Abstract 18109: β-Arrestins Regulate Collagen Synthesis in Human Cardiac Fibroblasts via GPCR-Dependent and Independent Signaling

Abstract

End-stage heart failure (HF) is characterized by high levels of circulating catecholamines to increase cardiac output and uncoupling of cardiac β-adrenergic receptors (β-ARs). β-arrestins are scaffold signaling molecules that also play a key role in G protein-coupled receptor (GPCR) desensitization, but also have other G protein independent functions including activation of MAPK signaling. This study investigates a potential novel role of β-arrestins in regulating cardiac fibroblasts (CF) biology and myocardial fibrosis which can lead to HF. Both isoforms of β-arrestins expressed in the heart, β-arrestin1 and 2 are upregulated in failing CF versus normal controls. This is a primary mechanism for impaired β-AR signaling as basal and β-agonist-stimulated cAMP production is much lower in the failing CF and there is loss of the β-agonist-mediated inhibition of collagen synthesis in the failing cells. siRNA-mediated knockdown of β-arrestins in failing CF led to decreased α-SMA and fibronectin expression indicative of a reversal from the activated myofibroblast phenotype to the normal quiescent state. β-arrestin knockdown also restored CF β-AR signaling as measured by β-agonist-stimulated cAMP production as well as β-agonist-stimulated inhibition of collagen synthesis. Overexpression of either β-arrestin1 or 2 in normal control CF uncoupled β-AR signaling and blunted the inhibition of collagen synthesis by β-agonist stimulation. To investigate potential non-GPCR effects of β-arrestins in CF, cells were treated with TGF-β. Knockdown of β-arrestin1 or 2 in failing CF significantly inhibited TGF-β-stimulated collagen synthesis and expression of collagen I and III were decreased under both basal conditions and with TGF-β. Pre-treatment of these CF with the pharmacological ERK inhibitor, UO126, abolished Smad phosphorylation in the setting of β-arrestin overexpression and inhibited TGF-β-stimulated collagen synthesis. Both of these isoforms of β-arrestin play a significant role in CF transformation and regulating collagen synthesis via GPCR-dependent and independent signaling pathways. Targeted inhibition of β-arrestins in CF may represent a novel therapeutic strategy to prevent pathological myocardial fibrosis and progression to HF.