p38 MAPK contributes to angiotensin II-induced COX-2 expression in aortic fibroblasts from normotensive and hypertensive rats
Objective To investigate the effect of angiotensin II on cyclooxygenase-2 (COX-2) expression in aortic adventitial fibroblasts from normotensive [Wistar¿Kyoto (WKY)] rats and spontaneously hypertensive rats (SHRs). Methods Protein expression was determined by western blot, mRNA levels by real-time PCR, transcriptional activity by luciferase assays, superoxide anion (O2.-) production by dihydroethidine fluorescence and prostaglandin E2 by enzyme immunoassay. Results Angiotensin II (0.1mmol/l, 0.5¿6 h) time dependently induced COX-2 protein expression, this effect being transient in fibroblasts from WKY rats and maintained over time in SHRs. Angiotensin II effect was abolished by valsartan (1mmol/l), an angiotensin II type 1 receptor antagonist. Angiotensin II-induced prostaglandin E2 production was reduced by valsartan and the COX-2 inhibitor NS398 (1mmol/l). Angiotensin II increased O2.- production more in SHR than WKY rats. This increase was reduced by apocynin (30mmol/l) and allopurinol (10mmol/ l), respective nicotinamide adenine dinucleotide phosphate (NADPH) and xanthine oxidase inhibitors. However, angiotensin II-induced COX-2 expression was unaffected by apocynin, allopurinol, tempol (1 mmol/l) or catalase (1000 U/ml). Angiotensin II (2¿30 min) induced p38 mitogen-activated protein kinase (MAPK) phosphorylation, transiently in WKY rats but sustained in SHRs. The p38 inhibitor SB203580 (10mmol/l) reduced angiotensin II-induced COX-2 protein and mRNA levels. The angiotensin II effect was not prevented by inhibition of mRNA synthesis, and angiotensin II was unable to modulate COX-2 transcriptional activity. Conclusions Angiotensin II increases COX-2 expression in aortic fibroblasts through mechanisms including p38 MAPK pathway, independent of reactive oxygen species production and nonmediated by COX-2 transcriptional activity modulation. The sustained angiotensin-induced p38 MAPK activation in SHR cells might be related to the maintained COX-2 expression in this strain.