Abstract 15271: Synergistic Benefits of Concurrent Inhibition of Both Caspase and Parp Activations During Ischemia/Reperfusion in Mice Hearts in vivo
Inhibition of caspase activation has been shown to be an effective strategy to limit apoptosis in heart. However, often times, caspase inhibition alone is only partially effective in preventing apoptosis in heart after ischemia/reperfusion (I/R) injury suggesting that other apoptotic mechanisms may be involved. In the present study, we examine to determine the contribution of caspase-independent apoptosis after I/R injury in heart in vivo.
Methods and Results: We generated transgenic mice with cardiac specific overexpression of cytokine response modifier A (CrmA), a known inhibitor of caspases, using αMHC promoter (CrmA Tg mice). We measured infarct size, apoptosis rate and cardiac function after I/R in both WT and CrmA Tg mice. Caspases were effectively inhibited by CrmA overexpression in heart. CrmA Tg mice showed a 54% decrease in apoptosis, a 34% reduction in infarct size, and a modest 18% increase in cardiac output compared to WT mice (p<0.05 for all) suggesting that inhibition of caspases is only partially beneficial after I/R-induced cardiac apoptosis. We also found that I/R produced a significant release of apoptosis inducing factor (AIF) from the mitochondria (evidence of AIF activation) and activated PARP-1 (an important regulator of AIF-induced apoptosis) in both WT and CrmA Tg mice. The activation of AIF and PARP-1 was significantly greater in CrmA Tg mice suggesting that AIF-induced, caspase-independent apoptosis may be significantly activated in the setting of caspase inhibition in CrmA Tg mice heart after I/R. To explore the effect of inhibiting PARP-1 activation, we pre-treated the mice using 4-AN (4-amino-1,8-napthalimide (3 mg/kg), a potent inhibitor of PARP, before I/R injury. Pre-treatment with 4-AN significantly blocked both the release of AIF and PARP-1 activation in CrmA Tg mice after I/R compared to the vehicle control. We also found that concurrent 4-AN pretreatment further inhibited apoptosis (80.3%), reduced infarct size (60.2%), and improved cardiac output (67.3%) after I/R compared to CrmA Tg mice with vehicle treatment.
Conclusion: The concurrent inhibition of caspase and PARP-1 is needed for an effective and complete inhibition of apoptosis after I/R in heart.
- © 2011 by American Heart Association, Inc.