GRK2-S670A Mice reveal cardioprotection post ischemia-reperfusion

Abstract

Background: 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. Animal and human studies have shown that GRK2 is elevated in HF pathogenesis. In addition to GRK2 being involved in pathological βAR our lab has uncovered non-canonical actions of this kinase 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 ischemia. Methods: To determine the ultimate role of this pathway in the post-ischemic heart we have developed and generated novel GRK2-S670A knock-in mice where all endogenous GRK2 cannot be regulated by phosphorylation at this residue. Baseline characterization of these mice show a minimal phenotype, however we have found significant differences after ischemia-reperfusion (I/R) injury. Results: Compared to control mice (WT) expressing wild-type GRK2, GRK2-S670A mice have significantly less infarction size and improved cardiac function post-24h I/R. GRK2-S670A showed improved ejection fraction post-IR (53.56%+/- 2.08 S670A vs 42.38%+/- 1.6 WT) and smaller infarcted areas (13.67%+/- 1.976 S670A vs 20.78%+/- 3.579 WT) when compared to control mice. Further, we found that mitochondrial GRK2 protein levels were lower in the GRK2-S670A mice at the area at risk post I/R when compared to WT mice (0.8103 +/- 0.1458 S670A vs 1.610 +/- 0.1983 WT). Conclusion: Overall, our data suggest that phosphorylation at Ser670 of GRK2 promotes translocation 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.