The aim of this study was to analyze both the constitutive and induced expression and function of double-stranded RNA (dsRNA; Toll-like receptor 3 [TLR-3], retinoic acid-inducible gene I [RIG-I], and melanoma differentiation-associated gene 5 [MDA5]) and single-stranded RNA (ssRNA; TLR-7) receptors in osteoarthritis (OA) and rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS), by studying the transcription factors involved and the subsequent effects on antiviral interferon-β (IFNβ), the proinflammatory CXCL8 chemokine, and matrix metalloproteinase 3 (MMP-3). An additional goal was to study the effect of vasoactive intestinal peptide (VIP).
The expression of TLR-3, TLR-7, RIG-I, and MDA5 in cultured FLS was studied by reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), immunofluorescence, and Western blotting. Transcription factors were studied using the ELISA-based TransAM transcription factor kit. The expression of IFNβ, CXCL8 (interleukin-8), and MMP-3 was analyzed by RT-PCR and ELISA.
FLS expressed TLR-3, TLR-7, RIG-I, and MDA5. The expression of TLR-3 and RIG-I was higher in RA FLS, while the expression of TLR-7 and MDA5 was higher in OA FLS. Stimulation with poly(I-C) induced the activation of IFN regulatory factor 3 (IRF-3), NF-κB, and activator protein 1 (AP-1) c-Jun as well as the subsequent production of IFNβ, CXCL8, and MMP-3. VIP reduced the activation of IRF-3 and the production of IFNβ in both OA and RA FLS. Imiquimod induced the activation of NF-κB, AP-1 c-Fos, and AP-1 c-Jun and the synthesis of CXCL8 and MMP-3. VIP significantly diminished MMP-3 production only in imiquimod-treated RA FLS.
The results of this study revealed a prominent function of FLS in the recognition of both dsRNA and ssRNA, which may be present in the joint microenvironment. This study also advances the healing function of the endogenous neuroimmune peptide VIP, which inhibited TLR-3-, RIG-I-, MDA5-, and TLR-7-mediated stimulation of antiviral, proinflammatory, and joint destruction mediators.