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

• Published in: Journal of hepatology Vol. 60; no. 1; pp. 143 - 151
• Main Authors: Grzelak, Candice Alexandra, Martelotto, Luciano Gastón, Sigglekow, Nicholas David, Patkunanathan, Bramilla, Ajami, Katerina, Calabro, Sarah Ruth, Dwyer, Benjamin James, Tirnitz-Parker, Janina Elke Eleonore, Watkins, D. Neil, Warner, Fiona Jane, Shackel, Nicholas Adam, McCaughan, Geoffrey William
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.01.2014
• Subjects: Animals; Chemical and Drug Induced Liver Injury - pathology; Chronic Disease; Cilia - physiology; Epithelial-Mesenchymal Transition; Gastroenterology and Hepatology; GLI; Hedgehog Proteins - physiology; Hedgehog signalling pathway; Kruppel-Like Transcription Factors - analysis; Kruppel-Like Transcription Factors - physiology; Liver - pathology; Liver progenitor cells; Male; Mice; Mice, Inbred C57BL; Non-canonical cell signalling; Nuclear Proteins - analysis; Primary cilia; Receptors, G-Protein-Coupled - physiology; Signal Transduction - physiology; Smoothened; Smoothened Receptor; Thioacetamide; Zinc Finger Protein GLI1; Zinc Finger Protein Gli2; Liver progenitor cells; EpCAM; GLI; primary cilia; IHH; alanine aminotransferase; ALT; cytokeratin; non-targeting control; N-terminal Hedgehog signalling peptide; α-SMA; SHH; Smoothened; Pc; HSC; Hh; HGF; liver progenitor cell; NT2; EMT; epithelial-to-mesenchymal transition; Hedgehog; alcoholic liver disease; GLI cleaved repressor; Indian Hedgehog; MCDE; SMO; GLI-A; Desert Hedgehog; Hedgehog signalling pathway; epidermal growth factor; LPC; epithelial cell adhesion molecule; α-smooth muscle actin; DHH; GLI-R; GLI-Kruppel family of transcription factors; hepatocyte growth factor; Sonic Hedgehog; hepatic stellate cell; N-Hh; Ptc1-lacZ reporter; EGF; PTCH1; methionine choline-deficient diet + ethionine; CK; thioacetamide; GLI full-length activator; Ptc1; TAA; Non-canonical cell signalling; Patched 1; ALD; Primary cilia; Thioacetamide; Ptc1(+/−); methionine choline-deficient diet+ethionine
• DOI: 10.1016/j.jhep.2013.08.012
• ISSN: 0168-8278

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/h Gli3-R overexpression reduced proliferation/viability in Pc+ progenitors, whilst increased proliferation occurred with h Gli1 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.