Mmu-microRNA-200a overexpression leads to implantation defect by targeting phosphatase and tensin homolog in mouse uterus

Decreased expression of miR-200a and miR-223-3p in endometriosis during the secretory phase of menstrual cycle: Insights from a case-control study on molecular biomarkers and disease-related infertility

Background

Endometriosis (EM) is a condition that causes infertility with decreasing uterine receptivity. It is reported that it affects about 20-25% of all infertile women. Some genetic markers play a crucial role in pathogenesis and infertility.

Objective

This study investigates the role of miR-200a and miR-223-3p in embryo implantation and their association with EM-related infertility.

Materials and Methods

In this case-control study, 36 women who referred to the Center for Research on Reproductive Health and Infertility of Babol University of Medical Sciences and Fatemeh Al-Zahra Infertility Specialized Treatment Center in Babol, Iran between June 2022 and July 2023 were evaluated. Participants were divided into 2 EM and control groups (n = 18/each). Endometrial samples were collected from participants between 17  th and 24  th days of their menstrual cycle. Histopathological examination (hematoxylin and eosin and periodic acid schiff) was performed to confirm the secretory stage, and miR-200a and miR-223-3p expressions were analyzed by quantitative reverse transcriptase-polymerase chain reaction.

Results

Histological analysis confirmed that both groups were in the secretory stage. Additionally, miRNA expression results showed a significant decrease in the miR-200a and miR-223-3p expression levels in EM group compared to control group. The expression level of miR-223-3p and miR-200a in the eutopic endometrial tissue of women with EM was notably lower than those in the control group.

Conclusion

Our results suggest that miR-200a and miR-223-3p are involved in the EM pathogenesis, while other genes and signaling pathways are probably involved in the implantation failure.

Dysregulated miR-124-3p in endometrial epithelial cells reduces endometrial receptivity by altering polarity and adhesion

The endometrium undergoes substantial remodeling in each menstrual cycle to become receptive to an implanting embryo. Abnormal endometrial receptivity is one of the major causes of embryo implantation failure and infertility. MicroRNA-124-3p is elevated in both the serum and endometrial tissue of women with chronic endometritis, a condition associated with infertility. MicroRNA-124-3p also has a role in cell adhesion, a key function during receptivity to allow blastocysts to adhere and implant. In this study, we aimed to determine the function of microRNA-124-3p on endometrial epithelial adhesive capacity during receptivity and effect on embryo implantation. Using a unique inducible, uterine epithelial-specific microRNA overexpression mouse model, we demonstrated that elevated uterine epithelial microRNA-124-3p impaired endometrial receptivity by altering genes associated with cell adhesion and polarity. This resulted in embryo implantation failure. Similarly in a second mouse model, increasing microRNA-124-3p expression only in mouse uterine surface (luminal) epithelium impaired receptivity and led to implantation failure. In humans, we demonstrated that microRNA-124-3p was abnormally increased in the endometrial epithelium of women with unexplained infertility during the receptive window. MicroRNA-124-3p overexpression in primary human endometrial epithelial cells (HEECs) impaired primary human embryo trophectoderm attachment in a 3-dimensional culture model of endometrium. Reduction of microRNA-124-3p in HEECs from infertile women normalized HEEC adhesive capacity. Overexpression of microRNA-124-3p or knockdown of its direct target IQGAP1 reduced fertile HEEC adhesion and its ability to lose polarity. Collectively, our data highlight that microRNA-124-3p and its protein targets contribute to endometrial receptivity by altering cell polarity and adhesion.

Transcriptomic Analysis of Vitrified-Warmed vs. Fresh Mouse Blastocysts: Cryo-Induced Physiological Mechanisms and Implantation Impact

Blastocyst vitrification has significantly improved embryo transfer methods, leading to higher implantation success rates and better pregnancy outcomes in subsequent frozen embryo transfer cycles. This study aimed to simulate the transcriptional changes caused by vitrifying human blastocysts using mouse blastocysts as a model and to further investigate these changes' effects. Utilizing a human vitrification protocol, we implanted both vitrified and fresh embryos into mice. We observed the implantation success rates and performed transcriptomic analysis on the blastocysts. To validate the results from messenger RNA sequencing, we conducted reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) to measure the expression levels of specific genes. Based on mRNA profiling, we predicted the microRNAs responsible for the regulation and used qPCR basic microRNA assays for validation. Our observations revealed a higher implantation success rate for vitrified embryos than fresh embryos. Transcriptomic analysis showed that vitrified-warmed blastocysts exhibited differentially expressed genes (DEGs) primarily associated with thermogenesis, chemical carcinogenesis-reactive oxygen species, oxidative phosphorylation, immune response, and MAPK-related signaling pathways. RT-qPCR confirmed increased expression of genes such as Cdk6 and Nfat2, and decreased expression of genes such as Dkk3 and Mapk10. Additionally, gene-microRNA interaction predictions and microRNA expression analysis identified twelve microRNAs with expression patterns consistent with the predicted results, suggesting potential roles in uterine epithelial cell adhesion, trophectoderm development, invasive capacity, and immune responses. Our findings suggest that vitrification induces transcriptomic changes in mouse blastocysts, and even small changes in gene expression can enhance implantation success. These results highlight the importance of understanding the molecular mechanisms underlying vitrification to optimize embryo transfer techniques and improve pregnancy outcomes.

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.

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.

Expression profile of genes related to pregnancy maintenance in Dromedary Camel during the first trimester

So far, few signals involved in embryo-maternal dialogue have been identified in pregnant she-camel. Our objective was to investigate expression profiles of genes relevant to uterine extracellular matrix remodeling (ITGB4, SLCO2A1, FOS, and JUN), uterine tissue vascularization, and placental formation (VEGFA, PGF, and PDGFA), embryonic growth and development (IGF1 and PTEN), plus cell death of uterine tissue (BCL2) in early pregnant versus non-pregnant she-camels. Forty genital tracts (20 pregnant and 20 non-pregnant) and blood samples were collected from abattoirs. Total RNA was extracted from uterine tissues and qRT-PCR was conducted for candidate genes. Serum concentrations of progesterone (P4) and estradiol17-β (E2) were measured. Expression of ITGB4, FOS, and PGF genes increased (P < 0.001) in the right uterine horn of pregnant versus non-pregnant she-camels. Moreover, JUN, SLCO2A1, VEGFA, and PTEN mRNAs were up-regulated (P < 0.001) in various segments of uterine tissues in pregnant groups. The PDGFA transcript was over-expressed (P < 0.001) in both uterine horns of pregnant groups. Additionally, IGF1 was higher (P < 0.001) in the right horn and the uterine body of pregnant groups, and expression of BCL2 was increased (P < 0.001) in the pregnant uterine body. Moreover, serum concentrations of P4 were higher (P < 0.001) and E2 lower (P < 0.05) in pregnant she-camels. Taken together, the fine-tuning of genes related to implantation, matrix formation, vascularization, and placental formation is highly required for successful pregnancy in she-camels.

Investigation of Sperm and Seminal Plasma Candidate MicroRNAs of Bulls with Differing Fertility and In Silico Prediction of miRNA-mRNA Interaction Network of Reproductive Function

Simple Summary

The objective of this study was to identify differentially expressed (DE) sperm and seminal plasma microRNAs (miRNAs) in high- and low-fertile Holstein bulls (four bulls per group), integrate miRNAs to their target genes, and categorize target genes based on predicted biological processes. Out of 84 bovine-specific, prioritized miRNAs analyzed by RT-PCR, 30 were differentially expressed in high-fertile sperm and seminal plasma compared to low-fertile sperm and seminal plasma, respectively (p ≤ 0.05, fold regulation ≥5 magnitudes). Interestingly, expression levels of DE-miRNAs in sperm and seminal plasma followed a similar pattern. Highly scored integrated genes of DE-miRNAs predicted various biological and molecular functions, cellular process, and pathways. Further in silico analysis revealed categorized genes may have a plausible association with pathways regulating sperm structure and function, fertilization, and embryo and placental development. In conclusion, highly DE-miRNAs in bovine sperm and seminal plasma could be used as a tool for predicting reproductive functions. Since the identified miRNA-mRNA interactions were mostly based on predictions from public databases, the causal regulations of miRNA-mRNA and the underlying mechanisms require further functional characterization in future studies.

Abstract

Recent advances in high-throughput in silico techniques portray experimental data as exemplified biological networks and help us understand the role of individual proteins, interactions, and their biological functions. The objective of this study was to identify differentially expressed (DE) sperm and seminal plasma microRNAs (miRNAs) in high- and low-fertile Holstein bulls (four bulls per group), integrate miRNAs to their target genes, and categorize the target genes based on biological process predictions. Out of 84 bovine-specific, prioritized miRNAs analyzed by RT-PCR, 30 were differentially expressed in high-fertile sperm and seminal plasma compared to low-fertile sperm and seminal plasma, respectively (p ≤ 0.05, fold regulation ≥ 5 magnitudes). The expression levels of DE-miRNAs in sperm and seminal plasma followed a similar pattern. Highly scored integrated genes of DE-miRNAs predicted various biological and molecular functions, cellular process, and pathways. Further, analysis of the categorized genes showed association with pathways regulating sperm structure and function, fertilization, and embryo and placental development. In conclusion, highly DE-miRNAs in bovine sperm and seminal plasma could be used as a tool for predicting reproductive functions. Since the identified miRNA-mRNA interactions were mostly based on predictions from public databases, the causal regulations of miRNA-mRNA and the underlying mechanisms require further functional characterization in future studies.

MicroRNAs in the Regulation of Endometrial Receptivity for Embryo Implantation

Development of endometrial receptivity is crucial for successful embryo implantation and pregnancy initiation. Understanding the molecular regulation underpinning endometrial transformation to a receptive state is key to improving implantation rates in fertility treatments such as IVF. With microRNAs (miRNAs) increasingly recognized as important gene regulators, recent studies have investigated the role of miRNAs in the endometrium. Studies on miRNAs in endometrial disorders such as endometriosis and endometrial cancer have been reviewed previously. In this minireview, we aim to provide an up-to-date knowledge of miRNAs in the regulation of endometrial receptivity. Since endometrial remodelling differs considerably between species, we firstly summarised the key events of the endometrial cycle in humans and mice and then reviewed the miRNAs identified so far in these two species with likely functional significance in receptivity establishment. To date, 29 miRNAs have been reported in humans and 15 miRNAs in mice within various compartments of the endometrium that may potentially modulate receptivity; miRNAs regulating the Wnt signalling and those from the let-7, miR-23, miR-30, miR-200 and miR-183 families are found in both species. Future studies are warranted to investigate miRNAs as biomarkers and/or therapeutic targets to detect/improve endometrial receptivity in human fertility treatment.

Differential Expression Pattern of Goat Uterine Fluids Extracellular Vesicles miRNAs during Peri-Implantation

Early pregnancy failure occurs when a mature embryo attaches to an unreceptive endometrium. During the formation of a receptive endometrium, extracellular vesicles (EVs) of the uterine fluids (UFs) deliver regulatory molecules such as small RNAs to mediate intrauterine communication between the embryo and the endometrium. However, profiling of small RNAs in goat UFs’ EVs during pregnancy recognition (day 16) has not been carried out. In this study, EVs were isolated from UFs on day 16 of the estrous cycle or gestation. They were isolated by Optiprep™ Density G radient (ODG) and verified by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blotting. Immunostaining demonstrated that CD63 was present both in the endometrial epithelium and glandular epithelium, and stain intensity was greater in the pregnant endometrium compared to the non-pregnant endometrium. Small RNA sequencing revealed that UFs’ EVs contained numerous sRNA families and a total of 106 differentially expressed miRNAs (DEMs). Additionally, 1867 target genes of the DEMs were obtained, and miRNA–mRNA interaction networks were constructed. GO and KEGG analysis showed that miRNAs were significantly associated with the formation of a receptive endometrium and embryo implantation. In addition, the fluorescence in situ hybridization assay (FISH) showed that chi-miR-451-5p was mainly expressed in stromal cells of the endometrium and a higher level was detected in the endometrial luminal epithelium in pregnant states. Moreover, the dual-luciferase reporter assay showed that chi-miR-451-5p directly binds to PSMB8 and may play an important role in the formation of a receptive endometrium and embryo implantation. In conclusion, these results reveal that UFs’ EVs contain various small RNAs that may be vital in the formation of a receptive endometrium and embryo implantation.

Endometrial Liquid Biopsy Provides a miRNA Roadmap of the Secretory Phase of the Human Endometrium

CONTEXT

Endometrial liquid biopsy (ELB) is a minimally invasive alternative for research and diagnosis in endometrial biology.

OBJECTIVE

We sought to establish an endometrial micro ribonucleic acid (miRNA) roadmap based on ELB during the secretory phase of the menstrual cycle in both natural and hormonal replacement therapy (HRT) cycles.

DESIGN

Human ELB samples (n = 58) were obtained from healthy ovum donors undergoing a natural and an HRT cycle consecutively. miRNA profiles were identified using next-generation sequencing (NGS). For functional analysis, messenger ribonucleic acid targets were chosen among those reported in the endometrial receptivity analysis.

RESULTS

The human endometrial secretory phase is characterized by a dynamic miRNA secretion pattern that varies from the prereceptive to the receptive stages. No differences in miRNA profiles were found among natural versus HRT cycles in the same women, reinforcing the similarities in functional and clinical outcomes in natural versus medicated cycles. Bioinformatic analysis revealed 62 validated interactions and 81 predicted interactions of miRNAs differentially expressed in the HRT cycle. Annotation of these genes linked them to 51 different pathways involved in endometrial receptivity.

CONCLUSION

This NGS-based study describes the miRNA signature in human ELB during the secretory phase of natural and HRT cycles. A consistent endometrial miRNA signature was observed in the acquisition of endometrial receptivity. Interestingly, no significant differences in miRNA expression were found in natural versus HRT cycles reinforcing the functional clinical similarities between both approaches.

The Role of MicroRNAs in Mammalian Fertility: From Gametogenesis to Embryo Implantation

The genetic codes inscribed during two key developmental processes, namely gametogenesis and embryogenesis, are believed to determine subsequent development and survival of adult life. Once the embryo is formed, its further development mainly depends on its intrinsic characteristics, maternal environment (the endometrial receptivity), and the embryo–maternal interactions established during each phase of development. These developmental processes are under strict genetic regulation that could be manifested temporally and spatially depending on the physiological and developmental status of the cell. MicroRNAs (miRNAs), one of the small non-coding classes of RNAs, approximately 19–22 nucleotides in length, are one of the candidates for post-transcriptional developmental regulators. These tiny non-coding RNAs are expressed in ovarian tissue, granulosa cells, testis, oocytes, follicular fluid, and embryos and are implicated in diverse biological processes such as cell-to-cell communication. Moreover, accumulated evidences have also highlighted that miRNAs can be released into the extracellular environment through different mechanisms facilitating intercellular communication. Therefore, understanding miRNAs mediated regulatory mechanisms during gametogenesis and embryogenesis provides further insights about the molecular mechanisms underlying oocyte/sperm formation, early embryo development, and implantation. Thus, this review highlights the role of miRNAs in mammalian gametogenesis and embryogenesis and summarizes recent findings about miRNA-mediated post-transcriptional regulatory mechanisms occurring during early mammalian development.

Administration of dexamethasone disrupts endometrial receptivity by alteration of expression of miRNA 223, 200a, LIF, Muc1, SGK1, and ENaC via the ERK1/2-mTOR pathway

Successful implantation of embryos requires endometrial receptivity. Glucocorticoids are one of the factors influencing the implantation window. In this study, 40 female BALB/c mice were used to study the impacts of dexamethasone administration on endometrial receptivity markers during implantation window. The mice mated and were randomly divided into four groups: control (vehicle), dexamethasone (100 μg/kg, IP), PP242 (30 mg/kg, IP), and dexamethasone + PP242 (Dex + PP242). On the Day 4th and 5th of gestation, mice received their respective treatments and were killed on the 5th day. To assess the expression of Muc1, leukemia inflammatory inhibitor (LIF), serum/glucocorticoid-inducible kinase 1 (SGK1), epithelial Na+ channel (ENaC), miRNA 200a, and miRNA 223-3p in the endometrium real-time polymerase chain reaction was performed. Furthermore, using Western blot analysis protein expressions of extracellular signal-regulated kinase 1/2 (ERK1/2), mammalian target of rapamycin (mTOR), and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) were evaluated. Periodic Acid-Schiff staining was used to examine the histomorphological changes of the uterus. According to the results dexamethasone declined the expression of LIF, whereas upregulated expression of Muc1, SGK1, ENaC mRNA, miRNA 200a, and miRNA 223-3p in the endometrium. In addition, PP242, an mTOR inhibitor, induced mRNA expression of Muc1, miRNA200a, and miRNa223-3p whereas it declined the expression of LIF. Moreover, activity of the ERK1/2-mTOR pathway in the endometrial cells was deterred by dexamethasone and PP242. Nonstop epithelium proliferation and elevated surface glycoproteins layer on epithelium of dexamethasone and/or PP242-received groups were divulged through histochemical analysis. According to the above mentioned results, uterine receptivity during implantation period was declined by dexamethasone, at least in part, through modulation of involved genes in endometrial receptivity and inhibition of the ERK1/2-mTOR pathway.

Roles of microRNAs in mammalian reproduction: from the commitment of germ cells to peri-implantation embryos

MicroRNAs (miRNAs) are active regulators of numerous biological and physiological processes including most of the events of mammalian reproduction. Understanding the biological functions of miRNAs in the context of mammalian reproduction will allow a better and comparative understanding of fertility and sterility in male and female mammals. Herein, we summarize recent progress in miRNA‐mediated regulation of mammalian reproduction and highlight the significance of miRNAs in different aspects of mammalian reproduction including the biogenesis of germ cells, the functionality of reproductive organs, and the development of early embryos. Furthermore, we focus on the gene expression regulatory feedback loops involving hormones and miRNA expression to increase our understanding of germ cell commitment and the functioning of reproductive organs. Finally, we discuss the influence of miRNAs on male and female reproductive failure, and provide perspectives for future studies on this topic.

Role of microRNAs in embryo implantation

Failure of embryo implantation is a major limiting factor in early pregnancy and assisted reproduction. Determinants of implantation include the embryo viability, the endometrial receptivity, and embryo-maternal interactions. Multiple molecules are involved in the regulation of implantation, but their specific regulatory mechanisms remain unclear. MicroRNA (miRNA), functioning as the transcriptional regulator of gene expression, has been widely reported to be involved in embryo implantation. Recent studies reveal that miRNAs not only act inside the cells, but also can be released by cells into the extracellular environment through multiple packaging forms, facilitating intercellular communication and providing indicative information associated with physiological and pathological conditions. The discovery of extracellular miRNAs shed new light on implantation studies. MiRNAs provide new mechanisms for embryo-maternal communication. Moreover, they may serve as non-invasive biomarkers for embryo selection and assessment of endometrial receptivity in assisted reproduction, which improves the accuracy of evaluation while reducing the mechanical damage to the tissue. In this review, we discuss the involvement of miRNAs in embryo implantation from several aspects, focusing on the role of extracellular miRNAs and their potential applications in assisted reproductive technologies (ART) to promote fertility efficiency.

Role of the microRNA 181 family in glioma development

MicroRNAs (miRNAs) are small, noncoding regulatory RNAs that regulate protein expression by reducing mRNA stability and/or translation, via base pairing with full or partial sequence‑complementary target mRNAs. Recent evidence indicates that miRNAs have roles as tumor suppressors and oncogenes. The members of the miRNA181 (miR181) family have been reported to be downregulated in early stage human glioma, and to be involved in glioma development. The current study demonstrated that all subtypes of the miRNA 181 family were downregulated at stages of human glioma, including miR181a1, a2, b1, b2, c and d. In the present study, the family members were detected by reverse transcription-quantitative polymerase chain reaction in glioma tissues of different stages. miR181c declined the most in the samples from patients with World Health Organization (WHO) grade I glioma. As glioma development progressed from grade I to IV, the expression of miRN181 family members continued to decline, with miR181b1 exhibiting the fastest decline rate. Furthermore, a lentivirus was used to overexpress miR181c in primary glioma cells; the result indicated that miR181c overexpression was able to significantly inhibit glioma cell proliferation. Thus, miR181 may be a useful biomarker for human glioma at early stages. Detection of the level of miR181 family members may be a potential method for glioma diagnosis, determining the tumor WHO grade and guiding clinical treatment.

Profile of MicroRNA Expression in Endometrial Cell during In Vitro Culture According to Progesterone Concentration

Artificial uterus using endometrium implant can be a novel treatment strategy for infertile women with refractory endometrial dysfunction. At early pregnancy, the function of uterine endometrial cells for the communication between the conceptus of pre-implantation period and maternal reproductive system is essential. MicroRNA (miR) expression profile of endometrial cells according to progesterone, a crucial pregnancy-maintaining hormone, provides important data for in vitro endometrial cell culture strategy that is useful for engineering artificial uteri using endometrial implants. The present study aimed to evaluate the miR expression profile of in vitro cultured endometrial cells under hormonal milieu mimicking early pregnancy period in terms of progesterone concentration. We cultured murine uterine endometrial cells, human uterine endometrial carcinoma cells, and immortalized human uterine endometrial cells using different progesterone concentrations, and analyzed the expression of miRs critical for early pregnancy. The expression of miR-20a, -21, -196a, -199a, and -200a was differently regulated according to progesterone concentration in different endometrial cell lines. The analysis of candidate target genes showed that the expression of phosphatase and tensin homolog, mucin 1 (MUC1), progesterone receptor, transforming growth factor β receptor II, matrix metallopeptidase-9 was up-regulated by progesterone treatment in mouse and human endometrial cell lines. These results indicate that physiological concentration range (10-7 and 10-9 M) of progesterone affect the survival and target gene expression via modulating miR expression. Taken together, progesterone can be a crucial factor in regulating miR expression on in vitro cultured endometrial cells.

Potential role of microRNAs in mammalian female fertility

Since the first evidence for the involvement of microRNAs (miRNAs) in various reproductive processes through conditional knockout of DICER, several studies have been conducted to investigate the expression pattern and role of miRNAs in ovarian follicular development, oocyte maturation, embryo development, embryo-maternal communication, pregnancy establishment and various reproductive diseases. Although advances in sequencing technology have fuelled miRNA studies in mammalian species, the presence of extracellular miRNAs in various biological fluids, including follicular fluid, blood plasma, urine and milk among others, has opened a new door in miRNA research for their use as diagnostic markers. This review presents data related to the identification and expression analysis of cellular miRNA in mammalian female fertility associated with ovarian folliculogenesis, oocyte maturation, preimplantation embryo development and embryo implantation. In addition, the relevance of miRNAs to female reproductive disorders, including polycystic ovary syndrome (PCOS), endometritis and abnormal pregnancies, is discussed for various mammalian species. Most importantly, the mechanism of release and the role of extracellular miRNAs in cell-cell communication and their potential role as non-invasive markers in female fertility are discussed in detail. Understanding this layer of regulation in female reproduction processes will pave the way to understanding the genetic regulation of female fertility in mammalian species.

Expression of mmu-miR-96 in the endometrium during early pregnancy and its regulatory effects on stromal cell apoptosis via Bcl2

Decidualization of endometrial stromal cells is an important feature of implantation and pregnancy. The molecular mechanism underlying decidualization remains unclear, particularly regarding the microRNA (miRNA/miR) regulation of this process. The present study revealed the temporal and spatial distribution of mmu-miR-96 in the mouse uterus during early pregnancy by reverse transcription-quantitative polymerase chain reaction and in situ hybridization. In addition, primary stromal cells were isolated from the mouse uterus and used to explore the role of mmu-miR-96 in decidualization. The results demonstrated that mmu-miR-96 was highly expressed in stromal cells during pregnancy, and was upregulated at implantation sites. In addition, mmu-miR-96 was strongly expressed during decidualization, which indicates that it may serve a role in the decidualization of stromal cells. Based on existing reports, mmu-miR-96 participates in apoptosis; therefore the present study investigated its effects on the apoptosis of primary endometrial stromal cells. The results indicated that overexpression of mmu-miR-96 may induce apoptosis of stromal cells. In further studies regarding the underlying mechanism, the target genes of mmu-miR-96 were screened by bioinformatics analysis, and it was confirmed that B-cell lymphoma 2, an anti-apoptotic gene, was the target of mmu-miR-96, as determined using a reporter gene assay. In conclusion, the present study suggested that mmu-miR-96 participates in the decidualization of endometrial stromal cells in mice, thereby serving a key role in pregnancy.

MicroRNA and Embryo Implantation

PROBLEM

In mammals, implantation involves interactions between an activated blastocyst and a receptive endometrium. There are controversies on the role of microRNAs in preimplantation embryo development. The actions of endometrial microRNAs on implantation are beginning to be understood.

METHOD OF STUDY

Review of literature on microRNAs in preimplantation embryos and endometrium.

RESULTS

Emerging evidence suggests a role of microRNAs in blastocyst activation and implantation. Differential expression of microRNAs is found between receptive and non-receptive endometria. Members of the let-7, miR-200, miR-30 families, and the miR-17-92 clusters are more commonly found to be associated with endometrial receptivity. Experimental studies show that the targets of the differentially expressed microRNAs affect endometrial receptivity, decidualization, and embryo implantation. Free and exosome/microvesicle containing microRNAs have been detected in human and ovine uterine luminal fluid (ULF). They may serve as mediators of embryo-endometrium dialog. Some observations suggest that the microRNAs in ULF may be used as biomarkers in infertility treatment.

CONCLUSION

MicroRNAs in endometrium and blastocysts are involved in the implantation process.

Let-7-mediated suppression of mucin 1 expression in the mouse uterus during embryo implantation

Mucin 1 (Muc1) is an integral transmembrane mucin glycoprotein expressed on the apical surface of most epithelia. It is considered to be a barrier to the regulation of embryo implantation by inhibiting attachment of the embryo to the endometrium. Therefore, loss of Muc1 on the surface of uterine epithelial cells is necessary for embryo implantation. Studies have demonstrated that microRNAs (miRNAs) play a key role in enhancing embryo implantation in mammals. In this study, we investigated the regulatory role of two miRNAs (let-7a and let-7b) on the expression of Muc1 in mouse uteri during implantation. Western blotting indicated that Muc1 expression was highest on day1 of pregnancy and constantly decreased thereafter until day 4. In contrast to Muc1 expression, increased expression of let-7a and let-7b was evident on day 4 of pregnancy as measured by real-time reverse transcription-polymerase chain reaction (real-time RT-PCR). We demonstrated direct binding of let-7a and let-7b to the 3’untranslated region of muc1. Furthermore, Muc1 expression was suppressed after transfection of mouse uterine epithelial cells isolated from day 1 of pregnancy with let-7a and let-7b. In summary, the present study provides evidence that Muc1 is a direct target of let-7a and let-7b. Additionally, the current study suggests that miRNAs are novel targets which can be used to facilitate a successful pregnancy and repair implantation failure.

MicroRNA-429 functions as a regulator of epithelial-mesenchymal transition by targeting Pcdh8 during murine embryo implantation

STUDY QUESTION

What is the role of miR-429 in murine embryo implantation?

SUMMARY ANSWER

miR-429 functions as a suppressor of epithelial-mesenchymal transition (EMT) during the process of embryo implantation by reverse regulation of Pcdh8.

WHAT IS KNOWN ALREADY

MicroRNAs (miRNAs) may serve as promising regulators of embryo implantation. miR-429 was recently found to be down-regulated during embryo implantation period in a microarray analysis.

STUDY DESIGN, SIZE, DURATION

The expression profile of miR-429 was clarified in a series of models, and the target gene was confirmed. The in vivo and in vitro effect of miR-429 on embryo implantation was examined.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pregnancy was produced by natural mating between female C57BL6/J mice and male mice, and a series of models, including pseudopregnancy, delayed implantation and artificial decidualization, were established. The expression profile of miR-429 during the embryo implantation period was clarified in these models. Candidate target genes of miR-429 were predicted by bioinformatic analysis and tested by luciferase activity assay. The in vivo effects of miR-429 on embryo implantation were also examined. The in vitro effects of miR-429 on EMT were studied by examining migratory and invasive capacities by transwell assay and expression profiles of cadherin family members by western blotting and qRT-PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

The expression profile of miR-429 in animal models suggested its down-regulation should be dependent on the presence and status of blastocysts and on endometrial decidualization. The luciferase activity assay showed that Pcdh8, a member of cadherin gene family, was the target gene of miR-429, and miR-429 suppressed the expression of Pcdh8 mRNA and protein. Gain-of-function of miR-429 in vivo resulted in a significant reduction of the number of implantation sites, but had little effect on fertilization. Up-regulation of miR-429 in vitro led to suppression of mesenchymal marker genes Vim, Cdh2, Zeb1 and Zeb2, and activation of epithelial marker gene Cdh1, resulting in suppression of the migratory and invasive capacities of cells. miR-429 also partially abrogated TGF-beta-induced EMT. The dysregulated expression profiles of EMT markers during embryo implantation period could be partially reversed by gain-of-function of miR-429 in vivo.

LIMITATIONS, REASONS FOR CAUTION

The association of miR-429 with other members of the miR-200 family in embryo implantation remains to be determined. The relationship between miR-429 and the cadherin family needs more intensive description and the detailed mechanism of miR-429 in regulating the cadherin family needs to be elucidated.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings indicate that miR-429 plays a major role in embryo implantation as a suppressor of EMT by targeting Pcdh8. This information could contribute to a better understanding of the mechanisms involved in the miRNA-mediated regulation of embryo implantation, and subsequently improve treatments for infertility. The findings are consistent with that from previous research of the other members in miR-200 family in embryo implantation and in the EMT.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by the Natural Science Foundation of China (Grant number: 81170592), and Special Fund from National Excellent Doctoral Dissertation (Grant number: 201079). There was no conflict of interest.

MicroRNA-451 plays a role in murine embryo implantation through targeting Ankrd46, as implicated by a microarray-based analysis

OBJECTIVE

To determine the potential microRNA (miRNA) regulators of embryo implantation, as a continuation of genomic and proteomic research.

DESIGN

Laboratory animal research.

SETTING

University hospital laboratory.

ANIMAL(S)

Adult healthy female C57BL6/J mice (age 6-8 weeks, nonfertile, weighing 18-20 g each).

INTERVENTION(S)

Female mice were mated naturally with fertile males to produce pregnancy. Luminal epithelium was collected by laser-capture microdissection during the implantation period. Mouse models of pseudopregnancy, delayed implantation, and artificial decidualization were established.

MAIN OUTCOME MEASURE(S)

The miRNA profile in luminal epithelium was clarified by microarray analysis and validated by real-time reverse transcription polymerase chain reaction (qRT-PCR) in a series of models. Target genes were predicted and confirmed by luciferase activity assay. The role of miRNA in implantation was examined by loss-of-function and gain-of-function of miRNA in vitro and in vivo.

RESULT(S)

A total of 29 and 15 miRNAs were up- and down-regulated, respectively, during the implantation period; 11 of these miRNAs were validated by qRT-PCR. The profile of miR-451 was clarified in a series of models. A dual-luciferase activity assay showed that Ankrd46 was a target gene of miR-451. Loss-of-function by LV-miR-451 sponge or miR-451 inhibitor led to a reduced number of embryo implantations, but had little effect on fertilization.

CONCLUSION(S)

miR-451 was specifically up-regulated during the implantation period, and it may play a major role in embryo implantation by targeting Ankrd46.

Modeling glands with PTEN deficient cells and microscopic methods for assessing PTEN loss: endometrial cancer as a model

PTEN is an important tumor suppressor gene. Interpreting PTEN deficiency in the appropriate microscopic context of cancer may be important to understand its role in tumor development and progression. This may be particularly relevant in heterogeneous tumors. Here, we discuss the usefulness of 3D cultures in understanding the consequences of PTEN inactivation in tissue architecture. Afterwards, we discuss the role of immunohistochemistry and fluorescent in situ hybridization in assessing PTEN loss in tumors. In this review, endometrial carcinoma is used as a model.

The role of miR-200a in mammalian epithelial cell transformation

Cancer is a multistep disease that begins with malignant cell transformation and frequently culminates in metastasis. MicroRNAs (miRNAs) are small regulatory 21-25 nt RNA molecules and are frequently deregulated in cancer. miR-200a is a member of the miR-200 family, which are known inhibitors of the epithelial-to-mesenchymal transition. As such, the tumor-suppressive role of miR-200a in oncogenesis has been well documented; however, recent studies have found a proliferative role for this miRNA as well as a prometastatic role in the later steps of cancer progression. Little is known about the role of this miRNA in the early stages of cancer, namely, malignant cell transformation. Here, we show that miR-200a alone transforms an immortalized rat epithelial cell line, and miR-200a cooperates with Ras to enhance malignant transformation of an immortalized human epithelial cell line. Furthermore, miR-200a induces cell transformation and tumorigenesis in immunocompromised mice by cooperating with a Ras mutant that activates only the RalGEF effector pathway, but not Ras mutants activating PI3K or Raf effector pathways. This transformative ability is in accordance with miR-200a targeting Fog2 and p53 to activate Akt and directly repress p53 protein levels, respectively. These results demonstrate an oncogenic role for miR-200a and provide a specific cellular context where miR-200a acts as an oncomiR rather than a tumor suppressor by cooperating with an oncogene in malignant cell transformation.

MicroRNA and gynecological reproductive diseases

MicroRNAs (miRNAs) are a class of small non-coding RNAs estimated to regulate the translation of mRNAs in 30% of all genes in animals by inhibiting translation. Aberrant miRNA expression is associated with many human diseases, including gynecological diseases, cancer, inflammatory diseases, and cardiovascular disorders. Abnormal expression of miRNAs has been observed in multiple human reproductive tract diseases including preeclampsia, endometrioid endometrial adenocarcinoma, uterine leiomyomata, ovarian carcinoma, endometriosis, and recurrent pregnancy loss. In the following review, an update of the role of microRNA and gynecological diseases is performed covering, not only impact of microRNA dysregulation in the origin of each disease, but also showing the potential useful diagnostic and therapeutic tool that miRNA may play in these gynecological pathologies.