Activin A Plays a Critical Role in Proliferation and Differentiation of Human Adipose Progenitors

International audienceAbstractObjective: Growth of white adipose tissue takes place in normal development and in obesity. A pool of adipose progenitors is responsible for the formation of new adipocytes and for the potential of this tissue to expand in response to chronic energy overload. However, factors controlling self-renewal of human adipose progenitors are largely unknown. We investigated the expression profile and the role of activin A in this process. Research Design and Methods: Expression of INHBA/activin A has been investigated in three types of human adipose progenitors. We then analyzed at the molecular level the function of activin A during human adipogenesis. We finally investigated the status of activin A in adipose tissues of lean and obese subjects and analyzed macrophage-induced regulation of its expression. Results: INHBA/activin A is expressed by adipose progenitors from various fat depots and its expression dramatically decreases as progenitors differentiate into adipocytes. Activin A regulates the number of undifferentiated progenitors. Sustained activation or inhibition of the activin A pathway impairs or promotes respectively adipocyte differentiation via C/EBPbeta-LAP and Smad2 pathway in an autocrine/paracrine manner. Activin A is expressed at higher levels in adipose tissue of obese patients compared to lean subjects. Indeed, activin A levels in adipose progenitors are dramatically increased by factors secreted by macrophages derived from obese adipose tissue. Conclusions: Altogether, our data show that activin A plays a significant role in human adipogenesis. We propose a model in which macrophages which are located in adipose tissue regulate adipose progenitor self-renewal through activin A

TGFbeta Family Members Are Key Mediators in the Induction of Myofibroblast Phenotype of Human Adipose Tissue Progenitor Cells by Macrophages

International audienceOBJECTIVE: The present study was undertaken to characterize the remodeling phenotype of human adipose tissue (AT) macrophages (ATM) and to analyze their paracrine effects on AT progenitor cells. RESEARCH DESIGN AND METHODS: The phenotype of ATM, immunoselected from subcutaneous (Sc) AT originating from subjects with wide range of body mass index and from paired biopsies of Sc and omental (Om) AT from obese subjects, was studied by gene expression analysis in the native and activated states. The paracrine effects of ScATM on the phenotype of human ScAT progenitor cells (CD34(+)CD31(-)) were investigated. RESULTS: Two main ATM phenotypes were distinguished based on gene expression profiles. For ScAT-derived ATM, obesity and adipocyte-derived factors favored a pro-fibrotic/remodeling phenotype whereas the OmAT location and hypoxic culture conditions favored a pro-angiogenic phenotype. Treatment of native human ScAT progenitor cells with ScATM-conditioned media induced the appearance of myofibroblast-like cells as shown by expression of both α-SMA and the transcription factor SNAIL, an effect mimicked by TGFβ1 and activinA. Immunohistochemical analyses showed the presence of double positive α-SMA and CD34 cells in the stroma of human ScAT. Moreover, the mRNA levels of SNAIL and SLUG in ScAT progenitor cells were higher in obese compared with lean subjects. CONCLUSIONS: Human ATM exhibit distinct pro-angiogenic and matrix remodeling/fibrotic phenotypes according to the adiposity and the location of AT, that may be related to AT microenvironment including hypoxia and adipokines. Moreover, human ScAT progenitor cells have been identified as target cells for ScATM-derived TGFβ and as a potential source of fibrosis through their induction of myofibroblast-like cells

Role of macrophage tissue infiltration in obesity and insulin resistance.

International audienceObesity is associated with systemic chronic low-grade inflammation, a major contributor to the aetiology of insulin resistance (IR). An inflammatory response in the presence of obesity appears to be triggered by, and to reside predominantly in, adipose tissue (AT). The discovery that the AT in obese mice and humans is infiltrated with macrophages has provided a major advance in our understanding of how obesity propagates inflammation. Interestingly, AT-infiltrating macrophages exhibit a proinflammatory phenotype (classical activation) whereas macrophages residing in AT have a reparative phenotype (alternative activation). In this review, the processes involved in monocyte/macrophage recruitment into the AT, and the events underlying the activation of infiltrating and/or resident AT macrophages (ATM) are described. Also, the localized roles of ATM on AT growth, metabolism and remodelling, as well as their systemic effects in promoting IR, are revealed. Finally, the new therapeutic targets that have recently emerged, and which have the potential to modulate the recruitment and/or activation of ATM, are discussed

Evidence of in situ proliferation of adult adipose tissue-derived progenitor cells: influence of fat mass microenvironment and growth.

International audienceCONTEXT: Adipocyte formation in human adult adipose tissue (hAT) originates from resident progenitor cell differentiation in the stroma vascular fraction of the AT. The processes involved in the self-renewal of this cell population remain to be defined. OBJECTIVE: The objective was to study in situ and in vitro hAT progenitor cell (defined as CD34(+)/CD31(-) cells) proliferation. DESIGN AND PARTICIPANTS: In situ progenitor cell proliferation was assessed by immunohistochemistry and flow cytometry analyses on hAT from lean to obese subjects using the proliferation marker Ki-67. The effects of adipokines, hypoxia, and conditioned media (CM) from adipocytes, capillary endothelial cells, and macrophages isolated by an immunoselection approach were studied on hAT progenitor cell growth. Cell death in hAT was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein end labeling method. RESULTS: Ki-67-positive staining was observed in AT progenitor cells. Fat mass enlargement in obese patients was associated with an increased Ki-67(+) progenitor cell population together with a new fraction of small adipocytes and increased cell death. HIF-1alpha mRNA expression in freshly harvested progenitor cells was positively correlated with body mass index. Adipocyte- and capillary endothelial cell-CM, hypoxia, leptin, IL-6, lysophosphatidic acid, and vascular endothelial growth factor, all increased hAT progenitor cell proliferation in vitro. Macrophage-CM had an antiproliferative effect that was suppressed by an antioxidant. CONCLUSIONS: The fraction of proliferative progenitor cells in adult hAT is modulated by the degree of adiposity. Changes in the progenitor cell microenvironment involving adipokines, hypoxia, and oxidative stress might play a key role in the control of the self-renewal of the local pool of AT progenitor cells

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

Influence of lipolysis and fatty acid availability on fuel selection during exercise.

International audienceThe aim of the present study was to investigate the influence of substrate availability on fuel selection during exercise. Eight endurance-trained male cyclists performed 90-min exercise at 70% of their maximal oxygen uptake in a cross-over design, either in rested condition (CON) or the day after 2-h exercise practised at 70% of maximal oxygen uptake (EX). Subjects were given a sucrose load (0.75 g kg(-1) body weight) 45 min after the beginning of the 90-min exercise test. Lipolysis was measured in subcutaneous abdominal adipose tissue (SCAT) by microdialysis and substrate oxidation by indirect calorimetry. Lipid oxidation increased during exercise and tended to decrease during sucrose ingestion in both conditions. Lipid oxidation was higher during the whole experimental period in the EX group (p = 0.004). Interestingly, fuel selection, assessed by the change in respiratory exchange ratio (RER), was increased in the EX session (p = 0.002). This was paralleled by a higher rate of SCAT lipolysis reflected by dialysate glycerol, plasma glycerol, and fatty acids (FA) levels (p < 0.001). Of note, we observed a significant relationship between whole-body fat oxidation and dialysate glycerol in both sessions (r (2) = 0.33, p = 0.02). In conclusion, this study highlights the limiting role of lipolysis and plasma FA availability to whole-body fat oxidation during exercise in endurance-trained subjects. This study shows that adipose tissue lipolysis is a determinant of fuel selection during exercise in healthy subjects

Interplay Between Human Adipocytes and T Lymphocytes in Obesity. CCL20 as an Adipochemokine and T Lymphocytes as Lipogenic Modulators.

International audienceOBJECTIVE: Adipose tissue (AT) plays a major role in the low-grade inflammatory state associated with obesity. The aim of the present study was to characterize the human AT lymphocytes (ATLs) and to analyze their interactions with adipocytes. METHODS AND RESULTS: Human ATL subsets were characterized by flow cytometry in subcutaneous ATs from 92 individuals with body mass index (BMI) ranging from 19 to 43 kg/m(2) and in paired biopsies of subcutaneous and visceral AT from 45 class II/III obese patients. CD3(+) ATLs were composed of effector and memory CD4(+) helper and CD8(+) cytotoxic T cells. The number of ATLs correlated positively with BMI and was higher in visceral than subcutaneous AT. Mature adipocytes stimulated the migration of ATLs and released the chemokine CCL20, the receptor of which (CCR6) was expressed in ATLs. The expression of adipocyte CCL20 was positively correlated with BMI and increased in visceral compared to subcutaneous adipocytes. ATLs expressed inflammatory markers and released interferon gamma (IFNgamma). Progenitor and adipocyte treatment with ATL-conditioned media reduced the insulin-mediated upregulation of lipogenic enzymes, an effect involving IFNgamma. CONCLUSIONS: Therefore, crosstalk occurs between adipocytes and lymphocytes within human AT involving T cell chemoattraction by adipocytes and modulation of lipogenesis by ATLs

Endurance exercise training up-regulates lipolytic proteins and reduces triglyceride content in skeletal muscle of obese subjects.

International audienceCONTEXT: Skeletal muscle lipase and intramyocellular triglyceride (IMTG) play a role in obesity-related metabolic disorders. OBJECTIVES: The aim of the present study was to investigate the impact of 8 weeks of endurance exercise training on IMTG content and lipolytic proteins in obese male subjects. DESIGN AND VOLUNTEERS: Ten obese subjects completed an 8-week supervised endurance exercise training intervention in which vastus lateralis muscle biopsy samples were collected before and after training. MAIN OUTCOME MEASURES: Clinical characteristics and ex vivo substrate oxidation rates were measured pre- and posttraining. Skeletal muscle lipid content and lipolytic protein expression were also investigated. RESULTS: Our data show that exercise training reduced IMTG content by 42% (P < .01) and increased skeletal muscle oxidative capacity, whereas no change in total diacylglycerol content and glucose oxidation was found. Exercise training up-regulated adipose triglyceride lipase, perilipin (PLIN) 3 protein, and PLIN5 protein contents in skeletal muscle despite no change in mRNA levels. Training also increased hormone sensitive-lipase Ser660 phosphorylation. No significant changes in comparative gene identification 58, G₀/G₁ switch gene 2, and PLIN2 protein and mRNA levels were observed in response to training. Interestingly, we noted a strong relationship between skeletal muscle comparative gene identification 58 and mitochondrial respiratory chain complex I protein contents at baseline (r = 0.87, P < .0001). CONCLUSIONS: Endurance exercise training coordinately up-regulates fat oxidative capacity and lipolytic protein expression in skeletal muscle of obese subjects. This physiological adaptation probably favors fat oxidation and may alleviate the lipotoxic lipid pressure in skeletal muscle. Enhancement of IMTG turnover may be required for the beneficial metabolic effects of exercise in obesity