Abstract 516: GRK5 Regulates Cardiac Fibroblast Differentiation and Fibrosis

Abstract

Pathological remodeling of the heart is a hallmark of heart failure (HF) and these structural changes further perpetuate the disease. Cardiac fibroblasts are the critical cell type that is responsible for maintaining the structural integrity of the heart. Stress conditions, such as a myocardial infarction (MI), can activate and induce the transdifferentiation of quiescent fibroblasts into synthetic and contractile myofibroblasts. G protein-coupled receptor (GPCR) kinases (GRKs) are important mediators of cardiovascular homeostasis through dampening of GPCR signaling. GRK5 is one isoform of these kinases that is expressed in the heart and has been shown to be up-regulated in human HF. Of note, GRK5 has been demonstrated to translocate to the nucleus in cardiomyocytes in a calcium-calmodulin (Ca 2+ -CAM)-dependent manner, promoting hypertrophic gene transcription through activation of NFAT and NFκB. Interestingly, these transcription factors are also involved in fibroblast activation. GRK5 is highly expressed and active in cardiac fibroblasts (CFs), however its pathophysiological role in these crucial cardiac cells is unknown. Utilizing adult mouse CFs in vitro , our preliminary data suggests a relevant role for GRK5 in the activation of fibroblasts. We observed that genetic deletion of GRK5 (GRK5KO) in CFs attenuated α-smooth muscle actin (α-SMA) expression, a myofibroblast marker, after stimulation with Angiotensin II (AngII). In addition, deletion of GRK5 diminished the expression of myofibroblast genes and proteins such as Collagen I and III after AngII stimulation. GRK5KO CF’s were also refractory to AngII mediated collagen gel contraction and protein translation. In vivo , mice with fibroblast-specific deletion of GRK5 were protected against cardiac fibrosis and hypertrophy after AngII infusion and post-MI compared to wild type mice. Mechanistically, GRK5 translocates to the nucleus after AngII stimulation and pharmacological inhibition of this event (via inhibition of Ca 2+ -CAM) prevented AngII mediated fibroblast transdifferentiation. These data support the hypothesis that GRK5 is an essential regulator of fibroblast activation and could be a novel therapeutic target to decrease adverse myocardial remodeling after injury.