Shear stress, tip cells and regulators of endothelial migration

A nanoporous hydrogel-based model to study chemokine gradient-driven angiogenesis under luminal flow

The growth of new blood vessels through angiogenesis is a highly coordinated process, which is initiated by chemokine gradients that activate endothelial cells within a perfused parent vessel to sprout into the surrounding 3D tissue matrix. While both biochemical signals from pro-angiogenic factors, as well as mechanical cues originating from luminal fluid flow that exerts shear stress on the vessel wall, have individually been identified as major regulators of endothelial cell sprouting, it remains unclear whether and how both types of cues synergize. To fill this knowledge gap, here, we created a 3D biomimetic model of chemokine gradient-driven angiogenic sprouting, in which a micromolded tube inside a hydrogel matrix is seeded with endothelial cells and connected to a perfusion system to control fluid flow rates and resulting shear forces on the vessel wall. To allow for the formation of chemokine gradients despite the presence of luminal flow, a nanoporous synthetic hydrogel that supports angiogenesis but limits the interstitial flow proved crucial. Using this system, we find that luminal flow and resulting shear stress is a major regulator of the speed and morphogenesis of angiogenic sprouting, whose action is mediated through changes in vascular permeability.

Analysis of brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving peripheral leukocytes and brain resident cells that contribute to both tissue injury and repair. However, their dynamics and diversity remain poorly understood. To address these limitations, we performed a single-cell transcriptomic study of brain and blood cells 2 or 14 days after ischemic stroke in mice. We observed a strong divergence of post-ischemic microglia, monocyte-derived macrophages and neutrophils over time, while endothelial cells and brain-associated macrophages showed altered transcriptomic signatures at 2 days poststroke. Trajectory inference predicted the in situ trans-differentiation of macrophages from blood monocytes into day 2 and day 14 phenotypes, while neutrophils were projected to be continuously de novo recruited from the blood. Brain single-cell transcriptomes from both female and male aged mice were similar to that of young male mice, but aged and young brains differed in their immune cell composition. Although blood leukocyte analysis also revealed altered transcriptomes after stroke, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification occurs within the brain in the early and recovery phases of ischemic stroke. A portal ( https://anratherlab.shinyapps.io/strokevis/ ) is provided to allow user-friendly access to our data.

Brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving both peripheral leukocytes and brain resident cells. Recent evidence indicates that their differentiation into a variety of functional phenotypes contributes to both tissue injury and repair. However, the temporal dynamics and diversity of post-stroke immune cell subsets remain poorly understood. To address these limitations, we performed a longitudinal single-cell transcriptomic study of both brain and mouse blood to obtain a composite picture of brain-infiltrating leukocytes, circulating leukocytes, microglia and endothelium diversity over the ischemic/reperfusion time. Brain cells and blood leukocytes isolated from mice 2 or 14 days after transient middle cerebral artery occlusion or sham surgery were purified by FACS sorting and processed for droplet-based single-cell transcriptomics. The analysis revealed a strong divergence of post-ischemic microglia, macrophages, and neutrophils over time, while such diversity was less evident in dendritic cells, B, T and NK cells. Conversely, brain endothelial cells and brain associated-macrophages showed altered transcriptomic signatures at 2 days post-stroke, but low divergence from sham at day 14. Pseudotime trajectory inference predicted the in-situ longitudinal progression of monocyte-derived macrophages from their blood precursors into day 2 and day 14 phenotypes, while microglia phenotypes at these two time points were not connected. In contrast to monocyte-derived macrophages, neutrophils were predicted to be continuously de-novo recruited from the blood. Brain single-cell transcriptomics from both female and male aged mice did not show major changes in respect to young mice, but aged and young brains differed in their immune cell composition. Furthermore, blood leukocyte analysis also revealed altered transcriptomes after stroke. However, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification into cellular subsets occurs within the brain in the early and the recovery phase of ischemic stroke. In addition, this resource report contains a searchable database https://anratherlab.shinyapps.io/strokevis/ to allow user-friendly access to our data. The StrokeVis tool constitutes a comprehensive gene expression atlas that can be interrogated at the gene and cell type level to explore the transcriptional changes of endothelial and immune cell subsets from mouse brain and blood after stroke.

Constructing interactive networks of functional genes and metabolites to uncover the cellular events related to colorectal cancer cell migration induced by arsenite

Tumor cell migration induced by arsenite (iAs^III) is closely associated with cancer progression. However, transcriptomic and metabolic traits of migrative human cells exposed to iAs^III remain to be well characterized. Here, the combination of transcriptomics and metabolomics approaches were employed to construct interactive networks of functional genes and metabolites in human colorectal cancer (DLD-1) cells exposed to iAs^III. The number of DLD-1 cells passing through the Transwell membrane was at least 6 times greater in the iAs^III-treated groups than in controls. Following iAs^III treatment, the expression of ZEB1 and SLUG protein was significantly upregulated while the expression of CRB2 was downregulated (p < 0.05), indicating the onset of epithelial to mesenchymal transition (EMT). Meanwhile, integrin- and collagen-mediated biological adhesion were enhanced by SLUG under iAs^III treatment. The expression of matrix metallopeptidase (MMP) genes was fostered by iAs^III, which have the functions to degrade extracellular matrix. Glutamine metabolism could be considerably interfered by iAs^III, and in turn glutamine supplementation could effectively enhance DLD-1 cell movement. Overall, our results suggested that DLD-1 cell migration could be promoted by iAs^III via a series of cellular events, including EMT activation, altered cell adhesion, MMP-dependent matrix degradation, accompanying with a metabolic focus on glutamine.

Mechanical regulation of the early stages of angiogenesis

Favouring or thwarting the development of a vascular network is essential in fields as diverse as oncology, cardiovascular disease or tissue engineering. As a result, understanding and controlling angiogenesis has become a major scientific challenge. Mechanical factors play a fundamental role in angiogenesis and can potentially be exploited for optimizing the architecture of the resulting vascular network. Largely focusing on in vitro systems but also supported by some in vivo evidence, the aim of this Highlight Review is dual. First, we describe the current knowledge with particular focus on the effects of fluid and solid mechanical stimuli on the early stages of the angiogenic process, most notably the destabilization of existing vessels and the initiation and elongation of new vessels. Second, we explore inherent difficulties in the field and propose future perspectives on the use of in vitro and physics-based modelling to overcome these difficulties.

Vascular Endothelial Cells: Heterogeneity and Targeting Approaches

Forming the inner layer of the vascular system, endothelial cells (ECs) facilitate a multitude of crucial physiological processes throughout the body. Vascular ECs enable the vessel wall passage of nutrients and diffusion of oxygen from the blood into adjacent cellular structures. ECs regulate vascular tone and blood coagulation as well as adhesion and transmigration of circulating cells. The multitude of EC functions is reflected by tremendous cellular diversity. Vascular ECs can form extremely tight barriers, thereby restricting the passage of xenobiotics or immune cell invasion, whereas, in other organ systems, the endothelial layer is fenestrated (e.g., glomeruli in the kidney), or discontinuous (e.g., liver sinusoids) and less dense to allow for rapid molecular exchange. ECs not only differ between organs or vascular systems, they also change along the vascular tree and specialized subpopulations of ECs can be found within the capillaries of a single organ. Molecular tools that enable selective vascular targeting are helpful to experimentally dissect the role of distinct EC populations, to improve molecular imaging and pave the way for novel treatment options for vascular diseases. This review provides an overview of endothelial diversity and highlights the most successful methods for selective targeting of distinct EC subpopulations.

CLEC14A deficiency exacerbates neuronal loss by increasing blood-brain barrier permeability and inflammation

Background

Ischemic stroke is a main cause of mortality. Blood-brain barrier (BBB) breakdown appears to play a critical role in inflammation in patients with ischemic stroke and acceleration of brain injury. The BBB has a protective function and is composed of endothelial cells, pericytes, and astrocytes. In ischemic stroke treatments, regulation of vascular endothelial growth factor (VEGF)-A and vascular endothelial growth factor receptor (VEGFR)-2 is a crucial target despite adverse effects. Our previous study found that loss of C-type lectin family 14 member A (CLEC14A) activated VEGF-A/VEGFR-2 signaling in developmental and tumoral angiogenesis. Here, we evaluate the effects of BBB impairment caused by CLEC14A deficiency in ischemia-reperfusion injury.

Methods

In vitro fluorescein isothiocyanate (FITC)-dextran permeability, transendothelial electrical resistance (TEER) assay, and immunostaining were used to evaluate endothelial integrity. BBB permeability was assessed using Evans blue dye and FITC-dextran injection in Clec14a^−/− (CLEC14A-KO) mice and wild-type mice. Middle cerebral artery occlusion surgery and behavioral assessments were performed to evaluate the neurologic damage. The change of tight junctional proteins, adhesion molecules, pro-inflammatory cytokines, and microglial were confirmed by immunofluorescence staining, Western blotting, and quantitative reverse transcription polymerase chain reaction of brain samples.

Results

In endothelial cells, knockdown of CLEC14A increased FITC-dextran permeability and decreased transendothelial electrical resistance; the severity of this effect increased with VEGF treatment. Immunofluorescence staining revealed that tight junctional proteins were attenuated in the CLEC14A knockdown endothelial cells. Consistent with the in vitro results, CLEC14A-KO mice that were injected with Evans blue dye had cerebral vascular leakage at postnatal day 8; wild-type mice had no leakage. We used a middle cerebral artery occlusion model and found that CLEC14A-KO mice had severe infarcted brain and neurological deficits with upregulated VEGFR-2 expression. FITC-dextran leakage was present in CLEC14A-KO mice after ischemia-reperfusion, and the numbers of tight junctional molecules were significantly decreased. Loss of CLEC14A increased the pro-inflammatory response through adhesion molecule expression, and glial cells were activated.

Conclusions

These results suggest that activation of VEGFR-2 in CLEC14A-KO mice aggravates ischemic stroke by exacerbating cerebral vascular leakage and increasing neuronal inflammation after ischemia-reperfusion injury.

Proteomics-based screening of the endothelial heparan sulfate interactome reveals that C-type lectin 14a (CLEC14A) is a heparin-binding protein

Animal cells express heparan sulfate proteoglycans that perform many important cellular functions by way of heparan sulfate-protein interactions. The identification of membrane heparan sulfate-binding proteins is challenging because of their low abundance and the need for extensive enrichment. Here, we report a proteomics workflow for the identification and characterization of membrane-anchored and extracellular proteins that bind heparan sulfate. The technique is based on limited proteolysis of live cells in the absence of denaturation and fixation, heparin-affinity chromatography, and high-resolution LC-MS/MS, and we designate it LPHAMS. Application of LPHAMS to U937 monocytic and primary murine and human endothelial cells identified 55 plasma membrane, extracellular matrix, and soluble secreted proteins, including many previously unidentified heparin-binding proteins. The method also facilitated the mapping of the heparin-binding domains, making it possible to predict the location of the heparin-binding site. To validate the discovery feature of LPHAMS, we characterized one of the newly-discovered heparin-binding proteins, C-type lectin 14a (CLEC14A), a member of the C-type lectin family that modulates angiogenesis. We found that the C-type lectin domain of CLEC14A binds one-to-one to heparin with nanomolar affinity, and using molecular modeling and mutagenesis, we mapped its heparin-binding site. CLEC14A physically interacted with other glycosaminoglycans, including endothelial heparan sulfate and chondroitin sulfate E, but not with neutral or sialylated oligosaccharides. The LPHAMS technique should be applicable to other cells and glycans and provides a way to expand the repertoire of glycan-binding proteins for further study.

Magic roundabout is an endothelial-specific ohnolog of ROBO1 which neo-functionalized to an essential new role in angiogenesis

BACKGROUND

Magic roundabout (ROBO4) is an unusual endothelial-specific paralog of the family of neuronally-expressed axon guidance receptors called roundabouts. Endothelial cells (ECs), whose uninterrupted sheet delimits the lumen of all vertebrate blood vessels and which are absent from invertebrate species, are a vertebrate-specific evolutionary novelty.

RESULTS

Herein, the evolutionary mechanism of the duplication, retention and divergence of ROBO4 was investigated for the first time. Phylogenetic analyses carried out suggested that ROBO4 is a fast-evolving paralog of ROBO1 formed at the base of vertebrates. The ancestral expression pattern was neuronal. ROBO4 dramatically shifted its expression and became exceptionally specific to ECs. The data-mining of FANTOM5 and ENCODE reveals that ROBO4's endothelial expression arises from a single transcription start site (TSS), conserved in mouse, controlled by a proximal promoter with a complex architecture suggestive of regulatory neo-functionalization. (An analysis of promoter probabilities suggested the architecture was not due to a chance arrangement of TFBSes). Further evidence for the neo-functionalization of ROBO4 comes from the analysis of its protein interactions, the rates of protein evolution, and of positively selected sites.

CONCLUSIONS

The neo-functionalization model explains why ROBO4 protein acquired new context-specific biological functions in the control of angiogenesis. This endothelial-specific roundabout receptor is an illustrative example of the emergence of an essential vertebrate molecular novelty and an endothelial-specific signaling sub-network through 2R-WGD. The emergence of novel cell types, such as ECs, might be a neglected evolutionary force contributing to the high rate of retention of duplicates post-2R-WGD. Crucially, expression neo-functionalization to evolutionarily novel sites of expression conceptually extends the classical model of neo-functionalization.

Abscisic acid - an anti-angiogenic phytohormone that modulates the phenotypical plasticity of endothelial cells and macrophages

Abscisic acid (ABA) has shown anti-inflammatory and immunoregulatory properties in preclinical models of diabetes and inflammation. Herein, we studied the effects of ABA on angiogenesis, a strictly controlled process that, when dysregulated, leads to severe angiogenic disorders including vascular overgrowth, exudation, cellular inflammation and organ dysfunction. By using a 3D sprouting assay, we show that ABA effectively inhibits migration, growth and expansion of endothelial tubes without affecting cell viability. Analyses of the retinal vasculature in developing normoxic and hyperoxic mice challenged by oxygen toxicity reveal that exogenously administered ABA stunts the development and regeneration of blood vessels. In these models, ABA downregulates endothelial cell (EC)-specific growth and migratory genes, interferes with tip and stalk cell specification, and hinders the function of filopodial protrusions required for precise guidance of vascular sprouts. In addition, ABA skews macrophage polarization towards the M1 phenotype characterized by anti-angiogenic marker expression. In accordance with this, ABA treatment accelerates macrophage-induced programmed regression of fetal blood vessels. These findings reveal protective functions of ABA against neovascular growth through modulation of EC and macrophage plasticity, suggesting the potential utility of ABA as a treatment in vasoproliferative diseases.

Expression patterns of Slit and Robo family members in adult mouse spinal cord and peripheral nervous system

The secreted glycoproteins, Slit1-3, are classic axon guidance molecules that act as repulsive cues through their well characterised receptors Robo1-2 to allow precise axon pathfinding and neuronal migration. The expression patterns of Slit1-3 and Robo1-2 have been most characterized in the rodent developing nervous system and the adult brain, but little is known about their expression patterns in the adult rodent peripheral nervous system. Here, we report a detailed expression analysis of Slit1-3 and Robo1-2 in the adult mouse sciatic nerve as well as their expression in the nerve cell bodies within the ventral spinal cord (motor neurons) and dorsal root ganglion (sensory neurons). Our results show that, in the adult mouse peripheral nervous system, Slit1-3 and Robo1-2 are expressed in the cell bodies and axons of both motor and sensory neurons. While Slit1 and Robo2 are only expressed in peripheral axons and their cell bodies, Slit2, Slit3 and Robo1 are also expressed in satellite cells of the dorsal root ganglion, Schwann cells and fibroblasts of peripheral nerves. In addition to these expression patterns, we also demonstrate the expression of Robo1 in blood vessels of the peripheral nerves. Our work gives important new data on the expression patterns of Slit and Robo family members within the peripheral nervous system that may relate both to nerve homeostasis and the reaction of the peripheral nerves to injury.

The Robo4 cytoplasmic domain is dispensable for vascular permeability and neovascularization

Vascular permeability and neovascularization are implicated in many diseases including retinopathies and diabetic wound healing. Robo4 is an endothelial-specific transmembrane receptor that stabilizes the vasculature, as shown in Robo4^−/− mice that develop hyperpermeability, but how Robo4 signals remained unclear. Here we show that Robo4 deletion enhances permeability and revascularization in oxygen-induced retinopathy (OIR) and accelerates cutaneous wound healing. To determine Robo4 signalling pathways, we generated transgenic mice expressing a truncated Robo4 lacking the cytoplasmic domain (Robo4ΔCD). Robo4ΔCD expression is sufficient to prevent permeability, and inhibits OIR revascularization and wound healing in Robo4^−/− mice. Mechanistically, Robo4 does not affect Slit2 signalling, but Robo4 and Robo4ΔCD counteract Vegfr2-Y949 (Y951 in human VEGFR2) phosphorylation by signalling through the endothelial UNC5B receptor. We conclude that Robo4 inhibits angiogenesis and vessel permeability independently of its cytoplasmic domain, while activating VEGFR2-Y951 via ROBO4 inhibition might accelerate tissue revascularization in retinopathy of prematurity and in diabetic patients.

Robo4 is a transmembrane protein that regulates vascular permeability. Zhang et al. now reveal the mechanism of Robo4 action and show that Robo4 and UncB are required for VEGF-mediated regulation of vascular barrier by suppressing VEGF-induced phosphorylation of its receptor Vegfr2 on Y949.

Natural products against cancer angiogenesis

The process of angiogenesis is quite well-known nowadays. Some medicines and extracts affecting this process are already used routinely in supporting the conventional treatment of many diseases that are considered angiogenic such as cancer. However, we must be aware that the area of currently used drugs of this type is much narrower than the theoretical possibilities existing in therapeutic angiogenesis. Plant substances are a large and diverse group of compounds that are found naturally in fruits, vegetables, spices, and medicinal plants. They also have different anticancer properties. The aim of this literature review article is to present the current state of knowledge concerning the molecular targets of tumor angiogenesis and the active substances (polyphenols, alkaloids, phytohormones, carbohydrates, and terpenes) derived from natural sources, whose activity against cancer angiogenesis has been confirmed.

Expression of a novel endothelial marker, C-type lectin 14A, in epithelial ovarian cancer and its prognostic significance

OBJECTIVE

The purpose of this study was to evaluate microvessel density (MVD) as assessed by C-type lectin 14A (CLEC14A), which is a new marker for endothelial cells, and compare its expression to CD31 and CD105 in epithelial ovarian cancer (EOC).

METHODS

MVD was evaluated in tumors (n = 50) from patients with EOC who underwent primary surgery and in patients with EOC who received preoperative chemotherapy (n = 49) using immunohistochemistry with antibodies to CLEC14A, CD31 and CD105. The median duration of follow-up was 24.5 months (range 1-101 months). The effect of prognostic factors on event-free survival (EFS) and overall survival (OS) was assessed using the Cox regression model.

RESULTS

The amount of residual disease was found to be an independent prognostic factor in multivariate analysis with respect to EFS (P = 0.009) and OS (P < 0.001). The mean MVD of CLEC14A (MVD = 6), in tumors from patients who underwent primary surgery, was significantly lower than that of CD31 (MVD = 25, P < 0.0001) and CD105 (MVD = 11, P = 0.018). However, there was no significant correlation between MVD as detected by these markers and clinical outcome. There was no expression of CLEC14A in tumors from patients who received preoperative chemotherapy and the MVD of CD31 and CD105 was significantly reduced (P = 0.001 and 0.006, respectively) in this set of patients.

CONCLUSION

This study demonstrates MVD as detected by CLEC14A in EOC. Treatment with chemotherapy reduces tumor blood vessels significantly. We suggest that CLEC14A may be a more specific endothelial marker to assess tumor angiogenesis.

The molecular landscape of antibody-mediated kidney transplant rejection: evidence for NK involvement through CD16a Fc receptors

The recent recognition that antibody-mediated rejection (ABMR) is the major cause of kidney transplant loss creates strong interest in its pathogenesis. We used microarray analysis of kidney transplant biopsies to identify the changes in pure ABMR. We found that the ABMR transcript changes in the initial Discovery Set were strongly conserved in a subsequent Validation Set. In the Combined Set of 703 biopsies, 2603 transcripts were significantly changed (FDR < 0.05) in ABMR versus all other biopsies. In cultured cells, the transcripts strongly associated with ABMR were expressed in endothelial cells, e.g. cadherins CDH5 and CDH13; IFNG-treated endothelial cells, e.g. phospholipase PLA1A and chemokine CXCL11; or NK cells, e.g. cytotoxicity molecules granulysin (GNLY) and FGFBP2. Other ABMR transcripts were expressed in normal kidney but not cell lines, either increased e.g. Duffy chemokine receptor (DARC) or decreased e.g. sclerostin (SOST). Pathway analysis of ABMR transcripts identified angiogenesis, with roles for angiopoietin and vascular endothelial growth factors; leukocyte-endothelial interactions; and NK signaling, including evidence for CD16a Fc receptor signaling elements shared with T cells. These data support a model of ABMR involving injury-repair in the microcirculation induced by cognate recognition involving antibody and CD16a, triggering IFNG release and antibody-dependent NK cell-mediated cytotoxicity.

Blocking CLEC14A-MMRN2 binding inhibits sprouting angiogenesis and tumour growth

We previously identified CLEC14A as a tumour endothelial marker. Here we show CLEC14A is a regulator of sprouting angiogenesis in vitro and in vivo. Using a HUVEC spheroid sprouting assay we found CLEC14A to be a regulator of sprout initiation. Analysis of endothelial sprouting in aortic ring and in vivo subcutaneous sponge assays from clec14a^+/+ and clec14a^−/− mice revealed defects in sprouting angiogenesis in CLEC14A deficient animals. Tumour growth was retarded and vascularity reduced in clec14a^−/− mice. Pulldown and co-immunoprecipitation experiments confirmed MMRN2 binds to the extracellular region of CLEC14A. The CLEC14A-MMRN2 interaction was interrogated using mouse monoclonal antibodies. Monoclonal antibodies were screened for their ability to block this interaction. Clone C4 but not C2 blocked CLEC14A-MMRN2 binding. C4 antibody perturbed tube formation and endothelial sprouting in vitro and in vivo, with a similar phenotype to loss of CLEC14A. Significantly, tumour growth was impaired in C4 treated animals and vascular density was also reduced in the C4 treated group. We conclude that CLEC14A-MMRN2 binding has a role in inducing sprouting angiogenesis during tumour growth, that has the potential to be manipulated in future anti-angiogenic therapy design.

Shear stress regulated gene expression and angiogenesis in vascular endothelium

The behavior of vascular EC is greatly altered in sites of pathological angiogenesis, such as a developing tumor or atherosclerotic plaque. Until recently it was thought that this was largely due to abnormal chemical signaling, i.e., endothelial cell chemo transduction, at these sites. However, we now demonstrate that the shear stress intensity encountered by EC can have a profound impact on their gene expression and behavior. We review the growing body of evidence suggesting that mechanotransduction, too, is a major regulator of pathological angiogenesis. This fits with the evolving story of physiological angiogenesis, where a combination of metabolic and mechanical signaling is emerging as the probable mechanism by which tight feedback regulation of angiogenesis is achieved in vivo.

Piezo1 integration of vascular architecture with physiological force

The mechanisms by which physical forces regulate endothelial cells to determine the complexities of vascular structure and function are enigmatic. Studies of sensory neurons have suggested Piezo proteins as subunits of Ca(2+)-permeable non-selective cationic channels for detection of noxious mechanical impact. Here we show Piezo1 (Fam38a) channels as sensors of frictional force (shear stress) and determinants of vascular structure in both development and adult physiology. Global or endothelial-specific disruption of mouse Piezo1 profoundly disturbed the developing vasculature and was embryonic lethal within days of the heart beating. Haploinsufficiency was not lethal but endothelial abnormality was detected in mature vessels. The importance of Piezo1 channels as sensors of blood flow was shown by Piezo1 dependence of shear-stress-evoked ionic current and calcium influx in endothelial cells and the ability of exogenous Piezo1 to confer sensitivity to shear stress on otherwise resistant cells. Downstream of this calcium influx there was protease activation and spatial reorganization of endothelial cells to the polarity of the applied force. The data suggest that Piezo1 channels function as pivotal integrators in vascular biology.

Robo4 vaccines induce antibodies that retard tumor growth

Tumor endothelial specific expression of Robo4 in adults identifies this plasma membrane protein as an anti-cancer target for immunotherapeutic approaches, such as vaccination. In this report, we describe how vaccination against Robo4 inhibits angiogenesis and tumor growth. To break tolerance to the auto-antigen Robo4, mice were immunised with the extracellular domain of mouse Robo4, fused to the Fc domain of human immunoglobulin within an adjuvant. Vaccinated mice show a strong antibody response to Robo4, with no objectively detectable adverse effects on health. Robo4 vaccinated mice showed impaired fibrovascular invasion and angiogenesis in a rodent sponge implantation assay, as well as a reduced growth of implanted syngeneic Lewis lung carcinoma. The anti-tumor effect of Robo4 vaccination was present in CD8 deficient mice but absent in B cell or IgG1 knockout mice, suggesting antibody dependent cell mediated cytotoxicity as the anti-vascular/anti-tumor mechanism. Finally, we show that an adjuvant free soluble Robo4-carrier conjugate can retard tumor growth in carrier primed mice. These results point to appropriate Robo4 conjugates as potential anti-angiogenic vaccines for cancer patients.

Retargeting of gene expression using endothelium specific hexon modified adenoviral vector

Adenovirus serotype 5 (Ad5) vectors are well suited for gene therapy. However, tissue-selective transduction by systemically administered Ad5-based vectors is confounded by viral particle sequestration in the liver. Hexon-modified Ad5 expressing reporter gene under transcriptional control by the immediate/early cytomegalovirus (CMV) or the Roundabout 4 receptor (Robo4) enhancer/promoter was characterized by growth in cell culture, stability in vitro, gene transfer in the presence of human coagulation factor X, and biodistribution in mice. The obtained data demonstrate the utility of the Robo4 promoter in an Ad5 vector context. Substitution of the hypervariable region 7 (HVR7) of the Ad5 hexon with HVR7 from Ad serotype 3 resulted in decreased liver tropism and dramatically altered biodistribution of gene expression. The results of these studies suggest that the combination of liver detargeting using a genetic modification of hexon with an endothelium-specific transcriptional control element produces an additive effect in the improvement of Ad5 biodistribution.

Clinical significance of UNC5B expression in bladder cancer

UNC5B is a membrane-bound receptor of the neural guidance factor netrin-1 family, with important roles in angiogenesis, neurogenesis, embryonic development, cancer, inflammation and various pathologies. However, its effect on bladder cancer has not been reported. To investigate the association of UNC5B expression with bladder cancer prognosis, 100 cases of clinical bladder cancer and adjacent noncancerous tissue samples, and four bladder cancer cell lines were selected using RT-PCR, Western blot, immunofluorescence and immunohistochemistry to investigate differential expression and cellular positioning of UNC5B, and its relationship with clinicopathological parameters. In 72 % of cases, UNC5B was expressed in both bladder cancer and adjacent noncancerous tissue samples. Expression of UNC5B in bladder cancer tissues increased significantly as cancer stage increased (P < 0.05); UNC5B emerged more in bladder cancer cell lines with lower degrees of malignancy than those with higher degrees of malignancy; UNC5B expression in bladder cancer cells was significantly reduced compared to normal bladder cells (P < 0.05). UNC5B mRNA was down-expressed in about 28 % of bladder cancer tissues. Low UNC5B expression was an independent risk factor for postoperative recurrence in patients with different stages and grades bladder cancer. Furthermore, patients with lower UNC5B expression in tumors had significantly higher recurrence rate after curative surgery and poorer prognosis than those with higher UNC5B expression, suggesting that UNC5B could be used to predict prognosis and recurrence.

Advances in the cellular and molecular biology of angiogenesis

Capillaries have been recognized for over a century as one of the most important components in regulating tissue oxygen transport, and their formation or angiogenesis a pivotal element of tissue remodelling during development and adaptation. Clinical interest stems from observations that both excessive and inadequate vascular growth plays a major role in human diseases, and novel developments in treatments for cancer and eye disease increasingly rely on anti-angiogenic therapies. Although the discovery of VEGF (vascular endothelial growth factor) provided the first clue for specificity of signalling in endothelial cell activation, understanding the integrative response that drives angiogenesis requires a much broader perspective. The Advances in the Cellular and Molecular Biology of Angiogenesis meeting brought together researchers at the forefront of this rapidly moving field to provide an update on current understanding, and the most recent insights into molecular and cellular mechanisms of vascular growth. The plenary lecture highlighted the integrative nature of the angiogenic process, whereas invited contributions from basic and clinician scientists described fundamental mechanisms and disease-associated issues of blood vessel formation, grouped under a number of themes to aid discussion. These articles will appeal to academic, clinical and pharmaceutical scientists interested in the molecular and cellular basis of angiogenesis, their modulation or dysfunction in human diseases, and application of these findings towards translational medicine.