Citrullination of synovial proteins in murine models of rheumatoid arthritis
Article first published online: 11 SEP 2003
Copyright © 2003 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 48, Issue 9, pages 2489–2500, September 2003
How to Cite
Vossenaar, E. R., Nijenhuis, S., Helsen, M. M. A., van der Heijden, A., Senshu, T., van den Berg, W. B., van Venrooij, W. J. and Joosten, L. A. B. (2003), Citrullination of synovial proteins in murine models of rheumatoid arthritis. Arthritis & Rheumatism, 48: 2489–2500. doi: 10.1002/art.11229
- Issue published online: 11 SEP 2003
- Article first published online: 11 SEP 2003
- Manuscript Accepted: 9 MAY 2003
- Manuscript Received: 23 DEC 2002
- Dutch Arthritis Association. Grant Number: NR-00-2-402
- Netherlands Foundation for Scientific Research. Grant Number: NWO grant 940-35-037
Antibodies directed to citrulline-containing proteins are highly specific for rheumatoid arthritis (RA) and can be detected in up to 80% of patients with RA. Citrulline is a nonstandard amino acid that can be incorporated into proteins only by posttranslational modification of arginine by peptidylarginine deiminase (PAD) enzymes. The objective of this study was to investigate the presence of anticitrulline antibodies, PAD enzymes, and citrullinated antigens in mouse models of both acute and chronic destructive arthritis: streptococcal cell wall (SCW)–induced arthritis and collagen-induced arthritis (CIA), respectively.
Synovial tissue biopsy specimens were obtained from naive mice, mice with CIA, and mice with SCW-induced arthritis. The expression of messenger RNA (mRNA) for PAD enzymes was analyzed by reverse transcriptase–polymerase chain reaction; the presence of PAD proteins and their products (citrullinated proteins) was analyzed by Western blotting and by immunolocalization. The presence of anticitrullinated protein antibodies was investigated by an anti–cyclic citrullinated peptide (anti-CCP) enzyme-linked immunosorbent assay (ELISA) and an ELISA using in vitro citrullinated fibrinogen.
In both mouse models, PAD type 2 (PAD2) mRNA was present in the synovium but was not translated into PAD2 protein. In contrast, PAD4 mRNA, although absent from healthy synovium, was readily transcribed and translated by polymorphonuclear neutrophils infiltrating the synovial tissue during inflammation. As a consequence, several synovial proteins were subjected to citrullination. One of these proteins was identified as fibrin, which has been reported to be citrullinated also in synovium of patients with RA. Although generation of citrullinated antigens during synovial inflammation in the mice was eminent, no anti-CCP antibodies could be detected.
Citrullination of synovial antigens is an active process during joint inflammation in both mice and humans, but the induction of autoantibodies directed to these proteins is a more specific phenomenon, detectable only in human RA patients.