Nox2-derived reactive oxygen species contribute to hypercholesterolemia-induced inhibition of neovascularization: Effects on endothelial progenitor cells and mature endothelial cells

Abstract

Background Hypercholesterolemia has been associated with impaired angiogenesis and reduced blood flow recuperation after ischemia. However, the precise mechanisms involved are unknown. Here we investigated the role of Nox2-derived reactive oxygen species (ROS) in the modulation of neovascularization by hypercholesterolemia. Methods and results Mice deficient for the Nox2-containing NADPH oxidase (Nox2 −/−) and control mice (Nox2 +/+) were put on a high cholesterol diet (HCD) for a total of 15 weeks. After three months, hindlimb ischemia was surgically induced by femoral artery removal. Nox2 expression and oxidative stress levels in ischemic tissues were significantly increased by HCD in control mice, but not in Nox2 −/− mice. Nox2 −/− mice were also protected against hypercholesterolemia-induced impairment of neovascularization, as demonstrated by faster blood flow recovery after ischemia and increased capillary density in ischemic muscles. Nox2 deficiency was associated with preserved activity of eNOS in ischemic tissues, and improved activity of endothelial progenitor cells (EPCs). In vitro, HUVECs treated with the NADPH oxidase inhibitor apocynin or endothelial cells isolated from the aorta of Nox2 −/− mice exhibited reduced ROS formation following exposure to oxLDL. This was associated with improved nitric oxide (NO) bioavailability and protection against oxLDL-induced inhibition of angiogenic activities. Conclusions Nox2-containing NADPH oxidase deficiency protects against hypercholesterolemia-induced impairment of neovascularization. The potential mechanisms involved include reduced ROS formation, preserved activation of angiogenic signals, and improved functional activities of EPCs and mature endothelial cells.