Oxidative stress controls mitochondrial coupling and energy homeostasis in vivo

Oxidative stress is implicated in many degenerative conditions, but the mechanisms linking oxidative stress to cell signaling and tissue degeneration are unclear. We hypothesize that oxidative stress induces uncoupling of oxidative phosphorylation, resulting in energy stress and activation of energy sensitive signaling pathways, without altering the functional capacity of mitochondria. To test the effects of oxidative stress in vivo , we treated mice with the ROS‐inducing agent paraquat (PQ) and measured mitochondrial function and energy state using magnetic resonance and optical spectroscopy. In vivo studies were followed with analyses of permeabilized muscle fibers using high resolution respirometry. PQ treatment resulted in a dose‐dependent decrease in mitochondrial coupling (P/O) and energy state (PCr/ATP) with no change in phosphorylation capacity in vivo . Phosphorylation of AMPK increased with PQ dose, linking oxidative stress to uncoupling, energy stress, and activation of downstream signals. Respirometry revealed no effect of PQ on leak, complex IV, or maximal respiration ex vivo , suggesting that in vivo changes are not caused by damage to the respiratory chain. These results indicate that oxidative stress exerts control over mitochondrial function in vivo that is not related to oxidative damage. This was supported by NIH grants AG036606 and AG028455 and the Ellison Medical Foundation.