Role of neuronal NO synthase in regulating vascular superoxide levels and mitogen-activated protein kinase phosphorylation.
OBJECTIVE
The present study is designed to investigate the role of neuronal nitric oxide synthase (nNOS) in the regulation of vascular mitogen-activated protein kinase (MAPK) activity under basal and angiotensin II (Ang II)-stimulated conditions.


RESULTS
Incubation with a potent nNOS inhibitor (L-VNIO) significantly increased superoxide (O2(-)) levels, with increased MAPK phosphorylation, in isolated aorta and vascular smooth muscle cells (VSMCs) from wild-type mice. Both increases were inhibited by the superoxide dismutase mimetic, tempol, but not by the peroxynitrite scavenger, FeTPPS. The levels of O2(-) and MAPK phosphorylation were higher in aorta from nNOS(-/-) mice than from wild-type mice. These parameters were suppressed by tempol and oxypurinal (a xanthine oxidase inhibitor). In isolated VSMCs or aorta from wild-type mice, Ang II stimulation markedly increased the levels of O2(-) and MAPK phosphorylation. L-VNIO significantly reduced Ang II-induced increases of these parameters. Apocynin, an NAD(P)H oxidase inhibitor, further inhibited Ang II-induced increases of these parameters compared with the L-VNIO-treated group. FeTPPS did not suppress the Ang II-induced increase of O2(-) levels, but markedly inhibited Ang II-induced MAPK phosphorylation. In contrast to the wild-type, in isolated aorta or VSMCs from nNOS(-/-) mice, Ang II failed to increase O2(-) levels and MAPK phosphorylation.


CONCLUSIONS
Under basal conditions, nNOS-derived NO acting as antioxidant reduces O2(-) accumulation and suppresses vascular MAPK phosphorylation. Under Ang II-stimulated conditions, NAD(P)H oxidase-derived O2(-), inducing nNOS uncoupling, potentiates the Ang II-induced increase of O2(-) generation. The generated O2(-) may react with NO to form peroxynitrite (ONOO(-)). Both O2(-) and ONOO(-) participate in Ang II-induced activation of vascular MAPK.
Zhang
Guo-Xing
GX
Department of Physiology II, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8521, Japan. gxzhang@naramed-u.ac.jp
Kimura
Shoji
S
Murao
Koji
K
Shimizu
Juichiro
J
Matsuyoshi
Hiroko
H
Takaki
Miyako
M
D000098:Acetophenones / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D003497:Cyclic N-Oxides / Q000494:pharmacology; D008297:Male; D008665:Metalloporphyrins / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000502:physiology*; D009952:Ornithine / Q000031:analogs & derivatives / Q000494:pharmacology; D010117:Oxypurinol / Q000494:pharmacology; D010766:Phosphorylation; D013113:Spin Labels; D013481:Superoxides / Q000097:blood*; D014969:Xanthine Oxidase / Q000502:physiology
C466420:5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron(III) chloride; D000098:Acetophenones; D003497:Cyclic N-Oxides; D008665:Metalloporphyrins; C111862:N(5)-(1-imino-3-butenyl)ornithine; D013113:Spin Labels; D013481:Superoxides; D000804:Angiotensin II; C056165:acetovanillone; D009952:Ornithine; D052248:Nitric Oxide Synthase Type I; D014969:Xanthine Oxidase; D020928:Mitogen-Activated Protein Kinases; D010117:Oxypurinol; C001803:tempol