Estrogen stimulation of proinflammatory cytokine and matrix metalloproteinase gene expression in human corneal epithelial cells

Purpose: Researchers have proposed that the secretion of proinflammatory cytokines and matrix metalloproteinases (MMPs) by corneal epithelial cells contributes to the development of ocular surface inflammation in dry eye syndromes. We hypothesize that this cytokine and MMP production is promoted by estrogens, given that dry eye syndromes occur predominantly in women and estrogen therapy is associated with an increase in dry eye signs and symptoms. Moreover, corneal epithelial cells contain estrogen receptors and estrogens are known to influence other aspects of corneal immunity. The purpose of this study was to test our hypothesis. Methods: Immortalized human corneal epithelial cells were exposed to vehicle, lipopolysaccharide (LPS), or varying concentrations of 17 beta-estradiol. After 6 or 24 hours of hormone treatment, cells were harvested and processed for total RNA isolation, cDNA synthesis, and the analysis of cytokine and MMP mRNA levels by multiplex and real-time PCR methods. Results: Our results demonstrate that 17 beta-estradiol upregulates the expression of proinflammatory cytokine and MMP genes in human corneal epithelial cells. Estrogen administration significantly increased the levels of IL-1 beta, IL-6, IL-8, and GM-CSF mRNAs, as well as MMP 2, 7, and 9 mRNAs, compared with those of placebo-treated controls. This estrogen effect was found after 6 and/or 24 hours of hormone treatment. An analogous stimulation of gene expression was observed following cellular exposure to LPS. Conclusions: Our findings show that 17 beta-estradiol increases the expression of inflammatory genes in human corneal epithelial cells. This hormone action may play an etiologic role in the ocular surface inflammation of dry eye.