Glucocorticoids regulate transendothelial fluid flow resistance and formation of intercellular junctions

The regulation of transendothelial fluid flow by glucocorticoids was studie d in vitro with use of human endothelial cells cultured from Schlemm's cana l (SCE) and the trabecular meshwork (TM) in conjunction with computer-linke d flowmeters. After 2-7 mk of 500 nM dexamethasone (Dex) treatment, the fol lowing physiological, morphometric, and biochemical alterations were observ ed: a 3- to 5-fold increase in fluid flow resistance, a 8-fold increase in the representation of tight junctions, a 10- to 30-fold reduction in the me an area occupied by interendothelial "gaps" or preferential flow channels, and a 3- to Ei-fold increase in the expression of the junction-associated p rotein ZO-1. The more resistive SCE cells expressed two isoforms of ZO-1; T M cells expressed only one. To investigate the role of ZO-1 in the aforemen tioned Dex effects, its expression was inhibited using antisense phosphorot hioate oligonucleotides, and the response was compared with that observed w ith the use of sense and nonsense phosphorothioate oligonucleotides. Inhibi tion of ZO-1 expression abolished the Dex-induced increase in resistance an d the accompanying alterations in cell junctions and gaps. These results su pport the hypothesis that intercellular junctions are necessary for the dev elopment and maintenance of transendothelial flow resistance in cultured SC E and TM cells and are likely involved in the mechanism of increased resist ance associated with glucocorticoid exposure.