Epigenetic clock and methylation study of oocytes from a bovine model of reproductive aging

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.

CRL4DCAF13 E3 ubiquitin ligase targets MeCP2 for degradation to prevent DNA hypermethylation and ensure normal transcription in growing oocytes

The DNA methylation is gradually acquired during oogenesis, a process sustained by successful follicle development. However, the functional roles of methyl-CpG-binding protein 2 (MeCP2), an epigenetic regulator displaying specifical binding with methylated DNA, remains unknown in oogenesis. In this study, we found MeCP2 protein was highly expressed in primordial and primary follicle, but was almost undetectable in secondary follicles. However, in aged ovary, MeCP2 protein is significantly increased in both oocyte and granulosa cells. Overexpression of MeCP2 in growing oocyte caused transcription dysregulation, DNA hypermethylation, and genome instability, ultimately leading to follicle growth arrest and apoptosis. MeCP2 is targeted by DCAF13, a substrate recognition adaptor of the Cullin 4-RING (CRL4) E3 ligase, and polyubiquitinated for degradation in both cells and oocytes. Dcaf13-null oocyte exhibited an accumulation of MeCP2 protein, and the partial rescue of follicle growth arrest induced by Dcaf13 deletion was observed following MeCP2 knockdown. The RNA-seq results revealed that large amounts of genes were regulated by the DCAF13-MeCP2 axis in growing oocytes. Our study demonstrated that CRL4DCAF13 E3 ubiquitin ligase targets MeCP2 for degradation to ensure normal DNA methylome and transcription in growing oocytes. Moreover, in aged ovarian follicles, deceased DCAF13 and DDB1 protein were observed, indicating a potential novel mechanism that regulates ovary aging.

Conservative Hypomethylation of Mesenchymal Stem Cells and Their Secretome Restored the Follicular Development in Cisplatin-Induced Premature Ovarian Failure Mice

Premature ovarian failure (POF) is one of the main causes of infertility in women under the age of 40 years. Recently, epigenetic reprogramming, particularly DNA hypomethylation, has emerged as a promising strategy to enhance the therapeutic potential of mesenchymal stem cells (MSCs). Thus, it is crucial to elucidate how far global hypomethylation of MSCs genome can maintain their pluripotency and viability and improve their therapeutic effect in chemotherapy-induced POF mice. Herein, the genomic DNA of bone marrow-derived MSCs (BM-MSCs) was hypomethylated by the DNA methyltransferase inhibitor (5-Aza-dC), and the degree of global hypomethylation was assessed by methylation-sensitive HepII/MspI restriction analysis. Next, mildly hypomethylated cells and their secretome were independently transplanted (or infused) in POF mice, established via cisplatin-mediated gonadotoxicity. We found that conservative global hypomethylation of BM-MSCs genome with low doses of 5-Aza-dC (≤0.5 μM) has maintained cell viability and MSCs-specific clusters of differentiation (CD). Engraftment of mildly hypomethylated cells in POF mice, or infusion of their secretome, improved the concentrations of estradiol (E2), follicle-stimulating hormone (FSH), and anti-Mullerian hormone (AMH). Furthermore, mice restored their normal body weight, ovarian size, and ovarian follicle count. This was associated with improved follicular development, where the populations of healthy primordial, primary, secondary, and tertiary follicles were significantly ameliorated, relative to mice transplanted with normally methylated cells. This observational study suggests that transplantation of mildly hypomethylated BM-MSCs cells and their secretome can restore the structural and functional integrity of the damaged ovaries in POF mice. Also, it presents conservative hypomethylation of BM-MSCs and their secretome as a promising alternative to MSCs transplantation.

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.

DNA methylation as a window into female reproductive aging

People with ovaries experience reproductive aging as their reproductive function and system declines. This has significant implications for both fertility and long-term health, with people experiencing an increased risk of cardiometabolic disorders after menopause. Reproductive aging can be assessed through markers of ovarian reserve, response to fertility treatment or molecular biomarkers, including DNA methylation. Changes in DNA methylation with age associate with poorer reproductive outcomes, and epigenome-wide studies can provide insight into genes and pathways involved. DNA methylation-based epigenetic clocks can quantify biological age in reproductive tissues and systemically. This review provides an overview of hallmarks and theories of aging in the context of the reproductive system, and then focuses on studies of DNA methylation in reproductive tissues.

Pan-primate studies of age and sex

Age and sex have a profound effect on cytosine methylation levels in humans and many other species. Here we analyzed DNA methylation profiles of 2400 tissues derived from 37 primate species including 11 haplorhine species (baboons, marmosets, vervets, rhesus macaque, chimpanzees, gorillas, orangutan, humans) and 26 strepsirrhine species (suborders Lemuriformes and Lorisiformes). From these we present here, pan-primate epigenetic clocks which are highly accurate for all primates including humans (age correlation R = 0.98). We also carried out in-depth analysis of baboon DNA methylation profiles and generated five epigenetic clocks for baboons (Olive-yellow baboon hybrid), one of which, the pan-tissue epigenetic clock, was trained on seven tissue types (fetal cerebral cortex, adult cerebral cortex, cerebellum, adipose, heart, liver, and skeletal muscle) with ages ranging from late fetal life to 22.8 years of age. Using the primate data, we characterize the effect of age and sex on individual cytosines in highly conserved regions. We identify 11 sex-related CpGs on autosomes near genes (POU3F2, CDYL, MYCL, FBXL4, ZC3H10, ZXDC, RRAS, FAM217A, RBM39, GRIA2, UHRF2). Low overlap can be observed between age- and sex-related CpGs. Overall, this study advances our understanding of conserved age- and sex-related epigenetic changes in primates, and provides biomarkers of aging for all primates.

Biological clocks as age estimation markers in animals: a systematic review and meta-analysis

Various biological attributes associated with individual fitness in animals change predictably over the lifespan of an organism. Therefore, the study of animal ecology and the work of conservationists frequently relies upon the ability to assign animals to functionally relevant age classes to model population fitness. Several approaches have been applied to determining individual age and, while these methods have proved useful, they are not without limitations and often lack standardisation or are only applicable to specific species. For these reasons, scientists have explored the potential use of biological clocks towards creating a universal age-determination method. Two biological clocks, tooth layer annulation and otolith layering have found universal appeal. Both methods are highly invasive and most appropriate for post-mortem age-at-death estimation. More recently, attributes of cellular ageing previously explored in humans have been adapted to studying ageing in animals for the use of less-invasive molecular methods for determining age. Here, we review two such methods, assessment of methylation and telomere length, describing (i) what they are, (ii) how they change with age, and providing (iii) a summary and meta-analysis of studies that have explored their utility in animal age determination. We found that both attributes have been studied across multiple vertebrate classes, however, telomere studies were used before methylation studies and telomere length has been modelled in nearly twice as many studies. Telomere length studies included in the review often related changes to stress responses and illustrated that telomere length is sensitive to environmental and social stressors and, in the absence of repair mechanisms such as telomerase or alternative lengthening modes, lacks the ability to recover. Methylation studies, however, while also detecting sensitivity to stressors and toxins, illustrated the ability to recover from such stresses after a period of accelerated ageing, likely due to constitutive expression or reactivation of repair enzymes such as DNA methyl transferases. We also found that both studied attributes have parentally heritable features, but the mode of inheritance differs among taxa and may relate to heterogamy. Our meta-analysis included more than 40 species in common for methylation and telomere length, although both analyses included at least 60 age-estimation models. We found that methylation outperforms telomere length in terms of predictive power evidenced from effect sizes (more than double that observed for telomeres) and smaller prediction intervals. Both methods produced age correlation models using similar sample sizes and were able to classify individuals into young, middle, or old age classes with high accuracy. Our review and meta-analysis illustrate that both methods are well suited to studying age in animals and do not suffer significantly from variation due to differences in the lifespan of the species, genome size, karyotype, or tissue type but rather that quantitative method, patterns of inheritance, and environmental factors should be the main considerations. Thus, provided that complex factors affecting the measured trait can be accounted for, both methylation and telomere length are promising targets to develop as biomarkers for age determination in animals.

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.

DNA methylation networks underlying mammalian traits

Using DNA methylation profiles (n = 15,456) from 348 mammalian species, we constructed phyloepigenetic trees that bear marked similarities to traditional phylogenetic ones. Using unsupervised clustering across all samples, we identified 55 distinct cytosine modules, of which 30 are related to traits such as maximum life span, adult weight, age, sex, and human mortality risk. Maximum life span is associated with methylation levels in HOXL subclass homeobox genes and developmental processes and is potentially regulated by pluripotency transcription factors. The methylation state of some modules responds to perturbations such as caloric restriction, ablation of growth hormone receptors, consumption of high-fat diets, and expression of Yamanaka factors. This study reveals an intertwined evolution of the genome and epigenome that mediates the biological characteristics and traits of different mammalian species.

Harnessing male germline epigenomics for the genetic improvement in cattle

Sperm is essential for successful artificial insemination in dairy cattle, and its quality can be influenced by both epigenetic modification and epigenetic inheritance. The bovine germline differentiation is characterized by epigenetic reprogramming, while intergenerational and transgenerational epigenetic inheritance can influence the offspring's development through the transmission of epigenetic features to the offspring via the germline. Therefore, the selection of bulls with superior sperm quality for the production and fertility traits requires a better understanding of the epigenetic mechanism and more accurate identifications of epigenetic biomarkers. We have comprehensively reviewed the current progress in the studies of bovine sperm epigenome in terms of both resources and biological discovery in order to provide perspectives on how to harness this valuable information for genetic improvement in the cattle breeding industry.

Novel insights into reproductive ageing and menopause from genomics

The post-reproductive phase or menopause in females is triggered by a physiological timer that depends on a threshold of follicle number in the ovary. Curiously, reproductive senescence appears to be decoupled from chronological age and is instead thought to be a function of physiological ageing. Ovarian ageing is associated with a decrease in oocyte developmental competence, attributed to a concomitant increase in meiotic errors. Although many biological hallmarks of general ageing are well characterized, the precise mechanisms underlying the programmed ageing of the female reproductive system remain elusive. In particular, the molecular pathways linking the external menopause trigger to the internal oocyte chromosome segregation machinery that controls fertility outcomes is unclear. However, recent large scale genomics studies have begun to provide insights into this process. Next-generation sequencing integrated with systems biology offers the advantage of sampling large datasets to uncover molecular pathways associated with a phenotype such as ageing. In this mini-review, we discuss findings from these studies that are crucial for advancing female reproductive senescence research. Targets identified in these studies can inform future animal models for menopause. We present three potential hypotheses for how external pathways governing ovarian ageing can influence meiotic chromosome segregation, with evidence from both animal models and molecular targets revealed from genomics studies. Although still in incipient stages, we discuss the potential of genomics studies combined with epigenetic age acceleration models for providing a predictive toolkit of biomarkers controlling menopause onset in women. We also speculate on future research directions to investigate extending female reproductive lifespan, such as comparative genomics in model systems that lack menopause. Novel genomics insights from such organisms are predicted to provide clues to preserving female fertility.

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.

Reprogramming of ovarian aging epigenome by resveratrol

Resveratrol is an antiaging, antioxidant, and anti-inflammatory natural polyphenolic compound. Growing evidence indicates that resveratrol has potential therapeutic effects for improving aging ovarian function. However, the mechanisms underlying prolonged reproductive longevity remain elusive. We found that resveratrol ameliorates ovarian aging transcriptome, some of which are associated with specific changes in methylome. In addition to known aging transcriptome of oocytes and granulosa cells such as decline in oxidoreductase activity, metabolism and mitochondria function, and elevated DNA damage and apoptosis, actin cytoskeleton are notably downregulated with age, and these defects are mostly rescued by resveratrol. Moreover, the aging-associated hypermethylation of actin cytoskeleton is decreased by resveratrol. In contrast, deletion of Tet2, involved in DNA demethylation, abrogates resveratrol-reprogrammed ovarian aging transcriptome. Consistently, Tet2 deficiency results in additional altered pathways as shown by increased mTOR and Wnt signaling, as well as reduced DNA repair and actin cytoskeleton with mouse age. Moreover, genes associated with oxidoreductase activity and oxidation-reduction process were hypermethylated in Tet2-deficient oocytes from middle-age mice treated with resveratrol, indicating that loss of Tet2 abolishes the antioxidant effect of resveratrol. Taking together, our finding provides a comprehensive landscape of transcriptome and epigenetic changes associated with ovarian aging that can be reprogrammed by resveratrol administration, and suggests that aberrantly increased DNA methylation by Tet2 deficiency promotes additional aging epigenome that cannot be effectively restored to younger state by resveratrol.

DNA methylation profile in beef cattle is influenced by additive genetics and age

DNA methylation (DNAm) has been considered a promising indicator of biological age in mammals and could be useful to increase the accuracy of phenotypic prediction in livestock. The objectives of this study were to estimate the heritability and age effects of site-specific DNAm (DNAm level) and cumulative DNAm across all sites (DNAm load) in beef cattle. Blood samples were collected from cows ranging from 217 to 3,192 days (0.6 to 8.7 years) of age (n = 136). All animals were genotyped, and DNAm was obtained using the Infinium array HorvathMammalMethylChip40. Genetic parameters for DNAm were obtained from an animal model based on the genomic relationship matrix, including the fixed effects of age and breed composition. Heritability estimates of DNAm levels ranged from 0.18 to 0.72, with a similar average across all regions and chromosomes. Heritability estimate of DNAm load was 0.45. The average age effect on DNAm level varied among genomic regions. The DNAm level across the genome increased with age in the promoter and 5′ UTR and decreased in the exonic, intronic, 3′ UTR, and intergenic regions. In addition, DNAm level increased with age in regions enriched in CpG and decreased in regions deficient in CpG. Results suggest DNAm profiles are influenced by both genetics and the environmental effect of age in beef cattle.

Epigenetic clock and methylation studies in marsupials: opossums, Tasmanian devils, kangaroos, and wallabies

The opossum (Monodelphis domestica), with its sequenced genome, ease of laboratory care and experimental manipulation, and unique biology, is the most used laboratory marsupial. Using the mammalian methylation array, we generated DNA methylation data from n = 100 opossum samples from the ear, liver, and tail. We contrasted postnatal development and later aging effects in the opossum methylome with those in mouse (Mus musculus, C57BL/6 J strain) and other marsupial species such as Tasmanian devil, kangaroos, and wallabies. While the opossum methylome is similar to that of mouse during postnatal development, it is distinct from that shared by other mammals when it comes to the age-related gain of methylation at target sites of polycomb repressive complex 2. Our immunohistochemical staining results provide additional support for the hypothesis that PRC2 activity increases with later aging in mouse tissues but remains constant in opossum tissues. We present several epigenetic clocks for opossums that are distinguished by their compatibility with tissue type (pan-tissue and blood clock) and species (opossum and human). Two dual-species human-opossum pan-tissue clocks accurately measure chronological age and relative age, respectively. The human-opossum epigenetic clocks are expected to provide a significant boost to the attractiveness of opossum as a biological model. Additional epigenetic clocks for Tasmanian devil, red kangaroos and other species of the genus Macropus may aid species conservation efforts.

Ribosomal DNA methylation in human and mouse oocytes increases with age

An age-dependent increase in ribosomal DNA (rDNA) methylation has been observed across a broad spectrum of somatic tissues and the male mammalian germline. Bisulfite pyrosequencing (BPS) was used to determine the methylation levels of the rDNA core promoter and the rDNA upstream control element (UCE) along with two oppositely genomically imprinted control genes (PEG3 and GTL2) in individual human germinal vesicle (GV) oocytes from 90 consenting women undergoing fertility treatment because of male infertility. Apart from a few (4%) oocytes with single imprinting defects (in either PEG3 or GTL2), the analyzed GV oocytes displayed correct imprinting patterns. In 95 GV oocytes from 42 younger women (26-32 years), the mean methylation levels of the rDNA core promoter and UCE were 7.4±4.0% and 9.3±6.1%, respectively. In 79 GV oocytes from 48 older women (33-39 years), methylation levels increased to 9.3±5.3% (P = 0.014) and 11.6±7.4% (P = 0.039), respectively. An age-related increase in oocyte rDNA methylation was also observed in 123 mouse GV oocytes from 29 4-16-months-old animals. Similar to the continuously mitotically dividing male germline, ovarian aging is associated with a gain of rDNA methylation in meiotically arrested oocytes. Oocytes from the same woman can exhibit varying rDNA methylation levels and, by extrapolation, different epigenetic ages.

A mammalian methylation array for profiling methylation levels at conserved sequences

Infinium methylation arrays are not available for the vast majority of non-human mammals. Moreover, even if species-specific arrays were available, probe differences between them would confound cross-species comparisons. To address these challenges, we developed the mammalian methylation array, a single custom array that measures up to 36k CpGs per species that are well conserved across many mammalian species. We designed a set of probes that can tolerate specific cross-species mutations. We annotate the array in over 200 species and report CpG island status and chromatin states in select species. Calibration experiments demonstrate the high fidelity in humans, rats, and mice. The mammalian methylation array has several strengths: it applies to all mammalian species even those that have not yet been sequenced, it provides deep coverage of conserved cytosines facilitating the development of epigenetic biomarkers, and it increases the probability that biological insights gained in one species will translate to others.

Methods to probe DNA methylation in the majority of non-human mammals are lacking. Here the authors developed a Mammalian Methylation Array that includes 36k well-conserved CpGs in mammals which will facilitate cross-species comparisons. They annotate the conserved CpGs in > 200 species. The array allows one to measure methylation in all mammalian species including unsequenced ones.

Development of Epigenetic Clocks for Key Ruminant Species

Robust biomarkers of chronological age have been developed in humans and model mammalian species such as rats and mice using DNA methylation data. The concept of these so-called "epigenetic clocks" has emerged from a large body of literature describing the relationship between genome-wide methylation levels and age. Epigenetic clocks exploit this phenomenon and use small panels of differentially methylated cytosine (CpG) sites to make robust predictions of chronological age, independent of tissue type. Here, we present highly accurate livestock epigenetic clocks for which we have used the custom mammalian methylation array "HorvathMammalMethyl40" to construct the first epigenetic clock for domesticated goat (Capra hircus), cattle (Bos taurus), Red (Cervus elaphus) and Wapiti deer (Cervus canadensis) and composite-breed sheep (Ovis aries). Additionally, we have constructed a 'farm animal clock' for all species included in the study, which will allow for robust predictions to be extended to various breeds/strains. The farm animal clock shows similarly high accuracy to the individual species' clocks (r > 0.97), utilizing only 217 CpG sites to estimate age (relative to the maximum lifespan of the species) with a single mathematical model. We hypothesise that the applications of this livestock clock could extend well beyond the scope of chronological age estimates. Many independent studies have demonstrated that a deviation between true age and clock derived molecular age is indicative of past and/or present health (including stress) status. There is, therefore, untapped potential to utilize livestock clocks in breeding programs as a predictor for age-related production traits.

chi-miR-324-3p Regulates Goat Granulosa Cell Proliferation by Targeting DENND1A

Granulosa cell (GC) proliferation provides essential conditions for ovulation in animals. A previous study showed that DENND1A plays a significant role in polycystic ovary syndrome. However, the modulation of DENND1A in GCs remains unclear. Our previous integrated analysis of miRNA–mRNA revealed that the 3'-untranslated region of DENND1A could be a target of chi-miR-324-3p. In this study, we used quantitative reverse transcription polymerase chain reaction (RT-qPCR) to investigate DENND1A expression in ovarian tissues of high- and low-yielding goats. Furthermore, dual-fluorescent reporter vector experiments, Cell Counting Kit-8 (CCK-8) assay, and RT-qPCR were used to elucidate the regulatory pathway of chi-miR-324-3p-DENND1A in GCs. The results revealed an opposite tendency between the expressions of chi-miR-324-3p and DENND1A in the ovaries of high- and low-yielding goats. The CCK-8 assay indicated that chi-miR-324-3p overexpression significantly suppressed GC proliferation, whereas chi-miR-324-3p inhibition promoted GC proliferation. In addition, the expressions of GC proliferation markers LHR, Cylin D2, and CDK4 showed the same tendency. The dual-fluorescent reporter assay revealed that chi-miR-324-3p directly targeted DENND1A, and the RT-qPCR results revealed that DENND1A expression was inhibited by chi-miR-324-3p. In summary, chi-miR-324-3p inhibited the proliferation of GCs by targeting DENND1A.

An Epigenetic Aging Clock for Cattle Using Portable Sequencing Technology

Extensively grazed cattle are often mustered only once a year. Therefore, birthdates are typically unknown or inaccurate. Birthdates would be useful for deriving important traits (growth rate; calving interval), breed registrations, and making management decisions. Epigenetic clocks use methylation of DNA to predict an individual's age. An epigenetic clock for cattle could provide a solution to the challenges of industry birthdate recording. Here we derived the first epigenetic clock for tropically adapted cattle using portable sequencing devices from tail hair, a tissue which is widely used in industry for genotyping. Cattle (n = 66) with ages ranging from 0.35 to 15.7 years were sequenced using Oxford Nanopore Technologies MinION and methylation was called at CpG sites across the genome. Sites were then filtered and used to calculate a covariance relationship matrix based on methylation state. Best linear unbiased prediction was used with 10-fold cross validation to predict age. A second methylation relationship matrix was also calculated that contained sites associated with genes used in the dog and human epigenetic clocks. The correlation between predicted age and actual age was 0.71 for all sites and 0.60 for dog and human gene epigenetic clock sites. The mean absolute deviation was 1.4 years for animals aged less than 3 years of age, and 1.5 years for animals aged 3-10 years. This is the first reported epigenetic clock using industry relevant samples in cattle.

Nicotinamide Adenine Nucleotide-The Fountain of Youth to Prevent Oocyte Aging?

According to the U.S. Special Operations Command (SOCOM), new clinical trials of an anti-aging oral treatment using nicotinamide adenine nucleotide are planned for 2022. All over the globe, the discovery of the fountain of youth is still a great goal to reach, not only among aging researchers, since people desire to stay longer healthy and feel young when reaching old age. Since the 1960s, women delaying pregnancy to pursue higher educational levels and a career path has contributed to drastically diminished overall female fertility rates (e.g., number of born offspring/woman). Consequently, a growing number of advanced-aged women depend on assisted reproductive technologies (ART) to become pregnant. In 2019, the Society for Assisted Reproductive Technology reported 293,672 cycles for oocyte retrieval. This change of demographics influenced women's age of having their first child, which has increased significantly. However, their reproductive tract shows hallmarks of aging very early in life without an effective preventive treatment. Therefore, we will present whether NAD+ could help to prevent oocyte aging.

Epigenetic age prediction

Advanced age is the main common risk factor for cancer, cardiovascular disease and neurodegeneration. Yet, more is known about the molecular basis of any of these groups of diseases than the changes that accompany ageing itself. Progress in molecular ageing research was slow because the tools predicting whether someone aged slowly or fast (biological age) were unreliable. To understand ageing as a risk factor for disease and to develop interventions, the molecular ageing field needed a quantitative measure; a clock for biological age. Over the past decade, a number of age predictors utilising DNA methylation have been developed, referred to as epigenetic clocks. While they appear to estimate biological age, it remains unclear whether the methylation changes used to train the clocks are a reflection of other underlying cellular or molecular processes, or whether methylation itself is involved in the ageing process. The precise aspects of ageing that the epigenetic clocks capture remain hidden and seem to vary between predictors. Nonetheless, the use of epigenetic clocks has opened the door towards studying biological ageing quantitatively, and new clocks and applications, such as forensics, appear frequently. In this review, we will discuss the range of epigenetic clocks available, their strengths and weaknesses, and their applicability to various scientific queries.