Uterine glands: biological roles in conceptus implantation, uterine receptivity and decidualization

Dynamic changes in AI-based analysis of endometrial cellular composition: Analysis of PCOS and RIF endometrium

Background

The human endometrium undergoes a monthly cycle of tissue growth and degeneration. During the mid-secretory phase, the endometrium establishes an optimal niche for embryo implantation by regulating cellular composition (e.g., epithelial and stromal cells) and differentiation. Impaired endometrial development observed in conditions such as polycystic ovary syndrome (PCOS) and recurrent implantation failure (RIF) contributes to infertility. Surprisingly, despite the importance of the endometrial lining properly developing prior to pregnancy, precise measures of endometrial cellular composition in these two infertility-associated conditions are entirely lacking. Additionally, current methods for measuring the epithelial and stromal area have limitations, including intra- and inter-observer variability and efficiency.

Methods

We utilized a deep-learning artificial intelligence (AI) model, created on a cloud-based platform and developed in our previous study. The AI model underwent training to segment both areas populated by epithelial and stromal endometrial cells. During the training step, a total of 28.36 mm2 areas were annotated, comprising 2.56 mm2 of epithelium and 24.87 mm2 of stroma. Two experienced pathologists validated the performance of the AI model. 73 endometrial samples from healthy control women were included in the sample set to establish cycle phase-dependent dynamics of the endometrial epithelial-to-stroma ratio from the proliferative (PE) to secretory (SE) phases. In addition, 91 samples from PCOS cases, accounting for the presence or absence of ovulation and representing all menstrual cycle phases, and 29 samples from RIF patients on day 5 after progesterone administration in the hormone replacement treatment cycle were also included and analyzed in terms of cellular composition.

Results

Our AI model exhibited reliable and reproducible performance in delineating epithelial and stromal compartments, achieving an accuracy of 92.40% and 99.23%, respectively. Moreover, the performance of the AI model was comparable to the pathologists' assessment, with F1 scores exceeding 82% for the epithelium and >96% for the stroma. Next, we compared the endometrial epithelial-to-stromal ratio during the menstrual cycle in women with PCOS and in relation to endometrial receptivity status in RIF patients. The ovulatory PCOS endometrium exhibited epithelial cell proportions similar to those of control and healthy women's samples in every cycle phase, from the PE to the late SE, correlating with progesterone levels (control SE, r2 = 0.64, FDR < 0.001; PCOS SE, r2 = 0.52, FDR < 0.001). The mid-SE endometrium showed the highest epithelial percentage compared to both the early and late SE endometrium in both healthy women and PCOS patients. Anovulatory PCOS cases showed epithelial cellular fractions comparable to those of PCOS cases in the PE (Anovulatory, 14.54%; PCOS PE, 15.56%, p = 1.00). We did not observe significant differences in the epithelial-to-stroma ratio in the hormone-induced endometrium in RIF patients with different receptivity statuses.

Conclusion

The AI model rapidly and accurately identifies endometrial histology features by calculating areas occupied by epithelial and stromal cells. The AI model demonstrates changes in epithelial cellular proportions according to the menstrual cycle phase and reveals no changes in epithelial cellular proportions based on PCOS and RIF conditions. In conclusion, the AI model can potentially improve endometrial histology assessment by accelerating the analysis of the cellular composition of the tissue and by ensuring maximal objectivity for research and clinical purposes.

Spatial local expressions of kisspeptin in the uterus and uterine tubes and its relationship to the reproductive potential in goats

Kisspeptins are neuropeptides encoded by the Kiss1 gene that was discovered as a metastasis suppressor gene in melanoma and breast cancer. Kisspeptin has pivotal functions for gonadotropin-releasing hormone secretion and plays integrated roles in the hypothalamic-pituitary-gonadal axis. However, little is known about the peripheral expression of kisspeptin in ruminants, especially in the female reproductive tract. Here, the objectives of the current study were to investigate the spatial localization of kisspeptin and mRNA expression of Kiss1 and its receptor (Kiss1r) in the fallopian tubes (FT) and uterus of goats at varied reproductive activity (cyclic versus true anoestrous goats, n=6, each). Specimens of the uterus and FT were collected and fixed using paraformaldehyde to investigate the localizations of kisspeptin in the selected tissues by immunohistochemistry. Another set of samples was snape-frozen to identify the expressions of mRNAs encoding Kiss1 and Kiss1r using real-time PCR. Results revealed immunolocalizations of kisspeptin in the uterus and the FT. The staining of kisspeptin was found mainly in the mucosal epithelium of the uterus the FT, and the endometrial glands. Very intense staining of kisspeptin was found in the uterine and FT specimens in the true anoestrous goats compared to that in cyclic ones. The expression of mRNA encoding Kiss1 gene was significantly higher in the uterine specimen of cyclic goats (1.00±0.09) compared to that in the true anoestrous goats (0.62±0.08) (P ˂0.05), while the expression of mRNA encoding Kiss1r was significantly (P ˂0.001) higher in the uterine tissues of true anoestrous goats (1.78±0.17) compared to that in cyclic ones (1.00±0.11). In conclusion, immunohistochemical localization of kisspeptin and the expression of mRNA encoding Kiss1/Kiss1r revealed spatial changes in the uterus and FT of goats according to the reproductive potential of goats (cyclic versus true anoestrous goats). However, the definitive local role of kisspeptin in the uterus and FT need further investigation.

Exposure to urban ambient particles (PM2.5) before pregnancy affects the expression of endometrial receptive markers to embryo implantation in mice: Preliminary results

Air pollution (AP) is one of the main recent concerns in reproductive healthy due to its potential to promote negative outcomes during pregnancy and male and female fertility. Several studies have demonstrated that AP exposure has been linked to increased embryonic implantation failures, alterations in embryonic, fetal and placental development. For a well-succeeded implantation, both competent blastocyst and receptive endometrium are required. Based on the lack of data about the effect of AP in endometrial receptivity, this study aimed to evaluate he particulate matter (PM) exposure impact on uterine receptive markers in mice and associate the alterations to increased implantation failures due to AP. For this study, ten dams per group were exposed for 39 days to either filter (F) or polluted air (CAP). At fourth gestational day (GD4), females were euthanized. Morphological, ultrastructural, immunohistochemical and molecular analysis of uterine and ovarian samples were performed. CAP-exposed females presented a reduced number of corpus luteum; glands and epithelial cells were increased with pinopodes formation impairment. Immunohistochemistry analysis revealed decreased LIF protein levels. These preliminary data suggests that PM exposure may exert negative effects on endometrial receptivity by affecting crucial parameters to embryonic implantation as uterine morphological differentiation, corpus luteum quantity and LIF expression during implantation window.

GnRH Induces Citrullination of the Cytoskeleton in Murine Gonadotrope Cells

Peptidylarginine deiminases (PADs or PADIs) catalyze the conversion of positively charged arginine to neutral citrulline, which alters target protein structure and function. Our previous work established that gonadotropin-releasing hormone agonist (GnRHa) stimulates PAD2-catalyzed histone citrullination to epigenetically regulate gonadotropin gene expression in the gonadotrope-derived LβT2 cell line. However, PADs are also found in the cytoplasm. Given this, we used mass spectrometry (MS) to identify additional non-histone proteins that are citrullinated following GnRHa stimulation and characterized the temporal dynamics of this modification. Our results show that actin and tubulin are citrullinated, which led us to hypothesize that GnRHa might induce their citrullination to modulate cytoskeletal dynamics and architecture. The data show that 10 nM GnRHa induces the citrullination of β-actin, with elevated levels occurring at 10 min. The level of β-actin citrullination is reduced in the presence of the pan-PAD inhibitor biphenyl-benzimidazole-Cl-amidine (BB-ClA), which also prevents GnRHa-induced actin reorganization in dispersed murine gonadotrope cells. GnRHa induces the citrullination of β-tubulin, with elevated levels occurring at 30 min, and this response is attenuated in the presence of PAD inhibition. To examine the functional consequence of β-tubulin citrullination, we utilized fluorescently tagged end binding protein 1 (EB1-GFP) to track the growing plus end of microtubules (MT) in real time in transfected LβT2 cells. Time-lapse confocal microscopy of EB1-GFP reveals that the MT average lifetime increases following 30 min of GnRHa treatment, but this increase is attenuated by PAD inhibition. Taken together, our data suggest that GnRHa-induced citrullination alters actin reorganization and MT lifetime in gonadotrope cells.

MicroRNA expression in specific segments of the pig periovulatory internal genital tract is differentially regulated by semen or by seminal plasma

microRNAs play pivotal roles during mammalian reproduction, including the cross-talk between gametes, embryos and the maternal genital tract. Mating induces changes in the expression of mRNA transcripts in the female, but whether miRNAs are involved remains to be elucidated. In the current study, we mapped 181 miRNAs in the porcine peri-ovulatory female reproductive tract: Cervix (Cvx), distal and proximal uterus (Dist-Ut, Prox-Ut), Utero-tubal-junction (UTJ), isthmus (Isth), ampulla (Amp), and infundibulum (Inf) when exposed to semen (natural mating (NM) or artificial insemination (AI-P1)) or to infusions of sperm-free seminal plasma (SP): the first 10 mL of the sperm rich fraction (SP-P1) or the entire ejaculate (SP-E). Among the most interesting findings, NM decreased mir-671, implicated in uterine development and pregnancy loss prior to embryo implantation, in Cvx, Dist-UT, Prox-UT, Isth, and Inf, while it increased in Amp. NM and SP-E induced the downregulation of miR-let7A-1 (Dist-UT, Prox-UT), a regulator of immunity during pregnancy. miR-34C-1, a regulator of endometrial receptivity gene expression, was increased in Dist-UT, UTJ and Amp (NM), in Prox-UT (AI-P1), and in Amp (SP-P1). miR-296, a modulator of the inflammatory response and apoptosis, was upregulated in the UTJ (all treatments). NM elicited the highest miRNA activity in the sperm reservoir (UTJ), suggesting that key-regulators such as miR-34c or miR-296 may modulate the metabolic processes linked to the adequate preparation for gamete encounter in the oviduct. Our results suggest that SP should be maintained in AI to warrant miRNA regulation within the female genital tract for reproductive success.

Endometrial Stem Cells: Orchestrating Dynamic Regeneration of Endometrium and Their Implications in Diverse Endometrial Disorders

The human endometrium, a vital component of the uterus, undergoes dynamic changes during the menstrual cycle to create a receptive environment for embryo implantation. Its remarkable regenerative capacity can be attributed to the presence of tissue-resident stem cell populations within the endometrium. Despite variations in characteristics among different subtypes, endometrial stem cells exhibit notably robust self-renewal capacity and the ability to differentiate into multiple lineages. This review offers a comprehensive insight into the current literature and recent advancements regarding the roles of various endometrial stem cell types during dynamic regeneration of the endometrium during the menstrual cycle. In addition, emerging evidence suggests that dysfunction or depletion of endometrial stem cells may play critical roles in the development and progression of various endometrial disorders, such as endometriosis, uterine fibroids, adenomyosis, infertility, and endometrial cancer. Therefore, we also highlight potential roles of endometrial stem cells in the development and progression of these endometrial diseases, including their ability to accumulate genetic mutations and express genes associated with endometrial diseases. Understanding the dynamic properties of the endometrium and the roles of endometrial stem cells in various endometrial disorders will shed light on potential therapeutic strategies for managing these conditions and improving women's fertility outcomes.

Single-cell insights into epithelial morphogenesis in the neonatal mouse uterus

The uterus is vital for successful reproduction in mammals, and two different types of epithelia (luminal and glandular) are essential for embryo implantation and pregnancy establishment. However, the essential cellular and molecular factors and pathways governing postnatal epithelium maturation, determination, and differentiation in developing uterus are yet to be elucidated. Here, the epithelium of the neonatal mouse uterus was isolated and subjected to single-cell transcriptome (scRNA-seq) analysis. Both the undifferentiated epithelium and determined luminal epithelium were heterogeneous and contained several different cell clusters based on single-cell transcription profiles. Substantial gene expression differences were evident as the epithelium matured and differentiated between postnatal days 1 to 15. Two new glandular epithelium-expressed genes (Gas6 and Cited4) were identified and validated by in situ hybridization. Trajectory analyses provided a framework for understanding epithelium maturation, lineage bifurcation, and differentiation. A candidate set of transcription factors and gene regulatory networks were identified that potentially direct epithelium lineage specification and morphogenesis. This atlas provides a foundation important to discover intrinsic cellular and molecular mechanisms directing uterine epithelium morphogenesis during a critical window of postnatal development.

Understanding conceptus-maternal interactions: what tools do we need to develop?

Communication between the maternal endometrium and developing embryo/conceptus is critical to support successful pregnancy to term. Studying the peri-implantation period of pregnancy is critical as this is when most pregnancy loss occurs in cattle. Our current understanding of these interactions is limited, due to the lack of appropriate in vitro models to assess these interactions. The endometrium is a complex and heterogeneous tissue that is regulated in a transcriptional and translational manner throughout the oestrous cycle. While there are in vitro models to study endometrial function, they are static and 2D in nature or explant models and are limited in how well they recapitulate the in vivo endometrium. Recent developments in organoid systems, microfluidic approaches, extracellular matrix biology, and in silico approaches provide a new opportunity to develop in vitro systems that better model the in vivo scenario. This will allow us to investigate in a more high-throughput manner the fundamental molecular interactions that are required for successful pregnancy in cattle.

Transcriptome changes associated with elongation of bovine conceptuses I: Differentially expressed transcripts in the conceptus on day 17 after insemination

The objective was to characterize transcriptome changes associated with elongation in bovine conceptuses during preimplantation stages. Nonlactating Holstein cows were euthanized 17 d after artificial insemination (AI) and the uterine horn ipsilateral to the CL was flushed with saline solution. Recovered conceptuses were classified as small (1.2 to 6.9 cm; n = 9), medium (10.5 to 16.0 cm; n = 9), or large (18.0 to 26.4 cm; n = 10). Total mRNA was extracted and subjected to transcriptome analyses using the Affymetrix Gene Chip Bovine array. Data were normalized using the GCRMA method and analyzed by robust regression using the Linear Models for Microarray library within Bioconductor in R. Transcripts with P ≤ 0.05 after adjustment for false discovery rate and fold change ≥1.5 were considered differentially expressed. Functional analyses were conducted using the Ingenuity Pathway Analysis platform. Comparisons between large versus small (LvsS), large versus medium (LvsM), and medium versus small (MvsS) conceptuses yielded a total of 634, 240, and 63 differentially expressed transcripts, respectively. Top canonical pathways of known involvement with embryo growth that were upregulated in large conceptuses included actin cytoskeleton (LvsS), integrin signaling (LvsS and LvsM), ephrin receptor (LvsS), mesenchymal transition by growth factor (LvsM), and regulation of calpain protease (LvsS). Transcripts involved with lipid metabolism pathways (LXR/RXR, FXR/RXR, hepatic fibrosis) were associated with the LvsS and LvsM, and some transcripts such as APOC2, APOH, APOM, RARA, RBP4, and PPARGC1A, were involved in these pathways. An overall network summary associated biological downstream effects of invasion of cells, proliferation of embryonic cells, and inhibition of organismal death in the LvsS. In conclusion, differently expressed transcripts in the LvsS comparison were associated with the cell growth, adhesion, and organismal development, although part of these findings could be attributed to differences in circulatory concentrations of progesterone of the cows that bore large and small conceptuses. The large and medium conceptuses developed under similar concentrations of progesterone and presented 240 differently expressed transcripts, associated with cell differentiation, metabolite regulation, and other biological processes.

Biallelic Dicer1 Mutations in the Gynecologic Tract of Mice Drive Lineage-Specific Development of DICER1 Syndrome-Associated Cancer

DICER1 is an RNase III enzyme essential for miRNA biogenesis through cleaving precursor-miRNA hairpins. Germline loss-of-function DICER1 mutations underline the development of DICER1 syndrome, a rare genetic disorder that predisposes children to cancer development in organs such as lung, gynecologic tract, kidney, and brain. Unlike classical tumor suppressors, the somatic "second hit" in DICER1 syndrome-associated cancers does not fully inactivate DICER1 but impairs its RNase IIIb activity only, suggesting a noncanonical two-hit hypothesis. Here, we developed a genetically engineered conditional compound heterozygous Dicer1 mutant mouse strain that fully recapitulates the biallelic DICER1 mutations in DICER1 syndrome-associated human cancers. Crossing this tool strain with tissue-specific Cre strains that activate Dicer1 mutations in gynecologic tract cells at two distinct developmental stages revealed that embryonic biallelic Dicer1 mutations caused infertility in females by disrupting oviduct and endometrium development and ultimately drove cancer development. These multicystic tubal and intrauterine tumors histologically resembled a subset of DICER1 syndrome-associated human cancers. Molecular analysis uncovered accumulation of additional oncogenic events (e.g., aberrant p53 expression, Kras mutation, and Myc activation) in murine Dicer1 mutant tumors and validated miRNA biogenesis defects in 5P miRNA strand production, of which, loss of let-7 family miRNAs was identified as a putative key player in transcriptomic rewiring and tumor development. Thus, this DICER1 syndrome-associated cancer model recapitulates the biology of human cancer and provides a unique tool for future investigation and therapeutic development.

SIGNIFICANCE

Generation of a Dicer1 mutant mouse model establishes the oncogenicity of missense mutations in the DICER1 RNase IIIb domain and provides a faithful model of DICER1 syndrome-associated cancer for further investigation.

CREB1 Is Involved in miR-134-5p-Mediated Endometrial Stromal Cell Proliferation, Apoptosis, and Autophagy

The successful establishment of endometrial receptivity is a key factor in ensuring the fertility of ewes and their economic benefits. Hu sheep have attracted attention due to their high fecundity and year-round estrus. In this study, we found that in the luteal phase, the uterine gland density, uterine coefficient, and number of uterine caruncles of high-fertility Hu sheep were higher than those of low-fertility Hu sheep. Thousands of differentially expressed genes were identified in the endometrium of Hu sheep with different fertility potential using RNA sequencing (RNA-Seq). Several genes involved in endometrial receptivity were screened using bioinformatics analysis. The qRT-PCR analysis further revealed the differential expression of cAMP reactive element binding protein-1 (CREB1) in the Hu sheep endometrium during the estrous cycle. Functionally, our results suggested that CREB1 significantly affected the expression level of endometrial receptivity marker genes, promoted cell proliferation by facilitating the transition from the G1 phase to the S phase, and inhibited cell apoptosis and autophagy. Moreover, we observed a negative linear correlation between miR-134-5p and CREB1 in the endometrium. In addition, CREB1 overexpression prevented the negative effect of miR-134-5p on endometrial stromal cell (ESC) growth. Taken together, these data indicated that CREB1 was regulated by miR-134-5p and may promote the establishment of uterine receptivity by regulating the function of ESCs. Moreover, this study provides new theoretical references for identifying candidate genes associated with fertility.

Single-cell transcriptomic characterization of sheep conceptus elongation and implantation

Bidirectional communication between the developing conceptus and endometrium is essential for pregnancy recognition and establishment in ruminants. We dissect the transcriptomic dynamics of sheep conceptus and corresponding endometrium at pre- and peri-implantation stages using single-cell RNA sequencing. Spherical blastocysts contain five cell types, with 68.62% trophectoderm cells. Strikingly, elongated conceptuses differentiate into 17 cell types, indicating dramatic cell fate specifications. Cell-type-specific gene expression delineates the features of distinctive trophectoderm lineages and indicates that the transition from polar trophectoderm to trophoblast increases interferon-tau expression and likely drives elongation initiation. We identify 13 endometrium-derived cell types and elucidate their molecular responses to conceptus development. Integrated analyses uncover multiple paired transcripts mediating the dialogues between extraembryonic membrane and endometrium, including IGF2-IGF1R, FGF19-FGFR1, NPY-NPY1R, PROS1-AXL, and ADGRE5-CD55. These data provide insight into the molecular regulation of conceptus elongation and represent a valuable resource for functional investigations of pre- and peri-implantation ruminant development.

Pathophysiological Insight into Fatty Acid-Binding Protein-4: Multifaced Roles in Reproduction, Pregnancy, and Offspring Health

Fatty acid-binding protein-4 (FABP4), commonly known as adipocyte-fatty acid-binding protein (A-FABP), is a pleiotropic adipokine that broadly affects immunity and metabolism. It has been increasingly recognized that FABP4 dysfunction is associated with various metabolic syndromes, including obesity, diabetes, cardiovascular diseases, and metabolic inflammation. However, its explicit roles within the context of women's reproduction and pregnancy remain to be investigated. In this review, we collate recent studies probing the influence of FABP4 on female reproduction, pregnancy, and even fetal health. Elevated circulating FABP4 levels have been found to correlate with impaired reproductive function in women, such as polycystic ovary syndrome and endometriosis. Throughout pregnancy, FABP4 affects maternal-fetal interface homeostasis by affecting both glycolipid metabolism and immune tolerance, leading to adverse pregnancy outcomes, including miscarriage, gestational obesity, gestational diabetes, and preeclampsia. Moreover, maternal FABP4 levels exhibit a substantial linkage with the metabolic health of offspring. Herein, we discuss the emerging significance and potential application of FABP4 in reproduction and pregnancy health and delve into its underlying mechanism at molecular levels.

Beclin-1-dependent autophagy, but not apoptosis, is critical for stem-cell-mediated endometrial programming and the establishment of pregnancy

The human endometrium shows a remarkable regenerative capacity that enables cyclical regeneration and remodeling throughout a woman's reproductive life. Although early postnatal uterine developmental cues direct this regeneration, the vital factors that govern early endometrial programming are largely unknown. We report that Beclin-1, an essential autophagy-associated protein, plays an integral role in uterine morphogenesis during the early postnatal period. We show that conditional depletion of Beclin-1 in the uterus triggers apoptosis and causes progressive loss of Lgr5+/Aldh1a1+ endometrial progenitor stem cells, with concomitant loss of Wnt signaling, which is crucial for stem cell renewal and epithelial gland development. Beclin-1 knockin (Becn1 KI) mice with disabled apoptosis exhibit normal uterine development. Importantly, the restoration of Beclin-1-driven autophagy, but not apoptosis, promotes normal uterine adenogenesis and morphogenesis. Together, the data suggest that Beclin-1-mediated autophagy acts as a molecular switch that governs the early uterine morphogenetic program by maintaining the endometrial progenitor stem cells.

Review: Endometrial function in pregnancy establishment in cattle

The endometrium is fundamentally required for successful pregnancy in ruminants and species where the posthatching conceptus undergoes a protracted elongation and peri-implantation phase of pregnancy. Moreover, there are substantial waves of pregnancy loss during this pre- and peri-implantation period of pregnancy the precise source of which has not been clearly defined i.e., the maternal uterine contribution to this loss. Understanding the molecular interactions required for successful pregnancy in cattle will allow us to intervene to support pregnancy success during this vulnerable window. The endometrium contributes to most key developmental milestones of pregnancy establishment, including (1) contributing to the regulation of the oestrus cycle, (2) nourishing the preimplantation conceptus, (3) responding to the conceptus to create a more receptive microenvironment, (4) providing essential biophysical support, and (5) signalling and producing factors which affect the mother systemically. This review will summarise what we currently know about conceptus-maternal interactions as well as identify the gaps in our knowledge that could be filled with newer in vitro model approaches. These include the use of microfluidics, organ-on-a-chip devices, and bioinformatic approaches. This will help maximise food production efficiency (both meat and dairy) and decrease the environmental burden, while enhancing our understanding of the fundamental processes required for successful implantation in cattle.

Integrated microRNA and secretome analysis of human endometrial organoids reveal the miR-3194-5p/Aquaporin/S100A9 module in regulating trophoblast functions

Successful placentation requires delicate communication between the endometrium and trophoblasts. The invasion and integration of trophoblasts into the endometrium during early pregnancy is crucial to placentation. Dysregulation of these functions is associated with various pregnancy complications, such as miscarriage and preeclampsia. The endometrial microenvironment has an important influence on trophoblast cell functions. The precise effect of the endometrial gland secretome on trophoblast functions remains uncertain. We hypothesized that the hormonal environment regulates the miRNA profile and secretome of the human endometrial gland, which subsequently modulates trophoblast functions during early pregnancy. Human endometrial tissues were obtained from endometrial biopsies with written consent. Endometrial organoids were established in matrix gel under defined culture conditions. They were treated with hormones mimicking the environment of the proliferative phase (Estrogen, E2), secretory phase (E2+Progesterone, P4), and early pregnancy (E2+P4+Human Chorionic Gonadotropin, hCG). miRNA-seq was performed on the treated organoids. Organoid secretions were also collected for mass spectrometric analysis. The viability and invasion/migration of the trophoblasts after treatment with the organoid secretome were determined by cytotoxicity assay and transwell assay, respectively. Endometrial organoids with the ability to respond to sex steroid hormones were successfully developed from human endometrial glands. By establishing the first secretome profiles and miRNA atlas of these endometrial organoids to the hormonal changes followed by trophoblast functional assays, we demonstrated that sex steroid hormones modulate aquaporin (AQP)1/9 and S100A9 secretions through miR-3194 activation in endometrial epithelial cells, which in turn enhanced trophoblast migration and invasion during early pregnancy. By using a human endometrial organoid model, we demonstrated for the first time that the hormonal regulation of the endometrial gland secretome is crucial to regulating the functions of human trophoblasts during early pregnancy. The study provides the basis for understanding the regulation of early placental development in humans.

The Cystic Anechoic Zone of Uterine Cavity Newly Observed during Controlled Ovarian Hyperstimulation Affects Pregnancy Outcomes of Fresh Embryo Transfer

During controlled ovarian hyperstimulation (COH), cystic anechoic zones in the uterine cavity are occasionally visible. This retrospective matched cohort study collected information on patients who underwent in vitro fertilization/intracytoplasmic injection (IVF/ICSI) from January 2014 to December 2020 at our center. The propensity score algorithm matched 179 cases that had uterine cystic anechoic zones, with 358 which did not have uterine cystic anechoic zones cases. After matching, the live birth rate (38.0% vs. 48.6%, p = 0.025) of patients with uterine cystic anechoic zones was lower than that in the no uterine cystic anechoic zone group, while for clinical pregnancy miscarriage rate (22.2% vs. 12.4%, p = 0.031), the rate was higher. The results showed no correlation in the association between live birth rate (r = −0.027, p = 0.718), clinical pregnancy rate (r = −0.037, p = 0.620) or biochemical pregnancy rate (r = −0.015, p = 0.840) and the diameters of the cystic anechoic zones in the uterine cavity. There was a significant difference in the type of endometrium between the two groups (p < 0.001). The result of this study can provide guidance to patients on whether to undergo fresh embryo transfer in the current cycle.

Prss29 Cre recombinase mice are useful to study adult uterine gland function

All mammalian uteri contain glands in their endometrium that develop only or primarily after birth. In mice, those endometrial glands govern post implantation pregnancy establishment via regulation of blastocyst implantation, stromal cell decidualization, and placental development. Here, we describe a new uterine glandular epithelium (GE) specific Cre recombinase mouse line that is useful for the study of uterine gland function during pregnancy. Utilizing CRISPR-Cas9 genome editing, Cre recombinase was inserted into the endogenous serine protease 29 precursor (Prss29) gene. Both Prss29 mRNA and Cre recombinase activity was specific to the GE of the mouse uterus following implantation, but was absent from other areas of the female reproductive tract. Next, Prss29-Cre mice were crossed with floxed forkhead box A2 (Foxa2) mice to conditionally delete Foxa2 specifically in the endometrial glands. Foxa2 was absent in the glands of the post-implantation uterus, and Foxa2 deleted mice exhibited complete infertility after their first pregnancy. These results establish that Prss29-Cre mice are a valuable resource to elucidate and explore the functions of glands in the adult uterus.

Human placental development and function

The placenta is a transient fetal organ that plays a critical role in the health and wellbeing of both the fetus and its mother. Functionally, the placenta sustains the growth of the fetus as it facilitates delivery of oxygen and nutrients and removal of waste products. Not surprisingly, defective early placental development is the primary cause of common disorders of pregnancy, including recurrent miscarriage, fetal growth restriction, pre-eclampsia and stillbirth. Adverse pregnancy conditions will also affect the life-long health of the fetus via developmental programming[1]. Despite its critical importance in reproductive success and life-long health, our understanding of placental development is not extensive, largely due to ethical limitations to studying early or chronological placental development, lack of long-term in vitro models, or comparative animal models. In this review, we examine current knowledge of early human placental development, discuss the critical role of the maternal endometrium and of the fetal-maternal dialogue in pregnancy success, and we explore the latest models of trophoblast and endometrial stem cells. In addition, we discuss the role of oxygen in placental formation and function, how nutrient delivery is mediated during the periods of histotrophic nutrition (uptake of uterine secretions) and haemotrophic nutrition (exchange between the maternal and fetal circulations), and how placental endocrine function facilitates fetal growth and development.

Three-dimensional culture models of human endometrium for studying trophoblast-endometrium interaction during implantation

During implantation, a symphony of interaction between the trophoblast originated from the trophectoderm of the implanting blastocyst and the endometrium leads to a successful pregnancy. Defective interaction between the trophoblast and endometrium often results in implantation failure, pregnancy loss, and a number of pregnancy complications. Owing to ethical concerns of using in vivo approaches to study human embryo implantation, various in vitro culture models of endometrium were established in the past decade ranging from two-dimensional cell-based to three-dimensional extracellular matrix (ECM)/tissue-based culture systems. Advanced organoid systems have also been established for recapitulation of different cellular components of the maternal-fetal interface, including the endometrial glandular organoids, trophoblast organoids and blastoids. However, there is no single ideal model to study the whole implantation process leaving more research to be done pursuing the establishment of a comprehensive in vitro model that can recapitulate the biology of trophoblast-endometrium interaction during early pregnancy. This would allow us to have better understanding of the physiological and pathological process of trophoblast-endometrium interaction during implantation.

Three-Dimensional Visualization of Mouse Endometrial Remodeling After Superovulation

Uterine status determines pregnancy success. Although it is well known that superovulation operations can disrupt uterine function, our understanding of the morphological changes in the uterine endometrium at the three-dimensional (3D) level is limited. Here, combining the tissue clearing with 3D deep imaging, we reveal an increase in epithelial density and angiogenesis after ovarian stimulation, which is accompanied by a circulating surge in P4 levels. Using an ovariectomized mouse model, we further detected the separate regulatory effects of P4 and E2 on the uterine endometrium, with P4 promoting endothelial cell growth and E2 inducing epithelial proliferation. Additionally, we observed that the effects of E2 can be partially neutralized by P4, and vice versa. By analyzing the 3D uterine imaging, we discovered an interesting phenomenon in which the growing blood vessels closely surround the remodeling uterine epithelium, indicating a close relationship between angiogenesis and epithelial growth. These findings provide new insight into the uterine epithelial changes and angiogenesis at the 3D level, and explain a potential reason for endometrial changes due to the low implantation rate in patients undergoing clinic super-ovulation.

The Role of Endometrial Stem/Progenitor Cells in Recurrent Reproductive Failure

Recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL), collectively referred to as recurrent reproductive failure (RRF), are both challenging conditions with many unanswered questions relating to causes and management options. Both conditions are proposed to be related to an aberrant endometrial microenvironment, with different proposed aetiologies related to a restrictive or permissive endometrium for an invading embryo. The impressive regenerative capacity of the human endometrium has been well-established and has led to the isolation and characterisation of several subtypes of endometrial stem/progenitor cells (eSPCs). eSPCs are known to be involved in the pathogenesis of endometrium-related disorders (such as endometriosis) and have been proposed to be implicated in the pathogenesis of RRF. This review appraises the current knowledge of eSPCs, and their involvement in RRF, highlighting the considerable unknown aspects in this field, and providing avenues for future research to facilitate much-needed advances in the diagnosis and management of millions of women suffering with RRF.

CRIPTO-1 Is Immunolocalized in the Syncytiotrophoblast of Ampullary Pregnancies

Introduction

Controlling the invasive activity of trophoblastic tissue has not been elucidated. In the accreta placenta, the invasion of placental tissue is directly related to the expression of CRIPTO-1 at the maternal-fetal interface. The aim of this study is to evaluate if the expression of the CRIPTO-1 is related to different degrees of trophoblast invasion into the tube wall in ampullary pregnancy.

Methods

Prospective study with 21 patients with ampullary tubal pregnancy undergoing salpingectomy. Anatomopathological evaluation determined the degree of invasion of trophoblast tissues into the tubal wall and grouped the samples into invasive degrees I, II, or III. The groups were compared for tissue expression of CRIPTO-1 using the Kruskal-Wallis nonparametric test. p values lower than 0.05 were considered significant.

Results

Quantitative expression of CRIPTO-1 differed in each of the three groups of trophoblast invasion in the tubal wall in ampullary pregnancies (p < 0.001). There is a difference between groups when grade I + grade II versus grade III (p < 0.001) and grade I versus grade II + grade III (p < 0.001). The tissue expression of CRIPTO-1 in ectopic trophoblasts showed that deeper invasion of the tubal wall was associated with stronger expression than in shallow invasion (p < 0.001). Discussion. In ampullary pregnancies, the depth of penetration of trophoblast tissue in the tubal wall is related to CRIPTO-1 tissue expression.

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.

A phenomenological-based model of the endometrial growth and shedding during the menstrual cycle

The human endometrium presents a remarkable growth dynamic with an outstanding regenerative capacity. This work aims to develop a phenomenological-based dynamic model to predict the volume changes in the functional layer of the endometrium in each phase of the menstrual cycle. This model considers changes in the endometrial tissue, the blood flow through the spiral arteries, the shedding of the endometrial cells, and the menstrual blood flow. The input variables are estrogen and progesterone; these hormone dynamics are taken from a pre-existing and validated model. Key parameters are modified in order to know their effect on the state variables. The model response was quantitatively assessed using the experimental data of the endometrial cycle reported in the literature. The proposed model provides a better insight into the interactions between ovarian hormones and the endometrial cycle by coupling both physiological processes.

Evaluation of bovine uterine gland functions in 2D and 3D culture system

In ruminants, uterine glands play key roles in the establishment of pregnancy by secreting various factors into the uterine lumen. Although a three-dimensional (3D) culture system has been used for investigating cellular functions in vitro, the detailed functions of uterine gland have not been fully elucidated. In this study, we examined the benefits of 3D culture system to examine the innate functions of bovine uterine glands. Isolated bovine uterine glands were cultured on Matrigel (2D) or in Matrigel (3D), respectively, and the mRNA levels of secreted proteins (SERPINA14, MEP1B, APOA1, ARSA, CTGF, and SPP1) were measured in isolated and cultured uterine glands. The protein expression of estrogen receptor β (ERβ) and progesterone receptor (PR) and the establishment of apico-basal polarity were examined. In isolated uterine glands, the mRNA levels of secreted proteins changed during the estrous cycle. Although uterine glands cultured in both 2D and 3D expressed ERβ and PR, progesterone did not affect SERPINA14 mRNA expression. The expression of APOA1 mRNA in 2D cultured uterine glands did not respond to estrogen and progesterone. Additionally, the mRNA levels of secreted proteins in the 3D culture system were significantly higher than those in the 2D culture system, which might be attributed to the different cellular morphology between them. The locations of ZO-1 and β-catenin in 2D cultured uterine glands were disordered compared with 3D cultured uterine glands. These results showed that the hormonal responsiveness of secreted factor expression and cellular morphology were different between 2D and 3D cultured bovine uterine glands.

Effects of progesterone concentrations and follicular wave during growth of the ovulatory follicle on conceptus and endometrial transcriptome in dairy cows

Objectives were to evaluate the effects of follicular wave and progesterone concentration on growth of the ovulatory follicle, conceptus elongation, uterine IFN-τ concentration, and transcriptome of conceptus and endometrium of pregnant cows on d 17 of gestation. Nonlactating nonpregnant Holstein cows were assigned randomly to one of 3 treatments: ovulation of a first-wave follicle (FW, n = 15); ovulation of a first-wave follicle and progesterone supplementation (FWP4, n = 12); and ovulation of a second-wave follicle (SW, n = 19). Ovulation of a first- or second-wave follicle was achieved by initiating the Ovsynch protocol (d -9 GnRH, d -2 and -1 PGF_2α, d 0 GnRH and artificial insemination, d 0.7 artificial insemination) on d 0 or 6 of a presynchronized estrous cycle, respectively. Cows in FWP4 received 3 intravaginal inserts containing progesterone at 12, 24, and 48 h after the first GnRH injection that were removed on d -2. Cows were killed on d 17 for collection of the reproductive tract. Transcriptome was evaluated by microarray using the Affymetrix Bovine Array. Orthogonal contrasts were built to assess the effects of progesterone concentration during follicle growth (FW vs. FWP4 + SW) and follicular wave (FWP4 vs. SW). Progesterone concentrations (LSM ± SEM) from d -9 to -2 were greater for SW, followed by FWP4 and FW (5.38 ± 0.24, 4.26 ± 0.28, and 1.17 ± 0.27 ng/mL). Diameter of the ovulatory follicle (FW = 19.6 ± 0.6; FWP4 = 15.6 ± 0.6; SW = 15.2 ± 0.5 mm) and concentrations of estradiol from d -2 to 1 (FW = 4.05 ± 0.33; FWP4 = 2.73 ± 0.35; SW = 2.48 ± 0.30 pg/mL) were greater for FW compared with FWP4 and SW. Progesterone concentrations from d 3 to 16 were greater for FW compared with FWP4 and SW. A total of 28 singleton conceptuses were collected (FW, n = 8; FWP4, n = 8; SW, n = 12) and only intact conceptuses were included in the analyses of length (FW, n = 8; FWP4, n = 6; SW, n = 12). Although conceptuses were longer for FW compared with FWP4 and SW (FW = 16.6 ± 2.3; FWP4 = 9.8 ± 2.2; SW = 9.6 ± 2.0 cm), treatment did not affect the amount of IFN-τ in uterine flushing. Transcriptome of conceptuses and endometrium of pregnant cows was not extensively affected by follicular wave (8 and 1 differentially expressed transcripts) or concentration of progesterone during follicle growth (0 and 3 differentially expressed transcripts), showing that these factors did not affect conceptuses and endometrium transcriptome in pregnancies that are maintained to d 17.

Effect of Overfeeding Shetland Pony Mares on Embryonic Glucose and Lipid Accumulation, and Expression of Imprinted Genes

Simple Summary

In pregnant individuals, maternal overnutrition is associated with disturbances in the expression of specific genes and nutrient transporters in the early embryo, which can affect both fetal and placental development and have lasting effects on the health of resulting offspring. To examine how maternal overfeeding affects the equine embryo, Shetland pony mares were fed either a high-energy (HE: 200% of net energy requirements) or maintenance (control) diet. Mares from both groups were inseminated, and day-seven embryos were recovered and transferred to recipients from the same or the alternate group. The expression of several genes, nutrient transporters and DNA methyltransferases (DNMTs; play an important role in regulating gene expression) were determined in extra-embryonic membranes after recovery on day 28 of gestation. The expression of nutrient transporters was also assessed in endometrium recovered from recipient mares immediately after embryo removal. In addition, glucose uptake by day-28 extra-embryonic membranes, and lipid droplet accumulation in day-seven embryos were assessed. Maternal overfeeding resulted in elevated expression of several genes, DNMTs and nutrient transporters following embryo transfer from an HE to a control mare. The expression of two amino acid transporters was also elevated in the endometrium after embryo transfer from HE to control. Maternal overfeeding did not affect lipid droplet accumulation in day-seven embryos, or glucose uptake by membranes of day-28 embryos. It remains to be seen whether the alterations in gene expression are maintained throughout gestation and into postnatal life.

Abstract

Maternal overfeeding is associated with disturbances in early embryonic epigenetic reprogramming, leading to altered expression of imprinted genes and nutrient transporters, which can affect both fetal and placental development and have lasting effects on the health of resulting offspring. To examine how maternal overfeeding affects the equine embryo, Shetland pony mares were fed either a high-energy (HE: 200% of net energy requirements) or maintenance (control) diet. Mares from both groups were inseminated, and day-seven embryos were recovered and transferred to recipients from the same or the alternate group. The expression of a panel of imprinted genes, glucose and amino acid transporters, and DNA methyltransferases (DNMTs) were determined in conceptus membranes after recovery on day 28 of gestation (late pre-implantation phase). The expression of nutrient transporters was also assessed in endometrium recovered from recipient mares immediately after conceptus removal. In addition, glucose uptake by day-28 extra-embryonic membranes, and lipid droplet accumulation in day-seven blastocysts were assessed. Maternal overfeeding resulted in elevated expression of imprinted genes (IGF2, IGF2R, H19, GRB10, PEG10 and SNRPN), DNMTs (DNMT1 and DNMT3B), glucose (SLC2A1), fructose (SLC2A5) and amino acid (SLC7A2) transporters following ET from an HE to a control mare. Expression of amino acid transporters (SLC1A5 and SLC7A1) was also elevated in the endometrium after ET from HE to control. Maternal overfeeding did not affect lipid droplet accumulation in blastocysts, or glucose uptake by day-28 membranes. It remains to be seen whether the alterations in gene expression are maintained throughout gestation and into postnatal life.

3D stem cell-laden artificial endometrium: successful endometrial regeneration and pregnancy

Thin endometrium lining or severe endometrial injury which may occur during artificial abortion can cause defective endometrial receptivity and subsequent infertility. Therefore, much effort has been devoted toward regenerating thin or damaged endometrial lining by applying multiple types of stem cells. Even though there are some positive preliminary outcomes, repairing the injured endometrium with stem cells is considerably challenging, due to the lack of an adequate microenvironment for the administrated stem cells within the tissues and subsequent poor therapeutic efficiency. In this context, as an alternative, we fabricated a 3D stem cell-laden artificial endometrium by incorporating several biodegradable biomaterials (collagen and hyaluronic acid) and multiple cellular components of endometrium (endometrial stem cells, stromal cells, and vessel cells) to properly recapitulate the multicellular microenvironment and multilayered structure. Agarose was used as an inert filler substrate to enhance the mechanical integrity of the three-layered artificial endometrium. Various mechanical characteristics, such as morphology, compression properties, swelling, and viscosity, have been evaluated. Various biological features, such as steroid hormone responsiveness, specific endometrial cell-surface marker expressions, and the secretion of multiple growth factors and steroid hormones, as well as the viability of encapsulated endometrial cells are relatively well maintained within the artificial endometrium. More importantly, severe tissue injuries were significantly relieved by transplanting our 3D artificial endometrium into endometrial ablation mice. Remarkably, artificial endometrium transplantation resulted in a successful pregnancy with subsequent live birth without any morphological or chromosomal abnormalities.

Analysis of the transcriptome of bovine endometrial cells isolated by laser micro-dissection (2): impacts of post-partum negative energy balance on stromal, glandular and luminal epithelial cells

BACKGROUND

In post-partum dairy cows, the energy needs to satisfy high milk production induces a status of more or less pronounced Negative Energy Balance (NEB). NEB associated with fat mobilization impairs reproductive function. In a companion paper, we described constitutive gene expression in the three main endometrial cell types (stromal, glandular and luminal epithelial cells) isolated by laser capture micro-dissection (LCM) showing the specificities of their transcriptomic profiles. This study investigates the specific impact of NEB on gene expression in these cells around 80 days after parturition at day 15 of the oestrus cycle and describes their specific response to NEB.

RESULTS

Following the description of their constitutive expression, the transcriptome profiles obtained by RNA sequencing of the three cells types revealed that differences related to the severity of NEB altered mainly specific patterns of expression related to individual cell types. Number of differentially expressed genes between severe NEB (SNEB) and mild NEB (MNEB) cows was higher in ST than in LE and GE, respectively. SNEB was associated with differential expression of genes coding for proteins involved in metabolic processes and embryo-maternal interactions in ST. Under-expression of genes encoding proteins with functions related to cell structure was found in GE whereas genes encoding proteins participating in pro-inflammatory pathways were over-expressed. Genes associated to adaptive immunity were under-expressed in LE.

CONCLUSION

The severity of NEB after calving is associated with changes in gene expression around 80 days after parturition corresponding to the time of breeding. Specific alterations in GEs are associated with activation of pro-inflammatory mechanisms. Concomitantly, changes in the expression of genes encoding proteins involved in cell interactions and maternal recognition of pregnancy takes place in ST. The combination of these effects possibly altering the uterine environment and embryo maternal interactions may negatively influence the establishment of pregnancy.

Reproductive roles of novel adipokines apelin, visfatin, and irisin in farm animals

The adipose tissue has a substantial impact on reproduction in mammals, specifically in females. As an energy depository organ, it is precisely associated with the reproductive success of mammals. Adipose tissue secretes many single molecules that are called 'adipokines' which mainly act as endocrine hormones. Adipokines homeostasis is fundamental to energy regulation, metabolic and cardiovascular diseases. The endocrine function of adipokines is influential for the long-term control of energy metabolism and performs an important function in metabolic state and fertility modulation. During the last years, new roles for adipokines have been appearing in the field of fertility. The adipokines have functions in reproduction at levels of the hypothalamus, the pituitary, and the gonads in humans, rodents, and other animals. Normal levels of adipokines are indispensable to protect the integrity of the hypothalamus-hypophysis-gonadal axis, regular ovulatory processes, and successful embryo implantation. Leptin and adiponectin are the most studied adipokines, but also the novel adipokines; apelin, visfatin, and irisin are important adipokines having several functions within the reproductive tract. Due to the known and unknown effects of these novel adipokines in the reproduction of farm animals, in this review, we will highlight the reproductive functions of apelin, visfatin, and irisin and summarize the known reproductive effects in farm animals to introduce the gaps for future studies in farm animals.

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.

Gut microbiota contributes to the development of endometrial glands in gilts during the ovary-dependent period

Background

The hyper-prolificacy Meishan gilts achieved a superior endometrial gland development (EGD) than white crossbred gilts during the ovary-independent period (before 60 d of age). Then, the EGD continues under the management of ovary-derived steroid hormones that regulated by gut microbiota (after 60 d of age). However, whether Meishan gilts’ superiority in EGD lasting to the ovary-dependent period (after 60 d of age) and the role of gut microbiota in this period both remain unclear.

Methods

Meishan gilts and Landrace x Yorkshire (LxY) gilts were raised under the same housing and feeding conditions until sexual maturity and then we compared their EGD and gut microbiota. Meanwhile, we transplanted fecal microbiota from Meishan gilts to L×Y gilts to explore the role of gut microbiota in EGD. We sampled plasma every 3 weeks and collected the uterus, ovary, liver, and rectal feces after the sacrifice. We then determined the hormone concentrations and expressions of the EGD-related genes. We also profiled the gut microbiota using 16S rDNA sequencing and metabolites of plasma and liver tissue using untargeted metabolomics. Finally, the correlation analysis and significant test was conducted between FMT-shifted gut microbes and EGD-related indices.

Results

Meishan gilts have larger endometrial gland area (P < 0.001), longer uterine horn length (P < 0.01) but lighter uterine horn weight (P < 0.05), a distinctive gut microbiota compared with L×Y gilts. Fecal microbiota transplantation (FMT) increased endometrial gland area (P < 0.01). FMT markedly shifted the metabolite profiles of both liver and plasma, and these differential metabolites enriched in steroid hormone biosynthesis pathway. FMT increased estradiol and insulin-like growth factor 1 but decreased progesterone dynamically. FMT also increased the expression of the EGD-related genes estrogen receptor 1 gene, epithelial cadherin, and forkhead box protein A2. There is a significant correlation between FMT-shifted gut microbes and EGD-related indices.

Conclusion

Sexually matured Meishan gilts achieved a superior EGD than LxY gilts. Meanwhile, gut microbiota contribute to the EGD potentially via regulating of steroid hormones during the ovary-dependent period.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00578-y.

Characterization of pregnancy-associated glycoproteins and progesterone as a predictor of twins and conceptus loss in high-risk-pregnancy Holstein cows

The objective of this study was to characterize plasma concentrations of pregnancy-associated glycoprotein (PAG) and progesterone (P4) as predictors of twins and pregnancy loss in Holstein cows with high-risk pregnancies. High-risk pregnancy was characterized using transrectal ultrasonography 37 d after artificial insemination (AI) based on the following criteria: small embryo size <15 mm, n = 10), slow heartbeat (<60 beats per minute, n = 11), and extra-amniotic membrane (additional amniotic membrane, n = 3). A cohort of twins (n = 41) diagnosed at d 37 post-AI was also enrolled. Each high-risk and twin pregnancy cow was paired with a cow of the same parity carrying a normal singleton at d 37 post-AI (control, n = 65). Blood samples were collected to measure PAG and P4 at d 37, 44, and 51 post-AI. Statistical analysis was performed using ANOVA, logistic regression, and receiver operator characteristic (ROC) curve with JMP software (SAS Institute Inc., Cary, NC). Pregnancy loss at d 51 post-AI was greater in high-risk pregnancies than in controls and twins (control = 1.5%; high-risk = 87.5%; twins = 12.2%). Concentration of PAG at d 37 post-AI did not differ among groups (control = 5.3 ± 0.7; high-risk = 4.8 ± 1.2; twins = 4.0 ± 0.9 ng/mL). Concentration of P4 at d 37 post-AI was greater in twins than in high-risk pregnancies and control, and lesser in high-risk pregnancies than in controls (control = 7.0 ± 0.3; high-risk = 5.9 ± 0.4; twins = 8.4 ± 0.3 ng/mL). Regression and ROC analysis for PAG at d 37 post-AI did not find a threshold to predict pregnancy loss or twins. Regression and ROC analysis for P4 at d 37 post-AI found that a threshold of 6.5 ng/mL predicted pregnancy loss with an area under the curve (AUC) of 0.64, and a threshold of 7.2 ng/mL predicted twins with AUC of 0.71. In summary, pregnancy loss and twins were predicted with only moderate accuracy by P4 concentration at d 37 post-AI, and the variability in PAG concentrations at d 37 post-AI was not sufficient to generate a threshold to predict pregnancy loss and twins in Holstein lactating cows.

Correlates of reproductive tract anatomy and uterine histomorphometrics with fertility in swine

Economic potential of the swine industry hinges upon the reproductive performance of sows, which may be enhanced by improving uterine capacity, a component trait of litter size and piglet productivity. Previous attempts at characterizing morphological traits indicative of high uterine volume have not been completely successful, resulting in the continued need for a reliable method of predicting reproductive value to improve production efficiency of the sow. Hence, the main objective of this study was to scrutinize macro- and micro-morphology of the sow's reproductive tract for quantitative correlations with fertility indices. Reproductive records from Polish Landrace × Polish Large White sows were used to examine the associations between fertility and ovarian/uterine morphology (n = 34) or uterine histomorphometry (n = 10). Several measures related to the ovary, including right and left ovarian weight (r = 0.50, p = 0.005 and r = 0.49, p = 0.006, respectively), were positively correlated with the litter size, while left ovarian number of corpora lutea (r = -0.38, p = 0.04) was negatively correlated with the mean litter size. Analysis of histomorphological characteristics of the uterine wall collected during the luteal phase of the estrous cycle revealed correlations between mean litter size and myometrial vascular content (r = 0.75, p = 0.03), the proportion of myometrial stroma (r = -0.68, p = 0.03), and the variability of endometrial thickness (r = -0.72, p = 0.02) in sows. Eight ovarian, vaginal and uterine characteristics were significantly correlated with mean lifetime numbers of live born and stillborn piglets/litter or the last litter size before slaughter. In conclusion, several anatomical and histomorphological metrics that relate to reproductive performance of swine may be used to inform production protocols and as a tool for selection of elite breeding sows, warranting future research into non-invasive or minimally invasive techniques for obtaining such measures.

Gene-expression profile and postpartum transition of bovine endometrial side population cells†

The mechanism of bovine endometrial regeneration after parturition remains unclear. Here, we hypothesized that bovine endometrial stem/progenitor cells participate in the postpartum regeneration of the endometrium. Flow cytometry analysis identified the presence of side population (SP) cells among endometrial stromal cells. Endometrial SP cells were shown to differentiate into osteoblasts and adipocytes. RNA-seq data showed that the gene expression pattern was different between bovine endometrial SP cells and main population cells. Gene Set Enrichment Analysis identified the enrichment of stemness genes in SP cells. Significantly (false discovery rate < 0.01) upregulated genes in SP cells contained several stem cell marker genes. Gene ontology (GO) analysis of the upregulated genes in SP cells showed enrichment of terms related to RNA metabolic process and transcription. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of upregulated genes in SP cells revealed enrichment of signaling pathways associated with maintenance and differentiation of stem/progenitor cells. The terms involved in TCA cycles were enriched in GO and KEGG pathway analysis of downregulated genes in SP cells. These results support the assumption that bovine endometrial SP cells exhibit characteristics of somatic stem/progenitor cells. The ratio of SP cells to endometrial cells was lowest on days 9-11 after parturition, which gradually increased thereafter. SP cells were shown to differentiate into epithelial cells. Collectively, these results suggest that bovine endometrial SP cells were temporarily reduced immediately after calving possibly due to their differentiation to provide new endometrial cells.

Placentation in Equids

This chapter focuses on the early stages of placental development in horses and their relatives in the genus Equus and highlights unique features of equid reproductive biology. The equine placenta is classified as a noninvasive, epitheliochorial type. However, equids have evolved a minor component of invasive trophoblast, the chorionic girdle and endometrial cups, which links the equine placenta with the highly invasive hemochorial placentae of rodents and, particularly, with the primate placenta. Two types of fetus-to-mother signaling in equine pregnancy are mediated by the invasive equine trophoblast cells. First, endocrinological signaling mediated by equine chorionic gonadotrophin (eCG) drives maternal progesterone production to support the equine conceptus between days 40 and 100 of gestation. Only in primates and equids does the placenta produce a gonadotrophin, but the evolutionary paths taken by these two groups of mammals to produce this placental signal were very different. Second, florid expression of paternal major histocompatibility complex (MHC) class I molecules by invading chorionic girdle cells stimulates strong maternal anti-fetal antibody responses that may play a role in the development of immunological tolerance that protects the conceptus from destruction by the maternal immune system. In humans, invasive extravillous trophoblasts also express MHC class I molecules, but the loci involved, and their likely function, are different from those of the horse. Comparison of the cellular and molecular events in these disparate species provides outstanding examples of convergent evolution and co-option in mammalian pregnancy and highlights how studies of the equine placenta have produced new insights into reproductive strategies.

Placentation in the Human and Higher Primates

Placentation in humans is precocious and highly invasive compared to other mammals. Implantation is interstitial, with the conceptus becoming completely embedded within the endometrium towards the end of the second week post-fertilization. Villi initially form over the entire surface of the chorionic sac, stimulated by histotrophic secretions from the endometrial glands. The secondary yolk sac never makes contact with the chorion, and a choriovitelline placenta is never established. However, recent morphological and transcriptomic analyses suggest that the yolk sac plays an important role in the uptake of nutrients from the coelomic fluid. Measurements performed in vivo demonstrate that early development takes place in a physiological, low-oxygen environment that protects against teratogenic free radicals and maintains stem cells in a multipotent state. The maternal arterial circulation to the placenta is only fully established around 10-12 weeks of gestation. By then, villi have regressed over the superficial, abembryonic pole, leaving the definitive discoid placenta, which is of the villous, hemochorial type. Remodeling of the maternal spiral arteries is essential to ensure a high-volume but low-velocity inflow into the mature placenta. Extravillous trophoblast cells migrate from anchoring villi and surround the arteries. Their interactions with maternal immune cells release cytokines and proteases that are key to remodeling, and a successful pregnancy.

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.

IFNT, ISGs, PPARs, RXRs and MUC1 in day 16 embryo and endometrium of repeat-breeder cows, with or without subclinical endometritis

Interferon-τ (IFNT), IFN stimulated genes (ISG15, CTSL1, RSAD2, SLC2A1, CXCL10, and SLC27A6), Peroxisome proliferator activated receptors (PPARA, D, and G), Retinoic acid receptors (RXRA, B, and G), and Mucin-1 (MUC1) play decisive roles in embryo elongation. The objective was to elucidate expressions of these genes in day 16 embryo [tubular (n = 4) vs. filamentous (n = 4)] and corresponding endometrium [without (n = 4) vs. with subclinical endometritis (SCE; n = 4)] of repeat breeder Holstein cows (2 × 2 factorial design). Results showed that the mRNA abundances (except PPARA and RXRB) were greater (P < 0.05) in filamentous embryo and endometrium without SCE compared with tubular embryo and endometrium with SCE, respectively. Overall, the mRNA abundances (except RSAD2, PPARA and RXRA) in filamentous embryo and corresponding endometrium of cows without SCE were greater (P < 0.05) than tubular embryo and corresponding endometrium of cows with SCE. Proteins IFNT, ISGs, PPARs and RXRs (except RXRB) were greater (P < 0.05) and protein MUC1 was lower (P < 0.01) in filamentous embryo and corresponding endometrium of cows without SCE compared to tubular embryo and corresponding endometrium of cows with SCE. On pairwise comparison, mRNA and protein abundances of MUC1 significantly differed between tubular embryo in uterus with or without SCE, and corresponding endometrium with or without SCE (P < 0.05). In conclusion, the mRNA and protein abundances of IFNT, ISG15, CXCL10, PPARG and MUC1 differed among filamentous and tubular conceptuses, and endometrium with or without SCE of repeat breeder cows on Day 16, indicating that these genes and their downstream signaling cascades play important roles in embryo elongation. Perhaps, interruptions in cross-talk between endometrium and conceptus impaired conceptus elongation in repeat breeder cows with SCE. In addition to disrupted signaling, the tubular conceptus (compared to filamentous conceptus) was unable to downregulate MUC1 (anti-adhesive glycocalyx) in repeat breeder cows with or without SCE, resulting in early embryonic demise.

The endometrial proteomic profile around the time of embryo implantation†

Embryo implantation is an intricate process which requires competent embryo and receptive endometrium. The failure of endometrium to achieve receptivity is a recognized cause of infertility. However, due to multiplicity of events involved, the molecular mechanisms governing endometrial receptivity are still not fully understood. Traditional one-by-one approaches, including western blotting and histochemistry, are insufficient to examine the extensive changes of endometrial proteome. Although genomics and transcriptomics studies have identified several significant genes, the underlying mechanism remains to be uncovered owing to post-transcriptional and post-translational modifications. Proteomic technologies are high throughput in protein identification, and they are now intensively used to identify diagnostic and prognostic markers in the field of reproductive medicine. There is a series of studies analyzing endometrial proteomic profile, which has provided a mechanistic insight into implantation failure. These published studies mainly focused on the difference between pre-receptive and receptive stages of endometrium, as well as on the alternation of endometrial proteomics in women with reproductive failure. Here, we review recent data from proteomic analyses regarding endometrium around the time of embryo implantation and propose possible future research directions.

Aldosterone from endometrial glands is benefit for human decidualization

Local renin-angiotensin system (RAS) in female reproductive system is involved in many physiological and pathological processes, such as follicular development, ovarian angiogenesis, ovarian, and endometrial cancer progress. However, studies on the functional relevance of RAS in human endometrium are limited, especially for renin-angiotensin-aldosterone system (RAAS). In this study, we defined the location of RAS components in human endometrium. We found that angiotensin II type-1 receptor (AT₁R) and aldosterone synthase (CYP11B2), major components of RAAS, are specifically expressed in endometrial gland during mid-secretory phase. Aldosterone receptor, mineralocorticoid receptor (MR), is elevated in stroma in mid-secretory endometrium. In vitro, MR is also activated by aldosterone during decidualization. Activated MR initiates LKB1 expression, followed by phosphorylating of AMPK that stimulates PDK4 expression. The impact of PDK4 on decidualization is independent on PDHE1α inactivation. Based on co-immunoprecipitation, PDK4 interacts with p-CREB to prevent its ubiquitination for facilitating decidualization via FOXO1. Restrain of MR activation interrupts LKB1/p-AMPK/PDK4/p-CREB/FOXO1 pathway induced by aldosterone, indicating that aldosterone action on decidualization is mainly dependent on MR stimulation. Aldosterone biosynthesized in endometrial gland during mid-secretory phase promotes decidualization via activating MR/LKB1/p-AMPK/PDK4/p-CREB/FOXO1 signaling pathway. This study provides the valuable information for understanding the underlying mechanism during decidualization.

Neonatal exposure to environment-relevant levels of tributyltin leads to uterine dysplasia in rats

Endocrine-disrupting chemicals (EDCs) are natural/synthetic compounds that mimic or inhibit the biological actions of endogenous hormones. Studies have revealed that environmental estrogen, such as bisphenol A (BPA), causes developmental defects in the uterus. Tributyltin (TBT) is a typical environmental androgen. In this study, we aimed to explore the effect and mechanism of TBT on uterine development. Neonatal female rats were exposed to TBT (10 and 100 ng/kg bw) from postnatal days 1 to 16. BPA (50 μg/kg bw) was used as a positive control. Neonatal exposure to environmental concentrations of TBT resulted in pathological changes in the uterus, including thickening of the uterine luminal epithelium, a low density of glands, endometrial inflammation and fibrosis. Further, TBT affected the Wnt signaling pathway, which might mediate developmental disorders of the endometrial epithelial cells and glands in the uterus. TBT exposure also activated the NF-κB signaling pathway, which triggered inflammation. Moreover, TBT exposure upregulated the TGF-β/Smads signaling pathway, possibly leading to endometrial fibrosis. In summary, our results demonstrate that neonatal exposure to an environment-relevant level of TBT leads to uterine dysplasia and provide potential molecular mechanisms. Our study is helpful for clarifying the effects of environmental androgens on the female reproduction system.

Effects of timing of artificial insemination and treatment of semen with a Slo3 potassium channel blocker on fertility of dairy heifers subjected to the 5-day CIDR-Synch protocol

Two experiments were conducted to evaluate the effects of the timing of artificial insemination (AI) and incorporation of the Slo3 K⁺ channel blocker 4-(4-chlorophenyl)butyl-diethyl-heptylammonium to semen extender (CSE) on pregnancy per AI (P/AI) and pregnancy loss in dairy heifers. In experiment 1, Holstein heifers were subjected to the 5-d CIDR-Synch protocol: d -8 GnRH and controlled internal drug-release device (CIDR); d -3 PGF_2α and CIDR removal; d -2 PGF_2α; d 0 GnRH) and assigned randomly to receive timed AI with control semen on d 0 (72-CON; n = 104), control semen on d -1 (48-CON; n = 100), or CSE-treated semen on d -1 (48-CSE; n = 98). Heifers were fitted with collar-mounted automated estrus detection devices to monitor physical activity and rumination. In experiment 2, Holstein heifers were subjected to the 5-d CIDR-Synch protocol and received a mount detection patch at the first PGF_2α injection. Heifers detected in estrus before d 0 were inseminated on the same day, whereas those not detected in estrus received the second GnRH injection and timed AI on d 0. Heifers were assigned randomly to receive AI with control (AI-CON; n = 148) or CSE-treated semen (AI-CSE; n = 110). Four bulls with proven fertility were used in both experiments, and ejaculates from each sire were divided and processed as CON or CSE. Pregnancy was diagnosed by transrectal ultrasonography at 29 and 54 d after AI. Data were analyzed by logistic regression, and statistical models included the fixed effects of treatment and enrollment week. In experiment 1, orthogonal contrasts were built to assess the effects of day of AI (72-CON vs. 48-CON + 48-CSE) and treatment of semen with CSE (48-CON vs. 48-CSE). Pregnancy per AI on d 29 (72-CON = 60.8, 48-CON = 35.2, 48-CSE = 39.8%) and d 54 (72-CON = 58.2, 48-CON = 31.6, 48-CSE = 36.2%) was greater for heifers inseminated on d 0 compared with d -1. However, no effect of semen extender on P/AI was observed in heifers inseminated on d -1. In experiment 2, P/AI tended to be greater for AI-CSE than for AI-CON on d 29 (58.6 vs. 47.3%) and d 54 after AI (55.6 vs. 43.7%). Advancing AI by 24 h decreased the likelihood of pregnancy, and use of CSE was unable to overcome the expected asynchrony between insemination and ovulation. Nevertheless, incorporation of CSE in semen processing tended to improve P/AI when heifers received AI upon detected estrus or timed AI concurrently with the final GnRH of the 5-d CIDR-Synch protocol.

Biochemical characterization of progesterone-induced alterations in bovine uterine fluid amino acid and carbohydrate composition during the conceptus elongation window†

Pregnancy establishment in cattle is contingent on conceptus elongation-a fundamental developmental event coinciding with the time during which most pregnancies fail. Elongation in vivo is directly driven by uterine secretions, indirectly influenced by systemic progesterone concentrations, and has yet to be recapitulated in vitro. To better understand the microenvironment evolved to facilitate this phenomenon, the amino acid and carbohydrate composition of uterine fluid was interrogated using high-throughput metabolomics on days 12, 13, and 14 of the estrous cycle from heifers with normal and high circulating progesterone. A total of 99 biochemicals (79 amino acids and 20 carbohydrates) were consistently identified, of which 31 showed a day by progesterone interaction. Fructose and mannitol/sorbitol did not exhibit a day by progesterone interaction, but displayed the greatest individual fluctuations (P ≤ 0.05) with respective fold increases of 18.39 and 28.53 in high vs normal progesterone heifers on day 12, and increases by 10.70-fold and 14.85-fold in the uterine fluid of normal progesterone animals on day 14 vs day 12. Moreover, enrichment analyses revealed that the phenylalanine, glutathione, polyamine, and arginine metabolic pathways were among the most affected by day and progesterone. In conclusion, progesterone had a largely stabilizing effect on amino acid flux, and identified biochemicals of likely importance to conceptus elongation initiation include arginine, fructose, glutamate, and mannitol/sorbitol.

Asynchronous Embryo Transfer Followed by Comparative Transcriptomic Analysis of Conceptus Membranes and Endometrium Identifies Processes Important to the Establishment of Equine Pregnancy

Preimplantation horse conceptuses require nutrients and signals from histotroph, the composition of which is regulated by luteal progesterone and conceptus-secreted factors. To distinguish progesterone and conceptus effects we shortened the period of endometrial progesterone-priming by asynchronous embryo transfer. Day 8 embryos were transferred to synchronous (day 8) or asynchronous (day 3) recipients, and RNA sequencing was performed on endometrium and conceptuses recovered 6 and 11 days later (embryo days 14 and 19). Asynchrony resulted in many more differentially expressed genes (DEGs) in conceptus membranes (3473) than endometrium (715). Gene ontology analysis identified upregulation in biological processes related to organogenesis and preventing apoptosis in synchronous conceptuses on day 14, and in cell adhesion and migration on day 19. Asynchrony also resulted in large numbers of DEGs related to 'extracellular exosome'. In endometrium, genes involved in immunity, the inflammatory response, and apoptosis regulation were upregulated during synchronous pregnancy and, again, many genes related to extracellular exosome were differentially expressed. Interestingly, only 14 genes were differentially expressed in endometrium recovered 6 days after synchronous versus 11 days after asynchronous transfer (day 14 recipient in both). Among these, KNG1 and IGFBP3 were consistently upregulated in synchronous endometrium. Furthermore bradykinin, an active peptide cleaved from KNG1, stimulated prostaglandin release by cultured trophectoderm cells. The horse conceptus thus responds to a negatively asynchronous uterus by extensively adjusting its transcriptome, whereas the endometrial transcriptome is modified only subtly by a more advanced conceptus.