title: Excessive bone formation in a mouse model of ankylosing spondylitis is associated with decreases in Wnt pathway inhibitors.
abstract: BACKGROUND
  Ankylosing spondylitis (AS) is unique in its pathology where inflammation commences at the entheses before progressing to an osteoproliferative phenotype generating excessive bone formation that can result in joint fusion. The underlying mechanisms of this progression are poorly understood. Recent work has suggested that changes in Wnt signalling, a key bone regulatory pathway, may contribute to joint ankylosis in AS. Using the proteoglycan-induced spondylitis (PGISp) mouse model which displays spondylitis and eventual joint fusion following an initial inflammatory stimulus, we have characterised the structural and molecular changes that underlie disease progression.
  
  
  METHODS
  PGISp mice were characterised 12 weeks after initiation of inflammation using histology, immunohistochemistry (IHC) and expression profiling.
  
  
  RESULTS
  Inflammation initiated at the periphery of the intervertebral discs progressing to disc destruction followed by massively excessive cartilage and bone matrix formation, as demonstrated by toluidine blue staining and IHC for collagen type I and osteocalcin, leading to syndesmophyte formation. Expression levels of DKK1 and SOST, Wnt signalling inhibitors highly expressed in joints, were reduced by 49% and 63% respectively in the spine PGISp compared with control mice (P < 0.05) with SOST inhibition confirmed by IHC. Microarray profiling showed genes involved in inflammation and immune-regulation were altered. Further, a number of genes specifically involved in bone regulation including other members of the Wnt pathway were also dysregulated.
  
  
  CONCLUSIONS
  This study implicates the Wnt pathway as a likely mediator of the mechanism by which inflammation induces bony ankylosis in spondyloarthritis, raising the potential that therapies targeting this pathway may be effective in preventing this process.
authors.forename: Katelin R
authors.initials: KR
authors.lastname: Haynes
authors.forename: Allison R
authors.initials: AR
authors.lastname: Pettit
authors.forename: Ran
authors.initials: R
authors.lastname: Duan
authors.forename: Hsu-Wen
authors.initials: HW
authors.lastname: Tseng
authors.forename: Tibor T
authors.initials: TT
authors.lastname: Glant
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Brown
authors.forename: Gethin P
authors.initials: GP
authors.lastname: Thomas
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D024042:Collagen Type I / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D020869:Gene Expression Profiling; D063990:Gene Ontology; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D007596:Joints / Q000378:metabolism / Q000473:pathology; D018345:Mice, Knockout; D020411:Oligonucleotide Array Sequence Analysis; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D010012:Osteogenesis / Q000235:genetics*; D011509:Proteoglycans; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013131:Spine / Q000378:metabolism; D013167:Spondylitis, Ankylosing / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism; D060449:Wnt Signaling Pathway / Q000235:genetics*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D024042:Collagen Type I; C501127:Dkk1 protein, mouse; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D011509:Proteoglycans; C486030:Sost protein, mouse; D015675:Osteocalcin