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.Abstract 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 μg 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-κB 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.

Virag JA, Dries JL, Easton PR, Friesland AM, DeAntonio JH, Chintalgattu V, Cozzi E, Lehmann BD, Ding JM, Lust RM. Attenuation of myocardial injury in mice with functional deletion of the circadian rhythm gene mPer2.

Variations in circadian patterns are evident in the incidence of cardiovascular disease and derangements in normal circadian patterns are demonstrated to precipitate the onset of chronic diseases. “Clock genes” such as Per-1 and -2, Cry-1 and -2, and clock/bmal , are found in all peripheral tissues, including the heart. It is clear that they are involved in synchronization of vascular function and cardiac metabolism however, the downstream effector genes have yet to be identified. To evaluate the function of mPer2 in post-infarct myocardial remodeling, we used an mPer2 mutant mouse which lacks functional mPer2 protein (mPer2-KO). In anesthetized, mechanically ventilated wild-type (WT) and mPer2-KO mice, Myocardial infarction was induced by permanent ligation of the left anterior descending coronary artery. Our data reveal that, although there is no difference in the initial area at risk between the WT and mPer2-KO mouse hearts, at 4 days post-MI there is a 50% reduction of infarct size in mPer2-KO mice compared to WT. This is coincident with a 40% increase in vascular density, 25% less macrophage infiltration, and 34% less apoptosis in the infarct zone. Cytokine array analysis showed 3-fold increase in IGFBP-3 and -5 and a 90% increase in SDF-1α, IL12p70, and lymphotactin in mPer2-KO relative to WT at 4 days post-MI. Conversely, in mPer2-KO the levels of L-selectin, sTNFRII, and IL-6 were approx. 70% less than the WT. These data suggest that mice lacking mPer2 protein have enhanced activation of anti-apoptotic and hypertrophic pathways, augmented chemotaxis for reparative cells, and blunted production of adverse inflammatory mediators post-MI. We conclude that deletion of the mPER2 gene is cardioprotective. Further mechanistic studies are being conducted to understand the signaling pathways that afford this protection. Long-term studies are also in progress to determine the duration of these protective effects and whether cardiac function is altered. Understanding the complex interactions between circadian rhythms and cardiovascular disease may provide insights into potential preventative and therapeutics for susceptible populations.