Upregulation of sphingosine-1-phosphate receptor 3 on fibroblast-like synoviocytes is associated with the development of collagen-induced arthritis via increased interleukin-6 production

by Takuya Inoue, Masataka Kohno, Hidetake Nagahara, Ken Murakami, Tomoya Sagawa, Akiko Kasahara, Shunya Kaneshita, Takashi Kida, Kazuki Fujioka, Makoto Wada, Hiroshi Nakada, Timothy Hla, Yutaka Kawahito

Background

Sphingosine-1-phosphate receptor 3 (S1P₃) is one of five receptors for sphingosine-1-phosphate (S1P). S1P/S1P₃ signaling is involved in numerous physiological and pathological processes including bone metabolism, sepsis, cancer, and immunity. In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLSs) are activated by several factors and promote abundant proinflammatory cytokine production and bone destruction. The aim of this study was to investigate whether S1P₃ is associated with the development of autoimmune arthritis and the pathogenic function of FLSs.

Methods

Wild-type (WT) and S1P₃ knockout (S1P₃-KO) collagen-induced arthritis (CIA) mice were evaluated with respect to clinical and histological disease severity, along with the levels of anti-collagen antibodies and expression of tumor necrosis factor-α (TNFα) and interleukin-6 (IL-6). S1P₃ expression in the synovium was analyzed by real-time reverse-transcription polymerase chain reaction (RT-PCR) and immunofluorescence staining. FLSs isolated from CIA mice were activated with TNFα and S1P₃ expression was analyzed by real-time RT-PCR. The role of S1P/S1P₃ signaling in activated and non-activated FLSs was investigated by measuring cell proliferation and cyto/chemokine production by real-time RT-PCR and/or enzyme-linked immunosorbent assay.

Results

Clinical and histological scores, and synovial IL-6 expression were significantly lower in S1P₃-KO mice with CIA than in WT mice. Arthritic synovia had higher S1P₃ expression than intact synovia and FLSs in arthritic joints expressed S1P₃ in vivo. Primary cultured FLSs produced IL-6 in a time-dependent manner in response to S1P stimulation and exhibited higher levels of S1P₃ expression after activation with TNFα. S1P₃-induced production of IL-6 and MMP-3 was increased in FLSs pre-activated with TNFα.

Conclusion

In this study, we demonstrated that S1P₃ expression is associated with the development of autoimmune arthritis via inflammation-induced increases in S1P/S1P₃ signaling that increase production of IL-6 in FLSs. Inhibition of S1P/S1P₃ signaling could open the door to the development of new therapies for RA.