Molecular mechanisms in H2O2-induced increase in AT1 receptor gene expression in cardiac fibroblasts: A role for endogenously generated Angiotensin II

The AT1 receptor (AT1R) mediates the manifold actions of angiotensin II in the cardiovascular system. This study probed the molecular mechanisms that link altered redox status to AT1R expression in cardiac fibroblasts. Real-time PCR and western blot analysis showed that H2O2 enhances AT1R mRNA and protein expression via NADPH oxidase-dependent reactive oxygen species induction. Activation of NF-κB and AP-1, demonstrated by electrophoretic mobility shift assay, abolition of AT1R expression by their inhibitors, Bay-11-7085 and SR11302, respectively, and luciferase and chromatin immunoprecipitation assays confirmed transcriptional control of AT1R by NF-κB and AP-1 in H2O2-treated cells. Further, inhibition of ERK1/2, p38 MAPK and c-Jun N-terminal kinase (JNK) using chemical inhibitors or by RNA interference attenuated AT1R expression. Inhibition of the MAPKs showed that while ERK1/2 and p38 MAPK suffice for NF-κB activation, all three kinases are required for AP-1 activation. H2O2 also increased collagen type I mRNA and protein expression. Interestingly, the AT1R antagonist, candesartan, attenuated H2O2-stimulated AT1R and collagen mRNA and protein expression, suggesting that H2O2 up-regulates AT1R and collagen expression via local Angiotensin II generation, which was confirmed by real-time PCR and ELISA. To conclude, oxidative stress enhances AT1R gene expression in cardiac fibroblasts by a complex mechanism involving the redox-sensitive transcription factors NF-κB and AP-1 that are activated by the co-ordinated action of ERK1/2, p38 MAPK and JNK. Importantly, by causally linking oxidative stress to Angiotensin II and AT1R up-regulation in cardiac fibroblasts, this study offers a novel perspective on the pathogenesis of cardiovascular diseases associated with oxidative stress.