Differential Involvement of Tight Junction Associated Proteins in Regulating Blood‐Brain Barrier Endothelial Cell Permeability

Abstract

Microvascular hyperpermeability of the blood‐brain barrier (BBB) leads to brain edema and neuroinflammation. The tight junction associated proteins of the BBB endothelial cells such as claudin‐5, occludin and zonula occludens‐1 (ZO‐1) are key molecules that regulate barrier integrity. Our objective was to determine if knockdown of various tight junction‐associated as well as adherens junction proteins in brain microvascular endothelial cells would lead to selective and differential barrier properties. Rat brain microvascular endothelial cell (RBMEC) monolayers grown on Transwell plates or on chamber slides were transfected with siRNAs for the tight junction associated proteins, claudin‐5, occludin and ZO‐1 and the adherens junction proteins β‐catenin and VE‐cadherin. FITC‐dextran flux across the monolayer was used as an indicator of the changes in permeability. The integrity of the monolayers were determined by using immunofluorescence localization of the above mentioned proteins followed by confocal microscopy. ZO‐1 siRNA trannsfected monolayers but not claudin‐ 5 or occludin siRNA transfected monolayers showed significant hyperpermeability (p<0.05). β‐Catenin or VE‐cadherin siRNA trasfected monolayers showed no significant change in permeability. Tight junction associated proteins of the BBB show differential involvement in regulating microvascular hyperpermeability. ZO‐1 plays a predominant role in maintaining the BBB integrity and permeability compared to the other tight junction associated and adherens junction proteins.