Arthritis is associated with T-cell-induced upregulation of Toll-like receptor 3 on synovial fibroblasts

Abstract

IntroductionToll-like receptors (TLRs) are likely to play crucial roles in the pathogenesis of rheumatoid arthritis (RA). The aim of this study was to determine the key TLRs in synovium and explore their roles in the activation of fibroblast-like synoviocytes (FLSs) mediated by T cells in arthritis.MethodsPristane-induced arthritis (PIA) was established by subcutaneous injection with pristane at the base of the rat's tail. TLR expression in synovium from PIA rats was detected at different time points by performing real-time PCR. Polyinosinic:polycytidylic acid (poly(I:C)) was intra-articularly administrated to PIA rats, and arthritis was monitored macroscopically and microscopically. Synovial TLR3 was detected by immunohistochemical staining. Rat FLSs were stimulated with pristane-primed T cells or pristane-primed, T-cell conditioned medium. The intervention of TLR3 in FLSs was achieved by specific short-hairpin RNA (shRNA) or an antibody. The migration ability of FLSs was measured by using the scratch test, and gene expression was detected by using real-time PCR. FLSs from RA patients were stimulated with various cytokines and TLR ligands, and TLR3 expression was detected by performing real-time PCR. In addition, with different concentrations of poly(I:C) stimulation, TLR3 expression of FLSs from RA patients and patients with osteoarthritis (OA) was compared.ResultsSynovium TLR3 displayed early and persistent overexpression in PIA rats. TLR3 was expressed in FLSs, and local treatment with poly(I:C) synergistically aggravated the arthritis. Rat FLSs co-cultured with pristane-primed T cells showed strengthened migration ability and significant upregulation of TLR3, IFN-β, IL-6 and matrix metalloproteinase 3 (MMP3) expression, which could also be induced by pristane-primed, T-cell conditioned medium. The upregulation of cytokines and MMPs was blocked by shRNA or TLR3 antibodies. In RA FLSs with cytokine or TLR ligand stimulation, TLR3 expression exhibited remarkable upregulation. Furthermore, RA FLSs showed higher reactivity than OA FLSs to poly(I:C).ConclusionsTLR3 in the synovium of PIA rats was overexpressed, and activation of the TLR3 signaling pathway could aggravate this arthritis. The induction of TLR3 in FLSs resulted from T cell-derived inflammatory stimulation and could further mediate FLS activation in arthritis. We conclude that TLR3 upregulation of FLSs activated by T cells results in articular inflammation.

Pristane primed rat T cells enhance TLR3 expression of fibroblast-like synoviocytes via TNF-α initiated p38 MAPK and NF-κB pathways

“…Yaron et al found that polyI:C, a synthetic ligand of TLR3, could induce acute joint inflammation in rats in 1979 [14]. Subsequent studies testified that the ligands of TLR3, polyI:C and dsRNA, did result in arthritis [5,15,16]. Our experiments also showed that polyI:C synergistically aggravates the pristane-induced arthritis (PIA) [4,5].…”

“…Subsequent studies testified that the ligands of TLR3, polyI:C and dsRNA, did result in arthritis [5,15,16]. Our experiments also showed that polyI:C synergistically aggravates the pristane-induced arthritis (PIA) [4,5]. Meanwhile, many researches showed that TLR3 expression was increased in some tissues such as synovium and spleen, and especially in some cells such as FLS, macrophages and dendritic cells (DC), in RA patients and arthritis animals [4,5,7,10].…”

“…Our experiments also showed that polyI:C synergistically aggravates the pristane-induced arthritis (PIA) [4,5]. Meanwhile, many researches showed that TLR3 expression was increased in some tissues such as synovium and spleen, and especially in some cells such as FLS, macrophages and dendritic cells (DC), in RA patients and arthritis animals [4,5,7,10]. The clinical symptom and pathological manifestation of arthritis were alleviated significantly when TLR3 expression was knocked down in vivo [4].…”

“…Accumulating evidence indicates that TLRs, in particular TLR2, TLR3, TLR4, TLR7/8 and TLR9, participate in the pathogenesis of RA and experimental arthritis by affecting the function of key cells including immune cells and FLS [4][5][6][7][8][9][10]. It has been found that the overexpressed TLR3 and TLR4 in RA FLS are more responsive to their ligands [5,7]. TLR3 and TLR7 in synovium could trigger the inflammatory cascade of RA via type I interferons [11].…”

“…As stimulated with their specific ligands, pathogen-associated molecular patterns and damage-associated molecular patterns, TLRs activate specific transcriptional factors by MyD88 dependent or independent pathway to regulate the inflammatory gene expression. Accumulating evidence indicates that TLRs, in particular TLR2, TLR3, TLR4, TLR7/8 and TLR9, participate in the pathogenesis of RA and experimental arthritis by affecting the function of key cells including immune cells and FLS [4][5][6][7][8][9][10]. It has been found that the overexpressed TLR3 and TLR4 in RA FLS are more responsive to their ligands [5,7].…”