Limited oxidative stress favors resistance to skeletal muscle atrophy in hibernating brown bears (Ursus Arctos)

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The microRNA Signature in Response to Insulin Reveals Its Implication in the Transcriptional Action of Insulin in Human Skeletal Muscle and the Role of a Sterol Regulatory Element–Binding Protein-1c/Myocyte Enhancer Factor 2C Pathway

International audienceOBJECTIVE: Factors governing microRNA expressions in response to changes of cellular environment are still largely unknown. Our aim was to determine whether insulin, the major hormone controlling whole-body energy homeostasis, is involved in the regulation of microRNA expressions in human skeletal muscle. RESEARCH DESIGN AND METHODS: We carried out comparative microRNA (miRNA) expression profiles in human skeletal muscle biopsies before and after a 3-h euglycemic-hyperinsulinemic clamp, with TaqMan low-density arrays. Then, using DNA microarrays, we determined the response to insulin of the miRNA putative target genes in order to determine their role in the transcriptional action of insulin. We further characterized the mechanism of action of insulin on two representative miRNAs, miR-1 and miR-133a, in human muscle cells. RESULTS: Insulin downregulated the expressions of 39 distinct miRNAs in human skeletal muscle. Their potential target mRNAs coded for proteins that were mainly involved in insulin signaling and ubiquitination-mediated proteolysis. Bioinformatic analysis suggested that combinations of different downregulated miRNAs worked in concert to regulate gene expressions in response to insulin. We further demonstrated that sterol regulatory element-binding protein (SREBP)-1c and myocyte enhancer factor 2C were involved in the effect of insulin on miR-1 and miR-133a expression. Interestingly, we found an impaired regulation of miRNAs by insulin in the skeletal muscle of type 2 diabetic patients, likely as consequences of altered SREBP-1c activation. CONCLUSIONS: This work demonstrates a new role of insulin in the regulation of miRNAs in human skeletal muscle and suggests a possible implication of these new modulators in insulin resistance

Grape polyphenols decrease circulating branched chain amino acids in overfed adults

Introduction and aims: Dietary polyphenols have long been associated with health benefits, including the prevention of obesity and related chronic diseases. Overfeeding was shown to rapidly induce weight gain and fat mass, associated with mild insulin resistance in humans, and thus represents a suitable model of the metabolic complications resulting from obesity. We studied the effects of a polyphenol-rich grape extract supplementation on the plasma metabolome during an overfeeding intervention in adults, in two randomized parallel controlled clinical trials. Methods: Blood plasma samples from 40 normal weight to overweight male adults, submitted to a 31-day overfeeding (additional 50% of energy requirement by a high calorie-high fructose diet), given either 2 g/day grape polyphenol extract or a placebo at 0, 15, 21, and 31 days were analyzed (Lyon study). Samples from a similarly designed trial on females (20 subjects) were collected in parallel (Lausanne study). Nuclear magnetic resonance (NMR)-based metabolomics was conducted to characterize metabolome changes induced by overfeeding and associated effects from polyphenol supplementation. The clinical trials are registered under the numbers NCT02145780 and NCT02225457 at ClinicalTrials.gov. Results: Changes in plasma levels of many metabolic markers, including branched chain amino acids (BCAA), ketone bodies and glucose in both placebo as well as upon polyphenol intervention were identified in the Lyon study. Polyphenol supplementation counterbalanced levels of BCAA found to be induced by overfeeding. These results were further corroborated in the Lausanne female study.Conclusion: Administration of grape polyphenol-rich extract over 1 month period was associated with a protective metabolic effect against overfeeding in adults

Integrative mixture of experts to combine clinical factors and gene markers

Motivation: Microarrays are being increasingly used in cancer research to better characterize and classify tumors by selecting marker genes. However, as very few of these genes have been validated as predictive biomarkers so far, it is mostly conventional clinical and pathological factors that are being used as prognostic indicators of clinical course. Combining clinical data with gene expression data may add valuable information, but it is a challenging task due to their categorical versus continuous characteristics. We have further developed the mixture of experts (ME) methodology, a promising approach to tackle complex non-linear problems. Several variants are proposed in integrative ME as well as the inclusion of various gene selection methods to select a hybrid signature

Persistent Organic Pollutant Exposure Leads to Insulin Resistance Syndrome

International audienceBackground: the incidence of the insulin resistance syndrome has increased at an alarming rate worldwide, creating a serious challenge to public health care in the 21st century. Recently, epide-miological studies have associated the prevalence of type 2 diabetes with elevated body burdens of persistent organic pollutants (POPs). However, experimental evidence demonstrating a causal link between POPs and the development of insulin resistance is lacking. Objective: We investigated whether exposure to POPs contributes to insulin resistance and meta-bolic disorders. Methods: Sprague-Dawley rats were exposed for 28 days to lipophilic POPs through the con-sumption of a high-fat diet containing either refined or crude fish oil obtained from farmed Atlantic salmon. In addition, differentiated adipocytes were exposed to several POP mixtures that mimicked the relative abundance of organic pollutants present in crude salmon oil. We measured body weight, whole-body insulin sensitivity, POP accumulation, lipid and glucose homeostasis, and gene expres-sion and we performed micro array analysis. Results: Adult male rats exposed to crude, but not refined, salmon oil developed insulin resis-tance, abdominal obesity, and hepatosteatosis. The contribution of POPs to insulin resistance was confirmed in cultured adipocytes where POPs, especially organochlorine pesticides, led to robust inhibition of insulin action. Moreover, POPs induced down-regulation of insulin-induced gene-1 (Insig-1) and Lpin1, two master regulators of lipid homeostasis. Conclusion: Our findings provide evidence that exposure to POPs commonly present in food chains leads to insulin resistance and associated metabolic disorder

Chronic Consumption of Farmed Salmon Containing Persistent Organic Pollutants Causes Insulin Resistance and Obesity in Mice

Background: Dietary interventions are critical in the prevention of metabolic diseases. Yet, the effects of fatty fish consumption on type 2 diabetes remain unclear. The aim of this study was to investigate whether a diet containing farmed salmon prevents or contributes to insulin resistance in mice. Methodology/Principal Findings: Adult male C57BL/6J mice were fed control diet (C), a very high-fat diet without or with farmed Atlantic salmon fillet (VHF and VHF/S, respectively), and Western diet without or with farmed Atlantic salmon fillet (WD and WD/S, respectively). Other mice were fed VHF containing farmed salmon fillet with reduced concentrations of persistent organic pollutants (VHF/S-POPs). We assessed body weight gain, fat mass, insulin sensitivity, glucose tolerance, ex vivo muscle glucose uptake, performed histology and immunohistochemistry analysis, and investigated gene and protein expression. In comparison with animals fed VHF and WD, consumption of both VHF/S and WD/S exaggerated insulin resistance, visceral obesity, and glucose intolerance. In addition, the ability of insulin to stimulate Akt phosphorylation and muscle glucose uptake was impaired in mice fed farmed salmon. Relative to VHF/S-fed mice, animals fed VHF/S-POPs had less body burdens of POPs, accumulated less visceral fat, and had reduced mRNA levels of TNFa as well as macrophage infiltration in adipose tissue. VHF/S-POPs-fed mice further exhibited better insulin sensitivity and glucose tolerance than mice fed VHF/S. Conclusions/Significance: Our data indicate that intake of farmed salmon fillet contributes to several metabolic disorders linked to type 2 diabetes and obesity, and suggest a role of POPs in these deleterious effects. Overall, these findings may participate to improve nutritional strategies for the prevention and therapy of insulin resistance

Regulation of gene expression by glucose

International audienceIn addition to its metabolic function, glucose modulates gene expression which is crucial in adapting cells to variations in glycaemia. We summarize recent advances in our understanding of regulation of gene expression by glucose

The ubiquitin-proteasome pathway is a new partner for the control of insulin signaling.

International audienceInsulin signaling is a transitory effect that has to be tightly controlled in magnitude and duration in order to maintain cell homeostasis. Recent reports have demonstrated that members of the ubiquitin-proteasome pathway represent new partners that have to be taken into account for the regulation of insulin action

La bétaïne, un élément régulateur des points de contacts entre la mitochondrie et le réticulum endoplasmique (MAMs) de l’hépatocyte

International audienceLes points de contact entre les mitochondries et le réticulum endoplasmique (RE), appelés MAMs pour Mitochondria-Associated Membranes, ont un rôle crucial dans le contrôle de l'homéostasie glucido-lipidique de l’hépatocyte. Des données récentes montrent que les MAMs sont altérées dans le foie de modèles murins de résistance à l’insuline et de stéatose, faisant des MAMs une cible thérapeutique privilégiée pour la prévention ou le traitement des pathologies métaboliques. Ces plateformes dynamiques peuvent être régulées par différents facteurs, notamment les nutriments. Nous avons fait l’hypothèse que la bétaïne (un acide aminé dérivé de la glycine), de par sa structure et ses propriétés, pourrait moduler la structure et la fonction des MAMs de l’hépatocyte. Des hépatocytes primaires de rats Wistar, mâles, âgés de 3 mois ont été isolés par une méthode de perfusion à la collagénase et cultivés dans du DMEM (3 g/l de glucose) complet. Les cellules ont été incubées pendant 18h dans le milieu de culture avec BSA (Bovine serum albumine, 200µM), supplémenté ou non avec de la bétaïne (5mM). La structure des MAMs a été explorée par microscopie électronique à transmission (MET) et par in situ proximity ligation assay (PLA) pour l’unité fonctionnelle formée par le récepteur IP3R1 (inositol 1,4,5-trisphosphate receptor) du RE et le canal VDAC1 (voltage dependent anion channel) de la mitochondrie. La respiration mitochondriale a été mesurée par oxygraphie sur cellules perméabilisées avec les substrats glutamate (5 mM)/malate (2,5 mM) et succinate (5 mM)/roténone (5 µM). L’expression génique et le contenu en protéines clés des MAMs (VDAC1, mitofusine 2 : Mfn2 et la chaperonne Grp75) ont également été analysés.Les résultats montrent que la bétaïne favorise l’intégrité des MAMs par rapport au contrôle :•La longueur des MAMs mesurée par MET par rapport à la circonférence mitochondriale est augmentée de 41% sous bétaïne par rapport au contrôle (bétaïne 16,2% vs. contrôle 11,5%, p<0,05). Les contacts de 20 à 30nm de largeur, responsables des transferts calciques du RE vers la mitochondrie, sont particulièrement augmentés suite au traitement à la bétaïne (bétaïne 3,5% vs. contrôle 2,0%, p<0,01 soit +75%).•Le nombre d’interaction VDAC1/IP3R1 par noyau analysé par in situ PLA est augmenté de 16,7% sous bétaïne par rapport au contrôle (p<0,05).Ces adaptations sont associées à une modification de la respiration cellulaire en glutamate/malate (+48%, p<0,01). Par ailleurs, l’expression génique de Mfn2, la protéine la plus retrouvée aux MAMs, est augmentée de 26,2% par rapport au contrôle (p<0,001) et son contenu protéique est augmenté de 15,2% (p=0.052). Nos résultats confirment notre hypothèse selon laquelle la bétaïne régule l’intégrité des MAMs. Ceci pourrait s’expliquer par un effet spécifique sur l’expression de la protéine de structure Mfn2. L'augmentation de la respiration cellulaire témoigne d'un effet bénéfique de l'amélioration de l'intégrité de la MAM sur la fonction oxydative mitochondriale

Betaine, a regulator of mitochondrial-endoplasmic reticulum (MAM) interactions in the hepatocyte

International audienceBackground and objectives : Interactions between mitochondria and the endoplasmic reticulum (ER), called MAMs, are impaired in the liver of obese mice, with insulin resistance (IR) and steatosis. As certain nutrients can regulate MAMs, we tested whether betaine (a methylated amino acid derived from glycine) could modulate the structure and function of hepatocyte MAMs. Methods : Primary hepatocytes from Wistar rats (male, 3 months, n=5) were incubated in the presence or absence of betaine (5mM). The structure of MAMs was explored by electron microscopy (TEM) and by in situ proximity ligation assay (PLA) for the functional unit formed by IP3R1 (inositol 1,4,5-trisphosphate receptor) at the ER and VDAC1 (voltage dependent anion channel) at the mitochondrion. Mitochondrial respiration was measured by oxygraphy in permeabilised cells. Gene expression and protein content of key actor at the MAMs (VDAC1, mitofusin 2: Mfn2, chaperone Grp75) were analysed. The results were analysed with Student's t-test.Results : Betaine promoted MAM integrity vs. control. The length of MAMs measured by TEM relative to the mitochondrial circumference was increased by 4.7 points under betaine vs. control (16.2 vs. 11.5%, p<0.05). The number of VDAC1/IP3R1 interactions per nucleus analysed by in situ PLA was increased by 16.7% under betaine vs. control (p<0.05). These adaptations were associated with an increase in glutamate (5mM)/malate (2.5mM) cellular respiration (+48%, p<0.01). Furthermore, the gene expression and protein content of Mfn2, the protein most commonly found at MAMs, were increased by 26.2 and 15.2% vs. control (p<0.001 and p=0.052), respectively. Conclusions : Our results evidenced that betaine regulates the integrity of MAMs. This could be explained by a specific effect on the expression of the structural protein Mfn2. The increase in cellular respiration indicates a beneficial effect of improved MAM integrity on mitochondrial oxidative function