p38 mitogen-activated protein kinase is a critical component of the redox-sensitive signaling pathways activated by angiotensin II. Role in vascular smooth muscle cell hypertrophy

Angiotensin II induces an oxidant stress-dependent hypertrophy in cultured vascular smooth muscle cells. To investigate the growth-related molecular targets of H₂O₂, we examined the redox sensitivity of agonist- stimulated activation of the mitogen-activated protein kinase (MAPK) family. We show here that angiotensin H elicits a rapid increase in intracellular H₂O₂ and a rapid and robust phosphorylation of both p42/44MAPK (16-fold) and p38MAPK (15-fold). However, exogenous H₂O₂ activates only p38MAPK (14- fold), and diphenylene iodonium, an NADH/NADPH oxidase inhibitor, attenuates angiotensin II-stimulated phosphorylation of p38MAPK, but not p42/44MAPK. Furthermore, in cells stably transfected with human catalase, angiotensin II- induced intracellular H₂O₂ generation is almost completely blocked, resulting in inhibition of phosphorylation of p38MAPK, but not p42/44MAPK, and a subsequent partial decrease in angiotensin II-induced hypertrophy. Specific inhibition of either the p38MAPK pathway with SB203580 (4-(4- fluorophenyl)-2-(4-methylsufinylphenyl)-5-(4-pyridyl)1H-imidazole) or the p42/44MAPK pathway with PD98059 (2-(2'-amino-3'-methoxyphenyl)oxanaphthalen- 4-one) also partially, but significantly, attenuates angiotensin II-induced hypertrophy; however, simultaneous blockade of both pathways has an additive inhibitory effect, indicating that the hypertrophic response to angiotensin II requires parallel, independent activation of both MAPK pathways. These results provide the first evidence that p38MAPK is a critical component of the oxidant stress (H₂O₂)-sensitive signaling pathways activated by angiotensin II in vascular smooth muscle cells and indicate that it plays a crucial role in vascular hypertrophy.