Abstract 13722: Dual Roles of cAMP In Cardiac Myocyte Apoptosis Induced by Beta-Adrenergic Agonists
β-Adrenergic (β-AR) overstimulation causes cardiomyocyte death contributing to heart disease development. Protein kinase A (PKA), exchange protein directly activated by cAMP (EPAC) and Ca2+/calmodulin-dependent kinase II are the major downstream molecules of the β-AR pathway. However, to date, the relative contribution of these molecules to myocyte apoptosis induced by β-AR overstimulation has not been well studied.
Methods: Adult feline ventricular myocytes (AFVMs) were isolated and cultured. β-AR agonists were used to induce AFVM apoptosis. Adenovirus with PKI-GFP (PKI) was used to infect AFVMs to inhibit PKA to separate the effects of PKA from CaMK II and EPAC.
Results: 1. PKA activity stimulated with cAMP in the crude protein extract from PKI-AFVMs is fully inhibited although isoproterenol (ISO) induced the same amount of cAMP as in GFP-VMs; 2. ISO (10uM), dobutamine+ICI 118551 induced >80% of GFP-AFVMs to die but <5% cell death in PKI-AFVMs at 72 hours post treatment; ISO induced significantly higher percentage of FLICA+ myocytes (65.6±2.3% GFP-AFVMs vs. 12.5±1.8% PKI-VMs) and TUNEL+ myocytes (19.7±1.5% GFP-AFVMs vs. 4.4±1.5% PKI-AFVMs), indicating caspase activation and myocyte apoptosis induced by ISO; 3. AFVM death by ISO was prevented by nifedipine, thapsigargin and KN-93 and myocyte ICa-L, contraction, Ca2+ transient and SR content in PKI-AFVMs did not respond to ISO stimulation, indicating the involvement of Ca2+ and CaMK II in b-AR stimulation induced apoptosis; 4. In the presence of PKI, ISO could not induce CaMK II activation although CaMK II in PKI-VMs can be activated by high extracelluar Ca2+ and an L-type Ca2+ channel agonist (BayK 8644), indicating that CaMK II activation by ISO is downstream to PKA; 5. In the presence of PKI, ISO reduced apoptosis induced by PKA-independent stimuli (high extracellular Ca2+ and H2O2), which can be mimicked by an EPAC activator, 8-cp-TOME-AM; 6. Examination of antiapoptotic signals in PKI-VMs stimulated by ISO revealed the activation of Rap1 and ERK but not Akt.
Conclusion: cAMP plays dual roles in b-adrenergic agonist-induced myocyte apoptosis, a proapoptotic effect mediated by PKA and its downstream CaMK II and an antiapoptotic effect mediated by the EPAC/Rap1/ERK pathway.
- © 2011 by American Heart Association, Inc.