Coralie Sengenès

Natriuretic peptides: a new lipolytic pathway in human adipocytes

Atrial natriuretic peptide (ANP) receptors have been described on rodent adipocytes and expression of their mRNA is found in human adipose tissue. However, no biological effects associated with the stimulation of these receptors have been reported in this tissue. A putative lipolytic effect of natriuretic peptides was investigated in human adipose tissue. On isolated fat cells, ANP and brain natriuretic peptide (BNP) stimulated lipolysis as much as isoproterenol, a nonselective β‐adrenergic receptor agonist, whereas C‐type natriuretic peptide (CNP) had the lowest lipolytic effect. In situ microdialysis experiments confirmed the potent lipolytic effect of ANP in abdominal s.c. adipose tissue of healthy subjects. A high level of ANP binding sites was identified in human adipocytes. The potency order defined in lipolysis (ANP > BNP > CNP) and the ANP‐induced cGMP production sustained the presence of type A natriuretic peptide receptor in human fat cells. Activation or inhibition of cGMP‐inhibited phosphodiesterase (PDE‐3B) (using insulin and OPC 3911, respectively) did not modify ANP‐induced lipolysis whereas the isoproterenol effect was decreased or increased. Moreover, inhibition of adenylyl cyclase activity (using a mixture of α2‐adrenergic and adenosine A1 agonists receptors) did not change ANP‐ but suppressed isoproterenol‐induced lipolysis. The noninvolvement of the PDE‐3B was finally confirmed by measuring its activity under ANP stimulation. Thus, we demonstrate that natriuretic pep tides are a new pathway controlling human adipose tissue lipolysis operating via a cGMP‐dependent pathway that does not involve PDE‐3B inhibition and cAMP production.—Sengenès, C., Berlan, M., De Glisezinski, I., Lafontan, M., Galitzky, J. Natriuretic peptides: a new lipolytic pathway in human adipocytes. FASEB J. 14, 1345–1351 (2000)

Remodeling Phenotype of Human Subcutaneous Adipose Tissue Macrophages

Background— Adipose tissue macrophages (ATMs) have become a focus of attention recently because they have been shown to accumulate with an increase in fat mass and to be involved in the genesis of insulin resistance in obese mice. However, the phenotype and functions of human ATMs are still to be defined. Methods and Results— The present study, performed on human subcutaneous AT, showed that ATMs from lean to overweight individuals are composed of distinct macrophage subsets based on the expression of several cell surface markers: CD45, CD14, CD31, CD44, HLA-DR, CD206, and CD16, as assessed by flow cytometry. ATMs isolated by an immunoselection protocol showed a mixed expression of proinflammatory (tumor necrosis factor-&agr;, interleukin-6 [IL-6], IL-23, monocyte chemoattractant protein-1, IL-8, cyclooxygenase-2) and antiinflammatory (IL-10, transforming growth factor-&bgr;, alternative macrophage activation–associated cc chemokine-1, cyclooxygenase-1) factors. Fat mass enlargement is associated with accumulation of the CD206+/CD16− macrophage subset that exhibits an M2 remodeling phenotype characterized by decreased expression of proinflammatory IL-8 and cyclooxygenase-2 and increased expression of lymphatic vessel endothelial hyaluronan receptor-1. ATMs specifically produced and released matrix metalloproteinase-9 compared with adipocytes and capillary endothelial cells, and secretion of matrix metalloproteinase-9 from human AT in vivo, assessed by arteriovenous difference measurement, was correlated with body mass index. Finally, ATMs exerted a marked proangiogenic effect on AT-derived endothelial and progenitor cells. Conclusions— The present results showed that the ATMs that accumulate with fat mass development exhibit a particular M2 remodeling phenotype. ATMs may be active players in the process of AT development through the extension of the capillary network and in the genesis of obesity-associated cardiovascular pathologies.

Control of lipolysis by natriuretic peptides and cyclic GMP.

Human fat cell lipolysis was, until recently, thought to be mediated exclusively by a cAMP-dependent protein kinase (PKA)-regulated pathway under the control of catecholamines and insulin. We have shown that atrial- and B-type natriuretic peptides (ANP and BNP respectively) stimulate lipolysis in human fat cells through a cGMP-dependent protein kinase (PKG) signaling pathway independent of cAMP production and PKA activity. Pharmacological or physiological (exercise) increases in plasma ANP levels stimulate lipid mobilization in humans. This pathway becomes important during chronic treatment with beta-adrenoceptor antagonists, which inhibit catecholamine-induced lipolysis but enhance cardiac ANP release. These findings have metabolic implications and point to potential problems when natriuretic peptide secretion is altered or during therapeutic use of recombinant BNP.

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

Objective—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/m2 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 (IFNγ). Progenitor and adipocyte treatment with ATL-conditioned media reduced the insulin-mediated upregulation of lipogenic enzymes, an effect involving IFNγ. Conclusions—Therefore, crosstalk occurs between adipocytes and lymphocytes within human AT involving T cell chemoattraction by adipocytes and modulation of lipogenesis by ATLs.

Chemotaxis and Differentiation of Human Adipose Tissue CD34+/CD31− Progenitor Cells: Role of Stromal Derived Factor‐1 Released by Adipose Tissue Capillary Endothelial Cells

The native CD34+/CD31− cell population present in the stroma‐vascular fraction of human adipose tissue (hAT) displays progenitor cell properties since they exhibit adipocyte‐ and endothelial cell‐like phenotypes under appropriate stimuli. To analyze the signals within hAT regulating their phenotypes, the influence of hAT‐derived capillary endothelial cells (CECs) was studied on the chemotaxis and differentiation of the hAT‐CD34+/CD31− cells. Conditioned medium from hAT‐CECs led to a strong chemotaxis of the hAT‐CD34+/CD31− cells that was inhibited with pretreatments with pertussis toxin, CXCR‐4 antagonist, or neutralizing antibodies. Furthermore, hAT‐CECs produced and secreted the CXCR‐4 ligand, that is, the stromal derived factor‐1 (SDF‐1). Finally, hAT‐CECs induced the differentiation of hAT‐CD34+/CD31− cells toward an endothelial cell (EC) phenotype. Indeed, hAT‐CECs and ‐CD34+/CD31− cell coculture stimulated in a two‐dimensional system the expression of the EC CD31 marker by the hAT‐progenitor cells and, in a three‐dimensional approach, the formation of capillary‐like structures via a SDF‐1/CXCR‐4 dependent pathway. Thus, the migration and differentiation of hAT progenitor cells are modulated by hAT‐CEC‐derived factors. SDF‐1, which is secreted by hAT‐derived CECs, and its receptor CXCR‐4, expressed by hAT‐derived progenitor cells, may promote chemotaxis and differentiation of hAT‐derived progenitor cells and thus contribute to the formation of the vascular network during the development of hAT.

Increased lipolysis in adipose tissue and lipid mobilization to natriuretic peptides during low-calorie diet in obese women.

OBJECTIVE: We recently demonstrated that natriuretic peptides (NP) are involved in a pathway inducing lipolysis in human adipose tissue. Atrial NP (ANP) and brain NP (BNP) operate via a cGMP-dependent pathway which does not involve phosphodiesterase-3B inhibition or cAMP. The study was performed to evaluate the effect of ANP on lipid mobilization in obese women and secondly to examine the possible effect of a low-calorie diet (LCD) on the lipolytic response of subcutaneous abdominal fat cells to NP and on the lipid mobilization induced by ANP infusion (1 µg/m2 min for 60 min).SUBJECTS: Ten obese women from 40.5±3.4 y old were selected for this study. Their body weight was 96.4±5.7 kg and their BMI was 35.3±1.7 kg/m2. They received a 2.5–2.9 MJ/day formula diet for 28 days.DESIGN: Before and during the LCD, an adipose tissue biospy was performed for in vitro studies and, moreover, ANP was perfused i.v. to evaluate its lipid mobilizing action in toto and in situ in subcutaneous abdominal adipose tissue (SCAAT) using microdialysis.RESULTS: The lipolytic effects of isoproterenol, ANP, BNP and bromo-cGMP (an analogue of cGMP) on fat cells increased by about 80–100% during LCD. The lipid mobilization during i.v. ANP infusion, assessed by plasma non-esterified fatty acids (NEFA) increase was enhanced during the LCD. However, during LCD, ANP infusion induced a biphasic effect on glycerol concentration in plasma and interstitial fluid of SCAAT; a significant increase was observed in glycerol levels during the first 30 min infusion period, followed by a steady decrease. The concentration of glycerol was lower during the post-infusion period than during the baseline period. This effect was stronger in obese subjects submitted to the LCD with a low-carbohydrate composition. Other plasma parameters were weakly increased (noradrenaline) or not modified (insulin, glucose) by ANP infusion and no difference was found before and during LCD treatment.CONCLUSION: The present study shows that NP are powerful lipolytic agents in subcutaneous fat cells and that both isoproterenol- and NP-induced lipolysis increase during LCD, in obese women. These changes seem to be associated with an improvement of the lipolytic pathway at a post-receptor level. Moreover, i.v. administration of ANP induced a lipid mobilizing effect which was enhanced by a LCD in these objects.

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

Objective 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.

The role of endothelial cells in inflamed adipose tissue.

In recent years, the general concept has emerged that chronic low‐grade inflammation can be the condition linking excessive development of adipose tissue (AT) and obesity‐associated pathologies such as type II diabetes and atherosclerosis. Moreover, the evidence that the growth of the fat mass was associated with an accumulation of adipose tissue macrophages (ATM) has raised the hypothesis that the development of an inflammatory process within the growing fat mass is a primary event involved in the genesis of systemic metabolic and vascular alterations. As ATM originate from the bone marrow/blood compartment, enhanced macrophage recruitment to growing AT is suspected. However, the mechanisms responsible for attracting the blood cells and their entry into the fat mass remain to be clearly defined. The present review highlights the key role of endothelial cells in the control of the inflammatory process and describes the potential involvement of AT‐endothelial cells as well as the factors involved in the regulation of their phenotype in the ‘inflamed fat tissue’.

Recent developments on lipolysis regulation in humans and discovery of a new lipolytic pathway.

In man, the major hormones controlling the lipolytic function are insulin (inhibition of lipolysis) and catecholamines (stimulation of lipolysis). Catecholamines are of major importance for the regulation of lipid mobilization in human adipose tissue and for the increase of non-esterified fatty acid supply to the working muscle. In vitro studies have shown that there are differences in the catecholaminergic control of fat cells from various fat deposits and a number of physiological and pathological alterations of catecholamine-induced lipolysis have been reported. Lipolytic resistance to catecholamines has been reported in subcutaneous adipose tissue, the major fat depot in obese subjects. Multiple alterations in catecholamine signal transduction pathways have been reported. In situ microdialysis allows a physiological exploration of adipose tissue biology. Recent data obtained on the catecholaminergic regulation of lipolysis and lipid mobilization, using microdialysis in humans, will be analysed. A potent lipolytic and lipomobilizing effect of atrial natriuretic peptide has recently been discovered; the mechanisms of action and physiological relevance will also be discussed.

Adipogenic progenitors from obese human skeletal muscle give rise to functional white adipocytes that contribute to insulin resistance

Background/Objectives:Recent reports indicate that inter/intramuscular adipose tissue (IMAT), composed by adipocytes underneath the deep fascia of the muscles, is positively correlated with aging, obesity and insulin resistance in humans. However, no molecular/cellular evidence is available to support these interactions. The current study aimed to better characterize human skeletal muscle-derived adipogenic progenitors obtained from obese volunteers and investigate the impact of derived adipocytes on insulin action in primary skeletal muscle cells.Methods:Primary cultured stroma-vascular fraction (SVF) obtained from vastus lateralis muscle biopsies of middle-aged obese subjects was immunoseparated (magnetic beads or flow cytometry). The characteristics and/or metabolic phenotype of CD56+, CD56− and CD56−CD15+ cellular fractions were investigated by complementary approaches (flow cytometry, cytology, quantitative PCR and metabolic assays). The effects of conditioned media from CD56−CD15+ cells differentiated into adipocytes on insulin action and signaling in human primary myotubes was also examined.Results:Our data indicate that CD56+ and CD56− cellular fractions isolated from cultured SVF of human muscle contain two distinct committed progenitors: CD56+ cells (that is, satellite cells) as myogenic progenitors and CD15+ cells as adipogenic progenitors, respectively. CD56−CD15+-derived adipocytes display the phenotype and metabolic properties of white adipocytes. Secretions of CD56−CD15+ cells differentiated into functional white adipocytes reduced insulin-mediated non-oxidative glucose disposal (P=0.0002) and insulin signaling.Conclusions:Using in-vitro models, we show for the first time that secretions of skeletal muscle adipocytes are able to impair insulin action and signaling of muscle fibers. This paracrine effect could explain, at least in part, the negative association between high levels of IMAT and insulin sensitivity in obesity and aging.