Transcription Factor Foxo3a Prevents Apoptosis by Regulating Calcium through the Apoptosis Repressor with Caspase Recruitment Domain *

Apoptosis can occur in the myocardium under a variety of pathological conditions, including myocardial infarction and heart failure. The forkhead family of transcription factor Foxo3a plays a pivotal role in apoptosis; however, its role in regulating cardiac apoptosis remains to be fully elucidated. We showed that enforced expression of Foxo3a inhibits cardiomyocyte apoptosis, whereas knockdown of endogenous Foxo3a sensitizes cardiomyocytes to undergo apoptosis. The a poptosis r epressor with c aspase recruitment domain (ARC) is a potent anti-apoptotic protein. Here, we demonstrate that it attenuates the release of calcium from the sarcoplasmic reticulum and inhibits calcium elevations in the cytoplasm and mitochondria provoked by oxidative stress in cardiomyocytes. Furthermore, Foxo3a is shown to maintain cytoplasmic and mitochondrial calcium homeostasis through ARC. We observed that Foxo3a knock-out mice exhibited enlarged myocardial infarction sizes upon ischemia/reperfusion, and ARC transgenic mice demonstrated reduced myocardial infarction and balanced calcium levels in mitochondria and sarcoplasmic reticulum. Moreover, we showed that Foxo3a activates ARC expression by directly binding to its promoter. This study reveals that Foxo3a maintains calcium homeostasis and inhibits cardiac apoptosis through trans-activation of the ARC promoter. These findings provided novel evidence that Foxo3a and ARC constitute an anti-apoptotic pathway that regulates calcium homeostasis in the heart.