Objective: The aim of this study was to understand the cellular/molecular mechanisms of periodontal breakdown in a collagen-induced arthritis (CIA) model in mice to enhance the understanding of rheumatoid arthritis (RA)-associated alveolar bone loss in humans. Materials and Methods: All analyses were performed on paired samples from CIA and control group mice. Mandibles were retrieved for micro-computed tomography (micro-CT), histomorphometric analysis, and isolation of alveolar bone cells (ABCs). In vitro steoclastogenic/osteogenic/adipogenic potentials of ABCs were evaluated and the mRNA expression of downstream effector genes was assessed. Bone formation of ABCs was assessed using an ectopic transplantation model. Results: Histomorphometric and micro-CT data showed that alveolar bone loss was significantly increased in the CIA group (p<0.05). Osteoclastogenesis was significantly increased in the CIA group in vivo (p<0.05), with upregulated mRNA expressions of osteoclastogenesis-associated genes. Osteoblasts appeared to undergo increased apoptosis, and the bone-forming activity of ABCs concomitantly decreased with in vitro osteogenic differentiation and in vivo ectopic transplantation (p<0.05). Also, adipogenesis-associated mRNA expression was highly expressed in the CIA group, resulting in significantly enhanced adipocyte differentiation in vitro (p<0.05). Conclusions: These data demonstrate that increased osteoclastic activity, decreased bone-forming activity and enhanced adipogenesis promote alveolar bone loss in a CIA model in mice, and they suggest that these mechanisms could account for the same outcome in human RA.
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