Abstract 17626: Sildenafil Prevents Progressive Hypertrophy and Normalizes the Enhanced Slow Force Response in Dystrophic Myocardium
Background Duchenne Muscular Dystrophy (DMD) is a frequent and devastating disease that affects both skeletal muscle and the heart, resulting in cardiomyopathy in virtually all patients. Key features include nNOS-dysregulation and excessive Ca2+ entry upon mechanical stress. A possible source of increased Ca2+ entry are mechano-sensitive TRPC channels. As TRPC3/6 channels can be suppressed by PKG phosphorylation, we hypothesized that augmentation of PKG stimulation ameliorates invivo function coupled to blunting of stretch-activated Ca2+ entry and the slow force response (SFR).
Methods Mdx, utrophin+/- mice were treated with sildenafil 200mg/kg/d for 2 months and followed-up by echocardiography; gene expression was assessed by qRT-PCR and PDE5 activity by fluorescence polarization. The SFR and Ca2+ transients were assessed in single cardiomyocytes attached to carbon fibers and papillary muscle preparations when exposed to stretch.
Results Mdx, utrophin+/- mice demonstrated marked hypertrophy when compared to WT or mdx-only mice, with up-regulation of fetal gene expression markers (ANP 4.5±0.8-fold, BNP 2.5±0.4-fold, bMHC 2.8±0.4-fold, p<0.05) and a trend towards up-regulation of TRPC6 (3.4±1.5-fold, p=n.s.). Myocardial PDE5 activity was increased 3.5±0.5-fold over controls (p<0.01). Sildenafil treatment prevented and reversed progressive myocardial hypertrophy, normalized PDE5 activity, decreased fetal gene and TRPC6 expression (all p<0.05). The morphological and molecular changes were accompanied by an enhanced SFR in dystrophic cardiomyocytes. Sildenafil treatment and/or direct TRPC3/6 antagonism using a selective blocker normalized the myocyte SFR (p<0.05).
Conclusion PDE5 inhibition is effective in preventing progressive hypertrophy and normalizing molecular markers of heart failure in dystrophic hearts. The SFR is enhanced in dystrophic cardiomyocytes and can be normalized by PDE5 inhibition or acute TRPC antagonism. These data support the involvement of TRPC channels in excessive Ca2+ entry and the enhanced SFR, offering a rationale for modifying TRPC Ca2+ entry, either by direct antagonism or by PKG phosphorylation of TRPC channels.
- © 2012 by American Heart Association, Inc.