Effect of resistance exercise under conditions of reduced blood insulin on AMPK{alpha} Ser485/491 inhibitory phosphorylation and AMPK pathway activation
AJP Regulatory Integrative and Comparative Physiology
Published online on May 17, 2017
Abstract
Insulin stimulates skeletal muscle glucose uptake via activation of the protein kinase B/Akt (Akt) pathway. Recent studies suggest that insulin down-regulates AMP-activated protein kinase (AMPK) activity via Ser485/491 phosphorylation of the AMPK α-subunit. Thus, lower blood insulin concentrations may induce AMPK signal activation. Acute exercise is one method to stimulate AMPK activation; however, no study has examined the relationship between blood insulin levels and acute resistance exercise-induced AMPK pathway activation. Based on previous findings, we hypothesized that the acute resistance exercise-induced AMPK pathway activation would be augmented by disruptions in insulin secretion through a decrease in AMPKα Ser485/491 inhibitory phosphorylation. To test the hypothesis, 10-week-old male Sprague-Dawley rats were administered the toxin streptozotocin (STZ; 55 mg/kg) to destroy the insulin secreting β-cells. Three-day post-injection, the right gastrocnemius muscle from STZ and control rats was subjected to resistance exercise by percutaneous electrical stimulation. Animals were sacrificed 0, 1, or 3 h later; activation of the Akt/AMPK and downstream pathways in the muscle tissue were analyzed by western blotting and real-time PCR. Notably, STZ rats showed a significant decrease in basal Akt and AMPKα Ser485/491 phosphorylation. However, substantial exercise caused increases in both AMPKα Thr172 and acetyl-CoA carboxylase (ACC) Ser79 phosphorylation. Although no significant impact on resistance exercise-induced Akt pathway activation or glucose uptake was found, resistance exercise–induced PGC-1α gene expression was augmented by STZ treatment. Collectively, these data suggest that circulating insulin levels may regulate acute resistance exercise-induced AMPK pathway activation and AMPK-dependent gene expression relating to basal AMPKα Ser485/491 phosphorylation.