Role of β-Catenin in Regulating Microvascular Endothelial Cell Hyperpermeability

Background: Paracellular microvascular hyperpermeability occurs mainly because of the disruption of the endothelial adherens junction complex. Vascular endothelial-cadherin that consists of an extracellular and intracellular domain to confer cell-cell contact is linked to the actin cytoskeletal assembly through beta-catenin. Our objective was to determine the functional role of beta-catenin during paracellular hyperpermeability and to evaluate whether exogenous beta-catenin would protect against vascular leak. Methods: beta-Catenin siRNA (2.5 mu g/mL) was administered to Sprague-Dawley rats through tail vein. FITC-albumin extravasation of the mesenteric postcapillary venules was evaluated after 48 hours using intravital microscopy. Parallel studies using rat lung microvascular endothelial cell monolayers were transfected with beta-catenin siRNA, and hyperpermeability was determined using monolayers after 48 hours. The effectiveness of beta-catenin siRNA was tested using immunofluorescence and Western blot. To study the protective effect of beta-catenin, rat lung microvascular endothelial cell monolayers were transfected with a beta-catenin gene expression construct for 48 hours or a recombinant beta-catenin protein (1 mu g/mL) for 2 hours, followed by transfection with proapoptotic BAK peptide (5 mu g/mL), a known inducer hyperpermeability. Results: beta-Catenin siRNA induced a significant increase in vascular hyperpermeability in vivo (p < 0.05) and monolayer permeability (in vitro; p < 0.05). beta-Catenin siRNA significantly altered the adherens junction complex and decreased beta-catenin protein levels. beta-Catenin gene expression construct or recombinant beta-catenin protein attenuated BAK-induced monolayer hyperpermeability significantly (p < 0.05). Conclusion: Posttranscriptional gene silencing of beta-catenin leads to vascular hyperpermeability in vivo and monolayer hyperpermeability in vitro. The enhancement of beta-catenin gene expression at the adherens junction or exogenous introduction of beta-catenin protein shows protection against vascular hyperpermeability.