Abstract 9485: Cardiac G Protein-Coupled Receptor Kinase 2 Knockdown Decreases Ischemia/Reperfusion-Induced Injury and Improves Cardiac Function through Anti-Apoptotic Mechanisms
Background: Studies from our lab have shown that decreasing myocardial G protein-coupled receptor kinase 2 (GRK2) expression or preventing GRK2 activation with an inhibitory peptide (βARKct) can prevent or rescue heart failure after myocardial infarction. In this study we investigated the acute cardiac effects associated with lowered myocyte GRK2 expression in a mouse model of ischemia/reperfusion (I/R) injury.
Methods: Cardiomyocyte-specific GRK2 knockout (KO) mice were used with either GRK2 deleted at birth or inducible GRK2 deletion along with appropriate control mice that included GRK2 floxed mice and αMHC-Cre and MerCreMer mice. All mice were subjected to sham or 30 min myocardial ischemia via coronary artery ligation followed by 24 hrs reperfusion. Cardiac function, infarct size, tissue apoptosis (TUNEL and Caspase activity) and changes in the activation state of various signaling molecules (Akt, GSK3β, ERK, p38, JNK and cytochrome C) were analyzed.
Results: Echo and hemodynamic measurements showed significantly improved post-I/R cardiac function in both lines of GRK2 KO mice with corresponding decreased infarct size compared to control groups. We found that cell death as measured by TUNEL staining was decreased in GRK2 KO mice, a finding that was supported by reduced activity of caspase 3 and 9 and lowered cytosolic cytochrome C levels in GRK2 KO mice (at birth — 0.65±0.04 or inducible – 0.66±0.045) compared to control mice (GRK2 floxed — 0.99±0.07 or MerCreMer — 1.22±0.11). Consistent with the in vivo results, we found that siRNA-silencing of GRK2 in neonatal ventricular myocytes resulted in decreased oxidative stress-induced activation of cleaved caspase-3, confirming the anti-apoptotic effect of lowered GRK2. Finally, following I/R, the activity of pAkt, pGSK3β, p38 and p-ERK were significantly increased in GRK2 KO hearts compared to controls, suggesting that activation of these signaling molecules promoted survival.
Conclusions: Loss of GRK2 expression in cardiomyocytes limits myocardial injury after I/R by decreasing myocyte apoptosis resulting in improved functional recovery acutely. Future experiments will be designed to investigate the mechanistic crosstalk between GRK2 and cell survival pathways.
- © 2010 by American Heart Association, Inc.