Hematopoietic stem cells mobilized by granulocyte colony-stimulating factor partly contribute to liver graft regeneration after partial orthotopic liver transplantation

On the basis of the recently recognized potential of hematopoietic stem cells (HSCs) to give rise to hepatocytes, we investigated whether HSCs mobilized by granulocyte colony-stimulating factor (G-CSF) or G-CSF per se could contribute to faster recovery and promote tissue reparation after rats' (cross-sex) partial orthotopic liver transplantation (PLTx). Sex-mismatched (female to male) syngeneic rat PLTx was established. The recipients were repeatedly administrated recombinant G-CSF for 5 consecutive days before (G-CSF + PLTx group) and after PLTx (PLTx + G-CSF group). Compared with those in PLTx group, CD34(+) cells in peripheral blood and portal tract region increased from day 1 to 7 after transplantation in G-CSF + PLTx group and from day 3 to 14 after transplantation in PLTx + G-CSF group, respectively, which suggested that CD34(+) HSCs were mobilized and migrated into liver graft. Compared with that in G-CSF + PLTx and PLTx groups, there was a higher survival rate in the PLTx + G-CSF group. On day 3 after surgery, the level of aspartate aminotransferase and alanine aminotransferase were lower, whereas the mitosis index, proliferating cell nuclear antigen-positive nuclei, bromodeoxyuridine (BrdU) incorporation, and graft-to-recipient weight ratio were higher in the PLTx + G-CSF group. In contrast, these parameters had no significant difference between G-CSF + PLTx and PLTx groups. To define the origin of proliferating cells reconstituting liver after injury, sry(+) (sex-determining region for Y chromosome) and sry(+)/cytokeratin 19(+) (CK19) cells were quantitated. Higher percentage of sry+ and sry(+)/CK19(+) cells in PLTx + G-CSF was detected than in G-CSF + PLTx groups on day 14 after surgery, although the liver engraftment rate still remained rather low. Some of the sry+/CK19(+) cells in the portal tract areas were similar to hepatic oval cells/cholangiocytes. In conclusion, G-CSF administration after PLTx greatly improved survival rate and liver regeneration of partial graft, partly by its mobilizing HSCs into the injured liver to differentiate into hepatocytes through hepatic oval cells'/cholangiocytes' engraftment.