A have been described as a normal response of the adult heart to damage [5]. Other acquired cardiac diseases like dilated cardiomyopathy are also characterized by fibrotic disorders [6].As already indicated, adult CICs are a heterogeneous population of cells [7]. The phenotypes of CICs range from the characteristic spindle-shaped profile of cardiac fibroblasts (CF) to the more spherical aspect of resident cardiac progenitor/stem cells [8]. From a molecular standpoint, CICs have been phenotyped and classified into different categories by the expression of fibroblastic markers like DDR-2, FSP-1, HSP47, collagen-I [9,10]; stemness markers such as c-Kit, CD34, or Sca-1 [11?5]; or molecules classically related to cardiac embryonic progenitors like Islet 1 (Isl1) or Gata4 [16,17]. The origin of CICs is also known to be diverse, as reported sources for these cells include bone marrow-derived circulating cells, perivascular cells, the endothelium/endocardium, and the epicardium [3,7]. Interestingly, only the epicardium shows a very early and persistent contribution to the cardiac interstitium, starting around midgestation [7,17?9]. The embryonic epicardium is an important Finafloxacin web tissue in cardiac development. It originates from the proepicardium, a cluster of coelomic cells at the caudal end of the developing heart (E9.0?.5 in the mouse). Proepicardial cells are transferred to the myocardial surface, where they attach and spread forming a continuousEpicardial-Derived Interstitial Cellsmonolayered epithelium, the epicardium [20]. While the epicardial epithelium forms, an epithelial-to-mesenchymal Etrasimod transition (EMT) is initiated, so that part of epicardial epithelial cells transform into a population of mesenchymal, highly invasive, epicardium-derived cells (EPDCs). Therefore, the proepicardialepicardial-EPDC transition should be considered as an anatomical and developmental continuum. EPDCs differentiate into coronary endothelial and smooth muscle cells [19,21?3], and interstitial fibroblasts both in vivo and in vitro [18,24,25]. Cardiomyocyte differentiation from epicardial progenitors has only been fully confirmed in vitro [24,26], being the in vivo differentiation scenario still under debate [17,27,28]. Taken together, these results suggest that cells in the epicardial lineage could indeed have multipotent properties [24,29,30]. Despite the biomedical importance of CICs, not many reports have characterized these cells as related to their embryonic origin. This approach is most relevant, as our knowledge on the biology of the embryonic sources of CICs can provide clues to understand the responses of the adult interstitium to stress or pathological conditions (e.g. myocardial ischemia). Since the number of EPDCs that can be retrieved from the embryo is really limited, the use of a tool such as a stable cell line is necessary for detailed molecular and experimental analyses. The main goal of this work is to analyze CICs of epicardial origin using a continuous cell line of epicardium-derived interstitial cells (EPIC) as a model, also comparing its properties to those of native epicardial embryonic derivatives. Our work provides data suggesting that the multipotent properties of cells in the embryonic epicardial lineage are progressively lost throughout development, and accordingly the EPIC line represents a post-EMT EPDC that can differentiate into myofibroblast-like (smooth muscle-like) and fibroblastic cells, but not into myocardial or endothelial cell.A have been described as a normal response of the adult heart to damage [5]. Other acquired cardiac diseases like dilated cardiomyopathy are also characterized by fibrotic disorders [6].As already indicated, adult CICs are a heterogeneous population of cells [7]. The phenotypes of CICs range from the characteristic spindle-shaped profile of cardiac fibroblasts (CF) to the more spherical aspect of resident cardiac progenitor/stem cells [8]. From a molecular standpoint, CICs have been phenotyped and classified into different categories by the expression of fibroblastic markers like DDR-2, FSP-1, HSP47, collagen-I [9,10]; stemness markers such as c-Kit, CD34, or Sca-1 [11?5]; or molecules classically related to cardiac embryonic progenitors like Islet 1 (Isl1) or Gata4 [16,17]. The origin of CICs is also known to be diverse, as reported sources for these cells include bone marrow-derived circulating cells, perivascular cells, the endothelium/endocardium, and the epicardium [3,7]. Interestingly, only the epicardium shows a very early and persistent contribution to the cardiac interstitium, starting around midgestation [7,17?9]. The embryonic epicardium is an important tissue in cardiac development. It originates from the proepicardium, a cluster of coelomic cells at the caudal end of the developing heart (E9.0?.5 in the mouse). Proepicardial cells are transferred to the myocardial surface, where they attach and spread forming a continuousEpicardial-Derived Interstitial Cellsmonolayered epithelium, the epicardium [20]. While the epicardial epithelium forms, an epithelial-to-mesenchymal transition (EMT) is initiated, so that part of epicardial epithelial cells transform into a population of mesenchymal, highly invasive, epicardium-derived cells (EPDCs). Therefore, the proepicardialepicardial-EPDC transition should be considered as an anatomical and developmental continuum. EPDCs differentiate into coronary endothelial and smooth muscle cells [19,21?3], and interstitial fibroblasts both in vivo and in vitro [18,24,25]. Cardiomyocyte differentiation from epicardial progenitors has only been fully confirmed in vitro [24,26], being the in vivo differentiation scenario still under debate [17,27,28]. Taken together, these results suggest that cells in the epicardial lineage could indeed have multipotent properties [24,29,30]. Despite the biomedical importance of CICs, not many reports have characterized these cells as related to their embryonic origin. This approach is most relevant, as our knowledge on the biology of the embryonic sources of CICs can provide clues to understand the responses of the adult interstitium to stress or pathological conditions (e.g. myocardial ischemia). Since the number of EPDCs that can be retrieved from the embryo is really limited, the use of a tool such as a stable cell line is necessary for detailed molecular and experimental analyses. The main goal of this work is to analyze CICs of epicardial origin using a continuous cell line of epicardium-derived interstitial cells (EPIC) as a model, also comparing its properties to those of native epicardial embryonic derivatives. Our work provides data suggesting that the multipotent properties of cells in the embryonic epicardial lineage are progressively lost throughout development, and accordingly the EPIC line represents a post-EMT EPDC that can differentiate into myofibroblast-like (smooth muscle-like) and fibroblastic cells, but not into myocardial or endothelial cell.
