Rapamycin treatment during in vitro maturation of oocytes improves embryonic development after parthenogenesis and somatic cell nuclear transfer in pigs

Role of programmed cell death in mammalian ovarian follicular atresia

Programmed cell death (PCD) is a fundamental process in the development process of organisms, including apoptosis, autophagy, ferroptosis, and pyroptosis. In mammalian ovaries, 99 % of follicles undergo atresia, while only 1 % mature and ovulate, which limits the reproductive efficiency of mammals. The PCD process is closely related to the regulation of follicle development and atresia. Recently, an increasing number of studies have reported that autophagy, pyroptosis, and ferroptosis of PCD are involved in regulating granulosa cell apoptosis and follicular atresia. Granulosa cell apoptosis is a hallmark of follicular atresia. Therefore, an understanding of molecular mechanisms regulating PCD events is required for future advances in the diagnosis and management of various disorders of follicular atresia. This review summarizes recent work on apoptosis, autophagy, pyroptosis, and ferroptosis of PCD that affect granulosa cell survival and follicular atresia, and further elucidating the mechanisms of follicular atresia and providing new directions for improving the reproductive capacity of humans and animals.

Mitochondria as therapeutic targets in assisted reproduction

Mitochondria are essential organelles with specialized functions, which play crucial roles in energy production, calcium homeostasis, and programmed cell death. In oocytes, mitochondrial populations are inherited maternally and are vital for developmental competence. Dysfunction in mitochondrial quality control mechanisms can lead to reproductive failure. Due to their central role in oocyte and embryo development, mitochondria have been investigated as potential diagnostic and therapeutic targets in assisted reproduction. Pharmacological agents that target mitochondrial function and show promise in improving assisted reproduction outcomes include antioxidant coenzyme Q10 and mitoquinone, mammalian target of rapamycin signaling pathway inhibitor rapamycin, and nicotinamide mononucleotide. Mitochondrial replacement therapies (MRTs) offer solutions for infertility and mitochondrial disorders. Autologous germline mitochondrial energy transfer initially showed promise but failed to demonstrate significant benefits in clinical trials. Maternal spindle transfer (MST) and pronuclear transfer hold potential for preventing mitochondrial disease transmission and improving oocyte quality. Clinical trials of MST have shown promising outcomes, but larger studies are needed to confirm safety and efficacy. However, ethical and legislative challenges complicate the widespread implementation of MRTs.

Dietary restriction and life-history trade-offs: insights into mTOR pathway regulation and reproductive investment in Japanese quail

Resources are needed for growth, reproduction and survival, and organisms must trade off limited resources among competing processes. Nutritional availability in organisms is sensed and monitored by nutrient-sensing pathways that can trigger physiological changes or alter gene expression. Previous studies have proposed that one such signalling pathway, the mechanistic target of rapamycin (mTOR), underpins a form of adaptive plasticity when individuals encounter constraints in their energy budget. Despite the fundamental importance of this process in evolutionary biology, how nutritional limitation is regulated through the expression of genes governing this pathway and its consequential effects on fitness remain understudied, particularly in birds. We used dietary restriction to simulate resource depletion and examined its effects on body mass, reproduction and gene expression in Japanese quails (Coturnix japonica). Quails were subjected to feeding at 20%, 30% and 40% restriction levels or ad libitum for 2 weeks. All restricted groups exhibited reduced body mass, whereas reductions in the number and mass of eggs were observed only under more severe restrictions. Additionally, dietary restriction led to decreased expression of mTOR and insulin-like growth factor 1 (IGF1), whereas the ribosomal protein S6 kinase 1 (RPS6K1) and autophagy-related genes (ATG9A and ATG5) were upregulated. The pattern in which mTOR responded to restriction was similar to that for body mass. Regardless of the treatment, proportionally higher reproductive investment was associated with individual variation in mTOR expression. These findings reveal the connection between dietary intake and the expression of mTOR and related genes in this pathway.

Addition of rapamycin or co-culture with cumulus cells from younger reproductive age women does not improve rescue in vitro oocyte maturation or euploidy rates in older reproductive age women

Both spontaneously conceived pregnancies and those achieved using assisted reproduction decline with advancing maternal age. In this study, we tested if rapamycin and/or cumulus cells (CCs) from young donors could improve oocyte maturation and euploidy rates of germinal vesicle (GV) stage oocytes obtained from older women of reproductive age. A total of 498 GVs from 201 women >38 years (40.6 ± 1.8, mean ± SD) were included. GVs were randomly assigned into five groups for rescue IVM: control (with no CCs and no rapamycin); with autologous CCs; with autologous CCs and rapamycin; with CCs from young women (<35 years); and with CCs from young women and rapamycin. After 24 h of culture, the first polar body (PB) was biopsied in metaphase II oocytes, and the cytogenetic constitution was assessed using next-generation sequencing for both oocytes and PBs. Comparable maturation rates were found (56.2%, 60.0%, 46.5%, 51.7%, and 48.5% for groups 1-5, respectively; P = 0.30). Similarly, comparable euploidy rates were observed in the five groups (41.5%, 37.8%, 47.2%, 43.6%, and 47.8% for Groups 1-5, respectively; P = 0.87). Our findings indicate that rescue IVM is effective for obtaining mature euploid oocytes in older women of reproductive age, and that incubation with rapamycin or CCs obtained from young donors does not improve the maturation or euploidy rate.

Rapamycin encourages the maintenance of mitochondrial dynamic balance and mitophagy activity for improving developmental competence of blastocysts in porcine embryos in vitro

Rapamycin induces autophagosome formation and activity during oocyte maturation, improved fertilization ability of matured oocytes, and early embryonic developmental competence. However, potential changes in mitochondrial fission and mitophagy via regulation of autophagy in early porcine embryonic development have not been previously studied. Here, we investigated embryonic developmental ability and quality of porcine embryos 2 days after in vitro fertilization and following treatment with 1 and 10 nM rapamycin. As a results, 1 nM rapamycin exposure significantly improved (p < 0.05) blastocyst developmental competence compared to that in nontreated embryos (nontreated: 26.2 ± 5.7% vs. 1 nM rapamycin: 35.3 ± 5.1%). We observed autophagic (LC3B) and mitochondrial fission protein expression (dynamin-related protein-1 [DRP1] and pDRP1-Ser616) at the cleavage stage of 1 and 10 nM rapamycin-treated porcine embryos, using Western blot and immunofluorescence analyses. Interestingly, 1 nM rapamycin treatment significantly improved autophagy formation, mitochondrial activation, and mitochondrial fission protein levels (p < 0.05; p-DRP1 [Ser616]) at the cleavage stage of porcine embryos. Additionally, mitophagy was significantly increased in blastocysts treated with 1 nM rapamycin. In conclusion, our results suggest that rapamycin promotes blastocyst development ability in porcine embryos through mitochondrial fission, activation, and mitophagy in in vitro culture.

Rapamycin improves the quality and developmental competence of in vitro matured oocytes in aged mice and humans

Women over age 35 suffer from the inadequate number and poor quality of oocytes during assisted reproductive treatment, and making full use of the oocytes by in vitro maturation (IVM) is crucial. Rapamycin could improve the developmental competences of the post-maturation oocytes during in vitro aging, yet its effects on the IVM process of oocytes from an aged population were not clear. In this study, the immature oocytes from aged mice or older women underwent IVM with or without 10 nM rapamycin, followed by parthenogenetic activation or insemination and embryo culture. The developmental competence and quality of IVM oocytes in both groups were compared. The results showed that in aged mice, the maturation rate, activation rate, and cleavage rate of IVM oocytes were significantly elevated in the rapamycin group. Additionally, oocytes cultured with rapamycin presented decreased ROS levels, reduced chromosome aberration, and attenuated levels of γ-H2AX. During IVM of oocytes from older women, the GVBD rate, 24 h maturation rate, and 48 h maturation rate were increased in the rapamycin group, compared with those in the control group, although without significant differences. After intracytoplasmic sperm injection (ICSI) and further culture of human oocytes, the high-quality embryo rate in the rapamycin group was significantly elevated. Overall, rapamycin improved IVM outcomes of oocytes from aged mice and older women. The specific mechanism of the positive effects of rapamycin on IVM outcomes might be reducing ROS levels, mitigating DNA damage, and promoting developmental potential.

Rapamycin improves the developmental competence of human oocytes by alleviating DNA damage during IVM

STUDY QUESTION

Can rapamycin improve the developmental competence of human oocytes during the IVM process?

SUMMARY ANSWER

Rapamycin at 10 nM could markedly improve the developmental competence of human oocytes undergoing IVM.

WHAT IS KNOWN ALREADY

Embryos derived from oocytes that mature in vitro have lower developmental competence than sibling embryos derived from oocytes matured in vivo. Rapamycin was shown to effectively improve IVM outcomes in mammalian oocytes; however, its effects on IVM of human oocytes have not been investigated.

STUDY DESIGN SIZE DURATION

In 2021, donated immature oocytes (n = 202) from 80 infertile couples receiving ICSI were included in a control group, and 156 oocytes from 72 couples were included in a rapamycin group. The oocytes underwent IVM with 10 nM rapamycin or without (control) rapamycin, followed by insemination by ICSI and embryo culture.

PARTICIPANTS/MATERIALS SETTING METHODS

The germinal vesicle breakdown (GVBD), maturation, normal fertilization, high-quality embryo (HQE) and blastocyst formation rates were calculated to evaluate the developmental competence of IVM oocytes, and fluorescence staining was used to assess DNA damage levels of oocytes in both groups. Whole-genome amplification and DNA sequencing were performed to analyze chromosome euploidy in embryos derived from the rapamycin group.

MAIN RESULTS AND THE ROLE OF CHANCE

The baseline characteristics of patients who donated oocytes for the two experimental groups were similar. In the control group, GVBD happened in 135 (66.8%) oocytes, and the maturation rate reached 52.5% at 24 h and 63.4% at 48 h. In the rapamycin group, 143 (91.7%) oocytes underwent GVBD, and the maturation rate reached 60.3% at 24 h and 82.7% at 48 h. Following ICSI, more HQEs were obtained in the rapamycin group versus control (34.2% versus 22.1%, respectively, P = 0.040), although with comparable fertilization rates in the two groups. In addition, the levels of histone γH2AX in oocytes cultured with 10 nM rapamycin were markedly decreased, compared with those in the control group (0.3 ± 0.0 versus 0.6 ± 0.1, respectively, P = 0.048). Embryos with normal karyotype could be obtained from oocytes cultured with rapamycin.

LIMITATIONS REASONS FOR CAUTION

Our preliminary results indicated that the addition of rapamycin during human oocyte IVM did not cause extra aneuploidy. However, this safety evaluation of rapamycin treatment was based on limited samples and more data are needed before possible application in the clinic.

WIDER IMPLICATIONS OF THE FINDINGS

In the current study, 10 nM rapamycin was applied in the IVM process of human oocytes for the first time and showed positive effects, providing new insights for potentially improving IVM outcomes in the clinic. There were subtle differences between the results presented here on human oocytes and our previous studies on mouse oocytes, indicating the necessity of more research on human samples.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the research grants from National Key Research and Development Project (2018YFC1002103) and Health Commission of Hubei Province scientific research project (WJ2021M110). All authors declared no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Rapamycin improves the quality and developmental competence of mice oocytes by promoting DNA damage repair during in vitro maturation

BACKGROUND

Increasing evidence has shown that the mammalian target of rapamycin (mTOR) pathway plays a critical role in oocyte meiosis and embryonic development, however, previous studies reporting the effects of rapamycin on oocyte IVM showed different or even opposite results, and the specific mechanisms were not clear.

METHODS

The immature oocytes from female mice underwent IVM with rapamycin at different concentrations to select an optimal dose. The maturation rate, activation rate, subsequent cleavage and blastocyst formation rates, spindle assembly, chromosome alignment, mitochondrial membrane potential (MMP), ROS levels, and DNA damage levels were evaluated and compared in oocytes matured with or without rapamycin. In addition, the expression levels of genes associated with mTORC1 pathway, spindle assembly, antioxidant function, and DNA damage repair (DDR) were also assessed and compared.

RESULTS

Rapamycin at 10 nM was selected as an optimal concentration based on the higher maturation and activation rate of IVM oocytes. Following subsequent culture, cleavage and blastocyst formation rates were elevated in activated embryos from the rapamycin group. Additionally, oocytes cultured with 10 nM rapamycin presented decreased ROS levels, reduced chromosome aberration, and attenuated levels of γ-H2AX. No significant effects on the percentages of abnormal spindle were observed. Correspondingly, the expressions of Nrf2, Atm, Atr, and Prkdc in IVM oocytes were markedly increased, following the inhibition of mTORC1 pathway by 10 nM rapamycin.

CONCLUSION

Rapamycin at 10 nM could ameliorate the developmental competence and quality of IVM oocytes of mice, mainly by improving the chromosome alignments. The inhibition of mTORC1 pathway, which involved in activating DDR-associated genes may act as a potential mechanism for oocyte quality improvement by rapamycin.

Beneficial Effects of Neurotrophin-4 Supplementation During in vitro Maturation of Porcine Cumulus-Oocyte Complexes and Subsequent Embryonic Development After Parthenogenetic Activation

Neurotrophin-4 (NT-4) is a neurotrophic factor that plays an important role in follicular development and oocyte maturation. However, it is not yet known whether NT-4 is related to oocyte maturation and follicular development in pigs. This study aims to investigate the effects of NT-4 supplementation during in vitro maturation (IVM) of porcine oocytes and subsequent embryonic development after parthenogenetic activation (PA). First, NT-4 and its receptors (TrkB and p75^NTR) were identified through fluorescent immunohistochemistry in porcine ovaries. NT-4 was mainly expressed in theca and granulosa cells; phospho-TrkB and total TrkB were expressed in theca cells, granulosa cells, and oocytes; p75^NTR was expressed in all follicular cells. During IVM, the defined maturation medium was supplemented with various concentrations of NT-4 (0, 1, 10, and 100 ng/mL). After IVM, the nuclear maturation rate was significantly higher in the 10 and 100 ng/mL NT-4 treated groups than in the control. There was no significant difference in the intracellular reactive oxygen species levels in any group after IVM, but the 1 and 10 ng/mL NT-4 treatment groups showed a significant increase in the intracellular glutathione levels compared to the control. In matured cumulus cells, the 10 ng/mL NT-4 treatment group showed significantly increased cumulus expansion-related genes and epidermal growth factor (EGF) signaling pathway-related genes. In matured oocytes, the 10 ng/mL treatment group showed significantly increased expression of cell proliferation-related genes, antioxidant-related genes, and EGF signaling pathway-related genes. We also investigated the subsequent embryonic developmental competence of PA embryos. After PA, the cleavage rates significantly increased in the 10 and 100 ng/mL NT-4 treatment groups. Although there was no significant difference in the total cell number of blastocysts, only the 10 ng/mL NT-4 treatment group showed a higher blastocyst formation rate than the control group. Our findings suggest that supplementation with the 10 ng/mL NT-4 can enhance porcine oocyte maturation by interacting with the EGF receptor signaling pathway. In addition, we demonstrated for the first time that NT-4 is not only required for porcine follicular development, but also has beneficial effects on oocyte maturation and developmental competence of PA embryos.

Effects of electromagnetic waves on oocyte maturation and embryonic development in pigs

Our living environment has been full of electromagnetic radiation (EMR) due to the prevailing electronic devices and equipment. Intermediate frequency electromagnetic field (IF-EMF) or waves constitute a significant part of EMR; therefore, an increasing number of household electrical appliances have become a source of IF-EMF, and concerns about IF-EMF on health are gaining more attention. However, little information is available about its impact on female reproductive traits, such as germ cell viability and early embryonic development, particularly at the cellular and molecular levels. In this study, we used porcine oocytes as a model system to explore the effect of IF-EMF at various intensities on the in vitro maturation (IVM) of oocytes and their subsequent embryonic development. Our results showed that no difference in oocyte maturation rates was detected among groups, but the cleavage and blastocyst rates of parthenotes derived from EMF-treated oocytes decreased with the weaker IF-EMF intensity (25 and 50 Gauss, G) groups compared to the control group (P < 0.05). For cytoplasmic maturation, the weaker IF-EMF intensity groups also showed a peripheral pattern of mitochondrial distribution resembling that of immature oocytes and increased autophagy activity. No obvious differences in cytoskeletal distribution and total cell numbers of blastocysts were investigated in the four IF-EMF treatments compared to those in the control group. Although the underlying mechanism associated with EMF effects on oocytes and embryos is still elusive, we have demonstrated that low intensity IF-EMF exerts harmful effects on porcine oocytes during the maturation stage, carrying over such effects to their subsequent embryonic development.

Characterization of the effects of heat stress on autophagy induction in the pig oocyte

BACKGROUND

Heat stress (HS) occurs when body heat accumulation exceeds heat dissipation and is associated with swine seasonal infertility. HS contributes to compromised oocyte integrity and reduced embryo development. Autophagy is a potential mechanism for the oocyte to mitigate the detrimental effects of HS by recycling damaged cellular components.

METHODS

To characterize the effect of HS on autophagy in oocyte maturation, we utilized an in vitro maturation (IVM) system where oocytes underwent thermal neutral (TN) conditions throughout the entire maturation period (TN/TN), HS conditions during the first half of IVM (HS/TN), or HS conditions during the second half of IVM (TN/HS).

RESULTS

To determine the effect of HS on autophagy induction within the oocyte, we compared the relative abundance and localization of autophagy-related proteins. Heat stress treatment affected the abundance of two well described markers of autophagy induction: autophagy related gene 12 (ATG12) in complex with ATG5 and the cleaved form of microtubule-associated protein 1 light chain 3 beta (LC3B-II). The HS/TN IVM treatment increased the abundance of the ATG12-ATG5 complex and exacerbated the loss of LC3B-II in oocytes. The B-cell lymphoma 2 like 1 protein (BCL2L1) can inhibit autophagy or apoptosis through its interaction with either beclin1 (BECN1) or BCL2 associated X, apoptosis regulator (BAX), respectively. We detected colocalization of BCL2L1 with BAX but not BCL2L1 with BECN1, suggesting that apoptosis is inhibited under the HS/TN treatment but not autophagy. Interestingly, low doses of the autophagy inducer, rapamycin, increased oocyte maturation.

CONCLUSIONS

Our results here suggest that HS increases autophagy induction in the oocyte during IVM, and that artificial induction of autophagy increases the maturation rate of oocytes during IVM. These data support autophagy as a potential mechanism activated in the oocyte during HS to recycle damaged cellular components and maintain developmental competence.

Contextualizing Autophagy during Gametogenesis and Preimplantation Embryonic Development

Mammals face environmental stressors throughout their lifespan, which may jeopardize cellular homeostasis. Hence, these organisms have acquired mechanisms to cope with stressors by sensing, repairing the damage, and reallocating resources to increase the odds of long-term survival. Autophagy is a pro-survival lysosome-mediated cytoplasm degradation pathway for organelle and macromolecule recycling. Furthermore, autophagy efflux increases, and this pathway becomes idiosyncratic depending upon developmental and environmental contexts. Mammalian germ cells and preimplantation embryos are attractive models for dissecting autophagy due to their metastable phenotypes during differentiation and exposure to varying environmental cues. The aim of this review is to explore autophagy during mammalian gametogenesis, fertilization and preimplantation embryonic development by contemplating its physiological role during development, under key stressors, and within the scope of assisted reproduction technologies.

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.

Glucose in a maturation medium with reduced NaCl improves oocyte maturation and embryonic development after somatic cell nuclear transfer and in vitro fertilization in pigs

This study was conducted to examine whether glucose in maturation medium containing reduced NaCl could improve oocyte maturation and embryonic development in pigs. The base medium was bovine serum albumin-free porcine zygote medium (PZM)-3 containing 10% (v/v) pig follicular fluid (FPZM) or 0.1% (w/v) polyvinyl alcohol (PPZM). Using each medium, the effects of NaCl concentrations (108 and 61.6 mM) and 5.56 mM glucose supplementation (designated as PZM108N, PZM108G, PZM61N, and PZM61G, respectively) were examined using a 2 × 2 factorial arrangement. When oocytes were matured in FPZM, glucose supplementation improved nuclear maturation compared with no supplementation, regardless of the NaCl concentrations. FPZM61G showed a higher blastocyst formation compared with FPZM108N and FPZM108G after parthenogenesis (PA). Blastocyst formations of somatic cell nuclear transfer (SCNT) embryos derived from FPZM61N and FPZM61G were higher compared with those of oocytes from FPZM108N. When oocytes were matured in PPZM, glucose added to PPZM108 and PPZM61 increased nuclear maturation compared with no supplementation. However, glucose added to PPZM108 did not alter embryonic development after PA. Additionally, oocytes matured in PPZM61G showed a higher blastocyst formation compared with those from PPZM61N. In SCNT, blastocyst formation was not influenced by glucose supplementation of PPZM108, but was increased by maturation in glucose-supplemented PPZM61. In embryonic development of in vitro fertilization (IVF), oocytes matured in medium with reduced NaCl and glucose showed significantly higher blastocyst formation compared with those matured in PPZM108G. Our results demonstrated that glucose in maturation medium containing 61.6 mM NaCl increased oocyte maturation and embryonic development after PA, SCNT, and IVF.

Autophagy in Female Fertility: A Role in Oxidative Stress and Aging

Significance: The precipitous age-related decline in female fertility is intimately associated with a reduction in both the quantity and quality of the germline (oocytes). Although complex etiologies undoubtedly contribute to the deterioration of oocyte quality, increasing attention has focused on the pervasive impact of oxidative stress. Indeed, the prolonged lifespan of the meiotically arrested oocyte places this cell at heightened risk of oxidative lesions, which commonly manifest in dysregulation of protein homeostasis (proteostasis). Although oocytes are able to mitigate this threat via the mobilization of a sophisticated network of surveillance, repair, and proteolytic pathways, these defenses are themselves prone to age-related defects, reducing their capacity to eliminate oxidatively damaged proteins. Recent Advances: Here, we give consideration to the quality control mechanisms identified within the ovary that afford protection to the female germline. Our primary focus is to review recent advances in our understanding of the autophagy pathway and its contribution to promoting oocyte longevity and modulating pathophysiological responses to oxidative stress. In addition, we explore the therapeutic potential of emerging strategies to fortify autophagic activity. Critical Issues: The complex interplay of oxidative stress and autophagy has yet to be fully elucidated within the context of the aging oocyte and surrounding ovarian environment. Future Directions: Emerging evidence provides a strong impetus to resolve the causal link between autophagy and oxidative stress-driven pathologies in the aging oocyte. Such research may ultimately inform novel therapeutic strategies to combat the age-related loss of female fertility via fortification of intrinsic autophagic activity.

Effect of autophagy induction and cathepsin B inhibition on developmental competence of poor quality bovine oocytes

The present study investigated the effect of autophagy induction and cathepsin B (CTSB) inhibition on developmental competence of poor quality oocytes. Bovine cumulus oocyte complexes (COCs) were classified as good or poor according to their morphology. Autophagy activity was detected in good and poor germinal vesicle (GV) oocytes. Then E-64, a CTSB inhibitor, rapamycin (Rapa), an autophagy inducer, and combined administration was achieved during in vitro maturation (IVM) of poor quality COCs followed by detection of autophagy activity. In the next experiment, E-64, Rapa, and E64 + Rapa, were added during IVM to good and poor quality COCs followed by in vitro fertilization and culture for 8 days to investigate whether inhibition of CTSB and/or induction of autophagy improve embryonic development and quality. Autophagy activity was significantly lower in poor quality GV oocytes than in good quality ones. E-64, Rapa and E-64 + Rapa treatment during IVM significantly increased autophagy activity in poor quality oocytes. Addition of Rapa in good quality COCs did not increase the blastocyst rate, whereas E-64 increased the blastocyst rate and total cell number (TCN) with decreasing TUNEL-positive cells. In contrast, Rapa treatment in poor quality COCs significantly increased the blastocyst rate and TCN with decreasing TUNEL-positive cells. These results indicate oocyte quality has different responses to intracellular autophagy induction and CTSB activity control by potential autophagy and catabolic status, however, synergetic effect of autophagy induction and CTSB inhibition can increase developmental competence of both good and poor quality COCs, especially rescue effect in poor quality COCs.

The autophagic inducer and inhibitor display different activities on the meiotic and developmental competencies of porcine oocytes derived from small and medium follicles

This study aimed to examine the effect of rapamycin (autophagy inducer) and 3-methyladenine (3-MA, autophagy inhibitor) on the meiotic and developmental competencies of porcine oocytes derived from medium follicles (MF, 3-6 mm in diameter) and small follicles (SF, 1-2 mm in diameter) during in vitro maturation (IVM) process. The presence of 1 nM but not 10 nM rapamycin significantly increased the maturation rate of MF-derived oocytes (P < 0.05). However, the maturation rate of SF-derived oocytes was not affected by rapamycin at both concentrations (1 nM and 10 nM). The maturation rate of MF-derived oocytes decreased significantly (P < 0.05) in the presence of 0.2 mM but not 2 mM 3-MA than non-supplemented control. In contrast, in SF-derived oocytes, 3-MA at both 0.2 and 2 mM concentrations did not affect the maturation rates. The presence of 1 nM rapamycin significantly increased the blastocyst formation rate of MF-derived mature oocytes following parthenogenetic activation (P < 0.05). However, the blastocyst formation rate of SF-derived mature oocytes was not affected by the presence of rapamycin. The presence of 3-MA significantly reduced the blastocyst formation rate of MF-derived mature oocytes but did not change that of SF-derived oocytes. In conclusion, our study results show differences in activity of the autophagy inducer and inhibitor on the meiotic and developmental competencies of MF- and SF-derived porcine oocytes.

Autophagy in Ovarian Follicular Development and Atresia

Autophagy is a mechanism that exists in all eukaryotes under a variety of physiological and pathological conditions. In the mammalian ovaries, less than 1% of follicles ovulate, whereas the remaining 99% undergo follicular atresia. Autophagy and apoptosis have been previously found to be involved in the regulation of both primordial follicular development as well as atresia. The relationship between autophagy, follicular development, and atresia have been summarized in this review with the aim to obtain a more comprehensive understanding of the role played by autophagy in follicular development and atresia.

Autophagy is required for proper meiosis of porcine oocytes maturing in vitro

Autophagy is an essential cellular mechanism that degrades cytoplasmic proteins and organelles to recycle their components; however, the contribution of autophagy during meiosis has not been studied in porcine oocytes maturing in vitro. In this study, we observed that the autophagy-related gene, LC3, was expressed in porcine oocytes during maturation for 44 h in vitro. Knockdown of the autophagy-related gene, BECN1, reduced both BECN1 and LC3 protein expression levels. Moreover, BECN1 knockdown and treatment with the autophagy inhibitor, LY294002, during maturation of porcine oocytes in vitro impaired polar body extrusion, disturbed mitochondrial function, triggered the DNA damage response, and induced early apoptosis in porcine oocytes. Autophagy inhibition during oocyte maturation also impaired the further developmental potential of porcine oocytes. These results indicate that autophagy is required for the in vitro maturation of porcine oocytes.

Role of autophagy in modulating post-maturation aging of mouse oocytes

Mechanisms for post-maturation oocyte aging (PMOA) are not fully understood, and whether autophagy plays any role in PMOA is unknown. To explore the role of autophagy in PMOA, expression of autophagosomes and effects of the autophagy (macro-autophagy) activity on PMOA were observed in mouse oocytes. Oocyte activation rates and active caspase-3 levels increased continuously from 0 to 18 h of in vitro aging. While levels of microtubule-associated protein light chain 3 (LC3)-II increased up to 12 h and decreased thereafter, contents of p62 decreased from 0 to 12 h and then elevated to basal level by 18 h. However, the LC3-II/I ratio remained unchanged following aging in different media or for different times. During in vitro aging up to 12 h, upregulating autophagy with rapamycin or lithium chloride decreased activation susceptibility, cytoplasmic calcium, p62 contents, oxidative stress, caspase-3 activation and cytoplasmic fragmentation while increasing developmental competence, LC3-II contents, LC3-II/I ratio, mitochondrial membrane potential, spindle/chromosome integrity and normal cortical granule distribution. Downregulating autophagy with 3-methyladenine (3-MA) produced opposite effects on all these parameters except cytoplasmic fragmentation. After 12 h of aging culture, however, regulating autophagy with either rapamycin/lithium chloride or 3-MA had no impact on oocyte activation susceptibility. It is concluded that autophagy plays an important role in regulating PMOA. Thus, during the early stage of PMOA, autophagy increases as an adaptive response to prevent further apoptosis, but by the late stage of PMOA, the activation of more caspases blocks the autophagic process leading to severer apoptosis.

Choosing a culture medium for SCNT and iSCNT reconstructed embryos: from domestic to wildlife species

Over the past decades, in vitro culture media have been developed to successfully support IVF embryo growth in a variety of species. Advanced reproductive technologies, such as somatic cell nuclear transfer (SCNT), challenge us with a new type of embryo, with special nutritional requirements and altered physiology under in vitro conditions. Numerous studies have successfully reconstructed cloned embryos of domestic animals for biomedical research and livestock production. However, studies evaluating suitable culture conditions for SCNT embryos in wildlife species are scarce (for both intra- and interspecies SCNT). Most of the existing studies derive from previous IVF work done in conventional domestic species. Extrapolation to non-domestic species presents significant challenges since we lack information on reproductive processes and embryo development in most wildlife species. Given the challenges in adapting culture media and conditions from IVF to SCNT embryos, developmental competence of SCNT embryos remains low. This review summarizes research efforts to tailor culture media to SCNT embryos and explore the different outcomes in diverse species. It will also consider how these culture media protocols have been extrapolated to wildlife species, most particularly using SCNT as a cutting-edge technical resource to assist in the preservation of endangered species.

Parthenogenetic activation and somatic cell nuclear transfer of porcine oocytes activated by an electric pulse and AZD5438 treatment

We examined the in vitro developmental competence of parthenogenetic activation (PA) oocytes activated by an electric pulse (EP) and treated with various concentrations of AZD5438 for 4 h. Treatment with 10 µM AZD5438 for 4 h significantly improved the blastocyst formation rate of PA oocytes in comparison with 0, 20, or 50 µM AZD5438 treatment (46.4% vs. 34.5%, 32.3%, and 24.0%, respectively; P 0.05). Furthermore, 66.67% of blastocysts derived from these AZD5438-treated PA oocytes had a diploid karyotype. The blastocyst formation rate of PA and somatic cell nuclear transfer (SCNT) embryos was similar between oocytes activated by an EP and treated with 2 mM 6-dimethylaminopurine for 4 h and those activated by an EP and treated with 10 µM AZD5438 for 4 h (11.11% vs. 13.40%, P > 0.05). In addition, the level of maturation-promoting factor (MPF) was significantly decreased in oocytes activated by an EP and treated with 10 µM AZD5438 for 4 h. Finally, the mRNA expression levels of apoptosis-related genes (Bax and Bcl-2) and pluripotency-related genes (Oct4, Nanog, and Sox2) were checked by RT-PCR; however, there were no differences between the AZD5438-treated and non-treated control groups. Our results demonstrate that porcine oocyte activation via an EP in combination with AZD5438 treatment can lead to a high blastocyst formation rate in PA and SCNT experiments.

Effect of rapamycin treatment during post-activation and/or in vitro culture on embryonic development after parthenogenesis and in vitro fertilization in pigs

This study investigated the effects of early induction of autophagy on embryonic development in pigs. For this, oocytes or embryos were treated with an autophagy inducer, rapamycin (RP), during post-activation (Pa), in vitro fertilization (IVF) and/or in vitro culture (IVC). When parthenogenesis (PA) embryos were untreated (control) or treated with various concentrations of RP for 4 hr during Pa, 100 nm RP showed a higher blastocyst formation (48.8 ± 2.7%) than the control (34.6 ± 3.0%). When PA embryos were treated during the first 24 hr of IVC, blastocyst formation was increased (p < .05) by 1 and 10 nm RP (61.9 ± 3.0 and 59.6 ± 3.0%, respectively) compared to the control (43.2 ± 1.8%) and 100 nm RP (47.8 ± 3.2%), with a higher embryo cleavage in response to 10 nm RP (87.3 ± 2.4%) than the control (74.1 ± 3.2%). RP treatment during IVC and Pa + IVC showed increased blastocyst formation (44.7 ± 2.5 and 44.1 ± 2.0%, respectively) compared to the control (33.2 ± 2.0%). In addition, RP treatment during Pa and/or IVC increased glutathione content and inversely reduced reactive oxygen species. In IVF, RP treatment for 6 hr during IVF significantly increased embryonic development (34.0 ± 2.6%) compared to the control (24.8 ± 1.6%), but treatment during IVC for 24 hr with RP did not (23.0 ± 3.8%). Autophagy was significantly increased in PA oocytes by the RP treatment during Pa but not altered by the treatment during the first 24 hr of IVC. Overall, RP treatment positively regulated the pre-implantation development of pig embryos, probably by regulating cellular redox state and stimulating autophagy.

Rex Rabbit Somatic Cell Nuclear Transfer with In Vitro-Matured Oocytes

Somatic cell nuclear transfer (SCNT) requires large numbers of matured oocytes. In vitro-matured (IVM) oocytes have been used in SCNT in many animals. We investigated the use of IVM oocytes in Rex rabbit SCNT using Rex rabbit ovaries obtained from a local abattoir. The meiotic ability of oocytes isolated from follicles of different diameters was studied. Rex rabbit SCNT was optimized for denucleation, activation, and donor cell synchronization. Rex rabbit oocytes grew to the largest diameter (110 μm) when the follicle diameter was 1.0 mm. Oocytes isolated from <0.5-mm follicles lacked the ability to resume meiosis. More than 90% of these oocytes remained in the germinal vesicle (GV) stage after in vitro culture (IVC) for 18 h. Oocytes isolated from >0.7-mm follicles acquired maturation ability. More than 90% of these oocytes matured after IVC for 18 h. The developmental potential of oocytes isolated from >1-mm follicles was greater than that of oocytes isolated from 0.7- to 1.0-mm follicles. The highest activation rates for IVM Rex rabbit oocytes were seen after treatment with 2.5 μM ionomycin for 5 min followed by 2 mM 6-dimethylaminopurine (6-DMAP) and 5 μg/mL cycloheximide (CHX) for 1 h. Ionomycin induced the chromatin of IVM oocytes to protrude from the oocyte surface, promoting denucleation. Fetal fibroblast cells (FFCs) and cumulus cells (CCs) were more suitable for Rex rabbit SCNT than skin fibroblast cells (SFCs) (blastocyst rate was 35.6 ± 2.2% and 38.0 ± 6.0% vs. 19.7 ± 3.1%). The best fusion condition was a 2DC interval for 1 sec, 1.6 kV/cm voltages, and 40 μsec duration in 0.28 M mannitol. In conclusion, the in vitro maturation of Rex rabbit oocytes and SCNT procedures were studied systematically and optimized in this study.