Delayed Disruption of Barrier Function in Cultured Human Corneal Epithelial Cells Induced by Tumor Necrosis Factor-α in a Manner Dependent on NF-κB

Abstract

The corneal epithelium provides a barrier that is both important for corneal homeostasis and dependent on tight junctions (TJs) between adjacent epithelial cells. The authors examined the effects of tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, on barrier function and the expression of TJ proteins in simian virus 40-transformed human corneal epithelial (HCE) cells. The barrier function of cultured HCE cells was evaluated by measurement of transepithelial electrical resistance (TER). The subcellular distribution of the TJ proteins zonula occludens-1 (ZO-1) and occludin and that of the p65 subunit of nuclear factor-kappaB (NF-kappaB) were determined by immunofluorescence staining. The expression of ZO-1 and occludin and the phosphorylation and degradation of the NF-kappaB inhibitory protein IkappaB-alpha were examined by immunoblot analysis. TNF-alpha induced a decrease in the TER of HCE cells in a concentration- and time-dependent manner. It also induced the disappearance of ZO-1 from the interfaces of neighboring HCE cells without affecting the localization of occludin. The abundance of neither ZO-1 nor occludin was affected by TNF-alpha. TNF-alpha induced the phosphorylation and downregulation of IkappaB-alpha and the translocation of the p65 subunit of NF-kappaB to the nucleus. The NF-kappaB inhibitor curcumin blocked the effects of TNF-alpha on TER and the subcellular localization of ZO-1 at late phase. TNF-alpha disrupted the barrier function of HCE cells, apparently by affecting the localization of ZO-1 at TJs in a manner dependent on NF-kappaB at late phase. This action of TNF-alpha may contribute to the loss of corneal epithelial barrier function associated with ocular inflammation.