Abstract 3990: Regulation of AIF Nuclear Translocation is a Critical Step in Cardiac Apoptosis in Mice Lacking Hsp70 During Ischemia/Reperfusion in vivo
Heat shock protein 70 (Hsp70) has been shown to have an anti-apoptotic effect, possibly by regulating apoptosis inducing factor (AIF), a key mediator of caspase-independent apoptosis. Here, we examined the anti-apoptotic mechanism of Hsp70 in AIF-induced apoptosis during ischemia/reperfusion (I/R) in vivo.
Method and Results: Hsp70 knockout (Hsp70 KO) and wild type (WT) mice underwent I/R surgery (45 minutes of ischemia followed by reperfusion) followed by molecular analysis, TUNEL, infarct size, and functional analyses of the heart. After 9 hours of reperfusion, we observed that while a similar amount of AIF was released from the mitochondria to the cytosol in WT and Hsp70 KO mice, Hsp70 KO mice showed a significantly greater (4.1-fold) accumulation of AIF in the nuclei. We also found that phosphorylated ERK expression was significantly up regulated after I/R in WT, but did not change in Hsp70 KO mice. Two days after I/R, there were greater increases in apoptosis (13%) and infarct size (23%) in Hsp70 KO compared to WT mice (p<0.05 for both). Furthermore, 2 weeks after I/R Hsp70 KO mice showed a 56% greater reduction in ejection fraction. Inhibiting PARP, a critical regulator of AIF-induced apoptosis, significantly blocked the release of AIF from mitochondria and the accumulation of AIF in the nuclei after I/R in both WT and Hsp70 KO mice, suggesting that PARP regulates the subcellular translocation of AIF. Pretreatment with PARP inhibitor also significantly inhibited apoptosis, reduced infarct size, and attenuated cardiac dysfunction in both WT and Hsp70 KO mice after I/R.
Conclusion: The anti-apoptotic mechanism of Hsp70 involves the inhibition of AIF nuclear translocation which might be involving an ERK-dependent pathway, and PARP inhibition is effective in blocking AIF-induced apoptosis after I/R.