Up-regulation of caspase-3, -9 expressions participates in hypoxia-induced cardiomyocyte apoptosis

Objective To explore the effects of hypoxia on the activation of caspases in cardiomyocytes. Methods At 0, 3, 6, 12, and 24 h after hypoxia, cell apoptosis and viability were determined with Hoechst 33342 staining and MTT method, respectively. Expressions of caspase-3, -9 mRNA and release of mitochondrial cytochrome c in primary culture of cardiomyocytes were determined by RT-PCR and Western blotting, respectively. Results Typical cell apoptosis was induced in cardiomyocytes at 24 h after hypoxia and cell viability decreased significantly. Elevation of Cyt c in cytosol was in accordance with the decline in mitochondrial Cyt c content. Significant increase in Cyt c in cytosol appeared at 12 h after hypoxia and peaked at 24 h while Cyt c in mitochondria could not be detected at 24 h after hypoxia. Hypoxia could up-regulate the caspase-3, -9 mRNA expressions at 3 h after exposure. Up-regulation of caspase-3, -9 mRNA expressions was maintained during 24 h hypoxic insult. Conclusion Hypoxia can induce mitochodrial Cyt c release into cytosol and up-regulate caspase-3, -9 mRNA expressions. These results demonstrate that hypoxia can induce mitochondrium-dependent caspase-3 activation in cardiomyocytes, resulting in cell apoptosis.