Complement factor H-related protein 5 alleviates joint inflammation and osteoclast differentiation by disrupting RANK-JNK signaling in collagen antibody-induced arthritis mouse model.

Background: Complement Factor H-Related protein 5 (CFHR5) belongs to the factor H/CFHR family and regulates the complement system by modulating factor H's inhibitory activity against C3b. Despite its known role, the impact of CFHR5 on autoimmune arthritis and its relationship to pathophysiological changes in arthritis and bone loss remain unclear. This study aimed to assess the effect of CFHR5 on aggressive osteoclast activity and arthritis using a murine model of collagen antibody-induced arthritis (CAIA).

Methods: The effect of recombinant CFHR5 protein (rCFHR5) on arthritis were evaluated in CAIA. The mice were divided into three group and intraperitoneally treated with rCFHR5, methotrexate (MTX) as positive control or PBS as negative control. In the CAIA mouse model, the rCFHR5-treated group significantly reduced the incidence and clinical arthritis equivalent to the MTX group. Clinical arthritis scores, incidence and body weight were measured, and histological analysis of ankle joints was performed by Hematoxylin and Eosin (H&E) and Safranin O - Fast green (SOFG), Tartrate-resistant acid phosphatase (TRAP) staining and Immunohistochemistry. Moreover, to investigate the rCFHR5 role, we isolated murine osteoclast precursor cells (OCPs) from each group, induced osteoclasts with M-CSF and RANKL, and performed TRAP and F-actin staining. To verify the mechanism, mRNA and protein analyses were performed in OCPs.

Results: Histological examination of ankle joints revealed substantial reductions in synovial hyperplasia, bone marrow inflammation, bone erosion, cartilage destruction and TRAP-positive cells in the rCFHR5 group compared to the vehicle group. The ankle joints of the rCFHR5 group showed markedly decreased expression of proinflammatory cytokines (TNF-α, IL-1β and IL-6). Mechanically, treatment with rCFHR5 inhibited RANKL-mediated osteoclast differentiation from OCPs and disrupted the RANK-JNK signaling. These findings demonstrate that treatment with rCFHR5 attenuates joint inflammation and reduces osteoclast differentiation, indicating its potential anti-inflammatory effect in autoimmune arthritis models.