Alyzed the phenotype and properties of the epicardium-derived component of cardiac interstitial cells (CICs). We have focused our research on this CIC subpopulation for three different reasons. First, because embryonic epicardial mesenchymal derivatives (EPDCs) pioneer the colonization of the cardiac interstitial space, remaining as part of the cardiac interstitium throughout adulthood [17,18,26,32?4]. Since the cardiac interstitium becomes more complex with time, interstitial cells of epicardial origin are likely to be involved in the progressive recruitment of cells from different origins to the cardiac interstitium. Second, EPDCs are known to invade multiple cardiac tissues, differentiating into a variety of cell kinds [18,19,35,36]. This phenomenon requires the active migration of EPDCs, and thus the activation of efficient mobilization andproteolytic programs. Third, some EPDCs have been shown to differentiate into CFs [18], a cell type responsible for the fibrotic ventricular remodeling that follows chronic cardiac infarction. Due to the complex biology of CICs (including CFs), new in vitro models to study the diversity and behavior of these cells under normal and pathologic conditions are needed. Other works have reported the use of epicardial continuous cell lines derived from neonatal rat epicardium [37,38] or mouse embryonic epicardium [39,40]. However, in most cases, these cell lines retain a full epithelial phenotype and are a poor model for epicardial mesenchymal derivatives, which display unique migratory and proteolytic properties. Our work uses a new immortalized embryonic epicardial cell line derived from ED11.5 24272870 mouse hearts (EPIC). Original embryonic epicardial epithelial cells explanted in vitro continuously proliferate and expand, acquiring a characteristic mesenchymal phenotype and expressing known mesenchymal markers like Sox9. We have however identified in our cell line a few, small clones of cells that display an epithelial-like phenotype (Pan-Cadherin+, ZO-1+) (Fig. 1). The appearance of such cells can be the result of the immortalization procedure, but also illustrate a dynamic phenotypical plasticity between embryonic epicardial epithelial cells and their mesenchymal derivatives. Since embryonic (pro)epicardial cells have been reported to differentiate into various cell types [18,19,24], and thus suggested to be multipotent [29], we have evaluated the differentiation potential of the EPIC line. In order to do so, we have first compared EPICs with epicardial progenitor cells (proepicardium) and E11.5 embryonic epicardial cells to screen the differentiation potential of the cells along the proepicardial-epicardial-EPDC developmental continuum. Mouse epicardial progenitor cellsEpicardial-Derived Interstitial CellsFigure 4. EPIC cell surface marker expression (FACS). EPIC expression of cell surface markers was evaluated by flow POR8 site cytometry. Additional FACS analyses on ephrin and Eph receptors can be found in Fig. S4. doi:10.1371/Sudan I site journal.pone.0053694.g(proepicardial cells) are shown to differentiate into endothelial and smooth muscle cells, cardiomyocytes and fibroblasts. In contrast, cultured E11.5 epicardial cells and EPICs only express markers for smooth muscle cells (a-SMA) and fibroblasts (FSP1), and seem to have lost their potential to spontaneously differentiate into endothelial cells (CD31) or cardiomyocytes (MF20) in vitro. These data could be interpreted as the result of a progressive restriction of the dev.Alyzed the phenotype and properties of the epicardium-derived component of cardiac interstitial cells (CICs). We have focused our research on this CIC subpopulation for three different reasons. First, because embryonic epicardial mesenchymal derivatives (EPDCs) pioneer the colonization of the cardiac interstitial space, remaining as part of the cardiac interstitium throughout adulthood [17,18,26,32?4]. Since the cardiac interstitium becomes more complex with time, interstitial cells of epicardial origin are likely to be involved in the progressive recruitment of cells from different origins to the cardiac interstitium. Second, EPDCs are known to invade multiple cardiac tissues, differentiating into a variety of cell kinds [18,19,35,36]. This phenomenon requires the active migration of EPDCs, and thus the activation of efficient mobilization andproteolytic programs. Third, some EPDCs have been shown to differentiate into CFs [18], a cell type responsible for the fibrotic ventricular remodeling that follows chronic cardiac infarction. Due to the complex biology of CICs (including CFs), new in vitro models to study the diversity and behavior of these cells under normal and pathologic conditions are needed. Other works have reported the use of epicardial continuous cell lines derived from neonatal rat epicardium [37,38] or mouse embryonic epicardium [39,40]. However, in most cases, these cell lines retain a full epithelial phenotype and are a poor model for epicardial mesenchymal derivatives, which display unique migratory and proteolytic properties. Our work uses a new immortalized embryonic epicardial cell line derived from ED11.5 24272870 mouse hearts (EPIC). Original embryonic epicardial epithelial cells explanted in vitro continuously proliferate and expand, acquiring a characteristic mesenchymal phenotype and expressing known mesenchymal markers like Sox9. We have however identified in our cell line a few, small clones of cells that display an epithelial-like phenotype (Pan-Cadherin+, ZO-1+) (Fig. 1). The appearance of such cells can be the result of the immortalization procedure, but also illustrate a dynamic phenotypical plasticity between embryonic epicardial epithelial cells and their mesenchymal derivatives. Since embryonic (pro)epicardial cells have been reported to differentiate into various cell types [18,19,24], and thus suggested to be multipotent [29], we have evaluated the differentiation potential of the EPIC line. In order to do so, we have first compared EPICs with epicardial progenitor cells (proepicardium) and E11.5 embryonic epicardial cells to screen the differentiation potential of the cells along the proepicardial-epicardial-EPDC developmental continuum. Mouse epicardial progenitor cellsEpicardial-Derived Interstitial CellsFigure 4. EPIC cell surface marker expression (FACS). EPIC expression of cell surface markers was evaluated by flow cytometry. Additional FACS analyses on ephrin and Eph receptors can be found in Fig. S4. doi:10.1371/journal.pone.0053694.g(proepicardial cells) are shown to differentiate into endothelial and smooth muscle cells, cardiomyocytes and fibroblasts. In contrast, cultured E11.5 epicardial cells and EPICs only express markers for smooth muscle cells (a-SMA) and fibroblasts (FSP1), and seem to have lost their potential to spontaneously differentiate into endothelial cells (CD31) or cardiomyocytes (MF20) in vitro. These data could be interpreted as the result of a progressive restriction of the dev.
