Melatonin Improves In Vitro Development of Vitrified-Warmed Mouse Germinal Vesicle Oocytes Potentially via Modulation of Spindle Assembly Checkpoint-Related Genes

The walnut-derived peptide TW-7 improves mouse parthenogenetic embryo development of vitrified MII oocytes potentially by promoting histone lactylation

BACKGROUND

Previous studies have shown that the vitrification of metaphase II (MII) oocytes significantly represses their developmental potential. Abnormally increased oxidative stress is the probable factor; however, the underlying mechanism remains unclear. The walnut-derived peptide TW-7 was initially isolated and purified from walnut protein hydrolysate. Accumulating evidences implied that TW-7 was a powerful antioxidant, while its prospective application in oocyte cryopreservation has not been reported.

RESULT

Here, we found that parthenogenetic activation (PA) zygotes derived from vitrified MII oocytes showed elevated ROS level and delayed progression of pronucleus formation. Addition of 25 μmol/L TW-7 in warming, recovery, PA, and embryo culture medium could alleviate oxidative stress in PA zygotes from vitrified mouse MII oocytes, furtherly increase proteins related to histone lactylation such as LDHA, LDHB, and EP300 and finally improve histone lactylation in PA zygotes. The elevated histone lactylation facilitated the expression of minor zygotic genome activation (ZGA) genes and preimplantation embryo development.

CONCLUSIONS

Our findings revealed the mechanism of oxidative stress inducing repressed development of PA embryos from vitrified mouse MII oocytes and found a potent and easy-obtained short peptide that could significantly rescue the decreased developmental potential of vitrified oocytes, which would potentially contribute to reproductive medicine, animal protection, and breeding.

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.

Exploring melatonin's multifaceted role in female reproductive health: From follicular development to lactation and its therapeutic potential in obstetric syndromes

BACKGROUND

Melatonin is mainly secreted by the pineal gland during darkness and regulates biological rhythms through its receptors in the suprachiasmatic nucleus of the hypothalamus. In addition, it also plays a role in the reproductive system by affecting the function of the hypothalamic-pituitary-gonadal axis, and by acting as a free radical scavenger thus contributing to the maintenance of the optimal physiological state of the gonads. Besides, melatonin can freely cross the placenta to influence fetal development. However, there is still a lack of overall understanding of the role of melatonin in the reproductive cycle of female mammals.

AIM OF REVIEW

Here we focus the role of melatonin in female reproduction from follicular development to delivery as well as the relationship between melatonin and lactation. We further summarize the potential role of melatonin in the treatment of preeclampsia, polycystic ovary syndrome, endometriosis, and ovarian aging.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Understanding the physiological role of melatonin in female reproductive processes will contribute to the advancement of human fertility and reproductive medicine research.

Effect of melatonin on developmental competence, mitochondrial distribution, and intensity of fresh and vitrified/thawed in vitro matured buffalo oocytes

BACKGROUND

In livestock breeding, oocyte cryopreservation is crucial for preserving and transferring superior genetic traits. This study was conducted to examine the additional effect of melatonin to maturation and vitrification media on the in vitro developmental capacity, mitochondrial distribution, and intensity of buffalo oocytes. The study involved obtaining ovaries from a slaughterhouse and conducting two phases. In the first phase, high-quality oocytes were incubated in a maturation medium with or without 10-9M melatonin for 22 h (at 38.5°C in 5% CO2). Matured oocytes were fertilized in vitro and cultured in SOF media for seven days. In the second phase, vitrified in vitro matured oocytes were stored in vitrified media (basic media (BM) containing a combination of cryoprotectants (20% Ethyl Glycol and 20% Dimethyl sulfoxide), with or without melatonin, and then stored in liquid nitrogen. Normal vitrified/thawed oocytes were fertilized in vitro and cultured as described. Finally, the matured oocytes from the fresh and vitrified/thawed groups, both with and without melatonin, were stained using DAPI and Mitotracker red to detect their viability (nuclear maturation), mitochondrial intensity, and distribution using a confocal microscope. The study found that adding 10-9M melatonin to the maturation media significantly increased maturation (85.47%), fertilization rate (84.21%)cleavage (89.58%), and transferable embryo (48.83%) rates compared to the group without melatonin (69.85%,79.88%, 75.55%, and 37.25% respectively). Besides that, the addition of melatonin to the vitrification media improved the recovery rate of normal oocytes (83.75%), as well as the cleavage (61.80%) and transferable embryo (27.00%) rates when compared to the vitrified TCM group (67.46%, 51.40%, and 17.00%, respectively). The diffuse mitochondrial distribution was higher in fresh with melatonin (TCM + Mel) (80%) and vitrified with melatonin (VS2 + Mel groups) (76.70%), Furthermore, within the same group, while the mitochondrial intensity was higher in the TCM + Mel group (1698.60) than other group. In conclusion, Melatonin supplementation improves the developmental competence and mitochondrial distribution in buffalo oocytes in both cases(in vitro maturation and vitrification).

Vitrification of Mammalian Oocytes: Recent Studies on Mitochondrial Dysfunction

Vitrification of reproductive cells is definitely essential and integral in animal breeding, as well as in assisted reproduction. However, issues accompanied with this technology such as decreased oocyte competency and relatively low embryo survival rates appear to be a tough conundrum that has long perplexed us. As significant organelles in cell metabolism, mitochondria play pivotal roles in numerous pathways. Nonetheless, extensive evidence has demonstrated that vitrification can seriously impair mitochondrial function in mammalian oocytes. Thus, in this article, we summarize the current progress in oocyte vitrification and particularly outline the common mitochondrial abnormalities alongside subsequent injury cascades seen in mammalian oocytes following vitrification. Based on existing literature, we tentatively come up with the potential mechanisms related to mitochondrial dysfunction and generalize efficacious ways which have been recommended to restore mitochondrial function.

Mito-TEMPO Improves the Meiosis Resumption and Mitochondrial Function of Vitrified Sheep Oocytes via the Recovery of Respiratory Chain Activity

Vitrification is a crucial method for preserving animal germ cells. Considering the increased oxidative stress and organelle damage incurred, it is still necessary to make the process more efficient for oocytes. As the energy source of oocytes, mitochondria are the most abundant organelle in oocytes and play a crucial role in their maturation. Here, we found that Mito-TEMPO, a mitochondria-targeted antioxidant, could efficaciously improve the oxidative stress injury of vitrified oocytes by recovering mitochondrial function via the mitochondrial respiratory chain. It was observed that Mito-TEMPO not only improves oocyte viability and meiosis but also maintains spindle structure. A subsequent study indicated that Mito-TEMPO effectively rescued mitochondrial dysfunction and attenuated vitrification-induced oxidative stress. Further investigation revealed that Mito-TEMPO regulates vitrified oocytes' intracellular Ca2+ homeostasis and ATP content and provides strong antioxidant properties. Additionally, an analysis of the transcriptome at the single-cell level revealed that the respiratory chain mediates the beneficial effect of Mito-TEMPO on vitrified oocytes. Overall, our findings indicate that supplementing oocytes with Mito-TEMPO is an effective method to shield them from the damage caused by vitrification. In addition, the beneficial effects of Mito-TEMPO on vitrified sheep oocytes could inspire further investigations of the principles underlying oocyte cryobiology in other animals.

C-Type Natriuretic Peptide Pre-Treatment Improves Maturation Rate of Goat Oocytes by Maintaining Transzonal Projections, Spindle Morphology, and Mitochondrial Function

C-type natriuretic peptide (CNP) is a peptide molecule naturally found in follicles and can be used to extend meiotic resumption and enhance the potential for oocytes to develop. However, the mechanism by which CNP improves goat oocyte quality remains unclear. In this study, cumulus-oocyte complexes (COCs) from goats were pre-treated with CNP prior to IVM, and the results showed that pre-treatment with CNP enhanced goat oocyte maturation. First, we discovered that CNP maintained communication between cumulus cells and oocytes by regulating the transzonal projections (TZPs). We then found that CNP treatment reduced abnormal spindle formation and increased the expression of genes associated with spindle assembly and the spindle assembly checkpoint. Moreover, further analysis showed that oocytes exhibited better antioxidant ability in the CNP treatment group, which mainly manifested in higher glutathione (GSH) and lower reactive oxygen species (ROS) concentrations. Enhanced mitochondrial activity was signified via the augmented expression of mitochondrial oxidative metabolism and fusion and fission-related genes, thus diminishing the apoptosis of the oocytes. Overall, these results provide novel insights into the potential mechanism by which CNP treatment before IVM can improve oocyte quality.

Transcriptome sequencing promotes insights on the molecular mechanism of SKP-SC-EVs mitigating denervation-induced muscle atrophy

BACKGROUND

Complex pathophysiological changes accompany denervation-induced skeletal muscle atrophy, but no effective treatment strategies exist. Our previous study indicated that extracellular vesicles derived from skin-derived precursors-derived Schwann cells (SKP-SC-EVs) can effectively mitigate denervation-induced muscle atrophy. However, the specific molecular mechanism remains unclear.

METHODS AND RESULTS

In this study, we used bioinformatics methods to scrutinize the impact of SKP-SC-EVs on gene expression in denervation-induced skeletal muscle atrophy. We found that SKP-SC-EVs altered the expression of 358 genes in denervated skeletal muscles. The differentially expressed genes were predominantly participated in biological processes, including cell cycle, inflammation, immunity, and adhesion, and signaling pathways, such as FoxO and PI3K.Using the Molecular Complex Detection (MCODE) plugin, we identified the two clusters with the highest score: cluster 1 comprised 37 genes, and Cluster 2 consisted of 24 genes. Then, fifty hub genes were identified using CytoHubba. The intersection of Hub genes and genes obtained by MCODE showed that all 23 genes related to the cell cycle in Cluster 1 were hub genes, and 5 genes in Cluster 2 were hub genes and associated with inflammation.

CONCLUSIONS

Overall, the differentially expressed genes in denervated skeletal muscle following SKP-SC-EVs treatment are primarily linked to the cell cycle and inflammation. Consequently, promoting proliferation and inhibiting inflammation may be the critical process in which SKP-SC-EVs delay denervation-induced muscle atrophy. Our findings contribute to a better understanding of the molecular mechanism of SKP-SC-EVs delaying denervation-induced muscle atrophy, offering a promising new avenue for muscle atrophy treatment.

New insights on mitochondrial heteroplasmy observed in ovarian diseases

BACKGROUND

The reportedly high mutation rate of mitochondrial DNA (mtDNA) may be attributed to the absence of histone protection and complete repair mechanisms. Mitochondrial heteroplasmy refers to the coexistence of wild-type and mutant mtDNA. Most healthy individuals carry a low point mutation load (<1 %) in their mtDNA, typically without any discernible phenotypic effects. However, as it exceeds a certain threshold, it may cause the onset of various diseases. Since the ovary is a highly energy-intensive organ, it relies heavily on mitochondrial function. Mitochondrial heteroplasmy can potentially contribute to a variety of significant ovarian disorders.

AIM OF REVIEW

In this review, we have elucidated the close relationship between mtDNA heteroplasmy and ovarian diseases, and summarized novel avenues and strategies for the potential treatment of these ovarian diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Mitochondrial heteroplasmy can potentially contribute to a variety of significant ovarian disorders, including polycystic ovary syndrome, premature ovarian insufficiency, and endometriosis. Current strategies related to mitochondrial heteroplasmy are untargeted and have low bioavailability. Nanoparticle delivery systems loaded with mitochondrial modulators, mitochondrial replacement/transplantation therapy, and mitochondria-targeted gene editing therapy may offer promising paths towards potentially more effective treatments for these diseases, despite ongoing challenges.

Melatonin promotes parthenogenetic development of vitrified-warmed mouse MII oocytes, potentially by reducing oxidative stress through SIRT1

Previous studies have demonstrated that melatonin could ameliorate oxidative stress during the cryopreservation of mouse MII oocytes and their in vitro culture after parthenogenetic activation. However, the underlying molecular mechanism remained poorly understood. This study was conducted to investigate whether melatonin could modulate the oxidative stress in the parthenogenetic 2-cell embryos derived from vitrified-warmed oocytes through SIRT1. The results showed that the reactive oxygen species levels increased, the glutathione levels and SIRT1 expression decreased significantly in parthenogenetic 2-cell embryos derived from cryopreserved oocyte, and the parthenogenetic blastocyst formation rates significantly decreased when compared to those derived from control oocytes. These unfavorable phenomena were prevented by the addition of either 10-9 mol/L melatonin or 10-6 mol/L SRT-1720 (SIRT1 agonist), and it was restored by the supplementation of 10-9 mol/L melatonin in combination with 2 × 10-5 mol/L EX527 (SIRT1 inhibitor). Therefore, the findings from the present study concluded that melatonin may reduce oxidative stress via regulating SIRT1, and potentially promote the parthenogenetic development of vitrified-warmed mouse MII oocytes.

Ru360 protects against vitrification-induced oocyte meiotic defects by restoring mitochondrial function

Oocyte vitrification has been widely application in female fertility preservation. Recent studies found that vitrification of immature (germinal vesicle stage, GV) oocytes increased the risk of aneuploidy during meiotic maturation; however, the underlying mechanisms and the strategies to prevent this defect remain unexplored. In this study, we found that vitrification of GV oocytes decreased the first polarbody extrusion rate (90.51 ± 1.04% vs. 63.89 ± 1.39%, p < 0.05) and increased the aneuploid rate (2.50% vs. 20.00%, p < 0.05), accompanied with a series of defects during meiotic maturation, including aberrant spindle morphology, chromosome misalignment, incorrect Kinetochore-Microtubule attachments (KT-MTs) and weakened spindle assembly checkpoint protein complex (SAC) function. We also found that vitrification disrupted mitochondrial function by increasing mitochondrial Ca²⁺ levels. Importantly, inhibition of mitochondrial Ca²⁺ entry by 1 μM Ru360 significantly restored mitochondrial function and rescued the meiotic defects, indicating that the increase of mitochondrial Ca²⁺, at least, was a cause of meiotic defects in vitrified oocytes. These results shed light on the molecular mechanisms of oocyte vitrification-induced adverse effects of meiotic maturation and provided a potential strategy to improve oocyte cryopreservation protocols further.

Combination of CNP, MT and FLI during IVM Significantly Improved the Quality and Development Abilities of Bovine Oocytes and IVF-Derived Embryos

Oocyte maturation is a critical step in the completion of female gametogenesis in the ovary; thus, for subsequent fertilization and embryogenesis. Vitrification of embryo also has been shown to be closely associated with oocyte maturation. To improve the quality and developmental potential of bovine oocytes derived from in vitro maturation (IVM), Pre-IVM with C-type natriuretic peptide (CNP), melatonin (MT) and in combination, IGF1, FGF2, LIF (FLI) were supplemented in the IVM medium. In this current study, we cultured bovine oocytes in Pre-IVM with CNP for 6 h before transferring them to the IVM medium supplemented with MT and FLI. The developmental potential of bovine oocytes was then investigated by measuring the reactive oxygen species (ROS), the intracellular glutathione (GSH) and ATP levels, the transzonal projections (TZP), the mitochondrial membrane potential (ΔΨm), cacline-AM, and the expression of related genes (cumulus cells (CCs), oocytes, blastocysts). The results revealed that oocytes treated with a combination of CNP, MT, and FLI had dramatically improved the percentage of oocytes developed to blastocyst, ATP content, GSH levels, TZP intensity, the ΔΨm, cacline-AM fluorescence intensity, and considerably reduced ROS levels of oocytes. Furthermore, the survival rate and the hatched rate after vitrification of the CNP+MT+FLI group were significantly higher than those other groups. Thus, we speculated that CNP+MT+FLI increases the IVM of bovine oocytes. In conclusion, our findings deepen our understanding and provide new perspectives on targeting the combination of CNP, MT and FLI to enhance the quality and developmental potential of bovine oocytes.

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).

Coping with Oxidative Stress in Reproductive Pathophysiology and Assisted Reproduction: Melatonin as an Emerging Therapeutical Tool

Infertility is an increasing global public health concern with socio-psychological implications for affected couples. Remarkable advances in reproductive medicine have led to successful treatments such as assisted reproductive techniques (ART). However, the search for new therapeutic tools to improve ART success rates has become a research hotspot. In the last few years, pineal indolamine melatonin has been investigated for its powerful antioxidant properties and its role in reproductive physiology. It is considered a promising therapeutical agent to counteract the detrimental effects associated with oxidative stress in fertility treatments. The aim of the present narrative review was to summarize the current state of the art on the importance of melatonin in reproductive physiology and to provide a critical evaluation of the data available encompassing basic, translational and clinical studies on its potential use in ART to improve fertility success rates.

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.

Antioxidant procyanidin B2 protects oocytes against cryoinjuries via mitochondria regulated cortical tension

BACKGROUND

Irreversible cryodamage caused by oocyte vitrification limited its wild application in female fertility preservation. Antioxidants were always used to antagonist the oxidative stress caused by vitrification. However, the comprehensive mechanism underlying the protective role of antioxidants has not been studied. Procyanidin B2 (PCB2) is a potent natural antioxidant and its functions in response to vitrification are still unknown. In this study, the effects of PCB2 on vitrified-thawed oocytes and subsequent embryo development were explored, and the mechanisms underlying the protective role of PCB2 were systematically elucidated.

RESULTS

Vitrification induced a marked decline in oocyte quality, while PCB2 could improve oocyte viability and further development after parthenogenetic activation. A subsequent study indicated that PCB2 effectively attenuated vitrification-induced oxidative stress, rescued mitochondrial dysfunction, and improved cell viability. Moreover, PCB2 also acts as a cortical tension regulator apart from strong antioxidant properties. Increased cortical tension caused by PCB2 would maintain normal spindle morphology and promote migration, ensure correct meiosis progression and finally reduce the aneuploidy rate in vitrified oocytes. Further study reveals that ATP biosynthesis plays a crucial role in cortical tension regulation, and PCB2 effectively increased the cortical tension through the electron transfer chain pathway. Additionally, PCB2 would elevate the cortical tension in embryo cells at morula and blastocyst stages and further improve blastocyst quality. What's more, targeted metabolomics shows that PCB2 has a beneficial effect on blastocyst formation by mediating saccharides and amino acids metabolism.

CONCLUSIONS

Antioxidant PCB2 exhibits multi-protective roles in response to vitrification stimuli through mitochondria-mediated cortical tension regulation.

Melatonin Improves Quality of Repeated-Poor and Frozen-Thawed Embryos in Human, a Prospective Clinical Trial

OBJECTIVE

In this study, two experiments were performed to assess the effect and the role of melatonin on human in vitro embryo quality.

METHODS

Experiment I: A total of 42 repeated-poor-quality-embryo patients were enrolled, with a total of 181 oocytes retrieval cycles. After IVF, for the same patient, the MT cycles group (10^-7 M melatonin added to the culture medium; n=48) were compared with the previous non-MT cycles group (n=133), following by in vitro culture to blastocyst stage and embryo transfer. 31 patients were transplanted with 65 embryo transfer, including 24 MT embryo transfer, 41 non-MT embryo transfer. Cycle outcomes were compared between the two groups. Experiment II:A total of 143 supernumerary human cleavage-stage embryos (from non-repeated-poor-quality-embryo patients) vitrified on Day 3 after IVF were warmed and randomized into two groups: melatonin group (10^-7 M melatonin added to the culture medium; n=71) and control group (n=72), and then cultured for 72 h. Rate of blastocyst and high-quality blastocyst, reactive oxygen species (ROS) levels of culture media as well as embryonic GPX1, CAT, Mn-SOD, Cu/Zn-SOD, BCL-2, BAX gene expression levels were analyzed.

RESULTS

Experiment I: Results showed that the rate of Day 3 high-quality embryos (29.6% vs.19.5%) in the MT cycles group was significantly higher than that in the non-MT cycles group (P<0.05). The rate of available blastocysts (17.1% vs.12.7%) and clinical pregnancy rate (25.0% vs.17.1%) were in tendency higher in the group treated with melatonin (P>0.05). Experiment II:Results showed that the blastocyst rates in the melatonin administered group were significantly higher than in control group (42.25% vs.26.38%, P<0.05). There were no significant differences in high-quality blastocyst rates. In addition, quantitative PCR showed that the expression of CAT was significantly upregulated by melatonin treatment (P<0.05), while there were no significant differences in the expression of GPX1, Mn-SOD, Cu/Zn-SOD, BAX and BCL-2 gene as well as the levels of ROS.

CONCLUSION

These data showed that melatonin supplement in the culture medium will improve Day 3 high-quality embryos rate of repeated-poor-quality-embryo patients and improve blastocyst rate of vitrified-warmed cleavage-stage embryos, suggesting that melatonin intervention may provide a potential rescue strategy for IVF failures.

CLINICAL TRIAL REGISTRATION

identifier [ChiCTR2200059773].

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.

Treatment of mouse cumulus-oocyte complexes with L-carnitine during vitrification and in vitro maturation affects maturation and embryonic developmental rate after parthenogenetic activation

The technique of oocyte vitrification remains a challenge in most animal species. The present study aimed to evaluate the effects of cumulus cell presence and L-carnitine (LC) treatment during vitrification of selected immature oocytes by brilliant cresyl blue (BCB) staining on maturation and embryonic developmental rate after parthenogenetic activation. Immature oocytes were obtained from C57BL/6 female mice ovaries and stained with BCB. The BCB⁺ cumulus-oocyte complexes (COCs) were then selected and random parts of COCs were denuded from cumulus cells (denuded oocytes: DOs). COCs and DOs were treated with/out LC (0.6 mg/ml) during vitrification and in vitro maturation (IVM) procedures. A number of non-vitrified COCs were also treated with LC during the IVM process (fresh group). Maturation rate, intracellular glutathione (GSH) contents, and developmental competence of oocytes were also examined. The GSH levels in vitrified DOs+LC and vitrified COCs+LC groups were significantly higher (p < 0.01) than untreated vitrified-warmed COCs and DOs. Maturation rate and blastocyst developmental rate were reduced after the vitrification-warming procedure compared with the fresh group. The vitrified COCs+LC group showed a higher percentage of mature oocytes and the ability to develop to blastocyst stage than the vitrified-warmed DOs group (p < 0.01). These data indicated that the presence of cumulus cells around the competent oocyte and LC treatment during vitrification and IVM procedure could improve parthenogenetic developmental competence of vitrified-warmed oocytes by increasing GSH levels and accelerating oocyte maturation.

Melatonin Promotes in vitro Development of Vitrified-Warmed Mouse GV Oocytes, Potentially by Modulating Phosphorylation of Drp1

Previous studies have shown that melatonin can mitigate cryopreservation-induced mitochondrial dysfunction in oocytes; however, the underlying molecular mechanism remains unclear. The objective of the present study was to investigate whether melatonin can improve the mitochondrial function during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes by modulating phosphorylation of dynamin related protein 1 (Drp1). Vitrification/warming procedures resulted in the following: (1) After cryopreservation of mouse GV oocytes, the phosphorylation level of Drp1 at Ser616 (p-Drp1 Ser616) in metaphase II (MII) oocytes was increased (P < 0.05). Furthermore, the rates of in vitro maturation, cleavage and blastocyst formation after parthenogenetic activation were decreased (P < 0.05). (2) In MII oocytes, the expression levels of translocase of the mitochondrial outer membrane 20 (TOMM20), mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) content, and mRNA levels of mitochondrial biogenesis-related genes (Sirt1, Pgc-1α, Tfam) were all decreased (P < 0.05), and (3) Reactive oxygen species (ROS) level, early apoptosis level, Cytochrome C release and mRNA levels of pro-apoptotic related genes (Bax, Caspase9, Caspase3) in MII oocytes were all increased (P < 0.05). The results of this study further revealed that negative impacts of GV oocyte cryopreservation were mitigated by supplementation of warming and in vitro maturation media with 10⁻⁷mol /L melatonin or 2 x 10⁻⁵mol/L Mdivi-1 (Drp1 inhibitor). Therefore, we concluded that 10⁻⁷mol/L melatonin improved mitochondrial function, reduced oxidative stress and inhibited apoptosis by regulating phosphorylation of Drp1, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

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.

Melatonin Promotes In Vitro Maturation of Vitrified-Warmed Mouse Germinal Vesicle Oocytes, Potentially by Reducing Oxidative Stress through the Nrf2 Pathway

Simple Summary

Cryopreservation of oocytes can cause high oxidative stress, reduce the quality of vitrified-warmed oocytes, and seriously hinder the application of oocyte cryopreservation technology in production and medicine. In this work, we found for the first time that melatonin can exert antioxidant effects through receptors and regulate the Nrf2 antioxidant pathway to respond to oxidative stress of vitrified-warmed oocytes, thereby improving both oocyte quality and the potential for subsequent development. The results illustrated the molecular mechanism of melatonin’s antioxidant effect in vitrified-warmed oocytes and provided a theoretical basis for the application of melatonin in the cryopreservation of oocytes. These findings are of great significance for the further application of oocyte cryopreservation technology to production and assisted reproduction in the future.

Abstract

Previously it was reported that melatonin could mitigate oxidative stress caused by oocyte cryopreservation; however, the underlying molecular mechanisms which cause this remain unclear. The objective was to explore whether melatonin could reduce oxidative stress during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes through the Nrf2 signaling pathway or its receptors. During in vitro maturation of vitrified-warmed mouse GV oocytes, there were decreases (p < 0.05) in the development rates of metaphase I (MI) oocytes and metaphase II (MII) and spindle morphology grades; increases (p < 0.05) in the reactive oxygen species (ROS) levels; and decreases (p < 0.05) in expressions of Nrf2 signaling pathway-related genes (Nrf2, SOD1) and proteins (Nrf2, HO-1). However, adding 10⁻⁷ mol/L melatonin to both the warming solution and maturation solutions improved (p < 0.05) these indicators. When the Nrf2 protein was specifically inhibited by Brusatol, melatonin did not increase development rates, spindle morphology grades, genes, or protein expressions, nor did it reduce vitrification-induced intracellular oxidative stress in GV oocytes during in vitro maturation. In addition, when melatonin receptors were inhibited by luzindole, the ability of melatonin to scavenge intracellular ROS was decreased, and the expressions of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1) were not restored to control levels. Therefore, we concluded that 10⁻⁷ mol/L melatonin acted on the Nrf2 signaling pathway through its receptors to regulate the expression of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1), and mitigate intracellular oxidative stress, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

Applications of Melatonin in Female Reproduction in the Context of Oxidative Stress

Oxidative stress has been recognized as one of the causal mediators of female infertility by affecting the oocyte quality and early embryo development. Improving oxidative stress is essential for reproductive health. Melatonin, a self-secreted antioxidant, has a wide range of effects by improving mitochondrial function and reducing the damage of reactive oxygen species (ROS). This minireview illustrates the applications of melatonin in reproduction from four aspects: physiological ovarian aging, vitrification freezing, in vitro maturation (IVM), and oxidative stress homeostasis imbalance associated with polycystic ovary syndrome (PCOS), emphasising the role of melatonin in improving the quality of oocytes in assisted reproduction and other adverse conditions.

Melatonin promotes in vitro maturation of vitrified-warmed mouse GV oocytes potentially by modulating MAD2 protein expression of SAC component through MTRs

Previous studies have shown that melatonin (MT) can ameliorate vitrification-inflicted damage in mouse germinal vesicle (GV) oocytes, however, the key mechanistic basis of this improvement still remains poorly understood. This study was conducted to investigate whether MT can improve in vitro developmental potential of vitrified-warmed GV oocytes through its receptors. The fresh oocytes were randomly divided into four groups: untreated (control group, F), vitrified by open-pulled straw method (vitrification group, V), vitrification group with 100 nmol/L MT supplementation (vitrification + MT group, VM), and with 100 nmol/L MT plus 100 nmol/L luzindole administration (vitrification + MT + luzindole group, VML) or with 50 nmol/L ramelteon addition (vitrification + ramelteon group; VR). After warming, oocytes were cultured in vitro, and MT receptors (MTRs), MAD2 (mitotic arrest deficient 2), Securin and CyclinB1 protein levels and spindle morphology were evaluated. The ratio of oocytes developed to the metaphase I (MI) and metaphase II (MII) stages was also assessed. The results showed that after vitrification-warming, the in vitro maturation rate of GV oocytes was significantly lower compared to the control (F) group. Vitrification also significantly impaired the spindle morphology, decreased the protein level of MTRs and Securin, and decreased MAD2 levels in MI oocytes. However, when MT or ramelteon (MTRs agonist) were added (group wise) to warming and maturation media, the maturation rate of GV oocytes was significantly increased, the normal proportion of the spindle morphology increased, and the expression level of MAD2 increased in their resulting MI oocytes compared to the vitrification group. However, following addition of both MT and ramelteon, the maturation rate of GV oocyte showed no significant difference between VML and vitrification groups. The spindle morphology and MAD2 levels in MI oocytes were comparable to the vitrification group but differed significantly from the VM group. Taken together, finding of the present study shows that MT (100 nmol/L) can ameliorate the in vitro maturation of vitrified-warmed mouse GV oocytes, potentially by improving the spindle morphology, modulating MAD2 protein level and promoting the development of MI stage oocytes through MTRs.

Melatonin improves the first cleavage of parthenogenetic embryos from vitrified-warmed mouse oocytes potentially by promoting cell cycle progression

Background

This study investigated the effect of melatonin (MT) on cell cycle (G1/S/G2/M) of parthenogenetic zygotes developed from vitrified-warmed mouse metaphase II (MII) oocytes and elucidated the potential mechanism of MT action in the first cleavage of embryos.

Results

After vitrification and warming, oocytes were parthenogenetically activated (PA) and in vitro cultured (IVC). Then the spindle morphology and chromosome segregation in oocytes, the maternal mRNA levels of genes including Miss, Doc1r, Setd2 and Ythdf2 in activated oocytes, pronuclear formation, the S phase duration in zygotes, mitochondrial function at G1 phase, reactive oxygen species (ROS) level at S phase, DNA damage at G2 phase, early apoptosis in 2-cell embryos, cleavage and blastocyst formation rates were evaluated. The results indicated that the vitrification/warming procedures led to following perturbations 1) spindle abnormalities and chromosome misalignment, alteration of maternal mRNAs and delay in pronucleus formation, 2) decreased mitochondrial membrane potential (MMP) and lower adenosine triphosphate (ATP) levels, increased ROS production and DNA damage, G1/S and S/G2 phase transition delay, and delayed first cleavage, and 3) increased early apoptosis and lower levels of cleavage and blastocyst formation. Our results further revealed that such negative impacts of oocyte cryopreservation could be alleviated by supplementation of warming, recovery, PA and IVC media with 10^− 9 mol/L MT before the embryos moved into the 2-cell stage of development.

Conclusions

MT might promote cell cycle progression via regulation of MMP, ATP, ROS and maternal mRNA levels, potentially increasing the first cleavage of parthenogenetic zygotes developed from vitrified–warmed mouse oocytes and their subsequent development.

Mitochondria: emerging therapeutic strategies for oocyte rescue

As the vital organelles for cell energy metabolism, mitochondria are essential for oocyte maturation, fertilization, and embryo development. Abnormalities in quantity, quality, and function of mitochondria are closely related to poor fertility and disorders, such as decreased ovarian reserve (DOR), premature ovarian aging (POA), and ovarian aging, as well as maternal mitochondrial genetic disease caused by mitochondrial DNA (mtDNA) mutations or deletions. Mitochondria have begun to become a therapeutic target for infertility caused by factors such as poor oocyte quality, oocyte aging, and maternal mitochondrial genetic diseases. Mitochondrial replacement therapy (MRT) has attempted to use heterologous or autologous mitochondria to rebuild healthy state of oocyte by increasing the amount of mitochondria (e.g., partial ooplasm transfer, autologous mitochondrial transfer), or to stop the transmission of mtDNA diseases by replacing abnormal maternal mitochondria (e.g., pronuclei transfer, spindle transfer, polar body transfer). Among them, autologous mitochondrial transfer is the most promising therapeutic technology as of today which does not involve using a third party, but its clinical efficacy is controversial due to many factors such as the aging phenomenon of germ line cells, the authenticity of the existence of ovarian stem cells (OSC), and secondary damage caused by invasive surgery to patients with poor ovarian function. Therefore, the research of optimal autologous cell type that can be applied in autologous mitochondrial transfer is an area worthy of further exploration. Besides, the quality of germ cells can also be probably improved by the use of compounds that enhance mitochondrial activity (e.g., coenzyme Q10, resveratrol, melatonin), or by innovative gene editing technologies which have shown capability in reducing the risk of mtDNA diseases (e.g., CRISPR/Cas9, TALENTs). Though the current evidences from animal and clinical trials are not sufficient, and some solutions of technical problems are still needed, we believe this review will guide a new direction in the possible clinical applied mitochondrial-related therapeutic strategies in reproductive medicine.

Highly successful production of viable mice derived from vitrified germinal vesicle oocytes

The vitrification of immature germinal vesicle (GV) oocytes is an important way to preserve genetic resources and female fertility. However, it is well known that cryopreserved GV oocytes have very poor developmental ability and that further improvement in this technique is needed. We previously reported the successful vitrification of matured mouse oocytes with enclosed cumulus cells using the calcium-free vitrification solution supplemented with ethylene glycol (EG) by the minimal volume cooling (MVC) method. In this study, we investigated whether our method is applicable to the vitrification of mouse oocytes at the GV stage (GV oocytes). Following maturation and fertilization in vitro, vitrified GV oocytes showed high survival (94.3 ± 2.0%) and maturation (94.3 ± 2.1%) rates. Although the fertilization and blastocyst rates of vitrified oocytes (fertilization: 46.6 ± 4.9% and blastocyst: 46.6 ± 3.0%) were significantly lower than those of fresh oocytes (fertilization: 73.0 ± 7.1% and blastocyst: 71.6 ± 8.0%) (P < 0.01), there were no differences in the ability to develop to term between fresh oocytes (50.0 ± 8.4%) and vitrified oocytes (37.5 ± 4.6%) (P > 0.05). In conclusion, we here show, for the first time, the efficient production of live mice derived from vitrified GV oocytes.

Melatonin improves the effect of cryopreservation on human oocytes by suppressing oxidative stress and maintaining the permeability of the oolemma

Cryopreservation causes cryoinjury to oocytes and impairs their developmental competence. Melatonin (MLT) can improve the effect of cryopreservation in animal oocytes. However, no such studies on human oocytes have been reported. In this study, collected in vitro-matured human oocytes were randomly divided into the following groups: fresh group, MLT-treated cryopreservation (MC) group, and no-MLT-treated cryopreservation (NC) group. After vitrification and warming, viable oocytes from these three groups were assessed for their mitochondrial function, ultrastructure, permeability of oolemma, early apoptosis, developmental competence, and cryotolerance-related gene expression. First, fluorescence staining results revealed that oocytes from the 10^-9  M subgroup showed the lowest intracellular reactive oxygen species and Ca²⁺ levels and highest mitochondrial membrane potential among the MC subgroups (10^-11 , 10^-9 , 10^-7 , and 10^-5  M). In subsequent experiments, oocytes from the 10^-9  M-MC group were observed to maintain the normal ultrastructural features and the permeability of the oolemma. Compared with those of the oocytes in the NC group, the early apoptosis rate significantly decreased (P < .01), whereas both the high-quality cleavage embryo and blastocyst rates significantly increased (both P < .05) in the oocytes of the 10^-9  M-MC group. Finally, single-cell RNA sequencing and immunofluorescence results revealed that aquaporin (AQP) 1/2/11 gene expression and AQP1 protein expression were upregulated in the MC group. Therefore, these results suggest that MLT can improve the effect of cryopreservation on human oocytes by suppressing oxidative stress and maintaining the permeability of the oolemma.

Enhanced Cryoprotective Effect of Melatonin and Resveratrol by Coencapsulation: Improved In Vitro Development of Vitrified-Warmed Mouse Germinal Vesicle Oocytes

Oocyte vitrification, as a vital step in reproductive medicine, is strongly associated with lower development caused by cryodamaging factors, such as oxidative stress. In this study, we evaluated the antioxidative synergistic effects of Melatonin (Mel) and Resveratrol (RES) coencapsulated by solid lipid nanocarriers (SLNs) against the pure antioxidant combination (Mel+RES). In this research, the formation of Mel+RES-SLN was confirmed by Fourier-transformed infrared spectroscopy. The average mean diameter, size distribution, polydispersity index, and zeta potential of particles were measured by Zetasizer, and the morphology was evaluated by scanning electron microscopy. In addition, the encapsulation efficiency (EE%) or drug loading capacity (DL%) of the nanocapsule was determined by spectrophotometric methods. Germinal vesicle (GV)-stage oocytes harvested from 6- to 12-week-old female NMRI mice were randomly divided into seven groups for in vitro studies. In these groups, (0, 10^-12 M + 0.5 μM, 10^-9 M + 2 μM, or 10^-6 M + 10 μM) of Mel+RES/Mel+RES-SLN were added into vitrification media. After thawing, oocytes were matured, fertilized, and cultured for 3 days. Extra/intracellular reactive oxygen species (ROS) levels were measured in in vitro maturation medium after 24 hours. Our results revealed a significant improvement in the normal morphology of warmed GV-stage oocytes, GV breakdown (GVBD) rate, Metaphase II (MII)-stage oocyte formation, fertilization rate, early embryo development, and a significant reduction in intra/extracellular ROS level when vitrification media was supplemented with the lowest Mel+RES-SLN concentration. In vitro studies also demonstrated that the highest concentration of Mel+RES-SLN was safe, without a detrimental effect on embryonic development upon treatment. In conclusion, the lowest concentration of Mel+RES-SLN supplementation in GV-stage oocyte vitrification media improved maturation, fertilization, and embryo development rate and decreased extra/intracellular ROS level through an enhanced/controlled intracellular penetration compared to the pure Mel+RES.

Ceratonia siliqua (Carob) extract improved in vitro development of vitrified-warmed mouse germinal vesicle oocytes: assessment of possible mechanism

Oocyte banking is a vital step for safekeeping and spreading genetic resources of animals. It is also used for fertility preservation of human. Oocyte vitrification is closely related to the lower developmental competence which includes the cryo-injury arisen during vitrification. The aim of the present study was to evaluate the maturation, embryonic development and production of reactive oxygen species (ROS) of mice oocytes following the supplementation vitrification media with different concentrations of Ceratonia siliqua (carob) extracts. In this experimental study, germinal vesicle oocytes collected from 8 to 10 week-old female NMRI mice (30-40 gr) were randomly divided into six groups of vitrification media supplemented with 0 (control), 5, 10, 20, 30 and 50 µg/ml C. siliqua. After thawing, oocytes were put in an in vitro maturation medium (IVM) (α-MEM: Alpha Minimum Essential Medium). 3-4 and 24 h (hr) later, the oocyte nuclear maturity was checked. Standard in vitro fertilization was performed on the matured oocytes (MII), and embryonic development was followed. Extra- and intra-cellular ROS was measured in IVM medium after 24 h of oocyte incubation. The addition of 20 and 30 μg/ml C. siliqua extract to vitrification media improved normal morphology of warmed germinal vesicle (GV) oocytes, rate of germinal vesicle break down (GVBD), and metaphase 2 (MII) oocyte formation significantly (p < 0.05). Fertilization rate, (embryonic development to 2 cells stage, 4-8 cells stage, and > 8 cells stage increased in the 30 μg/ml C. siliqua group significantly (p < 0.05). Furthermore, supplementation of 30 μg/ml C. siliqua in vitrification media significantly decreased extra- and intra-cellular of ROS as well as embryonic fragmentation (p < 0.05). In conclusion, supplementation of GV oocyte vitrification media with carob extract improved maturation, fertilization, and embryonic development rate and decreased extra- and intra-cellular ROS levels.

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 Error-Prone Kinetochore-Microtubule Attachments During Meiosis I in Vitrified Oocytes

Oocytes vitrification is frequently applied in assisted reproductive technologies. However, chromosomes segregation was error-prone during meiosis maturation of vitrified oocytes. The fidelity of chromosomes segregation depends on the correct kinetochore-microtubule attachments (KT-MTs). In meiosis I, the Aurora B/C would not spatially separate from the attachment sites upon bivalents stretched. Oocytes lack a mechanism for coordinating bivalent stretching and Aurora B/C inhibition in meiosis I. Thus, the KT-MTs are unstable in oocytes. In this study, we firstly found the incorrect KT-MTs were markedly increased in vitrified oocytes. The Aurora B/C activity in vitrified oocytes was significantly increased when the bivalents were stretched. This Aurora B/C activity could not induce a SAC response, as the SAC protein Mad2 was significantly decreased during MI stage in vitrified oocytes. Thus, the KT-MTs in vitrified oocytes were error-prone. This study, for the first time, revealed the mechanism of the incorrect KT-MTs occurred in vitrified oocytes and provided a theoretical basis for further improvement of oocytes vitrification.

Dietary Selenium Supplementation Ameliorates Female Reproductive Efficiency in Aging Mice

Female reproductive (ovarian) aging is distinctively characterized by a markedly reduced reproductive function due to a remarkable decline in quality and quantity of follicles and oocytes. Selenium (Se) has been implicated in playing many important biological roles in male fertility and reproduction; however, its potential roles in female reproduction, particularly in aging subjects, remain poorly elucidated. Therefore, in the current study we used a murine model of female reproductive aging and elucidated how different Se-levels might affect the reproductive efficiency in aging females. Our results showed that at the end of an 8-week dietary trial, whole-blood Se concentration and blood total antioxidant capacity (TAOC) were significantly reduced in Se-deficient (0.08 mg Se/kg; Se-D) mice, whereas both of these biomarkers were significantly higher in inorganic (0.33 mg/kg; ISe-S) and organic (0.33 mg/kg; OSe-S) Se-supplemented groups. Similarly, compared to the Se-D group, Se supplementation significantly ameliorated the maintenance of follicles and reduced the rate of apoptosis in ovaries. Meanwhile, the rate of in vitro-produced embryos resulting from germinal vesicle (GV) oocytes was also significantly improved in Se-supplemented (ISe-S and OSe-S) groups compared to the Se-D mice, in which none of the embryos developed to the hatched blastocyst stage. RT-qPCR results revealed that mRNA expression of Gpx1, Gpx3, Gpx4, Selenof, p21, and Bcl-2 genes in ovaries of aging mice was differentially modulated by dietary Se levels. A considerably higher mRNA expression of Gpx1, Gpx3, Gpx4, and Selenof was observed in Se-supplemented groups compared to the Se-D group. Similarly, mRNA expression of Bcl-2 and p21 was significantly lower in Se-supplemented groups. Immunohistochemical assay also revealed a significantly higher expression of GPX4 in Se-supplemented mice. Our results reasonably indicate that Se deficiency (or marginal levels) can negatively impact the fertility and reproduction in females, particularly those of an advancing age, and that the Se supplementation (inorganic and organic) can substantiate ovarian function and overall reproductive efficiency in aging females.