Abstract 028: CCN1 Enables Fas Ligand-Induced Apoptosis by Elevating Fas Expression in Primary Cardiomyocytes or by Increasing Cytoplasmic Smac in Cardiomyoblast H9c2 Cells
Fas/Fas ligand (FasL) is implicated in cardiac ischemia/reperfusion injury. However, cardiomyocytes in culture are resistant to FasL-induced apoptosis, suggesting that additional factor(s) are required for FasL-induced apoptosis. Matricellular protein CCN1 has been demonstrated to promote cytotoxicity of FasL in human skin fibroblasts. CCN1 is induced in a variety of cardiac pathologies. We assessed the hypothesis that CCN1 may be involved in the regulation of FasL-induced apoptosis in cardiomyocytes. We found that either FasL or CCN1 did not induce cell death in neonatal rat ventricular cardiomyocytes (NRVM). Interestingly, the combination of FasL+CCN1 generated 2-fold induction of apoptosis (vs. control p<0.001). An integrin-α6β1-binding defective mutant CCN1, CCN1-DM failed to exert synergy with FasL to induce apoptosis, indicating a critical role of α6β1. The engagement between CCN1 and α6β1 instigated the elevation of cellular reactive oxygen species (ROS), the activation of mitogen activated protein kinase p38, and followed by the induction of cell surface display of Fas, thereby sensitizing NRVM to FasL-induced apoptosis. Pretreatment of the p38 inhibitor SB202190 abolished the CCN1-induced cell-surface Fas expression and the apoptosis induced by FasL+CCN1. In addition, we tested the interaction between CCN1 and FasL on the cardiomyoblast H9c2 cells. We found that FasL or CCN1 alone did not cause apoptosis in H9c2, and required the combination of FasL+CCN1 to induced apoptosis (vs. control p<0.001) in H9c2 cells, reminiscent of the observation in NRVM. Mechanistically, CCN1 acted through binding to integrin α6β1, ROS generation, and p38 activation, however, did not increase the expression of cell surface Fas for its synergy with FasL in H9c2 cells. Instead, CCN1 induced Bax translocation to mitochondria, which in turn led to the release of Smac from mitochondria to cytosol. The cytosolic Smac functions to neutralize XIAP. Smac is critical for CCN1 action, because the knockdown of Smac blunted the apoptotic activities of CCN1. In conclusion, CCN1 may play a detrimental role in a stressed heart to both the differentiated cardiomyocytes and the proliferative cardioblasts through distinct signaling mechanisms.
- © 2013 by American Heart Association, Inc.