Embryo implantation

Uterine receptivity, embryo attachment, and embryo invasion: Multistep processes in embryo implantation

BACKGROUND

Recurrent implantation failure is a critical issue in IVF-ET treatment. Successful embryo implantation needs appropriate molecular and cellular communications between embryo and uterus. Rodent models have been used intensively to understand these mechanisms.

METHODS

The molecular and cellular mechanisms of embryo implantation were described by referring to the previous literature investigated by us and others. The studies using mouse models of embryo implantation were mainly cited.

RESULTS

Progesterone (P4) produced by ovarian corpus luteum provides the uterus with receptivity to the embryo, and uterine epithelial growth arrest and stromal proliferation, what we call uterine proliferation-differentiation switching (PDS), take place in the peri-implantation period before embryo attachment. Uterine PDS is a hallmark of uterine receptivity, and several genes such as HAND2 and BMI1, control uterine PDS by modulating P4-PR signaling. As the next implantation process, embryo attachment onto the luminal epithelium occurs. This process is regulated by FOXA2-LIF pathway and planar cell polarity signaling. Then, the luminal epithelium at the embryo attachment site detaches from the stroma, which enables trophoblast invasion. This process of embryo invasion is regulated by HIF2α in the stroma.

CONCLUSION

These findings indicate that embryo implantation contains multistep processes regulated by specific molecular pathways.

Magnetic Resonance Imaging Reveals Distinct Roles for Tissue Transglutaminase and Factor XIII in Maternal Angiogenesis During Early Mouse Pregnancy

OBJECTIVE

The early embryo implantation is characterized by enhanced uterine vascular permeability at the site of blastocyst attachment, followed by extracellular-matrix remodeling and angiogenesis. Two TG (transglutaminase) isoenzymes, TG2 (tissue TG) and FXIII (factor XIII), catalyze covalent cross-linking of the extracellular-matrix. However, their specific role during embryo implantation is not fully understood. Approach and Results: For mapping the distribution as well as the enzymatic activities of TG2 and FXIII towards blood-borne and resident extracellular-matrix substrates, we synthetized selective and specific low molecular weight substrate analogs for each of the isoenzymes. The implantation sites were challenged by genetically modifying the trophoblast cells in the outer layer of blastocysts, to either overexpress or deplete TG2 or FXIII, and the angiogenic response was studied by dynamic contrast-enhanced-magnetic resonance imaging. Dynamic contrast-enhanced-magnetic resonance imaging revealed a decrease in the permeability of decidual vasculature surrounding embryos in which FXIII were overexpressed in trophoblast cell. Reduction in decidual blood volume fraction was demonstrated when either FXIII or TG2 were overexpressed in embryonic trophoblast cell and was elevated when trophoblast cell was depleted of FXIII. These results were corroborated by histological analysis.

CONCLUSIONS

In this study, we report on the isoenzyme-specific roles of TG2 and FXIII during the early days of mouse pregnancy and further reveal their involvement in decidual angiogenesis. Our results reveal an important magnetic resonance imaging-detectable function of embryo-derived TG2 and FXIII on regulating maternal angiogenesis during embryo implantation in mice.Visual Overview: An online visual overview is available for this article.

Human endometrial stromal cell decidualization requires transcriptional reprogramming by PLZF

Infertility and early embryo miscarriage is linked to inadequate endometrial decidualization. Although transcriptional reprogramming is known to drive decidualization in response to progesterone, the key signaling effectors that directly mediate this hormone response are not fully known. This knowledge gap is clinically significant because identifying the early signals that directly mediate progesterone-driven decidualization will address some of the current limitations in diagnosing and therapeutically treating patients at most risk for early pregnancy loss. We recently revealed that the promyelocytic leukemia zinc finger (PLZF) is a direct target of the progesterone receptor and is essential for decidualization of human endometrial stromal cells (hESCs). The purpose of this current work was to identify the genome-wide transcriptional program that is controlled by PLZF during hESC decidualization using an established in vitro hESC culture model, siRNA-mediated knockdown methods, and RNA-sequencing technology followed by bioinformatic analysis and validation. We discovered that PLZF is critical in the regulation of genes that are involved in cellular processes that are essential for the archetypal morphological and functional changes that occur when hESCs transform into epithelioid decidual cells such as proliferation and cell motility. We predict that the transcriptome datasets identified in this study will not only contribute to a broader understanding of PLZF-dependent endometrial decidualization at the molecular level but may advance the development of more effective molecular diagnostics and therapeutics for the clinical management of female infertility and subfertility that is based on a dysfunctional endometrium.

Spatiotemporal expression and regulation of FoxO1 in mouse uterus during peri-implantation period

Recent studies indicate that FoxO1 has roles in female reproductive system, especially in maternal endometrium. Although various cellular aspects and molecular pathways have been identified, the exact molecular characteristics of embryo implantation are still not completely understood. In this study, we aimed to investigate uterine expression and regulation of FoxO1 during peri-implantation period in mice. Experimental mouse models including, normal pregnancy, pseudopregnancy, artificial decidualization, and delayed implantation and activation were performed. Our results showed that FoxO1 expression was spatiotemporal in mouse endometrial tissue throughout peri-implantation period and its expression was significantly upregulated in luminal and glandular epithelium at the time of implantation. Moreover, on day 5 morning (09:00 AM) of pregnancy, expression of FoxO1 was cytoplasmic in endometrial luminal epithelial cells where embryo homing takes place. With progressing time on day 5 evening (19:00 PM) of pregnancy FoxO1 expression was nuclear in luminal epithelium at implantation site. Pseudopregnancy and artificial decidualization models indicated that FoxO1 expression was regulated by pregnancy hormones. Delayed implantation and activation model indicated that FoxO1 expression at the time of implantation is dependent upon activation status of blastocyst due to E2 induction and uterine sensitivity to implantation. In conclusion, our findings highlight a perspective for FoxO1 expression and regulation in mouse uterus during peri-implantation period indicating that its expression is regulated by implanting embryo and pregnancy hormones.

Characterisation of Osteopontin in an In Vitro Model of Embryo Implantation

At the onset of pregnancy, embryo implantation is initiated by interactions between the endometrial epithelium and the outer trophectoderm cells of the blastocyst. Osteopontin (OPN) is expressed in the endometrium and is implicated in attachment and signalling roles at the embryo–epithelium interface. We have characterised OPN in the human endometrial epithelial Ishikawa cell line using three different monoclonal antibodies, revealing at least nine distinct molecular weight forms and a novel secretory pathway localisation in the apical domain induced by cell organisation into a confluent epithelial layer. Mouse blastocysts co-cultured with Ishikawa cell layers served to model embryo apposition, attachment and initial invasion at implantation. Exogenous OPN attenuated initial, weak embryo attachment to Ishikawa cells but did not affect the attainment of stable attachment. Notably, exogenous OPN inhibited embryonic invasion of the underlying cell layer, and this corresponded with altered expression of transcription factors associated with differentiation from trophectoderm (Gata2) to invasive trophoblast giant cells (Hand1). These data demonstrate the complexity of endometrial OPN forms and suggest that OPN regulates embryonic invasion at implantation by signalling to the trophectoderm.

A single post-ovulatory dose of ulipristal acetate impairs post-fertilization events in mice

Ulipristal acetate (UPA) is a selective progesterone receptor modulator used for emergency contraception that has proven to be highly effective in preventing pregnancy when taken up to 120 h after unprotected sexual intercourse. Even though it may act mainly by delaying or inhibiting ovulation, additional effects of UPA on post-fertilization events cannot be excluded. Therefore, the aim of this study was to determine whether a single post-ovulatory dose of UPA could prevent pregnancy using the mouse as a pre-clinical model. Mated females received a single dose of UPA (40 mg/kg) on Day E1.5 or E2.5 (E0.5: copulatory plug detection) and post-fertilization events were evaluated. Our studies revealed that UPA administration produced a significant decrease in the number of conceptuses compared to control. Moreover, UPA-treated females exhibited a lower number of early implantation sites on Day E5.5, despite normal in vivo embryo development and transport to the uterus at E3.5. Administration of UPA produced histological and functional alterations in the uterine horns, i.e., a dyssynchronous growth between endometrial glands and stroma, with non-physiological combination of both fractions compared to controls, and a completely impaired ability to respond to an artificial decidualization stimulus. Altogether, our results show that the administration of a single post-ovulatory dose of UPA impairs mouse pregnancy probably due to an effect on embryo-uterine interaction, supporting additional effects of the drug on post-fertilization events. Although these studies cannot be performed with human samples, our results with the mouse model provide new insights into the mechanism of action of UPA as an emergency contraception method.

Male-mediated prenatal loss: Functions and mechanisms

Sexually selected infanticide has been the subject of intense empirical and theoretical study for decades; a related phenomenon, male-mediated prenatal loss, has received much less attention in evolutionary studies. Male-mediated prenatal loss occurs when inseminated or pregnant females terminate reproductive effort following exposure to a nonsire male, either through implantation failure or pregnancy termination. Male-mediated prenatal loss encompasses two sub-phenomena: sexually selected feticide and the Bruce effect. In this review, we provide a framework that explains the relationship between feticide and the Bruce effect and describes what is known about the proximate and ultimate mechanisms involved in each. Using a simple model, we demonstrate that male-mediated prenatal loss can provide greater reproductive benefits to males than infanticide. We therefore suggest that, compared to infanticide, male-mediated prenatal loss may be more prevalent in mammalian species and may have played a greater role in their social evolution than has previously been documented.

Association of foetal size and sex with porcine foeto-maternal interface integrin expression

Integrins regulate adhesion at the foeto-maternal interface by interacting with secreted phosphoprotein 1 (SPP1) and fibronectin (FN). It is hypothesised that impaired foetal growth of ‘runt’ piglets is linked to altered integrin signalling at the foeto-maternal interface. Placental and endometrial samples associated with the lightest and closest to mean litter weight (CTMLW) (gestational day (GD18, 30, 45, 60 and 90), of both sex (GD30, 45, 60 and 90) (n = 5–8 litters/GD), Large White × Landrace conceptuses or foetuses were obtained. The mRNA expression of the integrin subunits (ITG) ITGA2, ITGAV, ITGB1, ITGB3, ITGB5, ITGB6, ITGB8, SPP1 and FN was quantified by qPCR. Temporal changes in mRNA expression were observed, with different profiles in the two tissues. Endometrial ITGB1 (P ≤ 0.05, GD45) and SPP1 (P ≤ 0.05, all GD combined and GD60) expression was decreased in samples supplying the lightest compared to the CTMLW foetuses. Placentas supplying female foetuses had decreased expression of ITGB6 (GD45, P ≤ 0.05) and FN (GD90, P ≤ 0.05) compared to those supplying male foetuses. Endometrial samples supplying females had increased ITGB3 (P ≤ 0.05, GD60) and FN (P ≤ 0.05, GD30) expression and decreased SPP1 (P ≤ 0.05, GD60) expression compared to male foetuses. Correlations between mean within-gilt mRNA expression and percentage prenatal survival, number of live foetuses or conceptuses and percentage male foetuses were observed. This study has highlighted novel and dynamic associations between foetal size, sex and integrin subunit mRNA expression at the porcine foeto-maternal interface. Further studies should be performed to improve the understanding of the mechanisms behind these novel findings.

Fine-tuned adaptation of embryo-endometrium pairs at implantation revealed by transcriptome analyses in Bos taurus

Interactions between embryo and endometrium at implantation are critical for the progression of pregnancy. These reciprocal actions involve exchange of paracrine signals that govern implantation and placentation. However, it remains unknown how these interactions between the conceptus and the endometrium are coordinated at the level of an individual pregnancy. Under the hypothesis that gene expression in endometrium is dependent on gene expression of extraembryonic tissues and genes expressed in extraembryonic tissues are dependent of genes expressed in the endometrium, we performed an integrative analysis of transcriptome profiles of paired extraembryonic tissue and endometria obtained from cattle (Bos taurus) pregnancies initiated by artificial insemination. We quantified strong dependence (|r| > 0.95, empirical false discovery rate [eFDR] < 0.01) in transcript abundance of genes expressed in the extraembryonic tissues and genes expressed in the endometrium. The profiles of connectivity revealed distinct coexpression patterns of extraembryonic tissues with caruncular and intercaruncular areas of the endometrium. Notably, a subset of highly coexpressed genes between extraembryonic tissue (n = 229) and caruncular areas of the endometrium (n = 218, r > 0.9999, eFDR < 0.001) revealed a blueprint of gene expression specific to each pregnancy. Gene ontology analyses of genes coexpressed between extraembryonic tissue and endometrium revealed significantly enriched modules with critical contribution for implantation and placentation, including “in utero embryonic development,” “placenta development,” and “regulation of transcription.” Coexpressing modules were remarkably specific to caruncular or intercaruncular areas of the endometrium. The quantitative association between genes expressed in extraembryonic tissue and endometrium emphasize a coordinated communication between these two entities in mammals. We provide evidence that implantation in mammalian pregnancy relies on the ability of the extraembryonic tissue and the endometrium to develop a fine-tuned adaptive response characteristic of each pregnancy.

An integrative analysis of interactions between conceptus and endometrium, in cattle, reveals complex regulatory networks operating at the time of implantation, highlighting the unique transcriptional blueprint of conceptus-maternal communication

Implantation in mammals requires a complex crosstalk between the conceptus (the embryo and associated membranes) and the uterus. An imbalanced regulation of the factors contributing to these interactions has negative impacts on the attachment of the fetus, the progression of the pregnancy, and the progeny. Focusing on paired conceptus–endometrium analyses of individual pregnancies in cows, we have determined that communication at implantation encompasses synchronized genome-wide coregulation of genes. Gene regulatory interactions between one conceptus and the surrounding maternal tissue vary between endometrial regions containing or lacking glands. Our data reveal new insights, to our knowledge, on the coordination of molecular mechanisms that contribute to implantation and pregnancy establishment in mammals. We conclude that the biological response of the endometrium is embryo-specific, a phenomenon that deserves further investigation in the context of assisted reproductive technologies.

Integrative analysis of the forkhead box A2 (FOXA2) cistrome for the human endometrium

The pioneer forkhead box (FOX)A2 transcription factor is specifically expressed in the glands of the uterus, which are central to endometrial function and fertility. In mice, FOXA2 is a critical regulator of uterine gland development in the neonate and gland function in the adult. An integrative approach was used here to define the FOXA2 cistrome in the human endometrium. Genome-wide mapping of FOXA2 binding intervals by chromatin immunoprecipitation sequencing was performed using proliferative (P)- and midsecretory (MS)-phase endometrium and integrated with the transcriptome determined by RNA sequencing. Distinctive FOXA2 binding intervals, enriched for different transcription factor binding site motifs, were detected in the P and MS endometrium. Pathway analysis revealed different biologic processes regulated by genes with FOXA2 binding intervals in the P and MS endometrium. Thus, FOXA2 is postulated to regulate gene expression in concert with other transcription factors and impact uterine gland development and function in a cycle phase-dependent manner. Analyses also identified potential FOXA2-regulated genes that influence uterine receptivity, blastocyst implantation, and stromal cell decidualization, which are key events in pregnancy establishment.-Kelleher, A. M., Behura, S. K., Burns, G. W., Young, S. L., DeMayo, F. J., Spencer, T. E. Integrative analysis of the forkhead box A2 (FOXA2) cistrome for the human endometrium.

Progesterone governs endometrial proliferation-differentiation switching and blastocyst implantation

Blastocyst implantation contains the following three processes: apposition, attachment, and invasion of the blastocyst. Ovarian hormone progesterone (P₄) regulates these processes exquisitely. P₄-induced molecular communications between the endometrial epithelium and stroma as well as endometrial proliferation-differentiation switching (PDS) until blastocyst attachment are fundamental steps in blastocyst implantation. Based on the knowledge obtained from the previous studies of mouse models by my group and others, this article outlines how P₄ directs the uterus to complete blastocyst implantation.

Cytometric assessment of uterine receptivity via epithelial β3 integrin expression

RESEARCH QUESTION

Many techniques now exist to assess the receptivity status of the endometrium. Can a simple low-cost flow cytometric technique be used to rapidly assess uterine receptivity via a luteal phase endometrial biopsy?

DESIGN

Epithelial β3 integrin (EB3) evaluation was undertaken in 300 women presenting with repeated implantation failure or recurrent pregnancy loss who subsequently underwent 710 assisted reproductive technology (ART) cycles. Endometrial tissue was mechanically dissociated and evaluated using specific antibodies to capture integrin expression. Autologous and donor oocyte embryo transfers were evaluated. A 'High', 'Borderline' and 'Low' grading system was developed based on the pattern and percentage expression of EB3 relative to the total endometrial epithelium. Clinical outcomes of the resulting embryo transfers (n = 559) were analysed according to EB3 grading.

RESULTS

Based on 180 completed transfers, the clinical pregnancy rate (CPR) per embryo transferred in the donor egg cycles was 41.7%. EB3 results from women with a 'High' grading showed a superior CPR (54.0%) compared with 'Low' (22.2% CPR) or 'Borderline' (37.4%) cases (P = 0.024). Similarly, following 379 autologous oocyte transfers, the CPR was 36.1% overall, with major variations between the 'High' (43.8%), 'Low' (17.5%) and 'Borderline' (34.8%) groups (P = 0.0008). Implantation rates showed similar significant trends in the 'High' versus 'Low' groups of 40.4% versus 16% (P = 0.048) in donor oocyte transfers, and 30.8% versus 16.1% (P = 0.025) in autologous oocyte transfers.

CONCLUSIONS

The distribution patterns and percentage expression of EB3 assessed by a flow cytometry grading system shows a significant relationship to implantation rate and CPR success in ART cycles and may thus represent a useful additional tool for the assessment of uterine receptivity.

Gestational age-specific reference values of placental thickness in normal pregnant women

The aim of this study was to determine the reference values of the placental thickness in 400 normal pregnant women during weeks 16-41 of gestation who were referred to the Mahdiyeh hospital during January 2014-February 2015. The placental thickness at the junction of the umbilical artery was measured using ultrasonography. Multivariable linear regression was used to model the mean placental thickness and assess associations with measured covariates, including gestational age (GA). Centiles for placental thickness distribution were estimated according to the modulus exponential-normal model. The mean and standard deviation of the age of the participants was 31.4 ± 5.7 years. The Pearson correlation coefficient indicated a very strong positive linear correlation between GA and placental thickness (p <.001; r = 0.93). A nonlinear increase of placental thickness with estimated fetal weights was observed. GA-specific placental thicknesses for the 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97.5th percentiles of placental thickness were calculated. By making use of the provided nomogram in this study, neonatal outcomes associated with the placental thickness, such as Hemoglobin Bart's disease, can be diagnosed early to improve maternal and newborn health.

Early Pregnancy Human Decidua is Enriched with Activated, Fully Differentiated and Pro-Inflammatory Gamma/Delta T Cells with Diverse TCR Repertoires

Pregnancy is a state where high and stage-dependent plasticity of the maternal immune system is necessary in order to equilibrate between immunosuppression of harmful responses towards the fetus and ability to fight infections. TCR γδ cells have been implicated in the responses in infectious diseases, in the regulation of immune responses, and in tissue homeostasis and repair. The variety of functions makes γδ T cells a particularly interesting population during pregnancy. In this study, we investigated the proportion, phenotype and TCR γ and δ repertoires of γδ T cells at the maternal–fetal interface and in the blood of pregnant women using FACS, immunohistochemistry and spectratyping. We found an enrichment of activated and terminally differentiated pro-inflammatory γδ T-cell effectors with specific location in the human decidua during early pregnancy, while no significant changes in their counterparts in the blood of pregnant women were observed. Our spectratyping data revealed polyclonal CDR3 repertoires of the δ1, δ2 and δ3 chains and γ2, γ3, γ4 and γ5 chains and oligoclonal and highly restricted CDR3γ9 repertoire of γδ T cells in the decidua and blood of pregnant women. Early pregnancy induces recruitment of differentiated pro-inflammatory γδ T-cell effectors with diverse TCR repertoires at the maternal–fetal interface.

Platelet-rich plasma or blood-derived products to improve endometrial receptivity?

The use of platelet-rich plasma (PRP) to improve endometrial receptivity is gaining increasing attention in assisted reproduction technologies. The authors report that autologous PRP intrauterine administration improves pregnancy and birth rates, particularly in cases of patients presenting poor endometrial growth. Different groups of scientists proposed a similar approach years ago using whole blood-derived products also to improve endometrial receptivity. The important role played by cytokines and growth factors during embryo implantation has been well-known for a long time. These signaling molecules are present and released by blood cells during physiological, normal endometrial growth and implantation. Similar blood mediators are released from platelet granules upon a blood vessel injury. Methods described for PRP preparation for intrauterine administration are not precise, and they seem to be similar to those used to prepare peripheral blood-derived products. Thus, it is possible that when preparing PRP from whole blood, the final plasma product used as "PRP" contains platelets in addition to the important cytokines and growth factors released by the peripheral blood mononuclear cells present in the whole blood. Precise knowledge of the identity, concentration, and effects of the individual blood factors, their origin, whether platelets or blood mononuclear cells, will greatly contribute to improve and to make results obtained in fertility treatments more repeatable.

Electroacupuncture facilitates implantation by enhancing endometrial angiogenesis in a rat model of ovarian hyperstimulation

Controlled ovarian hyperstimulation (COH) impairs the synchronized development of endometrium and embryo, resulting in the failure of embryo implantation. Here, we investigated what effects electroacupuncture had on embryo implantation in COH rats. Female rats were randomly assigned to four groups: normal (N), model (M), electroacupuncture (EA), and electroacupuncture pretreatment (PEA). Rats in groups M, EA, PEA were injected with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin to establish the COH model. Rats in group EA received electroacupuncture treatment from the PMSG injection day to the 3rd day of pregnancy (D3), while those in group PEA received electroacupuncture treatment for 3 days before the PMSG day and continuing to D3. Furthermore, another 30 female rats who received the same treatment as the rats in group PEA were injected with siVEGFR2 into uterine lumen. The endometrial microvascular density (MVD) and the expression levels of vascular endothelial growth factor-A, angiopoietin-1, and fibroblast growth factor-2 were significantly lower in groups M than in groups N and PEA. The percentage of dolichos biflorus agglutinin positive uterine natural killer cells in groups N, EA and PEA was higher than that in group M. After the siVEGFR2 injection, the protein expression levels of vascular endothelial growth factor receptor 2 (VEGFR2), PI3K, p-AKT and p-ERK, the embryo number and the MVD were significantly reduced. In conclusion, electroacupuncture can facilitate embryo implantation in COH rats by activating the VEGFR2/PI3K/AKT and VEGFR2/ERK signaling pathways which have a positive relationship with endometrial angiogenesis.

Role of mTOR Signaling in Female Reproduction

Mammalian target of rapamycin (mTOR) is a conserved serine/threonine kinase of the phosphatidylinositol kinase-related kinase family that regulates cell growth, metabolism, and autophagy. Extensive research has linked mTOR to several human diseases including cancer, neurodegenerative disorders, and aging. In this review, recent publications regarding the mechanisms underlying the role of mTOR in female reproduction under physiological and pathological conditions are summarized. Moreover, we assess whether strategies to improve or suppress mTOR expression could have therapeutic potential for reproductive diseases like premature ovarian failure, polycystic ovarian syndrome, and endometriosis.

Calcitonin administration improves endometrial receptivity via regulation of LIF, Muc-1 and microRNA Let-7a in mice

Calcitonin (CT) is one of the factors affecting the embryo implantation, but its effects on the implantation window have not been fully investigated. The current study investigated the effects of CT on the endometrium receptivity by morphological study and evaluation of leukemia inhibitory factor (LIF), mucin 1 (Muc-1), and microRNA (miRNA) Let-7a in the ovarian stimulation and the normal ovarian cycle. Then the mechanism of the CT effects through the mammalian target of rapamycin (mTOR) signaling pathway was studied by using PP242. A total of 64 BALB/c mice were divided into the normal ovarian cycle and ovarian stimulation groups. Each group consisted of four subgroups: control, calcitonin, PP242, and calcitonin+PP242. CT and PP242 were injected on the fourth of pregnancy into the mice and 24 hr later all the mice were killed. The uterine tissue samples were used for morphological analysis, and endometrial cells were mechanically isolated for evaluation of gene and protein expression. The results showed that ovarian stimulation induced mTOR phosphorylation as well as increased expression of the Let-7a miRNA. In addition, CT injection increased the expression of LIF and miRNA Let-7a in ovarian stimulation similar to that in normal ovarian cycles. However, injection of PP242 reduced expression of miRNA Let-7a and increased Muc-1 expression in ovarian stimulation group. In conclusion, the administration of CT improved endometrial receptivity in mice. This phenomenon occurred by upregulation of LIF, miRNA Let-7a and downregulation of Muc-1 via mTOR signaling pathway.

2-Methoxyoestradiol impairs mouse embryo implantation via F-spondin

The anti-implantation effects of high oestradiol (E2) concentrations could be mediated by E2 metabolites. Herein, we examined whether 2-methoxyoestradiol (2ME) impairs embryo implantation via its target protein F-spondin. Mice on Day 3 of pregnancy were treated with E2 concomitantly with the cathecol-O-methyl transferase inhibitor OR486 and the number of implanted embryos was recorded 5 days later. The effect of 2ME or 4-methoxyoestradiol (4ME) on embryo implantation was also investigated. Plasma and uterine levels of 2ME were measured 0.5, 1 or 3h after E2 treatment while the mRNA for spondin 1 (Spon1) and F-spondin were determined in the uterus 3, 6, 12 or 24h after 2ME treatment. Finally, the effect of a neutralising F-spondin antibody on the anti-implantation effect of 2ME was explored. OR486 blocked the anti-implantation effect of E2; 2ME, but not 4ME, affected embryo implantation. The 2ME concentration was increased after 0.5 and 1h in plasma and 3h in uterine fluid following E2 treatment. 2ME increased levels of Spon1 at 12 and 24h although F-spondin was increased at 12h. F-spondin antibody blocked the effect of 2ME on embryo implantation. We conclude that 2ME impairs mouse embryo implantation via activation of F-spondin in the uterus.

Retinoid signaling controlled by SRC-2 in decidualization revealed by transcriptomics

Establishment of a successful pregnancy requires not only implantation of a healthy embryo into a receptive uterus but also progesterone receptor (PGR)-dependent transformation of endometrial stromal cells (ESCs) into specialized decidual cells. Decidual cells support the developing embryo and are critical for placentation. We have previously shown that a known transcriptional coregulator of the PGR, steroid receptor coactivator-2 (SRC-2), is a critical driver of endometrial decidualization in both human and mouse endometrium. However, the full spectrum of genes transcriptionally controlled by SRC-2 in decidualizing ESCs has not been identified. Therefore, using an RNA- and chromatin immunoprecipitation-sequencing approach, we have identified the transcriptome of decidualizing human ESCs (hESCs) that requires SRC-2. We revealed that the majority of hESC genes regulated by SRC-2 are associated with decidualization. Over 50% of SRC-2-regulated genes are also controlled by the PGR. While ontology analysis showed that SRC-2-dependent genes are functionally linked to signaling processes known to underpin hESC decidualization, cell membrane processes were significantly enriched in this analysis. Follow-up studies showed that retinoid signaling is dependent on SRC-2 during hESC decidualization. Specifically, SRC-2 is required for full induction of the retinol transporter, stimulated by retinoic acid 6 (STRA6), which is essential for hESC decidualization. Together our findings show that a critical subset of genes transcriptionally reprogramed by PGR during hESC decidualization requires SRC-2. Among the multiple genes, pathways and networks that are dependent on SRC-2 during hESC decidualization, first-line analysis supports a critical role for this coregulator in maintaining retinoid signaling during progesterone-driven decidualization.

Partial ablation of endometrial glands in dogs after exposure to progestin during the neonatal period

Bitches with uteri devoid of endometrial glands should be sterile, and consequently could contribute to the population control of dogs. Considering that an inadequate exposure of the female reproductive system to steroids can lead to the formation of the uterine gland knock-out (UGKO) phenotype in some species, the aim of this study was to evaluate the effect of serial applications of medroxyprogesterone acetate (MPA) from birth until the age of six months on the development of endometrial glands in bitches. For this purpose, 16 female mongrel dogs from different litters were distributed into either an MPA group (n = 8), animals treated with 10 mg kg sc (Promone-E^®, Pfizer, Brasil) at 3-week intervals, from day one after birth until the age of six months, or a control group (n = 8), composed of animals that only received a 0.9% NaCl solution in place of MPA. At six months of age, ovariohysterectomy was performed and uterine horn samples were collected for histological and immunohistochemical examinations. The bitches from the MPA-treated group presented a 35% decrease in the number of endometrial glands, a larger diameter of the endometrial glands, a greater epithelial height, as well as a greater thickness of the uterine wall, endometrium, and myometrium. However, no significant differences were observed between the two groups in the expression of ER-α, ER-β, and PR on the surface epithelium and endometrial stroma. Therefore, the serial application of MPA from birth until the age of 6 months do not completely ablate the development of the endometrial glands in bitches, but impair it by 35%.

Soluble Delta-like ligand 1 alters human endometrial epithelial cell adhesive capacity

The endometrium undergoes substantial morphological and functional changes to become receptive to embryo implantation and to enable establishment of a successful pregnancy. Reduced Delta-like ligand 1 (DLL1, Notch ligand) in the endometrium is associated with infertility. DLL1 can be cleaved by 'a disintegrin and metalloprotease' (ADAM) proteases to produce a soluble ligand that may act to inhibit Notch signalling. We used an enzyme-linked immunosorbent assay to quantify soluble DLL1 in uterine lavages from fertile and infertile women in the secretory phase of the menstrual cycle. We also determined the cellular location and immunostaining intensity of ADAM12 and 17 in human endometrium throughout the cycle. Functional effects of soluble DLL1 in receptivity were analysed using in vitro adhesion and proliferation assays and gene expression analysis of Notch signalling targets. Soluble DLL1 was significantly increased in uterine lavage samples of infertile women compared with fertile women in the secretory phase of the menstrual cycle. This coincided with significantly increased ADAM17 immunostaining detected in the endometrial luminal epithelium in the mid-secretory phase in infertile women. Soluble DLL1 significantly inhibited the adhesive capacity of endometrial epithelial cells via downregulation of helix-loop-helix and hairy/enhancer of split family member HES1 mRNA. Thus, soluble DLL1 may serve as a suitable target or potential biomarker for receptivity.

Mechanisms for the establishment and maintenance of pregnancy: synergies from scientific collaborations

Research on the functions of interferon tau (IFNT) led to the theory of pregnancy recognition signaling in ruminant species. But IFNT does much more as it induces expression of interferon regulatory factor 2 (IRF2) in uterine luminal (LE), superficial glandular (sGE), but not glandular (GE) epithelia. First, IRF2 silences transcription of the estrogen receptor alpha gene and, indirectly, transcription of the oxytocin receptor gene to abrogate development of the luteolytic mechanism to prevent regression of the corpus luteum and its production of progesterone for establishing and maintaining pregnancy. Second, IRF2 silences expression of classical interferon-stimulated genes in uterine LE and sGE; however, uterine LE and sGE respond to progesterone (P4) and IFNT to increase expression of genes for transport of nutrients into the uterine lumen such as amino acids and glucose. Other genes expressed by uterine LE and sGE encode for adhesion molecules such as galectin 15, cathepsins, and cystatins for tissue remodeling, and hypoxia-inducible factor relevant to angiogenesis and survival of blastocysts in a hypoxic environment. IFNT is also key to a servomechanism that allows uterine epithelia, particularly GE, to proliferate and to express genes in response to placental lactogen and placental growth hormone in sheep. The roles of secreted phosphoprotein 1 are also discussed regarding its role in implantation in sheep and pigs, as well as its stimulation of expression of mechanistic target of rapamycin mRNA and protein which is central to proliferation, migration, and gene expression in the trophectoderm cells.

Endometrial response to conceptus-derived estrogen and interleukin-1β at the time of implantation in pigs

The establishment of pregnancy is a complex process that requires a well-coordinated interaction between the implanting conceptus and the maternal uterus. In pigs, the conceptus undergoes dramatic morphological and functional changes at the time of implantation and introduces various factors, including estrogens and cytokines, interleukin-1β2 (IL1B2), interferon-γ (IFNG), and IFN-δ (IFND), into the uterine lumen. In response to ovarian steroid hormones and conceptus-derived factors, the uterine endometrium becomes receptive to the implanting conceptus by changing its expression of cell adhesion molecules, secretory activity, and immune response. Conceptus-derived estrogens act as a signal for maternal recognition of pregnancy by changing the direction of prostaglandin (PG) F_2α from the uterine vasculature to the uterine lumen. Estrogens also induce the expression of many endometrial genes, including genes related to growth factors, the synthesis and transport of PGs, and immunity. IL1B2, a pro-inflammatory cytokine, is produced by the elongating conceptus. The direct effect of IL1B2 on endometrial function is not fully understood. IL1B activates the expression of endometrial genes, including the genes involved in IL1B signaling and PG synthesis and transport. In addition, estrogen or IL1B stimulates endometrial expression of IFN signaling molecules, suggesting that estrogen and IL1B act cooperatively in priming the endometrial function of conceptus-produced IFNG and IFND that, in turn, modulate endometrial immune response during early pregnancy. This review addresses information about maternal-conceptus interactions with respect to endometrial gene expression in response to conceptus-derived factors, focusing on the roles of estrogen and IL1B during early pregnancy in pigs.

Bushen Huoxue Recipe Alleviates Implantation Loss in Mice by Enhancing Estrogen-Progesterone Signals and Promoting Decidual Angiogenesis Through FGF2 During Early Pregnancy

Bushen Huoxue recipe (BSHXR) is a classic Chinese herbal prescription for nourishing the kidney and activating blood circulation. It consists of six herbs: Astragali radix, Angelicae sinensis radix, Ligustici Chuanxiong Rhizoma, Cuscutae semen, Taxilli Herba, and Dipsaci Radix, and the main active constituents of BSHXR are ferulic acid, calycosin-7-glucopyranoside, hyperoside, quercitrin, and asperosaponin VI. In clinical practice, BSHXR is traditionally used to treat failed pregnancy and its complications. However, little is known about the underlying mechanism of BSHXR for the treatment of implantation loss during early pregnancy. In the current study, controlled ovarian hyperstimulation was induced in mice as our implantation loss model, and we evaluated the effects of BSHXR on implantation, decidualization, decidual angiogenesis, and reproductive outcome. We showed that BSHXR could regulate the supraphysiological levels of serum estrogen and progesterone observed in these mice, and also act on estrogen and progesterone receptors in the stroma and epithelium. BSHXR also enhanced FGF2 expression in the vascular sinus folding area of the decidua, thus potentially reducing implantation loss during early pregnancy and contributing to placentation and survival of the fetuses. Taken together, our findings provide scientific evidence for the application of BSHXR in the clinic as a treatment for implantation loss during early pregnancy, and warrant further investigation of BSHXR as an effective treatment for failed pregnancy and its complications.

Growth regulation by estrogen in breast cancer 1 (GREB1) is a novel progesterone-responsive gene required for human endometrial stromal decidualization

STUDY QUESTION

Is Growth Regulation by Estrogen in Breast Cancer 1 (GREB1) required for progesterone-driven endometrial stromal cell decidualization?

SUMMARY ANSWER

GREB1 is a novel progesterone-responsive gene required for progesterone-driven human endometrial stromal cell (HESC) decidualization.

WHAT IS KNOWN ALREADY

Successful establishment of pregnancy requires HESCs to transform from fibroblastic to epithelioid cells in a process called decidualization. This process depends on the hormone progesterone, but the molecular mechanisms by which it occurs have not been determined.

STUDY DESIGN, SIZE, DURATION

Primary and transformed HESCs in which GREB1 expression was knocked down were decidualized in culture for up to 6 days. Wild-type and progesterone receptor (PR) knockout mice were treated with progesterone, and their uteri were assessed for levels of GREB1 expression.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Analysis of previous data included data mining of expression profile data sets and in silico transcription factor-binding analysis. Endometrial biopsies obtained from healthy women of reproductive age during the proliferative phase (Days 8-12) of their menstrual cycle were used for isolating HESCs. Experiments were carried out with early passage (no more than four passages) HESCs isolated from at least three subjects. Transcript levels of decidualization markers prolactin (PRL) and insulin-like growth factor-binding protein-1 (IGFBP-1) were detected by quantitative RT-PCR as readouts for HESC decidualization. Cells were also imaged by phase-contrast microscopy. To assess the requirement for GREB1, PR and SRC-2, cells were transfected with specifically targeted small interfering RNAs. Results are shown as mean and SE from three replicates of one representative patient-derived primary endometrial cell line. Experiments were also conducted with transformed HESCs.

MAIN RESULTS AND THE ROLE OF CHANCE

Progesterone treatment of mice and transformed HESCs led to an ~5-fold (5.6 ± 0.81, P < 0.05, and 5.2 ± 0.26, P < 0.01, respectively) increase in GREB1 transcript levels. This increase was significantly reduced in the uteri of PR knock-out mice (P < 0.01), in HESCs treated with the PR antagonist RU486 (P < 0.01), or in HESCs in which PR expression was knocked down (P < 0.05). When GREB1 expression was knocked down, progesterone-driven decidualization markers in both immortalized and primary HESCs was significantly reduced (P < 0.05 and P < 0.01). Finally, GREB1 knock down signficantly reduced expression of the PR target genes WNT4 and FOXOA1 (P < 0.05 and P < 0.01, respectively).

LARGE SCALE DATA

This study used the Nuclear Receptor Signaling Atlas.

LIMITATIONS, REASONS FOR CAUTION

Although in vitro cell culture studies indicate that GREB1 is required for endoemtrial decidualization, the in vivo role of GREB1 in endometrial function and dysfunction should be assessed by using knock-out mouse models.

WIDER IMPLICATIONS OF THE FINDINGS

Identification and functional analysis of GREB1 as a key molecular mediator of decidualization may lead to improved diagnosis and clinical management of women with peri-implantation loss due to inadequate endometrial decidualization.

STUDY FUNDING AND COMPETING INTEREST(S)

This research was funded in part by: a National Institutes of Health (NIH)/ National Institute of Child Health and Human Development (NICHD) grant (R00 HD080742) and Washington University School of Medicine start-up funds to R.K., an NIH/NICHD grant (RO1 HD-07857) to B.W.O.M., and a NIH/NICHD grant (R01 HD-042311) to J.P.L. The authors declare no conflicts of interests.

Expression and function of Pdcd4 in mouse endometrium during early pregnancy

Embryo implantation is a complex process involving synchronised crosstalk between a receptive endometrium and functional blastocysts. Apoptosis plays an important role in this process as well as in the maintenance of pregnancy. In this study, we analysed the expression pattern of programmed cell death 4 (Pdcd4), a gene associated with apoptosis in the mouse endometrium, during early pregnancy and pseudopregnancy by real-time quantitative polymerase chain reaction, in situ hybridisation, Western blotting and immunohistochemistry. The results showed that Pdcd4 was increased along with days of pregnancy and significantly reduced at implantation sites (IS) from day 5 of pregnancy (D5). The level of Pdcd4 at IS was substantially lower than that at interimplantation sites (IIS) on D6 and D7. In addition, Pdcd4 expression in the endometrium was reduced in response to artificially induced decidualisation in vivo and in vitro. Downregulation of Pdcd4 gene expression in cultured primary stromal cells promoted decidualisation, while upregulation inhibited the decidualisation process by increasing apoptosis. These results demonstrate that Pdcd4 is involved in stromal cell decidualisation by mediating apoptosis and therefore plays a role in embryo implantation in mice.

Selective estrogen receptor modulator ormeloxifene suppresses embryo implantation via inducing miR-140 and targeting insulin-like growth factor 1 receptor in rat uterus

Ormeloxifene, the non-steroidal SERM contraceptive, inhibits endometrial receptivity and embryo implantation via countering nidatory estrogen. However, the molecular mechanism of ormeloxifene action responsible for its contraceptive efficacy still remains unclear. Herein, we aimed to identify the miRNAs modulated under the influence of ormeloxifene and to explore their role in endometrial receptivity and embryo implantation. By doing microRNA sequencing analysis, a total of 168 miRNAs were found to be differentially expressed in uterine tissue of ormeloxifene-treated rats, on day 5 (10:00 h) of pregnancy i.e. peri-implantation period. Out of differentially expressed miRNAs, miR-140 expression was found to be elevated in ormeloxifene administered groups and was selected for detailed investigation. In-vivo gain-of-function of miR-140 resulted in a significant reduction of implantation sites indicating its role in embryo implantation. The experiment on delayed implantation showed that estradiol caused down-regulation of miR-140. It also suppressed the attachment and outgrowth of BeWo spheroids to RL95-2 endometrial cells. In transwell migration assay, miR-140 was found to be involved in suppression of migration and invasion of endometrial epithelial cells. The ormeloxifene treatment caused up-regulation of miR-140 along with down-regulated expression of its target IGF1R in endometrial epithelial and stromal cells which also led to the suppression of downstream effectors integrin β3 and FAK. In mimic miR-140 receiving horn, the reduced expression of IGF1R was observed along with suppressed downstream integrin β3 and FAK similar to that observed in uteri of ormeloxifene- treated rats. Taken together, these findings suggest that ormeloxifene-induced inhibition of embryo implantation occurs via inducing miR-140 and altering its target IGF1R in rat uterus.

Hyperglycemia-induced mouse trophoblast spreading is mediated by reactive oxygen species

During embryo implantation, the outer layer of the blastocyst interacts with the endometrium giving rise to the development of the trophoblast cell lineage. The cells in this lineage participate in the penetration of endometrium due to their motility and invasive properties. The mechanisms that regulate the differentiation and invasive ability of these cells are essential for the establishment and maintenance of an efficient exchange between maternal and fetal tissues during pregnancy. In this context, hyperglycemia can induce oxidative stress causing alterations in the placenta. This study evaluated the role of reactive oxygen species (ROS) in the actions of high glucose concentration (HG) on trophoblast spreading and the expression of extracellular proteases in cultured mouse conceptuses. Blastocysts from gestational day 4 (GD4) were cultured until GD7 in HAM-F10 medium and further treated for 48 hr with HG (25 mM glucose) from GD7 to GD9. This treatment induced larger trophoblast outgrowths and increased ROS concentration, which was associated with increased expression levels of urokinase-type plasminogen activator (PLAU), plasminogen activator inhibitor 1 (PAI-1), and matrix metalloproteinase 9 (MMP-9). These effects were prevented by treatment with the non-specific antioxidant N-acetylcysteine (NAC) or apocynin, an inhibitor of NADPH oxidase. Our data suggest that the HG-induced trophoblast spreading and the expression of PLAU, PAI-1, and MMP-9 were mediated by the production of ROS via NADPH oxidase activity. Our results shed light on placental alterations in gestational diabetes mellitus.

Roles of DEK in the endometrium of mice in early pregnancy

Embryo implantation is a complex process requiring reciprocal interactions between implantation-competent blastocysts and receptive uteri. Accumulating evidence from Digital Protein Expression Profiling indicates that DEK protein expression at implantation sites (ISs) was much higher than that at inter-implantation sites (IISs). In this study, we investigated the expression of DEK in mouse uterus by immunohistochemistry (IHC), Western blotting. We explored its function during decidualization of uterine stromal cells by inhibiting the expression of DEK. In further study of mechanism, the cell proliferation, apoptosis and DNA damage were detected after inhibiting DEK during decidualization of stromal cells. The results suggest that DEK participates in decidualization of stromal cells through mediating cell proliferation, apoptosis and DNA repair.

Leptin action in normal and pathological pregnancies

Leptin is now considered an important signalling molecule of the reproductive system, as it regulates the production of gonadotrophins, the blastocyst formation and implantation, the normal placentation, as well as the foeto-placental communication. Leptin is a peptide hormone secreted mainly by adipose tissue, and the placenta is the second leptin-producing tissue in humans. Placental leptin is an important cytokine which regulates placental functions in an autocrine or paracrine manner. Leptin seems to play a crucial role during the first stages of pregnancy as it modulates critical processes such as proliferation, protein synthesis, invasion and apoptosis in placental cells. Furthermore, deregulation of leptin levels has been correlated with the pathogenesis of various disorders associated with reproduction and gestation, including polycystic ovary syndrome, recurrent miscarriage, gestational diabetes mellitus, pre-eclampsia and intrauterine growth restriction. Due to the relevant incidence of the mentioned diseases and the importance of leptin, we decided to review the latest information available about leptin action in normal and pathological pregnancies to support the idea of leptin as an important factor and/or predictor of diverse disorders associated with reproduction and pregnancy.

Chromatin Remodelling Proteins and Cell Fate Decisions in Mammalian Preimplantation Development

The very first cell divisions in mammalian embryogenesis produce a ball of cells, each with the potential to form any cell in the developing embryo or placenta. At some point, the embryo produces enough cells that some are located on the outside of the embryo, while others are completely surrounded by other cells. It is at this point that cells undergo the very first lineage commitment event: outer cells form the trophectoderm and lose the potential to form embryonic lineages, while inner cells form the Inner Cell Mass, which retain embryonic potential. Cell identity is defined by gene expression patterns, and gene expression is largely controlled by how the DNA is packaged into chromatin. A number of protein complexes exist which are able to use the energy of ATP to remodel chromatin: that is, to alter the nucleosome topology of chromatin. Here, we summarise the evidence that chromatin remodellers play essential roles in the successful completion of preimplantation development in mammals and describe recent efforts to understand the molecular mechanisms through which chromatin remodellers facilitate the successful completion of the first cell fate decisions in mammalian embryogenesis.

Timing of exogenous progesterone administration is critical for embryo development and uterine gene expression in an ovine model of maternal constraint

Progesterone (P4) administration in early pregnancy enhances embryo growth in sheep but is associated with decreased embryo survival. This study examined the effects of exogenous P4 administered during specific time periods between pregnancy Day 0 and Day 6 to determine the critical time point for advancement of embryo growth without pregnancy loss and to examine Day 6 and Day 19 endometrial gene expression. Suffolk (S) embryos were transferred into Cheviot (C) ewes that received exogenous P4 (CP4) on Days 0–3 (CP40–3), Days 0–6 (CP40–6), Days 2–4 (CP42–4) or Days 3–6 (CP43–6). Additionally, S embryos were transferred to C and S ewes that did not receive P4 (CnP4 and SnP4). Day 19 embryos from CP4 ewes were longer (P < 0.05) than those from CnP4 ewes. CP42–4 ewes had embryos of similar size to those of CP40–3 and CP40–6 ewes but had higher pregnancy rates. There was altered expression of genes associated with embryo implantation and histotroph production: diacylglycerol-O-acyltransferase (DGAT2), hepatocyte growth factor (HGF) and prostaglandin endoperoxide synthase 2 (PTSG2) on Day 6 and endometrial galectin 15 (LGALS15) and mucin glycoprotein 1 (MUC1) on Day 19. This suggests that specific timing of P4 administration is critical to the enhanced embryo growth and survival observed. These findings provide a platform for further investigation aimed at advancing embryo development and survival.

Cytokines, growth factors and macromolecules as mediators of implantation in mammalian species

Implantation is one of the most critical steps in mammalian reproduction and implantation failure constitutes a major cause of infertility in both animals and humans. The mechanism of implantation is exclusively under the control of ovarian steroids progesterone and oestrogen whose actions are mediated in a complex phenomenon that involves a number of cytokines and growth factors. According to a plethora of literature on implantation in mammalian species, prominent of these cytokines and growth factor playing crucial roles in implantation include integrin, osteopontin, integrin, insulin-like growth factor and leukaemia inhibitory factor. Others are cluster domain 44, hyaluronan system and many non-adhesive molecules such as glycoprotein mucin 1. In this review, the specific roles played by these molecules are expatiated. Generally, they function as adhesive molecules that facilitate attachment of ligands/proteins on the trophectoderm to their respective receptors on endometrial luminal epithelia or vice versa. Sometimes, they also function as signalling molecules that enhance communication between implanting blastocyst and receptive endometrium. This is of particular importance in embryo culture and embryo transfer where in vitro derived blastocyst unlike the in vivo condition, is not exposed to these substances and hence, their absence may be partly responsible for the low implantation rate observed in the surrogate. Appreciation of the roles played by these cytokines, growth factors and molecules as revealed in this review will spur further research on these topics, facilitate their inclusion in embryo culture media (if positively required) and are considered as vital aspect while developing strategies to improve fertility.

Effect of exogenous progesterone on embryo size and ewe uterine gene expression in an ovine 'dam size' model of maternal constraint

Progesterone (P4), acting via its receptor, regulates uterine function and histotroph production, which are crucial to embryo growth. This study aimed to examine exogenous P4 effects on embryo size and differential endometrial gene expression at Day 19 of gestation using a 'dam size' sheep model of maternal constraint. Purebred Suffolk (S, genotypically large) embryos were transferred into recipient groups of Cheviot (C, genotypically small) or Suffolk ewes that had, or had not, been pre-treated with P4 from Days 0 to 6 of pregnancy. At Day 19S embryos were collected from four experimental groups: P4 pretreated S ewes (SP4; n=5), untreated S ewes (SnP4; n=15), P4 pretreated C ewes (CP4; n=7) and untreated C ewes (CnP4; n=21). Day-19 embryos from CP4 ewes were larger (P<0.05) than those from CnP4 ewes and similar in size (P>0.05) to embryos from SnP4 and SP4 ewes. Expression of mucin 1 (MUC1) and prostaglandin-endoperoxide synthase 2 (PTGS2) was upregulated in uterine horns ipsilateral to the corpus luteum from CP4 ewes. Prostaglandin receptor (PGR), MUC1 and PTGS2 expression was upregulated, whilst cathepsin L (CTSL) and radical S-adenosyl methionine domain-containing 2 (RSAD2) expression was downregulated in the ipsilateral horn of SP4 ewes. This suggests that pretreating ewes with exogenous P4 may alleviate early pregnancy maternal constraint via mechanisms that alter uterine function. However, further research is required to investigate the timing of P4 administration and its impact on conception rates.

Role of microRNAs in embryo implantation

Failure of embryo implantation is a major limiting factor in early pregnancy and assisted reproduction. Determinants of implantation include the embryo viability, the endometrial receptivity, and embryo-maternal interactions. Multiple molecules are involved in the regulation of implantation, but their specific regulatory mechanisms remain unclear. MicroRNA (miRNA), functioning as the transcriptional regulator of gene expression, has been widely reported to be involved in embryo implantation. Recent studies reveal that miRNAs not only act inside the cells, but also can be released by cells into the extracellular environment through multiple packaging forms, facilitating intercellular communication and providing indicative information associated with physiological and pathological conditions. The discovery of extracellular miRNAs shed new light on implantation studies. MiRNAs provide new mechanisms for embryo-maternal communication. Moreover, they may serve as non-invasive biomarkers for embryo selection and assessment of endometrial receptivity in assisted reproduction, which improves the accuracy of evaluation while reducing the mechanical damage to the tissue. In this review, we discuss the involvement of miRNAs in embryo implantation from several aspects, focusing on the role of extracellular miRNAs and their potential applications in assisted reproductive technologies (ART) to promote fertility efficiency.

Endometrial receptivity and conception outcome among women with light menstrual bleeding of unidentified etiology

OBJECTIVE

To investigate endometrial receptivity (ER), conception outcome, and other factors among women with light menstrual bleeding of unidentified etiology.

METHODS

A prospective study was undertaken at a center in China. Between January 1, 2011, and December 31, 2014, women meeting the inclusion criteria (aged 20-35 years, without any history of pregnancy, desire to conceive, follicle-stimulating hormone <10 IU on second or third day of cycle, and regular menstrual periods) were enrolled. Participants with a menstrual blood volume of 5-20 mL formed the study group; others were in the control group. ER measures were obtained by transvaginal Doppler ultrasonography. Serum estradiol and progesterone levels were measured and items of prethrombotic state were screened in mid-luteal phase. Participants were followed up for 1 year to establish conception outcome.

RESULTS

The ER (Salle) score was significantly lower in the study group (n=110) than in the control group (n=330; 9.41 ± 3.02 vs 15.67 ± 2.63, P<0.001). The natural rate of conception within 1 year was lower (60.0% [63/105] vs 72.1% [230/319], P=0.020), and the spontaneous abortion rate in early pregnancy was higher (34.4% [21/61] vs 18.1% [41/227], P=0.006) in the study group than in the control group.

CONCLUSION

Women with light menstrual bleeding of unidentified etiology had an increased prevalence of low ER and poor conception outcome.

Involvement of leptin in the molecular physiology of the placenta

Leptin is a homeostatic regulator in the placenta where it promotes proliferation, protein synthesis and the expression of tolerogenic maternal response molecules such as HLA-G. Leptin also exerts an anti-apoptotic action in placenta controlling the expression of p53 master cell cycle regulator under different stress conditions. On the other hand, leptin is an integrative target of different placental stimuli. The expression of leptin in placenta is regulated by hCG, insulin, steroids, hypoxia and many other growth hormones, suggesting that it might have an important endocrine function in the trophoblastic cells. The leptin expression is induced involving the cAMP/PKA or cAMP/Epac pathways which have profound actions upon human trophoblast function. The activation of PI3K and MAPK pathways also participates in the leptin expression. Estrogens play a central role during pregnancy, particularly 17β-estradiol upregulates the leptin expression in placental cells through genomic and non-genomic actions. The leptin promoter analysis reveals specific elements that are active in placental cells. The transcription factors CREB, AP1, Sp1, NFκB and the coactivator CBP are involved in the placental leptin expression. Moreover, placental leptin promoter is a target of epigenetic marks such as DNA methylation and histone acetylation that regulates not only the leptin expression in placenta during pregnancy but also determines the predisposition of acquiring adult metabolism diseases. Taken together, all these results allow a better understanding of leptin function and regulatory mechanisms of leptin expression in human placental trophoblasts, and support the importance of leptin during pregnancy and in programming adult health.

The TGF-β Family in the Reproductive Tract

The transforming growth factor β (TGF-β) family has a profound impact on the reproductive function of various organisms. In this review, we discuss how highly conserved members of the TGF-β family influence the reproductive function across several species. We briefly discuss how TGF-β-related proteins balance germ-cell proliferation and differentiation as well as dauer entry and exit in Caenorhabditis elegans. In Drosophila melanogaster, TGF-β-related proteins maintain germ stem-cell identity and eggshell patterning. We then provide an in-depth analysis of landmark studies performed using transgenic mouse models and discuss how these data have uncovered basic developmental aspects of male and female reproductive development. In particular, we discuss the roles of the various TGF-β family ligands and receptors in primordial germ-cell development, sexual differentiation, and gonadal cell development. We also discuss how mutant mouse studies showed the contribution of TGF-β family signaling to embryonic and postnatal testis and ovarian development. We conclude the review by describing data obtained from human studies, which highlight the importance of the TGF-β family in normal female reproductive function during pregnancy and in various gynecologic pathologies.

Development of an in vitro model to study uterine functions and early implantation using rat uterine explants

This study was conducted to develop an in vitro model using rat uterine explants to explore complex uterine functions. Rat uterine explants (1-2 mm) were isolated, cultured and further characterized. Steroid hormone treatment of cultured explants showed that both Muc1 and Pr were significantly up-regulated (P < 0.05) by E2. Areg was significantly up-regulated (P < 0.05) by P4 and Igfbp1 was significantly up-regulated (P < 0.05) by the combination of E2 and P4, although, in rat, Igfbp1 is E2-dependent. In vitro decidualization of cultured explants was induced and two potential markers of decidualization, Prl8a2 and Bmp2, were examined. Real-time quantitative PCR data revealed that both Prl8a2 and Bmp2 were significantly up-regulated (P < 0.05) in MPA- and db-cAMP-treated explants compared to the control group of explants. Then, an individual hatched blastocyst and cultured explant was placed in a 96-well (round-bottom U-shaped) plate. Co-culture results showed that stable attachments were observed after 48 h, where embryos were stably attached to the explants and could not be dislodged after mild shaking and/or pipetting. The rates of attachment of embryos to the explants were increased significantly in the P4-treated group (63.6%) compared to the control group (35.5%), after steroid hormone treatment. The rates of attachment were reduced significantly in the E2-treated group (0.0%), where no stable attachments were observed. Despite the necessity of comprehensive investigation, our results suggest that the cultured rat uterine explants can be a useful in vitro model to study uterine functions and early implantation.

IL‑33 restricts invasion and adhesion of trophoblast cell line JEG3 by downregulation of integrin α4β1 and CD62L

Interleukin-33 (IL-33) promotes migration of cancer cells through downregulating the expression of E-cadherin. Previous studies have demonstrated that IL-33 stimulates the proliferation of trophoblasts. However, the effect of IL-33 on the adhesion and invasion of trophoblasts has not been investigated in detail. In the present study, the expression of IL-33 and its receptor, IL-1 receptor-like 1 (ST2), was examined in villi from women during early pregnancy using immunohistochemistry. ST2 expression on human trophoblast and choriocarcinoma cell lines JAR, BeWo, JEG3 and HTR8 was confirmed by flow cytometry (FCM) assay. The effect of recombinant human IL-33 (rhIL-33) on adhesion, invasion and associated molecules was analyzed by cell adhesion, Matrigel invasion and FCM assays. The current study identified that human trophoblasts expressed IL-33 and ST2. RhIL-33 inhibited trophoblast invasion and adhesion, and decreased adhesion and invasion-associated molecules such as integrin α4β1 and CD62L. Therefore, these results suggest that IL-33 may serve an important role in limiting invasion and implantation of trophoblasts by adhesion and invasion-associated molecules, contributing to the formation of the placenta and maintenance of normal pregnancy during early pregnancy.

Endometrial receptivity in the eutopic endometrium of women with endometriosis: it is affected, and let me show you why

The endometrium maintains complex controls on proliferation and apoptosis as part of repetitive menstrual cycles that prepare the endometrium for the window of implantation and pregnancy. The reliance on inflammatory mechanisms for both implantation and menstruation creates the opportunity in the setting of endometriosis for establishment of chronic inflammation that is disruptive to endometrial receptivity, causing both infertility and abnormal bleeding. Clinically, there can be little doubt that the endometrium of women with endometriosis is less receptive to embryo implantation, and strong evidence exists to suggest that endometrial changes are associated with decreased cycle fecundity as a result of this disease. Here we provide unifying concepts regarding those changes and how they are coordinated to promote progesterone resistance and estrogen dominance through aberrant cell signaling pathways and reduced expression of key homeostatic proteins in eutopic endometrium of women with endometriosis.

Effects of Excess Copper Ions on Decidualization of Human Endometrial Stromal Cells

The aim of this study was to investigate the effects of copper ions on decidualization of human endometrial stromal cells (HESCs) cultured in vitro. Firstly, non-toxic concentrations of copper D-gluconate were screened in HESCs based on cell activity. Then, the effects of non-toxic concentrations of copper ions (0~250 μM) were examined on decidualization of human endometrial stromal cells. Our data demonstrated that the mRNA expressions of insulin-like growth factor binding protein (IGFBP-1), prolactin (PRL), Mn-SOD, and FOXO1were down-regulated during decidualization following the treatments with 100 or 250 μM copper ions. Meanwhile, the amount of malonaldehyde (MDA) in the supernatant of HESCs was increased. These results showed that in vitro decidualization of HESCs was impaired by copper treatment.

Increased Krüppel-like factor 12 in recurrent implantation failure impairs endometrial decidualization by repressing Nur77 expression

BACKGROUND

Decidualization is a prerequisite for successful implantation and the establishment of pregnancy. A critical role of impaired decidualization in subfertility has been established. In human endometrial stromal cells (hESCs), Krüppel-like factor 12 (KLF12) and Nur77 are novel regulators of decidualization. We investigated whether KLF12 impaired the decidualization of hESCs in recurrent implantation failure (RIF) patients.

METHODS

Endometrial tissues and hESCs were collected from RIF patients (n = 34) and fertile controls (n = 30) for in vitro analysis. Primary hESCs isolated from RIF endometrial tissues were used to evaluate the biological functions of KLF12 and Nur77. In addition, their molecular mechanisms were investigated by adenovirus-mediated overexpression. Gene expression regulation was examined by real-time-quantitative PCR (qRT-PCR), immunostaining and luciferase reporter assay. Further, blastocyst-like spheroid (BLS) and blastocyst implantation models were performed to examine the roles of KLF12 and Nur77 during embryo expansion on hESCs.

RESULTS

hESCs from the RIF patients showed a poor decidual response, mainly characterized by decreased decidual prolactin (dPRL) secretion, impaired transformation and limited BLS expansion. In addition, KLF12 expression was increased in endometrial tissues from the RIF patients compared with those from the fertile controls, especially in stromal compartments. The opposite results were observed for Nur77 expression in these tissues. KLF12 repressed hESC decidualization by decreasing Nur77 expression. Mechanistically, KLF12 bound to a conserved site in the Nur77 promoter region. Nur77 overexpression significantly reversed the KLF12-mediated repression of dPRL expression, decidual transformation and BLS/blastocyst expansion.

CONCLUSIONS

KLF12 impairs endometrial decidualization by transcriptionally repressing Nur77, and Nur77 overexpression reverses the poor decidual response of hESCs in RIF patients.