Genetic deletion of the hydrogen peroxide producing NADPH oxidase 4 (Nox4), as shown in the present study, leads to endothelial dysfunction and increased atherosclerosis under pathological conditions. Consequently, endothelial activation of Nox4 may represent a promising novel strategy for preventing endothelial dysfunction and atherosclerosis and its severe clinical complications. This also suggests that in contrast to the deleterious effects of oxidative stress certain reactive oxygen species might mediate beneficial effects in the vessel wall.
Endothelial dysfunction is an early step in the development of atherosclerosis. Increased formation of superoxide anions by NADPH oxidase Nox1, 2, and 5 reduces nitric oxide availability and can promote endothelial dysfunction. In contrast, recent evidence supports a vasoprotective role of H 2O 2 produced by main endothelial isoform Nox4. Therefore, we analysed the impact of genetic deletion of Nox4 on endothelial dysfunction and atherosclerosis in the low-density lipoprotein receptor (Ldlr) knockout model.
Ex vivo analysis of endothelial function by Mulvany myograph showed impaired endothelial function in thoracic aorta of Nox4 −/−/Ldlr −/− mice. Further progression of endothelial dysfunction due to high-fat diet increased atherosclerotic plaque burden and galectin-3 staining in Nox4 −/−/Ldlr −/− mice compared with Ldlr −/− mice. Under physiological conditions, loss of Nox4 does not influence aortic vascular function. In this setting, loss of Nox4-derived H 2O 2 production could be partially compensated for by nNOS upregulation. Using an innovative optical coherence tomography approach, we were able to analyse endothelial function by flow-mediated vasodilation in the murine saphenous artery in vivo. This new approach revealed an altered flow-mediated dilation in Nox4 −/− mice, indicating a role for Nox4 under physiological conditions in peripheral arteries in vivo.
Nox4 plays an important role in maintaining endothelial function under physiological and pathological conditions. Loss of Nox4-derived H 2O 2 could be partially compensated for by nNOS upregulation, but severe endothelial dysfunction is not reversible. This leads to increased atherosclerosis under atherosclerotic prone conditions.