Opposing roles of p47phox in basal versus angiotensin II-stimulated alterations in vascular O2- production, vascular tone, and mitogen-activated protein kinase activation.

BACKGROUND: NADPH oxidase is a major source of vascular superoxide (O2-) production and is implicated in angiotensin II (Ang II)-induced oxidant stress. The p47phox subunit plays an important role in Ang II-induced oxidase activation, but its role in basal oxidase activity and vascular function is unclear. METHODS AND
RESULTS: Aortae from p47phox-/- and matched wild-type (WT) mice (n=9/group) were incubated ex vivo with or without Ang II (200 nmol/L, 30 minutes) and then examined for (1) NADPH-dependent O2- production, (2) endothelium-dependent and -independent vascular relaxation, and (3) activation of mitogen-activated protein kinases (MAPKs). In the absence of Ang II, p47phox-/- vessels had slightly but significantly higher (1.3+/-0.1-fold; P<0.05) NADPH-dependent O2- production than WT; impaired relaxation to acetylcholine (maximum 54+/-4% versus 80+/-3%; P<0.05), which was normalized to WT levels by the O2- scavenger tiron or by Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride, and increased basal phosphorylation of ERK1/2, p38MAPK, and JNK compared with WT. In WT aortae, Ang II increased NADPH-dependent O2- production (2.5+/-0.5-fold; P<0.05), impaired relaxation to acetylcholine (maximum 60+/-6% versus 80+/-3%; P<0.05), and increased ERK1/2, p38MAPK, and JNK phosphorylation (P<0.05). In contrast, Ang II failed to increase O2- production, impair acetylcholine responses, or increase MAPK activation in p47phox-/- aortae.
CONCLUSIONS: p47phox plays a complex dual role in the vasculature. It inhibits basal NADPH oxidase activity but is critical for Ang II-induced vascular dysfunction via activation of NADPH oxidase.