Abstract 3509: Inhibition of G-Protein Coupled Receptor Kinase-2 Protects From Myocardial Ischemia-Reperfusion Injury via an Anti-Apoptotic Effect
Morbidity and mortality of acute myocardial infarction remains significant, with resultant left ventricular systolic function presenting a major determinant of clinical outcome. Activation of pro-survival kinases such as AKT have been proven to pose powerful targets for cardiopro-tection in ischemia-reperfusion injury (I/R) models. G-protein-coupled receptors can confer cardioprotection by activating AKT signaling. The carboxyl-terminus of GRK2 (βARKct) has been shown to have beneficial effects in heart failure by inhibiting G-protein coupled receptor kinase 2 (GRK2), leading to improved cardiac performance. This study elucidates a deleterious effect of increased GRK2-activity in the model of myocardial I/R and rescue via βARKct. Non-transgenic littermate controls (NLC) and myocardial-specific βARKct-expressing or GRK2-transgenic mice were subjected to I/R. Neonatal ventricular cardiomyocytes (NVCM) overexpressing βARKct or GRK2 were subjected to oxidative stress via H2O2 stimulation. Infarct size was measured by triphenyltetrazoliumchloride staining and myocardial apoptosis was assessed with TUNEL staining and Caspase-3 cleavage assay in vitro and in vivo. Protein expression reflecting AKT phosphorylation was measured in NVCMs after H2O2 treatment and the ischemic area at 4 hours after I/R. Infarct size was enlarged in GRK2 overexpressing mice (45.0±2.8%) compared to controls (31.3±2.3%), βARKct expression reduced it significantly to 16.8±1.3% (p<0.05). Selective blocking of β2-adrenergic receptor signaling abolished the effect in βARKct hearts. Apoptotic index was also significantly decreased in the hearts expressing βARKct compared to increased cell death in GRK2 transgenic mice. These results were reflected by a two-fold higher increase of AKT activation in the bARKct-group compared to the GRK2-overexpressing group in vivo and in vitro. GRK2 overexpression was deleterious in ischemic myocardium whereas inhibition via βARKct was cardioprotective resulting in reduced apoptosis and increased AKT signaling. GRK2 inhibition represents a therapeutic approach reducing acute ischemic injury in the myocardium, thus GRK2 inhibition appears a valuable strategy limiting acute myocardial ischemia.
This research has received full or partial funding support from the American Heart Association, Great Rivers Affiliate (Delaware, Kentucky, Ohio, Pennsylvania & West Virginia).