TNF promotes osteoclastogenesis by secreting miR-31-5p into small extracellular vesicles via the autotaxin–LPA–LPAR1 axis in arthritic fibroblast-like synoviocytes

Abstract

Fibroblast-like synoviocytes (FLSs) play a crucial role in the pathogenesis of arthritis. However, the impact of small extracellular vesicles (sEVs) secreted by FLSs on osteoclastogenesis remains incompletely understood. In this study, we aimed to investigate the role of tumor necrosis factor (TNF)- and lysophosphatidic acid (LPA)-activated FLSs in sEV-mediated release of osteoclastogenic miRNAs and elucidate their functional contribution to osteoclastogenesis. Stimulation of SW982 cells with LPA or TNF significantly increased sEV secretion. TNF upregulated autotaxin expression and promoted sEV release; however, small interfering RNA (siRNA)-mediated knockdown (KD) of LPAR1 attenuated the increase in sEV release induced by the TNF–autotaxin–LPA axis. Notably, stimulation with TNF or LPA elevated syntenin-1 expression without altering its mRNA level. Furthermore, KD of the syntenin-1 gene (SDCBP) suppressed the LPA-induced increase in sEV release, indicating that syntenin-1 may mediate sEV secretion induced by the TNF–autotaxin–LPA–LPAR1 axis. sEVs derived from TNF- or LPA-treated SW982 cells stimulated osteoclastogenesis. We identified miR-31-5p as an osteoclastogenic miRNA enriched in sEVs. Expression levels of miR-31-5p in sEVs from TNF- and LPA-stimulated rheumatoid arthritis (RA) FLSs were significantly higher than in those from unstimulated RA FLSs. Treatment with a miR-31-5p mimic enhanced osteoclastogenesis by targeting large tumor suppressor kinase 2 (LATS2), whereas treatment with its inhibitor suppressed the sEV-mediated promotion of osteoclastogenesis. These findings reveal a mechanism by which TNF- and LPA-activated FLSs may facilitate sEV-mediated delivery of osteoclastogenic miRNAs, such as miR-31-5p, to osteoclast precursors, thereby contributing to osteoclast formation and bone destruction.