Abstract 9815: Cardioprotective Effect Of Neuregulin-1 In Myocardial Ischemia-Reperfusion Injury Relies On eNos.

Abstract

Background: The neuregulin-1 (NRG1)/erbB system is an endothelium-controlled paracrine system, which protects the heart during myocardial stress. Subcellular mechanisms of this protection have not been identified. We previously observed that NRG1 activates cardiomyocyte endothelial nitric oxide synthase (eNOS), leading to desensitization of the myocardium for beta-1-adrenergic inotropic effects. In this study, we tested whether eNOS also participates during NRG1-mediated protection against myocardial ischemia-reperfusion (I/R) injury. Methods: C57BL/6 (wild type, WT) and eNOS knockout (KO) mice were pre-treated with rNRG1 (20μ g/kg/d, ip) or vehicle for 3 days. Next, they were subjected to 30 min of ischemia by coronary artery ligation, followed by 4h reperfusion. Sham operated littermates served as control. Investigators were blinded for pre-treatment of mice. Results: Left ventricular (LV) NRG1 expression, erbB2 and erbB4 receptor activity remained unaffected by I/R injury (30min/4h) or by genetic background. rNRG1 significantly increased LV erbB2 and erbB4 phosphorylation in WT and KO mice. I/R injury blunted eNOS phosphorylation in WT mice (-57±15%, p<0,05), which was completely prevented by rNRG1. In WT mice, rNRG1 reduced infarct area by 9±2% as compared to vehicle. In contrast, rNRG1 had no effect on infarct area in eNOS KO mice (= 7/group, p =0.001 for NRG1 treatment, p=0.02 for interaction). Also, in WT but not in eNOS KO mice, rNRG1 increased fractional shortening by 11±4% (p<0.05). Interestingly, rNRG1 reduced polymorphonuclear cell influx into infarct and border zones in WT (157±17 cells/mm 2 in vehicle versus 78±18 cells/mm 2 in NRG1 treated WT mice) but had no effect on polymorphonuclear influx in eNOS KO (144±15 cells/mm 2 in vehicle versus 126±10 cells/mm 2 in NRG1 treated KO mice, p=0.008 for NRG1 treatment, p=0.07 for interaction). Conclusions: An activated NRG1/erbB system prevents blunting of myocardial eNOS phosphorylation during I/R, and attenuates myocardial I/R injury. These events are causally related as indicated by the loss of rNRG1-induced protection in eNOS KO mice.