Myocardial regeneration after embryonic cryoinjury influenced by epicardium

Abstract

One of the unexplored topics of medicine that could significantly affect the treatment of myocardial infarction is the regenerative potential of the epicardium. The embryonic epicardium is the outermost layer of the heart, which undergoes epithelial-to-mesenchymal transformation, contributing cells for formation of coronary vasculature and valves. It is also a source of paracrine cues that are essential for fetal cardiac growth, coronary vessel patterning, and regenerative heart repair.We have modified an established model of early embryonic transmural myocardial cryoinjury by performing it at the stage, where the heart is already covered by the epicardium.We induced myocardial injury by cryoprobe on ventricle of avian embryos (chicken and quail) at HH stage 21. Embryos were then re-incubated until HH31. We analyzed myocardial regeneration electrophysiologically by epicardial optical mapping, and morphologically by immunohistochemical markers.Morphological analysis confirmed changes in the epicardial region. As a result of the cryoinjury, the epicardium was wrinkled, detached, and thus the subepicardial area increased. In the subepicardium we detected many cells participating in the epithelial-mesenchymal transition (positive for α-SMA, WT1, N2.261, CK). Regenerative potential was also confirmed by increased neovascularization (QH1+) or proliferation (EdU+) after cryoinjury. Functional analysis shows temporal loss of epicardial activation in the cryoinjury zone, but heart activation was restored within four days.Our study confirmed the importance of the epicardium in the healing of myocardial injury, increased neovascularization, and cell proliferation, which led to restoration of the electrical conduction. Myocardial healing was complete and without a fibrotic scar. This could be potentially used for devising novel regenerative strategies in humans, where properly activated epicardium may repair myocardial infraction.