Decrease of Toll like Receptor 4 During Conjunctival Epithelial Cell Apoptosis Induced by Lipopolysaccharide

Abstract

Purpose:: Toll like receptor 4 (TLR4) is the principal receptor for bacterial lipopolysaccharide (LPS). Recent observations define it as a modulator of cellular apoptosis. The purpose of this study was to investigate the relationship between TLR4 expression and apoptosis in conjunctival epithelial cells in vitro.

Methods:: A human conjunctiva-derived cell line (Wong-Kilbourne derivative of Chang conjunctiva) was treated with different concentrations (from 1 to 1000 ng/ml) of LPS. After 24, 48, and 72 hours of treatment, membrane and cytoplasmic TLR4 expressions were evaluated by flow cytometry (FCM) and/or Western blot analysis. Immunostaining of TLR4 was evaluated in cells cultured in Labtek® chambers. The measurements of subG1 population by FCM and TUNEL assay were used to study LPS-induced apoptosis under different concentrations of LPS treatments.

Results:: Exposure of conjunctiva-derived epithelial cells to high concentrations LPS revealed a significant increase in apoptosis compared with controls. However, in these conditions, a significant decrease of TLR4 expressions was observed by FCM and by Western blot analysis in cellular extracts, compared with controls. Immunostaining of TLR4 in cells became faint after high concentration LPS (1000ng/ml) treatments.

Conclusions:: This study showed a negative relationship between TLR4 expression and apoptosis in a conjunctiva-derived cell line. TLR4 could be implicated in modulation of conjunctival epithelial cell apoptosis.

Keywords: conjunctiva • apoptosis/cell death • receptors