Abstract 5559: Role of AMP-activated Protein Kinase in Ischemia-Reperfusion-Induced Barrier Failure in Endothelial Monolayers

Abstract

Background: Ischemia-reperfusion provokes endothelial barrier dysfunction leading to edema formation and organ failure. The AMP-activated protein kinase (AMPK) is a fuel sensor which becomes activated under ischemia. It is now apparent that AMPK may also play important roles in stabilization of cell-adhesion. Here, it is hypothesized that AMPK may play an important role in protection barrier function under metabolic stress. Methods and Results: Overexpression of a dominant negative AMPK mutant in endothelial monolayers from human umbilical veins (EC) caused a 2-fold increase in basal permeability (albumin flux across the monolayers). In accordance, downregulation of AMPK by siRNA (~60%) leads to gap formation between adjacent EC, disintegration of cell adhesion structures and alterations of the cytoskeleton (loss of VE-cadherin at cell borders, actin stress fiber formation; immunocytochemistry), indicating that AMPK plays an important role in maintenance of barrier integrity. To analyse the role of AMPK on barrier function EC were exposed to ischemia (40 min, Po 2 <5 mm Hg; pH 6.4) followed by reperfusion (40 min, Po 2 =140 mm Hg; pH 7.4). Ischemia caused an immediate increase in permeability (gap formation, video-imaging technique) and a 3-fold increase in AMPK activity (AMPK phosphorylation; western blot) after 40 min. During reperfusion gap formation was further increased by 307± 9 % (P<0.05, n=5) within the ongoing 40 min. In contrast, AMPK phosphorylation rapidly declined to basal level within the first 10 minutes of reperfusion. However, addition of AICAR (AMPK activator; 5-aminoimidizole-4-carboxamide riboside), at the onset of reperfusion caused a rapid increase in AMPK phosphorylation and abolished the reperfusion-induced gap formation. Pretreatment of the cells with AICAR before the onset of ischemia reduced reperfusion-induced gap formation by 50 %. Conclusion: AMPK is involved in maintenance of cell-cell contacts and stabilization of basal barrier function. Pharmacological activation of AMPK within the first minutes of reperfusion can prevent hyperpermeability induced by reperfusion stress. Hence, activation of AMPK may provide a new therapeutic option to prevent ischemia-reperfusion barrier failure.