Compartmentalized ocular lymphatic system mediates eye-brain immunity

The eye, an anatomical extension of the central nervous system (CNS), exhibits many molecular and cellular parallels to the brain. Emerging research demonstrates that changes in the brain are often reflected in the eye, particularly in the retina1. Still, the possibility of an immunological nexus between the posterior eye and the rest of the CNS tissues remains unexplored. Here, studying immune responses to herpes simplex virus in the brain, we observed that intravitreal immunization protects mice against intracranial viral challenge. This protection extended to bacteria and even tumours, allowing therapeutic immune responses against glioblastoma through intravitreal immunization. We further show that the anterior and posterior compartments of the eye have distinct lymphatic drainage systems, with the latter draining to the deep cervical lymph nodes through lymphatic vasculature in the optic nerve sheath. This posterior lymphatic drainage, like that of meningeal lymphatics, could be modulated by the lymphatic stimulator VEGFC. Conversely, we show that inhibition of lymphatic signalling on the optic nerve could overcome a major limitation in gene therapy by diminishing the immune response to adeno-associated virus and ensuring continued efficacy after multiple doses. These results reveal a shared lymphatic circuit able to mount a unified immune response between the posterior eye and the brain, highlighting an understudied immunological feature of the eye and opening up the potential for new therapeutic strategies in ocular and CNS diseases.

Human mesenchymal stem cells derived from adipose tissue showed a more robust effect than those from the umbilical cord in promoting corneal graft survival by suppressing lymphangiogenesis

BACKGROUND

Mesenchymal stem cells (MSCs) have shown promising potential in allograft survival. However, few reports have focused on comparing the immunosuppressive capacity of MSCs from different sources and administered via different routes in inhibiting transplant rejection. Moreover, virtually nothing is known about the role of MSCs in the regulation of graft neovascularization and lymphangiogenesis. In this study, we compared the efficacy of human adipose MSCs (hAD-MSCs) and human umbilical cord MSCs (hUC-MSCs) in vitro and in corneal transplantation models to explore the underlying molecular mechanisms and provide a powerful strategy for future clinical applications.

METHODS

hAD-MSCs and hUC-MSCs were generated, and their self-renewal and multi-differentiation abilities were evaluated. The inhibitory effect of human MSCs (hMSCs) was examined by T-cell proliferation assays with or without transwell in vitro. Two MSCs from different sources were separately adoptively transferred in mice corneal transplantation (5 × 105 or 1 × 106/mouse) via topical subconjunctival or intravenous (IV) routes. Allograft survival was evaluated every other day, and angiogenesis and lymphomagenesis were quantitatively analyzed by immunofluorescence staining. The RNA expression profiles of hMSCs were revealed by RNA sequencing (RNA-seq) and verified by quantitative real-time PCR (qRT‒PCR), western blotting or ELISA. The function of the differentially expressed gene FAS was verified by a T-cell apoptosis assay.

RESULTS

hAD-MSCs induced stronger immunosuppression in vitro than hUC-MSCs. The inhibitory effect of hUC-MSCs but not hAD-MSCs was mediated by cell-cell contact-dependent mechanisms. Systemic administration of a lower dose of hAD-MSCs showed better performance in prolonging corneal allograft survival than hUC-MSCs, while subconjunctival administration of hMSCs was safer and further prolonged corneal allograft survival. Both types of hMSCs could inhibit corneal neovascularization, while hAD-MSCs showed greater superiority in suppressing graft lymphangiogenesis. RNA-seq analysis and confirmation experiments revealed the superior performance of hAD-MSCs in allografts based on the lower expression of vascular endothelial growth factor C (VEGF-C) and higher expression of FAS.

CONCLUSIONS

The remarkable inhibitory effects on angiogenesis/lymphangiogenesis and immunological transplantation effects support the development of hAD-MSCs as a cell therapy against corneal transplant rejection. Topical administration of hMSCs was a safer and more effective route for application than systemic administration.

Inhibition of PFKFB3 Expression Stimulates Macrophage-Mediated Lymphangiogenesis Post-Acute Myocardial Infarction

BACKGROUND

The dilation of lymphatic vessels plays a critical role in maintaining heart function, while a lack thereof could contribute to heart failure (HF), and subsequently to an acute myocardial infarction (AMI). Macrophages participate in the induction of lymphangiogenesis by secreting vascular endothelial cell growth factor C (VEGF-C), although the precise mechanism remains unclear.

METHODS

Intramyocardial injections of adeno-associated viruses (AAV9) to inhibit the expression of VEGFR3 (VEGFR3 shRNA) or promote the expression of VEGFR3 (VEGFR3 ORF) in the heart; Myh6-mCherry B6 D2-tg mice and flow cytometry were used to evaluate the number of myocellular debris in the mediastinal lymph nodes; fluorescence staining and qPCR were used to evaluate fluorescence analysis; seahorse experiment was used to evaluate the level of glycolysis of macrophages; Lyz2𝐶𝑟𝑒, VEGFCfl/fl, and PFKFB3fl/fl mice were used as a model to knock out the expression of VEGF-C and PFKFB3 in macrophages.

RESULTS

The escalation of VEGFR3 in cardiac tissue can facilitate the drainage of myocardial debris to the mediastinal lymph nodes, thereby improving cardiac function and reducing fibrosis after reperfusion injury. Conversely, myeloid VEGF-C deficiency displayed an increase in macrophage counts and inflammation levels following reperfusion injury. The inhibition of the critical enzyme PFKFB3 in macrophage glycolysis can stimulate the manifestation of VEGF-C in macrophages. A deficiency in myeloid PFKFB3 is associated with induced lymphangiogenesis following reperfusion injury.

CONCLUSIONS

Our initial investigations suggest that the suppression of PFKFB3 expression in macrophages could potentially stimulate the production of VEGF-C in these immune cells, which in turn may facilitate lymphangiogenesis and mitigate the inflammatory effects of I/R injury.

The Effect of Lymphangiogenesis in Transplant Arteriosclerosis

BACKGROUND

Transplant arteriosclerosis is a major complication in long-term survivors of heart transplantation. Increased lymph flow from donor heart to host lymph nodes has been reported to play a role in transplant arteriosclerosis, but how lymphangiogenesis affects this process is unknown.

METHODS

Vascular allografts were transplanted among various combinations of mice, including wild-type, Lyve1-CreERT2;R26-tdTomato, CAG-Cre-tdTomato, severe combined immune deficiency, Ccr2KO, Foxn1KO, and lghm/lghdKO mice. Whole-mount staining and 3-dimensional reconstruction identified lymphatic vessels within the grafted arteries. Lineage tracing strategies delineated the cellular origin of lymphatic endothelial cells. Adeno-associated viral vectors and a selective inhibitor were used to regulate lymphangiogenesis.

RESULTS

Lymphangiogenesis within allograft vessels began at the anastomotic sites and extended from preexisting lymphatic vessels in the host. Tertiary lymphatic organs were identified in transplanted arteries at the anastomotic site and lymphatic vessels expressing CCL21 (chemokine [C-C motif] ligand 21) were associated with these immune structures. Fibroblasts in the vascular allografts released VEGF-C (vascular endothelial growth factor C), which stimulated lymphangiogenesis into the grafts. Inhibition of VEGF-C signaling inhibited lymphangiogenesis, neointima formation, and adventitial fibrosis of vascular allografts. These studies identified VEGF-C released from fibroblasts as a signal stimulating lymphangiogenesis extending from the host into the vascular allografts.

CONCLUSIONS

Formation of lymphatic vessels plays a key role in the immune response to vascular transplantation. The inhibition of lymphangiogenesis may be a novel approach to prevent transplant arteriosclerosis.

The binding of kaempferol-3-O-rutinoside to vascular endothelial growth factor potentiates anti-inflammatory efficiencies in lipopolysaccharide-treated mouse macrophage RAW264.7 cells

BACKGROUND

Vascular Endothelial Growth Factors (VEGFs) are a group of growth factor in regulating development and maintenance of blood capillary. The VEGF family members include VEGF-A, placenta growth factor (PGF), VEGF-B, VEGF-C and VEGF-D. VEGF receptor activation leads to multiple complex signaling pathways, particularly in inducing angiogenesis. Besides, VEGF is produced by macrophages and T cells, which is playing roles in inflammation. In macrophages, VEGF receptor-3 (VEGFR-3) and its ligand VEGF-C are known to attenuate the release of pro-inflammatory cytokines.

METHODS

Immunoprecipitation and molecular docking assays showed the binding interaction of kaempferol-3-O-rutinoside and VEGF-C. Western blotting and qRT-PCR methods were applied to explore the potentiating effect of kaempferol-3-O-rutinoside in VEGF-C-mediated expressions of proteins and genes in endothelial cells and LPS-induced macrophages. Enzyme-linked immunosorbent assay (ELISA) was employed to reveal the release of proinflammatory cytokines in LPS-induced macrophages. Immunofluorescence assay was performed to determine the effect of kaempferol-3-O-rutinoside in regulating nuclear translocation of NF-κB p65 subunit in the VEGF-C-treated cultures. In addition, Transwell® motility assay was applied to detect the ability of cell migration after drug treatment in LPS-induced macrophages.

RESULTS

We identified kaempferol-3-O-rutinoside, a flavonoid commonly found in vegetable and fruit, was able to act on cultured macrophages in inhibiting inflammatory response, and the inhibition was mediated by its specific binding to VEGF-C. The kaempferol-3-O-rutinoside-bound VEGF-C showed high potency to trigger the receptor activation. In LPS-treated cultured macrophages, applied kaempferol-3-O-rutinoside potentiated inhibitory effects of exogenous applied VEGF-C on the secretions of pro-inflammatory cytokines, i.e. IL-6 and TNF-α, as well as expressions of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). This inhibition was in parallel to transcription and translocation of NF-κB. Moreover, the binding of kaempferol-3-O-rutinoside with VEGF-C suppressed the LPS-induced migration of macrophage.

CONCLUSION

Taken together, our results suggested the pharmacological roles of kaempferol-3-O-rutinoside in VEGF-C-mediated anti-inflammation.

Lymphangiogenic therapy prevents cardiac dysfunction by ameliorating inflammation and hypertension

The lymphatic vasculature is involved in the pathogenesis of acute cardiac injuries, but little is known about its role in chronic cardiac dysfunction. Here, we demonstrate that angiotensin II infusion induced cardiac inflammation and fibrosis at 1 week and caused cardiac dysfunction and impaired lymphatic transport at 6 weeks in mice, while co-administration of VEGFCc156s improved these parameters. To identify novel mechanisms underlying this protection, RNA sequencing analysis in distinct cell populations revealed that VEGFCc156s specifically modulated angiotensin II-induced inflammatory responses in cardiac and peripheral lymphatic endothelial cells. Furthermore, telemetry studies showed that while angiotensin II increased blood pressure acutely in all animals, VEGFCc156s-treated animals displayed a delayed systemic reduction in blood pressure independent of alterations in angiotensin II-mediated aortic stiffness. Overall, these results demonstrate that VEGFCc156s had a multifaceted therapeutic effect to prevent angiotensin II-induced cardiac dysfunction by improving cardiac lymphatic function, alleviating fibrosis and inflammation, and ameliorating hypertension.

Functional Nanocomplexes with Vascular Endothelial Growth Factor A/C Isoforms Improve Collateral Circulation and Cardiac Function

Protein-based therapies are potential treatments for cancer, immunological, and cardiovascular diseases. However, effective delivery systems are needed because of their instability, immunogenicity, and so on. Crosslinked negatively charged heparin polysaccharide nanoparticle (HepNP) is proposed for protein delivery. HepNP can efficiently condense vascular endothelial growth factor (VEGF) because of the unique electronegative sulfonic acid and carboxyl domain of heparin. HepNP is then assembled with VEGF-C (Hep@VEGF-C) or VEGF-A (Hep@VEGF-A) protein for the therapy of myocardial infarction (MI) via intravenous (iv) injection. Hep@VEGF-A-mediated improvement of cardiac function by promoting angiogenesis is limited because of elevated vascular permeability, while Hep@VEGF-C effectively promotes lymphangiogenesis and reduces edema. On this basis, a graded delivery of VEGF-C (0.5-1 h post-MI) and VEGF-A (5 d post-MI) using HepNP is developed. At the dose ratio of 3:1 (Hep@VEGF-C vs Hep@VEGF-A), Hep@VEGF functional complexes substantially reduce the scar formation (≈-39%; p < 0.05) and improve cardiac function (≈+74%; p < 0.05). Such a HepNP delivery system provides a simple and effective therapeutic strategy for cardiovascular diseases by delivering functional proteins. Because of the unique binding ability of heparin with cytokines and growth factors, HepNP also has considerable application prospects in protein therapy for other serious diseases.

Antibody-mediated delivery of VEGF-C potently reduces chronic skin inflammation

VEGF-C is an important mediator of lymphangiogenesis and has been shown to alleviate chronic inflammation in a variety of disease models. In this study, we investigated whether targeted delivery of VEGF-C to sites of inflammation and site-specific activation of lymphatic vessels would represent a clinically feasible strategy for treating chronic skin inflammation. To this end, we generated a fusion protein consisting of human VEGF-C fused to the F8 antibody (F8-VEGF-C), which is specific for the alternatively spliced, angiogenesis-marking extradomain A (EDA) of fibronectin. In two mouse models of psoriasis-like skin inflammation, mediated by transgenic VEGF-A overexpression or repeated application of imiquimod, intravenous treatment with F8-VEGF-C but not with untargeted VEGF-C significantly reduced ear skin edema and was as effective as the clinically used TNF-α receptor-Fc fusion protein (TNFR-Fc). Treatment with F8-VEGF-C led to a marked expansion of lymphatic vessels in the inflamed skin and significantly improved lymphatic drainage function. At the same time, treatment with F8-VEGF-C significantly reduced leukocyte numbers, including CD4+ and γδ T cells. In sum, our results reveal that targeted delivery of VEGF-C and site-specific induction of lymphatic vessels represent a potentially new and promising approach for the treatment of chronic inflammatory diseases.

Vascular endothelial growth factor C promotes cervical cancer cell invasiveness via regulation of microRNA-326/cortactin expression

Vascular endothelial growth factor C (VEGF-C) accelerates cervical cancer metastasis, while the detailed mechanism remains largely unknown. Recent evidence indicates that microRNA play a crucial role in controlling cancer cell invasiveness. In the present study, we investigated the role of miR-326 in VEGF-C-induced cervical cancer cell invasion. VEGF-C expression was higher and miR-326 was much lower in primary cervical cancer specimens than that in non-cancerous specimens, and a negative correlation between VEGF-C and miR-326 was found. On cervical carcinoma cell line SiHa cells, treatment with VEGF-C downregulated miR-326 level and increased cortactin protein expression. Transfection with miR-326 mimic reversed cortactin expression induced by VEGF-C, suggesting that VEGF-C increased cortactin via downregulation of miR-326. VEGF-C activated c-Src and c-Src inhibitor PP2 abolished VEGF-C effect on miR-326 and cortactin expression, implying that VEGF-C regulated miR-326/cortactin via c-Src signaling. VEGF-C promoted SiHa cell invasion index, which was largely inhibited by transfection with miR-326 antagonist or by siRNA against cortactin. In conclusion, our findings implied that VEGF-C reduced miR-326 expression and increased cortactin expression through c-Src signaling, leading to enhanced cervical cancer invasiveness. This may shed light on potential therapeutic strategies for cervical cancer therapy.

Pannexin-1 in Human Lymphatic Endothelial Cells Regulates Lymphangiogenesis

The molecular mechanisms governing the formation of lymphatic vasculature are not yet well understood. Pannexins are transmembrane proteins that form channels which allow for diffusion of ions and small molecules (<1 kDa) between the extracellular space and the cytosol. The expression and function of pannexins in blood vessels have been studied in the last few decades. Meanwhile, no studies have been conducted to evaluate the role of pannexins during human lymphatic vessel formation. Here we show, using primary human dermal lymphatic endothelial cells (HDLECs), pharmacological tools (probenecid, Brilliant Blue FCF, mimetic peptides [¹⁰Panx]) and siRNA-mediated knockdown that Pannexin-1 is necessary for capillary tube formation on Matrigel and for VEGF-C-induced invasion. These results newly identify Pannexin-1 as a protein highly expressed in HDLECs and its requirement during in vitro lymphangiogenesis.

Antitumor and Antimetastatic Activity of Synthetic Hydroxystilbenes Through Inhibition of Lymphangiogenesis and M2 Macrophage Differentiation of Tumor-associated Macrophages

An increase in tumor-associated macrophages (TAMs) around the tumor microenvironment has been closely associated with a poor prognosis in patients with cancer, and M2 TAMs promote tumor growth and tumor metastasis by stimulating angiogenesis or lymphangiogenesis in tumors. We herein examined the effects of nine synthetic hydroxystilbenes on M2 macrophage activation and differentiation, and three selected dihydroxystilbenes on vascular endothelial cell growth factor (VEGF)-C-induced tube formation in human lymphatic endothelial cells (HLECs) (in vitro). We also investigated the antitumor and antimetastatic effects of three synthetic dihydroxystilbenes in LM8-bearing mice in vivo. The three selected synthetic stilbenes (at concentrations of 5, 10, 25, and 50 μM) inhibited the production of interleukin-10 and monocyte chemoattractant protein-1 in M2 macrophages, but promoted that of transforming growth factor-β1. The three dihydroxystilbenes (at concentrations of 10-50 μM) inhibited the phosphorylation of signal transducer and activator of transcript 3 without affecting its expression in the differentiation of M2 macrophages. Furthermore, the 2,3- and 4,4'-dihydroxystilbene inhibited VEGF-C-induced lymphangiogenesis in HLECs. Both 2,3- and 4,4'-dihydroxystilbene (at 10 and 25 mg/kg, twice daily) inhibited tumor growth and metastasis to the lung in mice. These results suggested that the antitumor and antimetastatic effects of 2,3- and 4,4'-dihydroxystilbene were partly due to anti-lymphangiogenesis, and the regulation of M2 macrophage activation and differentiation.

Therapeutic lymphangiogenesis ameliorates established acute lung allograft rejection

Lung transplantation is the only viable option for patients suffering from otherwise incurable end-stage pulmonary diseases such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. Despite aggressive immunosuppression, acute rejection of the lung allograft occurs in over half of transplant recipients, and the factors that promote lung acceptance are poorly understood. The contribution of lymphatic vessels to transplant pathophysiology remains controversial, and data that directly address the exact roles of lymphatic vessels in lung allograft function and survival are limited. Here, we have shown that there is a marked decline in the density of lymphatic vessels, accompanied by accumulation of low-MW hyaluronan (HA) in mouse orthotopic allografts undergoing rejection. We found that stimulation of lymphangiogenesis with VEGF-C156S, a mutant form of VEGF-C with selective VEGFR-3 binding, alleviates an established rejection response and improves clearance of HA from the lung allograft. Longitudinal analysis of transbronchial biopsies from human lung transplant recipients demonstrated an association between resolution of acute lung rejection and decreased HA in the graft tissue. Taken together, these results indicate that lymphatic vessel formation after lung transplantation mediates HA drainage and suggest that treatments to stimulate lymphangiogenesis have promise for improving graft outcomes.

The indolinone MAZ51 induces cell rounding and G2/M cell cycle arrest in glioma cells without the inhibition of VEGFR-3 phosphorylation: involvement of the RhoA and Akt/GSK3β signaling pathways

MAZ51 is an indolinone-based molecule originally synthesized as a selective inhibitor of vascular endothelial growth factor receptor (VEGFR)-3 tyrosine kinase. This study shows that exposure of two glioma cell lines, rat C6 and human U251MG, to MAZ51 caused dramatic shape changes, including the retraction of cellular protrusions and cell rounding. These changes were caused by the clustering and aggregation of actin filaments and microtubules. MAZ51 also induced G2/M phase cell cycle arrest. This led to an inhibition of cellular proliferation, without triggering significant cell death. These alterations induced by MAZ51 occurred with similar dose- and time-dependent patterns. Treatment of glioma cells with MAZ51 resulted in increased levels of phosphorylated GSK3β through the activation of Akt, as well as increased levels of active RhoA. Interestingly, MAZ51 did not affect the morphology and cell cycle patterns of rat primary cortical astrocytes, suggesting it selectively targeted transformed cells. Immunoprecipitation–western blot analyses indicated that MAZ51 did not decrease, but rather increased, tyrosine phosphorylation of VEGFR-3. To confirm this unanticipated result, several additional experiments were conducted. Enhancing VEGFR-3 phosphorylation by treatment of glioma cells with VEGF-C affected neither cytoskeleton arrangements nor cell cycle patterns. In addition, the knockdown of VEGFR-3 in glioma cells did not cause morphological or cytoskeletal alterations. Furthermore, treatment of VEGFR-3-silenced cells with MAZ51 caused the same alterations of cell shape and cytoskeletal arrangements as that observed in control cells. These data indicate that MAZ51 causes cytoskeletal alterations and G2/M cell cycle arrest in glioma cells. These effects are mediated through phosphorylation of Akt/GSK3β and activation of RhoA. The anti-proliferative activity of MAZ51 does not require the inhibition of VEGFR-3 phosphorylation, suggesting that it is a potential candidate for further clinical investigation for treatment of gliomas, although the precise mechanism(s) underlying its effects remain to be determined.

Vascular endothelial growth factor-C enhances radiosensitivity of lymphatic endothelial cells

Radiation therapy after lymph node dissection increases the risk of developing painful and incurable lymphedema in breast cancer patients. Lymphedema occurs when lymphatic vessels become unable to maintain proper fluid balance. The sensitivity of lymphatic endothelial cells (LECs) to ionizing radiation has not been reported to date. Here, the radiosensitivity of LECs in vitro has been determined using clonogenic survival assays. The ability of various growth factors to alter LEC radiosensitivity was also examined. Vascular endothelial growth factor (VEGF)-C enhanced radiosensitivity when LECs were treated prior to radiation. VEGF-C-treated LECs exhibited higher levels of entry into the cell cycle at the time of radiation, with a greater number of cells in the S and G2/M phases. These LECs showed higher levels of γH2A.X-an indicator of DNA damage-after radiation. VEGF-C did not increase cell death as a result of radiation. Instead, it increased the relative number of quiescent LECs. These data suggest that abundant VEGF-C or lymphangiogenesis may predispose patients to radiation-induced lymphedema by impairing lymphatic vessel repair through induction of LEC quiescence.

Vascular endothelial growth factor C enhances cervical cancer migration and invasion via activation of focal adhesion kinase

Vascular endothelial growth factor C (VEGF-C) is correlated positively with clinical cervical cancer metastasis and survival. Previously we showed that VEGF-C directly activated actin-binding protein moesin, leading to the formation of membrane protrusions. However, whether VEGF-C alters cervical cancer cell adhesion to the extra-cellular matrix is currently unknown. In this study, we investigated the effects of VEGF-C on the formation of focal adhesion complexes, which provide anchoring sites for cell attachment to the extracellular matrix. On cultured cervical carcinoma cell line SiHa cells, VEGF-C enhanced focal adhesion kinase (FAK) phosphorylation. As a result, VEGF-C led to increased formation of focal adhesion complexes and enhanced migration and invasion, which was reversed by siRNA abrogating FAK. VEGF-C resulted in increased interaction of its receptor Flt-4 with non-receptor tyrosine kinase c-Src, leading to c-Src phosphorylation. The specific inhibitor of c-Src kinase, PP2, or the transfection with specific c-Src siRNA largely impaired VEGF-C-enhanced FAK phosphorylation, suggesting that Flt-4/c-Src cascade plays a central role in these processes. These results implied that VEGF-C promotes cervical cancer metastasis by activation of FAK protein through Flt-4/c-Src pathway.

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.

Monocytes can be induced to express lymphatic phenotypes

Although it has been recently shown that monocytes can transdifferentiate into blood vascular endothelial cells which are involved in angiogenesis, little attention has been paid to their potential to transdifferentiate into lymphatic endothelial cells. Therefore, we examined this question in our study. We first stimulated monocytes with either fibronectin (FN), VEGF-C, TNF-alpha, LPS, or IL-3 for 24h. Then we examined the expression of several markers of lymphatic endothelium and found that the monocytes expressed specific lymphatic endothelial markers, LYVE-1, Podoplanin, and Prox-1, but not common endothelial markers vWF or eNOS. Next, monocytes were incubated in endothelial growth medium with FN and VEGF-C for 6d. These monocytes were also found to express LYVE-1, Podoplanin and Prox-1, but not vWF or eNOS. Our results indicate that monocytes in vitro can be easily induced to present lymphatic phenotypes in an inflammatory environment.

Low molecular weight heparin suppresses lymphatic endothelial cell proliferation induced by vascular endothelial growth factor C in vitro

BACKGROUND

Pancreatic cancer is one of the most aggressive human malignancies. Lymphangiogenesis plays an important role in lymph node metastasis of many solid tumors. It is well known that low molecular weight heparins (LMWHs) can inhibit cell growth, cell invasion and angiogenesis, which are key processes in tumor progression.

METHODS

We measured the expression of vascular endothelial growth factor C (VEGF-C) in pancreatic cancer cells (PANC-1) using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. We used an in vitro assay to evaluate the anti-lymphangiogenic effect of an LMWH, Fragmin, on human lymphatic endothelial cell (HLEC) proliferation.

RESULTS

Fragmin at a low concentration can effectively inhibits HLEC proliferation induced by VEGF-C. VEGF-C secreted by PANC-1 cells stimulated HLEC proliferation. Low concentration LMWH suppressed HLEC proliferation induced by VEGF-C but did not affect proliferation or VEGF-C expression of PANC-1 cells, whereas high concentrations of LMWH inhibited PANC-1 cell proliferation.

CONCLUSIONS

These results suggest that VEGF-C released by cancer cells plays an important role in promoting HLEC proliferation. The LMWH Fragmin has anti-lymphangiogenic effects and may inhibit lymphatic metastasis in pancreatic cancer.

Hepatitis B x antigen up-regulates vascular endothelial growth factor receptor 3 in hepatocarcinogenesis

Hepatitis B x antigen (HBxAg) is a trans-activating protein that contributes to liver cancer, in part, by altering the expression of cellular genes. However, few natural effectors of HBxAg have been identified. Hence, HBxAg positive and negative HepG2 cells were prepared and analyzed by PCR select cDNA subtraction. The results identified elevated vascular endothelial growth factor receptor-3 short form splice variant (VEGFR-3(S)) expression in HBxAg positive compared to negative cells. Normally, VEGFR-3 activates Akt signaling in lymphatic endothelial cells, resulting in lymphangiogenesis. In contrast, the results here show that the expression of VEGFR-3(S) is up-regulated in >75% of HBxAg positive hepatocellular carcinoma (HCC) nodules. VEGFR-3(S) up-regulation correlates with the expression of HBxAg, is associated with decreased survival in tumor bearing patients, and when over-expressed in HepG2 cells, strongly stimulated cell growth in culture, in soft agar, and accelerated tumor formation in a ligand independent manner. VEGFR-3(S) siRNA partially blocked the ability of HBxAg to promote hepatocellular growth. In conclusion, HBxAg may short circuit VEGFR-3(S) signaling in liver cancer. Blocking VEGFR-3(S) signaling may be effective in preventing tumor development and/or prolonging survival in tumor bearing patients.

Distinct Architecture of Lymphatic Vessels Induced by Chimeric Vascular Endothelial Growth Factor-C/Vascular Endothelial Growth Factor Heparin-Binding Domain Fusion Proteins

Vascular endothelial growth factor (VEGF)-C and VEGF-D are composed of the receptor-binding VEGF homology domain and a carboxy-terminal silk homology domain that requires proteolytic cleavage for growth factor activation. Here, we explored whether the C-terminal heparin-binding domain of the VEGF 165 or VEGF 189 isoform also containing neuropilin-binding sequences could substitute for the silk homology domain of VEGF-C. Such VEGF-C/VEGF–heparin-binding domain chimeras were produced and shown to activate VEGF-C receptors, and, when expressed in tissues via adenovirus or adeno-associated virus vectors, stimulated lymphangiogenesis in vivo. However, both chimeras induced a distinctly different pattern of lymphatic vessels when compared with VEGF-C. Whereas VEGF-C–induced vessels were initially a dense network of small diameter vessels, the lymphatic vessels induced by the chimeric growth factors tended to form directly along tissue borders, along basement membranes that are rich in heparan sulfate. For example, in skeletal muscle, the chimeras induced formation of lumenized lymphatic vessels more efficiently than wild-type VEGF-C. We conclude that the matrix-binding domain of VEGF can target VEGF-C activity to heparin-rich basement membrane structures. These properties may prove useful for tissue engineering and attempts to regenerate lymphatic vessels in lymphedema patients.

Enhanced capillary formation stimulated by a chimeric vascular endothelial growth factor/vascular endothelial growth factor-C silk domain fusion protein

Vascular endothelial growth factor (VEGF)-C and VEGF-D require proteolytic cleavage of the carboxy terminal silk-homology domain for activation. To study the functions of the VEGF-C propeptides, we engineered a chimeric growth factor protein, VEGF-CAC, composed of the amino- and carboxy-terminal propeptides of VEGF-C fused to the receptor-activating core domain of VEGF. Like VEGF-C, VEGF-CAC underwent proteolytic cleavage, and like VEGF, it bound to and activated VEGF receptor-1 and VEGF receptor-2, but not the VEGF-C receptor VEGF receptor-3. VEGF-CAC also bound to neuropilins in a heparin-dependent manner. Strikingly, when VEGF-CAC was expressed via an adenovirus vector in the ear skin of immunodeficient mice, it proved to be a more potent inducer of capillary angiogenesis than VEGF. The VEGF-CAC-induced vessels differed greatly from those induced by VEGF, as they formed a very dense and fine network of pericyte and basement membrane-covered capillaries that were functional, as shown by lectin perfusion experiments. VEGF-CAC could prove useful in proangiogenic therapies in patients experiencing tissue ischemia.

Vascular endothelial growth factor-C secreted by pancreatic cancer cell line promotes lymphatic endothelial cell migration in an in vitro model of tumor lymphangiogenesis

OBJECTIVES

To investigate mechanisms underlying lymphatic node metastasis in pancreatic cancer, we examined roles of vascular endothelial growth factor-C (VEGF-C) in tumor lymphangiogenesis.

METHODS

We measured VEGF-C secretion by pancreatic cancer cell lines using enzyme-linked immunosorbent assay and examined effects of different cell lines on lymphatic endothelial cells (LECs) in vitro.

RESULTS

We identified VEGF-C high-secretion (MIA PaCa-2) and low-secretion cell lines (BxPC-3). The trend of enhancement of LEC proliferation by recombinant human VEGF-C (rVEGF-C) was not statistically significant. Numbers of migrating cells were increased by rVEGF-C treatment in a dose-dependent manner. The MIA PaCa-2 cell culture supernatant caused greater LEC migration than the BxPC-3 supernatant. The VEGF-C effects were significantly inhibited by rVEGF receptor 3 (rVEGF R3)/Fc chimera. In LEC/fibroblast coculture on collagen gel, LEC capillary formation was significantly enhanced by coculture with MIA PaCa-2 cells compared with BxPC-3 cells. Enhanced capillary formation with MIA PaCa-2 cells was inhibited by rVEGF R3/Fc chimera, implying VEGF-C involvement in progression of LEC sprouting in a tumor microenvironment.

CONCLUSIONS

Because VEGF-C secreted by pancreatic cancer cells plays an important role in LEC migration in pancreatic cancer lymphangiogenesis, it is possible that rVEGF R3/Fc chimera might have a role in controlling lymph node metastasis.

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.

[Sorting of lymphatic endothelial progenitor cells from canine peripheral blood and their differentiation induction towards endothelial cells]

OBJECTIVE

To investigate the biological properties of CD34+/CD133 +/VEGFR-3 + lymphatic endothelial progenitor cells in peripheral blood and explore the effects of the VEGF-C/VEGFR-3 signaling pathway on differentiation of lymphatic endothelial progenitor cells to lymphatic endothelial cells.

METHODS

Mononuclear cells were isolated from peripheral blood by density centrifugation with Percoll solution, and VEGFR-3+ cells were sorted from them with flow cytometry. Differentiation of VEGFR-3+ cells was induced with VEGF-C. The morphology and ultrastructures of the cells were observed with scanning and transmission electron microscopes. Expression of surface markers were examined with a confocal laser scanning microscope.

RESULTS

VEGFR-3+ cells expressed CD34 and CD133 antigen. The percentage of CD34+/ VEGFR-3+ and VEGFR-3+/CD133+ cells were 0.13% and 0.08% of peripheral blood MNC respectively. The size of CD34+/CD133+/VEGFR-3+ cells was about 15 microm in the diameter. After induction with VEGFC, they were increased. The cells were shuttle-like in shape and extended the lamellipodia and many filopodia. After 1 week induction with VEGF-C, they expressed coagulation factor VII related antigen, and at 2 week induction, they showed caveolae on the surface and Weibel-Palade body inside the cells. The specific lymphatic endothelial marker LYVE-1 was expressed on the cells, and no longer expressed CD133.

CONCLUSIONS

CD34+/CD133+/VEGFR-3+ lymphatic endothelial progenitor cells from peripheral blood may differentiate into lymphatic endothelial cells. The VEGF-C/VEGFR-3 signaling pathway has important effects on the differentiation of the lymphatic endothelial progenitor cells.

VEGF-C-induced lymphangiogenesis in sentinel lymph nodes promotes tumor metastasis to distant sites

The mechanisms by which tumors metastasize to sentinel and distant lymph nodes, and beyond, are poorly understood. We developed transgenic mice that overexpress vascular endothelial growth factor-C (VEGF-C) and green fluorescent protein specifically in the skin and studied the effects of chemically-induced skin carcinogenesis in this model. We found that in contrast to VEGF-A, VEGF-C does not increase the growth of primary tumors, but instead induces expansion of lymphatic networks within sentinel lymph nodes, even before the onset of metastasis. Once the metastatic cells arrived at the sentinel lymph nodes, the extent of lymphangiogenesis at these sites increased. Of importance, in mice with metastasis-containing sentinel lymph nodes, tumors that expressed VEGF-C were more likely to metastasize to additional organs, such as distal lymph nodes and lungs. No metastases were observed in distant organs in the absence of lymph node metastases. These findings indicate an important role of VEGF-C-induced lymph node lymphangiogenesis in the promotion of cancer metastasis beyond the sentinel lymph nodes. VEGF-C is therefore a good target to slow or even prevent the onset of metastasis.

Tumor-Induced Activation of Lymphatic Endothelial Cells via Vascular Endothelial Growth Factor Receptor-2 Is Critical for Prostate Cancer Lymphatic Metastasis

Prostate cancer disseminates initially and primarily to regional lymph nodes. However, the nature of interactions between tumor cells and lymphatic endothelial cells (LEC) is poorly understood. In the current study, we have isolated prostate LECs and developed a series of two-dimensional and three-dimensional in vitro coculture systems and in vivo orthotopic prostate cancer models to investigate the interactions of prostate cancer cells with prostate LECs. In vitro, highly lymph node metastatic prostate cancer cell lines (PC-3 and LNCaP) and their conditioned medium enhanced prostate LEC tube formation and migration, whereas poorly lymph node metastatic prostate cancer cells (DU145) or normal prostate epithelial cells (RWPE-1) or their conditioned medium had no effect. In vivo, the occurrence of lymphatic invasion and lymph node metastasis was observed in PC-3 and LNCaP xenografts but not in DU145 xenografts. Furthermore, vascular endothelial growth factor (VEGF) receptor (VEGFR)-2 is expressed by prostate LECs, and its ligands VEGF-A, VEGF-C, and VEGF-D are up-regulated in highly lymph node metastatic prostate cancer cells. Recombinant VEGF-A and VEGF-C, but not VEGF-C156S, potently promoted prostate LEC tube formation, migration, and proliferation in vitro, indicating that signaling via VEGFR-2 rather than VEGFR-3 is involved in these responses. Consistent with this, blockade of VEGFR-2 significantly reduced tumor-induced activation of LECs. These results show that the interaction of prostate tumor cells with LECs via VEGFR-2 modulates LEC behavior and is related to the ability of tumor cells to form lymph node metastases.

Apoptosis of human macrophages by Flt-4 signaling: implications for atherosclerotic plaque pathology

BACKGROUND

Neointimal inflammation and angiogenesis are important contributors of progression and destabilization of the atherosclerotic plaque. While the role of vascular endothelial growth factor (VEGF) and its receptors VEGF-R1 (Flt-1) and VEGF-R2 (Flk-1) in this process has clearly been defined, expression of the VEGF-R3 (Flt-4) has only been documented on lymphatic and tumor endothelium. This study examined Flt-4 expression in human atherosclerotic plaque and explored its implications for atherosclerotic disease.

METHODS AND RESULTS

Carotid artery thrombendartherectomy specimens from 10 patients with unstable plaque were stained for Flt-4 and its specific growth factors VEGF-C and VEGF-D. Microvascular endothelial cells (MVEC) stained positive for VEGF-C and -D, but not for Flt-4. Interestingly, macrophages within inflammatory perivascular regions coexpressed Flt-4, VEGF-C and VEGF-D. In vitro studies confirmed the expression of Flt-4, VEGF-C and VEGF-D in human monocytes and cultured macrophages. Treatment of macrophages with VEGF-D induced apoptosis as determined by annexin V staining, by immunoblotting of activated caspase 3, and by the ratio of Bcl-2/Bax as well as by DNA fragmentation. Immunohistochemical studies of advanced human carotid atherosclerotic plaque confirmed the coexpression of Flt-4 with activated caspase 3 and TUNEL staining in macrophages, indicating an ongoing apoptotic process.

CONCLUSION

Human monocytes/macrophages express VEGF-C and -D and their receptor Flt-4 in vitro and in vivo within advanced atherosclerotic lesions. Flt-4, in turn, mediates monocyte/macrophage apoptosis and may this way alter plaque stability.

Differentiation of lymphatic endothelial cells from embryonic stem cells on OP9 stromal cells

OBJECTIVE

The discovery of vascular endothelial growth factor C (VEGF-C) and VEGF receptor-3 (VEGFR-3) has started to provide an understanding of the molecular mechanisms of lymphangiogenesis. The homeobox gene prox1 has been proven to specify lymphatic endothelial cells (ECs) from blood ECs. We investigated the process of lymphatic EC (LEC) differentiation using embryonic stem (ES) cells.

METHODS AND RESULTS

VEGFR-2+ cells derived from ES cells differentiated into LECs at day 3 on OP9 stromal cells defined by the expression of prox1, VEGFR-3, and another lymphatic marker podoplanin. VEGFR-2+ cells gave rise to LYVE-1+ embryonic ECs, which were negative for prox1 on day 1 but turned to prox1+ LECs by day 3. VEGFR-3-Fc or Tie2-Fc, sequestering VEGF-C or angiopoietin1 (Ang1), suppressed colony formation of LECs on OP9 cells. However, addition of VEGF-C and Ang1 in combination with VEGF to the culture of VEGFR-2+ cells on collagen-coated dishes failed to induce LECs. LEC-inducing activity of OP9 cells was fully reproduced on paraformaldehyde-fixed OP9 cells with the conditioned medium.

CONCLUSIONS

We succeeded in differentiating LECs from ES cells and revealed the requirements of VEGF-C, Ang1, and other unknown factors for LEC differentiation.

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.

Early Lymph Vessel Development From Embryonic Stem Cells

Objective— The purpose of this study was to establish a model system for lymph vessel development based on directed differentiation of murine embryonic stem cells.

Methods and Results— Stem cells were aggregated to form embryoid bodies, and subsequently cultured in 3-dimensional collagen matrix for up to 18 days. Treatment with vascular endothelial growth factor (VEGF)-C and VEGF-A individually enhanced formation of lymphatic vessel structures, although combined treatment with VEGF-C and VEGF-A was most potent and gave rise to a network of LYVE-1, podoplanin, Prox1, and VEGF receptor-3 positive lymphatic vessel structures running parallel to and apparently emanating from, capillaries. In contrast, fibroblast growth factor-2, hepatocyte growth factor, or hypoxia had little or no effect on the development of the early lymphatics. Further, cells of hematopoietic origin were shown to express lymphatic markers. In summary, different subpopulations of lymphatic endothelial cells were identified on the basis of differential expression of several lymphatic and blood vessel markers, indicating vascular heterogeneity.

Conclusions— We conclude that the present model closely mimics the early steps of lymph vessel development in mouse embryos.

Neuropilin-2 interacts with VEGFR-2 and VEGFR-3 and promotes human endothelial cell survival and migration

Neuropilin 2 (NRP2) is a receptor for the vascular endothelial growth factor (VEGF) and the semaphorin (SEMA) families, 2 unrelated ligand families involved in angiogenesis and neuronal guidance. NRP2 specifically binds VEGF-A and VEGF-C, although the biological relevance of these interactions in human endothelial cells is poorly understood. In this study, we show that both VEGF-A and VEGF-C induce the interaction of NRP2 with VEGFR-2. This interaction correlated with an enhancement of the VEGFR-2 phosphorylation threshold. Overexpression of NRP2 in primary human endothelial cells promoted cell survival induced by VEGF-A and VEGF-C. In contrast, SEMA3F, another ligand for NRP2, was able to inhibit human endothelial cell survival and migration induced by VEGF-A and VEGF-C. Moreover, a siRNA targeting specifically NRP2 was a potent inhibitor of human endothelial cell migration induced by VEGF-A and VEGF-C. Thus, our data indicate that NRP2 acts as a coreceptor that enhances human endothelial cell biological responses induced by VEGF-A and VEGF-C.

Vascular endothelial growth factor stimulates rat cholangiocyte proliferation via an autocrine mechanism

BACKGROUND & AIMS

Vascular endothelial growth factor (VEGF) is secreted by several epithelia and modulates cellular functions by autocrine and paracrine mechanisms. The role of VEGF in cholangiocyte pathophysiology is unknown. We evaluated the role of VEGF in the regulation of cholangiocyte proliferation in rats that underwent bile duct ligation.

METHODS

The expression of VEGF-A and VEGF-C and their receptors in cholangiocytes from normal and BDL rats was evaluated. Normal or BDL rats were treated with recombinant-VEGF-A or recombinant-VEGF-C or anti-VEGF antibodies, and proliferation of cholangiocytes was evaluated in situ by morphometry and in vitro by proliferating cell nuclear antigen immunoblots and MTS assay. In vitro, normal rat cholangiocyte cultures were stimulated with r-VEGF-A or r-VEGF-C and proliferation and signal transduction were evaluated.

RESULTS

We found that (1) cholangiocytes express messenger RNA and protein for VEGF-A, VEGF-C, VEGF receptor 2 (VEGFR-2), and VEGF receptor 3 (VEGFR-3) and secrete VEGF; (2) secretion of VEGF and expression of VEGFR-2 and VEGFR-3 increases in BDL cholangiocytes; (3) blocking VEGF in vivo by anti-VEGF-A or anti-VEGF-C antibodies decreases cholangiocyte proliferation; (4) the in vivo administration of r-VEGF-A or r-VEGF-C induces cholangiocyte proliferation in normal rats; and (5) in vitro, VEGF-A increases normal rat cholangiocyte culture proliferation by activation of inositol 1,4,5-triphosphate/Ca2+/protein kinase C alpha and phosphorylation of Src/ERK1/2.

CONCLUSIONS

Cholangiocytes secrete VEGF and express VEGFR-2 and VEGFR-3, all of which are amplified in BDL cholangiocytes. VEGF induces cholangiocyte proliferation by activation of inositol 1,4,5-triphosphate/[Ca2+]i/protein kinase C alpha and phosphorylation of Src/ERK1/2. VEGF mediates the adaptive proliferative response of cholangiocytes to cholestasis.

Isolation and characterization of lymphatic microvascular endothelial cells from human tonsils

Human lymphatic endothelial cells (LECs) have isolated prevalently from human derma and tumors. As specialized lymphatic organs within the oropharynx, palatine tonsils are easily obtained and rich in lymphatic venules. Using a two-step purification method based on the sorting of endothelial cells with Ulex Europaeus Agglutinin 1 (UEA-1)-coated beads, followed by purification with monoclonal antibody D2-40, we successfully purified LECs from human palatine tonsils. The LECs were expanded on flasks coated with collagen type 1 and fibronectin for up to 8-10 passages and then analyzed for phenotypic and functional properties. Cultured cells retained the phenotypic pattern of the lymphatic endothelium of palatine tonsils and expressed functional VEGFR-3 molecules. In fact, stimulation with VEGFR-3 ligand, the vascular endothelium grow factor C, induced a marked increase in cell proliferation. Similarly to blood endothelial cells (BECs), LECs were able to form tube-like structure when seeded in Cultrex basement membrane extract. Comparative studies performed on LECs derived from palatine tonsils and iliac lymphatic vessels (ILVs), obtained with the same procedures, showed substantial discrepancies in the expression of various lymphatic markers. This points to the existence of micro- and macrovessel-derived LECs with different phenotypes, possibly involving different biological activities and functions. Palatine tonsil- and ILV-derived LECs may, therefore, represent new models for investigating function and biochemical properties of these lymphatic endothelia.

Vascular endothelial growth factor C promotes lymph node metastasis in a rectal cancer orthotopic model

PURPOSE

Vascular endothelial growth factor C (VEGF-C), a novel member of the vascular endothelial growth factor family, is a relatively specific lymphangiogenic growth factor. It has been suggested that increased expression of VEGF-C in primary tumors is correlated with lymph node metastasis. We conducted this study to determine whether VEGF-C directly affects lymphangiogenesis and lymph node metastasis in colorectal cancer.

METHODS

For an accurate analysis and clear visualization of metastases, the rectal cancer cell line, DLD1, was engineered to stably express green fluorescent protein (GFP) (DLD1/GFP). We implanted DLD1/GFP cells overexpressing VEGF-C orthotopically into the rectal walls of nude mice.

RESULTS

Lymph node metastasis was confirmed in all (100%) of the mice bearing DLD1/GFP-VEGF-C tumors, but in only 25% of the mice bearing control tumors. There were more lymph node metastases per mouse in the mice bearing DLD1/GFP-VEGF-C tumors than in the mice bearing control tumors. There were no differences in cell growth and motility in vitro or in the resulting tumor volume from the implanted cells between the two groups. Immunohistochemical staining revealed that VEGF-C induced the growth of lymphatic vessels, which were enlarged in the tumor periphery and contained tumor cell emboli.

CONCLUSION

These results suggest that VEGF-C-induced lymphangiogenesis mediates tumor spread and the formation of lymph node metastasis.

Roles of vascular endothelial growth factor receptor 3 signaling in differentiation of mouse embryonic stem cell–derived vascular progenitor cells into endothelial cells

Vascular endothelial growth factor receptor 2 (VEGFR2/Flk-1)–positive cells derived from embryonic stem (ES) cells serve as vascular progenitors, which differentiate into endothelial cells (ECs) in the presence of VEGF-A. VEGFR3/Flt-4 (fms-like tyrosine kinase 4) signaling is known to be important for the development of lymphatic endothelial cells (LECs). To elucidate the roles of VEGFR3 signaling in the differentiation of vascular progenitor cells into ECs, we introduced various types of VEGFR3 cDNAs into mouse ES cells. VEGF-C, a ligand for VEGFR2 and VEGFR3, stimulated the endothelial differentiation of the VEGFR2+ cells transfected with the VEGFR3 cDNA but not those transfected with kinasenegative mutants of VEGFR3. The VEGFR3-transfected ECs exhibited high expression levels of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), one of the markers of LECs, and showed efficient binding of hyaluronan. VEGF-C(C152S), which is able to activate VEGFR3 but not VEGFR2, failed to induce the endothelial differentiation of mock- and VEGFR3-transfected VEGFR2+ cells, suggesting the essential role of VEGFR2 signaling for endothelial differentiation. Furthermore, kinase-negative mutants of VEGFR3 prevented the VEGF-C–mediated endothelial differentiation of the vascular progenitor cells. Thus, VEGFR2 signaling is required for the endothelial differentiation of mouse ES cells induced by VEGF-C, and VEGFR3 signaling may confer lymphatic endothelial-like phenotypes to ECs.

Dose-dependent response of FGF-2 for lymphangiogenesis

Spatio-temporal studies on the growth of capillary blood vessels and capillary lymphatic vessels in tissue remodeling have suggested that lymphangiogenesis is angiogenesis-dependent. We revisited this concept by using fibroblast growth factor 2 (FGF-2) (80 ng) to stimulate the growth of both vessel types in the mouse cornea. When we lowered the dose of FGF-2 in the cornea 6.4-fold (12.5 ng), the primary response was lymphangiogenic. Further investigation revealed that vascular endothelial growth factor-C and -D are required for this apparent lymphangiogenic property of FGF-2, and when the small amount of accompanying angiogenesis was completely suppressed, lymphangiogenesis remained unaffected. Our findings demonstrate that there is a dose-dependent response of FGF-2 for lymphangiogenesis, and lymphangiogenesis can occur in the absence of a preexisting or developing vascular bed, i.e., in the absence of angiogenesis, in the mouse cornea.

Involvement of the VEGF receptor 3 in tubular morphogenesis demonstrated with a human anti-human VEGFR-3 monoclonal antibody that antagonizes receptor activation by VEGF-C

In this report we utilize a novel antagonist antibody to the human VEGFR-3 to elucidate the role of this receptor in in vitro tubular morphogenesis of bovine and human endothelial cells (EC cells) induced by VEGF-C. The antibody hF4-3C5 was obtained by panning a human phage display library on soluble human VEGFR-3. The binding affinity constant of hF4-3C5 significantly exceeds that of the interaction of VEGFR-3 with VEGF-C. hF4-3C5 strongly inhibits the binding of soluble VEGFR-3 to immobilized VEGF-C and abolishes the VEGF-C-mediated mitogenic response of cells that expresses a chimeric human VEGFR-3-cFMS receptor. In fluorescence experiments, hF4-3C5 reactivity is observed with human lymphatic endothelial cells (LECs) and human umbilical vein endothelial cells (HUVECs). Binding of hF4-3C5 shows that about half of bovine aortic endothelial (BAE) cells express VEGFR-3 and cells in this subpopulation are primarily responsible for the chemotactic response to the mature form of VEGF-C (VEGF-C(DeltaNDeltaC)). This response was strongly inhibited by the addition of hF4-3C5. In vitro tube formation by BAE cells induced by VEGF-C(DeltaNDeltaC) was reduced by greater than 60% by hF4-3C5 whereas the response to VEGF(165) was unaffected. Addition of hF4-3C5 together with an antagonist antibody to VEGFR-2 completely abolished the response to VEGF-C(DeltaNDeltaC). Similar results were obtained with HUVECs. Together, these findings point to a role for VEGFR-3 in vascular tubular morphogenesis and highlight the utility of hF4-3C5 as a tool for the investigation of the biology of VEGFR-3.

Comparative evaluation of FGF-2-, VEGF-A-, and VEGF-C-induced angiogenesis, lymphangiogenesis, vascular fenestrations, and permeability

Several endothelial growth factors induce both blood and lymphatic angiogenesis. However, a systematic comparative study of the impact of these factors on vascular morphology and function has been lacking. In this study, we report a quantitative analysis of the structure and macromolecular permeability of FGF-2-, VEGF-A-, and VEGF-C-induced blood and lymphatic vessels. Our results show that VEGF-A stimulated formation of disorganized, nascent vasculatures as a result of fusion of blood capillaries into premature plexuses with only a few lymphatic vessels. Ultrastructural analysis revealed that VEGF-A-induced blood vessels contained high numbers of endothelial fenestrations that mediated high permeability to ferritin, whereas the FGF-2-induced blood vessels lacked vascular fenestrations and showed only little leakage of ferritin. VEGF-C induced approximately equal amounts of blood and lymphatic capillaries with endothelial fenestrations present only on blood capillaries, mediating a medium level of ferritin leakage into the perivascular space. No endothelial fenestrations were found in FGF-2-, VEGF-A-, or VEGF-C-induced lymphatic vessels. These findings highlight the structural and functional differences between blood and lymphatic vessels induced by FGF-2, VEGF-A, and VEGF-C. Such information is important to consider in development of novel therapeutic strategies using these angiogenic factors.