THE ROLE OF G PROTEIN-COUPLED RECEPTOR KINASE 4 IN CARDIOMYOCYTE INJURY AFTER MYOCARDIAL INFARCTION

Abstract

Objective: G-protein-coupled receptor kinase 4 (GRK4) has been reported to play a regulatory role in hypertension, but little is known of its role in cardiomyocytes and myocardial infarction (MI). The goal of present study is to explore the role of cardiac-restricted GRK4 overexpression in the pathogenesis and progression of MIDesign and method: GRK4 WT/ A486 V transgenic mice and GRK4 cardiac specific knocked out mice were generated and subjected to MI surgery. Then the survival, scar size, cardiac function and cardiomyocyte apoptosis were examined. The LC3 B protein level and GFP-LC3B were assessed to determine the autophagic activity in different groups. The phosphorylation resistant mutant HDAC4 S3A were used to investigated the how GRK4 affect autophagy. Con-focal microscope and co-immunoprecipitation were performed to reveal the interaction between GRK4 and HDAC4. We also investigated the cardiac function of MI patient between GRK4 WT and A486 V carrier. Results: The mRNA and protein expressions of GRK4 were increased in heart tissue injured by MI injury. Mice with cardiac overexpression of human GRK4 wild-type or human GRK4–486A > V were vulnerable to MI, evidenced by exaggerated cardiomyocyte apoptosis and cardiac dysfunction and remodeling. By contrast, the MI-induced cardiac dysfunction and remodeling were reduced in GRK4 knockout mice. GRK4 overexpression in cardiomyocytes had aggravated apoptosis, decreased autophagy, and decreased beclin1 expression, which were ameliorated by the autophagy agonist rapamycin. MI also induced the nuclear aggregation of GRK4. GRK4 inhibited autophagy by decreasing HDAC4 nuclear localization. A constitutively nuclear-localized mutant HDAC4 S3A partially restored the GRK4-induced inhibition of autophagy. Patients with MI carrying the constitutively active GRK4 486A > V variant had greater impairment of cardiac function than wild-type carriers. Conclusions: GRK4 increases cardiomyocyte injury caused by MI by inhibiting autophagy and promoting cardiomyocyte apoptosis. These GRK4 effects are mediated by phosphorylation of HDAC4 and a decrease in beclin1 expression.