Role of vascular endothelial-cadherin in vascular morphogenesis

The sprouting angiogenesis and vascular dysfunction triggered by bisphenol S and tetrabromobisphenol S through disrupting vascular endothelial-cadherin in zebrafish

Exogenous chemical toxicants may be important inducers of pathological angiogenesis diseases. However, few studies have investigated the associations between pathological angiogenesis diseases and chemical toxicant exposures, and the specific mechanism by which chemical toxicants induce sprouting angiogenesis is unclear. In this study, zebrafish were exposed to bisphenol S (BPS, 1-100 μg/L) and tetrabromobisphenol S (TBBPS, 0.1 and 10 μg/L) from the embryonic stage to the larval stage to investigate how pollutants interfere with angiogenesis and the function of ectopic sprouting vessels. The results showed that BPS and TBBPS promoted ectopic sprouting angiogenesis in different types of vascular plexuses, including the posterior cardinal vein (PCV) and superficial choroidal vessels (SOVs), at different developmental time points. Proteomic analyses of eGFP-positive endothelial cells (ECs) isolated from Tg(flk1: eGFP) zebrafish revealed that both BPS and TBBPS induced ectopic angiogenesis by acting on vascular endothelial-cadherin (VE-cadherin) and activating downstream proangiogenic signaling. In ectopic sprouting vessels induced by BPS and TBBPS, increased endothelial permeability resulted in white blood cell recruitment. Human oxidized lipids also tended to deposit in these ectopic vessels following BPS and TBBPS exposure. These findings suggest that chemical toxicant-induced ectopic angiogenesis is an important cause of vascular dysfunction and related diseases.

VE-cadherin may suppress inflammation depending on the phase of inflammation of rheumatoid arthritis

OBJECTIVES

A disintegrin and metalloproteinase (ADAM)-15 and vascular endothelial (VE)-cadherin are involved in angiogenesis. We investigated the relationship between ADAM-15 and VE-cadherin expressions in rheumatoid arthritis (RA).

METHODS

VE-cadherin concentrations in the serum of patients with RA were measured using the enzyme linked immunosorbent assay. We stimulated fibroblast-like synoviocytes (RA-FLS) with VE-cadherin and measured the vascular endothelial growth factor (VEGF) and inflammatory cytokine levels using ELISA. We also examined the correlation between serum VE-cadherin levels and DAS-28ESR, and used the Matrigel assay to examine VE-cadherin involvement in angiogenesis.

RESULTS

Serum VE-cadherin levels were significantly higher in patients with RA than in healthy controls. A negative correlation was observed between VE-cadherin and DAS-28ESR. VEGF, chemokine ligand 16, intercellular adhesion molecule-1, and interleukin-8 levels in the supernatant of RA-FLS or human umbilical vein endothelial cells stimulated with VE-cadherin were significantly lower than those in the controls. The number of intercellular bridges formed by endothelial cells using Matrigel significantly decreased in RA synovial fluids from which VE-cadherin had been removed compared to synovial fluids treated with control immunoglobulin G.

CONCLUSION

VE-cadherin may have an inhibitory effect on inflammation depending on the phase of RA inflammation.

Falsifying computational models of endothelial cell network formation through quantitative comparison with in vitro models

During angiogenesis, endothelial cells expand the vasculature by migrating from existing blood vessels, proliferating and collectively organizing into new capillaries. In vitro and in vivo experimentation is instrumental for identifying the molecular players and cell behaviour that regulate angiogenesis. Alongside experimental work, computational and mathematical models of endothelial cell network formation have helped to analyse if the current molecular and cellular understanding of endothelial cell behaviour is sufficient to explain the formation of endothelial cell networks. As input, the models take (a subset of) the current knowledge or hypotheses of single cell behaviour and capture it into a dynamical, mathematical description. As output, they predict the multicellular behaviour following from the actions of many individual cells, i.e., formation of a vascular-like network. Paradoxically, computational modelling based on different assumptions, i.e., completely different, sometimes non-intersecting sets of observed single cell behaviour, can reproduce the same angiogenesis-like multicellular behaviour, making it practically impossible to decide which, if any, of these models is correct. Here we present dynamical analyses of time-lapses of in vitro endothelial cell network formation experiments and compare these with dynamic analyses of three mathematical models: (1) the cell elongation model; (2) the contact-inhibited chemotaxis model; and (3) the mechanical cell-cell communication model. We extract a variety of dynamical characteristics of endothelial cell network formation using a custom time-lapse video analysis pipeline in ImageJ. We compare the dynamical network characteristics of the in vitro experiments to those of the cellular networks produced by the computational models. We test the response of the in silico dynamical cell network characteristics to changes in cell density and make related changes in the in vitro experiments. Of the three computational models that we have considered, the cell elongation model best captures the remodelling phase of in vitro endothelial cell network formation. Furthermore, in the in vitro model, the final size and number of lacunae in the network are independent of the initial cell density. This observation is also reproduced in the cell elongation model, but not in the other two models that we have considered. Altogether, we present an approach to model validation based on comparisons of time-resolved data and variations of model conditions.

Densely vascularized thick 3D tissue shows enhanced protein secretion constructed with intermittent positive pressure

Constructing a dense vascular endothelial network within engineered tissue is crucial for successful engraftment. The present study investigated the effects of air-compressing intermittent positive pressure (IPP) on co-cultured mesenchymal stem cells and vascular endothelial cells and evaluated the potential of IPP-cultured cell sheets for transplantation therapy. The results demonstrated that the IPP (+) group exhibited a denser vascular endothelial network and significantly increased cell sheet thickness compared to the IPP (-) group. Furthermore, in vivo experiments showed that IPP-cultured cell sheets enhanced the secretion of Gaussian luciferase by genetically modified mesenchymal stem cells. These findings highlight the IPP method as a technique that simultaneously enables the thickening of planar tissues and the construction of vascular networks. This approach demonstrates promise for fabricating functional, transplantable, and thick tissues with dense vascularization and a high capacity for protein secretion, paving the way for novel applications in regenerative medicine.

Identification of Amino Acid Residues Critical for the Interaction of Fibrin with N-Cadherin

We recently identified N-cadherin as a novel receptor for fibrin and localized complementary binding sites within the fibrin βN-domains and the third and fifth extracellular domains (EC3 and EC5) of N-cadherin. We also hypothesized that the His16 and Arg17 residues of the βN-domains and the (Asp/Glu)-X-(Asp/Glu) motifs present in the EC3 and EC5 domains may play roles in the interaction between fibrin and N-cadherin. The primary objectives of this study were to test these hypotheses and to further clarify the structural basis for this interaction. To test our hypotheses, we first mutated His16 and Arg17 in the recombinant (β15-66)2 fragment, which mimics the dimeric arrangement of the βN-domains in fibrin, using site-directed mutagenesis. The results revealed that the mutations of both His16 and Arg17 are critical for the interaction. Next, we mutated Asp/Glu residues in the three (Asp/Glu)-X-(Asp/Glu) motifs, M1 (Asp-Phe-Glu), M2 (Glu-Ala-Glu), and M3 (Asp-Tyr-Asp), of the fibrin-binding N-cad(3-5) fragment of N-cadherin. The results showed that Asp292 and Glu294 of M1, and Asp468 and Asp470 of M3, are critical for the interaction. Our molecular modeling of the 3D structure of the EC3-EC4-EC5 domains revealed that these residues are located at the interfaces of EC3-EC4 and EC4-EC5 and that some may also be involved in calcium binding. In conclusion, our study identified amino acid residues in the fibrin βN-domains and the EC3 and EC5 domains of N-cadherin that are critical for the interaction of fibrin with N-cadherin and localized the fibrin-binding residues in the 3D structure of N-cadherin.

Complement System and Adhesion Molecule Skirmishes in Fabry Disease: Insights into Pathogenesis and Disease Mechanisms

Fabry disease is a rare X-linked lysosomal storage disorder caused by mutations in the galactosidase alpha (GLA) gene, resulting in the accumulation of globotriaosylceramide (Gb3) and its deacetylated form, globotriaosylsphingosine (Lyso-Gb3) in various tissues and fluids throughout the body. This pathological accumulation triggers a cascade of processes involving immune dysregulation and complement system activation. Elevated levels of complement 3a (C3a), C5a, and their precursor C3 are observed in the plasma, serum, and tissues of patients with Fabry disease, correlating with significant endothelial cell abnormalities and vascular dysfunction. This review elucidates how the complement system, particularly through the activation of C3a and C5a, exacerbates disease pathology. The activation of these pathways leads to the upregulation of adhesion molecules, including vascular cell adhesion molecule 1 (VCAM1), intercellular adhesion molecule 1 (ICAM1), platelet and endothelial cell adhesion molecule 1 (PECAM1), and complement receptor 3 (CR3) on leukocytes and endothelial cells. This upregulation promotes the excessive recruitment of leukocytes, which in turn exacerbates disease pathology. Targeting complement components C3a, C5a, or their respective receptors, C3aR (C3a receptor) and C5aR1 (C5a receptor 1), could potentially reduce inflammation, mitigate tissue damage, and improve clinical outcomes for individuals with Fabry disease.

Netrin‑4 promotes VE‑cadherin expression in endothelial cells through the NF‑κB signaling pathway

Netrin-4 (NTN4), a secreted protein from the Netrin family, has been recognized for its role in vascular development, endothelial homeostasis and angiogenesis. Vascular endothelial (VE)-cadherin is a specialized adhesion protein located at the intercellular junctions of endothelial cells (ECs), and regulates migration, proliferation and permeability. To date, the relationship between NTN4 and VE-cadherin in ECs remains unclear. In the present study, human umbilical vein ECs (HUVECs) were transfected with NTN4 overexpression plasmid, resulting in NTN4 overexpression. Reverse transcription-quantitative PCR and western blotting were used to determine gene and protein expression. CCK8, wound healing, and Transwell assays were performed to evaluate cell proliferation, migration and permeability. NTN4 overexpression decreased HUVEC viability and migration. In addition, NTN4 overexpression increased the expression of VE-cadherin and decreased the permeability of HUVECs. Subsequent studies showed that NTN4 overexpression increased the NF-κB protein level and decreased IκB-α protein expression in HUVECs. In HUVECs treated with NF-κB inhibitor pyrrolidine dithiocarbamate, the expression of VE-cadherin failed to increase with NTN4 overexpression. Taken together, the results indicated that NTN4 overexpression increased VE-cadherin expression through the activation of the NF-κB signaling pathway in HUVECs. The present findings revealed a novel regulatory mechanism for VE-cadherin expression and suggested a novel avenue for future research on the role of NTN4 in endothelial barrier-related diseases.

Rare genetic variation in VE-PTP is associated with central serous chorioretinopathy, venous dysfunction and glaucoma

Central serous chorioretinopathy (CSC) is a fluid maculopathy whose etiology is not well understood. Abnormal choroidal veins in CSC patients have been shown to have similarities with varicose veins. To identify potential mechanisms, we analyzed genotype data from 1,477 CSC patients and 455,449 controls in FinnGen. We identified an association for a low-frequency (AF=0.5%) missense variant (rs113791087) in the gene encoding vascular endothelial protein tyrosine phosphatase (VE-PTP) (OR=2.85, P=4.5×10-9). This was confirmed in a meta-analysis of 2,452 CSC patients and 865,767 controls from 4 studies (OR=3.06, P=7.4×10-15). Rs113791087 was associated with a 56% higher prevalence of retinal abnormalities (35.3% vs 22.6%, P=8.0×10-4) in 708 UK Biobank participants and, surprisingly, with varicose veins (OR=1.31, P=2.3×10-11) and glaucoma (OR=0.82, P=6.9×10-9). Predicted loss-of-function variants in VEPTP, though rare in number, were associated with CSC in All of Us (OR=17.10, P=0.018). These findings highlight the significance of VE-PTP in diverse ocular and systemic vascular diseases.

Collateral Damage in the Placenta during Viral Infection in Pregnancy: A Possible Mechanism for Vertical Transmission and an Adverse Pregnancy Outcome

In mammals, the placenta is a connection between a mother and a new developing organism. This tissue has a protective function against some microorganisms, transports nutrients, and exchanges gases and excretory substances between the mother and the fetus. Placental tissue is mainly composed of chorionic villi functional units called trophoblasts (cytotrophoblasts, the syncytiotrophoblast, and extravillous trophoblasts). However, some viruses have developed mechanisms that help them invade the placenta, causing various conditions such as necrosis, poor perfusion, and membrane rupture which, in turn, can impact the development of the fetus and put the mother's health at risk. In this study, we collected the most relevant information about viral infection during pregnancy which can affect both the mother and the fetus, leading to an increase in the probability of vertical transmission. Knowing these mechanisms could be relevant for new research in the maternal-fetal context and may provide options for new therapeutic targets and biomarkers in fetal prognosis.

A mechanical modeling framework to study endothelial permeability

The inner lining of blood vessels, the endothelium, is made up of endothelial cells. Vascular endothelial (VE)-cadherin protein forms a bond with VE-cadherin from neighboring cells to determine the size of gaps between the cells and thereby regulate the size of particles that can cross the endothelium. Chemical cues such as thrombin, along with mechanical properties of the cell and extracellular matrix are known to affect the permeability of endothelial cells. Abnormal permeability is found in patients suffering from diseases including cardiovascular diseases, cancer, and COVID-19. Even though some of the regulatory mechanisms affecting endothelial permeability are well studied, details of how several mechanical and chemical stimuli acting simultaneously affect endothelial permeability are not yet understood. In this article, we present a continuum-level mechanical modeling framework to study the highly dynamic nature of the VE-cadherin bonds. Taking inspiration from the catch-slip behavior that VE-cadherin complexes are known to exhibit, we model the VE-cadherin homophilic bond as cohesive contact with damage following a traction-separation law. We explicitly model the actin cytoskeleton and substrate to study their role in permeability. Our studies show that mechanochemical coupling is necessary to simulate the influence of the mechanical properties of the substrate on permeability. Simulations show that shear between cells is responsible for the variation in permeability between bicellular and tricellular junctions, explaining the phenotypic differences observed in experiments. An increase in the magnitude of traction force due to disturbed flow that endothelial cells experience results in increased permeability, and it is found that the effect is higher on stiffer extracellular matrix. Finally, we show that the cylindrical monolayer exhibits higher permeability than the planar monolayer under unconstrained cases. Thus, we present a contact mechanics-based mechanochemical model to investigate the variation in the permeability of endothelial monolayer due to multiple loads acting simultaneously.

Identification of Neural (N)-Cadherin as a Novel Endothelial Cell Receptor for Fibrin and Localization of the Complementary Binding Sites

Based on the high structural homology between vascular endothelial (VE)-cadherin and neural (N)-cadherin, we hypothesized that fibrin, which is known to interact with VE-cadherin and promote angiogenesis through this interaction, may also interact with N-cadherin. To test this hypothesis, we prepared fibrin and its plasmin-produced and recombinant fragments covering practically all parts of the fibrin molecule. We also prepared the soluble extracellular portion of N-cadherin (sN-cadherin), which includes all five extracellular N-cadherin domains, and studied its interaction with fibrinogen, fibrin, and the aforementioned fibrin fragments using two independent methods, ELISA and SPR. The experiments confirmed our hypothesis, revealing that fibrin interacts with sN-cadherin with high affinity. Furthermore, the experiments localized the N-cadherin binding site within the fibrin βN-domains. Notably, the recombinant dimeric (β15-66)2 fragment, corresponding to these domains and mimicking their dimeric arrangement in fibrin, preserved the N-cadherin-binding properties of fibrin. To localize the fibrin binding site within N-cadherin, we performed ELISA and SPR experiments with (β15-66)2 and recombinant N-cadherin fragments representing its individual extracellular domains and combinations thereof. The results obtained indicate that the interaction of fibrin with N-cadherin occurs through the third and fifth extracellular domains of the latter. This is in contrast to our previous study, which revealed that fibrin interacts only with the third extracellular domain of VE-cadherin. In conclusion, our study identified N-cadherin as a novel receptor for fibrin and localized complementary binding sites within both fibrin and N-cadherin. The pathophysiological role of this interaction remains to be established.

Retinal vascular remodeling in photoreceptor degenerative disease

Abnormal vasculature in the retina, specifically tortuous vessels and capillary degeneration, is common in many of the most prevalent retinal degenerative diseases, currently affecting millions of people across the world. However, the formation and development of abnormal vasculature in the context of retinal degenerative diseases are still poorly understood. The FVB/N (rd1) and rd10 mice are well-studied animal models of retinal degenerative diseases, but how photoreceptor degeneration leads to vascular abnormality in the diseases remains to be elucidated. Here, we used advancements in confocal microscopy, immunohistochemistry, and image analysis software to systematically characterize the pathological vasculature in the FVB/N (rd1) and rd10 mice, known as a chronic, rapid and slower retinal degenerative model, respectively. We demonstrated that there was plexus-specific vascular degeneration in the retinal trilaminar vascular network paralleled to photoreceptor degeneration in the diseased retinas. We also quantitatively analyzed the vascular structural architecture in the wild-type and diseased retinas to provide valuable information on vascular remodeling in retinal degenerative disease.

Molecular Mechanisms of Endothelialitis in SARS-CoV-2 Infection: Evidence for VE-Cadherin Cleavage by ACE2

Long COVID-19 syndrome appears after Severe Acute Respiratory Syndrome-Corona Virus (SARS-CoV-2) infection with acute damage to microcapillaries, microthrombi, and endothelialitis. However, the mechanisms involved in these processes remain to be elucidated. All blood vessels are lined with a monolayer of endothelial cells called vascular endothelium, which provides a the major function is to prevent coagulation. A component of endothelial cell junctions is VE-cadherin, which is responsible for maintaining the integrity of the vessels through homophilic interactions of its Ca++-dependent adhesive extracellular domain. Here we provide the first evidence that VE-cadherin is a target in vitro for ACE2 cleavage because its extracellular domain (hrVE-ED) contains two amino acid sequences for ACE2 substrate recognition at the positions 256P-F257 and 321PMKP-325L. Indeed, incubation of hrVE-ED with the active ectopeptidase hrACE2 for 16 hrs in the presence of 10 μM ZnCl2 showed a dose-dependent (from 0.2 ng/μL to 2 ng/μL) decrease of the VE-cadherin immunoreactive band. In vivo, in the blood from patients having severe COVID-19 we detected a circulating form of ACE2 with an apparent molecular mass of 70 kDa, which was barely detectable in patients with mild COVID-19. Of importance, in the patients with severe COVID-19 disease, the presence of three soluble fragments of VE-cadherin (70, 62, 54 kDa) were detected using the antiEC1 antibody while only the 54 kDa fragment was present in patients with mild disease. Altogether, these data clearly support a role for ACE2 to cleave VE-cadherin, which leads to potential biomarkers of SARS-CoV-2 infection related with the vascular disease in "Long COVID-19".

Coordinated linear and rotational movements of endothelial cells compartmentalized by VE-cadherin drive angiogenic sprouting

Angiogenesis is a sequential process to extend new blood vessels from preexisting ones by sprouting and branching. During angiogenesis, endothelial cells (ECs) exhibit inhomogeneous multicellular behaviors referred to as "cell mixing," in which ECs repetitively exchange their relative positions, but the underlying mechanism remains elusive. Here we identified the coordinated linear and rotational movements potentiated by cell-cell contact as drivers of sprouting angiogenesis using in vitro and in silico approaches. VE-cadherin confers the coordinated linear motility that facilitated forward sprout elongation, although it is dispensable for rotational movement, which was synchronous without VE-cadherin. Mathematical modeling recapitulated the EC motility in the two-cell state and angiogenic morphogenesis with the effects of VE-cadherin-knockout. Finally, we found that VE-cadherin-dependent EC compartmentalization potentiated branch elongations, and confirmed this by mathematical simulation. Collectively, we propose a way to understand angiogenesis, based on unique EC behavioral properties that are partially dependent on VE-cadherin function.

PI(4,5)P2-dependent regulation of endothelial tip cell specification contributes to angiogenesis

Dynamic positioning of endothelial tip and stalk cells, via the interplay between VEGFR2 and NOTCH signaling, is essential for angiogenesis. VEGFR2 activates PI3K, which phosphorylates PI(4,5)P₂ to PI(3,4,5)P₃, activating AKT; however, PI3K/AKT does not direct tip cell specification. We report that PI(4,5)P₂ hydrolysis by the phosphoinositide-5-phosphatase, INPP5K, contributes to angiogenesis. INPP5K ablation disrupted tip cell specification and impaired embryonic angiogenesis associated with enhanced DLL4/NOTCH signaling. INPP5K degraded a pool of PI(4,5)P₂ generated by PIP5K1C phosphorylation of PI(4)P in endothelial cells. INPP5K ablation increased PI(4,5)P₂, thereby releasing β-catenin from the plasma membrane, and concurrently increased PI(3,4,5)P₃-dependent AKT activation, conditions that licensed DLL4/NOTCH transcription. Suppression of PI(4,5)P₂ in INPP5K-siRNA cells by PIP5K1C-siRNA, restored β-catenin membrane localization and normalized AKT signaling. Pharmacological NOTCH or AKT inhibition in vivo or genetic β-catenin attenuation rescued angiogenesis defects in INPP5K-null mice. Therefore, PI(4,5)P₂ is critical for β-catenin/DLL4/NOTCH signaling, which governs tip cell specification during angiogenesis.

Dialogue between VE-Cadherin and Sphingosine 1 Phosphate Receptor1 (S1PR1) for Protecting Endothelial Functions

The endothelial cells (EC) of established blood vessels in adults remain extraordinarily quiescent in the sense that they are not actively proliferating, but they fulfill the necessary role to control the permeability of their monolayer that lines the interior of blood vessels. The cell-cell junctions between ECs in the endothelium comprise tight junctions and adherens homotypic junctions, which are ubiquitous along the vascular tree. Adherens junctions are adhesive intercellular contacts that are crucial for the organization of the EC monolayer and its maintenance and regulation of normal microvascular function. The molecular components and underlying signaling pathways that control the association of adherens junctions have been described in the last few years. In contrast, the role that dysfunction of these adherens junctions has in contributing to human vascular disease remains an important open issue. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid mediator found at high concentrations in blood which has important roles in the control of the vascular permeability, cell recruitment, and clotting that follow inflammatory processes. This role of S1P is achieved through a signaling pathway mediated through a family of G protein-coupled receptors designated as S1PR1. This review highlights novel evidence for a direct linkage between S1PR1 signaling and the mediation of EC cohesive properties that are controlled by VE-cadherin.

Characterization of the roles of amphiregulin and transforming growth factor β1 in microvasculature-like formation in human granulosa-lutein cells

Vascular endothelial-cadherin (VE-cadherin) is an essential component that regulates angiogenesis during corpus luteum formation. Amphiregulin (AREG) and transforming growth factor β1 (TGF-β1) are two intrafollicular factors that possess opposite functions in directing corpus luteum development and progesterone synthesis in human granulosa-lutein (hGL) cells. However, whether AREG or TGF-β1 regulates the VE-cadherin expression and subsequent angiogenesis in the human corpus luteum remains to be elucidated. Results showed that hGL cells cultured on Matrigel spontaneously formed capillary-like and sprout-like microvascular networks. Results of specific inhibitor treatment and small interfering RNA-mediated knockdown revealed that AREG promoteed microvascular-like formation in hGL cells by upregulating the VE-cadherin expression mediated by the epidermal growth factor receptor (EGFR)-extracellular signal-regulated kinase1/2 (ERK1/2) signaling pathway. However, TGF-β1 suppressed microvascular-like formation in hGL cells by downregulating VE-cadherin expression mediated by the activin receptor-like kinase (ALK)5-Sma- and Mad-related protein (SMAD)2/3/4 signaling pathway. Collectively, this study provides important insights into the underlying molecular mechanisms by which TGF-β1 and AREG differentially regulate corpus luteum formation in human ovaries.

Modeling Transposition of the Great Arteries with Patient-Specific Induced Pluripotent Stem Cells

The dextro-transposition of the great arteries (d-TGA) is one of the most common congenital heart diseases. To identify biological processes that could be related to the development of d-TGA, we established induced pluripotent stem cell (iPSC) lines from two patients with d-TGA and from two healthy subjects (as controls) and differentiated them into endothelial cells (iPSC-ECs). iPSC-EC transcriptome profiling and bioinformatics analysis revealed differences in the expression level of genes involved in circulatory system and animal organ development. iPSC-ECs from patients with d-TGA showed impaired ability to develop tubular structures in an in vitro capillary-like tube formation assay, and interactome studies revealed downregulation of biological processes related to Notch signaling, circulatory system development and angiogenesis, pointing to alterations in vascular structure development. Our study provides an iPSC-based cellular model to investigate the etiology of d-TGA.

DHA-enriched phosphatidylcholine suppressed angiogenesis by activating PPARγ and modulating the VEGFR2/Ras/ERK pathway in human umbilical vein endothelial cells

Docosahexaenoic acid-enriched phosphatidylcholine (DHA-PC) is a new generation of omega-3 lipids, which contains an ester bond linking DHA at the sn-2 position of phospholipid. DHA-PC has become the interest recently as its better bioavailability and anti-oxidation capacity. In this study, the anti-angiogenic effect of DHA-PC was evaluated. The capacities of proliferation, migration, tube formation of human umbilical vein endothelial cells were significantly declined after DHA-PC treatment. Furthermore, DHA-PC inhibited the neovascularization of the chick chorioallantoic membrane in vivo. Mechanism results indicated that DHA-PC enhances the expression of peroxisome proliferator-activated receptor γ (PPARγ) at transcriptional and translational level, subsequently down-regulates the VEGFR2 expression and VEGFR2-mediated downstream Ras/ERK pathway, resulting in significant reduction in proliferation and differentiation. Additionally, PPARγ-specific antagonist GW9662 partly reversed the inhibition effects of DHA-PC on tube formation and neovascularization, suggesting that DHA-PC exerts anti-angiogenesis effect through activating PPARγ. These findings indicated that DHA-PC has a great prospect of anti-tumor angiogenesis therapy.

Embryonic lethal genetic variants and chromosomally normal pregnancy loss

OBJECTIVE

To examine whether rare damaging genetic variants are associated with chromosomally normal pregnancy loss and estimate the magnitude of the association.

DESIGN

Case-control.

SETTING

Cases were derived from a consecutive series of karyotyped losses at one New Jersey hospital. Controls were derived from the National Database for Autism Research.

PATIENT(S)

Cases comprised 19 chromosomally normal loss conceptus-parent trios. Controls comprised 547 unaffected siblings of autism case-parent trios.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The rate of damaging variants in the exome (loss of function and missense-damaging) and the proportions of probands with at least one such variant among cases vs. controls.

RESULTS

The proportions of probands with at least one rare damaging variant were 36.8% among cases and 22.9% among controls (odds ratio, 2.0; 99% confidence interval, 0.5-7.3). No case had a variant in a known fetal anomaly gene. The proportion with variants in possibly embryonic lethal genes increased in case probands (odds ratio, 14.5; 99% confidence interval, 1.5-89.7); variants occurred in BAZ1A, FBN2, and TIMP2.

CONCLUSION(S)

Rare genetic variants in the conceptus may be a cause of chromosomally normal pregnancy loss. A larger sample is needed to estimate the magnitude of the association with precision and identify relevant biologic pathways.

Cartiotonic steroids affect monolayer permeability in lymphatic endothelial cells

Edema is common in preeclampsia (preE), a hypertensive disorder of pregnancy. Cardiotonic steroids (CTSs) such as marinobufagenin (MBG) are involved in the pathogenesis of preE. To assess whether CTSs are involved in the leakage of lymphatic endothelial cell (LEC), we evaluated their effect on monolayer permeability of LECs (MPLEC) in culture. A rat mesenteric LECs were treated with DMSO (vehicle), and CTSs (MBG, CINO, OUB) at concentrations of 1, 10, and 100 nM. Some LECs were pretreated with 1 μM L-NAME (N-Nitro-L-Arginine Methyl Ester) before adding 100 nM MBG or cinobufotalin (CINO). Expression of β-catenin and vascular endothelial (VE)-cadherin in CTS-treated LECs was measured by immunofluorescence and MPLEC was quantified using a fluorescence plate reader. Western blot was performed to measure β-catenin and VE-cadherin protein levels and myosin light chain 20 (MLC20) phosphorylation. MBG (≥ 1 nM) and CINO (≥ 10 nM) caused an increase (p < 0.05) in the MPLEC compared to DMSO while ouabain (OUB) had no effect. Pretreatment of LECs with 1 μM L-NAME attenuated (p < 0.05) the MPLEC. The β-catenin expression in LECs was downregulated (p < 0.05) by MBG and CINO. However, there was no effect on the LECs tight junctions for the CINO group. VE-cadherin expression was downregulated (p < 0.05) by CINO, and MLC20 phosphorylation was upregulated (p < 0.05) by MBG. We demonstrated that MBG and CINO caused an increase in the MPLEC, which were attenuated by L-NAME pretreatment. The data suggest that CTSs exert their effect via nitric-oxide-dependent signaling pathway and may be involved in vascular leak syndrome of LEC lining in preE.

Mapping the regulatory landscape of auditory hair cells from single-cell multi-omics data

Auditory hair cells transduce sound to the brain and in mammals these cells reside together with supporting cells in the sensory epithelium of the cochlea, called the organ of Corti. To establish the organ's delicate function during development and differentiation, spatiotemporal gene expression is strictly controlled by chromatin accessibility and cell type-specific transcription factors, jointly representing the regulatory landscape. Bulk-sequencing technology and cellular heterogeneity obscured investigations on the interplay between transcription factors and chromatin accessibility in inner ear development. To study the formation of the regulatory landscape in hair cells, we collected single-cell chromatin accessibility profiles accompanied by single-cell RNA data from genetically labeled murine hair cells and supporting cells after birth. Using an integrative approach, we predicted cell type-specific activating and repressing functions of developmental transcription factors. Furthermore, by integrating gene expression and chromatin accessibility datasets, we reconstructed gene regulatory networks. Then, using a comparative approach, 20 hair cell-specific activators and repressors, including putative downstream target genes, were identified. Clustering of target genes resolved groups of related transcription factors and was utilized to infer their developmental functions. Finally, the heterogeneity in the single-cell data allowed us to spatially reconstruct transcriptional as well as chromatin accessibility trajectories, indicating that gradual changes in the chromatin accessibility landscape were lagging behind the transcriptional identity of hair cells along the organ's longitudinal axis. Overall, this study provides a strategy to spatially reconstruct the formation of a lineage specific regulatory landscape using a single-cell multi-omics approach.

Regulation of endothelial cell differentiation in embryonic vascular development and its therapeutic potential in cardiovascular diseases

During vertebrate development, the cardiovascular system begins operating earlier than any other organ in the embryo. Endothelial cell (EC) forms the inner lining of blood vessels, and its extensive proliferation and migration are requisite for vasculogenesis and angiogenesis. Many aspects of cellular biology are involved in vasculogenesis and angiogenesis, including the tip versus stalk cell specification. Recently, epigenetics has attracted growing attention in regulating embryonic vascular development and controlling EC differentiation. Some proteins that regulate chromatin structure have been shown to be directly implicated in human cardiovascular diseases. Additionally, the roles of important EC signaling such as vascular endothelial growth factor and its receptors, angiopoietin-1 and tyrosine kinase containing immunoglobulin and epidermal growth factor homology domain-2, and transforming growth factor-β in EC differentiation during embryonic vasculature development are briefly discussed in this review. Recently, the transplantation of human induced pluripotent stem cell (iPSC)-ECs are promising approaches for the treatment of ischemic cardiovascular disease including myocardial infarction. Patient-specific iPSC-derived EC is a potential new target to study differences in gene expression or response to drugs. However, clinical application of the iPSC-ECs in regenerative medicine is often limited by the challenges of maintaining cell viability and function. Therefore, novel insights into the molecular mechanisms underlying EC differentiation might provide a better understanding of embryonic vascular development and bring out more effective EC-based therapeutic strategies for cardiovascular diseases.

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.

Blood flow-mediated gene transfer and siRNA-knockdown in the developing vasculature in a spatio-temporally controlled manner in chicken embryos

We describe a method by which early developing vasculature can be gene-manipulated independently of the heart in a spatio-temporally controlled manner. Lipofectamine 2000 or 3000, an easy-to-use lipid reagent, has been found to yield a high efficiency of transfection when co-injected with GFP DNA within a critical range of lipid concentration. By exploiting developmentally changing patterns of vasculature and blood flow, we have succeed in controlling the site of transfection: injection with a lipid-DNA cocktail into the heart before or after the blood circulation starts results in a limited and widely spread patterns of transfection, respectively. Furthermore, a cocktail injection into the right dorsal aorta leads to transgenesis of the right half of embryonic vasculature. In addition, this method combined with the siRNA technique has allowed, for the first time, to knockdown the endogenous expression of VE-cadherin (also called Cdh5), which has been implicated in assembly of nasant blood vessels: when Cah5 siRNA is injected into the right dorsal aorta, pronounced defects in the right half of vasculature are observed without heart defects. Whereas infusion-mediated gene transfection method has previously been reported using lipid reagents that were elaborately prepared on their own, Lipofectamine is an easy-use reagent with no requirement of special expertise. The methods reported here would overcome shortcomings of conventional vascular-transgenic animals, such as mice and zebrafish, in which pan-endothelial enhancer-driven transgenesis often leads to the heart malformation, which, in turn, indirectly affects peripheral vasculature due to flow defects. Since a variety of subtypes in vasculature have increasingly been appreciated, the spatio-temporally controllable gene manipulation described in this study offers a powerful tool to understand how the vasculature is established at the molecular level.

Cadherin Signaling in Cancer: Its Functions and Role as a Therapeutic Target

Cadherin family includes lists of transmembrane glycoproteins which mediate calcium-dependent cell-cell adhesion. Cadherin-mediated adhesion regulates cell growth and differentiation throughout life. Through the establishment of the cadherin-catenin complex, cadherins provide normal cell-cell adhesion and maintain homeostatic tissue architecture. In the process of cell recognition and adhesion, cadherins act as vital participators. As results, the disruption of cadherin signaling has significant implications on tumor formation and progression. Altered cadherin expression plays a vital role in tumorigenesis, tumor progression, angiogenesis, and tumor immune response. Based on ongoing research into the role of cadherin signaling in malignant tumors, cadherins are now being considered as potential targets for cancer therapies. This review will demonstrate the mechanisms of cadherin involvement in tumor progression, and consider the clinical significance of cadherins as therapeutic targets.

VE-Cadherin Is Required for Lymphatic Valve Formation and Maintenance

The lymphatic vasculature requires intraluminal valves to maintain forward lymph flow. Lymphatic valves form and are constantly maintained by oscillatory fluid flow throughout life, yet the earliest steps of how lymphatic endothelial cells are able to respond to fluid shear stress remain unknown. Here, we show that the adherens junction protein VE-cadherin is required for the upregulation of valve-specific transcription factors. Conditional deletion of VE-cadherin in vivo prevented valve formation in the embryo and caused postnatal regression of nearly all lymphatic valves in multiple tissues. Since VE-cadherin is known to signal through β-catenin and the VEGFR/AKT pathway, each pathway was probed. Expression of a constitutively active β-catenin mutant or direct pharmacologic activation of AKT in vivo significantly rescued valve regression in the VE-cadherin-deficient lymphatic vessels. In conclusion, VE-cadherin-dependent signaling is required for lymphatic valve formation and maintenance and therapies to augment downstream pathways hold potential to treat lymphedema in patients.

VE-PTP inhibition stabilizes endothelial junctions by activating FGD5

Inhibition of VE-PTP, an endothelial receptor-type tyrosine phosphatase, triggers phosphorylation of the tyrosine kinase receptor Tie-2, which leads to the suppression of inflammation-induced vascular permeability. Analyzing the underlying mechanism, we show here that inhibition of VE-PTP and activation of Tie-2 induce tyrosine phosphorylation of FGD5, a GTPase exchange factor (GEF) for Cdc42, and stimulate its translocation to cell contacts. Interfering with the expression of FGD5 blocks the junction-stabilizing effect of VE-PTP inhibition in vitro and in vivo. Likewise, FGD5 is required for strengthening cortical actin bundles and inhibiting radial stress fiber formation, which are each stimulated by VE-PTP inhibition. We identify Y820 of FGD5 as the direct substrate for VE-PTP. The phosphorylation of FGD5-Y820 is required for the stabilization of endothelial junctions and for the activation of Cdc42 by VE-PTP inhibition but is dispensable for the recruitment of FGD5 to endothelial cell contacts. Thus, activation of FGD5 is a two-step process that comprises membrane recruitment and phosphorylation of Y820. These steps are necessary for the junction-stabilizing effect stimulated by VE-PTP inhibition and Tie-2 activation.

The biology of the extracorporeal vasculature of Botryllus schlosseri

The extracorporeal vasculature of the colonial ascidian Botryllus schlosseri plays a key role in several biological processes: transporting blood, angiogenesis, regeneration, self-nonself recognition, and parabiosis. The vasculature also interconnects all individuals in a colony and is composed of a single layer of ectodermally-derived cells. These cells form a tube with the basal lamina facing the lumen, and the apical side facing an extracellular matrix that consists of cellulose and other proteins, known as the tunic. Vascular tissue is transparent and can cover several square centimeters, which is much larger than any single individual within the colony. It forms a network that ramifies and expands to the perimeter of each colony and terminates into oval-shaped protrusions known as ampullae. Botryllus individuals replace themselves through a weekly budding cycle, and vasculature is added to ensure the interconnection of each new individual, thus there is continuous angiogenesis occurring naturally. The vascular tissue itself is highly regenerative; surgical removal of the ampullae and peripheral vasculature triggers regrowth within 24-48 h, which includes forming new ampullae. When two individuals, whether in the wild or in the lab, come into close contact and their ampullae touch, they can either undergo parabiosis through anastomosing vessels, or reject vascular fusion. The vasculature is easily manipulated by direct means such as microinjections, microsurgeries, and pharmacological reagents. Its transparent nature allows for in vivo analysis by bright field and fluorescence microscopy. Here we review the techniques and approaches developed to study the different biological processes that involve the extracorporeal vasculature.

Hypoxia and matrix viscoelasticity sequentially regulate endothelial progenitor cluster-based vasculogenesis

Vascular morphogenesis is the formation of endothelial lumenized networks. Cluster-based vasculogenesis of endothelial progenitor cells (EPCs) has been observed in animal models, but the underlying mechanism is unknown. Here, using O2-controllabe hydrogels, we unveil the mechanism by which hypoxia, co-jointly with matrix viscoelasticity, induces EPC vasculogenesis. When EPCs are subjected to a 3D hypoxic gradient ranging from <2 to 5%, they rapidly produce reactive oxygen species that up-regulate proteases, most notably MMP-1, which degrade the surrounding extracellular matrix. EPC clusters form and expand as the matrix degrades. Cell-cell interactions, including those mediated by VE-cadherin, integrin-β2, and ICAM-1, stabilize the clusters. Subsequently, EPC sprouting into the stiffer, intact matrix leads to vascular network formation. In vivo examination further corroborated hypoxia-driven clustering of EPCs. Overall, this is the first description of how hypoxia mediates cluster-based vasculogenesis, advancing our understanding toward regulating vascular development as well as postnatal vasculogenesis in regeneration and tumorigenesis.

Colloidal Gels with Tunable Mechanomorphology Regulate Endothelial Morphogenesis

Endothelial morphogenesis into capillary networks is dependent on the matrix morphology and mechanical properties. In current 3D gels, these two matrix features are interdependent and their distinct roles in endothelial organization are not known. Thus, it is important to decouple these parameters in the matrix design. Colloidal gels can be engineered to regulate the microstructural morphology and mechanics in an independent manner because colloidal gels are formed by the aggregation of particles into a self-similar 3D network. In this work, gelatin based colloidal gels with distinct mechanomorphology were developed by engineering the electrostatic interaction mediated aggregation of particles. By altering the mode of aggregation, colloidal gels showed either compact dense microstructure or tenuous strand-like networks, and the matrix stiffness was controlled independently by varying the particle fraction. Endothelial Cell (EC) networks were favored in tenuous strand-like microstructure through increased cell-matrix and cell-cell interactions, while compact dense microstructure inhibited the networks. For a given microstructure, as the gel stiffness was increased, the extent of EC network was reduced. This result demonstrates that 3D matrix morphology and mechanics provide distinct signals in a bidirectional manner during EC network formation. Colloidal gels can be used to interrogate the angiogenic responses of ECs and can be developed as a biomaterial for vascularization.

The precise molecular signals that control endothelial cell-cell adhesion within the vessel wall

Endothelial cell–cell adhesion within the wall of the vasculature controls a range of physiological processes, such as growth, integrity and barrier function. The adhesive properties of endothelial cells are tightly controlled by a complex cascade of signals transmitted from the surrounding environment or from within the cells themselves, with the dynamic nature of cellular adhesion and the regulating signalling networks now beginning to be appreciated. Here, we summarise the current knowledge of the mechanisms controlling endothelial cell–cell adhesion in the developing and mature blood vasculature.

Distinct roles of VE-cadherin for development and maintenance of specific lymph vessel beds

Endothelial cells line blood and lymphatic vessels and form intercellular junctions, which preserve vessel structure and integrity. The vascular endothelial cadherin, VE-cadherin, mediates endothelial adhesion and is indispensible for blood vessel development and permeability regulation. However, its requirement for lymphatic vessels has not been addressed. During development, VE-cadherin deletion in lymphatic endothelial cells resulted in abortive lymphangiogenesis, edema, and prenatal death. Unexpectedly, inducible postnatal or adult deletion elicited vessel bed-specific responses. Mature dermal lymph vessels resisted VE-cadherin loss and maintained button junctions, which was associated with an upregulation of junctional molecules. Very different, mesenteric lymphatic collectors deteriorated and formed a strongly hyperplastic layer of lymphatic endothelial cells on the mesothelium. This massive hyperproliferation may have been favored by high mesenteric VEGF-C expression and was associated with VEGFR-3 phosphorylation and upregulation of the transcriptional activator TAZ Finally, intestinal lacteals fragmented into cysts or became highly distended possibly as a consequence of the mesenteric defects. Taken together, we demonstrate here the importance of VE-cadherin for lymphatic vessel development and maintenance, which is however remarkably vessel bed-specific.

Erythro-myeloid progenitors contribute endothelial cells to blood vessels

The earliest blood vessels in mammalian embryos are formed when endothelial cells differentiate from angioblasts and coalesce into tubular networks. Thereafter, the endothelium is thought to expand solely by proliferation of pre-existing endothelial cells. Here we show that a complementary source of endothelial cells is recruited into pre-existing vasculature after differentiation from the earliest precursors of erythrocytes, megakaryocytes and macrophages, the erythro-myeloid progenitors (EMPs) that are born in the yolk sac. A first wave of EMPs contributes endothelial cells to the yolk sac endothelium, and a second wave of EMPs colonizes the embryo and contributes endothelial cells to intraembryonic endothelium in multiple organs, where they persist into adulthood. By demonstrating that EMPs constitute a hitherto unrecognized source of endothelial cells, we reveal that embryonic blood vascular endothelium expands in a dual mechanism that involves both the proliferation of pre-existing endothelial cells and the incorporation of endothelial cells derived from haematopoietic precursors.

CMTM4 regulates angiogenesis by promoting cell surface recycling of VE-cadherin to endothelial adherens junctions

Vascular endothelial (VE) cadherin is a key component of endothelial adherens junctions (AJs) and plays an important role in maintaining vascular integrity. Endocytosis of VE-cadherin regulates junctional strength and a decrease of surface VE-cadherin reduces vascular stability. However, disruption of AJs is also a requirement for vascular sprouting. Identifying novel regulators of endothelial endocytosis could enhance our understanding of angiogenesis. Here, we evaluated the angiogenic potential of (CKLF-like MARVEL transmembrane domain 4) CMTM4 and assessed in which molecular pathway CMTM4 is involved during angiogenesis. Using a 3D vascular assay composed of GFP-labeled HUVECs and dsRED-labeled pericytes, we demonstrated in vitro that siRNA-mediated CMTM4 silencing impairs vascular sprouting. In vivo, CMTM4 silencing by morpholino injection in zebrafish larvae inhibits intersomitic vessel growth. Intracellular staining revealed that CMTM4 colocalizes with Rab4⁺ and Rab7⁺ vesicles, both markers of the endocytic trafficking pathway. CMTM4 colocalizes with both membrane-bound and internalized VE-cadherin. Adenovirus-mediated CMTM4 overexpression enhances the endothelial endocytic pathway, in particular the rapid recycling pathway, shown by an increase in early endosomal antigen-1 positive (EEA1⁺), Rab4⁺, Rab11⁺ , and Rab7⁺ vesicles. CMTM4 overexpression enhances membrane-bound VE-cadherin internalization, whereas CMTM4 knockdown decreases internalization of VE-cadherin. CMTM4 overexpression promotes endothelial barrier function, shown by an increase in recovery of transendothelial electrical resistance (TEER) after thrombin stimulation. We have identified in this study a novel regulatory function for CMTM4 in angiogenesis. CMTM4 plays an important role in the turnover of membrane-bound VE-cadherin at AJs, mediating endothelial barrier function and controlling vascular sprouting.

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.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Endothelial Progenitor Cells for the Vascularization of Engineered Tissues

Self-assembled microvasculature from cocultures of endothelial cells (ECs) and stromal cells has significantly advanced efforts to vascularize engineered tissues by enhancing perfusion rates in vivo and producing investigative platforms for microvascular morphogenesis in vitro. However, to clinically translate prevascularized constructs, the issue of EC source must be resolved. Endothelial progenitor cells (EPCs) can be noninvasively supplied from the recipient through adult peripheral and umbilical cord blood, as well as derived from induced pluripotent stem cells, alleviating antigenicity issues. EPCs can also differentiate into all tissue endothelium, and have demonstrated potential for therapeutic vascularization. Yet, EPCs are not the standard EC choice to vascularize tissue constructs in vitro. Possible reasons include unresolved issues with EPC identity and characterization, as well as uncertainty in the selection of coculture, scaffold, and culture media combinations that promote EPC microvessel formation. This review addresses these issues through a summary of EPC vascular biology and the effects of tissue engineering design parameters upon EPC microvessel formation. Also included are perspectives to integrate EPCs with emerging technologies to produce functional, organotypic vascularized tissues.

Dual-functional drug liposomes in treatment of resistant cancers

Efficacy of regular chemotherapy is significantly hampered by multidrug resistance (MDR) and severe systemic toxicity. The reduced toxicity has been evidenced after administration of drug liposomes, consisting of the first generation of regular drug liposomes, the second generation of long-circulation drug liposomes, and the third generation of targeting drug liposomes. However, MDR of cancers remains as an unsolved issue. The objective of this article is to review the dual-functional drug liposomes, which demonstrate the potential in overcoming MDR. Herein, dual-functional drug liposomes are referring to the drug-containing phospholipid bilayer vesicles that possess a dual-function of providing the basic efficacy of drug and the extended effect of the drug carrier. They exhibit unique roles in treatment of resistant cancer via circumventing drug efflux caused by adenosine triphosphate binding cassette (ABC) transporters, eliminating cancer stem cells, destroying mitochondria, initiating apoptosis, regulating autophagy, destroying supply channels, utilizing microenvironment, and silencing genes of the resistant cancer. As the prospect of an estimation, dual-functional drug liposomes would exhibit more strength in their extended function, hence deserving further investigation for clinical validation.

CMTM3 (CKLF-Like Marvel Transmembrane Domain 3) Mediates Angiogenesis by Regulating Cell Surface Availability of VE-Cadherin in Endothelial Adherens Junctions

OBJECTIVE

Decrease in VE-cadherin adherens junctions reduces vascular stability, whereas disruption of adherens junctions is a requirement for neovessel sprouting during angiogenesis. Endocytosis plays a key role in regulating junctional strength by altering bioavailability of cell surface proteins, including VE-cadherin. Identification of new mediators of endothelial endocytosis could enhance our understanding of angiogenesis. Here, we assessed the function of CMTM3 (CKLF-like MARVEL transmembrane domain 3), which we have previously identified as highly expressed in Flk1⁺ endothelial progenitor cells during embryonic development.

APPROACH AND RESULTS

Using a 3-dimensional coculture of human umbilical vein endothelial cells-GFP (green fluorescent protein) and pericytes-RFP (red fluorescent protein), we demonstrated that siRNA-mediated CMTM3 silencing in human umbilical vein endothelial cells impairs angiogenesis. In vivo CMTM3 inhibition by morpholino injection in developing zebrafish larvae confirmed that CMTM3 expression is required for vascular sprouting. CMTM3 knockdown in human umbilical vein endothelial cells does not affect proliferation or migration. Intracellular staining demonstrated that CMTM3 colocalizes with early endosome markers EEA1 (early endosome marker 1) and Clathrin⁺ vesicles and with cytosolic VE-cadherin in human umbilical vein endothelial cells. Adenovirus-mediated CMTM3 overexpression enhances endothelial endocytosis, shown by an increase in Clathrin⁺, EEA1⁺, Rab11⁺, Rab5⁺, and Rab7⁺ vesicles. CMTM3 overexpression enhances, whereas CMTM3 knockdown decreases internalization of cell surface VE-cadherin in vitro. CMTM3 promotes loss of endothelial barrier function in thrombin-induced responses, shown by transendothelial electric resistance measurements in vitro.

CONCLUSIONS

In this study, we have identified a new regulatory function for CMTM3 in angiogenesis. CMTM3 is involved in VE-cadherin turnover and is a regulator of the cell surface pool of VE-cadherin. Therefore, CMTM3 mediates cell-cell adhesion at adherens junctions and contributes to the control of vascular sprouting.

Distinct and redundant functions of Esama and VE-cadherin during vascular morphogenesis

The cardiovascular system forms during early embryogenesis and adapts to embryonic growth by sprouting angiogenesis and vascular remodeling. These processes require fine-tuning of cell-cell adhesion to maintain and re-establish endothelial contacts, while allowing cell motility. We have compared the contribution of two endothelial cell-specific adhesion proteins, VE-cadherin (VE-cad/Cdh5) and Esama (endothelial cell-selective adhesion molecule a), during angiogenic sprouting and blood vessel fusion (anastomosis) in the zebrafish embryo by genetic analyses. Different combinations of mutant alleles can be placed into a phenotypic series with increasing defects in filopodial contact formation. Contact formation in esama mutants appears similar to wild type, whereas esama^-/-; ve-cad^+/- and ve-cad single mutants exhibit intermediate phenotypes. The lack of both proteins interrupts filopodial interaction completely. Furthermore, double mutants do not form a stable endothelial monolayer, and display intrajunctional gaps, dislocalization of Zo-1 and defects in apical-basal polarization. In summary, VE-cadherin and Esama have distinct and redundant functions during blood vessel morphogenesis, and both adhesion proteins are central to endothelial cell recognition during anastomosis.

Computational Screening of Tip and Stalk Cell Behavior Proposes a Role for Apelin Signaling in Sprout Progression

Angiogenesis involves the formation of new blood vessels by sprouting or splitting of existing blood vessels. During sprouting, a highly motile type of endothelial cell, called the tip cell, migrates from the blood vessels followed by stalk cells, an endothelial cell type that forms the body of the sprout. To get more insight into how tip cells contribute to angiogenesis, we extended an existing computational model of vascular network formation based on the cellular Potts model with tip and stalk differentiation, without making a priori assumptions about the differences between tip cells and stalk cells. To predict potential differences, we looked for parameter values that make tip cells (a) move to the sprout tip, and (b) change the morphology of the angiogenic networks. The screening predicted that if tip cells respond less effectively to an endothelial chemoattractant than stalk cells, they move to the tips of the sprouts, which impacts the morphology of the networks. A comparison of this model prediction with genes expressed differentially in tip and stalk cells revealed that the endothelial chemoattractant Apelin and its receptor APJ may match the model prediction. To test the model prediction we inhibited Apelin signaling in our model and in an in vitro model of angiogenic sprouting, and found that in both cases inhibition of Apelin or of its receptor APJ reduces sprouting. Based on the prediction of the computational model, we propose that the differential expression of Apelin and APJ yields a "self-generated" gradient mechanisms that accelerates the extension of the sprout.

Hypobaric hypoxia down-regulated junctional protein complex: Implications to vascular leakage

Acute mountain sickness (AMS) can cause capillary hyper-permeability and vasogenic edema. However, its underlying mechanisms remained unclear and there is no previous in vitro study on AMS. We therefore conducted an in vitro study and examined whether continuous hypobaric hypoxia (CHH) could alter expression of junctional protein complex of vascular endothelial cells, causing hyper-permeabilization. EA.hy926 human endothelial cells were exposed to either CHH or normoxia for up to 24 h. Flow cytometry using annexin V/propidium iodide co-staining demonstrated that cell death had no significant difference at 12-h, but was increased by CHH at 24-h. Transendothelial resistance (TER) of endothelial cell monolayer was progressively decreased by CHH from 1-h to 24-h. Western blot analysis and immunofluorescence study demonstrated decreased expression levels of VE-cadherin, PECAM-1 and ZO-1 junctional proteins at both 12-h and 24-h exposure time-points. Interestingly, while the main form of ZO-1 (220 kDa) was decreased, its degraded form (100 kDa) was increased by 24-h CHH that might be linked to the increased cell death. Our data have demonstrated that CHH caused vascular endothelial hyper-permeability and defective junctional protein complex by reducing expression levels of VE-cadherin, PECAM-1, and ZO-1. Taken together, these data may explain pathophysiology underlying vascular hyper-permeability in AMS.

Endothelial exocytosis of angiopoietin-2 resulting from CCM3 deficiency contributes to cerebral cavernous malformation

Cerebral cavernous malformations (CCMs) are vascular malformations that affect the central nervous system and result in cerebral hemorrhage, seizure and stroke. CCMs arise from loss-of-function mutations in one of three genes: KRIT1 (also known as CCM1), CCM2 or PDCD10 (also known as CCM3). PDCD10 mutations in humans often result in a more severe form of the disease relative to mutations in the other two CCM genes, and PDCD10-knockout mice show severe defects, the mechanistic basis for which is unclear. We have recently reported that CCM3 regulates exocytosis mediated by the UNC13 family of exocytic regulatory proteins. Here, in investigating the role of endothelial cell exocytosis in CCM disease progression, we found that CCM3 suppresses UNC13B- and vesicle-associated membrane protein 3 (VAMP3)-dependent exocytosis of angiopoietin 2 (ANGPT2) in brain endothelial cells. CCM3 deficiency in endothelial cells augments the exocytosis and secretion of ANGPT2, which is associated with destabilized endothelial cell junctions, enlarged lumen formation and endothelial cell-pericyte dissociation. UNC13B deficiency, which blunts ANGPT2 secretion from endothelial cells, or treatment with an ANGPT2-neutralizing antibody normalizes the defects in the brain and retina caused by endothelial-cell-specific CCM3 deficiency, including the disruption of endothelial cell junctions, vessel dilation and pericyte dissociation. Thus, enhanced secretion of ANGPT2 in endothelial cells contributes to the progression of CCM disease, providing a new therapeutic approach for treating this devastating pathology.

Endothelial lipid phosphate phosphatase-3 deficiency that disrupts the endothelial barrier function is a modifier of cardiovascular development

Aims

Lipid phosphate phosphatase-3 (LPP3) is expressed at high levels in endothelial cells (ECs). Although LPP3 is known to hydrolyse the phosphate group from lysolipids such as spingosine-1-phosphate and its structural homologues, the function of Lpp3 in ECs is not completely understood. In this study, we investigated how tyrosine-protein kinase receptor (TEK or Tie2) promoter–dependent deletion of Lpp3 alters EC activities.

Methods and results

Lpp3^fl/fl mice were crossed with the tg.Tie2^Cre transgenic line. Vasculogenesis occurred normally in embryos with Tie2^Cre-mediated deletion of Lpp3 (called Lpp3^ECKO), but embryonic lethality occurred in two waves, the first wave between E8.5 and E10.5, while the second between E11.5 and E13.5. Lethality in Lpp3^ECKO embryos after E11.5 was accompanied by vascular leakage and haemorrhage, which likely resulted in insufficient cardiovascular development. Analyses of haematoxylin- and eosin-stained heart sections from E11.5 Lpp3^ECKO embryos showed insufficient heart growth associated with decreased trabeculation, reduced growth of the compact wall, and absence of cardiac cushions. Staining followed by microscopic analyses of Lpp3^ECKO embryos revealed the presence of apoptotic ECs. Furthermore, Lpp3-deficient ECs showed decreased gene expression and protein levels of Cyclin-D1, VE-cadherin, Fibronectin, Klf2, and Klf4. To determine the underlying mechanisms of vascular leakage and barrier disruption, we performed knockdown and rescue experiments in cultured ECs. LPP3 knockdown decreased transendothelial electrical resistance and increased permeability. Re-expression of β-catenin cDNA in LPP3-knockdown ECs partially restored the effect of the LPP3 loss, whereas re-expression of p120ctn cDNA did not.

Conclusion

These findings demonstrate the essential roles of LPP3 in the maturation of EC barrier integrity and normal cardiovascular development.

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.

Prevascularization of biofunctional calcium phosphate cement for dental and craniofacial repairs

OBJECTIVES

Calcium phosphate cement (CPC) is promising for dental and craniofacial repairs. Vascularization in bone tissue engineering constructs is currently a major challenge. The objectives of this study were to investigate the prevascularization of macroporous CPC via coculturing human umbilical vein endothelial cells (HUVEC) and human osteoblasts (HOB), and determine the effect of RGD in CPC on microcapillary formation for the first time.

METHODS

Macroporous CPC scaffold was prepared using CPC powder, chitosan liquid and gas-foaming porogen. Chitosan was grafted with Arg-Gly-Asp (RGD) to biofunctionalize the CPC. HUVEC and HOB were cocultured on macroporous CPC-RGD and CPC control without RGD for up to 42d. The osteogenic and angiogenic differentiation, bone matrix mineral synthesis, and formation of microcapillary-like structures were measured.

RESULTS

RGD-grafting in CPC increased the gene expressions of osteogenic and angiogenic differentiation markers than those of CPC control without RGD. Cell-synthesized bone mineral content also increased on CPC-RGD, compared to CPC control (p<0.05). Immunostaining with endothelial marker showed that the amount of microcapillary-like structures on CPC scaffolds increased with time. At 42d, the cumulative vessel length for CPC-RGD scaffold was 1.69-fold that of CPC control. SEM examination confirmed the morphology of self-assembled microcapillary-like structures on CPC scaffolds.

SIGNIFICANCE

HUVEC+HOB coculture on macroporous CPC scaffold successfully achieved prevascularization. RGD incorporation in CPC enhanced osteogenic differentiation, bone mineral synthesis, and microcapillary-like structure formation. The novel prevascularized CPC-RGD constructs are promising for dental, craniofacial and orthopedic applications.

Comparative Phosphoproteomics Analysis of VEGF and Angiopoietin-1 Signaling Reveals ZO-1 as a Critical Regulator of Endothelial Cell Proliferation

VEGF and angiopoietin-1 (Ang-1) are essential factors to promote angiogenesis through regulation of a plethora of signaling events in endothelial cells (ECs). Although pathways activated by VEGF and Ang-1 are being established, the unique signaling nodes conferring specific responses to each factor remain poorly defined. Thus, we conducted a large-scale comparative phosphoproteomic analysis of signaling pathways activated by VEGF and Ang-1 in ECs using mass spectrometry. Analysis of VEGF and Ang-1 networks of regulated phosphoproteins revealed that the junctional proteins ZO-1, ZO-2, JUP and p120-catenin are part of a cluster of proteins phosphorylated following VEGF stimulation that are linked to MAPK1 activation. Down-regulation of these junctional proteins led to MAPK1 activation and accordingly, increased proliferation of ECs stimulated specifically by VEGF, but not by Ang-1. We identified ZO-1 as the central regulator of this effect and showed that modulation of cellular ZO-1 levels is necessary for EC proliferation during vascular development of the mouse postnatal retina. In conclusion, we uncovered ZO-1 as part of a signaling node activated by VEGF, but not Ang-1, that specifically modulates EC proliferation during angiogenesis.

Leukocytes Crossing the Endothelium: A Matter of Communication

Leukocytes cross the endothelial vessel wall in a process called transendothelial migration (TEM). The purpose of leukocyte TEM is to clear the causing agents of inflammation in underlying tissues, for example, bacteria and viruses. During TEM, endothelial cells initiate signals that attract and guide leukocytes to sites of tissue damage. Leukocytes react by attaching to these sites and signal their readiness to move back to endothelial cells. Endothelial cells in turn respond by facilitating the passage of leukocytes while retaining overall integrity. In this review, we present recent findings in the field and we have endeavored to synthesize a coherent picture of the intricate interplay between endothelial cells and leukocytes during TEM.