title: Depletion of protease-activated receptor 2 but not protease-activated receptor 1 may confer protection against osteoarthritis in mice through extracartilaginous mechanisms.
abstract: OBJECTIVE
  To explore the involvement of protease-activated receptor 1 (PAR-1) and PAR-2 in the pathologic processes of osteoarthritis (OA) and to identify the cells/tissues primarily affected by ablation of PAR-1 or PAR-2 in mice.
  
  
  METHODS
  OA was induced in the joints of wild-type (WT), PAR-1(+/+) , PAR-1(-/-) , and PAR-2(-/-) mice by destabilization of the medial meniscus (DMM), and scores of histologic features (cartilage aggrecan loss and erosion, subchondral bone sclerosis, osteophytes, and synovitis) were compared at 1, 4, and 8 weeks post-DMM. The effects of PAR ablation on cartilage degradation and chondrocyte metalloproteinase expression/activity were studied in cultures of mouse femoral head tissue with or without interleukin-1α (IL-1α). At 1 week post-DMM, synovial expression of cytokines and metalloproteinase genes was measured by reverse transcription-polymerase chain reaction, and populations of inflammatory cells were quantified by flow cytometry.
  
  
  RESULTS
  Deletion of PAR-2, but not that of PAR-1, in mice significantly delayed the progression of cartilage damage and inhibited subchondral bone sclerosis following DMM. There was no inhibitory effect of PAR-1 or PAR-2 ablation on IL-1α-induced cartilage degradation or chondrocyte metalloproteinase expression/activation. A low but significant level of synovitis persisted in mice subjected to DMM compared to that in control mice subjected to sham surgery, but no differences between the genotypes were seen 4 or 8 weeks post-DMM. One week after DMM, increased synovial expression of proinflammatory cytokines and metalloproteinase genes, along with increased levels of CD4+ T cells, inflammatory monocytes, and activated macrophages, were seen in all genotypes. However, there was a significant reduction in the percentage of activated macrophages in PAR-2(-/-) mice compared to PAR-1(-/-) and WT mice.
  
  
  CONCLUSIONS
  Deletion of PAR-2, but not that of PAR-1, results in a significant decrease in DMM-induced cartilage damage. The chondroprotection in PAR-2(-/-) mice appears to occur indirectly through modulation of extracartilaginous events such as subchondral bone remodeling and synovial macrophage activation, rather than through alteration of chondrocyte catabolic responses.
authors.affiliation: Kolling Institute of Medical Research and the University of Sydney at Royal North Shore Hospital, St. Leonards, New South Wales, Australia.
authors.forename: Miriam T
authors.initials: MT
authors.lastname: Jackson
authors.forename: Babak
authors.initials: B
authors.lastname: Moradi
authors.forename: Sanaa
authors.initials: S
authors.lastname: Zaki
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Smith
authors.forename: Sharon
authors.initials: S
authors.lastname: McCracken
authors.forename: Susan M
authors.initials: SM
authors.lastname: Smith
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Jackson
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Little
mesh_terms: D051722:ADAM Proteins / Q000235:genetics / Q000378:metabolism; D053674:Aggrecans / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism*; D019902:Chondrocytes / Q000378:metabolism*; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000235:genetics*; D008592:Menisci, Tibial / Q000601:surgery*; D045726:Metalloproteases / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010003:Osteoarthritis / Q000235:genetics* / Q000378:metabolism; D065840:Protective Factors; D011509:Proteoglycans / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis*; D044463:Receptor, PAR-1 / Q000235:genetics*; D044464:Receptor, PAR-2 / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D053674:Aggrecans; D011509:Proteoglycans; D012333:RNA, Messenger; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D045726:Metalloproteases; D051722:ADAM Proteins