F4/80+CD206+ M2-like macrophages contribute to bone erosion in collagen-induced arthritis by differentiating into osteoclasts

Abstract

Rheumatoid arthritis is an autoimmune disease characterized by synovial inflammation-driven cartilage and bone destruction, a process mainly mediated by osteoclasts. In recent years M2-like macrophages have been found to play an important role in the pathological process of RA by mediating pro-inflammatory effects, but their roles in the bone destruction of autoimmune arthritis have not been reported. In this study we identified that an abundant cell population of CD45+CD11b+Gr-1-F4/80+CD206+ cells, which were normally classified as M2-like macrophages, was present in synovium of collagen-induced arthritis (CIA) mice, and these cells had the potential to differentiate into osteoclasts. These M2-like macrophages sorted from CIA synovium highly expressed RANK and could be activated by RANKL and M-CSF to acquire osteoclast markers and bone resorption function both in vitro and in vivo. Furthermore, in vitro differentiated M2 macrophages from both CIA mouse bone marrow and RA patient peripheral blood mononuclear cells were also able to differentiate into osteoclasts, confirming the general osteoclastogenesis capability of M2 subtype macrophages. All these results suggest that synovial F4/80+CD206+ M2-like macrophages in RA may be novel osteoclast precursors and contribute significantly to bone erosive changes seen in RA. Our studies provided new directions and targets for the diagnosis and treatment of rheumatoid arthritis.