Wnt/beta-catenin signaling in murine hepatic transit amplifying progenitor cells.
OBJECTIVE
Oval cells are postnatal hepatic progenitors with high proliferative potential and bipotent differentiation ability to become hepatocytes and cholangiocytes. Because Wnt/beta-catenin signaling is a known regulatory pathway for liver development and regeneration, we studied the role of Wnt signaling in oval cells using a mouse model of chronic liver injury.


METHODS
A 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-enriched diet was used to stimulate oval cell proliferation. Livers were harvested for histologic analysis and determination of Wnt family gene expression by quantitative reverse transcription-polymerase chain reaction and in situ hybridization. The transgenic beta-catenin reporter mouse (TOPGAL) was use to confirm canonical Wnt/beta-catenin signal transduction in proliferating oval cells within atypical ductal proliferations (ADPs). Confocal fluorescence microscopy and immunohistochemistry was used to confirm colocalization of beta-catenin with the oval cell antigen A-6.


RESULTS
Several Wnt ligands were significantly induced in the liver of DDC-fed mice and localized to proliferating cells in and adjacent to the ADPs. Oval cells isolated from DDC-fed mouse livers showed the presence of active beta-catenin in the nucleus along with cell-cycle entry in response to purified Wnt3a in vitro. Moreover, Wnt3a-induced beta-catenin/T-cell factor/lymphoid enhancer factor (TCF/LEF) transcriptional activation was quantified by TCF/LEF luciferase reporter assays.


CONCLUSIONS
From these data, we conclude that oval cells respond to Wnt ligands (Wnt3a) in vitro with an increase in amino-terminus dephosphorylated beta-catenin and cell-cycle entry and that canonical Wnt/beta-catenin/TCF signaling is active in proliferating facultative hepatic progenitor cells in vivo. These findings may lend insight to the consequences of increased canonical Wnt signaling during periods of chronic liver injury.
Hu
Min
M
Department of Surgery, Stanford University School of Medicine, Stanford, California, USA.
Kurobe
Masashi
M
Jeong
Yeon Jun
YJ
Fuerer
Christophe
C
Ghole
Saif
S
Nusse
Roel
R
Sylvester
Karl G
KG
D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003997:Dicarbethoxydihydrocollidine / Q000494:pharmacology; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects; D006500:Hepatic Duct, Common / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008107:Liver Diseases / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D015398:Signal Transduction / Q000502:physiology*; D013234:Stem Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051820:TCF Transcription Factors / Q000235:genetics / Q000378:metabolism; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
D051820:TCF Transcription Factors; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; C555511:Wnt3a protein, mouse; D051176:beta Catenin; D003997:Dicarbethoxydihydrocollidine