Abstract 368: Cardiac Expression of a Mutant p53 Protects Against Doxorubicin-induced Cardiomyocyte Apoptosis and Preserves Heart Function
Cardiomyocyte apoptosis plays a key role in the development of heart failure. Doxorubicin, a topoisomerase II inhibitor that is used in cancer therapy, induces p53-mediated cardiomyocyte apoptosis leading to heart failure. Studies from our laboratory have demonstrated that cardiac-restricted expression a mutant p53 (CB7) protects cardiomyocytes from E1A-induced apoptosis. We hypothesize that the cardiac-restricted expression of CB7 will protect cardio-myocytes from doxorubicin-induced apoptosis in vivo. Transgenic mice expressing cardiomy-ocyte restricted nuclear beta-galactosidase, with or without expression of CB7 (CB7/nLAC vs. nLAC) were treated with a total of 20mg/kg of doxorubicin (2 intraperitoneal injections of 10mg/kg at 3-day interval). The prevalence of cardiomyocyte apoptosis was assessed using anti-active caspase-3 antibody and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) staining. We also determined the level of the cleavage poly (ADP-ribose) polymerases (PARP), a substrate of caspase-3, and the level of the anti-apoptotic protein Bcl-xL in the heart. In addition, we measured global cardiac function using the two dimensional echocardiography. Our results show that the prevalence of cardiomyocyte apoptosis is higher in the nLAC mice than in the CB7/nLAC mice 4 days following doxorubicin injection using anti-active caspase-3 staining (1.98±0.24/mm2 vs. 0.85±0.14/mm2, p<0.05, n=6) and TUNEL staining (0.146±0.009% vs. 0.045±0.006%, p<0.01, n=5). In addition, cleavage PARP was detected in the doxorubicin-treated nLAC mouse hearts but not in the doxorubicin-treated CB7/nLAC hearts. Moreover, higher level of Bcl-xL was observed in treated CB7/nLAC mice than in the treated nLAC mice (n=3). Finally, echocardiography revealed greater reduction of fractional shortening in the nLAC mice than in the CB7/nLAC mice post-injection (28.8±5.48% vs. 7.79±1.35%, p<0.05, n=6). In conclusion, cardiac expression of CB7 protects against doxorubicin-induced cardiomyocyte apoptosis and preserves heart function. The anti-apoptotic effects of CB7 might result from the increased level of Bcl-xL.