Directed expression of dominant-negative p73 enables proliferation of cardiomyocytes in mice

Previous studies have shown that p53 plays an important role in maintaining cell cycle arrest of cardiomyocytes, which might account for the inability of human hearts to regenerate adequately after injury. Therefore, inhibition of p53 represents an attractive strategy to restore cell cycle progression in cardiomyocytes although such an approach is hampered by the potential danger of concomitant tumor induction. During normal development, N-terminal truncated isoforms of the p53-related protein p73 are naturally occurring antagonists of p53 and p73, which are not related to tumor induction. We have generated recombinant adenoviruses encoding dominant-interfering p73 (Ad-p73DD) to inhibit p53/p73 in murine hearts at different developmental stages. We found that the expression of p73DD(wt) in newborn mice led to the increase of the relative heart weights after 14 days which is paralleled by a significant increase of proliferating cardiomyocytes as seen by ICC (BrdU-incorporation, phosphorylation of histone3, expression of AuroraB) without induction of apoptosis. Stimulation of cell cycle progression in cardiomyocytes went along with a significant down-regulation of the p53-dependent cdk-inhibitor p21WAF both on mRNA and protein level. Furthermore, mRNA levels and protein expression of D-type cyclins and cyclins A, B2, and E were selectively increased after expression of p73DD. We further show that the cell cycle entry of cardiomyocytes is not restricted to neonatal hearts but is also found in adult mouse hearts 5 days after intramyocardial injection of Ad-p73DD. Taken together we reason that directed expression of dominant-negative p73 might be utilized to stimulate proliferation of cardiomyocytes to improve cardiac regeneration.