NLRX1 is a critical neutrophil checkpoint modulating ferroptosis and suppressing NETosis to attenuate joint damage in...

Neutrophil extracellular traps (NETs) are key drivers of inflammation and tissue damage in rheumatoid arthritis (RA), yet the mechanisms that restrain NETs overproduction remain unclear. Here, we identify the mitochondrial NOD-like receptor NLRX1 as a critical checkpoint limiting NETs production. The expression of NLRX1 is dysregulated in RA patients. NLRX1 deficiency leads to a profound expansion of the neutrophil population, and neutrophil-specific NLRX1 deficiency results in broad production of cytokines, chemokines, autoantibodies and complement accompanied by markedly accelerated arthritis, exaggerated NETs formation, and enhanced joint damage. Single-cell RNA sequencing reveals that NLRX1 restrains a Padi4-high neutrophil population that is central to NETosis. Mechanistically, NLRX1 deficiency promotes sustained TRAF6-NF-κB signaling and activates the NRF2-mediated oxidative defense pathway, which confers ferroptosis resistance to extend neutrophil lifespan and provides a prolonged temporal window for continuous NETs formation. NLRX1-knockdown cells exhibit increased NETs release, with a more ordered periodic distribution of myeloperoxidase (MPO) along the citrullinated histone H3 (CitH3)-decorated DNA backbone forming the typical 'beads-on-a-string' pattern, suggesting enhanced structural organization of NETs. NETs, known to directly degrade bone matrix through proteolytic enzymes, also promote TNFα production, with the cytokine enriched on NETs structures. TNFα in turn stimulates synovial macrophages to express the pro-osteoclastic factor RANKL, thereby fueling bone destruction. Pharmacological activation of the NLRX1 checkpoint attenuates osteoclast differentiation and joint damage. Collectively, these findings unveil the new role of NLRX1 in regulating neutrophil ferroptosis and NETs production and its potential as a therapeutic target for mitigating cartilage and bone damage in RA.