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 (~50% higher in eNOS ^hep-/- vs. eNOS ^fl/fl mice) was completely ablated with EX. Interestingly, EX increased [1- ¹⁴ C] palmitate oxidation in eNOS ^fl/fl male mice, but this was blunted in the eNOS ^hep-/- male mice. eNOS ^hep-/- mice 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 mitochondrial biogenesis (transcription factor A, mitochondrial, peroxisome proliferator-activated receptor-gamma coactivator 1α).
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.
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