TGFβ Receptor Activation Enhances Cardiac Apoptosis Via SMAD Activation and Concomitant NO Release

Transforming growth factor beta(TGF beta) expression is induced in the myocardium during transition from compensated hypertrophy to heart failure. In cardiomyocytes, stimulation with TGF beta results in restricted contractile function and enhanced apoptosis. Nitric oxide (NO) also induces apoptosis and influences cardiac function. Therefore, we wanted to know whether NO is causally involved in TGF beta-induced apoptosis. In isolated ventricular cardiomyocytes of adult rat incubation with TGF beta(1) increased NO release which was inhibited by NOS inhibitor ETU but not with iNOS inhibitor (1400 W) or nNOS inhibitor (TFA). In addition, TGF beta-induced apoptosis was blocked with ETU and ODQ, but not with 1400 W or TFA. The consequent assumption that endothelial NOS is involved in TGF beta-induced NO formation and apoptosis was supported by increased phosphorylation of eNOS at serine 1177 and by the fact that TGF beta did not increase NO release in eNOS KO mice. Furthermore, TGF beta-induced apoptosis, NO formation, SMAD binding activity and SMAD2 phosphorylation were blocked by a TGF beta receptor antagonist, but only apoptosis and NO formation could be blocked with ETU. Expression of SMAD7 was increased after TGF beta stimulation and blocked with TGF beta receptor antagonist but not after blocking NO synthase with ETU. Conclusion: In cardiomyocytes TGF beta-induced apoptosis is mediated via TGF beta receptor activation that concomitantly activates SMAD transcription factors and the eNOS/NO/sGC pathway. Both of these pathways are needed for apoptosis induction by TGF beta. This reveals a new pathway of cardiac NO release and identifies NO as a possible contributor to heart failure progression mediated by TGF beta. J. Cell. Physiol. 226: 2683-2690, 2011. (C) 2010 Wiley-Liss, Inc.