Lack of correlation between vascular endothelial growth factor production and endothelial cell proliferation in the human endometrium

Three-Dimensional Visualization of Mouse Endometrial Remodeling After Superovulation

Uterine status determines pregnancy success. Although it is well known that superovulation operations can disrupt uterine function, our understanding of the morphological changes in the uterine endometrium at the three-dimensional (3D) level is limited. Here, combining the tissue clearing with 3D deep imaging, we reveal an increase in epithelial density and angiogenesis after ovarian stimulation, which is accompanied by a circulating surge in P4 levels. Using an ovariectomized mouse model, we further detected the separate regulatory effects of P4 and E2 on the uterine endometrium, with P4 promoting endothelial cell growth and E2 inducing epithelial proliferation. Additionally, we observed that the effects of E2 can be partially neutralized by P4, and vice versa. By analyzing the 3D uterine imaging, we discovered an interesting phenomenon in which the growing blood vessels closely surround the remodeling uterine epithelium, indicating a close relationship between angiogenesis and epithelial growth. These findings provide new insight into the uterine epithelial changes and angiogenesis at the 3D level, and explain a potential reason for endometrial changes due to the low implantation rate in patients undergoing clinic super-ovulation.

Endometrial delay is found to be part of a normal individual dynamic transformation process

Purpose

Limited information is clinically available concerning endometrial receptivity; assessing endometrial transformation status is therefore an urgent topic in assisted reproductive technology. This study aimed to investigate individual endometrial transformation rates during the secretory phase in subfertile patients using personal endometrial transformation analysis.

Methods

Monitoring was carried out during the secretory phase to obtain endometrial receptivity profiles. For the investigation, two endometrial biopsies were taken within one menstrual cycle. The extended endometrial dating was based on the Noyes criteria, combined with immunohistochemical analyses of hormone receptors and proliferation marker Ki-67. Biopsies were taken mainly at days ovulation (OV, n = 76)/hormone replacement therapy (HRT, n = 58) + 5 and + 10.

Results

The results of the two biopsies were correlated with the clinically expected day of the cycle and showed temporal delays or hypercompensations, diverging from the expected cycle days by 0.5–5 days. In comparison with the first biopsies, the transformation rate in the second biopsies showed compensation, augmented delay, or constant transformation in 48.69, 22.37, and 28.94% of cases for ovulation in natural cycles and 56.89, 25.85, and 17.26% for HRT cycles, respectively.

Conclusion

The study revealed an individually dynamic transformation process of the endometrium, with the ability to compensate or enlarge an initial “delay”, which is now identified as a normal individual transformation process during the secretory phase. This information is of great importance for the scientific investigation of dynamic changes in endometrial tissue, as well as for the timing of embryo transfers.

Histological component quantification for the evaluation of endometrial receptivity in women with natural cycles undergoing in vitro fertilization/intracytoplasmic sperm injection

OBJECTIVE

Our aim was to evaluate the value of the volumetric fraction of vascular endothelial cells (EnVF) for determining endometrial receptivity in women undergoing in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI).

MATERIALS AND METHODS

The records of women undergoing IVF/ICSI between 2006 and 2010 were retrospectively reviewed. An endometrial biopsy was performed in the cycle prior to IVF/ICSI. EnVF was calculated from endometrial biopsy staining.

RESULTS

Twenty-seven patients who did not become pregnant, 8 who had a miscarriage, and 21 with a clinical pregnancy were included. The three groups were similar with respect to infertility and IVF characteristics. An EnVF ≤3.85 was associated with not becoming pregnant, an EnVF >5.29 with miscarriage, and a level between 3.86 and 5.29 was associated with clinical pregnancy (p = 0.001).

CONCLUSIONS

EnVF examined in the prior cycle may be a marker of endometrial receptivity and predict the chance of pregnancy in women undergoing IVF/ICSI.

Evaluation of Progesterone and Ovulation-stimulating Drugs on the Glandular Epithelium and Angiogenesis in Mice

Background:

Human endometrium is a dynamic tissue during the menstrual cycle can be influenced by ovarian hormones. The purpose of this study was to evaluate the endometrium angiogenesis under the influence of human menopausal gonadotropin and human chorionic gonadotropin (HMG and HCG) that stimulate ovulation and progesterone.

Materials and Methods:

In this study, thirty adult female mice were randomly divided into three groups as: control, gonadotropin and gonadotropin + progesterone. The mice in the other two groups except the control group received 7.5 IU HMG and later HCG. Subsequently, the mice were placed in a cage for mating. Gonadotropin + progesterone group was administered, 1 mg/mouse progesterone in 24, 48, and 72 h interval, after HMG injection. Ninety-six hours after HMG injection, animals were sacrificed, and their uterine specimens were prepared by immunohistochemistry technique for light microscopic studies, and statistical analysis was carried out.

Results:

Endometrium angiogenesis in control group showed that mean ± standard deviation was 24.15 ± 11.15, gonadotropin group was 62.50 ± 24.16, and gonadotropin + progesterone group was 41.85 ± 19.54. Significant difference between the control group and gonadotropin group and between the control group and gonadotropin + progesterone was observed. Statistically significant differences were observed in all groups in the endometrial angiogenesis (P < 0.05).

Conclusion:

Ovarian induction with gonadotropins and gonadotropins + progesterone could not change the morphometrically index of endometrial glandular epithelium in mice. Ovarian stimulation followed by progesterone injection could modify the angiogenesis of mice endometrium.

Insufficient Angiogenesis: Cause of Abnormally Thin Endometrium in Subfertile Patients?

INTRODUCTION

This study investigated subfertile patients with abnormally thin endometrium after infertility treatment. As they had adequate serum concentrations of hormones, an endometrial factor for subfertility was suspected.

METHODS

To elucidate the cause of subfertility, endometrial biopsies were taken in each patient in the late proliferative and mid-secretory phases of one menstrual cycle. Endometrial biopsies from women with normal menstrual cycles and confirmed fertility who were undergoing hysterectomy for benign uterine disease were used as positive controls. The tissue samples were investigated for steroid hormone receptor expression and for the proliferation marker Ki-67. Immunohistochemistry was performed with antibodies against the marker molecules for endometrial receptivity - β ₃ integrin, VEGF, LIF, and CD56 (large granular lymphocytes, LGLs).

RESULTS

The steroid hormone receptors for estrogen (E2) and progesterone (P) were expressed normally (at the first biopsy) and were down-regulated (at the second biopsy) within the cycle. Strikingly, all of the marker molecules investigated showed negative or weak and inadequate expression in the mid-secretory phase. Numbers of LGLs remained as low as in the proliferative phase. In contrast, fertile patients were found to express these marker molecules distinctly in the mid-secretory phase.

CONCLUSIONS

It may be hypothesized that a severe deficiency of these angiogenesis-related marker molecules leads to defective development of the endometrium, which remains thin. Deficient angiogenetic development may thus provide an explanation for the endometrial factor that causes infertility. Further investigations will need to focus on identifying the regulating factors that act between steroid receptor activation and the expression of these marker molecules.

Associations between Individual and Combined Polymorphisms of the TNF and VEGF Genes and the Embryo Implantation Rate in Patients Undergoing In Vitro Fertilization (IVF) Programs

BACKGROUND

A multiple pregnancy is now considered to be the most common adverse outcome associated with in vitro fertilization (IVF). As a consequence, the identification of women with the best chances of embryo implantation is a challenge in IVF program, in which the objective is to offer elective single-embryo transfer (eSET) without decreasing the pregnancy rate. To date, a range of hormonal and clinical parameters have been used to optimize eSET but none have significant predictive value. This variability could be due to genetic predispositions related to single-nucleotide polymorphisms (SNPs). Here, we assessed the individual and combined impacts of thirteen SNPs that reportedly influence the outcome of in vitro fertilisation (IVF) on the embryo implantation rate for patients undergoing intracytoplasmic sperm injection program (ICSI).

MATERIALS AND METHODS

A 13 gene polymorphisms: FSHR(Asn680Ser), p53(Arg72Pro), AMH(Ile49Ser), ESR2(+1730G>A), ESR1(-397T>C), BMP15(-9C>G), MTHFR1(677C>T), MTHFR2(1298A>C), HLA-G(-725C>G), VEGF(+405G>C), TNFα(-308A>G), AMHR(-482A>G), PAI-1(4G/5G), multiplex PCR assay was designed to genotype women undergoing ICSI program. We analyzed the total patients population (n = 428) and a subgroup with homogeneous characteristics (n = 112).

RESULTS

Only the VEGF(+405G>C) and TNFα(-308A>G) polymorphisms impacted fertilization, embryo implantation and pregnancy rates. Moreover, the combined VEGF+405.GG and TNFα-308.AG or AA genotype occurred significantly more frequently in women with high implantation potential. In contrast, the VEGF+405.CC and TNFα-308.GG combination was associated with a low implantation rate.

CONCLUSION

We identified associations between VEGF(+405G>C) and TNFα(-308A>G) polymorphisms (when considered singly or as combinations) and the embryo implantation rate. These associations may be predictive of embryo implantation and could help to define populations in which elective single-embryo transfer should be recommended (or, conversely, ruled out). However, the mechanism underlying the function of these polymorphisms in embryo implantation remains to be determined and the associations observed here must be confirmed in a larger, more heterogeneous cohort.

Mifepristone-exposured human endometrial endothelial cells in vitro

The antiprogestin mifepristone has been used for more than 20 years as a medical alternative for early pregnancy termination. After mifepristone administration, significant changes have been observed in the endometrial vessels, with cell injury and cell death in capillary endothelial cells. In this study, the effect of mifepristone on human endometrial endothelial cells (HEECs) in vitro was evaluated using proliferation and viability assays, quantitative polymerase chain reaction of markers important for the regulation of angiogenesis, and by tube formation assay. There were no detectable effects of mifepristone on HEECs messenger RNA expression of the studied markers. Exposure to mifepristone did not alter tube formation. However, mifepristone exposure to HEECs cocultured with endometrial stromal cells significantly reduced the activity in the tube formation assay compared with mifepristone exposure of HEECs in monoculture. This implies that mifepristone causes changes in HEEC-associated angiogenic activity and that this effect is mediated through stromal cells via paracrine mechanisms.

Receptivity assessment of an ultrasonographic homogeneous endometrium in the late follicular phase of infertile women with natural cycles

OBJECTIVE

The purpose of this study was to assess the receptivity of the homogeneous endometrium in the late follicular phase in infertile women with natural cycles.

STUDY DESIGN

Twenty-eight infertile women with ultrasonographically homogeneous (group 1) or trilaminar (group 2) endometria in the late follicular phase underwent endometrial biopsies. Some molecular markers and development of pinopodes were evaluated.

RESULTS

In the late follicular phase, the mean level of vascular endothelial growth factor was significantly lower in group 1 than in group 2 (0.96 ± 0.37 marks vs 1.39 ± 0.46 marks; P = .010). In the mid luteal phase, a decreased leukemia inhibitory factor and integrin alpha v beta 3 levels were found in group 1 (1.58 ± 0.99 marks vs 2.59 ± 0.61 marks; 1.85 ± 0.72 marks vs 2.60 ± 0.73 marks; 1.92 ± 0.91 marks vs 2.83 ± 0.57 marks; P = .003; P = .011; P = .004). The rate of fully developed pinopodes in the mid luteal phase was significantly decreased in group 1 (P = .018).

CONCLUSION

An ultrasonographically homogeneous endometrium in the late follicular phase was associated with poor receptivity in infertile women with natural cycles.

Coronary artery disease in aging women: a menopause of endothelial progenitor cells?

The cardiovascular protection provided to women during the reproductive age and the unique angiogenic properties of the female reproductive system provide insights into the complex regulatory network of female sex hormones, angiogenic growth factors, and stem cell regulatory molecules. The intricate and interwoven endometrial physiology of the female menstrual cycle shows that in order to harness the physiologic cardioprotection provided by nature to women of reproductive age, for better cardiovascular therapies in postmenopausal women and the population in general, a coherent and systematic approach is needed.

Is sildenafil citrate affect endometrial receptivity? An immunohistochemical study

The authors aimed to investigate the effect of sildenafil citrate (Sc) on expressions of β(3) integrin and vascular endothelial growth factor (VEGF), which is taking part in endometrium receptivity in implantation window period in controlled ovarian hyperstimulation (COH) performed rats. In this study, Wistar albino female rats were used and were divided into four groups as control, COH, Sc, and COH + Sc groups. They were sacrificed on the third, fourth, and fifth day of pregnancy, uteruses were resected, and uteri sections were stained with immunohistochemical method and evaluated. β(3) integrin immunoreactivity was most intensely observed in the endometrial glandular epithelium (GE) and stromal cells in the Sc group on the third day, whereas immunoreactivity was most intensely detected in the luminal epithelium (LE), GE, and stromal cells in the Sc group on the fourth day. VEGF immunoreactivity was most intensely observed in the endometrial LE in the Sc group on the third day, in the Sc and COH + Sc groups on the fourth day, and in the COH + Sc group on the fifth day. Our results indicated that Sc plays a role in both implantation and decidualization by affecting β(3) integrin and VEGF expressions in implantation window period in rats.

Three dimensional microvascular measurements in human endometrium using optical slices from laser scanning confocal microscopy (LSCM)

There is increasing interest in the structure of the microvascular environment in human endometrium because of the recognition of the complexity and functional importance of this tissue. Endometrial microcirculatory networks and their relationships have rarely been studied in three-dimensions. Longitudinal uterine slices containing endometrial tissue were carefully selected from women undergoing a hysterectomy. Formalin-fixed endometrial sections (≤ 50 μm) representing the fundal and isthmic regions were immunofluorescently labeled with monoclonal antibody (CD34) to target the endothelium of microvessel and fluorescein isothiocyanate (FITC) labeled goat anti-mouse. Digital images were acquired using a Nikon Eclipse E800 microscope equipped with a Radiance 2000 confocal scanning laser attachment. ImarisBasic 4.1 visualization suite was utilized for qualitative interpretation. NeuronTracer 1.0 software was utilized to derive the length and numerical densities. There were significant changes across the phases of the menstrual cycle in functional and basal endometrial layers in vessel length density (LD(v)) and branch point density (ND(v)) within both fundal and isthmic regions of the uterus (P<0.001). There was also a significant effect of menstrual cycle phase on mean vessel segment length (SL(v)) within each region and within each of the layers (P<0.001). The capillary radial diffusion distance r(diff) was negatively correlated with LD(v). In general, within each of the menstrual cycle phases, LD(v), ND(v) were greater in the fundal than the isthmic regions while, in contrast, SL(v) was found to be greatest in the isthmic region. Utilization of immunofluorescence and laser scanning confocal microscopy has enabled us to demonstrate significant vascular changes in human endometrial layers illustrating that in general, within each of the menstrual cycle phases, vessel length and branch point densities were greater in the fundal than the isthmic regions, while vessel segment lengths were found to be greatest in the isthmic region.

Long-term progestin-only contraception in humans versus animal models

Abnormal uterine bleeding is the leading indication for discontinuation of long-term progestin-only contraceptives. Histological sections of endometria from long-term progestin-treated patients display abnormally enlarged blood vessels that are prone to bleed in a nonuniform manner. Because it has been complex to attain patients willing to complete long-term studies, and good quality endometrial tissues have proven difficult to obtain, animal models have been used to obviate this problem. In this review, we describe these models including the guinea pig, an animal model we have previously investigated, to assess the mechanisms involved in abnormal uterine bleeding following long-term progestin-only contraception.

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.

The role of vascular endothelial growth factor and estradiol in the regulation of endometrial angiogenesis and cell proliferation in the marmoset

The present studies explore the roles of vascular endothelial growth factor (VEGF) and estradiol on angiogenesis and stromal and epithelial cell proliferation in the marmoset endometrium during the proliferative phase of the ovulatory cycle. At the start of the proliferative phase, marmosets were 1) treated with vehicle, 2) treated with a VEGF inhibitor (VEGF Trap, aflibercept), 3) ovariectomized, 4) ovariectomized and given replacement estradiol, or 5) treated with VEGF Trap and given replacement estradiol. The uterus was examined 10 d later in the late proliferative phase. Changes in endothelial and epithelial cell proliferation were quantified using a volumetric density method after immunohistochemistry for bromodeoxyuridine to localize proliferating cells, CD31 to visualize endothelial cells, and dual staining to distinguish endothelial cell proliferation. Endothelial proliferation was elevated in late proliferative controls but virtually absent after VEGF Trap. Ovariectomy had a similar inhibitory effect, whereas angiogenesis was restored by estrogen replacement. Estradiol replacement in VEGF Trap-treated marmosets resulted in only a small increase in endothelial cell proliferation that remained significantly below control values. VEGF Trap treatment and ovariectomy also markedly reduced stromal cell proliferation but resulted in increased stromal cell density associated with a reduction in overall endometrial volume. Estrogen replacement in both ovariectomized and VEGF Trap-treated animals restored stromal proliferation rates and cell density. These results show that endometrial angiogenesis and stromal proliferation during the proliferative phase are driven by estradiol and that the effect of estrogen on angiogenesis is mediated largely by VEGF.

The relationship between microvessel density, proliferative activity and expression of vascular endothelial growth factor-A and its receptors in eutopic endometrium and endometriotic lesions

Studies were performed to elucidate the possible relationship between microvessel density, proliferative activity and angiogenesis in eutopic endometrium from women with and without endometriosis and peritoneal endometriotic lesions. The question whether changes in these parameters in endometriotic lesions were reflected by the level of vascular endothelial growth factor-A (VEGF-A) in serum and peritoneal fluid was also studied. Biopsy specimens of both eutopic endometrium and peritoneal endometriotic lesions from women with endometriosis (n = 25) as well as eutopic endometrium from women without endometriosis (n = 14) were analysed immunohistochemically regarding microvessel density, proliferative activity, and expression of VEGF-A and its receptors vascular endothelial growth factor receptors 1 and 2 (VEGFR-1 and VEGFR-2) in stroma, glands and blood vessels. The VEGF-A concentration was measured in peritoneal fluid and serum. Secretory phase eutopic endometrium from women with endometriosis had significantly higher microvessel density, expression of VEGF-A in glandular epithelium and VEGFR-2 in endometrial blood vessels than those from women without endometriosis. Endometriotic lesions with high proliferative activity had a higher microvessel density and showed higher vascular expression of VEGFR-2 as well as being accompanied by higher levels of VEGF-A in peritoneal fluid and serum, compared with lesions with low proliferative activity. In conclusion, there seems to be a dysregulation of angiogenic activity in the eutopic endometrium of women with endometriosis and endometriotic lesions with high proliferative activity were accompanied by higher local angiogenic activity and higher levels of VEGF in serum and peritoneal fluid.

Angiogenic factors in normal endometrium and endometrial adenocarcinoma

In the endometrium, angiogenesis plays important roles not only in tumor growth but also in the menstrual cycle. The purpose of the present paper was to investigate immunohistochemically the correlation between angiogenic factor expression and angiogenic score in normal and neoplastic endometrium. Immunohistochemical staining for vascular endothelial growth factor (VEGF), angiopoietin (Ang)-1, Ang2, Tie2, CD34 and CD105 was performed on formalin-fixed and paraffin-embedded tissues from 31 normal endometrium and 85 endometrial adenocarcinoma. VEGF, Ang1, Ang2 and Tie2 expression was localized in the cytoplasm of glandular and tumor cells. The levels of each angiogenic factor were different in the phases of the menstrual cycle and each layer of normal endometrium. In general, VEGF and Tie2 expression was higher in adenocarcinoma than in normal epithelial cells. Conversely, Ang1 and Ang2 expression was higher in normal epithelium than in adenocarcinoma. The angiogenic score (CD105/CD34) tended to be higher in the adenocarcinoma than in the normal epithelium. It is suggested that the angiogenic pathway and the role of these factors seem to differ between normal tissue and carcinoma of the endometrium.

Endocrine regulation of menstruation

In women, endometrial morphology and function undergo characteristic changes every menstrual cycle. These changes are crucial for perpetuation of the species and are orchestrated to prepare the endometrium for implantation of a conceptus. In the absence of pregnancy, the human endometrium is sloughed off at menstruation over a period of a few days. Tissue repair, growth, angiogenesis, differentiation, and receptivity ensue to prepare the endometrium for implantation in the next cycle. Ovarian sex steroids through interaction with different cognate nuclear receptors regulate the expression of a cascade of local factors within the endometrium that act in an autocrine/paracrine and even intracrine manner. Such interactions initiate complex events within the endometrium that are crucial for implantation and, in the absence thereof, normal menstruation. A clearer understanding of regulation of normal endometrial function will provide an insight into causes of menstrual dysfunction such as menorrhagia (heavy menstrual bleeding) and dysmenorrhea (painful periods). The molecular pathways that precipitate these pathologies remain largely undefined. Future research efforts to provide greater insight into these pathways will lead to the development of novel drugs that would target identified aberrations in expression and/or of local uterine factors that are crucial for normal endometrial function.

Recent advances in endometrial angiogenesis research

This review summarises recent research into the mechanisms and regulation of endometrial angiogenesis. Understanding of when and by what mechanisms angiogenesis occurs during the menstrual cycle is limited, as is knowledge of how it is regulated. Significant endometrial endothelial cell proliferation occurs at all stages of the menstrual cycle in humans, unlike most animal models where a more precise spatial relationship exists between endothelial cell proliferation and circulating levels of oestrogen and progesterone. Recent stereological data has identified vessel elongation as a major endometrial angiogenic mechanism in the mid-late proliferative phase of the cycle. In contrast, the mechanisms that contribute to post-menstrual repair and secretory phase remodelling have not yet been determined. Both oestrogen and progesterone/progestins appear to have paradoxical actions, with recent studies showing that under different circumstances both can promote as well as inhibit endometrial angiogenesis. The relative contribution of direct versus indirect effects of these hormones on the vasculature may help to explain their pro- or anti-angiogenic activities. Recent work has also identified the hormone relaxin as a player in the regulation of endometrial angiogenesis. While vascular endothelial growth factor (VEGF) is fundamental to endometrial angiogenesis, details of how and when different endometrial cell types produce VEGF, and how production and activity is controlled by oestrogen and progesterone, remains to be elucidated. Evidence is emerging that the different splice variants of VEGF play a major role in regulating endometrial angiogenesis at a local level. Intravascular neutrophils containing VEGF have been identified as having a role in stimulating endometrial angiogenesis, although other currently unidentified mechanisms must also exist. Future studies to clarify how endometrial angiogenesis is regulated in the human, as well as in relevant animal models, will be important for a better understanding of diseases such as breakthrough bleeding, menorrhagia, endometriosis and endometrial cancer.

Putative stem cell activity of human endometrial epithelial and stromal cells during the menstrual cycle

OBJECTIVE

To determine whether menstrual cycle stage or activity has an effect on the clonogenic activity of human endometrial epithelial and stromal cells.

DESIGN

Clonal analysis of human endometrial epithelial and stromal cells derived from full-thickness endometrium.

SETTING

University research laboratory.

PATIENT(S)

Twenty-six women of varying age and race undergoing hysterectomy for nonendometrial pathologies.

INTERVENTION(S)

Full-thickness human endometrial tissue was dissociated into single cells. Epithelial and stromal cells were separated using magnetic beads, and cloning assays were performed in serum-containing or growth factor-supplemented serum-free medium.

MAIN OUTCOME MEASURE(S)

Clonogenic activity of epithelial and stromal cells.

RESULT(S)

Clonogenicity of epithelial and stromal cells did not vary significantly between proliferative, secretory, and inactive endometrium. However, epithelial and stromal cells did show a trend for greater numbers of clonogenic cells in secretory and proliferative endometrium respectively. A large variation between samples was observed, which may have masked any significant differences.

CONCLUSION(S)

We found that clonogenicity does not vary from the proliferative to secretory stage of the menstrual cycle, or between active, cycling and inactive endometrium for both epithelial and stromal cells. We have demonstrated for the first time that inactive endometrium contains clonogenic epithelial and stromal cells.

Microvascular density, vascular endothelial growth factor A, and its receptors in endometrial blood vessels in patients with menorrhagia

OBJECTIVE

To analyze the expression of vascular endothelial growth factor A (VEGF-A) and receptors (VEGFR-1 and VEGFR-2) in endometrial blood vessels, as well as microvascular density (MVD), in endometrial biopsy samples from idiopathic menorrhagia patients.

DESIGN

Prospective clinical study.

SETTING

University hospital, unit of gynecology.

PATIENT(S)

Twenty-four patients with idiopathic menorrhagia and 18 healthy fertile women.

INTERVENTION(S)

Blood sampling for hormone measurement, hysteroscopy, and endometrial biopsy sampling. Endometrial biopsy samples were used for immunohistochemistry assessments and image analysis of stained endothelial structures for VEGF-A, VEGFR-1, VEGFR-2, and CD34.

MAIN OUTCOME MEASURE(S)

Appearance of the endometrial vascular immunoreactivity for VEGF-A, VEGFR-1, and VEGFR-2, MVD and computer-assisted stereological analysis of immunoassayed blood vessels.

RESULT(S)

Although the MVD did not differ between patients and controls, we observed that vascular expression of VEGF-A, VEGFR-1, and VEGFR-2 in capillaries was 1.8-fold, 1.8-fold, and 2.0-fold higher, respectively, in the menorrhagia group when assessed as the number of stained capillaries per unit area. There were also a twofold higher number of arterioles, which were VEGFR-2 positive in the menorrhagia group.

CONCLUSION(S)

Up-regulation of VEGF-A and receptors VEGFR-1 and VEGFR-2 in capillaries in menorrhagia could be involved in abnormal endometrial vascular structure and permeability.

Influence of different hormonal regimens on endometrial microvascular density and VEGF expression in women suffering from breakthrough bleeding

BACKGROUND

The aim of this study was to quantify blood vessel density (BVD) and immunoreactive vascular endothelial growth factor (VEGF) levels in endometrial biopsies taken from women suffering breakthrough bleeding (BTB) under different exogenous hormonal regimes.

METHODS

Endometrial biopsies from women in Melbourne with BTB were divided into four groups: combined-continuous hormone therapy (HT) (estrogen and progestin taken daily), cyclical HT (daily estrogen with progestin for 14 days each cycle), progestin-only, or no HT. Subjects from Barcelona were using the Mirena intrauterine levonorgestrel-releasing system for contraceptive purposes, with menstrual diaries for classification into four groups (amenorrhea, infrequent, regular and prolonged). Control biopsies from Melbourne were included in the study. Endometrial samples were immunostained for VEGF and blood vessel localization using an antibody to CD34.

RESULTS

Results showed that BVD was significantly reduced in the progestin-only treated group compared with the other three treatment groups (P = 0.028). In addition, all four Mirena BTB groups had significantly reduced BVD compared with controls. Considerable heterogeneity was observed in VEGF immunostaining within and between individual samples with no major differences between HT or Mirena.

CONCLUSION

These results provide strong evidence that unopposed progestins reduce endometrial BVD and that there is no link between VEGF immunostaining and BVD or BTB.

Soluble factors from human endometrium promote angiogenesis and regulate the endothelial cell transcriptome

BACKGROUND

Angiogenesis and vascular remodeling play critical roles in the cyclical growth and regression of endometrium. They also appear to play roles in the pathogenesis of endometriosis.

METHODS AND RESULTS

Supernatants were collected from cultured endometrium isolated from women with and without endometriosis. These supernatants induced endothelial cell proliferation and angiogenesis in vitro. They contained vascular endothelial growth factor (VEGF)-A, and their proliferative effects on endothelial cells were partially abrogated by a blocking anti-VEGF-A antibody. Gene array analysis showed that culture supernatants from proliferative phase endometrium, and to a lesser extent secretory phase endometrium, induced significant changes in the transcriptome of endothelial cells. We could not detect any association between endometriosis and the ability of endometrial-derived soluble factors to promote angiogenesis or to regulate the endothelial transcriptome. In addition, we could not detect any association between endometriosis and the concentration of VEGF-A in supernatants from cultured endometrium or in menstrual effluent.

CONCLUSIONS

We have shown that endometrium cultured in vitro produced soluble factors, including VEGF-A, that promoted angiogenesis. Proliferative phase endometrium promoted significant endothelial cell transcriptome changes that appear overall to be pro-angiogenic. These transcriptome changes provide insight into the dynamic control of vessel structure on which both eutopic endometrium and endometriotic lesions depend.

Intravascular neutrophils partially mediate the endometrial endothelial cell proliferative response to oestrogen in ovariectomised mice

The aim of this study was to investigate the role of intravascular neutrophils in initiating endothelial cell proliferation following oestrogen treatment in ovariectomised mouse endometrium. Uterine tissues were collected from ovariectomised C57/CBA female mice 24 h after oestrogen treatment with or without systemic neutrophil depletion. Neutropenia was achieved with either an in-house anti-neutrophil serum (ANS) or Gr-1 monoclonal antibody. All mice received an i.p. injection of bromodeoxyuridine (BrdU) 4 h prior to dissection to allow visualisation of proliferating cells using immunocytochemistry. Endometrial sections were immunostained for BrdU, vascular endothelial growth factor (VEGF), and neutrophils (using ANS). Oestrogen treatment of ovariectomised mice significantly increased the number of intravascular neutrophils, whereas induction of neutropenia with either ANS or Gr-1 in conjunction with oestrogen treatment prevented this increase. Oestrogen treatment of ovariectomised mice also significantly increased the number of intravascular VEGF-positive cells; however, whereas induction of neutropenia with ANS significantly reduced this increase, Gr-1 did not. In both studies, neutropenia significantly reduced, but did not eliminate, the amount of endometrial endothelial cell proliferation. These results suggest a role for neutrophils in endometrial angiogenesis following acute oestrogen treatment; however, the presence of VEGF-positive cells even after induction of neutropenia suggests that more than one type of leukocyte may be involved.

Clonogenicity of human endometrial epithelial and stromal cells

The human endometrium regenerates from the lower basalis layer, a germinal compartment that persists after menstruation to give rise to the new upper functionalis layer. Because adult stem cells are present in tissues that undergo regeneration, we hypothesized that human endometrium contains small populations of epithelial and stromal stem cells responsible for cyclical regeneration of endometrial glands and stroma and that these cells would exhibit clonogenicity, a stem-cell property. The aims of this study were to determine 1) the clonogenic activity of human endometrial epithelial and stromal cells, 2) which growth factors support this clonogenic activity, and 3) determine the cellular phenotypes of the clones. Endometrial tissue was obtained from women undergoing hysterectomy. Purified single- cell suspensions of epithelial and stromal cells were cultured at cloning density (300-500/cm(2)) in serum medium or in serum- free medium supplemented with one of eight growth factors. Small numbers of epithelial (0.22%) and stromal cells (1.25%) initiated colonies in serum-containing medium. The majority of colonies were small, containing large, loosely arranged cells, and 37% of epithelial and 1 in 60 of stromal colonies were classified as large, comprising small, densely packed cells. In serum-free medium, transforming growth factor-alpha (TGF alpha), epidermal growth factor (EGF), platelet-derived growth factor-BB (PDGF-BB) strongly supported clonogenicity of epithelial cells, while leukemia-inhibitory factor (LIF), hepatocyte growth factor (HGF), stem-cell factor (SCF), insulin-like growth factor-I (IGF- I) were weakly supportive, and basic fibroblast growth factor (bFGF) was without effect. TGF alpha, EGF, PDGF-BB, and bFGF supported stromal cell clonogenicity, while HGF, SCF, LIF, and IGF- I were without effect. Small epithelial colonies expressed three epithelial markers but not stromal markers; however, large epithelial colonies showed little reactivity for all markers except alpha(6)-integrin. All stromal colonies contained fibroblasts, expressing stromal markers, and in some colonies, myofibroblasts were also identified. This analysis of human endometrium has demonstrated the presence of rare clonogenic epithelial and stromal cells with high proliferative potential, providing the first evidence for the existence of putative endometrial epithelial and stromal stem cells.

Human uterine vascular structures in normal and diseased states

Menstrual bleeding disorders are one of the most common problems presenting to the gynaecologist. There is increasing evidence that alterations in human uterine vascular structures are associated with spontaneous and sex steroid-induced changes in menstrual bleeding patterns. This article will discuss the normal anatomy and physiology of uterine vascular growth, breakdown, and repair and will indicate where altered anatomy and function may contribute to menstrual disorder. In particular, impact of low-dose progestogens on the endometrial vasculature and endometrial vascular fragility will be discussed. Disturbances of myometrial vascular growth and remodeling, including fibroids, adenomyosis, implantation, and arterio-venous malformations will also be addressed.

Expression of vascular endothelial growth/permeability factor by endometrial glandular epithelial and stromal cells in baboons during the menstrual cycle and after ovariectomy

Vascular endothelial growth/permeability factor (VEG/PF) has a crucial role in angiogenesis, and neovascularization is essential in preparing the uterine endometrium for implantation. However, the regulation of VEG/PF synthesis by particular cell types of the endometrium during the human menstrual cycle is not well understood. Therefore, in the present study the baboon was used as a nonhuman primate to determine the role of the ovary in vivo in endometrial VEG/PF expression. VEG/PF mRNA levels were quantified by competitive RT-PCR in whole uterine endometrium and in glandular epithelial and stromal cells isolated from the endometrium by laser capture microdissection of baboons during the normal menstrual cycle and after ovariectomy, which decreased serum estradiol and progesterone to undetectable levels. Mean (+/-SE) levels (attomoles per micrograms of total RNA) of the 323-bp VEG/PF mRNA product, which reflected collective expression of all VEG/PF isoforms, in whole endometrium were 785 and 727 +/- 158 during the mid and late follicular phases, respectively, and 1108 +/- 320 during the midcycle surge in serum estradiol. VEG/PF mRNA levels then declined briefly before increasing to 1029 +/- 365 attomoles/ micro g RNA during the late luteal phase of the menstrual cycle. VEG/PF mRNA levels (attomoles per femtomole of 18S rRNA) were similar in glandular epithelial (2.27 +/- 1.11) and stromal (2.54 +/- 0.70) cells at the midcycle estradiol peak and the midluteal phase of the menstrual cycle (2.34 +/- 1.30 and 1.49 +/- 0.53, respectively). Immunocytochemical expression of VEG/PF protein was abundant in glandular and luminal epithelium, stroma, and vascular endothelium. Endometrial vessel density and percent vascularized area, determined by morphometric image analysis, were similar during the various stages of the baboon menstrual cycle. After ovariectomy, VEG/PF mRNA levels (attomoles per femtomole of 18S rRNA) in the endometrial glands (0.52 +/- 0.21) and stroma (0.22 +/- 0.11) were decreased to values that were approximately 20% and 10% (P < 0.05), respectively, of those in intact baboons during the midcycle estrogen surge. Moreover, there was relatively little VEG/PF protein immunostaining in the endometrial glands, stroma, and vascular endothelium after ovariectomy. In summary, VEG/PF mRNA and protein expression in glandular epithelial and stromal cells were markedly suppressed after ovariectomy, indicating that synthesis of this angiogenic factor in these endometrial cells is dependent upon a product(s) secreted by the ovary. Moreover, endometrial VEG/PF expression remained relatively constant and thus was available as a component of the angiogenic system throughout the menstrual cycle, presumably to progressively promote vascular reconstruction of the endometrium.

Vascular proliferation and vascular endothelial growth factor expression in the rhesus macaque endometrium

The relationship between vascular endothelial growth factor (VEGF) expression and the pattern of vascular proliferation in the rhesus macaque endometrium has not been studied. In this report, we used in situ hybridization to evaluate VEGF, VEGF receptor type 1 and VEGF receptor type 2 mRNA expression during hormonally regulated menstrual cycles in ovariectomized macaques. Proliferating endothelial cells were identified by a double immunocytochemistry procedure that detected Ki-67 antigen and von Willebrand factor in the same endothelial cells. One and 2 d after progesterone withdrawal (premenstrual), VEGF mRNA was up-regulated in the glands and stroma of the superficial endometrial zones, a finding that supports our previous suggestion that VEGF may play a role in the menstrual induction cascade. During the postmenstrual repair phase, the healing surface epithelium showed a further, dramatic increase in expression of VEGF mRNA, accompanied by strong increases in signals for VEGF receptor types 1 and 2 in multiple profiles of small blood vessels immediately below the surface epithelium. This finding implicates VEGF in the early angiogenic processes associated with endometrial healing and regeneration. Vascular endothelial proliferation persisted throughout the cycle in the upper endometrial zones and showed a dramatic estrogen- dependent peak during the midproliferative phase. This proliferative peak coincided with a peak in VEGF expression in the endometrial stroma. Endothelial proliferation was also significantly correlated with the degree of stromal VEGF expression during the proliferative and secretory stages of the cycle. These results implicate VEGF of stromal origin in endometrial vascular proliferation.

Vascular endothelial growth factor mRNA in eutopic and ectopic endometrium

OBJECTIVE

To evaluate changes in expression levels of vascular endothelial growth factor (VEGF) mRNA in human endometrial explants in a chicken chorioallantoic membrane model of endometriosis.

DESIGN

Experimental prospective study.

SETTING

University hospital.

PATIENT(S)

Endometrial biopsy samples were obtained from healthy, ovulating women undergoing elective surgery.

INTERVENTION(S)

Endometrial fragments were placed on the chicken chorioallantoic membrane and removed for analysis after 0, 24, 48, and 72 hours.

MAIN OUTCOME MEASURE(S)

Expression of different VEGF mRNA splice variants was tested. Expression of VEGF(165) mRNA was assessed by using competitive polymerase chain reaction and normalized to expression of the housekeeping gene human glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA.

RESULT(S)

After 0, 24, 48, and 72 hours of incubation, all grafts expressed VEGF(121), VEGF(145), VEGF(165), and VEGF(189) mRNA. Expression of VEGF(165) mRNA increased up to 10-fold at 24 to 72 hours compared with precultivation values.

CONCLUSION(S)

Levels of VEGF(165) mRNA in endometrial grafts increase after implantation on chicken chorioallantoic membrane. Hypoxic induction of VEGF mRNA expression in endometrial cell cultures has been reported previously. Induction of VEGF expression might indicate relative hypoxia of the specimen due to insufficient vascularization. Expression of VEGF may assist in vascularization of endometrial explants after retrograde menstruation.

Endocrine and paracrine regulation of endometrial angiogenesis

The human endometrium is a complex tissue comprised of different cell types, including epithelial, stromal, inflammatory, perivascular, and blood vessel cells. The hormonal receptivity and distribution of these cell populations change during the menstrual cycle. Cyclical endometrial growth is dependent on its ability to regenerate a vascular capillary network, which grows in parallel with the proliferation and differentiation of the endometrial lining. Natural hormonal effects on the endometrium and endocrine manipulation of this tissue, in response to the use of exogenous steroid therapies, can affect endometrial capillary proliferation and function, leading to clinical abnormalities of uterine bleeding. We propose that the regulation of endometrial angiogenesis is mediated indirectly via complex interactions among cell types. Our laboratory has focused on a prototypical member of the angiogenic proteins, vascular endothelial growth factor (VEGF)-A. In this paper we present data demonstrating that VEGF-A expression in normal endometrial epithelial and stromal cells and in Ishikawa adenocarcinoma cells is increased by an ovarian steroid, estradiol. Infiltrating immune cells, particularly polymorphonuclear granulocytes, also are sources of VEGF-A. In inflammatory conditions involving the endometrium (e.g., endometriosis), a proinflammatory cytokine, IL-1beta, can mediate neoangiogenesis by inducing VEGF-A gene transcription. Thus, endometrial vascularization is effected by both endocrine and paracrine pathways.

Enhanced angiogenic capacity and urokinase-type plasminogen activator expression by endothelial cells isolated from human endometrium

The endometrium is a tissue unique for its cyclic destruction and rapid regeneration of blood vessels. Angiogenesis, indispensable for the regeneration process, provides a richly vascularized, receptive endometrium fundamental for implantation, placentation, and embryogenesis. Human endometrial microvascular endothelial cells (hEMVEC) were isolated to better understand the properties and angiogenic behavior of these cells. Unlike human foreskin microvascular endothelial cells (hFMVEC), which proliferated better upon stimulation by basic fibroblast growth factor, hEMVEC were much more sensitive to vascular endothelial growth factor A (VEGF-A) stimulation, probably due to enhanced VEGF receptor 2 expression. In addition, hEMVEC displayed an enhanced expression of the urokinase-type plasminogen activator (u-PA) compared with hFMVEC. No differences were found in tissue-type PA, PA inhibitor-1, and u-PA receptor expression. The high expression of u-PA by hEMVEC was also found in tissue sections. hEMVEC formed capillary-like structures when cultured in 20% human serum on top of three-dimensional fibrin matrices, and VEGF-A or basic fibroblast growth factor increased this tube formation. This is in contrast with hFMVEC, which formed tubes only after simultaneous stimulation by a growth factor and tumor necrosis factor-alpha. The high basal level of u-PA contributes to and may explain the higher angiogenic properties of hEMVEC (in vitro).

Evidence for telomerase involvement in the angiogenesis of astrocytic tumors: expression of human telomerase reverse transcriptase messenger RNA by vascular endothelial cells

OBJECT

Evidence from recent in vitro studies indicates that reactivation of telomerase, the enzyme that synthesizes the telomere ends of chromosomes, is a crucial event in the unlimited clonal expansion of endothelial cells that precedes the neoplastic conversion of these cells. It is known that high-grade gliomas express telomerase and that, in these neoplasms, proliferating endothelial cells may undergo transformational changes with development of sarcomatous components within the primitive tumor. To assess whether telomerase is involved in the endothelial cell proliferation that characterizes brain tumor angiogenesis, the authors investigated at the single-cell level the expression of messenger (m)RNA for the human telomerase catalytic subunit human telomerase reverse transcriptase (hTERT) by vascular cells of astrocytic tumors.

METHODS

The in situ hybridization (ISH) method was performed by processing histological sections with specific riboprobes for hTERT and for c-myc, an oncogene that is known to upregulate hTERT. Results of the ISH studies were compared with proliferative activity, as estimated by Ki-67 immunostaining. The expression of hTERT mRNA by vascular endothelial cells was related to the histological grade of the tumor because it was detected in five (29%) of 17 low-grade astrocytomas, nine (56%) of 16 anaplastic astrocytomas, and 19 (100%) of 19 glioblastomas multiforme (GBMs). Expression of c-myc mRNA was strictly correlated with that of hTERT mRNA. In low-grade astrocytomas and anaplastic astrocytomas, a dissociation was noted between hTERT mRNA expression and the proliferation rate of endothelial cells. Conversely, GBMs displayed a significant correlation between the level of hTERT mRNA expression and endothelial cell proliferation. Data from an in vitro assay in which human umbilical vein endothelial cells were stimulated to proliferate by adding vascular endothelial growth factor and an ISH study of newly formed vessels surrounding brain infarcts confirmed that expression of hTERT mRNA does not merely reflect the proliferative status of endothelial cells but represents a specific feature of brain tumor neovascularization.

CONCLUSIONS

The results of this study are consistent with a role of telomerase in the angiogenesis of astrocytic tumors. Expression of hTERT mRNA by tumor vascular cells is an early event during the progression of astrocytic tumors, which precedes endothelial cell proliferation and may represent a first sign of dedifferentiation. Other than elucidating the mechanisms of tumor angiogenesis, these results encourage research on antitelomerase drugs for the treatment of malignant gliomas.

Vascular repair after menstruation involves regulation of vascular endothelial growth factor-receptor phosphorylation by sFLT-1

Regeneration of the endometrium after menstruation requires a rapid and highly organized vascular response. Potential regulators of this process include members of the vascular endothelial growth factor (VEGF) family of proteins and their receptors. Although VEGF expression has been detected in the endometrium, the relationship between VEGF production, receptor activation, and endothelial cell proliferation during the endometrial cycle is poorly understood. To better ascertain the relevance of VEGF family members during postmenstrual repair, we have evaluated ligands, receptors, and activity by receptor phosphorylation in human endometrium throughout the menstrual cycle. We found that VEGF is significantly increased at the onset of menstruation, a result of the additive effects of hypoxia, transforming growth factor-alpha, and interleukin-1beta. Both VEGF receptors, FLT-1 and KDR, followed a similar pattern. However, functional activity of KDR, as determined by phosphorylation studies, revealed activation in the late menstrual and early proliferative phases. The degree of KDR phosphorylation was inversely correlated with the presence of sFLT-1. Endothelial cell proliferation analysis in endometrium showed a peak during the late menstrual and early proliferative phases in concert with the presence of VEGF, VEGF receptor phosphorylation, and decrease of sFLT-1. Together, these results suggest that VEGF receptor activation and the subsequent modulation of sFLT-1 in the late menstrual phase likely contributes to the onset of angiogenesis and endothelial repair in the human endometrium.

Endometrial angiogenesis

The endometrium is one of the few tissues in the adult where physiological angiogenesis occurs. Studies of endometrial angiogenesis are complicated by the continual changes in tissue growth and regression during the menstrual cycle, and differences between the two different zones of the endometrium--the functionalis and basalis. The mechanisms of angiogenesis in the endometrium may be different to those in solid tumours, requiring a re-evaluation of the relative importance of various angiogenesis promoters and inhibitors. None of the angiogenesis promoters or inhibitors have yet been demonstrated beyond doubt to have a biological role in endometrial angiogenesis in vivo. Thus, the mechanisms, timing and control of angiogenesis in the endometrium are far from being fully understood.

Clinical implications of disturbances of uterine vascular morphology and function

Menstrual disturbances are one of the most common problems presenting to the gynaecologist. In order for the endometrium to bleed, vessels must break down. Disruption in the regulation of endometrial vascular growth and function has been found in association with spontaneous and sex steroid-induced disturbances of menstrual bleeding. Although circulating oestrogens and progestogens influence the endometrial vessels, this effect appears to be indirect, and regulation is primarily via local factors. Deficient vasoconstriction and haemostasis with excessive fibrinolysis is seen in menorrhagia. Breakthrough bleeding in users of progestogen-only contraceptives is associated with increased superficial vascular fragility and disruptions in the supporting basement membrane. Blood vessels in uterine fibroids are abnormal in distribution and appearance. Adenomyosis is also commonly associated with menstrual disturbance, and alterations in vascular distribution suggest altered angiogenesis. Successful human embryo implantation requires endometrial vascular breakdown. Excessive thrombosis associated with the antiphospholipid syndrome may interfere with this re-modelling and compromise implantation. Arteriovenous malformations are a rare but important cause of excessive or irregular vaginal bleeding. Abundant vessels with abnormal morphology, associated with aberrant angiogenesis can be seen, and embolization of these vessels may be an effective conservative treatment. Improved understanding of the regulation of the uterine vasculature is likely to lead to targeted therapies to prevent unscheduled vascular breakdown and to control menstrual disturbance at an endometrial level.