Gut-bone axis in rheumatoid arthritis: microbiota-driven barrier dysfunction, immune crosstalk, and therapeutic strategies.

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent synovial inflammation and progressive bone destruction in which immune dysregulation plays a central role. Recent evidence has highlighted the gut-bone axis as a critical framework linking gut microbiota to skeletal and immune homeostasis. Gut microbiota dysbiosis disrupts intestinal barrier integrity by altering tight junction proteins and increasing intestinal permeability, facilitating microbial translocation and triggering systemic inflammatory responses. Microbiota-derived metabolites, including short-chain fatty acids, bile acids, and tryptophan metabolites, act as key mediators along the gut-bone axis. These metabolites regulate multiple signaling pathways and immune cell functions, particularly by modulating the balance between T helper 17 and regulatory T cells, suppressing B-cell hyperactivation, promoting macrophage M2 polarization, and inhibiting dendritic cell maturation. These actions may contribute to immune homeostasis and bone metabolism associated with RA. This review systematically summarizes the role of gut microbiota dysbiosis, intestinal barrier dysfunction, and microbial metabolites in RA pathogenesis within the framework of the gut-bone axis. Furthermore, microbiota-targeted therapeutic strategies, including probiotics, prebiotics, dietary interventions, fecal microbiota transplantation, and traditional Chinese medicine, are discussed as potential approaches to restore host-microbiota balance. However, most current evidence is derived from preclinical studies, highlighting the need for further clinical validation. Despite these limitations, a deeper understanding of microbiota-driven mechanisms along the gut-bone axis may provide novel insights into RA pathogenesis and facilitate the development of targeted and personalized therapeutic strategies.