Objective Animal models for human diseases are especially valuable for clarifying molecular mechanisms before or around the onset. As a model for rheumatoid arthritis (RA), we utilise knock-in mice gp130F759. They have a Y759F mutation in gp130, a common receptor subunit for interleukin 6 (IL-6) family cytokines. Definitive arthritis develops around 8 months old and the incidence reaches 100% around 1 year old. Careful examination in the clinical course revealed very subtle resistance in flexibility of joints at 5 months old. Therefore, pathophysiological changes in gp130F759 were examined to dissect molecular mechanisms for preclinical phase of RA.
Methods Severity of arthritis in gp130F759 was evaluated with a clinical score system and histological quantification. Serum cytokines, autoantibodies and C reactive protein (CRP) were measured. Changes in the synovium were analysed by real-time PCR, flow cytometry and immunohistochemistry.
Results Around 5 months old, various types of cytokines, rheumatoid factor (RF), anti-circular citrullinated peptide IgM and CRP increased in the sera of gp130F759. Enhancement of neovascularisation, synovial hyperplasia and fibrosis was observed. Also, increases in haematopoietic cells dominated by innate immune cells and gene expression of Il6 and Padi4 were detected in the joints. Il6 was expressed by non-haematopoietic synovial cells, whereas PAD4 protein was detected in the synovial neutrophils. Padi4 is induced in neutrophils in vitro by IL-6. Increases of phospho-STAT3 and PAD4 protein were detected in the synovium. Deletion of IL-6 in gp130F759 normalised the amount of PAD4 protein in the joints.
Conclusion The IL-6-PAD4 axis operates in the earliest phase of arthritis in gp130F759, implicating it in early RA.
- early rheumatoid arthritis
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
Statistics from Altmetric.com
Contributors AY, YS and KI contributed to the conception and study design. AY, TS, MT-I, HI and KI acquired and analysed the data. AY, TS, HH, MT-I, HI, YS and KI contributed to interpretation of the data. AY and KI wrote the first version of the manuscript and FT, HA, MI, YM, HI and YS revised it critically. All authors read and approved the final manuscript.
Funding This work was supported by JSPS KAKENHI Grant Numbers JP17K16217 to AY and JP21590448, JP17K08798 to KI. This work was also supported by Research Project Grants from Kawasaki Medical School to AY and KI and The KAWASAKI Foundation for Medical Science & Medical Welfare to AY.
Competing interests HH and YM have received research support from Chugai pharmaceutical Co.
Patient consent for publication Not required.
Ethics approval The study was approved by the Animal Care and Use Committee of Kawasaki Medical School.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All data relevant to the study are included in the article or uploaded as supplementary information.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.