Modulation of VEGF signalling output by the Notch pathway

Defining the Functional Influence of Endothelial Cell-Expressed Oncogenic Activating Mutations on Vascular Morphogenesis and Capillary Assembly

This study sought to define key molecules and signals controlling major steps in vascular morphogenesis, and how these signals regulate pericyte recruitment and pericyte-induced basement membrane deposition. The morphogenic impact of endothelial cell (EC) expression of activating mutants of Kirsten rat sarcoma virus (kRas), mitogen-activated protein kinase 1 (Mek1), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), Akt serine/threonine kinase 1 (Akt1), Ras homolog enriched in brain (Rheb) Janus kinase 2 (Jak2), or signal transducer and activator of transcription 3 (Stat3) expression versus controls was evaluated, along with EC signaling events, pharmacologic inhibitor assays, and siRNA suppression experiments. Primary stimulators of EC lumen formation included kRas, Akt1, and Mek1, whereas PIK3CA and Akt1 stimulated a specialized type of cystic lumen formation. In contrast, the key drivers of EC sprouting behavior were Jak2, Stat3, Mek1, PIK3CA, and mammalian target of rapamycin (mTor). These conclusions are further supported by pharmacologic inhibitor and siRNA suppression experiments. EC expression of active Akt1, kRas, and PIK3CA led to markedly dysregulated lumen formation coupled to strongly inhibited pericyte recruitment and basement membrane deposition. For example, activated Akt1 expression in ECs excessively stimulated lumen formation, decreased EC sprouting behavior, and showed minimal pericyte recruitment with reduced mRNA expression of platelet-derived growth factor-BB, platelet-derived growth factor-DD, and endothelin-1, critical EC-derived factors known to stimulate pericyte invasion. The study identified key signals controlling fundamental steps in capillary morphogenesis and maturation and provided mechanistic details on why EC activating mutations induced a capillary deficiency state with abnormal lumens, impaired pericyte recruitment, and basement deposition: predisposing stimuli for the development of vascular malformations.

Vascular endothelial cell development and diversity

Vascular endothelial cells form the inner layer of blood vessels where they have a key role in the development and maintenance of the functional circulatory system and provide paracrine support to surrounding non-vascular cells. Technical advances in the past 5 years in single-cell genomics and in in vivo genetic labelling have facilitated greater insights into endothelial cell development, plasticity and heterogeneity. These advances have also contributed to a new understanding of the timing of endothelial cell subtype differentiation and its relationship to the cell cycle. Identification of novel tissue-specific gene expression patterns in endothelial cells has led to the discovery of crucial signalling pathways and new interactions with other cell types that have key roles in both tissue maintenance and disease pathology. In this Review, we describe the latest findings in vascular endothelial cell development and diversity, which are often supported by large-scale, single-cell studies, and discuss the implications of these findings for vascular medicine. In addition, we highlight how techniques such as single-cell multimodal omics, which have become increasingly sophisticated over the past 2 years, are being utilized to study normal vascular physiology as well as functional perturbations in disease.

JAG1 is correlated to suppressive immune microenvironment and predicts immunotherapy resistance in lung adenocarcinoma

Background

The current exploration of the tumor immune microenvironment is enthusiastic, but few studies explored the impact of angiogenesis on the immune microenvironment. Immunotherapy combined with anti-angiogenesis therapy has become one of the first-line treatment for lung adenocarcinoma. Our study aimed to explore the reasons for resistance of immunotherapy, and explore markers for immunotherapy combined with anti-angiogenesis therapy.

Methods

First, by unsupervised clustering of 36 angiogenesis-related genes in lung adenocarcinoma patients from TCGA database, AGS1 and AGS2 groups were distinguished with significantly different clinical outcomes. Secondly, the immune microenvironment and metabolic characteristics were analyzed. Next, we used the GDSC and GEO database to analyze therapeutic responses. Then, through multivariate Cox regression, the hub gene: JAG1, significantly related to prognosis was selected, and further verified by multi-omics data. Finally, we validated that patient with high JAG1 expression had a low immune-infiltrating tumor microenvironment through single-cell transcriptomic data.

Results

Compared with the AGS1 group, AGS2 showed an immune "cold" phenotype with lower lymphocyte infiltration, and was associated with worse prognoses. At the same time, the immunosuppressive TGF-β response was significantly higher in AGS2. Furthermore, the glycolysis ability of the AGS2 was stronger than AGS1. The expression of JAG1 was significantly higher in the AGS2, and was significantly negatively correlated with the degree of immune infiltration, accompanying with higher glycolytic capacity. The above results indicate that patients with high expression of JAG1 may lead to immunosuppressive phenotype due to its strong glycolytic capacity, thus making immunotherapy resistance.

Conclusion

Patients with high expression of JAG1 enhanced glycolytic capacity was likely to cause suppressed immune microenvironment. JAG1 may be a marker for resistance of immunotherapy. Combining anti-angiogenesis therapy could be considered to improve the prognosis of those patients.

Mutations in MINAR2 encoding membrane integral NOTCH2-associated receptor 2 cause deafness in humans and mice

Discovery of deafness genes and elucidating their functions have substantially contributed to our understanding of hearing physiology and its pathologies. Here we report on DNA variants in MINAR2, encoding membrane integral NOTCH2-associated receptor 2, in four families underlying autosomal recessive nonsyndromic deafness. Neurologic evaluation of affected individuals at ages ranging from 4 to 80 y old does not show additional abnormalities. MINAR2 is a recently annotated gene with limited functional understanding. We detected three MINAR2 variants, c.144G > A (p.Trp48*), c.412_419delCGGTTTTG (p.Arg138Valfs*10), and c.393G > T, in 13 individuals with congenital- or prelingual-onset severe-to-profound sensorineural hearing loss (HL). The c.393G > T variant is shown to disrupt a splice donor site. We show that Minar2 is expressed in the mouse inner ear, with the protein localizing mainly in the hair cells, spiral ganglia, the spiral limbus, and the stria vascularis. Mice with loss of function of the Minar2 protein (Minar2^tm1b/tm1b) present with rapidly progressive sensorineural HL associated with a reduction in outer hair cell stereocilia in the shortest row and degeneration of hair cells at a later age. We conclude that MINAR2 is essential for hearing in humans and mice and its disruption leads to sensorineural HL. Progressive HL observed in mice and in some affected individuals and as well as relative preservation of hair cells provides an opportunity to interfere with HL using genetic therapies.

Interaction of transcription factors Islet2 and Nr2f1b to control vascular patterning during zebrafish development

Many regulators controlling arterial identity are well described; however, transcription factors that promote vein identity and vascular patterning have remained largely unknown. We previously identified the transcription factors Islet2 (Isl2) and Nr2f1b required for specification of the vein and tip cell identity mediated by notch pathway in zebrafish. However, the interaction between Isl2 and Nr2f1b is not known. In this study, we report that Nr2f2 plays minor roles on vein and intersegmental vessels (ISV) growth and dissect the genetic interactions among the three transcription factors Isl2, Nr2f1b, and Nr2f2 using a combinatorial knockdown strategy. The double knockdown of isl2/nr2f1b, isl2/nr2f2, and nr2f1b/nr2f2 showed the enhanced defects in vasculature including less completed ISV, reduced veins, and ISV cells. We further tested the genetic relationship among these three transcription factors. We found isl2 can regulate the expression of nr2f1b and nr2f2, suggesting a model where Isl2 functions upstream of Nr2f1b and Nr2f2. We hypothsized that Isl2 and Nr2f1b can function together through cis-regulatory binding motifs. In-vitro luciferase assay results, we showed that Isl2 and Nr2f1b can cooperatively enhance gene expression. Moreover, co-immunoprecipitation results indicated that Isl2 and Nr2f1b interact physically. Together, we showed that the interaction of the Nr2f1b and Nr2f2 transcription factors in combination with the Islet2 play coordinated roles in the vascular development of zebrafish.

Notch1 promotes ordered revascularization through Semaphorin 3g modulation of downstream vascular patterning signalling factors

Here we genetically and functionally addressed potential pathways of Notch signalling in mediating vascular regeneration in mouse models. We first used transgenic adult mice with either gain- or loss-of-function Notch signalling in vascular endothelial cells and monitored perfusion in the hindlimb following ischaemia induced by femoral artery ligation. Mice deficient in Notch signalling showed defective perfusion recovery and expansion of collateral arteries. Transcriptomics analysis of arterial endothelial cells in the Notch mutants identified the guidance factor Sema3g as a candidate gene mediating reperfusion downstream of Notch. Studies in the retinal circulation showed the central role of SEMA3G downstream of Notch signalling in the orderly regulation of vascular patterning. These studies in multiple vascular beds show the primacy of Notch signalling and downstream generation of guidance peptides such as SEMA3G in promoting well-ordered vascular regeneration. KEY POINTS: Notch signalling is a critical mediator of revascularization. Yet the cellular processes activated during recovery following vascular injury are incompletely understood. Here we used genetic and cellular approaches in two different vascular beds and cultured endothelial cells to address the generalizability of mechanisms. By utilizing a highly reproducible murine model of hindlimb ischaemia in transgenic mice in which Notch signalling was inhibited at the transcriptional level, we demonstrated the centrality of Notch signalling in perfusion recovery and revascularization. RNA-sequencing of Notch mutants identified class 3 Semaphorins regulated by Notch signalling as downstream targets. Studies in retinal vessels and endothelial cells showed an essential role of guidance peptide Sema3g as a modulator of angiogenesis and orderly vascular patterning. The Notch to Sema3g signalling axis functions as a feedback mechanism to sculpt the growing vasculature in multiple beds.

The role of the Notch pathway in the pathogenesis of systemic sclerosis: clinical implications

INTRODUCTION

Systemic sclerosis (SSc) is a chronic debilitating disease characterized by vascular insufficiency, widespread fibrosis and immune activation. Current understanding of its pathophysiology remains incomplete, which translates into inefficient therapies. Notch signaling is a central player in the development of physiological and pathological fibrosis not only in general but also in the context of SSc and is most likely involved in the vascular dysfunction that characterizes the disease.

AREAS COVERED

This review explores the role of the Notch pathway in the pathophysiology of SSc and the potential implications for the diagnosis, evaluation, and management of this yet incurable disease.

EXPERT OPINION

Although major issues still exist about the comprehension of SSc and the design of effective treatments, the knowledge of the role of the Notch pathway in fibrogenesis and vascular biology has shed light and enthusiasm over the field. Drugs that target components of Notch signaling are currently in development including already some in clinical trials. As such, Notch may become a very important topic in the near future (considering both the pathophysiology and treatment perspectives), not only in the context of SSc but also in the vascular-dependent fibrotic processes present in a multitude of diseases.

Endothelial Semaphorin 3fb regulates Vegf pathway-mediated angiogenic sprouting

Vessel growth integrates diverse extrinsic signals with intrinsic signaling cascades to coordinate cell migration and sprouting morphogenesis. The pro-angiogenic effects of Vascular Endothelial Growth Factor (VEGF) are carefully controlled during sprouting to generate an efficiently patterned vascular network. We identify crosstalk between VEGF signaling and that of the secreted ligand Semaphorin 3fb (Sema3fb), one of two zebrafish paralogs of mammalian Sema3F. The sema3fb gene is expressed by endothelial cells in actively sprouting vessels. Loss of sema3fb results in abnormally wide and stunted intersegmental vessel artery sprouts. Although the sprouts initiate at the correct developmental time, they have a reduced migration speed. These sprouts have persistent filopodia and abnormally spaced nuclei suggesting dysregulated control of actin assembly. sema3fb mutants show simultaneously higher expression of pro-angiogenic (VEGF receptor 2 (vegfr2) and delta-like 4 (dll4)) and anti-angiogenic (soluble VEGF receptor 1 (svegfr1)/ soluble Fms Related Receptor Tyrosine Kinase 1 (sflt1)) pathway components. We show increased phospho-ERK staining in migrating angioblasts, consistent with enhanced Vegf activity. Reducing Vegfr2 kinase activity in sema3fb mutants rescues angiogenic sprouting. Our data suggest that Sema3fb plays a critical role in promoting endothelial sprouting through modulating the VEGF signaling pathway, acting as an autocrine cue that modulates intrinsic growth factor signaling.

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.

ETS factors are required but not sufficient for specific patterns of enhancer activity in different endothelial subtypes

Correct vascular differentiation requires distinct patterns of gene expression in different subtypes of endothelial cells. Members of the ETS transcription factor family are essential for the transcriptional activation of arterial and angiogenesis-specific gene regulatory elements, leading to the hypothesis that they play lineage-defining roles in arterial and angiogenic differentiation directly downstream of VEGFA signalling. However, an alternative explanation is that ETS binding at enhancers and promoters is a general requirement for activation of many endothelial genes regardless of expression pattern, with subtype-specificity provided by additional factors. Here we use analysis of Ephb4 and Coup-TFII (Nr2f2) vein-specific enhancers to demonstrate that ETS factors are equally essential for vein, arterial and angiogenic-specific enhancer activity patterns. Further, we show that ETS factor binding at these vein-specific enhancers is enriched by VEGFA signalling, similar to that seen at arterial and angiogenic enhancers. However, while arterial and angiogenic enhancers can be activated by VEGFA in vivo, the Ephb4 and Coup-TFII venous enhancers are not, suggesting that the specificity of VEGFA-induced arterial and angiogenic enhancer activity occurs via non-ETS transcription factors. These results support a model in which ETS factors are not the primary regulators of specific patterns of gene expression in different endothelial subtypes.

•

Vein-specific enhancers can contain essential ETS motifs.

•

VEGFA induced an increase in ETS binding at vein, arterial and angiogenic enhancers.

•

VEGFA stimulation cannot induce vein-specific enhancer activity.

AIBP, Angiogenesis, Hematopoiesis, and Atherogenesis

PURPOSE OF REVIEW

The goal of this manuscript is to summarize the current understanding of the secreted APOA1 binding protein (AIBP), encoded by NAXE, in angiogenesis, hematopoiesis, and inflammation. The studies on AIBP illustrate a critical connection between lipid metabolism and the aforementioned endothelial and immune cell biology.

RECENT FINDINGS

AIBP dictates both developmental processes such as angiogenesis and hematopoiesis, and pathological events such as inflammation, tumorigenesis, and atherosclerosis. Although cholesterol efflux dictates AIBP-mediated lipid raft disruption in many of the cell types, recent studies document cholesterol efflux-independent mechanism involving Cdc42-mediated cytoskeleton remodeling in macrophages. AIBP disrupts lipid rafts and impairs raft-associated VEGFR2 but facilitates non-raft-associated NOTCH1 signaling. Furthermore, AIBP can induce cholesterol biosynthesis gene SREBP2 activation, which in turn transactivates NOTCH1 and supports specification of hematopoietic stem and progenitor cells (HSPCs). In addition, AIBP also binds TLR4 and represses TLR4-mediated inflammation. In this review, we summarize the latest research on AIBP, focusing on its role in cholesterol metabolism and the attendant effects on lipid raft-regulated VEGFR2 and non-raft-associated NOTCH1 activation in angiogenesis, SREBP2-upregulated NOTCH1 signaling in hematopoiesis, and TLR4 signaling in inflammation and atherogenesis. We will discuss its potential therapeutic applications in angiogenesis and inflammation due to selective targeting of activated cells.

Notch Signaling Function in the Angiocrine Regulation of Tumor Development

The concept of tumor growth being angiogenesis dependent had its origin in the observations of Judah Folkman in 1969 of a retinoblastoma in a child. Tumor angiogenesis is initiated when endothelial cells (ECs) respond to local stimuli and migrate towards the growing mass, which results in the formation of tubular structures surrounded by perivascular support cells that transport blood to the inner tumor. In turn, the neo-vasculature supports tumor development and eventual metastasis. This process is highly regulated by several signaling pathways. Central to this process is the Notch signaling pathway. Beyond the role of Notch signaling in tumor angiogenesis, a major hallmark of cancer development, it has also been implicated in the regulation of tumor cell proliferation and survival, in epithelial-to-mesenchymal transition, invasion and metastasis and in the regulation of cancer stem cells, in a variety of hematologic and solid malignancies. There is increasing evidence for the tumor vasculature being important in roles other than those linked to blood perfusion. Namely, endothelial cells act on and influence neighboring tumor cells by use of angiocrine factors to generate a unique cellular microenvironment, thereby regulating tumor stem-like cells’ homeostasis, modulating tumor progression, invasiveness, trafficking and metastasis. This review will focus on Notch signaling components that play a part in angiocrine signaling in a tumor setting.

Co-Culture of Primary Human Coronary Artery and Internal Thoracic Artery Endothelial Cells Results in Mutually Beneficial Paracrine Interactions

Although saphenous veins (SVs) are commonly used as conduits for coronary artery bypass grafting (CABG), internal thoracic artery (ITA) grafts have significantly higher long-term patency. As SVs and ITA endothelial cells (ECs) have a considerable level of heterogeneity, we suggested that synergistic paracrine interactions between CA and ITA ECs (HCAECs and HITAECs, respectively) may explain the increased resistance of ITA grafts and adjacent CAs to atherosclerosis and restenosis. In this study, we measured the gene and protein expression of the molecules responsible for endothelial homeostasis, pro-inflammatory response, and endothelial-to-mesenchymal transition in HCAECs co-cultured with either HITAECs or SV ECs (HSaVECs) for an ascending duration. Upon the co-culture, HCAECs and HITAECs showed augmented expression of endothelial nitric oxide synthase (eNOS) and reduced expression of endothelial-to-mesenchymal transition transcription factors Snail and Slug when compared to the HCAEC–HSaVEC model. HCAECs co-cultured with HITAECs demonstrated an upregulation of HES1, a master regulator of arterial specification, of which the expression was also exclusively induced in HSaVECs co-cultured with HCAECs, suggestive of their arterialisation. In addition, co-culture of HCAECs and HITAECs promoted the release of pro-angiogenic molecules. To conclude, co-culture of HCAECs and HITAECs results in reciprocal and beneficial paracrine interactions that might contribute to the better performance of ITA grafts upon CABG.

The vascular endothelial cell-expressed prion protein doppel promotes angiogenesis and blood-brain barrier development

The central nervous system (CNS) contains a complex network of blood vessels that promote normal tissue development and physiology. Abnormal control of blood vessel morphogenesis and maturation is linked to the pathogenesis of various neurodevelopmental diseases. The CNS-specific genes that regulate blood vessel morphogenesis in development and disease remain largely unknown. Here, we have characterized functions for the gene encoding prion protein 2 (Prnd) in CNS blood vessel development and physiology. Prnd encodes the glycosylphosphatidylinositol (GPI)-linked protein doppel, which is expressed on the surface of angiogenic vascular endothelial cells, but is absent in quiescent endothelial cells of the adult CNS. During CNS vascular development, doppel interacts with receptor tyrosine kinases and activates cytoplasmic signaling pathways involved in endothelial cell survival, metabolism and migration. Analysis of mice genetically null for Prnd revealed impaired CNS blood vessel morphogenesis and associated endothelial cell sprouting defects. Prnd^-/- mice also displayed defects in endothelial barrier integrity. Collectively, these data reveal novel mechanisms underlying doppel control of angiogenesis in the developing CNS, and may provide new insights about dysfunctional pathways that cause vascular-related CNS disorders.

Mechanism of Notch1‑saRNA‑1480 reversing androgen sensitivity in human metastatic castration‑resistant prostate cancer

The aim of the present study was to explore the mechanism by which Notch1-small activating (sa)RNA restored androgen sensitivity in human metastatic castration-resistant prostate cancer (CRPC). After transfection of Notch1-saRNA-1480 in PC3 cells, the expression of Notch1 and androgen receptor (AR) was investigated by reverse transcription quantitative PCR (RT-qPCR) and western blotting. Furthermore, the protein expression level of vascular endothelial growth factor (VEGF) was measured. Then, flow cytometry was used to analyze the cell cycle and apoptosis after transfection. Moreover, the migration and invasion ability of PC3 cells were assessed by transwell assays. Then, angio-genesis experiments were conducted to analyze the abilities of PC3 cells to form blood vessels. Furthermore, in vivo experiments detected the antitumor activity of Notch1-saRNA-1480. The mRNA and protein expression levels of Notch1 were significantly increased after transfection, while the expression levels of AR and VEGF were decreased. After transfection, the cell cycle was arrested at the G0/G1 checkpoint. Notch1-saRNA-1480 significantly increased the proportion of apoptotic cells after transfection. In addition, transwell assay results showed that PC3 cell migration and invasion were inhibited. The total vessel length was significantly decreased based on angiogenesis experiments, which indicated that PC3 cell angiogenesis was inhibited. In vivo experiments showed that Notch1-saRNA-1480 could inhibit tumor growth and volume. The protein expression of Notch1, AR, VEGF receptor 2 (VEGFR2) and VEGF in tumor tissues was consistent with in vitro levels. Notch1-saRNA-1480 could significantly inhibit the proliferation of PC3 cells in vitro and the growth of tumors in vivo, which is associated with the inhibition of the AR and VEGF pathways.

Combined treatment of melatonin and sodium tanshinone IIA sulfonate reduced the neurological and cardiovascular toxicity induced by deltamethrin in zebrafish

The pyrethroid insecticide deltamethrin has been reported to have an effect on vertebrate development and cardiovascular disease. Sodium tanshinone IIA sulfonate (STS) is considered to have cardioprotective effects and melatonin is known to regulate sleep-waking cycles. In this experiment, we used transgenic zebrafish Tg (kdrl:mCherry) and Tg (myl7:GFP) to investigate whether STS and melatonin could reverse the cardiovascular toxicity and neurotoxicity induced by deltamethrin. Zebrafish embryos were exposed to 25 μg/L deltamethrin at 10 hpf and treated with 100 mmol/L STS and 1 μmol/L melatonin showed that deltamethrin treatment affected normal cardiovascular development. In situ hybridization and qRT-PCR results showed that deltamethrin could interfere with the normal expression of cardiovascular development-related genes vegfr2, shh, gata4, nkx2.5, causing functional defects in the cardiovascular system. In addition, deltamethrin could affect the sleep-waking behavior of larvae, increasing the activity of larvae, decreasing the rest behavior and the expression of hcrt, hcrtr, aanat2 were down-regulated. The addition of melatonin and STS can significantly alleviate cardiovascular toxicity and sleep-waking induced by deltamethrin, while restoring the expression of related genes to normal levels. Our study demonstrates the role of STS and melatonin in protecting cardiovascular and sleep-waking behavior caused by deltamethrin.

Blood Vessel Patterning on Retinal Astrocytes Requires Endothelial Flt-1 (VEGFR-1)

Feedback mechanisms are critical components of many pro-angiogenic signaling pathways that keep vessel growth within a functional range. The Vascular Endothelial Growth Factor-A (VEGF-A) pathway utilizes the decoy VEGF-A receptor Flt-1 to provide negative feedback regulation of VEGF-A signaling. In this study, we investigated how the genetic loss of flt-1 differentially affects the branching complexity of vascular networks in tissues despite similar effects on endothelial sprouting. We selectively ablated flt-1 in the post-natal retina and found that maximum induction of flt-1 loss resulted in alterations in endothelial sprouting and filopodial extension, ultimately yielding hyper-branched networks in the absence of changes in retinal astrocyte architecture. The mosaic deletion of flt-1 revealed that sprouting endothelial cells flanked by flt-1^−/− regions of vasculature more extensively associated with underlying astrocytes and exhibited aberrant sprouting, independent of the tip cell genotype. Overall, our data support a model in which tissue patterning features, such as retinal astrocytes, integrate with flt-1-regulated angiogenic molecular and cellular mechanisms to yield optimal vessel patterning for a given tissue.

Phenotypic characteristics of human bone marrow-derived endothelial progenitor cells in vitro support cell effectiveness for repair of the blood-spinal cord barrier in ALS

Amyotrophic lateral sclerosis (ALS) was recently recognized as a neurovascular disease. Accumulating evidence demonstrated blood-spinal-cord barrier (BSCB) impairment mainly via endothelial cell (EC) degeneration in ALS patients and animal models. BSCB repair may be a therapeutic approach for ALS. We showed benefits of human bone marrow endothelial progenitor cell (hBMEPC) transplantation into symptomatic ALS mice on barrier restoration; however, cellular mechanisms remain unclear. The study aimed to characterize hBMEPCs in vitro under normogenic conditions. hBMEPCs were cultured at different time points. Enzyme-linked immunosorbent assay (ELISA) was used to detect concentrations of angiogenic factors (VEGF-A, angiogenin-1, and endoglin) and angiogenic inhibitor endostatin in conditioned media. Double immunocytochemical staining for CD105, ZO-1, and occludin with F-actin was performed. Results showed predominantly gradual significant post-culture increases of VEGF-A and angiogenin-1 levels. Cultured cells displayed distinct rounded or elongated cellular morphologies and positively immunoexpressed for CD105, indicating EC phenotype. Cytoskeletal F-actin filaments were re-arranged according to cell morphologies. Immunopositive expressions for ZO-1 were detected near inner cell membrane and for occludin on cell membrane surface of adjacent hBMEPCs. Together, secretion of angiogenic factors by cultured cells provides evidence for a potential mechanism underlying endogenous EC repair in ALS through hBMEPC transplantation, leading to restored barrier integrity. Also, ZO-1 and occludin immunoexpressions, confirming hBMEPC interactions in vitro, may reflect post-transplant cell actions in vivo.

Notch and breast cancer metastasis: Current knowledge, new sights and targeted therapy

Breast cancer is the most common type of invasive cancer in females and metastasis is one of the major causes of breast cancer-associated mortality. Following detachment from the primary site, disseminated tumor cells (DTCs) enter the bloodstream and establish secondary colonies during the metastatic process. An increasing amount of studies have elucidated the importance of Notch signaling in breast cancer metastasis; therefore, the present review focuses on the mechanisms by which Notch contributes to the occurrence of breast cancer DTCs, increases their motility, establishes interactions with the tumor microenvironment, protects DTCs from host surveillance and finally facilitates secondary colonization. Identification of the underlying mechanisms of Notch-associated breast cancer metastasis will provide additional insights that may contribute towards the development of novel Notch-targeted therapeutic strategies, which may aid in reducing metastasis, culminating in an improved patient prognosis.

Veins and Arteries Build Hierarchical Branching Patterns Differently: Bottom-Up versus Top-Down

A tree-like hierarchical branching structure is present in many biological systems, such as the kidney, lung, mammary gland, and blood vessels. Most of these organs form through branching morphogenesis, where outward growth results in smaller and smaller branches. However, the blood vasculature is unique in that it exists as two trees (arterial and venous) connected at their tips. Obtaining this organization might therefore require unique developmental mechanisms. As reviewed here, recent data indicate that arterial trees often form in reverse order. Accordingly, initial arterial endothelial cell differentiation occurs outside of arterial vessels. These pre-artery cells then build trees by following a migratory path from smaller into larger arteries, a process guided by the forces imparted by blood flow. Thus, in comparison to other branched organs, arteries can obtain their structure through inward growth and coalescence. Here, new information on the underlying mechanisms is discussed, and how defects can lead to pathologies, such as hypoplastic arteries and arteriovenous malformations.

The regulatory roles of VEGF-Notch signaling pathway on aplastic anemia with kidney deficiency and blood stasis

OBJECTIVE

Vascular endothelial growth factor (VEGF)-Notch signaling pathway plays an important role in aplastic anemia (AA). This study aimed to evaluate the regulatory roles of VEGF-Notch signaling pathway on mesenchymal stem cells (MSCs) isolated from AA patients with kidney deficiency and blood stasis (KB) (AA MSCs).

METHODS

Expression of VEGF-Notch signaling related factors, including VEGF, VEGFR, Notch-1, Jagged1, Delta-like1, and hes1 was detected in bone marrow (BM) tissues and AA MSCs by Western blot analysis. VEGF (100 ng/mL) and γ-secretase inhibitor (DAPT) (10 μM) was used to active and inhibit VEGF-Notch signaling in AA MSCs, respectively. After treatment, the proliferation, apoptosis, and adipogenic differentiation of AA MSCs was detected by Cell Counting Kit-8, flow cytometry, and Oil red O staining, respectively. Lentivirus short hairpin RNA (shRNA) were constructed to downregulate Notch-1 and VEGF in normal bone marrow mesenchymal stem cells (BMSCs), and the effects of VEGF/Notch-1 shRNA transfected BMSCs on the proliferation, migration, and angiogenesis of human umbilical vein endothelial cells (HUVECs) were evaluated.

RESULTS

Significantly lower expression of VEGF, VEGFR, Notch-1, Jagged1, Delta-like1, and hes1 was revealed in AA BM tissues and AA MSCs when compared with the normal control (P < 0.05). The intervention of DAPT significantly inhibited the proliferation, and promoted the apoptosis and adipogenic differentiation of AA MSCs, while VEGF intervention exhibited opposite results (P < 0.05). Meanwhile, the proliferation, migration, and angiogenesis of HUVECs were significantly promoted by normal BMSCs, while inhibited by VEGF/Notch-1 shRNA transfected BMSCs (P < 0.05).

CONCLUSION

The activation of VEGF-Notch signaling pathway may be a potential therapeutic target for AA with KB.

Excess vascular endothelial growth factor-A disrupts pericyte recruitment during blood vessel formation

Pericyte investment into new blood vessels is essential for vascular development such that mis-regulation within this phase of vessel formation can contribute to numerous pathologies including arteriovenous and cerebrovascular malformations. It is critical therefore to illuminate how angiogenic signaling pathways intersect to regulate pericyte migration and investment. Here, we disrupted vascular endothelial growth factor-A (VEGF-A) signaling in ex vivo and in vitro models of sprouting angiogenesis, and found pericyte coverage to be compromised during VEGF-A perturbations. Pericytes had little to no expression of VEGF receptors, suggesting VEGF-A signaling defects affect endothelial cells directly but pericytes indirectly. Live imaging of ex vivo angiogenesis in mouse embryonic skin revealed limited pericyte migration during exposure to exogenous VEGF-A. During VEGF-A gain-of-function conditions, pericytes and endothelial cells displayed abnormal transcriptional changes within the platelet-derived growth factor-B (PDGF-B) and Notch pathways. To further test potential crosstalk between these pathways in pericytes, we stimulated embryonic pericytes with Notch ligands Delta-like 4 (Dll4) and Jagged-1 (Jag1) and found induction of Notch pathway activity but no changes in PDGF Receptor-β (Pdgfrβ) expression. In contrast, PDGFRβ protein levels decreased with mis-regulated VEGF-A activity, observed in the effects on full-length PDGFRβ and a truncated PDGFRβ isoform generated by proteolytic cleavage or potentially by mRNA splicing. Overall, these observations support a model in which, during the initial stages of vascular development, pericyte distribution and coverage are indirectly affected by endothelial cell VEGF-A signaling and the downstream regulation of PDGF-B-PDGFRβ dynamics, without substantial involvement of pericyte Notch signaling during these early stages.

Retinal vasculature development in health and disease

Development of the retinal vasculature is based on highly coordinated signalling between different cell types of the retina, integrating internal metabolic requirements with external influences such as the supply of oxygen and nutrients. The developing mouse retinal vasculature is a useful model system to study these interactions because it is experimentally accessible for intra ocular injections and genetic manipulations, can be easily imaged and develops in a similar fashion to that of humans. Research using this model has provided insights about general principles of angiogenesis as well as pathologies that affect the developing retinal vasculature. In this review, we discuss recent advances in our understanding of the molecular and cellular mechanisms that govern the interactions between neurons, glial and vascular cells in the developing retina. This includes a review of mechanisms that shape the retinal vasculature, such as sprouting angiogenesis, vascular network remodelling and vessel maturation. We also explore how the disruption of these processes in mice can lead to pathology - such as oxygen induced retinopathy - and how this translates to human retinopathy of prematurity.

Notch Signaling: Linking Embryonic Lung Development and Asthmatic Airway Remodeling

Lung development is mediated by assorted signaling proteins and orchestrated by complex mesenchymal-epithelial interactions. Notch signaling is an evolutionarily conserved cell-cell communication mechanism that exhibits a pivotal role in lung development. Notably, both aberrant expression and loss of regulation of Notch signaling are critically linked to the pathogenesis of various lung diseases, in particular, pulmonary fibrosis, lung cancer, pulmonary arterial hypertension, and asthmatic airway remodeling; implying that precise regulation of intensity and duration of Notch signaling is imperative for appropriate lung development. Moreover, evidence suggests that Notch signaling links embryonic lung development and asthmatic airway remodeling. Herein, we summarized all-recent advances associated with the mechanistic role of Notch signaling in lung development, consequences of aberrant expression or deletion of Notch signaling in linking early-impaired lung development and asthmatic airway remodeling, and all recently investigated potential therapeutic strategies to treat asthmatic airway remodeling.

The presence of VEGF and Notch2 during preantral-antral follicular transition in infantile rats: Anatomical evidence and its implications

Folliculogenesis is a process that depends on angiogenesis, in which VEGF and Notch signaling pathway members are involved. Although this pathway is present in preantral and antral follicular structures during the second stage of folliculogenesis, this association has not been described. Therefore, this study aimed to identify VEGF and Notch2 in ovary structures of infantile rats after induction of follicular development with a gonadotropin stimulus. In order to explore this possibility we analyzed rat ovary morphology from days 10-25 after birth; subsequently, the transition from preantral follicle to an antral stage was analyzed by the induction of follicular development with equine chorionic gonadotropin (eCG) and VEGF and Notch were identified in the rat ovary by fluorescence. The histological analysis revealed that the ovary of a 10-day-old rat has the highest percentage of preantral follicles and based on this a 10IU eCG dose promoted an increase in the number of antral follicles, as well as a decrease in the number of preantral follicles, related to which there was an increase in ovary weight and size. In addition, a higher concentration of circulating estradiol was observed, proliferation of granulosa cells in both follicle groups was stimulated, and the accumulation of VEGF in granulosa and theca cells and in the antral follicle oocyte was increased (p<0.05), whereas the presence of Notch2 was limited to mural granulosa cells, in granulosa cells that formed the cumulus oophorus and in the oocyte of both groups of follicles. The multiple correspondence analysis allowed us to support an association between VEGF and Notch2 during the transition from preantral to antral follicles in the ovary of an infantile rat.

SUMOylation Negatively Regulates Angiogenesis by Targeting Endothelial NOTCH Signaling

RATIONALE

The highly conserved NOTCH (neurogenic locus notch homolog protein) signaling pathway functions as a key cell-cell interaction mechanism controlling cell fate and tissue patterning, whereas its dysregulation is implicated in a variety of developmental disorders and cancers. The pivotal role of endothelial NOTCH in regulation of angiogenesis is widely appreciated; however, little is known about what controls its signal transduction. Our previous study indicated the potential role of post-translational SUMO (small ubiquitin-like modifier) modification (SUMOylation) in vascular disorders.

OBJECTIVE

The aim of this study was to investigate the role of SUMOylation in endothelial NOTCH signaling and angiogenesis.

METHODS AND RESULTS

Endothelial SENP1 (sentrin-specific protease 1) deletion, in newly generated endothelial SENP1 (the major protease of the SUMO system)-deficient mice, significantly delayed retinal vascularization by maintaining prolonged NOTCH1 signaling, as confirmed in cultured endothelial cells. An in vitro SUMOylation assay and immunoprecipitation revealed that when SENP1 associated with N1ICD (NOTCH1 intracellular domain), it functions as a deSUMOylase of N1ICD SUMOylation on conserved lysines. Immunoblot and immunoprecipitation analyses and dual-luciferase assays of natural and SUMO-conjugated/nonconjugated NOTCH1 forms demonstrated that SUMO conjugation facilitated NOTCH1 cleavage. This released N1ICD from the membrane and stabilized it for translocation to the nucleus where it functions as a cotranscriptional factor. Functionally, SENP1-mediated NOTCH1 deSUMOylation was required for NOTCH signal activation in response to DLL4 (Delta-like 4) stimulation. This in turn suppressed VEGF (vascular endothelial growth factor) receptor signaling and angiogenesis, as evidenced by immunoblotted signaling molecules and in vitro angiogenesis assays.

CONCLUSIONS

These results establish reversible NOTCH1 SUMOylation as a regulatory mechanism in coordinating endothelial angiogenic signaling; SENP1 acts as a critical intrinsic mediator of this process. These findings may apply to NOTCH-regulated biological events in nonvascular tissues and provide a novel therapeutic strategy for vascular diseases and tumors.

Fine-tune regulation of carboxypeptidase N1 controls vascular patterning during zebrafish development

Vascular development is regulated by complicated signals and molecules in vertebrates. In this study, we characterized a novel function of carboxypeptidase N1 (Cpn1) in the vasculature. We show that cpn1 mRNA is expressed in developing vessels. The knockdown of cpn1 by morpholino injection impairs the growth of intersegmental vessels (ISV) and caudal vein plexus (CVP), suggesting the role of cpn1 in vascular development. We showed that vascular defects are not caused by cell death but are due to the impairment of migration and proliferation. Consistent with vascular growth defects, loss of cpn1 affects the expression of the vascular markers flt4, mrc1, flk, stabilin, and ephrinb2. Furthermore, the overexpression of cpn1 impaired the growth of ISV and CVP, but the remodeling expression of vascular markers was different from the knockdown of cpn1, indicating the differential regulation mechanisms in cpn1-overexpressing embryos. We examine the interaction between cpn1 and multiple signals and observed that cpn1 is regulated by Notch/VEGF signals for ISV growth and likely regulates BMP signals for CVP patterning. In conclusion, we demonstrate that cpn1 has a critical role in the vascular development of zebrafish. We also reveal a fine-tune regulation of cpn1 that controls vascular patterning mediated by multiple signals.

Ftr82 Is Critical for Vascular Patterning during Zebrafish Development

Cellular components and signaling pathways are required for the proper growth of blood vessels. Here, we report for the first time that a teleost-specific gene ftr82 (finTRIM family, member 82) plays a critical role in vasculature during zebrafish development. To date, there has been no description of tripartite motif proteins (TRIM) in vascular development, and the role of ftr82 is unknown. In this study, we found that ftr82 mRNA is expressed during the development of vessels, and loss of ftr82 by morpholino (MO) knockdown impairs the growth of intersegmental vessels (ISV) and caudal vein plexus (CVP), suggesting that ftr82 plays a critical role in promoting ISV and CVP growth. We showed the specificity of ftr82 MO by analyzing ftr82 expression products and expressing ftr82 mRNA to rescue ftr82 morphants. We further showed that the knockdown of ftr82 reduced ISV cell numbers, suggesting that the growth impairment of vessels is likely due to a decrease of cell proliferation and migration, but not cell death. In addition, loss of ftr82 affects the expression of vascular markers, which is consistent with the defect of vascular growth. Finally, we showed that ftr82 likely interacts with vascular endothelial growth factor (VEGF) and Notch signaling. Together, we identify teleost-specific ftr82 as a vascular gene that plays an important role for vascular development in zebrafish.

The role of the semaphorins in cancer

The semaphorins were initially characterized as axon guidance factors, but have subsequently been implicated also in the regulation of immune responses, angiogenesis, organ formation, and a variety of additional physiological and developmental functions. The semaphorin family contains more then 20 genes divided into 7 subfamilies, all of which contain the signature sema domain. The semaphorins transduce signals by binding to receptors belonging to the neuropilin or plexin families. Additional receptors which form complexes with these primary semaphorin receptors are also frequently involved in semaphorin signaling. Recent evidence suggests that semaphorins also fulfill important roles in the etiology of multiple forms of cancer. Some semaphorins have been found to function as bona-fide tumor suppressors and to inhibit tumor progression by various mechanisms while other semaphorins function as inducers and promoters of tumor progression.

Preparation and characterization of pro-angiogenic gel derived from small intestinal submucosa

Gels derived from decellularized small intestinal submucosa (SIS) have been used to repair ischemic myocardium and deliver protein drug. However, their material properties and effects on cell behavior are not well understood, in part because of the difficulty of gelling in vitro. In this study, soluble SIS matrix, which was easily handled and could effectively gel, was successfully prepared using a modified method. Fourier transform infrared spectroscopy confirmed that the SIS gel contained not only collagen but also sulfated glycosaminoglycans (sGAGs). Interestingly, the sustained release of vascular endothelial growth factor and basic fibroblast growth factor within the SIS gel was detected, and no initial burst release was observed. The SIS gel was more capable of evoking neovascularization than collagen type I gel, as determined by tube formation experiments in human umbilical vein endothelial cells, the mouse aortic ring assay, and animal experiments. The upregulated expression of kinase insert domain receptor (KDR), Notch1, and Ang2, the key genes in angiogenesis that were evaluated in HUVECs seeded on the SIS gel, confirmed that angiogenesis bioactive factors contained in the SIS gel are indeed active and effective. The SIS gel significantly promoted neovascularization compared to the collagen type I gel in vivo. Histology revealed adequate host tissue response in engraftment both types of gels. Together, these data demonstrate that the SIS gel is a promising and attractive candidate for tissue engineering, especially in promoting vessel formation.

STATEMENT OF SIGNIFICANCE

The material properties of small intestinal submucosa (SIS) gel and the effect of these properties upon cell behavior are not well understood, in part due to the difficulty of gelling in vitro. In this study, soluble SIS matrix, which was easily handled and gelled was prepared using modified method. The material properties and biocompatibility of SIS gel were explored. The sustained release of growth factors from this gel was observed along with its degradation in vitro. The results demonstrate that the SIS gel promote angiogenesis in vitro and in vivo. The SIS gel biological properties suggest that the constituent ECM molecules released from the gel remain activity. These findings suggested that the SIS gel was a promising candidate for tissue engineering, especially in promoting vessel formation.

Regulation of signaling interactions and receptor endocytosis in growing blood vessels

Blood vessels and the lymphatic vasculature are extensive tubular networks formed by endothelial cells that have several indispensable functions in the developing and adult organism. During growth and tissue regeneration but also in many pathological settings, these vascular networks expand, which is critically controlled by the receptor EphB4 and the ligand ephrin-B2. An increasing body of evidence links Eph/ephrin molecules to the function of other receptor tyrosine kinases and cell surface receptors. In the endothelium, ephrin-B2 is required for clathrin-dependent internalization and full signaling activity of VEGFR2, the main receptor for vascular endothelial growth factor. In vascular smooth muscle cells, ephrin-B2 antagonizes clathrin-dependent endocytosis of PDGFRβ and controls the balanced activation of different signal transduction processes after stimulation with platelet-derived growth factor. This review summarizes the important roles of Eph/ephrin molecules in vascular morphogenesis and explains the function of ephrin-B2 as a molecular hub for receptor endocytosis in the vasculature.

Emodin inhibits the proliferation of PC3 prostate cancer cells in vitro via the Notch signaling pathway

The aim of the present study was to examine the anticarcinogenic effects of emodin on the Notch signaling pathway and vascular endothelial growth factor (VEGF) in the PC3 androgen-independent prostate cancer cell line in vitro. The cell viability was assessed using an 3‑(4,5)‑dimethylthiahiazo(‑z‑y1)‑3,5‑di‑phenytetrazolium bromide assay. Cell apoptosis and cell cycle were detected using flow cytometry. Morphological alterations were observed using transmission electron microscopy. The mRNA and protein expression levels of Notch1, Jagged1, VEGF and bFGF were detected using reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. Laser scanning confocal microscope (LSCM) immunofluorescence analysis was performed to detect the levels of expression and the sub‑cellular localization of the Notch1 receptor protein. Growth of the PC3 cells was inhibited by emodin. Flow cytometry demonstrated that emodin induced apoptosis in the PC3 cells and arrested the cell cycle of the PC3 cells at the G2/M phase. The mRNA and protein expression of Notch1 in the PC3 cells was markedly increased, whereas the mRNA and protein expression levels of Jagged1, VEGF and bFGF were significantly decreased following exposure to emodin for 24 h. The LSCM assay revealed that the Notch1 was not only localized in the membrane and cytoplasm, but was also present in the nucleolus of the PC3 cells, and the expression of Notch1 in the nuclei gradually increased following treatment with emodin. These results demonstrated that emodin suppressed the growth of androgen‑independent prostate cancer cell lines and induced apoptosis and cell cycle arrest. The Notch signaling pathway was activated in the PC3 cells following exposure to emodin, which suggested that the Notch signaling pathway is involved in the prostate tumor‑suppressing mechanisms of emodin, the activation of which may depend on CBF1 protein in the nucleus by classic pathways. The antitumor function of emodin, attributed to the Notch signaling pathway, induced the downregulation of VEGF by suppressing tumorigenesis and angiogenesis, which indicated a novel mechanism underlying the emodin-mediated anti-prostate cancer effect.

Lipid rafts: integrated platforms for vascular organization offering therapeutic opportunities

Research on the nanoscale membrane structures known as lipid rafts is relevant to the fields of cancer biology, inflammation and ischaemia. Lipid rafts recruit molecules critical to signalling and regulation of the invasion process in malignant cells, the leukocytes that provide immunity in inflammation and the endothelial cells that build blood and lymphatic vessels, as well as the patterning of neural networks. As angiogenesis is a common denominator, regulation of receptors and signalling molecules critical to angiogenesis is central to the design of new approaches aimed at reducing, promoting or normalizing the angiogenic process. The goal of this review is to highlight some of the key issues that indicate the involvement of endothelial cell lipid rafts at each step of so-called 'sprouting angiogenesis', from stimulation of the vascular endothelial growth factor to the choice of tip cells, activation of migratory and invasion pathways, recruitment of molecules that guide axons in vascular patterning and maturation of blood vessels. Finally, the review addresses opportunities for future studies to define how these lipid domains (and their constituents) may be manipulated to stimulate the so-called 'normalization' of vascular networks within tumors, and be identified as the main target, enabling the development of more efficient chemotherapeutics and cancer immunotherapies.

Notch ligand Delta-like 1 promotes in vivo vasculogenesis in human cord blood-derived endothelial colony forming cells

BACKGROUND AIMS

Human cord blood (CB) is enriched in circulating endothelial colony forming cells (ECFCs) that display high proliferative potential and in vivo vessel forming ability. Because Notch signaling is critical for embryonic blood vessel formation in utero, we hypothesized that Notch pathway activation may enhance cultured ECFC vasculogenic properties in vivo.

METHODS

In vitro ECFC stimulation with an immobilized chimeric Notch ligand (Delta-like1(ext-IgG)) led to significant increases in the mRNA and protein levels of Notch regulated Hey2 and EphrinB2 that were blocked by treatment with γ-secretase inhibitor addition. However, Notch stimulated preconditioning in vitro failed to enhance ECFC vasculogenesis in vivo. In contrast, in vivo co-implantation of ECFCs with OP9-Delta-like 1 stromal cells that constitutively expressed the Notch ligand delta-like 1 resulted in enhanced Notch activated ECFC-derived increased vessel density and enlarged vessel area in vivo, an effect not induced by OP9 control stromal implantation.

RESULTS

This Notch activation was associated with diminished apoptosis in the exposed ECFC.

CONCLUSIONS

We conclude that Notch pathway activation in ECFC in vivo via co-implanted stromal cells expressing delta-like 1 promotes vasculogenesis and augments blood vessel formation via diminishing apoptosis of the implanted ECFC.

FGF signalling restricts haematopoietic stem cell specification via modulation of the BMP pathway

Haematopoietic stem cells (HSCs) are produced during embryogenesis from the floor of the dorsal aorta. The localization of HSCs is dependent on the presence of instructive signals on the ventral side of the vessel. The nature of the extrinsic molecular signals that control the aortic haematopoietic niche is currently poorly understood. Here we demonstrate a novel requirement for FGF signalling in the specification of aortic haemogenic endothelium. Our results demonstrate that FGF signalling normally acts to repress BMP activity in the subaortic mesenchyme through transcriptional inhibition of bmp4, as well as through activation of two BMP antagonists, noggin2 and gremlin1a. Taken together, these findings demonstrate a key role for FGF signalling in establishment of the developmental HSC niche via its regulation of BMP activity in the subaortic mesenchyme. These results should help inform strategies to recapitulate the development of HSCs in vitro from pluripotent precursors.

Flk-1/KDR mediates ethanol-stimulated endothelial cell Notch signaling and angiogenic activity

We previously reported that ethanol (EtOH) stimulates endothelial angiogenic activity mediated via a notch- and angiopoietin-1 (Ang-1) pathway. As crosstalk exists between notch and vascular endothelial growth factor (VEGF) signaling, we examined whether the VEGF receptor (VEGFR) Flk-1 (fetal liver kinase 1) mediates EtOH-stimulated notch signaling and angiogenic activity.

METHODS AND RESULTS

Treatment of human coronary artery endothelial cells (HCAECs) with EtOH (1-50 mM, 24 h) dose-dependently increased Flk-1 expression with a maximum increase observed at 25 mM EtOH. Ethanol treatment activated both Flk-1 and Flt-1 (FMS-like tyrosine kinase 1) as indicated by their phosphorylation, and subsequent stimulation of Akt. EtOH activation of Flk-1 was inhibited by the VEGFR inhibitor SU5416. Gene silencing of Flk-1 using small interfering RNA inhibited the EtOH-induced increase in notch receptors 1 and 4 and notch target gene (hairy enhancer of split-related transcription factor 1) mRNA. Knockdown of Flk-1 inhibited EtOH-induced Ang-1/Tie-2 mRNA expression and blocked EtOH-induced HCAEC network formation on Matrigel, a response that was restored by notch ligand, notch ligand delta-like ligand 4, treatment. In vivo, moderate alcohol feeding increased vascular remodeling in mouse ischemic hindlimbs.

CONCLUSIONS

These data demonstrate that EtOH activates Flk-1 and Flt-1 receptors in HCAECs and promotes angiogenic activity via an Flk-1/notch pathway. These effects of EtOH may be relevant to the influence of moderate alcohol consumption on cardiovascular health.

Inhibition of Delta-like 4 mediated signaling induces abortion in mice due to deregulation of decidual angiogenesis

OBJECTIVE

To explore whether the Dll4/Notch1 pathway plays a key role in regulating the vascular endothelial growth factor (VEGF)/VEGF receptor 2 (VEGFR2) driven decidual angiogenesis and related pregnancy through induction of a tip/stalk phenotype.

METHODS

Progesterone-replaced ovariectomized pregnant mice received a single injection of YW152F (Dll4 blocking antibody, BAb) or placebo at embryonic day (E) 4.5. Animals were sacrificed at different time points; blood and uterus were collected for further analysis. Number of embryos and implantation site, uteri weight, and serum progesterone levels were assessed. Alterations in the tip/stalk phenotype were determined by quantitative immunofluorescent analysis of vascularization, Dll4 expression, cellular proliferation and apoptosis in uterine sections.

RESULTS

Abrogation of Dll4 signaling leads to a promiscuous expression of Dll4, increased cell proliferation, apoptosis and vascularization at E 6.5. Such an abrogation was associated with a dramatic disruption of embryo growth and development starting at E 9.5.

DISCUSSION

The observed promiscuous expression of Dll4 and the increase in cell proliferation, apoptosis and vascularization are events compatible with loss of the tip/stalk phenotype. Excessive (although very likely defective) decidual angiogenesis due to such vascular alterations is the most likely cause of subsequent interruption of embryo development and related pregnancy in Dll4 treated mice.

CONCLUSIONS

Dll4 plays a key role in regulating decidual angiogenesis and related pregnancy through induction of a tip/stalk phenotype.

Zebrafish models of dyslipidemia: relevance to atherosclerosis and angiogenesis

Lipid and lipoprotein metabolism in zebrafish and in humans are remarkably similar. Zebrafish express all major nuclear receptors, lipid transporters, apolipoproteins and enzymes involved in lipoprotein metabolism. Unlike mice, zebrafish express cetp and the Cetp activity is detected in zebrafish plasma. Feeding zebrafish a high cholesterol diet, without any genetic intervention, results in significant hypercholesterolemia and robust lipoprotein oxidation, making zebrafish an attractive animal model to study mechanisms relevant to early development of human atherosclerosis. These studies are facilitated by the optical transparency of zebrafish larvae and the availability of transgenic zebrafish expressing fluorescent proteins in endothelial cells and macrophages. Thus, vascular processes can be monitored in live animals. In this review article, we discuss recent advances in using dyslipidemic zebrafish in atherosclerosis-related studies. We also summarize recent work connecting lipid metabolism with regulation of angiogenesis, the work that considerably benefited from using the zebrafish model. These studies uncovered the role of aibp, abca1, abcg1, mtp, apoB, and apoC2 in regulation of angiogenesis in zebrafish and paved the way for future studies in mammals, which may suggest new therapeutic approaches to modulation of excessive or diminished angiogenesis contributing to the pathogenesis of human disease.

Neovascularization and hematopoietic stem cells

Vasculogenesis and angiogenesis are the major forms of blood vessel formation. Angiogenesis is the process where new vessels grow from pre-existing blood vessels, and is very important in the functional recovery of pathological conditions, such as wound healing and ischemic heart diseases. The development of better animal model and imaging technologies in past decades has greatly enriched our understanding on vasculogenesis and angiogenesis processes. Hypoxia turned out to be an important driving force for angiogenesis in various ischemic conditions. It stimulates expression of many growth factors like vascular endothelial growth factor, platelet-derived growth factor, insulin-like growth factor, and fibroblast growth factor, which play critical role in induction of angiogenesis. Other cellular components like monocytes, T cells, neutrophils, and platelets also play significant role in induction and regulation of angiogenesis. Various stem/progenitor cells also being recruited to the ischemic sites play crucial role in the angiogenesis process. Pre-clinical studies showed that stem/progenitor cells with/without combination of growth factors induce neovascularization in the ischemic tissues in various animal models. In this review, we will discuss about the fundamental factors that regulate the angiogenesis process and the use of stem cells as therapeutic regime for the treatment of ischemic diseases.

Regulation of angiogenesis via Notch signaling in breast cancer and cancer stem cells

Breast cancer angiogenesis is elicited and regulated by a number of factors including the Notch signaling. Notch receptors and ligands are expressed in breast cancer cells as well as in the stromal compartment and have been implicated in carcinogenesis. Signals exchanged between neighboring cells through the Notch pathway can amplify and consolidate molecular differences, which eventually dictate cell fates. Notch signaling and its crosstalk with many signaling pathways play an important role in breast cancer cell growth, migration, invasion, metastasis and angiogenesis, as well as cancer stem cell (CSC) self-renewal. Therefore, significant attention has been paid in recent years toward the development of clinically useful antagonists of Notch signaling. Better understanding of the structure, function and regulation of Notch intracellular signaling pathways, as well as its complex crosstalk with other oncogenic signals in breast cancer cells will be essential to ensure rational design and application of new combinatory therapeutic strategies. Novel opportunities have emerged from the discovery of Notch crosstalk with inflammatory and angiogenic cytokines and their links to CSCs. Combinatory treatments with drugs designed to prevent Notch oncogenic signal crosstalk may be advantageous over λ secretase inhibitors (GSIs) alone. In this review, we focus on the more recent advancements in our knowledge of aberrant Notch signaling contributing to breast cancer angiogenesis, as well as its crosstalk with other factors contributing to angiogenesis and CSCs.

Etv5a regulates the proliferation of ventral mesoderm cells and the formation of hemato-vascular derivatives

Hematopoietic and vascular endothelial cells constitute the circulatory system and are both generated from the ventral mesoderm. However, the molecules and signaling pathways involved in ventral mesoderm formation and specification remain unclear. We found that zebrafish etv5a was expressed in the ventral mesoderm during gastrulation. Knockdown of Etv5a using morpholinos increased the proliferation of ventral mesoderm cells and caused defects in hematopoietic derivatives and in vascular formation. By contrast, the formation of other mesodermal derivatives, such as pronephros, somites and the gut wall, was not affected. Knockdown specificity was further confirmed by overexpression of an etv5a construct lacking its acidic domain. In conclusion, our data reveal that etv5a is essential for the inhibition of ventral mesoderm cell proliferation and for the formation of the hemato-vascular lineage.

CCR2 deficiency, dysregulation of Notch signaling, and spontaneous pulmonary arterial hypertension

In pulmonary arterial hypertension (PAH), there is overexpression of the chemokine, C-C chemokine ligand type 2 (CCL2), and infiltration of myeloid cells into the pulmonary vasculature. Inhibition of CCL2 in animals decreases PAH, suggesting that the CCL2 receptor (CCR2) plays a role in PAH development. To test this hypothesis, we exposed wild-type (WT) and CCR2-deficient (Ccr2(-/-)) mice to chronic hypobaric hypoxia to induce PAH. After hypoxic stress, Ccr2(-/-) mice displayed a more severe PAH phenotype, as demonstrated by increased right ventricular (RV) systolic pressures, RV hypertrophy, and tachycardia relative to WT mice. However, these mice also exhibited increased RV systolic pressures and increased pulmonary artery muscularization under normoxic conditions. Moreover, Ccr2(-/-) mice displayed decreased pulmonary vascular branching at 3 weeks of age and increased vascular muscularization at birth, suggesting that an abnormality in pulmonary vascular development leads to spontaneous PAH in these animals. No significant differences in cytokine responses were observed between WT and Ccr2(-/-) mice during either normoxia or hypoxia. However, Ccr2(-/-) mice displayed increased Notch-3 signaling and dysregulated Notch ligand expression, suggesting a possible cause for their abnormal pulmonary vascular development. Our findings imply that CCR2 does not directly contribute to the development of PAH, but does play a previously unrecognized role in pulmonary vasculature development and remodeling wherein the absence of CCR2 results in spontaneous PAH, most likely via dysregulation of Notch signaling. Our results demonstrate that CCR2 has impacts beyond leukocyte recruitment, and is required for the proper expression of Notch signaling molecules.

Inhibition of patched-1 prevents injury-induced neointimal hyperplasia

OBJECTIVE

To determine the role of patched receptor (Ptc)-1 in mediating pulsatile flow-induced changes in vascular smooth muscle cell growth and vascular remodeling.

APPROACH AND RESULTS

In vitro, human coronary arterial smooth muscle cells were exposed to normal or pathological low pulsatile flow conditions for 24 hours using a perfused transcapillary flow system. Low pulsatile flow increased vascular smooth muscle cell proliferation when compared with normal flow conditions. Inhibition of Ptc-1 by cyclopamine attenuated low flow-induced increases in Notch expression while concomitantly decreasing human coronary arterial smooth muscle cell growth to that similar under normal flow conditions. In vivo, ligation injury-induced low flow increased vascular smooth muscle cell growth and vascular remodeling, while increasing Ptc-1/Notch expression. Perivascular delivery of Ptc-1 small interfering RNA by pluronic gel inhibited the pathological low flow-induced increases in Ptc-1/Notch expression and markedly reduced the subsequent vascular remodeling.

CONCLUSIONS

These results suggest that pathological low flow stimulates smooth muscle cell growth in vitro and vascular remodeling in vivo via Ptc-1 regulation of Notch signaling.