Exogenous clustered neuropilin 1 enhances vasculogenesis and angiogenesis

Alteration of Neuropilin-1 and Heparan Sulfate Interaction Impairs Murine B16 Tumor Growth

Neuropilin-1 acts as a coreceptor with vascular endothelial growth factor receptors to facilitate binding of its ligand, vascular endothelial growth factor. Neuropilin-1 also binds to heparan sulfate, but the functional significance of this interaction has not been established. A combinatorial library screening using heparin oligosaccharides followed by molecular dynamics simulations of a heparin tetradecasaccharide suggested a highly conserved binding site composed of amino acid residues extending across the b1 and b2 domains of murine neuropilin-1. Mutagenesis studies established the importance of arginine513 and lysine514 for binding of heparin to a recombinant form of Nrp1 composed of the a1, a2, b1, and b2 domains. Recombinant Nrp1 protein bearing R513A,K514A mutations showed a significant loss of heparin-binding, heparin-induced dimerization, and heparin-dependent thermal stabilization. Isothermal calorimetry experiments suggested a 1:2 complex of heparin tetradecasaccharide:Nrp1. To study the impact of altered heparin binding in vivo, a mutant allele of Nrp1 bearing the R513A,K514A mutations was created in mice (Nrp1D) and crossbred to Nrp1+/- mice to examine the impact of altered heparan sulfate binding. Analysis of tumor formation showed variable effects on tumor growth in Nrp1D/D mice, resulting in a frank reduction in tumor growth in Nrp1D/- mice. Expression of mutant Nrp1D protein was normal in tissues, suggesting that the reduction in tumor growth was due to the altered binding of heparin/heparan sulfate to neuropilin-1. These findings suggest that the interaction of neuropilin-1 with heparan sulfate modulates its stability and its role in tumor formation and growth.

Relationship between soluble neuropilin-1 in the gingival crevicular fluid of early pregnant women and different severities of periodontitis: A cross-sectional study

Background

Pregnancy exacerbates the periodontal inflammation; however, the biological mediators involved are not well characterized. Neuropilins (NRPs) are transmembrane glycoproteins involved in physiological and pathogenic processes such as angiogenesis and immunity but its relationship with periodontal disease in pregnant women has not been studied.

Objective

To explore the soluble Neuropilin-1 (sNRP-1) levels in gingival crevicular fluid (GCF) samples during early pregnancy and its association with the periodontitis severity and periodontal clinical parameters.

Methods

80 pregnant women were recruited, and GCF samples were collected. Clinical data and periodontal clinical parameters were recorded. sNRP-1 expression was determined by ELISA assay. The relationship between sNRP-1(+) pregnant women with the severity of periodontitis and periodontal clinical parameters was determined by Kruskal-Wallis and Mann-Whitney tests. Spearman's test estimated the correlation between sNRP-1 levels and periodontal clinical parameters.

Results

Periodontitis was classified as mild in 27.5% (n = 22) women, moderate in 42.5% (n = 34), and severe in 30% (n = 24). sNRP-1 expression was higher in the GCF of pregnant with severe (41.67%) and moderate (41.17%) periodontitis compared than in those with mild periodontitis (18.8%). The sNRP-1(+) pregnant had a higher BOP (76.5% v/s 57%; p = 0.0071) and PISA (1199.5 mm2 v/s 880.2 mm2; p = 0.0282) compared with sNRP-1(-). A positive correlation between sNRP-1 levels in GCF and BOP (p = 0.0081) and PISA (p = 0.0398) was observed.

Conclusions

The results suggest that sNRP-1 could be involved in periodontal inflammation during pregnancy.

Neuropilin-1 deficiency in vascular smooth muscle cells is associated with hereditary hemorrhagic telangiectasia arteriovenous malformations

Patients with hereditary hemorrhagic telangiectasia (HHT) have arteriovenous malformations (AVMs) with genetic mutations involving the activin-A receptor like type 1 (ACVRL1 or ALK1) and endoglin (ENG). Recent studies have shown that Neuropilin-1 (NRP-1) inhibits ALK1. We investigated the expression of NRP-1 in livers of patients with HHT and found that there was a significant reduction in NRP-1 in perivascular smooth muscle cells (SMCs). We used Nrp1^SM22KO mice (Nrp1 was ablated in SMCs) and found hemorrhage, increased immune cell infiltration with a decrease in SMCs, and pericyte lining in lungs and liver in adult mice. Histologic examination revealed lung arteriovenous fistulas (AVFs) with enlarged liver vessels. Evaluation of the retina vessels at P5 from Nrp1^SM22KO mice demonstrated dilated capillaries with a reduction of pericytes. In inflow artery of surgical AVFs from the Nrp1^SM22KO versus WT mice, there was a significant decrease in Tgfb1, Eng, and Alk1 expression and phosphorylated SMAD1/5/8 (pSMAD1/5/8), with an increase in apoptosis. TGF-β1–stimulated aortic SMCs from Nrp1^SM22KO versus WT mice have decreased pSMAD1/5/8 and increased apoptosis. Coimmunoprecipitation experiments revealed that NRP-1 interacts with ALK1 and ENG in SMCs. In summary, NRP-1 deletion in SMCs leads to reduced ALK1, ENG, and pSMAD1/5/8 signaling and reduced cell death associated with AVM formation.

Maternal plasma soluble neuropilin-1 is downregulated in fetal growth restriction complicated by abnormal umbilical artery Doppler: a pilot study

OBJECTIVES

Placental expression of neuropilin-1 (NRP1), a proangiogenic member of the vascular endothelial growth factor receptor family involved in sprouting angiogenesis, was recently discovered to be downregulated in pregnancies with fetal growth restriction (FGR) and abnormal umbilical artery (UA) Doppler. Soluble NRP1 (sNRP1) is an antagonist to NRP1; however, little is known about its role in normal and FGR pregnancies. This study tested the hypotheses that, first, sNRP1 would be detectable in maternal circulation and, second, its concentration would be upregulated in FGR pregnancies compared to those with normal fetal growth and this would correlate with the severity of the disease as assessed by UA Doppler.

METHODS

This was a prospective case-control pilot study of 40 singleton pregnancies (20 FGR cases and 20 uncomplicated controls) between 24 + 0 and 40 + 0 weeks' gestation followed in an academic perinatal center from January 2015 to May 2017. FGR was defined as an ultrasound-estimated fetal weight < 10^th percentile for gestational age. The control group was matched to the FGR group for maternal age and gestational age at assessment. Fetal ultrasound biometry and UA Doppler were performed using standard protocols. Maternal plasma sNRP1 measurements were performed using a commercially available ELISA.

RESULTS

Contrary to the study hypothesis, maternal plasma sNRP1 levels were significantly decreased in FGR pregnancies as compared to those with normal fetal growth (137.4 ± 44.8 pg/mL vs 166.7 ± 36.9 pg/mL; P = 0.03). However, there was no significant difference in sNRP1 concentration between the control group and FGR pregnancies that had normal UA Doppler. Plasma sNRP1 was downregulated in FGR pregnancies with elevated UA systolic/diastolic ratio (P = 0.023) and those with UA absent or reversed end-diastolic flow (P = 0.005) in comparison to FGR pregnancies with normal UA Doppler. This suggests that biometrically small fetuses without hemodynamic compromise are small-for-gestational age rather than FGR.

CONCLUSIONS

This study demonstrated a significant decrease in maternal plasma sNRP1 concentration in growth-restricted pregnancies with fetoplacental circulatory compromise. These findings suggest a possible role of sNRP1 in modulating fetal growth and its potential as a biomarker for FGR. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Susceptibility to Cardiac Arrhythmias and Sympathetic Nerve Growth in VEGF-B Overexpressing Myocardium

VEGF-B gene therapy is a promising proangiogenic treatment for ischemic heart disease, but, unexpectedly, we found that high doses of VEGF-B promote ventricular arrhythmias (VAs). VEGF-B knockout, alpha myosin heavy-chain promoter (αMHC)-VEGF-B transgenic mice, and pigs transduced intramyocardially with adenoviral (Ad)VEGF- B186 were studied. Immunostaining showed a 2-fold increase in the number of nerves per field (76 vs. 39 in controls, p < 0.001) and an abnormal nerve distribution in the hypertrophic hearts of 11- to 20-month-old αMHC-VEGF-B mice. AdVEGF-B186 gene transfer (GT) led to local sprouting of nerve endings in pig myocardium (141 vs. 78 nerves per field in controls, p < 0.05). During dobutamine stress, 60% of the αMHC-VEGF-B hypertrophic mice had arrhythmias as compared to 7% in controls, and 20% of the AdVEGF-B186-transduced pigs and 100% of the combination of AdVEGF-B186- and AdsVEGFR-1-transduced pigs displayed VAs and even ventricular fibrillation. AdVEGF-B186 GT significantly increased the risk of sudden cardiac death in pigs when compared to any other GT with different VEGFs (hazard ratio, 500.5; 95% confidence interval [CI] 46.4-5,396.7; p < 0.0001). In gene expression analysis, VEGF-B induced the upregulation of Nr4a2, ATF6, and MANF in cardiomyocytes, molecules previously linked to nerve growth and differentiation. Thus, high AdVEGF-B186 overexpression induced nerve growth in the adult heart via a VEGFR-1 signaling-independent mechanism, leading to an increased risk of VA and sudden cardiac death.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

VEGF (Vascular Endothelial Growth Factor) Induces NRP1 (Neuropilin-1) Cleavage via ADAMs (a Disintegrin and Metalloproteinase) 9 and 10 to Generate Novel Carboxy-Terminal NRP1 Fragments That Regulate Angiogenic Signaling

Objective- NRP1(neuropilin-1) acts as a coreceptor for VEGF (vascular endothelial growth factor) with an essential role in angiogenesis. Recent findings suggest that posttranslational proteolytic cleavage of VEGF receptors may be an important mechanism for regulating angiogenesis, but the role of NRP1 proteolysis and the NRP1 species generated by cleavage in endothelial cells is not known. Here, we characterize NRP1 proteolytic cleavage in endothelial cells, determine the mechanism, and investigate the role of NRP1 cleavage in regulation of endothelial cell function. Approach and Results- NRP1 species comprising the carboxy (C)-terminal and transmembrane NRP1 domains but lacking the ligand-binding A and B regions are constitutively expressed in endothelial cells. Generation of these C-terminal domain NRP1 proteins is upregulated by phorbol ester and Ca²⁺ ionophore, and reduced by pharmacological inhibition of metalloproteinases, by small interfering RNA-mediated knockdown of 2 members of ADAM (a disintegrin and metalloproteinase) family, ADAMs 9 and 10, and by a specific ADAM10 inhibitor. Furthermore, VEGF upregulates expression of these NRP1 species in an ADAM9/10-dependent manner. Transduction of endothelial cells with adenoviral constructs expressing NRP1 C-terminal domain fragments inhibited VEGF-induced phosphorylation of VEGFR2 (VEGF receptor tyrosine kinase)/KDR (kinase domain insert receptor) and decreased VEGF-stimulated endothelial cell motility and angiogenesis in coculture and aortic ring sprouting assays. Conclusions- These findings identify novel NRP1 species in endothelial cells and demonstrate that regulation of NRP1 proteolysis via ADAMs 9 and 10 is a new regulatory pathway able to modulate VEGF angiogenic signaling.

Neuropilins in the Context of Tumor Vasculature

Neuropilin-1 and Neuropilin-2 form a small family of plasma membrane spanning receptors originally identified by the binding of semaphorin and vascular endothelial growth factor. Having no cytosolic protein kinase domain, they function predominantly as co-receptors of other receptors for various ligands. As such, they critically modulate the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. This review highlights the diverse neuropilin ligands and interacting partners on endothelial cells, which are relevant in the context of the tumor vasculature and the tumor microenvironment. In addition to tumor cells, the latter contains cancer-associated fibroblasts, immune cells, and endothelial cells. Based on the prevalent neuropilin-mediated interactions, the suitability of various neuropilin-targeted substances for influencing tumor angiogenesis as a possible building block of a tumor therapy is discussed.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

Potential beneficial effect of some adipokines positively correlated with the adipose tissue content on the cardiovascular system

Obesity is a risk factor of cardiovascular diseases. However, in the case of heart failure, obese and overweight patients have a more favourable prognosis compared to patients who have a normal body weight. This phenomenon is referred to as the "obesity paradox," and it is explained by, among others, a positive effect of adipokines produced by adipose tissue, particularly by the tissue located in the direct vicinity of the heart and blood vessels. The favourable effect on the cardiovascular system is mostly associated with adiponectin and omentin, but the levels of these substances are reduced in obese patients. Among the adipokines which levels are positively correlated with the adipose tissue content, favourable activity is demonstrated by apelin, progranulin, chemerin, TNF-α (tumour necrosis factor-)α, CTRP-3 (C1q/tumour necrosis factor (TNF) related protein), leptin, visfatin and vaspin. This activity is associated with the promotion of regeneration processes in the damaged myocardium, formation of new blood vessels, reduction of the afterload, improvement of metabolic processes in cardiomyocytes and myocardial contractile function, inhibition of apoptosis and fibrosis of the myocardium, as well as anti-inflammatory and anti-atheromatous effects. The potential use of these properties in the treatment of heart failure and ischaemic heart disease, as well as in pulmonary hypertension, arterial hypertension and the limitation of the loss of cardiomyocytes during cardioplegia-requiring cardiosurgical procedures, is studied. The most advanced studies focus on analogues of apelin and progranulin.

An Overview of VEGF-Mediated Signal Transduction

Vascular endothelial growth factor (VEGF) plays a fundamental role in angiogenesis and endothelial cell biology, and has been the subject of intense study as a result. VEGF acts via a diverse and complex range of signaling pathways, with new targets constantly being discovered. This review attempts to summarize the current state of knowledge regarding VEGF cell signaling in endothelial and cardiovascular biology, with a particular emphasis on its role in angiogenesis.

VEGFA splicing: divergent isoforms regulate spermatogonial stem cell maintenance

Despite being well-known for regulating angiogenesis in both normal and tumorigenic environments, vascular endothelial growth factor A (VEGFA) has been recently implicated in male fertility, namely in the maintenance of spermatogonial stem cells (SSC). The VEGFA gene can be spliced into multiple distinct isoforms that are either angiogenic or antiangiogenic in nature. Although studies have demonstrated the alternative splicing of VEGFA, including the divergent roles of the two isoform family types, many investigations do not differentiate between them. Data concerning VEGFA in the mammalian testis are limited, but the various angiogenic isoforms appear to promote seminiferous cord formation and to form a gradient across which cells may migrate. Treatment with either antiangiogenic isoforms of VEGFA or with inhibitors to angiogenic signaling impair these processes. Serendipitously, expression of KDR, the primary receptor for both types of VEGFA isoforms, was observed on male germ cells. These findings led to further investigation of the way that VEGFA elicits avascular functions within testes. Following treatment of donor perinatal male mice with either antiangiogenic VEGFA165b or angiogenic VEGFA164 isoforms, seminiferous tubules were less colonized following transplantation with cells from VEGFA165b-treated donors. Thus, VEGFA165b and possibly other antiangiogenic isoforms of VEGFA reduce SSC number either by promoting premature differentiation, inducing cell death, or by preventing SSC formation. Thus, angiogenic isoforms of VEGFA are hypothesized to promote SSC self-renewal, and the divergent isoforms are thought to balance one another to maintain SSC homeostasis in vivo.

Neuropilin Functions as an Essential Cell Surface Receptor

The Neuropilins (Nrps) are a family of essential cell surface receptors involved in multiple fundamental cellular signaling cascades. Nrp family members have key functions in VEGF-dependent angiogenesis and semaphorin-dependent axon guidance, controlling signaling and cross-talk between these fundamental physiological processes. More recently, Nrp function has been found in diverse signaling and adhesive functions, emphasizing their role as pleiotropic co-receptors. Pathological Nrp function has been shown to be important in aberrant activation of both canonical and alternative pathways. Here we review key recent insights into Nrp function in human health and disease.

Regulation of soluble neuropilin 1, an endogenous angiogenesis inhibitor, in liver development and regeneration

Neuropilin-1 (NRP1) is a receptor for vascular endothelial growth factor (VEGF). A soluble isoform of Nrp1 (sNrp1) has not been described in the mouse. Our goal was to examine the expression of mouse sNrp1 during liver development and regeneration.sNrp1 was cloned from mouse liver. The expression of sNrp1 and VEGF was examined in mouse liver during post-natal development and regeneration using northern blot, western blot, in situ hybridisation, and immunohistochemical analyses. HGF/NRP1 binding was examined in vitro.A novel 588-amino acid sNrp1 isoform was found to contain the ligand binding regions of Nrp1. The adult liver expressed more sNrp1 than full-length Nrp1. In vivo, hepatocytes constitutively expressed VEGF and sNrp1 in the quiescent state. sNrp1 was highly up-regulated at P20, a time point coinciding with a plateau in liver and body weights. Following hepatectomy, endogenous levels of sNrp1 decreased during the rapid growth phase, and VEGF levels were highest just prior to and during the angiogenic phase. sNrp1 levels again rose 5-10 days post-hepatectomy, presumably to control regeneration. HGF protein bound NRP1 and binding was competed with sNRP1.We cloned a novel mouse sNrp1 isoform from liver and provide evidence that this endogenous angiogenesis inhibitor may regulate VEGF or HGF bioavailability during normal physiological growth and development as well as during liver regeneration.

Vascular Endothelial Growth Factor (VEGF)-D Stimulates VEGF-A, Stanniocalcin-1, and Neuropilin-2 and Has Potent Angiogenic Effects

Objective—

The mature form of human vascular endothelial growth factor-D (hVEGF-D ΔNΔC ) is an efficient angiogenic factor, but its full mechanism of action has remained unclear. We studied the effects of hVEGF-D ΔNΔC in endothelial cells using gene array, signaling, cell culture, and in vivo gene transfer techniques.

Methods and Results—

Concomitant with the angiogenic and proliferative responses, hVEGF-D ΔNΔC enhanced the phosphorylation of VEGF receptor-2, Akt, and endothelial nitric oxide synthase. Gene arrays, quantitative reverse transcription–polymerase chain reaction, and Western blot revealed increases in VEGF-A, stanniocalcin-1 (STC1), and neuropilin (NRP) 2 expression by hVEGF-D ΔNΔC stimulation, whereas induction with hVEGF-A 165 altered the expression of STC1 and NRP1, another coreceptor for VEGFs. The effects of hVEGF-D ΔNΔC were seen only under high-serum conditions, whereas for hVEGF-A 165 , the strongest response was observed under low-serum conditions. The hVEGF-D ΔNΔC -induced upregulation of STC1 and NRP2 was also evident in vivo in mouse skeletal muscle treated with hVEGF-D ΔNΔC by adenoviral gene delivery. The importance of NRP2 in hVEGF-D ΔNΔC signaling was further studied with NRP2 small interfering RNA and NRP antagonist, which were able to block hVEGF-D ΔNΔC -induced survival of endothelial cells.

Conclusion—

In this study, the importance of serum and upregulation of NRP2 and STC1 for VEGF-D ΔNΔC effects were demonstrated. Better knowledge of VEGF-D ΔNΔC signaling and regulation is valuable for the development of efficient and safe VEGF-D ΔNΔC -based therapeutic applications for cardiovascular diseases.

Adjuvant effects of formalin-inactivated HSV through activation of dendritic cells and inactivation of myeloid-derived suppressor cells in cancer immunotherapy

Use of adequate adjuvant is necessary for induction of effective antitumor immune responses. To develop an effective adjuvant for cancer immunotherapy, we selected formalin-inactivated (f)-HSV as an adjuvant component, and analyzed the mechanisms underlying its adjuvant effects. First, we found that f-HSV can induce the tumor antigen-specific CTLs by enhancing antigen cross-presentation by dendritic cells (DCs), mainly through TLR2, but not TLR9. Next, f-HSV was also found to prevent the accumulation of myeloid-derived suppressor cells (MDSCs). We demonstrated that the expansion of MDSCs in the blood and spleen during tumor progression required B cells producing the inflammatory angiogenesis factors, vascular endothelial growth factor (VEGF)-A and neuropilin-1 (NRP-1), a co-receptor for VEGF receptor-2 (VEGFR-2). Interestingly, the transmembrane-type NRP-1 on B cells changed to soluble-type NRP-1 (sNRP-1) by f-HSV treatment. We further showed that the sNRP-1 and VEGF-A secreted from B cells by f-HSV treatment could abrogate the immunosuppressive ability of MDSCs. These results suggest that f-HSV can enhance antitumor immune responses as an adjuvant, not only through activation of DCs, but also inactivation of MDSCs via B cells.

Exogenous recombinant dimeric neuropilin-1 is sufficient to drive angiogenesis

Neuropilin-1 (NRP-1) is present on the cell surface of endothelial cells, or as a soluble truncated variant. Membrane NRP-1 is proposed to enhance angiogenesis by promoting the formation of a signaling complex between vascular endothelial growth factor-A(165) (VEGF-A(165)), VEGF receptor-2 (VEGFR-2) and heparan sulfate, whereas the soluble NRP-1 is thought to act as an antagonist of signaling complex formation. We have analyzed the angiogenic potential of a chimera comprising the entire extracellular NRP-1 region dimerized through an Fc IgG domain and a monomeric truncated NRP-1 variant. Both NRP-1 proteins stimulated tubular morphogenesis and cell migration in HDMECs and HUVECs. Fc rNRP-1 was able to induce VEGFR-2 phosphorylation and expression of the VEGFR-2 specific target, regulator of calcineurin-1 (RCAN1.4). siRNA mediated gene silencing of VEGFR-2 revealed that VEGFR-2 was required for Fc rNRP-1 mediated activation of the intracellular signaling proteins PLC-γ, AKT, and MAPK and tubular morphogenesis. The stimulatory activity was independent of VEGF-A(165). This was evidenced by depleting the cell culture of exogenous VEGF-A(165), and using instead for routine culture VEGF-A(121), which does not interact with NRP-1, and by the inability of VEGF-A sequestering antibodies to inhibit the angiogenic activity of the NRP proteins. Analysis of angiogenesis over a period of 6 days in an in vitro fibroblast/endothelial co-culture model revealed that Fc rNRP-1 could induce endothelial cell tubular morphogenesis. Thus, we conclude that soluble Fc rNRP-1 is a VEGF-A(165)-independent agonist of VEGFR-2 and stimulates angiogenesis in endothelial cells.

Structure-function analysis of VEGF receptor activation and the role of coreceptors in angiogenic signaling

Vascular endothelial growth factors (VEGFs) constitute a family of six polypeptides, VEGF-A, -B, -C, -D, -E and PlGF, that regulate blood and lymphatic vessel development. VEGFs specifically bind to three type V receptor tyrosine kinases (RTKs), VEGFR-1, -2 and -3, and to coreceptors such as neuropilins and heparan sulfate proteoglycans (HSPG). VEGFRs are activated upon ligand-induced dimerization mediated by the extracellular domain (ECD). A study using receptor constructs carrying artificial dimerization-promoting transmembrane domains (TMDs) showed that receptor dimerization is necessary, but not sufficient, for receptor activation and demonstrates that distinct orientation of receptor monomers is required to instigate transmembrane signaling. Angiogenic signaling by VEGF receptors also depends on cooperation with specific coreceptors such as neuropilins and HSPG. A number of VEGF isoforms differ in binding to coreceptors, and ligand-specific signal output is apparently the result of the specific coreceptor complex assembled by a particular VEGF isoform. Here we discuss the structural features of VEGF family ligands and their receptors in relation to their distinct signal output and angiogenic potential.

Vascular endothelial growth factor-B induces myocardium-specific angiogenesis and arteriogenesis via vascular endothelial growth factor receptor-1- and neuropilin receptor-1-dependent mechanisms

BACKGROUND

New revascularization therapies are urgently needed for patients with severe coronary heart disease who lack conventional treatment options.

METHODS AND RESULTS

We describe a new proangiogenic approach for these no-option patients using adenoviral (Ad) intramyocardial vascular endothelial growth factor (VEGF)-B186 gene transfer, which induces myocardium-specific angiogenesis and arteriogenesis in pigs and rabbits. After acute infarction, AdVEGF-B186 increased blood vessel area, perfusion, ejection fraction, and collateral artery formation and induced changes toward an ischemia-resistant myocardial phenotype. Soluble VEGF receptor-1 and soluble neuropilin receptor-1 reduced the effects of AdVEGF-B186, whereas neither soluble VEGF receptor-2 nor inhibition of nitric oxide production had this result. The effects of AdVEGF-B186 involved activation of neuropilin receptor-1, which is highly expressed in the myocardium, via recruitment of G-protein-alpha interacting protein, terminus C (GIPC) and upregulation of G-protein-alpha interacting protein. AdVEGF-B186 also induced an antiapoptotic gene expression profile in cardiomyocytes and had metabolic effects by inducing expression of fatty acid transport protein-4 and lipid and glycogen accumulation in the myocardium.

CONCLUSIONS

VEGF-B186 displayed strikingly distinct effects compared with other VEGFs. These effects may be mediated at least in part via a G-protein signaling pathway. Tissue-specificity, high efficiency in ischemic myocardium, and induction of arteriogenesis and antiapoptotic and metabolic effects make AdVEGF-B186 a promising candidate for the treatment of myocardial ischemia.

Angiogenic signalling pathways

Hypoxia is widely recognised as a key driving force for tumor angiogenesis by its induction of vascular endothelial growth factor (VEGF) and other direct-acting angiogenic factors. We describe the effect of hypoxia on gene expression and downstream angiogenic signalling; however, the angiogenic process is complex, and many other signalling pathways beyond VEGF are implicated in the formation of new vessels. These include extra-cellular signalling pathways such as the notch/delta, ephrin/Eph receptor, roundabout/slit, and netrin/UNC (uncoordinated) receptor families as well as intracellular proteins such as hedgehog and sprouty. The remarkable diversity in angiogenic signalling pathways provides many opportunities for therapeutic intervention, and anti-angiogenesis is currently a major area of oncology research.

Neuropilins: structure, function and role in disease

NRPs (neuropilins) are co-receptors for class 3 semaphorins, polypeptides with key roles in axonal guidance, and for members of the VEGF (vascular endothelial growth factor) family of angiogenic cytokines. They lack a defined signalling role, but are thought to mediate functional responses as a result of complex formation with other receptors, such as plexins in the case of semaphorins and VEGF receptors (e.g. VEGFR2). Mutant mouse studies show that NRP1 is essential for neuronal and cardiovascular development, whereas NRP2 has a more restricted role in neuronal patterning and lymphangiogenesis, but recent findings indicate that NRPs may have additional biological roles in other physiological and disease-related settings. In particular, NRPs are highly expressed in diverse tumour cell lines and human neoplasms and have been implicated in tumour growth and vascularization in vivo. However, despite the wealth of information regarding the probable biological roles of these molecules, many aspects of the regulation of cellular function via NRPs remain uncertain, and little is known concerning the molecular mechanisms through which NRPs mediate the functions of their various ligands in different cell types.

Gating of Sema3E/PlexinD1 signaling by neuropilin-1 switches axonal repulsion to attraction during brain development

The establishment of functional neural circuits requires the guidance of axons in response to the actions of secreted and cell-surface molecules such as the semaphorins. Semaphorin 3E and its receptor PlexinD1 are expressed in the brain, but their functions are unknown. Here, we show that Sema3E/PlexinD1 signaling plays an important role in initial development of descending axon tracts in the forebrain. Early errors in axonal projections are reflected in behavioral deficits in Sema3E null mutant mice. Two distinct signaling mechanisms can be distinguished downstream of Sema3E. On corticofugal and striatonigral neurons expressing PlexinD1 but not Neuropilin-1, Sema3E acts as a repellent. In contrast, on subiculo-mammillary neurons coexpressing PlexinD1 and Neuropilin-1, Sema3E acts as an attractant. The extracellular domain of Neuropilin-1 is sufficient to convert repulsive signaling by PlexinD1 to attraction. Our data therefore reveal a "gating" function of neuropilins in semaphorin-plexin signaling during the assembly of forebrain neuronal circuits.

Lentiviral rescue of vascular endothelial growth factor receptor-2 expression in flk1-/- embryonic stem cells shows early priming of endothelial precursors

The vascular endothelial growth factor (VEGF) family and its receptors are important for vascular development and maintenance of blood vessels, as well as for angiogenesis, the formation of new vessels. Loss of VEGF receptor-2 (VEGFR-2; designated Flk-1 in mouse) results in arrest of vascular and hematopoietic development in vivo. We used lentiviral transduction to reconstitute VEGFR-2 expression in flk1-/- embryonic stem (ES) cells. VEGF-induced vasculogenesis and sprouting angiogenesis were rescued in transduced ES cultures differentiating in vitro as EBs. Although the transgene was expressed in the pluripotent stem cells and lacked linage restriction during differentiation, the extent of endothelial recruitment was similar to that in wild-type EBs. Reconstitution of VEGFR-2 in flk1-/- ES cells allowed only precommitted precursors to differentiate into functional endothelial cells able to organize into vascular structures. Chimeric EB cultures composed of wild-type ES cells mixed with flk1-/- ES cells or reconstituted VEGFR-2-expressing ES cells were created. In the chimeric cultures, flk1-/- endothelial precursors were excluded from wild-type vessel structures, whereas reconstituted VEGFR-2-expressing precursors became integrated together with wild-type endothelial cells to form chimeric vessels. We conclude that maturation of endothelial precursors, as well as organization into vascular structures, requires expression of VEGFR-2. Disclosure of potential conflicts of interest is found at the end of this article.

Inhibition of axonal outgrowth in the tumor environment: involvement of class 3 semaphorins

That tumors lack innervation is dogma in the field of pathology, but the molecular determinants of this phenomenon remain elusive. We studied the effects of conditioned media from Colon 26 and B16 mouse tumor cell lines on the axonal outgrowth and cellular differentiation of embryonic Institute of Cancer Research (ICR) mouse dorsal root ganglion cells. Tumor-conditioned media suppressed dorsal root ganglion axonal extension but had no effect on neuronal or glial differentiation. We found that the tumor cells expressed most of the class 3 semaphorins - axon guidance molecules. Blocking the activity of class 3 semaphorins with the soluble receptor neuropilin-1 significantly counteracted the tumor-induced inhibition of axonal extension. Together, these results suggest a role for tumor-secreted class 3 semaphorins in selectively inhibiting axonal outgrowth of dorsal root ganglion neurons.

Cardiac stem cells in brown adipose tissue express CD133 and induce bone marrow nonhematopoietic cells to differentiate into cardiomyocytes

Recently, there has been noteworthy progress in the field of cardiac regeneration therapy. We previously reported that brown adipose tissue (BAT) contained cardiac progenitor cells that were relevant to the regeneration of damaged myocardium. In this study, we found that CD133-positive, but not c-Kit- or Sca-1-positive, cells in BAT differentiated into cardiomyocytes (CMs) with a high frequency. Moreover, we found that CD133(+) brown adipose tissue-derived cells (BATDCs) effectively induced bone marrow cells (BMCs) into CMs. BMCs are considered to have the greatest potential as a source of CMs, and two sorts of stem cell populations, the MSCs and hematopoietic stem cells (HSCs), have been reported to differentiate into CMs; however, it has not been determined which population is a better source of CMs. Here we show that CD133-positive BATDCs induce BMCs into CMs, not through cell fusion but through bivalent cation-mediated cell-to-cell contact when cocultured. Moreover, BMCs induced by BATDCs are able to act as CM repletion in an in vivo infarction model. Finally, we found that CD45(-)CD31(-) CD105(+) nonhematopoietic cells, when cocultured with BATDCs, generated more than 20 times the number of CMs compared with lin(-)c-Kit(+) HSCs. Taken together, these data suggest that CD133-positive BATDCs are a useful tool as CM inducers, as well as a source of CMs, and that the nonhematopoietic fraction in bone marrow is also a major source of CMs. Disclosure of potential conflicts of interest is found at the end of this article.

A novel approach for myocardial regeneration with educated cord blood cells cocultured with cells from brown adipose tissue

Umbilical cord blood (CB) is a promising source for regeneration therapy in humans. Recently, it was shown that CB was a source of mesenchymal stem cells as well as hematopoietic stem cells, and further that the mesenchymal stem cells could differentiate into a number of cells types of mesenchymal lineage, such as cardiomyocytes (CMs), osteocytes, chondrocytes, and fat cells. Previously, we reported that brown adipose tissue derived cells (BATDCs) differentiated into CMs and these CMs could adapt functionally to repair regions of myocardial infarction. In this study, we examined whether CB mononuclear cells (CBMNCs) could effectively differentiate into CMs by coculturing them with BATDCs and determined which population among CBMNCs differentiated into CMs. The results show that BATDCs effectively induced CBMNCs that were non-hematopoietic stem cells (HSCs) (educated CB cells: e-CBCs) into CMs in vitro. E-CBCs reconstituted infarcted myocardium more effectively than non-educated CBMNCs or CD34-positive HSCs. Moreover, we found that e-CBCs after 3 days coculturing with BATDCs induced the most effective regeneration for impaired CMs. This suggests that e-CBCs have a high potential to differentiate into CMs and that adequate timing of transplantation supports a high efficiency for CM regeneration. This strategy might be a promising therapy for human cardiac disease.

Dendritic cells can turn CD4+ T lymphocytes into vascular endothelial growth factor-carrying cells by intercellular neuropilin-1 transfer

Neuropilin-1 (NRP1) is a transmembrane protein expressed on neuronal and endothelial cells where it plays a crucial role in guiding axons and regulating angiogenesis. We have recently shown that NRP1 also is expressed on dendritic cells (DC) in the human immune system and have proposed a role for NRP1 in the first stages of the immune response. In these studies, we show that NRP1 can be transferred with a high efficiency from human DC to T lymphocytes by trogocytosis. The NRP1 transfer can occur independently of T lymphocyte activation; the amount of NRP1 transferred depends on the NRP1 expression level on APC and is enhanced when T cells are activated through the TCR. Moreover, the NRP1 transfer occurs between specific donor and recipient cells, because no NRP1 transfer is observed between endothelial cells and T lymphocytes or between APCs and CD34(+) hemopoietic cells. Finally, we show that a major NRP1 ligand, vascular endothelial growth factor (VEGF)(165), is secreted by mature human DCs and binds to NRP1 captured by T lymphocytes. These results show that NRP1 transfer to T lymphocytes during the immune synapse can convert T lymphocytes into VEGF(165)-carrying cells. Together with the enhanced signaling of VEGF-R2 on endothelial cells in the presence, in trans, of the NRP1-VEGF(165) complex, our results suggest that the intercellular transfer of NRP1 might participate in the Ag-independent remodelling of the endothelial vessels in secondary lymphoid organs during inflammation.

Role of hematopoietic lineage cells as accessory components in blood vessel formation

In adults, the vasculature is normally quiescent, due to the dominant influence of endogenous angiogenesis inhibitors over angiogenic stimuli. However, blood vessels in adults retain the capacity for brisk initiation of angiogenesis, the growth of new vessels from pre-existing vessels, during tissue repair and in numerous diseases, including inflammation and cancer. Because of the role of angiogenesis in tumor growth, many new cancer therapies are being conducted against tumor angiogenesis. It is thought that these anti-angiogenic therapies destroy the tumor vessels, thereby depriving the tumor of oxygen and nutrients. Therefore, a better understanding of the molecular mechanisms in the process of sprouting angiogenesis may lead to more effective therapies not only for cancer but also for diseases involving abnormal vasculature. It is widely believed that after birth, endothelial cells (EC) in new blood vessels are derived from resident EC of pre-existing vessels. However, evidence is now emerging that cells derived from the bone marrow may also contribute to postnatal angiogenesis. Most studies have focused initially on the contribution of endothelial progenitor cells in this process. However, we have proposed a concept in which cells of the hematopoietic lineage are mobilized and then entrapped in peripheral tissues, where they function as accessory cells that promote the sprouting of resident EC by releasing angiogenic signals. Most recently we found that hematopoietic cells play major roles in tumor angiogenesis by initiating sprouting angiogenesis and also in maturation of blood vessels in the fibrous cap of tumors. Therefore, manipulating these entrapment signals may offer therapeutic opportunities to stimulate or inhibit angiogenesis.

Nuchal edema and venous-lymphatic phenotype disturbance in human fetuses and mouse embryos with aneuploidy

OBJECTIVE

Nuchal edema (NE) is a clinical indicator for aneuploidy, cardiovascular anomalies, and several genetic syndromes. Its etiology, however, is unknown. In the nuchal area, the endothelium of the jugular lymphatic sacs (JLS) develops by budding from the blood vascular endothelium of the cardinal veins. Abnormal distension of the jugular sacs is associated with NE. We hypothesize that a disturbed lymphatic endothelial differentiation and sac formation causes NE. We investigated endothelial differentiation of the jugular lymphatic system in human and mouse species with NE.

METHODS

Aneuploid human fetuses (trisomy 21; trisomy 18) were compared with euploid controls (gestational age 12 to 18 weeks). Trisomy 16 mouse embryos were compared with wild type controls (embryonic day 10 to 18). Trisomy 16 mice are considered an animal model for human trisomy 21. Endothelial differentiation was investigated by immunohistochemistry using lymphatic markers (prox-1, podoplanin, lymphatic vessel endothelial hyaluronan receptor [LYVE]-1) and en blood vessel markers (neuropilin [NP]-1 and ligand vascular endothelial growth factor [VEGF]-A). Smooth muscle actin (SMA) was included as a smooth muscle cell marker.

RESULTS

We report a disturbed venous-lymphatic phenotype in aneuploid human fetuses and mouse embryos with enlarged jugular sacs and NE. Our results show absent or diminished expression of the lymphatic markers Prox-1 and podoplanin in the enlarged jugular sac, while LYVE-1 expression was normal. Additionally, the enlarged JLS showed blood vessel characteristics, including increased NP-1 and VEGF-A expression. The lumen contained blood cells and smooth muscle cells lined the wall.

CONCLUSION

A loss of lymphatic identity seems to be the underlying cause for clinical NE. Also, abnormal endothelial differentiation provides a link to the cardiovascular anomalies associated with NE.

Neuropilin-2 interacts with VEGFR-2 and VEGFR-3 and promotes human endothelial cell survival and migration

Neuropilin 2 (NRP2) is a receptor for the vascular endothelial growth factor (VEGF) and the semaphorin (SEMA) families, 2 unrelated ligand families involved in angiogenesis and neuronal guidance. NRP2 specifically binds VEGF-A and VEGF-C, although the biological relevance of these interactions in human endothelial cells is poorly understood. In this study, we show that both VEGF-A and VEGF-C induce the interaction of NRP2 with VEGFR-2. This interaction correlated with an enhancement of the VEGFR-2 phosphorylation threshold. Overexpression of NRP2 in primary human endothelial cells promoted cell survival induced by VEGF-A and VEGF-C. In contrast, SEMA3F, another ligand for NRP2, was able to inhibit human endothelial cell survival and migration induced by VEGF-A and VEGF-C. Moreover, a siRNA targeting specifically NRP2 was a potent inhibitor of human endothelial cell migration induced by VEGF-A and VEGF-C. Thus, our data indicate that NRP2 acts as a coreceptor that enhances human endothelial cell biological responses induced by VEGF-A and VEGF-C.

The neuropilins and their role in tumorigenesis and tumor progression

The neuropilins were originally described as receptors for the six axon guidance factors belonging to the class-3 semaphorins. They were subsequently found to function in addition as receptors for specific splice forms of angiogenic factors belonging to the VEGF family. The neuropilins are expressed in many types of cancer cells, in endothelial cells and in additional many types of normal diploid cell types. Recent findings indicate that the neuropilins and their associated plexin and tyrosine-kinase VEGF receptors play a regulatory role in developmental angiogenesis as well as in tumor angiogenesis. The neuropilin ligands belonging to the semaphorin family as well as the various VEGF's function as modulators of angiogenesis and tumor angiogenesis. Furthermore, since many types of cancer cells express neuropilins and neuropilin associated receptors, it is not surprising that various neuropilin ligands can modulate the behavior of cancer cells directly leading to the potentiation or inhibition of tumor progression.

Cardiac progenitor cells in brown adipose tissue repaired damaged myocardium

Cardiomyocyte (CM) regeneration is limited in adult life and is not sufficient to prevent myocardial infarction. Hence, the identification of a useful source of CM progenitors is of great interest for possible use in regenerative therapy. Mesenchymal stem cells in bone marrow, embryonic stem cells, and skeletal myoblasts are known sources of CM repletion; however, there are a number of critical problems for clinical application. In this study, we succeeded to identify CM progenitor cells in brown adipose tissue (BAT). Moreover, we showed that CM progenitor cells in BAT that existed in CD29-positive population could differentiate into CM with high efficiency. To confirm the in vivo effect of CD29(+)BAT-derived cells (BATDCs), we transplanted these cells into infarct border zone of an acute myocardial infarction model in rat. Results clearly indicated that implantation of CD29(+) BATDCs led to the reduction of the infarction area and improvement of left ventricular function by replacing newly developed CMs in comparison with that by CD29(+) white adipose tissue-derived cells or control saline. These findings suggest that BATDCs are one of the useful sources for a new strategy in CM regeneration.

Increased NCAM expression and vascular development in trisomy 16 mouse embryos: relationship with nuchal translucency

Increased nuchal translucency in the human fetus is associated with chromosomal abnormalities, enlarged jugular lymphatic sacs, cardiac defects and changed flow through the ductus venosus. The developmental background of this nuchal edema in relation to the associated anomalies remains elusive. We studied the morphologic correlation between neurogenesis and vasculogenesis in neck, heart, and ductus venosus region of wild type and trisomy 16 mice embryos (E10- E18), using an antibody against Neural Cell Adhesion Molecule (NCAM). Trisomy 16 mice are a model for the above described human phenotype. From E12 trisomy 16 mice showed an altered arrangement of cranial nerves IX, X and XI, which are positioned between the carotid artery, jugular vein and enlarged lymphatic sac. The vagal nerve was significantly smaller, compared with wild type embryos. NCAM was over expressed in both neuronal and cardiovascular structures in trisomy 16 mice, being particularly prominent in the 4th and 6th pharyngeal arch arteries, and the ductus venosus. In the 4th and 6th pharyngeal arch arteries, NCAM over expression was located to the part of the vessel wall that is closely related to the vagal and recurrent nerve. In case of 4th pharyngeal arch artery abnormalities NCAM expression, on the other hand, was reduced. In conclusion, the interaction between neurogenesis and vasculogenesis is disturbed in the trisomy 16 mouse model, and might be a common denominator in the spectrum of anomalies associated with increased nuchal translucency.

Soluble neuropilin targeted to the skin inhibits vascular permeability

Neuropilin 1 (NRP1) is a co-receptor for vascular endothelial growth factor (VEGF(165)), an inducer of vascular permeability and angiogenesis. Numerous physiological factors enhance VEGF expression and function but only a few have been shown to be negative regulators. Previously, we have shown that the naturally occurring soluble form of NRP1 (sNRP1) inhibits binding of VEGF(165) to endothelial cells in vitro and impairs tumor growth in vivo. To investigate the role of sNRP1 in the regulation of vascular development and function, sNRP1 expression was targeted to the skin, where it is not normally expressed, using a keratin 14 (K14) promoter expression construct. K14-sNRP1 transgenic mice displayed normal skin architecture with a subtle abnormal vascular phenotype. While the overall number of skin blood vessels remained unchanged, the lumen size of smooth muscle-associated dermal vessels was reduced. K14-sNRP1 mice had reduced vascular permeability in response to VEGF(165), but also to VEGF(121) and platelet activating factor, suggesting that the lack of permeability was not solely due to the sequestration of VEGF. sNRP1 also reversed the increase in inflammation and edema induced by transgenic VEGF overexpression in cutaneous delayed-type hypersensitivity reactions. In summary, sNRP1 appears to primarily regulate vessel permeability while its effect on physiological angiogenesis is less evident in this model.

Roles of neuropilins in neuronal development, angiogenesis, and cancers

Neuropilin-1 (NRP1) and neuropilin-2 (NRP2) are transmembrane glycoproteins that have been characterized as receptors for both semaphorins for neuronal guidance and vascular endothelial growth factor (VEGF) for angiogenesis. Biologic properties of NRPs have been linked to their unique domain structures. However, molecular interaction among NRPs, VEGF, and VEGF receptors is still not clear. Although several types of cancer cells can express NRPs, the role of NRPs in tumor pathogenesis is largely unknown. Thus, future investigations should include determining the effects and mechanisms of NRPs on proliferation, apoptosis, and migration of neuronal , endothelial, and cancer cells. Study of protein-protein interaction, signal transduction pathways, and NRP-mediated gene expression is particularly important to understand NRPs functions, which may have significant clinical applications in the treatment of neurological disorders, cardiovascular diseases, and certain cancers.

Neuropilin-1 is required for endothelial tip cell guidance in the developing central nervous system

Recent evidence indicates that sprouting angiogenesis in the central nervous system (CNS) is a guided process similar to the guidance of axons and insect tracheal tubes. Specialized tip cells of vessel sprouts navigate in response to local depots or gradients of vascular endothelial growth factor (VEGF-A). Neuropilin-1 (Nrp-1) is a transmembrane receptor with a repulsive function in axon guidance. Nrp-1 also binds the VEGF-A splice isoform VEGF165, stimulates angiogenesis, and is necessary for vascular development in the mouse. However, the morphogenetic events controlled by Nrp-1 in angiogenesis have not been defined. Here, we analyzed endothelial tip cell guidance in the CNS of Nrp-1-deficient mice. We focused our attention on the developing hindbrain, which is normally vascularized in a stereotyped manner. Initially, angiogenic sprouts extend along radial glia from the pial surface toward the ventricles, but in the subventricular zone (SVZ), they leave the radial path, turn laterally, and fuse to form a capillary plexus. Radial sprout elongation correlated with tip cell filopodia extensions along nestin-positive radial glial processes, but in the SVZ, the tip cell filopodia also extended perpendicular to the glial tracks and made contact with filopodia of the neighboring sprouts. In Nrp-1-deficient mice, the tip cell filopodia remained associated with the radial glia in the SVZ, which correlated with a failure of sprout turning and elongation across this region. As a result, the sprouts remained blind-ended forming glomeruloid tufts in the SVZ. These observations suggest that Nrp-1 plays an important role in allowing the endothelial tip cell filopodia to switch substrate and protrude in a new direction at a specific location in the developing brain.

Effects of cyclophilin A on cell proliferation and gene expressions in human vascular smooth muscle cells and endothelial cells

BACKGROUND

Cyclophilin A (CypA) is a cytosolic protein which involves many biological functions including immune modulation, cell growth, tumorigenesis, and vascular disease. The objective of this study was to determine the effect of CypA on cell proliferation and several gene expressions in human endothelial cells and vascular smooth muscle cells.

METHODS

Human coronary artery endothelial cells (HCAEC), human lung microvascular endothelial cells (HMVEC-L), and human aorta smooth muscle cells (HAoSMC) were used in this study. Cells were treated with 10 nM CypA for 24 h. The cell proliferation was determined by [3H]thymidine incorporation. The mRNA levels of 13 genes including CD147 (receptor for CypA), PDGF-BB, endothelin-1 (ET-1), vascular endothelial growth factor receptor-1 (VEGFR-1), VEGFR-2, VEGFR-3, neuropilin-1 (NRP-1), NRP-2, eNOS, iNOS, nNOS, ICAM-1, and PECAM-1 were semiquantitatively determined by real time RT-PCR as standardized with a house keeping gene beta-actin.

RESULTS

CypA significantly increased cell proliferation of HAoSMC and HMVEC-L by 31% and 45%, respectively, as compared to controls, but had no effect on HCAEC. Blocking CD147 did not affect the mitogenic action of CypA. In addition, CypA also significantly increased the mRNA expression of CD147 by 43% and VEGFR-2 by 65% in HAoSMCs (P < 0.05, t test). HAoSMCs expressed much higher CD147 and neuropilin-1 (NRP-1) mRNA than HMVECs-L and HCAECs (P < 0.017, ANOVA). Furthermore, CypA increased ET-1 mRNA by 22% and VEGFR-1 mRNA by 23% in HMVECs-L, but had limited effects on HCAECs. HMVECs-L had much higher expressions of PDGF-BB, ET-1, VEGFR-2, VEGFR-1, VEGFR-3, and NRP-2 than HAoSMCs and HCAECs (P < 0.017, ANOVA). By contrast, HCAECs had much higher ICAM-1 mRNA levels than HMVECs-L and HAoSMCs (P < 0.017, ANOVA).

CONCLUSIONS

These data demonstrate that CypA has a mitogenic effect on HAoSMCs and HMVECs-L, but not HCAECs. CD147 may not mediate the action of CypA. In addition, CypA substantially alters the mRNA levels of several key genes in human vascular cells, indicating potential multifunctional roles of CypA in vascular system. Furthermore, this study provides several new aspects of gene expressions in vascular cells.

Interactions of multiple heparin binding growth factors with neuropilin-1 and potentiation of the activity of fibroblast growth factor-2

The hypothesis that neuropilin-1 (Npn-1) may interact with heparin-binding proteins other than vascular endothelial growth factor has been tested using an optical biosensor-based binding assay. The results show that fibroblast growth factor (FGF) 1, 2, 4, and 7, FGF receptor 1, hepatocyte growth factor/scatter factor (HGF/SF), FGF-binding protein, normal protease sensitive form of prion protein, antithrombin III, and Npn-1 itself are all able to interact with Npn-1 immobilized on the sensor surface. FGF-2, FGF-4, and HGF/SF are also shown to interact with Npn-1 in a solution assay. Moreover, these protein-protein interactions are dependent on the ionic strength of the medium and are inhibited by heparin, and the kinetics of binding of FGF-2, FGF-4 and HGF/SF to Npn-1 are characterized by fast association rate constants (270,000-1,600,000 m(-1) s(-1)). These results suggest that Npn-1 possesses a "heparin" mimetic site that is able to interact at least in part through ionic bonding with the heparin binding site on many of the proteins studied. Npn-1 was also found to potentiate the growth stimulatory activity of FGF-2 on human umbilical vein endothelial cells, indicating that Npn-1 may not just bind but also regulate the activity of heparin-binding proteins.

Hematopoietic cells regulate the angiogenic switch during tumorigenesis

Hematopoietic cells (HCs) promote blood vessel formation by producing various proangiogenic cytokines and chemokines and matrix metalloproteinases. We injected mouse colon26 colon cancer cells or human PC3 prostate adenocarcinoma cells into mice and studied the localization of HCs during tumor development. HCs were distributed in the inner tumor mass in all of the tumor tissues examined; however, the localization of HCs in the tumor tissue differed depending on the tumor cell type. In the case of colon26 tumors, as the tumor grew, many mature HCs migrated into the tumor mass before fine capillary formation was observed. On the other hand, although very few HCs migrated into PC3 tumor tissue, c-Kit+ hematopoietic stem/progenitor cells accumulated around the edge of the tumor. Bone marrow suppression induced by injection of anti-c-Kit neutralizing antibody suppressed tumor angiogenesis by different mechanisms according to the tumor cell type: bone marrow suppression inhibited the initiation of sprouting angiogenesis in colon26 tumors, while it suppressed an increase in the caliber of newly developed blood vessels at the tumor edge in PC3 tumors. Our findings suggest that HCs are involved in tumor angiogenesis and regulate the angiogenic switch during tumorigenesis.

Semaphorin 3B (SEMA3B) induces apoptosis in lung and breast cancer, whereas VEGF165 antagonizes this effect

Semaphorin 3B (SEMA3B) is a secreted member of the semaphorin family, important in axonal guidance. We and others have shown that SEMA3B can act as a tumor suppressor by inducing apoptosis either by reexpression in tumor cells or applied as a soluble ligand. The common method of inactivation of SEMA3B is by allele loss and tumor-acquired promoter methylation. We studied the mechanism of SEMA3B-induced tumor cell apoptosis and found that vascular endothelial growth factor (VEGF)165 significantly decreased the proapoptotic and antimitotic effect of transfected or secreted SEMA3B on lung and breast cancer cells. VEGF165 binds to neuropilin, receptors for SEMA3B, and we found that SEMA3B competed for binding of 125I-VEGF165 to lung and breast cancer cells. We also found that small interfering RNA knockdown of tumor-produced VEGF-A or the use of an anti-VEGF neutralizing antibody (Ab) significantly inhibited tumor cell growth in vitro. By contrast, VEGF121, a VEGF variant that lacks binding to neuropilin (NP)-1 or NP-2 receptors, was not expressed in tumor cells and had no effect on SEMA3B growth-suppressing activities. In conclusion, we hypothesize that VEGF165, produced by tumor cells, acts as an autocrine survival factor and that SEMA3B mediates its tumor-suppressing effects, at least in part, by blocking this VEGF autocrine activity.

Discrete Types of Osteoclast Precursors Can Be Generated from Embryonic Stem Cells

Osteoclast precursors (OCPs) share some characteristics with the monocyte/macrophage lineages, but the early events of OCP development are not yet clear. To investigate osteoclastogenesis from the earliest stage, we used step-wise cultures of embryonic stem (ES) cells to induce mature osteoclasts and assessed the effect of vascular endothelial growth factor receptor (VEGFR)-1/Fc chimeric protein on osteoclast development. Addition of VEGFR-1/Fc for the first 5 days of culture (phase I) severely inhibited the development of OCPs. Although OCPs were detected after culturing for a further 5 days (phase II), the reduction of OCPs in phase I was maintained in phase II. The generation of OCPs in phase I was resistant to signal blocking mediated by Kit receptors, but that in phase II was partially inhibited by either an anti-Kit antagonistic antibody or VEGFR-1/Fc and was severely inhibited by the combination of both reagents. Moreover, the OCPs in phase I gave rise to larger numbers of osteoclasts but required a longer period for maturation than the OCPs in phase II. We thus showed that OCPs expanded in phase II, but the majority of OCPs arose from ES cells in a manner dependent on VEGFR-1 binding factor(s) in phase I.

The role of neuropilin in vascular and tumor biology

Neuropilin-1 (NRP1) and NRP2 are related transmembrane receptors that function as mediators of neuronal guidance and angiogenesis. NRPs bind members of the class 3 semaphorin family, regulators of neuronal guidance, and of the vascular endothelial growth factor (VEGF) family of angiogenesis factors. There is substantial evidence that NRPs serve as mediators of developmental and tumor angiogenesis. NRPs are expressed in endothelial cells (EC) and bind VEGF165. NRP1 is a co-receptor for VEGF receptor-2 (VEGFR2) that enhances the binding of VEGF165 to VEGFR2 and VEGF165-mediated chemotaxis. NRP1 expression is regulated in EC by tumor necrosis factor-alpha, the transcription factors dHAND and Ets-1, and vascular injury. During avian blood vessel development NRP1 is expressed only in arteries whereas NRP2 is expressed in veins. Transgenic mouse models demonstrate that NRP1 plays a critical role in embryonic vascular development. Overexpression of NRP1 results in the formation of excess capillaries and hemorrhaging. NRP1 knockouts have defects in yolk sac, embryo and neuronal vascularization, and in development of large vessels in the heart. Tumor cells express NRPs and bind VEGF165. NRP1 upregulation is positively correlated with the progression of various tumors. Overexpression of NRPI in rat tumor cells results in enlarged tumors and substantially enhanced tumor angiogenesis. On the other hand, soluble NRP1 (sNRP1) is an antagonist of tumor angiogenesis. Semaphorin 3A binds to EC and tumor cells. It also inhibits EC motility and capillary sprouting in vitro. VEGF165 and Sema3A are competitive inhibitors for NRP1 mediated functions in EC and neurons. These results suggest that NRP1 is a novel regulator of the vascular system.

The interaction of Neuropilin-1 and Neuropilin-2 with tyrosine-kinase receptors for VEGF

The Neuropilin-1 (NRP1) and Neuropilin-2 (NRP2) receptors were initially described as receptors for axon guidance factors belonging to the class-3 Semaphorin sub-family. Subsequently, it was found the Neuropilins also function as receptors for some forms of vascular endothelial growth factor (VEGF). VEGF165 binds to both NRP1 and to NRP2 but VEGF121, does not bind to either of these receptors. VEGF145 on the other hand, binds to NRP2 but not to NRP1. Additional VEGF family members such as the heparin binding form of placenta growth factor (PlGF-2) and VEGF-B bind to NRP1, and it was also shown that both PlGF-2 and VEGF-C bind to NRP2. The intracellular domains of the Neuropilins are short, and do not suffice for independent transduction of biological signals subsequent to Semaphorin or VEGF binding. It was shown that both Neuropilins can form complexes with receptors belonging to the Plexin family, and that such Plexin/Neuropilin complexes are able to transduce signals following the binding of class-3 Semaphorins to Neuropilins. The VEGF165 induced proliferation and migration of cells that express the VEGF tyrosine-kinase receptor VEGFR2 is enhanced in the presence of NRP1, suggesting that Neuropilins may also form complexes with VEGF tyrosine-kinase receptors such as VEGFR2. However, it is not yet clear whether VEGFR2 and NRPI form complexes and contrasting results have been reported with regard to this issue. In contrast, it was recently reported by two laboratories that Neuropilins can form complexes with the second tyrosine-kinase receptor of VEGF, VEGFR1. However, the biological function of these complexes is still unclear.

Neurovascular congruence results from a shared patterning mechanism that utilizes Semaphorin3A and Neuropilin-1

Peripheral nerves and blood vessels have similar patterns in quail forelimb development. Usually, nerves extend adjacent to existing blood vessels, but in a few cases, vessels follow nerves. Nerves have been proposed to follow vascular smooth muscle, endothelium, or their basal laminae. Focusing on the major axial blood vessels and nerves, we found that when nerves grow into forelimbs at E3.5-E5, vascular smooth muscle was not detectable by smooth muscle actin immunoreactivity. Additionally, transmission electron microscopy at E5.5 confirmed that early blood vessels lacked smooth muscle and showed that the endothelial cell layer lacks a basal lamina, and we did not observe physical contact between peripheral nerves and these endothelial cells. To test more generally whether lack of nerves affected blood vessel patterns, forelimb-level neural tube ablations were performed at E2 to produce aneural limbs; these had completely normal vascular patterns up to at least E10. To test more generally whether vascular perturbation affected nerve patterns, VEGF(165), VEGF(121), Ang-1, and soluble Flt-1/Fc proteins singly and in combination were focally introduced via beads implanted into E4.5 forelimbs. These produced significant alterations to the vascular patterns, which included the formation of neo-vessels and the creation of ectopic avascular spaces at E6, but in both under- and overvascularized forelimbs, the peripheral nerve pattern was normal. The spatial distribution of semaphorin3A protein immunoreactivity was consistent with a negative regulation of neural and/or vascular patterning. Semaphorin3A bead implantations into E4.5 forelimbs caused failure of nerves and blood vessels to form and to deviate away from the bead. Conversely, semaphorin3A antibody bead implantation was associated with a local increase in capillary formation. Furthermore, neural tube electroporation at E2 with a construct for the soluble form of neuropilin-1 caused vascular malformations and hemorrhage as well as altered nerve trajectories and peripheral nerve defasciculation at E5-E6. These results suggest that neurovascular congruency does not arise from interdependence between peripheral nerves and blood vessels, but supports the hypothesis that it arises by a shared patterning mechanism that utilizes semaphorin3A.

Neuropilin-1 on hematopoietic cells as a source of vascular development

Neuropilin-1 (NP-1) is a receptor for vascular endothelial growth factor-165 (VEGF165) and acts as a coreceptor that enhances the function of VEGF165 through VEGF receptor-2 (VEGFR-2). Studies using transgenic and knock-out mice of NP-1 indicated that this molecule is important for vascular development as well as neuronal development. We recently reported that clustered soluble NP-1 phosphorylates VEGFR-2 on endothelial cells with a low dose of VEGF165 and rescues the defective vascularity of the NP-1-/- embryo in vitro and in vivo. Here we show that NP-1 is expressed by CD45+ hematopoietic cells in the fetal liver, can bind VEGF165, and phosphorylates VEGFR-2 on endothelial cells. CD45+NP-1+ cells rescued the defective vasculogenesis and angiogenesis in the NP-1-/- P-Sp (para-aortic splanchnopleural mesodermal region) culture, although CD45+NP-1- cells did not. Moreover, CD45+NP-1+ cells together with VEGF165 induced angiogenesis in an in vivo Matrigel assay and cornea neovascularization assay. The extracellular domain of NP-1 consists of "a," "b," and "c" domains, and it is known that the "a" and "c" domains are necessary for dimerization of NP-1. We found that both the "a" and "c" domains are essential for such rescue of defective vascularities in the NP-1 mutant. These results suggest that NP-1 enhances vasculogenesis and angiogenesis exogenously and that dimerization of NP-1 is important for enhancing vascular development. In NP-1-/- embryos, vascular sprouting is impaired at the central nervous system (CNS) and pericardium where VEGF is not abundant, indicating that NP-1-expressing cells are required for normal vascular development.

Recent advances in angiogenesis, anti-angiogenesis and vascular targeting

Angiogenesis, the development of new blood vessels, has become a major focus of research. This has been stimulated by the therapeutic opportunities offered by the ability to manipulate the vasculature in pathologies such as cancer. Here, we present an overview of recent advances in angiogenesis. Especially noteworthy is the large volume of information from developmental studies, particularly those that involve transgenic and gene knockout mice. We also discuss the increasing repertoire of drugs with which to manipulate angiogenesis and new endothelial-specific genes with which to target the vasculature.

The pattern of neurovascular development in the forelimb of the quail embryo

Peripheral nerve and vascular patterns are congruent in the adult vertebrate, but this has been disputed in vertebrate embryos. The most detailed of these studies have used the avian forelimb as a model system, yet neurovascular anatomical relationships and critical vascular remodeling events remain inadequately characterized in this model. To address this, we have used a combination of intravascular marker injection, multilabel fluorescent stereomicroscopy, and confocal microscopy to analyze the spatiotemporal relationships between peripheral nerves and blood vessels in the forelimb of 818 quail embryos from E2 (HH13) to E15 (HH41). We find that the neurovascular anatomical relationships established during development are highly stereotypic and congruent. Blood vessels typically arise before their corresponding nerves, but there are several critical exceptions to this rule. The vascular pattern is extensively remodeled from the earliest stage examined (E2; HH13), whereas the peripheral nerves, the first of which enter the forelimb at E3.5-E4 (HH21-HH24), have a progressively unfolding pattern that, once formed, remains essentially unchanged. The adult neurovascular pattern is not established until E8 (HH34). Peripheral nerves are always found to track close and parallel to the vasculature. As they track distally, peripheral nerves always lie on the side of the vasculature away from the center of the forelimb. Neurovascular patterns have a hierarchy of congruence that is highest in the dorsoventral plane, followed by the anteroposterior, and lastly the proximodistal planes.

Neuropilin-1 is required for vascular development and is a mediator of VEGF-dependent angiogenesis in zebrafish

Neuropilin-1 (NRP1) is a cell-surface receptor for both vascular endothelial growth factor(165) (VEGF(165)) and class 3 semaphorins that is expressed by neurons and endothelial cells. NRP1 is required for normal developmental angiogenesis in mice. The zebrafish is an excellent system for analyzing vascular development. Zebrafish intersegmental vessels correspond to mammalian capillary sprouts, whereas the axial vessels correspond to larger blood vessels, such as arteries. The zebrafish NRP1 gene (znrp1) was isolated and when overexpressed in cells, zNRP1 protein was a functional receptor for human VEGF(165). Whole-mount in situ hybridization showed that transcripts for znrp1 during embryonic and early larval development were detected mainly in neuronal and vascular tissues. Morpholino-mediated knockdown of zNRP1 in embryos resulted in vascular defects, most notably impaired circulation in the intersegmental vessels. Circulation via trunk axial vessels was not affected. Embryos treated with VEGF receptor-2 kinase inhibitor had a similar intersegmental vessel defect suggesting that knockdown of zNRP1 reduces VEGF activity. To determine whether NRP1 and VEGF activities were interdependent in vivo, zNRP1 and VEGF morpholinos were coinjected into embryos at concentrations that individually did not significantly inhibit blood vessel development. The result was a potent inhibition of blood cell circulation via both intersegmental and axial vessels demonstrating that VEGF and NRP1 act synergistically to promote a functional circulatory system. These results provide the first physiological demonstration that NRP1 regulates angiogenesis through a VEGF-dependent pathway.

VEGF165 mediates formation of complexes containing VEGFR-2 and neuropilin-1 that enhance VEGF165-receptor binding

Co-expression of NRP1 and (VEGFR-2) KDR on the surface of endothelial cells (EC) enhances VEGF165 binding to KDR and EC chemotaxis in response to VEGF165. Overexpression of NRP1 by prostate tumor cells in vivo results in increased tumor angiogenesis and growth. We investigated the molecular mechanisms underlying NRP1-mediated angiogenesis by analyzing the association of NRP1 and KDR. An intracellular complex containing NRP1 and KDR was immunoprecipitated from EC by anti-NRP1 antibodies only in the presence of VEGF165. In contrast, VEGF121, which does not bind to NRP1, did not support complex formation. Complexes containing VEGF165, NRP1, and KDR were also formed in an intercellular fashion by co-culture of EC expressing KDR only, with cells expressing NRP1 only, for example, breast carcinoma cells. VEGF165 also mediated the binding of a soluble NRP1 dimer to cells expressing KDR only, confirming the formation of such complexes. Furthermore, the formation of complexes containing KDR and NRP1 markedly increased 125I-VEGF165 binding to KDR. Our results suggest that formation of a ternary complex of VEGF165, KDR, and NRP1 potentiates VEGF165 binding to KDR. These complexes are formed on the surface of EC and in a juxtacrine manner via association of tumor cell NRP1 and EC KDR.