The effects of vitrification on gene expression in mature mouse oocytes by nested quantitative PCR

Effects and Mechanisms of Imperatorin on Vitrified Mouse Oocytes

Imperatorin (IMP) is a naturally occurring furanocoumarin with beneficial biological activities such as anticancer, antioxidant, and neuromodulatory properties. Currently, the protective effects and mechanisms of IMP on oxidative stress experienced by mouse oocytes after vitrification-thawing remain unclear. To investigate the influence of IMP on mouse oocyte development after vitrification-thawing, we added different concentrations of IMP to the vitrification and thawing media. Results indicated that the addition of 40 μM IMP enhanced post-thaw fertilization capacity, reduced intracellular reactive oxygen species (ROS) levels, and increased intracellular glutathione (GSH) levels. IMP also improved mitochondrial health by alleviating the decrease in mitochondrial membrane potential (MMP) and enhancing mitochondrial distribution. IMP reduced intracellular ROS levels by affecting the transcription of the antioxidant genes SOD2, NRF2, and HO-1 and enhancing SOD activity. It also elevated GSH levels via GPX1, improved mitochondrial function, and decreased early apoptosis through Bcl-2. In conclusion, IMP enhanced ovum health through the alleviation of oxidative stress. The present study provides useful information for further exploration of the molecular mechanisms of IMP in female reproductive cells and offers a novel approach for the improvement of vitrification technology.

Oxidative Stress and Oocyte Cryopreservation: Recent Advances in Mitigation Strategies Involving Antioxidants

Oocyte cryopreservation is widely used in assisted-reproductive technology and animal production. However, cryopreservation not only induces a massive accumulation of reactive oxygen species (ROS) in oocytes, but also leads to oxidative-stress-inflicted damage to mitochondria and the endoplasmic reticulum. These stresses lead to damage to the spindle, DNA, proteins, and lipids, ultimately reducing the developmental potential of oocytes both in vitro and in vivo. Although oocytes can mitigate oxidative stress via intrinsic antioxidant systems, the formation of ribonucleoprotein granules, mitophagy, and the cryopreservation-inflicted oxidative damage cannot be completely eliminated. Therefore, exogenous antioxidants such as melatonin and resveratrol are widely used in oocyte cryopreservation to reduce oxidative damage through direct or indirect scavenging of ROS. In this review, we discuss analysis of various oxidative stresses induced by oocyte cryopreservation, the impact of antioxidants against oxidative damage, and their underlying mechanisms. We hope that this literature review can provide a reference for improving the efficiency of oocyte cryopreservation.

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.

Cryopreservation and oxidative stress in porcine oocytes

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

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.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

Comparison of The Effects of Vitrification on Gene Expression of Mature Mouse Oocytes Using Cryotop and Open Pulled Straw

Background

Oocyte cryopreservation is an essential part of the assisted reproductive technology (ART), which was recently introduced into clinical practice. This study aimed to evaluate the effects of two vitrification systems-Cryotop and Open Pulled Straw (OPS)-on mature oocytes gene expressions.

MATERIALS AND METHODS

In this experimental study, the survival rate of metaphase II (MII) mouse oocytes were assessed after cryopreservation by vitrification via i. OPS or ii. Cryotop. Then we compared the fertilization rate of oocytes produced via these two methods. In the second experiment, we determined the effects of the two vitrification methods on the expression of Hspa1a, mn-Sod, and ß-actin genes in vitrified-warmed oocytes. Denuded MII oocytes were vitrified in two concentrations of vitrification solution (VS1 and VS2) by Cryotop and straw. We then compared the results using the two vitrification methods with fresh control oocytes.

RESULTS

mn-Sod expression increased in the vitrified-warmed group both in OPS and Cryotop compared with the controls. We only detected Hspa1a in VS1 and control groups using Cryotop. The survival rate of the oocytes was 91.2% (VS1) and 89.2% (VS2) in the Cryotop groups (P=0.902) and 85.5% (VS1) and 83.6% (VS2) in the OPS groups (P=0.905). There were no significant differences between the Cryotop and the OPS groups (P=0.927). The survival rate in the Cryotop or the OPS groups was, nevertheless, significantly lower than the control group (P<0.001). The fertilization rates of the oocytes were 39% (VS1) and 34% (VS2) in the Cryotop groups (P=0.902) and 29 %( VS1) and 19.7% (VS2) in the OPS groups (P=0.413). The fertilization rates were achieved without significant differences among the Cryotop and OPS groups (P=0.755).

CONCLUSION

Our results indicated that Cryotop vitrification increases both cooling and warming rates, but both Cryotop and OPS techniques have the same effect on the mouse oocytes after vitrification.

State of the art on oocyte cryopreservation in female cancer patients: A critical review of the literature

During the last decades, important advances in therapeutic options have led to increased survival rates in cancer patients; however, cancer treatments are associated with several potential adverse effects including infertility in those diagnosed during their reproductive years. A proper discussion about fertility preservation options before the use of therapies with potential gonadotoxicity (i.e. oncofertility counseling) is standard of care and should be offered to all patients of childbearing age. Temporary ovarian suppression with LH-RH analogs, oocyte and embryo cryopreservation are standard strategies for fertility preservation in female cancer patients. Oocyte cryopreservation should be preferred to embryo cryopreservation when this latter is prohibited by law, avoided for ethical or religious issues and in single women refusing sperm donation. Despite the increasing use of this strategy, data are still lacking about the efficacy and safety of the procedure in female cancer patients, with most of the evidence on this regard deriving from infertile non-oncologic women. This article aims at critically review the available evidence about the success of oocyte cryopreservation in female cancer patients with the final goal to further improve the oncofertility counseling of these women.

Storage time does not modify the gene expression profile of cryopreserved human metaphase II oocytes

STUDY QUESTION

Does storage time have any impact on the transcriptome of slowly frozen cryopreserved human metaphase II (MII) oocytes?

SUMMARY ANSWER

The length of cryostorage has no effect on the gene expression profile of human MII oocytes.

WHAT IS KNOWN ALREADY

Oocyte cryopreservation is a widely used technique in IVF for storage of surplus oocytes, as well as for fertility preservation (i.e. women undergoing gonadotoxic therapies) and oocyte donation programs. Although cryopreservation has negative impacts on oocyte physiology and it is associated with decrease of transcripts, no experimental data about the effect of storage time on the oocyte molecular profile are available to date.

STUDY DESIGN, SIZE, DURATION

This study included 27 women, ≤38 years aged, without any ovarian pathology, undergoing IVF treatment. Surplus MII oocytes were donated after written informed consent. A total of 31 non-cryopreserved oocytes and 68 surviving slow-frozen/rapid-thawed oocytes (32 oocytes cryostored for 3 years and 36 cryostored for 6 years) were analyzed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pools of ≈10 oocytes for each group were prepared. Total RNA was extracted from each pool, amplified, labeled and hybridized on oligonucleotide microarrays. Analyses were performed by R software using the limma package.

MAIN RESULTS AND THE ROLE OF CHANCE

Comparison of gene expression profiles between surviving thawed oocytes after 3 and 6 years of storage in liquid nitrogen found no differently expressed genes. The expression profiles of cryopreserved MII oocytes significantly differed from those of non-cryopreserved oocytes in 107 probe sets corresponding to 73 down-regulated and 29 up-regulated unique transcripts. Gene Ontology analysis by DAVID bioinformatics resource disclosed that cryopreservation deregulates genes involved in oocyte function and early embryo development, such as chromosome organization, RNA splicing and processing, cell cycle, cellular response to DNA damage and to stress, DNA repair, calcium ion binding, malate dehydrogenase activity and mitochondrial activity. Among the probes significantly up-regulated in cryopreserved oocytes, two corresponded to ovary-specific expressed large intergenic noncoding (linc)RNAs.

LIMITATIONS, REASONS FOR CAUTION

Data validation in a larger cohort of samples would be beneficial, although we applied stringent criteria for gene selection (fold-change >3 or <1/3 and FDR < 0.1). Further research should be undertaken to verify experimentally that the length of cryostorage has no effect on gene expression profile of vitrified/warmed MII oocytes, as well as to include in analyses 'older' frozen oocytes.

WIDER IMPLICATIONS OF THE FINDINGS

Confirmation that the length of storage does not alter the gene expression profile of frozen oocytes is noteworthy for the safety issue of long-term oocyte banking, i.e. fertility preservation, gamete donation.

STUDY FUNDING/COMPETING INTEREST

This study was supported by a grant of the Italian Ministry of Health (CCM 2012) and by Ferring Pharmaceutical company. The authors have no conflicts of interest to declare.

Maternal-Effect Gene Expression in Cultured Preantral Follicles Derived from Vitrified-Warmed Mouse Ovary

Objective

This study was conducted to assess survival of follicles, their oocyte maturation and fertilization potential as well as expression of early embryo developmental genes in in vitro cultured pre-antral follicles derived from vitrified-warmed mouse ovary.

Materials and Methods

In this experimental study, ovaries of 12-day old Naval Medical Research Institute (NMRI) female mice were placed into non-vitrified and vitrifiedwarmed groups. Isolated preantral follicles from experimental groups were cultured in vitro for 12 days. On the 12^th day of culture, oocyte maturation was induced and then matured oocytes were in vitro fertilized. The rates of oocyte maturation and two-cell stage embryo formation were assessed. Relative expression of Mater and Zar1 was evaluated on days 1, 6, 10 and 12 of culture. Data analysis was performed by t test and two-way ANOVA (P<0.05).

Results

Our data showed no significant difference between the control and vitrification groups in the rate of follicular survival, oocyte maturation and two-cell stage embryo formation. The level of gene expression was higher on the 6^thand 10^thdays of culture for Mater and Zar1 in vitrified-warmed group compared with non-vitrified group, however, there was no significant difference between the two groups.

Conclusion

It seems that the applied vitrification method did not reveal any negative effect on maturation and developmental competence of oocytes surrounded in preantral follicles and therefore could preserve follicular reserves efficiently.

The effect of vitrification of immature bovine oocytes to the subsequent in vitro development and gene expression

Immature bovine oocytes were vitrified using the cryotop method and their post-warming survivability and capability to undergo in vitro maturation, fertilization and subsequent embryonic development were evaluated. In addition throughout the embryonic 2-cell, 4-cell, morula and blastocyst stages, the expression of four developmentally important genes (Cx43, CDH1, DNMT1 and HSPA14) was analysed using the real-time polymerase chain reaction (PCR). Immature oocytes (n = 550) were randomly assigned to non-vitrified (fresh) or cryotop vitrification groups using ethylene glycol (EG) with 1,2 propanediol (PROH) or dimethylsulphoxide (DMSO). After warming, oocytes survivability, embryo cleavage and embryonic developmental rates were not statistically different between the two cryoprotectants groups. However, the DMSO group had a lower (P < 0.05) oocyte maturation rate compared with the fresh and PROH groups. For morula and blastocyst rates, the DMSO group achieved a lower (P < 0.05) morula rate compared with the fresh group, while at the blastocyst stage, there were no differences between fresh and both cryoprotectants groups. For molecular analysis, at the 4-cell stage, most studied genes showed an inconsistent pattern of expression either from the PROH or DMSO groups. Noteworthily, these differences were limited at the morula and blastocyst stages. In conclusion, the cryotop method is sufficient for vitrification of immature bovine oocytes, both for embryonic developmental competence and at the molecular level. Moreover, PROH showed some advantage over DMSO as a cryoprotectant.

Exposing mouse oocytes to necrostatin 1 during in vitro maturation improves maturation, survival after vitrification, mitochondrial preservation, and developmental competence

Necrostatin 1 (Nec1) is widely used in disease models to examine the contribution of receptor-interacting protein kinase 1 in cell death. The biological actions of Nec1 are blocking necrotic cell death. The purpose of this study was to investigate whether adding Nec1 into in vitro maturation (IVM) media, followed by vitrification procedures, could enhance the survival and developmental competency of oocytes. Germinal vesicle oocytes were matured in IVM medium containing 2 different doses of Nec1 (0.5 and 1 μmol/L). After IVM, the oocytes were vitrified using a 2-step exposure to equilibrium and vitrification solutions. After warming, the rates of survival, fertilization, embryonic development up to blastocyst in vitro, morphology of spindle and chromosome, membrane integrity, mitochondria integrity, and several gene expressions were evaluated. The survival and developmental competency of oocytes were higher in the 1 μmol/L Nec1-treated group than control. The proportion with intact spindles/chromosomes and stable membranes was similar in all the groups. The mitochondrial integrity of all Nec1-treated groups showed a higher score with strong staining. The 1 μmol/L Nec1 showed significantly increased expressions of Mad2, Gdf9, and Bcl2. The Cirp level had a tendency to be downregulated in the 0.5 µmol/L Nec1 but upregulated in the 1 μmol/L Nec1, compared with the control. The Mtgenome expressions were significantly decreased in both Nec1 groups. The supplementation of 1 μmol/L Nec1 into the IVM medium could be beneficial for the survival and development of immature oocytes after vitrification.

The protective role of antifreeze protein 3 on the structure and function of mature mouse oocytes in vitrification

Several studies have reported the oocyte damage in mice during vitrification; however, little has been known about the protective role that antifreeze protein 3 (Afp3) plays on their cellular structure and function during vitrification. In order to observe the extracellular cryo-protective role of Afp3, four groups were divided randomly. The observations were made for changes in cytoskeleton, expression of the related genes before and after vitrification, and also for changes in the in vitro developmental potential of oocytes. The outcomes were as follows: (i) microtubules, actin filaments and chromosomal integrity were more intact in the vitrification group supplemented with additional Afp3 compared to the vitrification group. In the fresh control group and the group with additional cryoprotectant containing ethylene glycol (EG), dimethyl sulfoxide (Me2SO) and sucrose, the organelles were more intact than the other two vitrification groups. (ii) Real-time PCR analysis revealed that the relative quantification of mitotic arrest deficient 2 (Mad2) and centromere protein E (Cenp-e) were significantly higher in the vitrification group with additional Afp3, the fresh control group and the one group with additional cryoprotectant, in comparison to the vitrification group. On the contrary, the expression of cold inducible RNA-binding protein (Cirbp) and kinesin-5 motor protein (Eg5) were up-regulated in the vitrification group compared to the remaining groups. (iii) The fertilization rate and the recovery rate in the fresh control group and the group with additional cryoprotectant were higher than the other two vitrification groups; furthermore, the recovery rate and the fertilization rate in the vitrification group with Afp3 were higher than the vitrification group. However, the blastocyst formation rate in all the four groups showed no statistical significance. In conclusion, Afp3 plays a positive role in the structure and function of mice oocytes in vitrification.

Mitochondrial Distribution and ATP Content of Vitrified, In vitro Matured Mouse Oocytes

BACKGROUND

The objective of this study was to investigate the effect of vitrification and in vitro maturation on the mitochondrial distribution and ATP content of oocytes.

METHODS

The oocytes at Germinal Vesicle (GV) and Metaphase II (MII) stages were recovered from 6-8 week old NMRI strain female mice. The oocytes were divided into vitrified and non-vitrified groups. Vitrification was done by the cryotop method using ethylene glycol, dimethylsulfoxide and sucrose as cryoprotectants. The GV oocytes were cultured in maturation medium for 24 hrs. The collected in vitro matured oocytes (IVM-MII) and ovulated metaphase II (OV-MII) oocytes were inseminated with capacitated sperm. The ATP content of the oocytes was measured by luciferin-luciferase reaction. Distribution of oocyte mitochondria was studied using Mito Tracker Green staining under fluorescent microscope.

RESULTS

The survival rates of vitrified oocytes at GV and MII stages were 87.39 and 89.5%, respectively. There was no significant difference in the developmental and hatching rates of vitrified and non-vitrified oocytes. The ATP content of GV and MII oocytes derived from in vivo and in vitro condition was not significantly different in vitrified and non-vitrified samples. The pattern of mitochondrial distribution in vitrified and non-vitrified GV and MII oocytes was similar but it was different between MII oocytes collected from fallopian tube and in vitro matured MII oocytes. However, the florescent intensity of mitochondrial staining was different in all the groups in the study.

CONCLUSION

Vitrification did not affect mouse oocyte developmental competence, ATP content at different developmental stages but some alteration was seen in mitochondria distribution of in vitro matured oocytes in comparison to their controls.

The beneficial effects of antifreeze proteins in the vitrification of immature mouse oocytes

Antifreeze proteins (AFPs) are a class of polypeptides that permit organismal survival in sub-freezing environments. The purpose of this study was to investigate the effect of AFP supplementation on immature mouse oocyte vitrification. Germinal vesicle-stage oocytes were vitrified using a two-step exposure to equilibrium and vitrification solution in the presence or absence of 500 ng/mL of AFP III. After warming, oocyte survival, in vitro maturation, fertilization, and embryonic development up to the blastocyst stage were assessed. Spindle and chromosome morphology, membrane integrity, and the expression levels of several genes were assessed in in vitro matured oocytes. The rate of blastocyst formation was significantly higher and the number of caspase-positive blastomeres was significantly lower in the AFP-treated group compared with the untreated group. The proportion of oocytes with intact spindles/chromosomes and stable membranes was also significantly higher in the AFP group. The AFP group showed increased Mad2, Hook-1, Zar1, Zp1, and Bcl2 expression and lower Eg5, Zp2, Caspase6, and Rbm3 expression compared with the untreated group. Supplementation of the vitrification medium with AFP has a protective effect on immature mouse oocytes, promoting their resistance to chilling injury. AFPs may preserve spindle forming ability and membrane integrity at GV stage. The fertilization and subsequent developmental competence of oocytes may be associated with the modulation of Zar1, Zp1/Zp2, Bcl2, Caspase6, and Rbm3.

Effect of antifreeze protein supplementation in vitrification medium on mouse oocyte developmental competence

OBJECTIVE

To investigate the effect of antifreeze protein (AFP) supplementation during mouse oocyte vitrification on the survival, fertilization and embryonic development.

DESIGN

Animal study.

SETTING

University laboratory.

ANIMAL(S)

BDF-1 mice.

INTERVENTION(S)

In vivo-matured metaphase II oocytes were vitrified with the use of CryoTop by two-step exposure to equilibrium and vitrification solution supplemented or not with 500 ng/mL AFP III.

MAIN OUTCOME MEASURE(S)

Postwarming survival, fertilization, embryonic development up to blastocyst in vitro, morphology of spindle and chromosome, membrane integrity, adenosine triphosphate (ATP) contents, and several gene expressions.

RESULT(S)

In the AFP-treated group, blastocyst formation rate was significantly higher and blastomere count with positive caspase was significantly lower compared with the nontreated group. Rate of intact spindle/chromosome, stable membrane, and ATP contents were significantly higher in AFP group. AFP group showed higher Mad2 and lower Eg5 gene expression. Both vitrification groups showed increased Hsf1, Zar1, and Zp1/Zp2 expression and decreased Hook1 and Zp3 expression compared with fresh control samples.

CONCLUSION(S)

Supplementation of AFP in vitrification medium has a protective effect on mouse oocytes for chilling injury; it can preserve spindle/membrane integrity and intracellular ATP contents. More stable spindle integrity in the AFP group may be associated with higher Mad2 and lower Eg5 gene expression.