Adiponectin Stimulates Autophagy and Reduces Oxidative Stress to Enhance Insulin Sensitivity During High-Fat Diet Feeding in Mice

Abstract

Numerous studies have characterized the antidiabetic 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 a high-fat diet (HFD) to induce obesity and insulin resistance in wild-type (WT) or adiponectin knockout (Ad-KO) mice with and without adiponectin replenishment. Temporal analysis of glucose tolerance and insulin sensitivity using hyperinsulinemic-euglycemic clamp and muscle insulin receptor substrate and Akt phosphorylation demonstrated exaggerated and more rapid HFD-induced insulin resistance in skeletal muscle of Ad-KO mice. Superoxide dismutase activity, the reduced glutathione-to-glutathione disulfide ratio, and lipid peroxidation indicated that HFD-induced oxidative stress was corrected by adiponectin. Gene array analysis implicated several antioxidant enzymes, including Gpxs, Prdx, Sod, and Nox4, in mediating this effect. Adiponectin also attenuated palmitate-induced reactive oxygen species 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, induced fibroblast growth factor-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.Adiponectin normally circulates abundantly in the concentration range of 2 to 20 mg/mL, and decreased plasma adiponectin, in particular the high-molecular-weight form, has been found in patients with obesity and type 2 diabetes (1). Extensive studies have shown that adiponectin exerts beneficial antidiabetic actions by direct metabolic and insulin-sensitizing effects in various tissues (2). Skeletal muscle is the major site for glucose disposal, and maintenance of insulin sensitivity is critical for optimal glucose homeostasis. Generation of reactive oxygen species (ROS) and the resulting oxidative stress, mitochondrial dysfunction, and accumulation of triglyceride and lipotoxic metabolites have all been shown to contribute to insulin resistance (3,4). Transgenic mice overexpressing adiponectin show improved insulin sensitivity and mitochondrial function (5,6), whereas adiponectin knockout (Ad-KO) mice are more susceptible to insulin resistance induced by a high-...

Unacylated Ghrelin Reduces Skeletal Muscle Reactive Oxygen Species Generation and Inflammation and Prevents High-Fat Diet–Induced Hyperglycemia and Whole-Body Insulin Resistance in Rodents

“…Most importantly, circulating UnAG upregulation prevented HFD-induced hyperglycemia and systemic insulin resistance, whereas muscle oxidative stress markers, inflammation, and impaired insulin signaling were preserved overall at levels comparable with lean Tg Myh6/Ghrl or wild-type animals. UnAG-dependent stimulation of muscle autophagy was also confirmed in vivo in HFD-fed obese Tg Myh6/Ghrl by a higher LC3II/ LC3I ratio and, therefore, could have potentially directly contributed to beneficial effects of UnAG overexpression (40). Of note, obese Tg Myh6/Ghrl animals showed no increments in pIRS-1 S312 compared with wild-type counterparts, and lack of effect was associated with lack of stimulation of insulin signaling activation at P70S6K levels.…”

Insulin resistance and sarcopenia: mechanistic links between common co-morbidities

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Health markers in obese adolescents improved by a 12-week recreational soccer program: a randomised controlled trial

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