Co-activation of PKCdelta/ERK1/2 and P38 MAPK mediates angiotensin II-induced cyclooxygenase-2 up-regulation in endothelial cells and the clinical implications

Abstract

Elevated angiotensin II (AngII) levels have been implicated in patients with hypertension and diabetic vascular complications, while cyclooxy-genase-2 (COX-2) is regarded as a culprit of vascular inflammation. However, it remains elusive whether COX-2 acts directly as a downstream effector in mediating AngII-induced vascular pathogenesis. The present study aimed to investigate this relationship and the intracellular signalling cascades linking these two factors. Primary endothelial cells were freshly cultivated from rat thoracic aortas. The COX-2 expression was minimal in untreated endothelial cells but reached a maximum after 8-hour incubation with 100 nM AngII. Losartan and RNA synthesis inhibitor (actinomycin-D) inhibited COX-2 over-expression. Of known transcriptional pathways examined, only inhibitors of p38 MAPK and ERK1/2 (SB-202190 and PD-98059) decreased COX-2 expression, and co-treatment caused additive effect, suggesting a joint mediation through both kinases. PKC inhibitor (GF109203X), and particularly, the specific PKCδ inhibitor (rottlerin), prevented AngII-induced phosphorylation of ERK1/2 and COX-2 expression, suggesting an upstream regulation of ERK1/2 by PKCδ. Pivotal role of PKC in AngII-induced COX-2 expression was further supported by a similar stimulatory effect of PKC activator, signified by the translocation of PKCδ to the membrane and confirmed by its phosphorylation (Tyr311). Aortae of AngII-infused rats and renal arteries from patients with hypertension and diabetes exhibited an increased endothelial COX-2 expression. The present novel findings indicate that activation of p38 MAPK and PKCδ/ERK1/2 is critical in AngII-mediated COX-2 up-regulation. This study provides an important molecular basis for further elucidation on how the COX-2-derived products participate in vascular inflammation in hypertension and diabetes.