Oocyte mitochondrial function and reproduction

Oocyte mitochondria – Key regulators of oocyte function and potential therapeutic targets for improving fertility

The development of oocytes and early embryos is dependent on mitochondrial ATP production. This reliance on mitochondrial activity, together with the exclusively maternal inheritance of mitochondria in development, places mitochondria as central regulators of both fertility and transgenerational inheritance mechanisms. Mitochondrial mass and mtDNA content massively increase during oocyte growth. They are highly dynamic organelles and oocyte maturation is accompanied by mitochondrial trafficking around subcellular compartments. Due to their key roles in generation of ATP and reactive oxygen species, oocyte mitochondrial defects have largely been linked with energy deficiency and oxidative stress. Pharmacological treatments and mitochondrial supplementation have been proposed to improve oocyte quality and fertility by enhancing ATP generation and reducing reactive oxygen species levels. More recently, the role of mitochondria-derived metabolites in controlling epigenetic modifiers has provided a mechanistic basis for mitochondria-nuclear crosstalk, allowing adaptation of gene expression to specific metabolic states. Here, we discuss the multi-faceted mechanisms by which mitochondrial function influence oocyte quality, as well as longer-term developmental events within and across generations.

Glutathione protects against the meiotic defects of ovine oocytes induced by arsenic exposure via the inhibition of mitochondrial dysfunctions

Accumulating evidences revealed the connections between arsenic exposure and mitochondrial dysfunctions induced reproductive toxicology. Meanwhile, production declines were found in livestock suffering from arsenic exposure. However, the connections between arsenic exposure and livestock meiotic defects remain unclear. In this study, the effects of sodium arsenite (NaAsO2) exposure during the in vitro maturation (IVM) on the meiotic potentials of ovine oocytes were analyzed. Furthermore, the effects of glutathione (GSH) supplementation on the meiotic defects of NaAsO2 exposed ovine oocytes were investigated by the assay of nuclear maturation, spindle organization, chromosome alignment, cytoskeleton assembly, cortical granule (CGs) dynamics, mitochondrial dysfunctions, reactive oxygen species (ROS) accumulation, oxidative DNA damages, cellular apoptosis, epigenetic modifications and fertilization capacities. The results showed that the meiotic defects of NaAsO2 exposed ovine oocytes were effectively ameliorated by the GSH supplementation via the inhibition of mitochondrial dysfunctions, which not only promoted the nuclear maturation, spindle organization, chromosome alignment, cytoskeleton assembly, CGs dynamic and fertilization capacities, but also inhibited the ROS accumulation, oxidative DNA damages and apoptosis of ovine MII oocytes. The abnormal expressions of 5mC, H3K4me3 and H3K9me3 in NaAsO2 exposed ovine oocytes, indicating the abnormal epimutations of DNA methylation and histone methylation, were also effectively ameliorated by the GSH supplementation. Taken together, this study confirmed the connections between arsenic exposure and meiotic defects of ovine oocytes. Meanwhile, the effects of GSH supplementation on the developmental competence of livestock oocytes, especially for these suffering from arsenic exposure were also founded, benefiting the extended researches for the GSH applications.

The mitochondrial protease LONP1 maintains oocyte development and survival by suppressing nuclear translocation of AIFM1 in mammals

Background

Oogenesis is a fundamental process of human reproduction, and mitochondria play crucial roles in oocyte competence. Mitochondrial ATP-dependent Lon protease 1 (LONP1) functions as a critical protein in maintaining mitochondrial and cellular homeostasis in somatic cells. However, the essential role of LONP1 in maintaining mammalian oogenesis is far from elucidated.

Methods

Using conditional oocyte Lonp1-knockout mice, RNA sequencing (RNA-seq) and coimmunoprecipitation/liquid chromatography–mass spectrometry (Co-IP/LC–MS) technology, we analysed the functions of LONP1 in mammalian oogenesis.

Findings

Conditional knockout of Lonp1 in mouse oocytes in both the primordial and growing follicle stages impairs follicular development and causes progressive oocyte death, ovarian reserve loss, and infertility. LONP1 directly interacts with apoptosis inducing factor mitochondria-associated 1 (AIFM1), and LONP1 ablation leads to the translocation of AIFM1 from the cytoplasm to the nucleus, causing apoptosis in mouse oocytes. In addition, women with pathogenic variants of LONP1 lack large antral follicles (>10 mm) in the ovaries, are infertile and present premature ovarian insufficiency.

Interpretation

We demonstrated the function of LONP1 in regulating oocyte development and survival, and in-depth analysis of LONP1 will be crucial for elucidating the mechanisms underlying premature ovarian insufficiency.

Funding

This work was supported by grants from the National Key Research and Development Program of China (2018YFC1004701), the National Nature Science Foundation of China (82001629, 81871128, 81571391, 81401166, 82030040), the Jiangsu Province Social Development Project (BE2018602), the Jiangsu Provincial Medical Youth Talent (QNRC2016006), the Youth Program of the Natural Science Foundation of Jiangsu Province (BK20200116) and Jiangsu Province Postdoctoral Research Funding (2021K277B).

Follicular fluid steroid and gonadotropic hormone levels and mitochondrial function from exosomes predict embryonic development

PURPOSE

Human follicular fluid (FF) is a complex biological fluid that contributes to the micro-environment of oocyte development. The aim of this study was to evaluate the role of steroid and gonadotropic hormones levels and mitochondrial function in embryo development during in vitro fertilization cycles.

METHODS

This was a cohort study of 138 women receiving IVF/ICSI, including 136 FF samples from 109 infertile women. FF steroid and gonadotropic hormones levels were tested by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunoassays. The mRNA expression levels of mitochondrial electron transport chain (ETC) complex genes from FF exosomes were detected by qPCR.

RESULTS

Analysis of these individual FF concentrations revealed that LH and FSH concentrations were higher in follicles in which the oocyte developed into a top quality (TQ) blastocyst (LH: 9.44 ± 2.32mIU/ml, FSH: 9.32 ± 1.01mIU/ml) than those in which there was a failure of fertilization (LH: 5.30 ± 0.84mIU/ml, FSH: 6.91 ± 0.62mIU/ml). In contrast, follicular cortisone concentrations were lower for oocytes that resulted in a TQ blastocyst (12.20 ± 0.82mIU/ml). The receiver operating characteristic analysis showed that FF LH and FSH levels predicted TQ blastocyst with excellent AUC value of 0.711 and 0.747. Mitochondrial ETC complex I and III mRNA levels were increased in the FF exosomes of TQ blastocyst. Correlation analysis showed that mRNA levels of ETC complex I was positively correlated with LH and FSH levels in FF.

CONCLUSION

The levels of FF steroid and gonadotropic hormones from single follicle can predetermine subsequent embryo development to some extent. Furthermore, impaired exosome mitochondrial dysfunction is a potiential event that causes hormone change in embryo development.

Extensive analysis of mitochondrial DNA quantity and sequence variation in human cumulus cells and assisted reproduction outcomes

STUDY QUESTION

Are relative mitochondrial DNA (mtDNA) content and mitochondrial genome (mtGenome) variants in human cumulus cells (CCs) associated with oocyte reproductive potential and assisted reproductive technology (ART) outcomes?

SUMMARY ANSWER

Neither the CC mtDNA quantity nor the presence of specific mtDNA genetic variants was associated with ART outcomes, although associations with patient body mass index (BMI) were detected, and the total number of oocytes retrieved differed between major mitochondrial haplogroups.

WHAT IS KNOWN ALREADY

CCs fulfil a vital role in the support of oocyte developmental competence. As with other cell types, appropriate cellular function is likely to rely upon adequate energy production, which in turn depends on the quantity and genetic competence of the mitochondria. mtDNA mutations can be inherited or they can accumulate in somatic cells over time, potentially contributing to aging. Such mutations may be homoplasmic (affecting all mtDNA in a cell) or they may display varying levels of heteroplasmy (affecting a proportion of the mtDNA). Currently, little is known concerning variation in CC mitochondrial genetics and how this might influence the reproductive potential of the associated oocyte.

STUDY DESIGN, SIZE, DURATION

This was a prospective observational study involving human CCs collected with 541 oocytes from 177 IVF patients. mtDNA quantity was measured in all the samples with a validated quantitative PCR method and the entire mtGenome was sequenced in a subset of 138 samples using a high-depth massively parallel sequencing approach. Associations between relative mtDNA quantity and mtGenome variants in CCs and patient age, BMI (kg/m2), infertility diagnosis and ART outcomes were investigated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Massively parallel sequencing permitted not only the accurate detection of mutations but also the precise quantification of levels of mutations in cases of heteroplasmy. Sequence variants in the mtDNA were evaluated using Mitomaster and HmtVar to predict their potential impact.

MAIN RESULTS AND THE ROLE OF CHANCE

The relative mtDNA CC content was significantly associated with BMI. No significant associations were observed between CC mtDNA quantity and patient age, female infertility diagnosis or any ART outcome variable. mtGenome sequencing revealed 4181 genetic variants with respect to a reference genome. The COXI locus contained the least number of coding sequence variants, whereas ATPase8 had the most. The number of variants predicted to affect the ATP production differed significantly between mitochondrial macrohaplogroups. The total number of retrieved oocytes was different between the H-V and J-T as well as the U-K and J-T macrohaplogroups. There was a non-significant increase in mtDNA levels in CCs with heteroplasmic mitochondrial mutations.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although a large number of samples were analysed in this study, it was not possible to analyse all the CCs from every patient. Also, the results obtained with respect to specific clinical outcomes and macrohaplogroups should be interpreted with caution due to the smaller sample sizes when subdividing the dataset.

WIDER IMPLICATIONS OF THE FINDINGS

These findings suggest that the analysis of mtDNA in CCs is unlikely to provide an advantage in terms of improved embryo selection during assisted reproduction cycles. Nonetheless, our data raise interesting biological questions, particularly regarding the interplay of metabolism and BMI and the association of mtDNA haplogroup with oocyte yield in ovarian stimulation cycles.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by National Institutes of Health grant 5R01HD092550-02. D.J.N. and C.R. co-hold patent US20150346100A1 and D.J.N. holds US20170039415A1, both for metabolic imaging methods. D.W. receives support from the NIHR Oxford Biomedical Research Centre. The remaining authors have no conflicts of interest to declare.

Looking at the Future Through the Mother's Womb: Gestational Diabetes and Offspring Fertility

Altered nutrition or intrauterine exposure to various adverse conditions during fetal development or earlier in a mother's life can lead to epigenetic changes in fetal tissues, predisposing those tissues to diseases that manifest when offspring become adults. An example is a maternal obesity associated with gestational diabetes (GDM), where fetal exposure to a hyperglycemic, hyperinsulinemic, and/or hyperlipidemic gestational environment can provoke epigenetic changes that predispose offspring to various diseased conditions later in life. While it is now well established that offspring exposed to GDM have an increased risk of developing obesity, metabolic disorders, and/or cardiovascular disease in adult life, there are limited studies assessing the reproductive health of these offspring. This mini-review discusses the long-term effect of in utero exposure to GDM-associated adverse prenatal environment on the reproductive health of the offspring. Moreover, using evidence from various animal models and human epidemiological studies, this review offers molecular insight and understanding of how epigenetic reprogramming of genes culminates in reproductive dysfunction and the development of subfertility or infertility later in adult life.

Perfluorooctane sulfonate affects mouse oocyte maturation in vitro by promoting oxidative stress and apoptosis induced bymitochondrial dysfunction

Perfluorooctane sulphonate (PFOS), as a surfactant, is widely applied in the agricultural production activities and has become a potential menace to human health. The mechanism of its effect on the maturation of mammalian oocytes is unclear. This study explored the toxic effect of PFOS on mouse oocyte maturation in vitro. The results revealed that PFOS under a concentration of 600 μM could significantly reduce the polar body extrusion rate (PBE) of mouse oocytes and cause symmetrical cell division. Further experiments showed that PFOS resulted in the abnormal cytoskeleton of the oocytes, causing the abnormal spindles and misplaced chromosomes, as well as the impaired dynamics of actin. Moreover, PFOS exposure inhibited the process of oocyte meiosis, which reflected in the slower spindle migration and continuous activation of spindle assembly checkpoint (SAC), then ultimately increased the probability of aneuploidy. Most importantly, PFOS exposure reduced the quality of oocytes, specifically by disrupting the function of mitochondria, inducing cell oxidative stress, and triggering early apoptosis. Furthermore, the level of methylation of histones is additionally influenced. In summary, our findings showed that PFOS exposure interfered with the maturation of mouse oocytes through affecting cytoskeletal dynamics, meiotic progression, oocyte quality, and histone modifications.

Mitochondrial proteome of mouse oocytes and cisplatin-induced shifts in protein profile

Mitochondria are essential organelles that provide energy for mammalian cells and participate in multiple functions, such as signal transduction, cellular differentiation, and regulation of apoptosis. Compared with the mitochondria in somatic cells, oocyte mitochondria have an additional level of importance since they are required for germ cell maturation, dysfunction in which can lead to severe inherited disorders. Thus, a systematic proteomic profile of oocyte mitochondria is urgently needed to support the basic and clinical research, but the acquisition of such a profile has been hindered by the rarity of oocyte samples and technical challenges associated with capturing mitochondrial proteins from live oocytes. Here, in this work, using proximity labeling proteomics, we established a mitochondria-specific ascorbate peroxidase (APEX2) reaction in live GV-stage mouse oocytes and identified a total of 158 proteins in oocyte mitochondria. This proteome includes intrinsic mitochondrial structural and functional components involved in processes associated with “cellular respiration”, “ATP metabolism”, “mitochondrial transport”, etc. In addition, mitochondrial proteome capture after oocyte exposure to the antitumor chemotherapeutic cisplatin revealed differential changes in the abundance of several oocyte-specific mitochondrial proteins. Our study provides the first description of a mammalian oocyte mitochondrial proteome of which we are aware, and further illustrates the dynamic shifts in protein abundance associated with chemotherapeutic agents.

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.

Correlation between Pre-Ovulatory Follicle Diameter and Follicular Fluid Metabolome Profiles in Lactating Beef Cows

Induced ovulation of small pre-ovulatory follicles reduced pregnancy rates, embryo survival, day seven embryo quality, and successful embryo cleavage in beef cows undergoing fixed-time artificial insemination. RNA-sequencing of oocytes and associated cumulus cells collected from pre-ovulatory follicles 23 h after gonadotropin-releasing hormone (GnRH) administration to induce the pre-ovulatory gonadotropin surge suggested reduced capacity for glucose metabolism in cumulus cells of follicles ≤11.7 mm. We hypothesized that the follicular fluid metabolome influences metabolic capacity of the cumulus-oocyte complex and contributes to reduced embryo cleavage and quality grade observed following induced ovulation of small follicles. Therefore, we performed a study to determine the correlation between pre-ovulatory follicle diameter and follicular fluid metabolome profiles in lactating beef cows (Angus, n = 130). We synchronized the development of a pre-ovulatory follicle and collected the follicular contents approximately 20 h after GnRH administration. We then performed ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) metabolomic studies on 43 follicular fluid samples and identified 38 metabolites within pre-ovulatory follicles of increasing size. We detected 18 metabolites with a significant, positive correlation to follicle diameter. Individual and pathway enrichment analysis of significantly correlated metabolites suggest that altered glucose and amino acid metabolism likely contribute to reduced developmental competence of oocytes when small pre-ovulatory follicles undergo induced ovulation.

Hyperandrogenemia alters mitochondrial structure and function in the oocytes of obese mouse with polycystic ovary syndrome

Capsule

Hyperandrogenemia in an obese PCOS mouse model results in altered glucose/insulin metabolism and mitochondrial structure and function in the oocytes, in part explaining adverse outcomes and inheritance patterns seen in PCOS.

Objective

To study the oocyte quality by means of mitochondrial structure and function in a well-established classic PCOS mouse model.

Design

Animal study using an obese PCOS mouse model compared with control.

Setting

Animal research facility in a tertiary care university hospital setting.

Animals

C57/B6J mice.

Intervention

Three week old mice had subdermal implants of DHT controlled release pellet or placebo for 90 days.

Main Outcome Measures

The mouse model was validated by performing glucose tolerance test, HbA1c levels, body weight and estrous cycle analyses. Oocytes were subsequently isolated and were used to investigate mitochondrial membrane potential, oxidative stress, lipid peroxidation, ATP production, mtDNA copy number, transcript abundance, histology and electron microscopy.

Results

Results showed glucose intolerance and hyperinsulinemia along with dysregulated estrus cycle. Analysis of the oocytes demonstrated impaired inner mitochondrial membrane function, increased ATP production and mtDNA copy number, altered RNA transcript abundance and aberrant ovarian histology. Electron microscopy of the oocytes showed severely impaired mitochondrial ultrastructure.

Conclusion

The obese PCOS mouse model shows a decreased oocyte quality related to impaired mitochondrial function.

Human oocyte meiotic maturation is associated with a specific profile of alternatively spliced transcript isoforms

The transition from a transcriptionally active state (GV) to a transcriptionally inactive state (mature MII oocytes) is required for the acquisition of oocyte developmental competence. We hypothesize that the expression of specific genes at the in vivo matured (MII) stage could be modulated by posttranscriptional mechanisms, particularly regulation of alternative splicing (AS). In this study, we examined the transcriptional activity of GV oocytes after ovarian stimulation followed by oocyte pick-up and the landscape of alternatively spliced isoforms in human MII oocytes. Individual oocytes were processed and analyzed for transcriptional activity (GV), gene expression (GV and MII), and AS signatures (GV and MII) on HTA 2.0 microarrays. Samples were grouped according to maturation stage, and then subgrouped according to women's age and antral follicular count (AFC); array results were validated by quantitative polymerase chain reaction. Differentially expressed genes between GV and MII oocytes clustered mainly in biological processes related to mitochondrial metabolism. Interestingly, 16 genes that were related to the regulation of transcription and mitochondrial translation showed differences in alternatively spliced isoform profiles despite not being differentially expressed between groups. Altogether, our results contribute to our understanding of the role of AS in oocyte developmental competence acquisition.

Pigment epithelium-derived factor negates oxidative stress in mouse oocytes

Molecular changes, caused by various environmental factors, affect the quality and developmental potential of oocytes. Oxidative stress (OS) is a major factor involved in various gynecologic disorders and/or in aging. Recent studies suggest that elevated reactive oxygen species (ROS) hamper oocyte quality and future embryonic development. Pigment epithelium-derived factor (PEDF) is a pleiotropic protein, known for its antiangiogenic, anti-inflammatory, and antioxidative properties. Our previous findings demonstrate the antioxidative role of rPEDF in maintaining granulosa cell viability. In the current study, we examined the ability of PEDF to negate the adverse impact of OS on oocytes. Maturation rate of oocytes exposed to OS was significantly lower than that of control oocytes. The number of mtDNA copies in OS-exposed oocytes was significantly higher than in control oocytes (>3 times), whereas ATP concentration was significantly lower. Oocytes exposed to OS demonstrated impaired chromosome arrangement at the metaphase plate. PEDF significantly improved maturation rate of untreated OS-exposed oocytes. Moreover, mtDNA copy number, ATP concentration, and chromosome arrangement at the metaphase plate in rPEDF-treated OS-exposed oocytes were restored to the level of control oocytes. Our findings demonstrate that OS hampers the ability of oocytes to undergo proper in vitro maturation. The energetic balance of OS-exposed oocyte is characterized by excessive mtDNA replication and reduced ATP concentration; it hampers the ability of oocytes to perform high fidelity chromosome segregation. PEDF alleviates this damage, improves the rate of oocyte maturation, and preserves mtDNA level and ATP content, thus enabling oocytes to form proper metaphase plate and improve oocyte competence.

Tributyltin Oxide Exposure During in vitro Maturation Disrupts Oocyte Maturation and Subsequent Embryonic Developmental Competence in Pigs

Tributyltin oxide (TBTO), an organotin compound, has been demonstrated to have toxic effects on several cell types. Previous research has shown that TBTO impairs mouse denuded oocyte maturation. However, limited information is available on the effects of TBTO exposure on livestock reproductive systems, especially on porcine oocytes in the presence of dense cumulus cells. In the present research, we evaluated the effects of TBTO exposure on porcine oocyte maturation and the possible underlying mechanisms. Porcine cumulus-oocyte complexes were cultured in maturation medium with or without TBTO for 42 h. We found that TBTO exposure during oocyte maturation prevented polar body extrusion, inhibited cumulus expansion and impaired subsequent blastocyst formation after parthenogenetic activation. Further analysis revealed that TBTO exposure not only induced intracellular reactive oxygen species (ROS) accumulation but also caused a loss of mitochondrial membrane potential and reduced intracellular ATP generation. In addition, TBTO exposure impaired porcine oocyte quality by disrupting cellular iron homeostasis. Taken together, these results demonstrate that TBTO exposure impairs the porcine oocyte maturation process by inducing intracellular ROS accumulation, causing mitochondrial dysfunction, and disrupting cellular iron homeostasis, thus decreasing the quality and impairing the subsequent embryonic developmental competence of porcine oocytes.

Bioengineering Approaches to Improve In Vitro Performance of Prepubertal Lamb Oocytes

Juvenile in vitro embryo technology (JIVET) provides exciting opportunities in animal reproduction by reducing the generation intervals. Prepubertal oocytes are also relevant models for studies on oncofertility. However, current JIVET efficiency is still unpredictable, and further improvements are needed in order for it to be used on a large-scale level. This study applied bioengineering approaches to recreate: (1) the three-dimensional (3D) structure of the cumulus–oocyte complex (COC), by constructing—via bioprinting technologies—alginate-based microbeads (COC-microbeads) for 3D in vitro maturation (3D-IVM); (2) dynamic IVM conditions, by culturing the COC in a millifluidic bioreactor; and (3) an artificial follicular wall with basal membrane, by adding granulosa cells (GCs) and type I collagen (CI) during bioprinting. The results show that oocyte nuclear and cytoplasmic maturation, as well as blastocyst quality, were improved after 3D-IVM compared to 2D controls. The dynamic 3D-IVM did not enhance oocyte maturation, but it improved oocyte bioenergetics compared with static 3D-IVM. The computational model showed higher oxygen levels in the bioreactor with respect to the static well. Microbead enrichment with GCs and CI improved oocyte maturation and bioenergetics. In conclusion, this study demonstrated that bioengineering approaches that mimic the physiological follicle structure could be valuable tools to improve IVM and JIVET.

Effects of a gel culture system made of polysaccharides (xanthan gum and locust bean gum) on in vitro bovine oocyte development and gene expression of the granulosa cells

Xanthan gum (XG) and locust bean gum (LBG) are nontoxic polysaccharides that produce culture substrates. The present study examined the effect of XG-LBG gel on in vitro bovine oocyte growth and gene expression in granulosa cells. Oocytes and granulosa cell complexes (OGCs) were cultured in vitro on plastic culture plate (Plate) or XG-LBG gel for 16 days. OGCs formed a dome-like cavity surrounding the oocytes on plate but formed a spherical follicle structure on XG-LBG gel. The total granulosa cell numbers of the OGCs and their survival rate was greater for OGCs cultured on XG-LBG gel than for those cultured on plate. Oocytes grown on XG-LBG gels had higher lipid and mitochondrial content, as well as a larger diameter, than their plate counterparts. When oocytes grown in vitro were subjected to in vitro maturation and fertilization, the normal fertilization rate was significantly higher for oocytes developed on XG-LBG gel than that of oocytes cultured on the plate counterpart. RNAseq of the granulosa cells revealed that genes associated with focal adhesion, phosphatidylinositol 3'-kinase-Akt and Hippo signaling, and regulation of actin cytoskeleton were upregulated in granulosa cells of OGCs cultured on XG-LBG gel compared with those cultured on plate.

The Molecular Regulation in the Pathophysiology in Ovarian Aging

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

Podophyllotoxin Exposure Affects Organelle Distribution and Functions in Mouse Oocyte Meiosis

Podophyllotoxin (POD) is one of the most characterized lignans that is commonly found in podophyllum, and its preparations and derivatives are widely used in clinical treatment due to strong antitumor and antivirus activities. POD has been reported for its neurotoxicity, liver toxicity, and potential reproductive toxicity. In the present study, we investigated the effects of POD on the organelles of mouse oocytes during meiosis. Our results showed that exposure to POD significantly reduced the developmental competence of mouse oocytes. Further analysis revealed that the endoplasmic reticulum (ER) failed to accumulate to the spindle periphery, suggesting that POD exposure might affect protein synthesis during oocyte meiotic maturation. Similarly, abnormal Golgi apparatus distribution was found after POD exposure, which could be confirmed by the aberrant localization of Rab11a-related vesicles, indicating that POD induced vesicle-based protein transport disorder. We also found the aberrant accumulation of lysosomes in the cytoplasm of POD-exposed oocytes, which implied that POD might lead to aberrant protein degradation. Moreover, the perinuclear distribution of mitochondria was also significantly disturbed, indicating the mitochondrial dysfunction after POD exposure. In all, our study illustrated that exposure to POD might disrupt protein synthesis, transport, degradation, and ATP production by its effects on the distribution and functions of organelles during mouse oocyte meiotic maturation.

Gallic acid promotes the in vitro development of sheep secondary isolated follicles involving the phosphatidylinositol 3-kinase pathway

This study was conducted to evaluate the effect of addition of gallic acid as the single antioxidant to the base medium for in vitro culture of sheep secondary follicles and if the phosphatidylinositol 3-kinase (PI3K) pathway is involved in the action of gallic acid. Secondary follicles were isolated and cultured for 12 days in α-MEM supplemented with bovine serum albumin (BSA), insulin, glutamine, hypoxanthine, transferrin, selenium, and ascorbic acid (control medium: α-MEM⁺) or in α-MEM supplemented with BSA, insulin, glutamine, hypoxanthine and different concentrations of gallic acid (25, 50 or 100 μM), thus replacing transferrin, selenium and ascorbic acid in the medium. Follicle morphology, glutathione (GSH), and mitochondrial activity, and meiotic resumption were evaluated. Furthermore, inhibition of PI3K pathway was performed by pretreatment with LY294002. After 12 days of culture, the follicle survival in a medium containing 100 μM gallic acid was similar (P > 0.05) to α-MEM⁺ and greater (P < 0.05) compared with other gallic acid concentrations. Antrum formation, follicle diameter, GSH, and mitochondrial activity, and meiotic resumption, however, were greater (P < 0.05) when 100 μM gallic acid was included in the α-MEM⁺ culture medium compared with the control medium. Furthermore, LY294002 inhibited (P < 0.05) follicle survival, development, and meiotic resumption stimulated by 100 μM gallic acid. In conclusion, concentration of 100 μM of gallic acid can be a substitute for transferrin, selenium, and ascorbic acid in the base medium during in vitro culture of sheep secondary follicles, inducing follicle development likely through the PI3K pathway.

Oxidative stress induced by methomyl exposure reduces the quality of early embryo development in mice

Methomyl is a widely used carbamate insecticide and environmental oestrogen that has adverse effects on the reproductive system. However, there have been no reports on the effect of methomyl on early embryos in mammals. In this study, we explored the effect of methomyl exposure on the quality of early embryonic development in mice and the possible mechanisms. During in vitro culture, different concentrations of methomyl (10, 20, 30 and 35 μM) were added to mouse zygote medium. The results showed that methomyl had an adverse effect on early embryonic development. Compared with the control group, the addition of 30 μM methomyl significantly reduced the rate of early embryo blastocyst formation. Methomyl exposure can increase oxidative stress and impair mitochondrial function, which may be the cause of blastocyst formation. In addition, we found that methomyl exposure promoted apoptosis and autophagy in mouse blastocysts. The toxic effect of methomyl on early embryos may be the result of oxidative stress induction. Taken together, our results indicate that methomyl can cause embryonic development defects in mice, thereby reducing the quality of early embryo development.

Evaluation of mitochondria in mouse oocytes following cisplatin exposure

BACKGROUND

Cisplatin is a platinum-based chemotherapeutic that damages genomic DNA leading to cell death. It also damages mitochondrial DNA and induces high levels of mitochondrial reactive oxygen species (mtROS), further sensitising cells to apoptosis. Notably, immature oocytes are particularly vulnerable to cisplatin treatment, a common side effect of which is depletion of the primordial follicle reserve, leading to infertility and early menopause. Cisplatin is known to damage the DNA of oocytes, but the possibility that cisplatin also compromises oocyte survival and quality by damaging mitochondria, has not been investigated. To begin to address this question, neonatal mice were treated with saline or cisplatin (2 mg/kg or 4 mg/kg) and the short and long-term impacts on mitochondria in oocytes were characterised.

RESULTS

At 6 and 24 h after treatment, mitochondrial localisation, mass and ATP content in immature oocytes were similar between groups. However, TMRM staining intensity, a marker of mitochondrial membrane potential, was decreased in immature oocytes from cisplatin treated mice compared to saline treated controls, consistent with the induction of apoptosis. When mice were super ovulated 5 weeks after exposure, the number of mature oocytes harvested from cisplatin treated mice was significantly lower than controls. Mitochondrial localisation, mass, membrane potential and ATP levels showed no differences between groups.

CONCLUSIONS

These findings suggest that mitochondrial dysfunction may contribute to the depletion of the ovarian reserve caused by cisplatin, but long-term impacts on mitochondria may be minimal as those immature oocytes that survive cisplatin treatment develop into mature oocytes with normal mitochondrial parameters.

Trophectoderm Mitochondrial DNA Content Associated with Embryo Quality and Day-5 Euploid Blastocyst Transfer Outcomes

Mitochondria play a critical role in cell function and embryo development. Recently, increasing studies have investigated whether mitochondrial DNA (mtDNA) can be used as a predictive biomarker of embryo implantation. However, the results of its effect on implantation are still controversial. To further understand the clinical application value of mtDNA content for reproductive potential, we analyzed the influence of relative mtDNA quantity on embryo quality and transfer outcomes based on the results of second-generation sequencing of preimplantation genetic testing patients in our center. Biopsied trophectoderm (TE) from aneuploid blastocysts contained much larger amounts of mtDNA than those from euploid blastocysts (p < 0.000). In an analysis of only euploid blastocysts (n = 769), female age had no effect on mtDNA content (p = 0.216). TE cells biopsied on day 5 (n = 355) contained significantly higher amounts of mtDNA compared to those biopsied on day 6 (n = 388) or day 7 (n = 26) (p < 0.000). Higher quality trophoblast was associated with lower mtDNA content (p = 0.026), but quality of inner cell mass was not correlated with quantity of mtDNA (p = 0.112). For transferred embryos, the biopsied date and mtDNA content were significantly associated with embryo implantation and live birth outcomes. Day-5 euploid blastocysts with lower quantities of mtDNA exhibited higher implantation rate and live birth rate. However, our data indicated that mtDNA content may not be considered an independent predictive marker, it may be a useful reference for the selection of day-5 transferred euploid blastocysts.

The mitochondrial DNA copy number of cumulus granulosa cells may be related to the maturity of oocyte cytoplasm

STUDY QUESTION

Is the mitochondrial DNA (mtDNA) copy number of cumulus granulosa cells (CGCs) related to the maturation of oocyte cytoplasm?

SUMMARY ANSWER

Compared with the mtDNA copy number of CGCs from germinal vesicles (GV), CGCs from Metaphase I (MI) oocytes appear to have a lower mtDNA copy number.

WHAT IS KNOWN ALREADY

The growth and development of CGCs and oocyte are synchronised. The interaction between CGCs and the oocyte provides the appropriate balance of energy, which is necessary for mammalian oocyte development. Moreover, in the oocyte-cumulus complex (OCC), mature oocytes with higher mtDNA copy numbers tend to have corresponding CGCs with higher mtDNA copy numbers.

STUDY DESIGN, SIZE, DURATION

This is a prospective study of 302 OCCs obtained from 70 women undergoing in vitro fertilisation with intracytoplasmic sperm injection (ICSI) at the Reproductive and Genetic Hospital of CITIC-Xiangya, between 24 February 2018 and 21 December 2019. The CGCs were divided into three groups (GV, MI and MII stages) based on the maturation status of their corresponding oocyte. The sample sizes (n = 302) of CGCs in the three stages were 63 (CGCGV), 70 (CGCMI) and 169 (CGCMII), respectively. Some of the samples (n = 257) was used to quantify the mtDNA copy number, while the rest (n = 45) were used to analyse the expression level of mitochondrial genes. Furthermore, we retrieved 82 immature oocytes from among the 257 OCCs used for mtDNA copy numbers, including 36 GV oocytes and 46 MI oocytes, for analysis of oocyte mtDNA.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We selected genes with high consistency of real-time PCR results to accurately measure the mtDNA copy number by testing the efficacy and the reproducibility in whole genome amplification (WGA) samples from a human embryonic stem cell line. The CGCs of each oocyte were individually isolated. The mtDNA copy number and gene expression of the CGCs were assessed using real-time PCR techniques. Mitochondrial DNA copy number of the corresponding immature oocytes was also evaluated.

MAIN RESULTS AND THE ROLE OF CHANCE

MT-ND1, MT-CO1 and β-globin genes were chosen for the assessment of mtDNA content, and mRNA expressions of MT-ND1, MT-CO1, PGC-1α and TFAM were also measured. The genome of 257 CGCs and 82 immature oocytes were amplified according to the multiple displacement amplification (MDA) protocol, and RNA was extracted from 45 CGCs. Compared with CGCGV, CGCMI had a significantly lower mtDNA copy number. In the MT-ND1 assay, the CGCGV: CGCMI was [270 ± 302]: [134 ± 201], P = 0.015. In the MT-CO1 assay, CGCGV: CGCMI was [205 ± 228]: [92 ± 112], P = 0.026. There was no statistical difference in mtDNA between CGCGV and CGCMII. In the MT-ND1 assay, CGCGV: CGCMII was [270 ± 302]: [175 ± 223], P = 0.074. In the MT-CO1 assay, CGCGV: CGCMII was [205 ± 228]: [119 ± 192], P = 0.077. No statistical difference of mtDNA copy number was observed between CGCMI and CGCMII. In the MT-ND1 assay, CGCMI: CGCMII was [134 ± 201]: [175 ± 223], P = 0.422. In the MT-CO1 assay, CGCMI: CGCMII was [92 ± 112]: [119 ± 192], P = 0.478. To verify the reliability of the above results, we further analysed the mtDNA copy number of CGCs of 14 patients with GV, MI and MII oocytes, and the results showed that the mtDNA copy number of CGCMI may be lower. The mtDNA copy number of CGCGV and CGCMI was statistically different in the MT-ND1 assay where CGCGV: CGCMI was [249 ± 173]: [118 ± 113], P = 0.016, but in the MT-CO1 assay, CGCGV: CGCMI was [208 ± 199]: [83 ± 98], P = 0.109. There was no significant difference in mtDNA between CGCGV and CGCMII. In the MT-ND1 assay, CGCGV: CGCMII was [249 ± 173]: [185 ± 200], P = 0.096. In the MT-CO1 assay, CGCGV: CGCMII was [208 ± 199]: [114 ± 139], P = 0.096. There was also no significant difference in mtDNA between CGCMI and CGCMII. In the MT-ND1 assay, CGCMI: CGCMII was [118 ± 113]: [185 ± 200], P = 0.198. In the MT-CO1 assay, CGCMI: CGCMII was [83 ± 98]: [114 ± 139], P = 0.470. Moreover, there were no statistical differences in the expression levels of MT-ND1, MT-CO1, PGC-1α and TFAM between CGCGV, CGCMI and CGCMII (P > 0.05).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Due to the ethical issues, the study did not quantify the mtDNA content of MII oocytes. Thus, whether the change in mtDNA copy number in CGCs is related to the different developmental stages of oocytes has not been further confirmed. Moreover, the sample size was relatively small.

WIDER IMPLICATIONS OF THE FINDINGS

The mtDNA copy number of CGCs decreases from the GV phase to the MI phase and stays steady from the MI to MII stage. At different stages of oocyte maturation, the mtDNA of CGCs may undergo self-degradation and replication to meet the energy requirements of the corresponding oocyte and the maturation of the oocyte cytoplasm.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was provided by the National Key R&D Program of China (Grant 2018YFC1003100, to L.H.), the science and technology major project of the Ministry of Science and Technology of Hunan Province, China (grant 2017SK1030, to G.L.), the National Natural Science Foundation of China (grant 81873478, to L.H.), and Merck Serono China Research Fund for Fertility Experts (to L.H.). There is no conflict of interest.

UCH-L1 inhibitor LDN-57444 hampers mouse oocyte maturation by regulating oxidative stress and mitochondrial function and reducing ERK1/2 expression

Oocyte maturation is a prerequisite for successful fertilization and embryo development. Incomplete oocyte maturation can result in infertility. Ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) has been found to be implicated in oocyte maturation and embryo development. However, the cellular and molecular mechanisms of UCH-L1 underlying oocyte maturation have not been fully elucidated. In the present study, we observed that the introduction of UCH-L1 inhibitor LDN-57444 suppressed first polar body extrusion during mouse oocyte maturation. The inhibition of UCH-L1 by LDN-57444 led to the notable increase in reactive oxygen species (ROS) level, conspicuous reduction in glutathione (GSH) content and mitochondrial membrane potential (MMP), and blockade of spindle body formation. As a conclusion, UCH-L1 inhibitor LDN-57444 suppressed mouse oocyte maturation by improving oxidative stress, attenuating mitochondrial function, curbing spindle body formation and down-regulating extracellular signal-related kinases (ERK1/2) expression, providing a deep insight into the cellular and molecular basis of UCH-L1 during mouse oocyte maturation.

Ultrastructure of mitochondria of human oocytes in different clinical conditions during assisted reproduction

Infertility affects around 8% of couples with a slight change in percentage in the last years. Despite the significant efforts made in Assisted Reproductive Technologies (ARTs) in handling this disorder, oocyte quality remains a crucial factor for a positive outcome. A better understanding of the dynamics underlying oocyte maturation, fertilization, and embryo development remains one of the main areas for progress in the ARTs field. Mitochondria are believed to play an essential role in these processes. Mitochondria have a crucial part in producing energy for oocyte maturation and embryo development throughout precise cellular functions comprising Ca²⁺ homeostasis regulation, glycolysis, amino acid and fatty acid metabolism, and regulation of apoptosis. Recent studies suggest that mitochondrial structure, content, and function may be related to oocyte competence, embryo viability, and implantation success during ARTs. Their defects could lead to low fertilization rates and embryonic development failure. This review aimed to provide an overview of the available literature data surrounding the correlation between changes at ultrastructural level of mitochondria or correlated-mitochondrial aggregates and oocyte quality and ARTs treatments. Our reported data demonstrated that oocyte mitochondrial ultrastructural alterations could be partial or complete recovery during the early embryo stages. However, these changes could persist as quiescent during the pre-implantation embryo development, causing abnormalities that become evident only during fetal and postnatal life. These factors led to consider the mitochondria as a crucial marker of oocyte and embryo quality, as well as a strategic target for further prospective therapeutical approaches.

Nicotinamide Supplementation Improves Oocyte Quality and Offspring Development by Modulating Mitochondrial Function in an Aged Caenorhabditis elegans Model

Aging is associated with a decline in the quality of biological functions. Among the aging processes, reproductive aging is a critical process because of its intergenerational effects. However, the mechanisms underlying reproductive aging remain largely unknown. Female reproductive aging is the primary reason for limited fertility in mammals. Therefore, we attempted to investigate a modulator that can control female reproductive aging using a Caenorhabditis elegans model. In the present study, we examined the role of nicotinamide (NAM) in oocyte quality and offspring development. The levels of reactive oxygen species (ROS) and oxidative stress responses in aged oocytes, embryonic lethality, and developmental growth of the offspring were examined with maternal NAM supplementation. Supplementation with NAM improved oocyte quality, decreased embryonic lethality, and promoted germ cell apoptosis. Furthermore, NAM supplementation in aged mothers reduced ROS accumulation and improved mitochondrial function in oocytes. Consequently, the developmental growth and motility of offspring were improved. These findings suggest that NAM supplementation improves the health of the offspring produced by aged mothers through improved mitochondrial function. Taken together, our results imply that NAM supplementation in the aged mother improves oocyte quality and protects offspring by modulating mitochondrial function.

Lipid Metabolism in Bovine Oocytes and Early Embryos under In Vivo, In Vitro, and Stress Conditions

Lipids are a potential reservoir of energy for initial embryonic development before activation of the embryonic genome and are involved in plasma membrane biosynthesis. Excessive lipid droplet formation is detrimental to cryotolerance and is related to alterations in mitochondrial function, which likely affects lipid metabolism. Increased lipid accumulation in in vitro produced embryos is a consequence of the stress during in vitro embryonic development process. There are several open questions concerning embryo lipid metabolism and developmental potential. Oocyte maturation and embryo development in vivo and in vitro may vary if the donors are subjected to any type of stress before follicle puncture because crucial changes in oocyte/embryonic metabolism occur in response to stress. However, little is known about lipid metabolism under additional stress (such as heat stress). Therefore, in this review, we aimed to update the information regarding the energy metabolism of oocytes and early bovine embryos exhibiting developmental competence, focusing on lipid metabolic pathways observed under in vivo, in vitro, and stress conditions.

Bisphenol A Exposure Disrupts Organelle Distribution and Functions During Mouse Oocyte Maturation

Bisphenol A (BPA) is one of the ubiquitous environmental endocrine disruptors (EEDs). Previous studies have shown that the reproduction toxicity of BPA could cause severe effects on the mammal oocytes and disturb the quality of mature oocytes. However, the toxic effects of BPA on the organelles of mouse oocytes have not been reported. In this study, to investigate whether BPA can be toxic to the organelles, we used different concentrations of BPA (50, 100, and 200 μM) to culture mouse oocytes in vitro. The results showed that 100 μM BPA exposure could significantly decrease the developmental capacity of oocytes. Then, we used the immunofluorescence staining, confocal microscopy, and western blotting to investigate the toxic effects of BPA on the organelles. The results revealed that mitochondrial dysfunction is manifested by abnormal distribution and decreased mitochondrial membrane potential. Moreover, the endoplasmic reticulum (ER) is abnormally distributed which is accompanied by ER stress showing increased expression of GRP78. For the Golgi apparatus, BPA-exposed dose not disorder the Golgi apparatus distribution but caused abnormal structure of Golgi apparatus, which is manifested by the decrease of GM130 protein expression. Moreover, we also found that BPA-exposed led to the damage of lysosome, which were shown by the increase of LAMP2 protein expression. Collectively, our findings demonstrated that the exposure of BPA could damage the normal function of the organelles, which may explain the reduced maturation quality of oocytes.

Understanding oocyte ageing: can we influence the process as clinicians?

PURPOSE OF REVIEW

Oocyte quality is rate-limiting for pregnancy success and declines with age. Here, I review animal-study evidence showing dramatic reversal of oocyte ageing with mitochondrial nutrients and explore clinical evidence related to their usage.

RECENT FINDINGS

Oocyte ageing is strongly tied to mitochondrial dysfunction and oxidative stress. Quality-defining events occur over a protracted period (2-3 months in humans) when oocyte volume increases over 100-fold. Treating mice during the growth phase with mitochondrial modifiers such as CoQ10 combats oocyte ageing. Exciting new work shows that raising oocyte NAD+ levels also dramatically rejuvenate aged oocytes. However, evidence that any of these agents can reproducibly improve quality in humans is lacking. This is largely because there has been a focus on patients with poor ovarian response during IVF and/or low ovarian follicular pool size, rather than patients with poor oocyte quality. In addition, studies have used short-term treatment during ovarian stimulation after oocyte growth is already complete.

SUMMARY

Mitochondrial therapeutics such as NAD+-boosting used during the oocyte's growth phase markedly improve oocyte quality in mice. Evaluating them in humans should focus on patients with poor oocyte quality and utilise per-oocyte (rather than per-cycle) endpoints after adequate treatment that captures the growth phase when quality is defined.

Mogroside V Protects Porcine Oocytes From Lipopolysaccharide-Induced Meiotic Defects

Accumulating evidence has demonstrated that lipopolysaccharide (LPS) compromises female reproduction, especially oocyte maturation and competence. However, methods to protect oocyte quality from LPS-induced deterioration remain largely unexplored. We previously found that mogroside V (MV) can promote oocyte maturation and embryonic development. However, whether MV can alleviate the adverse effects of LPS exposure on oocyte maturation is unclear. Thus, in this study, we used porcine oocytes as a model to explore the effects of MV administration on LPS-induced oocyte meiotic defects. Our findings show that supplementation with MV protected oocytes from the LPS-mediated reduction in the meiotic maturation rate and the subsequent blastocyst formation rate. In addition, MV alleviated the abnormalities in spindle formation and chromosome alignment, decrease in α-tubulin acetylation levels, the disruption of actin polymerization, and the reductions in mitochondrial contents and lipid droplet contents caused by LPS exposure. Meanwhile, LPS reduced m⁶A levels in oocytes, but MV restored these epigenetic modifications. Furthermore, MV reduced reactive oxygen species (ROS) levels and early apoptosis in oocytes exposed to LPS. In summary, our study demonstrates that MV can protect oocytes from LPS-induced meiotic defects in part by reducing oxidative stress and maintaining m⁶A levels.

Fetal programming of polycystic ovary syndrome: Effects of androgen exposure on prenatal ovarian development

Polycystic ovary syndrome (PCOS) is a common form of anovulatory infertility with a strong hereditary component but no candidate genes have been found. The inheritance pattern may be due to in utero androgen programming on gene expression and mitochondria. Mitochondria are maternally inherited and alterations to mitochondria after fetal androgen exposure may explain one of the mechanisms of fetal programming in PCOS. Our aim was to investigate the role of excessive prenatal androgens in ovarian development by identifying how hyperandrogenemia affects gene expression and mitochondria in neonatal ovary. Pregnant dams were injected with dihydrotestosterone on days 16-18 of pregnancy. Day 0 ovaries were collected for gene expression and mitochondrial studies. RNAseq showed differential gene expressions which were related to mitochondrial dysfunction, fetal gonadal development, oocyte maturation, metabolism, angiogenesis, and PCOS. Top 20 up and downregulated genes were validated with qPCR and Western Blot. Transcriptional pathways involved in folliculogenesis and genes involved in ovarian and mitochondrial function were dysregulated. Further, DHT exposure altered mitochondrial ultrastructure and function by increasing mitochondrial oxygen consumption and decreasing mitochondrial efficiency with increased proton leak within the first day of life. Our data indicates that one path that leads to PCOS begins at birth and is programmed in utero by androgens.

Reproductive toxicity of Roundup WG® herbicide: impairments in ovarian follicles of model organism Danio rerio

Glyphosate-based herbicides are widely used in global agriculture, and their effects on different non-target animal organisms have been the focus of many toxicological studies. Regarding the potential role of glyphosate-based herbicides as an endocrine disruptor, the present study aims to investigate the effects of the herbicide Roundup WG® (RWG) on female reproduction, specifically on the ovarian maturation of Danio rerio. Adult females were exposed to low concentrations of RWG (0.065, 0.65, and 6.5 mg L^-1) for 15 days, and then the ovaries were submitted to structural and morphometric procedures, accompanied by analysis of the vitellin protein content. Our results showed an increase of initial ovarian follicle numbers, decrease of late ovarian follicles, and smaller diameter of ovarian follicles in fish exposed to 0.065 and 6.5 mg L^-1. The thickness of vitelline envelope was reduced, and the vitellin protein content was increased in the ovarian follicle in the two highest concentrations. Ultrastructural changes in the ovarian follicular component were evident and expressed by the cell index; vacuolization in follicular cells, increase of perivitelline space, and impaired mitochondria in oocytes were observed. Therefore, RWG adversely affects the ovarian maturation in D. rerio, and these changes can lead to reproductive toxicity, compromising population dynamics.

Shared aspects of mRNA expression associated with oocyte maturation failure in humans and rhesus monkeys indicating compromised oocyte quality

Oocyte maturation failure observed in assisted reproduction technology (ART) cycles can limit the number of quality oocytes obtained and present a pronounced barrier for some patients. The potential exists to use unmatured oocytes for ART through in vitro maturation. Understanding the molecular basis of oocyte maturation failure is pertinent to minimizing this loss of oocytes and considerations of whether such oocytes can be used safely for ART. We identified shared transcriptome abnormalities for rhesus monkey and human failed-to-mature (FTM) oocytes relative to healthy matured MII stage oocytes. We discovered that, although the number of shared affected genes was comparatively small, FTM oocytes in both species shared effects for several pathways and functions, including predicted activation of oxidative phosphorylation (OxPhos) with additional effects on mitochondrial function, lipid metabolism, transcription, nucleotide excision repair, endoplasmic reticulum stress, unfolded protein response, and cell viability. RICTOR emerged as a prominent upstream regulator with predicted inhibition across all analyses. Alterations in KDM5A, MTOR, MTORC1, INSR, CAB39L, and STK11 activities were implicated along with RICTOR in modulating mitochondrial activity and OxPhos. Defects in cell cycle progression were not a prominent feature of FTM oocytes. These results identify a common set of transcriptome abnormalities associated with oocyte maturation failure. While our results do not demonstrate causality, they indicate that fundamental aspects of cellular function are abnormal in FTM oocytes and raise significant concerns about the potential risks of using FTM oocytes for ART.

Lycopene Improves In Vitro Development of Porcine Embryos by Reducing Oxidative Stress and Apoptosis

In vitro culture (IVC) for porcine embryo development is inferior compared to in vivo development because oxidative stress can be induced by the production of excessive reactive oxygen species (ROS) under high oxygen tension in the in vitro environment. To overcome this problem, we investigated the effect of lycopene, an antioxidant carotenoid, on developmental competence and the mechanisms involved in mitochondria-dependent apoptosis pathways in porcine embryos. In vitro fertilized (IVF) embryos were cultured in IVC medium supplemented with 0, 0.02, 0.05, 0.1, or 0.2 μM lycopene. The results indicate that 0.1 μM lycopene significantly increased the rate of blastocyst formation and the total cell numbers, including trophectoderm cell numbers, on Day In terms of mitochondria-dependent apoptosis, IVF embryos treated with 0.1 μM lycopene exhibited significantly decreased levels of ROS, increased mitochondrial membrane potential, and decreased expression of cytochrome c on Days 2 and Furthermore, 0.1 μM lycopene significantly decreased the number and percentage of caspase 3-positive and apoptotic cells in Day-6 blastocysts. In addition, Day-2 embryos and Day-6 blastocysts treated with 0.1 μM lycopene showed significantly reduced mRNA expression related to antioxidant enzymes (SOD1, SOD2, CATALASE) and apoptosis (BAX/BCL2L1 ratio). These results indicate that lycopene supplementation during the entire period of IVC enhanced embryonic development in pigs by regulating oxidative stress and mitochondria-dependent apoptosis.

Gefitinib reduces oocyte quality by disturbing meiotic progression

Gefitinib is a first-line anti-cancer drug for the treatment of advanced non-small cell lung cancer (NSCLC). It has been reported that gefitinib can generate several drug-related adverse effects, including nausea, peripheral edema, decreased appetite and rash. However, the reproductive toxicity of gefitinib has not been clearly defined until now. Here we assessed the effects of gefitinib on oocyte quality by examining the critical events and molecular changes of oocyte maturation. Gefitinib at 1, 2, 5 or 10 μM concentration was added to culture medium (M2). We found that gefitinib at its median peak concentration of 1 μM did not affect oocyte maturation, but 5 μM gefitinib severely blocked oocyte meiotic progression as indicated by decreased rates of germinal vesicle breakdown (GVBD) and polar body extrusion (PBE). We further showed that gefitinib treatment increased phosphorylation of CDK1 at the site of Try15, inhibited cyclin B1 entry into the nucleus, and disrupted normal spindle assembly, chromosome alignment and mitochondria dynamics, finally leading to the generation of aneuploidy and early apoptosis of oocytes. Our study reported here provides valuable evidence for reproductive toxicity of gefitinib administration employed for the treatment of cancer patients.

Ovarian Aging: Molecular Mechanisms and Medical Management

This is a short review of the basic molecular mechanisms of ovarian aging, written with a particular focus on the use of this data to improve the diagnostic and therapeutic protocols both for women affected by physiological (age-related) ovarian decay and for those suffering premature ovarian insufficiency. Ovarian aging has a genetic basis that conditions the ovarian activity via a plethora of cell-signaling pathways that control the functions of different types of cells in the ovary. There are various factors that can influence these pathways so as to reduce their efficiency. Oxidative stress, often related to mitochondrial dysfunction, leading to the apoptosis of ovarian cells, can be at the origin of vicious circles in which the primary cause feeds back other abnormalities, resulting in an overall decline in the ovarian activity and in the quantity and quality of oocytes. The correct diagnosis of the molecular mechanisms involved in ovarian aging can serve to design treatment strategies that can slow down ovarian decay and increase the quantity and quality of oocytes that can be obtained for an in vitro fertilization attempt. The available treatment options include the use of antioxidants, melatonin, growth hormones, and mitochondrial therapies. All of these treatments have to be considered in the context of each couple's history and current clinical condition, and a customized (patient-tailored) treatment protocol is to be elaborated.

In vitro rescue immature oocytes - a literature review

Immature oocytes retrieved from in vitro fertilization (IVF) and clinical in vitro maturation (IVM) is a common problem, especially in patients with advanced age, poor ovarian response (POR), or polycystic ovary syndrome (PCOS). Considering there is no common name to describe this group of oocytes, we suggest naming all of immature oocytes retrieved from IVF and clinical IVM cycles as 'Medical Unusable Oocytes' (MUO) as none of them will be used for subsequent treatment and will eventually be discarded. Scientists attempt to improve the clinical utilization rate of MUO instead of discarding them. Rescue IVM and mitochondria supplementation may be available approaches to mature MUO. We propose a specific definition of rescue IVM, namely the cultivation and maturation of immature oocytes in vitro collected from IVF cycles with human chorionic gonadotropin (hCG) trigger. Rescue IVM is usually mixed up with clinical IVM. Clarification of the differences between rescue IVM and clinical IVM is necessary. This manuscript aims to clarify the rather confusing IVM procedures and review existing methods of improving rescue IVM, currently available information on the success rate, and explore the future possibility of rescue IVM serving as a promising tool in reproductive medicine.

Effects of tris (2-carboxyethyl) phosphine hydrochloride treatment on porcine oocyte in vitro maturation and subsequent in vitro fertilized embryo developmental capacity

Oocyte in vitro maturation (IVM) is a crucial process that determines subsequent in vitro embryo production. The present study investigated the effects of the antioxidant tris (2-carboxyethyl) phosphine hydrochloride (TCEP-HCL) on the in vitro maturation of porcine oocytes and in vitro developmental competence of fertilized embryos. Oocytes were matured in IVM medium based on four concentration groups of TCEP-HCL (0, 50, 100, and 200 μM) treatment. 100 μM TCEP-HCL treatment significantly increased the oocyte first polar body extrusion rate, monospermy rate and subsequent in vitro fertilized embryo developmental capacity (cleavage rate, blastocyst formation rate, and blastocyst total cell number) compared to those in the control group. Furthermore, 100 μM TCEP-HCL treatment significantly reduced the levels of reactive oxygen species, significantly increased glutathione levels and mitochondrial content compared to those in the control group. Moreover, 100 μM TCEP-HCL treatment significantly decreased the oocyte apoptosis, blastocyst apoptosis compared to that in the controls. In summary, these results indicate that 100 μM TCEP-HCL treatment improves the quality and developmental capacity of in vitro-fertilized embryos by decreasing oxidative stress in porcine oocytes.

Systemic Regulation of Host Energy and Oogenesis by Microbiome-Derived Mitochondrial Coenzymes

Gut microbiota have been shown to promote oogenesis and fecundity, but the mechanistic basis of remote influence on oogenesis remained unknown. Here, we report a systemic mechanism of influence mediated by bacterial-derived supply of mitochondrial coenzymes. Removal of microbiota decreased mitochondrial activity and ATP levels in the whole-body and ovary, resulting in repressed oogenesis. Similar repression was caused by RNA-based knockdown of mitochondrial function in ovarian follicle cells. Reduced mitochondrial function in germ-free (GF) females was reversed by bacterial recolonization or supplementation of riboflavin, a precursor of FAD and FMN. Metabolomics analysis of GF females revealed a decrease in oxidative phosphorylation and FAD levels and an increase in metabolites that are degraded by FAD-dependent enzymes (e.g., amino and fatty acids). Riboflavin supplementation opposed this effect, elevating mitochondrial function, ATP, and oogenesis. These findings uncover a bacterial-mitochondrial axis of influence, linking gut bacteria with systemic regulation of host energy and reproduction.

The toxic effects and possible mechanisms of decabromodiphenyl ethane on mouse oocyte

Decabromodiphenyl ethane (DBDPE), a widely used new brominated flame retardant, is added into flammable materials to achieve fire retardation. As it is continuously detected in the environment, it has become an emerging environmental pollutant. However, the effects of DBDPE exposure on oocyte maturation and its underlying mechanisms remain unknown. This study found that DBDPE exposure inhibited the rate of germinal vesicle breakdown (GVBD), first polar body extrusion (PBE) and fertilization of mouse oocytes. After 14 h of exposure to DBDPE, metaphase II (MII) oocytes showed that the hardness of zona pellucida (ZP) markedly increased and that the spindle morphology was abnormal. Moreover, DBDPE exposure induced abnormal mitochondrial distribution, mitochondrial dysfunction, and ATP deficiency. Simultaneously, DBDPE exposure down-regulated the expression of antioxidant-related genes (Sod2, Gpx1) and increased the level of reactive oxygen species (ROS) in oocytes. The results of immunofluorescence and qRT-PCR revealed that autophagy occurred in DBDPE-treated oocytes with high expression of autophagy-related protein (LC3) and genes (Lc3, Beclin1). Meanwhile, DBDPE significantly up-regulated the protein (Bax) and mRNA (Bax, Caspase3) levels of pro-apoptosis genes. However, the protein and mRNA expression of anti-apoptosis genes Bcl-2 was dramatically down-regulated in DBDPE-exposed oocytes. Collectively, DBDPE exposure impaired mitochondrial function, causing oxidative damage, autophagy and apoptosis in oocytes.

Ovarian Aging: Role of Pituitary-Ovarian Axis Hormones and ncRNAs in Regulating Ovarian Mitochondrial Activity

The number of mitochondria in the oocyte along with their functions (e.g., energy production, scavenger activity) decline with age progression. Such multifaceted functions support several processes during oocyte maturation, ranging from energy supply to synthesis of the steroid hormones. Hence, it is hardly surprising that their impairment has been reported in both physiological and premature ovarian aging, wherein they are crucial players in the apoptotic processes that arise in aged ovaries. In any form, ovarian aging implies the progressive damage of the mitochondrial structure and activities as regards to ovarian germ and somatic cells. The imbalance in the circulating hormones and peptides (e.g., gonadotropins, estrogens, AMH, activins, and inhibins), active along the pituitary-ovarian axis, represents the biochemical sign of ovarian aging. Despite the progress accomplished in determining the key role of the mitochondria in preserving ovarian follicular number and health, their modulation by the hormonal signalling pathways involved in ovarian aging has been poorly and randomly explored. Yet characterizing this mechanism is pivotal to molecularly define the implication of mitochondrial dysfunction in physiological and premature ovarian aging, respectively. However, it is fairly difficult considering that the pathways associated with ovarian aging might affect mitochondria directly or by altering the activity, stability and localization of proteins controlling mitochondrial dynamics and functions, either unbalancing other cellular mediators, released by the mitochondria, such as non-coding RNAs (ncRNAs). We will focus on the mitochondrial ncRNAs (i.e., mitomiRs and mtlncRNAs), that retranslocate from the mitochondria to the nucleus, as active players in aging and describe their role in the nuclear-mitochondrial crosstalk and its modulation by the pituitary-ovarian hormone dependent pathways. In this review, we will illustrate mitochondria as targets of the signaling pathways dependent on hormones and peptides active along the pituitary/ovarian axis and as transducers, with a particular focus on the molecules retrieved in the mitochondria, mainly ncRNAs. Given their regulatory function in cellular activities we propose them as potential diagnostic markers and/or therapeutic targets.

Treatment of cattle oocytes with C-type natriuretic peptide before in vitro maturation enhances oocyte mitochondrial function

The present study was conducted to evaluate the effects in vitro on oocyte mitochondrial function of C-type natriuretic peptide (CNP) when treatments were imposed before in vitro maturation (IVM). Immature oocytes were either directly matured in vitro for 24 h (Control, no pre-IVM), or cultured in basic medium not supplemented or supplemented with CNP (100 nM) (Control pre-IVM and CNP pre-IVM, respectively) for 6 h, followed by IVM for 24 h. The results indicated treatment with CNP before IVM affected patterns of distribution of mitochondria, increased the mitochondrial content, membrane potential, and decreased the ROS content in cattle oocytes before and after IVM. Furthermore, treatment of immature cattle oocytes with CNP before IVM induced marked increases in the relative abundance of mRNA transcripts and proteins related to mitochondria development and antioxidative defense mechanisms. Treatment with CNP before oocyte IVM also resulted in an enhanced relative abundance of sirtuin-1 (SIRT1) mRNA transcript in cattle oocytes. Taken together, these results provide evidence that treatment of cattle oocytes with CNP before IVM improved mitochondrial function and antioxidant defense mechanisms in cattle oocytes. Findings in the present study provide insights into the potential mechanisms by which CNP has positive effects on oocyte cytoplasmic organelles, specifically mitochondria.

Mitochondrial Stress Response Gene Clpp Is Not Required for Granulosa Cell Function

Mitochondrial unfolded protein response (UPR^mt) is a highly conserved mechanism, which is activated upon cellular or metabolic stress and aims to help cells maintain homeostasis. CLPP (caseinolytic peptidase P) plays a crucial factor for UPR^mt; it promotes the degradation of unfolded mitochondrial proteins. Global germline deletion of Clpp in mice results in female infertility and accelerated follicular depletion. Here, we asked whether CLPP is necessary for granulosa/cumulus cell function. Clpp^flox/flox mice were generated and crossbred with Cyp19a1-Cre mice to generate mice with granulosa/cumulus cell-specific Clpp deletion (Clpp^-/-). Mature (8-week-old) Clpp^-/- female mice (8-week-old) were compared to same age wild type (WT) mice. We found that mature Clpp^-/- female mice were fertile and produced a similar number of pups per litter compared to WT. Folliculogenesis was not affected by the loss of CLPP in granulosa/cumulus cells as Clpp^-/- and WT mice had a similar number of primordial, primary, secondary, early antral, and antral follicles. The number of germinal vesicles (GV) and MII oocytes collected from Clpp^-/- and WT female mice were also similar. Our findings demonstrate that fertility in female mice is not affected by granulosa/cumulus cell-specific UPR^mt disruption through CLPP deletion.

Cybrid Model Supports Mitochondrial Genetic Effect on Pig Litter Size

In pigs, mitochondrial DNA (mtDNA) polymorphism and the correlation to reproductive performance across breeds and individuals have been largely reported, however, experimental proof has never been provided. In this study, we analyzed 807 sows for correlation of total number born (TNB) and mitotype, which presented the maximum of 1.73 piglets for mtDNA contribution. Cybrid models representing different mitotypes were generated for identification of the mtDNA effect. Results indicated significant differences on cellular and molecular characteristics among cybrids, including energy metabolic traits, mtDNA copy numbers and transcriptions, mRNA and protein expressions on mitochondrial biogenesis genes and reproduction-related genes. Referring to mitotypes, the cybrids with prolific mitotypes presented significantly higher oxygen consumption rate (OCR) productions, mtDNA transcriptions and copy numbers than those with common mitotypes, while both mRNA and protein expressions of PPARA, TFAM, ER1, ER2, and ESRRG in prolific cybrids were significantly higher than those with common mitotypes. Cybrid models reflected the mtDNA effect on pig litter size, suggesting the potential application of mtDNA polymorphism in pig selection and breeding practices.

Mitochondrial Ca2+ Overload Leads to Mitochondrial Oxidative Stress and Delayed Meiotic Resumption in Mouse Oocytes

Overweight or obese women seeking pregnancy is becoming increasingly common. Human maternal obesity gives rise to detrimental effects during reproduction. Emerging evidence has shown that these abnormities are likely attributed to oocyte quality. Oxidative stress induces poor oocyte conditions, but whether mitochondrial calcium homeostasis plays a key role in oocyte status remains unresolved. Here, we established a mitochondrial Ca²⁺ overload model in mouse oocytes. Knockdown gatekeepers of the mitochondrial Ca²⁺ uniporters Micu1 and Micu2 as well as the mitochondrial sodium calcium exchanger NCLX in oocytes both increased oocytes mitochondrial Ca²⁺ concentration. The overload of mitochondria Ca²⁺ in oocytes impaired mitochondrial function, leaded to oxidative stress, and changed protein kinase A (PKA) signaling associated gene expression as well as delayed meiotic resumption. Using this model, we aimed to determine the mechanism of delayed meiosis caused by mitochondrial Ca²⁺ overload, and whether oocyte-specific inhibition of mitochondrial Ca²⁺ influx could improve the reproductive abnormalities seen within obesity. Germinal vesicle breakdown stage (GVBD) and extrusion of first polar body (PB1) are two indicators of meiosis maturation. As expected, the percentage of oocytes that successfully progress to the germinal vesicle breakdown stage and extrude the first polar body during in vitro culture was increased significantly, and the expression of PKA signaling genes and mitochondrial function recovered after appropriate mitochondrial Ca²⁺ regulation. Additionally, some indicators of mitochondrial performance-such as adenosine triphosphate (ATP) and reactive oxygen species (ROS) levels and mitochondrial membrane potential-recovered to normal. These results suggest that the regulation of mitochondrial Ca²⁺ uptake in mouse oocytes has a significant role during oocyte maturation as well as PKA signaling and that proper mitochondrial Ca²⁺ reductions in obese oocytes can recover mitochondrial performance and improve obesity-associated oocyte quality.

Molecular profiling and functional delineation of peroxiredoxin 3 (HaPrx3) from the big-belly seahorses (Hippocampus abdominalis) and understanding their immunological responses

Peroxiredoxins (Prxs) are ubiquitously expressed antioxidant proteins that can protect aerobic organisms from oxidative stress. Here, we characterized the HaPrx3 homolog at the molecular level from big-belly seahorse (Hippocampus abdominalis) and analyzed its functional activities. The coding sequence of HaPrx3 consists of 726 bp, which encodes 241 amino acids. The predicted molecular weight and theoretical isoelectric point (pI) of HaPrx3 was 26.20 kDa and 7.04, respectively. Multiple sequence alignments revealed that the arrangements of domains, catalytic triads, dimers, and decamer interfaces of HaPrx3 were conserved among Prx sequences of other organisms. According to the phylogenetic analysis, HaPrx3 is clustered with the teleost Prx3 subclade. The highest transcript level of HaPrx3 was detected in the ovary tissue among fourteen healthy fish tissues. The mRNA levels of HaPrx3 in blood and liver tissues were significantly (P < 0.05) upregulated in response to lipopolysaccharide (LPS), polyinosinic-polycytidylic (poly I:C), Edwardsiella tarda, and Streptococcus iniae, suggesting its involvement in immune responses. Under functional properties, insulin disulfide reduction assay confirmed the oxidoreductase activity of recombinant HaPrx3. A cell viability assay and Hoechst staining indicated cell survival ability and reduction of apoptotic activity, respectively. Moreover, a peroxidase activity assay verified peroxidase activity, while a metal-catalyzed oxidation (MCO) assay indicated the DNA protection ability of HaPrx3. Collectively, it is concluded that HaPrx3 may play a significant role in oxidative stress and immune responses against pathogenic infections in big-belly seahorses.

Clinical Application of Antioxidants to Improve Human Oocyte Mitochondrial Function: A Review

Mitochondria produce adenosine triphosphate (ATP) while also generating high amounts of reactive oxygen species (ROS) derived from oxygen metabolism. ROS are small but highly reactive molecules that can be detrimental if unregulated. While normally functioning mitochondria produce molecules that counteract ROS production, an imbalance between the amount of ROS produced in the mitochondria and the capacity of the cell to counteract them leads to oxidative stress and ultimately to mitochondrial dysfunction. This dysfunction impairs cellular functions through reduced ATP output and/or increased oxidative stress. Mitochondrial dysfunction may also lead to poor oocyte quality and embryo development, ultimately affecting pregnancy outcomes. Improving mitochondrial function through antioxidant supplementation may enhance reproductive performance. Recent studies suggest that antioxidants may treat infertility by restoring mitochondrial function and promoting mitochondrial biogenesis. However, further randomized, controlled trials are needed to determine their clinical efficacy. In this review, we discuss the use of resveratrol, coenzyme-Q10, melatonin, folic acid, and several vitamins as antioxidant treatments to improve human oocyte and embryo quality, focusing on the mitochondria as their main hypothetical target. However, this mechanism of action has not yet been demonstrated in the human oocyte, which highlights the need for further studies in this field.

The Role of Oocyte Quality in Explaining "Unexplained" Infertility

Infertility is described as unexplained when pregnancy does not occur despite ovulation, patent Fallopian tubes, and normal semen parameters. Oocyte developmental competence (or quality) is rate-limiting for pregnancy success as oocytes provide virtually all the cellular building blocks including mitochondria required during embryogenesis. However, available tests estimate oocyte numbers (anti-Müllerian hormone, follicle-stimulating hormone and antral follicle count) and ovulation (luteal phase serum progesterone) but not the third, and most pivotal, oocyte-specific parameter, quality. Severe depletion of the follicular reserve manifests as premature ovarian insufficiency and is an obvious cause of anovulation with overt symptoms and clear diagnostic criteria. In contrast, there are no biomarkers of poor oocyte quality other than through in vitro fertilization when readouts of oocyte quality such as preimplantation embryo development can be assessed. The most common cause of poor oocyte quality is natural aging, which is strongly tied to reduced oocyte mitochondrial efficiency and increased oxidative stress. In younger women, quality may also be impaired due to accelerated aging or sporadic genetic mutations which cause severe defects during oocyte and embryo development. Thus, poor oocyte quality often provides an explanation for infertility, but because it cannot be measured using conventional tests, many cases of infertility are often incorrectly labeled "unexplained." Since female age remains the best predictor of oocyte quality, age over 37 years should be considered an independent diagnostic criterion.