Interrelationship between lymphocytes and leptin in fat depots of obese mice revealed by changes in nutritional status

The mechanisms underlying the relationships between nutritional status and immunity remain to be fully characterized. The present study was undertaken to analyze by flow cytometry, in the context of diet-induced obesity, the status of immune cells in subcutaneous, and epididymal fat depots in wild-type and immunodeficient Rag2−/− mice submitted to nutritional challenge, i.e., 48-h fasting and 1-week refeeding. In parallel, the responsiveness of mature adipocytes and immune cells in bone marrow, lymph node, and liver were also analyzed. The results show that fasting in obese wild-type mice induces a prominent lipolysis in epididymal AT and immunosuppression restricted to both subcutaneous and epididymal AT, characterized by reduced number of CD4+ T and B lymphocytes and M1/M2 macrophages associated with reduced leptin and increased FGF21 expression in mature adipocytes. One-week refeeding was sufficient to reverse the fasting-induced effects. Obese immunodeficient mice under nutritional challenge exhibited no changes in adipocyte leptin expression and no marked trafficking of AT macrophages or NK cells, while the fasted-induced upregulation of FGF21 expression was maintained as well as the lipolytic responses. The present results demonstrate that, in a context of diet-induced obesity, fasting-induced immunosuppression is restricted to fat depots in immunocompetent mice. Lack of adipocyte leptin regulation and fasting-induced immunosuppression in obese immunodeficient mice strongly suggests that lymphocytes are involved in the modulation of adipocyte leptin expression on one hand and on the other that leptin is involved in the immune changes in AT according to nutritional status

Interrelationship between lymphocytes and leptin in fat depots of obese mice revealed by changes in nutritional status.

The mechanisms underlying the relationships between nutritional status and immunity remain to be fully characterized. The present study was undertaken to analyze by flow cytometry, in the context of diet-induced obesity, the status of immune cells in subcutaneous, and epididymal fat depots in wild-type and immunodeficient Rag2-/- mice submitted to nutritional challenge, i.e., 48-h fasting and 1-week refeeding. In parallel, the responsiveness of mature adipocytes and immune cells in bone marrow, lymph node, and liver were also analyzed. The results show that fasting in obese wild-type mice induces a prominent lipolysis in epididymal AT and immunosuppression restricted to both subcutaneous and epididymal AT, characterized by reduced number of CD4+ T and B lymphocytes and M1/M2 macrophages associated with reduced leptin and increased FGF21 expression in mature adipocytes. One-week refeeding was sufficient to reverse the fasting-induced effects. Obese immunodeficient mice under nutritional challenge exhibited no changes in adipocyte leptin expression and no marked trafficking of AT macrophages or NK cells, while the fasted-induced upregulation of FGF21 expression was maintained as well as the lipolytic responses. The present results demonstrate that, in a context of diet-induced obesity, fasting-induced immunosuppression is restricted to fat depots in immunocompetent mice. Lack of adipocyte leptin regulation and fasting-induced immunosuppression in obese immunodeficient mice strongly suggests that lymphocytes are involved in the modulation of adipocyte leptin expression on one hand and on the other that leptin is involved in the immune changes in AT according to nutritional status.

Defective NOD2 peptidoglycan sensing promotes diet-induced inflammation, dysbiosis, and insulin resistance.

Pattern recognition receptors link metabolite and bacteria-derived inflammation to insulin resistance during obesity. We demonstrate that NOD2 detection of bacterial cell wall peptidoglycan (PGN) regulates metabolic inflammation and insulin sensitivity. An obesity-promoting high-fat diet (HFD) increased NOD2 in hepatocytes and adipocytes, and NOD2(-/-) mice have increased adipose tissue and liver inflammation and exacerbated insulin resistance during a HFD. This effect is independent of altered adiposity or NOD2 in hematopoietic-derived immune cells. Instead, increased metabolic inflammation and insulin resistance in NOD2(-/-) mice is associated with increased commensal bacterial translocation from the gut into adipose tissue and liver. An intact PGN-NOD2 sensing system regulated gut mucosal bacterial colonization and a metabolic tissue dysbiosis that is a potential trigger for increased metabolic inflammation and insulin resistance. Gut dysbiosis in HFD-fed NOD2(-/-) mice is an independent and transmissible factor that contributes to metabolic inflammation and insulin resistance when transferred to WT, germ-free mice. These findings warrant scrutiny of bacterial component detection, dysbiosis, and protective immune responses in the links between inflammatory gut and metabolic diseases, including diabetes.

Adipocyte size threshold matters: link with risk of type 2 diabetes and improved insulin resistance after gastric bypass.

CONTEXT: Adipocyte volume has been associated with insulin resistance and type 2 diabetes. OBJECTIVE: Our purpose was to identify an adipocyte volume threshold linked with increased insulin resistance risk, and to examine its association with insulin resistance improvement after bariatric surgery. SETTING AND DESIGN: We investigated two cohorts of Caucasian women, candidates for bariatric surgery, from two institutional centers in France (age 42.0 ± 11.5 years; body mass index, 47.6 ± 6.9 kg/m(2)) and Germany (age 41.3 ± 11.2 years; body mass index, 49.5 ± 8.1 kg/m(2)). 38% of the subjects had gastric bypass surgery and were followed for 6 months after the intervention. We defined a group of subjects with type 2 diabetes or at risk of type 2 diabetes (DRD) and investigated the relations between adipocyte volume and this status before and after surgery. RESULTS: In both cohorts, subjects with DRD presented enlarged adipocytes (France, P = 3×10(-4); Germany, P =3×10(-10)) and we were able to determine thresholds in each cohort above which diabetes risk was potentially increased (France: 1003±42 pL, Germany: 798±32 pL). Subjects above those adipocyte thresholds were less prone to disappearance of the DRD status after bypass surgery (France, risk ratio = 2.1, P = .024; Germany, risk ratio = 1.3, P = .05). CONCLUSIONS: We show in two cohorts of morbidly obese subjects that a specific adipocyte volume threshold may predict an increased risk for obesity-associated type 2 diabetes. However, this threshold might be established for each specific investigation site. Having a high adipocyte size is associated with a lower improvement of insulin resistance after bypass surgery in both cohorts.

7ß-Hydroxycholesterol-induced energy stress leads to sequential opposing signaling responses and to death of C6 glioblastoma cells.

7ß-Hydroxycholesterol cytotoxicity has been shown in vivo and in vitro to be dependent on the accumulation of its esters. We show in our study, using a detergent-free raft preparation and LC/MS lipid content analysis, that membrane microdomains isolated from 7ß-hydroxycholesterol-treated C6 cells have a reduced cholesterol: cholesterol ester ratio and accumulate 7keto-hydroxycholesterol, 7ß-hydroxycholesterol and 7ß-hydroxycholesterol esters. These modifications in lipid content are accompanied by a redistribution of flotillin-1 in the lipid rafts. Transient increases of AMPK phosphorylation and mitochondrial activity during the first 12 h of 7ß-hydroxycholesterol treatment indicate that C6 cells undergo energy stress and increase oxidative phosphorylation. Even so, ATP levels are maintained during 15 h until glucose uptake decreases. The cell's answers to raft modifications and energy stress are sequential activations of different signaling pathways such as ERK, AMPK and PI3K/Akt. These pathways, known to be activated under energy stress conditions, are transiently activated at 6 h (ERK, AMPK) and 12 h (Akt) of treatment respectively suggesting a shift from cell survival to cell proliferation. The persistence of 7ß-hydroxycholesterol-induced stress led after 24 h to P38 activation, loss of GSK3ß activation and to cell death. Finally we demonstrate that the observed signaling responses depend on 7ß-hydroxycholesterol esterification, confirming that esterification of 7ß-hydroxycholesterol is essential for cytotoxicity.

Inflammatory and alternatively activated human macrophages attract vessel-associated stem cells, relying on separate HMGB1- and MMP-9-dependent pathways.

Inflammatory macrophages recruited at the site of damaged muscles progressively acquire an alternative activation profile. Inflammatory (M1) and alternatively activated (M2) macrophages exert various and even opposite functions. M1 cells amplify tissue damage, and M2 cells dispose of necrotic fibers and deliver survival signals to myogenic precursors, finally supporting healing. A critical step in muscle healing is the recruitment of myogenic stem cells, including vessel-associated stem cells (mesoangioblasts), which have been demonstrated to home to damaged skeletal muscle selectively and preferentially. Little information is available about the signals involved and the role played by infiltrating macrophages. Here, we report that the polarization of macrophages dramatically skews the secretion of high mobility group box 1 (HMGB1), TNF-alpha, vascular endothelial growth factor, and metalloproteinase 9 (MMP-9), molecules involved in the regulation of cell diapedesis and migration. All polarized macrophage populations were strikingly effective at inducing mesoangioblast migration. By means of specific inhibitors, we verified that the recruitment of mesoangioblasts requires the secretion of HMGB1 and TNF-alpha by M1 cells and of MMP-9 by M2 cells. Together, these data demonstrate a feature, unrecognized previously, of macrophages: their ability to attract stem cells, which is conserved throughout their polarization. Moreover, they open the possibility of novel strategies, aimed at interfering selectively with signals that recruit blood-derived stem cells toward pro- or anti-inflammatory macrophages.

Circulating chromogranin A reveals extra-articular involvement in patients with rheumatoid arthritis and curbs TNF-alpha-elicited endothelial activation.

TNF-alpha plays an important role in the natural history of rheumatoid arthritis (RA), a systemic disease characterized by endothelial activation and synovial involvement with bone erosions. Neuroendocrine signals contribute as well to RA, but their role is poorly understood. We measured in 104 RA patients and in an equal number of sex- and age-matched, healthy controls the blood levels of chromogranin A (CgA), a candidate marker linking the neuroendocrine system to TNF-alpha-mediated vascular inflammation. CgA levels were significantly higher in patients with RA and remained stable over time. High levels of CgA were significantly associated with severe extra-articular manifestations, namely pulmonary fibrosis, rheumatoid vasculitis, serositis, and peripheral neuropathy. RA sera curbed the response of human microvascular endothelial cells to TNF-alpha, as assessed by the expression of ICAM-1, the release of MCP-1/CCL2, and the export of nuclear high-mobility group box 1; the effect abated in the presence of anti-CgA antibodies. The efficacy of the blockade was significantly correlated with the CgA concentration in the serum. The recombinant aminoterminal portion of CgA, corresponding to residues 1-78, had similar inhibitory effects on endothelial cells challenged with TNF-alpha. Our results suggest that enhanced levels of CgA identify patients with extra-articular involvement and reveal a negative feedback loop that limits the activation of endothelial cells in RA.

Profiling of adipokines secreted from human subcutaneous adipose tissue in response to PPAR agonists.

The role of PPARs in the regulation of human adipose tissue secretome has received little attention despite its potential importance in the therapeutic actions of PPAR agonists. Here, we have investigated the effect of selective PPARgamma, PPARalpha, and PPARbeta/delta agonists on the production of adipokines by human subcutaneous adipose tissue. Antibody arrays were used to measure secreted factors in media from cultured adipose tissue explants. Sixteen proteins were produced in significant amounts. Activation of PPARs regulated the production of five proteins. Treatments with the three PPAR agonists decreased the secretion of leptin and interleukin-6. PPARalpha and beta/delta agonists markedly enhanced hepatocyte growth factor secretion whereas PPARbeta/delta down-regulated angiogenin and up-regulated TIMP-1 release. Hepatocyte growth factor, interleukin-6, and TIMP-1 are chiefly expressed in cells from the stromal vascular fraction whereas angiogenin is expressed in both adipocytes and cells from the stromal vascular fraction. Our data show that PPAR agonists modulate secretion of bioactive molecules from the different cell types composing human adipose tissue.

Role of macrophage tissue infiltration in metabolic diseases.

PURPOSE OF REVIEW: White adipose tissue is necessary for optimal energy homeostasis and the excessive development of fat mass is clearly associated with the metabolic syndrome. The fact that adipocytes secrete a number of specific factors or 'adipokines' has forced a reassessment of the involvement of adipose tissue in a wide range of physiological and pathophysiological processes. Obesity has recently been described as a 'low-grade' inflammatory condition, a state proposed to represent a common determinator in the genesis of obesity-associated pathologies, i.e. diabetes and atherosclerosis. RECENT FINDINGS: Recent reports of an increase in the number of macrophages that infiltrate the fat mass in obese individuals led to the suggestion that adipose tissue itself is a source and site of inflammation. SUMMARY: This review summarizes recent data on the characterization of the macrophage population in fat tissue. Their origin, fate and activation will be considered. The potential involvement of adipose tissue macrophages in the development of insulin resistance and vascular pathologies, as well as in the control of adipose tissue growth and metabolism, will be examined.

Preadipocytes in the human subcutaneous adipose tissue display distinct features from the adult mesenchymal and hematopoietic stem cells.

The stroma-vascular fraction (SVF) of human adipose tissue has recently been described to be composed of endothelial cells identified as CD34+/CD31+ cells, infiltrated/resident macrophages defined as CD14+/CD31+ cells, and a new cell population characterized as CD34+/CD31- cells. To elucidate the cell identity of the adipocyte precursor cells, fluorescent activating cell sorter (FACS) analyses were performed on crude SVF cultured under adipogenic conditions, i.e., serum-deprived medium containing insulin, cortisol, triiodothyronine, and supplemented with a PPARgamma agonist for the first 3 days. The progressive accumulation of lipid droplets was associated with a selective enrichment of the CD34+/CD31- cell population whereas control experiments performed in medium supplemented with 10% serum showed an overall downregulation of the three cell markers without adipogenesis. Among the different cell subsets, the CD34+/CD31- subset was the unique cell fraction able to answer to adipogenic culture conditions. Indeed, a time-dependent expression of adipocyte markers as well as acquisition of adipocyte-typical metabolic activities were observed. In parallel, the gene expression of lipogenic and lipolytic enzymes increased. The ability to differentiate into adipocytes was restricted to cells that did not express the mesenchymal stem cell marker CD105. Furthermore, the CD34+/CD31- cells did not respond to culture conditions used for hematopoietic colony assays. Taken together, the present study demonstrates that adipocyte progenitor cells, i.e., the preadipocytes, are included in the CD34+/CD31- cell fraction, which displays distinct features from the adult mesenchymal and hematopoietic stem cells.