A role for VEGF as a negative regulator of pericyte function and vessel maturation

Angiogenesis does not only depend on endothelial cell invasion and proliferation: it also requires pericyte coverage of vascular sprouts for vessel stabilization. These processes are coordinated by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) through their cognate receptors on endothelial cells and vascular smooth muscle cells (VSMCs), respectively. PDGF induces neovascularization by priming VSMCs/pericytes to release pro-angiogenic mediators. Although VEGF directly stimulates endothelial cell proliferation and migration, its role in pericyte biology is less clear. Here we define a role for VEGF as an inhibitor of neovascularization on the basis of its capacity to disrupt VSMC function. Specifically, under conditions of PDGF-mediated angiogenesis, VEGF ablates pericyte coverage of nascent vascular sprouts, leading to vessel destabilization. At the molecular level, VEGF-mediated activation of VEGF-R2 suppresses PDGF-Rbeta signalling in VSMCs through the assembly of a previously undescribed receptor complex consisting of PDGF-Rbeta and VEGF-R2. Inhibition of VEGF-R2 not only prevents assembly of this receptor complex but also restores angiogenesis in tissues exposed to both VEGF and PDGF. Finally, genetic deletion of tumour cell VEGF disrupts PDGF-Rbeta/VEGF-R2 complex formation and increases tumour vessel maturation. These findings underscore the importance of VSMCs/pericytes in neovascularization and reveal a dichotomous role for VEGF and VEGF-R2 signalling as both a promoter of endothelial cell function and a negative regulator of VSMCs and vessel maturation.     

Regulation of angiogenesis by a non-canonical Wnt-Flt1 pathway in myeloid cells

Myeloid cells are a feature of most tissues. Here we show that during development, retinal myeloid cells (RMCs) produce Wnt ligands to regulate blood vessel branching. In the mouse retina, where angiogenesis occurs postnatally, somatic deletion in RMCs of the Wnt ligand transporter Wntless results in increased angiogenesis in the deeper layers. We also show that mutation of Wnt5a and Wnt11 results in increased angiogenesis and that these ligands elicit RMC responses via a non-canonical Wnt pathway. Using cultured myeloid-like cells and RMC somatic deletion of Flt1, we show that an effector of Wnt-dependent suppression of angiogenesis by RMCs is Flt1, a naturally occurring inhibitor of vascular endothelial growth factor (VEGF). These findings indicate that resident myeloid cells can use a non-canonical, Wnt-Flt1 pathway to suppress angiogenic branching.     

Oxidative stress induces angiogenesis by activating TLR2 with novel endogenous ligands

Reciprocity of inflammation, oxidative stress and neovascularization is emerging as an important mechanism underlying numerous processes from tissue healing and remodelling to cancer progression. Whereas the mechanism of hypoxia-driven angiogenesis is well understood, the link between inflammation-induced oxidation and de novo blood vessel growth remains obscure. Here we show that the end products of lipid oxidation, ω-(2-carboxyethyl)pyrrole (CEP) and other related pyrroles, are generated during inflammation and wound healing and accumulate at high levels in ageing tissues in mice and in highly vascularized tumours in both murine and human melanoma. The molecular patterns of carboxyalkylpyrroles are recognized by Toll-like receptor 2 (TLR2), but not TLR4 or scavenger receptors on endothelial cells, leading to an angiogenic response that is independent of vascular endothelial growth factor. CEP promoted angiogenesis in hindlimb ischaemia and wound healing models through MyD88-dependent TLR2 signalling. Neutralization of endogenous carboxyalkylpyrroles impaired wound healing and tissue revascularization and diminished tumour angiogenesis. Both TLR2 and MyD88 are required for CEP-induced stimulation of Rac1 and endothelial migration. Taken together, these findings establish a new function of TLR2 as a sensor of oxidation-associated molecular patterns, providing a key link connecting inflammation, oxidative stress, innate immunity and angiogenesis.     

Blockade of Dll4 inhibits tumour growth by promoting non-productive angiogenesis

Tumour growth requires accompanying expansion of the host vasculature, with tumour progression often correlated with vascular density. Vascular endothelial growth factor (VEGF) is the best-characterized inducer of tumour angiogenesis. We report that VEGF dynamically regulates tumour endothelial expression of Delta-like ligand 4 (Dll4), which was previously shown to be absolutely required for normal embryonic vascular development. To define Dll4 function in tumour angiogenesis, we manipulated this pathway in murine tumour models using several approaches. Here we show that blockade resulted in markedly increased tumour vascularity, associated with enhanced angiogenic sprouting and branching. Paradoxically, this increased vascularity was non-productive-as shown by poor perfusion and increased hypoxia, and most importantly, by decreased tumour growth-even for tumours resistant to anti-VEGF therapy. Thus, VEGF-induced Dll4 acts as a negative regulator of tumour angiogenesis; its blockade results in a striking uncoupling of tumour growth from vessel density, presenting a novel therapeutic approach even for tumours resistant to anti-VEGF therapies.     

Expression of vascular endothelial growth factor in rat uterus during peri-implantation

The first distinct mark of rodent implantation is the increased vascular permeability and significant angiogenesis at the sites of blastocyst implantation, but its mechanism is not clearly defined. Vascular endothelial growth factor (VEGF) is the key mediator for angiogenesis during embryogenesis and adult span and also serves as a vascular permeability factor. The aim of this study is to explore VEGF regulation mechanism and the possible role that VEGF plays in implantation by studying the VEGF expression and angiogenesis in the rat uterus during estrous cycle, ovarioectomized and peri-implantation stages usingin situ message RNA hybridization and confocal laser scanning techniques. The results indicated that VEGF was regulated by ovarian steroid hormones. VEGF expression before implantation was localized at luminal epithelium, shifted to stroma as implantation initiated and extensively located at the decidualizing stroma region after implantation. Bandeiraea simplicifolia-1 (BS-1) agglutinin and antibody against von Willebrand factor (vWF) were used to mark the endothelial cells and blood vessels. The results showed that the active angiogenesis occurred during the implantation process and this effect was probably mediated by VEGF. The results suggest that under the regulation of ovarian steroid hormones, VEGF plays an essential role in angiogenesis and increasing vascular permeability in endometrium, which are necessary for successful implantation.     

Vascular endothelial growth factor is a potential tumour angiogenesis factor in human gliomas in vivo.

Clinical and experimental studies suggest that angiogenesis is a prerequisite for solid tumour growth. Several growth factors with mitogenic or chemotactic activity for endothelial cells in vitro have been described, but it is not known whether these mediate tumour vascularization in vivo. Glioblastoma, the most common and most malignant brain tumour in humans, is distinguished from astrocytoma by the presence of necroses and vascular proliferations. Here we show that expression of an endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), is induced in astrocytoma cells but is dramatically upregulated in two apparently different subsets of glioblastoma cells. The high-affinity tyrosine kinase receptor for VEGF, flt, although not expressed in normal brain endothelium, is upregulated in tumour endothelial cells in vivo. These observations strongly support the concept that tumour angiogenesis is regulated by paracrine mechanisms and identify VEGF as a potential tumour angiogenesis factor in vivo.     

PM2.5引起的肿瘤新生血管形成和转移研究进展

 PM_2.5指直径≤2.5 μm 的颗粒物质,它很容易穿过呼吸道屏障,进入血液循环,可诱发肺癌等多种恶性肿瘤,已成为恶性肿瘤新的诱因。近年研究揭示,PM_2.5可刺激肿瘤细胞合成和分泌血管内皮生长因子（VEGF）,促进血管内皮细胞介导的肿瘤血管新生;并可激活肿瘤细胞,使其通过血管生成拟态直接形成肿瘤血管;还能使肿瘤干细胞向肿瘤内皮细胞转化,促进肿瘤新生血管形成。此外,PM_2.5可促进肿瘤细胞及其他多种细胞分泌趋化因子和白细胞介素,招募骨髓和血液中白细胞进入肿瘤组织,诱发局部慢性炎症反应,诱导上皮细胞-间充质细胞转化（EMT）的发生,增加肿瘤细胞干性、迁移和转移能力;还可破坏血管稳态,增加血管通透性,为肿瘤细胞的转移打开方便之门。PM_2.5在肿瘤的新生血管形成和转移中起了重要作用,然而,至今对其作用机制知之甚少。因此,进一步深入研究PM_2.5诱导的肿瘤新生血管形成及转移机制,能为PM_2.5引起的恶性肿瘤防治提供可靠的理论依据和新的应对策略。     

Identification of an angiogenic mitogen selective for endocrine gland endothelium

The known endothelial mitogens stimulate growth of vascular endothelial cells without regard to their tissue of origin. Here we report a growth factor that is expressed largely in one type of tissue and acts selectively on one type of endothelium. This molecule, called endocrine-gland-derived vascular endothelial growth factor (EG-VEGF), induced proliferation, migration and fenestration (the formation of membrane discontinuities) in capillary endothelial cells derived from endocrine glands. However, EG-VEGF had little or no effect on a variety of other endothelial and non-endothelial cell types tested. Similar to VEGF, EG-VEGF possesses a HIF-1 binding site, and its expression is induced by hypoxia. Both EG-VEGF and VEGF resulted in extensive angiogenesis and cyst formation when delivered in the ovary. However, unlike VEGF, EG-VEGF failed to promote angiogenesis in the cornea or skeletal muscle. Expression of human EG-VEGF messenger RNA is restricted to the steroidogenic glands, ovary, testis, adrenal and placenta and is often complementary to the expression of VEGF, suggesting that these molecules function in a coordinated manner. EG-VEGF is an example of a class of highly specific mitogens that act to regulate proliferation and differentiation of the vascular endothelium in a tissue-specific manner.     

Angiogenesis selectively requires the p110alpha isoform of PI3K to control endothelial cell migration

Phosphoinositide 3-kinases (PI3Ks) signal downstream of multiple cell-surface receptor types. Class IA PI3K isoforms couple to tyrosine kinases and consist of a p110 catalytic subunit (p110alpha, p110beta or p110delta), constitutively bound to one of five distinct p85 regulatory subunits. PI3Ks have been implicated in angiogenesis, but little is known about potential selectivity among the PI3K isoforms and their mechanism of action in endothelial cells during angiogenesis in vivo. Here we show that only p110alpha activity is essential for vascular development. Ubiquitous or endothelial cell-specific inactivation of p110alpha led to embryonic lethality at mid-gestation because of severe defects in angiogenic sprouting and vascular remodelling. p110alpha exerts this critical endothelial cell-autonomous function by regulating endothelial cell migration through the small GTPase RhoA. p110alpha activity is particularly high in endothelial cells and preferentially induced by tyrosine kinase ligands (such as vascular endothelial growth factor (VEGF)-A). In contrast, p110beta in endothelial cells signals downstream of G-protein-coupled receptor (GPCR) ligands such as SDF-1alpha, whereas p110delta is expressed at low level and contributes only minimally to PI3K activity in endothelial cells. These results provide the first in vivo evidence for p110-isoform selectivity in endothelial PI3K signalling during angiogenesis.     

Dll4 signalling through Notch1 regulates formation of tip cells during angiogenesis

In sprouting angiogenesis, specialized endothelial tip cells lead the outgrowth of blood-vessel sprouts towards gradients of vascular endothelial growth factor (VEGF)-A. VEGF-A is also essential for the induction of endothelial tip cells, but it is not known how single tip cells are selected to lead each vessel sprout, and how tip-cell numbers are determined. Here we present evidence that delta-like 4 (Dll4)-Notch1 signalling regulates the formation of appropriate numbers of tip cells to control vessel sprouting and branching in the mouse retina. We show that inhibition of Notch signalling using gamma-secretase inhibitors, genetic inactivation of one allele of the endothelial Notch ligand Dll4, or endothelial-specific genetic deletion of Notch1, all promote increased numbers of tip cells. Conversely, activation of Notch by a soluble jagged1 peptide leads to fewer tip cells and vessel branches. Dll4 and reporters of Notch signalling are distributed in a mosaic pattern among endothelial cells of actively sprouting retinal vessels. At this location, Notch1-deleted endothelial cells preferentially assume tip-cell characteristics. Together, our results suggest that Dll4-Notch1 signalling between the endothelial cells within the angiogenic sprout serves to restrict tip-cell formation in response to VEGF, thereby establishing the adequate ratio between tip and stalk cells required for correct sprouting and branching patterns. This model offers an explanation for the dose-dependency and haploinsufficiency of the Dll4 gene, and indicates that modulators of Dll4 or Notch signalling, such as gamma-secretase inhibitors developed for Alzheimer's disease, might find usage as pharmacological regulators of angiogenesis.     

血管内皮生长因子研究进展

血管内皮生长因子是一种有效的血管形成和血管通透性诱导因子,特异性地作用于血管内皮细胞,具有维持血管正常状态和完整性、增加血管通透性、促进血管生成的作用。在正常成人和动物组织中表达水平较低,一些代谢旺盛、血供丰富的组织中VEGF表达水平略高,一些病理情况下可以过度表达。     

血管内皮生长因子与急性白血病骨髓的血管新生

目的:探讨血管内皮生长因子(VEGF)在急性白血病及其骨髓的新生血管之间的关系,为白血病的治疗寻找新的治疗方法。方法:查阅总结近15年来国内外相关文献,对VEGF的性质作用特点以及与急性白血病的关系进行综述。结果:白血病细胞表达较高的VEGF,VEGF促使血管生成和内皮细胞增生,白血病细胞与骨髓新生血管之间存在密切的关系。结论:抗VEGF和抗新生血管治疗有可能成为治疗急性白血病的新的思路和方法。     

Pathophysiological consequences of VEGF-induced vascular permeability

Although vascular endothelial growth factor (VEGF) induces angiogenesis, it also disrupts vascular barrier function in diseased tissues. Accordingly, VEGF expression in cancer and ischaemic disease has unexpected pathophysiological consequences. By uncoupling endothelial cell-cell junctions VEGF causes vascular permeability and oedema, resulting in extensive injury to ischaemic tissues after stroke or myocardial infarction. In cancer, VEGF-mediated disruption of the vascular barrier may potentiate tumour cell extravasation, leading to widespread metastatic disease. Therefore, by blocking the vascular permeability promoting effects of VEGF it may be feasible to reduce tissue injury after ischaemic disease and minimize the invasive properties of circulating tumour cells.     

Blocking VEGFR-3 suppresses angiogenic sprouting and vascular network formation

Angiogenesis, the growth of new blood vessels from pre-existing vasculature, is a key process in several pathological conditions, including tumour growth and age-related macular degeneration. Vascular endothelial growth factors (VEGFs) stimulate angiogenesis and lymphangiogenesis by activating VEGF receptor (VEGFR) tyrosine kinases in endothelial cells. VEGFR-3 (also known as FLT-4) is present in all endothelia during development, and in the adult it becomes restricted to the lymphatic endothelium. However, VEGFR-3 is upregulated in the microvasculature of tumours and wounds. Here we demonstrate that VEGFR-3 is highly expressed in angiogenic sprouts, and genetic targeting of VEGFR-3 or blocking of VEGFR-3 signalling with monoclonal antibodies results in decreased sprouting, vascular density, vessel branching and endothelial cell proliferation in mouse angiogenesis models. Stimulation of VEGFR-3 augmented VEGF-induced angiogenesis and sustained angiogenesis even in the presence of VEGFR-2 (also known as KDR or FLK-1) inhibitors, whereas antibodies against VEGFR-3 and VEGFR-2 in combination resulted in additive inhibition of angiogenesis and tumour growth. Furthermore, genetic or pharmacological disruption of the Notch signalling pathway led to widespread endothelial VEGFR-3 expression and excessive sprouting, which was inhibited by blocking VEGFR-3 signals. Our results implicate VEGFR-3 as a regulator of vascular network formation. Targeting VEGFR-3 may provide additional efficacy for anti-angiogenic therapies, especially towards vessels that are resistant to VEGF or VEGFR-2 inhibitors.     

A vascular niche and a VEGF-Nrp1 loop regulate the initiation and stemness of skin tumours

Angiogenesis is critical during tumour initiation and malignant progression. Different strategies aimed at blocking vascular endothelial growth factor (VEGF) and its receptors have been developed to inhibit angiogenesis in cancer patients. It has become increasingly clear that in addition to its effect on angiogenesis, other mechanisms including a direct effect of VEGF on tumour cells may account for the efficiency of VEGF-blockade therapies. Cancer stem cells (CSCs) have been described in various cancers including squamous tumours of the skin. Here we use a mouse model of skin tumours to investigate the impact of the vascular niche and VEGF signalling on controlling the stemness (the ability to self renew and differentiate) of squamous skin tumours during the early stages of tumour progression. We show that CSCs of skin papillomas are localized in a perivascular niche, in the immediate vicinity of endothelial cells. Furthermore, blocking VEGFR2 caused tumour regression not only by decreasing the microvascular density, but also by reducing CSC pool size and impairing CSC renewal properties. Conditional deletion of Vegfa in tumour epithelial cells caused tumours to regress, whereas VEGF overexpression by tumour epithelial cells accelerated tumour growth. In addition to its well-known effect on angiogenesis, VEGF affected skin tumour growth by promoting cancer stemness and symmetric CSC division, leading to CSC expansion. Moreover, deletion of neuropilin-1 (Nrp1), a VEGF co-receptor expressed in cutaneous CSCs, blocked VEGF's ability to promote cancer stemness and renewal. Our results identify a dual role for tumour-cell-derived VEGF in promoting cancer stemness: by stimulating angiogenesis in a paracrine manner, VEGF creates a perivascular niche for CSCs, and by directly affecting CSCs through Nrp1 in an autocrine loop, VEGF stimulates cancer stemness and renewal. Finally, deletion of Nrp1 in normal epidermis prevents skin tumour initiation. These results may have important implications for the prevention and treatment of skin cancers.     

Functions of VEGF in female reproductive system

As a homodimeric glycoprotein,vascular endothelial growth factor(VEGF)is a highly specific mitogen of vascular endothelial cells.It can induce proliferation and migration,and inhibit apoptosis of endothelial cell.VEGF is involved in many processes in the female reproductive system,such as ovulation,periodical changes of endometrium,embryo implantation and development,VEGF plays important roles in some reproductive diseases,including preeclampsia and fetal hypoevolutism in uterus.Based on our studies on angiogenesis and its relevant factors in the female reproductive system these years,the functions of VEGF in female reproductive system are reviewed,and the research prospect and application of VEGF are also discussed.     

鼻咽癌细胞凋亡与血管生成的关系

摘要：为了探讨鼻咽癌（NPC）细胞凋亡及瘤内血管生成与患者预后的关系,采用TdT酶介导的生物素化dUTP缺口末端标记技术（TUNEL）和免疫组化S-P法,分别检测20例正常鼻咽粘膜组织及73例NPC组织的细胞凋亡率（Apoptosis Rate AR）、瘤内微血管密度（MVD）及血管内皮细胞生长因子（VEGF）的表达。其中,NPC复发转移组24例,未复发组49例。结果表明,正常鼻咽粘膜AR显著高于NPC（P〈0．01）,NPC复发转移组的MVD及VEGF显著高于未复发组（P〈0．05）,而AR则显著低于未复发组（P〈0．05）,MVD与VEGF、MVD与AR呈正相关（P〈0.05）。在NPC发展过程中,细胞凋亡明显受到抑制,VEGF是血管生成的重要因子,并通过促进血管生成影响患者的预后,说明细胞凋亡与NPC患者的预后有关系。