Interference With ESAM (Endothelial Cell-Selective Adhesion Molecule) Plus Vascular Endothelial-Cadherin Causes Immediate Lethality and Lung-Specific Blood Coagulation.

Objective: Vascular endothelial (VE)-cadherin is of dominant importance for the formation and stability of endothelial junctions, yet induced gene inactivation enhances vascular permeability in the lung but does not cause junction rupture. This study aims at identifying the junctional adhesion molecule, which is responsible for preventing endothelial junction rupture in the pulmonary vasculature in the absence of VE-cadherin. Approach and Results: We have compared the relevance of ESAM (endothelial cell-selective adhesion molecule), JAM (junctional adhesion molecule)-A, PECAM (platelet endothelial cell adhesion molecule)-1, and VE-cadherin for vascular barrier integrity in various mouse tissues. Gene inactivation of ESAM enhanced vascular permeability in the lung but not in the heart, skin, and brain. In contrast, deletion of JAM-A or PECAM-1 did not affect barrier integrity in any of these organs. Blocking VE-cadherin with antibodies caused lethality in ESAM(-/-) mice within 30 minutes but had no such effect in JAM-A(-/-), PECAM-1(-/-) or wild-type mice. Likewise, induced gene inactivation of VE-cadherin caused rapid lethality only in the absence of ESAM. Ultrastructural analysis revealed that only combined interference with VE-cadherin and ESAM disrupted endothelial junctions and caused massive blood coagulation in the lung. Mechanistically, we could exclude a role of platelet ESAM in coagulation, changes in the expression of other junctional proteins or a contribution of cytoplasmic signaling domains of ESAM. Conclusions: Despite well-documented roles of JAM-A and PECAM-1 for the regulation of endothelial junctions, only for ESAM, we detected an essential role for endothelial barrier integrity in a tissue-specific way. In addition, we found that it is ESAM which prevents endothelial junction rupture in the lung when VE-cadherin is absent.