Anticitrullinated protein antibodies facilitate migration of synovial tissue-derived fibroblasts

Objectives Rheumatoid arthritis (RA)-specific anti-citrullinated protein/peptide antibodies (AC PAs) might contribute to bone loss and arthralgia before the onset of joint inflammation. We aimed to dissect additional mechanisms by which AC PAs might contribute to development of joint pathology. Methods Fibroblast-like synoviocytes (FLS) were isolated from the synovial membrane of patients with RA. The FLS cultures were stimulated with polyclonal AC PAs (anti-CCP-2 antibodies) purified from the peripheral blood of patients with RA or with monoclonal AC PAs derived from single synovial fluid B cells. We analysed how AC PAs modulate FLS by measuring cell adhesion and mobility as well as cytokine production. Expression of protein arginine deiminase (PAD) enzymes and protein citrullination were analysed by immunofluorescence, and signal transduction was studied using immunoblotting. Results Challenge of FLS by starvation-induced stress or by exposure to the chemokine interleukin-8 was essential to sensitise the cells to AC PAs. These challenges led to an increased PAD expression and protein citrullination and an AC PA-mediated induction of FLS migration through a mechanism involving phosphoinositide 3-kinase activation. Inhibition of the PAD enzymes or competition with soluble citrullinated proteins or peptides completely abolished the AC PA-induced FLS migration. Different monoclonal AC PAs triggered distinct cellular effects in either fibroblasts or osteoclasts, suggesting unique roles for individual AC PA clones in disease pathogenesis. Conclusion We propose that transient synovial insults in the presence of a certain pre-existing AC PA repertoire might result in an AC PA-mediated increase of FLS migration.