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 (O-2(-)) production and is implicated in angiotensin II (Ang II) - induced oxidant stress. The p47(phox) 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 p47(phox-/-) 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 O-2(-) production, (2) endothelium-dependent and - independent vascular relaxation, and (3) activation of mitogen-activated protein kinases (MAPKs). In the absence of Ang II, p47(phox-/-) vessels had slightly but significantly higher (1.3 +/- 0.1-fold; P < 0.05) NADPH-dependent O-2(-) production than WT; impaired relaxation to acetylcholine (maximum 54 +/- 4% versus 80 +/- 3%; P < 0.05), which was normalized to WT levels by the O-2(-) 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 O-2(-) 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 O-2(-) production, impair acetylcholine responses, or increase MAPK activation in p47(phox-/-) aortae. Conclusions - p47(phox) 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.