Background Damage-associated molecular patterns (DAMPs) are proposed to drive aberrant stimulation of Toll-like receptors (TLRs) in the rheumatoid arthritis (RA) joints resulting in increased expression of proinflammatory cytokines and chemokines. In the recent study we demonstrated that the neutrophil-derived lactoferrin (LTF) induces inflammatory response in RA synovial fibroblasts (RASF) via TLR-4 (Ref.). However, the molecular mechanisms of TLR-4 signaling in activated RASF are still unclear.
Objectives To clarify the molecular mechanisms of TLR-4 signaling pathways in activated RASF.
Methods Recombinant human neutrophil-derived LTF was used as one of the TLR-4 ligands. RASF were treated with LTF and/or TNF-α, and the expression of proinflammatory cytokines and chemokines, such as IL-6, IL-8 and CCL20 in RASF was measured by RT-qPCR and ELISA. To repress the TLR-4 signaling pathways, a small molecular inhibitor of TLR-4 (TAK-242), TAK1 inhibitor (5Z-7-Oxozeaenol), nuclear factor kappa B (NF-kB) inhibitor (BMS345541), and p38 mitogen activated protein kinase (MAPK) inhibitor (SB202190) were used. The role of nuclear factor of activated T cells 5 (NFAT5) in the TLR-4 signaling in RASF was investigated using a small interfering RNA targeting NFAT5.
Results Stimulation of RASF with LTF significantly increased the expression of IL-6, IL-8 and CCL20 mRNA and proteins (p=0.01). LTF enhanced the expression of these cytokine and chemokine mRNA in RASF stimulated by TNFα. TAK-242 completely repressed the expression of these cytokines and chemokines in RASF stimulated by LTF, while the TAK-1 inhibitor did not suppress the expression of these cytokines and chemokines in RASF. The NF-kB inhibitor, but not the p38MAPK inhibitor, partially repressed the expression of IL-6 and IL-8 mRNA induced by LTF. However, neither the NF-kB inhibitor nor p38MAPK inhibitor repressed the expression of CCL20 mRNA. Interestingly, silencing of NFAT5 significantly decreased the basal expression of IL-6, IL-8 and CCL20 mRNA in RASF. Additionally, silencing of NFAT5 significantly repressed the expression of not only IL-6, IL-8, but also of CCL20 mRNA in RASF treated by LTF.
Conclusions These findings suggest that NFAT5 plays an important role as a critical regulator in the proinflammatory response of RASF mediated by the TLR-4 signaling pathway.
Umekita K, et al. Neutrophil-Derived Lactoferrin Regulates the Activity of NFAT5 in Rheumatoid Arthritis Synovial Fibroblasts Via Toll-like Receptor 4. 2015 ACR/ARHP Annual Meeting (San Francisco)
Acknowledgement We thank Ms. Yuki Kaseda, Ms. Ayaka Miyamoto and Dr. Yatsuki Aratake for their excellent technical assistance.
Disclosure of Interest None declared