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 β-catenin. Our objective was to determine the functional role of β-catenin during paracellular hyperpermeability and to evaluate whether exogenous β-catenin would protect against vascular leak.
Methods: β-Catenin siRNA (2.5 μg/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 β-catenin siRNA, and hyperpermeability was determined using monolayers after 48 hours. The effectiveness of β-catenin siRNA was tested using immunofluorescence and Western blot. To study the protective effect of β-catenin, rat lung microvascular endothelial cell monolayers were transfected with a β-catenin gene expression construct for 48 hours or a recombinant β-catenin protein (1 μg/mL) for 2 hours, followed by transfection with proapoptotic BAK peptide (5 μg/mL), a known inducer hyperpermeability.
Results: β-Catenin siRNA induced a significant increase in vascular hyperpermeability in vivo (p<0.05) and monolayer permeability (in vitro; p<0.05). β-Catenin siRNA significantly altered the adherens junction complex and decreased β-catenin protein levels. β-Catenin gene expression construct or recombinant β-catenin protein attenuated BAK-induced monolayer hyperpermeability significantly (p<0.05).
Conclusion: Posttranscriptional gene silencing of β-catenin leads to vascular hyperpermeability in vivo and monolayer hyperpermeability in vitro. The enhancement of β-catenin gene expression at the adherens junction or exogenous introduction of β-catenin protein shows protection against vascular hyperpermeability.