The presence of pinopodes in the human endometrium does not delineate the implantation window

When the Embryo Meets the Endometrium: Identifying the Features Required for Successful Embryo Implantation

Evaluation of the optimal number of embryos, their quality, and the precise timing for transfer are critical determinants in reproductive success, although still remaining one of the main challenges in assisted reproduction technologies (ART). Indeed, the success of in vitro fertilization (IVF) treatments relies on a multitude of events and factors involving both the endometrium and the embryo. Despite concerted efforts on both fronts, the overall success rates of IVF techniques continue to range between 25% and 30%. The role of the endometrium in implantation has been recently recognized, leading to the hypothesis that both the "soil" and the "seed" play a central role in a successful pregnancy. In this respect, identification of the molecular signature of endometrial receptivity together with the selection of the best embryo for transfer become crucial in ART. Currently, efforts have been made to develop accurate, predictive, and personalized tests to identify the window of implantation and the best quality embryo. However, the value of these tests is still debated, as conflicting results are reported in the literature. The purpose of this review is to summarize and critically report the available criteria to optimize the success of embryo transfer and to better understand current limitations and potential areas for improvement.

Expression of HOXA10 Gene in Women with Endometriosis: A Systematic Review

The homeobox A10 (HOXA10) gene is known to be related to endometriosis; however, due to a lack of knowledge/evidence in the pathogenesis of endometriosis, the mechanisms that link HOXA10 to endometriosis still need to be clarified. This review addresses the difference in the expression of the HOXA10 gene in endometriotic women versus non-endometriotic women across populations by country and discusses its influences on women's fertility. An organized search of electronic databases was conducted in Scopus, ScienceDirect, PubMed, and Web of Science. The keywords used were (HOXA10 OR "homeobox A10" OR PL OR HOX1 OR HOX1H OR HOX1.8) AND ("gene expression") AND (endometriosis). The initial search resulted in 623 articles, 10 of which were included in this review. All ten papers included in this study were rated fair in terms of the quality of the studies conducted. The expression of the HOXA10 gene was found to be downregulated in most studies. However, one study provided evidence of the downregulation and upregulation of HOXA10 gene expression due to the localization of endometriotic lesions. Measuring the expression of the HOXA10 gene in women is clinically essential to predicting endometriosis, endometrial receptivity, and the development of pinopodes in the endometrium during the luteal phase.

The RNA-seq based endometrial receptivity test (rsERT) compared to pinopode: A better diagnostic tool for endometrial receptivity for patients with recurrent implantation failure in Chinese population

Displaced window of implantation (WOI) is one of the endometrial origins that accounts for implantation failure, especially for patients with recurrent implantation failure (RIF), yet no standard diagnostic tool has been recognized. The study consists of two parts, aiming to compare the concordance and efficacy of the diagnostic tools, the newly developed RNA-seq based endometrial receptivity test (rsERT) to the conventional pinopode, in diagnosing WOI and guiding personalized embryo transfer (pET). With the same group of RIF patients, the rsERT diagnosed 32 patients (65.31%) with normal WOIs, and most of the displacements were advancements (30.61%). While according to pinopode, only 14 patients (28.57%) were found with normal WOIs, and most patients (63.27%) presented delayed growth patterns. After conducting pET, patients in the rsERT group had higher successful pregnancy rates while requiring fewer ET cycles (50.00% vs. 16.67%, p=0.001). The study proved poor consistency between the diagnostic tools of endometrial receptivity based on cellular structure and gene profiling, and it supported rsERT as a reliable tool with potential clinical value.

Granulocyte Colony-Stimulating Factor Combined With Transcutaneous Electrical Acupoint Stimulation in Treatment of Unresponsive Thin Endometrium in Frozen Embryo Transfer Cycles

Objective: This trial was designed to assess the treatment effects of granulocyte colony-stimulating factor (G-CSF) and transcutaneous electrical acupoint stimulation (TEAS) on thin endometrium in frozen-thawed embryo transfer (FET) cycles.

Methods: Ninety-nine patients with previous cancellations of embryo transfer were included, 56 of whom were prospectively treated with intrauterine perfusion of G-CSF in subsequent FET cycles. The selected patients were randomized into the G-CSF perfusion only group and the G-CSF perfusion combined with TEAS group. The other 43 patients were retrospectively included as controls.

Results: Compared to previous cycles, endometrial thickness was statistically significantly increased in the two treatment groups (5.97 ± 0.60, 7.52 ± 0.56, 6.14 ± 0.52, and 7.66 ± 0.44; P = 0.00 and 0.00, respectively). The increases in endometrial thickness suggested that no statistically significant difference was found between the two treatment groups. The G-CSF with TEAS group suggested a higher embryo implantation rate than the G-CSF perfusion only and control groups (33.33 and 29.1% and 33.33 and 17.39%; P = 0.412 and 0.091, respectively). The G-CSF combined with TEAS group demonstrated nominally higher clinical and ongoing pregnancy rates than the G-CSF perfusion-only group and controls, though, the difference was not statistically significant.

Conclusion: G-CSF has a potential role in improving endometrium thickness in patients with thin unresponsive endometrium in FET treatment cycles. In addition, when combined with TEAS, G-CSF perfusion treatment also improves the embryo implantation rate; however, randomized controlled trials are highly demanded to provide high-grade evidence regarding clinical pregnancy rate after G-CSF perfusion treatment.

Mother and Embryo Cross-Communication

Endometrial receptivity is a biosensor for embryo quality, as embryos with reduced developmental potential are rejected. However, embryo quality only accounts for an estimated one-third of implantation failures, with suboptimal endometrial receptivity accounting for the remaining two-thirds. As pregnancy progresses, a uterus continues to engage in close communication with an embryo/fetus, exchanging information in the form of endocrine, paracrine, and other cues. Given the long mammalian gestation period, this dialogue is intricate, diverse, and, currently, not fully understood. Recent progress and the availability of high-throughput techniques, including transcriptomics, proteomics, and metabolomics, has allowed the simultaneous examination of multiple molecular changes, enhancing our knowledge in this area. This review covers the known mechanisms of mother–embryo cross-communication gathered from animal and human studies.

Pinopodes: Recent advancements, current perspectives, and future directions

Successful embryo implantation is a complex and highly regulated process involving precise synchronization between the fetal-derived trophoblast cells and maternal uterine luminal epithelium. Multiple endocrine-driven factors are important for controlling the timely receptivity of the uterus, and this complexity underscores implantation failure as a major cause of recurrent infertility associated with assisted reproductive technologies. One particular cellular structure often hypothesized to promote receptivity is the pinopode or uterodome - a hormonally regulated, large cellular protrusion on the uterine epithelial surface. Recent clinical studies associate pinopodes with favorable fertility outcomes in women, and because they are directly linked to an increase in progesterone levels, the potential utility of these hormone-regulated cell biological structures in predicting or improving implantation in a clinical setting holds promise. In this review, we aim to generate interest in pinopodes from the broader cell biology and endocrinology communities, re-examine methodologies in pinopode research, and identify priorities for future investigation of pinopode structure and function in women's reproductive health.

Molecular Signaling Regulating Endometrium-Blastocyst Crosstalk

Implantation of the embryo into the uterine endometrium is one of the most finely-regulated processes that leads to the establishment of a successful pregnancy. A plethora of factors are released in a time-specific fashion to synchronize the differentiation program of both the embryo and the endometrium. Indeed, blastocyst implantation in the uterus occurs in a limited time frame called the "window of implantation" (WOI), during which the maternal endometrium undergoes dramatic changes, collectively called "decidualization". Decidualization is guided not just by maternal factors (e.g., estrogen, progesterone, thyroid hormone), but also by molecules secreted by the embryo, such as chorionic gonadotropin (CG) and interleukin-1β (IL-1 β), just to cite few. Once reached the uterine cavity, the embryo orients correctly toward the uterine epithelium, interacts with specialized structures, called pinopodes, and begins the process of adhesion and invasion. All these events are guided by factors secreted by both the endometrium and the embryo, such as leukemia inhibitory factor (LIF), integrins and their ligands, adhesion molecules, Notch family members, and metalloproteinases and their inhibitors. The aim of this review is to give an overview of the factors and mechanisms regulating implantation, with a focus on those involved in the complex crosstalk between the blastocyst and the endometrium.

Acupuncture in improving endometrial receptivity: a systematic review and meta-analysis

Background

This systematic review aimed at summarizing and evaluating the evidence of randomized controlled trials (RCTs) using acupuncture to improve endometrial receptivity (ER).

Methods

We searched 12 databases electronically through August 2018 without language restrictions. We included RCTs of women of infertility due to low ER, and excluded infertility caused by other reasons or non-RCTs. Two independent reviewers extracted the characteristics of studies and resolved the differences through consensus. Data were pooled and expressed as standard mean difference (SMD) or mean difference (MD) for continuous outcomes and risk ratio (RR) for dichotomous outcomes, with 95% confidence interval (CI).

Results

We found very low to moderate level of evidence that acupuncture may improve pregnancy rate (RR = 1.23 95%CI[1.13, 1.34] P < 0.00001) and embryo transfer rate (RR = 2.04 95%CI[1.13, 3.70] P = 0.02), increase trilinear endometrium (RR = 1.47 95%CI [1.27, 1.70] P < 0.00001), thicken endometrium (SMD = 0.41 95% CI [0.11, 0.72] P = 0.008), reduce resistive index (RI) (MD = -0.08 95% CI [− 0.15, − 0.02] P = 0.01), pulse index (PI) (SMD = -2.39 95% CI [− 3.85, − 0.93] P = 0.001) and peak systolic velocity/ end-diastolic blood velocity (S/D) (SMD = -0.60 95% CI [− 0.89, − 0.30] P < 0.0001), compared with medication, sham acupuncture or physiotherapy. Acupuncture was statistically significant as a treatment approach.

Conclusion

The efficacy and safety of acupuncture on key outcomes in women with low ER is statistically significant, but the level of most evidence was very low or low. More large-scale, long-term RCTs with rigorous methodologies are needed.

Ultrastructural markers of tissue endometrial receptivity in patients with recurrent implantation failure

The scanning electron microscopy of the endometrial surface epithelium during the 'implantation window' was performed in 119 patients with uterine factor of infertility or recurrent miscarriage due to endometrial hypoplasia. Ultramorphological picture of the surface endometrial epithelium was characterized by aplasia and hypoplasia of pinopodes (67.39%), dense cell - cell contacts (69.53%), heteromorphy of secretory cells (15.22%) in combination with atypia of microenvironment cells (50%) in patients with infertility. The asynchronous development of pinopodes (46.67%) and the absence of intercellular contacts separation during the 'implantation window' (84.44%) was observed in patients with recurrent miscarriage. The revealed disturbance determines the mechanisms of the blastocyst adhesion violation and trophoblast invasion in the different stages of implantation in patients with uterine factor of infertility and recurrent miscarriage.

Wenshen Yangxue decoction improves endometrial receptivity recovery and promotes endometrial angiogenesis in a rat model

CONTEXT

Wenshen Yangxue decoction (WSYXD) is a famous traditional Chinese medicine (TCM) formula and has been used in infertility treatment, but the exact mechanism is still unknown.

OBJECTIVES

To determine if WSYXD improves endometrial receptivity recovery and promotes endometrial angiogenesis in a rat model.

MATERIALS AND METHODS

A total of 100 proestrus female SPF Wistar rats were randomly assigned into five groups: control (saline), model (saline and hydroxyurea solution), high (5.2/100 g), middle (2.6/100 g) and low (1.3/100 g) WSYXD dose groups for 10 d. The microvessel densities, endometrial microstructure, as well as blastocysts number, were observed, followed by detection of angiogenesis-related gene/protein expression by immunohistochemistry, western blot and quantitative real-time polymerase chain reaction (RT-PCR), respectively.

RESULTS

Compared with the model group, the blastocyst number in WSYXD middle and high groups were significantly increased (4.50 ± 3.11 vs. 13.00 ± 2.12, 14.00 ± 1.83, p < 0.01). Lower MVD can be found in the model group (4.7) when compared with the normal control (13.7), middle (8.4) and high (9.7) dose groups. Additionally, significant differences were observed in VEGF, HIF-1α, p-AKT, p-PI3K, Ang1 and Ang2 (all p < 0.01) among different groups.

DISCUSSION AND CONCLUSIONS

In conclusion, WSYXD could help endometrial receptivity recovery and promote endometrial angiogenesis through PI3K, HIF-1α signalling and VEGF expression regulation. This study provides molecular evidence for application of WSYXD in the clinic and promotes new drug development from TCM.

Pinopode score around the time of implantation is predictive of successful implantation following frozen embryo transfer in hormone replacement cycles

STUDY QUESTION

Is pinopode measurement of any prognostic value?

SUMMARY ANSWER

Pinopode expression was significantly associated with the occurrence of pregnancy after frozen embryo transfer.

WHAT IS KNOWN ALREADY

Pinopodes are expressed in the endometrium during the implantation period. Pinopode measurement has been proposed as a marker of endometrial receptivity.

STUDY DESIGN, SIZE, DURATION

A prospective cohort study was conducted at the Center of Reproductive Medicine, Sir Run Run Shaw Hospital, between 2014 and 2016, recruiting 172 women with infertility and undergoing frozen embryo transfer following IVF treatment. Among 172 participants, 46 women took part in the first study to quantify the daily changing pattern of pinopodes 3-7 days after the initiation of progesterone therapy in the hormone replacement cycles and the remaining 126 women with infertility participated in a study to examine the relationship between pinopode count and pregnancy outcome following frozen embryo transfer in hormone replacement cycles.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The mean age of participants was 29 years old. All participants received an artificial hormone replacement protocol capable of supporting successful implantation. Endometrial biopsies from 46 women were obtained 3, 4, 5, 6 and 7 days after the initiation of progesterone therapy (P + 3, n = 6; P + 4, n = 6; P + 5, n = 11; P + 6, n = 13; P + 7, n = 10, respectively). Another 126 endometrial biopsies were obtained precisely 6 days after the initiation of progesterone. Scanning electron microscopy was used to capture the pinopode images, followed by use of the image J program to quantify the count and subtype of the pinopodes.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that at least 60 microscopic fields were necessary to achieve a reproducible result. An intra-observer variability study showed good agreement between two measurements regarding the developing pinopode (DP) subtype (r = 0.95) and the fully developed pinopode (FDP) subtype (r = 0.86) but not for the regressing (RP) pinopode subtype (r = 0.39). The proportion of DP/total pinopodes (TP) declined rapidly form day P + 4 to a minimum on day P + 6. The percentage of FDP/TP increased rapidly from day P + 4 to reach a peak on day P + 6. On the other hand, the percentage of RP/TP reached a peak on day P + 7. Participants who conceived had a significantly (P = 0.011) higher percentage of FDP/TP on day P + 6 and significantly (P = 0.005) lower percentage of DP/TP on the same day compared with participants who did not become pregnant. Using a scoring system incorporating the percentages of DP and FDP, it was found that the pregnancy rate and the embryo implantation rate of women with a high pinopode score (82.3%; 63.0%) was significantly (P = 0.001; P = 0.046) higher than that of women with a low pinopode score (53.3%; 46.7%), respectively. There remains a possibility that the observations could have arisen due to chance.

LIMITATIONS, REASONS FOR CAUTION

This study examined pinopode count and subtype in the HRT cycles, and it is uncertain whether the same observations apply to in natural cycles.

WIDER IMPLICATIONS OF THE FNDINGS

Pinopodes have been questioned as a potential marker of endometrial receptivity for many years. Our results suggested that pinopode measurement may be of value in predicting pregnancy.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by the grants from the general project of medicine and health in Zhejiang Province of China (2015KYA142; 2018KY106), the Key Research and Development Program of Zhejiang Province (2017C03022) and the National Natural Science Foundation of China (81701514).The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript. We have no competing interests to declare.

TRIAL REGISTRATION NUMBER

ISRCTN26300668.

Changes in Morphology and Presence of Pinopodes in Endometrial Cells during the Luteal Phase in Women with Infertility Problems: A Pilot Study

Objective: To investigate morphological changes in the endometrial epithelial cells of patients with infertility problems. Materials and methods: Endometrial biopsies were obtained from 10 women who have undergone several unsuccessful in vitro fertilisation (IVF) procedures. Endometrial biopsies were performed between luteinizing hormone surge days LH+6 to +10 of the natural menstrual cycle. Each sample was divided into three parts, which were processed for histological, transmission (TEM), and scanning electron microscopy (SEM) investigations. Results: Histological investigations demonstrated significant alterations in the apical part of epithelial cells of one patient; in four patients, the gland maturity was low, not matching the cycle day, and thus a phase lag had developed. By TEM examination, we ascertained changes in secretory and ciliated cells in three patients (decreased amount or missing microvilli, irregular cilia in ciliated cells). SEM examination found pinopodes in five patients: three samples contained fully developed pinopodes-larger and completely smooth, with only some wrinkles; one sample contained regressing small pinopodes, with wrinkled surfaces; and one sample had both developed and regressing pinopodes. Conclusions: To conclude, our study shows that the endometrium of patients with poor IVF outcome has either significant changes in the morphology or the endometrial maturation is inhibited and a phase lag often develops. Our study shows that endometrial pinopodes are found throughout the mid-luteal phase up to day LH+10.

Molecular mechanisms of embryonic implantation in mammals: Lessons from the gene manipulation of mice

BACKGROUND

Human infertility has become a serious and social issue all over the world, especially in developed countries. Numerous types of assisted reproductive technology have been developed and are widely used to treat infertility. However, pregnancy outcomes require further improvement. It is essential to understand the cross-talk between the uterus (mother) and the embryo (fetus) in pregnancy, which is a very complicated event.

METHODS

The mammalian uterus requires many physiological and morphological changes for pregnancy-associated events, including implantation, decidualization, placentation, and parturition, to occur. Here is discussed recent advances in the knowledge of the molecular mechanisms underlying these reproductive events - in particular, embryonic implantation and decidualization - based on original and review articles.

MAIN FINDINGS RESULTS

In mice, embryonic implantation and decidualization are regulated by two steroid hormones: estrogen and progesterone. Along with these hormones, cytokines, cell-cycle regulators, growth factors, and transcription factors have essential roles in implantation and decidualization in mice.

CONCLUSION

Recent studies using the gene manipulation of mice have given considerable insight into the molecular mechanisms underlying embryonic implantation and decidualization. However, as most of the findings are based on mice, comparative research using different mammalian species will be useful for a better understanding of the species-dependent differences that are associated with reproductive events, including embryonic implantation.

Adrenomedullin improves fertility and promotes pinopodes and cell junctions in the peri-implantation endometrium

Implantation is a complex event demanding contributions from both embryo and endometrium. Despite advances in assisted reproduction, endometrial receptivity defects persist as a barrier to successful implantation in women with infertility. We previously demonstrated that maternal haploinsufficiency for the endocrine peptide adrenomedullin (AM) in mice confers a subfertility phenotype characterized by defective uterine receptivity and sparse epithelial pinopode coverage. The strong link between AM and implantation suggested the compelling hypothesis that administration of AM prior to implantation may improve fertility, protect against pregnancy complications, and ultimately lead to better maternal and fetal outcomes. Here, we demonstrate that intrauterine delivery of AM prior to blastocyst transfer improves the embryo implantation rate and spacing within the uterus. We then use genetic decrease-of-function and pharmacologic gain-of-function mouse models to identify potential mechanisms by which AM confers enhanced implantation success. In epithelium, we find that AM accelerates the kinetics of pinopode formation and water transport and that, in stroma, AM promotes connexin 43 expression, gap junction communication, and barrier integrity of the primary decidual zone. Ultimately, our findings advance our understanding of the contributions of AM to uterine receptivity and suggest potential broad use for AM as therapy to encourage healthy embryo implantation, for example, in combination with in vitro fertilization.

GnRH agonist improves pregnancy outcome in mice with induced adenomyosis by restoring endometrial receptivity

Purpose

Adenomyosis has a negative impact on female fertility. GnRH agonist treatment can improve pregnancy outcomes in women with adenomyosis. However, the impact of GnRH agonist upon endometrium receptivity of patients with adenomyosis remains unclear. In this study, endometrial receptivity and pregnancy outcome were investigated using a mouse model of adenomyosis.

Materials and methods

Adenomyosis was induced in 12 female ICR mice, neonatally treated with tamoxifen, while another six female mice (control group) received solvent only. At 75 days, the induced adenomyosis group was randomly divided into two groups: an untreated group and a group treated with GnRH agonist (n = 6 each). Sixty days later, the mice were mated and pregnancy outcomes were observed and compared among the three groups (n = 6 each). In a parallel experiment using the same treatment regimes, uterus samples were collected on day 4 of pregnancy for immunohistochemistry, gene (quantitative polymerase chain reaction) and protein expression (Western blot), and scanning electron microscopy analyses.

Results

We found that the average live litter size was reduced in the adenomyosis compared with control group (8 ± 0.56 versus 13 ± 0.71; P = 0.03). However, the litter size was significantly increased in the treated with GnRH agonist group compared with the untreated group (12 ± 0.35 versus 8 ± 0.56; P = 0.04). The uterine expression levels of Hoxa10, Hoxa11, Lif and integrin b3 mRNA and protein were decreased in the adenomyosis group, and were significantly increased after GnRH agonist treatment. Additionally, pinopodes were reduced in number and poorly developed in mice with induced adenomyosis. However, pinopodes were abundant and well-developed in the GnRH agonist treatment group.

Conclusion

Adenomyosis may have an adverse impact on endometrial receptivity and reduce pregnancy outcomes in mice. However, GnRH agonist may improve the pregnancy outcome by partially restoring endometrial receptivity.

[Effects of raloxifene at two different doses for ovulation induction on endometrial pinopodes in mice during the implantation window]

OBJECTIVE

To compare the expression of pinopodes, the marker of endometrial receptivity, during the implantation window in Kunming mice stimulated with two different doses of raloxifene (RAL).

METHODS

Forty-eight 8-week-old female Kunming mice were randomly divided into 4 groups (n=12), namely saline group, clomiphene citrate (CC, 18 mg/kg) group, RAL (33 mg/kg) group and RAL (44 mg/kg group). In each group, the mice received intragastric administration of 1 mL of normal saline containing CC or RAL at the specified doses or saline only as indicated for ovulation induction, once daily for 2 days. The mice received then injection with 5 IU human chorionic gonadotropin (HCG) and mated and on day 4.5 of gestation, the pregnant mice were sacrificed for examination of the uterus with scanning electron microscopy.

RESULTS

Abundant and well developed pinopodes were observed in the endometrium of the mice in the 2 RAL groups and in the saline control group. The mice in CC group showed obviously reduced endometrial pinopodes with poor development.

CONCLUSIONS

RAL at two different doses does not obviously affect the expression of pinopodes in the uterine epithelium of mice, suggesting the safety of RAL at these two doses for ovulation induction without causing adverse effects on endometrial receptivity.

Clinical validation of pinopode as a marker of endometrial receptivity: a randomized controlled trial

OBJECTIVE

To determine the clinical value of pinopodes in the human.

DESIGN

Randomized controlled trial.

SETTING

Academic fertility center.

PATIENT(S)

From December 2014 to December 2016, in a phase I trial, 363 patients were recruited in their first IVF cycles. In a phase II trial, 136 patients with at least two previous embryo implantation failures were recruited.

INTERVENTION(S)

In the phase I trial, in the midluteal phase, endometrial tissues were obtained for scanning electron microscopy, and their IVF treatment outcomes were followed up. In the phase II trial, participants were allocated into two groups by random number table, and the experimental group had twice the number of the control group. Individual ETs (iETs) were performed in the experimental group, while frozen-thawed embryos were routinely transferred in the control group.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy rate (CPR) and ongoing pregnancy rate (OPR).

RESULT(S)

In the phase I trial, through receiver operation characteristic curve analysis, the optimal pinopode scoring for successful clinical pregnancy was determined to be 85. The CPR (74.29% vs. 19.77%) and OPR (62.86% vs 11.86%) were significantly higher in the patients whose pinopode scoring was >85. In the phase II trial, the CPR was dramatically higher in the iET group (33.82% vs. 8.11%).

CONCLUSION(S)

Pinopode scoring is a reliable marker of endometrial receptivity, and iET based on pinopode scoring is a promising solution for recurrent implantation failure.

TRIAL REGISTRATION NUMBERS

ChiCTR-OOC-14005617; ChiCTR-OOC-15005882.

Endometrial Receptivity Markers in Mice Stimulated With Raloxifene Versus Clomiphene Citrate and Natural Cycles

Ovulation induction therapy with clomiphene citrate can suppress endometrial receptivity. Raloxifene may be an alternative therapeutic for women with ovulatory disorders. This study aimed to compare the expression of endometrial receptivity markers, including homeobox gene 10 (HOXA10), integrin β3, and leukemia inhibitory factor (LIF), as well as pinopode production during the implantation window in mice stimulated with raloxifene and clomiphene citrate and natural cycles. Thirty-six 8-week-old female Kunming mice were randomly divided into 3 groups (n = 12) and administered daily raloxifene (22 mg/kg), clomiphene citrate (18 mg/kg), and normal saline (1 mL), respectively, by gavage. Two days later, mice were injected with 5 IU human chorionic gonadotropin and mated. Successfully mated female animals were identified with vaginal plugs designated gestation day 1. At day 4.5, pregnant donor mice were euthanized, and uterus samples were collected for immunohistochemistry, quantitative polymerase chain reaction, Western blot, and scanning electron microscopy analyses. Homeobox gene 10, integrin β3, and LIF messenger RNA (mRNA) and protein levels were significantly higher in the raloxifene-treated animals compared with the clomiphene citrate group (all P < .05) but not significantly different from saline group values, except for LIF and integrin β3 mRNA levels (P < .05). Pinopodes were abundant and well developed in the raloxifene and saline groups; however, in the clomiphene citrate-treated mice, fewer and poorly developed pinopodes were obtained. In mice, raloxifene had no effect on HOXA10, integrin β3, and LIF expression as well as pinopode production, suggesting it has no adverse effects on endometrial receptivity. Raloxifene may provide a viable alternative oral ovulation induction agent to clomiphene citrate.

MicroRNA-31 is significantly elevated in both human endometrium and serum during the window of implantation: a potential biomarker for optimum receptivity

The window of implantation of human embryos into the endometrium spans Cycle Days 20-24 of the 28-day menstrual cycle. However, uterine receptivity may not be reliably replicated in infertile patients throughout this span. Thus, it is of importance to be able to determine optimal receptivity through a minimally invasive measure. We screened expression of a number of candidate micro-RNAs (miRNAs) in endometrial tissues and serum collected from a panel of fertile women during both the proliferative phase and the secretory phase of a normal menstrual cycle. We found that several miRNAs were significantly elevated in endometrial tissues in the secretory phase versus the proliferative phase. One of these, miR-31, was found to be not only detectable in serum samples but also significantly elevated in the secretory phase versus the proliferative phase. MiR-31 is known to target several immunomodulatory factors, such as FOXP3 and CXCL12. We find that both of these factors are significantly downregulated in endometrial tissues during the secretory phase. Our data suggest that miR-31 is a potential biomarker for optimal endometrial receptivity, possibly operating through an immunosuppressive mechanism.

The role of progesterone and the progesterone receptor in human reproduction and cancer

Insufficient progesterone, effect possibly more on immune factors rather than adequate endometrial development, can be an easy remedial cause of infertility by simply supplementing the luteal phase with either vaginal or intramuscular or oral (dydrogesterone) progesterone. Progesterone will also help to reduce miscarriage rates when follicle maturing drugs are used for those with regular menses but follicular maturation defects, or women with recurrent miscarriages. One mechanism of action seems to be related to production of an immunomodulatory protein, the progesterone-induced blocking factor either in the cytoplasm or in the circulation. PIBF inhibits cytotoxicity of natural killer cells. Cancer cells may 'borrow' the same mechanism to escape NK cell immunosurveillance.

Pinopodes, leukemia inhibitory factor, integrin-β3, and mucin-1 expression in the peri-implantation endometrium of women with unexplained recurrent pregnancy loss

OBJECTIVE

To compare pinopode morphology and coverage, and expression of leukemia inhibitory factor (LIF), integrin-β3, and mucin-1 (MUC1) in the peri-implantation endometrium of women with unexplained recurrent pregnancy loss (RPL) versus normal fertile women.

DESIGN

Exploratory clinical study.

SETTING

University-affiliated assisted reproductive center.

PATIENT(S)

Women undergoing assisted reproduction at centers of reproductive medicine in two university teaching hospitals.

INTERVENTION(S)

Endometrial biopsy samples were obtained from women with RPL (test group, n = 30) and normal fertile women (control group, n = 26) 7 days after the day of luteinizing hormone peak. Pinopode morphology and coverage were assessed by use of scanning electron microscopy. Expression of LIF, integrin β3, and MUC1 were evaluated by immunohistochemical staining.

MAIN OUTCOME MEASURE(S)

Pinopode morphology and coverage, and the expression of LIF, integrin-β3, and MUC1 in both groups.

RESULT(S)

Pinopode morphology and coverage, and the expression of LIF and integrin-β3 showed no statistically significant differences between the two groups. The expression of MUC1 was statistically significantly reduced in the glandular epithelial cells and endometrial lumen of the RPL group compared with controls.

CONCLUSION(S)

The morphology and the coverage of pinopodes and expression of LIF and integrin-β3 did not change, but MUC1 expression was statistically significantly reduced in women with RPL compared with normal women.

Molecular aspects of implantation failure

Despite expanding global experience with advanced reproductive technologies, the majority of IVF attempts do not result in a successful pregnancy, foremost as a result of implantation failure. The process of embryo implantation, a remarkably dynamic and precisely controlled molecular and cellular event, appears inefficient in humans and is poorly understood. However, insights gained from clinical implantation failure, early pregnancy loss, and emerging techologies that enable molecular interrogation of endometrial-embryo interactions are unravelling this major limiting step in human reproduction. We review current molecular concepts thought to underlie implantation failure, consider the contribution of embryonic and endometrial factors, and discuss the clinical value of putative markers of impaired endometrial receptivity. Finally we highlight the nature of the dialogue between the maternal endometrium and the implanting embryo and discuss the concept of natural embryo selection. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Assessment of endometrial receptivity

OBJECTIVE

To provide a focused review of the scientific literature pertaining to endometrial receptivity.

DESIGN

Review of the literature and appraisal of relevant articles.

SETTING

Academic teaching hospital.

PATIENT(S)

Women with infertility.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Critical review of the literature.

RESULT(S)

Although a consensus has been achieved regarding the existence of a temporally defined period during which embryo attachment and invasion can occur (called the "window of implantation"), reliable methods to assess "receptivity" have not been established or adequately validated. In women with certain gynecologic disorders, including endometriosis, tubal disease, and polycystic ovary syndrome, endometrial receptivity seems to be compromised, leading to infertility and pregnancy loss. The establishment of reliable biomarkers for the detection of defects in endometrial receptivity has been a long-sought goal that remains an elusive target. The validation of endometrial biomarkers will require properly designed and implemented studies based on the recognition that endometrial receptivity defects are not equally distributed in women with endometriosis or these other conditions.

CONCLUSION(S)

Rapidly advancing technologies are bringing new biomarkers to the clinical arena that promise to further reveal the complexities of the implantation process.

The nucleolar channel system reliably marks the midluteal endometrium regardless of fertility status: a fresh look at an old organelle

OBJECTIVE

To determine whether nucleolar channel systems (NCSs) in the midluteal endometrium are associated with overall fertility status and/or with unexplained infertility.

DESIGN

Retrospective and prospective clinical studies.

SETTING

Repository of stored specimens from prior multicenter study and private infertility center.

PATIENT(S)

Retrospective study that included 97 women (49 fertile couples, 48 infertile couples) who had been randomized for endometrial biopsy during the midluteal or late luteal phase. The prospective study included 78 women with a variety of infertility diagnoses.

INTERVENTION(S)

Endometrial biopsies were obtained and assessed for the presence of NCSs by indirect immunofluorescence.

MAIN OUTCOME MEASURE(S)

The presence of NCS was graded semiquantitatively and dichotomized as normal versus low or absent.

RESULT(S)

Normal presence of NCS was significantly associated with the midluteal phase compared with the late luteal phase (80% vs. 29%). However, there was no association between presence of NCS and fertility status or between presence of NCS and unexplained infertility.

CONCLUSION(S)

Midluteal phase endometrium consistently forms NCSs regardless of fertility status, including unexplained infertility. This indicates a possible role for the NCS in initiating the window of endometrial receptivity. However, the consistent presence of NCSs across several different types of infertility challenges the likelihood that inadequate secretory transformation is a cause of infertility.

Effects of hydrosalpinx on pinopodes, leukaemia inhibitory factor, integrin beta3 and MUC1 expression in the peri-implantation endometrium

OBJECTIVES

To compare the expression of pinopodes, LIF, integrin beta(3) and MUC1 in the peri-implantation endometrium of women with and without hydrosalpinx.

STUDY DESIGN

A prospective observational study in an assisted reproductive unit in a university teaching hospital, including 20 women with hydrosalpinx and 21 women without hydrosalpinx. Endometrial biopsies were performed on day LH+7 or +8. The proportion and density of pinopodes were assessed by scanning electron microscopy. LIF, integrin beta3 and MUC1 were evaluated with immunohistochemical staining.

RESULTS

The proportion and the density of pinopodes were not significantly different between the hydrosalpinx and control groups. The LIF, integrin beta(3), and MUC1 expression were significantly reduced in both glandular epithelial cells and endometrial lumen of the hydrosalpinx group when compared with those of the control group. The expression of integrin beta(3) in stromal cells was also significantly lower in the hydrosalpinx group.

CONCLUSIONS

The proportion and the density of pinopodes in the peri-implantation endometrium were not affected by the presence of hydrosalpinx while LIF, integrin beta(3) and MUC1 were significantly reduced in patients with hydrosalpinx.

Disturbances in the LIF pathway in the endometrium among women with unexplained infertility

OBJECTIVE

To study the expression of leukemia inhibitory factor (LIF), its receptors LIFR and gp130, and its inhibitor SOCS1 in endometria from fertile women and infertile women with unexplained infertility. Signaling through the LIF pathway is involved in maintenance of a receptive state of human endometrium. Impaired endometrial receptivity may be a cause of female infertility.

DESIGN

Prospective clinical study.

SETTING

Hospital-based IVF unit and university-affiliated reproductive research laboratories.

PATIENT(S)

Twenty-six healthy fertile women and 14 women with unexplained infertility.

INTERVENTION(S)

Endometrial biopsy.

MAIN OUTCOME MEASURE(S)

Pinopode formation, expression of LIF, LIFR, gp130, and SOCS1 protein and mRNA in endometrial biopsies.

RESULT(S)

The expression of LIFR in the endometrium was negatively correlated to the expression of SOCS1 and positively correlated to the formation of pinopodes. In control fertile women, simultaneous intense apical staining of LIFR and gp130 together with faint SOCS1 staining was observed in epithelial cells, whereas the opposite was seen in most women with unexplained infertility.

CONCLUSION(S)

Unexplained infertility in some women might be explained by disturbances in the LIF pathway in midsecretory-phase endometrium.

Nuclear pore complex proteins mark the implantation window in human endometrium

Nucleolar channel systems (NCSs) are membranous organelles appearing transiently in the epithelial cell nuclei of postovulatory human endometrium. Their characterization and use as markers for a healthy receptive endometrium have been limited because they are only identifiable by electron microscopy. Here we describe the light microscopic detection of NCSs using immunofluorescence. Specifically, the monoclonal nuclear pore complex antibody 414 shows that NCSs are present in about half of all human endometrial epithelial cells but not in any other cell type, tissue or species. Most nuclei contain only a single NCS of uniform 1 microm diameter indicating a tightly controlled organelle. The composition of NCSs is as unique as their structure; they contain only a subset each of the proteins of nuclear pore complexes, inner nuclear membrane, nuclear lamina and endoplasmic reticulum. Validation of our robust NCS detection method on 95 endometrial biopsies defines a 6-day window, days 19-24 (+/-1) of an idealized 28 day cycle, wherein NCSs occur. Therefore, NCSs precede and overlap with the implantation window and serve as potential markers of uterine receptivity. The immunodetection assay, combined with the hitherto underappreciated prevalence of NCSs, now enables simple screening and further molecular and functional dissection.

Revealing the enigmas of implantation: what is the true impact of ovarian hyperstimulation?

It is agreed that ovarian stimulation results in histopathologic changes and variations in gene expression when compared to natural cycles. However, the enigma is still present: What is the true impact of variable degrees of embryo-endometrium developmental asynchrony in the presence of high clinical embryo implantation rates in IVF? It is postulated that the temporal characterization of gene expression and protein profiles of isolated endometrial compartments might unveil patterns that are critical for the establishment of the window of implantation.

Pinopodes are present in Lif null and Hoxa10 null mice

OBJECTIVE

To assess pinopode formation in Lif null and Hoxa10 null mice with infertility secondary to failed implantation.

DESIGN

Controlled animal experiment.

SETTING

Animal research and laboratory facility.

ANIMAL(S)

Lif null, Hoxa10 null, and ICR mice and Sprague-Dawley rats.

INTERVENTION(S)

Endometrial tissue was collected during the peri-implantation period and after ovariectomy.

MAIN OUTCOME MEASURE(S)

Endometrial epithelial tissue was examined under scanning-electron microscopy and assigned a score depending on the number of pinopodes present.

RESULT(S)

Pinopode scores in ICR, Lif null, and Hoxa10 null mice were comparable throughout the peri-implantation period, rising on day 3.5 of pregnancy and remaining elevated through to day 7.5, suggesting that pinopodes are not a good indicator of receptivity in mice. In contrast, pinopode scores in rats clearly demarcated the window of receptivity, appearing on day 4 of pregnancy and declining sharply on day 6. Pinopode scores were low in E(2)-treated ovariectomized mice, but unexpectedly, pinopode scores in vehicle-injected ovariectomized ICR mice were markedly elevated.

CONCLUSION(S)

Lif null and Hoxa10 null mice, in which implantation is impaired, have a similar number of pinopodes to fertile ICR mice. Pinopodes do not define a window of implantation in mice.

The nucleolar channel system of human endometrium is related to endoplasmic reticulum and R-rings

The nucleolar channel system (NCS) is a well-established ultrastructural hallmark of the postovulation endometrium. Its transient presence has been associated with human fertility. Nevertheless, the biogenesis, composition, and function of these intranuclear membrane cisternae are unknown. Membrane systems with a striking ultrastructural resemblance to the NCS, termed R-rings, are induced in nuclei of tissue culture cells by overexpression of the central repeat domain of the nucleolar protein Nopp140. Here we provide a first molecular characterization of the NCS and compare the biogenesis of these two enigmatic organelles. Like the R-rings, the NCS consists of endoplasmic reticulum harboring the marker glucose-6-phosphatase. R-ring formation initiates at the nuclear envelope, apparently by a calcium-mediated Nopp140-membrane interaction, as supported by the calcium-binding ability of Nopp140, the inhibition of R-ring formation by calcium chelators, and the concentration of Nopp140 and complexed calcium in R-rings. Although biogenesis of the NCS may initiate similarly, the reduced presence of complexed calcium and Nopp140 suggests the involvement of additional factors.

Delayed blastocyst transfer: is the window shutting?

Data suggest that dyssynchrony between day 6 blastocysts and endometrium may impair pregnancy rates in fresh transfer cycles.