Cyclic AMP promotes cell death in cardiac fibroblasts

Abstract

Cardiac fibrosis, which occurs in response to cardiac damage, such as myocardial infarction, is at least in part caused by fibroblast-to-myofibroblast transformation and the resultant excess accumulation of extracellular matrix (ECM). Previous studies indicate that the second messenger cyclic AMP (cAMP) blocks fibroblast-to-myofibroblast transformation. We sought to investigate if cAMP could also reverse cardiac fibrosis by inducing apoptosis of cardiac fibroblasts (CFs). MTT assay showed that primary rat CFs treated for 48 h with drugs that increase endogenous cAMP or cAMP analogs that selectively target PKA (but not ones that target the cAMP mediator Epac) produce ~30% increase in cell death. FACS identified CFs apoptosis based on the DNA content that places them in the sub-G1 phase of the cell cycle and immunoblotting indicated that cleaved caspase 3 is released into the culture media after cAMP treatment. Real-time PCR and immunoblotting revealed that cAMP treatment increased mRNA and protein expression of the pro-apoptotic Bcl2-interacting mediator (Bim) in CFs. We conclude that cAMP induces apoptosis of rat CFs in a PKA-dependent manner and that up-regulation of Bim likely contributes to this apoptosis. These findings suggest that targeting the cAMP/PKA pathway may be a mean to induce apoptosis of CFs and perhaps attenuate or reverse cardiac fibrosis. (Supported by NIH and the Ellison Medical Edn)