Cardiac stem cells in adult human heart originate from epithelial-mesenchymal transition of epicardial mesothelium.

Recently, the presence of numerous cardiac stem cells in the subepicardium of the adult human heart has been described. Hence, we assessed the hypothesis that epithelial-mesenchymal transition (EMT) takes place in the adult human heart and investigated a possible link between epicardium, epicardially-derive cells (EPDCs) and cardiac stem cells. Fragments of adult human normal (n = 11) and pathological hearts with ischemic cardiomyopathy (n= 20) were examined by immunohistochemistry. In the normal hearts, cells positive for epithelial markers, cytokeratin-5/6, β-catenin, Bves, were confined to epicardium. In contrast, rare positive cells were distributed throughout the subepicardium in the pathological hearts. Noticeably, cells were absent from epicardium of diseased hearts. RT-PCR analysis of mRNA revealed that the expression of E-cadherin, cytokeratin 5, and BVES was significantly higher in the normal hearts, while that of mesenchymal markers, M-cadherin, Tie-2, and vimentin was predominant in the hearts with ischemic cardiomyopathy. Toluidine blue staining excluded that EPDCs can be CD117(+) mast cells. Next, we cultured the fragments of epicardium from the normal hearts on the specific substrate formed by extracellular matrix produced by cardiac fibroblasts in vitro, thus obtaining the outgrowth of cells with preserved epithelial phenotype. TGFβ induced cellular and molecular changes typical of epithelial-mesenchymal transition, which were confirmed by morphological study, immunofluorescence and RT-PCR. In particular, the expression of E-cadherin and cytokeratin-5 in EPDCs diminished 2.27-fold and 5-fold, respectively. Moreover, mesenchymal gene RT-PCR products of vimentin and M-cadherin were readily detected, with the 1.84-fold increase of the latter. Interestingly, 32±1.8%; of EPDCs were CD117(+). These cells expressed markers of cardiomyocyte, endothelial and smooth muscle cell cardiac progenitors and precursors.In conclusion, our results provide evidence that cardiac stem cells originate from epicardial cells which undergo EMT in the adult human heart. EPDCs can be promising candidates for clinical application in ischemic hearts – the more so considering that a subset of them represents cardiac CD117(+) stem cells.