title: Endochondral Growth Defect and Deployment of Transient Chondrocyte Behaviors Underlie Osteoarthritis Onset in a Natural Murine Model.
abstract: OBJECTIVE
  To explore whether aberrant transient chondrocyte behaviors occur in the joints of STR/Ort mice (which spontaneously develop osteoarthritis [OA]) and whether they are attributable to an endochondral growth defect.
  
  
  METHODS
  Knee joints from STR/Ort mice with advanced OA and age-matched CBA (control) mice were examined by Affymetrix microarray profiling, multiplex polymerase chain reaction (PCR) analysis, and immunohistochemical labeling of endochondral markers, including sclerostin and MEPE. The endochondral phenotype of STR/Ort mice was analyzed by histologic examination, micro-computed tomography, and ex vivo organ culture. A novel protocol for quantifying bony bridges across the murine epiphysis (growth plate fusion) using synchrotron x-ray computed microtomography was developed and applied.
  
  
  RESULTS
  Meta-analysis of transcription profiles showed significant elevation in functions linked with endochondral ossification in STR/Ort mice (compared to CBA mice; P < 0.05). Consistent with this, immunolabeling revealed increased matrix metalloproteinase 13 (MMP-13) and type X collagen expression in STR/Ort mouse joints, and multiplex quantitative reverse transcriptase-PCR showed differential expression of known mineralization regulators, suggesting an inherent chondrocyte defect. Support for the notion of an endochondral defect included accelerated growth, increased zone of growth plate proliferative chondrocytes (P < 0.05), and widespread type X collagen/MMP-13 labeling beyond the expected hypertrophic zone distribution. OA development involved concomitant focal suppression of sclerostin/MEPE in STR/Ort mice. Our novel synchrotron radiation microtomography method showed increased numbers (P < 0.001) and mean areal growth plate bridge densities (P < 0.01) in young and aged STR/Ort mice compared to age-matched CBA mice.
  
  
  CONCLUSIONS
  Taken together, our data support the notion of an inherent endochondral defect that is linked to growth dynamics and subject to regulation by the MEPE/sclerostin axis and may represent an underlying mechanism of pathologic ossification in OA.
authors.affiliation: Royal Veterinary College, University of London, London, UK, and Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, UK.
authors.forename: K A
authors.initials: KA
authors.lastname: Staines
authors.affiliation: Manchester X-Ray Imaging Facility, University of Manchester, Manchester, UK.
authors.forename: K
authors.initials: K
authors.lastname: Madi
authors.affiliation: Royal Veterinary College, University of London, London, UK;
authors.forename: S M
authors.initials: SM
authors.lastname: Mirczuk
authors.affiliation: Royal Veterinary College, University of London, London, UK;
authors.forename: S
authors.initials: S
authors.lastname: Parker
authors.affiliation: Royal Veterinary College, University of London, London, UK;
authors.forename: A
authors.initials: A
authors.lastname: Burleigh
authors.affiliation: University College London Medical School, London, UK.
authors.forename: B
authors.initials: B
authors.lastname: Poulet
authors.affiliation: Royal Veterinary College, University of London, London, UK;
authors.forename: M
authors.initials: M
authors.lastname: Hopkinson
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Bodey
authors.affiliation: Royal Veterinary College, University of London, London, UK;
authors.forename: R C
authors.initials: RC
authors.lastname: Fowkes
authors.affiliation: Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, UK.
authors.forename: C
authors.initials: C
authors.lastname: Farquharson
authors.affiliation: Manchester X-Ray Imaging Facility, University of Manchester, Manchester, UK.
authors.forename: P D
authors.initials: PD
authors.lastname: Lee
authors.affiliation: Royal Veterinary College, University of London, London, UK;
authors.forename: A A
authors.initials: AA
authors.lastname: Pitsillides
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000378:metabolism*; D016022:Case-Control Studies; D019902:Chondrocytes / Q000378:metabolism*; D024121:Collagen Type X / Q000378:metabolism; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006132:Growth Plate / Q000000981:diagnostic imaging / Q000254:growth & development / Q000378:metabolism*; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D051379:Mice; D008808:Mice, Inbred CBA; D060885:Multiplex Polymerase Chain Reaction; D020411:Oligonucleotide Array Sequence Analysis; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000378:metabolism*; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000378:metabolism*; D053495:Osteopontin / Q000235:genetics; D053402:PHEX Phosphate Regulating Neutral Endopeptidase / Q000235:genetics; D028061:Phosphate Transport Proteins / Q000235:genetics; D010750:Phosphoproteins / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000235:genetics; D011755:Pyrophosphatases / Q000235:genetics; D055114:X-Ray Microtomography
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D024121:Collagen Type X; C513308:Dmp1 protein, mouse; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; C518716:Mepe protein, mouse; D028061:Phosphate Transport Proteins; D010750:Phosphoproteins; C486030:Sost protein, mouse; C506896:Spp1 protein, mouse; C410982:ank protein, mouse; D053495:Osteopontin; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D053509:Matrix Metalloproteinase 13; C507081:Mmp13 protein, mouse; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506232:Phex protein, mouse; D011755:Pyrophosphatases