Abstract ID : 108266
 

Carvedilol effectively blocks the oxidative stress-mediated downregulation of sarcoplasmic reticulum Ca2+ ATPase 2 gene expression independent of its β blocking activity in neonatal rat cardiac myocytes

Norimichi Koitabashi
Authors: Masahiko Kurabayashi; Kazuo Niwano; Kohichi Tomaru; Takako Takizawa; Masashi Arai; Norimichi Koitabashi

Background: Carvedilol, a vasodilating β blocker and a potent antioxidant, improves cardiac function and survival in patients with heart failure. We have previously demonstrated that oxidative stress reduces the sarcoplasmic reticulum Ca2+-ATPase (SERCA2) gene transcription. In this study, we tested the hypothesis that carvedilol inhibits the reduction of SERCA2 gene expression in cardiac myocytes exposed to oxidative stress.

Methods and Results: We examined the effect of carvedilol, and its metabolite BM910228, which has no β blocking activity, on the expression of SERCA2 gene by using cultured neonatal rat cardiac myocytes. Hydrogen peroxide decreased SERCA2 mRNA and protein levels in a dose dependent manner. Transient transfection assays showed that Hydrogen peroxide decreased the transcription of the SERCA2 gene promoter. Treatment of cardiac myocytes with either carvedilol (1-10μM) or BM910228 (0.01-0.5μM) attenuated the Hydrogen peroxide-mediated decrease in SERCA2 promoter activity, SERCA2 mRNA expression and its protein levels. In contrast, metoprolol, a β1 selective blocker, failed to exert these effects. To delineate the carvedilol-responsive element in the 5'-upstream regulatory region of the SERCA2 gene, we transfected 5´-deletion constructs. Carvedilol increased the transcription from the SERCA2 gene promoter, and deletion of the G+C-rich sequence spanning between -284 and -72 markedly abolished this induction, suggesting that GC-box in this region may be responsible for the upregulation of SERCA2 gene expression by carvedilol.

Conclusion: We have demonstrated that carvedilol effectively attenuated the downregulation of Ca2+ cycling protein, SERCA2, evoked by oxidative stress. The effect of carvedilol on the SERCA2 gene expression is exerted through its antioxidant action but not its β blocking action. Given that SERCA2 expression levels are critical determinant of cardiac function, our results provide a mechanistic explanation for clinical effects of carvedilol in heart failure.