Introduction: Causality of the association between impairments in mitochondrial function and insulin resistance remains debatable. We have previously demonstrated that mitochondrial ADP sensitivity is impaired in high-fat diet (HFD)-induced insulin resistance, which contributes to bioenergetic imbalance and higher reactive oxygen species (ROS) production. However, insulin regulates several metabolic processes within skeletal muscle, and we tested the hypothesis that insulin could rapidly improve mitochondrial ADP sensitivity, a phenomenon possibly lost in HFD-induced insulin resistance.
Methods: Male and female C57Bl/6 mice were fed a control diet (10% fat) or HFD (60% fat) for 8 weeks. At the end of treatment, insulin was injected intraperitoneally (3 U/kg) twice (0 and 30 minutes). At 60 minutes red gastrocnemius muscle was excised to evaluate mitochondrial bioenergetics, ADP sensitivity, and ROS production.
Results: In control mice, insulin increased respiration by ∼2-fold in the presence of submaximal (100-1000 μM ADP) but not maximal ADP-supported respiration. As a result, insulin decreased the apparent ADP Km from 700 to 380 μM ADP. Despite these respiratory changes, insulin had no effect on mitochondrial maximal succinate-supported ROS emission or the ability of ADP to suppress ROS emission. HFD consumption impaired whole-body glucose intolerance, skeletal muscle insulin resistance (decreased insulin-stimulated Akt Thr-308 and Ser-473 phosphorylation) and impaired mitochondrial submaximal ADP-supported respiration by ∼50% (ADP Km ∼1100 μM). However, despite the reduction in insulin signaling following HFD, insulin increased submaximal ADP-supported respiration by ∼2-fold, decreased the apparent ADP Km to ∼400 μM and improved the ability of ADP to suppress mitochondrial ROS emission.
Conclusion: Insulin rapidly improves mitochondrial ADP sensitivity, mitigating the apparent HFD-induced mitochondrial dysfunction.
H. Brunetta: None. H.L. Petrick: None. E.A. Nunes: None. G. Holloway: None.
Natural Sciences and Engineering Research Council of Canada (400360); Coordination for the Improvement of Higher Education Personnel