The resolution of lymphedema by interstitial flow in the mouse tail skin

Lymphangiogenesis is considered a promising approach for increasing fluid drainage during secondary lymphedema. However, organization of lymphatics into functional capillaries may be dependent upon interstitial flow (IF). The present study was undertaken to determine the importance of lymphangiogenesis for lymphedema resolution. We created a lymphatic obstruction that produces lymphedema in mouse tail skin. The relatively scar-free skin regeneration that occurred across the obstruction allowed the progression of lymphangiogenesis to be observed and compared with the evolution of lymphedema. The role of vascular endothelial growth factor-C (VEGF-C)/VEGF receptor (VEGFR)-3 signaling in lymphedema resolution was investigated by exogenous administration of VEGF-C or neutralizing antibodies against VEGFR-3. VEGF-C protein improved lymphedema at 15 days [reducing dermal thickness from 742 +/- 105 to 559 +/- 141 microm with 95% confidence intervals (CIs), P < 0.05] without increasing lymphatic capillary coverage (11.6 +/- 6.4% following VEGF-C treatment relative to 9.6 +/- 6.2% with 95% CIs, P > 0.50). Blocking VEGFR-3 signaling did not inhibit lymphedema resolution at 25 days (dermal thickness of 462 +/- 127 microm following VEGFR-3 inhibition relative to 502 +/- 87 microm with 95% CIs) or inhibit IF, although VEGFR-3 blocking prevented lymphangiogenesis (reducing lymphatic coverage to 0.2 +/- 0.7% relative to 8.7 +/- 7.3% with 95% CIs, P < 0.005). A second mouse tail lymphedema model was employed to investigate the ability of VEGF-C to increase fluid drainage across a scar. We found that neither neutralization of VEGFR-3 nor administration of VEGF-C affected the course of skin swelling over 25 days. These findings suggest that resolution of lymphedema in the mouse tail skin may be more dependent upon IF and regeneration of the extracellular matrix across the obstruction than lymphatic capillary regeneration.     

In vitro assays using primary embryonic mouse lymphatic endothelial cells uncover key roles for FGFR1 signalling in lymphangiogenesis

Despite the importance of blood vessels and lymphatic vessels during development and disease, the signalling pathways underpinning vessel construction remain poorly characterised. Primary mouse endothelial cells have traditionally proven difficult to culture and as a consequence, few assays have been developed to dissect gene function and signal transduction pathways in these cells ex vivo. Having established methodology for the purification, short-term culture and transfection of primary blood (BEC) and lymphatic (LEC) vascular endothelial cells isolated from embryonic mouse skin, we sought to optimise robust assays able to measure embryonic LEC proliferation, migration and three-dimensional tube forming ability in vitro. In the course of developing these assays using the pro-lymphangiogenic growth factors FGF2 and VEGF-C, we identified previously unrecognised roles for FGFR1 signalling in lymphangiogenesis. The small molecule FGF receptor tyrosine kinase inhibitor SU5402, but not inhibitors of VEGFR-2 (SU5416) or VEGFR-3 (MAZ51), inhibited FGF2 mediated LEC proliferation, demonstrating that FGF2 promotes proliferation directly via FGF receptors and independently of VEGF receptors in primary embryonic LEC. Further investigation revealed that FGFR1 was by far the predominant FGF receptor expressed by primary embryonic LEC and correspondingly, siRNA-mediated FGFR1 knockdown abrogated FGF2 mediated LEC proliferation. While FGF2 potently promoted LEC proliferation and migration, three dimensional tube formation assays revealed that VEGF-C primarily promoted LEC sprouting and elongation, illustrating that FGF2 and VEGF-C play distinct, cooperative roles in lymphatic vascular morphogenesis. These assays therefore provide useful tools able to dissect gene function in cellular events important for lymphangiogenesis and implicate FGFR1 as a key player in developmental lymphangiogenesis in vivo.     

Inhibition of Lymphangiogenesis of Endothelial Progenitor Cells with VEGFR-3 siRNA Delivered with PEI-alginate Nanoparticles

Lymphangiogenesis is implicated in lymphatic metastasis of tumor cells. Recently, growing evidences show that endothelial progenitor cells (EPCs) are involved in lymphangiogenesis. This study has investigated effects of VEGF-C/VEGFR-3 (vascular endothelial growth factor receptor-3) signaling pathway on EPC differentiation and effectiveness of inhibiting lymphatic formation of EPCs with VEGFR-3 siRNA delivered in PEI (polyethylenimine)-alginate nanoparticles. CD34⁺VEGFR-3⁺ EPCs were sorted from mononuclear cells of human cord blood. Under induction with VEGF-C, the cells differentiated toward lymphatic endothelial cells. The nanoparticles were formulated with 25 kDa branched PEI and alginate. The size and surface charge of PEI-alginate nanoparticles loading VEGFR-3 siRNA (N/P = 16) are 139.1 nm and 7.56 mV respectively. VEGFR-3 siRNA specifically inhibited expression of VEGFR-3 mRNA in the cells. After treatment with PEI-alginate/siRNA nanocomplexes, EPCs could not differentiate into lymphatic endothelial cells, and proliferation, migration and lymphatic formation of EPC-derived cells were suppressed significantly. These results demonstrate that VEGFR-3 signaling plays an important role in differentiation of CD34⁺VEGFR-3⁺ EPCs. VEGFR-3 siRNA delivered with PEI-alginate nanoparticles can effectively inhibit differentiation and lymphangiogenesis of EPCs. Inhibiting VEGFR-3 signaling with siRNA/nanocomplexes would be a potential therapy for suppression of tumor lymphangiogenesis and lymphatic metastasis.     

Signalling via vascular endothelial growth factor receptor-3 is sufficient for lymphangiogenesis in transgenic mice

Vascular endothelial growth factor receptor-3 (VEGFR-3) has an essential role in the development of embryonic blood vessels; however, after midgestation its expression becomes restricted mainly to the developing lymphatic vessels. The VEGFR-3 ligand VEGF-C stimulates lymphangiogenesis in transgenic mice and in chick chorioallantoic membrane. As VEGF-C also binds VEGFR-2, which is expressed in lymphatic endothelia, it is not clear which receptors are responsible for the lymphangiogenic effects of VEGF-C. VEGF-D, which binds to the same receptors, has been reported to induce angiogenesis, but its lymphangiogenic potential is not known. In order to define the lymphangiogenic signalling pathway we have created transgenic mice overexpressing a VEGFR-3-specific mutant of VEGF-C (VEGF-C156S) or VEGF-D in epidermal keratinocytes under the keratin 14 promoter. Both transgenes induced the growth of lymphatic vessels in the skin, whereas the blood vessel architecture was not affected. Evidence was also obtained that these growth factors act in a paracrine manner in vivo. These results demonstrate that stimulation of the VEGFR-3 signal transduction pathway is sufficient to induce specifically lymphangiogenesis in vivo.     

Blocking Fibroblast Growth Factor receptor signaling inhibits tumor growth, lymphangiogenesis, and metastasis

Fibroblast Growth Factor receptor (FGFR) activity plays crucial roles in tumor growth and patient survival. However, FGF (Fibroblast Growth Factor) signaling as a target for cancer therapy has been under-investigated compared to other receptor tyrosine kinases. Here, we studied the effect of FGFR signaling inhibition on tumor growth, metastasis and lymphangiogenesis by expressing a dominant negative FGFR (FGFR-2DN) in an orthotopic mouse mammary 66c14 carcinoma model. We show that FGFR-2DN-expressing 66c14 cells proliferate in vitro slower than controls. 66c14 tumor outgrowth and lung metastatic foci are reduced in mice implanted with FGFR-2DN-expressing cells, which also exhibited better overall survival. We found 66c14 cells in the lumen of tumor lymphatic vessels and in lymph nodes. FGFR-2DN-expressing tumors exhibited a decrease in VEGFR-3 (Vascular Endothelial Growth Factor Receptor-3) or podoplanin-positive lymphatic vessels, an increase in isolated intratumoral lymphatic endothelial cells and a reduction in VEGF-C (Vascular Endothelial Growth Factor-C) mRNA expression. FGFs may act in an autocrine manner as the inhibition of FGFR signaling in tumor cells suppresses VEGF-C expression in a COX-2 (cyclooxygenase-2) or HIF1-α (hypoxia-inducible factor-1 α) independent manner. FGFs may also act in a paracrine manner on tumor lymphatics by inducing expression of pro-lymphangiogenic molecules such as VEGFR-3, integrin α9, prox1 and netrin-1. Finally, in vitro lymphangiogenesis is impeded in the presence of FGFR-2DN 66c14 cells. These data confirm that both FGF and VEGF signaling are necessary for the maintenance of vascular morphogenesis and provide evidence that targeting FGFR signaling may be an interesting approach to inhibit tumor lymphangiogenesis and metastatic spread.     

VEGFR-3基因转染淋巴管内皮祖细胞后可溶性VEGFR-3蛋白的分泌

目的研究携带BABL/c小鼠VEGFR-3（1-3Ig）基因的重组腺病毒转染淋巴管内皮祖细胞（LEPCs）后,对可溶性VEGFR-3蛋白分泌及其生物学特性的作用。方法采用巢式RT-PCR技术从BABL/c小鼠胎盘组织中扩增VEGFR-3（1-3Ig）的编码基因,并通过重组PCR技术在基因的N端加上人CD33的信号肽。将该基因片段亚克隆入腺病毒表达载体（pDC316-IRES-EGFP）,重组质粒经酶切及测序验证后,与包装质粒共转染293细胞以产生重组腺病毒。将构建好的携带有小鼠VEGFR-3（1-3Ig）基因的重组腺病毒转染淋巴管内皮祖细胞,通过ELISA检测转染细胞上清液中可溶性VEGFR-3蛋白的分泌及其对VEGF-C的中和作用。结果成功构建了带有信号肽的BABL/c小鼠VEGFR-3（1-3Ig）基因的腺病毒表达质粒,并获得高滴度的携带有小鼠VEGFR-3（1-3Ig）基因的重组腺病毒,重组腺病毒转染淋巴管内皮祖细胞后,可使转染细胞分泌可溶性VEGFR-3蛋白,该蛋白具有中和VEGF-C的作用。结论成功地制备了携带BABL/c小鼠VEGFR-3（1-3Ig）基因的重组腺病毒,用该病毒转染淋巴管内皮祖细胞可使其分泌可溶性VEGFR-3,该蛋白在体外具有中和VEGF-C的作用,这为临床抑制肿瘤淋巴管新生奠定了基础。     

Characterization of lymphangiogenesis in a model of adult skin regeneration

To date, adult lymphangiogenesis is not well understood. In this study we describe the evolution of lymphatic capillaries in regenerating skin and correlate lymphatic migration and organization with the expression of matrix metalloproteinases (MMPs), immune cells, the growth factors VEGF-A and VEGF-C, and the heparan sulfate proteogylcan perlecan, a key component of basement membrane. We show that while lymphatic endothelial cells (LECs) migrate and organize unidirectionally, in the direction of interstitial fluid flow, they do not sprout into the region but rather migrate as single cells that later join together into vessels. Furthermore, in a modified "shunted flow" version of the model, infiltrated LECs fail to organize into functional vessels, indicating that interstitial fluid flow is necessary for lymphatic organization. Perlecan expression on new lymphatic vessels was only observed after vessel organization was complete and also appeared first in the distal region, consistent with the directionality of lymphatic migration and organization. VEGF-C expression peaked at the initiation of lymphangiogenesis but was reduced to lower levels throughout organization and maturation. In mice lacking MMP-9, lymphatics regenerated normally, suggesting that MMP-9 is not required for lymphangiogenesis, at least in mouse skin. This study thus characterizes the process of adult lymphangiogenesis and differentiates it from sprouting blood angiogenesis, verifies its dependence on interstitial fluid flow for vessel organization, and correlates its temporal evolution with those of relevant environmental factors.     

卵巢上皮肿瘤淋巴转移与血管内皮生长因子C的表达

The aim of the present study was to explore the role of vascular endothelial growth factor-C (VEGF-C) in the process of angiogenesis, lymphangiogenesis and lymphatic metastasis in epithelial ovarian tumors. In situ hybridization and immunohistochemical staining for VEGF-C were performed in 30 epithelial ovarian carcinomas, 9 borderline tumors and 26 benign cystadenomas. Endothelial cells were immunostained with anti-VEGFR-3 pAb and anti-CD31 mAb, and VEGFR-3 positive vessels and microvessel density (MVD) were assessed by image analysis. VEGF-C mRNA and protein expression in ovarian epithelial carcinomas were significantly higher than that in borderline tumors and benign cystadenomas (p < 0.05 or p < 0.01). In ovarian epithelial carcinomas, VEGF-C protein expression, VEGFR-3 positive vessels and MVD were significantly higher in the cases of clinical stage III-IV and with lymphatic metastasis than those of clinical stage I-II and without lymphatic metastasis respectively (p < 0.05 or p < 0.01), VEGFR-3 positive vessels and MVD was significantly higher in the VEGF-C protein positive tumors than negative tumors (p < 0.05), VEGFR-3 positive vessels was significantly correlated with MVD(p < 0.01). These data suggest that VEGF-C might play a role in lymphatic metastasis via lymphangiogenesis and angiogenesis in epithelial ovarian carcinomas, and VEGF-C could be used as a biologic marker of metastasis in ovarian epithelial carcinomas.     

Expression of vascular endothelial growth factor C in human pterygium

Vascular endothelial growth factor C (VEGF-C) and its receptor VEGFR-3 mediate lymphangiogenesis. In this study, we analyzed the expression of VEGF-C and VEGFR-3 as well as lymphatic vessels in the pterygium and normal conjunctiva of humans. Fifteen primary nasal pterygia and three normal bulbar conjunctivas, surgically removed, were examined in this study. The lymphatic vessel density (LVD) and blood vessel density were determined by the immunolabeling of D2-40 and CD31, markers for lymphatic and blood vessels, respectively. VEGF-C and VEGFR-3 expression in pterygial and conjunctival tissue proteins was detected by Western blotting and were evaluated using immunohistochemistry. The LVD was significantly higher in the pterygium than normal conjunctiva (p < 0.05). Western blot demonstrated high-level expression of VEGF-C and VEGFR-3 in the pterygium compared with normal conjunctiva. VEGF-C immunoreactivity was detected in the cytoplasm of pterygial and normal conjunctival epithelial cells. The number of VEGF-C-immunopositive cells in pterygial epithelial cells was significantly higher than in normal conjunctival cells (p < 0.05). VEGFR-3 immunoreactivity was localized in the D2-40-positive lymphatic endothelial cells. The present findings suggest the potential role of VEGF-C in the pathogenesis and development of a pterygium through lymphangiogenesis and the VEGF-C/VEGFR-3 pathway as a novel therapeutic target for the human pterygium.     

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.     

The good,the bad and the ugly: A neuropilin-2 story from normal to tumor-associated lymphangiogenesis

VEGF-C is a crucial player in lymphangiogenesis. Besides VEGFR-2 and VEGFR-3, it also binds NRP2. NRP2 enhances VEGF-C/VEGFR-3 effects in developmental lymphangiogenesis, but its role in adult and tumoral lymphangiogenesis is not known. In their study, Bagri and colleagues demonstrate that blocking NRP2 results in a decrease of metastasis formation, a phenomenon relying on tumoral lymphangiogenesis. Thus, they identified NRP2 as an attractive new target for modulating metastasis.Key words: VEGF-C, NRP2, VEGFR-3, tumoral lymphangiogenesis, metastasisBesides developmental and adult lymphangiogenesis, formation of new lymphatic vessels also occurs during tumor growth. This abnormal lymphangiogenesis enables tumor cells to escape from the solid tumor and to invade the body through the newly formed lymphatics. The resulting metastases are responsible for most cancer-associated deaths. Interestingly, inhibition of VEGF-C/VEGFR-3 axis has been shown to block metastasis formation in preclinical models.¹ However, treatment with VEGFR3_ECD may result in compromise of the normal lymphatic system leading to complications such as lymphedema. VEGF-C belongs to the VEGF family and is particularly involved in lymphangiogenesis. VEGF-C binds VEGFR-2 but mostly associates with high affinity with the third tyrosine kinase VEGF receptor, VEGFR-3.² Recently, it has been proved that VEGF-C also binds a receptor from the neuropilin family, NRP2. NRP2 associates with VEGFR-3, and binding of VEGF-C to NRP2 enhances VEGF-C/VEGFR-3-induced biological effects.³ NRP2 thus modulates developmental lymphangiogenesis, but its significance in adult or tumoral lymphangiogenesis remained unknown until a recent study by Bagri and colleagues who analyzed NRP2 function in tumor cell metastasis.⁴     

Involvement of lysosomal degradation in VEGF-C-induced down-regulation of VEGFR-3

The vascular endothelial growth factor (VEGF)-C-induced down-regulation of VEGF receptor (VEGFR)-3 is important in lymphangiogenesis. Here, we demonstrate that VEGF-C, -D, and -C156S, but not VEGF-A, down-regulate VEGFR-3. VEGF-C stimulates VEGFR-3 tyrosyl phosphorylation and transient phosphorylation of extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinases in lymphatic endothelial cells. VEGF-C-induced down-regulation of VEGFR-3 was blocked by a VEGF-C trap, tyrosine kinase inhibitor, and leupeptin, pepstatin, and E64 (LPE), but was unaffected by Notch 1 activator and γ-secretase inhibitors. Our findings indicate that VEGF-C down-regulates VEGFR-3 in lymphatic endothelial cells through VEGFR-3 kinase activation and, in part, via lysosomal degradation.     

Molecular control of lymphangiogenesis

The lymphatic vasculature plays a critical role in the regulation of body fluid volume and immune function. Extensive research into the molecular mechanisms that control blood vessel growth has led to identification of molecules that also regulate development and growth of the lymphatic vessels. This is generating a great deal of interest in the molecular control of the lymphatics in the context of embryogenesis, lymphatic disorders and tumor metastasis. Studies in animal models carried out over the past three years have shown that the soluble protein growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. Furthermore, disfunction of VEGFR-3 has recently been shown to cause lymphedema. The capacity to induce lymphangiogenesis by manipulation of the VEGF-C/VEGF-D/VEGFR-3 signaling pathway offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders.     

Vascular endothelial growth factor-C stimulates the lymphatic pump by a VEGF receptor-3-dependent mechanism

Vascular endothelial growth factor (VEGF)-C plays an important role in lymphangiogenesis; however, functional responses of lymphatic vessels to VEGF-C have not been characterized. We tested the hypothesis that VEGF-C-induced activation of VEGF receptor (VEGFR)-3 increases lymphatic pump output. We examined the in vivo pump activity of rat mesenteric collecting lymphatics using intravital microscopy during basal conditions and during treatment with 1 nM recombinant VEGF-C, the selective VEGFR-3 agonist VEGF-Cys(156)Ser mutation (C156S; 1 nM), or 0.1 nM VEGF-A. Their specific responses were also analyzed during selective inhibition of VEGFR-3 with MAZ-51. Contraction frequency, end-diastolic diameter, end-systolic diameter, stroke volume index, pump flow index, and ejection fraction were evaluated. We also assessed arteriolar diameter and microvascular extravasation of FITC-albumin. The results show that both VEGF-C and VEGF-C156S significantly increased contraction frequency, end-diastolic diameter, stroke volume index, and pump flow index in a time-dependent manner. VEGF-A caused a different response characterized by a significantly increased stroke volume after 30 min of treatment. MAZ-51 (5 muM) caused tonic constriction and decreased contraction frequency. In addition, 0.5 and 5 muM MAZ-51 attenuated VEGF-C- and VEGF-C156S-induced lymphatic pump activation. VEGF-A caused vasodilation of arterioles, whereas VEGF-C and VEGF-C156S did not significantly alter arteriolar diameter. Also, VEGF-A and VEGF-C caused increased microvascular permeability, whereas VEGF-C156S did not. Our results demonstrate that VEGF-C increases lymphatic pumping through VEGFR-3. Furthermore, changes in microvascular hemodynamics are not required for VEGFR-3-mediated changes in lymphatic pump activity.     

Differential mRNA and tissue expression of lymphangiogenic growth factors (VEGF-C and -D) and their receptor (VEGFR-3) during tail regeneration in a gecko

Lymphangiogenesis, the growth of new lymph vessels, has important roles in both normal and pathological lymphatic function. Despite recent advances, the precise molecular mechanisms behind the lymphangiogenic process remain unclear. The Australian marbled gecko, Christinus marmoratus, voluntarily drops its tail (autotomy) as a predator avoidance strategy. Following autotomy a new tail is regenerated including lymphatic drainage pathways. We examined the molecular control of lymphangiogenesis within the unique model of the regenerating gecko tail. Partial sequences were obtained of the gecko lymphangiogenic growth factors, vascular endothelial growth factor C (VEGF-C) and VEGF-D along with their receptor VEGFR-3. These were highly homologous to other vertebrates. Quantitative real-time polymerase chain reaction (PCR) demonstrated up-regulation of VEGF-C, VEGF-D and VEGFR-3 mRNA expression during the early and middle stages of tail regeneration (between 4 and 9 weeks following autotomy), in late regeneration (12 weeks) and during mid-regeneration (7 and 9 weeks), respectively. VEGF-C and VEGF-D immunostaining was observed lining some lymphatic-like and blood vessels in early–mid tail regeneration, indicating possible associations of the proteins with VEGFRs on endothelia. Keratinocytes and fibroblasts also showed positive staining of VEGF-C and VEGF-D in early–mid tail regeneration. Additionally, VEGF-C was localised in adipose tissue in all tail states examined. This work suggests that specific timings exist for the expression of the lymphangiogenic growth factors, VEGF-C and VEGF-D, and their receptor, VEGF-R3, throughout the regeneration of a functional lymphatic network. Along with localisation data, this suggests potential functions for the growth factors in lymphangiogenesis and angiogenesis throughout tail regeneration.     

Role of macrophages in inflammatory lymphangiogenesis: Enhanced production of vascular endothelial growth factor C and D through NF-kappaB activation

The close association of inflammation, angiogenesis and cancer progression is now highlighted, and in this study we especially focused on a close association of inflammation and lymphangiogenesis. We found that proinflammatory cytokine, interleukin-1β (IL-1β), could induce lymphangiogenesis in mouse cornea through enhanced production of potent lymphangiogenic factors, VEGF-A, VEGF-C and VEGF-D. IL-1β-induced lymphangiogenesis, but not angiogenesis, was inhibited by administration of a selective anti-VEGF receptor-3 (VEGFR-3) neutralizing antibody. And in mouse cornea we observed recruitment of monocyte/macrophages and neutrophils by IL-1β implanted cornea. Depletion of macrophages by a bisphosphonate encapsulated in liposomes inhibited this IL-1β-induced lymphangiogenesis and also up-regulation of VEGF-A, VEGF-C, and VEGF-D. Furthermore, IL-1β-induced lymphangiogenesis and angiogenesis were suppressed by NF-κB inhibition with marked suppression of VEGF-A, VEGF-C, and VEGF-D expression.     

Inhibition of lymphangiogenesis with resulting lymphedema in transgenic mice expressing soluble VEGF receptor-3

The lymphatic vasculature transports extravasated tissue fluid, macromolecules and cells back into the blood circulation. Recent reports have focused on the molecular mechanisms regulating the lymphatic vessels. Vascular endothelial growth factor (VEGF)-C and VEGF-D have been shown to stimulate lymphangiogenesis and their receptor, VEGFR-3, has been linked to human hereditary lymphedema. Here we show that a soluble form of VEGFR-3 is a potent inhibitor of VEGF-C/VEGF-D signaling, and when expressed in the skin of transgenic mice, it inhibits fetal lymphangiogenesis and induces a regression of already formed lymphatic vessels, though the blood vasculature remains normal. Transgenic mice develop a lymphedema-like phenotype characterized by swelling of feet, edema and dermal fibrosis. They survive the neonatal period in spite of a virtually complete lack of lymphatic vessels in several tissues, and later show regeneration of the lymphatic vasculature, indicating that induction of lymphatic regeneration may also be possible in humans.     

Characterization of the interaction between endostatin short Peptide and VEGF receptor 3

Corneal angiogenesis and lymphangiogenesis are induced by vascular endothelial growth factors (VEGFs) signaling through its receptors VEGFR-1, -2, and -3. Endostatin is a peptide antagonist of these receptors that causes inhibition of bFGF-induced corneal angiogenesis and lymphangiogenesis. Here we show that binding of VEGF-C and endostatin to recombinant VEGFR-3 is competitive. Alignments of the primary amino acid sequences of VEGF-C and the C-terminal endostatin peptide (mEP: LEQKAASCHNSYIVLCIENSFMTSFSK) identified two conserved cysteine residues separated by seven amino acids. Peptides of VEGF-C and mEP containing these conserved residues bound toVEGFR-3. However, substitution of alanine for either of the cysteines in the mEP peptide perturbed the secondary structure, and this mutated peptide was unable to bind to VEGFR-3. Analysis by surface plasmon resonance demonstrated that the binding of the mEP peptide for recombinant VEGFR-3 had a Ka of 1.41x107M-1s-1, Kd of 0.6718 s-1, and a KD of 4.78x10-8M. Characterization of the mechanism of endostatin binding to VEGFR-3 may lead to the development of novel therapies for lymphangiogenesis-related disorders, such as transplant rejection, lymphedema, and cancer metastasis.     

Expression of vascular endothelial growth factors VEGF- C and D, VEGFR-3, and comparison of lymphatic vessels density labeled with D2-40 antibodies as a prognostic factors in vulvar intraepithelial neoplasia (VIN) and invasive vulvar cancer

OBJECTIVE: The aim of this study was to compare the immunohistochemical expression of vascular endothelial growth factors VEGF-C and D, as well as the expression of VEGFR-3 in VIN and vulvar invasive cancer and to compare the density of lymphatic marker D2-40 antibody in both groups, and to compare them with different clinicopathologic features. Materials & Methods: The study was performed using tissue material and clinical data from 100 women diagnosed with VIN and 100 women diagnosed with invasive vulvar cancer. Results: No significant differences were found in the expression of VEGF-C and -D or VEGFR-3 between those patients with VIN and those with invasive vulvar cancers. Weak expression of VEGF-C was confirmed only in two cases of the analyzed series; in all cases, expression of VEGF-D and VEGFR-3 was observed. The strongest expression of VEGF-D and VEGFR-3 was observed in the group of invasive cancers. The highest density of lymphatic vessels per 2 mm was observed in VIN. In the cancer group, small lymphatic vessels with a narrow oval lumen were observed. Moreover, in two cases of vulvar cancer, the presence of intratumoral lymphatic vessels was observed. Conclusions: These results suggest that lymphangiogenesis begins at the preinvasive stage of vulvar carcinogenesis and suggests the important role of VEGF-C, VEGF-D, VEGFR-3 and LV (D2-40) as prognostic factors in the process of carcinogenesis in the vulvar area.     

The specificity of receptor binding by vascular endothelial growth factor-d is different in mouse and man

Human vascular endothelial growth factor-D (VEGF-D) binds and activates VEGFR-2 and VEGFR-3, receptors expressed on vascular and lymphatic endothelial cells. As VEGFR-2 signals for angiogenesis and VEGFR-3 is thought to signal for lymphangiogenesis, it was proposed that VEGF-D stimulates growth of blood vessels and lymphatic vessels into regions of embryos and tumors. Here we report the unexpected finding that mouse VEGF-D fails to bind mouse VEGFR-2 but binds and cross-links VEGFR-3 as demonstrated by biosensor analysis with immobilized receptor domains and bioassays of VEGFR-2 and VEGFR-3 cross-linking. Mutation of amino acids in mouse VEGF-D to those in the human homologue indicated that residues important for the VEGFR-2 interaction are clustered at, or are near, the predicted receptor-binding surface. Coordinated expression of VEGF-D and VEGFR-3 in mouse embryos was detected in the developing skin where the VEGF-D gene was expressed in a layer of cells beneath the developing epidermis and VEGFR-3 was localized on a network of vessels immediately beneath the VEGF-D-positive cells. This suggests that VEGF-D and VEGFR-3 may play a role in establishing vessels of the skin by a paracrine mechanism. Our study of receptor specificity suggests that VEGF-D may have different biological functions in mouse and man.