Abstract P290: RhoA Protects Against Myocardial Ischemia/Reperfusion Injury

Abstract

The small GTPase RhoA has established effects on cytoskeletal dynamics and gene expression but its role in regulating cardiac physiology and disease remains elusive. To characterize the in vivo role of RhoA signaling in cardiomyocytes, we generated conditional cardiac-specific RhoA transgenic mice (CA-RhoA) with 2–5 fold increases in RhoA activation in the adult heart. CA-RhoA mice show no overt cardiomyopathy but when challenged by in vivo or ex vivo I/R, these mice exhibit strikingly increased tolerance to injury. Compared to control mice, myocardial infarct size in CA-RhoA mice is reduced by 60–70% (20% vs. 50%, ex vivo; 10% vs. 37%, in vivo) and recovery of contractile function is significantly improved. Protein kinase D (PKD) is robustly activated in CA-RhoA hearts and inhibiting PKD reverses the cardioprotection afforded by RhoA. Both RhoA and PKD are also activated during I/R and blocking PKD augments I/R injury in WT mouse hearts. To further confirm that RhoA and PKD play a protective role during I/R, cardiac-specific RhoA knockout mice generated in the Molkentin laboratory were tested and demonstrated to show decreased tolerance to I/R injury, manifests as increased infarct size (42% vs. 23%) and lactate dehydrogenase release relative to control mice. This was accompanied by attenuated PKD activation during I/R. Taken together, our data indicates that RhoA signaling in adult cardiomyocytes promotes survival and reveals an unexpected role of PKD as a downstream mediator of RhoA and on cardioprotection against I/R.