Neuropilin-1 regulates vascular endothelial growth factor-mediated endothelial permeability

Vascular endothelial growth factor receptor-2: structure, function, intracellular signalling and therapeutic inhibition

Vascular endothelial growth factors (VEGFs) regulate vascular development, angiogenesis and lymphangiogenesis by binding to a number of receptors. VEGFR-1 is required for the recruitment of haematopoietic stem cells and the migration of monocytes and macrophages, VEGFR-2 regulates vascular endothelial function and VEGFR-3 regulates lymphatic endothelial cell function. Over the last decade, considerable progress has been made in delineating the VEGFR-2 specific intracellular signalling cascades leading to proliferation, migration, survival and increased permeability, each of which contributes to the angiogenic response. Furthermore, therapeutic inhibition of VEGFR-2 action is now having an impact in the clinic for the treatment of a number of diseases.

Expression of Neuropilin-1 In Kidney Graft Biopsies: What Is the Significance?

OBJECTIVE

Recent work has suggested that neuropilin-1 (NRP-1) is a surface marker of regulatory T cells (Treg). However, no further relative evidence has been provided to confirm this finding. Since Treg should decline during rejection, the expression of NRP-1 on lymphocytes should decline in a rejected graft. To test this proposal, we examined NRP-1 expression in kidney graft biopsies.

MATERIALS AND METHODS

Tissue samples were obtained from 20 kidney graft biopsies with pathologically confirmed acute rejection and from 10 without rejections. We performed immunohistochemistry assays using an anti-NRP-1 monoclonal antibody. The positive cells were counted and the ratios among lymphocytes analyzed.

RESULTS

Compared with samples from nonrejected graft biopsies (18.71 +/- 20.60), the number of positive cells among lymphocytes in the rejected samples showed a lower percentage (3.16 +/- 1.72; P < .05).

CONCLUSIONS

NRP-1 has an important role in directing the growth of nervous synapses and immune synapses. We found in rejected grafts that the percentage of NRP-1 positive cells among lymphocytes decreased significantly. Therefore, NRP-1 may have a previously unrecognized role to predict the immune state of the graft as a potential marker for Treg.

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

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

Vascular endothelial growth factor (VEGF) in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS): paradox or paradigm?

Acute respiratory distress syndrome (ARDS), the most severe form of acute lung injury (ALI), remains a devastating condition with a high mortality. It is characterised by alveolar injury and increased pulmonary vascular permeability. Vascular endothelial cell growth factor (VEGF) was identified by its properties to increase permeability and act as a cellular growth factor, hence its potential for a key role in the pathogenesis of ALI/ARDS. This review describes the basic biology of VEGF and its receptors as an essential prerequisite to discussing the available and sometimes paradoxical published data, before considering a paradigm for the role of VEGF in the human lung.

Chimeric VEGF-E(NZ7)/PlGF promotes angiogenesis via VEGFR-2 without significant enhancement of vascular permeability and inflammation

OBJECTIVE

Vascular endothelial growth factor (VEGF) plays critical roles in the regulation of angiogenesis and lymphangiogenesis. However, tissue edema, hemorrhage, and inflammation occur when VEGF-A is used for angiogenic therapy. To design a novel angiogenic factor without severe side effects, we examined the biological function of chimeric VEGF-E(NZ7)/placental growth factor (PlGF), which is composed of Orf-Virus(NZ7)-derived VEGF-E(NZ7) and human PlGF1, in a transgenic (Tg) mouse model.

METHODS AND RESULTS

A strong angiogenic response was observed in both VEGF-E(NZ7)/PlGF and VEGF-A165 Tg mice. Notably, the vascular leakage of VEGF-E(NZ7)/PlGF-induced blood vessels was 4-fold lower than that of VEGF-A165-induced blood vessels. Furthermore, the monocyte/macrophage recruitment in the skin of VEGF-E(NZ7)/PlGF Tg mice was approximately 8-fold decreased compared with that of VEGF-A165 Tg mice. In addition, the lymphatic vessels in VEGF-E(NZ7)/PlGF Tg mice were structurally normal, whereas they were markedly dilated in VEGF-A165 Tg mice, possibly because of the high vascular leakage. Receptor binding assay demonstrated that VEGF-E(NZ7)/PlGF was the ligand only activating VEGF receptor (VEGFR)-2.

CONCLUSIONS

These results indicated that neither the hyperpermeability in response to simultaneous stimulation of VEGFR-1 and VEGFR-2 nor VEGFR-1-mediated severe inflammation was associated with VEGF-E(NZ7)/PlGF-induced angiogenesis. The unique receptor binding property may shed light on VEGF-E(NZ7)/PlGF as a novel candidate for therapeutic angiogenesis.

Früher antiexsudativer Effekt – OCT-Monitoring nach intravitrealer Bevacizumab-Applikation

VEGF is more potent than histamine by a factor of 50,000 for inducing increased vessel permeability. Already in the first few minutes, hydraulic conductivity and diffusive permeability are significantly increased, followed by a longer-lasting, marked leakage over 20 h. Specific inhibition of the angiogenic, vasoactive, and permeability-inducing protein VEGF is now possible by new drugs, one of which is the first available (off-label) treatment in Germany for routine clinical use (Avastin). Retinal edema is composed of increased outflow of water and low molecular substances in the interstitial environment and is an important determinate of functional development in different ocular diseases. First experiences with the anti-hyperpermeability effect show early response and high potential in pathologic leakage. Future examinations have to assess when a permanent benefit can be achieved in respect to the other antiproliferative capabilities of the drug.

Pigment epithelium-derived factor inhibits advanced glycation end product-induced retinal vascular hyperpermeability by blocking reactive oxygen species-mediated vascular endothelial growth factor expression

Pigment epithelium-derived factor (PEDF) is the most potent inhibitor of angiogenesis, suggesting that loss of PEDF contributes to proliferative diabetic retinopathy. However, the role of PEDF against retinal vascular hyperpermeability remains to be elucidated. We investigated here whether and how PEDF could inhibit the advanced glycation end product (AGE) signaling to vascular hyperpermeability. Intravenous administration of AGEs to normal rats not only increased retinal vascular permeability by stimulating vascular endothelial growth factor (VEGF) expression but also decreased retinal PEDF levels. Simultaneous treatments with PEDF inhibited the AGE-elicited VEGF-mediated permeability by down-regulating mRNA levels of p22(phox) and gp91(phox), membrane components of NADPH oxidase, and subsequently decreasing retinal levels of an oxidative stress marker, 8-hydroxydeoxyguanosine. PEDF also inhibited the AGE-induced vascular hyperpermeability evaluated by transendothelial electrical resistance by suppressing VEGF expression. Furthermore, PEDF decreased reactive oxygen species (ROS) generation in AGE-exposed endothelial cells by suppressing NADPH oxidase activity via down-regulation of mRNA levels of p22(PHOX) and gp91(PHOX). This led to blockade of the AGE-elicited Ras activation and NF-kappaB-dependent VEGF gene induction in endothelial cells. These results indicate that the central mechanism for PEDF inhibition of the AGE signaling to vascular permeability is by suppression of NADPH oxidase-mediated ROS generation and subsequent VEGF expression. Substitution of PEDF may offer a promising strategy for halting the development of diabetic retinopathy.

Neuropilins in neoplasms: expression, regulation, and function

Neuropilins (NRP) are membranous receptors capable of binding two disparate ligands, class 3 semaphorins (SEMA) and vascular endothelial growth factors (VEGF), and regulating two diverse systems, neuronal guidance and angiogenesis. The neuropilin genes, NRP1 and NRP2, share similar protein structure, but differ in their expression patterns, regulation, and ligand-binding specificities. NRPs vary in their expression patterns; for example, endothelial cells express both NRP1 and NRP2, lymphatic endothelial cells predominantly express NRP2, and epidermal cells predominantly express NRP1. NRP expression can be differentially regulated by transcription factors, e.g. prox-1 induces NRP2 while suppressing NRP1, or by growth factors, e.g. epidermal growth factor (EGF) induces NRP1 but not NRP2. Nearly all tumor cells express NRP1, NRP2, or both. Carcinomas express NRP1, whereas neuronal tumors and melanomas predominantly express NRP2. SEMAs play a role in neoplasms as angiogenesis inhibitors. For example, SEMA3F, which binds specifically to NRP2, inhibits tumor angiogenesis and metastasis. Metastatic tumor cells lose SEMA3F expression during progression. Therefore, SEMA3F may have therapeutic potential. This article focuses on the role of NRPs and SEMAs in tumor progression and angiogenesis.