Csk controls leukocyte extravasation via local regulation of Src family kinases and cortactin signaling.

C-terminal Src kinase (Csk) targets Src family kinases (SFKs) and thereby inactivates them. We have previously shown that Csk binds to phosphorylated tyrosine 685 of VE-cadherin, an adhesion molecule of major importance for the regulation of endothelial junctions. This tyrosine residue is an SFK target, and its mutation (VE-cadherin-Y685F) inhibits the induction of vascular permeability in various inflammation models.

Ubiquitination of VE-cadherin regulates inflammation-induced vascular permeability in vivo.

VE-cadherin is a major component of the cell adhesion machinery which provides integrity and plasticity of the barrier function of endothelial junctions. Here, we analyze whether ubiquitination of VE-cadherin is involved in the regulation of the endothelial barrier in inflammation in vivo. We show that histamine and thrombin stimulate ubiquitination of VE-cadherin in HUVEC, which is completely blocked if the two lysine residues K626 and K633 are replaced by arginine.

Sinusoidal and lymphatic vessel growth is controlled by reciprocal VEGF-C-CDH5 inhibition.

Sinusoids are specialized, low pressure blood vessels in the liver, bone marrow, and spleen required for definitive hematopoiesis. Unlike other blood endothelial cells (ECs), sinusoidal ECs express high levels of VEGFR3. VEGFR3 and its ligand VEGF-C are known to support lymphatic growth, but their function in sinusoidal vessels is unknown.

Shear stress control of vascular leaks and atheromas through Tie2 activation by VE-PTP sequestration.

Vascular endothelial protein tyrosine phosphatase (VE-PTP) influences endothelial barrier function by regulating the activation of tyrosine kinase receptor Tie2. We determined whether this action is linked to the development of atherosclerosis by examining the influence of arterial shear stress on VE-PTP, Tie2 activation, plasma leakage, and atherogenesis. We found that exposure to high average shear stress led to downstream polarization and endocytosis of VE-PTP accompanied by Tie2 activation at cell junctions.

Targeting Procalcitonin Protects Vascular Barrier Integrity.

Capillary leakage frequently occurs during sepsis and after major surgery and is associated with microvascular dysfunction and adverse outcome. Procalcitonin is a well-established biomarker in inflammation without known impact on vascular integrity. We determined how procalcitonin induces endothelial hyperpermeability and how targeting procalcitonin protects vascular barrier integrity.

Force-induced changes of α-catenin conformation stabilize vascular junctions independently of vinculin.

Cadherin-mediated cell adhesion requires anchoring via the β-catenin-α-catenin complex to the actin cytoskeleton, yet, α-catenin only binds F-actin weakly. A covalent fusion of VE-cadherin to α-catenin enhances actin anchorage in endothelial cells and strongly stabilizes endothelial junctions in vivo, blocking inflammatory responses. Here, we have analyzed the underlying mechanism.

A Small Molecule Inhibitor of VE-PTP Activates Tie2 in Schlemm's Canal Increasing Outflow Facility and Reducing Intraocular Pressure.

Purpose: Tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (Tie2) activation in Schlemm's canal (SC) endothelium is required for the maintenance of IOP, making the angiopoietin/Tie2 pathway a target for new and potentially disease modifying glaucoma therapies. The goal of the present study was to examine the effects of a Tie2 activator, AKB-9778, on IOP and outflow function.

Methods: AKB-9778 effects on IOP was evaluated in humans, rabbits, and mice.

Extracellular Vesicle Transfer from Endothelial Cells Drives VE-Cadherin Expression in Breast Cancer Cells, Thereby Causing Heterotypic Cell Contacts.

Cadherins mediate cohesive contacts between isotypic cells by homophilic interaction and prevent contact between heterotypic cells. Breast cancer cells neighboring endothelial cells (ECs) atypically express vascular endothelial (VE)-cadherin. To understand this EC-induced VE-cadherin expression in breast cancer cells, MCF7 and MDA-MB-231 cells expressing different endogenous cadherins were co-cultured with ECs and analyzed for VE-cadherin at the transcriptional level and by confocal microscopy, flow cytometry, and immunoblotting.

Platelets docking to VWF prevent leaks during leukocyte extravasation by stimulating Tie-2.

Neutrophil extravasation requires opening of the endothelial barrier but does not necessarily cause plasma leakage. Leaks are prevented by contractile actin filaments surrounding the diapedesis pore, keeping this opening tightly closed around the transmigrating neutrophils. We have identified the receptor system that is responsible for this.

Local microvascular leakage promotes trafficking of activated neutrophils to remote organs.

Increased microvascular permeability to plasma proteins and neutrophil emigration are hallmarks of innate immunity and key features of numerous inflammatory disorders. Although neutrophils can promote microvascular leakage, the impact of vascular permeability on neutrophil trafficking is unknown. Here, through the application of confocal intravital microscopy, we report that vascular permeability-enhancing stimuli caused a significant frequency of neutrophil reverse transendothelial cell migration (rTEM).

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.

Interfering with VE-PTP stabilizes endothelial junctions in vivo via Tie-2 in the absence of VE-cadherin.

Vascular endothelial (VE)-protein tyrosine phosphatase (PTP) associates with VE-cadherin, thereby supporting its adhesive activity and endothelial junction integrity. VE-PTP also associates with Tie-2, dampening the tyrosine kinase activity of this receptor that can support stabilization of endothelial junctions. Here, we have analyzed how interference with VE-PTP affects the stability of endothelial junctions in vivo.

Similarities and differences in the regulation of leukocyte extravasation and vascular permeability.

Leukocyte extravasation is regulated and mediated by a multitude of adhesion and signaling molecules. Many of them enable the capturing and docking of leukocytes to the vessel wall. Others allow leukocytes to crawl on the apical surface of endothelial cells to appropriate sites of exit.

Phosphatases and kinases as regulators of the endothelial barrier function.

The endothelial layer of blood vessels controls the passage of cells and solutes from the blood into the surrounding tissue. Crucial for this regulation is the integrity of endothelial cell-cell junctions. Various molecular mechanisms control junctional integrity of the endothelial layer including GTPases, modulation of the actomyosin cytoskeleton and phosphorylation and dephosphorylation of junctional proteins.

Leukocyte extravasation and vascular permeability are each controlled in vivo by different tyrosine residues of VE-cadherin.

Tyrosine phosphorylation of the adhesion molecule VE-cadherin is assumed to affect endothelial junction integrity. However, it remains unclear whether tyrosine residues of VE-cadherin are required for the induction of vascular permeability and the regulation of leukocyte extravasation in vivo. We found here that knock-in mice expressing a Y685F mutant of VE-cadherin had impaired induction of vascular permeability, but those expressing a Y731F mutant did not.

Dissociation of VE-PTP from VE-cadherin is required for leukocyte extravasation and for VEGF-induced vascular permeability in vivo.

We have recently shown that vascular endothelial protein tyrosine phosphatase (VE-PTP), an endothelial membrane protein, associates with VE-cadherin and is required for optimal VE-cadherin function and endothelial cell contact integrity. The dissociation of VE-PTP from VE-cadherin is triggered by vascular endothelial growth factor (VEGF) and by the binding of leukocytes to endothelial cells in vitro, suggesting that this dissociation is a prerequisite for the destabilization of endothelial cell contacts. Here, we show that VE-cadherin/VE-PTP dissociation also occurs in vivo in response to LPS stimulation of the lung or systemic VEGF stimulation.

VE-PTP controls blood vessel development by balancing Tie-2 activity.

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is an endothelial-specific receptor-type tyrosine phosphatase that associates with Tie-2 and VE-cadherin. VE-PTP gene disruption leads to embryonic lethality, vascular remodeling defects, and enlargement of vascular structures in extraembryonic tissues. We show here that antibodies against the extracellular part of VE-PTP mimic the effects of VE-PTP gene disruption exemplified by vessel enlargement in allantois explants.

VE-PTP maintains the endothelial barrier via plakoglobin and becomes dissociated from VE-cadherin by leukocytes and by VEGF.

We have shown recently that vascular endothelial protein tyrosine phosphatase (VE-PTP), an endothelial-specific membrane protein, associates with vascular endothelial (VE)-cadherin and enhances VE-cadherin function in transfected cells (Nawroth, R., G. Poell, A.

Cell adhesion dynamics at endothelial junctions: VE-cadherin as a major player.

The regulation of endothelial cell contacts is of central importance for the barrier function of the blood vessel wall and for the control of leukocyte extravasation. In addition, the plasticity of endothelial cell contacts is regulated during angiogenesis by growth factors, such as vascular endothelial growth factor and angiopoietin-1. Despite the participation of several adhesion molecules and receptors in the control of endothelial cell contacts, most of the currently known mechanisms involve vascular endothelial cadherin (VE-cadherin), an essential adhesion molecule for the stability of endothelial junctions.

Angiopoietins assemble distinct Tie2 signalling complexes in endothelial cell-cell and cell-matrix contacts.

The receptor tyrosine kinase Tie2, and its activating ligand Angiopoietin-1 (Ang1), are required for vascular remodelling and vessel integrity, whereas Ang2 may counteract these functions. However, it is not known how Tie2 transduces these different signals. Here, we show that Ang1 induces unique Tie2 complexes in mobile and confluent endothelial cells.