Regulation of soluble vascular endothelial growth factor receptor (sFlt-1/sVEGFR-1) expression and release in endothelial cells by human follicular fluid and granulosa cells

BACKGROUND: During the female reproductive cycle, follicular development and corpus luteum formation crucially depend on the fast generation of new blood vessels. The importance of granulosa cells and follicular fluid in controlling this angiogenesis is still not completely understood. Vascular endothelial growth factor (VEGF) produced by granulosa cells and secreted into the follicular fluid plays an essential role in this process. On the other hand, soluble VEGF receptor-1 (sFlt-1) produced by endothelial cells acts as a negative modulator for the bioavailability of VEGF. However, the regulation of sFlt-1 production remains to be determined. METHODS: We analyzed the influence of human follicular fluid obtained from FSH-stimulated women as well as of human granulosa cell conditioned medium on sFlt-1 production in and release from human umbilical vein endothelial cells (HUVEC) in vitro. Soluble Flt-1 gene expression was determined by RT-PCR analysis, amount of sFlt-1-protein was quantified by Sandwich-ELISA. RESULTS: Human follicular fluid as well as granulosa cell-conditioned medium significantly inhibit the production of sFlt-1 by endothelial cells on a posttranscriptional level. Treatment of cultured granulosa cells with either hCG or FSH had not impact on the production of sFlt-1 inhibiting factors. We further present data suggesting that this as yet unknown sFlt-1 regulating factor secreted by granulosa cells is not heat-sensitive, not steroidal, and it is of low molecular mass (< 1000 Da). CONCLUSION: We provide strong support that follicular fluid and granulosa cells control VEGF availability by down regulation of the soluble antagonist sFlt-1 leading to an increase of free, bioactive VEGF for maximal induction of vessel growth in the ovary

VEGF and VEGF-C: Specific Induction of Angiogenesis and Lymphangiogenesis in the Differentiated Avian Chorioallantoic Membrane

AbstractThe lymphangiogenic potency of endothelial growth factors has not been studied to date. This is partially due to the lack ofin vivolymphangiogenesis assays. We have studied the lymphatics of differentiated avian chorioallantoic membrane (CAM) using microinjection of Mercox resin, semi- and ultrathin sectioning, immunohistochemical detection of fibronectin and α-smooth muscle actin, andin situhybridization with VEGFR-2 and VEGFR-3 probes. CAM is drained by lymphatic vessels which are arranged in a regular pattern. Arterioles and arteries are accompanied by a pair of interconnected lymphatics and form a plexus around bigger arteries. Veins are also associated with lymphatics, particularly larger veins, which are surrounded by a lymphatic plexus. The lymphatics are characterized by an extremely thin endothelial lining, pores, and the absence of a basal lamina. Patches of the extracellular matrix can be stained with an antibody against fibronectin. Lymphatic endothelial cells of differentiated CAM show ultrastructural features of this cell type. CAM lymphatics do not possess mediae. In contrast, the lymphatic trunks of the umbilical stalk are invested by a single but discontinuous layer of smooth muscle cells. CAM lymphatics express VEGFR-2 and VEGFR-3. Both the regular pattern and the typical structure of these lymphatics suggest that CAM is a suitable site to study thein vivoeffects of potential lymphangiogenic factors. We have studied the effects of VEGF homo- and heterodimers, VEGF/PlGF heterodimers, and PlGF and VEGF-C homodimers on Day 13 CAM. All the growth factors containing at least one VEGF chain are angiogenic but do not induce lymphangiogenesis. PlGF-1 and PlGF-2 are neither angiogenic nor lymphangiogenic. VEGF-C is the first lymphangiogenic factor and seems to be highly chemoattractive for lymphatic endothelial cells. It induces proliferation of lymphatic endothelial cells and development of new lymphatic sinuses which are directed immediately beneath the chorionic epithelium. Our studies show that VEGF and VEGF-C are specific angiogenic and lymphangiogenic growth factors, respectively

Mouse lung contains endothelial progenitors with high capacity to form blood and lymphatic vessels

<p>Abstract</p> <p>Background</p> <p>Postnatal endothelial progenitor cells (EPCs) have been successfully isolated from whole bone marrow, blood and the walls of conduit vessels. They can, therefore, be classified into circulating and resident progenitor cells. The differentiation capacity of resident lung endothelial progenitor cells from mouse has not been evaluated.</p> <p>Results</p> <p>In an attempt to isolate differentiated mature endothelial cells from mouse lung we found that the lung contains EPCs with a high vasculogenic capacity and capability of <it>de novo </it>vasculogenesis for blood and lymph vessels.</p> <p>Mouse lung microvascular endothelial cells (MLMVECs) were isolated by selection of CD31⁺cells. Whereas the majority of the CD31⁺cells did not divide, some scattered cells started to proliferate giving rise to large colonies (> 3000 cells/colony). These highly dividing cells possess the capacity to integrate into various types of vessels including blood and lymph vessels unveiling the existence of local microvascular endothelial progenitor cells (LMEPCs) in adult mouse lung. EPCs could be amplified > passage 30 and still expressed panendothelial markers as well as the progenitor cell antigens, but not antigens for immune cells and hematopoietic stem cells. A high percentage of these cells are also positive for Lyve1, Prox1, podoplanin and VEGFR-3 indicating that a considerabe fraction of the cells are committed to develop lymphatic endothelium. Clonogenic highly proliferating cells from limiting dilution assays were also bipotent. Combined <it>in vitro </it>and <it>in vivo </it>spheroid and matrigel assays revealed that these EPCs exhibit vasculogenic capacity by forming functional blood and lymph vessels.</p> <p>Conclusion</p> <p>The lung contains large numbers of EPCs that display commitment for both types of vessels, suggesting that lung blood and lymphatic endothelial cells are derived from a single progenitor cell.</p

VEGFR-3 is expressed on megakaryocyte precursors in the murine bone marrow and plays a regulatory role in megakaryopoiesis

Introduction VEGFR-3 is a member of the VEGFR receptor tyrosine kinase family. It is expressed on lymphatic endothelial cells (LECs) and plays a central role in the regulation of lymphangiogenesis. 1 On binding to its ligands, VEGF-C and VEGF-D, VEGFR-3 is activated and orchestrates the outgrowth of lymphatic vessels. During murine hematopoiesis, Sca-1 ϩ hematopoietic stem cells give rise to the precursors of all hematopoietic lineages. 10 Megakaryocytes develop from CD34 ϩ progenitors. Methods Cell culture HEL cells were obtained from DSMZ and cultivated in RPMI (Gibco-BRL) containing 10% FCS and 1% penicillin-streptomycin. Differentiation was induced with 10nM tetradecanoyl phorbol acetate (TPA; Sigma-Aldrich). Primary human microvascular LECs (Cambrex) from the dermis (HMVECdLyNeo) were cultivated in EGM-2MV (Lonza) and 5% FCS supplemented with growth factors provided by the manufacturer. Bovine lymphatic endothelial cells were cultivated in DMEM (Gibco-BRL) containing 20% FCS and 1% penicillin-streptomycin on gelatin-coated plastic. HEK-293 cells were cultivated in DMEM supplemented with 10% FCS and 1% penicillin-streptomycin. Western blot analysis Cell lysates were analyzed using standard Western blotting techniques. The membranes were probed with Abs specific for VEGFR-3 (R&amp;D Systems), CD31 (Santa Cruz Biotechnology), CD34 (Abcam), CD42a (Santa Cruz Biotechnology), CD61 (R&amp;D Systems), CD144 (Santa Cruz Biotechnology), or GpA (International Blood Group Reference Laboratory). Probing with hypoxanthine phosphoribosyltransferase (HPRT) Abs (Santa Cruz Biotechnology) served as a loading control. PCR analysis RNA was prepared using peqGOLD RNAPure (PeqLab). Synthesis of cDNA using Superscript II (Invitrogen) was performed according to the manufacturer&apos;s recommendations. For PCR, cDNAs were amplified as follows: 94°C for 30 seconds, 60°C for 30 seconds, and 72°C for 90 seconds (VEGFR-2, Prox1, LYVE-1, Podoplanin, HPRT, Fli-1, Fog-2, Gata-2, and Elf-1) or 94°C for 30 seconds, 54°C for 30 seconds, and 72°C for 90 seconds (VEGFR-3). Details of the primers used are in supplemental Methods (available on the Blood Web site; see the Supplemental Materials link at the top of the online article). Tubule formation on collagen gels Collagen type 1 was prepared from rat tails. Tendons were isolated, dissolved in acetic acid, then filtered, lyophilized, and redissolved in 0.1% acetic acid at 4 mg/mL. Cells were seeded on collagen gels (2 mg/mL) and cultured in the presence of 30 ng/mL of VEGF 165 (Promokine) for 8 days. Tubule formation was analyzed as described previously. 22 Immunohistochemistry For the immunohistochemical analysis of VEGFR-3 expression in the BM, cryosections of decalcified murine femurs embedded in tissue-freezing medium (Leica) were fixed in acetone and stained with VEGFR-3 Abs (eBiosciences). The stained sections were then analysed at room temperature using an Axioskop (Zeiss) equipped with a PlanNeoflur 20ϫ/0.50 and an Axiocam (Zeiss) and Axiovision software (Ziess). MACS BM cells isolated from femurs and tibias of C57BL/6 mice were treated with Fc-block (BD Biosciences) and then incubated with Abs against VEGFR-3 (R&amp;D Systems), Sca-1, CD41, or CD38 (BD Biosciences), followed by specific secondary MACS Abs (Miltenyi-Biotec) according to the manufacturerЈs recommendations. Cell populations were then either enriched or depleted for the labeled epitope using LS or LD columns (Miltenyi-Biotec), respectively. The purity of the sorted populations was controlled by flow cytometry. CD42 FACS BM was isolated from femurs and tibias of C57BL/6 mice and stained with Abs specific for VEGFR-3 (R&amp;D Systems) and/or CD42a (Emfret) and analyzed by FACS. Lethal irradiation and BM transplantation C57BL/6 mice were irradiated with lethal doses (9 Gy) from a ␥ source. After 24 hours, the mice were all transplanted in parallel by IV injection with either complete BM, BM depleted of VEGFR-3 ϩ cells, or BM mock depleted with an appropriate isotype control using MACS. EDTA blood samples were taken from all animals on days 0, Isolation and culture of primary murine BM cells BM was isolated from femurs and tibias of C57BL6 mice. After lysis of RBCs with ammonium-chloride-potassium buffer, the cells were transferred to IMDM (Gibco-BRL) supplemented with 1% penicillin/streptomycin, 10% HEK-293 cell-conditioned DMEM, Nutridoma SP (Roche), L-glutamine, and 100 pg/mL of recombinant murine TPO (RDI Diagnostics). Depending on the experiment, the cells were cultured with either 100 g/mL of mF4-31C1 VEGFR-3-blocking Abs (kindly provided by ImClone Systems), 100 g/mL of rat IgG isotype control, or 400 ng/mL of VEGF-C-Cys, a mutant form of VEGF-C that activates VEGFR-3 but not VEGFR-2. Long-term injections C57BL/6 mice were injected daily with 25 g of VEGF-C-Cys for 3 weeks. Blood was taken on days 0, 3, 7, 10, 14, 17, and 21. In the blocking Ab experiments, mice were injected with 600 g/animal/injection of mF4-31C1 VEGFR-3-blocking Ab, isotype control Ig, or PBS on a MondayWednesday-Friday schedule for 6 weeks. Blood was taken on days 0, Recovery kinetics after sublethal irradiation Experimental C57BL/6 mice were sublethally irradiated (4.5 Gy) in a ␥ source. They were then either injected daily with VEGF-C-Cys (25 g/animal/injection) or PBS or were intraperitoneally injected with 600 g/animal/injection of mF4-31C1 VEGFR-3-blocking Abs, isotype control Ig, or PBS every other day. Blood was taken on days 0, 7, 11, 14, 18, and 21 after irradiation and analyzed. In each experiment, all animals were treated at the same time and on the same day and all animals were bled at each time point. BM was isolated from femurs and tibias 20 days after irradiation, and the number and ploidy of CD41 ϩ cells in the BM was assessed. Significance was tested using 2-tailed unpaired t tests assuming equal variance. TPO administration C57BL/6 mice were administered with 5 g of recombinant murine TPO (RDI), followed by daily injections of either 25 g of VEGF-C-Cys or PBS. One group received only PBS throughout. Blood was taken and analyzed 0, 3, 5, 7, and 10 days after TPO administration. All animals were treated at the same time and on the same day and all animals were bled at each time point. After 10 days, the animals were killed and the number and ploidy of CD41 ϩ 1900 THIELE et al BLOOD, 30 AUGUST 2012 ⅐ VOLUME 120, NUMBER 9 For personal use only. on October 6, 2016. by guest www.bloodjournal.org From cells in the BM was assessed. Significance was tested using 2-tailed unpaired t tests assuming equal variance. 5-FU treatment C57BL/6 mice were intraperitoneally injected with a single dose of 5-FU (Sigma-Aldrich) at 150 mg/kg. Control mice remained untreated. The 5-FU-treated mice then received daily injections of either 25 g of VEGF-C-Cys or PBS throughout the experiment. Blood was taken and analyzed 0, All animal experiments were approved by the local regulatory authorities and were performed according to German legal requirements. Results Expression of VEGFR-3 and other lymphatic endothelial markers is up-regulated on phorbol diester-induced megakaryocytic differentiation of HEL cells VEGFR-3 is widely used as a marker for lymphatic endothelium. Originally, however, the receptor was cloned from the HEL cell line. 7 This cell line can be induced to differentiate into the erythrocyte lineage by EPO treatment 23 and into the megakaryocyte lineage in response to TPA. Consistent with the notion that HEL cells differentiate into the megakaryocyte lineage on TPA treatment, we detected strong up-regulation of several markers and transcription factors associated with megakaryocytic differentiation A survey of the literature revealed that virtually all markers described to date as being expressed on megakaryocytes can also be expressed on endothelial cells (supplemental These observations raised the question of whether HEL cells really undergo megakaryocytic differentiation after TPA treatment or if they adopt an endothelial phenotype with LEC characteristics. To address this point, we investigated whether TPA-treated HEL cells are capable of forming capillaries, reasoning that if the cells differentiated into endothelial cells, this should be the case. However, in contrast to control bovine LECs, TPA-treated HEL cells could not be induced to form capillaries VEGFR-3 IN MEGAKARYOPOIESIS 1901 BLOOD, 30 AUGUST 2012 ⅐ VOLUME 120, NUMBER 9 For personal use only. on October 6, 2016. by guest www.bloodjournal.org From VEGFR-3 is expressed on megakaryocytic progenitors through to the promegakaryoblast stage in the BM The up-regulation of VEGFR-3 during HEL cell megakaryocytic differentiation suggested to us that VEGFR-3 may play a role in megakaryopoiesis. Because of the limited megakaryocytic differentiation capacity of HEL cells and their cancerous nature, we explored this possibility further using murine BM. First we characterized VEGFR-3 expression in the BM. FACS staining revealed that approximately 2% of murine BM cells were VEGFR-3 ϩ ( To define further the stages of megakaryopoiesis during which VEGFR-3 is expressed, costainings with the stem cell marker Sca-1 and with CD38, CD41, and VEGFR-3 were performed. Expression of Sca-1 is lost during myeloid differentiation. 25 CD38 expression, in turn, is increased early in megakaryopoiesis from the BFU-MK stage on. These observations suggested to us that VEGFR-3 might be expressed on hematopoietic stem cells through to the promegakaryoblast stage. However, Sca1 is not just expressed on hematopoietic stem cells, but also on the immediate progenitors arising from the stem cells. These data are consistent with the notion that VEGFR-3 is not expressed on hematopoietic stem cells, but rather on megakaryocyte precursors through to the premegakaryoblast stage, and that VEGFR-3 expression is lost as megakaryocytes further mature. This notion is further substantiated by the observation that VEGFR-3 ϩ BM cells coexpressed CD42, a marker for megakaryocytes that is not expressed on hematopoietic precursor cells (supplemental Manipulation of VEGFR-3 influences megakaryopoiesis in vitro To examine the role that VEGFR-3 plays during megakaryopoiesis, we cultivated primary murine BM cells with physiologic concentrations of TPO to maintain the megakaryocyte precursors. The cells were grown for 3 days in the presence or absence of VEGF-C-Cys, a mutant form of VEGF-C that specifically activates VEGFR-3 but not VEGFR-2, 20 because VEGFR-2 is also present on megakaryocytic cells. Our data suggest that the specific activation of VEGFR-3 during megakaryopoiesis impairs the transition to polyploid stages, whereas blocking the receptor promotes differentiation and endoreplication. For personal use only. on October 6, 2016. by guest www.bloodjournal.org From Neither activation nor blocking of VEGFR-3 influences steady-state megakaryopoiesis or thrombopoiesis in vivo To study the potential effects of VEGFR-3 manipulation on megakaryopoiesis and thrombopoiesis in vivo, we first injected VEGF-C-Cys to activate VEGFR-3, or PBS as a control, into mice on a daily basis for 3 weeks. Thrombocyte concentrations in the blood were monitored regularly. After 3 weeks of treatment, the mice were killed. BM cells were isolated and stained for CD41 and DNA content to evaluate the number and ploidy of the CD41 ϩ population. We observed a significant decrease in apoptotic CD41 ϩ BM cells in the VEGF-C-Cys-treated group (P Ͻ .01), a trend toward reduced polyploidy, and an increase in 2n CD41 ϩ cells, which were consistent with our in vitro observations. VEGF-C-Cys had no effect on platelet counts or the number of CD41 ϩ cells in the BM (supplemental To determine the effect of inhibiting VEGFR-3 activation on megakaryopoiesis and thrombopoiesis in vivo, mice were injected daily with VEGFR-3-blocking Abs or an appropriate isotype control for 6 weeks. Platelet counts were monitored regularly and the numbers and ploidy distribution of CD41 ϩ BM cells were analyzed at the end of the experiment. Under these conditions, no effects on the measured parameters were observed (supplemental Activation of VEGFR-3 increases platelet counts in TPO-stimulated animals, modulates 5-FU-induced thrombocytopenia and thrombocytosis, and influences ploidy distribution and numbers of CD41 ؉ BM cells after sublethal irradiation Thrombocyte homeostasis is tightly controlled in mammals, and alternative mechanisms exist that can compensate for perturbation . FACS analysis showed that 1.85% Ϯ 0.31% SEM (n ϭ 9) of the murine BM cells expressed VEGFR-3. Dot plots of 1 representative experiment are depicted. Density plots were used to define a region in which 95% (the 2 outer contours) of the negative control events were excluded. The region was then applied to a plot displaying the stained sample. The number of positive events in both the negative control and the actual sample was then assessed. The percentage of true positive cells was calculated by subtraction of the number of events in the negative control within the defined region from the number of events found in the same region for the actual sample. Identical numbers of events were acquired. (B) VEGFR-3 is expressed on isolated mononuclear cells in the murine BM. Sections of murine femurs were stained with VEGFR-3-specific Abs (left panel, VEGFR-3; right panel, control). MK indicates megakaryocyte. Scale bars indicate 100 m. (C) Ploidy of VEGFR-3 ϩ cells in the murine BM. VEGFR-3 ϩ BM cells were enriched by MACS and then analyzed in FACS. As a control, cells were treated with an appropriate isotype control. Clumping cells mimicking polyploidy were excluded from the analysis by appropriate gating strategies. The resulting histogram plot shows the DNA content of VEGFR-3 ϩ cells. Dot plots of the DNA content of the cells were used for the quantification of VEGFR-3 ϩ and isotype-treated cells within different ploidy classes or cell cycle stages, respectively (a detailed scheme of the gating strategy is provided in supplementa

Elevated expression of VEGFR-3 in lymphatic endothelial cells from lymphangiomas

<p>Abstract</p> <p>Background</p> <p>Lymphangiomas are neoplasias of childhood. Their etiology is unknown and a causal therapy does not exist. The recent discovery of highly specific markers for lymphatic endothelial cells (LECs) has permitted their isolation and characterization, but expression levels and stability of molecular markers on LECs from healthy and lymphangioma tissues have not been studied yet. We addressed this problem by profiling LECs from normal dermis and two children suffering from lymphangioma, and also compared them with blood endothelial cells (BECs) from umbilical vein, aorta and myometrial microvessels.</p> <p>Methods</p> <p>Lymphangioma tissue samples were obtained from two young patients suffering from lymphangioma in the axillary and upper arm region. Initially isolated with anti-CD31 (PECAM-1) antibodies, the cells were separated by FACS sorting and magnetic beads using anti-podoplanin and/or LYVE-1 antibodies. Characterization was performed by FACS analysis, immunofluorescence staining, ELISA and micro-array gene analysis.</p> <p>Results</p> <p>LECs from foreskin and lymphangioma had an almost identical pattern of lymphendothelial markers such as podoplanin, Prox1, reelin, cMaf and integrin-α1 and -α9. However, LYVE-1 was down-regulated and VEGFR-2 and R-3 were up-regulated in lymphangiomas. Prox1 was constantly expressed in LECs but not in any of the BECs.</p> <p>Conclusion</p> <p>LECs from different sources express slightly variable molecular markers, but can always be distinguished from BECs by their Prox1 expression. High levels of VEGFR-3 and -2 seem to contribute to the etiology of lymphangiomas.</p

DNA methylation regulates expression of VEGF-R2 (KDR) and VEGF-R3 (FLT4)

Abstract Background Vascular Endothelial Growth Factors (VEGFs) and their receptors (VEGF-Rs) are important regulators for angiogenesis and lymphangiogenesis. VEGFs and VEGF-Rs are not only expressed on endothelial cells but also on various subtypes of solid tumors and leukemias contributing to the growth of the malignant cells. This study was performed to examine whether VEGF-R2 (KDR) and VEGF-R3 (FLT4) are regulated by DNA methylation. Methods Real-time (RT) PCR analysis was performed to quantify KDR and FLT4 expression in some ninety leukemia/lymphoma cell lines, human umbilical vein endothelial cells (HUVECs) and dermal microvascular endothelial cells (HDMECs). Western blot analyses and flow cytometric analyses confirmed results at the protein level. After bisulfite conversion of DNA we determined the methylation status of KDR and FLT4 by DNA sequencing and by methylation specific PCR (MSP). Western blot analyses were performed to examine the effect of VEGF-C on p42/44 MAPK activation. Results Expression of KDR and FLT4 was observed in cell lines from various leukemic entities, but not in lymphoma cell lines: 16% (10/62) of the leukemia cell lines expressed KDR, 42% (27/65) were FLT4 positive. None of thirty cell lines representing six lymphoma subtypes showed more than marginal expression of KDR or FLT4. Western blot analyses confirmed KDR and FLT4 protein expression in HDMECs, HUVECs and in cell lines with high VEGF-R mRNA levels. Mature VEGF-C induced p42/44 MAPK activation in the KDR- /FLT4+ cell line OCI-AML1 verifying the model character of this cell line for VEGF-C signal transduction studies. Bisulfite sequencing and MSP revealed that GpG islands in the promoter regions of KDR and FLT4 were unmethylated in HUVECs, HDMECs and KDR + and FLT4 + cell lines, whereas methylated cell lines did not express these genes. In hypermethylated cell lines, KDR and FLT4 were re-inducible by treatment with the DNA demethylating agent 5-Aza-2'deoxycytidine, confirming epigenetic regulation of both genes. Conclusions Our data show that VEGF-Rs KDR and FLT4 are silenced by DNA methylation. However, if the promoters are unmethylated, other factors (e.g. transactivation factors) determine the extent of KDR and FLT4 expression

Cortactin deficiency is associated with reduced neutrophil recruitment but increased vascular permeability in vivo

Cortactin is required for endothelial barrier function and leukocyte recruitment in vivo