Intramyocardial administration of chimeric ephrinA1-Fc promotes tissue salvage following myocardial infarction in mice

Non-technical summary Following a myocardial infarction, cardiac muscle becomes irreversibly damaged and over time this may lead to heart failure. Strategies to reduce ischaemic damage, enhance new vessel growth, and/or replace damaged heart muscle are currently being investigated. We have identified a novel non-angiogenic role for ephrinA1, a membrane-bound ligand receptor tyrosine kinase, in promoting myocardial tissue salvage after non reperfused myocardial infarction. Treating the heart with this protein at the time of injury reduced infarct size and overall damage, presumably by preventing cardiomyocyte loss after ischaemia. Further studies are in progress to determine the cellular mechanisms by which this occurs and the extent to which adverse remodelling is attenuated.The purpose of this study was to investigate the role of intramyocardial administration of chimeric ephrinA1-Fc in modulating the extent of injury and inflammation in non reperfused myocardial infarction (MI). Our results show that intramyocardial injection of 6 mu g ephrinA1-Fc into the border zone immediately after permanent coronary artery ligation in B6129s mice resulted in 50% reduction of infarct size, 64% less necrosis, 35% less chamber dilatation and 32% less left ventricular free wall thinning at 4 days post-MI. In the infarct zone, Ly6G+ neutrophil density was 57% reduced and CD45+ leukocyte density was 21% reduced. Myocyte damage was also reduced in ephrinA1-Fc-treated hearts, as evidenced by 54% reduced serum cardiac troponin I. Further, we observed decreased cleaved PARP, increased BAG-1 protein expression, increased phosphorylated AKT/total AKT protein, and reduced NF-kappa B protein with ephrinA1-Fc administration, indicating improved cellular survival. Of the eight EphA receptors known to be expressed in mice (A1-A8), RT-PCR revealed that A1-A4, A6 and A7 were expressed in the uninjured adult myocardium. Expression of EphA1-A3 and EphA7 were significantly increased following MI while EphA6 expression decreased. Treatment with ephrinA1-Fc further increased EphA1 and EphA2 gene expression and resulted in a 2-fold increase in EphA4. Upregulation and combinatorial activation of these receptors may promote tissue survival. We have identified a novel, beneficial role for ephrinA1-Fc administration at the time of MI, and propose this as a promising new target for infarct salvage in non reperfused MI. More experiments are in progress to identify receptor-expressing cell types as well as the functional implications of receptor activation.