Abstract 1378: Cardiac-Specific Deletion of GRK2 using Cre-LoxP-Technology
We have previously shown that G protein-coupled receptor kinase 2 (GRK2 or βARK1) is a critical regulator of cardiac β-adrenergic receptor (β-AR) signaling and cardiac function. Inhibition of GRK2 activity can rescue disparate models of heart failure (HF) and we remain interested to determine if loss of GRK2 expression, which is up-regulated in failing myocardium, also is therapeutic. Non-targeted deletion of the GRK2 gene in mice resulted in embryonic lethality, which precluded an analysis of the functional consequences of complete loss of GRK2 in the adult myocardium. To overcome this limitation we have generated mice with cardiac-specific knockout of GRK2 using the Cre/LoxP system. GRK2-loxP-targeted mice (GRK2fl/fl) were crossed with mice containing α-MHC-Cre, which produced viable mice that survived into adulthood. The biochemical and physiological phenotype of these mice were characterized with RT-PCR, immunoblotting, βAR signaling and cardiac function using echocardiography, and left-ventricular hemodymanics. Cardiac-specific deletion of the GRK2 gene at birth resulted in a 65% reduction of GRK2 mRNA (p<0.05) and 77% decline of GRK2 protein (p<0.05) compared to wild-type control mice when comparing whole heart extracts. Normal levels of cardiac GRK3 and GRK5 suggested no compensation for the loss of GRK2 by other GRKs. The deletion of GRK2 was limited to cardiac tissue, as lung and liver revealed normal GRK2 mRNA and protein levels. Echocardiography showed normal baseline contractility compared to control mice (FS 34±1% vs. 31±1%, n.s.) without signs of hypertrophy. Hemodynamic measurements indicate enhanced LV contractile function following stimulation with increasing doses of isoproterenol. Therefore, cardiac specific deletion of GRK2 using Cre/LoxP technology is feasible and produced viable mice that survived into adulthood. The cardiac-specific knockout mouse for GRK2 will serve as a powerful model to further characterize the functional impact of the loss of this GRK in the development and progression of heart failure.