Abstract 537: Sildenafil Suppresses Cardiac Hypertrophy through Inhibition of Canonical Transient Receptor Potential Cation Channel 6 Expression in Cardiac Myocytes

Abstract

Background: We have shown that a phosphodiesterase 5A (PDE5A) inhibitor, sildenafil blocks cardiac pathological hypertrophy through inhibition of Gαq mediated signaling and calcineurin (Cn) signaling. However, the precise molecular mechanism is still unknown. Recently canonical transient receptor potential cation channel 6 (TRPC6) and its up-regulation have been shown to play a critical role for Gαq-mediated Cn activation in pathogenesis of cardiac hypertrophy. Therefore, we hypothesized that PDE5A inhibition blocks TRPC6 gene induction in cardiac myocytes and thus prevents cardiac hypertrophy. Methods and Results: We examined TRPC6 expression levels using real-time RT-PCR in hypertrophied mouse heart created by transverse aortic constriction (TAC). TRPC6 mRNA expression was significantly increased after TAC. Sildenafil effectively attenuated TAC-induced hypertrophy, Cn protein level and upregulation of TRPC6 mRNA. To investigate role of TRPC6 in sildenafil’s anti-hypertrophic effects, we studied cultured adult mouse cardiac myocytes (AMCM) and neonatal rat cardiac myocytes (NRCM). Stimulation with Endothelin 1 (ET1) or angiotensin II (AngII) increased cell surface area, leucine uptake, Cn protein expression and TRPC6 gene expression. Sildenafil dose-dependently blocked these increases. 8-bromo cGMP also blocked TRPC6 induction by ET1 and AngII. In addition, 8-bromo cGMP stimulation following adenovirus-mediated overexpression of cGMP-dependent protein kinase I-α (PKG) showed a marked decrease in TRPC6 expression. These results suggest that PKG activation regulates TRPC6 gene in cardiac myocytes. Using adenovirus-based expression of artificial PDE5A-gene silencing miRNA, PDE5 protein was effectively knocked down both in NRCM and AMCM. Importantly, PDE5-miRNA completely blocked ET1-mediated increase of Cn and TRPC6 same as sildenafil. Conclusion: Sildenafil effectively blocks TRPC6 induction both in vivo and in vitro . TRPC6 gene regulation is PKG and PDE5A dependent in cardiac myocytes. Given that TRPC6 induction triggers Gαq-mediated maladaptive signaling, especially Cn, these data show that the inhibition of TRPC6 gene expression contributes to the Gαq-coupled anti-hypertrophic mechanism of sildenafil.