Adipose tissue immunology, inflammation and exosomes in regulating insulin sensitivity in people with obesity and nonalcoholic fatty liver disease. Adipose tissue immunology, inflammation and exosomes in regulating insulin sensitivity in people with obesity and nonalcoholic fatty liver disease

Background and Aims: Insulin resistance is a key factor in the pathogenesis of NAFLD. We evaluated the importance of subcutaneous abdominal adipose tissue (SAAT) inflammation and both plasma and SAAT-derived exosomes in regulating insulin sensitivity in people with obesity and NAFLD. Methods: Adipose tissue inflammation (macrophage and T cell content and gene expression of proinflammatory cytokines), liver and whole-body insulin sensitivity (assessed by a hyperinsulinemic-euglycemic clamp and glucose tracer infusion), and 24-hour serial plasma cytokine concentrations were evaluated in three groups stratified by adiposity, insulin sensitivity and intrahepatic triglyceride (IHTG) content: 1) metabolically-healthy lean (LEAN; n=14); 2) metabolically-healthy obese with normal IHTG content (OB-NL; n=28); and 3) metabolically-unhealthy obese with NAFLD (OB-NAFLD; n=28). The effect of plasma and SAAT-derived exosomes on insulin action (insulin-stimulated Akt phosphorylation) in human skeletal muscle myotubes was assessed in a subset of participants. Results: Proinflammatory macrophages, proinflammatory CD4 and CD8 T cell populations, and gene expression of several cytokines in SAAT were greater in the OB-NAFLD than the OB-NL and LEAN groups. However, with the exception of PAI-1, which was greater in the OB-NAFLD than the LEAN and OB-NL groups, 24-hour plasma cytokine concentration areas-under-the-curve (AUC) were not different between groups. The percentage of proinflammatory macrophages and plasma PAI-1 concentration AUC were inversely correlated with both hepatic and whole-body insulin sensitivity. Compared with exosomes from OB-NL participants, plasma and SAAT-derived exosomes obtained from the OB-NAFLD group impaired insulin action in myotubes. Conclusion: These results suggest SAAT-derived exosomes and PAI-1 are involved in the pathogenesis of systemic insulin resistance in people with obesity and NAFLD. ClinicalTrials.gov number: NCT02706262. Overall design: We obtained subcutaneous adipose tissue samples from people who were metabolically-healthy lean (MHL), metabolically-healthy obese (MHO), and metabolically-unhealthy obese (MUO) n=66).