Dysfunctional intercellular communication and metabolic signaling pathways in thin endometrium

Exploring the mechanism of action of aspirin in improving endometrial receptivity in PCOS rats based on uterine lavage fluid metabolomics

BACKGROUNDS

Aspirin has been shown to enhance endometrial receptivity (ER) during the window of implantation in patients with polycystic ovary syndrome (PCOS). However, the underlying mechanisms remain unclear. This study aimed to elucidate the mechanisms by which aspirin improves ER through metabolic analysis of uterine lavage fluid.

METHODS

A PCOS rat model was established using letrozole. Body weight and estrous cycles were monitored, and the number of implanted embryos was assessed across groups. We evaluated endometrial ultrastructure, ovarian and endometrial histomorphometry. Serum levels of estradiol(E2) and progesterone(P)were measured. Moreover, through ultra-performance liquid chromatography-mass spectrometry, the study of uterine lavage fluid metabolites revealed the potential mechanism of action of aspirin.

RESULTS

Compared with the model group, aspirin treatment significantly increased embryo implantation rates, improved endometrial morphology and hormone levels. Metabolomic analysis identified 48 differential metabolites, among which five-2, 6-dihydroxypurine, gluconolactone, Oxaceprol, PC (18:1/18:1), and PC (20:3e/17:1)-were identified as potential biomarkers for aspirin-mediated improvement of ER in PCOS rats. Pathway analysis revealed that aspirin primarily modulates the pentose phosphate pathway, arginine and proline metabolism, and glycerophospholipid metabolism.

CONCLUSIONS

Aspirin may enhance glucose metabolism, alleviate insulin resistance, promote angiogenesis, and improve vascular permeability and endometrial receptivity. These effects are likely mediated through the regulation of biomarkers involved in the pentose phosphate pathway, arginine and proline metabolism, and glycerophospholipid pathways in uterine lavage fluid.

Comprehensive single-cell transcriptome analysis of autologous platelet-rich plasma therapy on human thin endometrium

Therapeutics for thin endometrium (TE) have emerged, with autologous platelet-rich plasma (PRP) therapy gaining significant attention. In the present study, ten eligible TE patients were recruited for PRP infusion. Endometrial tissue biopsies collected before and after PRP therapy (paired samples) were subjected to single-cell RNA sequencing (scRNA-seq). Additionally, haematoxylin and eosin (HE) and immunohistochemistry (IHC) were employed to validate changes in protein markers. The results demonstrated PRP therapy increased the average endometrial thickness in these patients. Cellular trajectory reconstruction analysis using gene counts and expression (CytoTRACE) scores indicated that high-stemness cells were more enriched in proliferating stromal cells (pStr) or stromal cells (Str) in post-PRP samples, while greater stemness was observed in glandular epithelial cells (GE) and luminal epithelial cells (LE). Gene set variation analysis (GSVA) revealed significant differences in mesenchymal‒epithelial transition (MET)-related gene signature scores between paired samples. Furthermore, an increased number of macrophages, particularly M1-type macrophages, was detected in post-PRP samples. As the first study to investigate the effects of PRP therapy via transcriptomic analysis, our findings suggest PRP therapy may enhance high-stemness, stimulate MET, and boost macrophage function. These insights contribute to a better understanding of the mechanisms underlying PRP therapy and its potential in treating TE patients.

"Thin endometrium" at single-cell resolution

Thin endometrium is defined as an endometrial thickness of less than 7 mm in the midluteal phase of the menstrual cycle, a condition often seen in women of childbearing age with a history of uterine trauma, such as dilation and curettage or intrauterine adhesion separation. This inadequate thickness poses a substantial threat to endometrial receptivity and subsequent pregnancy, particularly during infertility treatments. Despite efforts to stimulate endometrial growth through agents such as high doses of estrogen, improvements in both endometrial thickness and pregnancy rates have been marginal. Consequently, it is referred to as "unresponsive endometrium or refractory thin endometrium." To explore novel therapeutic avenues, a deeper understanding of the underlying mechanisms is urgently needed. In this review, we examine recent single-cell sequencing studies that have identified key alterations in cell populations, signaling pathways, and cell-cell communication in the endometrium during the late proliferative phase, comparing normal endometrium and thin endometrium following uterine injuries. Evidence suggests that endometrial injury acted as a primary contributor, initiating an accelerated aging process across diverse cell types and establishing an environment characterized by immune incompetence and dysfunction. Senescence, a consequence of this injury, may impede endometrial proliferation, disrupt vascular development, and lead to fibrosis, creating a milieu of abnormal receptivity-a critical downstream event associated with implantation failure and infertility. Addressing these identified challenges necessitates advancing research to comprehend and target the key factors contributing to thin endometrium, a crucial step for clinical translation.

Integrating Single-Cell RNA-Seq and ATAC-Seq Analysis Reveals Uterine Cell Heterogeneity and Regulatory Networks Linked to Pimpled Eggs in Chickens

Pimpled eggs have defective shells, which severely impacts hatching rates and transportation safety. In this study, we constructed single-cell resolution transcriptomic and chromatin accessibility maps from uterine tissues of chickens using single-cell RNA sequencing (scRNA-seq) and single-cell ATAC sequencing (scATAC-seq). We identified 11 major cell types and characterized their marker genes, along with specific transcription factors (TFs) that determine cell fate. CellChat analysis showed that fibroblasts had the most extensive intercellular communication network and that the chickens laying pimpled eggs had amplified immune-related signaling pathways. Differential expression and enrichment analyses indicated that inflammation in pimpled egg-laying chickens may lead to disruptions in their circadian rhythm and changes in the expression of ion transport-related genes, which negatively impacts eggshell quality. We then integrated TF analysis to construct a regulatory network involving TF-target gene-Gene Ontology associations related to pimpled eggs. We found that the transcription factors ATF3, ATF4, JUN, and FOS regulate uterine activities upstream, while the downregulation of ion pumps and genes associated with metal ion binding directly promotes the formation of pimpled eggs. Finally, by integrating the results of scRNA-seq and scATAC-seq, we identified a rare cell type-ionocytes. Our study constructed single-cell resolution transcriptomic and chromatin accessibility maps of chicken uterine tissue and explored the molecular regulatory mechanisms underlying pimpled egg formation. Our findings provide deeper insights into the structure and function of the chicken uterus, as well as the molecular mechanisms of eggshell formation.

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.

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).

Varied cellular abnormalities in thin vs. normal endometrium in recurrent implantation failure by single-cell transcriptomics

BACKGROUND

Reduced endometrium thickness and receptivity are two important reasons for recurrent implantation failure (RIF). In order to elucidate differences between these two types of endometrial defects in terms of molecular signatures, cellular interactions, and structural changes, we systematically investigated the single-cell transcriptomic atlas across three distinct groups: RIF patients with thin endometrium (≤ 6 mm, TE-RIF), RIF patients with normal endometrium thickness (≥ 8 mm, NE-RIF), and fertile individuals (Control).

METHODS

The late proliferative and mid-secretory phases of the endometrium were collected from three individuals in the TE-RIF group, two in the NE-RIF group, and three in the control group. The study employed a combination of advanced techniques. Single-cell RNA sequencing (scRNA-seq) was utilized to capture comprehensive transcriptomic profiles at the single-cell level, providing insights into gene expression patterns within specific cell types. Scanning and transmission electron microscopy were employed to visualize ultrastructural details of the endometrial tissue, while hematoxylin and eosin staining facilitated the examination of tissue morphology and cellular composition. Immunohistochemistry techniques were also applied to detect and localize specific protein markers relevant to endometrial receptivity and function.

RESULTS

Through comparative analysis of differentially expressed genes among these groups and KEGG pathway analysis, the TE-RIF group exhibited notable dysregulations in the TNF and MAPK signaling pathways, which are pivotal in stromal cell growth and endometrial receptivity. Conversely, in the NE-RIF group, disturbances in energy metabolism emerged as a primary contributor to reduced endometrial receptivity. Additionally, using CellPhoneDB for intercellular communication analysis revealed aberrant interactions between epithelial and stromal cells, impacting endometrial receptivity specifically in the TE-RIF group.

CONCLUSION

Overall, our findings provide valuable insights into the heterogeneous molecular pathways and cellular interactions associated with RIF in different endometrial conditions. These insights may pave the way for targeted therapeutic interventions aimed at improving endometrial receptivity and enhancing reproductive outcomes in patients undergoing ART. Further research is warranted to validate these findings and translate them into clinical applications for personalized fertility treatments.

TRIAL REGISTRATION

Not applicable.

Bioengineering approaches for the endometrial research and application

The endometrium undergoes a series of precise monthly changes under the regulation of dynamic levels of ovarian hormones that are characterized by repeated shedding and subsequent regeneration without scarring. This provides the potential for wound healing during endometrial injuries. Bioengineering materials highlight the faithful replication of constitutive cells and the extracellular matrix that simulates the physical and biomechanical properties of the endometrium to a larger extent. Significant progress has been made in this field, and functional endometrial tissue bioengineering allows an in-depth investigation of regulatory factors for endometrial and myometrial defects in vitro and provides highly therapeutic methods to alleviate obstetric and gynecological complications. However, much remains to be learned about the latest progress in the application of bioengineering technologies to the human endometrium. Here, we summarize the existing developments in biomaterials and bioengineering models for endometrial regeneration and improving the female reproductive potential.

Impaired bone morphogenetic protein (BMP) signaling pathways disrupt decidualization in endometriosis

Endometriosis is linked to increased infertility and pregnancy complications due to defective endometrial decidualization. We hypothesized that identification of altered signaling pathways during decidualization could identify the underlying cause of infertility and pregnancy complications. Our study reveals that transforming growth factor β (TGFβ) pathways are impaired in the endometrium of individuals with endometriosis, leading to defective decidualization. Through detailed transcriptomic analyses, we discovered abnormalities in TGFβ signaling pathways and key regulators, such as SMAD4, in the endometrium of affected individuals. We also observed compromised activity of bone morphogenetic proteins (BMP), a subset of the TGFβ family, that control endometrial receptivity. Using 3-dimensional models of endometrial stromal and epithelial assembloids, we showed that exogenous BMP2 improved decidual marker expression in individuals with endometriosis. Our findings reveal dysfunction of BMP/SMAD signaling in the endometrium of individuals with endometriosis, explaining decidualization defects and subsequent pregnancy complications in these individuals.

Crosstalk among podocytes, glomerular endothelial cells and mesangial cells in diabetic kidney disease: an updated review

Diabetic kidney disease (DKD) is a long-term and serious complication of diabetes that affects millions of people worldwide. It is characterized by proteinuria, glomerular damage, and renal fibrosis, leading to end-stage renal disease, and the pathogenesis is complex and involves multiple cellular and molecular mechanisms. Among three kinds of intraglomerular cells including podocytes, glomerular endothelial cells (GECs) and mesangial cells (MCs), the alterations in one cell type can produce changes in the others. The cell-to-cell crosstalk plays a crucial role in maintaining the glomerular filtration barrier (GFB) and homeostasis. In this review, we summarized the recent advances in understanding the pathological changes and interactions of these three types of cells in DKD and then focused on the signaling pathways and factors that mediate the crosstalk, such as angiopoietins, vascular endothelial growth factors, transforming growth factor-β, Krüppel-like factors, retinoic acid receptor response protein 1 and exosomes, etc. Furthermore, we also simply introduce the application of the latest technologies in studying cell interactions within glomerular cells and new promising mediators for cell crosstalk in DKD. In conclusion, this review provides a comprehensive and updated overview of the glomerular crosstalk in DKD and highlights its importance for the development of novel intervention approaches.

Impaired bone morphogenetic protein (BMP) signaling pathways disrupt decidualization in endometriosis

Endometriosis is linked to increased infertility and pregnancy complications due to defective endometrial decidualization. We hypothesized that identification of altered signaling pathways during decidualization could identify the underlying cause of infertility and pregnancy complications. Our study reveals that transforming growth factor β (TGFβ) pathways are impaired in the endometrium of individuals with endometriosis, leading to defective decidualization. Through detailed transcriptomic analyses, we discovered abnormalities in TGFβ signaling pathways and key regulators, such as SMAD4, in the endometrium of affected individuals. We also observed compromised activity of bone morphogenetic proteins (BMP), a subset of the TGFβ family, that control endometrial receptivity. Using 3-dimensional models of endometrial stromal and epithelial assembloids, we showed that exogenous BMP2 improved decidual marker expression in individuals with endometriosis. Our findings unveil a previously unidentified dysfunction in BMP/SMAD signaling in the endometrium of individuals with endometriosis, explaining decidualization defects and subsequent pregnancy complications in these individuals.

Impaired bone morphogenetic protein signaling pathways disrupt decidualization in endometriosis

It is hypothesized that impaired endometrial decidualization contributes to decreased fertility in individuals with endometriosis. To identify the molecular defects that underpin defective decidualization in endometriosis, we subjected endometrial stromal cells from individuals with or without endometriosis to time course in vitro decidualization with estradiol, progesterone, and 8-bromo-cyclic-AMP (EPC) for 2, 4, 6, or 8 days. Transcriptomic profiling identified differences in key pathways between the two groups, including defective bone morphogenetic protein (BMP)/SMAD4 signaling (ID2, ID3, FST), oxidate stress response (NFE2L2, ALOX15, SLC40A1), and retinoic acid signaling pathways (RARRES, RARB, ALDH1B1). Genome-wide binding analyses identified an altered genomic distribution of SMAD4 and H3K27Ac in the decidualized stromal cells from individuals without endometriosis relative to those with endometriosis, with target genes enriched in pathways related to signaling by transforming growth factor β (TGFβ), neurotrophic tyrosine kinase receptors (NTRK), and nerve growth factor (NGF)-stimulated transcription. We found that direct SMAD1/5/4 target genes control FOXO, PI3K/AKT, and progesterone-mediated signaling in decidualizing cells and that BMP2 supplementation in endometriosis patient-derived assembloids elevated the expression of decidualization markers. In summary, transcriptomic and genome-wide binding analyses of patient-derived endometrial cells and assembloids identified that a functional BMP/SMAD1/5/4 signaling program is crucial for engaging decidualization.

Ferroptosis contributes to endometrial fibrosis in intrauterine adhesions

Intrauterine adhesions (IUA), characterized by endometrial fibrosis, is a challenging clinical issue in reproductive medicine. We previously demonstrated that epithelial-mesenchymal transition (EMT) and fibrosis of endometrial stromal cells (HESCs) played a vital role in the development of IUA, but the precise pathogenesis remains elucidated. Ferroptosis has now been recognized as a unique form of oxidative cell death, but whether it is involved in endometrial fibrosis remains unknown. In the present study, we performed an RNA-seq of the endometria from 4 severe IUA patients and 4 normal controls. Enrichment analysis and protein-protein interactions (PPIs) network analysis of differentially expressed genes (DEGs) were conducted. Immunohistochemistry was used to assess ferroptosis levels and cellular localization. The potential role of ferroptosis for IUA was investigated by in vitro and in vivo experiments. Here, we demonstrated that ferroptosis load is increased in IUA endometria. In vitro experiments showed that erastin-induced ferroptosis promoted EMT and fibrosis in endometrial epithelial cells (P < 0.05), but did not lead to pro-fibrotic differentiation in endometrial stromal cells (HESCs). Cell co-culture experiments showed that erastin-stimulated epithelial cell supernatants promoted fibrosis in HESCs (P < 0.05). In vivo experiments suggested that elevation of ferroptosis level in mice by erastin led to mild endometrial EMT and fibrosis. Meanwhile, the ferroptosis inhibitor Fer-1 significantly ameliorated endometrial fibrosis in a dual-injury IUA murine model. Overall, our findings revealed that ferroptosis may serve as a potential therapeutic target for endometrial fibrosis in IUA.

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.