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beta-Adrenergic pathway induces apoptosis through calcineurin activation in cardiac myocytes
1Department of Cardiovascular Medicine, University of Tokyo Graduate School of Medicine, Tokyo 113-8655, Japan.
Abstract:
Apoptosis of cardiac myocytes is one of the causes of heart failure. Here we examine the mechanism by which the activation of beta-adrenergic receptor induces cardiomyocyte apoptosis. Terminal deoxynucleotide transferase-mediated dUTP nick end labeling and DNA ladder analyses revealed that isoproterenol (Iso) induced the apoptosis of cardiac myocytes of neonatal rats through an increase in intracellular Ca(2+) levels. The Iso-induced cardiomyocyte apoptosis was strongly inhibited by the L-type Ca(2+) channel antagonist nifedipine and by the calcineurin inhibitors cyclosporin A and FK506. Iso reduced the phosphorylation levels of the proapoptotic Bcl-2 family protein Bad and induced cytochrome c release from mitochondria to the cytosol through calcineurin activation. Infusion of Iso increased calcineurin activity by approximately 3-fold in the hearts of wild-type mice but not in the hearts of transgenic mice that overexpress dominant negative mutants of calcineurin. Terminal deoxynucleotide transferase-mediated dUTP nick end labeling analysis revealed that infusion of Iso induced apoptosis of cardiac myocytes and that the number of apoptotic cardiomyocytes was significantly less in the hearts of the transgenic mice compared with the wild-type mice. These results suggest that calcineurin plays a critical role in Iso-induced apoptosis of cardiac myocytes, possibly through dephosphorylating Bad.
Insights
Beta-adrenergic receptor activation triggers heart cell death (cardiomyocyte apoptosis) by increasing intracellular calcium. Calcineurin activation is key to this process, leading to heart failure.
Area of Science:
- Cardiology
- Molecular Biology
- Cell Biology
Background:
- Cardiomyocyte apoptosis contributes to heart failure.
- Beta-adrenergic receptor (β-AR) activation is implicated in cardiac dysfunction.
Purpose of the Study:
- To elucidate the mechanism of beta-adrenergic receptor-induced cardiomyocyte apoptosis.
- To investigate the role of intracellular calcium and calcineurin in this process.
Main Methods:
- Terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay and DNA laddering.
- Assessment of intracellular calcium levels.
- Pharmacological inhibition using nifedipine and calcineurin inhibitors (cyclosporin A, FK506).
- Analysis of Bad protein phosphorylation and cytochrome c release.
- In vivo studies using wild-type and calcineurin-transgenic mice.
Main Results:
- Isoproterenol (Iso), a β-AR agonist, induced cardiomyocyte apoptosis via increased intracellular calcium.
- Iso-induced apoptosis was inhibited by nifedipine and calcineurin inhibitors.
- Iso reduced Bad phosphorylation and promoted cytochrome c release through calcineurin activation.
- Calcineurin activity was elevated by Iso in wild-type mice but not in transgenic mice.
- Transgenic mice overexpressing dominant-negative calcineurin showed significantly reduced Iso-induced cardiomyocyte apoptosis.
Conclusions:
- Calcineurin plays a critical role in beta-adrenergic receptor-mediated cardiomyocyte apoptosis.
- Calcineurin may induce apoptosis by dephosphorylating the proapoptotic protein Bad.
- Targeting calcineurin could be a therapeutic strategy for heart failure caused by β-AR overactivation.