Molecular and cellular mechanisms of lymphangiogenesis

Exosomal circ_0026611 contributes to lymphangiogenesis by reducing PROX1 acetylation and ubiquitination in human lymphatic endothelial cells (HLECs)

BACKGROUND

Esophageal squamous carcinoma (ESCC) is a common malignancy that originates in the digestive tract. Lymph node metastasis (LNM) is a complicated process, and tumor lymphangiogenesis has been reported to be associated with the spread of tumor cells to lymph nodes (LNs), including in ESCC. However, little is currently known about the mechanisms involved in lymphangiogenesis in ESCC tumors. According to previous literature, we know that hsa_circ_0026611 expresses at a high level in serum exosomes of patients with ESCC and shows a close association with LNM and poor prognosis. However, details on the functions of circ_0026611 in ESCC remain unclear. We aim to explore the effects of circ_0026611 in ESCC cell-derived exosomes on lymphangiogenesis and its potential molecular mechanism.

METHODS

We firstly examined how circ_0026611 may express in ESCC cells and exosomes by quantitative reverse transcription real-time polymerase chain reaction (RT-qPCR). The potential effects circ_0026611 may exert on lymphangiogenesis in ESCC cell-derived exosomes were assessed afterward via mechanism experiments.

RESULTS

circ_0026611 high expression pattern was confirmed in ESCC cells and exosomes. ESCC cell-derived exosomes promoted lymphangiogenesis by transferring circ_0026611. Besides, circ_0026611 interacted with N-α-acetyltransferase 10 (NAA10) to inhibit NAA10-mediated prospero homeobox 1 (PROX1) acetylation with subsequent ubiquitination and degradation. Furthermore, circ_0026611 was verified to promote lymphangiogenesis in a PROX1-mediated manner.

CONCLUSIONS

Exosomal circ_0026611 inhibited PROX1 acetylation and ubiquitination to promote lymphangiogenesis in ESCC.

Detection of Lymphatic Vessels in Dental Pulp

Simple Summary

Our studies and results suggest a moderate correlation between pulp inflammation and the formation of new vessels, including lymphatic vessels. In view of the above, it can be concluded that as inflammation increases, the size of the vascular bed that enables circulation of body fluids, blood, and lymph increases as well. However, microscopic and immunohistochemical studies did not conclusively demonstrate if these vessels form systems within the pulp that facilitate drainage of the tooth cavity.

Abstract

The literature lacks conclusive evidence that lymphatic vessels can form in the dental pulp. Lymphangiogenesis is believed to occur in an inflamed pulp. If one defines lymphangiogenesis as the development of lymphatic vessels from already existing ones, such a mechanism is possible only when lymphatic vessels are present in healthy teeth. This paper aims to identify lymphatic vessels in the dental pulp using microscopic and immunohistochemical methods under physiological and pathological conditions. The tissue material consisted of human teeth intended for extraction. Our studies and results suggest a moderate correlation between pulp inflammation and the formation of new vessels, including lymphatic vessels.

EGR1 Enhances Lymphangiogenesis via SOX18-Mediated Activation of JAK2/STAT3 Pathway

Background. Lymphangiogenesis is a process involved in the pathogenesis of many diseases. Identifying key molecules and pathway targeting this process is critical for lymphatic regeneration-associated disorders. EGR1 is a transcription factor, but its function in lymphangiogenesis is not yet known. This study is aimed at exploring the functional activity and molecular mechanism of EGR1 implicated in lymphangiogenesis. Methods. The CCK-8 method, transwell migration assay, and tube formation assay were used to detect the cell viability, motility, and tube formation of HDLEC cells, respectively. The luciferase reporter assay was applied to detect the impact of EGR1 on SOX18 promoter activity. CHIP assay was used to analyze the direct binding of EGR1 to the SOX18 promoter. qRT-PCR and Western blot analysis were performed to investigate molecules and pathway involved in lymphangiogenesis. Results. The EGR1 ectopic expression markedly increased the cell growth, mobility, tube formation, and the expression of lymphangiogenesis-associated markers (LYVE-1 and PROX1) in HDLEC cells. EGR1 interacted with the SXO18 gene promoter and transcriptionally regulated the SXO18 expression in HDLEC cells. Silencing of SOX18 abrogated the promotional activities of EGR1 on the cell viability, mobility, tube formation, and LYVE-1/PROX1 expression in HDLEC cells. SOX18 overexpression activated JAK/STAT signaling, which resulted in an increase in lymphangiogenesis in HDLEC cells. Conclusions. ERG1 can promote lymphangiogenesis, which is mediated by activating the SOX18/JAK/STAT3 cascade. ERG1 may serve as a promising target for the therapy of lymphatic vessel-related disorders.

The Role of Methionine Aminopeptidase 2 in Lymphangiogenesis

During the metastasis process, tumor cells invade the blood circulatory system directly from venous capillaries or indirectly via lymphatic vessels. Understanding the relative contribution of each pathway and identifying the molecular targets that affect both processes is critical for reducing cancer spread. Methionine aminopeptidase 2 (MetAp2) is an intracellular enzyme known to modulate angiogenesis. In this study, we investigated the additional role of MetAp2 in lymphangiogenesis. A histological staining of tumors from human breast-cancer donors was performed in order to detect the level and the localization of MetAp2 and lymphatic capillaries. The basal enzymatic level and activity in vascular and lymphatic endothelial cells were compared, followed by loss of function studies determining the role of MetAp2 in lymphangiogenesis in vitro and in vivo. The results from the histological analyses of the tumor tissues revealed a high MetAp2 expression, with detectable sites of co-localization with lymphatic capillaries. We showed slightly reduced levels of the MetAp2 enzyme and MetAp2 mRNA expression and activity in primary lymphatic cells when compared to the vascular endothelial cells. The genetic and biochemical manipulation of MetAp2 confirmed the dual activity of the enzyme in both vascular and lymphatic remodulation in cell function assays and in a zebrafish model. We found that cancer-related lymphangiogenesis is inhibited in murine models following MetAp2 inhibition treatment. Taken together, our study provides an indication that MetAp2 is a significant contributor to lymphangiogenesis and carries a dual role in both vascular and lymphatic capillary formation. Our data suggests that MetAp2 inhibitors can be effectively used as anti-metastatic broad-spectrum drugs.

A novel role of HIF-1α/PROX-1/LYVE-1 axis on tissue regeneration after renal ischaemia/reperfusion in mice

Context: Renal ischaemia reperfusion (I/R) is a common clinical condition with a high morbidity and mortality rate. To date, I/R-induced renal injury remains an ineffective treatment. Objective: We hypothesis that angiogenesis and lymphangiogenesis markers, prospero homeobox-1 (PROX-1) and lymphatic endothelial hyaluronan receptor-1 (LYVE-1), are critical during I/R. Material and methods: Kunming mice were subjected to I/R and observed for the following eight consecutive days. Pathology analysis and protein distribution were detected by H&E staining, immunohistochemistry and immunofluorescence confocal analysis. Results: After I/R treatment, renal pathology was changed. HIF-1α was induced in the early stage and colocalisation with PROX-1 mainly in the renal tubular region, whereas PROX-1 and LYVE-1 were colocalised in the glomerulus of the endothelial region. Conclusions: In this study, we revealed HIF-1α/PROX-1/LVYE-1 axis dynamic changes in different regions after I/R and demonstrated for the first time it activates during I/R repair.

The correlation between serum vascular endothelial growth factor (VEGF) and tumor VEGF receptor 3 in colorectal cancer

Purpose

Despite plasma biomarkers offering a number of advantages over tissue-based markers, the relationship between serum vascular endothelial growth factor (VEGF) and VEGF receptor (VEGF-R) tumor expression in colorectal cancer (CRC) is still unclear. This study was designed to establish the relationship between the concentration of serum VEGF and tumor VEGF-R expression in patients with CRC.

Methods

A prospective study of consecutive patients undergoing elective colorectal surgery during 1 year. Preoperative VEGF was determined by enzyme-linked immunosorbent assay and VEGF-R3 by immunochemistry.

Results

The initial sample included 134 patients with CRC diagnosis. Results showed significant association of serum values of VEGF with VEGF-R3 expression (P < 0.001), even in the presence of confounders (sex, age, body mass index, tumor location, and surgical approach). The estimated effect size was high (η² = 0.35).

Conclusion

Serum VEGF has a significant correlation with tumoral VEGF-R3 expression in CRC.

The Telocytes in the Subepicardial Niche

A great interest has developed over the last several years in research on interstitial Cajal-like cells (ICLCs), later renamed to telocytes (TCs). Such studies are restricted by diverse limitations. We aimed to critically review (sub)epicardial ICLCs/TCs and to bring forward supplemental immunohistochemical evidence on (sub)epicardial stromal niche inhabitants. We tested the epicardial expressions of CD117/c-kit, CD34, Cytokeratin 7 (CK7), Ki67, Platelet-Derived Growth Factor Receptor (PDGFR)-α and D2-40 in adult human cardiac samples. The mesothelial epicardial cells expressed D2-40, CK7, CD117/c-kit and PDGFR-α. Subepicardial D2-40-positive lymphatic vessels and isolated D2-40-positive and CK7-positive subepicardial cells were also found. Immediate submesothelial spindle-shaped cells expressed Ki-67. Submesothelial stromal cells and endothelial tubes were PDGFR-α-positive and CD34-positive. The expression of CD34 was pan-stromal, so a particular stromal cell type could not be distinguished. The stromal expression of CD117/c-kit was also noted. It seems that epicardial TCs could not be regarded as belonging to a unique cell type until (pre)lymphatic endothelial cells are inadequately excluded. Markers such as CD117/c-kit or CD34 seem to be improper for identifying TCs as a distinctive cell type. Care should be taken when using the immunohistochemical method and histological interpretations, as they may not produce accurate results.

Lymphatic Contribution to the Cellular Niche in Heterotopic Ossification

OBJECTIVE

The objective of this study was to determine the contribution of lymphatic tissue to heterotopic ossification (HO).

BACKGROUND

HO is the pathologic development of ectopic bone within soft tissues often following severe trauma. Characterization of the tissue niche supporting HO is critical to identifying therapies directed against this condition. Lymphangiogenesis is upregulated during incidents of trauma, thereby coincident with the niche supportive of HO. We hypothesized that lymphatic tissues play a critical role in HO formation.

METHODS

Mice underwent hindlimb Achilles' tendon transection and dorsal burn injury (burn/tenotomy) to induce HO. The popliteal and inguinal lymph nodes were excised ipsilateral to the tenotomy site. Flow cytometry and immunostaining were used to quantify and localize lymphoendothelium. MicroCT was used to quantify HO.

RESULTS

Enrichment of mature lymphatic tissues was noted 2 weeks after injury at the tendon transection sites when compared with the contralateral, intact tendon based on LYVE1+ tubules (10.9% vs 0.8%, P < 0.05). Excision of the inguinal and popliteal nodes with draining popliteal lymphatic vessel significantly decreased the presence of mature lymphoendothelium 2 weeks after injury (10.9% vs 3.3%, P < 0.05). Bone-cartilage-stromal progenitor cells (CD105+/AlphaV+/Tie2-/CD45-/CD90-/BP1-) were also significantly decreased after lymph node excision (10.2% vs 0.5%, P < 0.05). A significant decrease was noted in the volume of de novo HO present within the soft tissues (0.12 mm vs 0.02 mm).

CONCLUSION

These findings suggest that lymphatic vessels are intimately linked with the de novo formation bone within soft tissues following trauma, and their presence may facilitate bone formation.

Evaluation of Podoplanin in Oral Leukoplakia and Oral Squamous Cell Carcinoma

Background. Recent studies have demonstrated that podoplanin was expressed in some dysplastic lesions adjacent to primary oral cancers suggesting that podoplanin expression may occur in early oral tumorigenesis and lymphangiogenesis and therefore is related to tumor growth. The purpose of this study is to determine the role of podoplanin as a biomarker for cancer risk assessment in oral leukoplakia and correlation of podoplanin expression with grades of oral squamous cell carcinoma (OSCC). Materials and Methods. In the present retrospective study, podoplanin expression was investigated immunohistochemically in 40 patients each of oral leukoplakia and OSCC. The scores were analyzed statistically using one-way ANOVA test followed by Tukey HSD. Results. By applying one-way ANOVA test, there was a highly significant increase of the podoplanin expression from mild to severe dysplasia and from well to poorly differentiated OSCC (P < 0.01). Statistically highly significant difference was present between scores of mild to moderate dysplasia, moderate to severe dysplasia, well to poorly differentiated OSCC, and moderately to poorly differentiated OSCC (Tukey HSD test, P < 0.01). Conclusion. Podoplanin can be used as a biomarker for early oral tumorigenesis and for malignant transformation risk assessment of premalignant lesions and as a tumor progression biomarker for advanced grades of OSCC.

Identification of high-affinity VEGFR3-binding peptides through a phage-displayed random peptide library

Objective

Vascular endothelial growth factor (VEGF) interaction with its receptor, VEGFR-3/Flt-4, regulates lymphangiogenesis. VEGFR-3/Flt-4 expression in cancer cells has been correlated with clinical stage, lymph node metastasis, and lymphatic invasion. The objective of this study is to identify a VEGFR-3/Flt-4-interacting peptide that could be used to inhibit VEGFR-3 for ovarian cancer therapy.

Methods

The extracellular fragment of recombinant human VEGFR-3/Flt-4 (rhVEGFR-3/Flt-4) fused with coat protein pIII was screened against a phage-displayed random peptide library. Using affinity enrichment and enzyme-linked immunosorbent assay (ELISA) screening, positive clones of phages were amplified. Three phage clones were selected after four rounds of biopanning, and the specific binding of the peptides to rhVEGFR-3 was detected by ELISA and compared with that of VEGF-D. Immunohistochemistry and immunofluorescence analyses of ovarian cancer tissue sections was undertaken to demonstrate the specificity of the peptides.

Results

After four rounds of biopanning, ELISA confirmed the specificity of the enriched bound phage clones for rhVEGFR-3. Sequencing and translation identified three different peptides. Non-competitive ELISA revealed that peptides I, II, and III had binding affinities for VEGFR-3 with K_aff (affinity constant) of 16.4±8.6 µg/mL (n=3), 9.2±2.1 µg/mL (n=3), and 174.8±31.1 µg/mL (n=3), respectively. In ovarian carcinoma tissue sections, peptide III (WHWLPNLRHYAS), which had the greatest binding affinity, also co-localized with VEGFR-3 in endothelial cells lining lymphatic vessels; its labeling of ovarian tumors in vivo was also confirmed.

Conclusion

These finding showed that peptide III has high specificity and activity and, therefore, may represent a potential therapeutic approach to target VEGF-VEGFR-3 signaling for the treatment or diagnosis of ovarian cancer.

Lymphangiogenesis and Inflammation-Looking for the "Missing Pieces" of the Puzzle

Several papers about lymphangiogenesis and inflammation focused on the detailed and complicated descriptions of the molecular pathways accompanying both non-tumor and tumor inflammatory-induced lymphatic vessel development. Many authors are tempted to present inflammatory-induced lymphangiogenesis in pathologic conditions neglecting the role of inflammatory cells during embryonic lymphatic vessel development. Some of the inflammatory cells are largely characterized in inflammatory-induced lymphangiogenesis, while others as mast cells, eosinophils, or plasma cells are less studied. No phenotypic characterization of inflammation-activated lymphatic endothelial cell is available in this moment. Another paradox is related to the existence of few papers regarding lymphangiogenesis inside lymphoid organs and for their related pathology. There are still several "missing pieces of such a big puzzle" of lymphangiogenesis and inflammation, with a direct impact on the ineffectiveness of the anti-inflammatory therapy as lymphangiogenesis inhibitors. The present paper will focus on the controversial issues of lymphangiogenesis and inflammation.

Interleukin-8: A potent promoter of human lymphatic endothelial cell growth in gastric cancer

Lymphatic metastasis is a major progression route of gastric cancer. Interleukin-8 (IL-8), as an inflammatory cytokine, is induced by Helicobacter pylori infection and is strongly associated with gastric cancer development and metastasis. The blood and lymphatic systems are similar in their function and gene expression profiles. It has been proposed that IL-8 activates angiogenesis. However, the direct role of IL-8 in lymphangiogenesis in gastric cancer remains unclear. We investigated the effect of IL-8 on the growth of human lymphatic endothelial cells (LECs). In addition, protein and mRNA expression of selected lymphangiogenesis markers was assessed in these cells. LECs were co-cultured with gastric cancer SGC7901 cells and exposed to various concentrations of IL-8 (0, 0.2, 0.5, 0.8 and 1.0 ng/ml). The Cell Counting Kit-8 was used to evaluate LEC proliferation (cultured for 1-6 days). Then, protein (immunofluorescence and western blotting) and mRNA [quantitative transcription-polymerase chain reaction (qPCR)] levels were measured in samples obtained from the 24-h cultured cells, for lymphatic vessel endothelial hyaluronic acid receptor-1 (LYVE-1), vascular endothelial growth factor (VEGF)-C, VEGF-D and vascular endothelial growth factor receptor-3 (VEGFR-3). The data presented herein demonstrated that IL-8 promotes the proliferation of LECs and enhances the protein and mRNA expression of LYVE-1. Notably, IL-8 inhibited VEGF-C, VEGF-D and VEGFR-3 protein expression as well as VEGF-D and VEGFR-3 mRNA expression. These findings suggest that IL-8 may be a potent inducer of LECs, although this effect does not appear to involve the VEGF-C/VEGF-D and VEGFR-3 signaling pathway.

Expression of lymphatic markers and lymphatic growth factors in psoriasis before and after anti-TNF treatment

BACKGROUND

Angiogenesis is an early stage of psoriatic lesion development, but less is known about lymphagiogenesis and its role in the development of psoriasis.

OBJECTIVE

To examine the expression of specific lymphatic markers and lymphatic growth factors in untreated psoriatic skin, in the unaffected skin of patients and skin of healthy volunteers, as well as their alteration after treatment with an anti-TNF agent.

METHODS

Immunohistochemistry for the lymphatic markers D2-40 and LYVE-1, in addition to the VEGF-C and VEGF-D growth factors, was performed in the skin biopsies of psoriatic lesions and adjacent non-psoriatic skin of 19 patients before and after treatment with etanercept, as well as in the skin biopsies of 10 healthy volunteers.

RESULTS

The expressions of D2-40, VEGF-C and VEGF-D on lymphatic vessels underwent statistically significant increases in untreated psoriatic skin compared with non-lesional skin, in contrast to LYVE-1, which did not involve significant increase in expression in psoriatic skin. VEGF-C expression on lymphatic vessels diminished after treatment with etanercept. Moreover VEGF-C and VEGF-D staining on fibroblasts presented with higher expression in lesional skin than in non-lesional adjacent skin.

CONCLUSION

Remodeling of lymphatic vessels possibly occurs during psoriatic lesion development, parallel to blood vessel formation. The exact role of this alteration is not yet clear and more studies are necessary to confirm these results.

Head and neck squamous cell carcinoma lymphatic spread and survival: Relevance of vascular endothelial growth factor family for tumor evaluation

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is primarily a locoregional disease in which the cervical lymph nodes are the chief site of metastasis. The purpose of this study was to examine the relationship between lymphangiogenesis and clinicopathological aspects of HNSCC and its metastasis.

METHODS

Fifty-two patients with HNSCC and metastatic lymph nodes from 21 of these subjects were analyzed by immunohistochemistry.

RESULTS

The HNSCC samples were predominantly negative for vascular endothelial growth factor (VEGF)-C, VEGF-D, and vascular endothelial growth factor receptor (VEGFR)3. There was an association between the density of lymph vessels (measured by D2-40 staining) in the lymph nodes and advanced-stage tumors. There was no link between the expression of these proteins and survival rates.

CONCLUSION

Although lymphatic spread is a significant event in the progression of HNSCC, the expression of VEGF-C, VEGF-D, and VEGFR3 does not correlate with clinicopathological characteristics, suggesting that other signaling pathways mediate lymphangiogenesis in HNSCC.

The link between lymphedema, breast reconstruction and microsurgery

SUMMARY 

This management perspective will explore the relationship between lymphedema and breast reconstruction surgery. Little data exist, but early reports suggest breast reconstruction may be associated with a lower risk of lymphedema. Theories surrounding this relationship, as well as available data on lymphatic repair theories, will be discussed. In addition, the emerging role of lymphatic surgery to prevent or reverse lymphedema will be discussed. The refinement of advanced microsurgical techniques has resulted in a renewed interest in lymphatic surgery to cure lymphedema. However, efficacy, validation of surgical results, and surgery's ability to eliminate from patients the need for daily compression garments and therapy need further study.

Lymphatic invasion as a prognostic biomarker in primary cutaneous melanoma

Melanoma has a propensity for lymph node metastasis. However, the incidence of lymphatic invasion detected by histology alone in primary melanoma is disproportionately low in comparison to the incidence of positive sentinel lymph nodes (SLN). With the discovery of lymphatic endothelial cell markers, such as podoplanin and LYVE-1, lymphatic vessels can be reliably detected in formalin-fixed paraffin-embedded (FFPE) tissues. There is a now consensus that lymphatic invasion detected by immunohistochemical stains in primary melanoma is much more common than previously reported by histological examination alone. Immunohistochemical stains show that lymphangiogenesis and lymphatic invasion in primary melanoma may occur intratumorally or peritumorally, and lymphatic invasion is common across the range of tumor thicknesses in primary vertical growth phase (VGP) melanomas. A number of studies have shown that lymphatic invasion in primary melanoma is associated with a positive sentinel lymph node biopsy and a worse clinical outcome. Although not currently a part of the standard of care for staging of melanoma, the detection of lymphatic invasion in primary melanoma using immunohistochemical markers may be helpful in planning of therapy in some cases and may find a routine role in primary melanoma microscopic attributes in future.

Serum VEGF and VEGF-C values before surgery and after postoperative treatment in gastric cancer

INTRODUCTION

Angiogenesis and lymphangiogenesis are essential processes for the formation of blood and lymphatic vessels that allow tumour growth and spread. The binding of VEGF and VEGF-C factors with their receptors (VEGFR2, VEGFR3) in endothelial cells triggers signals that regulate these processes. We compared preoperative serum VEGF and VEGF-C levels with samples obtained after completion of surgery and adjuvant treatment in patients with gastric cancer. In addition, we determined the prognostic value and relationship to survival of serum VEGF and VEGF-C levels.

METHODS

We used a prospective cohort study of 59 gastric cancer patients who underwent surgery. Serum VEGF and VEGF-C were measured by enzyme-linked immunosorbent assay (ELISA) the day before surgery and 6 months later, after completion of adjuvant treatment.

RESULTS

Serum VEGF values decreased after treatment in patients with resectable tumours (mean ± SD) (405.42 ± 298.38 vs. 306.38 ± 212.47 pg/ml; p < 0.01), poorly differentiated and undifferentiated tumours (G3, G4) (438 ± 339.71 vs. 322.47 ± 210.71 pg/ml; p = 0.01), locally advanced gastric tumours (T4 stage) (424.27 ± 323.08 vs. 333.62 ± 221.72 pg/ml; p = 0.03) and tumours with a greater number of involved regional lymph nodes (N3) (442.38 ± 311.52 vs. 337.4 ± 203.64 pg/ml; p = 0.04). Serum preoperative VEGF values over 761 pg/ml were associated with shorter patient survival. The mean overall survival time for patients with serum VEGF levels higher than 761 pg/ml was 7 ± 2.99 months (95 % CI 1.14-12.86) while for patients with serum VEGF levels of less than 761 pg/ml was 21.18 ± 2.88 (95 % CI 15.54-26.83) The mean disease-specific survival time for patients with serum VEGF levels higher than 761 pg/ml was 6.25 ± 2.53 months (95 % CI 1.29-11.21) while for patients with serum VEGF levels of less than 761 pg/ml was 27.57 ± 3.45 (95 % CI 20.80-34.35). Multivariate analysis identified preoperative serum VEGF levels as an independent prognostic factor (HR = 0.144; p = 0.03).

CONCLUSIONS

Serum VEGF levels decreased after the completion of treatment in patients with resected tumours, suggesting VEGF tracking may be useful in monitoring progression. Preoperative measurement of serum VEGF may help us identify patients with a poor prognosis.

Development of lymphatic vasculature and morphological characterization in rat kidney

BACKGROUND

The mechanisms and morphological characteristics of lymphatic vascular development in embryonic kidneys remain uncertain.

METHODS

We examined the distribution and characteristics of lymphatic vessels in developing rat kidneys using immunostaining for podoplanin, prox-1, Ki-67, type IV collagen (basement membrane: BM), and α-smooth muscle actin (αSMA: pericytes or mural cells). We also examined the expression of VEGF-C.

RESULTS

At embryonic day 17 (E17), podoplanin-positive lymphatic vessels were observed mainly in the kidney hilus. At E20, lymphatic vessels extended further into the developing kidneys along the interlobar vasculature. In 1-day-old pups (P1) to P20, lymphatic vessels appeared around the arcuate arteries and veins of the kidneys, with some reaching the developing cortex via interlobular vessels. In 8-week-old adult rats, lymphatic vessels were extensively distributed around the blood vasculature from the renal hilus to cortex. Only lymphatic capillaries lacking continuous BM and αSMA-positive cells were present within adult kidneys, with none observed in renal medulla. VEGF-C was upregulated in the developing kidneys and expressed mainly in tubules. Importantly, the developing lymphatic vessels were characterized by endothelial cells immunopositive for podoplanin, prox-1, and Ki-67, with no surrounding BM or αSMA-positive cells.

CONCLUSION

During nephrogenesis, lymphatic vessels extend from the renal hilus into the renal cortex along the renal blood vasculature. Podoplanin, prox-1, Ki-67, type IV collagen, and αSMA immunostaining can detect lymphatic vessels during lymphangiogenesis.

Expression of lymphatic endothelium-specific hyaluronan receptor LYVE-1 in the developing mouse kidney

Our knowledge of the embryonic development of the lymphatic vessels within the kidney is limited. The aim of this study was to establish the time of appearance and the distribution of intra-renal lymphatic vessels in the developing mouse kidney by using the lymphatic marker, LYVE-1. Kidneys from embryonic day 12 (E12) to E18, from neonates at post-natal day 1 (P1) to P21, and from adults were studied. In the adult mouse kidney, LYVE-1 was expressed mainly in the lymphatic endothelial cells (LECs) and in a subset of endothelial cells in the glomerular capillaries. However, in the developing mouse kidney, LYVE-1 was also expressed transiently in F4/80(+)/CD11b(-) immature macrophages/dendritic cells and in the developing renal vein. LYVE-1(+) lymphatic vessels connected with extra-renal lymphatics were detected in the kidney at E13. F4/80(+)/CD11b(-)/LYVE-1(+) immature macrophages/dendritic cells appeared prior to the appearance of LYVE-1(+) renal lymphatic vessels and were closely intermingled or even formed part of the lymphatic vascular wall. Prox1 was expressed only in the LYVE-1(+) LECs from fetus to adult-hood, but not in LYVE-1(+) endothelial cells of the developing renal vein and macrophages/dendritic cells. Thus, lymphatic vessels of the kidney might originate by extension of extra-renal lymphatics through an active branching process possibly associated with F4/80(+)/CD11b(-)/LYVE-1(+) macrophages/dendritic cells.

Development and hormonal regulation of the ovarian lymphatic vasculature

The lymphatic vasculature plays a number of essential physiological roles including maintaining fluid homeostasis, providing a network for the transport of immune cells, and facilitating the uptake of fat-soluble nutrients from the gastrointestinal tract. Although the critical importance and remodeling capacity of the blood vasculature has been well described within the ovary, just a few reports describe the lymphatic vasculature. Using histological and molecular techniques, we report the kinetics of ovarian lymphangiogenesis and the hormonal regulation of lymphangiogenic growth factors associated with key stages of ovarian follicle growth. We exploited the Adamts1-null mouse model, a model with a previously characterized lymphatic defect to further interrogate the mechanisms controlling ovarian lymphangiogenesis. The establishment and development of the ovarian lymphatic vascular network in postnatal developing ovaries was associated with the presence and hormonal regulation of the lymphangiogenic growth factors and their receptors, including Vegfc, Vegfd, and Vegfr3. We characterized the hormonally regulated remodeling of the ovarian lymphatic vasculature in response to FSH and estradiol. The lymphatic network was defective in the Adamts1-null ovary, clearly demonstrating both the involvement of FSH/estradiol and the Adamts1 (a disintegrin and metalloproteinase with thrombospondin motifs 1) protease in ovarian lymphangiogenesis. This study provides the first evidence of a malleable lymphatic system responsive to hormonal changes of the female reproductive cycle, at least in the mouse ovary, suggesting a role for lymphatic vessel functions in normal folliculogenesis.

Study of intussusceptive angiogenesis in inflammatory regional lymph nodes by scanning electron microscopy

The aim of the present study was to verify the occurrence of intussusceptive angiogenesis in blood vessels from submandibular lymph nodes responsible for lymphatic drainage of the tongue. A surgical wound inflicted on the ventral tongue of male Wistar rats and submandibular regional lymph nodes were evaluated at different postoperative periods. Scanning electron microscopy (SEM) was used to observe 123 lymph nodes at times 2, 3, 7, 10, 14, and 21 postoperative days. During the analysis of the vascular models with SEM, intussusceptive angiogenesis was observed in all groups evaluated. This was more extensive on the second and third postoperative days (83.33% and 80%, respectively), representing in these groups the expansion of the vascular chain of lymph nodes. At 21 postoperative days, intussusceptive angiogenesis (42.85%) was suggestive of vascular remodeling.

Existence of the lymphatic system in the primate corpus luteum

To date, there have been no detailed studies on the lymphatic system in the primate corpus luteum (CL); early reports suggested that the presence of this "secondary circulation" in luteal tissue is species-dependant. Therefore, studies were designed to determine if (a) lymphatic vessels exist, and (b) recently discovered lymphangiogenic factors and their receptor are expressed in the macaque CL during the menstrual cycle. Immunohistochemistry (IHC) detected the lymphatic endothelial cell marker, lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), in some endothelial cells and vessels within the ovarian stroma and theca layer of preovulatory follicles and in the CL. Dual fluorescent IHC demonstrated that LYVE1 co-localized with another lymphatic endothelial cell marker D2-40, but a blood vascular endothelial cell marker (von Willebrand Factor, VWF) was in different cells. The numbers and staining intensity of LYVE1-positive cells in the CL appeared to increase from early to mid luteal phase, and remained elevated thereafter. RT-PCR detected cDNA fragments for mRNAs encoding VEGFC, FIGF, and their receptor FLT4 in CL. Real-time PCR analyses revealed similar patterns of VEGFC and FLT4 expression during the luteal lifespan; mRNA levels increased (p < 0.05) from early to mid luteal phase and decreased (p < 0.05) by late luteal phase. In contrast, FIGF levels were elevated initially, declined (p < 0.05) at mid luteal phase, and then increased (p < 0.05) to very late luteal phase. The data strongly suggest that lymphatic vessels are present in the primate CL, and that the VEGFC/FIGF-FLT4 system regulates lymphangiogenesis and luteal structure-function during the menstrual cycle.

Bone marrow-derived mononuclear cell therapy induces distal angiogenesis after local injection in critical leg ischemia

Critical leg ischemia is associated with a high risk of amputation when revascularization is not possible. Cell therapy based on bone marrow-derived mononuclear cells or with peripheral mononuclear cells, collected after stimulation with G-CSF has been used in an attempt to stimulate angiogenesis. Although several studies have raised the hope that such cell therapy may be effective in critical leg ischemia, no direct demonstration of angiogenesis induced by bone marrow-derived mononuclear cell/peripheral mononuclear cell injection has been reported in man. The aim of this study was to identify and to evaluate the extent of the angiogenic process associated with cell therapy in critical leg ischemia in man. To address this question, this pathological study was conducted in patients enrolled in the OPTIPEC clinical trial (Optimization of Progenitor Endothelial Cells in the Treatment of Critical leg ischemia), an interventional cell therapy study in critical leg ischemia. Amputation specimens from these patients were submitted to a standardized dissection protocol. In three patients, an active angiogenesis was observed in the distal part of the ischemic limb but not in the gastrocnemius muscle, the site of bone marrow cell injection. All the newly formed vessels were positive for endothelial cell markers (CD31, CD34, von Willebrand factor) and negative for markers of lymphatic vessels (podoplanin). Immunohistochemical staining for Ki-67 and c-kit showed extensive endothelial cell proliferation within the new vessels. Bone marrow-derived mononuclear cell therapy in patients with critical leg ischemia induces an active, substained angiogenesis in the ischemic and distal parts of the treated limb, although this may not prevent amputation in some patients with very severe ischemia.

Lymphangiogenesis induced by VEGF-C and VEGF-D promotes metastasis and a poor outcome in breast carcinoma: a retrospective study of 61 cases

PURPOSE

To evaluate lymphangiogenesis in patients with breast carcinoma, explore the underlying mechanism, and study the relationship between lymphangiogenesis and progression of breast carcinoma.

METHODS

Sixty-one cases of breast carcinoma with complete clinical and pathological data were analyzed. Using an anti-podoplanin monoclonal antibody, an immunohistochemical study was made of all specimens to detect lymphatic vessel density (LVD) and to investigate its clinicopathological and prognostic value. VEGF-C and VEGF-D were observed by RT-PCR and immunostaining to investigate their clinicopathological and prognostic values and their relationship with lymphangiogenesis.

RESULTS

LVD in breast carcinoma (6.28+/-3.73) was significantly higher than in benign mammary lesions (0.50+/-1.27), P<0.01 and was significantly associated with lymphatic metastasis and high TNM stage, P<0.01. The level of VEGF-C and VEGF-D expression was also significantly higher in breast carcinomas than in benign mammary lesions, P<0.01. LVD increased significantly with higher expression of VEGF-C and VEGF-D, P<0.01. Patients with high expression of VEGF-C and VEGF-D were observed to be more likely to have a bad outcome, P<0.05.

CONCLUSIONS

Lymphangiogenesis was significantly associated with lymph node metastasis, high TNM, and poor outcome in breast carcinoma. LVD may serve as a predictor of lymph node metastasis and a prognostic factor in breast carcinoma. VEGF-C and VEGF-D play an important role in lymphangiogenesis making the carcinoma more aggressive and leading to a poor prognosis.

Lymphatic and angiogenic characteristics in breast cancer: morphometric analysis and prognostic implications

Controversy exists regarding the topography of lymph vessels in breast cancer, their usefulness as prognostic factors, relationship with angiogenesis and whether active lymphangiogenesis occurs within the tumour. A series of 177 well-characterized breast cancers, with long term follow up, were stained with D2-40, CD31 and CD34. Distribution of lymphatics and lymph vessel density (LVD) were assessed in three areas, intratumoural, peripheral and peritumoural and correlated with clinicopathological criteria and patient prognosis. Microvessel density (MVD) was assessed and correlated with LVD. Double immunohistochemical staining with D2-40 and MIB-1 was carried out to assess the proliferative status of lymphatics and of the tumour emboli within. Peritumoural lymphatics were detected in all tumours whereas peripheral and intratumoural lymphatics were detected in 86 and 41% of specimens, respectively. Tumours with higher total LVD were significantly associated with the presence of lymph node (LN) metastasis and shorter overall survival (OS). In multivariate analysis, tumour grade, LN status and the presence of lymphovascular invasion, but not LVD, were independent poor prognostic factors. No association was found between LVD and MVD. Proliferating lymphatics were detected in 29% of specimens and were significantly associated with dense inflammatory infiltrate. In conclusion, lymphatics are located primarily in the peritumoural and peripheral areas in breast cancer and seem to play an important role in disease progression by being routes for tumour dissemination. The lack of correlation between lymphangiogenic and angiogenic characteristics suggests two distinct processes and the presence of active lymphangiogenesis, albeit in a small portion of specimens, may have important therapeutic implications.

Coexpression of VEGF-C and COX-2 and its association with lymphangiogenesis in human breast cancer

Background

Lymphangiogenesis has become a new research frontier in tumor metastasis since the discovery of reliable lymphatic markers that have allowed observation and isolation of lymphatic endothelium. Cyclooxygenase-2 (COX-2) has been reported to be involved in the critical steps in carcinogenesis. However, possible role of COX-2 in lymphangiogenesis and lymphatic metastasis is still poorly understood. In present study, we aimed to investigate the relationship between vascular endothelial growth factor-C (VEGF-C) and COX-2 in human breast cancer, and correlations with lymphangiogenesis and prognosis.

Methods

Tissue samples of primary tumors from 70 patients undergoing intentionally curative surgical resections for breast cancer were immunohistochemically examined for VEGF-C, COX-2, and D2-40 expressions. The association between COX-2 and VEGF-C expressions and clinicopathological parameters as well as prognosis were analysised. To demonstrate the presence of proliferating lymphatic endothelial cells, 10 random cases with high LVD counts were selected for D2-40/Ki-67 double immunostaining.

Results

A significant correlation was found between the expression of VEGF-C and COX-2 (r = 0.529, P < 0.001), and both elevated VEGF-C expression and elevated COX-2 expression were associated with higher lymph vessel density (LVD), lymph node metastasis and D2-40 positive lymphatic invasion (LVI) as well as worse disease free survival (DFS) and overall survival (OS) in a univariate analysis. In the double immunostain for the lymph vessel marker D2-40 and the proliferation marker Ki-67, the results confirmed Ki-67-positive nuclei in a proportion of lymph vessel endothelial cells.

Conclusion

There is indeed lymphangiogenesis in breast cancer, the most compelling evidence being the presence of proliferating lymphatic endothelial cells. VEGF-C and COX-2 are coexpressed and significantly associated with lymphangiogenesis and prognosis in invasive breast cancer. Suggesting COX-2 may up-regulate VEGF-C expression and thus promote lymph node metastasis via lymphangiogenesis pathway in human breast cancer.

Molecular epidemiologic features of inflammatory breast cancer: a comparison between Egyptian and US patients

BACKGROUND

Inflammatory breast cancer (IBC) is a lethal form of breast cancer with unknown etiology. A higher frequency of IBC and a more aggressive IBC phenotype was reported in Egypt than in the United States. This difference in disease frequency and presentation might be related to molecular epidemiologic factors.

METHODS

We used tumor blocks and demographic, epidemiologic, and clinical data of 48 IBC patients from Egypt and 12 patients from the United States. We counted tumor emboli in tumors before and after immunohistochemical staining with lymphatic vessel endothelial receptor-1 (LYVE-1), and measured the expression of RhoC GTPase protein in the two groups.

RESULTS

Erythema, edema, and peau d'orange were found in 77% of the Egyptian patients as compared with 29% found in the US patients (P=0.02). The number of tumor emboli was significantly higher in tumors from Egypt (mean+/-SD, 14.1+/-14.0) than in the tumors from the United States (5.0+/-4.0, P=0.01). The number of tumor emboli in LYVE-1 positive vessels was higher in tumors from Egypt (3.5+/-2.8) than tumors from the United States (1.6+/-0.5, P=0.15). We detected a high level of RhoC in 87% of the tumors from Egypt and 14% of the tumors from the United States (P=0.0003).

CONCLUSION

Patients from Egypt have a more aggressive form of IBC than those in the United States. Our analysis of IBC patients shows that distinct molecular phenotypes can be found when these two study populations are compared. Future studies should explore the epidemiologic and environmental exposures and the genetic factors that might lead to the different clinical and molecular features of IBC in patients from these two countries.

Lymphatic vessel endothelial hyaluronan receptor 1 immunocytochemical staining for pancreatic islets and pancreatic endocrine tumors

OBJECTIVES

Immunocytochemical staining for lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) is able to recognize lymphatic vessel endothelium and pancreatic endocrine cells (PETs). Pancreatic endocrine tumors were studied for LYVE-1 immunocytochemical staining compared with normal pancreatic islets to detect possible presence of LYVE-1 in PETs.

METHODS

Twenty-five cases of primary and metastatic PETs were immunocytochemically stained for LYVE-1, including insulinomas, glucagonomas, somatostatinoma, pancreatic polypeptidomas, gastrinomas, and nonfunctioning tumors. With routinely formalin-fixed and paraffin-embedded tissues, LYVE-1 immunostaining was performed with polyclonal goat antihuman LYVE-1.

RESULTS

All normal pancreatic islet cells were positive for LYVE-1, whereas 2 cases of 25 PETs, 1 each of gastrinoma and nonfunctioning tumor, were positive for LYVE-1, retaining immunocytochemical reactivity of islet cells.

CONCLUSIONS

Normal pancreatic islets were positive for LYVE-1, whereas only 2 of 25 PETs were positive, suggesting that most PETs lost LYVE-1 or contained below detectable levels of LYVE-1. The presence of LYVE-1 in pancreatic islets and in some PETs may suggest structure-function relationship of LYVE-1/lymphatic vessel in hormone synthesis and secretion.

Lymphatic vessel density in pulmonary adenocarcinoma immunohistochemically evaluated with anti-podoplanin or anti-D2-40 antibody is correlated with lymphatic invasion or lymph node metastases

In lung cancers, lymph node metastasis of cancer cells is one of the most important prognostic factors, and lymphatic vessel invasion (LVI) is very important in the stage preceding lymph node metastases. Recently, it has been reported that lymphatic vessel density (LVD) is associated with lymph node metastasis. The aim of the present study was to evaluate the relationship between LVD and LVI based on the immunohistochemical expression of podoplanin or D2-40, which are new specific markers for lymphatic endothelium. Using 76 cases of pulmonary adenocarcinoma, the relationship between LVD and LVI, lymph node metastases, vascular endothelial growth factor C (VEGF-C), VEGF-D or hepatocyte growth factor (HGF) expression was investigated. LVD was significantly associated with LVI, lymph node metastases and VEGF-D expression. LVI was also associated with lymph node metastases, histological subtype, VEGF-C or VEGF-D expression. High LVD, induced by VEGF-C or VEGF-D expression of cancer cells, is a good indicator of lymphatic metastases and LVI in pulmonary adenocarcinoma.

Lymphotoxin beta receptor signaling is required for inflammatory lymphangiogenesis in the thyroid

Infiltration of lymphocytes into the thyroid gland and formation of lymph node-like structures is a hallmark of Hashimoto's thyroiditis. Here we demonstrate that lymphatic vessels are present within these infiltrates. Mice overexpressing the chemokine CCL21 in the thyroid (TGCCL21 mice) developed similar lymphoid infiltrates and lymphatic vessels. TGCCL21 mice lacking mature T and B cells (RAGTGCCL21 mice) did not have cellular infiltrates or increased number of lymphatic vessels compared with controls. Transfer of CD3(+)CD4(+) T cells into RAGTGCCL21 mice promoted the development of LYVE-1(+)podoplanin(+)Prox-1(+) vessels in the thyroid. Genetic deletion of lymphotoxin beta receptor or lymphotoxin alpha abrogated development of lymphatic vessels in the inflamed areas in the thyroid but did not affect development of neighboring lymphatics. These results define a model for the study of inflammatory lymphangiogenesis in the thyroid and implicate lymphotoxin beta receptor signaling in this process.

Study on the relationship between lymphatic vessel density and distal intramural spread of rectal cancer

BACKGROUND

The smallest safe margin of distal clearance for lower rectal cancer is very important for the operation. In a previous study, a few factors were found to play a role in distal intramural spread (DIS), but there are few data regarding the influence of lymphangiogenesis. We studied the relationship between lymphatic vessel density (LVD) and DIS of rectal cancer, analyzing the probable value of LVD in determining the length of distal resection of lower rectal cancer.

METHODS

Nine-two patients who had undergone curative resection of lower rectal cancer were included. The length of DIS, LVD and other clinicopathological factors were evaluated. Immunohistochemical lymphatic vessel staining with LYVE-1 (lymphatic vessel endothelial hyaluronan receptor) were performed to detect the LVD.

RESULTS

44 cases had DIS (range 0.1-2.44, mean 0.31 cm), and cancer emboli were the most common modalities of DIS. The LVD of a peritumoral lesion was significantly higher than that of an intratumoral lesion; the LVD of the DIS subgroup was significantly higher than that of the no DIS subgroup, and the LVD of the 2 subgroups was significantly higher than that of normal rectal tissue. A significant correlation was shown by a rank correlation test between the length of DIS and the LVD at the periphery of the rectal cancer (n = 44, r = 0.755, p < 0.01). The LVD was also related to the extent of infiltration, lymphatic invasion and lymph node metastases.

CONCLUSIONS

Lymphangiogenesis plays an important role in rectal cancer cell metastasis and patients with a higher LVD have a better prognosis. The LVD is closely correlated with DIS. These findings may be helpful in determining the distal clearance length of rectal cancer.

Papillary carcinoma of the thyroid: low expression of NCAM (CD56) is associated with downregulation of VEGF-D production by tumour cells

The expression of NCAM was investigated in tissue sections of 61 cases of papillary carcinoma and in 14 lymph node metastases using immunohistochemistry. Tumour cells of 18 primary tumours were not stained, whereas in the remaining 43 cases, NCAM was expressed in less than 5% tumour cells. Similar results were obtained when NCAM expression was evaluated at the RNA level. Reduced expression of NCAM is an early event since 6/15 cases (40%) of micro-carcinoma were NCAM-negative. NCAM-positive tumour cells were more often located at the invasion front of the tumour. It has been reported that NCAM expression may affect lymphangiogenesis. In tissue sections immunostained for podoplanin, it was found that lymphatic vessels were extremely rare inside the body of the tumour, and were mostly associated with foci of chronic inflammation and/or of reparative fibrosis. Lymphangiogenesis is sustained by VEGF-C, VEGF-D, and FGF2. Analysis of micro-dissected samples of the tumour and of the paired normal thyroid tissue revealed that RNA transcripts for VEGF-D were significantly less numerous in the tumour tissue (p = 0.001). The potential role of NCAM in tumour cell biology was investigated by silencing the NCAM gene in the TPC1 thyroid papillary carcinoma cell line. It was found that NCAM down-regulation caused a significant reduction (p < 0.05) in the expression of both VEGF-C and VEGF-D mRNAs. In addition, NCAM-silenced TPC-1 cells were more adhesive to different extracellular matrix components, and were less efficient in cell migration (59% reduction; p < 0.05) and invasiveness (68% reduction). These latter results confirm that modifications of NCAM expression cause profound alterations in the adhesive and migratory properties of tumour cells, but are in apparent discrepancy with the observation that loss of NCAM is usually associated with increased tumour invasiveness in vivo.

Renal lymphatics, and lymphatic involvement in sinus vein invasive (pT3b) clear cell renal cell carcinoma: a study of 40 cases

Although renal sinus vein invasion is the most common site of extrarenal involvement in clear cell renal cell carcinoma (CC), CC also spreads by lymphatics. As cortical lymphatics drain into the sinus, some involved sinus structures may be lymphatics, not veins. This possibility was investigated with podoplanin, a specific lymphatic endothelial marker, in 40 CC with sinus vein invasion. Ten blocks of uninvolved kidney, serving as controls, showed lymphatics within the adventitia of midcortical intralobular arteries. Lymphatics became more numerous and enlarged with progression towards the medulla. No lymphatics were among glomeruli or within the medulla unless associated with inflammation. The largest lymphatics occurred within the sinus, and were also noted within pelvic muscularis, and media of large veins. Intralymphatic tumor was observed and divided into two Groups. Group 1 (four cases) involved lymphatics within the invasive edge of tumors lacking a pseudocapsule. The lymphatics were small (0.045-0.19 mm), irregularly shaped, often incomplete, and contained single cells or small clusters of tumor cells. Group 2 (four cases) involved sinus lymphatics separate from tumor. One case each also involved adventitial lymphatics of an intralobular artery, the muscularis of the renal pelvis, and media of a muscular vein. The intralymphatic tumor in Group 2 often appeared discohesive, not endothelial cell invested, and larger than in Group 1 (0.4-0.5 mm). Conversely, tumor within muscular veins was cohesive, contained a capillary plexis, and was endothelial cell invested. In conclusion, intralymphatic tumor can be demonstrated in CC. Lymphatic involvement is less frequent than venous involvement and involves smaller structures. The potential for lymphatic spread may not be equal among involved lymphatics. Small peritumoral lymphatics may be destined for destruction by tumor growth. However, involved lymphatics within sinus and associated with renal pelvis, are likely sources for lymphatic spread and lymph node metastases.

Blood and lymph vessels in embryonic tumors

Formation of embryonic blood and lymph vessels is mediated by different steps of vasculogenesis and angiogenesis. The vascular endothelial growth factor family (VEGF) as well as the VEGF-receptors on the surface of blood endothelial cells and lymph endothelial cells are responsible for both processes. In addition to the embryonic development of the vessel systems, the interactions of angiogenesis factors and receptors are also present in solid tumors. Embryonic tumors in children offer an interesting target for new substances developed for anti-angiogenesis. Some data on the role of blood vessels and anti-blood-angiogenesis are available on embryonic tumors. However, studies of lymph-angiogenesis are not found and anti-lymph-angiogenesis is not at all examined in embryonic tumors. This review gives an overview of the challenging field of angiogenesis and anti-angiogenesis of both blood and lymph vessels with a focus on embryonic tumors.

Biomedicine and diseases: the Klippel-Trenaunay syndrome, vascular anomalies and vascular morphogenesis

Vascular morphogenesis is a vital process for embryonic development, normal physiologic conditions (e.g. wound healing) and pathological processes (e.g. atherosclerosis, cancer). Genetic studies of vascular anomalies have led to identification of critical genes involved in vascular morphogenesis. A susceptibility gene, VG5Q (formally named AGGF1), was cloned for Klippel-Trenaunay syndrome (KTS). AGGF1 encodes a potent angiogenic factor, and KTS-associated mutations enhance angiogenic activity of AGGF1, defining 'increased angiogenesis' as one molecular mechanism for the pathogenesis of KTS. Similar studies have identified other genes involved in vascular anomalies as important genes for vascular morphogenesis, including TIE2, VEGFR-3, RASA1, KRIT1, MGC4607, PDCD10, glomulin, FOXC2, NEMO, SOX18, ENG, ACVRLK1, MADH4, NDP, TIMP3, Notch3, COL3A1 and PTEN. Future studies of vascular anomaly genes will provide insights into the molecular mechanisms for vascular morphogenesis, and may lead to the development of therapeutic strategies for treating these and other angiogenesis-related diseases, including coronary artery disease and cancer.