title: Analysis of germline GLI1 variation implicates hedgehog signalling in the regulation of intestinal inflammatory pathways.
abstract: BACKGROUND
  Ulcerative colitis (UC) and Crohn's disease (CD) are polygenic chronic inflammatory bowel diseases (IBD) of high prevalence that are associated with considerable morbidity. The hedgehog (HH) signalling pathway, which includes the transcription factor glioma-associated oncogene homolog 1 (GLI1), plays vital roles in gastrointestinal tract development, homeostasis, and malignancy. We identified a germline variation in GLI1 (within the IBD2 linkage region, 12q13) in patients with IBD. Since this IBD-associated variant encodes a GLI1 protein with reduced function and our expression studies demonstrated down-regulation of the HH response in IBD, we tested whether mice with reduced Gli1 activity demonstrate increased susceptibility to chemically induced colitis.
  
  
  RESULTS
  Using a gene-wide haplotype-tagging approach, germline GLI1 variation was examined in three independent populations of IBD patients and healthy controls from Northern Europe (Scotland, England, and Sweden) totalling over 5,000 individuals. On log-likelihood analysis, GLI1 was associated with IBD, predominantly UC, in Scotland and England (p < 0.0001). A nonsynonymous SNP (rs2228226C-->G), in exon 12 of GLI1 (Q1100E) was strongly implicated, with pooled odds ratio of 1.194 (confidence interval = 1.09-1.31, p = 0.0002). GLI1 variants were tested in vitro for transcriptional activity in luciferase assays. Q1100E falls within a conserved motif near the C terminus of GLI1; the variant GLI protein exhibited reduced transactivation function in vitro. In complementary expression studies, we noted the colonic HH response, including GLI1, patched (PTCH), and hedgehog-interacting protein (HHIP), to be down-regulated in patients with UC. Finally, Gli1(+/lacZ) mice were tested for susceptibility to dextran sodium sulphate (DSS)-induced colitis. Clinical response, histology, and expression of inflammatory cytokines and chemokines were recorded. Gli1(+/lacZ) mice rapidly developed severe intestinal inflammation, with considerable morbidity and mortality compared with wild type. Local myeloid cells were shown to be direct targets of HH signals and cytokine expression studies revealed robust up-regulation of IL-12, IL-17, and IL-23 in this model.
  
  
  CONCLUSIONS
  HH signalling through GLI1 is required for appropriate modulation of the intestinal response to acute inflammatory challenge. Reduced GLI1 function predisposes to a heightened myeloid response to inflammatory stimuli, potentially leading to IBD.
authors.affiliation: Gastrointestinal Unit, Molecular Medicine Centre, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Charlie W
authors.initials: CW
authors.lastname: Lees
authors.forename: William J
authors.initials: WJ
authors.lastname: Zacharias
authors.forename: Mark
authors.initials: M
authors.lastname: Tremelling
authors.forename: Colin L
authors.initials: CL
authors.lastname: Noble
authors.forename: Elaine R
authors.initials: ER
authors.lastname: Nimmo
authors.forename: Albert
authors.initials: A
authors.lastname: Tenesa
authors.forename: Jennine
authors.initials: J
authors.lastname: Cornelius
authors.forename: Leif
authors.initials: L
authors.lastname: Torkvist
authors.forename: John
authors.initials: J
authors.lastname: Kao
authors.forename: Susan
authors.initials: S
authors.lastname: Farrington
authors.forename: Hazel E
authors.initials: HE
authors.lastname: Drummond
authors.forename: Gwo-Tzer
authors.initials: GT
authors.lastname: Ho
authors.forename: Ian D R
authors.initials: ID
authors.lastname: Arnott
authors.forename: Henry D
authors.initials: HD
authors.lastname: Appelman
authors.forename: Lauri
authors.initials: L
authors.lastname: Diehl
authors.forename: Harry
authors.initials: H
authors.lastname: Campbell
authors.forename: Malcolm G
authors.initials: MG
authors.lastname: Dunlop
authors.forename: Miles
authors.initials: M
authors.lastname: Parkes
authors.forename: Sarah E M
authors.initials: SE
authors.lastname: Howie
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Gumucio
authors.forename: Jack
authors.initials: J
authors.lastname: Satsangi
mesh_terms: D000328:Adult; D000818:Animals; D004739:England; D005260:Female; D020869:Gene Expression Profiling; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D018095:Germ-Line Mutation; D053823:Hedgehog Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007249:Inflammation / Q000235:genetics; D015212:Inflammatory Bowel Diseases / Q000235:genetics*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D020641:Polymorphism, Single Nucleotide; D012606:Scotland; D015398:Signal Transduction / Q000235:genetics* / Q000276:immunology; D013548:Sweden; D014157:Transcription Factors / Q000235:genetics*; D000071676:Zinc Finger Protein GLI1
chemical_list: C400551:GLI1 protein, human; D053823:Hedgehog Proteins; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1