MicroRNA Expression in Bovine Cumulus Cells in Relation to Oocyte Quality

Role of miRNAs in assisted reproductive technology

Cellular proteins and the mRNAs that encode them are key factors in oocyte and sperm development, and the mechanisms that regulate their translation and degradation play an important role during early embryogenesis. There is abundant evidence that expression of microRNAs (miRNAs) is crucial for embryo development and are highly involved in regulating translation during oocyte and early embryo development. MiRNAs are a group of short (18-24 nucleotides) non-coding RNA molecules that regulate post-transcriptional gene silencing. The miRNAs are secreted outside the cell by embryos during preimplantation embryo development. Understanding regulatory mechanisms involving miRNAs during gametogenesis and embryogenesis will provide insights into molecular pathways active during gamete formation and early embryo development. This review summarizes recent findings regarding multiple roles of miRNAs in molecular signaling, plus their transport during gametogenesis and embryo preimplantation.

Transcriptomic Analysis and Finding of Potential Key mRNA Expression Profile in Human Cumulus Cells During in Vitro Culture and Different Passages Based on Integrated Bioinformatics Analysis

This study leveraged microarray datasets to investigate differentially expressed genes (DEGs) in cumulus cells and their relevance in predicting the successful implantation of embryos in human in-vitro fertilization procedures. The microarray data were obtained from the GEO database, encompassing samples of cumulus cells during in vitro culture and different passages. To ensure data consistency, inter-batch normalization was performed, and Principal Component Analysis (PCA) was applied to assess the impact of normalization on sample group clustering. The integrated dataset included samples from cumulus cells during in vitro culture, comprising 17,662 genes. Utilizing the "limma" software package, 1906 DEGs were identified, with 437 genes downregulated and 589 genes upregulated in the cumulus cells of infertility cases, while 748 genes were upregulated, and 1317 genes were downregulated in cumulus cells of successful implantation cases. Functional enrichment analysis utilized Gene Ontology, Metascape, and Kyoto Encyclopedia of Genes and Genomes pathway enrichment tools. Biological processes and molecular functions were enriched, including protein targeting, mRNA processing, and molecular binding among the identified DEGs. Furthermore, target prediction and functional enrichment analysis of microRNAs (miRNAs) revealed 25 key genes and 13 relevant miRNAs were identified. Notably, hsa-miR-149, hsa-miR23b, hsa-miR-877, hsa-miR593, hsa-miR-18a, hsa-miR25, hsa-miR185, mmu-miR-207, hsa-miR425, hsa-miR214, hsa-miR-129, hsa-miR-629, and hsa-miR-194 emerged as the most prominent miRNAs with potential regulatory roles in successful embryo implantation. This comprehensive analysis provides valuable insights into the molecular mechanisms underlying embryo implantation, offering potential targets for further research and therapeutic interventions in assisted reproductive technologies.

miRNA expression profiles of peripheral white blood cells from beef heifers with varying reproductive potential

Reproductive performance is the most critical factor affecting production efficiency in the cow-calf industry. Heifers with low reproductive efficiency may fail to become pregnant during the breeding season or maintain a pregnancy. The cause of reproductive failure often remains unknown, and the non-pregnant heifers are not identified until several weeks after the breeding season. Therefore, improving heifer fertility utilizing genomic information has become increasingly important. One approach is using microRNAs (miRNA) in the maternal blood that play an important role in regulating the target genes underlying pregnancy success and thereby in selecting reproductively efficient heifers. Therefore, the current study hypothesized that miRNA expression profiles from peripheral white blood cells (PWBC) at weaning could predict the future reproductive outcome of beef heifers. To this end, we measured the miRNA profiles using small RNA-sequencing in Angus-Simmental crossbred heifers sampled at weaning and retrospectively classified as fertile (FH, n = 7) or subfertile (SFH, n = 7). In addition to differentially expressed miRNAs (DEMIs), their target genes were predicted from TargetScan. The PWBC gene expression from the same heifers were retrieved and co-expression networks were constructed between DEMIs and their target genes. We identified 16 differentially expressed miRNAs between the groups (p-value ≤0.05 and absolute (log2 fold change ≥0.05)). Interestingly, based on a strong negative correlation identified from miRNA-gene network analysis with PCIT (partial correlation and information theory), we identified miRNA-target genes in the SFH group. Additionally, TargetScan predictions and differential expression analysis identified bta-miR-1839 with ESR1 , bta-miR-92b with KLF4 and KAT2B, bta-miR-2419-5p with LILRA4, bta-miR-1260b with UBE2E1, SKAP2 and CLEC4D, and bta-let-7a-5p with GATM, MXD1 as miRNA-gene targets. The miRNA-target gene pairs in the FH group are over-represented for MAPK, ErbB, HIF-1, FoxO, p53, mTOR, T-cell receptor, insulin and GnRH signaling pathways, while those in the SFH group include cell cycle, p53 signaling pathway and apoptosis. Some miRNAs, miRNA-target genes and regulated pathways identified in this study have a potential role in fertility; other targets are identified as novel and need to be validated in a bigger cohort that could help to predict the future reproductive outcomes of beef heifers.

Evaluation of the potential of miR-21 as a diagnostic marker for oocyte maturity and embryo quality in women undergoing ICSI

MicroRNAs are small molecules that play a crucial role in regulating a woman's reproductive system. The present study evaluates the expression of miR-21 in the serum, follicular fluid (FF), and cumulus cells (CCs) and their association with oocyte maturity and embryo quality in women undergoing intracytoplasmic sperm injection. Women subjects were divided into the case (54 Patients with female factor infertility) and control groups (33 patients with male factor infertility). The level of miR-21 was measured using Real-Time PCR. The level of miR-21 was significantly lower in the CCs, FF, and serum in the case compared to the control group (p < 0.05). MiR-21 abundance was higher in FF and CCs samples than in serum. Furthermore, there was a significant increase in CCs to FF in the case group (p < 0.05). A significant decrease in oocyte count, MII oocytes, and percentage of mature oocytes were observed in the case group (p < 0.05). The expression of miR-21 in FF and CCs was positively related to oocyte maturation, but no correlation with embryo development was observed. This study found that miR-21 is expressed less in women with female factor infertility, and human oocytes' development is crucially affected by the expression of miR-21. Therefore, miR-21 could provide new helpful biomarkers of oocyte maturity.

BPA Decreases PDCD4 in Bovine Granulosa Cells Independently of miR-21 Inhibition

microRNAs (miRNAs) are susceptible to environmental factors that might affect cellular function and impose negative effects on female reproduction. miR-21 is the most abundant miRNA in bovine granulosa cells and is widely reported as affected by Bisphenol A (BPA) exposure, yet the cause and consequences are not entirely elucidated. BPA is a synthetic endocrine disruptor associated with poor fertility. miR-21 function in bovine granulosa cells is investigated utilizing locked nucleic acid (LNA) oligonucleotides to suppress miR-21. Before measuring apoptosis and quantifying miR-21 apoptotic targets PDCD4 and PTEN, transfection was optimized and validated. BPA was introduced to see how it affects miR-21 regulation and which BPA-mediated effects are influenced by miR-21. miR-21 knockdown and specificity against additional miRNAs were confirmed. miR-21 was found to have antiapoptotic effects, which could be explained by its effect on the proapoptotic target PDCD4, but not PTEN. Previous findings of miR-21 overexpression were validated using BPA treatments, and the temporal influence of BPA on miR-21 levels was addressed. Finally, BPA effects on upstream regulators, such as VMP1 and STAT3, explain the BPA-dependent upregulation of miR-21 expression. Overall, this research enhances our understanding of miR-21 function in granulosa cells and the mechanisms of BPA-induced reproductive impairment.

MicroRNA-21 is involved in oocyte maturation, blastocyst formation, and pre-implantation embryo development

Follicular fluid is one source of microRNAs (miRNAs). These miRNAs originate from oocytes and their neighboring cells. The changes in the miRNAs profile in the follicular fluid could alter folliculogenesis and oocyte maturation, and lead to infertility. Polycystic ovary syndrome (PCOS) patients have increased miR-21 levels in their sera, granulosa cells, and follicular fluid, and this mi-RNA plays a role in the pathophysiology and follicular dysfunction of PCOS patients. In the current study, we intend to examine whether expression levels of miR-21 influence oocyte maturation and embryo development. We examined miR-21 over-expression and down-regulation of miR-21 by miR-off 21 during in vitro maturation (IVM) to assess its influence on oocyte maturation and embryo development in mice. Over-expression of miR-21 in cumulus cells decreased expansion, meiotic progression, Glutathione-S-transferase GSH levels, and decreased expressions of Bmpr2 and Ptx3 genes. Subsequently, we noted that in vitro fertilization, and the cleavage rate and blastocyst formation significantly increased in cumulus oocyte complexes (COCs) that over-expressed miR-21. Inhibition of miR-21 by miR-off 21 led to increased cumulus expansion and GSH levels, along with decreased cleavage rate and blastocyst formation by alterations in Cdk2ap1 and Oct4 gene expressions. However, oocyte progression from the germinal vesicle (GV) to the metaphase II (MII) stage was not significant. miR-21 altered the gene expression levels in cumulus cells and influenced cytoplasmic oocyte maturation, cumulus expansion, and subsequent embryonic development in mice.

Murine Blastocysts Release Mature MicroRNAs Into Culture Media That Reflect Developmental Status

Extracellular microRNA (miRNA) sequences derived from the pre-implantation embryo have attracted interest for their possible contributions to the ongoing embryonic-uterine milieu, as well as their potential for use as accessible biomarkers indicative of embryonic health. Spent culture media microdroplets used to culture late-stage E4.0 murine blastocysts were screened for 641 mature miRNA sequences using a reverse transcription-quantitative polymerase chain reaction-based array. We report here 39 miRNAs exclusively detected in the conditioned media, including the implantation-relevant miR-126a-3p, miR-101a, miR-143, and miR-320, in addition to members of the highly expressed embryonic miR-125 and miR-290 families. Based on these results, an miRNA panel was assembled comprising five members of the miR-290 family (miR-291-295) and five conserved sequences with significance to the embryonic secretome (miR-20a, miR-30c, miR-142-3p, miR-191, and miR-320). Panel profiling of developing embryo cohort lysates and accompanying conditioned media microdroplets revealed extensive similarities in relative quantities of miRNAs and, as a biomarker proof of concept, enabled distinction between media conditioned with differently staged embryos (zygote, 4-cell, and blastocyst). When used to assess media conditioned with embryos of varying degrees of degeneration, the panel revealed increases in all extracellular panel sequences, suggesting cell death is an influential and identifiable factor detectable by this assessment. In situ hybridization of three panel sequences (miR-30c, miR-294, and miR-295) in late-stage blastocysts revealed primarily inner cell mass expression with a significant presence of miR-294 throughout the blastocyst cavity. Furthermore, extracellular miR-290 sequences responded significantly to high centrifugal force, suggesting a substantial fraction of these sequences may exist within a vesicle such as an exosome, microvesicle, or apoptotic bleb. Together, these results support the use of extracellular miRNA to assess embryonic health and enable development of a non-invasive viability diagnostic tool for clinical use.

In vitro maturation in the presence of Leukemia Inhibitory Factor modulates gene and miRNA expression in bovine oocytes and embryos

Members of the interleukin-6 (IL-6) family of cytokines are important for reproductive function that are mediated through changes in gene and miRNA expression. Herein, we characterized the expression of miR-21, miR-155, miR-34c and miR-146a in bovine oocytes and cumulus cells during in vitro maturation (IVM) with leukemia inhibitory factor (LIF), IL-6 and IL-11 or unsupplemented controls. LIF-exposed COCs showed higher expression of miR-21 and miR-155 in oocytes, whereas miR-146a expression was increased in oocytes matured with IL-6 and IL-11. In cumulus cells, miR-155 expression was elevated by all treatments while only LIF increased miR-21 expression. Based on these results, we next examined how LIF exposure during IVM affected oocyte competence, through IVF and the expression of specific genes in GV- and MII-oocytes, in 2- and 8-cell embryos, and in Day 8-blastocysts. LIF supplementation did not affect cleavage rate, blastocyst yield or several other developmental parameters, but did increase hatching rate. LIF suppressed DPPA3, ZAR1 and NPM2 expression in 2 cell- and/or 8-cell embryos. LIF increased the expression of KAT2A and HSPA1A in MII-oocytes, and that of HDAC1, KAT2A and HSP90AA1 and the BAX:BCL2L1 ratio in 2-cell embryos. In contrast, HDAC1, KAT2A and HSP90AA1 expression and BAX:BCL2L1 ratio was lower in 8-cell embryos derived from LIF oocytes. IVM with LIF also increased the expression of DNMT3A, HSPA1A and HSP90AA1 in blastocysts. In conclusion, supplementation with LIF during IVM was consistently associated with changes in the relative abundance of transcripts in mature bovine oocytes and in specific embryo developmental stages.

Raman spectroscopy-based approach to study the female gamete

In the last years, an increasing interest has emerged on the development of new non-invasive methods for the assessment of oocyte quality in order to improve outcomes of assisted reproductive technologies (ARTs) either in medical or veterinary fields. Raman microspectroscopy (RMS) has been proposed as a promising tool for the examination of the mammalian female gamete and identification of markers of its developmental competence. This technique provides a unique spectral fingerprint indicative of molecular composition of the cell and allows probing subcellular compartments. Studies have been carried out analysing by RMS fixed or living oocytes derived from different animal models. RMS imaging has been successfully applied to discriminate the biochemical changes of the global molecular architecture of mouse oocytes at different stages of maturation and those occurring in different conditions of maturation and oocyte aging. RMS can also detect modifications of specific structural components, including the oocyte zona pellucida and F-actin subcortical cytoskeleton in fresh sheep oocytes and those underwent to vitrification procedures. Finally, the recent application of Coherent anti-Stokes Raman scattering (CARS) microscopy for examination of oocyte lipid component will be briefly discussed. CARS overcomes some limits of RMS providing vibrational and spectral information with higher sensitivity, spatial resolution which is ideal to study living oocytes. This review summarizes the research on RMS approaches for oocyte evaluation showing the high potential use, current limitations and new improvements.

Bovine herpesvirus 1 can impact the bovine oocyte development during in vitro maturation

Bovine herpesvirus 1 (BoHV-1) disseminates easily, is difficult to control, and is widely spread in cattle herds worldwide. BoHV-1 causes a broad range of losses to the cattle industry, mainly concerning reproduction. Previous studies involving experimental infection of BoHV-1 in an in vitro embryo production system have reported impairment of embryonic development by BoHV-1. In this study, we evaluated the interference of BoHV-1 in the in vitro maturation system of cumulus-oocyte complexes (COCs) and denuded oocytes (DOs) cultured with a cumulus cell suspension. Blood samples and ovaries were collected from slaughterhouse cows unvaccinated against BoHV-1. Using virus neutralization assays, the seropositive animals were classified according to their antibody titers. The oocytes were recovered by follicular aspiration and divided into two groups, COCs and DOs, which were evaluated for their nuclear maturation capacity using immunofluorescence assays by laser scanning confocal microscopy. Two experiments were carried out: (I) in vitro maturation of COCs and DOs after artificial infection of seronegative animals and (II) in vitro maturation of COCs and DOs of seropositive animals. In experiment I, a difference (P < 0.01) was observed between the maturation rates of the control group COCs (78.2%) and the infected COCs (43.6%). In experiment II, there was a difference (P < 0.01) in the maturation rate between animals with antibody titers ≥16 (56.9%) and the control group (79.4%). Immunofluorescence assays identified BoHV-1 in the COCs and DOs. Therefore, it was concluded that BoHV-1 affects the in vitro maturation process in both in vitro and natural infections.

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.

STAT3 signaling stimulates miR-21 expression in bovine cumulus cells during in vitro oocyte maturation

MicroRNAs are potent regulators of gene expression that have been widely implicated in reproduction and embryo development. Recent studies have demonstrated that miR-21, a microRNA extensively studied in the context of disease, is important in multiple facets of reproductive biology including folliculogenesis, ovulation, oocyte maturation and early mammalian development. Surprisingly, little is known about the mechanisms that regulate miR-21 and no studies have characterized these regulatory pathways in cumulus-oocyte complexes (COCs). We therefore investigated miR-21 in an in vitro model of bovine oocyte maturation. Levels of the primary transcript of miR-21 (pri-miR-21) and mature miR-21 increased markedly in COCs over the maturation period. Cloning of the bovine pri-miR-21 gene and promoter by 5′3′RACE (rapid amplification of cDNA ends) revealed a highly conserved region immediately upstream of the transcription start site and two alternatively-spliced variants of pri-miR-21. The promoter region contained several putative transcription factor binding sites, including two for signal transducer and activator of transcription 3 (STAT3). Mutation of these sites significantly decreased both the intrinsic activity of pri-miR-21 promoter-luciferase constructs and the response to leukemia inhibitory factor (LIF) (a STAT3 activator) in cultured MCF7 cells. In COCs, treatment with a STAT3 pathway inhibitor markedly decreased pri-miR-21 expression and prevented cumulus expansion. Pri-miR-21 expression was also inhibited by the protein synthesis inhibitor cycloheximide, suggesting that a protein ligand or signaling cofactor synthesized during maturation is necessary for transcription. Together these studies represent the first investigation of signaling pathways that directly influence miR-21 expression in bovine oocytes and cumulus cells.