Objective: To address the relative importance of tumor necrosis factor-receptor 1 (TNF-R1)/TNF-R2 and their signaling pathways for pro-inflammatory and pro- destructive features of early-passage synovial fibroblasts (SFB) from rheumatoid arthritis (RA) and osteoarthritis (OA).
Methods: Cells were stimulated with TNF-alpha or agonistic anti-TNF-R1/TNF-R2 mAbs. Phosphorylation of p38, ERK, and JNK kinases was assessed by western blot; proliferation by bromodesoxyuridine incorporation; IL-6, IL-8, PGE2, and MMP-1 secretion by ELISA and MMP-3 secretion by western-blot. Functional assays were performed with/without inhibition of p38 (SB203580), ERK (U0126), or JNK (SP600125).
Results: In RA- and OA-SFB, TNF-alpha-induced phosphorylation of p38, ERK, or JNK was exclusively mediated via TNF-R1. Reduction of proliferation and induction of IL-6, IL-8, and MMP-1 were solely mediated by TNF-R1, whereas PGE2 and MMP-3 secretion was mediated by both TNF-Rs. In general, inhibition of ERK or JNK did not significantly alter the TNF-alpha influence on these effector molecules. In contrast, inhibition of p38 reversed TNF-alpha effects on proliferation and IL- 6/PGE2 secretion (but not on IL-8 and MMP-3 secretion). The above effects were comparable in RA- and OA-SFB, except that TNF-alpha-induced MMP-1 secretion was reversed by p38 inhibition only in OA-SFB.
Conclusion: In early-passage RA/OA-SFB, activation of MAPK cascades and pro-inflammatory/pro- destructive features by TNF-alpha is predominantly mediated by TNF-R1 and, for proliferation and IL-6/PGE2, exclusively regulated by p38. Strikingly, RA-SFB are insensitive to p38 inhibition of MMP-1 secretion. This indicates a resistance of RA-SFB to the inhibition of pro-destructive functions and suggests underlying structural/functional alterations of the p38 pathway, which may contribute to the pathogenesis and/or therapeutic sensitivity of RA.
- p38 MAP kinase
- synovial fibroblast