NLRP3 inflammasome promotes PAD2/PAD4 release and protein citrullination in rheumatoid arthritis

Anti-citrullinated protein antibodies (ACPAs), a hallmark of rheumatoid arthritis (RA), arise from citrullinated proteins presenting immunogenic neoepitopes that break self-tolerance. Citrullination is a post-translational modification catalyzed by peptidylarginine deiminases (PADs). Among five isoforms, PAD2 and PAD4 expressed in immune cells are most closely associated with RA pathogenesis. Although typically intracellular, PAD2 and PAD4 are detectable extracellularly in RA, yet the mechanisms governing their release remain unclear. Here, we show that NLRP3 inflammasome activation triggers PAD release from human neutrophils via an NLRP3-caspase-1-gasdermin D axis, independent of cell death. Inflammasome activation increases citrullination of intracellular proteins, while released PADs retain enzymatic activity and citrullinate extracellular substrates. In RA serum, PAD concentrations and PAD activity correlate with IL-1β, suggesting an analogous inflammasome-driven mechanism for extracellular PAD release in vivo. Collectively, these findings indicate that the NLRP3 inflammasome may promote autoimmunity in RA by amplifying citrullinated neoepitope generation that fuels ACPA production.