Identification of Indian hedgehog as a progesterone-responsive gene in the murine uterus

Research Progress on the Impact of Human Chorionic Gonadotropin on Reproductive Performance in Sows

Human chorionic gonadotropin is a glycoprotein hormone produced by human or humanoid syncytiotrophoblasts that differentiate during pregnancy. Due to its superior stability and long-lasting effects compared to luteinizing hormone, it is often used to replace luteinizing hormone to regulate reproductive performance in sows. Human chorionic gonadotropin promotes oocyte maturation, follicle development, and luteinization, thereby increasing conception rates and supporting early embryonic development. In sow reproductive management, the application of human chorionic gonadotropin not only enhances ovulation synchrony but also improves the success rate of embryo implantation by regulating endometrial receptivity and immune mechanisms, significantly enhancing overall reproductive performance. This article primarily reviews the application of human chorionic gonadotropin in sow follicle development, luteal maintenance, and embryo implantation, providing theoretical support for its use in improving reproductive performance in sows.

Progesterone in frozen embryo transfer cycles: assays, circulating concentrations, metabolites, and molecular action

Programmed or medicated frozen embryo transfer cycles rely on exogenous progesterone (P) administration to prepare the endometrium for implantation and maintain pregnancy. Presently, the optimal route and dose of P replacement for frozen embryo transfer are not known. In addition, there is a paucity of data and insufficient understanding regarding the metabolism and actions of P in implantation and pregnancy maintenance. In the present review, we discuss how different P assay methodologies affect the determination of P thresholds for implantation and pregnancy maintenance. In addition, we discuss the importance of free P and its regulation in the endometrium and show the complexity of molecular signaling that is required for P-dependent endometrial receptivity. We concluded that future studies should focus on defining accurate circulating and endometrial P concentrations, both for total and free P, and how these concentrations correlate with endometrial receptivity and clinical outcomes.

Molecular approaches to mammalian uterine receptivity for conceptus implantation

Mammalian reproduction is more inefficient than expected and embryo/conceptus implantation into the maternal endometrium is considered to be a rate-limiting process. Although extensive physiological and structural diversity exists among mammalian species, the basic molecular mechanisms underlying successful implantation are conserved. The extensive use of genetically engineered mouse models has provided considerable information on uterine receptivity for embryo implantation. The molecular mechanisms and cellular processes identified thus far require further validation in other mammalian species. In this review, representative ovarian steroid hormone-induced signaling pathways controlling uterine adaptation are presented based on the results of rodent studies. Selected examples of functional conservation in mammals, such as humans and cattle, are briefly described. To date, molecular therapeutic trials for fertility improvement have not been conducted. Considerable efforts are required to provide further understanding of these molecular mechanisms. Such understanding will contribute to the development of reliable clinical diagnostics and therapeutics for implantation failure, leading to reproductive success in a wide variety of mammals in the future.

ST6GALNAC1-mediated sialylation in uterine endometrial epithelium facilitates the epithelium-embryo attachment

INTRODUCTION

Embryo implantation requires synergistic interaction between the embryo and the receptive endometrium. Glycoproteins and glycan-binding proteins are involved in endometrium-embryo attachment. Sialyl Tn (sTn), a truncated O-glycan, is catalyzed by ST6 N-Acetylgalactosaminide Alpha-2,6-Sialyltransferase 1 (ST6GALNAC1) and can be detected by specific Sialic-acid-binding immunoglobulin-like lectins (Siglecs). Whether the sTn-Siglecs axis supports embryo implantation remains unknown.

OBJECTIVES

This paper aims to study the role of ST6GALNAC1/sTn-Siglecs axis in embryo implantation.

METHODS

ST6GALNAC1 and sTn in human endometrium were analyzed by immunohistochemistry. An in vitro implantation model was conducted to evaluate the effects of ST6GALNAC1/sTn on the receptivity of human endometrial AN3CA cells to JAR spheroids. Immunoprecipitation combined with mass spectrometry analysis was carried out to identify the key proteins modified by sTn in endometrial cells. Siglec-6 in human embryos was analyzed by published single-cell RNA sequencing (scRNA-seq) datasets. Protein interaction assay was applied to verify the bond between the Siglec-6 with sTn-modified CD44. St6galnac1 siRNAs and anti-sTn antibodies were injected into the uterine horn of the mouse at the pre-implantation stage to evaluate the role of endometrial St6galnac1/sTn in embryo implantation. Siglec-G in murine embryos was analyzed by immunofluorescence staining. The function of Siglec-G is evidenced by uterine horn injection and protein interaction assay.

RESULTS

Both human and murine endometrium at the receptive stage exhibit higher ST6GALNAC1 and sTn levels compared to the non-receptive stage. Overexpression of ST6GALNAC1 significantly enhanced the receptivity of AN3CA cells to JAR spheroids. Inhibition of endometrial ST6GALNAC1/sTn substantially impaired embryo implantation in vivo. CD44 was identified as a carrier for sTn in the endometrial cells of both species. Siglec-6 and Siglec-G, expressed in the embryonic trophectoderm, were found to promote embryo attachment, which may be achieved through binding with sTn-modified CD44.

CONCLUSION

ST6GALNAC1-regulated sTn in the endometrium aids in embryo attachment through interaction with trophoblastic Siglecs.

Unraveling the Dynamics of Estrogen and Progesterone Signaling in the Endometrium: An Overview

The endometrium is crucial for the perpetuation of human species. It is a complex and dynamic tissue lining the inner wall of the uterus, regulated throughout a woman's life based on estrogen and progesterone fluctuations. During each menstrual cycle, this multicellular tissue undergoes cyclical changes, including regeneration, differentiation in order to allow egg implantation and embryo development, or shedding of the functional layer in the absence of pregnancy. The biology of the endometrium relies on paracrine interactions between epithelial and stromal cells involving complex signaling pathways that are modulated by the variations of estrogen and progesterone levels across the menstrual cycle. Understanding the complexity of estrogen and progesterone receptor signaling will help elucidate the mechanisms underlying normal reproductive physiology and provide fundamental knowledge contributing to a better understanding of the consequences of hormonal imbalances on gynecological conditions and tumorigenesis. In this narrative review, we delve into the physiology of the endometrium, encompassing the complex signaling pathways of estrogen and progesterone.

The uterine secretory cycle: recurring physiology of endometrial outputs that setup the uterine luminal microenvironment

Conserved in female reproduction across all mammalian species is the estrous cycle and its regulation by the hypothalamic-pituitary-gonadal (HPG) axis, a collective of intersected hormonal events that are crucial for ensuring uterine fertility. Nonetheless, knowledge of the direct mediators that synchronously shape the uterine microenvironment for successive yet distinct events, such as the transit of sperm and support for progressive stages of preimplantation embryo development, remain principally deficient. Toward understanding the timed endometrial outputs that permit luminal events as directed by the estrous cycle, we used Bovidae as a model system to uniquely surface sample and study temporal shifts to in vivo endometrial transcripts that encode for proteins destined to be secreted. The results revealed the full quantitative profile of endometrial components that shape the uterine luminal microenvironment at distinct phases of the estrous cycle (estrus, metestrus, diestrus, and proestrus). In interpreting this comprehensive log of stage-specific endometrial secretions, we define the "uterine secretory cycle" and extract a predictive understanding of recurring physiological actions regulated within the uterine lumen in anticipation of sperm and preimplantation embryonic stages. This repetitive microenvironmental preparedness to sequentially provide operative support was a stable intrinsic framework, with only limited responses to sperm or embryos if encountered in the lumen within the cyclic time period. In uncovering the secretory cycle and unraveling realistic biological processes, we present novel foundational knowledge of terminal effectors controlled by the HPG axis to direct a recurring sequence of vital functions within the uterine lumen.NEW & NOTEWORTHY This study unravels the recurring sequence of changes within the uterus that supports vital functions (sperm transit and development of preimplantation embryonic stages) during the reproductive cycle in female Ruminantia. These data present new systems knowledge in uterine reproductive physiology crucial for setting up in vitro biomimicry and artificial environments for assisted reproduction technologies for a range of mammalian species.

The presence of blastocyst within the uteri facilitates lumenal epithelium transformation for implantation via upregulating lysosome proteostasis activity

ABBREVIATIONS

ACTB: actin beta; AREG: amphiregulin; ATP6V0A4: ATPase, H+ transporting, lysosomal V0 subunit A4; Baf A1: bafilomycin A1; BSA: bovine serum albumin; CLDN1: claudin 1; CTSB: cathepsin B; DEGs: differentially expressed genes; E2: 17β-estradiol; ESR: estrogen receptor; GATA2: GATA binding protein 2; GLA: galactosidase, alpha; GO: gene ontology; HBEGF: heparin-binding EGF-like growth factor; IGF1R: insulin-like growth factor 1 receptor; Ihh: Indian hedgehog; ISH: in situ hybridization; LAMP1: lysosomal-associated membrane protein 1; LCM: laser capture microdissection; Le: lumenal epithelium; LGMN: legumain; LIF: leukemia inhibitory factor; LIFR: LIF receptor alpha; MSX1: msh homeobox 1; MUC1: mucin 1, transmembrane; P4: progesterone; PBS: phosphate-buffered saline; PCA: principal component analysis; PPT1: palmitoyl-protein thioesterase 1; PGR: progesterone receptor; PSP: pseudopregnancy; PTGS2/COX2: prostaglandin-endoperoxide synthase 2; qPCR: quantitative real-time polymerase chain reaction; SP: pregnancy; TFEB: transcription factor EB.

Endometrial TGFβ signaling fosters early pregnancy development by remodeling the fetomaternal interface

The endometrium is a unique and highly regenerative tissue with crucial roles during the reproductive lifespan of a woman. As the first site of contact between mother and embryo, the endometrium, and its critical processes of decidualization and immune cell recruitment, play a leading role in the establishment of pregnancy, embryonic development, and reproductive capacity. These integral processes are achieved by the concerted actions of steroid hormones and a myriad of growth factor signaling pathways. This review focuses on the roles of the transforming growth factor β (TGFβ) pathway in the endometrium during the earliest stages of pregnancy through the lens of immune cell regulation and function. We discuss how key ligands in the TGFβ family signal through downstream SMAD transcription factors and ultimately remodel the endometrium into a state suitable for embryo implantation and development. We also focus on the key roles of the TGFβ signaling pathway in recruiting uterine natural killer cells and their collective remodeling of the decidua and spiral arteries. By providing key details about immune cell populations and TGFβ signaling within the endometrium, it is our goal to shed light on the intricate remodeling that is required to achieve a successful pregnancy.

Hedgehog signaling is required for endometrial remodeling and myometrial homeostasis in the cycling mouse uterus

Decades of work demonstrate that the mammalian estrous cycle is controlled by cycling steroid hormones. However, the signaling mechanisms that act downstream, linking hormonal action to the physical remodeling of the cycling uterus, remain unclear. To address this issue, we analyzed gene expression at all stages of the mouse estrous cycle. Strikingly, we found that several genetic programs well-known to control tissue morphogenesis in developing embryos displayed cyclical patterns of expression. We find that most of the genetic architectures of Hedgehog signaling (ligands, receptors, effectors, and transcription factors) are transcribed cyclically in the uterus, and that conditional disruption of the Hedgehog receptor smoothened not only elicits a failure of normal cyclical thickening of the endometrial lining but also induces aberrant deformation of the uterine smooth muscle. Together, our data shed light on the mechanisms underlying normal uterine remodeling specifically and cyclical gene expression generally.

The endometrial transcriptome transition preceding receptivity to embryo implantation in mice

BACKGROUND

Receptivity of the uterus is essential for embryo implantation and progression of mammalian pregnancy. Acquisition of receptivity involves major molecular and cellular changes in the endometrial lining of the uterus from a non-receptive state at ovulation, to a receptive state several days later. The precise molecular mechanisms underlying this transition and their upstream regulators remain to be fully characterized. Here, we aimed to generate a comprehensive profile of the endometrial transcriptome in the peri-ovulatory and peri-implantation states, to define the genes and gene pathways that are different between these states, and to identify new candidate upstream regulators of this transition, in the mouse.

RESULTS

High throughput RNA-sequencing was utilized to identify genes and pathways expressed in the endometrium of female C57Bl/6 mice at estrus and on day 3.5 post-coitum (pc) after mating with BALB/c males (n = 3-4 biological replicates). Compared to the endometrium at estrus, 388 genes were considered differentially expressed in the endometrium on day 3.5 post-coitum. The transcriptional changes indicated substantial modulation of uterine immune and vascular systems during the pre-implantation phase, with the functional terms Angiogenesis, Chemotaxis, and Lymphangiogenesis predominating. Ingenuity Pathway Analysis software predicted the activation of several upstream regulators previously shown to be involved in the transition to receptivity including various cytokines, ovarian steroid hormones, prostaglandin E2, and vascular endothelial growth factor A. Our analysis also revealed four candidate upstream regulators that have not previously been implicated in the acquisition of uterine receptivity, with growth differentiation factor 2, lysine acetyltransferase 6 A, and N-6 adenine-specific DNA methyltransferase 1 predicted to be activated, and peptidylprolyl isomerase F predicted to be inhibited.

CONCLUSIONS

This study confirms that the transcriptome of a receptive uterus is vastly different to the non-receptive uterus and identifies several genes, regulatory pathways, and upstream drivers not previously associated with implantation. The findings will inform further research to investigate the molecular mechanisms of uterine receptivity.

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.

CRC Therapy Identifies Indian Hedgehog Signaling in Mouse Endometrial Epithelial Cells and Inhibition of Ihh-KLF9 as a Novel Strategy for Treating IUA

Intrauterine adhesion (IUA) causes menstrual disturbance and infertility. There is no effective treatment available for moderate to severe IUA cases. Stem cell-based therapy has been investigated for treating IUA but is limited in clinical applications due to issues including the precise induction of differentiation, tumorigenesis, and unclear molecular mechanisms. In our recent study, we isolated and expanded the long-term cultures of conditional reprogrammed (CR) mouse endometrial epithelial cells. Treating IUA mice with these CR cells (CRCs) restored the morphology and structure of the endometrium and significantly improved the pregnancy rate. In this study, our data with high-throughput sequencing, CRISPR knockout Ihh^-/-CRCs, and transplantation identified for the first time that the Indian hedgehog (Ihh) gene plays a critical role in the regulation of endometrial epithelial cell proliferation. We also found that aberrant activated Ihh-krüppel-like factor 9 (KLF9) signaling contributes to the inhibition of normal progesterone receptor (PR) function in IUA mice. Thus, we hypothesized that inhibition of the Ihh-KLF9 pathway may be a novel strategy to treat IUA. Our data demonstrated that treatment with the hedgehog signaling inhibitor Vismodegib restored the morphology, structure, and microenvironment of the endometrium, and greatly improved the pregnancy rate in IUA mice. This study suggests a promising application of hedgehog inhibitors as a targeted drug in the IUA clinic.

Chronic Estrus Disrupts Uterine Gland Development and Homeostasis

Female mice homozygous for an engineered Gnrhr E90K mutation have reduced gonadotropin-releasing hormone signaling, leading to infertility. Their ovaries have numerous antral follicles but no corpora lutea, indicating a block to ovulation. These mutants have high levels of circulating estradiol and low progesterone, indicating a state of persistent estrus. This mouse model provided a unique opportunity to examine the lack of cyclic levels of ovarian hormones on uterine gland biology. Although uterine gland development appeared similar to controls during prepubertal development, it was compromised during adolescence in the mutants. By age 20 weeks, uterine gland development was comparable to controls, but pathologies, including cribriform glandular structures, were observed. Induction of ovulations by periodic human chorionic gonadotropin treatment did not rescue postpubertal uterine gland development. Interestingly, progesterone receptor knockout mice, which lack progesterone signaling, also have defects in postpubertal uterine gland development. However, progesterone treatment did not rescue postpubertal uterine gland development. These studies indicate that chronically elevated levels of estradiol with low progesterone and therefore an absence of cyclic ovarian hormone secretion disrupts postpubertal uterine gland development and homeostasis.

Progesterone Actions and Resistance in Gynecological Disorders

Estrogen and progesterone and their signaling mechanisms are tightly regulated to maintain a normal menstrual cycle and to support a successful pregnancy. The imbalance of estrogen and progesterone disrupts their complex regulatory mechanisms, leading to estrogen dominance and progesterone resistance. Gynecological diseases are heavily associated with dysregulated steroid hormones and can induce chronic pelvic pain, dysmenorrhea, dyspareunia, heavy bleeding, and infertility, which substantially impact the quality of women's lives. Because the menstrual cycle repeatably occurs during reproductive ages with dynamic changes and remodeling of reproductive-related tissues, these alterations can accumulate and induce chronic and recurrent conditions. This review focuses on faulty progesterone signaling mechanisms and cellular responses to progesterone in endometriosis, adenomyosis, leiomyoma (uterine fibroids), polycystic ovary syndrome (PCOS), and endometrial hyperplasia. We also summarize the association with gene mutations and steroid hormone regulation in disease progression as well as current hormonal therapies and the clinical consequences of progesterone resistance.

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.

Uterine kisspeptin receptor critically regulates epithelial estrogen receptor α transcriptional activity at the time of embryo implantation in a mouse model

Embryo implantation failure is a major cause of infertility in women of reproductive age and a better understanding of uterine factors that regulate implantation is required for developing effective treatments for female infertility. This study investigated the role of the uterine kisspeptin receptor (KISS1R) in the molecular regulation of implantation in a mouse model. To conduct this study, a conditional uterine knockout (KO) of Kiss1r was created using the Pgr-Cre (progesterone receptor-CRE recombinase) driver. Reproductive profiling revealed that while KO females exhibited normal ovarian function and mated successfully to stud males, they exhibited significantly fewer implantation sites, reduced litter size and increased neonatal mortality demonstrating that uterine KISS1R is required for embryo implantation and a healthy pregnancy. Strikingly, in the uterus of Kiss1r KO mice on day 4 (D4) of pregnancy, the day of embryo implantation, KO females exhibited aberrantly elevated epithelial ERα (estrogen receptor α) transcriptional activity. This led to the temporal misexpression of several epithelial genes [Cftr (Cystic fibrosis transmembrane conductance regulator), Aqp5 (aquaporin 5), Aqp8 (aquaporin 8) and Cldn7 (claudin 7)] that mediate luminal fluid secretion and luminal opening. As a result, on D4 of pregnancy, the lumen remained open disrupting the final acquisition of endometrial receptivity and likely accounting for the reduction in implantation events. Our data clearly show that uterine KISS1R negatively regulates ERα signaling at the time of implantation, in part by inhibiting ERα overexpression and preventing detrimentally high ERα activity. To date, there are no reports on the regulation of ERα by KISS1R; therefore, this study has uncovered an important and powerful regulator of uterine ERα during early pregnancy.

A high level of KLF12 causes folic acid-resistant neural tube defects by activating the Shh signalling pathway in mice

Although adequate periconceptional folic acid (FA) supplementation has reduced the occurrence of pregnancies affected by neural tube defects (NTDs), the mechanisms underlying FA-resistant NTDs are poorly understood, and thus NTDs still remain a global public health concern. A high level of Krüppel-like factor 12 (KLF12) exerts deleterious effects on heath in most cases, but evidence for its roles in development has not been published. We observed KLF12-overexpressing mice showed disturbed neural tube development. KLF12-overexpressing foetuses died in utero at approximately 10.5 days post coitus, with 100% presenting cranial NTDs. Neither FA nor formate promoted normal neural tube closure in mutant foetuses. The RNA-seq results showed that a high level of KLF12 caused NTDs in mice via overactivating the sonic hedgehog (Shh) signalling pathway, leading to the upregulation of patched 1, GLI-Krüppel family member GLI1, hedgehog-interacting protein, etc., while FA metabolism-related enzymes did not express differently. PF-5274857, an antagonist of the Shh signalling pathway, significantly promoted dorsolateral hinge point formation and partially rescued the NTDs. The regulatory hierarchy between a high level of KLF12 and FA-resistant NTDs might provide new insights into the diagnosis and treatment of unexplained NTDs in the future.

Endometrial receptivity and implantation require uterine BMP signaling through an ACVR2A-SMAD1/SMAD5 axis

During early pregnancy in the mouse, nidatory estrogen (E2) stimulates endometrial receptivity by activating a network of signaling pathways that is not yet fully characterized. Here, we report that bone morphogenetic proteins (BMPs) control endometrial receptivity via a conserved activin receptor type 2 A (ACVR2A) and SMAD1/5 signaling pathway. Mice were generated to contain single or double conditional deletion of SMAD1/5 and ACVR2A/ACVR2B receptors using progesterone receptor (PR)-cre. Female mice with SMAD1/5 deletion display endometrial defects that result in the development of cystic endometrial glands, a hyperproliferative endometrial epithelium during the window of implantation, and impaired apicobasal transformation that prevents embryo implantation and leads to infertility. Analysis of Acvr2a-PRcre and Acvr2b-PRcre pregnant mice determined that BMP signaling occurs via ACVR2A and that ACVR2B is dispensable during embryo implantation. Therefore, BMPs signal through a conserved endometrial ACVR2A/SMAD1/5 pathway that promotes endometrial receptivity during embryo implantation.

Building on the known role of BMP signalling in implantation, the authors define the role of uterine ACVR2A and ALK3 (via SMAD1/5) in vivo in regulating murine endometrial receptivity and embryo implantation.

The endometrial response to modulation of ligand-progesterone receptor pathways is reversible

OBJECTIVE

To study the impact of the progesterone receptor modulator (PRM), ulipristal acetate (UPA), on endometrial morphology and function.

DESIGN

Cross-sectional.

SETTING

University Research Institute.

PATIENT(S)

Endometrial biopsies from 16 patients with heavy menstrual bleeding with a structurally normal uterus or in association with structural abnormalities identified on radiological imaging (fibroids, adenomyosis or a combination of fibroids and adenomyosis).

INTERVENTION(S)

Participants received UPA (5 mg once daily) for three 12-week courses, each separated by 4 weeks without treatment.

MAIN OUTCOME MEASURE(S)

Gene expression by real-time quantitative reverse transcription polymerase chain reaction, immunohistochemistry, and digital image analysis were analyzed to investigate the endometrial impact of modulation of progesterone receptor pathways upon expression of steroid receptors, steroid metabolizing enzymes, cell proliferation, and progesterone-regulated genes in the same patients at 3 time points: before, during, and after discontinuation of PRM treatment.

RESULT(S)

Ulipristal acetate treatment resulted in increased messenger ribonucleic acid (mRNA) levels of steroid receptors compared with pretreatment secretory endometrium; decreased mRNA levels of 17- and 11-beta-hydroxysteroid dehydrogenases compared with pretreatment proliferative endometrium and pretreatment secretory endometrium; reduced cell proliferation compared with pretreatment proliferative endometrium; and altered mRNA levels of progesterone-regulated genes. A strong consistency between immunohistochemistry-digital image analysis and real-time quantitative reverse transcription polymerase chain reaction results was evident. Alterations in the mRNA levels and endometrial morphology returned to a pretreatment phenotype after the cessation of PRM exposure.

CONCLUSION(S)

The endometrial impact of the modulation of progesterone receptor pathways with PRM (UPA) treatment is reversible.

CLINICAL TRIAL REGISTRATION NUMBER

Ulipristal acetate versus conventional management of heavy menstrual bleeding (UCON) trial (EudraCT 2014-003408-65; REC14/LO/1602).

Illuminating the "Black Box" of Progesterone-Dependent Embryo Implantation Using Engineered Mice

Synchrony between progesterone-driven endometrial receptivity and the arrival of a euploid blastocyst is essential for embryo implantation, a prerequisite event in the establishment of a successful pregnancy. Advancement of embryo implantation within the uterus also requires stromal fibroblasts of the endometrium to transform into epithelioid decidual cells, a progesterone-dependent cellular transformation process termed decidualization. Although progesterone is indispensable for these cellular processes, the molecular underpinnings are not fully understood. Because human studies are restricted, much of our fundamental understanding of progesterone signaling in endometrial periimplantation biology comes from in vitro and in vivo experimental systems. In this review, we focus on the tremendous progress attained with the use of engineered mouse models together with high throughput genome-scale analysis in disclosing key signals, pathways and networks that are required for normal endometrial responses to progesterone during the periimplantation period. Many molecular mediators and modifiers of the progesterone response are implicated in cross talk signaling between epithelial and stromal cells of the endometrium, an intercellular communication system that is critical for the ordered spatiotemporal control of embryo invasion within the maternal compartment. Accordingly, derailment of these signaling systems is causally linked with infertility, early embryo miscarriage and gestational complications that symptomatically manifest later in pregnancy. Such aberrant progesterone molecular responses also contribute to endometrial pathologies such as endometriosis, endometrial hyperplasia and cancer. Therefore, our review makes the case that further identification and functional analysis of key molecular mediators and modifiers of the endometrial response to progesterone will not only provide much-needed molecular insight into the early endometrial cellular changes that promote pregnancy establishment but lend credible hope for the development of more effective mechanism-based molecular diagnostics and precision therapies in the clinical management of female infertility, subfertility and a subset of gynecological morbidities.

Binding of microRNA-135a (miR-135a) to homeobox protein A10 (HOXA10) mRNA in a high-progesterone environment modulates the embryonic implantation factors beta3-integrin (ITGβ3) and empty spiracles homeobox-2 (EMX2)

Background

Patients with elevated circulating progesterone concentrations on the day of the human chorionic gonadotropin (hCG) trigger had relatively low implantation rates during assisted reproductive treatments. In this study, we assess the hypothesis that different concentrations of progesterone regulate the expression of homeobox protein A10 (HOXA10) and its downstream genes through miRNA-135a.

Methods

MicroRNA-135a (miR-135a), HOXA10, beta3-integrin (ITGβ3), and empty spiracles homeobox-2 (EMX2) expression levels in endometrial tissues from patients with elevated progesterone were measured. To determine the threshold of progesterone level which can impair implantation, Ishikawa cells were used to determine the expression of the aforementioned 4 genes after exposure to 5 graded concentrations of progesterone. The dual-luciferase reporter assay was used to verify whether miR-135a regulated the expression of HOXA10. Furthermore, the effects of HOXA10 on the expression of key endometrial receptivity genes ITGβ3 and EMX2 were confirmed.

Results

High progesterone levels promoted miR-135a expression in vivo, and miR-135a bound to the 3'-untranslated region (3'-UTR) of HOXA10 mRNA to inhibit HOXA10 expression. Reduction of HOXA10 promoted EMX2 expression and inhibited ITG-3 production. Progesterone promoted the expression of HOXA10 in vitro at low concentrations. However, when the concentration was greater than 10⁻⁷ ng/mL, progesterone inhibited HOXA10 by promoting miR-135a expression, thereby altering the expression of related genes and affecting endometrial receptivity.

Conclusions

In vitro, the trend in miR-135a expression (which first decreased and then increased) was in direct contrast to that of HOXA10 expression (which first increased and then decreased) as progesterone levels increased. The key factors regulating endometrial receptivity included ITGβ3 and EMX2, which were confirmed to be regulated by HOXA10. High progesterone levels affected miR-135a expression, and miR-135a inhibited HOXA10 expression, thereby affecting endometrial receptivity.

90 YEARS OF PROGESTERONE: New insights into progesterone receptor signaling in the endometrium required for embryo implantation

Progesterone's ability to maintain pregnancy in eutherian mammals highlighted this steroid as the 'hormone of pregnancy'. It was the unique 'pro-gestational' bioactivity of progesterone that enabled eventual purification of this ovarian steroid to crystalline form by Willard Myron Allen in the early 1930s. While a functional connection between normal progesterone responses ('progestational proliferation') of the uterus with the maintenance of pregnancy was quickly appreciated, an understanding of progesterone's involvement in the early stages of pregnancy establishment was comparatively less well understood. With the aforementioned as historical backdrop, this review focuses on a selection of key advances in our understanding of the molecular mechanisms by which progesterone, through its nuclear receptor (the progesterone receptor), drives the development of endometrial receptivity, a transient uterine state that allows for embryo implantation and the establishment of pregnancy. Highlighted in this review are the significant contributions of advanced mouse engineering and genome-wide transcriptomic and cistromic analytics which reveal the pivotal molecular mediators and modifiers that are essential to progesterone-dependent endometrial receptivity and decidualization. With a clearer understanding of the molecular landscape that underpins uterine responsiveness to progesterone during the periimplantation period, we predict that common gynecologic morbidities due to abnormal progesterone responsiveness will be more effectively diagnosed and/or treated in the future.

Interleukin-13 receptor subunit alpha-2 is a target of progesterone receptor and steroid receptor coactivator-1 in the mouse uterus†

The endometrium, composed of epithelial and stromal cell compartments, is tightly regulated by the ovarian steroid hormones estrogen (E2) and progesterone (P4) during early pregnancy. Through the progesterone receptor (PGR), steroid receptor coactivators, and other transcriptional coregulators, progesterone inhibits E2-induced cell proliferation and induces the differentiation of stromal cells in a process called decidualization to promote endometrial receptivity. Although interleukin-13 receptor subunit alpha-2 (Il13ra2) is expressed in the human and mouse endometrium, its potential role in the steroid hormone regulation of the endometrium has not been thoroughly examined. In this study, we employed PGR knockout mice and steroid receptor coactivator-1 knockout mice (SRC-1-/-) to profile the expression of Il13ra2 in the murine endometrium and determine the role of these transcriptional regulators in the hormone-responsiveness of Il13ra2 expression. Furthermore, we utilized a well-established decidualization-inducing steroidogenic cocktail and a siRNA-based knockdown of IL13RA2 to determine the importance of IL13RA2 in the decidualization of primary human endometrial stromal cells. Our findings demonstrate that Il13ra2 is expressed in the subepithelial stroma of the murine endometrium in response to ovarian steroid hormones and during early pregnancy in a PGR- and SRC-1-dependent manner. Furthermore, we show that knockdown of IL13RA2 before in vitro decidualization of primary human endometrial stromal cells partially compromises the full decidualization response. We conclude that Il13ra2 is a downstream target of progesterone through PGR and SRC-1 and plays a role in mediating the stromal action of ovarian steroid hormones.

Human Endometrial Transcriptome and Progesterone Receptor Cistrome Reveal Important Pathways and Epithelial Regulators

CONTEXT

Poor uterine receptivity is one major factor leading to pregnancy loss and infertility. Understanding the molecular events governing successful implantation is hence critical in combating infertility.

OBJECTIVE

To define Progesterone Receptor (PGR)-regulated molecular mechanisms and epithelial roles in receptivity.

DESIGN

RNA-sequencing and PGR-ChIP-seq were conducted in parallel to identify PGR-regulated pathways during the Window of implantation (WOI) in endometrium of fertile women.

SETTING

Endometrial biopsies from the proliferative and mid-secretory phases were analyzed.

PATIENTS OR OTHER PARTICIPANTS

Participants were fertile, reproductive aged (18-37 years) women with normal cycle length, and without any history of dysmenorrhea, infertility, or irregular cycles. In total, 42 endometrial biopsies obtained from 42 women were analyzed in this study.

INTERVENTIONS

There were no interventions during this study.

MAIN OUTCOME MEASURES

Here we measured the alterations in gene expression and PGR occupancy in the genome during the WOI, based on the hypothesis that PGR binds uterine chromatin cycle dependently to regulate genes involved in uterine cell differentiation and function.

RESULTS

653 genes were identified with regulated PGR binding and differential expression during the WOI. These were involved in regulating inflammatory response, xenobiotic metabolism, epithelial mesenchymal transition, cell death, interleukin/Signal Transducer And Activator Of Transcription (STAT) signaling, estrogen response, and Mammalian target of rapamycin complex 1 (MTORC1) response. Transcriptome of the epithelium identified 3052 differentially expressed genes, of which 658 were uniquely regulated. Transcription factors Interferon Regulatory Factor 8 (IRF8) and Myocyte Enhancer Factor 2C (MEF2C) were found to be regulated in the epithelium during the WOI at the protein level, suggesting potentially important functions that are previously unrecognized.

CONCLUSION

PGR binds the genomic regions of genes regulating critical processes in uterine receptivity and function.

Molecular Signaling Regulating Endometrium-Blastocyst Crosstalk

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

Evaluation of uterine receptivity after gonadotropin releasing hormone agonist administration as an oocyte maturation trigger: a rodent model

In natural cycle or minimal stimulation cycle IVF, buserelin acetate (buserelin), a gonadotropin-releasing hormone agonist, is often used as a maturation trigger; however, its effect on pregnancy outcomes remains unclear. Therefore, in the present study, we compared uterine receptivity in buserelin-administered mice with that in human chorionic gonadotropin (hCG)-administered mice during the peri-implantation period. Implantation, decidualisation, and term-pregnancy were impaired following hCG, but not buserelin administration. hCG stimulated the synthesis and secretion of progesterone and oestradiol, whereas ovarian steroidogenesis in the buserelin-treated group was comparable with that in the control group. Furthermore, similar to the observation in controls, the buserelin-treated group exhibited activation of progesterone receptor signalling and inhibition of oestrogen receptor signalling in the endometrial epithelium on the day of implantation. However, epithelial progesterone signalling was not detected, and a high expression of genes downstream to oestrogen was observed on day 4 following hCG administration. These results suggest that buserelin administration does not impact uterine receptivity as it did not affect ovarian steroidogenesis and endometrial steroid signalling. Therefore, buserelin is preferred as an oocyte maturation trigger to optimise uterine receptivity during treatments involving timed intercourse, intrauterine insemination, or fresh embryo transfer following in vitro fertilisation.

Tissue-specific progesterone receptor-chromatin binding and the regulation of progesterone-dependent gene expression

Progesterone receptor (PGR) co-ordinately regulates ovulation, fertilisation and embryo implantation through tissue-specific actions, but the mechanisms for divergent PGR action are poorly understood. Here we characterised PGR activity in mouse granulosa cells using combined ChIP-seq for PGR and H3K27ac and gene expression microarray. Comparison of granulosa, uterus and oviduct PGR-dependent genes showed almost complete tissue specificity in PGR target gene profiles. In granulosa cells 82% of identified PGR-regulated genes bound PGR within 3 kb of the gene and PGR binding sites were highly enriched in proximal promoter regions in close proximity to H3K27ac-modified active chromatin. Motif analysis showed highly enriched PGR binding to the PGR response element (GnACAnnnTGTnC), but PGR also interacted significantly with other transcription factor binding motifs. In uterus PGR showed far more tendency to bind intergenic chromatin regions and low evidence of interaction with other transcription factors. This is the first genome-wide description of PGR action in granulosa cells and systematic comparison of diverse PGR action in different reproductive tissues. It clarifies finely-tuned contextual PGR-chromatin interactions with implications for more targeted reproductive medicine.

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.

Myometrial progesterone hyper-responsiveness associated with increased risk of human uterine fibroids

BACKGROUND

Uterine Fibroids (UFs) growth is ovarian steroid-dependent. Previous studies have shown that estrogen and progesterone play an important role in UF development. However, the mechanism underlying progesterone induced UF pathogenesis is largely unknown. In this study, we determined the expression of progesterone receptor and compared the expression level of progesterone-regulated genes (PRGs) in human myometrial cells from normal uteri (MyoN) versus uteri with UFs (MyoF) in response to progesterone.

METHODS

Primary human myometrial cells were isolated from premenopausal patients with structurally normal uteri (PrMyoN). Primary human myometrial cells were also isolated from uterus with UFs (PrMyoF). Isolated tissues were excised at least 2 cm from the closest UFs lesion(s). Progesterone receptor (PR) expression was assessed using Western blot (WB). Expression levels of 15 PRGs were measured by qRT-PCR in PrMyoN and PrMyoF cells in the presence or absence of progesterone.

RESULTS

WB analysis revealed higher expression levels of PR in PrMyoF cells as compared to PrMyoN cells. Furthermore, we compared the expression patterns of 15 UF-related PRGs in PrMyoN and PrMyoF primary cells in response to progesterone hormone treatment. Our studies demonstrated that five PRGs including Bcl2, FOXO1A, SCGB2A2, CYP26a1 and MMP11 exhibited significant progesterone-hyper-responsiveness in human PrMyoF cells as compared to PrMyoN cells (P < 0.05). Another seven PRGs, including CIDEC, CANP6, ADHL5, ALDHA1, MT1E, KIK6, HHI showed gain in repression in response to progesterone treatment (P > 0.05). Importantly, these genes play crucial roles in cell proliferation, apoptosis, cell cycle, tissue remodeling and tumorigenesis in the development of UFs.

CONCLUSION

These data support the idea that progesterone acts as contributing mechanism in the origin of UFs. Identification and analysis of these PRGs will help to further understand the role of progesterone in UF development.

New Gene Markers of Angiogenesis and Blood Vessels Development in Porcine Ovarian Granulosa Cells during Short-Term Primary Culture In Vitro

The physiological processes that drive the development of ovarian follicle, as well as the process of oogenesis, are quite well known. Granulosa cells are major players in this occurrence, being the somatic element of the female gamete development. They participate directly in the processes of oogenesis, building the cumulus-oocyte complex surrounding the ovum. In addition to that, they have a further impact on the reproductive processes, being a place of steroid sex hormone synthesis and secretion. It is known that the follicle development creates a major need for angiogenesis and blood vessel development in the ovary. In this study, we use novel molecular approaches to analyze markers of these processes in porcine granulosa cultured primarily in vitro. The cells were recovered from mature sus scrofa specimen after slaughter. They were then subjected to enzymatic digestion and culture primarily for a short term. The RNA was extracted from cultures in specific time periods (0h, 24h, 48h, 96h, and 144h) and analyzed using expression microarrays. The genes that exhibited fold change bigger than |2|, and adjusted p-value lower than 0.05, were considered differentially expressed. From these, we have chosen the members of “angiogenesis,” “blood vessel development,” “blood vessel morphogenesis,” “cardiovascular system development,” and “vasculature development” for further selection. CCL2, FGFR2, SFRP2, PDPN, DCN, CAV1, CHI3L1, ITGB3, FN1, and LOX which are upregulated, as well as CXCL10, NEBL, IHH, TGFBR3, SCUBE1, IGF1, EDNRA, RHOB, PPARD, and SLITRK5 genes whose expression is downregulated through the time of culture, were chosen as the potential markers, as their expression varied the most during the time of culture. The fold changes were further validated with RT-qPCR. The genes were described, with special attention to their possible function in GCs during culture. The results broaden the general knowledge about GC's in vitro molecular processes and might serve as a point of reference for further in vivo and clinical studies.

Inside the Endometrial Cell Signaling Subway: Mind the Gap(s)

Endometrial cells perceive and respond to their microenvironment forming the basis of endometrial homeostasis. Errors in endometrial cell signaling are responsible for a wide spectrum of endometrial pathologies ranging from infertility to cancer. Intensive research over the years has been decoding the sophisticated molecular means by which endometrial cells communicate to each other and with the embryo. The objective of this review is to provide the scientific community with the first overview of key endometrial cell signaling pathways operating throughout the menstrual cycle. On this basis, a comprehensive and critical assessment of the literature was performed to provide the tools for the authorship of this narrative review summarizing the pivotal components and signaling cascades operating during seven endometrial cell fate “routes”: proliferation, decidualization, implantation, migration, breakdown, regeneration, and angiogenesis. Albeit schematically presented as separate transit routes in a subway network and narrated in a distinct fashion, the majority of the time these routes overlap or occur simultaneously within endometrial cells. This review facilitates identification of novel trajectories of research in endometrial cellular communication and signaling. The meticulous study of endometrial signaling pathways potentiates both the discovery of novel therapeutic targets to tackle disease and vanguard fertility approaches.

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.

Progesterone Receptor Regulation of Uterine Adaptation for Pregnancy

Progesterone acts through the progesterone receptor to direct physiological adaption of the uterus in preparation and completion of pregnancy. Genome-wide transcriptome and cistrome analyses have uncovered new members and novel modifiers of the progesterone signaling pathway. Genetically engineered mice allow functional assessment of newly identified genes in vivo and provide insights on the impact of progesterone receptor-dependent molecular mechanisms on pregnancy at the organ system level. Progesterone receptor isoforms collectively mediate progesterone signaling via their distinct and common downstream target genes, which makes the stoichiometry of isoforms relevant in modifying the progesterone activity. This review discusses recent advances on the discovery of the progesterone receptor network, with special focus on the endometrium at early pregnancy and myometrium during parturition.

Heparan Sulfate Proteoglycan Sulfation Regulates Uterine Differentiation and Signaling During Embryo Implantation

To prepare for embryo implantation, the uterus must undergo a series of reciprocal interactions between the uterine epithelium and the underlying stroma, which are orchestrated by ovarian hormones. During this process, multiple signaling pathways are activated to direct cell proliferation and differentiation, which render the uterus receptive to the implanting blastocysts. One important modulator of these signaling pathways is the cell surface and extracellular matrix macromolecules, heparan sulfate proteoglycans (HSPGs). HSPGs play crucial roles in signal transduction by regulating morphogen transport and ligand binding. In this study, we examine the role of HSPG sulfation in regulating uterine receptivity by conditionally deleting the N-deacetylase/N-sulfotransferase (NDST) 1 gene (Ndst1) in the mouse uterus using the Pgr-Cre driver, on an Ndst2- and Ndst3-null genetic background. Although development of the female reproductive tract and subsequent ovarian function appear normal in Ndst triple-knockout females, they are infertile due to implantation defects. Embryo attachment appears to occur but the uterine epithelium at the site of implantation persists rather than disintegrates in the mutant. Uterine epithelial cells continued to proliferate past day 4 of pregnancy, accompanied by elevated Fgf2 and Fgf9 expression, whereas uterine stroma failed to undergo decidualization, as evidenced by lack of Bmp2 induction. Despite normal Indian hedgehog expression, transcripts of Ptch1 and Gli1, both components as well as targets of the hedgehog (Hh) pathway, were detected only in the subepithelial stroma, indicating altered Hh signaling in the mutant uterus. Taken together, these data implicate an essential role for HSPGs in modulating signal transduction during mouse implantation.

Oestrogen, progesterone and stem cells: the discordant trio in endometriosis?

Oestrogen–progesterone signalling is highly versatile and critical for the maintenance of healthy endometrium in humans. The genomic and nongenomic signalling cascades initiated by these hormones in differentiated cells of endometrium have been the primary focus of research since 1920s. However, last decade of research has shown a significant role of stem cells in the maintenance of a healthy endometrium and the modulatory effects of hormones on these cells. Endometriosis, the growth of endometrium outside the uterus, is very common in infertile patients and the elusiveness in understanding of disease pathology causes hindrance in selection of treatment approaches to enhance fertility. In endometriosis, the stem cells are dysfunctional as it can confer progesterone resistance to their progenies resulting in disharmony of hormonal orchestration of endometrial homeostasis. The bidirectional communication between stem cell signalling pathways and oestrogen–progesterone signalling is found to be disrupted in endometriosis though it is not clear which precedes the other. In this paper, we review the intricate connection between hormones, stem cells and the cross-talks in their signalling cascades in normal endometrium and discuss how this is deregulated in endometriosis. Re-examination of the oestrogen–progesterone dependency of endometrium with a focus on stem cells is imperative to delineate infertility associated with endometriosis and thereby aid in designing better treatment modalities.

The high concentration of progesterone is harmful for endometrial receptivity and decidualization

Progesterone is required for the establishment and maintenance of mammalian pregnancy and widely used for conservative treatment of luteal phase deficiency in clinics. However, there are limited solid evidences available for the optimal timing and dose of progesterone therapy, especially for the possible adverse effects on implantation and decidualization when progesterone is administrated empirically. In our study, mouse models were used to examine effects of excess progesterone on embryo implantation and decidualization. Our data indicate that excess progesterone is not only harmful for mouse implantation, but also impairs mouse decidualization. In excess progesterone-treated mice, the impaired LIF/STAT3 pathway and dysregulated endoplasmic reticulum stress may lead to the inhibition of embryo implantation and decidualization. It is possible that the decrease in birth weight of excess progesterone-treated mice is due to a compromised embryo implantation and decidualization. Furthermore, excess progesterone compromises in vitro decidualization of human endometrial stromal cells.

Hormone dependent uterine epithelial-stromal communication for pregnancy support

Human fertility is a relatively inefficient process. Despite the presence of visibly healthy embryos, 30% of pregnancies generated by assisted reproductive technology (ART) fail before the second trimester. The uterine microenvironment plays a critical role in establishing and maintaining a successful pregnancy that requires coordinated communication between the epithelial and stromal cells of the endometrium. The epithelial cells must cease proliferation and become permissive for the conceptus (embryo and associated extraembryonic membranes), while the stromal cells undergoes mesenchymal-to-epithelioid transformation to form the decidua in support of subsequent embryo development. The ovarian steroids Estrogen (E2) and Progesterone (P4) are the major hormones governing these processes. These hormones act via their nuclear receptors, the estrogen receptor, ESR1, and progesterone receptor, PGR, to direct the transcription of genes that orchestrate epithelial and stromal cell communication. This review will discuss the molecular mechanisms utilized by steroid hormones that regulate uterine receptivity, as well, establish and maintain pregnancy.

Genetic Intersection of Tsix and Hedgehog Signaling during the Initiation of X-Chromosome Inactivation

X-chromosome inactivation (XCI) silences one X chromosome in the female mammal and is essential to peri-implantation development. XCI is thought to be cell autonomous, with all factors required being produced within each cell. Nevertheless, external cues may exist. Here, we search for such developmental signals by combining bioinformatic, biochemical, and genetic approaches. Using ex vivo and in vivo models, we identify the Hedgehog (HH) paracrine system as a candidate signaling cascade. HH signaling keeps XCI in check in pluripotent cells and is transduced by GLI transcription factors to binding sites in Tsix, the antisense repressor of XCI. GLI potentiates Tsix expression and impedes XCI. In vivo, mutating Indian Hedgehog results in a sex ratio bias against females, and the female lethality is rescued by a second-site mutation in Tsix. These data demonstrate a genetic and functional intersection between HH and XCI and support a role for intercellular signaling during XCI.

The regulation of Hh/Gli1 signaling cascade involves Gsk3β- mediated mechanism in estrogen-derived endometrial hyperplasia

The present study was undertaken to explore the functional involvement of Hh signaling and its regulatory mechanism in endometrial hyperplasia. Differential expression of Hh signaling molecules i.e., Ihh, Shh, Gli1 or Gsk3β was observed in endometrial hyperplasial (EH) cells as compared to normal endometrial cells. Estradiol induced the expression of Hh signaling molecules and attenuated the expression of Gsk3β whereas anti-estrogen (K1) or progestin (MPA) suppressed these effects in EH cells. Cyclopamine treatment or Gli1 siRNA knockdown suppressed the growth of EH cells and reduced the expression of proliferative markers. Estradiol also induced the nuclear translocation of Gli1 which was suppressed by both MPA and K1 in EH cells. While exploring non-canonical mechanism, LY-294002 (Gsk3β activator) caused a decrease in Gli1 expression indicating the involvement of Gsk3β in Gli1 regulation. Further, Gsk3β silencing promoted the expression and nuclear translocation of Gli1 demonstrating that Gsk3β serves as a negative kinase regulator of Gli1 in EH cells. Similar attenuation of Hh signaling molecules was observed in rats with uterine hyperplasia undergoing anti-estrogen treatment. The study suggested that Hh/Gli1 cascade (canonical pathway) as well as Gsk3β-Gli1 crosstalk (non-canonical pathway) play crucial role in estrogen-dependent cell proliferation in endometrial hyperplasia.

G-protein coupled receptor 64 is required for decidualization of endometrial stromal cells

Although GPR64 has an important role for male fertility, its physiological roles in the female reproductive system are still unknown. In the present study, immunohistochemical analysis reveals a spatiotemporal expression of GPR64 in the uterus during early pregnancy. Observation of remarkable induction of GPR64 expression in uterine decidual cells points to its potential physiological significance on decidualization. The decidualization of uterine stromal cells is a key event in implantation. Progesterone (P4) signaling is crucial for the decidualization of the endometrial stromal cells for successful pregnancy. Therefore, we examined ovarian steroid hormone regulation of GPR64 expression in the murine uterus. P4 induced GPR64 expression in the epithelial and stromal cells of the uterus in ovariectomized wild-type mice, but not in PRKO mice. ChIP analysis confirmed that PGR proteins were recruited on progesterone response element of Gpr64 gene in the uteri of wild-type mice treated with P4. Furthermore, the expression of GPR64 was increased in human endometrial stromal cells (hESCs) during in vitro decidualization. Interestingly, small interfering RNA (siRNA)-mediated knockdown of GPR64 in hESCs remarkably reduced decidualization. These results suggest that Gpr64 has a crucial role in the decidualization of endometrial stromal cells.

Molecular and cellular events during blastocyst implantation in the receptive uterus: clues from mouse models

The success of implantation is an interactive process between the blastocyst and the uterus. Synchronized development of embryos with uterine differentiation to a receptive state is necessary to complete pregnancy. The period of uterine receptivity for implantation is limited and referred to as the “implantation window”, which is regulated by ovarian steroid hormones. Implantation process is complicated due to the many signaling molecules in the hierarchical mechanisms with the embryo-uterine dialogue. The mouse is widely used in animal research, and is uniquely suited for reproductive studies, i.e., having a large litter size and brief estrous cycles. This review first describes why the mouse is the preferred model for implantation studies, focusing on uterine morphology and physiological traits, and then highlights the knowledge on uterine receptivity and the hormonal regulation of blastocyst implantation in mice. Our recent study revealed that selective proteolysis in the activated blastocyst is associated with the completion of blastocyst implantation after embryo transfer. Furthermore, in the context of blastocyst implantation in the mouse, this review discusses the window of uterine receptivity, hormonal regulation, uterine vascular permeability and angiogenesis, the delayed-implantation mouse model, morphogens, adhesion molecules, crosslinker proteins, extracellular matrix, and matricellular proteins. A better understanding of uterine and blastocyst biology during the peri-implantation period should facilitate further development of reproductive technology.

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.

Selective progesterone receptor modulator (SPRM) ulipristal acetate (UPA) and its effects on the human endometrium

STUDY QUESTION

What is the impact of administration of the selective progesterone receptor modulator (SPRM), ulipristal acetate (UPA) on the endometrium of women with fibroids?

SUMMARY ANSWER

UPA administration altered expression of sex-steroid receptors and progesterone-regulated genes and was associated with low levels of glandular and stromal cell proliferation.

WHAT IS KNOWN ALREADY

Administration of all SPRM class members results in PAEC (progesterone receptor modulator associated endometrial changes). Data on the impact of the SPRM UPA administration on endometrial sex-steroid receptor expression, progesterone (P)-regulated genes and cell proliferation are currently lacking.

STUDY DESIGN SIZE, DURATION

Observational study with histological and molecular analyses to delineate impact of treatment with UPA on endometrium. Endometrial samples (n = 9) were collected at hysterectomy from women aged 39 to 49 with uterine fibroids treated with UPA (oral 5 mg daily) for 9-12 weeks. Control proliferative (n = 9) and secretory (n = 9) endometrium from women aged 38-52 with fibroids were derived from institutional tissue archives.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Study setting was a University Research Institute. Endometrial biopsies were collected with institutional ethical approval and written informed consent. Concentrations of mRNAs encoded by steroid receptors, P-regulated genes and factors in decidualised endometrium were quantified with qRT-PCR. Immunohistochemistry was employed for localization of progesterone (PR, PRB), androgen (AR), estrogen (ERα) receptors and expression of FOXO1, HAND2, HOXA10, PTEN homologue. Endometrial glandular and stromal cell proliferation was objectively quantified using Ki67.

MAIN RESULTS AND THE ROLE OF CHANCE

UPA induced morphological changes in endometrial tissue consistent with PAEC. A striking change in expression patterns of PR and AR was detected compared with either proliferative or secretory phase samples. There were significant changes in pattern of expression of mRNAs encoded by IGFBP-1, FOXO1, IL-15, HAND2, IHH and HOXA10 compared with secretory phase samples consistent with low agonist activity in endometrium. Expression of mRNA encoded by FOXM1, a transcription factor implicated in cell cycle progression, was low in UPA-treated samples. Cell proliferation (Ki67 positive nuclei) was lower in samples from women treated with UPA compared with those in the proliferative phase.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

A small number of well-characterized patients were studied in-depth. The impacts on morphology, molecular and cellular changes with SPRM, UPA administration on symptom control remains to be determined.

WIDER IMPLICATIONS OF THE FINDINGS

P plays a pivotal role in endometrial function. P-action is mediated through interaction with the PR. These data provide support for onward development of the SPRM class of compounds as effective long-term medical therapy for heavy menstrual bleeding.

STUDY FUNDING/COMPETING INTEREST(S)

H.O.D.C. received has clinical research support for laboratory consumables and staff from Bayer Pharma Ag and provides consultancy advice (no personal remuneration) for Bayer Pharma Ag, PregLem SA, Gedeon Richter, Vifor Pharma UK Ltd, AbbVie Inc.; A.R.W.W. has received consultancy payments from Bayer, Gedeon Richter, Preglem SA, HRA Pharma; L.H.R.W., A.A.M., R.M., G.S. and P.T.K.S. have no conflicts of interest. Study funded in part from each of: Medical Research Council (G1002033; G1100356/1; MR/N022556/1); National Health Institute for Health Research (12/206/520) and TENOVUS Scotland.

Porcupine-dependent Wnt signaling controls stromal proliferation and endometrial gland maintenance through the action of distinct WNTs

Wnt signaling has been shown to be important in orchestrating proper development of the female reproductive tract. In the uterus, six members of the Wnt family are expressed in the neonatal endometrium and deletion of individual Wnt genes often leads to similar phenotypes, suggesting an interaction of these genes in uterine development and function. Furthermore, Wnts may have complementary functions, which could mask the identification of their individual functional role in single gene deletions. To circumvent this issue, we have generated a deletion of the Porcupine homolog within the female reproductive tract using progesterone receptor-Cre mice (Pgr^Cre/+); preventing Wnt secretion from the producing cells. We show that Porcupine-dependent Wnt signaling, unlike previously reported, is dispensable for postnatal gland formation but is required for post-pubertal gland maintenance as well as for stromal cell proliferation. Furthermore, our results demonstrate that WNT7a is sufficient to restore post-pubertal endometrial gland formation. Although WNT5a did not restore gland formation, it rescued stromal cell proliferation; up-regulating several secreted factors including Fgf10 and Ihh. Our results further elucidate the roles of Wnt signaling in uterine development and function as well as provide an ideal system to address individual Wnt functions in the uterus.

miR-200 Regulates Endometrial Development During Early Pregnancy

For successful embryo implantation, endometrial stromal cells must undergo functional and morphological changes, referred to as decidualization. However, the molecular mechanisms that regulate implantation and decidualization are not well defined. Here we demonstrate that the estradiol- and progesterone-regulated microRNA (miR)-200 family was markedly down-regulated in mouse endometrial stromal cells prior to implantation, whereas zinc finger E-box binding homeobox-1 and -2 and other known and predicted targets were up-regulated. Conversely, miR-200 was up-regulated during in vitro decidualization of human endometrial stromal cells. Knockdown of miR-200 negatively affected decidualization and prevented the mesenchymal-epithelial transition-like changes that accompanied decidual differentiation. Notably, superovulation of mice and humans altered miR-200 expression. Our findings suggest that hormonal alterations that accompany superovulation may negatively impact endometrial development and decidualization by causing aberrant miR-200 expression.

Use of a Conditional Ubr5 Mutant Allele to Investigate the Role of an N-End Rule Ubiquitin-Protein Ligase in Hedgehog Signalling and Embryonic Limb Development

Hedgehog (Hh) signalling is a potent regulator of cell fate and function. While much is known about the events within a Hh-stimulated cell, far less is known about the regulation of Hh-ligand production. Drosophila Hyperplastic Discs (Hyd), a ubiquitin-protein ligase, represents one of the few non-transcription factors that independently regulates both hh mRNA expression and pathway activity. Using a murine embryonic stem cell system, we revealed that shRNAi of the mammalian homologue of hyd, Ubr5, effectively prevented retinoic-acid-induced Sonic hedgehog (Shh) expression. We next investigated the UBR5:Hh signalling relationship in vivo by generating and validating a mouse bearing a conditional Ubr5 loss-of-function allele. Conditionally deleting Ubr5 in the early embryonic limb-bud mesenchyme resulted in a transient decrease in Indian hedgehog ligand expression and decreased Hh pathway activity, around E13.5. Although Ubr5-deficient limbs and digits were, on average, shorter than control limbs, the effects were not statistically significant. Hence, while loss of UBR5 perturbed Hedgehog signalling in the developing limb, there were no obvious morphological defects. In summary, we report the first conditional Ubr5 mutant mouse and provide evidence for a role for UBR5 in influencing Hh signalling, but are uncertain to whether the effects on Hedgehog signaling were direct (cell autonomous) or indirect (non-cell-autonomous). Elaboration of the cellular/molecular mechanism(s) involved may help our understanding on diseases and developmental disorders associated with aberrant Hh signalling.

Expression of genes involved in progesterone receptor paracrine signaling and their effect on litter size in pigs

Background

Embryonic mortality during the period of implantation strongly affects litter size in pigs. Progesterone receptor (PGR) paracrine signaling has been recognized to play a significant role in embryonic implantation. IHH, NR2F2, BMP2, FKBP4 and HAND2 were proved to involve in PGR paracrine signaling. The objective of this study was to evaluate the expression of IHH, NR2F2, BMP2, FKBP4 and HAND2 in endometrium of pregnant sows and to further investigate these genes’ effect on litter size in pigs. Real-time PCR, western blot and immunostaining were used to study target genes/proteins expression in endometrium in pigs. RFLP-PCR was used to detect single nucleotide polymorphisms (SNPs) of target genes.

Results

The results showed that the mRNA and protein expression levels of IHH, NR2F2 and BMP2 were up-regulated during implantation period (P < 0.05 or P < 0.01). All target proteins were mainly observed in luminal epithelium and glandular epithelium. Interestingly, the staining of NR2F2 and HAND2 was also strong in stroma. SNPs detection revealed that there was a -204C > A mutation in promoter region of NR2F2 gene. Three genotypes were found in Large White, Landrace and Duroc sows. A total of 1847 litter records from 625 sows genotyped at NR2F2 gene were used to analyze the total number born (TNB) and number born alive (NBA). The study of the effect on litter size suggested that sows with genotype CC tend to have higher litter size.

Conclusions

These results showed the expression patterns of genes/proteins involved in PGR paracrine signaling over implantation time. And the candidate gene for litter size was identified from genes involved in this signaling. This study could be a resource for further studies to identify the roles of these genes for embryonic implantation in pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-016-0090-z) contains supplementary material, which is available to authorized users.

Effect of purmorphamine on the mRNA expression of Sonic Hedgehog signaling downstream molecules in ovine embryo

Abstract. Sonic Hedgehog (SHH) is a signaling pathway mediated through a receptor system which seems to have effects on oocyte maturation and embryonic development. Purmorphamine is an SHH agonist that performs a crucial role in the regulation of the activity of SHH receptors and downstream transcription factors. The aim of this study was to analyze the effect of purmorphamine on the mRNA expression of SHH signaling downstream molecules (Patched1, Glioma-Associated Oncogene1, Smoothened, Histone Deacetylase1, Histone Deacetylase2 and Histone Deacetylase3) in ovine two-cell embryo. Ovaries were obtained from a slaughterhouse, and cumulus–oocyte complexes were aspirated and cultured in maturation media containing 0, 250 or 500 ng mL−1 purmorphamine. Then, oocytes were fertilized and cultured in a CR1 culture medium and after 24 h, two-cell embryos were collected for RNA extraction. Gene expression was evaluated by real-time polymerase chain reaction (PCR). Results indicated that in 250 ng mL−1 purmorphamine, Smo, Ptch1 and Hdac3 expression reduced, Hdac1 expression increased, and Gli1 and Hdac2 expression levels did not change. In 500 ng mL−1 purmorphamine, Gli1 and Smo transcripts increased, while Ptch1, Hdac2 and Hdac3 transcripts decreased. Regarding to the presence of SHH signaling molecules in two-cell embryos and their response to purmorphamine, it can be suggested that SHH signaling is probably active before embryonic genome activation in ovine embryos.

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.

Effect of single post-ovulatory administration of mifepristone (RU486) on transcript profile during the receptive period in human endometrium

Progesterone regulates uterine function during the luteal phase and is essential for the acquisition of endometrial receptivity. The objective of the present study was to identify endometrial transcripts whose expression is altered during the window of implantation after the administration of 200 mg of the antiprogestin mifepristone, 48 h after the LH peak (LH+2, LH+0=LH peak), and to determine the relationship of these transcripts with those regulated during the acquisition of receptivity. Endometrial samples were obtained in LH+7 from seven women of proven fertility, each one contributing with one cycle treated with placebo and another with mifepristone. Additionally, endometrial samples were obtained in LH+2 and LH+7 during a single untreated spontaneous cycle from seven normal fertile women as a reference. DNA microarrays were used to identify transcripts significantly regulated (defined as ≥2.0-fold change with false discovery rate below 1% usingt-test) with the administration of mifepristone vs placebo, or during the transition from pre-receptive to receptive (LH+2 vs LH+7). Approximately 2000 transcripts were significantly regulated in both comparisons (mifepristone vs placebo and LH+2 vs LH+7), but only 777 of them were coincident and displayed opposite regulation except for 25. The mRNA level for eight selected genes regulated by mifepristone was confirmed by real-time RT-PCR. We conclude that not all changes in endometrial transcript levels occurring in the transition from LH+2 to LH+7 seem to be regulated by the progesterone receptor and ∼37% of the genes whose transcript levels changed by effect of mifepristone could be associated with the acquisition of receptivity.