PURPOSE: To examine the effects of platelet-activating factor (PAF) on tight junction permeability in cultured retinal pigment epithelial (RPE) cells. METHODS: A human RPE cell line (ARPE-19) cultured on microporous filter supports was used. PAF and WEB2086, which is a specific PAF-receptor (PAF-R) antagonist, were added to the culture medium. RPE monolayer permeability was measured using transepithelial electrical resistance (TER) and sodium fluorescein flux. The expression of the tight junction protein zonula occludens (ZO)-1 was assessed using immunohistochemistry. We also measured the vascular endothelial growth factor (VEGF) level in cultures treated with PAF, and RPE monolayer permeability was measured again in the presence of neutralizing antibodies to VEGF. RESULTS: PAF significantly decreased the TER of the RPE monolayer and enhanced sodium fluorescein flux. ZO-1 expression was downregulated in PAF-supplemented medium. These effects were abolished with PAF-R blockage. PAF stimulation increased VEGF expression in RPE cells, and neutralization of VEGF with antibodies caused partial recovery of barrier properties. CONCLUSIONS: The tight junctions of ARPE-19 cells are altered by PAF, and these effects are partly mediated by the upregulation of VEGF expression in these cells. Our results contribute to growing evidence supporting the role of PAF in choroidal neovascularization, and our findings suggest that PAF is a novel therapeutic target for increased permeability of the RPE monolayer.
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