Abstract 16375: eNOS-Phosphorylation Regulates Myocardial Perfusion and the Outcome of Ischemic Postconditioning
Introduction: Endothelial nitric oxide synthase (eNOS) is an important regulator of myocardial ischemic postconditioning (IPOC). There is evidence suggesting that IPOC induces cardioprotection by phosphorylation of eNOS through the PI3K-Akt pathway. We previously reported that mice expressing a phosphomimetic S1176D form of eNOS show improved vascular reactivity and less severe cerebral ischemia. S1176D eNOS mutant mice carry knock-in mutations (serine to aspartate substitution) that render eNOS ‘constitutively active’. In the present study we tested the hypothesis that eNOS phosphorylation is an important determinant of myocardial perfusion and infarct-size during myocardial ischemia-reperfusion injury.
Methods: 10-12 week old C57BL6/J, eNOS knockout and S1176D knockin mice were subjected to 45 mins of myocardial ischemia followed by reperfusion. Mice were randomly divided into 2 groups receiving ischemia with reperfusion (IR) or ischemia with IPOC (six cycles of 10sec reperfusion separated by 10sec of no-flow ischemia). TTC-staining was used to determine infarct size at 24 hours and protein levels of p-eNOS (at Ser 1176) were measured in heart tissue by western blot. Myocardial perfusion was obtained by myocardial contrast echocardiography (MCE) and replenishment curves were obtained using a custom shape-based snake model for automatic segmentation of the left ventricular wall.
Results: IPOC treatment in C57 mice improved myocardial blood flow 30 mins after reperfusion in the apical anteroseptal region from 19±3% in IR mice to 40±4% in IPOC mice (expressed as % of blood flow before ischemia). IPOC reduced infarct size (% Inf/AAR) in C57 mice (54±4% in IR vs. 23±5% in IPOC groups) and increased protein expression of p-eNOS (Ser 1176). The effects of IPOC were abolished in IR and IPOC treated eNOS knockout mice (53±3% and 59±2% respectively) while both S1176D IR and IPOC groups showed reduced infarct sizes (18±2% and 23±5% respectively).
Conclusions: These findings show that phosphorylation of eNOS at S1176 has cardioprotective effects on IR injury in vivo. Our data supports the notion that the p-eNOS pathway is involved in the IPOC protection and that improved myocardial perfusion may play an important role in reducing myocardial infarct size.
- © 2011 by American Heart Association, Inc.