Blockade of Caspase-2 Activity Inhibits Ischemia/ Reperfusion-Induced Mitochondrial Reactive Oxygen Burst and Cell Death in Cardiomyocytes

We previously showed that initiator caspases-2 and -8 are prominently activated in ischemia/reperfusion (I/R)-induced injury in cardiomyocytes, but while blockade of caspase-2 activity enhanced cell survival, blockade of caspase-8 activity did not protect cardiomyocytes. Because apoptotic death in these cells is characterized by a burst of reactive oxygen species (ROS) at reperfusion and their survival by inhibition of this burst, we examined the effects of blocking caspase-2 and caspase-8 activities on ROS production. Caspase-2 inhibition blocked the reperfusion-induced ROS burst, while inhibition of caspase-8 did not. We also examined effects of caspase inhibition on mitochondrial membrane potential ( ψ m) and mitochondrial function and found that blocking caspase-2, but not caspase-8, allowed recovery of ψ m and mitochondrial functionality. Furthermore, knockdown of caspase-2 by small-interfering (si)RNA confirmed caspase-2 participation in cytochrome c release, which correlates with loss of ψm and cell death in these cardiomyocytes.