Etude du rôle des lipases musculaires dans la régulation du métabolisme des lipides et de la sensibilité à l'insuline

Mon travail de thèse à été axé sur l'étude le la lipolyse musculaire. Nous avons notamment étudié son impact sur la sensibilité à l'insuline ainsi que sur la régulation du métabolisme lipidique et oxydatif. Nous avons pu montrer que l'expression musculaire de l'adipose triglycéride lipase (ATGL), enzyme limitante de la lipolyse, était corrélée négativement avec la sensibilité à l'insuline dans une cohorte de personnes de poids normal, obèses et diabétiques. Afin d'identifier l'impact de cette augmentation d'expression de l'ATGL musculaire nous avons surexprimé la protéine dans des myocytes primaires humains. La signalisation ainsi que la sensibilité à l'insuline étaient diminuées dans ces cellules. Nous avons pu établir que ceci passait par une augmentation de la production de diacylglycérols (DAG) et l'activation de protéines kinases C (PKC) connus pour phosphoryler négativement l'insulin receptor substrate 1. Pour compléter ce travail nous avons étudié dans un modèle murin soumis à un régime riche en graisse, s'il existait une détérioration de l'expression des lipases associée à la perte de sensibilité à l'insuline. Nous avons ainsi pu montrer que le régime hyper lipidique entrainait un déséquilibre de la lipolyse musculaire avec une augmentation de l'expression de comparative gene identification 58 (CGI-58) (co-activateur de l'ATGL) et une baisse de la phosphorylation activatrice de la lipase hormono-sensible en sérine 660. Ceci était associé à une augmentation de l'activation des PKC-? et -e et à une accumulation de DAG. En parallèle, nous avons étudié la fonction de CGI-58 dans le muscle squelettique. Pour cela nous avons réalisé des expériences de surexpression ou d'extinction de CGI-58 dans des myocytes. Nous avons montré que, comme dans l'adipocyte, CGI-58 était un co-activateur de l'ATGL dans le muscle squelettique. De façon intéressante, nous avons également observé que la diminution de la lipolyse, résultant de l'extinction de CGI-58, passait par une diminution de l'oxydation des lipides et une hausse de celle des glucides. Ces effets pourraient s'expliquer par la baisse de l'expression de la pyruvate dehydrogenase kinase 4. Cette baisse d'expression est du dans notre modèle à une diminution de l'activation de peroxysome proliferator-activated receptor bêta/d par les acides gras de la lipolyse. Ces travaux ont montré pour la première fois un lien causal entre une dérégulation de la lipolyse musculaire et l'insulino-résistance. Nos données participent également à l'élargissement des connaissances existantes sur le contrôle physiologique et moléculaire de la lipolyse musculaire.During my PhD thesis, we studied the pathophysiological link between skeletal muscle lipolysis and insulin-resistance. We also evaluated the role of skeletal muscle lipolysis in the regulation of lipid and oxidative metabolism. We have shown that the expression of adipose triglyceride lipase (ATGL) in skeletal muscle, a limiting enzyme of lipolysis, was negatively correlated with insulin sensitivity in a cohort of lean, obese and type 2 diabetic subjects. To study the effect of ATGL up-regulation on insulin sensitivity, we next over-expressed ATGL in human primary myocytes. Insulin-sensitivity and signaling were both reduced. We also showed that these effects were dependant on diacylglycerol (DAG) production and protein kinase C (PKC) activation. PKC are known to inhibit insulin receptor substrate 1 by serine phosphorylation. We next studied, in a murine mouse model, the effect of high fat feeding on insulin resistance and skeletal muscle lipase expression. We have shown an increase of comparative gene identification 58 (CGI-58) expression (a co-activator of ATGL) and a decrease of hormone sensitive lipase phosphorylation on its activating residue at serine 660. This deregulation of lipolysis was associated with a strong increase of total DAG concentration and PKC ? and e membrane translocationin skeletal muscle. In parallel to this work, we studied the metabolic role of CGI-58 in skeletal muscle through overexpression and knockdown studies in primary human myocytes. We have shown that CGI-58 is a co-activator of ATGL in skeletal muscle. Moreover we observed during the knockdown of CGI-58 a decrease of lipid oxidation and an increase of glucose oxidation. These effects were partly explained by the down-regulation of pyruvate dehydrogenase kinase 4 expression. These effects were mostly mediated by a decrease of peroxysome proliferator-activated receptor beta/d activation by fatty acid from lipolysis. Finally our work shows for the first time a pathophysiological link between lipases deregulation and insulin-resistance in skeletal muscle. These data also significantly contribute to a better understanding of the molecular and physiological regulation of skeletal muscle lipolysis

Relation between mean arterial pressure and renal function in the early phase of shock: a prospective, explorative cohort study

International audienceIntroduction: Because of disturbed renal autoregulation, patients experiencing hypotension-induced renal insult might need higher levels of mean arterial pressure (MAP) than the 65 mmHg recommended level in order to avoid the progression of acute kidney insufficiency (AKI)

Étude du rôle des lipases musculaires dans la régulation du métabolisme des lipides et de la sensibilité à l'insuline

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Muscle Arnt/Hif1β Is Dispensable in Myofiber Type Determination, Vascularization and Insulin Sensitivity

<div><p>Aryl Hydrocarbon Receptor Nuclear Translocator/ hypoxia-inducible factor 1 beta (ARNT/ HIF1β), a member of bHLH-PAS family of transcriptional factors, plays a critical role in metabolic homeostasis, insulin resistance and glucose intolerance. The contributions of ARNT in pancreas, liver and adipose tissue to energy balance through gene regulation have been described. Surprisingly, the impact of ARNT signaling in the skeletal muscles, one of the major organs involved in glucose disposal, has not been investigated, especially in type II diabetes. Here we report that ARNT is expressed in the skeletal muscles, particularly in the energy-efficient oxidative slow-twitch myofibers, which are characterized by increased oxidative capacity, mitochondrial content, vascular supply and insulin sensitivity. However, muscle-specific deletion of ARNT did not change myofiber type distribution, oxidative capacity, mitochondrial content, capillarity, or the expression of genes associated with these features. Consequently, the lack of ARNT in the skeletal muscle did not affect weight gain, lean/fat mass, insulin sensitivity and glucose tolerance in lean mice, nor did it impact insulin resistance and glucose intolerance in high fat diet-induced obesity. Therefore, skeletal muscle ARNT is dispensable for controlling muscle fiber type and metabolic regulation, as well as diet-induced weight control, insulin sensitivity and glucose tolerance.</p></div

Comment les exceptions des handicaps révèlent les universaux phonologiques : contraintes visuelles et auditives des systèmes consonantiques des langues du monde

National audienc

Comment les exceptions des handicaps révèlent les universaux phonologiques : contraintes visuelles et auditives des systèmes consonantiques des langues du monde

National audienc

Comment les exceptions des handicaps révèlent des universaux phonologiques bimodaux: contraintes audiovisuelles des systèmes consonantiques des langues du monde.

National audienc

Modèles géométriques de croissance du cerveau, cervelet, tronc cérébral et modification des angles de la base du crâne au cours de la période fœtale

International audienc

High-fat diet-mediated lipotoxicity and insulin resistance is related to impaired lipase expression in mouse skeletal muscle.

International audienceElevated 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 <.01) phosphorylation. We next showed that HFD strongly reduced HSL phosphorylation at Ser660. HFD significantly up-regulated the muscle protein content of the ATGL coactivator comparative gene identification 58 and triacylglycerol hydrolase activity, despite a lower ATGL protein content. We further show a defective skeletal muscle insulin signaling and DAG accumulation in HSL knockout compared with wild-type mice. Together, these data suggest a pathophysiological link between altered skeletal muscle lipase expression and DAG-mediated insulin resistance in mice

ARNT expression in different tissues.

<p><b>(A)</b> ARNT protein expression in different organs [sub-cutaneous adipose tissue (Sc), perigonadic adipose tissue (Pg), brown adipose tissue (Bat), heart (He), liver (Li), brain (Br), kidney (Ki), pancreas (Pa), gastrocnemius muscle (Ga)] of 4 months old mice (N = 1). <b>(B)</b> Arnt gene expression in the soleus and the extensor digitorum longus (EDL) of 3 month old mice (N = 4–5). <b>(C-D)</b> ARNT expression in control and MKO muscle groups ranging from the most oxidative (soleus) to most glycolytic (EDL) (N = 3). (C) Representative images. (D) Densitometry for protein expression. (E) Arnt gene expression in EDL control and MKO muscles of 4 months old mice (N = 4–5). (*p<0.05,**p<0.01,***p<0.001, Unpaired Student’s t-test or One-way ANOVA with Tukey’s multiple comparison post-hoc test.)</p