Lymphangiogenesis of normal endometrium and endometrial adenocarcinoma

Nanomedicines for Endometriosis: Lessons Learned from Cancer Research

Endometriosis is an incurable gynecological disease characterized by the abnormal growth of endometrium-like tissue, characteristic of the uterine lining, outside of the uterine cavity. Millions of people with endometriosis suffer from pelvic pain and infertility. This review aims to discuss whether nanomedicines that are promising therapeutic approaches for various diseases have the potential to create a paradigm shift in endometriosis management. For the first time, the available reports and achievements in the field of endometriosis nanomedicine are critically evaluated, and a summary of how nanoparticle-based systems can improve endometriosis treatment and diagnosis is provided. Parallels between cancer and endometriosis are also drawn to understand whether some fundamental principles of the well-established cancer nanomedicine field can be adopted for the development of novel nanoparticle-based strategies for endometriosis. This review provides the state of the art of endometriosis nanomedicine and perspective for researchers aiming to realize and exploit the full potential of nanoparticles for treatment and imaging of the disorder.

Absence of lymphatic vessels in term placenta

Background

There has been debate about the existence of lymphatic vessels in placenta. Lymphatic endothelial cell (LEC) markers such as LYVE-1 and podoplanin/D2–40 have been found, although PROX1 has not been detected. The most reliable marker for LECs is the double staining for CD31 and PROX1, which has not been performed yet.

Methods

We studied three term placentas and dissected them into three areas: i.) basal plate area, ii.) intermediate area, and iii.) chorionic plate area. We used immunofluorescence single and double staining with antibodies against CD31, PROX1, LYVE-1, VEGFR-3, D2–40/PDPN, CD34, CCBE-1, and vimentin, as well as nested PCR, qPCR, Western blot and transmission electron microscopy (TEM).

Results

At TEM level we observed structures that have previously mistakenly been interpreted as lymphatics, however, we did not find any CD31/PROX1 double-positive cells in placenta. Absence of PROX1 was also noted by nested PCR, qPCR and Western blot. Also, LEC marker VEGFR-3 was expressed only in a small number of scattered leukocytes but was absent from vessels. The LEC marker D2–40/PDPN was expressed in most stromal cells, and the LEC marker LYVE-1 was found in a considerable number of stromal cells, but not in endothelial cells, which were positive for CD31, CD34, CCBE-1 and vimentin. Additionally, vimentin was found in stromal cells.

Conclusions

Our studies clearly show absence of lymphatics in term placenta. We also show that the functional area of the mother’s endometrium is not penetrated by lymphatics in term pregnancy.

Expression Profile of VEGF-C, VEGF-D, and VEGFR-3 in Different Grades of Endometrial Cancer

BACKGROUND

Vascular endothelial growth factor (VEGF)-C, -D, and VEGF receptor-3 are proteins characterized as crucial for tumor lymphangiogenesis. It is accompanied by angiogenesis during wound healing, but also in the neoplastic process. The research studies have shown that the lymphatic system plays a key role in the progression of carcinogenesis.

OBJECTIVE

The aim of this study was to evaluate changes in the expression of VEGF-C, VEGF-D and VEGFR-3 in different grades of endometrial cancer (G1-G3).

METHODS

The study included 45 patients diagnosed with endometrial cancer (G1=17; G2=15; G3=13) and 15 patients without neoplastic changes. The expression of VEGF-C, VEGF-D, and VEGFR-3 was assessed using microarray technique and immunohistochemistry. Statistical analysis was performed using the one-way ANOVA and Tukey's post-hoc test.

RESULTS

Statistically significant changes in the expression at the transcriptome level were found only in the case of VEGF-C (G1 vs. C, fold change - FC = -1.15; G2 vs. C, FC = -2.33; G3 vs. C, FC = - 1.68). However, VEGF-D and VEGFR-3 were expressed at the protein level. Analysis of VEGF-D expression showed that the optical density of the reaction product in G1 reached 101.7, while the values in G2 and G3 were 142.7 and 184.4, respectively. For VEGF-R3, the optical density of the reaction product reached the following levels: 72 in control, 118.77 in G1, 145.8 in G2, and 170.9 in G3.

CONCLUSION

An increase in VEGF-D and VEGFR-3 levels may indicate that VEGF-D-dependent processes are intensified along with the dedifferentiation of tumor cells. The lack of VEGF-C expression in endometrial cancer samples may suggest that this tumor is characterized by a different mechanism of metastasis than EMT. Our study emphasizes that when analyzing the metastatic potential of cancer, the expression of more than one factor should be taken into account.

Lymphatic Function and Dysfunction in the Context of Sex Differences

Endothelial cells are the building blocks of the blood vascular system and exhibit well-characterized sexually dimorphic phenotypes with regard to chromosomal and hormonal sex, imparting innate genetic and physiological differences between male and female vascular systems and cardiovascular disease. However, even though females are predominantly affected by disorders of lymphatic vascular function, we lack a comprehensive understanding of the effects of sex and sex hormones on lymphatic growth, function, and dysfunction. Here, we attempt to comprehensively evaluate the current understanding of sex as a biological variable influencing lymphatic biology. We first focus on elucidating innate and fundamental differences between the sexes in lymphatic function and development. Next, we delve into lymphatic disease and explore the potential underpinnings toward bias prevalence in the female population. Lastly, we incorporate more broadly the role of the lymphatic system in sex-biased diseases such as cancer, cardiovascular disease, reproductive disorders, and autoimmune diseases to explore whether and how sex differences may influence lymphatic function in the context of these pathologies.

Epithelial to Mesenchymal Transition and Cell Biology of Molecular Regulation in Endometrial Carcinogenesis

Endometrial carcinogenesis is involved in several signaling pathways and it comprises multiple steps. The four major signaling pathways-PI3K/AKT, Ras/Raf/MEK/ERK, WNT/β-catenin, and vascular endothelial growth factor (VEGF)-are involved in tumor cell metabolism, growth, proliferation, survival, and angiogenesis. The genetic mutation and germline mitochondrial DNA mutations also impair cell proliferation, anti-apoptosis signaling, and epithelial⁻mesenchymal transition by several transcription factors, leading to endometrial carcinogenesis and distant metastasis. The PI3K/AKT pathway activates the ransforming growth factor beta (TGF-β)-mediated endothelial-to-mesenchymal transition (EMT) and it interacts with downstream signals to upregulate EMT-associated factors. Estrogen and progesterone signaling in EMT also play key roles in the prognosis of endometrial carcinogenesis. In this review article, we summarize the current clinical and basic research efforts regarding the detailed molecular regulation in endometrial carcinogenesis, especially in EMT, to provide novel targets for further anti-carcinogenesis treatment.

Failure of Decidualization and Maternal Immune Tolerance Underlies Uterovascular Resistance in Intra Uterine Growth Restriction

Failure of uterine vascular transformation is associated with pregnancy complications including Intra Uterine Growth Restriction (IUGR). The decidua and its immune cell populations play a key role in the earliest stages of this process. Here we investigate the hypothesis that abnormal decidualization and failure of maternal immune tolerance in the second trimester may underlie the uteroplacental pathology of IUGR. Placental bed biopsies were obtained from women undergoing elective caesarian delivery of a healthy term pregnancy, an IUGR pregnancy or a pregnancy complicated by both IUGR and preeclampsia. Decidual tissues were also collected from second trimester terminations from women with either normal or high uterine artery Doppler pulsatile index (PI). Immunohistochemical image analysis and flow cytometry were used to quantify vascular remodeling, decidual leukocytes and decidual status in cases vs. controls. Biopsies from pregnancies complicated by severe IUGR with a high uterine artery pulsatile index (PI) displayed a lack of: myometrial vascular transformation, interstitial, and endovascular extravillous trophoblast (EVT) invasion, and a lower number of maternal leukocytes. Apoptotic mural EVT were observed in association with mature dendritic cells and T cells in the IUGR samples. Second trimester pregnancies with high uterine artery PI displayed a higher incidence of small for gestational age fetuses; a skewed decidual immunology with higher numbers of; CD8 T cells, mature CD83 dendritic cells and lymphatic vessels that were packed with decidual leukocytes. The decidual stromal cells (DSCs) failed to differentiate into the large secretory DSC in these cases, remaining small and cuboidal and expressing lower levels of the nuclear progesterone receptor isoform B, and DSC markers Insulin Growth Factor Binding protein-1 (IGFBP-1) and CD10 as compared to controls. This study shows that defective progesterone mediated decidualization and a hostile maternal immune response against the invading endovascular EVT contribute to the failure of uterovascular remodeling in IUGR pregnancies.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Presence of trophoblast in the uterine lumen affects VEGF-C expression in porcine endometrium

Early pregnancy is associated with morphological and functional changes within the uterus, accompanied by angiogenesis, increased vascular permeability and activation of immune tolerance. Intensive angiogenesis leads to accelerated vascular leakage and accumulation of interstitial fluid in endometrium. To protect the trophoblast from the harmful effect of extracellular fluid, process known as lymphangiogenesis is crucial. These studies are focused on VEGF-C, factor responsible of lymphatic vessels creating, and its receptors: Flk1 (VEGFR2) and Flt4 (VEGFR3) during the time of implantation as well as the effect of trophoblast signals (IFNG and E2) on VEGF-C production. Endometrial samples were collected from mature gilts from days 8, 10, 12, 14 of estrous cycle and pregnancy. Real-Time PCR analysis revealed increased mRNA expression of VEGF-C on days 10, 12, 14 of pregnancy compared to corresponding days of estrous cycle. The highest VEGF-C mRNA expression was observed on 14 day of pregnancy (p < 0.05). Increased mRNA expression of Flk1 and Flt4 was noticed on day 14 of pregnancy in comparison to day 10. Enhanced Flk1 mRNA expression during 14 day of pregnancy was observed compared to corresponding day of estrous cycle (p < 0.05). No significant difference on the protein level was revealed. VEGF-C and its receptors were localized mainly in luminal and glandular epithelial cells, but their presence were confirmed also in endothelial cells of blood and lymphatic vessels and 14 d trophoblasts. In vitro studies revealed positive effect of IFNG on VEGF-C mRNA expression in stromal cells and protein content in medium after stromal cells culture (p < 0.05). Our studies demonstrated the presence of VEGF-C system in porcine endometrium and indicated its possible important role during the time of implantation.

Abnormal lymphatic vessel development is associated with decreased decidual regulatory T cells in severe preeclampsia

PROBLEM

The lymphatic vasculature controls leukocytes trafficking and limits the adaptive immune response. In previous models of preeclampsia (PE), defective immune function caused by disruption of lymphangiogenesis was shown to be involved in the disease pathophysiology. Especially, the dysfunction of regulatory T cells (Treg) at the maternal-fetal interface may be one of the causes of severe PE. In particular, activation of Tregs to obtain immune tolerance requires adequate antigen presentation through the lymphatic system. We hypothesized that impaired lymphangiogenesis and imbalanced Tregs at the maternal-fetal interface are associated with the pathophysiology of severe PE. However, the current research addressing this hypothesis is limited. Therefore, to compare differences in lymphangiogenesis in severe PE and normal conditions, we aimed to examine the location of lymphatics at the maternal-fetal interface and to investigate the association between lymphangiogenesis and Tregs in severe PE.

METHOD OF STUDY

We obtained entire uterus from normal pregnant mice. Placental and fetal membranes, including decidua, were obtained from 10 pregnant women with severe PE and 10 gestational age-matched controls. Immunohistochemistry for LYVE1 was used to localize the distribution of lymphatic vessels and CD4, CD25, and FOXP3 for Treg.

RESULTS

LYVE1-positive vessels were present in the uterine wall of mice. LYVE1-positive lymphatic vessels were localized on the human decidua. Tubular lymphatics were abundant in the control decidua, but significantly reduced in severe PE. Furthermore, lymphatic vessel density correlated with the number of decidual Tregs.

CONCLUSION

Abnormal decidual lymphangiogenesis is associated with reduced numbers of decidual Tregs in severe PE.

Blood microvasculature and lymphatic densities in endometrial polyps and adjacent and distant endometrium

Objective:

Endometrial polyps are localised growths of endometrial tissue containing glands, stroma and blood vessels, covered with epithelium. The reported prevalence of endometrial polyps is dependent upon the population being studied and the uterine imaging technique utilised. The light microscopy literature provides very little information regarding their microvasculature and lymphatic systems; however, a plethora of ultrasound data demonstrating single central arteries in most medium- or large-sized endometrial polyps are well documented.

Methods:

Archived formalin-fixed paraffin-embedded blocks of endometrial curettings were retrieved from files for women with confirmed endometrial polyps (n = 20) and women with normal endometrium (control endometrium; n = 32). Immunohistochemistry was performed with the antibodies CD31 (blood vessels) and D2-40 (lymphatics). Blood vessels and lymphatics were quantified in endometrial polyps and adjacent, distant and control endometrium.

Results:

CD31 and D2-40 staining was present in all specimens, although there were no significant differences in blood vessel (F(3,70) = 2.36, p = 0.079) and lymphatic (F(3,70) = 0.16, p = 0.920) densities between endometrial polyps as well as adjacent, distant and control endometrium. There were also no significant differences in women with endometrial polyp-associated bleeding and those with no bleeding. In relation to infertility, there were no significant differences found in blood and lymphatic densities between women with endometrial polyps who were infertile and those with endometrial polyps who were fertile.

Conclusion:

Small blood vessel wall and perivascular structures rather than the distribution of vessels may be associated with abnormal bleeding.

Uterine Lymphatic and Blood Micro-Vessels in Women with Endometriosis through the Menstrual Cycle

Purpose

Endometriosis is a common disease, associated with persistent and severe symptoms including infertility and pain, however, pathogenesis remains poorly understood. It has been hypothesized that fragments of viable endometrial tissue shed at menstruation reach the peritoneal cavity and other distant sites by retrograde menstruation and dissemination into the lymphatic system. In this study, uterine lymphatic and blood micro-vessel populations were compared in women with and without endometriosis during the menstrual cycle.

Methods

Paraffin-embedded hysterectomy specimens from premenopausal women with histologically normal endometrium (37 control and 42 endometriosis) were obtained. Immunohistochemical staining was performed with antibodies for D2–40 (lymphatic endothelium), CD31 (pan-endothelial marker), and endoglin (activated endothelial cells in angiogenesis). Lymphatic (LVD) and blood (BVD) micro-vessel density were quantified with an automated cellular imaging system using color and morphometric properties to identify micro-vessels.

Results

Subtle but significant differences in uterine BVD and LVD were detected in endometriosis. LVD was significantly increased in basal layer endometrium of endometriosis patients during the proliferative phase (mean ± SD = 54.3 ± 20.1 vs. 41.4 ± 9.9, p = 0.025). Endoglin-positive BVD was increased in the subepithelial region of endometrium in endometriosis during the secretory phase (19.3 ± 16.6 vs. 6.4 ± 8.2, p = 0.038).

Conclusions

This report for the first time demonstrates that endometrial LVD is altered in women with endometriosis and supports changes in BVD in these women. These alterations are likely to contribute to pathogenesis of endometriosis, through lymphatic spread and increased angiogenic potential of shed endometrial fragments.

Vascular Notch proteins and Notch signaling in the peri-implantation mouse uterus

Background

Angiogenesis is essential for uterine decidualization, the progesterone-mediated transformation of the uterus allowing embryo implantation and initiation of pregnancy. In the current study, we define the vasculature, expression of Notch proteins and Notch ligands, and Notch activity in both endothelial cells and vascular-associated mural cells of blood vessels in the pre-implantation endometrium and post-implantation decidua of the mouse uterus.

Methods

We used immunofluorescence to determine the expression of Notch in endothelial cells and mural cells by co-staining for the endothelial cell marker, CD31, the pan-mural cell marker, platelet-derived growth factor receptor beta (PDGFR-β), the pericyte markers, neural/glial antigen 2 (NG2) and desmin, or the smooth muscle cell marker, alpha smooth muscle actin (SMA). A fluorescein isothiocyanate-labeled dextran tracer, was used to identify functional peri-implantation vasculature. CBF:H2B-Venus Notch reporter transgenic mice were used to determine Notch activity.

Results

Notch signaling is observed in endothelial cells and pericytes in the peri-implantation uterus. Prior to implantation, Notch1, Notch2 and Notch4 and Notch ligand, Delta-like 4 (Dll4) are expressed in capillary endothelial cells, while Notch3 is expressed in the pericytes. Jagged1 is expressed in both capillary endothelial cells and pericytes. After implantation, Notch1, Notch4 and Dll4 are expressed in endothelial cells of newly formed decidual capillaries. Jagged1 is expressed in endothelial cells of spiral arteries and a subset of decidual pericytes. Notch proteins are not expressed in lymphatic vessels or macrophages in the peri-implantation uterus.

Conclusions

We show Notch activity and distinct expression patterns for Notch proteins and ligands, suggesting unique roles for Notch1, Notch4, Dll4, and Jag1 during decidual angiogenesis and early placentation. These data set the stage for loss-of-function and gain-of-function studies that will determine the cell-type specific requirements for Notch proteins in decidual angiogenesis and placentation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13221-015-0034-y) contains supplementary material, which is available to authorized users.

Influence of Cancer-Associated Endometrial Stromal Cells on Hormone-Driven Endometrial Tumor Growth

Cancer-associated fibroblasts have been shown to inhibit or stimulate tumor growth depending on stage, grade, and tumor type. It remains unclear, however, the effect of endometrial-cancer-associated fibroblasts on hormone-driven responses in endometrial cancer. In this study, we investigated the effect of normal and cancer-associated stromal cells from patients with and without endometrial cancer on endometrial tumor growth in response to estradiol (E2) and progesterone (P4). Compared to benign endometrial stromal cells, the low-grade and high-grade cancer-associated stromal cells exhibited a blunted hormone response for proliferation as well as IGFBP1 secretion. Additional analysis of the influence of stromal cells on hormone-driven tumor growth was done by mixing stromal cells from benign, low-grade, or high-grade tumors, with Ishikawa cells for subcutaneous tumor formation. The presence of both benign and high-grade cancer-associated stromal cells increased estradiol-driven xenografted tumor growth compared to Ishikawa cells alone. Low-grade cancer-associated stromal cells did not significantly influence hormone-regulated tumor growth. Addition of P4 attenuated tumor growth in Ishikawa + benign or high-grade stromal cells, but not in Ishikawa cells alone or with low-grade stromal cells. Using an angiogenesis focused real-time array TGFA, TGFB2 and TGFBR1 and VEGFC were identified as potential candidates for hormone-influenced growth regulation of tumors in the presence of benign and high-grade stromal cells. In summary, endometrial-cancer-associated cells responded differently to in vitro hormone treatment compared to benign endometrial stromal cells. Additionally, presence of stromal cells differentially influenced hormone-driven xenograft growth in vivo depending on the disease status of the stromal cells.

Effects of levonorgestrel-releasing intrauterine system on lymphangiogenesis of adenomyosis

OBJECTIVES

Lymphangiogenesis may be involved in the pathogenesis of adenomyosis. We investigated the lymphatic vessels of patients with adenomyosis, including those treated with levonorgestrel-releasing intrauterine system (LNG-IUS).

METHODS

Full-thickness uterine samples were obtained from patients who received hysterectomies. Twenty-one patients with adenomyosis and 17 patients with adenomyosis who were treated with LNG-IUS were included. Eighteen patients with cervical intraepithelial neoplasia served as controls. Immunohistochemical staining was performed with antibodies against podoplanin and lymphatic vessel endothelial hyaluronan receptor 1. The lymphovascular density (LVD) was analyzed in each sample by the "hot spot" method.

RESULTS

The LVDs were significantly higher in the endometrial and myometrial tissues of patients with adenomyosis compared with those of patients treated with the LNG-IUS or controls. No significant differences were noted between the LNG-IUS-treated group and controls. Evaluation of the LVDs according to the menstrual cycle showed that the differences in the endometrial tissues of the adenomyosis group and those of the LNG-IUS-treated group or the controls were more prominent during the secretory phase.

CONCLUSIONS

Treatment with the LNG-IUS resulted in reduced lymphangiogenesis and LVD in the endometrial and myometrial tissues of patients with adenomyosis. Reduced lymphangiogenesis may be one mechanism by which the LNG-IUS reduces adenomyosis-related symptoms.

The defect of both angiogenesis and lymphangiogenesis is involved in preeclampsia

INTRODUCTION

Pre-eclampsia (PE) is characterized by failed remodeling of maternal vessels perfusing the placenta. Blood vessels and lymphatic system are involved in vessel remodeling and flow homeostasis in the uterus during pregnancy. This study aims to investigate the involvement of angiogenesis and lymphangiogenesis in PE.

METHODS

Placental and decidual tissues were obtained from pregnancies with PE (n = 90), including PE cases with decidual vasculopathy (DV) (n = 52) and without DV (n = 38), and healthy pregnancies (control, n = 20). The clinical characteristics of these groups were analyzed. The expression levels of VEGF1, CD34, PROX-1, VEGFR3, and CD31 in the placenta and decidua were detected through immunohistochemistry, reverse-transcription polymerase chain reaction, and Western blot.

RESULTS

The lymphangiogenic markers PROX-1 and VEGFR3 were negatively expressed in the placenta but positively expressed in the decidua. The expression levels of the angiogenic markers VEGF1 and CD34 and the panendothelial marker CD31 were significantly lower in the placenta and decidua of the PE group than in those of the control group. The expression levels of VEGF1, CD34, and CD31 were significantly lower in the placenta and decidua with DV than in those without DV. Furthermore, the expression trends of PROX-1 and VEGFR3 was similar to those of VEGF1, CD34, and CD31 among the groups.

CONCLUSIONS

Lymphangiogenesis occurred in the decidua but not in the placenta. Impaired angiogenesis and lymphangiogenesis were associated with PE, particularly in the presence of DV.

Expression profiling and significance of VEGF-A, VEGFR2, VEGFR3 and related proteins in endometrial carcinoma

BACKGROUND

Angiogenesis plays a key role in the progression of various tumors, including endometrial carcinomas. Several cytokines and their associated receptors are shown to be involved, particularly VEGF-A with VEGFR1, -2 and -3.

METHODS

The expressions of VEGF-A, VEGFR2 and VEGFR3 were studied in by immunohistochemistry in 76 endometrial carcinoma specimens. VEGFR2 and VEGFR3 receptor expression were also studied by qRT-PCR in 17 tumors in comparison to normal endometrium. The expression profiles were correlated with tumor type, grade, stage, lymphovascular invasion, disease free survival, and the expressions of other cytokine receptors (EGFR, CXCR1 and CXCR2).

RESULTS

Immunohistochemically, 63% of endometrial cancers expressed VEGF-A, 55% VEGFR2 and 26% VEGFR3. VEGFR3 was significantly correlated with tumor stage (p=0.02), with a trend towards poorer disease free survival (p=0.09). VEGF-A was significantly correlated with microvessel density (p<0.01). Using qRT-PCR, increased expression of VEGFR2 (17.2-fold) and VEGFR3 (21.9-fold) was seen in endometrial carcinomas compared with normal endometrium, with significant correlations among the expression levels of VEGFR2, VEGFR3, EGFR, CXCR1 and CXCR2.

CONCLUSION

Our study suggests that evaluation of VEGFR3 expression in tumors may provide prognostic data, and help identify patients who would best benefit from anti-angiogenic therapeutic agents. This is the first report showing correlations between the expressions levels of the different receptors.

VEGF-c expression in an in vivo model of orthotopic endometrial cancer and retroperitoneal lymph node metastasis

BACKGROUND

Retroperitoneal lymph node (RLN) metastasis is an important indicator of endometrial cancer (EC) prognosis. Because vascular endothelial growth factor c (VEGF-c) is known to influence lymphangiogenesis and thereby lymph node metastasis, this study assessed the relationship of VEGF-c mRNA expression with RLN metastasis in EC.

METHODS

The uterine muscularis mucosae of New Zealand white rabbits were inoculated with a VX2 tumor cell suspension after which they were sacrificed at 15, 18, 21, 24, 27 and 30 days. Control groups consisted of those receiving no treatment or an injection of saline. EC and metastatic RLN tissues along with peripheral blood samples were collected, and VEGF-c mRNA expression was evaluated using fluorescence real-time quantitative PCR.

RESULTS

The establishment of an in vivo model of EC with complete RLN metastasis was pathologically confirmed at day 21 post-injection with VX2 cells. As compared to the control groups, VEGF-c mRNA expression increased significantly over time in the tumor site, RLN, and peripheral white blood cells of EC rabbits. Significantly higher VEGF-c mRNA expression was observed in metastatic RLNs as compared to those without metastasis (P < 0.001). In addition, increased VEGF-c mRNA expression was observed in peripheral white blood cells of rabbits with RLN metastasis (P < 0.002).

CONCLUSION

Injection of a VX2 cell suspension is a simple method of establishing an in vivo EC model. VEGF-c may play an important role in the development of EC and its metastasis to RLN and may be useful marker to predict RLN metastasis.

The endometrial lymphatic vasculature: function and dysfunction

The endometrium has a complex and dynamic blood and lymphatic vasculature which undergoes regular cycles of growth and breakdown. While we now have a detailed picture of the endometrial blood vasculature, our understanding of the lymphatic vasculature in the endometrium is limited. Recent studies have illustrated that the endometrium contains a population of lymphatic vessels with restricted distribution in the functional layer relative to the basal layer. The mechanisms responsible for this restricted distribution and the consequences for endometrial function are not known. This review will summarise our current understanding of endometrial lymphatics, including the mechanisms regulating their growth and function. The potential contribution of lymphatic vessels and lymphangiogenic growth factors to various endometrial disorders will be discussed.

SiRNA-mediated down-regulation of vascular endothelial growth factor receptor 3 inhibits the growth of human colorectal cancer cell xenografts in nude mice

AIM: To investigate the inhibory effect of siRNA-mediated down-regulation of vascular endothelial growth factor receptor 3 (VEGFR-3) on the growth of human colorectal carcinoma cell xenografts in nude mice.

METHODS: Human colorectal carcinoma LoVo cells were transplanted subcutaneously into Balb/c nude mice to establish a xenograft tumor model. Fifteen model mice were randomized into three groups and were injected with recombinant plasmid carrying the siRNA (pG-siRNA/VEGFR-3), empty plasmid (pG-HK), and tranfection reagent (control), respectively. Tumor volume and weight were measured, and the reduced rate of tumor growth was calculated. VEGFR-3 mRNA and protein expression was detected by qRT-PCR and Western blot. Microlyphamatic vessels were counted by immunohistochemistry.

RESULTS: Tumor volume and weight were significantly less in the pG-siRNA/VEGFR-3 group than in the pG-HK and control group (both P < 0.001). Compared to the control group, the reduced rate of tumor growth was 52.75%, and VEGFR-3 expression was down-regulated in the pG-siRNA/VEGFR-3 group. However, there was no similar inhibitory effect in the control group and pG-HK group. Significant differences in microlymphatic counts were noted between the pG-siRNA/VEGFR-3 group and the two control groups (both P < 0.05).

CONCLUSION: SiRNA-mediated down-regulation of VEGFR-3 could inhibit the growth of human colorectal cancer cell xenografts in nude mice and reduce lymphangiogenesis.

Dilated thin-walled blood and lymphatic vessels in human endometrium: a potential role for VEGF-D in progestin-induced break-through bleeding

Progestins provide safe, effective and cheap options for contraception as well as the treatment of a variety of gynaecological disorders. Episodes of irregular endometrial bleeding or breakthrough bleeding (BTB) are a major unwanted side effect of progestin treatment, such that BTB is the leading cause for discontinued use of an otherwise effective and popular medication. The cellular mechanisms leading to BTB are poorly understood. In this study, we make the novel finding that the large, dilated, thin walled vessels characteristic of human progestin-treated endometrium include both blood and lymphatic vessels. Increased blood and lymphatic vessel diameter are features of VEGF-D action in other tissues and we show by immunolocalisation and Western blotting that stromal cell decidualisation results in a significant increase in VEGF-D protein production, particularly of the proteolytically processed 21 kD form. Using a NOD/scid mouse model with xenografted human endometrium we were able to show that progestin treatment causes decidualisation, VEGF-D production and endometrial vessel dilation. Our results lead to a novel hypothesis to explain BTB, with stromal cell decidualisation rather than progestin treatment per se being the proposed causative event, and VEGF-D being the proposed effector agent.

The expression and regulation of adrenomedullin in the human endometrium: a candidate for endometrial repair

After menstruation, the endometrium has a remarkable capacity for repair, but the factors involved remain undefined. We hypothesize adrenomedullin (AM) plays a role in this process. Premenstrually progesterone levels decline, stimulating prostaglandin (PG) synthesis, vasoconstriction, and hypoxia. This study aimed to determine 1) AM expression throughout the menstrual (M) cycle and 2) its regulation by PG and hypoxia. Human endometrial biopsies (n = 51) were collected with ethical approval and consent. AM mRNA expression was examined by quantitative RT-PCR and was found to be selectively elevated in endometrium from the menstrual (M) phase (P < 0.001). AM immunohistochemical staining was maximal in M and proliferative (P) endometrium. Culture of secretory, but not P, explants with 100 nm PGF(2α) or hypoxia (0.5% O2) increased AM mRNA (P < 0.05). P explants were induced to increase AM expression using in vitro progesterone withdrawal but required the presence of hypoxia (P < 0.05). Short hairpin sequences against hypoxia-inducible factor-1α (HIF-1α) inhibited AM hypoxic up-regulation but did not alter PGF(2α)-induced expression. The AM receptor was immunolocalized to endothelial cells in both lymphatic and blood vessels. Conditioned medium from PGF(2α)-treated cells increased endothelial cell proliferation and branching (P < 0.05). This was abolished by AM receptor antagonists. In conclusion, AM is elevated at the time of endometrial repair and induces both angiogenesis and lymphangiogenesis by stimulating endothelial cell proliferation and tube formation. In the human endometrium, AM expression is up-regulated by two mechanisms: a HIF-1α-mediated hypoxic induction and a HIF-1α-independent PGF(2α) pathway. These physiological mechanisms may provide novel therapeutic targets for disorders such as heavy menstrual bleeding.

Neither normal nor diseased placentas contain lymphatic vessels

BACKGROUND

Scant data on placental lymphatic vessels have pointed to the absence of lymphatic circulation. A recent study on mesenchymal dysplasia (MD), however, has identified pathologic lymphangiogenesis using the D2-40 lymphatic marker. These conflicting data have prompted us to investigate whether lymphatic vessels are present in normal developing placentas and in placental disorders characterized by cistern formation.

DESIGN

Seventeen human placentas without significant pathological abnormality ranging from 12 to 39 weeks of gestational age were studied. Cisternal placental disorders were represented by mesenchymal dysplasia (n = 1), partial hydatitiform mole (n = 2), spontaneous abortion (n = 3) and complete hydatiform mole (n = 2). To identify lymphatic vessels, we used lymphatic endothelial markers Prox-1 and D2-40. The pan-endothelial marker CD31 was used to highlight overall placental vasculature and to determine if the lining cells of cisterns were of endothelial origin. Lymphatic marker positivity was assessed in maternal (decidual) as well as in fetal (chorionic villous) vasculature.

RESULTS

No staining with Prox-1 or D2-40 was identified in fetal vessels in developing or term placentas, or in selected cisternal placental disorders, although both markers highlighted a number of thin-walled decidual vessels. Cistern lining cells were negative for Prox-1, D2-40 and CD31. D2-40 consistently marked stromal cells in chorionic villi and highlighted perivascular/pericellular extracellular matrix.

CONCLUSION

We established that no lymphatic vasculature is present in the chorionic villi during development, at term or in selected edematous placental disorders. The cisternal lining cells are not endothelial cells; most likely they are of stromal cell origin. Lymphangiogenesis is a part of decidual vascular remodeling during gestation.

Lymphatic Vessels in Peritoneal Endometriotic Lesions

Purpose

While the exact pathogenesis of endometriosis remains unclear, it has been hypothesized that fragments of viable endometrial tissue shed at menstruation can transit via the lymphatic circulation and establish endometriotic lesions at distant sites. Mounting evidence suggests that related parameters such as immune cell densities are altered in peritoneal endometriotic lesions. However, lymphatic vessels in lesions have not been previously investigated. In this study, the presence and distribution of lymphatic micro-vessels were characterized in peritoneal endometriotic lesions and surrounding tissues.

Methods

Immunohistochemical staining was performed with an antibody specific for lymphatic endothelium (podoplanin, D2–40 clone) on 48 peritoneal endometriotic lesion specimens and 15 samples of normal surface peritoneum. Lymphatic micro-vessel density (LVD) was quantified in and around endometriotic lesions, and in normal surface peritoneum using an automated cellular imaging system.

Results

LVD in endometriotic stroma (mean ± SD = 31.1 ± 28.8 vessels per mm2) was significantly increased compared to both adjacent (8.8 ± 7.6, P<.001) and distant sub-peritoneum (17.7 ± 12.0, P=.002). In addition, lesion-adjacent LVD was significantly lower than distant (P<.001). No statistically significant differences in LVD were observed between endometriotic stroma and normal surface peritoneum from women without endometriosis (31.1 ± 26.5) or at different phases of the menstrual cycle.

Conclusions

This is the first report of LVD in peritoneal endometriotic lesions. LVD is increased in the stroma of peritoneal lesions compared to the surrounding sub-peritoneal tissue. Lymphatic micro-vessels play an important role in the trafficking of immune cells within endometriotic lesions and may be involved in lesion establishment.

Association between intratumoral lymphatic microvessel density (LMVD) and clinicopathologic features in endometrial cancer: a retrospective cohort study

BACKGROUND

Lymph node metastasis in endometrial cancer significantly decreases survival rate. Few data on the influence of intratumoral lymphatic microvessel density (LMVD) on survival in endometrial cancer are available. Our aim was to assess the intratumoral LMVD of endometrial carcinomas and to investigate its association with classical pathological factors, lymph node metastasis and survival.

METHODS

Fifty-seven patients with endometrial carcinoma diagnosed between 2000 and 2008 underwent complete surgical staging and evaluation of intratumoral LMVD and other histologic variables. Lymphatic microvessels were identified by immunohistochemical staining using monoclonal antibody against human podoplanin (clone D2-40) and evaluated by counting the number of immunostained lymphatic vessels in 10 hot spot areas at 400× magnification. The LMVD was expressed by the mean number of vessels in these 10 hot spot microscopic fields. We next investigated the association of LMVD with the clinicopathologic findings and prognosis.

RESULTS

The mean number of lymphatic vessels counted in all cases ranged between 0 and 4.7. The median value of mean LMVD was 0.5, and defined the cut-off for low and high LMVD. We identified low intratumoral LMVD in 27 (47.4%) patients and high LMVD in 30 (52.6%) patients. High intratumoral LMVD was associated with lesser miometrial and adnaexal infiltration, lesser cervical and peritoneal involvement, and fewer fatal cases. Although there was lower lymph node involvement among cases with high LMVD, the difference did not reach significance. No association was seen between LMVD and FIGO staging, histological type, or vascular invasion. On the other hand, low intratumoral LMVD was associated with poor outcome. Seventy-five percent of deaths occurred in patients with low intratumoral LMVD.

CONCLUSION

Our results show association of high intratumoral LMVD with features related to more localized disease and better outcome. We discuss the role of lymphangiogenesis as an early event in the endometrial carcinogenesis.

Lymphatics in the human endometrium disappear during decidualization

BACKGROUND

The mammalian placenta plays a central role in maternal tolerance of the semi-allogeneic fetus and fluid balance between the maternal and fetal compartments. The lymphatics play a role in both these function. The aim of this study was to describe the distribution of lymphatic vessels in human decidua, with particular focus on the lymphatics that surround remodelling spiral arteries during decidualization and trophoblast invasion.

METHODS

Placental bed and non-placental bed (decidua parietalis) biopsies were obtained from 41 women undergoing elective termination of pregnancy at 6-18 weeks gestational age as well as placental bed biopsies from 5 women undergoing elective Caesarean section at term. In addition to routine haematoxylin and eosin staining, double immunohistochemical labelling was performed on serial 3-µm sections to identify lymphatic vessels in conjunction with one of the following: blood vessels, smooth muscle, epithelial and trophoblast cells or proliferating cells. Representative photomicrographs of all sections were obtained from a total of 273 areas (46 samples, average 6 range 3-15 areas per sample). Descriptive findings of the organization of lymphatics in human placental bed and decidua parietalis were made from a total of 1638 images.

RESULTS

Lymphatic vessels positive for podoplanin were abundant in non-decidualized hypersecretory endometrium at all stages of gestation. By contrast, the decidua was nearly always devoid of lymphatics. In some samples, structures that appeared to be regressing lymphatics could be observed at the boundary between non-decidualized hypersecretory and decidualized endometrium. Lymphatic vessels were notably absent from the vicinity of spiral arteries that were surrounded by decidualized stromal cells. Lymphatic vessels in non-decidualized hypersecretory endometrium appeared larger and more elongated as gestation progressed. Proliferating lymphatic vascular endothelial cells were identified in both large vessels, and in streaks of D2-40 positive cells that could have been newly forming lymphatic vessels. Placental bed lymphatics exhibited limited and variable staining with LYVE-1 at all stages of pregnancy apart from term.

CONCLUSIONS

We have made novel observations on lymphatics in the placental bed and their relationship with other structures throughout pregnancy. Endometrial stromal cell decidualization results in a loss of lymphatics, with this phenomenon being particularly apparent around the spiral arteries.

Vascular endothelial growth factor-D over-expressing tumor cells induce differential effects on uterine vasculature in a mouse model of endometrial cancer

BACKGROUND

It has been hypothesised that increased VEGF-D expression may be an independent prognostic factor for endometrial cancer progression and lymph node metastasis; however, the mechanism by which VEGF-D may promote disease progression in women with endometrial cancer has not been investigated. Our aim was to describe the distribution of lymphatic vessels in mouse uterus and to examine the effect of VEGF-D over-expression on these vessels in a model of endometrial cancer. We hypothesised that VEGF-D over-expression would stimulate growth of new lymphatic vessels into the endometrium, thereby contributing to cancer progression.

METHODS

We initially described the distribution of lymphatic vessels (Lyve-1, podoplanin, VEGFR-3) and VEGF-D expression in the mouse uterus during the estrous cycle, early pregnancy and in response to estradiol-17beta and progesterone using immunohistochemistry. We also examined the effects of VEGF-D over-expression on uterine vasculature by inoculating uterine horns in NOD SCID mice with control or VEGF-D-expressing 293EBNA tumor cells.

RESULTS

Lymphatic vessels positive for the lymphatic endothelial cell markers Lyve-1, podoplanin and VEGFR-3 profiles were largely restricted to the connective tissue between the myometrial circular and longitudinal muscle layers; very few lymphatic vessel profiles were observed in the endometrium. VEGF-D immunostaining was present in all uterine compartments (epithelium, stroma, myometrium), although expression was generally low. VEGF-D immunoexpression was slightly but significantly higher in estrus relative to diestrus; and in estradiol-17beta treated mice relative to vehicle or progesterone treated mice. The presence of VEGF-D over-expressing tumor cells did not induce endometrial lymphangiogenesis, although changes were observed in existing vessel profiles. For myometrial lymphatic and endometrial blood vessels, the percentage of profiles containing proliferating endothelial cells, and the cross sectional area of vessel profiles were significantly increased in response to VEGF-D in comparison to control tumor cells. In contrast, no significant changes were noted in myometrial blood vessels. In addition, examples of invading cells or tumor emboli were observed in mice receiving VEGF-D expressing 293EBNA cells.

CONCLUSIONS

These results illustrate that VEGF-D over-expression has differential effects on the uterine vasculature. These effects may facilitate VEGF-D's ability to promote endometrial cancer metastasis and disease progression.

High density of peritumoral lymphatic vessels is a potential prognostic marker of endometrial carcinoma: a clinical immunohistochemical method study

Background

The lymphatic system is a major route for cancer cell dissemination and also a potential target for antitumor therapy. To investigate whether increased lymphatic vessel density (LVD) is a prognostic factor for nodal metastasis and survival, we studied peritumoral LVD (P-LVD) and intratumoral LVD (I-LVD) in samples from 102 patients with endometrial carcinoma;

Methods

Endometrial carcinoma tissues were analyzed for lymphatic vessels by immunohistochemical staining with an antibody against LYVE-1. Univariate analysis was performed with Kaplan-Meier life-table curves to estimate survival, and was compared using the log rank test. Prognostic models used multivariate Cox regression analysis for multivariate analyses of survival;

Results

Our study showed that P-LVD, but not I-LVD, was significantly correlated with lymph vascular space invasion (LVSI), lymph node metastasis, tumor stage, and CD44 expression in endometrial carcinoma. Moreover, P-LVD was an independent prognostic factor for progression-free survival and overall survival of endometrial carcinoma;

Conclusions

P-LVD may serve as a prognostic factor for endometrial carcinoma. The peritumoral lymphatics might play an important role in lymphatic vessel metastasis.

The hidden maternal-fetal interface: events involving the lymphoid organs in maternal-fetal tolerance

The genetic disparity between the mother and fetus has long enticed immunologists to search for mechanisms of maternal tolerance to fetal antigens. The study of antigen-specific tolerance in murine and human pregnancy has gained new momentum in recent years through the focus on antigen-presenting cells, uterine lymphatics and fetal antigen-specific maternal T cell responses. In mice, we now know that these responses occur within the secondary lymphoid structures as they can be conveniently tracked through the use of defined, often transgenic fetal antigens and maternal T cell receptors. Although the secondary lymphoid organs are sites of both immunization and tolerization to antigens, the immunological processes that occur in response to fetal antigens during the healthy pregnancy must invariably lead to tolerance. The molecular properties of these maternal-fetal tolerogenic interactions are still being unraveled, and are likely to be greatly influenced by tissue-specific microenvironments and the hormonal milieu of pregnancy. In this article, we discuss the events leading to antigen-specific maternal tolerance, including the trafficking of fetal antigens to secondary lymphoid organs, the properties of the antigen-presenting cells that display them to maternal T lymphocytes, and the nature of the ensuing tolerogenic response. Experimental data generated from human biological specimens as well as murine transgenic models are considered.

Regulation of endometrial vascular remodelling: role of the vascular endothelial growth factor family and the angiopoietin–TIE signalling system

Angiogenesis, lymphangiogenesis and vascular maturation occur on a regular, physiological basis in human endometrium. These processes form part of a continuum of vascular remodelling involving numerous regulatory factors. Key factors include vascular endothelial growth factor (VEGF)A, VEGFC and VEGFD, and their associated receptors VEGFR1, VEGFR2 and VEGFR3. A second group of vascular regulatory proteins belongs to the angiopoietin (ANG)–TIE system. Although members of the VEGF family and the ANG–TIE system are represented in the endometrium, our understanding of how these different molecules interact to regulate remodelling of the blood and lymphatic vasculature present in the endometrium is still limited. A review of the current information is provided.

Vascular endothelial growth factor receptor 2 (VEGFR-2) functions to promote uterine decidual angiogenesis during early pregnancy in the mouse

Implantation of an embryo induces rapid proliferation and differentiation of uterine stromal cells, forming a new structure, the decidua. One salient feature of decidua formation is a marked increase in maternal angiogenesis. Vascular endothelial growth factor (VEGF)-dependent pathways are active in the ovary, uterus, and embryo, and inactivation of VEGF function in any of these structures might prevent normal pregnancy development. We hypothesized that decidual angiogenesis is regulated by VEGF acting through specific VEGF receptors (VEGFRs). To test this hypothesis, we developed a murine pregnancy model in which systemic administration of a receptor-blocking antibody would act specifically on uterine angiogenesis and not on ovarian or embryonic angiogenesis. In our model, ovarian function was replaced with exogenous progesterone, and blocking antibodies were administered prior to embryonic expression of VEGFRs. After administration of a single dose of the anti-VEGFR-2 antibody during the peri-implantation period, no embryos were detected on embryonic d 10.5. The pregnancy was disrupted because of a significant reduction in decidual angiogenesis, which under physiological conditions peaks on embryonic d 5.5 and 6.5. Inactivation of VEGFR-3 reduced angiogenesis in the primary decidual zone, whereas administration of VEGFR-1 blocking antibodies had no effect. Pregnancy was not disrupted after administration of anti-VEGFR-3 or anti-VEGFR-1 antibodies. Thus, the VEGF/VEGFR-2 pathway plays a key role in the maintenance of early pregnancy through its regulation of peri-implantation angiogenesis in the uterine decidua. This newly formed decidual vasculature serves as the first exchange apparatus for the developing embryo until the placenta becomes functionally active.

SRB Reproduction, Fertility and Development Award Lecture 2008. Regulation and manipulation of angiogenesis in the ovary and endometrium

The marked cyclical physiological angiogenesis in the developing follicle, corpus luteum and endometrium implies a critical role in health and disease. Our approach to understanding its regulation has been to localise and quantify the temporal changes in putative angiogenic factors, and their receptors, in human and non-human primate tissue and to use antagonists to dissect their role by specific inhibition at defined periods during the ovulatory cycle in non-human primates in vivo. The course of angiogenesis throughout the cycle and the cellular and molecular effects of inhibitory treatments have been investigated in the marmoset ovary and uterus, whereas consequences on pituitary-ovarian function have been monitored in macaques. Inhibition of vascular endothelial growth factor (VEGF) at the time of follicle recruitment or selection prevents endothelial cell proliferation, leading to inhibition of follicular development. VEGF inhibition during the early luteal phase prevents angiogenesis and restricts development of the luteal microvasculature. Inhibition of angiogenesis at all stages of the cycle leads to profound suppression of ovarian function. Even during the 'post-angiogenic' period of the luteal phase, inhibition of VEGF precipitates a suppression of progesterone secretion, pointing to additional roles for VEGF in the ovary. In the endometrium, oestrogen drives endometrial angiogenesis through VEGF. Thus, oestrogen can restore angiogenesis after ovariectomy, but not in the presence of VEGF inhibitors. These investigations enhance our understanding of the regulation of angiogenesis in the ovary and uterus and inform studies on conditions with abnormal vascularisation, such as polycystic ovary syndrome, endometriosis, uterine fibroids and menstrual dysfunction.

Localization of angiogenic growth factors and their receptors in the human placental bed throughout normal human pregnancy

During early human pregnancy invasion of uterine spiral arteries by extravillous trophoblast cells contributes to their remodelling characterised by loss of musculo-elastic media and replacement by fibrinoid containing trophoblast. Despite its importance for successful pregnancy, the mechanisms underlying 'transformation' of spiral arteries are not well understood. The aim of this study was to localize expression of members of the angiopoietin (Ang) family (Ang-1, Ang-2 and their receptor Tie-2) and the vascular endothelial growth factor (VEGF) family (VEGF-A, VEGF-C, VEGF-D and their receptors VEGF-R1, VEGF-R2 and VEGF-R3) in the placental bed throughout normal human pregnancy. Placental bed biopsies were obtained from women undergoing elective termination of pregnancy at 8-10, 12-14 and 16-20 weeks' gestation and elective caesarean section at term (n=6 each group). Paraffin-embedded sections were immunostained for Ang-1, Ang-2, Tie-2, VEGF-A, VEGF-C, VEGF-D, VEGF-R1, VEGF-R2 and VEGF-R3 using an avidin biotin peroxidase technique. Reactivity of endovascular, interstitial, intramural and multinucleate extravillous trophoblast populations in the placental bed was analysed semi-quantitatively. There was an increase in the level of immunostaining of intramural EVT for Tie-2 and VEGF-C with increasing gestational age. In addition, there was a reduction in Ang-1 and Ang-2 expression by multinucleate interstitial EVT and of VEGF-R1 and VEGF-R2 by endovascular EVT with increasing gestational age. At the earlier gestational ages studied, immunostaining for Ang-1, Ang-2, Tie-2, VEGF-C, VEGF-R1 and VEGF-R2 on intramural EVT was reduced compared to both mononuclear interstitial and endovascular EVT. These findings suggest that the Ang and VEGF families may play a role in the process of spiral artery remodelling in normal pregnancy.

Promotion of angiogenesis by human endometrial lymphocytes

The human endometrium is a unique tissue that undergoes dramatic monthly remodeling during the menstrual cycle in preparation for an implanting conceptus. This remodeling involves sequential proliferation and differentiation of endometrial stromal and epithelial cells, coupled with extensive angiogenesis and infiltration of a specific specialized immune cell subset. Increasing evidence points to an essential role for these maternal leukocytes in stimulating the endometrial angiogenesis, and we propose that they also play a key role in the decidual vascular transformation. Aberrant endometrial angiogenesis, decidualisation and vascular transformation is thought to underlie many pathologies of pregnancy, from infertility to the development of preeclampsia and Intra Uterine Growth Restriction. In this chapter we review the cellular processes associated with each stage of endometrial and decidual transformation, detailing the role of the immune cell populations and the angiogenic and chemotactic factors secreted by them.

Endometrial angiogenesis, vascular maturation, and lymphangiogenesis

Angiogenesis, arteriogenesis or vessel maturation, and lymphangiogenesis comprise a continuum of vascular development, with overlap and interaction between the mechanisms by which they are controlled. These processes are of clinical interest because they play roles in endometrial repair, placental development, and in gynecological disorders including endometrial cancer, endometriosis and abnormal uterine bleeding. Using mouse models we have shown that estrogen can be either proangiogenic or antiangiogenic in endometrium. Progesterone alone is proangiogenic, although this can be moderated by pretreatment with estrogen. Arteriogenesis also increases in response to progesterone, and this effect is not inhibited by estrogen. Lymphatics account for 13% of all vessels in the human functionalis compared to 57% in the basalis. Many of the basalis lymphatic vessels are closely associated with spiral arterioles and this intimate connection may provide a mechanism for paracrine communication between the functionalis and the arteries supplying the endometrium.

Midkine and its clinical significance in endometrial carcinoma

Midkine (MK) is a secreted heparin-binding growth factor. Several types of human cancer have increased MK expression with elevated serum levels. The purpose of this study was to determine whether MK was expressed in endometrial carcinoma and to evaluate the clinicopathological significance of serum MK in patients with endometrial carcinoma. Immunohistochemical expression of MK was evaluated in 85 endometrial carcinoma samples and 33 controls. MK expression was significantly higher in the carcinomas than in normal endometrium (P < 0.001). Interestingly, MK expression was highest at the margins of invasion and low in the superficial areas of the tumor samples. Using ELISA, we compared serum MK concentration in 120 endometrial carcinoma patients with the concentration in 46 patients with benign gynecologic tumors. Serum MK value in patients with cancer was significantly higher than that in the patients with benign diseases (P = 0.01). Patients with positive lymph node metastasis or recurrence, or cancer death, had a higher serum MK level (P = 0.008, P = 0.009, respectively). In conclusion, MK immunoreactivity in endometrial carcinoma is significantly higher than in normal endometrium. Additionally, preoperative serum MK levels are significantly correlated with prognosis and the presence of lymph node metastasis. Thus, MK may be a useful serum biomarker for identifying high risk patients of endometrial carcinoma.

Dynamic changes occur in patterns of endometrial EFNB2/EPHB4 expression during the period of spiral arterial modification in mice

Transient, human and murine decidua-associated, Natural Killer lymphocytes (uNK cells) have special, localized roles in early gestational endometrial remodeling and angiogenesis. To determine if uNK cells promote a specific vessel subtype, a histological time-course study of implantation site endothelia was undertaken using normal C57BL/6J (B6) and uNK-deficient B6.129-Rag2 tm1Fwa Il2rg tm2Cgn (alymphoid) mice, a strain lacking pregnancy-induced structural modifications of spiral arteries. Antibodies to EFNB2, EPHB4, and LYVE1, respectively, identified arterial, venous, and lymphatic endothelia. Unexpectedly, many uNK cells in B6 endometrium showed strong EFNB2 expression early in gestation, then became EPHB4+. This molecular transition coincided with structural modifications of spiral arteries that shifted from EFNB2+/EPHB4(-) to EFNB2+/EPHB4+. NK cells from B6 spleen and liver did not express EFNB2. LYVE1 expression was similar in endometrium from B6 and alymphoid mice, but EFNB2 and EPHB4 expression in alymphoid mice was dramatically different. Strong stromal expression of both molecules developed mesometrially, and this was reduced by B6 lymphocyte transfer. Trophoblasts reacted with each marker in both strains. Expression of EFNB2 by uNK cells and trophoblasts may be the key regulatory mechanism that drives their positional association with EFNB2+ arteries and prevents association of both cell types with EPHB4+ veins. Gain of EPHB4 by midgestation spiral arteries may signal completion of pregnancy-induced arterial modification and provide a repulsion mechanism that limits subsequent interactions of the modified vessel with uNK cells and trophoblasts.

Proliferating mesodermal cells in murine embryos exhibiting macrophage and lymphendothelial characteristics

BACKGROUND

The data on the embryonic origin of lymphatic endothelial cells (LECs) from either deep embryonic veins or mesenchymal (or circulating) lymphangioblasts presently available remain inconsistent. In various vertebrates, markers for LECs are first expressed in specific segments of embryonic veins arguing for a venous origin of lymph vessels. Very recently, studies on the mouse have strongly supported this view. However, in the chick, we have observed a dual origin of LECs from veins and from mesodermal lymphangioblasts. Additionally, in murine embryos we have detected mesenchymal cells that co-express LEC markers and the pan-leukocyte marker CD45. Here, we have characterized the mesoderm of murine embryos with LEC markers Prox1, Lyve-1 and LA102 in combination with macrophage markers CD11b and F4/80.

RESULTS

We observed cells co-expressing both types of markers (e.g. Prox1 - Lyve-1 - F4/80 triple-positive) located in the mesoderm, immediately adjacent to, and within lymph vessels. Our proliferation studies with Ki-67 antibodies showed high proliferative capacities of both the Lyve-1-positive LECs of lymph sacs/lymphatic sprouts and the Lyve-1-positive mesenchymal cells.

CONCLUSION

Our data argue for a dual origin of LECs in the mouse, although the primary source of embryonic LECs may reside in specific embryonic veins and mesenchymal lymphangioblasts integrated secondarily into lymph vessels. The impact of a dual source of LECs for ontogenetic, phylogenetic and pathological lymphangiogenesis is discussed.

Uterine NK cells in murine pregnancy

Murine uterine natural killer (uNK) cells are transient, short-lived, terminally differentiated lymphocytes found in decidualized endometrium. Cells expressing natural killer cell surface markers are present in uteri of infant mice. Terminal uNK cell differentiation coincides with mesometrial decidual development subsequent to blastocyst implantation and begins about gestation day 5. uNK cells proliferate rapidly and, within 3 days, senescent uNK cells appear in normal implantation sites. Mid-gestation, senescent cells become dominant and uNK cell numbers decline until term when remaining cells are shed with the placenta. Transplantable uNK cell progenitors occur outside the uterus, suggesting that blood cell homing augments any in-utero progenitors. Early in healthy pregnancies, uNK cells produce cytokines and angiogenic molecules. Their lytic capacity in normal gestation and in pregnancy failure is incompletely defined. A significant shift recently occurred in thinking about major uNK cell functions. Activated uNK cells are now considered critical for appropriate endometrial angiogenesis in early implantation site development and in non-gestational endometrium. Because analogous cells appear in the endometria of women during each menstrual cycle and become abundant in early pregnancy, studies involving experimental pregnancy termination in genetically manipulated mice continue to have great importance for understanding regulation at the human maternal-fetal interface.

Lymphatic vessel dynamics in the uterine wall

During pregnancy, maternal uterine blood vessels undergo dramatic vascular remodeling. However, until now, little was known about whether the lymphatic circulation experiences similar changes and whether these vessels interact with placental cells that invade maternal tissue. Recent studies demonstrate that lymphatic vessels in the uterine wall are highly compartmentalized where their presence is mostly restricted to the deeper layers. In humans, this arrangement changes during pregnancy when extensive lymphangiogenesis occurs at the maternal-fetal interface. Placental cytotrophoblasts stimulate lymphatic growth in vivo and in vitro suggesting that they play a role in triggering pregnancy-induced decidual lymphangiogenesis. These data indicate that lymphatic vessels may have important functions at the implantation site during pregnancy.