Human leukocytes express ephrinB2 which activates microvascular endothelial cells

Inhibition of EphA2 by Dasatinib Suppresses Radiation-Induced Intestinal Injury

Radiation-induced multiorgan dysfunction is thought to result primarily from damage to the endothelial system, leading to a systemic inflammatory response that is mediated by the recruitment of leukocytes. The Eph–ephrin signaling pathway in the vascular system participates in various disease developmental processes, including cancer and inflammation. In this study, we demonstrate that radiation exposure increased intestinal inflammation via endothelial dysfunction, caused by the radiation-induced activation of EphA2, an Eph receptor tyrosine kinase, and its ligand ephrinA1. Barrier dysfunction in endothelial and epithelial cells was aggravated by vascular endothelial–cadherin disruption and leukocyte adhesion in radiation-induced inflammation both in vitro and in vivo. Among all Eph receptors and their ligands, EphA2 and ephrinA1 were required for barrier destabilization and leukocyte adhesion. Knockdown of EphA2 in endothelial cells reduced radiation-induced endothelial dysfunction. Furthermore, pharmacological inhibition of EphA2–ephrinA1 by the tyrosine kinase inhibitor dasatinib attenuated the loss of vascular integrity and leukocyte adhesion in vitro. Mice administered dasatinib exhibited resistance to radiation injury characterized by reduced barrier leakage and decreased leukocyte infiltration into the intestine. Taken together, these data suggest that dasatinib therapy represents a potential approach for the protection of radiation-mediated intestinal damage by targeting the EphA2–ephrinA1 complex.

Ephs and Ephrins in Adult Endothelial Biology

Eph receptors and their ephrin ligands are important guidance molecules during neurological and vascular development. In recent years, it has become clear that the Eph protein family remains functional in adult physiology. A subset of Ephs and ephrins is highly expressed by endothelial cells. As endothelial cells form the first barrier between the blood and surrounding tissues, maintenance of a healthy endothelium is crucial for tissue homeostasis. This review gives an overview of the current insights of the role of ephrin ligands and receptors in endothelial function and leukocyte recruitment in the (patho)physiology of adult vascular biology.

Essential roles of EphrinB2 in mammalian heart: from development to diseases

EphrinB2, a membrane-tethered ligand preferentially binding to its receptor EphB4, is ubiquitously expressed in all mammals. Through the particular bidirectional signaling, EphrinB2 plays a critical role during the development of cardiovascular system, postnatal angiogenesis physiologically and pathologically, and cardiac remodeling after injuries as an emerging role. This review highlights the pivotal involvement of EphrinB2 in heart, from developmental cardiogenesis to pathological cardiac remodeling process. Further potential translational therapies will be discussed in targeting EphrinB2 signaling, to better understand the prevention and treatment of cardiovascular diseases.

Shear stress, arterial identity and atherosclerosis

In the developing embryo, the vasculature first takes the form of a web-like network called the vascular plexus. Arterial and venous differentiation is subsequently guided by the specific expression of genes in the endothelial cells that provide spatial and temporal cues for development. Notch1/4, Notch ligand delta-like 4 (Dll4), and Notch downstream effectors are typically expressed in arterial cells along with EphrinB2, whereas chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) and EphB4 characterise vein endothelial cells. Haemodynamic forces (blood pressure and blood flow) also contribute importantly to vascular remodelling. Early arteriovenous differentiation and local blood flow may hold the key to future inflammatory diseases. Indeed, despite the fact that atherosclerosis risk factors such as smoking, hypertension, hypercholesterolaemia, and diabetes all induce endothelial cell dysfunction throughout the vasculature, plaques develop only in arteries, and they localise essentially in vessel branch points, curvatures and bifurcations, where blood flow (and consequently shear stress) is low or oscillatory. Arterial segments exposed to high blood flow (and high laminar shear stress) tend to remain plaque-free. These observations have led many to investigate what particular properties of arterial or venous endothelial cells confer susceptibility or protection from plaque formation, and how that might interact with a particular shear stress environment.

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.

The multidrug-resistance transporter Abcc3 protects NK cells from chemotherapy in a murine model of malignant glioma

Abcc3, a member of the ATP-binding cassette transporter superfamily, plays a role in multidrug resistance. Here, we found that Abcc3 is highly expressed in blood-derived NK cells but not in CD8(+) T cells. In GL261 glioma-bearing mice treated with the alkylating agent temozolomide (TMZ) for 5 d, an early increased frequency of NK cells was observed. We also found that Abcc3 is strongly upregulated and functionally active in NK cells from mice treated with TMZ compared to controls. We demonstrate that Abcc3 is critical for NK cell survival during TMZ administration; more importantly, Akt, involved in lymphocyte survival, is phosphorylated only in NK cells expressing Abcc3. The resistance of NK cells to chemotherapy was accompanied by increased migration and homing in the brain at early time points. Cytotoxicity, evaluated by IFNγ production and specific lytic activity against GL261 cells, increased peripherally in the later phases, after conclusion of TMZ treatment. Intra-tumor increase of the NK effector subset as well as in IFNγ, granzymes and perforin-1 expression, were found early and persisted over time, correlating with a profound modulation on glioma microenvironment induced by TMZ. Our findings reveal an important involvement of Abcc3 in NK cell resistance to chemotherapy and have important clinical implications for patients treated with chemo-immunotherapy.

Eph/ephrin-B-mediated cell-to-cell interactions govern MTS20(+) thymic epithelial cell development

Thymus development is a complex process in which cell-to-cell interactions between thymocytes and thymic epithelial cells (TECs) are essential to allow a proper maturation of both thymic cell components. Although signals that control thymocyte development are well known, mechanisms governing TEC maturation are poorly understood, especially those that regulate the maturation of immature TEC populations during early fetal thymus development. In this study, we show that EphB2-deficient, EphB2LacZ and EphB3-deficient fetal thymuses present a lower number of cells and delayed maturation of DN cell subsets compared to WT values. Moreover, deficits in the production of chemokines, known to be involved in the lymphoid seeding into the thymus, contribute in decreased proportions of intrathymic T cell progenitors (PIRA/B(+)) in the mutant thymuses from early stages of development. These features correlate with increased proportions of MTS20(+) cells but fewer MTS20(-) cells from E13.5 onward in the deficient thymuses, suggesting a delayed development of the first epithelial cells. In addition, in vitro the lack of thymocytes or the blockade of Eph/ephrin-B-mediated cell-to-cell interactions between either thymocytes-TECs or TECs-TECs in E13.5 fetal thymic lobes coursed with increased proportions of MTS20(+) TECs. This confirms, for the first time, that the presence of CD45(+) cells, corresponding at these stages to DN1 and DN2 cells, and Eph/ephrin-B-mediated heterotypic or homotypic cell interactions between thymocytes and TECs, or between TECs and themselves, contribute to the early maturation of MTS20(+) TECs.

EphrinB2/EphA4-mediated activation of endothelial cells increases monocyte adhesion

The membrane anchored ligand ephrinB2 belongs to the broad Eph/ephrin system and is able to activate different Eph receptors. The Eph receptors belong to the huge group of receptor-tyrosine kinases. Eph receptors as well as their corresponding ephrin ligands are cell-membrane attached proteins. Therefore, direct cell-cell contact is essentially for interaction. It is known that ephrinB2 plays a pivotal role in developmental and in tumour angiogenesis. Previous studies point to a crucial role of the EphA4-receptor in the process of monocyte adhesion. Since ephrinB2 is known as an interaction partner of EphA4, the aim of the present study was to investigate a possible interplay of EphA4-receptor with ephrinB2 during monocyte adhesion to the endothelium. As verified by bulk adhesion assays and atomic-force microscopy based single-cell force spectroscopy, temporary stimulation of endothelial cells from different sources with the soluble ligand ephrinB2 increased monocyte adhesion to endothelial cells. The proadhesive effect of ephrinB2 was independent of an active transcription, but is mediated via the Rho signaling pathway with subsequent modulation of the actin cytoskeleton. Furthermore, ephrinB2 mediated its impact on monocyte adhesion via the receptor EphA4 as shown by siRNA-mediated silencing. Interestingly, ephrinB2 was induced by TNF-α treatment. Silencing of ephrinB2 led to a lowering of the TNF-α mediated monocyte adhesion to endothelial cells. Furthermore, immunohistochemical staining of human atherosclerotic plaque revealed expression of ephrinB2 in macrophages. The results of the present study point to a crucial role of ephrinB2 induced EphA4 forward signaling in the context of monocyte adhesion to endothelial cells. This transcription-independent effect is mediated by Rho signaling induced actin-filament polymerization.

TNF-α-mediated adhesion of monocytes to endothelial cells-The role of ephrinA1

The ligand ephrin A1 is more often discussed to play a role in the development of the atherosclerotic plaque and in this context especially in the monocyte adhesion to endothelial cells. As tumor necrosis factor-α (TNF-α) is known to induce monocyte adhesion to endothelium and ephrin A1 expression, the present study focuses on the involvement of ephrin A1 in TNF-α-mediated monocyte adhesion. The analysis of different members of the Eph/ephrin system in TNF-α-treated human umbilical vein endothelial cells (HUVEC) revealed that especially ephrinA1 was found to be highly regulated by TNF-α compared to other members of the Eph family. This effect is also present in arterial endothelial cells from the umbilical artery and from the coronary artery. This regulation is dependent on NFκB-activation as shown by the expression of a constitutive-active IκB-mutant. By using siRNA-mediated silencing and adenoviral overexpression of ephrinA1 in HUVEC, the involvement of ephrinA1 in the TNF-α triggered monocyte adhesion to endothelial cells could be demonstrated. In addition, these results could be verified by quantitative adhesion measurement using atomic force microscopy-based single-cell force spectroscopy and under flow conditions. Furthermore, this effect is mediated via the EphA4 receptor. EphrinA1 does not influence the mRNA or protein expression of the adhesion receptors VCAM-1 and ICAM-1 in endothelial cells. However, the surface presentation of these adhesion receptors is modulated in an ephrinA1-dependent manner. In conclusion, these data demonstrate that ephrinA1 plays an important role in the TNF-α-mediated adhesion of monocytes to endothelial cells, which might be of great importance in the context of atherosclerosis.

Evaluation of six synthetic surgical meshes implanted subcutaneously in a rat model

The long-term efficacy and mechanical integrity of implanted materials is largely determined by early host response. Therefore, implanting materials with well-characterized tissue responses provides the greatest chance of 'one-hit' surgical successes, without repeated interventions to replace, repair or remove non-compliant biomaterials. Six synthetic meshes were implanted subcutaneously in a rat model to deduce and quantify modulations in host response, based on material fabrication variables. The materials consisted of knitting variations of polypropylene (PP), polyethyleneterephthalate (PET) and polyglycolic acid (PGA) yarns and were implanted for 2, 5, 7, 14 and 28 days before fixation and both semi- and fully quantitative histopathology. In a subcutaneous niche, material weight did not influence foreign body response. PET stimulated earlier inflammation than PP and PGA, which normalized over 28 days. Multifilament meshes recruited foreign body giant cells, which were largely absent from monofilaments. Using CD68, PGA was demonstrated to be the greatest leukocyte-activating polymer at a number of the time points analysed. This research therefore highlights that underlying polymer composition may be more over-arching in deciding the inflammatory properties of surgical meshes, based on increased macrophagic responses to PGA vs alternative base polymers of comparable weights and porosities. Copyright © 2013 John Wiley & Sons, Ltd.

Ephrin-A1/EphA4-mediated adhesion of monocytes to endothelial cells

The Eph receptors represent the largest family of receptor tyrosine kinases. Both Eph receptors and their ephrin ligands are cell-surface proteins, and they typically mediate cell-to-cell communication by interacting at sites of intercellular contact. The major aim of the present study was to investigate the involvement of EphA4-ephrin-A1 interaction in monocyte adhesion to endothelial cells, as this process is a crucial step during the initiation and progression of the atherosclerotic plaque. Immunohistochemical analysis of human atherosclerotic plaques revealed expression of EphA4 receptor and ephrin-A1 ligand in major cell types within the plaque. Short-time stimulation of endothelial cells with the soluble ligand ephrin-A1 leads to a fourfold increase in adhesion of human monocytes to endothelial cells. In addition, ephrin-A1 further increases monocyte adhesion to already inflamed endothelial cells. EphrinA1 mediates its effect on monocyte adhesion via the activated receptor EphA4. This ephrinA1/EphA4 induced process involves the activation of the Rho signaling pathway and does not require active transcription. Rho activation downstream of EphA4 leads to increased polymerization of actin filaments in endothelial cells. This process was shown to be crucial for the proadhesive effect of ephrin-A1. The results of the present study show that ephrin-A1-induced EphA4 forward signaling promotes monocyte adhesion to endothelial cells via activation of RhoA and subsequent stress-fiber formation by a non-transcriptional mechanism.

Inhibition of choroidal neovascularization by anti-EphB4 monoclonal antibody

The aim of this study was to determine the effect of the EphB4 monoclonal antibody on experimental choroidal neovascularization (CNV) progression. Experimental CNV was established by argon laser photocoagulation. In the experimental group, the EphB4 monoclonal antibody was injected into the vitreous space in the eye specimens on days 0, 3, 6 and 9 after CNV model establishment. In the control group, an equal amount of balanced salt solution was injected at the same time points. On day 10 after CNV model establishment, fluorescein isothiocyanate-dextran endocardial perfusion and choroidal stretched preparation were conducted, respectively, for the two groups. The CNV area in each light spot and the mean values were determined. Histopathological examination was conducted and the ratio of the maximum thickness of the CNV in each light spot to the surrounding normal choroidal thickness, as well as the mean ratio, were calculated. Choroidal stretched preparation confirmed that the CNV of the experimental group was smaller, whereas the CNV of the control group was wider and larger. Quantitative analysis revealed that CNV in the experimental group was significantly inhibited (t=11.84, P<0.01) and that CNV progression in the experimental group was significantly suppressed (t=7.45, P<0.01). Histopathological examination revealed that CNV in the experimental group was thinner and smaller. Vitreous injection of the EphB4 monoclonal antibody inhibits experimental CNV progression. However, its specific mechanism remains unclear. Endogenous EphrinB2/EphB4 regulates ocular neovascularization and may become a new target in treating CNV diseases.

Eph/Ephrin signaling in injury and inflammation

The Eph/ephrin receptor-ligand system plays an important role in embryogenesis and adult life, principally by influencing cell behavior through signaling pathways, resulting in modification of the cell cytoskeleton and cell adhesion. There are 10 EphA receptors, and six EphB receptors, distinguished on sequence difference and binding preferences, that interact with the six glycosylphosphatidylinositol-linked ephrin-A ligands and the three transmembrane ephrin-B ligands, respectively. The Eph/ephrin proteins, originally described as developmental regulators that are expressed at low levels postembryonically, are re-expressed after injury to the optic nerve, spinal cord, and brain in fish, amphibians, rodents, and humans. In rodent spinal cord injury, the up-regulation of EphA4 prevents recovery by inhibiting axons from crossing the injury site. Eph/ephrin proteins may be partly responsible for the phenotypic changes to the vascular endothelium in inflammation, which allows fluid and inflammatory cells to pass from the vascular space into the interstitial tissues. Specifically, EphA2/ephrin-A1 signaling in the lung may be responsible for pulmonary inflammation in acute lung injury. A role in T-cell maturation and chronic inflammation (heart failure, inflammatory bowel disease, and rheumatoid arthritis) is also reported. Although there remains much to learn about Eph/ephrin signaling in human disease, and specifically in injury and inflammation, this area of research raises the exciting prospect that novel therapies will be developed that precisely target these pathways.

Soluble EphB4 inhibition of PDGF-induced RPE migration in vitro

PURPOSE

EphB4 receptor (EphB4) and its ligand (EphrinB2) play an important role in the regulation of cell adhesion, growth, and migration. The purpose of this study was to determine the effects of EphB4 blockade by soluble EphB4 (sEphB4) on retinal pigment epithelial (RPE) cell migration and proliferation, induced by platelet-derived growth factor-BB (PDGF), and to establish its relevance to proliferative vitreoretinopathy (PVR).

METHODS

The expression of EphB4 and EphrinB2 in early-passage human RPE cells and in human PVR membranes was evaluated by confocal microscopy. The effect of sEphB4 (0.1-3 microg/mL) on PDGF (20 ng/mL)-induced RPE migration and proliferation was evaluated using a modified Boyden chamber assay and an MTT assay, respectively. Attachment to basement membrane matrix and fibronectin was assayed by MTT. Phosphorylation of FAK and p42/44 mitogen-activated protein kinase (MAPK) in retinal pigment epithelium was determined by Western blot analysis after exposure to sEphB4. The effect of sEphB4 on the phosphorylation of EphB4/EphrinB2 was demonstrated with the use of immunoprecipitation assays.

RESULTS

EphrinB2 and EphB4 were expressed on human RPE cells in vitro and in cells within human PVR membranes. sEphB4 blocked EphB4 and EphrinB2 phosphorylation in RPE cells in vitro. sEphB4 reduced RPE migration in response to PDGF stimulation (P < 0.01). Similarly, sEphB4 inhibited RPE attachment and proliferation in a dose-dependent manner (P < 0.05). PDGF-induced phosphorylation of FAK and MAPK was inhibited by sEphB4.

CONCLUSIONS

EphB4 and EphrinB2 are expressed in RPE cells and PVR membranes. sEphB4 inhibits PDGF-induced RPE cell attachment, proliferation, and migration. This effect may result from the inhibition of FAK and MAPK phosphorylation.

Treatment with ephrin B2 positively impacts the abnormal metabolism of human osteoarthritic chondrocytes

Introduction

Members of the ephrin system, the ephrin receptor erythropoietin-producing hepatocellular B4 (EphB4) and its specific ligand, ephrin B2, appear to be involved in the bone remodelling process. We recently showed that their interaction inhibits the resorptive activity of human osteoarthritic (OA) subchondral bone osteoblasts. Hence, we further investigated the possible implication of these ephrin members on the catabolic/anabolic activities of human OA chondrocytes.

Methods

EphB4 receptor and ephrin B2 levels were determined by quantitative PCR and immunohistochemistry, and the effects of ephrin B2 on the expression/production of factors involved in the OA process.

Results

EphB4 receptors and ephrin B2 ligands are expressed and produced by human normal and OA chondrocytes. Ephrin B2 protein was found at similar levels in both cartilage types, whereas EphB4 receptor expression (P < 0.0001) and production (P < 0.01) levels were significantly increased in OA chondrocytes/cartilage. Ephrin B2 treatment significantly inhibited the interleukin (IL)-1beta, IL-6, matrix metalloproteinase-1 (MMP-1), MMP-9, MMP-13, and proteinase-activated receptor-2 (PAR-2) gene expression levels, whereas MMP-2 was unaffected, and significantly increased collagen type II, a cartilage specific macromolecule. It also inhibited the IL-1beta stimulated protein production of IL-6, MMP-1 and MMP-13.

Conclusions

Our study is the first to provide data on the presence and role of ephrin B2/EphB4 receptors in human chondrocytes/cartilage. Data showed that ephrin B2 treatment positively impacts the abnormal metabolism of OA cartilage by inhibiting important catabolic factors involved in this disease at the same time as increasing anabolic activity.

Involvement of endothelial ephrin-B2 in adhesion and transmigration of EphB-receptor-expressing monocytes

The vascular endothelium is a crucial interface that controls the recruitment of circulating leukocytes. Based on the luminal expression of the ephrin-B2 ligand by endothelial cells (ECs) and the expression of EphB receptors (EphBRs) by circulating monocytes, we hypothesized that EphBR-ephrinB interactions are involved in monocyte adhesion. Adhesion experiments with monocytic cells were performed on ECs that overexpressed either full-length ephrin-B2 or cytoplasmically truncated ephrin-B2 (DeltaC-ephrin-B2). Atomic force microscopy confirmed similar adhesive strengths of EphBR-expressing J774 cells to ECs that either overexpressed full-length ephrin-B2 or truncated DeltaC-ephrin-B2 (1-minute interaction). Yet, adhesion experiments under static or flow conditions for 30 minutes demonstrated the preferential adhesion of monocytic cells to ECs that overexpressed full-length ephrin-B2 but not to DeltaC-ephrin-B2 or to ECs that had been mock transduced. Adhesion was blocked by ephrin-B2-specific and EphBR-specific antibodies. Correspondingly, adhesion of EphB4-receptor-overexpressing monocytes to ephrin-B2-positive ECs was further augmented. Trafficking experiments of cell-surface molecules revealed that, prior to internalization, the resulting EphB4-receptor-ephrin-B2 complex translocated from the luminal surface to inter-endothelial junctions. Lastly, full-length ephrin-B2 in ECs was also involved in monocyte transmigration. Collectively, our study identifies a role of EphBR-ephrinB interactions as a new step in the cascade of events leading to monocyte adhesion and transmigration through the vascular endothelium.

Dynamic changes occur in patterns of endometrial EFNB2/EPHB4 expression during the period of spiral arterial modification in mice

Transient, human and murine decidua-associated, Natural Killer lymphocytes (uNK cells) have special, localized roles in early gestational endometrial remodeling and angiogenesis. To determine if uNK cells promote a specific vessel subtype, a histological time-course study of implantation site endothelia was undertaken using normal C57BL/6J (B6) and uNK-deficient B6.129-Rag2 tm1Fwa Il2rg tm2Cgn (alymphoid) mice, a strain lacking pregnancy-induced structural modifications of spiral arteries. Antibodies to EFNB2, EPHB4, and LYVE1, respectively, identified arterial, venous, and lymphatic endothelia. Unexpectedly, many uNK cells in B6 endometrium showed strong EFNB2 expression early in gestation, then became EPHB4+. This molecular transition coincided with structural modifications of spiral arteries that shifted from EFNB2+/EPHB4(-) to EFNB2+/EPHB4+. NK cells from B6 spleen and liver did not express EFNB2. LYVE1 expression was similar in endometrium from B6 and alymphoid mice, but EFNB2 and EPHB4 expression in alymphoid mice was dramatically different. Strong stromal expression of both molecules developed mesometrially, and this was reduced by B6 lymphocyte transfer. Trophoblasts reacted with each marker in both strains. Expression of EFNB2 by uNK cells and trophoblasts may be the key regulatory mechanism that drives their positional association with EFNB2+ arteries and prevents association of both cell types with EPHB4+ veins. Gain of EPHB4 by midgestation spiral arteries may signal completion of pregnancy-induced arterial modification and provide a repulsion mechanism that limits subsequent interactions of the modified vessel with uNK cells and trophoblasts.