Journal of angiogenesis research最新文献

Vascular exploration of small animals requires imaging hardware with a very high spatial resolution, capable of differentiating large as well as small vessels, in both in vivo and ex vivo studies. Micro Computed Tomography (micro-CT) has emerged in recent years as the preferred modality for this purpose, providing high resolution 3D volumetric data suitable for analysis, quantification, validation, and visualization of results. The usefulness of micro-CT, however, can be adversely affected by a range of factors including physical animal preparation, numerical quantification, visualization of results, and quantification software with limited possibilities. Exacerbating these inherent difficulties is the lack of a unified standard for micro-CT imaging. Most micro-CT today is aimed at particular applications and the software tools needed for quantification, developed mainly by imaging hardware manufacturers, lack the level of detail needed to address more specific aims. This review highlights the capabilities of micro-CT for vascular exploration, describes the current state of imaging protocols, and offers guidelines and suggestions aimed at making micro-CT more accurate, replicable, and robust.

Endothelial Progenitor Cells (EPC) were first described in 1997 and have since been the subject of numerous investigative studies exploring the potential of these cells in the process of cardiovascular damage and repair. Whilst their exact definition and mechanism of action remains unclear, they are directly influenced by different cardiovascular risk factors and have a definite role to play in defining cardiovascular risk. Furthermore, EPCs may have important therapeutic implications and further understanding of their pathophysiology has enabled us to explore new possibilities in the management of cardiovascular disease. This review article aims to provide an overview of the vast literature on EPCs in relation to clinical cardiology.

Background: Recent cancer therapies include drugs that target both tumor growth and angiogenesis including mammalian target of rapamycin (mTOR) inhibitors. Since mTOR inhibitor therapy is associated with significant side effects, we examined potential agents that can reduce the therapeutic dose.

Methods: Methylnaltrexone (MNTX), a peripheral mu opioid receptor (MOR) antagonist, in combination with the mTOR inhibitors temsirolimus and/or rapamycin, was evaluated for inhibition of VEGF-induced human pulmonary microvascular endothelial cell (EC) proliferation and migration as well as in vivo angiogenesis (mouse Matrigel plug assay).

Results: MNTX inhibited VEGF-induced EC proliferation and migration with an IC50 of approximately 100 nM. Adding 10 nM MNTX to EC shifted the IC50 of temsirolimus inhibition of VEGF-induced proliferation and migration from approximately 10 nM to approximately 1 nM and from approximately 50 to approximately 10 nM respectively. We observed similar effects with rapamycin. On a mechanistic level, we observed that MNTX increased EC plasma membrane-associated tyrosine phosphate activity. Inhibition of tyrosine phosphatase activity (3,4-dephostatin) blocked the synergy between MNTX and temsirolimus and increased VEGF-induced tyrosine phosphorylation of Src with enhanced PI3 kinase and mTOR Complex 2-dependent phosphorylation of Akt and subsequent activation of mTOR Complex 1 (rapamycin and temsirolimus target), while silencing Src, Akt or mTOR complex 2 components blocked VEGF-induced angiogenic events.

Conclusions: Our data indicate that MNTX exerts a synergistic effect with rapamycin and temsirolimus on inhibition of VEGF-induced human EC proliferation and migration and in vivo angiogenesis. Therefore, addition of MNTX could potentially lower the dose of mTOR inhibitors which could improve therapeutic index.

Epidermal growth factor-like domain 7, Egfl7, is a largely endothelial restricted gene which is thought to have a role during the differentiation of embryonic stem cells (ESCs) along the endothelial lineage. While it has been shown that Egfl7 knock-down in zebrafish impairs endothelial cord formation, the role of the gene in mammals has been unresolved. Interpretation of mouse knockout studies has been complicated by the fact that deletion of miR-126, an intronic microRNA located within Egfl7, results in vascular defects. Here we use an siRNA knock-down approach to target specific regions of Egfl7 without affecting miR-126 expression. Egfl7 was knocked down in mouse ESCs and the effect on vascular development was assessed using the in vitro embryoid body (EB) model after either 7 or 14 days of differentiation. Knock-down of Egfl7 resulted in the formation of abnormal sheet-like CD31+ structures that were abundant within EBs after 7 days of differentiation. Only up to 60% of these sheets co-expressed basement membrane and endothelial cell junction markers. Similar CD31+ sheets were also seen as outgrowths from 7 day EBs into collagen gels. A partial remodelling occurred by 14 days of differentiation when fewer CD31+ sheets were seen both within EBs, and as outgrowths from EBs. Formation of these sheets was due, at least in part, to increased proliferation specifically of CD31+ cells. Cell death within EBs was unaffected by Egfl7 knock-down. In conclusion, our work shows that knock-down of Egfl7 causes defects in early vascular cord formation, and results in the development of CD31+ sheet-like structures. This suggests that Egfl7 is vital for the formation of endothelial cell cords, and that the gene has an important role during both vasculogenesis and angiogenesis in mammalian cells.

Notch is a critical regulator of angiogenesis and arterial specification. We show that ectopic expression of activated Notch1 induces endothelial morphogenesis in human umbilical vein endothelial cells (HUVEC) in a VEGFR-1-dependent manner. Notch1-mediated upregulation of VEGFR-1 in HUVEC increased their responsiveness to the VEGFR-1 specific ligand, Placental Growth Factor (PlGF). In mice and human endothelial cells, inhibition of Notch signaling resulted in decreased VEGFR-1 expression during VEGF-A-induced neovascularization. In summary, we show that Notch1 plays a role in endothelial cells by regulating VEGFR-1, a function that may be important for physiological and pathological angiogenesis.

Background: Angiogenesis is critical to tumor growth and is therefore a potential target for cancer therapy. As many current inhibitors of angiogenesis exhibit host toxicity, natural alternatives are needed. At millimolar concentrations, ascorbate (vitamin C) inhibits migration and tubule formation by mature endothelial cells and endothelial progenitors. In the present study, we examined the effects of ascorbate, at levels relevant during intravenous infusion therapy, on angiogenesis using an ex vivo an in vivo assay.

Methods: Two assays were used to evaluate effect of high-doses ascorbic acid on angiogenesis: ex vivo rat aortic ring explant assay in Matrigel matrices and in vivo Matrigel plug assay. In aortic rings, we quantified microvessel growth, branching and vessel regression under different treatment conditions. In murine angiogenesis assay, male C57 mice 6-8 weeks old were treated by high-dose ascorbic acid and the number of microvessels was analyzed by histological method. To characterize the population of cells that formed capillary network and microvessels, the sections were stained by CD34 and CD31 antibodies.

Results: Results show that sprouting of endothelial tubules from aortic rings was reduced in a concentration-dependent fashion by ascorbate: while controls roughly tripled sprout densities during the study, ascorbate (1 mg/mL, 5.5 mM) actually reduced sprout density. In vivo, the ability of mice to vascularize subcutaneously implanted Matrigel plug was diminished if the mice were treated with 430 mg/kg vitamin C: numbers of vessels, and vessel densities, in plugs from treated mice were roughly 30% less than those in plugs from untreated mice.

Conclusions: We conclude that the inhibition of angiogenesis by ascorbate suggested in vitro is confirmed in vivo, and that angiogenesis inhibition may be one mechanism by which intravenous ascorbate therapy shows efficacy in animal experiments and clinical case studies.

Vascularization of the vertebrate brain takes place during embryonic development from a preformed perineural vascular plexus. As a consequence of the intimate contact with neuroectodermal cells the vessels, which are entering the brain exclusively via sprouting angiogenesis, acquire and maintain unique barrier properties known as the blood-brain barrier (BBB). The endothelial BBB depends upon the close association of endothelial cells with pericytes, astrocytes, neurons and microglia, which are summarized in the term neuro-vascular unit. Although it is known since decades that the CNS tissue provides the cues for BBB induction and differentiation in endothelial cells, the molecular mechanism remained obscure.Only recently, the canonical Wnt/beta-catenin pathway and the Wnt7a/7b growth factors have been implicated in brain angiogenesis on the one hand and in BBB induction on the other. This breakthrough in understanding the differentiation of the brain vasculature prompted us to review these findings embedded in the emerging concepts of Wnt signaling in the vasculature. In particular, interactions with other pathways that are crucial for vascular development such as VEGF, Notch, angiopoietins and Sonic hedgehog are discussed. Finally, we considered the potential role of the Wnt pathway in vascular brain pathologies in which BBB function is hampered, as for example in glioma, stroke and Alzheimer's disease.

Background: Circulating progenitor cells (PCs) are considered to contribute to the remodeling of atherosclerotic plaques. Their surface receptor CXCR4 plays an important role in the recruitment of PCs to their target. This study compares the mobilization of PCs and their functional characteristics in asymptomatic subjects with stable and with unstable carotid plaques. This could provide insight into plaque remodeling and help to develop biomarkers for plaque stability.

Methods: In 31 subjects with asymptomatic carotid artery stenosis we analyzed the number of CD133+ PCs, VEGFR2+CD34+ PCs and the surface expression of CXCR4 on CD133+ PCs by flow cytometry. Subjects underwent bilateral carotid MRI in a 1.5-T scanner in order to allow the categorization of plaques, following the modified criteria of the American Heart Association.

Results: The number of CD133+ PCs and VEGFR2+CD34+ PCs showed no significant difference between subjects with stable and unstable carotid plaques. The expression of CXCR4 on CD133+ PCs was higher in subjects with unstable plaques than in subjects with stable plaques (p = 0.009).

Conclusions: This study demonstrates an association between functional characteristics of circulating CD133+ PCs and plaque stability in subjects with asymptomatic carotid artery stenosis. The higher expression of CXCR4 on CD133+ PCs suggests a difference in the recruitment of PCs to the injured tissue in subjects with unstable plaques and subjects with stable plaques. As surface expression of CXCR4 on CD133+ PCs differs in subjects with unstable and with stable plaques, CXCR4 is a promising candidate for a serological biomarker for plaque stability.

VEGF-induced angiogenesis significantly contributes to tumor growth, invasion and metastasis. However, little is known about its hematopoietic activity during malignant development and progression. Here we show that in a mouse tumor model, tumor-derived VEGF acts as an endocrine-like hormone to induce extramedullary hematopoiesis by targeting distal organs in the host. In tumor-bearing mice, circulating VEGF induced hepatomegaly and splenomegaly owing to vessel dilation, tortuosity and activation of hematopoiesis. Furthermore, VEGFR1 and VEGFR2 were primarily localized in blood vessels rather than hepatocytes or splenocytes, demonstrating that alteration of angiogenic profiles modulates hematopoiesis in these organs. Stimulation of extramedullary hematopoiesis sheds new light on complex biological functions of VEGF and significantly increases our understanding of molecular mechanisms underlying VEGF-induced tumor growth.

The Notch signaling pathway is a critical component of vascular formation and morphogenesis in both development and disease. Compelling evidence indicates that Notch signaling is required for the induction of arterial-cell fate during development and for the selection of endothelial tip and stalk cells during sprouting angiogenesis. In mammals, two of the four Notch receptors (Notch1 and Notch4) and three of the five Notch ligands (Jagged1, Dll1, and Dll4) are predominantly expressed in vascular endothelial cells and are important for many aspects of vascular biology. During arterial cell-fate selection and angiogenesis, the roles of Notch1 and Notch4 are thought to be similar, and the function of Dll4 is well-characterized. However, the molecular mechanisms that determine the functional similarities and differences of Notch ligands in vascular endothelial cells remain largely unknown; consequently, additional research is needed to elucidate the ligand-specific functions and mechanisms associated with Notch activation in the vascular endothelium. Results from recent studies indicate that Dll1 and Dll4 have distinct roles in the specification and maintenance of arterial cell identity, while Dll4 and Jagged1 have opposing functions in tip- and stalk-cell selection during sprouting angiogenesis. This review will focus on the newly discovered, distinct functions of several Notch ligands in the regulation of blood vessel formation and will provide perspectives for future research in the field.