Vascular Endothelial Growth Factor and Its Receptors in Embryonic Zebrafish Blood Vessel Development

Topical Application of Baicalin Combined with Echinacoside Ameliorates Psoriatic Skin Lesions by Suppressing the Inflammation-Related TNF Signaling Pathway and the Angiogenesis-Related VEGF Signaling Pathway

Baicalin (BAI), the main active component of Scutellaria baicalensis, has significant anti-inflammatory and antibacterial effects. Echinacoside (ECH), an active component from Echinacea purpurea, has significant antiangiogenesis and antioxidant effects. In previous studies, BAI or ECH has been used for some skin inflammation problems by topical treatment. Psoriasis (PSO) is a common inflammatory skin disease with typical features such as excessive inflammatory response and vascular proliferation in skin lesions. Because of the anti-inflammatory effect of BAI and the antiangiogenic activity of ECH, it is proposed that the combination of BAI and ECH can ameliorate psoriatic skin lesions better than a single component. This study aims to explore the effects and potential mechanisms of BAI combined with ECH on imiquimod (IMQ)-induced psoriatic skin lesions by topical treatment. Transcriptome analysis first showed that the TNF signaling pathway and the VEGF signaling pathway were significantly enriched in IMQ-induced psoriatic skin lesions. Topical application of BAI combined with ECH could ameliorate IMQ-induced skin lesions in mice, especially the better effects of B2-E1 (BAI/ECH = 2:1). Network pharmacology analysis and molecular docking indicated that BAI-treated PSO on the skin by regulating the TNF signaling pathway, and ECH treated PSO on the skin by regulating the VEGF signaling pathway. Meanwhile, the ELISA test and the qPCR assay showed that BAI combined with ECH could inhibit the expression of key cytokines and genes related to the TNF signaling pathway and the VEGF signaling pathway. Zebrafish experiments demonstrated the anti-inflammatory and antiangiogenic effects of BAI combined with ECH and revealed the potential mechanisms associated with regulating the inflammation-related TNF signaling pathway and the angiogenesis-related VEGF signaling pathway. This suggested that BAI combined with ECH may be a promising topical agent to ameliorate psoriatic skin lesions in the future.

Zebrafish functional xenograft vasculature platform identifies PF-502 as a durable vasculature normalization drug

Tumor vasculature often exhibits disorder and inefficiency. Vascular normalization offers potential for alleviating hypoxia and optimizing drug delivery in tumors. However, identifying effective agents is hindered by a lack of robust screening. We aimed to establish a comprehensive method using the zebrafish functional xenograft vasculature platform (zFXVP) to visualize and quantify tumor vasculature changes. Employing zFXVP, we systematically screened compounds, identifying PF-502 as a robust vascular normalization agent. Mechanistic studies showed PF-502 induces endothelial cell-cycle arrest, streamlines vasculature, and activates Notch1 signaling, enhancing stability and hemodynamics. In murine models, PF-502 exhibited pronounced vascular normalization and improved drug delivery at a sub-maximum tolerated dose. These findings highlight zFXVP's utility and suggest PF-502 as a promising adjunctive for vascular normalization in clinical settings.

Nanoplastics exposure induces vascular malformation by interfering with the VEGFA/VEGFR pathway in zebrafish (Danio rerio)

The widespread accumulation and adverse effects of nanoplastics (NPs) are a growing concern for environmental and human health. However, the potential toxicological effects of nanoplastics, especially on vascular development, have not been well studied. In this study, the zebrafish model was utilized to systematically study the developmental toxicity of nanoplastics exposure at different concentrations with morphological, histological, and molecular levels. The results revealed developmental defects in zebrafish embryos after exposure to different concentrations of nanoplastics. Specifically, the morphological deformities, including pericardial oedema and spine curvature, as well as the abnormal body length and the rates of survival and hatching were induced after nanoplastics exposure in zebrafish embryos. In addition, we found that nanoplastics exposure could induce vascular malformation, including the ectopic sprouting of intersegmental vessels (ISVs), malformation of superficial ocular vessels (SOVs), and overgrowth of the common cardinal vein (CCV), as well as the disorganized vasculature of the subintestinal venous plexus (SIVP). Moreover, further study indicated that SU5416, a specific vascular endothelial growth factor receptor (VEGFR) inhibitor, partially rescued the nanoplastics exposure-impaired vasculature, suggesting that the VEGFA/VEGFR pathway might be associated with nanoplastics-induced vascular malformation in zebrafish embryos. Further quantitative polymerase chain reaction assays revealed that the mRNA levels of VEGFA/VEGFR pathway-related genes, including vegfa, nrp1, klf6a, flt1, fih-1, flk1, cldn5a, and rspo3, were altered in different groups, indicating that nanoplastics exposure interferes with the VEGFA/VEGFR pathway, thereby inducing vascular malformation during the early developmental stage in zebrafish embryos. Therefore, our findings illustrated that nanoplastics might induce vascular malformation by regulating VEGFA/VEGFR pathway-related genes at the early developmental stage in zebrafish.

Zebrafish xenografts as a fast screening platform for bevacizumab cancer therapy

Despite promising preclinical results, average response rates to anti-VEGF therapies, such as bevacizumab, are reduced for most cancers, while incurring in remarkable costs and side effects. Currently, there are no biomarkers available to select patients that can benefit from this therapy. Depending on the individual tumor, anti-VEGF therapies can either block or promote metastasis. In this context, an assay able to predict individual responses prior to treatment, including the impact on metastasis would prove of great value to guide treatment options. Here we show that zebrafish xenografts are able to reveal different responses to bevacizumab in just 4 days, evaluating not only individual tumor responses but also the impact on angiogenesis and micrometastasis. Importantly, we perform proof-of-concept experiments where clinical responses in patients were compared with their matching zebrafish Patient-Derived Xenografts - zAvatars, opening the possibility of using the zebrafish model to screen bevacizumab therapy in a personalized manner.

Rebelo de Almeida et al. describe the application of zebrafish tumor xenografts (zAvatars) to analyse the efficacy of bevacizumab (FDA approved drug) to treat cancer patients with highly variable outcomes. The authors suggest that these zAvatars could be used as a predictive model to determine whether or not bevacizumab treatment would be efficient for individual patients.

Competitive binding between Seryl-tRNA synthetase/YY1 complex and NFKB1 at the distal segment results in differential regulation of human vegfa promoter activity during angiogenesis

Vascular endothelial growth factor (VEGF) plays a pivotal role in angiogenesis. Previous studies focused on transcriptional regulation modulated by proximal upstream cis-regulatory elements (CREs) of the human vegfa promoter. However, we hypothesized that distal upstream CREs may also be involved in controlling vegfa transcription. In this study, we found that the catalytic domain of Seryl-tRNA synthetase (SerRS) interacted with transcription factor Yin Yang 1 (YY1) to form a SerRS/YY1 complex that negatively controls vegfa promoter activity through binding distal CREs at -4654 to -4623 of vegfa. Particularly, we demonstrated that the -4654 to -4623 segment, which predominantly controls vegfa promoter activity, is involved in competitive binding between SerRS/YY1 complex and NFKB1. We further showed that VEGFA protein and blood vessel development were reduced by overexpression of either SerRS or YY1, but enhanced by the knockdown of either SerRS or yy1. In contrast, these same parameters were enhanced by overexpression of NFKB1, but reduced by knockdown of nfkb1. Therefore, we suggested that SerRS does not bind DNA directly but form a SerRS/YY1 complex, which functions as a negative effector to regulate vegfa transcription through binding at the distal CREs; while NFKB1 serves as a positive effector through competing with SerRS/YY1 binding at the overlapping CREs.

Dose-dependent effects of gamma radiation on the early zebrafish development and gene expression

Ionizing radiation from natural sources or anthropogenic activity has the potential to cause oxidative stress or genetic damage in living organisms, through the ionization and excitation of molecules and the subsequent production of free radicals and reactive oxygen species (ROS). The present work focuses on radiation-induced biological effects using the zebrafish (Danio rerio) vertebrate model. Changes in developmental traits and gene expression in zebrafish were assessed after continuous external gamma irradiation (0.4, 3.9, 15 and 38 mGy/h) with corresponding controls, starting at 2.5 hours post fertilization (hpf) and lasting through embryogenesis and the early larval stage. The lowest dose rate corresponded to recommended benchmarks at which adverse effects are not expected to occur in aquatic ecosystems (2-10 mGy/day). The survival observed at 96 hours post fertilization (hpf) in the 38 mGy/h group was significantly lower, while other groups showed no significant difference compared to controls. The total hatching was significantly lower from controls in the 15 mGy/h group and a delay in hatching onset in the 0.4 mGy/h group was observed. The deformity frequency was significantly increased by prolonged exposure duration at dose rates ≥ 0.4 mGy/h. Molecular responses analyzed by RNA-seq at gastrulation (5.5 hpf transcriptome) indicate that the radiation induced adverse effects occurred during the earliest stages of development. A dose-response relationship was found in the numbers of differentially regulated genes in exposure groups compared to controls at a total dose as low as 1.62 mGy. Ingenuity Pathway Analysis identified retinoic acid receptor activation, apoptosis, and glutathione mediated detoxification signaling as the most affected pathways in the lower dose rate (0.54 mGy/h), while eif2 and mTOR, i.e., involved in the modulation of angiogenesis, were most affected in higher dose rates (5.4 and 10.9 mGy/h). By comparing gene expression data, myc was found to be the most significant upstream regulator, followed by tp53, TNF, hnf4a, TGFb1 and cebpa, while crabp2b and vegfab were identified as most frequent downstream target genes. These genes are associated with various developmental processes. The present findings show that continuous gamma irradiation (≥ 0.54 mGy/h) during early gastrula causes gene expression changes that are linked to developmental defects in zebrafish embryos.

Current Perspectives on the Use of Anti-VEGF Drugs as Adjuvant Therapy in Glaucoma

The approval of one of the first anti-vascular endothelial growth factor (VEGF) agents for the treatment of neovascular age-related macular degeneration one decade ago marked the beginning of a new era in the management of several sight-threatening retinal diseases. Since then, emerging evidence has demonstrated the utility of these therapies for the treatment of other ocular conditions characterized by elevated VEGF levels. In this article we review current perspectives on the use of anti-VEGF drugs as adjuvant therapy in the management of neovascular glaucoma (NVG). The use of anti-VEGFs for modifying wound healing in glaucoma filtration surgery (GFS) is also reviewed. Selected studies investigating the use of anti-VEGF agents or antimetabolites in GFS or the management of NVG have demonstrated that these agents can improve surgical outcomes. However, anti-VEGF agents have yet to demonstrate specific advantages over the more established agents commonly used today. Further studies are needed to evaluate the duration of action, dosing intervals, and toxicity profile of these treatments.

GUCA1A mutation causes maculopathy in a five-generation family with a wide spectrum of severity

PURPOSE

The aim of this study was to investigate the genetic basis and pathogenic mechanism of variable maculopathies, ranging from mild photoreceptor degeneration to central areolar choroidal dystrophy, in a five-generation family.

METHODS

Clinical characterizations, whole-exome sequencing, and genome-wide linkage analysis were carried out on the family. Zebrafish models were used to investigate the pathogenesis of GUCA1A mutations.

RESULTS

A novel mutation, GUCA1A p.R120L, was identified in the family and predicted to alter the tertiary structure of guanylyl cyclase-activating protein 1, a photoreceptor-expressed protein encoded by the GUCA1A gene. The mutation was shown in zebrafish to cause significant disruptions in photoreceptors and retinal pigment epithelium, together with atrophies of retinal vessels and choriocapillaris. Those phenotypes could not be fully rescued by exogenous wild-type GUCA1A, suggesting a likely gain-of-function mechanism for p.R120L. GUCA1A p.D100E, another mutation previously implicated in cone dystrophy, also impaired the retinal pigment epithelium and photoreceptors in zebrafish, but probably via a dominant negative effect.

CONCLUSION

We conclude that GUCA1A mutations could cause significant variability in maculopathies, including central areolar choroidal dystrophy, which represents a severe pattern of maculopathy. The diverse pathogenic modes of GUCA1A mutations may explain the phenotypic diversities.Genet Med advance online publication 26 January 2017.

Vascular toxicity of ultra-small TiO2 nanoparticles and single walled carbon nanotubes in vitro and in vivo

Ultra-small nanoparticles (USNPs) at 1-3 nm are a subset of nanoparticles (NPs) that exhibit intermediate physicochemical properties between molecular dispersions and larger NPs. Despite interest in their utilization in applications such as theranostics, limited data about their toxicity exist. Here the effect of TiO2-USNPs on endothelial cells in vitro, and zebrafish embryos in vivo, was studied and compared to larger TiO2-NPs (30 nm) and to single walled carbon nanotubes (SWCNTs). In vitro exposure showed that TiO2-USNPs were neither cytotoxic, nor had oxidative ability, nevertheless were genotoxic. In vivo experiment in early developing zebrafish embryos in water at high concentrations of TiO2-USNPs caused mortality possibly by acidifying the water and caused malformations in the form of pericardial edema when injected. Myo1C involved in glomerular development of zebrafish embryos was upregulated in embryos exposed to TiO2-USNPs. They also exhibited anti-angiogenic effects both in vitro and in vivo plus decreased nitric oxide concentration. The larger TiO2-NPs were genotoxic but not cytotoxic. SWCNTs were cytotoxic in vitro and had the highest oxidative ability. Neither of these NPs had significant effects in vivo. To our knowledge this is the first study evaluating the effects of TiO2-USNPs on vascular toxicity in vitro and in vivo and this strategy could unravel USNPs potential applications.

Anti-angiogenic effect of auranofin on HUVECs in vitro and zebrafish in vivo

Angiogenesis plays an essential role in many physiological and pathological processes. Auranofin (Ridaura®), an important gold(I) complex, is used to treat rheumatoid arthritis. However, the effect of auranofin on blood vessel formation is still unclear. In this study, we investigated the anti-angiogenic activity of auranofin on human umbilical vein endothelial cells (HUVEC) in vitro and zebrafish in vivo. Our results showed that auranofin could inhibit the proliferation, migration and tube formation of HUVECs and disrupted the formation of intersegmental vessels and the subintestinal vessels of zebrafish embryos. Auranofin inhibited the phosphorylation of vascular endothelial growth factor 2 (p-VEGFR2) on HUVECs and suppressed the vascular endothelial growth factor (VEGF) signaling pathway (vegfa, flt-1, kdr) but not thioredoxin reductase (TrxR) on zebrafish. Our study suggested that auranofin might serve as a potential anti-angiogenic compound candidate.

Embryonic exposure to sodium arsenite perturbs vascular development in zebrafish

Exposure to arsenic in its inorganic form, arsenite, causes adverse effects to many different organs and tissues. Here, we have investigated arsenite-induced adverse effects on vascular tissues in the model organism zebrafish, Danio rerio. Zebrafish embryos were exposed to arsenite at different exposure windows and the susceptibility to vascular tissue damage was recorded at 72hours post fertilization (hpf). Intersegmental vessel sprouting and growth was most perturbed by exposure to arsenite during the 24-48hpf window, while disruption in the condensation of the caudal vein plexus was more often observed at the 48-72hpf exposure window, reflecting when these structures develop during normal embryogenesis. The vascular growth rate was decreased by arsenite exposure, and deviated from that of control embryos at around 24-26.5hpf. We further mapped changes in expression of key regulators of angiogenesis and vasculogenesis. Downregulation of vascular endothelial growth factor receptor 1/fms-related tyrosine kinase 1 (vegfr1/flt1) expression was evident already at 24hpf, coinciding with the decreased vascular growth rate. At later time points, matrix metalloproteinase 9 (mmp9) expression was upregulated, suggesting that arsenite affects the composition of the extracellular matrix. In total, the expression of eight key factors involved in different aspects of vascularization was significantly altered by arsenic exposure. In conclusion, our results show that arsenite is a potent vascular disruptor in the developing zebrafish embryo, a finding that calls for an evaluation of arsenite as a developmental vascular toxicant in mammalian model systems.

Dihydroartemisinin promotes angiogenesis during the early embryonic development of zebrafish

AIM

To investigate the embryotoxicity of dihydroartemisinin (DHA), the main active metabolite of artemisinin, in zebrafish, and explore the corresponding mechanisms.

METHODS

The embryos of wild type and TG (flk1:GFP) transgenic zebrafish were exposed to DHA. Developmental phenotypes of the embryos were observed. Development of blood vessels was directly observed in living embryos of TG (flk1:GFP) transgenic zebrafish under fluorescence microscope. The expression of angiogenesis marker genes vegfa, flk1, and flt1 in the embryos was detected using real-time PCR and RNA in situ hybridization assays.

RESULTS

Exposure to DHA (1-10 mg/L) dose-dependently caused abnormal zebrafish embryonic phenotypes in the early developmental stage. Furthermore, exposure to DHA (10 mg/L) resulted in more pronounced embryonic angiogenesis in TG (flk1:GFP) zebrafish line. Exposure to DHA (10 mg/L) significantly increased the mRNA expression of vegfa, flk1, and flt1 in the embryos. Knockdown of the flk1 protein partially blocked the effects of DHA on embryogenesis.

CONCLUSION

DHA causes abnormal embryonic phenotypes and promotes angiogenesis in zebrafish early embryonic development, demonstrating the potential embryotoxicity of DHA.

Microarray profiling reveals CXCR4a is downregulated by blood flow in vivo and mediates collateral formation in zebrafish embryos

The response to hemodynamic force is implicated in a number of pathologies including collateral vessel development. However, the transcriptional effect of hemodynamic force is extremely challenging to examine in vivo in mammals without also detecting confounding processes such as hypoxia and ischemia. We therefore serially examined the transcriptional effect of preventing cardiac contraction in zebrafish embryos which can be deprived of circulation without experiencing hypoxia since they obtain sufficient oxygenation by diffusion. Morpholino antisense knock-down of cardiac troponin T2 (tnnt2) prevented cardiac contraction without affecting vascular development. Gene expression in whole embryo RNA from tnnt2 or control morphants at 36, 48, and 60 h postfertilization (hpf) was assessed using Affymetrix GeneChip Zebrafish Genome Arrays (>14,900 transcripts). We identified 308 differentially expressed genes between tnnt2 and control morphants. One such (CXCR4a) was significantly more highly expressed in tnnt2 morphants at 48 and 60 hpf than controls. In situ hybridization localized CXCR4a upregulation to endothelium of both tnnt2 morphants and gridlock mutants (which have an occluded aorta preventing distal blood flow). This upregulation appears to be of functional significance as either CXCR4a knock-down or pharmacologic inhibition impaired the ability of gridlock mutants to recover blood flow via collateral vessels. We conclude absence of hemodynamic force induces endothelial CXCR4a upregulation that promotes recovery of blood flow.

Neuropilin-1 in regulation of VEGF-induced activation of p38MAPK and endothelial cell organization

Vascular endothelial growth factor (VEGF)-A regulates vascular development and angiogenesis. VEGF isoforms differ in ability to bind coreceptors heparan sulfate (HS) and neuropilin-1 (NRP1). We used VEGF-A165 (which binds HS and NRP1), VEGF-A121 (binds neither HS nor NRP1), and parapoxvirus VEGF-E-NZ2 (binds NRP1 but not HS) to investigate the role of NRP1 in organization of endothelial cells into vascular structures. All 3 ligands induced similar level of VEGFR-2 tyrosine phosphorylation in the presence of NRP1. In contrast, sprouting angiogenesis in differentiating embryonic stem cells (embryoid bodies), formation of branching pericyte-embedded vessels in subcutaneous matrigel plugs, and sprouting of intersegmental vessels in developing zebrafish were induced by VEGF-A165 and VEGF-E-NZ2 but not by VEGF-A121. Analyses of recombinant factors with NRP1-binding gain- and loss-of-function properties supported the conclusion that NRP1 is critical for VEGF-induced sprouting and branching of endothelial cells. Signal transduction antibody arrays implicated NRP1 in VEGF-induced activation of p38MAPK. Inclusion of the p38MAPK inhibitor SB203580 in VEGF-A165-containing matrigel plugs led to attenuated angiogenesis and poor association with pericytes. Our data strongly indicate that the ability of VEGF ligands to bind NRP1 influences p38MAPK activation, and formation of functional, pericyte-associated vessels.

Zebrafish Sox7 and Sox18 function together to control arterial-venous identity

Sox7 and Sox18 are members of the F-subgroup of Sox transcription factors family and are mostly expressed in endothelial compartments. In humans, dominant mutations in Sox18 are the underlying cause of the severe hypotrichosis-lymphedema-telangiectasia disorder characterized by vascular defects. However little is known about which vasculogenic processes Sox7 and Sox18 regulate in vivo. We cloned the orthologs of Sox7 and Sox18 in zebrafish, analysed their expression pattern and performed functional analyses. Both genes are expressed in the lateral plate mesoderm during somitogenesis. At later stages, Sox18 is expressed in all axial vessels whereas Sox7 expression is mainly restricted to the dorsal aorta. Knockdown of Sox7 or Sox18 alone failed to reveal any phenotype. In contrast, blocking the two genes simultaneously led to embryos displaying dysmorphogenesis of the proximal aorta and arteriovenous shunts, all of which can account for the lack of circulation observed in the trunk and tail. Gene expression analyses performed with general endothelial markers on double morphants revealed that Sox7 and Sox18 are dispensable for the initial specification and positioning of the major trunk vessels. However, morphants display ectopic expression of the venous Flt4 marker in the dorsal aorta and a concomitant reduction of the artery-specific markers EphrinB2a and Gridlock. The striking similarities between the phenotype of Sox7/Sox18 morphants and Gridlock mutants strongly suggest that Sox7 and Sox18 control arterial-venous identity by regulating Gridlock expression.

Angiomotin regulates endothelial cell migration during embryonic angiogenesis

The development of the embryonic vascular system into a highly ordered network requires precise control over the migration and branching of endothelial cells (ECs). We have previously identified angiomotin (Amot) as a receptor for the angiogenesis inhibitor angiostatin. Furthermore, DNA vaccination targeting Amot inhibits angiogenesis and tumor growth. However, little is known regarding the role of Amot in physiological angiogenesis. We therefore investigated the role of Amot in embryonic neovascularization during zebrafish and mouse embryogenesis. Here we report that knockdown of Amot in zebrafish reduced the number of filopodia of endothelial tip cells and severely impaired the migration of intersegmental vessels. We further show that 75% of Amot knockout mice die between embryonic day 11 (E11) and E11.5 and exhibit severe vascular insufficiency in the intersomitic region as well as dilated vessels in the brain. Furthermore, using ECs differentiated from embryonic stem (ES) cells, we demonstrate that Amot-deficient cells have intact response to vascular endothelial growth factor (VEGF) in regard to differentiation and proliferation. However, the chemotactic response to VEGF was abolished in Amot-deficient cells. We provide evidence that Amot is important for endothelial polarization during migration and that Amot controls Rac1 activity in endothelial and epithelial cells. Our data demonstrate a critical role for Amot during vascular patterning and endothelial polarization.

Duplicate VegfA genes and orthologues of the KDR receptor tyrosine kinase family mediate vascular development in the zebrafish

Vascular endothelial growth factor A (VEGFA) and the type III receptor tyrosine kinase receptors (RTKs) are both required for the differentiation of endothelial cells (vasculogenesis) and for the sprouting of new capillaries (angiogenesis). We have isolated a duplicated zebrafish VegfA locus, termed VegfAb, and a duplicate RTK locus with homology to KDR/FLK1 (named Kdrb). Morpholino-disrupted VegfAb embryos develop a normal circulatory system until approximately 2 to 3 days after fertilization (dpf), when defects in angiogenesis permit blood to extravasate into many tissues. Unlike the VegfAa(121) and VegfAa(165) isoforms, the VegfAb isoforms VegfAb(171) and VegfAb(210) are not normally secreted when expressed in mammalian tissue culture cells. The Kdrb locus encodes a 1361-amino acid transmembrane receptor with strong homology to mammalian KDR. Combined knockdown of both RTKs leads to defects in vascular development, suggesting that they cooperate in mediating the vascular effects of VegfA in zebrafish development. Both VegfAa and VegfAb can individually bind and promote phosphorylation of both Flk1 (Kdra) and Kdrb proteins in vitro. Taken together, our data support a model in the zebrafish, in which duplicated VegfA and multiple type III RTKs mediate vascular development.

Site-directed Mutagenesis in the B-Neuropilin-2 Domain Selectively Enhances Its Affinity to VEGF165, but Not to Semaphorin 3F

Neuropilins (NRPs) are 130-kDa receptors that bind and respond to the class 3 semaphorin family of axon guidance molecules (SEMAs) and to members of the vascular endothelial growth factor (VEGF) family of angiogenic factors. Two NRPs have been reported so far, NRP1 and NRP2. Unlike NRP1, little is known about NRP2 interactions with its ligands, VEGF165 and SEMA3F. Cell binding studies reveal that VEGF165 and SEMA3F bind NRP2 with similar affinities, 5.2 and 3.9 nM, respectively, and are competitive NRP2 ligands. Immunoprecipitation studies show that the B (b1b2) extracellular domain of NRP2 is sufficient for VEGF165 binding, whereas SEMA3F requires both the A (a1a2) and B domains. To identify residues of B-NRP2 involved in VEGF165 binding, point mutations were introduced by site-directed mutagenesis. VEGF165 is a basic protein. Reduction of the electronegative potential of B-NRP2 by exchanging acidic residues for uncharged alanine (B-NRP2 E284A,E291A) in the 280-290 b1-NRP2 loop resulted in a 2-fold reduction in VEGF165 affinity. Conversely, enhancing the electronegative potential (B-NRP2 R287E,N290D and R287E,N290S) significantly increased VEGF165 affinity for B-NRP2 by 8- and 6.6-fold, respectively. The mutagenesis did not affect SEMA3F/B-NRP2 interactions. These results demonstrate that it is possible to alter VEGF165 affinity for NRP2 without affecting SEMA3F affinity. They also identify NRP2 residues involved in VEGF165 binding and suggest that modifications of B-NRP2 could lead to potentially high affinity selective inhibitors of VEGF165/NRP2 interactions.

Endothelial cell migration during angiogenesis

Endothelial cell migration is essential to angiogenesis. This motile process is directionally regulated by chemotactic, haptotactic, and mechanotactic stimuli and further involves degradation of the extracellular matrix to enable progression of the migrating cells. It requires the activation of several signaling pathways that converge on cytoskeletal remodeling. Then, it follows a series of events in which the endothelial cells extend, contract, and throw their rear toward the front and progress forward. The aim of this review is to give an integrative view of the signaling mechanisms that govern endothelial cell migration in the context of angiogenesis.

Endothelial signalling by the Notch ligand Delta-like 4 restricts angiogenesis

Notch signalling by the ligand Delta-like 4 (Dll4) is essential for normal vascular remodelling, yet the precise way in which the pathway influences the behaviour of endothelial cells remains a mystery. Using the embryonic zebrafish, we show that, when Dll4-Notch signalling is defective, endothelial cells continue to migrate and proliferate when they should normally stop these processes. Artificial overactivation of the Notch pathway has opposite consequences. When vascular endothelial growth factor (Vegf) signalling and Dll4-Notch signalling are both blocked, the endothelial cells remain quiescent. Thus, Dll4-Notch signalling acts as an angiogenic ;off' switch by making endothelial cells unresponsive to Vegf.

AlphaA-crystallin expression prevents gamma-crystallin insolubility and cataract formation in the zebrafish cloche mutant lens

Cataracts, the loss of lens transparency, are the leading cause of human blindness. The zebrafish embryo, with its transparency and relatively large eyes, is an excellent model for studying ocular disease in vivo. We found that the zebrafish cloche mutant, both the cloche(m39) and cloche(S5) alleles, which have defects in hematopoiesis and blood vessel development, also have lens cataracts. Quantitative examination of the living zebrafish lens by confocal microscopy showed significant increases in lens reflectance. Histological analysis revealed retention of lens fiber cell nuclei owing to impeded terminal differentiation. Proteomics identified gamma-crystallin as a protein that was substantially diminished in cloche mutants. Crystallins are the major structural proteins in mouse, human and zebrafish lens. Defects in crystallins have previously been shown in mice and humans to contribute to cataracts. The loss of gamma-crystallin protein in cloche was not due to lowered mRNA levels but rather to gamma-crystallin protein insolubility. AlphaA-crystallin is a chaperone that protects proteins from misfolding and becoming insoluble. The cloche lens is deficient in both alphaA-crystallin mRNA and protein during development from 2-5 dpf. Overexpression of exogenous alphaA-crystallin rescued the cloche lens phenotype, including solubilization of gamma-crystallin, increased lens transparency and induction of lens fiber cell differentiation. Taken together, these results indicate that alphaA-crystallin expression is required for normal lens development and demonstrate that cataract formation can be prevented in vivo. In addition, these results show that proteomics is a valuable tool for detecting protein alterations in zebrafish.

Neuron Restrictive Silencer Factor NRSF/REST Is a Transcriptional Repressor of Neuropilin-1 and Diminishes the Ability of Semaphorin 3A to Inhibit Keratinocyte Migration

Neuropilin-1 (NRP1) is expressed by endothelial cells and neurons and serves as a receptor for both vascular endothelial growth factor (VEGF), an angiogenesis factor, and semaphorin 3A (Sema3A), a mediator of axonal guidance. We show here that NRP1 is also expressed in keratinocytes in vitro and in vivo. However, nothing has been reported about the regulation or function of keratinocyte NRP1. Using NRP1 promoter constructs in HaCaT cells, a keratinocyte cell line, we could demonstrate that a neuron restrictive silencer element (NRSE) was implicated in transcriptional repression of the NRP1 gene. Electrophoretic mobility shift assays demonstrated that the neuron restrictive silencer factor (NRSF) binds to NRSE. Overexpression of NRSF in HaCaT cells decreased NRP1 RNA and protein, whereas a dominant negative NRSF increased NRP1. Furthermore, the histone deacetylase inhibitor trichostatin A, an inhibitor of NRSF silencing activity, also increased NRP1 levels. NRP2 expression was not affected. Epidermal growth factor (EGF) and heparin-binding EGF-like growth factor (HB-EGF) strongly up-regulated NRP1 expression, concomitant with down-regulation of NRSF. Other keratinocyte mitogens such as keratinocyte growth factor (KGF) had no effect. To address function, HaCaT cells were exposed to two NRP1 ligands, VEGF165 and Sema3A. Neither had an effect on proliferation, whereas Sema3A, but not VEGF165, inhibited cell migration. Down-regulation of NRP1 by NRSF overexpression reduced Sema3A activity. It was concluded that NRSF is a transcription factor that silences NRP1 expression and thereby diminishes the Sema3A mediated inhibition of HaCaT keratinocyte migration.