Mechanical stretch induces mitochondria-dependent apoptosis in neonatal rat cardiomyocytes and G_(2)/M accumulation in cardiac fibroblasts

摘要

Heart remodeling is associated with the loss of cardiomyocytes and increase of fibrous tissue owing to abnormal mechanical load in a number of heart disease conditions. In present study,a well-described in vitro sustained stretch model was employed to study mechanical stretch-induced responses in both neonatal cardiomyocytes and cardiac fibroblasts. Cardiomyocytes,but not cardiac fibroblasts,underwent mitochondria-dependent apoptosis as evidenced by cytochrome c (cyto c) and Smac/DIABLO release from mitochondria into cytosol accompanied by mitochondrial membrane potential (△ψm) reduction,indicative of mitochondrial permeability transition pore (PTP)opening. Cyclosporin A,an inhibitor of PTP,inhibited stretch-induced cyto c release,△ψm reduction and apoptosis,suggesting an important role of mitochondrial PTP in stretch-induced apoptosis. The stretch also resulted in increased expression of the pro-apoptotic Bcl-2 family proteins,including Bax and Bad,in cardiomyocytes,but not in fibroblasts. Bax was accumulated in mitochondria following stretch. Cell permeable Bid-BH3 peptide could induce and facilitate stretch-induced apoptosis and △ψm reduction in cardiomyocytes. These results suggest that Bcl-2 family proteins play an important role in coupling stretch signaling to mitochondrial death machinery,probably by targeting to PTP. Interestingly,the levels of p53 were increased at 12 h after stretch although we observed that Bax upregulation and apoptosis occurred as early as 1 h. Adenovirus delivered dominant negative p53 blocked Bax upregulation in cardiomyocytes but showed partial effect on preventing stretch-induced apoptosis,suggesting that p53 was only partially involved in mediating stretch-induced apoptosis. Furthermore,we showed that p21 was upregulated and cyclin B l was downregulated only in cardiac fibroblasts,which may be associated with G2/M accumulation in response to mechanical stretch.