Abstract P224: β-arrestin2 Stimulates SERCA2a SUMOylation and Activity in Cardiac Myocytes to Promote Contractility

Abstract

Background: Heart failure (HF) is the most lethal disease worldwide and new treatments are needed. The β 1 -adrenergic receptor (AR) mediates the positive inotropy of catecholamines, partly via Sarco(Endo)plasmic Reticulum Ca 2+ -ATPase (SERCA)-2a activation. Agonist-activated β 1 ARs, however, are desensitized/downregulated in human HF due to the actions of the βarrestins (βarrestin1 and 2). βarrestins are GPCR adapter proteins and signal transducers. βarrestin1 is by far the predominant isoform in the heart and reduces contractility by desensitizing the β 1 AR, whereas βarrestin2 is expressed at negligible levels and is beneficial post-myocardial infarction (MI), as it combats inflammation and apoptosis. Herein, we sought to investigate whether cardiac βarrestin2 exerts any inotropic effects. Methods: We used βarrestin knockout (KO) mouse hearts and also performed intra-cardiac adenoviral gene transfer of βarrestin2 (Adβarrestin2) in post-MI mice in vivo. For mechanistic signaling studies we used the cardiomyocyte cell line H9c2. Results: SERCA2a SUMO (small ubiquitin-like modifier)ylation and activity and, consequently, cardiac contractility were increased in βarrestin1 KO`s vs. WT`s post-MI. The opposite was true for βarrestin2 KO`s post-MI. Additionally, βarrestin2, but not βarrestin1, was found to directly bind SERCA2a and induce its SUMOylation and activation in mouse hearts in vivo, as well as in cardiomyocytes in vitro acutely in response to β 1 AR stimulation. Interestingly, βarrestin2 did not affect the classic β 1 AR cAMP-dependent pro-contractile signaling pathway in cardiomyocytes, again contrary to βarrestin1. Importantly, and consistent with these findings, Adβarrestin2 gene transfer in post-MI mouse hearts in vivo resulted in enhanced cardiac function (post-MI ejection fraction of Adβarrestin2 vs. control (AdGFP) mice: 40.3 + 1.3% vs. 23.1 + 1.2%, respectively, p<0.05, n=5). Conclusions: Cardiac β 1 AR-activated βarrestin2, but not βarrestin1, promotes SERCA2a SUMOylation and activity, increasing cardiac contractility. Given also its anti-inflammatory and anti-apoptotic effects post-MI, cardiac-specific βarrestin2 gene transfer may be a novel and safe inotropic therapy for both acute and chronic HF.