Thy1-positive bone marrow stem cells express liver-specific genes in vitro and can mature into hepatocytes in vivo

The bone marrow contains stem cells that have the potential to differentiate into a variety of organ-specific mature cells, including the liver and the pancreas. Recently, the origin of hepatic progenitors and hepatocytes was identified to be the bone marrow. However, evidence that describes which cells, among all bone marrow cells, differentiate into hepatocytes, has not yet been presented. Based on recent reports, hematopoietic and hepatic stem cells share characteristic markers such as CD34, c-kit, and Thy1. In particular, both hematopoietic and hepatic stem cells express the Thy1 antigen. We investigated whether rat Thy1-positive bone marrow cells express liver-specific genes in vitro, and whether transplanted Thy1 BM cells differentiate into mature hepatocytes in vivo. For collection of Thy1 cells from bone marrow, FITC-conjugated anti-Thy1.1 monoclonal antibody was used with a Fluorescence-Activated Cell Sorter system. A coculture system of 2 separate layers was used for culture of Thy bone marrow cells. Cultured Thy1 cells expressed albumin protein, which was analyzed by immunofluorescent staining. Thy1 bone marrow cells obtained from wild-type dipeptidyl peptidase IV (DPPIV(+)) male rat were directly transplanted into the injured liver of DPPIV mutant (DPPIV(-)) Fisher 344 female rats and differentiated into mature hepatocytes in recipient liver on 60 days. Donor-derived hepatocytes were confirmed by DPPIV staining and Y-chromsome in situ hybridization. Our results suggest that Thy1-positive bone marrow cells have the potential to generate liver-specific genes in vitro and can differentiate into mature hepatocytes in adult liver in vivo. Thy1-positive bone marrow stem cells may represent preexisting hepatocyte-specific stem cells.