Effect of pro-inflammatory mediators on membrane-associated mucins expressed by human ocular surface epithelial cells

Membrane-associated mucins are altered on the ocular surface in non-Sjögren's dry eye. This study sought to determine if inflammatory mediators, present in tears of dry eye patients, regulate membrane-associated mucins MUC1 and -16 at the level of gene expression, protein biosynthesis and/or ectodomain release. A human corneal limbal epithelial cell line (HCLE), which produces membrane-associated mucins, was used. Cells were treated with interleukin (IL)-6, -8, or -17, tumor necrosis factor-α (TNF-α), and Interferon-gamma (IFN-γ), or a combination of TNF-α and IFN-γ, or IFN-γ and IL-17, for 1, 6, 24, or 48 h. Presence of receptors for these mediators was verified by RT-PCR. Effects of the cytokines on expression levels of MUC1 and -16 were determined by real-time PCR, and on mucin protein biosynthesis and ectodomain release in cell lysates and culture media, respectively, by immunoblot analysis. TNF-α and IFN-γ each significantly induced MUC1 expression, cellular protein content and ectodomain release over time. Combined treatment with the two cytokines was not additive. By comparison, one of the inflammatory mediators, IFN-γ, affected all three parameters-gene expression, cellular protein, and ectodomain release-for MUC16. Combined treatment with TNF-α and IFN-γ showed effects similar to IFN-γ alone, except that ectodomain release followed that of TNF-α, which induced MUC16 ectodomain release. In conclusion, inflammatory mediators present in tears of dry eye patients can affect MUC1 and -16 on corneal epithelial cells and may be responsible for alterations of surface mucins in dry eye.