ACPA-Induced ATP release and K+ efflux trigger NLRP3 inflammasome activation in rheumatoid arthritis

Objectives: Anti-citrullinated protein antibodies (ACPA) is one of the key inducers of the initiation and maintenance of the immune-inflammatory response in Rheumatoid arthritis (RA), yet evidence is lacking on how ACPA drives the inflammatory response.

Methods: Citrullinated collagen-induced arthritis (C-CIA) were performed to evaluate the inflammatory response, especially NLRP3 inflammasome activation, in ACPA + arthritis model. Macrophages differentiated from THP-1 cell line were stimulated by ACPA purified from RA patients' serum, and the localization and interaction of molecules involved in NLRP3 inflammasome were analyzed by confocal microscopy and immunoprecipitation.

Results: Mice with arthritis induced by citrullinated Collagen showed higher levels of ACPA and enhanced activation of the NLRP3 inflammasome. This was evidenced by increased levels of IL-1β in the peripheral blood and more pronounced Pyroptosis and Caspase-1 (p20) expression in the synovial tissue, compared to mice induced with common Collagen. ACPA induced overactivation of NLRP3 inflammasome in THP-1-differentiated macrophages in vitro. ACPA recruits SFK kinase by binding to Integrin α₅β₁, induces C-terminal phosphorylation of Panx-1, and opens pannexin channel to release ATP; In addition, ACPA mediates the outflow of K⁺ into the extracellular by activating TWIK2 channel. These two signaling axes collectively lead to the activation of the NLRP3 inflammasome.

Conclusion: Our study demonstrates that ACPA can trigger both the priming and activation of the NLRP3 inflammasome. This process involves the release of ATP and the efflux of K⁺.