Lipopolysaccharide Regulation of Toll-Like Receptor-4 and Matrix Metalloprotease-9 in Human Primary Corneal Fibroblasts

Abstract

Toll-like receptor 4 (TLR4) is a key component of the innate immune response related to microbial keratitis (MK). Pathways and downstream effectors relating to TLR signaling remain unknown in human bacterial MK. To this effect, by activating the TLR4 signaling cascade with lipopolysaccharide (LPS), the authors investigated whether TLR4, matrix metalloproteases (MMP)-2, MMP-9, and cytokine expression in diseased human primary corneal fibroblasts (CFs) were altered. Human primary CFs from patients with severe corneal ulceration were cultured in conjunction with healthy control CFs and treated with LPS derived from Pseudomonas aeruginosa. TLR4, MMP-2, and MMP-9 were constitutively expressed in both ulcerated and control CFs. Diseased CFs showed greater responsiveness to LPS stimulation. TLR4 and MMP-9 expression was dose-dependently increased by LPS. MMP-2 expression was not affected by LPS. Analysis on cytokine expression revealed that IL-2, IL-8, IL-10, IL-12p70, GM-CSF, IFNγ, and TNFα expression increased after LPS treatment but only in diseased cells. TLR4 activation with LPS increases TLR4, MMP-9, and cytokine expression in CFs cultured from patients with microbial keratitis. Overexpression of these products may provide a local mechanism to eradicate bacterial infection but may also aid corneal ulceration and perforation.