Martine Laville

Tissue distribution and quantification of the expression of mRNAs of peroxisome proliferator-activated receptors and liver X receptor-alpha in humans: no alteration in adipose tissue of obese and NIDDM patients

Members of the peroxisome proliferator–activated receptor (PPAR) family might be involved in pathologies with altered lipid metabolism. They participate in the control of the expression of genes involved in lipid metabolism and adipocyte differentiation. In addition, thiazolidinediones improve insulin resistance in vivo by activating PPARγ. However, little is known regarding their tissue distribution and relative expression in humans. Using a quantitative and sensitive reverse transcription (RT)-competitive polymerase chain reaction (PCR) assay, we determined the distribution and relative mRNA expression of the four PPARs (α, β, γ1, and γ2) and liver X receptor-α (LXRα) in the main tissues implicated in lipid metabolism. PPARα and LXRα were mainly expressed in liver, while PPARγ1 predominated in adipose tissue and large intestine. We found that PPARγ2 mRNA was a minor isoform, even in adipose tissue, thus causing question of its role in humans. PPARβ mRNA was present in all the tissues tested at low levels. In addition, PPARγ mRNA was barely detectable in skeletal muscle, suggesting that improvement of insulin resistance with thiazolidinediones may not result from a direct effect of these agents on PPARγ in muscle. Obesity and NIDDM were not associated with change in PPARs and LXRα expression in adipose tissue. The mRNA levels of PPARγ1, the predominant form in adipocytes, did not correlate with BMI, leptin mRNA levels, or fasting insulinemia in 29 subjects with various degrees of obesity. These results indicated that obesity is not associated with alteration in PPAR gene expression in abdominal subcutaneous adipose tissue in humans.

Weight loss regulates inflammation-related genes in white adipose tissue of obese subjects

Adipose tissue produces inflammation and immunity molecules suspected to be involved in obesity‐related complications. The pattern of expression and the nutritional regulation of these molecules in humans are poorly understood. We analyzed the gene expression profiles of subcutaneous white adipose tissue from 29 obese subjects during very low calorie diet (VLCD) using cDNA microarray and reverse transcription quantitative PCR. The patterns of expression were compared with that of 17 non‐obese subjects. We determined whether the regulated genes were expressed in adipocytes or stromavascular fraction cells. Gene expression profiling identified 100 inflammation‐related transcripts that are regulated in obese individuals when eating a 28 day VLCD but not a 2 day VLCD. Cluster analysis showed that the pattern of gene expression in obese subjects after 28 day VLCD was closer to the profile of lean subjects than to the pattern of obese subjects before VLCD. Weight loss improves the inflammatory profile of obese subjects through a decrease of proinflammatory factors and an increase of anti‐inflammatory molecules. The genes are expressed mostly in the stromavascular fraction of adipose tissue, which is shown to contain numerous macrophages. The beneficial effect of weight loss on obesity‐related complications may be associated with the modification of the inflammatory profile in adipose tissue.— Clément, K., Viguerie, N., Poitou, C., Carette, C., Pelloux, V., Curat, C. A., Sicard, A., Rome, S., Benis, A., Zucker, J.‐D., Vidal, H., Laville, M., Barsh, G. S., Basdevant, A., Stich, V., Cancello R., Langin, D. Weight loss regulates inflammation‐related genes in white adipose tissue of obese subjects. FASEB J. 18, 1657–1669 (2004)

Emulsified lipids increase endotoxemia: possible role in early postprandial low-grade inflammation.

Low-grade inflammation is a risk factor for the onset of atherosclerosis. Little is known about the involvement of endotoxin absorption from the gut during the digestion of lipids. In the present study, we first investigated in humans the impact of a mixed meal containing dispersed lipids on postprandial endotoxemia and inflammation. We then investigated the effect of (i) oil emulsification in vivo in rats and (ii) fatty acid amounts in vitro using Caco-2 cells on postprandial endotoxemia. In humans, postprandial endotoxemia increased early after the meal. Moreover, we evidenced that the endotoxin receptor sCD14 increased during digestion and that chylomicrons could contribute to absorbed endotoxin transport. This could explain the significant peak of inflammatory cytokine IL-6 that we observed 2 h after the mixed meal. Interestingly, in rats, the emulsion led to both higher endotoxemia and hypertriglyceridemia than oil and compared to a control saline load. In vitro, incubation of Caco-2 cells with increasing fatty acid concentrations enhanced epithelial absorption of endotoxin. To our knowledge, this is the first study evidencing in healthy humans that, following a mixed meal containing lipids, increased endotoxemia is associated with raised sCD14 and a peak of IL-6. On a repeated basis, this may thus be a triggering cascade for the onset of atherosclerosis. In this respect, optimizing both dietary fat amount and structure could be a possible strategy to limit such low-grade endotoxemia and inflammation by the control of postprandial lipemia.

The effects of exercise and protein-energy supplements on body composition and muscle function in frail elderly individuals: a long-term controlled randomised study

Fighting against inactivity and inadequate nutritional intake are of utmost importance in the elderly. To our knowledge, the few studies which have been performed were conducted for only a short period and the results do not permit formal conclusions to be drawn. We therefore tried to fill this gap in our knowledge by determining whether an intervention combining an acceptable progressive exercise programme and nutritional supplements would be feasible for a long-term period in the very frail elderly, and would bring about concomitant benefits in body composition and muscle power. Accordingly, this exercise and nutritional combination was assessed in the frail elderly in a 9-month randomised trial with a factorial design. Fifty-seven elderly volunteers over 72 years, from sixteen retirement homes in Lyon, France participated in the study. Dietary supplements were compared with placebo, and physical exercise was compared with memory training. Main outcome measures were fat-free mass (FFM) and muscle power. FFM was determined by labelled water, and muscle power was measured by a leg-extensor machine. At 9 months, the compliance was 63 % for exercise sessions, and 54 % for nutritional supplements. In patients with dietary supplements, muscle power increased by 57 % at 3 months (P=0.03), and showed only a tendency at 9 months; although FFM increased by 2.7 % at 9 months, the difference was not significant (P=0.10). Exercise did not improve muscle power at 9 months, but improved functional tests (five-time-chair rise, P=0.01). BMI increased with supplements (+3.65 %), but decreased with placebo (-0.5 %) at 9 months (P=0.007). A long-term combined intervention is feasible in frail elderly individuals with a good rate of compliance. Nutritional supplements and exercise may improve muscle function. Despite no significant results on FFM, due to the limited number of volunteers, combined intervention should be suggested to counteract muscle weakness in the frail elderly.

Dual Peroxisome Proliferator–Activated Receptor α/δ Agonist GFT505 Improves Hepatic and Peripheral Insulin Sensitivity in Abdominally Obese Subjects

OBJECTIVE The development of new insulin sensitizers is an unmet need for the treatment of type 2 diabetes. We investigated the effect of GFT505, a dual peroxisome proliferator–activated receptor (PPAR)-α/δ agonist, on peripheral and hepatic insulin sensitivity. RESEARCH DESIGN AND METHODS Twenty-two abdominally obese insulin-resistant males (homeostasis model assessment of insulin resistance >3) were randomly assigned in a randomized crossover study to subsequent 8-week treatment periods with GFT505 (80 mg/day) or placebo, followed by a two-step hyperinsulinemic-euglycemic insulin clamp with a glucose tracer to calculate endogenous glucose production (EGP). The primary end point was the improvement in glucose infusion rate (GIR). Gene expression analysis was performed on skeletal muscle biopsy specimens. RESULTS GFT505 improved peripheral insulin sensitivity, with a 21% (P = 0.048) increase of the GIR at the second insulin infusion period. GFT505 also enhanced hepatic insulin sensitivity, with a 44% (P = 0.006) increase of insulin suppression of EGP at the first insulin infusion period. Insulin-suppressed plasma free fatty acid concentrations were significantly reduced on GFT505 treatment (0.21 ± 0.07 vs. 0.27 ± 0.11 mmol/L; P = 0.006). Neither PPARα nor PPARδ target genes were induced in skeletal muscle, suggesting a liver-targeted action of GFT505. GFT505 significantly reduced fasting plasma triglycerides (−21%; P = 0.003) and LDL cholesterol (−13%; P = 0.0006), as well as liver enzyme concentrations (γ-glutamyltranspeptidase: −30.4%, P = 0.003; alanine aminotransferase: −20.5%, P = 0.004). There was no safety concern or any indication of PPARγ activation with GFT505. CONCLUSIONS The dual PPARα/δ agonist GFT505 is a liver-targeted insulin-sensitizer that is a promising drug candidate for the treatment of type 2 diabetes and nonalcoholic fatty liver disease.

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

OBJECTIVE 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.

Subcutaneous Adipose Tissue Remodeling during the Initial Phase of Weight Gain Induced by Overfeeding in Humans

CONTEXT Deciphering the early processes occurring in adipose tissue during weight gain is a major issue for understanding the development of fat mass and obesity. Experimental overfeeding in humans is a unique situation to tackle these events. OBJECTIVE Our aim was to identify the pathways involved in sc adipose tissue remodeling during the initial phase of weight gain. RESEARCH DESIGN AND METHODS Forty-four healthy men were involved in an overfeeding protocol with a lipid-enriched diet (+760 kcal/d) for 2 months. Subcutaneous abdominal adipose tissue biopsies were taken for histology, transcriptomics, and Western blotting in the basal state, after 14 d, and at the end of the protocol. RESULTS Overfeeding significantly increased body weight (+2.5 kg) and fat mass. Reorganization of gene expression patterns occurred in adipose tissue with an up-regulation of numerous genes involved in lipid metabolism and storage, followed by clusters of genes related to angiogenesis and extracellular matrix remodeling. Histological examination showed increased microvascular density and connective tissue deposition after 56 d of overfeeding, with no changes in the number of macrophages or inflammatory cells. Inhibition of the canonical Wnt/β-catenin signaling pathway and induction of the renin-angiotensin system might be implicated in the remodeling of sc adipose tissue. CONCLUSIONS We characterize the coordinated and time-dependent processes that occur in human adipose tissue during the early phase of weight gain in healthy subjects and identify pathways representing potential targets in pathologies of adipose development, including obesity.

Apelin and APJ regulation in adipose tissue and skeletal muscle of type 2 diabetic mice and humans

Apelin, an adipocyte-secreted factor upregulated by insulin, is increased in adipose tissue (AT) and plasma with obesity. Apelin was recently identified as a new player in the control of glucose homeostasis. However, the regulation of apelin and APJ (apelin receptor) expression in skeletal muscle in relation to insulin resistance or type 2 diabetes is not known. Thus we studied apelin and APJ expression in AT and muscle in different mice models of obesity and in type 2 diabetic patients. In insulin-resistant high-fat (HF)-fed mice, apelin and APJ expression were increased in AT compared with control. This was not the case in AT of highly insulin-resistant db/db mice. In skeletal muscle, apelin expression was similar in control and HF-fed mice and decreased in db/db mice. APJ expression was decreased in both HF-fed and db/db mice. Control subjects and type 2 diabetic patients were subjected to a hyperinsulinemic-euglycemic clamp, and tissues biopsies were obtained before and at the end of the clamp. There was no significant difference in basal apelin and APJ expression in AT and muscle between control and diabetic patients. However, apelin plasma levels were significantly increased in diabetic patients. During the clamp, hyperinsulinemia increased apelin and APJ expression in AT of control but not in diabetic subjects. In muscle, only APJ mRNA levels were increased in control but also in diabetic patients. Taken together, these data show that apelin and APJ expression in mice and humans is regulated in a tissue-dependent manner and according to the severity of insulin resistance.

Waist circumference and the metabolic syndrome predict the development of elevated albuminuria in non-diabetic subjects: the DESIR Study.

Objective Metabolic determinants of microalbuminuria remain poorly understood in non-diabetic individuals and particularly in women. We investigated in both sexes whether an elevated waist circumference (WC) or the presence of the metabolic syndrome (MetS) predict the development of elevated albuminuria at 6 years. Design and patients We studied 2738 subjects from the DESIR cohort without microalbuminuria or diabetes at baseline and who were followed up for 6 years. Results At 6 years, 254 individuals [9.3%; 95% confidence interval (CI) 8.2–10.4%] had developed elevated albuminuria (≥ 20 mg/l), which was significantly and positively associated with WC and blood pressure, but not with fasting glucose, lipids or body mass index in either sex. In both sexes, subjects with a high WC or with MetS at baseline were more likely to develop elevated albuminuria at 6 years compared with those with a normal WC or absence of MetS. In multivariate logistic analysis, WC as a continuous variable or a WC of 94 cm or greater for men and a WC greater than 88 cm for women were predictive of the development of elevated albuminuria, after adjusting for age, hypertension, the use of angiotensin-converting enzyme inhibitors, fibrinogen and glycaemia. MetS was a risk factor for elevated albuminuria in men (odds ratio 1.87; 95% CI 1.25–2.81), with differences according to the MetS definition. Conclusion Abdominal adiposity is related to the development of elevated albuminuria in both sexes, suggesting that the measurement of WC may improve the identification of non-diabetic individuals at risk of developing microalbuminuria and emphasizing the interest of screening for albuminuria among those with MetS.

Increasing intakes of the long-chain ω-3 docosahexaenoic acid: effects on platelet functions and redox status in healthy men

Docosahexaenoic acid (DHA) can prevent cardiovascular events. However, few studies have addressed the effects of DHA on both platelet reactivity and redox status in healthy subjects, and dose‐related studies are scarce. The main objectives of the present study were to determine the effects of increasing doses of DHA on platelets and redox status in humans. Twelve healthy male volunteers (aged 53–65 yr) were assigned to consume an intake of successively 200, 400, 800, and 1600 mg/d DHA, as the only ω‐3 fatty acid, for 2 wk each dose. Blood and urine samples were collected before and after each dose of DHA and at 8 wk after arrest of supplementation. DHA was incorporated in a dose‐response fashion in platelet phospholipids. After supplementation with 400 and 800 mg/d DHA, platelet reactivity was significantly decreased. Platelet vitamin E concentration increased only after 200 mg/d DHA, while p38 MAP kinase phosphorylation decreased. Urinary isoprostane was also significantly lowered after 200 mg/d DHA but was increased after 1600 mg/d. Therefore, supplementation with only 200 mg/d DHA for 2 wk induced an antioxidant effect. It is concluded that low consumption of DHA could be an effective and nonpharmacological way to protect healthy men from platelet‐related cardiovascular events.—Guillot, N., Caillet, E., Laville, M., Calzada, C., Lagarde, M., Vericel, E. Increasing intakes of the long‐chain ω‐3 docosahexaenoic acid: effects on platelet functions and redox status in healthy men. FASEB J. 23, 2909–2916 (2009). www.fasebj.org