Nox2 regulates endothelial cell cycle arrest and apoptosis via p21cip1 and p53

Endothelial cells (EC) express constitutively two major isoforms (Nox2 and Nox4) of the catalytic subunit of NADPH oxidase, which is a major source of endothelial reactive oxygen species. However, the individual roles of these Noxes in endothelial function remain unclear. We have investigated the role of Nox2 in nutrient deprivation-induced cell cycle arrest and apoptosis. In proliferating human dermal microvascular EC, Nox2 mRNA expression was low relative to Nox4 (Nox2:Nox4 ∼ 1:13), but was upregulated 24 h after starvation and increased to 8 ± 3.5-fold at 36 h of starvation. Accompanying the upregulation of Nox2, there was a 2.28 ± 0.18-fold increase in O2− production, a dramatic induction of p21cip1 and p53, cell cycle arrest, and the onset of apoptosis (all p < 0.05). All these changes were inhibited significantly by in vitro deletion of Nox2 expression and in coronary microvascular EC isolated from Nox2 knockout mice. In Nox2 knockout cells, although there was a 3.8 ± 0.5-fold increase in Nox4 mRNA expression after 36 h of starvation (p < 0.01), neither O2− production nor the p21cip1 or p53 expression was increased significantly and only 0.46% of cells were apoptotic. In conclusion, Nox2-derived O2−, through the modulation of p21cip1 and p53 expression, participates in endothelial cell cycle regulation and apoptosis.