Hormonal control of ovoimplantation

Expression of Cystatin C in the rat endometrium during the peri-implantation period

Endometrial receptivity for embryo implantation in the rat is a transient state occurring on day 5 of pregnancy or pseudopregnancy and is controlled by estrogen and progesterone. To identify genes potentially involved in receptivity, a uterine cDNA library was screened. An interesting pattern for Cystatin C (Cst3) expression was discovered with a peak in abundance just prior to embryo implantation (day 4 of pregnancy) followed by a significant drop the following day when implantation is initiated. Histology localized Cst3 mRNA and CST3 protein to the glandular epithelium on day 4 of pregnancy suggesting that it is secreted into the uterine lumen at this time. In ovariectomized rats endometrial Cst3 mRNA levels decreased within 3h of treatment with estradiol; this effect was inhibited by the anti-estrogen, ICI 182, 780. The data suggest that the endometrial expression of the cysteine protease inhibitor, Cst3, is modulated by estrogen during the peri-implantation period.

Apoptosis is not altered by clomiphene citrate in pseudopregnant rat uteri

Clomiphene citrate (CC) remains one of the most often prescribed synthetic oestrogens used in the treatment of infertility even though the ensuing pregnancy rates are low. CC alters the uterine environment on most levels. Ovariectomised rats were treated with 5 mg progesterone (P) for 3 days and a 0.5 microg injection of oestrogen (E) on the third day (PP(PE)) thus inducing pseudopregnancy and rendering the uterus receptive to implantation 24 h later. Using this model, we investigated apoptosis in the rat uterus treated with 0.25 mg CC given prior to the PP(PE) treatment. Apoptotic cells in the uterus were localised using TUNEL and visualised with a FITC marker. There was a similar increase in apoptosis in the uterine luminal epithelium in the PP(PE) and CCPP(PE) treated animals; no changes were observed in apoptosis in the other uterine compartments when compared to the control. The CCPP(PE)-treated tissue showed tall epithelial cells with long microvilli while the PP(PE) tissue had short microvilli and low cuboidal epithelium. These results suggest that CC does not disrupt the normal apoptotic activity seen at implantation, but does change the morphology of the luminal epithelium, suggesting that these cellular changes could influence successful implantation.

Metoclopramide-induced hyperprolactinaemia caused marked decline in pinopodes and pregnancy rates in mice

BACKGROUND

The impact of hyperprolactinaemia on endometrial function, along with embryo implantation, has been the subject of discussion. This article examines whether experimental hyperprolactinaemia can affect mouse ovarian function, endometrial pinopodes and embryo implantation.

METHODS

For pinopode analysis, 60 female mice were randomly divided into two groups: control (vehicle) and experimental [metoclopramide (MCP) 200 microg per day]. Injections were given subcutaneously for 50 days, and then, normally cycling females were housed with male mice for copulation during proestrus. The animals were killed on the fifth day following coitus when the antimesometrium portions of the uterine horns were removed for endometrial analysis. Blood was collected for prolactin (PRL) determination. In the second experiment, 60 female mice were used to evaluate the ovarian function by measuring estrogen and progesterone levels and counting luteal bodies and oocytes in the oviduct and uterus during estrus.

RESULTS

The highest pregnancy rates and the largest population of pinopodes were both found in the vehicle group (P<0.01). Estrogen and progesterone levels in MCP-treated mice were lower than those in control mice (P<0.05). Also, the number of implantations was significantly lower in the MCP-treated group compared with the vehicle group after embryo transfer (P<0.001).

CONCLUSION

PRL seems to have suppressive effects on ovarian function and the number of pinopodes; conceivably, hyperprolactinaemia has a negative effect on mouse embryo implantation.

Is there a role for preparatory cycle in ovum donation recipients?

PURPOSE OF REVIEW

In ovum donation cycles, the role of preparatory cycles to ensure proper endometrial development in the recipient remains controversial. As evidenced in the literature, endometrial receptivity is critical in conception. Therefore, endometrial preparation with exogenous hormones in addition to synchronization of the recipient and donor are essential in achieving a successful outcome.

RECENT FINDINGS

There are very limited data specifically examining the benefit of recipients undergoing preparatory cycles prior to their actual egg donation cycle. One study concluded that trial hormone replacement treatment cycles with endometrial biopsies may be useful in older reproductive-age women but not in younger women. Another study showed no difference in pregnancy rates between those who did and did not undergo preparatory cycles.

SUMMARY

Since one of the integral elements of preparatory cycles is determining endometrial dating, with relatively conflicting data, these mock cycles may not be as beneficial as expected. Therefore, for those who routinely use preparatory cycles, the potential risks, benefits, and costs of these cycles, increased hormonal exposure, the relatively invasive nature of the procedure, and time prior to performing them must be considered.

Identification of a signaling pathway involving progesterone receptor, calcitonin, and tissue tranglutaminase in Ishikawa endometrial cells

Previous studies indicated that calcitonin (CT), a peptide hormone involved in calcium (Ca(2+)) homeostasis, is transiently induced by steroid hormone progesterone (P) in the uterine epithelia of the rat and human within the window of implantation. Targeted disruption of uterine CT expression markedly impaired implantation in the rat. To gain insight into the molecular events underlying CT action in the endometrium, we performed gene expression profiling in response to CT in a human endometrial adenocarcinoma cell line, Ishikawa. We identified the gene encoding tissue tranglutaminase type II (tTGase), which participates in Ca(2+)-dependent, protein-protein cross-linking, as a downstream target of CT. Interestingly, addition of P alone to Ishikawa cells led to a marked induction in the level of both CT and tTGase, indicating the existence of a pathway involving P receptors, CT, and tTGase in these cells. Other studies revealed that regulation of the tTGase gene by CT occurs via its cell surface receptor and uses both cAMP and Ca(2+) signaling pathways. We also noted that tTGase protein is expressed in human endometrium during the P-dominated midsecretory phase of the menstrual cycle, and it is localized at the basal membrane of glandular epithelium and the surrounding stroma. The spatio-temporal expression of tTGase in human endometrium during the cycle closely overlapped with that of CT. In summary, we have uncovered a novel steroid-regulated signaling cascade in which P induces CT, which, in turn, induces tTGase and potentially plays a critical role in the human endometrium during implantation.

Endometrium estradiol receptors type I and type II during early pregnancy of rat

By centrifugation in a sucrose density gradient we studied the citosol 17beta-estradiol binding sites of blastocyst receptive and non-receptive endometrial zones, as well as uterine horn endometrium whose ovary was extirpated three weeks before pregnancy. The cytosol was prelabelled with [3H]-17beta-estradiol 2 and 25 nM. In this work two incubation temperatures were studied. On the other hand, at 4 degrees C unoccupied receptors were identified as different from the classic receptor 8S type I. At the same time, we found that 25 degrees C is the optimal temperature for the assay of total receptors to achieve complete exchange of [3H]-17beta-estradiol by 17beta-estradiol in the binding sites. In these conditions, the major component was the 4S type II receptor, mainly in the endometrium from ovariectomized uteri. Furthermore, 17beta-estradiol content was determined in the total homogenized by radioimmunoassay and the results were: 1.42+/-0.16, 1.22+/-0.15 and 1.75+/-0.27 pmol/g wet tissue for receptive, non-receptive and ovariectomized uteri, respectively.

Interleukin-11, IL-11 receptorα and leukemia inhibitory factor are dysregulated in endometrium of infertile women with endometriosis during the implantation window

Interleukin (IL)-11 is essential for embryo implantation in the mouse and evidence suggests it has a role in implantation in humans. This study has evaluated immunoreactive IL-11, IL-11 receptor (R) alpha and leukemia inhibitory factor (LIF) in endometrium of infertile women with endometriosis (I/E) and normal fertile women (controls) during the implantation window. Endometrial biopsies from I/E (N = 7) were timed from the LH surge and were post-ovulatory days (POD) 5-10. Control biopsies (N = 8) from women were between days 19 and 24 of the menstrual cycle. Staining intensity of IL-11, IL-11Ralpha and LIF evaluated using semi-quantitative immunohistochemistry scores. Immunoreactive IL-11, IL-11Ralpha and LIF were present predominantly in glandular epithelium, while luminal epithelium showed patchy staining. All controls stained positively for IL-11, IL-11Ralpha and LIF in glandular epithelium. IL-11 and IL-11Ralpha staining was absent from glandular epithelium in cohorts of I/E. LIF staining intensity in glandular epithelium was significantly lower in I/E compared to controls. The results suggest that reduced endometrial IL-11 and/or LIF may contribute to infertility in some endometriotic women.

Cytokine expression in the endometrium of women with implantation failure and recurrent miscarriage

One potential cause of reproductive failure such as infertility and recurrent miscarriage may be an endometrial defect. Numerous studies in mice have suggested the importance of various different cytokines in successful pregnancy outcome. This article reviews the literature available on the role of T helper cytokines and IL-1, IL-11, LIF, IL-12 and IL-18 in infertility and recurrent miscarriage, with particular emphasis on the role that endometrial cytokines may play. Although there are numerous studies on cytokines in recurrent miscarriage, much less has been reported on their role in infertility with or without failure after IVF. There is also considerable variation in the results obtained from various different studies, which may be due to different populations studied, the different timing of the sample collection, and whether the cytokines were measured in whole tissue or a specific cell population. The presence of complicated networks of cytokines and their overlapping biological activities means that alteration of one cytokine is likely to affect others and this also makes the study of their role in implantation failure very difficult. There is an urgent need to re-examine the role played by various cytokines in reproductive failure through carefully planned and vigorously designed studies and to compare the different types of reproductive failure.

The role of aromatase inhibitors in ameliorating deleterious effects of ovarian stimulation on outcome of infertility treatment

Clinical utilization of ovulation stimulation to facilitate the ability of a couple to conceive has not only provided a valuable therapeutic approach, but has also yielded extensive information on the physiology of ovarian follicular recruitment, endometrial receptivity and early embryo competency. One of the consequences of the use of fertility enhancing agents for ovarian stimulation has been the creation of a hyperestrogenic state, which may influence each of these parameters. Use of aromatase inhibitors reduces hyperestrogenism inevitably attained during ovarian stimulation. In addition, the adjunct use of aromatase inhibitors during ovarian stimulation reduces amount of gonadotropins required for optimum stimulation. The unique approach of reducing hyperestrogenism, as well as lowering amount of gonadotropins without affecting the number of mature ovarian follicles is an exciting strategy that could result in improvement in the treatment outcome by ameliorating the deleterious effects of the ovarian stimulation on follicular development, endometrial receptivity, as well as oocyte and embryo quality.

Molecular and Pharmacological Properties of a Potent and Selective Novel Nonsteroidal Progesterone Receptor Agonist Tanaproget

Progesterone receptor (PR) agonists have several important applications in women's health, such as in oral contraception and post-menopausal hormone therapy. Currently, all PR agonists used clinically are steroids. Because of their interactions with other steroid receptors, steroid-metabolizing enzymes, or other steroid-signaling pathways, these drugs can pose significant side effects in some women. Efforts to discover novel nonsteroidal PR agonists with improved biological properties led to the discovery of tanaproget (TNPR). TNPR binds to the PR from various species with a higher relative affinity than reference steroidal progestins. In T47D cells, TNPR induces alkaline phosphatase activity with an EC(50) value of 0.1 nm, comparable with potent steroidal progestins such as medroxyprogesterone acetate (MPA) and trimegestone (TMG), albeit with a reduced efficacy ( approximately 60%). In a mammalian two-hybrid assay to measure PR agonist-induced interaction between steroid receptor co-activator-1 and PR, TNPR showed similar potency (EC(50) value of 0.02 nm) and efficacy to MPA and TMG. Importantly, in key animal models such as the rat ovulation inhibition assay, TNPR demonstrates full efficacy and an enhanced progestational potency (30-fold) when compared with MPA and TMG. Furthermore, TNPR has relatively weak interactions with other steroid receptors and binding proteins and little effect on cytochrome P450 metabolic pathways. Finally, the three-dimensional crystal structure of the PR ligand binding domain with TNPR has been delineated to demonstrate how this nonsteroidal ligand achieves its high binding affinity. Therefore, TNPR is a structurally novel and very selective PR agonist with an improved preclinical pharmacological profile.

Differential expression and activation of Stat3 during mouse embryo implantation and decidualization

Signal transducer and activator of transcription (STATs) can be activated by many cytokines and growth factors. Stat3, a member of STAT family, is essential for embryonic development. Stat3 is specifically activated during mouse embryo implantation. This study was to investigate the expression, activation, and regulation of Stat3 in mouse uterus during early pregnancy, pseudopregnancy, delayed implantation, artificial decidualization, and hormonal treatments using in situ hybridization and immunohistochemistry. There was a strong level of Stat3 phosphorylation in the luminal epithelium only at the midnight of day 4 pregnancy, which coincides with attachment reaction between the blastocyst and luminal epithelium. However, there was no detectable Stat3 phosphorylation at the corresponding period during pseudopregnancy. On day 5 of pregnancy, Stat3 phosphorylation was strongly observed in the luminal epithelium and the stroma surrounding the implanting blastocyst at implantation sites, but not at the inter-implantation sites. Stat3 phosphorylation was also not detected on day 5 of pseudopregnancy. Stat3 phosphorylation was at a high level in the decidual cells on days 6-8 of pregnancy. Under artificial decidualization, Stat3 was also phosphorylated in the decidual cells. In the ovariectomized mice, there was no Stat3 expression and activation in the uterus. Progesterone had no obvious effects. However, Stat3 mRNA expression and phosphorylation were significantly stimulated by estrogen treatment. Our data suggest that Stat3 phosphorylation may be important for mouse embryo implantation and decidualization, and may also be regulated by maternal estrogen.

Uterine receptivity and the plasma membrane transformation

This review begins with a brief commentary on the diversity of placentation mechanisms, and then goes on to examine the extensive alterations which occur in the plasma membrane of uterine epithelial cells during early pregnancy across species. Ultrastructural, biochemical and more general morphological data reveal that strikingly common phenomena occur in this plasma membrane during early pregnancy despite the diversity of placental types--from epitheliochorial to hemochorial, which ultimately form in different species. To encapsulate the concept that common morphological and molecular alterations occur across species, that they are found basolaterally as well as apically, and that moreover they are an ongoing process during much of early pregnancy, not just an event at the time attachment, the term 'plasma membrane transformation' is suggested which also emphasises that alterations in this plasma membrane during early pregnancy are key to uterine receptivity.

Progesterone treatment and the progress of early pregnancy reduce desmoglein 1&2 staining along the lateral plasma membrane in rat uterine epithelial cells

Uterine epithelium undergoes dramatic changes during early pregnancy in preparation for implantation. We have studied distribution patterns of the desmosomal marker, desmoglein 1&2, in rat uterine epithelial cells during early pregnancy as well as in hormonally stimulated ovariectomised animals. On day 1 of pregnancy as well as in oestradiol treated rats, desmoglein 1&2 staining was localized along the entire length of the lateral plasma membrane. By day 3 and on subsequent days of pregnancy as well as in ovariectomised animals treated with progesterone alone or in combination with oestradiol, desmoglein 1&2 staining was concentrated at the apical portion of the lateral plasma membrane. We suggest that the reorganisation of these desmosomal cadherins is an important component of uterine epithelial receptivity and this relocation is under the control of the ovarian hormone progesterone.

Effect of estradiol on mouse uterine epithelial cell transepithelial resistance (TER)

PROBLEM

The effects of estradiol on epithelial cell function in the uterus may either be direct or indirect through the paracrine effects of underlying stromal cells. The aim of this study was to test whether estradiol-17beta (E(2)) acts directly to regulate uterine epithelial cell monolayer integrity.

METHODS OF STUDY

Mouse uterine epithelial cells were isolated and grown on cell culture inserts to form confluent, polarized monolayers, as indicated by the development of high transepithelial resistance (TER).

RESULTS

When polarized epithelial cells were treated with E(2), TER was significantly decreased within 24 hr of exposure. Epithelial cells remained hormonally responsive in culture for at least 10 days. In contrast to estradiol, incubation with progesterone, cortisol, aldosterone, and DHT had no effect on uterine epithelial cell TER. The ability of E(2) to decrease TER was inhibited following co-incubation with ICI 182,780, a pure estrogen receptor antagonist. To further investigate the mechanism involved in estradiol-induced decreases in TER, we tested the effect of TAPI-0, an inhibitor of matrix metalloproteinases. Our findings indicate that TAPI-0 reversed the inhibitory effect of E(2) on TER.

CONCLUSIONS

These studies demonstrate that epithelial monolayer integrity is directly influenced by E(2) and ER mediated. Further, it suggests that the mechanism through which estradiol decreases TER is mediated by matrix metalloproteinases.

Urinary gonadotrophins but not recombinant gonadotrophins reduce expression of VEGF120 and its receptors flt-1 and flk-1 in the mouse uterus during the peri-implantation period

BACKGROUND

Ovarian stimulation in humans might affect the perinatal outcome and be considered as a stress factor in the implantation process. In this study we compared the effects of recombinant and urinary gonadotrophins during the mouse peri-implantation period.

METHODS

Adult female CD1 mice were treated as follows (a) urinary hFSH and urinary hCG, (b) recombinant hFSH and recombinant hLH and (c) saline. The effects of the gonadotrophins on the expression of vascular endothelial growth factor120 (VEG120) and its receptors and the corticotrophin releasing hormone (CRH) system during the peri-implantation period were studied. The specific effects of the different gonadotrophins on the onset of implantation were also studied.

RESULTS

Urinary gonadotrophin treatment caused lower levels of VEGF120, flt-1 and flk-1 mRNA levels, reduced the size of the embryo implantation site, delayed implantation and prolonged the gestational period. Both urinary hFSH and urinary hCG contributed to the adverse effects. Levels of CRH and CRHR1 expression were not influenced. Recombinant gonadotrophin treatment did not alter any of the parameters studied.

CONCLUSIONS

Our results show that the VEGF system of the mouse uterus during the peri-implantation period is adversely affected by urinary gonadotrophins but not by recombinant gonadotrophins. The CRH system was not affected by the two types of gonadotrophins.

Differential effects of estrogens and progestins on the anticoagulant tissue factor pathway inhibitor in the rat

Oral contraceptives (OC) and postmenopausal hormone therapy (HT) modulate plasma levels of proteins that regulate blood coagulation. It remains unclear whether the progestin component contributes to these changes. The present study was designed to determine whether progestins modulate two essential plasma anticoagulants, antithrombin (AT) and tissue factor pathway inhibitor (TFPI), in an animal model. Ovariectomized rats were treated orally with three progestins, norethindrone acetate (NETA), trimegestone (TMG), or drospirenone (DSP), either alone or combined with 17alpha-ethyinylestradiol (EE). Plasma AT levels were unchanged. However, TFPI activity was reduced by EE alone (10-100 microg/kg/day) in a dose-dependent manner; NETA (3 or 10 mg/kg/day) reduced TFPI by approximately 40 or approximately 80%, respectively, while TMG and DSP had no effect. NETA and EE effects were blocked by co-administration of ICI-182,780, an estrogen receptor antagonist, suggesting that both responses were likely estrogen receptor-mediated. Reduced TFPI after NETA or EE treatment was not accompanied by changes in TFPI mRNA levels in tissues that express TFPI, but there was a positive correlation between plasma TFPI and total cholesterol. Sex hormone effects on TFPI in this model and as reported in women may help to shift the coagulation balance to a more prothrombotic state. Progestins such as TMG and DSP that lack estrogenic activity could potentially have an improved clinical profile.

Increased endometrial thickness is associated with improved treatment outcome for selected patients undergoing in vitro fertilization–embryo transfer

OBJECTIVE

To examine possible relationships between endometrial thickness and treatment outcome after IVF and embryo transfer, and to explore the role of potential confounding factors that may influence such relationships.

DESIGN

Retrospective study.

SETTING

A university-affiliated clinical IVF center.

PATIENT(S)

Patients undergoing IVF-embryo transfer with their own oocytes.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Endometrial thickness was determined on the day of hCG administration, 2 days before oocyte retrieval. Clinical pregnancy was confirmed by ultrasound observation of fetal heart activity.

RESULT(S)

The study analyzed 897 IVF-embryo transfer cycles. Treatment outcome (clinical pregnancy) after IVF-embryo transfer was positively associated with increased endometrial thickness and peak E(2) concentrations in serum, and negatively associated with advanced age. Endometrial thickness was dependent on peak E(2) concentrations in serum, but was independent of patient age or duration of ovarian stimulation. Thin endometrium reduced PRs in relatively young patients (<38 years old), in patients who required more than 10 days of gonadotropin stimulation, or in patients whose embryo transfers consisted of poor quality embryos.

CONCLUSION(S)

Increased endometrial thickness was associated with improved treatment outcome, but this association was dependent on patient age, duration of ovarian stimulation, and embryo quality.

Localisation of sulphated glycoconjugates during hyaline layer formation in rat molars by ultrastructural cytochemistry

In order to study the presence of sulphated glycoconjugates in the first mineralised layer juxtaposed to the root dentine (the hyaline layer), we have examined the early stages of molar root development by ultrastructural cytochemistry using Cuprolinic Blue combined with enzymatic pretreatment. Upper molars from 10 to 13 day-old Wistar rats were fixed in 2.5% glutaraldehyde containing 0.05% Cuprolinic Blue in 25 mM sodium acetate, pH 5.6, containing 0.3 M MgCl2. Some specimens were previously treated with heparitinase or chondroitinase ABC. Our results showed sulphated glycoconjugate--Cuprolinic Blue complexes that appeared as electron opaque ribbon-like deposits in the unmineralised hyaline layer. Few complexes were detected adjacent to the dentinal surface. These complexes were removed by heparitinase, indicating that they contained heparan sulphate chains. In contrast, the complexes found in unmineralised cementum and root dentine were removed by chondroitinase, indicating that they contained chondroitin or dermatan sulphate chains. The complexes decreased after the initiation of mineralisation of hyaline layer and root dentine and they were no longer present in stages of fully mineralisation. We conclude that the hyaline layer only contains sulphated glycoconjugates prior to mineralisation, and that they may play a role in the regulation of the mineralisation.

Developmental diethylstilbestrol exposure alters genetic pathways of uterine cytodifferentiation

The formation of a simple columnar epithelium in the uterus is essential for implantation. Perturbation of this developmental process by exogenous estrogen, such as diethylstilbestrol (DES), results in uterine metaplasia that contributes to infertility. The cellular and molecular mechanism underlying this transformation event is not well understood. Here we use a combination of global gene expression analysis and a knockout mouse model to delineate genetic pathways affected by DES. Global gene expression profiling experiment revealed that neonatal DES treatment alters uterine cell fate, particularly in the luminal epithelium by inducing abnormal differentiation, characterized by the induction of stratified epithelial markers including members of the small proline-rich protein family and epidermal keratins. We show that Msx2, a homeodomain transcription factor, functions downstream of DES and is required for the proper expression of several genes in the uterine epithelium including Wnt7a, PLAP, and K2.16. Finally, Msx2-/- uteri were found to exhibit abnormal water trafficking upon DES exposure, demonstrating the importance of Msx2 in tissue responsiveness to estrogen exposure. Together, these results indicate that developmental exposure to DES can perturb normal uterine development by affecting genetic pathways governing uterine differentiation.

Regulation of matrix metalloproteinases (MMPS) and their inhibitors (TIMPS) during mouse peri-implantation: role of nitric oxide

Nitric oxide (NO) is believed to play pivotal roles in embryo implantation. The purpose of this study was to investigate the effect of NO on matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs), as well as the mechanism of NO during mouse implantation. Nitric oxide synthase (NOS) inhibitor, L-NAME was administered with or without sodium nitroprusside (SNP), NO donor, into one uterine horn on day 3 of pregnancy, and the contralateral uterine horn served as the control. We collected the uteri on days 5, 6, and 7 of pregnancy and examined the mRNA expression of MMP-2, -9, and TIMP-1, -2, -3, as well as the activities of MMP-2 and -9 by using in situ hybridization and gelatin zymography, respectively. The results showed that, compared with the control, the expression of MMP-2 and -9 mRNAs was decreased in L-NAME-treated uteri during peri-implantation. Treatment of mice with L-NAME had slight effect on the expression of TIMP-1 mRNA on day 5 of pregnancy, and no effect on TIMP-2 mRNA expression during peri-implantation. However, the expression of TIMP-3 mRNA was increased. The gelatin zymography results indicated that the activity of MMP-9 was decreased during peri-implantation, but the activity of MMP-2 did not change significantly in these time points examined. The L-NAME-mediated effect on MMPs and TIMPs were significantly reversed when SNP was co-administered with L-NAME. These data suggest that inhibition of NO production regulates the gene expression of MMP-2, -9, and TIMP-3, together with the activity of MMP-9 during peri-implantation, which may have serious consequence on embryo implantation.

Histological dating of timed endometrial biopsy tissue is not related to fertility status

OBJECTIVE

To assess the ability of histological dating to discriminate between women of fertile and infertile couples. The utility of histological dating of endometrium in the evaluation of infertile couples is uncertain.

DESIGN

Prospective multicenter study, with subjects randomly assigned to biopsy timing. Criterion standard for infertility was 12 months of unprotected, regular intercourse without conception and for fertility at least one live birth within 2 years.

SETTING

University-based infertility practices.

PATIENT(S)

Volunteer subjects (847) recruited at 12 clinical sites participating in the National Institutes of Health-funded Reproductive Medicine Network. Inclusion criteria included ages 20-39 years, regular menstrual cycles, and no hormonal treatment or contraceptive use for 1 month before the study. Fertile controls were excluded if they had a history of infertility, recurrent pregnancy loss, or recent breastfeeding.

INTERVENTION(S)

Subjects underwent daily urinary LH testing. After detection of the LH surge, subjects were randomized to biopsy in the mid (days 21-22) or the late (days 26-27) luteal phase. Pathologists at each site estimated the cycle day based on standard criteria. For the primary analysis, an out-of-phase biopsy was defined as a greater than 2-day delay in the histological maturation of the endometrium.

MAIN OUTCOME MEASURE(S)

The proportion of out-of-phase biopsies in fertile and infertile women was compared using logistic regression models with age at randomization as a covariate. Comparisons were also made between fertile vs. infertile at the midluteal or late luteal phase time points.

RESULT(S)

Biopsies were evaluated (301 mid and 318 late; N = 619). Out-of-phase biopsy results poorly discriminated between women from fertile and infertile couples in either the midluteal (fertile: 49.4%, infertile: 43.2%) or late luteal phase (fertile: 35.3%, infertile 23.0%). Results did not substantially differ using alternative definitions of "out-of-phase" or standardized cycle day.

CONCLUSION(S)

Histological dating of the endometrium does not discriminate between women of fertile and infertile couples and should not be used in the routine evaluation of infertility.

Role of energy metabolism in the pregnancy interceptive action of Ferula assafoetida and Melia azedarach extracts in rat

Ethanolic extract of Ferula assafoetida and chloroform fraction of Melia azedarach, both devoid of estrogenic activity, were examined for their pregnancy interceptive property. Treatment of rats from days 1 to 7 of pregnancy with either of the plant extracts resulted in pregnancy failure in about 65-85% of the animals. The possible role of energy metabolism in the antifertility action was investigated by measuring changes in activities of the key enzymes of carbohydrate metabolism in uterus on day 7 of pregnancy. It was observed that on the day 7 of pregnancy, one key enzyme of glycolytic pathway (phosphofructokinase) was significantly reduced in the uteri of treated rats as compared to controls. Hexosemonophosphate pathway also appeared to be sensitive to treatment with the plant extracts and showed an inhibitory effect on the enzyme activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Oxidative energy metabolism through tricarboxylic acid cycle, which is considered to be the main source of energy to the uterus at this stage, was maximally affected by the treatment with several enzymes showing significant inhibition. The two plant materials appeared to interrupt the latter metabolic pathway more significantly. It is thus concluded that plants lacking phytoestrogens may intercept pregnancy by their ability to disrupt energy metabolism in rat uterus during implantation, especially the oxidative pathway.

Expression of glucosamine trisaccharides on the rat uterine surface is altered by clomiphene citrate. III. Relationship with implantation regimes and pregnancy

The present study further elucidates the complex effects of a commonly-prescribed fertility drug upon a target organ in an animal model. In the human condition, its effects are rarely observed without the influence of endogenous ovarian hormones. The aim of the study was to investigate how the administration of a single dose of clomiphene citrate (CC) given prior to an implantation-priming sequence of ovarian hormones would affect the expression of surface oligosaccharides and membrane architecture of uterine epithelium. Ovariectomized rats were given a single dose of either 0.25 mg or 1.25 mg of CC prior to a hormone-priming regime of progesterone (P4) for 3 days with a single additional administration of oestradiol 17beta (E2) on day 3. Animals were killed 24 h after final treatment. Uterine tissue was labelled with the lectin Phytolacca americana conjugated with avidin, subsequently labelled with biotinylated ferritin and prepared for transmission electron microscopy. Results indicate that CC, when administered prior to the implantation hormone-priming regime, is able to act as a super oestrogen and upregulates expression of oligosaccharides on the plasma membrane surface and increases the density and length of microvilli on the surface of the cells when compared with other treatment regimes. Understanding of the effects of CC at the uterine level at the time of implantation enables manipulation of uterine receptivity to control fertility and to improve the outcome of assisted reproductive procedures.

Molecular cues to implantation

Successful implantation is the result of reciprocal interactions between the implantation-competent blastocyst and receptive uterus. Although various cellular aspects and molecular pathways of this dialogue have been identified, a comprehensive understanding of the implantation process is still missing. The receptive state of the uterus, which lasts for a limited period, is defined as the time when the uterine environment is conducive to blastocyst acceptance and implantation. A better understanding of the molecular signals that regulate uterine receptivity and implantation competency of the blastocyst is of clinical relevance because unraveling the nature of these signals may lead to strategies to correct implantation failure and improve pregnancy rates. Gene expression studies and genetically engineered mouse models have provided valuable clues to the implantation process with respect to specific growth factors, cytokines, lipid mediators, adhesion molecules, and transcription factors. However, a staggering amount of information from microarray experiments is also being generated at a rapid pace. If properly annotated and explored, this information will expand our knowledge regarding yet-to-be-identified unique, complementary, and/or redundant molecular pathways in implantation. It is hoped that the forthcoming information will generate new ideas and concepts for a process that is essential for maintaining procreation and solving major reproductive health issues in women.

Two pathways of progesterone action in the human endometrium: implications for implantation and contraception

The endometrium is the site of implantation and pregnancy. Preparation for this important biological event relies primarily on progesterone, which takes the estrogen-primed endometrium toward a state of receptivity. As a steroid target tissue, the endometrium is also prone to abnormal growth sometimes leading to the development of hyperplasia or cancer. It is the balance between estrogen and progesterone that maintains the endometrium in a state of health and provides the synchronous timing necessary for a successful implantation to occur. In our efforts to understand the role of progesterone in the endometrium we have focused on the use of specific protein biomarkers. Based on examination of a cell adhesion molecule, the alphavbeta3 integrin, and its ligand, osteopontin, we have come to conclude that progesterone action can be direct or indirect. Progesterone acting on the stromal compartment provides paracrine mediators that influence epithelial gene expression. Conversely, acting directly, progesterone may primarily stimulate gene expression of the endometrial epithelium. The complexity of the system is extended since progesterone itself works through two different receptor isoforms. Regulated differential expression of PR-A versus PR-B also appears to fine tune the effect of progesterone on specific genes. Progesterone may also inhibit specific genes that undergo cyclic variation during the menstrual cycle. Together, using in vitro models we have shown that progesterone dynamically regulates gene expression in the endometrium and that imbalances between estrogen and progesterone may have far reaching consequences on normal cycle fecundity and on the balance between health and disease in this hormone-target tissue.

Asoprisnil (J867): a selective progesterone receptor modulator for gynecological therapy

Asoprisnil is a novel selective steroid receptor modulator that shows unique pharmacodynamic effects in animal models and humans. Asoprisnil, its major metabolite J912, and structurally related compounds represent a new class of progesterone receptor (PR) ligands that exhibit partial agonist and antagonist activities in vivo. Asoprisnil demonstrates a high degree of receptor and tissue selectivity, with high-binding affinity for PR, moderate affinity for glucocorticoid receptor (GR), low affinity for androgen receptor (AR), and no binding affinity for estrogen or mineralocorticoid receptors. In the rabbit endometrium, both asoprisnil and J912 induce partial agonist and antagonist effects. Asoprisnil induces mucification of the guinea pig vagina and has pronounced anti-uterotrophic effects in normal and ovariectomized guinea pigs. Unlike antiprogestins, asoprisnil shows only marginal labor-inducing activity during mid-pregnancy and is completely ineffective in inducing preterm parturition in the guinea pig. Asoprisnil exhibits only marginal antiglucocorticoid activity in transactivation in vitro assays and animal models. In male rats, asoprisnil showed weak androgenic and anti-androgenic properties. In toxicological studies in female cynomolgus monkeys, asoprisnil treatment abolished menstrual cyclicity and endometrial atrophy. Early clinical studies of asoprisnil in normal volunteers demonstrated a dose-dependent suppression of menstruation irrespective of the effects on ovulation, with no change in basal estrogen concentrations and no antiglucocorticoid effects. Unlike progestins, asoprisnil does not induce breakthrough bleeding. With favorable safety and tolerability profiles thus far, asoprisnil appears promising as a novel treatment of gynecological disorders, such as uterine fibroids and endometriosis.

Viviparous lizard,Eulamprus tympanum, shows changes in the uterine surface epithelium during early pregnancy that are similar to the plasma membrane transformation of mammals

The "plasma membrane transformation" describes a series of ultrastructural, biochemical, and morphological changes that occur in the uterus of many mammals at the time of blastocyst attachment. These changes, regardless of placental type or length of gestation, include alterations to microvillar length and density and the presence or absence of pinopods or uterodomes. Scanning electron microscopy (SEM) was used to 1) document the topographical ultrastructure of the uterus of Eulamprus tympanum, an eastern Australian viviparous skink with a simple chorioallantoic placenta, for the first time; and 2) determine whether changes identified as "plasma membrane transformation" in mammals occur in E. tympanum. Tissues collected over three seasons from nonreproductive subadult females, preovulatory, postovulatory, and early to mid-gestational females were examined. At low magnification the uterine epithelium of subadults displays a distinctive pattern of tissue folding that includes rectangular areas of tissue delineated by deep lateral and transverse folds. At higher magnification, the uterine epithelium surface is composed of two dominant cell types, i.e., those covered by microvilli and ciliated cells. The folding pattern observed in subadults is less evident in vitellogenic females and the cell surfaces appear highly secretory, with bulging cell apices. Tissue from postovulatory lizards has no distinctive folding pattern and cell surfaces are frequently smooth and lack microvilli. Uterine egg chambers lack ciliated cells at the embryonic pole, but display abundant secretory droplets. Thus, the uterus of E. tympanum undergoes a plasma membrane transformation. The scope of this transformation is not fully understood but may be related to the complexity of placental structure and the development of the embryo/fetus at parturition.

The matrix metalloproteinase system: changes, regulation, and impact throughout the ovarian and uterine reproductive cycle

The ovary and uterus undergo extensive tissue remodeling throughout each reproductive cycle. This remodeling of the extracellular environment is dependent upon the cyclic hormonal changes associated with each estrous or menstrual cycle. In the ovary, tissue remodeling is requisite for growth and expansion of the follicle, breakdown of the follicular wall during the ovulatory process, transformation of the postovulatory follicle into the corpus luteum, as well as the structural dissolution of the corpus luteum during luteal regression. In the uterus, there is extraordinary turnover of the endometrial connective tissue matrix during each menstrual cycle. This turnover encompasses the complete breakdown and loss of this layer, followed by its subsequent regrowth. With implantation, extensive remodeling of the uterus occurs to support placentation. These dynamic changes in the ovarian and uterine extracellular architecture are regulated, in part, by the matrix metalloproteinase (MMP) system. The MMP system acts to control connective tissue remodeling processes throughout the body and is comprised of both a proteolytic component, the MMPs, and a regulatory component, the associated tissue inhibitors of metalloproteinases. The current review will highlight the key features of the MMPs and tissue inhibitors of metalloproteinases, focus on the changes and regulation of the MMP system that take place throughout the estrous and menstrual cycles, and address the impact of the dynamic tissue remodeling processes on ovarian and uterine physiology.

Relationship between peak serum estradiol levels and treatment outcome in in vitro fertilization cycles after embryo transfer on day 3 or day 5

OBJECTIVE

To examine the relationships between peak serum estradiol (E(2)) levels and treatment outcome in in vitro fertilization (IVF) cycles after embryo transfer (ET) on day 3 or day 5.

DESIGN

Retrospective analysis of 697 IVF-ET cycles between January 1999 and December 2001.

SETTING

A university-affiliated assisted reproduction program.

PATIENT(S)

Infertile patients undergoing IVF-ET cycles.

INTERVENTION(S)

Peak E(2) concentration in serum was determined on the day of human chorionic gonadotropin (hCG) administration. The IVF-generated embryos were cultured for 2 days until transfer on day 3. If more than four 8-cell embryos were present on day 3, embryo culture was continued until day 5 for blastocyst transfer.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy rates.

RESULT(S)

High peak E(2) levels did not adversely affect treatment outcome. After the cycles were divided according to the day of ET, high peak E(2) levels were associated with improved pregnancy rates after ET on day 5 but not on day 3.

CONCLUSION(S)

Increasing peak E(2) levels in IVF cycles are associated with improved pregnancy rates after ET on day 5.

Aquaporin water channel genes are differentially expressed and regulated by ovarian steroids during the periimplantation period in the mouse

The periimplantation period is marked by edematous changes in the uterus. In the mouse, increased uterine vascular permeability occurs in response to estrogen and certain vasoactive mediators, but the mechanisms that regulate fluid transport during implantation are not fully understood. Aquaporins (AQPs) are a family of membrane channel proteins that facilitate bulk water transport. To assess their role in implantation, we examined the expression of AQPs 0-9 in the mouse uterus on d 1-8 of pregnancy. Our results show distinct uterine expression patterns for AQP1, AQP4, and AQP5. AQP1 is localized to the inner circular myometrium throughout the periimplantation period. AQP4 is highly expressed in the luminal epithelium on d 1 of pregnancy but barely detectable at the time of implantation. AQP5 is expressed at low levels in the glandular epithelium during early pregnancy but is markedly increased on d 5. By immunohistochemistry, AQP5 is localized in the basolateral region of the uterine glands. Treatment of adult ovariectomized mice with replacement steroids demonstrates an estrogen-induced shift in AQP1 signals from the myometrium to the uterine stromal vasculature, suggesting a role in uterine fluid imbibition. In contrast, AQP5 is induced only in estrogen-treated, progesterone-primed uteri. We also observed expression of AQP8 in the inner-cell mass and AQP9 in the mural trophectoderm of the implanting blastocyst. Collectively, these results suggest that members of the AQP family are involved in embryo and uterine fluid homeostasis during implantation.

A role for alphavbeta3 integrin during implantation in the rabbit model

The study of implantation has been facilitated by the identification of specific biomarkers that are associated with uterine receptivity. The alpha(v)beta(3) integrin is a cell surface adhesion receptor, whose expression has been shown to be elevated in the endometrium at the time of implantation in both humans and other mammalian species; however, the distribution of alpha(v)beta(3) in the rabbit model is unknown. The rabbit has been shown to be an excellent model for the study of implantation. As an obligate ovulator, the timing of pregnancy can be precisely established, and embryonic attachment occurs through specialized trophoblast-endometrial structures known as trophoblastic knobs. In the present study, the expression of alpha(v)beta(3) integrin subunit in the rabbit uterus was examined by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and in situ hybridization. Expression of the alpha(v)beta(3) integrin was examined in Day 6.5 embryos, flushed from pregnant does. Immunofluorescence demonstrated strong immunostaining on the rabbit blastocyst (Day 6.5). RT-PCR analyses showed higher levels of mRNA for beta(3) subunit at the implantation site, with reduced expression in nonimplantation sites and in nonpregnant adult and immature endometrium. Immunohistochemistry demonstrated little, if any, beta(3) immunoreactivity on the endometrial epithelium. In contrast, in situ hybridization showed expression of the beta(3) integrin subunit mRNA in the uterine myometrium and on the trophoblast. To further determine the functional significance of alpha(v)beta(3) integrin expression during implantation, pregnant female rabbits that underwent ventral laparotomy on the morning of Day 6 received intrauterine injection of the following into the right uterine horn: 1) the monoclonal alpha(v)beta(3) neutralizing antibody (LM609), 2) arg-gly-asp (RGD) hexapeptides (GRGDSP), 3) non-RGD hexapeptides (GRGESP), and 4) IgG isotype matched control antibody. The left horn served as a control and received only saline injections. A significant reduction in the number of implantation sites was observed in the horns receiving anti-alpha(v)beta(3) antibody (P < 0.001) and the RGD peptides (P = 0.03). In the rabbit, the alpha(v)beta(3) integrin is present on the embryo and trophoblast and appears to be involved in early embryo-maternal interaction.

Muc4/sialomucin complex, the intramembrane ErbB2 ligand, in cancer and epithelia: to protect and to survive

The membrane mucin Muc4, also called sialomucin complex (SMC), is a heterodimeric complex of two subunits, ASGP-1 and ASGP-2, derived from a single gene. It is produced by multiple epithelia in both membrane and soluble forms and serves as a protective agent for the epithelia. The membrane form of Muc4 acts as a steric barrier to the apical cell surface of epithelial or tumor cells. An important example is the uterus of the rat, in which Muc4 expression is downregulated for blastocyst implantation. The soluble form facilitates the protection and lubrication of epithelia by mucous gels composed of gel-forming mucins, as in the airway, where Muc4 is proposed to participate in mucociliary transport as a constituent of the periciliary fluid. The soluble form is also found in body fluids, such as milk, tears, and saliva. The transmembrane subunit ASGP-2 acts as an intramembrane ligand and activator for the receptor tyrosine kinase ErbB2. Formation of this ligand-receptor complex is proposed to repress apopotosis in epithelial and cancer cells in which the ligand-receptor complex is formed, providing a second type of cell protective mechanism. Muc4 expression is regulated in epithelial tissues in a cell- and tissue-specific manner during epithelial differentiation. In stratified epithelia, it is predominantly in the most superficial, differentiated layers, often coincident with ErbB2. Dysregulation of Muc4 expression may contribute to cell and tissue dysfunction, such as the proposed contribution of Muc4 to mammary tumor progression. These observations clearly show that Muc4 has multiple roles in epithelia, which may provide insights into aberrant behaviors of these tissues and their derivative carcinomas.

Transcription of cholesterol side-chain cleavage cytochrome P450 in the placenta: activating protein-2 assumes the role of steroidogenic factor-1 by binding to an overlapping promoter element

Progesterone is essential to the sustenance of pregnancy in humans and other mammals. From the second trimester on, the human placenta is the sole origin of de novo synthesized steroid hormones. In mice, placentation at midgestation is accompanied by a temporal rise of steroid hormone synthesis commencing in the giant cells of the mouse trophoblast. In doing so, the giant trophoblasts, as any other steroidogenic cell, express high levels of the key steroidogenic enzyme, cholesterol side-chain cleavage cytochrome P450 (P450scc). Because steroidogenic factor 1 (SF-1), the transcription factor required for expression of P450scc in the adrenals and the gonads, is not expressed in the placenta, we hypothesized that placenta-specific nuclear factor(s) (PNF) assumes the role of SF-1 by binding to the same promoter region that harbors the SF-1 recognition site in the P450scc gene. To address this possibility, we used SCC1, a well conserved proximal region in the P450scc genes (-60/-32 in the rat gene) to purify PNF from human term placenta. Sequencing of the purified PNF revealed that it is the alpha isoform of the human activating protein-2 (AP-2alpha). Specific antibodies tested in EMSA confirmed that AP-2alpha is the predominant isoform that binds SCC1 in the human placenta, whereas AP-2gamma is the only mouse placental protein that binds this oligonucleotide. Functional studies showed that coexpression of the rat P450scc promoter (-378/+8 CAT) and AP-2 isoforms (alpha or gamma) in human embryonic kidney 293 cells results in a marked activation of chloramphenicol acetyltransferase (CAT) transcription that is dependent on an intact AP-2 motif, GCCTTGAGC. This motif conforms with consensus sequences previously determined for binding of the AP-2 alpha and gamma isoforms. Mutations of the AP-2 element ablated binding of AP-2 to SCC1, as well as severely diminished the promoter activity in primary mouse giant trophoblasts and human choriocarcinoma JAR cells. Collectively, these studies suggest that expression of placental P450scc is governed by AP-2 factors that bind to a cis-element that largely overlaps the sequence required for recognition of SF-1 in other steroidogenic tissues.

Deciphering the cross-talk of implantation: advances and challenges

Implantation involves a series of steps leading to an effective reciprocal signaling between the blastocyst and the uterus. Except for a restricted period when ovarian hormones induce a uterine receptive phase, the uterus is an unfavorable environment for blastocyst implantation. Because species-specific variations in implantation strategies exist, these differences preclude the formulation of a unifying theme for the molecular basis of this event. However, an increased understanding of mammalian implantation has been gained through the use of the mouse model. This review summarizes recognized signaling cascades and new research in mammalian implantation, based primarily on available genetic and molecular evidence from implantation studies in the mouse. Although the identification of new molecules associated with implantation in various species provides valuable insight, important questions remain regarding the common molecular mechanisms that govern this process. Understanding the mechanisms of implantation promises to help alleviate infertility, enhance fetal health, and improve contraceptive design. The success of any species depends on its reproductive efficiency. For sexual reproduction, an egg and sperm must overcome many obstacles to fuse and co-mingle their genetic material at fertilization. The zygote develops into a blastocyst with two cell lineages (the inner cell mass and the trophectoderm), migrates within the reproductive tract, and ultimately implants into a transiently permissive host tissue, the uterus. However, the molecular basis of the road map connecting the blastocyst with the endometrium across species is diverse (1) and not fully understood. Recent advances have identified numerous molecules involved in implantation (1-4), yet new discoveries have not yielded a unifying scheme for the mechanisms of implantation.

Gonadotrophin stimulation reduces VEGF(120) expression in the mouse uterus during the peri-implantation period

BACKGROUND

Ovarian stimulation by gonadotrophin treatment exerts negative effects on implantation and embryonic development. We investigated whether gonadotrophin treatment affects VEGF(120) mRNA expression during the peri-implantation period.

METHODS

Two groups of adult female CD1 mice were used: the hormone-treated group was injected i.p. with urinary human FSH (5 IU in 0.1 ml saline) and urinary HCG (5 IU in 0.1 ml saline). Spontaneously ovulating mice served as controls and received saline injections. The pregnant mice were killed on embryonic development (ED) days 0, 3, 4, 5 and 6 (day of vaginal plug detection is considered as ED0). The uteri with the implanted embryos were processed for in-situ hybridization for VEGF(120). A separate group of control and hormone-treated pregnant mice were allowed to give birth. Litter size, birthweight and length of gestational period were noted.

RESULTS

Gonadotrophin treatment decreased VEGF(120) mRNA levels, delayed implantation, reduced the size of the embryo implantation site on ED5 and ED6 and prolonged the gestational period.

CONCLUSIONS

Gonadotrophin treatment reduces VEGF(120) expression which may have serious consequences for normal embryonic development. The present data cannot establish whether this effect is a cause or consequence of delayed implantation.

Molecules in blastocyst implantation: uterine and embryonic perspectives

Synchronized development of the embryo to the active stage of the blastocyst, differentiation of the uterus to the receptive state, and a "cross talk" between the blastocyst and uterine luminal epithelium are essential to the process of implantation. In spite of considerable accumulation of information and the present state of the knowledge, our understanding of the definitive mechanisms that regulate these events remains elusive. Although there are species variations in the process of implantation, many basic similarities do exist among various species. This review focuses on specific aspects of the implantation process in mice with the hope that many of the findings will be relevant to the process in humans. To establish signaling mechanisms of embryo-uterine interactions during implantation, studies on both embryonic and uterine consequences are required to generate more meaningful information. Due to ethical restriction and experimental limitation, it is difficult to generate such information in humans. This review has attempted to provide a comprehensive, but not complete, narration of a number of embryonic and uterine factors that are involved in the process of implantation in autocrine, paracrine, and/or juxtacrine manners in mice at the physiological, cellular, molecular, and genetic levels.

Pinopode expression during human implantation

Implantation failure is considered the major impediment to successful in vitro fertilization pregnancy rate. Despite recent advances in reproductive medicine, the role played by uterine receptivity in contributing to human infertility remains unclear. Several clinical studies suggest the importance of blastocyst implantation in a narrow window of uterine receptivity, between 6 and 8 days after ovulation. This brief and precise period, called "implantation or nidation window", lasts less than 48 h and coincides with the formation of large and smooth projections, called "pinopodes", on the apical membranes of the endometrial epithelial cells. Pinopode expression appears to advance or retard depending on the hormonal treatments and an individual's particular response. This displacement can be followed through endometrial biopsy and scanning electron microscopy (SEM). Therefore, pinopode expression could be considered a useful biological marker to assess endometrial receptivity and to locate the implantation window.

Uterine and placental expression of steroidogenic genes during rodent pregnancy

The ontogeny and functional role of steroidogenesis during mammalian gestation is poorly understood. This review provides a summary of our recent findings on the spatio-temporal expression of key steroidogenic genes controlling progesterone synthesis in the uterus during mouse pregnancy. We have shown that onset of cholesterol side chain cleavage cytochrome P450 (P450scc) and a newly identified isoform of murine 3beta-hydroxysteroid dehydrogenase/isomerase type VI (3betaHSD VI) expression occurs upon decidualization of the uterine wall induced by implantation. This unexpected early expression of the enzymes in the maternal decidua is terminated at mid-pregnancy when the steroidogenic ability reappears in the extraembryonic giant cells at the time of placentation. The giant cells express another protein indispensable for steroid hormone synthesis in the adrenal and gonads, Steroidogenic Acute Regulatory (StAR) protein. Unlike the human placenta, the steroidogenic genes are not expressed in the cells of the mature mouse placenta during the second half of gestation. Finally, our studies suggest that transcriptional regulation of P450scc is mediated by a non-SF-1 protein that substitutes SF-1 functions in the extraembryonic cells. Collectively, the results of the present study suggest that, during early phases of pregnancy, local progesterone synthesis in the maternal decidua and the trophoblast layers surrounding the embryonal cavity is important for successful implantation and/or maintenance of pregnancy. We propose that the local production of progesterone acts as an immunosuppressant at the maternofetal interface preventing the rejection of the fetal allograft.

Progesterone-action in the decidual mesometrium of pregnancy

The mesometrial decidua is absolutely dependent on progesterone action for its maintenance and growth. Hormone action is mediated by intranuclear progesterone receptors (PR) that regulate target cell gene transcription. In early pregnancy of the rat gene expression is particularly enhanced for regulators of cell cycle progression, growth factors and their cognate receptors; cell cycle arrest proteins are suppressed. Cell survival proteins such as Bcl2 are also up-regulated. These events are associated with abundant expression of PR-A and PR-B isoforms and STAT (signal transducers and activators of transcription) family members. Proliferation of decidual cells no longer occurs after mid-pregnancy despite high levels of circulating progesterone and the decidua begins a slow process of regression, which continues to term. Regression is characterized by an increase in abundance of proteins that promote apoptosis such as p27, Bax and Caspase-3. These late pregnancy changes are associated with a relative increase in PR-C, a third form of the PR molecule, that binds progesterone but probably has limited transcriptional activity. Protein kinase C, which is suppressed by progesterone in early pregnancy, may be a key mediator of these processes.

Assessing uterine receptivity in 2001: ultrasonographic glances at the new millennium

The understanding and control of embryo implantation represents the major challenge for assisted reproductive technologies. Along with developments in basic research and efforts to optimize embryo quality, the improvement of noninvasive and reliable methods to assess uterine receptivity constitutes an important step toward meeting such a challenge. Today, ultrasound-based approaches to evaluate endometrial echogenicity and uterine perfusion and contractility are available for practical use. Increasing evidence indicates that echogenic patterns of the endometrium reflect histologic processes that are involved in the establishment of receptivity. This constitutes a possible explanation for the reported association between premature hyperechogenic patterns of the endometrium and poor implantation rates. Nevertheless, additional studies aiming at correlating further morpho-biochemical events in the endometrium with its echogenicity patterns are needed. Further, developments in vascular assessment by Doppler, Doppler-related, and vascular detection technologies will also be instrumental in monitoring and improving vascular changes that lead to uterine receptivity. Finally, data supporting the hypothesis that uterine contractility, as visualized by ultrasound, influences in vitro fertilization-embryo transfer (IVF-ET) pregnancy rates encourage further investigation on both the regulation and control of uterine contractions. This article discusses some of the advantages and limitations of ultrasonographic assessments of uterine receptivity in the perspective of the new millennium.

Rat uterine complement C3 expression as a model for progesterone receptor modulators: characterization of the new progestin trimegestone

Progestins have a wide variety of activities in female reproduction. There are also pharmacological applications for progestins, including hormone replacement therapy and contraception. Here we report the development and characterization of the rat uterine complement component C3 mRNA as a molecular target for the evaluation of the antiestrogenic activity of progestins in the uterus. In this assay, ethinyl estradiol (EE) is used to stimulate C3 expression and progestins are then evaluated for their ability to inhibit this expression. The three reference progestins, progesterone (P4), levonorgestrel (LNG), and medroxyprogesterone acetate (MPA) blocked the increase in C3 mRNA levels induced by EE. Dexamethasone (DEX) and 17alpha-methyl testosterone did not inhibit the estrogen induced C3 mRNA levels; in fact, DEX caused a further increase in C3 mRNA levels. Finally, the antiprogestin RU486 was able to block the MPA inhibition of C3 message. RU486, like DEX, caused an increase in C3 mRNA levels above that of estrogen treatment alone. The model was also used to evaluate trimegestone (TMG), a new steroidal progestin, that has been shown to be a potent and selective progesterone receptor agonist. The activity of TMG in the rat uterine decidualization and ovulation inhibition assays was similar to MPA. However, in the C3 model, TMG caused a dose-dependent inhibition of the EE induced C3 message and was approximately five-fold more potent in this model than MPA (EC(50) of 4.7 microg/kg and 26.5 microg/kg, respectively). Therefore, TMG was a more potent antagonist of estrogenic activity in the uterine endometrium than any of the reference progestins tested and therefore may be more effective in protecting the endometrium in hormone replacement therapy.

Understanding the apical surface markers of uterine receptivity: pinopods-or uterodomes?

The plasma membrane of uterine epithelial cells is very sensitive to ovarian hormones and protrusions of the apical portion of this membrane have been used as indicators of endocrine status and preparation for implantation in the human uterus in particular. Protrusions of the apical plasma membrane were first identified in rats and mice where their established pinocytotic function gave rise to the name 'pinopod'. In humans and many other animals however, little evidence of the functional nature of such protrusions is available but what is available suggests that human 'pinopods' (useful though they are as indicators of endocrine status) might be more similar morphologically to other, larger, membrane protrusions, or apical domes, which have been shown not to be pinocytotic. Hence, I propose that these latter protrusions, including those in the human uterus, should be referred to by a term which does not imply a particular function and have settled on the name 'uterodome'.

Effects of leukaemia inhibitory factor on embryo implantation in the mouse

Leukaemia inhibitory factor (LIF) is a pleiotrophic cytokine. Recent reports indicate that LIF is relevant to murine embryo implantation. In this work, results of indirect immunofluorescence under a confocal microscope illustrated that LIF was mainly located in the uterine lumen and uterine epithelial cells in pregnant mice on day 4. The number of embryos implanted in pregnant mice on day 8 decreased significantly after injection of 3 microg LIF antibodies into a uterine horn (P<0.001), which demonstrated again that LIF is a critical factor for embryo implantation. In a co-culture system, LIF (0.1 ng/ml, 1 ng/ml, 10 ng/ml and 100 ng/ml) significantly enhanced the blastocyst outgrowth after 24, 48 or 72 h of co-culture, and outgrowth areas after 72 h of co-culture. Conversely, 5 microg/ml and 10 microg/ml, but not 1 microg/ml, LIF antibodies decreased the percentage of blastocysts with outgrowth; only 10 microg/ml LIF antibody inhibited blastocyst outgrowth area significantly (P<0.001). However, neither LIF nor its antibodies changed embryo attachment. Analysis of correlation showed that the effects of LIF or its antibodies on the blastocyst outgrowth were dose-dependent. In summary, different pathways may exist to regulate the blastocyst attachment and outgrowth on a monolayer of uterine epithelial cells. LIF protein from the maternal uterus exerts an essential role in embryo implantation in the mouse, which is mediated by stimulating trophoblast outgrowth, but not by promoting the attachment.

Regulation of sialomucin complex/Muc4 expression in rat uterine luminal epithelial cells by transforming growth factor-beta: implications for blastocyst implantation

Blastocyst implantation is arguably the most critical stage of mammalian embryogenesis and requires that the uterus be in a receptive state. Initiation of receptivity involves loss of anti-adhesive molecules from the apical surface of the uterine luminal epithelium, one of which is sialomucin complex (SMC/Muc4), a highly O-glycosylated, anti-adhesive glycoprotein composed of mucin ascites sialoglycoprotein-1 (ASGP-1) and transmembrane (ASGP-2) subunits. SMC expression at the uterine luminal surface, but not in glandular epithelium, is hormonally regulated and varies with the estrous cycle. SMC is lost from the luminal uterine surface at the period of receptivity. However, the mechanism by which SMC is hormonally regulated is not understood. Analyses of SMC regulation in hormone-responsive primary cultures of rat uterine luminal epithelial cells (RULEC) demonstrated robust SMC expression by the RULEC, which is not altered by treatments with estrogen or progesterone. However, both SMC protein and transcript are downregulated by transforming growth factor-beta (TGF-beta1). SMC is also downregulated when RULEC are co-cultured with isolated uterine stromal cells. Estradiol and anti-TGF-beta block the stromal cell effect. These results suggest an indirect hormonal regulation of RULEC SMC, in which TGF-beta acts as a hormonally regulated, mesenchymal paracrine factor to repress SMC production by the epithelial cells and permit implantation.

Endometrial receptivity and the window of implantation

Implantation is a highly co-ordinated event that involves both embryonic and endometrial participation. The endometrium expresses a sophisticated repertoire of proteins during the menstrual cycle many of which help to define a period of receptivity collectively known as the 'window of implantation'. Many of these factors, which are temporally aligned with this window, are now seen as chemical messengers that are recognized by the embryo and facilitate embryonic growth and differentiation. The use of such proteins as biomarkers has also advanced our understanding of the implantation process and may identify women with implantation failure and infertility. While the study of endometrial receptivity is still evolving, the field is growing rapidly and will probably enhance our ability to diagnose and treat couples with infertility, especially in the arena of assisted reproductive technologies (ART).

Endometrial cell death during early pregnancy in the rat

In a study of early pregnancy in the rat, a high proportion of morphologically apoptotic, TUNEL and P2X7 positive cells were found to be present in the luminal epithelium and stroma prior to implantation. At the time of implantation on Day 6, apoptosis as measured by these indicators was reduced up to 4-fold in the non-implantation uterine epithelium but was markedly increased adjacent to the implanting blastocyst. It is proposed that apoptotic cell death is an important regulatory factor involved in uterine remodelling prior to and during implantation.

Presence of uterine peroxidase activity in the rat early pregnancy

Peroxidase has been associated with estrogen action in the uterus. This enzyme plays an important role in the control of hydrogen peroxide levels and in catechol estrogen production. Since the uterus, during early pregnancy, is subjected to estrogen and progesterone regulation, we analyzed the changes of peroxidase activity in relation to receptivity and uterine early response to the embryo. Soluble and microsomal peroxidase activity were determined in the rat uterus during the estrus phase and early pregnancy (days 3 through 6). Soluble peroxidase activity increased significantly (p < 0.01) from day 3 (1.50 +/- 0.24) to day 4 (3.5 +/- 0.3) and 5 (5 +/- 0.5 U/mg protein, mean +/- S.D., n = 6) of pregnancy. During day 6, a significant decrease was noted in both the implantation site and the nonimplantation uterine tissue. Microsomal calcium-extractable peroxidase showed a similar pattern, with lower specific activity than, the soluble peroxidase. During estrus, the uterine tissue showed the highest activity of calcium-extracted peroxidase (8.7 +/- 1.35 U/mg protein), statistically greater when compared with days 3, 4, 5 and 6 of pregnancy. In conclusion, high peroxidase activity was associated with uterine receptivity. The decrease of activity on day 6 might be due to a progesterone-estrogen interaction, and consequently, hydrogen peroxide can be utilized for hydroxile production by means of the Fenton reaction. Lipoperoxidation may be necessary for changes in membrane fluidity for embryo attachment to endometrial epithelium.

Retinoic acid synthesis and expression of cellular retinol-binding protein and cellular retinoic acid-binding protein type II are concurrent with decidualization of rat uterine stromal cells

Decidualization of stromal cells at the site of embryo implantation in the rat uterus is accompanied by expression of cellular retinol-binding protein and cellular retinoic acid-binding protein [CRABP(II)], whose presence has been shown to correlate with gain of ability to synthesize retinoic acid in other cells. Here we examined whether decidual cells also acquired the ability to synthesize retinoic acid, which would have important implications for understanding the implantation process. Decidual cells were isolated from the uterus on day 8 of pregnancy and cultured. When provided with retinol, they indeed synthesized and released retinoic acid to the medium. To follow acquisition of this ability more closely, artificial induction of decidualization was exploited. Ovariectomized rats were placed on a hormonal regimen that allows decidualization to occur in vivo, with oil stimulation, or in vitro, if cells are isolated on day 5 of the regimen and then cultured. Decidualization in vivo reproduced the expression of cellular retinol-binding protein and CRABP(II) seen during pregnancy. Stromal cells isolated on regimen day 2 synthesized little retinoic acid and expressed little alkaline phosphatase, a marker of decidualization. Stromal cells isolated on regimen day 5 had elevated levels of alkaline phosphatase, increasing during the 3 days of culture examined. The ability of the stromal cells to synthesize retinoic acid showed the same pattern: a substantially elevated production from that previously observed, on day 2, with production increasing significantly over the next 2 culture days. Thus, expression of CRABP(II) was correlated with gain of ability to synthesize retinoic acid. Retinoid signaling may be an important part of the process of embryo implantation.

Preimplantation access to maternal insulin and albumin increases fetal growth rate in mice

Provision of the maternal factors, albumin and/or insulin to embryos in vitro restores preimplantation morphological development and cell proliferation to that seen in vivo. The hypothesis that the preimplantation effects of insulin or albumin would be reflected in increased fetal growth rate was examined. Two-cell embryos were cultured 48-50 h in medium supplemented with 0.17 micromol/l, 15 micromol/l albumin or 0.17 micromol/l insulin and the resultant blastocysts transferred to pseudopregnant recipients. Fetal and placental mass and skeletal development were determined at E19 or E20 (day 19 or 20 of embryonic development). Preimplantation access to insulin or albumin increased fetal growth by 4-6%. Combining insulin and albumin did not produce a further increment in fetal growth. The fetal growth achieved by providing preimplantation access to insulin, albumin or both was equivalent to that of in-vivo developed blastocysts. The conclusions are that: (i) preimplantation access to maternal insulin and albumin is required for normal fetal growth rates in the mouse and (ii) the increments in inner cell mass cell number and metabolic rates induced by insulin (and possibly albumin) reflect a requirement for maternal growth factors during preimplantation stages to optimize fetal development.