Thy1-Positive Cells Have Bipotential Ability to Differentiate into Hepatocytes and Biliary Epithelial Cells in Galactosamine-induced Rat Liver Regeneration

in galactosamine (Ga1N)-induced rat liver injury, hepatic stem/progenitor cells, small hepatocytes (SHs) and oval cells, transiently appear in the initial period of liver regeneration. To clarify the relationship between SHs and oval cells, CD44(+) and Thy1(+) cells were sorted from Ga1N-treated livers and used as candidates for SHs and oval cells, respectively. Some Thy1(+) cells isolated 3 days after GaIN-treatment (GaIN-D3) formed CD44(+) cell colonies, but those from GalN-D2 could form few. GeneChip (Affymetrix, Inc, Santa Clara, CA) analysis of the sorted cells and cultured Thy1(+) cells suggested that hepatocytic differentiation progressed in the order Thy1(+) (GaIN-D3), Thy1(+) cell colony (Thy1-C), and CD44(+) (GaIN-D4) cells. When Thy1(+), Thy1-C, and CD44+ cells were transplanted into retrorsine/PH rat livers, they could proliferate to form hepatocytic foci. At 30 days after transplantation most cells forming the foci derived from CD44(+) cells possessed C/EBP alpha(+) nuclei, whereas only a few cells derived from Thy1-C showed this positivity. When Thy1(+) (GaIN-D3) cells were cultured between collagen gels in medium with hepatocyte growth factor(+)/dexamethasone-/dimethyl sulfoxide(-), ducts/cysts consisting of biliary epithelial cells appeared, whereas with CD44(+) and Thy1(+) (GaIN-D2) cells they did not. Taken together, these results indicate that the conunitment of Thy1(+) cells to differentiate into hepatocytes or biliary epithetial cells may occur between Day 2 and Day 3. Furthermore, some Thy1(+) cells may differentiate into hepatocytes via CD44+ SHs. (Am J Pathol 2009, 175:2362-2371; DOI: 10.2353/ajpath.2009.080338)