Trabecular bone loss in collagen antibody-induced arthritis.

Introduction: Postmenopausal women with rheumatoid arthritis (RA) have increased risk of developing osteoporosis due to chronic inflammation and estrogen deprivation. Collagen antibody-induced arthritis (CAIA), an experimental polyarthritis model representing the effector phase of arthritis, is mainly mediated by the innate immune system. Compared to the widely used collagen-induced arthritis model, CAIA is conveniently short and can be used in C57BL/6 mice, enabling studies with knock-out mice. However, the impact on bone of the CAIA model in C57BL/6 mice has not previously been studied. Therefore, the aim of this study was to determine if CAIA can be used to study postmenopausal arthritis-induced osteoporosis.

Methods: CAIA was induced by administration of collagen-type II antibodies and lipopolysaccharide to ovariectomized female C57BL/6J mice. Control mice received lipopolysaccharide, but no antibodies. Nine days later, femurs were collected for high-resolution micro-CT and histomorphometry. Serum was used to assess cartilage breakdown and levels of complement. Frequencies of immune cell subsets from bone marrow and lymph nodes were analyzed by flow cytometery.

Results: Trabecular bone mass was decreased and associated with increased number of osteoclasts per bone surface in the CAIA model. Also, the frequency of interleukin-17(+) cells in lymph nodes was increased in CAIA.

Conclusion: The present study show that CAIA, a short reproducible arthritis model that is compatible with C57BL/6 mice, is associated with increased number of osteoclasts and trabecular bone loss.