title: Adult mice lacking the type 2 iodothyronine deiodinase have increased subchondral bone but normal articular cartilage.
abstract: BACKGROUND
  Although osteoarthritis (OA) is the commonest joint disorder and has a rising prevalence as the population ages, no drugs are available that prevent or delay the onset and progression of disease. Recent studies identified the DIO2 gene encoding type 2 deiodinase (D2) as a susceptibility locus for OA, and further data suggest deiodinase-regulated local availability of triiodothyronine (T3) in the joint plays an important role in cartilage maintenance and repair. To investigate the hypothesis that reduced tissue T3 availability protects joints from development of OA, the joint phenotypes of adult mice lacking D2 (D2KO) or lacking both D1 and D2 (D1D2KO), the only enzymes that catalyze conversion of the prohormone thyroxine to active T3, were determined.
  
  
  METHODS
  Knee joints were prepared from male 16-week-old adult wild type (WT; n=9), D2KO (n=5), and D1D2KO (n=3) mice. Articular cartilage pathology was scored using the Osteoarthritis Research Society International (OARSI) histopathology scale for murine OA to determine the severity and extent of disease. Digital X-ray microradiography was used to determine the area and mineral content of subchondral bone immediately beneath the articular cartilage surface.
  
  
  RESULTS
  There were no differences in maximum and standardized OA scores, cartilage erosion indices, or articular cartilage cellularity among WT, D2KO, and D1D2KO mice. Subchondral bone area did not differ among genotypes, but mineral content was markedly increased in both D2KO and D1D2KO mice compared to WT.
  
  
  CONCLUSIONS
  Although adult D2KO mice have normal articular cartilage and no other features of spontaneous joint damage, they exhibit increased subchondral bone mineral content.
authors.affiliation: Molecular Endocrinology Group, Department of Medicine, Imperial College London , London, United Kingdom .
authors.forename: Julian A
authors.initials: JA
authors.lastname: Waung
authors.forename: J H Duncan
authors.initials: JH
authors.lastname: Bassett
authors.forename: Graham R
authors.initials: GR
authors.lastname: Williams
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D002358:Cartilage, Articular / Q000378:metabolism*; D004195:Disease Models, Animal; D053595:Embryonic Stem Cells / Q000166:cytology; D005838:Genotype; D007453:Iodide Peroxidase / Q000235:genetics* / Q000502:physiology; D007596:Joints / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D014284:Triiodothyronine / Q000378:metabolism; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D007453:Iodide Peroxidase; D014284:Triiodothyronine; D000097564:Iodothyronine Deiodinase Type II