Three weeks of DDC treatment produced the same findings despite clear expression of these mesenchymal proteins by other cells in the surrounding stroma (Figs. 6, 7). Therefore, we conclude that EMT does not occur in this model of biliary fibrosis characterized by bipotential progenitor cell proliferation. We report here a broad-based approach to the study of EMT in liver fibrosis. Employing a heritable marker expressed in nearly all bipotential progenitor this website cells,

cholangiocytes, and hepatocytes, we found no evidence in three different fibrosis models that epithelial cells in the adult liver undergo transition to fibrogenic myofibroblasts or other mesenchymal cells during hepatic injury. Our labeling strategy click here enabled us to bypass potential problems associated with the use of the cholangiocyte marker K19 for fate mapping. Several studies have suggested that K19 is expressed in only a subset of biliary epithelial cells.47 Tan et al.27 demonstrated in diseased human livers that K19 is absent in some keratin 7-positive biliary cells, and additionally, studies with human and rodent livers affected by biliary pathology found that a significant number of putative hepatic progenitor cells are K19-negative, even in the ducts.48, 49 Unlike K19, AFP is expressed in mice beginning at embryonic day (E)8.25-8.5. In the Alfp-Cre strain, Cre recombinase

activity is detectible by E9.5, and its efficient recombination results in labeling of more than 98% of cholangiocytes and hepatocytes (Figs. 1, 2B; Supporting

Information Fig. 1B).28.29,32 A significant advantage of this approach is the marking of K19-negative cholangiocyte progenitors. These potentially include hepatocytes, which stop expressing K19 after maturation but may transdifferentiate into cholangiocytes,19-23 and AFP-positive/K19-negative progenitor cells.24-26, 50 An important part of our study was the use of the DDC model, which permits a more complete assessment of bipotential progenitor cell fate during the ductular reaction than is possible with the CCl4 and BDL models. Bipotential progenitor cell activation is central to the “ductular reaction” that characterizes biliary Roflumilast fibrosis.43, 51 Recent studies have demonstrated a direct association between the degree of the ductular reaction and the severity of fibrosis in diseases including biliary atresia and hepatitis C.52 We have previously shown that costaining of epithelial and mesenchymal markers primarily occurs in diseases with a marked ductular reaction. Notably, in livers from patients with primary biliary cirrhosis, marker costaining was limited to epithelial cells of the ductular reaction and was not seen in mature ducts.4 Using the DDC model, in which bipotential progenitor cell expansion is associated with fibrosis, we observed no evidence of EMT.