The intrahepatic signalling niche of hedgehog is defined by primary cilia positive cells during chronic liver injury

Candice Alexandra Grzelak, Luciano Gastón Martelotto, Nicholas David Sigglekow, Bramilla Patkunanathan, Katerina Ajami, Sarah Ruth Calabro, Benjamin James Dwyer, Janina Elke Eleonore Tirnitz-Parker, D Neil Watkins, Fiona Jane Warner, Nicholas Adam Shackel, Geoffrey William McCaughan

Research output: Contribution to journalArticlepeer-review

Abstract

BACKGROUND & AIMS: In vertebrates, canonical Hedgehog (Hh) pathway activation requires Smoothened (SMO) translocation to the primary cilium (Pc), followed by a GLI-mediated transcriptional response. In addition, a similar gene regulation occurs in response to growth factors/cytokines, although independently of SMO signalling. The Hh pathway plays a critical role in liver fibrosis/regeneration, however, the mechanism of activation in chronic liver injury is poorly understood. This study aimed to characterise Hh pathway activation upon thioacetamide (TAA)-induced chronic liver injury in vivo by defining Hh-responsive cells, namely cells harbouring Pc and Pc-localised SMO.

METHODS: C57BL/6 mice (wild-type or Ptc1(+/-)) were TAA-treated. Liver injury and Hh ligand/pathway mRNA and protein expression were assessed in vivo. SMO/GLI manipulation and SMO-dependent/independent activation of GLI-mediated transcriptional response in Pc-positive (Pc(+)) cells were studied in vitro.

RESULTS: In vivo, Hh activation was progressively induced following TAA. At the epithelial-mesenchymal interface, injured hepatocytes produced Hh ligands. Progenitors, myofibroblasts, leukocytes and hepatocytes were GLI2(+). Pc(+) cells increased following TAA, but only EpCAM(+)/GLI2(+) progenitors were Pc(+)/SMO(+). In vitro, SMO knockdown/hGli3-R overexpression reduced proliferation/viability in Pc(+) progenitors, whilst increased proliferation occurred with hGli1 overexpression. HGF induced GLI transcriptional activity independently of Pc/SMO. Ptc1(+/-) mice exhibited increased progenitor, myofibroblast and fibrosis responses.

CONCLUSIONS: In chronic liver injury, Pc(+) progenitors receive Hh ligand signals and process it through Pc/SMO-dependent activation of GLI-mediated transcriptional response. Pc/SMO-independent GLI activation likely occurs in Pc(-)/GLI2(+) cells. Increased fibrosis in Hh gain-of-function mice likely occurs by primary progenitor expansion/proliferation and secondary fibrotic myofibroblast expansion, in close contact with progenitors.

Original languageEnglish
Pages (from-to)143-51
Number of pages9
JournalJournal of Hepatology
Volume60
Issue number1
DOIs
Publication statusPublished - Jan 2014

Keywords

  • Animals
  • Chemical and Drug Induced Liver Injury
  • Chronic Disease
  • Cilia
  • Epithelial-Mesenchymal Transition
  • Hedgehog Proteins
  • Kruppel-Like Transcription Factors
  • Liver
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Nuclear Proteins
  • Receptors, G-Protein-Coupled
  • Signal Transduction
  • Smoothened Receptor
  • Thioacetamide
  • Zinc Finger Protein GLI1
  • Zinc Finger Protein Gli2
  • Journal Article
  • Research Support, Non-U.S. Gov't

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