Abstract 1782: Activation of Puma is Required for p53-dependent Apoptosis in Murine Dilated Cardiomyopathy
Background: Recent studies indicate that p53-dependent apoptosis may be critical for the development of dilated cardiomyopathy. The downstream mediators of this apoptotic pathway, however, have not yet been identified. Earlier we showed that the proapoptotic Bcl-2 family protein Puma represents an essential component of the apoptotic machinery in isolated cardiac myocytes in vitro. In the current study we investigated the role of Puma in apoptosis during dilated cardiomyopathy in vivo.
Methods: We applied two mouse models of dilated cardiomyopathy to analyze the downstream targets of p53 in apoptosis. The first model was the transverse aortic constriction (TAC), which causes adaptive hypertrophy 1 week after operation and leads to left ventricular dilation 4 weeks later. We compared the response of puma+/+ (wild-type) and puma−/− (mutant) mice to TAC. The second model was a heart-specific mdm4 (an inhibitor of p53) knockout mouse line, which spontaneously develops dilated cardiomyopathy from 3 months of age. These mdm4−/− mice were crossed with puma−/− mice and the mdm4−/−/puma+/+ animals were compared with mdm4−/−/puma−/− counterparts from the same litters.
Results: In both mouse models knocking out puma attenuated the signs of dilated cardiomyopathy. The endpoints of the study included heart weight/body weight ratio, hypertrophy, apoptosis, fibrosis and fractional shortening. In the first model in the presence of Puma, 4 weeks after TAC we observed a significant increase of apoptosis and fibrosis with concomitant elevation of Puma, p53 and Mdm4 expression. Interestingly, in the absence of Puma the elevated expression of p53 and Mdm4 was retained, however, less apoptosis, fibrosis and smaller functional changes were observed. In the second model, knocking out puma in mdm4−/− mice significantly slowed down the development of dilated cardiomyopathy, having the first signs of apoptosis only after 6 months.
Conclusions: Puma appears to be a critical component of the p53-dependent apoptosis pathway in cardiomyocytes in vivo, therefore, inhibition of Puma may be a suitable therapeutic approach in heart diseases based on dilated cardiomyopathy. Our present studies provide the proof of concept to develop Puma inhibitors to target cardiac apoptosis.