Abstract P033: β-Adrenergic Signaling Mediates Cardiac Stem Cell Survival
Rationale:Adrenergic activity serves to increase acute cardiac contractility but chronic adrenergic drive is detrimental. Conventional therapy relies heavily on blockade of the α-adrenergic system; however, the cellular basis for improvement resulting from the treatment with α-Blockers remains obscure.
Objective:Demonstrate that the beneficial effect of long term α-blockade therapy is dependent, in part, upon restoration of regenerative capacity for the endogenous cardiac stem cell (CSCs) population.
Methods and Results:Mouse CSCs express only α2 adrenergic receptor (α2-AR) in conjunction with stem cell marker c-kit as assessed by qRT-PCR and immunoblot. Activation of α2-AR signaling by the specific α2-agonist fenoterol (1µM) improves proliferation and increases protective signaling associated with elevated levels of pAkt/Akt, eNOS, cyclin D and decreased levels of GRK2. Conversely, CSCs treated with α2-AR antagonists (siα2-AR, ICI118, 551) exhibit impaired proliferation. Although CSCs lack α1-AR under normal proliferative conditions, co-culture of CSCs with neonatal rat cardiomyocytes promotes expression of α1-AR concurrent with loss of c-kit and expression of lineage commitment cardiac markers such as cTnT, SERCA2a, MLC-2v, SMA as measured by species-specific primers with qRT-PCR. Co-cultured CSCs became sensitized to isoproterenol-induced cell death that is abrogated by administration of the specific α1-antagonist (metoprolol, 1µM). Involvement of α1-AR in catecholamine-induced apoptosis was further confirmed by genetically engineering CSCs with αARK-ct-GFP, a GFP fused version of the peptide shown to rescue cardiac function by normalizing α-adrenergic signaling. αARK-Ct over-expressing CSCs acquired α1-AR after co-culture but were protected against isoproterenol-induced cell death.
Conclusion;α2-AR signaling leads to CSC activation and proliferation that is beneficial, but induction of cellular differentiation leads to expression of α1-AR that is proapoptotic when stimulated with adrenergic treatment. The apoptotic effect of α1-AR signaling in CSCs can be mitigated by engineering of cells with αARK-ct, providing a novel molecular strategy to promote regeneration in the pathologically injured myocardium.
- © 2011 by American Heart Association, Inc.