Abstract 206: Mitofilin Knockdown Induces Cell Death by Apoptosis via an AIF-PARP-dependent Mechanism and Cell Cycle Arrest

Abstract

Introduction: Mitochondrial activity plays an essential role in the efficient function of cardiomyocytes. Mitofilin is an inner membrane protein that has been defined as a mitochondria-shaping protein in controlling and maintaining mitochondrial cristae structure and remodeling. In this study, we determined the role of mitofilin in H9c2 and C2C12 myoblasts survival by investigating the mechanism underlying mitofilin knockdown-induced cell death by apoptosis. Methods: H9c2 and C2C12 cells were cultured and treated with mitofilin siRNA or scramble siRNA for 24 hours. Cell death (apoptosis), caspase 3 activity, and cell cycle phases were assessed by flow-cytometry, cytochrome C release and intracellular ATP production were measured by ELISA. Mitofilin, AIF and PARP expression was measured by Western blot analysis and calpain activity assessed using calpain kit. Mitochondria images were taken using electron microscopy. Results: We found that mitofilin knockdown increases cell death by apoptosis mainly via activation of AIF pathway leading to nuclear fragmentation and subsequent PARP1 activation in the nucleus that is correlated with S phase arrest of the cell cycle. Knockdown of mitofilin in H9c2 as well as C2C12 myoblasts with siRNA led to mitochondrial swelling and damage of mitochondrial cristae that is associated with the increase in ROS production, decrease in intracellular ATP production and a marked decrease in mitochondrial membrane potential. Moreover, cells treated with mitofilin siRNA displayed an increase in calpain activity versus scramble siRNA. Conclusion: Together, these results indicate that mitofilin knockdown by siRNA increases calpain activity that presumably leads to mitochondrial structural degradation resulting in a critical reduction of mitochondrial function that is responsible for the increase in cell death by apoptosis via AIF-PARP mechanism which is associated with nuclear fragmentation and S phase arrest of cell cycle.