Necessity of Lysophosphatidic Acid Receptor 1 for Development of Arthritis

Objective. Lysophosphatidic acid (LPA) is a bioactive lipid that binds to a group of cell surface G protein-coupled receptors (LPA receptors 1-6 [LPA(1-6)]) and has been implicated as an important mediator of angiogenesis, inflammation, and cancer growth. This study was undertaken to analyze the effects of LPA(1) on the development of arthritis. Methods. Expression of LPA receptors on synovial tissue was analyzed by immunohistochemistry and quantitative reverse transcription-polymerase chain reaction. The effects of abrogation of LPA(1) on collagen-induced arthritis (CIA) were evaluated using LPA(1)-deficient mice or LPA(1) antagonist. Migrating fluorescence-labeled CD11b+ splenocytes, which were transferred into the synovium of mice with CIA, were counted. CD4+ naive T cells were incubated under Th1-, Th2-, or Th17-polarizing conditions, and T helper cell differentiation was assessed. Osteoclast formation from bone marrow cells was examined. Results. LPA(1) was highly expressed in the synovium of patients with rheumatoid arthritis (RA) compared with that of patients with osteoarthritis. LPA(1)-deficient mice did not develop arthritis following immunization with type II collagen (CII). LPA(1) antagonist also ameliorated murine CIA. Abrogation of LPA(1) was associated with reductions in cell infiltration, bone destruction in the joints, and interleukin-17 production from CII-stimulated splenocytes. Infiltration of transferred CD11b+ macrophages from LPA(1)-deficient mice into the synovium was suppressed compared with infiltration of macrophages from wild-type mice. LPA(1) antagonist inhibited the infiltration of macrophages from wild-type mice. Differentiation into Th17, but not Th1 or Th2, and osteoclast formation were also suppressed under conditions of LPA(1) deficiency or LPA(1) inhibition in vitro. Conclusion. Collectively, these results indicate that LPA/LPA(1) signaling contributes to the development of arthritis via cellular infiltration, Th17 differentiation, and osteoclastogenesis. Thus, LPA(1) may be a promising target molecule for RA therapy.