VEGF-A promotes tissue repair-associated lymphatic vessel formation via VEGFR-2 and the alpha1beta1 and alpha2beta1 integrins

Lymphatic vessels in osteoarthritic human knees

OBJECTIVES

The distribution and function of lymphatic vessels in normal and diseased human knees are understood incompletely. This study aimed to investigate whether lymphatic density is associated with clinical, histological or radiographic parameters in osteoarthritis (OA).

METHODS

Sections of synovium from 60 knees from patients with OA were compared with 60 post mortem control knees (from 37 individuals). Lymphatic vessels were identified using immunohistochemistry for podoplanin, and quantified as lymphatic vessel density (LVD) and lymphatic endothelial cell (LEC) fractional area. Effusion status was determined by clinical examination, radiographs were scored for OA changes, and inflammation grading used haematoxylin and eosin stained sections of synovium.

RESULTS

Lymphatic vessels were present in synovia from both disease groups, but were not identified in subchondral bone. Synovial lymphatic densities were independent of radiological severity and age. Synovia from patients with OA displayed lower LVD (z=-3.4, P=0.001) and lower LEC fractional areas (z=-4.5, P<0.0005) than non-arthritic controls. In patients with OA, low LVD was associated with clinically detectable effusion (z=-2.2, P=0.027), but not with histological evidence of synovitis. The negative associations between lymphatics and OA/effusion appeared to be independent of other measured confounders.

CONCLUSION

Lymphatic vessels are present in lower densities in OA synovia. Abnormalities of synovial fluid drainage may confound the value of effusion as a clinical sign of synovitis in OA.

Co-expression of α9β1 integrin and VEGF-D confers lymphatic metastatic ability to a human breast cancer cell line MDA-MB-468LN

Introduction and Objectives

Lymphatic metastasis is a common occurrence in human breast cancer, mechanisms remaining poorly understood. MDA-MB-468LN (468LN), a variant of the MDA-MB-468GFP (468GFP) human breast cancer cell line, produces extensive lymphatic metastasis in nude mice. 468LN cells differentially express α9β1 integrin, a receptor for lymphangiogenic factors VEGF-C/-D. We explored whether (1) differential production of VEGF-C/-D by 468LN cells provides an autocrine stimulus for cellular motility by interacting with α9β1 and a paracrine stimulus for lymphangiogenesis in vitro as measured with capillary-like tube formation by human lymphatic endothelial cells (HMVEC-dLy); (2) differential expression of α9 also promotes cellular motility/invasiveness by interacting with macrophage derived factors; (3) stable knock-down of VEGF-D or α9 in 468LN cells abrogates lymphangiogenesis and lymphatic metastasis in vivo in nude mice.

Results

A comparison of expression of cyclo-oxygenase (COX)-2 (a VEGF-C/-D inducer), VEGF-C/-D and their receptors revealed little COX-2 expression by either cells. However, 468LN cells showed differential VEGF-D and α9β1 expression, VEGF-D secretion, proliferative, migratory/invasive capacities, latter functions being stimulated further with VEGF-D. The requirement of α9β1 for native and VEGF-D-stimulated proliferation, migration and Erk activation was demonstrated by treating with α9β1 blocking antibody or knock-down of α9. An autocrine role of VEGF-D in migration was shown by its impairment by silencing VEGF-D and restoration with VEGF-D. 468LN cells and their soluble products stimulated tube formation, migration/invasiveness of HMVEC-dLy cell in a VEGF-D dependent manner as indicated by the loss of stimulation by silencing VEGF-D in 468LN cells. Furthermore, 468LN cells showed α9-dependent stimulation of migration/invasiveness by macrophage products. Finally, capacity for intra-tumoral lymphangiogenesis and lymphatic metastasis in nude mice was completely abrogated by stable knock-down of either VEGF-D or α9 in 468LN cells.

Conclusion

Differential capacity for VEGF-D production and α9β1 integrin expression by 468LN cells jointly contributed to their lymphatic metastatic phenotype.

Correlations between SUVmax and expression of GLUT1 and growth factors inducing lymphangiogenesis

RATIONALE AND OBJECTIVES

The purpose of this study was to assess the correlations between the maximum standardized uptake value (SUVmax) of colorectal carcinoma and hepatocyte growth factor (HGF), vascular endothelial growth factor C (VEGF-C), and their respective receptors using (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT).

METHODS

Fluorine-18-FDG PET/CT scans were performed on 33 patients with colorectal carcinoma before any treatment. The SUVmax of colorectal carcinoma and the clinicopathologic data associated with lymphatic metastases were analyzed. The expression of glucose transporter 1 (GLUT1), HGF, c-Met, VEGF-C, and vascular endothelial growth factor receptor 3 (VEGFR-3) in tumor tissues was analyzed using immunohistochemical methods. Lymphatic endothelial cells were marked with D2-40, and lymphatic vessel density (LVD) was recorded. The correlations were analyzed among the SUVmax of colorectal carcinoma, LVD, and the expression of GLUT1, HGF, c-Met, VEGF-C, and VEGFR-3 in tumor tissues.

RESULTS

SUVmax and LVD in 15 patients with lymphatic metastases were 13.00 ± 4.51 and 6.25 ± 1.54, respectively, whereas in 18 patients with nonmetastatic nodes, SUVmax and LVD were 9.66 ± 4.82 and 4.54 ± 1.02, respectively. The differences of SUVmax and LVD between metastatic and nonmetastatic patients were statistically significant (F = 4.153, P = .025, and F = 14.501, P = .001, respectively). There were no statistical differences of SUVmax and LVD in variably differentiated colorectal carcinoma (F = 0.708, P = .502, and F = 0.311, P = .735, respectively). The expression rates of GLUT1 in neoplastic and normal tissue were 72.7% (24 of 33) and 21.2% (seven of 33), respectively (P = .001). Moreover, the expression rates of GLUT1 in metastatic and nonmetastatic tissue were 93.33% (14 of 15) and 61.11% (11 of 18), respectively (P = .038). LVD and the integrated optical density of GLUT1 were 5.31 ± 1.53 and 8.21 × 10(4) ± 4.30 × 10(4), respectively, in tumor tissue, and there were linear correlations between SUVmax and LVD (r = 0.373, P = .033) and between SUVmax and expression of GLUT1 (r = 0.428, P = .013). The differences of SUVmax in HGF, c-Met, and VEGF-C groups with different expressions were statistically significant (P = .007, P = .009, and P = .030, respectively). No correlation was found between the expression of VEGFR-3 and SUVmax. The expression of GLUT1 and HGF as well as of GLUT1 and VEGF-C was rank correlated (r = 0.521, P = .002, and r = 0.505, P = .003, respectively). No rank correlations were found between the expression of GLUT1 and c-Met, GLUT1, and VEGFR-3.

CONCLUSIONS

The SUVmax of colorectal carcinoma was significantly higher in metastatic patients; the uptake of colorectal carcinoma was associated with LVD and the expression of HGF and VEGF-C but not with the expression of VEGFR-3.

Macrophages are important mediators of either tumor- or inflammation-induced lymphangiogenesis

The lymphatic system provides important functions for tissue fluid homeostasis and immune response. Lymphangiogenesis, the formation of new lymphatics, comprises a series of complex cellular events in vitro or in vivo, e.g., proliferation, differentiation, and sprouting. Recent evidence has implied that macrophages act as a direct structural contributor to lymphatic endothelial walls or secret VEGF-C/-D and VEGF-A to initiate lymphangiogenesis in inflamed or tumor tissues. Bone marrow-derived macrophages are versatile cells that express different functional programs in response to exposure to microenvironmental signals, and can be identified by specific expression of a number of proteins, F4/80, CD11b, and CD68. Several causative factors, e.g., NF-κB, IL-1β, TNF-α, SDF-1, M-CSF, especially TonEBP/VEGF-C signaling, may be actively involved in macrophage-induced lymphangiogenesis. Alteration of macrophage phenotype and function has a profound effect on the development and progression of inflammation and malignancy, and macrophage depletion for controlling lymphangiogenesis may provide a novel approach for prevention and treatment of lymphatic-associated diseases.

Integrins and their extracellular matrix ligands in lymphangiogenesis and lymph node metastasis

In the 1970s, the late Judah Folkman postulated that tumors grow proportionately to their blood supply and that tumor angiogenesis removed this limitation promoting growth and metastasis. Work over the past 40 years, varying from molecular examination to clinical trials, verified this hypothesis and identified a host of therapeutic targets to limit tumor angiogenesis, including the integrin family of extracellular matrix receptors. However, the propensity for some tumors to spread through lymphatics suggests that lymphangiogenesis plays a similarly important role. Lymphangiogenesis inhibitors reduce lymph node metastasis, the leading indicator of poor prognosis, whereas inducing lymphangiogenesis promotes lymph node metastasis even in cancers not prone to lymphatic dissemination. Recent works highlight a role for integrins in lymphangiogenesis and suggest that integrin inhibitors may serve as therapeutic targets to limit lymphangiogenesis and lymph node metastasis. This review discusses the current literature on integrin-matrix interactions in lymphatic vessel development and lymphangiogenesis and highlights our current knowledge on how specific integrins regulate tumor lymphangiogenesis.

Integrin-dependent Akt1 activation regulates PGC-1 expression and fatty acid oxidation

BACKGROUND

Poly-N-acetyl glucosamine nanofibers derived from a marine diatom have been used to increase cutaneous wound healing. These nanofibers exert their activity by specifically activating integrins, which makes them a useful tool for dissecting integrin-mediated pathways. We have shown that short-fiber poly-N-acetyl glucosamine nanofiber (sNAG) treatment of endothelial cells results in increased cell motility and metabolic rate in the absence of increased cell proliferation.

RESULTS

Using a Seahorse Bioanalyzer to measure oxygen consumption in real time, we show that sNAG treatment increases oxygen consumption rates, correlated with an integrin-dependent activation of Akt1. Akt1 activation leads to an increase in the expression of the transcriptional coactivator, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α). This is not due to increased mitochondrial biogenesis, but is associated with an increase in the expression of pyruvate dehydrogenase kinase 4 (PDK4), suggesting regulation of fatty acid oxidation. Blockade of fatty acid oxidation with etomoxir, an O-carnitine palmitoyltransferase-1 inhibitor, blocks the sNAG-dependent increased oxygen consumption. (3)H-palmitate uptake experiments indicate a PDK4-dependent increase in fatty acid oxidation, which is required for nanofiber-induced cell motility.

CONCLUSIONS

Our findings imply a linear pathway whereby an integrin-dependent activation of Akt1 leads to increased PGC-1α and PDK4 expression resulting in increased energy production by fatty acid oxidation.

Interaction of tumor cells and lymphatic vessels in cancer progression

Metastatic spread of cancer through the lymphatic system affects hundreds of thousands of patients yearly. Growth of new lymphatic vessels, lymphangiogenesis, is activated in cancer and inflammation, but is largely inactive in normal physiology, and therefore offers therapeutic potential. Key mediators of lymphangiogenesis have been identified in developmental studies. During embryonic development, lymphatic endothelial cells derive from the blood vascular endothelium and differentiate under the guidance of lymphatic-specific regulators, such as the prospero homeobox 1 transcription factor. Vascular endothelial growth factor-C (VEGF-C) and VEGF receptor 3 signaling are essential for the further development of lymphatic vessels and therefore they provide a promising target for inhibition of tumor lymphangiogenesis. Lymphangiogenesis is important for the progression of solid tumors as shown for melanoma and breast cancer. Tumor cells may use chemokine gradients as guidance cues and enter lymphatic vessels through intercellular openings between endothelial cell junctions or, possibly, by inducing larger discontinuities in the endothelial cell layer. Tumor-draining sentinel lymph nodes show enhanced lymphangiogenesis even before cancer metastasis and they may function as a permissive 'lymphovascular niche' for the survival of metastatic cells. Although our current knowledge indicates that the development of anti-lymphangiogenic therapies may be beneficial for the treatment of cancer patients, several open questions remain with regard to the frequency, mechanisms and biological importance of lymphatic metastases.

Mechanoinduction of lymph vessel expansion

In the mammalian embryo, few mechanical signals have been identified to influence organ development and function. Here, we report that an increase in the volume of interstitial or extracellular fluid mechanically induces growth of an organ system, that is, the lymphatic vasculature. We first demonstrate that lymph vessel expansion in the developing mouse embryo correlates with a peak in interstitial fluid pressure and lymphatic endothelial cell (LEC) elongation. In 'loss-of-fluid' experiments, we then show that aspiration of interstitial fluid reduces the length of LECs, decreases tyrosine phosphorylation of vascular endothelial growth factor receptor-3 (VEGFR3), and inhibits LEC proliferation. Conversely, in 'gain-of-fluid' experiments, increasing the amount of interstitial fluid elongates the LECs, and increases both VEGFR3 phosphorylation and LEC proliferation. Finally, we provide genetic evidence that β1 integrins are required for the proliferative response of LECs to both fluid accumulation and cell stretching and, therefore, are necessary for lymphatic vessel expansion and fluid drainage. Thus, we propose a new and physiologically relevant mode of VEGFR3 activation, which is based on mechanotransduction and is essential for normal development and fluid homeostasis in a mammalian embryo.

Phosphorylation of Akt and ERK1/2 is required for VEGF-A/VEGFR2-induced proliferation and migration of lymphatic endothelium

There is growing evidence that vascular endothelial growth factor-A (VEGF-A), a ligand of the receptor tyrosine kinases VEGFR1 and VEGFR2, promotes lymphangiogenesis. However, the underlying mechanisms by which VEGF-A induces the growth of lymphatic vessels remain poorly defined. Here we report that VEGFR2, not VEGFR1, is the primary receptor regulating VEGF-A-induced lymphangiogenesis. We show that specific inhibition of VEGF-A/VEGFR2 signaling with the fully human monoclonal antibody r84 significantly inhibits lymphangiogenesis in MDA-MB-231 tumors. In vitro experiments with primary human dermal lymphatic endothelial cells (LECs) demonstrate that blocking VEGF-A activation of VEGFR2, not VEGFR1, significantly inhibits VEGF-A-induced proliferation and migration of LECs. We show that VEGF-A stimulation of LECs leads to the phosphorylation of VEGFR2 (Tyr 951, 1054, 1059, 1175, and 1214) which subsequently triggers PKC dependent phosphorylation of ERK1/2 and PI3-K dependent phosphorylation of Akt. Additionally, we demonstrate that inhibitors that suppress the phosphorylation of ERK1/2 and Akt significantly block VEGF-A- induced proliferation and migration of LECs. Together, these results shed light on the mechanisms regulating VEGF-A-induced proliferation and migration of LECs, reveal that VEGFR2 is the primary signaling VEGF-A receptor on lymphatic endothelium, and suggest that therapeutic agents targeting the VEGF-A/VEGFR2 axis could be useful in blocking the pathological formation of lymphatic vessels.

Relation between bevacizumab dose intensity and high-grade glioma survival: a retrospective study in two large cohorts

Bevacizumab is one of the rare drugs that could improve high-grade glioma outcome after failure of chemoradiotherapy. However, to date, there is no biomarker predictive for efficacy of bevacizumab therapy in terms of survival improvement for patients with high-grade glioma. We performed a retrospective analysis of clinical factors associated with patient survival using a training cohort of 110 consecutive patients treated with bevacizumab for recurrent high-grade glioma and an independent validation cohort of 109 patients. In the training cohort, 110 consecutive patients received bevacizumab-based therapy. The number of chemotherapy cycles delivered was 1,411. Median follow-up was 12 months. Thirty-four patients (31%) had objective partial response and 24% had stable disease on magnetic resonance imaging evaluation. Median progression-free survival (PFS) and overall survival (OS) were 4.3 and 9.2 months, respectively. On univariate analysis, among classical prognosis factors, only Karnofsky status ≥70% was associated with improved outcome. Surprisingly, patients with low bevacizumab dose intensity (<5 mg/kg/week) had better PFS (12 vs. 2 months, P < 0.0001) and OS (16 vs. 6 months, P = 0.0002). On multivariate analysis, low bevacizumab dose intensity was the most significant independent prognostic factor of survival. Analysis of the validation cohort yielded similar results, externally validating this observation. This large retrospective study using two independent cohorts of high-grade glioma suggests that the currently recommended dosage of bevacizumab (5 mg/kg/week) is not optimal. Further prospective randomized trials using lower dosages are warranted.

An overview of lymphatic vessels and their emerging role in cardiovascular disease

Over the past decade, molecular details of lymphatic vessels (lymphatics) have been rapidly acquired due to the identification of lymphatic endothelial-specific markers. Separate from the cardiovascular system, the lymphatic system is also an elaborate network of vessels that are important in normal physiology. Lymphatic vessels have the unique task to regulate fluid homeostasis, assist in immune surveillance, and transport dietary lipids. However, dysfunctional lymphatic vessels can cause pathology, while normal lymphatics can exacerbate pathology. This review summarizes the development and growth of lymphatic vessels in addition to highlighting their critical roles in physiology and pathology. Also, we discuss recent work that suggests a connection between lymphatic dysfunction and cardiovascular disease.

Apelin attenuates UVB-induced edema and inflammation by promoting vessel function

Apelin, the ligand of the G protein-coupled receptor APJ, is involved in the regulation of cardiovascular functions, fluid homeostasis, and vessel formation. Recent reports indicate that apelin secreted from endothelial cells mediates APJ regulation of blood vessel caliber size; however, the function of apelin in lymphatic vessels is unclear. Here we report that APJ was expressed by human lymphatic endothelial cells and that apelin induced migration and cord formation of lymphatic endothelial cells dose-dependently in vitro. Furthermore, permeability assays demonstrated that apelin stabilizes lymphatic endothelial cells. In vivo, transgenic mice harboring apelin under the control of keratin 14 (K14-apelin) exhibited attenuated UVB-induced edema and a decreased number of CD11b-positive macrophages. Moreover, activation of apelin/APJ signaling inhibited UVB-induced enlargement of lymphatic and blood vessels. Finally, K14-apelin mice blocked the hyperpermeability of lymphatic vessels in inflamed skin. These results indicate that apelin plays a functional role in the stabilization of lymphatic vessels in inflamed tissues and that apelin might be a suitable target for prevention of UVB-induced inflammation.

Active lymphangiogenesis is a major risk factor for anastomotic leakage following sphincter-sparing resection of rectal cancer

OBJECTIVE

Anastomotic leakage is a major complication of rectal surgery and controversy about its risk factors still exists. The aim of present study was to identify risk factors for anastomotic leakage following sphincter-sparing resection of rectal cancer, focusing on the role of tissular lymphatic vessel density (LVD) in tumorous margin and distal clearance margin.

METHODS

In a 9-year period, from September 1999 to September 2009, 750 consecutive patients who underwent anterior resection with restoration of the bowel continuity were included. Univariate and multivariate analysis were applied to identify risk factors for anastomotic leakage.

RESULTS

The rate of anastomotic leakage was 7.6% (57 of 750 patients). In a multivariate analysis, high LVD in tumorous margin [P=0.0017; odds ratio (OR)=5.93; 95% confidence interval (CI)=2.61-8.514], high LVD in distal clearance margin (P=0.0011; OR=6.05; 95% CI=2.72-10.108) and lower tumor location (P=0.006; OR=4.620; 95% CI=1.76-6.97) were identified as independent factors for anastomotic leakage. A significant LVD correlation was shown by Spearman's rank test between the tumorous and distal clearance margin (r=0.796).

CONCLUSIONS

Tissular LVD in tumorous or distal clearance margin and lower tumor location are important risk factors for anastomotic leakage.

The role of vascular endothelial growth factor in fractional laser resurfacing with the carbon dioxide laser

The aim of this study was to analyze the role of vascular endothelial growth factor (VEGF) in mechanisms of cutaneous remodeling induced by fractional CO(2) laser treatment. The dorsal skin of Kunming mice was exposed to a single-pass fractional CO(2) laser treatment. Biopsies were taken 1 h, and 1, 3, 7, 14, 28 and 56 days after treatment. Skin samples VEGF expression was evaluated by immunohistochemistry and ELISA, fibroblasts by hematoxylin-eosin staining, and types I and III collagen by ELISA. Staining for VEGF was found in many types of cell including fibroblasts. The amount of VEGF in the skin of laser-treated areas had increased significantly compared to that in the control areas on days 1 and 3 (P < 0.05, P < 0.01, respectively), then decreased by day 7 after treatment and returned to the baseline level. The number of fibroblasts in the skin of the laser-treated areas had increased significantly compared to that in control areas on days 3, 7, 14, 28 and 56 after irradiation (P < 0.05, P < 0.01, P < 0.01, P < 0.01, P < 0.01, respectively). The amount of type I collagen was significantly higher in the skin of the laser-treated areas compared to that in control areas from day 28 to day 56 (P < 0.05, respectively), and type III collagen was significantly higher from day 3 to day 56 (P < 0.05, P < 0.05, P < 0.05, P < 0.05, P < 0.01, respectively). There was a positive correlation between the level of VEGF and fibroblast proliferation early stage after laser treatment (r = 0.853, P < 0.01), but there was no correlation after the first week (r = -0.124, P > 0.05). The amounts of type I and III collagen showed no significant correlations with the expression of VEGF in the late stages after laser treatment (r = 0.417, P > 0.05 and r = 0.340, P > 0.05, respectively). The results suggest that VEGF might be mainly involved in the early stages of wound healing, including the stages of acute inflammation, fibroblast proliferation and vessel formation induced by fractional CO(2) laser resurfacing.

Role of the lymphatics in cancer metastasis and chemotherapy applications

The lymphatic system was first described centuries ago. The recent discovery of various molecular markers has allowed for more in-depth research of the lymphatic system and its role in health and disease. The lymphatic system has recently been elucidated as playing an active role in cancer metastasis. The knowledge of the active processes involved in lymphatic metastasis provides novel treatment targets for various malignancies.

Recombinant canstatin inhibits angiopoietin-1-induced angiogenesis and lymphangiogenesis

We describe the effect of recombinant canstatin, the NC1 domain of the α2 chain of Type IV collagen, on suppression of angiogenesis and lymphangiogenesis both in vitro and in vivo. Recombinant canstatin produced from stably transformed Drosophila S2 cells reduced the expression of angiopoietin-1 in hypoxia mimetic agent, CoCl(2) -treated CT-26 cells. Recombinant canstatin inhibited proliferation, tube formation and migration of human angiopoietin-1 (rhAngpt-1)-treated human umbilical vein endothelial cells (HUVEC) and lymphatic endothelial cells (LEC). Recombinant canstatin suppressed the expression of Tie-2 and vascular endothelial growth factor-3 (VEGFR-3) transcripts in rhAngpt-1-treated HUVEC and LEC, respectively. The inhibitory effect of recombinant canstatin on tumor growth was also investigated using a heterotopic CT-26 colon carcinoma animal (BALB/c mice) model. Recombinant canstatin reduced the final volume and weight of tumors, and blood and lymphatic vessel densities of tumors, which were evaluated by CD-31 and LYVE-1 immunostaining. Immunohistochemical analysis showed that recombinant canstatin dramatically reduced the expression of angiopoietin-1 in CT-26 colon carcinoma-induced tumor, but not the expression of VEGF-C. Tie-2 and VEGFR-3 expressions were also reduced in recombinant canstatin-treated tumors. These results indicate that recombinant canstatin has anti-tumoral activities against CT-26 colon carcinoma cells. Recombinant canstatin reduces the expression of angiopoietin-1 in hypoxia-induced CT-26 cells and inhibits the angiogenic and lymphangiogenic signaling induced by angiopoietin-1. Recombinant canstatin probably inhibits angiogenesis and lymphangiogenesis via suppression of the integrin-dependent FAK signaling induced by angiopoietin-1/Tie-2 and/or VEGFR-3.

VIP and growth factors in the infected cornea

PURPOSE

Vasoactive intestinal peptide (VIP) is an anti-inflammatory neuropeptide that downregulates proinflammatory cytokines and promotes healing in a susceptible model of P. aeruginosa keratitis. Growth factors also play a role in corneal healing and restoration of tissue homeostasis after wounding. However, whether VIP treatment modulates growth factors to promote healing in the infected cornea remains untested and is the purpose of this study.

METHODS

C57BL/6 (B6) mice were injected with VIP and mRNA and protein levels, and immunostaining for EGF, FGF, HGF, and VEGF-A were done. Exogenous treatment with a mixture of the growth factors also was tested and levels of cytokines, defensins, and bacterial counts were determined.

RESULTS

Real-time RT-PCR, immunostaining, and ELISA data demonstrated that treatment with VIP enhanced levels of EGF, FGF, and HGF during disease, and that VEGF-A, and associated angiogenic molecules also were increased by VIP. Moreover, immunohistochemical studies confirmed that both epithelial and stromal cells participated in growth factor production. Most notably, treatment with a mixture of EGF, FGF, and HGF after disease onset, prevented corneal perforation when compared with controls. This outcome was associated with downregulation of proinflammatory cytokines such as macrophage inflammatory protein-2 (MIP-2), upregulation of anti-inflammatory cytokines such as TGF-β, and antimicrobials β-defensins 2 and 3, as well as decreased plate counts at 1 day postinfection (p.i.) (P = 0.0001).

CONCLUSIONS

Collectively, the data provide evidence that VIP treatment modulates growth factors, angiogenic molecules, and defensins in the infected cornea and that this in turn promotes healing and restoration of tissue homeostasis.

Nuclear translocation of phosphorylated STAT3 regulates VEGF-A-induced lymphatic endothelial cell migration and tube formation

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific growth factor that regulates endothelial functions, and signal transducers and activators of transcription (STATs) are known to be important during VEGF receptor signaling. The aim of this study was to determine whether STAT3 regulates VEGF-induced lymphatic endothelial cell (LEC) migration and tube formation. VEGF-A (33 ng/ml) enhanced LEC migration by 2-fold and increased tube length by 25% compared with the control, as analyzed using a Boyden chamber and Matrigel assay, respectively. Western blot analysis and immunostaining revealed that VEGF-A induced the nuclear translocation of phosphorylated STAT3 in LECs, and this translocation was blocked by the transfection of LECs with an adenovirus vector expressing a dominant-negative mutant of STAT3 (Ax-STAT3F). Transfection with Ax-STAT3F also almost completely inhibited VEGF-A-induced LEC migration and tube formation. These results indicate that STAT3 is essential for VEGF-A-induced LEC migration and tube formation and that STAT3 regulates LEC functions.

Why integrin as a primary target for imaging and therapy

Integrin-mediated cell adhesion is involved in many essential normal cellular and pathological functions including cell survival, growth, differentiation, migration, inflammatory responses, platelet aggregation, tissue repair and tumor invasion. 24 different heterodimerized transmembrane integrin receptors are combined from 18 different α and 8 different β subunits. Each integrin subunit contains a large extracellular domain, a single transmembrane domain and a usually short cytoplasmic domain. Integrins bind extracellular matrix (ECM) proteins through their large extracellular domain, and engage the cytoskeleton via their short cytoplasmic tails. These integrin-mediated linkages on either side of the plasma membrane are dynamically linked. Thus, integrins communicate over the plasma membrane in both directions, i.e., outside-in and inside-out signaling. In outside-in signaling through integrins, conformational changes of integrin induced by ligand binding on the extracellular domain altered the cytoplasmic domain structures to elicit various intracellular signaling pathways. Inside-out signaling originates from non-integrin cell surface receptors or cytoplasmic molecules and it activates signaling pathways inside the cells, ultimately resulting in the activation/deactivation of integrins. Integrins are one of key family proteins for cell adhesion regulation through binding to a large number of ECM molecules and cell membrane proteins. Lack of expression of integrins may result in a wide variety of effects ranging from blockage in pre-implantation to embryonic or perinatal lethality and developmental defects. Based on both the key role they played in angiogenesis, leukocytes function and tumor development and easy accessibility as cell surface receptors interacting with extracellular ligands, the integrin superfamily represents the best opportunity of targeting both antibodies and small-molecule antagonists for both therapeutic and diagnostic utility in various key diseases so far.

Lymphatic vessels and related factors in adenoid cystic carcinoma of the salivary gland

Adenoid cystic carcinoma of the salivary gland preferentially metastasizes to distant organs. It rarely metastasizes to lymph nodes. Recently, lymphangiogenesis has been associated with lymph node metastasis. Therefore, lymphangiogenesis in adenoid cystic carcinoma was evaluated from the number of lymphatic vessels and the expression of lymphangiogenic factors. Immunohistochemistry and molecular analysis were performed on clinical materials (29 cases for immunohistochemistry and 9 cases for molecular analysis). Normal submandibular gland was used as a negative control of lymphangiogenesis (10 cases for immunohistochemistry and 5 cases for molecular analysis). In adenoid cystic carcinoma, podoplanin-positive lymphatic vessels were small and often constricted, and localized to the tumor periphery. They did not have Ki67-positive endothelial cells. The lymphatic vessel density of the tumor did not exceed that of the salivary gland. By reverse transcriptase-polymerase chain reaction, adenoid cystic carcinoma and the salivary gland expressed vascular endothelial growth factor receptor-3 (VEGFR-3) similarly but VEGF-C and VEGF-D differently. Adenoid cystic carcinoma expressed VEGF-C, whereas the salivary gland expressed both VEGF-C and VEGF-D. VEGF-C was weak in adenoid cystic carcinoma and strong in the salivary gland. Real-time reverse transcriptase-polymerase chain reaction of VEGF-C showed that the ratio of the tumor to the salivary gland was 1 to 30 (P<0.01). Immunohistochemistry barely detected VEGF-C in adenoid cystic carcinoma. VEGF-C was expressed faintly by the tumor cells. VEGF-C and VEGF-D were detected in the serous acinar and duct cells and in the duct contents in the salivary gland. VEGFR-3 appeared to be expressed by lymphatic vessels in both adenoid cystic carcinoma and the salivary gland. These results indicate that lymphangiogenesis does not occur in adenoid cystic carcinoma. This condition would lead to the uncommon lymphatic metastasis.

The Transcriptional Control of Lymphatic Vascular Development

More than 100 years ago, Florence Sabin suggested that lymphatic vessels develop by sprouting from preexisting blood vessels, but it is only over the past decade that the molecular mechanisms underpinning lymphatic vascular development have begun to be elucidated. Genetic manipulations in mice have identified a transcriptional hub comprised of Prox1, CoupTFII, and Sox18 that is essential for lymphatic endothelial cell fate specification. Recent work has identified a number of additional transcription factors that regulate later stages of lymphatic vessel differentiation and maturation. This review highlights recent advances in our understanding of the transcriptional control of lymphatic vascular development and reflects on efforts to better understand the activities of transcriptional networks during this discrete developmental process. Finally, we highlight the transcription factors associated with human lymphatic vascular disorders, demonstrating the importance of understanding how the activity of these key molecules is regulated, with a view toward the development of innovative therapeutic avenues.

Lymphangiogenesis in post-natal tissue remodeling: lymphatic endothelial cell connection with its environment

The main physiological function of the lymphatic vasculature is to maintain tissue fluid homeostasis. Lymphangiogenesis or de novo lymphatic formation is closely associated with tissue inflammation in adults (i.e. wound healing, allograft rejection, tumor metastasis). Until recently, research on lymphangiogenesis focused mainly on growth factor/growth factor-receptor pathways governing this process. One of the lymphatic vessel features is the incomplete or absence of basement membrane. This close association of endothelial cells with the underlying interstitial matrix suggests that cell-matrix interactions play an important role in lymphangiogenesis and lymphatic functions. However, the exploration of interaction between extracellular matrix (ECM) components and lymphatic endothelial cells is in its infancy. Herein, we describe ECM-cell and cell-cell interactions on lymphatic system function and their modification occurring in pathologies including cancer metastasis.

Pleiotropic stromal effects of vascular endothelial growth factor receptor 2 antibody therapy in renal cell carcinoma models

The benefits of inhibiting vascular endothelial growth factor (VEGF) signaling in cancer patients are predominantly attributed to effects on tumor endothelial cells. Targeting non-endothelial stromal cells to further impact tumor cell growth and survival is being pursued through the inhibition of additional growth factor pathways important for the survival and/or proliferation of these cells. However, recent data suggest that VEGF receptor (VEGFR)-specific inhibitors may target lymphatic vessels and pericytes in addition to blood vessels. Here, in fact, we demonstrate that DC101 (40 mg/kg, thrice a week), an antibody specific to murine VEGFR2, significantly reduces all three of these stromal components in subcutaneous (SKRC-29) and orthotopic (786-O-LP) models of renal cell carcinoma (RCC) established in nu/nu athymic mice. Sunitinib (40 mg/kg, once daily), a receptor tyrosine kinase inhibitor of VEGFR2 and other growth factor receptors, also caused significant loss of tumor blood vessels in RCC models but had weaker effects than DC101 on pericytes and lymphatic vessels. In combination, sunitinib did not significantly add to the effects of DC101 on tumor blood vessels, lymphatic vessels, or pericytes. Nevertheless, sunitinib increased the effect of DC101 on tumor burden in the SKRC-29 model, perhaps related to its broader specificity. Our data have important implications for combination therapy design, supporting the conclusion that targeting VEGFR2 alone in RCC has the potential to have pleiotropic effects on tumor stroma.

Proteolytic processing of vascular endothelial growth factor-D is essential for its capacity to promote the growth and spread of cancer

VEGF-D is a mitogen for endothelial cells that promotes tumor growth and metastatic spread in animal models, and expression of which correlates with lymph node metastasis in some human cancers. It is secreted from the cell as a full-length form with propeptides flanking a central region containing binding sites for VEGFR-2 and VEGFR-3, receptors that signal for angiogenesis and lymphangiogenesis. The propeptides can be cleaved from VEGF-D, enhancing affinity for VEGFR-2 and VEGFR-3 in vitro; however, the importance of this processing in cancer is unclear. To explore the necessity of processing for the effects of VEGF-D in cancer, we use a mutant full-length form that cannot be processed, and show that, in contrast to full-length VEGF-D that is processed, this mutant does not promote tumor growth and lymph node metastasis in a mouse tumor model. Processing of VEGF-D is required for tumor angiogenesis, lymphangiogenesis, and recruitment of tumor-associated macrophages. These observations may be explained by the requirement of processing for VEGF-D to bind neuropilin receptors and activate VEGFR-2. Our results indicate that proteolytic processing is necessary for VEGF-D to promote the growth and spread of cancer, and suggest that enzymes catalyzing this processing could be targets for antimetastatic therapeutics.

VEGF-C promotes the development of esophageal cancer via regulating CNTN-1 expression

Vascular endothelial growth factor C (VEGF-C) is a key regulator of angiogenesis and lymphangiogenesis. VEGF-C is also implicated in the development of esophageal cancer. We investigated the mRNA levels of VEGF-C and its receptors in 38 esophageal squamous cell carcinoma specimens (ESCCs) and matched adjacent normal esophageal tissues via real-time PCR. The mRNA levels of VEGF-C, VEGFR-2 and VEGFR-3 were significantly upregulated in ESCCs versus respective side normal tissues. To explore the influence of VEGF-C on esophageal cancer progression, the expression of VEGF-C was manipulated in esophageal cancer cell lines TE-1 and Eca-109. VEGF-C transcription, translation and secretion were significantly enhanced in cells stably transfected with a VEGF-C overexpression vector or attenuated in VEGF-C shRNA-transfected cell lines. In vitro, TE-1 cells stably transfected with a VEGF-C overexpression vector exhibited an increased rate of cell proliferation, migration and focus formation, whereas knockdown of VEGF-C inhibited cell proliferation, migration and focus formation. Similar results were obtained for Eca-109 cells. VEGF-C mediated biological function through transcription of CNTN-1, which is implicated in tumor invasion and metastasis. The expression of VEGF-C was correlated with that of CNTN-1 and cell proliferation and migration induced by VEGF-C were reversed by silencing of CNTN-1. In addition, nude mice inoculated with VEGF-C shRNA-transfected cells exhibited a significantly decreased tumor size in vivo via reduced VEGFR-2 and VEGFR-3 phosphorylation and microvessel formation. VEGF-C upregulation may be involved in esophageal tumor progression. Vector-based RNA interference (RNAi) targeting VEGF-C is a potential therapeutic method for human esophageal carcinoma.

β1 integrin regulates MMP-10 dependant tubulogenesis in human lymphatic endothelial cells

Lymphatic vessel growth requires extensive remodeling of the extracellular matrix, a process hypothesized to be related to the expression and function of the matrix metalloproteinases. We used a protein based screening strategy to demonstrate increased matrix matalloproteinase-10 expression in human lymphatic endothelial cells undergoing collagen I induced tubulogenesis. Knock-down experiments showed that matrix metalloproteinase-10 regulated lymphatic endothelial cell tubulogenesis. β1 integrin signaling via the ERK/MAPK pathway increased matrix metalloproteinase-10 mRNA and protein expression in human lymphatic endothelial cells. These findings demonstrate a novel mechanism by which β1 integrin regulates matrix metalloproteinase-10 expression during lymphatic vessel remodeling.

Vitreous and plasma concentrations of apelin and vascular endothelial growth factor after intravitreal bevacizumab in eyes with proliferative diabetic retinopathy

PURPOSE

To evaluate vitreous and plasma concentrations of vascular endothelial growth factor (VEGF) and apelin and to detect the expressions of VEGF and apelin on epiretinal fibrovascular membranes obtained during vitrectomy in eyes with proliferative diabetic retinopathy after intravitreal bevacizumab injection.

METHODS

Forty-four eyes of 44 patients affected by active proliferative diabetic retinopathy were investigated. The bevacizumab study group consisted of 20 eyes that received an intravitreal bevacizumab injection (1.25 mg) 7 days before pars plana vitrectomy. The control group included 24 eyes that underwent pars plana vitrectomy without previous intravitreal bevacizumab injection. Using enzyme-linked immunosorbent assay, the concentrations of VEGF and apelin were measured in vitreous and plasma samples. The expressions of VEGF and apelin in the excised epiretinal membranes were examined by fluorescence immunostaining.

RESULTS

Vitreous and plasma concentrations of VEGF were significantly lower in the bevacizumab group than in the control group (P , 0.001 and P = 0.003, respectively), while the vitreous and plasma concentrations of apelin did not vary significantly between the 2 groups (P = 0.62 and P = 0.09, respectively). In the epiretinal fibrovascular membranes of both the groups, a colocalization of the endothelial marker CD31 with the markers for apelin was observed.

CONCLUSION

Intravitreal bevacizumab injection may lead to a decrease in the intraocular and systemic concentrations of VEGF, suggesting a local and potentially a systemic effect on VEGF but may have no effect on apelin. Apelin may be associated with the development of epiretinal membranes in proliferative diabetic retinopathy and may not directly correlate with VEGF.

MAPK and PI3K signalling differentially regulate angiogenic and lymphangiogenic cytokine secretion in squamous cell carcinoma of the head and neck

Vascular endothelial growth factors (VEGF-C and VEGF-A) play important roles in tumour-induced lymphangiogenesis and angiogenesis, respectively, key processes implicated in promoting tumour growth and metastatic spread. Previous work from our laboratory has shown that EGFR overexpression in squamous carcinomas of the head and neck (SCCHN) is linked to high levels of VEGF-A and VEGF-C (but low levels of VEGF-D) and is associated with poor prognosis. The present study explored the signalling pathways regulating the induction of VEGF-C and VEGF-A in the SCCHN cell lines CAL 27 and Detroit 562. The addition of exogenous EGF induced the expression of VEGF-C and VEGF-A in a concentration-dependent manner and this was blocked by a selective EGFR inhibitor, gefitinib. In both cell lines stimulated with endogenous or exogenous ligand, inhibition of MEK1/2 (with U0126 or PD98059) or PI3K (with PI-103 or LY294002) resulted in a marked reduction of EGFR-induced VEGF-A expression, whereas exogenous EGF-induced VEGF-C upregulation was blocked by inhibitors of MEK but not PI3K. Inhibition of p38 MAPK suppressed EGF-induced VEGF-C upregulation in CAL 27 cells, but inhibited EGF-induced VEGF-A upregulation in Detroit 562. Taken together, our evidence suggests that both endogenous and exogenous EGFR activation induces VEGF-A expression requiring both PI3K and MAPK signalling whereas VEGF-C expression is dependent on MAPK, but not the PI3K or mTOR pathways in SCCHN cell lines. p38 MAPK appears to be differentially linked to either VEGF-A or VEGF-C regulation in different cellular contexts.

A phase 2 trial of single-agent bevacizumab given in an every-3-week schedule for patients with recurrent high-grade gliomas

BACKGROUND

The authors evaluated a 3-week schedule of bevacizumab in patients with recurrent high-grade glioma (HGG).

METHODS

Patients received bevacizumab 15 mg/kg every 3 weeks and were evaluated every 6 weeks until tumor progression. Tissue correlates were used to quantify tumor content of vascular endothelial growth factor A (VEGFA) and vascular endothelial growth factor receptor-2 (VEGFR2).

RESULTS

Of 61 patients who were treated (35 men and 26 women; median age, 52 years; age range, 21-78 years), 50 patients had glioblastoma multiforme (GBM), and 11 patients had anaplastic glioma (AG). The median number of previous chemotherapies was 2 (range, 1-5 previous chemotherapies), and 16 patients had received ≥3 previous chemotherapies. The median number of bevacizumab doses was 4 (range, 1-20 doses), and 45% of patients received >5 doses. The toxicities observed were primarily grade 1 and 2, and the most common were fatigue, hypertension, and headache. One grade 2 intratumoral bleed and 1 bowel perforation were reported. For patients with GBM, the 6-month progression-free survival rate was 25%, the median time to tumor progression was 10.8 weeks, and the median overall survival was 25.6 weeks. The best response included a partial response in 15 patients (24.5%) and stable disease in 31 patients (50.8%) patients; radiographic recurrence patterns included increased changes in fluid attenuation inversion recovery (24%) and multifocal recurrence (20%). The median survival after bevacizumab failure was 10 weeks. The ratio of tumor VEGFA/VEGFR2 was increased in patients aged >55 years; an increased VEGFA/VEGFR2 ratio was correlated nonsignificantly with decreased survival (P = .052).

CONCLUSIONS

An every-3-week schedule of bevacizumab had antitumor activity and was relatively nontoxic for patients with recurrent HGG. The predictive value of VEGFA/VEGFR2 in tumor will require validation in a larger patient cohort.

A case of ocular benign lymphoid hyperplasia treated with bevacizumab injection

We report the first case of ocular benign lymphoid hyperplasia (BLH) treated with subconjunctival injection of bevacizumab (Avastin). A 27-year-old man presented to our clinic with conjunctival masses and limbal neovascularization. An incisional biopsy yielded the diagnosis of BLH. The patient was subsequently given a subconjunctival injection of bevacizumab (1.25 mg / 0.1 mL). The patient did not experience recurrence or malignant metaplasia during the one-year follow-up period. In patients with conjunctival BLH, subconjunctival injection of bevacizumab can be a useful treatment option in patients unable to undergo a surgical procedure due to limbal neovascularization.

Integrins in tumor angiogenesis and lymphangiogenesis

Angiogenesis, the formation of new blood vessel, plays an important role for the growth and metastasis of malignant tumors. The recent identification of specific growth factors for lymphatic vessels and of new lymphatic-specific markers provided evidence for an active role of the lymphatic system during the tumor growth and metastasis processes. Tumor lymphangiogenesis has been shown to play a role in promoting tumor growth and metastasis of tumor cells to distant sites. Integrins play keys roles in the regulation of angiogenesis and lymphangiogenesis during normal development and several diseases. Indeed, integrins control vascular and lymphatic endothelial cell adhesion, migration, and survival. Importantly, integrin inhibitors can block angiogenesis and lymphangiogenesis. In this chapter, we will highlight the role of integrins during angiogenesis and lymphangiogenesis as well as the function of individual integrins during vascular development, postnatal angiogenesis, and lymphangiogenesis. We discuss the role of integrins as potential therapeutic targets for the control of tumor angiogenesis, lymphangiogenesis, and metastatic spread in the treatment of cancer. We also describe methods to analyze expression and function of integrins during angiogenesis and lymphangiogenesis.

Interaction between the extracellular matrix and lymphatics: consequences for lymphangiogenesis and lymphatic function

The lymphatic system is important for body fluid balance as well as immunological surveillance. Due to the identification of new molecular markers during the last decade, there has been a recent dramatic increase in our knowledge on the molecular mechanisms involved in lymphatic vessel growth (lymphangiogenesis) and lymphatic function. Here we review data showing that although it is often overlooked, the extracellular matrix plays an important role in the generation of new lymphatic vessels as a response to physiological and pathological stimuli. Extracellular matrix-lymphatic interactions as well as biophysical characteristics of the stroma have consequences for tumor formation, growth and metastasis. During the recent years, anti-lymphangiogenesis has emerged as an additional therapeutic modality to the clinically applied anti-angiogenesis strategy. Oppositely, enhancement of lymphangiogenesis in situations of lymph accumulation is seen as a promising strategy to a set of conditions where few therapeutic avenues are available. Knowledge on the interaction between the extracellular matrix and the lymphatics may enhance our understanding of the underlying mechanisms and may ultimately lead to better therapies for conditions where reduced or increased lymphatic function is the therapeutic target.

Functional analyses of the bone marrow kinase in the X chromosome in vascular endothelial growth factor-induced lymphangiogenesis

OBJECTIVE

The goal of this study was to investigate the novel hypothesis that bone marrow kinase in the X chromosome (Bmx), an established inflammatory mediator of pathological angiogenesis, promotes lymphangiogenesis.

METHODS AND RESULTS

We have recently demonstrated a critical role for Bmx in inflammatory angiogenesis. However, the role of Bmx in lymphangiogenesis has not been investigated. Here, we show that in wild-type mice, Bmx is upregulated in lymphatic vessels in response to vascular endothelial growth factor (VEGF). In comparison with wild-type mice, Bmx-deficient mice mount weaker lymphangiogenic responses to VEGF-A and VEGF-C in 2 mouse models. In vitro, Bmx is expressed in cultured human dermal microvascular lymphatic endothelial cells. Furthermore, pharmacological inhibition and short interfering RNA mediated silencing of Bmx reduces VEGF-A and VEGF-C-induced signaling and lymphatic endothelial cell tube formation. Mechanistically, we demonstrated that Bmx differentially regulates VEGFR-2 and VEGFR-3 receptor signaling pathways: Bmx associates with and directly regulates VEGFR-2 activation, whereas Bmx associates with VEGFR-3 and regulates downstream signaling without an effect on the receptor autophosphorylation.

CONCLUSIONS

Our in vivo and in vitro results provide the first insight into the mechanism by which Bmx mediates VEGF-dependent lymphangiogenic signaling.

Podoplanin-expressing cells derived from bone marrow play a crucial role in postnatal lymphatic neovascularization

BACKGROUND

Emerging evidence has suggested a contribution of bone marrow (BM) cells to lymphatic vessel formation; however, the exact phenotype of the cells with lymphatic endothelial progenitor cell function has yet to be identified. Here, we investigate the identity of BM-derived lymphatic endothelial progenitor cells and their role in lymphatic neovascularization.

METHODS AND RESULTS

Culture of BM-mononuclear cells in the presence of vascular endothelial growth factors A and C and endothelial growth factor resulted in expression of lymphatic endothelial cell markers. Among these cells, podoplanin(+) cells were isolated by magnetic-activated cell sorting and characterized by fluorescence-activated cell sorter analysis and immunocytochemistry. These podoplanin(+) cells highly express markers for lymphatic endothelial cells, hematopoietic lineages, and stem/progenitor cells; on further cultivation, they generate lymphatic endothelial cells. We further confirmed that podoplanin(+) cells exist in small numbers in BM and peripheral blood of normal mice but are significantly (15-fold) augmented on lymphangiogenic stimuli such as tumor implantation. Next, to evaluate the potential of podoplanin(+) cells for the formation of new lymphatic vessels in vivo, we injected culture-isolated or freshly isolated BM-derived podoplanin(+) cells into wound and tumor models. Immunohistochemistry demonstrated that the injected cells were incorporated into the lymphatic vasculature, displayed lymphatic endothelial cell phenotypes, and increased lymphatic vascular density in tissues, suggesting lymphvasculogenesis. Podoplanin(+) cells also expressed high levels of lymphangiogenic cytokines and increased proliferation of lymphatic endothelial cells during coculture, suggesting a lymphangiogenic or paracrine role.

CONCLUSIONS

Our results provide compelling evidence that BM-derived podoplanin(+) cells, a previously unrecognized cell type, function as lymphatic endothelial progenitor cells and participate in postnatal lymphatic neovascularization through both lymphvasculogenesis and lymphangiogenesis.

The effect of bevacizumab on corneal neovascularization in rabbits

Purpose

To determine the efficacy of topical application and subconjunctival injection of bevacizumab in the treatment of corneal neovascularization.

Methods

Corneal neovascularization was induced with a silk suture of the corneal stroma in 12 rabbits (24 eyes). One week after suturing, four rabbits were treated with topical bevacizumab at 5 mg/mL (group A) and another four rabbits were treated with topical bevacizumab 10 mg/mL (group B) in the right eyes twice a day for two weeks. A subconjunctival injection of bevacizumab 1.25 mg/mL was done in the right eyes of four rabbits (group C). All of the left eyes (12 eyes) were used as controls. The area of corneal neovascularization was measured after one and two weeks, and the concentration of vascular endothelial growth factor (VEGF) in corneal tissue was measured after two weeks.

Results

The neovascularized area was smaller in all treated groups than in the control group (p<0.001). Upon analysis of the neovascularized area, there was no significant difference between groups A and B. However, the mean neovascularized area of group B was significantly smaller than that of group C after two weeks of treatment (p=0.043). The histologic examination revealed fewer new corneal vessels in all treated groups than the control group. The concentration of VEGF was significantly lower in all treated groups compared to the control group (p<0.01), but no difference was shown between treated groups.

Conclusions

Topical and subconjunctival bevacizumab application may be useful in the treatment of corneal neovascularization and further study is necessary.

Heterogeneity and plasticity of lymphatic endothelial cells

Endothelial cells are found in most organs and tissues in our body. Despite their apparent morphological and functional similarities, endothelial cells exhibit remarkable heterogeneity and plasticity. In a strict sense, no two endothelial cells are identical in terms of their biological, immunological, functional, metabolic, morphological, and anatomical aspects. Their heterogeneity and plasticity are now known to be dependent upon and conferred by their microenvironments, arteriovenous-lymphatic cell identity, organ-specific vascular beds, fluid dynamics, vessel sizes, anatomical locations, physiological and pathological states, and more. Although abundant evidence is available to demonstrate endothelial heterogeneity in the blood vascular system, studies of heterogeneity and plasticity of lymphatic endothelial cells are limited because of the short history of lymphatic research. Nonetheless, a growing body of exciting work has begun to discover that lymphatic endothelial cells are as heterogeneous as blood vascular endothelial cells. In this article, we discuss the heterogeneity and plasticity of lymphatic endothelial cells.

Activation of vascular endothelial growth factor receptor 2 in a cellular model of loricrin keratoderma

Loricrin is a major constituent of the epidermal cornified cell envelope. Recently, heterozygous loricrin gene mutations have been identified in two dominantly inherited skin diseases, Vohwinkel syndrome with ichthyosis and progressive symmetric erythrokeratoderma, collectively termed loricrin keratoderma. We generated stable HaCaT cell lines that express wild-type (WT) loricrin and a mutant form found in Vohwinkel syndrome with ichthyosis, using an ecdysone-inducible promoter system. The cells expressing the mutant loricrin grew more rapidly than those expressing WT loricrin after induction for 5 days. Confocal immunofluorescence microscopy revealed that phospho-Akt occurred in the nucleolus where the mutant loricrin was also located. The level of activity of Akt kinase was about nine times higher in cells with the mutant than in those with WT loricrin. ERK1/2, the epidermal growth factor receptor, vascular endothelial growth factor (VEGF) receptor 2 and Stat3 were all phosphorylated in cells with the mutant loricrin. The docking proteins, Gab1 and c-Cbl, were also tyrosine-phosphorylated in these cells. Furthermore, chromatin immunoprecipitation assays showed that Stat3 protein bound to the VEGF promoter in cells with the mutant. Thus, this study suggests that VEGF release and the subsequent activation of VEGF receptor 2 link loricrin gene mutations to rapid cell proliferation in a cellular model of loricrin keratoderma.

Lymphangiogenesis in cancer: current perspectives

Although the lymphatic system has been initially described in the sixteenth century, basic research has been limited. Despite its importance for the maintenance of tissue fluid homeostasis and for the afferent immune response, research of the molecular mechanisms of lymphatic vessel formation and function has for a long time been hampered. One reason could be because of the difficulties of visibility due to the lack of lymphatic markers. But since the discovery of several molecules specifically expressed in lymphatic endothelial cells, a rediscovery of the lymphatic vasculature has taken place. New scientific insights has facilitated detailed analysis of the nature and organization of the lymphatic system in physiological and pathophysiological conditions, such as in chronic inflammation and metastatic cancer spread. Knowledge about the molecules that control lymphangiogenesis and tumor-associated lymphangiogenesis is now expanding, allowing better opportunities for the development of drugs interfering with the relevant signaling pathways. Advances in our understanding of the mechanisms have translated into a number of novel therapeutic studies.

VEGF-D deficiency in mice does not affect embryonic or postnatal lymphangiogenesis but reduces lymphatic metastasis

Vascular endothelial growth factor-D (VEGF-D) is one of the two ligands of the VEGFR-3 receptor on lymphatic endothelial cells. Gene-silencing studies in mice and Xenopus tadpoles recently showed that the role of endogenous VEGF-D in lymphatic development is moderate. By contrast, exogenous VEGF-D is capable of stimulating lymphangiogenesis. Nonetheless, its endogenous role in pathological conditions remains largely unknown. Hence, we reassessed its role in disease, using Vegf-d(null) mice. Vegf-d(null) mice were generated that, under physiological conditions, displayed normal embryonic and postnatal lymphangiogenesis and lymphatic remodelling, efficient lymphatic functioning and normal health. Vegf-d(null) mice also reponded normally in models of skin wound healing and healing of infarcted myocardium, despite enhanced expression of VEGF-D in these models in wild-type mice. In contrast, Vegf-d(null) mice displayed reduced peritumoral lymphangiogenesis and lymph node metastasis in an orthotopic pancreatic tumour model. Together, our data indicate that endogenous VEGF-D in mice is dispensible for lymphangiogenesis during development, in postnatal and adult physiology and in several pathological conditions, but significantly contributes to lymphatic metastasis.

Neuropilin-2 mediates VEGF-C-induced lymphatic sprouting together with VEGFR3

If neuropilin-2 and the growth factor VEGF-C don’t come together, lymphatic vessels don’t branch apart.

Vascular sprouting is a key process-driving development of the vascular system. In this study, we show that neuropilin-2 (Nrp2), a transmembrane receptor for the lymphangiogenic vascular endothelial growth factor C (VEGF-C), plays an important role in lymphatic vessel sprouting. Blocking VEGF-C binding to Nrp2 using antibodies specifically inhibits sprouting of developing lymphatic endothelial tip cells in vivo. In vitro analyses show that Nrp2 modulates lymphatic endothelial tip cell extension and prevents tip cell stalling and retraction during vascular sprout formation. Genetic deletion of Nrp2 reproduces the sprouting defects seen after antibody treatment. To investigate whether this defect depends on Nrp2 interaction with VEGF receptor 2 (VEGFR2) and/or 3, we intercrossed heterozygous mice lacking one allele of these receptors. Double-heterozygous nrp2vegfr2 mice develop normally without detectable lymphatic sprouting defects. In contrast, double-heterozygote nrp2vegfr3 mice show a reduction of lymphatic vessel sprouting and decreased lymph vessel branching in adult organs. Thus, interaction between Nrp2 and VEGFR3 mediates proper lymphatic vessel sprouting in response to VEGF-C.

Histological and transcriptional study of angiogenesis and lymphangiogenesis in uninvolved skin, acute pinpoint lesions and established psoriasis plaques: an approach of vascular development chronology in psoriasis

BACKGROUND

Dysregulation of angiogenesis and lymphangiogenesis could participate in psoriasis pathogenesis. Analysis of nascent psoriasis lesions should help at identifying early vascular anomalies.

OBJECTIVE

To analyse vascular development, angiogenesis and lymphangiogenesis markers expression in uninvolved skin in psoriatic patients (N), early psoriasis lesions or pinpoints (PP) and psoriasis plaques (PSO).

METHODS

Skin biopsies were taken in 17 patients in N and in PSO and/or PP. The mRNA steady-state level of angiogenesis and lymphangiogenesis markers was measured by RT-PCR. Immunohistochemistry was performed for von Willebrand factor, podoplanin, Ki-67 and VEGFR3. Blood (BV) and lymphatic (LV) vessels expansion was measured by computer-assisted morphometry.

RESULTS

Clinical and epidermal aspects indicated that PP are intermediate between N and PSO. While total BV area was already increased in PP similarly to PSO as compared to N, LV area in PP was intermediate between N and PSO. Mean LV size was identical in N and PP and increased in PSO, mean BV size in PP being intermediate between N and PSO. VEGF-A 189 variant was increased in PP as compared to N and PSO. As compared to N, angiogenesis markers (VEGF-A isoforms, PlGF, VEGFR2, NRP-1), VEGF-C and NRP-2 were similarly increased in PP and PSO. Keratin 16 and the lymphangiogenesis markers (VEGFR3, prox-1) were intermediate in PP.

CONCLUSION

These data suggest that the expansion of lymphatic vessels occurs after blood vascular development in psoriasis. Expansion of BV in PP could be followed by vessel enlargement during progression to PSO, in parallel with a decreased VEGF-A 189/VEGF-A 121 balance in plaques.

Vascular integrins: therapeutic and imaging targets of tumor angiogenesis

Cells, including endothelial cells, continuously sense their surrounding environment and rapidly adapt to changes in order to assure tissues and organs homeostasis. The extracellular matrix (ECM) provides a physical scaffold for cell positioning and represents an instructive interface allowing cells to communicate over short distances. Cell surface receptors of the integrin family emerged through evolution as essential mediators and integrators of ECM-dependent communication. In preclinical studies, pharmacological inhibition of vascular integrins suppressed angiogenesis and inhibited tumor progression. alpha(V)beta(3) and alpha(V)beta(5) were the first integrins targeted to suppress tumor angiogenesis. Subsequently, additional integrins, in particular alpha(1)beta(1), alpha(2)beta(1), alpha(5)beta(1), and alpha(6)beta(4), emerged as potential therapeutic targets. Integrin inhibitors are currently tested in clinical trials for their safety and antiangiogenic/antitumor activity. In this chapter, we review the role of integrins in angiogenesis and present recent advances in the use of integrin antagonists as potential therapeutics in cancer and discuss future perspectives.

Tumor-derived VEGF modulates hematopoiesis

VEGF-induced angiogenesis significantly contributes to tumor growth, invasion and metastasis. However, little is known about its hematopoietic activity during malignant development and progression. Here we show that in a mouse tumor model, tumor-derived VEGF acts as an endocrine-like hormone to induce extramedullary hematopoiesis by targeting distal organs in the host. In tumor-bearing mice, circulating VEGF induced hepatomegaly and splenomegaly owing to vessel dilation, tortuosity and activation of hematopoiesis. Furthermore, VEGFR1 and VEGFR2 were primarily localized in blood vessels rather than hepatocytes or splenocytes, demonstrating that alteration of angiogenic profiles modulates hematopoiesis in these organs. Stimulation of extramedullary hematopoiesis sheds new light on complex biological functions of VEGF and significantly increases our understanding of molecular mechanisms underlying VEGF-induced tumor growth.

VEGF-A expression by HSV-1-infected cells drives corneal lymphangiogenesis

Inflammatory lymphangiogenesis plays a crucial role in the development of inflammation and transplant rejection. The mechanisms of inflammatory lymphangiogenesis during bacterial infection, toll-like receptor ligand administration, and wound healing are well characterized and depend on ligands for the vascular endothelial grow factor receptor (VEGFR) 3 that are produced by infiltrating macrophages. But inflammatory lymphangiogenesis in nonlymphoid tissues during chronic viral infection is unstudied. Herpes simplex virus 1 (HSV-1) infection of the cornea is a leading cause of blindness and depends on aberrant host immune responses to antigen within the normally immunologically privileged cornea. We report that corneal HSV-1 infection drives lymphangiogenesis and that corneal lymphatics persist past the resolution of infection. The mechanism of HSV-1–induced lymphangiogenesis was distinct from the described mechanisms of inflammatory lymphangiogenesis. HSV-1–elicited lymphangiogenesis was strictly dependent on VEGF-A/VEGFR-2 signaling but not on VEGFR-3 ligands. Macrophages played no role in the induction of lymphangiogenesis and were not a detectable source of VEGF-A. Rather, using VEGF-A reporter transgenic mice, we have identified infected epithelial cells as the primary source of VEGF-A during HSV-1 infection. Our results indicate that HSV-1 directly induces vascularization of the cornea through up-regulation of VEGF-A expression.