Transition of compensated hypertrophy to heart failure is accompanied by increased TGFb expression in the heart. In cardiomyocytes stimulation with TGFb leads to decrease in contractile function and apoptosis, two processes in the development of heart failure that also could be seen with nitric oxide (NO). The aim of this study was to analyze the impact of NO in TGFb-induced apoptosis. Therefore, we stimulated adult cardiomyocytes of rat with TGFb₁ (1ng/ml) and measured NO. NO release increased significantly within two hours and could be blocked with the NO synthase inhibitor ETU (1 mM). Use of iNOS-specific inhibitor 1400W (100 nM), or nNOS-specific inhibitor TFA (10 mM) did not inhibit NO formation. Similarly, TGFb-induced apoptosis was totally blocked if all NOS isoforms were inhibited with ETU, but not by specific inhibition of iNOS or nNOS. These results indicate that the quick NO release was a result of eNOS activation under TGFb. This was affirmed by phosphorylation of eNOS at serine 1177 under TGFb stimulation. NO release was mediated via TGFb-receptor I (ALK5), since ALK5 receptor blocker SB431542 (1 mM) impeded NO formation. Also, TGFb-induced apoptosis was blocked with SB431542. Additionally, TGFb-induced apoptosis was significantly reduced by use of PI3-kinase inhibitors Ly294002 (10 mM) und wortmannin (100nM).

Conclusion: 

TGFb activates eNOS via TGFb-receptor I in adult cardiomyocytes of rat. This results in increased NO release and apoptosis induction. In addition, apoptosis is regulated via PI3-kinase activation. So, NO was identified as an important signalling molecule in TGFb-induced apoptosis.