Expression of vascular endothelial growth factor receptors 1, 2, and 3 in quiescent endothelia

Rescue from lethal Shiga toxin 2-induced renal failure with a cell-permeable peptide

Intestinal infection with Shiga toxin (Stx)-producing E.coli is a leading cause of hemolytic uremic syndrome and acute renal injury in otherwise healthy children in the US. Antibiotics are contraindicated and a therapeutic priority is agents that act intracellularly against the bacterial toxins that drive kidney injury. Our aim was to evaluate whether intravenous administration of a cell-permeable peptide (TVP) that binds to Stx2 will reduce disease severity and rescue juvenile baboons from a lethal Stx2 dose (50 ng/kg). TVP (5 mg/kg) was delivered i.v. simultaneously with toxin (prevention protocol) or at 6 or 24 h after toxin with daily 1 mg/kg supplements up to day 4 (rescue protocols). Biomarkers were monitored in blood and urine up to 28 days. TVP therapy resulted in either absence of clinical signs of acute kidney injury and normal urine output (prevention), or delayed and reduced BUN and creatinine levels (rescue) with concomitant survival. Delayed peptide administration significantly reduced thrombocytopenia, but surprisingly did not alter anemia even when monitored for 28 days in rescued survivors. This is the first successful cell-permeable therapeutic that counteracts Stx2 lethality in an animal model, which recapitulates many of the human responses to enteric infection.

The patterns and expression of KDR in normal tissues of human internal organs

KDR has been implicated for playing an important role in the formation of new blood vessels and in solid tumor growth. It was considered as one of the most important regulators of angiogenesis and a key target in anticancer treatment. In the present study, we characterized KDR mRNA and protein expression in normal tissues of perinatal and adult tissues using One-step Real-Time RT-PCR and immunohistochemistry with a self-made anti-KDR antibody. The expression of KDR mRNA and protein in perinatal internal organs were all higher than in adult organs including brain, kidney, liver, lung and heart, respectively. KDR protein was presented in the cell plasma membrane of human internal tissues. The expression of KDR protein was raised in macrophage of spleen, and decreased in neurons of brain, myocardium, bronchial epithelial cells and alveolar epithelial cell, proximal and distal tubules cells, and hepatic cells with the maturity process of human organs. Notably, the order of KDR protein expression from highest to lowest is as follows: brain, liver, heart, kidney, and lung in adult tissues with statistically significant. It follows that how to balance the potential therapeutic side effect with human internal organs in targeted therapy of over-expressing KDR tumor.

Therapeutic action of the mitochondria-targeted antioxidant SkQ1 on retinopathy in OXYS rats linked with improvement of VEGF and PEDF gene expression

The incidence of age-related macular degeneration (AMD), the main cause of blindness in older patients in the developed countries, is increasing with the ageing population. At present there is no effective treatment for the prevailing geographic atrophy, dry AMD, whereas antiangiogenic therapies successful used in managing the wet form of AMD. Recently we showed that mitochondria-targeted antioxidant plastoquinonyl-decyl-triphenylphosphonium (SkQ1) is able to prevent the development and moreover caused regression of pre-existing signs of the retinopathy in OXYS rats, an animal model of AMD. Here we examine the effects of SkQ1 on expression of key regulators of angiogenesis vascular endothelial growth factor A (VEGF) and its antagonist pigment epithelium-derived factor (PEDF) genes in the retina of OXYS rats as evidenced by real-time PCR and an ELISA test for VEGF using Wistar rats as control. Ophthalmoscopic examinations confirmed that SkQ1 supplementation (from 1.5 to 3 months of age, 250 nmol/kg) prevented development while eye drops SkQ1 (250 nM, from 9 to 12 months) caused some reduction of retinopathy signs in OXYS rats and did not reveal any negative effects on the control Wistar rat's retina. Prevention of premature retinopathy by SkQ1 was connected with an increase of VEGF mRNA and protein in OXYS rat's retina up to the levels corresponding to the Wistar rats, and did not involve changes in PEDF expression. In contrast the treatment with SkQ1 drops caused a decrease of VEGF mRNA and protein levels and an increase in the PEDF mRNA level in the middle-aged OXYS rats, but in Wistar rats the changes of gene expression were the opposite. Conclusions: The beneficial effects of SkQ1 on retinopathy connected with normalization of expression of VEGF and PEDF in the retina of OXYS rats and depended on age of the animals and the stage of retinopathy.

Alterations of retinal pigment epithelium cause AMD-like retinopathy in senescence-accelerated OXYS rats

Pathogenesis of age-related macular degeneration (AMD), the leading cause of blindness in the world, remains poorly understood. This makes it necessary to create animal models for studying AMD pathogenesis and to design new therapeutic approaches. Here we showed that retinopathy in OXYS rats is similar to human AMD according to clinical signs, morphology, and vascular endothelium growth factor (VEGF) and pigment epithelium-derived factor (PEDF) genes expression. Clinical signs of retinopathy OXYS rats manifest by the age 3 months against the background of significantly reduced expression level of VEGF and PEDF genes due to the decline of the amount of retinal pigment epithelium (RPE) cells and alteration of choroidal microcirculation. The disruption in OXYS rats' retina starts at the age of 20 days and appears as reduce the area of RPE cells but does not affect their ultrastructure. Ultrastructural pathological alterations of RPE as well as develop forms of retinopathy are observed in OXYS rats from age 12 months and manifested as excessive accumulation of lipofuscin in RPE regions adjacent to the rod cells, whirling extentions of the basement membrane into the cytoplasm. These data suggest that primary cellular degenerative alterations in the RPE cells secondarily lead to choriocapillaris atrophy and results in complete loss of photoreceptor cells in the OXYS rats' retina by the age of 24 months.

Vascular endothelial growth factor in the circulation in cancer patients may not be a relevant biomarker

BACKGROUND

Levels of circulating vascular endothelial growth factor (VEGF) have widely been used as biomarker for angiogenic activity in cancer. For this purpose, non-standardized measurements in plasma and serum were used, without correction for artificial VEGF release by platelets activated ex vivo. We hypothesize that "true" circulating (c)VEGF levels in most cancer patients are low and unrelated to cancer load or tumour angiogenesis.

METHODOLOGY

We determined VEGF levels in PECT, a medium that contains platelet activation inhibitors, in citrate plasma, and in isolated platelets in 16 healthy subjects, 18 patients with metastatic non-renal cancer (non-RCC) and 12 patients with renal cell carcinoma (RCC). In non-RCC patients, circulating plasma VEGF levels were low and similar to VEGF levels in controls if platelet activation was minimized during the harvest procedure by PECT medium. In citrate plasma, VEGF levels were elevated in non-RCC patients, but this could be explained by a combination of increased platelet activation during blood harvesting, and by a two-fold increase in VEGF content of individual platelets (controls: 3.4 IU/10(6), non-RCC: 6.2 IU/10(6) platelets, p = 0.001). In contrast, cVEGF levels in RCC patients were elevated (PECT plasma: 64 pg/ml vs. 21 pg/ml, RCC vs. non-RCC, p<0.0001), and not related to platelet VEGF concentration.

CONCLUSIONS

Our findings suggest that "true" freely cVEGF levels are not elevated in the majority of cancer patients. Previously reported elevated plasma VEGF levels in cancer appear to be due to artificial release from activated platelets, which in cancer have an increased VEGF content, during the blood harvest procedure. Only in patients with RCC, which is characterized by excessive VEGF production due to a specific genetic defect, were cVEGF levels elevated. This observation may be related to limited and selective success of anti-VEGF agents, such as bevacizumab and sorafenib, as monotherapy in RCC compared to other forms of cancer.

Characterization of Prox1 and VEGFR-3 expression and lymphatic phenotype in normal organs of mice lacking p50 subunit of NF-κB

OBJECTIVE

Inflammation and NF-κB are highly associated with lymphangiogenesis but the underlying mechanisms remain unclear. We recently established that activated NF-κB p50 subunit increases expression of the main lymphangiogenic mediators, VEGFR-3 and its transcriptional activator, Prox1. To elucidate the role of p50 in lymphatic vasculature, we compared LVD and phenotype in p50 KO and WT mice.

METHODS

Normal tissues from KO and WT mice were stained for LYVE-1 to calculate LVD. VEGFR-3 and Prox1 expressions were analyzed by immunofluorescence and qRT-PCR.

RESULTS

Compared with WT, LVD in the liver and lungs of KO mice was reduced by 39% and 13%, respectively. This corresponded to 25-44% decreased VEGFR-3 and Prox1 expression. In the MFP, LVD was decreased by 18% but VEGFR-3 and Prox1 expression was 80-140% higher than in WT. Analysis of p65 and p52 NF-κB subunits and an array of inflammatory mediators showed a significant increase in p50 alternative pathways in the MFP but not in other organs.

CONCLUSIONS

These findings demonstrate the role of NF-κB p50 in regulating the expression of VEGFR-3, Prox1 and LVD in the mammary tissue, liver, and lung.

Isolated lymphoid follicles in colon: switch points between inflammation and colorectal cancer?

Gut-associated lymphoid tissue is supposed to play a central role in both the organization of colonic repair mechanisms and colorectal carcinogenesis. In inflammatory conditions, the number, diameter and density of isolated lymphoid follicles (ILFs) increases. They are not only involved in immune surveillance, but their presence is also indispensable in normal mucosal regeneration of the colon. In carcinogenesis, ILFs may play a dual role. On the one hand they may support tumor growth and the metastatic process by vascular endothelial growth factor receptor signaling and producing a specific cytokine and cellular milieu, but on the other hand their presence is sometimes associated with a better prognosis. The relation of ILFs to bone marrow derived stem cells, follicular dendritic cells, subepithelial myofibroblasts or crypt formation, which are all involved in mucosal repair and carcinogenesis, has not been directly studied. Data about the putative organizer role of ILFs is scattered in scientific literature.

The expression of vascular endothelial growth factor and its receptors (flt1/fms, flk1/KDR, flt4) and vascular endothelial growth inhibitor in the bovine uterus during the sexual cycle and their correlation with serum sex steroids

The present study was conducted to demonstrate of the immunohistochemical localization of vascular endothelial growth factor (VEGF) and its receptors (flt1/fms, flk1/KDR and flt4) as well as vascular endothelial growth inhibitor (VEGI) and to determine the correlation of VEGF and its receptors and VEGI with serum sex steroids (estrogen and progesterone) in the bovine uterus during the sexual cycle. The stage of the estrous cycle in 30 Holstein cattle was assessed based on the gross and histological appearance of the ovaries and uterus and on blood steroid hormone levels. Tissue samples obtained from the uterus were fixed in 10% formaldehyde for routine histological processing. During both follicular and luteal phases, positive cytoplasmic and membrane staining was achieved for VEGF and its receptors (flt1/fms, flk1/KDR and flt4) as well as VEGI in the luminal and glandular epithelial cells, the connective tissue and smooth muscle cells, and the vascular endothelial cells and smooth muscle cells in the uterus. The intensity, proportional and total scores determined for VEGF and its receptors (flt1/fms and flt4) as well as VEGI were greater in the luminal and glandular epithelial cells compared to the connective tissue and smooth muscle cells (P < 0.05). Furthermore, the number and intensity of the flk1/KDR positive cells were greater among the connective tissue cells compared to the luminal and glandular epithelial cells (P < 0.05). As a result, it was determined that the expression of VEGF and its receptors as well as VEGI in the bovine uterus during the follicular and luteal phases varied with different cell types. This suggests that depending on the stage of the sexual cycle, these factors may mediate the establishment of an appropriate environment for the nutritional supply and implantation of the embryo primarily due to the stimulation of angiogenesis but also through the increase in the secretory activity of the epithelial cells in the uterus. Furthermore, this indicates that ovarian steroid hormones play a significant role in regulating the expression of VEGF and its receptors as well as VEGI.

Optical advances in skeletal imaging applied to bone metastases

Optical Imaging has evolved into one of the standard molecular imaging modalities used in pre-clinical cancer research. Bone research however, strongly depends on other imaging modalities such as SPECT, PET, x-ray and μCT. Each imaging modality has its own specific strengths and weaknesses concerning spatial resolution, sensitivity and the possibility to quantify the signal. An increasing number of bone specific optical imaging models and probes have been developed over the past years. This review gives an overview of optical imaging modalities, models and probes that can be used to study skeletal complications of cancer in small laboratory animals.

Antibody drug-conjugates targeting the tumor vasculature: Current and future developments

Reducing the blood supply of tumors is one modality to combat cancer. Monoclonal antibodies are now established as a key therapeutic approach for a range of diseases. Owing to the ability of antibodies to selectively target endothelial cells within the tumor vasculature, vascular targeting programs have become a mainstay in oncology drug development. However, the antitumor activity of single agent administration of conventional anti-angiogenic compounds is limited and the improvements in patient survival are most prominent in combinations with chemotherapy. Furthermore, prolonged treatment with conventional anti-angiogenic drugs is associated with toxicity and drug resistance. These circumstances provide a strong rationale for novel approaches to enhance the efficacy of mAbs targeting tumor vasculature such as antibody-drug conjugates (ADCs).Here, we review trends in the development of ADCs targeting tumor vasculature with the aim of informing future research and development of this class of therapeutics.

'In vivo' optical approaches to angiogenesis imaging

In recent years, molecular imaging gained significant importance in biomedical research. Optical imaging developed into a modality which enables the visualization and quantification of all kinds of cellular processes and cancerous cell growth in small animals. Novel gene reporter mice and cell lines and the development of targeted and cleavable fluorescent "smart" probes form a powerful imaging toolbox. The development of systems collecting tomographic bioluminescence and fluorescence data enabled even more spatial accuracy and more quantitative measurements. Here we describe various bioluminescent and fluorescent gene reporter models and probes that can be used to specifically image and quantify neovascularization or the angiogenic process itself.

Expression of vascular endothelial growth factor receptor-3 mRNA in the rat developing forebrain and retina

Vascular endothelial growth factor receptor (VEGFR)-3, a receptor for VEGF-C and VEGF-D, is expressed in neural progenitor cells, but there has been no comprehensive study of its distribution in the developing brain. Here, the temporal and cell-specific expression of VEGFR-3 mRNA was studied in the developing rat forebrain and eye. Expression appeared along the ventricular and subventricular zones of the lateral and third ventricles showing ongoing neurogenesis as early as embryonic day 13 but was progressively down-regulated during development and remained in the subventricular zone and rostral migratory stream of the adult forebrain. VEGFR-3 expression was also detectable in some differentiating and postmitotic neurons in the developing cerebral cortex, including Cajal-Retzius cells, cortical plate neurons, and subplate neurons. Expression in the subplate increased significantly during the early postnatal period but was absent by postnatal day 14. It was also highly expressed in nonneural tissues of the eye during development, including the retinal pigment epithelium, the retinal ciliary margin, and the lens, but persisted in a subset of cells in the pigmented ciliary epithelium of the adult eye. In contrast, there was weak or undetectable expression in the early neural retina, but a subset of retinal neurons in the postnatal and mature retina showed intense signals. These unique spatiotemporal mRNA expression patterns suggest that VEGFR-3 might mediate the regulation of both neurogenesis and adult neuronal function in the rat forebrain and eye.

Progress on antiangiogenic therapy for patients with malignant glioma

Glioblastoma (GBM) is the most common primary brain tumor occurring in America. Despite recent advances in therapeutics, the prognosis for patients with newly diagnosed GBM remains dismal. As these tumors characteristically show evidence of angiogenesis (neovascularization) there has been great interest in developing anti-angiogenic therapeutic strategies for the treatment of patients with this disease and some anti-angiogenic agents have now been used for the treatment of patients with malignant glioma tumors. Although the results of these clinical trials are promising in that they indicate an initial therapeutic response, the anti-angiogenic therapies tested to date have not changed the overall survival of patients with malignant glioma tumors. This is due, in large part, to the development of resistance to these therapies. Ongoing research into key features of the neovasculature in malignant glioma tumors, as well as the general angiogenesis process, is suggesting additional molecules that may be targeted and an improved response when both the neovasculature and the tumor cells are targeted. Prevention of the development of resistance may require the development of anti-angiogenic strategies that induce apoptosis or cell death of the neovasculature, as well as an improved understanding of the potential roles of circulating endothelial progenitor cells and vascular co-option by tumor cells, in the development of resistance.

The possible role of isolated lymphoid follicles in colonic mucosal repair

The continuous reformation and rapid repair of the colonic mucosa is essential for avoiding the aggregation of pernicious mutations induced by bacterial, toxic, or mitogenic factors. Gut-associated lymphoid tissue is supposed to play a central role in the organization of the repair mechanisms. In inflammatory conditions, the number, the diameter and the density of isolated lymphoid follicles (ILFs) are increasing. They are involved not just in immune surveillance, but their presence is also indispensable in normal mucosal regeneration of the colon. The relation of ILFs to the components of mucosal renewal such as bone marrow derived stem cells, follicular dendritic cells, subepithelial myofibroblasts or crypt formation has not been directly studied, and data about their putative organizer role are scattered in scientific literature. Whether they act as a regenerative pool containing stem cells in case of mucosal damage, or they are responsible only for the optimal cytokine milieu for the differentiation of immigrating stem cells is a question under debate. Our aim is to review the relation of ILFs to the different elements of colonic mucosal repair.

Imaging angiogenesis of genitourinary tumors

Angiogenesis is a key process in the growth and metastasis of cancer, and genitourinary tumors are no exception. The evolution of angiogenesis as an important target for novel anticancer therapeutics has brought with it new challenges for in vivo imaging. Most imaging techniques quantify physiological parameters, such as blood volume and capillary endothelial permeability. Although CT, PET and ultrasonography have shown promise, MRI is the most common method used to evaluate angiogenesis in clinical trials of genitourinary tumors. Pilot studies of MRI, CT and ultrasonography in patients with renal cancer have produced promising results; reductions in vascular permeability and blood flow have been correlated with progression-free survival. The vascular characteristics of prostate cancer have been evaluated by MRI, and this has been suggested as a means of assessing tumor response to hormone deprivation therapy. Current evidence highlights the potential of angiogenesis imaging in the diagnosis, staging and possibly response monitoring of bladder cancer. In the future, assessment of the angiogenic process at the structural, functional and molecular levels, before, during and after antiangiogenic therapy will undoubtedly be integrated into wider clinical practice.

VEGF-C regulates lymphangiogenesis and capillary stability by regulation of PDGF-B

Emerging evidence indicates that the tight communication between vascular endothelial cells and mural cells using platelet-derived growth factor (PDGF)-BB is essential for capillary stabilization during the angiogenic process. However, little is known about the related regulator that determines PDGF-BB expression. Using murine models of therapeutic neovascularization, we here show that a typical lymphangiogenic factor, vascular endothelial growth factor (VEGF)-C, is an essential regulator determining PDGF-BB expression for vascular stabilization via a paracrine mode of action. The blockade of VEGF type 3 receptor (VEGFR3) using neutralizing antibody AFL-4 abrogated FGF-2-mediated limb salvage and blood flow recovery in severely ischemic hindlimb. Interestingly, inhibition of VEGFR3 activity not only diminished lymphangiogenesis, but induced marked dilatation of capillary vessels, showing mural cell dissociation. In these mice, VEGF-C and PDGF-B were upregulated in the later phase after induced ischemia, on day 7, when exogenous FGF-2 expression had already declined, and blockade of VEGFR3 or PDGF-BB activities diminished PDGF-B or VEGF-C expression, respectively. These results clearly indicate that VEGF-C is a critical mediator, not only for lymphangiogenesis, but also for capillary stabilization, the essential molecular mechanism of communication between endothelial cells and mural cells during neovascularization.

Coordinated regulation of angiopoietin-1 and vascular endothelial growth factor by arsenite in human brain microvascular pericytes: implications of arsenite-induced vascular dysfunction

Arsenite is an environmental toxicant that is associated with vascular disease; however, the underlying mechanism of its toxicity has yet to be elucidated. Vascular stability appears to be tightly regulated by several vasoactive proteins produced by two adjacent vascular cells, endothelial cells (EC) and pericytes. The disruption of vascular stability may be involved in arsenite toxicity. The roles of angipoietins (Ang) and vascular endothelial growth factor (VEGF) in this process have been evaluated, but these studies have mostly been limited to EC. In this study, we used human brain microvascular pericytes (HBMP) to evaluate the effects of arsenite on Ang-1 and VEGF regulation. Ang-2 was reported to be not detected in HBMP. Arsenite decreased Ang-1 secretion in a time and dose-dependent manner, while it increased VEGF secretion. Although arsenite did not alter Ang-1 mRNA expression, it increased intracellular Ang-1 protein levels in a dose-dependent manner, suggesting a role for arsenite in the intracellular trapping of Ang-1. Contrary to Ang-1, the expression of VEGF mRNA was dose-dependently up-regulated by arsenite. Treatment with N-actyl-l:-cysteine (NAC) alone decreased the release of Ang-1, but failed to attenuate the arsenite-induced decrease in Ang-1 secretion, while NAC completely blocked the arsenite-stimulated VEGF secretion. These results indicate that reactive oxygen species are involved in the regulation of VEGF, but not of Ang-1, secretion in response to arsenite treatment in pericytes. Furthermore, immunocytochemical analysis using confocal microscopy revealed a colocalization of Ang-1 with actin filaments that occurred independently of tubulin. In conclusion, arsenite decreases Ang-1 secretion and increases VEGF secretion, which may offer new insight into understanding the arsenite toxicity associated with vascular instability and subsequent development of vascular disease.

Analysis of in situ and ex vivo vascular endothelial growth factor receptor expression during experimental aortic aneurysm progression

OBJECTIVE

Mural inflammation and neovascularization are characteristic pathological features of abdominal aortic aneurysm (AAA) disease. Vascular endothelial growth factor receptor (VEGFR) expression may also mediate AAA growth and rupture. We examined VEGFR expression as a function of AAA disease progression in the Apolipoprotein E-deficient (Apo E(-/-)) murine AAA model.

METHODS AND RESULTS

Apo E(-/-) mice maintained on a high-fat diet underwent continuous infusion with angiotensin II at 1000 ng/kg/min (Ang II) or vehicle (Control) via subcutaneous osmotic pump. Serial transabdominal ultrasound measurements of abdominal aortic diameter were recorded (n=16 mice, 3 to 4 time points per mouse) for up to 28 days. Near-infrared receptor fluorescent (NIRF) imaging was performed on Ang II mice (n=9) and Controls (n=5) with scVEGF/Cy, a single-chain VEGF homo-dimer labeled with Cy 5.5 fluorescent tracer (7 to 18 microg/mouse IV). NIRF with inactivated single chain VEGF/Cy tracer (scVEGF/In, 18 microg/mouse IV) was performed on 2 additional Ang II mice to control for nonreceptor-mediated tracer binding and uptake. After image acquisition and sacrifice, aortae were harvested for analysis. An additional AAA mouse cohort received either an oral angiogenesis inhibitor or suitable negative or positive controls to clarify the significance of angiogenesis in experimental aneurysm progression. Aneurysms developed in the suprarenal aortic segment of all Ang II mice. Significantly greater fluorescent signal was obtained from aneurysmal aorta as compared to remote, uninvolved aortic segments in Ang II scVEGF/Cy mice or AAA in scVEGF/In mice or suprarenal aortic segments in Control mice. Signal intensity increased in a diameter-dependent fashion in aneurysmal segments. Immunostaining confirmed mural VEGFR-2 expression in medial smooth muscle cells. Treatment with an angiogenesis inhibitor attenuated AAA formation while decreasing mural macrophage infiltration and CD-31(+) cell density.

CONCLUSIONS

Mural VEGFR expression, as determined by scVEGF/Cy fluorescent imaging and VEGFR-2 immunostaining, increases in experimental AAAs in a diameter-dependent fashion. Angiogenesis inhibition limits AAA progression. Clinical VEGFR expression imaging strategies, if feasible, may improve real-time monitoring of AAA disease progression and response to suppressive strategies.

Treatment of retinal diseases with VEGF antagonists

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are the most prevalent causes of blindness in the Western world. The pathogenesis of neovascularization and vascular leakage, both hallmarks of these diseases, appears to have one common denominator: vascular endothelial growth factor (VEGF). Since the recent introduction of anti-VEGF therapy, intravitreal injections with these agents have become standard care in neovascular AMD, and have been found to be a valuable additional treatment strategy in several other vascular retinal diseases. This review provides an overview of the history of anti-VEGF treatment in the eye, its rationale, its efficacy, and its potential drawbacks.

FLT1 and its ligands VEGFB and PlGF: drug targets for anti-angiogenic therapy?

Less than 5 years ago, it was still not clear whether anti-angiogenic drugs would prove successful in the clinic. After numerous patients with cancer or age-related macular degeneration have been treated with these drugs, they have now become part of the standard range of therapeutic tools. Despite this milestone, anti-angiogenic therapy still faces a number of clinical hurdles, such as improving efficacy, avoiding escape and resistance, and minimizing toxicity. Hopefully, other agents with complementary mechanisms, such as those that target placental growth factor, will offer novel opportunities for improved treatment.

Differential regulation of vascular endothelial growth factor-C and its receptor in the rat hippocampus following transient forebrain ischemia

We investigated the changes in the expression of vascular endothelial growth factor-C (VEGF-C) and its receptor, VEGFR-3, in the rat hippocampus following transient forebrain ischemia. The expression profiles of VEGF-C and VEGFR-3 were very similar in the control hippocampi, where both genes were constitutively expressed in neurons in the pyramidal cell and granule cell layers. The spatiotemporal expression pattern of VEGF-C was similar to that of VEGFR-3 in the ischemic hippocampus, and in the CA1 and dentate hilar regions both VEGF-C and VEGFR-3 were strongly expressed in activated glial cells rather than in neurons. Most of the activated glial cells expressing both genes were reactive astrocytes, although some were a subpopulation of brain macrophages. In the dentate gyrus, however, VEGFR-3 expression was transiently increased in the innermost layer of granule cells on days 7-10 after reperfusion, coinciding with an increase in polysialylated neural cell adhesion molecule staining--a marker for immature neurons. These data suggest that VEGF-C may be involved in glial reaction via paracrine or autocrine mechanisms in the ischemic brain and may carry out specific roles in adult hippocampal neurogenesis during ischemic insults.

Vascular endothelial growth factor-C, a potential paracrine regulator of glomerular permeability, increases glomerular endothelial cell monolayer integrity and intracellular calcium

We have previously reported expression of vascular endothelial growth factor (VEGF)-A and -C in glomerular podocytes and actions of VEGF-A on glomerular endothelial cells (GEnC) that express VEGF receptor-2 (VEGFR-2). Here we define VEGFR-3 expression in GEnC and investigate the effects of the ligand VEGF-C. Renal cortex and cultured GEnC were examined by microscopy, and both cell and glomerular lysates were assessed by Western blotting. VEGF-C effects on trans-endothelial electrical resistance and albumin flux across GEnC monolayers were measured. The effects of VEGF-C156S, a VEGFR-3-specific agonist, and VEGF-A were also studied. VEGF-C effects on intracellular calcium ([Ca2+]i) were measured using a fluorescence technique, receptor phosphorylation was examined by immunoprecipitation assays, and phosphorylation of myosin light chain-2 and VE-cadherin was assessed by blotting with phospho-specific antibodies. GEnC expressed VEGFR-3 in tissue sections and culture, and VEGF-C increased trans-endothelial electrical resistance in a dose-dependent manner with a maximal effect at 120 minutes of 6.8 Omega whereas VEGF-C156S had no effect. VEGF-C reduced labeled albumin flux by 32.8%. VEGF-C and VEGF-A increased [Ca2+]i by 15% and 39%, respectively. VEGF-C phosphorylated VEGFR-2 but not VEGFR-3, myosin light chain-2, or VE-cadherin. VEGF-C increased GEnC monolayer integrity and increased [Ca2+]i, which may be related to VEGF-C-S particular receptor binding and phosphorylation induction characteristics. These observations suggest that podocytes direct GEnC behavior through both VEGF-C and VEGF-A.

New molecular targets in angiogenic vessels of glioblastoma tumours

Antiangiogenesis approaches have the potential to be particularly effective in the treatment of glioblastoma tumours. These tumours exhibit extremely high levels of neovascularisation, which may contribute to their extremely aggressive behaviour, not only by providing oxygenation and nutrition, but also by establishing a leaky vasculature that lacks a blood-brain barrier. This leaky vasculature enables migration of tumour cells, as well as the build up of fluid, which exacerbates tissue damage due to increased intracranial pressure. Here, we discuss the considerable progress that has been made in the identification of the pro- and antiangiogenic factors produced by glioblastoma tumours and the effects of these molecules in animal models of the disease. The safety and efficacy of some of these approaches have now been demonstrated in clinical trials. However, the ability of tumours to overcome these therapies and to re-establish angiogenesis requires further clinical research regarding potential multimodality therapies, as well as basic research into the regulation of angiogenesis by as yet unidentified factors. Optimisation of noninvasive procedures for monitoring of angiogenesis would greatly facilitate such research.

Cellular distribution of vascular endothelial growth factor A (VEGFA) and B (VEGFB) and VEGF receptors 1 and 2 in focal cortical dysplasia type IIB

Members of the vascular endothelial growth factor (VEGF) family are key signaling proteins in the induction and regulation of angiogenesis, both during development and in pathological conditions. However, signaling mediated through VEGF family proteins and their receptors has recently been shown to have direct effects on neurons and glial cells. In the present study, we immunocytochemically investigated the expression and cellular distribution of VEGFA, VEGFB, and their associated receptors (VEGFR-1 and VEGFR-2) in focal cortical dysplasia (FCD) type IIB from patients with medically intractable epilepsy. Histologically normal temporal cortex and perilesional regions displayed neuronal immunoreactivity (IR) for VEGFA, VEGFB, and VEGF receptors (VEGFR-1 and VEGFR-2), mainly in pyramidal neurons. Weak IR was observed in blood vessels and there was no notable glial IR within the grey and white matter. In all FCD specimens, VEGFA, VEGFB, and both VEGF receptors were highly expressed in dysplastic neurons. IR in astroglial and balloon cells was observed for VEGFA and its receptors. VEGFR-1 displayed strong endothelial staining in FCD. Double-labeling also showed expression of VEGFA, VEGFB and VEGFR-1 in cells of the microglia/macrophage lineage. The neuronal expression of both VEGFA and VEGFB, together with their specific receptors in FCD, suggests autocrine/paracrine effects on dysplastic neurons. These autocrine/paracrine effects could play a role in the development of FCD, preventing the death of abnormal neuronal cells. In addition, the expression of VEGFA and its receptors in glial cells within the dysplastic cortex indicates that VEGF-mediated signaling could contribute to astroglial activation and associated inflammatory reactions.

Roles for VEGF in the adult

The role of VEGF during development and in pathology is well known, but its function in normal adult tissues is poorly understood. Adverse effects associated with the use of anti-angiogenic therapies targeting VEGF in human pathologies have begun to reveal potential functions of VEGF in quiescent vasculature. Further clues from expression studies of VEGF and its receptors in the adult, from the disease preeclampsia, and from experimental neutralization studies, have suggested that VEGF is involved in endothelial cell survival and fenestration, as well as in the signaling and maintenance of non-endothelial cells. The various biochemical properties of VEGF, and its interaction with other growth factors, may be an important point in determining whether VEGF functions as a maintenance factor versus an angiogenic factor. A thorough understanding of the function of VEGF in the adult may lead to more efficacious pro- and anti-angiogenic therapies.

Integrin alpha9beta1 directly binds to vascular endothelial growth factor (VEGF)-A and contributes to VEGF-A-induced angiogenesis

Vascular endothelial growth factor A (VEGF-A) is a potent inducer of angiogenesis. We now show that VEGF-A-induced adhesion and migration of human endothelial cells are dependent on the integrin alpha9beta1 and that VEGF-A is a direct ligand for this integrin. Adhesion and migration of these cells on the 165 and 121 isoforms of VEGF-A depend on cooperative input from alpha9beta1 and the cognate receptor for VEGF-A, VEGF receptor 2 (VEGF-R2). Unlike alpha3beta1or alphavbeta3 integrins, alpha9beta1 was also found to bind the 121 isoform of VEGF-A. This interaction appears to be biologically significant, because alpha9beta1-blocking antibody dramatically and specifically inhibited angiogenesis induced by VEGF-A165 or -121. Together with our previous findings that alpha9beta1 directly binds to VEGF-C and -D and contributes to lymphangiogenesis, these results identify the integrin alpha9beta1 as a potential pharmacotherapeutic target for inhibition of pathogenic angiogenesis and lymphangiogenesis.

Molecular imaging of VEGF receptors in angiogenic vasculature with single-chain VEGF-based probes

We describe a new generation of protein-targeted contrast agents for multimodal imaging of the cell-surface receptors for vascular endothelial growth factor (VEGF). These receptors have a key role in angiogenesis and are important targets for drug development. Our probes are based on a single-chain recombinant VEGF expressed with a cysteine-containing tag that allows site-specific labeling with contrast agents for near-infrared fluorescence imaging, single-photon emission computed tomography or positron emission tomography. These probes retain VEGF activities in vitro and undergo selective and highly specific focal uptake into the vasculature of tumors and surrounding host tissue in vivo. The fluorescence contrast agent shows long-term persistence and co-localizes with endothelial cell markers, indicating that internalization is mediated by the receptors. We expect that multimodal imaging of VEGF receptors with these probes will be useful for clinical diagnosis and therapeutic monitoring, and will help to accelerate the development of new angiogenesis-directed drugs and treatments.

Vascular endothelial growth factor receptor-3 activity is modulated by its association with caveolin-1 on endothelial membrane

Vascular endothelial growth factor receptor-3 (VEGFR-3) is constitutively expressed in lymphatic vessels and transiently in endothelial cells of blood vessels during angiogenesis. Here we report that VEGFR-3 localizes in the caveolae membrane of endothelial cells and co-immunoprecipitates with caveolin-1. Caveolin-1 silencing or its depletion from the cell membrane by cholesterol increases VEGFR-3 autophosphorylation, suggesting that caveolin acts as a negative regulator of VEGFR-3 activity. Receptor activation induces caveolin-1 phosphorylation on tyrosine residues including tyrosine 14. Cell treatment with Src or Abl inhibitors PP2 or STI571, prior to receptor stimulation, affects caveolin-1 phosphorylation without affecting receptor autophosphorylation, suggesting that both Src and Abl are involved in VEGFR-3-dependent caveolin-1 phosphorylation. Caveolin-1 phosphorylation in Src/Fyn/Yes knockout cells demonstrated that Abl phosphorylates caveolin-1 independently from Src family members. These results suggest a functional interaction between VEGFR-3 and caveolin-1 to modulate endothelial cell activation during angiogenesis.

Angiogenesis inhibition with bevacizumab and the surgical management of colorectal cancer

BACKGROUND

Bevacizumab is an angiogenesis inhibitor and a new therapy for the treatment of colorectal cancer. It is a humanized monoclonal antibody that targets vascular endothelial growth factor.

METHODS

This review is based on a literature search of Medline, Pubmed, ISI web of knowledge and other published work for original articles, reviews and abstracts relevant to the surgical management of colorectal cancer with bevacizumab.

RESULTS AND CONCLUSION

Combined with current chemotherapy regimens, bevacizumab offers a significant survival advantage, making it likely to see widespread use. Despite being generally well tolerated, serious toxicities, including wound complications and gastrointestinal perforation, have been reported that affect surgical management. Consideration should be given to the timing of surgical and adjuvant intervention when using this drug.

Vitreous fluid biomarkers

Interactions between cells and the network of secreted proteins are associated with the ocular disease. In most cases, clinical appearcance is sufficiently diagnostic. However, in cases of nonspecific or atypical clinical presentation, diagnostic sampling of vitreous fluid can aid diagnosis and treatment for ocular disease. Progresses in the basic sciences, particularly molecular biology, and advances in surgical instrumentation have greatly enhanced the diagnostic armamentarium. These developments also have led to a better understanding of the pathophysiological processes involved in ocular diseases and have prompted evolution of new therapeutic modalities. In this chapter, we review techniques for vitreous fluid sampling and biomarker quantitation thereof. The molecular biology of bioactive vitreous fluid factors is also discussed with respect to their clinical involvement in the development of ocular disease.

Expression of VEGFR3 in glioma endothelium correlates with tumor grade

Angiogenic processes are regulated by vascular endothelial growth factors (VEGFs) and their receptors VEGFR1 (Flt-1), 2 (Flk-1) and 3 (Flt-4). While VEGFR2 is thought to play a central role in tumor angiogenesis, anti-angiogenic therapies targeting VEGFR2 in glioma models can show escape phenomena with secondary onset of angiogenesis. The purpose of this study was to find explanations for these processes by searching for alternative pathways regulating glioma angiogenesis and reveal a correlation with tumor grade. Thus, VEGFR3, which is not expressed in normal brain, and its ligands VEGF-C and -D, were assessed in high grade (WHO degrees IV, glioblastomas, GBM) and low grade gliomas [WHO degrees II astrocytomas (AII)]. In all GBM, a strong protein expression of VEGFR3 was found on tumor endothelium, VEGF-C and -D expression was found on numerous cells in areas of high vascularization. On RNA level, a significant up-regulation of VEGFR3 was detected in GBM compared to AII and non-neoplastic brain. In AII, only very moderate VEGFR3, VEGF-C and -D expression was found on protein and RNA level indicating a correlation of VEGFR3 expression with tumor grade. VEGFR3 signal in both grades was found predominantly on endothelial cells, confirmed by VEGFR3 expression on isolated CD31 positive cells and the expression of various endothelial markers on VEGFR3-positive cells isolated from GBM. The demonstration of a complete angiogenic signaling system that is dependent on tumor grade may influence the traditional paradigm of glioma angiogenesis and may provide a basis for more effective anti-angiogenic treatment strategies.

Localization of Ang-1, -2, Tie-2, and VEGF expression at endothelial-pericyte interdigitation in rat angiogenesis

Endothelial cells and pericytes play critical role in angiogenesis, which is controlled, in part, by the angiopoietin (Ang)/Tie-2 system and vascular endothelial growth factor (VEGF). Here, we investigated Ang, Tie-2, and VEGF expression within endothelial cells and pericyte interdigitations (EPI), which consist of cytoplasmic projections of pericytes and corresponding endothelial indentations. After subcutaneous implantation of a thermoreversible gelation polymer disc in rats, the capillary density was low on day 5, increased to a peak on day 7, and then decreased on days 10-20. A small number of EPI were observed on day 5, then increased sharply to a peak on day 10, but had decreased on day 20. Light and electron microscopy immunohistochemical and RNA in situ hybridization analyses revealed that Tie-2 localized at endothelial cells, and Ang-2 localized at endothelial cells and pericytes, while Ang-1 and VEGF localized at pericytes, and Ang-1 was most intensely observed at EPI of pericytes. Conventional quantitative RT-PCR and Western blot analyses revealed that the level of Ang-1 was low on days 5-7, then increased on days 10-20, while the level of VEGF was high on days 5-10, but had decreased on day 20. The level of Ang-2 remained high and Tie-2 remained at the level of the control on days 5-20. The present study showed that the angiogenic phase might be initiated by increases in Ang-2 and VEGF, while the microvessel maturation phase might be initiated by a relative increase in Ang-1 and a decrease in VEGF. Moreover, EPI might serve as a pathway for the Ang-1/Tie-2 system, with VEGF promoting pericyte recruitment for microvascular integrity.

The regulation of vascular endothelial growth factors (VEGF-A, -C, and -D) expression in the retinal pigment epithelium

The vascular endothelial growth factor (VEGF) family plays an essential role in vascular development, angiogenesis and lymphangiogenesis. VEGF-A is a key regulator of endothelial cell functions and VEGF-C and VEGF-D are known to stimulate both angiogenesis and lymphangiogenesis. In a surgically removed subretinal vascular membrane of an age-related macular degeneration (AMD) patient, both VEGF-C and VEGF-D were confirmed, in addition to VEGF-A, to be markedly positive in the retinal pigment epithelium (RPE). There is no lymph vessel in ocular tissue, so it is possible that VEGF-C and VEGF-D expression in the RPE play some role in ocular angiogenesis, as well as VEGF-A. Next, we assessed the transition of VEGF-A, -C, and -D expression on several conditions, in human RPE. Hypoxia proverbially induced VEGF-A mRNA expression, meanwhile VEGF-C and VEGF-D mRNA expression was down-regulated. The Ca(2+) deprivation from culture medium strongly up-regulated VEGF-A and VEGF-D mRNA expression. Culture on plastic flasks precoated with poly-2-hydroxyethyl methacrylate up-regulated VEGF-D expression. Meanwhile, no significant change of VEGF-C mRNA expression was found in the blockade of cell-cell and/or cell-matrix adhesion. These findings suggest the possibility that VEGF-C and VEGF-D expression in RPE modify the ocular angiogenesis as angiogenic stimulators.

Interleukin-1beta regulates vascular endothelial growth factor and soluble fms-like tyrosine kinase-1 secretion by human oviductal epithelial cells and stromal fibroblasts

The aim of the present study was to evaluate the effects of interleukin (IL)-1beta on the production of vascular endothelial growth factor (VEGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) in the human fallopian tube. Human oviductal epithelial cells (OECs) and oviductal stromal fibroblasts (OSFs) were isolated from ten premenopausal patients. The secretion of VEGF and sFlt-1 by cultured OECs and OSFs in response to IL-1beta and IL-1 receptor antagonist (IL-1RA) was measured using an enzyme-linked immunosorbent assay. The secretion of VEGF and sFlt-1 was detected in cultured OECs and OSFs under untreated conditions; secretion of these angiogenic modulators was significantly stimulated with IL-1beta administration in these cells. IL-1beta-induced production of VEGF and sFlt-1 by these cells was significantly inhibited by the addition of IL-1RA. The present findings suggest that IL-1beta in the local environment may stimulate oviductal vascular permeability by inducing the production of VEGF by oviductal cells via both autocrine and paracrine mechanisms. Simultaneous upregulation of sFlt-1 secretion by these cells after IL-1beta stimulation may prevent an excessive upregulation of vascular permeability. The modulation of the ratio of VEGF and sFlt-1 in the fallopian tube may contribute to the normal and pathological processes of oviductal fluid secretion by regulating oviductal vascular permeability during the menstrual cycle and during the peri-implantation period.

Molecular Profile and Proliferative Responses of Rat Lymphatic Endothelial Cells in Culture

BACKGROUND

Lymphangiogenesis plays an important role in metastasis of many solid tumors. To study lymphangiogenesis under controlled conditions, an in vitro model is needed. The goal of this work was to establish such an in vitro model by determining a molecular profile of rat mesenteric lymphatic endothelial cells (RMLEC) and characterizing their proliferative responses to angiogenic and lymphangiogenic factors, such as vascular endothelial growth factor A and C (VEGF-A and VEGF-C).

METHODS AND RESULTS

RMLEC strongly expressed most lymphatic-specific markers, including Prox-1, LYVE-1, and VEGFR-3. Proliferation of RMLEC was serum and heparin dependent. In the presence of low (2%) serum concentration, exogenously added VEGF-A and VEGFC stimulated RMLEC in a linear and dose-dependent manner. This effect was abrogated by anti-VEGF-A and VEGF-C antibodies, as well as by soluble Tie-2 and Flt-4 fusion proteins. Abrogation was reversed by VEGF-A, suggesting that this factor as an important regulator of lymphangiogenesis.

CONCLUSIONS

Cultured RMLEC preserved a molecular profile consistent with the phenotype of lymphatic endothelium in vivo and respond to either VEGF-A or VEGF-C factors. VEGFA was able to rescue RMLEC proliferation inhibited by a neutralizing VEGF-C antibody or soluble Tie-2 fusion protein. These results support the existence of cross-talk among angiogenic and lymphangiogenic factors. This work established experimental conditions that allow in vitro modeling of lymphatic endothelial responses to lymphangiogenic regulators. Preliminary results using this model suggest that VEGF-A, VEGF-C, and angiopoietins work in concert to promote lymphangiogenesis in vivo.

Promising new treatments for neovascular age-related macular degeneration

Angiogenesis, the growth of new blood vessels from existing blood vessels, is responsible for vision loss in a variety of ophthalmic diseases. In neovascular age-related macular degeneration (AMD), the leading cause for legal blindness in many industrialised countries, abnormal blood vessels grow in the macula and cause blindness. There are a number of factors important in the angiogenic cascade but VEGF-A has been implicated in recent years as the major factor responsible for neovascular and exudative diseases of the eye. Numerous antiangiogenic drugs are in development but anti-VEGF drugs have shown great promise in treating neovascular AMD and other ocular diseases, and many of these drugs have been adopted from oncology where antiangiogenic therapy is gaining wide acceptance. For the first time in neovascular AMD, anti-VEGF drugs have brought the hope of vision improvement to a significant proportion of patients. This review provides an overview on angiogenic mechanisms, potential antiangiogenic treatment strategies and different antiangiogenic drugs with special focus on neovascular AMD.

Thiol regulation of vascular endothelial growth factor-A and its receptors in human retinal pigment epithelial cells

We investigated the secretion and expression of VEGF-A and its receptors in human retinal pigment epithelial cells (RPE) under conditions of oxidative stress induced by glutathione (GSH) depletion. RPE cells were treated with 500 microM DL-buthionine-(S,R)-sulfoximine (BSO) for varying times up to 24 h. Cellular GSH levels, GSH:GSSG ratios, VEGF-A mRNA and protein expression, as well as VEGF-A secretion, and VEGFR-1 and VEGFR-2 receptor expression were determined. Treatment with BSO caused a significant decrease in intracellular GSH and in GSH/GSSG ratios. Treatment with BSO increased VEGF-A mRNA linearly with time which was significant at 24h (p<0.01 vs untreated controls). An increase was also found for VEGF-A secretion with BSO treatment; incubation of RPE with GSH monoethyl ester (GSH-MEE) caused an 84% decrease in VEGF-A secretion. Further, thiol depletion by BSO caused a significant induction of VEGFR-1 and VEGFR-2. Thus, our studies show that cellular redox status plays an important role in VEGF regulation in RPE cells.

Smoking impairs angiogenesis during maturation of human oocytes

OBJECTIVE

This study determines whether smoking influences ovarian vascularization which thus may impair follicular development.

DESIGN

Prospective laboratory study of follicular fluids and granulosa cells from patients undergoing in vitro fertilization.

SETTING

University Hospital Aachen, Germany.

PATIENT(S)

Fifty smoking women and 50 nonsmoking women.

INTERVENTION(S)

Cultivation of human granulosa cells. Cultivation of human umbilical vein endothelial cells (HUVECs) with either granulosa cell-conditioned medium or follicular fluid. Determination of clinical parameters.

MAIN OUTCOME MEASURE(S)

Quantification of soluble vascular endothelial growth factor receptor 1 (sVEGFR-1) and cotinine.

RESULT(S)

Mean sVEGFR-1 concentration in follicular fluid of smokers was 499.6 pg/mL compared with 159.2 pg/mL in nonsmokers. Correspondingly, supernatant of HUVECs cultured with follicular fluid from smoking and nonsmoking women showed, respectively, 1,174.1 pg/mL versus 794.2 pg/mL sVEGFR-1. The HUVECs incubated with conditioned medium from smokers' granulosa cells at culturing days 5, 9, 13, and 17 secreted, respectively, 1,712.4, 1,560.6, 1,619.0, and 1,635.0 pg/mL sVEGFR-1, whereas nonsmokers showed, respectively, 1,147.6, 1,067.2, 1,135.9, and 1,206.3 pg/mL sVEGFR-1. Mean cotinine concentration in smoking women was 83.9 ng/mL and in nonsmoking was 2.8 ng/mL. In all four comparisons, differences between groups reached statistical significance.

CONCLUSION(S)

This study showed that smokers secrete significantly higher amounts of sVEGFR-1 than nonsmokers, which may result in decreased ovarian vascularization and reduced oocyte maturation.

VEGF-A regulates the expression of VEGF-C in human retinal pigment epithelial cells

AIM

To determine the expression and regulation of vascular endothelial growth factor C (VEGF-C), and its receptor VEGFR-3, in human retinal pigment epithelial (RPE) cells and to consider their angiogenic role in choroidal neovascularisation (CNV).

METHOD

The expression of VEGF-C and VEGFR-3 in cultured human RPE was confirmed by immunostaining, PCR, western blotting, and ELISA. Cultured RPE cells were exposed to VEGF-A and glucose and VEGF-C and VEGFR-3 changes in gene expression determined by RT-PCR. Secreted VEGF-C protein in conditioned media from RPE was examined by western blotting and ELISA analysis. The ability of VEGF-C to elicit tube formation in choroidal endothelial cells was assayed by an in vitro Matrigel model.

RESULT

VEGF-A and glucose upregulated VEGF-C mRNA expression and increased the secretion of VEGF-C protein into the culture medium. VEGF-A, but not glucose alone, stimulated VEGFR-3 mRNA expression. VEGF-C acted synergistically with VEGF-A to promote in vitro tube formation by choroidal endothelial cells.

CONCLUSION

VEGF-A has a critical role in the orchestration of VEGF-C expression in RPE cells and the synergistic action of VEGF-C with VEGF-A may play an important part in the aetiology of CNV.

Hypoxia regulates vascular endothelial growth factor and soluble fms-like tyrosine kinase-1 secretion by human oviductal epithelial cells and stromal fibroblasts

OBJECTIVE

To evaluate the effect of hypoxia on the production of vascular endothelial growth factor (VEGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) in the human fallopian tube.

DESIGN

The secretion of VEGF and sFlt-1 by cultured oviductal epithelial cells (OECs) and oviductal stromal fibroblasts (OSFs) in response to hypoxia was investigated.

SETTING

Research laboratory at a medical school.

PATIENT(S)

Normal oviducts obtained from seven premenopausal patients were used.

INTERVENTION(S)

Oviductal epithelial cells and OSFs were incubated under normoxic (20% O2) or hypoxic (2% O2) conditions.

MAIN OUTCOME MEASURE(S)

The concentrations of VEGF and sFlt-1 in the culture media of OECs and OSFs were measured by enzyme-linked immunosorbent assays.

RESULT(S)

The secretion of both VEGF and sFlt-1 was detected in cultured OECs and OSFs and was found to have been stimulated under hypoxic conditions in these cells.

CONCLUSION(S)

The present findings suggest that hypoxia in the local environment may stimulate oviductal vascular permeability by inducing the production of VEGF by oviductal cells. Simultaneous up-regulation of sFlt-1 secretion by these cells under hypoxic conditions may prevent excessive up-regulation of vascular permeability. The modulation of the bias of VEGF and sFlt-1 in the fallopian tubes may contribute to the normal and pathological processes of oviductal fluid secretion by regulating oviductal vascular permeability during the menstrual cycle.

Tumor-induced lymphangiogenesis: a target for cancer therapy?

Recent advances in understanding the biology of lymphangiogenesis, the new growth of lymphatic vessels, have cast new light on the molecular basis of metastasis to regional lymph nodes. The receptor tyrosine kinase VEGFR-3 is virtually exclusively expressed on lymphatic but not blood endothelium in the adult, and activation of VEGFR-3 by its ligands VEGF-C and VEGF-D is sufficient to induce lymphangiogenesis. Correlative studies with human tumors and functional studies using animal tumor models show that increased levels of VEGF-C or VEGF-D in tumors lead to enhanced numbers of lymphatic vessels in the vicinity of tumors, which in turn promotes metastasis to regional lymph nodes by providing a greater number of entry sites into the lymphatic system for invading tumor cells. These findings have prompted studies to investigate whether inhibitors of VEGFR-3 activation might represent novel therapeutic agents for the suppression of metastasis. However, a number of points regarding the therapeutic potential of anti-lymphangiogenic treatments in the context of cancer remain to be addressed. The spectrum and relative importance of molecules that induce lymphangiogenesis and the regulation of their expression during tumor progression, the reversibility of tumor-induced lymphangiogenesis, and possible side-effects of anti-lymphangiogenesis-based therapies all need to be investigated. Most importantly, the extent to which lymph node metastases contribute to the formation of metastases in other organs remains to be elucidated. These aspects are the focus of this review, and their investigation should serve as a roadmap to possible translational application.

Vascular Endothelial Growth Factor A Signaling in the Podocyte-Endothelial Compartment Is Required for Mesangial Cell Migration and Survival

The glomerular filtration barrier separates the blood from the urinary space and consists of two major cell types: podocytes and fenestrated endothelial cells. Mesangial cells sit between the capillary loops and provide structural support. Proliferation and loss of mesangial cells both are central findings in a number of renal diseases, including diabetic nephropathy and mesangiolysis, respectively. Using cell-specific gene targeting, it was shown previously that vascular endothelial growth factor A (VEGF-A) production by podocytes is required for glomerular endothelial cell migration, differentiation, and survival. For further investigation of the effect of gene dose and VEGF-A knockdown within the glomerulus, mice that carry one hypomorphic VEGF-A allele and one podocyte-specific null VEGF-A allele (VEGFhypo/loxP,Neph-Cre+/-) were generated; in these mice, the "allelic dose" of VEGF-A is intermediate between glomerular-specific heterozygous and null states. VEGFhypo/loxP,Neph-Cre+/- mice die at 3 wk of age from renal failure. Although endothelial cell defects are observed, striking loss of mesangial cells occurs postnatally. In addition, differentiated mesangial cells cannot be found in glomeruli of podocyte-specific null VEGF-A mice (VEGFloxP/loxP,Cre+/-). Together, these results demonstrate a key role for VEGF-A production in the podocyte for mesangial cell survival and differentiation.

Direct recruitment of CRK and GRB2 to VEGFR-3 induces proliferation, migration, and survival of endothelial cells through the activation of ERK, AKT, and JNK pathways

Vascular endothelial growth factor receptor-3 (VEGFR-3) plays a key role for the remodeling of the primary capillary plexus in the embryo and contributes to angiogenesis and lymphangiogenesis in the adult. However, VEGFR-3 signal transduction pathways remain to be elucidated. Here we investigated VEGFR-3 signaling in primary human umbilical vein endothelial cells (HUVECs) by the systematic mutation of the tyrosine residues potentially involved in VEGFR-3 signaling and identified the tyrosines critical for its function. Y1068 was shown to be essential for the kinase activity of the receptor. Y1063 signals the receptor-mediated survival by recruiting CRKI/II to the activated receptor, inducing a signaling cascade that, via mitogen-activated protein kinase kinase-4 (MKK4), activates c-Jun N-terminal kinase-1/2 (JNK1/2). Inhibition of JNK1/2 function either by specific peptide inhibitor JNKI1 or by RNA interference (RNAi) demonstrated that activation of JNK1/2 is required for a VEGFR-3–dependent prosurvival signaling. Y1230/Y1231 contributes, together with Y1337, to proliferation, migration, and survival of endothelial cells. Phospho-Y1230/Y1231 directly recruits growth factor receptor–bonus protein (GRB2) to the receptor, inducing the activation of both AKT and extracellular signal–related kinase 1/2 (ERK1/2) signaling. Finally, we observed that Y1063 and Y1230/Y1231 signaling converge to induce c-JUN expression, and RNAi experiments demonstrated that c-JUN is required for growth factor–induced prosurvival signaling in primary endothelial cells.

Immunohistochemical study about the Flt-1/VEGFR1 expression in the gastrointestinal tract of mouse, rat, dog, swine and monkey

Fms-like tyrosine kinase 1 (Flt-1) performs a subordinate effector role in mesenchymal angiogenesis and potentially serves an equally important functional role as a self-contained receptor in epithelial cells. In both endothelial cells and epithelial cells, Flt-1/vascular endothelial growth factor receptor 1 (VEGFR1) downstream signalling is involved in regulating cellular processes such as cytoskeletal changes and cellular survival protection. Cellular renewal of the gastrointestinal mucosa is based on these processes and might involve Flt-1/VEGFR1 pathway activities; the molecular mechanisms regulating these cellular dynamics remain unclear. This study was performed to investigate the presence and distribution of Flt-1/VEGFR1 in epithelial cells of the gastrointestinal tract by immunohistochemistry (IHC). Gastrointestinal tissues were taken from eight anatomical sites from mouse, rat, dog, swine and monkey. Present results revealed a cytosolic Flt-1/VEGFR1 staining pattern in mucosal epithelial cells for all investigated species. Non-epithelial structures also displayed a distinct Flt-1/VEGFR1 positivity and included vascular smooth muscle walls, enteric smooth muscle layers, the enteric nervous system and capillary endothelial cells. Diverse intensities of the Flt-1/VEGFR1 binding reaction within each species were observed in the intestinal mucosa with a strong immunoreaction in enterocytes and with a low protein expression in the ileum in most species. Crypt cells in the large intestine were mostly negative for Flt-1/VEGFR1. A peculiar and mainly intranuclear antibody binding reaction was found in Brunner's gland epithelial cells of mouse and rat whereas Brunner's glands of dog, swine and monkey remained completely negative. These results indicate a potential involvement of Flt-1/VEGFR1 in normal restitution of gastrointestinal structures in the species studied. Additionally, intranuclear Flt-1/VEGFR1 antibody binding in Brunner's glands of rodents may suggest a nuclear translocation of the transmembrane VEGFR1 which has not previously been described.

Cellular changes in normal blood capillaries undergoing regression after inhibition of VEGF signaling

The vasculature of the embryo requires vascular endothelial growth factor (VEGF) during development, but most adult blood vessels lose VEGF dependence. However, some capillaries in the respiratory tract and selected other organs of adult mice regress after VEGF inhibition. The present study sought to identify the sequence of events and the fate of endothelial cells, pericytes, and vascular basement membrane during capillary regression in mouse tracheas after VEGF signaling was blocked with a VEGF-receptor tyrosine kinase inhibitor AG-013736 or soluble receptor construct (VEGF Trap or soluble adenoviral VEGFR-1). Within 1 day, patency was lost and fibrin accumulated in some tracheal capillaries. Apoptotic endothelial cells marked by activated caspase-3 were present in capillaries without blood flow. VEGF inhibition was accompanied by a 19% decrease in tracheal capillaries over 7 days and 30% over 21 days. During this period, desmin/NG2-immunoreactive pericytes moved away from regressing capillaries onto surviving vessels. Empty sleeves of basement membrane, left behind by regressing endothelial cells, persisted for about 2 wk and served as a scaffold for vascular regrowth after treatment ended. The amount of regrowth was limited by the number of surviving basement membrane sleeves. These findings demonstrate that, after inhibition of VEGF signaling, some normal capillaries regress in a systematic sequence of events initiated by a cessation of blood flow and followed by apoptosis of endothelial cells, migration of pericytes away from regressing vessels, and formation of empty basement membrane sleeves that can facilitate capillary regrowth.

VEGF-dependent plasticity of fenestrated capillaries in the normal adult microvasculature

Unlike during development, blood vessels in the adult are generally thought not to require VEGF for normal function. However, VEGF is a survival factor for many tumor vessels, and there are clues that some normal blood vessels may also depend on VEGF. In this study, we sought to identify which, if any, vascular beds in adult mice depend on VEGF for survival. Mice were treated with a small-molecule VEGF receptor (VEGFR) tyrosine kinase inhibitor or soluble VEGFRs for 1-3 wk. Blood vessels were assessed using immunohistochemistry or scanning or transmission electron microscopy. In a study of 17 normal organs after VEGF inhibition, we found significant capillary regression in pancreatic islets, thyroid, adrenal cortex, pituitary, choroid plexus, small-intestinal villi, and epididymal adipose tissue. The amount of regression was dose dependent and varied from organ to organ, with a maximum of 68% in thyroid, but was less in normal organs than in tumors in RIP-Tag2-transgenic mice or in Lewis lung carcinoma. VEGF-dependent capillaries were fenestrated, expressed high levels of both VEGFR-2 and VEGFR-3, and had normal pericyte coverage. Surviving capillaries in affected organs had fewer fenestrations and less VEGFR expression. All mice appeared healthy, but distinct physiological changes, including more efficient blood glucose handling, accompanied some regimens of VEGF inhibition. Strikingly, most capillaries in the thyroid grew back within 2 wk after cessation of treatment for 1 wk. Our findings of VEGF dependency of normal fenestrated capillaries and rapid regrowth after regression demonstrate the plasticity of the adult microvasculature.

Vascular endothelial growth factor levels in vitreous and serum of patients with either proliferative diabetic retinopathy or proliferative vitreoretinopathy

PURPOSES

To confirm the role of vascular endothelial growth factor (VEGF) in the pathogenesis of proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR) and to investigate the relationship between the level of VEGF in serum and its vitreal level in patients with either disease.

METHODS

Venous blood and vitreous of 18 patients with PDR, 15 patients with PVR and 20 patients forming a control group were collected during vitrectomy. The VEGF level was quantified by using ELISA methods in either serum or vitreous.

RESULTS

The VEGF level in serum and vitreous was similarly high in the case of PDR, but its level was only high in serum in the case of PVR.

DISCUSSION

PDR is closely linked with systemic diabetes mellitus whereas PVR is more localized. More selective systemic anti-VEGF medications with reduced side effects are required to treat PDR successfully.