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henolic compounds have emerged in recent years as an option to face insulin resistance and diabetes. The central aim of this study was: (1) to demonstrate that physiological doses of resveratrol (RSV) or quercetin (Q) can influence glucose metabolism in human myotubes, (2) to establish whether AMP-activated protein kinase (AMPK) and protein kinase B –PKB- (Akt) pathways are involved in this effect. In addition, the effects of these polyphenols on mitochondrial biogenesis and fatty acid oxidation were analysed. Myotubes from healthy donors were cultured for 24 h with either 0.1 μM of RSV or with 10 μM of Q. Glucose metabolism, such as glycogen synthesis, glucose oxidation, and lactate production, were measured with D[U-14C]glucose. β-oxidation using [1–14C]palmitate as well as the expression of key metabolic genes and proteins by Real Time PCR and Western blot were also assessed. Although RSV and Q increased pgc1α expression, they did not significantly change either glucose oxidation or β-oxidation. Q increased AMPK, insulin receptor substrate 1 (IRS-1), and AS160 phosphorylation in basal conditions and glycogen synthase kinase 3 (GSK3β) in insulin-stimulated conditions. RSV tended to increase the phosphorylation rates of AMPK and GSK3β. Both of the polyphenols increased insulin-stimulated glycogen synthesis and reduced lactate production in human myotubes. Thus, physiological doses of RSV or Q may exhibit anti-diabetic actions in human myotubes. This research has been supported by Instituto de Salud Carlos III (CIBERObn) under Grant CB12/03/30007 (01/2013) and by the University of the Basque Country under Grant GIU18-173 (07/2018).

Apelin treatment has been shown to improve insulin sensitivity in insulin resistant mice by acting in skeletal muscles. However, the effects of systemic apelin on the hepatic energy metabolism have not been addressed. We thus aimed to determine the effect of chronic apelin treatment on the hepatic lipid metabolism in insulin resistant mice. The apelin receptor (APJ) expression was also studied in this context since its regulation has only been reported in severe liver pathologies. Mice were fed a high-fat diet (HFD) in order to become obese and insulin resistant compared to chow fed mice (CD). HFD mice then received a daily intraperitoneal injection of apelin (0.1 µmol/kg) or PBS during 28 days. Triglycerides content and the expression of different lipogenesis-related genes were significantly decreased in the liver of HFD apelin-treated compared to PBS-treated mice. Moreover, at this stage of insulin resistance, the beta-oxidation was increased in liver homogenates of HFD PBS-treated mice compared to CD mice and reduced in HFD apelin-treated mice. Finally, APJ expression was not up-regulated in the liver of insulin resistant mice. In isolated hepatocytes from chow and HFD fed mice, apelin did not induce significant effect. Altogether, these results suggest that systemic apelin treatment decreases steatosis in insulin resistant mice without directly targeting hepatocytes.

cope In recent years, several studies reported the role of eIF4E-binding proteins (4E-BPs) on the development of diet-induced obesity and insulin resistance. Our aim was to investigate the effect of 4E-BP protein deletion on lipid accumulation and metabolism in skeletal muscle in response to a high fat diet-induced obesity in 4E-BP1/2 DKO mice. Methods and results Diet-induced obesity engendered increased ectopic accumulation of lipotoxic species in skeletal muscle of 4E-BP1 and 4E-BP2 double-knockout mice (4E-BP1/2 DKO), namely diacylglycerols and ceramides. Increased lipid accumulation was associated with alterations in the expression of genes involved in fatty acid transport (FATP, CD36), diacylglycerol/triacylglycerol biosynthesis (GPAT1, AGPAT1, DGAT1) and β-oxidation (CPT1b, MCAD). Diet-induced obesity resulted in increased lean mass and muscle in 4E-BP1/2 DKO mice despite the development of a more severe systemic insulin resistance. Since increased expression of genes of several proteolytic systems (MuRF1, Atrogin/MAFbx and Cathepsin-L) in 4EBP1/2 DKO skeletal muscle was reported, the increased of skeletal muscle mass in 4E-BP1/2 DKO mice suggests that ablation of 4E-BPs compensate with activation of muscle anabolism. Conclusions These findings indicate that 4E-BP proteins may prevent excess lipid accumulation in skeletal muscle and suggest that 4E-BPs are key regulators of muscle homeostasis regardless of insulin sensitivity. This article is protected by copyright. All rights reserved

International audience; Adipose tissue fibrosis development blocks adipocyte hypertrophy and favors ectopic lipid accumulation. Here, we show that adipose tissue fibrosis is associated with obesity and insulin resistance in humans and mice. Kinetic studies in C3H mice fed a high-fat diet show activation of macrophages and progression of fibrosis along with adipocyte metabolic dysfunction and death. Adipose tissue fibrosis is attenuated by macrophage depletion. Impairment of Toll-like receptor 4 signaling protects mice from obesity-induced fibrosis. The presence of a functional Toll-like receptor 4 on adipose tissue hematopoietic cells is necessary for the initiation of adipose tissue fibrosis. Continuous low-dose infusion of the Toll-like receptor 4 ligand, lipopolysaccharide, promotes adipose tissue fibrosis. Ex vivo, lipopolysaccharide-mediated induction of fibrosis is prevented by antibodies against the profibrotic factor TGFβ1. Together, these results indicate that obesity and endotoxemia favor the development of adipose tissue fibrosis, a condition associated with insulin resistance, through immune cell Toll-like receptor 4.

Lipid droplets (LD) play a central role in lipid homeostasis by controlling transient fatty acid (FA) storage and release from triacylglycerols stores, while preventing high levels of cellular toxic lipids. This crucial function in oxidative tissues is altered in obesity and type 2 diabetes. Perilipin 5 (PLIN5) is a LD protein whose mechanistic and causal link with lipotoxicity and insulin resistance has raised controversies. We investigated here the physiological role of PLIN5 in skeletal muscle upon various metabolic challenges. We show that PLIN5 protein is elevated in endurance-trained (ET) subjects and correlates with muscle oxidative capacity and whole-body insulin sensitivity. When overexpressed in human skeletal muscle cells to recapitulate the ET phenotype, PLIN5 diminishes lipolysis and FA oxidation under basal condition, but paradoxically enhances FA oxidation during forskolin- and contraction- mediated lipolysis. Moreover, PLIN5 partly protects muscle cells against lipid-induced lipotoxicity. In addition, we demonstrate that down-regulation of PLIN5 in skeletal muscle inhibits insulin-mediated glucose uptake under normal chow feeding condition, while paradoxically improving insulin sensitivity upon high-fat feeding. These data highlight a key role of PLIN5 in LD function, first by finely adjusting LD FA supply to mitochondrial oxidation, and second acting as a protective factor against lipotoxicity in skeletal muscle.

Dissecting exercise-mimicking pathways that can replicate the benefits of exercise in obesity and diabetes may lead to promising treatments for metabolic disorders. Muscle estrogen-related receptor gamma (ERRγ) is induced by exercise, and when over-expressed in the skeletal muscle mimics exercise by stimulating glycolytic-to-oxidative myofiber switch, mitochondrial biogenesis and angiogenesis in lean mice. The objective of this study was to test whether muscle ERRγ in obese mice mitigates weight gain and insulin resistance. To do so, ERRγ was selectively over-expressed in the skeletal muscle of obese and diabetic db/db mice. Muscle ERRγ over-expression successfully triggered glycolytic-to-oxidative myofiber switch, increased functional mitochondrial content and boosted vascular supply in the db/db mice. Despite aerobic remodeling, ERRγ surprisingly failed to improve whole-body energy expenditure, block muscle accumulation of triglycerides, toxic diacylglycerols (DAG) and ceramides or suppress muscle PKCε sarcolemmal translocation in db/db mice. Consequently, muscle ERRγ did not mitigate impaired muscle insulin signaling or insulin resistance in these mice. In conclusion, obesity and diabetes in db/db mice are not amenable to selective ERRγ-directed programming of classic exercise-like effects in the skeletal muscle. Other biochemical pathways or integrated whole-body effects of exercise may be critical for resisting diabetes and obesity.

Apelin is a bioactive peptide involved in the control of energy metabolism. In the hypothalamus, chronic exposure to high levels of apelin is associated with an increase in hepatic glucose production, and then contributes to the onset of type 2 diabetes. However, the molecular mechanisms behind deleterious effects of chronic apelin in the brain and consequences on energy expenditure and thermogenesis are currently unknown. We aimed to evaluate the effects of chronic intracerebroventricular (icv) infusion of apelin in normal mice on hypothalamic inflammatory gene expression, energy expenditure, thermogenesis and brown adipose tissue functions. We have shown that chronic icv infusion of apelin increases the expression of pro-inflammatory factors in the hypothalamus associated with an increase in plasma interleukin-1 beta. In parallel, mice infused with icv apelin exhibit a significant lower energy expenditure coupled to a decrease in PGC1alpha, PRDM16 and UCP1 expression in brown adipose tissue which could explain the alteration of thermogenesis in these mice. These data provide compelling evidence that central apelin contributes to the development of type 2 diabetes by altering energy expenditure, thermogenesis and fat browning.

International audience; We investigated here the specific role of CGI-58 in the regulation of energy metabolism in skeletal muscle. We first examined CGI-58 protein expression in various muscle types in mice, and next modulated CGI-58 expression during overexpression and knockdown studies in human primary myotubes and evaluated the consequences on oxidative metabolism. We observed a preferential expression of CGI-58 in oxidative muscles in mice consistent with triacylglycerol hydrolase activity. We next showed by pulse-chase that CGI-58 overexpression increased by more than 2-fold the rate of triacylglycerol (TAG) hydrolysis, as well as TAG-derived fatty acid (FA) release and oxidation. Oppositely, CGI-58 silencing reduced TAG hydrolysis and TAG-derived FA release and oxidation (-77%, P < 0.001), whereas it increased glucose oxidation and glycogen synthesis. Interestingly, modulations of CGI-58 expression and FA release are reflected by changes in pyruvate dehydrogenase kinase 4 gene expression. This regulation involves the activation of the peroxisome proliferator activating receptor-δ (PPARδ) by lipolysis products. Altogether, these data reveal that CGI-58 plays a limiting role in the control of oxidative metabolism by modulating FA availability and the expression of PPARδ-target genes, and highlight an important metabolic function of CGI-58 in skeletal muscle.

OBJECTIVE Insulin resistance is associated with elevated content of skeletal muscle lipids, including triacylglycerols (TAGs) and diacylglycerols (DAGs). DAGs are by-products of lipolysis consecutive to TAG hydrolysis by adipose triglyceride lipase (ATGL) and are subsequently hydrolyzed by hormone-sensitive lipase (HSL). We hypothesized that an imbalance of ATGL relative to HSL (expression or activity) may contribute to DAG accumulation and insulin resistance. RESEARCH DESIGN AND METHODS We first measured lipase expression in vastus lateralis biopsies of young lean (n = 9), young obese (n = 9), and obese-matched type 2 diabetic (n = 8) subjects. We next investigated in vitro in human primary myotubes the impact of altered lipase expression/activity on lipid content and insulin signaling. RESULTS Muscle ATGL protein was negatively associated with whole-body insulin sensitivity in our population (r = −0.55, P = 0.005), whereas muscle HSL protein was reduced in obese subjects. We next showed that adenovirus-mediated ATGL overexpression in human primary myotubes induced DAG and ceramide accumulation. ATGL overexpression reduced insulin-stimulated glycogen synthesis (−30%, P < 0.05) and disrupted insulin signaling at Ser1101 of the insulin receptor substrate-1 and downstream Akt activation at Ser473. These defects were fully rescued by nonselective protein kinase C inhibition or concomitant HSL overexpression to restore a proper lipolytic balance. We show that selective HSL inhibition induces DAG accumulation and insulin resistance. CONCLUSIONS Altogether, the data indicate that altered ATGL and HSL expression in skeletal muscle could promote DAG accumulation and disrupt insulin signaling and action. Targeting skeletal muscle lipases may constitute an interesting strategy to improve insulin sensitivity in obesity and type 2 diabetes.

OBJECTIVE—Rosiglitazone displays powerful antidiabetes benefits but is associated with increased body weight and adipogenesis. Keeping in mind the concept of selective peroxisome proliferator–activated receptor (PPAR)γ modulator, the aim of this study was to characterize the properties of a new PPARγ ligand, S 26948, with special attention in body-weight gain. RESEARCH DESIGN AND METHODS—We used transient transfection and binding assays to characterized the binding characteristics of S 26948 and GST pull-down experiments to investigate its pattern of coactivator recruitment compared with rosiglitazone. We also assessed its adipogenic capacity in vitro using the 3T3-F442A cell line and its in vivo effects in ob/ob mice (for antidiabetes and antiobesity properties), as well as the homozygous human apolipoprotein E2 knockin mice (E2-KI) (for antiatherogenic capacity). RESULTS—S 26948 displayed pharmacological features of a high selective ligand for PPARγ with low potency in promoting adipocyte differentiation. It also displayed a different coactivator recruitment profile compared with rosiglitazone, being unable to recruit DRIP205 or PPARγ coactivator-1α. In vivo experiments showed that S 26948 was as efficient in ameliorating glucose and lipid homeostasis as rosiglitazone, but it did not increase body and white adipose tissue weights and improved lipid oxidation in liver. In addition, S 26948 represented one of the few molecules of the PPARγ ligand class able to decrease atherosclerotic lesions. CONCLUSIONS—These findings establish S 26948 as a selective PPARγ ligand with distinctive coactivator recruitment and gene expression profile, reduced adipogenic effect, and improved biological responses in vivo.

Circulating natriuretic peptide (NP) levels are reduced in obesity and predict the risk of type 2 diabetes (T2D). Since skeletal muscle was recently shown as a key target tissue of NP, we aimed to investigate muscle NP receptor (NPR) expression in the context of obesity and T2D. Muscle NPRA correlated positively with whole-body insulin sensitivity in humans and was strikingly downregulated in obese subjects and recovered in response to diet-induced weight loss. In addition, muscle NP clearance receptor (NPRC) increased in individuals with impaired glucose tolerance and T2D. Similar results were found in obese diabetic mice. Although no acute effect of brain NP (BNP) on insulin sensitivity was observed in lean mice, chronic BNP infusion improved blood glucose control and insulin sensitivity in skeletal muscle of obese and diabetic mice. This occurred in parallel with a reduced lipotoxic pressure in skeletal muscle due to an upregulation of lipid oxidative capacity. In addition, chronic NP treatment in human primary myotubes increased lipid oxidation in a PGC1α-dependent manner and reduced palmitate-induced lipotoxicity. Collectively, our data show that activation of NPRA signaling in skeletal muscle is important for the maintenance of long-term insulin sensitivity and has the potential to treat obesity-related metabolic disorders.

Introduction Bien qu'une association robuste entre une diminution des niveaux circulants de peptides natriuretiques (PN) et un risque accru de diabete de type 2 a ete rapportee chez l'homme, il n'y a, a ce jour, aucune evidence directe d'une effet des PN sur la sensibilite a l'insuline globale ou dans un tissu cible. Materiels et Methodes L'expression genique des recepteurs aux PN a ete mesuree par RT-qPCR dans des biopsies de tissu adipeux sous-cutane de deux cohortes europeennes independantes. Le transport de glucose a ete mesure sur des adipocytes humains isoles et sur des adipocytes hMADS ( human multipotent adipose-derived stem cell ) en culture. Les experiences de flux metaboliques et de signalisation ont ete effectuees sur hMADS en culture. Resultats Nous demontrons ici que l'expression du recepteur biologiquement actif aux PN de type A (NPRA) diminue tandis que celle du recepteur de clairance de type C (NPRC) augmente avec le degre d'obesite. L'expression du NPRA correle negativement avec la glycemie a jeun et est diminue chez des individus pre-diabetiques et diabetiques de type 2. L'expression du NPRA correle aussi negativement avec l'insulino-resistance (r=− 0,65, p Conclusions Collectivement, nos donnees supportent un role des PN dans la regulation du metabolisme du glucose et de la sensibilite a l'insuline en stimulant le transport de glucose dans l'adipocyte humain. La signalisation aux PN pourrait constituer une cible potentielle pour ameliorer l'insulinoresistance associee a l'obesite.

The presence of brown adipose tissue (BAT) in human adults opens attractive perspectives to treat metabolic disorders. Indeed, BAT dissipates energy as heat via uncoupling protein (UCP)1. Brown adipocytes are located in specific deposits or can emerge among white fat through the so-called browning process. Although numerous inducers have been shown to drive this process, no study has investigated whether it could be controlled by specific metabolites. Here, we show that lactate, an important metabolic intermediate, induces browning of murine white adipose cells with expression of functional UCP1. Lactate-induced browning also occurs in human cells and in vivo. Lactate controls Ucp1 expression independently of hypoxia-inducible factor-1α and PPARα pathways but requires active PPARγ signaling. We demonstrate that the lactate effect on Ucp1 is mediated by intracellular redox modifications as a result of lactate transport through monocarboxylate transporters. Further, the ketone body β-hydroxybutyrate, another metabolite that impacts redox state, is also a strong browning inducer. Because this redox-dependent increase in Ucp1 expression promotes an oxidative phenotype with mitochondria, browning appears as an adaptive mechanism to alleviate redox pressure. Our findings open new perspectives for the control of adipose tissue browning and its physiological relevance.

It was suggested that human cultured primary myotubes retain the metabolic characteristics of their donor in vitro.The aim of the present study was to investigate whether the metabolic responses to endurance training are also conserved in culture.Middle-aged obese subjects completed an 8-week supervised aerobic exercise training program in which vastus lateralis muscle biopsies were collected before and after training.Anthropometric and blood parameters, as well as aerobic capacity, were assessed before and after training. Muscle biopsies were either used for Western blot analysis or digested to harvest myogenic progenitors that were differentiated into myotubes. Glucose oxidation, palmitate oxidation, and glycogen synthesis assays were performed on myotubes before and after training. Gene expression was assessed by real-time quantitative PCR.Our data indicate that in parallel of in vivo improvement of whole-body aerobic capacity and glucose metabolism, biopsy-derived primary myotubes showed similar patterns in vitro. Indeed, glucose oxidation, glycogen synthesis, and inhibition of palmitate oxidation by glucose were enhanced in myotubes after training. This was associated with consistent changes in the expression of metabolism-linked genes such as GLUT1, PDK4, and PDHA1. Interestingly, no difference in myogenic differentiation capacity was observed before and after training.Aerobic exercise training is associated with metabolic adaptations in vivo that are preserved in human cultured primary myotubes. It can be hypothesized that skeletal muscle microenvironmental changes induced by endurance training lead to metabolic imprinting on myogenic progenitor cells.

It has been suggested that the metabolic benefits of physical exercise could be mediated by myokines. We examined here the effect of exercise training on skeletal muscle expression of a panel of myokines in humans. Pathways regulating myokine expression were investigated in human myotubes.Eleven obese non-diabetic male subjects were enrolled in an 8-week endurance training program. Insulin sensitivity was assessed by an oral glucose tolerance test. Subcutaneous adipose tissue and Vastus lateralis muscle biopsy samples were collected before and after training. RNAs were prepared from adipose tissue and skeletal muscle. Primary culture of myoblasts was established.As expected, exercise training improved aerobic capacity and decreased fat mass. No significant change in interleukin 6, fibroblast growth factor 21, myostatin (MSTN) or irisin mRNA level was found in muscle after training. A twofold increase in apelin mRNA level was found in muscle but not in adipose tissue. No change in circulating myokine and adipokine plasma levels was observed in the resting state in response to training. Interestingly, apelin was significantly expressed and secreted in primary human myotubes. Apelin gene expression was upregulated by cyclic AMP and calcium, unlike the other myokines investigated. Importantly, changes in muscle apelin mRNA levels were positively related to whole-body insulin sensitivity improvement.Collectively, our data show that exercise training upregulates muscle apelin expression in obese subjects. Apelin expression is induced by exercise signaling pathways and secreted in vitro in human primary myotubes, and may behave as a novel exercise-regulated myokine with autocrine/paracrine action.

Elevated expression/activity of adipose triglyceride lipase (ATGL) and/or reduced activity of hormone-sensitive lipase (HSL) in skeletal muscle are causally linked to insulin resistance in vitro. We investigated here the effect of high-fat feeding on skeletal muscle lipolytic proteins, lipotoxicity, and insulin signaling in vivo. Five-week-old C3H mice were fed normal chow diet (NCD) or 45% kcal high-fat diet (HFD) for 4 weeks. Wild-type and HSL knockout mice fed NCD were also studied. Whole-body and muscle insulin sensitivity, as well as lipolytic protein expression, lipid levels, and insulin signaling in skeletal muscle, were measured. HFD induced whole-body insulin resistance and glucose intolerance and reduced skeletal muscle glucose uptake compared with NCD. HFD increased skeletal muscle total diacylglycerol (DAG) content, protein kinase Cθ and protein kinase Cϵ membrane translocation, and impaired insulin signaling as reflected by a robust increase of basal Ser1101 insulin receptor substrate 1 phosphorylation (2.8-fold, P < .05) and a decrease of insulin-stimulated v-Akt murine thymoma viral oncogene homolog Ser473 (−37%, P < .05) and AS160 Thr642 (−47%, P

Partial inhibition of adipose tissue lipolysis does not increase fat mass but improves glucose metabolism and insulin sensitivity through modulation of fatty acid turnover and induction of fat cell de novo lipogenesis., When energy is needed, white adipose tissue (WAT) provides fatty acids (FAs) for use in peripheral tissues via stimulation of fat cell lipolysis. FAs have been postulated to play a critical role in the development of obesity-induced insulin resistance, a major risk factor for diabetes and cardiovascular disease. However, whether and how chronic inhibition of fat mobilization from WAT modulates insulin sensitivity remains elusive. Hormone-sensitive lipase (HSL) participates in the breakdown of WAT triacylglycerol into FAs. HSL haploinsufficiency and treatment with a HSL inhibitor resulted in improvement of insulin tolerance without impact on body weight, fat mass, and WAT inflammation in high-fat-diet–fed mice. In vivo palmitate turnover analysis revealed that blunted lipolytic capacity is associated with diminution in FA uptake and storage in peripheral tissues of obese HSL haploinsufficient mice. The reduction in FA turnover was accompanied by an improvement of glucose metabolism with a shift in respiratory quotient, increase of glucose uptake in WAT and skeletal muscle, and enhancement of de novo lipogenesis and insulin signalling in liver. In human adipocytes, HSL gene silencing led to improved insulin-stimulated glucose uptake, resulting in increased de novo lipogenesis and activation of cognate gene expression. In clinical studies, WAT lipolytic rate was positively and negatively correlated with indexes of insulin resistance and WAT de novo lipogenesis gene expression, respectively. In obese individuals, chronic inhibition of lipolysis resulted in induction of WAT de novo lipogenesis gene expression. Thus, reduction in WAT lipolysis reshapes FA fluxes without increase of fat mass and improves glucose metabolism through cell-autonomous induction of fat cell de novo lipogenesis, which contributes to improved insulin sensitivity., Author Summary In periods of energy demand, mobilization of fat stores in mammals (i.e., adipose tissue lipolysis) is essential to provide energy in the form of fatty acids. In excess, however, fatty acids induce resistance to the action of insulin, which serves to regulate glucose metabolism in skeletal muscle and liver. Insulin resistance (or low insulin sensitivity) is believed to be a cornerstone of the complications of obesity such as type 2 diabetes and cardiovascular diseases. In this study, our clinical observation of natural variation in fat cell lipolysis in individuals reveals that a high lipolytic rate is associated with low insulin sensitivity. Furthermore, partial genetic and pharmacologic inhibition of hormone-sensitive lipase, one of the enzymes involved in the breakdown of white adipose tissue lipids, results in improvement of insulin sensitivity in mice without gain in body weight and fat mass. We undertake a series of mechanistic studies in mice and in human fat cells to show that blunted lipolytic capacity increases the synthesis of new fatty acids from glucose in fat cells, a pathway that has recently been shown by others to be a major determinant of whole body insulin sensitivity. In conclusion, partial inhibition of adipose tissue lipolysis is a plausible strategy in the treatment of obesity-related insulin resistance.

Introduction L'apeline est une adipokine dont les effets benefiques sur le metabolisme energetique ont ete decrits notamment chez les souris obeses et resistantes a l'insuline. Elle permet, entre autre, d'augmenter l'utilisation des lipides et la biogenese mitochondriale dans le muscle. Par contre, les effets de l'apeline sur le metabolisme hepatique ne sont pas connus. Il est vrai que le foie exprime tres faiblement le recepteur APJ en situation physiologique. Le but de cette etude a donc ete de determiner quels sont les effets d'un traitement a l'apeline chez des souris obeses et insulino-resistantes sur le metabolisme lipidique hepatique. Materiels et Methodes Des souris mâles adultes ont ete nourries soit avec un regime standard soit hyperlipidique (HFD) pendant 10 semaines puis traitees pendant 28 jours avec une injection ip d'apeline (0,1 μmol/kg/j) ou de PBS. L'etat d'insulino-resistance a ete evalue. Au sacrifice, le foie a ete preleve afin de mesurer differentes fonctions metaboliques. En parallele, des hepatocytes isoles de souris standard ont ete traites au palmitate (250 μm) et a l'apeline (10 – 7M) a court (20 min) et moyen terme (7 h). Resultats Le traitement apeline chez les souris HFD reduit le gain de masse grasse et l'hyperinsulinemie comme precedemment montre. Dans le foie, le contenu en TG est diminue ainsi que l'expression de genes impliques dans la lipogenese de novo (SREBP-1c, FAS…). L'augmentation de la β-oxydation observee chez les souris HFD est reduite apres le traitement apeline ainsi que la secretion de VLDL. Sur les hepatocytes isoles traites au palmitate, l'apeline n'a pas d'effet sur l'expression des genes de la lipogenese de novo. En aigu l'apeline n'a pas d'effet sur la phosphorylation d'Akt decrite auparavant dans d'autres tissus. Conclusions La steatose hepatique est attenuee chez les souris insulino-resistantes traitees a l'apeline. Cependant il semblerait que les effets de l'apeline sur le metabolisme hepatique soient indirects et une consequence de l'amelioration globale de la sensibilite a l'insuline.

Cardiac natriuretic peptides (NP) are major activators of human fat cell lipolysis and have recently been shown to control brown fat thermogenesis. Here, we investigated the physiological role of NP on the oxidative metabolism of human skeletal muscle. NP receptor type A (NPRA) gene expression was positively correlated to mRNA levels of PPARγ coactivator-1α (PGC1A) and several oxidative phosphorylation (OXPHOS) genes in human skeletal muscle. Further, the expression of NPRA, PGC1A, and OXPHOS genes was coordinately upregulated in response to aerobic exercise training in human skeletal muscle. In human myotubes, NP induced PGC-1α and mitochondrial OXPHOS gene expression in a cyclic GMP–dependent manner. NP treatment increased OXPHOS protein expression, fat oxidation, and maximal respiration independent of substantial changes in mitochondrial proliferation and mass. Treatment of myotubes with NP recapitulated the effect of exercise training on muscle fat oxidative capacity in vivo. Collectively, these data show that activation of NP signaling in human skeletal muscle enhances mitochondrial oxidative metabolism and fat oxidation. We propose that NP could contribute to exercise training–induced improvement in skeletal muscle fat oxidative capacity in humans.

Introduction Les triglycerides intramusculaires constituent une source d’energie importante pour le muscle squelettique notamment au cours d’un exercice physique. Des travaux recents suggerent que l’ATGL (adipose triglyceride lipase) joue un role cle dans ce processus. Cependant, peu de donnees sont actuellement disponibles sur le controle de son activite. L’objectif de ce travail etait d’etudier le role de la proteine G0/G1 Switch Gene 2 (G0S2), recemment decrite comme inhibitrice de l’ATGL dans le tissu adipeux, dans la regulation de la lipolyse et du metabolisme oxydatif musculaire. Materiels et methodes L’expression de G0S2 a ete diminuee, a l’aide de lentivirus contenant des shRNA, dans des cultures primaires de cellules musculaires squelettiques humaines (i.e. myotubes) issues de biopsies de rectus abdominis obtenues chez des volontaires sains. L’activite de l’ATGL, le contenu en triglycerides, la mobilisation et l’oxydation des acides gras, l’oxydation du glucose et la synthese de glycogene ont ete evalues a l’aide de substrats radiomarques. Les approches metaboliques ont ete completees par des etudes d’immunofluorescence des mitochondries et d’expression de genes cles par RT-qPCR. Resultats Nos resultats montrent que G0S2 est exprime dans les myotubes et qu’il inhibe l’activite de l’ATGL. Son invalidation induit une diminution du pool de triglycerides et une augmentation de la mobilisation et de l’oxydation des acides gras. L’oxydation du glucose et la synthese de glycogene sont diminuees. L’augmentation du flux d’acides gras s’accompagne d’une hausse de la masse et du potentiel de membrane des mitochondries. Ces effets seraient potentiellement medies par l’induction de genes cibles du Peroxysome Proliferator Activated Receptor δ (PPARδ). Conclusion Ces resultats indiquent que G0S2 joue un role majeur dans la regulation de la lipolyse et du metabolisme oxydatif musculaire, en modulant le flux d’acides gras et l’expression de genes cibles de PPARδ.

Rosiglitazone displays powerful antidiabetes benefits but is associated with increased body weight and adipogenesis. Keeping in mind the concept of selective peroxisome proliferator-activated receptor (PPAR)gamma modulator, the aim of this study was to characterize the properties of a new PPARgamma ligand, S 26948, with special attention in body-weight gain.We used transient transfection and binding assays to characterized the binding characteristics of S 26948 and GST pull-down experiments to investigate its pattern of coactivator recruitment compared with rosiglitazone. We also assessed its adipogenic capacity in vitro using the 3T3-F442A cell line and its in vivo effects in ob/ob mice (for antidiabetes and antiobesity properties), as well as the homozygous human apolipoprotein E2 knocking mice (E2-KI) (for antiatherogenic capacity).S 26948 displayed pharmacological features of a high selective ligand for PPARgamma with low potency in promoting adipocyte differentiation. It also displayed a different coactivator recruitment profile compared with rosiglitazone, being unable to recruit DRIP205 or PPARgamma coactivator-1 alpha. In vivo experiments showed that S 26948 was as efficient in ameliorating glucose and lipid homeostasis as rosiglitazone, but it did not increase body and white adipose tissue weights and improved lipid oxidation in liver. In addition, S 26948 represented one of the few molecules of the PPARgamma ligand class able to decrease atherosclerotic lesions.These findings establish S 26948 as a selective PPARgamma ligand with distinctive coactivator recruitment and gene expression profile, reduced adipogenic effect, and improved biological responses in vivo.

Introduction L'obesite et le diabete de type 2 (DT2) se caracterisent par une diminution des niveaux circulants de peptides natriuretiques (PN) chez l'homme. Nous avons recemment demontre une signalisation fonctionnelle des PN dans le muscle squelettique. L'objectif de ce travail est d'etudier l'influence de l'obesite et du DT2 sur la signalisation aux PN chez l'homme et la souris. Materiels et methodes Nous avons mesure l'expression proteique des recepteurs aux PN, biologiquement actif (NPRA) et de clairance (NPRC) dans des biopsies musculaires issues de patients normoponderes ou obeses et dans un modele murin d'obesite/diabete (souris db/db et db/+). Nous avons ensuite etudie l'influence d'une perfusion continue de Brain-NP (BNP) par mini-pompe osmotique pendant 4 semaines chez des souris engraissees pendant 16 semaines. Des mesures de poids, composition corporelle et tolerance au glucose ont ete realisees. Resultats Nos resultats demontrent une correlation positive entre l'expression proteique du NPRA musculaire et la sensibilite a l'insuline ( r =0,51, p p Conclusion Nous demontrons pour la premiere fois que la signalisation musculaire aux PN est associee a la sensibilite a l'insuline et que l'obesite et le DT2 se caracterisent par une diminution de la signalisation musculaire aux PN chez l'homme et la souris. Declaration d’interet Les auteurs declarent ne pas avoir d'interet direct ou indirect (financier ou en nature) avec un organisme prive, industriel ou commercial en relation avec le sujet presente.

Introduction Les triglycerides intramusculares constituent une source d'energie importante pour le muscle squelettique, notamment au cours d'un exercice physique. Des travaux precedents chez le rongeur indiquent que la perilipine 5 (PLIN5), proteine localisee a la surface de gouttelettes lipidiques de triglycerides, pourrait jouer un role dans le metabolisme lipidique musculaire. L'objec-tif de ce travail etait de caracteriser et d'etudier le role de PLIN5 dans la regulation de la lipolyse et du metabolisme oxydatif musculaire. Materiels et methodes Nous avons caracterise l'expression proteique de PLIN5 dans differents muscles de souris et chez des individus de poids normal sedentaires, entraines en endurance, et obeses intolerants au glucose (IGT). Nous avons egalement surexprime PLIN5 par une approche adenovirale dans des cultures primaires de cellules musculaires squelettiques humaines pour etudier son role fonctionnel dans la regulation du metabolisme energetique. Resultats Nos resultats montrent que PLIN5 est fortement exprime dans les muscles oxydatifs par rapport aux muscles glycolytiques. Nous montrons egalement une forte correlation positive de PLIN5 avec la sensibilite a l'insuline (r 2 = 0,42, p p = 0,0025), ainsi que la mobilisation et l'utilisation des acides gras issus de la lipolyse des triglycerides (− 46 %, p = 0,0035). Ceci s'accompagne d'une augmentation de l'oxydation du glucose et de la synthese de glycogene, concomitante avec une diminution de l'expression genique de PDK4 (Pyruvate Dehydrogenase Kinase 4). Conclusion Ces resultats indiquent que PLIN5 joue un role important dans la regulation de la lipolyse et du metabolisme oxydatif musculaire. PLIN5 pour-rait en partie determiner la sensibilite a l'insuline en modulant le flux d'acides gras dans le muscle squelettique. Declaration d’interet Les auteurs declarent ne pas avoir d'interet direct ou indirect (financier ou en nature) avec un organisme prive, industriel ou commercial en relation avec le sujet presente.

A series of 1,3-dicarbonyl compounds having 2(3 H )-benzazolonic heterocycles has been synthesized and tested for PPARγ agonist activity. SAR were developed and revealed that 6-acyl-2(3 H )-benzothiazolone derivatives with 1,3-dicarbonyl group were the most potent. IP administration of compound 22 exhibited comparable levels of glucose and triglyceride correction to PO administration of rosiglitazone in the ob / ob mouse studies.

Introduction L’obesite et le diabete de type 2 (DT2) se caracterisent par une diminution des niveaux circulants de peptides natriuretiques (PN) chez l’homme. Les PN jouent un role important dans la regulation de differentes voies metaboliques. L’objectif de ce travail est d’etudier le lien entre deficit en PN, obesite et DT2 dans differents modeles murins. Materiels et methodes Nous avons mesure le niveau d’expression proteique des recepteurs aux PN (NPRA et C) par Western blot dans un modele murin d’obesite/diabete genetique (souris db/db et db/+). Nous avons ensuite etudie l’influence d’une perfusion continue de brain-NP (BNP) par mini-pompe alzet pendant 4 semaines chez des souris db/db a 10 ng/kg/min et chez des souris engraissees par un regime hyperlipidique pendant 16 semaines a 50 ng/kg/min. Des mesures de poids, de composition corporelle, et de tolerances a l’insuline et au glucose ont ete realisees. Resultats Nos resultats montrent une diminution tres nette du ratio NPRA/NPRC (recepteur biologiquement actif/recepteur de clairance) dans les muscles, le foie, et les tissus adipeux blancs et bruns des souris db/db par rapport aux db/+. De plus, le BNP a faible dose diminue significativement la glycemie a jeun, l’hemoglobine glyquee (HbA1c) et ameliore l’insulinosensibilite chez les souris db/db independamment du poids corporel. A plus forte dose, le BNP previent la prise de poids et la degradation de la tolerance au glucose en regime hyperlipidique. Conclusion Nos donnees suggerent que l’obesite est associee a une perte de sensibilite des principaux organes metaboliques aux PN, ce qui pourrait contribuer au developpement du DT2. Une elevation des taux circulant de PN ameliore le controle glycemique et la tolerance au glucose chez des souris obeses et diabetiques.

Introduction Une association inverse entre le contenu en lipides intramyocellulaires et la sensibilite a l'insuline existe chez les sujets sedentaires. Cette relation disparait chez des individus entraines en endurance et refere au paradoxe des athletes. Une deregulation de l'expression des lipases musculaire pourrait contribuer a l'insulino-resistance. L'objectif de ce travail etait d'etudier l'association entre contenu en lipides intramyocellulaires, expression des lipases, capacite oxydative et sensibilite a l'insuline chez des sedentaires, des athletes et des obeses intolerants au glucose avant et apres perte de poids. Materiels et methodes Nous avons etudie des sujets de poids normal sedentaires et entraines en endurance, ainsi que des obeses intolerants au glucose avant et apres perte de poids induite par un regime hypocalorique. La sensibilite a l'insuline a ete evaluee par clamp hyperinsulinemique-euglycemique, les triacylglycerols et diacylglycerols ont ete mesures par chromatographie gazeuse. L'expression des lipases a ete etudiee par Western-blot et la capacite oxydative evaluee par mesure de l'activite citrate synthase. Resultats Nos donnees montrent une forte association entre la sensibilite a l'insuline, la capacite oxydative et l'expression des lipases. Ces trois parametres sont augmentes chez les athletes et diminues chez les obeses compares aux sedentaires. Nous observons une dissociation entre contenu en lipides intramyocellulaires toxiques et sensibilite a l'insuline avec une augmentation du contenu en diacylglycerols a la fois chez l'obese et chez l'athlete. Nous observons egalement une diminution nette des triacylglycerols et diacylglycerols et de l'expression des lipases apres perte de poids chez les obeses. Ces changements interviennent vis-a-vis d'une amelioration de la sensibilite a l'insuline et sans modification de la capacite oxydative musculaire. Conclusion Ces resultats suggerent que les lipides intramyocellulaires totaux, l'expression des lipases et la capacite oxydative musculaire ne sont pas systematiquement associes, et ne constituent donc pas de bons marqueurs de la sensibilite a l'insuline.

Objectif Un traitement aigu ou chronique a l’apeline ameliore la sensibilite a l’insuline de souris insulino-resistantes. Cependant, les effets de l’apeline sur le metabolisme lipidique au cours de la resistance a l’insuline n’ont pas ete clairement definis. Le but de cette etude est de determiner l’effet d’un traitement chronique a l’apeline sur le stockage et l’utilisation des lipides dans deux organes cles du metabolisme : le muscle squelettique et le foie. Materiels et methodes Des souris obeses et resistantes a l’insuline soumises a un regime hyperlipidique ont ete traitees par injection ip quotidienne d’apeline (0,1 μmol/kg/jour) ou de PBS (groupe controle) durant 4 semaines. Le metabolisme energetique a ete etudie in vivo par calorimetrie indirecte, et ex vivo en mesurant l’oxydation du [14C] palmitate et le stockage des triglycerides (TG) dans les deux organes. Resultats Les souris traitees a l’apeline ont un quotient respiratoire diminue par rapport aux souris du groupe controle, indiquant globalement une utilisation des lipides plus importante. En effet, le traitement a l’apeline augmente l’oxydation complete du [14C] palmitate sans augmenter son oxydation incomplete dans le muscle soleaire. Cet effet s’accompagne d’une diminution des taux de malonyl-coA et d’acylcarnitines musculaires. Par contre les taux de TG intramusculaires ne sont pas modifies. Dans le foie, le stockage des TG est reduit chez les souris traitees a l’apeline ainsi que l’expression genique du facteur de transcription SREBP1c et de la FAS (Fatty Acid Synthase). L’oxydation complete du [14C] palmitate mesuree sur des homogenats de foie est elle aussi diminuee chez ces souris sans que l’oxydation incomplete ne soit modifiee. Conclusion Un traitement chronique a l’apeline chez la souris insulino-resistante favorise la diminution du stockage des lipides dans le foie et leur meilleure utilisation par le muscle squelettique, ce qui pourrait contribuer a l’amelioration de la sensibilite a l’insuline observee chez ces souris.

Introduction L’obesite et le diabete de type 2 sont caracterises par un muscle « gras ». Cette graisse musculaire inclus (i) les adipocytes intra/intermusculaires (IMAT) et (ii) les lipides intramyocellulaires majoritairement dus a l’accumulation de triglycerides (IMTG). Afin de mieux comprendre les liens entre accumulation lipidique et insulino-resistance musculaire, une caracterisation approfondie des progeniteurs myocytaires (i. e, cellules satellites) et adipocytaires a ete entreprise. Materiels et methodes Les cellules issues de digestats de biopsies de muscle vastus lateralis de volontaires obeses sont ensemencees et cultivees jusqu’a sub-confluence puis trypsinees afin d’etre, ou non, triees par immunoselection en fonction de l’expression d’un marqueur membranaire des cellules satellites, le CD56. Les 3 fractions cellulaires (Non Triee, CD56 +, CD56−) sont, apres une etape de proliferation, cultivees en milieu de differentiation myogenique (MM) et adipogenique (MA). La nature des cellules presentes ainsi que la purete du tri sont examinees par cytometrie en flux. La differentiation myogenique et adipogenique est evaluee par l’expression de marqueurs specifiques en qPCR et immunocytochimie. Resultats Les donnees preliminaires indiquent que les fractions NT (naturellement riche en cellules exprimant le CD56) et CD56 + s’organisent spontanement en myotubes, quelque soit le milieu de differentiation (MM et MA), et expriment des marqueurs de differentiation myogenique. A l’inverse, la fraction CD56 – ne s’organise pas en myotube (MM), se charge en gouttelettes lipidiques et exprime des marqueurs de differentiation adipogenique (MA). Cette fraction renferme une forte proportion de cellules CD15 +, recemment identifiees comme de potentiels progeniteurs adipocytaires musculaires chez l’homme. Conclusion Deux progeniteurs differents, isolables et cultivables semblent etre a l’origine des fibres musculaires et des adipocytes au sein du muscle chez l’homme obese. L’etude de leur metabolisme et de l’empreinte laissee par leur microenvironnement in situ devrait permettre l’obtention de donnees pertinentes concernant la relation entre lipides musculaires et sensibilite a l’insuline.

Objectif Nous avons etudie le role du co-activateur de l’adipose triglyceride lipase, CGI-58 (Comparative Gene Identification-58) dans le metabolisme energetique du muscle squelettique. Materiels et methodes Nous avons d’abord etudie l’expression de CGI-58 dans divers types de muscles chez la souris. Ensuite nous avons evalue les effets d’un gain ou d’une perte de fonction de CGI-58 sur le metabolisme lipidique, glucidique et oxydatif de cultures primaires de cellules musculaires humaines. Pour cela nous avons mesure, dans ces cellules, le flux lipolytique, l’oxydation des acides gras (AG) ou du glucose et l’expression de genes oxydatifs. Resultats Nous avons observe chez la souris que CGI-58 etait preferentiellement exprime dans les muscles oxydatifs qui possedent une forte activite d’hydrolyse des triacylglycerols (TAG). Nous avons egalement montre qu’une surexpression de CGI-58 augmentait de plus de 2 fois l’hydrolyse des TAG, ainsi que le relargage et l’oxydation des AG derivants des TAG. A l’inverse une invalidation ciblee de CGI-58 diminue l’hydrolyse des TAG, le flux intracellulaire d’AG et leur oxydation (− 77%, p Conclusion Nos resultats demontrent un role important de CGI-58 dans le controle du metabolisme lipidique, glucidique et oxydatif du muscle squelettique.

Recent reports indicate that inter/intramuscular adipose tissue (IMAT), composed by adipocytes underneath the deep fascia of the muscles, is positively correlated with aging, obesity and insulin resistance in humans. However, no molecular/cellular evidence is available to support these interactions. The current study aimed to better characterize human skeletal muscle-derived adipogenic progenitors obtained from obese volunteers and investigate the impact of derived adipocytes on insulin action in primary skeletal muscle cells.Primary cultured stroma-vascular fraction (SVF) obtained from vastus lateralis muscle biopsies of middle-aged obese subjects was immunoseparated (magnetic beads or flow cytometry). The characteristics and/or metabolic phenotype of CD56(+), CD56(-) and CD56(-)CD15(+) cellular fractions were investigated by complementary approaches (flow cytometry, cytology, quantitative PCR and metabolic assays). The effects of conditioned media from CD56(-)CD15(+) cells differentiated into adipocytes on insulin action and signaling in human primary myotubes was also examined.Our data indicate that CD56(+) and CD56(-) cellular fractions isolated from cultured SVF of human muscle contain two distinct committed progenitors: CD56(+) cells (that is, satellite cells) as myogenic progenitors and CD15(+) cells as adipogenic progenitors, respectively. CD56(-)CD15(+)-derived adipocytes display the phenotype and metabolic properties of white adipocytes. Secretions of CD56(-)CD15(+) cells differentiated into functional white adipocytes reduced insulin-mediated non-oxidative glucose disposal (P=0.0002) and insulin signaling.Using in-vitro models, we show for the first time that secretions of skeletal muscle adipocytes are able to impair insulin action and signaling of muscle fibers. This paracrine effect could explain, at least in part, the negative association between high levels of IMAT and insulin sensitivity in obesity and aging.