Inhibitory effects of luteolin on TLR3-mediated inflammation caused by TAK/NF-κB signaling in human corneal fibroblasts

AIM: To study the role of luteolin (LUT) in the expression of toll-like receptors 3 (TLR3) ligand polyl:C stimulated inflammatory factors in human corneal fibroblasts (HCFs). METHODS: HCFs cells were cultivated with or without LUT or polyl:C. The expression levels of interleukin (IL)-6, IL-8, monocyte chemotactic protein-1 (MCP-1), vascular cell adhesion molecule (VCAM)-1, as well as intercellular adhesion molecule (ICAM)-1 were measured using enzyme-linked immunosorbent assay (ELISA), immunoblotting or reverse transcription-quantitative polymerase chain reaction (PCR) analyses. Immunoblotting was used to assess tollinterleukin-1 receptor-domain-containing adapter-inducing interferon-beta (TRIF), TLR3, transforming growth factor-bactivated kinase 1 (TAK1), tumor necrosis factor receptor-associated factor 6 (TRAF6), the transcription factor AP-1, as well as transcription factor nuclear factor (NF-kappa B)-inhibitory protein I kappa B-alpha degradation and phosphorylation. Immunofluorescence assays were used to localize the cellular location of the p65 subunit of NF-kappa B. RESULTS: Corneal fibroblasts exposed to polyl:C demonstrated decreased VCAM-1, ICAM-1, MCP-1, IL-6, and IL-8 expression levels upon exposure to LUT in a timedependent and concentration-dependent manner. LUT was observed to suppress polyl:C-triggered expression of TLR3, the translocation of NF-kappa B p65 into cell nuclei, as well as the phosphorylation of TAK, c-Jun, and IKB-alpha, while no impact on the expression levels of TRIF and TRAF6 were observed. CONCLUSION: LUT suppress the expression of proinflammatory adhesion molecules, chemokines, and cytokines in polyl:C exposed HCFs. These effects are likely mediated through TAK/NF-kappa B signal attenuation. Therefore, LUT is a candidate molecule that can prevent the TLR3-mediated inflammation response associated with corneal viral infection.