Abstract 449: GRK2-S670A Mice Reveal Cardioprotection Post Ischemia-reperfusion

Abstract

β-adrenergic receptors (βARs) are critical regulators of cardiac contractility whose function are drastically impaired during heart failure (HF). Activated βARs are regulated via phosphorylation by G-protein coupled receptor kinase-2 (GRK2) and subsequent interaction with β-arrestin. Numerous studies have shown that GRK2 is elevated in human HF and animal models demonstrate that it contributes to HF pathogenesis after ischemic injury (IR). Further, our lab has uncovered non-canonical actions of GRK2 that are involved in HF development. One such novel action of GRK2 is within mitochondria where we have shown increased GRK2 localization after oxidative stress. Our lab has shown that in the heart, phosphorylation of GRK2 via Map kinase at residue Ser670 promotes binding to Hsp90 and further enhances translocation of GRK2 to the mitochondria after oxidative stress such as ischemia. To determine the ultimate role of this pathway in the post-ischemic heart we have generated novel GRK2-S670A mice where all endogenous GRK2 cannot be phosphorylated at this residue. Baseline characterization of these mice along with their controls, show a minimal phenotype, however we have found significant differences post-IR. Compared to control mice (NLC), GRK2-S670A have significantly less infarction size 24 hrs after IR and echocardiography and hemodynamics revealed significantly improved cardiac function in GRK2-S670A mice post-IR. GRK2-S670A mice showed improved ejection fraction (52.83%+/- 2.826 S670A vs 42.38%+/- 1.603 NLC) and smaller infarcted areas (9.942%+/- 1.763 S670A vs 20.78%+/- 3.579 NLC) when compared to NLC mice. Further, we found that mitochondrial GRK2 protein levels were lower in the GRK2-S670A mice at the area at risk (0.1428+/-0.02485 S670A vs 0.2327+/- 0.023 NLC). Overall, our data suggest that phosphorylation at Ser670 of GRK2 might act as a “biological switch” in cardiomyocytes, where un-phosphorylated GRK2 is readily available in the cytoplasm to desensitize receptors such as βARs, but upon phosphorylation, GRK2 translocates to the mitochondria leading to detrimental effects including cell death. This mechanism suggests a novel way to develop pharmacological interventions to aid in the treatment of HF.