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. |