Stage-specific regulation of adhesion molecule expression segregates epithelial stem/progenitor cells in fetal and adult human livers

Abstract

Purpose Regulated expression of cell adhesion molecules could be critical in the proliferation, sequestration, and maintenance of stem/progenitor cells. Therefore, we determined fetal and adult stage-specific roles of cell adhesion in liver cell compartments. Methods We performed immunostaining for the adhesion molecules, E-cadherin and Ep-CAM, associated proteins, b-catenin and a-actinin, hepatobiliary markers, albumin, a-fetoprotein, and cytokeratin-19, and the proliferation marker, Ki-67. Expression of albumin was verified by in situ mRNA hybridization. Results In the fetal liver, hepatoblasts showed extensive proliferation with wide expression of E-cadherin, b-catenin, and a-actinin, although Ep-CAM was expressed in these cells less intensely and focally in the cell membrane to indicate weak cell adhesion. Hepatoblasts in ductal plate and bile ducts showed less proliferation and Ep-CAM was intensely expressed in these cells throughout the cell membrane, indicating strong adhesion. In some ductal plate cells, b-catenin was additionally in the cytoplasm and nucleus, suggesting active cell signaling by adhesion molecules. In adult livers, cells were no longer proliferating and E-cadherin, b-catenin, and a-actinin were expressed in hepatocytes throughout, whereas Ep-CAM was expressed in only bile duct cells. Some cells in ductal structures of the adult liver with Ep-CAM coexpressed albumin and cytokeratin-19, indicating persistence of fetal-like stem/progenitor cells. Conclusions Regulated expression of Ep-CAM supported proliferation in fetal hepatoblasts through weak adhesion and helped in biliary morphogenesis by promoting stronger adhesion in hepatoblasts during this process. Restriction of Ep-CAM expression to bile ducts in the adult liver presumably facilitated sequestration of stem/progenitor cells. This stage-specific and cell compartment-related regulation of adhesion molecules should be relevant for defining how liver stem/progenitor cells enter, exit, and remain in hepatic niches during both health and disease.

Spontaneous origin from human embryonic stem cells of liver cells displaying conjoint meso-endodermal phenotype with hepatic functions

“…Our prediction was that if hESC-MECs represent endodermal cells, these will share their identity with naturally occurring fetal human liver stem cells (Inada et al, 2008a). This was confirmed by multiple assays as described above.…”

“…Lentiviral vectors expressing green fluorescent protein (GFP) under PGK, mouse albumin enhancer-promoter, transthyretrin (TTR) and a-1-antitrypsin promoters were prepared (Inada et al, 2008a). Cells were transduced with lentiviral vectors at multiplicity of infection (MOI) of 10.…”

“…In studies of fetal liver development and of isolated fetal liver stem or progenitor cells, significant differences were noted in these cells compared with mature hepatocytes, including multilineage gene expression patterns in fetal cells (Inada et al, 2008a;Inada et al, 2008b). The discovery of an unexpected conjoint meso-endodermal phenotype in fetal liver stem cells, which was characterized by simultaneous expression of epithelial and mesenchymal properties, was in agreement with their ability to generate endodermal and mesodermal lineages, such as adipocytes, osteocytes or endothelial cells, as well as hepatocytes or biliary cells (Inada et al, 2008b).…”

Phenotype reversion in fetal human liver epithelial cells identifies the role of an intermediate meso-endodermal stage before hepatic maturation

“…This molecule is selectively displayed by epithelial cells and characterizes subsets of hepatic stem cells (Winter et al, 2003;Inada et al, 2007). From 7 to 24 weeks of fetal liver development, EpCAM-positive cells are in a state of extensive proliferation, with coexpression of hepatic markers, such as albumin (Alb) and α-fetoprotein (AFP), and biliary markers, such as cytokeratin (CK)-19 and γ-glutamyltranspeptidase (GGT).…”

Liver Regenerative Medicine: Advances and Challenges

“…Liver progenitor cells of the human fetus express several surface markers such as delta-like kinase-1, E-cadherin, THYmocyte differentiation antigen (Thy)-1 and fetal hepatoblast surface marker 2 [Terrace et al, 2007;Inada et al, 2008], thereby suggesting the possibility of selective isolation of these cells via cell sorting. Human hepatic progenitors have already been isolated from fetal livers using immunoselection against the surface marker, an epithelial cell adhesion molecule (EpCAM) .…”