Artemether Targets Raptor-Induced Actin Polymerization and Suppresses Migration of Fibroblast-like Synoviocytes in Rheumatoid Arthritis

Abstract

Background: Fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) may cause articular damage as a result of its aggressive features including direct adhesion and invasion of surface cartilage in joints. Artemether (ART), one of the artemisinin derivatives with antimalarial properties, showed inhibitory effect on inflammation and destruction of joints in collagen-induced arthritis rats, which might be applied in RA treatment. However, whether ART has effects on the aggressive properties of human RA-FLS remains unexplored. Methods: Synovium was obtained from patients with active RA (n=18) and FLS were isolated in vitro. RA-FLS were subjected to cell migration, invasion assays, live-cell imaging analysis and Rho GTPase activation assay after ART treatment. To identify the therapeutic target of ART, key signaling molecules of PI3K/Akt, AMPK, MAPK, NF-κB and mTOR pathways from RA-FLS were examined by Western Blot after ART treatment. Raptor was knockdown or overexpressed by siRNA or lentivirus transfection to reveal its role on regulating the aggressive properties of RA-FLS.Results: ART treatment significantly suppressed the transwell migration and invasion of synovial FLS from RA patients. Time-lapse microscopy revealed that ART treatment reduced random migration velocity of RA-FLS, as well as the directional persistence. ART also impaired the formation of filopodia and lamellipodia in RA-FLS. Further mechanism investigation showed that ART reduced the protein level of Raptor, a critical component of the mTOR pathway, and its downstream target 4E-BP1. It also inhibited the activation of Rho GTPases and the expression of actin binding proteins, including Profilin 1 and p-Cofilin. Raptor overexpression could reverse the anti-migration and anti-invasion effects of ART on RA-FLS as well as the suppression of Rho GTPases activation and the expression of actin binding proteins. Conclusion: ART can inhibit migration of RA-FLS by blocking Raptor-induced actin polymerization. ART might be a potential agent targeting FLS in RA treatment.