The barrier function of the corneal epithelium maintains corneal homeostasis and is mediated by tight junctions (TJs) and adherens junctions (AJs). It is also susceptible to disruption by hypoxia. We have now examined the effects of hypoxia on TJs and AJs as well as on barrier function in human corneal epithelial (HCE) cells. Moreover, we investigated whether such effects of hypoxia might be modulated by hepatocyte growth factor (HGF). The subcellular distribution of the TJ proteins ZO-1 and occludin, the AJ proteins E-cadherin and beta-catenin, and actin filaments was examined by fluorescence microscopy. The abundance of junctional proteins as well as of myosin light chain kinase (MLCK) was determined by immunoblot analysis. Barrier function was evaluated by measurement of transepithelial electrical resistance (TER). Hypoxia-induced both the disappearance of ZO-1 from the borders of neighboring HCE cells as well as the down-regulation of ZO-1 expression without affecting the distribution or abundance of occludin, E-cadherin, or beta-catenin. It also induced the formation of actin stress fibers, the up-regulation of MLCK expression, and a reduction in the TER of HCE cells. All these effects of hypoxia were inhibited by HGF. Neither hypoxia nor HGF exhibited a mitogenic or cytotoxic effect on HCE cells. HGF thus protects HCE cells from hypoxia-induced disruption of barrier function by maintaining the expression and distribution of ZO-1. Inhibition of the effects of hypoxia on the organization of the actin cytoskeleton might also contribute to this protective action of HGF.
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