title: Elevation of activated protein C in synovial joints in rheumatoid arthritis and its correlation with matrix metalloproteinase 2.
abstract: OBJECTIVE
  To investigate the involvement of the anticoagulant serine protease activated protein C (APC) in tissue remodeling in rheumatoid arthritis (RA).
  
  
  METHODS
  PC/APC, matrix metalloproteinase 2 (MMP-2), and MMP-9 were detected in synovial fluid by Western blotting, and their antigen levels were quantified by enzyme-linked immunosorbent assay in patients with osteoarthritis (OA) or RA. Enzymatic activity of MMP-2 was assayed using a specific fluorogenic substrate. We developed an improved assay to measure APC activity in synovial fluid utilizing a chromogenic substrate following immunoprecipitation with a specific PC/APC antibody. PC/APC and MMP-2 were localized by immunohistochemistry in RA, OA, and normal synovial tissues.
  
  
  RESULTS
  Synovial fluid analysis demonstrated that APC is present in both RA and OA synovial fluid, with APC activity being markedly higher in RA (mean +/- SEM 462 +/- 112 ng/ml versus 136 +/- 42 ng/ml; P < 0.02). A correlation (r(2) = 0.61) was found between APC and MMP-2 activity levels in RA patients, but not in OA patients. Immunohistochemical studies of synovial sections showed colocalization of APC and MMP-2 in endothelial and synovial lining cells. Additionally, APC and MMP-2 coimmunoprecipitated with an anti-PC/APC antibody.
  
  
  CONCLUSIONS
  Our results show, for the first time, that APC and MMP-2 are coordinately up-regulated and tightly bound in RA synovial fluid and colocalized in synovia. Their association suggests that APC may modulate MMP-2 activity in RA.
authors.affiliation: Institute of Bone and Joint Research, University of Sydney, Sydney, New South Wales, Australia. nathalie@med.usyd.edu.au
authors.forename: Nathalie
authors.initials: N
authors.lastname: Buisson-Legendre
authors.forename: Sue
authors.initials: S
authors.lastname: Smith
authors.forename: Lyn
authors.initials: L
authors.lastname: March
authors.forename: Christopher
authors.initials: C
authors.lastname: Jackson
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D010003:Osteoarthritis / Q000378:metabolism; D011233:Precipitin Tests; D011486:Protein C / Q000378:metabolism*; D013582:Synovial Fluid / Q000378:metabolism*; D013583:Synovial Membrane / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D011486:Protein C; D020778:Matrix Metalloproteinase 2