Abstract
Rheumatoid arthritis (RA) is a systemic inflammatory disease that mainly affects the synovial joints. Although involvement of the fibroblast growth factor (FGF) signaling pathway has been suggested as an important modulator in RA development, no clear evidence has been provided. In this study, we found that synovial fluid basic FGF (bFGF) concentration was significantly higher in RA than in osteoarthritis (OA) patients. bFGF stimulates proliferation and migration of human fibroblast-like synoviocytes (FLSs) by activation of the bFGF-FGF receptor 3 (FGFR3)-ribosomal S6 kinase 2 (RSK2) signaling axis. Moreover, a molecular docking study revealed that kaempferol inhibited FGFR3 activity by binding to the active pocket of the FGFR3 kinase domain. Kaempferol forms hydrogen bonds with the FGFR3 backbone oxygen of Glu555 and Ala558 and the side chain of Lys508. Notably, the inhibition of bFGF-FGFR3–RSK2 signaling by kaempferol suppresses the proliferation and migration of RA FLSs and the release of activated T-cell-mediated inflammatory cytokines, such as IL-17, IL-21, and TNF-α. We further found that activated phospho-FGFR3 and -RSK2 were more highly observed in RA than in OA synovium. The hyperplastic lining and sublining lymphoid aggregate layers of RA synovium showed p-RSK2-expressing CD68+ macrophages with high frequency, while pRSK2-expressing CD4+ T-cells was observed at a lower frequency. Notably, kaempferol administration in collagen-induced arthritis mice relieved the frequency and severity of arthritis. Kaempferol reduced osteoclast differentiation in vitro and in vivo relative to the controls and was associated with the inhibition of osteoclast markers, such as tartrate-resistant acid phosphatase, integrin β3, and MMP9. Conclusively, our data suggest that bFGF-induced FGFR3–RSK2 signaling may play a critical role during the initiation and progression of RA in terms of FLS proliferation and enhanced osteoclastogenesis, and that kaempferol may be effective as a new treatment for RA.
Highlights
Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by infiltration of immune cells into the synovium and hyperplasia of the synovial lining
Data were obtained from three independent experiments, and values are represented as means ± SEM. *p < 0.001 by Student’s t-test. d Representative photographs (×40) of triple immunohistofluorescence analysis of tissues obtained from OA (n = 5) and RA (n = 5) patients. p-ribosomal S6 kinase 2 (RSK2) and p-FGF receptor 3 (FGFR3) were co-stained with CD4- or CD68- specific antibodies as indicated and analyzed by confocal microscopy
Data were obtained from three independent experiments, and values are represented as means ± SEM. *p < 0.01; **p < 0.001. d, e Kaempferol binding to FGFR3 was confirmed by a cyanogen bromide (CNBr)-kaempferol pull-down assay using a commercial FGFR3 kinase domain (c) and a membrane fraction of MH7A cells (d)
Summary
Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by infiltration of immune cells into the synovium and hyperplasia of the synovial lining. Since the angiogenesis and proliferation of fibroblast-like synoviocytes (FLSs) play pivotal roles in mechanisms involved in RA pathogenesis[5], altered activities of angiogenic and growth factors in RA synovium or synovial fluids (SF) have been considered as treatment targets for the disease[5,6,7]. The pathophysiological roles of bFGF in RA and its signaling in immune cells or FLSs have not been well understood Proinflammatory cytokines such as TNF-α, IL-1, and IL-6 induce inflammatory reaction and chemokine production in FLSs, resulting in the increased influx of additional proinflammatory cells, including macrophages, into the synovium[11]. We found that kaempferol was identified as a compound that inhibits FGFR3 kinase activity in RA FLSs, resulting in significant inhibition of FLS proliferation and migration. Kaempferol treatment in arthritis mice attenuated arthritis severity and osteoclastogenesis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
