A contribution of mast cells and its mediators in the pathogenesis of arthritis has been postulated. We aimed to clarify the role of mast cell-derived serine protease tryptase and proteinase activated receptor (PAR)-2-mediated signaling in chondrocytes.
Human articular cartilage specimens were obtained from patients with osteoarthritis (OA), rheumatoid arthritis (RA) and with traumatic fracture without arthritis (PT; as controls) who underwent joint surgery. Isolated chondrocytes were cultured in vitro by monolayer, and confluent cells were incubated with recombinant human lung Beta tryptase or with a PAR-2 agonist peptide. The secreted level of vascular endothelial growth factor (VEGF) in culture supernatant was measured using commercially available ELISA kits, and expression of VEGF mRNA was analyzed using real-time PCR.
The tryptase-stimulated chondrocytes from OA or RA, but not from PT patients, produced significantly higher amount of VEGF in their supernatants. The response was blocked by a G-protein receptor inhibitor pertussis toxin, however, was not reproduced by incubation of cells with the PAR-2 agonist, suggesting a presence of non-PAR-2 dependent signals for the VEGF induction. In addition, actinomycin D and cycloheximide did not exert significant inhibition, indicating a regulation of VEGF release by tryptase.
The inflammatory mediator, mast cell-derived protease tryptase may modulate chondrocyte metabolism through induction of VEGF release.