Netrin-4 inhibits angiogenesis via binding to neogenin and recruitment of Unc5B.

Netrins are secreted molecules with roles in axon guidance and angiogenesis. We identified Netrin-4 as a gene specifically overexpressed in VEGF-stimulated endothelial cells (EC) in vitro as well as in vivo. Knockdown of Netrin-4 expression in EC increased their ability to form tubular structures on Matrigel. To identify which receptor is involved, we showed by quantitative RT-PCR that EC express three of the six Netrin-1 cognate receptors: neogenin, Unc5B, and Unc5C. In contrast to Netrin-1, Netrin-4 bound only to neogenin but not to Unc5B or Unc5C receptors. Neutralization of Netrin-4 binding to neogenin by blocking antibodies abolished the chemotactic effect of Netrin-4. Furthermore, the silencing of either neogenin or Unc5B abolished Netrin-4 inhibitory effect on EC migration, suggesting that both receptors are essential for its function in vitro. Coimmunoprecipitation experiments demonstrated that Netrin-4 increased the association between Unc5B and neogenin on VEGF- or FGF-2-stimulated EC. Finally, we showed that Netrin-4 significantly reduced pathological angiogenesis in Matrigel and laser-induced choroidal neovascularization models. Interestingly, Netrin-4, neogenin, and Unc5B receptor expression was up-regulated in choroidal neovessel EC after laser injury. Moreover, Netrin-4 overexpression delayed tumor angiogenesis in a model of s.c. xenograft. We propose that Netrin-4 acts as an antiangiogenic factor through binding to neogenin and recruitment of Unc5B.

PSGL-1-mediated activation of EphB4 increases the proangiogenic potential of endothelial progenitor cells.

Endothelial progenitor cell (EPC) transplantation has beneficial effects for therapeutic neovascularization; however, only a small proportion of injected cells home to the lesion and incorporate into the neocapillaries. Consequently, this type of cell therapy requires substantial improvement to be of clinical value. Erythropoietin-producing human hepatocellular carcinoma (Eph) receptors and their ephrin ligands are key regulators of vascular development. We postulated that activation of the EphB4/ephrin-B2 system may enhance EPC proangiogenic potential. In this report, we demonstrate in a nude mouse model of hind limb ischemia that EphB4 activation with an ephrin-B2-Fc chimeric protein increases the angiogenic potential of human EPCs. This effect was abolished by EphB4 siRNA, confirming that it is mediated by EphB4. EphB4 activation enhanced P selectin glycoprotein ligand-1 (PSGL-1) expression and EPC adhesion. Inhibition of PSGL-1 by siRNA reversed the proangiogenic and adhesive effects of EphB4 activation. Moreover, neutralizing antibodies to E selectin and P selectin blocked ephrin-B2-Fc-stimulated EPC adhesion properties. Thus, activation of EphB4 enhances EPC proangiogenic capacity through induction of PSGL-1 expression and adhesion to E selectin and P selectin. Therefore, activation of EphB4 is an innovative and potentially valuable therapeutic strategy for improving the recruitment of EPCs to sites of neovascularization and thereby the efficiency of cell-based proangiogenic therapy.

Coadministration of endothelial and smooth muscle progenitor cells enhances the efficiency of proangiogenic cell-based therapy.

Cell-based therapy is a promising approach designed to enhance neovascularization and function of ischemic tissues. Interaction between endothelial and smooth muscle cells regulates vessels development and remodeling and is required for the formation of a mature and functional vascular network. Therefore, we assessed whether coadministration of endothelial progenitor cells (EPCs) and smooth muscle progenitor cells (SMPCs) can increase the efficiency of cell therapy. Unilateral hindlimb ischemia was surgically induced in athymic nude mice treated with or without intravenous injection of EPCs (0.5 x 10(6)), SMPCs (0.5 x 10(6)) and EPCs+SMPCs (0.25 x 10(6)+0.25 x 10(6)). Vessel density and foot perfusion were increased in mice treated with EPCs+SMPCs compared to animals receiving EPCs alone or SMPCs alone (P<0.001). In addition, capillary and arteriolar densities were enhanced in EPC+SMPC-treated mice compared to SMPC and EPC groups (P<0.01). We next examined the role of Ang-1/Tie2 signaling in the beneficial effect of EPC and SMPC coadministration. Small interfering RNA directed against Ang-1-producing SMPCs or Tie2-expressing EPCs blocked vascular network formation in Matrigel coculture assays, reduced the rate of incorporated EPCs within vascular structure, and abrogated the efficiency of cell therapy. Production of Ang-1 by SMPCs activates Tie2-expressing EPCs, resulting in increase of EPC survival and formation of a stable vascular network. Subsequently, the efficiency of EPC- and SMPC-based cotherapy is markedly increased. Therefore, coadministration of different types of vascular progenitor cells may constitute a novel therapeutic strategy for improving the treatment of ischemic diseases.

Cross-talk between the VEGF-A and HGF signalling pathways in endothelial cells.

BACKGROUND INFORMATION: Endothelial cells play a major role in angiogenesis, the process by which new blood vessels arise from a pre-existing vascular bed. VEGF-A (vascular endothelial growth factor-A) is a key regulator of angiogenesis during both development and in adults. HGF (hepatocyte growth factor) is a pleiotropic cytokine that may promote VEGF-A-driven angiogenesis, although the signalling mechanisms underlying this co-operation are not completely understood. RESULTS: We analysed the effects of the combination of VEGF-A and HGF on the activation of VEGFR-2 (VEGF receptor-2) and c-met receptors, and on the stimulation of downstream signalling pathways in endothelial cells. We found that VEGFR-2 and c-met do not physically associate and do not transphosphorylate each other, suggesting that co-operation involves signalling events more distal from receptor activation. We demonstrate that the VEGF isoform VEGF-A(165) and HGF stimulate a similar set of MAPKs (mitogen-activated protein kinases), although the kinetics and strengths of the activation differ depending on the growth factor and pathway. An enhanced activation of the signalling was observed when endothelial cells were stimulated by the combination of VEGF-A(165) and HGF. Moreover, the combination of VEGF-A and HGF results in a statistically significant synergistic activation of ERK1/2 (extracellular-signal-regulated kinase 1/2) and p38 kinases. We demonstrated that VEGF-A(165) and HGF activate FAK (focal adhesion kinase) with different kinetics and stimulate the recruitment of phosphorylated FAK to different subsets of focal adhesions. VEGF-A(165) and HGF regulate distinct morphogenic aspects of the cytoskeletal remodelling that are associated with the preferential activation of Rho or Rac respectively, and induce structurally distinct vascular-like patterns in vitro in a Rho- or Rac-dependent manner. CONCLUSIONS: Under angiogenic conditions, combining VEGF-A with HGF can promote neovascularization by enhancing intracellular signalling and allowing more finely regulated control of the signalling molecules involved in the regulation of the cytoskeleton and cellular migration and morphogenesis.

New anti angiogenesis developments through electro-immunization: optimization by in vivo optical imaging of intradermal electro gene transfer.

Direct application of high voltage electric pulses of milliseconds duration to the skin of a mouse enhances in vivo intradermal delivery of injected therapeutic molecules such as DNA. The efficacy of gene transfer and expression is dependent on electrical parameters. DNA electrotransfer in tissues increases the associated DNA expression vaccine potency. This protocol is called "electro-immunization". In the present study, we report a new strategy for optimizing electro-immunization. In vivo fluorescence imaging was used to detect the expression of a fluorescent protein (DsRed) and therefore allowed rapid optimization of the protocol. In vivo electrogenetransfer in the skin was well tolerated and DsRed expression was followed for over 2 weeks. Expression was voltage dependent under our conditions. Parameters were selected giving the highest level of expression. Under these optimized conditions, electrotransfer of a plasmid encoding VEGF was evaluated for its immune response as a gene therapy of interest involved in anti-angiogenic strategies. Anti VEGF 165 antibodies in sera of mice were evaluated by ELISA and compared to those obtained after conventional immunization. Comparable titres of antibodies were obtained in both groups. An IgG2a predominance was found in mice immunized with the plasmid whereas a IgG1 predominance was observed in mice immunized classically. Skin electro-immunization is therefore shown as a good route for DNA immunization for anti-angiogenesis concern.

[Effects of dihydroartiminisin on the adhesion, migration, and invasion of epithelial ovarian cancer cells].

OBJECTIVE: To investigate the effects of dihydroartiminisin (DHA) on the adhesion, migration, and invasion ovarian cancer cells. METHODS: Human ovarian cancer cells of the lines SKOV3 and OVCAR3 were cultured. Suspensions of SKOV3 and OVCAR3 cells were treated with DHA of the concentrations of 0.5, 2.5, 12.5, and 62.5 micromol/L respectively, and then inoculated on the plate coated with Matrigel. MTT method was used to -determine the adhesion rate. Transwell membrane chamber model was used to evaluate the effect of DHA on the migration and invasion of the SKOV3 and OVCAR3 cells. Western blotting and reverse transcriptase polymerase chain reaction were used to detect the effect of DHA on the phosphorylation of focal adhesion kinase (FAK) and on the effect of expression of metal matrix proteinases (MMPs) and their tissue inhibitors (TIMPs) respectively. RESULTS: (1) Compared to the cells without DHA treatment, the cell adhesion ability levels of the SKOV3 and OVCAR3 cells treated with 12.5 micromol/L DHA decreased by 76.1% and 57.9% respectively (P < 0.05), while their migration ability levels decreased by 59.3% and 69.7% respectively (P < 0.05). (2) Both SKOV3 and OVCAR3 showed weak invasion ability, and DHA only showed a slight inhibitory effect on the cell invasion of these 2 lines (both P > 0.05). (3) Compared to the cells without DHA treatment, the phosphorylation level of FAK of the SKOV3 and OVCAR3 cells treated with 12.5 micromol/L DHA decreased by 42.9% and 44.8% respectively (both P < 0.05). (4) RT-PCR showed mRNA expression of MMP2, TIMP1, and TIMP2, but not mRNA expression of MMP9 in both SKOV3 and OVCAR3 cells. The mRNA expression levels of the SKOV3 and OVCAR3 cells treated with 12.5 micromol/L DHA increased by 1.5 and 2.6 times respectively (both P < 0.05). CONCLUSION: DHA has inhibitory effects on the adhesion and migration of epithelial ovarian cancer cells, which may be related to its down-regulation of the phosphorylation of FAK in these cells.

[Effects of dihydroartiminisin on proliferation and phosphorylation of mitogen-activated protein kinase in epithelial ovarian cancer cell lines].

OBJECTIVE: To determine the effect of dihydroartiminisin on the proliferation and phosphorylation of mitogen-activated protein kinase (MAPK) in SKOV3 and OVCAR3 ovarian cancer cell lines. METHODS: Methyl thiazolyl tetrazolium assay was performed to evaluate the anti-proliferative effect of dihydroartiminisin in SKOV3 and OVCAR3 cells, and Western blot was used to determine its effect on phosphorylation level of MAPK, including extra-cell regulated kinase (ERK) 1/2 and p38 protein kinase, in the two cell lines. RESULTS: Dihydroartiminisin inhibited the proliferation of ovarian cancer cells in vitro, with a mean of 50% inhibition concentration (IC(50)) at 72 h of (9.0 +/- 1.4) micromol/L for SKOV3 and (5.5 +/- 1.2) micromol/L for OVCAR3 respectively. Compared to cells without dihydroartiminisin treatment, phosphorylation level of ERK 1/2 in SKOV3 and OVCAR3 cells treated with dihydroartiminisin decreased by 64.2% and 75.3% respectively (P < 0.05), while phosphorylation of p38 protein kinase in SKOV3 and OVCAR3 only decreased by 8.5%and 6.4%respectively (P > 0.05). CONCLUSION: Dihydroartiminisin can inhibit the proliferation of ovarian cancer cell in vitro, probably through down-regulation of the phosphorylation of ERK 1/2 in ovarian cancer cells.

Direct FGF receptor 1 activation through an anti-idiotypic strategy mimicks the biological activity of FGF-2 and inhibits the progression of the bladder carcinoma derived from NBT-II cells.

The hypothesis that tumor growth is angiogenesis-dependent has been documented by a considerable body of direct and indirect experimental data. Since the discovery of the vascular endothelial growth factor (VEGF), most attention has been focused on the VEGF system. Although fibroblast growth factors 1 and 2 (FGF-1 and FGF-2) can exert a strong angiogenic activity when they are supplied as a single pharmacological agent, their role in pathological angiogenesis in preclinical models remains controversial. To decipher the contribution of FGF receptors in various models of angiogenesis, we took advantage of the anti-idiotypic strategy to obtain circulating agonists specific for FGFR-1 and FGFR-2 (AIdF-1 and AIdF-2). They mimicked FGF-1 and FGF-2 for receptor binding, signal transduction, proliferation of endothelial cells and differentiation of the bladder carcinoma cell NBT-II which expresses FGFR-2b but not FGFR-1. The constitutive expression of FGFR-1 allowed binding of FGF-2 and AIdF-2 and inhibition of the proliferation of NBT-II cells. AIdF-1 and AIdF-2 induced angiogenesis in the corneal pocket assay. Although FGFR-1 dimerization achieved by AIdF-2 injection led to highly differentiated and smaller NBT-II tumors, no sign of reduction of tumor angiogenesis was observed, thus suggesting that endothelial cells are resistant to FGF.

Heparin affin regulatory peptide binds to vascular endothelial growth factor (VEGF) and inhibits VEGF-induced angiogenesis.

Heparin affin regulatory peptide (HARP) is an heparin-binding molecule involved in the regulation of cell proliferation and differentiation. Here, we report that HARP inhibited the biological activity induced by the 165-amino-acid form of vascular endothelial growth factor (VEGF165) on human umbilical vein endothelial cells. Endothelial-cell proliferation induced by VEGF165 showed about 50% inhibition in the presence of HARP in a concentration of 3 nM. In similar range of concentrations, HARP blocked tube formation induced by VEGF165 in three-dimensional angiogenesis assay. In vivo studies showed that HARP inhibited the VEGF165-induced Matrigel trade mark infiltration of endothelial cells. We then investigated the mechanisms of this inhibition and shown that HARP inhibited the binding of 125I-VEGF165 to the VEGF receptors of endothelial cells. Additional studies using VEGF soluble receptors indicated that binding of 125I-VEGF165 to kinase insert domain-containing receptor and neuropilin receptor was inhibited by HARP, but conversely the binding of 125I-VEGF165 to fms-like tyrosine kinase I receptor was unaffected. A competitive affinity-binding assay demonstrated that HARP interacted directly with VEGF165 with a dissociation coefficient of 1.38 nM. Binding assay using deletion mutants of HARP revealed that the thrombospondin type-1 repeats domains were involved in this interaction. These data demonstrate for the first time that the angiogenic factor HARP can also negatively regulates the angiogenic activity of VEGF165.

Extracellular matrix-bound vascular endothelial growth factor promotes endothelial cell adhesion, migration, and survival through integrin ligation.

Vascular endothelial growth factor (VEGF), a major factor mediating endothelial cell survival, migration, and proliferation during angiogenesis, is expressed as five splice variants (121, 145, 165, 189, and 206 aminoacids) encoded by a single gene. Although the three shorter isoforms are mainly diffusible, the two longer ones are sequestered in cell membranes after secretion. However, their potential role as true components of the extracellular matrix has not been investigated. We determined that endothelial cells could adhere and spread on VEGF189 and VEGF165, but not on VEGF121. Adhesion was mediated by the alpha3beta1 and alpha(v)beta3 integrins and other alpha(v) integrins but not by the cognate VEGF receptors. Cells migrated on VEGF165 and VEGF189 and displayed a stellate morphology with numerous lamellopodia and FAK staining but no actin stress fibers. Tumstatin, an antiangiogenic peptide that interacts with the alpha(v)beta3 integrin, could inhibit adhesion on VEGF, and this effect was potentiated by anti-alpha(v)beta3 blocking antibody. Immobilized VEGF almost totally abolished endothelial cell apoptosis through interactions with integrins. The inhibition of alpha(v)beta3 engagement with immobilized VEGF by tumstatin inhibited most of its survival activity. We have thus determined a new VEGF receptor-independent role for immobilized VEGF in supporting cell adhesion and survival through interactions with integrins.

Increase of both angiogenesis and bone mass in response to exercise depends on VEGF.

UNLABELLED: Physiological angiogenesis during bone remodeling is undefined. Treadmill-running rats displayed bone marrow angiogenesis concomitant with bone formation increase and resorption decrease and upregulation of VEGF and its R1 receptor mRNA in proximal tibia. VEGF blockade over 5 weeks of training fully prevented the exercise-induced bone mass gain. INTRODUCTION: We investigated the role of vascular endothelial growth factor (VEGF) and angiogenesis in the osteogenic response to exercise. MATERIALS AND METHODS: Nine-week-old male Wistar rats were treadmill-trained at 60% Vo(2max) for various periods. Bone and vascular histomorphometry was performed after 2- and 5-week experiments. On-line RT PCR for VEGF and its receptors R1 and R2 was done after a 10-day experiment. In the 5-week experiment, running rats received either a VEGF inhibitory antibody or a placebo. RESULTS: After 2 weeks, tibial BMD did not change; however, vessel number in the proximal metaphysis increased by 20% in running versus sedentary rats. In running rats, vessel number correlated positively (r = 0.88) with bone formation rate and negatively (r = -0.85) with active resorption surfaces. After 10 days of training, upregulation of VEGF and VEGF receptor R1 mRNA was detected in periosteum and metaphyseal bone. VEGF blockade in 5-week trained rats fully prevented the exercise-induced increase in metaphyseal BMD (9%) and cancellous bone volume (BV/TV; 25%), as well as the increased vessel number (25%). In 5-week placebo-treated running rats, bone formation rate returned to initial values, whereas osteoclastic surfaces continued to decline compared with both sedentary and anti-VEGF-treated running rats. CONCLUSION: VEGF signaling-mediated bone angiogenesis is tightly related to exercise-induced bone cellular uncoupling and is indispensable for bone gain induced by exercise.

Netrin-4 promotes mural cell adhesion and recruitment to endothelial cells.

Netrins are secreted molecules involved in axon guidance and angiogenesis. We previously showed that Netrin-4 acts as an anti-angiogenic factor by inhibiting endothelial cell (EC) functions. In this study, we investigated the effects of Netrin-4 on vascular smooth muscle cell (VSMC) activity in vitro and in vivo. We show that exogenous Netrin-4 stimulated VSMC adhesion and migration, and increased their coverage on EC tubes (grown on a Matrigel substrate). siRNA knock-down of endogenous Netrin-4 expression in VSMC decreased their recruitment to EC tubes. VSMC expressed Netrin-4 and three of the six Netrin-1 cognate receptors: DCC, Neogenin, and Unc5B. Silencing of these receptors reduced Netrin-4 adhesion to VSMC, strongly suggesting that these receptors were involved in the recruitment process. We previously showed that Netrin-4 overexpression in PC3 cancer cells delayed tumor growth in a model of subcutaneous xenograft by reducing tumor vessel density. Here, we show that Netrin-4 overexpression improved tumor blood vessel structure and increased VSMC coverage. Thus, Netrin-4 induced mural cell recruitment may play a role in the inhibition of tumor growth. Our data suggest that Netrin-4 is important for blood vessel normalization through the regulation of both endothelial and perivascular cells.

Brain pericytes from stress-susceptible pigs increase blood-brain barrier permeability in vitro.

BACKGROUND: The function of pericytes remains questionable but with improved cultured technique and the use of genetically modified animals, it has become increasingly clear that pericytes are an integral part of blood-brain barrier (BBB) function, and the involvement of pericyte dysfunction in certain cerebrovascular diseases is now emerging. The porcine stress syndrome (PSS) is the only confirmed, homologous model of malignant hyperthermia (MH) in veterinary medicine. Affected animals can experience upon slaughter a range of symptoms, including skeletal muscle rigidity, metabolic acidosis, tachycardia and fever, similar to the human syndrome. Symptoms are due to an enhanced calcium release from intracellular stores. These conditions are associated with a point mutation in ryr1/hal gene, encoding the ryanodine receptor, a calcium channel. Important blood vessel wall muscle modifications have been described in PSS, but potential brain vessel changes have never been documented in this syndrome. METHODS: In the present work, histological and ultrastructural analyses of brain capillaries from wild type and ryr1 mutated pigs were conducted to investigate the potential impairment of pericytes, in this pathology. In addition, brain pericytes were isolated from the three porcine genotypes (wild-type NN pigs; Nn and nn pigs, bearing one or two (n) mutant ryr1/hal alleles, respectively), and tested in vitro for their influence on the permeability of BBB endothelial monolayers. RESULTS: Enlarged perivascular spaces were observed in ryr1-mutant samples, corresponding to a partial or total detachment of the astrocytic endfeet. These spaces were electron lucent and sometimes filled with lipid deposits and swollen astrocytic feet. At the ultrastructural level, brain pericytes did not seem to be affected because they showed regular morphology and characteristics, so we aimed to check their ability to maintain BBB properties in vitro. Our results indicated that pericytes from the three genotypes of pigs had differing influences on the BBB. Unlike pericytes from NN pigs, pericytes from Nn and nn pigs were not able to maintain low BBB permeability. CONCLUSIONS: Electron microscopy observations demonstrated brain capillary modifications in PSS condition, but no change in pericyte morphology. Results from in vitro experiments suggest that brain pericytes from ryr1 mutated pigs, even if they are not affected by this condition at the ultrastructural level, are not able to maintain BBB integrity in comparison with pericytes from wild-type animals.

Neuropilin-1 and neuropilin-2 act as coreceptors, potentiating proangiogenic activity.

Neuropilin-1 and -2 (NRP1 and NRP2) are the transmembrane glycoproteins interacting with 2 types of ligands: class III semaphorins and several members of the VEGF family, the main regulators of blood and lymphatic vessel growth. We show here that both NRP1 and NRP2 can also bind hepatocyte growth factor (HGF). HGF is a pleiotropic cytokine and potent proangiogenic molecule that acts on its target cells by binding to the c-met receptor. We found that the N-terminal domain of HGF is involved in the interaction with neuropilins. We demonstrated that invalidation of NRP1 or NRP2 by RNA interference in human umbilical vein endothelial cells (HUVECs) decreased HGF-induced c-met phosphorylation and VEGF-A(165)- and HGF-mediated intracellular signaling. Accordingly, the disruption of NRP1 or NRP2 binding to VEGF-A(165) or HGF with a blocking antibody, decreased the proliferation and migration of endothelial cells. This effect may be further enhanced if VEGF-A(165) or HGF binding to both NRP1 and NRP2 was disrupted. Using a mouse Matrigel model, we demonstrated that NRP1 is essential for HGF-mediated angiogenesis in vivo. Our results suggest that, in endothelial cells, both NRP1 and NRP2 function as proangiogenic coreceptors, potentiating the activity of at least 2 major proangiogenic cytokines, VEGF-A(165) and HGF.

Inhibiting angiogenesis: interview with Dr Jean Plouët. Interview by Emma Quigley.

Dr Jean Plouët (Centre de Recherche Cardiovasculaire, INSERM U 689/Institut des Vaisseaux et du Sang) was interviewed by Emma Quigley (Commissioning Editor, Expert Opinion) on 20th June 2006. Born in Brittany, France, Dr Jean Plouët received his MD degree from Nantes University in 1977 and his PhD in Molecular Biology from Paris VII University in 1981. His first research topic, under the supervision of Dr Courtois and Dr Barritault was devoted to the purification and the description of the mechanisms of action of eye-derived growth factor, which turned out to be the retinal fibroblast growth factor (FGF)-2. He was appointed as Charge de Recherche by the Centre National de la Recherche Scientifique in 1981. He later conducted his research on the effect of FGF-2 on light transduction and demonstrated the role of opsin phosphorylation on FGF-2 release from retinal discs in Dr Pouliquen's laboratory. From 1987 to 1989, Dr Plouët worked in the Cancer Research Institute at the University of California, San Francisco, in Dr Gospodarowicz's laboratory where he co-discovered vascular endothelial growth factor (VEGF) with Dr Napoleone Ferrara. He established his own group in Toulouse where he worked on the mechanisms of action of VEGF and vascular targeting by anti-idiotypoc antibodies against VEGF and FGF. In 2005, Dr Plouët moved to Paris where he now works mainly on endogenous inhibitors of angiogenesis acting downstream of VEGF.

The role of the vascular endothelial growth factor-Delta-like 4 ligand/Notch4-ephrin B2 cascade in tumor vessel remodeling and endothelial cell functions.

Vascular endothelial growth factor (VEGF) and Delta-like 4 ligand (DLL4) are the only genes whose haploinsufficiency results in vascular abnormalities. Although many common pathways are up-regulated in both vascular development and tumor angiogenesis and in vascular remodeling, the role of the Delta/Notch pathway has not been clearly defined in tumor angiogenesis. In this study, we assessed the expression of DLL4, Notch4, and ephrin B2 in transgenic mice developing hepatocarcinoma characterized by a strong remodeling of the tumor sinusoids. We also investigated the role of VEGF in the expression and biological functions of these molecules on human venous endothelial cells. In transgenic livers, we showed that DLL4, active Notch4, and ephrin B2 were gradually up-regulated within the hepatocarcinoma progression and expressed on tumor sinusoidal endothelial cells. In venous endothelial cells, we showed that VEGF up-regulates DLL4 and presenilin, and increased the activation of Notch4, leading to an up-regulation of ephrin B2 with a down-regulation of Eph B4. We also showed that the activation of Notch4 is required for VEGF-induced up-regulation of ephrin B2 and the differentiation of human venous endothelial cells in vitro. Accordingly, the disruption of Notch4 signaling by pharmacologic inhibition of presenilin or addition of soluble DLL4 inhibited the effect of VEGF on human venous endothelial cell migration and differentiation. Our study strongly suggests that a coordinated activation of DDL4/Notch4 and ephrin B2 pathways downstream of VEGF plays a key role in the abnormal remodeling of tumor vessels.

Soluble HLA-G1 inhibits angiogenesis through an apoptotic pathway and by direct binding to CD160 receptor expressed by endothelial cells.

HLA-G is a major histocompatibility complex class Ib molecule whose constitutive tissue distribution is restricted mainly to trophoblast cells at the maternal-fetal interface during pregnancy. In this study, we demonstrated the ability of the soluble HLA-G1 (sHLA-G1) isoform to inhibit fibroblast growth factor-2 (FGF2)-induced capillary-like tubule formation. Using a rabbit corneal neovascularization model, we further showed that sHLA-G1 inhibits FGF2-induced angiogenesis in vivo. We also demonstrated that sHLA-G1 induces endothelial cell apoptosis through binding to BY55/CD160, a glycosylphosphatidylinositolanchored receptor expressed by endothelial cells. Furthermore, we showed that the specific CL1-R2 anti-CD160 monoclonal antibody mimics sHLA-G1-mediated inhibition of endothelial cell tube formation and induction of apoptosis. Thus, the engagement of CD160 in endothelial cells may be essential for the inhibition of angiogenesis. sHLA-G1/CD160-mediated antiangiogenic property may participate in the vascular remodeling of maternal spiral arteries during pregnancy, and, given that we found that CD160 is strongly expressed in the vasculature of a murine tumor, it offers an attractive therapeutic target for preventing pathologic neovascularization.

Pigment epithelium-derived factor exerts opposite effects on endothelial cells of different phenotypes.

The anti-angiogenic activity of pigment epithelium-derived factor (PEDF) has recently been discovered on the basis of its inhibition of ischemia-induced retinal neovascularization in an animal model of retinopathy of the premature. Moreover PEDF inhibits the migration and proliferation of various endothelial cells maintained in culture with FGF(2). Since vascular endothelial growth factor (VEGF) is the main angiogenic factor expressed in hypervascularized retinas, we investigated the functions of PEDF on retinal endothelial cells whose angiogenic phenotype is controlled or not by long term exposure to VEGF as observed in human pathologies such as diabetic retinopathy. Here, we observed that PEDF exerts opposite effects on endothelial cells depending on their phenotype. We determined that when PEDF inhibits endothelial cell growth, it inhibits VEGF-induced MAPK activation. However, in endothelial cells cultured with VEGF, PEDF has a synergistic action on cell proliferation with VEGF, and this corresponds to increased MAPK activation.

A dynamic shift of VEGF isoforms with a transient and selective progesterone-induced expression of VEGF189 regulates angiogenesis and vascular permeability in human uterus.

A key mechanism underlying physiological angiogenesis of the human endometrium is its ability to regenerate the vascular capillary network and to perform vascular remodeling (i.e., development of spiral arteries). Vascular endothelial growth factor (VEGF) is associated with angiogenesis and capillary permeability in this tissue. VEGF is expressed as several spliced variants, its main human isoforms contain 121 and 165 aa; 17beta-estradiol (E(2)) increases endometrial VEGF, possibly in all isoforms. Here we show that progesterone (P) selectively increases the expression of the VEGF(189) (V(189)) isoform in the human uterus. V(189) is identified in the conditioned medium of stromal cells treated with E(2) + P; its presence in this in vitro model of decidual stromal cells is detected after 6-8 days, using ELISA, and after 8-10 days, using Western blot analysis with different antibodies, including one specific for V(189). The secretion pattern of V(189) parallels that of the decidual protein IGFBP-1. V(189) is secreted as a native isoform, as compared with the migration of recombinant V(189) by SDS/PAGE. In situ hybridization and immunocytochemistry(,) performed on the same biopsies, suggest that decidual cells express V(189) during the mid-late secretory phase of the menstrual cycle and early gestation. Finally, using an in vivo permeability assay, we show that native V(189) increases capillary permeability. These observations demonstrate that P regulates V(189) expression in decidual cells, which could have important implications for understanding uterine vascular remodeling and implantation, and may be relevant in a range of disease states such as edema and irregular bleeding.