Decreased adiponectin links elevated adipose tissue autophagy with adipocyte endocrine dysfunction in obesity

Abstract

Background/objectives: Adipose tissue (AT) autophagy gene expression is elevated in human obesity, correlating with increased metabolic risk, but mechanistic links between the two remain unclear. Thus, the objective of this study was to assess whether elevated autophagy may cause AT endocrine dysfunction, emphasizing the putative role of adiponectin in fat-liver endocrine communication.

Subjects/methods: We utilized a large (N=186) human AT biobank to assess clinical associations between human visceral AT autophagy genes, adiponectin and leptin, by multivariate models. A broader view of adipocytokines association with elevated autophagy was assessed using adipocytokine array. Finally, to establish causality, ex vivo studies utilizing a murine AT-hepatocyte cell line co-culture system was used.

Results: Circulating high-molecular-weight adiponectin and leptin levels were associated with human omental-AT expression of ATG5 mRNA, associations that remained significant (β=-0.197, P=0.011; β=0.267, P<0.001, respectively) in a multivariate model adjusted for age, sex, body mass index and interleukin-6 (IL-6). A similar association was observed with omental-AT LC3A mRNA levels. Bafilomycin-A1 (Baf A) pretreatment of AT explants from high-fat-fed (HFF) mice had no effect on the secretion of some AT-derived endocrine factors, but partially or fully reversed obesity-related changes in secretion of a subset of adipocytokines by >30%, including the obesity-associated upregulation of IL-6, vascular endothelial growth factor, tumor necrosis factor alpha (TNFα) and certain insulin-like growth factor-binding proteins, and the HFF-induced downregulated secretion of IL-10 and adiponectin. Similarly, decreased adiponectin and increased leptin secretion from cultured adipocytes stimulated with TNFα+IL-1β was partially reversed by small interfering RNA-mediated knockdown of ATG7. AT explants from HFF mice co-cultured with Hepa1c hepatoma cells impaired insulin-induced Akt and GSK3 phosphorylation. This effect was significantly reversed by pretreating explants with Baf A, but not if adiponectin was immunodepleted from the conditioned media.

Conclusions: Reduced secretion of adiponectin may link obesity-associated elevated AT autophagy/lysosomal activity with adipose endocrine dysfunction.