Epigenetic Clock Deceleration and Maternal Reproductive Efforts: Associations With Increasing Gray Matter Volume of the Precuneus

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.

Evaluation of the pooled sample method in Infinium MethylationEPIC BeadChip array by comparison with individual samples

BACKGROUND

The pooled sample method is used in epigenomic research and expression analysis and is a cost-effective screening approach for small amounts of DNA. Evaluation of the pooled sample method in epigenomic studies is performed using the Illumina Infinium Methylation 450K BeadChip array; however, subsequent reports on the updated 850K array are lacking. A previous study demonstrated that the methylation levels obtained from individual samples were accurately replicated using pooled samples but did not address epigenome-wide association study (EWAS) statistics. The DNA quantification method, which is important for the homogeneous mixing of DNA in the pooled sample method, has since become fluorescence-based, and additional factors need to be considered including the resolution of batch effects of microarray chips and the heterogeneity of the cellular proportions from which the DNA samples are derived. In this study, four pooled samples were created from 44 individual samples, and EWAS statistics for differentially methylated positions (DMPs) and regions (DMRs) were conducted for individual samples and compared with the statistics obtained from the pooled samples.

RESULTS

The methylation levels could be reproduced fairly well in the pooled samples. This was the case for the entire dataset and when limited to the top 100 CpG sites, consistent with a previous study using the 450K BeadChip array. However, the statistical results of the EWAS for the DMP by individual samples were not replicated in pooled samples. Qualitative analyses highlighting methylation within an arbitrary candidate gene were replicable. Focusing on chr 20, the statistical results of EWAS for DMR from individual samples showed replicability in the pooled samples as long as they were limited to regions with a sufficient effect size.

CONCLUSIONS

The pooled sample method replicated the methylation values well and can be used for EWAS in DMR. This method is sample amount-effective and cost-effective and can be utilized for screening by carefully understanding the effective features and disadvantages of the pooled sample method and combining it with candidate gene analyses.

Correlates of estimated lifetime cruciate ligament survival inform potential rupture risk reduction strategies: findings from the Exceptional Aging in Rottweilers Study

Cranial cruciate ligament (CCL) rupture is one of the most commonly diagnosed orthopedic conditions of pet dogs, making estimated lifetime cruciate ligament survival an attractive endpoint for studies attempting to define clinical and genetic correlates of rupture risk reduction. Early life experiences contribute significantly to the origins of adult health outcomes, yet our current understanding of modifiable susceptibility factors that drive the high frequency of CCL rupture remains limited. We reasoned that combining lifetime medical history with standardized late-life assessment of lifetime cruciate ligament survival and detailed phenotyping of each dog for selected risk variables would provide a sensitive approach to identify factors that would differentiate between lifelong avoidance versus susceptibility to ligament rupture. Here, we report results of Kaplan-Meier analysis of estimated lifetime cruciate ligament survival and Cox proportional hazards modeling to assess risk variables in a lifetime cohort study of 123 purebred Rottweilers, a breed at high risk for veterinarian-diagnosed CCL rupture. We show that gonad removal during the 24-month developmental period is adversely associated with three measures of susceptibility-increased incidence of CCL rupture, multiplicity (bilateral rupture), and accelerated time to initial CCL failure. Our analysis reveals two other phenotypes-short adult height and the production of offspring (in females)-are associated with significant CCL rupture risk reduction. Together, the results provide clues to an early endocrine influence on lifetime cruciate ligament survival. Further, we identify two distinct clinical syndromes of CCL failure, providing a disease subtyping framework to advance future progress in genetic epidemiology, pathogenesis, and prediction. By conducting an evaluation of estimated lifetime CCL survival in dogs, we show that cruciate ligament survival may be jeopardized by gonad removal during the developmental period. Avoidance of such early environmental adversity may represent an actionable method for the control of canine CCL disease in certain breeds.

Epigenetic clocks and female fertility timeline: A new approach to an old issue?

Worldwide increase in life expectancy has boosted research on aging. Overcoming the concept of chronological age, higher attention has been addressed to biological age, which reflects a person's real health state, and which may be the resulting combination of both intrinsic and environmental factors. As epigenetics may exert a pivotal role in the biological aging, epigenetic clocks were developed. They are based on mathematical models aimed at identifying DNA methylation patterns that can define the biological age and that can be adopted for different clinical scopes (i.e., estimation of the risks of developing age-related disorders or predicting lifespan). Recently, epigenetic clocks have gained a peculiar attention in the fertility research field, in particular in the female counterpart. The insight into the possible relations between epigenetic aging and women's infertility might glean additional information about certain conditions that are still not completely understood. Moreover, they could disclose significant implications for health promotion programs in infertile women. Of relevance here is that the impact of biological age and epigenetics may not be limited to fertility status but could translate into pregnancy issues. Indeed, epigenetic alterations of the mother may transfer into the offspring, and pregnancy itself as well as related complications could contribute to epigenetic modifications in both the mother and newborn. However, even if the growing interest has culminated in the conspicuous production of studies on these topics, a global overview and the availability of validated instruments for diagnosis is still missing. The present narrative review aims to explore the possible bonds between epigenetic aging and fertility timeline. In the "infertility" section, we will discuss the advances on epigenetic clocks focusing on the different tissues examined (endometrium, peripheral blood, ovaries). In the "pregnancy" section, we will discuss the results obtained from placenta, umbilical cord and peripheral blood. The possible role of epigenetic aging on infertility mechanisms and pregnancy outcomes represents a question that may configure epigenetic clock as a bond between two apparently opposite worlds: infertility and pregnancy.