Citrullinated fibronectin inhibits apoptosis and promotes the secretion of pro-inflammatory cytokines in fibroblast-like synoviocytes in rheumatoid arthritis

Lieying Fan,Dongyi He,Ming Zong,Rongqing Liu,Hui Zhang,Yuanyuan Ding,Qiang Wang,Jianwei Ma

doi:10.1186/ar4112

Abstract

IntroductionRheumatoid arthritis (RA) is characterized by synovial lining hyperplasia, in which there may be an imbalance between the growth and death of fibroblast-like synoviocytes (FLSs). Antibodies against citrullinated proteins are proposed to induce RA. This study aimed to investigate the pathogenic role of citrullinated fibronectin (cFn) in RA.MethodsThe distribution of fibronectin (Fn) and cFn in synovial tissues from RA and osteoarthritis (OA) patients was examined by immunohistochemical and double immunofluorescence analysis. FLSs were isolated from RA and OA patients and treated with Fn or cFn. Apoptosis was detected by flow cytometry and TUNEL assay. The expression of survivin, caspase-3, cyclin-B1, Bcl-2 and Bax was detected by real-time PCR. The secretion of proinflammatory cytokines was measured by ELISA.ResultsFn formed extracellular aggregates that were specifically citrullinated in synovial tissues of RA patients, but no Fn deposits were observed in those of OA patients. Fn induced the apoptosis of RA and OA FLSs while cFn inhibited the apoptosis of RA and OA FLSs. Fn significantly increased the expression of caspase-3 and decreased the expression of survivin and cyclin-B1 in FLSs from RA and OA patients. cFn significantly increased the expression of survivin in RA FLSs. Furthermore, cFn increased the secretion of TNF-α and IL-1 by FLSs.ConclusionscFn plays a potential pathophysiologic role in RA by inhibiting apoptosis and increasing proinflammatory cytokine secretion of FLSs.

Highlights

Rheumatoid arthritis (RA) is characterized by synovial lining hyperplasia, in which there may be an imbalance between the growth and death of fibroblast-like synoviocytes (FLSs)
Results citrullinated fibronectin (cFn) is abundant in arthritic synovial tissues To clarify the distribution of cFn in synovial tissues from RA and OA, we performed immunostaining and double immunofluorescent staining
Extracellular accumulation of Fn and citrullination of proteins were undetectable in OA synovial tissue except for the deep subling region where some fibrous materials and endothelial cells were immunostained by anti-MC antibody

Summary

Introduction

Rheumatoid arthritis (RA) is characterized by synovial lining hyperplasia, in which there may be an imbalance between the growth and death of fibroblast-like synoviocytes (FLSs). Fibroblast-like synoviocytes (FLSs) play important role in the initiation and perpetuation of RA [1]. Anti-CCP antibodies are produced locally in the synovium of RA patients [3] These antibodies recognize the proteins containing citrulline amino acid residues, which is generated via post-translational modification of arginine residues by peptidylarginine deiminase (PADI) [4,5]. Arginine residues often play a central role in the structural integrity of a protein, due to their ability to participate in ionic interactions with negatively charged amino acid side chains, substrates, and cofactors, and form multiple hydrogen bonds to the peptide backbone and other amino acid side chains [6]. The citrullinated forms of fibrinogen, fibronectin (Fn), fibrin, vimentin, collagen type II and a-enolase are common in the inflamed synovium and citrullinated fibrinogen, citrullinated fibronectin (cFn), citrullinated fibrin and citrullinated vimentin in the inflamed synovium and plasma have been considered as important citrullinated autoantigens in RA [4,7,8,9,10,11,12]

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