Hepatocyte-specific eNOS deletion impairs exercise-induced adaptations in hepatic mitochondrial function and autophagy

Objective: Endothelial nitric oxide synthase (eNOS) is a potential mediator of exercise-induced hepatic mitochondrial adaptations. Methods: Here, male and female hepatocyte-specific eNOS knockout (eNOS(hep-/-)) and intact hepatic eNOS (eNOS(fl/fl)) mice performed voluntary wheel-running exercise (EX) or remained in sedentary cage conditions for 10 weeks. Results: EX resolved the exacerbated hepatic steatosis in eNOS(hep-/-) male mice. Elevated hydrogen peroxide emission (similar to 50% higher in eNOS(hep-/- )vs. eNOS(fl/fl) mice) was completely ablated with EX. Interestingly, EX increased [1-C-14] palmitate oxidation in eNOS(fl/fl) male mice, but this was blunted in the eNOS(hep-/-) male mice. eNOS(hep-/- )imice had lower markers of the energy sensors AMP-activated protein kinase (AMPK)/phospho- (p)AMPK and mammalian target of rapamycin (mTOR) and p-mTOR, as well as the autophagy initiators serine/threonine-protein kinase ULK1 and pULK1, compared with eNOS(fl/fl) mice. Females showed elevated electron transport chain protein content and markers of mitochondria! biogenesis (transcription factor A, mitochondrial. peroxisome proliferator-activated receptor-gamma coactivator 1 alpha). Conclusions: Collectively, this study demonstrates for the first time, to the authors' knowledge, the requirement of eNOS in hepatocytes in the EX-induced increases in hepatic fatty acid oxidation in male mice. Deletion of eNOS in hepatocytes also appears to impair the energy-sensing ability of the cell and inhibit the activation of the autophagy initiating factor ULK1. These data uncover the important and novel role of hepatocyte eNOS in EX-induced hepatic mitochondrial adaptations.

Automated summary

This study demonstrates for the first time the requirement of eNOS in hepatocytes for the exercise-induced increase in hepatic fatty acid oxidation in male mice. Deletion of eNOS in hepatocytes also appears to impair the energy-sensing ability of the cell and inhibit the activation of the autophagy initiating factor ULK1.