Ephrin B2 and EphB4 selectively mark arterial and venous vessels in cerebral arteriovenous malformation

Comment on, "Increased expression of ephrin A1 in brain arteriovenous malformation: DNA microarray analysis"

This study by Sasahara et al. explores the role of ephrin A1 in brain arteriovenous malformations (AVM) using DNA microarray analysis, quantitative real-time RT-PCR, and immunohistochemistry. The research identifies significant upregulation of ephrin A1 in AVM, suggesting its potential involvement in the abnormal vascular architecture characteristic of this condition. The study's innovative methodology and thorough exploration of gene expression patterns contribute valuable insights into AVM pathogenesis, highlighting ephrin A1 as a potential therapeutic target. However, the study's limitations include clinical variability among patient samples and the use of draining veins as controls, which may affect the robustness of the findings. Future research should address these limitations by using more homogeneous samples and expanding the investigation to include other ephrin family members. This could provide a broader understanding of ephrin signaling in AVM and guide the development of targeted therapies.

Pathophysiology in Brain Arteriovenous Malformations: Focus on Endothelial Dysfunctions and Endothelial-to-Mesenchymal Transition

Brain arteriovenous malformations (bAVMs) substantially increase the risk for intracerebral hemorrhage (ICH), which is associated with significant morbidity and mortality. However, the treatment options for bAVMs are severely limited, primarily relying on invasive methods that carry their own risks for intraoperative hemorrhage or even death. Currently, there are no pharmaceutical agents shown to treat this condition, primarily due to a poor understanding of bAVM pathophysiology. For the last decade, bAVM research has made significant advances, including the identification of novel genetic mutations and relevant signaling in bAVM development. However, bAVM pathophysiology is still largely unclear. Further investigation is required to understand the detailed cellular and molecular mechanisms involved, which will enable the development of safer and more effective treatment options. Endothelial cells (ECs), the cells that line the vascular lumen, are integral to the pathogenesis of bAVMs. Understanding the fundamental role of ECs in pathological conditions is crucial to unraveling bAVM pathophysiology. This review focuses on the current knowledge of bAVM-relevant signaling pathways and dysfunctions in ECs, particularly the endothelial-to-mesenchymal transition (EndMT).

Biological Significance of EphB4 Expression in Cancer

Eph receptors and their Eph receptor-interacting (ephrin) ligands comprise a vital cell communication system with several functions. In cancer cells, there was evidence of bilateral Eph receptor signaling with both tumor-suppressing and tumor-promoting actions. As a member of the Eph receptor family, EphB4 has been linked to tumor angiogenesis, growth, and metastasis, which makes it a viable and desirable target for drug development in therapeutic applications. Many investigations have been conducted over the last decade to elucidate the structure and function of EphB4 in association with its ligand ephrinB2 for its involvement in tumorigenesis. Although several EphB4-targeting drugs have been investigated, and some selective inhibitors have been evaluated in clinical trials. This article addresses the structure and function of the EphB4 receptor, analyses its possibility as an anticancer therapeutic target, and summarises knowledge of EphB4 kinase inhibitors. To summarise, EphB4 is a difficult but potential treatment option for cancers.

Endothelial deletion of EPH receptor A4 alters single-cell profile and Tie2/Akap12 signaling to preserve blood-brain barrier integrity

Neurobiological consequences of traumatic brain injury (TBI) result from a complex interplay of secondary injury responses and sequela that mediates chronic disability. Endothelial cells are important regulators of the cerebrovascular response to TBI. Our work demonstrates that genetic deletion of endothelial cell (EC)-specific EPH receptor A4 (EphA4) using conditional EphA4f/f/Tie2-Cre and EphA4f/f/VE-Cadherin-CreERT2 knockout (KO) mice promotes blood-brain barrier (BBB) integrity and tissue protection, which correlates with improved motor function and cerebral blood flow recovery following controlled cortical impact (CCI) injury. scRNAseq of capillary-derived KO ECs showed increased differential gene expression of BBB-related junctional and actin cytoskeletal regulators, namely, A-kinase anchor protein 12, Akap12, whose presence at Tie2 clustering domains is enhanced in KO microvessels. Transcript and protein analysis of CCI-injured whole cortical tissue or cortical-derived ECs suggests that EphA4 limits the expression of Cldn5, Akt, and Akap12 and promotes Ang2. Blocking Tie2 using sTie2-Fc attenuated protection and reversed Akap12 mRNA and protein levels cortical-derived ECs. Direct stimulation of Tie2 using Vasculotide, angiopoietin-1 memetic peptide, phenocopied the neuroprotection. Finally, we report a noteworthy rise in soluble Ang2 in the sera of individuals with acute TBI, highlighting its promising role as a vascular biomarker for early detection of BBB disruption. These findings describe a contribution of the axon guidance molecule, EphA4, in mediating TBI microvascular dysfunction through negative regulation of Tie2/Akap12 signaling.

Shaping the brain vasculature in development and disease in the single-cell era

The CNS critically relies on the formation and proper function of its vasculature during development, adult homeostasis and disease. Angiogenesis - the formation of new blood vessels - is highly active during brain development, enters almost complete quiescence in the healthy adult brain and is reactivated in vascular-dependent brain pathologies such as brain vascular malformations and brain tumours. Despite major advances in the understanding of the cellular and molecular mechanisms driving angiogenesis in peripheral tissues, developmental signalling pathways orchestrating angiogenic processes in the healthy and the diseased CNS remain incompletely understood. Molecular signalling pathways of the 'neurovascular link' defining common mechanisms of nerve and vessel wiring have emerged as crucial regulators of peripheral vascular growth, but their relevance for angiogenesis in brain development and disease remains largely unexplored. Here we review the current knowledge of general and CNS-specific mechanisms of angiogenesis during brain development and in brain vascular malformations and brain tumours, including how key molecular signalling pathways are reactivated in vascular-dependent diseases. We also discuss how these topics can be studied in the single-cell multi-omics era.

Genetics of brain arteriovenous malformations and cerebral cavernous malformations

Cerebrovascular malformations comprise abnormal development of cerebral vasculature. They can result in hemorrhagic stroke due to rupture of lesions as well as seizures and neurological defects. The most common forms of cerebrovascular malformations are brain arteriovenous malformations (bAVMs) and cerebral cavernous malformations (CCMs). They occur in both sporadic and inherited forms. Rapidly evolving molecular genetic methodologies have helped to identify causative or associated genes involved in genesis of bAVMs and CCMs. In this review, we highlight the current knowledge regarding the genetic basis of these malformations.

Molecular and genetic mechanisms in brain arteriovenous malformations: new insights and future perspectives

Brain arteriovenous malformations (bAVMs) are rare vascular lesions made of shunts between cerebral arteries and veins without the interposition of a capillary bed. The majority of bAVMs are asymptomatic, but some may be revealed by seizures and potentially life-threatening brain hemorrhage. The management of unruptured bAVMs remains a matter of debate. Significant progress in the understanding of their pathogenesis has been made during the last decade, particularly using genome sequencing and biomolecular analysis. Herein, we comprehensively review the recent molecular and genetic advances in the study of bAVMs that not only allow a better understanding of the genesis and growth of bAVMs, but also open new insights in medical treatment perspectives.

Cellular loci involved in the development of brain arteriovenous malformations

Brain arteriovenous malformations (bAVMs) are abnormal vessels that are prone to rupture, causing life-threatening intracranial bleeding. The mechanism of bAVM formation is poorly understood. Nevertheless, animal studies revealed that gene mutation in endothelial cells (ECs) and angiogenic stimulation are necessary for bAVM initiation. Evidence collected through analyzing bAVM specimens of human and mouse models indicate that cells other than ECs also are involved in bAVM pathogenesis. Both human and mouse bAVMs vessels showed lower mural cell-coverage, suggesting a role of pericytes and vascular smooth muscle cells (vSMCs) in bAVM pathogenesis. Perivascular astrocytes also are important in maintaining cerebral vascular function and take part in bAVM development. Furthermore, higher inflammatory cytokines in bAVM tissue and blood demonstrate the contribution of inflammatory cells in bAVM progression, and rupture. The goal of this paper is to provide our current understanding of the roles of different cellular loci in bAVM pathogenesis.

Vascular Injury in the Zebrafish Tail Modulates Blood Flow and Peak Wall Shear Stress to Restore Embryonic Circular Network

Mechano-responsive signaling pathways enable blood vessels within a connected network to structurally adapt to partition of blood flow between organ systems. Wall shear stress (WSS) modulates endothelial cell proliferation and arteriovenous specification. Here, we study vascular regeneration in a zebrafish model by using tail amputation to disrupt the embryonic circulatory loop (ECL) at 3 days post fertilization (dpf). We observed a local increase in blood flow and peak WSS in the Segmental Artery (SeA) immediately adjacent to the amputation site. By manipulating blood flow and WSS via changes in blood viscosity and myocardial contractility, we show that the angiogenic Notch-ephrinb2 cascade is hemodynamically activated in the SeA to guide arteriogenesis and network reconnection. Taken together, ECL amputation induces changes in microvascular topology to partition blood flow and increase WSS-mediated Notch-ephrinb2 pathway, promoting new vascular arterial loop formation and restoring microcirculation.

Review of treatment and therapeutic targets in brain arteriovenous malformation

Brain arteriovenous malformations (bAVM) are an important cause of intracranial hemorrhage (ICH), especially in younger patients. The pathogenesis of bAVM are largely unknown. Current understanding of bAVM etiology is based on studying genetic syndromes, animal models, and surgically resected specimens from patients. The identification of activating somatic mutations in the Kirsten rat sarcoma viral oncogene homologue (KRAS) gene and other mitogen-activated protein kinase (MAPK) pathway genes has opened up new avenues for bAVM study, leading to a paradigm shift to search for somatic, de novo mutations in sporadic bAVMs instead of focusing on inherited genetic mutations. Through the development of new models and understanding of pathways involved in maintaining normal vascular structure and functions, promising therapeutic targets have been identified and safety and efficacy studies are underway in animal models and in patients. The goal of this paper is to provide a thorough review or current diagnostic and treatment tools, known genes and key pathways involved in bAVM pathogenesis to summarize current treatment options and potential therapeutic targets uncovered by recent discoveries.

The role of mural cells in hemorrhage of brain arteriovenous malformation

Brain arteriovenous malformation (bAVM) is the most common cause of intracranial hemorrhage (ICH), particularly in young patients. However, the exact cause of bAVM bleeding and rupture is not yet fully understood. In bAVMs, blood bypasses the entire capillary bed and directly flows from arteries to veins. The vessel walls in bAVMs have structural defects, which impair vascular integrity. Mural cells are essential structural and functional components of blood vessels and play a critical role in maintaining vascular integrity. Changes in mural cell number and coverage have been implicated in bAVMs. In this review, we discussed the roles of mural cells in bAVM pathogenesis. We focused on 1) the recent advances in human and animal studies of bAVMs; 2) the importance of mural cells in vascular integrity; 3) the regulatory signaling pathways that regulate mural cell function. More specifically, the platelet-derived growth factor-B (PDGF-B)/PDGF receptor-β (PDGFR-β), EphrinB2/EphB4, and angiopoietins/tie2 signaling pathways that regulate mural cell-recruitment during vascular remodeling were discussed in detail.

Review on the current treatment status of vein of Galen malformations and future directions in research and treatment

INTRODUCTION

Vein of Galen malformations (VOGMs) represent a rare pathologic entity with often catastrophic natural history. The advances in endovascular treatment in recent years have allowed for a paradigm shift in the treatment and outcome of these high-flow shunts, even though their pathogenetic mechanisms and evolution remain in part obscure.

AREAS COVERED

The overall management of VOGMs requires a tailored case-to-case approach, starting with in utero detection and reserving endovascular treatment for indicated cases. Lately, the advances in translational research with whole-genome sequencing and the coupling with cellular-level hemodynamics attempt to shed more light in the pathogenesis and evolution of these lesions. At the same time the advances in endovascular techniques allow for more safety and tailored technical strategy planning. Furthermore, the advances in MRI techniques allow a better understanding of their vascular anatomy. In view of these recent advances and by performing a PUBMED literature review of the last 15 years, we attempt a review of the evolutions in the imaging, management, endovascular treatment and understanding of underlying mechanisms for VOGMs.

EXPERT OPINION

The progress in the fields detailed in this review appears very promising in better understanding VOGMs and expanding the available therapeutic arsenal.

Effects of shear stress on differentiation of stem cells into endothelial cells

Stem cell transplantation is an appealing potential therapy for vascular diseases and an indispensable key step in vascular tissue engineering. Substantial effort has been made to differentiate stem cells toward vascular cell phenotypes, including endothelial cells (ECs) and smooth muscle cells. The microenvironment of vascular cells not only contains biochemical factors that influence differentiation but also exerts hemodynamic forces, such as shear stress and cyclic strain. More recently, studies have shown that shear stress can influence the differentiation of stem cells toward ECs. A deep understanding of the responses and underlying mechanisms involved in this process is essential for clinical translation. This review highlights current data supporting the role of shear stress in stem cell differentiation into ECs. Potential mechanisms and signaling cascades for transducing shear stress into a biological signal are proposed. Further study of stem cell responses to shear stress will be necessary to apply stem cells for pharmacological applications and cardiovascular implants in the realm of regenerative medicine.

Vascular dysfunction and pathology: focus on mechanical forces

The role of mechanical forces is emerging as a new player in the pathophysiologic programming of the cardiovascular system. The ability of the cells to 'sense' mechanical forces does not relate only to perception of movement or flow, as intended traditionally, but also to the biophysical properties of the extracellular matrix, the geometry of the tissues, and the force distribution inside them. This is also supported by the finding that cells can actively translate mechanical cues into discrete gene expression and epigenetic programming. In the present review, we will contextualize these new concepts in the vascular pathologic programming.

Selective Endothelial Hyperactivation of Oncogenic KRAS Induces Brain Arteriovenous Malformations in Mice

OBJECTIVE

Brain arteriovenous malformations (bAVMs) are a leading cause of hemorrhagic stroke and neurological deficits in children and young adults, however, no pharmacological intervention is available to treat these patients. Although more than 95% of bAVMs are sporadic without family history, the pathogenesis of sporadic bAVMs is largely unknown, which may account for the lack of therapeutic options. KRAS mutations are frequently observed in cancer, and a recent unprecedented finding of these mutations in human sporadic bAVMs offers a new direction in the bAVM research. Using a novel adeno-associated virus targeting brain endothelium (AAV-BR1), the current study tested if endothelial KRAS^G12V mutation induces sporadic bAVMs in mice.

METHODS

Five-week-old mice were systemically injected with either AAV-BR1-GFP or -KRAS^G12V . At 8 weeks after the AAV injection, bAVM formation and characteristics were addressed by histological and molecular analyses. The effect of MEK/ERK inhibition on KRAS^G12V -induced bAVMs was determined by treatment of trametinib, a US Food and Drug Administration (FDA)-approved MEK/ERK inhibitor.

RESULTS

The viral-mediated KRAS^G12V overexpression induced bAVMs, which were composed of a tangled nidus mirroring the distinctive morphology of human bAVMs. The bAVMs were accompanied by focal angiogenesis, intracerebral hemorrhages, altered vascular constituents, neuroinflammation, and impaired sensory/cognitive/motor functions. Finally, we confirmed that bAVM growth was inhibited by trametinib treatment.

INTERPRETATION

Our innovative approach using AAV-BR1 confirms that KRAS mutations promote bAVM development via the MEK/ERK pathway, and provides a novel preclinical mouse model of bAVMs which will be useful to develop a therapeutic strategy for patients with bAVM. ANN NEUROL 2021;89:926-941.

Germline Mutation Enrichment in Pathways Controlling Endothelial Cell Homeostasis in Patients with Brain Arteriovenous Malformation: Implication for Molecular Diagnosis

Brain arteriovenous malformation (bAVM) is a congenital defect affecting brain microvasculature, characterized by a direct shunt from arterioles to venules. Germline mutations in several genes related to transforming growth factor beta (TGF-β)/BMP signaling are linked to both sporadic and hereditary phenotypes. However, the low incidence of inherited cases makes the genetic bases of the disease unclear. To increase this knowledge, we performed a whole exome sequencing on five patients, on DNA purified by peripheral blood. Variants were filtered based on frequency and functional class. Those selected were validated by Sanger sequencing. Genes carrying selected variants were prioritized to relate these genes with those already known to be linked to bAVM development. Most of the prioritized genes showed a correlation with the TGF-βNotch signaling and vessel morphogenesis. However, two novel pathways related to cilia morphogenesis and ion homeostasis were enriched in mutated genes. These results suggest novel insights on sporadic bAVM onset and confirm its genetic heterogeneity. The high frequency of germline variants in genes related to TGF-β signaling allows us to hypothesize bAVM as a complex trait resulting from the co-existence of low-penetrance loci. Deeper knowledge on bAVM genetics can improve personalized diagnosis and can be helpful with genotype–phenotype correlations.

Pathophysiologic Role of Molecules Determining Arteriovenous Differentiation in Adult Life

The structural differences between arteries and veins are genetically predetermined. Vascular identity markers, the molecular markers specific to veins and arteries, determine the differential development of vessels during embryogenesis and their expression persists in adult vessels. It is revealed that they can be reactivated under various pathophysiologic conditions even after vessel differentiation. Thus, once considered as quiescent in adults, vascular identity markers may actually play significant roles in vascular remodeling. Manipulation of vascular identity and the underlying molecular mechanisms might be a novel strategy to improve vascular remodeling for clinical application.

The critical role of the interplays of EphrinB2/EphB4 and VEGF in the induction of angiogenesis

The significant role of VEGF (vascular endothelial growth factor) as an angiogenesis inducer is well recognized. Besides VEGF, EphrinB2/EphB4 also plays essential roles in vascular development and postnatal angiogenesis. Compared with classical proangiogenic factors, not only does EphrinB2/EphB4 promote sprouting of new vessels, it is also involved in the vessel maturation. Given their involvement in many physiologic and pathological conditions, EphB4 and EphrinB2 are increasingly recognized as attractive therapeutic targets for angiogenesis-related diseases through modulating their expression and function. Previous works mainly focused on the individual role of VEGF and EphrinB2/EphB4 in angiogenesis, respectively, but the correlation between EphrinB2/EphB4 and VEGF in angiogenesis has not been fully disclosed. Here, we summarize the structure and bidirectional signaling of EphrinB2/EphB4, provide an overview on the relationship between EphrinB2/EphB4 signaling and VEGF pathway in angiogenesis and highlight the associated potential usefulness in anti-angiogenetic therapy.

Dysregulation of the EphrinB2-EphB4 ratio in pediatric cerebral arteriovenous malformations is associated with endothelial cell dysfunction in vitro and functions as a novel noninvasive biomarker in patients

We investigated (1) EphrinB2 and EphB4 receptor expression in cerebral AVMs, (2) the impact of an altered EphrinB2:EphB4 ratio on brain endothelial cell function and (3) potential translational applications of these data. The following parameters were compared between AVM endothelial cells (AVMECs) and human brain microvascular endothelial cells (HBMVECs): quantified EphrinB2 and EphB4 expression, angiogenic potential, and responses to manipulation of the EphrinB2:EphB4 ratio via pharmacologic stimulation/inhibition. To investigate the clinical relevance of these in vitro data, Ephrin expression was assessed in AVM tissue (by immunohistochemistry) and urine (by ELISA) from pediatric patients with AVM (n = 30), other cerebrovascular disease (n = 14) and control patients (n = 29), and the data were subjected to univariate and multivariate statistical analyses. Compared to HBMVECs, AVMECs demonstrated increased invasion (p = 0.04) and migration (p = 0.08), impaired tube formation (p = 0.06) and increased EphrinB2:EphB4 ratios. Altering the EphrinB2:EphB4 ratio (by increasing EphrinB2 or blocking EphB4) in HBMVECs increased invasion (p = 0.03 and p < 0.05, respectively). EphrinB2 expression was increased in AVM tissue, which correlated with increased urinary EphrinB2 levels in AVM patients. Using the optimal urinary cutoff value (EphrinB2 > 25.7 pg/μg), AVMs were detected with high accuracy (80% vs. controls) and were distinguished from other cerebrovascular disease (75% accuracy). Post-treatment urinary EphrinB2 levels normalized in an index patient. In summary, AVMECs have an EphrinB2:EphB4 ratio that is increased compared to that of normal HBMVECs. Changing this ratio in HBMVECs induces AVMEC-like behavior. EphrinB2 is clinically relevant, and its levels are increased in AVM tissue and patient urine. This work suggests that dysregulation of the EphrinB2:EphB4 signaling cascade and increases in EphrinB2 may play a role in AVM development, with potential utility as a diagnostic and therapeutic target.

Tangled blood vessel growths in the brain, known as arteriovenous malformations (AVMs), can be identified with a urine test, and the test protein may also help in treatment. AVMs often have no symptoms and can go undiagnosed, but when they rupture they can cause deadly brain hemorrhage. Better diagnostic tools and nonsurgical treatments are needed. Katie Fehnel and Edward Smith at Boston Children’s Hospital, USA, and co-workers identified an imbalance in a pair of signal/receptor proteins called ephrins in AVMs. Disturbing the balance of ephrin levels in blood vessel-forming cells disrupted growth, causing disorganized vessel formation with too many sprouts and insufficient junctions. Testing ephrin levels in patients’ urine reliably identified AVMs. These results offer a rapid and noninvasive new diagnostic tool and may help find new treatments for this mostly invisible and potentially fatal condition.

Characterization of Endothelial Cells Associated with Cerebral Arteriovenous Malformation

INTRODUCTION

Cerebral arteriovenous malformation (cAVM) is a disease characterized by the angiogenesis and remodeling of veins. However, whether vascular endothelial cells (ECs) exhibit morphological and functional changes during cAVM remains unclear. This study aimed to investigate the role of ECs in the pathogenesis of cAVM.

METHODS

Rat model of cAVM was established by anastomosing the common carotid artery with the external jugular vein. The digital subtraction angiography (DSA), HE, Masson and immunohistochemical staining were performed to evaluate the model. ECs were isolated from AVM rat model or control rats, and characterized by MTT, cell scratch, and tube formation assays. The secretion of vascular endothelial growth factor (VEGF) was detected by ELISA.

RESULTS

AVM rat model showed typical pathological characteristics of cAVM. In addition, the proliferation, migration and tube formation abilities of ECs of arterialized vein (AV-ECs) were significantly better than those of ECs of normal vein (NV-ECs). Moreover, the levels of secreted VEGF were significantly higher in AV-ECs than in NV-ECs.

CONCLUSION

AV-ECs isolated from AVM rat model showed increased proliferation, migration and angiogenesis and may be potential target for the treatment of cAVM.

The prostaglandin H2 analog U-46619 improves the differentiation efficiency of human induced pluripotent stem cells into endothelial cells by activating both p38MAPK and ERK1/2 signaling pathways

Background

We have shown that the differentiation of human-induced pluripotent stem cells (hiPSCs) into endothelial cells (ECs) is more efficient when performed with a 3-dimensional (3D) scaffold of biomaterial than in monolayers. The current study aims to further increase hiPSC-EC differentiation efficiency by deciphering the signaling pathways in 3D scaffolds.

Methods and results

We modified our 3D protocol by using U-46619 to upregulate both p38 mitogen-activated protein kinase (p38MAPK) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, which increased the differentiation efficiency (as measured by CD31 expression) to as high as 89% in two established hiPSC lines. The differentiated cells expressed arteriovenous, but not lymphatic, markers; formed tubular structures and EC lumen in vitro; had significantly shorter population-doubling times than monolayer-differentiated hiPSC-ECs; and restored perfusion and vascularity in a murine hind limb ischemia model. The differentiation efficiency was also > 85% in three hiPSC lines that had been derived from patients with diseases or disease symptoms that have been linked to endothelial dysfunction.

Conclusions

These observations demonstrate that activating both p38MAPK and ERK1/2 signaling pathways with U-46619 improves the efficiency of arteriovenous hiPSC-EC differentiation and produces cells with greater proliferative capacity.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1061-4) contains supplementary material, which is available to authorized users.

Shear stress promotes differentiation of stem cells from human exfoliated deciduous teeth into endothelial cells via the downstream pathway of VEGF-Notch signaling

Effects of shear stress on endotheliaxl differentiation of stem cells from human exfoliated deciduous teeth (SHEDs) were investigated. SHEDs were treated with shear stress, then reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to analyse the mRNA expression of arterial markers and western blot analysis was performed to analyse protein expression of angiogenic markers. Additionally, in vitro matrigel angiogenesis assay was performed to evaluate vascular-like structure formation. The secreted protein expression levels of the vascular endothelial growth factor (VEGF) of SHEDs after shear stress was also quantified using corresponding ELISA kits. Untreated SHEDs seeded on Matrigel cannot form vessel-like structures at any time points, whereas groups treated with shear stress formed a few vessel-like structures at 4, 8 and 12 h. When SHEDs were treated with EphrinB2-siRNA for 24, the capability of vessel-like structure formation was suppressed. After being treated with shear stress, the expression of VEGF, VEGFR2, DLL4, Notch1, EphrinB2, Hey1 and Hey2 (arterial markers) gene expression was significantly upregulated, moreover, the protein levels of VEGFR2, EphrinB2, CD31, Notch1, DLL4, Hey1, and Hey2 were also significantly up-regulated. Both the mRNA and protein expression levels of EphB4 (venous marker) were downregulated. The average VEGF protein concentration in supernatants secreted by shear stress treated SHEDs groups increased significantly. In conclusion, shear stress was able to induce arterial endothelial differentiation of stem cells from human exfoliated deciduous teeth, and VEGF-DLL4/Notch‑EphrinB2 signaling was involved in this process.

Stromal cells of hemangioblastomas exhibit mesenchymal stem cell-derived vascular progenitor cell properties

Hemangioblastoma is composed of neoplastic stromal cells and a prominent capillary network. To date, the identity of stromal cells remains unclear. Mesenchymal stem cells can give rise to committed vascular progenitor cells, and ephrin-B2/EphB4 and Notch signaling have crucial roles in these steps. The aim of our study was to elucidate that stromal cells of central nervous system hemangioblastomas have mesenchymal stem cell-derived vascular progenitor cell properties. Ten hemangioblastomas were investigated immunohistochemically. CD44, a mesenchymal stem cell marker, was detected in stromal cells of all cases, suggesting that stromal cells have mesenchymal stem cell-like properties. Neither CD31 nor α-SMA was expressed in stromal cells, suggesting that stromal cells have not acquired differentiated vascular cell properties. Both ephrin-B2 and EphB4, immature vascular cell markers, were detected in stromal cells of all cases. Jagged1, Notch1, and Hesr2/Hey2, which are known to be detected in both immature endothelial cells and mural cells, were expressed in stromal cells of all cases. Notch3, which is known to be detected in differentiating mural cells, was also expressed in all cases. These results suggest that stromal cells also have vascular progenitor cell properties. In conclusion, stromal cells of hemangioblastomas exhibit mesenchymal stem cell-derived vascular progenitor cell properties.

Gene expression analysis of nidus of cerebral arteriovenous malformations reveals vascular structures with deficient differentiation and maturation

Objective

Arteriovenous malformations (AVMs) are characterised by tangles of dysplastic blood vessels which shunt blood from arteries to veins with no intervening capillary bed. It is not known at what stage of development and differentiation, AVM vessels became aberrant. To address this, we have analysed the expression of vascular differentiation, vascular maturation and brain capillary specific genes in AVM nidus.

Methodology

We performed immunohistochemistry and western blot analysis of vascular differentiation (HEY2, DLL4, EFNB2, and COUP-TFII), vascular maturation (ENG and KLF2) and brain capillary specific genes (GGTP and GLUT1) on ten surgically excised human brain AVMs and ten normal human brain tissues.

Results

Immunohistochemical analysis revealed that AVM vessels co-express both artery and vein differentiation genes. H-score analysis revealed that there is statistically significant (P < 0.0001) increase in expression of these proteins in AVM vessels compared to control vessels. These findings were further confirmed by western blot analysis and found to be statistically significant (P < 0.0001 and P < 0.001) for all proteins except Hey2. Both immunostaining and western blot analysis revealed that AVM vessels express GGTP and GLUT1, markers specific to brain capillaries. Immunofluorescent staining demonstrated that expression of KLF2, a vascular maturation marker is significantly (P <0.001) decreased in AVM vessels and was further confirmed by western blot analysis (P < 0.001). Immunohistochemical and western blot analysis demonstrated that another vascular maturation protein Endoglin had high expression in AVM vessels compared to control vessels. The results were found to be statistically significant (P < 0.0001).

Summary

Our findings suggest that vascular structures of AVMs co-express markers specific for arteries, veins and capillaries. We conclude that AVM nidus constitutes of aberrant vessels which are not terminally differentiated and inadequately matured.

Contribution of Endothelial-to-Mesenchymal Transition to the Pathogenesis of Human Cerebral and Orbital Cavernous Malformations

BACKGROUND

The analysis of gene-targeted mouse mutants has demonstrated that endothelial-to-mesenchymal transition (EndMT) is crucial to the onset and progression of cerebral cavernous malformations (CMs). It has also been shown that Notch and ephrin/Eph signaling are involved in EndMT. However, their roles in the pathogenesis of human intracranial CMs remain unclear.

OBJECTIVE

To elucidate the contribution of EndMT, the Notch pathway, and ephrin-B2/EphB4 signaling to the pathogenesis of human intracranial CMs.

METHODS

Eight human intracranial CMs (5 cerebral and 3 orbital CMs) were immunohistochemically investigated.

RESULTS

CD31 (an endothelial marker) and EndMT markers, such as α-smooth muscle actin (a mesenchymal marker) and CD44 (a mesenchymal stem cell marker), were expressed in the endothelial layer of vascular sinusoids in all cases, suggesting that endothelial cells (ECs) have acquired mesenchymal and stem-cell-like characteristics and undergone EndMT in all cerebral and orbital CMs. EndMT was observed in about 70% and 35% of ECs in cerebral and orbital CMs, respectively. In all cases, Notch3 was expressed in the endothelial layer, indicating that ECs of vascular sinusoids have acquired mesenchymal features. In all cases, both ephrin-B2 and EphB4 were detected in the endothelial layer, suggesting that ECs of vascular sinusoids are immature or malformed cells and have both arterial and venous characteristics.

CONCLUSION

EndMT plays a critical role in the pathogenesis of human cerebral and orbital CMs. Modulating EndMT is expected to be a new therapeutic strategy for cerebral and orbital CMs.

Cardiovascular Disease: An Introduction

Cardiovascular disease (CVD) is a collective term designating all types of affliction affecting the blood circulatory system, including the heart and vasculature, which, respectively, displaces and conveys the blood.

Targeting receptor tyrosine kinase EphB4 in cancer therapy

Eph receptors and their Eph receptor-interacting (ephrin) ligands together form an important cell communication system with diverse roles. Experimental evidence demonstrated Eph receptor bidirectional signaling with both tumor-suppressing and tumor-promoting activities in cancer cells. The tyrosine kinase EphB4, a member of the Eph receptor family, has been associated with tumor angiogenesis, growth and metastasis, thus making it a valuable and attractive target for drug design for therapeutic applications. In the past decade, many studies have focused on elucidating the structure and function of EphB4 in complex with its ligand ephrinB2 for their role in carcinogenesis. Meanwhile, an array of compounds targeting EphB4 have been studied and several selective inhibitors have been tested in clinical studies. This review discusses the structure and function of the EphB4 receptor, analyzes its potential as a target for anticancer therapy, and summarizes the information about inhibitors of EphB4 kinase activity. Conclusively, EphB4 is a challenging but promising therapeutic target in cancer.

Germline Loss-of-Function Mutations in EPHB4 Cause a Second Form of Capillary Malformation-Arteriovenous Malformation (CM-AVM2) Deregulating RAS-MAPK Signaling

BACKGROUND

Most arteriovenous malformations (AVMs) are localized and occur sporadically. However, they also can be multifocal in autosomal-dominant disorders, such as hereditary hemorrhagic telangiectasia and capillary malformation (CM)-AVM. Previously, we identified RASA1 mutations in 50% of patients with CM-AVM. Herein we studied non-RASA1 patients to further elucidate the pathogenicity of CMs and AVMs.

METHODS

We conducted a genome-wide linkage study on a CM-AVM family. Whole-exome sequencing was also performed on 9 unrelated CM-AVM families. We identified a candidate gene and screened it in a large series of patients. The influence of several missense variants on protein function was also studied in vitro.

RESULTS

We found evidence for linkage in 2 loci. Whole-exome sequencing data unraveled 4 distinct damaging variants in EPHB4 in 5 families that cosegregated with CM-AVM. Overall, screening of EPHB4 detected 47 distinct mutations in 54 index patients: 27 led to a premature stop codon or splice-site alteration, suggesting loss of function. The other 20 are nonsynonymous variants that result in amino acid substitutions. In vitro expression of several mutations confirmed loss of function of EPHB4. The clinical features included multifocal CMs, telangiectasias, and AVMs.

CONCLUSIONS

We found EPHB4 mutations in patients with multifocal CMs associated with AVMs. The phenotype, CM-AVM2, mimics RASA1-related CM-AVM1 and also hereditary hemorrhagic telangiectasia. RASA1-encoded p120RASGAP is a direct effector of EPHB4. Our data highlight the pathogenetic importance of this interaction and indicts EPHB4-RAS-ERK signaling pathway as a major cause for AVMs.

Comprehensive study of angiogenic factors in women with endometriosis compared to women without endometriosis

OBJECTIVE

Endometriosis is a benign gynaecological disease, affecting women during their reproductive years. Angiogenesis represents a crucial step in the pathogenesis of endometriosis, because endometriotic lesions require neovascularization. In this study several angiogenesis-related genes have been studied in the context of endometriosis. Some of the analyzed angiogenic factors as well as their interactions were studied the first time regarding a possible association with endometriosis.

STUDY DESIGN

This case-control study consisted of 205 biopsies of 114 patients comprising 61 endometriosis patients and 53 control patients. Among them in 29 cases paired samples were obtained. VEGFA, VEGFR2, HIF1A, HGF, NRP1, PDGFB, FGF18, TNFα, TGFB2, EPHB4, EPO and ANG mRNA expression was analyzed by qRT-PCR in ectopic tissue samples, in eutopic endometrium of women with and without endometriosis, and in unaffected peritoneum of women with and without endometriosis.

RESULTS

VEGFR2, HIF1A, HGF, PDGFB, NRP1 and EPHB4 are overexpressed in ectopic lesions compared to eutopic tissues. VEGFR2, HGF, PDGFB, NRP1, and EPHB4 showed highest mRNA levels in peritoneal implants, in contrast HIF1A showed the highest expression in ovarian endometriomas. Correlation analyses of angiogenic factors in ectopic lesions revealed the strongest associations between VEGFR2, PDGFB, and EPHB4. We further showed a significant upregulation of VEGFR2, HIF1A and EPHB4 in eutopic endometrium of women with endometriosis compared to that of controls and a trend towards upregulation of HGF. Additionally, a significant downregulation for HIF1A, HGF and EPHB4 was observed in unaffected peritoneal tissues of women with endometriosis compared to controls.

CONCLUSION

We identified new genes (EPHB4 and NRP1) that may contribute to angiogenesis in endometriosis beside known factors (VEGFA, VEGFR2, HIF1A, HGF, and PDGFB). Correlation studies revealed the putative importance of EBHB4 in association with endometriosis. Our analyses support preliminary reports that angiogenic factors seem to be differently expressed in peritoneal implants, ovarian endometriomas and deep infiltrating endometriosis. Our observation that angiogenic factors are differently expressed in the unaffected peritoneum of women with endometriosis compared to women without endometriosis underlines the importance of the peritoneum in the establishment of endometriosis.

EphrinB2/EphB4 pathway in postnatal angiogenesis: a potential therapeutic target for ischemic cardiovascular disease

Ischemic cardiovascular disease remains one of the leading causes of morbidity and mortality in the world. Proangiogenic therapy appears to be a promising and feasible strategy for the patients with ischemic cardiovascular disease, but the results of preclinical and clinical trials are limited due to the complicated mechanisms of angiogenesis. Facilitating the formation of functional vessels is important in rescuing the ischemic cardiomyocytes. EphrinB2/EphB4, a novel pathway in angiogenesis, plays a critical role in both microvascular growth and neovascular maturation. Hence, investigating the mechanisms of EphrinB2/EphB4 pathway in angiogenesis may contribute to the development of novel therapeutics for ischemic cardiovascular disease. Previous reviews mainly focused on the role of EphrinB2/EphB4 pathway in embryo vascular development, but their role in postnatal angiogenesis in ischemic heart disease has not been fully illustrated. Here, we summarized the current knowledge of EphrinB2/EphB4 in angiogenesis and their interaction with other angiogenic pathways in ischemic cardiovascular disease.

EphB4 promotes the proliferation, invasion, and angiogenesis of human colorectal cancer

OBJECTIVE

Eph/Ephrin signalling plays an important role in tumorigenesis, neovascularization, and vasculogenesis. However, studies concerning the role of EphB4 in colorectal cancer (CRC) show inconsistent results, and the function of EphB4 in the formation of CRC-related blood vessels is not fully understood. The aim of this study is to investigate the EphB4 expression in CRC and the role of EphB4 in tumour angiogenesis.

MATERIALS AND METHODS

EphB4 and EphrinB2 expressions were detected in 200 CRC samples and 50 paired colorectal mucosae by immunohistochemistry. Xenograft animal models were established by stable knockdown and stable overexpression of EphB4, and control cell lines were used to investigate the role of EphB4 in CRC. Microvessels were stained with anti-CD34, and microvessel density (MVD) was assessed.

RESULTS

EphB4 protein was more highly expressed in CRC tissues compared with adjacent normal mucosae (P<0.05), while EphrinB2 levels were unchanged. Modulation of EphB4 levels in colon cancer cell line SW480 resulted in significant effects on tumour growth and invasion in vivo, with stable overexpression of EphB4 associated with faster growth and invasion. Furthermore, microvessel density values in xenograft tumours were significantly correlated with EphB4 (P<0.05).

CONCLUSION

EphB4 acts as a tumour promoter associated with proliferation, invasion, and angiogenesis, and may be used as a potential CRC therapeutic target.

Cartilage-specific deletion of ephrin-B2 in mice results in early developmental defects and an osteoarthritis-like phenotype during aging in vivo

BACKGROUND

Ephrins and their related receptors have been implicated in some developmental events. We have demonstrated that ephrin-B2 (EFNB2) could play a role in knee joint pathology associated with osteoarthritis (OA). Here, we delineate the in vivo role of EFNB2 in musculoskeletal growth, development, and in OA using a cartilage-specific EFNB2 knockout (EFNB2(Col2)KO) mouse model.

METHODS

EFNB2(Col2)KO was generated with Col2a1-Cre transgenic mice. The skeletal development was evaluated using macroscopy, immunohistochemistry, histomorphometry, radiology, densitometry, and micro-computed tomography. Analyses were performed at P0 (birth) and on postnatal days P15, P21, and on 8-week- and 1-year-old mice.

RESULTS

EFNB2(Col2)KO mice exhibited significant reduction in size, weight, length, and in long bones. At P0, the growth plates of EFNB2(Col2)KO mice displayed increased type X collagen, disorganized hyphertrophic zone, and decreased mineralization. At P15, mutant mice demonstrated a significant reduction in VEGF and TRAP at the chondro-osseous junction and a delay in the secondary ossification, including a decrease in bone volume and trabecular thickness. At P21 and 8 weeks old, EFNB2(Col2)KO mice exhibited reduced bone mineral density in the total skeleton, femur and spine. One-year-old EFNB2(Col2)KO mice demonstrated OA phenotypic features in both the knee and hip. By P15, 27 % of the EFNB2(Col2)KO mice developed a hip locomotor phenotype, which further experiments demonstrated reflected the neurological midline abnormality involving the corticospinal tract.

CONCLUSION

This in vivo study demonstrated, for the first time, that EFNB2 is essential for normal long bone growth and development and its absence leads to a knee and hip OA phenotype in aged mice.

Ephs and Ephrins in malignant gliomas

Eph receptor tyrosine kinases and the corresponding ephrin ligands play a pivotal role in the glioma development and progression. Aberrant protein expression levels of the Eph receptors and ephrins are often associated with higher tumor grade and poor prognosis. Their function in tumorigenesis is complex due to the intricate network of possible co-occurring interactions between neighboring tumor cells and tumor microenvironment. Both Ephs and ephrins localize on the surface of tumor cells, tumor vasculature, glioma stem cells, tumor cells infiltrating brain, and immune cells infiltrating tumors. They can both promote and inhibit tumorigenicity depending on the downstream forward and reverse signalling generated. All the above-mentioned features make the Ephs/ephrins system an intriguing candidate for the development of new therapeutic strategies in glioma treatment. This review will give a general overview on the structure and the function of Ephs and ephrins, with a particular emphasis on the state of the knowledge of their role in malignant gliomas.