Widespread GLI expression but limited canonical hedgehog signaling restricted to the ductular reaction in human chronic liver disease

PLoS One. 2017 Feb 10;12(2):e0171480. doi: 10.1371/journal.pone.0171480. eCollection 2017.

Abstract

Canonical Hedgehog (Hh) signaling in vertebrate cells occurs following Smoothened activation/translocation into the primary cilia (Pc), followed by a GLI transcriptional response. Nonetheless, GLI activation can occur independently of the canonical Hh pathway. Using a murine model of liver injury, we previously identified the importance of canonical Hh signaling within the Pc+ liver progenitor cell (LPC) population and noted that SMO-independent, GLI-mediated signals were important in multiple Pc-ve GLI2+ intrahepatic populations. This study extends these observations to human liver tissue, and analyses the effect of GLI inhibition on LPC viability/gene expression. Human donor and cirrhotic liver tissue specimens were evaluated for SHH, GLI2 and Pc expression using immunofluorescence and qRT-PCR. Changes to viability and gene expression in LPCs in vitro were assessed following GLI inhibition. Identification of Pc (as a marker of canonical Hh signaling) in human cirrhosis was predominantly confined to the ductular reaction and LPCs. In contrast, GLI2 was expressed in multiple cell populations including Pc-ve endothelium, hepatocytes, and leukocytes. HSCs/myofibroblasts (>99%) expressed GLI2, with only 1.92% displaying Pc. In vitro GLI signals maintained proliferation/viability within LPCs and GLI inhibition affected the expression of genes related to stemness, hepatocyte/biliary differentiation and Hh/Wnt signaling. At least two mechanisms of GLI signaling (Pc/SMO-dependent and Pc/SMO-independent) mediate chronic liver disease pathogenesis. This may have significant ramifications for the choice of Hh inhibitor (anti-SMO or anti-GLI) suitable for clinical trials. We also postulate GLI delivers a pro-survival signal to LPCs whilst maintaining stemness.

MeSH terms

  • Adult
  • Aged
  • Cilia / metabolism
  • Endothelium / metabolism
  • Female
  • Hedgehog Proteins / genetics*
  • Hedgehog Proteins / metabolism
  • Hepatocytes / metabolism
  • Humans
  • Kruppel-Like Transcription Factors / genetics*
  • Kruppel-Like Transcription Factors / metabolism
  • Leukocytes / metabolism
  • Liver Diseases / metabolism*
  • Male
  • Middle Aged
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism
  • Signal Transduction*
  • Zinc Finger Protein Gli2

Substances

  • GLI2 protein, human
  • Hedgehog Proteins
  • Kruppel-Like Transcription Factors
  • Nuclear Proteins
  • SHH protein, human
  • Zinc Finger Protein Gli2

Grants and funding

This project was funded by the National Health and Medical Research Council, Program Grant #571408 (GWM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.