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

Progesterone receptor in uterine glands is required for pregnancy establishment in mice

Embryo implantation is a critical event in the establishment of pregnancy, and implantation failure is a major cause of pregnancy loss in women. Coordinated, cell-type specific responses to the ovarian steroid hormones, estrogen, and progesterone, within the endometrium underlie successful embryo implantation and pregnancy establishment. In this study, we utilized a glandular epithelium (GE) specific Cre recombinase mouse line that is only active in the adult (Prss29-Cre) to determine the biological role of progesterone receptor (PGR) in uterine glands during pregnancy. Conditional ablation of PGR specifically in the GE compromised fertility due to defects in uterine receptivity and embryo implantation. Histological and transcriptomic analyses uncovered disruption of multiple PGR-regulated genes in the GE during the window of receptivity, including leukemia inhibitory factor (LIF), a cytokine produced specifically by the GE that is essential for embryo implantation. Interestingly, intraperitoneal injections of recombinant LIF in Pgr conditional knockout mice rescued embryo implantation and supported successful pregnancy to term. These findings underscore the vital role of PGR in regulating Lif expression in the GE, while suggesting that PGR in the glands of the uterus is unessential once pregnancy is established. Overall, these findings reveal a previously unrecognized role of PGR in uterine glands and support the hypothesis that glandular secretions, governed by PGR, are indispensable for pregnancy establishment.

FOXA2 loss results in an increase of endometriosis development and LIF reveals a therapeutic effect for endometriosis

Endometriosis, characterized by the growth of uterine-like tissue outside the uterus, causes chronic pain and infertility. Current diagnostic and therapeutic strategies have notable limitations, including delayed diagnosis and adverse effects. The transcription factor forkhead box A2 (FOXA2), which is exclusively expressed in the uterine glandular epithelium, regulates key genes involved in endometrial proliferation, differentiation, fertility, and hormone response. While FOXA2 expression is reduced in the endometrial tissue of women with endometriosis, its pathophysiological role in the disease is not well understood. In this study, we report that endometriosis significantly reduced FOXA2 expression in the eutopic endometrium of mice with endometriosis compared to sham controls, accompanied by decreased expression of its downstream gene, CXCL15. To evaluate the effect of FOXA2 loss in endometriosis, we surgically induced endometriosis by transplanting control Rosa26mTmG/+ or Pgrcre/+Foxa2f/fRosa26mTmG/+ (Foxa2d/dRosa26mTmG/+) endometrial tissue into the peritoneal cavity of mice. The number and weight of ectopic lesions were significantly increased in the mice with Foxa2d/dRosa26mTmG/+ ectopic lesions compared to controls. Furthermore, progesterone receptor expression was significantly reduced in the endometrial epithelium from mice with Foxa2d/dRosa26mTmG/+ ectopic lesions compared to mice with control ectopic lesions. Importantly, treatment with leukemia inhibitory factor (LIF), a cytokine regulated by FOXA2, significantly reduced ectopic lesion formation in Foxa2d/dRosa26mTmG/+ endometriosis mice compared to vehicle-treated mice. This study demonstrates that FOXA2 loss results in an increase in endometriosis incidence and that treatment with LIF offers a novel promising therapeutic approach for endometriosis.

Foxa2-dependent uterine glandular cell differentiation is essential for successful implantation

Uterine receptivity is essential for successful implantation. In mice, uterine receptivity begins with the secretion of LIF from uterine glands stimulated by estrogen on the morning of day 4 pregnancy. We hypothesize that gland readiness for estrogen stimulation is indispensable for uterine receptivity. The current study reveals that uterine glands undergo a differentiation process with expanded branching during the preimplantation period. The single-cell RNA profiling of glandular cells identifies that LIF is expressed exclusively in a Prss29+ subgroup of glandular cells on day 4 of pregnancy. Interestingly, Foxa2-deficient glands lacking LIF production fail to develop branches and the functional Prss29+ subgroup. This Prss29+ subgroup develops prior to estrogen secretion. Collectively, our findings show that uterine glands undergo a FOXA2-dependent maturation process to acquire the competence, named "transitional phase", for entering the receptive phase. The "transitional phase", predicting uterine receptivity one day before implantation, is a landmark concept in uterine receptivity.

Prevention of Intrauterine Adhesion with Platelet-Rich Plasma Double-Network Hydrogel

Intrauterine adhesion (IUA) can negatively impact on pregnancy outcomes, leading to reduced pregnancy rates, secondary infertility, and an increased risk of pregnancy complications. Studies have shown that the application of platelet-rich plasma (PRP) in IUA patients is effective. However, the clinical readhesive rate of IUA after treatment is still high, especially in severe cases. Platelet-rich plasma double-network hydrogel (DN gel) is an engineered PRP double network hydrogel, which is a sodium alginate (SA) based PRP hydrogel with egg carton ion cross-linking and fibrin double network. The results of this study show that intrauterine injection of DN gel has a better effect on promoting endometrial regeneration and enhancing endometrial receptivity than PRP gel. The mechanism is analyzed through single-cell sequencing, which may be achieved by increasing the expression of neutrophils (Neut), natural killer cells (NK), and type I classical dendritic cells (cDC1) in the endometrium and inhibiting the infiltration of M2 macrophages. Overall, based on the good healing efficiency and good biocompatibility of DN gel, it is expected to become a method of treating IUA with better efficacy and faster clinical translation.

The endometrial transcriptome of infertile women with and without implantation failure

INTRODUCTION

Implantation failure after transferring morphologically "good-quality" embryos in in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) may be explained by impaired endometrial receptivity. Analyzing the endometrial transcriptome analysis may reveal the underlying processes and could help in guiding prognosis and using targeted interventions for infertility. This exploratory study investigated whether the endometrial transcriptome profile was associated with short-term or long-term implantation outcomes (ie success or failure).

MATERIAL AND METHODS

Mid-luteal phase endometrial biopsies of 107 infertile women with one full failed IVF/ICSI cycle, obtained within an endometrial scratching trial, were subjected to RNA-sequencing and differentially expressed genes analysis with covariate adjustment (age, body mass index, luteinizing hormone [LH]-day). Endometrial transcriptomes were compared between implantation failure and success groups in the short term (after the second fresh IVF/ICSI cycle) and long term (including all fresh and frozen cycles within 12 months). The short-term analysis included 85/107 women (33 ongoing pregnancy vs 52 no pregnancy), excluding 22/107 women. The long-term analysis included 46/107 women (23 'fertile' group, ie infertile women with a live birth after ≤3 embryos transferred vs 23 recurrent implantation failure group, ie no live birth after ≥3 good quality embryos transferred), excluding 61/107 women not fitting these categories. As both analyses drew from the same pool of 107 samples, there was some sample overlap. Additionally, cell type enrichment scores and endometrial receptivity were analyzed, and an endometrial development pseudo-timeline was constructed to estimate transcriptomic deviations from the optimum receptivity day (LH + 7), denoted as ΔWOI (window of implantation).

RESULTS

There were no significantly differentially expressed genes between implantation failure and success groups in either the short-term or long-term analyses. Principal component analysis initially showed two clusters in the long-term analysis, unrelated to clinical phenotype and no longer distinct following covariate adjustment. Cell type enrichment scores did not differ significantly between groups in both analyses. However, endometrial receptivity analysis demonstrated a potentially significant displacement of the WOI in the non-pregnant group compared with the ongoing pregnant group in the short-term analysis.

CONCLUSIONS

No distinct endometrial transcriptome profile was associated with either implantation failure or success in infertile women. However, there may be differences in the extent to which the WOI is displaced.

Long-term maintenance of human endometrial epithelial organoids and their stem cell properties

The endometrium undergoes dynamic changes throughout the menstrual cycle and pregnancy, which is unique to primates. Endometrium remodeling is essential for the implantation and nutritional support of the conceptus. Despite this, the role of uterine glands in driving endometrial tissue remodeling is still poorly understood. To address this, a 3-dimensional culture system was used to generate endometrial epithelial organoids from human endometrium biopsies. These organoids are genetically stable, long-term expandability. They reproduce some functions of uterine glands in vivo. The epithelial organoids exhibit characteristics of stem cells, with the proportion of stem cells increasing with culture time and passage number. Long-term maintenance of organoids strongly expressed stemness related genes accompanied by a decrease expression in mature epithelial gene, which suggests the organoids had switched from a mature stage to a progenitor stage. Thus we proposed the possible markers for epithelial progenitors. Meanwhile, long-term cultured organoids exhibit an increase in the proportion of luminal epithelial stem cells, accompanied by a decrease of glandular epithelial stem cells. Organoids also show hormone responsiveness, reflecting the various stages of the menstrual cycle and early pregnancy.

An Integrative ATAC-Seq and RNA-Seq Analysis of the Endometrial Tissues of Meishan and Duroc Pigs

Meishan pigs are a well-known indigenous pig breed in China characterized by a high fertility. Notably, the number of endometrial grands is significantly higher in Meishan pigs than Duroc pigs. The characteristics of the endometrial tissue are related to litter size. Therefore, we used the assay for transposase-accessible chromatin with sequencing (ATAC-seq) and RNA-sequencing (RNA-seq) to analyze the mechanisms underlying the differences in fecundity between the breeds. We detected the key transcription factors, including Double homeobox (Dux), Ladybird-like homeobox gene 2 (LBX2), and LIM homeobox 8 (Lhx8), with potentially pivotal roles in the regulation of the genes related to endometrial development. We identified the differentially expressed genes between the breeds, including SOX17, ANXA4, DLX3, DMRT1, FLNB, IRF6, CBFA2T2, TFCP2L1, EFNA5, SLIT2, and CYFIP2, with roles in epithelial cell differentiation, fertility, and ovulation. Interestingly, ANXA4, CBFA2T2, and TFCP2L1, which were upregulated in the Meishan pigs in the RNA-seq analysis, were identified again by the integration of the ATAC-seq and RNA-seq data. Moreover, we identified genes in the cancer or immune pathways, FoxO signaling, Wnt signaling, and phospholipase D signaling pathways. These ATAC-seq and RNA-seq analyses revealed the accessible chromatin and potential mechanisms underlying the differences in the endometrial tissues between the two types of pigs.

Deciphering a shared transcriptomic regulation and the relative contribution of each regulator type through endometrial gene expression signatures

BACKGORUND

While various endometrial biomarkers have been characterized at the transcriptomic and functional level, there is generally a poor overlap among studies, making it unclear to what extent their upstream regulators (e.g., ovarian hormones, transcription factors (TFs) and microRNAs (miRNAs)) realistically contribute to menstrual cycle progression and function. Unmasking the intricacies of the molecular interactions in the endometrium from a novel systemic point of view will help gain a more accurate perspective of endometrial regulation and a better explanation the molecular etiology of endometrial-factor infertility.

METHODS

An in-silico analysis was carried out to identify which regulators consistently target the gene biomarkers proposed in studies related to endometrial progression and implantation failure (19 gene lists/signatures were included). The roles of these regulators, and of genes related to progesterone and estrogens, were then analysed in transcriptomic datasets compiled from samples collected throughout the menstrual cycle (n = 129), and the expression of selected TFs were prospectively validated in an independent cohort of healthy participants (n = 19).

RESULTS

A total of 3,608 distinct genes from the 19 gene lists were associated with endometrial progression and implantation failure. The lists' regulation was significantly favoured by TFs (89% (17/19) of gene lists) and progesterone (47% (8 /19) of gene lists), rather than miRNAs (5% (1/19) of gene lists) or estrogen (0% (0/19) of gene lists), respectively (FDR < 0.05). Exceptionally, two gene lists that were previously associated with implantation failure and unexplained infertility were less hormone-dependent, but primarily regulated by estrogen. Although endometrial progression genes were mainly targeted by hormones rather than non-hormonal contributors (odds ratio = 91.94, FDR < 0.05), we identified 311 TFs and 595 miRNAs not previously associated with ovarian hormones. We highlight CTCF, GATA6, hsa-miR-15a-5p, hsa-miR-218-5p, hsa-miR-107, hsa-miR-103a-3p, and hsa-miR-128-3p, as overlapping novel master regulators of endometrial function. The gene expression changes of selected regulators throughout the menstrual cycle (FDR < 0.05), dually validated in-silico and through endometrial biopsies, corroborated their potential regulatory roles in the endometrium.

CONCLUSIONS

This study revealed novel hormonal and non-hormonal regulators and their relative contributions to endometrial progression and pathology, providing new leads for the potential causes of endometrial-factor infertility.

Basolateral secretions of human endometrial epithelial organoids impact stromal cell decidualization

Uterine glands and, by inference, their secretions impact uterine receptivity, blastocyst implantation, stromal cell decidualization, and placental development. Changes in gland function across the menstrual cycle are primarily governed by the steroid hormones estrogen (E2) and progesterone (P4) but can also be influenced by extrinsic factors from the stroma. Using a human endometrial epithelial organoid system, transcriptome and proteome analyses identified distinct responses of the organoids to steroid hormones and prostaglandin E2 (PGE2). Notably, P4 and PGE2 modulated the basolateral secretion of organoid proteins, particularly cystatin C (CST3), serpin family A member 3 (SERPINA3), and stanniocalcin 1 (STC1). CST3, but not SERPINA3 or STC1, attenuated the in vitro stromal decidualization response to steroid hormones and PGE2. These findings provide evidence that uterine gland-derived factors impact stromal cell decidualization, which has implications for pregnancy establishment and fertility in women.

Role of EZH2 in Uterine Gland Development

Enhancer of zeste homolog 2 (EZH2) is a core component of polycomb repressive complex 2 that plays a vital role in transcriptional repression of gene expression. Conditional ablation of EZH2 using progesterone receptor (Pgr)-Cre in the mouse uterus has uncovered its roles in regulating uterine epithelial cell growth and stratification, suppressing decidual myofibroblast activation, and maintaining normal female fertility. However, it is unclear whether EZH2 plays a role in the development of uterine glands, which are required for pregnancy success. Herein, we created mice with conditional deletion of Ezh2 using anti-Mullerian hormone receptor type 2 (Amhr2)-Cre recombinase that is expressed in mesenchyme-derived cells of the female reproductive tract. Strikingly, these mice showed marked defects in uterine adenogenesis. Unlike Ezh2 Pgr-Cre conditional knockout mice, deletion of Ezh2 using Amhr2-Cre did not lead to the differentiation of basal-like cells in the uterus. The deficient uterine adenogenesis was accompanied by impaired uterine function and pregnancy loss. Transcriptomic profiling using next generation sequencing revealed dysregulation of genes associated with signaling pathways that play fundamental roles in development and disease. In summary, this study has identified an unrecognized role of EZH2 in uterine gland development, a postnatal event critical for pregnancy success and female fertility.

Single-cell transcriptomic analysis highlights origin and pathological process of human endometrioid endometrial carcinoma

Endometrial cancers are complex ecosystems composed of cells with distinct phenotypes, genotypes, and epigenetic states. Current models do not adequately reflect oncogenic origin and pathological progression in patients. Here we use single-cell RNA sequencing to profile cells from normal endometrium, atypical endometrial hyperplasia, and endometrioid endometrial cancer (EEC), which altogether represent the step-by-step development of endometrial cancer. We find that EEC originates from endometrial epithelial cells but not stromal cells, and unciliated glandular epithelium is the source of EEC. We also identify LCN2 + /SAA1/2 + cells as a featured subpopulation of endometrial tumorigenesis. Finally, the stromal niche and immune environment changes during EEC progression are described. This study elucidates the evolution of cell populations in EEC development at single-cell resolution, which would provide a direction to facilitate EEC research and diagnosis.

Mouse Cre drivers: tools for studying disorders of the human female neuroendocrine-reproductive axis†

Benign disorders of the human female reproductive system, such primary ovarian insufficiency and polycystic ovary syndrome are associated with infertility and recurrent miscarriage, as well as increased risk of adverse health outcomes, including cardiovascular disease and type 2 diabetes. For many of these conditions, the contributing molecular and cellular processes are poorly understood. The overarching similarities between mice and humans have rendered mouse models irreplaceable in understanding normal physiology and elucidating pathological processes that underlie disorders of the female reproductive system. The utilization of Cre-LoxP recombination technology, which allows for spatial and temporal control of gene expression, has identified the role of numerous genes in development of the female reproductive system and in processes, such as ovulation and endometrial decidualization, that are required for the establishment and maintenance of pregnancy in mammals. In this comprehensive review, we provide a detailed overview of Cre drivers with activity in the neuroendocrine-reproductive axis that have been used to study disruptions in key intracellular signaling pathways. We first summarize normal development of the hypothalamus, pituitary, ovary, and uterus, highlighting similarities and differences between mice and humans. We then describe human conditions resulting from abnormal development and/or function of the organ. Finally, we describe loss-of-function models for each Cre driver that elegantly recapitulate some key features of the human condition and are associated with impaired fertility. The examples we provide illustrate use of each Cre driver as a tool for elucidating genetic and molecular underpinnings of reproductive dysfunction.

Roles of WNT6 in Sheep Endometrial Epithelial Cell Cycle Progression and Uterine Glands Organogenesis

The uterus, as part of the female reproductive tract, is essential for embryo survival and in the maintenance of multiple pregnancies in domestic animals. This study was conducted to investigate the effects of WNT6 on Hu sheep endometrial epithelial cells (EECs) and uterine glands (UGs) in Hu sheep, with high prolificacy rates. In the present study, Hu sheep with different fecundity, over three consecutive pregnancies, were divided into two groups: high prolificacy rate group (HP, litter size = 3) and low prolificacy rate group (LP, litter size = 1). A comparative analysis of the endometrial morphology was performed by immunofluorescence. RNA-seq was used to analyze the gene’s expression in endometrium of HP and LP Hu sheep, providing a candidate gene, which was investigated in EECs and organoid culture. Firstly, higher density of UGs was found in the HP Hu sheep groups (p < 0.05). The RNA-seq data revealed the importance of the WNT signaling pathway and WNT6 gene in Hu sheep endometrium. Functionally, WNT6 could promote the cell cycle progression of EECs via WNT/β-catenin signal and enhance UGs organogenesis. Taken together, WNT6 is a crucial regulator for sheep endometrial development; this finding may offer a new insight into understanding the regulatory mechanism of sheep prolificacy.

Uterine glands impact embryo survival and stromal cell decidualization in mice

Uterine glands are essential for the establishment of pregnancy and have critical roles in endometrial receptivity to blastocyst implantation, stromal cell decidualization, and placentation. Uterine gland dysfunction is considered a major contributing factor to pregnancy loss, however our understanding of how glands impact embryo survival and stromal cell decidualization is incomplete. Forkhead box A2 (FOXA2) is expressed only in the glandular epithelium and regulates its development and function. Mice with a conditional deletion of FOXA2 in the uterus are infertile due to defective embryo implantation arising from a lack of leukemia inhibitory factor (LIF), a critical factor of uterine gland origin. Here, a glandless FOXA2-deficient mouse model, coupled with LIF repletion to rescue the implantation defect, was used to investigate the roles of uterine glands in embryo survival and decidualization. Studies found that embryo survival and decidualization were compromised in glandless FOXA2-deficient mice on gestational day 6.5, resulting in abrupt pregnancy loss by day 7.5. These findings strongly support the hypothesis that uterine glands secrete factors other than LIF that impact embryo survival and stromal cell decidualization for pregnancy success.

Generation and analysis of Prss28 and Prss29 deficient mice using CRISPR-Cas9 genome-editing

Glands of the uterus are essential for the establishment of pregnancy in mice and their products regulate embryo implantation and stromal cell decidualization critical for pregnancy establishment. Forkhead box A2 (FOXA2) is expressed specifically in the glands and a critical regulator of their differentiation, development and function. Progesterone and FOXA2 regulate members of a serine proteinase gene family (Prss28 and Prss29). Here, CRISPR-Cas9 genome-editing was used to create mice with a heterozygous or homozygous deletion of Prss28 or/and Prss29 to determine their biological roles in uterine function. Female mice lacking Prss28 and Prss29 or both developed normally and were fertile without alterations in uterine histoarchitecture, uterine gland number, or and gene expression. Thus, Prss28 and Prss29 are dispensable for female fertility and do not impact endometrial gland development or uterine function mice.

Endometrial epithelial ARID1A is critical for uterine gland function in early pregnancy establishment

Though endometriosis and infertility are clearly associated, the pathophysiological mechanism remains unclear. Previous work has linked endometrial ARID1A loss to endometriosis-related endometrial non-receptivity. Here, we show in mice that ARID1A binds and regulates transcription of the Foxa2 gene required for endometrial gland function. Uterine-specific deletion of Arid1a compromises gland development and diminishes Foxa2 and Lif expression. Deletion of Arid1a with Ltf-iCre in the adult mouse endometrial epithelium preserves the gland development while still compromising the gland function. Mice lacking endometrial epithelial Arid1a are severely sub-fertile due to defects in implantation, decidualization, and endometrial receptivity from disruption of the LIF-STAT3-EGR1 pathway. FOXA2 is also reduced in the endometrium of women with endometriosis in correlation with diminished ARID1A, and both ARID1A and FOXA2 are reduced in nonhuman primates induced with endometriosis. Our findings describe a role for ARID1A in the endometrial epithelium supporting early pregnancy establishment through the maintenance of gland function.

In vitro models of the human endometrium: evolution and application for women's health

The endometrium is the inner lining of the uterus that undergoes complex regeneration and differentiation during the human menstrual cycle. The process of endometrial shedding, regeneration, and differentiation is driven by ovarian steroid hormones and prepares the endometrium and intrauterine environment for embryo implantation and pregnancy establishment. Endometrial glands and their secretions are essential for pregnancy establishment, and cross talk between the glandular epithelium and stromal cells appears vital for decidualization and placental development. Despite being crucial, the biology of the human endometrium during pregnancy establishment and most of pregnancy is incomplete, given the ethical and practical limitations of obtaining and studying endometrium from pregnant women. As such, in vitro models of the human endometrium are required to fill significant gaps in understanding endometrial biology. This review is focused on the evolution and development of in vitro three-dimensional models of the human endometrium and provides insight into the challenges and promises of those models to improve women's reproductive health.

Single-cell transcriptomic atlas of the human endometrium during the menstrual cycle

In a human menstrual cycle the endometrium undergoes remodeling, shedding and regeneration, all of which are driven by substantial gene expression changes in the underlying cellular hierarchy. Despite its importance in human fertility and regenerative biology, our understanding of this unique type of tissue homeostasis remains rudimentary. We characterized the transcriptomic transformation of human endometrium at single-cell resolution across the menstrual cycle, resolving cellular heterogeneity in multiple dimensions. We profiled the behavior of seven endometrial cell types, including a previously uncharacterized ciliated cell type, during four major phases of endometrial transformation, and found characteristic signatures for each cell type and phase. We discovered that the human window of implantation opens with an abrupt and discontinuous transcriptomic activation in the epithelia, accompanied with a widespread decidualization feature in the stromal fibroblasts. Our study provides a high-resolution molecular and cellular characterization of human endometrial transformation across the menstrual cycle, providing insights into this essential physiological process.

Sexually dimorphic effects of forkhead box a2 (FOXA2) and uterine glands on decidualization and fetoplacental development

Glands of the uterus are essential for pregnancy establishment. Forkhead box A2 (FOXA2) is expressed specifically in the glands of the uterus and a critical regulator of glandular epithelium (GE) differentiation, development, and function. Mice with a conditional deletion of FOXA2 in the adult uterus, created using the lactotransferrin iCre (Ltf-iCre) model, have a morphologically normal uterus with glands, but lack FOXA2-dependent GE-expressed genes, such as leukemia inhibitory factor (LIF). Adult FOXA2 conditional knockout (cKO; Ltf ^iCre/+ Foxa2 ^f/f ) mice are infertile due to defective embryo implantation arising from a lack of LIF, a critical implantation factor of uterine gland origin. However, intraperitoneal injections of LIF can initiate embryo implantation in the uterus of adult FOXA2 cKO mice with pregnancies maintained to term. Here, we tested the hypothesis that FOXA2-regulated genes in the uterine glands impact development of the decidua, placenta, and fetus. On gestational day 8.5, the antimesometrial and mesometrial decidua transcriptome was noticeably altered in LIF-replaced FOXA2 cKO mice. Viable fetuses were reduced in FOXA2 cKO mice on gestational days 12.5 and 17.5. Sex-dependent differences in fetal weight, placenta histoarchitecture, and the placenta and metrial gland transcriptome were observed between control and FOXA2 cKO mice. The transcriptome of the placenta with a female fetus was considerably more altered than the placenta with a male fetus in FOXA2 cKO dams. These studies reveal previously unrecognized sexually dimorphic effects of FOXA2 and uterine glands on fetoplacental development with potential impacts on offspring health into adulthood.

Self-renewing endometrial epithelial organoids of the human uterus

The human endometrium is essential in providing the site for implantation and maintaining the growth and survival of the conceptus. An unreceptive endometrium and disrupted maternal-conceptus interactions can cause infertility due to pregnancy loss or later pregnancy complications. Despite this, the role of uterine glands in first trimester human pregnancy is little understood. An established organoid protocol was used to generate and comprehensively analyze 3-dimensional endometrial epithelial organoid (EEO) cultures from human endometrial biopsies. The derived EEO expand long-term, are genetically stable, and can be cryopreserved. Using endometrium from 2 different donors, EEO were derived and then treated with estrogen (E2) for 2 d or E2 and medroxyprogesterone acetate (MPA) for 6 d. EEO cells were positive for the gland marker, FOXA2, and exhibited appropriate hormonal regulation of steroid hormone receptor expression. Real-time qPCR and bulk RNA-sequencing analysis revealed effects of hormone treatment on gene expression that recapitulated changes in proliferative and secretory phase endometrium. Single-cell RNA sequencing analysis revealed that several different epithelial cell types are present in the EEO whose proportion and gene expression changed with hormone treatment. The EEO model serves as an important platform for studying the physiology and pathology of the human endometrium.

Uterine Glands: Developmental Biology and Functional Roles in Pregnancy

All mammalian uteri contain glands in the endometrium that develop only or primarily after birth. Gland development or adenogenesis in the postnatal uterus is intrinsically regulated by proliferation, cell-cell interactions, growth factors and their inhibitors, as well as transcription factors, including forkhead box A2 (FOXA2) and estrogen receptor α (ESR1). Extrinsic factors regulating adenogenesis originate from other organs, including the ovary, pituitary, and mammary gland. The infertility and recurrent pregnancy loss observed in uterine gland knockout sheep and mouse models support a primary role for secretions and products of the glands in pregnancy success. Recent studies in mice revealed that uterine glandular epithelia govern postimplantation pregnancy establishment through effects on stromal cell decidualization and placental development. In humans, uterine glands and, by inference, their secretions and products are hypothesized to be critical for blastocyst survival and implantation as well as embryo and placental development during the first trimester before the onset of fetal-maternal circulation. A variety of hormones and other factors from the ovary, placenta, and stromal cells impact secretory function of the uterine glands during pregnancy. This review summarizes new information related to the developmental biology of uterine glands and discusses novel perspectives on their functional roles in pregnancy establishment and success.