Objectives:In the synovial membrane of rheumatoid arthritis (RA)patients, a strong expression of laminins and matrix degrading proteases was reported. We therefore investigated the regulation of matrix metalloproteinases (MMP) in synovial fibroblasts (SF) of osteoarthritis (OA) and RA patients by attachment to laminin-1 (LM-111)and in the presence or absence of co- stimulatory signals provided by transforming growth factor- (TGF-ß).
Methods:SF were seeded in laminin-coated flasks and activated by addition of TGF-ß. The expression of genes was investigated by qRT-PCR, immunocytochemistry, and ELISA, and intracellular signaling pathways by immunoblotting, and by poisoning p38MAPK by SB203580, MEK-ERK by PD98059, and SMAD2 by A-83-01.
Results:Attachment of SF to LM-111 did not activate the expression of MMPs, but addition of TGF-ß induced a five-fold higher expression of MMP-3. Incubation of SF on LM-111 in the presence of TGF-ß induced a significant twelve fold higher expression of MMP-3 mRNA and secretion of MMP-3 was elevated twenty fold above controls. Functional blocking of LM-111 - integrin interaction reduced the laminin-activated MMP-3 expression significantly. Stimulation of SF by LM-111 and TGF-ß activated the p38MAPK, ERK and SMAD2 pathways and inhibition of these pathways by utilizing SB203580, PD98059, or A-83-01, confirmed the involvement of these pathways in the regulation of MMP-3.
Conclusion:Attachment of SF to LM-111 by itself has only minor effects on the expression of MMP-1 or MMP- 3 but it facilitates the TGF- induced expression of MMP-3 significantly. This mode of MMP-3 induction may therefore contribute to inflammatory joint destruction in RA independent of the pro-inflammatory cytokines IL- 1ß or TNF-.
- signal transduction,
- synovial fibroblast,