Meta-signature of human endometrial receptivity: a meta-analysis and validation study of transcriptomic biomarkers

MicroRNAs as Biomarkers and Therapeutic Targets in Female Infertility

The study of microRNAs (miRNAs) has emerged in recent decades as a key approach to understanding the pathophysiology of many diseases, exploring their potential role as biomarkers, and testing their use as future treatments. Not only have neurological, cardiovascular diseases, or cancer benefited from this research but also infertility. Female infertility, as a disease, involves alterations at multiple levels, such as ovarian and uterine alterations. This review compiles the latest studies published in humans that link female disorders that affect fertility with altered miRNA profiles. Studies on ovarian alterations, including diminished ovarian reserve (DOR), poor ovarian response to stimulation (POR), premature ovarian insufficiency (POI), and polycystic ovary syndrome (PCOS), are summarized and classified based on the expression and type of sample analyzed. Regarding uterine disorders, this review highlights upregulated and downregulated miRNAs primarily identified as biomarkers for endometriosis, adenomyosis, decreased endometrial receptivity, and implantation failure. However, despite the large number of studies in this field, the same limitations that reduce reproducibility are often observed. Therefore, at the end of this review, the main limitations of this type of study are described, as well as specific precautions or safety measures that should be considered when handling miRNAs.

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.

AI-algorithm training and validation for identification of endometrial CD138+ cells in infertility-associated conditions; polycystic ovary syndrome (PCOS) and recurrent implantation failure (RIF)

Background

Endometrial CD138+ plasma cells serve as a diagnostic biomarker for endometrial inflammation, and their elevated occurrence correlates positively with adverse pregnancy outcomes. Infertility-related conditions like polycystic ovary syndrome (PCOS) and recurrent implantation failure (RIF) are closely associated with systemic and local chronic inflammatory status, wherein endometrial CD138+ plasma cell accumulation could also contribute to endometrial pathology. Current methods for quantifying CD138+ cells typically involve laborious and time-consuming microscopic assessments of only a few random areas from a slide. These methods have limitations in accurately representing the entire slide and are susceptible to significant biases arising from intra- and interobserver variations. Implementing artificial intelligence (AI) for CD138+ cell identification could enhance the accuracy, reproducibility, and reliability of analysis.

Methods

Here, an AI algorithm was developed to identify CD138+ plasma cells within endometrial tissue. The AI model comprised two layers of convolutional neural networks (CNNs). CNN1 was trained to segment epithelium and stroma across 28,363 mm2 (2.56 mm2 of epithelium and 24.87 mm2 of stroma), while CNN2 was trained to distinguish stromal cells based on CD138 staining, encompassing 7345 cells in the object layers (6942 CD138- cells and 403 CD138+ cells). The training and performance of the AI model were validated by three experienced pathologists. We collected 193 endometrial tissues from healthy controls (n = 73), women with PCOS (n = 91), and RIF patients (n = 29) and compared the CD138+ cell percentages based on cycle phases, ovulation status, and endometrial receptivity utilizing the AI model.

Results

The AI algorithm consistently and reliably distinguished CD138- and CD138+ cells, with total error rates of 6.32% and 3.23%, respectively. During the training validation, there was a complete agreement between the decisions made by the pathologists and the AI algorithm, while the performance validation demonstrated excellent accuracy between the AI and human evaluation methods (intraclass correlation; 0.76, 95% confidence intervals; 0.36-0.93, p = 0.002) and a positive correlation (Spearman's rank correlation coefficient: 0.79, p < 0.01). In the AI analysis, the AI model revealed higher CD138+ cell percentages in the proliferative phase (PE) endometrium compared to the secretory phase or anovulatory PCOS endometrium, irrespective of PCOS diagnosis. Interestingly, CD138+ percentages differed according to PCOS phenotype in the PE (p = 0.03). On the other hand, the receptivity status had no impact on the cell percentages in RIF samples.

Conclusion

Our findings emphasize the potential and accuracy of the AI algorithm in detecting endometrial CD138+ plasma cells, offering distinct advantages over manual inspection, such as rapid analysis of whole slide images, reduction of intra- and interobserver variations, sparing the valuable time of trained specialists, and consistent productivity. This supports the application of AI technology to help clinical decision-making, for example, in understanding endometrial cycle phase-related dynamics, as well as different reproductive disorders.

Reproductomics: Exploring the Applications and Advancements of Computational Tools

Over recent decades, advancements in omics technologies, such as proteomics, genomics, epigenomics, metabolomics, transcriptomics, and microbiomics, have significantly enhanced our understanding of the molecular mechanisms underlying various physiological and pathological processes. Nonetheless, the analysis and interpretation of vast omics data concerning reproductive diseases are complicated by the cyclic regulation of hormones and multiple other factors, which, in conjunction with a genetic makeup of an individual, lead to diverse biological responses. Reproductomics investigates the interplay between a hormonal regulation of an individual, environmental factors, genetic predisposition (DNA composition and epigenome), health effects, and resulting biological outcomes. It is a rapidly emerging field that utilizes computational tools to analyze and interpret reproductive data, with the aim of improving reproductive health outcomes. It is time to explore the applications of reproductomics in understanding the molecular mechanisms underlying infertility, identification of potential biomarkers for diagnosis and treatment, and in improving assisted reproductive technologies (ARTs). Reproductomics tools include machine learning algorithms for predicting fertility outcomes, gene editing technologies for correcting genetic abnormalities, and single cell sequencing techniques for analyzing gene expression patterns at the individual cell level. However, there are several challenges, limitations and ethical issues involved with the use of reproductomics, such as the applications of gene editing technologies and their potential impact on future generations are discussed. The review comprehensively covers the applications and advancements of reproductomics, highlighting its potential to improve reproductive health outcomes and deepen our understanding of reproductive molecular mechanisms.

Development of a New Personalized Molecular Test Based on Endometrial Receptivity and Maternal-Fetal Dialogue: Adhesio

Successful embryo implantation relies on a receptive endometrium and a maternofetal dialogue. Abnormal receptivity is a common cause of implantation failure in assisted reproductive techniques. This study aimed to develop a novel transcriptomic-based diagnostic assay, Adhesio, for assessing endometrial receptivity and guiding personalized embryo transfer. Adhesio was developed based on an initial dataset of 74 endometrial biopsies. Two types of biopsy samples were involved: 45 endometrial biopsies collected during the optimal theoretical window of implantation (WOI) and 29 endometrial biopsies which cells have been cultured with or without an autologous embryo. Microarray analysis was performed to identify differentially expressed genes associated with endometrial receptivity and selected candidate genes were assessed using quantitative real-time polymerase chain reaction (RT-qPCR) on biopsy samples. Statistical analyses were conducted to assess the performance and accuracy of Adhesio. The microarray analysis identified three distinct clusters of endometrial samples with differential gene expression patterns. Cluster 1 exhibited 1717 differentially expressed genes involved in biological processes associated with endometrial receptivity. A specific transcriptomic signature of 60 genes associated with endometrial co-culture was obtained using class prediction approach. Thereafter, an original panel of 10 genes was selected as potential biomarkers for endometrial receptivity based on their expression profiles in both endometrial biopsies and co-cultured cells. This article outlines the methodology employed to develop Adhesio, a test that assesses endometrial receptivity using an original panel of 10 genes. These genes are not only involved during the WOI but are also influenced by the maternal-fetal dialogue.

Altered Expressions of IL-15, IFNG, and HPRT1 Genes in the Thin Endometria of Patients with Reproductive Disorders: A Prospective Comparative Study

Reproductive disorders are common events in modern reproductive medicine, occurring both in spontaneous and assisted pregnancies. Studies on the molecular mechanisms of implantation disorders in thin endometria, including the study of gene transcriptional activities, have shed light on the identification of the potential biological markers of endometrial receptivity. Background/Objectives: The goal of this study was to reveal the significantly dysregulated selected gene expressions between RIF and RPL patients with thin endometria. Methods: Endometrial samples were collected from RIF patients (n = 20) and RPL patients (n = 19) during the implantation window days (LH + 7-LH + 10) of their natural menstrual cycles. Ten genes were chosen as the target genes regarding their possible relations with the implantation process. The total RNA was purified and reverse-transcribed, and gene expressions were quantified by RT-PCR. Results: The expressions of the IL-15, INFG, and HPRT1 genes were significantly decreased in the RIF patients with thin endometria compared to the RPL patients (log2 fold change = 0.92, p = 0.023 for IL-15; log2 fold change = 1.24, p = 0.046 for INFG; and log2 fold change = 0.579, p = 0.046 for HPRT1). There were no significant differences in the expressions of the CXCL8, CXCL1, MMP10, C4BPA, TNC, VEGFB, and HAND2 genes between the groups. Conclusions: Decreased expressions of the IL-15, INFG, and HPRT1 genes were found in patients with RIF with thin endometria compared to the endometria of women with RPL. This has practical significance for clinicians for the differentiated prescription of immunomodulatory therapy in patients undergoing ART programs.

The Role of the Endometrium in Implantation: A Modern View

According to the current data, the endometrium acts as a "sensor" of embryo quality, which promotes the implantation of euploid embryos and prevents the implantation and/or subsequent development of genetically abnormal embryos. The present review addresses the nature of the "sensory function" of the endometrium and highlights the necessity for assessing its functional status. The first section examines the evolutionary origin of the "sensory" ability of the endometrium as a consequence of spontaneous decidualization that occurred in placental animals. The second section details the mechanisms for implementing this function at the cellular level. In particular, the recent findings of the appearance of different cell subpopulations during decidualization are described, and their role in implantation is discussed. The pathological consequences of an imbalance among these subpopulations are also discussed. Finally, the third section summarizes information on currently available clinical tools to assess endometrial functional status. The advantages and disadvantages of the approaches are emphasized, and possible options for developing more advanced technologies for assessing the "sensory" function of the endometrium are proposed.

Altered Expression of C4BPA and CXCL1 Genes in the Endometrium of Patients with Recurrent Implantation Failure after In Vitro Fertilization and Thin Endometrium

Currently, recurrent implantation failure (RIF) after in vitro fertilization is a problem that is commonly faced by reproductive specialists. The phenomenon of a thin endometrium in RIF patients is not yet completely understood or sufficiently treated. This study aimed to reveal the dysregulated expression of selected genes between RIF patients with a thin endometrium and fertile women. Endometrial samples were collected in the implantation window (21-24 days of the natural menstrual cycle) from RIF patients (n = 20) and fertile women (n = 14). Ten genes were chosen as target genes regarding their possible relations with the implantation process. The endometrial gene expression levels showed differences in RIF samples compared to fertile samples. Significant downregulation was observed for the CXCL1 (p = 0.005) and C4BPA (p = 0.03) genes. There was no statistically significant difference between the RIF group and the fertile group in the expression of eight genes: CXCL8, HPRT1, MMP10, INFG, VEGFB, HAND2, IL-15, and TNC (p > 0.05). The use of a combination of two markers (C4BPA + CXCL1) allows for the good discrimination of RIF patients from fertile women (AUC 0.806).

Stanniocalcin Protein Expression in Female Reproductive Organs: Literature Review and Public Cancer Database Analysis

Stanniocalcin (STC) 1 and 2 serve as antihyperglycemic polypeptide hormones with critical roles in regulating calcium and phosphate homeostasis. They additionally function as paracrine and/or autocrine factors involved in numerous physiological processes, including female reproduction. STC1 and STC2 contribute to the pathophysiology of several diseases, including female infertility- and pregnancy-associated conditions, and even tumorigenesis of reproductive organs. This comprehensive review highlights the dynamic expression patterns and potential dysregulation of STC1 and STC2, restricted to female fertility, and infertility- and pregnancy-associated diseases and conditions, such as endometriosis, polycystic ovary syndrome (PCOS), abnormal uterine bleeding, uterine polyps, and pregnancy complications, like impaired decidualization, preeclampsia, and preterm labor. Furthermore, the review elucidates the role of dysregulated STC in the progression of cancers of the reproductive system, including endometrial, cervical, and ovarian cancers. Additionally, the review evaluates the expression patterns and prognostic significance of STC in gynecological cancers by utilizing existing public datasets from The Cancer Genome Atlas to help decipher the multifaceted roles of these pleiotropic hormones in disease progression. Understanding the intricate mechanisms by which STC proteins influence all these reviewed conditions could lead to the development of targeted diagnostic and therapeutic strategies in the context of female reproductive health and oncology.

LnCRNAs in the Regulation of Endometrial Receptivity for Embryo Implantation

The development of endometrial receptivity is crucial for successful embryo implantation and the initiation of pregnancy. Understanding the molecular regulatory processes that transform the endometrium into a receptive phase is essential for enhancing implantation rates in fertility treatments, such as in vitro fertilization (IVF). Long non-coding RNAs (lncRNAs) play a pivotal role as gene regulators and have been examined in the endometrium. This review offers current insights into the role of lncRNAs in regulating endometrial receptivity. Considering the significant variation in endometrial remodeling among species, we summarize the key events in the human endometrial cycle and discuss the identified lncRNAs in both humans and other species, which may play a crucial role in establishing receptivity. Notably, there are 742 lncRNAs in humans and 4438 lncRNAs that have the potential to modulate endometrial receptivity. Additionally, lncRNAs regulating matrix metalloproteinases (MMPs) and Let-7 have been observed in both species. Future investigations should explore the potential of lncRNAs as therapeutic targets and/or biomarkers for diagnosing and improving endometrial receptivity in human fertility therapy.

Tailor-made embryo transfer considering embryonic developmental speed to overcome the dilemma of personalized embryo transfer

RESEARCH QUESTION

Does tailor-made embryo transfer (TmET), timed with respect to embryonic developmental speed, affect pregnancy outcomes in patients with recurrent implantation failure?

DESIGN

Among 741 patients identified as receptive through endometrial receptivity testing, the clinical pregnancy rates and live birth rates were retrospectively compared between those who underwent standard personalized embryo transfer and those who underwent TmET in hormone replacement therapy cycles. Personalized embryo transfer was performed according to endometrial receptivity test results (standard personalized embryo transfer group) or considering embryonic developmental speed (TmET group). For TmET, the expansion grade of warmed blastocysts was estimated based on each patient's previous embryonic developmental pattern. The embryo transfer days were set so that estimated blastocyst grades 3, 4, 5 and 6 were transferred on days P+5, P+5.5, P+6.0 and P+6.5, respectively.

RESULTS

In a propensity score matching analysis, the clinical pregnancy rate was significantly higher in the TmET group than the standard personalized embryo transfer group (P = 0.014), whereas the live birth rates were similar between the two groups (P = 0.65). In a subgroup analysis with euploid embryo transfers, the clinical pregnancy rate was significantly higher in the TmET group than the standard personalized embryo transfer group, although there was no difference in live birth rate between the two groups (P = 0.045 and P = 0.057, respectively).

CONCLUSIONS

For patients experiencing recurrent implantation failure and identified as receptive through endometrial receptivity testing, subsequent TmET strategies may further enhance pregnancy outcomes.

Aging promotes accumulation of senescent and multiciliated cells in human endometrial epithelium

STUDY QUESTION

What changes occur in the endometrium during aging, and do they impact fertility?

SUMMARY ANSWER

Both the transcriptome and cellular composition of endometrial samples from women of advanced maternal age (AMA) are significantly different from that of samples from young women, suggesting specific changes in epithelial cells that may affect endometrial receptivity.

WHAT IS KNOWN ALREADY

Aging is associated with the accumulation of senescent cells in aging tissues. Reproductive aging is mostly attributed to the decline in ovarian reserve and oocyte quality, whereas the endometrium is a unique complex tissue that is monthly renewed under hormonal regulation. Several clinical studies have reported lower implantation and pregnancy rates in oocyte recipients of AMA during IVF. Molecular studies have indicated the presence of specific mutations within the epithelial cells of AMA endometrium, along with altered gene expression of bulk endometrial tissue.

STUDY DESIGN SIZE DURATION

Endometrial transcriptome profiling was performed for 44 women undergoing HRT during the assessment of endometrial receptivity before IVF. Patients younger than 28 years were considered as the young maternal age (YMA) group (age 23-27 years) and women older than 45 years were considered as the AMA group (age 47-50 years). Endometrial biopsies were obtained on Day 5 of progesterone treatment and RNA was extracted. All endometrial samples were evaluated as being receptive based on the expression of 68 common endometrial receptivity markers. Endometrial samples from another 24 women classified into four age groups (YMA, intermediate age group 1 (IMA1, age 29-35), intermediate age group 2 (IMA2, age 36-44), and AMA) were obtained in the mid-secretory stage of a natural cycle (NC) and used for validation studies across the reproductive lifespan.

PARTICIPANTS/MATERIALS SETTING METHODS

A total of 24 HRT samples (12 YMA and 12 AMA) were subject to RNA sequencing (RNA-seq) and differential gene expression analysis, 20 samples (10 YMA and 10 AMA) were used for qPCR validation, and 24 NC samples (6 YMA, 6 IMA1, 6 IMA2 and 6AMA) were used for RNA-seq validation of AMA genes across the woman's reproductive lifespan. Immunohistochemistry (IHC) was used to confirm some expression changes at the protein level. Computational deconvolution using six endometrial cell type-specific transcriptomic profiles was conducted to compare the cellular composition between the groups.

MAIN RESULTS AND THE ROLE OF CHANCE

Comparisons between YMA and AMA samples identified a lower proportion of receptive endometria in the AMA group (P = 0.007). Gene expression profiling identified 491 differentially expressed age-sensitive genes (P adj < 0.05) that revealed the effects of age on endometrial epithelial growth and receptivity, likely contributing to decreased reproductive performance. Our results indicate that changes in the expression of the cellular senescence marker p16INK4a and genes associated with metabolism, inflammation, and hormone response are involved in endometrial aging. Importantly, we demonstrate that the proportion of multi-ciliated cells, as discovered based on RNA-seq data deconvolution and tissue IHC results, is affected by endometrial aging, and propose a putative onset of age-related changes. Furthermore, we propose that aging has an impact on the transcriptomic profile of endometrial tissue in the context of endometrial receptivity.

LARGE SCALE DATA

The raw sequencing data reported in this article are deposited at the Gene Expression Omnibus under accession code GSE236128.

LIMITATIONS REASONS FOR CAUTION

This retrospective study identified changes in the endometrium of patients undergoing hormonal replacement and validated these changes using samples obtained during a NC. However, future studies must clarify the importance of these findings on the clinical outcomes of assisted reproduction.

WIDER IMPLICATIONS OF THE FINDINGS

The findings reported in this study have important implications for devising future strategies aimed at improving fertility management in women of advanced reproductive age.

STUDY FUNDING/COMPETING INTERESTS

This research was funded by the Estonian Research Council (grant no. PRG1076), Horizon 2020 innovation grant (ERIN, grant no. EU952516), Enterprise Estonia (grant no. EU48695), MSCA-RISE-2020 project TRENDO (grant no. 101008193), EU 874867 project HUTER, the Horizon Europe NESTOR grant (grant no. 101120075) of the European Commission, the EVA specialty program (grant no. KP111513) of the Maastricht University Medical Center (MUMC+), MICIU/AEI/10.13039/501100011033 and FEDER, EU projects Endo-Map (grant no. PID2021-12728OB-100), ROSY (grant no. CNS2022-135999), and the National Science Fund of Bulgaria (grant no. KII-06 H31/2). The authors declare no competing interests.

Predicting risk of endometrial failure: a biomarker signature that identifies a novel disruption independent of endometrial timing in patients undergoing hormonal replacement cycles

OBJECTIVE

To propose a new gene expression signature that identifies endometrial disruptions independent of endometrial luteal phase timing and predicts if patients are at risk of endometrial failure.

DESIGN

Multicentric, prospective study.

SETTING

Reproductive medicine research department in a public hospital affiliated with private fertility clinics and a reproductive genetics laboratory.

PATIENTS

Caucasian women (n = 281; 39.4 ± 4.8 years old with a body mass index of 22.9 ± 3.5 kg/m2) undergoing hormone replacement therapy between July 2018 and July 2021. Endometrial samples from 217 patients met RNA quality criteria for signature discovery and analysis.

INTERVENTION(S)

Endometrial biopsies collected in the mid-secretory phase.

MAIN OUTCOME MEASURE(S)

Endometrial luteal phase timing-corrected expression of 404 genes and reproductive outcomes of the first single embryo transfer (SET) after biopsy collection to identify prognostic biomarkers of endometrial failure.

RESULTS

Removal of endometrial timing variation from gene expression data allowed patients to be stratified into poor (n = 137) or good (n = 49) endometrial prognosis groups on the basis of their clinical and transcriptomic profiles. Significant differences were found between endometrial prognosis groups in terms of reproductive rates: pregnancy (44.6% vs. 79.6%), live birth (25.6% vs. 77.6%), clinical miscarriage (22.2% vs. 2.6%), and biochemical miscarriage (20.4% vs. 0%). The relative risk of endometrial failure for patients predicted as a poor endometrial prognosis was 3.3 times higher than those with a good prognosis. The differences in gene expression between both profiles were proposed as a biomarker, coined the endometrial failure risk (EFR) signature. Poor prognosis profiles were characterized by 59 upregulated and 63 downregulated genes mainly involved in regulation (17.0%), metabolism (8.4%), immune response, and inflammation (7.8%). This EFR signature had a median accuracy of 0.92 (min = 0.88, max = 0.94), median sensitivity of 0.96 (min = 0.91, max = 0.98), and median specificity of 0.84 (min = 0.77, max = 0.88), positioning itself as a promising biomarker for endometrial evaluation.

CONCLUSION(S)

The EFR signature revealed a novel endometrial disruption, independent of endometrial luteal phase timing, present in 73.7% of patients. This EFR signature stratified patients into 2 significantly distinct and clinically relevant prognosis profiles providing opportunities for personalized therapy. Nevertheless, further validations are needed before implementing this gene signature as an artificial intelligence (AI)-based tool to reduce the risk of patients experiencing endometrial failure.

Inflammatory mechanisms of preterm labor and emerging anti-inflammatory interventions

Preterm birth is a major public health concern, requiring a deeper understanding of its underlying inflammatory mechanisms and to develop effective therapeutic strategies. This review explores the complex interaction between inflammation and preterm labor, highlighting the pivotal role of the dysregulation of inflammation in triggering premature delivery. The immunological environment of pregnancy, characterized by a fragile balance of immune tolerance and resistance, is disrupted in preterm labor, leading to a pathological inflammatory response. Feto-maternal infections, among other pro-inflammatory stimuli, trigger the activation of toll-like receptors and the production of pro-inflammatory mediators, promoting uterine contractility and cervical ripening. Emerging anti-inflammatory therapeutics offer promising approaches for the prevention of preterm birth by targeting key inflammatory pathways. From TLR-4 antagonists to chemokine and interleukin receptor antagonists, these interventions aim to modulate the inflammatory environment and prevent adverse pregnancy outcomes. In conclusion, a comprehensive understanding of the inflammatory mechanisms leading to preterm labor is crucial for the development of targeted interventions in hope of reducing the incidence of preterm birth and improving neonatal health outcomes.

Comprehensive transcriptional atlas of human adenomyosis deciphered by the integration of single-cell RNA-sequencing and spatial transcriptomics

Adenomyosis is a poorly understood gynecological disorder lacking effective treatments. Controversy persists regarding "invagination" and "metaplasia" theories. The endometrial-myometrial junction (EMJ) connects the endometrium and myometrium and is important for diagnosing and classifying adenomyosis, but its in-depth study is just beginning. Using single-cell RNA sequencing and spatial profiling, we mapped transcriptional alterations across eutopic endometrium, lesions, and EMJ. Within lesions, we identified unique epithelial (LGR5+) and invasive stromal (PKIB+) subpopulations, along with WFDC1+ progenitor cells, supporting a complex interplay between "invagination" and "metaplasia" theories of pathogenesis. Further, we observed endothelial cell heterogeneity and abnormal angiogenic signaling involving vascular endothelial growth factor and angiopoietin pathways. Cell-cell communication differed markedly between ectopic and eutopic endometrium, with aberrant signaling in lesions involving pleiotrophin, TWEAK, and WNT cascades. This study reveals unique stem cell-like and invasive cell subpopulations within adenomyosis lesions identified, dysfunctional signaling, and EMJ abnormalities critical to developing precise diagnostic and therapeutic strategies.

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.

In Vitro Human Endometrial Cells and In Vivo Rat Model Studies Suggest That Ulipristal Acetate Impacts Endometrial Compatibility for Embryo Implantation

BACKGROUND

Ulipristal acetate (UPA) and levonorgestrel are used as emergency hormonal contraceptives. Although both are highly effective in preventing pregnancy, UPA shows efficacy even when taken up to 120 h after unprotected sexual intercourse.

AIMS

To investigate whether the mechanism of UPA's contraceptive action involves post-fertilization effects.

METHODS

In vitro and in vivo studies using cultured human endometrial cells and a pre-clinical rat model.

RESULTS

Endometrial cells treated with UPA showed changes in the expression of receptivity gene markers and a significant decrease in trophoblast spheroids attached to the cultured cells. In addition, administration of UPA to female unmated rats decreased the expression of implantation-related genes in the endometrium and inhibited the number of implantation sites in the mated group compared to the non-treated group.

CONCLUSIONS

These results support that UPA as an emergency contraceptive might have post-fertilization effects that may affect embryo implantation.

Rapid generation of functional nanovesicles from human trophectodermal cells for embryo attachment and outgrowth

Extracellular vesicles (EVs) are important mediators of embryo attachment and outgrowth critical for successful implantation. While EVs have garnered immense interest in their therapeutic potential in assisted reproductive technology by improving implantation success, their large-scale generation remains a major challenge. Here, we report a rapid and scalable production of nanovesicles (NVs) directly from human trophectoderm cells (hTSCs) via serial mechanical extrusion of cells; these NVs can be generated in approximately 6 h with a 20-fold higher yield than EVs isolated from culture medium of the same number of cells. NVs display similar biophysical traits (morphologically intact, spherical, 90-130 nm) to EVs, and are laden with hallmark players of implantation that include cell-matrix adhesion and extracellular matrix organisation proteins (ITGA2/V, ITGB1, MFGE8) and antioxidative regulators (PRDX1, SOD2). Functionally, NVs are readily taken up by low-receptive endometrial HEC1A cells and reprogram their proteome towards a receptive phenotype that support hTSC spheroid attachment. Moreover, a single dose treatment with NVs significantly enhanced adhesion and spreading of mouse embryo trophoblast on fibronectin matrix. Thus, we demonstrate the functional potential of NVs in enhancing embryo implantation and highlight their rapid and scalable generation, amenable to clinical utility.

Expression of miRNA from spent pre-implantation embryos culture media

This study examines the expression of three microRNAs (hsa-miR-661, hsa-miR-21-5p, hsa-miR-372-5p) in spent pre-implantation embryos culture media to identify possible new non-invasive biomarkers of embryo competence, predictive of development to the blastocyst stage. A preliminary analysis on 16 patients undergoing IVF cycles was performed by collecting and stored spent culture media on the fifth/sixth day of embryo culture. Expression of miRNAs was evaluated according to the embryos' fate: 1) NE/DG: non-evolved or degenerate embryos; 2) BLOK: embryos developed to the blastocyst stage. Preliminary results revealed a higher miRNAs expression in NE/DG spent media. To elucidate the roles of these miRNAs, we employed a robust bioinformatics pipeline involving: 1) in-silico miRNA Target Prediction using RNAHybrid, which identified the most-likely gene targets; 2) Construction of a Protein-Protein Interaction network via GeneMania, linking genes with significant biological correlations; 3) application of modularity-based clustering with the gLay app in Cytoscape, resulting in three size-adapted subnets for focused analysis; 4) Enrichment Analysis to discern the biological pathways influenced by the miRNAs. Our bioinformatics analysis revealed that hsa-miR-661 was closely associated with pathways regulating cell shape and morphogenesis of the epithelial sheet. These data suggest the potential use of certain miRNAs to identify embryos with a higher likelihood of developing to the blastocyst stage. Further analysis will be necessary to explore the reproducibility of these findings and to understand if miRNAs here investigated can be used as biomarkers for embryo selection before implantation into the uterus or if they may be reliable predictors of IVF outcome.

Uterine fluid microRNAs in repeated implantation failure

Recurrent implantation failure (RIF) is a significant obstacle in assisted reproductive procedures, primarily because of compromised receptivity. As such, there is a need for a dependable and accurate clinical test to evaluate endometrial receptiveness, particularly during embryo transfer. MicroRNAs (miRNAs) have diverse functions in the processes of implantation and pregnancy. Dysregulation of miRNAs results in reproductive diseases such as recurrent implantation failure (RIF). The endometrium secretes several microRNAs (miRNAs) during the implantation period, which could potentially indicate whether the endometrium is suitable for in vitro fertilization (IVF). The goal of this review is to examine endometrial miRNAs as noninvasive biomarkers that successfully predict endometrium receptivity in RIF.

Endometrial Proliferative Phase-Centered View of Transcriptome Dynamics across the Menstrual Cycle

The endometrium, the inner mucosal lining of the uterus, undergoes complex molecular and cellular changes across the menstrual cycle in preparation for embryo implantation. Transcriptome-wide analyses have mainly been utilized to study endometrial receptivity, the prerequisite for successful implantation, with most studies, so far, comparing the endometrial transcriptomes between (i) secretory and proliferative endometrium or (ii) mid-secretory and early secretory endometrium. In the current study, we provide a complete transcriptome description of the endometrium across the entire menstrual cycle and, for the first time, comprehensively characterize the proliferative phase of the endometrium. Our temporal transcriptome analysis includes five time points including the mid-proliferative, late proliferative (peri-ovulatory phase), early secretory, mid-secretory, and late secretory phases. Thus, we unveil exhaustively the transitions between the consecutive proliferative and secretory phases, highlighting their unique gene expression profiles and possible distinct biological functions. The transcriptome analysis reveals many differentially expressed genes (DEGs) across the menstrual cycle, most of which are phase-specific. As an example of coordinated gene activity, the expression profile of histone-encoding genes within the HIST cluster on chromosome 6 shows an increase in cluster activity during the late proliferative and a decline during the mid-secretory phase. Moreover, numerous DEGs are shared among all phases. In conclusion, in the current study, we delineate the endometrial proliferative phase-centered view of transcriptome dynamics across the menstrual cycle. Our data analysis highlights significant transcriptomic and functional changes occurring during the late proliferative phase-an essential transition point from the proliferative phase to the secretory phase. Future studies should explore how the biology of the late proliferative phase endometrium impacts the achievement of mid-secretory endometrial receptivity or contributes to molecular aberrations leading to embryo implantation failure.

Meta-analysis of endometrial transcriptome data reveals novel molecular targets for recurrent implantation failure

PURPOSE

Gene expression analysis of the endometrium has been shown to be a useful approach for identifying the molecular signatures and pathways involved in recurrent implantation failure (RIF). Nevertheless, individual studies have limitations in terms of study design, methodology and analysis to detect minor changes in expression levels or identify novel gene signatures associated with RIF.

METHOD

To overcome this, we conducted an in silico meta-analysis of nine studies, the systematic collection and integration of gene expression data, utilizing rigorous selection criteria and statistical techniques to ensure the robustness of our findings.

RESULTS

Our meta-analysis successfully unveiled a meta-signature of 49 genes closely associated with RIF. Of these genes, 38 were upregulated and 11 downregulated in RIF patients' endometrium and believed to participate in key processes like cell differentiation, communication, and adhesion. GADD45A, IGF2, and LIF, known for their roles in implantation, were identified, along with lesser-studied genes like OPRK1, PSIP1, SMCHD1, and SOD2 related to female infertility. Many of these genes are involved in MAPK and PI3K-Akt pathways, indicating their role in inflammation. We also investigated to look for key miRNAs regulating these 49 dysregulated mRNAs as potential diagnostic biomarkers. Along with this, we went to associate protein-protein interactions of 49 genes, and we could recognize one cluster consisting of 11 genes (consisted of 22 nodes and 11 edges) with the highest score (p = 0.001). Finally, we validated some of the genes by qRT-PCR in our samples.

CONCLUSION

In summary, the meta-signature genes hold promise for improving RIF patient identification and facilitating the development of personalized treatment strategies, illuminating the multifaceted nature of this complex condition.

Enhancing endometrial receptivity: the roles of human chorionic gonadotropin in autophagy and apoptosis regulation in endometrial stromal cells

Inadequate endometrial receptivity often results in embryo implantation failure and miscarriage. Human chorionic gonadotropin (hCG) is a key signaling molecule secreted during early embryonic development, which regulates embryonic maternal interface signaling and promotes embryo implantation. This study aimed to examine the impact of hCG on endometrial receptivity and its underlying mechanisms. An exploratory study was designed, and endometrial samples were obtained from women diagnosed with simple tubal infertility or male factor infertile (n = 12) and recurrent implantation failure (RIF, n = 10). Using reverse transcription-quantitative PCR and western blotting, luteinizing hormone (LH)/hCG receptor (LHCGR) levels and autophagy were detected in the endometrial tissues. Subsequently, primary endometrial stromal cells (ESCs) were isolated from these control groups and treated with hCG to examine the presence of LHCGR and markers of endometrial receptivity (HOXA10, ITGB3, FOXO1, LIF, and L-selectin ligand) and autophagy-related factors (Beclin1, LC3, and P62). The findings revealed that the expressions of receptivity factors, LHCGR, and LC3 were reduced in the endometrial tissues of women with RIF compared with the control group, whereas the expression of P62 was elevated. The administration of hCG to ESCs specifically activated LHCGR, stimulating an increase in the endometrial production of HOXA10, ITGB3, FOXO1, LIF and L-selectin ligands. Furthermore, when ESCs were exposed to 0.1 IU/mL hCG for 72 h, the autophagy factors Beclin1 and LC3 increased within the cells and P62 decreased. Moreover, the apoptotic factor Bax increased and Bcl-2 declined. However, when small interfering RNA was used to knock down LHCGR, hCG was less capable of controlling endometrial receptivity and autophagy molecules in ESCs. In addition, hCG stimulation enhanced the phosphorylation of ERK1/2 and mTOR proteins. These results suggest that women with RIF exhibit lower levels of LHCGR and compromised autophagy function in their endometrial tissues. Thus, hCG/LHCGR could potentially improve endometrial receptivity by modulating autophagy and apoptosis.

Effect of endometrial biopsy method on ribonucleic acid quality and gene expression analysis in patients with leiomyoma

Objective

To compare ribonucleic acid (RNA) quantity and purity in tissue collected with different endometrial sampling methods to establish the optimal tool for use in endometrial gene expression studies.

Design

Observational study.

Setting

University hospital.

Patients

Fourteen patients with submucosal leiomyomas.

Interventions

Unguided biopsies were obtained using a low-pressure suction device before hysteroscopy from 14 patients with submucosal leiomyomas followed by guided biopsy with a resectoscope loop. Fifty-seven samples were collected: 25 obtained using a suction device and 32 with a loop.

Main Outcome Measures

Total biopsy weight, RNA purity, and RNA yield for each collection method. After complementary deoxyribonucleic acid synthesis, HOXA10 expression was measured by quantitative polymerase chain reaction in the endometrium overlying and remote from the leiomyoma, as similar expression throughout the cavity was a prerequisite for the use of unguided biopsy method.

Results

The median weight of the samples was significantly larger when obtained with the low-pressure suction device than with the resectoscope loop (153 vs. 20 mg). The RNA yield was similar (suction curette, 1,625 ng/mg; resectoscope loop, 1,779 ng/mg). The A260-to-A280 ratio was satisfactory for 94.7 % of the samples, with no difference between the groups. The endometrial expression of HOXA10 was similar in areas overlying the leiomyoma compared with that in remote endometrial sites (2-ΔCt = 0.0224 vs. 0.0225).

Conclusions

Low-pressure endometrial suction devices provide tissue samples with acceptable RNA purity and quantity for gene expression studies. The expression of HOXA10 did not differ between endometrial sampling sites even in the presence of leiomyomas.

When the Embryo Meets the Endometrium: Identifying the Features Required for Successful Embryo Implantation

Evaluation of the optimal number of embryos, their quality, and the precise timing for transfer are critical determinants in reproductive success, although still remaining one of the main challenges in assisted reproduction technologies (ART). Indeed, the success of in vitro fertilization (IVF) treatments relies on a multitude of events and factors involving both the endometrium and the embryo. Despite concerted efforts on both fronts, the overall success rates of IVF techniques continue to range between 25% and 30%. The role of the endometrium in implantation has been recently recognized, leading to the hypothesis that both the "soil" and the "seed" play a central role in a successful pregnancy. In this respect, identification of the molecular signature of endometrial receptivity together with the selection of the best embryo for transfer become crucial in ART. Currently, efforts have been made to develop accurate, predictive, and personalized tests to identify the window of implantation and the best quality embryo. However, the value of these tests is still debated, as conflicting results are reported in the literature. The purpose of this review is to summarize and critically report the available criteria to optimize the success of embryo transfer and to better understand current limitations and potential areas for improvement.

An unbiased approach of molecular characterization of the endometrium: toward defining endometrial-based infertility

Infertility is a complex condition affecting millions of couples worldwide. The current definition of infertility, based on clinical criteria, fails to account for the molecular and cellular changes that may occur during the development of infertility. Recent advancements in sequencing technology and single-cell analysis offer new opportunities to gain a deeper understanding of these changes. The endometrium has a potential role in infertility and has been extensively studied to identify gene expression profiles associated with (impaired) endometrial receptivity. However, limited overlap among studies hampers the identification of relevant downstream pathways that could play a role in the development of endometrial-related infertility. To address these challenges, we propose sequencing the endometrial transcriptome of healthy and infertile women at the single-cell level to consistently identify molecular signatures. Establishing consensus on physiological patterns in endometrial samples can aid in identifying deviations in infertile patients. A similar strategy has been used with great success in cancer research. However, large collaborative initiatives, international uniform protocols of sample collection and processing are crucial to ensure reliability and reproducibility. Overall, the proposed approach holds promise for an objective and accurate classification of endometrial-based infertility and has the potential to improve diagnosis and treatment outcomes.

MiR-124-3p negatively impacts embryo implantation via suppressing uterine receptivity formation and embryo development

During embryo implantation, blastocyst interacts with the receptivity endometrium and the endometrial epithelium secretes nurturing fluid to support embryonic development. Interferon-λ (IFN-λ) is a novel, non-redundant regulator that participates in the fetal-maternal interaction; however, the precise molecular mechanism underlying its impact on uterine receptivity remains elusive. Here, microarray profiling revealed that 149 specific miRNAs were differentially expressed in the human endometrial cells following IFN-λ treatment. In particular, miR-124-3p expression was significantly reduced after IFN-λ treatment (p < 0.05). An in vivo mouse pregnancy model showed that miR-124-3p overexpression notably decreased embryo implantation rate and led to an aberrant epithelial phenotype. Furthermore, miR-124-3p negatively impacted the migration and proliferation of endometrial cells, and hindered embryonic developmental competence in terms of blastocyst formation and global DNA re-methylation. Downstream analysis showed that LIF, MUC1 and BCL2 are potential target genes for miR-124-3p, which was confirmed using western blotting and immunofluorescence assays. In conclusion, IFN-λ-driven downregulation of miR-124-3p during embryo implantation modulates uterine receptivity. The dual functional role of miR-124-3p suggests a cross-talk model wherein, maternal endometrial miRNA acts as a transcriptomic modifier of the peri-implantation endometrium and embryo development.

Endometrial transcriptome profiling of patients with recurrent implantation failure during hormone replacement therapy cycles

Background

The molecular mechanisms underlying window of implantation (WOI) displacement in patients with recurrent implantation failure (RIF) remain unclear. This study aims to explore the transcriptomic signatures of endometrium with normal and displaced WOIs and to identify the causes of endometrial receptivity (ER) abnormalities and WOI displacement in RIF patients.

Methods

In this study, 40 RIF patients were recruited and underwent personalized embryo transfer (pET) guided by the predicted results of endometrial receptivity diagnosis (ERD) model. Transcriptome analysis of endometrium from patients with clinical pregnancies after pET was performed to identify differentially expressed genes (DEGs) associated with WOI displacement. Gene expression data from HRT and natural cycle endometrium were compared to identify specific gene expression patterns of ER-related genes during WOI.

Results

The ERD results indicated that 67.5% of RIF patients (27/40) were non-receptive in the conventional WOI (P+5) of the HRT cycle. The clinical pregnancy rate in RIF patients improved to 65% (26/40) after ERD-guided pET, indicating the effectiveness of transcriptome-based WOI prediction. Among the 26 patients with clinical pregnancy, the gene expression profiles of P+5 endometrium from advanced (n=6), normal (n=10) and delayed (n=10) WOI groups were significantly different from each other. Furthermore, 10 DEGs identified among P+5 endometrium of 3 groups were involved in immunomodulation, transmembrane transport and tissue regeneration, which could accurately classify the endometrium with different WOIs. Additionally, a large number of ER-related genes showed significant correlation and similar gene expression patterns in P+3, P+5, and P+7 endometrium from HRT cycles and LH+5, LH+7, and LH+9 endometrium from natural cycles.

Conclusion

Our study shows that ER-related genes share similar gene expression patterns during WOI in both natural and HRT cycles, and their aberrant expression is associated with WOI displacements. The improvement of pregnancy outcomes in RIF patients by adjusting ET timing according to ERD results demonstrates the importance of transcriptome-based endometrial receptivity assessment and the clinical efficiency of ERD model.

Single-Cell RNA Transcriptome of the Human Endometrium Reveals Epithelial Characterizations Associated with Recurrent Implantation Failure

Recurrent implantation failure (RIF) remains a complex and poorly characterized disorder despite significant advancements in assisted reproductive technology. This study utilizes single-cell transcriptome sequencing (scRNA-seq) to characterize the mid-secretory endometrium of RIF patients. Stromal fibroblast-enriched and epithelium-enriched populations are collected using a two-step dissociation process. After quality control, 25,315 individual cells from 3 RIF patients are analyzed. The analysis identifies 12 distinct cell types, including 6 subtypes of epithelial cells. Significantly, the study reveals the replacement of glandular epithelia with MAP2K6+ EPCAMDIM epithelia in the endometrial glands of RIF patients. Furthermore, the study demonstrates that endometrial gland organoids derived from RIF patients exhibit diminished responses to sex steroids compared to the controls. Single-cell regulatory network inference and clustering (SCENIC) analysis identifies cell-specific cis-regulatory elements and constructed regulatory networks in both groups, showing alterations gene-regulatory networks in RIF patients. Cell-cell communication analysis distinguishes intercellular communication between the two groups, shedding light on disrupted cellular interactions associated with RIF. In summary, these findings provide valuable insights into the cellular and molecular mechanisms underlying RIF, highlighting the roles of epithelial cells in the implantation process.

Assessing the endometrium: An update on current and potential novel biomarkers of receptivity

A cyclical evolvement of the endometrium into a transient state of receptivity is crucial for acceptance of the semi-allogeneic foetus, conducive to pregnancy. Despite documentation of aberrances in this process within patients experiencing repeated embryo implantation failures and miscarriages, the endometrium is often overlooked in IVF clinics as the cause for failure. Focus instead is usually given to embryo-derived factors, such as aneuploidy. Nevertheless, failure of approximately 30 % of euploid embryos to implant demonstrates that other factors such as the endometrium require clinical exploration. Here, we review both traditional and novel methods used to assess endometrial receptivity such as identifying the WOI, endometrial immune profiling and transcriptomics panel testing. Where reported, we will also discuss their clinical application, as well as novel potential biomarkers within the pre-clinical research stages which show promise in their ability to assess endometrial receptivity.

Endometrial receptivity in women of advanced age: an underrated factor in infertility

BACKGROUND

Modern lifestyle has led to an increase in the age at conception. Advanced age is one of the critical risk factors for female-related infertility. It is well known that maternal age positively correlates with the deterioration of oocyte quality and chromosomal abnormalities in oocytes and embryos. The effect of age on endometrial function may be an equally important factor influencing implantation rate, pregnancy rate, and overall female fertility. However, there are only a few published studies on this topic, suggesting that this area has been under-explored. Improving our knowledge of endometrial aging from the biological (cellular, molecular, histological) and clinical perspectives would broaden our understanding of the risks of age-related female infertility.

OBJECTIVE AND RATIONALE

The objective of this narrative review is to critically evaluate the existing literature on endometrial aging with a focus on synthesizing the evidence for the impact of endometrial aging on conception and pregnancy success. This would provide insights into existing gaps in the clinical application of research findings and promote the development of treatment options in this field.

SEARCH METHODS

The review was prepared using PubMed (Medline) until February 2023 with the keywords such as 'endometrial aging', 'receptivity', 'decidualization', 'hormone', 'senescence', 'cellular', 'molecular', 'methylation', 'biological age', 'epigenetic', 'oocyte recipient', 'oocyte donation', 'embryo transfer', and 'pregnancy rate'. Articles in a language other than English were excluded.

OUTCOMES

In the aging endometrium, alterations occur at the molecular, cellular, and histological levels suggesting that aging has a negative effect on endometrial biology and may impair endometrial receptivity. Additionally, advanced age influences cellular senescence, which plays an important role during the initial phase of implantation and is a major obstacle in the development of suitable senolytic agents for endometrial aging. Aging is also accountable for chronic conditions associated with inflammaging, which eventually can lead to increased pro-inflammation and tissue fibrosis. Furthermore, advanced age influences epigenetic regulation in the endometrium, thus altering the relation between its epigenetic and chronological age. The studies in oocyte donation cycles to determine the effect of age on endometrial receptivity with respect to the rates of implantation, clinical pregnancy, miscarriage, and live birth have revealed contradictory inferences indicating the need for future research on the mechanisms and corresponding causal effects of women's age on endometrial receptivity.

WIDER IMPLICATIONS

Increasing age can be accountable for female infertility and IVF failures. Based on the complied observations and synthesized conclusions in this review, advanced age has been shown to have a negative impact on endometrial functioning. This information can provide recommendations for future research focusing on molecular mechanisms of age-related cellular senescence, cellular composition, and transcriptomic changes in relation to endometrial aging. Additionally, further prospective research is needed to explore newly emerging therapeutic options, such as the senolytic agents that can target endometrial aging without affecting decidualization. Moreover, clinical trial protocols, focusing on oocyte donation cycles, would be beneficial in understanding the direct clinical implications of endometrial aging on pregnancy outcomes.

Changes in the immunophenotype of endometrium during implantation window receptivity formation in healthy fertile women

INTRODUCTION

Endometrial receptivity is largely determined by the immunophenotype of endometrium, especially uterine NK-cells (uNK). Immune component is directly involved in the formation of favourable microenvironment for the blastocyst implantation and placenta formation, but the way it changes during the maturation of endometrial tissue in healthy fertile women is still underexplored.

METHODS

The endometrium was collected from 47 healthy oocyte donors after controlled ovarian stimulation: 23 women on the day of oocytes retrieval (OR) and 24 women on the term of implantation window (IW). The OR group was analysed, published previously and used as a comparison group to show the dynamic of changes. Isolated endometrial lymphocytes and peripheral blood samples were stained with monoclonal antibodies and analysed according to the three-color flow cytometry protocol.

RESULTS

The proportion of NK-cells (CD3-CD56+) in endometrium grew significantly in the implantation window compared to the oocytes retrieval day. NK-cells acquired a more differentiated phenotype from the day of OR until IW: the expression of CD8 and CD158a significantly increased, while the expression of HLA-DR significantly decreased. Significant correlations between peripheral blood and endometrial NK-cells were found in CD8 expression during OR and IW, CD335(p46)neg and CD335(p46)++ subsets during IW term.

DISCUSSION

Immunophenotype of receptive endometrium forms due to the accumulation of uNK-cells, which actively proliferate, become mature, differentiative, and ready to meet the embryo. Endometrial immunophenotype is peculiar and specific but not autonomic and isolated. Differentiation (CD8 on NK-cells), and activity (p46 on NK-cells) of peripheral blood lymphocytes is reflected in endometrial lymphocytes profile, and therefore the research of peripheral blood immunophenotype is relevant.

Current knowledge on the role of extracellular vesicles in endometrial receptivity

Endometrial receptivity has been widely understood as the capacity of the endometrium to receive implantable embryos. The establishment of endometrial receptivity involves multiple biological processes including decidualization, tissue remodeling, angiogenesis, immune regulation, and oxidative metabolism. Extracellular vesicles (EVs) are lipid-bilayer-membrane nanosized vesicles mediating cell-to-cell communication. Recently, EVs and their cargo have been proven as functional factors in the establishment of endometrial receptivity. In this review, we comprehensively summarized the alteration of endometrium/embryo-derived EVs during the receptive phase and retrospected the current findings which revealed the pivotal role and potential mechanism of EVs to promote successful implantation. Furthermore, we highlight the potentiality and limitations of EVs being translated into clinical applications such as biomarkers of endometrial receptivity or reproductive therapeutic mediators, and point out the direction for further research.

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.

Dynamic peripheral blood microRNA expression landscape during the peri-implantation stage in women with successful pregnancy achieved by single frozen-thawed blastocyst transfer

STUDY QUESTION

What are the dynamic expression features of plasma microRNAs (miRNAs) during the peri-implantation period in women with successful pregnancy via single frozen-thawed blastocyst transfer?

SUMMARY ANSWER

There is a significant change in the plasma miRNA expression profile before and after blastocyst transfer, during the window of implantation.

WHAT IS KNOWN ALREADY

The expression of miRNAs in peripheral blood has indicative functions during the peri-implantation period. Nevertheless, the dynamic expression profile of circulating miRNAs during the peri-implantation stage in women with a successful pregnancy has not been studied.

STUDY DESIGN SIZE DURATION

Seventy-six women treated for infertility with a single frozen-thawed blastocyst transfer in a natural cycle were included in this study. Among them, 57 women had implantation success and a live birth, while 19 patients experienced implantation failure. Peripheral blood samples were collected at five different time points throughout the peri-implantation period, including D0 (ovulation day), D3, D5, D7, and D9 in this cycle of embryo transfer. The plasma miRNAs in women with blastocyst transfer were isolated, sequenced, and analyzed.

PARTICIPANTS/MATERIALS SETTING METHODS

Peripheral blood samples were collected in EDTA tubes and stored at -80°C until further use. miRNAs were isolated from blood, cDNA libraries were constructed, and the resulting sequences were mapped to the human genome. The plasma miRNAs were initially analyzed in a screening cohort (n = 34) with successful pregnancy. Trajectory analysis, including a global test and pairwise comparisons, was performed to detect dynamic differentially expressed (DE) miRNAs. Fuzzy c-means clustering was conducted for all dynamic DE miRNAs. The correlation between DE miRNAs and clinical characteristics of patients was investigated using a linear mixed model. Target genes of the miRNAs were predicted, and functional annotation analysis was performed. The expression of DE miRNAs was also identified in a validation set consisting of women with successful (n = 23) and unsuccessful (n = 19) pregnancies.

MAIN RESULTS AND THE ROLE OF CHANCE

Following small RNA sequencing, a total of 2656 miRNAs were determined as valid read values. After trajectory analysis, 26 DE miRNAs (false discovery rate < 0.05) were identified by the global test, while pairwise comparisons in addition identified 20 DE miRNAs. A total of seven distinct clusters representing different temporal patterns of miRNA expression were discovered. Nineteen DE miRNAs were further identified to be associated with at least one clinical trait. Endometrium thickness and progesterone level showed a correlation with multiple DE miRNAs (including two of the same miRNAs, hsa-miR-1-3p and hsa-miR-6741-3p). Moreover, the 19 DE miRNAs were predicted to have 403 gene targets, and there were 51 (12.7%) predicted genes likely involved in both decidualization and embryo implantation. Functional annotation for predicted targets of those clinically related DE miRNAs suggested the involvement of vascular endothelial growth factor and Wnt signaling pathways, as well as responses to hormones, immune responses, and cell adhesion-related signaling pathways during the peri-implantation stage.

LARGE SCALE DATA

The raw miRNA sequence data reported in this article have been deposited in the Genome Sequence Archive (GSA-Human: HRA005227) and are publicly accessible at https://ngdc.cncb.ac.cn/gsa-human/browse/HRA005227.

LIMITATIONS REASONS FOR CAUTION

Although the RNA sequencing results revealed the global dynamic changes of miRNA expression, further experiments examining the clinical significance of the identified DE miRNAs in embryo implantation outcome and the relevant regulatory mechanisms involved are warranted.

WIDER IMPLICATIONS OF THE FINDINGS

Understanding the dynamic landscape of the miRNA transcriptome could shed light on the physiological mechanisms involved from ovulation to the post-implantation stage, as well as identifying biomarkers that characterize stage-related biological process.

STUDY FUNDING/COMPETING INTERESTS

The study was funded by the Major clinical research project of Tangdu Hospital (2021LCYJ004) and the Discipline Platform Improvement Plan of Tangdu Hospital (2020XKPT003). The funders had no influence on the study design, data collection, and analysis, decision to publish, or preparation of the article. There are no conflicts of interest to declare.

Targeted gene expression profiling for accurate endometrial receptivity testing

Expressional profiling of the endometrium enables the personalised timing of the window of implantation (WOI). This study presents and evaluates a novel analytical pipeline based on a TAC-seq (Targeted Allele Counting by sequencing) method for endometrial dating. The expressional profiles were clustered, and differential expression analysis was performed on the model development group, using 63 endometrial biopsies spanning over proliferative (PE, n = 18), early-secretory (ESE, n = 18), mid-secretory (MSE, n = 17) and late-secretory (LSE, n = 10) endometrial phases of the natural cycle. A quantitative predictor model was trained on the development group and validated on sequenced samples from healthy women, consisting of 52 paired samples taken from ESE and MSE phases and five LSE phase samples from 31 individuals. Finally, the developed test was applied to 44 MSE phase samples from a study group of patients diagnosed with recurrent implantation failure (RIF). In validation samples (n = 57), we detected displaced WOI in 1.8% of the samples from fertile women. In the RIF study group, we detected a significantly higher proportion of the samples with shifted WOI than in the validation set of samples from fertile women, 15.9% and 1.8% (p = 0.012), respectively. The developed model was evaluated with an average cross-validation accuracy of 98.8% and an accuracy of 98.2% in the validation group. The developed beREADY screening model enables sensitive and dynamic detection of selected transcriptome biomarkers, providing a quantitative and accurate prediction of endometrial receptivity status.

Circulating miRNAs as a Tool for Early Diagnosis of Endometrial Cancer-Implications for the Fertility-Sparing Process: Clinical, Biological, and Legal Aspects

This review article explores the possibility of developing an integrated approach to the management of the different needs of endometrial cancer (EC) patients seeking to become pregnant. Life preservation of the woman, health preservation of the baby, a precocious and-as much as possible-minimally invasive characterization of the health and fertility parameters of the patient, together with the concerns regarding the obstetric, neonatal, and adult health risks of the children conceived via assisted reproductive techniques (ART) are all essential aspects of the problem to be taken into consideration, yet the possibility to harmonize such needs through a concerted and integrated approach is still very challenging. This review aims to illustrate the main features of EC and how it affects the normal physiology of pre-menopausal women. We also focus on the prospect of a miR-based, molecular evaluation of patient health status, including both EC early diagnosis and staging and, similarly, the receptivity of the woman, discussing the possible evaluation of both aspects using a single specific panel of circulating miRs in the patient, thus allowing a relatively fast, non-invasive testing with a significantly reduced margin of error. Finally, the ethical and legal/regulatory aspects of such innovative techniques require not only a risk-benefit analysis; respect for patient autonomy and equitable health care access allocation are fundamental issues as well.

Impact of Endometrial Receptivity Analysis on Pregnancy Outcomes In Patients Undergoing Embryo Transfer: A Systematic Review and Meta-Analysis

To analyze the influence of endometrial receptivity analysis (ERA) on embryo transfer (ET) results in patients undergoing in vitro fertilization (IVF) treatment. PubMed, Embase, Cochrane Central Register of Controlled Trials, and BioMed Central databases were searched from inception up to December 2022 for studies comparing pregnancy outcomes in patients undergoing personalized embryo transfer (pET) by ERA versus standard ET. Data were pooled by meta-analysis using a random effects model. We identified twelve studies, including 14,224 patients. No differences were observed between patients undergoing ERA test and those not undergoing ERA test prior to ET in terms of live birth (OR 1.00, 95% CI 0.63-1.58, I2 = 92.7%), clinical pregnancy (OR 1.20, 95% CI 0.90-1.61, I2 = 86.5%), biochemical pregnancy (OR 0.83, 95% CI 0.46-1.49, I2 = 87%), positive pregnancy test (OR 0.99, 95% CI 0.80-1.22, I2 = 0%), miscarriage (OR 0.91, 95% CI 0.62-1.34, I2 = 67.1%), and implantation rate (OR 1.18, 95% CI 0.44-3.14, I2 = 93.2%). pET with ERA is not associated with any significant differences in pregnancy outcomes as compared to standard ET protocols. Therefore, the utility of ERA in patients undergoing IVF should be revisited.

Cyclic processes in the uterine tubes, endometrium, myometrium, and cervix: pathways and perturbations

This review leads the 2023 Call for Papers in MHR: 'Cyclical function of the female reproductive tract' and will outline the complex and fascinating changes that take place in the reproductive tract during the menstrual cycle. We will also explore associated reproductive tract abnormalities that impact or are impacted by the menstrual cycle. Between menarche and menopause, women and people who menstruate living in high-income countries can expect to experience ∼450 menstrual cycles. The primary function of the menstrual cycle is to prepare the reproductive system for pregnancy in the event of fertilization. In the absence of pregnancy, ovarian hormone levels fall, triggering the end of the menstrual cycle and onset of menstruation. We have chosen to exclude the ovaries and focus on the other structures that make up the reproductive tract: uterine tubes, endometrium, myometrium, and cervix, which also functionally change in response to fluctuations in ovarian hormone production across the menstrual cycle. This inaugural paper for the 2023 MHR special collection will discuss our current understanding of the normal physiological processes involved in uterine cyclicity (limited specifically to the uterine tubes, endometrium, myometrium, and cervix) in humans, and other mammals where relevant. We will emphasize where knowledge gaps exist and highlight the impact that reproductive tract and uterine cycle perturbations have on health and fertility.

Obesity and female infertility

Infertility is a significant global health issue, with a negative impact on people's wellbeing and human rights. Despite the longstanding association between obesity and infertility, there remains uncertainty, about the precise mechanisms underpinning this association and best management strategies. In this article, we aimed to address these uncertainties by reviewing the recent literature, and focusing on studies which evaluated live birth rates. We found that just over half of the studies, investigating the relationship between preconception maternal weight and live birth rates found an inverse correlation. There was, however, insufficient evidence, that preconception maternal lifestyle or pharmacological interventions in obese women with infertility, resulted in improved live birth rates. The implications for clinical practice and future research are highlighted. For example, the need to consider some flexibility in applying strict preconception body mass index targets, limiting access to fertility treatment, and a need for large clinical trials of new pharmacological options and bariatric surgery.

MicroRNAs, small regulatory elements with significant effects on human implantation: a review

Embryo implantation is a critical process for achieving a successful pregnancy and live birth. The proper implantation must have a synchronized interaction between blastocyst and a receptive endometrium. Many genes are involved in the modulation of precise molecular events during implantation. MicroRNAs (miRNAs) have been extensively reported as gene regulatory molecules on post-transcriptional levels involved in various biological processes such as gametogenesis, embryogenesis, and the quality of sperm, oocyte, and embryos. A plethora of evidence has demonstrated critical roles for miRNAs in regulating genes involved in the implantation process; hence, dysregulation of miRNAs could be associated with significant impairments in implantation, such as recurrent implantation failure. In addition to the indispensable role of miRNAs in the intracellular control of gene expression, they can also be secreted into extracellular fluid and circulation. Therefore, miRNAs in body fluids and blood may be exploited as non-invasive diagnostic biomarkers for different pathological and physiological conditions. Recently, several studies have focused on the discovery of miRNAs function in the implantation process by appraising miRNAs and their target genes in human embryos, endometrial tissue, and cell culture models. Moreover, it was revealed that there could be a significant association between endometrial receptivity or implantation status and the expression of miRNAs in human body fluids, reinforcing their role as non-invasive biomarkers. In the current work, we reviewed the studies concerning the role of intracellular and extracellular miRNAs in human implantation and the influence of their dysregulation on implantation disorders.

Exosomes: The role in mammalian reproductive regulation and pregnancy-related diseases

Exosomes are a kind of extracellular vesicles that are produced and secreted by different mammalian cells. They serve as cargo proteins and can transfer different kinds of biomolecules, including proteins, lipids, and nucleic acids, which consequently act on target cells to exert different biological effects. Recent years have witnessed a significant increase in the number of studies on exosomes due to the potential effects of exosomes in the diagnosis and treatment of cancers, neurodegenerative diseases, and immune disorders. Previous studies have demonstrated that exosomal contents, especially miRNAs, are implicated in numerous physiological processes such as reproduction, and are crucial regulators of mammalian reproduction and pregnancy-related diseases. Here, we describe the origin, composition, and intercellular communication of exosomes, and discuss their functions in follicular development, early embryonic development, embryonic implantation, male reproduction and development of pregnancy-related diseases in humans and animals. We believe this study will provide a foundation for revealing the mechanism of exosomes in regulating mammalian reproduction, and providing new approaches and ideas for the diagnosis and treatment of pregnancy-related diseases.

Can biomarkers identified from the uterine fluid transcriptome be used to establish a noninvasive endometrial receptivity prediction tool? A proof-of-concept study

BACKGROUND

Embryo implantation in a receptive endometrium is crucial for successful pregnancy. Endometrial receptivity (ER) prediction tools based on endometrial transcriptome biomarkers by endometrial biopsy have been used to guide successful embryo implantation in in vitro fertilization (IVF) patients. However, no reliable noninvasive ER prediction method has been established, and one is greatly needed. We aimed to identify biomarkers from uterine fluid transcriptomic sequencing data for establishing noninvasive ER prediction tool and to evaluate its clinical application potential in patients undergoing IVF.

METHODS

The non-invasive RNA-seq based endometrial receptivity test (nirsERT) was established by analyzing transcriptomic profile of 144 uterine fluid specimens (LH + 5, LH + 7, and LH + 9) at three different receptive status from 48 IVF patients with normal ER in combination with random forest algorithm. Subsequently, 22 IVF patients who underwent frozen-thaw blastocyst transfer were recruited and analyzed the correlation between the predicted results of nirsERT and pregnancy outcomes.

RESULTS

A total of 864 ER-associated differentially expressed genes (DEGs) involved in biological processes associated with endometrium-embryo crosstalk, including protein binding, signal reception and transduction, biomacromolecule transport and cell-cell adherens junctions, were selected. Subsequently, a nirsERT model consisting of 87 markers and 3 hub genes was established using a random forest algorithm. 10-fold cross-validation resulted in a mean accuracy of 93.0%. A small cohort (n = 22) retrospective observation shows that 77.8% (14/18) of IVF patients predicted with a normal WOI had successful intrauterine pregnancies, while none of the 3 patients with a displaced WOI had successful pregnancies. One patient failed due to poor sequencing data quality.

CONCLUSIONS

NirsERT based on uterine fluid transcriptome biomarkers can predict the WOI period relatively accurately and may serve as a noninvasive, reliable and same cycle test for ER in reproductive clinics.

TRIAL REGISTRATION

Chinese Clinical Trial Registry: ChiCTR-DDD-17013375. Registered 14 November 2017, http://www.chictr.org.cn/index.aspx .

Trophectoderm non-coding RNAs reflect the higher metabolic and more invasive properties of young maternal age blastocysts

Increasing female age is accompanied by a corresponding fall in her fertility. This decline is influenced by a variety of factors over an individual's life course including background genetics, local environment and diet. Studying both coding and non-coding RNAs of the embryo could aid our understanding of the causes and/or effects of the physiological processes accompanying the decline including the differential expression of sub-cellular biomarkers indicative of various diseases. The current study is a post-hoc analysis of the expression of trophectoderm RNA data derived from a previous high throughput study. Its main aim is to determine the characteristics and potential functionalities that characterize long non-coding RNAs. As reported previously, a maternal age-related component is potentially implicated in implantation success. Trophectoderm samples representing the full range of maternal reproductive ages were considered in relation to embryonic implantation potential, trophectoderm transcriptome dynamics and reproductive maternal age. The long non-coding RNA (lncRNA) biomarkers identified here are consistent with the activities of embryo-endometrial crosstalk, developmental competency and implantation and share common characteristics with markers of neoplasia/cancer invasion. Corresponding genes for expressed lncRNAs were more active in the blastocysts of younger women are associated with metabolic pathways including cholesterol biosynthesis and steroidogenesis.

Prolactin Relationship with Fertility and In Vitro Fertilization Outcomes-A Review of the Literature

Hyperprolactinemia is a known cause of amenorrhea and infertility. However, there is an increasing body of evidence suggesting that prolactin is involved in multiple physiological aspects of normal reproduction. Thus, the present paper aims to review the current literature regarding the relationship between serum prolactin level and in vitro fertilization (IVF)/intracytoplasmic sperm injection outcome and the role of dopamine agonists treatment in IVF success. Moreover, the mechanisms by which prolactin may exert its role in fertility and infertility were summarized. Although not all studies agree, the available evidence suggests that higher prolactin levels in follicular fluid are associated with increased oocytes competence, but also with positive effects on corpus luteum formation and survival, endometrial receptivity, blastocyst implantation potential and survival of low-motile sperm. Transient hyperprolactinemia found in IVF cycles was reported in most of the studies not to be related to IVF outcome, although a few reports suggested that it may be associated with higher implantation and pregnancy rates, and better-cumulated pregnancy outcomes. Administration of dopamine agonists for hyperprolactinemia preceding IVF treatment does not seem to negatively impact the IVF results, while treatment of transient hyperprolactinemia during IVF might be beneficial in terms of fertilization rates and conception rates. Due to limited available evidence, future studies are necessary to clarify the optimal level of circulating prolactin in patients performing IVF and the role of dopamine agonist treatment.

Integrating Analysis to Identify Differential circRNAs Involved in Goat Endometrial Receptivity

Endometrial receptivity is one of the main factors underlying a successful pregnancy, with reports substantiating the fact that suboptimal endometrial receptivity accounts for two-thirds of early implantation event failures. The association between circRNAs and endometrial receptivity in the goat remains unclear. This study aims to identify potential circRNAs and regulatory mechanisms related to goat endometrial receptivity. Therefore, the endometrial samples on day 16 of pregnancy and day 16 of the estrous cycle were analyzed using high-throughput RNA-seq and bioinformatics. The results show that 4666 circRNAs were identified, including 7 downregulated and 11 upregulated differentially expressed circRNAs (DE-circRNAs). Back-splicing and RNase R resistance verified the identified circRNAs. We predicted the competing endogenous RNA (ceRNA) regulatory mechanism and potential target genes of DE-circRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of these predicted target genes suggest that DE-circRNAs were significantly involved in establishing endometrial receptivity. Furthermore, Sanger sequencing, qPCR, correlation analysis and Fluorescence in Situ Hybridization (FISH) show that circ_MYRF derived from the host gene myelin regulatory factor (MYRF) might regulate the expression of interferon stimulating gene 15 (ISG15), thereby promoting the formation of endometrial receptivity. These novel findings may contribute to a better understanding of the molecular mechanisms regulating endometrial receptivity and promoting the maternal recognition of pregnancy (MRP).

Endometrial whole metabolome profile at the receptive phase: influence of Mediterranean Diet and infertility

Introduction

Several metabolite classes have been identified in human endometrium, including lipids, nucleotides, amino acids, organic acids, and sugars. The first studies suggest the importance of metabolites in endometrial functions, as imbalance in uterine metabolites has been associated with low implantation rate and endometriosis. Nevertheless, most of studies have put emphasis on specific metabolite classes, and we lack the knowledge of the whole metabolome composition in human uterus. Further, a healthy dietary pattern has been shown to potentially protect against different endometrial dysfunctions and is a potential modulator of metabolomic composition and, consequently, the intrauterine microenvironment. The Mediterranean Diet (MD), characterized by a high intake of fruits, vegetables, cereals, nuts, legumes, fish, and olive oil, and a low consumption of meat, dairy products, and processed foods, has been associated with a wide range of benefits for health. Indeed, the MD pattern has displayed a beneficial role in endometriosis management and fertility; however, the relationship between the MD and the endometrial metabolome is still unknown. In our study, we set out to analyze receptive-phase endometrial metabolome profiles among women with infertility and their associations with MD.

Methods

The study included women with male factor infertility (n=8), unexplained infertility (n=10), recurrent implantation failure (n=14), and endometriosis (n=13). The endometrial metabolome was analyzed with ultrahigh-performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS). The MD adherence of the participants was assessed using the 14-point MEDAS questionnaire of adherence to the MD.

Results

We provide the whole metabolome profile of the endometrium, where 925 different metabolites were identified. Among these metabolites, lipids comprised the largest part, where polyunsaturated fatty acids (PUFAs) prevailed. Women with endometriosis and recurrent implantation failure were found to have lower levels of PUFAs compared to women with male factor and unexplained infertility (i.e., no clear endometrial alterations), identifying a metabolome profile associated with infertility diagnoses where altered endometrial functions are suspected. Moreover, MD adherence seemed to be associated with the endometrial metabolomic profile in a manner dependent on the health status of the uterus.

Conclusion

The study findings provide insight into the molecular background of female infertility and lead to identification of potential molecular biomarkers and possibilities for modulating the endometrial microenvironment and, thereby, endometrial functions involved in embryo implantation and infertility.

Expression of Markers of Endometrial Receptivity in Obese Infertile PCOS Women before and after the Weight Loss Program-A Preliminary Study

Obesity is an increasing worldwide problem, and it is common in women with polycystic ovaries syndrome (PCOS). It is well known that women with PCOS have lower chances of spontaneous conception as well as lower success with IVF procedures. The mechanisms by which obesity causes lower fertility are not yet fully understood. The aim of the present study was to determine the effect of a lifestyle intervention weight loss program on the expression of the endometrial genes during the window of implantation (WOI). For this purpose, 15 infertile women with obesity and PCOS were included in the study. Endometrial samples were taken during the WOI before and at the end of the program, and RNASeq analysis was performed. There were no significantly differentially expressed genes before and after the weight loss program. We then compared the results of our study with previously published studies on markers of endometrial receptivity. The biomarker genes that were found to be down-regulated during the WOI in previous studies were more down-regulated after the weight loss program in the present study. Furthermore, 25% of the women who achieved the desired 5% or more weight reduction conceived spontaneously. Our study shows that weight loss might positively impact endometrial receptivity. which may lead towards the improved fertility of obese women with PCOS.