Pyruvate utilization by mouse oocytes is influenced by meiotic status and the cumulus oophorus

Mitochondria as determinants of reproductive senescence and competence: implications for diagnosis of embryo competence in assisted reproduction

Mitochondria are commonly recognized as the powerhouses of the cell, primarily responsible for energy production through oxidative phosphorylation. Alongside this vital function, they also play crucial roles in regulating calcium signaling, maintaining membrane potential, and modulating apoptosis. Their involvement in various cellular pathways becomes particularly evident during oogenesis and embryogenesis, where mitochondrial quantity, morphology, and distribution are tightly controlled. The efficiency of the mitochondrial network is maintained through multiple quality control mechanisms that are essential for reproductive success. These include mitochondrial unfolded protein response, mitochondrial dynamics, and mitophagy. Not surprisingly, mitochondrial dysfunction has been implicated in infertility and ovarian aging, prompting investigation into mitochondria as diagnostic and therapeutic targets in assisted reproduction. To date, mitochondrial DNA copy number in oocytes, cumulus cells, and trophectoderm biopsies, and fluorescent lifetime imaging microscopy-based assessment of NADH and flavin adenine dinucleotide content have been explored as potential predictors of embryo competence, yielding limited success. Despite challenges in the clinical application of mitochondrial diagnostic strategies, these enigmatic organelles have a significant impact on reproduction, and their potential role as diagnostic targets in assisted reproduction is likely to remain an active area of investigation in the foreseeable future.

Metabolic imaging of human cumulus cells reveals associations with pregnancy and live birth

STUDY QUESTION

Can fluorescence lifetime imaging microscopy (FLIM) detect associations between the metabolic state of cumulus cell (CC) samples and the clinical outcome of the corresponding embryos?

SUMMARY ANSWER

FLIM can detect significant variations in the metabolism of CC associated with the corresponding embryos that resulted in a clinical pregnancy versus those that did not.

WHAT IS KNOWN ALREADY

CC and oocyte metabolic cooperativity are known to be necessary for the acquisition of developmental competence. However, reliable CC biomarkers that reflect oocyte viability and embryo developmental competency have yet to be established. Quantitative measures of CC metabolism could be used to aid in the evaluation of oocyte and embryo quality in ART.

STUDY DESIGN, SIZE, DURATION

A prospective observational study was carried out. In total, 223 patients undergoing IVF with either conventional insemination or ICSI at a tertiary care center from February 2018 to May 2020 were included, with no exclusion criteria applied.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This cohort had a mean maternal age of 36.5 ± 4.4 years and an average oocyte yield of 16.9 (range 1-50). One to four CC clusters from each patient were collected after oocyte retrieval and vitrified. CC metabolic state was assessed using FLIM to measure the autofluorescence of the molecules NAD(P)H and FAD+, which are essential for multiple metabolic pathways. CC clusters were tracked with their corresponding oocytes and associated embryos. Patient age, Day 3 and Day 5/6 embryo morphological grades, and clinical outcomes of embryos with traceable fate were recorded. Nine FLIM quantitative parameters were obtained for each CC cluster. We investigated associations between the FLIM parameters and patient maternal age, embryo morphological rank, ploidy, and clinical outcome, where false discovery rate P-values of <0.05 were considered statistically significant.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 851 CC clusters from 851 cumulus-oocyte complexes from 223 patients were collected. Of these CC clusters, 623 were imaged using FLIM. None of the measured CC FLIM parameters were correlated with Day 3 morphological rank or ploidy of the corresponding embryos, but FAD+ FLIM parameters were significantly associated with morphological rank of blastocysts. There were significant differences for FAD+ FLIM parameters (FAD+ fraction engaged and short lifetime) from CC clusters linked with embryos resulting in a clinical pregnancy compared with those that did not, as well as for CC clusters associated with embryos that resulted in a live birth compared those that did not.

LIMITATIONS, REASONS FOR CAUTION

Our data are based on a relatively low number of traceable embryos from an older patient population. Additionally, we only assessed CCs from 1 to 4 oocytes from each patient. Future work in a younger patient population with a larger number of traceable embryos, as well as measuring the metabolic state of CCs from all oocytes from each patient, would provide a better understanding of the potential utility of this technology for oocyte/embryo selection.

WIDER IMPLICATIONS OF THE FINDINGS

Metabolic imaging via FLIM is able to detect CC metabolic associations with maternal age and detects variations in the metabolism of CCs associated with oocytes leading to embryos that result in a clinical pregnancy and a live birth versus those that do not. Our findings suggest that FLIM of CCs may be used as a new approach to aid in the assessment of oocyte and embryo developmental competence in clinical ART.

STUDY FUNDING/COMPETING INTEREST(S)

National Institutes of Health grant NIH R01HD092550-03 (to C.R., and D.J.N.). Becker and Hickl GmbH and Boston Electronics sponsored research with the loaning of equipment for FLIM. D.J.N. and C.R. are inventors on patent US20170039415A1.

TRIAL REGISTRATION NUMBER

N/A.

The role of mitochondrial dynamics in oocyte and early embryo development

Mitochondrial dysfunction is widely implicated in various human diseases, through mechanisms that go beyond mitochondria's well-established role in energy generation. These dynamic organelles exert vital control over numerous cellular processes, including calcium regulation, phospholipid synthesis, innate immunity, and apoptosis. While mitochondria's importance is acknowledged in all cell types, research has revealed the exceptionally dynamic nature of the mitochondrial network in oocytes and embryos, finely tuned to meet unique needs during gamete and pre-implantation embryo development. Within oocytes, both the quantity and morphology of mitochondria can significantly change during maturation and post-fertilization. These changes are orchestrated by fusion and fission processes (collectively known as mitochondrial dynamics), crucial for energy production, content exchange, and quality control as mitochondria adjust to the shifting energy demands of oocytes and embryos. The roles of proteins that regulate mitochondrial dynamics in reproductive processes have been primarily elucidated through targeted deletion studies in animal models. Notably, impaired mitochondrial dynamics have been linked to female reproductive health, affecting oocyte quality, fertilization, and embryo development. Dysfunctional mitochondria can lead to fertility problems and can have an impact on the success of pregnancy, particularly in older reproductive age women.

Role of miRNAs in glucose metabolism of mouse cumulus cells†

It is known that the oocyte has a limited capacity to acquire and metabolize glucose, and it must rely on cumulus cells (CCs) to take up glucose and produce pyruvate for use to produce ATP through oxidative phosphorylation. We therefore propose that miRNAs might regulate glucose metabolism (GM) in CCs and might be used as markers for oocyte quality assessment. Here, mouse CC models with impaired glycolysis or pentose phosphate pathway (PPP) were established, and miRNAs targeting the key enzymes in glycolysis/PPP were predicted using the miRNA target prediction databases. Expression of the predicted miRNAs was compared between CCs with normal and impaired glycolysis/PPP to identify candidate miRNAs. Function of the candidate miRNAs was validated by transfecting CCs or cumulus-oocyte-complexes (COCs) with miRNA inhibitors and observing effects on glucose metabolites of CCs and on competence of oocytes. The results validated that miR-23b-3p, let-7b-5p, 34b-5p and 145a-5p inhibited glycolysis, and miR-24-3p, 3078-3p,183-5p and 7001-5p inhibited PPP of CCs. Our observation using a more physiologically relevant model (intact cultured COCs) further validated the four glycolysis-targeting miRNAs we identified. Furthermore, miR-let-7b-5p, 34b-5p and 145a-5p may also inhibit PPP, as they decreased the production of glucose-6-phosphate. In conclusion, miRNAs play critical roles in GM of CCs and may be used as markers for oocyte quality assessment. Summary sentence:  We identified and validated eight new miRNAs that inhibit glycolysis and/or pentose phosphate pathways in cumulus cells (CCs) suggesting that miRNAs play critical roles in glucose metabolism of CCs and may be used for oocyte quality markers.

Diminished NAD+ levels and activation of retrotransposons promote postovulatory aged oocyte (POAO) death

Death is the fate of postovulatory aged or unfertilized oocytes (POAO) in many animals. However, precise molecular mechanisms are yet to be discovered. Here, we demonstrate that increased amounts of reactive oxygen species (ROS), calcium ion (Ca+2) channels, and retrotransposon activity induce apoptosis, which in turn causes POAO death. Notably, suppression of ROS, Ca+2 channels, and retrotransposons delayed POAO death. Further, we found that the histone H4K12 and K16 acetylation increased via downregulation of NAD+ and NAD+ -dependent histone deacetylase SIRT3. Furthermore, adding NMN, sodium pyruvate, or CD38 inhibition delayed the death of postovulatory aged oocytes. Finally, we demonstrate the conservation of retrotransposon-induced DNA damage-dependent POAO death in higher-order vertebrates. Our findings suggest that POAO mortality is caused by cyclic cascade metabolic interactions in which low NAD+ levels increase histone acetylation by inhibiting histone deacetylases, resulting in an increase in retrotransposons, ROS, and Ca+2 channel activity and thus contributing to DNA damage-induced apoptosis.

Ovarian ERβ cistrome and transcriptome reveal chromatin interaction with LRH-1

BACKGROUND

Estrogen receptor beta (ERβ, Esr2) plays a pivotal role in folliculogenesis and ovulation, yet its exact mechanism of action is mainly uncharacterized.

RESULTS

We here performed ERβ ChIP-sequencing of mouse ovaries followed by complementary RNA-sequencing of wild-type and ERβ knockout ovaries. By integrating the ERβ cistrome and transcriptome, we identified its direct target genes and enriched biological functions in the ovary. This demonstrated its strong impact on genes regulating organism development, cell migration, lipid metabolism, response to hypoxia, and response to estrogen. Cell-type deconvolution analysis of the bulk RNA-seq data revealed a decrease in luteal cells and an increased proportion of theca cells and a specific type of cumulus cells upon ERβ loss. Moreover, we identified a significant overlap with the gene regulatory network of liver receptor homolog 1 (LRH-1, Nr5a2) and showed that ERβ and LRH-1 extensively bound to the same chromatin locations in granulosa cells. Using ChIP-reChIP, we corroborated simultaneous ERβ and LRH-1 co-binding at the ERβ-repressed gene Greb1 but not at the ERβ-upregulated genes Cyp11a1 and Fkbp5. Transactivation assay experimentation further showed that ERβ and LRH-1 can inhibit their respective transcriptional activity at classical response elements.

CONCLUSIONS

By characterizing the genome-wide endogenous ERβ chromatin binding, gene regulations, and extensive crosstalk between ERβ and LRH-1, along with experimental corroborations, our data offer genome-wide mechanistic underpinnings of ovarian physiology and fertility.

Effects of lactate, super-GDF9, and low oxygen tension during bi-phasic in vitro maturation on the bioenergetic profiles of mouse cumulus-oocyte complex†

In vitro maturation (IVM) is an alternative assisted reproductive technology with reduced hormone-related side effects and treatment burden compared to conventional IVF. Capacitation (CAPA)-IVM is a bi-phasic IVM system with improved clinical outcomes compared to standard monophasic IVM. Yet, CAPA-IVM efficiency compared to conventional IVF is still suboptimal in terms of producing utilizable blastocysts. Previously, we have shown that CAPA-IVM leads to a precocious increase in cumulus cell (CC) glycolytic activity during cytoplasmic maturation. In the current study, considering the fundamental importance of CCs for oocyte maturation and cumulus-oocyte complex (COC) microenvironment, we further analyzed the bioenergetic profiles of maturing CAPA-IVM COCs. Through a multi-step approach, we (i) explored mitochondrial function of the in vivo and CAPA-IVM matured COCs through real-time metabolic analysis with Seahorse analyzer, and to improve COC metabolism (ii) supplemented the culture media with lactate and/or super-GDF9 (an engineered form of growth differentiation factor 9) and (iii) reduced culture oxygen tension. Our results indicated that the pre-IVM step is delicate and prone to culture-related disruptions. Lactate and/or super-GDF9 supplementations failed to eliminate pre-IVM-induced stress on COC glucose metabolism and mitochondrial respiration. However, when performing pre-IVM culture under 5% oxygen tension, CAPA-IVM COCs showed similar bioenergetic profiles compared to in vivo matured counterparts. This is the first study providing real-time metabolic analysis of the COCs from a bi-phasic IVM system. The currently used analytical approach provides the quantitative measures and the rational basis to further improve IVM culture requirements.

Oocyte-cumulus cells crosstalk: New comparative insights

Mammalian follicles are constituted of a complex structure composed of several layers of granulosa cells surrounding the oocyte and of theca cells that reside beneath its basement membrane. During folliculogenesis, granulosa cells separate into two anatomically and functionally distinct sub-types; the mural cells lining the follicle wall and the oocyte-surrounding cumulus cells, i.e. those in intimate metabolic contact with the oocyte. The cumulus cells connecting with the oocyte have trans-zonal cytoplasmic projections which, penetrating the zona pellucida, form the cumulus-oocyte complex. The connections through gap junctions allow the transfer of small molecules between oocyte and cumulus cells, such as ions, metabolites, and amino acids necessary for oocyte growth, as well as small regulatory molecules that control oocyte development. The bi-directional communication between the oocyte and cumulus cells is crucial for the development and functions of both cell types. Our current knowledge of the relationship between the oocyte and its surrounding cumulus cells continues to change as we gain a greater understanding of factors regulating oocyte development and folliculogenesis. This review will mainly focus on the reciprocal interaction between oocytes and cumulus cells during the latter stages of follicle development i.e. through antral development to periovulatory events including oocyte maturation, expansion, and degradation of the cumulus matrix.

Biotin levels in blood and follicular fluid and their associations with pregnancy outcomes in IVF/ICSI patients

It has been shown that biotin, a water-soluble vitamin (B7), plays roles in reproductive functions, such as oocyte maturation and embryo development, in experimental animals. On the other hand, little is known about the clinical effects of biotin on human reproduction. In this study, serum and follicular fluid biotin levels were measured in patients who underwent in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI), and their associations with reproductive outcomes were evaluated. As a result, biotin was detected in follicular fluid, as well as serum, and the biotin levels of follicular fluid were found to be positively correlated with those of serum. The biotin levels of serum were higher than those of follicular fluid, suggesting that biotin may be taken up into the follicular fluid from the blood. Although serum and follicular fluid biotin levels tended to be higher in pregnant patients than in non-pregnant patients, these data did not show the significant statistical difference. These findings indicate that biotin does not contribute to the maintenance of oocyte quality, and hence, it does not increase fertilization and pregnancy rates. J. Med. Invest. 69 : 65-69, February, 2022.

The putative roles of FSH and AMH in the regulation of oocyte developmental competence: from fertility prognosis to mechanisms underlying age-related subfertility

BACKGROUND

Fertility loss during female ageing is associated with increasing basal FSH and decreasing anti-Müllerian hormone (AMH) concentrations, together with compromised oocyte quality, presumably due to increased oxidative stress (OS) and DNA damage, as well as reduced metabolic and meiotic competences. Basal FSH and AMH circulatory concentrations have been broadly utilized as IVF success predictors, regardless of fluctuations in prognostic accuracy; basal FSH and AMH perform better in pre-advanced maternal age (AMA: >35 years) and AMA patients, respectively. The relationships between FSH and AMH intrafollicular levels and IVF outcomes suggest, nevertheless, that both hormones regulate oocyte competence, supporting the hypothesis that changes in FSH/AMH levels cause, at least in part, oocyte quality degradation during ageing. To understand the reasons behind the fluctuations in FSH and AMH prognostic accuracies and to clarify their participation in mechanisms determining oocyte competence and age-related subfertility, a deeper knowledge of the regulation of FSH and AMH intrafollicular signalling during the female reproductive lifespan, and of their effects on the cumulus-oocyte complex, is required.

OBJECTIVE AND RATIONALE

An extensive body of information on the regulation of FSH and AMH intrafollicular availability and signalling, as well as on the control of folliculogenesis and oocyte metabolism, has been accumulated. However, these datasets have been explored within the relatively narrow boundaries of their specific subjects. Given the aforementioned gaps in knowledge and their clinical relevance, herein we integrate clinical and basic data, within a wide biological perspective, aiming to shed light on (i) the reasons for the variability in the accuracy of serum FSH and AMH as fertility markers, and on (ii) the potential roles of these hormones in mechanisms regulating oocyte quality, particularly those associated with ageing.

SEARCH METHODS

The PubMed database encompassing the period between 1960 and 2021 was searched. Principal search terms were FSH, FSH receptor, AMH, oocyte, maternal age, cumulus, transzonal projections (TZPs), actin, OS, redox, reactive oxygen species, mitochondria, DNA damage, DNA repair, aneuploidy, spindle, meiosis, gene expression, transcription, translation, oocyte secreted factors (OSFs), cAMP, cyclic guanosine monophosphate, natriuretic peptide C, growth differentiation factor 9, bone morphogenetic protein 15 and fibroblast growth factor.

OUTCOMES

Our analysis suggests that variations in the accuracy of fertility prognosis reflect a modest association between circulatory AMH levels and oocyte quality as well as increasing basal FSH inter-cycle variability with age. In addition, the basic and clinical data articulated herein support the hypothesis that increased intrafollicular FSH levels, as maternal age advances, may override the physiological protective influences of AMH and OSFs against excessive FSH signalling in cumulus cells. This would result in the disruption of oocyte homeostasis via reduced TZP-mediated transfer of cumulus-derived molecules essential for meiotic competence, gene expression, redox activity and DNA repair.

WIDER IMPLICATIONS

In-depth data analysis, encompassing a wide biological perspective has revealed potential causative mechanisms of age-related subfertility triggered by alterations in FSH/AMH signalling during the female reproductive life. Insights from new mechanistic models arising from this analysis should contribute to advancing our comprehension of oocyte biology in humans and serve as a valuable reference for novel AMA subfertility treatments aimed at improving oocyte quality through the modulation of AMH/FSH action.

Uncovering the important role of mitochondrial dynamics in oogenesis: impact on fertility and metabolic disorder transmission

Oocyte health is tightly tied to mitochondria given their role in energy production, metabolite supply, calcium (Ca2+) buffering, and cell death regulation, among others. In turn, mitochondrial function strongly relies on these organelle dynamics once cyclic events of fusion and fission (division) are required for mitochondrial turnover, positioning, content homogenization, metabolic flexibility, interaction with subcellular compartments, etc. Importantly, during oogenesis, mitochondria change their architecture from an "orthodox" elongated shape characterized by the presence of numerous transversely oriented cristae to a round-to-oval morphology containing arched and concentrically arranged cristae. This, along with evidence showing that mitochondrial function is kept quiescent during most part of oocyte development, suggests an important role of mitochondrial dynamics in oogenesis. To investigate this, recent works have downregulated/upregulated in oocytes the expression of key effectors of mitochondrial dynamics, including mitofusins 1 (MFN1) and 2 (MFN2) and the dynamin-related protein 1 (DRP1). As a result, both MFN1 and DRP1 were found to be essential to oogenesis and fertility, while MFN2 deletion led to offspring with increased weight gain and glucose intolerance. Curiously, neither MFN1/MFN2 deficiency nor DRP1 overexpression enhanced mitochondrial fragmentation, indicating that mitochondrial size is strictly regulated in oocytes. Therefore, the present work seeks to discuss the role of mitochondria in supporting oogenesis as well as recent findings connecting defective mitochondrial dynamics in oocytes with infertility and transmission of metabolic disorders.

Metabolic imaging of human cumulus cells reveals associations among metabolic profiles of cumulus cells, patient clinical factors, and oocyte maturity

OBJECTIVE

To determine whether fluorescence lifetime imaging microscopy (FLIM) detects differences in metabolic state among cumulus cell samples and whether their metabolic state is associated with patient age, body mass index (BMI), and antimüllerian hormone (AMH) level and maturity of the oocyte.

DESIGN

Prospective observational study.

SETTING

Academic laboratory.

PATIENT(S)

Cumulus cell (CC) clusters from cumulus-oocyte complexes were collected from patients undergoing assisted reproductive technology treatment after oocyte retrieval and vitrified.

INTERVENTION(S)

Cumulus cell metabolism was assessed using FLIM to measure autofluorescence of nicotinamide adenine (phosphate) dinucleotide and flavine adenine dinucleotide, endogenous coenzymes essential for cellular respiration and glycolysis. Patient age, BMI, and AMH level and the maturity of the corresponding oocytes were recorded.

MAIN OUTCOME MEASURE(S)

Quantitative information from FLIM was obtained regarding metabolite concentrations from fluorescence intensity and metabolite enzyme engagement from fluorescence lifetimes. Associations were investigated between each FLIM parameter and oocyte maturity and patient age, BMI, and AMH. Variance between CC clusters within and between patients was determined.

RESULT(S)

Of 619 CC clusters from 193 patients, 90 were associated with immature oocytes and 505 with metaphase II oocytes. FLIM enabled quantitative measurements of the metabolic state of CC clusters. These parameters were significantly correlated with patient age and AMH independently, but not with BMI. Cumulus cell nicotinamide adenine (phosphate) dinucleotide FLIM parameters and redox ratio were significantly associated with maturity of the enclosed oocyte.

CONCLUSION(S)

FLIM detects variations in the metabolic state of CCs, showing a greater variance among clusters from each patient than between patients. Fluorescence lifetime imaging microscopy can detect CC metabolic associations with patient age and AMH and variations between mature and immature oocytes, suggesting the potential utility of this technique to help identify superior oocytes.

Metabolic co-dependence of the oocyte and cumulus cells: essential role in determining oocyte developmental competence

BACKGROUND

Within the antral follicle, the oocyte is reliant on metabolic support from its surrounding somatic cells. Metabolism plays a critical role in oocyte developmental competence (oocyte quality). In the last decade, there has been significant progress in understanding the metabolism of the cumulus-oocyte complex (COC) during its final stages of growth and maturation in the follicle. Certain metabolic conditions (e.g. obesity) or ART (e.g. IVM) perturb COC metabolism, providing insights into metabolic regulation of oocyte quality.

OBJECTIVE AND RATIONALE

This review provides an update on the progress made in our understanding of COC metabolism, and the metabolic conditions that influence both meiotic and developmental competence of the oocyte.

SEARCH METHODS

The PubMed database was used to search for peer-reviewed original and review articles. Searches were performed adopting the main terms 'oocyte metabolism', 'cumulus cell metabolism', 'oocyte maturation', 'oocyte mitochondria', 'oocyte metabolism', 'oocyte developmental competence' and 'oocyte IVM'.

OUTCOMES

Metabolism is a major determinant of oocyte quality. Glucose is an essential requirement for both meiotic and cytoplasmic maturation of the COC. Glucose is the driver of cumulus cell metabolism and is essential for energy production, extracellular matrix formation and supply of pyruvate to the oocyte for ATP production. Mitochondria are the primary source of ATP production within the oocyte. Recent advances in real-time live cell imaging reveal dynamic fluctuations in ATP demand throughout oocyte maturation. Cumulus cells have been shown to play a central role in maintaining adequate oocyte ATP levels by providing metabolic support through gap junctional communication. New insights have highlighted the importance of oocyte lipid metabolism for oocyte oxidative phosphorylation for ATP production, meiotic progression and developmental competence. Within the last decade, several new strategies for improving the developmental competence of oocytes undergoing IVM have emerged, including modulation of cyclic nucleotides, the addition of precursors for the antioxidant glutathione or endogenous maturation mediators such as epidermal growth factor-like peptides and growth differentiation factor 9/bone morphogenetic protein 15. These IVM additives positively alter COC metabolic endpoints commonly associated with oocyte competence. There remain significant challenges in the study of COC metabolism. Owing to the paucity in non-invasive or in situ techniques to assess metabolism, most work to date has used in vitro or ex vivo models. Additionally, the difficulty of measuring oocyte and cumulus cell metabolism separately while still in a complex has led to the frequent use of denuded oocytes, the results from which should be interpreted with caution since the oocyte and cumulus cell compartments are metabolically interdependent, and oocytes do not naturally exist in a naked state until after fertilization. There are emerging tools, including live fluorescence imaging and photonics probes, which may provide ways to measure the dynamic nature of metabolism in a single oocyte, potentially while in situ.

WIDER IMPLICATIONS

There is an association between oocyte metabolism and oocyte developmental competence. Advancing our understanding of basic cellular and biochemical mechanisms regulating oocyte metabolism may identify new avenues to augment oocyte quality and assess developmental potential in assisted reproduction.

DPAGT1-Mediated Protein N-Glycosylation Is Indispensable for Oocyte and Follicle Development in Mice

Post-translational modification of proteins by N-linked glycosylation is crucial for many life processes. However, the exact contribution of N-glycosylation to mammalian female reproduction remains largely undefined. Here, DPAGT1, the enzyme that catalyzes the first step of protein N-glycosylation, is identified to be indispensable for oocyte development in mice. Dpagt1 missense mutation (c. 497A>G; p. Asp166Gly) causes female subfertility without grossly affecting other functions. Mutant females ovulate fewer eggs owing to defective development of growing follicles. Mutant oocytes have a thin and fragile zona pellucida (ZP) due to the reduction in glycosylation of ZP proteins, and display poor developmental competence after fertilization in vitro. Moreover, completion of the first meiosis is accelerated in mutant oocytes, which is coincident with the elevation of aneuploidy. Mechanistically, transcriptomic analysis reveals the downregulation of a number of transcripts essential for oocyte meiotic progression and preimplantation development (e.g., Pttgt1, Esco2, Orc6, and Npm2) in mutant oocytes, which could account for the defects observed. Furthermore, conditional knockout of Dpagt1 in oocytes recapitulates the phenotypes observed in Dpagt1 mutant females, and causes complete infertility. Taken together, these data indicate that protein N-glycosylation in oocytes is essential for female fertility in mammals by specific control of oocyte development.

The insulin signaling pathway is dysregulated in cumulus cells from obese, infertile women with polycystic ovarian syndrome with an absence of clinical insulin resistance

Methods:

This is a cohort study, conducted at a university-based reproductive medicine center and private reproductive medicine center that aimed to evaluate granulosa cumulus cell gene expression in the insulin signaling pathway in Polycystic Ovary Syndrome (PCOS) patients undergoing in vitro fertilization (IVF) treatment and to compare the cumulus gene expression between normal weight and obese women without clinical insulin resistance. Fifteen PCOS patients, nine normal weight patients and six obese patients presenting normal HOMA IR (Homeostasis Model Assessment–Insulin Resistance), participated. Patients underwent oocyte retrieval for IVF and after the procedure, granulosa cumulus cells were removed from the oocytes for RNA extraction. Quantitative polymerase chain reaction (PCR) array analysis of 84 genes from insulin signaling pathway was conducted. The results were expressed as fold up- or fold down-expression in obese patients compared with normal weight patients. Any fold change ⩾3 or ⩽3 and any p ⩽ 0.05 were considered statistically significant.

Results:

There were 10 genes that were overexpressed in obese compared with normal weight women, BCL2L1, BRAF, CBL, DOK1, FBP1, FRS2, MTOR, PCK2, RPS6KA1, and SORBS1, that had a fold change ⩾3 and p ⩽ 0.05.

Discussion:

In the obese group, the overexpressed genes are mainly responsible for the proliferation and differentiation of cumulus cells during oocyte maturation, insulin resistance, apoptosis regulation, and glucose metabolism during early embryogenesis, suggesting that in the follicular environment, insulin resistance is present even in the absence of clinical signs.

Conclusion:

Together, our findings and the related literature suggest that those alterations may be associated with the worse prognosis of follicular development and oocyte maturation observed in PCOS obese women.

Mitochondrial dynamics and metabolism in induced pluripotency

Somatic cells can be reprogrammed to pluripotency by either ectopic expression of defined factors or exposure to chemical cocktails. During reprogramming, somatic cells undergo dramatic changes in a wide range of cellular processes, such as metabolism, mitochondrial morphology and function, cell signaling pathways or immortalization. Regulation of these processes during cell reprograming lead to the acquisition of a pluripotent state, which enables indefinite propagation by symmetrical self-renewal without losing the ability of reprogrammed cells to differentiate into all cell types of the adult. In this review, recent data from different laboratories showing how these processes are controlled during the phenotypic transformation of a somatic cell into a pluripotent stem cell will be discussed.

Expanded equine cumulus-oocyte complexes exhibit higher meiotic competence and lower glucose consumption than compact cumulus-oocyte complexes

Equine cumulus-oocyte complexes (COCs) are classified as compact (cCOC) or expanded (eCOC) and vary in their meiotic competence. This difference could be related to divergent glucose metabolism. To test this hypothesis in the present study, eCOCs, cCOCs and expanded or compact mural granulosa cells (EC and CC respectively) were matured in vitro for 30h, at which time maturation rate, glucose metabolism and the expression of genes involved in glucose transport, glycolysis, apoptosis and meiotic competence were determined. There were significant differences between eCOCs and cCOCs in maturation rate (50% vs 21.7% (n=192 and 46) respectively; P<0.001), as well as mean (±s.e.m.) glucose consumption (1.8±0.5 vs 27.9±5.9 nmol per COC respectively) and pyruvate (0.09±0.01 vs 2.4±0.8 nmol per COC respectively) and lactate (4.7±1.3 vs 64.1±20.6 nmol per COC respectively; P<0.05 for all) production. Glucose consumption in EC and CC did not differ significantly. Expression of hyaluronan-binding protein (tumour necrosis factor alpha induced protein 6; TNFAIP6) was increased in eCOCs and EC, and solute carrier family 2 member 1 (SLC2A1) expression was increased in eCOCs, but there were no differences in the expression of glycolysis-related enzymes and solute carrier family 2 member 3 (SLC2A3) between the COC or mural granulosa cell types. The findings of the present study demonstrate that metabolic and genomic differences exist between eCOCs and cCOCs and mural granulosa cells in the horse.

Effects of Subacute Administration of Co-Trimoxazole and Folic Acid on Ovarian Tissue in Adult Female Rats

BACKGROUND

Previous studies have reported the antifertility activities of sulfonamides. This study was designed to evaluate the effects of co-trimoxazole and its co-administration with folic acid on ovarian tissue in female rats.

METHODS

A total of 54 rats were randomly divided into 9 groups (n=6). Group I served as the control and group II (vehicle) received saline. Other groups, III to IX, received co-trimoxazole (30, 60, and 120 mg/kg; i.p.), folic acid (1 mg/kg; i.p.) or their combination for 14 days, respectively. The oocytes were obtained from each group at the end of the 14th days and scored for maturational status as germinal vesicle (GV), metaphase I (MI), or metaphase II (MII). The number of primordial follicle (PrF), primary follicle (PF), and secondary follicle in formalin-fixed ovaries were counted under light microscopy. The data were analyzed by one-way ANOVA followed by post-hoc Dunnet test using SPSS statistical software (version 17.0). Results were considered statistically significant at P<0.05.

RESULTS

Co-trimoxazole (60 and 120 mg/kg) treatment for 14 days caused a significant decrease in the number of GV (P=0.02, P<0.001), MI and MII (P=0.03, P<0.001), a significant increase in structural abnormalities, including PrF, PF and secondary follicle (P<0.001) as well as congestion, inflammation and necrosis of ovarian tissue compared to the vehicle group. Folic acid co-administration with co-trimoxazole reversed partially all these parameters compared to the co-trimoxazole group (P<0.001).

CONCLUSION

The data showed the adverse effects of co-trimoxazole on the ovarian maturational status and tissue structure which was reversed partially by folic acid co-administration in rats.

Insulin signalling and glucose transport in the ovary and ovarian function during the ovarian cycle

Data derived principally from peripheral tissues (fat, muscle and liver) show that insulin signals via diverse interconnecting intracellular pathways and that some of the major intersecting points (known as critical nodes) are the IRSs (insulin receptor substrates), PI3K (phosphoinositide kinase)/Akt and MAPK (mitogen-activated protein kinase). Most of these insulin pathways are probably also active in the ovary and their ability to interact with each other and also with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) signalling pathways enables insulin to exert direct modulating influences on ovarian function. The present paper reviews the intracellular actions of insulin and the uptake of glucose by ovarian tissues (granulosa, theca and oocyte) during the oestrous/menstrual cycle of some rodent, primate and ruminant species. Insulin signals through diverse pathways and these are discussed with specific reference to follicular cell types (granulosa, theca and oocyte). The signalling pathways for FSH in granulosa cells and LH in granulosa and theca cells are summarized. The roles of glucose and of insulin-mediated uptake of glucose in folliculogenesis are discussed. It is suggested that glucose in addition to its well-established role of providing energy for cellular function may also have insulin-mediated signalling functions in ovarian cells, involving AMPK (AMP-dependent protein kinase) and/or hexosamine. Potential interactions of insulin signalling with FSH or LH signalling at critical nodes are identified and the available evidence for such interactions in ovarian cells is discussed. Finally the action of the insulin-sensitizing drugs metformin and the thiazolidinedione rosiglitazone on follicular cells is reviewed.

Survival of glucose phosphate isomerase null somatic cells and germ cells in adult mouse chimaeras

The mouse Gpi1 gene encodes the glycolytic enzyme glucose phosphate isomerase. Homozygous Gpi1(-/-) null mouse embryos die but a previous study showed that some homozygous Gpi1(-/-) null cells survived when combined with wild-type cells in fetal chimaeras. One adult female Gpi1(-/-)↔Gpi1(c/c) chimaera with functional Gpi1(-/-) null oocytes was also identified in a preliminary study. The aims were to characterise the survival of Gpi1(-/-) null cells in adult Gpi1(-/-)↔Gpi1(c/c) chimaeras and determine if Gpi1(-/-) null germ cells are functional. Analysis of adult Gpi1(-/-)↔Gpi1(c/c) chimaeras with pigment and a reiterated transgenic lineage marker showed that low numbers of homozygous Gpi1(-/-) null cells could survive in many tissues of adult chimaeras, including oocytes. Breeding experiments confirmed that Gpi1(-/-) null oocytes in one female Gpi1(-/-)↔Gpi1(c/c) chimaera were functional and provided preliminary evidence that one male putative Gpi1(-/-)↔Gpi1(c/c) chimaera produced functional spermatozoa from homozygous Gpi1(-/-) null germ cells. Although the male chimaera was almost certainly Gpi1(-/-)↔Gpi1(c/c), this part of the study is considered preliminary because only blood was typed for GPI. Gpi1(-/-) null germ cells should survive in a chimaeric testis if they are supported by wild-type Sertoli cells. It is also feasible that spermatozoa could bypass a block at GPI, but not blocks at some later steps in glycolysis, by using fructose, rather than glucose, as the substrate for glycolysis. Although chimaera analysis proved inefficient for studying the fate of Gpi1(-/-) null germ cells, it successfully identified functional Gpi1(-/-) null oocytes and revealed that some Gpi1(-/-) null cells could survive in many adult tissues.

Effects of glucose metabolism during in vitro maturation on cytoplasmic maturation of mouse oocytes

Although there are many reports on the effect of glucose metabolism on oocyte nuclear maturation, there are few studies on its effect on ooplasmic maturation. By manipulating glucose metabolism pathways using a maturation medium that could support oocyte nuclear maturation but only a limited blastocyst formation without glucose, this study determined effects of glucose metabolism pathways on ooplasmic maturation. During maturation of cumulus-oocyte-complexes (COCs) with glucose, the presence of PPP inhibitor, DHEA or glycolysis inhibitor, iodoacetate significantly decreased blastocyst rates, intraoocyte glutathione and ATP. While blastocyst rates, GSH/GSSG ratio and NADPH were higher, ROS was lower significantly in COCs matured with iodoacetate than with DHEA. Fructose-6-phosphate overcame the inhibitory effect of DHEA on PPP. During maturation of COCs with pyruvate, electron transport inhibitor, rotenone or monocarboxylate transfer inhibitor, 4-CIN significantly decreased blastocyst rates. Cumulus-denuded oocytes had a limited capacity to use glucose or lactate, but they could use pyruvate to support maturation. In conclusion, whereas glycolysis promoted ooplasmic maturation mainly by supplying energy, PPP facilitated ooplasmic maturation to a greater extent by both reducing oxidative stress and supplying energy through providing fructose-6-phosphate for glycolysis. Pyruvate was transferred by monocarboxylate transporters and utilized through mitochondrial electron transport to sustain ooplasmic maturation.

Gene Expression of Monocarboxylate Transporters and Oocyte-secreted Factors in Bovine Cumulus-oocyte Complexes Selected by Brilliant Cresyl Blue

Oocyte selection based on the brilliant cresyl blue (BCB) staining test has been successfully used to differentiate between competent and incompetent bovine oocytes. Here, the expression of genes involved in transport of monocarboxylates (Mct1-4) and oogenesis specific genes (Bmp15, Gdf9 and Has2) in BCB+ and BCB- selected immature and mature bovine cumulus-oocyte complexes (COC) was evaluated. In order to find specific molecular markers to characterize successful oocyte maturation, our study was also aimed at identifying the expression of Mcts and oogenesis specific genes in denuded oocytes and cumulus cells. Immature COCs morphological appropriate were (i) stained with 26 mm BCB for 90 min before IVM, (ii) exposed to same incubation conditions as stained COCs, but without BCB (holding group) or (iii) transferred into a maturation medium immediately after morphological selection (control group). mRNA expression was investigated by RT-PCR in COCs before and after IVM. No relationship was observed in the relative expression of Has2, Gdf9, Bmp15 or Mct1, 2 and 4 transcripts between BCB+ and BCB- COCs. Transcripts analysis showed that Gdf9 and Bmp15 in BCB+, BCB- and holding groups were up-regulated (p < 0.05) before IVM, while Has2 was up-regulated (p < 0.01) after IVM in the control group. Other genes remained stable during maturation (Mct1, 2 and 4). Our results showed, for the first time, Mct1, 2 and 4 expression in bovine COCs. Mct1 and Mct4 transcripts were present in denuded oocytes and cumulus cell, while Mct2 was detected only in cumulus cells. These differences between the three isoforms in localization suggest unique roles for each in monocarboxylate transport during maturation.

Mcl-1 is a key regulator of the ovarian reserve

A majority of ovarian follicles are lost to natural death, but the disruption of factors involved in maintenance of the oocyte pool results in a further untimely follicular depletion known as premature ovarian failure. The anti-apoptotic B-cell lymphoma 2 (Bcl-2) family member myeloid cell leukemia-1 (MCL-1) has a pro-survival role in various cell types; however, its contribution to oocyte survival is unconfirmed. We present a phenotypic characterization of oocytes deficient in Mcl-1, and establish its role in maintenance of the primordial follicle (PMF) pool, growing oocyte survival and oocyte quality. Mcl-1 depletion resulted in the premature exhaustion of the ovarian reserve, characterized by early PMF loss because of activation of apoptosis. The increasingly diminished surviving cohort of growing oocytes displayed elevated markers of autophagy and mitochondrial dysfunction. Mcl-1-deficient ovulated oocytes demonstrated an increased susceptibility to cellular fragmentation with activation of the apoptotic cascade. Concomitant deletion of the pro-apoptotic Bcl-2 member Bcl-2-associated X protein (Bax) rescued the PMF phenotype and ovulated oocyte death, but did not prevent the mitochondrial dysfunction associated with Mcl-1 deficiency and could not rescue long-term breeding performance. We thus recognize MCL-1 as the essential survival factor required for conservation of the postnatal PMF pool, growing follicle survival and effective oocyte mitochondrial function.

Nutrient pathways regulating the nuclear maturation of mammalian oocytes

Oocyte maturation is defined as that phase of development whereby a fully grown oocyte reinitiates meiotic maturation, completes one meiotic division with extrusion of a polar body, then arrests at MII until fertilisation. Completion of maturation depends on many different factors, not the least of which is the proper provision of energy substrates to fuel the process. Interaction of the oocyte and somatic compartment of the follicle is critical and involves numerous signals exchanged between the two cell types in both directions. One of the prominent functions of the cumulus cells is the channelling of metabolites and nutrients to the oocyte to help stimulate germinal vesicle breakdown and direct development to MII. This entails the careful integration and coordination of numerous metabolic pathways, as well as oocyte paracrine signals that direct certain aspects of cumulus cell metabolism. These forces collaborate to produce a mature oocyte that, along with accompanying physiological changes called cytoplasmic maturation, which impart subsequent developmental competence to the oocyte, can be fertilised and develop to term. This review focuses on nuclear maturation and the metabolic interplay that regulates it, with special emphasis on data generated in the mouse.

Reversible meiotic arrest in feline oocytes

Increasing intracellular concentrations of cyclic adenosine monophosphate (cAMP) within the cumulus-oocyte complex (COC) inhibits or delays spontaneous oocyte maturation and improves the developmental competence of the oocyte in many species, but information for carnivores is limited. The objectives of the present study were to describe the effects of isobutyl methylxanthine (IBMX), which decreases cAMP degradation, and forskolin, which increases cAMP production, on spontaneous and induced maturation (by equine chorionic gonadotrophin (eCG) and epidermal growth factor (EGF)) of feline oocytes and to evaluate the reversibility of IBMX-induced arrest by measuring the resumption of meiosis and embryonic development following IVF. IBMX decreased (P<0.05) the incidence of spontaneous (6.7% vs 42.0%, metaphase II (MII)) and induced (5.6% vs 66.1% MII) maturation after 24 h of culture. In contrast, forskolin stimulated meiosis (81.7% MII; P<0.05). Following 12 h of culture with IBMX and an additional 24h with eCG and EGF in the absence of IBMX, the proportions of oocytes reaching MII (66.1%), cleaving (79.9%) and developing to the blastocyst stage (15.3%) were similar (P>0.05) to oocytes cultured continuously with eCG and EGF (70.2%, 83.0% and 18.1%, respectively). These results demonstrate that IBMX reversibly inhibits both spontaneous and eCG+EGF-induced meiosis in feline oocytes without compromising the oocyte's developmental competence.

Measurement of ATP in single oocytes: impact of maturation and cumulus cells on levels and consumption

Mitochondria provide the primary source of ATP in the oocyte and early embryo and mitochondrial dysfunction and deficit of mitochondria-derived ATP has been linked to suboptimal developmental competence. We have undertaken a study of ATP in the maturing mouse oocyte using a novel recombinant FRET based probe, AT1.03. We show that AT1.03 can be successfully used to monitor cytosolic ATP levels in single live oocytes over extended time periods. We find that ATP levels undergo dynamic changes associated with specific maturational events and that oocytes display altered rates of ATP consumption at different stages of maturation. Cumulus enclosed oocytes have a higher ATP level during maturation than denuded oocytes and this can be abolished by inhibition of gap junctional communication between the oocyte and cumulus cells. Our work uses a new approach to shed light on regulation of ATP levels and ATP consumption during oocyte maturation.

Oxidative stress and ageing of the post-ovulatory oocyte

With extended periods of time following ovulation, the metaphase II stage oocyte experiences deterioration in quality referred to as post-ovulatory oocyte ageing. Post-ovulatory ageing occurs both in vivo and in vitro and has been associated with reduced fertilization rates, poor embryo quality, post-implantation errors and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been established, the molecular mechanisms controlling this process are not well defined. This review analyses the relationships between biochemical changes exhibited by the ageing oocyte and the symptoms associated with the ageing phenotype. We also discuss molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We propose that oxidative stress may act as the initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to cause a decline in levels of critical cell cycle factors such as maturation-promoting factor, impair calcium homoeostasis, induce mitochondrial dysfunction and directly damage multiple intracellular components of the oocyte such as lipids, proteins and DNA. Finally, this review addresses current strategies for delaying post-ovulatory oocyte ageing with a particular focus on the potential use of compounds such as caffeine or selected antioxidants in the development of more refined media for the preservation of oocyte integrity during IVF procedures.

Oxidative stress and ageing of the post-ovulatory oocyte

With extended periods of time following ovulation, the metaphase II stage oocyte experiences deterioration in quality referred to as post-ovulatory oocyte ageing. Post-ovulatory ageing occurs both in vivo and in vitro and has been associated with reduced fertilization rates, poor embryo quality, post-implantation errors and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been established, the molecular mechanisms controlling this process are not well defined. This review analyses the relationships between biochemical changes exhibited by the ageing oocyte and the symptoms associated with the ageing phenotype. We also discuss molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We propose that oxidative stress may act as the initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to cause a decline in levels of critical cell cycle factors such as maturation-promoting factor, impair calcium homoeostasis, induce mitochondrial dysfunction and directly damage multiple intracellular components of the oocyte such as lipids, proteins and DNA. Finally, this review addresses current strategies for delaying post-ovulatory oocyte ageing with a particular focus on the potential use of compounds such as caffeine or selected antioxidants in the development of more refined media for the preservation of oocyte integrity during IVF procedures.

A requirement for fatty acid oxidation in the hormone-induced meiotic maturation of mouse oocytes

We have previously shown that fatty acid oxidation (FAO) is required for AMP-activated protein kinase (PRKA)-induced maturation in vitro. In the present study, we have further investigated the role of this metabolic pathway in hormone-induced meiotic maturation. Incorporating an assay with (3)H-palmitic acid as the substrate, we first examined the effect of PRKA activators on FAO levels. There was a significant stimulation of FAO in cumulus cell-enclosed oocytes (CEO) treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and RSVA405. In denuded oocytes (DO), AICAR stimulated FAO only in the presence of carnitine, the molecule that facilitates fatty acyl CoA entry into the mitochondria. The carnitine palmitoyltransferase 1 activator C75 successfully stimulated FAO in CEO. All three of these activators trigger germinal vesicle breakdown. Meiotic resumption induced by follicle-stimulating hormone (FSH) or amphiregulin was completely inhibited by the FAO inhibitors etomoxir, mercaptoacetate, and malonyl CoA. Importantly, FAO was increased in CEO stimulated by FSH and epidermal growth factor, and this increase was blocked by FAO inhibitors. Moreover, compound C, a PRKA inhibitor, prevented the FSH-induced increase in FAO. Both carnitine and palmitic acid augmented hormonal induction of maturation. In a more physiological setting, etomoxir eliminated human chorionic gonadotropin (hCG)-induced maturation in follicle-enclosed oocytes. In addition, CEO and DO from hCG-treated mice displayed an etomoxir-sensitive increase in FAO, indicating that this pathway was stimulated during in vivo meiotic resumption. Taken together, our data indicate that hormone-induced maturation in mice requires a PRKA-dependent increase in FAO.

Microarray analysis of mRNA from cumulus cells following in vivo or in vitro maturation of mouse cumulus–oocyte complexes

The IVM of mammalian cumulus–oocyte complexes (COCs) yields reduced oocyte developmental competence compared with oocytes matured in vivo. Altered cumulus cell function during IVM is implicated as one cause for this difference. We have conducted a microarray analysis of cumulus cell mRNA following IVM or in vivo maturation (IVV). Mouse COCs were sourced from ovaries of 21-day-old CBAB6F1 mice 46 h after equine chorionic gonadotrophin (5 IU, i.p.) or from oviducts following treatment with 5 IU eCG (61 h) and 5 IU human chorionic gonadotrophin (13 h). IVM was performed in α-Minimal Essential Medium with 50 mIU FSH for 17 h. Three independent RNA samples were assessed using the Affymetrix Gene Chip Mouse Genome 430 2.0 array (Affymetrix, Santa Clara, CA, USA). In total, 1593 genes were differentially expressed, with 811 genes upregulated and 782 genes downregulated in IVM compared with IVV cumulus cells; selected genes were validated by real-time reverse transcription–polymerase chain reaction (RT-PCR). Surprisingly, haemoglobin α (Hba-a1) was highly expressed in IVV relative to IVM cumulus cells, which was verified by both RT-PCR and western blot analysis. Because haemoglobin regulates O2 and/or nitric oxide availability, we postulate that it may contribute to regulation of these gases during the ovulatory period in vivo. These data will provide a useful resource to determine differences in cumulus cell function that are possibly linked to oocyte competence.

The ability to achieve meiotic maturation in the dog oocyte is linked to glycolysis and glutamine oxidation

We tested the hypothesis that meiotic competence of dog oocytes is tightly linked with donor follicle size and energy metabolism. Oocytes were recovered from small (<1 mm diameter, n = 327), medium (1-<2 mm, n = 292) or large (≥2 mm, n = 102) follicles, cultured for 0, 24, or 48 hr, and then assessed for glycolysis, glucose oxidation, pyruvate uptake, glutamine oxidation, and nuclear status. More oocytes (P < 0.05) from large follicles (37%) reached the metaphase-II (MII) stage than from the small group (11%), with the medium-sized class being intermediate (18%; P > 0.05). Glycolytic rate increased (P < 0.05) as oocytes progressed from the germinal vesicle (GV) to MII stage. After 48 hr of culture, oocytes completing nuclear maturation had higher (P < 0.05) glycolytic rates than those arrested at earlier stages. GV oocytes recovered from large follicle oocytes had higher (P < 0.05) metabolism than those from smaller counterparts at culture onset. MII oocytes from large follicles oxidized more (P < 0.05) glutamine than the same stage gametes recovered from smaller counterparts. In summary, larger-sized dog follicles contain a more metabolically active oocyte with a greater chance of achieving nuclear maturation in vitro. These findings demonstrate a significant role for energy metabolism in promoting dog oocyte maturation, information that will be useful for improving culture systems for rescuing intraovarian genetic material.

Dynamics of intra-follicular glucose during luteinization of macaque ovarian follicles

Glucose is important to the maturation of the oocyte and development of the embryo, while hyperglycemia results in profound reproductive and developmental consequences. However, the normal physiology of glucose in the ovary remains poorly understood. The goal of this study was to determine intra-follicular glucose dynamics during the periovulatory interval in non-human primates undergoing controlled ovarian stimulation protocols. Follicular fluid and mural granulosa cells were isolated before or up to 24h after an ovulatory hCG bolus, and the human granulosa-lutein cell line hGL5 was used. Intra-follicular glucose increased 3h after hCG, and remained at that level until 12h when levels decline back to pre-hCG concentrations. Pyruvate and lactate concentrations in the follicle were not strongly altered by hCG. Mural granulosa cell expression of hexokinase 1 and 2, and glucose-6-phosphate dehydrogenase mRNA decreased following hCG, while glycogen phosphorylase (liver form) increased following hCG. Glucose uptake by hGL5 cells was delayed until 24h following stimulation. In summary, intra-follicular glucose increases following an ovulatory stimulus and mural granulosa cells do not appear able to utilize it, sparing the glucose for the cumulus-oocyte complex.

Role of AMPK throughout meiotic maturation in the mouse oocyte: evidence for promotion of polar body formation and suppression of premature activation

This study was conducted to assess the role of AMPK in regulating meiosis in mouse oocytes from the germinal vesicle stage to metaphase II. Exposure of mouse cumulus cell-enclosed oocytes (CEO) and denuded oocytes (DO) during spontaneous maturation in vitro to AMPK-activating agents resulted in augmentation of the rate and frequency of polar body formation. Inhibitors of AMPK had an opposite, inhibitory effect. In addition, the AMPK inhibitor, compound C (Cmpd C) increased the frequency of oocyte activation. The stimulatory action of the AMPK-activating agent, AICAR, and the inhibitory action of Cmpd C were diminished if exposure was delayed, indicating an early action of AMPK on polar body formation. The frequency of spontaneous and Cmpd C-induced activation in CEO was reduced as the period of hormonal priming was increased, and AMPK stimulation eliminated the activation response. Immunostaining of oocytes with antibody to active AMPK revealed an association of active kinase with chromatin, spindle poles, and midbody during maturation. Immunolocalization of the α1 catalytic subunit of AMPK showed an association with condensed chromatin and the meiotic spindle but not in the spindle poles or midbody; α2 stained only diffusely throughout the oocyte. These data suggest that AMPK is involved in a regulatory capacity throughout maturation and helps promote the completion of meiosis while suppressing premature activation.

Association between amino acid turnover and chromosome aneuploidy during human preimplantation embryo development in vitro

This study investigated the relationship between human preimplantation embryo metabolism and aneuploidy rates during development in vitro. One hundred and eighty-eight fresh and cryopreserved embryos from 59 patients (33.9 +/- 0.6 years) were cultured for 2-5 days. The turnover of 18 amino acids was measured in spent media by high-performance liquid chromatography. Embryos were either fixed for interphase fluorescent in situ hybridization analysis of chromosomes 13, 18, 19, 21, X or Y, or were assayed for mitochondrial activity. Amino acid turnover was different (P < 0.05) between stage-matched fresh and cryopreserved embryos due to blastomere loss following warming. The proportion of embryos with aneuploid cells increased as cell division progressed from pronucleate- (23%) to late cleavage stages (50-70%). Asparagine, glycine and valine turnover was significantly different between uniformly genetically normal and uniformly abnormal embryos on Days 2-3 of culture. By Days 3-4, the profiles of serine, leucine and lysine differed between uniformly euploid versus aneuploid embryos. Gender significantly (P < 0.05) affected the metabolism of tryptophan, leucine and asparagine by cleavage-stage embryos. Pronucleate zygotes had a significantly higher proportion of active:inactive mitochondria compared with cleavage-stage embryos. Furthermore, mitochondrial activity was correlated (P < 0.05) with altered aspartate and glutamine turnover. These results demonstrate the association between the metabolism, cytogenetic composition and health of human embryos in vitro.

Nongenomic steroid-triggered oocyte maturation: of mice and frogs

Luteinizing hormone (LH) mediates many important processes in ovarian follicles, including cumulus cell expansion, changes in gap junction expression and activity, sterol and steroid production, and the release of paracrine signaling molecules. All of these functions work together to trigger oocyte maturation (meiotic progression) and subsequent ovulation. Many laboratories are interested in better understanding both the extra-oocyte follicular processes that trigger oocyte maturation, as well as the intra-oocyte molecules and signals that regulate meiosis. Multiple model systems have been used to study LH-effects in the ovary, including fish, frogs, mice, rats, pigs, and primates. Here we provide a brief summary of oocyte maturation, focusing primarily on steroid-triggered meiotic progression in frogs and mice. Furthermore, we present new studies that implicate classical steroid receptors rather than alternative non-classical membrane steroid receptors as the primary regulators of steroid-mediated oocyte maturation in both of these model systems.

Pyruvate prevents aging of mouse oocytes

Inhibiting oocyte aging is important not only for healthy reproduction but also for the success of assisted reproduction techniques. Although our previous studies showed that cumulus cells accelerated aging of mouse oocytes, the underlying mechanism is unknown. The objective of this paper was to study the effects of pyruvate and cumulus cells on mouse oocyte aging. Freshly ovulated mouse cumulus-oocyte complexes (COCs) or cumulus-denuded oocytes (DOs) were cultured in Chatot-Ziomek-Bavister (CZB) medium or COC-conditioned CZB medium supplemented with different concentrations of pyruvate before being examined for aging signs and developmental potential. Pyruvate supplementation to CZB medium decreased rates of ethanol-induced activation in both COCs and DOs by maintaining their maturation-promoting factor activities, but more pyruvate was needed for COCs than for DOs. Addition of pyruvate to the COC-conditioned CZB also alleviated aging of DOs. Observations on cortical granules, level of BCL2 proteins, histone acetylation, intracellular concentration of glutathione, and embryo development all confirmed that pyruvate supplementation inhibited aging of mouse oocytes. It is concluded that the aging of mouse oocytes, facilitated by culture in COCs, can be partially prevented by the addition of pyruvate to the culture medium.

Mouse oocyte control of granulosa cell development and function: paracrine regulation of cumulus cell metabolism

Bidirectional communication between oocytes and the companion granulosa cells is essential for the development and functions of both compartments. Oocytes are deficient in their ability to transport certain amino acids and in carrying out glycolysis and cholesterol biosynthesis. Cumulus cells must provide them with the specific amino acids and the products in these metabolic pathways. Oocytes control metabolic activities in cumulus cells by promoting the expression of genes in cumulus cells encoding specific amino acid transporters and enzymes essential for the oocyte-deficient metabolic processes. Hence oocytes outsource metabolic functions to cumulus cells to compensate for oocyte metabolic deficiencies. Oocyte control of granulosa cell metabolism may also participate in regulating the rate of follicular development in coordination with endocrine, paracrine, and autocrine signals. Oocytes influence granulosa cell development mainly by secretion of paracrine factors, although juxtacrine signals probably also participate. Key oocyte-derived paracrine factors include growth differentiation factor 9, bone morphogenetic protein 15, and fibroblast growth factor 8B.

Inactivation of glucocorticoids by 11beta-hydroxysteroid dehydrogenase enzymes increases during the meiotic maturation of porcine oocytes

Recent reports have shown that glucocorticoids can modulate oocyte maturation in both teleost fish and mammals. Within potential target cells, the actions of physiological glucocorticoids are modulated by 11beta-hydroxysteroid dehydrogenase (HSD11B) isoenzymes that catalyse the interconversion of cortisol and cortisone. Hence, the objective of this study was to establish whether HSD11B enzymes mediate cortisol-cortisone metabolism in porcine oocytes and, if so, whether the rate of glucocorticoid metabolism changes during oocyte maturation. Enzyme activities were measured in cumulus-oocyte complexes (COCs) and denuded oocytes (DOs) using radiometric conversion assays. While COCs and DOs oxidised cortisol to inert cortisone, there was no detectable regeneration of cortisol from cortisone. The rate of cortisol oxidation was higher in expanded COCs than in compact COCs containing germinal vesicle (GV) stage oocytes (111+/-6 vs 2041+/-115 fmol cortisone/oocyte.24 h; P<0.001). Likewise, HSD11B activities were 17+/-1 fold higher in DOs from expanded COCs than in those from compact COCs (P<0.001). When GV stage oocytes were subject to a 48 h in vitro maturation protocol, the enzyme activities were significantly increased from 146+/-18 to 1857+/-276 fmol cortisone/oocyte.24 h in GV versus MII stage oocytes respectively (P<0.001). Cortisol metabolism was inhibited by established pharmacological inhibitors of HSD11B (glycyrrhetinic acid and carbenoxolone), and by porcine follicular and ovarian cyst fluid. We conclude that an HSD11B enzyme (or enzymes) functions within porcine oocytes to oxidise cortisol, and that this enzymatic inactivation of cortisol increases during oocyte maturation.

Supplemented tissue culture medium 199 is a better medium for in vitro maturation of oocytes from women with polycystic ovary syndrome women than human tubal fluid

OBJECTIVE

To compare oocyte maturation, fertilization and cleavage rates, and embryonic developmental quality after culture of human immature oocytes from polycystic ovary syndrome (PCOS) patients in human tubal fluid (HTF) or tissue culture medium (TCM) 199.

DESIGN

Prospective, randomized, controlled trial.

SETTING

University hospital.

PATIENT(S)

Thirteen women undergoing 23 in vitro maturation cycles, from whom 119 oocytes were retrieved.

INTERVENTION(S)

Cumulus-enclosed germinal vesicle-stage oocytes matured in TCM-199-supplemented or HTF-supplemented media.

MAIN OUTCOME MEASURE(S)

Oocyte maturation and fertilization rates, embryonic developmental quality.

RESULT(S)

Significant differences were observed between TCM 199 and HTF regarding maturation rate (82% vs. 56.9%), fertilization rate (70% vs. 39.4%), and embryo quality (81.3% vs. 41.7%).

CONCLUSION(S)

Human tubal fluid medium, although widely used for embryo fertilization and maintenance in IVF techniques, is not an appropriate medium for the maturation of oocytes obtained from PCOS patients in nonstimulated cycles.

Carbohydrate metabolism by murine ovarian follicles and oocytes grown in vitro

Metabolic markers are potentially valuable for assessment of follicle development in vitro. Carbohydrate metabolism of murine preantral follicles grown to maturity over 13 days in vitro has been measured, and metabolism of resulting oocyte-cumulus complexes (OCCs) and denuded oocytes has been compared with in vivo ovulated control counterparts. Spent follicle culture media were analysed for glucose, lactate and pyruvate concentrations. During follicle in vitro growth, glycolysis accounted for a rise from approximately 24 to 60% of all glucose consumed. Ovulation induction caused a significant increase in glucose uptake and lactate production by in vitro-grown follicles to 71.7+/-1.2 and 96.6+/-4.8 nmoles/day respectively. OCCs grown in vitro had significantly higher rates of glucose consumption and lactate and pyruvate production (110.1+/- 3.5, 191.8+/- 8.9 and 31.7+/- 1.7 pmoles/h respectively) than in vivo ovulated controls (67.4+/- 8.1, 113.9+/- 17.1 and 20.2+/- 4.0 pmoles/h respectively), but a reduced capacity for pyruvate consumption (1.13+/- 0.06 vs 1.49+/- 0.06 pmoles/h by in vivo ovulated oocytes). Metabolism of OCCs was affected by the quality of the original follicle. In vitro-grown oocytes had a reduced cytoplasmic volume when compared with controls (168.3+/- 2.0 vs 199.0+/- 3.2 proportionately respectively) but a similar rate of metabolism per unit volume. Meiotic status influenced metabolism of both OCCs and denuded oocytes. In conclusion, glucose consumption and lactate production by cultured follicles increased in tandem with developmental progression and were stimulated prior to ovulation. Additionally, the metabolic profiles of in vitro produced OCCs and the oocytes within them are affected by long-term exposure to the culture environment.

Requirement for, and patterns of, pyruvate and glutamine metabolism in the domestic dog oocyte in vitro

Supplementation of energy substrates to culture medium is essential for resumption and completion of meiosis in vitro for many mammalian species. Objectives were to study the dog oocyte, specifically the influences of pyruvate and glutamine on maturation and the utilization of these two substrates at various developmental stages and incubation times. Ovarian oocytes (n=681) were obtained from spayed bitches and cultured for 48 hr in TCM 199 medium containing various concentrations of pyruvate (0-2.5 mM) and glutamine (0-4 mM) before being assessed for nuclear status. For analyzing metabolic activity, 259 dog oocytes were cultured for 0, 12, 24, 36, or 48 hr, assessed for pyruvate and glutamine metabolism using the hanging drop method and then evaluated for nuclear status. Neither pyruvate nor glutamine had influence (P > 0.05) on oocyte maturation in vitro (IVM). However, both culture interval and meiotic status influenced pyruvate uptake (P < 0.05). Specifically, pyruvate uptake declined as the oocyte progressed from the germinal vesicle (GV) to metaphase II (MII) stage. Glutamine oxidation decreased as culture duration progressed (P < 0.05). In summary, pyruvate or glutamine is not required to promote successful IVM of dog oocytes. But, both substrates are being metabolized, and in patterns different to the domestic cat, another carnivore species. Pyruvate played an important role earlier in the maturational process, and less glutamine was oxidized as the oocyte neared nuclear maturation. These variations emphasize the importance of defining species specificities in carnivores before expecting consistently successful IVM/IVF.

A comparative analysis of metabolism and viability in porcine oocytes during in vitro maturation

The importance of oocyte quality cannot be overstated, because it impacts all subsequent events during development of the embryo, the fetus and even the resulting offspring. Oocyte metabolism plays a critical role in supporting developmental competence via multiple mechanisms. It is beginning to be understood that metabolic pathways not only affect cytoplasmic maturation but may control nuclear maturation as well. A complete understanding of the precise roles that metabolism plays in determining oocyte quality is crucial for developing efficient in vitro maturation systems to support acquisition of oocyte competence. To date, this pursuit has not been entirely successful. Work in our laboratory on porcine oocyte metabolism has elucidated some of the intricate control mechanisms at work within the oocyte, not only for energy production, but also encompassing progression of nuclear maturation, mitochondrial activity and distribution, and oxidative and ionic stresses. We hypothesize that by utilizing oocyte metabolic data, we can develop more appropriate in vitro maturation systems that result in increased oocyte and embryo developmental competence.

Cracking the egg: molecular dynamics and evolutionary aspects of the transition from the fully grown oocyte to embryo

Fully grown oocytes (FGOs) contain all the necessary transcripts to activate molecular pathways underlying the oocyte-to-embryo transition (OET). To elucidate this critical period of development, an extensive survey of the FGO transcriptome was performed by analyzing 19,000 expressed sequence tags of the Mus musculus FGO cDNA library. Expression of 5400 genes and transposable elements is reported. For a majority of genes expressed in mouse FGOs, homologs transcribed in eggs of Xenopus laevis or Ciona intestinalis were found, pinpointing evolutionary conservation of most regulatory cascades underlying the OET in chordates. A large proportion of identified genes belongs to several gene families with oocyte-restricted expression, a likely result of lineage-specific genomic duplications. Gene loss by mutation and expression in female germline of retrotransposed genes specific to M. musculus is documented. These findings indicate rapid diversification of genes involved in female reproduction. Comparison of the FGO and two-cell embryo transcriptomes demarcated the processes important for oogenesis from those involved in OET and identified novel motifs in maternal mRNAs associated with transcript stability. Discovery of oocyte-specific eukaryotic translation initiation factor 4E distinguishes a novel system of translational regulation. These results implicate conserved pathways underlying transition from oogenesis to initiation of development and illustrate how genes acquire and lose reproductive functions during evolution, a potential mechanism for reproductive isolation.

Selective degradation of transcripts during meiotic maturation of mouse oocytes

There is massive destruction of transcripts during the maturation of mouse oocytes. The objective of this project was to identify and characterize the transcripts that are degraded versus those that are stable during the transcriptionally silent germinal vesicle (GV)-stage to metaphase II (MII)-stage transition using a microarray approach. A system for oocyte transcript amplification using both internal and 3'-poly(A) priming was utilized to minimize the impact of complex variations in transcript polyadenylation prevalent during this transition. Transcripts were identified and quantified using the Affymetrix Mouse Genome 430 v2.0 GeneChip. The significantly changed and stable transcripts were analyzed using Ingenuity Pathways Analysis and GenMAPP/MAPPFinder to characterize the biological themes underlying global changes in oocyte transcripts during maturation. It was concluded that the destruction of transcripts during the GV to MII transition is a selective rather than promiscuous process in mouse oocytes. In general, transcripts involved in processes that are associated with meiotic arrest at the GV-stage and the progression of oocyte maturation, such as oxidative phosphorylation, energy production, and protein synthesis and metabolism, were dramatically degraded. In contrast, transcripts encoding participants in signaling pathways essential for maintaining the unique characteristics of the MII-arrested oocyte, such as those involved in protein kinase pathways, were the most prominent among the stable transcripts.

Differential response of cumulus cell-enclosed and denuded mouse oocytes in a meiotic induction model system

In this study we have examined the effects of denuded oocyte coculture with dissociated cumulus cells (CC) or intact oocyte-CC complexes on meiotic resumption. When denuded oocytes (DO) or cumulus cell-enclosed oocytes (CEO) were cultured in 40-microl drops of medium under oil, and held in meiotic arrest with 4 mM hypoxanthine plus 25 microM dbcAMP, they underwent germinal vesicle breakdown (GVB) at similar frequencies (34%-35%). Coculture of DO with complexes or dissociated CCs stimulated maturation (50% and 61% GVB, respectively), with no effect of DO on maturation of cocultured CEO (32% GVB). This coculture effect was increased with the number of CCs added to the culture drop. When either glucose or glutamine was eliminated from the medium, no meiotic induction resulted from cocultured CCs. When CEO were cultured alone in microdrops, increasing their number from 10 to 50 significantly lowered the percentage resuming maturation, an effect also reduced by removing glucose and/or glutamine from the medium. This effect was not observed with DO. When inhibitory medium was conditioned overnight with complexes, subsequent culture with DO led to higher maturation percentages than culture in unconditioned medium; however, when CEO were cultured in conditioned medium, there was either no effect or increased inhibition of maturation. Assay of glucose and pyruvate in spent medium showed that DO cultured alone consumed glucose and pyruvate, but under CC coculture conditions more glucose was consumed and significant amounts of pyruvate accumulated in the medium, changes that led to an increase in the maturation of DO. Further experiments showed that DO were more sensitive than CEO to the meiosis-inducing effect of pyruvate. These results demonstrate different responsiveness of DO and CEO to coculture conditions and question the physiological relevance of denuded oocyte/CC coculture to study meiotic induction.