It has been reported that at the end stage, apoptosis is involved in the progression of heart failure. It is suggested that cardiac energy metabolism is impaired during the progression of heart failure. Although the mechanism of induction of apoptosis in the failing heart varies according to the model of heart failure, it is not known whether an impairment of energy metabolism in cardiomyocytes is a primary cause of apoptosis. In this study, we applied mitochondrial inhibitors, such as rotenone, cobalt chloride and antimycin A, which inhibit mitochondrial function at different sites of the mitochondrial respiratory chain, to cardiomyocytes. All these reagents markedly decreased 3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay (MTT) reduction activity, an indicator of mitochondrial function, of cardiomyocytes and greatly increased glucose consumption, suggesting that cardiac energy metabolism is switched from β-oxidation of fatty acid to glycolysis. It was shown that after 48-72 h of treatment with each reagent, apoptosis was shown to occur by DNA laddering and increase in caspase activity. Interestingly, each reagent with a different action site greatly activated caspase-3, but not caspase-8 activity, suggesting that mitochondria are involved in induction of apoptosis. On the other hand, within 24 h of the treatment, when apoptosis of cardiomyocytes was not observed, the treated cardiomyocytes showed a marked increase in preproendothelin-1 and atrial natriuretic peptide (ANP) gene expressions. In conclusion, the present study suggests that mitochondrial dysfunction with impaired energy metabolism elevates gene expression of cardiac ET-1, an aggravating factor in heart failure, and then finally induces apoptosis in cardiomyocytes. The finding of marked increases in expression of molecular markers (ET-1 mRNA and ANP mRNA) in the failing heart, followed by apoptosis in the treated cardiomyocytes suggests that the inhibition of mitochondrial function of cultured cardiomyocytes provides a possible new in vitro model of heart failure.
Cardiovascular Division, Department of Internal Medicine, Institute of Clinical Medicine, and *Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
Address correspondence and reprint requests to Takashi Miyauchi, Cardiovascular Division, Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan. E-mail: [email protected]
© 2000 Lippincott Williams & Wilkins, Inc.