Abstract 15445: Beta-Adrenergic Receptor Stimulation Regulates Bcl-2 and Enhances Cardiomyocytes Sensitivity to Apoptosis
Background: Loss of terminally differentiated cardiac myocytes contributes to the development of heart failure. Increased β-adrenergic receptors (βAR) stimulation regulates myocardial function in the normal heart, but contributes to myocardial pathology in heart failure. We characterized a novel mechanism by which βAR stimulation regulates Bcl-2, a major anti-apoptotic protein, and dictates cell fate.
Methods and results: Western Blot analysis from subcellular fractionated cells (HL-1 and Beas-2bs) subjected to β1-and/or β2 stimulation (1 hour 10 μM isoproterenol) and/or overexpression, or from hearts isolated from transgenic mice overexpressing cardiac β1 or β2 reveals induction of Bcl-2 translocation from the mitochondrial membrane to the cytosol. We further establish that Bcl-2-induced-translocation via βAR stimulation sensitizes cells towards apoptotic stimuli (DNA fragmentation, caspase-3 activity), such as staurosporine or actinomycin D. We demonstrate that artificial elevation of cytosolic cAMP, using 10 μM forskolin or 100 μM DBcAMP, was sufficient to induce Bcl-2 relocation. Further, PKA and CaMKII were required for the transduction of the signal form β1AR but not from β2AR suggesting an alternative mechanism for β2AR. However β1-and β2AR stimulation both lead to calpain activation (luminescence assay). In vitro experiments demonstrate that recombinant calpain protein cleaves Bcl-2 from isolated mitochondria, thereby enabling its release into the cytosol. Furthermore 30 minutes pretreatment with 10 μM calpeptin, a calpain inhibitor, completely prevented Bcl-2 cytosolic redistribution induced by βAR stimulation. Thus, βAR stimulation induces cAMP elevation, which leads to calpain activation, Bcl-2 cleavage and ultimately renders cells more sensitive to apoptosis.
Conclusion: We demonstrate a direct link between β-adrenergic receptor stimulation and the regulation of Bcl-2 a major anti apoptotic member of the Bcl-2 family. These data provide a potential underlying mechanism by which the increase in cardiac sympathetic stimulation sensitizes cardiac myocytes towards apoptosis.
- © 2011 by American Heart Association, Inc.