Induction of RANKL expression and osteoclast maturation by the binding of fibroblast growth factor 2 to heparan sulfate proteoglycan on rheumatoid synovial fibroblasts.
OBJECTIVE: Rheumatoid arthritis (RA) is characterized by progressive joint destruction. The aim of this study was to clarify the relevance of RA synovial fibroblasts (RASFs) and fibroblast growth factor 2 ( FGF-2), which is produced abundantly by RASFs, to the osteoclastogenesis and bone resorption in RA. METHODS: Synovial fibroblasts were prepared from the synovial tissues of 10 patients with active RA and 7 patients with osteoarthritis (OA). The expression of RANKL, intercellular adhesion molecule 1 (ICAM-1), FGF receptor 1 (FGFR-1), and heparan sulfate proteoglycan ( HSPG) on synovial fibroblasts was measured by FACScan. Osteoclast formation in cocultures of RASFs and peripheral blood mononuclear cells (PBMCs) was evaluated by tartrate-resistant acid phosphatase staining and a pit-formation assay using dentin slices. RESULTS: FGF-2 induced the expression of both RANKL and ICAM-1 on RASFs more so than on OA synovial fibroblasts (OASFs). FGF-2- induced up-regulation of RANKL and ICAM-1 was inhibited by anti- FGF-2 antibody. Although FGFR-1 was equally expressed on RASFs and OASFs, HSPG was highly expressed on RASFs. Up-regulation of RANKL by FGF-2 on RASFs was diminished by the removal of heparan sulfate with heparitinase. Osteoclast formation from PBMCs induced by RASFs was inhibited by the addition of either heparitinase, anti-ICAM-1 antibody, anti- FGF-2 antibody, or osteoprotegerin. FGF-2- induced RANKL on RASFs and osteoclast formation were suppressed by an inhibitor of ERK. CONCLUSION: FGF-2 was transferred to FGFR-1 through binding to HSPG, which is characteristically expressed on RASFs, resulting in RANKL- and ICAM-1- mediated maturation of osteoclasts via ERK activation. Thus, we propose that FGF-2 not only augments the proliferation of RASFs, but also is involved in osteoclast maturation, which leads to bone destruction in RA.[1]References
- Induction of RANKL expression and osteoclast maturation by the binding of fibroblast growth factor 2 to heparan sulfate proteoglycan on rheumatoid synovial fibroblasts. Nakano, K., Okada, Y., Saito, K., Tanaka, Y. Arthritis Rheum. (2004) [Pubmed]
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