Role of the netrin system of repellent factors on synovial fibroblasts in rheumatoid arthritis and osteoarthritis.

Changes in the expression of repellent factors, i.e., Netrins and their receptors, may be responsible for the invasive behavior of the synovial tissue cells in patients with rheumatoid arthritis (RA) and osteoarthritis (OA). This study was carried out to analyze the expression of Netrins and their receptors in synovial cells of patients with RA, OA, and control subjects without synovial inflammation. Quantitative RT-PCR was performed to measure the expression of Netrin-1, -3, -4, Neogenin, DCC, UNC5A-D. The influence of Netrin-1 on synovial fibroblasts (SF) was analyzed by determining proliferation, migration, and their ability to organize collagen. SF expressed all repellent factors of the Netrin family. When comparing SF of healthy donors to patients with RA and OA, a stronger expression of UNC5B (4 fold) and UNC5C (769 fold) in RA and OA was found, whereas expression of the other molecules revealed no significant differences. Treating the SF-cells with recombinant Netrin-1 resulted in inhibition of migration of RA- and OA-SFs whereas control cells were not affected. The stronger expression of UNC5B and UNC5C receptors might contribute to the disordered phenotype of RA- and OA-SFs. Addition of Netrin-1 reduces the migratory ability of SFs, potentially by repulsion, as seen in neuronal cells in embryonic development. Due to its function, Netrin-1 may constitute a novel target in the treatment of OA and RA.