Implantation in the baboon: endometrial responses

iTRAQ-based Proteomic Analysis Unveils ACSL4 as a Novel Potential Regulator of Human Endometrial Receptivity

Competent endometrial receptivity is a prerequisite for successful embryo implantation. Identification of novel key molecules involved in endometrial receptivity is essential to better interpret human implantation and improve pregnancy rates in assisted reproduction treatment. Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics was performed to profile the proteomes of the prereceptive (luteinizing hormone [LH] + 2, n = 4) and receptive (LH + 7, n = 4) endometrial tissues. A total of 173 differentially expressed proteins (DEPs) between LH + 2 and LH + 7 endometrial samples were identified. Integrated analysis of the proteomic data and published transcriptomic data was performed to identify the concordant DEPs with differential expression at both the messenger RNA and protein levels. Protein-protein interaction (PPI) network analysis was performed on concordant DEPs. We first identified 63 novel concordant DEPs and 5 hub proteins (ACSL4, ACSL5, COL1A1, PTGS1, and PLA2G4F) between LH + 2 and LH + 7 endometrial samples. ACSL4 was predominantly expressed in endometrial epithelial cells and its expression was significantly upregulated by progesterone in the LH + 7 endometrium and significantly downregulated in repeated implantation failure patients. Knockdown of ACSL4 in endometrial epithelial cells induced the downregulation of endometrial receptivity markers (HOXA10, COX2, and LIF) and the significant decrease of implantation rate during in vitro implantation analysis. This study provides the first gel-independent quantitative proteomes of the LH + 2 and LH + 7 human endometrium using iTRAQ technology. The identified concordant DEPs and hub proteins open a new avenue for future studies aimed at elucidating the underlying mechanisms governing endometrial receptivity. ACSL4 was identified as a novel regulatory molecule in the establishment of endometrial receptivity and might play important roles during implantation.

Increased METTL3-mediated m6A methylation inhibits embryo implantation by repressing HOXA10 expression in recurrent implantation failure

BACKGROUND

Recurrent implantation failure (RIF) is a major limitation of assisted reproductive technology, which is associated with impaired endometrial receptivity. Although N⁶-methyladenosine (m⁶A) has been demonstrated to be involved in various biological processes, its potential role in the endometrium of women with RIF has been poorly studied.

METHODS

Global m⁶A levels and major m⁶A methyltransferases/demethylases mRNA levels in mid-secretory endometrium from normal and RIF women were examined by colorimetric m⁶A quantification strategy and quantitative real-time PCR, respectively. The effects of METTL3-mediated m⁶A modification on embryo attachment were evaluated by an vitro model of a confluent monolayer of Ishikawa cells co-cultured with BeWo spheroids, and the expression levels of homeo box A10 (HOXA10, a well-characterized marker of endometrial receptivity) and its downstream targets were evaluated by quantitative real-time PCR and Western blotting in METTL3-overexpressing Ishikawa cells. The molecular mechanism for METTL3 regulating HOXA10 expression was determined by methylated RNA immunoprecipitation assay and transcription inhibition assay.

RESULTS

Global m⁶A methylation and METTL3 expression were significantly increased in the endometrial tissues from women with RIF compared with the controls. Overexpression of METTL3 in Ishikawa cells significantly decreased the ration of BeWo spheroid attachment, and inhibited HOXA10 expression with downstream decreased β3-integrin and increased empty spiracles homeobox 2 expression. METTL3 catalyzed the m⁶A methylation of HOXA10 mRNA and contributed to its decay with shortened half-life. Enforced expression of HOXA10 in Ishikawa cells effectively rescued the impairment of METTL3 on the embryo attachment in vitro.

CONCLUSION

Increased METTL3-mediated m⁶A modification represents an adverse impact on embryo implantation by inhibiting HOXA10 expression, contributing to the pathogenesis of RIF.

The role of miRNAs in polycystic ovary syndrome with insulin resistance

PURPOSE

This review aims to summarize the key findings of several miRNAs and their roles in polycystic ovary syndrome with insulin resistance, characterize the disease pathogenesis, and establish a new theoretical basis for diagnosing, treating, and preventing polycystic ovary syndrome.

METHODS

Relevant scientific literature was covered from 1992 to 2020 by searching the PubMed database with search terms: insulin/insulin resistance, polycystic ovary syndrome, microRNAs, and metabolic diseases. References of relevant studies were cross-checked.

RESULTS

The related miRNAs (including differentially expressed miRNAs) and their roles in pathogenesis, and possible therapeutic targets and pathways, are discussed, highlighting controversies and offering thoughts for future directions.

CONCLUSION

We found abundant evidence on the role of differentially expressed miRNAs with its related phenotypes in PCOS. Considering the essential role of insulin resistance in the pathogenesis of PCOS, the alterations of associated miRNAs need more research attention. We speculate that race/ethnicity or PCOS phenotype and differences in methodological differences might lead to inconsistencies in research findings; thus, several miRNA profiles need to be investigated further to qualify for the potential therapeutic targets for PCOS-IR.

Diagnostic and therapeutic options in recurrent implantation failure

Recurrent implantation failure (RIF) is an uncommon, imprecisely defined clinical disorder characterized by failure to achieve pregnancy after repeated embryo transfers. The diverse etiologies and incomplete understanding of RIF provide significant diagnostic and therapeutic challenges to patients and providers. Careful clinical evaluation prior to assisted reproduction can uncover many treatable causes, including thyroid dysfunction, submucosal myomas, and tobacco use. The more-subtle causes often require a more-targeted assessment. Undetected, small polyps or small areas of intrauterine synechiae are relatively common and easily treated contributors to RIF. Molecular and cellular abnormalities pose a greater therapeutic challenge. Putative causes of RIF, including progesterone resistance, shifted window of receptivity, decreased integrin expression, and immunologic disturbances, should be considered in the evaluation of a patient with otherwise unexplained RIF. It may also be true that a more complex and standardized definition of RIF would be helpful in these cases. In this paper, we review the diagnostic and therapeutic approaches to RIF, with emphasis on disorders of endometrial receptivity.

Nonsteroidal Anti-inflammatory Drug Interaction with Prostacyclin Synthase Protects from Miscarriage

This study evaluates the relationship between single nucleotide polymorphisms (SNPs) in nonsteroidal anti-inflammatory drug (NSAID) metabolism and related pathways and spontaneous abortion (SAB, gestation < 20 weeks) risk. Women were enrolled in Right from the Start (2004–2010) prospective cohort. Periconceptional NSAIDs reported through the sixth week of pregnancy were obtained from study interviews. We evaluated 201 SNPs in 600 European American women. Interaction analyses between NSAID use and SNPs were conducted using logistic regression, adjusted for confounders. We also evaluated prostaglandin E2 urinary metabolite (PGE-M) in an independent population for association with SNPs using linear regression. NSAID use was reported by 63% of cases and 62% controls. The most significant interaction was at prostacyclin synthase (PGIS) rs5602 (OR = 0.34, 95% CI 0.19–0.60, p = 2.45 × 10⁻⁴) and was significant after a Bonferroni correction. NSAID users were protected from SAB (OR = 0.78, 95% CI 0.56–1.10), while non-NSAID users were at increased risk (OR = 2.11, 95% CI 1.35–3.29) in rs5602 stratified analyses. rs5602 also associated with increased PGE-M levels (Beta = 0.09, 95% CI −0.002–0.19, p = 0.033). We identified an association between a PGIS variant and SAB risk that is modified by NSAIDs use during pregnancy and directly associated with increased levels of PGE metabolites. This suggests the potential use of genetic information to guide pharmaceutical intervention to prevent adverse pregnancy outcomes.

Coexistence of adenomyosis uteri and endometrial cancer is associated with an improved prognosis compared with endometrial cancer only

The present study aimed to identify differences in protein expression in cases of endometrioid endometrial cancer (EEC) with and without coexisting adenomyosis uteri (AM), and to evaluate the histopathological and prognostic distinctions. The total cohort included 22 patients in Group A (patients with concomitant AM and EEC) and 35 patients in Group B (patients affected only by EEC). Evaluation of the following factors was performed: Tumour grade, International Federation of Gynaecology and Obstetrics (FIGO) stage, survival, and expression of estrogen receptor β (ERβ), glycodelin and inhibin βB. Group A (AM and EEC) was associated with a lower tumour grade (G1, 90.9 vs. 45.7%; P=0.001) and a lower FIGO stage (FIGO stage I, 100 vs. 80%; P=0.002) compared with Group B (EEC only). In the survival analysis, Group A was associated with a significantly higher 5-year survival rate (95 vs. 82%; P=0.024) than Group B. In addition, the expression of ERβ in Group A was significantly higher (P<0.001), whereas the expression of glycodelin is significantly lower (P=0.028), compared with Group B. The results of the present study indicate that the presence of AM in cases of EEC may be a positive prognostic factor.

The role of the placenta in the initiation of spiral artery remodelling in an early pregnant chimpanzee uterus

INTRODUCTION

In this study we evaluated the full extent of placental bed changes (centre to periphery) in a pregnant chimpanzee uterus, kept at the Museum for Central Africa in Tervuren, Belgium. According to placental size the specimen was equivalent to an 8 weeks pregnant human uterus.

METHODS

Histological sections from central to peripheral tissue blocks of the placental bed were stained to reveal the presence of trophoblast, endothelium, vascular smooth muscle and elastic laminae. As an indicator for early arterial remodelling, we evaluated endothelial nuclear rounding and subendothelial vascular changes within the maternal vasculature in decidua and adjacent inner myometrium.

RESULTS

While interstitially invading trophoblasts were present, endovascular trophoblast invasion seemed about to start into one spiral artery outlet at the centre of the placental bed, confirming our previous impression of a later onset of endovascular trophoblast invasion as compared to the human. An early sign of spiral artery remodelling was rounding of the endothelial nuclei. This phenomenon was not related to the local presence of interstitial trophoblast.

DISCUSSION

Endothelial nuclear rounding turned out to be a feature of the placental bed as a whole, being significantly less prominent in the adjacent non-placental bed part of the uterus, indicating an effect of the presence of the placenta. The different time-course of early spiral artery remodelling in the chimpanzee as compared to the human may have had a significant impact upon our evolution.

Murine uterine decidualization is a novel function of autoimmune regulator-beyond immune tolerance

PROBLEM

Autoimmune polyendocrinopathy, candidiasis, and ectodermal dystrophy (APECED, APS-1) patients characterized by Aire (autoimmune regulator) mutations and Aire homozygous knockouts (Aire(-/-) ) exhibit infertility. It is not clear as to what contributes to infertility in the above.

METHOD OF STUDY

This study investigates the expression of "AIRE in the uterus" and its contribution to early pregnancy of mice by using quantitative real-time PCR analysis, immunohistochemistry, Western blotting, and in vivo Aire silencing experiments.

RESULTS

Aire (Isoform 1a) is expressed in the uterus during the "window of implantation" and decidualization. In vivo Aire silencing interfered with formation of implantation sites and stromal cell transformation by regulating bone morphogenetic protein-2,4 (Bmp2, Bmp4), homeobox A10 (Hoxa10), and insulin-like growth factor-binding protein 1(Igfbp1) leading to pregnancy failure.

CONCLUSION

Our consolidated results on extrathymic uterine expression of AIRE during early pregnancy and decidualization and impaired fertility on in vivo silencing are suggestive of its importance in pregnancy via a role beyond immune tolerance.

Induction of Insulin-Like Growth Factor Binding Protein-1 Expression in Baboon Endometrial Stromal Cells by Cells of Trophoblast Origin

OBJECTIVE

To determine the influence of the conceptus on the induction of decidualization in endometrial stromal cells from the baboon.

METHODS

For in vivo studies, implantation sites from day 22 of pregnancy in the baboon were analyzed for insulin-like growth factor-II (IGF-II) and insulin-like growth factor binding protein-1 (IGFBP-1) mRNAs using in situ hybridization. For in vitro studies, Jeg-3 cells or primary cytotrophoblasts isolated from term placenta were cocultured with a monolayer of stromal cells from the baboon endometrium. Cytotrophoblasts were placed either directly on top of the stromal cell monolayer or in transwell cell culture inserts and cultured for 7 days. No exogenous hormones were added. Stromal cells were analyzed for IGFBP-1 mRNA and protein by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry.

RESULTS

Examination of early implantation sites in the baboon revealed a high expression of IGF-II mRNA in the invading cytotrophoblasts. Conversely, the stromal cells of the endometrium directly adjacent to the cytotrophoblasts expressed IGFBP-1 mRNA. Endometrial stromal cells cocultured with Jeg-3 cells or primary cytotrophoblasts for 7 days expressed IGFBP-1 mRNA and protein. This expression occurred in both the direct coculture system and coculture using the cell culture inserts. Cytotrophoblasts also induced the expression of prolactin in stromal fibroblasts following coculture.

CONCLUSIONS

The conceptus is capable of inducing decidualization of endometrial stromal cells. This is shown in both the in vivo and in vitro systems.

Implantation and Establishment of Pregnancy in Human and Nonhuman Primates

Implantation and the establishment of pregnancy are critical for the propagation of the species, but yet remain the limiting steps in human and primate reproduction. Successful implantation requires a competent blastocyst and a receptive endometrium during a specific window of time during the menstrual cycle to initiate the bilateral communication required for the establishment of a successful pregnancy. This chapter provides an overview of these processes and discusses the molecular mechanisms associated with implantation of the blastocyst and decidualization of the uterus in primates.

Cytokines from the pig conceptus: roles in conceptus development in pigs

Establishment of pregnancy in pigs involves maintaining progesterone secretion from the corpora lutea in addition to regulating a sensitive interplay between the maternal immune system and attachment of the rapidly expanding trophoblast for nutrient absorption. The peri-implantation period of rapid trophoblastic elongation followed by attachment to the maternal uterine endometrium is critical for establishing a sufficient placental-uterine interface for subsequent nutrient transport for fetal survival to term, but is also marked by the required conceptus release of factors involved with stimulating uterine secretion of histotroph and modulation of the maternal immune system. Many endometrial genes activated by the conceptus secretory factors stimulate a tightly controlled proinflammatory response within the uterus. A number of the cytokines released by the elongating conceptuses stimulate inducible transcription factors such as nuclear factor kappa B (NFKB) potentially regulating the maternal uterine proinflammatory and immune response. This review will establish the current knowledge for the role of conceptus cytokine production and release in early development and establishment of pregnancy in the pig.

Vital and vulnerable functions of the primate placenta critical for infant health and brain development

The placenta is essential to mammalian pregnancy with many roles beyond just nutrient supply, including both endocrine and immune functions. During the course of evolution, the placenta of higher primates has acquired some unique features, including the capacity to secrete corticotropin-releasing hormone (CRH). In addition, a placental receptor for IgG enables particularly high levels of protective maternal antibody to reach the fetus before birth. This paper reviews the placental biology of primates, and discusses its involvement in adrenocortical hormone activity during pregnancy, the transfer of maternal antibody, and finally the delivery of maternal iron to the fetus, which is needed for normal brain development. An understanding of these vital functions during a full-term, healthy pregnancy provides insights into the consequences of gestational disturbances, such as maternal stress, illness, and undernutrition, which have even larger ramifications if the infant is born premature.

The expression of cyclooxygenase-2 and vascular endothelial growth factor in the endometrium during the peri-implantation period in women with and without polyps

OBJECTIVE

This prospective study was designed to determine whether the expression of cyclooxygenase-2 (COX-2) and vascular endothelial growth factor (VEGF) in the endometrial tissue obtained from the peri-implantation period of women with endometrial polyp (EP) differs from that of control subjects without a polyp.

METHODS

Endometrial samples were collected from 30 patients with EP and 30 control subjects without EP, in the mid-secretory phase. The expression of COX-2 and VEGF in the endometrium was examined with the use of immunohistochemistry.

RESULTS

COX-2 and VEGF were predominantly expressed in endometrial glands. The expression of COX-2 and VEGF in the endometrium obtained from women with EP was lower than that of control subjects.

CONCLUSION

The reduced expression of COX-2 and VEGF in the endometrium of women with EP may account for the association between EP and infertility.

Racial differences in risk of spontaneous abortions associated with periconceptional over-the-counter nonsteroidal anti-inflammatory drug exposure

PURPOSE

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most common medications reported in pregnancy. NSAIDs directly impact prostaglandin pathways and have been proposed as potential risk factors for spontaneous abortions (SABs, gestation <20 weeks). SAB risk and drug response across several medications differ by race; therefore, we evaluated whether associations between NSAIDs and SAB risk differ by race.

METHODS

Women were enrolled in the Right from the Start (2004-2010) prospective cohort. Data regarding over-the-counter NSAIDs up to the sixth week of pregnancy were obtained from interviews. Race was self-reported. Cox proportional hazards regression models were used to estimate the association between NSAID exposure and SAB, adjusted for confounders.

RESULTS

Among 2493 pregnancies, 12% were African American and 88% were Caucasian. NSAID exposure was reported by 40% (n = 124) of African Americans and 43% (n = 945) of Caucasians. Race-stratified analyses showed protection from SAB among African Americans (adjusted hazard ratio [aHR], 0.84; 95% confidence interval [CI], 0.73-0.96) but no effect in Caucasians (aHR, 1.01; 95% CI 0.88-1.16).

CONCLUSIONS

Our findings suggest that risk for SAB due to over-the-counter NSAIDs in early pregnancy is modified by race. Further investigation of dose, timing in gestation, and indication may help to further reconcile the relationship between race, NSAIDs, and SAB.

Changes in eutopic endometrial gene expression during the progression of experimental endometriosis in the baboon, Papio anubis

Endometriosis is associated with aberrant gene expression in the eutopic endometrium of women with disease. To determine if the development of endometriotic lesions directly impacts eutopic endometrial gene expression, we sequentially analyzed the eutopic endometrium across the time course of disease progression in a baboon model of induced disease. Endometriosis was induced in baboons (n = 4) by intraperitoneal inoculation of autologous menstrual endometrium. Eutopic endometria were collected during the midsecretory phase (Days 9-11 postovulation) at 1, 3, 6-7, 10-12, and 15-16 mo after disease induction and compared with tissue from disease-free baboons. RNA was hybridized to Human Genome U133 Plus 2.0 Arrays, and data were extracted using Gene-Chip Operating Software. Subsequently, both Gene Set Enrichment Analysis and Ingenuity Pathways Analysis were used to find biological states that have a statistically significant enrichment concomitant with pairwise comparison of human endometriosis arrays. Within 1 mo of induction of the disease, 4331 genes were differentially expressed (P < 0.05). Hierarchical clustering revealed self-segregation into two groups-a) 1, 3, and 10-12 mo and b) 6-7 and 15-16 mo-together with controls. Clustering analysis at each stage of disease validated dysregulation of several signaling pathways, including Nodal-like receptor, EGF, ERK/MAPK, and PI3/AKT. Sequential analysis of the same animals during disease progression demonstrated an early disease insult and a transitory dominance of an estrogenic phenotype; however, as the disease progressed, a progesterone-resistant phenotype became evident. Furthermore, we demonstrate a 38.6% differential gene expression overlap with endometrial samples in the midsecretory phase from women with endometriosis, concomitant with similar dysregulation in human disease candidate genes Fos, Nodal, Suclg2, and Kras, among others. Molecular changes in the eutopic endometrium, associated with endometriosis, are directly impacted by endometriotic lesions, providing strong evidence that it is the disease rather than inherent defective endometrium that results in aberrant gene expression in the eutopic endometrium. Furthermore, this baboon model provides a powerful means whereby the early events associated with the pathology of disease and the resulting infertility may be elucidated.

Aromatase inhibitor treatment limits progression of peritoneal endometriosis in baboons

OBJECTIVE

To determine the effect of inhibiting aromatase activity on endometrial lesion growth and aromatase expression in a baboon model of induced endometriosis.

DESIGN

Prospective study.

SETTING

Primate research institute.

ANIMAL(S)

Sixteen olive baboons.

INTERVENTION(S)

Sixteen olive baboons with induced endometriosis were examined with laparoscopy 10 months after disease inoculation. Animals in group 1 (n = 10) were treated with 1.25 mg/d of the aromatase inhibitor (AI) letrozole, and animals in group 2 (n = 6) were given a placebo for a total of 6 months.

MAIN OUTCOME MEASURE(S)

Total number of endometriotic lesions, morphology, and volume of lesions, as well as semiquantitative reverse transcription-polymerase chain reaction and quantitative polymerase chain reaction for levels of aromatase cytochrome messenger RNA were measured. Ovarian volumes were evaluated before treatment initiation and every 2 months during the study.

RESULT(S)

Treatment of group 1 animals with an AI significantly decreased lesion volume from baseline measurements, whereas the placebo-treated animals showed an increase in lesion volume. Aromatase messenger RNA levels in lesions in the AI-treated animals were significantly lower compared with the placebo-treated animals. Ovarian volumes were significantly increased at 6 months of AI treatment compared with pretreatment volumes.

CONCLUSION(S)

These findings suggest that suppression of aromatase cytochrome P450 may inhibit the in vivo growth of endometriotic lesions in baboons.

Periconceptional over-the-counter nonsteroidal anti-inflammatory drug exposure and risk for spontaneous abortion

OBJECTIVE

To estimate the association between over-the-counter nonsteroidal anti-inflammatory drug (NSAID) exposure during the early first trimester and risk for spontaneous abortion (gestation before 20 weeks of gestation) in a prospective cohort.

METHODS

Women were enrolled in the Right from the Start study (2004-2010). Exposure data regarding over-the-counter NSAID use from the last menstrual period (LMP) through the sixth week of pregnancy were obtained from intake and first-trimester interviews. Pregnancy outcomes were self-reported and verified by medical records. Gestational age was determined from the LMP. Stage of development before loss was determined from study ultrasonography. Cox proportional hazards regression models were used to estimate the association between NSAID exposure and pregnancy outcome taking into account candidate confounders.

RESULTS

Among 2,780 pregnancies, 367 women (13%) experienced a spontaneous abortion. NSAID exposure was reported by 1,185 (43%) women. NSAID exposure was not associated with spontaneous abortion risk in unadjusted models (hazard ratio [HR] 1.01, 95% confidence interval [CI] 0.82-1.24) or models adjusted for maternal age (adjusted HR 1.00, 95% CI 0.81-1.23).

CONCLUSION

Our findings suggest that use of nonprescription over-the-counter NSAIDs in early pregnancy does not put women at increased risk of spontaneous abortion.

Interaction of the conceptus and endometrium to establish pregnancy in mammals: role of interleukin 1β

Implantation and the establishment of pregnancy in mammals involves an intricate interplay of hormones, cytokines, growth factors, proteins, lipids, ions and the extracellular matrix between the uterine epithelium, stroma, immune cells and the conceptus trophectoderm. The divergent nature of implantation in the mouse, human and pig provides not only an interesting contrast in the establishment of pregnancy and early embryonic development but also intriguing similarities with regard to early endometrial-conceptus signaling. An interesting pro-inflammatory cytokine expressed in a number of mammalian species during the period of implantation is interleukin-1β (IL1B). The presence of IL1B might be involved with immunotolerance at the maternal-placental interface and has been proposed as one of the mediators in placental viviparity. The production of IL1B and other proinflammatory cytokines might play a role in establishing pregnancy through modulation of the nuclear factor kappa-B (NFKB) system in a number of species. A model for the regulation of cellular progesterone receptor expression and NFKB activation for endometrial receptivity and conceptus attachment is continuing to evolve and is discussed in the present review.

Activation of the transcription factor, nuclear factor kappa-B, during the estrous cycle and early pregnancy in the pig

Establishment and maintenance of pregnancy in the pig involves intricate communication between the developing conceptuses and the maternal endometrium. This process occurs during trophoblast elongation which is spaciotemporally associated with conceptus synthesis and release of IL1B concomitant with pregnancy-specific endometrial up-regulation of IL-1 receptors, providing the potential for activation of the transcription factor, NFKB. The objective of the current investigation was to determine changes in expression and cellular localization of NFKB and associated factors during the estrous cycle and early pregnancy in the pig. In situ hybridization was used to localize changes in PGR, ESR1, and TNFRSF11A during the peri-implantation period. Quantitative RT-PCR was utilized to demonstrate gene expression changes for NFKB1, RELA, TNFRSF11A, TLR4, NFKBIA and NFKBIB. Transcription factor ELISA demonstrated an overall increase in RELA during the peri-implantation period in both cyclic and pregnant gilts. While the presence of TNFSF11A and TLR4 were both detected, TLR4 expression changes were temporally associated with NFKB expression and activation. Collectively, these data demonstrate that NFKB activation may occur during the period of uterine receptivity in both the cyclic and pregnant endometrium.

The transcription factor C/EBPβ is a marker of uterine receptivity and expressed at the implantation site in the primate

During early pregnancy, the endometrium undergoes pronounced hormone-dependent functional changes in preparation for embryo implantation. Local autocrine-paracrine signaling at the fetal-maternal interface is crucial for the establishment of pregnancy. We previously reported that the transcription factor C/ EBPbeta, which is expressed at the implantation sites (ISs) in pregnant mice, acts as a key mediator of steroid hormone responsiveness in the endometrium. Mice lacking C/EBPbeta fail to support implantation due to defects in epithelial proliferation and stromal cell differentiation. In the current study, C/EBPbeta expression was dramatically stimulated in the endometrium of baboons (Papio anubis) during the window of uterine receptivity in response to a local infusion of chorionic gonadotropin, an embryonic signal. A robust induction of C/EBPbeta expression was also seen at the IS in the baboon and the human. Collectively, our results indicate that C/EBPbeta is a biomarker of endometrial receptivity and plays a conserved functional role during implantation in the primate.

Endometrial gene expression analysis at the time of embryo implantation in women with unexplained infertility

Successful embryo implantation depends on the quality of the embryo, as well as on the receptivity of the endometrium. The aim of this study was to investigate the endometrial gene expression profile in women with unexplained infertility in comparison with fertile controls at the time of embryo implantation in order to find potential predictive markers of uterine receptivity and to identify the molecular mechanisms of infertility. High-density oligonucleotide gene arrays, comprising 44 000 gene targets, were used to define the endometrial gene expression profile in infertile (n = 4) and fertile (n = 5) women during the mid-secretory phase (day LH + 7). Microarray results were validated using real-time PCR. Analyses of expression data were carried out using non-parametric methods. Hierarchical clustering and principal component analysis showed a clear distinction in endometrial gene expression between infertile and fertile women. In total we identified 145 significantly (>3-fold change) up-regulated and 115 down-regulated genes in infertile women versus controls. Via Database for Annotation, Visualization and Integrated Discovery functional analysis we detected a substantial number of dysregulated genes in the endometria of infertile women, involved in cellular localization (21.1%) and transport (18.8%) and transporter activity (13.1%) and with major localization in extracellular regions (19.2%). Ingenuity Pathways Analysis of the gene list showed dysregulation of gene pathways involved in leukocyte extravasation signalling, lipid metabolism and detoxification in the endometria of infertile women. In conclusion, endometrial gene expression in women with unexplained infertility at the time of embryo implantation is markedly different from that in fertile women. These results provide new information on genes and pathways that may have functional significance as regards to endometrial receptivity and subsequent embryo implantation.

Epithelial human chorionic gonadotropin is expressed and produced in human secretory endometrium during the normal menstrual cycle

The objective of this study was to determine whether beta human chorionic gonadotropin (hCG) (CGB) subunits and alpha hCG (CGA) subunits are expressed and the hCG dimer is produced in normal human cyclic endometrium. Endometrial specimens were collected for histological dating from women undergoing treatment in our division of human reproduction. RNA from normal secretory endometrium was extracted, and CGB and CGA gene expression was assessed by semiquantitative PCR. Adequate secretory endometrial specimens were homogenized using protease inhibitors. Proteins present in the supernatant were separated electrophoretically, and molecular hCG isoforms were detected by Western blot. The supernatant hCG concentrations were measured by ELISA. We characterized hCG and leukocytes in endometrial specimens by immunohistochemistry. Uterine flushing was performed to confirm endometrial hCG secretion into the uterine fluid. A full-length CGB mRNA encompassing the exon 1 promoter region and the structure exons 2 and 3 (including the C-terminal peptide) was expressed in normal secretory endometrial specimens (similar to CGA) during the early secretory phase of the menstrual cycle, up to an optimum at the midsecretory to late secretory phases. In homogenate supernatants obtained from normal secretory endometrium, hormone concentrations of dimeric hCG were approximately 5 mU per 10 mg of tissue, compared with considerably smaller concentrations of corresponding single free CGB subunit. Single chains of CGB, CGA, and dimeric molecular hCG isoforms were found in endometrial specimens by Western blot. Glandular endometrial hCG production is demonstrated immunohistochemically, with an increase toward the late secretory phase vs. the early secretory phase of the normal secretory menstrual cycle. However, glandular hCG release is diminished or absent in the dyssynchronous or missing endometrial secretory transformation. Endogenous endometrial hCG may be important for implantation and maintenance of pregnancy.

Hormone control and expression of androgen receptor coregulator MAGE-11 in human endometrium during the window of receptivity to embryo implantation

The androgen receptor (AR) is a ligand-activated transcription factor of the male and female reproductive tracts whose activity is modulated by coregulator binding. We recently identified melanoma antigen gene protein-11 (MAGE-11) of the MAGEA gene family that functions as an AR coregulator by binding the AR N-terminal FXXLF motif. Here we report that MAGE-11 is expressed in a temporal fashion in endometrium of normally cycling women. Highest levels of MAGE-11 mRNA and protein occur in the mid-secretory stage, coincident with the window of uterine receptivity to embryo implantation. Studies in human endometrial cell lines together with the hormone profile of the menstrual cycle and pattern of estrogen receptor-alpha expression in cycling endometrium suggest the rise in MAGE-11 mRNA results from down-regulation by estradiol during the proliferative phase and up-regulation by cyclic AMP signaling in the early and mid-secretory stage. In agreement with its coregulatory function, MAGE-11 localizes with AR in glandular epithelial cell nuclei in the mid-secretory stage. The increase in AR protein in the mid-secretory endometrium without an increase in AR mRNA suggests MAGE-11 stabilizes AR in glandular epithelial cell nuclei. This was supported by expression studies at low androgen levels indicating AR stabilization by MAGE-11 dependent on the AR N-terminal transactivation domain. The results suggest that MAGE-11 functions as a coregulator that increases AR transcriptional activity during the establishment of uterine receptivity in the human female.

Angiogenic activity of human chorionic gonadotropin through LH receptor activation on endothelial and epithelial cells of the endometrium

Successful embryo development requires an extensive endometrial angiogenesis in proximity of implantation site. The glycoprotein hCG is produced even before implantation by trophoblast in normal pregnancy. In this manuscript, we demonstrate an angiogenic effect of hCG in several in vivo (chick chorioallantoïc membrane, matrigel plug assay, aortic ring assay) and in vitro experimental models. In contrast, human placental lactogen (hPL) did not display angiogenic properties. LH/hCG receptor was detected in endothelial cells by reverse-transcriptase polymerase chain reaction (RT-PCR) and by Western blotting. In mice aortic ring assay, angiostimulation by hCG was abrogated by deletion of LH/hCG receptor (LuRKO mice). Use of recombinant hCG and anti-hCG antibody (Ab) further confirmed the specificity of this angiogenic activity. By using dibutyryl cAMP, adenylate cyclase, or protein kinase A inhibitors, we demonstrate that hCG-mediated angiogenesis involves adenylyl-cyclase-protein kinase A activation. Addition of hCG to endometrial epithelial epithelial cells, but not to cultured endothelial cells, stimulated vascular endothelial growth factor (VEGF). VEGF and hCG also displayed additive activities. Altogether, these data demonstrate that peritrophoblastic angiostimulation may result from a paracrine dialogue between trophoblast, epithelial, and endothelial cells through hCG and VEGF.

Induced Endometriosis in the Baboon (Papio anubis) Increases the Expression of the Proangiogenic Factor CYR61 (CCN1) in Eutopic and Ectopic Endometria1

The expression of human CYR61 (cysteine-rich, angiogenic inducer, 61; CCN1) mRNA has been previously shown to be deregulated in the endometrium of women with endometriosis. We have chosen the baboon model (Papio anubis) of induced endometriosis to clarify whether CYR61 mRNA upregulation is predisposed to an inappropriately differentiated endometrium or is deregulated as a response to the presence of ectopic lesions. In the baboon, endometrial CYR61 mRNA expression underwent moderate cyclical variation, with a significant 7.3-fold increase detected at Day 2 postmenses when compared to endometrium from the proliferative and secretory phases. The CYR61 transcript was extensively upregulated in the eutopic endometrium from all baboons with induced endometriosis, as early as 1 mo postinoculation of menstrual tissue into the peritoneal cavity. CYR61 mRNA expression then decreased throughout progression of the disease, but remained higher compared to control tissues. Ectopic endometriotic lesions showed a further increase in CYR61 mRNA, with highest expression found in red lesions. Moreover, the expression levels of CYR61 transcripts correlated significantly with those of VEGF. Immunohistochemistry revealed the presence of CYR61 protein in glandular and luminal epithelial cells as well as in blood vessels of eutopic and ectopic endometrium. As in humans, increased levels of CYR61 mRNA correlated with the development of endometriosis in baboons. The increase of CYR61 mRNA in eutopic endometrium of baboons following peritoneal inoculation with menstrual endometrium provides evidence for a feedback mechanism from resulting lesions to induce a shift in gene expression patterns in the eutopic endometrium.

Stromal cells from endometriotic lesions and endometrium from women with endometriosis have reduced decidualization capacity

OBJECTIVE

To evaluate the phenotype, proliferative, and differentiation capacities in vitro of stromal cells derived from peritoneal, ovarian, and deeply infiltrating endometriosis.

DESIGN

Experimental study using phase contrast microscopy, immunocytochemistry, and functional bioassays.

SETTING

University-based laboratory.

PATIENT(S)

Women with and without endometriosis undergoing surgery for benign indications.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The stability in vitro of stromal cells derived from peritoneal (n = 18), ovarian (n = 29), and deeply infiltrating (n = 14) endometriotic lesions, as well as endometrium from women with (n = 5) and without endometriosis (n = 5) was evaluated by detection of endometrial markers. The proliferative and differentiation capacity of the cells was assessed by the use of cell doubling estimation and in vitro decidualization assays.

RESULT(S)

The expression of the progesterone receptor and CD10 in stromal cells derived from the three types of endometriotic lesions is retained in culture up to passage 10. The doubling time of stromal cells from deeply infiltrating lesions is lower than that of endometrial stromal cells. Levels of prolactin and insulin-like growth factor binding protein-1 (IGFBP-1) are reduced in supernatants from stromal cells derived from the three types of lesions and from the endometrium of women with endometriosis.

CONCLUSION(S)

The peritoneal, ovarian, and deeply infiltrating endometriotic stromal cell lines we describe retain in vivo tissue markers. Loss of differentiation capacity of the endometriotic cell lines and endometrial cells from women with endometriosis may influence the capacity for proliferation and survival of these cells in the ectopic environment.

Embryo-maternal interactive factors regulating the implantation process: implications in assisted reproductive

The embryo-maternal dialogue that starts very early in the life of the embryo is crucial for its own implantation. A disturbance in this dialogue is the major reason for which 60% of all pregnancies are terminated at the end of the periimplantation period. Many studies have been performed to improve the understanding of the molecular mechanisms involved in this dialogue. Both partners, the mother and the embryo, are equally involved in this exchange of signals. Much progress has been done in understanding the role of (i) chorionic gonadotrophin, (ii) growth factors and cytokines, and (iii) steroid hormones and other mediators, produced either by the embryo, by the mother, or by both, during the peri-implantation period. Today it is clear that their production dictates changes in the endometrium, in the immunological system of the mother and in embryo metabolism, that enable the embryo to implant. Knowledge of the molecular mechanisms involved in the embryo-maternal interaction are reviewed in this article.

Spontaneous epithelial plaques in the uterus of a non-pregnant cynomolgus monkey (Macaca fascicularis)

Two epithelial plaques were observed in the uterus of a 4 years 8 month old non-pregnant cynomolgus monkey. Normally, epithelial plaques occur near the implantation site of primates during early pregnancy but can also be induced by various procedures. Both plaques consisted of clusters and nest of cells with large nuclei and a faintly basophilic cytoplasm. Marked cellular pleomorphism was seen, including cells with giant nuclei and binucleated cells. Further histological features were vacuolation, mitosis and PAS-positive granules in several cells and polymorphonuclear infiltration in the periphery of the plaque. This is the second description of a spontaneous epithelial plaque in a primate and the first in a cynomolgus monkey.

Immunohistological localization of insulin-like growth factor binding protein-1 in primary implantation sites and trauma-induced deciduomal tissues of the rhesus monkey

We have earlier demonstrated that there is a close similarity in the temporo-spatial pattern in the onset of oedema, epithelial-plaque transformation, stromal decidualization and influx of granulated lymphocytes in artificially trauma-induced deciduomal endometrium with such events in maternal endometrium at the primary implantation site during early stages of pregnancy in the rhesus monkey. In the present study, we have immunohistochemically examined whether the pattern of insulin-like growth factor-binding protein 1 (IGFBP-1) protein expression in conceptus tissue and maternal endometrium during lacunae and villous placenta stages of gestation in the rhesus monkey is developmental stage-specific and whether a discernible difference exists in the temporo-spatial characteristics of IGFBP-1 protein expression between conceptus associated implantation-decidualization and trauma induced deciduoma in the rhesus monkey. Trophoblast cells failed to exhibit IGFBP-1 immunopositive staining at any stage of implantation-placentation studied. Epithelial cells in plaque acini, endothelial cells, and vascular smooth muscle also did not show any immunopositive staining for IGFBP-1 in samples of primary implantation sites and trauma-induced deciduoma. Maternal endometrial epithelial and stromal-decidual cells however exhibited a temporal and spatial pattern of IGFBP-1 expression in cell-type specific manner and clear distinctions were observed between conception and deciduoma samples. Our results suggest that IGFBP-1 expression is highly tissue and development-specific and that conceptus-derived signals are necessary to initiate the glandular expression of IGFBP-1 during the early stage of gestation.

Biomarkers of endometrial receptivity--a review

Implantation is a phenomenon that involves an interaction between the embryo and maternal endometrium. There is, in the menstrual cycle, a short and precise period of time in which the maternal-embryonic interaction is optimal and culminates with adhesion and invasion of the blastocyst into the progesterone-induced secretory endometrium. This period is called nidation or implantation window. In the implantation window changes occur in endometrial epithelial morphology, characterized by the appearance of membrane projections called pinopodes. Pinopodes are progesterone-dependent organelles, that look like apical cellular protrusions appearing between days 20 and 21 of the natural menstrual cycle. There are many factors that regulate the changes typical of the implantation window and the appearance of the pinopodes. The embryonic and maternal expression of growth factors and cytokines, calcitonin, HOX genes and cell adhesion molecules might all play a major role in the phenomenon of implantation. The cytokines function as chemical messengers and can serve as biomarkers of uterine receptivity. Understanding the function of these biomarkers and their role in determining the implantation window in women, will help us to diagnose and treat infertile couples more efficiently.

Differential Expression of Genes in the Endometrium at Implantation: Upregulation of a Novel Member of the E2 Class of Ubiquitin-Conjugating Enzymes1

The process of embryo attachment and implantation is accompanied by dramatic cellular and functional changes in the endometrium, the control and mechanisms of which are not clearly understood. The cDNA cloning of differentially expressed genes, specifically at implantation sites in the rabbit endometrium, was used to identify genes controlling functional and remodeling changes. Tissue from the endometrium of Day 6(3/4) (preimplantation) and Day 8 (implantation initiation) pregnant rabbits was used to screen for differentially expressed genes by combined cDNA subtraction/suppressive hybridization. Twenty-nine differentially expressed genes were identified encoding protein modification enzymes, signaling proteins, structural proteins, and enzymes. One of these is a novel member of the E2 ubiquitin-conjugating enzyme family we have designated UBCi (i for implantation), which displayed dramatic nucleotide and deduced amino acid sequence conservation between rabbits, humans, and mice. In situ hybridization indicated UBCi expression exclusively in the luminal epithelium of the endometrium while glandular epithelium, trophoblast, and myometrium were negative. Expression was specific for epithelial cells at implantation sites and was not detected in non-implant-site endometrium. UBCi mRNA was detected in both the mesometrial and antimesometrial epithelial cells of the implantation sites, sites undergoing both differentiation and/or apoptosis. These results identify a group of differentially expressed genes in the endometrium including UBCi and provide new focal targets for studying processes controlling cellular remodeling during implantation. The important roles of ubiquitination in controlling the activities and turnover of key signaling proteins suggest potential roles in controlling critical aspects of implantation.

Reproductive adaptations to a large-brained fetus open a vulnerability to anovulation similar to polycystic ovary syndrome

During the ovarian or menstrual cycle, prior to ovulation, many female primates exhibit a relatively prolonged follicular phase and terminate the postovulatory luteal phase with menstrual bleeding. The prolonged follicular phase is a trait that distinguishes primate from nonprimate species. It enables extended estrogen-induced proliferation and growth of the uterine endometrium prior to progesterone-induced maturation during the luteal phase to accommodate a potential pregnancy with a rapidly invading placenta. Progressive development of both an extended duration of estrogen-induced, preimplantation endometrial proliferation and a rapidly invading placenta across the Primate order may well have been necessary to accommodate differentiation and growth of an increasingly large fetal brain. Prolongation of the follicular phase in primates has also led to the isolation of the final stages of follicle selection (growth deviation of the dominant follicle from its contemporaries) solely within the follicular phase and thus outside the protection of luteal phase progesterone inhibition of pituitary luteinizing hormone (LH) secretion. Such primate reproductive characteristics put the latter stages of ovarian follicle selection at risk of exposure to excessive pituitary secretion of LH. Excessive secretion of LH during follicle selection could result not only in impaired follicle development, excessive ovarian androgen secretion, and ovulation failure, but also in excessive estrogenic stimulation of the uterine endometrium without intervening menstrual periods. Such reproductive abnormalities are all found in a single, prevalent infertility syndrome afflicting women in their reproductive years: polycystic ovary syndrome (PCOS). We propose that successful female reproductive adaptations to accommodate the growth demands of large-brained primate fetuses have facilitated a particular vulnerability of higher primates to hypergonadotropic disruption of ovulatory function, as found in PCOS.

Embryo-maternal signalling: how the embryo starts talking to its mother to accomplish implantation

The process of implantation and trophoblast invasion is currently considered as the most limiting factor for the establishment of pregnancy. Molecular interactions at the embryo-maternal interface during the time of adhesion and subsequent invasion are crucial to the process of embryonic implantation. Both partners, the mother as well as the embryo, play equal roles in the embryo-maternal dialogue, the embryonic part being the main topic in this study. Investigations of the proteins in the extra-embryonic matrices (i.e. zona pellucida) indicate that the embryo participates intensively in this early embryo-maternal signalling. One unique feature during implantation process of primate embryos is the release of chorionic gonadotrophin, which seems to influence endometrial activity by two different mechanisms: (i) luteotrophic activity with increasing progesterone release and (ii) a direct action on the endometrium. Furthermore, embryonic interleukin-1beta may be involved in embryo-maternal signalling. Other significant signals in this interaction are most likely leukaemia inhibitory factor (LIF) and colony-stimulating factor (CSF), which stimulate matrix metalloproteinase (MMP)/insulin-like growth factor binding protein-1 (IGFBP-1) activity and the insulin-like growth factor (IGF) system, which is modulated by embryonic IGFBP-3. Similar significances are discussed for uteroglobin and haptoglobin. Finally, the phenomenon of maternal immunological tolerance, triggered by the presence of the early embryo, is fundamental to the understanding of implantation and trophoblast invasion. A tightly regulated balance between activated and inactivated T cells at the implantation site may control the beginning of adequate trophoblast invasion and also limit this invasion to a tolerable extent for the maternal system, consequently ensuring a biologically healthy haemo-chorial placenta.

A modified baboon model for endometriosis

Endometriosis is one of the most common causes of infertility and chronic pelvic pain and affects 1 in 10 women in the reproductive-age group. Although existence of this disease has been known for over 100 years, our current knowledge of its pathogenesis, the pathophysiology of related infertility, and its spontaneous evolution is limited. Several reasons contribute to our lack of knowledge, the most critical being the difficulty in carrying out objective long-term studies in women. Thus, we and others have developed the baboon as an appropriate nonhuman primate to study the etiology of this disease. We suggested that endometriosis develops in two distinct phases. Phase I is invasive and dependent on ovarian steroids. Phase II, which is the active phase of the disease, is characterized by endogenous estrogen biosynthesis. Following inoculation with menstrual endometrial tissues in two consecutive menstrual cycles, baboons develop lesions that are similar to those seen in humans. Laparoscopy at 1, 4, and 10 months revealed a preponderance of red raised nodules at the first month, while both red lesions and reddish-blue proliferative endometriotic lesions were evident at 4 and 10 months. The presence of glandular tissue and stromal fibroblasts in these lesions was confirmed by histology. Lesions obtained at 1 and 4 months expressed estrogen receptor beta (ERbeta), matrix metalloproteinase-7 (MMP-7), and vascular endothelial growth factor (VEGF) predominantly. However, aromatase expression was only readily evident at 10 months, although some lesions obtained at 4 months expressed low levels of aromatase. Therefore, our preliminary data suggest that endometriosis can be artificially induced in baboons, and the role of exogenous and endogenous estradiol in proliferation, angiogenesis, and immune modulations can now be evaluated in a potentially systemic manner.

Molecular markers of implantation: clinical implications

The endometrium has been conventionally studied using histologic criteria. Our understanding of endometrial physiology has been advanced tremendously by research into the molecules that mediate its development and function. These molecules demonstrate a dynamic expression pattern through the menstrual cycle and have been implicated in endometrial growth, differentiation, and receptivity. These molecules include secreted proteins (endometrial bleeding-associated factor, glycodelin-A, insulin-like growth factor binding protein-1), cell-surface receptors (integrins), and nuclear transcription factors (HOXA10 and HOXA11). The homeobox genes Hoxa10 and Hoxa11 are necessary for implantation because mice with mutations in these genes exhibit a failure of implantation. HOXA10 and HOXA11 have been shown to be important for implantation in humans as well. Knowledge of endometrial molecular dynamics may now be used to enhance our ability to diagnose implantation defects. It may soon be possible to treat individual molecular defects by protein supplementation or gene therapy.