Inhibition of vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation by a peptide corresponding to the exon 7-encoded domain of VEGF165

Analysis of RNA Interference Targeted Against Human Antigen R (HuR) to Reduce Vascular Endothelial Growth Factor (VEGF) Protein Expression in Human Retinal Pigment Epithelial Cells

VEGF-A or vascular endothelial growth factor-A is an important factor in enabling neovascularization and angiogenesis. VEGF-A is regulated transcriptionally as well as post transcriptionally. Human antigen R (HuR) belonging to the embryonic lethal abnormal vision (ELAV) family is a key regulator promoting stabilization of VEGF-A mRNA. In this research we investigate, whether HuR targeted RNA interference would enable the reduction of the VEGF-A protein in human retinal pigment epithelial cells (ARPE-19) in-vitro, in normoxic conditions. Three siRNA molecules with sequences complementary to three regions of the HuR mRNA were designed. The three designed siRNA molecules were individually transfected in ARPE-19 cells using Lipofectamine™2000 reagent. Post-transfection (24 h, 48 h, 72 h), downregulation of HuR mRNA was estimated by real-time polymerase reaction, while HuR protein and VEGF-A protein levels were semi-quantitatively determined by western blotting techniques. VEGF-A protein levels were additionally quantified using ELISA techniques. All experiments were done in triplicate. The designed siRNA could successfully downregulate HuR mRNA with concomitant decreases in HuR and VEGF-A protein. The study reveals that HuR downregulation can prominently downregulate VEGF-A, making the protein a target for therapy against pathological angiogenesis conditions such as diabetic retinopathy.

VEGF-Encoding, Gene-Activated Collagen-Based Matrices Promote Blood Vessel Formation and Improved Wound Repair

Disruption in vascularization during wound repair can severely impair healing. Proangiogenic growth factor therapies have shown great healing potential; however, controlling growth factor activity and cellular behavior over desired healing time scales remains challenging. In this study, we evaluated collagen-mimetic peptide (CMP) tethers for their capacity to control growth factor gene transfer and growth factor activity using our recently developed gene-activated hyaluronic acid-collagen matrix (GAHCM). GAHCM was comprised of DNA/polyethyleneimine (PEI) polyplexes that were retained on hyaluronic acid (HA)-collagen hydrogels using CMPs. We hypothesized that using CMP-collagen tethers to control vascular endothelial growth factor-A (VEGF-A) gene delivery in fibroblasts would provide a powerful strategy to modulate the proangiogenic behaviors of endothelial cells (ECs) for blood vessel formation, resulting in enhanced wound repair. In co-culture experiments, we observed that CMP-modified GAHCM induced tunable gene delivery in fibroblasts as predicted, and correspondingly, VEGF-A produced by the fibroblasts led to increased growth and persistent migration of ECs for at least 7 days, as compared to non-CMP-modified GAHCM. Moreover, when ECs were exposed to fibroblast-containing VEGF-GAHCM with higher levels of CMP modification (50% CMP-PEI, or 50 CP), high CD31 expression was stimulated, resulting in the formation of an interconnected EC network with a significantly higher network volume and a larger diameter network structure than controls. Application of VEGF-GAHCM with 50 CP in murine splinted excisional wounds facilitated prolonged prohealing and proangiogenic responses resulting in increased blood vessel formation, improved granulation tissue formation, faster re-epithelialization, and overall enhanced repair. These findings suggest the benefits of CMP-collagen tethers as useful tools to control gene transfer and growth factor activity for improved treatment of wounds.

Lowry M, Almasri R, Gorgun C, Eichholz K, Stavenschi E, Hokamp K, Roche F, O’Driscoll L, Hoey D. Mechanically activated mesenchymal-derived bone cells drive vessel formation via an extracellular vesicle mediated mechanism

Blood vessel formation is an important initial step for bone formation during development as well as during remodelling and repair in the adult skeleton. This results in a heavily vascularized tissue where endothelial cells and skeletal cells are constantly in crosstalk to facilitate homeostasis, a process that is mediated by numerous environmental signals, including mechanical loading. Breakdown in this communication can lead to disease and/or poor fracture repair. Therefore, this study aimed to determine the role of mature bone cells in regulating angiogenesis, how this is influenced by a dynamic mechanical environment, and understand the mechanism by which this could occur. Herein, we demonstrate that both osteoblasts and osteocytes coordinate endothelial cell proliferation, migration, and blood vessel formation via a mechanically dependent paracrine mechanism. Moreover, we identified that this process is mediated via the secretion of extracellular vesicles (EVs), as isolated EVs from mechanically stimulated bone cells elicited the same response as seen with the full secretome, while the EV-depleted secretome did not elicit any effect. Despite mechanically activated bone cell-derived EVs (MA-EVs) driving a similar response to VEGF treatment, MA-EVs contain minimal quantities of this angiogenic factor. Lastly, a miRNA screen identified mechanoresponsive miRNAs packaged within MA-EVs which are linked with angiogenesis. Taken together, this study has highlighted an important mechanism in osteogenic-angiogenic coupling in bone and has identified the mechanically activated bone cell-derived EVs as a therapeutic to promote angiogenesis and potentially bone repair.

Synthesis, Physicochemical and Biological Study of Gallium-68- and Lutetium-177-Labeled VEGF-A165/NRP-1 Complex Inhibitors Based on Peptide A7R and Branched Peptidomimetic

Neuropilin-1 (NRP-1) is a surface receptor found on many types of cancer cells. The overexpression of NRP-1 and its interaction with vascular endothelial growth factor-165 (VEGF₁₆₅) are associated with tumor growth and metastasis. Therefore, compounds that block the VEGF₁₆₅/NRP-1 interaction represent a promising strategy to image and treat NRP-1-related pathologies. The aim of the presented work was to design and synthesize radioconjugates of two known peptide-type inhibitors of the VEGF₁₆₅/NRP-1 complex: A7R peptide and its shorter analog, the branched peptidomimetic Lys(hArg)-Dab-Pro-Arg. Both peptide-type inhibitors were coupled to a radionuclide chelator (DOTA) via a linker (Ahx) and so radiolabeled with Ga-68 and Lu-177 radionuclides, for diagnostic and therapeutic uses, respectively. The synthesized radioconjugates were tested for their possible use as theranostic-like radiopharmaceuticals for the imaging and therapy of cancers that overexpress NRP-1. The obtained results indicate good efficiency of the radiolabeling reaction and satisfactory stability, at least 3t_1/2 for the ⁶⁸Ga- and 1t_1/2 for the ¹⁷⁷Lu-radiocompounds, in solutions mimicking human body fluids. However, enzymatic degradation of both the studied inhibitors caused insufficient stability of the radiocompounds in human serum, indicating that further modifications are needed to sufficiently stabilize the peptidomimetics with inhibitory properties against VEGF₁₆₅/NRP-1 complex formation.

Urea-Peptide Hybrids as VEGF-A165/NRP-1 Complex Inhibitors with Improved Receptor Affinity and Biological Properties

Neuropilin-1 (NRP-1), the major co-receptor of vascular endothelial growth factor receptor-2 (VEGFR-2), may also independently act with VEGF-A₁₆₅ to stimulate tumour growth and metastasis. Therefore, there is great interest in compounds that can block VEGF-A165/NRP-1 interaction. Peptidomimetic type inhibitors represent a promising strategy in the treatment of NRP-1-related disorders. Here, we present the synthesis, affinity, enzymatic stability, molecular modeling and in vitro binding evaluation of the branched urea–peptide hybrids, based on our previously reported Lys(hArg)-Dab-Oic-Arg active sequence, where the Lys(hArg) branching has been modified by introducing urea units to replace the peptide bond at various positions. One of the resulting hybrids increased the affinity of the compound for NRP-1 more than 10-fold, while simultaneously improving resistance for proteolytic stability in serum. In addition, ligand binding to NRP-1 induced rapid protein stock exocytotic trafficking to the plasma membrane in breast cancer cells. Examined properties characterize this compound as a good candidate for further development of VEGF₁₆₅/NRP-1 inhibitors.

ACE2: Evidence of role as entry receptor for SARS-CoV-2 and implications in comorbidities

Pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus 19 disease (COVID-19) which presents a large spectrum of manifestations with fatal outcomes in vulnerable people over 70-years-old and with hypertension, diabetes, obesity, cardiovascular disease, COPD, and smoking status. Knowledge of the entry receptor is key to understand SARS-CoV-2 tropism, transmission and pathogenesis. Early evidence pointed to angiotensin-converting enzyme 2 (ACE2) as SARS-CoV-2 entry receptor. Here, we provide a critical summary of the current knowledge highlighting the limitations and remaining gaps that need to be addressed to fully characterize ACE2 function in SARS-CoV-2 infection and associated pathogenesis. We also discuss ACE2 expression and potential role in the context of comorbidities associated with poor COVID-19 outcomes. Finally, we discuss the potential co-receptors/attachment factors such as neuropilins, heparan sulfate and sialic acids and the putative alternative receptors, such as CD147 and GRP78.

In vitro combination therapy of pathologic angiogenesis using anti-vascular endothelial growth factor and anti-neuropilin-1 nanobodies

OBJECTIVES

Emergence of resistant tumor cells to the current therapeutics is the main hindrance in cancer treatment. Combination therapy, which mixes two or more drugs, is a way to overcome resistant problems of cancer cells to current treatments. Nanobodies are promising tools in cancer therapy due to their high affinity as well as high penetration to tumor sites.

MATERIALS AND METHODS

Here, the inhibitory effect of mixtures of two nanobodies (anti-vascular endothelial growth factor (VEGF) and anti-neuropilin-1 (NRP-1) nanobodies) on tube formation of human endothelial cells in vitro and ex vivo were analyzed.

RESULTS

Results showed that combination of two drugs significantly inhibited proliferation and tube formation of human endothelial cells. In addition, mixtures of two nanobodies inhibited angiogenesis in chick chorioallantoic membrane (CAM) assay efficiently compared with each individual nanobody.

CONCLUSION

Results highlight the efficacy of combination therapy of cancer compared with mono-therapy and promises development of novel anti-cancer therapeutics based on nanobodies targeting two or more targets of tumor cells.

Vascular NRP2 triggers PNET angiogenesis by activating the SSH1-cofilin axis

Background

Angiogenesis is a critical step in the growth of pancreatic neuroendocrine tumors (PNETs) and may be a selective target for PNET therapy. However, PNETs are robustly resistant to current anti-angiogenic therapies that primarily target the VEGFR pathway. Thus, the mechanism of PNET angiogenesis urgently needs to be clarified.

Methods

Dataset analysis was used to identify angiogenesis-related genes in PNETs. Immunohistochemistry was performed to determine the relationship among Neuropilin 2 (NRP2), VEGFR2 and CD31. Cell proliferation, wound-healing and tube formation assays were performed to clarify the function of NRP2 in angiogenesis. The mechanism involved in NRP2-induced angiogenesis was detected by constructing plasmids with mutant variants and performing Western blot, and immunofluorescence assays. A mouse model was used to evaluate the effect of the NRP2 antibody in vivo, and clinical data were collected from patient records to verify the association between NRP2 and patient prognosis.

Results

NRP2, a VEGFR2 co-receptor, was positively correlated with vascularity but not with VEGFR2 in PNET tissues. NRP2 promoted the migration of human umbilical vein endothelial cells (HUVECs) cultured in the presence of conditioned medium PNET cells via a VEGF/VEGFR2-independent pathway. Moreover, NRP2 induced F-actin polymerization by activating the actin-binding protein cofilin. Cofilin phosphatase slingshot-1 (SSH1) was highly expressed in NRP2-activating cofilin, and silencing SSH1 ameliorated NRP2-activated HUVEC migration and F-actin polymerization. Furthermore, blocking NRP2 in vivo suppressed PNET angiogenesis and tumor growth. Finally, elevated NRP2 expression was associated with poor prognosis in PNET patients.

Conclusion

Vascular NRP2 promotes PNET angiogenesis by activating the SSH1/cofilin/actin axis. Our findings demonstrate that NRP2 is an important regulator of angiogenesis and a potential therapeutic target of anti-angiogenesis therapy for PNET.

Overview of Brain-to-Gut Axis Exposed to Chronic CNS Bacterial Infection(s) and a Predictive Urinary Metabolic Profile of a Brain Infected by Mycobacterium tuberculosis

A new paradigm in neuroscience has recently emerged - the brain-gut axis (BGA). The contemporary focus in this paradigm has been gut → brain ("bottom-up"), in which the gut-microbiome, and its perturbations, affects one's psychological state-of-mind and behavior, and is pivotal in neurodegenerative disorders. The emerging brain → gut ("top-down") concept, the subject of this review, proposes that dysfunctional brain health can alter the gut-microbiome. Feedback of this alternative bidirectional highway subsequently aggravates the neurological pathology. This paradigm shift, however, focuses upon non-communicable neurological diseases (progressive neuroinflammation). What of infectious diseases, in which pathogenic bacteria penetrate the blood-brain barrier and interact with the brain, and what is this effect on the BGA in bacterial infection(s) that cause chronic neuroinflammation? Persistent immune activity in the CNS due to chronic neuroinflammation can lead to irreversible neurodegeneration and neuronal death. The properties of cerebrospinal fluid (CSF), such as immunological markers, are used to diagnose brain disorders. But what of metabolic markers for such purposes? If a BGA exists, then chronic CNS bacterial infection(s) should theoretically be reflected in the urine. The premise here is that chronic CNS bacterial infection(s) will affect the gut-microbiome and that perturbed metabolism in both the CNS and gut will release metabolites into the blood that are filtered (kidneys) and excreted in the urine. Here we assess the literature on the effects of chronic neuroinflammatory diseases on the gut-microbiome caused by bacterial infection(s) of the CNS, in the context of information attained via metabolomics-based studies of urine. Furthermore, we take a severe chronic neuroinflammatory infectious disease - tuberculous meningitis (TBM), caused by Mycobacterium tuberculosis, and examine three previously validated CSF immunological biomarkers - vascular endothelial growth factor, interferon-gamma and myeloperoxidase - in terms of the expected changes in normal brain metabolism. We then model the downstream metabolic effects expected, predicting pivotal altered metabolic pathways that would be reflected in the urinary profiles of TBM subjects. Our cascading metabolic model should be adjustable to account for other types of CNS bacterial infection(s) associated with chronic neuroinflammation, typically prevalent, and difficult to distinguish from TBM, in the resource-constrained settings of poor communities.

Does Cysteine Rule (CysR) Complete the CendR Principle? Increase in Affinity of Peptide Ligands for NRP-1 Through the Presence of N-Terminal Cysteine

The structure-activity relationship of branched H-Lys(hArg)-Dab-Dhp-Arg-OH sequence analogues, modified with Cys-Asp or Cys at N-terminal amino acids (Lys, hArg), in VEGF-A₁₆₅/Neuropilin-1 complex inhibition is presented. The addition of Cys residue led to a 100-fold decrease in the IC₅₀ value, compared to the parent peptide. The change occurred regardless of coupling Cys to the free N-terminal amino group present in the main or the side chain. A few analogues extended by the attachment of Cys at the N-terminus of several potent NRP-1 peptide ligands documented in the literature are also presented. In all studied cases, the enhancement of inhibitory properties after the addition of Cys at the N-terminus is observed. It is particularly evident for the tetrapeptide derived from the C-terminus of VEGF-A₁₆₅ (KPRR), suggesting that extending the K/RXXK/R motif (CendR) with the Cys moiety can significantly improve affinity to NRP-1 of CendR peptides.

Synchronous inhibition of mTOR and VEGF/NRP1 axis impedes tumor growth and metastasis in renal cancer

Clear cell renal cell carcinoma (ccRCC) is known for its highly vascular phenotype which is associated with elevated expression of vascular endothelial growth factor A (VEGF), also known as vascular permeability factor (VPF). Accordingly, VEGF has been an attractive target for antiangiogenic therapies in ccRCC. Two major strategies have hitherto been utilized for VEGF-targeted antiangiogenic therapies: targeting VEGF by antibodies, ligand traps or aptamers, and targeting the VEGF receptor signaling via antibodies or small-molecule tyrosine-kinase inhibitors (TKIs). In the present article we utilized two entirely different approaches: targeting mammalian target of rapamycin (mTOR) pathway that is known to be involved in VEGF synthesis, and disruption of VEGF/Neuroplin-1 (NRP1) axis that is known to activate proangiogenic and pro-tumorigenic signaling in endothelial and tumor cells, respectively. Everolimus (E) and a small-molecule inhibitor EG00229 (G) were used for the inhibition of mTOR and the disruption of VEGF/NRP1 axis, respectively. We also exploited a liposomal formulation decorated with a proprietary tumor-targeting-peptide (TTP) to simultaneously deliver these two agents in a tumor-targeted manner. The TTP-liposomes encapsulating both Everolimus and EG00229 (EG-L) demonstrated higher in vitro and in vivo growth retardation than the single drug-loaded liposomes (E-L and G-L) in two different ccRCC models and led to a noticeable reduction in lung metastasis in vivo. In addition, EG-L displayed remarkable inhibition of tumor growth in a highly aggressive syngeneic immune-competent mouse model of ccRCC developed in Balb/c mice. Taken together, this study demonstrates an effective approach to achieve improved therapeutic outcome in ccRCC.

A portable oligonucleotide-based microfluidic device for the detection of VEGF165 in a three-step suspended-droplet mode

Vascular endothelial growth factor (VEGF165), an important glycosylated protein from the VEGF family, is a type of signal protein highly associated with the development and progression of cancers. In this work, we designed a G-quadruplex-based aptasensing platform for the sensitive and selective detection of VEGF165 in aqueous solution and red blood cell solution. A long-lived phosphorescence iridium(iii) complex (1) with promising photophysical properties and a large Stokes shift was chosen as a selective G-quadruplex probe. The platform could achieve a limit of detection (LOD) down to the picomolar level using a conventional fluorometer. Furthermore, we successfully applied the platform to a three-step suspended droplet (SD)-based microfluidic device for the monitoring of VEGF165. In contrast to the channel-based and digital microfluidic chips, SD-based chips allow easy introduction of liquid samples, valve-free manipulation of multiple reaction steps and flexible volume range. Importantly, polypropylene (PP), a hydrophobic and thermally stable material, was chosen as a substrate to fabricate the chip for the SD-based microfluidic device. The PP-based chip allows the combination of superhydrophobic force, gravity and surface tension for effective driving of the suspended droplet throughout the channel without reverse migration. After assembling all the major components, including a UV lamp, a rotatable chip holder, a filter and a camera into the portable device, we successfully demonstrated the applicability of the device to detect VEGF165 in aqueous solution with a LOD of 0.33 nM at a signal-to-noise ratio (S/N) of 3 and a linear range of 1-100 nM.

Urea moiety as amide bond mimetic in peptide-like inhibitors of VEGF-A165/NRP-1 complex

NRP-1 is an important co-receptor of vascular endothelial growth factor receptor-2 (VEGFR-2). Many reports suggested that NRP-1 might also serve as a separate receptor for VEGF-A₁₆₅ causing stimulation of tumour growth and metastasis. Therefore, compounds interfering with VEGF-A₁₆₅/NRP-1 complex triggered interest in the design of new molecules, including peptides, as anti-angiogenic and anti-tumour drugs. Here, we report the synthesis, affinity and stability evaluation of the urea-peptide hybrids, based on general Lys(hArg)-AA²-AA³-Arg sequence, where hArg residue was substituted by Arg urea unit. Such substitution does not substantially affected affinity of compounds for NRP-1 but significantly increased their proteolytic stability in plasma.

Triazolopeptides Inhibiting the Interaction between Neuropilin-1 and Vascular Endothelial Growth Factor-165

Inhibiting the interaction of neuropilin-1 (NRP-1) with vascular endothelial growth factor (VEGF) has become an interesting mechanism for potential anticancer therapies. In our previous works, we have obtained several submicromolar inhibitors of this interaction, including branched pentapeptides of general structure Lys(Har)-Xxx-Xxx-Arg. With the intent to improve the proteolytic stability of our inhibitors, we turned our attention to 1,4-disubstituted 1,2,3-triazoles as peptide bond isosteres. In the present contribution, we report the synthesis of 23 novel triazolopeptides along with their inhibitory activity. The compounds were synthesized using typical peptide chemistry methods, but with a conversion of amine into azide completely on solid support. The inhibitory activity of the synthesized derivatives spans from 9.2% to 58.1% at 10 μM concentration (the best compound Lys(Har)-GlyΨ[Trl]GlyΨ[Trl]Arg, 3, IC₅₀ = 8.39 μM). Synthesized peptidotriazoles were tested for stability in human plasma and showed remarkable resistance toward proteolysis, with half-life times far exceeding 48 h. In vitro cell survival test resulted in no significant impact on bone marrow derived murine cells 32D viability. By means of molecular dynamics, we were able to propose a binding mode for compound 3 and discuss the observed structure–activity relationships.

The Role of Endothelial Surface Glycocalyx in Mechanosensing and Transduction

The endothelial cells (ECs) forming the inner wall of every blood vessel are constantly exposed to the mechanical forces generated by blood flow. The EC responses to these hemodynamic forces play a critical role in the homeostasis of the circulatory system. A variety of mechanosensors and transducers, locating on the EC surface, intra- and trans-EC membrane, and within the EC cytoskeleton, have thus been identified to ensure proper functions of ECs. Among them, the most recent candidate is the endothelial surface glycocalyx (ESG), which is a matrix-like thin layer covering the luminal surface of the EC. It consists of various proteoglycans, glycosaminoglycans, and plasma proteins and is close to other prominent EC mechanosensors and transducers. This chapter summarizes the ESG composition, thickness, and structure observed by different labeling and visualization techniques and in different types of vessels. It also presents the literature in determining the ESG mechanical properties by atomic force microscopy and optical tweezers. The molecular mechanisms by which the ESG plays the role in EC mechanosensing and transduction are described as well as the ESG remodeling by shear stress, the actin cytoskeleton, the membrane rafts, the angiogenic factors, and the sphingosine-1-phosphate.

Matrix Stiffness Enhances VEGFR-2 Internalization, Signaling, and Proliferation in Endothelial Cells

Vascular endothelial growth factor (VEGF) can mediate endothelial cell migration, proliferation, and angiogenesis. During cancer progression, VEGF production is often increased to stimulate the growth of new blood vessels to supply growing tumors with the additional oxygen and nutrients they require. Extracellular matrix stiffening also occurs during tumor progression, however, the crosstalk between tumor mechanics and VEGF signaling remains poorly understood. Here, we show that matrix stiffness heightens downstream endothelial cell response to VEGF by altering VEGF receptor-2 (VEGFR-2) internalization, and this effect is influenced by cell confluency. In sub-confluent endothelial monolayers, VEGFR-2 levels, but not VEGFR-2 phosphorylation, are influenced by matrix rigidity. Interestingly, more compliant matrices correlated with increased expression and clustering of VEGFR-2; however, stiffer matrices induced increased VEGFR-2 internalization. These effects are most likely due to actin-mediated contractility, as inhibiting ROCK on stiff substrates increased VEGFR-2 clustering and decreased internalization. Additionally, increasing matrix stiffness elevates ERK 1/2 phosphorylation, resulting in increased cell proliferation. Moreover, cells on stiff matrices generate more actin stress fibers than on compliant substrates, and the addition of VEGF stimulates an increase in fiber formation regardless of stiffness. In contrast, once endothelial cells reached confluency, stiffness-enhanced VEGF signaling was no longer observed. Together, these data show a complex effect of VEGF and matrix mechanics on VEGF-induced signaling, receptor dynamics, and cell proliferation that is mediated by cell confluency.

Revisiting the expression and function of follicle-stimulation hormone receptor in human umbilical vein endothelial cells

Expression of follicle-stimulation hormone receptor (FSHR) is confined to gonads and at low levels to some extragonadal tissues like human umbilical vein endothelial cells (HUVEC). FSH-FSHR signaling was shown to promote HUVEC angiogenesis and thereafter suggested to have an influential role in pregnancy. We revisited hereby the expression and functionality of FSHR in HUVECs angiogenesis, and were unable to reproduce the FSHR expression in human umbilical cord, HUVECs or immortalized HUVECs (HUV-ST). Positive controls as granulosa cells and HEK293 cells stably transfected with human FSHR cDNA expressed FSHR signal. In contrast to positive control VEGF, FSH treatment showed no effects on tube formation, nitric oxide production, wound healing or cell proliferation in HUVEC/HUV-ST. Thus, it remains open whether the FSH-FSHR activation has a direct regulatory role in the angiogenesis of HUVECs.

Crystal Structure of the Neuropilin-1 MAM Domain: Completing the Neuropilin-1 Ectodomain Picture

Neuropilins (NRPs) are single-pass transmembrane receptors involved in several signaling pathways that regulate key physiological processes such as vascular morphogenesis and axon guidance. The MAM domain of NRP, which has previously been implicated in receptor multimerization, was the only portion of the ectopic domain of the NRPs for which the structure, until now, has been elusive. Using site-directed mutagenesis in the linker region preceding the MAM domain we generated a protein construct amenable to crystallization. Here we present the crystal structure of the MAM domain of human NRP1 at 2.24 Å resolution. The protein exhibits a jellyroll topology, with Ca2+ ions bound at the inter-strand space enhancing the thermostability of the domain. We show that the MAM domain of NRP1 is monomeric in solution and insufficient to drive receptor dimerization, which leads us to propose a different role for this domain in the context of NRP membrane assembly and signaling.

Molecular modelling, synthesis and biological evaluation of peptide inhibitors as anti-angiogenic agent targeting neuropilin-1 for anticancer application

Vascular endothelial growth factor (VEGF) and its co-receptor neuropilin-1 (NRP-1) are important targets of many pro-angiogenic factors. In this study, nine peptides were synthesized and evaluated for their molecular interaction with NRP-1 and compared to our previous peptide ATWLPPR. Docking study showed that the investigated peptides shared the same binding region as shown by tuftsin known to bind selectively to NRP-1. Four pentapeptides (DKPPR, DKPRR, TKPPR and TKPRR) and a hexapeptide CDKPRR demonstrated good inhibitory activity against NRP-1. In contrast, peptides having arginine residue at sites other than the C-terminus exhibited low activity towards NRP-1 and this is confirmed by their inability to displace the VEGF₁₆₅ binding to NRP-1. Docking study also revealed that replacement of carboxyl to amide group at the C-terminal arginine of the peptide did not affect significantly the binding interaction to NRP-1. However, the molecular affinity study showed that these peptides have marked reduction in the activity against NRP-1. Pentapeptides having C-terminal arginine showed strong interaction and good inhibitory activity with NRP thus may be a good template for anti-angiogenic targeting agent.

Targeting VEGF-A with a vaccine decreases inflammation and joint destruction in experimental arthritis

OBJECTIVES

Inflammation and angiogenesis are two tightly linked processes in arthritis, and therapeutic targeting of pro-angiogenic factors may contribute to control joint inflammation and synovitis progression. In this work, we explored whether vaccination against vascular endothelial growth factor (VEGF) ameliorates collagen-induced arthritis (CIA).

METHODS

Anti-VEGF vaccines were heterocomplexes consisting of the entire VEGF cytokine (or a VEGF-derived peptide) linked to the carrier protein keyhole limpet hemocyanin (KLH). Two kinds of vaccines were separately tested in two independent experiments of CIA. In the first, we tested a kinoid of the murine cytokine VEGF (VEGF-K), obtained by conjugating VEGF-A to KLH. For the second, we selected two VEGF-A-derived peptide sequences to produce heterocomplexes (Vpep1-K and Vpep2-K). DBA/1 mice were immunized with either VEGF-K, Vpep1-K, or Vpep2-K, before CIA induction. Clinical and histological scores of arthritis, anti-VEGF, anti-Vpep Ab titers, and anti-VEGF Abs neutralizing capacity were determined.

RESULTS

Both VEGF-K and Vpep1-K significantly ameliorated clinical arthritis scores and reduced synovial inflammation and joint destruction at histology. VEGF-K significantly reduced synovial vascularization. None of the vaccines reduced anti-collagen Ab response in mice. Both VEGF-K and Vpep1-K induced persistently high titers of anti-VEGF Abs capable of inhibiting VEGF-A bioactivity.

CONCLUSION

Vaccination against the pro-angiogenic factor VEGF-A leads to the production of anti-VEGF polyclonal Abs and has a significant anti-inflammatory effect in CIA. Restraining Ab response to a single peptide sequence (Vpep1) with a peptide vaccine effectively protects immunized mice from joint inflammation and destruction.

Neuropilin-1 as Therapeutic Target for Malignant Melanoma

Neuropilin-1 (NRP-1) is a transmembrane glycoprotein that acts as a co-receptor for various members of the vascular endothelial growth factor (VEGF) family. Its ability to bind or modulate the activity of a number of other extracellular ligands, such as class 3 semaphorins, TGF-β, HGF, FGF, and PDGF, has suggested the involvement of NRP-1 in a variety of physiological and pathological processes. Actually, this co-receptor has been implicated in axon guidance, angiogenesis, and immune responses. NRP-1 is also expressed in a variety of cancers (prostate, lung, pancreatic, or colon carcinoma, melanoma, astrocytoma, glioblastoma, and neuroblastoma), suggesting a critical role in tumor progression. Moreover, a growing amount of evidence indicates that NRP-1 might display important functions independently of other VEGF receptors. In particular, in the absence of VEGFR-1/2, NRP-1 promotes melanoma invasiveness, through the activation of selected integrins, by stimulating VEGF-A and metalloproteinases secretion and modulating specific signal transduction pathways. This review is focused on the role of NRP-1 in melanoma aggressiveness and on the evidence supporting its use as target of therapies for metastatic melanoma.

Effect of switching therapy to pegaptanib in eyes with the persistent cases of exudative age-related macular degeneration

Purpose of this study was to evaluate the efficacy of switching to pegaptanib monotherapy for persistent cases of exudative age-related macular degeneration (AMD).Out of 296 eyes of 296 patients treated with ranibizumab or ranibizumab combined with photodynamic therapy (PDT), 50 eyes of 50 AMD patients were found to be resistant to these treatments. Over a 12-month period, intravitreal pegaptanib (IVP) 0.3 mg was administered at intervals of 6 weeks until the exudation disappeared prospectively. All patients were examined with the following tests: best-corrected visual acuity (BCVA) and central retinal thickness (CRT), determined at the initial visit, before the first IVP (baseline), and at 12 months. The factors responsible for achieving dry macula with IVP were examined statistically.The rate of persistent cases with intravitreal ranibizumab (IVR) and/or PDT was 17.0%. The mean number of IVPs administered was 5.4 (range, 2-9). Logarithm of the minimal angle of resolution BCVA at 12 months was stable or improved by ≥ 0.3 in 49 eyes (98.0%), with a significant improvement noted between the baseline and final BCVA (P=0.01, paired t test). The CRT (mean ± standard deviation) was 446.9 ± 150.6 µm at the initial visit, 414.5 ± 146.5 µm at baseline, and 318.7 ± 99.0 µm at 12 months. There was a significant decrease in the mean CRT between the measurements at baseline and at 12 months after the first IVP (P=0.002, Bonferroni correction). At 12 months, the exudative change was completely resolved in 27 eyes (54.0%) and reduced in 21 eyes (42.0%). The number of previous IVR treatments was significantly correlated with dry macula at 12 months.After switching therapy to pegaptanib in persistent cases of AMD, most patients maintained or improved their BCVA and exhibited a positive treatment response at 12 months.

Surface density of vascular endothelial growth factor modulates endothelial proliferation and differentiation

Therapeutic strategies aim to regulate vasculature either by encouraging vessel growth for tissue engineering or inhibiting vascularization around a tumor. Vascular endothelial growth factor (VEGF) is essential to these processes, and there are several strategies that manipulate VEGF signaling. Here we develop a method to control the surface density of VEGF, which is covalently attached to tissue culture polystyrene (TCPS), and explore cellular responses to surfaces with varying VEGF densities. We show that the crosslinker reduces but does not eliminate the biological activity of soluble VEGF as measured by endothelial proliferation. However, endothelial cells cultured on surfaces of covalently bound VEGF did not proliferate in response to surface cues. Interestingly, compared to cells incubated with soluble VEGF (10 ng/ml) and cultured on TCPS, lower cell proliferation was observed when endothelial cells were cultured on high VEGF surface densities (5.9 ng/cm(2)), whereas higher cell proliferation occurred when cells were cultured on low surface densities (0.04 ng/cm(2)). High density surfaces (5.9 ng/cm(2)) also acted in synergy with an inhibitor of VEGF receptors to further suppress endothelial cell proliferation. We also examined the effect of VEGF surfaces on endothelial differentiation of mesenchymal stem cells. No effect was observed when cells were cultured on VEGF surfaces; however, the VEGF surfaces acted in synergy with an inhibitor of VEGF receptors to decrease the ability of differentiated cells to form vascular networks. Together, these results suggest that surface density of bound VEGF can be used to modulate cell behavior and inhibit an angiogenic response.

Characterisation of the interaction of neuropilin-1 with heparin and a heparan sulfate mimetic library of heparin-derived sugars

Background. Neuropilin-1 (NRP-1) is a multidomain membrane protein with soluble isoforms interacting with a complex network of other membrane receptors, their respective ligands and heparan sulfate (HS). It is involved in the development of vasculature, neural patterning, immunological responses and pathological angiogenesis. Methods. We have characterised the binding of a Fc fusion of rat NRP-1 (Fc rNRP-1) and of a soluble isoform, corresponding to the first four extracellular domains of human NRP-1, shNRP-1, using optical biosensor-based binding assays with a library of heparin derivatives. Selective labelling of lysines protected upon heparin binding allowed their identification by mass spectrometry. Results. Fc rNRP-1 bound to heparin with high affinity (2.5 nM) and fast ka (9.8 × 10(6) M(-1)s(-1)). Unusually, NRP-1 bound both highly sulfated and completely desulfated stretches of heparin and exhibited a complex pattern of preferences for chemically modified heparins possessing one or two sulfate groups, e.g., it bound heparin with just a 6-O sulfate group better than heparin with any two of N-sulfate, 6-O sulfate and 2-O sulfate. Mass-spectrometry based mapping identified that, in addition to the expected the b1 domain, the a1, and c domains and the L2 linker were also involved in the interaction. In contrast, shNRP-1 bound heparin far more weakly. This could only be shown by affinity chromatography and by differential scanning fluorimetry. Discussion. The results suggest that the interaction of NRP-1 with HS is more complex than anticipated and involving a far greater extent of the protein than just the b1-b2 domains. NRP-1's preference for binding long saccharide structures suggests it has the potential to bind large segments of HS chains and so organise their local structure. In contrast, the four domain soluble isoform, shNRP-1 binds heparin weakly and so would be expected to diffuse away rapidly from the source cell.

Serum-dependence of affinity-mediated VEGF release from biomimetic microspheres

Vascular endothelial growth factor (VEGF) activity is highly regulated via sequestering within the ECM and cell-demanded proteolysis to release the sequestered VEGF. Numerous studies have demonstrated that VEGF activity mediates cellular events leading to angiogenesis and capillary formation in vivo. This has motivated the study of biomaterials to sustain VEGF release, and in many cases, the materials are inspired by the structure and function of the native ECM. However, there remains a need for materials that can bind to VEGF with high specificity, as the in vivo environment is rich in a variety of growth factors (GFs) and GF-binding moieties. Here we describe a strategy to control VEGF release using hydrogel microspheres with tethered peptides derived from VEGF receptor 2 (VEGFR2). Using biomaterials covalently modified with varying concentrations of two distinct VEGFR2-derived peptides with varying serum stability, we analyzed both biomaterial and environmental variables that influence VEGF release and activity. The presence of tethered VEGF-binding peptides (VBPs) resulted in significantly extended VEGF release relative to control conditions, and the resulting released VEGF significantly increased the expansion of human umbilical vein endothelial cells in culture. VEGF release rates were also strongly influenced by the concentration of serum. The presence of Feline McDonough Sarcoma-like tyrosine kinase 1 (sFlt-1), a serum-borne receptor fragment derived from VEGF receptor 1, increased VEGF release rates, although sFlt-1 was not sufficient to recapitulate the release profile of VEGF in serum. Further, the influence of serum on VEGF release was not due to protease activity or nonspecific VEGF interactions in the presence of serum-borne heparin. VEGF release kinetics correlated well with a generalizable mathematical model describing affinity-mediated release of VEGF from hydrogel microspheres in defined conditions. Modeling results suggest a potential mechanism whereby competition between VEGF and multiple VEGF-binding serum proteins including sFlt-1, soluble kinase insert domain receptor (sKDR), and α2-macroglobulin (α2-M) likely influenced VEGF release from microspheres. The materials and mathematical model described in this approach may be useful in a range of applications in which sustained, biologically active GF release of a specific GF is desirable.

Differential expression of capillary VEGF isoforms following traumatic brain injury

OBJECTIVES

While it is known that angiogenesis occurs after trauma, we sought to characterize the expression of vascular endothelial growth factor (VEGF) subtypes, vascular endothelial growth factor receptor 2 (VEGFR2) and angiopoietin within capillaries of animals subjected to traumatic brain injury (TBI). Further, we sought to characterize pericyte cell death in isolated capillaries.

METHODS

We used Marmarou's acceleration impact model to induce head trauma and measured VEGF, VEGFR2 and angiopoietin levels in isolated capillaries. TUNEL was used to determine pericyte cell death.

RESULTS

The VEGF response was restricted to the VEGF120 isoform. No increase in transcripts for VEGF164 and VEGF188 was observed. VEGFR2 was marginally increased and angiopoietin was increased. A subset of pericytes were TUNEL-positive.

DISCUSSION

These results show a distinct expression pattern of angiogenic factors following injury and suggest that pericyte involvement in adaptive angiogenesis may be altered following TBI.

Targeting VEGF signalling via the neuropilin co-receptor

The blockade of tumour vascularisation and angiogenesis continues to be a focus for drug development in oncology and other pathologies. Historically, targeting vascular endothelial growth factor (VEGF) activity and its association with VEGF receptors (VEGFRs) has represented the most promising line of attack. More recently, the recognition that VEGFR co-receptors, neuropilin-1 and -2 (NRP1 and NRP2), are also engaged by specific VEGF isoforms in tandem with the VEGFRs has expanded the landscape for the development of modulators of VEGF-dependent signalling. Here, we review the recent structural characterisation of VEGF interactions with NRP subdomains and the impact this has had on drug development activity in this area.

Comparative molecular developmental aspects of the mammalian- and the avian lungs, and the insectan tracheal system by branching morphogenesis: recent advances and future directions

Gas exchangers fundamentally form by branching morphogenesis (BM), a mechanistically profoundly complex process which derives from coherent expression and regulation of multiple genes that direct cell-to-cell interactions, differentiation, and movements by signaling of various molecular morphogenetic cues at specific times and particular places in the developing organ. Coordinated expression of growth-instructing factors determines sizes and sites where bifurcation occurs, by how much a part elongates before it divides, and the angle at which branching occurs. BM is essentially induced by dualities of factors where through feedback- or feed forward loops agonists/antagonists are activated or repressed. The intricate transactions between the development orchestrating molecular factors determine the ultimate phenotype. From the primeval time when the transformation of unicellular organisms to multicellular ones occurred by systematic accretion of cells, BM has been perpetually conserved. Canonical signalling, transcriptional pathways, and other instructive molecular factors are commonly employed within and across species, tissues, and stages of development. While much still remain to be elucidated and some of what has been reported corroborated and reconciled with rest of existing data, notable progress has in recent times been made in understanding the mechanism of BM. By identifying and characterizing the morphogenetic drivers, and markers and their regulatory dynamics, the elemental underpinnings of BM have been more precisely explained. Broadening these insights will allow more effective diagnostic and therapeutic interventions of developmental abnormalities and pathologies in pre- and postnatal lungs. Conservation of the molecular factors which are involved in the development of the lung (and other branched organs) is a classic example of nature's astuteness in economically utilizing finite resources. Once purposefully formed, well-tested and tried ways and means are adopted, preserved, and widely used to engineer the most optimal phenotypes. The material and time costs of developing utterly new instruments and routines with every drastic biological change (e.g. adaptation and speciation) are circumvented. This should assure the best possible structures and therefore functions, ensuring survival and evolutionary success.

Differential effects of a soluble or immobilized VEGFR-binding peptide

Regulating endothelial cell behavior is a key step in understanding and controlling neovascularization for both pro-angiogenic and anti-angiogenic therapeutic strategies. Here, we characterized the effects of a covalently immobilized peptide mimic of vascular endothelial growth factor, herein referred to as VEGF receptor-binding peptide (VR-BP), on human umbilical vein endothelial cell (HUVEC) behavior. Self-assembled monolayer arrays presenting varied densities of covalently immobilized VR-BP and varied densities of the fibronectin-derived cell adhesion peptide Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) were used to probe for changes in HUVEC attachment, proliferation and tubulogenesis. In a soluble form, VR-BP exhibited pro-angiogenic effects in agreement with previous studies, indicated by increases in HUVEC proliferation. However, when presented to cells in an insoluble context, covalently immobilized VR-BP inhibited several pro-angiogenic HUVEC behaviors, including attachment and proliferation, and also inhibited HUVEC response to soluble recombinant VEGF protein. Furthermore, substrates with covalently immobilized VR-BP also modulated HUVEC tubulogenesis when a matrigel overlay assay was used to provide cells with a pseudo-three dimensional environment. Taken together, these results demonstrate that the context in which ligands are presented to cell surface receptors strongly influences their effects, and that the same ligand can be an agonist or an antagonist depending on the manner of presentation to the cell.

Preparation and characterization of a VEGF-Fc fusion protein matrix for enhancing HUVEC growth

To enhance vascularization of hydrophobic implants in vivo, a VEGF-Fc fusion protein consisting of vascular endothelial growth factor (VEGF) fused to the immunoglobulin G Fc domain was prepared as an artificial extracellular matrix (ECM). VEGF-Fc was stably immobilized on a polystyrene plate due to the hydrophobicity of the Fc domain, and significantly enhanced the adhesion of human umbilical vein endothelial cells (HUVECs). Additionally, the use of VEGF-Fc as an ECM markedly promoted the proliferation of HUVECs longer than 72 h and induced the reorganization of actin filaments into larger stress fibers within these cells. The VEGF-Fc fusion protein may be a promising artificial ECM for enhancing endothelial cell growth.

Neuropilin signalling in angiogenesis

VEGFs (vascular endothelial growth factors) are master regulators of vascular development and of blood and lymphatic vessel function during health and disease in adults. This family of five mammalian ligands acts through three RTKs (receptor tyrosine kinases). In addition, co-receptors such as NRPs (neuropilins) associate with the ligand-receptor signalling complex and modulate the output. Therapeutics to block several of the VEGF signalling components as well as NRP function have been developed with the aim of halting blood vessel formation, angiogenesis, in diseases that involve tissue growth and inflammation, such as cancer. The present review outlines the current understanding of NRPs in relation to blood and lymphatic vessel biology.

Neuropilins: expression and roles in the epithelium

Initially found expressed in neuronal and then later in endothelial cells, it is well established that the transmembrane glycoproteins neuropilin-1 (NRP1) and neuropilin-2 (NRP2) play essential roles in axonal growth and guidance and in physiological and pathological angiogenesis. Neuropilin expression and function in epithelial cells has received little attention when compared with neuronal and endothelial cells. Overexpression of NRPs is shown to enhance growth, correlate with invasion and is associated with poor prognosis in various tumour types, especially those of epithelial origin. The contribution of NRP and its ligands to tumour growth and metastasis has spurred a strong interest in NRPs as novel chemotherapy drug targets. Given NRP's role as a multifunctional co-receptor with an ability to bind with disparate ligand families, this has sparked new areas of research implicating NRPs in diverse biological functions. Here, we review the growing body of research demonstrating NRP expression and role in the normal and neoplastic epithelium.

Structural basis for selective vascular endothelial growth factor-A (VEGF-A) binding to neuropilin-1

Neuropilin-1 (Nrp1) is an essential receptor for angiogenesis that binds to VEGF-A. Nrp1 binds directly to VEGF-A with high affinity, but the nature of their selective binding has remained unclear. Nrp1 was initially reported to bind to the exon 7-encoded region of VEGF-A and function as an isoform-specific receptor for VEGF-A(164/165). Recent data have implicated exon 8-encoded residues, which are found in all proangiogenic VEGF-A isoforms, in Nrp binding. We have determined the crystal structure of the exon 7/8-encoded VEGF-A heparin binding domain in complex with the Nrp1-b1 domain. This structure clearly demonstrates that residues from both exons 7 and 8 physically contribute to Nrp1 binding. Using an in vitro binding assay, we have determined the relative contributions of exon 7- and 8-encoded residues. We demonstrate that the exon 8-encoded C-terminal arginine is essential for the interaction of VEGF-A with Nrp1 and mediates high affinity Nrp binding. Exon 7-encoded electronegative residues make additional interactions with the L1 loop of Nrp1. Although otherwise conserved, the primary sequences of Nrp1 and Nrp2 differ significantly in this region. We further show that VEGF-A(164) binds 50-fold more strongly to Nrp1 than Nrp2. Direct repulsion between the electronegative exon 7-encoded residues of the heparin binding domain and the electronegative L1 loop found only in Nrp2 is found to significantly contribute to the observed selectivity. The results reveal the basis for the potent and selective binding of VEGF-A(164) to Nrp1.

Increased endothelial progenitor cells and vasculogenic factors in higher-staged arteriovenous malformations

ACKGROUND:: Arteriovenous malformations cause significant morbidity, primarily because they expand over time and recur after treatment. The authors hypothesized that neovascularization might contribute to arteriovenous malformation progression.

METHODS

Arteriovenous malformation tissue was collected prospectively from 12 patients after resection. Schobinger stage was determined by clinical history. Neovascularization in stage II lesions (n=7) was compared with stage III arteriovenous malformations (n=5) that had progressed. Specimens were analyzed using immunohistochemistry for CD31, Ki67, and CD34/CD133. Quantitative real-time reverse-transcriptase polymerase chain reaction was used to determine mRNA expression of factors that recruit endothelial progenitor cells: vascular endothelial growth factor (VEGF), stromal cell-derived factor-1α (SDF-1α), and hypoxia-inducible factor-1α (HIF-1α). VEGF receptors (VEGFR1, VEGFR2, neuropilin 1, and neuropilin 2) also were quantified using quantitative real-time reverse-transcriptase polymerase chain reaction.

RESULTS

Stage III arteriovenous malformations showed greater microvessel density (5.8 percent) than stage II lesions (1.3 percent) (p=0.004); no difference in proliferating endothelial cells was noted (p=0.67). CD133CD34 endothelial progenitor cells were elevated in stage III (0.53 percent) compared with stage II arteriovenous malformations (0.25 percent) (p=0.03). HIF-1α and SDF-1α were increased 7.6- and 7.9-fold in stage III compared with stage II lesions (1.7-fold and 3.3-fold), respectively (p=0.02). Neuropilin 1 and neuropilin 2 expression was greater in stage III (5.8-fold and 4.6-fold) than stage II arteriovenous malformations (3.0-fold and 2.4-fold) (p=0.03).

CONCLUSIONS

Higher-staged arteriovenous malformations exhibit increased expression of endothelial progenitor cells and factors that stimulate their recruitment. Neovascularization by vasculogenesis may be involved in progression of arteriovenous malformation.

Tissue kallikrein inhibits retinal neovascularization via the cleavage of vascular endothelial growth factor-165

OBJECTIVE

Tissue kallikrein, a widely used vasodilator for the treatment of hypertension and peripheral circulatory disorder, acts by releasing kinin, a potent vasodilator peptide. To identify the role of tissue kallikrein in retinal neovascularization, we investigated the antiangiogenic effect by using an in vitro and in vivo angiogenesis model.

METHODS AND RESULTS

Tissue kallikrein in vitreous fluid was markedly elevated in proliferative diabetic retinopathy patients compared with that in control patients with macular hole and epiretinal membrane. Tissue kallikrein inhibited vascular endothelial growth factor-165 (VEGF165)-induced tube formation, proliferation, and migration in vitro angiogenesis model via suppression of the VEGF165-induced phosphorylation of VEGF receptor-2. Furthermore, tissue kallikrein cleavage of VEGF165 was on the C-terminal side, which was analyzed by Western blotting and mass spectrometry. When administered subcutaneously, tissue kallikrein reduced the pathological vascular changes in retinal neovascularization induced in neonatal mice by returning the retina to normoxia after exposure to hyperoxia.

CONCLUSIONS

These findings indicate that tissue kallikrein is partly involved in pathogenesis of proliferative diabetic retinopathy and may be a promising therapeutic agent that could cleave VEGF165 itself when administered by a peripheral route.

Anti-neuropilin-1 peptide inhibition of synoviocyte survival, angiogenesis, and experimental arthritis

OBJECTIVE

To delineate the role of neuropilin-1 (NP-1), a vascular endothelial growth factor receptor (VEGFR), in rheumatoid inflammation and to determine whether blockade of NP-1 could suppress synoviocyte survival and angiogenesis.

METHODS

VEGF(111-165) peptide, which encompasses the NP-1 binding domain of VEGF(165), was generated by cleaving VEGF(165) with plasmin. The effect of this peptide on the interaction between VEGF(165) and its receptor was determined by (125)I-VEGFR binding assay. Assays to determine synoviocyte apoptosis, adhesion, and migration were performed in the presence of VEGF(165) and/or the peptide. VEGF(165)-induced angiogenesis was assessed by measuring the proliferation, tube formation, and wounding migration of endothelial cells (ECs). Mice were immunized with type II collagen to induce experimental arthritis.

RESULTS

VEGF(111-165) peptide specifically inhibited the binding of (125)I-VEGF(165) to NP-1 on rheumatoid synoviocytes and ECs. The peptide eliminated the VEGF(165)-mediated increase in synoviocyte survival and activation of p-ERK and Bcl-2. The peptide also completely inhibited a VEGF(165)-induced increase in synoviocyte adhesion and migration. In addition, the anti-NP-1 peptide blocked VEGF(165)-stimulated proliferation, capillary tube formation, and wounding migration of ECs in vitro. VEGF(165)-induced neovascularization in a Matrigel plug in mice was also blocked by treatment with the peptide. Finally, subcutaneous injection of anti-NP-1 peptide suppressed arthritis severity and autoantibody formation in mice with experimental arthritis and inhibited synoviocyte hyperplasia and angiogenesis in arthritic joints.

CONCLUSION

Anti-NP-1 peptide suppressed VEGF(165)-induced increases in synoviocyte survival and angiogenesis, and thereby blocked experimental arthritis. Our findings suggest that anti-NP-1 peptide could be useful in alleviating chronic arthritis.

Pulmonary epithelial neuropilin-1 deletion enhances development of cigarette smoke-induced emphysema

RATIONALE

Cigarette smoke (CS) exposure is an important risk factor for chronic obstructive pulmonary disease; however, not all smokers develop disease, suggesting that other factors influence disease development.

OBJECTIVES

We sought to determine whether neuropilin-1 (Nrp1), an integral component of receptor complexes mediating alveolar septation and vascular development, was involved in maintenance of normal alveolar structure, and/or altered susceptibility to the effects of CS.

METHODS

Transgenic mice were generated to achieve inducible lung-specific deletion of epithelial Nrp1. We determined whether conditional Nrp1 deletion altered airspace size, then compared the effects of chronic CS or filtered air exposure on airspace size, inflammation, and the balance between cell death and proliferation in conditionally Nrp1-deficient adult mice and littermate controls. Finally, we evaluated the effects of Nrp1 silencing on cell death after acute exposure of A549 cells to cigarette smoke extract or short chain ceramides.

MEASUREMENTS AND MAIN RESULTS

Genetic deletion of epithelial Nrp1 in either postnatal or adult lungs resulted in a small increase in airspace size. More notably, both airspace enlargement and apoptosis of type I and type II alveolar epithelial cells were significantly enhanced following chronic CS exposure in conditionally Nrp1-deficient adult mice. Silencing of Nrp1 in A549 cells did not alter cell survival after vehicle treatment but significantly augmented apoptosis after exposure to cigarette smoke extract or ceramide.

CONCLUSIONS

These data support a role for epithelial Nrp1 in the maintenance of normal alveolar structure and suggest that dysregulation of Nrp1 expression may promote epithelial cell death in response to CS exposure, thereby enhancing emphysema development.

HTLV-1 uses HSPG and neuropilin-1 for entry by molecular mimicry of VEGF165

Human T-cell lymphotropic virus type 1 (HTLV-1) entry involves the interaction between the surface (SU) subunit of the Env proteins and cellular receptor(s). Previously, our laboratories demonstrated that heparan sulfate proteoglycans (HSPGs) and neuropilin-1 (NRP-1), a receptor of VEGF(165), are essential for HTLV-1 entry. Here we investigated whether, as when binding VEGF(165), HSPGs and NRP-1 work in concert during HTLV-1 entry. VEGF(165) binds to the b domain of NRP-1 through both HSPG-dependent and -independent interactions, the latter involving its exon 8. We show that VEGF(165) is a selective competitor of HTLV-1 entry and that HTLV-1 mimics VEGF(165) to recruit HSPGs and NRP-1: (1) the NRP-1 b domain is required for HTLV-1 binding; (2) SU binding to target cells is blocked by the HSPG-binding domain of VEGF(165); (3) the formation of Env/NRP-1 complexes is enhanced by HSPGs; and (4) the HTLV SU contains a motif homologous to VEGF(165) exon 8. This motif directly binds to NRP-1 and is essential for HTLV-1 binding to, internalization into, and infection of CD4(+) T cells and dendritic cells. These findings demonstrate that HSPGs and NRP-1 function as HTLV-1 receptors in a cooperative manner and reveal an unexpected mimicry mechanism that may have major implications in vivo.

Elongation, proliferation & migration differentiate endothelial cell phenotypes and determine capillary sprouting

BACKGROUND

Angiogenesis, the growth of capillaries from preexisting blood vessels, has been extensively studied experimentally over the past thirty years. Molecular insights from these studies have lead to therapies for cancer, macular degeneration and ischemia. In parallel, mathematical models of angiogenesis have helped characterize a broader view of capillary network formation and have suggested new directions for experimental pursuit. We developed a computational model that bridges the gap between these two perspectives, and addresses a remaining question in angiogenic sprouting: how do the processes of endothelial cell elongation, migration and proliferation contribute to vessel formation?

RESULTS

We present a multiscale systems model that closely simulates the mechanisms underlying sprouting at the onset of angiogenesis. Designed by agent-based programming, the model uses logical rules to guide the behavior of individual endothelial cells and segments of cells. The activation, proliferation, and movement of these cells lead to capillary growth in three dimensions. By this means, a novel capillary network emerges out of combinatorially complex interactions of single cells. Rules and parameter ranges are based on literature data on endothelial cell behavior in vitro. The model is designed generally, and will subsequently be applied to represent species-specific, tissue-specific in vitro and in vivo conditions. Initial results predict tip cell activation, stalk cell development and sprout formation as a function of local vascular endothelial growth factor concentrations and the Delta-like 4 Notch ligand, as it might occur in a three-dimensional in vitro setting. Results demonstrate the differential effects of ligand concentrations, cell movement and proliferation on sprouting and directional persistence.

CONCLUSION

This systems biology model offers a paradigm closely related to biological phenomena and highlights previously unexplored interactions of cell elongation, migration and proliferation as a function of ligand concentration, giving insight into key cellular mechanisms driving angiogenesis.

Neuropilin-2-mediated tumor growth and angiogenesis in pancreatic adenocarcinoma

PURPOSE

Neuropilin-2 (NRP-2) is a coreceptor for vascular endothelial growth factor (VEGF) on endothelial cells. NRP-2 is overexpressed in pancreatic ductal adenocarcinoma (PDAC) cells relative to nonmalignant ductal epithelium. This study determined the role of NRP-2 in PDAC cells.

EXPERIMENTAL DESIGN

NRP-2 expression was reduced in PDAC cells with stable short-hairpin RNA (shRNA) transfection. Western blotting was done to evaluate signaling intermediates. Migration and invasion studies were carried out in Boyden chambers. Anchorage-independent growth was assessed by soft-agar colony formation. In vivo growth was evaluated using murine subcutaneous and orthotopic xenograft models. Immunohistochemical analysis evaluated in vivo proliferation and angiogenesis.

RESULTS

shRNA-NRP-2 decreased NRP-2 levels without affecting neuropilin-1 levels. Akt activation was decreased in clones with reduced NRP-2 (shRNA-NRP-2). shRNA-NRP-2 cells showed decreased migration, invasion, and anchorage-independent growth compared with control cells. In vitro proliferation rates were similar in control- and shRNA-transfected cells. Subcutaneous and orthotopic xenografts from shRNA-transfected cells were significantly smaller than those resulting from control-transfected cells (P < 0.05). Furthermore, shRNA-NRP-2 tumors exhibited less cellular proliferation and decreased microvascular area relative to control tumors (P < 0.05). Constitutive expression of the angiogenic mediator Jagged-1 was reduced in shRNA-NRP-2 cells, whereas vascular endothelial growth factor levels were unchanged.

CONCLUSION

Reduction of NRP-2 expression in PDAC cells decreased survival signaling, migration, invasion, and ability to grow under anchorage-independent conditions. In vivo, reduction of NRP-2 led to decreased growth of xenograft tumors and decreased vascular area, which was associated with decreased Jagged-1 levels. NRP-2 is a potential therapeutic target on PDAC cells.

Orf virus VEGF-E NZ2 promotes paracellular NRP-1/VEGFR-2 coreceptor assembly via the peptide RPPR

Vascular endothelial growth factors (VEGFs) interact with the receptor tyrosine kinases (RTKs) VEGFR-1, -2, and -3; neuropilins (NRPs); and heparan sulfate (HS) proteoglycans. VEGF RTKs signal to downstream targets upon ligand-induced tyrosine phosphorylation, while NRPs and HS act as coreceptors that lack enzymatic activity yet modulate signal output by VEGF RTKs. VEGFs exist in various isoforms with distinct receptor specificity and biological activity. Here, a series of mammalian VEGF-A splice variants and orf virus VEGF-Es, as well as chimeric and mutant VEGF variants, were characterized to determine the motifs required for binding to NRP-1 in the absence (VEGF-E) or presence (VEGF-A(165)) of an HS-binding sequence. We identified the carboxyterminal peptides RPPR and DKPRR as the NRP-1 binding motifs of VEGF-E and VEGF-A, respectively. RPPR had significantly higher affinity for NRP-1 than DKPRR. VEGFs containing an RPPR motif promoted HS-independent coreceptor complex assembly between VEGFR-2 and NRP-1, independent of whether these receptors were expressed on the same or separate cells grown in cocultures. Functional studies showed that stable coreceptor assembly by VEGF correlated with its ability to promote vessel formation in an embryoid body angiogenesis assay.

Catalytically inactive phospholipase A2 homologue binds to vascular endothelial growth factor receptor-2 via a C-terminal loop region

VEGF (vascular endothelial growth factor) regulates neovascularization through binding to its receptor KDR (kinase insert domain-containing receptor; VEGF receptor-2). We recently identified a catalytically inactive PLA2 (phospholipase A2) homologue (KDR-bp) in the venom of eastern cottonmouth (Agkistrodon piscivorus piscivorus) as a third KDR-binding protein, in addition to VEGF165 and tissue inhibitor of metalloproteinase-3. KDR-bp binds to the extracellular domain of KDR with a Kd of 10−8 M, resulting in specific blockade of endothelial cell growth induced by VEGF165. Inactive PLA2 homologues are widely distributed in the venoms of Viperidae snakes and are known to act as myotoxins. In the present study, we demonstrated that KDR-binding ability is a common characteristic for inactive PLA2 homologues in snake venom, but not for active PLA2s such as neurotoxic and platelet aggregation-modulating PLA2s. To understand better the KDR and KDR-bp interaction, we resolved the binding region of KDR-bp using eight synthetic peptides designed based on the structure of KDR-bp. A synthetic peptide based on the structure of the C-terminal loop region of KDR-bp showed high affinity for KDR, but other peptides did not, suggesting that the C-terminal loop region of KDR-bp is involved in the interaction with KDR. The results of the present study provide insight into the binding of inactive PLA2 homologues to KDR, and may also assist in the design of novel anti-KDR molecules for anti-angiogenic therapy.