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

Abstract

AIMS: Physical activity is one of the most potent strategies to prevent endothelial dysfunction. Recent evidence suggests vaso-protective properties of hydrogen peroxide (H$_{2}$O$_{2}$) produced by main endothelial NADPH oxidase isoform 4 (Nox4) in the vasculature. Therefore, we hypothesized that Nox4 connects physical activity with vaso-protective effects.

METHODS AND RESULTS: 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 H$_{2}$O$_{2}$ release in the aorta of WT mice with increased phosphorylation of eNOS pathway member AKT serine/threonine kinase 1 (AKT1). Both H$_{2}$O$_{2}$ 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. H$_{2}$O$_{2}$ scavenger catalase reduced phenylephrine-induced contraction in WT mice. Supplementing H$_{2}$O$_{2}$ 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.

CONCLUSIONS: Nox4 derived H$_{2}$O$_{2}$ 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.

TRANSLATIONAL PERSPECTIVE: Reactive oxygen species are generally regarded as harmful. However, we demonstrated that Nox4, one of the main sources for reactive oxygen species is essential for exercise-mediated adaptations in the vasculature and the skeletal muscle. Hence, testing the safety and efficacy of Nox4 inhibitors in treating fibrotic disease, for example, should include cardiovascular endpoints to rule out side-effects.