Involvement of caspase 3-and 8-like proteases in ceramide-induced apoptosis of cardiomyocytes

Ceramides are the metabolic products of sphingolipids of the eukaryotic cell membranes and are believed to function as signaling molecules in a variety of biological processes. Ceramide induces apoptosis in cultured cardiomyocytes. However, the molecular pathway underlying ceramide-induced apoptosis is not clear. In this study, we investigated the role of the cysteinyl aspartate-specific proteases (caspases) in cardiomyocyte apoptosis induced by ceramide. Treatment of in vitro cultured rat neonatal cardiomyocytes with ceramide results in robust cell death, of which the majority is apoptotic, as shown by positive staining for terminal deoxyribonuclease transferase-mediated deoxyuridine triphosphate nick end-labeling and the appearance of pyknotic nuclei with Hoechst staining. Caspase 3- and 8-like protease activities are induced in cardiomyocytes by ceramide treatment. Addition of the tetrapeptide inhibitors for caspases attenuated ceramide-induced apoptosis. The nonselective caspase inhibitor (B-D-FMK) and the caspase 3 (Z-DEVD-FMK) and caspase 8 (Z-IETD-FMK) inhibitors reduced ceramide-induced cardiomyocyte death and significantly inhibited the activation of caspase 3. However, the inhibitors specific for caspases 1, 2, 4, 6, and 9 have no significant effects on cardiomyocyte survival under the same conditions. These data suggest that caspases 3- and 8-related proteases are involved in ceramide-induced cardiomyocyte apoptosis.