title: Enhanced Wnt/β-catenin and Notch signalling in the activated canine hepatic progenitor cell niche.
abstract: BACKGROUND
  The liver has a large regenerative capacity. Hepatocytes can replicate and regenerate a diseased liver. However, as is the case in severe liver diseases, this replication may become insufficient or exhausted and hepatic progenitor cells (HPCs) can be activated in an attempt to restore liver function. Due to their bi-potent differentiation capacity, these HPCs have great potential for regenerative approaches yet over-activation does pose potential health risks. Therefore the mechanisms leading to activation must be elucidated prior to safe implementation in the veterinary clinic. Wnt/β-catenin and Notch signalling have been implicated in the activation of HPCs in mouse models and in humans. Here we assessed the involvement in canine HPC activation. Gene-expression profiles were derived from laser microdissected HPC niches from lobular dissecting hepatitis (LDH) and normal liver tissue, with a focus on Wnt/β-catenin and Notch signalling. Immunohistochemical and immunofluorescent studies were combined to assess the role of the pathways in HPCs during LDH.
  
  
  RESULTS
  Gene-expression confirmed higher expression of Wnt/β-catenin and Notch pathway components and target genes in activated HPC niches in diseased liver compared to quiescent HPC niches from normal liver. Immunofluorescence confirmed the activation of these pathways in the HPCs during disease. Immunohistochemistry showed proliferating HPCs during LDH, and double immunofluorescence showed downregulation of Wnt/β-catenin and Notch in differentiating HPCs. Vimentin, a mesenchymal marker, was expressed on a subset of undifferentiated HPCs.
  
  
  CONCLUSIONS
  Together these studies clearly revealed that both Wnt/β-catenin and Notch signalling pathways are enhanced in undifferentiated, proliferating and potentially migrating HPCs during severe progressive canine liver disease (LDH).
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. B.A.Schotanus@uu.nl.
authors.forename: Baukje A
authors.initials: BA
authors.lastname: Schotanus
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. H.S.Kruitwagen@uu.nl.
authors.forename: Hedwig S
authors.initials: HS
authors.lastname: Kruitwagen
authors.affiliation: TCCI Consultancy BV, Utrecht, The Netherlands. t.s.g.a.m.vandeningh@online.nl.
authors.forename: Ted S G A M
authors.initials: TS
authors.lastname: van den Ingh
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. M.E.vanWolferen@uu.nl.
authors.forename: Monique E
authors.initials: ME
authors.lastname: van Wolferen
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. J.Rothuizen@uu.nl.
authors.forename: Jan
authors.initials: J
authors.lastname: Rothuizen
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. L.C.Penning@uu.nl.
authors.forename: Louis C
authors.initials: LC
authors.lastname: Penning
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. B.Spee@uu.nl.
authors.forename: Bart
authors.initials: B
authors.lastname: Spee
mesh_terms: D000818:Animals; D004283:Dog Diseases / Q000503:physiopathology; D004285:Dogs; D005455:Fluorescent Antibody Technique / Q000662:veterinary; D005786:Gene Expression Regulation / Q000502:physiology; D008099:Liver / Q000166:cytology* / Q000502:physiology; D008107:Liver Diseases / Q000503:physiopathology / Q000662:veterinary; D008115:Liver Regeneration / Q000502:physiology; D051880:Receptors, Notch / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D055153:Stem Cell Niche / Q000502:physiology*; D013234:Stem Cells / Q000502:physiology*; D051153:Wnt Proteins / Q000502:physiology; D060449:Wnt Signaling Pathway / Q000502:physiology*; D051176:beta Catenin / Q000502:physiology
chemical_list: D051880:Receptors, Notch; D051153:Wnt Proteins; D051176:beta Catenin