Activated protein C utilizes the angiopoietin/Tie2 axis to promote endothelial barrier function

Abstract

Activated protein C (APC) is an anticoagulant, approved as a treatment for severe sepsis, that can prevent apoptosis, inflammation, and vascular leakage. The aim of this study was to investigate whether APC protects endothelial barrier function through the angiopoietin (Ang)/Tie2 axis. APC significantly up‐regulated gene and protein expression of Tie2 and Ang1 in a dose (0.01–10 μg/ml)‐ and time (0.5–24 h)‐dependent manner in human umbilical vein endothelial cells (HUVECs). Interestingly, it markedly inhibited Ang2 with an IC 50 of ~0.1 μg/ml. HUVEC permeability, measured using Evans blue dye transfer, was significantly reduced in the presence of APC, and, in concordance, the tight junction associated protein zona occludens (ZO)‐1 was up‐regulated and localized peripherally around cells, compared with controls. Smooth muscle cell migration toward APC‐stimulated HUVECs was elevated compared with unstimulated cells. Blocking antibodies and small interfering (si) RNA treatment, compared with isotype (IgG) or scrambled siRNA controls, showed that APC requires 3 receptors, the endothelial protein C receptor, protease‐activated receptor 1, and Tie2 to perform all these barrier stabilization functions. In summary, this study demonstrates that APC has novel effects on the Ang/Tie2 axis, which enhance endothelial barrier function and are likely to contribute to its therapeutic effect in sepsis and other diseases associated with vascular leakage.—Minhas, N., Xue, M., Fukudome, K., Jackson, C. J. Activated protein C utilizes the angiopoietin/Tie2 axis to promote endothelial barrier function. FASEB J. 24, 873–881 (2010). www.fasebj.org