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Peripheral neuropeptide Y Y1 receptors regulate lipid oxidation and fat accretion
Abstract
Neuropeptide Y and its Y receptors are important players in the regulation of energy homeostasis. However, while their functions in feeding regulation are well recognized, functions in other critical aspects of energy homeostasis are largely unknown. To investigate the function of Y1 receptors in the regulation of energy homeostasis, we examined energy expenditure, physical activity, body composition, oxidative fuel selection and mitochondrial oxidative capacity in germline Y1(-/-) mice as well as in a conditional Y1-receptor-knockdown model in which Y1 receptors were knocked down in peripheral tissues of adult mice.
Germline Y1(-/-) mice of both genders not only exhibit a decreased respiratory exchange ratio, indicative of increased lipid oxidation, but interestingly also develop late-onset obesity. However, the increased lipid oxidation is a primary effect of Y1 deletion rather than secondary to increased adiposity, as young Y1(-/-) mice are lean and show the same effect. The mechanism behind this is likely because of increased liver and muscle protein levels of carnitine palmitoyltransferase-1 (CPT-1) and maximal activity of key enzymes involved in beta-oxidation; beta-hydroxyacyl CoA dehydrogenase (betaHAD) and medium-chain acyl-CoA dehydrogenase (MCAD), leading to increased mitochondrial capacity for fatty acid transport and oxidation. These effects are controlled by peripheral Y1-receptor signalling, as adult-onset conditional Y1 knockdown in peripheral tissues also leads to increased lipid oxidation, liver CPT-1 levels and betaHAD activity. Importantly, these mice are resistant to diet-induced obesity.
This work shows the primary function of peripheral Y1 receptors in the regulation of oxidative fuel selection and adiposity, opening up new avenues for anti-obesity treatments by targeting energy utilization in peripheral tissues rather than suppressing appetite by central effects.
... In cultured 3T3-L1 adipocytes, NPY increased lipogenesis (PPARγ, C/EBP, ap2, and DGAT1) while inhibiting lipolysis (decreasing pHSL (ser563)), via NPY1R activation, suggesting a direct action of NPY in adipocytes to mediate this metabolic response [18,19,31,97]. Peripheral Npy1r knockdown in mice prevented diet-induced obesity (DIO), exclusively due to decreased adiposity, rather than alterations in food intake or excretion and physical activity, which can be the result of augmented lipid oxidation capacity [98]. NPY2R also plays an obesogenic role in WAT [19]. ...
... However, NPY also plays a direct role in hepatic lipid oxidation despite the downstream pathways of NPY1R and NPY2R still remaining unknown [19]. The peripheral Npy1r abolition increases carnitine palmitoyltransferase I (CPT-1) levels in the liver, which is a protein required for the mitochondrial β-oxidation of long-chain fatty acids ( Figure 2C) [98,100]. This suggests that at the hepatic level, NPY1R downregulates CPT-1 expression in the outer mitochondrial membrane (OMM). ...
... The skeletal muscle also plays an important role in lipid homeostasis. The deletion of Npy1r on the periphery has the same outcome regarding CPT-1 on skeletal muscle; however, it also increases oxidative phosphorylation (OXPHOS) and peroxisome proliferator-activated receptor-γ coactivator-1α (Pgc-1α) levels in a sex-dependent manner ( Figure 2D) [98]. Thus, the NPY system is a crucial regulator of overall lipid metabolism, on one hand by directly stimulating lipid accumulation on WAT reservoirs, and on the other hand by limiting lipid oxidation in the BAT (only via SNS inhibition), liver, and muscle, or indirectly by inhibiting lipolysis. ...
Energy balance is regulated by several hormones and peptides, and neuropeptide Y is one of the most crucial in feeding and energy expenditure control. NPY is regulated by a series of peripheral nervous and humoral signals that are responsive to nutrient sensing, but its role in the energy balance is also intricately related to the energetic status, namely mitochondrial function. During fasting, mitochondrial dynamics and activity are activated in orexigenic neurons, increasing the levels of neuropeptide Y. By acting on the sympathetic nervous system, neuropeptide Y modulates thermogenesis and lipolysis, while in the peripheral sites, it triggers adipogenesis and lipogenesis instead. Moreover, both central and peripheral neuropeptide Y reduces mitochondrial activity by decreasing oxidative phosphorylation proteins and other mediators important to the uptake of fatty acids into the mitochondrial matrix, inhibiting lipid oxidation and energy expenditure. Dysregulation of the neuropeptide Y system, as occurs in metabolic diseases like obesity, may lead to mitochondrial dysfunction and, consequently, to oxidative stress and to the white adipose tissue inflammatory environment, contributing to the development of a metabolically unhealthy profile. This review focuses on the interconnection between mitochondrial function and dynamics with central and peripheral neuropeptide Y actions and discusses possible therapeutical modulations of the neuropeptide Y system as an anti-obesity tool.
... This is consistent with a previous study conducted by Zhang et al. where conditional knockdown of Y1 receptors in the periphery exhibited reduced RER, indicating increased lipid oxidation [42]. Mechanisms underlying the increased lipid oxidation under peripheral Y1 antagonism were reported to be associated with increased carnitine palmitoyltransferase-1 (CPT-1) and upregulation of key enzymes involved in b-oxidation, consequently increasing the capacity of mitochondrial lipid oxidation and fatty acid transportation, particularly in the liver and muscle [42]. ...
... where conditional knockdown of Y1 receptors in the periphery exhibited reduced RER, indicating increased lipid oxidation [42]. Mechanisms underlying the increased lipid oxidation under peripheral Y1 antagonism were reported to be associated with increased carnitine palmitoyltransferase-1 (CPT-1) and upregulation of key enzymes involved in b-oxidation, consequently increasing the capacity of mitochondrial lipid oxidation and fatty acid transportation, particularly in the liver and muscle [42]. Interestingly, a recent study by Yan et al. demonstrated that the oral administration of BIBO3304 enhances thermogenesis through its effect on brown adipose tissue in dietinduced obese mice [22], although our study does not identify any noticeable change in Akt activity in adipose tissues in response to BIBO3304. ...
... The insulin sensitizing effect observed in db/db mice might be, at least in part, due to reduced body weight and adiposity or muscle fat content. In line with our finding in primary human myotubes, previous studies showed that deficiency of the peripheral Y1 receptor results in increased mitochondrial capacity in the muscle [42], supporting a role of the Y1 receptor antagonism acting directly on muscle insulin receptor signaling. Nonetheless, these results are consistent with the notion that increasing muscle glucose uptake improves glycemic control and suggesting that, in addition to reduced adiposity, these effects may at least in part be responsible for the observed improvement in glucose homeostasis in BIBO3304-treated db/ db mice. ...
Objectives
Loss of functional β-cell mass is a key factor contributing to poor glycaemic control in advanced type 2 diabetes. We previously reported that inhibition of the neuropeptide Y1 receptor improves islet transplantation outcome in type 1 diabetes. The aim of this study was to identify the pathophysiological role of the neuropeptide Y system in human type 2 diabetes, and further evaluate the therapeutic potential of using the neuropeptide Y1 receptor antagonist, BIBO3304 to improve β-cell function and survival in type 2 diabetes.
Methods
The gene expression of the NPY system in human islets from non-diabetic and subjects with type 2 diabetes was determined and correlated with stimulation index. The glucose lowering and β-cell protective effects of BIBO3304, a selective orally bioavailable neuropeptide Y1 receptor antagonist, in high-fat-diet/multiple low-dose streptozotocin- and genetic obese (db/db) type 2 diabetic mouse models were assessed.
Results
In this study, we identified a more than 2-fold increase in neuropeptide Y1 receptor and its ligand, neuropeptide Y mRNA expression in primary human islets from subjects with type 2 diabetes, which was significantly associated with reduced insulin secretion. Consistently, pharmacological inhibition of Y1 receptors by BIBO3304 significantly protected β cells from dysfunction and death under multiple diabetogenic conditions in islets. In preclinical study, we demonstrated that inhibition of Y1 receptors by BIBO3304 led to reduced adiposity and enhanced insulin action in skeletal muscle. Importantly, Y1 receptor antagonist BIBO3304 treatment also improved β-cell function and preserved functional β-cell mass, thereby resulting in better glycaemic control in both high-fat-diet/multiple low-dose streptozotocin- and db/db type 2 diabetic mice.
Conclusions
Our results uncovered a novel causal link of increased islet NPY-Y1 receptor gene expression to β-cell dysfunction and failure in human type 2 diabetes, contributing to the understanding of the pathophysiology of type 2 diabetes. Furthermore, our results demonstrate that inhibition of Y1 receptor by BIBO3304 represents a potential β-cell protective therapy for improving functional β-cell mass and glycaemic control in type 2 diabetes.
... Importantly, however, NPY and its Y-receptors are also prominently expressed in the periphery where NPY is co-stored and co-released with noradrenaline from postganglionic sympathetic neurons and chromaffin cells of the adrenal medulla 8 . In addition, peripheral tissues and cells such as adipose tissue, pancreas, liver, skeletal muscle, and osteoblasts have been shown to express NPY 9 . While the pharmacologically similar acting other members of the NPY family, peptide YY (PYY) and pancreatic polypeptide (PP), can also be found in the pancreas and the gut 10 . ...
... However, the nature and mechanisms whereby Y-receptor signalling that modulate metabolism and energy homeostasis in the periphery are largely unknown. The few exceptions are the recent identification of the inhibitory tone that the Y1R signalling has on insulin secretion in pancreatic β cells 11 and the beneficial effects that partial knockdown of Y1R signalling inhibition in peripheral tissues has on fat mass and lipid oxidation 9 . These results lead us to hypothsize that blocking Y1R signalling in peripheral tissues may ameliorate diet-induced obesity (DIO) and improve whole-body glucose metabolism. ...
... Elevated NPY level in the circulation and various adipose tissue sites has been linked to the development of obesity and metabolic diseases in mice 29 and humans [13][14][15]30 . In fact, NPY is locally produced by pre-adipocytes and mature differentiated adipocytes in humans and mice, with increased expression of NPY and Y1R in adipose tissue favouring the storage of lipids over thermogenesis 9,31 . This NPY-induced storage of energy is an important survival mechanism in mice and humans during times of energy shortage; however, with current overnutrition and sedentary behaviour, this powerful energy conservation capacity can translate into comorbidities, exacerbating already existing diet-induced weight gain and fat accretion. ...
Obesity is caused by an imbalance between food intake and energy expenditure (EE). Here we identify a conserved pathway that links signalling through peripheral Y1 receptors (Y1R) to the control of EE. Selective antagonism of peripheral Y1R, via the non-brain penetrable antagonist BIBO3304, leads to a significant reduction in body weight gain due to enhanced EE thereby reducing fat mass. Specifically thermogenesis in brown adipose tissue (BAT) due to elevated UCP1 is enhanced accompanied by extensive browning of white adipose tissue both in mice and humans. Importantly, selective ablation of Y1R from adipocytes protects against diet-induced obesity. Furthermore, peripheral specific Y1R antagonism also improves glucose homeostasis mainly driven by dynamic changes in Akt activity in BAT. Together, these data suggest that selective peripheral only Y1R antagonism via BIBO3304, or a functional analogue, could be developed as a safer and more effective treatment option to mitigate diet-induced obesity.
... Intracerebral administration of an Y 1 receptor antagonist suppressed physiological food intake after overnight fasting in mice [589], whereas the deletion of hypothalamic Y 1 receptors in mice did not alter food intake [77]. Y1 receptor knockout mice are associated with hyperinsulinemia but do not show alterations in food intake [671,1368,77]. Hyperphagia induced by i.c.v. ...
... Results from different research groups have shown that Y 1 receptor knockout mice showed a decreased respiratory exchange ratio, indicating an increase in lipid oxidation and/or reduced lipogenesis, designating a role to the Y 1 receptor controlling oxidative fuel selection [974,1368]. These effects seem to be controlled by peripheral Y 1 receptor signaling [1368]. ...
... Results from different research groups have shown that Y 1 receptor knockout mice showed a decreased respiratory exchange ratio, indicating an increase in lipid oxidation and/or reduced lipogenesis, designating a role to the Y 1 receptor controlling oxidative fuel selection [974,1368]. These effects seem to be controlled by peripheral Y 1 receptor signaling [1368]. According to another study, the Y 1 receptor showed a direct influence on the very-low-density lipoproteins and triglyceride levels in rats. ...
Neuropeptide tyrosine (neuropeptide Y or NPY) is one of the most abundant neuropeptides in the mammalian central nervous system and also widely distributed in the peripheral nervous system. Among the many mediators involved in important physiological and psychological systems, NPY in particular appears to be a multisignaling key peptide. The biological actions of NPY are vast and mediated via the Y1, Y2, Y4, and Y5 receptors, which are involved in both essential physiological and pathophysiological processes. Here, we discuss various roles of NPY in seven systems: a) regulation of energy homeostasis, b) thermoregulation, c) circadian system, d) sleep, e) nociception, f) emotional behavior, and g) the autonomic nervous system.
NPY regulates a) energy homeostasis with actions at different sites (central and peripheral), via different receptors in various neuronal tissues. Due to its prominent actions in the brain, including stimulating appetite, NPY function has gained importance. However, NPY is more than just an orexigenic peptide. Food intake and decrease in energy expenditure are exerted together by the Y1 and Y5 receptors. While the Y4 receptor exerts anorexigenic effects, the Y2 receptor has central anorexigenic and peripheral orexigenic properties. The involvement of NPY in b) thermoregulation remains unclear. Although it has been reported that cold exposure activates NPY. Increased or decreased thermogenesis has been observed as a result of NPY administration to different central sites. Central Y1 and Y5 receptors inhibit sympatho-adrenal transmitted thermogenesis in peripheral brown adipose tissue. NPY functions as a chemical messenger autonomous of the light-dark-cycle in the c) circadian rhythm and exerts similar phase-shifting effects to those of light. NPY leads to a shortened d) sleep onset and reduced REM latency, but its role in the circadian rhythm seems to be elusive and has not been established. NPY is implicated in e) pain perception and modulates nociception. It has been shown to cause both nociceptive and anti-nociceptive responses.
Moreover, Y receptors are thought to form heterodimers with those of galanin and glutamate to enhance their nociceptive modulatory effects. Especially the role of the Y2 receptor within this system and all the other systems reveals opposite properties. The different effects of Y2 receptors are dependent on their central or peripheral location.These opposing effects can be observed in other receptors as well and are likely explained by tissue-specific differences in receptor expression (number and distribution of receptors). Differences in cell type-specific second messenger coupling also play a role. Therefore, centrally located receptors can have a completely different function than peripherally located receptors. The regulation of f) emotional behavior through NPY and its receptors is biphasic. The Y1 and Y5 receptor are anxiolytic, whereas the Y2 and Y4 receptors lead to anxiety- and depression-like behavior. Moreover, the Y2 receptor enhances dopamine mediated anxious behavior but can also reverse the dopamine effects. Comparison of several studies showed that NPY mainly exerts anxiolytic, anti-depressant effects, and is implicated in memory processing. Moreover, it seems to be the ‘peptide of success.’ Polymorphisms in NPY genes may predispose different kinds of human affective disorders. Lower levels of NPY are associated with major depression and bipolar disorder. These findings are consistent with NPY modulating emotional behavior and may help to explain interindividual variation in resiliency to stress. In the g) autonomic nervous system effects are mediated predominantly via Y1, Y2, and Y5 receptors. These receptors are expressed in neurons supplying the vascular smooth muscle cells, the cardiomyocytes and are involved in physiological processes including vasoconstriction and -dilatation, heart rate variability, cardiac remodeling, and angiogenesis. However, additional peripheral mediated Y receptor-ligand effects have received far less attention than central. Besides its several physiological roles, NPY has been implicated in several common diseases, such as chronic pain, depression, hypertension, and atherosclerosis. Therefore, the NPY-multi-signaling-system could be a therapeutic target but as well an interesting neurotransmitter which plays obviously an important role in human adaptation to extreme environments, including space.
... Mice were culled when 20 weeks old between 1200 and 1500 h by cervical dislocation followed by decapitation. White adipose tissue depots (inguinal, epididymal, mesenteric and retroperitoneal) were removed and weighed as published previously 59 . Brain and BAT were removed and frozen for further analysis by quantitative real-time PCR and western blotting, respectively, as described below. ...
... Indirect calorimetry and measurement of physical activity. Metabolic rate was measured by indirect calorimetry using an eight chamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, Columbus, OH, USA) as described previously 59 . Briefly, mice were housed individually in specially built Plexiglas cages (20.1 × 10.1 × 12.7 cm). ...
... Western blotting. Western blotting was performed on BAT samples following procedures described previously 59 , in order to determine the protein levels of UCP-1 and PGC-1α. Briefly, BAT samples were resuspended in radioimmunoprecipitation assay buffer (PBS, pH 7.5; 1% nonident NP-40; 0.5% sodium deoxy-cholate; and 0.1% SDS), supplemented with protease and phosphatase inhibitors (10 µg/ml phenylmethylsulfonyl fluoride, 10 µg/ml aprotinin, 10 µg/ml leupeptin, 1 mmol/l Na 3 VO 4 and 10 mmol/l NaF) and solubilized for 2 h at 4°C. ...
Excess caloric intake results in increased fat accumulation and an increase in energy expenditure via diet-induced adaptive thermogenesis; however, the underlying mechanisms controlling these processes are unclear. Here we identify the neuropeptide FF receptor-2 (NPFFR2) as a critical regulator of diet-induced thermogenesis and bone homoeostasis. Npffr2−/− mice exhibit a stronger bone phenotype and when fed a HFD display exacerbated obesity associated with a failure in activating brown adipose tissue (BAT) thermogenic response to energy excess, whereas the activation of cold-induced BAT thermogenesis is unaffected. NPFFR2 signalling is required to maintain basal arcuate nucleus NPY mRNA expression. Lack of NPFFR2 signalling leads to a decrease in BAT thermogenesis under HFD conditions with significantly lower UCP-1 and PGC-1α levels in the BAT. Together, these data demonstrate that NPFFR2 signalling promotes diet-induced thermogenesis via a novel hypothalamic NPY-dependent circuitry thereby coupling energy homoeostasis with energy partitioning to adipose and bone tissue.
... Consistently, NPY has been implicated in the stressinduced obesity, directly affecting the adipogenic and lipogenic regulation of WAT (Kuo et al. 2007, Zhang et al. 2014). In addition, chronic peripheral NPY administration induces obesity (Xie et al. 2012), and knockdown of peripheral NPY Y1-or Y2-receptors protects from dietinduced obesity by changing fuel oxidation (Zhang et al. 2010, Shi et al. 2011. ...
... It predicts the incidence of T2D (Vozarova et al. 2002, Lee et al. 2003, and together with diabetes increases the risk for cardiovascular events (Targher et al. 2005). In various murine models, NPY has been shown to contribute to hepatic lipogenesis, VLDLtriglyceride (TG) and VLDL-cholesterol secretion, fatty acid (FA) oxidation and increased serum cholesterol levels (Zarjevski et al. 1993, Stafford et al. 2008, Zhang et al. 2010, Bruinstroop et al. 2012, Xie et al. 2012, Zhang et al. 2014), but it is not known, whether chronic excess of NPY causes hepatosteatosis, or which hepatic mechanisms contribute to dyslipidemias and development of the metabolic syndrome. ...
... Body composition was measured on days -14, 0 and 30 by quantitative NMR followed by tissue collection (after 3-h fast). As peripheral Y1-knockdown was shown to reduce respiratory exchange ratio (RER) without significantly affecting adiposity (Zhang et al. 2010), the effects of BIBO3304 vs vehicle (for 7 days preceded by 7 days habituation) were elucidated on 24-h energy expenditure (EE), RER and activity in 3-month-old WT mice (n = 4/ group) with an indirect calorimetry (Oxylet System, Panlab, Barcelona, Spain). ...
A gain-of-function polymorphism in human neuropeptide Y (NPY) gene (rs16139) associates with metabolic disorders and earlier onset of type 2 diabetes (T2D). Similarly, mice overexpressing NPY in noradrenergic neurons (OE-NPY(DBH)) display obesity and impaired glucose metabolism. In this study, the metabolic syndrome -like phenotype was characterized and mechanisms of impaired hepatic fatty acid, cholesterol and glucose metabolism in pre-obese (2-month-old) and obese (4-7-month-old) OE-NPY(DBH) mice were elucidated. Susceptibility to T2D was assessed by subjecting mice to high caloric diet combined with low-dose streptozotocin. Contribution of hepatic Y1-receptor to the phenotype was studied using chronic treatment with a Y1-receptor antagonist, BIBO3304. Obese OE-NPY(DBH) mice displayed hepatosteatosis and hypercholesterolemia preceded by decreased fatty acid oxidation and accelerated cholesterol synthesis. Hyperinsulinemia in early obese state inhibited pyruvate- and glucose-induced hyperglycemia, and deteriation of glucose metabolism of OE-NPY(DBH) mice developed with aging. Furthermore, streptozotocin induced T2D only in OE-NPY(DBH) mice. Hepatic inflammation was not morphologically visible, but up-regulated hepatic anti-inflammatory pathways and increased 8-isoprostane combined with increased serum resistin and decreased interleukin 10 pointed to increased NPY-induced oxidative stress that may predispose OE-NPY(DBH) mice to insulin resistance. Chronic treatment with BIBO3304 did not improve the metabolic status of OE-NPY(DBH) mice. Instead, down-regulation of beta1-adrenoceptors suggests indirect actions of NPY via inhibition of sympathetic nervous system. In conclusion, changes in hepatic fatty acid, cholesterol and glucose metabolism favoring energy storage contribute to the development of NPY-induced metabolic syndrome, and the effect is likely mediated via changes in sympathetic nervous system activity.
... Energy expenditure and respiratory exchange ratio were calculated by measurement of the rate of oxygen consumption (VO 2 ) and carbon dioxide output (VCO 2 ) via indirect calorimetry, in ad libitum-fed mice using an eight-chamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, OH) as previously described [38]. Physical activity was also determined in the calorimetry cages using an OPTO-M3 sensor system (Columbus Instruments) as previously described [38]. ...
... Energy expenditure and respiratory exchange ratio were calculated by measurement of the rate of oxygen consumption (VO 2 ) and carbon dioxide output (VCO 2 ) via indirect calorimetry, in ad libitum-fed mice using an eight-chamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, OH) as previously described [38]. Physical activity was also determined in the calorimetry cages using an OPTO-M3 sensor system (Columbus Instruments) as previously described [38]. Studies were conducted after 24 h of acclimatisation to calorimetry chambers. ...
... Interestingly, recent data has linked several bone-active molecules to BAT activation, including parathyroid hormone-related peptide (PTHrP) [51] and interleukin 6 [52]. Thus it appears that the integration of BAT with skeletal metabolism displays a level of complexity akin to the integration of WAT with bone (38,40). ...
Brown adipose tissue (BAT), largely controlled by the sympathetic nervous system (SNS), has the ability to dissipate energy in the form of heat through the actions of uncoupling protein-1 (UCP-1), thereby critically influencing energy expenditure. Besides BAT, the SNS also strongly influences bone, and recent studies have demonstrated a positive correlation between BAT activity and bone mass, albeit the interactions between BAT and bone remain unclear. Here we show that UCP-1 is critical for protecting bone mass in mice under conditions of permanent mild cold stress for this species (22°C). UCP-1(-/-) mice housed at 22°C showed significantly lower cancellous bone mass, with lower trabecular number and thickness, a lower bone formation rate and mineralising surface, but unaltered osteoclast number, compared to wild type mice housed at the same temperature. UCP-1(-/-) mice also displayed shorter femurs than wild types, with smaller cortical periosteal and endocortical perimeters. Importantly, these altered bone phenotypes were not observed when UCP-1(-/-) and wild type mice were housed in thermo-neutral conditions (29°C), indicating a UCP-1 dependent support of bone mass and bone formation at the lower temperature. Furthermore, at 22°C UCP-1(-/-) mice showed elevated hypothalamic expression of neuropeptide Y (NPY) relative to wild type, which is consistent with the lower bone formation and mass of UCP-1(-/-) mice at 22°C caused by the catabolic effects of hypothalamic NPY-induced SNS modulation. The results from this study suggest that during mild cold stress, when BAT-dependent thermogenesis is required, UCP-1 activity exerts a protective effect on bone mass possibly through alterations in central NPY pathways known to regulate SNS activity.
Copyright © 2015. Published by Elsevier Inc.
... While the expression pattern of Y receptors in the CNS has been extensively studied [14], their distribution in the periphery and precise functions remains largely unexplored. Nevertheless, recent evidence suggests the presence of Y1 receptors in white adipose tissue, the liver, skeletal muscle, immune cells [15], and the pancreas [16], implying a crucial role of Y1 receptors for modulating the function of these peripheral tissues. Similarly, the Y2 receptor is mostly found in epididymal white adipose tissue, skeletal muscle, and the liver [17], but not in other peripheral tissues such as the pancreas [17]. ...
... Consistent with the initial recognition as a feeding receptor to mediate NPY-induced hyperphagia [50], activation of central Y1 receptors using selective Y1 receptor agonists via ICV administration into wild type mice leads to a marked increase in food intake [51,52]. Paradoxically, germline Y1 knockout mice do not exhibit any major abnormalities with regard to food intake, but develop late-onset obesity in association with hyperinsulinaemia that could contribute to the greater adiposity observed [7,16,53]. However, the hyperphagia induced by ICV administration of NPY was abolished in germline Y1 knockout mice, strongly indicating that the Y1 receptor is involved in mediating NPYinduced hyperphagia [54,55]. ...
... In addition to its role in mediating NPY-induced food intake, several studies have demonstrated that Y1 receptor deletion leads to altered physical activity and respiratory exchange ratio (RER) [7,16], although contradicting data have also been published [53,54,57]. Nonetheless, results from different research groups have shown that germline Y1 receptor knockout mice display decreased RER, indicating an increase in lipid oxidation and/or reduced lipogenesis, and highlighting a role of the Y1 receptor in controlling oxidative fuel selection [16,54]. ...
Obesity develops when energy intake exceeds energy expenditure over time. Numerous neurotransmitters, hormones, and factors have been implicated to coordinately control energy homeostasis, centrally and peripherally. However, the neuropeptide Y (NPY) system has emerged as the one with the most critical functions in this process. While NPY centrally promotes feeding and reduces energy expenditure, peptide YY (PYY) and pancreatic polypeptide (PP), the other family members, mediate satiety. Importantly, recent research has uncovered additional functions for these peptides that go beyond the simple feeding/satiety circuits and indicate a more extensive function in controlling energy homeostasis. In this review, we will discuss the actions of the NPY system in the regulation of energy balance, with a particular focus on energy expenditure.
Copyright © 2015 Elsevier Ltd. All rights reserved.
... At 16 weeks of age, animals were culled between 13:00 and 16:00 h by cervical dislocation followed by decapitation. White adipose tissue depots (inguinal, epididymal, mesenteric and retroperitoneal) were removed and weighed as published previously [15,16]. A subset of 9-week-old WT, NPY À/À and catNPY mice were fed on a high-fat diet (HFD, 43% calories from fat, 17% calories from protein and 20 MJ/kg; Specialty Feeds, Glen Forrest, WA, Australia) for 7 weeks. ...
... 2.8. Examination of energy metabolism, respiratory exchange ratio and physical activity Metabolic rate was measured by indirect calorimetry using an eightchamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, Columbus, OH, USA) as described previously [16]. Briefly, mice were housed individually in specially built Plexiglas cages (20.1 Â 10.1 Â 12.7 cm). ...
... Western analysis was performed on liver samples following procedures described previously [16] in order to determine protein levels of acetyl-CoA carboxylase (ACC) levels, the key enzymes involved in fatty acid synthesis and overall energy metabolism in lipogenic tissues. Briefly, liver samples were resuspended in radioimmunoprecipitation assay buffer (PBS, pH 7.5; 1% nonident NP-40; 0.5% sodium deoxycholate; and 0.1% SDS), supplemented with protease and phosphatase inhibitors (10 mg/ml phenylmethylsulfonyl fluoride, 10 mg/ml aprotinin, 10 mg/ml leupeptin, 1 mmol/l Na 3 VO 4 , and 10 mmol/l NaF) and solubilized for 2 h at 4 C. Equal amounts of tissue lysate (20 mg protein) were resolved by SDS-PAGE and immunoblotted with antibodies against phospho-Ser79 acetyl-CoA carboxylase (pACC), total acetyl-CoA carboxylase (tACC) (Cell Signalling Technology, Danvers, MA, USA), carnitine palmitoyltransferase-1 (CPT-1) (Alpha Diagnostic Intl., San Antonio, Texas, USA), fatty acid synthase (FAS) (Cell Signalling Technology, Danvers, MA, USA), glyceraldehyde 3phosphate dehydrogenase (GAPDH) (Cell Signalling Technology, Danvers, MA, USA). ...
Neuropeptide Y (NPY) and noradrenaline are commonly co-expressed in sympathetic neurons. Both are key regulators of energy homeostasis and critical for stress-coping. However, little is known about the specific function of NPY in the catechoalminergic system in these regulations. Here we show that mice with NPY expression only in the noradrenergic and adrenergic cells of the catecholaminergic system (catNPY) exhibited exacerbated diet-induced obesity, lower body and brown adipose tissue temperatures compared to WT and NPY-/- mice under a HFD. Furthermore, chronic stress increased adiposity and serum corticosterone level in WT but not NPY-/- mice. Re-introducing NPY specifically to the catecholaninergic system in catNPY mice restored stress responsiveness associated with increased respiratory exchange ratio and decreased liver pACC to tACC ratio. These results demonstrate catecholaminergic NPY signalling is critical in mediating diet- and chronic stress-induced fat gain via effects on diet-induced thermogenesis and stress-induced increases in corticosterone levels and lipogenic capacity.
... Y1 and Y5 receptors have been strongly implicated in mediating the hyperphagic effects of NPY or energy restriction [10]–[12]. However, whereas male and female germline Y1 receptor deficient mice exhibit reduced fasting-induced food intake, they exhibit slight or no reductions in total daily food intake or NPY-stimulated feeding, and they also develop late-onset obesity [13]–[16]. Paradoxically, male and female germline Y5 receptor knockout mice are obese with increases in total daily food intake, fasting-induced food intake, body weight and adiposity, and they are not protected against leptin-deficiency-induced obesity [17], [18]. Additionally, chronic intracerebroventricular NPY administration to Y1 or Y5 receptor knockout mice induces a similar hyperphagic obesity syndrome as that seen in wildtype mice [6]. ...
... Energy expenditure and respiratory exchange ratio were calculated by measurement of the rate of oxygen consumption (VO2) and carbon dioxide output (VCO2) via indirect calorimetry in ad libitum-fed mice using an eight-chamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, Columbus, OH, USA) as previously described by us [16]. Physical activity was also determined in the calorimetry cages using an OPTO-M3 sensor system (Columbus Instruments) as previously described [16]. Studies were conducted after 24 hours of acclimatisation to calorimetry chambers. ...
... The strong hypophagic phenotype of our Y1Y5 double knockout models suggests that Y1 and Y5 receptors play redundant roles in the regulation of food intake. Whereas single germline deletion of Y1 receptors in male and female mice has been consistently shown to reduce fasting-induced but not spontaneous food intake [13]–[16], and whereas single germline deletion of Y5 receptors actually increases spontaneous and fasting-induced food intake in both sexes [17], [18], our male germline Y1Y5 receptor double knockout mice exhibited hypophagia under both fasted and non-fasted conditions. These findings imply that when either the Y1 or the Y5 receptor is missing, the remaining receptor is able to compensate or overcompensate to protect against hypophagia. ...
Neuropeptide Y (NPY) acting in the hypothalamus is one of the most powerful orexigenic agents known. Of the five known Y receptors, hypothalamic Y1 and Y5 have been most strongly implicated in mediating hyperphagic effects. However, knockout of individual Y1 or Y5 receptors induces late-onset obesity--and Y5 receptor knockout also induces hyperphagia, possibly due to redundancy in functions of these genes. Here we show that food intake in mice requires the combined actions of both Y1 and Y5 receptors. Germline Y1Y5 ablation in Y1Y5(-/-) mice results in hypophagia, an effect that is at least partially mediated by the hypothalamus, since mice with adult-onset Y1Y5 receptor dual ablation targeted to the paraventricular nucleus (PVN) of the hypothalamus (Y1Y5(Hyp/Hyp)) also exhibit reduced spontaneous or fasting-induced food intake when fed a high fat diet. Interestingly, despite hypophagia, mice with germline or hypothalamus-specific Y1Y5 deficiency exhibited increased body weight and/or increased adiposity, possibly due to compensatory responses to gene deletion, such as the decreased energy expenditure observed in male Y1Y5(-/-) animals relative to wildtype values. While Y1 and Y5 receptors expressed in other hypothalamic areas besides the PVN--such as the dorsomedial nucleus and the ventromedial hypothalamus--cannot be excluded from having a role in the regulation of food intake, these studies demonstrate the pivotal, combined role of both Y1 and Y5 receptors in the mediation of food intake.
... In contrast to great research efforts investigating effects of PYY3-36, little attention has been paid to the role of PYY1-36, or the possible interactions between PYY1-36 and PYY3-36, in the regulation of energy balance and glucose homeostasis. PYY1-36 might be expected to have a broader and more complex profile of effects, since in addition to having a higher affinity for Y2 receptors than PYY3-36, it also has a high affinity for other Y receptors, such as the Y1 receptor, which elicits prominent but differential effects on energy balance and glucose homeostasis compared to Y2 receptor (Shi et al., 2010(Shi et al., , 2011Zhang et al., 2010bZhang et al., ,c, 2011. For instance, lack of Y1 signalling promotes lipid oxidation (Henry et al., 2005;Zhang et al., 2010b), whereas lack of Y2 signalling appears to have opposite effects on oxidative fuel selection (Shi et al., 2010(Shi et al., , 2011Zhang et al., 2010c). ...
... PYY1-36 might be expected to have a broader and more complex profile of effects, since in addition to having a higher affinity for Y2 receptors than PYY3-36, it also has a high affinity for other Y receptors, such as the Y1 receptor, which elicits prominent but differential effects on energy balance and glucose homeostasis compared to Y2 receptor (Shi et al., 2010(Shi et al., , 2011Zhang et al., 2010bZhang et al., ,c, 2011. For instance, lack of Y1 signalling promotes lipid oxidation (Henry et al., 2005;Zhang et al., 2010b), whereas lack of Y2 signalling appears to have opposite effects on oxidative fuel selection (Shi et al., 2010(Shi et al., , 2011Zhang et al., 2010c). Furthermore, Y1 receptor deficiency leads to pronounced hyperinsulinemia which is not observed in Y2 receptor deficient mice (Kushi et al., 1998;Sainsbury et al., 2003;Zhang et al., 2010b), suggesting that Y1 but not Y2 signalling plays an important role in regulating insulin secretion. ...
... For instance, lack of Y1 signalling promotes lipid oxidation (Henry et al., 2005;Zhang et al., 2010b), whereas lack of Y2 signalling appears to have opposite effects on oxidative fuel selection (Shi et al., 2010(Shi et al., , 2011Zhang et al., 2010c). Furthermore, Y1 receptor deficiency leads to pronounced hyperinsulinemia which is not observed in Y2 receptor deficient mice (Kushi et al., 1998;Sainsbury et al., 2003;Zhang et al., 2010b), suggesting that Y1 but not Y2 signalling plays an important role in regulating insulin secretion. Based on the differential effects of Y1 and Y2 signalling on energy and glucose homeostasis, and considering that PYY1-36 and PYY3-36 coexist in the circulation in varying ratios depending on nutritional status (Grandt et al., 1994), PYY1-36 and PYY3-36 may act in a co-ordinate or synergistic manner to regulate energy and glucose metabolism in fasted and postprandial states. ...
... This can function in a local manner, with NPY secreted by visceral adipose tissue and local macrophages to promote proliferation in adipocyte cell populations [9]. Peripheral Y1R on adipocytes has also been shown to be a critical regulator of fat mass and lipid oxidation [38]. Y1R peripheral knockdowns show resistance to diet-induced obesity, whereas global Y1R null mice show no such resistance and become obese with increasing age [38]. ...
... Peripheral Y1R on adipocytes has also been shown to be a critical regulator of fat mass and lipid oxidation [38]. Y1R peripheral knockdowns show resistance to diet-induced obesity, whereas global Y1R null mice show no such resistance and become obese with increasing age [38]. This is similar to the antagonism seen in Y2R between central and peripheral receptors; hypothalamic Y1R deletion reduces obesity and adipocytic Y1R acts to stimulate fat accretion. ...
Neural pathways are now a well-appreciated factor in the regulatory milieu controlling the maintenance of bone mass. A number of neural pathways from the brain to bone have been identified. These pathways often involve elements of the energy homeostatic apparatus, indicating links between the regulation of bone metabolism and energy balance. Neuropeptide Y is one such factor that co-regulates these two processes. Initial studies outlined the skeletal actions of NPY from within the brain and the interactions with energy homeostatic processes. However, in recent years, an appreciation for the actions of NPY within bone cells has expanded. Cells of the osteoblastic lineage express both NPY ligand and a cognate receptor NPY, Y1R. Murine studies have demonstrated that both ligand and receptor actively control bone mass and osteoblast activity and interact with mechanical signals to integrate with the local loading environment. Local NPY signalling regulates osteoprogenitor production and differentiation, to cover the entire osteoblastic lineage. In addition, several recent studies have demonstrated extra-skeletal actions of osteoblastic NPY signalling, to regulate energy expenditure and with it adiposity, and in a separate study, to control release of a factor-controlling beta cell mass and insulin production/release and with it glucose tolerance. Thus, osteoblastic neuropeptide production and signalling illustrates the rapidly widening sphere of influence of skeletal tissue, and suggests a far more complex and interconnected physiology then is currently appreciated.
... Intraperitoneal NPY administration partially rescues the adipose phenotype of p38a osteoblast-specific KO mice These data indicated that p38 ablation in osteoblasts reduces the expression of NPY in bone and plasma. It has been reported that NPY promotes adiposity through the enhancement of adipogenesis and inhibition of lipolysis (42)(43)(44). Based on all these observations, we examined whether NPY affects the adipose phenotype of KO animals. ...
... Peripherally, NPY is considered an obesogenic hormone with antilipolytic and adipogenic effects (32,42,49). The peripheral deletion of NPY receptors reduces weight and fat pad accretion and increases energy expenditure and lipid oxidation (42)(43)(44). We confirmed that adipose cells express Npy, but in KO mice, neither a decrease in Npy mRNA levels nor Cre recombinase expression was observed in adipose tissue or the adrenal glands. ...
The skeleton acts as an endocrine organ that regulates energy metabolism and calcium and phosphorous homeostasis through the secretion of osteocalcin (Oc) and fibroblast growth factor 23 (FGF23). However, evidence suggests that osteoblasts secrete additional unknown factors that contribute to the endocrine function of bone. To search for these additional factors, we generated mice with a conditional osteoblast-specific deletion of p38α MAPK known to display profound defects in bone homeostasis. Herein, we show that impaired osteoblast function is associated with a strong decrease in body weight and adiposity (P < 0.01). The differences in adiposity were not associated with diminished caloric intake, but rather reflected 20% increased energy expenditure and the up-regulation of uncoupling protein-1 (Ucp1) in white adipose tissue (WAT) and brown adipose tissue (BAT) (P < 0.05). These alterations in lipid metabolism and energy expenditure were correlated with a decrease in the blood levels of neuropeptide Y (NPY) (40% lower) rather than changes in the serum levels of insulin, Oc, or FGF23. Among all Npy-expressing tissues, only bone and primary osteoblasts showed a decline in Npy expression (P < 0.01). Moreover, the intraperitoneal administration of recombinant NPY partially restored the WAT weight and adipocyte size of p38α-deficient mice (P < 0.05). Altogether, these results further suggest that, in addition to Oc, other bone-derived signals affect WAT and energy expenditure contributing to the regulation of energy metabolism.-Rodríguez-Carballo, E., Gámez, B., Méndez-Lucas, A., Sánchez-Freutrie, M., Zorzano, A., Bartrons, R., Alcántara, S., Perales, J. C., and Ventura, F. p38α function in osteoblasts influences adipose tissue homeostasis.
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... The Y receptors are widely distributed in the central and peripheral tissues. Each Y receptor has a varying distribution across central and peripheral tissues [105,106]. Basal plasma PYY levels are low but rise in response to food, and postprandially they remain elevated for several hours. [107]. ...
Obesity remains a common metabolic disorder and a threat to health as it is associated with numerous complications. Lifestyle modifications and caloric restriction can achieve limited weight loss. Bariatric surgery is an effective way of achieving substantial weight loss as well as glycemic control secondary to weight-related type 2 diabetes mellitus. It has been suggested that an anorexigenic gut hormone response following bariatric surgery contributes to weight loss. Understanding the changes in gut hormones and their contribution to weight loss physiology can lead to new therapeutic treatments for weight loss. Two distinct types of neurons in the arcuate hypothalamic nuclei control food intake: proopiomelanocortin neurons activated by the anorexigenic (satiety) hormones and neurons activated by the orexigenic peptides that release neuropeptide Y and agouti-related peptide (hunger centre). The arcuate nucleus of the hypothalamus integrates hormonal inputs from the gut and adipose tissue (the anorexigenic hormones cholecystokinin, polypeptide YY, glucagon-like peptide-1, oxyntomodulin, leptin, and others) and orexigeneic peptides (ghrelin). Replicating the endocrine response to bariatric surgery through pharmacological mimicry holds promise for medical treatment. Obesity has genetic and environmental factors. New advances in genetic testing have identified both monogenic and polygenic obesity-related genes. Understanding the function of genes contributing to obesity will increase insights into the biology of obesity. This review includes the physiology of appetite control, the influence of genetics on obesity, and the changes that occur following bariatric surgery. This has the potential to lead to the development of more subtle, individualised, treatments for obesity.
... However, Stevanović-Silva et al. showed no lipid accumulation in female offspring [49,50]. Interestingly, the liver of female offspring presented lower levels of NPY1R, which suggests less inhibition of CTP-1 and lipid accumulation [55], regardless of PPARα level reduction. ...
Obesogenic environments such as Westernized diets, overnutrition, and exposure to glycation during gestation and lactation can alter peripheral neuroendocrine factors in offspring, predisposing for metabolic diseases in adulthood. Thus, we hypothesized that exposure to obesogenic environments during the perinatal period reprograms offspring energy balance mechanisms. Four rat obesogenic models were studied: maternal diet-induced obesity (DIO); early-life obesity induced by postnatal overfeeding; maternal glycation; and postnatal overfeeding combined with maternal glycation. Metabolic parameters, energy expenditure, and storage pathways in visceral adipose tissue (VAT) and the liver were analyzed. Maternal DIO increased VAT lipogenic [NPY receptor-1 (NPY1R), NPY receptor-2 (NPY2R), and ghrelin receptor], but also lipolytic/catabolic mechanisms [dopamine-1 receptor (D1R) and p-AMP-activated protein kinase (AMPK)] in male offspring, while reducing NPY1R in females. Postnatally overfed male animals only exhibited higher NPY2R levels in VAT, while females also presented NPY1R and NPY2R downregulation. Maternal glycation reduces VAT expandability by decreasing NPY2R in overfed animals. Regarding the liver, D1R was decreased in all obesogenic models, while overfeeding induced fat accumulation in both sexes and glycation the inflammatory infiltration. The VAT response to maternal DIO and overfeeding showed a sexual dysmorphism, and exposure to glycotoxins led to a thin-outside-fat-inside phenotype in overfeeding conditions and impaired energy balance, increasing the metabolic risk in adulthood.
... 142 Moreover, NPY greatly promotes adipocyte proliferation and differentiation, and fat accumulation. 143,144 Dyslipidemia Previous studies have shown that OSAHS can promote dyslipidemia. 145,146 Dyslipidemia is a recognized risk factor for AS. ...
Cardiovascular disease is a common cause of death worldwide, and atherosclerosis (AS) and obstructive sleep apnea–hypopnea syndrome (OSAHS) critically contribute to the initiation and progression of cardiovascular diseases. OSAHS promotes endothelial injury, vascular smooth muscle cell (VSMC) proliferation, abnormal lipid metabolism, and elevated arterial blood pressure. However, the exact OSAHS mechanism that causes AS remains unclear. The nervous system is widely distributed in the central and peripheral regions. It regulates appetite, energy metabolism, inflammation, oxidative stress, insulin resistance, and vasoconstriction by releasing regulatory factors and participates in the occurrence and development of AS. Studies showed that OSAHS can cause changes in neurophysiological plasticity and affect modulator release, suggesting that neuroendocrine dysfunction may be related to the OSAHS mechanism causing AS. In this article, we review the possible mechanisms of neuroendocrine disorders in the pathogenesis of OSAHS-induced AS and provide a new basis for further research on the development of corresponding effective intervention strategies.
... For phenotype characterization of our stress-induced obesity study (SIO), NPY ablation study, overexpression study, metabolic rate was measured by indirect calorimetry using an eight-chamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, Columbus, OH, USA) as described previously ( Zhang et al., 2010). Briefly, mice were housed individually in specially built Plexiglas cages (20.1 x 10.1 x 12.7 cm) 48 h before the actual monitoring. ...
Neuropeptide Y (NPY) exerts a powerful orexigenic effect in the hypothalamus. However, extra-hypothalamic nuclei also produce NPY, but its influence on energy homeostasis is unclear. Here we uncover a previously unknown feeding stimulatory pathway that is activated under conditions of stress in combination with calorie-dense food; NPY neurons in the central amygdala are responsible for an exacerbated response to a combined stress and high-fat-diet intervention. Central amygdala NPY neuron-specific Npy overexpression mimics the obese phenotype seen in a combined stress and high-fat-diet model, which is prevented by the selective ablation of Npy. Using food intake and energy expenditure as readouts, we demonstrate that selective activation of central amygdala NPY neurons results in increased food intake and decreased energy expenditure. Mechanistically, it is the diminished insulin signaling capacity on central amygdala NPY neurons under combined stress and high-fat-diet conditions that leads to the exaggerated development of obesity.
... PYY exists in two forms, PYY 1−36 has affinity for all three receptors while PYY 3−36 , the cleaved form of PYY 1−36, has increased affinity for Y2r (Berglund et al., 2003). Expression of the Y receptors is documented in rodent myoblasts (Zhang et al., 2010) but, to our knowledge, their expression in human MPCs (hMPCs) and SkM has not been identified. ...
Peptide YY (PYY) is considered a gut peptide with roles in post-prandial appetite and glucose regulation. Circulating PYY protein levels increase during aerobic exercise. Furthermore, people who have greater increases in muscle progenitor cells (hMPCs), the adult stem cell population responsible for skeletal muscle (SkM) repair, after resistance training have higher PYY transcript levels in SkM prior to training. Currently, examination of PYY expression patterns in SkM and/or hMPCs is lacking. Our objective was to identify the expression patterns of PYY in SkM and hMPCs. PYY and the associated Y receptors were analyzed in SkM biopsy tissue and cultured hMPCs from young and old human participants. Additional experiments to assess the role and regulation of PYY in hMPCs were performed. In SkM, PYY and one of the three Y receptors (Y1r) were detectable, but expression patterns were not affected by age. In expanding hMPCs, PYY and all three Y receptor (Y1r, Y2r, and Y5r) proteins were expressed in a temporal fashion with young hMPCs having greater levels of Y receptors at various time points. Exogenous PYY did not affect hMPC population expansion. hMPC PYY levels increased following the metabolic stimulus, 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR), but were not affected by the inflammatory stimulus, tumor necrosis factor alpha (TNFα). In conclusion, PYY and Y receptor expression are not impacted by age in SkM tissue but are reduced in old vs. young expanding hMPCs. Furthermore, endogenous PYY production is stimulated by low energy states and thus may be integral for skeletal muscle and hMPC responses to metabolic stimuli.
... NPY is implicated in the regulation of whole body energy homeostasis; Y1 deficient mice develop adult-onset obesity at around 12-15 weeks of age (Baldock et al., 2007;Zhang et al., 2010). In our global NPY-deficient model, at 14 weeks of age, no difference in body weight (Fig. 3C) or lean mass (Fig. 3D) was present in male WT and NPYKO mice. ...
Neuropeptide Y (NPY) is involved in multiple processes such as behavior, energy and bone metabolism. Previous studies have relied on global NPY depletion to examine its effects on bone. However, this approach is unable to distinguish the central or local source of NPY influencing bone. Our aim was to identify which cells within the skeleton express Npy and establish a model that will enable us to differentiate effects of NPY derived from different cell types. We have generated the NPY floxed (NPYflox) mice using CRISPR technology. By crossing the NPYflox mice with Hypoxanthine Phosphoribosyltransferase 1 (Hprt)-cre to generate a global knockout, we were able to validate and confirm loss of Npy transcript and protein in our global NPYKO. Global deletion of NPY results in a smaller femoral cortical cross-sectional area (−12%) and reduced bone strength (−18%) in male mice. In vitro, NPY-deficient bone marrow stromal cells (BMSCs) showed increase in osteogenic differentiation detected by increases in alkaline phosphatase staining and bone sialoprotein and osteocalcin expression. Despite both sexes presenting with increased adiposity, female mice had no alterations in bone mass, suggesting that NPY may have sex-specific effects on bone. In this study we identified Npy expression in the skeleton and examined the effect of global NPY depletion to bone mass. The differential impact of NPY deletion in cortical and cancellous compartments along with differences in phenotypes between in vitro and in vivo, highlights the complex nature of NPY signaling, indicative of distinct sources that can be dissected in the future using this NPYflox model.
... In order to determine protein levels of Akt in the total and phosphorylated forms, western blot analysis was performed on quadriceps muscle samples as previously described [25]. Briefly, powdered muscle samples were resuspended in buffer (PBS, pH 7.5; 1% nonident NP-40; 0.5% sodium deoxy-cholate; and 0.1% SDS), supplemented with protease and phosphatase inhibitors (10 mg/ml phenylmethylsulfonyl fluoride, 10 mg/ml aprotinin, 10 mg/ml leupeptin, 1 mmol/l Na 3 VO 4 , and 10 mmol/l NaF) and solubilized for 2 h at 4 C. Equal amounts of tissue lysate (25 mg protein) were resolved by SDS-PAGE, transferred to immobilon-P membranes (Millipore, Billerica, MA,USA) and immunoblotted with antibodies against phospho-Akt (Ser473) (pAkt (473)) and Akt (Cell Signaling Technology, Danvers, MA, USA), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) (Cell Signaling Technology, Danvers, MA, USA). ...
Objective:
The skeleton, which is strongly controlled by endocrine factors, has recently been shown to also play an active endocrine role itself, specifically influencing energy metabolism. However, much less is known about this role. Therefore, we sought to identify novel endocrine factors involved in the regulation of both bone mass and whole-body glucose homeostasis.
Methods:
We used transcriptomic and proteomic analysis of Y1 receptor deficient osteoblasts combined with the generation of a novel osteoglycin deficient mouse model and performed comprehensive in vivo phenotype profiling, combined with osteoglycin administration in wildtype mice and human studies.
Results:
Here we identify a novel role for osteoglycin, a secreted proteoglycan, in coordinating bone accretion with changes in energy balance. Using an osteoglycin knockout mouse model, we show that at a whole body level, osteoglycin acts to suppress bone formation and modulate whole body energy supplies by altering glucose uptake through changes in insulin secretion and sensitivity, as well as by altering food intake through central signaling. Examining humans following gastric surgery as a model of negative energy balance, we show that osteoglycin is associated with BMI and lean mass as well as changes in weight, BMI, and glucose levels.
Conclusions:
Thus, we identify osteoglycin as a novel factor involved in the regulation of energy homeostasis and identify a role for it in facilitating the matching of bone acquisition to alterations in energy status.
... During this period, both WT-HFD and NPYKO-HFD groups gained weight compared to chow (~4 g and~8 g, respectively) ( Fig. 5a, b), attributed primarily to increased fat mass (Fig. 5c). In contrast to younger mice, NPYKO-HFD had a greater accrual of fat mass (~9 g) than WT-HFD (~5 g) (Fig. 5c, d), consistent with previous studies [34]. Fat pad weight increased across the four fat pads dissected-inguinal, epididymal, retroperitoneal, mesenteric and total ( Fig. 5e-i). ...
Objective:
To determine whether age and neuropeptide Y (NPY) were involved in the skeletal response to extended periods of diet-induced obesity.
Methods:
Male wild-type (WT) and NPY null (NPYKO) mice were fed a mild (23% fat) high-fat diet for 10 weeks from 6 or 16 weeks of age. Metabolism and bone density were assessed during feeding. Skeletal changes were assessed by microCT and histomorphometry.
Results:
High-fat feeding in 6-week-old WT mice led to significantly increased body weight, adiposity and serum leptin levels, accompanied with markedly suppressed cortical bone accrual. NPYKO mice were less susceptible to fat accrual but, importantly, displayed a complete lack of suppression of bone accrual or cortical bone loss. In contrast, when skeletally mature (16 week old) mice underwent 10 weeks of fat feeding, the metabolic response to HFD was similar to younger mice, however bone mass was not affected in either WT or NPYKO. Thus, growing mice are particularly susceptible to the detrimental effects of HFD on bone mass, through suppression of bone accrual involving NPY signalling.
Conclusion:
This study provides new insights into the relationship between the opposing processes of a positive weight/bone relationship and the negative 'metabolic' effect of obesity on bone mass. This negative effect is particularly active in growing skeletons, which have heightened sensitivity to changes in obesity. In addition, NPY is identified as a fundamental driver of this negative 'metabolic' pathway to bone.
... Our results are consistent with previous studies which showed the capability of the yeast extract to increase igf-1 gene expression which in turn activates GH, and promotes cell growth (Merten et al., 2001;Zhang et al., 2010). (Craig, Wood, & McClelland, 2007). ...
Due to the undesirable consequences associated with antibiotics use, researchers and food producers have studied alternative feeding, for the control of fish diseases and animal welfare improvement. However, the beneficial properties of RNA yeasts extract in aquaculture have been barely considered. The present study investigated the beneficial properties of RNA yeast extract from Kluyveromyces fragilis on survival rate, weight and length as well as on molecular pathways involved in growth, immuno-system and oxidative stress using zebrafish (Danio rerio) as an experimental model. The yeast extract has been administrated to zebrafish at three different concentrations (60–180–300 ppm) via zooplankton (Artemia salina) for 21 days. Results highlighted yeast extract RNA capability to enhance growth and to improve larvae survival rate in a dose-dependent manner. In fact, gene expression data showed the ability of the RNA yeast extract to up-regulate genes involved in growth and to restore stress-related condition due to the early larval development coupled with the RNA yeast extract administration. In addition, gene expression showed that RNA yeast extract acts as inflammatory-reducer, but did not enhance the immune response. Histological analysis showed that all three treated groups displayed a thicker gut epithelium, higher intestinal crypts coupled with higher enterocytes lengths compared to control group. In conclusion, these findings provide a large gene network through which yeast RNA extract acts and, by inducing transcriptional changes, modulate the physiological control of growth and inflammatory response coupled with the increase in length and dry weight, together with a higher survival ratio and an intestinal architecture amelioration.
... For instance, increasing cAMP levels, as a result of glucagon-likepeptide 1 (GLP-1) signaling in β-cells potentiates insulin secretion 12 , highlighting this pathway as a critical control point. Importantly, Y-receptors (Y1, Y2, Y4, Y5, and y6) 13,14 which are activated by neuropeptide Y (NPY) family members preferentially associate with G i/o G-proteins and, therefore, act in an inhibitory fashion reducing cAMP levels [15][16][17] . Particularly, Y1 receptors are highly expressed in β-cells, indicating the potential for an inhibitory effect of Y1 receptor signaling to directly regulate insulin release from β-cells. ...
Failure to secrete sufficient quantities of insulin is a pathological feature of type-1 and type-2 diabetes, and also reduces the success of islet cell transplantation. Here we demonstrate that Y1 receptor signaling inhibits insulin release in β-cells, and show that this can be pharmacologically exploited to boost insulin secretion. Transplanting islets with Y1 receptor deficiency accelerates the normalization of hyperglycemia in chemically induced diabetic recipient mice, which can also be achieved by short-term pharmacological blockade of Y1 receptors in transplanted mouse and human islets. Furthermore, treatment of non-obese diabetic mice with a Y1 receptor antagonist delays the onset of diabetes. Mechanistically, Y1 receptor signaling inhibits the production of cAMP in islets, which via CREB mediated pathways results in the down-regulation of several key enzymes in glycolysis and ATP production. Thus, manipulating Y1 receptor signaling in β-cells offers a unique therapeutic opportunity for correcting insulin deficiency as it occurs in the pathological state of type-1 diabetes as well as during islet transplantation.
... 28,29 Moreover, it is worth noting that noradrenergic NPY, co-localized with noradrenaline in the same neurons of the brainstem or sympathetic nervous system, 30,31 takes part in energy metabolism in response to long-term stress. [32][33][34] Recent studies of OE-NPY DβH mouse models overexpressing noradrenergic NPY showed that NPY in noradrenergic neurons indeed contributed to the development of stress-induced obesity accompanied with impaired glucose metabolism and IR. 35,36 Taken together, both central and peripheral NPY are crucial for the development of obesity and adiposity. ...
Diabetes-induced atherosclerotic cardiovascular disease is the leading cause of death of diabetic patients. Neuronal regulation plays a critical role in glucose metabolism and cardiovascular function under physiological and pathological conditions, among which, neurotransmitter neuropeptide Y has been shown to be closely involved in these two processes. Elevated central neuropeptide Y level promotes food intake and reduces energy expenditure, thereby increasing adiposity. Neuropeptide Y is co-localized with noradrenaline in central and sympathetic nervous systems. As a major peripheral vascular contractive neurotransmitter, through interactions with its receptors, neuropeptide Y has been implicated in the pathology and progression of diabetes, by promoting the proliferation of endothelial cells and vascular fibrosis, which may contribute to diabetes-induced cardiovascular disease. Neuropeptide Y also participates in the pathogenesis of atherosclerosis, the major form of cardiovascular disease, via aggravating endothelial dysfunction, growth of vascular smooth muscle cells, formation of foam cells and platelets aggregation. This review highlights the causal role of neuropeptide Y and its receptor system in the development of diabetes mellitus and one of its complications: atherosclerotic cardiovascular disease. The information from this review provides both critical insights onto the mechanisms underlying the pathogenesis of atherosclerosis and evidence for the development of therapeutic strategies.
... It has been demonstrated that CB1 receptor increases hepatic lipid accumulation through the stimulation of the lipogenic transcription factor SREBP-1c and increases de novo fatty acid synthesis 23 . Like CB1, NPY and its Y receptors also stimulate food intake 24 . In the rat model, NPY has acute effects on glucose metabolism by increasing glucagon, insulin, and corticosterone 25 ; moreover, a recent study demonstrated the role of NPY in stimulating lipid accumulation through pre-adipocyte proliferation, suggesting an important emergent role of NPY on adipogenesis 26 . ...
The gut microbiota regulates metabolic pathways that modulate the physiological state of hunger or satiety. Nutrients in the gut stimulate the release of several appetite modulators acting at central and peripheral levels to mediate appetite and glucose metabolism. After an eight-day exposure of zebrafish larvae to probiotic Lactobacillus rhamnosus, high-throughput sequence analysis evidenced the ability of the probiotic to modulate the microbial composition of the gastrointestinal tract. These changes were associated with a down-regulation and up-regulation of larval orexigenic and anorexigenic genes, respectively, an up-regulation of genes related to glucose level reduction and concomitantly reduced appetite and body glucose level. BODIPY-FL-pentanoic-acid staining revealed higher short chain fatty acids levels in the intestine of treated larvae. These results underline the capability of the probiotic to modulate the gut microbiota community and provides insight into how the probiotic interacts to regulate a novel gene network involved in glucose metabolism and appetite control, suggesting a possible role for L. rhamnosus in the treatment of impaired glucose tolerance and food intake disorders by gut microbiota manipulation.
... The potentially direct effects of NPY on the liver and skeletal muscle have been elucidated using mice with conditional knockdown of Y1 or Y2 receptors in peripheral tissues. Both models showed resistance to diet-induced obesity (Shi et al., 2011;Zhang et al., 2010b). This was attributed to increased respiratory quotient and expression of lipid oxidizing enzymes, which suggests that NPY could inhibit lipid oxidation by acting directly on peripheral tissues. ...
... 13,14 NPY and its receptors, like the endocannabinoids and CB1, are located in key metabolic tissues, such as the adipose tissue, liver and pancreas, and recent evidence suggests that they have an important role in promoting fat storage and accompanying metabolic disturbances. [15][16][17] The source of peripheral NPY is the sympathetic nervous system, where NPY is a co-transmitter with norepinephrine. 18 To characterize the role of NPY co-localized with norepinephrine in sympathetic nervous system and brain noradrenergic neurons, we previously created a transgenic mouse model overexpressing NPY under the promoter of the dopamine-β-hydroxylase (DβH) gene (OE-NPY DβH mice). ...
Objective:
Endocannabinoids and neuropeptide Y (NPY) promote energy storage via central and peripheral mechanisms. In the hypothalamus, the two systems were suggested to interact. To investigate such interplay also in non-hypothalamic tissues, we evaluated endocannabinoid levels in obese OE-NPY(DβH) mice, which overexpress NPY in the noradrenergic neurons in the sympathetic nervous system and the brain.
Methods:
The levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) were measured in key regulatory tissues, that is, hypothalamus, pancreas, epididymal white adipose tissue (WAT), liver and soleus muscle, over the development of metabolic dysfunctions in OE-NPY(DβH) mice. The effects of a 5-week treatment with the CB1 receptor inverse agonist AM251 on adiposity and glucose metabolism were studied.
Results:
2-AG levels were increased in the hypothalamus and epididymal WAT of pre-obese and obese OE-NPY(DβH) mice. Anandamide levels in adipose tissue and pancreas were increased at 4 months concomitantly with higher fat mass and impaired glucose tolerance. CB1 receptor blockage reduced body weight gain and glucose intolerance in OE-NPY(DβH) to the level of vehicle-treated wild-type mice.
Conclusions:
Altered endocannabinoid tone may underlie some of the metabolic dysfunctions in OE-NPY(DβH) mice, which can be attenuated with CB1 inverse agonism suggesting interactions between endocannabinoids and NPY also in the periphery. CB1 receptors may offer a target for the pharmacological treatment of the metabolic syndrome with altered NPY levels.
... In the adipose tissue, NPY inhibits lipolysis (Bradley et al. 2005) and stimulates adipogenesis and angiogenesis (Zukowska-Grojec et al. 1998, Kuo et al. 2007. Furthermore, conditional knockdown of peripheral NPY receptors Y2 (Shi et al. 2011) or Y1 (Zhang et al. 2010) protects mice from high-fat diet-induced obesity via increased energy expenditure or lipid oxidation respectively. Sympathetic NPY has been suggested to play a role in stressinduced obesity as WAT-targeted knockdown of NPY Y2-receptors reduced obesity induced by chronic mild stress in mice (Kuo et al. 2007). ...
Neuropeptide Y (NPY) co-localized with noradrenaline in central and sympathetic nervous systems seems to play a role in the control of energy metabolism. In this study, the aim was to elucidate the effects and pathophysiological mechanisms of increased NPY in catecholaminergic neurons on accumulation of body adiposity.
Transgenic mice overexpressing NPY under the dopamine-beta-hydroxylase promoter (OE-NPY(D) (βH) ) and wildtype control mice were followed for body weight gain and body fat content. Food intake, energy expenditure, physical activity, body temperature, serum lipid content and markers of glucose homeostasis were monitored. Thermogenic and lipolytic responses in adipose tissues, and urine catecholamine and tissue catecholamine synthesizing enzyme levels were analysed as indices of sympathetic tone.
Homozygous OE-NPY(D) (βH) mice showed significant obesity accompanied with impaired glucose tolerance and insulin resistance. Increased adiposity was explained by neither increased food intake or fat absorption nor by decreased total energy expenditure or physical activity. Adipocyte hypertrophy and decreased circulating lipid levels suggested decreased lipolysis and increased lipid uptake. Brown adipose tissue thermogenic capacity was decreased and brown adipocytes filled with lipids. Enhanced response to adrenergic stimuli, downregulation of catecholamine synthesizing enzyme expressions in the brainstem and lower adrenaline excretion supported the notion of low basal catecholaminergic activity.
Increased NPY in catecholaminergic neurons induces obesity that seems to be a result of preferential fat storage. These results support the role of NPY as a direct effector in peripheral tissues and an inhibitor of sympathetic activity in the pathogenesis of obesity. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
... Dual energy X-ray absorptiometry (DEXA) scanning was performed using a Lunar PIXImus2 (GE Healthcare, Port Washington, NY, USA) as previously reported [22]. ...
Insulin secretion increases in normal pregnancy to meet increasing demands. Inability to increase beta-cell function results in gestational diabetes mellitus (GDM). We have previously shown that the expression of the transcription factor ARNT (Aryl-hydrocarbon Receptor Nuclear Translocator) is reduced in the islets of humans with type 2 diabetes. Mice with a beta-cell specific deletion of ARNT (β-ARNT mice) have impaired glucose tolerance secondary to defective insulin secretion. We hypothesised that ARNT is required to increase beta-cell function during pregnancy, and that β-ARNT mice would be unable to compensate for the beta-cell stress of pregnancy. The aims of this study were to investigate the mechanisms of ARNT regulation of beta-cell function and glucose tolerance in pregnancy.
β-ARNT females were mated with floxed control (FC) males and FC females with β-ARNT males.
During pregnancy, β-ARNT mice had a marked deterioration in glucose tolerance secondary to defective insulin secretion. There was impaired beta-cell proliferation in late pregnancy, associated with decreased protein and mRNA levels of the islet cell-cycle regulator cyclinD2. There was also reduced expression of Irs2 and G6PI. In contrast, in control mice, pregnancy was associated with a 2.1-fold increase in ARNT protein and a 1.6-fold increase in cyclinD2 protein, and with increased beta-cell proliferation.
Islet ARNT increases in normal murine pregnancy and beta-cell ARNT is required for cyclinD2 induction and increased beta-cell proliferation in pregnancy.
... [44] The peripheral action of NPY can also involve the tonic regulation of fat oxidation and energy expenditure as shown in recent studies using conditional peripheral Y 1 and Y 2 null mice. [45,46] Furthermore, SNS NPY could induce lipogenesis by inhibiting lipolysis via adipocyte-located Y 1 -receptors. [47] Hence, all these data combined show that NPY can induce obesity by extrahypothalamic pathways influencing generation, differentiation and function of adipocytes and use of lipids as energy source rather than by infl uencing appetite via hypothalamic sites or brainstem -hypothalamus projections. ...
Neuropeptide Y (NPY) is a neuropeptide widely expressed in the brain and a peptide transmitter of sympathetic nervous system (SNS) co-released with noradrenaline (NA) in prolonged stress. Association of a gain-of-function polymorphism in the human NPY gene with dyslipideamia, diabetes and vascular diseases suggests that increased NPY plays a role in the pathogenesis of the metabolic syndrome in humans. In the hypothalamus, NPY plays an established role in the regulation of body energy homeostasis. However, the effects of NPY elsewhere in the brain and in the SNS are less explored. In order to understand the role of NPY co-expressed with NA in the sympathetic nerves and brain noradrenergic neurons, a novel mouse model overexpressing NPY in noradrenergic neurons was generated. The mouse displays metabolic defects such as increased adiposity, hepatosteatosis, and impaired glucose tolerance as well as stress-related hypertension and increased susceptibility to vascular wall hypertrophy. The mouse phenotype closely reflects the findings of the several association studies with human NPY gene polymorphisms, and fits with the previous work on the effects of stress-induced NPY release on metabolism and vasculature. Thus, in addition of promoting feeding and obesity in the hypothalamus, NPY expressed in the noradrenergic neurons in the brain and in the SNS induces the development of cardiometabolic diseases.
... Based on the essential role of lipid metabolism in cardiovascular dysfunction of DM, we measured the plasma lipid concentration and found that BIBP 3226 and BIIE 0246 rescued the aberrant lipid level. Previous studies suggest that peripheral Y1R participates in the regulation of energy homeostasis mainly via fatty acid oxidation [28], while Y2R located in abdominal adipocytes takes part in the process of stress-induced obesity on peripheral fat tissue [29]. These properties of Y1R/Y2R implied that they might also similarly influence the fat metabolism and lipid modulation in a DM model. ...
Background/Aims: Abnormal baroreceptor reflex sensitivity (BRS) and elevated plasma neuropeptide Y (NPY) are prevalent in diabetic patients. The present study was conducted to determine whether NPY Y1 receptor (Y1R) and NPY Y2 receptor (Y2R) contribute to the regulatin of BRS in diabetic rats. Methods: Diabetes mellitus (DM) rats with hyperlipidemia were developed by an emulsion diet enriched with fat, sucrose and fructose followed by streptozocin (STZ). Y1R and Y2R specific antagonists (BIBP 3226 and BIIE 0246) were administered by a mini-osmotic pump. Systolic blood pressure (SBP), heart rate (HR), BRS and heart functions, as well as the plasma NPY and lipid level were measured after treatment for 4 weeks. Results: Both BIBP 3226 and BIIE 0246 treatment reversed the elevated total cholesterol (TC) and low density lipoprotein (LDL-C) level, and reduced high density lipoprotein (HDL-C) level in DM rats. BIIE 0246 may attenuate the increased triglyceride (TG) level in DM rats. In addition, neither BIBP 3226 nor BIIE 0246 treatment produced significant effects on BRS, SBP or HR (P>0.05) in DM rats, even after PE and SNP challenge. However, BIBP 3226 and BIIE 0246 further impaired LVSP, LVEDP, +dp/dtmax and -dp/dtmax. Conclusion: This study provided us with the evidence that the inhibition of peripheral Y1R and Y2R did not affect impaired BRS but amplified the deterioration of the compromised cardiac function in STZ-induced DM rats with hyperlipidemia.
... They were housed under conditions of controlled temperature (22 C) with a 12:12 hr light-dark cycle (lights on at 07:00 hr) and fed a standard chow diet with ad libitum access to water, except where noted. Generation of the NPY À/À , Y1 À/À , Y2 À/À , and conditional Y1 lox/lox mice has been described previously (Howell et al., 2003;Karl et al., 2008;Sainsbury et al., 2002;Zhang et al., 2010). NPYCre knockin mice were generated as described in the Supplemental Experimental Procedures. ...
Neuropepetide Y (NPY) is best known for its powerful stimulation of food intake and its effects on reducing energy expenditure. However, the pathways involved and the regulatory mechanisms behind this are not well understood. Here we demonstrate that NPY derived from the arcuate nucleus (Arc) is critical for the control of sympathetic outflow and brown adipose tissue (BAT) function. Mechanistically, a key change induced by Arc NPY signaling is a marked Y1 receptor-mediated reduction in tyrosine hydroxylase (TH) expression in the hypothalamic paraventricular nucleus (PVN), which is also associated with a reduction in TH expression in the locus coeruleus (LC) and other regions in the brainstem. Consistent with this, Arc NPY signaling decreased sympathetically innervated BAT thermogenesis, involving the downregulation of uncoupling protein 1 (UCP1) expression in BAT. Taken together, these data reveal a powerful Arc-NPY-regulated neuronal circuit that controls BAT thermogenesis and sympathetic output via TH neurons.
... Sexually dimorphic responses to NPY-associated metabolic changes have been reported in NPY Y1 receptor knock-out mice, which develop late-onset obesity without hyperphagia that is more pronounced in female than male mice [22]. The difference was attributed to decreased skeletal muscle mitochondrial oxidative capacity in female Y1 knock-out mice [23]. Gonadal steroid hormones seem to play a role in the fat accumulation in the Y1 knock-out mice as weight gain does not start until puberty [24, 25]. ...
Neuropeptide Y (NPY) is a neurotransmitter associated with feeding and obesity. We have constructed an NPY transgenic mouse model (OE-NPY(DBH) mouse), where targeted overexpression leads to increased levels of NPY in noradrenergic and adrenergic neurons. We previously showed that these mice become obese on a normal chow. Now we aimed to study the effect of a Western-type diet in OE-NPY(DBH) and wildtype (WT) mice, and to compare the genotype differences in the development of obesity, insulin resistance, and diabetes. Weight gain, glucose, and insulin tolerance tests, fasted plasma insulin, and cholesterol levels were assayed. We found that female OE-NPY(DBH) mice gained significantly more weight without hyperphagia or decreased activity, and showed larger white and brown fat depots with no difference in UCP-1 levels. They also displayed impaired glucose tolerance and decreased insulin sensitivity. OE-NPY(DBH) and WT males gained weight robustly, but no difference in the degree of adiposity was observed. However, 40% of OE-NPY(DBH) but none of the WT males developed hyperglycaemia while on the diet. The present study shows that female OE-NPY(DBH) mice were not protected from the obesogenic effect of the diet suggesting that increased NPY release may predispose females to a greater risk of weight gain under high caloric conditions.
... Indirect calorimetry studies were carried out on ob/ob, NPY -/ob/ob, and wild-type littermates of both genders at 14 to 15 weeks of age as described. (23) Briefly, the metabolic rate was measured by indirect calorimetry using an eight-chamber open-circuit calorimeter (Oxymax Series; Columbus Instruments, Columbus, OH, USA). Preweighed mice were housed individually in specially built Plexiglas cages (20.1 Â 10.1 Â 12.7 cm). ...
Leptin signaling is required for normal bone homeostasis, however, loss of leptin results in differing effects on cortical and cancellous bone, as well as altered responses between the axial and appendicular regions. Local β-adrenergic actions are responsible for the greater cancellous bone volume in leptin-deficient (ob/ob) mice, however, the mechanism responsible for the opposing reduction in cortical bone in ob/ob is not known. Here we show that blocking the leptin-deficient increase in neuropeptide Y expression reverses the cortical bone loss in ob/ob mice. Mice null for both NPY and leptin (NPY(-/-) ob/ob), display greater cortical bone mass in both long bone and vertebra, with NPY(-/-) ob/ob mice exhibiting thicker and denser cortical bone, associated with greater endocortical and periosteal MAR, compared to ob/ob animals. Importantly, these cortical changes occurred without significant increases in body weight, with NPY(-/-) ob/ob mice showing significantly reduced adiposity compared to ob/ob controls most likely due to the reduced respiratory exchange ratio seen in these animals. Interestingly, cancellous bone volume was not different between NPY(-/-) ob/ob and ob/ob, suggesting that NPY is not influencing the adrenergic axis. Taken together, this work demonstrates the critical role of NPY signaling in the regulation of bone and energy homeostasis, and more importantly, suggests that reduced leptin levels or leptin resistance, which occurs in obesity, could potentially inhibit cortical bone formation via increased central NPY signaling. © 2012 American Society for Bone and Mineral Research.
Background:
Obesity is a complex condition that is affected by a variety of factors, including the environment, behavior, and genetics. However, the genetic mechanisms underlying obesity remains poorly elucidated. Therefore, our study aimed at identifying key genes for human obesity using bioinformatics analysis.
Methods:
The microarray datasets of adipose tissue in humans were downloaded from the Gene Expression Omnibus (GEO) database. After the selection of differentially expressed genes (DEGs), we used Lasso regression and Support Vector Machine (SVM) algorithm to further identify the feature genes. Moreover, immune cell infiltration analysis, gene set variation analysis (GSVA), GeneCards database and transcriptional regulation analysis were conducted to study the potential mechanisms by which the feature genes may impact obesity. We utilized receiveroperatingcharacteristic(ROC)curve to analysis the diagnostic efficacy of feature genes. Finally, we verified the feature genes in cell experiments and animal experiments. The statistical analyses in validation experiments were conducted using SPSS version 28.0, and the graph were generated using GraphPadPrism 9.0 software. The bioinformatics analyses were conducted using R language (version 4.2.2), with a significance threshold of p<0.05 used.
Results:
199 DEGs were selected using Limma package, and subsequently, 5 feature genes (EGR2, NPY1R, GREM1, BMP3 and COL8A1) were selected through Lasso regression and SVM algorithm. Through various bioinformatics analyses, we found some signaling pathways by which feature genes influence obesity and also revealed the crucial role of these genes in the immune microenvironment, as well as their strong correlations with obesity-related genes. Additionally, ROC curve showed that all the feature genes had good predictive and diagnostic efficiency in obesity. Finally, after validation through in vitro experiments, EGR2, NPY1R and GREM1 were identified as the key genes.
Conclusions:
This study identified EGR2, GREM1 and NPY1R as the potential key genes and potential diagnostic biomarkers for obesity in humans. Moreover, EGR2 was discovered as a key gene for obesity in human adipose tissue for the first time, which may provide novel targets for diagnosing and treating obesity.
Thermogenesis is a centrally regulated physiological process integral for thermoregulation and energy homeostasis. However, the mechanisms and pathways involved remain poorly understood. Importantly, in this study we uncovered that in an environment of 28 °C that is within the mouse thermoneutral zone, lack of NPFF signalling leads to significant increases in energy expenditure, resting metabolic rate and brown adipose tissue (BAT) thermogenesis, which is associated with decreased body weight gain and lean tissue mass. Interestingly, when exposed to a high-fat diet (HFD) at 28 °C, Npff−/− mice lost the high energy expenditure phenotype observed under chow condition and exhibited an impaired diet-induced thermogenesis. On the other hand, under conditions of increasing levels of thermal demands, Npff−/− mice exhibited an elevated BAT thermogenesis at mild cold condition (22 °C), but initiated comparable BAT thermogenic responses as WT mice when thermal demand increased, such as an exposure to 4 °C. Together, these results reveal NPFF signalling as a novel and critical player in the control of thermogenesis, where it regulates thermosensory thermogenesis at warm condition and adjusts thermoregulation under positive energy balance to regulate diet-induced thermogenesis.
Type 2 diabetes and obesity have reached pandemic proportions throughout the world, so much so that the World Health Organisation coined the term “Globesity” to help encapsulate the magnitude of the problem. G protein-coupled receptors (GPCRs) are highly tractable drug targets due to their wide involvement in all aspects of physiology and pathophysiology, indeed, GPCRs are the targets of approximately 30% of the currently approved drugs. GPCRs are also broadly involved in key physiologies that underlie type 2 diabetes and obesity including feeding reward, appetite and satiety, regulation of blood glucose levels, energy homeostasis and adipose function. Despite this, only two GPCRs are the target of approved pharmaceuticals for treatment of type 2 diabetes and obesity. In this review we discuss the role of these, and select other candidate GPCRs, involved in various facets of type 2 diabetic or obese pathophysiology, how they might be targeted and the potential reasons why pharmaceuticals against these targets have not progressed to clinical use. Finally, we provide a perspective on the current development pipeline of anti-obesity drugs that target GPCRs.
Loss of functional β-cell mass is a key factor contributing to the poor glycaemic control in type 2 diabetes. However, therapies that directly target these underlying processes remains lacking. Here we demonstrate that gene expression of neuropeptide Y1 receptor and its ligand, neuropeptide Y, was significantly upregulated in human islets from subjects with type 2 diabetes. Importantly, the reduced insulin secretion in type 2 diabetes was associated with increased neuropeptide Y and Y1 receptor expression in human islets. Consistently, pharmacological inhibition of Y1 receptors by BIBO3304 significantly protected β-cells from dysfunction and death under multiple diabetogenic conditions in islets. In a preclinical study, Y1 receptor antagonist BIBO3304 treatment improved β-cell function and preserved functional β-cell mass, thereby resulting in better glycaemic control in both high-fat-diet/multiple low dose streptozotocin- and db/db type 2 diabetic mice. Collectively, our results uncovered a novel causal link of increased islet NPY-Y1 receptor signaling to β-cell dysfunction and failure in human type 2 diabetes. These results further demonstrate that inhibition of Y1 receptor by BIBO3304 represents a novel and effective β-cell protective therapy for improving functional β-cell mass and glycaemic control in type 2 diabetes.
Central action of the adipocyte hormone leptin via the neuropeptide Y (NPY) system is considered critical for energy homeostatic control. However, the precise mechanisms for this control are still not clear. To specifically investigate how leptin signalling on NPY neuron contributes to the control of energy homeostasis, we generated an inducible adult‐onset NPY neuron‐specific leptin receptor (Lepr) knockout model and performed a comprehensive metabolic phenotyping study. Here we show that the subpopulation of NPY neurons that is directly responsive to leptin is not required for leptin’s inhibition on fasting‐induced hyperphagia, but is essential for the regulation of adiposity that is independent of changes in energy balance or diet composition. Furthermore, under obesogenic conditions such as a high‐fat diet, lack of Lepr signalling on NPY neurons results in significant increases in food intake and concomitant reductions in energy expenditure leading to accelerated accumulation of fat mass. Collectively, these findings support the notion that Lepr‐expressing NPY neurons act as the key relay point where peripheral adipose storage information is sensed, and corresponding responses are initiated to protect adipose reserves.
Aims:
NPY-Y1R plays an important role in dietary regulation. Although germline knockdown of NPY-Y1R in mice alleviates high-fat-diet-induced obesity and increases CPT1α levels in the liver, the role of the Y1 receptor in specific tissues has not been studied.
Main methods:
MCD diet is the most widely used method to establish a model of lean NASH in a short time. We therefore evaluated the role of liver NPY-Y1R in NASH progression.
Key findings:
In mice with liver-specific knockout of NPY-Y1R (LivKO) and wild-type control littermates fed MCD diet for 4 weeks, NPY-Y1R deficiency significantly decreased body and liver weight. Moreover, NPY-Y1R deletion protected mice against hepatic steatosis and injury. LivKO decreased TG, TC, and FFA levels in the liver and alanine aminotransferase activity in plasma. To clarify the mechanism, we evaluated the key enzymes involved in triglyceride hydrolase and fatty-acid oxidase. Expression of ATGL, CPT1α, and ACO was significantly increased in LivKO mice, whereas expression of fatty-acid synthase was significantly decreased. mRNA expression analysis revealed a marked reduction of genes involved in de-novo lipogenesis and monosaturated fatty-acid synthesis, including sterol-regulatory element-binding protein 1c and fatty-acid synthase. Moreover, liver injury-related factors were significantly decreased in LivKO mice, such as TNF-α, inducible nitric oxide synthase, and MCP-1. Thus, NPY-Y1R deficiency in the liver alleviates lipid deposition and injury. However, NPY-Y1R did not affect inflammation and fibrosis.
Significance:
NPY-Y1R deficiency in the liver directly suppresses not only hepatic steatosis, but also liver injury, and thus provides a treatment option for NASH.
Genetic and pharmacological functional studies have provided evidence that the lack of Neuropeptide Y‐Y1 receptor (Y1R) signaling pathway induces a high bone mass phenotype in mice. However, clinical observations have shown that drug or genetic mediated improvement of bone mass might be associated to alterations to bone extracellular matrix (ECM) properties, leading to bone fragility. Hence, in this study we propose to characterize the physical, chemical and biomechanical properties of mature bone ECM of germline NPY‐Y1R knockout (Y1R−/−) mice, and compare to their wild‐type (WT) littermates. Our results demonstrated that the high bone mass phenotype observed in Y1R−/− mice involves alterations in Y1R−/− bone ECM ultrastructure, as a result of accelerated deposition of organic and mineral fractions. In addition, Y1R−/− bone ECM displays enhanced matrix maturation characterized by greater number of mature/highly packed collagen fibers without pathological accumulation of immature/mature collagen crosslinks nor compromise of mineral crystallinity. These unique features of Y1R−/− bone ECM improved the biochemical properties of Y1R−/− bones, reflected by mechanically robust bones with diminished propensity to fracture, contributing to greater bone strength. These findings support the future usage of drugs targeting Y1R signaling as a promising therapeutic strategy to treat bone loss‐related pathologies.
Neuropeptide Y (NPY) is a member of the pancreatic peptide family of neuropeptides that play a crucial role in numerous central and peripheral nervous system responses. Recently, it has been shown that NPY protected cells against neurotoxic damage from β-amyloid peptides (Aβ) in Alzheimer's disease (AD). Heme is a common factor linking several metabolic perturbations in AD and altered heme metabolism has been shown a relationship to the pathologies of AD. Thus, heme may have a chance to meet NPY and potentially counteract its function. To explore this, UV-Visible spectroscopy, fluorescence spectroscopy and differential pulse voltammetry (DPV) were used to demonstrate that NPY can bind with heme to form a NPY-heme complex and the binding enhances the peroxidase activity of heme. Dot blotting result indicates that NPY is easily to be nitrated by binding with heme when H2O2 and NO2- are present. Furthermore, LC-MS/MS results confirm that tyrosine36 (Y36), an important amino acid residue of NPY in binding and activating for neuropeptide receptors, can be nitrated during the nitration process. Thereafter, we used mutant peptide NPY（3N）with Y36 replaced by 3-nitrtotyrosine to investigate the impact of nitration on the structure and bioactive of the peptide. Our results show that Y36 nitration destabilizes the α-helix conformation of the peptide, and counteract NPY-induced inhibition of cAMP accumulation in SK-N-MC cells. Collectively, these data imply that the self-association of NPY with heme potentially induces tyrosine nitration, destroys active monomeric conformation of the peptide and thereby counteracts its bioactivity
Hypothalamic alpha-melanocyte-stimulating hormone (α-MSH) is a key catabolic mediator of energy homeostasis. Its anorexigenic and hypermetabolic effects show characteristic age-related alterations that may be part of the mechanism of middle-aged obesity and geriatric anorexia/cachexia seen in humans and other mammals. We aimed to investigate the role of α-MSH in mitochondrial energy metabolism during the course of aging in a rodent model.
To determine the role of α-MSH in mitochondrial energy metabolism in muscle, we administered intracerebroventricular (ICV) infusions of α-MSH for 7-days to different age-groups of male Wistar rats. The activities of oxidative phosphorylation complexes I to V and citrate synthase were determined and compared to those of age-matched controls. We also quantified mitochondrial DNA (mtDNA) copy number and measured the expression of the master regulators of mitochondrial biogenesis, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and peroxisome proliferator-activated receptor gamma (PPARγ).
The peptide reduced weight gain in juvenile rats to one fifth of that of controls and increased the weight loss in older animals by about five fold. Mitochondrial DNA copy number inversely correlated with changes in body weight in controls, but not in α-MSH-treated animals. The strong increase in body weight in young rats was associated with a low mtDNA copy number and high PPARγ mRNA levels in controls. Expression of PGC-1α and PPARγ declined with age, whereas OXPHOS and citrate synthase enzyme activities were unchanged. In contrast, α-MSH treatment suppressed OXPHOS enzyme and citrate synthase activity.
In conclusion, our results showed age-related differences in the metabolic effects of α-MSH. In addition, administration of α-MSH suppressed citrate synthase and OXPHOS activities independent of age. These findings suggest that α-MSH exposure may inhibit mitochondrial biogenesis.
With average life expectancy rising greatly, the incidence rate of arteriosclerotic cardiovascular disease (ASCVD) has significantly increased. The heart disease has now become the number one killer that threatens the global population health, the second is stroke. It will be of great significance to investigate the pathophysiological mechanisms underlying ASCVD in order to promote illicit prevention and treatment. The neuropeptide Y (NPY) has now been discovered for more than thirty years and is widely distributed in the central nervous system (CNS) and peripheral tissues. By combining with certain receptors, NPY performs a variety of physiological functions, including the regulation of food intake, cardiovascular effects, development, hormonal secretion, sexual behavior, biological rhythms, temperature and emotion. In ASCVD, increased peripheral NPY was involved in the pathophysiological process of atherosclerosis through affecting the vascular endothelial dysfunction, the formation of foam cells, the proliferation of vascular smooth muscle cells, the local inflammatory response of plaques and the activation and aggregation of platelets. Via central and/or the peripheral nervous system, increased NPY was associated with dyslipidemia, hypertension, obesity, diabetes, impaired glucose tolerance, and smoking which are all risk factors for ASCVD. In this review, we summarize the development that shows the role of neuropeptide Y in atherosclerotic cardiovascular disease.
Neuropeptide Y (NPY) plays an important role in maintaining energy homeostasis. Within the hypothalamus, Npy is primarily expressed in the arcuate nucleus (Arc) and the dorsomedial hypothalamus (DMH). ARC NPY acts as an orexigenic neuromodulator integrating energy-related systemic signals (such as the adiposity signal leptin) to modulate food intake and energy balance. In contrast, DMH NPY acts independently of leptin. In addition to its feeding effects, DMH NPY has specific actions on brown adipocyte formation and thermoregulation. Knockdown of NPY in the DMH promotes development of brown adipocytes in white adipose tissue and increases brown adipocyte activity, leading to increased energy expenditure and lowered fat contents. DMH NPY knockdown prevents high-fat diet-induced obesity. Peripheral NPY also directly acts on adipose tissue and promotes white adipogenesis. Overall, NPY plays critical roles in the control of energy balance through affecting food intake, body adiposity, and energy expenditure. These actions provide evidence for the potential target(s) for combatting obesity and diabetes.
Accumulating evidence suggests that neuropeptide Y (NPY) has a role in aging and lifespan determination. In this review, we critically discuss age-related changes in NPY levels in the brain, together with recent findings concerning the contribution of NPY to, and impact on, six hallmarks of aging, specifically: loss of proteostasis, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing, cellular senescence, and mitochondrial dysfunction. Understanding how NPY contributes to, and counteracts, these hallmarks of aging will open new avenues of research on limiting damage related to aging.
Selection of broiler chickens for growth has led to increased adipose tissue accretion. To investigate the post-hatch development of adipose tissue, the abdominal, clavicular, and subcutaneous adipose tissue depots were collected from broiler chicks at 4 and 14days post-hatch. As a percent of body weight, abdominal fat increased (P<0.001) with age. At day 4, clavicular and subcutaneous fat depots were heavier (P<0.003) than abdominal fat whereas at day 14, abdominal and clavicular weighed more (P<0.003) than subcutaneous fat. Adipocyte area and diameter were greater in clavicular and subcutaneous than abdominal fat at 4 and 14days post-hatch (P<0.001). Glycerol-3-phosphate dehydrogenase (G3PDH) activity increased (P<0.001) in all depots from day 4 to 14, and at both ages was greatest in subcutaneous, intermediate in clavicular, and lowest in abdominal fat (P<0.05). In clavicular fat, peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer binding protein (CEBP)α, CEBPβ, fatty acid synthase (FASN), fatty acid binding protein 4 (FABP4), lipoprotein lipase (LPL), neuropeptide Y (NPY), and NPY receptor 5 (NPYR5) mRNA increased and NPYR2 mRNA decreased from day 4 to 14 (P<0.001). Thus, there are site-specific differences in broiler chick adipose development, with larger adipocytes and greater G3PDH activity in subcutaneous fat at day 4, more rapid growth of abdominal fat, and clavicular fat intermediate for most traits. Adipose tissue expansion was accompanied by changes in gene expression of adipose-associated factors.
Copyright © 2015. Published by Elsevier Inc.
Obesity is no longer considered to provide protection against osteoporosis. Moreover, treatments for obesity are now suspected of reducing bone mass. With the escalating incidence of obesity, combined with increases in the frequency, duration and intensity of interventions used to combat it, we face a potential increase in health burden due to osteoporotic fractures. The neuropeptide Y-ergic system offers a potential target for the prevention and anabolic treatment of bone loss in obesity, due to its dual role in the regulation of energy homeostasis and bone mass. Although the strongest stimulation of bone mass by this system appears to occur via indirect hypothalamic pathways involving Y2 receptors (one of the five types of receptors for neuropeptide Y), Y1 receptors on osteoblasts (bone-forming cells) induce direct effects to enhance bone mass. This latter pathway may offer a suitable target for anti-osteoporotic treatment while also minimizing the risk of adverse side effects.
Objective:
Elevated very low-density lipoprotein (VLDL)-triglyceride (TG) secretion from the liver contributes to an atherogenic dyslipidemia that is associated with obesity, diabetes and the metabolic syndrome. Numerous models of obesity and diabetes are characterized by increased central nervous system (CNS) neuropeptide Y (NPY); in fact, a single intracerebroventricular (icv) administration of NPY in lean fasted rats elevates hepatic VLDL-TG secretion and does so, in large part, via signaling through the CNS NPY Y1 receptor. Thus, our overarching hypothesis is that elevated CNS NPY action contributes to dyslipidemia by activating central circuits that modulate liver lipid metabolism.
Methods:
Chow-fed Zucker fatty (ZF) rats were pair-fed by matching their caloric intake to that of lean controls and effects on body weight, plasma TG, and liver content of TG and phospholipid (PL) were compared to ad-libitum (ad-lib) fed ZF rats. Additionally, lean 4-h fasted rats with intact or disrupted hepatic sympathetic innervation were treated with icv NPY or NPY Y1 receptor agonist to identify novel hepatic mechanisms by which NPY promotes VLDL particle maturation and secretion.
Results:
Manipulation of plasma TG levels in obese ZF rats, through pair-feeding had no effect on liver TG content; however, hepatic PL content was substantially reduced and was tightly correlated with plasma TG levels. Treatment with icv NPY or a selective NPY Y1 receptor agonist in lean fasted rats robustly activated key hepatic regulatory proteins, stearoyl-CoA desaturase-1 (SCD-1), ADP-ribosylation factor-1 (ARF-1), and lipin-1, known to be involved in remodeling liver PL into TG for VLDL maturation and secretion. Lastly, we show that the effects of CNS NPY on key liporegulatory proteins are attenuated by hepatic sympathetic denervation.
Conclusions:
These data support a model in which CNS NPY modulates mediators of hepatic PL remodeling and VLDL maturation to stimulate VLDL-TG secretion that is dependent on the Y1 receptor and sympathetic signaling to the liver.
Recently, Neuropeptide Y (NPY) and Y1 receptor (Y1R) were found to be expressed and synthesized in adipose tissue. This study aimed to compare NPY and Y1R mRNA expression in subcutaneous and visceral fat tissues as well as serum NPY in normal weight and obese humans and their correlations with clinical parameters and peripheral metabolic factors. We demonstrate that NPY mRNA expression was higher in obese than in normal weight humans (p<0.05) in both subcutaneous and visceral adipose tissues and was significantly greater in visceral when compared with subcutaneous fat in overall subjects (p<0.01), obese (p<0.05) and normal weight humans (p<0.05). Y1R mRNA expression was higher in obese than normal weight subjects in visceral (p<0.01) but not in subcutaneous adipose tissue and was statistically greater in subcutaneous when compared to visceral adipose tissues in obese (p<0.05) and overall subjects (p<0.05). Serum NPY was higher in obese than normal weight groups (p<0.05). Obese subjects showed significantly greater levels of systolic blood pressure (SBP) (P<0.01), diastolic blood pressure (DBP) (P<0.05), plasma insulin (P<0.05) and HOMA-IR (P<0.05) when compared with normal weight subjects. Additionally, Y1R mRNA expression in visceral adipose tissue was positively correlated with body weight (R=0.586), BMI (R=0.611), waist (R=0.474) and hip (R=0.483) circumferences, insulin levels (R=0.539), and HOMA-IR (0.480). As the result, Y1R expression in visceral adipose tissue might be an indicator of increased risk of metabolic syndrome. Further studies about blocking specific Y1R may propose strategies for risk reduction in metabolic syndrome and prevention or treatment of obesity.
Neuropeptide Y (NPY) and peptide YY (PYY) are regulatory peptides that have considerable sequence homology with pancreatic polypeptide. Because (a) NPY has been shown to be colocalized with noradrenaline in peripheral as well as central catecholaminergic neurons, and (b) alpha 2-adrenergic receptors of adipocytes play a major role in the regulation of lipolysis, we investigated the effect of NPY and PYY on isolated fat cells. In human fat cells NPY and PYY promoted a dose-dependent inhibition of lipolysis elicited by 2 micrograms/ml adenosine deaminase (removal of adenosine) whatever the lipolytic index used (glycerol or nonesterified fatty acids). In dog fat cells NPY and PYY inhibited adenosine deaminase-, isoproterenol- and forskolin-induced lipolysis. In humans and dogs the effects of NPY or PYY were abolished by treatment of cells with Bordetella pertussis toxin, clearly indicating the involvement of a Gi protein in the antilipolytic effects. This study indicates that, in addition to alpha 2-adrenergic agonists, NPY and PYY are also involved in the regulation of lipolysis in human and dog adipose tissue as powerful antilipolytic agents. Further studies are needed to characterize the pharmacological nature of the receptor mediating the inhibitory effect of NPY and PYY in fat cells.
Daily human energy requirements calculated from separate components of energy expenditure are inaccurate and usually in poor agreement with measured energy intakes. Measurement of energy expenditure over periods of 24 h or longer is needed to determine more accurately rates of daily energy expenditure in humans. We provide a detailed description of a human respiratory chamber and methods used to determine rates of energy expenditure over 24-h periods in 177 subjects. The results show that: fat-free mass (FFM) as estimated by densitometry is the best available determinant of 24-h energy expenditures (24EE) and explains 81% of the variance observed between individuals (24EE [kcal/d] = 597 + 26.5 FFM); 24EE in an individual is very reproducible (coefficient of variation = 2.4%); and even when adjusted for differences in FFM, there is still considerable interperson variability of the daily energy expenditure. A large portion of the variability of 24EE among individuals, independent of differences in body size, was due to variability in the degree of spontaneous physical activity, i.e., "fidgeting," which accounted for 100-800 kcal/d in these subjects.
No current treatment for obesity reliably sustains weight loss, perhaps because compensatory metabolic processes resist the maintenance of the altered body weight. We examined the effects of experimental perturbations of body weight on energy expenditure to determine whether they lead to metabolic changes and whether obese subjects and those who have never been obese respond similarly.
We repeatedly measured 24-hour total energy expenditure, resting and nonresting energy expenditure, and the thermic effect of feeding in 18 obese subjects and 23 subjects who had never been obese. The subjects were studied at their usual body weight and after losing 10 to 20 percent of their body weight by underfeeding or gaining 10 percent by overfeeding.
Maintenance of a body weight at a level 10 percent or more below the initial weight was associated with a mean (+/- SD) reduction in total energy expenditure of 6 +/- 3 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 5 kcal per kilogram per day in the obese subjects (P < 0.001). Resting energy expenditure and nonresting energy expenditure each decreased 3 to 4 kcal per kilogram of fat-free mass per day in both groups of subjects. Maintenance of body weight at a level 10 percent above the usual weight was associated with an increase in total energy expenditure of 9 +/- 7 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 4 kcal per kilogram per day in the obese subjects (P < 0.001). The thermic effect of feeding and nonresting energy expenditure increased by approximately 1 to 2 and 8 to 9 kcal per kilogram of fat-free mass per day, respectively, after weight gain. These changes in energy expenditure were not related to the degree of adiposity or the sex of the subjects.
Maintenance of a reduced or elevated body weight is associated with compensatory changes in energy expenditure, which oppose the maintenance of a body weight that is different from the usual weight. These compensatory changes may account for the poor long-term efficacy of treatments for obesity.
The present literature characterising the pharmacology of the hypothalamic receptor(s) responsible for mediating the hyperphagic effect of NPY is fragmented and far from comprehensive. Different groups of workers have studied NPY, its fragments and substituted analogues in the rat by administering these substances into the lateral or third brain ventricle or via direct administration into discrete hypothalamic nuclei [ 1-51. Much of this work has been performed using single doses of agonists and has utilised the porcine rather than the native series of neuropeptides. In the present work, we have performed a systematic analysis of the dose-feeding response relationship for hNPY and a number of its fragments and derivatives in order to define their relative potency and intrinsic activity for this action. These agents or vehicle were administered icv, during the light phase, to free-fed conscious male Sprague Dawley rats with an implanted lateral ventricular cannula. Food intake was measured hourly for 4 hours. Results were analysed by ANOVA using the 4 hour data.
The potential blockade of the neuropeptide Y (NPY) Y1 receptor agonist [Leu31,Pro34]NPY-induced modulation of the characteristics of alpha 2-adrenoceptor agonist [3H]p-aminoclonidine binding sites by a selective non-peptide NPY Y1 receptor antagonist BIBP3226, was studied in the nucleus tractus solitarii of the rat by means of quantitative receptor autoradiography. [Leu31,Pro34]NPY at a concentration of 10 nM significantly increased the Kd value of [3H]p-aminoclonidine binding sites in the nucleus tractus solitarii without influencing the Bmax, suggesting the existence of an antagonistic modulation by NPY Y1 receptors of alpha 2-adrenoceptors in the nucleus tractus solitarii. BIBP3226 at 100 nM fully blocked the [Leu31,Pro34]NPY-induced increase in Kd of the [3H]p-aminoclonidine binding sites. The present results therefore provide evidence, by use of a NPY Y1 receptor antagonist, for the existence of a NPY Y1/alpha 2 receptor interaction in the nucleus tractus solitarii.
During development, gene expression of medium-chain acyl-CoA dehydrogenase (MCAD), a nuclear-encoded mitochondrial enzyme that catalyses the first step of medium-chain fatty acid beta-oxidation, is highly regulated in tissues in accordance with fatty acid utilization, but the factors involved in this regulation are largely unknown. To investigate a possible role of thyroid hormones, rat pups were made hypothyroid by the administration of propylthiouracyl to the mother from day 12 of gestation, and their kidneys, heart and liver were removed on postnatal day 16 to determine MCAD mRNA abundance, protein level and enzyme activity. Similar experiments were run in 3,3',5-tri-iodothyronine (T3)-replaced hypothyroid (1 microg of T3/100 g body weight from postnatal day 5 to 15) and euthyroid pups. Hypothyroidism led to an increase in MCAD mRNA abundance in kidney and a decrease in abundance in heart, but had no effect in liver. The protein levels and enzyme activity were lowered in hypothyroid heart and kidney, suggesting that hypothyroidism affects post-transcriptional steps of gene expression in the kidney. All the effects of hypothyroidism were completely reversed in both heart and kidney by T3 replacement. Injection of a single T3 dose into 16-day-old euthyroid rats also led to tissue-specific changes in mRNA abundance. Nuclear run-on assays performed from hypothyroid and hypothyroid plus T3 rats showed that T3 stimulates MCAD gene transcription in heart and represses it in the kidney. These results indicate that the postnatal rise in circulating T3 is essential to the developmental regulation of the MCAD gene in vivo.
Neuropeptide Y in the hypothalamus is a potent physiological stimulator of feeding, and may contribute to the characteristic metabolic defects of obesity when hypothalamic levels remain chronically elevated. Since corticosterone and insulin are important regulators of fuel metabolism, the longitudinal effects of chronic (6 days) intracerebroventricular infusion of neuropeptide Y in normal rats on the hypothalamo-pituitary-adrenal axis and on insulin secretion were studied. Neuropeptide Y-infused rats were either allowed to eat ad libitum, or were pair-fed with normophagic control rats. Neuropeptide Y increased the basal plasma concentrations of adrenocorticotropic hormone and corticosterone during the first 2 days of its intracerebroventricular infusion and increased cold stress-induced plasma adrenocorticotropic hormone concentrations. After 4-6 days of central neuropeptide Y infusion, however, basal plasma adrenocorticotropic hormone and corticosterone concentrations were no different from control values (except in ad libitum-fed rats in which corticosteronaemia remained elevated), they were unaffected by the stress of cold exposure, and the hypothalamic content of corticotropin-releasing factor immunoreactivity was significantly decreased. A state of hyperinsulinaemia was present throughout the 6 days of intracerebroventricular neuropeptide Y infusion, being more marked in the ad libitum-fed than in the pair-fed group. The proportions of insulin, proinsulin, and conversion intermediates in plasma and pancreas were unchanged. Hyperinsulinaemia of the pair-fed neuropeptide Y-infused rats was accompanied by muscle insulin resistance and white adipose tissue insulin hyperresponsiveness, as assessed by the in vivo uptake of 2-deoxyglucose. Finally, bilateral subdiaphragmatic vagotomy prevented both the basal and the marked glucose-induced hyperinsulinaemia of animals chronically infused with neuropeptide Y, demonstrating that central neuropeptide Y-induced hyperinsulinaemia is mediated by the parasympathetic nervous system.
Humans show considerable interindividual variation in susceptibility to weight gain in response to overeating. The physiological
basis of this variation was investigated by measuring changes in energy storage and expenditure in 16 nonobese volunteers
who were fed 1000 kilocalories per day in excess of weight-maintenance requirements for 8 weeks. Two-thirds of the increases
in total daily energy expenditure was due to increased nonexercise activity thermogenesis (NEAT), which is associated with
fidgeting, maintenance of posture, and other physical activities of daily life. Changes in NEAT accounted for the 10-fold
differences in fat storage that occurred and directly predicted resistance to fat gain with overfeeding (correlation coefficient
= 0.77, probability < 0.001). These results suggest that as humans overeat, activation of NEAT dissipates excess energy to
preserve leanness and that failure to activate NEAT may result in ready fat gain.
The three peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure known as the PP-fold. There are four known human G-protein coupled receptors for the PP-fold peptides, namely Y1, Y2, Y4, and Y5, each of them being able to bind at least two of the three endogenous ligands. All three peptides are found in the circulation acting as hormones. Although NPY is only released from neurons, PYY and PP are primarily found in endocrine cells in the gut, where they exert such effects as inhibition of gall bladder secretion, gut motility, and pancreatic secretion. However, when PYY is administered in an experimental setting to animals, cloned receptors, or tissue preparations, it can mimic the effects of NPY in essentially all studies, making it difficult to study the effects of PP-fold peptides and to delineate what receptor and peptide accounts for a particular effect. Initial studies with transgenic animals confirmed the well-established action of NPY on metabolism, food-intake, vascular systems, memory, mood, neuronal excitability, and reproduction. More recently, using transgenic techniques and novel antagonists for the Y1, Y2, and Y5 receptors, NPY has been found to be a key player in the regulation of ethanol consumption and neuronal development.
Objectives. The effects of menopause transition on metabolic and cardiovascular disease risk in women are unclear. It is unknown whether estrogen deficiency, aging, or a combination of both factors are independent contributors to a worsening health profile in women. We considered the effects of menopause transition and hormone replacement therapy on body composition, regional body fat, energy expenditure, and insulin sensitivity. Methods. A brief review of current literature that has considered the role of menopause transition and hormone replacement therapy on body composition, energy expenditure, and insulin sensitivity with an emphasis on longitudinal investigations. Results. Preliminary evidence suggests that natural menopause is associated with reduced energy expenditure during rest and physical activity, an accelerated loss of fat-free mass, and increased central adiposity and fasting insulin levels. Hormone replacement therapy has been shown to attenuate these changes. Longitudinal and longer intervention studies are needed to confirm these initial findings. Conclusions. Menopause transition may represent a risky period in a woman's life, 'triggering' adverse metabolic and cardiovascular processes that predispose women to a greater incidence of obesity-related comorbidities. Dietary, exercise, and hormonal interventions specifically targeted at premenopausal women may help mitigate the worsening cardiovascular and metabolic risk profile associated with menopause.
Neuropeptide Y (NPY) is a 36-amino-acid neurotransmitter which is widely distributed throughout the central and peripheral nervous system1. NPY involvement has been suggested in various physiological responses including cardiovascular homeostasis2 and the hypothalamic control of food intake3. At least six subtypes of NPY receptors have been described4,5. Because of the lack of selective antagonists, the specific role of each receptor subtype has been difficult to establish. Here we describe mice deficient for the expression of the Y1 receptor subtype. Homozygous mutant mice demonstrate a complete absence of blood pressure response to NPY, whereas they retain normal response to other vasoconstrictors. Daily food intake, as well as NPY-stimulated feeding, are only slightly diminished, whereas fast-induced refeeding is markedly reduced. Adult mice lacking the NPY Y1 receptor are characterized by increased body fat with no change in protein content. The higher energetic efficiency of mutant mice might result, in part, from the lower metabolic rate measured during the active period, associated with reduced locomotor activity. These results demonstrate the importance of NPY Y1 receptors in NPY-mediated cardiovascular response and in the regulation of body weight through central control of energy expenditure. In addition, these data are also indicative of a role for the Y1 receptor in the control of food intake.
Corticotropin releasing hormone (CRH) acts on the central nervous system to alter energy balance and influence both food intake and sympathetically-mediated thermogenesis. CRH is also reported to inhibit food intake in several models of hyperphagia including neuropeptide Y (NPY)-induced eating. The recently identified CRH-related peptide, urocortin (UCN), also binds with high affinity to CRH receptor subtypes and decreases food intake in food-deprived and non-deprived rats. The present experiment characterized further the feeding and metabolic effects of UCN by examining its impact after direct injections into the paraventricular nucleus (PVN) of the hypothalamus. In feeding tests (n=8), UCN (50–200 pmol) was injected into the PVN at the onset of the dark cycle and food intake was measured 1, 2 and 4 h postinjection. In separate rats (n=8), the metabolic effects of UCN were monitored using an open circuit calorimeter which measured oxygen consumption (Vo2) and carbon dioxide production (Vco2). Respiratory quotient (RQ) was calculated as Vco2/Vo2. UCN suppressed feeding at all times studied and reliably decreased RQ within 30 min of infusion. Additional work examined the effect of UCN (50–100 pmol) pretreatment on the feeding and metabolic effects of NPY. NPY, injected at the start of the dark period, reliably increased 2 h food intake. This effect was blocked by PVN UCN administration. Similarly, UCN blocked the increase in RQ elicited by NPY alone. These results suggest that UCN-sensitive mechanisms within the PVN may modulate food intake and energy substrate utilization, possibly through an interaction with hypothalamic NPY.
Neuropeptide Y (NPY) is known to induce robust feeding through the action of NPY receptors in the hypothalamus. Among the subtypes of NPY receptors, Y1 receptors may play a key role in feeding regulation. In the present study, we demonstrated that a novel Y1 antagonist, J-104870, shows high selectivity and potency for the Y1 receptor with an anorexigenic effect on NPY-mediated feeding. J-104870 displaced [125I]peptide YY (PYY) binding to cloned human and rat Y1 receptors with Ki values of 0.29 and 0.54 nM, respectively, and inhibited the NPY (10 nM)-induced increase in intracellular calcium levels (IC50 = 3.2 nM) in cells expressing human Y1 receptors. In contrast, J-104870 showed low affinities for human Y2 (Ki > 10 μM), Y4 (Ki > 10 μM), and Y5 receptors (Ki = 6 μM). In rat hypothalamic membranes, J-104870 also completely displaced the binding of [125I]1229U91, which is known to bind to the typical Y1 receptor, with a high affinity (Ki = 2.0 nM). Intracerebroventricular (ICV) injection of J-104870 (200 μg) significantly suppressed NPY (5 μg)-induced feeding in satiated Sprague–Dawley rats by 74%. Furthermore, ICV and oral administration of J-104870 (200 μg and 100 mg/kg, respectively) significantly suppressed spontaneous food intake in Zucker fatty rats. These findings suggested that J-104870 is a selective and potent nonpeptide Y1 antagonist with oral bioavailability and brain penetrability. In addition, the anorexigenic effect of J-104870 clearly revealed the participation of the Y1 receptor in NPY-mediated feeding regulation. The potent and orally active Y1 antagonist J-104970 is a useful tool for elucidating the physiological roles of NPY in obesity.
Neuropeptide Y (NPY), a putative neurotransmitter abundant in the brain, has recently been shown to act within the hypothalamus, inducing a powerful eating response and a specific appetite for carbohydrates. In the present study, NPY (235 pmol) injected bilaterally in the paraventricular nucleus three times a day for 10 days caused approximately a two-fold increase in daily food intake, a six-fold increase in the rate of body weight gain and a three-fold increase in the body fat of female rats. Subsequently, the food intake and body weight of these subjects decreased precipitously, reaching control levels 20 days postinjection. These findings, demonstrating that exogenous NPY is capable of overriding mechanisms of satiety and body weight control, suggest that disturbances in NPY function may play a role in some disorders of eating behavior and body weight regulation.
Labelle, M., Y. Boulanger, A. Fournier, S. St.-Pierre and R. Savard. Tissue-specific regulation of fat cell lipolysis by Npy in 6-Ohda-treated rats. Peptides 18(6) 801–808, 1997.—The effects of neuropeptide Y (NPY), peptide YY (PYY), [Leu31, Pro34]NPY, and NPY(13–36) on adipocyte lipolysis have been studied in subcutaneous (inguinal) and visceral (parametrial) rat adipose tissues. A 48-h fasting period and chemical sympathectomy were used to evaluate the regulation of Y1 and Y2 pathways in rat adipocytes. NPY, PYY, and [Leu31, Pro34]NPY significantly inhibited fat cell lipolysis by about 25% in both tissues (p ≤ 0.05). This inhibition was achieved mainly through the Y1 pathway. No significant response to NPY(13–36) was observed, suggesting a lack of involvement of the Y2 pathway in the antilipolytic effect of NPY and PYY. The 48-h fasting period led to the loss of the Y1 inhibitory effect previously observed in control rats. On the other hand, the chemical sympathectomy induced a 35% increase of fat cell lipolysis (p ≤ 0.05). The latter involved the Y2 pathway as stimulated by NPY(13–36), and was observed in the parametrial tissue exclusively. These results suggest that: a) rat Y receptors reported to exhibit Gi responses can also express Gs-like responses, and b) visceral and subcutaneous adipose tissues exhibit specific regulation of fat cell lipolysis.
Medium chain acyl-CoA dehydrogenase (MCAD) catalyzes the first reaction of the beta-oxidation cycle for 4-10-carbon fatty acids. MCAD deficiency is one of the most frequent inborn metabolic disorders in populations of northwestern European origin. In the compilation of data from a worldwide study of 172 unrelated patients each representing an independent pedigree, a total of 8 different mutations have been identified. Among them, a single prevalent mutation, 985A-->G, was found in 90% of 344 variant alleles. 985A-->G causes glutamate substitution for lysine-304 in the mature MCAD subunit, which causes impairment of tetramer assembly and instability of the protein. Three of 7 rarer mutations have been identified in a few unrelated patients, while the remaining 4 have each been found in only a single pedigree. In addition to tabulating the mutations, the acyl-CoA dehydrogenase gene family, the structure of the MCAD gene and the evolution of 985A-->G mutation are briefly discussed.
The distribution of nerve fibers displaying neuropeptide Y immunoreactivity in relationship to the catecholaminergic innervation of rat, guinea pig, and rabbit liver was investigated by single- and double-label immunofluorescence methods. In all three species, neuropeptide Y-immunoreactive fibers are prominent in association with the vasculature, biliary pathway, and stromal compartment. The neuropeptide Y innervation of the parenchyma, on the other hand, differs among the three species in term of density. It is quite sparse in the rat and rabbit, particularly in the former species. In the guinea pig liver, numerous single, varicose neuropeptide Y-containing nerve fibers innervate the hepatic parenchyma; often, thin processes surround single hepatocytes and lie close to sinusoids. The immunoreactive pattern of tyrosine hydroxylase, a marker for catecholaminergic neurons and fibers, is comparable to that of neuropeptide Y. Most neuropeptide Y-containing nerve fibers also contain tyrosine hydroxylase immunoreactivity, in all three species, with the exception of the rabbit parenchyma, where a substantial proportion of catecholaminergic fibers lack immunoreactivity for neuropeptide Y. Finally, systemic administration of the sympathetic neurotoxin, 6-hydroxydopamine, in rats and guinea pigs resulted in virtually complete elimination of both neuropeptide Y- and tyrosine hydroxylase-immunoreactive fibers. These findings are consistent with the hypothesis that neuropeptide Y-containing nerve fibers form a subpopulation of the sympathetic innervation of the mammalian liver, which is likely to originate from prevertebral sympathetic ganglia.
To investigate the effects of neuropeptide Y (NPY) on sympathetic nerve activity to interscapular brown adipose tissue (IBAT), we injected NPY into the third cerebroventricle (icv), medial preoptic area (MPOA), anterior hypothalamic area (AHA), paraventricular hypothalamic nucleus (PVN), ventromedial hypothalamic nucleus (VMN), and lateral hypothalamic area (LHA) of anesthetized rats. Multiunit discharges from sympathetic nerves to IBAT were recorded electrophysiologically. The icv injection of NPY suppressed sympathetic nerve activity in a dose-dependent manner, followed by a gradual recovery. The microinjection of NPY (25 pmol) unilaterally into the PVN also significantly suppressed the sympathetic nerve activity to IBAT. In contrast, microinjection of NPY into the MPOA significantly increased the sympathetic nerve activity. The injection of saline into either the PVN or MPOA had no significant effect on sympathetic nerve activity. The microinjection of NPY (25 pmol) into the AHA, VMN, or LHA did not change sympathetic nerve activity to IBAT. We conclude that central administration of NPY affects the sympathetic nerve activity to IBAT and that the suppressive effect of NPY, which may act in part through the PVN, is dominant to the stimulatory effect. The result is consistent with the hypothesis that NPY is a neurochemical modulator of the sympathetic nervous system which controls energy expenditure in IBAT.
Our objective was to find out if central injection of neuropeptide Y (NPY) would alter brown fat thermogenesis and white fat lipoprotein lipase activity. The following three groups of Sprague-Dawley rats received five injections over 24 h into the right lateral ventricle: 1) NPY (5 micrograms/injection) and ad libitum food; 2) NPY (5 micrograms/injection) and food restricted to control intake; 3) saline injection and ad libitum food. The NPY ad libitum-fed group consumed more food than the saline controls or NPY food-restricted animals. Brown fat thermogenic activity, assessed by GDP binding, was decreased relative to saline controls in both NPY-treated groups. White fat lipoprotein lipase activity was greatly increased in both NPY treatment groups compared with saline controls. The NPY effects on brown and white fat were not explained by measures of serum insulin, glucagon, glucose, or other metabolites. In a follow-up experiment, we asked whether food was necessary for expression of the NPY effects. Brown fat mitochondrial GDP binding indicated NPY effect even when no food was ingested. We conclude that intracerebroventricular administration of NPY promotes white fat lipid storage and decreases brown fat thermogenesis in addition to its known effect of stimulating food intake.
The effects of physiological hyperinsulinemia (approximately 75 mU/l) on glucose storage, oxidation, and glycolysis in skeletal muscle were assessed with euglycemic clamps performed in seven healthy volunteers, in conjunction with leg balance for glucose, lactate, alanine, O2, and CO2. Infusion of insulin increased leg glucose uptake, storage, and oxidation but did not alter net release of lactate and alanine. The respiratory quotient (RQ) across the leg increased from a basal value of 0.74 +/- 0.02 to 0.99 +/- 0.02 during hyperinsulinemia. Under conditions of insulin stimulation, 49 +/- 5% of leg glucose uptake was stored, 37 +/- 4% was oxidized, and 14 +/- 2% was released as lactate and alanine. We conclude that during physiological hyperinsulinemia and euglycemia 1) skeletal muscle lipid oxidation is nearly entirely suppressed and glucose becomes the primary oxidative substrate of muscle, 2) glucose storage and oxidation are the major pathways of skeletal muscle glucose metabolism and are quantitatively similar at physiological insulin levels, and 3) the majority of insulin-stimulated glycolysis is oxidized, with only a small portion released as lactate or alanine.
The metabolic effects of single injections of neuropeptide Y (NPY) into the paraventricular hypothalamus were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. Over the dose range of 10-156 pmol NPY had large effects on respiratory quotient (RQ) while having no effect on energy expenditure or locomotor activity. The effects of NPY on RQ were unusual both in respect to their dose-response and time-dose-response characteristics. The lowest dose (10 pmol) produced a very low latency reduction in RQ which indicates a decreased utilization of carbohydrates as an energy substrate. The next higher dose (20 pmol) had no effect, whereas the next three doses (39, 78 and 156 pmol) produced increases in RQ which indicate an increased utilization of carbohydrates as an energy substrate. Surprisingly, the latencies of the increased RQs were dose-dependent over the range of 30 min to 20 h with the highest dose producing the longest latency effect. The finding of a positive relation of dose to response latency over a time range of from a few minutes to 20 h is unprecedented and appears to represent a neuromodulatory effect of NPY that acts in concert with its neurotransmitter effects. These data highlight the central role of NPY in modulating energy substrate utilization and indicate the importance of elucidating time-dose-response relationships when investigating the effects of NPY.
Indirect calorimetry is the method by which the type and rate of substrate utilization, and energy metabolism are estimated in vivo starting from gas exchange measurements. This technique provides unique information, is noninvasive, and can be advantageously combined with other experimental methods to investigate numerous aspects of nutrient assimilation, thermogenesis, the energetics of physical exercise, and the pathogenesis of metabolic diseases. Since its use as a research tool in metabolism is growing, the theoretical bases of indirect calorimetry are here reviewed in a detailed and orderly fashion. Special cases, such as the occurrence of net lipid synthesis or gluconeogenesis, are formally considered with derivation of explicit stoichiometric equations. The limitations of indirect calorimetry, both theoretical and technical, are discussed in the context of circumstances of clinical interest in metabolism.
The requirement for carnitine and the malonyl-CoA sensitivity of carnitine palmitoyl-transferase I (EC 2.3.1.21) were measured in isolated mitochondria from eight tissues of animal or human origin using fixed concentrations of palmitoyl-CoA (50 microM) and albumin (147 microM). The Km for carnitine spanned a 20-fold range, rising from about 35 microM in adult rat and human foetal liver to 700 microM in dog heart. Intermediate values of increasing magnitude were found for rat heart, guinea pig liver and skeletal muscle of rat, dog and man. Conversely, the concentration of malonyl-CoA required for 50% suppression of enzyme activity fell from the region of 2-3 microM in human and rat liver to only 20 nM in tissues displaying the highest Km for carnitine. Thus, the requirement for carnitine and sensitivity to malonyl-CoA appeared to be inversely related. The Km of carnitine palmitoyltransferase I for palmitoyl-CoA was similar in tissues showing large differences in requirement for carnitine. Other experiments established that, in addition to liver, heart and skeletal muscle of fed rats contain significant quantities of malonyl-CoA and that in all three tissues the level falls with starvation. Although its intracellular location in heart and skeletal muscle is not known, the possibility is raised that malonyl-CoA (or a related compound) could, under certain circumstances, interact with carnitine palmitoyltransferase I in non-hepatic tissues and thereby exert control over long chain fatty acid oxidation.
This paper reviews the assumptions involved in calculating rates of carbohydrate and fat oxidation from measurements of O2 consumption, CO2 production, and urinary nitrogen excretion. It is shown that erroneous results are obtained in the presence of metabolic processes such as lipogenesis and gluconeogenesis. The apparent rates calculated under these conditions can, however, be interpreted as net rates of "utilization." Thus the apparent rate of carbohydrate oxidation is the sum of the rates of utilization for oxidation and for lipogenesis minus the rate at which carbohydrate is formed from amino acids. The apparent rate of fat oxidation is the difference between the rates of oxidation and synthesis from carbohydrate, so that the apparently negative rates encountered in patients infused with glucose do quantitatively represent net rates of synthesis. Other processes such as synthesis of ketone bodies or lactate at rates greater than their utilization can also disturb the calculations, but the magnitude of the effect can be estimated from appropriate measurements. Methods of correcting the observed gaseous exchange in these circumstances are given.
The present study investigated the effects of neuropeptide Y (NPY) on food intake and body temperature (Tbo) in free-feeding unrestrained rats following injection into the medial hypothalamic paraventricular nucleus (PVN) or the lateral perifornical hypothalamus (PFH). NPY (78-235 pmol) or saline was infused unilaterally into the PVN or PFH in a volume of 0.4 microliter and simultaneous measures of food intake and Tbo were taken every 30 min for 3 h. Results indicated that NPY evoked changes in eating behavior and Tbo that were dependent upon the site of hypothalamic injection. Although PVN and PFH administration of NPY both increased food intake dose dependently within 30 min of treatment, PFH NPY-injected rats (n = 9) showed a stronger behavioral response compared to rats (n = 9) receiving NPY injections into the PVN. In PVN-treated rats, however, the increased eating was associated with a significant decline in Tbo evident within the first 30-min test interval. A mean maximal decline of 0.92 +/- 0.26 degree C occurred within 90 min of PVN treatment of the highest dose, which produced a reduction in Tbo that was maintained for 2.5 h. In contrast, NPY infusion into the PFH failed to reliably alter Tbo at any of the doses tested. These findings are consistent with evidence that NPY in the PVN and PFH may have distinct functions and suggest that although PFH NPY acts to stimulate a robust and relatively specific ingestive response, PVN NPY may participate in the complex integrative mechanisms responsible for the simultaneous regulation of feeding, thermoregulatory, and metabolic processes.
Neuropeptide Y (NPY) is one of the most abundant peptide transmitters in the mammalian brain. In the periphery it is costored and coreleased with norepinephrine from sympathetic nerve terminals. However, the physiological functions of this peptide remain unclear because of the absence of specific high-affinity receptor antagonists. Three potent NPY receptor antagonists were synthesized and tested for their biological activity in in vitro, ex vivo, and in vivo functional assays. We describe here the effects of these antagonists inhibiting specific radiolabeled NPY binding at Y1 and Y2 receptors and antagonizing the effects of NPY in human erythroleukemia cell intracellular calcium mobilization perfusion pressure in the isolated rat kidney, and mean arterial blood pressure in anesthetized rats.
A method of gene targeting that allows the inducible inactivation of a target gene in mice is presented. The method uses an
interferon-responsive promoter to control the expression of Cre recombinase. Here, Cre was used to delete a segment of the
DNA polymerase beta gene flanked by IoxP recombinase recognition sites. Deletion was complete in liver and nearly complete
in lymphocytes within a few days, whereas partial deletion was obtained in other tissues. This method can be used for the
inducible inactivation of any other gene in vivo.
Lipolysis is stimulated by different hormones, depending on the species, but is also regulated by antilipolytic modulators, such as catecholamines (alpha 2-agonists), neuropeptide Y (NPY), adenosine, and prostaglandin E1 (PGE1), for which species-specific variations are poorly described. Comparison of the efficiency of these antilipolytic systems showed that PGE1 or phenylisopropyladenosine was able to totally inhibit lipolysis activation in nine mammalian species. However, the antilipolytic responses to clonidine or UK-14304 were fully developed in hamster and rabbit but blunted in the adipocytes of jerboa, rat, guinea pig, garden dormouse, and dormouse. A powerful antilipolytic effect of NPY was found only in the garden dormouse. Only human and dog adipocytes exhibited antilipolytic responses to alpha 2-adrenergic and NPY stimulation. These observations were explained by differences in alpha 2-adrenergic and NPY/peptide YY receptor number. Thus, inhibitory regulation of lipolysis in white adipocytes seems to be composed of two systems: a constitutive one that is related to paracrine mediators (adenosine, prostaglandins) and a regulatory one including neuroendocrine messengers such as catecholamines and NPY.
Intracerebroventricular injection of neuropeptide Y (NPY) has two effects on energy metabolism in addition to increased feeding: decreased brown fat thermogenesis and increased white fat lipoprotein lipase (LPL) enzymatic activity. We hypothesized that the paraventricular nucleus (PVN) of the hypothalamus is the controlling neural site for these responses. We further hypothesized that NPY stimulation at PVN would reduce gene expression for the critical brown fat thermogenic protein, uncoupling protein (UCP), and increase gene expression for the key white fat storage enzyme, LPL. In the first experiment, three groups of rats received injections every 6 h for 24 h (5 injections total) into the PVN:1) NPY (1 micrograms/1 microliters injection) and ad libitum food; 2) NPY (1 micrograms/1 microliters injection) and food restricted to control intake; 3) saline injection (1 microliter) and ad libitum food. Both NPY-treated groups showed significant reductions (P < 0.05) in brown fat UCP mRNA levels and marked stimulation of LPL mRNA levels relative to controls. In the second experiment, four groups of seven rats had NPY injected into the PVN:0 (vehicle control); 0.1 microgram; 0.5 microgram; and 1 microgram. Injections were made every 6 h for 24 h. There was a dose-related reduction in UCP mRNA produced by the NPY treatment. NPY treatment increased LPL mRNA, but a smooth dosing effect was not evident. The observation that NPY in the PVN can coordinate more than one component of energy metabolism is significant when considered with many reports of responsiveness of NPY activity in the arcuate nucleus-PVN neural circuit to perturbations of energy balance such as fasting and feeding, diabetes, and genetic obesity.(ABSTRACT TRUNCATED AT 250 WORDS)
1. In order to characterize the thermoregulatory actions of brain neuropeptide Y (NPY), the effects of intra-third ventricular (I3V) injection of NPY on temperatures of colon (Tco), brown adipose tissue (TBAT) and tail skin (Ts) were observed at ambient temperatures (Ta) of 19 and 8 degrees C. 2. The injection of NPY in a dose of 8 mcg/100 g body wt evoked a fall of Tco by about 2 degrees C in both neutral and cold environments. NPY (4 and 8 mcg/100 g body wt) induced dose-dependent Tco falls in rats at thermoneutral environment. The thermolytic reactions induced by I3V administration of NPY were associated with a fall in TBAT but no changes in Is were observed. 3. The results suggest that NPY may mediate hypothermic response in neutral and cold environments mainly by its effects on the brown adipose tissues in the rat.
Given that several genetically obese rodents characterized by hyperphagia, hyperinsulinemia, and insulin resistance have increased hypothalamic neuropeptide Y (NPY) mRNA and peptide content, the impact of NPY administered intracerebroventricularly (i.c.v.) for 7 days to normal, awake rats was investigated. NPY produced marked hyperphagia, increased body weight gain, increased basal insulinemia, and, more importantly, a much greater insulin response to meal feeding than that of saline-infused controls. NPY administration also resulted in a pronounced increase in the in vivo insulin-stimulated glucose uptake by adipose tissue but in a marked decrease in uptake by eight different muscle types. Increased insulin responsiveness of the glucose transport process by adipose tissue was accompanied by increases in both GLUT4 mRNA and protein levels. In contrast, the decreased insulin responsiveness of glucose uptake in muscles from NPY-administered rats was not related to GLUT4 expression. We conclude that i.c.v. NPY administration to normal rats produces a hormonal-metabolic situation that is similar to that reported in the dynamic phase of the genetic obesity of the fa/fa strain. Thus, NPY could be of primary importance in the establishment of obesity syndromes with incipient insulin resistance.
To determine whether the liver or gut releases neuropeptide Y (NPY) from their sympathetic nerves, we performed bilateral thoracic sympathetic nerve stimulation (BTSNS) in halothane-anesthetized dogs and calculated gut and liver NPY spillover. BTSNS markedly increased hepatic NPY spillover (delta = +32 +/- 8 ng/min) and arterial NPY concentration (delta = +220 +/- 56 pg/ml), despite no effect on gut NPY spillover (delta = +8 +/- 7 ng/min). To determine the liver's contribution to this increase of circulating NPY, hepatic nerves were selectively stimulated (HNS). Liver NPY spillover increased markedly (delta = +114 +/- 42 ng/min, P < 0.025) during HNS, causing a large increase of arterial NPY (delta = +586 +/- 237 pg/ml, P < 0.025). Using this ratio of liver spillover to arterial increments of NPY, we calculated that the liver makes a major contribution (70%) to circulating NPY levels during BTSNS. The predominant form of canine NPY coeluted with synthetic [Met17]NPY and the minor form of canine NPY coeluted with the oxidized form of [Met17]NPY on high-performance liquid chromatography. We therefore conclude that dog NPY is likely [Met17]NPY and that the liver, rather than the gut, is a major source of circulating NPY during sympathetic nerve stimulation and perhaps stress.
Chronic intracerebroventricular (icv) administration of neuropeptide-Y (NPY; 10 micrograms/day) was performed in normal female rats to investigate its hormonal and metabolic consequences. Intracerebroventricular NPY produced hyperphagia, increased basal insulinemia, as well as liver and adipose tissue lipogenic activity. It also increased basal morning corticosteronemia. When NPY-induced hyperphagia was prevented by pair-feeding, the icv NPY treatment resulted in the same increases in basal insulinemia and corticosteronemia, and liver and white adipose tissue lipogenesis was still higher than that in respective controls. Under the ad libitum and pair-feeding conditions, icv NPY stimulated glucose uptake as well as total lipoprotein lipase activity in white adipose tissue; it resulted in an increase total activity of hepatic and white adipose tissue acetyl coenzyme-A-carboxylase. As all hormonal and metabolic changes elicited by icv NPY remained present (at the same or to a lesser extent depending upon the parameter considered) when hyperphagia was prevented by pair-feeding, it was, thus, shown that icv NPY per se induces peripheral hormonal and metabolic alterations via efferent routes, which remain to be determined. The effects of icv NPY reported in this study are similar to the defects observed in the early phase of genetic obesity in rodents, the hypothalamus of which has increased NPY levels. NPY could, thus, be of relevance in the occurrence of genetically induced obesity.
The Y-receptors belong to the G protein-coupled receptor superfamily and mediate a wide variety of physiological effects, such as regulation of blood pressure, anxiety, memory retention, hormone release and food intake. Since the first human Y-receptor was cloned in 1992, the search for additional subtypes has been an area of intense study. Recently four new NPY-receptor subtypes have been isolated, revealing surprisingly limited sequence identity with values as low as 30%. Several reports indicate further heterogeneity of this receptor family, for example a peripheral Y2 receptor. However, since many studies have been carried out with different peptide analogs and radioligands in different species, there is substantial confusion regarding the pharmacological profile of the receptors. This may have led to an exaggeration of the potential number of discrete receptors.
In the liver, the in vivo assessment of metabolic functions is limited by methodologic problems. The present evidence suggests that the liver contributes to 20-30% of whole body energy expenditure. Hepatic fuel selection can change considerably under different circumstances. During tissue catabolism (i.e., depletion of glycogen stores, increased lipid oxidation), the "hepatic respiratory quotient (RQ)" is lower than whole body RQ, suggesting that hepatic catabolism exceeds whole body catabolism. By contrast, the hepatic RQ may exceed whole body RQ during tissue anabolism (i.e., after full repletion of hepatic glycogen stores and significant lipogenesis). In cirrhosis, both the hepatic RQ and the whole body RQ are markedly reduced. When compared with the whole body level, the cirrhosis-induced decrease in the hepatic RQ is more pronounced. Given that liver catabolism exceeds (or possibly precedes) whole body catabolism, early nutritional support is mandatory in cirrhotic patients. The assessment of hepatic, in addition to whole body, energy metabolism may provide a basis for future recommendations of more specific nutritional support in patients with liver diseases.
Neuropeptide Y (NPY), a 36-amino-acid neuromodulator abundantly expressed in the brain, has been implicated in the regulation of food intake and body weight. Pharmacological data suggest that NPY's stimulatory effect on appetite is transduced by the G-protein-coupled NPY Y5 receptor (Y5R). We have inactivated the Y5R gene in mice and report that younger Y5R-null mice feed and grow normally; however, they develop mild late-onset obesity characterized by increased body weight, food intake and adiposity. Fasting-induced refeeding is unchanged in younger Y5R-null mice and they exhibit normal sensitivity to leptin. Their response to intracerebroventricular (i.c.v.) administration of NPY and related peptides is either reduced or absent. NPY deficiency attenuates the obesity syndrome of mice deficient for leptin (ob/ob), but these effects are not mediated by NPY signaling through the Y5R because Y5R-null ob/ob mice are equally obese. These results demonstrate that the Y5R contributes to feeding induced by centrally administered NPY and its analogs, but is not a critical physiological feeding receptor in mice.
Peptide YY (PYY), neuropeptide Y (NPY) and pancreatic polypeptide (PP) are structurally related peptides which have potent antisecretory effects in small and/or large intestines. Receptors mediating these effects are still unknown with the exception of a PYY-preferring receptor expressed in small intestinal crypts. In the present study, expression of recently cloned Y1, Y2, and Y5 receptors which have similar affinity for PYY and NPY and Y4 receptors which have a high affinity for PP was investigated in gut by RT-PCR analysis. The data show that all Y receptors are expressed in small intestine and/or colon but with specific distributions. Y1 receptors are only expressed in nonepithelial colonic tissue, whereas Y2 and Y4 receptors are present in both epithelial and nonepithelial tissue of the small or large intestine. In contrast, Y5 receptor expression appears to be restricted to epithelial crypts of the small intestine and nonepithelial tissue of colon. Sequencing of PCR products showed 100% identity with the corresponding sequences of the cloned Y1, Y4, or Y5 receptors. The PCR product obtained with Y2 primers from rat crypt cells showed 84% identity with the cloned human Y2 receptor. These data indicate a wide distribution of Y receptors in small intestine and colon. They also suggest that Y1, Y2, Y4, and Y5 receptors may be responsible for still unexplained effects of PYY, NPY, or PP on secretion in small and large intestines.
Neuropeptide Y (NPY) injected into the paraventricular nucleus (PVN) increases feeding and decreases brown adipose tissue (BAT) uncoupling protein (UCP) and lipoprotein lipase (LPL) mRNA. Previously we reported that the feeding and BAT effects induced by NPY in the PVN are blocked by 50 microg naltrexone (NTX) in the rostral nucleus of the solitary tract (rNTS). We sought to determine whether the effect of rNTS NTX on PVN NPY-induced alterations in energy metabolism occurred at lower doses of NTX. Male Sprague-Dawley rats were fitted with cannulas into two sites: PVN and rNTS. Feeding response, BAT UCP, and LPL mRNA were measured after injection of 0, 5, 10, and 25 microg NTX in the rNTS +/- 1 microg NPY in the PVN. One-hour feeding response to PVN NPY was significantly and dose dependently decreased by 10 and 25 microg rNTS NTX (-23 and -31%, respectively). However, rNTS NTX did not block the PVN NPY-induced decrease in BAT UCP or LPL mRNA. BAT beta-actin mRNA (as a measure of overall changes in gene expression) was unchanged among treatment groups. These results indicate a possible divergence in the PVN NPY feeding-stimulatory/BAT-inhibitory pathway, such that PVN NPY feeding effects may be routed through the rNTS whereas BAT effects may be due to alterations at another neural site.
1. We have investigated the neurotransmitters and receptor subtypes involved in nerve-mediated vasoconstriction in small arteries of the rat hepatic mesentery. 2. A dense sympathetic innervation was demonstrated antibodies against the synaptic vesicle protein synaptophysin. 3. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated very strong expression of the α(1A)-adrenergic, neuropeptide Y (NPY) Y1, P(2X1)- and P(2X4)-purinergic receptors, moderate expression of the α(2B)-adrenergic receptor and the purinergic P(2X5)- and P(2X7)-receptors and weak expression of the α(1B)-, α(1D)-, α(2A)- and α(2C)-adrenergic receptors and the P(2X2)- and P(2X3)-purinergic receptors. NPY2 and P(2X6) receptor expression was absent. 4. Electrical field stimulation (10 Hz, 10 s) produced contractions which were abolished by tetrodotoxin (10-6 M) and/or guanethidine (GE, 5 x 10-6 M) and a combination of benextramine (10-5 M) and α,β-methylene ATP, (α,β-mATP, 3 x 10-6 M) or PPADS (10-5 M). Selective α1-adrenergic receptor antagonists showed the potency order of prazosin > WB-4101 > 5-methyl-urapidil > BMY 7378. Yohimbine (10-8 M, 10-7 M), α,β-mATP (3 x 10-6 M) and PPADS (10-5 M) each enhanced the response to nerve stimulation. 5. Some experiments demonstrated a slow neurogenic contraction which was abolished by GE or the selective NPY1 receptor antagonist 1229U91 (6 x 10-7 M). 6. We conclude that nerve-mediated vasoconstriction results from the activation of postsynaptic α(1A)-adrenergic and P(2X)-purinergic receptors and under some conditions, NPY1 receptors. Neurotransmitter release is modulated by presynaptic α2-adrenergic receptors and possibly also P(2X)-purinoceptors. The major postsynaptic subtypes involved were well predicted by mRNA expression as measured by RT-PCR, suggesting that this technique may be a useful adjunct to studies aimed at identifying functional receptor subtypes.
Mechanisms regulating adipocyte lipolysis are reviewed in three stages. The first stage examines plasma membrane hormone receptors and G-proteins. The primary regulators of adipose tissue lipolysis, the catecholamines, bind to the alpha 2, beta 1, beta 2, and beta 3 adrenergic receptors. The alpha 2 receptor couples with Gi-proteins to inhibit cyclic AMP formation and lipolysis, while the beta receptors couple with Gs-proteins to stimulate cyclic AMP formation and lipolysis. The beta 1 receptor may mediate low level catecholamine stimulation, while the beta 3 receptor, which is activated by higher levels of catecholamines, may deliver a more sustained signal. The second stage examines the regulation of cyclic AMP, the intracellular messenger that activates protein kinase A. Adenylyl cyclase synthesizes cyclic AMP from ATP and is regulated by the G-proteins. Phosphodiesterase 3B hydrolyzes cyclic AMP to AMP and is activated and phosphorylated by both insulin and the catecholamines norepinephrine and epinephrine. The third stage focuses on the rate-limiting enzyme of lipolysis, hormone-sensitive lipase (HSL). This 82 to 88 kDa protein is regulated by reversible phosphorylation. Protein kinase A activates and phosphorylates the enzyme at 2 sites, and 3 phosphatases have been implicated in HSL dephosphorylation. The translocation of HSL from the cytosol to the lipid droplet in response to lipolytic stimulation may be facilitated by a family of lipid-associated droplets called perilipins that are heavily phosphorylated by protein kinase A and dephosphorylated by insulin. As the mechanisms regulating adipocyte lipolysis continue to be uncovered, we look forward to the challenges of integrating these findings with research at the in situ and in vivo levels.
Food intake was measured in freely fed rats following intracerebroventricular administration of neuropeptide Y (NPY) and several of its analogues and antagonists to investigate the hypothesis that the NPY Y5 receptor mediates feeding. Rat NPY (rNPY), rNPY(2-36) and rNPY(3-36) produced similar feeding responses over the dose range 0.7-7.0 nmol. Rat peptide YY (rPYY) was more potent and at least as efficacious as rNPY. [Leu31 Pro34]-rNPY (agonist potency: Y1 > Y5 > Y4 = y6) and human pancreatic polypeptide (hPP) produced flatter dose-response curves, suggesting partial agonism at the receptor(s). rNPY(13-36) (agonist potency: Y2 > Y5) had little activity and rPP was inactive. [D-Trp32]-NPY was a weak orexigenic agent given alone and, consistent with partial agonism, it markedly antagonised the response to porcine NPY (pNPY). Similarly, the receptor antagonist (Y1 > Y4) 1229U91 stimulated feeding slightly, and markedly inhibited rNPY-induced feeding. In contrast to a previous report, BIBP 3226 (70 nmol), another Y1 receptor antagonist, failed to inhibit the response to rNPY. Our data in vivo are inconsistent with findings that hPP, [Leu31 Pro34]-rNPY and [D-Trp32]-rNPY are full agonists at the rat cloned Y5 receptor. Thus, whilst the Y5 receptor may be involved, its participation as the sole receptor mediating the orexigenic action of NPY in the rat remains unproven.
To elucidate the role of neuropeptide Y (NPY)-Y1 receptor (Y1-R) in food intake, energy expenditure, and other possible functions, we have generated Y1-R-deficient mice (Y1-R-/-) by gene targeting. Contrary to our hypothesis that the lack of NPY signaling via Y1-R would result in impaired feeding and weight loss, Y1-R-/- mice showed a moderate obesity and mild hyperinsulinemia without hyperphagia. Although there was some variation between males and females, typical characteristics of Y1-R-/- mice include: greater body weight (females more than males), an increase in the weight of white adipose tissue (WAT) (approximately 4-fold in females), an elevated basal level of plasma insulin (approximately 2-fold), impaired insulin secretion in response to glucose administration, and a significant changes in mitochondrial uncoupling protein (UCP) gene expression (up-regulation of UCP1 in brown adipose tissue and down-regulation of UCP2 in WAT). These results suggest either that the Y1-R in the hypothalamus is not a key molecule in the leptin/NPY pathway, which controls feeding behavior, or that its deficiency is compensated by other receptors, such as NPY-Y5 receptor. We believe that the mild obesity found in Y1-R-/- mice (especially females) was caused by the impaired control of insulin secretion and/or low energy expenditure, including the lowered expression of UCP2 in WAT. This model will be useful for studying the mechanism of mild obesity and abnormal insulin metabolism in noninsulin-dependent diabetes mellitus.
Researchers using animals are beginning to elucidate the control of fatty acid metabolism in muscle at the molecular and enzymatic level. This review examines the physiological data that has been collected from human subjects in the context of the proposed control mechanisms. A number of factors, including the availability of free fatty acids and the abundance of fatty acid transporters, may influence the rate of muscle fatty acid oxidation. However, the predominant point of control appears to be the rate at which fatty acyl-coenzyme A is transported into the mitochondria by the carnitine palmitoyl transferase system. In turn, evidence suggests that the intracellular concentration of malonyl-coenzyme A in muscle is an important regulator of carnitine palmitoyl transferase-I activity. Malonyl-coenzyme A is increased by glucose, which is likely the mechanism whereby glucose intake suppresses the transfer of fatty acids into the mitochondria for subsequent oxidation. In contrast, malonyl-coenzyme A levels decrease during exercise, which enables increased fatty acid oxidation. However, for any given carnitine palmitoyl transferase-I activity, there may be an effect of free fatty acid availability on fatty acid oxidation, particularly at low levels of free fatty acids. Nonetheless, the rate of glucose or glycogen metabolism is probably the primary regulator of the balance between glucose and fatty acid oxidation in muscle.
Intracerebroventricular (ICV) administration of neuropeptide Y (NPY) has been shown to decrease energy expenditure, induce hypothermia, and stimulate food intake. Recent evidence has suggested that the Y5 receptor may be a significant mediator of NPY-stimulated feeding. The present study attempts to further characterize the role of NPY Y5-receptor subtypes in feeding and energy expenditure regulation. Satiated Long-Evans rats with temperature transponders implanted in the interscapular brown adipose tissue (BAT) displayed a dose-dependent decrease in BAT temperature and an increase in food intake after ICV infusion of NPY. Similar effects were induced by ICV administration of peptide analogs of NPY that activate the Y5 receptor, but not by analogs that activate Y1, Y2, or Y4 receptors. Furthermore, ICV infusion of the Y5 selective agonist D-[Trp(32)]-NPY significantly reduced oxygen consumption and energy expenditure of rats as measured by indirect calorimetry. These data suggest that the NPY Y5-receptor subtype not only mediates the feeding response of NPY but also contributes to brown fat temperature and energy expenditure regulation.
Resting energy expenditure (REE) and components of fat-free mass (FFM) were assessed in 26 healthy nonobese adults (13 males, 13 females). Detailed body composition analyses were performed by the combined use of dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), bioelectrical impedance analysis (BIA), and anthropometrics. We found close correlations between REE and FFM(BIA) (r = 0.92), muscle mass(DEXA) (r = 0.89), and sum of internal organs(MRI) (r = 0.90). In a multiple stepwise regression analysis, FFM(BIA) alone explained 85% of the variance in REE (standard error of the estimate 423 kJ/day). Including the sum of internal organs(MRI) into the model increased the r(2) to 0.89 with a standard error of 381 kJ/day. With respect to individual organs, only skeletal muscle(DEXA) and liver mass(MRI) significantly contributed to REE. Prediction of REE based on 1) individual organ masses and 2) a constant metabolic rate per kilogram organ mass was very close to the measured REE, with a mean prediction error of 96 kJ/day. The very close agreement between measured and predicted REE argues against significant variations in specific REEs of individual organs. In conclusion, the mass of internal organs contributes significantly to the variance in REE.
In order to characterize neuropeptide Y (NPY) receptors present in human adipocytes, we used selective ligands together with specific molecular probes able to recognize the different NPY receptor subtypes. RT-PCR experiments revealed the presence of Y(1) receptor transcripts with Y(4) and Y(5) and absence of Y(2) signals. Binding studies, using selective radioiodinated ligands, detected a high number (B(max)=497+/-124 fmol/mg protein) of a high affinity binding site only with [(125)I]peptide YY (PYY) and [(125)I](Leu(31), Pro(34))PYY. These sites exhibited a typical Y(1) profile as indicated by the rank order of affinity of NPY analogs and the high affinity of two selective NPY receptor antagonists, SR120819A and BIBP3226. In [(35)S]GTPgammaS binding experiments, PYY activation was totally inhibited by SR120819A and BIBP3226. Both compounds antagonized, with similar efficiency, the antilipolytic effect exerted by NPY in isolated adipocytes. Finally, PYY and Y(1) ligands enhanced adipocyte leptin secretion, an effect totally prevented by SR120819A. Thus, highly expressed in human adipocytes, the Y(1) receptor sustains the strong antilipolytic effect of NPY and exerts a positive action on leptin secretion.