Abstract P339: The Mechanistic Relationship Between GRK2 and eNOS During Cardiac Ischemia/Reperfusion Injury

Background: Previous studies have shown that both cardiac-specific GRK2 transgenic (TG) (αMHC-GRK2) mice and eNOS knockout (KO) mice have larger infarcts after I/R compared to control mice. In contrast, cardiac-targeted eNOS TG mice and cardiac specific GRK2 KO mice show cardioprotection after I/R, suggesting a dynamic interaction between the two proteins. Mechanistically, GRK2 can be inhibited by cellular NO through S-nitrosylation with Cys340 being the major site; meanwhile GRK2 has been shown to directly bind to and inhibit Akt, which is a strong activator of eNOS. Aim: to investigate the potential novel interaction between GRK2 and eNOS, and the consequent functional impact on the protein activity and cardiac phenotype after I/R injury. Methods: αMHC-GRK2 mice were crossed with either eNOS TG or eNOS KO mice. All mice were subjected to sham or 30min myocardial ischemia via coronary artery ligation followed by 24hrs of reperfusion. Infarct size, cardiac function, and tissue apoptosis were examined. Co-IP was used to test the interaction between GRK2 and eNOS, and phosphorylation of eNOS was studied in neonatal myocytes. Results: 1).αMHC-GRK2/eNOS TG hybrid mice showed a significantly reduced infarct size after I/R compared to αMHC-GRK2 mice, accompanied by improved cardiac function measured by echocardiography and hemodynamics, and significantly less apoptosis tested by TUNEL assay, implying a rescue effect by eNOS. 2). αMHC-GRK2/eNOS KO mice exhibited a bigger infarct size compared to either αMHC-GRK2 mice or eNOS KO mice. 3). CO-IP confirmed the interaction between GRK2 and eNOS in cardiac tissue, which was increased upon β-AR agonist treatment. 4). In neonatal ventricular myocytes, GRK2 overexpression significantly decreased eNOS phosphorylation at Ser1177 after exposure to H2O2, while GRK2 knockdown by siRNA led to slight increase in pSer1177. Conclusions: eNOS interacts with and may be a downstream target of GRK2 in the heart. Decreased activation of eNOS may mediate the deleterious effect of GRK2 overexpression during cardiac I/R injury.