Featured ArticlesVolume 6 | No. 1 | January 2017
|A Critical Role for ChREBP-Mediated FGF21 Secretion in Hepatic Fructose MetabolismFructose, but not glucose, ingestion acutely and robustly activates hepatic Carbohydrate Responsive-Element Binding Protein (ChREBP), a key carbohydrate sensing transcription factor. Fibroblast growth factor 21 (FGF21) is a metabolic hormone synthesized by multiple tissues and released into circulation largely by the liver. Fisher and colleagues show that the acute FGF21 response to fructose ingestion observed in humans is conserved in mice. Furthermore, using ChREBP KO mice and FGF21 KO mice, they demonstrate that ChREBP is essential for fructose-induced increases in circulating FGF21. Moreover, they show that FGF21 is required for a normal hepatic metabolic response to fructose consumption and that the absence of FGF21 leads to liver disease in mice on high-fructose diets. |
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Objective: Increased fructose consumption is a contributor to the burgeoning epidemic of non-alcoholic fatty liver disease (NAFLD). Recent evidence indicates that the metabolic hormone FGF21 is regulated by fructose consumption in humans and rodents and may play a functional role in this nutritional context. Here, we sought to define the mechanism by which fructose ingestion regulates FGF21 and determine whether FGF21 contributes to an adaptive metabolic response to fructose consumption.
Methods: We tested the role of the transcription factor carbohydrate responsive-element binding protein (ChREBP) in fructose-mediated regulation of FGF21 using ChREBP knockout mice. Using FGF21 knockout mice, we investigated whether FGF21 has a metabolic function in the context of fructose consumption. Additionally, we tested whether a ChREBP-FGF21 interaction is likely conserved in human subjects.
Results: Hepatic expression of ChREBP-β and Fgf21 acutely increased 2-fold and 3-fold, respectively, following fructose gavage, and this was accompanied by increased circulating FGF21. The acute increase in circulating FGF21 following fructose gavage was absent in ChREBP knockout mice. Induction of ChREBP-β and its glycolytic, fructolytic, and lipogenic gene targets were attenuated in FGF21 knockout mice fed high-fructose diets, and this was accompanied by a 50% reduction in de novo lipogenesis a, 30% reduction VLDL secretion, and a 25% reduction in liver fat compared to fructose-fed controls. In human subjects, serum FGF21 correlates with de novo lipogenic rates measured by stable isotopic tracers (R = 0.55, P = 0.04) consistent with conservation of a ChREBP-FGF21 interaction. After 8 weeks of high-fructose diet, livers from FGF21 knockout mice demonstrate atrophy and fibrosis accompanied by molecular markers of inflammation and stellate cell activation; whereas, this did not occur in controls.
Conclusions: In summary, ChREBP and FGF21 constitute a signaling axis likely conserved in humans that mediates an essential adaptive response to fructose ingestion that may participate in the pathogenesis of NAFLD and liver fibrosis.[Hide abstract]
|Circulating FGF21 is potently induced by overfeeding of carbohydratesThe hormone fibroblast growth factor 21 (FGF21) has received increasing interest due to its role in the regulation of energy homeostasis and its potential antidiabetic and lipid-lowering properties. FGF21 holds promise as a therapeutic target. Lundsgaard et al. evaluate the role of dietary carbohydrates, without restricting protein intake, in the regulation of circulating FGF21. For this purpose, they performed a controlled randomized three-day cross-over dietary intervention study in healthy men. Short term overfeeding of carbohydrates revealed a paramount and remarkable stimulating effect on FGF21 secretion. In contrast, energy excess per se, induced by a hypercaloric fat-rich diet, did not induce a detectable increase in circulating FGF21. This suggests that FGF21 secretion provides a mechanism for peripheral disposal of the carbohydrate load.|
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Objective: Fibroblast-growth factor 21 (FGF21) is thought to be important in metabolic regulation. Recently, low protein diets have been shown to increase circulating FGF21 levels. However, when energy contribution from dietary protein is lowered, other macronutrients, such as carbohydrates, must be increased to meet eucaloric balance. This raises the possibility that intake of a diet rich in carbohydrates may induce an increase in plasma FGF21 levels per se. Here we studied the role of dietary carbohydrates on the levels of circulating FGF21 and concomitant physiologic effects by feeding healthy men a carbohydrate rich diet without reducing protein intake.
Methods: A diet enriched in carbohydrates (80 E% carbohydrate; CHO) and a eucaloric control diet (CON) were provided to nine healthy men for three days. The energy intake during the CHO diet was increased (+75% energy) to ensure similar dietary protein intake in CHO and CON. To control for the effect of caloric surplus, we similarly overfed (+75% energy) the same subjects for three days with a fat-rich diet (78 E% fat; FAT), consisting of primarily unsaturated fatty acids. The three diets were provided in random order.
Results: After CHO, plasma FGF21 concentration increased 8-fold compared to CON (329 ± 99 vs. 39 ± 9 pg ml-1, p < 0.05). In contrast, after FAT only a non-significant tendency (p = 0.073) to an increase in plasma FGF21 concentration was found. The increase in FGF21 concentration after CHO correlated closely (r = 0.88, p < 0.01) with increased leg glucose uptake (62%, p < 0.05) and increased hepatic glucose production (17%, p < 0.01), indicating increased glucose turnover. Plasma fatty acid (FA) concentration was decreased by 68% (p < 0.01), supported by reduced subcutaneous adipose tissue HSL Ser660 phosphorylation (p < 0.01) and perilipin 1 protein content (p < 0.01), pointing to a suppression of adipose tissue lipolysis. Concomitantly, a 146% increase in the plasma marker of hepatic de novo lipogenesis C16:1 n-7 FA (p < 0.01) was observed together with 101% increased plasma TG concentration (p < 0.001) in association with CHO intake and increased plasma FGF21 concentration.
Conclusions: Excess dietary carbohydrate, but not fat, led to markedly increased FGF21 secretion in humans, notably without protein restriction, and affected glucose and lipid homeostasis.[Hide abstract]
|Deletion of Histone Deacetylase 3 in Beta Cells Improves Glucose ToleranceHistone deacetylase 3 (HDAC3) functions as part of multi-protein complexes that deacetylate histone tails, modifying chromatin structure and resulting in gene repression. Remsberg et al. deleted HDAC3 in beta cells of adult mice and demonstrated that HDAC3 in beta cells regulates insulin secretion and glucose metabolism. They identified several target genes that may in combination act to increase glucose-stimulated insulin secretion in vivo.|
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Objective: Histone deacetylases are epigenetic regulators known to control gene transcription in various tissues. A member of this family, histone deacetylase 3 (HDAC3), has been shown to regulate metabolic genes. Cell culture studies with HDAC-specific inhibitors and siRNA suggest that HDAC3 plays a role in pancreatic β-cell function, but a recent genetic study in mice has been contradictory. Here we address the functional role of HDAC3 in β-cells of adult mice.
Methods: An HDAC3 β-cell specific knockout was generated in adult MIP-CreERT transgenic mice using the Cre-loxP system. Induction of HDAC3 deletion was initiated at 8 weeks of age with administration of tamoxifen in corn oil (2 mg/day for 5 days). Mice were assayed for glucose tolerance, glucose-stimulated insulin secretion, and islet function 2 weeks after induction of the knockout. Transcriptional functions of HDAC3 were assessed by ChIP-seq as well as RNA-seq comparing control and β-cell knockout islets.
Results: HDAC3 β-cell specific knockout (HDAC3βKO) did not increase total pancreatic insulin content or β-cell mass. However, HDAC3βKO mice demonstrated markedly improved glucose tolerance. This improved glucose metabolism coincided with increased basal and glucose-stimulated insulin secretion in vivo as well as in isolated islets. Cistromic and transcriptomic analyses of pancreatic islets revealed that HDAC3 regulates multiple genes that contribute to glucose-stimulated insulin secretion.
Conclusions: HDAC3 plays an important role in regulating insulin secretion in vivo, and therapeutic intervention may improve glucose homeostasis.[Hide abstract]
|Interaction of iron homeostasis with glucose metabolismDifferent iron phenotypes such as obesity-related iron deficiency and iron overload have been observed in association with obesity. A high serum ferritin concentration has been identified as a risk factor for the development of diabetes. Felder, Aigner, and colleagues confirm that high serum ferritin concentrations are linked to impaired glucose homeostasis. Their study identifies novel associations of iron excess with distinct subsets of phosphatidylcholines as well as a pathway involving sarcosine and citrulline. These metabolic pathways may be involved in iron-induced augmentation of insulin resistance.|
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Objective: Elevated serum ferritin has been linked to type 2 diabetes (T2D) and adverse health outcomes in subjects with the Metabolic Syndrome (MetS). As the mechanisms underlying the negative impact of excess iron have so far remained elusive, we aimed to identify potential links between iron homeostasis and metabolic pathways.
Methods: In a cross-sectional study, data were obtained from 163 patients, allocated to one of three groups: (1) lean, healthy controls (n = 53), (2) MetS without hyperferritinemia (n = 54) and (3) MetS with hyperferritinemia (n = 56). An additional phlebotomy study included 29 patients with biopsy-proven iron overload before and after iron removal. A detailed clinical and biochemical characterization was obtained and metabolomic profiling was performed via a targeted metabolomics approach.
Results: Subjects with MetS and elevated ferritin had higher fasting glucose (p < 0.001), HbA1c (p = 0.035) and 1 h glucose in oral glucose tolerance test (p = 0.002) compared to MetS subjects without iron overload, whereas other clinical and biochemical features of the MetS were not different. The metabolomic study revealed significant differences between MetS with high and low ferritin in the serum concentrations of sarcosine, citrulline and particularly long-chain phosphatidylcholines. Methionine, glutamate, and long-chain phosphatidylcholines were significantly different before and after phlebotomy (p < 0.05 for all metabolites).
Conclusions: Our data suggest that high serum ferritin concentrations are linked to impaired glucose homeostasis in subjects with the MetS. Iron excess is associated to distinct changes in the serum concentrations of phosphatidylcholine subsets. A pathway involving sarcosine and citrulline also may be involved in iron-induced impairment of glucose metabolism.[Hide abstract]
|Fermentable carbohydrate to increase satietyThe resident intestinal microbiota plays an important role in determining susceptibility to obesity. This is partly due to the production of physiologically active metabolites during the process of microbial fermentation. To determine if the beneficial metabolic effects of fermentable carbohydrate are mediated by free fatty acid receptor 2 signaling, Brooks, Viardot et al. used mice with targeted deletion of this receptor. They demonstrate that this receptor is essential for mediating inulin’s ability to reduce food intake and protect against diet-induced obesity.|
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Objective: Dietary supplementation with fermentable carbohydrate protects against body weight gain. Fermentation by the resident gut microbiota produces short-chain fatty acids, which act at free fatty acid receptor 2 (FFAR2). Our aim was to test the hypothesis that FFAR2 is important in regulating the beneficial effects of fermentable carbohydrate on body weight and to understand the role of gut hormones PYY and GLP-1.
Methods: Wild-type or Ffar2-/- mice were fed an inulin supplemented or control diet. Mice were metabolically characterized and gut hormone concentrations, enteroendocrine cell density measurements were carried out. Intestinal organoids and colonic cultures were utilized to substantiate the in vivo findings.
Results: We provide new mechanistic insight into how fermentable carbohydrate regulates metabolism. Using mice that lack FFAR2, we demonstrate that the fermentable carbohydrate inulin acts via this receptor to drive an 87% increase in the density of cells that produce the appetite-suppressing hormone peptide YY (PYY), reduce food intake, and prevent diet-induced obesity.
Conclusions: Our results demonstrate that FFAR2 is predominantly involved in regulating the effects of fermentable carbohydrate on metabolism and does so, in part, by enhancing PYY cell density and release. This highlights the potential for targeting enteroendocrine cell differentiation to treat obesity.[Hide abstract]
|Intestinal invalidation of GLUT2 delays tissue distribution of glucose The glucose transporter GLUT2 facilitates the passage of dietary sugars towards the bloodstream. Schmitt and colleagues generated an inducible model of GLUT2 invalidation in intestinal epithelial cells. They revealed unexpected functions for GLUT2 in regulating gut homeostasis such as modulating enteroendocrine L-cell density, microvillus length, gut permeability, and inflammation. Therefore, specifically blocking intestinal GLUT2 activity using drugs could be a strategy to protect against weight gain and metabolic perturbations.|
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Objective: Intestinal glucose absorption is orchestrated by specialized glucose transporters such as SGLT1 and GLUT2. However, the role of GLUT2 in the regulation of glucose absorption remains to be fully elucidated.
Methods: We wanted to evaluate the role of GLUT2 on glucose absorption and glucose homeostasis after intestinal-specific deletion of GLUT2 in mice (GLUT2ΔIEC mice).
Results: As anticipated, intestinal GLUT2 deletion provoked glucose malabsorption as visualized by the delay in the distribution of oral sugar in tissues. Consequences of intestinal GLUT2 deletion in GLUT2ΔIEC mice were limiting body weight gain despite normal food intake, improving glucose tolerance, and increasing ketone body production. These features were reminiscent of calorie restriction. Other adaptations to intestinal GLUT2 deletion were reduced microvillus length and altered gut microbiota composition, which was associated with improved inflammatory status. Moreover, a reduced density of glucagon-like peptide-1 (GLP-1) positive cells was compensated by increased GLP-1 content per L-cell, suggesting a preserved enteroendocrine function in GLUT2ΔIEC mice.
Conclusions: Intestinal GLUT2 modulates glucose absorption and constitutes a control step for the distribution of dietary sugar to tissues. Consequently, metabolic and gut homeostasis are improved in the absence of functional GLUT2 in the intestine, thus mimicking calorie restriction.[Hide abstract]
|IP6K1 deletion enhances temperature modulated energy expenditure IP6 kinases (IP6Ks) regulate cell metabolism and survival. Mice with deletion of IP6K1 are protected from diet induced obesity (DIO). Zhu and colleagues determine effects of global IP6K1 deletion on body weight and energy expenditure at various diet and temperature conditions. Deletion of global IP6K1 dramatically protects mice from DIO and insulin resistance due to increased energy expenditure, which is not entirely dependent on environmental temperature condition.|
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Objective: IP6 kinases (IP6Ks) regulate cell metabolism and survival. Mice with global (IP6K1-KO) or adipocyte-specific (AdKO) deletion of IP6K1 are protected from diet induced obesity (DIO) at ambient (23 °C) temperature. AdKO mice are lean primarily due to increased AMPK mediated thermogenic energy expenditure (EE). Thus, at thermoneutral (30 °C) temperature, high fat diet (HFD)-fed AdKO mice expend energy and gain body weight, similar to control mice. IP6K1 is ubiquitously expressed; thus, it is critical to determine to what extent the lean phenotype of global IP6K1-KO mice depends on environmental temperature. Furthermore, it is not known whether IP6K1 regulates AMPK mediated EE in cells, which do not express UCP1.
Methods: Q-NMR, GTT, food intake, EE, QRT-PCR, histology, mitochondrial oxygen consumption rate (OCR), fatty acid metabolism assays, and immunoblot studies were conducted in IP6K1-KO and WT mice or cells.
Results: Global IP6K1 deletion mediated enhancement in EE is impaired albeit not abolished at 30 °C. As a result, IP6K1-KO mice are protected from DIO, insulin resistance, and fatty liver even at 30 °C. Like AdKO, IP6K1-KO mice display enhanced adipose tissue browning. However, unlike AdKO mice, thermoneutrality only partly abolishes browning in IP6K1-KO mice. Cold (5 °C) exposure enhances carbohydrate expenditure, whereas 23 °C and 30 °C promote fat oxidation in HFD-KO mice. Furthermore, IP6K1 deletion diminishes cellular fat accumulation via activation of the AMPK signaling pathway.
Conclusions: Global deletion of IP6K1 ameliorates obesity and insulin resistance irrespective of the environmental temperature conditions, which strengthens its validity as an anti-obesity target.[Hide abstract]
|DNA promoter methylation and transcriptome analysis unravels novel candidate genes for obesityIn order to gain insight into adipose tissue specific principles of epigenetic gene regulation and to elucidate how the provoke the well-known physiological differences between subcutaneous adipose tissue (SAT) and omental visceral adipose tissue (OVAT), Keller et al. studied DNA promoter methylation levels in SAT and OVAT. They confirmed obesity and fat distribution candidate genes and identified genes which have been previously unrecognized in the pathophysiology of obesity. Their data suggest that DNA promoter methylation of specific genes is directly associated with BMI and obesity and clearly demonstrates adipose tissue depot specific differences.|
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Objective/methods: DNA methylation plays an important role in obesity and related metabolic complications. We examined genome-wide DNA promoter methylation along with mRNA profiles in paired samples of human subcutaneous adipose tissue (SAT) and omental visceral adipose tissue (OVAT) from non-obese vs. obese individuals.
Results: We identified negatively correlated methylation and expression of several obesity-associated genes in our discovery dataset and in silico replicated ETV6 in two independent cohorts. Further, we identified six adipose tissue depot-specific genes (HAND2, HOXC6, PPARG, SORBS2, CD36, and CLDN1). The effects were further supported in additional independent cohorts. Our top hits might play a role in adipogenesis and differentiation, obesity, lipid metabolism, and adipose tissue expandability. Finally, we show that in vitro methylation of SORBS2 directly represses gene expression.
Conclusions: Taken together, our data show distinct tissue specific epigenetic alterations which associate with obesity.[Hide abstract]
|Conserved Function of the Long Noncoding RNA Blnc1 in Brown Adipocyte Differentiation Brown fat is present in adult humans and appears highly responsive to physiological and environmental stimuli. Mi and colleagues previously identified Blnc1 as a highly inducible long noncoding RNA that promotes brown and beige adipocyte differentiation. In the present study, they demonstrate that Blnc1 is highly conserved and drives the induction of a thermogenic gene program during brown adipocyte differentiation. In addition, both mouse and human Blnc1 physically interact with the RNA-binding protein hnRNPU and the transcription factor EBF2 to form a ribonucleoprotein complex that regulates the transcription of genes involved in thermogenesis.|
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Objective: Long noncoding RNAs (lncRNAs) are emerging as important regulators of diverse biological processes. Recent work has demonstrated that the inducible lncRNA Blnc1 stimulates thermogenic gene expression during brown and beige adipocyte differentiation. However, whether Blnc1 is functionally conserved in humans has not been explored. In addition, the molecular basis of the Blnc1 ribonucleoprotein complex in thermogenic gene induction remains incompletely understood. The aims of the current study were to: i) investigate functional conservation of Blnc1 in mice and humans and ii) elucidate the molecular mechanisms by which Blnc1 controls the thermogenic gene program in brown adipocytes.
Methods: Full-length human Blnc1 was cloned and examined for its ability to stimulate brown adipocyte differentiation. Different truncation mutants of Blnc1 were generated to identify functional RNA domains responsible for thermogenic gene induction. RNA-protein interaction studies were performed to delineate the molecular features of the Blnc1 ribonucleoprotein complex.Results: Blnc1 is highly conserved in mice and humans at the sequence and function levels, both capable of stimulating brown adipocyte gene expression. A conserved RNA domain was identified to be required and sufficient for the biological activity of Blnc1. We identified hnRNPU as an RNA-binding protein that facilitates the assembly and augments the transcriptional function of the Blnc1/EBF2 ribonucleoprotein complex.
Conclusions: Blnc1 is a conserved lncRNA that promotes thermogenic gene expression in brown adipocytes through formation of the Blnc1/hnRNPU/EBF2 ribonucleoprotein complex.[Hide abstract]
|Development of White Adipose Tissue is Dependent on Zfp423 Zfp423 is a multi zinc-finger transcription factor expressed in preadipocytes and mature adipocytes in vivo. Shao et al. reveal that the loss of adipose Zfp423 during fetal white adipose tissue development leads to arrested terminal differentiation of inguinal white adipocytes by the time of birth. Upon high-fat diet feeding as adults, Zfp423-deficient animals become obese but exhibit a metabolic phenotype similar to that of partial lipodystrophy. This developmental defect can be rescued by administering rosiglitazone. These data define Zfp423 as a critical regulator of adipose development and illustrate the systemic metabolic consequences of pathological subcutaneous adipose tissue expansion in obesity.|
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Objective: Zfp423 is a multi zinc-finger transcription factor expressed in preadipocytes and mature adipocytes in vivo. Our recent work has revealed a critical role for Zfp423 in maintaining the fate of white adipocytes in adult mice through suppression of the beige cell thermogenic gene program; loss of Zfp423 in mature adipocytes of adult mice results in a white-to-beige phenotypic switch. However, the exact requirements of Zfp423 in the fetal stages of early adipose development in vivo have not been clarified.
Methods: Here, we utilize two models that confer adipose-specific Zfp423 inactivation during fetal adipose development (Adiponectin-Cre; Zfp423loxP/loxP and Adiponectin-rtTA; TRE-Cre; Zfp423loxP/loxP). We assess the impact of fetal adipose Zfp423 deletion on the initial formation of adipose tissue and evaluate the metabolic consequences of challenging these animals with high-fat diet feeding.Results: Deletion of Zfp423 during fetal adipose development results in a different phenotype than is observed when deleting Zfp423 in adipocytes of adult mice. Inactivation of Zfp423 during fetal adipose development results in arrested differentiation, specifically of inguinal white adipocytes, rather than a white-to-beige phenotypic switch that occurs when Zfp423 is inactivated in adult mice. This is likely explained by the observation that adiponectin driven Cre expression is active at an earlier stage of the adipocyte life cycle during fetal subcutaneous adipose development than in adult mice. Upon high-fat diet feeding, obese adipose Zfp423-deficient animals undergo a pathological adipose tissue expansion, associated with ectopic lipid deposition and systemic insulin resistance.
Conclusions: Our results reveal that Zfp423 is essential for the terminal differentiation of subcutaneous white adipocytes during fetal adipose tissue development. Moreover, our data highlight the striking adverse effects of pathological subcutaneous adipose tissue remodeling on visceral adipose function and systemic nutrient homeostasis in obesity. Importantly, these data reveal the distinct phenotypes that can occur when adiponectin driven transgenes are activated in fetal vs. adult adipose tissue.[Hide abstract]
|Insulin sensitivity is regulated by GPS2 inhibition of AKT ubiquitination and activationGPS2 plays an important anti-inflammatory role in adipose tissue and macrophages and is required for the expression of genes regulating cholesterol and triglyceride metabolism. Cederquist et al. demonstrate that GPS2 is required for restricting the activation of the insulin signaling pathway through inhibition of Ubc13-mediated ubiquitination of the kinase AKT. Insulin-mediated ubiquitination of AKT, via Ubc13-mediated synthesis of K63 ubiquitin chains, is an unexpected, critical step for the activation of downstream signaling events. GPS2 deletion in mice adipose tissue results in constitutive ubiquitination and activation of AKT, leading to disrupted lipid metabolism and increased adiposity but also to elevated adiponectin levels.|
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Objective: Insulin signaling plays a unique role in the regulation of energy homeostasis and the impairment of insulin action is associated with altered lipid metabolism, obesity, and Type 2 Diabetes. The main aim of this study was to provide further insight into the regulatory mechanisms governing the insulin signaling pathway by investigating the role of non-proteolytic ubiquitination in insulin-mediated activation of AKT.
Methods: The molecular mechanism of AKT regulation through ubiquitination is first dissected in vitro in 3T3-L1 preadipocytes and then validated in vivo using mice with adipo-specific deletion of GPS2, an endogenous inhibitor of Ubc13 activity (GPS2-AKO mice).Results: Our results indicate that K63 ubiquitination is a critical component of AKT activation in the insulin signaling pathway and that counter-regulation of this step is provided by GPS2 preventing AKT ubiquitination through inhibition of Ubc13 enzymatic activity. Removal of this negative checkpoint, through GPS2 downregulation or genetic deletion, results in sustained activation of insulin signaling both in vitro and in vivo. As a result, the balance between lipid accumulation and utilization is shifted toward storage in the adipose tissue and GPS2-AKO mice become obese under normal laboratory chow diet. However, the adipose tissue of GPS2-AKO mice is not inflamed, the levels of circulating adiponectin are elevated, and systemic insulin sensitivity is overall improved.
Conclusions: Our findings characterize a novel layer of regulation of the insulin signaling pathway based on non-proteolytic ubiquitination of AKT and define GPS2 as a previously unrecognized component of the insulin signaling cascade. In accordance with this role, we have shown that GPS2 presence in adipocytes modulates systemic metabolism by restricting the activation of insulin signaling during the fasted state, whereas in absence of GPS2, the adipose tissue is more efficient at lipid storage, and obesity becomes uncoupled from inflammation and insulin resistance.[Hide abstract]
|Celastrol Ameliorates Liver Metabolic Damage through Sirt1 Celastrol was recently identified as a potential novel treatment for obesity. Nonalcoholic fatty liver disease (NAFLD) is currently the most common chronic liver disease worldwide. In this study, Zhang et al. report that Celastrol ameliorates NAFLD by decreasing lipid synthesis and improving the anti-oxidative and anti-inflammatory status. Celastrol aggravates liver metabolic damage in liver specific Silent mating type information regulation 2 homolog 1 (Sirt1)-deficient mice fed a high fat diet through inhibiting the phosphorylation of AMP-activated protein kinase a and boosting the translocation of nuclear factor kappa B into the nucleus, thereby increasing expression of Srebp-1c and the mRNA levels of liver proinflammatory cytokines.|
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Objective: Celastrol was recently identified as a potential novel treatment for obesity. However, the effect of Celastrol on nonalcoholic fatty liver disease (NAFLD) remains elusive. The aim of this study is to evaluate the role of Celastrol in NAFLD.
Methods: Functional studies were performed using wild-type C57BL/6J (WT) mice and liver specific Sirt1-deficient (LKO) mice. The molecular mechanism was explored in primary mouse liver and primary hepatocytes.Results: When WT mice receiving a high-fat diet (HFD) were treated with Celastrol, reductions in body weight, subcutaneous and visceral fat content, and liver lipid droplet formation were observed, along with reduced hepatic intracellular triglyceride and serum triglyceride, free fatty acid, and ALT concentrations. Furthermore, Celastrol decreased hepatic sterol regulatory element binding protein 1c (Srebp-1c) expression, enhanced the phosphorylation of hepatic AMP-activated protein kinase α (AMPKα), and increased the expression of hepatic serine–threonine liver kinase B1 (LKB1). Additionally, Celastrol treatment improved glucose tolerance and insulin sensitivity in WT mice fed the HFD. Celastrol administration also improved the anti-inflammatory and anti-oxidative status by inhibiting nuclear factor kappa B (NFκB) activity and the mRNA levels of proinflammatory cytokines and increasing mitochondrial DNA copy number and anti-oxidative stress genes expression in WT mice liver, in vivo and in vitro. Moreover, Celastrol induced hepatic Sirt1 expression in WT mice, in vivo and in vitro. These Celastrol-mediated protective effects in WT mice fed a HFD were abolished in LKO mice fed a HFD. It was more interesting that Celastrol aggravated HFD-induced liver damage in LKO mice fed a HFD by inhibiting the phosphorylation of AMPKα and boosting the translocation of NFκB into the nucleus, thereby resulting in the increase of Srebp-1c expression and the mRNA levels of liver proinflammatory cytokines.
Conclusions: Celastrol ameliorates NAFLD by decreasing lipid synthesis and improving the anti-oxidative and anti-inflammatory status. And Sirt1 has an important role in Celastrol-ameliorating liver metabolic damage caused by HFD.[Hide abstract]
|The neuropeptide TLQP-21 opposes obesity Cero and colleagues identified a novel lipolytic and anti-obesity mechanism exerted by TLQP-21, a neuropeptide encoded by the pro-peptide VGF (non-acronymic). Their study significantly advances the mechanistic understanding of lipolysis by the identification of a calcium-regulated pathway mediated by TLQP-21 and C3aR1. This pathway could be targeted to safely treat obesity and reverse catecholamine resistance, bypassing the side effects associated with the use of Gs-coupled receptor agonists and other potent prolipolytic mechanisms, which often lead to the development of insulin resistance and other metabolic diseases.|
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Objective: Obesity is characterized by excessive fat mass and is associated with serious diseases such as type 2 diabetes. Targeting excess fat mass by sustained lipolysis has been a major challenge for anti-obesity therapies due to unwanted side effects. TLQP-21, a neuropeptide encoded by the pro-peptide VGF (non-acronymic), that binds the complement 3a receptor 1 (C3aR1) on the adipocyte membrane, is emerging as a novel modulator of adipocyte functions and a potential target for obesity-associated diseases. The molecular mechanism is still largely uncharacterized.
Methods: We used a combination of pharmacological and genetic gain and loss of function approaches. 3T3-L1 and mature murine adipocytes were used for in vitro experiments. Chronic in vivo experiments were conducted on diet-induced obese wild type, β1, β2, β3-adrenergic receptor (AR) deficient and C3aR1 knockout mice. Acute in vivo lipolysis experiments were conducted on Sprague Dawley rats.Results: We demonstrated that TLQP-21 does not possess lipolytic properties per se. Rather, it enhances β-AR activation-induced lipolysis by a mechanism requiring Ca2+ mobilization and ERK activation of Hormone Sensitive Lipase (HSL). TLQP-21 acutely potentiated isoproterenol-induced lipolysis in vivo. Finally, chronic peripheral TLQP-21 treatment decreases body weight and fat mass in diet induced obese mice by a mechanism involving β-adrenergic and C3a receptor activation without associated adverse metabolic effects.
Conclusions: In conclusion, our data identify an alternative pathway modulating lipolysis that could be targeted to diminish fat mass in obesity without the side effects typically observed when using potent pro-lipolytic molecules.[Hide abstract]
|Endospanin 1 affects oppositely body weight regulation and glucose homeostasis Endospanin1 (Endo1), a small four-transmembrane protein, behaves as a negative regulator of leptin receptor function. Vauthier, Roujeau et al. investigated whether silencing Endo1 in the hypothalamic arcuate nucleus (ARC), associated with reduced body weight, could also ameliorate glucose homeostasis accordingly. They reveal that the depletion of Endo1 in the ARC surprisingly worsens glucose homeostasis under conditions of enriched food. Interestingly, at the cellular level, Endo1 silencing has differential effects on leptin signal transduction. |
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Objective: Herein we investigated whether decreased Endo1 expression in the hypothalamic ARC, associated with reduced obesity, could also ameliorate glucose homeostasis accordingly.
Methods: We studied glucose homeostasis in lean or obese mice silenced for Endo1 in the ARC via stereotactic injection of shRNA-expressing lentiviral vectors.Results: We observed that despite being leaner, Endo1-silenced mice showed impaired glucose homeostasis on HFD. Mechanistically, we show that Endo1 interacts with p85, the regulatory subunit of PI3K, and mediates leptin-induced PI3K activation.
Conclusions: Our results thus define Endo1 as an important hypothalamic integrator of leptin signaling, and its silencing differentially regulates the OBR-dependent functions.[Hide abstract]