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Glucose transporter proteins in brain: Delivery of glucose to neurons and glia
Abstract
Glucose is the principle energy source for the mammalian brain. Delivery of glucose from the blood to the brain requires transport across the endothelial cells of the blood-brain barrier and into the neurons and glia. The facilitative glucose transporter proteins mediate these processes. The primary isoforms in brain are GLUT1, detected at high concentrations as a highly glycosylated form, (55 kDa) in blood-brain barrier, and also as a less glycosylated, 45 kDa form, present in parenchyma, predominantly glia; GLUT3 in neurons; and GLUT5 in microglia. The rest of the transporter family, GLUTs 2, 4, and 7, have also been detected in brain but at lower levels of expression and confined to more discrete regions. All of the transporters probably contribute to cerebral glucose utilization, as part of overall metabolism and metabolic interactions among cells. We discuss the properties, regulation, cell-specific location, and kinetic characteristics of the isoforms, their potential contributions to cerebral metabolism, and several experimental paradigms in which alterations in energetic demand and/or substrate supply affect glucose transporter expression.
... Due to the increased energy requirements for neuronal signaling, neurotransmitter release, ionic balance, and synaptic plasticity [13][14][15][16], glucose is actively "drawn" into the brain [17,18]. Glucose transport is accomplished by the coordinated activation of glucose transporters on the capillary endothelium (GLUT1) [19][20][21][22][23][24][25], astrocytes (GLUT1 [26], GLUT2 [27], and GLUT7 [28]), oligodendrocytes (GLUT1) [29], and neurons (GLUT3 [28,30] and GLUT4) [26,[31][32][33][34]. Blood glucose diffuses either directly from capillaries to neurons via the extracellular space, or is mediated by the astrocyte end-feet surrounding the capillary walls [25,[35][36][37]. The distribution of energy and metabolic support inside the brain is greatly aided by astrocytes. ...
... Due to the increased energy requirements for neuronal signaling, neurotransmitter release, ionic balance, and synaptic plasticity [13][14][15][16], glucose is actively "drawn" into the brain [17,18]. Glucose transport is accomplished by the coordinated activation of glucose transporters on the capillary endothelium (GLUT1) [19][20][21][22][23][24][25], astrocytes (GLUT1 [26], GLUT2 [27], and GLUT7 [28]), oligodendrocytes (GLUT1) [29], and neurons (GLUT3 [28,30] and GLUT4) [26,[31][32][33][34]. Blood glucose diffuses either directly from capillaries to neurons via the extracellular space, or is mediated by the astrocyte end-feet surrounding the capillary walls [25,[35][36][37]. The distribution of energy and metabolic support inside the brain is greatly aided by astrocytes. ...
... Additionally, altered distribution or localization of glucose transporters within the cell membrane may contribute to impaired glucose uptake in AD. In AD, GLUT1 expression is reduced in regions such as the hippocampus and frontal cortex [28,100,157,158]. This reduction in expression may impair glucose uptake from the bloodstream into the brain. ...
The brain is a highly dynamic organ that requires a constant energy source to function normally. This energy is mostly supplied by glucose, a simple sugar that serves as the brain’s principal fuel source. Glucose transport across the blood–brain barrier (BBB) is primarily controlled via sodium-independent facilitated glucose transport, such as by glucose transporter 1 (GLUT1) and 3 (GLUT3). However, other glucose transporters, including GLUT4 and the sodium-dependent transporters SGLT1 and SGLT6, have been reported in vitro and in vivo. When the BBB endothelial layer is crossed, neurons and astrocytes can absorb the glucose using their GLUT1 and GLUT3 transporters. Glucose then enters the glycolytic pathway and is metabolized into adenosine triphosphate (ATP), which supplies the energy to support cellular functions. The transport and metabolism of glucose in the brain are impacted by several medical conditions, which can cause neurological and neuropsychiatric symptoms. Alzheimer’s disease (AD), Parkinson’s disease (PD), epilepsy, traumatic brain injury (TBI), schizophrenia, etc., are a few of the most prevalent disorders, characterized by a decline in brain metabolism or hypometabolism early in the course of the disease. Indeed, AD is considered a metabolic disorder related to decreased brain glucose metabolism, involving brain insulin resistance and age-dependent mitochondrial dysfunction. Although the conventional view is that reduced cerebral metabolism is an effect of neuronal loss and consequent brain atrophy, a growing body of evidence points to the opposite, where hypometabolism is prodromal or at least precedes the onset of brain atrophy and the manifestation of clinical symptoms. The underlying processes responsible for these glucose transport and metabolic abnormalities are complicated and remain poorly understood. This review article provides a comprehensive overview of the current understanding of hypometabolism in AD and potential therapeutic targets.
... Glucose is considered to be the primary substrate fueling oxidative metabolism and neural activity [6,7]. Glucose is transported to neural tissue through the capillaries, entering cells through specialized glucose transporters (GLUTs) [8]. Blood-borne glucose transport across the blood-brain barrier occurs through the glucose transporter 1 (GLUT1), whereas glucose uptake in neurons and astrocytes is regulated by GLUT3 and GLUT1, respectively [8]. ...
... Glucose is transported to neural tissue through the capillaries, entering cells through specialized glucose transporters (GLUTs) [8]. Blood-borne glucose transport across the blood-brain barrier occurs through the glucose transporter 1 (GLUT1), whereas glucose uptake in neurons and astrocytes is regulated by GLUT3 and GLUT1, respectively [8]. Interestingly, PET imaging indicates a possible uncoupling between glucose utilization and oxygen consumption [9,10]. ...
Neural tissue requires a great metabolic demand despite negligible intrinsic energy stores. As a result, the central nervous system (CNS) depends upon a continuous influx of metabolic substrates from the blood. Disruption of this process can lead to impairment of neurological functions, loss of consciousness, and coma within minutes. Intricate neurovascular networks permit both spatially and temporally appropriate metabolic substrate delivery. Lactate is the end product of anaerobic or aerobic glycolysis, converted from pyruvate by lactate dehydrogenase-5 (LDH-5). Although abundant in the brain, it was traditionally considered a byproduct or waste of glycolysis. However, recent evidence indicates lactate may be an important energy source as well as a metabolic signaling molecule for the brain and astrocytes—the most abundant glial cell—playing a crucial role in energy delivery, storage, production, and utilization. The astrocyte–neuron lactate-shuttle hypothesis states that lactate, once released into the extracellular space by astrocytes, can be up-taken and metabolized by neurons. This review focuses on this hypothesis, highlighting lactate’s emerging role in the brain, with particular emphasis on its role during development, synaptic plasticity, angiogenesis, and disease.
... In the CNS, GLUT1 is expressed by endothelial cells of the blood brain barrier enabling glucose access into the extracellular space where it can be taken up by astrocytes (Vannucci et al., 1997) and ...
... oligodendrocytes (Saab et al., 2016) also via GLUT1, or via GLUT3 into neurones (Vannucci et al., 1997). In the PNS glucose can diffuse from epineurial microvessels that lack a blood nerve barrier into the extracellular space of the epineurium (Allt & Lawrenson, 2000) then across the perineurium and endoneurium via GLUT1 (Magnani et al., 1996). ...
Astrocytes of the central nervous system (CNS) provide glycogen derived lactate to axons when energy substrate availability is low and when axons have an increased energy demand. Signals, including glutamate and K+, released from axons communicate the need for metabolic support and trigger astrocyte lactate production. Whether similar metabolic interactions occur between axons and Schwann cells of the peripheral nervous system (PNS) is less well understood. The association of peripheral neuropathy with the metabolic disease diabetes makes the study of axon-Schwann cell metabolic interactions valuable. Myelinating Schwann cells possess glycogen and glycolytically metabolise this to lactate, which their associated axons, known as A fibres, benefit from as an energy substrate when glucose availability is reduced. The aim of this thesis was to use the mouse sciatic nerve to investigate the role of Schwann cells in providing lactate to A fibres during increased axonal activity and the ability of K+ to act as a metabolic signal. Fructose metabolism of the mouse sciatic nerve was also investigated. Stimulus evoked compound action potential (CAP) electrophysiology was used to measure the conduction of, and lactate biosensors were used to record the lactate released from, the mouse sciatic nerve ex vivo. The method of stimulus evoked CAP electrophysiology was first adapted to record from paired, rather than single nerves, reducing the number of required animals whilst maintaining statistical power. Using this adapted method nerves were subjected to high frequency stimulation (HFS) to increase energy demand. A fibre conduction was maintained through increased glucose supply or Schwann cell derived lactate. The importance of Schwann cell lactate was evident by the loss and inability to maintain recovery of conduction when cinnamate (CIN), an inhibitor that prevents the shuttling of lactate from Schwann cells to axons, was present under normoglycaemic conditions. These findings prompted investigations into K+ as a trigger of Schwann cell lactate production. Increasing the concentration of extracellular K+ increased the concentration of extracellular lactate, a relationship which was logarithmic in response to global changes in K+ within the artificial cerebrospinal fluid (aCSF), but not in response to local changes in K+ as the result of increasing stimulus frequency. This suggests the Schwann cell membrane potential influences lactate production. When fructose is supplied to the ex vivo sciatic nerve preparation, Schwann cells provide lactate to A fibres, with these axons unable to directly benefit from fructose. Using fluorescent immunohistochemistry, the expression of the fructose specific transporter, GLUT5, and the fructose metabolism specific enzyme, fructokinase, was not found to parallel these electrophysiology findings. With fructokinase expressed exclusively by A fibres and GLUT5 expressed by A fibres and myelinating Schwann cells. These molecular findings might reflect a neuroprotective strategy in which Schwann cells convert excess glucose to fructose via the polyol pathway, a pathway upregulated during diabetes. This fructose may then be shuttled to A fibres for metabolism via fructokinase. These findings further our understanding of the metabolic role of Schwann cells and provide insight into the potential signal that enables metabolic communication between axons and Schwann cells.
... Of importance, the brain density of both GLUT1 and GLUT3 is significantly reduced in the cerebral cortex of AD patients [16]; though, GLUT3 demonstrates a more substantial reduction (by about two-fold in the hippocampi), even being corrected for concomitant synaptic and neuronal loss [17]. Taking into account a strong positive correlation between the glucose transporters expression levels and the glucose utilization rate in the brain tissue [18], GLUT3 deficit is considered a potential cause of the brain glucose metabolism deficits associated with AD [17]. ...
... Positron emission tomography (PET) is a well-established, reliable, non-invasive, widely used in the preclinical and clinical AD studies technique. 18 F-Fluorodeoxyglucose (18F-FDG) PET is a reliable imaging biomarker that allows the evaluation of cerebral glucose metabolism [34]. ...
Alzheimer's disease (AD) is an insidious neurodegenerative disorder representing a serious continuously escalating medico-social problem. The AD-associated progressive dementia is followed by gradual formation of amyloid plaques and neurofibrillary tangles in the brain. Though, converging evidence indicates apparent metabolic dysfunctions as key AD characteristic. In particular, late-onset AD possesses a clear metabolic signature. Considerable brain insulin signaling impairment and a decline in glucose metabolism are common AD attributes. Thus, positron emission tomography (PET) with glucose tracers is a reliable non-invasive tool for early AD diagnosis and treatment efficacy monitoring. Various approaches and agents have been trialed to modulate insulin signaling. Accumulating data point to arginase inhibition as a promising direction to treat AD via diverse molecular mechanisms involving, inter alia, the insulin pathway. Here, we use a transgenic AD mouse model, demonstrating age-dependent brain insulin signaling abnormalities, reduced brain insulin receptor levels, and substantial energy metabolism alterations, to evaluate the effects of arginase inhibition with Norvaline on glucose metabolism. We utilize fluorodeoxyglucose whole-body micro-PET to reveal a significant treatment-associated increase in glucose uptake by the brain tissue in-vivo. Additionally, we apply advanced molecular biology and bioinformatics methods to explore the mechanisms underlying the effects of Norvaline on glucose metabolism. We demonstrate that treatment-associated improvement in glucose utilization is followed by significantly elevated levels of insulin receptor and glucose transporter-3 expression in the mice hippocampi. Additionally, Norvaline diminishes the rate of Tau protein phosphorylation. Our results suggest that Norvaline interferes with AD pathogenesis. These findings open new avenues for clinical evaluation and innovative drug development.
... In the human brain, the primary source of energy is glucose as neurons cannot produce or store glucose themselves. The transport of glucose into the brain and its various cells is facilitated by specific carrier proteins, known as glucose transporters [84]. There are two types of AD: type 1 AD, accounting for a small percentage, is linked to genetic abnormalities, while the majority of cases are sporadic or type 2 AD. ...
Alzheimer’s disease (AD) is a distressing neurodegenerative condition characterized by the accumulation of amyloid-beta (Aβ) plaques and tau tangles within the brain. The interconnectedness between membrane transporters (SLCs) and microRNAs (miRNAs) in AD pathogenesis has gained increasing attention. This review explores the localization, substrates, and functions of SLC transporters in the brain, emphasizing the roles of transporters for glutamate, glucose, nucleosides, and other essential compounds. The examination delves into the significance of SLCs in AD, their potential for drug development, and the intricate realm of miRNAs, encompassing their transcription, processing, functions, and regulation. MiRNAs have emerged as significant players in AD, including those associated with mitochondria and synapses. Furthermore, this review discusses the intriguing nexus of miRNAs targeting SLC transporters and their potential as therapeutic targets in AD. Finally, the review underscores the interaction between SLC transporters and miRNA regulation within the context of Alzheimer’s disease, underscoring the need for further research in this area. This comprehensive review aims to shed light on the complex mechanisms underlying the causation of AD and provides insights into potential therapeutic approaches.
... Because plasma glucose levels were normal in PKU patients (Fig. 1), a hypothetical explanation for low CSF glucose would be that there is a negative impact of chronic hyperphenylalanemia on GLUT1-mediated transport of glucose across the BBB. If this impact is limited to GLUT1, then the primary effects would involve red blood cells, vascular endothelium, oligodendrocytes, and astrocytes [39,41], retina [42] and other cells, that express this transporter, as opposed to neurons that express GLUT3 [39]. Interestingly, visual problems [43] and morphological changes of the retina have been described in PKU patients [44]. ...
... Because plasma glucose levels were normal in PKU patients (Fig. 1), a hypothetical explanation for low CSF glucose would be that there is a negative impact of chronic hyperphenylalanemia on GLUT1-mediated transport of glucose across the BBB. If this impact is limited to GLUT1, then the primary effects would involve red blood cells, vascular endothelium, oligodendrocytes, and astrocytes [39,41], retina [42] and other cells, that express this transporter, as opposed to neurons that express GLUT3 [39]. Interestingly, visual problems [43] and morphological changes of the retina have been described in PKU patients [44]. ...
... Glucose consumption is frequently related to the metabolic demand of neurons, but glia cells also require energy to function under normal or pathological conditions. Glucose uptake by glial cells facilitates glycogen storage, fuels glutamate uptake, participates in glutamine biosynthesis, and these cells are also responsible for exporting metabolic intermediate molecules [66]. The vascular processes of endfeet astrocytes express glucose transporters on their luminal surface [67]. ...
Objectives:
Neurons and glial cells are the main functional and structural elements of the brain, and the former depends on the latter for their nutritional, functional and structural organization, as well as for their energy maintenance.
Methods:
Glucose is the main metabolic source that fulfills energetic demands, either by direct anaplerosis or through its conversion to metabolic intermediates. Development of some neurodegenerative diseases have been related with modifications in the expression and/or function of glial glucose transporters, which might cause physiological and/or pathological disturbances of brain metabolism. In the present contribution, we summarized the experimental findings that describe the exquisite adjustment in expression and function of glial glucose transporters from physiologic to pathologic metabolism, and its relevance to neurodegenerative diseases.
Results:
A exhaustive literature review was done in order to gain insight into the role of brain energetics in neurodegenerative disease. This study made evident a critical involvement of glucose transporters and thus brain energetics in the development of neurodegenerative diseases.
Discussion:
An exquisite adjustment in the expression and function of glial glucose transporters from physiologic to pathologic metabolism is a biochemical signature of neurodegenerative diseases.
... 106-109 GLUT5 is primarily located on microglia. 110 Additional research into the intersection between peripheral and central glucose metabolism and its role in aging and neurodegeneration is ongoing and warranted. In addition to the mechanisms reviewed in this section, obesity is associated with reduced cerebral perfusion [111][112][113] and individuals with obesity exhibit cortical thinning even in the absence of cognitive impairment. ...
Obesity is increasing in prevalence across all age groups. Long-term obesity can lead to the development of metabolic and cardiovascular diseases through its effects on adipose, skeletal muscle, and liver tissue. Pathological mechanisms associated with obesity include immune response and inflammation as well as oxidative stress and consequent endothelial and mitochondrial dysfunction. Recent evidence links obesity to diminished brain health and neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Both AD and PD are associated with insulin resistance, an underlying syndrome of obesity. Despite these links, causative mechanism(s) resulting in neurodegenerative disease remain unclear. This review discusses relationships between obesity, AD, and PD, including clinical and preclinical findings. The review then briefly explores nonpharmacological directions for intervention.
... Glucose metabolism plays a vital role in brain development, producing ATP via the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPOS). Glucose crosses the BBB to enter the brain region through the glucose transporter-1 (GLUT1) and subsequently via GLUT3 and GLUT1 to enter inside the neuron and glia, respectively (Vannucci et al. 1997;Arnold et al. 2018;Bazrgar et al. 2021). Various studies have reported that the brains of people with AD and amnestic mild cognitive impairment (aMCI) have markedly reduced levels of GLUT1 and GLUT3 and glucose metabolism (Weise et al. 2018;Cho et al. 2021;Zhang et al. 2021b). ...
Small non-coding RNAs (miRNAs) regulate gene expression by binding to mRNA and mediating its degradation or inhibiting translation. Since miRNAs can regulate the expression of several genes, they have multiple roles to play in biological processes and human diseases. The majority of miRNAs are known to be expressed in the brain and are involved in synaptic functions, thus marking their presence and role in major neurodegenerative disorders, including Alzheimer’s disease (AD). In AD, amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) are known to be the major hallmarks. The clearance of Aβ and tau is known to be associated with miRNA dysregulation. In addition, the β-site APP cleaving enzyme (BACE 1), which cleaves APP to form Aβ, is also found to be regulated by miRNAs, thus directly affecting Aβ accumulation. Growing evidences suggest that neuroinflammation can be an initial event in AD pathology, and miRNAs have been linked with the regulation of neuroinflammation. Inflammatory disorders have also been associated with AD pathology, and exosomes associated with miRNAs are known to regulate brain inflammation, suggesting for the role of systemic miRNAs in AD pathology. Several miRNAs have been related in AD, years before the clinical symptoms appear, most of which are associated with regulating the cell cycle, immune system, stress responses, cellular senescence, nerve growth factor (NGF) signaling, and synaptic regulation. Phytochemicals, especially polyphenols, alter the expression of various miRNAs by binding to miRNAs or binding to the transcriptional activators of miRNAs, thus control/alter various metabolic pathways. Awing to the sundry biological processes being regulated by miRNAs in the brain and regulation of expression of miRNAs via phytochemicals, miRNAs and the regulatory bioactive phytochemicals can serve as therapeutic agents in the treatment and management of AD.
... Glycogen metabolism is subject to complex regulation in various tissues, including the brain. Glucose is transported to brain cells through different glucose transporters, with astrocytes and oligodendrocytes utilizing GLUT1 and microglial cells utilizing GLUT5 [22]. Neurons, on the other hand, primarily rely on GLUT3 for glucose uptake. ...
This comprehensive narrative review explores the concept of neuro-vulnerability in energy metabolism regulation and its implications for metabolic disorders. The review highlights the complex interactions among the neural, hormonal, and metabolic pathways involved in the regulation of energy metabolism. The key topics discussed include the role of organs, hormones, and neural circuits in maintaining metabolic balance. The review investigates the association between neuro-vulnerability and metabolic disorders, such as obesity, insulin resistance, and eating disorders, considering genetic, epigenetic, and environmental factors that influence neuro-vulnerability and subsequent metabolic dysregulation. Neuroendocrine interactions and the neural regulation of food intake and energy expenditure are examined, with a focus on the impact of neuro-vulnerability on appetite dysregulation and altered energy expenditure. The role of neuroinflammation in metabolic health and neuro-vulnerability is discussed, emphasizing the bidirectional relationship between metabolic dysregulation and neuroinflammatory processes. This review also evaluates the use of neuroimaging techniques in studying neuro-vulnerability and their potential applications in clinical settings. Furthermore, the association between neuro-vulnerability and eating disorders, as well as its contribution to obesity, is examined. Potential therapeutic interventions targeting neuro-vulnerability, including pharmacological treatments and lifestyle modifications, are reviewed. In conclusion, understanding the concept of neuro-vulnerability in energy metabolism regulation is crucial for addressing metabolic disorders. This review provides valuable insights into the underlying neurobiological mechanisms and their implications for metabolic health. Targeting neuro-vulnerability holds promise for developing innovative strategies in the prevention and treatment of metabolic disorders, ultimately improving metabolic health outcomes.
... The excessive stressor led to the concentrates of dysfunctional mitochondria producing ROS and the release of several pro-death mediators to further initiate various cell death events, such as apoptosis and autophagy. One such kind of stressor is high glucose in the cellular milieu where increase glucose entry in neurons through diffusion could induce susceptibility to hyperglycemic stress [74]. The present study is carried out to explore the neuroprotective effect of PCN at in vitro stage against high glucoseinduced neurotoxicity in the N2A cell line and STZ-induced experimental DN in SD rats. ...
... However, in states of low glucose availability, other substrates, such as ketone bodies, can be used as a substitute [56]. Under normal physiologic conditions, glucose is transported primarily into neurons via glucose transporters [57]. Glucose can then be phosphorylated, where its metabolic fate can be determined by either proceeding through glycolysis or being shunted into the pentose phosphate pathway (PPP) [58,59]. ...
(Motor Neuron Diseases (MND) are neurological disorders characterized by a loss of varying motor neurons resulting in decreased physical capabilities. Current research is focused on hindering disease progression by determining causes of motor neuron death. Metabolic malfunction has been proposed as a promising topic when targeting motor neuron loss. Alterations in metabolism have also been noted at the neuromuscular junction (NMJ) and skeletal muscle tissue, emphasizing the importance of a cohesive system. Finding metabolism changes consistent throughout both neurons and skeletal muscle tissue could pose as a target for therapeutic intervention. This review will focus on metabolic deficits reported in MNDs and propose potential therapeutic targets for future intervention.
... In living systems, endogenous H2S is produced from the sulfur amino acids cysteine (Cys) and methionine under the catalysis of cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and cysteine aminotransferase [8]. In the central nervous system, CBS which is highly distributed in hippocampus and cerebellum, is the main enzyme that produces H2S [9]. ...
Purpose: To investigate the potential protective effect of hydrogen sulfide against neural cell damage induced by a high-concentration of adenosine triphosphate (ATP).Methods: PC12 cells were incubated with ATP in order to induce cell damage. The extracellular level of H2S and protein expression of cystathionine-β-synthase (CBS) were determined. The PC12 cells pretreated with NaHS, aminooxyacetic acid (AOAA) and KN-62, prior to further incubation with ATP, and the effect of the treatments on cell viability was investigated.Results: High-concentration ATP induced cell death in PC12 cells, and this was accompanied by markedly increased contents of extracellular H2S and CBS expression (p < 0.05). The ATP-induced cytotoxicity was significantly compromised after pretreatment with H2S. (p < 0.05). The viability of PC12 cells pretreated with NaHS and AOAA was significantly higher than that of PC12 cells treated with ATP alone. In addition, the viability of ATP-treated PC12 cells was further markedly increased after pretreatment with NaHS and KN-62 (p < 0.05).Conclusion: ATP induced a concentration- and time-dependent cytotoxicity in PC12 cells via theendogenous H2S/CBS system. Supplementation with exogenous H2S mitigated the cell damageinduced by high concentration of ATP via a specific mechanism which may be specifically related to P2X7R.
... Our study observed the activation of GSDMD in BV2 and HT22 cells after OGD/R. The results showed that HT22 cells developed cell pyroptosis earlier than BV2 cells, which may help explain the cell type-specific susceptibility in vivo because neurons are more vulnerable to ischemiainduced injury than microglia [31][32][33]. In our study, we also found no changes in GSDME activation in both neuronal cells and microglia after OGD/R. ...
Pyroptosis is a new type of programmed cell death, which induces a strong pro-inflammatory reaction. However, the mechanism of pyroptosis after brain ischemia/reperfusion (I/R) and the interaction between different neural cell types are still unclear. This study comprehensively explored the mechanisms and interactions of microglial and neuronal pyroptosisin the simulated I/R environment in vitro. The BV2 (as microglial) and HT22(as neuronal) cells were treated by oxygen–glucose deprivation/reoxygenation (OGD/R). Both BV2 and HT22 cells underwent pyroptosis after OGD/R, and the pyroptosis occurred at earlier time point in HT22than that of BV2. Caspase-11 and Gasdermin E expression in BV2 and HT22 cells did not change significantly after OGD/R. Inhibition of caspase-1 or GSDMD activity, or down-regulation of GSDMD expression, alleviated pyroptosis in both BV2 and HT22 cells after OGD/R. Transwell studies further showed that OGD/R-treated HT22 or BV2 cells aggravated pyroptosis of adjacent non-OGD/R-treated cells, which could be relieved by inhibition of caspase-1 or GSDMD. These results suggested that OGD/R induces pyroptosis of microglia and neuronal cells and aggravates cell injury via activation of caspase-1/GSDMD signaling pathway. Our findings indicated that caspase-1 and GSDMD may be therapeutic targets after cerebral I/R.
... We next examined the impact of GLUT3KO on glucose levels at the synapse, where GLUT3 may be enriched. 54 At baseline, GLUT3KO neurons had lower glucose level at the synapse than controls (Figure 6F), and their glucose levels were unresponsive to changes in the extracellular glucose level ( Figure 6G). Moreover, in the presence of extracellular glucose, intracellular glucose levels declined far more rapidly and to a greater extent in GLUT3KO neurons than controls in response to electrical field stimulation ( Figure 6H, left). ...
Neurons require large amounts of energy, but whether they can perform glycolysis or require glycolysis to maintain energy remains unclear. Using metabolomics, we show that human neurons do metabolize glucose through glycolysis and can rely on glycolysis to supply tricarboxylic acid (TCA) cycle metabolites. To investigate the requirement for glycolysis, we generated mice with postnatal deletion of either the dominant neuronal glucose transporter (GLUT3cKO) or the neuronal-enriched pyruvate kinase isoform (PKM1cKO) in CA1 and other hippocampal neurons. GLUT3cKO and PKM1cKO mice show age-dependent learning and memory deficits. Hyperpolarized magnetic resonance spectroscopic (MRS) imaging shows that female PKM1cKO mice have increased pyruvate-to-lactate conversion, whereas female GLUT3cKO mice have decreased conversion, body weight, and brain volume. GLUT3KO neurons also have decreased cytosolic glucose and ATP at nerve terminals, with spatial genomics and metabolomics revealing compensatory changes in mitochondrial bioenergetics and galactose metabolism. Therefore, neurons metabolize glucose through glycolysis in vivo and require glycolysis for normal function.
... GLUT3 is a high-affinity subclass; it allows glucose transport to occur in all cases, even when glucose levels are intracellularly low-a phenomenon required for neurons [52], placenta, and fetal cells [53]. This transporter protein has a significantly greater transport capacity than GLUT1 and GLUT4, as well as a higher glucose affinity than other subclasses, namely, GLUT1, GLUT2, and GLUT4 [54]. ...
Insulin is the main metabolic regulator of fuel molecules in the diet, such as carbohydrates, lipids, and proteins. It does so by facilitating glucose influx from the circulation into the liver, adipose tissue, and skeletal myocytes. The outcome of which is subjected to glycogenesis in skeletal muscle and lipogenesis in adipose tissue, as well as in the liver. Therefore, insulin has an anabolic action while, on the contrary, hypoinsulinemia promotes the reverse process. Protein breakdown in myocytes is also encountered during the late stages of diabetes mellitus. The balance of the blood glucose level in physiological conditions is maintained by virtue of the interactive functions of insulin and glucagon. In insulin resistance (IR), the balance is disturbed because glucose transporters (GLUTs) of cell membranes fail to respond to this peptide hormone, meaning that glucose molecules cannot be internalized into the cells, the consequence of which is hyperglycemia. To develop the full state of diabetes mellitus, IR should be associated with the impairment of insulin release from beta-cells of the pancreas. Periodic screening of individuals of high risk, such as those with obesity, hypercholesterolemia, and pregnant nulliparous women in antenatal control, is vital, as these are important checkpoints to detect cases of insulin resistance. This is pivotal as IR can be reversed, provided it is detected in its early stages, through healthy dietary habits, regular exercise, and the use of hypoglycemic agents. In this review, we discuss the pathophysiology, etiology, diagnosis, preventive methods, and management of IR in brief.
... The excessive stressor led to the concentrates of dysfunctional mitochondria producing ROS and the release of several pro-death mediators to further initiate various cell death events, such as apoptosis and autophagy. One such kind of stressor is high glucose in the cellular milieu where increase glucose entry in neurons through diffusion could induce susceptibility to hyperglycemic stress [74]. The present study is carried out to explore the neuroprotective effect of PCN at in vitro stage against high glucoseinduced neurotoxicity in the N2A cell line and STZ-induced experimental DN in SD rats. ...
Piceatannol (PCN), a SIRT1 activator, regulates multiple oxidative stress mechanism and has anti-inflammatory potential in various inflammatory conditions. However, its role in Diabetic insulted peripheral neuropathy (DN) remains unknown. Oxidative stress and mitochondrial dysfunction are major contributing factors to DN. Myriad
studies have proven that sirtuin1 (SIRT1) stimulation convalesce nerve functions by activating mitochondrial functions like mitochondrial biogenesis and mitophagy. Diabetic neuropathy (DN) was provoked by injecting streptozotocin (STZ) at a dose of 55 mg/kg, i.p to male Sprague Dawley (SD) rats. Mechanical, thermal hyper-
algesia was evaluated by using water immersion, Vonfrey Aesthesiometer, and Randall Sellito Calipers. Motor, sensory nerve conduction velocity was measured using Power Lab 4sp system whereas The Laser Doppler system was used to evaluate nerve blood flow. To induce hyperglycemia for the in vitro investigations, high glucose (HG) (30 mM) conditions were applied to Neuro2a cells. At doses of 5 and 10 µM, PCN was examined for its role in SIRT1 and Nrf2 activation. HG-induced N2A cells, reactive oxygen exposure, mitochondrial superoxides and mitochondrial membrane potentials were restored by PCN exposure, and their neurite outgrowth was enhanced.
Peroxisome proliferator activated receptor-gamma coactivator-1α (PGC-1α) directed mitochondrial biogenesis was induced by increased SIRT1 activation by piceatannol. SIRT1 activation also enhanced Nrf2-mediated antioxidant signalling. Our study results inferred that PCN administration can counteract the decline in mitochondrial function
... high drug-loading efficiency, and facile surface modification [22][23][24]. Next, we select biotin as a brain-targeting moiety among several known moieties, including transferrin, lectin, ApoE, glutathione, biotin, and so on, because it has known to exist in abundance in the brain, especially in the hippocampus, which is most closely related to AD and memory [25][26][27][28][29][30]. Therefore, we hypothesized that more drugs could be delivered to the hippocampus region by surface modification using biotin. ...
There has been a lot of basic and clinical research on Alzheimer's disease (AD) over the last 100 years, but its mechanisms and treatments have not been fully clarified. Despite some controversies, the amyloid-beta hypothesis is one of the most widely accepted causes of AD. In this study, we disclose a new amyloid-beta plaque disaggregating agent and an AD brain-targeted delivery system using porous silicon nanoparticles (pSiNPs) as a therapeutic nano-platform to overcome AD. We hypothesized that the negatively charged sulfonic acid functional group could disaggregate plaques and construct a chemical library. As a result of the in vitro assay of amyloid plaques and library screening, we confirmed that 6-amino-2-naphthalenesulfonic acid (ANA) showed the highest efficacy for plaque disaggregation as a hit compound. To confirm the targeted delivery of ANA to the AD brain, a nano-platform was created using porous silicon nanoparticles (pSiNPs) with ANA loaded into the pore of pSiNPs and biotin-polyethylene glycol (PEG) surface functionalization. The resulting nano-formulation, named Biotin-CaCl2-ANA-pSiNPs (BCAP), delivered a large amount of ANA to the AD brain and ameliorated memory impairment of the AD mouse model through the disaggregation of amyloid plaques in the brain. This study presents a new bioactive small molecule for amyloid plaque disaggregation and its promising therapeutic nano-platform for AD brain-targeted delivery.
... Glucose transporter 1 deficiency syndrome (Glut1DS; OMIM #606777) is caused by haploinsufficiency of solute carrier family 2 member 1 (SLC2A1; cytogenic location: 1p34.2), which encodes GLUT1. GLUT1 is expressed mainly on the endothelial cells of the blood-brain barrier, but also on other cell types including astrocytes, oligodendrocytes, and neurons of the central nervous system [1][2][3][4][5]. Impaired hexose transport by heterozygous mutation of SLC2A1 causes energy failure and results in irreversible neurologic dysfunction [6][7][8]. ...
Objective
We assessed the usefulness of flow cytometry as a functional assay to measure glucose transporter 1 (GLUT1) levels on the surface of red blood cells (RBCs) from Japanese patients with glucose transporter 1 deficiency syndrome (Glut1DS).
Methods
We recruited 13 genetically confirmed Glut1DS patients with a solute carrier family 2 member 1 (SLC2A1) mutation (eight missense, one frameshift, two nonsense, and two deletion) and one clinically suspected Glut1DS-like patient without an SLC2A1 mutation, and collected whole blood with informed consent. We stained pelleted RBCs (1 μL) from the patients with a Glut1.RBD ligand and anti-glycophorin A antibody, which recognizes a human RBC membrane protein, and analyzed the cells using flow cytometry.
Results
Relative GLUT1 levels quantified by flow cytometry in 11 of 13 patients with definite Glut1DS were 90% below those of healthy controls. Relative GLUT1 levels were not reduced in two of 13 Glut1DS patients who had a missense mutation and no intellectual disability and one Glut1DS-like patient without an SLC2A1 mutation. Relative GLUT1 levels were significantly reduced in Glut1DS patients with an SLC2A1 mutation, more severe intellectual disability, and spasticity.
Conclusions
This method to detect GLUT1 levels on RBCs is simple and appears to be an appropriate screening assay to identify severe Glut1DS patients in the early stage before the development of irreversible neurologic damage caused by chronic hypoglycorrhachia.
... Specifically, to reach brain cells, blood glucose is transported across endothelial membranes via glucose transporter 1 (GLUT1). Endothelial cells are ensheathed by the endfeet of astrocytes, whose major glucose transporter is also GLUT1 9,10 . Thus, astrocytes are located in a privileged position to control the access of glucose into the brain 11 . ...
Astrocytes are considered an essential source of blood-borne glucose or its metabolites to neurons. Nonetheless, the necessity of the main astrocyte glucose transporter, i.e. GLUT1, for brain glucose metabolism has not been defined. Unexpectedly, we found that brain glucose metabolism was paradoxically augmented in mice with astrocytic GLUT1 ablation (GLUT1GFAP mice). These mice also exhibited improved peripheral glucose metabolism especially in obesity, rendering them metabolically healthier. Importantly, GLUT1GFAP mice did not present cognitive alterations. Mechanistically, we observed that GLUT1-ablated astrocytes exhibited increased insulin receptor-dependent ATP release, and both astrocyte insulin signalling and brain purinergic signalling are essential for improved brain function and systemic glucose metabolism. Collectively, we demonstrate that astrocytic GLUT1 is central to the regulation of brain energetics, yet its ablation triggers a reprogramming of brain metabolism sufficient to sustain energy requirements, peripheral glucose homeostasis and cognitive function.
... The excessive stressor led to the concentrates of dysfunctional mitochondria producing ROS and the release of several pro-death mediators to further initiate various cell death events, such as apoptosis and autophagy. One such kind of stressor is high glucose in the cellular milieu where increase glucose entry in neurons through diffusion could induce susceptibility to hyperglycemic stress [74]. The present study is carried out to explore the neuroprotective effect of PCN at in vitro stage against high glucoseinduced neurotoxicity in the N2A cell line and STZ-induced experimental DN in SD rats. ...
Background:
Silibinin (SBN), a sirtuin 1 (SIRT1) activator, has been evaluated for its anti-inflammatory activity in many inflammatory diseases. However, its role in diabetes-induced peripheral neuropathy (DPN) remains unknown. The SIRT1 activation convalesces nerve functions by improving mitochondrial biogenesis and mitophagy.
Methods:
DPN was induced by streptozotocin (STZ) at a dose of 55 mg/kg, i.p. in the male SD rats whereas neurotoxicity was induced in Neuro2A cells by 30 mM (high glucose) glucose. Neurobehavioural (nerve conduction velocity and nerve blood flow) western blot, immunohistochemistry, and immunocytochemistry were performed to evaluate the protein expression and their cellular localisation.
Results:
Two-week SBN treatment improved neurobehavioural symptoms, SIRT1, PGC-1α, and TFAM expression in the sciatic nerve and HG insulted N2A cells. It has also maintained the mitophagy by up-regulating PARL, PINK1, PGAM5, LC3 level and provided antioxidant defence by upregulating Nrf2.
Conclusion:
SBN has shown neuroprotective potential in DPN through SIRT1 activation and antioxidant mechanism.
... Glucose entry into the CNS is primarily mediated by the glucose transporter 1 (GLUT1, SLC2A1), abundantly expressed in astrocytes (Koepsell, 2020;Vannucci et al., 1997). Expression of GLUT1 is decreased in the cerebral cortex and the hippocampus of AD patients (Liu et al., 2008;Mooradian et al., 1997;Simpson et al., 1994) indicating reduced capacity of astrocyte glucose transport. ...
Astrocytes contribute to the complex cellular pathology of Alzheimer’s disease (AD). Neurons and astrocytes function in close collaboration through neurotransmitter recycling, collectively known as the glutamate/GABA-glutamine cycle, which is essential to sustain neurotransmission. Neurotransmitter recycling is intimately linked to astrocyte energy metabolism. In the course of AD, astrocytes undergo extensive metabolic remodeling, which may profoundly affect the glutamate/GABA-glutamine cycle. The consequences of altered astrocyte function and metabolism in relation to neurotransmitter recycling are yet to be comprehended. Metabolic alterations of astrocytes in AD deprive neurons of metabolic support, thereby contributing to synaptic dysfunction and neurodegeneration. In addition, several astrocyte-specific components of the glutamate/GABA-glutamine cycle, including glutamine synthesis and synaptic neurotransmitter uptake, are perturbed in AD. Integration of the complex astrocyte biology within the context of AD is essential for understanding the fundamental mechanisms of the disease, while restoring astrocyte metabolism may serve as an approach to arrest or even revert clinical progression of AD.
... This was concordant with the results of Viglianti et al. [10] and Sarikaya et al. [12] and could be explained by the competition of 18F-FDG and glucose on the membrane glucose transporters (GLUTs) in the blood-brain barrier. [13,14] On subgroup analysis, the effect of blood glucose level on tracer uptake in the brain was stronger in diabetic than in non-diabetic patients (r = −0.537, P-value = 0.001 on the first occasion and r = −0.314, ...
Objectives
To investigate the effect of serum glucose level and other confounding factors on the variability of maximum standardized uptake value (SUVmax) in normal tissues within the same patient on two separate occasions and to suggest an ideal reference tissue.
Materials and Methods
We retrospectively reviewed 334 18F-FDG PET/CT scans of 167 cancer patients including 38 diabetics. All patients had two studies, on average 152 ± 68 days apart. Ten matched volumes of interest were drawn on the brain, right tonsil, blood pool, heart, lung, liver, spleen, bone marrow, fat, and iliopsoas muscle opposite third lumber vertebra away from any pathological 18F-FDG uptake to calculate SUVmax.
Results
SUVmax of the lungs and heart were significantly different in the two studies ( P = 0.003 and P = 0.024 respectively). Only the brain uptake showed a significant moderate negative correlation with the level of blood glucose in diabetic patients (r = −0.537, P = 0.001) in the first study, while the SUVmax of other tissues showed negligible or weak correlation with the level of blood glucose in both studies.
The liver showed significant moderate positive correlation with body mass index (BMI) in both studies (r = .416, P = <0.001 versus r = 0.453, P = <0.001, respectively), and blood pool activity showed significant moderate positive correlation with BMI in the first study only (r = 0.414, P = <0.001). The liver and blood pool activities showed significant moderate negative correlation with 18F-FDG uptake time in first study only (r = −0.405, P -value = <0.001; and r = −0.409, P -value = <0.001, respectively).
In the multivariate analysis, the liver showed a consistent effect of the injected 18F-FDG dose and uptake duration on its SUVmax on the two occasions. In comparison, spleen and muscle showed consistent effect only of the injected dose on the two occasions.
Conclusion
The liver, muscle, and splenic activities showed satisfactory test/retest stability and can be used as reference activities. The spleen and muscle appear to be more optimal reference than the liver, as it is only associated with the injected dose of 18F-FDG.
... and glutamine (Gln) as major energy substrates [122]. In microglia, glucose is uptaken by GLUT3 and GLUT5 [123,124]. Microglia express acyl-CoA synthetases that catalyze a β-oxidation of fatty acid into acyl-CoA, and they also express high levels of lipoprotein lipase, thus suggesting that microglia use fatty acid as well as glucose to produce ATP [122]. Gln is known to be used as an energy source in the brain, and microglia highly express glutaminase, glutamate dehydrogenase, and soluble linked carrier family 1 member 5A (SLC1A5), preferably metabolizing Gln to generate ATP [122]. ...
Transection of the rat facial nerve leads to a variety of alterations not only in motoneurons, but also in glial cells and inhibitory neurons in the ipsilateral facial nucleus. In injured motoneurons, the levels of energy metabolism-related molecules are elevated, while those of neurofunction-related molecules are decreased. In tandem with these motoneuron changes, microglia are activated and start to proliferate around injured motoneurons, and astrocytes become activated for a long period without mitosis. Inhibitory GABAergic neurons reduce the levels of neurofunction-related molecules. These facts indicate that injured motoneurons somehow closely interact with glial cells and inhibitory neurons. At the same time, these events allow us to predict the occurrence of tissue remodeling in the axotomized facial nucleus. This review summarizes the events occurring in the axotomized facial nucleus and the cellular and molecular mechanisms associated with each event.
... Glucose is transported from plasma to the brain via glucose transporters (GLUTs), primarily GLUT1 expressed in the bloodbrain barrier/astrocytes and GLUT3 expressed in neurons (4). Glucose is then phosphorylated by hexokinase to glucose-6-phosphate in cells and metabolized in the glycolytic pathway to produce adenosine triphosphate (2). ...
Since the invention of 18F-FDG as a neurochemical tracer in the 1970s, 18F-FDG PET has been used extensively for dementia research and clinical applications. FDG, a glucose analog, is transported into the brain via glucose transporters and metabolized in a concerted process involving astrocytes and neurons. Although the exact cellular mechanisms of glucose consumption are still under investigation, 18F-FDG PET can sensitively detect altered neuronal activity due to neurodegeneration. Various neurodegenerative disorders affect different areas of the brain, which can be depicted as altered 18F-FDG uptake by PET. The spatial patterns and severity of such changes can be reproducibly visualized by statistical mapping technology, which has become widely available in the clinic. The differentiation of 3 major neurodegenerative disorders by 18F-FDG PET, Alzheimer disease (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB), has become standard practice. As the nosology of FTD evolves, frontotemporal lobar degeneration, the umbrella term for pathology affecting the frontal and temporal lobes, has been subclassified clinically into behavioral variant FTD; primary progressive aphasia with 3 subtypes, semantic, nonfluent, and logopenic variants; and movement disorders including progressive supranuclear palsy and corticobasal degeneration. Each of these subtypes is associated with differential 18F-FDG PET findings. The discovery of new pathologic markers and clinicopathologic correlations via larger autopsy series have led to newly recognized or redefined disease categories, such as limbic-predominant age-related TDP-43 encephalopathy, hippocampus sclerosis, primary age-related tauopathy, and argyrophilic grain disease, which have become a focus of investigations by molecular imaging. These findings need to be integrated into the modern interpretation of 18F-FDG PET. Recent pathologic investigations also have revealed a high prevalence, particularly in the elderly, of mixed dementia with overlapping and coexisting pathologies. The interpretation of 18F-FDG PET is evolving from a traditional dichotomous diagnosis of AD versus FTD (or DLB) to a determination of the most predominant underlying pathology that would best explain the patient's symptoms, for the purpose of care guidance. 18F-FDG PET is a relatively low cost and widely available imaging modality that can help assess various neurodegenerative disorders in a single test and remains the workhorse in clinical dementia evaluation.
... In living systems, endogenous H2S is produced from the sulfur amino acids cysteine (Cys) and methionine under the catalysis of cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and cysteine aminotransferase [8]. In the central nervous system, CBS which is highly distributed in hippocampus and cerebellum, is the main enzyme that produces H2S [9]. ...
Purpose: To investigate the potential protective effect of hydrogen sulfide against neural cell damage induced by a high-concentration of adenosine triphosphate (ATP).Methods: PC12 cells were incubated with ATP in order to induce cell damage. The extracellular level of H2S and protein expression of cystathionine-β-synthase (CBS) were determined. The PC12 cells pretreated with NaHS, aminooxyacetic acid (AOAA) and KN-62, prior to further incubation with ATP, and the effect of the treatments on cell viability was investigated.Results: High-concentration ATP induced cell death in PC12 cells, and this was accompanied by markedly increased contents of extracellular H2S and CBS expression (p < 0.05). The ATP-induced cytotoxicity was significantly compromised after pretreatment with H2S. (p < 0.05). The viability of PC12 cells pretreated with NaHS and AOAA was significantly higher than that of PC12 cells treated with ATP alone. In addition, the viability of ATP-treated PC12 cells was further markedly increased after pretreatment with NaHS and KN-62 (p < 0.05).Conclusion: ATP induced a concentration- and time-dependent cytotoxicity in PC12 cells via theendogenous H2S/CBS system. Supplementation with exogenous H2S mitigated the cell damageinduced by high concentration of ATP via a specific mechanism which may be specifically related to P2X7R.
... The brain microenvironment heavily depends on the supply of solutes, nutrients, and ions for its normal physiological functioning and metabolism (Bélanger et al., 2011). The brain uses glucose as its primary fuel for ATP production, and the transporters involved in its uptake are the isoforms GLUT1 and GLUT3 within various cells in the brain (Maher et al., 1994;Vannucci et al., 1997;Lundgaard et al., 2015). However, the transport of glucose across the BBB mostly occurs from facilitative GLUT1 expressed by the brain endothelial cells in a 1:4 ratio on its luminal and abluminal membranes, respectively (Shah et al., 2012). ...
Nicotine, the major component of tobacco smoke (TS) and electronic cigarette (e-cig) vape, has been reported in some cases to be prodromal to cerebrovascular toxicity as well as a promoting factor for the onset of various neurological diseases. In some conditions, pre-exposure to nicotine can lead to a state of compromised blood-brain barrier (BBB) integrity, including altered BBB-related protein expression, BBB leakage, and defective ion and glucose homeostasis within the brain. Moreover, drugs used to treat central nervous system disorders (CNS) have been reported to interact with nicotine and other components of TS/e-cig through both transporter and enzyme-based mechanisms. Herein we discuss nicotine’s potential toxicity at the brain cerebrovasculature and explain how nicotine (from smoking/vaping) may interfere with the uptake of CNS drugs through a CNS drug interaction perspective.
... The brain microenvironment heavily depends on the supply of solutes, nutrients, and ions for its normal physiological functioning and metabolism (Bélanger et al., 2011). The brain uses glucose as its primary fuel for ATP production, and the transporters involved in its uptake are the isoforms GLUT1 and GLUT3 within various cells in the brain (Maher et al., 1994;Vannucci et al., 1997;Lundgaard et al., 2015). However, the transport of glucose across the BBB mostly occurs from facilitative GLUT1 expressed by the brain endothelial cells in a 1:4 ratio on its luminal and abluminal membranes, respectively (Shah et al., 2012). ...
Nicotine, the major component of tobacco smoke (TS) and electronic cigarette (e-cig) vape, has been reported in some cases to be prodromal to cerebrovascular toxicity as well as a promoting factor for the onset of various neurological diseases. In some conditions, pre-exposure to nicotine can lead to a state of compromised blood-brain barrier (BBB) integrity, including altered BBB-related protein expression, BBB leakage, and defective ion and glucose homeostasis within the brain. Moreover, drugs used to treat central nervous system disorders (CNS) have been reported to interact with nicotine and other components of TS/e-cig through both transporter and enzyme-based mechanisms. Herein we discuss nicotine’s potential toxicity at the brain cerebrovasculature and explain how nicotine (from smoking/vaping) may interfere with the uptake of CNS drugs through a CNS drug interaction perspective.
... Glucose transporters are important for glucose uptake in the brain and classical indicators of this uptake [65]. GLUT1 is expressed in oligodendrocytes and astrocytes [66], GLUT3 is expressed in neurons, and GLUT5 is expressed in microglia [67]. Reduced GLUT1 and GLUT3 have been reported in AD [68,69]. ...
Background
The role of physical exercise in the prevention of Alzheimer’s disease (AD) has been widely studied. Microglia play an important role in AD. Triggering receptor expressed in myeloid cells 2 (TREM2) is expressed on microglia and is known to mediate microglial metabolic activity and brain glucose metabolism. However, the relationship between brain glucose metabolism and microglial metabolic activity during running exercise in APP/PS1 mice remains unclear.
Methods
Ten-month-old male APP/PS1 mice and wild-type mice were randomly divided into sedentary groups or running groups (AD_Sed, WT_Sed, AD_Run and WT_Run, n = 20/group). Running mice had free access to a running wheel for 3 months. Behavioral tests, [18]F-FDG-PET and hippocampal RNA-Seq were performed. The expression levels of microglial glucose transporter (GLUT5), TREM2, soluble TREM2 (sTREM2), TYRO protein tyrosine kinase binding protein (TYROBP), secreted phosphoprotein 1 (SPP1), and phosphorylated spleen tyrosine kinase (p-SYK) were estimated by western blot or ELISA. Immunohistochemistry, stereological methods and immunofluorescence were used to investigate the morphology, proliferation and activity of microglia.
Results
Long-term voluntary running significantly improved cognitive function in APP/PS1 mice. Although there were few differentially expressed genes (DEGs), gene set enrichment analysis (GSEA) showed enriched glycometabolic pathways in APP/PS1 running mice. Running exercise increased FDG uptake in the hippocampus of APP/PS1 mice, as well as the protein expression of GLUT5, TREM2, SPP1 and p-SYK. The level of sTREM2 decreased in the plasma of APP/PS1 running mice. The number of microglia, the length and endpoints of microglial processes, and the ratio of GLUT5 ⁺ /IBA1 ⁺ microglia were increased in the dentate gyrus (DG) of APP/PS1 running mice. Running exercise did not alter the number of 5-bromo-2′-deoxyuridine (BrdU) ⁺ /IBA1 ⁺ microglia but reduced the immunoactivity of CD68 in the hippocampus of APP/PS1 mice.
Conclusions
Running exercise inhibited TREM2 shedding and maintained TREM2 protein levels, which were accompanied by the promotion of brain glucose metabolism, microglial glucose metabolism and morphological plasticity in the hippocampus of AD mice. Microglia might be a structural target responsible for the benefits of running exercise in AD. Promoting microglial glucose metabolism and morphological plasticity modulated by TREM2 might be a novel strategy for AD treatment.
In glucose transporter 1 deficiency syndrome (Glut1DS), glucose transport into brain is reduced due to impaired Glut1 function in endothelial cells at the blood–brain barrier. This can lead to shortages of glucose in brain and is thought to contribute to seizures. Ketogenic diets are the first‐line treatment and, among many beneficial effects, provide auxiliary fuel in the form of ketone bodies that are largely metabolized by neurons. However, Glut1 is also the main glucose transporter in astrocytes. Here, we review data indicating that glucose shortage may also impact astrocytes in addition to neurons and discuss the expected negative biochemical consequences of compromised astrocytic glucose transport for neurons. Based on these effects, auxiliary fuels are needed for both cell types and adding medium chain triglycerides (MCTs) to ketogenic diets is a biochemically superior treatment for Glut1DS compared to classical ketogenic diets. MCTs provide medium chain fatty acids (MCFAs), which are largely metabolized by astrocytes and not neurons. MCFAs supply energy and contribute carbons for glutamine and γ‐aminobutyric acid synthesis, and decanoic acid can also block α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid glutamate receptors. MCTs do not compete with metabolism of ketone bodies mostly occurring in neurons. Triheptanoin, an anaplerotic but also gluconeogenic uneven MCT, may be another potential addition to ketogenic diets, although maintenance of “ketosis” can be difficult. Gene therapy has also targeted both endothelial cells and astrocytes. Other approaches to increase fuel delivery to the brain currently investigated include exchange of Glut1DS erythrocytes with healthy cells, infusion of lactate, and pharmacological improvement of glucose transport. In conclusion, although it remains difficult to assess impaired astrocytic energy metabolism in vivo, astrocytic energy needs are most likely not met by ketogenic diets in Glut1DS. Thus, we propose prospective studies including monitoring of blood MCFA levels to find optimal doses for add‐on MCT to ketogenic diets and assessing of short‐ and long‐term outcomes.
In the face of flourishing industrialization and global trade, heavy metal and metalloid contamination of the environment is a growing concern throughout the world. The widespread presence of highly toxic compounds of arsenic, antimony, and cadmium in nature poses a particular threat to human health. Prolonged exposure to these toxins has been associated with severe human diseases, including cancer, diabetes, and neurodegenerative disorders. These toxins are known to induce analogous cellular stresses, such as DNA damage, disturbance of redox homeostasis, and proteotoxicity. To overcome these threats and improve or devise treatment methods, it is crucial to understand the mechanisms of cellular detoxification in metal and metalloid stress. Membrane proteins are key cellular components involved in the uptake, vacuolar/lysosomal sequestration, and efflux of these compounds; thus, deciphering the multilevel regulation of these proteins is of the utmost importance. In this review, we summarize data on the mechanisms of arsenic, antimony, and cadmium detoxification in the context of membrane proteome. We used yeast Saccharomyces cerevisiae as a eukaryotic model to elucidate the complex mechanisms of the production, regulation, and degradation of selected membrane transporters under metal(loid)-induced stress conditions. Additionally, we present data on orthologues membrane proteins involved in metal(loid)-associated diseases in humans.
Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD⁺, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research. image
Diabetes microangiopathy, a hallmark complication of diabetes, is characterised by structural and functional abnormalities within the intricate network of microvessels beyond well-known and documented target organs, i.e., the retina, kidney, and peripheral nerves. Indeed, an intact microvascular bed is crucial for preserving each organ’s specific functions and achieving physiological balance to meet their respective metabolic demands. Therefore, diabetes-related microvascular dysfunction leads to widespread multiorgan consequences in still-overlooked non-traditional target organs such as the brain, the lung, the bone tissue, the skin, the arterial wall, the heart, or the musculoskeletal system. All these organs are vulnerable to the physiopathological mechanisms that cause microvascular damage in diabetes (i.e., hyperglycaemia-induced oxidative stress, inflammation, and endothelial dysfunction) and collectively contribute to abnormalities in the microvessels’ structure and function, compromising blood flow and tissue perfusion. However, the microcirculatory networks differ between organs due to variations in haemodynamic, vascular architecture, and affected cells, resulting in a spectrum of clinical presentations. The aim of this review is to focus on the multifaceted nature of microvascular impairment in diabetes through available evidence of specific consequences in often overlooked organs. A better understanding of diabetes microangiopathy in non-target organs provides a broader perspective on the systemic nature of the disease, underscoring the importance of recognising the comprehensive range of complications beyond the classic target sites.
Parkinson's disease (PD) is a slowly progressive neurodegenerative disease characterized by α-synuclein aggregation and dopaminergic neuronal death. Recent evidence suggests that neuroinflammation is an early event in the pathogenesis of PD. Microglia are resident immune cells in the central nervous system that can be activated into either pro-inflammatory M1 or anti-inflammatory M2 phenotypes as found in peripheral macrophages. To exert their immune functions, microglia respond to various stimuli, resulting in the flexible regulation of their metabolic pathways. Inflammasomes activation in microglia induces metabolic shift from oxidative phosphorylation to glycolysis, and leads to the polarization of microglia to pro-inflammatory M1 phenotype, finally causing neuroinflammation and neurodegeneration. In addition, iron accumulation induces microglia take an inflammatory and glycolytic phenotype. M2 phenotype microglia is more sensitive to ferroptosis, inhibition of which can attenuate neuroinflammation. Therefore, this review highlights the interplay between microglial polarization and metabolic reprogramming of microglia. Moreover, it will interpret how inflammasomes and iron regulate microglial metabolism and phenotypic shifts, which provides a promising therapeutic target to modulate neuroinflammation and neurodegeneration in PD and other neurodegenerative diseases.
Traumatic spinal cord injury (SCI) causes secondary damage in injured and adjacent regions due to temporal deprivation of oxygen and energy supply. Peroxisome proliferator-activated receptor γ (PPARγ) is known to regulate cell survival mechanisms such as hypoxia, oxidative stress, inflammation, and energy homeostasis in various tissues. Thus, PPARγ has the potential to show neuroprotective properties. However, the role of endogenous spinal PPARγ in SCI is not well established. In this study, under isoflurane inhalation, a 10 g rod was freely dropped onto the exposed spinal cord after T10 laminectomy using a New York University impactor in male Sprague-Dawley rats. Cellular localization of spinal PPARγ, locomotor function, and mRNA levels of various genes including NFκB-targeted pro-inflammatory mediators after intrathecal administration of PPARγ antagonists, agonists, or vehicles in SCI rats were then analyzed. In both sham and SCI rats, spinal PPARγ was presented in neurons but not in microglia or astrocytes. Inhibition of PPARγ induced IκB activation and increased mRNA levels of pro-inflammatory mediators. It also suppressed recovery of locomotor function with myelin-related gene expression in SCI rats. However, a PPARγ agonist showed no beneficial effects on locomotor performances of SCI rats, although it further increased protein expression of PPARγ. In conclusion, endogenous PPARγ has a role in anti-inflammation after SCI. Inhibition of PPARγ might have a negative influence on motor function recovery through accelerated neuroinflammation. Nonetheless, exogenous PPARγ activation does not appear to effectively help with functional improvement after SCI.
The changes of metabolites of tricarboxylic acid (TCA) cycle in cells under hypoxia play a key role in drug screening. In order to dynamically monitor the drug metabolism changes of Scutellarin in the hypoxia environment induced by deferoxamine (DFO), a microfluidic-chip mass spectrometry method was used to study the real-time monitoring of drug metabolism changes under hypoxia conditions. This system has six drug-loading units, cell culture chamber, metabolite collection, filtration, HPLC separation and mass spectrometer. The cells in each microchannel were incubated with continuous flow of culture medium, metabolites will be collected by the fixed card slot, automatic sampling needle will be precise positioned and sampled. Through this new system combined with molecular biological methods, the changes of metabolites in TCA cycle of BV2 cells and drug metabolism of Scutellarin can be determined in real-time. In general, we illustrated a new mechanism of Scutellarin for reducing BV2 cell hypoxia injury and presented a novel analysis strategy that opened a way for real-time online monitoring of the energy metabolic mechanism of the effect of drugs on cells and further provided a superior strategy to screen natural drug candidates for hypoxia-related brain disease treatment.
The area postrema (AP) of the brain is exposed to circulating metabolites and hormones. However, whether AP detects glucose changes to exert biological responses remains unknown. Its neighboring nuclei, the nucleus tractus solitarius (NTS), responds to acute glucose infusion by inhibiting hepatic glucose production, but the mechanism also remains elusive. Herein, we characterized AP and NTS glucose-sensing mechanisms. Infusion of glucose into the AP, like the NTS, of chow rats suppressed glucose production during the pancreatic (basal insulin)-euglycemic clamps. Glucose transporter-1 or pyruvate kinase lentiviral-mediated knockdown in the AP negated AP glucose infusion to lower glucose production, while the glucoregulatory effect of NTS glucose infusion was also negated by knocking down glucose transporter-1 or pyruvate kinase in the NTS. Furthermore, we determined that high-fat (HF) feeding disrupts glucose infusion to lower glucose production in association with a modest reduction in expression of glucose transporter-1, but not pyruvate kinase, in the AP and NTS. However, pyruvate dehydrogenase activator dichloroacetate infusion into the AP or NTS that enhanced downstream pyruvate metabolism and recapitulated the glucoregulatory effect of glucose in chow rats still failed to lower glucose production in HF rats. We discovered that a glucose transporter-1 and pyruvate kinase-dependent glucose-sensing mechanism in the AP (as well as the NTS) lowers glucose production in chow rats, and that HF disrupts the glucose-sensing mechanism that is downstream of pyruvate metabolism in the AP and NTS. These findings highlight the role of AP and NTS in mediating glucose to regulate hepatic glucose production.
Insulin is a hormone secreted by pancreatic β cells. The concentration of glucose in circulation is proportional to the secretion of insulin by these cells. In target cells, insulin binds to its receptors and activates phosphatidylinositol-3-kinase/protein kinase B, inducing different mechanisms depending on the cell type. In the liver it activates the synthesis of glycogen, in adipose tissue and muscle it allows the capture of glucose, and in the hypothalamus, it regulates thermogenesis and appetite. Defects in insulin function [insulin resistance (IR)] are related to the development of neurodegenerative diseases in obese people. Furthermore, in obesity and diabetes, its role as an anorexigenic hormone in the hypothalamus is diminished during IR. Therefore, hyperphagia prevails, which aggravates hyper-glycemia and IR further, becoming a vicious circle in which the patient cannot regulate their need to eat. Uncontrolled calorie intake induces an increase in reactive oxygen species, overcoming cellular antioxidant defenses (oxidative stress). Reactive oxygen species activate stress-sensitive kinases, such as c-Jun N-terminal kinase and p38 mitogen-activated protein kinase, that induce phos-phorylation in serine residues in the insulin receptor, which blocks the insulin signaling pathway, continuing the mechanism of IR. The brain and pancreas are organs mainly affected by oxidative stress. The use of drugs that regulate food intake and improve glucose metabolism is the conventional therapy to improve the quality of life of these patients. Currently, the use of antioxidants that regulate oxidative stress has given good results because they reduce oxidative stress and inflammatory processes, and they also have fewer side effects than synthetic drugs.
Cholesterol serves a vital role in the occurrence and development of glioblastoma multiforme (GBM). Furthermore, cholesterol synthesis is regulated by sterol regulatory element-binding protein 2 (SREBP2), and certain glucose transporters (GLUTs) and Ras-related protein Rab11 (Rab11) small GTPase family members (Rab11s) may contribute to the process. The Cancer Genome Atlas was used to analyze the relationship between prognosis and GLUT gene expressions. To investigate the regulatory effect of Rab11s and SREBP2 on GLUTs during tumor progression, single cell RNA sequencing (scRNA-seq), western blotting and reverse transcription-quantitative PCR were performed on glioma tissues and the T98G GBM cell line. Cell viability and migration were assessed by performing MTT and wound healing assays, respectively. Moreover, the dual-luciferase reporter gene assay was conducted to predict the sterol regulatory elements in the promoter regions of the target genes. The results demonstrated that high SREBP2, GLUT1 and GLUT6 expression was associated with poor survival of patients with GBM. ScRNA-seq distinguished glioblastoma cells by EGFR and indicated the related lipid metabolism signaling pathways. Moreover, the results indicated that GLUT1 and GLUT6 were regulated by SREBP2 and Rab11s. Rab11s and SREBP2 also contributed to T98G cell viability and migration. Additionally, the results indicated that Rab11s, GLUT1 and GLUT6 were transcriptionally regulated by SREBP2. Therefore, the present study suggested that the SREBP2/Rab11/GLUT network promoted T98G cell growth, thus, identifying potential therapeutic targets for GBM.
Background
Glut1 deficiency syndrome (Glut1-DS) is a rare metabolic encephalopathy. Familial forms are poorly investigated, and no previous studies have explored aspects of Glut1-DS over the course of life: clinical pictures, intelligence, life achievements, and quality of life in adulthood.
Clinical, biochemical and genetic data in a cohort of familial Glut1-DS cases were collected from medical records. Intelligence was assessed using Raven’s Standard Progressive Matrices and Raven’s Colored Progressive Matrices in adults and children, respectively. An ad hoc interview focusing on life achievements and the World Health Organization Quality of Life Questionnaire were administered to adult subjects.
Results
The clinical picture in adults was characterized by paroxysmal exercise-induced dyskinesia (PED) (80%), fatigue (60%), low intelligence (60%), epilepsy (50%), and migraine (50%). However, 20% of the adults had higher-than-average intelligence. Quality of Life (QoL) seemed unrelated to the presence of PED or fatigue in adulthood. An association of potential clinical relevance, albeit not statistically significant, was found between intelligence and QoL. The phenotype of familial Glut1-DS in children was characterized by epilepsy (83.3%), intellectual disability (50%), and PED (33%).
Conclusion
The phenotype of familial Glut1-DS shows age-related differences: epilepsy predominates in childhood; PED and fatigue, followed by epilepsy and migraine, characterize the condition in adulthood. Some adults with familial Glut1-DS may lead regular and fulfilling lives, enjoying the same QoL as unaffected individuals. The disorder tends to worsen from generation to generation, with new and more severe symptoms arising within the same family. Epigenetic studies might be useful to assess the phenotypic variability in Glut1-DS.
Glial cells are the most abundant cells of the brain, outnumbering neurons. These multifunctional cells are crucial for maintaining brain homeostasis by providing trophic and nutritional support to neurons, sculpting synapses, and providing an immune defense. Glia are highly plastic and undergo both structural and functional alterations in response to changes in the brain microenvironment. Glial phenotypes are intimately regulated by underlying metabolic machinery, which dictates the effector functions of these cells. Altered brain energy metabolism and chronic neuroinflammation are common features of several neurodegenerative diseases. Microglia and astrocytes are the major glial cells fueling the ongoing neuroinflammatory process, exacerbating neurodegeneration. Distinct metabolic perturbations in microglia and astrocytes, including altered carbohydrate, lipid, and amino acid metabolism have been documented in neurodegenerative diseases. These disturbances aggravate the neurodegenerative process by potentiating the inflammatory activation of glial cells. This review covers the recent advances in the molecular aspects of glial metabolic changes in the pathophysiology of neurodegenerative diseases. Finally, we discuss studies exploiting glial metabolism as a potential therapeutic avenue in neurodegenerative diseases.
We used next‐generation metabolic screening to identify new biomarkers for improved diagnosis and pathophysiological understanding of glucose transporter type 1 deficiency syndrome (GLUT1DS), comparing metabolic CSF profiles from 12 patients to those of 116 controls. This confirmed decreased CSF glucose and lactate levels in patients with GLUT1DS and increased glutamine at group level. We identified three novel biomarkers significantly decreased in patients, namely gluconic + galactonic acid, xylose‐α1‐3‐glucose and xylose‐α1‐3‐xylose‐α1‐3‐glucose, of which the latter two have not previously been identified in body fluids. CSF concentrations of gluconic + galactonic acid may be reduced as these metabolites could serve as alternative substrates for the pentose phosphate pathway. Xylose‐α1‐3‐glucose and xylose‐α1‐3‐xylose‐α1‐3‐glucose may originate from glycosylated proteins; their decreased levels are hypothetically the consequence of insufficient glucose, one of two substrates for O‐glucosylation. Since many proteins are O‐glucosylated, this deficiency may affect cellular processes and thus contribute to GLUT1DS pathophysiology. The novel CSF biomarkers have the potential to improve the biochemical diagnosis of GLUT1DS. Our findings imply that brain glucose deficiency in GLUT1DS may cause disruptions at the cellular level that go beyond energy metabolism, underlining the importance of developing treatment strategies that directly target cerebral glucose uptake.
Early sporadic Alzheimer’s disease (SAD) caused by abnormal glucose/energy metabolism and disrupted insulin signaling is associated with a brain insulin-resistant state, which is the root cause of neurodegenerative changes. In preclinical studies, mainly in rodents, intracerebroventricular (ICV) administration of streptozotocin (STZ) at subdiabetogenic doses leads to a perturbed brain insulin-resistant state. Furthermore, ICV-STZ infused animals display memory loss, progressive cholinergic dysfunction, oxidative stress, impaired glucose metabolism, and neurodegeneration that are akin to the pathological changes in human SAD. Animal models which mimic many of these pathological features of human SAD play an important role to test the therapeutic potential of newer molecules including phytochemicals for the prevention and treatment of SAD. The present chapter aims to explore the cellular pathways involved in the ICV-STZ-induced model of SAD. Moreover, the therapeutic potential of phytochemicals which have been evaluated so far in the ICV-STZ animal model of SAD has been also included and appraised for their potential usefulness as possible molecules for pharmaceutical or dietary application in SAD.
We used next-generation metabolic screening to identify new biomarkers for improved diagnosis and pathophysiological understanding of glucose transporter type 1 deficiency syndrome (GLUT1DS), comparing metabolic CSF profiles from 11 patients to those of 116 controls. This confirmed decreased CSF glucose and lactate levels in patients with GLUT1DS and increased glutamine at group level. We identified three novel biomarkers significantly decreased in patients, namely gluconic + galactonic acid, xylose-α1-3-glucose and xylose-α1-3-xylose-α1-3-glucose, of which the latter two have not previously been identified in body fluids. CSF concentrations of gluconic + galactonic acid may be reduced as these metabolites could serve as alternative substrates for the pentose phosphate pathway. Xylose-α1-3-glucose and xylose-α1-3-xylose-α1-3-glucose may originate from O-glycosylated proteins; their decreased levels are hypothetically the consequence of insufficient glucose, one of two substrates for O-glucosylation. Since many proteins are O-glucosylated, this deficiency may affect cellular processes and thus contribute to GLUT1DS pathophysiology. The novel CSF biomarkers have the potential to improve the biochemical diagnosis of GLUT1DS. Our findings imply that brain glucose deficiency in GLUT1DS may cause disruptions at the cellular level that go beyond energy metabolism, underlining the importance of developing treatment strategies that directly target cerebral glucose uptake.
Background:
Delirium, an acute confusion status, is associated with adverse effects, including the development of Alzheimer's disease. However, the etiology and underlying mechanisms of delirium remain largely to be determined. Many patients have urinary catheterization (UC), and UC is associated with delirium. However, the cause effects of UC-associated delirium and the underlying mechanisms remain largely unknown. We, therefore, established an animal model of UC, without urinary tract infection, in mice and determined whether UC could induce delirium-like behavior in the mice and the underlying mechanism of these effects.
Methods:
Adult female mice (16 weeks old) had UC placement under brief isoflurane anesthesia. The delirium-like behavior was determined using our established mice model at 3, 6, 9, and 24 hours after UC placement. We measured the amounts of glucose in both blood and brain interstitial fluid, adenosine triphosphate (ATP) concentration in the cortex, and glucose transporter 1 in the cortex of mice using western blot, immunohistochemistry imaging, reverse transcriptase-polymerase chain reaction (RT-PCR), and fluorescence at 6 hours after the UC placement. Finally, we used vascular endothelial growth factor (VEGF) in the interaction studies.
Results:
We found that UC induced delirium-like behavior in mice at 3, 6, 9, but not 24 hours after the UC placement. UC decreased glucose amounts in brain interstitial fluid (86.38% ± 4.99% vs 100% ± 6.26%, P = .003), but not blood of mice and reduced ATP amounts (84.49% ± 8.85% vs 100% ± 10.64%, P = .031) in the cortex of mice. Finally, UC reduced both protein amount (85.49% ± 6.83% vs 100% ± 11.93%, P = .040) and messenger ribonucleic acid (mRNA) expression (41.95% ± 6.48% vs 100% ± 19.80%, P = .017) of glucose transporter 1 in the cortex of mice. VEGF attenuated these UC-induced changes.
Conclusions:
These data demonstrated that UC decreased brain glucose and energy amounts via impairing the glucose transport from blood to brain, leading to delirium-like behavior in mice. These findings will promote more research to identify the etiologies and underlying mechanisms of delirium.
Background
Advances in genetic science have led to the identification of many rare treatable pediatric movements disorders (MDs). We explored the phenotypic–genotypic spectrum of pediatric patients presenting with MDs. By this, we aimed at raising awareness about such rare disorders, especially in our region. Over the past 3 years, we reviewed the demographic data, clinical profile, molecular genetics and other diagnostic workups of pediatric patients presenting with MDs.
Results
Twelve patients were identified; however, only six patients were genetically confirmed. The phenomenology of MDs ranged from paroxysmal kinesigenic choreoathetosis (1 patient), exercise-induced dyskinesia (2 patients), ataxia (2 patients) and dystonia (2 patients). Whole-exome sequencing in addition to the functional studies for some patients revealed a specific genetic diagnosis being responsible for their MDs. The genetic diagnosis of our patients included infantile convulsions and paroxysmal choreoathetosis syndrome and episodic ataxia due to “pathogenic homozygous mutation of PRRT2 gene,” glucose transporter type 1 deficiency-exercise induced dyskinesia due to “De Novo pathogenic heterozygous missense mutation of exon 4 of SLC2A1 gene,” aromatic L amino acid decarboxylase deficiency due to “pathogenic homozygous mutation of the DDC gene,” myopathy with extrapyramidal signs due to “likely pathogenic homozygous mutations of the MICU1 gene,” mitochondrial trifunctional protein deficiency due to “homozygous variant of uncertain significance (VUS) of HADHB gene” and glutaric aciduria II with serine deficiency due to “homozygous VUS for both ETFDH and PHGDH genes.” After receiving the treatment as per recognized treatment protocols, two patients showed complete resolution of symptoms and the rest showed variable responses.
Conclusion
Identifying the genetic etiology of our patients guided us to provide either disease-specific treatment or redirected our management plan. Hence, highlighting the value of molecular genetic analysis to avoid the diagnostic odyssey and identify treatable MDs.
The transport of glucose across the brain capillary endothelium, which makes up the blood-brain barrier (BBB) in vivo, is developmentally up-regulated in the postnatal period, as the brain switches from combustion of circulating ketone bodies to glucose. The principle transporter mediating the uptake of circulating glucose across the BBB is the GLUT1 isoform. To further define molecular mechanisms underlying developmental modulation of the BBB GLUT1 transporter, the amounts of brain microvessel GLUT1 mRNA and immunoreactive protein were quantitated. In addition, an immunocytochemical analysis of GLUT1 expression at the choroid plexus in developing brain was performed, since this transporter isoform is selectively expressed at the choroid plexus epithelium basolateral membrane. Quantitative Western blotting employing purified human erythrocyte glucose transporter as an assay standard showed that the concentration of immunoreactive GLUT1 protein in 70-day-old rabbit brain microvessels (111 +/- 3 pmol/mg pro...
We recently reported that the glucose transporter isoform, GLUT5, is expressed on the brush border membrane of human small intestinal enterocytes (Davidson, N. O., Hausman, A. M. L., Ifkovits, C. A., Buse, J. B., Gould, G. W., Burant, C. F., and Bell, G. I. (1992) Am. J. Physiol. 262, C795-C800). To define its role in sugar transport, human GLUT5 was expressed in Xenopus oocytes and its substrate specifiicity and kinetic properties determined. GLUT5 exhibits selectivity for fructose transport, as determined by inhibition studies, with a K(m) of 6 mM. In addition, fructose transport by GLUT5 is not inhibited by cytochalasin B, a competitive inhibitor of facilitative glucose transporters. RNA and protein blotting studies showed the presence of high levels of GLUT5 mRNA and protein in human testis and spermatozoa, and immunocytochemical studies localize GLUT5 to the plasma membrane of mature spermatids and spermatozoa. The biochemical properties and tissue distribution of GLUT5 are consistent with a physiological role for this protein as a fructose transporter.
Physiological stimulation of the hypothalamo-neurohypophysial system by salt loading of rats resulted in a dramatically increased glucose utilization in the posterior pituitary but not in the paraventricular or supraoptic nuclei. The good correlation between glucose utilization and neural activity in the posterior pituitary (that is, nerve terminals) contrasted with the lack of correlation in the paraventricular and supraoptic nuclei (that is, the sites of the cell bodies of the same neurons). This difference in the metabolic response to functional activity between the two regions of these neurons can be explained by the differences in surface-to-volume ratios of these regions.
— The kinetics of the uptake from blood to brain of pyruvate, lactate and glucose have been determined in rats of different ages. The carotid artery single injection technique was used in animals anaesthetized with pentobarbital. The rates of influx for each substrate were determined over a range of concentrations for the different age-groups. Data were analysed in terms of the Michaelis-Menten equation with a component to allow for non-saturable diffusion. Values are given for Km, Vmax and Kd. In suckling rats (15-21 days) the Vmax values for both pyruvate and lactate were 2.0 μmol g−1 min−1. In 28-day-old rats the Vmax values had fallen to one-half and in adults they were less than one-tenth. Km, values were higher in the younger animals. The rate of glucose transport in suckling rats was half that of 28-day-old and adults although there was no difference with age in the Km values.The results are discussed in relation to the net flux of these substrates in and out of brain during different stages of post-natal development.
The type 1 glucose transporter (GLUT1) gene encodes an integral membrane glycoprotein responsible for facilitating transfer of glucose across plasma membrane and is rapidly activated by serum, growth factors, and by oncogenic transformation. To elucidate the molecular mechanisms of regulation of GLUT1 gene expression, we isolated and characterized the mouse GLUT1 gene. DNA elements regulating transcription of the gene were analyzed in transient expression assays after transfection of NIH/3T3 cells with a low background chloramphenicol acetyltransferase (CAT) vector system pSVOOCAT. We identified two enhancer elements; the first one is located 2.7 kilobases upstream of the cap site of the gene which contains the homologous sequences with two 12-O-tetradecanoylphorbol-13-acetate-responsive elements (TREs), a serum response element, a cyclic AMP-responsive element (CRE) and three GC boxes, and the second one is located in the second intron of the gene which contains the homologous sequences with two TREs and one CRE. With the promoter alone the transcription of the gene is activated by src, only slightly activated by ras and is not activated by serum and platelet-derived growth factor. When the gene is accompanied by one of these enhancers, the transcription is activated by all these stimuli.
A recent study by C.F. Burant et al. (13) demonstrates that GLUT5 is a high-affinity fructose transporter with a much lower capacity to transport glucose. To characterize the potential role of GLUT5 in fructose and glucose transport in insulin-sensitive tissues, we investigated the distribution and insulin-stimulated translocation of the GLUT5 protein in human tissues by immunoblotting with an antibody to the COOH-terminus of the human GLUT5 sequence. GLUT5 was detected in postnuclear membranes from the small intestine, kidney, heart, four different skeletal muscle groups, and the brain, and in plasma membranes from adipocytes. Cytochalasin-B photolabeled a 53,000-M(r) protein in small intestine membranes that was immunoprecipitated by the GLUT5 antibody; labeling was inhibited by D- but not L-glucose. N-glycanase treatment resulted in a band of 45,000 M(r) in all tissues. Plasma membranes were prepared from isolated adipocytes from 5 nonobese and 4 obese subjects. Incubation of adipocytes from either group with 7 nM insulin did not recruit GLUT5 to the plasma membrane, in spite of a 54% insulin-stimulated increase in GLUT4 in nonobese subjects. Thus, GLUT5 appears to be a constitutive sugar transporter that is expressed in many tissues. Further studies are needed to define its overall contribution to fructose and glucose transport in insulin-responsive tissues and brain.
Aminoalkylcarbamate derivatives of forskolin have been synthesized at the 6- and 7-hydroxyl positions which have different selectivity for adenylyl cyclase and a glucose transporter, respectively. They were radioiodinated using the Bolton-Hunter reagent to yield [125I]-2-[3-(4-hydroxy-3-iodophenyl)propanamido]-N-ethyl-6- (aminocarbonyl)forskolin ([125I]6-IHPP-Fsk) and [125I]-2-[3-(4-hydroxy-3-iodophenyl)(propanamidol]-N-ethyl-7- (aminocarbonyl)-7-desacetylforskolin ([125I]7-IHPP-Fsk) and tested as autoradiographic probes for adenylyl cyclase and a glucose transporter. In slide-mounted rat brain sections [125I]6-IHPP-Fsk binding was potently inhibited by 1 microM 6-HPP-Fsk (95%) but unaffected by 500 mM D-glucose. In contrast, [125I]7-IHPP-Fsk was only partially inhibited by 1 microM 6-HPP-Fsk (37%), but residual [125I]7-IHPP-Fsk binding was further inhibited 56% by 500 mM D-glucose. These data suggest that while [125I]6-IHPP-Fsk binds exclusively to adenylyl cyclase, a significant fraction of [125I]7-IHPP-Fsk is binding to a glucose transporter in brain. Autoradiographic patterns of [125I]6-IHPP-Fsk and glucose-sensitive [125I]7-IHPP-Fsk binding were different. [125I]6-IHPP-Fsk binding was heterogeneously distributed and resembled [3H] forskolin binding. Highest densities of binding sites were noted in olfactory tubercle, caudate putamen, nucleus accumbens, pyramidal and granule cell layers of hippocampus, molecular layer of cerebellum and substantia nigra. In contrast, of glucose-sensitive [125I]7-IHPP-Fsk, binding appeared more homogeneous and similar to [3H]cytochalasin B, a compound which inhibits glucose transport. Highest densities of binding were noted in caudate putamen, nucleus accumbens, cerebral cortex and molecular layer of cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)
We have examined the expression and cellular location of facilitated glucose transporter proteins (GLUT1, -3, and -5) in a human colonic epithelial cell line (Caco-2) by using peptide-specific antibodies. A differential cellular distribution of these transporters was observed in differentiated (greater than 14 days postconfluence) Caco-2 cells by immunofluorescence and immunoelectron microscopy. GLUT1 was localized primarily to the basolateral membrane, whereas GLUT3 was predominantly localized to the apical membrane. GLUT5, which was detected in only approximately 40% of fully differentiated Caco-2 cells, was found primarily in the apical membrane but was also present in both basolateral and intracellular membranes. A Na(+)-independent glucose transport system in the apical membrane of Caco-2 cells has been described previously [Blais, A., Bissonnette, A. & Berteloot, A. (1987) J. Membr. Biol. 99, 113-125], and we propose that GLUT3 mediates this process. The amino acid sequence identity (57%) and structural conservation between GLUT1 and GLUT3 may make these transporters an ideal model system for examining the molecular basis for polarized sorting of membrane proteins.
Antibodies raised against a 52 kDa rat liver microsomal glucose-transport protein were used to screen a rat liver cDNA library. Six positive clones were isolated. Two clones were found to be identical with the liver plasma-membrane glucose-transport protein termed GLUT 2. The sequence of the four remaining clones indicates that they encode a unique microsomal facilitative glucose-transport protein which we have termed GLUT 7. Sequence analysis revealed that the largest GLUT 7 clone was 2161 bp in length and encodes a protein of 528 amino acids. The deduced amino acid sequence of GLUT 7 shows 68% identity with the deduced amino acid sequence of rat liver GLUT 2. The GLUT 7 sequence is six amino acids longer than rat liver GLUT 2, and the extra six amino acids at the C-terminal end contain a consensus motif for retention of membrane-spanning proteins in the endoplasmic reticulum. When the largest GLUT 7 clone was transfected into COS 7 cells the expressed protein was found in the endoplasmic reticulum and nuclear membrane, but not in the plasma membrane. Microsomes isolated from the transfected COS 7 cells demonstrated an increase in their microsomal glucose-transport capacity, demonstrating that the GLUT 7 clone encodes a functional endoplasmic-reticulum glucose-transport protein.
We investigated the diversity of cellular localization of the GLUT-1 glucose transporter protein at epithelial and endothelial barriers either possessing or lacking occluding junctions. The avidin-biotin immunoperoxidase and the immunogold-silver staining (IGSS) techniques were used. A rabbit polyclonal antiserum prepared against a synthetic peptide encoding the 13 amino acids at the carboxyl terminus of the GLUT-1 glucose transporter protein was used. Both techniques were found to have comparable sensitivity in detecting immunoreactive GLUT-1. The IGSS experiments employed a light-insensitive stabilizer, and no immunoreactive GLUT-1 was found in brain cells (neurons, glial cells), but abundant immunoreactive GLUT-1 was found in brain capillary endothelium, which is composed of cells with occluding junctions. However, immunoreactive GLUT-1 was also found in endothelium known not to contain occluding junctions, such as testicular microvascular endothelium and endothelium on the fetal side of the syncytiotrophoblast of the placenta. In epithelial barriers, GLUT-1 was also found in the basolateral membrane of renal collecting duct epithelium, choroid plexus, and the placental syncytiotrophoblast layer. However, immunoreactive GLUT-1 was found in the apical membrane of ependymal epithelium near the lower portion of the third ventricle. In conclusion, there is diversity underlying the expression of the GLUT-1 glucose transporter protein in different cell types, and the transporter protein can be found in endothelium with and without occluding junctions, and in both apical and basolateral membranes of epithelial barriers.
In the present study, we have investigated the expression of both the erythrocyte-type (GLUT1) and the brain-type (GLUT3) glucose transporter isoforms in primary human brain tumors. In situ hybridization made it possible to localize and semiquantify both GLUT1 and GLUT3 mRNAs of individual cells in all 18 samples examined. More signals for GLUT3 mRNA than for GLUT1 mRNA were found over astrocytoma cells, while the reverse was the case in all 6 meningiomas. In astrocytomas, for both mRNAs, the density of silver grains over tumor cells was well correlated with the malignancy of the cells. This correlation was, as was also confirmed by Northern blot analysis, more marked with GLUT3 mRNA than with GLUT1 mRNA. In 2 of 5 anaplastic astrocytomas and in all 3 glioblastomas, numerous tumor cells with large amounts of both mRNAs tended to surround the perivascular regions. "Tumor vessels" with endothelial proliferation, an almost pathognomonic feature of glioblastomas, expressed much GLUT3 mRNA but no significant GLUT1 mRNA, while a single- or a few-layered capillary endothelium expressed much GLUT1 mRNA. The distribution of both mRNAs was in good accordance with that of both proteins. Our results suggest that the expression of both glucose transporter isoforms may contribute to the maintenance of human brain tumors and that the expression of the GLUT3 isoform may be closely related to the malignant change of astrocytomas and particularly related to the aberrant neovascularization which accompanies glioblastomas.
Two novel facilitative glucose transporter-like cDNAs have been isolated from human small intestine and fetal skeletal muscle cDNA libraries by low stringency cross-hybridization with a fragment of the human erythrocyte/GLUT1 facilitative glucose transporter cDNA. One encodes a 501-amino acid facilitative glucose transporter, designated as the small intestine/GLUT5 isoform, having 41.7, 40.0, 38.7, and 41.6% identity with the previously described human erythrocyte/GLUT1, liver/GLUT2, brain/GLUT3, and muscle-fat/GLUT4 isoforms, respectively. GLUT5 mRNA is expressed at highest levels in small intestine and at much lower levels in kidney, skeletal muscle, and adipose tissue. Expression of in vitro synthesized human GLUT5 mRNA in Xenopus laevis oocytes indicates that the GLUT5 protein is a cytochalasin B-sensitive glucose carrier. The gene encoding the GLUT5 protein is located on the short arm of human chromosome 1. The second facilitative transporter-like cDNA sequence, designated GLUT6, is part of an 11-kilobase transcript that is expressed in all tissues examined. The sequence of a partial-length GLUT6 cDNA having an insert of 3.4 kilobase pairs revealed a region of 1.5 kilobase pairs that has 79.6% identity with the human brain/GLUT3 facilitative glucose transporter cDNA. However, because of the presence of multiple stop codons and frame shifts, this sequence cannot encode a functional glucose transporter protein. The region of facilitative glucose transporter nucleotide sequence homology in the GLUT6 transcript may have arisen by insertion of a reverse-transcribed GLUT3 transcript into the untranslated region of another gene. The GLUT6 gene is located on the long arm of human chromosome 5.
Marie Hully, Sandrine Vuillaumier-Barrot, Christiane Le Bizec, Nathalie Boddaert, Anna Kaminska, Karine Lascelles, Pascale de Lonlay, Claude Cances, Vincent des Portes, Agathe Roubertie, Diane Doummar, Anne LeBihannic, Bertrand Degos, Anne de Saint Martin, Elisabeth Flori, Jean Michel Pedespan, Alice Goldenberg, Catherine Vanhulle, Soumeya Bekri, Anne Roubergue, Bénédicte Heron, Marie-Anne Cournelle, Alice Kuster, Alexis Chenouard, Marie-Noelle Loiseau, Vassili Valayannopoulos, Nicole Chemaly, Cyril Gitiaux, Nathalie Seta, Nadia Bahi-Buisson. (2015) From splitting GLUT1 deficiency syndromes to overlapping phenotypes. European Journal of Medical Genetics 58, 443-454
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W. G. Leen, J. Klepper, M. M. Verbeek, M. Leferink, T. Hofste, B. G. van Engelen, R. A. Wevers, T. Arthur, N. Bahi-Buisson, D. Ballhausen, J. Bekhof, P. van Bogaert, I. Carrilho, B. Chabrol, M. P. Champion, J. Coldwell, P. Clayton, E. Donner, A. Evangeliou, F. Ebinger, K. Farrell, R. J. Forsyth, C. G. E. L. de Goede, S. Gross, S. Grunewald, H. Holthausen, S. Jayawant, K. Lachlan, V. Laugel, K. Leppig, M. J. Lim, G. Mancini, A. D. Marina, L. Martorell, J. McMenamin, M. E. C. Meuwissen, H. Mundy, N. O. Nilsson, A. Panzer, B. T. Poll-The, C. Rauscher, C. M. R. Rouselle, I. Sandvig, T. Scheffner, E. Sheridan, N. Simpson, P. Sykora, R. Tomlinson, J. Trounce, D. Webb, B. Weschke, H. Scheffer, M. A. Willemsen. (2010) Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder. Brain 133, 655-670
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Complementary DNAs encoding the mouse GLUT3/brain facilitative glucose transporter have been isolated and sequenced. The predicted amino acid sequence indicates that mouse GLUT3 is composed of 493 amino acids and has 83 and 89% identity and similarity, respectively, to the sequence of human GLUT3. In contrast to human GLUT3 mRNA, which can be readily detected by RNA blotting in all human tissues that have been examined, mouse GLUT3 mRNA was only present at significant levels in brain. In situ hybridization showed differential expression of GLUT3 mRNA in several regions of adult mouse brain. Specific expression was observed in the hippocampus, with GLUT3 mRNA levels being higher in areas CA1 to CA3 than in the dentate gyrus. It was also detected in the Purkinje cell layer of the cerebellum and in the cerebral cortex, with higher expression in the piriform cortex than in other regions of the cortex. Antisera to mouse GLUT3 immunoblotted a series of proteins of 45-50 kDa in mouse brain plasma membranes. These results are consistent with GLUT3 being a neuronal glucose transporter.
Glucose is the main fuel for energy metabolism in the normal human brain. It is generally assumed that glucose transport into the brain is not rate-limiting for metabolism. Since brain glucose concentrations cannot be determined directly by radiotracer techniques, we used 13C NMR spectroscopy after infusing enriched D-[1-13C]glucose to measure brain glucose concentrations at euglycemia and at hyperglycemia (range, 4.5-12.1 mM) in six healthy children (13-16 years old). Brain glucose concentrations averaged 1.0 +/- 0.1 mumol/ml at euglycemia (4.7 +/- 0.3 mM plasma) and 1.8-2.7 mumol/ml at hyperglycemia (7.3-12.1 mM plasma). Michaelis-Menten parameters of transport were calculated to be Kt = 6.2 +/- 1.7 mM and Tmax = 1.2 +/- 0.1 mumol/g.min from the relationship between plasma and brain glucose concentrations. The brain glucose concentrations and transport constants are consistent with transport not being rate-limiting for resting brain metabolism at plasma levels greater than 3 mM.
The glucose transporter (GLUT) isoforms responsible for glucose uptake in early mouse embryos have been identified. GLUT 1, the isoform present in nearly every tissue examined including adult brain and erythrocytes, is expressed throughout preimplantation development. GLUT 2, which is normally present in adult liver, kidney, intestine and pancreatic beta cells is expressed from the 8-cell stage onward. GLUT 4, an insulin-recruitable isoform, which is expressed in adult fat and muscle, is not expressed at any stage of preimplantation development or in early postimplantation stage embryos. Genetic mapping studies of glucose transporters in the mouse show that Glut-1 is located on chromosome 4, Glut-2 on chromosome 3, Glut-3 on chromosome 6, and Glut-4 on chromosome 11.
The increase in glucose transport that occurs when chicken embryo fibroblasts (CEFs) are transformed by src is associated with an increase in the amount of type 1 glucose transporter protein, and we have previously shown that this effect is due to a decrease in the degradation rate of this protein. The rate of CEF type 1 glucose transporter biosynthesis and the level of its mRNA are unaffected by src transformation. To study the molecular basis of this phenomenon, we have been isolating chicken glucose transporter cDNAs by hybridization to a rat type 1 glucose transporter probe at low stringency. Surprisingly, these clones corresponded to a message encoding a protein which has most sequence similarity to the human type 3 glucose transporter and which we refer to as CEF-GT3. CEF-GT3 is clearly distinct from the CEF type 1 transporter that we have previously described. Northern (RNA) analysis of CEF RNA with CEF-GT3 cDNA revealed two messages of 1.7 and 3.3 kb which were both greatly induced by src transformation. When the CEF-GT3 cDNA was expressed in rat fibroblasts, a three-to fourfold enhancement of 2-deoxyglucose uptake was observed, indicating that CEF-GT3 is a functional glucose transporter. Northern analyses using a CEF-GT3 and a rat type 1 probe demonstrated that there is no hybridization between different isoforms but that there is cross-species hybridization between the rat type 1 probe and the chicken homolog. Southern blot analyses confirmed that the chicken genomic type 1 and type 3 transporters are encoded by distinct genes. We conclude that CEFs express two types of transporter, type 1 (which we have previously reported to be regulated posttranslationally by src) and a novel type 3 isoform which, unlike type 1, shows mRNA induction upon src transformation. We conclude that src regulates glucose transport in CEFs simultaneously by two different mechanisms.
Steady-state distribution spaces of 2-[14C]deoxyglucose ([14C]DG), glucose, and 3-O-[14C]methylglucose at various concentrations of glucose in brain and plasma ranging from hypoglycemic to hyperglycemic levels have been determined by direct chemical analyses in the brains of conscious rats. The hexose concentrations were measured chemically in freeze-blown brain extracted with ethanol to avoid the degradation of acid-labile products of [14C]DG back to free [14C]DG that has been found to occur with the more commonly used perchloric acid extraction of brain. Corrections were also made for nonphosphorylatable, labeled products of [14C]DG found in the nonacidic fractions of the brain extracts, which were previously included with the assayed [14C]DG, and for the contribution of the hexose contents in the blood in the brain, which was found to be particularly critical for the determination of the glucose distribution space, especially in hypoglycemic states. From the measured contents of the hexoses in brain and plasma, the relationships of the tissue concentrations and distribution spaces of each of the hexoses and of the lambda (i.e., ratio of tissue distribution space of DG to that of glucose) of the DG method to the tissue glucose concentration were derived. The lambda was then quantitatively related to the measured equilibrium ratio for [14C]methylglucose over the full range of brain and plasma glucose levels. By combining these new data with the values for the lumped constant, the factor that converts the rate of DG phosphorylation to glucose phosphorylation, previously determined in rats over the same range of plasma glucose levels, the phosphorylation coefficient was calculated and the lumped constant graphed as a function of the measured distribution space in brain for [14C]methylglucose.
Dynamic positron emission tomography with [18F]fluorodeoxyglucose was used in six patients with Alzheimer's disease (AD) and seven healthy age-matched control subjects to estimate the kinetic parameters K1*, k2*, and k3* that describe glucose transport and phosphorylation. A high-resolution tomograph was used to acquire brain uptake data in one tomographic plane, and a radial artery catheter connected to a plastic scintillator was used to acquire arterial input data. A nonlinear iterative least-squares fitting procedure that included terms for the vascular fraction and time delay to the peripheral sampling site was used to fit a three-compartment model to the brain data. Regions studied included frontal, temporal, occipital, and the entire cortex and subcortical white matter. The values obtained for the individual rate constants and regional CMRglc (rCMRglc; calculated using regional values of the rate constants) were higher than those reported previously. A significant (p less than 0.05) decrease was found in K1* in frontal and temporal cortex in the AD patients compared with the controls, with values of 0.157 and 0.161 ml/g/min in frontal and temporal cortex, respectively, of controls and 0.127 and 0.126 ml/g/min in frontal and temporal cortex of the AD patients. rCMRglc was also significantly (p less than 0.02) lower in the AD patients than controls in all cortical brain regions. Lower values of k3* were found in all brain regions in the AD patients, although these were not statistically significant. These findings provide evidence of an in vivo abnormality of forward glucose transport in AD.(ABSTRACT TRUNCATED AT 250 WORDS)
It is generally assumed that there is symmetric distribution of the glucose transporter on the lumenal and ablumenal membranes of the brain capillary endothelial cell that makes up the blood-brain barrier (BBB) in vivo. However, the presence of brain endothelial tight junctions allows for asymmetric distribution of BBB plasma membrane proteins. Glucose transporter isoform 1 (GLUT-1), the principal glucose transporter at the BBB, was assessed in rat brain in the present studies using immunogold electron microscopy. The distribution of the immunoreactive GLUT-1 protein on the endothelial lumenal membrane, the ablumenal membrane, and the cytoplasmic compartment was 12%, 48%, and 40%, respectively, and no significant immunolabeling of the neuropil was measurable. These studies suggest (i) that GLUT-1 is asymmetrically distributed on the BBB plasma membrane with an approximately 4-fold greater abundance on the ablumenal membrane as compared to the lumenal membrane; (ii) that approximately 40% of the endothelial glucose transporter protein is contained within the cytoplasmic space, which provides a mechanism for rapid up-regulation of the transporter by altered distribution of transporter between cytoplasmic and plasma membrane compartments; and (iii) that no significant labeling of neuropil is found with antisera directed against the GLUT-1 protein. These studies also suggest mechanisms of regulation of glucose transport from blood to brain that involve differential distribution of the BBB glucose transporter in subcellular compartments of brain capillary endothelial cells.
The recently cloned Glut-5, glucose transporter isoform, is expressed in human jejunum and kidney. Employing previously characterized polyclonal antibodies directed towards the C-terminus region of the derived human Glut-5 peptide and Western blot analysis, a 50-55 kilodalton Glut-5 protein was detected in adult human brain homogenates. The amount of Glut-5 protein in brain was 4-fold lower when compared to the levels in adult kidney. Immunohistochemical analysis using cerebral and cerebellar sections demonstrated Glut-5 immunoreactivity in only some of the Glut-1 and factor VIII-positive brain microvascular endothelial cells, the intravascular red and white blood cells being negative. This selective localization pattern was confirmed by the 5-fold enrichment of Glut-5 vs. a 20-fold enrichment of Glut-1 in an isolated human cerebral cortical microvascular preparation, when compared to whole cerebral homogenates. We conclude that Glut-5 is localized in the endothelial cells of human brain microvasculature....
Under normal circumstances, a mixture of α- and β-D-glucopyranose (D-glucose) is the only fuel of brain energy metabolism (Pardridge 1983). The breakdown of D-glucose is regulated by complex mechanisms that influence the activities of phos phofructokinase and hexokinase. The metabolism depends heavily on the glucose concentration of the brain intracellular and interstitial fluids. As the tissue glucose concentration, in turn, depends on the glucose phosphorylation rate, the blood–brain transfer assumes a pivotal role in the supply of glucose to the brain.
As neurons rely almost exclusively on glucose as an energy substrate, glucose transport is of critical importance to cerebral function. Two specific facilitative glucose transporters, GT1 and -3, predominate in brain, with the latter exclusively expressed by neurons, whereas GT1 is expressed by astrocytes and vascular elements. Little is known about the regulation of these transporters at the genetic level or the extent to which their expression may change in response to acute or chronic changes in metabolic demands. Thus, we employed in situ hybridization to evaluate changes in glucose transporter gene expression in the rat brain in response to ischemia induced by middle cerebral artery occlusion (MCAO). The most remarkable responses were demonstrated by GT1, which within an hour of ischemic insult demonstrated a global increase in gene expression throughout the forebrain. In the ensuing hours, GT1 expression further intensified and became lateralized to the lesioned hemisphere, with normalization of exp...
Simple motor and cognition tasks are associated with regionally specific and rapid changes in cerebral blood flow. Examination of these phenomena in man has been made possible by Positron Emission Tomography. Improvements in the spatial and temporal resolution of the tomograph, together with the development and application of dynamic tracer modelling techniques, have in particular allowed repeat studies to be carried out in the same individual, so that comparisons can be made between resting and activated states over short periods. For example it can be shown that wilful movements of the hand and arm are accompanied by increased blood flow in the ipsilateral cerebellum, supplementary motor area and in the contralateral motor cortex. Specific regional changes in flow are also characteristic of visual stimulation and of the performance of mental tasks. The simplest interpretation of these phenomena is that they are in some way related to increased energy demands arising from increased neuronal activity, and they illustrate the rapidity with which metabolic and physiological adaptation can occur
Under normal circumstances, a mixture of α-and β-D-glucopyranose (D-glucose) is the only fuel of brain energy metabolism (Pardridge 1983). The breakdown of D-glucose is regulated by complex mechanisms that influence the activities of phosphofructokinase and hexokinase. The metabolism depends indirectly on the glucose concentration of the brain intracellular and interstitial fluids. Since the tissue glucose concentration, in turn, depends directly on the glucose phosphorylation rate, the blood-brain transfer assumes a pivotal role in the supply of glucose to the brain.
This article provides a brief review of recent developments regarding the pathophysiology of ischemic brain damage, and offers hypotheses explaining the pathogenesis of selective neuronal vulnerability and of tissue infarction, respectively. It is suggested that selective neuronal vulnerability, observed after brief periods of ischemia and after hypoglycemic coma, qualifies as an excitotoxic lesion, which causes postsynaptic damage to neurons innervated by excitatory amino acids by enhancing calcium influx. However, ischemic damage often involves glial and vascular cells as well, and causes infarction. It is hypothesized that this type of brain damage is related to acidosis and that enhanced acidosis is detrimental because it accelerates delocalization of protein-bound iron, with an ensuing free-radical damage to membrane lipids and proteins.
Introduction
Since alkaline phosphatase was first reported in the retina by deConciliis in 1934,1 much study has gone into the chemical and histochemical demonstration of various phosphatases in the eye. Until recently most attention was directed to acid and alkaline phosphatase. In the past few years interest has shifted to certain "specific" phosphatases whose optimal activity occurs within or close to the physiological range of tissue pH and whose substrates are known to play important roles in intermediary metabolism.Various types of adenosine triphosphatase (ATPase) have been demonstrated in retina, ciliary body, iris sphincter, choroid, corneal epithelium, corneal endothelium, and lens capsule and epithelium.2 In certain of these loci the enzyme is thought to be concerned with cation transport. 5′-Nucleotidase has been detected in the choroid and retina.3 Yet there is little histochemical evidence for the localization of these enzymes in the eye. In 1957 Wachstein and
Astrocytes exposed to hypoxia (H) or hypoxia/reoxygenation (H/R) maintain cell viability and display changes in protein biosynthesis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of metabolically labeled astrocytes exposed to H showed induction of an ≈78-kDa polypeptide that demonstrated sequence identity with glucose-regulated protein (GRP) 78. Cell lysates from H/R astrocytes displayed induction of neuroprotective interleukin (IL) 6, which was present in a high-molecular-weight complex also containing GRP78, suggesting that GRP78 might be functioning as a chaperone during cellular stress consequent on H/R. Introduction of anti-sense oligonucleotide to GRP78 into astrocytes prevented expression of the protein and suppressed H/R-induced astrocyte release of IL-6 by ≈50%. These data indicate that modulation of astrocyte properties during oxygen deprivation results, in part, from intracellular glucose depletion and subsequent expression of GRP78, which sustains generation of neuroprotective IL-6 under the stress of H/R.
The incorporation of 14C into glycogen in rat brain has been measured under the same conditions that exist during the measurement of local cerebral glucose utilization by the autoradiographic 2-[14C]deoxyglucose method. The results demonstrate that approximately 2% of the total 14C in brain 45 min after the pulse of 2-[14C]deoxyglucose is contained in the glycogen portion, and, in fact, incorporated into α-1-4 and α-1-6 deoxyglucosyl linkages. When the brain is removed by dissection, as is routinely done in the course of the procedure of the 2-[14C]deoxyglucose method to preserve the structure of the brain for autoradiography, the portion of total brain 14C contained in glycogen falls to less than 1%, presumably because of postmortem glycogenolysis which restores much of the label to deoxyglucose-phosphates. In any case, the incorporation of the 14C into glycogen is of no consequence to the validity of the autoradiographic deoxyglucose method, not because of its small magnitude, but because 2-[14C]deoxyglucose is incorporated into glycogen via [14C]deoxyglucose-6-phosphate, and the label in glycogen represents, therefore, an additional “trapped” product of deoxyglucose phosphorylation by hexokinase. With the autoradiographic 2-[14C]deoxyglucose method, in which only total 14C concentration in the brain tissue is measured by quantitative autoradiography, it is essential that all the labeled products derived directly or indirectly from [14C]deoxyglucose phosphorylation by hexokinase be retained in the tissue; their chemical identity is of no significance.
The precise histologic localization of GLUT3, a glucose transporter thought to be restricted to neurons, is unknown. Using a high-affinity, specific antiserum against rodent GLUT3 for immunocytochemistry, light microscopic staining concentrates heterogeneously in the neuropil in a region- and lamina-specific manner; intense staining characterizes areas with high rates of glucose utilization such as inferior colliculus and pyriform cortex. Neuropil localization with little perikaryal staining suggests that GLUT3 may provide the energy needed locally for synaptic transmission.
Patterns of gene expression for the facilitative glucose transporters 1-4 (GTs 1-4) were mapped using in situ hybridization on rat brains from embryonic day 11 (E 11) through adulthood. GT2 and GT4 mRNAs were not detected at any stage of development. Prior to the formation of the blood-brain barrier (BBB), GT1 mRNA was localized in the germinal neuroepithelium. During and after formation of the BBB, GT1 mRNA was abundant in brain and spinal cord vascular endothelium and in condensations of mesenchyme forming the meninges. With the gradual disappearance of the germinal neuroepithelium, GT1 mRNA was retained in the ependymal cell layer lining the ventricles. Postnatally, GT1 mRNA appeared in numerous small parenchymal cells, demonstrating characteristic glial cell morphology and distribution, and was not detected in neurons. GT3 mRNA, in contrast, was detected only in differentiated neurons, indicating that there is a switch from GT1 to GT3 gene expression by neuroepithelial cell lineages during the process of terminal neural differentiation. GT3 mRNA increased gradually from E14, attaining adult levels in most regions by postnatal day 20. The highest levels were found in large projection neurons of the olfactory system, hippocampal formation, neocortex (VI), and deep cerebellar, pontine, and brain stem nuclei. The ontogeny and neuroanatomical distribution of GT3 gene expression correlates with developmental and regional patterns of brain glucose utilization, suggesting that-while GT1 may have a role in the transfer of glucose across the BBB-GT3 expression determines brain glucose utilization.
The brain is dependent on glucose as an energy source and thus requires the expression of glucose transporter proteins to enable passage of glucose across both the endothelial cells of the blood-brain barrier and the plasma membranes of neurons and glia. The GLUT 1 isoform of the facilitative glucose transporter family is expressed in the blood-brain barrier; however, the major glucose transporter isoform(s) in neurons and glia have not been identified. We have investigated the expression of glucose transporters in cultured rat cerebellar granule neurons. Two isoforms, GLUT1 and GLUT3, were detected by Western and Northern blot analyses. Expression of both isoforms increased as neurons differentiated in culture, corresponding to an increase in glucose uptake. Localization of glucose transporters by immunofluorescence indicated the presence of both isoforms in neuronal processes and in the cell body. GLUT1 was detected in both plasma membrane and cytoplasm, whereas GLUT3 appeared only in plasma membrane. Significant GLUT3 expression was also detected in the neuronal cell lines PC12 and NG108 but not in primary cultured glia or C6 glioma cells. Our findings indicate that, in the rat brain, GLUT3 expression is predominantly in neurons, suggesting that this isoform may play a major role in neuronal glucose transport.
1. Rats aged from 1 to 116 weeks were studied. 2. Influx of glucose into the brain is low in suckling rats but rises after weaning, to reach its highest level in the young adult, thenceforward declining slowly as age increases. 3. The blood-brain barrier for glucose is fully developed in the rat by the age of 18 days and glucose enters the brain, at this stage, by carrier-mediated transport, as in the adult. 4. The results show that the low influx of glucose into the brain of the suckling animal is due to a low maximum rate of transport of glucose rather than to a low affinity of the carrier-molecule for glucose. 5. In the young adult rat, efflux of glucose back from the brain into the blood is greater than in either the suckling or the old animals. Thus the margin of safety, i.e. the extent to which the blood glucose can be reduced without affecting the utilization of glucose by the brain, is highest in the young adult. 6. The lower margin of safety in the suckling animals is compensated for by the high influx of the ketone bodies which provide an alternative source of energy at this age. In the old animals there is no alternative source of energy, so that the older brain is at greatest risk in hypoglycaemia.
— A method has been developed for the simultaneous measurement of the rates of glucose consumption in the various structural and functional components of the brain in vivo. The method can be applied to most laboratory animals in the conscious state. It is based on the use of 2-deoxy-D-[14C]glucose ([14C]DG) as a tracer for the exchange of glucose between plasma and brain and its phosphorylation by hexokinase in the tissues. [14C]DG is used because the label in its product, [14C]deoxyglucose-6-phosphate, is essentially trapped in the tissue over the time course of the measurement. A model has been designed based on the assumptions of a steady state for glucose consumption, a first order equilibration of the free [14C]DG pool in the tissue with the plasma level, and relative rates of phosphorylation of [14C]DG and glucose determined by their relative concentrations in the precursor pools and their respective kinetic constants for the hexokinase reaction. An operational equation based on this model has been derived in terms of determinable variables. A pulse of [14C]DG is administered intravenously and the arterial plasma [14C]DG and glucose concentrations monitored for a preset time between 30 and 45min. At the prescribed time, the head is removed and frozen in liquid N2-chilled Freon XII, and the brain sectioned for autoradiography. Local tissue concentrations of [14C]DG are determined by quantitative autoradiography. Local cerebral glucose consumption is calculated by the equation on the basis of these measured values.The method has been applied to normal albino rats in the conscious state and under thiopental anesthesia. The results demonstrate that the local rates of glucose consumption in the brain fall into two distinct distributions, one for gray matter and the other for white matter. In the conscious rat the values in the gray matter vary widely from structure to structure (54-197 μmol/100 g/min) with the highest values in structures related to auditory function, e.g. medial geniculate body, superior olive, inferior colliculus, and auditory cortex. The values in white matter are more uniform (i.e. 33–40 μmo1/100 g/min) at levels approximately one-fourth to one-half those of gray matter. Heterogeneous rates of glucose consumption are frequently seen within specific structures, often revealing a pattern of cytoarchitecture. Thiopental anesthesia markedly depresses the rates of glucose utilization throughout the brain, particularly in gray matter, and metabolic rate throughout gray matter becomes more uniform at a lower level.
To investigate the tissue distribution of the GLUT3 glucose transporter isoform in human tissue we produced affinity purified antibodies to the COOH terminus of the human GLUT3. Both antibodies recognize a specific GLUT3 band in oocytes injected with GLUT3 mRNA but not in those injected with H2O or GLUT1, 2, 4, 5 mRNA. This immunoreactive band in GLUT3 injected oocytes is photolabelled by cytochalasin-B in the presence of L- but not D-glucose indicating that it is a glucose transporter. A high cross reactivity between the human GLUT3 antibodies and a 43 kDa cytoskeletal actin band was identified in all oocyte lysates and many human tissues. However, the specific GLUT3 band could be distinguished from the actin band by carbonate treatment which preferentially solubilized the actin band. Using these antibodies we show that GLUT3 is present as a 45-48 kDa protein in human brain with lower levels detectable in heart, placenta, liver and a barely detectable level in kidney. No GLUT3 was detected in membranes from any of 3 skeletal muscle groups investigated. We conclude that a major role of GLUT3 in humans is as the brain neuronal glucose transporter.
We have studied the developmental and regional expression of mRNAs encoding sodium-dependent and facilitative glucose transporter proteins in human fetal and adult small intestine. The abundance of mRNAs encoding the Na(+)-glucose cotransporter isoform SGLT1 and the facilitative glucose transporter isoforms GLUT2 and GLUT5 is developmentally modulated with highest levels in adult small intestine. By contrast, the levels of GLUT1 mRNA are higher in fetal than adult small intestine. Immunohistochemical analysis of adult small intestine localized GLUT5 to the luminal surface of mature enterocytes, a finding confirmed by Western blot analysis of purified human jejunal brush-border membranes. By contrast, in the fetal small intestine, GLUT5 was localized along the intercellular junctions of the developing villus, indicating that both its expression and localization are developmentally regulated. The localization of GLUT5 to the luminal surface of mature absorptive epithelial cells implies that this protein participates in the uptake of dietary sugars.
We recently reported that the glucose transporter isoform, GLUT5, is expressed on the brush border membrane of human small intestinal enterocytes (Davidson, N. O., Hausman, A. M. L., Ifkovits, C. A., Buse, J. B., Gould, G. W., Burant, C. F., and Bell, G. I. (1992) Am. J. Physiol. 262, C795-C800). To define its role in sugar transport, human GLUT5 was expressed in Xenopus oocytes and its substrate specificity and kinetic properties determined. GLUT5 exhibits selectivity for fructose transport, as determined by inhibition studies, with a Km of 6 mM. In addition, fructose transport by GLUT5 is not inhibited by cytochalasin B, a competitive inhibitor of facilitative glucose transporters. RNA and protein blotting studies showed the presence of high levels of GLUT5 mRNA and protein in human testis and spermatozoa, and immunocytochemical studies localize GLUT5 to the plasma membrane of mature spermatids and spermatozoa. The biochemical properties and tissue distribution of GLUT5 are consistent with a physiological role for this protein as a fructose transporter.
The complementary DNA for the human brain type glucose transporter (GLUT3) was used to determine its tissue specific expression in human, monkey, rabbit, rat, and mouse. Under high stringent conditions, 4.1 and 3.2 kilobase (kb) GLUT3 transcripts in monkey and a single 4.1 kb GLUT3 mRNA in rabbit, rat, and mouse were detected by RNA blot analysis. Although the GLUT3 transcripts were widely distributed, as are the erythrocyte type glucose transporter (GLUT1) transcripts, this mRNA is most abundant in the brain. However, the relative abundance of GLUT3 mRNA in the various regions of the monkey brain shows a different pattern from that of GLUT1 mRNA: GLUT3 is most highly expressed in the frontal lobe of the cerebrum, whereas GLUT1 is most abundant in the basal ganglia and the thalamus. Moderately higher GLUT3 mRNA levels were detected in the parietal lobe of the cerebrum, hippocampus, and cerebellum than the levels of GLUT1 transcripts. We also detected GLUT3 mRNA in adult human psoas major muscle, although it has been reported that the GLUT3 gene is scarcely expressed in adult human skeletal muscle of the thigh. In addition, in the rat and the mouse, no transcripts of the GLUT3 gene were detected in liver, kidney, small intestine, skeletal muscle, or fat besides in brain. Thus, the expression of the GLUT3 gene seems to be restricted to the brain in rodents. These results suggest that the expression of GLUT1 and GLUT3 genes might be regulated by different mechanisms.
In mammals, glucose transport is mediated by five structurally related glucose transporters that show a characteristic cell-specific expression. However, the rat brain/HepG2/erythrocyte-type glucose transporter GLUT-1 is expressed at low levels in most cells. The reason for this coexpression is not clear. GLUT-1 is negatively regulated by glucose. Another family of proteins, glucose-regulated proteins (GRPs), is also ubiquitously expressed and stimulated by glucose deprivation and other cellular stresses. We therefore hypothesized that GLUT-1 may be a glucose-regulated stress protein. This was tested by subjecting L8 myocytes and NIH 3T3 fibroblasts to glucose starvation or exposure to the calcium ionophore A23187, 2-mercaptoethanol, or tunicamycin, all known to increase GRP levels. The mRNA for GLUT-1 was augmented by 50-300% in a time-dependent manner, similarly to the changes in GRP-78 mRNA. Ex vivo incubation of rat soleus muscles induced a marked and concomitant rise in the mRNA levels of GLUT-1 and GRP-78. Finally, calcium ionophore A23187 and 2-mercaptoethanol induced a 2- to 3-fold increase in the levels of the GLUT-1 protein and hexose uptake. In all instances in which GRP-78 and GLUT-1 responded to stress, the transcription of the cell-specific muscle/adipocyte-type insulin-responsive glucose transporter (GLUT-4) did not change. Thus, despite the lack of structural similarity, GLUT-1 and GRP-78 expression is regulated similarly, whereas the regulation of GLUT-4, which is structurally related to GLUT-1, is different. We propose that GLUT-1 belongs to the GRP family of stress proteins and that its ubiquitous expression may serve a specific purpose during cellular stress.
To elucidate glucose transport mechanisms in brain and to demonstrate the cellular expression of the brain-type glucose transporter (GLUT3), antisera to a synthetic peptide corresponding to the C terminus were prepared and used as probes for this isoform of the facilitative glucose transporter family. Immunocytochemistry of frozen sections of dog and rat brain demonstrated GLUT3 antigen in pyramidal cell bodies and processes, in microvessels, and in intima pia or glia limitans. Immunoanalysis of Western blots identified a protein (Mr, 45,000) that was present in both neuron/neuropil and microvessel fractions. The presence of the GLUT3 message in brain was confirmed by Northern blot analysis and by amplifying and partially sequencing GLUT3 cDNA by PCR. These findings demonstrate a neuron glucose transporter in tissue and suggest that GLUT3 may play an important role in brain metabolism under physiological and pathophysiological conditions.
Polyclonal anti-peptide antisera were raised to the C-terminal sequence of mouse- and human-GLUT3 glucose transporter isoforms. GLUT3 protein and mRNA expression were investigated by Western blot and Northern blot assays, in a range of tissues and cell lines. Mouse-GLUT3 protein was detected only in rat brain, where it was present in most regions except adenohypophysis and pineal gland. Mouse-GLUT3 was also detected in primary cultured rat cerebellar neurons and the neuronal cell lines PC12 and NG108-15, but not in cultured astroglia. Human-GLUT3 protein was detected in CHO cells transfected with the human-GLUT3 cDNA and in human brain, but not in human placenta or fat. The expression of GLUT3 in rat brain and neurons indicates it is a major neuronal glucose transporter.
Cerebral hypoxia-ischemia remains a major cause of acute perinatal brain injury, leading ultimately to neurologic dysfunction manifest as cerebral palsy, mental retardation, and epilepsy. Research in experimental animals over the past 10 or more years has expanded greatly our understanding of the cellular and molecular events that occur during a hypoxic-ischemic insult to brain, and recent discoveries have suggested that metabolic perturbations arising in the recovery period after resuscitation contribute substantially to the nature and extent of neuronal destruction. The review focuses on those neurochemical processes responsible for the maintenance of cellular homeostasis and how these mechanisms fail in hypoxia-ischemia to culminate in brain damage. Knowledge of these critical events has opened new avenues of potential therapy for the fetus and newborn infant subjected to cerebral hypoxia-ischemia to prevent the serious delayed effects of perinatal brain injury.
Mammals have low cerebral metabolic rates immediately after birth and, by inference, also before birth. In this study, we extended the deoxyglucose method to the fetal rat brain in utero. Rate constants for deoxyglucose transfer across the maternal placental and fetal blood-brain barriers, and lumped constant, have not been reported. Therefore, we applied a new method of determining the lumped constant regionally to the fetal rat brain in utero. The lumped constant averaged 0.55 +/- 0.15 relative to the maternal circulation. On this basis, we determined the glucose metabolic rate of the fetal rat brain to be one third of the corresponding maternal value, or 19 +/- 2 mumol hg-1 min-1.