Meiotic Cohesin and Variants Associated With Human Reproductive Aging and Disease

Changes in DNA repair compartments and cohesin loss promote DNA damage accumulation in aged oocytes

Oocyte loss, a natural process that accelerates as women approach their mid-30s, poses a significant challenge to female reproduction. Recent studies have identified DNA damage as a primary contributor to oocyte loss, but the mechanisms underlying DNA damage accumulation remain unclear. Here, we show that aged oocytes have a lower DNA repair capacity and reduced mobility of DNA damage sites compared to young oocytes. Incomplete DNA repair in aged oocytes results in defective chromosome integrity and partitioning, thereby compromising oocyte quality. We found that DNA repair proteins are arranged in spatially distinct DNA repair compartments that form during the late stages of oocyte growth, accompanied by changes in the activity of DNA repair pathways. We demonstrate alterations in these compartments with age, including substantial changes in the levels of key DNA repair proteins and a shift toward error-prone DNA repair pathways. In addition, we show that reduced cohesin levels make aged oocytes more vulnerable to persistent DNA damage and cause changes in DNA repair compartments. Our study links DNA damage accumulation in aged oocytes, a leading cause of oocyte loss, to cohesin deterioration and changes in the organization, abundance, and response of DNA repair machinery.

Positive Selection Drives the Evolution of the Structural Maintenance of Chromosomes (SMC) Complexes

Structural Maintenance of Chromosomes (SMC) complexes are an evolutionary conserved protein family. In most eukaryotes, three SMC complexes have been characterized, as follows: cohesin, condensin, and SMC5/6 complexes. These complexes are involved in a plethora of functions, and defects in SMC genes can lead to an increased risk of chromosomal abnormalities, infertility, and cancer. To investigate the evolution of SMC complex genes in mammals, we analyzed their selective patterns in an extended phylogeny. Signals of positive selection were identified for condensin NCAPG, for two SMC5/6 complex genes (SMC5 and NSMCE4A), and for all cohesin genes with almost exclusive meiotic expression (RAD21L1, REC8, SMC1B, and STAG3). For the latter, evolutionary rates correlate with expression during female meiosis, and most positively selected sites fall in intrinsically disordered regions (IDRs). Our results support growing evidence that IDRs are fast evolving, and that they most likely contribute to adaptation through modulation of phase separation. We suggest that the natural selection signals identified in SMC complexes may be the result of different selective pressures: a host-pathogen arms race in the condensin and SMC5/6 complexes, and an intragenomic conflict for meiotic cohesin genes that is similar to that described for centromeres and telomeres.

The oocyte microenvironment is altered in adolescents compared to oocyte donors

STUDY QUESTION

Do the molecular signatures of cumulus cells (CCs) and follicular fluid (FF) of adolescents undergoing fertility preservation differ from that of oocyte donors?

SUMMARY ANSWER

The microenvironment immediately surrounding the oocyte, including the CCs and FF, is altered in adolescents undergoing fertility preservation compared to oocyte donors.

WHAT IS KNOWN ALREADY

Adolescents experience a period of subfecundity following menarche. Recent evidence suggests that this may be at least partially due to increased oocyte aneuploidy. Reproductive juvenescence in mammals is associated with suboptimal oocyte quality.

STUDY DESIGN SIZE DURATION

This was a prospective cohort study. Adolescents (10-19 years old, n = 23) and oocyte donors (22-30 years old, n = 31) undergoing ovarian stimulation and oocyte retrieval at a single center between 1 November 2020 and 1 May 2023 were enrolled in this study.

PARTICIPANTS/MATERIALS SETTING METHODS

Patient demographics, ovarian stimulation, and oocyte retrieval outcomes were collected for all participants. The transcriptome of CCs associated with mature oocytes was compared between adolescents (10-19 years old, n = 19) and oocyte donors (22-30 years old, n = 19) using bulk RNA-sequencing. FF cytokine profiles (10-19 years old, n = 18 vs 25-30 years old, n = 16) were compared using cytokine arrays.

MAIN RESULTS AND THE ROLE OF CHANCE

RNA-seq analysis revealed 581 differentially expressed genes in CCs of adolescents relative to oocyte donors, with 361 genes downregulated and 220 upregulated. Genes enriched in pathways involved in cell cycle and cell division (e.g. GO: 1903047, P = 3.5 × 10-43; GO: 0051983, P = 4.1 × 10-30; GO: 0000281, P = 7.7 × 10-15; GO: 0044839, P = 5.3 × 10-13) were significantly downregulated, while genes enriched in several pathways involved in cellular and vesicle organization (e.g. GO: 0010256, P = 1.2 × 10-8; GO: 0051129, P = 6.8 × 10-7; GO: 0016050, P = 7.4 × 10-7; GO: 0051640, P = 8.1 × 10-7) were upregulated in CCs of adolescents compared to oocyte donors. The levels of nine cytokines were significantly increased in FF of adolescents compared to oocyte donors: IL-1 alpha (2-fold), IL-1 beta (1.7-fold), I-309 (2-fold), IL-15 (1.6-fold), TARC (1.9-fold), TPO (2.1-fold), IGFBP-4 (2-fold), IL-12-p40 (1.7-fold), and ENA-78 (1.4-fold). Interestingly, seven of these cytokines have known pro-inflammatory roles. Importantly, neither the CC transcriptomes nor FF cytokine profiles were different in adolescents with or without cancer.

LARGE SCALE DATA

Original high-throughput sequencing data have been deposited in Gene Expression Omnibus (GEO) database with the accession number GSE265995.

LIMITATIONS REASONS FOR CAUTION

This study aims to gain insights into the associated gamete quality by studying the immediate oocyte microenvironment. The direct study of oocytes is more challenging due to sample scarcity, as they are cryopreserved for future use, but would provide a more accurate assessment of oocyte reproductive potential.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings have implications for the adolescent fertility preservation cycles. Understanding the expected quality of cryopreserved eggs in this age group will lead to better counseling of these patients about their reproductive potential and may help to determine the number of eggs that is recommended to be banked to achieve a reasonable chance of future live birth(s).

STUDY FUNDING/COMPETING INTERESTS

This project was supported by Friends of Prentice organization SP0061324 (M.M.L. and E.B.), Gesualdo Family Foundation (Research Scholar: M.M.L.), and NIH/NICHD K12 HD050121 (E.B.). The authors have declared that no conflict of interest exists.

The oocyte microenvironment is altered in adolescents compared to oocyte donors

Study question

Are the molecular signatures of cumulus cells (CCs) and follicular fluid (FF) of adolescents undergoing fertility preservation differ from that of reproductively adult oocyte donors?

Summary answer

The microenvironment immediately surrounding the oocyte, including the CCs and FF, is altered in adolescents undergoing fertility preservation compared to oocyte donors.

What is known already

Adolescents experience a period of subfecundity following menarche. Recent evidence suggests that this may be at least partially due to increased oocyte aneuploidy. Reproductive juvenescence in mammals is associated with suboptimal oocyte quality.

Study design size duration

This was a prospective cohort study. Adolescents (10-19 years old, N=23) and oocyte donors (22-30 years old, N=31) undergoing ovarian stimulation and oocyte retrieval at the Northwestern Fertility and Reproductive Medicine Center between November 1, 2020 and May 1, 2023 were enrolled in this study.

Participants/materials setting methods

Patient demographics, ovarian stimulation, and oocyte retrieval outcomes were collected for all participants. The transcriptome of CCs associated with mature oocytes was compared between adolescents (10-19 years old, n=19), and oocyte donors (22-30 years old, n=19) using bulk RNA-sequencing. FF cytokine profiles (10-19 years old, n=18 vs. 25-30 years old, n=16) were compared using cytokine arrays.

Main results and the role of chance

RNA-seq analysis revealed 581 differentially expressed genes (DEGs) in cumulus cells of adolescents relative to oocyte donors, with 361 genes downregulated and 220 upregulated. Genes enriched in pathways involved in cell cycle and cell division (e.g., GO:1903047, p= 3.5 × 10-43; GO:0051983, p= 4.1 × 10-30; GO:0000281, p= 7.7 × 10-15; GO:0044839, p= 5.3 × 10-13) were significantly downregulated, while genes enriched in several pathways involved in cellular and vesicle organization (e.g., GO:0010256, p= 1.2 × 10-8; GO:0051129, p= 6.8 × 10-7; GO:0016050, p= 7.4 × 10-7; GO:0051640, p= 8.1 × 10-7) were upregulated in CCs of adolescents compared to oocyte donors. The levels of 9 cytokines were significantly increased in FF of adolescents compared to oocyte donors: IL-1 alpha (2-fold), IL-1 beta (1.7-fold), I-309 (2-fold), IL-15 (1.6-fold), TARC (1.9-fold), TPO (2.1-fold), IGFBP-4 (2-fold), IL-12-p40 (1.7-fold) and ENA-78 (1.4-fold). Interestingly, 7 of these cytokines have known pro-inflammatory roles. Importantly, neither the CC transcriptomes or FF cytokine profiles were different in adolescents with or without cancer.

Large scale data

Original high-throughput sequencing data will be deposited in Gene Expression Omnibus (GEO) before publication, and the GEO accession number will be provided here.

Limitations reasons for caution

This study aims to gain insights into the associated gamete quality by studying the immediate oocyte microenvironment. The direct study of oocytes is more challenging due to sample scarcity, as they are cryopreserved for future use, but will provide a more accurate assessment of oocyte reproductive potential.

Wider implications of the findings

Understanding the underpinnings of altered immediate oocyte microenvironment of adolescent patients may provide insights into the reproductive potential of the associated gametes in the younger end of the age spectrum. This has implications for the fertility preservation cycles for very young patients.

Study funding/competing interests

This project was supported by Friends of Prentice organization SP0061324 (M.M.L and E.B.), Gesualdo Family Foundation (Research Scholar: M.M.L.), and NIH/NICHD K12 HD050121 (E.B.). The authors have declared that no conflict of interest exists.

Cumulus expansion is impaired with advanced reproductive age due to loss of matrix integrity and reduced hyaluronan

Reproductive aging is associated with ovulatory defects. Age-related ovarian fibrosis partially contributes to this phenotype as short-term treatment with anti-fibrotic compounds improves ovulation in reproductively old mice. However, age-dependent changes that are intrinsic to the follicle may also be relevant. In this study, we used a mouse model to demonstrate that reproductive aging is associated with impaired cumulus expansion which is accompanied by altered morphokinetic behavior of cumulus cells as assessed by time-lapse microscopy. The extracellular matrix integrity of expanded cumulus-oocyte complexes is compromised with advanced age as evidenced by increased penetration of fluorescent nanoparticles in a particle exclusion assay and larger open spaces on scanning electron microscopy. Reduced hyaluronan (HA) levels, decreased expression of genes encoding HA-associated proteins (e.g., Ptx3 and Tnfaip6), and increased expression of inflammatory genes and matrix metalloproteinases underlie this loss of matrix integrity. Importantly, HA levels are decreased with age in follicular fluid of women, indicative of conserved reproductive aging mechanisms. These findings provide novel mechanistic insights into how defects in cumulus expansion contribute to age-related infertility and may serve as a target to extend reproductive longevity.

Meiotic Chromosome Structure, the Synaptonemal Complex, and Infertility

In meiosis, homologous chromosome synapsis is mediated by a supramolecular protein structure, the synaptonemal complex (SC), that assembles between homologous chromosome axes. The mammalian SC comprises at least eight largely coiled-coil proteins that interact and self-assemble to generate a long, zipper-like structure that holds homologous chromosomes in close proximity and promotes the formation of genetic crossovers and accurate meiotic chromosome segregation. In recent years, numerous mutations in human SC genes have been associated with different types of male and female infertility. Here, we integrate structural information on the human SC with mouse and human genetics to describe the molecular mechanisms by which SC mutations can result in human infertility. We outline certain themes in which different SC proteins are susceptible to different types of disease mutation and how genetic variants with seemingly minor effects on SC proteins may act as dominant-negative mutations in which the heterozygous state is pathogenic.

The Aging Ovary and the Tales Learned Since Fetal Development

BACKGROUND

While the term "aging" implies a process typically associated with later life, the consequences of ovarian aging are evident by the time a woman reaches her forties, and sometimes earlier. This is due to a gradual decline in the quantity and quality of oocytes which occurs over a woman's reproductive lifespan. Indeed, the reproductive potential of the ovary is established even before birth, as the proper formation and assembly of the ovarian germ cell population during fetal life determines the lifetime endowment of oocytes and follicles. In the ovary, sophisticated molecular processes have been identified that regulate the timing of ovarian aging and these are critical to ensuring follicular maintenance.

SUMMARY

The mechanisms thought to contribute to overall aging have been summarized under the term the "hallmarks of aging" and include such processes as DNA damage, mitochondrial dysfunction, telomere attrition, genomic instability, and stem cell exhaustion, among others. Similarly, in the ovary, molecular processes have been identified that regulate the timing of ovarian aging and these are critical to ensuring follicular maintenance. In this review, we outline critical processes involved in ovarian aging, highlight major achievements for treatment of ovarian aging, and discuss ongoing questions and areas of debate.

KEY MESSAGES

Ovarian aging is recognized as what may be a complex process in which age, genetics, environment, and many other factors contribute to the size and depletion of the follicle pool. The putative hallmarks of reproductive aging outlined herein include a diversity of plausible processes contributing to the depletion of the ovarian reserve. More research is needed to clarify if and to what extent these putative regulators do in fact govern follicle and oocyte behavior, and how these signals might be integrated in order to control the overall pattern of ovarian aging.

Towards prevention of aneuploidy-associated cellular senescence and aging: more questions than answers?

The aim of this review is to discuss how aneuploidy contributes to the aging process, and to identify plausible strategies for its prevention. After an overview of mechanisms leading to aneuploidy and the major features of cellular senescence, we discuss the link between (i) aneuploidy and cellular senescence; (ii) aneuploidy and aging; and (iii) cellular senescence and aging. We also consider (i) interactions between aneuploidy, micronuclei, cellular senescence and aging, (ii) the potential of nutritional treatments to prevent aneuploidy-associated senescence and aging, and (iii) knowledge and technological gaps. Evidence for a causal link between aneuploidy, senescence and aging is emerging. In vitro, aneuploidy accompanies the entry into cellular senescence and can itself induce senescence. How aneuploidy contributes in vivo to cellular senescence is less clear. Several routes depending on aneuploidy and/or senescence converge towards chronic inflammation, the major driver of unhealthy aging. Aneuploidy can induce the pro-inflammatory Senescence Associated Secretory Phenotype (SASP), either directly or as a result of micronucleus (MN) induction leading to leakage of DNA into the cytoplasm and triggering of the cGAS-STING pathway of innate immune response. A major difficulty in understanding the impact of aneuploidy on senescence and aging in vivo, results from the heterogeneity of cellular senescence in different tissues at the cytological and molecular level. Due to this complexity, there is at the present time no biomarker or biomarker combination characteristic for all types of senescent cells. In conclusion, a deeper understanding of the critical role aneuploidy plays in cellular senescence and aging is essential to devise practical strategies to protect human populations from aneuploidy-associated pathologies. We discuss emerging evidence, based on in vitro and in vivo studies, that adequate amounts of specific micronutrients are essential for prevention of aneuploidy in humans and that precise nutritional intervention may be essential to help avoid the scourge of aneuploidy-driven diseases.

Granulosa cell mevalonate pathway abnormalities contribute to oocyte meiotic defects and aneuploidy

With aging, abnormalities during oocyte meiosis become more prevalent. However, the mechanisms of aging-related oocyte aneuploidy are not fully understood. Here we performed Hi-C and SMART-seq of oocytes from young and old mice and reveal decreases in chromosome condensation and disrupted meiosis-associated gene expression in metaphase I oocytes from aged mice. Further transcriptomic analysis showed that meiotic maturation in young oocytes was correlated with robust increases in mevalonate (MVA) pathway gene expression in oocyte-surrounding granulosa cells (GCs), which was largely downregulated in aged GCs. Inhibition of MVA metabolism in GCs by statins resulted in marked meiotic defects and aneuploidy in young cumulus-oocyte complexes. Correspondingly, supplementation with the MVA isoprenoid geranylgeraniol ameliorated oocyte meiotic defects and aneuploidy in aged mice. Mechanically, we showed that geranylgeraniol activated LHR/EGF signaling in aged GCs and enhanced the meiosis-associated gene expression in oocytes. Collectively, we demonstrate that the MVA pathway in GCs is a critical regulator of meiotic maturation and euploidy in oocytes, and age-associated MVA pathway abnormalities contribute to oocyte meiotic defects and aneuploidy.

Characterization of Oogonial Stem Cells in Adult Mouse Ovaries with Age and Comparison to In Silico Data on Human Ovarian Aging

Many adult somatic stem cell lineages are comprised of subpopulations that differ in gene expression, mitotic activity, and differentiation status. In this study, we explored if cellular heterogeneity also exists within oogonial stem cells (OSCs), and how chronological aging impacts OSCs. In OSCs isolated from mouse ovaries by flow cytometry and established in culture, we identified subpopulations of OSCs that could be separated based on differential expression of stage-specific embryonic antigen 1 (SSEA1) and cluster of differentiation 61 (CD61). Levels of aldehyde dehydrogenase (ALDH) activity were inversely related to OSC differentiation, whereas commitment of OSCs to differentiation through transcriptional activation of stimulated by retinoic acid gene 8 was marked by a decline in ALDH activity and in SSEA1 expression. Analysis of OSCs freshly isolated from ovaries of mice between 3 and 20 months of age revealed that these subpopulations were present and persisted throughout adult life. However, expression of developmental pluripotency associated 3 (Dppa3), an epigenetic modifier that promotes OSC differentiation into oocytes, was lost as the mice transitioned from a time of reproductive compromise (10 months) to reproductive failure (15 months). Further analysis showed that OSCs from aged females could be established in culture, and that once established the cultured cells reactivated Dppa3 expression and the capacity for oogenesis. Analysis of single-nucleus RNA sequence data sets generated from ovaries of women in their 20s versus those in their late 40s to early 50s showed that the frequency of DPPA3-expressing cells decreased with advancing age, and this was paralleled by reduced expression of several key meiotic differentiation genes. These data support the existence of OSC subpopulations that differ in gene expression profiles and differentiation status. In addition, an age-related decrease in Dppa3/DPPA3 expression, which is conserved between mice and humans, may play a role in loss of the ability of OSCs to maintain oogenesis with age.

Identification of Common and Specific Genes Involved in Mouse Models of Age-Related and Cyclophosphamide-Induced Diminished Ovarian Reserve

Diminished ovarian reserve (DOR) is an etiologically heterogeneous disorder that usually leads to poor reproductive outcomes. Does a specific or common pathogenesis exist for DOR subtypes with different etiologies? Two frequently used mouse models, age-related DOR (AR-DOR) and cyclophosphamide (CTX)-induced DOR (CTX-DOR), were successfully established, and RNA sequencing was performed on ovarian tissue samples. Differentially expressed genes (DEGs) in each subtype and common DEGs (co-DEGs) in the two subtypes were identified. Subsequently, we performed comprehensive bioinformatics analyses, including an evaluation of immune cell infiltration. Finally, the genes of interest were further validated by performing RT-qPCR and immunohistochemistry. In AR-DOR mice, functional enrichment analyses showed that upregulated DEGs were mainly involved in the inflammatory/immune response, while downregulated DEGs were involved in DNA damage repair. In CTX-DOR mice, the inflammatory/immune response and cell apoptosis played significant roles. Meanwhile, 406 co-DEGs were identified from the two models. The biological functions of these co-DEGs were associated with inflammatory/immune responses. The analysis of immune cell infiltration showed reduced infiltration of Treg cells, as well as increased infiltration of M0 macrophages, NK resting, and T cells CD4 follicular in both DOR subtypes. The results of the validation experiments were consistent with the RNA sequencing data. In conclusion, the inflammatory/immune response might be the common pathogenesis for the two DOR subtypes, while DNA repair and cell apoptosis may have different roles in the two subtypes. These results may provide potential insights for mechanistic research and therapeutic targets of DOR.

Age-associated changes in cumulus cells and follicular fluid: the local oocyte microenvironment as a determinant of gamete quality

The ovary is the first organ to age in humans with functional decline evident already in women in their early 30s. Reproductive aging is characterized by a decrease in oocyte quantity and quality, which is associated with an increase in infertility, spontaneous abortions, and birth defects. Reproductive aging also has implications for overall health due to decreased endocrinological output. Understanding the mechanisms underlying reproductive aging has significant societal implications as women globally are delaying childbearing and medical interventions have greatly increased the interval between menopause and total lifespan. Age-related changes inherent to the female gamete are well-characterized and include defects in chromosome and mitochondria structure, function, and regulation. More recently, it has been appreciated that the extra-follicular ovarian environment may have important direct or indirect impacts on the developing gamete, and age-dependent changes include increased fibrosis, inflammation, stiffness, and oxidative damage. The cumulus cells and follicular fluid that directly surround the oocyte during its final growth phase within the antral follicle represent additional critical local microenvironments. Here we systematically review the literature and evaluate the studies that investigated the age-related changes in cumulus cells and follicular fluid. Our findings demonstrate unique genetic, epigenetic, transcriptomic, and proteomic changes with associated metabolomic alterations, redox status imbalance, and increased apoptosis in the local oocyte microenvironment. We propose a model of how these changes interact, which may explain the rapid decline in gamete quality with age. We also review the limitations of published studies and highlight future research frontiers.

Role and Clinical Utility of Cancer/Testis Antigens in Head and Neck Squamous Cell Carcinoma

Cancer/testis (CT) antigens exhibit selective expression predominantly in immunoprivileged tissues in non-pathological contexts but are aberrantly expressed in diverse cancers. Due to their expression pattern, they have historically been attractive targets for immunotherapies. A growing number of studies implicate CT antigens in almost all hallmarks of cancer, suggesting that they may act as cancer drivers. CT antigens are expressed in head and neck squamous cell carcinomas. However, their role in the pathogenesis of these cancers remains poorly studied. Given that CT antigens hold intriguing potential as therapeutic targets and as biomarkers for prognosis and that they can provide novel insights into oncogenic mechanisms, their further study in the context of head and squamous cell carcinoma is warranted.