NADPH oxidase 4 mediates the protective effects of physical activity against obesity-induced vascular dysfunction

Physical activity is one of the most potent strategies to prevent endothelial dysfunction. Recent evidence suggests vaso-protective properties of hydrogen peroxide (H₂O₂) produced by main endothelial NADPH oxidase isoform 4 (Nox4) in the vasculature. Therefore, we hypothesized that Nox4 connects physical activity with vaso-protective effects.

Analysis of the endothelial function using Mulvany Myograph showed endothelial dysfunction in wild-type (WT) as well as in C57BL/6J/ Nox4^−/− (Nox4^−/−) mice after 20 weeks on high-fat diet (HFD). Access to running wheels during the HFD prevented endothelial dysfunction in WT but not in Nox4^−/− mice. Mechanistically, exercise led to an increased H₂O₂ release in the aorta of WT mice with increased phosphorylation of eNOS pathway member AKT serine/threonine kinase 1 (AKT1). Both H₂O₂ release and phosphorylation of AKT1 were diminished in aortas of Nox4^−/− mice. Deletion of Nox4 also resulted in lower intracellular calcium release proven by reduced phenylephrine-mediated contraction, whilst potassium-induced contraction was not affected. H₂O₂ scavenger catalase reduced phenylephrine-induced contraction in WT mice. Supplementing H₂O₂ increased phenylephrine-induced contraction in Nox4^−/− mice. Exercise-induced peroxisome proliferative-activated receptor gamma, coactivator 1 alpha (Ppargc1a), as key regulator of mitochondria biogenesis in WT but not Nox4^−/− mice. Furthermore, exercise-induced citrate synthase activity and mitochondria mass were reduced in the absence of Nox4. Thus, Nox4^−/− mice became less active and ran less compared with WT mice.

Nox4 derived H₂O₂ plays a key role in exercise-induced adaptations of eNOS and Ppargc1a pathway and intracellular calcium release. Hence, loss of Nox4 diminished physical activity performance and vascular protective effects of exercise.