Correlation of protease-activated receptor-2 expression and synovitis in rheumatoid and osteoarthritis

Rheumatol Int. 2012 Oct;32(10):3077-86. doi: 10.1007/s00296-011-2102-9. Epub 2011 Sep 13.


Protease-activated receptor-2 (PAR-2) is known to be pro-inflammatory and increasing evidence points to an inflammatory component in osteoarthritis. This investigation examined the relationship between synovitis and PAR-2 expression, histological and immunohistochemical analysis being performed on synovial samples obtained from OA and RA patients, along with non-arthritic samples obtained by post mortem (PM). Samples were also analysed for PAR-4 expression, this receptor also having putative pro-inflammatory roles. Analysis involved comparison of inflammatory indices (synovial thickness and monocyte infiltration) with expression of PAR-2 and PAR-4. Synovial explants were also analysed for TNFα generation in the presence of a PAR-2 antagonist (ENMD-1068) or vehicle. OA synovia showed heterogeneity of inflammatory indicators, some samples overlapping with those from the RA cohort whilst others appeared similar to the PM cohort. PAR-2 expression, both in the lining layer and the interstitium, correlated strongly and significantly with synovial thickness (r = 0.91) and monocyte infiltration (r = 0.83), respectively (P < 0.001 in both cases), and this remains significant on individual cohort analysis. PAR-2 was co-localised to CD3 and CD68 cells in RA and OA synovium as well as fibroblasts derived from these synovia. PAR-4 was also expressed, but the relationship with inflammatory indicators was substantially weaker. Inflammatory indicators in OA synovia showed considerable variability, but correlated strongly with PAR-2 expression, suggesting PAR-2 upregulation in synovitis. Heterogeneity of inflammatory indicators was paralleled by wide variation in TNFα generation between samples. Secretion of this cytokine was dose-dependently inhibited by ENMD-1068, providing evidence of a functional role for PAR-2 in promoting synovitis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Arthritis, Rheumatoid / immunology
  • Arthritis, Rheumatoid / metabolism*
  • Arthritis, Rheumatoid / pathology
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Female
  • Humans
  • Immunohistochemistry
  • Inflammation Mediators / metabolism*
  • Male
  • Middle Aged
  • Osteoarthritis / immunology
  • Osteoarthritis / metabolism*
  • Osteoarthritis / pathology
  • Piperazines / pharmacology
  • Receptor, PAR-2 / antagonists & inhibitors
  • Receptor, PAR-2 / metabolism*
  • Receptors, Thrombin / metabolism
  • Synovial Membrane / drug effects
  • Synovial Membrane / immunology
  • Synovial Membrane / metabolism*
  • Synovial Membrane / pathology
  • Synovitis / immunology
  • Synovitis / metabolism*
  • Synovitis / pathology
  • Tumor Necrosis Factor-alpha / metabolism


  • 1-3-methylbutyryl-N4-6-aminohexanoyl-piperazine
  • Inflammation Mediators
  • Piperazines
  • Receptor, PAR-2
  • Receptors, Thrombin
  • Tumor Necrosis Factor-alpha
  • protease-activated receptor 4