Background/Purpose: CD13 is an ectopeptidase expressed on myeloid cells, endothelial cells, and rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS). Soluble (s) CD13 is generated by matrix metalloproteinase 14 (MMP14) cleavage of surface CD13 on FLS, and a high level of sCD13 is found in RA synovial fluid. We have identified bradykinin receptor B1 (B1R) as a receptor for sCD13. We also reported that B1R is expressed in RA synovial tissue and that sCD13 causes inflammatory arthritis via B1R. Furthermore, B1R is expressed on inflammation-stimulated monocytes and the sCD13/B1R axis is involved in monocyte migration. In RA, osteoclasts derived from monocytes play a pivotal role in the pathogenesis of bone destruction. We hypothesized that the sCD13/B1R axis is involved in differentiation from monocytes into osteoclasts.

Methods: RAW264.7 cells, mouse bone marrow derived osteoclast precursor cells (mOCPs), and human monocytes were obtained. These cells were incubated with macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor‑κB ligand (RANKL) with or without SSR240612, a B1R antagonist. The cells were stained for tartrate-resistant acid phosphatase (TRAP). TRAP-positive multinucleated (three or more nuclei) cells were counted as osteoclasts. A resorption assay was conducted using plates coated with calcium phosphate thin films. The surface expression of CD13, B1R, and MMP14 on these cells was analyzed by flow cytometry and sCD13 was measured using ELISA. Gene expression was analyzed by qPCR. Immunocytochemistry for CD13 and B1R was also conducted. One-way ANOVA was used to compare differences between groups. P values of less than 0.05 were considered statistically significant.

Results: RAW264.7 cells, which express high levels of CD13, B1R, and MMP14, differentiated into osteoclasts by incubation with RANKL and showed resorption activity; both are significantly blocked by B1R inhibition. sCD13-induced ERK1/2 phosphorylation was also blocked by SSR240612 in these cells. Similarly, mOCPs-derived osteoclasts differentiation was inhibited by addition of SSR240612. In addition, osteoclast suppression by SSR240612 was also observed in mOCPs derived from male and female mice, regardless of age. In human monocytes, SSR240612 showed significant inhibition of differentiation into osteoclasts by addition of M-CSF and RANKL. Interestingly, the expression of CD13 and B1R was increased after RANKL incubation.

Conclusion: The broad consistency of these effects across various models underscores the potential involvement of the sCD13/B1R pathway in osteoclast biology. These studies reveal an autocrine loop involving engagement of B1R by sCD13, that is downstream from the interaction between RANK and RANKL. This insight opens new avenues for therapeutic strategies targeting B1R to prevent or mitigate bone erosions in RA and other conditions in which pathologic bone loss occurs. The compelling evidence provided by this study on the sCD13/B1R axis as a novel contributor to inflammation-induced bone damage highlights the possibility of developing B1R antagonists as a therapeutic measure against RA-associated osteoclastogenesis.

« Back to ACR Convergence 2024

ACR Meeting Abstracts - https://acrabstracts.org/abstract/bradykinin-receptor-b1-blockade-suppresses-soluble-cd13-induced-differentiation-of-osteoclasts-from-monocytes/