Toll- Like Receptor Expression is Modulated in Response in Experimental Dry Eye

Abstract

Purpose: : Dry eye is a multifactorial syndrome in which inflammation is thought to be a significant component. The human ocular surface epithelia express a number of toll-like receptors (TLRs) that stimulate the production of proinflammatory cytokines and chemokines upon activation by host or microbial ligands. Our previous studies have shown that TLRs are modulated during dry eye associated conditions (hyperosmolar stress and desiccation) in human corneal epithelial cells in vitro. Therefore we have begun in vivo studies to investigate TLR mRNA expression in mice with experimentally-induced dry eye (EDE).

Methods: : EDE was induced in 6-8 week old C57BL/6 mice (5 animals per experiment) by subcutaneous scopolamine injection (2.5 mg/ml) four times a day and exposure to low humidity and an air draft for 5 days (n=3). Untreated C57BL/6 mice were used as the control. Following treatment the corneal epithelium was removed by scraping and the entire conjunctiva was removed by dissection. Total RNA was extracted and the fold change in TLR2, 3 and 5 mRNA expression between the treated and untreated mice was determined by real-time PCR.

Results: : In the conjunctiva, EDE significantly (P=0.02) increased the mRNA expression of TLR2 by 2.48 ± 0.38 fold and TLR3 by 11.2 ± 2.90 fold compared to the untreated control group. A similar trend was found in the corneal epithelium where EDE significantly (P≤0.01) increased the expression of TLR2 by 2.46 ± 0.26 fold and TLR5 by 2.21 ± 0.19. We also found corneal epithelial TLR3 mRNA elevated by 4.25 ± 2.22 (P=0.12) fold and conjunctival TLR5 mRNA by 3.81 ± 1.47 (P=0.08) fold however these changes did not achieve statistical significance since two of the three samples gave comparable fold changes while the third sample was lower.

Conclusions: : EDE increases TLR2, 3 and 5 mRNA expression in the corneal epithelium and conjunctiva of C57BL/6 mice. These findings suggest that TLRs may be involved in the rapid detection of pathogens to help protect the compromised EDE ocular surface and/or they may be involved in ocular surface response to desiccating stress.

Keywords: cornea: tears/tear film/dry eye • conjunctiva • inflammation