Abstract 295: Enhanced Cardiac Function And Lower Circulating Aldosterone Levels In βArrestin1 Knockout Mice During Post-myocardial Infarction Heart Failure Progression

Introduction: Chronic heart failure (HF) is characterized by enhanced circulating cardiotoxic hormones, among the most prominent of which is aldosterone, which contributes to the increased morbidity and mortality of the disease by promoting cardiac adverse remodeling post-myocardial infarction (MI). Cardiac β-adrenergic receptor (ΑR) desensitization and downregulation are a hallmark abnormality in HF at the molecular level and are due to the concerted action of cardiac G protein-coupled receptor kinase-2 (GRK2), together with its co-factors in receptor desensitization, the βarrestins (βarrs). We have also recently established that βarr1 promotes angiotensin II-dependent aldosterone production in the adrenal cortex, and this leads to elevated circulating aldosterone levels in vivo, both under normal conditions and during post-MI HF progression. Hypothesis: Herein, we sought to investigate the effects of genetically deleting βarr1 on post-MI cardiac function and hyperaldosteronic status in mice progressing to HF. Methods: We uitilized the βarr1KO mouse model and studied these mice at 4 weeks after surgically induced MI, in parallel with C57/B6 wild type (WT) controls. Cardiac function was assessed by echocardiography and in vivo catheterization. Plasma aldosterone was measured by ELISA. Results: Cardiac function is markedly improved in βarr1KO`s at 4 weeks post-MI, as evidenced by increased ejection fraction compared to WT mice (41.5 + 2.8 % vs. 21.8 + 2.4 %, respectively, n=9, p<0.0001) and increased isoproterenol-induced contractility. Additionally, cardiac dimensions are significantly reduced compared to WT`s, indicating attenuation of adverse cardiac remodeling. Importantly, plasma circulating aldosterone levels are significantly lowered and cardiac βAR signaling and function appear elevated in post-MI βarr1KO`s compared to control WT`s. Conclusions: Genetic deletion of βarr1 substantially improves cardiac function, adverse remodeling, hyperaldosteronism, and cardiac βAR function during post-MI HF progression. The underlying mechanism is attenuation of both cardiac βAR desensitization/downregulation and adrenal aldosterone production, which is βarr1-dependent.