Hematopoietic mobilization in mice increases the presence of bone marrow-derived hepatocytes via in vivo cell fusion

The mechanisms for in vivo production of bone marrow-derived hepatocytes (BMDHs) remain largely unclear. We investigated whether granulocyte colony-stimulating factor (G-CSF)-mediated mobilization of hematopoietic cells increases the phenomenon. Recurrent liver injury in mice expressing green fluorescent protein (EGFP) in all hematopoietic-derived cells was produced by 3 months of carbon tetrachloride (CCL4) injections. Histologically, there were necrotic foci with histiocyte-rich infiltrates, but little oval cell proliferation. Subsequently, some animals were mobilized with G-CSF for 1, 2, or 3 weeks. Animals were sacrificed 1 month after growth factor treatment. BMDH percentages were lower than previously reported, though G-CSF mobilization significantly augmented BMDH production in injured livers. BMDHs originating from in vivo fusion were evaluated by transplanting female EGFP(+) cells into male mice. Binucleated, EGFP(+) hepatocytes with one Y chromosome, indicating fusion, were identified. In conclusion, (1) mobilization of hematopoietic cells increases BMDH production and (2) as with the FAH-null model, the first model demonstrating hematopoietic/hepatocyte fusion, recurring CCl4-induced injury has macrophage-rich infiltrates, a blunted oval cell response, and a predominantly in vivo fusion process for circulating cell engraftment into the liver. These findings open the possibility of using hematopoietic growth factors to treat nonhematopoietic degenerative diseases. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.htm l).