Rheumatoid arthritis (RA) is a complex autoimmune disease characterized by chronic inflammation and joint destruction, with its pathogenesis not yet fully elucidated. In recent years, the dysbiosis of gut microbiota has garnered significant attention regarding its role in the development of RA. Hypoxia-inducible factor 1 alpha (HIF-1α) serves as a pivotal transcription factor that connects hypoxic conditions with immune responses. It participates in the regulation of gut barrier function and local immune reactions, affecting the composition of gut microbiota. Our research indicates that this regulatory function is closely linked to peptidylarginine deiminase 4 (PAD4). Therefore, the present study aims to investigate the mechanisms by which HIF-1α regulates gut microbiome homeostasis through PAD4 during the progression of RA, revealing its potential biological significance in the pathogenesis of the disease, and providing new therapeutic targets for RA.

This study utilized a collagen-induced arthritis (CIA) mouse model. HIF-1α expression was induced through cobalt chloride injection, accompanied by the administration of the PAD4-specific inhibitor GSK484. Arthritis severity and bone destruction were assessed using immunohistochemistry, ELISA, Micro-CT, and hematoxylin and eosin (HE) staining. The composition of gut microbiota was analyzed via 16S rDNA sequencing, while non-targeted metabolomics techniques were employed to evaluate fecal metabolic profiles. Principal component analysis, LEfSe analysis, and Spearman correlation analysis were utilized to systematically assess the variations in microbiota and metabolites, along with their associations.

 The study found that cobalt chloride significantly intensified arthritis, synovial hyperplasia, and bone degradation in CIA mice, accompanied by an upregulation of PAD4 expression in the synovium and spleen. Treatment with GSK484 effectively reversed these pathological changes. Gut microbiota analysis demonstrated that cobalt chloride exacerbated dysbiosis in CIA mice, with combined GSK484 treatment partially correcting this microbial imbalance. Additionally, metabolomic analysis revealed significant alterations in fecal metabolite profiles induced by cobalt chloride, with GSK484 reversing some of these changes. Correlation analyses indicated strong associations between specific gut bacteria and metabolic changes, with these associations disrupted by cobalt chloride but partially restored by GSK484.

 This study provides the first evidence that the HIF-1α-PAD4 signaling axis exacerbates joint damage in RA models by modulating gut microbiota dysbiosis and metabolic imbalances. These findings offer new insights into the pathological mechanisms underlying the “gut-joint” axis in RA and suggest that targeting HIF-1α may represent a novel therapeutic strategy for managing RA through the regulation of gut microbiota.