Impact of Oxidative Stress on Age-Associated Decline in Oocyte Developmental Competence

Toxic effects of 4-methylimidazole on the maturation and fertilization of mouse oocytes

Individuals of all ages, including children and teenagers, consume 4-methylimidazole (4-MI) in their food. 4-MI is a caramel-colored waste product that has previously been linked to human carcinogenesis and has shown possible signs of reproductive toxicity. This study aimed to determine whether 4-MI is harmful to oocytes during meiosis and fertilization. Female mice were intragastrically administered 0, 50, or 100 mg/kg body weight of 4-MI daily for 10 days. We found that 4-MI affects the quality of oocytes by affecting their meiotic ability and fertility potential. Specifically, 4-MI rendered the meiotic spindles and chromosomes less stable, which halted oocyte maturation and resulted in aneuploidy. 4-MI also slowed the decrease in the levels of cortical granules and their component ovastacin; consequently, sperms could not be bound and fertilization could not occur. We also found that mitochondrial dysfunction was associated with oocytes deterioration. This led to reactive oxygen species accumulation and cell death. Altogether, our findings reveal that the poor condition of oocytes subjected to 4-MI is primarily attributable to mitochondrial malfunction and redox alterations.

Epitalon protects against post-ovulatory aging-related damage of mouse oocytes in vitro

The developmental potential of oocytes decreases with time after ovulation in vivo or in vitro. Epitalon is a synthetic short peptide made of four amino acids (alanine, glutamic acid, aspartic acid, and glycine), based on a natural peptide called epithalamion extracted from the pineal gland. It is a potent antioxidant, comparable to melatonin, that may confer longevity benefits. The current study aims to test the protective effects of Epitalon on the quality of post-ovulatory aging oocytes. Epitalon at 0.1mM was added to the culture medium, and the quality of oocytes was evaluated at 6h, 12h, and 24h of culture. We found that 0.1mM Epitalon reduced intracellular reactive oxygen species. Epitalon treatment significantly decreased frequency of spindle defects and abnormal distribution of cortical granules during aging for 12h and 24h, while increased mitochondrial membrane potential and DNA copy number of mitochondria, thus decreasing apoptosis of oocytes by 24h of in vitro aging. Our results suggest that Epitalon can delay the aging process of oocytes in vitro via modulating mitochondrial activity and ROS levels.

Procyanidin B2 Protects Aged Oocytes Against Meiotic Defects Through Cortical Tension Modulation

Defects in meiotic process are the main factors responsible for the decreased developmental competence in aged oocytes. Our recent research indicated that natural antioxidant procyanidin B2 (PCB2) promoted maturation progress in oocytes from diabetic mice. However, the effect of PCB2 on aging-induced chromosome abnormalities and the underlying mechanism have not been explored. Here, we found that PCB2 recovered aging-caused developmental arrest during meiotic maturation, germinal vesicle breakdown (GVBD) rate was significantly higher in aged oocytes treated with PCB2 (P < 0.05). Furthermore, we discovered that cortical mechanics were altered during aging process, cortical tension-related proteins were aberrantly expressed in aged oocytes (P < 0.001). PCB2 supplementation efficaciously antagonized aging-induced decreased cortical tension (P < 0.001). Moreover, PCB2 restored spindle morphology (P < 0.01), maintained proper chromosome alignment (P < 0.05), and dramatically reduced reactive oxygen species (ROS) level (P < 0.05) in aged oocytes. Collectively, our results reveal that PCB2 supplementation is a feasible approach to protect oocytes from reproductive aging, contributing to the improvement of oocytes quality.

Fertilization, embryo culture, and clinical results using low lactate embryo culture medium for pre‐culture, insemination, and beyond

Purpose

We focused on the metabolism of oocytes in pre‐culture and insemination and compared these results between our existing fertilization medium, GEMS Fertilisation Medium (GEMS group) (Merck BioPharma) and Continuous Single Culture Medium—NX Complete (CSCM‐NXC group) (FUJIFILM Irvine Scientific).

Methods

Patients under 42 years of age were received controlled ovarian stimulation and oocytes were retrieved. Those were pre‐cultured and fertilized with either GEMS fertilization medium or CSCM‐NXC. After fertilization was confirmed, embryos were cultured using CSCM‐NXC in both groups. The embryos were cryopreserved at blastocyst stage (3BB or more, Gardner classification) and then transferred in HRT cycles.

Results

The fertilization rate of both groups was the same, but the 3PN rate was significantly lower in the CSCM‐NXC group. In terms of embryo culture results, the CSCM‐NXC group had a significantly higher rate of good quality blastocysts, high‐grade embryos, and embryos with a high degree of expansion.

Conclusions

The use of CSCM‐NXC, a low lactate embryo culture medium, from pre‐culture and for insemination, increases the energy metabolic efficiency of oocytes and cumulus cells, making it possible to supply sufficient energy ATP for fertilization and early division, which is thought to promote good embryonic development.

Protecting the future: balancing proteostasis for reproduction

The proteostasis network (PN) regulates protein synthesis, folding, and degradation and is critical for the health and function of all cells. The PN has been extensively studied in the context of aging and age-related diseases, and loss of proteostasis is regarded as a major contributor to many age-associated disorders. In contrast to somatic tissues, an important feature of germ cells is their ability to maintain a healthy proteome across generations. Accumulating evidence has now revealed multiple layers of PN regulation that support germ cell function, determine reproductive capacity during aging, and prioritize reproduction at the expense of somatic health. Here, we review recent insights into these different modes of regulation and their implications for reproductive and somatic aging.

The role of cellular senescence in female reproductive aging and the potential for senotherapeutic interventions

BACKGROUND

Advanced maternal age is associated with decreased oocyte quantity and quality as well as uterine and placental dysfunctions. These changes lead to infertility, pregnancy complications and birth defects in the offspring. As the mean age of giving birth is increasing worldwide, prevention of age-associated infertility and pregnancy complications, along with the more frequent use of ART, become extremely important. Currently, significant research is being conducted to unravel the mechanisms underlying female reproductive aging. Among the potential mechanisms involved, recent evidence has suggested a contributing role for cellular senescence, a cellular state of irreversible growth arrest characterized by a hypersecretory and pro-inflammatory phenotype. Elucidating the role of senescence in female reproductive aging holds the potential for developing novel and less invasive therapeutic measures to prevent or even reverse female reproductive aging and increase offspring wellbeing.

OBJECTIVE AND RATIONALE

The review will summarize the positive and negative implications of cellular senescence in the pathophysiology of the female reproductive organs during aging and critically explore the use of novel senotherapeutics aiming to reverse and/or eliminate their detrimental effects. The focus will be on major senescence mechanisms of the ovaries, the uterus, and the placenta, as well as the potential and risks of using senotherapies that have been discovered in recent years.

SEARCH METHODS

Data for this review were identified by searches of MEDLINE, PubMed and Google Scholar. References from relevant articles using the search terms 'Cellular Senescence', 'Aging', 'Gestational age', 'Maternal Age', 'Anti-aging', 'Uterus', 'Pregnancy', 'Fertility', 'Infertility', 'Reproduction', 'Implant', 'Senolytic', 'Senostatic', 'Senotherapy' and 'Senotherapeutic' where selected. A total of 182 articles published in English between 2005 and 2020 were included, 27 of which focus on potential senotherapies for reproductive aging. Exclusion criteria were inclusion of the terms 'male' and 'plants'.

OUTCOMES

Aging is a major determinant of reproductive wellbeing. Cellular senescence is a basic aging mechanism, which can be exploited for therapeutic interventions. Within the last decade, several new strategies for the development and repurposing of drugs targeting senescent cells have emerged, such as modulators of the anti-inflammatory response, oxidative stress, DNA damage, and mitochondria and protein dysfunctions. Several studies of female reproductive aging and senotherapies have been discussed that show promising results for future interventions.

WIDER IMPLICATIONS

In most countries of the Organization for Economic Co-operation and Development, the average age at which women give birth is above 30 years. Currently, in countries such as the Netherlands, Australia, Spain, Finland, Germany and the UK, birth rates among 30- to 34-year-olds are now higher than in any other age groups. This review will provide new knowledge and scientific advancement on the senescence mechanisms during female reproductive aging, and benefit fundamental and clinical scientists and professionals in the areas of reproduction, cancer, immunobiology and fibrosis.

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.

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.

Direct Imaging of Lipid Metabolic Changes in Drosophila Ovary During Aging Using DO-SRS Microscopy

Emerging studies have shown that lipids and proteins play versatile roles in various aspects of aging. High-resolution in situ optical imaging provides a powerful approach to study the metabolic dynamics of lipids and proteins during aging. Here, we integrated D2O probing and stimulated Raman scattering (DO-SRS) microscopy to directly visualize metabolic changes in aging Drosophila ovary. The subcellular spatial distribution of de novo protein synthesis and lipogenesis in ovary was quantitatively imaged and examined. Our Raman spectra showed that early stages follicles were protein-enriched whereas mature eggs were lipid-enriched. DO-SRS imaging showed a higher protein synthesis in the earlier developing stages and an increased lipid turned over at the late stage. Aged (35 days) flies exhibited a dramatic decrease in metabolic turnover activities of both proteins and lipids, particularly, in the germ stem cell niche of germarium. We found an accumulation of unsaturated lipids in the nurse cells and oocytes in old flies, suggesting that unsaturated lipids may play an important role in the processes of oocyte maturation. We further detected changes in mitochondrial morphology and accumulation of Cytochrome c during aging. To our knowledge, this is the first study that directly visualizes spatiotemporal changes in lipid and protein metabolism in Drosophila ovary during development and aging processes. Our study not only demonstrates the application of a new imaging platform in visualizing metabolic dynamics of lipids and proteins in situ but also unravels how the metabolic activity and lipid distribution change in Drosophila ovary during aging.

Melatonin improves the quality of maternally aged oocytes by maintaining intercellular communication and antioxidant metabolite supply

In mammalian ovaries, oocytes are physically coupled to somatic granulosa cells, and this coupling is crucial for the growth and development of competent oocytes as it mediates the transfer of metabolic support molecules. However, aging-mediated dysregulation in communication between the oocytes and granulosa cells affects the oocyte quality. In the present study, we examined the defected germline-soma communication and reduced mRNA levels encoding key structural components of transzonal projections (TZPs) in maternally aged oocytes. Oral administration of melatonin to aged mice substantially increased TZPs and maintained the cumulus cells-oocyte communication, which played a central role in the production of adequate oocyte ATP levels and reducing the accumulation of reactive oxygen species (ROS), apoptosis, DNA damage, endoplasmic reticulum (ER) stress and spindle/chromosomal defects. This beneficial effect of melatonin was inhibited by carbenoxolone (CBX), a gap junctional uncoupler, which disrupts bidirectional communications between oocyte and somatic cells. Simultaneously, melatonin significantly increased the mRNA and protein levels corresponding to genes associated with TZPs and prevented TZP retraction in in vitro-cultured cumulus-oocyte complex (COCs). Furthermore, we infused melatonin and CBX into the COCs in vitro culture system and monitored the levels of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione (GSH) in cumulus cells and oocytes. Notably, COCs treated with melatonin demonstrated improved NADPH and GSH levels. Of note, CBX was capable of reducing NADPH and GSH levels, aggravated the ROS accumulation and ER stress. Collectively, our data demonstrate the role of melatonin in preventing age-associated germline-soma communication defects, aiding the relay of antioxidant metabolic molecules for the maintenance of oocyte quality from cumulus cells, which have important potential for improving deficient phenotypes of maternally aged oocytes and the treatment of woman infertility.

In Vivo and In Vitro Matured Oocytes From Mice of Advanced Reproductive Age Exhibit Alternative Splicing Processes for Mitochondrial Oxidative Phosphorylation

The mean age of women seeking infertility treatment has gradually increased over recent years. This has coincided with the emergence of in vitro maturation (IVM), a method used in assisted reproductive technology for patients with special requirements. However, when compared with conventional in vitro fertilization, IVM is associated with poor embryonic development potential and low live birth rates, thus limiting the widespread application of this technique. In this study, we performed RNA-sequencing transcriptomic assays and identified a total of 2,627 significant differentially expressed genes (DEGs) between IVM oocytes and in vivo matured oocytes from mice of advanced reproductive age. Next, Kyoto Encyclopedia of Genes and Genomes pathway analysis was used to identify the potential functions of the DEGs. The most significantly enriched pathway was oxidative phosphorylation (OXPHOS). In addition, we constructed a protein-protein interaction network to identify key genes and determined that most of the hub genes were mtDNA-encoded subunits of respiratory chain complex I. Antioxidant supplementation lead to an increase in ATP production and reduced the gene expression profile of the OXPHOS pathway in the IVM group. Moreover, alternative splicing (AS) events were identified during in vivo or in vitro oocyte maturation; data showed that skipped exons were the most frequent type of AS event. A number of genes associated with the OXPHOS pathway exhibited alterations in AS events, including Ndufa7, Ndufs7, Cox6a2, Ndufs5, Ndufb1, and Uqcrh. Furthermore, the process of IVO promoted the skipping of exon 2 in Ndufa7 and exon 3 in Ndufs7 compared with the IVM oocytes, as determined by semi-quantitative RT-PCR. Collectively, these findings provide potential new therapeutic targets for improving IVM of aged women who undergo infertility treatment.

Salidroside alleviates oxidative stress and apoptosis via AMPK/Nrf2 pathway in DHT-induced human granulosa cell line KGN

In the past few years, emerging evidence established persistent oxidative stress to be a key player in the pathogenesis of polycystic ovary syndrome (PCOS). Particularly, it damages the function of granulosa cells, and thus hinders the development of follicles. The present study aimed to explore and establish the protective effects of salidroside on dihydrotestosterone (DHT)-induced Granulosa-like tumor cell line (KGN), mediated via antioxidant mechanisms. The study assessed the positive effects of salidroside on DHT-induced apoptosis, reactive oxygen species (ROS) accumulation, damage of antioxidant capacity, and mitochondrial membrane potential depolarization. Interestingly, salidroside partly reversed DHT mediated effects, via stimulation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and the downstream antioxidant proteins heme oxygenase-1(HO-1) and quinine oxidoreductase 1(NQO1). Additionally, the knockdown of Nrf2 partly moderated the antioxidant and anti-apoptosis effects of salidroside in DHT-treated KGN cells. Mechanistically, AMP-activated protein kinase (AMPK) was identified to be the upstream signaling involved in salidroside-induced Nrf2 activation, as silencing of AMPK partly prevented the upregulation of Nrf2 and the downstream proteins HO-1 and NQO1. Altogether, the present study is the first to effectively demonstrate the inhibitory effect of salidroside on DHT-stimulated oxidative stress and apoptosis in KGN cells, which was dependent on Nrf2 activation that involved AMPK.

Effects of BPA, BPS, and BPF on Oxidative Stress and Antioxidant Enzyme Expression in Bovine Oocytes and Spermatozoa

Bisphenol A (BPA) and its analogs, bisphenol S (BPS) and bisphenol F (BPF), might impact fertility by altering oxidative stress pathways. Here, we hypothesize that bisphenols-induced oxidative stress is responsible for decreased gamete quality. In both female (cumulus-oocyte-complexes-COCs) and male (spermatozoa), oxidative stress was measured by CM-H2DCFDA assay and key ROS scavengers (SOD1, SOD2, GPX1, GPX4, CAT) were quantified at the mRNA and protein levels using qPCR and Western blot (COCs)/immunofluorescence (sperm). Either gamete was treated in five groups: control, vehicle, and 0.05 mg/mL of BPA, BPS, or BPF. Our results show elevated ROS in BPA-treated COCs but decreased production in BPS- and BPF-treated spermatozoa. Additionally, both mRNA and protein expression of SOD2, GPX1, and GPX4 were decreased in BPA-treated COCs (p < 0.05). In sperm, motility (p < 0.03), but not morphology, was significantly altered by bisphenols. SOD1 mRNA expression was significantly increased, while GPX4 was significantly reduced. These results support BPA's ability to alter oxidative stress in oocytes and, to a lesser extent, in sperm. However, BPS and BPF likely act through different mechanisms.

PQQ Dietary Supplementation Prevents Alkylating Agent-Induced Ovarian Dysfunction in Mice

Alkylating agents (AAs) that are commonly used for cancer therapy cause great damage to the ovary. Pyrroloquinoline-quinine (PQQ), which was initially identified as a redox cofactor for bacterial dehydrogenases, has been demonstrated to benefit the fertility of females. The aim of this study was to investigate whether PQQ dietary supplementation plays a protective role against alkylating agent-induced ovarian dysfunction. A single dose of busulphan (20 mg/kg) and cyclophosphamide (CTX, 120 mg/kg) were used to establish a mouse model of ovarian dysfunction. Feed containing PQQNa₂ (5 mg/kg) was provided starting 1 week before the establishment of the mouse model until the date of sacrifice. One month later, estrous cycle period of mice were examined and recorded for consecutive 30 days. Three months later, some mice were mated with fertile male mice for fertility test. The remaining mice were sacrificed to collect serum samples and ovaries. One day before sacrifice, some mice received a single injection of BrdU to label proliferating cells. Serum samples were used for test hormonal levels. Ovaries were weighted and used to detect follicle counts, cell proliferation, cell apoptosis and cell senescence. In addition, the levels of inflammation, oxidative damage and Pgc1α expression were detected in ovaries. Results showed that PQQ treatment increased the ovarian weight and size, partially normalized the disrupted estrous cycle period and prevented the loss of follicles of mice treated with AAs. More importantly, we found that PQQ treatment significantly increased the pregnancy rate and litter size per delivery of mice treated with AAs. The protective effects of PQQ appeared to be directly mediated by promoting cell proliferation of granulosa, and inhibiting cell apoptosis of granulosa and cell senescence of ovarian stromal cells. The underlying mechanisms may attribute to the anti-oxidative stress, anti-inflammation and pro-mitochondria biogenesis effects of PQQ.Our study highlights the therapeutic potential of PQQ against ovarian dysfunction caused by alkylating agents.

Sorbitol accumulation decreases oocyte quality in aged mice by altering the intracellular redox balance

Sorbitol is a product of glucose metabolism through the polyol pathway. Many studies have demonstrated that excessive sorbitol can disrupt the intracellular redox balance. However, we still know very little about the impact of excessive intracellular sorbitol on oocyte quality, oocyte maturation, and embryo developmental potential. This study explored whether intracellular sorbitol accumulates in the oocytes of aged mice during in vitro maturation (IVM) and what roles sorbitol plays in oocyte development and maturation. Our results showed that sorbitol levels were significantly higher in in vitro-matured oocytes from aged mice than in oocytes from young mice (14.08 ± 3.78 vs. 0.23 ± 0.04 ng/oocyte). The expression of aldose reductase (AR) mRNA was significantly higher in the in vitro-cultured oocytes from 9-month-old mice than prior to culture. To decrease the excessive intracellular sorbitol in oocytes from aged mice, sorbinil, a specific inhibitor of aldose reductase, was supplemented in IVM medium, and the sorbitol level was significantly decreased (14.08 ± 3.78 vs. 0.48 ± 0.19 ng/oocyte). Our results indicated that the percentage of oocytes with first polar body extrusion (PBE) was significantly higher in the sorbinil group than in the aged group (82.4% ± 7.2% vs. 66.1% ± 6.9%), and the content of sorbitol was drastically increased in the aged group. The ROS fluorescence intensity in the sorbinil group was drastically lower than that in the aged group, while the GSH fluorescence intensity was significantly higher. Interestingly, SOD1 was upregulated in the sorbinil group. The present study suggests that excessive sorbitol accumulation is induced during IVM in aged mouse oocytes, which negatively influences oocyte quality by altering the intracellular redox balance. Inhibition of sorbitol accumulation may be a potential method to improve the nuclear maturation of aged oocytes.

CDC26 is a key factor in human oocyte aging

STUDY QUESTION

Is CDC26 a key factor in human oocyte aging?

SUMMARY ANSWER

The lack of CDC26 disrupts the oocytes maturation process, leading to oocyte aging, but these defects could be partially rescued by overexpression of the CDC26 protein.

WHAT IS KNOWN ALREADY

Age-related oocyte aging is the main cause of female fertility decline. In mammalian oocytes, aberrant meiosis can cause chromosomal abnormalities that might lead to infertility and developmental disorders. CDC26 participates in the meiosis process.

STUDY DESIGN, SIZE, DURATION

Differential gene expression in young and old women oocytes were screened by single-cell RNA-seq technology, and the functions of differentially genes were verified on mouse oocytes. Finally, transfection technology was used to evaluate the effect of a differentially expressed gene in rescuing human oocyte from aging.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Discarded human oocytes were collected for single-cell RNA-seq, q-PCR and immunocytochemical analyses to screen for and identify differential gene expression. Female KM mice oocytes were collected for IVM of oocytes, q-PCR and immunocytochemical analyses to delineate the relationships between oocyte aging and differential gene expression. Additionally, recombinant lentiviral vectors encoding CDC26 were transfected into the germinal vesicle oocytes of older women, to investigate the effects of the CDC26 gene expression on oocyte development.

MAIN RESULTS AND THE ROLE OF CHANCE

Many genes were found to be differentially expressed in the oocytes of young versus old patients via RNA-seq technology. CDC26 mRNA and protein levels in aged oocytes were severely decreased, when compared with the levels observed in young oocytes. Moreover, aged oocytes lacking CDC26 were more prone to aneuploidy. These defects in aged oocytes could be partially rescued by overexpression of the CDC26 protein.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Our study delineated key steps in the oocyte aging process by identifying the key role of CDC26 in the progression of oocyte maturation. Future studies are required to address whether other signaling pathways play a role in regulating oocyte maturation via CDC26 and which genes are the direct molecular targets of CDC26.

WIDER IMPLICATIONS OF THE FINDINGS

Our results using in vitro systems for both mouse and human oocyte maturation provide a proof of principle that CDC26 may represent a novel therapeutic approach against maternal aging-related spindle and chromosomal abnormalities.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the National Natural Science Foundation of China (81571442 and 81170571), the outstanding Talent Project of Shanghai Municipal Commission of Health (XBR2011067) and Clinical Research and Cultivation Project in Shanghai Municipal Hospitals (SHDC12019X32). The authors declare no conflict of interest.

CENP-V is required for proper chromosome segregation through interaction with spindle microtubules in mouse oocytes

Proper chromosome segregation is essential to avoid aneuploidy, yet this process fails with increasing age in mammalian oocytes. Here we report a role for the scarcely described protein CENP-V in oocyte spindle formation and chromosome segregation. We show that depending on the oocyte maturation state, CENP-V localizes to centromeres, to microtubule organizing centers, and to spindle microtubules. We find that Cenp-V-/- oocytes feature severe deficiencies, including metaphase I arrest, strongly reduced polar body extrusion, increased numbers of mis-aligned chromosomes and aneuploidy, multipolar spindles, unfocused spindle poles and loss of kinetochore spindle fibres. We also show that CENP-V protein binds, diffuses along, and bundles microtubules in vitro. The spindle assembly checkpoint arrests about half of metaphase I Cenp-V-/- oocytes from young adults only. This finding suggests checkpoint weakening in ageing oocytes, which mature despite carrying mis-aligned chromosomes. Thus, CENP-V is a microtubule bundling protein crucial to faithful oocyte meiosis, and Cenp-V-/- oocytes reveal age-dependent weakening of the spindle assembly checkpoint.

The impact of maternal age on gene expression during the GV to MII transition in euploid human oocytes

STUDY QUESTION

Are there age-related differences in gene expression during the germinal vesicle (GV) to metaphase II (MII) stage transition in euploid human oocytes?

SUMMARY ANSWER

A decrease in mitochondrial-related transcripts from GV to MII oocytes was observed, with a much greater reduction in MII oocytes with advanced age.

WHAT IS KNOWN ALREADY

Early embryonic development is dependent on maternal transcripts accumulated and stored within the oocyte during oogenesis. Transcriptional activity of the oocyte, which dictates its ultimate developmental potential, may be influenced by age and explain the reduced competence of advanced maternal age (AMA) oocytes compared with the young maternal age (YMA). Gene expression has been studied in human and animal oocytes; however, RNA sequencing could provide further insights into the transcriptome profiling of GV and in vivo matured MII euploid oocytes of YMA and AMA patients.

STUDY DESIGN, SIZE, DURATION

Fifteen women treated for infertility in a single IVF unit agreed to participate in this study. Five GV and 5 MII oocytes from 6, 21-26 years old women (YMA cohort) and 5 GV and 6 MII oocytes from 6, 41-44 years old women (AMA cohort) undergoing IVF treatment were donated. The samples were collected within a time frame of 4 months. RNA was isolated and deep sequenced at the single-cell level. All donors provided either GV or MII oocytes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Cumulus dissection from donated oocytes was performed 38 h after hCG injection, denuded oocytes were inserted into lysis buffer supplemented with RNase inhibitor. The samples were stored at -80°C until further use. Isolated RNA from GV and MII oocytes underwent library preparation using an oligo deoxy-thymidine (dT) priming approach (SMART-Seq v4 Ultra Low Input RNA assay; Takara Bio, Japan) and Nextera XT DNA library preparation assay (Illumina, USA) followed by deep sequencing. Data processing, quality assessment and bioinformatics analysis were performed using source-software, mainly including FastQC, HISAT2, StringTie and edgeR, along with functional annotation analysis, while scploid R package was employed to determine the ploidy status.

MAIN RESULTS AND THE ROLE OF CHANCE

Following deep sequencing of single GV and MII oocytes in both YMA and AMA cohorts, several hundred transcripts were found to be expressed at significantly different levels. When YMA and AMA MII oocyte transcriptomes were compared, the most significant of these were related to mitochondrial structure and function, including biological processes, mitochondrial respiratory chain complex I assembly and mitochondrial translational termination (false discovery rate (FDR) 6.0E-10 to 1.2E-7). These results indicate a higher energy potential of the YMA MII cohort that is reduced with ageing. Other biological processes that were significantly higher in the YMA MII cohort included transcripts involved in the translation process (FDR 1.9E-2). Lack of these transcripts could lead to inappropriate protein synthesis prior to or upon fertilisation of the AMA MII oocytes.

LARGE SCALE DATA

The RNA sequencing data were deposited in the Gene Expression Omnibus (https://www.ncbi.nlm.nih.gov/geo), under the accession number: GSE164371.

LIMITATIONS, REASONS FOR CAUTION

The relatively small sample size could be a reason for caution. However, the RNA sequencing results showed homogeneous clustering with low intra-group variation and five to six biological replicates derived from at least three different women per group minimised the potential impact of the sample size.

WIDER IMPLICATIONS OF THE FINDINGS

Understanding the effects of ageing on the oocyte transcriptome could highlight the mechanisms involved in GV to MII transition and identify biomarkers that characterise good MII oocyte quality. This knowledge has the potential to guide IVF regimes for AMA patients.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Medical Research Council (MRC Grant number MR/K020501/1).

Antral follicle count, oocyte production and embryonic developmental competence of senescent Nellore (Bos indicus) cows

Information on the follicular population and oocyte quality of cows in the final period of reproductive life is scarce. The present study aimed to compare the antral follicle count (AFC), oocyte production and embryonic developmental competence of young versus long-lived and senescent Bos indicus beef cows. Nellore cows (Bos indicus) were classified into three groups according to age: young (4-9 years, n = 10), long-lived (14-17 years, n = 10) and senescent (17-23 years, n = 10). At a random time in the estrus cycle, the cows received cloprostenol sodium salt (0.5 mg, IM), estradiol benzoate (1 mg, IM) and an intravaginal P4 device (1.4 g). Five days later, the P4 devise was removed and oocyte collection (OPU1) was performed. A second OPU (OPU2) was performed 5 days after the first in order to aspirate only growing follicles. During each OPU, AFC and the number and quality of cumulus-oocyte complexes (COCs) were evaluated. Then, the COCs were placed in standard maturation medium (IVM), fertilized and incubated for 9 days. The data were subjected to ANOVA and Multinomial Logistic Regression. The AFC was smaller in long-lived and senescent cows in both OPU1 and OPU2 when compared to younger cows. There was no difference in AFC between OPU1 (19.9 ± 1.8) and OPU2 (17.6 ± 1.9) in young cows, however, more follicles were punctured in long-lived and senescent cows in OPU1 (12.0 ± 2.6 and 19.3 ± 4.6) than in OPU2 (9.2 ± 1.9 and 10.3 ± 2.3), respectively (P < 0.01). The numbers of COCs recovered from young cows (OPU1 = 14.2 ± 1.8; OPU2 = 8.4 ± 0.9) were higher than those obtained from long-lived cows (OPU1 = 5.9 ± 2.3; OPU2 = 4.3 ± 1.0) and senescent cows (OPU1 = 7.2 ± 3.0; OPU2 = 4.1 ± 1.7), respectively (P < 0.05). The cleavage rate did not differ between groups. However, the rate of blastocyst formation was higher for young (64.8%) and long-lived (65.0%) compared to senescent (16.5%) cows (P < 0.01). In conclusion our results indicate that the AFC is lower in long-lived and senescent cows compared with young cows. However, unlike in senescent cows, the embryonic development of long-lived cows is similar to that of young cows. This suggests that Nellore cows aged >17 years begin to have reduced embryonic development capacity due to ovarian aging.

Melatonin Promotes in vitro Development of Vitrified-Warmed Mouse GV Oocytes, Potentially by Modulating Phosphorylation of Drp1

Previous studies have shown that melatonin can mitigate cryopreservation-induced mitochondrial dysfunction in oocytes; however, the underlying molecular mechanism remains unclear. The objective of the present study was to investigate whether melatonin can improve the mitochondrial function during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes by modulating phosphorylation of dynamin related protein 1 (Drp1). Vitrification/warming procedures resulted in the following: (1) After cryopreservation of mouse GV oocytes, the phosphorylation level of Drp1 at Ser616 (p-Drp1 Ser616) in metaphase II (MII) oocytes was increased (P < 0.05). Furthermore, the rates of in vitro maturation, cleavage and blastocyst formation after parthenogenetic activation were decreased (P < 0.05). (2) In MII oocytes, the expression levels of translocase of the mitochondrial outer membrane 20 (TOMM20), mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) content, and mRNA levels of mitochondrial biogenesis-related genes (Sirt1, Pgc-1α, Tfam) were all decreased (P < 0.05), and (3) Reactive oxygen species (ROS) level, early apoptosis level, Cytochrome C release and mRNA levels of pro-apoptotic related genes (Bax, Caspase9, Caspase3) in MII oocytes were all increased (P < 0.05). The results of this study further revealed that negative impacts of GV oocyte cryopreservation were mitigated by supplementation of warming and in vitro maturation media with 10⁻⁷mol /L melatonin or 2 x 10⁻⁵mol/L Mdivi-1 (Drp1 inhibitor). Therefore, we concluded that 10⁻⁷mol/L melatonin improved mitochondrial function, reduced oxidative stress and inhibited apoptosis by regulating phosphorylation of Drp1, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

Roles of melatonin in the field of reproductive medicine

Melatonin, mostly released by the pineal gland, is a circadian rhythm-regulated and multifunctional hormone. Great advances in melatonin research have been made, including its role in rhythms of the sleep-wake cycle, retardation of ageing processes, as well as antioxidant or anti-inflammatory functions. Melatonin can scavenge free radicals such as reactive oxygen species (ROS), a key factor in reproductive functions. Melatonin plays an important role in oocyte maturation, fertilization and embryonic development as well. The concurrent use of melatonin increases the number of mature oocytes, the fertilization rate, and number of high-quality embryos, which improves the clinical outcome of assisted reproductive technology (ART). This review discusses the relationship between melatonin and human reproductive function, and potential clinical applications of melatonin in the field of reproductive medicine.

Transcriptomic study of the mechanism by which the Kai Yu Zhong Yu recipe improves oocyte quality in a stressed mouse model

ETHNOPHARMACOLOGICAL RELEVANCE

The Kai Yu Zhong Yu recipe (KYZY) is a classic herbal formula in traditional Chinese medicine (TCM) that has been used to treat infertility associated with psychological stress for more than three hundred years.

AIM OF THE STUDY

Psychological stress has major impacts on fertility, with variable outcomes depending on the nature, strength, and duration of the stress. Stress can directly disturb ovulation, oocyte quality, maturation, and embryo development. The aim of this study is to investigate the molecular mechanism by which KYZY improves oocyte developmental potential under psychological stress.

MATERIALS AND METHODS

ICR female mice aged 4-5 weeks were randomly divided into five groups: control, stressed in the chronic unpredictable stress model (CUSM), and stressed plus KYZY treatment at 38.2 g/kg (KYZYH), 19.1 g/kg (KYZYM), or 9.6 g/kg (KYZYL). Ovary function was assessed by measuring serum levels of estradiol (E2), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and anti-Müllerian hormone (AMH). Oocyte quality was evaluated in terms of reactive oxygen species (ROS) levels, apoptotic DNA fragmentation, and mitochondria distribution. We used RNA sequencing (RNAseq) to identify differentially expressed genes (DEGs) between groups and then further analyzed the DEGs for gene ontology (GO) term enrichment and protein-protein interactions.

RESULTS

Mice in the stressed group had reduced serum E2, LH, and FSH as well as increased ROS levels, increased apoptosis, and disturbed mitochondria distribution in oocytes. Treatment with KYZY at all three doses reversed or ameliorated these negative effects of stress. DEG analysis identified 187 common genes between the two comparisons (stressed vs. control and KYZYM vs. stressed), 33 of which were annotated with six gene ontology (GO)'s biological process (BP) terms: cell differentiation, apoptosis, ATP synthesis, protein homo-oligomerization, neuron migration, and negative regulation of peptidase activity. Protein-protein interaction network analysis of DEGs identified key hub genes. Notably, the genes Atp5o and Cyc1 were both involved in the ATP synthesis and among the top three hub genes, suggesting that regulation of oocyte mitochondrial electron transport and ATP synthesis is important in the response to stress and also is a possible mechanism of action for KYZY.

CONCLUSIONS

KYZY was effective in ameliorating the adverse effects of stress on oocyte competence, possibly by targeting the mitochondrial respiratory chain and ATP synthase.

Advanced Maternal Age-associated SIRT1 Deficiency Compromises Trophoblast Epithelial-Mesenchymal Transition through an Increase in Vimentin Acetylation

Advanced maternal age (AMA) pregnancies are rapidly increasing and are associated with aberrant trophoblast cell function, poor placentation, and unfavorable pregnancy outcomes, presumably due to premature placental senescence. SIRT1 is an NAD⁺ -dependent deacetylase with well-known antiaging effects, but its connection with placental senescence is unreported. In this study, human term placentas and first-trimester villi were collected from AMA and normal pregnancies, and a mouse AMA model was established by cross breeding young and aged male and female C57 mice. SIRT1 expression and activity in HTR8/SVneo cells were genetically or pharmacologically manipulated. Trophoblast-specific Sirt1-knockout (KO) mouse placentas were generated by mating Elf5-Cre and Sirt1^fl/fl mice. Trophoblast cell mobility was assessed with transwell invasion and wound-healing assays. SIRT1-binding proteins in HTR8/SVneo cells and human placental tissue were identified by mass spectrometry. We identified SIRT1 as the only differentially expressed sirtuin between AMA and normal placentas. It is downregulated in AMA placentas early in the placental life cycle and is barely impacted by paternal age. SIRT1 loss upregulates P53 acetylation and P21 expression and impairs trophoblast invasion and migration. Sirt1-KO mouse placentas exhibit senescence markers and morphological disruption, along with decreased fetal weight. In trophoblasts, SIRT1 interacts with vimentin, regulating its acetylation. In conclusion, SIRT1 promotes trophoblast epithelial-mesenchymal transition (EMT) to enhance invasiveness by modulating vimentin acetylation. AMA placentas are associated with premature senescence during placentation due to SIRT1 loss. Therefore, SIRT1 may be an antiaging therapeutic target for improving placental development and perinatal outcomes in AMA pregnancies.

Local DNA synthesis is critical for DNA repair during oocyte maturation

Mammalian oocytes can be very long-lived cells and thereby are very likely to encounter DNA damage during their lifetime. Defective DNA repair may result in oocytes that are developmentally incompetent or give rise to progeny with congenital disorders. During oocyte maturation, damaged DNA is repaired primarily by non-homologous end joining (NHEJ) or homologous recombination (HR). Although these repair pathways have been studied extensively, the associated DNA synthesis is poorly characterized. Here, using porcine oocytes, we demonstrate that the DNA synthesis machinery is present during oocyte maturation and dynamically recruited to sites of DNA damage. DNA polymerase δ is identified as being crucial for oocyte DNA synthesis. Furthermore, inhibiting synthesis causes DNA damage to accumulate and delays the progression of oocyte maturation. Importantly, inhibition of the spindle assembly checkpoint (SAC) bypassed the delay of oocyte maturation caused by DNA synthesis inhibition. Finally, we found that ∼20% of unperturbed oocytes experienced spontaneously arising damage during maturation. Cumulatively, our findings indicate that oocyte maturation requires damage-associated DNA synthesis that is monitored by the SAC. This article has an associated First Person interview with the first author of the paper.

PI3K/PTEN/AKT Signaling Pathways in Germ Cell Development and Their Involvement in Germ Cell Tumors and Ovarian Dysfunctions

Several studies indicate that the PI3K/PTEN/AKT signaling pathways are critical regulators of ovarian function including the formation of the germ cell precursors, termed primordial germ cells, and the follicular pool maintenance. This article reviews the current state of knowledge of the functional role of the PI3K/PTEN/AKT pathways during primordial germ cell development and the dynamics of the ovarian primordial follicle reserve and how dysregulation of these signaling pathways may contribute to the development of some types of germ cell tumors and ovarian dysfunctions.

Does Coenzyme Q10 Supplementation Improve Human Oocyte Quality?

Acquiring oocyte competence requires optimal mitochondrial function and adequate ATP levels. In this context, CoQ10 supplementation may improve human oocyte quality and subsequent reproductive performance given its role in ATP synthesis and mitochondrial protection from ROS oxidative damage. In infertility treatments, CoQ10 therapy can be orally supplied to promote a more favorable environment for oocyte development in vivo or by its addition to culture media in an attempt to improve its quality in vitro. Human clinical studies evaluating the impact of CoQ10 on reproductive performance are summarized in this review, although the available data do not clearly prove its ability to improve human oocyte quality. The main objective is to provide readers with a complete overview of this topic's current status as well as the keys for potential future research lines that may help to take this therapy to clinical practice. Indeed, further clinical trials are needed to confirm these results along with molecular studies to evaluate the impact of CoQ10 supplementation on oxidative stress status and mitochondrial function in human gametes.

Bezafibrate prevents aging in in vitro-matured porcine oocytes

Bezafibrate, a fibrate drug used as a lipid-lowering agent to treat hyperlipidemia, is a pan-agonist of peroxisome proliferator-activated receptor alpha. It can enhance mitochondrial fatty acid oxidation, oxidative phosphorylation, and mitochondrial biogenesis. After ovulation, oocytes may get arrested at the metaphase II (MII) stage until fertilization beyond optimal timing, which is termed as post-ovulatory aging. Post-ovulatory aging is a disease that degrades DNA, mitochondria, and oxidative system, and has a negative impact on embryo development and quality; however, the impact of bezafibrate during post-ovulatory aging has not been fully defined. In the present study, we assessed the ability of bezafibrate to prevent the progression of aging in in vitro conditions as well as the underlying mechanisms in pigs. An appropriate concentration of this drug (50 μM) was added, and then oxidative stress, reactive oxygen species downstream, mitochondrial biogenesis, and mitochondrial function were analyzed via immunofluorescence staining and real-time polymerase chain reaction. Bezafibrate significantly alleviated reactive oxygen species and ameliorated glutathione production simultaneously in oocytes and embryos. Moreover, it diminished H2A.X and attenuated CASPASE 3 expression produced by oxidative stress in oocytes and embryos. Furthermore, bezafibrate remarkably improved the mitochondrial function and blastocyst quality as well as markedly reduced the mitochondria/TOM20 ratio and mtDNA copy number. The elevated PARKIN level indicated that mitophagy was induced by bezafibrate treatment after post-ovulatory aging. Collectively, these results suggest that bezafibrate beneficially affects against porcine post-ovulatory oocyte aging in porcine by its antioxidant property and mitochondrial protection.

Coenzyme Q10 ameliorates the quality of mouse oocytes during in vitro culture

Oxidative stress causes several diseases and dysfunctions in cells, including oocytes. Clearly, oxidative stress influences oocyte quality during in vitro maturation and fertilization. Here we tested the ability of coenzyme Q10 (CoQ10) to reduce reactive oxygen species (ROS) and improve mouse oocyte quality during in vitro culture. Treatment with 50 μM CoQ10 efficiently reduced ROS levels in oocytes cultured in vitro. The fertilizable form of an oocyte usually contains a cortical granule-free domain (CGFD). CoQ10 enhanced the ratio of CGFD-oocytes from 35% to 45%. However, the hardening of the zona pellucida in oocytes was not affected by CoQ10 treatment. The in vitro maturation capacity of oocytes, which was determined by the first polar body extrusion, was enhanced from 48.9% to 75.7% by the addition of CoQ10 to the culture medium. During the parthenogenesis process, the number of two-cell embryos was increased by CoQ10 from 43.5% to 67.3%. Additionally, treatment with CoQ10 increased the expression of Bcl2 and Sirt1 in cumulus cells. These results suggested that CoQ10 had a positive effect on ROS reduction, maturation rate and two-cell embryo formation in mouse oocyte culture.

Mitochondrial Functional Assessment in Mammalian Gametes Using Fluorescent Probes

A positive relationship between mitochondrial functionality and gamete quality, ultimately contributing to fertilization success and normal embryo development has been established for some years now. Both mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) production are major indicators of mitochondrial function, and the need for accurate biomarkers mirroring gamete quality highlights the importance of a precise assessment of mitochondrial quality and function. In this chapter, we discuss the use of some mitochondrial fluorescent probes coupled to flow cytometry and/or fluorescence microscopy to specifically assess mitochondrial ROS production and MMP in both sperm and oocytes. Furthermore, as the distribution/aggregation of mitochondria in the oocyte is of interest to determine its quality, a detailed protocol is also given. These methodologies are easy, accurate and can be safely applied in research- and/or clinical-based contexts.

Effect of exogenous glutathione supplementation on the in vitro developmental competence of ovine oocytes

The beneficial effect of glutathione (GSH) on the in vitro maturation (IVM) of bovine/porcine oocytes has been confirmed; however, the antioxidant effect of exogenous GSH supplementation on the IVM of ovine oocytes has not been determined. In this study, ovine cumulus oocyte complexes (COCs) were classified into three groups according to the layer number of cumulus cells (the Grade A group has more than five layers, the Grade B group has three to four layers and the Grade C group has less than three layers). After in vitro culture of COCs in the presence of exogenous GSH, the meiotic competence of ovine oocytes was assessed by analyzing nuclear maturation to metaphase II (MII) stage, cortical granules (CGs) dynamics, astacin like metalloendopeptidase (ASTL) distribution, histone methylation pattern, reactive oxygen species (ROS) production, mitochondrial activities and genes expression. After in vitro fertilization (IVF), assessments of embryonic development were conducted to confirm the effects of exogenous GSH supplementation. The results showed that exogenous GSH not only enhanced the maturation rates of the Grade B and Grade C groups but also promoted CGs dynamics and ASTL distribution of the Grade A, B and C groups (p < 0.05). Exogenous GSH increased the mitochondrial activities of the Grade A, B and C groups and decreased the ROS production levels of oocytes (p < 0.05), regardless of the layer number of cumulus cells. Moreover, exogenous GSH promoted the expression levels of genes related with oocyte maturation, antioxidant activity and antiapoptotic effects in the Grade B and Grade C groups (p < 0.05). The expression levels of H3K4me3 and H3K9me3 in the Grade B and Grade C groups were promoted after exogenous GSH supplementation (p < 0.05), consistent with the expression levels of genes related with histone methylation (p < 0.05). In addition, exogenous GSH strongly promoted the embryonic developmental competence of Grade B and Grade C groups (p < 0.05). Taken together, our findings provide foundational evidence for the free radical scavenging potential of exogenous GSH in the in vitro developmental competence of ovine oocytes, especially oocytes from COCs lacking cumulus cells. These findings, which demonstrated the potential for improving the quality of ovine oocytes during IVM, will contribute to researches on GSH applications and the efficiency of assisted reproductive technology for ovine breeding.

Curcumin as Prospective Anti-Aging Natural Compound: Focus on Brain

The nutrients and their potential benefits are a new field of study in modern medicine for their positive impact on health. Curcumin, the yellow polyphenolic compound extracted from Curcuma longa species, is widely used in traditional Ayurvedic medicine to prevent and contrast many diseases, considering its antioxidant, immunomodulatory, anti-inflammatory, anti-microbial, cardio-protective, nephron-protective, hepato-protective, anti-neoplastic, and anti-rheumatic proprieties. In recent years, the investigations of curcumin have been focused on its application to aging and age-associated diseases. Aging is a physiological process in which there is a decreasing of cellular function due to internal or external stimuli. Oxidative stress is one of the most important causes of aging and age-related diseases. Moreover, many age-related disorders such as cancer, neuroinflammation, and infections are due to a low-grade chronic systemic inflammation. Curcumin acting on different proteins is able to contrast both oxidative stress than inflammation. In the brain, curcumin is able to modulate inflammation induced by microglia. Finally in brain tumors curcumin is able to reduce tumor growth by inhibition of telomerase activity. This review emphasizes the anti-aging role of curcumin focusing on its mechanism to counteract aging in the brain. Moreover, new formulations to increase the bioavailability of curcumin are discussed.

Melatonin Promotes In Vitro Maturation of Vitrified-Warmed Mouse Germinal Vesicle Oocytes, Potentially by Reducing Oxidative Stress through the Nrf2 Pathway

Simple Summary

Cryopreservation of oocytes can cause high oxidative stress, reduce the quality of vitrified-warmed oocytes, and seriously hinder the application of oocyte cryopreservation technology in production and medicine. In this work, we found for the first time that melatonin can exert antioxidant effects through receptors and regulate the Nrf2 antioxidant pathway to respond to oxidative stress of vitrified-warmed oocytes, thereby improving both oocyte quality and the potential for subsequent development. The results illustrated the molecular mechanism of melatonin’s antioxidant effect in vitrified-warmed oocytes and provided a theoretical basis for the application of melatonin in the cryopreservation of oocytes. These findings are of great significance for the further application of oocyte cryopreservation technology to production and assisted reproduction in the future.

Abstract

Previously it was reported that melatonin could mitigate oxidative stress caused by oocyte cryopreservation; however, the underlying molecular mechanisms which cause this remain unclear. The objective was to explore whether melatonin could reduce oxidative stress during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes through the Nrf2 signaling pathway or its receptors. During in vitro maturation of vitrified-warmed mouse GV oocytes, there were decreases (p < 0.05) in the development rates of metaphase I (MI) oocytes and metaphase II (MII) and spindle morphology grades; increases (p < 0.05) in the reactive oxygen species (ROS) levels; and decreases (p < 0.05) in expressions of Nrf2 signaling pathway-related genes (Nrf2, SOD1) and proteins (Nrf2, HO-1). However, adding 10⁻⁷ mol/L melatonin to both the warming solution and maturation solutions improved (p < 0.05) these indicators. When the Nrf2 protein was specifically inhibited by Brusatol, melatonin did not increase development rates, spindle morphology grades, genes, or protein expressions, nor did it reduce vitrification-induced intracellular oxidative stress in GV oocytes during in vitro maturation. In addition, when melatonin receptors were inhibited by luzindole, the ability of melatonin to scavenge intracellular ROS was decreased, and the expressions of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1) were not restored to control levels. Therefore, we concluded that 10⁻⁷ mol/L melatonin acted on the Nrf2 signaling pathway through its receptors to regulate the expression of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1), and mitigate intracellular oxidative stress, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

Proteins from the DNA Damage Response: Regulation, Dysfunction, and Anticancer Strategies

Cells respond to genotoxic stress through a series of complex protein pathways called DNA damage response (DDR). These monitoring mechanisms ensure the maintenance and the transfer of a correct genome to daughter cells through a selection of DNA repair, cell cycle regulation, and programmed cell death processes. Canonical or non-canonical DDRs are highly organized and controlled to play crucial roles in genome stability and diversity. When altered or mutated, the proteins in these complex networks lead to many diseases that share common features, and to tumor formation. In recent years, technological advances have made it possible to benefit from the principles and mechanisms of DDR to target and eliminate cancer cells. These new types of treatments are adapted to the different types of tumor sensitivity and could benefit from a combination of therapies to ensure maximal efficiency.

RAB7 activity is required for the regulation of mitophagy in oocyte meiosis and oocyte quality control during ovarian aging

There is increasing evidence that mitophagy, a specialized form of autophagy to degrade and clear long-lived or damaged mitochondria, is impaired in aging and age-related disease. Previous study has demonstrated the obesity-exposed oocytes accumulate and transmit damaged mitochondria due to an inability to activate mitophagy. However, it remains unknown whether mitophagy functions in oocyte and what's the regulatory mechanism in oocyte aging. In the study, when fully grown oocytes were treated with CCCP, an uncoupling agent to induce mitophagy, we found the activation of the PRKN-mediated mitophagy pathway accompanied the blockage of meiosis at metaphase I stage. Our result then demonstrated its association with the decreased activity of RAB7 and all the observed defects in CCCP treated oocytes could be effectively rescued by microinjection of mRNA encoding active RAB7^Q67L or treatment with the RAB7 activator ML098. Further study indicated PRKN protein level as a rate-limiting factor to facilitate degradation of RAB7 and its GEF (guanine nucleotide exchange factor) complex CCZ1-MON1 through the ubiquitin-proteasome system. In GV oocytes collected during ovarian aging, we found the age-related increase of PINK1 and PRKN proteins and a significant decrease of RAB7 which resulted in defects of mitophagosome formation and the accumulation of damaged mitochondria. The age-related retardation of female fertility was improved after in vivo treatment of ML098. Thus, RAB7 activity is required to maintain the balance between mitophagy and chromosome stability and RAB7 activator is a good candidate to ameliorate age-related deterioration of oocyte quality.Abbreviations: ATG9: autophagy related 9A; ATP: adenosine triphosphate; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CCZ1: CCZ1 vacuolar protein trafficking and biogenesis associated; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GAPs: GTPase-activating proteins; GEF: guanine nucleotide exchange factor; GV: germinal vesicle; GVBD: germinal vesicle breakdown; LAMP1: lysosomal-associated membrane protein 1; MI: metaphase I stage of meiosis; MII: metaphase II stage of meiosis; Mito: MitoTracker; mtDNA: mitochondrial DNA; MON1: MON1 homolog, secretory trafficking associated; OPTN: optineurin; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RAB7: RAB7, member RAS oncogene family; ROS: reactive oxygen species; TEM: transmission electron microscopy; TOMM20/TOM20: translocase of outer mitochondrial membrane 20; TUBB: tubulin, beta; UB: ubiquitin.

Oxidative stress in oocyte aging and female reproduction

In a healthy body, reactive oxygen species (ROS) and antioxidants remain balanced. When the balance is broken toward an overabundance of ROS, oxidative stress appears and may lead to oocyte aging. Oocyte aging is mainly reflected as the gradual decrease of oocyte quantity and quality. Here, we aim to review the relationship between oxidative stress and oocyte aging. First, we introduced that the defective mitochondria, the age-related ovarian aging, the repeated ovulation, and the high-oxygen environment were the ovarian sources of ROS in vivo and in vitro. And we also introduced other sources of ROS accumulation in ovaries, such as overweight and unhealthy lifestyles. Then, we figured that oxidative stress may act as the "initiator" for oocyte aging and reproductive pathology, which specifically causes follicular abnormally atresia, abnormal meiosis, lower fertilization rate, delayed embryonic development, and reproductive disease, including polycystic ovary syndrome and ovary endometriosis cyst. Finally, we discussed current strategies for delaying oocyte aging. We introduced three autophagy antioxidant pathways like Beclin-VPS34-Atg14, adenosine 5'-monophosphate (AMP)-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR), and p62-Keap1-Nrf2. And we also describe the different antioxidants used to combat oocyte aging. In addition, the hypoxic (5% O₂ ) culture environment for oocytes avoiding oxidative stress in vitro. So, this review not only contribute to our general understanding of oxidative stress and oocyte aging but also lay the foundations for the therapies to treat premature ovarian failure and oocyte aging in women.

Reproductive senescence and energetic metabolism of human luteinized granulosa cells: is it all about ATP? A prospective cohort and critical view

Mitochondria are known to play a key role in the regulation of reproductive capacity. Senescence is known to impair mitochondrial function and, ultimately, cellular energetic metabolism. Therefore, as women age, a deficient energy supply is likely to affect oocyte quality. The analysis of granulosa cells is considered a valuable noninvasive strategy to assess factors implicated in oocyte competence. Thus, we conducted an observational prospective cohort to evaluate the impact of aging on energy production by luteinized granulosa cells (LGCs). The control group comprised 13 young oocyte donors, whereas the comparison group included 13 infertile women over 38 years of age undergoing in vitro fertilization. Women with diseases that could potentially impact mitochondrial function were excluded. No differences were detected in the ATP levels in LGCs from young donors and infertile patients of advanced reproductive age (1.9 ± 0.99 picomoles in the control group vs. 2.1 ± 0.59 picomoles; p-value = .139). Likewise, the ATP levels in our series did not correlate with either oocyte number or maturity. Despite the similar ATP levels in LGCs, an age effect on the bioenergetic status cannot be excluded. Energy metabolism is very complex, and ATP does not seem to be the most important and reliable parameter.

Effects of coenzyme Q10 on ovarian surface epithelium-derived ovarian stem cells and ovarian function in a 4-vinylcyclohexene diepoxide-induced murine model of ovarian failure

BACKGROUND

Several studies have shown that coenzyme Q10 (CoQ10) can rescue ovarian aging and that ovarian surface epithelium (OSE)-derived ovarian stem cells (OSCs) are useful for treating infertility due to ovarian aging. However, few studies have examined the effect of CoQ10 on OSCs. This study was aimed to investigate whether CoQ10 activates OSCs and recovers ovarian function in a 4-vinylcyclohexene diepoxide (VCD)-induced mouse model of ovarian failure.

METHODS

Forty female C57BL/6 mice aged 6 weeks were randomly divided into four groups (n = 10/group): a control group administered saline orally, a CoQ10 group administered 150 mg/kg/day of CoQ10 orally in 1 mL of saline daily for 14 days, a VCD group administered 160 mg/kg/day of VCD i.p. in 2.5 mL of saline/kg for 5 days, and a VCD + CoQ10 group administered VCD i.p. for 5 days injection and CoQ10 (150 mg/kg/day) orally for 14 days. After treatment, follicle counts were evaluated by hematoxylin and eosin (H&E) staining, and ovarian mRNA expressions of Bmp-15, Gdf-9, and c-Kit were examined by quantitative real-time PCR. Serum FSH, AMH, and ROS levels were also measured. Oocyte-like structure counts and the expressions of Oct-4 and MVH were also evaluated after culturing OSE for 3 weeks. In a second experiment, 32 female mice were administered CoQ10 as described above, induced to superovulate using PMSG and hCG, and mated. Numbers of zygotes and embryo development rate were examined.

RESULTS

Postcultured OSE showed significant increases in the numbers of oocyte-like structure and that the expression of Oct-4 and MVH were higher in the VCD + CoQ10 group than in the VCD group (p < 0.05). Numbers of surviving follicles from primordial to antral follicles, numbers of zygotes retrieved and embryo development rate to blastocyst were significantly greater in the VCD + CoQ10 group than in the VCD group (p < 0.01). Serum AMH level and ovarian expressions of Bmp-15, Gdf-9 and c-Kit were also significantly greater in the VCD + CoQ10 group than in the VCD group (p < 0.05). In contrast, serum ROS level was significantly lower in the VCD + CoQ10 group than in the VCD group (p < 0.05).

CONCLUSION

This study shows that CoQ10 stimulates the differentiation of OSE-derived OSCs and confirms that CoQ10 can reduce ROS levels and improve ovarian function and oocyte quality in mice with VCD-induced ovarian failure.

Melatonin rescues the reproductive toxicity of low-dose glyphosate-based herbicide during mouse oocyte maturation via the GPER signaling pathway

Glyphosate-based herbicides (GBHs) are a group of widely used broad-spectrum agricultural pesticides. Due to the recalcitrance of GBH, it has been found in food and environment as a contaminant, posing a threat to public health. The health risks associated with GBH have been indicated by reporting acute toxicity data (an acute exposure of GBH at a 0.5% dose), which primarily discuss toxicity in relation to accidental high-rate exposure. Currently, there is little information regarding the toxicity of GBH at environmentally relevant levels. In this study, we used mature mouse oocytes to study the toxic effects of low-dose GBH exposure in vitro (0.00001%-0.00025%) and in vivo (0.0005%, orally administered through daily drinking water) during meiotic maturation. GBH exposure led to meiotic maturation failure with spindle defects and chromosome misalignment. In addition, GBH treatment severely reduced sperm-binding ability and disrupted early embryo cleavage. Moreover, GBH exposure significantly increased the reactive oxygen species (ROS) levels and apoptotic rates. Evidence indicates that such effects in GBH-exposed oocytes are likely due to overexpression of the G-protein estrogen receptor (GPER/GPR30). Remarkably, we found that melatonin administration elicited significant protection against GBH-induced oocyte deterioration via preserving the expression of GPR30, along with activation of its downstream signaling event (pERK/ERK). Taken together, these results revealed that low-dose glyphosate has a certain adverse effect on oocyte maturation and early embryo cleavage, and highlight the protective roles of melatonin.

Comparison of Embryo and Clinical Outcomes in Different Types of Incubator Between Two Different Embryo Culture Systems

This study aimed to compare the clinical outcomes of an oxidative stress-reducing embryo culture system (ORES) containing compounds that minimize intercellular oxidative stress, with those of a standard embryo culture system (StES). Furthermore, we investigated the efficiency of the ORES regarding the type of incubator used (time-lapse incubator [TLI] or non-time-lapse dry incubator [non-TLI]) and maternal age. In this retrospective study, we analyzed 3610 oocyte retrieval cycles (in 2537 patients) and 1726 single vitrified-warmed blastocyst transfer (SVBT) cycles (in 1726 patients) performed in a single center between April 2018 and July 2019. Transfers of single vitrified-warmed blastocysts, confirmed by fetal heartbeat, were used to assess clinical outcomes. The clinical outcomes of ORES and StES were compared in both TLI and non-TLI. Groups were stratified according to maternal age (≤39 years old, young age group; ≥40 years old, advanced age group). A significant difference in ongoing pregnancy rates was observed between the ORES and StES groups when non-TLI was used (34.9 vs. 27.0%, respectively; p < 0.05), unlike when TLI was used. Furthermore, ongoing pregnancy rates were significantly higher in the ORES group (24.8%) than in the StES group (14.9%) in the advanced age group, unlike in the young age group when non-TLI was used. In conclusion, compared to StEs, the ORES during all in vitro fertilization procedures improved ongoing pregnancy rates in the advanced age group using the non-TLI.

Reprogramming of glucose metabolism of cumulus cells and oocytes and its therapeutic significance

The aim of this review is to summarize our current understanding of the molecular mechanism for the glucose metabolism, especially pyruvate dehydrogenase (PDH), during oocyte maturation, as well as future perspectives of therapeutic strategies for aging focusing on metabolic regulation between aerobic glycolysis and the tricarboxylic acid (TCA) cycle/oxidative phosphorylation (OXPHOS). Each keyword alone or in combination was used to search from PubMed. Glucose metabolism is a dynamic process involving "On" and "Off" switches by the pyruvate dehydrogenase kinase (PDK)-PDH axis, which is crucial for energy metabolism and mitochondrial efficiency in cumulus cell differentiation and oocyte maturation. Activation of PDK suppresses the conversion of pyruvate to acetyl-coenzyme A (acetyl-CoA) through the inactivation of PDH, which allows the cumulus cells to supply sufficient amounts of pyruvate, lactate, and nicotinamide adenine dinucleotide phosphate (NADPH) to the oocytes. On the other hand, inactivation of PDK in oocytes can produce adenosine triphosphate (ATP) through a metabolic shift from aerobic glycolysis to the TCA cycle/OXPHOS. The metabolic balance between aerobic glycolysis and TCA cycle/OXPHOS presents us with a number of enzymes, ligands, receptors, and antioxidants that are potential therapeutic targets, some of which have already been successfully pursued to improve fertility outcomes. However, there are also many reports that question their efficacy. In conclusion, understanding the molecular mechanisms involved in the PDK-PDH axis is a crucial step to advance in novel therapeutic strategies to improve oocyte quality.

Genetics of Menopause and Primary Ovarian Insufficiency: Time for a Paradigm Shift?

This review summarizes the existing information concerning the genetic background of menopause and primary ovarian insufficiency (POI). There is overwhelming evidence that majority of genes are involved in double-strand break repair, mismatch repair, and base excision repair. The remaining loci were involved in cell energy metabolism and immune response. Gradual (or in case of rapid POI) accumulation of unrepaired DNA damage causes (premature) cell death and cellular senescence. This in turn leads to exhaustion of cell renewal capacity and cellular dysfunction in affected organs and eventually to aging of the entire soma. Similar erosion of the genome occurs within the germ cell line and the ovaries. Subsequently, the systemic "survival" response intentionally suppresses the sex-steroid hormonal output, which in turn may contribute to the onset of menopause. The latter occurs in particular when age-dependent DNA damage accumulation does not cease. Both effects are expected to synergize to promote (premature) ovarian silencing and install (early) menopause. Consequently, aging of the soma seems to be a primary driver for the loss of ovarian function in women. This challenges the current dogma which implies that loss of ovarian function initiates aging of the soma. It is time for a paradigm shift!

Exploring the mechanism of (-)-Epicatechin on premature ovarian insufficiency based on network pharmacology and experimental evaluation

METHODS

Relevant potential targets for EC were obtained based on Traditional Chinese Medicine System Pharmacology Database (TCMSP), a bioinformatics analysis tool for molecular mechanism of Traditional Chinese Medicine (BATMAN-TCM) and STITCH databases. The Online Mendelian Inheritance in Man (OMIM) and GeneCards databases were utilized to screen the known POI-related targets, while Cytoscape software was used for network construction and visualization. Then, the Gene Ontology (GO) and pathway enrichment analysis were carried out by the Database for Annotation, Visualization and Integrated Discovery (DAVID) database. Furthermore, KGN cells were performed to validate the predicted results in oxidative stress (OS) model, and antioxidant effect was examined.

RESULTS

A total of 70 potential common targets for EC in the treatment of POI were obtained through network pharmacology. Metabolic process, response to stimulus and antioxidant activity occupied a leading position of Gene Ontology (GO) enrichment. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that PI3K/protein kinase B (AKT), TNF, estrogen, VEGF and MAPK signaling pathways were significantly enriched. In addition, cell experiments showed that EC exhibited antioxidant effects in an H2O2-mediated OS model in ovarian granulosa cells by regulating the expression of PI3K/AKT/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and multiple downstream antioxidant enzymes.

CONCLUSION

EC could regulate multiple signaling pathways and several biological processes (BPs). EC had the ability to down-regulate elevated OS level through the PI3K/AKT/Nrf2 signaling pathway and represented a potential novel treatment for POI.

Mitochondrial Dysfunction and Oxidative Stress Caused by Cryopreservation in Reproductive Cells

Mitochondria, fundamental organelles in cell metabolism, and ATP synthesis are responsible for generating reactive oxygen species (ROS), calcium homeostasis, and cell death. Mitochondria produce most ROS, and when levels exceed the antioxidant defenses, oxidative stress (OS) is generated. These changes may eventually impair the electron transport chain, resulting in decreased ATP synthesis, increased ROS production, altered mitochondrial membrane permeability, and disruption of calcium homeostasis. Mitochondria play a key role in the gamete competence to facilitate normal embryo development. However, iatrogenic factors in assisted reproductive technologies (ART) may affect their functional competence, leading to an abnormal reproductive outcome. Cryopreservation, a fundamental technology in ART, may compromise mitochondrial function leading to elevated intracellular OS that decreases sperm and oocytes' competence and the dynamics of fertilization and embryo development. This article aims to review the role played by mitochondria and ROS in sperm and oocyte function and the close, biunivocal relationships between mitochondrial damage and ROS generation during cryopreservation of gametes and gonadal tissues in different species. Based on current literature, we propose tentative hypothesis of mechanisms involved in cryopreservation-associated mitochondrial dysfunction in gametes, and discuss the role played by antioxidants and other agents to retain the competence of cryopreserved reproductive cells and tissues.

Biodynamic digital holographic speckle microscopy for oocyte and embryo metabolic evaluation

Assisted reproductive technologies seek to improve the success rate of pregnancies. Morphology scoring is a common approach to evaluate oocyte and embryo viability prior to embryo transfer in utero, but the efficacy of the method is low. We apply biodynamic imaging, based on dynamic light scattering and low-coherence digital holography, to assess the metabolic activity of oocytes and embryos. A biodynamic microscope, developed to image small and translucent biological specimens, is inserted into the bay of a commercial inverted microscope that can switch between conventional microscopy channels and biodynamic microscopy. We find intracellular Doppler spectral features that act as noninvasive proxies for embryo metabolic activity that may relate to embryo viability.

MicroRNA-Mediated Gene Regulatory Mechanisms in Mammalian Female Reproductive Health

Mammalian reproductive health affects the entire reproductive cycle starting with the ovarian function through implantation and fetal growth. Various environmental and physiological factors contribute to disturbed reproductive health status leading to infertility problems in mammalian species. In the last couple of decades a significant number of studies have been conducted to investigate the transcriptome of reproductive tissues and organs in relation to the various reproductive health issues including endometritis, polycystic ovarian syndrome (PCOS), intrauterine growth restriction (IUGR), preeclampsia, and various age-associated reproductive disorders. Among others, the post-transcriptional regulation of genes by small noncoding miRNAs contributes to the observed transcriptome dysregulation associated with reproductive pathophysiological conditions. MicroRNAs as a class of non-coding RNAs are also known to be involved in various pathophysiological conditions either in cellular cytoplasm or they can be released to the extracellular fluid via membrane-bounded extracellular vesicles and proteins. The present review summarizes the cellular and extracellular miRNAs and their association with the etiology of major reproductive pathologies including PCOS, endometritis, IUGR and age-associated disorders in various mammalian species.

The Role of Oxidative Stress and Natural Antioxidants in Ovarian Aging

The ovarian system comprises vital organs in females and is of great significance for the maintenance of reproductive potential and endocrine stability. Although complex pathogenesis undoubtedly contributes to ovarian aging, increasing attention is being paid to the extensive influence of oxidative stress. However, the role of oxidative stress in ovarian aging is yet to be fully elucidated. Exploring oxidative stress-related processes might be a promising strategy against ovarian aging. In this review, compelling evidence is shown that oxidative stress plays a role in the etiology of ovarian aging and promotes the development of other ovarian aging-related etiologies, including telomere shortening, mitochondrial dysfunction, apoptosis, and inflammation. In addition, some natural antioxidants such as quercetin, resveratrol, and curcumin have a protective role in the ovaries through multiple mechanisms. These findings raise the prospect of oxidative stress modulator-natural antioxidants as therapeutic interventions for delaying ovarian aging.

The Impact of Unbalanced Maternal Nutritional Intakes on Oocyte Mitochondrial Activity: Implications for Reproductive Function

Accumulating evidence on the effect of nutrition on reproduction is emerging from both animal and human studies. A healthy dietary pattern and nutrient supplementation, especially during the peri-conceptional period, might be helpful to achieve a live birth, although the mechanisms implicated are not fully understood. The endocrine system and the ooplasmic organelles apparatus, in particular the mitochondria, are clearly key elements during oogenesis and subsequent embryo development, and their proper functioning is associated with nutrition, even beyond maternal aging. Several studies in animal models have reported various adverse effects on mitochondria caused by unbalanced dietary intakes such as high fat diet, high fat high sugar diet, and low protein diet. The alterations produced might include mitochondrial intracellular distribution, content, structure, biogenesis, and functioning. This review summarizes the key role of mitochondria in female reproduction and the effects of different dietary macronutrient compositions on oocyte mitochondrial activity with their possible short-, medium-, and long-term effects.

Cryopreservation and oxidative stress in porcine oocytes

Several vitrification protocols have been established for porcine oocytes so as to facilitate gene banking of female germplasm. Although live piglets have been successfully produced from pig oocytes vitrified at the germinal vesicle (GV) stage, the competence of vitrified oocytes to develop into the blastocyst stage is greatly compromised following cryopreservation. The focus of this review is to elucidate the impact of cryopreservation on the redox balance of pig oocytes, making special reference to the relevance of non-enzymatic and enzymatic antioxidant defences. Besides, the regulation of gene expression in response to oxidative stress is also considered. Finally, we discuss the effects of supplementing maturation and vitrification media with the exogenous non-enzymatic antioxidants that have hitherto yielded the most relevant results.