title: Hepatocyte growth factor/c-met signaling is required for stem-cell-mediated liver regeneration in mice.
abstract: Hepatocyte growth factor (HGF)/c-Met supports a pleiotrophic signal transduction pathway that controls stem cell homeostasis. Here, we directly addressed the role of c-Met in stem-cell-mediated liver regeneration by utilizing mice harboring c-met floxed alleles and Alb-Cre or Mx1-Cre transgenes. To activate oval cells, the hepatic stem cell (HSC) progeny, we used a model of liver injury induced by diet containing the porphyrinogenic agent, 3,5-diethocarbonyl-1,4-dihydrocollidine (DDC). Deletion of c-met in oval cells was confirmed in both models by polymerase chain reaction analysis of fluorescence-activated cell-sorted epithelial cell adhesion molecule (EpCam)-positive cells. Loss of c-Met receptor decreased the sphere-forming capacity of oval cells in vitro as well as reduced oval cell pool, impaired migration, and decreased hepatocytic differentiation in vivo, as demonstrated by double immunofluorescence using oval- (A6 and EpCam) and hepatocyte-specific (i.e. hepatocyte nuclear factor 4-alpha) antibodies. Furthermore, lack of c-Met had a profound effect on tissue remodeling and overall composition of HSC niche, which was associated with greatly reduced matrix metalloproteinase (MMP)9 activity and decreased expression of stromal-cell-derived factor 1. Using a combination of double immunofluorescence of cell-type-specific markers with MMP9 and gelatin zymography on the isolated cell populations, we identified macrophages as a major source of MMP9 in DDC-treated livers. The Mx1-Cre-driven c-met deletion caused the greatest phenotypic impact on HSCs response, as compared to the selective inactivation in the epithelial cell lineages achieved in c-Met(fl/fl); Alb-Cre(+/-) mice. However, in both models, genetic loss of c-met triggered a similar cascade of events, leading to the failure of HSC mobilization and death of the mice.
  
  
  CONCLUSIONS
  These results establish a direct contribution of c-Met in the regulation of HSC response and support a unique role for HGF/c-Met as an essential growth-factor-signaling pathway for regeneration of diseased liver.
authors.affiliation: Laboratory of Experimental Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4262, USA.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Valentina M
authors.initials: VM
authors.lastname: Factor
authors.forename: Jens U
authors.initials: JU
authors.lastname: Marquardt
authors.forename: Chiara
authors.initials: C
authors.lastname: Raggi
authors.forename: Daekwan
authors.initials: D
authors.lastname: Seo
authors.forename: Mitsuteru
authors.initials: M
authors.lastname: Kitade
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Conner
authors.forename: Snorri S
authors.initials: SS
authors.lastname: Thorgeirsson
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D056486:Chemical and Drug Induced Liver Injury / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D054377:Chemokine CXCL12 / Q000378:metabolism; D004195:Disease Models, Animal; D017228:Hepatocyte Growth Factor / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D008115:Liver Regeneration / Q000502:physiology*; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D008822:Mice, Transgenic; D019859:Proto-Oncogene Proteins c-met / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011725:Pyridines / Q000009:adverse effects; D015398:Signal Transduction / Q000502:physiology*; D033581:Stem Cell Transplantation; D013234:Stem Cells / Q000166:cytology / Q000502:physiology*
chemical_list: C530773:3,5-diethoxycarbonyl-1,4-dihydrocollidine; D054377:Chemokine CXCL12; D011725:Pyridines; D017228:Hepatocyte Growth Factor; D019859:Proto-Oncogene Proteins c-met; D020780:Matrix Metalloproteinase 9
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