Recent insights into oocyte-follicle cell interactions provide opportunities for the development of new approaches to in vitro maturation

Effect of human chorionic gonadotropin on oocyte maturation and developmental competence in buffalo

We hypothesized that human chorionic gonadotropic (hCG) could replace LH in the maturation media for buffalo oocytes, and hCG administration before ovum pick-up (OPU) enhances in-vitro development of buffalo oocytes. Objectives were 1) to investigate the effect of hCG supplementation on nuclear maturation, oocyte development, and granulosa cell mRNA abundance of genes related to growth and antioxidant pathways and 2) to determine the effect of hCG administration before OPU on in-vitro oocyte development. In Experiment 1, buffalo oocytes retrieved from slaughterhouse ovaries were maturated in the media supplemented with 0.5 μg of LH or 2 IU of hCG. After fertilization, cleavage and embryo were assessed on 48 h and 7 d of the culture, respectively. The nuclear maturation of the oocytes and granulosa cells mRNA abundance of genes (AREG,EREG,NRG1,CYP19A1,GDF9,CASP9,SOD1) were assessed after maturation. In Experiment 2, buffaloes were synchronized and superstimulated with FSH and 6 h before OPU, randomly assigned to either receive saline (CON, n = 4) or 1500 IU of hCG (hCG, n = 6). Four OPU sessions per buffalo were conducted at weekly intervals and retrieved oocytes were maturated and fertilized in-vitro. In Experiment 1, nuclear maturation, cleavage, embryo production, and mRNA abundance of the genes related to growth and steroidogenesis did not differ between treatments but SOD1 gene expression tended (P = 0.10) to lower in hCG treatment as compared with LH. In Experiment 2, oocytes retrieved from hCG-treated buffaloes resulted in a higher proportion of cleavage (84.0 vs. 42.5 ± 8.9 %, P = 0.02) and embryo (84.0 vs 24.0 ± 7.3, P < 0.01) than CON. In conclusion, hCG supplementation in the maturation media yielded comparable outcomes to that of LH, and hCG administration 6 h before OPU enhanced the in-vitro developmental competency of the buffalo oocytes.

Relationship between chromatin configuration and maturation ability of rat oocytes in vitro and in vivo

PURPOSE

Embryo engineering requires a large number of oocytes, which undergo in vitro maturation (IVM). Understanding how to select the best quality oocytes is key to improving IVM efficiency. Oocytes have different germinal vesicle (GV) chromatin configurations, which may explain the heterogeneity in oocyte quality during IVM. However, no reports have categorized, the chromatin configuration of rat GVs or evaluated, the association between the chromatin configuration and oocytes development.

METHODS

The GV chromatin configuration of rat oocytes was divided into seven types according to the degree of chromatin compaction: non-surrounded nucleolus (NSN), prematurely condensed NSN, partly NSN, partly surrounded nucleolus (SN-1), SN-1, condensed SN-1, and aggregated (SN-2). The chromatin configuration distribution was compared during the different stages of oocyte growth and maturation. We also analyzed the changes in the chromatin configuration at different GV stages during IVM. Moreover, the factors affecting the chromatin configuration were analyzed.

RESULTS

The SN-2 configuration increased with rat oocyte growth and maturation, suggesting that SN-2 facilitates oocyte development. RNA transcription activity in rat oocyte GVs was inversely correlated with oocyte IVM.

CONCLUSIONS

The SN-2 chromatin configuration was related to rat oocyte growth and maturation. RNA transcription activity in rat oocytes in the GV stage was inversely correlated with oocyte maturation.

Effect of Alpha-Lipoic Acid on the Development, Oxidative Stress, and Cryotolerance of Bovine Embryos Produced In Vitro

Oxidative stress (OS) induced by an imbalance in reactive oxygen species (ROS) levels in vitro impairs embryonic development. Here, we assessed the effects of alpha-lipoic acid (ALA) in in vitro production media on OS reduction, embryonic development, and cryotolerance of bovine embryos. We evaluated the effects of adding different concentrations of ALA (2.5, 5, 10, and 25 μM) to in vitro maturation (IVM) or in vitro culture (IVC) medium on embryonic development. We also determined the effects of adding ALA (25 μM) to the IVM and IVC medium in the same routine on the development and quality of embryos, ROS levels, and cryotolerance. Embryos were produced in vitro using conventional protocols for each treatment. The inclusion of ALA in the IVM and IVC media did not affect the development or quality of embryos; however, it reduced ROS levels in grade II embryos and increased hatching after 12 h on day 7 in grade I embryos and on day 8 in grade II embryos after warming. These findings prompt questions regarding the potential of ALA in improving embryo metabolism, considering the initial embryo recovery in the first few hours of embryo warming.

Current status and hotspots of in vitro oocyte maturation: a bibliometric study of the past two decades

PURPOSE

In vitro maturation (IVM) of oocytes is a promising technique among assisted reproductive technologies. Although IVM has been used for many years, its efficiency is still relatively low compared to that of traditional in vitro fertilization (IVF) procedures. Therefore, we aimed to explore the hotspots and frontiers of IVM research over the past two decades and provide direction for IVM advancement.

METHODS

The articles and reviews related to IVM in the Web of Science Core Collection (WoSCC) were retrieved on June 03, 2024. Three bibliometric tools, VOSviewer 1.6.18 (2010), CiteSpace 6.1. R6 (2006), and Bibliometrix R package 4.1.0 (2017), were used to generate network maps and explore knowledge frontiers and trends. To uncover the latest research advancements and frontiers in the IVM field, we conducted an analysis of the entire IVM field, including all species. Given our focus on human IVM developments, we identified the leading countries, institutions, authors, and journals driving progress in human IVM.

RESULTS

A total of 5150 publications about IVM and 1534 publications in the specific context of human IVM were retrieved from the WoSCC. The number of publications on both overall IVM and human IVM fields has increased steadily. In human IVM, the United States (USA) and McGill University were the most prolific country and institution, respectively. Human Reproduction was both the most published in and the most cited journal in human IVM. Seang Lin, Tan was the most productive author, and Ri-Cheng, Chian's papers were the most cited in human IVM. Furthermore, five hotspot topics were summarized, namely, culture system, supplementation, cooperation in the ovarian follicle, gene expression, and oocyte cryopreservation.

CONCLUSIONS

Further studies could concentrate on the following topics: (1) the mechanisms involved in oocyte maturation in vivo and in vitro, especially in energy metabolism and intercellular communications; (2) the establishment of IVM culture systems, including standardization of the biphasic IVM culture system and supplementation; (3) the genetic differences between oocytes matured in vivo and in vitro; and (4) the mechanism of cryopreservation-inflicted damage and solutions to this challenge. For human IVM, it is necessary to precisely assess the developmental stages of oocytes and adjust the IVM process accordingly to develop tailored culture media. Concurrently, clinical trials are essential for evaluating the effectiveness and safety of IVM.

Hormone-free vs. follicle-stimulating hormone-primed infertility treatment of women with polycystic ovary syndrome using biphasic in vitro maturation: a randomized controlled trial

OBJECTIVE

To compare oocyte maturation rates and pregnancy outcomes in women with polycystic ovary syndrome (PCOS) undergoing biphasic in vitro maturation (capacitation in vitro maturation [CAPA-IVM]) with vs. without follicle-stimulating hormone (FSH) priming.

DESIGN

Randomized, controlled, assessor-blinded trial.

SUBJECTS

Women aged 18-37 years with PCOS and an indication for CAPA-IVM.

INTERVENTION(S)

Participants were randomized (1:1) to undergo CAPA-IVM with or without FSH priming. The FSH priming group had 2 days of FSH injections before oocyte pickup; no FSH was given in the non-FSH group. After CAPA-IVM, day-5 embryos were vitrified for transfer in a subsequent cycle.

MAIN OUTCOME MEASURE(S)

The primary endpoint was number of matured oocytes. Secondary outcomes included rates of live birth, implantation, clinical pregnancy, ongoing pregnancy, pregnancy complications, obstetric and perinatal complications, and neonatal complications.

RESULT(S)

The number (interquartile range) of matured oocytes did not differ significantly in the non-FSH vs. FSH group (13 [9-18] vs. 14 [7-18]; absolute difference -1 [95% confidence interval -5 to 4]); other oocyte and embryology outcomes did not differ between groups. Rates of ongoing pregnancy and live birth were 38.3% in the non-FSH group and 31.7% in the FSH group (risk ratio for both outcomes: 1.21, 95% confidence interval 0.74-1.98). Maternal complications were infrequent and occurred at a similar rate in the two groups; there were no preterm deliveries before 32 weeks gestation.

CONCLUSION(S)

These findings open the possibility of a new, hormone-free approach to infertility treatment of women with PCOS.

CLINICAL TRAIL REGISTRATION NUMBER

NCT05600972.

In vitro maturation of oocytes: what is already known?†

Assisted reproductive technologies (ARTs) involve the laboratory manipulation of gametes and embryos to help couples with fertility problems become pregnant. One of these procedures, controlled ovarian stimulation, uses pharmacological agents to induce ovarian and follicular maturation in vivo. Despite the effectiveness in achieving pregnancy and live births, some patients may have complications due to over-response to gonadotropins and develop ovarian hyperstimulation syndrome. In vitro maturation (IVM) of oocytes has emerged as a technique to reduce the risk of ovarian hyperstimulation syndrome, particularly in women with polycystic ovary syndrome, and for fertility preservation in women undergoing oncological treatment. Although there are some limitations, primarily due to oocyte quality, recent advances have improved pregnancy success rates and neonatal and infant outcomes. Different terms have been coined to describe variations of IVM, and the technique has evolved with the introduction of hormones to optimize results. In this review, we provide a comprehensive overview of IVM relating hormonal priming, culture system and media, and clinical indications for IVM with its reproductive outcomes during ARTs.

Screening and identification of nanobody against inhibin α-subunit from a Camelus bactrianus phage display library

Background

Inhibin is a member of the transforming growth factor family that influences reproduction in animals.

Objective

The purpose of this study was to obtain nanobodies from the phage antibody library constructed by us that can specifically bind to inhibin α-subunit.

Methods

In this study, camels were immunized with Kazakh sheep inhibin-α protein that expressed in BL21 E. coli, and the camel VHH nanobody phage display library was prepared using nested PCR. The nanobodies specifically binding to inhibin α-subunit in the library were screened by three rounds of immunoaffinity screening and phage enzyme-linked immunosorbent assay (phage ELISA). The functions of the selected nanobodies were identified using molecular simulation docking, ELISA affinity test, and sheep immunity test.

Results

A nanobody display library was successfully constructed with a capacity of 1.05 × 1012 CFU, and four inhibin-α-subunit-specific nanobodies with an overall similarity of 69.34 % were screened from the library, namely, Nb-4, Nb-15, Nb-26, and Nb-57. The results of molecular simulation docking revealed that four types of nanobodies were complexed with inhibin-α protein mainly through hydrophobic bonds. Immunity tests revealed that the nanobody Nb-4 could effectively inhibit sheep inhibin A/B and could significantly improve the FSH level in sheep.

Conclusion

Four inhibin α-subunit-specific nanobodies with biological functions were successfully screened. To the best of our knowledge, this is a new reproductive immunomodulatory pathway of inhibin α-subunit, which may change the secretion of FSH in the ovary, thus changing the estrous cycle of organisms.

In vitro maturation of oocytes in light of ovarian mitochondrial improvement: effectiveness and safety

In vitro maturation of oocytes (IVM) represents an assisted reproductive technique that involves the minimal or absence of ovarian stimulation and is beneficial to specific groups of patients. These may include women with polycystic ovarian syndrome and/or patients who need a fertility preservation option before undergoing gonadotoxic treatment. However, when IVM is applied in cases where it is not recommended, it can be considered as an add-on technique, as described by the ESHRE Guideline Group on Female Fertility Preservation. Interestingly, IVM has not been proven yet to be as effective as conventional IVF in the laboratory, in terms of clinical pregnancy and live birth rates, while concerns have been raised for its long-term safety. As a result, both safety and efficacy of IVM remain still questionable and additional data are needed to draw conclusions.

A fresh start for IVM: capacitating the oocyte for development using pre-IVM

BACKGROUND

While oocyte IVM is practiced sporadically it has not achieved widespread clinical practice globally. However, recently there have been some seminal advances in our understanding of basic aspects of oocyte biology and ovulation from animal studies that have led to novel approaches to IVM. A significant recent advance in IVM technology is the use of biphasic IVM approaches. These involve the collection of immature oocytes from small antral follicles from minimally stimulated patients/animals (without hCG-priming) and an ∼24 h pre-culture of oocytes in an advanced culture system ('pre-IVM') prior to IVM, followed by routine IVF procedures. If safe and efficacious, this novel procedure may stand to make a significant impact on human ART practices.

OBJECTIVE AND RATIONALE

The objectives of this review are to examine the major scientific advances in ovarian biology with a unique focus on the development of pre-IVM methodologies, to provide an insight into biphasic IVM procedures, and to report on outcomes from animal and clinical human data, including safety data. The potential future impact of biphasic IVM on ART practice is discussed.

SEARCH METHODS

Peer review original and review articles were selected from PubMed and Web of Science searches for this narrative review. Searches were performed using the following keywords: oocyte IVM, pre-IVM, biphasic IVM, CAPA-IVM, hCG-triggered/primed IVM, natural cycle IVF/M, ex-vivo IVM, OTO-IVM, oocyte maturation, meiotic competence, oocyte developmental competence, oocyte capacitation, follicle size, cumulus cell (CC), granulosa cell, COC, gap-junction communication, trans-zonal process, cAMP and IVM, cGMP and IVM, CNP and IVM, EGF-like peptide and IVM, minimal stimulation ART, PCOS.

OUTCOMES

Minimizing gonadotrophin use means IVM oocytes will be collected from small antral (pre-dominant) follicles containing oocytes that are still developing. Standard IVM yields suboptimal clinical outcomes using such oocytes, whereas pre-IVM aims to continue the oocyte's development ex vivo, prior to IVM. Pre-IVM achieves this by eliciting profound cellular changes in the oocyte's CCs, which continue to meet the oocyte's developmental needs during the pre-IVM phase. The literature contains 25 years of animal research on various pre-IVM and biphasic IVM procedures, which serves as a large knowledge base for new approaches to human IVM. A pre-IVM procedure based on c-type natriuretic peptide (named 'capacitation-IVM' (CAPA-IVM)) has undergone pre-clinical human safety and efficacy trials and its adoption into clinical practice resulted in healthy live birth rates not different from conventional IVF.

WIDER IMPLICATIONS

Over many decades, improvements in clinical IVM have been gradual and incremental but there has likely been a turning of the tide in the past few years, with landmark discoveries in animal oocyte biology finally making their way into clinical practice leading to improved outcomes for patients. Demonstration of favorable clinical results with CAPA-IVM, as the first clinically tested biphasic IVM system, has led to renewed interest in IVM as an alternative, low-intervention, low-cost, safe, patient-friendly ART approach, and especially for patients with PCOS. The same new approach is being used as part of fertility preservation in patients with cancer and holds promise for social oocyte freezing.

Mammalian embryo culture media: now and into the future

For over 70years, since the culture of the first mammalian embryo in vitro , scientists have undertaken studies to devise and optimise media to support the manipulation and culture of gametes and embryos. This area of research became especially active in the late 1970s onwards following the successful birth of the first human in vitro fertilised embryo. This review summarises some of the key advances in mammalian embryo culture media over time based on a greater understanding of the biochemical milieu of the reproductive tract. It highlights how learnings from studies in mice and agricultural species have informed human culture media compositions, in particular the inclusion of albumin, growth factors, cytokines, and antioxidants into contemporary culture media formulations, and how these advances may then in turn help to inform and guide development of in vitro culture systems used in other arenas, in particular agriculture. Additionally, it will highlight how the introduction of new technologies, such as timelapse, can influence current trends in media composition and usage that may see a return to a single step medium.

Ovarian follicle transcriptome dynamics reveals enrichment of immune system process during transition from small to large follicles in cyclic Indian Ghoongroo pigs

Ovarian follicular development is a critical determinant of reproductive performance in litter bearing species like pigs, wherein economic gains depend on litter size. The study aimed to gain insight into the differentially expressed genes (DEGs) and signalling pathways regulating follicular growth and maturation in Ghoongroo pigs. Transcriptome profiling of porcine small follicles (SF) and large follicles (LF) was conducted using NovaSeq600 sequencing platform and DEGs were identified using DESeq2 with threshold of Padj. < 0.05 and log2 fold change cut off 0.58 (LF vs. SF). Functional annotations and bioinformatics analysis of DEGs were performed to find out biological functions, signalling pathways and hub genes regulating follicular dynamics. Transcriptome analysis revealed 709 and 479 genes unique to SF and LF stages, respectively, and 11,993 co-expressed genes in both the groups. In total, 507 DEGs (284 upregulated and 223 downregulated) were identified, which encoded for diverse proteins including transcription factors (TFs). These DEGs were functionally linked to response to stimulus, lipid metabolic process, developmental process, extracellular matrix organisation along with the immune system process, indicating wide-ranging mechanisms associated with follicular transition. The enriched KEGG pathways in LF stage consisted of ovarian steroidogenesis, cholesterol and retinol metabolism, cell adhesion molecules, cytokine receptor interaction and immune signalling pathways, depicting intra-follicular control of varied ovarian function. The hub gene analysis revealed APOE, SCARB1, MMP9, CYP17A1, TYROBP as key regulators of follicular development. This study identified candidate genes and TFs providing steroidogenic advantage to LFs which makes them fit for selection into the ovulatory pool of follicles.

The effect of ACVR1B/TGFBR1/ACVR1C signaling inhibition on oocyte and granulosa cell development during in vitro growth culture

The signals of the transforming growth factor β (TGF-β) superfamily play a critical role in follicular development in mammals. ACVR1B/TGFBR1/ACVR1C receptors mediate the signaling of several TGF-β superfamily ligands in granulosa cells. Although the requirement for ACVR1B/TGFBR1/ACVR1C receptor signaling in follicular development has been confirmed using mutant mouse models, the detailed roles of the signaling in granulosa cell and oocyte development have not been clearly defined. In the present study, we examined the requirement for ACVR1B/TGFBR1/ACVR1C receptor signaling in granulosa cells using an in vitro growth culture of oocyte-granulosa cell complexes (OGCs) and SB431542, a potent inhibitor of the receptor signaling. Although cumulus-oocyte complexes isolated from the control OGCs were able to undergo cumulus expansion, those isolated from OGCs grown with the inhibitor were not competent, even in the presence of in vivo-grown oocytes. The diameter of the oocytes in the SB431542-treated OGCs was comparable with that of the control; however, these oocytes were not competent for complete meiotic maturation or preimplantation development. Therefore, ACVR1B/TGFBR1/ACVR1C receptor signaling is not required for oocytes to increase their volume but is essential for the normal development of cumulus cells and oocyte developmental competence.

Pre-maturational culture promotes the developmental competence of bovine oocytes derived from an 8-day in vitro growth culture system

In this study, we evaluated the effects of pre-maturational culture (pre-IVM) on the developmental competence of bovine oocytes derived from an 8-day in vitro growth (IVG) culture system. IVG oocytes were subjected to 5 h pre-IVM before in vitro maturation, followed by in vitro fertilization (IVF). The proportion of oocytes that progressed to the germinal vesicle breakdown stage was similar between groups with and without pre-IVM. Although metaphase II oocytes and cleavage rates after IVF were similar regardless of pre-IVM culture, the blastocyst rate was significantly higher in the group with pre-IVM (22.5%) than without pre-IVM (11.0%, P < 0.05). In conclusion, pre-IVM culture improved the developmental competence of bovine oocytes derived from an 8-day IVG system.

Developmental Hurdles That Can Compromise Pregnancy during the First Month of Gestation in Cattle

Several key developmental events are associated with early embryonic pregnancy losses in beef and dairy cows. These developmental problems are observed at a greater frequency in pregnancies generated from in-vitro-produced bovine embryos. This review describes critical problems that arise during oocyte maturation, fertilization, early embryonic development, compaction and blastulation, embryonic cell lineage specification, elongation, gastrulation, and placentation. Additionally, discussed are potential remediation strategies, but unfortunately, corrective actions are not available for several of the problems being discussed. Further research is needed to produce bovine embryos that have a greater likelihood of surviving to term.

Human Follicular Fluid and Mesenchymal Stem Cell Conditioned Medium Improves in Vitro Development of Vitrified-Warmed Mouse Oocytes

BACKGROUND: In vitro maturation (IVM) and oocyte cryopreservation are therapeutic options in assisted reproductive technology which is used to preserve fertility in patients with different causes of infertility. OBJECTIVE: To analyze in vitro development of vitrified-warmed oocytes in the presence of human follicular fluid (FF) and bone marrow mesenchymal stem cell-conditioned medium (BMSC- CM) as a rescue strategy in fertility preservation. MATERIALS AND METHODS: BMSC-CM and FF media were used as two natural media. Not only osteogenic and adipogenic differentiation but also flow cytometry was carried out to confirm the nature of mesenchymal stem cells. A total of 327 vitrified-warmed oocytes were randomly assigned to three groups with different maturation media. After 24 h the maturation rate was evaluated. In vitro fertilization and also embryo development were also assessed. RESULTS: Oocytes matured in the BMSC-CM and FF groups showed a significant increase compared to the control group (76.6±2.9, 53.2±1.0 , and 40.8±6.1, respectively) (P < 0.05). Embryo cleavage rates in the BMSC-CM were dramatically higher than FF and control groups (85.6±2.2, 70.5±2.2, and 60.7±1.5, respectively). Blastocyst formation rates in the BMSC-CM group were statically different compared to FF and control groups (73.6±1.0, 58.5±1.0, and 45.8±4.2, respectively). CONCLUSION: BMSC-CM and FF media not only improve the maturation rate of vitrified warmed oocytes but also significantly increase embryo cleavage and blastocyst rates.

Regulation of human oocyte maturation in vivo during the final maturation of follicles

STUDY QUESTION

Which substances and signal transduction pathways are potentially active downstream to the effect of FSH and LH in the regulation of human oocyte maturation in vivo?

SUMMARY ANSWER

The regulation of human oocyte maturation appears to be a multifactorial process in which several different signal transduction pathways are active.

WHAT IS KNOWN ALREADY

Many studies in animal species have provided insight into the mechanisms that govern the final maturation of oocytes. Currently, these studies have identified several different mechanisms downstream to the effects of FSH and LH. Some of the identified mechanisms include the regulation of cAMP/cGMP levels in oocytes involving C-type natriuretic peptide (CNP), effects of epidermal growth factor (EGF)-related peptides such as amphiregulin (AREG) and/or epiregulin (EREG), effect of TGF-β family members including growth differentiation factor 9 (GDF9) and morphogenetic protein 15 (BMP15), activins/inhibins, follicular fluid meiosis activating sterol (FF-MAS), the growth factor midkine (MDK), and several others. However, to what extent these pathways and mechanisms are active in humans in vivo is unknown.

STUDY DESIGN, SIZE, DURATION

This prospective cohort study included 50 women undergoing fertility treatment in a standard antagonist protocol at a university hospital affiliated fertility clinic in 2016-2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We evaluated the substances and signalling pathways potentially affecting human oocyte maturation in follicular fluid (FF) and granulosa cells (GCs) collected at five time points during the final maturation of follicles. Using ELISA measurement and proteomic profiling of FF and whole genome gene expression in GC, the following substances and their signal transduction pathways were collectively evaluated: CNP, the EGF family, inhibin-A, inhibin-B, activins, FF-MAS, MDK, GDF9, and BMP15.

MAIN RESULTS AND THE ROLE OF CHANCE

All the evaluated substances and signal transduction pathways are potentially active in the regulation of human oocyte maturation in vivo except for GDF9/BMP15 signalling. In particular, AREG, inhibins, and MDK were significantly upregulated during the first 12-17 h after initiating the final maturation of follicles and were measured at significantly higher concentrations than previously reported. Additionally, the genes regulating FF-MAS synthesis and metabolism were significantly controlled in favour of accumulation during the first 12-17 h. In contrast, concentrations of CNP were low and did not change during the process of final maturation of follicles, and concentrations of GDF9 and BMP15 were much lower than reported in small antral follicles, suggesting a less pronounced influence from these substances.

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

Although GC and cumulus cells have many similar features, it is a limitation of the current study that information for the corresponding cumulus cells is not available. However, we seldom recovered a cumulus-oocyte complex during the follicle aspiration from 0 to 32 h.

WIDER IMPLICATIONS OF THE FINDINGS

Delineating the mechanisms governing the regulation of human oocyte maturation in vivo advances the possibility of developing a platform for IVM that, as for most other mammalian species, results in healthy offspring with good efficacy. Mimicking the intrafollicular conditions during oocyte maturation in vivo in small culture droplets during IVM may enhance oocyte nuclear and cytoplasmic maturation. The primary outlook for such a method is, in the context of fertility preservation, to augment the chances of achieving biological children after a cancer treatment by subjecting oocytes from small antral follicles to IVM. Provided that aspiration of oocytes from small antral follicles in vivo can be developed with good efficacy, IVM may be applied to infertile patients on a larger scale and can provide a cheap alternative to conventional IVF treatment with ovarian stimulation. Successful IVM has the potential to change current established techniques for infertility treatment.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the University Hospital of Copenhagen, Rigshospitalet, the Independent Research Fund Denmark (grant number 0134-00448), and the Interregional EU-sponsored ReproUnion network. There are no conflicts of interest to be declared.

Supplement of secreted recombinant low molecular weight human fibroblast growth factor 2 in culture media enhances in vitro bovine maturation

With the annual increase in in vitro bovine embryo production, understanding oocyte maturation is becoming more important. Previous studies have shown that oocyte maturation can be improved by adding bovine additives to in vitro maturation media. Among the additives, human fibroblast growth factor 2 (hFGF2) is well known for its positive influence on the growth rate and quality of cells and oocytes. However, the effect of LMW-hFGF2, one of the isoforms of hFGF2, on bovine in vitro maturation has not yet been identified. Therefore, the goal of this study was to elucidate the effect of LMW-hFGF2 on bovine oocyte maturation. Vectors expressing LMW-hFGF2 were cloned and transfected into cells. Afterward, secretion of LMW-hFGF2 from cells was confirmed, and used to assess the effect LMW-hFGF2 on cells and bovine oocytes. LMW-hFGF2 improved bovine oocyte maturation and embryo developmental competence. Laboratories can use LMW-hFGF2 in bovine oocyte culture media to improve in vitro embryo production success rates.

Intrafollicular Concentrations of the Oocyte-secreted Factors GDF9 and BMP15 Vary Inversely in Polycystic Ovaries

CONTEXT

The oocyte-secreted factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) play essential roles in follicle development and oocyte maturation, and aberrant regulation might contribute to the pathogenesis of polycystic ovary syndrome.

OBJECTIVE

Are there measurable differences in concentrations of GDF9, BMP15, and the GDF9/BMP15 heterodimer in small antral follicle fluids from women with and without polycystic ovaries (PCO)?

DESIGN AND SETTING

Follicle fluids (n = 356) were collected from 4- to 11-mm follicles in unstimulated ovaries of 87 women undergoing ovarian tissue cryopreservation for fertility preservation.

PATIENTS

Twenty-seven women with PCO were identified and 60 women without PCO-like characteristics (non-PCO women) were matched according to age and follicle size.

MAIN OUTCOME MEASURES

Intrafollicular concentrations of GDF9, BMP15, GDF9/BMP15 heterodimer, anti-Mullerian hormone (AMH), inhibin-A and -B, total inhibin, activin-B and -AB, and follistatin were measured using enzyme-linked immunosorbent assays.

RESULTS

The detectability of GDF9, BMP15, and the GDF9/BMP15 heterodimer were 100%, 94.4%, and 91.5%, respectively, and concentrations were significantly negatively correlated with increasing follicle size (P < 0.0001). GDF9 was significantly higher in women with PCO (PCO: 4230 ± 189 pg/mL [mean ± SEM], n = 188; non-PCO: 3498 ± 199 pg/mL, n = 168; P < 0.03), whereas BMP15 was lower in women with PCO (PCO: 431 ± 40 pg/mL, n = 125; non-PCO: 573 ± 55 pg/mL, n = 109; P = 0.10), leading to a significantly higher GDF9:BMP15 ratio in women with PCO (P < 0.01). Significant positive associations between BMP15 and AMH, activins, and inhibins in non-PCO women switched to negative associations in women with PCO.

CONCLUSIONS

Intrafollicular concentrations of GDF9 and BMP15 varied inversely in women with PCO reflecting an aberrant endocrine environment. An increased GDF9:BMP15 ratio may be a new biomarker for PCO.

Sequential IVM by CNP preincubation and cooperating of PGE2 with AREG enhances developmental competence of SCNT reconstructs in goat

Developmental competence of in vitro matured cumulus oocyte complexes (COCs) in conventional IVM (C.IVM) is lower than in vivo maturated COCs and is related to unsynchronized nuclear and cytoplasmic maturation. To overcome this dearth, COCs can be exposed to granulosa secreted factors in a two-step system. Therefore, in the first experiment, 1000 nM of C-type natriuretic peptide for 8 h was determined (CAPA), as the best time and concentration to retain oocytes in germinal vesicle stage. This condition, also reduces lipid droplets and increases the expression of ATGL and PLIN2 involved in lipolysis and lipogenesis, respectively. In the second experiment, maturation was stimulated with prostaglandin E2 and amphiregulin for 18 h (CAPA-IVM), and their optimal concentrations based on blastocyst formation rates through in vitro fertilization (IVF) were determined as 1 and 600 nM, respectively. In the third experiment, the in vitro and in vivo developmental competency of SCNT embryos in CAPA-IVM group were determined. Despite similar blastocyst formation rates in IVF and SCNT between CAPA-IVM and C.IVM, the quality of blastocysts were quality was higher in CAPA-IVM, which reflected itself, as higher ICM/TE ratio and also expression of NANOG in SCNT blastocysts. Pregnancy rate, live births rate and SCNT efficiency were not significant between CAPA-IVM and C.IVM groups. Therefore, CAPA-IVM can improve the developmental competency of SCNT derived embryos.

Physiological parameters related to oocyte nuclear differentiation for the improvement of IVM/IVF outcomes in women and cattle

In vitro maturation (IVM) has been applied in numerous different contexts and strategies in humans and animals, but in both cases it represents a challenge still far from being overcome. Despite the large dataset produced over the last two decades on the mechanisms that govern antral follicular development and oocyte metabolism and differentiation, IVM outcomes are still unsatisfactory. This review specifically focuses on data concerning the potential consequences of using supraphysiological levels of FSH during IVM, as well as on the regulation of oocyte chromatin dynamics and its utility as a potential marker of oocyte developmental competence. Taken together, the data revisited herein indicate that a significant improvement in IVM efficacy may be provided by the integration of pre-OPU patient-specific protocols preparing the oocyte population for IVM and more physiological culture systems mimicking more precisely the follicular environment that would be experienced by the recovered oocytes until completion of metaphase II.

Cytosine-phosphate-guanine oligodeoxynucleotides regulate the cell cycle, apoptosis, and steroidogenesis of mouse ovarian granulosa cells by targeting inhibin alpha (1 ~ 32) fragments

Cytosine-phosphate-guanine oligodeoxynucleotides (CpG-ODNs), which exist in vertebrate, bacterial, and viral genomes, are regarded as strong immune adjuvants. To date, the biological activities of CpG-ODNs in reproduction remain unknown. Here, we investigated the effects of CpG-ODNs on the cell cycle, apoptosis, and steroidogenesis in mouse granulosa cells (mGCs), in combination with inhibin alpha (1 ~ 32) fragments. mGCs were transfected with pEGFP (containing green fluorescent protein, as a control), pEGISI (containing inhibin alpha (1 ~ 32) fragments), or pEGISI-CpG-ODNs (containing inhibin alpha (1 ~ 32) fragments and CpG-ODNs motifs) plasmid for 48 h in vitro. Our results showed that the mRNA and protein expression levels of inhibin alpha were downregulated in mGCs transfected with pEGISI-CpG-ODNs, compared to those transfected with pEGISI. Flow cytometry demonstrated that pEGISI-CpG-ODNs transfection promoted cell proliferation (for example, increasing the number of cells in S and G2 phases) and decreased apoptosis, compared to pEGISI transfection. The present study also indicated that the expression of cell cycle-related genes (cyclin D2, cyclin D3, cyclin E1, Cdk2, and Cdk6) was increased, while the expression of apoptosis-related factors (Fas, FasL, caspase-8, and caspase-3) decreased after pEGISI-CpG-ODNs treatment. Additionally, pEGISI-CpG-ODNs reversed the effect of pEGISI on the secretion of estradiol in mGCs, which was further validated by upregulating the levels of its synthesis-related factors (StAR, Cyp11a1, and 17β-HSD II). Nevertheless, pEGISI-CpG-ODNs or pEGISI did not affect the concentration of progesterone nor changed the expression levels of its synthesis-related factors (3β-HSD I and Cyp19a1). In conclusion, this study demonstrated that CpG-ODNs may affect the cell cycle, apoptosis, and steroidogenesis by targeting the effects of inhibin alpha (1 ~ 32) fragments, supporting the potential role of CpG-ODNs in the development of granulosa cells.

Proteomic Exploration of Porcine Oocytes During Meiotic Maturation in vitro Using an Accurate TMT-Based Quantitative Approach

The dynamic changes in protein expression are well known to be required for oocyte meiotic maturation. Although proteomic analysis has been performed in porcine oocytes during in vitro maturation, there is still no full data because of the technical limitations at that time. Here, a novel tandem mass tag (TMT)-based quantitative approach was used to compare the proteomic profiles of porcine immature and in vitro mature oocytes. The results of our study showed that there were 763 proteins considered with significant difference−450 over-expressed and 313 under-expressed proteins. The GO and KEGG analyses revealed multiple regulatory mechanisms of oocyte nuclear and cytoplasmic maturation such as spindle and chromosome configurations, cytoskeletal reconstruction, epigenetic modifications, energy metabolism, signal transduction and others. In addition, 12 proteins identified with high-confidence peptide and related to oocyte maturation were quantified by a parallel reaction monitoring technique to validate the reliability of TMT results. In conclusion, we provided a detailed proteomics dataset to enrich the understanding of molecular characteristics underlying porcine oocyte maturation in vitro.

Effect of cumulin and super-GDF9 in standard and biphasic mouse IVM

PURPOSE

In vitro maturation (IVM) is a technology that generates mature oocytes following culture of immature cumulus-oocyte complexes (COC) in vitro. IVM is characterized by minimal patient stimulation, making it attractive for certain patient groups. Recently, a biphasic IVM system, capacitation (CAPA)-IVM, has shown improved clinical outcomes relative to standard IVM; however, it remains less efficient than IVF. This study assessed whether supplementation of CAPA-IVM culture media with the novel TGFβ superfamily proteins cumulin and super-GDF9 improves subsequent mouse embryo development.

METHODS

Immature mouse COCs were cultured by standard IVM or biphasic IVM ± cumulin or super-GDF9.

RESULTS

Both cumulin and super-GDF9 in standard IVM significantly improved day-6 blastocyst rate (53.9% control, 73.6% cumulin, 70.4% super-GDF9; p = 0.006; n = 382-406 oocytes). Cumulin or super-GDF9 in CAPA-IVM did not alter embryo yield or blastocyst cell allocation in an unstimulated model. Moreover, cumulin did not alter these outcomes in a mild PMSG stimulation model. Cumulin in CAPA-IVM significantly increased cumulus cell expression of cumulus expansion genes (Ptgs2, Ptx3, Adamts1, Gfat2) and decreased Lhr expression relative to control. However, cumulin-induced mRNA expression of cumulus cell (Ptgs2, Ptx3) and oocyte genes (Gdf9, Bmp15, Oct4, Stella) in CAPA-IVM remained significantly lower than that of in vivo matured cells.

CONCLUSION

Cumulin did not provide an additional beneficial effect in biphasic IVM in terms of blastocyst yield and cell allocation; however in standard IVM, cumulin and super-GDF9 significantly improve oocyte developmental competence.

Factors Influencing the In Vitro Maturation (IVM) of Human Oocyte

In vitro maturation (IVM) of oocytes is a promising assisted reproductive technology (ART) deemed as a simple and safe procedure. It is mainly used in patients with impaired oocyte maturation and in fertility preservation for women facing the risk of losing fertility. However, to date, it is still not widely used in clinical practice because of its underperformance. The influencing factors, such as biphasic IVM system, culture medium, and the supplementation, have a marked effect on the outcomes of oocyte IVM. However, the role of different culture media, supplements, and follicular priming regimens in oocyte IVM have yet to be fully clarified and deserve further investigation.

Approaches to oocyte meiotic arrest in vitro and impact on oocyte developmental competence

Oocytes are maintained in a state of meiotic arrest following the first meiotic division until ovulation is triggered. Within the antral follicle, meiotic arrest is actively suppressed in a process facilitated by the cyclic nucleotides cGMP and cAMP. If removed from this inhibitory follicular environment and cultured in vitro, mammalian oocytes undergo spontaneous meiotic resumption in the absence of the usual stimulatory follicular stimuli, leading to asynchronicity with oocyte cytoplasmic maturation and lower developmental competence. For more than 50 years, pharmacological agents have been used to attenuate oocyte germinal vesicle (GV) breakdown in vitro. Agents which increase intra-oocyte cAMP or prevent its degradation have been predominantly used, however agents such as kinase and protein synthesis inhibitors have also been trialled. Twenty years of research demonstrates that maintaining GV arrest for a period before in vitro maturation (IVM) improves oocyte developmental competence, and is likely attributed to maintenance of bidirectional communication with cumulus cells leading to improved oocyte metabolic function. However, outcomes are influenced by various factors including the mode of action of the modulators, dose, treatment duration, species, and the degree of hormonal priming of the oocyte donor. Cyclic GMP and/or cAMP modulation in a prematuration step (called pre-IVM) prior to IVM has shown the greatest consistency in improving oocyte developmental competence, whereas kinase and protein synthesis inhibitors have proven less effective at improving IVM outcomes. Such pre-IVM approaches have shown potential to alter current use of artificial reproductive technologies in medical and veterinary practice.

A Nuclear and Cytoplasmic Characterization of Bovine Oocytes Reveals That Cysteamine Partially Rescues the Embryo Development in a Model of Low Ovarian Reserve

Simple Summary

Women’s reproductive performance starts declining in the mid-30s, and by age 40–45, the possibility of becoming pregnant becomes very small. Reproductive aging is a physiological process of fertility decline characterized by a decrease in quality and stockpile of eggs (also called ovarian reserve) in most mammals. However, young individuals too can show an accelerated reproductive aging that similarly results in a low ovarian reserve and hypofertility. This syndrome, called premature ovarian failure (POF), is becoming a relevant problem due to the general tendency to postpone the first pregnancy. In this study, we used bovine ovaries that were classified in two categories, according to the number of follicles visible on the ovarian surface, and analyzed some parameters of egg maturation. We observed that eggs from the ‘aging-like’ ovaries carry several defects that impair maturation. However, one of the parameters was improved upon supplementation with a scavenger of free radicals, providing a proof of concept that in-depth knowledge of the cellular mechanisms is essential to find solutions to everyday-life problems.

Abstract

Decreased oocyte quality is a major determinant of age-associated fertility decline. Similarly, individuals affected by early ovarian aging carry low-quality oocytes. Using an established bovine model of early ovarian aging, we investigated key features of ‘quality’ oocyte maturation, associated with the onset of egg aneuploidy and reproductive aging, such as histone modifications, mitochondria distribution and activity, reduced glutathione (GSH) content, and gap junction functionality. Bovine ovaries were classified according to the antral follicle count (AFC), and the retrieved oocytes were processed immediately or matured in vitro. We observed alterations in several cellular processes, suggesting a multifactorial etiology of the reduced oocyte quality. Furthermore, we performed a rescue experiment for one of the parameters considered. By adding cysteamine to the maturation medium, we experimentally increased the free radical scavenger ability of the ‘low competence’ oocytes and obtained a higher embryo development. Our findings show that adopting culture conditions that counteract the free radicals has a positive impact on the quality of ‘compromised’ oocytes. Specifically, cysteamine treatment seems to be a promising option for treating aging-related deficiencies in embryo development.

Perspectives on the development and future of oocyte IVM in clinical practice

Oocyte in vitro maturation (IVM) is an assisted reproductive technology designed to obtain mature oocytes following culture of immature cumulus-oocyte complexes collected from antral follicles. Although IVM has been practiced for decades and is no longer considered experimental, the uptake of IVM in clinical practice is currently limited. The purpose of this review is to ensure reproductive medicine professionals understand the appropriate use of IVM drawn from the best available evidence supporting its clinical potential and safety in selected patient groups. This group of scientists and fertility specialists, with expertise in IVM in the ART laboratory and/or clinic, explore here the development of IVM towards acquisition of a non-experimental status and, in addition, critically appraise the current and future role of IVM in human ART.

Enhancing Oocyte Competence With Milrinone as a Phosphodiesterase 3A Inhibitor to Improve the Development of Porcine Cloned Embryos

The objective of this study was to investigate the effect of milrinone supplementation as a phosphodiesterase 3A inhibitor during in vitro maturation (IVM) to coordinate the cytoplasmic and nuclear maturation of porcine oocytes and subsequent development of porcine cloned embryos. Brilliant cresyl blue (BCB)-stained (BCB +) oocytes, classified as well-developed, and BCB− oocytes were used in parthenogenesis (PA) and cloning, and their preimplantation development was compared. In PA embryos, BCB + oocytes had significantly higher rates of development than BCB− oocytes in terms of maturation (87.5 vs. 71.3%), cleavage (88.6 vs. 76.3%), and blastocyst development (34.3 vs. 25.3%) and also had higher cell numbers (46.9 vs. 38.9%), respectively (p < 0.05). In cloned embryos, the BCB + group also had a significantly higher blastocyst formation rate than the BCB− group (30.6 vs. 20.1%; p < 0.05). Supplementation with 75 μM milrinone during IVM of BCB− oocytes showed improvement in maturation and blastocyst development rates, which may be due to the coordinated maturation of the cytoplasm with the nucleus as an effect of milrinone. Moreover, the analysis of nuclear reprogramming via the examination of the expression levels of the reprogramming-related genes POU5F1, DPPA2, and NDP52IL in milrinone-supplemented BCB− oocytes showed higher expression levels than that in non-treated BCB− oocytes. These findings demonstrate that milrinone is useful in improving developmental competence in less competent oocytes during IVM and for proper nuclear reprogramming in the production of porcine cloned embryos by coordinating cytoplasmic and nucleus maturation.

Bone morphogenetic protein 15 supplementation enhances cumulus expansion, nuclear maturation and progesterone production of in vitro-matured bovine cumulus-oocyte complexes

In vitro embryo production (IVP) efficiency is reduced when compared to in vivo. The basic knowledge of bovine in vitro oocyte maturation (IVM) mechanisms provides support to improve in vitro embryo production yields. The present study assessed the effects of bone morphogenetic protein 15 (BMP15), fibroblast growth factor 16 (FGF16) and their combined action on cumulus cells (CC) expansion, oocyte and CC DNA fragmentation, oocyte nuclear maturation, energetic metabolism and progesterone production in bovine IVM. Cumulus-oocyte complexes (COC) were matured in control or supplemented media containing BMP15 (100 ng/ml), FGF16 (10 ng/ml) or BMP15 combined with FGF16; and assessed at 0 and 22 hr of IVM. BMP15 alone or its association with FGF16 enhanced cumulus expansion. BMP15 decreased DNA fragmentation in both CC and oocytes, and improved oocyte nuclear maturation rate. In addition, BMP15 increased CC progesterone production, an effect not previously reported. The present study reinforces previous data pointing to a beneficial influence of BMP15 during IVM, while providing novel evidence that the underlying mechanisms involve increased progesterone production.

R-Spondin 2 and WNT/CTNNB1 Signaling Pathways Are Required for Porcine Follicle Development and In Vitro Maturation

The secretion of oocyte-derived paracrine factors, such as R-spondin2, is an essential mechanism for follicle growth by promoting the proliferation and differentiation of cumulus cells around oocytes. In the present study, we aimed to identify the effect of R-spondin2 during follicular development. First, R-spondin2-related factors (R-spondin2, CTNNB1, LGR4, and LGR5) were identified through immunofluorescence in porcine ovarian tissue. CTNNB1 was expressed in ooplasm, and CTNNB1 and LGR4 were expressed in granulosa cells. In addition, R-spondin2, LGR4, and LGR5 were expressed in the theca interna. These results imply that these proteins play a major role in porcine follicular development. In addition, the effects of R-spondin2 on the in vitro maturation process of porcine cumulus oocyte complexes and subsequent embryonic development were confirmed. A treatment of 100 ng/mL R-spondin2 in the in vitro maturation (IVM) process increased nuclear maturation and increased the expression of EGFR mRNA in cumulus cells. The EGFR-ERK signal is essential for oocyte maturation, ovulation, and luteinization. R-spondin2 treatment also increased the expression of CTNNB1 and EGFR in primary cultured cumulus cells. In conclusion, RSPO2 and WNT/CTNNB1 signaling pathways are required for porcine follicle development and are predicted to be involved in the EGFR-ERK signaling pathway.

Treatment of in vitro-Matured Bovine Oocytes With Tauroursodeoxycholic Acid Modulates the Oxidative Stress Signaling Pathway

In several species, oocyte and embryo competence are improved by the addition of endoplasmic reticulum (ER) stress inhibitors to in vitro maturation (IVM) medium and/or in vitro culture (IVC) medium. This study aimed to evaluate the effects of three concentrations of tauroursodeoxycholic acid (TUDCA; 50, 200, and 1,000 μM), a chemical chaperone for relieving ER stress, during IVM of bovine cumulus-oocyte complexes (COCs) for 24 h. Treated oocytes were analyzed for nuclear maturation, reactive oxygen species (ROS) production, mitochondrial activity, and abundance of target transcripts. In addition, the number of pronuclei in oocytes was evaluated after 18-20 h of insemination, and the rates of blastocyst and hatched blastocyst formation were evaluated after 7 and 8/9 days of culture, respectively. We further evaluated the transcript abundance of embryonic quality markers. Our findings showed that supplementation of IVM medium with 200 μM of TUDCA decreased ROS production and increased abundance of transcripts related to antioxidant activity in oocytes (CAT, GPX1, and HMOX1) and embryos (GPX1 and PRDX3). Interestingly, high concentration of TUDCA (1,000 μM) was toxic to oocytes, reducing the nuclear maturation rate, decreasing mitochondrial activity, and increasing the abundance of ER stress (HSPA5) and cellular apoptosis (CASP3 and CD40) related transcripts. The results of this study suggest that treatment with 200 μM of TUDCA is associated with a greater resistance to oxidative stress and indirectly with ER stress relief in bovine oocytes.

Molecular characteristics of oocytes and somatic cells of follicles at different sizes that influence in vitro oocyte maturation and embryo production

During the last 10 to 15 yr, in vitro research to predict antral follicle growth and oocyte maturation has delivered interesting advances in the knowledge of processes regulating follicle growth and developmental competence of oocytes. This review discusses the contribution of cumulus and mural granulosa cells in the process of oocyte maturation and cumulus expansion in cumulus-oocyte complexes (COCs) from follicles of different sizes and shows that differences in gene expression in oocytes, granulosa, and theca cells of small and large follicles impact the success of in vitro blastocyst development. In addition, the molecular mechanisms by which COC metabolism and antioxidant defense provide oocyte competence are highlighted. Furthermore, new insights and perspectives on molecular and cellular regulation of in vitro oocyte maturation are emphasized.

miR-532-3p: a possible altered miRNA in cumulus cells of infertile women with advanced endometriosis

RESEARCH QUESTION

Is the profile of microRNA (miRNA) altered in cumulus cells of infertile women with early (EI/II) and advanced (EIII/IV) endometriosis?

DESIGN

In this prospective case-control study, a miRNA profile including 754 targets was evaluated in samples of cumulus cells from infertile women with endometriosis (5 EI/II, 5 EIII/IV) and infertile controls (5, male and/or tubal factor) undergoing ovarian stimulation for intracytoplasmic sperm injection, using TaqMan® Array Human MicroRNA Cards A and B. The groups were compared with Kruskal-Wallis test, followed by Benjamini-Hochberg correction and Dunn's post hoc test. An in silico enrichment analysis was performed to list the possibly altered pathways in which the altered miRNA target genes are involved.

RESULTS

Only the miRNA miR-532-3p showed significant differences among the analysed groups, being down-regulated in the EIII/IV group compared with the infertile control group, as well as compared with the EI/II group. The enrichment analysis showed that some genes regulated by this miRNA are involved in important pathways for the acquisition of oocyte competence, such as the oxytocin, calcium, Wnt, FoxO, ErbB and Ras signalling pathways, as well as the oocyte meiosis pathway.

CONCLUSION

The present findings bring new perspectives to understanding the follicular microenvironment of infertile women with different stages of endometriosis. It is suggested that the dysregulation of miR-532-3p may be a potential mechanism involved in the aetiopathogenesis of endometriosis-related infertility. Further studies are needed to evaluate these pathways in cumulus cells of infertile women with the disease, as well as their impact on the acquisition of oocyte competence.

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.

Prokineticin 1 is a new biomarker of human oocyte competence: expression and hormonal regulation throughout late folliculogenesis

CONTEXT

Prokineticin 1 (PROK1) quantification in global follicular fluid (FF) has been recently reported as a predictive biomarker of in vitro fertilization (IVF) outcome. It is now necessary to evaluate its clinical usefulness in individual follicles.

OBJECTIVES

To evaluate the clinical value of PROK1 secretion in individual FF to predict oocyte competence. To determine the impact of follicular size, oocyte maturity, and gonadotropin treatments on PROK1 secretion.

DESIGN AND SETTING

Prospective cohort study from May 2015 to May 2017 at the University Hospital of Grenoble.

PATIENTS

A total of 69 infertile couples underwent IVF.

INTERVENTION(S)

Collection of 298 individual FF from 44 women undergoing IVF; 52 individual cumulus cell (CC) samples and 15 CC primary cultures from 25 women undergoing IVF-intracytoplasmic sperm injection (ICSI).

MAIN OUTCOME MEASURE(S)

Oocyte competence was defined as the ability to sustain embryo development to the blastocyst stage. Follicular size was measured by 2D-sonography. PROK1 concentration was quantified by ELISA assay.

RESULTS

PROK1 concentration was correlated to follicular size (r = 0.85, P = 2.2 × 10-16). Normalized PROK1 concentration in FF was predictive of subsequent oocyte competence (AUROC curve = 0.76 [95% CI, 0.69-0.83]; P = 1.7 × 10-9), irrespectively of day-2 embryo morphokinetic parameters. The expression and secretion of PROK1 were increased in FF and CC of mature oocytes (P < 0.01). Follicle Stimulating Hormone and hCG up-regulated PROK1 secretion in CC primary cultures (P < 0.01; P < 0.05), probably through the cAMP pathway (P < 0.01).

CONCLUSIONS

PROK1 quantification in individual FF could constitute a new predictive biomarker of oocyte competence in addition with embryo morphokinetic parameters.

TRIAL REGISTRATION NUMBER

none.

The SPOM-adapted IVM system improves in vitro production of bovine embryos

This study aimed to test the effects of an IVM SPOM adaptation (SPOM-adapted IVM) on the production, total number of cells (TNC), apoptosis, and cryotolerance (post-warming survival and cytoskeleton actin integrity) of bovine IVP embryos. Two experiments were conducted with two experimental groups based on IVM treatment: A control group (TCM 199 without FCS) and an SPOM-adapted group (TCM 199 with forskolin and IBMX in pre-IVM and IVM with cilostamide). The first experiment evaluated embryo in vitro production, TNC, and apoptosis rate on D9 of development. In the second experiment, embryos were vitrified/warmed at D7 (control fresh and vitrified; SPOM-adapted fresh and vitrified) and assessed regarding post-warming survival rates and cytoskeleton actin integrity. Statistical analysis was performed using GraphPad INSTAT software at a significance level of 5%. An increase (p < 0.05) in blastocyst production was observed in the SPOM-adapted group comparing to the control group. There was no difference (p > 0.05) in the TNC or apoptosis rate between the groups. Regarding cryopreservation, no differences were found (p > 0.05) in actin integrity or post-warming survival rates between the vitrified groups. In both vitrified groups, we observed a significantly lower uninjured pattern of actin integrity compared to the fresh groups (p < 0.05). We conclude that the SPOM-adapted IVM system is beneficial for blastocyst production and does not affect the quality and cryotolerance of the produced embryos.

In vivo and in vitro activation of dormant primordial follicles by EGF treatment in mouse and human

In the mammalian ovaries, dormant primordial follicles represent the reproductive reserve of individual females. Recently, stimulating the activation of primordial follicles in vitro has been practiced, making the utilization of those dormant follicles to treat female infertility possible. However, there are still lacks of effective upstream molecule and strategy to elevate follicle activation in vivo. In the current study, we revealed that growth factor EGF improved a transiently primordial follicle activation in mice by elevating the CDC42-PI3K signaling activity, and EGF treatment also improved the activation and development of human follicles in ovarian cortical pieces. Using a liquid-solid phase transition bio-gel as a carrier, an efficient in vivo activation system was established by ovarian topical EGF administration to living mice. We found that EGF treatment led to an increase of primordial follicle activation in short time but had no effect on long-term fertility in females. By establishing an inducible premature ovarian insufficiency (POI) mouse model through selectively ablating growing follicles in Zp3-Cre;iDTR mice, we further revealed that our in vivo EGF treatment system improved primordial follicle activation and ovulation of POI ovaries significantly. Taken together, our results revealed that in situ ovarian EGF administration could improve the activation of primordial follicles in living animals, and manipulating activation and development of primordial follicles in vivo might be an efficient approach to improve reproductive health in women.

In Vitro Maturation of Fully Grown Mouse Antral Follicles in the Presence of 1 nM 2-Hydroxyestradiol Improves Oocytes' Developmental Competence

Cathecolestrogens are estradiol metabolites produced during folliculogenesis in the mammalian ovary. 2-Hydroxyestradiol (2-OHE₂) is one of the most abundant although its role remains unknown. The aim of this study is to investigate whether the presence of 2-OHE₂ during the germinal vesicle-to-metaphase II transition affects oocyte meiotic and preimplantation developmental competence. Mouse cumulus-oocyte complexes (COCs), isolated from fully grown antral follicles, were in vitro–matured (IVM) in the presence of 2-OHE₂ (0.1, 1, 10 or 100 nM) for 6 or 15 h; then, their meiotic and developmental competence was evaluated using a number of cytological quality markers. With the exception of the highest dose (100 nM), the addition of 2-OHE₂ to the IVM medium, did not alter, compared with untreated control, the frequency of oocytes that reached the MII stage. Instead, IVM in the presence of 1 nM 2-OHE₂ highly increased the rate of preimplantation development and blastocyst quality. To understand whether this positive effect could be attributed to the events occurring during meiosis resumption, we analysed a number of specific cytological quality markers of the asymmetric division, such as PB-I volume and position, presence and extension of the cortical F-actin cap, meiotic spindle shape and area, and microtubule organisation centre localisation. The results highlighted how the presence of 1 nM 2-OHE₂ significantly improved the overall cytological organisation required for a correct asymmetric division. Our results contribute a first step to acknowledge a potential role of this estradiol metabolite during the GV-to-MII transition, contributing to the acquisition of oocytes developmental competence.

Effect of environmental contamination on female and male gametes - A lesson from bovines

Endocrine-disrupting compounds (EDCs) and foodborne contaminants are environmental pollutants that are considered reproductive toxicants due to their deleterious effects on female and male gametes. Among the EDCs, the phthalate plasticizers are of growing concern. In-vivo and in-vitro models indicate that the oocyte is highly sensitive to phthalates. This review summarizes the effects of di(2-ethylhexyl) phthalate and its major metabolite mono(2-ethyhexyl) phthalate (MEHP) on the oocyte. MEHP reduces the proportion of oocytes that fertilize, cleave and develop to the blastocyst stage. This is associated with negative effects on meiotic progression, and disruption of cortical granules, endoplasmic reticulum and mitochondrial reorganization. MEHP alters mitochondrial membrane polarity, increases reactive oxygen species levels and induces alterations in genes associated with oxidative phosphorylation. A carryover effect from the oocyte to the blastocyst is manifested by alterations in the transcriptomic profile of blastocysts developed from MEHP-treated oocytes. Among foodborne contaminants, the pesticide atrazine (ATZ) and the mycotoxin aflatoxin B1 (AFB1) are of high concern. The potential hazards associated with exposure of spermatozoa to these contaminants and their carryover effect to the blastocyst are described. AFB1 and ATZ reduce spermatozoa's viability, as reflected by a high proportion of cells with damaged plasma membrane; induce acrosome reaction, expressed as damage to the acrosomal membrane; and interfere with mitochondrial function, characterized by hyperpolarization of the membrane. ATZ and AFB1-treated spermatozoa show a high proportion of cells with fragmented DNA. Exposure of spermatozoa to AFB1 and ATZ reduces fertilization and cleavage rates, but not that of blastocyst formation. However, fertilization with AFB1- or ATZ-treated spermatozoa impairs transcript expression in the formed blastocysts, implying a carryover effect. Taken together, the review indicates the risk of exposing farm animals to environmental contaminants, and their deleterious effects on female and male gametes and the developing embryo.

Can extracellular vesicles from bovine ovarian follicular fluid modulate the in-vitro oocyte meiosis progression similarly to the CNP-NPR2 system?

C-type natriuretic peptide (CNP) and its natriuretic peptide receptors subtype 2 (NPR2) are essential for the maintenance of oocyte meiotic arrest in different species. Extracellular vesicles (EVs) in bovine follicular fluid (FF) are important for cell communication within the ovarian follicle. This study investigated the involvement of EVs from FF of bovine ovarian follicles in the CNP-NPR2 system, first by analyzing the presence of CNP in the EV contents, followed by addition of EVs to in-vitro maturation (IVM) medium, to evaluate the effect on maintenance of oocyte meiosis arrest and improvements in in-vitro embryo production. As expected, CNP was observed in FF and granulosa cells from the ovarian follicles. To the best of our knowledge, this is the first time that CNP has been found in the EV contents. To evaluate the possible effect of EVs on the progression of oocyte meiosis, the IVM was performed under three conditions: CNP and EV supplementation and control condition. Both the CNP and EV treatments inhibited meiosis resumption in the oocyte within 9 h of IVM. CNP treatment increased cGMP levels in cumulus cells within 6 h of IVM compared to the control group, but the EV treatment did not. In contrast, the relative mRNA abundance of adenylate cyclase 3 and 9 (ADCY3 and ADCY9) was upregulated in oocytes after 6 h of IVM under EV treatment compared to the control group, but not under CNP treatment. Last, these treatments in the IVM medium had no significant effect on the in-vitro embryo production. In conclusion, we demonstrated the presence of endogenous CNP in bovine reproductive structures, especially in the EVs from the FF of antral follicles. The presence of CNP in the EVs suggests an important involvement of this cell-communication system in the CNP-NPR2 system. Therefore, we indeed observed that the EVs from FF can modulate the arrest of oocyte meiosis, acting similarly to the CNP-NPR2 system to block the oocyte in the GV state. However, the mechanism of each system might be different; the CNP-NPR2 system seems to be involved in modulating the cGMP levels, while the contents of EVs might be involved in modulating the cAMP levels.

Effects of Short-Term Inhibition of Rho Kinase on Dromedary Camel Oocyte In Vitro Maturation

Simple Summary

Our results revealed, for the first time, that short-term inhibition of Rho-associated protein kinases (ROCK) for 4 h prior to in vitro maturation (IVM) in a biphasic IVM approach improved oocyte nuclear maturation, producing more MII oocyte, through modulating the expression of cytokinesis- and antiapoptosis-related mRNA transcripts. This positive result suggests ROCK inhibitor as a potential candidate molecule to exploit in the control of oocyte meiotic maturation.

Abstract

This is the first report on a biphasic in vitro maturation (IVM) approach with a meiotic inhibitor to improve dromedary camel IVM. Spontaneous meiotic resumption poses a major setback for in vitro matured oocytes. The overall objective of this study was to improve in vitro maturation of dromedary camel oocytes using ROCK inhibitor (Y-27632) in a biphasic IVM to prevent spontaneous meiotic resumption. In the first experiment, we cultured immature cumulus–oocyte complexes (COCs, n = 375) in a prematuration medium supplemented with ROCK inhibitor (RI) for 2 h, 4 h, 6 h, and 24 h before submission to normal in vitro maturation to complete 28 h. The control was cultured for 28 h in the absence of RI. In the first phase of experiment two, we cultured COCs (n = 480) in the presence or absence (control) of RI for 2 h, 4 h, 6 h, and 24 h, and conducted real-time relative quantitative PCR (qPCR) on selected mRNA transcripts. The same was done in the second phase, but qPCR was done after completion of normal IVM. Assessment of nuclear maturation showed that pre-IVM for 4 h yielded an increase in MII oocyte (54.67% vs. 26.6% of control; p < 0.05). As expected, the same group showed the highest degree (2) of cumulus expansion. In experiment 2, qPCR results showed significantly higher expression of ACTB and BCL2 in the RI group treated for 4 h when compared with the other groups. However, their relative quantification after biphasic IVM did not reveal any significant difference, except for the positive response of BCL2 and BAX/BCL2 ratio after 4 and 6 h biphasic IVM. In conclusion, RI prevents premature oocyte maturation and gave a significantly positive outcome during the 4 h treatment. This finding is a paradigm for future investigation on dromedary camel biphasic IVM and for improving the outcome of IVM in this species.

Granulosa secreted factors improve the developmental competence of cumulus oocyte complexes from small antral follicles in sheep

Oocyte in vitro maturation can be improved by mimicking the intra-follicular environment. Oocyte, cumulus cells, granulosa cells, and circulating factors act as meiotic regulators in follicles and maintain oocyte in the meiotic phase until oocyte becomes competent and ready to be ovulated. In a randomized experimental design, an ovine model was used to optimize the standard in vitro maturation media by Granulosa secreted factors. At first, the development capacity of oocyte derived from medium (>4 to 6 mm) and small (2 to ≤4 mm) size follicles was determined. Differential gene expression of granulosa secreted factors and their receptors were compared between the cumulus cells of the two groups. Then, the best time and concentration for arresting oocytes at the germinal vesicle stage by natriuretic peptide type C (CNP) were determined by nuclear staining in both groups. Oocyte quality was further confirmed by calcein uptake and gene expression. The developmental competence of cumulus oocyte complexes derived from small size follicles that were cultured in the presence of CNP in combination with amphiregulin (AREG) and prostaglandin E2 (PGE2) for 24 h was determined. Finally, embryo quality was specified by assessing expressions of NANOG, SOX2, CDX2, OCT4, and TET1. The cumulus oocyte complexes derived from small size follicles had a lower capacity to form blastocyst in comparison with cumulus oocyte complexes derived from medium size follicles. Prostaglandin E receptor 2 and prostaglandin-endoperoxide synthase 2 had significantly lower expression in cumulus cells derived from small size follicles in comparison with cumulus cells derived from medium size follicles. Natriuretic peptide type C increased the percentage of cumulus oocyte complexes arresting at the germinal vesicle stage in both oocytes derived from medium and small follicles. Gap junction communication was also improved in the presence of natriuretic peptide type C. In oocytes derived from small size follicles; best blastocyst rates were achieved by sequential exposure of cumulus oocyte complexes in [TCM+CNP (6 h), then cultured in TCM+AREG+PGE2 (18h)] and [TCM+CNP (6 h), then cultured in conventional IVM supplements+AREG+PGE2 (18h)]. Increased SOX2 expression was observed in [TCM+CNP (6 h), then cultured in TCM+AREG+PGE2 (18h)], while decreased OCT4 expression was observed in [TCM+CNP (6 h), then cultured in conventional IVM supplements+AREG+PGE2 (18h)]. It seems that the natriuretic peptide type C modulates meiotic progression, and oocyte development is probably mediated by amphiregulin and prostaglandin E2. These results may provide an alternative IVM method to optimize in vitro embryo production in sheep and subsequently for humans.

Extracellular vesicle mediated molecular signaling in ovarian follicle: Implication for oocyte developmental competence

The bidirectional communication between the oocyte and the companion somatic cells in the follicular environment is known to be mediated by either a direct communication via gap junction or transzonal projections or indirectly through endocrine, paracrine and autocrine signaling factors. Extracellular vesicles (EVs), which are found in various biological fluids, including follicular fluid (FF) are known to play important roles in mediating the communication between the oocyte and the surrounding somatic cells through shuttling bioactive molecules to facilitate follicular growth and oocyte maturation. As vesicles in the extracellular space are known to reflect the physiological status of the donor or the releasing cells, molecules carried by the EVs in the follicular environment could be markers of the internal and external stressors. EVs exhibit greater degree of heterogeneity in their size, biogenesis and the bioactive molecule they carry. The process of biogenesis of EVs is known to be regulated by several proteins associated with the endosomal sorting complex required for transport (ESCRT) proteins. The type of EVs and surface proteins markers vary according to the type of protein involved in their biogenesis. EVs are recently reported to play indispensable role in promoting cell-to-cell communication during follicular growth. Recent advancements in EV research opened the possibilities to load EVs with specific molecules like miRNA, siRNA, CRISPR-cas9 complex and protein, which showed a new horizon for their application in therapeutics. The present review explores the biogenesis, the role and the future prospects of EVs with a special emphasis given to follicular growth and oocyte maturation.

Effects of glucose metabolism pathways on nuclear and cytoplasmic maturation of pig oocytes

The developmental competence of IVM porcine oocytes is still low compared with that in their in vivo counterparts. Although many studies reported effects of glucose metabolism (GM) on oocyte nuclear maturation, few reported on cytoplasmic maturation. Previous studies could not differentiate whether GM of cumulus cells (CCs) or that of cumulus-denuded oocytes (DOs) supported oocyte maturation. Furthermore, species differences in oocyte GM are largely unknown. Our aim was to address these issues by using enzyme activity inhibitors, RNAi gene silencing and special media that could support nuclear but not cytoplasmic maturation when GM was inhibited. The results showed that GM in CCs promoted pig oocyte maturation by releasing metabolites from both pentose phosphate pathway and glycolysis. Both pyruvate and lactate were transferred into pig DOs by monocarboxylate transporter and pyruvate was further delivered into mitochondria by mitochondrial pyruvate carrier in both pig DOs and CCs. In both pig DOs and CCs, pyruvate and lactate were utilized through mitochondrial electron transport and LDH-catalyzed oxidation to pyruvate, respectively. Pig and mouse DOs differed in their CC dependency for glucose, pyruvate and lactate utilization. While mouse DOs could not, pig DOs could use the lactate-derived pyruvate.

A novel role of SIRT2 in regulating gap junction communications via connexin-43 in bovine cumulus-oocyte complexes

SIRT2, the predominantly cytosolic sirtuin, plays important role in multiple biological processes, including metabolism, stress response, and aging. However, the function of SIRT2 in gap junction intercellular communications (GJICs) of cumulus-oocyte complexes (COCs) is not yet known. The purpose of the present study was to evaluate the effect and underlining mechanism of SIRT2 on GJICs in COCs. Here, we found that treatment with SIRT2 inhibitors (SirReal2 or TM) inhibited bovine oocyte nuclear maturation. Further analysis revealed that SIRT2 inactivation disturbed the GJICs of COCs during in vitro maturation. Correspondingly, both the Cx43 phosphorylation levels and MEK/MER signaling pathways were induced by SIRT2 inhibition. Importantly, SIRT2-mediated Cx43 phosphorylation was completely abolished by treatment with MEK1/2 inhibitor (Trametinib). Furthermore, treatment with SIRT2 inhibitors resulted in the high levels of MEK1/2 acetylation. Functionally, downregulating the MER/ERK pathways with inhibitors (Trametinib or SCH772984) could attenuate the closure of GJICs caused by SIRT2 inactivation in partly. In addition, inhibition of SIRT2 activity significantly decreased the membrane and zona pellucida localization of Cx43 by upregulating the levels of Cx43 acetylation. Taken together, these results demonstrated a novel role that SIRT2 regulates GJICs via modulating the phosphorylation and deacetylation of Cx43 in COCs.

Effects of cyclic adenosine monophosphate modulators on maturation and quality of vitrified-warmed germinal vesicle stage mouse oocytes

BACKGROUND

It is still one of the unresolved issues if germinal vesicle stage (GV) oocytes can be successfully cryopreserved for fertility preservation and matured in vitro without damage after warming. Several studies have reported that the addition of cyclic adenosine monophosphate (cAMP) modulators to in vitro maturation (IVM) media improved the developmental potency of mature oocytes though vitrification itself provokes cAMP depletion. We evaluated whether the addition of cAMP modulators after GV oocytes retrieval before vitrification enhances maturation and developmental capability after warming of GV oocytes.

METHODS

Retrieved GV oocytes of mice were divided into cumulus-oocyte complexes (COCs) and denuded oocytes (DOs). Then, GV oocytes were cultured with or without dibutyryl-cAMP (dbcAMP, cAMP analog) and 3-isobutyl-l-methylxanthine (phosphodiesterase inhibitor) during the pre-vitrification period for 30 min.

RESULTS

One hour after warming, the ratio of oocytes that stayed in the intact GV stage was significantly higher in groups treated with cAMP modulators. After 18 h of IVM, the percentage of maturation was significantly higher in the COC group treated with dbcAMP. The expression of F-actin, which is involved in meiotic spindle migration and chromosomal translocation, is likewise increased in this group. However, there was no difference in chromosome and spindle organization integrity or developmental competence between the MII oocytes of all groups.

CONCLUSIONS

Increasing the intracellular cAMP level before vitrification of the GV oocytes maintained the cell cycle arrest, and this process may facilitate oocyte maturation after IVM by preventing cryodamage and synchronizing maturation between nuclear and cytoplasmic components. The role of cumulus cells seems to be essential for this mechanism.

Luteinizing Hormone Action in Human Oocyte Maturation and Quality: Signaling Pathways, Regulation, and Clinical Impact

The ovarian follicle luteinizing hormone (LH) signaling molecules that regulate oocyte meiotic maturation have recently been identified. The LH signal reduces preovulatory follicle cyclic nucleotide levels which releases oocytes from the first meiotic arrest. In the ovarian follicle, the LH signal reduces cyclic nucleotide levels via the CNP/NPR2 system, the EGF/EGF receptor network, and follicle/oocyte gap junctions. In the oocyte, reduced cyclic nucleotide levels activate the maturation promoting factor (MPF). The activated MPF induces chromosome segregation and completion of the first and second meiotic divisions. The purpose of this paper is to present an overview of the current understanding of human LH signaling regulation of oocyte meiotic maturation by identifying and integrating the human studies on this topic. We found 89 human studies in the literature that identified 24 LH follicle/oocyte signaling proteins. These studies show that human oocyte meiotic maturation is regulated by the same proteins that regulate animal oocyte meiotic maturation. We also found that these LH signaling pathway molecules regulate human oocyte quality and subsequent embryo quality. Remarkably, in vitro maturation (IVM) prematuration culture (PMC) protocols that manipulate the LH signaling pathway improve human oocyte quality of cultured human oocytes. This knowledge has improved clinical human IVM efficiency which may become a routine alternative ART for some infertile patients.

Capacitation IVM improves cumulus function and oocyte quality in minimally stimulated mice

PURPOSE

Oocyte in vitro maturation (IVM) is a patient-friendly reproductive technology but lower success rates than IVF have limited its uptake. Capacitation-IVM (CAPA-IVM) is an innovative new IVM system currently undergoing clinical evaluation. This study aimed to determine temporal effects of the pre-IVM phase of CAPA-IVM on cumulus function and oocyte developmental competence in mildly-stimulated mice.

METHODS

Immature cumulus oocyte complexes (COCs) derived from mildly stimulated (23 h PMSG) 28-day-old mice underwent pre-IVM for 0-24 h in medium containing c-type natriuretic peptide (CNP), E₂, FSH and insulin, prior to IVM (CAPA-IVM). The effect of pre-IVM duration on cumulus cell function and embryo development post-CAPA-IVM/IVF was assessed.

RESULTS

Day 6 blastocyst rate increased incrementally with increasing pre-IVM duration: 40.6 ± 2.0%, 45.8 ± 1.2%, 52.2 ± 3.5%, 53.3 ± 5.9%, and 59.9 ± 2.5% for 0, 2, 6, 12, and 24 h pre-IVM, respectively (P < 0.01). DNA content/COC, a measure of cumulus cell proliferation, was significantly higher with 24 h pre-IVM group compared to 0, 2, or 6 h pre-IVM (P < 0.001). Pre-IVM for 24 h significantly increased cumulus expansion and mRNA expression of matrix genes Has2 and Tnfaip6 and Areg relative to no pre-IVM control (P < 0.01). Cumulus-oocyte gap-junctional communication (GJC) was maintained throughout 24 h pre-IVM (P < 0.0001), and GJC loss was slowed during the subsequent IVM phase, whilst meiotic resumption was accelerated (P < 0.05). Pre-IVM increased COC ATP and ADP content (P < 0.05), but not AMP, ATP/ADP, and energy charge.

CONCLUSION

The pre-IVM phase of CAPA-IVM improves the quality of IVM oocytes in a temporally dependent manner and significantly influences cumulus cell function including increased cell proliferation, cumulus expansion, and prolonged cumulus-oocyte GJC.