A rare missense mutation in a type 2 diabetes patient decreases the transcriptional activity of human sterol regulatory element binding protein-1

11 pages, 3figures, 1 table.-PMID: 16429400 [PubMed]Sterol regulatory element binding protein 1 (SREBP-1) transcription factors play a key role in energy homeostasis by regulating genes involved in both carbohydrate and lipid metabolism, and in adipocyte differentiation. The 5' end of the mRNA-encoding SREBP-1 exists in two forms, designated 1a and 1c. The divergence results from the use of two transcription start sites that produce two separate 5' exons, each of which is spliced to a common exon 2. Mutations in the sterol regulatory element binding protein gene (SREBF)-1 may contribute to insulin resistance states. However, the variants described to date do not affect the SREBP function. In this study, we investigated the functional consequences of a novel missense mutation common to both SREBP-1 isoforms identified in a Spanish Type 2 diabetic patient (c.677C>T, SREBP-1a p.T226M; c.605C>T, SREBP-1c p.T202M). Using reporter gene analysis and electrophoretic mobility shift assays, we found that this variant impaires the transcriptional activity and reduces DNA binding ability despite its comparable protein stability to the wild-type SREBP-1. This decreased activity impaires the expression of known downstream targets, such as the LDL receptor and fatty acid synthase genes. Our findings suggest that the threonine residue and/or surrounding region play an important role in the SREBP-1 functionThis study was supported by grants from Instituto de Salud Carlos III, Red de Centros (RCMN) C03/08, and from Ministerio de Educación y Ciencia (SAF2003-01262). S.V. is supported by a fellowship from Consejo Superior de Investigaciones Científicas I3P-BPD2001-1.Peer reviewe

SETDB2 Links Glucocorticoid to Lipid Metabolism through Insig2a Regulation

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Activation of AMPK-Regulated CRH Neurons in the PVH is Sufficient and Necessary to Induce Dietary Preference for Carbohydrate over Fat

Food selection is essential for metabolic homeostasis and is influenced by nutritional state, food palatability, and social factors such as stress. However, the mechanism responsible for selection between a high-carbohydrate diet (HCD) and a high-fat diet (HFD) remains unknown. Here, we show that activation of a subset of corticotropin-releasing hormone (CRH)-positive neurons in the rostral region of the paraventricular hypothalamus (PVH) induces selection of an HCD over an HFD in mice during refeeding after fasting, resulting in a rapid recovery from the change in ketone metabolism. These neurons manifest activation of AMP-activated protein kinase (AMPK) during food deprivation, and this activation is necessary and sufficient for selection of an HCD over an HFD. Furthermore, this effect is mediated by carnitine palmitoyltransferase 1c (CPT1c). Thus, our results identify the specific neurons and intracellular signaling pathway responsible for regulation of the complex behavior of selection between an HCD and an HFD

Characterising the inhibitory actions of ceramide upon insulin signaling in different skeletal muscle cell models:a mechanistic insight

International audienceCeramides are known to promote insulin resistance in a number of metabolically important tissues including skeletal muscle, the predominant site of insulin-stimulated glucose disposal. Depending on cell type, these lipid intermediates have been shown to inhibit protein kinase B (PKB/Akt), a key mediator of the metabolic actions of insulin, via two distinct pathways: one involving the action of atypical protein kinase C (aPKC) isoforms, and the second dependent on protein phosphatase-2A (PP2A). The main aim of this study was to explore the mechanisms by which ceramide inhibits PKB/Akt in three different skeletal muscle-derived cell culture models; rat L6 myotubes, mouse C2C12 myotubes and primary human skeletal muscle cells. Our findings indicate that the mechanism by which ceramide acts to repress PKB/Akt is related to the myocellular abundance of caveolin-enriched domains (CEM) present at the plasma membrane. Here, we show that ceramide-enriched-CEMs are markedly more abundant in L6 myotubes compared to C2C12 myotubes, consistent with their previously reported role in coordinating aPKC-directed repression of PKB/Akt in L6 muscle cells. In contrast, a PP2A-dependent pathway predominantly mediates ceramide-induced inhibition of PKB/Akt in C2C12 myotubes. In addition, we demonstrate for the first time that ceramide engages an aPKC-dependent pathway to suppress insulin-induced PKB/Akt activation in palmitate-treated cultured human muscle cells as well as in muscle cells from diabetic patients. Collectively, this work identifies key mechanistic differences, which may be linked to variations in plasma membrane composition, underlying the insulin-desensitising effects of ceramide in different skeletal muscle cell models that are extensively used in signal transduction and metabolic studies

Hypothalamic AgRP-neurons control peripheral substrate utilization and nutrient partitioning

Obesity-related diseases such as diabetes and dyslipidemia result from metabolic alterations including the defective conversion, storage and utilization of nutrients, but the central mechanisms that regulate this process of nutrient partitioning remain elusive. As positive regulators of feeding behaviour, agouti-related protein (AgRP) producing neurons are indispensible for the hypothalamic integration of energy balance. Here, we demonstrate a role for AgRP-neurons in the control of nutrient partitioning. We report that ablation of AgRP-neurons leads to a change in autonomic output onto liver, muscle and pancreas affecting the relative balance between lipids and carbohydrates metabolism. As a consequence, mice lacking AgRP-neurons become obese and hyperinsulinemic on regular chow but display reduced body weight gain and paradoxical improvement in glucose tolerance on high-fat diet. These results provide a direct demonstration of a role for AgRP-neurons in the coordination of efferent organ activity and nutrient partitioning, providing a mechanistic link between obesity and obesity-related disorders

Etude du facteur de transcription SREBP-1c et de son implication dans le métabolisme glucido-lipidique hépatique

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

La réponse UPR

Le réticulum endoplasmique est le compartiment par lequel transitent obligatoirement les protéines sécrétées. Les protéines y subissent un contrôle de qualité qui les conduira soit vers l’appareil de Golgi pour être sécrétées, soit vers la dégradatio nen cas de mauvaise conformation. L’accumulation de protéines dans la lumière du réticulum endoplasmique,de nature physiologique (cellules sécrétrices) ou physiopathologique (protéines malrepliées) entraîne l’apparition d’une réponse UPR(unfolded protein response). Celle-ci se met en place à partir de l’activation de trois protéines transmembranaires du réticulum endoplasmique : PERK (PKR-like ER protein kinase), ATF6 (activatingtranscription factor 6) et IRE-1 (inositol requiring enzyme 1), et a pour but d’augmenter les capacités de repliement, de maturation, voire de dégradation du réticulum endoplasmique. La réponse UPR est une réponse physiologique qui joue un rôle majeur dans les cellules à forte capacité sécrétrice comme les plasmocytes ou les cellules β du pancréas. Des altérations dans sa qualité ou dans son intensité sont à l’origine de nombreuses pathologies humaines comme certains types de diabète ou des maladies neurodégénératives

Effet de l AMP activated protein kinase sur la lipolyse dans l adipocyte humain

L AMP-activated protein kinase (AMPK) joue un rôle majeur dans la régulation du métabolisme énergétique. L AMPK stimule les voies cataboliques et inhibe les voies anaboliques. Pour approfondir les mécanismes par lesquels l AMPK contrôle l homéostasie énergétique, nous avons exploré son rôle dans la régulation de la lipolyse adipocytaire humaine. Dans l adipocyte murin, l AMPK inhibe la lipolyse. Comme les biguanides et les thiazolidinediones activent cette enzyme, nous avons testé l hypothèse que ceux-ci pourraient avoir un effet anti-lipolytique dans l adipocyte humain. Pour répondre à cette question, les adipocytes, obtenus chez des patients bénéficiant d une plastie abdominale, ont été incubés avec différents agents lipolytiques (isoprénaline et peptide atrial natriuretique/ANP) en présence ou non de biguanides ou de thiazolidinediones. Dans l adipocyte humain, ces antidiabétiques activent l AMPK et inhibent la lipolyse induite par l isoprénaline et l ANP de 30 à 40%, probablement par l inhibition de la translocation de la lipase hormono-sensible à la gouttelette lipidique. La stimulation de la lipolyse induit par ailleurs l activation de l AMPK. Nous avons montré pour la première fois dans l adipocyte humain que les biguanides et les thiazolidinediones activent l AMPK, inhibant ainsi la lipolyse induite par l isoprénaline et l ANP. Par ailleurs, les agonistes adrénergiques ainsi que l ANP stimulent l activité AMPK via l augmentation du rapport AMP/ATP, lié à l activation des acides gras en acyl-CoA. L AMPK pourrait être utilisée pour restreindre de manière pharmacologique la libération d acides gras dans la circulation.AMP-activated protein kinase (AMPK) plays a key role in regulating energy metabolism. AMPK switches-on catabolic pathways and switches-off anabolic pathways. In order to understand further how AMPK controls energy homeostasis, we have investigated its role in the regulation of human adipose tissue lipolysis. In rodent adipocytes, activated AMPK reduces the lipolytic rate. As metformin and thiazolidinediones activate this enzyme, we tested the hypothesis that they could have an anti-lipolytic effect in human adipocytes. Adipocytes, obtained from individuals undergoing plastic surgery, were isolated and incubated with lipolytic agents (isoprenaline, atrial natriuretic peptide/ANP) and biguanides or thiazolidinediones. Biguanides and thiazolidinediones activated AMPK and inhibited lipolysis induced by isoprenaline and ANP by 30-40%, at least in part by inhibiting hormone-sensitive lipase translocation to the lipid droplet. Inhibition of AMPK by compound C precluded this inhibitory effect on lipolysis. Stimulation of lipolysis also induced an activation of AMP-activated protein kinase concomitant with a drop in ATP concentration. We show for the first time in human adipocytes that biguanides and thiazolidinediones activate AMP-activated protein kinase, thus counteracting lipolysis induced by lipolytic agents. In addition, induction of lipolysis increases AMPK activity, because of an increase in the AMP/ATP ratio, linked to activation of some of the released fatty acids into acyl-CoA. AMPK activation could represent a physiological means of avoiding a deleterious drain of energy during lipolysis but could be used to restrain pharmacological release of fatty acids.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF