In vitro transdifferentiation of adult bone marrow Sca-1+ cKit- cells cocultured with fetal liver cells into hepatic-like cells without fusion

Several research groups have recently reported that certain bone marrow cells (BMCs) differentiate into hepatocytes in vitro as well as in vivo in rodents. However, it has yet to be elucidated what factors effectively trigger and sustain transdifferentiation of BMCs. In the present study, we specifically asked whether the presence of murine fetal liver cells (FLCs) triggered and supported in vitro transdifferentiation of murine BMCs. Fractionated BMCs from green fluorescence protein (GFP)-expressing transgenic mice and FLCs from ROSA26 mice (X-gal(+) FLCs) were cocultured in the presence of hepatocyte growth factor in laminin-coated dishes. We found that Sca-1(+) BMCs gave rise to adherent hepatic-like cells, which expressed albumin as assessed with immunocytochemistry and RNA-polymerase chain reaction (PCR), and alpha-fetoprotein and cytokeratin 19 as examined with RNA-PCR. When GFP(+)Sca-1(+)cKit(-) cells were cocultured with X-gal(+) FLCs, all GFP(+) albumin-producing cells were negative for X-gal, showing that cell fusion was not associated in the observed BMCs' differentiation into hepatic-like cells. Titration analysis revealed that 1 of 5,943 Sca-1(+)cKit(-) cells had the ability to proliferate and differentiate into hepatic-like cells. These data strongly suggest that BMCs differentiate into hepatic-like cells in the presence of FLCs and that the present method may be useful for propagating BMC-derived hepatocytic progenitors and for investigating the nature of those cells.