Zebrafish Tie-2 shares a redundant role with Tie-1 in heart development and regulates vessel integrity

Angpt1 binding to Tie1 regulates the signaling required for lymphatic vessel development in zebrafish

Development of the vascular system is regulated by multiple signaling pathways mediated by receptor tyrosine kinases. Among them, angiopoietin (Ang)/Tie signaling regulates lymphatic and blood vessel development in mammals. Of the two Tie receptors, Tie2 is well known as a key mediator of Ang/Tie signaling, but, unexpectedly, recent studies have revealed that the Tie2 locus has been lost in many vertebrate species, whereas the Tie1 gene is more commonly present. However, Tie1-driven signaling pathways, including ligands and cellular functions, are not well understood. Here, we performed comprehensive mutant analyses of angiopoietins and Tie receptors in zebrafish and found that only angpt1 and tie1 mutants show defects in trunk lymphatic vessel development. Among zebrafish angiopoietins, only Angpt1 binds to Tie1 as a ligand. We indirectly monitored Ang1/Tie1 signaling and detected Tie1 activation in sprouting endothelial cells, where Tie1 inhibits nuclear import of EGFP-Foxo1a. Angpt1/Tie1 signaling functions in endothelial cell migration and proliferation, and in lymphatic specification during early lymphangiogenesis, at least in part by modulating Vegfc/Vegfr3 signaling. Thus, we show that Angpt1/Tie1 signaling constitutes an essential signaling pathway for lymphatic development in zebrafish.

Response of lipid metabolism, energy supply, and cell fate in yellowstripe goby (Mugilogobius chulae) exposed to environmentally relevant concentrations atorvastatin

The usage of typical pharmaceuticals and personal care products (PPCPs) such as cardiovascular and lipid-modulating drugs in clinical care accounts for the largest share of pharmaceutical consumption in most countries. Atorvastatin (ATV), one of the most commonly used lipid-lowering drugs, is frequently detected with lower concentrations in aquatic environments owing to its wide application, low removal, and degradation rates. However, the adverse effects of ATV on non-target aquatic organisms, especially the molecular mechanisms behind the toxic effects, still remain unclear. Therefore, this study investigated the potentially toxic effects of ATV exposure (including environmental concentrations) on yellowstripe goby (Mugilogobius chulae) and addressed the multi-dimensional responses. The results showed that ATV caused typical hepatotoxicity to M. chulae. ATV interfered with lipid metabolism by blocking fatty acid β-oxidation and led to the over-consumption of lipids. Thus, the exposed organism was obliged to alter the energy supply patterns and substrates utilization pathways to keep the normal energy supply. In addition, the higher concentration of ATV exposure caused oxidative stress to the organism. Subsequently, M. chulae triggered the autophagy and apoptosis processes with the help of key stress-related transcriptional regulators FOXOs and Sestrins to degrade the damaged organelles and proteins to maintain intracellular homeostasis.

Angiopoietin 1 and integrin beta 1b are vital for zebrafish brain development

Introduction

Angiopoietin 1 (angpt1) is essential for angiogenesis. However, its role in neurogenesis is largely undiscovered. This study aimed to identify the role of angpt1 in brain development, the mode of action of angpt1, and its prime targets in the zebrafish brain.

Methods

We investigated the effects of embryonic brain angiogenesis and neural development using qPCR, in situ hybridization, microangiography, retrograde labeling, and immunostaining in the angpt1sa14264, itgb1bmi371, tekhu1667 mutant fish and transgenic overexpression of angpt1 in the zebrafish larval brains.

Results

We showed the co-localization of angpt1 with notch, delta, and nestin in the proliferation zone in the larval brain. Additionally, lack of angpt1 was associated with downregulation of TEK tyrosine kinase, endothelial (tek), and several neurogenic factors despite upregulation of integrin beta 1b (itgb1b), angpt2a, vascular endothelial growth factor aa (vegfaa), and glial markers. We further demonstrated that the targeted angpt1sa14264 and itgb1bmi371 mutant fish showed severely irregular cerebrovascular development, aberrant hindbrain patterning, expansion of the radial glial progenitors, downregulation of cell proliferation, deficiencies of dopaminergic, histaminergic, and GABAergic populations in the caudal hypothalamus. In contrast to angpt1sa14264 and itgb1bmi371 mutants, the tekhu1667 mutant fish regularly grew with no apparent phenotypes. Notably, the neural-specific angpt1 overexpression driven by the elavl3 (HuC) promoter significantly increased cell proliferation and neuronal progenitor cells but decreased GABAergic neurons, and this neurogenic activity was independent of its typical receptor tek.

Discussion

Our results prove that angpt1 and itgb1b, besides regulating vascular development, act as a neurogenic factor via notch and wnt signaling pathways in the neural proliferation zone in the developing brain, indicating a novel role of dual regulation of angpt1 in embryonic neurogenesis that supports the concept of angiopoietin-based therapeutics in neurological disorders.

Svep1 is a binding ligand of Tie1 and affects specific aspects of facial lymphatic development in a Vegfc-independent manner

Multiple factors are required to form functional lymphatic vessels. Here, we uncover an essential role for the secreted protein Svep1 and the transmembrane receptor Tie1 during the development of subpopulations of the zebrafish facial lymphatic network. This specific aspect of the facial network forms independently of Vascular endothelial growth factor C (Vegfc) signalling, which otherwise is the most prominent signalling axis in all other lymphatic beds. Additionally, we find that multiple specific and newly uncovered phenotypic hallmarks of svep1 mutants are also present in tie1, but not in tie2 or vegfc mutants. These phenotypes are observed in the lymphatic vasculature of both head and trunk, as well as in the development of the dorsal longitudinal anastomotic vessel under reduced flow conditions. Therefore, our study demonstrates an important function for Tie1 signalling during lymphangiogenesis as well as blood vessel development in zebrafish. Furthermore, we show genetic interaction between svep1 and tie1 in vivo, during early steps of lymphangiogenesis, and demonstrate that zebrafish as well as human Svep1/SVEP1 protein bind to the respective Tie1/TIE1 receptors in vitro. Since compound heterozygous mutations for SVEP1 and TIE2 have recently been reported in human glaucoma patients, our data have clinical relevance in demonstrating a role for SVEP1 in TIE signalling in an in vivo setting.

An integrated model for Gpr124 function in Wnt7a/b signaling among vertebrates

Within the central nervous system, Wnt7a/b are unambiguously discriminated from other Wnt ligands by an endothelial receptor complex made of the glycosylphosphatidylinositol (GPI)-anchored Reck and the adhesion G protein-coupled receptor (GPCR) Gpr124. Reck is a Wnt7a/b-specific receptor, while Gpr124 facilitates the delivery of Reck-bound Wnt7a/b ligands to Frizzled, through partially characterized mechanisms. We report that, in zebrafish, the Gpr124-Frizzled interactions are dominated by intracellular scaffolds that exploit the striking molecular mimicry between Gpr124 and Frizzled intracellular domains (ICDs): an internal Dvl-binding motif and a C-terminal ETTV motif that recruits Dlg4 and Magi3. By contrast, mammalian Gpr124 receptors exhibit an ICD-independent interaction mechanism governed by species-specific attributes of their transmembrane and extracellular domains. This mechanism seemingly evolved to replace the Dvl-mediated mechanism. By contrasting zebrafish, mouse, and human Gpr124, this study provides insights into the evolution of Gpr124/Reck function across the vertebrate clade, a receptor complex uniquely implicated in Wnt ligand-specific cellular responses.

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Gpr124 displays mechanistic diversification in vertebrates

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At least two partially redundant mechanisms operate in each Gpr124 ortholog

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The distinct mechanisms converge on mediating Gpr124/Frizzled interactions

Enhanced phototransformation of atorvastatin by polystyrene microplastics: Critical role of aging

Reactive oxygen species (ROS) generated from light irradiation of microplastics (MPs) can potentially affect the environmental fate of organic contaminants when they coexist in the same environment. This study investigated the effect of polystyrene (PS) MPs with different aging degrees on the phototransformation of atorvastatin (ATV) under simulated sunlight. Results showed that the presence of PS MPs facilitated the phototransformation of ATV, and the degradation rate was linearly correlated with the aging degree (i.e., carbonyl index) of MPs. The enhanced effects mainly depended on the contents of oxygen-containing functional groups of PS MPs, which increased the absorption of light energy and the generation of ROS (e.g., singlet oxygen (¹O₂) and triplet-excited state PS (³PS*)). Quenching experiments indicated that ¹O₂ generated from photosensitization of PS was the major contributor to the increased phototransformation of ATV. Additionally, the role of ³PS* became more important in the photodegradation mediated by higher degree aged MPs because much more ¹O₂ was generated from the ³PS* . PS MPs also increased the types and yields of degradation products, especially for higher degree aged MPs, despite the low effect on leachate toxicity. The findings provide a novel insight into the critical role of MPs in the fate of organic contaminants in aquatic environments.

Evaluation of VEGF mediated pro-angiogenic and hemostatic effects and chemical marker investigation for Typhae Pollen and its processed product

ETHNOPHARMACOLOGICAL RELEVANCE

Typhae Pollen (TP) is a well-known Traditional Chinese Medicine (TCM) to remove blood stasis. Carbonized Typhae Pollen (CTP), a processed product of TP after being stir-fried, has been widely applied to clinical practice with its capability of hemostasis. However, the underlying mechanism of TP and CTP are still not fully elucidated and discrimination against TP and CTP remains a challenge.

AIM OF STUDY

The aim of this study is to investigate whether TP could remove blood stasis by promoting angiogenesis and the process of carbonizing it could enhance hemostatic effect. Meanwhile, some chemical markers for quality control of CTP had better to be found.

MATERIAL AND METHODS

The changes of constituents between TP and CTP were analyzed by UPLC-QTOF-MS/MS. We investigated pro-angiogenic and hemostatic effects of TP and CTP in two zebrafish models: VRI-induced ISV insufficiency model and Ator-induced cerebral hemorrhage model. Subsequently, quantitative real-time PCR (qRT-PCR) was applied to investigate the mechanism of pharmacological effects. Finally, chemometric method was applied to find chemical markers.

RESULTS

A total of 19 compounds were identified in qualitative analysis. The loss rate of each compound was calculated and compared. Two compounds (huaicarbon A/B) could only be detected in CTP and the content of flavonoid glycosides in CTP was significantly decreased compared with TP. The average content of the three identified flavonoid aglycones (quercetin, isorhamnetin and kaempferol) was increased about 30 percent in CTP. TP promoted pro-angiogenesis by up-regulating the expression of VEGFA, flt1 and kdr. After heating process, the pro-angiogenic activity was reduced and hemostatic activity was enhanced in CTP. Then qRT-PCR analysis found that CTP could significantly up-regulate the expression of VEGFA and vWF. In the discovery of markers, 6 chemical markers for discrimination of TP and CTP were obtained by chemometric method.

CONCLUSION

Our research indicated that the pro-angiogenic activity of TP was involved in VEGF signaling pathway. After processing, hemostatic activity of CTP has been enhanced by up-regulating the expression of VEGFA and vWF. A chemical marker database was established to provide a scientific evidence for quality control, mechanism and the clinical application of TP and CTP.

A Multi-Model Pipeline for Translational Intracerebral Haemorrhage Research

Apart from acute and chronic blood pressure lowering, we have no specific medications to prevent intracerebral haemorrhage (ICH) or improve outcomes once bleeding has occurred. One reason for this may be related to particular limitations associated with the current pre-clinical models of ICH, leading to a failure to translate into the clinic. It would seem that a breakdown in the 'drug development pipeline' currently exists for translational ICH research which needs to be urgently addressed. Here, we review the most commonly used pre-clinical models of ICH and discuss their advantages and disadvantages in the context of translational studies. We propose that to increase our chances of successfully identifying new therapeutics for ICH, a bi-directional, 2- or 3-pronged approach using more than one model species/system could be useful for confirming key pre-clinical observations. Furthermore, we highlight that post-mortem/ex-vivo ICH patient material is a precious and underused resource which could play an essential role in the verification of experimental results prior to consideration for further clinical investigation. Embracing multidisciplinary collaboration between pre-clinical and clinical ICH research groups will be essential to ensure the success of this type of approach in the future.

Singlet oxygen production abilities of oxidated aromatic compounds in natural water

Singlet oxygen (¹O₂) is well known to be formed through energy transfer from excited state organic matters to O₂, playing an important role in the transformations of contaminants. However, the contribution of small oxidated aromatic compounds (OACs) to the production of ¹O₂ in surface water is unclear. In this study, 28 OACs were selected to investigate the correlations between their photochemical production abilities of ¹O₂ and molecular structures. Our results showed that the steady-state concentrations and quantum yields of ¹O₂ (Φ_1O2) generated by OACs were in the range of 7.0 × 10^-14-1.4 × 10^-12 M and 2.2 × 10^-4-4.7 × 10^-2, respectively, indicating that the photochemical production abilities of ¹O₂ by OACs varied greatly with types and positions of functional groups on the molecule. More importantly, the observed photochemical production of ¹O₂ was most notable in cases of molecules containing -OCH₃ group and benzoquinone. A good quantitative structure-property relationship model was established between ¹O₂ producing ability, energy of the lowest unoccupied molecular orbitals (E_LUMO) and the most positive net charge of hydrogen atoms (qH⁺) of OACs. In addition, the role of ¹O₂ produced by 2, 6-dimethoxy-1, 4-benzoquinone, the OAC with the highest Φ_1O2, in the photodegradation of organic contaminants was validated by the enhanced degradation of atorvastatin under simulated sunlight, suggesting that OACs ubiquitously existed in surface water may greatly affect the fate and ecological risks of organic contaminants.

Tek (Tie2) is not required for cardiovascular development in zebrafish

Angiopoietin/TIE signalling plays a major role in blood and lymphatic vessel development. In mouse, Tek (previously known as Tie2) mutants die prenatally due to a severely underdeveloped cardiovascular system. In contrast, in zebrafish, previous studies have reported that although embryos injected with tek morpholinos (MOs) exhibit severe vascular defects, tek mutants display no obvious vascular malformations. To further investigate the function of zebrafish Tek, we generated a panel of loss-of-function tek mutants, including RNA-less alleles, an allele lacking the MO-binding site, an in-frame deletion allele and a premature termination codon-containing allele. Our data show that all these mutants survive to adulthood with no obvious cardiovascular defects. MO injections into tek mutants lacking the MO-binding site or the entire tek locus cause similar vascular defects to those observed in MO-injected +/+ siblings, indicating off-target effects of the MOs. Surprisingly, comprehensive phylogenetic profiling and synteny analyses reveal that Tek was lost in the largest teleost clade, suggesting a lineage-specific shift in the function of TEK during vertebrate evolution. Altogether, these data show that Tek is dispensable for zebrafish development, and probably dispensable in most teleost species.

Insights on photochemical activities of organic components and minerals in dissolved state biochar in the degradation of atorvastatin in aqueous solution

This study systematically investigated the photocatalytic activity of dissolved state biochar (DSB) with different pyrolysis temperature to the degradation of atorvastatin (ATV), a medicine widely used to combat hyperlipidemia. It was found that the photocatalytic efficiency of DSB increased with the decrease of pyrolysis temperature, that is, DSB300 (DSB with 300 °C of pyrolysis temperature) had the greatest photocatalytic activity in same condition, which was attributed to the dual role of DSB300 as heterogeneous photocatalyst and photosensitizer. The mineral components were responsible for the heterogeneous photocatalytic activity of DSB300. Organic carbon components could synergistically enhance the heterogeneous photocatalytic activity by enhancement of electron-hole separation, and contribute to the formation of singlet oxygen (¹O₂) and triplet-excited state (³DSB*) as well. The identification of intermediate products and X-ray photoelectron spectroscopy (XPS) analysis of irradiated DSB300/ATV revealed that cross-coupling reaction between ATV and DSB existed in the photodegradation process of ATV. The detailed photodegradation pathways of ATV were proposed, which was triggered by oxygen insertion of pyrrole ring and hydroxyl addition. Meanwhile, the modification of DSB300 under irradiation was evidently attenuated with ATV as shown by multiple characterizations, which helped to keep the stability of DSB300 in photochemical reaction process.

Chronic exposure to environmentally relevant levels of simvastatin disrupts zebrafish brain gene signaling involved in energy metabolism

Simvastatin (SIM), a hypocholesterolaemic drug belonging to the statins group, is a widely prescribed pharmaceutical for prevention of cardiovascular diseases. Several studies showed that lipophilic statins, as SIM, cross the blood-brain barrier and interfere with the energy metabolism of the central nervous system in humans and mammalian models. In fish and other aquatic organisms, the effects of SIM on the brain energy metabolism are unknown, particularly following exposure to low environmentally relevant concentrations. Therefore, the present study aimed at investigating the influence of SIM on gene signaling pathways involved in brain energy metabolism of adult zebrafish (Danio rerio) following chronic exposure (90 days) to environmentally relevant SIM concentrations ranging from 8 ng/L to 1000 ng/L. Real-time PCR was used to determine the transcript levels of several genes involved in different pathways of the brain energy metabolism (glut1b, gapdh, acadm, accα, fasn, idh3a, cox4i1, and cox5aa). The findings here reported integrated well with ecological and biochemical responses obtained in a parallel study. Data demonstrated that SIM modulates transcription of key genes involved in the mitochondrial electron transport chain, in glucose transport and metabolism, in fatty acid synthesis and β-oxidation. Further, SIM exposure led to a sex-dependent transcription profile for some of the studied genes. Overall, the present study demonstrated, for the first time, that SIM modulates gene regulation of key pathways involved in the energy metabolism in fish brain at environmentally relevant concentrations.

Lessons learned from a lncRNA odyssey for two genes with vascular functions, DLL4 and TIE1

Pervasive transcription is a feature of the human genome that requires better understanding. Over the last decade or so, RNA species longer than 200 nucleotides-dubbed long non-coding RNA (lncRNAs)-had been found in sense or anti-sense orientation within or outside of genes that encode proteins. Importantly, lncRNA-mediated gene regulation and the elements that control lncRNA expression are a source of fascination among molecular biologists. In vascular biology, a dozen or so lncRNAs had been identified, and progress occurs each day. In this review, we highlighted our laboratories' contribution to the lncRNA field by discussing lessons learned from two lncRNAs in the tyrosine kinase containing immunoglobulin and epidermal growth factor homology1 (Tie1) and delta-like 4 (Dll4) loci. These genes are responsible for basic vascular patterning and pathophysiological remodeling in angiogenesis.

Vascular defects of DYRK1A knockouts are ameliorated by modulating calcium signaling in zebrafish

DYRK1A is a major causative gene in Down syndrome (DS). Reduced incidence of solid tumors such as neuroblastoma in DS patients and increased vascular anomalies in DS fetuses suggest a potential role of DYRK1A in angiogenic processes, but in vivo evidence is still scarce. Here, we used zebrafish dyrk1aa mutant embryos to understand DYRK1A function in cerebral vasculature formation. Zebrafish dyrk1aa mutants exhibited cerebral hemorrhage and defects in angiogenesis of central arteries in the developing hindbrain. Such phenotypes were rescued by wild-type dyrk1aa mRNA, but not by a kinase-dead form, indicating the importance of DYRK1A kinase activity. Chemical screening using a bioactive small molecule library identified a calcium chelator, EGTA, as one of the hits that most robustly rescued the hemorrhage. Vascular defects of mutants were also rescued by independent modulation of calcium signaling by FK506. Furthermore, the transcriptomic analyses supported the alterations of calcium signaling networks in dyrk1aa mutants. Together, our results suggest that DYRK1A plays an essential role in angiogenesis and in maintenance of the developing cerebral vasculature via regulation of calcium signaling, which may have therapeutic potential for DYRK1A-related vascular diseases.

Summary: The roles of DYRK1A in angiogenesis and maintenance of the developing cerebral vasculature mediated by calcium signaling were revealed using zebrafish dyrk1aa knockout mutants.

Photolysis of atorvastatin in aquatic environment: Influencing factors, products, and pathways

Atorvastatin (ATV), a second generation cholesterol-lowering drug, is detected frequently in natural water because of its extensive use and incomplete removal from wastewater. In this study, the photochemical behavior of ATV under simulated solar irradiation was systematically investigated in order to assess the potential of photolysis as its transformation pathway in aquatic environment. The quantum yield of ATV direct photolysis was determined to be 0.0041. Among various water components investigated, including pH, Suwannee River Fulvic Acid (SRFA), Fe³⁺, HCO₃^-, SO₄^2- and NO₃^-, the major factors contributing to the indirect photolysis of ATV were SRFA and NO₃^-, and the co-existence of SRFA and NO₃^- showed no interaction in synthetic water containing the above water components. The results were further verified in natural water samples. Singlet oxygen (¹O₂) played dominant role in the indirect photolysis of ATV, and the contributions of ¹O₂ and ·OH to the photolysis of ATV in the solution with optimum combination of water components were calculated to be 67.14% and 0.66%, respectively. Nine phototransformation intermediates were identified by liquid chromatography - time-of-flight - mass spectrometry (LC-TOF-MS), and the degradation pathways were speculated as hydroxyl addition, pyrrole-ring open and debenzamide reactions. In addition, the evolution of products in the degradation process showed that the ring-opened product P416 and hydroxylation product P575 still remained at a certain level after two days of photodegradation, which may accumulate and cause additional ecological risks. This study provides significant information for understanding the risk and fate of ATV in aquatic environment.

Temporal and Spatial Post-Transcriptional Regulation of Zebrafish tie1 mRNA by Long Noncoding RNA During Brain Vascular Assembly

Supplemental Digital Content is available in the text.

Objective—

Tie1 (tyrosine kinase containing immunoglobulin and epidermal growth factor homology 1), an endothelial and hematopoietic cell–specific receptor tyrosine kinase, is an important regulator of angiogenesis and critical for maintaining vascular integrity. The post-transcriptional regulation of tie1 mRNA expression is not understood, but it might partly explain Tie1’s differential expression pattern in endothelium. Following up on our previous work that identified natural antisense transcripts from the tie1 locus—tie1 antisense (tie1AS), which regulates tie1 mRNA levels in zebrafish—we attempted to identify the mechanism of this regulation.

Approach and Results—

Through in vitro and in vivo ribonucleoprotein binding studies, we demonstrated that tie1AS long noncoding RNA interacts with an RNA binding protein—embryonic lethal and abnormal vision Drosophila-like 1 (Elavl1)—that regulates tie1 mRNA levels. When we disrupted the interaction between tie1AS and Elavl1 by using constitutively active antisense morpholino oligonucleotides or photoactivatable morpholino oligonucleotides, tie1 mRNA levels increased between 26 and 31 hours post-fertilization, particularly in the head. This increase correlated with dilation of primordial midbrain channels, smaller eyes, and reduced ventricular space. We also observed these phenotypes when we used CRISPR (clustered regularly interspaced short palindromic repeats)–mediated CRISPRi (CRISPR-mediated interference) to knock down tie1AS. Treatment of the morpholino oligonucleotide–injected embryos with a small molecule that decreased tie1 mRNA levels rescued all 3 abnormal phenotypes.

Conclusions—

We identified a novel mode of temporal and spatial post-transcriptional regulation of tie1 mRNA. It involves long noncoding RNA, tie1AS, and Elavl1 (an interactor of tie1AS).

Molecular Regulation of Sprouting Angiogenesis

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

How to Plumb a Pisces: Understanding Vascular Development and Disease Using Zebrafish Embryos

Our vasculature plays diverse and critical roles in homeostasis and disease. In recent decades, the use of zebrafish has driven our understanding of vascular development into new areas, identifying new genes and mechanisms controlling vessel formation and allowing unprecedented observation of the cellular and molecular events that shape the developing vasculature. Here, we highlight key mechanisms controlling formation of the zebrafish vasculature and investigate how knowledge from this highly tractable model system has informed our understanding of vascular disease in humans.

Discovery of a ROCK inhibitor, FPND, which prevents cerebral hemorrhage through maintaining vascular integrity by interference with VE-cadherin

Hemorrhagic stroke occurs when a weakened vessel ruptures and bleeds into the surrounding brain, leading to high rates of death and disability worldwide. A series of complex pathophysiological cascades contribute to the risk of hemorrhagic stroke, and no therapies have proven effective to prevent hemorrhagic stroke. Stabilization of vascular integrity has been considered as a potential therapeutic target for hemorrhagic stroke. ROCKs, which belong to the serine/threonine protein kinase family and participate in the organization of actin cytoskeleton, have become attractive targets for the treatment of strokes. In this study, in vitro enzyme-based assays revealed that a new compound (FPND) with a novel scaffold identified by docking-based virtual screening could inhibit ROCK1 specifically at low micromolar concentration. Molecular modeling showed that FPND preferentially interacted with ROCK1, and the difference between the binding affinity of FPND toward ROCK1 and ROCK2 primarily resulted from non-polar contributions. Furthermore, FPND significantly prevented statin-induced cerebral hemorrhage in a zebrafish model. In addition, in vitro studies using the xCELLigence RTCA system, immunofluorescence and western blotting revealed that FPND prevented statin-induced cerebral hemorrhage by enhancing endothelial cell–cell junctions through inhibiting the ROCK-mediated VE-cadherin signaling pathway. As indicated by the extremely low toxicity of FPND against mice, it is safe and can potentially prevent vascular integrity loss-related diseases, such as hemorrhagic stroke.

Polydom Is an Extracellular Matrix Protein Involved in Lymphatic Vessel Remodeling

RATIONALE

Lymphatic vasculature constitutes a second vascular system essential for immune surveillance and tissue fluid homeostasis. Maturation of the hierarchical vascular structure, with a highly branched network of capillaries and ducts, is crucial for its function. Environmental cues mediate the remodeling process, but the mechanism that underlies this process is largely unknown.

OBJECTIVE

Polydom (also called Svep1) is an extracellular matrix protein identified as a high-affinity ligand for integrin α9β1. However, its physiological function is unclear. Here, we investigated the role of Polydom in lymphatic development.

METHODS AND RESULTS

We generated Polydom-deficient mice. Polydom^-/- mice showed severe edema and died immediately after birth because of respiratory failure. We found that although a primitive lymphatic plexus was formed, it failed to undergo remodeling in Polydom^-/- embryos, including sprouting of new capillaries and formation of collecting lymphatic vessels. Impaired lymphatic development was also observed after knockdown/knockout of polydom in zebrafish. Polydom was deposited around lymphatic vessels, but secreted from surrounding mesenchymal cells. Expression of Foxc2 (forkhead box protein c2), a transcription factor involved in lymphatic remodeling, was decreased in Polydom^-/- mice. Polydom bound to the lymphangiogenic factor Ang-2 (angiopoietin-2), which was found to upregulate Foxc2 expression in cultured lymphatic endothelial cells. Expressions of Tie1/Tie2 receptors for angiopoietins were also decreased in Polydom^-/- mice.

CONCLUSIONS

Polydom affects remodeling of lymphatic vessels in both mouse and zebrafish. Polydom deposited around lymphatic vessels seems to ensure Foxc2 upregulation in lymphatic endothelial cells, possibly via the Ang-2 and Tie1/Tie2 receptor system.

Identification of vascular disruptor compounds by analysis in zebrafish embryos and mouse embryonic endothelial cells

To identify vascular disruptor compounds (VDCs), this study utilized an in vivo zebrafish embryo vascular model in conjunction with a mouse endothelial cell model to screen a subset of the U.S. Environmental Protection Agency (EPA) ToxCast Phase I chemical inventory. In zebrafish, 161 compounds were screened and 34 were identified by visual inspection as VDCs, of which 28 were confirmed as VDCs by quantitative image analysis. Testing of the zebrafish VDCs for their capacity to inhibit endothelial tube formation in the murine yolk-sac-derived endothelial cell line C166 identified 22 compounds that both disrupted zebrafish vascular development and murine endothelial in vitro tubulogenesis. Putative molecular targets for the VDCs were predicted using EPA's Toxicological Prioritization Index tool and a VDC signature based on a proposed adverse outcome pathway for developmental vascular toxicity. In conclusion, our screening approach identified 22 novel VDCs, some of which were active at nanomolar concentrations.

Alterations in zebrafish development induced by simvastatin: Comprehensive morphological and physiological study, focusing on muscle

The cholesterol synthesis inhibitor simvastatin, which is used to treat cardiovascular diseases, has severe collateral effects. We decided to comprehensively study the effects of simvastatin in zebrafish development and in myogenesis, because zebrafish has been used as a model to human diseases, due to its handling easiness, the optical clarity of its embryos, and the availability of physiological and structural methodologies. Furthermore, muscle is an important target of the drug. We used several simvastatin concentrations at different zebrafish developmental stages and studied survival rate, morphology, and physiology of the embryos. Our results show that high levels of simvastatin induce structural damage whereas low doses induce minor structural changes, impaired movements, and reduced heart beating. Morphological alterations include changes in embryo and somite size and septa shape. Physiological changes include movement reduction and slower heartbeat. These effects could be reversed by the addition of exogenous cholesterol. Moreover, we quantified the total cell number during zebrafish development and demonstrated a large reduction in cell number after statin treatment. Since we could classify the alterations induced by simvastatin in three distinct phenotypes, we speculate that simvastatin acts through more than one mechanism and could affect both cell replication and/or cell death and muscle function. Our data can contribute to the understanding of the molecular and cellular basis of the mechanisms of action of simvastatin.

Calmodulin Mediates Ca2+-Dependent Inhibition of Tie2 Signaling and Acts as a Developmental Brake During Embryonic Angiogenesis

OBJECTIVE

Angiogenesis, the process of building complex vascular structures, begins with sprout formation on preexisting blood vessels, followed by extension of the vessels through proliferation and migration of endothelial cells. Based on the potential therapeutic benefits of preventing angiogenesis in pathological conditions, many studies have focused on the mechanisms of its initiation as well as control. However, how the extension of vessels is terminated remains obscure. Thus, we investigated the negative regulation mechanism.

APPROACH AND RESULTS

We report that increased intracellular calcium can induce dephosphorylation of the endothelial receptor tyrosine kinase Tie2. The calcium-mediated dephosphorylation was found to be dependent on Tie2-calmodulin interaction. The Tyr1113 residue in the C-terminal end loop of the Tie2 kinase domain was mapped and found to be required for this interaction. Moreover, mutation of this residue into Phe impaired both the Tie2-calmodulin interaction and calcium-mediated Tie2 dephosphorylation. Furthermore, expressing a mutant Tie2 incapable of binding to calmodulin or inhibiting calmodulin function in vivo causes unchecked growth of the vasculature in Xenopus. Specifically, knockdown of Tie2 in Xenopus embryo retarded the sprouting and extension of intersomitic veins. Although human Tie2 expression in the Tie2-deficient animals almost completely rescued the retardation, the Tie2(Y1113F) mutant caused overgrowth of intersomitic veins with strikingly complex and excessive branching patterns.

CONCLUSIONS

We propose that the calcium/calmodulin-dependent negative regulation of Tie2 can be used as an inhibitory signal for vessel growth and branching to build proper vessel architecture during embryonic development.

Zebrafish as an Emerging Model Organism to Study Angiogenesis in Development and Regeneration

Angiogenesis is the process through which new blood vessels are formed from preexisting ones and plays a critical role in several conditions including embryonic development, tissue repair and disease. Moreover, enhanced therapeutic angiogenesis is a major goal in the field of regenerative medicine and efficient vascularization of artificial tissues and organs is one of the main hindrances in the implementation of tissue engineering approaches, while, on the other hand, inhibition of angiogenesis is a key therapeutic target to inhibit for instance tumor growth. During the last decades, the understanding of cellular and molecular mechanisms involved in this process has been matter of intense research. In this regard, several in vitro and in vivo models have been established to visualize and study migration of endothelial progenitor cells, formation of endothelial tubules and the generation of new vascular networks, while assessing the conditions and treatments that either promote or inhibit such processes. In this review, we address and compare the most commonly used experimental models to study angiogenesis in vitro and in vivo. In particular, we focus on the implementation of the zebrafish (Danio rerio) as a model to study angiogenesis and discuss the advantages and not yet explored possibilities of its use as model organism.

THSD1 preserves vascular integrity and protects against intraplaque haemorrhaging in ApoE-/- mice

AIMS

Impairment of the endothelial barrier leads to microvascular breakdown in cardiovascular disease and is involved in intraplaque haemorrhaging and the progression of advanced atherosclerotic lesions that are vulnerable to rupture. The exact mechanism that regulates vascular integrity requires further definition. Using a microarray screen for angiogenesis-associated genes during murine embryogenesis, we identified thrombospondin type I domain 1 (THSD1) as a new putative angiopotent factor with unknown biological function. We sought to characterize the role of THSD1 in endothelial cells during vascular development and cardiovascular disease.

METHODS AND RESULTS

Functional knockdown of Thsd1 in zebrafish embryos and in a murine retina vascularization model induced severe haemorrhaging without affecting neovascular growth. In human carotid endarterectomy specimens, THSD1 expression by endothelial cells was detected in advanced atherosclerotic lesions with intraplaque haemorrhaging, but was absent in stable lesions, implying involvement of THSD1 in neovascular bleeding. In vitro, stimulation with pro-atherogenic factors (3% O2 and TNFα) decreased THSD1 expression in human endothelial cells, whereas stimulation with an anti-atherogenic factor (IL10) showed opposite effect. Therapeutic evaluation in a murine advanced atherosclerosis model showed that Thsd1 overexpression decreased plaque vulnerability by attenuating intraplaque vascular leakage, subsequently reducing macrophage accumulation and necrotic core size. Mechanistic studies in human endothelial cells demonstrated that THSD1 activates FAK-PI3K, leading to Rac1-mediated actin cytoskeleton regulation of adherens junctions and focal adhesion assembly.

CONCLUSION

THSD1 is a new regulator of endothelial barrier function during vascular development and protects intraplaque microvessels against haemorrhaging in advanced atherosclerotic lesions.

Discovery of Novel ROCK1 Inhibitors via Integrated Virtual Screening Strategy and Bioassays

Rho-associated kinases (ROCKs) have been regarded as promising drug targets for the treatment of cardiovascular diseases, nervous system diseases and cancers. In this study, a novel integrated virtual screening protocol by combining molecular docking and pharmacophore mapping based on multiple ROCK1 crystal structures was utilized to screen the ChemBridge database for discovering potential inhibitors of ROCK1. Among the 38 tested compounds, seven of them exhibited significant inhibitory activities of ROCK1 (IC₅₀ < 10 μM) and the most potent one (compound TS-f22) with the novel scaffold of 4-Phenyl-1H-pyrrolo [2,3-b] pyridine had an IC₅₀ of 480 nM. Then, the structure-activity relationships of 41 analogues of TS-f22 were examined. Two potent inhibitors were proven effective in inhibiting the phosphorylation of the downstream target in the ROCK signaling pathway in vitro and protecting atorvastatin-induced cerebral hemorrhage in vivo. The high hit rate (28.95%) suggested that the integrated virtual screening strategy was quite reliable and could be used as a powerful tool for identifying promising active compounds for targets of interest.

Endothelial cell-cell adhesion during zebrafish vascular development

The vertebrate vasculature is an essential organ network with major roles in health and disease. The establishment of balanced cell-cell adhesion in the endothelium is crucial for the functionality of the vascular system. Furthermore, the correct patterning and integration of vascular endothelial cell-cell adhesion drives the morphogenesis of new vessels, and is thought to couple physical forces with signaling outcomes during development. Here, we review insights into this process that have come from studies in zebrafish. First, we describe mutants in which endothelial adhesion is perturbed, second we describe recent progress using in vivo cell biological approaches that allow the visualization of endothelial cell-cell junctions. These studies underline the profound potential of this model system to dissect in great detail the function of both known and novel regulators of endothelial cell-cell adhesion.

The TIE Receptor Family

The endothelial TIE1 and TIE2 receptor tyrosine kinases form a distinct subfamily characterized by their unique extracellular domains. Together with the angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG), the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietins exist in multimeric forms that activate the TIE receptors via unique mechanism. In endothelial cell–cell contacts, angiopoietins induce the formation of homomeric in trans TIE receptor complexes extending across the cell junctions, whereas matrix-bound angiopoietin-1 (ANG1) activates the TIE receptors in a cis configuration. In comparison to the vascular endothelial growth factor receptors, the TIE receptors undergo little ubiquitin-mediated degradation after activation, whereas TIE2 signaling is negatively regulated by the vascular endothelial protein tyrosine phosphatase, VE-PTP. ANG1 activation of TIE2 supports vascular stabilization, whereas angiopoietin-2 (ANG2), a context-dependent weak TIE2 agonist/antagonist, promotes pathological tumor angiogenesis, vascular permeability, and inflammation. Recently, ANG2 has been found to mediate some of its vascular destabilizing and angiogenic functions via integrin signalling. The circulating levels of ANG2 are increased in cancer, and in several human diseases associated with inflammation and vascular leak, for example, in sepsis. Blocking of ANG2 has emerged as a potential novel therapeutic strategy for these diseases. In addition, preclinical results demonstrate that genetic TIE1 deletion in mice inhibits the vascularization and growth of tumor isografts and protects from atherosclerosis, with little effect on normal vascular homeostasis in adult mice. The ability of the ANG-TIE pathway to control vessel stability and angiogenesis makes it an interesting vascular target for the treatment of the various diseases.

Endothelial cilia are essential for developmental vascular integrity in zebrafish

The cilium is a signaling platform of the vertebrate cell. It has a critical role in polycystic kidney disease and nephronophthisis. Cilia have been detected on endothelial cells, but the function of these organelles in the vasculature remains incompletely defined. In this study, using genetic and chemical genetic tools in the model organism zebrafish, we reveal an essential role of cilia in developmental vascular integrity. Embryos expressing mutant intraflagellar transport genes, which are essential and specific for cilia biogenesis, displayed increased risk of developmental intracranial hemorrhage, whereas the morphology of the vasculature remained normal. Moreover, cilia were present on endothelial cells in the developing zebrafish vasculature. We further show that the involvement of cilia in vascular integrity is endothelial autonomous, because endothelial-specific re-expression of intraflagellar transport genes in respective mutants rescued the intracranial hemorrhage phenotype. Finally, whereas inhibition of Hedgehog signaling increased the risk of intracranial hemorrhage in ciliary mutants, activation of the pathway rescued this phenotype. In contrast, embryos expressing an inactivating mutation in pkd2, one of two autosomal dominant cystic kidney disease genes, did not show increased risk of developmental intracranial hemorrhage. These results suggest that Hedgehog signaling is a major mechanism for this novel role of endothelial cilia in establishing vascular integrity.

Nanosuspension development of scutellarein as an active and rapid orally absorbed precursor of its BCS class IV glycoside scutellarin

This work addressed solubility and membrane permeability problems of Biopharmaceutics Classification System (BCS) Class IV glycoside scutellarin (SG) by developing a nanosuspension of its aglycone scutellarein (S) as a precursor. An S nanosuspension containing poloxamer 188 was prepared using antisolvent precipitation where hydroxypropyl-β-cyclodextrin was utilized as a lyophilizing protectant. Particle size and polydispersity index after redispersion were 342.6 ± 18.2 and 0.32 ± 0.06 nm, respectively. The dissolution rate of the S nanosuspension was superior compared with the physical mixture. No free S, but SG and SG's isomer were detected in plasma following oral delivery of SG or S, S nanosuspension or physical mixture of S. The Cmax values of SG after dosing with the S nanosuspension were 12.0, 8.0, and 4.5-fold higher than the SG, S, or physical mixture, respectively. The Tmax and mean residence time (MRTlast ) of SG after dosing with the S nanosuspension were significantly shorter than S and SG. Treatments with SG, S, or S nanosuspensions reduced the hemorrhage rate in a zebrafish model, but the S nanosuspension exhibited the strongest rescue effect. This study highlights a new strategy to circumvent BCS Class IV flavonoid glycosides using a formulation of their aglycone as a precursor to accelerate oral absorption and improve bioactivity.

Regulatory pathways affecting vascular stabilization via VE-cadherin dynamics: insights from zebrafish (Danio rerio)

The endothelial-specific transmembrane glycoprotein, vascular endothelial (VE)-cadherin, is required for the organization of a stable vascular endothelium. A number of cerebrovascular disorders are associated with mutations in genes that otherwise regulate vascular integrity through VE-cadherin dynamics. Hence, identification and characterization of regulatory pathways contributing to endothelial cell-cell adhesion is of clinical relevance, particularly in the treatment of aneurysms and cerebral cavernous malformations. The zebrafish (Danio rerio) have recently emerged as a powerful paradigm for studies geared toward elucidating the etiology of cerebrovascular disorders, principally in uncovering the genetic and mechanistic basis controlling endothelial adhesive barrier function.

Oceans of opportunity: exploring vertebrate hematopoiesis in zebrafish

Exploitation of the zebrafish model in hematology research has surged in recent years, becoming one of the most useful and tractable systems for understanding regulation of hematopoietic development, homeostasis, and malignancy. Despite the evolutionary distance between zebrafish and humans, remarkable genetic and phenotypic conservation in the hematopoietic system has enabled significant advancements in our understanding of blood stem and progenitor cell biology. The strengths of zebrafish in hematology research lie in the ability to perform real-time in vivo observations of hematopoietic stem, progenitor, and effector cell emergence, expansion, and function, as well as the ease with which novel genetic and chemical modifiers of specific hematopoietic processes or cell types can be identified and characterized. Further, myriad transgenic lines have been developed including fluorescent reporter systems to aid in the visualization and quantification of specified cell types of interest and cell-lineage relationships, as well as effector lines that can be used to implement a wide range of experimental manipulations. As our understanding of the complex nature of blood stem and progenitor cell biology during development, in response to infection or injury, or in the setting of hematologic malignancy continues to deepen, zebrafish will remain essential for exploring the spatiotemporal organization and integration of these fundamental processes, as well as the identification of efficacious small molecule modifiers of hematopoietic activity. In this review, we discuss the biology of the zebrafish hematopoietic system, including similarities and differences from mammals, and highlight important tools currently utilized in zebrafish embryos and adults to enhance our understanding of vertebrate hematology, with emphasis on findings that have impacted our understanding of the onset or treatment of human hematologic disorders and disease.

Conservation and early expression of zebrafish tyrosine kinases support the utility of zebrafish as a model for tyrosine kinase biology

Tyrosine kinases have significant roles in cell growth, apoptosis, development, and disease. To explore the use of zebrafish as a vertebrate model for tyrosine kinase signaling and to better understand their roles, we have identified all of the tyrosine kinases encoded in the zebrafish genome and quantified RNA expression of selected tyrosine kinases during early development. Using profile hidden Markov model analysis, we identified 122 zebrafish tyrosine kinase genes and proposed unambiguous gene names where needed. We found them to be organized into 39 nonreceptor and 83 receptor type, and 30 families consistent with human tyrosine kinase family assignments. We found five human tyrosine kinase genes (epha1, bmx, fgr, srm, and insrr) with no identifiable zebrafish ortholog, and one zebrafish gene (yrk) with no identifiable human ortholog. We also found that receptor tyrosine kinase genes were duplicated more often than nonreceptor tyrosine kinase genes in zebrafish. We profiled expression levels of 30 tyrosine kinases representing all families using direct digital detection at different stages during the first 24 hours of development. The profiling experiments clearly indicate regulated expression of tyrosine kinases in the zebrafish, suggesting their role during early embryonic development. In summary, our study has resulted in the first comprehensive description of the zebrafish tyrosine kinome.

MicroRNA 218 mediates the effects of Tbx5a over-expression on zebrafish heart development

tbx5, a member of the T-box gene family, encodes one of the key transcription factors mediating vertebrate heart development. Tbx5 function in heart development appears to be exquisitely sensitive to gene dosage, since both haploinsufficiency and gene duplication generate the cardiac abnormalities associated with Holt−Oram syndrome (HOS), a highly penetrant autosomal dominant disease characterized by congenital heart defects of varying severity and upper limb malformation. It is suggested that tight integration of microRNAs and transcription factors into the cardiac genetic circuitry provides a rich and robust array of regulatory interactions to control cardiac gene expression. Based on these considerations, we performed an in silico screening to identify microRNAs embedded in genes highly sensitive to Tbx5 dosage. Among the identified microRNAs, we focused our attention on miR-218-1 that, together with its host gene, slit2, is involved in heart development. We found correlated expression of tbx5 and miR-218 during cardiomyocyte differentiation of mouse P19CL6 cells. In zebrafish embryos, we show that both Tbx5 and miR-218 dysregulation have a severe impact on heart development, affecting early heart morphogenesis. Interestingly, down-regulation of miR-218 is able to rescue the heart defects generated by tbx5 over-expression supporting the notion that miR-218 is a crucial mediator of Tbx5 in heart development and suggesting its possible involvement in the onset of heart malformations.

Formation of a PKCζ/β-catenin complex in endothelial cells promotes angiopoietin-1-induced collective directional migration and angiogenic sprouting

Angiogenic sprouting requires that cell-cell contacts be maintained during migration of endothelial cells. Angiopoietin-1 (Ang-1) and vascular endothelial growth factor act oppositely on endothelial cell junctions. We found that Ang-1 promotes collective and directional migration and, in contrast to VEGF, induces the formation of a complex formed of atypical protein kinase C (PKC)-ζ and β-catenin at cell-cell junctions and at the leading edge of migrating endothelial cells. This complex brings Par3, Par6, and adherens junction proteins at the front of migrating cells to locally activate Rac1 in response to Ang-1. The colocalization of PKCζ and β-catenin at leading edge along with PKCζ-dependent stabilization of cell-cell contacts promotes directed and collective endothelial cell migration. Consistent with these results, down-regulation of PKCζ in endothelial cells alters Ang-1-induced sprouting in vitro and knockdown in developing zebrafish results in intersegmental vessel defects caused by a perturbed directionality of tip cells and by loss of cell contacts between tip and stalk cells. These results reveal that PKCζ and β-catenin function in a complex at adherens junctions and at the leading edge of migrating endothelial cells to modulate collective and directional migration during angiogenesis.

From omics to drug metabolism and high content screen of natural product in zebrafish: a new model for discovery of neuroactive compound

The zebrafish (Danio rerio) has recently become a common model in the fields of genetics, environmental science, toxicology, and especially drug screening. Zebrafish has emerged as a biomedically relevant model for in vivo high content drug screening and the simultaneous determination of multiple efficacy parameters, including behaviour, selectivity, and toxicity in the content of the whole organism. A zebrafish behavioural assay has been demonstrated as a novel, rapid, and high-throughput approach to the discovery of neuroactive, psychoactive, and memory-modulating compounds. Recent studies found a functional similarity of drug metabolism systems in zebrafish and mammals, providing a clue with why some compounds are active in zebrafish in vivo but not in vitro, as well as providing grounds for the rationales supporting the use of a zebrafish screen to identify prodrugs. Here, we discuss the advantages of the zebrafish model for evaluating drug metabolism and the mode of pharmacological action with the emerging omics approaches. Why this model is suitable for identifying lead compounds from natural products for therapy of disorders with multifactorial etiopathogenesis and imbalance of angiogenesis, such as Parkinson's disease, epilepsy, cardiotoxicity, cerebral hemorrhage, dyslipidemia, and hyperlipidemia, is addressed.

Molecular regulation of lymphangiogenesis in development and tumor microenvironment

A rapid progress has been made in the field of lymphatic research during the last 15 years. This includes better understanding of the cellular events and molecular players involved in the lymphatic vessel formation and remodeling in development. The key players identified in developmental lymphangiogenesis, including vascular endothelial cell growth factor-C (VEGF-C) / VEGFR-3 and angiopoietins (ANGPTs)/ TIE pathways, are also crucial for pathological lymphatic vessel growth. In solid tumor, tumor cells as well as tumor-associated stromal cells, such as tumor-infiltrating leukocytes, contribute to intra- and peri-tumoral lymphangiogenesis via secreting lymphangiogenic growth factors. Tumor-associated lymphatic endothelial cells also interact actively with tumor cells and leukocytes via secreting various chemokines. It has been well established that tumor lymphangiogenesis promotes tumor cell dissemination to regional lymph nodes. Thus manipulation of lymphangiogenic microenvironment could become another valuable approach in the combat of tumor progression.

Development and validation of an automated high-throughput system for zebrafish in vivo screenings

The zebrafish is a vertebrate model compatible with the paradigms of drug discovery. The small size and transparency of zebrafish embryos make them amenable for the automation necessary in high-throughput screenings. We have developed an automated high-throughput platform for in vivo chemical screenings on zebrafish embryos that includes automated methods for embryo dispensation, compound delivery, incubation, imaging and analysis of the results. At present, two different assays to detect cardiotoxic compounds and angiogenesis inhibitors can be automatically run in the platform, showing the versatility of the system. A validation of these two assays with known positive and negative compounds, as well as a screening for the detection of unknown anti-angiogenic compounds, have been successfully carried out in the system developed. We present a totally automated platform that allows for high-throughput screenings in a vertebrate organism.

Studying synthetic lethal interactions in the zebrafish system: insight into disease genes and mechanisms

The post-genomic era is marked by a pressing need to functionally characterize genes through understanding gene-gene interactions, as well as interactions between biological pathways. Exploiting a phenomenon known as synthetic lethality, in which simultaneous loss of two interacting genes leads to loss of viability, aids in the investigation of these interactions. Although synthetic lethal screening is a powerful technique that has been used with great success in many model organisms, including Saccharomyces cerevisiae, Drosophila melanogaster and Caenorhabditis elegans, this approach has not yet been applied in the zebrafish, Danio rerio. Recently, the zebrafish has emerged as a valuable system to model many human disease conditions; thus, the ability to conduct synthetic lethal screening using zebrafish should help to uncover many unknown disease-gene interactions. In this article, we discuss the concept of synthetic lethality and provide examples of its use in other model systems. We further discuss experimental approaches by which the concept of synthetic lethality can be applied to the zebrafish to understand the functions of specific genes.

Lymphatic vascular morphogenesis in development, physiology, and disease

The lymphatic vasculature constitutes a highly specialized part of the vascular system that is essential for the maintenance of interstitial fluid balance, uptake of dietary fat, and immune response. Recently, there has been an increased awareness of the importance of lymphatic vessels in many common pathological conditions, such as tumor cell dissemination and chronic inflammation. Studies of embryonic development and genetically engineered animal models coupled with the discovery of mutations underlying human lymphedema syndromes have contributed to our understanding of mechanisms regulating normal and pathological lymphatic morphogenesis. It is now crucial to use this knowledge for the development of novel therapies for human diseases.

Zebrafish as a model for hemorrhagic stroke

Blood vessels perform the fundamental role of providing conduits for the circulation of oxygen and nutrients and the removal of waste products throughout the body. Disruption of tissue perfusion by ischemia or hemorrhage of blood vessels has a range of devastating consequences including stroke. Stroke is a complex trait that includes both genetic and environmental risk factors. The zebrafish is an attractive model for the study of hemorrhagic stroke due to the conservation of the molecular mechanisms of blood vascular development among vertebrates and the experimental advantages that can be applied to zebrafish embryos and larva. This chapter will focus on the maintenance of vascular integrity and some of the seminal experimentation carried out in the zebrafish.