HMGB1-LPS complex promotes the transformation of SFs to a RASF-like phenotype (P4168)

Abstract

Abstract The specific pathogenesis of rheumatoid arthritis (RA) remains unclear. Current views hold that some inflammatory antigens recognize the Toll-like receptors on the synovial fibroblasts (SFs) and then activate downstream signals, leading to the formation of RASFs and the induction of RA. Our previous studies showed that intra-articular injection of the complex of HMGB1 and lipopolysaccharide (LPS) directly induced experimental arthritis in DBA/1 mice; histopathological analysis further revealed synovial thickening with excessive proliferation of SFs. In the present study, osteoarthritis synovial fibroblasts (OASFs) were co-cultured with HMGB1-LPS complex in vitro for 5-8 generations to induce the transformation of human SFs to RA-like SFs (tOASFs). Then the pathogenicity of tOASFs was evaluated, both in vitro and in vivo. Our results showed that tOASFs attached to, invaded and degraded co-implanted cartilage in a SCID mouse model. In addition, histochemistry showed excessive proliferation of tOASFs and the expression of MMPs. In vitro, cell cycle analysis showed more tOASFs passing through the G1/S checkpoint and moving to S or G2 phase. Flow cytometry and confocal microscopy showed significantly reduced apoptosis and enhanced autophagy in tOASFs compared to OASFs, respectively. Finally, we showed upregulated expression of certain receptors and adhesion molecules in tOASFs. This accumulated evidence led to the conclusion that HMGB1-LPS complex promoted the formation of RASFs.