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A model for the activation of the UPR in the absence of H6PD. 1, H6PD deletion disrupts the redox balance of the ER, resulting in unfolded protein accumulation and activation of the PERK, ATF6, and IRE1 pathways. 2, a PERK-induced translational block of transcripts without an internal ribosome entry site decreases secretory protein flow through the ER, and if rescue mechanisms are unsuccessful, induces the expression of pro-apoptotic genes. 3, ATF6 induced expression of ER resident chaperones speeds up protein folding. 4, IRE1 induced splicing and activation of XBP1 up-regulates both ER-associated protein degradation (ERAD) and phospholipid metabolism involved in ER membrane biogenesis. 5, the dysregulation of proteins involved in calcium metabolism increases intracellular calcium which activates the calcineurin pathway. Dashed lines indicate presumed interactions. Small arrows denote up-or down-regulation of gene expression. GRP94, glucose-regulated protein 94 (HSP90B1); BiP, immunoglobulin heavy chainbinding protein (GRP78, HSPA5) CHOP10-C/EBP-homologous protein (DDIT3); CALR, calreticulin; Derlin, Der1p-like protein; Hsp40, heat shock protein 40; IRE1, inositol-requiring enzyme 1; IRES, internal ribosome entry site; PERK, PKR-like ER kinase; PGC-1, peroxisome proliferator-activated receptor coactivator-1 ; XBP1, X-box-binding protein 1; sXBP1, spliced XBP1.
Source publication
Hexose-6-phosphate dehydrogenase (H6PD) is the initial component of a pentose phosphate pathway inside the endoplasmic reticulum (ER) that generates NADPH for ER enzymes. In liver H6PD is required for the 11-oxoreductase activity of 11beta-hydroxysteroid dehydrogenase type 1, which converts inactive 11-oxo-glucocorticoids to their active 11-hydroxy...
Context in source publication
Context 1
... we propose that the loss of H6PD and the consequent change in NADPH/NADP ratio is a specific stressor that affects the redox balance and ultimately disrupts the normal protein-folding environment of the SR (Fig. 7). The subsequent accumulation of unfolded proteins activates the UPR pathway in an effort to relieve the stress and restore homeostasis. Activation of the UPR pathway slows general protein translation and induces the expression of specific chaperones, degradative proteins, and enzymatic pathways that increase SR volume. Insufficient ...
Citations
... On the other hand, H6PD deficiency leads to serious diseases. The H6PD knockout mouse has severe skeletal muscle disease [87], and the H6PD gene has been identified as a risk factor for multiple sclerosis [88]. ...
... Glycogen decomposition depends on PYGL [32]. Gluconeogenesis is regulated by PEPCK, G6PC and PC [33][34][35]. Here, higher PK, PC and G6PC concentrations were detected in the liver of the MCS group than in the MC group. Both glycolytic and gluconeogenic pathways were enhanced in Min pigs. ...
Background
Cold regions have long autumn and winter seasons and low ambient temperatures. When pigs are unable to adjust to the cold, oxidative damage and inflammation may develop. However, the differences between cold and non-cold adaptation regarding glucose and lipid metabolism, gut microbiota and colonic mucosal immunological features in pigs are unknown. This study revealed the glucose and lipid metabolic responses and the dual role of gut microbiota in pigs during cold and non-cold adaptation. Moreover, the regulatory effects of dietary glucose supplements on glucose and lipid metabolism and the colonic mucosal barrier were evaluated in cold-exposed pigs.
Results
Cold and non-cold-adapted models were established by Min and Yorkshire pigs. Our results exhibited that cold exposure induced glucose overconsumption in non-cold-adapted pig models (Yorkshire pigs), decreasing plasma glucose concentrations. In this case, cold exposure enhanced the ATGL and CPT-1α expression to promote liver lipolysis and fatty acid oxidation. Meanwhile, the two probiotics ( Collinsella and Bifidobacterium ) depletion and the enrichment of two pathogens ( Sutterella and Escherichia-Shigella ) in colonic microbiota are not conducive to colonic mucosal immunity. However, glucagon-mediated hepatic glycogenolysis in cold-adapted pig models (Min pigs) maintained the stability of glucose homeostasis during cold exposure. It contributed to the gut microbiota (including the enrichment of the Rikenellaceae RC9 gut group , [Eubacterium] coprostanoligenes group and WCHB1-41 ) that favored cold-adapted metabolism.
Conclusions
The results of both models indicate that the gut microbiota during cold adaptation contributes to the protection of the colonic mucosa. During non-cold adaptation, cold-induced glucose overconsumption promotes thermogenesis through lipolysis, but interferes with the gut microbiome and colonic mucosal immunity. Furthermore, glucagon-mediated hepatic glycogenolysis contributes to glucose homeostasis during cold exposure.
... Knockdown of Hsd11b1 was achieved in adipose tissue in the AKO colony compared to control littermates and is demonstrated in Supplementary Fig. 1 (see section on supplementary materials given at the end of this article) (~87% knockdown in subcutaneous, ~73% in epidydimal and ~50% in mesenteric adipose tissues). Mice lacking H6pdh (generated using homologous recombination in embryonic stem cells to replace exons 2 and 3 with a neomycin resistance cassette (Lavery et al. 2006(Lavery et al. , 2008) and their wild-type controls on a C57BL/6J background were generated in the University of Birmingham by heterozygous breeding and transferred to Edinburgh at the age of 3 months, under supervision of the Named Veterinary Surgeons at the Universities of Birmingham and Edinburgh. C57Bl/6J mice (Harlan Olac, Bicester, UK) were used to assess parameters for infusion to achieve steady state. ...
11β-Hydroxysteroid dehydrogenase 1 (11βHSD1) is a drug target to attenuate adverse effects of chronic glucocorticoid excess. It catalyses intracellular regeneration of active glucocorticoids in tissues including brain, liver and adipose tissue (coupled to hexose-6-phosphate dehydrogenase, H6PDH). 11βHSD1 activity in individual tissues is thought to contribute significantly to glucocorticoid levels at those sites, but its local contribution versus glucocorticoid delivery via the circulation is unknown. Here, we hypothesised that hepatic 11βHSD1 would contribute significantly to the circulating pool. This was studied in mice with Cre-mediated disruption of Hsd11b1 in liver (Alac-Cre) versus adipose tissue (aP2-Cre) or whole-body disruption of H6pdh. Regeneration of [9,12,12-2H3]-cortisol (d3F) from [9,12,12-2H3]-cortisone (d3E), measuring 11βHSD1 reductase activity was assessed at steady state following infusion of [9,11,12,12-2H4]-cortisol (d4F) in male mice. Concentrations of steroids in plasma and amounts in liver, adipose tissue and brain were measured using mass spectrometry interfaced with matrix assisted laser desorption ionisation or liquid chromatography. Amounts of d3F were higher in liver, compared with brain and adipose tissue. Rates of appearance of d3F were ~6-fold slower in H6pdh-/- mice, showing the importance of whole-body 11βHSD1 reductase activity. Disruption of liver 11βHSD1 reduced amounts of d3F in liver (by ~36%), without changes elsewhere. In contrast disruption of 11βHSD1 in adipose tissue reduced rates of appearance of circulating d3F (by ~67%) and also reduced regeneration of d3F in liver and brain (both by ~30%). Thus, the contribution of hepatic 11βHSD1 to circulating glucocorticoid levels and amounts in other tissues is less than that of adipose tissue.
... However, the detailed architecture and ECM composition of NRK KO mice was not evaluated. Given the reported implication in muscle architecture as well as the observation that Nmrk2 is a damage-inducible transcript in muscle and even in non-muscle tissues (i.e. during neuronal injury) (Sasaki et al., 2006;Lavery et al., 2008;Aguilar et al., 2015;Xu et al., 2015;Diguet et al., 2018), we hypothesized that NRKs may be important for muscle plasticity during atrophy and regeneration. ...
Nicotinamide riboside kinases (NRKs) control the conversion of dietary Nicotinamide Riboside (NR) to NAD+, but little is known about their contribution to endogenous NAD+ turnover and muscle plasticity during skeletal muscle growth and remodeling. Using NRK1/2 double KO (NRKdKO) mice, we investigated the influence of NRKs on NAD+ metabolism and muscle homeostasis, and on the response to neurogenic muscle atrophy and regeneration following muscle injury. Muscles from NRKdKO animals have altered nicotinamide (NAM) salvage and a decrease in mitochondrial content. In single myonuclei RNAseq of skeletal muscle, NRK2 mRNA expression is restricted to type IIx muscle fibers, and perturbed NAD+ turnover and mitochondrial metabolism shifts the fiber type composition of NRKdKO muscle to fast glycolytic IIB fibers. NRKdKO does not influence muscle atrophy during denervation but alters muscle repair after myofiber injury. During regeneration, muscle stem cells (MuSCs) from NRKdKO animals hyper-proliferate but fail to differentiate. NRKdKO also alters the recovery of NAD+ during muscle regeneration as well as mitochondrial adaptations and extracellular matrix remodeling required for tissue repair. These metabolic perturbations result in a transient delay of muscle regeneration which normalizes during myofiber maturation at late stages of regeneration via over-compensation of anabolic IGF1-Akt signaling. Altogether, we demonstrate that NAD+ synthesis controls mitochondrial metabolism and fiber type composition via NRK1/2 and is rate-limiting for myogenic commitment and mitochondrial maturation during skeletal muscle repair.
... A striking element in this observation is that NRK2 levels are undetectable in the brain under normal conditions [163]. In muscle, Nrmk2 expression was also largely increased in mouse models of traumatic lower limb injury [178] or severe muscle myopathy [179]. Also, increased Nmrk2 expression levels were observed in muscle in response to high-fat feeding [173]. ...
Alterations in cellular nicotinamide adenine dinucleotide (NAD⁺) levels have been observed in multiple lifestyle and age-related medical conditions. This has led to the hypothesis that dietary supplementation with NAD⁺ precursors, or vitamin B3s, could exert health benefits. Among the different molecules that can act as NAD⁺ precursors, Nicotinamide Riboside (NR) has gained most attention due to its success in alleviating and treating disease conditions at the pre-clinical level. However, the clinical outcomes for NR supplementation strategies have not yet met the expectations generated in mouse models. In this review we aim to provide a comprehensive view on NAD⁺ biology, what causes NAD⁺ deficits and the journey of NR from its discovery to its clinical development. We also discuss what are the current limitations in NR-based therapies and potential ways to overcome them. Overall, this review will not only provide tools to understand NAD⁺ biology and assess its changes in disease situations, but also to decide which NAD⁺ precursor could have the best therapeutic potential.
... Following ER oxidation, H6PD depletion causes an increase in SERCA expression, leading to increased ER Ca 2+ levels and impairing cancer cell proliferation and migration (Tsachaki et al., 2018). Dysregulated SERCA expression has also been observed in H6pd knockout mice (Lavery et al., 2008). ...
Calcium ion (Ca²⁺) signaling is critical to many physiological processes, and its kinetics and subcellular localization are tightly regulated in all cell types. All Ca²⁺ flux perturbations impact cell function and may contribute to various diseases, including cancer. Several modulators of Ca²⁺ signaling are attractive pharmacological targets due to their accessibility at the plasma membrane. Despite this, the number of specific inhibitors is still limited, and to date there are no anticancer drugs in the clinic that target Ca²⁺ signaling. Ca²⁺ dynamics are impacted, in part, by modifications of cellular metabolic pathways. Conversely, it is well established that Ca²⁺ regulates cellular bioenergetics by allosterically activating key metabolic enzymes and metabolite shuttles or indirectly by modulating signaling cascades. A coordinated interplay between Ca²⁺ and metabolism is essential in maintaining cellular homeostasis. In this review, we provide a snapshot of the reciprocal interaction between Ca²⁺ and metabolism and discuss the potential consequences of this interplay in cancer cells. We highlight the contribution of Ca²⁺ to the metabolic reprogramming observed in cancer. We also describe how the metabolic adaptation of cancer cells influences this crosstalk to regulate protumorigenic signaling pathways. We suggest that the dual targeting of these processes might provide unprecedented opportunities for anticancer strategies. Interestingly, promising evidence for the synergistic effects of antimetabolites and Ca²⁺-modulating agents is emerging.
... Our understanding of the control of NADP(H) redox homeostasis within muscle sarcoplasmic reticulum (SR) and its influence over cellular metabolism is developing [1][2][3][4]. A major enzyme that reduces NADP + within the SR lumen is hexose-6-phosphate dehydrogenase (H6PD) which oxidises glucose-6-phosphate derived from glycolysis to generate NADPH [5,6]. ...
... Skeletal muscle of H6PD knockout mice develop a progressively deteriorating myopathy associated with large intrafibrillar membranous vacuoles, abnormal sarcoplasmic reticulum (SR) structure, dysregulated expression of SR proteins involved in calcium metabolism and switching of type II to type I fibers and impaired force generation [4]. Associated with myopathy is ER stress and activation of the unfolded protein responsepartially attributed to altered SR lumen protein folding capacity [2,4]. ...
... Skeletal muscle of H6PD knockout mice develop a progressively deteriorating myopathy associated with large intrafibrillar membranous vacuoles, abnormal sarcoplasmic reticulum (SR) structure, dysregulated expression of SR proteins involved in calcium metabolism and switching of type II to type I fibers and impaired force generation [4]. Associated with myopathy is ER stress and activation of the unfolded protein responsepartially attributed to altered SR lumen protein folding capacity [2,4]. Metabolically H6PDKO demonstrate dysfunction in glucose homeostasis, characterised by fasting hypoglycaemia, increased skeletal muscle insulin sensitivity (particularly in type II fibre-rich muscles) and increased glycogen content [4,13]. ...
Background:
Hexose-6-Phosphate Dehydrogenase (H6PD) is a generator of NADPH in the Endoplasmic/Sarcoplasmic Reticulum (ER/SR). Interaction of H6PD with 11β-hydroxysteroid dehydrogenase type 1 provides NADPH to support oxo-reduction of inactive to active glucocorticoids, but the wider understanding of H6PD in ER/SR NAD(P)(H) homeostasis is incomplete. Lack of H6PD results in a deteriorating skeletal myopathy, altered glucose homeostasis, ER stress and activation of the unfolded protein response. Here we further assess muscle responses to H6PD deficiency to delineate pathways that may underpin myopathy and link SR redox status to muscle wide metabolic adaptation.
Methods:
We analysed skeletal muscle from H6PD knockout (H6PDKO), H6PD and NRK2 double knockout (DKO) and wild-type (WT) mice. H6PDKO mice were supplemented with the NAD+ precursor nicotinamide riboside. Skeletal muscle samples were subjected to biochemical analysis including NAD(H) measurement, LC-MS based metabolomics, Western blotting, and high resolution mitochondrial respirometry. Genetic and supplement models were assessed for degree of myopathy compared to H6PDKO.
Results:
H6PDKO skeletal muscle showed adaptations in the routes regulating nicotinamide and NAD+ biosynthesis, with significant activation of the Nicotinamide Riboside Kinase 2 (NRK2) pathway. Associated with changes in NAD+ biosynthesis, H6PDKO muscle had impaired mitochondrial respiratory capacity with altered mitochondrial acylcarnitine and acetyl-CoA metabolism. Boosting NAD+ levels through the NRK2 pathway using the precursor nicotinamide riboside elevated NAD+/NADH but had no effect to mitigate ER stress and dysfunctional mitochondrial respiratory capacity or acetyl-CoA metabolism. Similarly, H6PDKO/NRK2 double KO mice did not display an exaggerated timing or severity of myopathy or overt change in mitochondrial metabolism despite depression of NAD+ availability.
Conclusions:
These findings suggest a complex metabolic response to changes in muscle SR NADP(H) redox status that result in impaired mitochondrial energy metabolism and activation of cellular NAD+ salvage pathways. It is possible that SR can sense and signal perturbation in NAD(P)(H) that cannot be rectified in the absence of H6PD. Whether NRK2 pathway activation is a direct response to changes in SR NAD(P)(H) availability or adaptation to deficits in metabolic energy availability remains to be resolved.
... In contrast, H6PDH, which accounts for only 5% of NADPH production, causes 11β-HSD1 to act as a reductase in liver cells, because these two enzymes and the co-factors are compartmentalized in SER lumen. Therefore, when H6PDH was knocked out, 11β-HSD1 in the liver became a primary oxidase (13). ...
Background: The purpose of this study was to investigate cytochrome P450-7B1 (CYP7B1) in the human and rat testes to regulate 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity. We hypothesized that dehydroepiandrosterone (DHEA) and its product 7α-hydroxydehydroepiandrosterone (7αOHD) after catalysis of CYP7B1 played a critical role in driving the direction of 11β-HSD1, because 7αOHD is an alternative substrate for 11β-HSD1. Methods: We examined the influence of DHEA and 7αOHD on 11β-HSD1 activities in both intact Leydig cells and microsomes using radioactive substrates and identified the location of CYP7B1 in Leydig cells using immunohistochemical staining, Western blot, and qPCR. Results: We found that DHEA stimulated 11β-HSD1 oxidase activity in intact cells (EC50 = 0.97 ± 0.11 μM) and inhibited its reductase activity (IC50 = 1.04 ± 0.06 μM). In microsomes, DHEA was a competitive inhibitor of the reductase activity. The 11β-HSD1 oxidase activity in intact cells was inhibited by 7αOHD (IC50 = 1.18 ± 0.12 μM), and the reductase activity was enhanced (EC50 = 0.7 ± 0.04 μM). 7αOHD was a competitive inhibitor of 11β-HSD1 oxidase. CYP7B1 was present in rat Leydig cells, as shown by immunohistochemistry, Western blotting, and qPCR analysis. Conclusion: Our results are consistent with a conclusion that DHEA in the circulation driving 11β-HSD1 toward an oxidase in Leydig cells mainly through inhibiting the reductase of the enzyme, while 7αOHD (CYP7B1 catalytic product of DHEA) drives the enzyme toward the opposite direction.
... These data suggest that H6PDH AcKO mice effectively decrease adipose GC production through the reduction of the GC-amplifying effects of endogenous 11β-HSD1 in adipose tissue. This interaction is supported by recent studies reporting that intracellular GC reactivation is impaired in the metabolic tissues of adipose, liver and muscle in H6PDH knockout mice [24, 32,33]. ...
Excessive glucocorticoid (GC) production in adipose tissue promotes the development of visceral obesity and metabolic syndrome. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is critical for controlling intracellular GC production, and this process is tightly regulated by hexose-6-phosphate dehydrogenase (H6PDH). To better understand the integrated molecular physiological effects of adipose H6PDH, we created a tissue-specific knockout of the H6PDH gene mouse model in adipocytes (H6PDHAcKO mice). H6PDHAcKO mice exhibited almost complete absence of H6PDH expression and decreased intra-adipose corticosterone production with a reduction of 11β-HSD1 activity in adipose tissue. These mice also had decreased abdominal fat mass, which was paralleled by decreased adipose lipogenic ACC and ACL gene expression and reduction of their transcription factor C/EBPα mRNA levels. Moreover, H6PDHAcKO mice also had reduced fasting blood glucose levels, increased glucose tolerance, and increased insulin sensitivity. In addition, plasma FFA levels were decreased with a concomitant decrease in the expression of lipase ATGL and HSL in adipose tissue. These results indicate that inactivation of adipocyte H6PDH expression is sufficient to cause intra-adipose GC inactivation that leads to a favorable pattern of metabolic phenotypes. These data suggest that H6PDHAcKO mice may provide a good model for studying the potential contributions of fat-specific H6PDH inhibition to improve the metabolic phenotype in vivo. Our study suggests that suppression or inactivation of H6PDH expression in adipocytes could be an effective intervention for treating obesity and diabetes.
... ER stress is also involved in regulating metabolism [102,103]. IRE1-XBP1 axis of ER stress may regulate insulin function, lipogenesis, adipogenesis [104], glycolysis [102,105,106], and PPP [107]. For example, ER stress was reported to regulate glycolysis. ...
... For example, hexose-6-phosphate dehydrogenase (H6PD), belonging to the PPP metabolism, is located within the ER for NAPDH production. H6PD null mice showed UPR activation and skeletal myopathy [107]. ...
To achieve preferential effects against cancer cells but less damage to normal cells is one of the main challenges of cancer research. In this review, we explore the roles and relationships of oxidative stress-mediated apoptosis, DNA damage, ER stress, autophagy, metabolism, and migration of ROS-modulating anticancer drugs. Understanding preferential anticancer effects in more detail will improve chemotherapeutic approaches that are based on ROS-modulating drugs in cancer treatments.
