Lipopolysaccharide promotes rheumatoid arthritis by enhancing Wnt7b mediated macrophage-FLS communication

Our previous research has shown that lipopolysaccharide (LPS) derived from Gram-negative bacteria in the intestine promoted rheumatoid arthritis (RA) after entering peripheral blood, but the specific molecular mechanism was unclear.

This study used transcriptome and proteomic sequencing, western blotting, co-immunoprecipitation (Co-IP), cell co-culture, and other related methods to investigate whether LPS entering peripheral blood activated the Wnt7b secretion in macrophages, and used the Wnt7b as a messenger molecule to promote the communication between macrophage-fibroblast-like synoviocyte (FLSs), ultimately leading to the onset of RA.

The results showed that LPS significantly promoted the pathology of collagen induced arthritis (CIA) mice. Transcriptome and proteomic sequencing, as well as experimental validation, confirmed that the target of LPS may be the Wnt7b. Knocking down the Wnt7b in CIA mice could effectively alleviate the LPS induced pathology. Furthermore, in the M₀ macrophage-FLS co-culture system, overexpression of Wnt7b in M₀ macrophages promoted the expression of RA pathological factors in FLSs and activated the WNT/CTNNB1 signaling pathway of FLSs. However, knocking down the Wnt7b in M₁ macrophages resulted in the opposite effects. Interestingly, in the M₀ macrophage-FLS co-culture system, overexpression of Wnt7b in M₀ macrophages could enhance the expression of frizzled class receptor 8 (FZD8) on FLSs, activating the Wnt/β-catenin signaling pathway of FLSs. However, knocking down the FZD8 in FLSs after overexpression of Wnt7b could interfere with the effects of overexpression of Wnt7b. In addition, adding LPS to M₀ macrophages promoted the FZD8 expression of co-cultured FLSs and activated the Wnt/β-catenin signaling pathway. Knocking down FZD8 in FLSs after adding LPS to M0 macrophages could interfere with the effects of LPS.

This study suggested that circulating LPS stimulated macrophages to secrete Wnt7b, which acted as a messenger molecule and bound to the FZD8 receptor on the FLSs cell membrane in the synovial microenvironment, promoting the activation of the Wnt/β-catenin signaling pathway in FLSs and leading to RA.