Juvenile idiopathic arthritis (JIA) is a chronic inflammatory joint disease with limited disease-modifying therapeutic options and poorly defined metabolic drivers of persistent synovitis. Urolithin A (UA), a gut microbiota-derived metabolite, exhibits potent anti-inflammatory and mitochondrial-protective properties; however, its mechanistic role in JIA remains unknown. This study aimed to elucidate the therapeutic potential and molecular basis of UA in JIA.

The collagen-induced arthritis (CIA) mouse model was used to evaluate the effects of UA on JIA-like pathological progression. Joint pathological alterations were assessed by immunohistochemistry, immunofluorescence, and SO/FG staining. A TNF-α–stimulated macrophage model was employed to investigate the inhibitory effects of UA on reactive oxygen species (ROS) production, oxidative stress, and inflammatory cytokine release. In parallel, macrophages stimulated with synovial fluid derived from JIA patients were used to assess UA-mediated suppression of inflammatory responses. In addition, network pharmacology, molecular docking, and clinical correlation analyses were performed to identify xanthine dehydrogenase (XDH) as a potential key target of UA. Transcriptomic sequencing was further conducted to characterize the regulatory effects of UA on TNF-α–induced macrophage transcriptional programs. 

UA markedly alleviated pathological progression in CIA mice, as evidenced by reduced inflammatory cytokine and ROS production in synovial macrophages. Consistently, UA significantly suppressed inflammatory responses in macrophages stimulated with JIA patient–derived synovial fluid. Network pharmacology and molecular docking analyses identified XDH as a major functional target of UA, and UA treatment significantly downregulated XDH expression. Mechanistically, XDH was closely associated with JIA pathological activity, and UA-mediated regulation of Parkin/PINK1-dependent mitophagy and ROS production was largely achieved through suppression of XDH. Transcriptomic analyses further demonstrated that UA profoundly reshaped the TNF-α–induced macrophage transcriptome, prominently inhibiting TNF-α–related inflammatory signaling pathways. 

These findings demonstrate that UA significantly attenuates pathological progression in experimental JIA. The underlying mechanism likely involves targeted suppression of XDH by UA, leading to restoration of Parkin/PINK1-mediated mitophagy, improvement of mitochondrial homeostasis, and reduction of excessive ROS generation, thereby limiting inflammatory damage in synovial macrophages. This study provides a mechanistic and translational foundation for UA as a potential targeted therapeutic strategy for JIA.