Altered microRNA Profiles of Extracellular Vesicles Secreted by Endometrial Cells from Women with Recurrent Implantation Failure

Circulating microRNAs in Body Fluid: "Fingerprint" RNA Snippets Deeply Impact Reproductive Biology

Circulating miRNAs (C-miRNAs) occuring in a cell-free form within body fluids and other extracellular environments have garnered attention in recent times. They offer deeper insight into various physiological and pathological processes which include reproductive health. This review delves into their diagnostic potential across a spectrum of reproductive disorders, including conditions affecting ovarian function, male infertility and post pregnancy issues. Through analysis of C-miRNA profiles in bodily fluids, researchers uncover crucial markers indicative of reproductive challenges. Dysregulated C-miRNAs emerge as important players in the progression of several reproductive disorders which is the main focus of this review. Advancements in technology, facilitate precise detection and quantification of C-miRNAs, paving the way for innovative diagnostic approaches. Challenges in studying C-miRNAs, such as their low abundance and variability in expression levels, underscore the need for standardized protocols and rigorous validation methods. Despite these challenges, ongoing research endeavors aim to unravel the complex regulatory roles of C-miRNAs in reproductive biology, with potential implications for clinical practice and therapeutic interventions.

Endometrial extracellular vesicles regulate processes related to embryo development and implantation in human blastocysts

STUDY QUESTION

What is the transcriptomic response of human blastocysts following internalization of extracellular vesicles (EVs) secreted by the human endometrium?

SUMMARY ANSWER

EVs secreted by the maternal endometrium induce a transcriptomic response in human embryos that modulates molecular mechanisms related to embryo development and implantation.

WHAT IS KNOWN ALREADY

EVs mediate intercellular communication by transporting various molecules, and endometrial EVs have been postulated to be involved in the molecular regulation of embryo implantation. Our previous studies showed that endometrial EVs carry miRNAs and proteins associated with implantation events that can be taken up by human blastocysts; however, no studies have yet investigated the transcriptomic response of human embryos to this EV uptake, which is crucial to demonstrate the functional significance of this communication system.

STUDY DESIGN, SIZE, DURATION

A prospective descriptive study was performed. Primary human endometrial epithelial cells (pHEECs), derived from endometrial biopsies collected from fertile oocyte donors (n = 20), were cultured in vitro to isolate secreted EVs. Following EV characterization, Day 5 human blastocysts (n = 24) were cultured in the presence or absence of the EVs for 24 h and evaluated by RNA-sequencing.

PARTICIPANTS/MATERIALS, SETTING, METHODS

EVs were isolated from the conditioned culture media using ultracentrifugation, and characterization was performed using western blot, nanoparticle tracking analysis, and transmission electron microscopy. Human blastocysts were devitrified, divided into two groups (n = 12/group), and cultured in vitro for 24 h with or without previously isolated EVs. RNA-sequencing analysis was performed, and DESeq2 was used to identify differentially expressed genes (DEGs) (FDR < 0.05). QIAGEN Ingenuity Pathway Analysis was used to perform the functional enrichment analysis and integration with our recently published data from the pHEECs' EV-miRNA cargo.

MAIN RESULTS AND THE ROLE OF CHANCE

Characterization confirmed the isolation of EVs from pHEECs' conditioned culture media. Among the DEGs in blastocysts co-cultured with EVs, we found 519 were significantly upregulated and 395 were significantly downregulated. These DEGs were significantly enriched in upregulated functions related to embryonic development, cellular invasion and migration, cell cycle, cellular organization and assembly, gene expression, and cell viability; and downregulated functions related to cell death and DNA fragmentation. Further, the intracellular signaling pathways regulated by the internalization of endometrial EVs were previously related to early embryo development and implantation potential, for their role in pluripotency, cellular homeostasis, early embryogenesis, and implantation-related processes. Finally, integrating data from miRNA cargo of EVs, we found that the miRNAs carried by endometrial EVs targeted nearly 80% of the DEGs in human blastocysts.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study in which conditions of endometrial cell culture could not mimic the intrauterine environment.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides novel insights into the functional relevance of EVs secreted by the human endometrium, and particularly the role of EV-miRNA regulation on global transcriptome behavior of human blastocysts during early embryogenesis and embryo implantation. It provides potential biomarkers that could become useful diagnostic targets for predicting implantation success.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Spanish Ministry of Education through FPU awarded to M.S.-B. (FPU18/03735), Generalitat Valenciana through VALi+d Programme awarded to M.C.C.-G. (ACIF/2019/139), and Instituto de Salud Carlos III and cofounded by the European Social Fund (ESF) "Investing in your future" through the Miguel Servet Program (CP20/00120 [H.F.]; CP19/00149 [I.C.]). The authors have no conflicts of interest to disclose.

TRIAL REGISTRATION NUMBER

N/A.

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.

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.

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.

Impact of miRNAs in the pathoetiology of recurrent implantation failure

Recurrent implantation failure (RIF) is a condition with a multifactorial basis. Recent research has focused on the role of genetic factors in the pathophysiology of RIF. Of particular note, miRNAs have been found to contribute to the pathogenesis of RIF. Several miRNA polymorphisms have been investigated in this context. Moreover, dysregulation of expression of a number of miRNAs, including miR-374a-5p, miR-145-5p, miR-30b-5p, miR-196b-5p, miR-22, miR-181 and miR-145 has been found in RIF. This review concentrates on the role of miRNAs in RIF to help in identification of the molecular basis for this condition and design of more effective methods for management of RIF, especially in a personalized manner that relies on the expression profiles of miRNAs in the peripheral blood or endometrium.

Non-coding RNAs in Recurrent implantation failure

Recurrent implantation failure (RIF), defined as the inability to achieve conception following multiple consecutive in-vitro fertilization (IVF) attempts, represents a complex and multifaceted challenge in reproductive medicine. The emerging role of non-coding RNAs in RIF etiopathogenesis has only gained prominence over the last decade, illustrating a new dimension to our understanding of the intricate network underlying RIF. Successful embryo implantation demands a harmonious synchronization between an adequately decidualized endometrium, a competent blastocyst, and effective maternal-embryonic interactions. Emerging evidence has clarified the involvement of a sophisticated network of non-coding RNAs, including microRNAs, circular RNAs, and long non-coding RNAs, in orchestrating these pivotal processes. Disconcerted expression of these molecules can disrupt the delicate equilibrium required for implantation, amplifying the risk of RIF. This comprehensive review presents an in-depth investigation of the complex role played by non-coding RNAs in the pathogenesis of RIF. Furthermore, it underscores the vast potential of non-coding RNAs as diagnostic biomarkers and therapeutic targets, with the ultimate goal of enhancing implantation success rates in IVF cycles. As ongoing research continues to unravel the intercalated web of molecular interactions, exploiting the power of non-coding RNAs may offer promising avenues for mitigating the challenges posed by RIF and improving the outcomes of assisted reproduction.

Human blastocysts uptake extracellular vesicles secreted by endometrial cells containing miRNAs related to implantation

STUDY QUESTION

Are the extracellular vesicles (EVs) secreted by the maternal endometrium uptaken by human embryos and is their miRNA cargo involved in implantation and embryo development?

SUMMARY ANSWER

Data suggest that EVs secreted by human endometrial epithelial cells are internalized by human blastocysts, and transport miRNAs to modulate biological processes related to implantation events and early embryo development.

WHAT IS KNOWN ALREADY

Successful implantation is dependent on coordination between maternal endometrium and embryo, and EVs role in the required cell-to-cell crosstalk has recently been established. In this regard, our group previously showed that protein cargo of EVs secreted by primary human endometrial epithelial cells (pHEECs) is implicated in biological processes related to endometrial receptivity, embryo implantation, and early embryo development. However, little is known about the regulation of these biological processes through EVs secreted by the endometrium at a transcriptomic level.

STUDY DESIGN, SIZE, DURATION

A prospective descriptive study was performed. Endometrial biopsies were collected from healthy oocyte donors with confirmed fertility on the day of oocyte retrieval, 36 h after the LH surge. pHEECs were isolated from endometrial biopsies (n = 8 in each pool) and cultured in vitro. Subsequently, conditioned medium was collected and EVs were isolated and characterized. Uptake of EVs by human blastocysts and miRNA cargo of these EVs (n = 3 pools) was analyzed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

EVs were isolated from the conditioned culture media using ultracentrifugation, and characterization was performed using western blotting, nanoparticle tracking analysis, and transmission electron microscopy. EVs were fluorescently labeled with Bodipy-TR ceramide, and their uptake by human blastocysts was analyzed using confocal microscopy. Analysis of the miRNA cargo of EVs was performed using miRNA sequencing, target genes of the most expressed miRNA were annotated, and functional enrichment analysis was performed.

MAIN RESULTS AND THE ROLE OF CHANCE

EVs measured 100-300 nm in diameter, a concentration of 1.78 × 1011 ± 4.12 × 1010 (SD) particles/ml and expressed intraluminal protein markers Heat shock protein 70 (HSP70) and Tumor Susceptibility Gene 101 (TSG101), in addition to CD9 and CD81 transmembrane proteins. Human blastocysts efficiently internalized fluorescent EVs within 1-2 h, and more pronounced internalization was observed in the hatched pole of the embryos. miRNA-seq analysis featured 149 annotated miRNAs, of which 37 were deemed most relevant. The latter had 6592 reported gene targets, that in turn, have functional implications in several processes related to embryo development, oxygen metabolism, cell cycle, cell differentiation, apoptosis, metabolism, cellular organization, and gene expression. Among the relevant miRNAs contained in these EVs, we highlight hsa-miR-92a-3p, hsa-let-7b-5p, hsa-miR-30a-5p, hsa-miR-24-3p, hsa-miR-21-5p, and hsa-let-7a-5p as master regulators of the biological processes.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study in which conditions of endometrial cell culture could not mimic the intrauterine environment.

WIDER IMPLICATIONS OF THE FINDINGS

This study defines potential biomarkers of endometrial receptivity and embryo competence that could be useful diagnostic and therapeutic targets for implantation success, as well as open insight further investigations to elucidate the molecular mechanisms implicated in a successful implantation.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Spanish Ministry of Education through FPU awarded to M.S.-B. (FPU18/03735), the Health Institute Carlos III awarded to E.J.-B. (FI19/00110) and awarded to H.F. by the Miguel Servet Program 'Fondo Social Europeo «El FSE invierte en tu futuro»' (CP20/00120), and Generalitat Valenciana through VALi+d Programme awarded to M.C.C.-G. (ACIF/2019/139). The authors have no conflicts of interest to disclose.

TRIAL REGISTRATION NUMBER

N/A.

The biological functions of maternal-derived extracellular vesicles during pregnancy and lactation and its impact on offspring health

During pregnancy and lactation, mothers provide not only nutrients, but also many bioactive components for their offspring through placenta and breast milk, which are essential for offspring development. Extracellular vesicles (EVs) are nanovesicles containing a variety of biologically active molecules and participate in the intercellular communication. In the past decade, an increasing number of studies have reported that maternal-derived EVs play a crucial role in offspring growth, development, and immune system establishment. Hereby, we summarized the characteristics of EVs; biological functions of maternal-derived EVs during pregnancy, including implantation, decidualization, placentation, embryo development and birth of offspring; biological function of breast milk-derived EVs (BMEs) on infant oral and intestinal diseases, immune system, neurodevelopment, and metabolism. In summary, emerging studies have revealed that maternal-derived EVs play a pivotal role in offspring health. As such, maternal-derived EVs may be used as promising biomarkers in offspring disease diagnosis and treatment. However, existing research on maternal-derived EVs and offspring health is largely limited to animal and cellular studies. Evidence from human studies is needed.

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.

Isolation of extracellular vesicles from bitch's amnion-derived cells culture and their CD59 expression: Preliminary results

Extracellular vesicles (EVs) are small spherical particles surrounded by a membrane with an unusual lipid composition and a striking cholesterol/phospholipidic ratio. About 2000 lipid and 3500 protein species were identified in EVs secreted by different cell sources. EVs mediate cell to cell communication in proximity to or distant from the cell of origin. In particular, it was suggested that they represent modulators of multiple processes during pregnancy. The aim of this study was to identify the presence of EVs in canine amnion-derived cells (ASCs) culture and the expression of CD 59 on their surface. Amniotic membrane was collected in PBS with antibiotics added from 2 bitches during elective caesarean section. Cells culture was prepared and EVs were isolated. EVs were used to evaluate CD59 expression by flow cytofluorimetry. We found that the majority of EVs expressed CD59. Our results could increase the knowledge about the complex mechanisms that regulate the pregnancy in the bitch.

The role of extracellular vesicles in intercellular communication in human reproduction

Embryo-maternal cross-talk has emerged as a vitally important process for embryo development and implantation, which is driven by secreted factors and extracellular vesicles (EVs). The EV cargo of bioactive molecules significantly influences target cells and primes them for critical stages of reproductive biology, including embryo development, adhesion, and implantation. Recent research has suggested that EVs and their cargo represent a powerful non-invasive tool that can be leveraged to assess embryo and maternal tissue quality during assisted reproduction treatments. Here, we review the current scientific literature regarding the intercellular cross-talk between embryos and maternal tissues from fertilization to implantation, focusing on human biology and signaling mechanisms identified in animal models.

Immune alterations in recurrent implantation failure

A failure to achieve pregnancy after three or more embryo transfer cycles with high-quality blastocysts is referred to as recurrent implantation failure (RIF). RIF can be due to altered uterine factors or male factors or embryo factors. Disrupted endometrial receptivity, altered expression of genes in several pathways, immunologic disturbances in the peripheral blood and/or the endometrium, and epigenetic alterations are associated with RIF. Amongst the immunologic disturbances, altered Th1/Th2 ratio, altered NK cell and macrophage numbers are observed in women with RIF. However, not all women with RIF have the same kind of immune dysfunction suggesting that RIF is a heterogeneous condition associated with varied immune responses and one size may not fit all. Thus, personalized therapies based on the immune status of the patient are being tested in women with RIF. In general, women with a high Th1/Th2 ratio are offered Tacrolimus, while intravenous IgG is recommended in women with high NK cell numbers/HLA mismatch. Women with hyperactivated immune status in the uterus are offered progesterone support, prednisolone, vitamin E, and intralipid treatment to suppress inflammation and oxidative stress, while endometrial scratching and intrauterine hCG administration are offered to women with hypo-active immune status. There is a need for standardized tests for evaluation of immune status in patients and sufficiently powered randomized controlled trials for personalized therapies to determine which of these will be beneficial in women with RIF. Till then, the ART community should limit the use of such add-on interventions in women with RIF.

Extracellular vesicles-encapsulated microRNA in mammalian reproduction: A review

Extracellular vesicles (EVs) are nanoscale cell-derived lipid vesicles that participate in cell-cell communication by delivering cargo, including mRNAs, proteins and non-coding RNAs, to recipient cells. MicroRNA (miRNA), a non-coding RNA typically 22 nucleotides long, is crucial for nearly all developmental and pathophysiological processes in mammals by regulating recipient cells gene expression. Infertility is a worldwide health issue that affects 10-15% of couples during their reproductive years. Although assisted reproductive technology (ART) gives infertility couples hope, the failure of ART is mainly unknown. It is well accepted that EVs-encapsulated miRNAs have a role in different reproductive processes, implying that these EVs-encapsulated miRNAs could optimize ART, improve reproductive rate, and treat infertility. As a result, in this review, we describe the present understanding of EVs-encapsulated miRNAs in reproduction regulation.

Bone Marrow Mesenchymal Stem Cells (BMSCs) Enhance the In Vitro Activities of Endometrial Cells via Strengthening the Phosphorylation and Activation of Phosphoinositide 3-Kinase (PI3K)

Mancozeb (ethylene bis-dithiocarbamate) is an organometallic fungicide and is widely used in agriculture and is related to women’s spontaneous abortion and menstrual abnormalities. Bone marrow mesenchymal stem cells (BMSCs) can impede endometrial fibrosis via suppressing PI3K pathway, but its effect on the activity of endometrial cells induced by mancozeb/EDU is unclear. This study intends to explore the protective effects of co-culture with BMSCs on endometrial cells after mancozeb/EDU treatment. Endometrial cells were randomized into control group, mancozeb/EDU group (mancozeb/EDU treatment), BMSCs group (cells were co-cultured with BMSCs after mancozeb/EDU treatment), and inhibitor group (treated with PI3K-Akt-mTOR inhibitor) followed by analysis of the expression of PI3K-Akt-mTOR pathway-related proteins, cell viability by MTT and cell invasion and migration by Transwell and scratch test. Mancozeb/EDU treatment significantly inhibited PI3K-Akt-mTOR signals and cell proliferation, increased apoptosis and decreased cell invasion and migration, which were all reversed by co-culture with BMSCs. Additionally, the co-culture with BMSCs modulated the In Vitro viability of endometrial cells by influencing PI3K-Akt-mTOR signal transduction pathway, which can be inverted by PI3K-Akt-mTOR pathway-specific antagonists. In conclusion, BMSCs exerted a protective effect on the In Vitro viability of endometrial cells by manipulating the PI3K/Akt/mTOR signal transduction, which helped to protect endometrial cells from damage caused by mancozeb/ETU treatment.

PLP1 may serve as a potential diagnostic biomarker of uterine fibroids

Objective: We aim to identify the crucial genes or potential biomarkers associated with uterine fibroids (UFs), which may provide clinicians with evidence about the diagnostic biomarker of UFs and reveal the mechanism of its progression.

Methods: The gene expression and genome-wide DNA methylation profiles were obtained from Gene Expression Omnibus database (GEO). GSE45189, GSE31699, and GSE593 datasets were included. GEO2R and Venn diagrams were used to analyze the differentially expressed genes (DEGs) and extract the hub genes. Gene Ontology (GO) analysis was performed by the online tool Database for Annotation, Visualization, and Integrated Discovery (DAVID). The mRNA and protein expression of hub genes were validated by RT-qPCR, western blot, and immunohistochemistry. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value.

Results: We detected 22 DEGs between UFs and normal myometrium, which were enriched in cell maturation, apoptotic process, hypoxia, protein binding, and cytoplasm for cell composition. By finding the intersection of the data between differentially expressed mRNA and DNA methylation profiles, 3 hub genes were identified, including transmembrane 4 L six family member 1 (TM4SF1), TNF superfamily member 10 (TNFSF10), and proteolipid protein 1 (PLP1). PLP1 was validated to be up-regulated significantly in UFs both at mRNA and protein levels. The area under the ROC curve (AUC) of PLP1 was 0.956, with a sensitivity of 79.2% and a specificity of 100%. Conclusion: Overall, our results indicate that PLP1 may be a potential diagnostic biomarker for uterine fibroids.

Exosomes in the f ield of reproduction: A scientometric study and visualization analysis

Background: The diagnostic capabilities of exosomes in the field of reproductive biomedicine have attracted much attention. The aim of this scientometric study was to statistically and qualitatively assess the knowledge structure, hot issues, and research trends of papers about exosomes in the field of reproduction using visualization methods.

Methods: The Web of Science Core Collection was searched for studies on exosomes in the field of reproduction. We performed bibliometric and visual analyses using VOSviewer, CiteSpace, and Microsoft Excel.

Results: After database search, 1,011 articles were included, with number of studies being published every year continually increasing. These publications came from 61 nations or regions, with the US having the highest number. The University of Queensland was the main institution in which the research was conducted. The journal Placenta contained the highest number studies. There were 5,247 authors in total. Carlos Salomon had the highest number of papers with co-citations. Exosomes, extracellular vesicles, pregnancy, microRNAs, preeclampsia, placenta, microvesicles, gene expression, biomarkers, and first trimester were the most frequently used terms.

Conclusion: Exosome research is booming in reproductive biomedicine. Future studies will likely focus on exosomes as biomarkers in gamete formation and fertilization, pregnancy, and cancers associated with reproduction. In addition to focusing on fundamental research, we should concentrate on the application of the results and the investigation of exosomes in infertile patients.

Role of endometrial microRNAs in repeated implantation failure (mini-review)

MicroRNAs (miRNAs) play various roles in the implantation and pregnancy process. Abnormal regulation of miRNAs leads to reproductive disorders such as repeated implantation failure (RIF). During the window of implantation, different miRNAs are released from the endometrium, which can potentially reflect the status of the endometrium for in vitro fertilization (IVF). The focus of this review is to determine whether endometrial miRNAs may be utilized as noninvasive biomarkers to predict the ability of endometrium to implant and provide live birth during IVF cycles. The levels of certain miRNAs in the endometrium have been linked to implantation potential and pregnancy outcomes in previous studies. Endometrial miRNAs could be employed as non-invasive biomarkers in the assisted reproductive technology (ART) cycle to determine the optimal time for implantation. Few human studies have evaluated the association between ART outcomes and endometrial miRNAs in RIF patients. This review may pave the way for more miRNA transcriptomic studies on human endometrium and introduce a specific miRNA profile as a multivariable prediction model for choosing the optimal time in the IVF cycle.

Emerging trends and frontier research on recurrent implantation failure: a bibliometric analysis

Background

Recurrent implantation failure (RIF) has been recognized to be a major obstacle to the successful application of artificial reproduction technologies. In this study, the trends in RIF research were examined through a bibliometric analysis evaluating relevant literature quantitatively and qualitatively.

Methods

A total of 1,764 publications from 2000 to 2020 were downloaded from the Web of Science Core Collection (WoSCC). Relevant articles were searched using the term "recurrent implantation failure" and other synonyms of this term. Using Excel 2013, CiteSpace V, and VOSviewer 1.6.10 software, data extracted from the literature, including countries/regions, institutions, journals, keywords, and trends, were analyzed. Next, a clustered network was constructed based on 46,718 references cited by the 1,764 publications to determine the top 10 cocited articles.

Results

The annual number of publications on RIF progressively increased over time. The highest number of publications were from the United States. Analysis of the cocited reference cluster showed that "endometrial injury", "platelet-rich plasma", "chronic endometritis" and "extracellular vesicles" were the hotspots in RIF research. Burst detection analysis of the top keywords showed that "hysteroscopy" and "improvement" are emerging research foci.

Conclusions

This study clarifies the current research status and evolution of research in the field of RIF. New therapeutic interventions designed to improve pregnancy outcomes are the focus of current research and are expected to dominate future research in the field of RIF.

Integrated Analysis of Multiple Microarrays Based on Raw Data Identified Novel Gene Signatures in Recurrent Implantation Failure

BACKGROUND

Recurrent implantation failure (RIF) is an intricate complication following IVF-ET, which refers to the situation that good-quality embryos repeatedly fail to implant following two or more IVF cycles. Intrinsic molecular mechanisms underlying RIF have not yet been fully elucidated. With enormous improvement in high-throughput technologies, researchers screened biomarkers for RIF using microarray. However, the findings of published studies are inconsistent. An integrated study on the endometrial molecular determinants of implantation will help to improve pregnancy outcomes.

OBJECTIVE

To identify robust differentially expressed genes (DEGs) and hub genes in endometrium associated with RIF, and to investigate the diagnostic role of hub genes in RIF.

METHODS

Raw data from five GEO microarrays regarding RIF were analyzed. Integrated genetic expression analyses were performed using the Robust Rank Aggregation method to identify robust DEGs. Enrichment analysis and protein-protein interaction (PPI) analysis were further performed with the robust DEGs. Cytohubba was used to screen hub genes based on the PPI network. GSE111974 was used to validate the expression and diagnostic role of hub genes in RIF.

RESULTS

1532 Robust DEGs were identified by integrating four GEO datasets. Enrichment analysis showed that the robust DEGs were mainly enriched in processes associated with extracellular matrix remodeling, adhesion, coagulation, and immunity. A total of 18 hub genes (HMGCS1, SQLE, ESR1, LAMC1, HOXB4, PIP5K1B, GNG11, GPX3, PAX2, TF, ALDH6A1, IDH1, SALL1, EYA1, TAGLN, TPD52L1, ST6GALNAC1, NNMT) were identified. 10 of the 18 hub genes were significantly differentially expressed in RIF patients as validated by GSE111974. The 10 hub genes (SQLE, LAMC1, HOXB4, PIP5K1B, PAX2, ALDH6A1, SALL1, EYA1, TAGLN, ST6GALNAC1) were effective in predicting RIF with an accuracy rate of 85%, specificity rate of 100%, and sensitivity rate of 88.9%.

CONCLUSIONS

Our integrated analysis identified novel robust DEGs and hub genes in RIF. The hub genes were effective in predicting RIF and will contribute to the understanding of comprehensive molecular mechanisms in RIF pathogenesis.

MicroRNA signatures in plasma and plasma exosome during window of implantation for implantation failure following in-vitro fertilization and embryo transfer

BACKGROUND

MicroRNAs (miRNAs) are small, non-coding RNAs that are dysregulated in many diseases and can act as biomarkers. Although well-studied in cancer, the role of miRNAs in embryo implantation is poorly understood. Approximately 70% of embryos fail to implant following in-vitro fertilization and embryo transfer, 10% of patients experienced recurrent implantation failure. However, there are no well-established biomarkers that can predict implantation failure. Our purpose is to investigate distinct miRNA profiles in plasma and plasma exosomes during the window of implantation between patients with failed implantation and successful implantation.

METHODS

We select a nested case-control population of 12 patients with implantation failure or successfully clinical pregnancy using propensity score matching. RNA was extracted from plasma and plasma exosomes collected during the window of implantation (WOI). MicroRNA expression in all samples was quantified using microRNA sequencing. The intersection of differently expressed miRNAs in plasma and exosomes were further validated in the GEO dataset. Significantly altered microRNAs in both plasma and plasma exosomes were then subjected to target prediction and KEGG pathway enrichment analyses to search for key signaling pathways. WGCNA analysis was performed to identify hub miRNAs associated with implantation.

RESULTS

13 miRNAs were differentially expressed in both plasma and plasma exosomes in patients with implantation failure. Among them, miR-150-5p, miR-150-3p, miR-149-5p, and miR-146b-3p had consistent direction changes in endometrium of patients with recurrent implantation failure (RIF), miR-342-3p had consistent direction changes in blood samples of patients with RIF. Pathway enrichment analysis showed that the target genes of differentially expressed miRNAs are enriched in pathways related to embryo implantation. WGCNA analysis indicated that miR-150-5p, miR-150-3p, miR-146b-3p, and miR-342-3p are hub miRNAs.

CONCLUSIONS

Implantation failure is associated with distinct miRNA profiles in plasma and plasma exosomes during WOI.

The Complicated Effects of Extracellular Vesicles and Their Cargos on Embryo Implantation

As a rate-limiting step in pregnancy, embryo implantation is highly dependent on intercellular communication. Extracellular vesicles (EVs) are newly identified to be important in the course of intercellular communication. EVs have been isolated from a wide variety of biofluids and tissues, including plasma, liver, uterine, semen, embryo, etc. The present and future use of EVs not only as biomarkers, but also as targeting drug delivery system, is promisingly pave the way for advanced comprehension of implantation failure in reproductive diseases. However, as the precise mechanisms of EVs in embryo implantation has not been elucidated yet. Herein, we summarize the current knowledge on the diverse effects of EVs from various sources and their cargos such as microRNA, long non-coding RNA, protein, etc. on embryo implantation, and the potential mechanisms of EVs in reproductive diseases such as recurrent implantation failure, polycystic ovary syndrome and endometriosis. It is essential to note that many of the biologically plausible functions of EVs in embryo implantation discussed in present literatures still need further research in vivo.