Objectives Rheumatoid arthritis (RA) is an autoimmune polyarthritis, in which fibroblast-like synoviocytes (FLS) play a key role in cartilage and bone destruction through tumour-like proliferation and invasiveness. Considering still unsatisfactory remission rate in RA even under treatment with biological disease-modifying antirheumatic drugs, novel therapeutic strategy for treatment-resistant RA is still awaited. In this study, we analysed the expression and function of Ras guanine nucleotide-releasing proteins (RASGRPs), guanine exchange factors for small GTPase Ras, in FLS as a potential therapeutic target for RA.
Methods The expression of RASGRPs mRNA was quantified by a real-time PCR assay in FLS isolated from synovial tissue samples. RASGRP2 protein was also evaluated immunohistochemically. Then, we transiently transfected FLS with RASGRP2 expression vector and assessed their proliferation, adhesion, migration and invasion by cellular functional assays and downstream signalling activation using immunoblot. Finally, the therapeutic effect of RASGRP2 silencing was evaluated in type-II collagen-induced arthritis rats.
Results RASGRP2 was abundantly expressed in FLS from RA synovium, whereas scarcely found in those from osteoarthritis. Expression of RASGRP2 in RA-FLS was enhanced by transforming growth factor-beta. RASGRP2 activated RAP-1, subsequently affecting nuclear factor kappa-light-chain-enhancer of activated B cells pathway and actin dynamics in FLS. RASGRP2-overexpressed FLS had increased abilities of adhesion, migration and interleukin (IL)-6 production. Silencing of RASGRP2 using the intra-articular injection of Rasgrp2-specific siRNAs dampened experimental arthritis in rats by inhibiting pannus formation.
Conclusions RASGRP2 was identified to be involved in the pathogenesis of RA by promoting adhesion, migration and IL-6 production from FLS, proposed as a potential novel non-immunosuppressive therapeutic target for RA.
- rheumatoid arthritis
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HN and SS contributed equally.
Handling editor Josef S Smolen
Contributors HN, SS and SY conceptualised the study. HN, SS, SY and MK developed the methodology. HN, SS, MK and TS conducted the investigation. MK and NI provided resources. HN and SY wrote the original draft of the manuscript. YF, MK, KO, TB, NI and TA reviewed and edited the manuscript. SY and TA acquired funding. MK, YF, TB, NI and TA supervised the study.
Funding This work was supported by grants from The Japan Society for the Promotion of Science, Grant-in-Aid for scientific research (KAKENHI, project number: 15K09514 and 18K0838008), Japan Agency for Medical Research and Development (project number: PH42180003) and from Bristol Myers Squibb (Bristol-Myers Squibb RA Clinical Investigation Grant).
Competing interests SY has accepted honoraria from Mitsubishi Tanabe Pharma Co., Chugai Pharmaceutical Co., Astellas Pharma and GlaxoSmithKline and grant from Bristol-Myers Squibb. TA has accepted honoraria from Mitsubishi Tanabe Pharma Co., Chugai Pharmaceutical Co., Astellas Pharma and Pfizer. Other authors have declared that no conflict of interest exists.
Patient consent Not required.
Ethics approval Human and Animal Ethics Committee of the Hokkaido University Hospital (approval number: 008–0103 and 17–0031).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Data are available from the corresponding author upon request.
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