Hidden oral-joint-lung axis: Porphyromonas gingivalis Infection promotes the EMyT of RA-ILD by inhibiting the JUN-regulated palmitoylation balance.

BACKGROUND

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is a major cause of mortality among patients with rheumatoid arthritis (RA), yet the pathological mechanism linking joint and lung involvement remains poorly understood. The pathogenic role of Porphyromonas gingivalis (P.g) in RA has been established. This study investigated how P.g infection drives RA-ILD through palmitoylation-mediated epithelial-myofibroblast transition (EMyT), thereby uncovering a mechanistic basis for the oral-joint-lung connection.

METHODS

Metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid and 16S rRNA sequencing of fecal samples from patients with RA-ILD were analyzed to assess the association between P.g and RA-ILD. A collagen-induced arthritis (CIA) mouse model and human lung epithelial cell lines (A549 and BEAS-2B) infected with P.g were established. Palmitoylation dynamics, EMyT marker expression, and the function of the hub gene JUN were evaluated using immunopathology, qPCR, western blotting (WB), single-cell sequencing, and molecular docking. Mechanistic studies employed the JUN activator c2-ceramide, the JUN inhibitor pterostilbene, and the palmitoylation inhibitor 2-BP to determine how P.g regulates palmitoylation in promoting RA-ILD.

RESULTS

Both mNGS and 16S rRNA analyses revealed a strong association between Porphyromonas spp. infection and RA/RA-ILD. P.g infection significantly increased EMyT marker expression (collagen I, fibronectin, and vimentin) in vitro and induced pulmonary fibrosis in CIA-ILD mice, with palmitoylation playing a central role. Mechanistically, JUN was identified as a key regulator of palmitoylation. P.g suppressed JUN level, activated ZDHHC3, and inhibited PPT1, leading to palmitoylation imbalance. Activation of JUN by c2-ceramide, combined with inhibition of palmitoylation by 2-BP, effectively suppressed EMyT progression in RA-ILD.

CONCLUSION

This study identifies a novel "oral-joint-lung axis" in which P.g infection promotes EMyT and fibrosis in RA-ILD by disrupting JUN-regulated palmitoylation homeostasis. Modulation of this axis provides a promising therapeutic strategy for RA-ILD.