Oocyte Vitrification Reduces its Capability to Repair Sperm DNA Fragmentation and Impairs Embryonic Development

Oocytes play a crucial role in repairing sperm DNA damage, which can affect the next generation; however, certain factors can impair this ability. This study examined whether oocyte vitrification, a widely used method for fertility preservation, negatively affects repair ability. Male DBA/2 mice (n = 28) were injected with 101.60 µmol/100 g body weight of tert-Butyl hydroperoxide (tBHP) for 14 days to induce sperm DNA damage. Histological changes, sperm functions, and DNA fragmentation were assessed using the TUNEL assay. Cumulus-oocyte-complexes (COCs) of superovulated female DBA/2 mice (n = 28) were vitrified using the Cryotop method. Fresh and vitrified oocytes were then fertilized by tBHP-treated and untreated sperms, and subsequent embryonic development was monitored. Additionally, the expression of Mre11a, Rad51, Brca1, and Xrcc4 was assessed in resulting zygotes and blastocysts using real-time PCR. The sperm tBHP treatment reduced differentiated spermatogenic cells in the testicular tissue, sperm concentration, and motility, while increasing DNA fragmentation (P < 0.05). The fertilization rate was decreased in the tBHP-treated sperm-vitrified oocyte group (P < 0.05), and the two-cell rate diminished in tBHP-treated sperm-fresh and vitrified oocyte groups (P < 0.05). The four-cell to blastocyst rate decreased in the untreated sperm-vitrified oocyte and the tBHP-treated sperm-fresh and vitrified oocyte groups (P < 0.05), and the tBHP-treated sperm-vitrified oocyte groups had the lowest blastocyst rate. In zygotes, Brca1 was upregulated in the tBHP-treated sperm-vitrified oocyte group (P < 0.05). Also, in blastocysts, Rad51, Brca1, and Xrcc4 were significantly upregulated in the untreated sperm-vitrified oocytes group (P < 0.05). Damages to the oocyte due to vitrification can disrupt the repair of sperm DNA fragmentation and consequently impair the embryo development.

The Effect of Open and Closed Oocyte Vitrification Systems on Embryo Development: A Systematic Review and Network Meta-Analysis

Background/Objectives: Open and closed vitrification systems are commonly employed in oocyte cryopreservation; however, there is limited evidence regarding a comparison of their separate impact on oocyte competence. This study uniquely brings to the literature, data on the effect of open versus closed vitrification systems on laboratory and clinical outcomes, and the effect of cooling and warming rates. Methods: A systematic search of the literature was performed using the databases PubMed/MEDLINE and the Cochrane Central Library, limited to articles published in English up to January 2023. A network meta-analysis was conducted comparing each vitrification system versus fresh oocytes. Results: Twenty-three studies were included. When compared to fresh oocytes, both vitrification devices resulted in lower fertilization rates per MII oocyte retrieved. When comparing the two systems in terms of survival rates, no statistically significant difference was observed. However, interestingly open systems resulted in lower cleavage and blastocyst formation rates per 2 pronuclear (2PN) oocyte compared to fresh controls, while at the same time no statistically significant difference was detected when comparing closed devices with fresh oocytes. Conclusions: In conclusion, closed vitrification systems appear to exert a less detrimental impact on the oocytes' competence, which is reflected in the blastocyst formation rates. Proof of superiority of one system versus the other may lead to standardization, helping to ultimately determine optimal practice in oocyte vitrification.

Influx of zwitterionic buffer after intracytoplasmic sperm injection (ICSI) membrane piercing alters the transcriptome of human oocytes

PURPOSE/STUDY QUESTION

Does piercing oocyte membranes during ICSI allow the influx of surrounding zwitterionic buffer into human oocytes and result in altered developmental competence?

METHODS

Human oocytes directed to IRB-approved research were used to determine the unrestricted influx of surrounding buffer into the oocyte after piercing of membranes via confocal fluorescence microscopy (n = 80 human MII oocytes) and the influence of the select buffer influx of HEPES, MOPS, and bicarbonate buffer on the oocyte transcriptome using ultra-low input RNA sequencing (n = 40 human MII oocytes).

RESULTS

Piercing membranes of human MII oocytes during sham-ICSI resulted in the unrestricted influx of surrounding culture buffer into the oocyte that was beyond technician control. Transcriptome analysis revealed statistically significant decreased cytoskeletal transcripts in the pierced buffer cohorts, higher levels of embryo competency transcripts (IGF2 and G6PD) in the bicarbonate buffer cohort, higher levels of stress-induced transcriptional repressor transcripts (MAF1) in the HEPES and MOPS cohorts, and decreased levels of numerous chromosomal maintenance transcripts (SMC3) in the HEPES buffer cohort. The HEPES buffer cohort also revealed higher levels of transcripts suggesting increased oxidative (GPX1) and lysosomal stress (LAMP1).

CONCLUSION

The influence of zwitterionic buffer on intrinsic cellular mechanisms provides numerous concerns for their use in IVF clinical applications. The primary concern is the ICSI procedure, in which the surrounding buffer is allowed influx into the oocytes after membrane piercing. Selecting a physiological bicarbonate buffer may reduce imposed stress on oocytes, resulting in improved embryo development and clinical results because intracellular MOPS, and especially HEPES, may negatively impact intrinsic biological mechanisms, as revealed by transcriptome changes. These findings further support the utilization of bicarbonate buffer as the oocyte-holding medium during ICSI.

Enhancing the photodynamic effect of curcumin through modification with TiO2 nanoparticles and cationic polymers

Curcumin (CUR), a natural compound extracted from turmeric, has shown potential as a photosensitizer in photodynamic therapy (PDT). The aim of this work was to enhance the efficacy of CUR by modifying it using titanium dioxide (TiO2) nanoparticles and a cationic polymer called Sofast to create a nanocomposite TiO2-CUR-Sofast (TCS). Compared to unmodified CUR, TCS exhibited a broadening toward longer wavelength in the absorption wavelength within the 400-550 nm range, leading to improved CUR absorption. Cellular uptake efficiency of TCS was also enhanced, and it demonstrated nearly 4.7-fold higher reactive oxygen species (ROS) generation than CUR. Furthermore, TCS displayed the ability to attach to the cell membrane and enter cells within a 30-min incubation period. Upon irradiation, TCS exhibited remarkable cytotoxicity, resulting in a significant reduction in the viability of various cancer cells. Autofluorescence lifetime imaging of intracellular reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD) enzymes indicated that cancer cells treated with TCS and irradiation undergo a metabolic pathway shift from oxidative phosphorylation to glycolysis. These findings highlight the potential of TCS as an effective PDT agent for cancer treatment.

Overview of Gene Expression Dynamics during Human Oogenesis/Folliculogenesis

The oocyte transcriptome follows a tightly controlled dynamic that leads the oocyte to grow and mature. This succession of distinct transcriptional states determines embryonic development prior to embryonic genome activation. However, these oocyte maternal mRNA regulatory events have yet to be decoded in humans. We reanalyzed human single-oocyte RNA-seq datasets previously published in the literature to decrypt the transcriptomic reshuffles ensuring that the oocyte is fully competent. We applied trajectory analysis (pseudotime) and a meta-analysis and uncovered the fundamental transcriptomic requirements of the oocyte at any moment of oogenesis until reaching the metaphase II stage (MII). We identified a bunch of genes showing significant variation in expression from primordial-to-antral follicle oocyte development and characterized their temporal regulation and their biological relevance. We also revealed the selective regulation of specific transcripts during the germinal vesicle-to-MII transition. Transcripts associated with energy production and mitochondrial functions were extensively downregulated, while those associated with cytoplasmic translation, histone modification, meiotic processes, and RNA processes were conserved. From the genes identified in this study, some appeared as sensitive to environmental factors such as maternal age, polycystic ovary syndrome, cryoconservation, and in vitro maturation. In the future, the atlas of transcriptomic changes described in this study will enable more precise identification of the transcripts responsible for follicular growth and oocyte maturation failures.

Exploring the effect of cryopreservation in assisted reproductive technology and potential epigenetic risk

Since the birth of the first baby by in vitro fertilization in 1978, more than 9 million children have been born worldwide using medically assisted reproductive treatments. Fertilization naturally takes place in the maternal oviduct where unique physiological conditions enable the early healthy development of the embryo. During this dynamic period of early development major waves of epigenetic reprogramming, crucial for the normal fate of the embryo, take place. Increasingly, over the past 20 years concerns relating to the increased incidence of epigenetic anomalies in general, and genomic-imprinting disorders in particular, have been raised following assisted reproduction technology (ART) treatments. Epigenetic reprogramming is particularly susceptible to environmental conditions during the periconceptional period and non-physiological conditions such as ovarian stimulation, in vitro fertilization and embryo culture, as well as cryopreservation procedure, might have the potential to independently or collectively contribute to epigenetic dysregulation. Therefore, this narrative review offers a critical reappraisal of the evidence relating to the association between embryo cryopreservation and potential epigenetic regulation and the consequences on gene expression together with long-term consequences for offspring health and wellbeing. Current literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by vitrification, in terms of osmotic shock, temperature and pH changes, and toxicity of cryoprotectants, it is therefore, critical to have a more comprehensive understanding and recognition of potential unanticipated iatrogenic-induced perturbations of epigenetic modifications that may or may not be a consequence of vitrification.

Alterations in the expression pattern of some epigenetic-related genes and microRNAs subsequent to oocyte cryopreservation

MicroRNAs (miRNAs) are small non-encoding RNAs that actively regulate biological and physiological processes, and play an important role in regulating gene expression in all cells, especially in most animal cells, including oocytes and embryos. The expression of miRNAs at the right time and place is crucial for the oocyte's maturation and the embryo's subsequent development. Although assisted reproductive techniques (ART) have helped to solve many infertility problems, they cause changes in the expression of miRNA and genes in oocytes and preimplantation embryos, and the effect of these changes on the future of offspring is unknown, and has caused concerns. The relevant genomic alterations commonly imposed on embryos during cryopreservation may have potential epigenetic risks. Understanding the biological functions of miRNAs in frozen maturated oocytes may provide a better understanding of embryonic development and a comparison of fertility conservation in female mammals. With the development of new techniques for genomic evaluation of preimplantation embryos, it has been possible to better understand the effects of ART. The results of various articles have shown that freezing of oocytes and the cryopreservation method are effective for the expression of miRNAs and, in some cases, cause changes in the expression of miRNAs and epigenetic changes in the resulting embryo. This literature review study aimed to investigate the effects of oocyte cryopreservation in both pre-maturation and post-maturation stages, the cryopreservation method and the type of cryoprotectants (CPA) used on the expression of some epigenetic-related genes and miRNAs.

Long-term storage of vitrified oocytes does not affect pregnancy and live birth rates: analysis of 5362 oocyte donation cycles

RESEARCH QUESTION

Does long-term storage of vitrified oocytes affect laboratory and reproductive outcomes after intracytoplasmic sperm injection?

DESIGN

Retrospective cohort study including 41,783 vitrified-warmed oocytes from 5362 oocyte donation cycles between 2013 and 2021. Five categories of storage time were established to analyse its effect on clinical and reproductive outcomes (≤1 year [reference group], 1-2 years, 2-3 years, 3-4 years and >4 years).

RESULTS

The mean number of warmed oocytes was 8.0 ± 2.5 oocytes. Oocyte storage time ranged from 3 days to 8.2 years (mean: 0.7 ± 0.9). Mean oocyte survival (90.2% ± 14.7% overall) did not significantly decrease with longer storage time after adjusting for confounders (88.9% for time >4 years, P = 0.963). A linear regression model did not show a significant effect of oocyte storage time on fertilization rate (about 70% in all time categories) (P > 0.05). Reproductive outcomes after the first embryo transfer were statistically comparable across storage times (P > 0.05 for all categories). Longer term oocyte storage (>4 years) did not affect the chances of clinical pregnancy (OR 0.700, 95% CI 0.423 to 1.158, P = 0.2214) or live birth (OR 0.716, 95% CI 0.425 to 1.208, P = 0.2670).

CONCLUSIONS

Oocyte survival, fertilization rate, pregnancy and live birth rates are not affected by the time spent by vitrified oocytes in vapour-phase nitrogen tanks.

Ovarian tissue cryopreservation and transplantation: a review on reactive oxygen species generation and antioxidant therapy

Cancer is the leading cause of death worldwide. Fortunately, the survival rate of cancer continues to rise, owing to advances in cancer treatments. However, these treatments are gonadotoxic and cause infertility. Ovarian tissue cryopreservation and transplantation (OTCT) is the most flexible option to preserve fertility in women and children with cancer. However, OTCT is associated with significant follicle loss and an accompanying short lifespan of the grafts. There has been a decade of research in cryopreservation-induced oxidative stress in single cells with significant successes in mitigating this major source of loss of viability. However, despite its success elsewhere and beyond a few promising experiments, little attention has been paid to this key aspect of OTCT-induced damage. As more and more clinical practices adopt OTCT for fertility preservation, it is a critical time to review oxidative stress as a cause of damage and to outline potential ameliorative interventions. Here we give an overview of the application of OTCT for female fertility preservation and existing challenges; clarify the potential contribution of oxidative stress in ovarian follicle loss; and highlight potential ability of antioxidant treatments to mitigate the OTCT-induced injuries that might be of interest to cryobiologists and reproductive clinicians.

A comparison of the morphokinetic profiles of embryos developed from vitrified versus fresh oocytes

RESEARCH QUESTION

Do morphokinetic profiles and treatment outcomes differ between embryos developed from vitrified or fresh oocytes?

DESIGN

Retrospective multicentre analysis using data from eight CARE Fertility clinics across the UK between 2012 and 2019. Patients receiving treatment using embryos developed from vitrified oocytes (n = 118 women, n = 748 oocytes), providing 557 zygotes during this time period, were recruited and matched with patients undergoing treatment with embryos developed from fresh oocytes (n = 123 women, n = 1110 oocytes), providing 539 zygotes in the same time frame. Time-lapse microscopy was used to assess morphokinetic profiles, including early cleavage divisions (2- through to 8-cell), post-cleavage stages including time to start of compaction, time to morula, time to start of blastulation and time to full blastocyst. Duration of key stages such as the compaction stage were also calculated. Treatment outcomes were compared between the two groups (live birth rate, clinical pregnancy rate and implantation rate).

RESULTS

A significant delay of 2-3 h across all early cleavage divisions (2- through to 8-cell) and time to start of compaction occurred in the vitrified group versus fresh controls (all P ≤ 0.01). The compaction stage was significantly shorter in vitrified oocytes (19.02 ± 0.5 h) compared with fresh controls (22.45 ± 0.6 h, P < 0.001). There was no difference in the time that fresh and vitrified embryos reached the blastocyst stage (108.03 ± 0.7 versus 107.78 ± 0.6 h). There was no significant difference in treatment outcomes between the two groups.

CONCLUSION

Vitrification is a useful technique for extending female fertility with no effects on IVF treatment outcome.

Vitrification with Dimethyl Sulfoxide Induces Transcriptomic Alteration of Gene and Transposable Element Expression in Immature Human Oocytes

Despite substantial advancements in the field of cryobiology, oocyte and embryo cryopreservation still compromise developmental competence. Furthermore, dimethyl sulfoxide (DMSO), one of the most commonly used cryoprotectants, has been found to exert potent effects on the epigenetic landscape of cultured human cells, as well as mouse oocytes and embryos. Little is known about its impact on human oocytes. Additionally, few studies investigate the effects of DMSO on transposable elements (TE), the control of which is essential for the maintenance of genomic instability. The objective of this study was to investigate the impact of vitrification with DMSO-containing cryoprotectant on the transcriptome, including on TEs, of human oocytes. Twenty-four oocytes at the GV stage were donated by four healthy women undergoing elective oocyte cryopreservation. Oocytes were paired such that half from each patient were vitrified with DMSO-containing cryoprotectant (Vitrified Cohort), while the other half were snap frozen in phosphate buffer, unexposed to DMSO (Non-Vitrified Cohort). All oocytes underwent RNA sequencing via a method with high fidelity for single cell analysis, and which allows for the analysis of TE expression through Switching Mechanism at the 5'-end of the RNA Transcript sequencing 2 (SMARTseq2), followed by functional enrichment analysis. Of the 27,837 genes identified by SMARTseq2, 7331 (26.3%) were differentially expressed (p < 0.05). There was a significant dysregulation of genes involved in chromatin and histone modification. Mitochondrial function, as well as the Wnt, insulin, mTOR, HIPPO, and MAPK signaling pathways were also altered. The expression of TEs was positively correlated with the expression of PIWIL2, DNMT3A, and DNMT3B, and negatively correlated with age. These findings suggest that the current standard process of oocyte vitrification, involving DMSO-containing cryoprotectant, induces significant transcriptome changes, including those involving TEs.

The role of Hippo pathway in ovarian development

The follicle is the functional unit of the ovary, whereby ovarian development is largely dependent on the development of the follicles themselves. The activation, growth, and progression of follicles are modulated by a diverse range of factors, including reproductive endocrine system and multiple signaling pathways. The Hippo pathway exhibits a high degree of evolutionary conservation between both Drosophila and mammalian systems, and is recognized for its pivotal role in regulating cellular proliferation, control of organ size, and embryonic development. During the process of follicle development, the components of the Hippo pathway show temporal and spatial variations. Recent clinical studies have shown that ovarian fragmentation can activate follicles. The mechanism is that the mechanical signal of cutting triggers actin polymerization. This process leads to the disruption of the Hippo pathway and subsequently induces the upregulation of downstream CCN and apoptosis inhibitors, thereby promoting follicle development. Thus, the Hippo pathway plays a crucial role in both the activation and development of follicles. In this article, we focused on the development and atresia of follicles and the function of Hippo pathway in these processes. Additionally, the physiological effects of Hippo pathway in follicle activation are also explored.

Transcriptomics Reveal Molecular Differences in Equine Oocytes Vitrified before and after In Vitro Maturation

In the last decade, in vitro embryo production in horses has become an established clinical practice, but blastocyst rates from vitrified equine oocytes remain low. Cryopreservation impairs the oocyte developmental potential, which may be reflected in the messenger RNA (mRNA) profile. Therefore, this study aimed to compare the transcriptome profiles of metaphase II equine oocytes vitrified before and after in vitro maturation. To do so, three groups were analyzed with RNA sequencing: (1) fresh in vitro matured oocytes as a control (FR), (2) oocytes vitrified after in vitro maturation (VMAT), and (3) oocytes vitrified immature, warmed, and in vitro matured (VIM). In comparison with fresh oocytes, VIM resulted in 46 differentially expressed (DE) genes (14 upregulated and 32 downregulated), while VMAT showed 36 DE genes (18 in each category). A comparison of VIM vs. VMAT resulted in 44 DE genes (20 upregulated and 24 downregulated). Pathway analyses highlighted cytoskeleton, spindle formation, and calcium and cation ion transport and homeostasis as the main affected pathways in vitrified oocytes. The vitrification of in vitro matured oocytes presented subtle advantages in terms of the mRNA profile over the vitrification of immature oocytes. Therefore, this study provides a new perspective for understanding the impact of vitrification on equine oocytes and can be the basis for further improvements in the efficiency of equine oocyte vitrification.

The live birth rate of vitrified oocyte accumulation for managing diminished ovarian reserve: a retrospective cohort study

BACKGROUND

Vitrified M-II oocyte accumulation for later simultaneous insemination has been used for managing POR. Our study aimed to determine whether vitrified oocyte accumulation strategy improves live birth rate (LBR) for managing diminished ovarian reserve (DOR).

METHODS

A retrospective study included 440 women with DOR fulfilling Poseidon classification groups 3 and 4, defined as the presence of serum anti-Müllerian hormone (AMH) hormone level < 1.2 ng/ml or antral follicle count (AFC) < 5, from January 1, 2014, to December 31, 2019, in a single department. Patients underwent accumulation of vitrified oocytes (DOR-Accu) and embryo transfer (ET) or controlled ovarian stimulation (COS) using fresh oocytes (DOR-fresh) and ET. Primary outcomes were LBR per ET and cumulative LBR (CLBR) per intention to treat (ITT). Secondary outcomes were clinical pregnancy rate (CPR) and miscarriage rate (MR).

RESULTS

Two hundred eleven patients underwent simultaneous insemination of vitrified oocyte accumulation and ET in the DOR-Accu group (maternal age: 39.29 ± 4.23 y, AMH: 0.54 ± 0.35 ng/ml), and 229 patients underwent COS and ET in the DOR-fresh group (maternal age: 38.07 ± 3.77 y, AMH: 0.72 ± 0.32 ng/ml). CPR in the DOR-Accu group was similar in the DOR-fresh group (27.5% vs. 31.0%, p = 0.418). However, MR was statistically higher (41.4% vs. 14.1%, p = 0.001), while LBR per ET was statistically lower (15.2% vs. 26.2%, p < 0.001) in the DOR-Accu group. There is no difference in CLBR per ITT between groups (20.4% vs. 27.5%, p = 0.081). The secondary analysis categorized clinical outcomes into four groups regarding patients' age. CPR, LBR per ET, and CLBR did not improve in the DOR-Accu group. In the group of 31 patients, accumulated vitrified metaphase II (M-II) oocytes reached a total number of ≥ 15, and CPR improved among the DOR-Accu group (48.4% vs. 31.0%, p = 0.054); however, higher MR (40.0% vs. 14.1%, p = 0.03) resulted in similar LBR per ET (29.0% vs. 26.2%, p = 0.738).

CONCLUSIONS

Vitrified oocyte accumulation for managing DOR did not improve LBR. Higher MR resulted in lower LBR in the DOR-Accu group. Therefore, the vitrified oocyte accumulation strategy for managing DOR is not clinically practical.

TRIAL REGISTRATION

The study protocol was retrospectively registered and was approved by Institutional Review Board of Mackay Memorial Hospital (21MMHIS219e) on August 26, 2021.

Microenvironment factors promoting the quality of vitrified cat oocytes

In oocyte cryopreservation programs, vitrification has overthrown conventional slow freezing both in veterinary and human medicine. In animals, its feasibility in field conditions makes it the preferred technique for the safeguard of genetic resources from zoo or wild animals, including threatened felids, for which the domestic cat is an excellent model. However, many cellular injuries, such as cytoskeleton, mitochondria and meiotic spindle alterations, DNA damage, zona pellucida hardening and cumulus cell loss, might occur following vitrification. After warming, although the exact mechanisms are still unclear, degeneration is a frequent outcome for cat vitrified oocytes. For immature (germinal vesicle) gametes, in vitro maturation after warming is a challenge, and cleavage after fertilization barely reaches 15-30%, while for mature (metaphase II) cryopreserved gametes it can get to 30-50%. Anyway, the progression to late embryos stages is often impaired, and improvements are needed. Standard cryopreservation protocol and the use of conventional in vitro culture systems after warming may not be enough for vitrified oocytes to recover and demonstrate their full developmental potential. Physical or chemical factors applied to oocytes undergoing vitrification, as an enrichment to the vitrification step, or to the culture microenvironment, could create more favorable conditions and promote vitrified oocyte survival and development. From the use of three-dimensional culture systems to the regulation of metabolic activities and cellular pathways, this review aims to explore all the possibilities employed so far, including the studies performed by our own lab, and the future perspectives, to present the most effective strategies for cat oocyte vitrification and the best time for their application (i.e., before, during, or after vitrification-warming).

Comparison of oocyte vitrification using a semi-automated or a manual closed system in human siblings: survival and transcriptomic analyses

BACKGROUND

Indications of oocyte vitrification increased substantially over the last decades for clinical and ethical reasons. A semi-automated vitrification system was recently developed making each act of vitrification reproducible. In this study, we evaluated the efficiency of the semi-automated technique of oocyte vitrification by survival rate, morphometric assessment and resistance to empty micro-injection gesture as compared with a manual method. Additionally, we intended to evaluate transcriptomic consequences of both techniques using single-cell RNA-seq technology.

RESULTS

Post-warming survival rate, oocyte surfaces and resistance to empty micro-injection were comparable between semi-automated and manual vitrification groups. Both oocyte vitrification techniques showed limited differences in the resulting transcriptomic profile of sibling oocytes since only 5 differentially expressed genes were identified. Additionally, there was no difference in median transcript integrity number or percentage of mitochondrial DNA between the two groups. However, a total of 108 genes were differentially expressed between fresh and vitrified oocytes (FDR < 0.05) and showed over-represented of genes related to important cellular process.

CONCLUSIONS

Our results provide reassurance about the influence of semi-automation as compared with the manual vitrification method. Concerning oocyte vitrification itself, no tight common transcriptomic signature associated has been observed across studies.

TRIAL REGISTRATION

NCT03570073.

Cryopreservation increases accumulation of exogenous stearic acid in mouse embryos

Cryopreservation of preimplantation embryos is a widely used technique, but this procedure might impact the subsequent embryo development. The effect of slow freezing and vitrification on the lipid metabolism in preimplantation mammalian embryos is not well studied. In this work, we applied Raman spectroscopy of isotopically labeled molecules to address the effects of cryopreservation on fatty acid accumulation in mouse embryos. Embryos after slow freezing or vitrification were cultured for 20 h in a medium supplemented with bovine serum albumin saturated with deuterated stearic acid (dSA). After this period the concentration of dSA estimated from Raman spectra of frozen-thawed and vitrified-warmed embryos at the morula stage was almost twice higher compared to non-cryopreserved morulas. At the same time, frozen-thawed and vitrified-warmed 4-cell embryos did not demonstrate any difference in the level of stearic acid uptake from non-cryopreserved embryos of the same stage. After an additional 24 h culture, cryopreserved and non-cryopreserved embryos demonstrated similar dSA uptake.

Effects of oocyte vitrification on gene expression in the liver and kidney tissues of adult offspring

Oocyte vitrification is an important assisted reproductive technology (ART) that preserves the fertility of unmarried patients with malignant tumors, and promotes the development of the oocyte donation program. In recent years, the effects of ART, including the vitrification of oocytes and embryos on the health of offspring, have attracted much attention; however, it is difficult to conduct long-term follow-up and biochemical evaluation in humans. In this study, we detected the effect of oocyte vitrification on gene expression in the organs of adult mice offspring by RNA sequencing for the first time. Our results showed that only a small amount of gene expression was significantly affected. Seven genes (Tpm3, Hspe1-rs1, Ntrk2, Cyp4a31, Asic5, Cyp4a14, Retsat) were abnormally expressed in the liver, and ten genes (Lbp, Hspe1-rs1, Prxl2b, Pfn3, Gm9008, Bglap3, Col8a1, Hmgcr, Ero1lb, Ifi44l) were abnormal in the kidney. Several genes were related to metabolism and disease occurrence in the liver or kidney. Besides, we paid special attention to the expression of known imprinted genes and DNA methylation-related genes in adult organs, which are susceptible to oocyte cryopreservation in the preimplantation stage. As a result, some of these transcripts were detected in adult organs, but they were not affected by oocyte vitrification. In conclusion, we first report that oocyte vitrification did not significantly change the global gene expression in offspring organs; nonetheless, it can still influence the transcription of a few functional genes. The potential adverse effects caused by oocyte vitrification need attention and further study.

Exogenous L-Glutathione Improves Vitrification Outcomes in Murine Preimplantation Embryos

Vitrification is an important tool to store surplus embryos in assisted reproductive technology (ART). However, vitrification increases oxidative damage and results in decreased viability. Studies have reported that L-glutathione (GSH) supplementation improves the preimplantation development of murine embryos. Glutathione constitutes the major non-protein sulphydryl compound in mammalian cells, which confers protection against oxidative damage. However, the effect of GSH supplementation on embryonic vitrification outcomes has yet to be reported. This study aims to determine whether GSH supplementation in culture media improves in vitro culture and vitrification outcomes, as observed through embryo morphology and preimplantation development. Female BALB/c mice aged 6−8 weeks were superovulated through an intraperitoneal injection of 10 IU of pregnant mare serum gonadotrophin (PMSG), followed by 10 IU of human chorionic gonadotrophin (hCG) 48 h later. The mated mice were euthanized by cervical dislocation 48 h after hCG to harvest embryos. Two-cell embryos were randomly assigned to be cultured in either Group 1 (GSH-free medium), Group 2 (GSH-free medium with vitrification), Group 3 (0.01 mM GSH-supplemented medium), or Group 4 (0.01 mM GSH-supplemented medium with vitrification). Non-vitrified (Groups 1 and 3) and vitrified (Groups 2 and 4) embryos were observed for morphological quality and preimplantation development at 24, 48, 72, and 96 h. In the non-vitrified groups, there were significant increases in the number of Grade-1 blastocysts in GSH cultures (p < 0.05). Similarly, in the vitrified groups, GSH supplementation was also seen to significantly increase blastocyst formation. Exogenous GSH supplementation resulted in a significant increase in intracellular GSH, a release of cytochrome c from mitochondria, and a parallel decrease in intracellular reactive oxygen species (ROS) levels in vitrified eight-cell embryos (p < 0.05). GSH supplementation was shown to upregulate Bcl2 expression and downregulate Bax expression in the vitrified preimplantation embryo group. The action of exogenous GSH was concomitant with an increase in the relative abundance of Gpx1 and Sod1. In conclusion, our study demonstrated the novel use and practical applicability of GSH supplementation for improving embryonic cryotolerance via a decrease in ROS levels and the inhibition of apoptotic events by improvement in oxidative status.

WGBS combined with RNA-seq analysis revealed that Dnmt1 affects the methylation modification and gene expression changes during mouse oocyte vitrification

Understanding the molecular level changes of oocyte cryopreservation and the subsequent warming process is essential for improving the oocyte cryopreservation technologies. Here, we collected the mature metaphase II (MII) oocytes from mice and vitrified. After thawing, single-cell whole-genome bisulphite sequencing (scWGBS) and single-cell RNA sequencing (scRNA-seq) were used to investigate the molecular attributes of this process. Compared to the fresh oocytes, the vitrified oocytes had lower global methylation and gene expression levels, and 1426 genes up-regulated and 3321 genes down-regulated. The 1426 up-regulated differentially expressed genes (DEGs) in the vitrified oocytes were mainly associated with the histone ubiquitination, while the 3321 down-regulated genes were mainly enriched in the mitochondrion organisation and ATP metabolism processes. The differentially methylated regions (DMRs) were mainly located in promoter, intron and exon region of genes, and the length of DMRs in the vitrified oocytes were also significantly lower than that of the fresh oocytes. Notably, there were no significant difference in the expression levels of DNA demethylases (Tet1, Tet2 and Tet3) and methyltransferases (Dnmt3a and Dnmt3b) between two treatments of oocytes. However, Dnmt1 and kcnq1ot1, which are responsible for maintaining DNA methylation, were significantly down regulated in the vitrified oocytes. Gene regulatory network (GRN) analysis showed the Dnmt1 and kcnq1ot1 play a core role in regulating methylation and expression levels of downstream genes. Moreover, some genes associated with oocyte quality were significantly down-regulated in the vitrified oocytes. The present data provides a new perspective for understanding the impact of vitrification on oocytes.

Oocyte Cryopreservation in Domestic Animals and Humans: Principles, Techniques and Updated Outcomes

Oocyte cryopreservation plays important roles in basic research and the application of models for genetic preservation and in clinical situations. This technology provides long-term storage of gametes for genetic banking and subsequent use with other assisted reproductive technologies. Until recently, oocytes have remained the most difficult cell type to freeze, as the oocytes per se are large with limited surface area to cytoplasm ratio. They are also highly sensitive to damage during cryopreservation, and therefore the success rate of oocyte cryopreservation is generally poor when compared to noncryopreserved oocytes. Although advancement in oocyte cryopreservation has progressed rapidly for decades, the improvement of cryosurvival and clinical outcomes is still required. This review focuses on the principles, techniques, outcomes and prospects of oocyte cryopreservation in domestic animals and humans.

Cryopreservation of Gametes and Embryos and Their Molecular Changes

The process of freezing cells or tissues and depositing them in liquid nitrogen at -196 °C is called cryopreservation. Sub-zero temperature is not a physiological condition for cells and water ice crystals represent the main problem since they induce cell death, principally in large cells like oocytes, which have a meiotic spindle that degenerates during this process. Significantly, cryopreservation represents an option for fertility preservation in patients who develop gonadal failure for any condition and those who want to freeze their germ cells for later use. The possibility of freezing sperm, oocytes, and embryos has been available for a long time, and in 1983 the first birth with thawed oocytes was achieved. From the mid-2000s forward, the use of egg vitrification through intracytoplasmic sperm injection has improved pregnancy rates. Births using assisted reproductive technologies (ART) have some adverse conditions and events. These risks could be associated with ART procedures or related to infertility. Cryopreservation generates changes in the epigenome of gametes and embryos, given that ART occurs when the epigenome is most vulnerable. Furthermore, cryoprotective agents induce alterations in the integrity of germ cells and embryos. Notably, cryopreservation extensively affects cell viability, generates proteomic profile changes, compromises crucial cellular functions, and alters sperm motility. This technique has been widely employed since the 1980s and there is a lack of knowledge about molecular changes. The emerging view is that molecular changes are associated with cryopreservation, affecting metabolism, cytoarchitecture, calcium homeostasis, epigenetic state, and cell survival, which compromise the fertilization in ART.

Vitrification-induced activation of lysosomal cathepsin B perturbs spindle assembly checkpoint function in mouse oocytes

As the age of child-bearing increases and correlates with infertility, cryopreservation of female gametes is becoming common-place in ART. However, the developmental competence of vitrified oocytes has remained low. The underlying mechanisms responsible for reduced oocyte quality post-vitrification are largely unknown. Mouse cumulus-oocyte complexes were vitrified using a cryoloop technique and a mixture of dimethylsulphoxide, ethylene glycol and trehalose as cryoprotectants. Fresh and vitrified/thawed oocytes were compared for chromosome alignment, spindle morphology, kinetochore-microtubule attachments, spindle assembly checkpoint (SAC) and aneuploidy. Although the majority of vitrified oocytes extruded the first polar body (PB), they had a significant increase of chromosome misalignment, abnormal spindle formation and aneuploidy at metaphase II. In contrast to controls, vitrified oocytes extruded the first PB in the presence of nocodazole and etoposide, which should induce metaphase I arrest in a SAC-dependent manner. The fluorescence intensity of mitotic arrest deficient 2 (MAD2), an essential SAC protein, at kinetochores was reduced in vitrified oocytes, indicating that the SAC is weakened after vitrification/thawing. Furthermore, we found that vitrification-associated stress disrupted lysosomal function and stimulated cathepsin B activity, with a subsequent activation of caspase 3. MAD2 localization and SAC function in vitrified oocytes were restored upon treatment with a cathepsin B or a caspase 3 inhibitor. This study was conducted using mouse oocytes, therefore confirming these results in human oocytes is a prerequisite before applying these findings in IVF clinics. Here, we uncovered underlying molecular pathways that contribute to an understanding of how vitrification compromises oocyte quality. Regulating these pathways will be a step toward improving oocyte quality post vitrification and potentially increasing the efficiency of the vitrification program.

Elective oocyte cryopreservation for age-related fertility decline

PURPOSE

Women who pursue fertility at an advanced age are increasingly common. Family planning and sexual education have traditionally focused on contraception and prevention of sexually transmitted diseases. A focus should now also be placed on fertility awareness and fertility preservation. This manuscript aims to give an update on the existing evidence around elective oocyte cryopreservation, also highlighting the need for fertility education and evidence-based, individualized counselling.

METHODS

A thorough electronic search was performed from the start of databases to March 2020 aiming to summarize the existing evidence around elective egg freezing, the logic behind its use, patient counselling and education, success rates and risks involved, regulation, cost-effectiveness, current status and future perspectives.

RESULTS

Clinician-led counselling regarding reproductive aging and fertility preservation is often overlooked. Elective oocyte cryopreservation is not a guarantee of live birth, and the answer regarding cost-effectiveness needs to be individualized. The existing studies on obstetric and perinatal outcomes following the use of egg freezing are, until now, reassuring. Constant monitoring of short-term and long-term outcomes, uniform regulation and evidence-based, individualized counselling is of paramount importance.

CONCLUSIONS

Elective oocyte cryopreservation is one of the most controversial aspects of the world of assisted reproduction, and a lot of questions remain unanswered. However, women today do have this option which was not available in the past. Elective oocyte cryopreservation for age-related fertility decline should be incorporated in women's reproductive options to ensure informed decisions and reproductive autonomy.

Antioxidants increase blastocyst cryosurvival and viability post-vitrification

STUDY QUESTION

What is the effect of antioxidants acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid (A3) in vitrification and warming solutions on mouse blastocyst development and viability?

SUMMARY ANSWER

The combination of three antioxidants in vitrification solutions resulted in mouse blastocysts with higher developmental potential in vitro and increased viability as assessed by both an outgrowth model in vitro and fetal development following uterine transfer.

WHAT IS KNOWN ALREADY

The antioxidant combination of acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid present in IVF handling and embryo culture media has significant beneficial effects on mouse embryo and fetal development, especially under oxidative stress.

STUDY DESIGN, SIZE, DURATION

The study was a laboratory-based analysis of an animal model. Rapid cooling through vitrification was conducted on F1 mouse blastocysts, with antioxidants (A3) supplemented in vitrification and/or warming solutions, followed by culture and embryo transfer.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Pronucleate oocytes were collected and cultured in groups to Day 4 blastocysts. Expanded blastocysts were vitrified and warmed in solutions with and without the A3 antioxidants and cultured for a further 24 h. Blastocyst cell number and allocation, apoptosis and histone acetylation levels were all quantified, and viability through outgrowths and transfers assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Mouse blastocysts vitrified with no antioxidants had significantly lower cell numbers (P  < 0.001) and higher apoptotic cells (P  < 0.05) compared to non-vitrified embryos. Addition of combined A3 antioxidants to the vitrification and warming solutions resulted in a significant increase in inner cell mass cell (ICM) number (P  < 0.001) and total cell number (P  < 0.01), and an increase in outgrowth area (P < 0.05), which correlated with the increased fetal weight (P < 0.05), crown rump length (P < 0.05) and limb development (P < 0.05) determined following transfer compared to embryos with no antioxidants. Furthermore, while blastocyst vitrification significantly reduced acetylation levels (P < 0.05) compared to non-vitrified embryos, the inclusion of A3 antioxidants helped to ameliorate this.

LIMITATIONS, REASONS FOR CAUTION

Embryo development was only examined in the mouse.

WIDER IMPLICATIONS OF THE FINDINGS

Results in this study demonstrate that vitrification and warming of blastocysts have significant detrimental effects on embryo histone acetylation and subsequent viability. The presence of antioxidants in the vitrification solutions helps to alleviate the negative effects of cryopreservation. Our data indicate that antioxidants need to be present in the medium at the time of exposure to increased oxidative stress associated with vitrification and that prior exposure (i.e. during culture or IVF alone) is insufficient to protect cells against cryo-induced injury. Hence, A3 antioxidants may assist in maintaining the viability of vitrified human embryos in ART through the reduction of oxidative stress.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by a research grant from Vitrolife AB (Sweden). The authors have no conflict of interest to declare.

Oocyte vitrification induces loss of DNA methylation and histone acetylation in the resulting embryos derived using ICSI in dromedary camel

Oocyte cryopreservation has become an important component of assisted reproductive technology with increasing implication in female fertility preservation and animal reproduction. However, the possible adverse effects of oocyte cryopreservation on epigenetic status of the resulting embryos is still an open question. This study evaluated the effects of MII-oocyte vitrification on gene transcripts linked to epigenetic reprogramming in association with the developmental competence and epigenetic status of the resulting embryos at 2-cell and blastocyst stages in dromedary camel. The cleavage rate of vitrified oocytes following intracytoplasmic sperm injection was significantly increased compared with the control (98.2 ± 2 vs. 72.7 ± 4.1%, respectively), possibly due to the higher susceptibility of vitrified oocytes to spontaneous activation. Nonetheless, the competence of cleaved embryos derived from vitrified oocytes for development to the blastocyst and hatched blastocyst was significantly reduced compared with the control (7.7 ± 1.2 and 11.1 ± 11.1 compared with 28.1 ± 2.6 and 52.4 ± 9.9%, respectively). The relative transcript abundances of epigenetic reprogramming genes DNMT1, DNMT3B, HDAC1, and SUV39H1 were all significantly reduced in vitrified oocytes relative to the control. Evaluation of the epigenetic marks showed significant reductions in the levels of DNA methylation (6.1 ± 0.3 vs. 9.9 ± 0.5, respectively) and H3K9 acetylation (7.8 ± 0.2 vs. 10.7 ± 0.3, respectively) in 2-cell embryos in the vitrification group relative to the control. Development to the blastocyst stage partially adjusted the effects that oocyte vitrification had on the epigenetic status of embryos (DNA methylation: 4.9 ± 0.4 vs. 6.2 ± 0.6; H3K9 acetylation: 5.8 ± 0.3 vs. 8 ± 0.9, respectively). To conclude, oocyte vitrification may interfere with the critical stages of epigenetic reprogramming during preimplantation embryo development.

Loss of ESRP1 blocks mouse oocyte development and leads to female infertility

Alternative splicing (AS) contributes to gene diversification, but the AS program during germline development remains largely undefined. Here, we interrupted pre-mRNA splicing events controlled by epithelial splicing regulatory protein 1 (ESRP1) and found that it induced female infertility in mice. Esrp1 deletion perturbed spindle organization, chromosome alignment and metaphase-to-anaphase transformation in oocytes. The first polar body extrusion was blocked during oocyte meiosis owing to abnormal activation of spindle assembly checkpoint and insufficiency of anaphase-promoting complex/cyclosome in Esrp1-knockout oocytes. Esrp1-knockout hampered follicular development and ovulation; eventually, premature ovarian failure occurred in six-month-old Esrp1-knockout mouse. Using single-cell RNA-seq analysis, 528 aberrant AS events of maternal mRNA transcripts were revealed and were preferentially associated with microtubule cytoskeletal organization. Notably, we found that loss of ESRP1 disturbed a comprehensive set of gene-splicing sites - including those within Trb53bp1, Rac1, Bora, Kif2c, Kif23, Ndel1, Kif3a, Cenpa and Lsm14b - that potentially caused abnormal spindle organization. Collectively, our findings provide the first report elucidating the ESRP1-mediated AS program of maternal mRNA transcripts, which may contribute to oocyte meiosis and female fertility in mice.

Vitrification of camel oocytes transiently impacts mitochondrial functions without affecting the developmental potential after intracytoplasmic sperm injection and parthenogenetic activation

Oocyte vitrification preserves the female genetic resources of elite dromedary camels. In the current study, we aimed to explore the effects of vitrification of camel oocytes on mitochondrial activity, redox stress, and expression of genes related to mitochondrial function, apoptosis, pluripotency, and cytoskeleton. Moreover, we investigated developmental competence of vitrified oocytes after parthenogenetic activation. Oocytes vitrified with the Cryotop method were compared with the fresh oocytes. Our results showed that vitrification led to increased ROS production in oocytes as evidenced by an increase in the DCFDHA fluorescence intensity, and lower mitochondrial activity. At the molecular level, vitrification reduced mRNA expression of many genes, including those related to mitochondrial function (TFAM, MT-CO1, MFN1, ATP1A1, NRF1), pluripotency (SOX2 and POU5F1), and apoptosis (p53 and BAX). In contrast, expression of KLF4 and cytoskeleton-related genes (ACTB and KRT8) was not affected. However, we found no difference in the rates of oocyte survival, cleavage, and blastocyst development, and blastocyst hatching between fresh and vitrified oocytes after warming. Our results indicate that although vitrification of camel metaphase II (MII) oocytes adversely affected mitochondrial functions, the effect was transient without compromising the developmental potential of the oocytes after parthenogenetic activation.

Gender-specific aspects related to type of fertility preservation strategies and access to fertility care

Survivorship is an area of paramount importance to be addressed as early as possible after cancer diagnosis by all health care providers. On this regard, cancer care in young patients often poses several age-related considerations among which fertility and pregnancy-related issues have a crucial role. According to the available guidelines on the topic, all patients with cancer diagnosed during their reproductive years should be provided a proper oncofertility counselling before starting anticancer treatments. This is an important step in order to inform patients about the potential treatment-induced gonadotoxicity and the available strategies for fertility preservation so that they can be referred as early as possible to fertility specialists if potentially interested in these options.In this manuscript, we aim to provide an up to date overview on the available efficacy and safety data with the main strategies for fertility preservation in male and female cancer patients in order to help optimising the oncofertility counselling performed by healthcare providers involved in cancer care and dealing with young patients. In male patients with cancer, sperm cryopreservation is the standard technique for fertility preservation. Oocyte/embryo cryopreservation, ovarian tissue cryopreservation and temporary ovarian suppression with luteinising hormone-releasing hormone agonists during chemotherapy are the main options in female patients with cancer.A multidisciplinary management building a strong network between fertility and oncology/haematology units is crucial to properly address fertility care in all young patients with cancer, at both diagnosis and during oncologic follow-up. Discussing fertility and pregnancy-related issues with young patients with cancer has to be considered mandatory nowadays keeping in mind that returning to a normal life (including the possibility to have a family and to live with as few side effects as possible) should be considered an important ambition in cancer care in the 21st century .

Effects of vitrification and cryostorage duration on single-cell RNA-Seq profiling of vitrified-thawed human metaphase II oocytes

Oocyte cryopreservation is widely used for clinical and social reasons. Previous studies have demonstrated that conventional slow-freezing cryopreservation procedures, but not storage time, can alter the gene expression profiles of frozen oocytes. Whether vitrification procedures and the related frozen storage durations have any effects on the transcriptomes of human metaphase II oocytes remain unknown. Four women (30-32 years old) who had undergone IVF treatment were recruited for this study. RNA-Seq profiles of 3 fresh oocytes and 13 surviving vitrified-thawed oocytes (3, 3, 4, and 3 oocytes were cryostored for 1,2, 3, and 12 months) were analyzed at a single-cell resolution. A total of 1987 genes were differentially expressed in the 13 vitrified-thawed oocytes. However, no differentially expressed genes were found between any two groups among the 1-, 2-, 3-, and 12-month storage groups. Further analysis revealed that the aberrant genes in the vitrified oocytes were closely related to oogenesis and development. Our findings indicated that the effects of vitrification on the transcriptomes of mature human oocytes are induced by the procedure itself, suggesting that long-term cryostorage of human oocytes is safe.

What impact does oocyte vitrification have on epigenetics and gene expression?

Children conceived by assisted reproductive technologies (ART) have a moderate risk for a number of adverse events and conditions. The question whether this additional risk is associated with specific procedures used in ART or whether it is related to the intrinsic biological factors associated with infertility remains unresolved. One of the main hypotheses is that laboratory procedures could have an effect on the epigenome of gametes and embryos. This suspicion is linked to the fact that ART procedures occur precisely during the period when there are major changes in the organization of the epigenome. Oocyte freezing protocols are generally considered safe; however, some evidence suggests that vitrification may be associated with modifications of the epigenetic marks. In this manuscript, after describing the main changes that occur during epigenetic reprogramming, we will provide current information regarding the impact of oocyte vitrification on epigenetic regulation and the consequences on gene expression, both in animals and humans. Overall, the literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by oocyte vitrification, and it also underlines the need to improve our knowledge in this field.

Comparison of two different oocyte vitrification methods: a prospective, paired study on the same genetic background and stimulation protocol

STUDY QUESTION

Can two different methods for oocyte vitrification, one using an open tool and the other a closed tool, result in similar oocyte survival rates?

SUMMARY ANSWER

The oocyte survival rate was found to be higher in the closed method.

WHAT IS KNOWN ALREADY

Open vitrification is performed routinely in oocyte donation cycles. Closed oocyte vitrification may result in slower cooling rates and thus it is less used, even though it has been recommended in order to avoid the risk of cross-contamination between material from different patients.

STUDY DESIGN, SIZE, DURATION

This is a prospective cohort study with sibling oocytes carried out in a fertility center between July 2014 and January 2016. The study included 83 oocyte donors each providing a minimum of 12 mature oocytes (metaphase II: MII) at oocyte retrieval. Oocyte survival rate and fertilization rate, as well as reproductive outcomes (biochemical, clinical, ongoing pregnancy and live birth rates) per embryo transfer and also cumulatively between the two methods were compared by Chi2 tests.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Donor oocytes were denuded and six MII oocytes from each donor were vitrified using an open method and later assigned to one recipient, while another six MII oocytes were vitrified using a closed method and assigned to a different recipient (paired analysis). ICSI was used in all cases and embryo transfer was performed on Day 2-3 in all cases.

MAIN RESULTS AND THE ROLE OF CHANCE

Oocyte donors were 24.8 years old on average (SD 4.7). Recipient age (average 41.2 years, SD 4.7) and BMI (mean 23.8 kg/m2, SD 4.0) were similar between recipient groups. Oocytes vitrified using the closed method had higher survival rate (94.5% versus 88.9%, P = 0.002), but lower fertilization rate (57.1% versus 69.8%, P < 0.001) compared to the open method. The number of fresh embryos transferred in the two groups was 1.8 on average (SD 0.4). Biochemical (45% closed versus 50% open), clinical (40% versus 50%) and ongoing (37.5% versus 42.5%) pregnancy rates were not different between groups (P > 0.05) and neither were live birth rates (37.5% versus 42.5%, P > 0.05). Cumulative reproductive results (obtained after the transfer of all the embryos) were also similar between groups.

LIMITATIONS, REASONS FOR CAUTION

The participants of this study were oocyte donors, i.e. young women in good health, and care should be exerted in extending our results to other populations such as infertility patients, oncofertility patients and women freezing oocytes to delay childbearing.

WIDER IMPLICATIONS OF THE FINDINGS

Our results suggest that, in spite of different survival and fertilization rates, closed and open oocyte vitrification methods should offer similar reproductive outcomes up to cumulative live birth rates.

STUDY FUNDING/COMPETING INTEREST(S)

The authors report no conflict of interest. Vitrolife provided the media and the closed method tool needed for the study at no cost.

Effects of oocyte vitrification on the behaviors and physiological indexes of aged first filial generation mice

To evaluate the long-term effects of oocyte cryopreservation on the health of the first filial generation (F1), we used B6D2F1 mice for oocyte collection, in vitro fertilization, and breeding. The female F1 mice born from the offspring of fresh mature oocytes (control group) and from the offspring of vitrified oocytes with traditional vitrification medium (VM group) and new improved vitrification medium (2P10E7D group) were maintained until 14-15 months of age for behavioral tests and 16-17 months of age for physiological analyses. Behavioral indexes, including anxiety-like status, discrimination ability, learning and memory ability, were investigated. Physiological indexes including body weight, body fat, heart rate, blood pressure, and blood lipids were also analyzed. In our results, the behavioral indexes, body weight, body fat, heart rate, blood pressure, total cholesterol (TC), high-density lipoprotein cholesterol (HDL), and low-density lipoprotein cholesterol (LDL) did not show significant differences among the three groups. However, the triglyceride (TG) level of the VM group was higher than that of the 2P10E7D group. Moreover, compared with the control group, both the VM group and the 2P10E7D group showed greatly increased diastolic blood pressure. This study is the first to report that oocyte vitrification might affect metabolic physiological indexes via transgenerational inheritance rather than behaviors related to anxiety-like status and cognitive ability. Furthermore, different vitrification media might have differential transgenerational effects.

Impact of nicotine, alcohol, and cocaine exposure on germline integrity and epigenome

Converging evidence suggests that parental exposure to drugs of abuse can affect offspring phenotypes. The impacts of drug abuse on germ cell quality may mediate multigenerational and transgenerational inheritance, although biological pathways underlying this mode of inheritance are not yet characterized. Germline epigenetic marks are modified by drug exposure and have emerged as promising mechanistic candidates in recent work. Drug exposure also impacts overall germline integrity and reproductive functioning, although the role of these consequences in multi/transgenerational inheritance is unclear. This review synthesizes literature on effects of exposure to alcohol, cocaine, and nicotine on the germline with a focus on epigenetic modifications following drug exposure and broader impacts on germline integrity and reproductive functioning. We discuss potential interactions between reproductive functioning, germline integrity, and germline epigenome/transcriptome in pathways underlying multi/transgenerational inheritance. We find that existing data may support independent or interactive contributions of these germline impacts on offspring phenotypes in a manner that may mediate multi/transgenerational inheritance.

Probing lasting cryoinjuries to oocyte-embryo transcriptome

Clinical applications of oocytes cryopreservation include preservation of future fertility of young cancer patients, substitution of embryo freezing to avoid associated legal and ethical issues, and delaying childbearing years. While the outcome of oocyte cryopreservation has recently been improved, currently used vitrification method still suffer from increased biosafety risk and handling issues while slow freezing techniques yield overall low success. Understanding better the mechanism of cryopreservation-induced injuries may lead to development of more reliable and safe methods for oocyte cryopreservation. Using the mouse model, a microarray study was conducted on oocyte cryopreservation to identify cryoinjuries to transcriptionally active genome. To this end, metaphase II (MII) oocytes were subjected to standard slow freezing, and then analyzed at the four-cell stage after embryonic genome activation. Non-frozen four-cell embryos served as controls. Differentially expressed genes were identified and validated using RT-PCR. Embryos produced from the cryopreserved oocytes displayed 200 upregulated and 105 downregulated genes, associated with the regulation of mitochondrial function, protein ubiquitination and maintenance, cellular response to stress and oxidative states, fatty acid and lipid regulation/metabolism, and cell cycle maintenance. These findings reveal previously unrecognized effects of standard slow oocyte freezing on embryonic gene expression, which can be used to guide improvement of oocyte cryopreservation methods.

Desiccation and supra-zero temperature storage of cat germinal vesicles lead to less structural damage and similar epigenetic alterations compared to cryopreservation

Understanding cellular and molecular damages in oocytes during exposure to extreme conditions is essential to optimize long-term fertility preservation approaches. Using the domestic cat (Felis catus) model, we are developing drying techniques for oocytes' germinal vesicles (GVs) as a more economical alternative to cryopreservation. The objective of the study was to characterize the influence of desiccation on nuclear envelope conformation, chromatin configuration, and the relative fluorescent intensities of histone H3 trimethylation at lysine 4 (H3K4me3) and at lysine 9 (H3K9me3) compared to vitrification. Results showed that higher proportions of dried/rehydrated GVs maintained normal nuclear envelope conformation and chromatin configuration than vitrified/warmed counterparts. Both preservation methods had a similar influence on epigenetic patterns, lowering H3K4me3 intensity to under 40% while maintaining H3K9me3 levels. Further analysis revealed that the decrease of H3K4me3 intensity mainly occurred during microwave dehydration and subsequent rehydration, whereas sample processing (permeabilization and trehalose exposure) or storage did not significantly affect the epigenetic marker. Moreover, rehydration either directly or stepwise with trehalose solutions did not influence the outcome. This is the first report demonstrating that the incidence of GV damages is lower after desiccation/rehydration than vitrification/warming.

Effect of vitrification temperature and cryoprotectant concentrations on the mRNA transcriptome of bovine mature oocytes after vitrifying at immature stage

The present study aimed to investigate the effect of vitrification temperature (VT) and cryoprotective agent concentrations (CPAs) on the mRNA transcriptome of bovine mature oocytes after vitrifying at immature stage. Cumulus oocyte complexes (COCs) were randomly divided into the following five groups: fresh oocytes (control), oocytes vitrified in liquid helium (LHe; -269 °C) with 5.6 M CPAs (LHe 5.6 M), oocytes vitrified in LHe with 6.6 M CPAs (LHe 6.6 M), oocytes vitrified in liquid nitrogen (LN; -196 °C) with 5.6 M CPAs (LN 5.6 M), and oocytes vitrified in LN with 6.6 M CPAs (LN 6.6 M). We performed two experiments in this study. In experiment 1, after vitrification and thawing, oocytes of vitrified and control groups were subjected to in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture (IVC). The rates of normal morphology, maturation, cleavage, and blastocyst formation in LHe 5.6 M were higher than those in LN 5.6 M (P < 0.05). The rates of normal morphology and cleavage in LHe 6.6 M were higher than those in LN 6.6 M (P < 0.05). However, the maturation and blastocyst rates were similar (P > 0.05) between LHe 6.6 M and LN 6.6 M. The blastocyst rate of 13.31% in LHe 5.6 M was the highest among all vitrified groups (P < 0.05). In experiment 2, the mRNA transcriptome of each sample was analyzed by Smart-Seq4, and the differentially expressed genes (DEGs) were detected by edgeR (P ≤ 0.05; fold-change ≥ 2). A total of 505 DEGs (342 upregulated and 163 downregulated genes) were detected in LHe 5.6 M; 609 DEGs (493 upregulated and 116 downregulated genes) were detected in LHe 6.6 M; 218 DEGs (101 upregulated and 117 downregulated genes) were determined in LN 5.6 M; and 221 DEGs (104 upregulated and 117 downregulated genes) were detected in LN 6.6 M. LHe vitrification affected the mRNA transcriptome of bovine mature oocytes after vitrifying at immature stage mainly by upregulating gene expression. Decreased CPAs (5.6 M) reduced the effect of vitrification on mRNA transcriptome when LHe vitrification was used. Among the DEGs closely related to bovine oocytes, the genes possibly related to VT were ND2, MPV17L2, PIF1, LPIN1, IMP3, BRD1, DCTN3, DERA, ATP7B, NEK5, HVCN1, and MARK2. The gene that may be associated with CPAs is CC2D2A. Genes that may be affected by VT and CPAs included PGK1, SLC7A3, FITM2, NPM3, ISCU, CWC15, and PSAP.

Effect of oocyte vitrification on DNA damage in metaphase II oocytes and the resulting preimplantation embryos

As an assisted reproduction technology, vitrification has been widely used for oocyte and embryo cryopreservation. Many studies have indicated that vitrification affects ultrastructure, gene expression, and epigenetic status. However, it is still controversial whether oocyte vitrification could induce DNA damage in metaphase II (MII) oocytes and the resulting early embryos. This study determined whether mouse oocytes vitrification induce DNA damage in MII oocytes and the resulting preimplantation embryos, and causes for vitrification-induced DNA damage. The effects of oocyte vitrification on reactive oxygen species (ROS) levels, γ-H2AX accumulation, apoptosis, early embryonic development, and the expression of DNA damage-related genes in early embryos derived by in vitro fertilization were examined. The results indicated that vitrification significantly increased the number of γ-H2AX foci in zygotes and two-cell embryos. Trp53bp1 was upregulated in zygotes, two-cell embryos and four-cell embryos in the vitrified group, and Brca1 was increased in two-cell embryos after vitrification. Vitrification also increased the ROS levels in MII oocytes, zygotes, and two-cell embryos and the apoptotic rate in blastocysts. Resveratrol (3,5,4'-trihydroxystilbene) treatment decreased the ROS levels and the accumulation of γ-H2AX foci in zygotes and two-cell embryos and the apoptotic rate in blastocysts after vitrification. Overall, vitrification-induced abnormal ROS generation, γ-H2AX accumulation, an increase in the apoptotic rate and the disruption of early embryonic development. Resveratrol treatment could decrease ROS levels, γ-H2AX accumulation, and the apoptotic rate and improve early embryonic development. Vitrification-associated γ-H2AX accumulation is at least partially due to abnormal ROS generation.

Dynactin pathway-related gene expression is altered by aging, but not by vitrification

The storage of surplus oocytes by cryopreservation (OC) is a widely used tool in assisted reproductive technology, but there is a great debate about the effects of cryopreservation on oocyte competence. It is known that OC may affect meiotic spindles but remains unclear if OC may increase the risk of aneuploidy. The aim of this study was to test the effects of OC and women aging on the expression of cytokinesis-related genes playing an important role in the segregation of chromosomes (DCTN1, DCTN2, DCTN3, DCTN6 and PLK1). Results highlighted that OC do not modify the expression of the selected genes, whereas women aging modulate the expression of all transcripts, confirming that aging is the crucial factor affecting meiosis and aneuploidy risk. A new role for Dynactin and PLK1 was shed in light, providing information on the ageing process in the oocyte which may be associated to reduced fertility.

Lycium barbarum polysaccharide enhances development of previously-cryopreserved murine two-cell embryos via restoration of mitochondrial function and down-regulated generation of reactive oxygen species

Lycium barbarum polysaccharide (LBP) exhibits multiple pharmacological and biological effects, including displaying antioxidant and cytoprotective properties. The current study investigated the effects of LBP-supplemented culture medium on mitochondrial distribution, mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) production, mitochondrial deoxyribonucleic acid (mtDNA) copy number, reactive oxygen species (ROS) accumulation, and development of previously-cryopreserved murine two-cell embryos. Results indicate that LBP enhances development of such embryos, and that potential mechanisms include: (1) mitochondrial function enhancement via altering mitochondrial distribution and increasing MMP, ATP production, mtDNA copy number, and expression of genes involved in mitochondrial biogenesis and energy metabolism (NAD-dependent deacetyltransferase sirtuin-1 (SIRT1) and phosphorylated adenosine monophosphate-activated protein kinase (pAMPK)); (2) down-regulation of ROS generation and enhanced expression of the antioxidant genes glutathione peroxidase 4 (GPX4) and superoxide dismutase 1 (SOD1), thereby increasing embryo oxidative stress tolerance; and (3) increased expression of B-cell lymphoma-2 (BCL2), a critical gene for cell survival and embryo development. These results demonstrate that LBP improves development of previously-cryopreserved murine two-cell embryos via restoration of mitochondrial function and down-regulated generation of ROS.

Melatonin Improves Parthenogenetic Development of Vitrified⁻Warmed Mouse Oocytes Potentially by Promoting G1/S Cell Cycle Progression

This study aimed to investigate the effect of melatonin on the cell cycle of parthenogenetic embryos derived from vitrified mouse metaphase II (MII) oocytes. Fresh oocytes were randomly allocated into three groups: untreated (control), or vitrified by the open-pulled straw method without (Vitrification group) or with melatonin (MT) supplementation (Vitrification + MT group). After warming, oocytes were parthenogenetically activated and cultured in vitro, then the percentage of embryos in the G1/S phase, the levels of reactive oxygen species (ROS) and glutathione (GSH), and the mRNA expression of cell cycle-related genes (P53, P21 and E2F1) in zygotes and their subsequent developmental potential in vitro were evaluated. The results showed that the vitrification/warming procedures significantly decreased the frequency of the S phase, markedly increased ROS and GSH levels and the expression of P53 and P21 genes, and decreased E2F1 expression in zygotes at the G1 stage and their subsequent development into 2-cell and blastocyst stage embryos. However, when 10⁻⁹ mol/L MT was administered for the whole duration of the experiment, the frequency of the S phase in zygotes was significantly increased, while the other indicators were also significantly improved and almost recovered to the normal levels shown in the control. Thus, MT might promote G1-to-S progression via regulation of ROS, GSH and cell cycle-related genes, potentially increasing the parthenogenetic development ability of vitrified–warmed mouse oocytes.

An improved method for vitrification of in vitro matured ovine oocytes; beneficial effects of Ethylene Glycol Tetraacetic acid, an intracellular calcium chelator

Vitrification affects fertilization ability and developmental competence of mammalian oocytes. This effect may be more closely associated with an intracellular calcium rise induced by cryoprotectants. The present study aimed to assess whether addition of Ethylene Glycol Tetraacetic acid (EGTA) to vitrification solution could improve quality and developmental competence of in vitro matured ovine oocytes. Vitrified groups were designed according to the presence or absence of EGTA and/or calcium in base media, including: mPB1+ (modified PBS with Ca²⁺), mPB1^- (modified PBS without Ca²⁺), mPB1⁺/EGTA (mPB1⁺ containing EGTA), mPB1^-/EGTA (mPB1^- containing EGTA). In vitro development, numerical chromosome abnormalities, hardening of zona pellucida, mitochondrial distribution and function of viable oocytes were evaluated and compared between groups. Quality of blastocysts was assessed by differential and TUNEL staining. Also, mRNA expression levels of six candidate genes (KIF11, KIF2C, CENP-E, KIF20A, KIF4A and KIF2A), were quantitatively evaluated by RT-PCR. Our results showed that calcium-free vitrification and EGTA supplementation can significantly increase the percentage of normal haploid oocytes and maintain normal distribution and function of mitochondria in vitrified ovine oocytes, consequently improving developmental rate after in vitro fertilization. qRT-PCR analysis showed no significant difference in mRNA expression levels of kinesin genes between vitrified and fresh oocytes. Also, the presence of calcium in vitrification solution significantly increased zona hardening. In conclusion, we have shown for the first time that supplementation of vitrification solution with EGTA, as a calcium chelator, improved the ability of vitrified ovine oocytes to preserve mitochondrial distribution and function, as well as normal chromosome segregation.

Motoring through: the role of kinesin superfamily proteins in female meiosis

BACKGROUND

The kinesin motor protein family consists of 14 distinct subclasses and 45 kinesin proteins in humans. A large number of these proteins, or their orthologues, have been shown to possess essential function(s) in both the mitotic and the meiotic cell cycle. Kinesins have important roles in chromosome separation, microtubule dynamics, spindle formation, cytokinesis and cell cycle progression. This article contains a review of the literature with respect to the role of kinesin motor proteins in female meiosis in model species. Throughout, we discuss the function of each class of kinesin proteins during oocyte meiosis, and where such data are not available their role in mitosis is considered. Finally, the review highlights the potential clinical importance of this family of proteins for human oocyte quality.

OBJECTIVE AND RATIONALE

To examine the role of kinesin motor proteins in oocyte meiosis.

SEARCH METHODS

A search was performed on the Pubmed database for journal articles published between January 1970 and February 2017. Search terms included 'oocyte kinesin' and 'meiosis kinesin' in addition to individual kinesin names with the terms oocyte or meiosis.

OUTCOMES

Within human cells 45 kinesin motor proteins have been discovered, with the role of only 13 of these proteins, or their orthologues, investigated in female meiosis. Furthermore, of these kinesins only half have been examined in mammalian oocytes, despite alterations occurring in gene transcripts or protein expression with maternal ageing, cryopreservation or behavioral conditions, such as binge drinking, for many of them.

WIDER IMPLICATIONS

Kinesin motor proteins have distinct and important roles throughout oocyte meiosis in many non-mammalian model species. However, the functions these proteins have in mammalian meiosis, particularly in humans, are less clear owing to lack of research. This review brings to light the need for more experimental investigation of kinesin motor proteins, particularly those associated with maternal ageing, cryopreservation or exposure to environmental toxicants.