Localization of Mucin 1 in endometrial luminal epithelium and its expression in women with reproductive failure during implantation window

Motile Cilia in Female and Male Reproductive Tracts and Fertility

Motile cilia are evolutionarily conserved organelles. In humans, multiciliated cells (MCCs), assembling several hundred motile cilia on their apical surface, are components of the monolayer epithelia lining lower and upper airways, brain ventricles, and parts of the reproductive tracts, the fallopian tube and uterus in females, and efferent ductules in males. The coordinated beating of cilia generates a force that enables a shift of the tubular fluid, particles, or cells along the surface of the ciliated epithelia. Uncoordinated or altered cilia motion or cilia immotility may result in subfertility or even infertility. Here, we summarize the current knowledge regarding the localization and function of MCCs in the human reproductive tracts, discuss how cilia and cilia beating-generated fluid flow directly and indirectly contribute to the processes in these organs, and how lack or improper functioning of cilia influence human fertility.

FANCD2 as a ferroptosis-related target for recurrent implantation failure by integrated bioinformatics and Mendelian randomization analysis

Despite advancements in assisted reproductive technology, recurrent implantation failure (RIF) remains a challenge. Endometrial factors, including ferroptosis and immunity, may contribute to this issue. This study integrated bioinformatics analysis and Mendelian randomization (MR) to investigate the expression and significance of DEFRGs in RIF. We intersected 484 ferroptosis-associated genes with 515 differentially expressed genes (DEGs) to identify key DEFRGs. Subsequent analyses included enrichment analysis, molecular subtype identification, machine learning model development for biomarker discovery, immune cell infiltration assessment, single-cell RNA sequencing, and MR to explore the causal relationships of selected genes with RIF. In this study, we identified 11 differentially expressed ferroptosis-related genes (DEFRGs) between RIF and healthy individuals. Cluster analysis revealed two distinct molecular subtypes with different immune profiles and DEFRG expressions. Machine learning models highlighted MUC1, GJA1 and FANCD2 as potential diagnostic biomarkers, with high accuracy in RIF prediction. Single-cell analysis further revealed the cellular localization and interactions of DEFRGs. MR suggested a protective effect of FANCD2 against RIF. Validation in RIF patients confirmed the differential expression of key DEFRGs, consistent with bioinformatics findings. This comprehensive study emphasize the significant role of DEFRGs in the pathogenesis of RIF, suggesting that modulating these genes could offer new avenues for treatment. The FANCD2 is a potential gene contributing to RIF pathogenesis through a non-classical ferroptosis-dependent pathway, providing a foundation for personalized therapeutic strategies in RIF management.

Smoothelin-like protein 1 promotes insulin sensitivity and modulates the contractile properties of endometrial epithelial cells with insulin resistance

Introduction

The incidence of infertility is significantly higher in women with diseases linked to impaired glucose homeostasis, such as insulin resistance. Defective glucose metabolism interferes with fertilization; however, the molecular mechanism underlying this interference is unclear. Smoothelin-like protein 1 (SMTNL1) was isolated from muscle and steroid hormone-responsive tissues and regulates the contractile functions of various cell types through the inhibition of myosin phosphatase (MP) holoenzyme. In addition, SMTNL-1 after phosphorylation at Ser301 by protein kinase A translocates to the nucleus and functions as a transcriptional co-activator of the progesterone receptor-B. SMTNL1 null mice exhibit reduced reproductive fitness and are more prone to type 2 diabetes mellitus. However, the role of SMTNL1 in endometrial epithelial cells is not known.

Methods

The effect of SMTNL1 overexpression was investigated in pregnancy and in gestational diabetic endometrial epithelial cell models by immunofluorescent staining, cell migration, and semi quantitative Western blot analysis and glucose uptake assay.

Results

We show that SMTNL1 promotes the differentiation of endometrial epithelial cells in a progesterone-dependent manner to attenuate insulin resistance. Furthermore, SMTNL1 hampers the migration capacity of epithelial cells in a gestational diabetes model by inhibiting the expression of MYPT1, the regulatory subunit of MP, and the activity of the holoenzyme, resulting in increased phosphorylation of the 20 kDa regulatory myosin light chain. SMTNL1 also acts as an insulin-sensitizing agent by increasing the gene expression of PP2A and DUPS9 protein phosphatases, resulting in decreased ERK1/2 activity and, hence, decreasing the phosphorylation of IRS-1 at Ser612 under gestational diabetes conditions.

Conclusion

SMTNL1 may have therapeutic relevance to the progesterone-dependent inhibition of endometrial epithelial cell migration under hyperglycemic conditions and insulin sensitivity in the endometrium in gestational diabetes or other metabolic disorders.

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.

Ovarian sex steroid and epithelial control of immune responses in the uterus and oviduct: human and animal models†

The female reproductive tract (FRT), including the uterus and oviduct (Fallopian tube), is responsible for maintaining an optimal microenvironment for reproductive processes, such as gamete activation and transportation, sperm capacitation, fertilization, and early embryonic and fetal development. The mucosal surface of the FRT may be exposed to pathogens and sexually transmitted microorganisms due to the opening of the cervix during mating. Pathogens and endotoxins may also reach the oviduct through the peritoneal fluid. To maintain an optimum reproductive environment while recognizing and killing pathogenic bacterial and viral agents, the oviduct and uterus should be equipped with an efficient and rigorously controlled immune system. Ovarian sex steroids can affect epithelial cells and underlying stromal cells, which have been shown to mediate innate and adaptive immune responses. This, in turn, protects against potential infections while maintaining an optimal milieu for reproductive events, highlighting the homeostatic involvement of ovarian sex steroids and reproductive epithelial cells. This article will discuss how ovarian sex steroids affect the immune reactions elicited by the epithelial cells of the non-pregnant uterus and oviduct in the bovine, murine, and human species. Finally, we propose that there are regional and species-specific differences in the immune responses in FRT.

The functional roles of protein glycosylation in human maternal-fetal crosstalk

BACKGROUND

The establishment of maternal-fetal crosstalk is vital to a successful pregnancy. Glycosylation is a post-translational modification in which glycans (monosaccharide chains) are attached to an organic molecule. Glycans are involved in many physiological and pathological processes. Human endometrial epithelium, endometrial gland secretions, decidual immune cells, and trophoblasts are highly enriched with glycoconjugates and glycan-binding molecules important for a healthy pregnancy. Aberrant glycosylation in the placenta and uterus has been linked to repeated implantation failure and various pregnancy complications, but there is no recent review summarizing the functional roles of glycosylation at the maternal-fetal interface and their associations with pathological processes.

OBJECTIVE AND RATIONALE

This review aims to summarize recent findings on glycosylation, glycosyltransferases, and glycan-binding receptors at the maternal-fetal interface, and their involvement in regulating the biology and pathological conditions associated with endometrial receptivity, placentation and maternal-fetal immunotolerance. Current knowledge limitations and future insights into the study of glycobiology in reproduction are discussed.

SEARCH METHODS

A comprehensive PubMed search was conducted using the following keywords: glycosylation, glycosyltransferases, glycan-binding proteins, endometrium, trophoblasts, maternal-fetal immunotolerance, siglec, selectin, galectin, repeated implantation failure, early pregnancy loss, recurrent pregnancy loss, preeclampsia, and fetal growth restriction. Relevant reports published between 1980 and 2023 and studies related to these reports were retrieved and reviewed. Only publications written in English were included.

OUTCOMES

The application of ultrasensitive mass spectrometry tools and lectin-based glycan profiling has enabled characterization of glycans present at the maternal-fetal interface and in maternal serum. The endometrial luminal epithelium is covered with highly glycosylated mucin that regulates blastocyst adhesion during implantation. In the placenta, fucose and sialic acid residues are abundantly presented on the villous membrane and are essential for proper placentation and establishment of maternal-fetal immunotolerance. Glycan-binding receptors, including selectins, sialic-acid-binding immunoglobulin-like lectins (siglecs) and galectins, also modulate implantation, trophoblast functions and maternal-fetal immunotolerance. Aberrant glycosylation is associated with repeated implantation failure, early pregnancy loss and various pregnancy complications. The current limitation in the field is that most glycobiological research relies on association studies, with few studies revealing the specific functions of glycans. Technological advancements in analytic, synthetic and functional glycobiology have laid the groundwork for further exploration of glycans in reproductive biology under both physiological and pathological conditions.

WIDER IMPLICATIONS

A deep understanding of the functions of glycan structures would provide insights into the molecular mechanisms underlying their involvement in the physiological and pathological regulation of early pregnancy. Glycans may also potentially serve as novel early predictive markers and therapeutic targets for repeated implantation failure, pregnancy loss, and other pregnancy complications.

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.

Ligustilide enhances pregnancy outcomes via improvement of endometrial receptivity and promotion of endometrial angiogenesis in rats

Ligustilide (LIG) is the main active ingredient of Angelica sinensis (Oliv.) Diels, which could promote focal angiogenesis to exert neuroprotection. However, there was no report that verified the exact effects of LIG on endometrial angiogenesis and the pregnancy outcomes. To explore the effects of LIG on low endometrial receptivity (LER) and angiogenesis, pregnancy rats were assigned into Control (saline treatment), LER (hydroxyurea-adrenaline treatment), LIG 20 mg/kg and LIG 40 mg/kg groups. Hematoxylin and eosin (H&E) staining was performed to evaluate endometrial morphology. Quantitative real-time PCR, immunofluorescence staining, western blot and immunohistochemistry staining were employed to assess the expression of endometrial receptivity factors and angiogenesis-related gene/protein, respectively. RNA sequencing was used to analyze the effects of LIG on LER caused by Kidney deficiency and blood stasis. We found that endometrial thickness and the implanted embryo number were substantially reduced in the hydroxyurea-adrenaline-treated pregnancy rats. At the same time, the gene and protein expressions of ERα, LIF, VEGFA and CD31 in the endometrium were markedly reduced, while the expressions of MUC1, E-cadherin were increased in the LER group. Administration of LIG raised the endometrial thickness and implanted embryos, as well as reversed the expressions of these factors. Collectively, our findings revealed that LIG could facilitate embryo implantation via recovery of the endometrium receptivity and promotion of endometrial angiogenesis.

miRNA profiling in intrauterine exosomes of pregnant cattle on day 7

Intrauterine exosomes have been identified to be involved in the embryo development and implantation. The aim of this study was to explore the role of miRNAs in intrauterine exosomes in bovine pregnancy. Intrauterine exosomes were collected from uterine flushing fluids of three donor and three recipient Xianan cows 7 days after fertilization. Intrauterine exosomes miRNAs were extracted and the exosomal miRNAs expression levels were analyzed. Sixty miRNAs differed significantly in their amounts between donors and recipients (p-value < 0.05, |log2(FoldChange)| > 1). Twenty-two miRNAs were upregulated and 38 downregulated in the group of donor cows. The bta-miR-184 was the most significant (P _{Benjamini-Hochberg} < 0.001). A total of 9,775 target genes were predicted using the 60 miRNAs. GO and KEGG analysis showed that the target genes were enriched in several biological processes or pathways associated with embryo implantation and endometrial development, such as cell adhesion, cell junction, focal adhesion, and Rap1 signaling pathway. Our findings suggest that, in cattle early pregnancy stage, these differently expressed miRNAs in intrauterine exosomes involved in embryo implantation and endometrial development, which may exert a significant effect and influence the uterine microenvironment for embryo implantation. These results could provide reference for screening and exploring the intrauterine exosomal miRNA affecting embryo implantation.

Human implantation: The complex interplay between endometrial receptivity, inflammation, and the microbiome

Human embryo implantation is an intricate spatiotemporal process that involves the intimate association between the embryo and the endometrium of the mother. During implantation, the endometrium undergoes a dynamic cascade of gene activation and repression, largely driven by autocrine, paracrine, and endocrine action. Steroid hormones, such as estrogen and progesterone, act on a variety of targets including cellular adhesion molecules (CAMs), cytokines, and growth factors to facilitate the implantation process. Given the synchrony required to achieve implantation, it is unsurprising that embryo implantation represents a substantial problem for infertility patients. This is due to a complex interplay taking place at the level of the endometrium. This review discusses the intricacies of embryo implantation including the window of implantation, the cyclical phases of the endometrium, the implantation process itself, and features of endometrial receptivity. Additionally, we will discuss new research regarding inflammatory reproductive biology, epigenetics and microRNA, and the role of the vaginal and endometrial microbiome in implantation. A better understanding of embryo implantation and the interactions occurring at the level of the blastocyst and the endometrium will improve patient care for infertile patients who experience this frustrating challenge.

Morphological features of the secretory phase endometrium in women with unexplained infertility

In this study, we evaluated the structural features of the endometrial tissues, the immunohistochemical expression of MUC-1, which plays an important role in implantation, and the biochemical markers during the implantation window. Randomly chosen 18 fertile and 18 unexplained infertile women that have 27-32 days long menstrual cycle, normal hormonal values, normal USG findings of ovary and endometrium were included. Five, six, and seven days after ovulation, endometrial biopsies were taken and prepared in accordance with light and electron microscopy tissue preparation methods. Immunohistochemical methods were used to determine MUC-1 expression in the tissues. Serum hormone levels were determined. The MUC-1 immunoreactivity, as well as the serum levels of FSH, LH, TSH, estrogen, progesterone, and total testosterone did not differ significantly between the two groups; however, prolactin levels were higher in the infertile group. In the unexplained infertile samples, intraepithelial lymphocytes were frequently observed, the microvilli of the surface columnar epithelium were widespread, cells with pinopodes as well as vesiculated cells were minimal, pinopode development was insufficient, and the development of the endometrial glands was deficient. It was concluded that these structural differences observed in the surface and glandular epithelium of the endometrium in unexplained infertile patients may be due to the insufficiency of these cells in responding to steroid hormones; therefore, these changes may affect the implantation of the blastocyst in the endometrium.

Pinopodes: Recent advancements, current perspectives, and future directions

Successful embryo implantation is a complex and highly regulated process involving precise synchronization between the fetal-derived trophoblast cells and maternal uterine luminal epithelium. Multiple endocrine-driven factors are important for controlling the timely receptivity of the uterus, and this complexity underscores implantation failure as a major cause of recurrent infertility associated with assisted reproductive technologies. One particular cellular structure often hypothesized to promote receptivity is the pinopode or uterodome - a hormonally regulated, large cellular protrusion on the uterine epithelial surface. Recent clinical studies associate pinopodes with favorable fertility outcomes in women, and because they are directly linked to an increase in progesterone levels, the potential utility of these hormone-regulated cell biological structures in predicting or improving implantation in a clinical setting holds promise. In this review, we aim to generate interest in pinopodes from the broader cell biology and endocrinology communities, re-examine methodologies in pinopode research, and identify priorities for future investigation of pinopode structure and function in women's reproductive health.