Background: 

Ischemia-reperfusion causes capillary leakage leading to edema formation restricting functional recovery of the heart. The AMP-activated protein kinase (AMPK) is a fuel sensor which becomes activated under ischemia. However, it is now apparent that AMPK may also play an important role in stabilizing barrier function of endothelial cells (EC). Here the hypothesis was tested, whether targeted activation of AMPK protects EC barrier against reperfusion-induced failure.

Methods and Results: 

Downregulation of AMPK by siRNA (~80%) leads to disintegration of VE-cadherin-mediated cell adhesion structures, alterations of the actin cytoskeleton (immunocytochemistry) and gap formation (GF) between adjacent EC (morphometry, video-imaging technique). Exposure of EC to ischemia (40 min, Po₂<5 mmHg; pH 6.4) causes an immediate increase in GF and a 3-fold increase in AMPK activity (AMPK~P: AMPK phosphorylation; Western blot) after 40 min. During reperfusion (40 min, Po₂=140 mm Hg; pH 7.4) GF was further increased by 307 9% (P<0.05, n=5) within 40 min. In contrast, AMPK~P declined to basal level within the first 10 min of reperfusion. Addition of AICAR, a pharmacological activator of AMPK, at the onset of reperfusion enhanced AMPK~P above the end-ischemic level, induced VE-cadherin translocation to cell borders, and abolished reperfusion-induced GF.

Conclusion: 

AMPK is involved in maintenance of endothelial barrier. Targeted activation of AMPK at the onset of reperfusion abolishes reperfusion-induced hyperpermeability. Hence, activation of AMPK may provide a new therapeutic option to prevent reperfusion-induced endothelial barrier failure.