The control of vascular integrity by endothelial cell junctions: molecular basis and pathological implications

Developmental SMAD6 loss leads to blood vessel hemorrhage and disrupted endothelial cell junctions

The BMP pathway regulates developmental processes including angiogenesis, yet its signaling outputs are complex and context-dependent. Recently, we showed that SMAD6, an intracellular BMP inhibitor expressed in endothelial cells, decreases vessel sprouting and branching both in vitro and in zebrafish. Genetic deletion of SMAD6 in mice results in poorly characterized cardiovascular defects and lethality. Here, we analyzed the effects of SMAD6 loss on vascular function during murine development. SMAD6 was expressed in a subset of blood vessels throughout development, primarily in arteries, while expression outside of the vasculature was largely confined to developing cardiac valves with no obvious embryonic phenotype. Mice deficient in SMAD6 died during late gestation and early stages of postnatal development, and this lethality was associated with vessel hemorrhage. Mice that survived past birth had increased branching and sprouting of developing postnatal retinal vessels and disorganized tight and adherens junctions. In vitro, knockdown of SMAD6 led to abnormal endothelial cell adherens junctions and increased VE-cadherin endocytosis, indicative of activated endothelium. Thus, SMAD6 is essential for proper blood vessel function during murine development, where it appears to stabilize endothelial junctions to prevent hemorrhage and aberrant angiogenesis.

Differential Mechanisms of Septic Human Pulmonary Microvascular Endothelial Cell Barrier Dysfunction Depending on the Presence of Neutrophils

Sepsis is characterized by injury of pulmonary microvascular endothelial cells (PMVEC) leading to barrier dysfunction. Multiple mechanisms promote septic PMVEC barrier dysfunction, including interaction with circulating leukocytes and PMVEC apoptotic death. Our previous work demonstrated a strong correlation between septic neutrophil (PMN)-dependent PMVEC apoptosis and pulmonary microvascular albumin leak in septic mice in vivo; however, this remains uncertain in human PMVEC. Thus, we hypothesize that human PMVEC apoptosis is required for loss of PMVEC barrier function under septic conditions in vitro. To assess this hypothesis, human PMVECs cultured alone or in coculture with PMN were stimulated with PBS or cytomix (equimolar interferon γ, tumor necrosis factor α, and interleukin 1β) in the absence or presence of a pan-caspase inhibitor, Q-VD, or specific caspase inhibitors. PMVEC barrier function was assessed by transendothelial electrical resistance (TEER), as well as fluoroisothiocyanate-labeled dextran and Evans blue-labeled albumin flux across PMVEC monolayers. PMVEC apoptosis was identified by (1) loss of cell membrane polarity (Annexin V), (2) caspase activation (FLICA), and (3) DNA fragmentation [terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)]. Septic stimulation of human PMVECs cultured alone resulted in loss of barrier function (decreased TEER and increased macromolecular flux) associated with increased apoptosis (increased Annexin V, FLICA, and TUNEL staining). In addition, treatment of septic PMVEC cultured alone with Q-VD decreased PMVEC apoptosis and prevented septic PMVEC barrier dysfunction. In septic PMN-PMVEC cocultures, there was greater trans-PMVEC macromolecular flux (both dextran and albumin) vs. PMVEC cultured alone. PMN presence also augmented septic PMVEC caspase activation (FLICA staining) vs. PMVEC cultured alone but did not affect septic PMVEC apoptosis. Importantly, pan-caspase inhibition (Q-VD treatment) completely attenuated septic PMN-dependent PMVEC barrier dysfunction. Moreover, inhibition of caspase 3, 8, or 9 in PMN-PMVEC cocultures also reduced septic PMVEC barrier dysfunction whereas inhibition of caspase 1 had no effect. Our data demonstrate that human PMVEC barrier dysfunction under septic conditions in vitro (cytomix stimulation) is clearly caspase-dependent, but the mechanism differs depending on the presence of PMN. In isolated PMVEC, apoptosis contributes to septic barrier dysfunction, whereas PMN presence enhances caspase-dependent septic PMVEC barrier dysfunction independently of PMVEC apoptosis.

Cholesterol crystals increase vascular permeability by inactivating SHP2 and disrupting adherens junctions

To understand the adverse effects of cholesterol crystals on vascular homeostasis, we have studied their effects on endothelial barrier function. Cholesterol crystals increased endothelial barrier permeability in a dose and time dependent manner. In addition, cholesterol crystals induced tyrosine phosphorylation of VE-cadherin and α-catenin, disrupting endothelial AJ and its barrier function and these effects required xanthine oxidase-mediated H₂O₂ production, SHP2 inactivation and Frk activation. Similarly, feeding C57BL/6 mice with cholesterol-rich diet increased xanthine oxidase expression, H₂O₂ production, SHP2 inactivation and Frk activation leading to enhanced tyrosine phosphorylation of VE-cadherin and α-catenin, thereby disrupting endothelial AJ and increasing vascular permeability. Resolvin D1, a specialized proresolving mediator, prevented all these adverse effects of cholesterol crystals and cholesterol-rich diet in endothelial cells and mice, respectively. Based on these observations, it is likely that cholesterol crystals via disrupting AJ increase vascular permeability, a critical event of endothelial dysfunction and specialized proresolving mediators such as Resolvin D1 exert protection against these effects.

Cancer-derived exosomes trigger endothelial to mesenchymal transition followed by the induction of cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) play a pivotal role in tumor growth, but very little has been known about its characteristics and origin. Recently, cancer-derived exosome has been suggested to transdifferentiate CAFs, by a new mechanism of endothelial to mesenchymal transition (EndMT), initiating angiogenic processes and triggering metastatic evolution. However, an enabling tool in vitro is yet to be developed to investigate complicated procedures of the EndMT and the transdifferentiation under reconstituted tumor microenvironment. Here we proposed an in vitro microfluidic model which enables to monitor a synergetic effect of complex tumor microenvironment in situ, including extracellular matrix (ECM), interstitial flow and environmental exosomes. The number of CAFs differentiated from human umbilical vein endothelial cells (HUVECs) increased with melanoma-derived exosomes, presenting apparent morphological and molecular changes with pronounced motility. Mesenchymal stem cell (MSC)-derived exosomes were found to suppress EndMT, induce angiogenesis and maintain vascular homeostasis, while cancer-derived exosomes promoted EndMT. Capabilities of the new microfluidic model exist in precise regulation of the complex tumor microenvironment and therefore successful reconstitution of 3D microvasculature niches, enabling in situ investigation of EndMT procedure between various cell types.

STATEMENT OF SIGNIFICANCE

This study presents an in vitro 3D EndMT model to understand the progress of the CAF generation by recapitulating the 3D tumor microenvironment in a microfluidic device. Both cancer-derived exosomes and interstitial fluid flow synergetically played a pivotal role in the EndMT and consequent formation of CAFs through a collagen-based ECM. Our approach also enabled the demonstration of a homeostatic capability of MSC-derived exosomes, ultimately leading to the recovery of CAFs back to endothelial cells. The in vitro 3D EndMT model can serve as a powerful tool to validate exosomal components that could be further developed to anti-cancer drugs.

Hold Me, but Not Too Tight-Endothelial Cell-Cell Junctions in Angiogenesis

Endothelial cell-cell junctions must perform seemingly incompatible tasks during vascular development-providing stable connections that prevent leakage, while allowing dynamic cellular rearrangements during sprouting, anastomosis, lumen formation, and functional remodeling of the vascular network. This review aims to highlight recent insights into the molecular mechanisms governing endothelial cell-cell adhesion in the context of vascular development.

Isocitrate dehydrogenase 2 deficiency induces endothelial inflammation via p66sh-mediated mitochondrial oxidative stress

Isocitrate dehydrogenase 2 (IDH2) is an essential enzyme in the mitochondrial antioxidant system, which produces nicotinamide adenine dinucleotide phosphate, and thereby defends against oxidative stress. We have shown that IDH2 downregulation results in mitochondrial dysfunction and reactive oxygen species (ROS) generation in mouse endothelial cells. The redox enzyme p66shc is a key factor in regulating the level of ROS in endothelial cells. In this study, we hypothesized that IDH2 knockdown-induced mitochondrial dysfunction stimulates endothelial inflammation, which might be regulated by p66shc-mediated oxidative stress. Our results showed that IDH2 downregulation led to mitochondrial dysfunction by decreasing the expression of mitochondrial oxidative phosphorylation complexes I, II, and IV, reducing oxygen consumption, and depolarizing mitochondrial membrane potential in human umbilical vein endothelial cells (HUVECs). The dysfunction not only increased mitochondrial ROS levels but also activated p66shc expression in HUVECs and IDH2 knockout mice. IDH2 deficiency increased intercellular adhesion molecule (ICAM)-1 expression and mRNA levels of pro-inflammatory cytokines (tumor necrosis factor [TNF]-α, and interleukin [IL]-1β) in HUVECs. The mRNA expression of ICAM-1 in endothelial cells and plasma levels of TNF-α and IL-1β were also markedly elevated in IDH2 knockout mice. However, p66shc knockdown rescued IDH2 deficiency-induced mitochondrial ROS levels, monocyte adhesion, ICAM-1, TNF-α, and IL-1β expression in HUVECs. These findings suggest that IDH2 deficiency induced endothelial inflammation via p66shc-mediated mitochondrial oxidative stress.

Intravital imaging-based analysis tools for vessel identification and assessment of concurrent dynamic vascular events

The vasculature undergoes changes in diameter, permeability and blood flow in response to specific stimuli. The dynamics and interdependence of these responses in different vessels are largely unknown. Here we report a non-invasive technique to study dynamic events in different vessel categories by multi-photon microscopy and an image analysis tool, RVDM (relative velocity, direction, and morphology) allowing the identification of vessel categories by their red blood cell (RBC) parameters. Moreover, Claudin5 promoter-driven green fluorescent protein (GFP) expression is used to distinguish capillary subtypes. Intradermal injection of vascular endothelial growth factor A (VEGFA) is shown to induce leakage of circulating dextran, with vessel-type-dependent kinetics, from capillaries and venules devoid of GFP expression. VEGFA-induced leakage in capillaries coincides with vessel dilation and reduced flow velocity. Thus, intravital imaging of non-invasive stimulation combined with RVDM analysis allows for recording and quantification of very rapid events in the vasculature.

Different stimuli can induce dynamic changes in blood flow velocity, vessel diameter and permeability. Here the authors develop a multi-photon microscopy-based image analysis tool allowing the identification of vessels and the assessment of rapid changes in large vascular networks.

Zebrafish mutants and TEAD reporters reveal essential functions for Yap and Taz in posterior cardinal vein development

As effectors of the Hippo signaling cascade, YAP1 and TAZ are transcriptional regulators playing important roles in development, tissue homeostasis and cancer. A number of different cues, including mechanotransduction of extracellular stimuli, adhesion molecules, oncogenic signaling and metabolism modulate YAP1/TAZ nucleo-cytoplasmic shuttling. In the nucleus, YAP1/TAZ tether with the DNA binding proteins TEADs, to activate the expression of target genes that regulate proliferation, migration, cell plasticity, and cell fate. Based on responsive elements present in the human and zebrafish promoters of the YAP1/TAZ target gene CTGF, we established zebrafish fluorescent transgenic reporter lines of Yap1/Taz activity. These reporter lines provide an in vivo view of Yap1/Taz activity during development and adulthood at the whole organism level. Transgene expression was detected in many larval tissues including the otic vesicles, heart, pharyngeal arches, muscles and brain and is prominent in endothelial cells. Analysis of vascular development in yap1/taz zebrafish mutants revealed specific defects in posterior cardinal vein (PCV) formation, with altered expression of arterial/venous markers. The overactivation of Yap1/Taz in endothelial cells was sufficient to promote an aberrant vessel sprouting phenotype. Our findings confirm and extend the emerging role of Yap1/Taz in vascular development including angiogenesis.

In vitro models of molecular and nano-particle transport across the blood-brain barrier

The blood-brain barrier (BBB) is the tightest endothelial barrier in humans. Characterized by the presence of tight endothelial junctions and adherens junctions, the primary function of the BBB is to maintain brain homeostasis through the control of solute transit across the barrier. The specific features of this barrier make for unique modes of transport of solutes, nanoparticles, and cells across the BBB. Understanding the different routes of traffic adopted by each of these is therefore critical in the development of targeted therapies. In an attempt to move towards controlled experimental assays, multiple groups are now opting for the use of microfluidic systems. A comprehensive understanding of bio-transport processes across the BBB in microfluidic devices is therefore necessary to develop targeted and efficient therapies for a host of diseases ranging from neurological disorders to the spread of metastases in the brain.

Red Blood Cell Adhesion to Heme-Activated Endothelial Cells Reflects Clinical Phenotype in Sickle Cell Disease

In sickle cell disease (SCD), 'disease severity' associates with increased RBC adhesion to quiescent endothelium, but the impact on activated endothelium is not known. Increased concentrations of free heme result from intravascular hemolysis in SCD. Heme is essential for aerobic metabolism, and plays an important role in numerous biological processes. Excess free heme induces reactive oxygen species generation and endothelial activation, which are associated with cardiovascular disorders including atherosclerosis, hypertension, and thrombosis. Here, we utilized an endothelialized microfluidic platform (Endothelium-on-a-chip) to assess adhesion of sickle hemoglobin-containing red blood cells (HbS RBCs), from adults with homozygous SCD, to heme-activated human endothelial cells (EC) in vitro. Confluent EC monolayers in microchannels were treated with pathophysiologically relevant levels of heme in order to simulate the highly hemolytic intravascular milieu seen in SCD. RBC adhesion to heme-activated ECs varied from subject to subject, and was associated with plasma markers of hemolysis (LDH) and reticulocytosis, thereby linking those RBCs that are most likely to adhere with those that are most likely to hemolyze. These results re-emphasize the critical contribution made by heterogeneous adhesive HbS RBCs to the pathophysiology of SCD. We found that adhesion of HbS RBCs to heme-activated ECs varied amongst individuals in the study population, and associated with biomarkers of hemolysis and inflammation, age, and a recent history of transfusion. Importantly, the microfluidic approach described herein holds promise as a clinically feasible Endothelium-on-a-chip platform with which to study complex heterocellular adhesive interactions in SCD. This article is protected by copyright. All rights reserved.

Mesencephalic Astrocyte-Derived Neurotrophic Factor Prevents Traumatic Brain Injury in Rats by Inhibiting Inflammatory Activation and Protecting the Blood-Brain Barrier

BACKGROUND

Our previous studies have shown that mesencephalic astrocyte-derived neurotrophic factor (MANF) provides a neuroprotective effect against ischemia/reperfusion injury and is also involved in inflammatory disease models. This study investigates the potential role and mechanism of MANF in acute brain damage after traumatic brain injury (TBI).

METHODS

The model of TBI was induced by Feeney free falling methods with male Sprague-Dawley rats. The expression of MANF, 24 hours after TBI, was detected by the immunohistochemistry, immunofluorescence, Western blot, and reverse transcription polymerase chain reaction techniques. After treatment with recombinant human MANF after TBI, assessment was conducted 24 hours later for brain water content, cerebral edema volume in magnetic resonance imaging, neurobehavioral testing, and Evans blue extravasation. Moreover, by the techniques of Western blot and reverse transcription polymerase chain reaction, the expression of inflammatory cytokines (interleukin 1β and tumor necrosis factor α) and P65 was also analyzed to explore the underlying protective mechanism of MANF.

RESULTS

At 24 hours after TBI, we found that endogenous MANF was widely expressed in the rat's brain tissues and different types of cells. Treatment with a high dose of recombinant human MANF (20 μg/20 μL) significantly increased the modified Garcia score, and reduced brain water content as well as cerebral edema volume on magnetic resonance imaging. Furthermore, MANF alleviated not only the permeability of the blood-brain barrier (BBB) but also the expressions of interleukin 1β and tumor necrosis factor α messenger RNA and protein. Besides, the activation of P65 was also inhibited.

CONCLUSIONS

These results suggest that MANF provides a neuroprotective effect against acute brain injury after TBI, via attenuating blood-brain barrier disruption and intracranial neuroinflammation; the inhibition of the NF-κB signaling pathway might be a potential mechanism.

Ionizing Radiation Enhances Paracellular Permeability Through Alteration of Intercellular Junctions in Cultured Human Lymphatic Endothelial Cells

BACKGROUND

A problematic complication after radiation therapy is lymphedema. Development of lymphedema is associated with an increase in lymphatic paracellular permeability. The current study investigated the effects of radiation on intercellular junctions and paracellular permeability in cultured human dermal lymphatic endothelial cells (HDLECs).

METHODS AND RESULTS

Double immunofluorescence staining with vascular endothelial (VE)-cadherin and actin immediately after X-ray irradiation (5 or 20 Gy) was performed. Morphological changes induced by irradiation were assessed. Cell viability and paracellular permeability after irradiation were also evaluated. Broad junctions in which VE-cadherin was accumulated at cell-cell contacts and almost colocalized with actin were significantly decreased in a dose-dependent manner in confluent and sparse irradiated HDLECs. Irradiation shortened the width of VE-cadherin-positive areas at the cell-cell contacts. Actin filaments did not colocalize with VE-cadherin after 20 Gy irradiation. Although cell viability was not affected by irradiation, paracellular permeability significantly increased in a dose-dependent manner.

CONCLUSIONS

A dose of 5 or 20 Gy irradiation in HDLECs does not affect cell viability, but changes VE-cadherin mediated intercellular junctions and actin structure, resulting in an increase of paracellular permeability. Further investigations on the regulatory proteins involved in radiation-induced changes, which were observed in the current study, may contribute to development of lymphedema therapy.

A case report of targeted therapy with apatinib in a patient with recurrent high grade glioma

RATIONALE

Despite the approval of antiangiogenic therapy for high grade glioma (HGG) patients, survival benefits are still limited. New treatment plans have always been developed to improve the survival.

PATIENT CONCERNS

A 26-year-old woman was admitted to our hospital for distending pain of head and eye.

DIAGNOSES

Resonance imaging (MRI) revealed a large spherical heterogeneously enhancing, mixed cystic and solid mass in the right frontal region, and the midline shifted.

INTERVENTION

The patient received apatinib therapy for positive vascular endothelial growth factor.

OUTCOMES

A partial response was observed after 4 weeks and remains sustained until now.

LESSONS

It suggests that apatinib might be a feasible option for the treatment in advanced HGG patients or patients with poor physical condition.

Maternal and early-life vitamin D deficiency enhances allergic reaction in an ovalbumin-sensitized BALB/c mouse model

Background

Recent studies have shown that vitamin D deficiency may contribute to the high prevalence of food allergy but the underlying mechanisms are far from clear.

Objective

The present study was designed to investigate the effect of maternal and early-life vitamin D deficiency in the development of food allergy.

Design

BALB/c mice were treated with ovalbumin (OVA) to trigger allergic reactions, under vitamin D-deficient (by maternal and early-life feeding of vitamin D deprived chow diet) or vitamin D-sufficient conditions.

Results

Increased occurrence and severity of allergic diarrhea as well as decreased rectal temperature were observed after OVA sensitization. For vitamin D deficiency groups, OVA-specific IgE and IL-4 levels were significantly increased, while IFN-γ levels were unchanged. Vitamin D deficiency also attenuated the structure of small intestinal villi and decreased the expression of the tight junction protein between adjacent epithelial cells and the percentages of CD4⁺CD25⁺Foxp3⁺Treg cell in spleen and mesenteric lymph nodes.

Conclusions

Maternal and early-life vitamin D deficiency have notable influence on the susceptibility to food allergy, which may relate with the reduced population of Treg cell and the dysfunction of intestinal epithelial barrier.

VE-cadherin promotes vasculogenic mimicry by modulating kaiso-dependent gene expression

Aberrant extra-vascular expression of VE-cadherin (VEC) has been observed in metastasis associated with vasculogenic mimicry (VM); however, the ultimate reason why non-endothelial VEC favors the acquisition of this phenotype is not established. In this study, we show that human malignant melanoma cells have a constitutively high expression of phoshoVEC (pVEC) at Y658; pVEC is a target of focal adhesion kinase (FAK) and forms a complex with p120-catenin and the transcriptional repressor kaiso in the nucleus. FAK inhibition enabled kaiso to suppress the expression of its target genes and enhanced kaiso recruitment to KBS-containing promoters. Finally we have found that ablation of kaiso-repressed genes WNT11 and CCDN1 abolished VM. Thus, identification of pVEC as a component of the kaiso transcriptional complex establishes a molecular paradigm that links FAK-dependent phosphorylation of VEC as a major mechanism by which ectopical VEC expression exerts its function in VM.

Rho-Kinase Inhibition Ameliorates Dasatinib-Induced Endothelial Dysfunction and Pulmonary Hypertension

The multi-kinase inhibitor dasatinib is used for treatment of imatinib-resistant chronic myeloid leukemia, but is prone to induce microvascular dysfunction. In lung this can manifest as capillary leakage with pleural effusion, pulmonary edema or even pulmonary arterial hypertension. To understand how dasatinib causes endothelial dysfunction we examined the effects of clinically relevant concentrations of dasatinib on both human pulmonary arterial macro- and microvascular endothelial cells (ECs). The effects of dasatinib was compared to imatinib and nilotinib, two other clinically used BCR/Abl kinase inhibitors that do not inhibit Src. Real three-dimensional morphology and high resolution stiffness mapping revealed softening of both macro- and microvascular ECs upon dasatinib treatment, which was not observed in response to imatinib. In a dose-dependent manner, dasatinib decreased transendothelial electrical resistance/impedance and caused a permeability increase as well as disruption of tight adherens junctions in both cell types. In isolated perfused and ventilated rat lungs, dasatinib increased mean pulmonary arterial pressure, which was accompanied by a gain in lung weight. The Rho-kinase inhibitor Y27632 partly reversed the dasatinib-induced changes in vitro and ex vivo, presumably by acting downstream of Src. Co-administration of the Rho-kinase inhibitor Y27632 completely blunted the increased pulmonary pressure in response to dasatinib. In conclusion, a dasatinib-induced permeability increase in human pulmonary arterial macro- and microvascular ECs might explain many of the adverse effects of dasatinib in patients. Rho-kinase inhibition might be suitable to ameliorate these effects.

Sodium tanshinone IIA sulfonate promotes endothelial integrity via regulating VE-cadherin dynamics and RhoA/ROCK-mediated cellular contractility and prevents atorvastatin-induced intracerebral hemorrhage in zebrafish

Impaired vascular integrity leads to serious cerebral vascular diseases such as intracerebral hemorrhage (ICH). In addition, high-dose statin therapy is suggested to cause increased ICH risk due to unclear effects of general inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) on the vascular system. Here we evaluated the protective effects of sodium tanshinone IIA sulfonate (STS), which has high efficacy and safety in clinical studies of ischemic stroke, by using atorvastatin (Ator) induced ICH zebrafish embryos and human umbilical vein endothelial cells (HUVECs). By using double transgenic Tg(fli1a:EGFP)y1 & Tg(gata1a:dsRed)sd2 zebrafish, we demonstrated that STS effectively reduced the occurrence and area of hemorrhage induced by Ator in zebrafish and restored impairment in motor function. We further demonstrated that Ator-induced disruption in VE-cadherin (VEC)-containing cell-cell adherens junctions (AJs) in HUVECs by enhancing Src-induced VEC internalization and RhoA/ROCK-mediated cellular contraction. STS inhibited Ator-induced Src activation and subsequent VEC internalization and actin depolymerization near cell borders, reducing lesions between neighboring cells and increasing barrier functions. STS also inhibited the Ator-induced RhoA/ROCK-mediated cellular contraction by regulating downstream LIMK/cofilin and MYPT1/MLC phosphatase signaling. These results showed that STS significantly promoted the stability of cell junctions and vascular integrity. Moreover, we observed that regulations of both Src and RhoA/ROCK are required for the maintenance of vascular integrity, and Src inhibitor (PP2) or ROCK inhibitors (fasudil and H1152) alone could not reduce the occurrence Ator-induced ICH. Taken together, we investigated the underlying mechanisms of Ator-induced endothelial instability, and provided scientific evidences of STS as potential ICH therapeutics by promoting vascular integrity.

Plasma Biomarkers of Inflammation and Angiogenesis Predict Cerebral Cavernous Malformation Symptomatic Hemorrhage or Lesional Growth

RATIONALE

The clinical course of cerebral cavernous malformations is highly unpredictable, with few cross-sectional studies correlating proinflammatory genotypes and plasma biomarkers with prior disease severity.

OBJECTIVE

We hypothesize that a panel of 24 candidate plasma biomarkers, with a reported role in the physiopathology of cerebral cavernous malformations, may predict subsequent clinically relevant disease activity.

METHODS AND RESULTS

Plasma biomarkers were assessed in nonfasting peripheral venous blood collected from consecutive cerebral cavernous malformation subjects followed for 1 year after initial sample collection. A first cohort (N=49) was used to define the best model of biomarker level combinations to predict a subsequent symptomatic lesional hemorrhagic expansion within a year after the blood sample. We generated the receiver operating characteristic curves and area under the curve for each biomarker individually and each weighted linear combination of relevant biomarkers. The best model to predict lesional activity was selected as that minimizing the Akaike information criterion. In this cohort, 11 subjects experienced symptomatic lesional hemorrhagic expansion (5 bleeds and 10 lesional growths) within a year after the blood draw. Subjects had lower soluble CD14 (cluster of differentiation 14; P=0.05), IL (interleukin)-6 (P=0.04), and VEGF (vascular endothelial growth factor; P=0.0003) levels along with higher plasma levels of IL-1β (P=0.008) and soluble ROBO4 (roundabout guidance receptor 4; P=0.03). Among the 31 weighted linear combinations of these 5 biomarkers, the best model (with the lowest Akaike information criterion value, 25.3) was the weighted linear combination including soluble CD14, IL-1β, VEGF, and soluble ROBO4, predicting a symptomatic hemorrhagic expansion with a sensitivity of 86% and specificity of 88% (area under the curve, 0.90; P<0.0001). We then validated our best model in the second sequential independent cohort (N=28).

CONCLUSIONS

This is the first study reporting a predictive association between plasma biomarkers and subsequent cerebral cavernous malformation disease clinical activity. This may be applied in clinical prognostication and stratification of cases in clinical trials.

Deep Sequencing of Small RNAs in Blood of Patients with Brain Arteriovenous Malformations

BACKGROUND

Deregulation of circulating microRNAs (miRNAs) is always associated with development and progression of human diseases. We aimed to assess whether patients with brain arteriovenous malformations (BAVMs) possess a distinct miRNA signature compared with healthy subjects.

METHODS

Three patients with unruptured BAVMs and 3 normal control subjects were recruited as case and control groups. Peripheral blood was collected, and miRNA signature was obtained by next-generation sequencing, followed by comparative, functional, and network analyses. Quantitative reverse transcription polymerase chain reaction was performed to validate expression of specific miRNAs.

RESULTS

Deep sequencing detected 246 differentially expressed miRNAs in blood samples of patients with BAVMs compared with normal control subjects. For the top 5 miRNAs, 946 target genes were predicted, and a BAVM-specific miRNA-target gene regulatory network was constructed. Functional annotation suggested that 15 of the predicted miRNA-targeted genes were involved in vascular endothelial growth factor signaling, in which 3 critical miRNAs were involved: miR-7-5p, miR-199a-5p, and miR-200b-3p.

CONCLUSIONS

We explored the miRNA expression signature of BAVMs, which will provide an important foundation for future studies on the regulation of miRNAs involved in BAVMs.

Induction of VEGFA and Snail-1 by meningitic Escherichia coli mediates disruption of the blood-brain barrier

Escherichia coli is the most common Gram-negative bacterium that possesses the ability to cause neonatal meningitis, which develops as circulating bacteria penetrate the blood-brain barrier (BBB). However, whether meningitic E. coli could induce disruption of the BBB and the underlying mechanisms are poorly understood. Our current work highlight for the first time the participation of VEGFA and Snail-1, as well as the potential mechanisms, in meningitic E. coli induced disruption of the BBB. Here, we characterized a meningitis-causing E. coli PCN033, and demonstrated that PCN033 invasion could increase the BBB permeability through downregulating and remodeling the tight junction proteins (TJ proteins). This process required the PCN033 infection-induced upregulation of VEGFA and Snail-1, which involves the activation of TLR2-MAPK-ERK1/2 signaling cascade. Moreover, production of proinflammatory cytokines and chemokines in response to infection also promoted the upregulation of VEGFA and Snail-1, therefore further mediating the BBB disruption. Our observations reported here directly support the involvement of VEGFA and Snail-1 in meningitic E. coli induced BBB disruption, and VEGFA and Snail-1 would therefore represent the essential host targets for future prevention of clinical E. coli meningitis.

Regional differences in endothelial cell cytoskeleton, junctional proteins and phosphorylated tyrosine labeling in the porcine vortex vein system

We previously demonstrated endothelial phenotype heterogeneity in the vortex vein system. This study is to further determine whether regional differences are present in the cytoskeleton, junctional proteins and phosphorylated tyrosine labeling within the system. The vortex vein system of twenty porcine eyes was perfused with labels for f-actin, claudin-5, VE-Cadherin, phosphorylated tyrosine and nucleic acid. The endothelial cells of eight different regions (choroidal veins, pre-ampulla, anterior ampulla, mid-ampulla, posterior ampulla, post-ampulla, intra-scleral canal and the extra-ocular vortex vein) were studied using confocal microscopy. There were regional differences in the endothelial cell structures. Cytoskeleton labeling was relatively even in intensity throughout Regions 1 to 6. Overall VE-Cadherin had a non-uniform distribution and thicker width endothelial cell border staining than claudin-5. Progressing downstream there was an increased variation in thickness of VE-cadherin labeling. There was an overlap in phosphorylated tyrosine and VE-Cadherin labeling in the post-ampulla, intra-scleral canal and extra-ocular vortex vein. Intramural cells were observed that were immune-positive for VE-Cadherin and phosphorylated tyrosine. There were significant differences in the number of intramural cells in different regions. Significant regional differences with endothelial cell labeling of cytoskeleton, junction proteins, and phosphorylated tyrosine were found within the vortex vein system. These findings support existing data on endothelial cell phenotype heterogeneity, and may aid in the knowledge of venous pathologies by understanding regions of vulnerability to endothelial damage within the vortex vein system. It could be valuable to further investigate and characterize the VE-cadherin and phosphotyrosine immune-positive intramural cells.

Gene-Therapeutic Strategies Targeting Angiogenesis in Peripheral Artery Disease

The World Health Organization announced that cardiovascular disease is the number one cause of death globally, representing 31% of all global deaths. Coronary artery disease (CAD) affects approximately 5% of the US population aged 40 years and older. With an age-adjusted prevalence of approximately 12%, peripheral artery disease (PAD) affects at least 8 to 12 million Americans. Both CAD and PAD are caused by mainly atherosclerosis, the hardening and narrowing of arteries over the years by lipid deposition in the vascular bed. Despite the significant advances in interventions for revascularization and intensive medical care, patients with CAD or PAD who undergo percutaneous transluminal angioplasty have a persistent high rate of myocardial infarction, amputation, and death. Therefore, new therapeutic strategies are urgently needed for these patients. To overcome this unmet need, therapeutic angiogenesis using angiogenic growth factors has evolved in an attempt to stimulate the growth of new vasculature to compensate for tissue ischemia. After nearly 20 years of investigation, there is growing evidence of successful or unsuccessful gene therapy for ischemic heart and limb disease. This review will discuss basic and clinical data of therapeutic angiogenesis studies employing angiogenic growth factors for PAD patients and will draw conclusions on the basis of our current understanding of the biological processes of new vascularization.

The tyrosine-kinase inhibitor sunitinib targets vascular endothelial (VE)-cadherin: a marker of response to antitumoural treatment in metastatic renal cell carcinoma

Background

Vascular endothelial (VE)-cadherin is an endothelial cell-specific protein responsible for endothelium integrity. Its adhesive properties are regulated by post-translational processing, such as tyrosine phosphorylation at site Y⁶⁸⁵ in its cytoplasmic domain, and cleavage of its extracellular domain (sVE). In hormone-refractory metastatic breast cancer, we recently demonstrated that sVE levels correlate to poor survival. In the present study, we determine whether kidney cancer therapies had an effect on VE-cadherin structural modifications and their clinical interest to monitor patient outcome.

Methods

The effects of kidney cancer biotherapies were tested on an endothelial monolayer model mimicking the endothelium lining blood vessels and on a homotypic and heterotypic 3D cell model mimicking tumour growth. sVE was quantified by ELISA in renal cell carcinoma patients initiating sunitinib (48 patients) or bevacizumab (83 patients) in the first-line metastatic setting (SUVEGIL and TORAVA trials).

Results

Human VE-cadherin is a direct target for sunitinib which inhibits its VEGF-induced phosphorylation and cleavage on endothelial monolayer and endothelial cell migration in the 3D model. The tumour cell environment modulates VE-cadherin functions through MMPs and VEGF. We demonstrate the presence of soluble VE-cadherin in the sera of mRCC patients (n = 131) which level at baseline, is higher than in a healthy donor group (n = 96). Analysis of sVE level after 4 weeks of treatment showed that a decrease in sVE level discriminates the responders vs. non-responders to sunitinib, but not bevacizumab.

Conclusions

These data highlight the interest for the sVE bioassay in future follow-up of cancer patients treated with targeted therapies such as tyrosine-kinase inhibitors.

Fasudil inhibits neutrophil-endothelial cell interactions by regulating the expressions of GRP78 and BMPR2

Regulation of leukocyte-endothelial cell interactions and of vascular permeability plays a critical role in the maintenance of functional pulmonary microvascular barriers. Little is yet known about the effect of the Rho-associated protein kinase (ROCK) inhibitor fasudil on leukocyte-endothelial cell interactions or the underlying mechanism. In the present study, as evaluated using co-culture systems of neutrophils and human pulmonary microvascular endothelial cells (HPMECs), fasudil dose-dependently suppressed neutrophil chemotaxis by decreasing the production of chemotactic factors in lipopolysaccharide (LPS)-treated HPMECs. The inhibitory role of fasudil in neutrophil chemotaxis was mediated by down-regulation of the chaperone glucose-regulated protein 78 (GRP78), since the inhibition was abolished by 4-phenyl butyric acid (a chemical chaperone mimicking GRP78). In addition, fasudil inhibited LPS-induced neutrophil-endothelial adhesion by reducing the expression of intercellular adhesion molecule (ICAM)-1. By use of lentiviral transfection in HPMECs, bone morphogenic protein receptor 2 (BMPR2) overexpression suppressed the LPS-induced increase of both ICAM-1 expression and neutrophil-endothelial adhesion, whereas knocking down BMPR2 abolished the inhibitory role of fasudil in both ICAM-1 expression and neutrophil-endothelial adhesion. Moreover, fasudil alleviated LPS-induced hyperpermeability of HPMEC monolayers by leading to the recovery of intercellular junctions, thereafter reduced neutrophil transendothelial cell migration. Therefore, fasudil inhibited leukocyte-endothelial cell interactions and vascular hyperpermeability through modulation of GRP78 and BMPR2 expression, suggesting a potential role for ROCK as a switch for inhibiting leukocyte-endothelial cell interactions.

Angiogenic potential of YKL-40 in the dynamics of tumor niche

A multitude of clinical studies showed the elevation of YKL-40 in subjects with different kinds of tumors. It is predicted that an inherent correlation exists between survivals of cancer patients with total YKL-40 serum levels, making this factor as a potential novel biomarker. However, the crucial role of YKL-40 in the dynamics of cancers, especially angiogenesis, has not yet been completely addressed. In this review, we highlighted the various facets of YKL-40 and its importance in cancer biology as a bio-shuttle in gene therapy.

RhoA/ROCK Signaling Pathway Mediates Shuanghuanglian Injection-Induced Pseudo-allergic Reactions

Background: Shuanghuanglian injection (SHLI) is a famous Chinese medicine used as an intravenous preparation for the treatment of acute respiratory tract infections. In the recent years, the immediate hypersensitivity reactions induced by SHLI have attracted broad attention. However, the mechanism involved in these reactions has not yet been elucidated. The present study aims to explore the characteristics of the immediate hypersensitivity reactions induced by SHLI and deciphers the role of the RhoA/ROCK signaling pathway in these reactions.

Methods: SHLI-immunized mice or naive mice were intravenously injected (i.v.) with SHLI (600 mg/kg) once, and vascular leakage in the ears was evaluated. Passive cutaneous anaphylaxis test was conducted using sera collected from SHLI-immunized mice. Naive mice were administered (i.v.) with a single dose of 150, 300, or 600 mg/kg of SHLI, and vascular leakage, histamine release, and histopathological alterations in the ears, lungs, and intestines were tested. In vitro, human umbilical vein endothelial cell (HUVEC) monolayer was incubated with SHLI (0.05, 0.1, or 0.15 mg/mL), and the changes in endothelial permeability and cytoskeleton were observed. Western blot analysis was performed and ROCK inhibitor was employed to investigate the contribution of the RhoA/ROCK signaling pathway in SHLI-induced hypersensitivity reactions, both in HUVECs and in mice.

Results: Our results indicate that SHLI was able to cause immediate dose-dependent vascular leakage, edema, and exudates in the ears, lungs, and intestines, and histamine release in mice. These were pseudo-allergic reactions, as SHLI-specific IgE was not elicited during sensitization. In addition, SHLI induced reorganization of actin cytoskeleton and disrupted the endothelial barrier. The administration of SHLI directly activated the RhoA/ROCK signaling pathway both in HUVECs and in the ears, lungs, and intestines of mice. Fasudil hydrochloride, a ROCK inhibitor, ameliorated the SHLI-induced hypersensitivity reactions in both endothelial cells and mice indicating its protective effect. SHLI-induced pseudo-allergic reactions were mediated by the activation of the RhoA/ROCK signaling pathway.

Conclusion: This study presents a novel mechanism of SHLI-induced immediate hypersensitivity reactions and suggests a potential therapeutic strategy to prevent the associated adverse reactions.

The NLRP3 Inflammasome May Contribute to Pathologic Neovascularization in the Advanced Stages of Diabetic Retinopathy

Diabetic retinopathy (DR) is a retinal microvascular disease characterized by inflammatory and angiogenic pathways. In this study, we evaluated NLRP3 inflammasome in a double transgenic mouse model, Akimba (Ins2 Akita xVEGF+/-), which demonstrates hyperglycemia, vascular hyperpermeability and neovascularization seen in the proliferative DR. Retinal structural integrity, vascular leakage and function were examined by fundus photography, fluorescein angiography, optical coherence tomography, retinal flat mounts, laser speckle flowgraphy (LSFG), and electroretinography in Akimba and its parental strains, Akita (Ins2 Akita ) and Kimba (trVEGF029) mice. Inflammatory mechanisms involving NLRP3 inflammasome were investigated using real time-PCR, immunohistochemistry, ELISA and western blots. We observed an increased vascular leakage, reduced retinal thickness, and function in Akimba retina. Also, Akimba retina depicts decreased relative flow volume measured by LSFG. Most importantly, high levels of IL-1β along with increased NLRP3, ASC, and Caspase-1 at mRNA and protein levels were observed in Akimba retina. However, the in vivo functional role remains undefined. In conclusion, increased activation of macroglia (GFAP), microglia (Iba-1 and OX-42) and perivascular macrophages (F4/80 and CD14) together with pro-inflammatory (IL-1β and IL-6) and pro-angiogenic markers (PECAM-1, ICAM-1, VEGF, Flt-1, and Flk-1), suggested a critical role for NLRP3 inflammasome in the Akimba mouse model depicting advanced stages of DR pathogenesis.

Mass Spectrometry-Based Proteomic Profiling of Thrombotic Material Obtained by Endovascular Thrombectomy in Patients with Ischemic Stroke

Thrombotic material retrieved from acute ischemic stroke (AIS) patients represents a valuable source of biological information. In this study, we have developed a clinical proteomics workflow to characterize the protein cargo of thrombi derived from AIS patients. To analyze the thrombus proteome in a large-scale format, we developed a workflow that combines the isolation of thrombus by endovascular thrombectomy and peptide chromatographic fractionation coupled to mass-spectrometry. Using this workflow, we have characterized a specific proteomic expression profile derived from four AIS patients included in this study. Around 1600 protein species were unambiguously identified in the analyzed material. Functional bioinformatics analyses were performed, emphasizing a clustering of proteins with immunological functions as well as cardiopathy-related proteins with blood-cell dependent functions and peripheral vascular processes. In addition, we established a reference proteomic fingerprint of 341 proteins commonly detected in all patients. Protein interactome network of this subproteome revealed protein clusters involved in the interaction of fibronectin with 14-3-3 proteins, TGFβ signaling, and TCP complex network. Taken together, our data contributes to the repertoire of the human thrombus proteome, serving as a reference library to increase our knowledge about the molecular basis of thrombus derived from AIS patients, paving the way toward the establishment of a quantitative approach necessary to detect and characterize potential novel biomarkers in the stroke field.

PDE4-Mediated cAMP Signalling

cAMP is the archetypal and ubiquitous second messenger utilised for the fine control of many cardiovascular cell signalling systems. The ability of cAMP to elicit cell surface receptor-specific responses relies on its compartmentalisation by cAMP hydrolysing enzymes known as phosphodiesterases. One family of these enzymes, PDE4, is particularly important in the cardiovascular system, where it has been extensively studied and shown to orchestrate complex, localised signalling that underpins many crucial functions of the heart. In the cardiac myocyte, cAMP activates PKA, which phosphorylates a small subset of mostly sarcoplasmic substrate proteins that drive β-adrenergic enhancement of cardiac function. The phosphorylation of these substrates, many of which are involved in cardiac excitation-contraction coupling, has been shown to be tightly regulated by highly localised pools of individual PDE4 isoforms. The spatial and temporal regulation of cardiac signalling is made possible by the formation of macromolecular “signalosomes”, which often include a cAMP effector, such as PKA, its substrate, PDE4 and an anchoring protein such as an AKAP. Studies described in the present review highlight the importance of this relationship for individual cardiac PKA substrates and we provide an overview of how this signalling paradigm is coordinated to promote efficient adrenergic enhancement of cardiac function. The role of PDE4 also extends to the vascular endothelium, where it regulates vascular permeability and barrier function. In this distinct location, PDE4 interacts with adherens junctions to regulate their stability. These highly specific, non-redundant roles for PDE4 isoforms have far reaching therapeutic potential. PDE inhibitors in the clinic have been plagued with problems due to the active site-directed nature of the compounds which concomitantly attenuate PDE activity in all highly localised “signalosomes”.

Pharmacologic management of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of vision loss in working-age populations, primarily attributable to retinal vascular hyperpermeability, hypoperfusion, and neoangiogenesis. In the past decade, laser photocoagulation and surgical interventions to treat DR have been replaced by topical administrations of anti-vascular endothelial growth factor drugs and corticosteroids. Although these drugs have revolutionized clinical management of DR, their limited efficacy and adverse effects have raised an increasing demand for new drug development. Meanwhile, mouse retinas have been prevalently employed as an experimental model system for angiogenic research, which has greatly contributed to the understanding of general principles in vascular biology. Therefore, clinical ophthalmology and basic research have complimentarily accumulated invaluable information for DR drug discovery. This review highlights the current pharmacologic management of DR, the utility of experimental mouse retinal models, and the perspectives on new drugs targeting the angioepoitin-Tie2 signals.

Rap1B promotes VEGF-induced endothelial permeability and is required for dynamic regulation of the endothelial barrier

Vascular endothelial growth factor (VEGF), a key angiogenic and permeability factor, plays an important role in new blood vessel formation. However, abnormal VEGF-induced VEGFR2 signaling leads to hyperpermeability. We have shown previously that Rap1, best known for promoting cell adhesion and vessel stability, is a critical regulator of VEGFR2-mediated angiogenic and shear-stress EC responses. To determine the role of Rap1 role in endothelial barrier dynamics, we examined vascular permeability in EC-specific Rap1A- and Rap1B-knockout mice, cell-cell junction remodeling and EC monolayer resistivity in Rap1-deficient ECs under basal, inflammatory or elevated VEGF conditions. Deletion of either Rap1 isoform impaired de novo adherens junction (AJ) formation and recovery from LPS-induced barrier disruption in vivo However, only Rap1A deficiency increased permeability in ECs and lung vessels. Interestingly, Rap1B deficiency attenuated VEGF-induced permeability in vivo and AJ remodeling in vitro Therefore, only Rap1A is required for the maintenance of normal vascular integrity. Importantly, Rap1B is the primary isoform essential for normal VEGF-induced EC barrier dissolution. Deletion of either Rap1 isoform protected against hyper permeability in the STZ-induced diabetes model, suggesting clinical implications for targeting Rap1 in pathologies with VEGF-induced hyperpermeability.

In Development-A New Paradigm for Understanding Vascular Disease

Under physiological conditions, the arterial endothelium exerts a powerful protective influence to maintain vascular homeostasis. However, during the development of vascular disease, these protective activities are lost, and dysfunctional endothelial cells actually promote disease pathogenesis. Numerous investigations have analyzed the characteristics of dysfunctional endothelium with a view to understanding the processes responsible for the dysfunction and to determining their role in vascular pathology. This review adopts an alternate approach: reviewing the mechanisms that contribute to the initial formation of a healthy protective endothelium and on how those mechanisms may be disrupted, precipitating the appearance of dysfunctional endothelial cells and the progression of vascular disease. This approach, which highlights the role of endothelial adherens junctions and vascular endothelial-cadherin in endothelial maturation and endothelial dysfunction, provides new insight into the remarkable biology of this important cell layer and its role in vascular protection and vascular disease.

Mind the gap: mechanisms regulating the endothelial barrier

The endothelial barrier consists of intercellular contacts localized in the cleft between endothelial cells, which is covered by the glycocalyx in a sievelike manner. Both types of barrier-forming junctions, i.e. the adherens junction (AJ) serving mechanical anchorage and mechanotransduction and the tight junction (TJ) sealing the intercellular space to limit paracellular permeability, are tethered to the actin cytoskeleton. Under resting conditions, the endothelium thereby builds a selective layer controlling the exchange of fluid and solutes with the surrounding tissue. However, in the situation of an inflammatory response such as in anaphylaxis or sepsis intercellular contacts disintegrate in post-capillary venules leading to intercellular gap formation. The resulting oedema can cause shock and multi-organ failure. Therefore, maintenance as well as coordinated opening and closure of interendothelial junctions is tightly regulated. The two principle underlying mechanisms comprise spatiotemporal activity control of the small GTPases Rac1 and RhoA and the balance of the phosphorylation state of AJ proteins. In the resting state, junctional Rac1 and RhoA activity is enhanced by junctional components, actin-binding proteins, cAMP signalling and extracellular cues such as sphingosine-1-phosphate (S1P) and angiopoietin-1 (Ang-1). In addition, phosphorylation of AJ components is prevented by junction-associated phosphatases including vascular endothelial protein tyrosine phosphatase (VE-PTP). In contrast, inflammatory mediators inhibiting cAMP/Rac1 signalling cause strong activation of RhoA and induce AJ phosphorylation finally leading to endocytosis and cleavage of VE-cadherin. This results in dissolution of TJs the outcome of which is endothelial barrier breakdown.

Growth Differentiation Factor 6 Promotes Vascular Stability by Restraining Vascular Endothelial Growth Factor Signaling

OBJECTIVE

The assembly of a functional vascular system requires a coordinated and dynamic transition from activation to maturation. High vascular endothelial growth factor activity promotes activation, including junction destabilization and cell motility. Maturation involves junctional stabilization and formation of a functional endothelial barrier. The identity and mechanism of action of prostabilization signals are still mostly unknown. Bone morphogenetic protein receptors and their ligands have important functions during embryonic vessel assembly and maturation. Previous work has suggested a role for growth differentiation factor 6 (GDF6; bone morphogenetic protein 13) in vascular integrity although GDF6's mechanism of action was not clear. Therefore, we sought to further explore the requirement for GDF6 in vascular stabilization.

APPROACH AND RESULTS

We investigated the role of GDF6 in promoting endothelial vascular integrity in vivo in zebrafish and in cultured human umbilical vein endothelial cells in vitro. We report that GDF6 promotes vascular integrity by counteracting vascular endothelial growth factor activity. GDF6-deficient endothelium has increased vascular endothelial growth factor signaling, increased vascular endothelial-cadherin Y658 phosphorylation, vascular endothelial-cadherin delocalization from cell-cell interfaces, and weakened endothelial cell adherence junctions that become prone to vascular leak.

CONCLUSIONS

Our results suggest that GDF6 promotes vascular stabilization by restraining vascular endothelial growth factor signaling. Understanding how GDF6 affects vascular integrity may help to provide insights into hemorrhage and associated vascular pathologies in humans.

Defenders and Challengers of Endothelial Barrier Function

Regulated vascular permeability is an essential feature of normal physiology and its dysfunction is associated with major human diseases ranging from cancer to inflammation and ischemic heart diseases. Integrity of endothelial cells also play a prominent role in the outcome of surgical procedures and organ transplant. Endothelial barrier function and integrity are regulated by a plethora of highly specialized transmembrane receptors, including claudin family proteins, occludin, junctional adhesion molecules (JAMs), vascular endothelial (VE)-cadherin, and the newly identified immunoglobulin (Ig) and proline-rich receptor-1 (IGPR-1) through various distinct mechanisms and signaling. On the other hand, vascular endothelial growth factor (VEGF) and its tyrosine kinase receptor, VEGF receptor-2, play a central role in the destabilization of endothelial barrier function. While claudins and occludin regulate cell-cell junction via recruitment of zonula occludens (ZO), cadherins via catenin proteins, and JAMs via ZO and afadin, IGPR-1 recruits bullous pemphigoid antigen 1 [also called dystonin (DST) and SH3 protein interacting with Nck90/WISH (SH3 protein interacting with Nck)]. Endothelial barrier function is moderated by the function of transmembrane receptors and signaling events that act to defend or destabilize it. Here, I highlight recent advances that have provided new insights into endothelial barrier function and mechanisms involved. Further investigation of these mechanisms could lead to the discovery of novel therapeutic targets for human diseases associated with endothelial dysfunction.

PI3K/AKT/Afadin signaling pathway contributes to pathological vascularization in glioblastomas

Glioblastomas are brain tumors with extensive vascularization that are associated with tumor malignancy. The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway is activated in endothelial cell tumors, although its exact function in glioblastoma neovascularization is poorly characterized. The present study identified that endothelial cells derived from human glioblastomas exhibit increased permeability and motility compared with normal brain vascular endothelial cells. Furthermore, the phosphorylation of AKT was significantly induced in glioblastoma-derived endothelial cells and glioblastoma vessels. To the best of our knowledge, the present study demonstrated for the first time that the cell-cell adhesion junction protein Afadin is phosphorylated and re-localized in glioblastoma-derived endothelial cells, and the phosphorylation and re-localization of Afadin is PI3K/AKT pathway-dependent. AKT-mediated phosphorylation and re-localization of Afadin may be critically involved in the modulation of brain endothelial permeability and migration. Therapies targeting the PI3K/AKT/Afadin pathway may therefore be beneficial for reducing the angiogenic potential of glioblastoma.

Plakoglobin maintains the integrity of vascular endothelial cell junctions and regulates VEGF-induced phosphorylation of VE-cadherin

Plakoglobin, also known as γ-catenin, is a close homolog of β-catenin and interacts with shared protein partners. Functions of β-catenin in cell adhesion are well-documented in terms of maintaining endothelial barrier function by interacting with vascular endothelial (VE)-cadherin. Plakoglobin also interacts with VE-cadherin, but its function in cell adhesion is not well understood. Here, we investigated plakoglobin function in vascular endothelial cell (ECs)-cell junction integrity. Knock-down of plakoglobin expression in ECs did not prevent cell proliferation or cell migration, but induced destabilization of the membrane distribution of VE-cadherin and resulted in increased permeability. Plakoglobin contributes to VE-cadherin-dependent adhesion in the steady state, but on stimulation with vascular endothelial growth factor (VEGF), it is essential for inducing sufficient VE-cadherin phosphorylation on VEGF signaling, thereby destabilizing cell-cell junctions. Furthermore, knock-down of plakoglobin expression increased vascular endothelial protein tyrosine phosphatase activity, an endothelial-specific membrane protein associating with VE-cadherin. These results indicate that plakoglobin plays multiple roles in regulation of cell-cell adhesion in a context dependent manner.

Prospect of divergent roles for the CUL3 system in vascular endothelial cell function and angiogenesis

Tissue remodelling and regeneration in various pathophysiological conditions (e.g. the processes of development, pregnancy, inflammation, wound healing, tissue regeneration, tumor growth, etc.) require angiogenesis, a dynamically coordinated response to stimuli from the extracellular microenvironment. During angiogenic and angiostatic responses, endothelial cells play a central role in the blood vessel formation and regression. Angiostatic responses, which are evoked by crucial factors such as VEGF and DLL4, have been elucidated. However, it has not been revealed, how endothelial cells process these conflicting signals. The study of VEGFR-Notch cross-signalling provided some clues. We discuss here the potential roles of cullin 3-based ubiquitin E3 ligases as key players in the process of various signals in endothelial cell function and angiogenesis. Our recent findings show that they function as units to process conflicting signalling crosstalk, epigenetic regulation of key factors, and functional barrier maintenance. We also expect more divergent roles of cullin 3-based ubiquitin E3 ligases in endothelial cell function and angiogenesis, and for their potential use as therapeutic targets.

ASK1-dependent endothelial cell activation is critical in ovarian cancer growth and metastasis

We have recently reported that tumor-associated macrophages (TAMs) promote early transcoelomic metastasis of ovarian cancer by facilitating TAM-ovarian cancer cell spheroid formation. ASK1 is known to be important for macrophage activation and inflammation-mediated tumorigenesis. In the present study, we show that ASK1 deficiency attenuates TAM-spheroid formation and ovarian cancer progression in an orthotopic ovarian cancer model. Interestingly, ASK1 in stroma, but not in TAMs, is critical for peritoneal tumor growth of ovarian cancer. Moreover, overexpression of an ASK1 inhibitory protein (suppressor of cytokine signaling-1; SOCS1) in vascular endothelium attenuates vascular permeability, TAM infiltration, and ovarian cancer growth. Mechanistically, we show that ASK1 mediates degradation of endothelial junction protein VE-cadherin via a lysosomal pathway to promote macrophage transmigration. Importantly, a pharmacological ASK1 inhibitor prevents tumor-induced vascular leakage, macrophage infiltration, and tumor growth in two mouse models. Since transcoelomic metastasis is also associated with many other cancers, such as pancreatic and colon cancers, our study provides ASK1 as a therapeutic target for the treatment of ovarian cancer and other transcoelomic metastasis cancers.

Defining the molecular basis of interaction between R3 receptor-type protein tyrosine phosphatases and VE-cadherin

Receptor-type protein tyrosine phosphatases (RPTPs) of the R3 subgroup play key roles in the immune, vascular and nervous systems. They are characterised by a large ectodomain comprising multiple FNIII-like repeats, a transmembrane domain, and a single intracellular phosphatase domain. The functional role of the extracellular region has not been clearly defined and potential roles in ligand interaction, dimerization, and regulation of cell-cell contacts have been reported. Here bimolecular fluorescence complementation (BiFC) in live cells was used to examine the molecular basis for the interaction of VE-PTP with VE-cadherin, two proteins involved in endothelial cell contact and maintenance of vascular integrity. The potential of other R3-PTPs to interact with VE-cadherin was also explored using this method. Quantitative BiFC analysis, using a VE-PTP construct expressing only the ectodomain and transmembrane domain, revealed a specific interaction with VE-cadherin, when compared with controls. Controls were sialophorin, an unrelated membrane protein with a large ectodomain, and a membrane anchored C-terminal Venus-YFP fragment, lacking both ectodomain and transmembrane domains. Truncation of the first 16 FNIII-like repeats from the ectodomain of VE-PTP indicated that removal of this region is not sufficient to disrupt the interaction with VE-cadherin, although it occurs predominantly in an intracellular location. A construct with a deletion of only the 17th domain of VE-PTP was, in contrast to previous studies, still able to interact with VE-cadherin, although this also was predominantly intracellular. Other members of the R3-PTP family (DEP-1, GLEPP1 and SAP-1) also exhibited the potential to interact with VE-cadherin. The direct interaction of DEP-1 with VE-cadherin is likely to be of physiological relevance since both proteins are expressed in endothelial cells. Together the data presented in the study suggest a role for both the ectodomain and transmembrane domain of R3-PTPs in interaction with VE-cadherin.

Blood-Brain Barrier in a Haemophilus influenzae Type a In Vitro Infection: Role of Adenosine Receptors A2A and A2B

The blood-brain barrier (BBB) is mainly made up of tightly connected microvascular endothelial cells (BMECs), surrounded by pericytes (BMPCs) which regulate BBB tightness by providing soluble factors that control endothelial proliferation. Haemophilus influenzae type a (Hia) is able to reach the BBB, crossing it, thus causing meningitis. In this study, by using an in vitro model of BBB, performed with human BMECs and human BMPCs in co-culture, we demonstrated that, after Hia infection, the number of hBMPCs decreased whereas the number of hBMECs increased in comparison with non-infected cells. SEM and TEM images showed that Hia was able to enter hBMECs and reduce TEER and VE-cadherin expression. When the cells were infected in presence of SCH58261 and PSB603 but not DPCPX, an increase in TEER values was observed thus demonstrating that A_2A and A_2B adenosine receptors play a key role in BBB dysfunction. These results were confirmed by the use of adenosine receptor agonists CGS21680, CCPA, and NECA. In infected co-cultures cAMP and VEGF increased and TEER reduction was counter-balanced by VEGF-R1 or VEGF-R2 antibodies. Moreover, the phosphorylated CREB and Rho-A significantly increased in infected hBMECs and hBMPCs and the presence of SCH58261 and PSB603 significantly abrogated the phosphorylation. In conclusion, this study demonstrated that the infection stimulated A_2A and A_2B adenosine receptors in hBMECs and hBMPCs thus inducing the pericytes to release large amounts of VEGF. The latter could be responsible for both, pericyte detachment and endothelial cell proliferation, thus provoking BBB impairment.

Drebrin's Role in the Maintenance of Endothelial Integrity

The human endothelium forms a permeable barrier between the blood stream and surrounding tissues, strictly governing the passage of immune cells, fluids and metabolites. The regulation of cell-cell contact dynamics between endothelial cells is essential for this function and thus for the maintenance of vascular integrity. Intercellular adhesion within the endothelium is mainly dependent on adherens junctions, composed of cell-cell adhesion proteins such as VE-cadherin and nectin, and their associated proteins. Recent research points to a critical role of the actin cytoskeleton in endothelial integrity, by providing anchorage of adhesion complexes to the cell cortex. We could show that the F-actin-binding protein drebrin is a critical regulator of endothelial integrity, by linking nectin to the cortical actin cytoskeleton. In particular, the knockdown of drebrin leads to functional impairment of endothelial cells, characterized by rupturing of endothelial monolayers cultured under conditions mimicking vascular flow. This weakening of cell-cell contacts upon drebrin depletion is based on the destabilization of nectin at adherens junctions, followed by internalization and degradation in lysosomes. Conducting interaction studies, we showed that drebrin binds to nectin's interaction partner afadin, thus linking the nectin/afadin system to the cortical F-actin network. Drebrin, containing binding sites for both afadin and F-actin, is thus uniquely equipped to stabilize nectin at adherens junctions, thereby preserving endothelial integrity. Collectively, these results contribute to the current understanding of cell-cell junction regulation, introducing a new function of drebrin as a stabilizer of endothelial integrity.

Endothelial cell-cell adhesion and signaling

Endothelial cells line blood vessels and provide a dynamic interface between the blood and tissues. They remodel to allow leukocytes, fluid and small molecules to enter tissues during inflammation and infections. Here we compare the signaling networks that contribute to endothelial permeability and leukocyte transendothelial migration, focusing particularly on signals mediated by small GTPases that regulate cell adhesion and the actin cytoskeleton. Rho and Rap GTPase signaling is important for both processes, but they differ in that signals are activated locally under leukocytes, whereas endothelial permeability is a wider event that affects the whole cell. Some molecules play a unique role in one of the two processes, and could therefore be targeted to selectively alter either endothelial permeability or leukocyte transendothelial migration.

Improved Antithrombotic Function of Oriented Endothelial Cell Monolayer on Microgrooves

Achievement of an endothelial cell (EC) monolayer (re-endothelialization) on the vascular implant surface with competent and functioning features is critical for long-term safety after implantation. Oriented EC monolayer is beneficial to improve endothelial function such as enhanced athero-resistant property. However, the information about antithrombotic property of oriented EC monolayer is limited. Here, we used the microgrooved polydimethylsiloxane substrates to guide EC orientation and obtain oriented EC monolayer. The effects of anisotropic topography on EC behaviors and antithrombotic function of the EC monolayer were then evaluated. Our data demonstrated that ECs responded to grooves in a size-dependent way as shown in oriented cell cytoskeleton and nuclei, enhanced directed migration, and overall velocity. Furthermore, compared to the EC monolayer on the flat surface, the oriented EC monolayer formed on the grooved substrates exhibited improved antithrombotic capability as indicated by higher expression of functional related genes, production of prostacyclin and tissue plasminogen activator, and prolonged activated coagulation time. The improvement of antithrombotic function was especially notable on the smaller-size groove. These findings reveal the responses of ECs to varisized topography and antithrombotic function of the oriented EC monolayer, providing insights into optimal design of vascular implants.

The role of endothelium in the onset of antibody-mediated TRALI

Transfusion Related Acute Lung Injury (TRALI) is one of the leading causes of mortality and morbidity following blood transfusion. The mechanisms behind the disease are not yet fully understood but seem to involve many different activating pathways and donor factors, in synergy with patient susceptibility. Studies have focused mostly on neutrophil activation, as aggregates of neutrophils and edema in lungs are found in post-mortem histological sections. This review aims to highlight the role of the endothelium in TRALI, as activated endothelium is the main promoter of leukocyte transmigration, and creates the barrier between blood and tissue. Since recent evidence suggests that a strong endothelial barrier prevents leukocyte transmigration and vascular leakage, we suggest that strengthening this barrier may be key to TRALI prevention.