Uterine Epithelial Estrogen Receptor-α Controls Decidualization via a Paracrine Mechanism

The timing for embryo transfer after antibiotic therapy for chronic endometritis

OBJECTIVE

To explore the optimal timing of embryo transfer after the first round treatment of chronic endometritis (CE) in vitro.

MATERIALS AND METHODS

A total of 184 patients were recruited from a retrospective analysis of a large university-affiliated reproduction center in 2021. Some people chose to undergo embryo transfer in the same menstrual cycle with the first round of antibiotic treatment (Group 1, n = 29). Others received embryo transfer in the next cycle after the first round of treatment (Group 2, n = 69) or even one cycle later (Group 3，n = 96).

RESULTS

Patients in Group 1 got significantly lower biochemical pregnancy rate and clinical pregnancy rate and live birth rate than Group 2 (p < 0.05) and also Group 3 (p < 0.05). Then after comparing the influence factors, we found embryo transfer in the next cycle after antibiotic treatment had a higher clinical pregnancy rate than group 1 (OR = 3.2 p < 0.05) and group 3(OR = 2.5, p < 0.05). The live birth rate in group 2 was higher than group 1(OR = 3.5, p < 0.05).

CONCLUSION

These findings illustrate that embryo transfer in the next menstrual cycle is the optimal time. Embryo transfer in the same menstrual cycle with the first round of treatment reduces the pregnancy rate.

Immunohistochemistry of Leukemia Inhibitory Factor and Integrin αVβ3 in Mouse Endometrium Following Kisspeptin-54 Ovulation Trigger

Kisspeptin (KP) is a group of hypothalamic neuropeptides encoded by KISS-1 gene. KP-54, a 54-amino-acid peptide, helps regulate the hypothalamic-pituitary-ovarian axis and plays a potential role in implantation. C57BL/6 J female mice were superovulated via intraperitoneal injection of 5 International Units (IU) pregnant mare serum gonadotrophin (day 1). Forty-eight hours later, mice (5/group) were injected with phosphate-buffered saline (PBS) (group A), 5 IU human chorionic gonadotrophin (hCG) (group B), or 3 nmol KP-54 (group C). On day 7, mice were euthanized and uteri excised to create paraformaldehyde-fixed paraffin-embedded sections that were immunostained for the implantation markers: leukemia inhibitory factor (LIF) and integrin αVβ3 (ITG αVβ3). Slides were scored for intensity of staining in endometrial glandular epithelium (GE) and stromal cells (SCs) via histoscore (H-score). Data were analyzed using the Kruskal-Wallis test followed by the Mann-Whitney U test for pairwise comparisons. LIF expression was significantly higher in GE and SCs of mice triggered with KP-54 compared to placebo (P = .009 for both), but only higher than hCG trigger group in SCs (P = .009). Meanwhile, ITG αVβ3 expression was significantly higher in SCs of mice triggered with KP-54 compared to placebo (P = .028). In conclusion, using KP-54 as an ovulation trigger resulted in higher expression of the implantation markers LIF and ITG αVβ3 in mice endometrium compared to hCG or placebo. This suggests a potential role for KP-54 trigger in improving embryo implantation in clinical IVF. However, further studies are needed to correlate these results with clinical implantation rates and pregnancy outcomes.

Exposure to di-isononyl phthalate during early pregnancy disrupts decidual angiogenesis and placental development in mice

Di-isononyl phthalate (DiNP), an endocrine-disrupting chemical, is found in numerous consumer products and human exposure to this phthalate is becoming inevitable. The impact of DiNP exposure on the establishment and maintenance of pregnancy remains largely unknown. Thus, we conducted studies in which pregnant mice were exposed to an environmentally relevant dose (20 µg/kg BW/day) of DiNP on days 1-7 of gestation, then analyzed the effects of this exposure on pregnancy outcome. Our studies revealed that exposure to DiNP during this window led to fetal loss towards the end of gestation. Further studies showed that, although embryos were able to attach to the uterus, implantation sites in DiNP-exposed uteri exhibited impaired differentiation of stromal cells to decidual cells and an underdeveloped angiogenic network in the decidual bed. We also found that exposure to this phthalate has a significant effect on trophoblast differentiation and causes disorganization of the placental layers. The labyrinth was significantly reduced, resulting in compromised expression of nutrient transporters in the placentas of mice exposed to DiNP. These placental defects in DiNP-exposed females were the cause of fetal loss during the later stages of gestation.

Uterine-specific Ezh2 deletion enhances stromal cell senescence and impairs placentation, resulting in pregnancy loss

Maternal uterine remodeling facilitates embryo implantation, stromal cell decidualization and placentation, and perturbation of these processes may cause pregnancy loss. Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that epigenetically represses gene transcription; loss of uterine EZH2 affects endometrial physiology and induces infertility. We utilized a uterine Ezh2 conditional knockout (cKO) mouse to determine EZH2's role in pregnancy progression. Despite normal fertilization and implantation, embryo resorption occurred mid-gestation in Ezh2cKO mice, accompanied by compromised decidualization and placentation. Western blot analysis revealed Ezh2-deficient stromal cells have reduced amounts of the histone methylation mark H3K27me3, causing upregulation of senescence markers p21 and p16 and indicating that enhanced stromal cell senescence likely impairs decidualization. Placentas from Ezh2cKO dams on gestation day (GD) 12 show architectural defects, including mislocalization of spongiotrophoblasts and reduced vascularization. In summary, uterine Ezh2 loss impairs decidualization, increases decidual senescence, and alters trophoblast differentiation, leading to pregnancy loss.

Association of Polymorphisms in FSHR, INHA, ESR1, and BMP15 with Recurrent Implantation Failure

Recurrent implantation failure (RIF) refers to two or more unsuccessful in vitro fertilization embryo transfers in the same individual. Embryonic characteristics, immunological factors, and coagulation factors are known to be the causes of RIF. Genetic factors have also been reported to be involved in the occurrence of RIF, and some single nucleotide polymorphisms (SNPs) may contribute to RIF. We examined SNPs in FSHR, INHA, ESR1, and BMP15, which have been associated with primary ovarian failure. A cohort of 133 RIF patients and 317 healthy controls consisting of all Korean women was included. Genotyping was performed by Taq-Man genotyping assays to determine the frequency of the following polymorphisms: FSHR rs6165, INHA rs11893842 and rs35118453, ESR1 rs9340799 and rs2234693, and BMP15 rs17003221 and rs3810682. The differences in these SNPs were compared between the patient and control groups. Our results demonstrate a decreased prevalence of RIF in subjects with the FSHR rs6165 A>G polymorphism [AA vs. AG adjusted odds ratio (AOR) = 0.432; confidence interval (CI) = 0.206-0.908; p = 0.027, AA+AG vs. GG AOR = 0.434; CI = 0.213-0.885; p = 0.022]. Based on a genotype combination analysis, the GG/AA (FSHR rs6165/ESR1 rs9340799: OR = 0.250; CI = 0.072-0.874; p = 0.030) and GG-CC (FSHR rs6165/BMP15 rs3810682: OR = 0.466; CI = 0.220-0.987; p = 0.046) alleles were also associated with a decreased RIF risk. Additionally, the FSHR rs6165GG and BMP15 rs17003221TT+TC genotype combination was associated with a decreased RIF risk (OR = 0.430; CI = 0.210-0.877; p = 0.020) and increased FSH levels, as assessed by an analysis of variance. The FSHR rs6165 polymorphism and genotype combinations are significantly associated with RIF development in Korean women.

Ovarian Stimulation in Mice Resulted in Abnormal Placentation through Its Effects on Proliferation and Cytokine Production of Uterine NK Cells

Ovarian stimulation is associated with an increased incidence of abnormal placentation. Uterine natural killer (uNK) cells are the major subpopulation of decidual immune cells, which are crucial for placentation. In a previous study, we found that ovarian stimulation impairs uNK cell density on gestation day (GD) 8.5 in mice. However, it was not clear how ovarian stimulation led to a reduction in the density of uNK cells. In this study, we constructed two mouse models, an in vitro mouse embryo transfer model and an estrogen-stimulated mouse model. We used HE and PAS glycogen staining, immunohistochemical techniques, q-PCR, Western blot, and flow cytometry to analyze the mouse decidua and placenta, and the results showed that SO resulted in a fetal weight reduction, abnormal placental morphology, decreased placental vascular density, and abnormal density and function of uNK cells. Our results suggest that ovarian stimulation resulted in aberrant estrogen signaling and may contribute to the disorder of uNK cells caused by ovarian stimulation. Together, these results provide new insights into the mechanisms of aberrant maternal endocrine environments and abnormal placentation.

Estrogen Actions in Placental Vascular Morphogenesis and Spiral Artery Remodeling: A Comparative View between Humans and Mice

Estrogens, mainly 17β-estradiol (E2), play a critical role in reproductive organogenesis, ovulation, and fertility via estrogen receptors. E2 is also a well-known regulator of utero-placental vascular development and blood-flow dynamics throughout gestation. Mouse and human placentas possess strikingly different morphological configurations that confer important reproductive advantages. However, the functional interplay between fetal and maternal vasculature remains similar in both species. In this review, we briefly describe the structural and functional characteristics, as well as the development, of mouse and human placentas. In addition, we summarize the current knowledge regarding estrogen actions during utero-placental vascular morphogenesis, which includes uterine angiogenesis, the control of trophoblast behavior, spiral artery remodeling, and hemodynamic adaptation throughout pregnancy, in both mice and humans. Finally, the estrogens that are present in abnormal placentation are also mentioned. Overall, this review highlights the importance of the actions of estrogens in the physiology and pathophysiology of placental vascular development.

Optimization of estrogen dosage for uterine receptivity for implantation in post-coital bilaterally ovariectomized mice

Estrogens and progesterone, in unison and/or separately, synchronize the distinct events of blastocyst development, uterine priming and receptivity induction for implantation. In contrast to high implantation failure rates, the mechanistic concepts regarding the uterine receptivity for implantation still remain elusive. The present study aims to define the minimum estradiol (E₂) dose to induce uterine receptivity for successful implantation in post-coitus bilaterally ovariectomized (BLO) progesterone-primed uterus of mice. Post-coital sperm-positive adult female mice were divided into two groups. In both the groups, delayed implantation was induced by BLO on post-coitus Day 4 (D4). Group 1 received 2 mg of progesterone (P₄) from D5 until sacrifice, and E₂ injection of 3.0, 10.0, 25.0 and 50.0 ng on D7. On D8, all mice of this group were sacrificed except the mice that received second dose of 25.0 ng of E₂ on D8 and were sacrificed on D9. Group 2 followed the same doses, but were given simultaneously on D4, and sacrificed on D5. The mice that received second doses of 25.0 ng E₂ were sacrificed on D6. The minimum dose of E₂ required to induce uterine receptivity for implantation is a single dose of 50.0 ng E₂. The uterus remained refractory following short receptive period at E₂ doses lower than 50.0 ng, which is just sufficient to establish desired uterine receptivity. However, repeated administration of sub-threshold doses of 25.0 ng of E₂ could also not effectively sustain uterine receptivity towards successful implantation.

Progress on the Role of Estrogen and Progesterone Signaling in Mouse Embryo Implantation and Decidualization

Embryo implantation and decidualization are key steps in establishing a successful pregnancy. Defects in embryo implantation and decidualization can cause a series of adverse chain reactions which can contribute to harmful pregnancy outcomes, such as embryo growth retardation, preeclampsia, miscarriage, premature birth, and so on. Approximately 75% of failed pregnancies are considered to be due to embryo implantation failure or defects. Decidualization, characterized by proliferation and differentiation of uterine stromal cells, is one of the essential conditions for blastocyst implantation, placental formation, and maintenance of pregnancy and is indispensable for the establishment of pregnancy in many species. Embryo implantation and decidualization are closely regulated by estrogen and progesterone secreted by the ovaries. Many cellular events and molecular signaling network pathways are involved in this process. This article reviews the recent advances in the molecular mechanisms of estrogen- and progesterone-regulating uterine receptivity establishment, blastocyst implantation, and decidualization, in order to better understand the underlying molecular mechanisms of hormonal regulation of embryo implantation and to develop new strategies for preventing or treating embryo implantation defects and improving the pregnancy rate of women.

Shp2 in uterine stromal cells critically regulates on time embryo implantation and stromal decidualization by multiple pathways during early pregnancy

Approximately 75% of failed pregnancies are considered to be due to embryo implantation failure or defects. Nevertheless, the explicit signaling mechanisms governing this process have not yet been elucidated. Here, we found that conditional deletion of the Shp2 gene in mouse uterine stromal cells deferred embryo implantation and inhibited the decidualization of stromal cells, which led to embryonic developmental delay and to the death of numerous embryos mid-gestation, ultimately reducing female fertility. The absence of Shp2 in stromal cells increased the proliferation of endometrial epithelial cells, thereby disturbing endometrial epithelial remodeling. However, Shp2 deletion impaired the proliferation and polyploidization of stromal cells, which are distinct characteristics of decidualization. In human endometrial stromal cells (hESCs), Shp2 expression gradually increased during the decidualization process. Knockout of Shp2 blocked the decidual differentiation of hESCs, while Shp2 overexpression had the opposite effect. Shp2 knockout inhibited the proliferation of hESCs during decidualization. Whole gene expression profiling analysis of hESCs during the decidualization process showed that Shp2 deficiency disrupted many signaling transduction pathways and gene expression. Analyses of hESCs and mouse uterine tissues confirmed that the signaling pathways extracellular regulated protein kinases (ERK), protein kinase B (AKT), signal transducer and activator of transcription 3 (STAT3) and their downstream transcription factors CCAAT/enhancer binding protein β (C/EBPβ) and Forkhead box transcription factor O1 (FOXO-1) were involved in the Shp2 regulation of decidualization. In summary, these results demonstrate that Shp2 plays a crucial role in stromal decidualization by mediating and coordinating multiple signaling pathways in uterine stromal cells. Our discovery possibly provides a novel key regulator of embryo implantation and novel therapeutic target for pregnancy failure.

Embryo implantation includes the establishment of uterine receptivity, blastocyst attachment, and endometrial decidualization. Disorders of this process usually induce pregnancy failure, resulting in women infertility. But the signaling mechanisms governing this process remain unclear. Here, using gene knockout mouse model and human endometrial stromal cells (hESCs), we identified a novel key regulator of embryo implantation, Shp2, which plays a crucial role in stromal decidualization by mediating and coordinating multiple signaling pathways in uterine stromal cells. Shp2 deficiency in mouse uterine stromal cells inhibited the uterine stromal decidualization, disturbing embryo implantation and embryonic development, ultimately reducing female fertility. The absence of Shp2 in hESCs also blocked the decidual differentiation. Our findings not only promote the understanding of peri-implantation biology, but may also provide a critical target for more effectively diagnose and/or treat women with recurrent implantation failure or early pregnancy loss.

Research Progress on the Mechanism Between Polycystic Ovary Syndrome and Abnormal Endometrium

As a highly dynamic tissue, the endometrium is periodically shed in response to the secretion of estrogen and progesterone. After menarche, the endometrium of healthy women proliferates and differentiates under the action of steroid hormones (e.g., 17β-estradiol and progesterone) that are secreted by the ovaries to provide appropriate conditions for embryo implantation. Polycystic ovary syndrome (PCOS), a prevalent endocrine and metabolic disorder in reproductive-aged women, is usually associated with multiple cysts within the ovaries and excess levels of androgen and is characterized by hirsutism, acne, menstrual irregularity, infertility, and increased risk of insulin resistance. Multiple factors, such as anovulation, endocrine-metabolic abnormalities, and inflammation, can disrupt the endometrium in PCOS patients and can lead to endometrial hyperplasia, pregnancy complications, or even cancer. Despite many recent studies, the relationship between PCOS and abnormal endometrial function is still not fully understood. In this review, we investigate the correlation of PCOS patient endometrium with anovulation, hyperandrogenemia, insulin resistance, progesterone resistance, and inflammatory cytokines, aiming to provide a theoretical basis for the treatment of disorders caused by endometrial dysfunction in PCOS patients.

Female Reproductive Systems: Hormone Dependence and Receptor Expression

The female reproductive system which consists of the ovaries, uterus (myometrium, endometrium), Fallopian tubes, cervix and vagina is exquisitely sensitive to the actions of steroid hormones. The ovaries play a key role in the synthesis of bioactive steroids (oestrogens, androgens, progestins) that act both within the tissue (intracrine/paracrine) as well as on other reproductive organs following release into the blood stream (endocrine action). Sex steroid receptors encoded by the oestrogen (ESR1, ESR2), progesterone (PR) and androgen (AR) receptor genes, which are members of the superfamily of ligand activated transcription factors are widely expressed within these tissues. These receptors play critical role(s) in regulation of cell proliferation, ovulation, endometrial receptivity, myometrial cell function and inflammatory cell infiltration. Our understanding of their importance has been informed by studies on human tissues and cells, which have employed immunohistochemistry as well as a wide range of molecular and genetic methods to identify which processes are dependent steroid ligand activation. The development of mice with targeted deletions of each of these receptors has provided complementary data that has extended our appreciation of cell-cell interactions in the fine tuning of reproductive tissue function. This large body of work has formed the basis of new and improved therapeutics to treat conditions such as infertility.

Disrupted PGR-B and ESR1 signaling underlies defective decidualization linked to severe preeclampsia

Background:

Decidualization of the uterine mucosa drives the maternal adaptation to invasion by the placenta. Appropriate depth of placental invasion is needed to support a healthy pregnancy; shallow invasion is associated with the development of severe preeclampsia (sPE). Maternal contribution to sPE through failed decidualization is an important determinant of placental phenotype. However, the molecular mechanism underlying the in vivo defect linking decidualization to sPE is unknown.

Methods:

Global RNA sequencing was applied to obtain the transcriptomic profile of endometrial biopsies collected from nonpregnant women who suffer sPE in a previous pregnancy and women who did not develop this condition. Samples were randomized in two cohorts, the training and the test set, to identify the fingerprinting encoding defective decidualization in sPE and its subsequent validation. Gene Ontology enrichment and an interaction network were performed to deepen in pathways impaired by genetic dysregulation in sPE. Finally, the main modulators of decidualization, estrogen receptor 1 (ESR1) and progesterone receptor B (PGR-B), were assessed at the level of gene expression and protein abundance.

Results:

Here, we discover the footprint encoding this decidualization defect comprising 120 genes—using global gene expression profiling in decidua from women who developed sPE in a previous pregnancy. This signature allowed us to effectively segregate samples into sPE and control groups. ESR1 and PGR were highly interconnected with the dynamic network of the defective decidualization fingerprint. ESR1 and PGR-B gene expression and protein abundance were remarkably disrupted in sPE.

Conclusions:

Thus, the transcriptomic signature of impaired decidualization implicates dysregulated hormonal signaling in the decidual endometria in women who developed sPE. These findings reveal a potential footprint that could be leveraged for a preconception or early prenatal screening of sPE risk, thus improving prevention and early treatments.

Funding:

This work has been supported by the grant PI19/01659 (MCIU/AEI/FEDER, UE) from the Spanish Carlos III Institute awarded to TGG. NCM was supported by the PhD program FDGENT/2019/008 from the Spanish Generalitat Valenciana. IMB was supported by the PhD program PRE2019-090770 and funding was provided by the grant RTI2018-094946-B-100 (MCIU/AEI/FEDER, UE) from the Spanish Ministry of Science and Innovation with CS as principal investigator. This research was funded partially by Igenomix S.L.

Signaling through retinoic acid receptors is essential for mammalian uterine receptivity and decidualization

Retinoic acid (RA) signaling has long been speculated to regulate embryo implantation, because many enzymes and proteins responsible for maintaining RA homeostasis and transducing RA signals are tightly regulated in the endometrium during this critical period. However, due to a lack of genetic data, it was unclear whether RA signaling is truly required for implantation and which specific RA signaling cascades are at play. Herein we utilize a genetic murine model that expresses a dominant-negative form of RA receptor (RAR) specifically in female reproductive organs to show that functional RA signaling is fundamental to female fertility, particularly implantation and decidualization. Reduction in RA signaling activity severely affects the ability of the uterus to achieve receptive status and decidualize, partially through dampening follistatin expression and downstream activin B/bone morphogenetic protein 2 signaling. To confirm translational relevance of these findings to humans, human endometrial stromal cells (hESCs) were treated with a pan-RAR antagonist to show that in vitro decidualization is impaired. RNA interference perturbation of individual RAR transcripts in hESCs revealed that RARα in particular was essential for proper decidualization. These data provide direct functional evidence that uterine RAR-mediated RA signaling was crucial for mammalian embryo implantation, and its disruption led to failure of uterine receptivity and decidualization, resulting in severely compromised fertility.

Effects of Endocrine-Disrupting Chemicals on Endometrial Receptivity and Embryo Implantation: A Systematic Review of 34 Mouse Model Studies

Several available studies have already analyzed the systemic effects of endocrine-disrupting chemicals (EDCs) on fertile woman and neonatal outcomes, but little is still known in humans about the precise mechanisms of interference of these compounds with the endometrial receptivity. There is consistent evidence that continuous and prolonged exposure to EDCs is a risk factor for reduced fertility and fecundity in women. Preliminary studies on mammalian models provide robust evidence about this issue and could help gynecologists worldwide to prevent long term injury caused by EDCs on human fertility. In this systematic review, we aimed to systematically summarize all available data about EDC effects on blastocyst endometrial implantation. We performed a systematic review using PubMed^®/MEDLINE^® to summarize all in vivo studies, carried out on mice models, analyzing the molecular consequences of the prolonged exposure of EDC on the implantation process. 34 studies carried out on mouse models were included. Primary effects of EDC were a reduction of the number of implantation sites and pregnancy rates, particularly after BPA and phthalate exposure. Furthermore, the endometrial expression of estrogen (ER) and progesterone receptors (PR), as well as their activation pathways, is compromised after EDC exposure. Finally, the expression of the primary endometrial markers of receptivity (such as MUC1, HOXA10, Inn and E-cadherin) after EDC contact was analyzed. In conclusion EDC deeply affect blastocyst implantation in mouse model. Several players of the implantation mechanism are strongly influenced by the exposure to different categories of EDC.

Bushen Huoxue recipe attenuates early pregnancy loss via activating endometrial COX2-PGE2 angiogenic signaling in mice

BACKGROUND

During the fresh cycles of in vitro fertilization and embryo transfer, a disturbance in the reproductive endocrine environment following controlled ovarian hyperstimulation (COH) is closely related to compromised endometrial receptivity. This is a major disadvantage for women during pregnancy. Based on the theory of traditional Chinese medicine, Bushen Huoxue recipe (BSHXR) has been indicated to facilitate embryo implantation.

METHODS

The COH model (Kunming breed) was induced by injecting mice with pregnant mare serum gonadotrophin (0.4 IU/g) and human chorionic gonadotropin (1 IU/g), followed by treatment with BSHXR at three different concentrations (5.7, 11.4, and 22.8 g/kg), Bushen recipe (BSR) (5.7 g/kg), and Huoxue recipe (HXR) (5.7 g/kg). After successful mating, the pregnancy rate and implantation sites were examined on embryo day 8 (ED8), and the weight ratio of endometrium was calculated on ED4 midnight. Serum estrogen, progesterone, and endometrial PGE2 levels were measured using enzyme-linked immunosorbent assay. The endometrial microvasculature was evaluated using CD31 immunostaining. The protein and mRNA levels of the angiogenic factors in the endometrium were evaluated using western blot, immunohistochemistry, and polymerase chain reaction.

RESULTS

In the COH group, the pregnancy rate and implantation sites were significantly decreased, and abnormal serum hormone levels and impaired endometrial vascular development were observed. After BSHXR treatment, the supraphysiological serum progesterone level in COH mice was restored to normalcy. Moreover, the abnormal expression of the endometrial pro-angiogenic factors, including HIF1α, COX2-PGE2 pathway, and the down-stream factors, namely, MMP2, MMP9, TIMP2, and FGF2 after subjecting mice to COH was significantly improved after BSHXR treatment.

CONCLUSION

BSHXR could improve embryo implantation by regulating hormonal balance and modulating endometrial angiogenesis in mice, without inducing any side effects in normal pregnancy.

The detrimental effects of stress-induced glucocorticoid exposure on mouse uterine receptivity and decidualization

Glucocorticoids (GCs), stress-induced steroid hormones, are released by adrenal cortex and essential for stress adaptation. Recently, there has been renewed interest in the relationship between GCs and pregnancy following the discovery that glucocorticoid receptor is necessary for implantation. It has been widely recognized that stress is detrimental to pregnancy. However, effects of stress-induced GC exposure on uterine receptivity and decidualization are still poorly understood. This study aims to explore the effects of GCs exposure on uterine receptivity, decidualization, and their underlying mechanisms in mice. Single prolonged stress (SPS) and corticosterone (Cort) injection models were used to analyze effects of GC exposure on early pregnancy, respectively. SPS or Cort injection inhibits embryo implantation by interfering Lif signaling and stimulating the uterine deposition of collagen types I, III, and IV on day 4 of pregnancy. Uterine decidualization is also attenuated by SPS or Cort injection through suppressing Cox-2 expression. Cort-induced collagen disorder also suppresses decidualization through regulating mesenchymal-epithelial transition. Our data should shed lights for a better understanding for the effects of GCs on embryo implantation for clinical research.

Comparative Analysis of Mouse Decidualization Models at the Molecular Level

The mouse is widely used to study decidualization and there are three well-established mouse models of decidualization, namely natural pregnancy decidualization (NPD), artificial decidualization (AD), and in vitro decidualization (IVD). However, the extent of similarity and difference between these models at the molecular level remains largely unknown. Here, we performed a comparative analysis using the RNA-seq approach. In the NPD model, which is thought to be the golden standard of mouse decidualization, we found a total of 5277 differentially expressed genes, with 3158 genes being up-regulated and 2119 genes being down-regulated. A total of 4294 differentially expressed genes were identified in the AD model: 1127 up-regulated genes and 3167 down-regulated genes. In comparison to NPD, 1977 genes were consistently expressed, whereas only 217 genes were inconsistently expressed, indicating that AD is a reliable model for mouse decidualization. In the IVD model, RNA-seq analysis revealed that 513 genes were up-regulated and 988 genes were down-regulated. Compared to NPD, 310 genes were consistently expressed, whereas 456 genes were inconsistently expressed. Moreover, although the decidualization marker Prl8a2 (prolactin family 8 subfamily a member 2) was up-regulated, the widely-used marker Alpl (alkaline phosphatase liver/bone/kidney) was down-regulated in the IVD model. Therefore, we suggest that the IVD model should be optimized to mimic NPD at the transcriptomic level. Our study contributes to an increase in the knowledge about mouse models of decidualization.

Distribution of estrogen receptor in the rabbit cervix during pregnancy with special reference to stromal elements: an immunohistochemical study

The estrogen plays a critical role during pregnancy through their receptors. Although the rabbit is one of the most important lab animal estrogen receptor alpha (ERA) localization on basic cells, newly discovered cells including telocyte and neuroendocrine cells, vascular compartments and interstitium during pregnancy not been described. At 0 day pregnancy, the most prominent immunoreactivity was moderate to ERA and observed on the ciliated cells, secretory cells, blood plasma, and interstitium. The smooth muscles and the endothelial cells showed mild immunoreactivity to ERA. Lymphocytes only exhibited strong immunoreactivity to ERA. At 7 days pregnancy moderate immunoreactivity to ERA observed on ciliated cells, secretory cells, smooth muscles, interstitium, and lymphocytes. Strong immunoreactivity to ERA detected on endothelial cells and blood plasma. At 14 days of pregnancy, the most prominent immunoreactivity was strong and detected on ciliated cells, smooth muscles, lymphocytes, and interstitium. Moderate immunoreactivity detected on endothelial cells and blood plasma. Secretory cells only exhibited mild immunoreactivity to ERA. At 21 days of pregnancy, the immunoreactivity to ERA ranged between mild on ciliated cells, smooth muscles, blood plasma and interstitium and negative on secretory cells, endothelial cells and lymphocytes. Our results indicated that the frequency and intensity of ERA immunostaining in the rabbit cervix varied on different structural compartments of the cervix during different pregnancy stages.

Genome-wide estrogen receptor-α binding and action in human endometrial stromal cells

OBJECTIVE

To investigate the gene targets of estradiol (E2)-estrogen receptor-α (ESR1) in human endometrial stromal cells.

DESIGN

Basic science.

SETTING

University research center.

PATIENT(S)

Premenopausal women with or without endometriosis.

INTERVENTION(S)

Primary cultures of human endometrial stromal cells from healthy endometrium, with or without small-interfering RNA (siRNA) knockdown of ESR1 expression, were treated with E2 or vehicle control.

MAIN OUTCOME MEASURE(S)

Genome-wide RNA expression by RNA sequencing was compared in endometrial stromal cells with or without siRNA knockdown of ESR1 in the presence or absence of E2. Genome-wide recruitment of ESR1 to chromatin was assessed by chromatin immunoprecipitation sequencing. Gene expression by real-time qualitative polymerase chain reaction of a potential E2-ESR1 target gene was determined in endometrial stromal cells and endometriotic stromal cells.

RESULT(S)

We identified several important pathways that are dependent on E2-ESR1 signaling in endometrial stromal cells, including progesterone signaling, cell-matrix adhesion, and cytoskeleton rearrangement, as well as paracrine signaling by members of the fibroblast growth factor family. We detected a total of 709 ESR1 target sites on chromatin. By integrating data on genome-wide transcriptomic changes and E2-ESR1 binding sites, we identified inositol polyphosphate phosphatase type II (INPP4B) as a candidate E2-mediated suppressor of proliferation in healthy endometrial cells. INPP4B was downregulated in endometriosis-derived stromal cells.

CONCLUSION(S)

E2-ESR1 activates genes involved in human endometrial stromal cell cycle regulation, progesterone response, and production of stromal growth factors. Understanding the direct role of estrogen on the endometrial stroma and identifying downstream targets of E2-ESR1 can inform the development of targeted therapies for endometriosis and diminished endometrial receptivity.

Uterine Gpr83 mRNA is highly expressed during early pregnancy and GPR83 mediates the actions of PEN in endometrial and non-endometrial cells

OBJECTIVE

To characterize the expression and signaling of uterine GPR83 in vivo in the nonpregnant and pregnant mouse and in vitro in human endometrial and nonendometrial cells.

DESIGN

Controlled laboratory study.

SETTING

Not applicable.

PATIENTS

Not applicable.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Expression of uterine Gpr83 was determined by quantitative polymerase chain reaction throughout the estrous cycle and during early pregnancy in ovarian-stimulated and non-ovarian-stimulated mice and pregnant and pseudopregnant mice. Expression was also determined in ovariectomized mice after the administration of oil, E2, P4, or E2 + P4 and in stromal cells following 6 days of in vitro decidualization. GPR83 signaling was studied in human endometrial and embryonic kidney cell lines. Cells were treated by PEN, a GPR83 ligand, and PEN-induced extracellular signal-regulated kinase (ERK) phosphorylation was assayed under conditions that blocked Gα_q/11 and/or β-arrestin signaling.

RESULTS

Uterine Gpr83 is expressed throughout the estrous cycle and during early pregnancy; expression increases dramatically at the time of uterine receptivity, embryo implantation, and stromal cell decidualization. In the ovariectomized mouse, hormone add-back reveals that Gpr83 expression is highly responsive to the combined treatment of E2 and P4, and studies in the ovarian-stimulated mouse show that expression is also very sensitive to changes in E2 and P4 and is therefore tightly regulated by E2 and P4. At the implantation site, expression is elevated up to D6 of pregnancy and then declines rapidly on D7 and D8, suggesting that if there is any involvement in decidualization, it is likely associated with primary but not secondary stromal cell decidualization. This premise was supported by the observation that stromal cell decidualization in vitro progresses with a decline in Gpr83 expression. In ERα/PR-expressing endometrial Ishikawa cells, GPR83 mediates PEN signals in a Gα_q/11-dependent manner, and studies conducted in HEK 293 cells lacking β-arrestin revealed that GPR83 also signals via a β-arrestin-dependent manner. When signaling by either one or both pathways is downregulated, cells exhibit a major reduction in responsiveness to PEN treatment, demonstrating that signaling by both pathways is significant.

CONCLUSION

We hypothesize that PEN/GPR83 signaling regulates uterine receptivity, embryo implantation, and primary stromal cell decidualization by coupling to Gα_q/11- and β-arrestin-dependent pathways.

Potential roles for the kisspeptin/kisspeptin receptor system in implantation and placentation

BACKGROUND

Initially identified as suppressors of metastasis in various types of cancer, kisspeptins are a family of neuropeptides that are key regulators of the mammalian reproductive axis. Accumulating evidence has shown that kisspeptin is able to control both the pulsatile and surge GnRH release, playing fundamental roles in female reproduction, which include the secretion of gonadotropins, puberty onset, brain sex differentiation, ovulation and the metabolic regulation of fertility. Furthermore, recent studies have demonstrated the involvement of the kisspeptin system in the processes of implantation and placentation. This review summarizes the current knowledge of the pathophysiological role and utility of these local placental regulatory factors as potential biomarkers during the early human gestation.

OBJECTIVE AND RATIONALE

A successful pregnancy, from the initiation of embryo implantation to parturition, is a complex process that requires the orchestration of a series of events. This review aims to concisely summarize what is known about the role of the kisspeptin system in implantation, placentation, early human pregnancy and pregnancy-related disorders, and to develop strategies for predicting, diagnosing and treating these abnormalities.

SEARCH METHODS

Using the PubMed and Google Scholar databases, we performed comprehensive literature searches in the English language describing the advancement of kisspeptins and the kisspeptin receptor (KISS1R) in implantation, placentation and early pregnancy in humans, since its initial identification in 1996 and ending in July 2018.

OUTCOMES

Recent studies have shown the coordinated spatial and temporal expression patterns of kisspeptins and KISS1R during human pregnancy. The experimental data gathered recently suggest putative roles of kisspeptin signaling in the regulation of trophoblast invasion, embryo implantation, placentation and early pregnancy. Dysregulation of the kisspeptin system may negatively affect the processes of implantation as well as placentation. Clinical studies indicate that the circulating levels of kisspeptins or the expression levels of kisspeptin/KISS1R in the placental tissues may be used as potential diagnostic markers for women with miscarriage and gestational trophoblastic neoplasia.

WIDER IMPLICATIONS

Comprehensive research on the pathophysiological role of the kisspeptin/KISS1R system in implantation and placentation will provide a dynamic and powerful approach to understanding the processes of early pregnancy, with potential applications in observational and analytic screening as well as the diagnosis, prognosis and treatment of implantation failure and early pregnancy-related disorders.

Endometrial autophagy is essential for embryo implantation during early pregnancy

Embryo implantation is an essential and complex process in mammalian reproduction. However, little evidence has indicated the involvement of autophagy during embryo implantation. To determine the possible role of autophagy in uterine of pregnant mice during the peri-implantation stage, we first examined the expression of autophagy-related markers ATG5 and LC3 on day 4, 5, and 6 of pregnancy (D4, D5, and D6, respectively). Compared with expression on D4, downregulation of the autophagy-related markers was observed on D5 and D6, the days after the embryo attached to the receptivity endometrium. Further examination showed that autophagy-related markers ATG5, ATG12, LC3, cathepsin B, and P62 at the implantation site were significantly decreased when comparing with the inter-implantation site. Fewer number of autophagosomes at the implantation site were also observed by transmission electron microscopy. To confirm the functional role of autophagy during embryo implantation in mice, we administered the autophagy inhibitor 3-methyladenine and chloroquine to mice. After treated with 3-methyladenine, the expression of decidual markers HOXA10 and progesterone receptor were significantly reduced. Furthermore, a reduction in implantation sites and increase in the HOXA10 and PR protein levels were observed in response to chloroquine treatment. In addition, impaired uterine decidualization and dysregulation of the PR and HOXA10 protein levels was observed after autophagy inhibited by 3-methyladenine and chloroquine in in vivo artificial decidualization mouse model. In the last, LC3 and P62 were also observed in normal human proliferative, secretory, and decidua tissues. In conclusion, endometrial autophagy may be essential for embryo implantation, and it may be associated with endometrial decidualization during early pregnancy. KEY MESSAGE: • Autophagy-related markers were significantly decreased at implantation site. • Autophagy inhibition results in abnormal decidualization. • Autophagy is essential for embryo implantation.

Genome-wide analysis and functional prediction of the estrogen-regulated transcriptional response in the mouse uterus†

The ovarian hormones estrogen and progesterone orchestrate the transcriptional programs required to direct functions of the uterus for initiation and maintenance of pregnancy. Estrogen, acting via estrogen receptor alpha, regulates gene expression by activating and repressing distinct genes involved in signaling pathways that regulate cellular and physiological responses including cell division, water influx, and immune cell recruitment. Historically, these transcriptional responses have been postulated to reflect a biphasic physiological response. In this study, we explored the transcriptional responses of the ovariectomized mouse uterus to 17β-estradiol (E2) by RNA-seq to obtain global expression profiles of protein-coding transcripts (mRNAs) and long noncoding RNAs (lncRNAs) following 0.5, 1, 2, and 6 hours of treatment. The E2-regulated mRNA and lncRNA expression profiles in the mouse uterus indicate an association between lncRNAs and mRNAs that regulate E2-driven pathways and reproductive phenotypes in the mouse. The transient E2-regulated transcriptome is reflected in the time-dependent shifting of biological processes regulated in the uterus in response to E2. Moreover, high expression of some conserved lncRNAs that are E2 regulated in the mouse uterus are predictive of low overall survival in endometrial carcinoma patients (e.g., H19, KCNQ1OT1, MIR17HG, and FTX). Collectively, this study (1) describes a genomic approach for identifying E2-regulated lncRNAs that may serve critical function in the uterus and (2) provides new insights into our understanding of the regulation of hormone-regulated transcriptional responses with implications in pregnancy and endometrial pathologies.

Regulatory mechanisms of endometrial decidualization and pregnancy-related diseases

Endometrial decidualization is one of the earliest changes by which the uterus adapts to pregnancy. During this period, the endometrium undergoes complex changes in its biochemistry, physiology, and function at various levels, providing a suitable microenvironment for embryo implantation and development. Favorable decidualization lays an essential foundation for subsequent gestation, without which pregnancy failure or pregnancy complications may occur. The interaction between pregnancy-related hormones and cytokines produced by embryonic and uterine cells is known to be essential for decidualization, in which some transcription factors also play pivotal roles. Increasing evidence has revealed the importance of metabolism in regulating decidualization. Here, we summarize and discuss these crucial elements in decidualization and the relationship between decidualization and pregnancy complications. A better comprehension of these issues should help to improve the prediction of pregnancy outcomes and the use of appropriate intervention.

Uterine Luminal Epithelium as the Transient Gateway for Embryo Implantation

The uterine luminal epithelium (LE) is the first maternal contact for an implanting embryo. Intrauterine fluid resorption, cessation of LE proliferation and apoptosis, and LE structural changes are prerequisites for establishing transient uterine receptivity for embryo implantation. Vesicle trafficking in the LE and receptor-mediated paracrine and autocrine mechanisms are crucial both for LE preparation and LE communications with the embryo and stroma during the initiation of embryo implantation. This review mainly covers recent in vivo studies in LE of mouse models from 0.5 days post-coitus (D0.5) to ∼D4 20 h when the trophoblasts pass through the LE layer for embryo implantation. The review is organized into three interconnected sections: preimplantation LE preparation for embryo attachment, embryo-LE communications, and LE-stroma communications.

Hashimoto's thyroiditis impairs embryo implantation by compromising endometrial morphology and receptivity markers in euthyroid mice

BACKGROUND

Although thyroid dysfunction caused by Hashimoto's thyroiditis (HT) is believed to be related to implantation failure due to the underdevelopment of the receptive uterus, it is unknown whether HT itself, even in the euthyroid state, impairs embryo implantation associated with endometrial receptivity defects. To address whether HT itself can affect endometrial receptivity accompanied by implantation alterations, a euthyroid HT model was established in mice.

METHODS

Female NOD mice were immunized twice with thyroglobulin and adjuvant to induce the experimental HT model. Four weeks after the second treatment, the mice were normally mated, and pregnant ones were sacrificed in implantation window for thyroid-related parameter and steroid hormones measurements by electrochemiluminescence immunoassay and enzyme-linked immunosorbent assay and implantation site number calculation by uptake of Chicago Blue dye. In addition, certain morphological features of endometrial receptivity were observed by hematoxylin-eosin staining and scanning electron microscopy, and the expression of other receptivity markers were analyzed by immunohistochemistry, RT-qPCR or Western Blot.

RESULTS

HT mice displayed intrathyroidal monocyte infiltration and elevated serum thyroid autoantibody levels without thyroid dysfunction, defined as euthyroid HT in humans. Euthyroid HT resulted in implantation failure, fewer pinopodes, retarded pinopode maturation, and inhibited expression of receptivity markers: estrogen receptor α (ERα), integrin β3, leukemia inhibitory factor (LIF), and cell adhesion molecule-1 (ICAM-1). Interestingly, despite this compromised endometrial receptivity response, no statistical differences in serum estradiol or progesterone level between groups were found.

CONCLUSIONS

These findings are the first to indicate that HT induces a nonreceptive endometrial milieu in the euthyroid state, which may underlie the detrimental effects of HT itself on embryo implantation.

Chronic and Low Dose Exposure to Nonlyphenol or Di(2-Ethylhexyl) Phthalate Alters Cell Proliferation and the Localization of Steroid Hormone Receptors in Uterine Endometria in Mice

Based on our preliminary results, we examined the possible role of low-dose and chronic-exposing of the chemicals those are known as endocrine disrupting chemical (EDC), on the proliferation of uterine endometrium and the localization of steroid receptors. Immunohistochemical or immunofluorochemical methodology were employed to evaluate the localization of antigen identified by monoclonal antibody Ki 67 protein (MKI67), estrogen receptor 1 (ESR1), estrogen receptor 2 (ESR2), and progesterone receptor (PGR). In 133 μg/L and 1,330 μg/L di(2-ethylhexyl) phthalate (DEHP) and 50 μg/L nonylphenol (NP) groups, the ratio of MKI67 positive stromal cells was significantly increased but not in 500 μg/L NP group. The ratios of MKI67 positive glandular and luminal epithelial cells were also changed by the chronic administration of NP and DEHP in tissue with dose specific manner. ESR1 signals were localized in nucleus in glandular and luminal epithelia of control group but its localization was mainly in cytoplasm in DEHP and NP administered groups. On the other hand, it was decreased at nucleus of stromal cells in 1,330 μg/L DEHP group. The colocalization patterns of these nuclear receptors were also modified by the administration of these chemicals. Such a tissue specific and dose specific localization of ESR2 and PGR were detected as ESR1 in all the uterine endometrial tissues. These results show that the chronic lows-dose exposing of NP or DEHP modify the localization and colocalization of ESRs and PGR, and of the proliferation patterns of the endometrial tissues.

Reproductive functions of Kisspeptin/KISS1R Systems in the Periphery

Kisspeptin and its G protein-coupled receptor KISS1R play key roles in mammalian reproduction due to their involvement in the onset of puberty and control of the hypothalamic-pituitary-gonadal axis. However, recent studies have indicated a potential role of extra-hypothalamic kisspeptin in reproductive function. Here, we summarize recent advances in our understanding of the physiological significance of kisspeptin/KISS1R in the peripheral reproductive system (including the ovary, testis, uterus, and placenta) and the potential role of kisspeptin/KISS1R in reproductive diseases. A comprehensive understanding of the expression, function, and potential molecular mechanisms of kisspeptin/KISS1R in the peripheral reproductive system will contribute to the diagnosis, treatment and prevention of reproductive diseases.

Progesterone and Estrogen Signaling in the Endometrium: What Goes Wrong in Endometriosis?

In the healthy endometrium, progesterone and estrogen signaling coordinate in a tightly regulated, dynamic interplay to drive a normal menstrual cycle and promote an embryo-receptive state to allow implantation during the window of receptivity. It is well-established that progesterone and estrogen act primarily through their cognate receptors to set off cascades of signaling pathways and enact large-scale gene expression programs. In endometriosis, when endometrial tissue grows outside the uterine cavity, progesterone and estrogen signaling are disrupted, commonly resulting in progesterone resistance and estrogen dominance. This hormone imbalance leads to heightened inflammation and may also increase the pelvic pain of the disease and decrease endometrial receptivity to embryo implantation. This review focuses on the molecular mechanisms governing progesterone and estrogen signaling supporting endometrial function and how they become dysregulated in endometriosis. Understanding how these mechanisms contribute to the pelvic pain and infertility associated with endometriosis will open new avenues of targeted medical therapies to give relief to the millions of women suffering its effects.

Dietary exposure to mycotoxin zearalenone (ZEA) during post-implantation adversely affects placental development in mice

Zearalenone (ZEA) is a common food contaminant (ppb-ppm) derived from Fusarium fungi. With its estrogenicity and potential chronic exposure, ZEA poses a risk to pregnancy. Our previous studies implied post-implantational lethality by ZEA. Since a functional placenta is essential for fetal development and survival, it was hypothesized that ZEA may have adverse effects on placental development leading to post-implantational lethality. Exposure of young mice to 0, 0.8, 4, 10, and 40 ppm ZEA diets from gestation day 5.5 (D5.5) to D13.5 led to increased resorption of implantation sites, increased placental hemorrhage, decreased placental and fetal weights, proportionally reduced placental layers, and disorganized placental labyrinth vascular spaces in the 40 ppm ZEA group, as well as lipid accumulation in the labyrinth layer of all four ZEA treatment groups examined on D13.5. These data demonstrate adverse effects of ZEA on placental development.

Estrogen Receptors: New Directions in the New Millennium

Nineteen years have passed since our previous review in this journal in 1999 regarding estrogen receptors. At that time, we described the current assessments of the physiological activities of estrogen and estrogen receptors. Since that time there has been an explosion of progress in our understanding of details of estrogen receptor-mediated processes from the molecular and cellular level to the whole organism. In this review we discuss the basic understanding of estrogen signaling and then elaborate on the progress and current understanding of estrogen receptor actions that have developed using new models and continuing clinical studies.

A historical review of blastocyst implantation research

Research development on blastocyst implantation was reviewed in three sections: primate implantation, ungulate farm animal implantation, and the general process of blastocyst implantation in small rodents. Future research directions of this area are suggested.

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.

Association of body mass index with ER, PR and 14-3-3σ expression in tumor and stroma of type I and type II endometrial carcinoma

Obesity is a prominent risk factor for endometrial cancer (EC) and can impede on surgical and hormonal treatments. Markers of EC, estrogen receptor (ER), progesterone receptor (PR), phospho(Ser473)-AKT (pAKT) and 14-3-3 sigma (14-3-3σ) were measured in EC tissues in both the tumor and stroma and grouped by body mass index (BMI). Immunohistochemical scoring of 82 cases of Type 1 and Type II EC tissues revealed a significantly increased tumor expression of ER, PR and 14-3-3σ in women with Type I (BMI < 40) as compared to Type II (BMI < 30) EC. With higher BMI, only PR and 14-3-3σ in the tumor epithelium was significantly higher in Type I than Type II. In particular, Type I EC exhibited significantly increased levels of only PR from patients with BMI > 40 compared to BMI < 40. Type II EC showed increased expression of ER in the stroma only between high and low BMI. Analysis of the TCGA RNA-Seq mRNA expression of ER, PR, PIK3CA, PTEN and SFN (gene for 14-3-3σ) confirmed increased PR expression in EC of obese women. In conclusion, ER, PR and 14-3-3σ are differentially regulated in Type I compared to Type II EC while PR is dysregulated in obese women with Type I EC. These findings have potential implications for efficacy of progestin treatment in obese women.

hCG activates Epac-Erk1/2 signaling regulating Progesterone Receptor expression and function in human endometrial stromal cells

STUDY QUESTION

How does hCG signal in human endometrial stromal cells (ESCs) and what is its role in regulating ESC function?

SUMMARY ANSWER

hCG signaling in ESCs activates the extracellular signal-regulated protein kinases 1 and 2 (Erk1/2) pathway through exchange protein activated by cyclic AMP (cAMP) (Epac) and transiently increases progesterone receptor (PR) transcript and protein expression and its transcriptional function.

WHAT IS KNOWN ALREADY

hCG is one of the earliest embryo-derived secreted signals in the endometrium, which abundantly expresses LH/hCG receptors. hCG signals through cAMP/protein kinase A (PKA) in gonadal cells, but in endometrial epithelial cells, hCG induces Erk1/2 activation independent of the cAMP/PKA pathway. Few data exist concerning the signal transduction pathways triggered by hCG in ESCs and their role in regulation of ESC function.

STUDY DESIGN, SIZE, DURATION

This is an in vitro study comprising patients undergoing benign gynecological surgery (n = 46).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Endometrial samples were collected from normal cycling women during the mid-secretory phase for ESCs isolation. The study conducted in an academic research laboratory within a tertiary-care hospital. The activation of the Erk1/2 signal transduction pathway elicited by hCG was evaluated in ESC. Signaling pathway inhibitors were used to examine the roles of PKA, PI3K, PKC, adenylyl cyclase and Epac on the hCG-stimulated up-regulation of phospho-Erk1/2 (pErk1/2). Erk1/2 phosphorylation was determined by immunoblot. siRNA targeting Epac was used to investigate the molecular mechanisms. To assess the role of Erk1/2 signaling induced by hCG on ESC function, gene expression regulation was examined by immunofluorescence and real-time quantitative PCR. The role of PR on the regulation of transcript levels was studied using progesterone and the PR antagonist RU486. All experiments were conducted using at least three different cell culture preparations in triplicate.

MAIN RESULTS AND THE ROLE OF CHANCE

Addition of hCG to ESCs in vitro induced the phosphorylation of Erk1/2 through cAMP accumulation. Such induction could not be blocked by inhibitors for PKA, PKC and PI3K. Epac inhibition and knockdown with siRNA prevented pErk1/2 induction by hCG. ESCs stimulated with hCG for up to 72 h showed a significant increase in PR mRNA and immunofluorescent label at 48 h only; an effect that was abrogated with the mitogen-activated protein kinase kinase inhibitor UO126. In addition, the hCG-activated Erk1/2 pathway significantly decreased the mRNA levels for secreted frizzled-related protein 4 (SFRP4) at 24 h, whereas it increased those for homeobox A10 (HOXA10) at 48 h (P = 0.041 and P = 0.022 versus control, respectively). Prolactin mRNA levels were not significantly modified. HOXA10 mRNA up-regulation by hCG was not enhanced by co-stimulation with progesterone; however, it was completely abolished in the presence of RU486 (P = 0.036 hCG versus hCG + RU486).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study utilizing stromal cell cultures from human endometrial tissues. Furthermore, results obtained should also be confirmed in vivo in the context of the whole human endometrial tissue and hormonal milieu. The in vitro experiments using hCG have been conducted without other hormones/factors that may also modulate the ESCs response to hCG.

WIDER IMPLICATIONS OF THE FINDINGS

We have determined that hCG induces the PR through the Erk1/2 pathway in ESCs which may render them more sensitive to progesterone, increasing our understanding about the effects of hCG at the embryo-maternal interface. The activation of such a pathway in the context of the hormonal milieu during the window of implantation might contribute to a successful dialog between the embryo and the uterus, leading to appropriate endometrial function. Defective hCG signaling in the endometrial stromal tissue may lead to an incomplete uterine response, compromising embryo implantation and early pregnancy.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Fund for Scientific and Technological Development, Government of Chile (FONDECYT) grants 11100443 and 1140614 (A.T.-P.). The authors have no conflicts of interest to declare.

Uterine ERα epigenetic modifications are induced by the endocrine disruptor endosulfan in female rats with impaired fertility

High ERα activity may disrupt the window of uterine receptivity, causing defective implantation. We investigated whether implantation failures prompted by endosulfan are associated with aberrant ERα uterine expression and DNA methylation status during the pre-implantation period. ERα-dependent target genes that play a crucial role in the uterine receptivity for embryo attachment and implantation were also investigated. Newborn female rats received corn oil (vehicle, Control), 6 μg/kg/d of endosulfan (Endo6) or 600 μg/kg/d of endosulfan (Endo600) on postnatal days (PND) 1, 3, 5, and 7. On PND90, females were made pregnant and on gestational day 5 (GD5, pre-implantation period) uterine samples were collected. ERα expression was assessed at protein and mRNA levels by immunohistochemistry and real time RT-PCR, respectively. ERα transcript variants mRNA containing alternative 5'-untranslated regions (5'UTRs) were also evaluated. We searched for predicted transcription factors binding sites in ERα regulatory regions and assessed their methylation status by Methylation-Sensitive Restriction Enzymes-PCR technique (MSRE-PCR). The expression of the ERα-dependent uterine target genes, i.e. mucin-1 (MUC-1), insulin-like growth factor-1 (IGF-1), and leukemia inhibitory factor (LIF), was assessed by real time RT-PCR. Both doses of endosulfan increased the expression of ERα and its transcript variants ERα-OS, ERα-O, ERα-OT and ERα-E1. Moreover, a decreased DNA methylation levels were detected in some ERα regulatory regions, suggesting an epigenetic up-regulation of it transcription. ERα overexpression was associated with an induction of its downstream genes, MUC-1 and IGF-1, suggesting that endosulfan might alter the uterine estrogenic pathway compromising uterine receptivity. These alterations could account, at least in part, for the endosulfan-induced implantation failures.

Juxtacrine Activity of Estrogen Receptor α in Uterine Stromal Cells is Necessary for Estrogen-Induced Epithelial Cell Proliferation

Aberrant regulation of uterine cell growth can lead to endometrial cancer and infertility. To understand the molecular mechanisms of estrogen-induced uterine cell growth, we removed the estrogen receptor α (Esr1) from mouse uterine stromal cells, where the embryo is implanted during pregnancy. Without ESR1 in neighboring stroma cells, epithelial cells that line the inside of the uterus are unable to grow due to a lack of growth factors secreted from adjacent stromal cells. Moreover, loss of stromal ESR1 caused mice to deliver fewer pups due in part due to inability of some embryos to implant in the uterus, indicating that stromal ESR1 is crucial for uterine cell growth and pregnancy.

Membrane and Nuclear Estrogen Receptor Alpha Actions: From Tissue Specificity to Medical Implications

Estrogen receptor alpha (ERα) has been recognized now for several decades as playing a key role in reproduction and exerting functions in numerous nonreproductive tissues. In this review, we attempt to summarize the in vitro studies that are the basis of our current understanding of the mechanisms of action of ERα as a nuclear receptor and the key roles played by its two activation functions (AFs) in its transcriptional activities. We then depict the consequences of the selective inactivation of these AFs in mouse models, focusing on the prominent roles played by ERα in the reproductive tract and in the vascular system. Evidence has accumulated over the two last decades that ERα is also associated with the plasma membrane and activates non-nuclear signaling from this site. These rapid/nongenomic/membrane-initiated steroid signals (MISS) have been characterized in a variety of cell lines, and in particular in endothelial cells. The development of selective pharmacological tools that specifically activate MISS and the generation of mice expressing an ERα protein impeded for membrane localization have begun to unravel the physiological role of MISS in vivo. Finally, we discuss novel perspectives for the design of tissue-selective ER modulators based on the integration of the physiological and pathophysiological roles of MISS actions of estrogens.

Autotaxin-lysophosphatidic acid-LPA3 signaling at the embryo-epithelial boundary controls decidualization pathways

During pregnancy, up-regulation of heparin-binding (HB-) EGF and cyclooxygenase-2 (COX-2) in the uterine epithelium contributes to decidualization, a series of uterine morphological changes required for placental formation and fetal development. Here, we report a key role for the lipid mediator lysophosphatidic acid (LPA) in decidualization, acting through its G-protein-coupled receptor LPA₃ in the uterine epithelium. Knockout of Lpar3 or inhibition of the LPA-producing enzyme autotaxin (ATX) in pregnant mice leads to HB-EGF and COX-2 down-regulation near embryos and attenuates decidual reactions. Conversely, selective pharmacological activation of LPA₃ induces decidualization via up-regulation of HB-EGF and COX-2. ATX and its substrate lysophosphatidylcholine can be detected in the uterine epithelium and in pre-implantation-stage embryos, respectively. Our results indicate that ATX-LPA-LPA₃ signaling at the embryo-epithelial boundary induces decidualization via the canonical HB-EGF and COX-2 pathways.

Gain-of-function β-catenin in the uterine mesenchyme leads to impaired implantation and decidualization

Embryo implantation and endometrial decidualization are critical events that occur during early pregnancy in humans and mice, and perturbation in either can result in infertility. WNT signaling through the canonical β-catenin pathway plays a pivotal role in embryonic Müllerian duct development, postnatal uterine maturation and establishment of pregnancy. Loss of β-catenin in the Müllerian duct mesenchyme (MDM)-derived stroma and myometrium results in impaired decidualization and infertility, whereas gain-of-function (GOF) results in the formation of mesenchymal tumors and sub-fertility attributed to malformed oviducts. We hypothesized that GOF β-catenin further contributes to sub-fertility through improper stromal and epithelial cell signaling during embryo implantation and decidualization. We show that mice with GOF β-catenin in MDM-derived stroma and myometrium have reduced implantation sites after embryo transfer and decreased decidualization. On day 4.5 of pseudopregnancy or in mice treated with progesterone and estrogen to mimic early pregnancy, the estrogen-LIF-ERK and progesterone-IHH pathways remain predominantly intact in GOF β-catenin mice; however, JAK/STAT signaling is altered. pSTAT3 is significantly reduced in GOF β-catenin mice and expression of downstream epithelial junctional complex factors, Ctnna1 and Cldn1, is increased. We also show that purified stromal cells from GOF β-catenin uteri, when removed from epithelial cell influence and provided with the appropriate hormonal stimuli, are able to decidualize in vitro indicating that the cells are intrinsically capable of decidualization. Taken together, these results suggest that dysregulated β-catenin activity in the stroma affects epithelial cell STAT3 signaling and ultimately embryo implantation and stromal decidualization.

Estrogen Hormone Biology

The hormone estrogen is involved in both female and male reproduction, as well as numerous other biological systems including the neuroendocrine, vascular, skeletal, and immune systems. Therefore, it is also implicated in many different diseases and conditions such as infertility, obesity, osteoporosis, endometriosis, and a variety of cancers. Estrogen works through its two distinct nuclear receptors, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). Various transcriptional regulation mechanisms have been identified as the mode of action for estrogen, mainly the classical mechanism with direct DNA binding but also a nongenomic mode of action and one using tethered or indirect binding. The expression profiles of ERα and ERβ are unique with the primary sites of ERα expression being the uterus and pituitary gland and the main site of ERβ expression being the granulosa cells of the ovary. Mouse models with knockout or mutation of Esr1 and Esr2 have furthered our understanding of the role of each individual receptor plays in physiology. From these studies, it is known that the primary roles for ERα are in the uterus and neuroendocrine system, as female mice lacking ERα are infertile due to impaired ovarian and uterine function, whereas female mice lacking ERβ are subfertile due to ovarian defects. The development of effective therapies for estrogen-related diseases has relied on an understanding of the physiological roles and mechanistic functionalities of ERα and ERβ in human health and disease.

Forkhead box a2 (FOXA2) is essential for uterine function and fertility

Establishment of pregnancy is a critical event, and failure of embryo implantation and stromal decidualization in the uterus contribute to significant numbers of pregnancy losses in women. Glands of the uterus are essential for establishment of pregnancy in mice and likely in humans. Forkhead box a2 (FOXA2) is a transcription factor expressed specifically in the glands of the uterus and is a critical regulator of postnatal uterine gland differentiation in mice. In this study, we conditionally deleted FOXA2 in the adult mouse uterus using the lactotransferrin Cre (Ltf-Cre) model and in the neonatal mouse uterus using the progesterone receptor Cre (Pgr-Cre) model. The uteri of adult FOXA2-deleted mice were morphologically normal and contained glands, whereas the uteri of neonatal FOXA2-deleted mice were completely aglandular. Notably, adult FOXA2-deleted mice are completely infertile because of defects in blastocyst implantation and stromal cell decidualization. Leukemia inhibitory factor (LIF), a critical implantation factor of uterine gland origin, was not expressed during early pregnancy in adult FOXA2-deleted mice. Intriguingly, i.p. injections of LIF initiated blastocyst implantation in the uteri of both gland-containing and glandless adult FOXA2-deleted mice. Although pregnancy was rescued by LIF and was maintained to term in uterine gland-containing adult FOXA2-deleted mice, pregnancy failed by day 10 in neonatal FOXA2-deleted mice lacking uterine glands. These studies reveal a previously unrecognized role for FOXA2 in regulation of adult uterine function and fertility and provide original evidence that uterine glands and, by inference, their secretions play important roles in blastocyst implantation and stromal cell decidualization.

Embryo implantation triggers dynamic spatiotemporal expression of the basement membrane toolkit during uterine reprogramming

Basement membranes (BMs) are specialized extracellular scaffolds that influence behaviors of cells in epithelial, endothelial, muscle, nervous, and fat tissues. Throughout development and in response to injury or disease, BMs are fine-tuned with specific protein compositions, ultrastructure, and localization. These features are modulated through implements of the BM toolkit that is comprised of collagen IV, laminin, perlecan, and nidogen. Two additional proteins, peroxidasin and Goodpasture antigen-binding protein (GPBP), have recently emerged as potential members of the toolkit. In the present study, we sought to determine whether peroxidasin and GPBP undergo dynamic regulation in the assembly of uterine tissue BMs in early pregnancy as a tractable model for dynamic adult BMs. We explored these proteins in the context of collagen IV and laminin that are known to extensively change for decidualization. Electron microscopic analyses revealed: 1) a smooth continuous layer of BM in between the epithelial and stromal layers of the preimplantation endometrium; and 2) interrupted, uneven, and progressively thickened BM within the pericellular space of the postimplantation decidua. Quantification of mRNA levels by qPCR showed changes in expression levels that were complemented by immunofluorescence localization of peroxidasin, GPBP, collagen IV, and laminin. Novel BM-associated and subcellular spatiotemporal localization patterns of the four components suggest both collective pericellular functions and distinct functions in the uterus during reprogramming for embryo implantation.

Effects of neonatal exposure to a glyphosate-based herbicide on female rat reproduction

In this study, we investigated whether neonatal exposure to a glyphosate-based herbicide (GBH) alters the reproductive performance and the molecular mechanisms involved in the decidualization process in adult rats. Newborn female rats received vehicle or 2 mg/kg/day of a GBH on postnatal days (PND) 1, 3, 5 and 7. On PND90, the rats were mated to evaluate (i) the reproductive performance on gestational day (GD) 19 and (ii) the ovarian steroid levels, uterine morphology, endometrial cell proliferation, apoptosis and cell cycle regulators, and endocrine pathways that regulate uterine decidualization (steroid receptors/COUP-TFII/Bmp2/Hoxa10) at the implantation sites (IS) on GD9. The GBH-exposed group showed a significant increase in the number of resorption sites on GD19, associated with an altered decidualization response. In fact, on GD9, the GBH-treated rats showed morphological changes at the IS, associated with a decreased expression of estrogen and progesterone receptors, a downregulation of COUP-TFII (Nr2f2) and Bmp2 mRNA and an increased expression of HOXA10 and the proliferation marker Ki67(Mki67) at the IS. We concluded that alterations in endometrial decidualization might be the mechanism of GBH-induced post-implantation embryo loss.

Mechanisms of uterine estrogen signaling during early pregnancy in mice: an update

Adherence of an embryo to the uterus represents the most critical step of the reproductive process. Implantation is a synchronized event between the blastocyst and the uterine luminal epithelium, leading to structural and functional changes for further embryonic growth and development. The milieu comprising the complex process of implantation is mediated by estrogen through diverse but interdependent signaling pathways. Mouse models have demonstrated the relevance of the expression of estrogen-modulated paracrine factors to uterine receptivity and implantation window. More importantly, some factors seem to serve as molecular links between different estrogen pathways, promoting cell growth, acting as molecular chaperones, or amplifying estrogenic effects. Abnormal expression of these factors can lead to implantation failure and infertility. This review provides an overview of several well-characterized signaling pathways that elucidates the molecular cross talk involved in the uterus during early pregnancy.

Roles of Estrogen Receptor-α and the Coactivator MED1 During Human Endometrial Decidualization

The steroid hormones 17β-estradiol and progesterone are critical regulators of endometrial stromal cell differentiation, known as decidualization, which is a prerequisite for successful establishment of pregnancy. The present study using primary human endometrial stromal cells (HESCs) addressed the role of estrogen receptor-α (ESR1) in decidualization. Knockdown of ESR1 transcripts by RNA interference led to a marked reduction in decidualization of HESCs. Gene expression profiling at an early stage of decidualization indicated that ESR1 negatively regulates several cell cycle regulatory factors, thereby suppressing the proliferation of HESCs as these cells enter the differentiation program. ESR1 also controls the expression of WNT4, FOXO1, and progesterone receptor (PGR), well-known mediators of decidualization. Whereas ESR1 knockdown strongly inhibited the expression of FOXO1 and WNT4 transcripts within 24 hours of the initiation of decidualization, PGR expression remained unaffected at this early time point. Our study also revealed a major role of cAMP signaling in influencing the function of ESR1 during decidualization. Using a proteomic approach, we discovered that the cAMP-dependent protein kinase A (PKA) phosphorylates Mediator 1 (MED1), a subunit of the mediator coactivator complex, during HESC differentiation. Using immunoprecipitation, we demonstrated that PKA-phosphorylated MED1 interacts with ESR1. The PKA-dependent phosphorylation of MED1 was also correlated with its enhanced recruitment to estrogen-responsive elements in the WNT4 gene. Knockdown of MED1 transcripts impaired the expression of ESR1-induced WNT4 and FOXO1 transcripts and blocked decidualization. Based on these findings, we conclude that modulation of ESR1-MED1 interactions by cAMP signaling plays a critical role in human decidualization.

What's new in estrogen receptor action in the female reproductive tract

Estrogen receptor alpha (ERα) is a critical player in development and function of the female reproductive system. Perturbations in ERα response can affect wide-ranging aspects of health in humans as well as in livestock and wildlife. Because of its long-known and broad impact, ERα mechanisms of action continue to be the focus on cutting-edge research efforts. Consequently, novel insights have greatly advanced understanding of every aspect of estrogen signaling. In this review, we attempt to briefly outline the current understanding of ERα mediated mechanisms in the context of the female reproductive system.

The Multifaceted Actions of Leukaemia Inhibitory Factor in Mediating Uterine Receptivity and Embryo Implantation

Embryo implantation is mediated by the combined actions of the ovarian hormones E2 and P4 on the uterus. In addition, the pro-inflammatory cytokine, leukaemia inhibitory factor (LIF), plays a pivotal role in regulating uterine receptivity. LIF is expressed in the endometrial glands and has a robust action on the uterine luminal epithelium (LE). In mice, LIF is induced by nidatory E2 and functions to convert the LE from a non-receptive to an embryo-responsive state. LIF mediates its actions by activating the JAK-STAT pathway specifically in the LE. Activation of JAK-STAT pathway results in the induction of many additional pathways, including some 40 +  transcription factors, many of which initiate a cascade of changes affecting epithelial polarity, epithelial-mesenchymal interactions, angiogenesis, stromal cell decidualization, and inhibiting cell proliferation. This review discusses the role of LIF and the recent analysis of its action on the uterine LE in regulating endometrial receptivity and implantation.