Upregulation of Nox1 in vascular smooth muscle leads to impaired endothelium-dependent relaxation via eNOS uncoupling

Recent work has made it clear that oxidant systems interact. To investigate potential cross talk between NADPH oxidase (Nox) 1 upregulation in vascular smooth muscle and endothelial function, transgenic mice overexpressing Nox1 in smooth muscle cells (Tg(SMCnox1)) were subjected to angiotensin II (ANG II)-induced hypertension. As expected, NADPH-dependent superoxide generation was increased in aortas from Nox1-overexpressing mice. Infusion of ANG II (0.7 mg x kg(-1) x day(-1)) for 2 wk potentiated NADPH-dependent superoxide generation and hydrogen peroxide production compared with similarly treated negative littermate controls. Endothelium-dependent relaxation was impaired in transgenic mice, and bioavailable nitric oxide was markedly decreased. To test the hypothesis that eNOS uncoupling might contribute to endothelial dysfunction, the diet was supplemented with tetrahydrobiopterin (BH(4)). BH(4) decreased aortic superoxide production, partially restored bioavailable nitric oxide in aortas of ANG II-treated Tg(SMCnox1) mice, and significantly improved endothelium-dependent relaxation in these mice. Western blot analysis revealed less dimeric eNOS in Tg(SMCnox1) mice compared with the wild-type mice; however, total eNOS was equivalent. Pretreatment of mouse aortas with the eNOS inhibitor N(G)-nitro-L-arginine methyl ester decreased ANG II-induced superoxide production in Tg(SMCnox1) mice compared with wild-type mice, indicating that uncoupled eNOS is also a significant source of increased superoxide in transgenic mice. Thus overexpression of Nox1 in vascular smooth muscle leading to enhanced production of reactive oxygen species in response to ANG II causes eNOS uncoupling and a decrease in nitric oxide bioavailability, resulting in impaired vasorelaxation.