Abstract 8556: Inhibition of Grk2 Augments Cardiac Beta2-Adrenergic Receptor-Dependent Contractility via Prevention of Receptor Interaction with Phosphodiesterase Type 4d
β1- and β2-adrenergic receptors (βARs) are G-protein coupled receptors (GPCRs) that play clearly distinct roles in cardiac physiology/pathology. For instance, cardiomyocyte contraction is readily stimulated by β1AR but not β2AR signaling. This might be explained by differences in assembly of macromolecular signaling complexes: β1AR forms a signaling complex with phosphodiesterase (PDE) type 4D8 directly, and agonist binding dissociates this complex. Conversely, GPCR kinase (GRK)2-induced β2AR phosphorylation leads to recruitment of a complex consisting of β-arrestin (βarr), a universal GPCR adapter/scaffolding molecule, and another PDE4D variant, PDE4D5. This PDE4D recruitment is postulated to constrain β2AR pro-contractile signaling by limiting compartmentalization of 3′-5′-adenosine monophosphate signaling. Thus, herein, we sought to investigate the effect of inhibition of this complex recruitment on β2AR pro-contractile signaling in vivo. In order to block β2AR-PDE4D interaction in cardiac myocytes in vivo, we crossed β1AR knockout (B1KO) mice, which do not express β1AR, with M27 mice, which overexpress, specifically in cardiac myocytes, the GRK2 inhibitor GRK2ct (or βARKct). By blocking GRK2-mediated phosphorylation, βarr-dependent PDE4D recruitment to β2AR is prevented. We studied the offspring both under normal conditions and after surgically induced myocardial infarction (MI). Contractility was significantly augmented in M27/B1KO mice compared to B1KO's, both in healthy mice (ejection fraction (EF): 69+1.8% vs. 57+1.7% respectively, p<0.05, n=8) and at 4 weeks after MI (EF: 42.6+0.1% vs. 25+3.9% respectively, p<0.05, n=8). In addition, GRK2ct expression attenuated cardiac dilatation of B1KO's at 4 weeks post-MI. At the molecular level, M27/B1KO hearts displayed significantly less membrane recruitment of both PDE4D5 and PDE4D3 compared to B1KO hearts, as evidenced by western blotting in cardiac membrane preparations, indicating less β2AR-PDE4D interaction. Thus, cardiac GRK2 inhibition by GRK2ct increases β2AR-dependent contractility both normally and in post-MI heart failure. The underlying mechanism appears to involve inhibition of the GRK2/βarr-mediated PDE4D recruitment to the receptor.
- © 2011 by American Heart Association, Inc.