Aging changes the chromatin configuration and histone methylation of mouse oocytes at germinal vesicle stage

ZAR1/2-Regulated Epigenetic Modifications are Essential for Age-Associated Oocyte Quality Maintenance and Zygotic Activation

The developmental competence and epigenetic progression of oocytes gradually become dysregulated with increasing maternal age. However, the mechanisms underlying age-related epigenetic regulation in oocytes remain poorly understood. Zygote arrest proteins 1 and 2 (ZAR1/2) are two maternal factors with partially redundant roles in maintaining oocyte quality, mainly known by regulating mRNA stability. In addition to this known function, it is found that ZAR1/2 is required for oocyte epigenetic maturation and zygotic reprogramming. Zar1/2-deleted oocytes exhibited reduced levels of multiple histone modifications and of the expression of corresponding histone modifiers, along with over-condensed chromatin, leading to compromised minor zygotic genome activation and deficient embryo development following fertilization. Cytoplasmic ZAR1/2 participated in intranuclear epigenetic maturation by binding the transcripts encoding histone modifiers and regulating their stability and translational activity. Moreover, oocytes from aged mice exhibited similar histone-modification deficiencies as the Zar1/2-deleted oocytes. ZAR1/2 mRNA and protein levels are downregulated in oocytes from mice and women with advanced ages, suggesting ZAR1/2 as regulators of epigenetic changes with reproductive aging. This study presents a new nucleo-cytoplasmic interaction mechanism that is involved in preventing oocyte epigenetic aging. Further, ZAR1/2 represents potential gene targets for diagnosis and clinical interventions in age-associated deficiencies in oocyte and embryo development.

Unraveling the mysteries of early embryonic arrest: genetic factors and molecular mechanisms

Early embryonic arrest (EEA) is a critical impediment in assisted reproductive technology (ART), affecting 40% of infertile patients by halting the development of early embryos from the zygote to blastocyst stage, resulting in a lack of viable embryos for successful pregnancy. Despite its prevalence, the molecular mechanism underlying EEA remains elusive. This review synthesizes the latest research on the genetic and molecular factors contributing to EEA, with a focus on maternal, paternal, and embryonic factors. Maternal factors such as irregularities in follicular development and endometrial environment, along with mutations in genes like NLRP5, PADI6, KPNA7, IGF2, and TUBB8, have been implicated in EEA. Specifically, PATL2 mutations are hypothesized to disrupt the maternal-zygotic transition, impairing embryo development. Paternal contributions to EEA are linked to chromosomal variations, epigenetic modifications, and mutations in genes such as CFAP69, ACTL7A, and M1AP, which interfere with sperm development and lead to infertility. Aneuploidy may disrupt spindle assembly checkpoints and pathways including Wnt, MAPK, and Hippo signaling, thereby contributing to EEA. Additionally, key genes involved in embryonic genome activation-such as ZSCAN4, DUXB, DUXA, NANOGNB, DPPA4, GATA6, ARGFX, RBP7, and KLF5-alongside functional disruptions in epigenetic modifications, mitochondrial DNA, and small non-coding RNAs, play critical roles in the onset of EEA. This review provides a comprehensive understanding of the genetic and molecular underpinnings of EEA, offering a theoretical foundation for the diagnosis and potential therapeutic strategies aimed at improving pregnancy outcomes.

Hallmarks of female reproductive aging in physiologic aging mice

The female reproductive axis is one of the first organ systems to age, which has consequences for fertility and overall health. Here, we provide a comprehensive overview of the biological process of female reproductive aging across reproductive organs, tissues and cells based on research with widely used physiologic aging mouse models, and describe the mechanisms that underpin these phenotypes. Overall, aging is associated with dysregulation of the hypothalamic-pituitary-ovarian axis, perturbations of the ovarian stroma, reduced egg quantity and quality, and altered uterine morphology and function that contributes to reduced capacity for fertilization and impaired embryo development. Ultimately, these age-related phenotypes contribute to altered pregnancy outcomes and adverse consequences in offspring. Conserved mechanisms of aging, as well as those unique to the reproductive system, underlie these phenotypes. The knowledge of such mechanisms will lead to development of therapeutics to extend female reproductive longevity and support endocrine function and overall health.

The Reproductive Lifespan of Ovarian Follicle

The functional unit within mammalian ovaries is the ovarian follicle. The development of the ovarian follicle is a lengthy process beginning from the time of embryogenesis, passing through multiple different stages of maturation. The purpose of this review is to describe the most basic events in the journey of ovarian follicle development, discussing the importance of ovarian reserve and highlighting the role of several factors that affect oocyte quality and quantity during aging including hormonal, genetic and epigenetic factors. Novel, promising anti-aging strategies are also discussed.

The maintenance of oocytes in the mammalian ovary involves extreme protein longevity

Women are born with all of their oocytes. The oocyte proteome must be maintained with minimal damage throughout the woman's reproductive life, and hence for decades. Here we report that oocyte and ovarian proteostasis involves extreme protein longevity. Mouse ovaries had more extremely long-lived proteins than other tissues, including brain. These long-lived proteins had diverse functions, including in mitochondria, the cytoskeleton, chromatin and proteostasis. The stable proteins resided not only in oocytes but also in long-lived ovarian somatic cells. Our data suggest that mammals increase protein longevity and enhance proteostasis by chaperones and cellular antioxidants to maintain the female germline for long periods. Indeed, protein aggregation in oocytes did not increase with age and proteasome activity did not decay. However, increasing protein longevity cannot fully block female germline senescence. Large-scale proteome profiling of ~8,890 proteins revealed a decline in many long-lived proteins of the proteostasis network in the aging ovary, accompanied by massive proteome remodeling, which eventually leads to female fertility decline.

The impact of maternal age on aneuploidy in oocytes: Reproductive consequences, molecular mechanisms, and future directions

Age-related aneuploidy in human oocytes is a major factor contributing to decreased fertility and adverse reproductive outcomes. As females age, their oocytes are more prone to meiotic chromosome segregation errors, leading primarily to aneuploidy. Elevated aneuploidy rates have also been observed in oocytes from very young, prepubertal conceptions. A key barrier to developing effective treatments for age-related oocyte aneuploidy is our incomplete understanding of the molecular mechanisms involved. The challenge is becoming increasingly critical as more people choose to delay childbearing, a trend that has significant societal implications. In this review, we summarize current knowledge regarding the process of oocyte meiosis and folliculogenesis, highlighting the relationship between age and chromosomal aberrations in oocytes and embryos, and integrate proposed mechanisms of age-related meiotic disturbances across structural, protein, and genomic levels. Our goal is to spur new research directions and therapeutic avenues.

Ovarian aging: energy metabolism of oocytes

In women who are getting older, the quantity and quality of their follicles or oocytes and decline. This is characterized by decreased ovarian reserve function (DOR), fewer remaining oocytes, and lower quality oocytes. As more women choose to delay childbirth, the decline in fertility associated with age has become a significant concern for modern women. The decline in oocyte quality is a key indicator of ovarian aging. Many studies suggest that age-related changes in oocyte energy metabolism may impact oocyte quality. Changes in oocyte energy metabolism affect adenosine 5'-triphosphate (ATP) production, but how related products and proteins influence oocyte quality remains largely unknown. This review focuses on oocyte metabolism in age-related ovarian aging and its potential impact on oocyte quality, as well as therapeutic strategies that may partially influence oocyte metabolism. This research aims to enhance our understanding of age-related changes in oocyte energy metabolism, and the identification of biomarkers and treatment methods.

Multiomics insights into the female reproductive aging

The human female reproductive lifespan significantly diminishes with age, leading to decreased fertility, reduced fertility quality and endocrine function disorders. While many aspects of aging in general have been extensively documented, the precise mechanisms governing programmed aging in the female reproductive system remain elusive. Recent advancements in omics technologies and computational capabilities have facilitated the emergence of multiomics deep phenotyping. Through the application and refinement of various high-throughput omics methods, a substantial volume of omics data has been generated, deepening our comprehension of the pathogenesis and molecular underpinnings of reproductive aging. This review highlights current and emerging multiomics approaches for investigating female reproductive aging, encompassing genomics, epigenomics, transcriptomics, proteomics, metabolomics, and microbiomics. We elucidate their influence on fundamental cell biology and translational research in the context of reproductive aging, address the limitations and current challenges associated with multiomics studies, and offer a glimpse into future prospects.

Acute irradiation induces a senescence-like chromatin structure in mammalian oocytes

The mechanisms leading to changes in mesoscale chromatin organization during cellular aging are unknown. Here, we used transcriptional activator-like effectors, RNA-seq and superresolution analysis to determine the effects of genotoxic stress on oocyte chromatin structure. Major satellites are organized into tightly packed globular structures that coalesce into chromocenters and dynamically associate with the nucleolus. Acute irradiation significantly enhanced chromocenter mobility in transcriptionally inactive oocytes. In transcriptionally active oocytes, irradiation induced a striking unfolding of satellite chromatin fibers and enhanced the expression of transcripts required for protection from oxidative stress (Fermt1, Smg1), recovery from DNA damage (Tlk2, Rad54l) and regulation of heterochromatin assembly (Zfp296, Ski-oncogene). Non-irradiated, senescent oocytes exhibit not only high chromocenter mobility and satellite distension but also a high frequency of extra chromosomal satellite DNA. Notably, analysis of biological aging using an oocyte-specific RNA clock revealed cellular communication, posttranslational protein modifications, chromatin and histone dynamics as the top cellular processes that are dysregulated in both senescent and irradiated oocytes. Our results indicate that unfolding of heterochromatin fibers following acute genotoxic stress or cellular aging induced the formation of distended satellites and that abnormal chromatin structure together with increased chromocenter mobility leads to chromosome instability in senescent oocytes.

Impact of NAD+ metabolism on ovarian aging

Nicotinamide adenine dinucleotide (NAD+), a crucial coenzyme in cellular redox reactions, is closely associated with age-related functional degeneration and metabolic diseases. NAD exerts direct and indirect influences on many crucial cellular functions, including metabolic pathways, DNA repair, chromatin remodeling, cellular senescence, and immune cell functionality. These cellular processes and functions are essential for maintaining tissue and metabolic homeostasis, as well as healthy aging. Causality has been elucidated between a decline in NAD levels and multiple age-related diseases, which has been confirmed by various strategies aimed at increasing NAD levels in the preclinical setting. Ovarian aging is recognized as a natural process characterized by a decline in follicle number and function, resulting in decreased estrogen production and menopause. In this regard, it is necessary to address the many factors involved in this complicated procedure, which could improve fertility in women of advanced maternal age. Concerning the decrease in NAD+ levels as ovarian aging progresses, promising and exciting results are presented for strategies using NAD+ precursors to promote NAD+ biosynthesis, which could substantially improve oocyte quality and alleviate ovarian aging. Hence, to acquire further insights into NAD+ metabolism and biology, this review aims to probe the factors affecting ovarian aging, the characteristics of NAD+ precursors, and the current research status of NAD+ supplementation in ovarian aging. Specifically, by gaining a comprehensive understanding of these aspects, we are optimistic about the prominent progress that will be made in both research and therapy related to ovarian aging.

Epigenetic aging of mammalian gametes

The process of aging refers to physiological changes that occur to an organism as time progresses and involves changes to DNA, proteins, metabolism, cells, and organs. Like the rest of the cells in the body, gametes age, and it is well established that there is a decline in reproductive capabilities in females and males with aging. One of the major pathways known to be involved in aging is epigenetic changes. The epigenome is the multitude of chemical modifications performed on DNA and chromatin that affect the ability of chromatin to be transcribed. In this review, we explore the effects of aging on female and male gametes with a focus on the epigenetic changes that occur in gametes throughout aging. Quality decline in oocytes occurs at a relatively early age. Epigenetic changes constitute an important part of oocyte aging. DNA methylation is reduced with age, along with reduced expression of DNA methyltransferases (DNMTs). Histone deacetylases (HDAC) expression is also reduced, and a loss of heterochromatin marks occurs with age. As a consequence of heterochromatin loss, retrotransposon expression is elevated, and aged oocytes suffer from DNA damage. In sperm, aging affects sperm number, motility and fecundity, and epigenetic changes may constitute a part of this process. 5 methyl-cytosine (5mC) methylation is elevated in sperm from aged men, but methylation on Long interspersed nuclear elements (LINE) elements is reduced. Di and trimethylation of histone 3 lysine 9 (H3K9me2/3) is reduced in sperm from aged men and trimethylation of histone 3 lysine 27 (H3K27me3) is elevated. The protamine makeup of sperm from aged men is also changed, with reduced protamine expression and a misbalanced ratio between protamine proteins protamine P1 and protamine P2. The study of epigenetic reproductive aging is recently gaining interest. The current status of the field suggests that many aspects of gamete epigenetic aging are still open for investigation. The clinical applications of these investigations have far-reaching consequences for fertility and sociological human behavior.

Traffic-related air pollution and supplemental folic acid intake in relation to DNA methylation in granulosa cells

BACKGROUND

Higher exposure to traffic-related air pollution (TRAP) is related to lower fertility, with specific adverse effects on the ovary. Folic acid may attenuate these effects. Our goal was to explore the relation of TRAP exposure and supplemental folic acid intake with epigenetic aging and CpG-specific DNA methylation (DNAm) in granulosa cells (GC). Our study included 61 women undergoing ovarian stimulation at a fertility center (2005-2015). DNAm levels were profiled in GC using the Infinium MethylationEPIC BeadChip. TRAP was defined using a spatiotemporal model to estimate residence-based nitrogen dioxide (NO2) exposure. Supplemental folic acid intake was measured with a validated food frequency questionnaire. We used linear regression to evaluate whether NO2 or supplemental folic acid was associated with epigenetic age acceleration according to the Pan-tissue, mural GC, and GrimAge clocks or DNAm across the genome adjusting for potential confounders and accounting for multiple testing with a false discovery rate < 0.1.

RESULTS

There were no associations between NO2 or supplemental folic acid intake and epigenetic age acceleration of GC. NO2 and supplemental folic acid were associated with 9 and 11 differentially methylated CpG sites. Among these CpGs, only cg07287107 exhibited a significant interaction (p-value = 0.037). In women with low supplemental folic acid, high NO2 exposure was associated with 1.7% higher DNAm. There was no association between NO2 and DNAm in women with high supplemental folic acid. The genes annotated to the top 250 NO2-associated CpGs were enriched for carbohydrate and protein metabolism, postsynaptic potential and dendrite development, and membrane components and exocytosis. The genes annotated to the top 250 supplemental folic acid-associated CpGs were enriched for estrous cycle, learning, cognition, synaptic organization and transmission, and size and composition of neuronal cell bodies.

CONCLUSIONS

We found no associations between NO2, supplemental folic acid, and DNAm age acceleration of GC. However, there were 20 differentially methylated CpGs and multiple enriched GO terms associated with both exposures suggesting that differences in GC DNAm could be a plausible mechanism underlying the effects of TRAP and supplemental folic acid on ovarian function.

Reproductive-Toxicity-Related Endpoints in C. elegans Are Consistent with Reduced Concern for Dimethylarsinic Acid Exposure Relative to Inorganic Arsenic

Exposures to arsenic and mercury are known to pose significant threats to human health; however, the effects specific to organic vs. inorganic forms are not fully understood. Caenorhabditis elegans' (C. elegans) transparent cuticle, along with the conservation of key genetic pathways regulating developmental and reproductive toxicology (DART)-related processes such as germ stem cell renewal and differentiation, meiosis, and embryonic tissue differentiation and growth, support this model's potential to address the need for quicker and more dependable testing methods for DART hazard identification. Organic and inorganic forms of mercury and arsenic had different effects on reproductive-related endpoints in C. elegans, with methylmercury (meHgCl) having effects at lower concentrations than mercury chloride (HgCl2), and sodium arsenite (NaAsO2) having effects at lower concentrations than dimethylarsinic acid (DMA). Progeny to adult ratio changes and germline apoptosis were seen at concentrations that also affected gravid adult gross morphology. For both forms of arsenic tested, germline histone regulation was altered at concentrations below those that affected progeny/adult ratios, while concentrations for these two endpoints were similar for the mercury compounds. These C. elegans findings are consistent with corresponding mammalian data, where available, suggesting that small animal model test systems may help to fill critical data gaps by contributing to weight of evidence assessments.

The emerging role of lysine succinylation in ovarian aging

BACKGROUND

Ovarian aging is a process of decline in its reserve leading to ovary dysfunction and even reduced health quality in offspring. However, aging-related molecular pathways in the ovary remain obscure. Lysine succinylation (Ksuc), a newly post-translational modification (PTM), has been found to be broadly conserved in both eukaryotic and prokaryotic cells, and associated with multiple pathophysiological processes. There are no relevant reports revealing a link between the molecular mechanisms of ovarian aging and Ksuc.

METHODS

The level of Ksuc in ovaries of aged and premature ovarian insufficiency (POI) mice were detected by immunoblotting and immunohistochemical. To further explore the role of Ksuc in ovarian aging, using in vitro mouse ovary tissue culture and an in vivo mouse model with changed Ksuc level.

RESULTS

Increased Ksuc in ovaries of aged and POI mice and distribution of Ksuc in various types of mice ovarian cells and the high level of Ksuc in granulosa cells (GCs) were revealed. Histological assessments and hormone levels analyses showed that the high Ksuc level down-regulated the ovarian index and the anti-Müllerian hormone (AMH) and estrogen levels, and increased follicular atresia. Moreover, in the high Ksuc groups, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) intensities and the expression of Cleaved-caspase-3 increased and the expression of B-cell lymphoma-2 (Bcl-2) decreased together with positively-expressed P21, an aging-related marker. These results suggest that ovarian aging is likely associated with alteration in Ksuc.

CONCLUSION

The present study has identified Ksuc in mouse ovary and found that high Ksuc level most likely contributes to ovarian aging which is expected further investigation to provide new information for delaying physiological ovarian aging and treating pathological ovarian aging.

H3K4 Methylation Promotes Expression of Mitochondrial Dynamics Regulators to Ensure Oocyte Quality in Mice

Significantly decreased H3K4 methylation in oocytes from aged mice indicates the important roles of H3K4 methylation in female reproduction. However, how H3K4 methylation regulates oocyte development remains largely unexplored. In this study, it is demonstrated that oocyte-specific expression of dominant negative mutant H3.3-K4M led to a decrease of the level of H3K4 methylation in mouse oocytes, resulting in reduced transcriptional activity and increased DNA methylation in oocytes, disturbed oocyte developmental potency, and fertility of female mice. The impaired expression of genes regulating mitochondrial functions in H3.3-K4M oocytes, accompanied by mitochondrial abnormalities, is further noticed. Moreover, early embryos from H3.3-K4M oocytes show developmental arrest and reduced zygotic genome activation. Collectively, these results show that H3K4 methylation in oocytes is critical to orchestrating gene expression profile, driving the oocyte developmental program, and ensuring oocyte quality. This study also improves understanding of how histone modifications regulate organelle dynamics in oocytes.

Epigenetic regulation in premature ovarian failure: A literature review

Premature ovarian failure (POF), or premature ovarian insufficiency (POI), is a multifactorial and heterogeneous disease characterized by amenorrhea, decreased estrogen levels and increased female gonadotropin levels. The incidence of POF is increasing annually, and POF has become one of the main causes of infertility in women of childbearing age. The etiology and pathogenesis of POF are complex and have not yet been clearly elucidated. In addition to genetic factors, an increasing number of studies have revealed that epigenetic changes play an important role in the occurrence and development of POF. However, we found that very few papers have summarized epigenetic variations in POF, and a systematic analysis of this topic is therefore necessary. In this article, by reviewing and analyzing the most relevant literature in this research field, we expound on the relationship between DNA methylation, histone modification and non-coding RNA expression and the development of POF. We also analyzed how environmental factors affect POF through epigenetic modulation. Additionally, we discuss potential epigenetic biomarkers and epigenetic treatment targets for POF. We anticipate that our paper may provide new therapeutic clues for improving ovarian function and maintaining fertility in POF patients.

Improvement of oocyte quality through the SIRT signaling pathway

Background

Oocyte quality is one of the major deciding factors in female fertility competence.

Methods

PubMed database was searched for reviews by using the following keyword "oocyte quality" AND "Sirtuins". The methodological quality of each literature review was assessed using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2020 statement.

Main Findings

Oxidative stress has been recognized as the mechanism attenuating oocyte quality. Increasing evidence from animal experiments and clinical studies has confirmed the protective roles of the sirtuin family in improving oocyte quality via an antioxidant effect.

Conclusion

The protective roles in the oocyte quality of the sirtuin family have been increasingly recognized.

Aneuploidy in mammalian oocytes and the impact of maternal ageing

During fertilization, the egg and the sperm are supposed to contribute precisely one copy of each chromosome to the embryo. However, human eggs frequently contain an incorrect number of chromosomes - a condition termed aneuploidy, which is much more prevalent in eggs than in either sperm or in most somatic cells. In turn, aneuploidy in eggs is a leading cause of infertility, miscarriage and congenital syndromes. Aneuploidy arises as a consequence of aberrant meiosis during egg development from its progenitor cell, the oocyte. In human oocytes, chromosomes often segregate incorrectly. Chromosome segregation errors increase in women from their mid-thirties, leading to even higher levels of aneuploidy in eggs from women of advanced maternal age, ultimately causing age-related infertility. Here, we cover the two main areas that contribute to aneuploidy: (1) factors that influence the fidelity of chromosome segregation in eggs of women from all ages and (2) factors that change in response to reproductive ageing. Recent discoveries reveal new error-causing pathways and present a framework for therapeutic strategies to extend the span of female fertility.

Effects of putrescine on the quality and epigenetic modification of mouse oocytes during in vitro maturation

CONTEXT

Low ovarian putrescine levels and decreased peak values following luteinising hormone peaks are related to poor oocyte quantity and quality in ageing women.

AIMS

To investigate the effects of putrescine supplementation in in vitro maturation (IVM) medium on oocyte quality and epigenetic modification.

METHODS

Germinal vesicle oocytes retrieved from the ovaries of 8-week-old and 9-month-old mice were divided into four groups (the young, young+difluoromethylornithine (DFMO), ageing and ageing+putrescine groups) and cultured in IVM medium with or without 1mM putrescine or DFMO for 16h. The first polar body extrusion (PBE), cleavage and embryonic development were evaluated. Spindles, chromosomes, mitochondria and reactive oxygen species (ROS) were measured. The expression levels of SIRT1, H3K9ac, H3K9me2, H3K9me3, and 5mC levels were evaluated. Sirt1 and imprinted genes were detected.

RESULTS

The PBE was higher in the ageing+putrescine group than in the ageing group. Putrescine increased the total and inner cell mass cell numbers of blastocysts in ageing oocytes. Putrescine decreased aberrant spindles and chromosome aneuploidy, increased the mitochondrial membrane potential and decreased ROS levels. Putrescine increased SIRT1 expression and attenuated the upregulation of H3K9ac levels in ageing oocytes. Putrescine did not affect 5mC, H3K9me2 or H3K9me3 levels or imprinted gene expression.

CONCLUSIONS

Putrescine supplementation during IVM improved the maturation and quality of ageing oocytes and promoted embryonic development by decreasing ROS generation, maintaining mitochondrial and spindle function and correcting aberrant epigenetic modification.

IMPLICATIONS

Putrescine shows application potential for human-assisted reproduction, especially for IVM of oocytes from ageing women.

Expression of the histone lysine methyltransferases SETD1B, SETDB1, SETD2, and CFP1 exhibits significant changes in the oocytes and granulosa cells of aged mouse ovaries

Histone methylation is one of the main epigenetic mechanisms by which methyl groups are dynamically added to the lysine and arginine residues of histone tails in nucleosomes. This process is catalyzed by specific histone methyltransferase enzymes. Methylation of these residues promotes gene expression regulation through chromatin remodeling. Functional analysis and knockout studies have revealed that the histone lysine methyltransferases SETD1B, SETDB1, SETD2, and CFP1 play key roles in establishing the methylation marks required for proper oocyte maturation and follicle development. As oocyte quality and follicle numbers progressively decrease with advancing maternal age, investigating their expression patterns in the ovaries at different reproductive periods may elucidate the fertility loss occurring during ovarian aging. The aim of our study was to determine the spatiotemporal distributions and relative expression levels of the Setd1b, Setdb1, Setd2, and Cxxc1 (encoding the CFP1 protein) genes in the postnatal mouse ovaries from prepuberty to late aged periods. For this purpose, five groups based on their reproductive periods and histological structures were created: prepuberty (3 weeks old; n = 6), puberty (7 weeks old; n = 7), postpuberty (18 weeks old; n = 7), early aged (52 weeks old; n = 7), and late aged (60 weeks old; n = 7). We found that Setd1b, Setdb1, Setd2, and Cxxc1 mRNA levels showed significant changes among postnatal ovary groups (P < 0.05). Furthermore, SETD1B, SETDB1, SETD2, and CFP1 proteins exhibited different subcellular localizations in the ovarian cells, including oocytes, granulosa cells, stromal and germinal epithelial cells. In general, their levels in the follicles, oocytes, and granulosa cells as well as in the germinal epithelial and stromal cells significantly decreased in the aged groups when compared the other groups (P < 0.05). These decreases were concordant with the reduced numbers of the follicles at different stages and the luteal structures in the aged groups (P < 0.05). In conclusion, these findings suggest that altered expression of the histone methyltransferase genes in the ovarian cells may be associated with female fertility loss in advancing maternal age.

Loss of heterochromatin and retrotransposon silencing as determinants in oocyte aging

Mammalian oocyte quality reduces with age. We show that prior to the occurrence of significant aneuploidy (9M in mouse), heterochromatin histone marks are lost, and oocyte maturation is impaired. This loss occurs in both constitutive and facultative heterochromatin marks but not in euchromatic active marks. We show that heterochromatin loss with age also occurs in human prophase I-arrested oocytes. Moreover, heterochromatin loss is accompanied in mouse oocytes by an increase in RNA processing and associated with an elevation in L1 and IAP retrotransposon expression and in DNA damage and DNA repair proteins nuclear localization. Artificial inhibition of the heterochromatin machinery in young oocytes causes an elevation in retrotransposon expression and oocyte maturation defects. Inhibiting retrotransposon reverse-transcriptase through azidothymidine (AZT) treatment in older oocytes partially rescues their maturation defects and activity of the DNA repair machinery. Moreover, activating the heterochromatin machinery via treatment with the SIRT1 activating molecule SRT-1720, or overexpression of Sirt1 or Ezh2 via plasmid electroporation into older oocytes causes an upregulation in constitutive heterochromatin, downregulation of retrotransposon expression, and elevated maturation rates. Collectively, our work demonstrates a significant process in oocyte aging, characterized by the loss of heterochromatin-associated chromatin marks and activation of specific retrotransposons, which cause DNA damage and impair oocyte maturation.

FAM111A Is a Novel Molecular Marker for Oocyte Aging

Aging is the main cause of decline in oocyte quality, which can further trigger the failure of assisted reproductive technology (ART). Exploring age-related genes in oocytes is an important way to investigate the molecular mechanisms involved in oocyte aging. To provide novel insight into this field, we performed a pooled analysis of publicly available datasets, using the overlapping results of two statistical methods on two Gene Expression Omnibus (GEO) datasets. The methods utilized in the current study mainly include Spearman rank correlation, the Wilcoxon signed-rank test, t-tests, Venn diagrams, Gene Ontology (GO), Protein-Protein Interaction (PPI), Gene Set Enrichment Analysis (GSEA), Gene Set Variation Analysis (GSVA), and receiver operating characteristic (ROC) curve analysis. We identified hundreds of age-related genes across different gene expression datasets of in vitro maturation-metaphase II (IVM-MII) oocytes. Age-related genes in IVM-MII oocytes were involved in the biological processes of cellular metabolism, DNA replication, and histone modifications. Among these age-related genes, FAM111A expression presented a robust correlation with age, seen in the results of different statistical methods and different datasets. FAM111A is associated with the processes of chromosome segregation and cell cycle regulation. Thus, this enzyme is potentially an interesting novel marker for the aging of oocytes, and warrants further mechanistic study.

Stem Cell Rejuvenation by Restoration of Youthful Metabolic Compartmentalization

Stem cell dysfunction is a hallmark of aging. Much recent study suggests that epigenetic changes play a critical role in the loss of stem cell function with age. However, the underlying mechanisms require elucidation. A recent report describes a process by which mild mitochondrial stress associated with aging causes lysosomal-mediated decreases in CiC, the mitochondrial citrate transporter, in bone marrow-derived mesenchymal stem cells (MSCs). This, in turn, results in a deficit of acetyl-CoA in the nucleus and hypoacetylation of histones. The altered epigenome results in skewered stem cell differentiation favoring adipogenesis and disfavoring osteogenesis, which is problematic given the role the MSCs play in maintaining the integrity of bone tissue. Restoration of nuclear acetyl-CoA by either ectopic expression of CiC or acetate supplementation of MSCs in culture rejuvenates the MSC, restoring the potential to efficiently differentiate along the osteogenic lineage. Citrate, which has recently been reported to extend lifespan in Drosophila, chemically incorporates acetyl-CoA and may prove useful to restore cytoplasmic and nuclear acetyl-CoA levels. The general applicability of the CiC defect in old cells, particularly stem cells, should be established.

Introducing ADNP and SIRT1 as new partners regulating microtubules and histone methylation

Activity-dependent neuroprotective protein (ADNP) is essential for brain formation and function. As such, de novo mutations in ADNP lead to the autistic ADNP syndrome and somatic ADNP mutations may drive Alzheimer's disease (AD) tauopathy. Sirtuin 1 (SIRT1) is positively associated with aging, the major risk for AD. Here, we revealed two key interaction sites for ADNP and SIRT1. One, at the microtubule end-binding protein (EB1 and EB3) Tau level, with EB1/EB3 serving as amplifiers for microtubule dynamics, synapse formation, axonal transport, and protection against tauopathy. Two, on the DNA/chromatin site, with yin yang 1, histone deacetylase 2, and ADNP, sharing a DNA binding motif and regulating SIRT1, ADNP, and EB1 (MAPRE1). This interaction was linked to sex- and age-dependent altered histone modification, associated with ADNP/SIRT1/WD repeat-containing protein 5, which mediates the assembly of histone modification complexes. Single-cell RNA and protein expression analyses as well as gene expression correlations placed SIRT1-ADNP and either MAPRE1 (EB1), MAPRE3 (EB3), or both in the same mouse and human cell; however, while MAPRE1 seemed to be similarly regulated to ADNP and SIRT1, MAPRE3 seemed to deviate. Finally, we demonstrated an extremely tight correlation for the gene transcripts described above, including related gene products. This correlation was specifically abolished in affected postmortem AD and Parkinson's disease brain select areas compared to matched controls, while being maintained in blood samples. Thus, we identified an ADNP-SIRT1 complex that may serve as a new target for the understanding of brain degeneration.

Dynamic changes of histone methylation in mammalian oocytes and early embryos

Histone methylation is a key epigenetic mechanism and plays a major role in regulating gene expression during oocyte maturation and early embryogenesis. This mechanism can be briefly defined as the process by which methyl groups are transferred to lysine and arginine residues of histone tails extending from nucleosomes. While methylation of the lysine residues is catalyzed by histone lysine methyltransferases (KMTs), protein arginine methyltransferases (PRMTs) add methyl groups to the arginine residues. When necessary, the added methyl groups can be reversibly removed by histone demethylases (HDMs) by a process called histone demethylation. The spatiotemporal regulation of methylation and demethylation in histones contributes to modulating the expression of genes required for proper oocyte maturation and early embryonic development. In this review, we comprehensively evaluate and discuss the functional importance of dynamic histone methylation in mammalian oocytes and early embryos, regulated by KMTs, PRMTs, and HDMs.

The Molecular Regulation in the Pathophysiology in Ovarian Aging

The female reproductive system is of great significance to women’s health. Aging of the female reproductive system occurs approximately 10 years prior to the natural age-associated functional decline of other organ systems. With an increase in life expectancy worldwide, reproductive aging has gradually become a key health issue among women. Therefore, an adequate understanding of the causes and molecular mechanisms of ovarian aging is essential towards the inhibition of age-related diseases and the promotion of health and longevity in women. In general, women begin to experience a decline in ovarian function around the age of 35 years, which is mainly manifested as a decrease in the number of ovarian follicles and the quality of oocytes. Studies have revealed the occurrence of mitochondrial dysfunction, reduced DNA repair, epigenetic changes, and metabolic alterations in the cells within the ovaries as age increases. In the present work, we reviewed the possible factors of aging-induced ovarian insufficiency based on its clinical diagnosis and performed an in-depth investigation of the relevant molecular mechanisms and potential targets to provide novel approaches for the effective improvement of ovarian function in older women.

Altered transcriptome in cumulus cells of infertile women with advanced endometriosis with and without endometrioma

RESEARCH QUESTION

Is the transcriptome of cumulus cells of infertile women with advanced endometriosis (EIII/IV), with and without endometrioma, altered?

DESIGN

In this prospective case-control study, next-generation RNA sequencing was used to compare the transcript profile of cumulus cells among infertile patients undergoing ovarian stimulation for intracytoplasmic sperm injection with EIII/IV, with (n = 9) and without endometrioma (n = 9), and controls (n = 9). An in-silico enrichment analysis was conducted to establish the possibly altered pathways in cumulus cells of patients with endometriosis.

RESULTS

Most of the differentially expressed genes (DEG) were found when cumulus cells from women with EIII/IV with endometrioma were compared with controls (DEG, n = 461). In women with EIII/IV without endometrioma, only 66 DEG were verified compared with controls. The enrichment analysis showed that some DEG in cumulus cells of endometriosis are involved in important pathways for the oocyte competence acquisition, such as oxidative phosphorylation, metabolism, mitochondrial function, acetylation and steroid biosynthesis. No DEG were found when cumulus cells from women with EIII/IV with and without endometrioma were compared.

CONCLUSION

RNA sequencing results suggest that cumulus cells of infertile women with EIII/IV have an altered transcriptome, regardless of endometrioma. The present findings offer a better understanding of the genes and molecular mechanisms that may be involved in endometriosis-related infertility, mostly in the oocyte competence acquisition process.

Energy sensors and reproductive hypothalamo-pituitary ovarian axis (HPO) in female mammals: Role of mTOR (mammalian target of rapamycin), AMPK (AMP-activated protein kinase) and SIRT1 (Sirtuin 1)

In female, energy metabolism influences reproductive function by modulating the Hypothalamic Pituitary Ovarian axis including the hypothalamic GnRH neuronal network, the pituitary gonadotropin secretion and the ovarian follicle growth and steroidogenesis. Several hormones and neuropeptides or metabolites are important signals between energy balance and reproduction. These energy sensors mediate their action on reproductive cells through specific kinases or signaling pathways. This review focuses on the role of three main enzymes-specifically, mTOR, AMPK, and SIRT1 at the hypothalamic pituitary and ovarian axis in normal female fertility and then we discuss their possible involvement in some women reproductive disorders known to be associated with metabolic complications, such as polycystic ovary syndrome (PCOS) and premature ovarian failure (POF).

SIRT1 reduces epigenetic and non-epigenetic changes to maintain the quality of postovulatory aged oocytes in mice

Postovulatory oocyte aging has a major influence on the development potential of embryos. Many antioxidants can delay oocyte aging by regulating the expression of SIRT1. However, there is a lack of knowledge on SIRT1 function in postovulatory oocyte aging. In vitro transcribed RNA of Sirt1 was injected into fresh oocytes to investigate the function of SIRT1 during postovulatory oocyte aging. In the present study, SIRT1 was found to be down-regulated in aged oocytes compared with fresh oocytes. Meanwhile the intensity of acetylation of H3K9 (H3K9ac) and H3K4 methylation increased in postovulatory aged oocytes. After the oocytes were injected with SIRT1 and aged for 12 h, the intensity of H3K9ac and H3K4 methylation markedly decreased compared with controls. Furthermore, SIRT1 overexpression also reduced the aging-induced oocyte morphological changes and reactive oxygen species accumulation, maintained the spindle normal morphology and attenuated the aging-associated abnormalities of mitochondrial function. The role of SIRT1 in protecting oocyte aging was diminished when oocytes with overexpressed SIRT1 were cultured with SIRT1 inhibitor EX-527. Briefly, these present results show that SIRT1 not only reduced the non-epigenetic changes such as abnormal oocyte morphology, ROS accumulation, spindle defects and mitochondrial dysfunctions but also regulated the epigenetic changes in order to maintain the quality of postovulatory aged oocytes.

Increased transcriptome variation and localised DNA methylation changes in oocytes from aged mice revealed by parallel single-cell analysis

Advancing maternal age causes a progressive reduction in fertility. The decline in developmental competence of the oocyte with age is likely to be a consequence of multiple contributory factors. Loss of epigenetic quality of the oocyte could impair early developmental events or programme adverse outcomes in offspring that manifest only later in life. Here, we undertake joint profiling of the transcriptome and DNA methylome of individual oocytes from reproductively young and old mice undergoing natural ovulation. We find reduced complexity as well as increased variance in the transcriptome of oocytes from aged females. This transcriptome heterogeneity is reflected in the identification of discrete sub-populations. Oocytes with a transcriptome characteristic of immature chromatin configuration (NSN) clustered into two groups: one with reduced developmental competence, as indicated by lower expression of maternal effect genes, and one with a young-like transcriptome. Oocytes from older females had on average reduced CpG methylation, but the characteristic bimodal methylation landscape of the oocyte was preserved. Germline differentially methylated regions of imprinted genes were appropriately methylated irrespective of age. For the majority of differentially expressed transcripts, the absence of correlated methylation changes suggests a post-transcriptional basis for most age-related effects on the transcriptome. However, we did find differences in gene body methylation at which there were corresponding changes in gene expression, indicating age-related effects on transcription that translate into methylation differences. Interestingly, oocytes varied in expression and methylation of these genes, which could contribute to variable competence of oocytes or penetrance of maternal age-related phenotypes in offspring.

Heterochromatin Morphodynamics in Late Oogenesis and Early Embryogenesis of Mammals

During the period of oocyte growth, chromatin undergoes global rearrangements at both morphological and molecular levels. An intriguing feature of oogenesis in some mammalian species is the formation of a heterochromatin ring-shaped structure, called the karyosphere or surrounded "nucleolus", which is associated with the periphery of the nucleolus-like bodies (NLBs). Morphologically similar heterochromatin structures also form around the nucleolus-precursor bodies (NPBs) in zygotes and persist for several first cleavage divisions in blastomeres. Despite recent progress in our understanding the regulation of gene silencing/expression during early mammalian development, as well as the molecular mechanisms that underlie chromatin condensation and heterochromatin structure, the biological significance of the karyosphere and its counterparts in early embryos is still elusive. We pay attention to both the changes of heterochromatin morphology and to the molecular mechanisms that can affect the configuration and functional activity of chromatin. We briefly discuss how DNA methylation, post-translational histone modifications, alternative histone variants, and some chromatin-associated non-histone proteins may be involved in the formation of peculiar heterochromatin structures intimately associated with NLBs and NPBs, the unique nuclear bodies of oocytes and early embryos.

Mitochondria in early development: linking the microenvironment, metabolism and the epigenome

Mitochondria, originally of bacterial origin, are highly dynamic organelles that have evolved a symbiotic relationship within eukaryotic cells. Mitochondria undergo dynamic, stage-specific restructuring and redistribution during oocyte maturation and preimplantation embryo development, necessary to support key developmental events. Mitochondria also fulfil a wide range of functions beyond ATP synthesis, including the production of intracellular reactive oxygen species and calcium regulation, and are active participants in the regulation of signal transduction pathways. Communication between not only mitochondria and the nucleus, but also with other organelles, is emerging as a critical function which regulates preimplantation development. Significantly, perturbations and deficits in mitochondrial function manifest not only as reduced quality and/or poor oocyte and embryo development but contribute to post-implantation failure, long-term cell function and adult disease. A growing body of evidence indicates that altered availability of metabolic co-factors modulate the activity of epigenetic modifiers, such that oocyte and embryo mitochondrial activity and dynamics have the capacity to establish long-lasting alterations to the epigenetic landscape. It is proposed that preimplantation embryo development may represent a sensitive window during which epigenetic regulation by mitochondria is likely to have significant short- and long-term effects on embryo, and offspring, health. Hence, mitochondrial integrity, communication and metabolism are critical links between the environment, the epigenome and the regulation of embryo development.

Dynamic changes of histone acetylation and methylation in bovine oocytes, zygotes, and preimplantation embryos

Histone modifications play important roles in regulating chromatin dynamic changes. In this study, acetylated histone H3 lysine 9 and 18 (H3K9ac and H3K18ac), acetylated histone H4 lysine 5 and 8 (H4K5ac and H4K8ac), tri-methylation histone H3 lysine 4 (H3K4me3), di-methylation histone H3 lysine 9 (H3K9me2) are investigated in bovine oocytes, zygote, and preimplantation. During meiosis, H3K9ac and H3K18ac are erased after germinal vesicle breakdown, H4K8ac is erased after metaphase I (MI). Although H4K5ac is erased at MI, it is redetectable after this stage. However, histone methylations have no significant change during meiosis. During fertilization, intensive H4K5ac and H4K8ac are resumed on male and female chromatins at postfertilization 4 and 8 hr, respectively. H3K9ac and H3K18ac are resumed on both male and female chromatins at postfertilization 8 and 12 hr, respectively. H3K4me3 and H3K9me2 gradually increased on male chromatin after postfertilization 8 hr, while these two signals on female chromatin are detectable from postfertilization 2-18 hr. During embryo cleavage, H3K9ac, H3K18ac, and H3K4me3 are reduced at 8-cell stage, and then start to increase. H4K5ac, H4K8ac, and H3K9me2 increase after the 4-cell stage. At interphase, H4K5ac and H4K8ac are more intensive in nuclear periphery from 2- to 8-cell stages. During mitosis, the signal of H4K8ac is intensive at chromosome periphery. In summary, during both oocyte meiosis and fertilization, the dynamic changes of both histone acetylations and methylations happen in a process of lysine residue-specific and species-specific. During preimplantation development, the dynamic patterns of both H3K9ac and H3K18ac are similar to that of H3K4me3, while the dynamic pattern of H4K5ac is similar to that of H4K8ac. These results will be helpful for understanding the effect of histone posttranslational modifications on bovine reproduction and development.

Perturbations in imprinted methylation from assisted reproductive technologies but not advanced maternal age in mouse preimplantation embryos

Background

Over the last several decades, the average age of first-time mothers has risen steadily. With increasing maternal age comes a decrease in fertility, which in turn has led to an increase in the use of assisted reproductive technologies by these women. Assisted reproductive technologies (ARTs), including superovulation and embryo culture, have been shown separately to alter imprinted DNA methylation maintenance in blastocysts. However, there has been little investigation on the effects of advanced maternal age, with or without ARTs, on genomic imprinting. We hypothesized that ARTs and advanced maternal age, separately and together, alter imprinted methylation in mouse preimplantation embryos. For this study, we examined imprinted methylation at three genes, Snrpn, Kcnq1ot1, and H19, which in humans are linked to ART-associated methylation errors that lead to imprinting disorders.

Results

Our data showed that imprinted methylation acquisition in oocytes was unaffected by increasing maternal age. Furthermore, imprinted methylation was normally acquired when advanced maternal age was combined with superovulation. Analysis of blastocyst-stage embryos revealed that imprinted methylation maintenance was also not affected by increasing maternal age. In a comparison of ARTs, we observed that the frequency of blastocysts with imprinted methylation loss was similar between the superovulation only and the embryo culture only groups, while the combination of superovulation and embryo culture resulted in a higher frequency of mouse blastocysts with maternal imprinted methylation perturbations than superovulation alone. Finally, the combination of increasing maternal age with ARTs had no additional effect on the frequency of imprinted methylation errors.

Conclusion

Collectively, increasing maternal age with or without superovulation had no effect of imprinted methylation acquisition at Snrpn, Kcnq1ot1, and H19 in oocytes. Furthermore, during preimplantation development, while ARTs generated perturbations in imprinted methylation maintenance in blastocysts, advanced maternal age did not increase the burden of imprinted methylation errors at Snrpn, Kcnq1ot1, and H19 when combined with ARTs. These results provide cautious optimism that advanced maternal age is not a contributing factor to imprinted methylation errors in embryos produced in the clinic. Furthermore, our data on the effects of ARTs strengthen the need to advance clinical methods to reduce imprinted methylation errors in in vitro-produced embryos.

Roles of Resveratrol in Improving the Quality of Postovulatory Aging Oocytes In Vitro

After ovulation, mammalian oocytes will undergo a time-dependent process of aging if they are not fertilized. This postovulatory aging (POA) seriously affects the oocyte quality and then impairs the subsequent fertilization and early embryo development, which should be avoided especially in assisted reproductive technology (ART). Resveratrol is an antioxidant substance that can scavenge free radicals and is effective in improving ovary functions. Here, mouse oocytes were used to investigate the effects and mechanisms of resveratrol on POA oocytes in vitro. With 1.0 µM resveratrol treatment during aging process, the rates of fertilization and blastocyst in POA oocytes increased significantly compared with those in the POA group. Resveratrol can reduce the loss of sperm binding sites by stabilizing Juno. Resveratrol can maintain the normal morphology of spindle and mitochondrion distribution and alleviate the levels of ROS and early apoptosis. Additionally, resveratrol can reduce the changes of H3K9me2. Therefore, resveratrol can significantly improve the quality of POA oocytes in vitro to enhance the rates of fertilization and blastocyst, which may be very helpful during the ART process.

Epigenetics and Female Reproductive Aging

With more women than ever waiting until a more advanced age to have children, there exists a newfound urgency to identify the various implications aging has on human reproduction, and understand the disrupted biological processes that result in these changes. In this review, we focus on one recent area of study: the age related epigenetic changes that have been found in female reproductive organs, and the effect these changes may contribute to reproductive outcomes.

Serum and follicular fluid levels of sirtuin 1, sirtuin 6, and resveratrol in women undergoing in vitro fertilization: an observational, clinical study

Objective

This observational, clinical study was designed to assess the role of sirtuin 1 (SIRT1), sirtuin 6 (SIRT6), and resveratrol in in vitro fertilization (IVF).

Methods

Paired serum and follicular fluid (FF) samples were obtained from 30 consecutive patients (age: 36.43 ± 4.17 years, body mass index: 22.90 ± 2.05 kg/m², duration of infertility: 5.10 ± 2.80 years) who received IVF treatment. SIRT1, SIRT6, and resveratrol levels were measured by enzyme-linked immunosorbent assay.

Results

Ovarian hyperstimulation resulted in significantly higher serum SIRT1 levels in pregnant women (8 patients) compared with non-pregnant women (22 patients). SIRT6 levels remained unchanged after ovarian hyperstimulation, but were significantly lower in pregnant women compared with non-pregnant women before and after hyperstimulation. Both SIRTs were detected in FF, but they appeared to be independent of their serum levels. After correction for confounders, FF SIRT6 levels were positively related to mature oocytes (F = 6.609), whereas serum SIRT1 and SIRT6 levels were related to clinical pregnancy (F = 10.008, F = 5.268, respectively).

Conclusions

Our study shows that SIRT1 and SIRT6, but not resveratrol, are involved in human reproduction and they may have a role in oocyte maturation and clinical pregnancy in IVF.

The effects of biological aging on global DNA methylation, histone modification, and epigenetic modifiers in the mouse germinal vesicle stage oocyte

A cultural trend in developed countries is favoring a delay in maternal age at first childbirth. In mammals fertility and chronological age show an inverse correlation. Oocyte quality is a contributing factor to this multifactorial phenomenon that may be influenced by age-related changes in the oocyte epigenome. Based on previous reports, we hypothesized that advanced maternal age would lead to alterations in the oocyte’s epigenome. We tested our hypothesis by determining protein levels of various epigenetic modifications and modifiers in fully-grown (≥70 µm), germinal vesicle (GV) stage oocytes of young (10-13 weeks) and aged (69-70 weeks) mice. Our results demonstrate a significant increase in protein amounts of the maintenance DNA methyltransferase DNMT1 (P = 0.003) and a trend toward increased global DNA methylation (P = 0.09) with advanced age. MeCP2, a methyl DNA binding domain protein, recognizes methylated DNA and induces chromatin compaction and silencing. We hypothesized that chromatin associated MeCP2 would be increased similarly to DNA methylation in oocytes of aged female mice. However, we detected a significant decrease (P = 0.0013) in protein abundance of MeCP2 between GV stage oocytes from young and aged females. Histone posttranslational modifications can also alter chromatin conformation. Di-methylation of H3K9 (H3K9me2) is associated with permissive heterochromatin while acetylation of H4K5 (H4K5ac) is associated with euchromatin. Our results indicate a trend toward decreasing H3K9me2 (P = 0.077) with advanced female age and no significant differences in levels of H4K5ac. These data demonstrate that physiologic aging affects the mouse oocyte epigenome and provide a better understanding of the mechanisms underlying the decrease in oocyte quality and reproductive potential of aged females.

Age Alters Chromatin Structure and Expression of SUMO Proteins under Stress Conditions in Human Adipose-Derived Stem Cells

Adult stem cells play a critical role in tissue homeostasis and repair. Aging leads to a decline in stem cells’ regenerative capacity that contributes significantly to the maintenance of organ and tissue functions. Age-dependent genomic and epigenetic modifications together play a role in the disruption of critical cellular pathways. However, the epigenetic mechanisms responsible for the decline of adult stem cell functions remain to be well established. Here, we investigated age-dependent, genome-wide alterations in the chromatin accessibility of primary human adipose-derived stem cells (ASCs) in comparison to age-matched fibroblasts via ATAC-seq technology. Our results demonstrate that aging ASCs possess globally more stable chromatin accessibility profiles as compared to aging fibroblasts, suggesting that robust regulatory mechanisms maintain adult stem cell chromatin structure against aging. Furthermore, we observed age-dependent subtle changes in promoter nucleosome positioning in selective pathways during aging, concurrent with altered small ubiquitin-related modifier (SUMO) protein expression under stress conditions. Together, our data suggest a significant role for nucleosome positioning in sumoylation pathway regulation in stress response during adult stem cell aging. The differences described here between the chromatin structure of human ASCs and fibroblasts will further elucidate the mechanisms regulating gene expression during aging in both stem cells and differentiated cells.

Quercetin delays postovulatory aging of mouse oocytes by regulating SIRT expression and MPF activity

If no fertilization occurs at an appropriate time after ovulation, oocyte quality deteriorates rapidly as a process called postovulatory aging. Because the postovulatory aging of oocytes has detrimental effects on embryo development and offspring, many efforts have been made to prevent oocyte aging. Here we showed that quercetin prevented the decline in oocyte quality during postovulatory aging of oocytes. Quercetin treatment reduced aging-induced morphological changes and reactive oxygen species accumulation. Moreover, quercetin attenuated the aging-associated abnormalities in spindle organization and mitochondrial distribution, preventing decrease of SIRT expression and histone methylation. Quercetin also ameliorated the decrease in maturation-promoting factor activity and the onset of apoptosis during postovulatory aging. Furthermore, quercetin treatment during postovulatory aging improves early embryo development. Our results demonstrate that quercetin relieves deterioration in oocyte quality and improves subsequent embryo development.

The effects of superovulation and reproductive aging on the epigenome of the oocyte and embryo

A societal preference of delaying maternal age at first childbirth has increased reliance on assisted reproductive technologies/therapies (ART) to conceive a child. Oocytes that have undergone physiologic aging (≥35 years for humans) are now commonly used for ART, yet evidence is building that suboptimal reproductive environments associated with aging negatively affect oocyte competence and embryo development-although the mechanisms underlying these relationship are not yet well understood. Epigenetic programming of the oocyte occurs during its growth within a follicle, so the ovarian stimulation protocols that administer exogenous hormones, as part of the first step for all ART procedures, may prevent the gamete from establishing an appropriate epigenetic state. Therefore, understanding how oocyte. Therefore, understanding how hormone stimulation and oocyte physiologic age independently and synergistically physiologic age independently and synergistically affect the epigenetic programming of these gametes, and how this may affect their developmental competence, are crucial to improved ART outcomes. Here, we review studies that measured the developmental outcomes affected by superovulation and aging, focusing on how the epigenome (i.e., global and imprinted DNA methylation, histone modifications, and epigenetic modifiers) of gametes and embryos acquired from females undergoing physiologic aging and exogenous ovarian stimulation is affected.

Exercise and epigenetic inheritance of disease risk

Epigenetics is the study of gene expression changes that occur in the absence of altered genotype. Current evidence indicates a role for environmentally induced alterations to epigenetic modifications leading to health and disease changes across multiple generations. This phenomenon is called intergenerational or transgenerational epigenetic inheritance of health or disease. Environmental insults, in the form of toxins, plastics and particular dietary interventions, perturb the epigenetic landscape and influence the health of F1 through to F4 generations in rodents. There is, however, the possibility that healthy lifestyles and environmental factors, such as exercise training, could lead to favourable, heritable epigenetic modifications that augment transcriptional programmes protective of disease, including metabolic dysfunction, heart disease and cancer. The health benefits conferred by regular physical exercise training are unquestionable, yet many of the molecular changes may have heritable health implications for future generations. Similar to other environmental factors, exercise modulates the epigenome of somatic cells and researchers are beginning to study exercise epigenetics in germ cells. The germ cell epigenetic modifications affected by exercise offer a molecular mechanism for the inheritance of health and disease risk. The aims of this review are to: (i) provide an update on the expanding field of exercise epigenetics; (ii) offer an overview of data on intergenerational/transgenerational epigenetic inheritance of disease by environmental insults; (iii) to discuss the potential of exercise-induced intergenerational inheritance of health and disease risk; and finally, outline potential mechanisms and avenues for future work on epigenetic inheritance through exercise.

Role of glutathione in the regulation of epigenetic mechanisms in disease

Epigenetics is a rapidly growing field that studies gene expression modifications not involving changes in the DNA sequence. Histone H3, one of the basic proteins in the nucleosomes that make up chromatin, is S-glutathionylated in mammalian cells and tissues, making Gamma-L-glutamyl-L-cysteinylglycine, glutathione (GSH), a physiological antioxidant and second messenger in cells, a new post-translational modifier of the histone code that alters the structure of the nucleosome. However, the role of GSH in the epigenetic mechanisms likely goes beyond a mere structural function. Evidence supports the hypothesis that there is a link between GSH metabolism and the control of epigenetic mechanisms at different levels (i.e., substrate availability, enzymatic activity for DNA methylation, changes in the expression of microRNAs, and participation in the histone code). However, little is known about the molecular pathways by which GSH can control epigenetic events. Studying mutations in enzymes involved in GSH metabolism and the alterations of the levels of cofactors affecting epigenetic mechanisms appears challenging. However, the number of diseases induced by aberrant epigenetic regulation is growing, so elucidating the intricate network between GSH metabolism, oxidative stress and epigenetics could shed light on how their deregulation contributes to the development of neurodegeneration, cancer, metabolic pathologies and many other types of diseases.

Molecular Mechanisms Responsible for Increased Vulnerability of the Ageing Oocyte to Oxidative Damage

In their midthirties, women experience a decline in fertility, coupled to a pronounced increase in the risk of aneuploidy, miscarriage, and birth defects. Although the aetiology of such pathologies are complex, a causative relationship between the age-related decline in oocyte quality and oxidative stress (OS) is now well established. What remains less certain are the molecular mechanisms governing the increased vulnerability of the aged oocyte to oxidative damage. In this review, we explore the reduced capacity of the ageing oocyte to mitigate macromolecular damage arising from oxidative insults and highlight the dramatic consequences for oocyte quality and female fertility. Indeed, while oocytes are typically endowed with a comprehensive suite of molecular mechanisms to moderate oxidative damage and thus ensure the fidelity of the germline, there is increasing recognition that the efficacy of such protective mechanisms undergoes an age-related decline. For instance, impaired reactive oxygen species metabolism, decreased DNA repair, reduced sensitivity of the spindle assembly checkpoint, and decreased capacity for protein repair and degradation collectively render the aged oocyte acutely vulnerable to OS and limits their capacity to recover from exposure to such insults. We also highlight the inadequacies of our current armoury of assisted reproductive technologies to combat age-related female infertility, emphasising the need for further research into mechanisms underpinning the functional deterioration of the ageing oocyte.

Preovulatory Aging In Vivo and In Vitro Affects Maturation Rates, Abundance of Selected Proteins, Histone Methylation Pattern and Spindle Integrity in Murine Oocytes

Delayed ovulation and delayed fertilization can lead to reduced developmental competence of the oocyte. In contrast to the consequences of postovulatory aging of the oocyte, hardly anything is known about the molecular processes occurring during oocyte maturation if ovulation is delayed (preovulatory aging). We investigated several aspects of oocyte maturation in two models of preovulatory aging: an in vitro follicle culture and an in vivo mouse model in which ovulation was postponed using the GnRH antagonist cetrorelix. Both models showed significantly reduced oocyte maturation rates after aging. Furthermore, in vitro preovulatory aging deregulated the protein abundance of the maternal effect genes Smarca4 and Nlrp5, decreased the levels of histone H3K9 trimethylation and caused major deterioration of chromosome alignment and spindle conformation. Protein abundance of YBX2, an important regulator of mRNA stability, storage and recruitment in the oocyte, was not affected by in vitro aging. In contrast, in vivo preovulatory aging led to reduction in Ybx2 transcript and YBX2 protein abundance. Taken together, preovulatory aging seems to affect various processes in the oocyte, which could explain the low maturation rates and the previously described failures in fertilization and embryonic development.

Age-associated events in bovine oocytes and possible countermeasures

Maternal aging profoundly affects oocyte quality. This has become common knowledge in industrialized countries and extensive studies addressing the causes and possible countermeasures against age-associated deterioration of oocytes suggest that mitochondrial dysfunction is a causal factor in infertility. However, almost all studies addressing age-associated events in oocytes have used mice as an animal model, and the reproductive life of mice is very short, making it difficult to study the gradual decline in fertility observed in humans. In the present review, age-associated changes in the quality and quantity of bovine oocytes and possible countermeasures related to mitochondrial quality control are introduced.