Md. Dabeva et al., Liver regeneration and alpha-fetoprotein messenger RNA expression in the retrorsine model for hepatocyte transplantation, CANCER RES, 58(24), 1998, pp. 5825-5834
Recently, we described a new model for hepatocyte transplantation with near
ly total replacement of the liver by exogenous hepatocytes (E, Laconi et at
, Am. J. Pathol., 153: 319-329, 1998). The model is based on the mitoinhibi
tory effect of the pyrrolizidine alkaloid retrorsine on hepatocytes in the
resident liver while transplanted hepatocytes proliferate. In this study, w
e exploit this novel approach to address the important and controversial is
sue of whether hepatocytes, when proliferating extensively, undergo dediffe
rentiation and give rise to foci of undifferentiated hepatocytes. Genetical
ly marked hepatocytes (isolated from normal Dipeptidyl peptidase IV+ Fische
r 344 rats) were delivered intraportally (2 x 10(6) cells) into the liver o
f retrorsine-treated Dipeptidyl peptidase IV- mutant Fischer 344 rats in co
njunction with partial hepatectomy. Transplanted hepatocytes were detected
histochemically or immunohistochemically, and cell proliferation was studie
d by in situ hybridization for histone-3 mRNA. Expression of alpha-fetoprot
ein (AFP) mRNA, a marker of hepatocyte dedifferentiation, was also revealed
by ill situ hybridization. One day after partial hepatectomy and hepatocyt
e transplantation, endogenous hepatocytes and oval cells expanding in the l
iver expressed histone-3 mRNA (cells had entered S phase); 2 days later, tr
ansplanted hepatocytes and nonparenchymal cells also expressed histone-3 mR
NA. Although the majority of endogenous hepatocytes did not divide and beca
me arrested as quiescent megalocytes, the exogenous hepatocytes, as well as
newly formed small hepatocytes, most probably derived from liver progenito
r cells, underwent extensive proliferation. After 7-14 days, the nonparench
ymal cells stopped proliferating, but transplanted hepatocytes and small en
dogenous hepatocytes continued to proliferate for 1 month, forming foci of
dividing parenchymal cells. Although many of the hepatocytes in clusters we
re in S phase (histone-3 mRNA positive), none expressed AFP mRNA. In contra
st, high expression of AFP mRNA was observed in proliferating oval and tran
sitional cells, forming duct-like structures of cytokeratin-19-positive cel
ls. From these studies, we conclude that hepatocyte proliferation in the ad
ult liver is not associated with dedifferentiation.