Osteoimmunology of Osteoporosis in Rheumatoid Arthritis: Emerging Mechanisms and Therapeutic Implications

Patients with rheumatoid arthritis (RA) exhibit a significantly higher incidence of secondary osteoporosis compared to the general population, leading to substantially increased fracture risk, compromised quality of life, and poorer prognosis. Traditional views attribute this primarily to inflammatory activity, immobilization, and glucocorticoid use. However, the emergence of osteoimmunology has revealed deeper mechanisms, demonstrating that RA-induced osteoporosis represents a classic paradigm of osteoimmune dysregulation. This review systematically synthesizes recent advances (past 5-10 years) in understanding the pathophysiology of RA-induced osteoporosis from an osteoimmunological perspective. Research indicates that within the synovial and bone marrow microenvironments of RA, activated immune cells and stromal cells secrete abundant pro-inflammatory cytokines and express signaling molecules. This process severely disrupts core regulatory pathways of bone remodeling, leading to a profound imbalance characterized by excessive bone resorption and inadequate bone formation. Key mediators of this imbalance include dysregulation of the RANKL/RANK/OPG system and upregulation of potent inhibitors of the bone-forming Wnt pathway. Complex interactions between immune cells and bone cells are critical in establishing a localized bone-destructive microenvironment. Emerging research areas, including gut microbiota dysregulation, epigenetic mechanisms, and neuro-immune interactions, provide novel insights into these mechanisms. This review emphasizes that dysregulation of the osteoimmune system constitutes the core pathophysiological basis of RA-induced osteoporosis. A deeper understanding of these mechanisms is crucial for developing targeted bone-protective therapies and guiding future clinical strategies.