Melatonin enhances the in vitro maturation and developmental potential of bovine oocytes denuded of the cumulus oophorus

Improving the meiotic competence of small antral follicle-derived porcine oocytes by using dibutyryl-cAMP and melatonin

OBJECTIVE

We increased the nuclear maturation rate of antral follicle derived oocytes by using a pre-in vitro maturation (IVM) culture system and improved the developmental potential of these porcine pathenotes by supplementing with melatonin. Furthermore, we investigated the expression patterns of genes involved in cumulus expansion (HAS2, PTGS2, TNFAIP6, and PTX3) derived from small and medium antral follicles before and after oocyte maturation.

METHODS

Only the cumulus oocyte-complexes (COCs) derived from small antral follicles were induced with [Pre-SF(+)hCG] or without [Pre-SF(-)hCG] the addition of human chorionic gonadotropin (hCG) during the last 7 h of the pre-IVM period before undergoing the regular culture system. The mature oocytes were investigated on embryonic development after parthenogenetic activation (PA). Melatonin (10-7 M) was supplemented during in vitro culture (IVC) to improve the developmental potential of these porcine pathenotes.

RESULTS

A pre-IVM culture system with hCG added during the last 7 h of the pre-IVM period [Pre-SF(+)hCG] effectively supported small antral follicle-derived oocytes and increased their nuclear maturation rate. The oocytes derived from medium antral follicles exhibited the highest nuclear maturation rate in a regular culture system. Compared with oocytes cultured in a regular culture system, those cultured in the pre-IVM culture system exhibited considerable overexpression of HAS2, PTGS2, and TNFAIP6. Porcine embryos treated with melatonin during IVC exhibited markedly improved quality and developmental competence after PA. Notably, melatonin supplementation during the IVM period can reduce and increase the levels of intracellular reactive oxygen species (ROS) and glutathione (GSH), respectively.

CONCLUSION

Our findings indicate that the Pre-SF(+)hCG culture system increases the nuclear maturation rate of small antral follicle-derived oocytes and the expression of genes involved in cumulus expansion. Melatonin supplementation during IVC may improve the quality and increase the blastocyst formation rate of porcine embryos. In addition, it can reduce and increase the levels of ROS and GSH, respectively, in mature oocytes, thus affecting subsequent embryos.

Ferulic Acid Enhances Oocyte Maturation and the Subsequent Development of Bovine Oocytes

Improving the quality of oocytes matured in vitro is integral to enhancing the efficacy of in vitro embryo production. Oxidative stress is one of the primary causes of quality decline in oocytes matured in vitro. In this study, ferulic acid (FA), a natural antioxidant found in plant cell walls, was investigated to evaluate its impact on bovine oocyte maturation and subsequent embryonic development. Bovine cumulus-oocyte complexes (COCs) were treated with different concentrations of FA (0, 2.5, 5, 10, 20 μM) during in vitro maturation (IVM). Compared to the control group, supplementation with 5 μM FA significantly enhanced the maturation rates of bovine oocytes and the expansion of the cumulus cells area, as well as the subsequent cleavage and blastocyst formation rates after in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT). Furthermore, FA supplementation was observed to effectively decrease the levels of ROS in bovine oocytes and improve their mitochondrial function. Our experiments demonstrate that FA can maintain the levels of antioxidants (GSH, SOD, CAT) in oocytes, thereby alleviating the oxidative stress induced by H2O2. RT-qPCR results revealed that, after FA treatment, the relative mRNA expression levels of genes related to oocyte maturation (GDF-9 and BMP-15), cumulus cell expansion (HAS2, PTX3, CX37, and CX43), and embryo pluripotency (OCT4, SOX2, and CDX2) were significantly increased. In conclusion, these findings demonstrate that FA supplementation during bovine oocyte IVM can enhance oocyte quality and the developmental potential of subsequent embryos.

Modulation of Apoptosis and Autophagy by Melatonin in Juglone-Exposed Bovine Oocytes

Melatonin, an antioxidant hormone secreted by the pineal gland, has been recognized as a regulator for numerous biological events. The deleterious effects of juglone, a polyphenolic extract of walnut trees, on embryo development has been previously reported. In the current study, we aimed to display the impact of melatonin administrated during in vitro oocyte maturation (IVM) on juglone-treated oocytes. Thus, in vitro matured oocytes were collected after 24 h post incubation with juglone in the presence or absence of melatonin. Reactive oxygen species (ROS), glutathione (GSH) content, mitochondrial distribution, and the relative abundance of mRNA transcription levels were assessed in oocytes, in addition, oocytes were in vitro fertilized to check the competency levels of oocytes to generate embryos. We found that administration of melatonin during the maturation of oocytes under juglone stress significantly improved the cleavage rate, 8-16 cell-stage embryos and day-8 blastocysts when compared to the sole juglone treatment. In addition, the fluorescence intensity of ROS increased, whereas the GSH decreased in juglone-treated oocytes compared to melatonin-juglone co-treated and untreated ones. Additionally, a significant increase in the mitochondrial aberrant pattern, the pattern that was normalized following melatonin supplementation, was observed following juglone administration. The mRNA analysis using RT-qPCR revealed a significant upregulation of autophagy and oxidative-stress-specific markers in the juglone-treated group compared to the co-treatment and control. In conclusion, the study reveals, for the first time, a protective effect of melatonin against the oxidative stress initiated following juglone treatment during the in vitro maturation of oocytes.

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.

Improvement of Fertilization Capacity and Developmental Ability of Vitrified Bovine Oocytes by JUNO mRNA Microinjection and Cholesterol-Loaded Methyl-β-Cyclodextrin Treatment

Vitrification of oocytes is crucial for embryo biotechnologies, germplasm cryopreservation of endangered and excellent female animals, and the fertility of humans. However, vitrification significantly impairs the fertilization ability of oocytes, which significantly limits its widely used application. JUNO protein, a receptor for Izumo1, is involved in sperm-oocyte fusion and is an indispensable protein for mammalian fertilization, and its abundance is susceptible to vitrification. However, it is still unclear how vitrification reduces the fertilization capacity of bovine oocytes by affecting JUNO protein. This study was designed to investigate the effect of vitrification on the abundance and post-translational modifications of JUNO protein in bovine oocytes. Our results showed that vitrification did not alter the amino acid sequence of JUNO protein in bovine oocytes. Furthermore, the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis results showed that vitrification significantly reduced the number and changed the location of disulfide bonds, and increased the number of both phosphorylation and glycosylation sites of JUNO protein in bovine oocytes. Finally, the fertilization capacity and development ability of vitrified oocytes treated with 200 pg JUNO mRNA microinjection and cholesterol-loaded methyl-β-cyclodextrin (CLC/MβCD) were similar to those of fresh oocytes. In conclusion, our results showed that vitrification of bovine oocytes did not alter the protein sequence of JUNO, but induced post-translational modifications and changed protein abundance. Moreover, the fertilization and development ability of vitrified bovine oocytes were improved by the combination treatment of JUNO mRNA microinjection and CLC/MβCD.

Past, present and future of ICSI in livestock species

During the past 2 decades, intracytoplasmic sperm injection (ICSI) has become a routine technique for clinical applications in humans. The widespread use among domestic species, however, has been limited to horses. In horses, ICSI is used to reproduce elite individuals and, as well as in humans, to mitigate or even circumvent reproductive barriers. Failures in superovulation and conventional in vitro fertilization (IVF) have been the main reason for the use of this technology in horses. In pigs, ICSI has been successfully used to produce transgenic animals. A series of factors have resulted in implementation of ICSI in pigs: need to use zygotes for numerous technologies, complexity of collecting zygotes surgically, and problems of polyspermy when there is utilization of IVF procedures. Nevertheless, there have been very few additional reports confirming positive results with the use of ICSI in pigs. The ICSI procedure could be important for use in cattle of high genetic value by maximizing semen utilization, as well as for utilization of spermatozoa from prepubertal bulls, by providing the opportunity to shorten the generation interval. When attempting to utilize ICSI in ruminants, there are some biological limitations that need to be overcome if this procedure is going to be efficacious for making genetic improvements in livestock in the future. In this review article, there is an overview and projection of the methodologies and applications that are envisioned for ICSI utilization in these species in the future.

Importance of Antioxidant Supplementation during In Vitro Maturation of Mammalian Oocytes

The in vitro embryo production (IVEP) technique is widely used in the field of reproductive biology. In vitro maturation (IVM) is the first and most critical step of IVEP, during which, the oocyte is matured in an artificial maturation medium under strict laboratory conditions. Despite all of the progress in the field of IVEP, the quality of in vitro matured oocytes remains inferior to that of those matured in vivo. The accumulation of substantial amounts of reactive oxygen species (ROS) within oocytes during IVM has been regarded as one of the main factors altering oocyte quality. One of the most promising approaches to overcome ROS accumulation within oocytes is the supplementation of oocyte IVM medium with antioxidants. In this article, we discuss recent advancements depicting the adverse effects of ROS on mammalian oocytes. We also discuss the potential use of antioxidants and their effect on both oocyte quality and IVM rate.

Effects of EGF and melatonin on gene expression of cumulus cells and further in vitro embryo development in bovines

Despite previous research demonstrating the benefits of including growth factors and antioxidants to maturation medium to support embryo production, to date the effect of epidermal growth factor (EGF) and melatonin (Mel) on oocyte competency has not been studied. This study supplemented in vitro maturation (IVM) medium with EGF (10 ng/ml) and Mel (50 ng/ml) alone, or in combination, and evaluated cumulus cell (CC) gene expression and the development and quality of parthenogenetic blastocysts. No differences in CC gene expression levels indicative of developmental potential were found among the treatment groups. Antioxidant gene CuZnSOD was significantly (P < 0.05) decreased in CCs from the Mel group. Moreover, blastocyst rates on day 7 were significantly increased in EGF or Mel (P < 0.05), but not EGF+Mel. Significant decrease (P < 0.05) in GPX1, CuZnSOD, SLC2A1 and HSPA1A (P = 0.07) mRNA levels was observed in blastocysts from the Mel group. OCT4 gene expression was significantly increased (P < 0.05) in EGF+Mel and confirmed using immunofluorescence. Our results indicate that, despite the lack of changes of competence-related genes in CCs, IVM medium supplemented with Mel improved the culture environment sufficiently, resulting in improved blastocysts. Moreover, EGF and Mel combined during maturation increased OCT4 gene and protein expression in blastocysts, indicating its potential for stem cells.

Menstrual blood-derived stem cells and its mitochondrial treatment improve the ovarian condition of aged mice

Aging causes a decline in ovarian function and may contribute to ovarian failure and infertility. We investigated the effect of menstrual blood-derived mesenchymal stem cells (MenSCs) and their mitochondria on ovarian function in aged mice. We performed two treatment protocols: i) ovaries of recipient aged mice were treated in vivo with MenSCs 3D alginate gel; ii) ovaries were injected with mitochondria suspension and then incubated with mitochondrial 3D gel. Seven days after treatment, ovaries were harvested for histological assessment by HE staining and transcriptomic analysis by RNA-seq. Our data showed that after incubation with stem cell 3D gel, the MenSCs could be detected in the recipient mouse ovary. HE staining showed that the follicular state of aging ovary improved with both treatments. RNA-seq analysis showed that mitochondrial pathway-related genes were upregulated and significantly enriched in the ovaries treated by MenSCs or their mitochondria. Conclusions: Treatment with MenSCs or their mitochondria can enhance the expression of mitochondrial pathway-related genes and promote the recovery of ovarian function in aged mice.

Supplementation of EGF, IGF-1, and Connexin 37 in IVM Medium Significantly Improved the Maturation of Bovine Oocytes and Vitrification of Their IVF Blastocysts

The quality and developmental capacity of oocytes derived from in vitro maturation (IVM) remain unsatisfactory, which greatly impairs the efficiency and application of embryo technologies. The present experiment was designed to investigate the effect of the supplementation of EGF, IGF-1, and Cx37 in an IVM medium on the maturation quality and development ability of bovine oocytes. The cytoplasmic maturation events of oocytes and the quality of in vitro fertilization (IVF) blastocysts were examined to investigate the relative mechanisms. Our results showed that the nuclear maturation and blastocyst development after the IVF of oocytes treated with 25 μg/mL Cx37 or the combination of 50 ng/mL EGF and 100 ng/mL IGF-1 were significantly increased compared to those of the control group (p < 0.05). Furthermore, the blastocyst rate, and blastocyst total cell number and survival rate after vitrification of the EGF+IGF-1+Cx37 group, were significantly higher than those of the control group (p < 0.05), but lower than those of the FSH+LH+EGF+IGF-1+Cx37 group (p < 0.05). The transzonal projection (TZP) intensity, glutathione (GSH) level, and mitochondrial function of the EGF+IGF-1+Cx37 group were significantly higher than that of the control group, and lower than those of the FSH+LH+EGF+IGF-1+Cx37 group, in contrast to the results of the reactive oxygen species (ROS) levels. In conclusion, our results showed that the supplementation of 50 ng/mL EGF, 100 ng/mL IGF-1, and 25 μg/mL Cx37 in the IVM of bovine oocytes significantly improved their quality and developmental ability by increasing the TZP, mitochondrial function, and GSH level.

The boosting effects of melatonin on the expression of related genes to oocyte maturation and antioxidant pathways: a polycystic ovary syndrome- mouse model

Background

Melatonin, as a free radical scavenger exhibiting genomic actions, regulates the antioxidant genes expression and apoptosis mechanisms. In polycystic ovary syndrome (PCOS) patients, an imbalance between free radicals and antioxidants in follicular fluid leads to oxidative stress, aberrant folliculogenesis, and intrinsic defects in PCOS oocytes. In this experimental mouse model study, oocytes of PCOS and the control groups were cultured in different melatonin concentrations (10− 5, 10− 6, and 10− 7 M) to investigate the expression of oocyte maturation-related genes (Gdf9/Bmp15), antioxidant-related genes (Gpx1/Sod1), apoptotic biomarkers (Bcl2/Bax) and total intracellular ROS levels.

Results

Gdf9 and Bmp15, Gpx1 and Sod1 were up-regulated in PCOS and control oocytes cultured in all melatonin concentrations compared to those cultured in IVM basal medium (P < 0.05). A significant decrease in the total ROS level was observed in all groups cultured in the supplemented cultures. Melatonin increased Bcl2 and decreased Bax gene expression in PCOS and control oocytes compared to non-treated oocytes.

Conclusions

Melatonin increased antioxidant gene expression and regulated the apoptosis pathway, effectively reducing the adverse effects of culture conditions on PCOS oocytes. Furthermore, it influenced the expression of oocyte maturation-related genes in PCOS, providing valuable support during the IVM process.

Melatonin improves the maturation and developmental ability of bovine oocytes by up-regulating GJA4 to enhance gap junction intercellular communication

Melatonin (MT) increases oocyte maturation by reducing reactive oxygen species level and enhancing oocyte antioxidant capacity. However, the mechanisms via which MT works are still poorly understood. In the present study, the effects of MT on the maturation rate and development ability of bovine oocytes were investigated. Then, the transcriptome of oocytes treated by MT was sequenced. Finally, the expression of gap junction protein alpha 4 (GJA4) protein and cAMP level were detected in bovine oocytes, and isoprenaline (enhancer of gap junctional intercellular communication (GJIC)) and heptanol (inhibitor of GJIC) were used to investigate the effect of MT on GJIC activity in bovine oocytes. Our results showed that MT significantly improved the maturation, developmental ability and mRNA expression of GJA4 of bovine oocytes. Meanwhile, MT significantly increased GJA4 protein level and cAMP level in bovine oocytes. In contrast to heptanol, both isoproterenol and MT significantly increased GJIC activity, nuclear maturation and the development ability of bovine oocytes. However, MT significantly restored the nuclear maturation and developmental ability of oocytes treated by heptanol. In conclusion, our results showed that MT improves the maturation and developmental ability of bovine oocytes by enhancing GJIC activity via up-regulating GJA4 protein expression in IVM progress.

Use of melatonin as an inhibitor of apoptotic process for cryopreservation of zebrafish (Danio rerio) embryos

This study investigated the use of melatonin to arrest the effects of apoptosis in vitrified zebrafish (D. rerio) embryos. Dechorionated embryos at 22-24 somite-stage were divided (n = 60/treatment) into a non-vitrified (Control Group, 0 M melatonin) and vitrified treatments with 0 M (T1), 1 µM (T2) and 1 mM of melatonin (T3). For vitrified treatments, a solution methanol/propylene glycol based was used and the embryos stored in -196 °C for a week. After thaw, survival rate, scanning electron microscopy, expression of anti (bcl-2) and pro-apoptotic (bax/caspase-3) genes, reactive oxygen species (ROS) formation and DNA fragmentation analyses were performed. No live embryos were obtained from vitrified treatments, observing a rapid degeneration immediately after thawing, with the vitelline layer rupture and leakage of its content, followed by breakdown of epithelial cells and melanisation of the tissue. Regarding the apoptotic process, T3 had the highest relative gene expression, for the three genes (P < 0.05) furthermore, T2 had similar expression of pro-apoptotic genes to CG (P < 0.05). ROS formation revealed that CG presented lower percentage of embryo surface area affected (3.80 ± 0.40%) (P < 0.05), in contrast, no differences were found among the other groups. T1 was most significantly (P < 0.05) damaged by DNA fragmentation. The vitrified groups with melatonin had similar damage levels of CG (P > 0.05). The inclusion of 1 µM of melatonin in the vitrifying solution, countered the effects of apoptotic process in post-thaw embryos, suggesting its utility in cryopreserving fish embryos.

Induction of Oxidative Stress and Mitochondrial Dysfunction by Juglone Affects the Development of Bovine Oocytes

Juglone, a major naphthalenedione component of walnut trees, has long been used in traditional medicine as an antimicrobial and antitumor agent. Nonetheless, its impact on oocyte and preimplantation embryo development has not been entirely clarified. Using the bovine model, we sought to elucidate the impact of juglone treatment during the in vitro maturation (IVM) of oocytes on their maturation and development of embryos. Results showed a severe reduction in oocyte nuclear maturation and cumulus expansion and a significant increase in mitochondrial dysfunction and reactive oxygen species (ROS) levels in cumulus-oocyte complexes (COCs) treated with juglone (12.5, 25.0, and 50.0 µM). In addition, RT-qPCR showed downregulation of the expansion-related (HAS2, TNFAIP6, PTX3, and PTGS2) and mitochondrial (ATPase6 and ATP5F1E) genes in juglone-treated COCs. Moreover, the development rates of day 4 total cleavage and 8-16 cell stage embryos, as well as day 8 blastocysts, were significantly reduced following exposure to juglone. Using immunofluorescence, the apoptotic marker caspase-9 was overexpressed in oocytes exposed to juglone (25.0 µM) compared to the untreated control. In conclusion, our study reports that exposing bovine oocytes to 12.5-50.0 µM of juglone can reduce their development through the direct induction of ROS accumulation, apoptosis, and mitochondrial dysfunction.

Mitochondrial function, blastocyst development and live foals born after ICSI of immature vitrified/warmed equine oocytes matured with or without melatonin

Oocyte vitrification is considered experimental in the horse with only three live foals reported. The oxidative conditions induced by vitrification could in part explain the poor results and melatonin, a powerful antioxidant, could stimulate ROS metabolization and restore mitochondrial function in these oocytes. Our objective was to determine the oxidative status of vitrified equine oocytes and to analyze the effect of melatonin on mitochondrial-specific ROS (mROS), oocyte maturation, ICSI embryo development and viability. Immature, abattoir-derived oocytes were held for 15 h and vitrified in a final concentration of 20% EG, 20% DMSO and 0.65 M trehalose. In Experiment 1, overall ROS was determined by DCHF-DA; vitrification increased ROS production compared to non-vitrified controls (1.29 ± 0.22 vs 0.74 ± 0.25 a. u.; P = 0.0156). In Experiment 2, mROS was analyzed by MitoSOX™ in vitrified/warmed oocytes matured with (+) or without (-) supplementation of 10^-9 M melatonin; mROS decreased in vitrified and non-vitrified oocytes matured in presence of melatonin (P < 0.05). In Experiment 3, we assessed the effect of melatonin supplementation on oocyte maturation, embryo development after ICSI, and viability by pregnancy establishment. Melatonin did not improve oocyte maturation, cleavage or blastocyst rate of non-vitrified oocytes. However, vitrified melatonin (+) oocytes reached similar cleavage (61, 75 and 77%, respectively) and blastocyst rate (15, 29 and 26%, respectively) than non-vitrified, melatonin (+) and (-) oocytes. Vitrified, melatonin (-) oocytes had lower cleavage (46%) and blastocyst rate (9%) compared to non-vitrified groups (P < 0.05), but no significant differences were observed when compared to vitrified melatonin (+). Although the lack of available recipients precluded the transfer of every blastocyst produced in our study, transferred embryos from non-vitrified oocytes resulted in 50 and 83% pregnancy rates while embryos from vitrified oocytes resulted in 17 and 33% pregnancy rates, from melatonin (+) and (-) treatments respectively. Two healthy foals, one colt from melatonin (+) and one filly from melatonin (-) treatment, were born from vitrified/warmed oocytes. Gestation lengths (considering day 0 = day of ICSI) were 338 days for the colt and 329 days for the filly, respectively. Our work showed for the first time that in the horse, as in other species, intracellular reactive oxygen species are increased by the process of vitrification. Melatonin was useful in reducing mitochondrial-related ROS and improving ICSI embryo development, although the lower pregnancy rate in presence of melatonin should be further analyzed in future studies. To our knowledge this is the first report of melatonin supplementation to an in vitro embryo culture system and its use to improve embryo developmental competence of vitrified oocytes following ICSI.

Glutathione Ethyl Ester Protects In Vitro-Maturing Bovine Oocytes against Oxidative Stress Induced by Subsequent Vitrification/Warming

This study aimed to examine whether the addition of glutathione ethyl ester (GSH-OEt) to the in vitro maturation (IVM) medium would improve the resilience of bovine oocytes to withstand vitrification. The effects of GSH-OEt on spindle morphology, levels of reactive oxygen species (ROS), mitochondrial activity and distribution, and embryo developmental potential were assessed together with the expression of genes with a role in apoptosis (BAX, BCL2), oxidative-stress pathways (GPX1, SOD1), water channels (AQP3), implantation (IFN-τ) and gap junctions (CX43) in oocytes and their derived blastocysts. Vitrification gave rise to abnormal spindle microtubule configurations and elevated ROS levels. Supplementation of IVM medium with GSH-OEt before vitrification preserved mitochondrial distribution pattern and diminished both cytoplasmic and mitochondrial ROS contents and percentages of embryos developing beyond the 8-cell stage were similar to those recorded in fresh non-vitrified oocytes. Although not significantly different from control vitrified oocytes, vitrified oocytes after GSH-OEt treatment gave rise to similar day 8-blastocyst and hatching rates to fresh non-vitrified oocytes. No effects of GSH-OEt supplementation were noted on the targeted gene expression of oocytes and derived blastocysts, with the exception of GPX1, AQP3 and CX43 in derived blastocysts. The addition of GSH-OEt to the IVM medium before vitrification may be beneficial for embryo development presumably as the consequence of additional anti-oxidant protection during IVM.

One-step automated bioprinting-based method for cumulus-oocyte complex microencapsulation for 3D in vitro maturation

Three-dimensional in vitro maturation (3D IVM) is a promising approach to improve IVM efficiency as it could prevent cumulus-oocyte complex (COC) flattening and preserve its structural and functional integrity. Methods reported to date have low reproducibility and validation studies are limited. In this study, a bioprinting based production process for generating microbeads containing a COC (COC-microbeads) was optimized and its validity tested in a large animal model (sheep). Alginate microbeads were produced and characterized for size, shape and stability under culture conditions. COC encapsulation had high efficiency and reproducibility and cumulus integrity was preserved. COC-microbeads underwent IVM, with COCs cultured in standard 2D IVM as controls. After IVM, oocytes were analyzed for nuclear chromatin configuration, bioenergetic/oxidative status and transcriptional activity of genes biomarker of mitochondrial activity (TFAM, ATP6, ATP8) and oocyte developmental competence (KHDC3, NLRP5, OOEP and TLE6). The 3D system supported oocyte nuclear maturation more efficiently than the 2D control (P<0.05). Ooplasmic mitochondrial activity and reactive oxygen species (ROS) generation ability were increased (P<0.05). Up-regulation of TFAM, ATP6 and ATP8 and down-regulation of KHDC3, NLRP5 expression were observed in 3D IVM. In conclusion, the new bioprinting method for producing COC-microbeads has high reproducibility and efficiency. Moreover, 3D IVM improves oocyte nuclear maturation and relevant parameters of oocyte cytoplasmic maturation and could be used for clinical and toxicological applications.

The Immp2l Mutation Causes Ovarian Aging Through ROS-Wnt/β-Catenin-Estrogen Pathway: Preventive Effect of Melatonin

Mitochondria play important roles in ovarian follicle development. Mitochondrial dysfunction, including mitochondrial gene deficiency, impairs ovarian development. Here, we explored the role and mechanism of mitochondrial inner membrane gene Immp2l in ovarian follicle growth and development. Our results revealed that female Immp2l-/- mice were infertile, whereas Immp2l+/- mice were normal. Body and ovarian weights were reduced in the female Immp2l-/- mice, ovarian follicle growth and development were stunted in the secondary follicle stage. Although a few ovarian follicles were ovulated, the oocytes were not fertilized because of mitochondrial dysfunction. Increased oxidative stress, decreased estrogen levels, and altered genes expression of Wnt/β-catenin and steroid hormone synthesis pathways were observed in 28-day-old Immp2l-/- mice. The Immp2l mutation accelerated ovarian aging process, as no ovarian follicles were detected by age 5 months in Immp2l-/- mice. All the aforementioned changes in the Immp2l-/- mice were reversed by administration of antioxidant melatonin to the Immp2l-/- mice. Furthermore, our in vitro study using Immp2l knockdown granulosa cells confirmed that the Immp2l downregulation induced granulosa cell aging by enhancing reactive oxygen species (ROS) levels, suppressing Wnt16, increasing β-catenin, and decreasing steroid hormone synthesis gene cyp19a1 and estrogen levels, accompanied by an increase in the aging phenotype of granulosa cells. Melatonin treatment delayed granulosa cell aging progression. Taken together, Immp2l causes ovarian aging through the ROS-Wnt/β-catenin-estrogen (cyp19a1) pathway, which can be reversed by melatonin treatment.

Effect of melatonin on bovine sperm characteristics and ultrastructure changes following cryopreservation

The production of reactive oxygen species (ROS) during cryopreservation of semen alters the sperm motion and mobility characteristics, resulting in poor or failure of conception rate after artificial insemination (AI). Melatonin an antioxidant is able to modulate the effect of ROS and prevents spermatozoa by reducing the oxidative stress during freezing process. Eight ejaculates from eight healthy HF bulls diluted with Tris egg yolk glycerol extender were divided into five equal aliquots. The Computer Assisted Semen Analyser (CASA) results showed no significant difference between the control-post- thaw samples and melatonin-treated samples; however, the velocity of spermatozoa with regard to the VAP, VSL showed highest increase in the 0.25 mM MLT-treated semen followed by 0.1 mM MLT treated semen except for VCL where velocity increased with increase in the concentration of melatonin. The vigour of spermatozoa regard to BCF, STR and LIN recorded highest increase in the 0.25 mM MLT treated semen followed by 0.1 mM MLT-treated semen except for the ALH where vigour increased with increase in the concentration of melatonin. The electron micrography images illustrated that the addition of 0.1 mM melatonin protected the plasma membrane and acrosome region and maintained the ultrastructure integrity of the cryopreserved spermatozoa when compared to control group, whereas the electron micrography of spermatozoa treated with 0.2 and 0.25 mM melatonin illustrated highest damage to the plasma and acrosome membrane. Thus concluding that inclusion of melatonin to sperm extender can improve the post-thaw quality of cryopreserved bull spermatozoa.

Source and Follicular Fluid Treatment During the In Vitro Maturation of Recipient Oocytes Affects the Development of Cloned Pig Embryo

Pig cloning technique is valuable in agriculture, biomedicine, and life sciences. However, the full-term developmental efficiency of cloned pig embryos is only about 1%, which limits pig cloning application. The quality of recipient oocytes greatly affects the developmental competence of cloned pig embryos. Thus, this study investigated the effects of a recipient oocyte source (in vivo matured [IVVM] oocytes vs. slaughter house-derived in vitro matured [IVTM] oocytes), and follicular liquid treatment (slaughter house-derived immature follicle-derived fluid [IFF] vs. in vivo-matured follicle-derived fluid [MFF]) during the in vitro maturation (IVM) of oocytes on the development of the cloned pig embryos. Our results showed that using IVVM oocytes to replace IVTM oocytes as recipient oocytes, and using 10% MFF IVM medium to replace 10% IFF IVM medium could enhance the development of the cloned pig embryos. IFF and MFF contained different levels of oocyte quality-related proteins, resulting in different oocyte quality-related gene expression levels and reactive oxygen species levels between the 10% MFF medium-cultured oocytes and 10% IFF medium-cultured oocytes. This study provided useful information for enhancing the pig cloning efficiency by improving the quality of recipient oocytes.

Effect of Melatonin on the In Vitro Maturation of Porcine Oocytes, Development of Parthenogenetically Activated Embryos, and Expression of Genes Related to the Oocyte Developmental Capability

Simple Summary

Exogenous melatonin has beneficial effects on improving cumulus oophorus expansion; mitochondrial distribution; intracellular level of glutathione; and first polar body extrusion rate of porcine oocytes derived from in vitro maturation. Moreover; melatonin supplementation increases relative abundances of BMP15 and CAT mRNA; and decreases intracellular levels of reactive oxygen species; and expression values of P53 and BAX genes; which are related to in vitro development of porcine oocytes.

Abstract

Melatonin treatment can improve quality and in vitro development of porcine oocytes, but the mechanism of improving quality and developmental competence is not fully understood. In this study, porcine cumulus–oocyte complexes were cultured in TCM199 medium with non-treated (control), 10⁻⁵ M luzindole (melatonin receptor antagonist), 10⁻⁵ M melatonin, and melatonin + luzindole during in vitro maturation, and parthenogenetically activated (PA) embryos were treated with nothing (control), or 10⁻⁵ M melatonin. Cumulus oophorus expansion, oocyte survival rate, first polar body extrusion rate, mitochondrial distribution, and intracellular levels of reactive oxygen species (ROS) and glutathione of oocytes, and cleavage rate and blastocyst rate of the PA embryos were assessed. In addition, expression of growth differentiation factor 9 (GDF9), tumor protein p53 (P53), BCL2 associated X protein (BAX), catalase (CAT), and bone morphogenetic protein 15 (BMP15) were analyzed by real-time quantitative PCR. The results revealed that melatonin treatment not only improved the first polar body extrusion rate and cumulus expansion of oocytes via melatonin receptors, but also enhanced the rates of cleavage and blastocyst formation of PA embryos. Additionally, melatonin treatment significantly increased intraooplasmic level of glutathione independently of melatonin receptors. Furthermore, melatonin supplementation not only significantly enhanced mitochondrial distribution and relative abundances of BMP15 and CAT mRNA, but also decreased intracellular level of ROS and relative abundances of P53 and BAX mRNA of the oocytes. In conclusion, melatonin enhanced the quality and in vitro development of porcine oocytes, which may be related to antioxidant and anti-apoptotic mechanisms.

Melatonin promotes the development of immature oocytes from the COH cycle into healthy offspring by protecting mitochondrial function

Melatonin (MT) regulates reproductive performance as a potent antioxidant; however, its beneficial effects on oocyte development remain largely unknown, especially in human oocytes. The collected 193 immature oocytes from the controlled ovarian hyperstimulation (COH) cycle underwent in vitro maturation (IVM) in IVM medium contained 10 μmol/L MT (n = 105, M group) and no MT (n = 88, NM group), followed by insemination and embryo culture. The results showed that the high-quality blastocyst formation rate in the M group (28.4%) was significantly higher than that in the NM group (2.0%) (P = .0001), and the aneuploidy rate was low (15.8%). In the subsequent clinical trials, three healthy infants were delivered. Next, single-cell RNA-seq data revealed 1026 differentially expressed genes (DEGs) between the two groups, KEGG enrichment analysis revealed that the majority of DEGs involved in oxidative phosphorylation pathway, which associated with ATP generation, was upregulated in the M group. Finally, confocal fluorescence staining results revealed that the mitochondrial membrane potential in the oocytes significantly increased and intracellular ROS and Ca²⁺ levels greatly decreased in the M group. Melatonin can promote the development of immature human oocytes retrieved from the COH cycle into healthy offspring by protecting mitochondrial function.

Melatonin Abrogates the Anti-Developmental Effect of the AKT Inhibitor SH6 in Bovine Oocytes and Embryos

Melatonin, a nighttime-secreted antioxidant hormone produced by the pineal gland, and AKT, a serine/threonine-specific protein kinase, have been identified as regulators for several cellular processes essential for reproduction. The current study aimed to investigate the potential interplay between melatonin and AKT in bovine oocytes in the context of embryo development. Results showed that the inclusion of SH6, a specific AKT inhibitor, during in vitro maturation (IVM) significantly reduced oocyte maturation, cumulus cell expansion, cleavage, and blastocyst development that were rescued upon addition of melatonin. Oocytes treated with SH6 in the presence of melatonin showed lower levels of reactive oxygen species (ROS) and blastocysts developed exhibited low apoptosis while the mitochondrial profile was significantly improved compared to the SH6-treated group. The RT-qPCR results showed up-regulation of the mRNA of maturation-, mitochondrial-, and cumulus expansion-related genes including GDF-9, BMP-15, MARF1, ATPase, ATP5F1E, POLG2, HAS2, TNFAIP6, and PTGS2 and down-regulation of Bcl-2 associated X apoptosis regulator (BAX), caspase 3, and p21 involved in apoptosis and cell cycle arrest in melatonin-SH6 co-treated group compared to SH6 sole treatment. The immunofluorescence showed high levels of caspase 3 and caspase 9, and low AKT phosphorylation in the SH6-treated group compared to the control and melatonin-SH6 co-treatment. Taken together, our results showed the importance of both melatonin and AKT for overall embryonic developmental processes and, for the first time, we report that melatonin could neutralize the deleterious consequences of AKT inhibition, suggesting a potential role in regulation of AKT signaling in bovine oocytes.

Effects of melatonin on production of reactive oxygen species and developmental competence of bovine oocytes exposed to heat shock and oxidative stress during in vitro maturation

SummaryHeat shock may disrupt oocyte function by increasing the generation of reactive oxygen species (ROS). We evaluated the capacity of the antioxidant melatonin to protect oocytes using two models of oxidative stress - heat shock and the pro-oxidant menadione. Bovine cumulus-oocyte complexes (COC) were exposed in the presence or absence of 1 µM melatonin to the following treatments during maturation: 38.5°C, 41°C and 38.5°C+5 µM menadione. In the first experiment, COC were matured for 3 h with 5 µM CellROX® and analyzed by epifluorescence microscopy to quantify production of ROS. The intensity of ROS was greater for oocytes exposed to heat shock and menadione than for control oocytes. Melatonin reduced ROS intensity for heat-shocked oocytes and oocytes exposed to menadione, but not for control oocytes. In the second experiment, COC were matured for 22 h. After maturation, oocytes were fertilized and the embryos cultured for 7.5 days. The proportion of oocytes that cleaved after fertilization was lower for oocytes exposed to heat shock and menadione than for control oocytes. Melatonin increased cleavage for heat-shocked oocytes and oocytes exposed to menadione, but not for control oocytes. Melatonin tended to increase the developmental competence of embryos from heat-shocked oocytes but not for embryos from oocytes exposed to menadione or from control oocytes. In conclusion, melatonin reduced production of ROS of maturing oocytes and protected oocytes from deleterious effects of both stresses on competence of the oocyte to cleave after coincubation with sperm. These results suggest that excessive production of ROS compromises oocyte function.

Effects of melatonin on the synthesis of estradiol and gene expression in pig granulosa cells

The interaction of granulosa cells (GCs) with oocytes is important to regulate follicle development. The exogenous melatonin promoting the maturation of oocytes by GCs has been approved in pig, however, the transcriptome profile and the functions of the genes regulated by melatonin in GCs have not yet to be fully characterized. In this study, we found melatonin could stimulate the synthesis of estradiol in pig GCs. The RNA-seq was used to explore the effects of melatonin on gene expression, a total of 89 differentially expressed genes (DEGs) were identified. Gene ontology analysis showed DEGs which associated with regulation of cell proliferation, cell cycle, and anti-apoptosis were significantly enriched. The functions of two DEGs, NOTCH2 and FILIP1L, were studied in pig GCs. The results showed that NOTCH2 inhibited the synthesis of estradiol, but FILIP1L promoted the synthesis of estradiol. Furthermore, inhibiting NOTCH2 in granulosa cells cocultured with cumulus-oocyte-complexes had no obvious effect on the maturation of pig oocyte, but could upregulate the cleavage rate of oocyte. We proved that FILIP1L had no effect on the maturation and cleavage of pig oocytes. Our work deepens the understanding of melatonin's effects on GCs and oocyte. The DEGs we found will be beneficial to reveal mechanisms of melatonin acting on GCs and oocytes and design the pharmacological interventions.

Melatonin supplementation during prolonged in vitro maturation improves the quality and development of poor-quality porcine oocytes via anti-oxidative and anti-apoptotic effects

Poor-quality oocytes (those with 1-2 layers of cumulus cells) typically possess low meiotic competence and development. Prolonging the duration of in vitro maturation (IVM; 52 hr) can enhance the maturation rate of poor-quality oocytes, but it does not improve subsequent embryonic development. This likely reflects the increased reactive oxygen species (ROS) production and apoptosis seen in these oocytes compared with the non-prolonged IVM (44 hr) group. Melatonin is a free radical scavenger, anti-oxidant and anti-apoptotic agent that reported to enhance the quality of embryos by inhibiting ROS generation and apoptosis. Therefore, we herein investigated whether melatonin combined with prolonged IVM (52 hr) could improve the quality and development of poor-quality oocytes. We supplemented IVM and/or in vitro culture (IVC) media with various concentrations (0, 10^-7 , 10^-6 , 10^-5  M) of melatonin, and estimated parameters related to oocyte quality and development. The addition of melatonin (10^-6  M) to a prolonged IVM system improved the oocyte quality and development compared with those of the melatonin-free poor-quality oocytes group, and that this was due to decreases in ROS generation, apoptosis, and DNA damage. When melatonin was added during both IVM (10^-6  M) and IVC (10^-6  M), we observed a cumulative positive influence on the embryonic development and quality; this treatment enhanced the expression level of Oct4 and decreased the levels of ROS, DNA damage, and apoptosis. Together, these findings suggest that the combination of melatonin plus prolonged IVM can improve the quality and development of poor-quality porcine oocytes via anti-oxidative and anti-apoptotic effects.

Melatonin Improves The Developmental Competence of Goat Oocytes

Background

DNA methylation is one the epigenetic mechanisms, which is critically involved in gene expression. This phenomenon is mediated by DNA methyl-transferases and is affected by environmental stress, including in vitro maturation (IVM) of oocytes. Melatonin, as an antioxidant, may theoretically be involved in epigenetic regulation via reductions of reactive oxygen species. This study was performed to investigate DNA methylation and the possibility of goat oocyte development after treatment with different concentrations of melatonin.

MATERIALS AND METHODS

This experimental study was performed to investigate DNA methylation and the possibility of goat oocyte development after treatment with different concentrations of melatonin. For this purpose, oocytes with granulated cytoplasm were selected and co-cultured with at least two layers of cumulus cells in maturation medium with 10^-6 M, 10^-9 M, 10^-12 M and 0-M (as control group) of melatonin. Nucleus status, glutathione content and developmental competence of the oocytes in each experimental group were assessed. Also, expression of genes associated with DNA methylation, including DNA methyltransferase 1 (DNMT1), DNA methyltransferase 3b (DNMT3b) and DNA methyltransferase 3a (DNMT3a) was evaluated by quantitative real time-polymerase chain reaction (RT-PCR).

RESULTS

According to our findings, the percentage of oocytes that reached the M-II stage significantly increased in the 10-12 M group (P<0.05). Also, a significant elevation of glutathione content was observed in melatonin-treated oocytes (P<0.05). Analysis of blastocyst formation revealed that developmental competence of the oocytes was higher than the control group (P<0.05). It was observed that melatonin treatment decreased expression levels of DNA methyltransferases (DNMTs) and global DNA methylation (P<0.05). In addition, the expression of melatonin receptor1A (MTNR1A) was detected in both cumulus and oocyte by RT-PCR.

CONCLUSION

The results suggested that in goat model melatonin affects DNA methylation pattern, leading to an improvement in the developmental competence of the oocytes.

Melatonin Improves the Quality of Inferior Bovine Oocytes and Promoted Their Subsequent IVF Embryo Development: Mechanisms and Results

The inferior oocytes (IOs), which are not suitable for embryo development, occupy roughly one-third or more of the collected immature bovine oocytes. The IOs are usually discarded from the in vitro bovine embryo production process. Improving the quality of the inferior oocytes (IOs) and make them available in in vitro embryo production would have important biological, as well as commercial, value. This study was designed to investigate whether melatonin could improve the quality of IOs and make them usable in the in vitro maturation (IVM) and subsequent (in vitro fertilization) IVF embryo development. The results indicated that: the maturation rate of IOs and their subsequent IVF embryo developments were impaired compared to cumulus-oocyte complexes and melatonin treatment significantly improved the quality of IOs, as well as their IVF and embryo developments. The potential mechanisms are that: (1) melatonin reduced reactive oxygen species (ROS) and enhanced glutathione (GSH) levels in the IOs, thereby protecting them from oxidative stress; (2) melatonin improved mitochondrial normal distribution and function to increase ATP level in IOs; and (3) melatonin upregulated the expression of ATPase 6, BMP-15, GDF-9, SOD-1, Gpx-4, and Bcl-2, which are critical genes for oocyte maturation and embryo development and downregulated apoptotic gene expression of caspase-3.

Melatonin influences the sonic hedgehog signaling pathway in porcine cumulus oocyte complexes

Melatonin, which is synthesized in the pineal gland and peripheral reproductive organs, has antioxidant properties and regulates physiological processes. It is well known that melatonin affects in vitro maturation (IVM) of oocytes and embryonic development in many species. However, beneficial effects of melatonin on IVM have been explained mainly by indirect antioxidant effects and little information is available on the underlying mechanism by which melatonin directly acts on porcine cumulus oocyte complexes (COCs). Sonic hedgehog (Shh) signaling is important for follicle development, oocyte maturation, and embryo development, and there may be a relationship between melatonin and Shh signaling. To examine this, we designed three groups: (i) control, (ii) melatonin (10^-9  mol/L), and (iii) melatonin with cyclopamine (2 μmol/L; Shh signaling inhibitor). The aim of this study was to investigate the effects of these agents on cumulus expansion, oocyte maturation, embryo development after parthenogenetic activation (PA), gene expression in cumulus cells, oocytes and blastocysts, and protein expression in COCs. Melatonin significantly increased the proportion of COCs exhibiting complete cumulus expansion (degree 4), PA blastocyst formation rates, and total cell numbers, which were inhibited by addition of cyclopamine. Simultaneously, the expression of cumulus expansion-related genes (Ptgs1, Ptgs2, and Has2) and Shh signaling-related genes (Shh, Pthc1, Smo, and Gli1) and proteins (Ptch1, Smo, and Gli1) in cumulus cells was upregulated in the melatonin-treated group, and these effects were also inhibited by cyclopamine. In conclusion, our results suggest that Shh signaling mediates effects of melatonin to improve porcine cumulus expansion and subsequent embryo development.

Effects of melatonin on maturation, histone acetylation, autophagy of porcine oocytes and subsequent embryonic development

Melatonin (MLT) is an endogenous hormone with roles in animal germ cell development. However, the effect of MLT on porcine oocyte maturation and its underlying mechanisms remain largely unknown. Here, we investigated the effects of exogenous MLT on oocyte maturation, histone acetylation, autophagy and subsequent embryonic development. We found that 1 nmol/L MLT supplemented in maturation medium was the optimal concentration to promote porcine oocyte maturation and subsequent developmental competence and quality of parthenogenetic embryos. Interestingly, the beneficial effects of 1 nmol/L MLT treatment on porcine oocyte maturation and embryo development were mainly attributed to the first half period of in vitro maturation. Simultaneously, MLT treatment could also improve maturation of small follicle-derived oocytes, morphologically poor (cumulus cell layer ≤1) and even artificially denuded oocytes and their subsequent embryo development. Furthermore, MLT treatment not only could decrease the levels of H3K27ac and H4K16ac in metaphase II (MII) oocytes, but also could increase the expression abundances of genes associated with cumulus cell expansion, meiotic maturation, histone acetylation and autophagy in cumulus cells or MII oocytes. These results indicate that MLT treatment can facilitate porcine oocyte maturation and subsequent embryonic development probably, through improvements in histone acetylation and autophagy in oocytes.

Melatonin implantation improved the egg-laying rate and quality in hens past their peak egg-laying age

The egg-laying rates of hens approximately 470 days of age exhibited a positive correlation to blood melatonin levels. The hens with an egg-laying rate <30%, 30~90% and ≥90% had blood melatonin levels of 5.8 ± 2.6, 74.0 ± 32.9 and 445.9 ± 115.3 ng/ml, respectively. When 10 mg of melatonin was implanted into the hens at 300, 360, 470 and 550 days of age, the egg-laying rates increased 4.63 ± 0.46%, 8.38 ± 1.45%, 4.93 ± 0.85% and 7.93 ± 0.91%, respectively, compared to that of the controls. Melatonin implantation in hens at 300–470 days of age was observed to enhance egg production and reduce the rate of appearance of sharpei eggs. Melatonin (10 mg) implanted in hens 360 days of age did not influence the blood levels of progesterone (P4) or the gene expression levels of ovarian follicle stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), oestradiol receptor alpha (ERα), superoxide dismutase 2 (SOD2) or melatonin receptor 1 (MT1). In contrast, melatonin significantly elevated the serum oestradiol-17β (E2) content, down-regulated the gene expression of gonadotropin-inhibitory hormone receptor (GnIHR), and enhanced the expression of melatonin receptor 2 (MT2). This result indicates that the improved egg-laying rate by melatonin was the result of increased serum oestradiol and decreased ovarian GnIHR. These alterations may be mediated by MT2 activation.

Melatonin: A Mitochondrial Targeting Molecule Involving Mitochondrial Protection and Dynamics

Melatonin has been speculated to be mainly synthesized by mitochondria. This speculation is supported by the recent discovery that aralkylamine N-acetyltransferase/serotonin N-acetyltransferase (AANAT/SNAT) is localized in mitochondria of oocytes and the isolated mitochondria generate melatonin. We have also speculated that melatonin is a mitochondria-targeted antioxidant. It accumulates in mitochondria with high concentration against a concentration gradient. This is probably achieved by an active transportation via mitochondrial melatonin transporter(s). Melatonin protects mitochondria by scavenging reactive oxygen species (ROS), inhibiting the mitochondrial permeability transition pore (MPTP), and activating uncoupling proteins (UCPs). Thus, melatonin maintains the optimal mitochondrial membrane potential and preserves mitochondrial functions. In addition, mitochondrial biogenesis and dynamics is also regulated by melatonin. In most cases, melatonin reduces mitochondrial fission and elevates their fusion. Mitochondrial dynamics exhibit an oscillatory pattern which matches the melatonin circadian secretory rhythm in pinealeocytes and probably in other cells. Recently, melatonin has been found to promote mitophagy and improve homeostasis of mitochondria.

The sensitivity of the DNA damage checkpoint prevents oocyte maturation in endometriosis

Mouse oocytes respond to DNA damage by arresting in meiosis I through activity of the Spindle Assembly Checkpoint (SAC) and DNA Damage Response (DDR) pathways. It is currently not known if DNA damage is the primary trigger for arrest, or if the pathway is sensitive to levels of DNA damage experienced physiologically. Here, using follicular fluid from patients with the disease endometriosis, which affects 10% of women and is associated with reduced fertility, we find raised levels of Reactive Oxygen Species (ROS), which generate DNA damage and turn on the DDR-SAC pathway. Only follicular fluid from patients with endometriosis, and not controls, produced ROS and damaged DNA in the oocyte. This activated ATM kinase, leading to SAC mediated metaphase I arrest. Completion of meiosis I could be restored by ROS scavengers, showing this is the primary trigger for arrest and offering a novel clinical therapeutic treatment. This study establishes a clinical relevance to the DDR induced SAC in oocytes. It helps explain how oocytes respond to a highly prevalent human disease and the reduced fertility associated with endometriosis.

Effects of melatonin during IVM in defined medium on oocyte meiosis, oxidative stress, and subsequent embryo development

Melatonin may have beneficial effects when used in oocyte maturation and embryo development culture. The effect of melatonin during IVM on meiosis resumption and progression in bovine oocytes and on expression of antioxidant enzymes, nuclear fragmentation and free radicals, as well as on embryo development were assessed. Cumulus-oocyte complexes were matured in vitro with melatonin (10(-9) and 10(-6) M), FSH (positive control), or without hormones (negative control) in defined medium. Maturation rates were evaluated at 6, 12, 18, and 24 hours. Transcripts for antioxidant enzymes (CuZnSOD, MnSOD, and glutathione peroxidase 4 (GPX4)) in oocytes and cumulus cells, nuclear fragmentation in cumulus cells (TUNEL) and reactive oxygen species levels in oocytes (carboxy-H2 difluorofluorescein diacetate) were determined at 24 hours IVM. Effect of treatments on embryo development was determined after in vitro fertilization and culture. At 12 hours, meiosis resumption rates in FSH and melatonin-treated groups were similar (69.6%-81.8%, P > 0.05). At 24 hours, most oocytes were in metaphase II, with FSH showing highest rates (90.0%, P < 0.05) compared with the other groups (51.6%-69.1%, P > 0.05). In cumulus cells, MnSOD expression was higher in FSH group (P < 0.05) whereas Cu,ZnSOD transcripts were more abundant in melatonin group (10(-6)M; P < 0.05). Nuclear fragmentation in cumulus cells was highest in controls (37.4%/10,000 cells; P < 0.05) and lower in FSH and 10(-6)M melatonin (29.4% and 25.6%/10,000 cells, respectively). Reactive oxygen species levels were lower in oocytes matured with 10(-6)M melatonin than in control and FSH groups (P < 0.05). Embryo development from oocytes matured only with melatonin was similar to those matured in complete medium (P > 0.05). In conclusion, although melatonin during IVM in a defined medium does not stimulate nuclear maturation progression it does stimulate meiosis resumption and such treated oocytes support subsequent embryo development. Melatonin also shows cytoprotective effects on cumulus-oocyte complexes.