Adiponectin stimulates autophagy and reduces oxidative stress to enhance insulin sensitivity during high fat diet feeding in mice.

Abstract

Numerous studies have characterized the anti-diabetic effects of adiponectin yet the precise cellular mechanisms in skeletal muscle, in particular changes in autophagy, require further clarification. In the current study we used high fat diet (HFD) to induce obesity and insulin resistance in wild type (wt) or adiponectin knockout (Ad-KO) mice ± adiponectin replenishment. Temporal analysis of glucose tolerance and insulin sensitivity using hyperinsulinemic-euglycemic clamp and muscle IRS and Akt phosphorylation demonstrated exaggerated and more rapid HFD-induced insulin resistance in skeletal muscle of Ad-KO mice. SOD activity, GSH/GSSG ratio and lipid peroxidation indicated that HFD-induced oxidative stress was corrected by adiponectin and gene array analysis implicated several antioxidant enzymes, including Gpxs, Prdx, Sod and Nox4 in mediating this effect. Adiponectin also attenuated palmitate-induced ROS production in cultured myotubes and improved insulin-stimulated glucose uptake in primary muscle cells. Increased LC3-II and decreased p62 expression suggested that HFD induced autophagy in muscle of wt mice, however these changes were not observed in Ad-KO mice. Replenishing adiponectin in Ad-KO mice increased LC3-II and Beclin1 and decreased p62 protein levels, inducec FGF-21 expression and corrected HFD-induced decreases in LC3, beclin1 and ULK1 gene expression. In vitro studies examining changes in phospho-ULK1(Ser555), LC3-II and lysosomal enzyme activity confirmed that adiponectin directly induced autophagic flux in cultured muscle cells in an AMPK-dependent manner. We overexpressed an inactive mutant of Atg5 to create an autophagy-deficient cell model and, together with pharmacological inhibition of autophagy, demonstrated reduced insulin sensitivity under these conditions. In summary, adiponectin stimulated skeletal muscle autophagy and antioxidant potential to reduce insulin resistance caused by HFD.