Compromised global embryonic transcriptome associated with advanced maternal age

Changes in the Transcription of Proliferation- and Apoptosis-Related Genes in Embryos in Women of Different Ages under the Influence of Extracellular Vesicles from Donor Follicular Fluid In Vitro

We studied the influence of extracellular vesicles from the follicular fluid of a young donor on gene expression (MKI67, MYBL2, CCNB1, CCND1, CCNE1, CALM2, BAX, NDRG1, TP53I3, VEGF, VCAN, HAS2, CTSL2, PIBF1, RPL37, PFKP, GPX3, and AQP3) in embryos of women of different ages. According to nanoparticle tracking analysis data, the concentration of extracellular vesicles was 3.75±0.47×1011 particles/ml and the mean particle size was 138.78±9.90 nm. During co-culturing of the follicular fluid extracellular vesicles with blastocysts of young women, we observed significantly increased expression of mRNA for genes CTSL2, CCND1, CCNE1, VEGF and reduced expression of BAX gene mRNA in comparison with embryos in women of late reproductive age. We hypothesized that addition of extracellular vesicles of the oocyte follicular fluid from a young donor to the culture medium of embryos could slow down apoptosis process typical of blastocyst cells in women above 36 years.

Comprehensive bioinformation analysis of differentially expressed genes in recurrent pregnancy loss

Recurrent pregnancy loss (RPL) occurs frequently, and its causes are complex. The aetiology of nearly 50% of RPL cases is still unknown. This study aimed to ascertain differentially expressed genes (DEGs) and pathways by comprehensive bioinformatics analysis. We downloaded the gene expression microarray of GSE165004 from the Gene Expression Omnibus (GEO). Gene ontology (GO) analysis and Kyoto Encyclopaedia of Gene and Genome (KEGG) pathway enrichment analyses were performed on selected genes by using the R Programming Language. A protein-protein interaction (PPI) network was constructed with the Retrieval of Interacting Genes (STRING). Our analysis revealed that 1,869 genes were differentially expressed in RPL and control groups. GO analysis revealed that the interferon type 1 and the glycoprotein-related biological processes played irreplaceable roles, meanwhile KEGG enrichment analysis also revealed that the cAMP signalling pathway and the prolactin signalling pathway played important roles. In the following study, we found that there were many DEGs in the RPL group that were closely related to endometrial decidualization, such as IL17RD, IL16, SOX4, CREBBP, and POFUT1 as well as Notch1 and RBPJ in the Notch signalling pathway family were down-regulated in the RPL group. The results provided valuable information on the pathogenesis of RPL.

Advanced maternal age leads to changes within the insulin/IGF system and lipid metabolism in the reproductive tract and preimplantation embryo: insights from the rabbit model

Reproductive potential in women declines with age. The impact of ageing on embryo-maternal interactions is still unclear. Rabbits were used as a reproductive model to investigate maternal age-related alterations in reproductive organs and embryos on Day 6 of pregnancy. Blood, ovaries, endometrium, and blastocysts from young (16-20 weeks) and advanced maternal age phase (>108 weeks, old) rabbits were analysed at the mRNA and protein levels to investigate the insulin-like growth factor (IGF) system, lipid metabolism, and stress defence system. Older rabbits had lower numbers of embryos at Day 6 of pregnancy. Plasma insulin and IGF levels were reduced, which was accompanied by paracrine regulation of IGFs and their receptors in ovaries and endometrium. Embryos adapted to hormonal changes as indicated by reduced embryonic IGF1 and 2 levels. Aged reproductive organs increased energy generation from the degradation of fatty acids, leading to higher oxidative stress. Stress markers, including catalase, superoxide dismutase 2, and receptor for advanced glycation end products were elevated in ovaries and endometrium from aged rabbits. Embryonic fatty acid uptake and β-oxidation were increased in both embryonic compartments (embryoblast and trophoblast) in old rabbits, associated with minor changes in the oxidative and glycative stress defence systems. In summary, the insulin/IGF system, lipid metabolism, and stress defence were dysregulated in reproductive tissues of older rabbits, which is consistent with changes in embryonic metabolism and stress defence. These data highlight the crucial influence of maternal age on uterine adaptability and embryo development.

Embryonic poly(A)-binding protein interacts with translation-related proteins and undergoes phosphorylation on the serine, threonine, and tyrosine residues in the mouse oocytes and early embryos

Expression of the embryonic poly(A)-binding protein (EPAB) in frog, mouse, and human oocytes and early-stage embryos is maintained at high levels until embryonic genome activation (EGA) after which a significant decrease occurs in EPAB levels. Studies on the vertebrate oocytes and early embryos revealed that EPAB plays key roles in the translational regulation, stabilization, and protection of maternal mRNAs during oocyte maturation and early embryogenesis. However, it remains elusive whether EPAB interacts with other cellular proteins and undergoes phosphorylation to perform these roles. For this purpose, we identified a group of Epab-interacting proteins and its phosphorylation status in mouse germinal vesicle (GV)- and metaphase II (MII)-stage oocytes, and in 1-cell, 2-cell, and 4-cell preimplantation embryos. In the oocytes and early preimplantation embryos, Epab-interacting proteins were found to play roles in the translation and transcription processes, intracellular signaling and transport, maintenance of structural integrity, metabolism, posttranslational modifications, and chromatin remodeling. Moreover, we discovered that Epab undergoes phosphorylation on the serine, threonine, and tyrosine residues, which are localized in the RNA recognition motifs 2, 3, and 4 or C-terminal. Conclusively, these findings suggest that Epab not only functions in the translational control of maternal mRNAs through binding to their poly(A) tails but also participates in various cellular events through interacting with certain group proteins. Most likely, Epab undergoes a dynamic phosphorylation during the oocyte maturation and the early embryo development to carry out these functions.

Trophectoderm non-coding RNAs reflect the higher metabolic and more invasive properties of young maternal age blastocysts

Increasing female age is accompanied by a corresponding fall in her fertility. This decline is influenced by a variety of factors over an individual's life course including background genetics, local environment and diet. Studying both coding and non-coding RNAs of the embryo could aid our understanding of the causes and/or effects of the physiological processes accompanying the decline including the differential expression of sub-cellular biomarkers indicative of various diseases. The current study is a post-hoc analysis of the expression of trophectoderm RNA data derived from a previous high throughput study. Its main aim is to determine the characteristics and potential functionalities that characterize long non-coding RNAs. As reported previously, a maternal age-related component is potentially implicated in implantation success. Trophectoderm samples representing the full range of maternal reproductive ages were considered in relation to embryonic implantation potential, trophectoderm transcriptome dynamics and reproductive maternal age. The long non-coding RNA (lncRNA) biomarkers identified here are consistent with the activities of embryo-endometrial crosstalk, developmental competency and implantation and share common characteristics with markers of neoplasia/cancer invasion. Corresponding genes for expressed lncRNAs were more active in the blastocysts of younger women are associated with metabolic pathways including cholesterol biosynthesis and steroidogenesis.

The combination of DNA methylome and transcriptome revealed the intergenerational inheritance on the influence of advanced maternal age

BACKGROUND

The number of women delivering at advanced maternal age (AMA; > = 35) continuously increases in developed and high-income countries. Large cohort studies have associated AMA with increased risks of various pregnancy complications and adverse pregnancy outcomes, which raises great concerns about the adverse effect of AMA on the long-term health of offspring. Specific acquired characteristics of parents can be passed on to descendants through certain molecular mechanisms, yet the underlying connection between AMA-related alterations in parents and that in offspring remains largely uncharted.

METHODS

We profiled the DNA methylomes of paired parental peripheral bloods and cord bloods from 20 nuclear families, including 10 AMA and 10 Young, and additional transcriptomes of 10 paired maternal peripheral bloods and cord bloods.

RESULTS

We revealed that AMA induced aging-like changes in DNA methylome and gene expression in both parents and offspring. The expression changes in several genes, such as SLC28A3, were highly relevant to the disorder in DNA methylation. In addition, AMA-related differentially methylated regions (DMRs) identified in mother and offspring groups showed remarkable similarities in both genomic locations and biological functions, mainly involving neuron differentiation, metabolism, and histone modification pathways. AMA-related differentially expressed genes (DEGs) shared by mother and offspring groups were highly enriched in the processes of immune cell activation and mitotic nuclear division. We further uncovered developmental-dependent dynamics for the DNA methylation of intergenerationally correlated DMRs during pre-implantation embryonic development, as well as diverse gene expression patterns during gametogenesis and early embryonic development for those common AMA-related DEGs presenting intergenerational correlation, such as CD24. Moreover, some intergenerational DEGs, typified by HTRA3, also showed the same significant alterations in AMA MII oocyte or blastocyst.

CONCLUSIONS

Our results reveal potential intergenerational inheritance of both AMA-related DNA methylome and transcriptome and provide new insights to understand health problems in AMA offspring.

Glutamate can act as a signaling molecule in mouse preimplantation embryos

Free amino acids are present in the natural environment of the preimplantation embryo, and their availability can influence early embryo development. Glutamic acid is one of the amino acids with highest concentrations in female reproductive fluids, and we investigated whether glutamic acid/glutamate can affect preimplantation embryo development by acting through cell membrane receptors. Using RT-PCR, we detected 15 ionotropic glutamate receptor transcripts and 8 metabotropic glutamate receptor transcripts in mouse ovulated oocytes and/or in vivo developed blastocysts. Using immunohistochemistry, we detected expression of two AMPA receptor subunits, three kainate receptor subunits and member 5 metabotropic glutamate receptor protein in blastocysts. Extracellular concentrations of glutamic acid starting at 5 mM impaired mouse blastocyst development, and this fact may be of great practical importance since glutamic acid and its salts (mainly monosodium glutamate) are widely used as food additives. Experiments with glutamate receptor agonists (in combination with gene expression analysis) revealed that specific AMPA receptors (formed from GRIA3 and/or GRIA4 subunits), kainate receptors (formed from GRIK 3 and GRIK 4 or GRIK 5 subunits) and GRM5 glutamate receptor were involved in this effect. The glutamic acid-induced effects were prevented or reduced by pre-treatment of blastocysts with AMPA, kainate and GRM5 receptor antagonists, further confirming the involvement of these receptor types. Our results show that glutamic acid can act as a signaling molecule in preimplantation embryos, exerting its effects through activation of cell membrane receptors.

Maternal age affects equine day 8 embryo gene expression both in trophoblast and inner cell mass

BACKGROUND

Breeding a mare until she is not fertile or even until her death is common in equine industry but the fertility decreases as the mare age increases. Embryo loss due to reduced embryo quality is partly accountable for this observation. Here, the effect of mare's age on blastocysts' gene expression was explored. Day 8 post-ovulation embryos were collected from multiparous young (YM, 6-year-old, N = 5) and older (OM, > 10-year-old, N = 6) non-nursing Saddlebred mares, inseminated with the semen of one stallion. Pure or inner cell mass (ICM) enriched trophoblast, obtained by embryo bisection, were RNA sequenced. Deconvolution algorithm was used to discriminate gene expression in the ICM from that in the trophoblast. Differential expression was analyzed with embryo sex and diameter as cofactors. Functional annotation and classification of differentially expressed genes and gene set enrichment analysis were also performed.

RESULTS

Maternal aging did not affect embryo recovery rate, embryo diameter nor total RNA quantity. In both compartments, the expression of genes involved in mitochondria and protein metabolism were disturbed by maternal age, although more genes were affected in the ICM. Mitosis, signaling and adhesion pathways and embryo development were decreased in the ICM of embryos from old mares. In trophoblast, ion movement pathways were affected.

CONCLUSIONS

This is the first study showing that maternal age affects gene expression in the equine blastocyst, demonstrating significant effects as early as 10 years of age. These perturbations may affect further embryo development and contribute to decreased fertility due to aging.

Apoptotic qPCR gene expression array analysis demonstrates proof-of-concept for rapid blastocoel fluid-conditioned media molecular prediction

PURPOSE

Successful identification of transcriptomic biomarkers within human IVF embryos may enhance implantation prediction and provide insights not available through conventional embryo biopsy genomic analysis. We demonstrate proof-of-concept for a methodology to assess overall embryo gene expression using qPCR with blastocoel fluid-conditioned media by examining the comparative presence of apoptotic genes.

METHODS

Blastocoel fluid-conditioned media were collected from 19 embryos (11 euploid) following trophectoderm biopsy of day-5 ICSI-IVF blastocysts. Media were assessed for apoptotic gene expression via qPCR. Statistical analysis of gene expression was conducted via Wilcoxon Signed-Ranks test (overall expression), multivariate ANOVA (functional gene groups), and chi-square test of independence (gene level).

RESULTS

A significantly higher overall apoptotic gene expression within euploid versus aneuploid embryos (p = 0.001) was observed. There was significantly (p = 0.045) higher expression of pro-apoptotic genes between implanted and not implanted embryos. Pro- vs. anti-apoptotic gene expression from all euploid embryos approached significance (p = 0.053). The ploidy status-based claim is further substantiated at the gene level with significantly higher expression of BBC3 (p = 0.012) and BCL2L13 (p = 0.003) in euploid embryos compared to aneuploid embryos.

CONCLUSIONS

In this preliminary study, we demonstrate that (1) qualitative analysis of blastocoel fluid-conditioned media gene expression is possible, (2) global trends of expression are potentially related to clinical outcomes, and (3) gene-level expression trends exist and may be another viable metric for comparative expression between samples. The presence of statistical significance within analyses conducted with this sample size warrants a larger investigation of blastocoel fluid-conditioned media as an additional beneficial predictive tool for future IVF cases.

Biphasic (5-2%) oxygen concentration strategy significantly improves the usable blastocyst and cumulative live birth rates in in vitro fertilization

Oxygen (O₂) concentration is approximately 5% in the fallopian tube and 2% in the uterus in humans. A "back to nature" approach could increase in vitro fertilization (IVF) outcomes. This hypothesis was tested in this monocentric observational retrospective study that included 120 couples who underwent two IVF cycles between 2014 and 2019. Embryos were cultured at 5% from day 0 (D0) to D5/6 (monophasic O₂ concentration strategy) in the first IVF cycle, and at 5% O₂ from D0 to D3 and 2% O₂ from D3 to D5/6 (biphasic O₂ concentration strategy) in the second IVF cycle. The total and usable blastocyst rates (44.4% vs. 54.8%, p = 0.049 and 21.8% vs. 32.8%, p = 0.002, respectively) and the cumulative live birth rate (17.9% vs. 44.1%, p = 0.027) were significantly higher with the biphasic (5%-2%) O₂ concentration strategy. Whole transcriptome analysis of blastocysts donated for research identified 707 RNAs that were differentially expressed in function of the O₂ strategy (fold-change > 2, p value < 0.05). These genes are mainly involved in embryo development, DNA repair, embryonic stem cell pluripotency, and implantation potential. The biphasic (5-2%) O₂ concentration strategy for preimplantation embryo culture could increase the "take home baby rate", thus improving IVF cost-effectiveness and infertility management.

Integrative proteome analysis implicates aberrant RNA splicing in impaired developmental potential of aged mouse oocytes

Aging has many effects on the female reproductive system, among which decreased oocyte quality and impaired embryo developmental potential are the most important factors affecting female fertility. However, the mechanisms underlying oocyte aging are not yet fully understood. Here, we selected normal reproductively aging female mice and constructed a protein expression profile of metaphase II (MII) oocytes from three age groups. A total of 187 differentially expressed (DE) proteins were identified, and bioinformatics analyses showed that these DE proteins were highly enriched in RNA splicing. Next, RNA‐seq was performed on 2‐cell embryos from these three age groups, and splicing analysis showed that a large number of splicing events and genes were discovered at this stage. Differentially spliced genes (DSGs) in the two reproductively aging groups versus the younger group were enriched in biological processes related to DNA damage repair/response. Binding motif analysis suggested that PUF60 might be one of the core splicing factors causing a decline in DNA repair capacity in the subsequent development of oocytes from reproductively aging mice, and changing the splicing pattern of its potential downstream DSG Cdk9 could partially mimic phenotypes in the reproductively aging groups. Taken together, our study suggested that the abnormal expression of splicing regulation proteins in aged MII oocytes would affect the splicing of nascent RNA after zygotic genome activation in 2‐cell embryos, leading to the production of abnormally spliced transcripts of some key genes associated with DNA damage repair/response, thus affecting the developmental potential of aged oocytes.

The effects of aging on molecular modulators of human embryo implantation

Advancing age has a negative impact on female fertility. As implantation rates decline during the normal maternal life course, age-related, embryonic factors are altered and our inability to monitor these factors in an unbiased genome-wide manner in vivo has severely limited our understanding of early human embryo development and implantation. Our high-throughput methodology uses trophectoderm samples representing the full spectrum of maternal reproductive ages with embryo implantation potential examined in relation to trophectoderm transcriptome dynamics and reproductive maternal age. Potential embryo-endometrial interactions were tested using trophectoderm sampled from young women, with the receptive uterine environment representing the most 'fertile' environment for successful embryo implantation. Potential roles for extracellular exosomes, embryonic metabolism and regulation of apoptosis were revealed. These biomarkers are consistent with embryo-endometrial crosstalk/developmental competency, serving as a mediator for successful implantation. Our data opens the door to developing a diagnostic test for predicting implantation success in women undergoing fertility treatment.

Advanced maternal age perturbs mouse embryo development and alters the phenotype of derived embryonic stem cells

Advanced maternal age (AMA) is known to reduce fertility, increases aneuploidy in oocytes and early embryos and leads to adverse developmental consequences which may associate with offspring lifetime health risks. However, investigating underlying effects of AMA on embryo developmental potential is confounded by the inherent senescence present in maternal body systems further affecting reproductive success. Here, we describe a new model for the analysis of early developmental mechanisms underlying AMA by the derivation and characterisation of mouse embryonic stem cell (mESC-like) lines from naturally conceived embryos. Young (7-8 weeks) and Old (7-8 months) C57BL/6 female mice were mated with young males. Preimplantation embryos from Old dams displayed developmental retardation in blastocyst morphogenesis. mESC lines established from these blastocysts using conventional techniques revealed differences in genetic, cellular and molecular criteria conserved over several passages in the standardised medium. mESCs from embryos from AMA dams displayed increased incidence of aneuploidy following Giemsa karyotyping compared with those from Young dams. Moreover, AMA caused an altered pattern of expression of pluripotency markers (Sox2, OCT4) in mESCs. AMA further diminished mESC survival and proliferation and reduced the expression of cell proliferation marker, Ki-67. These changes coincided with altered expression of the epigenetic marker, Dnmt3a and other developmental regulators in a sex-dependent manner. Collectively, our data demonstrate the feasibility to utilise mESCs to reveal developmental mechanisms underlying AMA in the absence of maternal senescence and with reduced animal use.

Small Noncoding RNA Signatures for Determining the Developmental Potential of an Embryo at the Morula Stage

As part of the optimization of assisted reproductive technology programs, the aim of the study was to identify key small noncoding RNA (sncRNA) molecules that participate in maternal-to-zygotic transition and determine development potential and competence to form a healthy fetus. Small RNA deep sequencing followed by quantitative real-time RT-PCR was used to profile sncRNAs in 50 samples of spent culture medium from morula with different development potentials (no potential (degradation/developmental arrest), low potential (poor-quality blastocyst), and high potential (good/excellent quality blastocyst capable of implanting and leading to live birth)) obtained from 27 subfertile couples who underwent in vitro fertilization. We have shown that the quality of embryos at the morula stage is determined by secretion/uptake rates of certain sets of piRNAs and miRNAs, namely hsa_piR_011291, hsa_piR_019122, hsa_piR_001311, hsa_piR_015026, hsa_piR_015462, hsa_piR_016735, hsa_piR_019675, hsa_piR_020381, hsa_piR_020485, hsa_piR_004880, hsa_piR_000807, hsa-let-7b-5p, and hsa-let-7i-5p. Predicted gene targets of these sncRNAs included those globally decreased at the 8-cell–morula–blastocyst stage and critical to early embryo development. We show new original data on sncRNA profiling in spent culture medium from morula with different development potential. Our findings provide a view of a more complex network that controls human embryogenesis at the pre-implantation stage. Further research is required using reporter analysis to experimentally confirm interactions between identified sncRNA/gene target pairs.

Antioxidant Intervention Attenuates Aging-Related Changes in the Murine Ovary and Oocyte

Advanced maternal age (AMA) is associated with reduced fertility due in part to diminished ovarian follicle quantity, inferior oocyte quality, chromosome aneuploidy, and lower implantation rates. Ovarian aging is accompanied by increased oxidative stress and blunted antioxidant signaling, such that antioxidant intervention could improve reproductive potential. The first aim of this study was to determine the molecular effects of antioxidant intervention in the ovaries and oocytes of aged mice, utilizing a supplement containing only naturally occurring açaí (Euterpe oleracea) with an oxygen radical absorbance capacity of 208,628 μmol Trolox equivalent (TE)/100 g indicating high antioxidant activity. Nine month old female CF-1 mice were administered 80 mg/day antioxidants (n = 12) or standard diet (n = 12) for 12 weeks. In the ovary, antioxidant treatment upregulated β-adrenergic signaling, downregulated apoptosis and proinflammatory signaling, and variably affected cell growth and antioxidant pathways (p < 0.05). Exogenous antioxidants also increased the oocyte expression of antioxidant genes GPX1, SOD2, and GSR (p < 0.05). A feasibility analysis was then conducted on female AMA infertility patients as a proof-of-principle investigation. Patients (n = 121; <45 years old) consented to receiving 600 mg antioxidants three times daily for ≥8 weeks preceding infertility treatment. Preliminary results indicate promising outcomes for AMA patients, warranting further investigation.