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Context Oncostatin M (OSM) plays a key role in inflammation, but its regulation and function during obesity is not fully understood. Objective The aim of this study was to evaluate the relationship of OSM with the inflammatory state that leads to impaired glucose homeostasis in obesity. We also assessed whether OSM immunoneutralization could revert metabolic disturbances caused by a high-fat diet (HFD) in mice. Design 28 patients with severe obesity were included and stratified into two groups: (1) glucose levels <100 mg/dL and (2) glucose levels >100 mg/dL. White adipose tissue was obtained to examine OSM gene expression. Human adipocytes were used to evaluate the effect of OSM in the inflammatory response, and HFD-fed C57BL/6J mice were injected with anti-OSM antibody to evaluate its effects. Results OSM expression was elevated in subcutaneous and visceral fat from patients with obesity and hyperglycemia, and correlated with Glut4 mRNA levels, serum insulin, homeostatic model assessment of insulin resistance, and inflammatory markers. OSM inhibited adipogenesis and induced inflammation in human adipocytes. Finally, OSM receptor knockout mice had increased Glut4 mRNA levels in adipose tissue, and OSM immunoneutralization resulted in a reduction of glucose levels and Ccl2 expression in adipose tissue from HFD-fed mice. Conclusions OSM contributes to the inflammatory state during obesity and may be involved in the development of insulin resistance.

Samples from patients included in this study were provided by the IGTP HUGTP Biobank integrated in the Spanish National Biobanks Network of "Instituto de Salud Carlos III" Title Page 2 (PT13/0010/0009) and they were processed following standard operating procedures with the appropriate approval of the Ethical and Scientific Committees.

Summary S100A4 is a marker of subcutaneous adipose tissue dysfunction. Polycystic ovary syndrome (PCOS) is often driven by hepato‐visceral adiposity. PCOS phenotypes are normalized more by reduction of central fat with spironolactone/pioglitazone/metformin (SPIOMET) than by oral contraceptive (OC) treatment. We studied whether circulating S100A4 concentrations are high in adolescents with PCOS and, if so, whether they normalize more with OC or SPIOMET. Assessments included circulating S100A4, endocrine markers, body composition, abdominal fat partitioning in controls (n = 12) and girls with PCOS (n = 51; age 15.8 y; body mass index [BMI] 24.5 kg/m2), and 1‐year changes in girls with PCOS randomized for OC (n = 27) or SPIOMET (n = 24) treatment. Mean S100A4 concentrations were 71% higher (P < 0.001) in girls with PCOS than in controls and associated with hepato‐visceral adiposity (r = 0.47; P = 0.001); S100A4 concentrations decreased more (P < 0.01) with SPIOMET, those decreases associating to hepato‐visceral fat loss (r = 0.50; P < 0.0001). S100A4 may become a circulating marker of hepato‐visceral fat excess in adolescents with PCOS.

Context The endocrine and immunological properties of subcutaneous vs. visceral adipose tissue (sWAT and vWAT, respectively) have turned a milestone in the study of metabolic diseases. The cytokine S100A4 is increased in obesity and has a role in adipose tissue dysfunction. However, the cellular source and its potential role in hepatic damage in obesity has not been elucidated. Objective We aim to study the regulation of S100A4 in immune cells present in sWAT and vWAT, as well as its potential role as a circulating marker of hepatic inflammation and steatosis. Design A cohort of 60 patients with obesity and distinct metabolic status was analyzed. CD11b+ myeloid cells and T cells were isolated from sWAT and vWAT by magnetic-activating cell sorting, and RNA was obtained. S100A4 gene expression was measured, and correlation analysis with clinical data was performed. Liver biopsies were obtained from 20 patients, and S100A4 circulating levels were measured to check the link with hepatic inflammation and steatosis. Results S100A4 gene expression was strongly upregulated in sWAT- vs. vWAT-infiltrated CD11b+ cells, but this modulation was not observed in T cells. S100A4 mRNA levels from sWAT (and not from vWAT) CD11b+ cells positively correlated with glycemia, triglycerides, TNF-α gene expression and proliferation markers. Finally, circulating S100A4 directly correlated with liver steatosis and hepatic inflammatory markers. Conclusion Our data suggest that sWAT-infiltrated CD11b+ cells could be a major source of S100A4 in obesity. Moreover, our correlations identify circulating S100A4 as a potential novel biomarker of hepatic damage and steatosis.