Calcineurin Aβ Gene Targeting Predisposes the Myocardium to Acute Ischemia-Induced Apoptosis and Dysfunction

Cardiovascular disease is the leading cause of mortality and morbidity within the industrialized nations of the world, with coronary heart disease (CHD) accounting for as much as 66% of these deaths. Acute myocardial infarction is a typical sequelae associated with long-standing coronary heart disease resulting in large scale loss of ventricular myocardium through both apoptotic and necrotic cell death. In this study, we investigated the role that the calcium calmodulin-activated protein phosphatase calcineurin (PP2B) plays in modulating cardiac apoptosis after acute ischemia-reperfusion injury to the heart. Calcineurin Aβ gene-targeted mice showed a greater loss of viable myocardium, enhanced DNA laddering and TUNEL, and a greater loss in functional performance compared with strain-matched wild-type control mice after ischemia-reperfusion injury. RNA expression profiling was performed to uncover potential mechanisms associated with this loss of cardioprotection. Interestingly, calcineurin Aβ^-/- hearts were characterized by a generalized downregulation in gene expression representing approximately 6% of all genes surveyed, Consistent with this observation, nuclear factor of activated T cells (NFAT)-luciferase reporter transgenic mice showed reduced expression in calcineurin Aβ^-/- hearts at baseline and after ischemia-reperfusion injury. Finally, expression of an activated NFAT mutant protected cardiac myocytes from apoptotic stimuli, whereas directed inhibition of NFAT augmented cell death. These results represent the first genetic loss-of-function data showing a prosurvival role for calcineurin-NFAT signaling in the heart.