Mitochondrial distribution and adenosine triphosphate content of bovine oocytes before and after in vitro maturation: correlation with morphological criteria and developmental capacity after in vitro fertilization and culture

The role of mitochondrial dynamics in oocyte and early embryo development

Mitochondrial dysfunction is widely implicated in various human diseases, through mechanisms that go beyond mitochondria's well-established role in energy generation. These dynamic organelles exert vital control over numerous cellular processes, including calcium regulation, phospholipid synthesis, innate immunity, and apoptosis. While mitochondria's importance is acknowledged in all cell types, research has revealed the exceptionally dynamic nature of the mitochondrial network in oocytes and embryos, finely tuned to meet unique needs during gamete and pre-implantation embryo development. Within oocytes, both the quantity and morphology of mitochondria can significantly change during maturation and post-fertilization. These changes are orchestrated by fusion and fission processes (collectively known as mitochondrial dynamics), crucial for energy production, content exchange, and quality control as mitochondria adjust to the shifting energy demands of oocytes and embryos. The roles of proteins that regulate mitochondrial dynamics in reproductive processes have been primarily elucidated through targeted deletion studies in animal models. Notably, impaired mitochondrial dynamics have been linked to female reproductive health, affecting oocyte quality, fertilization, and embryo development. Dysfunctional mitochondria can lead to fertility problems and can have an impact on the success of pregnancy, particularly in older reproductive age women.

Nobiletin enhances mitochondrial function by regulating SIRT1/PGC-1α signaling in porcine oocytes during in vitro maturation

Nobiletin is a natural flavonoid found in citrus fruits with beneficial effects, including anti-inflammatory, anti-cancer and anti-oxidation effects. The aim of this study was to investigate whether nobiletin improves mitochondrial function in porcine oocytes and examine the underlying mechanism. Oocytes enclosed by cumulus cells were cultured in TCM-199 for 44 h with 0.1% dimethyl sulfoxide (control), or supplemented with 5, 10, 25, and 50 μM of nobiletin (Nob5, Nob10, Nob25, and Nob50, respectively). Oocyte maturation rate was significantly enhanced in Nob10 (70.26 ± 0.45%) compared to the other groups (control: 60.12 ± 0.47%; Nob5: 59.44 ± 1.63%; Nob25: 63.15 ± 1.38%; Nob50: 46.57 ± 1.19%). The addition of nobiletin reduced the levels of reactive oxygen species and increased glutathione levels. Moreover, Nob10 promoted mitochondrial biogenesis by upregulating the protein levels of sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α). This resulted in an increase in the number of active mitochondria, mitochondrial DNA copy number, mitochondrial membrane potential, and ATP production, thereby enhancing mitochondrial function. The protein level of p53 decreased, followed by the phosphorylation of B-cell lymphoma 2, suggesting a reduction in mitochondria-mediated apoptosis in the Nob10 group. Additionally, the release of cytochrome c from the mitochondria was significantly diminished along with a decrease in the protein expression of caspase 3. Thus, nobiletin has a great potential to promote the in vitro maturation of porcine oocytes by suppressing oxidative stress and promoting mitochondrial function through the upregulation of the SIRT1/PGC-1α signaling pathway.

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

BACKGROUND

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

AIM OF REVIEW

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

KEY SCIENTIFIC CONCEPTS OF REVIEW

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

Nicotinamide Mononucleotide improves oocyte maturation of mice with type 1 diabetes

BACKGROUND

The number of patients with type 1 diabetes rises rapidly around the world in recent years. Maternal diabetes has a detrimental effect on reproductive outcomes due to decreased oocyte quality. However, the strategies to improve the oocyte quality and artificial reproductive technology (ART) efficiency of infertile females suffering from diabetes have not been fully studied. In this study, we aimed to examine the effects of nicotinamide mononucleotide (NMN) on oocyte maturation of mouse with type 1 diabetes mouse and explore the underlying mechanisms of NMN's effect.

METHODS

Streptozotocin (STZ) was used to establish the mouse models with type 1 diabetes. The successful establishment of the models was confirmed by the results of body weight test, fasting blood glucose test and haematoxylin and eosin (H&E) staining. The in vitro maturation (IVM) rate of oocytes from diabetic mice was examined. Immunofluorescence staining (IF) was performed to examine the reactive oxygen species (ROS) level, spindle/chromosome structure, mitochondrial function, actin dynamics, DNA damage and histone modification of oocytes, which are potential factors affecting the oocyte quality. The quantitative reverse transcription PCR (RT-qPCR) was used to detect the mRNA levels of Sod1, Opa1, Mfn2, Drp1, Sirt1 and Sirt3 in oocytes.

RESULTS

The NMN supplementation increased the oocyte maturation rate of the mice with diabetes. Furthermore, NMN supplementation improved the oocyte quality by rescuing the actin dynamics, reversing meiotic defects, improving the mitochondrial function, reducing ROS level, suppressing DNA damage and restoring changes in histone modifications of oocytes collected from the mice with diabetes.

CONCLUSION

NMN could improve the maturation rate and quality of oocytes in STZ-induced diabetic mice, which provides a significant clue for the treatment of infertility of the patients with diabetes.

Effect of maternal age on ATP content and distribution of mitochondria in bovine oocytes

Our objective was to understand how maternal age influences the mitochondrial population and ATP content of in vivo matured bovine oocytes. We hypothesized that in vivo matured oocytes from older cows would have altered mitochondrial number and distribution patterns and lower cytoplasmic ATP content compared to the oocytes obtained from younger cows. Follicles ≥5mm were ablated in old cows (13 to 22 yrs, Old Group, n = 7) and their younger daughters (4 to 10 years old, Young Group; n = 7) to induce the emergence of a new follicular wave. Cows were treated twice daily with eight doses of FSH starting 24 hr after ablation (Day 0, day of wave emergence). Prostaglandin F2alpha (PGF) was given on Days 3 and 3.5, LH on Day 4.5, and cumulus-oocyte-complexes were collected 18-20 hours post-LH by ultrasound-guided follicular aspiration. Oocytes were either processed for staining with MitoTracker Deep Red FM or for ATP assay. Stained oocytes were imaged with a Zeiss LSM 710 confocal microscope, and mitochondria were segmented in the oocyte volume sets using Imaris Pro 7.4. In vivo matured oocytes obtained from old cows were similar in morphological grades to those from young cows. However, the oocytes of COC from older cows had 23% less intracellular ATP (27.4±1.9 vs 35.7±2.2 pmol per oocyte, P = 0.01) than those of young cows. Furthermore, the average volume of individual mitochondria, indicated by the number of image voxels, was greater (P<0.05) in oocytes from older cows than in those from younger cows. Oocytes from older cows also tended to have a greater number of mitochondrial clusters (P = 0.06) and an increased number of clusters in the central region of the oocytes (P = 0.04) compared to those from younger cows. In conclusion, our study demonstrated that maternal age was associated with a decrease in the cytoplasmic ATP content of in vivo mature oocytes and an altered distribution of mitochondrial structures. These findings suggest that maternal age may negatively influence the developmental competence of oocytes from older cows.

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

BACKGROUND

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

Supplementation of SkQ1 Increases Mouse In Vitro Oocyte Maturation and Subsequent Embryonic Development by Reducing Oxidative Stress

In vitro oocyte maturation (IVM) technology is important for assisted animal and human reproduction. However, the maturation rates and developmental potential of in vitro-matured oocytes are usually lower than those of in vivo-matured oocytes. Oxidative stress is a main factor that causes the lower maturation rates and quality of in vitro-matured oocytes. The purpose of this study was to investigate the effects of treatment with SkQ1, a mitochondria-targeted antioxidant, on mouse IVM and subsequent embryonic development. The results demonstrated that the supplementation of SkQ1 during IVM improves the maturation rates of mouse oocytes and the subsequent developmental competence of in vitro-fertilized embryos. The addition of SkQ1 to the IVM medium also decreased oxidative stress and apoptosis, and increased mitochondrial membrane potential in matured mouse oocytes. This study provides a new method through which to enhance the maturation rates and the quality of in vitro-matured mouse oocytes, thus promoting the application and development of assisted animal and human reproductive technology.

Pre-fertilization approach using α-l-fucosidase modulates zona pellucida hardening during bovine in vitro embryo production

The polyspermy occurrence is considerably lower under in vivo compared to in vitro embryo culture conditions, suggesting that the presence of some factors in the maternal environment is responsible for this. The α-L-fucosidase (FUCA) is a natural glycosidase present in the oviductal fluid, therefore, this study aimed at investigating the effect of adding FUCA to the hardening of the zona pellucida (ZP), polyspermy control, and embryonic yield and quality of bovine blastocysts produced in vitro. In the first experiment, the effect of FUCA (0.125 U/mL) was evaluated during the entire in vitro fertilization (IVF). However, it was demonstrated to be embryotoxic by completely inhibiting the blastocyst formation. In the second experiment, the FUCA (0.125 U/mL) was tested as short-term incubation before IVF (pre-fertilization step) for 30 min or 2 h, which demonstrated that FUCA treatment for 30 min resulted in ZP hardening. In the third experiment, a pre-fertilization FUCA treatment (1 h) at different concentrations (0, 0.0625, and 0.125 U/mL) showed that FUCA (0.0625 U/mL) improved pre-fertilization ZP hardening and tended to increase monospermic fertilization rates but did not improve embryo yield and quality. Together, it has been demonstrated that FUCA can induce oocyte pre-fertilization ZP hardening and might improve monospermic fertilization performance, and this effect is dependent on both variables (protein concentration and incubation time).

Mitochondrial deoxyguanosine kinase is required for female fertility in mice

Mitochondrial homeostasis plays a pivotal role in oocyte maturation and embryonic development. Deoxyguanosine kinase (DGUOK) is a nucleoside kinase that salvages purine nucleosides in mitochondria and is critical for mitochondrial DNA replication and homeostasis in non-proliferating cells. Dguok loss-of-function mutations and deletions lead to hepatocerebral mitochondrial DNA deletion syndrome. However, its potential role in reproduction remains largely unknown. In this study, we find that Dguok knockout results in female infertility. Mechanistically, DGUOK deficiency hinders ovarian development and oocyte maturation. Moreover, DGUOK deficiency in oocytes causes a significant reduction in mitochondrial DNA copy number and abnormal mitochondrial dynamics and impairs germinal vesicle breakdown. Only few DGUOK-deficient oocytes can extrude their first polar body during in vitro maturation, and these oocytes exhibit irregular chromosome arrangements and different spindle lengths. In addition, DGUOK deficiency elevates reactive oxygen species levels and accelerates oocyte apoptosis. Our findings reveal novel physiological roles for the mitochondrial nucleoside salvage pathway in oocyte maturation and implicate DGUOK as a potential marker for the diagnosis of female infertility.

Lipopolysaccharide impairs the in vitro growth, steroidogenesis, and maturation of oocyte-cumulus-granulosa cell complexes derived from bovine early antral follicles

In postpartum dairy cows, lipopolysaccharide (LPS) derived from gram-negative bacteria causes uterine or mammary inflammation, resulting in low fertility. The present study aimed to investigate the effect of LPS on the in vitro growth (IVG), steroidogenesis, and maturation of oocyte-cumulus-granulosa cell complexes (OCGCs) derived from bovine early antral follicles. OCGCs were isolated from bovine early antral follicles (0.5-1 mm in diameter) and cultured in vitro for 12 days using media containing 0 (control), 0.01, or 1 μg/mL of LPS. The viability, cavity formation, and oocyte diameter of the OCGCs, as well as the concentrations of estradiol (E2) and progesterone (P4) in the IVG culture media, were determined. After IVG culture, oocytes collected from viable OCGCs were matured in vitro (IVM) in a medium without LPS. The nuclear maturation rate and the mitochondrial membrane potential of oocytes were determined. Bovine oocytes and cumulus-granulosa complexes derived from early antral follicles expressed genes encoding LPS receptor complex, such as toll-like receptor 4 (TLR4). Immunohistochemistry analysis further localized TLR4 expression predominantly in follicular granulosa and theca cells of early antral follicles. The viability of OCGCs and cavity formation in OCGCs were lower in the 0.01 and 1 μg/mL LPS groups than in the control group. No significant difference in oocyte diameter was observed between the treatment groups throughout the culture period. Moreover, E2 production was suppressed in the 0.01 and 1 μg/mL LPS groups from Days 4-8, whereas P4 production increased in the 1 μg/mL LPS group from Days 0-8. The nuclear maturation rate after IVM was lower in the 0.01 and 1 μg/mL LPS groups than in the control group. The mitochondrial membrane potential of post-IVM oocytes was lower in the 0.01 and 1 μg/mL LPS groups than in the control group. Taken together, these results indicate that LPS inhibited the growth and steroidogenesis of OCGCs and the meiosis and mitochondrial function of oocytes derived from early antral follicles. This study suggests that the detrimental effects of LPS on developing oocytes may contribute to long-term decreased fertility in postpartum dairy cows.

Improvement of oocyte competence and in vitro oocyte maturation with EGF and IGF-I in Guinea pig model

In vitro maturation (IVM) system is an alternative method to superovulation protocols to obtain mature oocytes. Epidermal Growth Factor (EGF) and Insulin-like Growth Factor I (IGF-I) have been widely used in IVM medium in different species. Although the guinea pig is a valuable animal model for reproductive studies, IVM is rarely used. We aimed to establish a suitable in vitro production system using EGF and/or IGF-I during IVM to improve oocyte competence. Firstly, immunolocalization of EGF and IGF-I receptors in the ovary was assessed. An IVM dose-response experiment was performed with cumulus-oocyte complexes (COCs) supplemented with: 1) EGF [0, 10, 50, 100 ng/mL or 10% fetal calf serum (FCS)]; 2) IGF-I [0, 50, 100, 200 ng/mL or 10% FCS]; or 3) the concentrations of EGF and IGF-I which showed the best IVM index in the previous experiments, with or without Fetal Calf Serum (FCS). Cortical granule and mitochondria distribution patterns were determined in in vivo and in vitro-matured oocytes for the first time in this species. Apoptotic rate after IVM and oocyte competence by in vitro embryo development were evaluated. Immunohistochemistry results showed positive immunostaining of EGF and IGF receptors in corpus luteum, oocytes, granulosa and theca cells in follicles in all stages of development. Supplementation of IVM medium with 50 ng/mL EGF or 100 ng/mL IGF-I or their combination with FCS successfully led to oocyte nuclear and cytoplasmic maturation and reduced the apoptotic rate. Both growth factors improved oocyte competence during IVM in this species since early embryos were in vitro developed, showing better results when FCS was used in the IVM medium.

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

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

Monomethyl Phthalate Causes Early Embryo Development Delay, Apoptosis, and Energy Metabolism Disruptions Through Inducing Redox Imbalance

Phthalates are a class of environmental endocrine disrupting chemicals which can cause reproductive system damages. However, data about reproductive toxicity spectrum of phthalate metabolites among Chinese women undergoing in vitro fertilization (IVF) treatments are scarce yet. Previous studies regarding underlying embryo toxicities focused on oxidative stress and apoptosis, while energy metabolism abnormality might be another key cause for embryo developmental disruptions. Here, we found that among the measured eight phthalate metabolites, monomethyl phthalate (MMP) had the second highest urinary concentration in women receiving IVF. Compare to the lowest exposure level group, MMP in tertile 3 was associated with fewer counts of oocyte retrieved and good-quality embryos, and MMP in tertile 2 was correlated with reduced good-quality embryo rate. The direct embryo toxicities of MMP were studied using mouse 2-cell embryos. Consistent to results found in human populations, exposure to MMP induced mouse early embryo developmental delay. Furthermore, MMP exposure led to excessive reactive oxygen species production in early embryos, and antioxidant can partially rescue the early embryo development slow down. Embryo apoptosis could also be caused by oxidative stress. To be noted, elevated apoptosis level was not found in live "slow" embryos but dead embryos, which suggested that apoptosis was not related to early embryo developmental delay. Additionally, MMP exposure depleted adenosine triphosphate (ATP) synthesis of early embryos, which could be reversed by antioxidant. In conclusion, MMP, as the newly found embryonic toxicant in Chinese women, resulted in early embryo development delay, apoptosis, and energy metabolism disruptions via inducing redox imbalance.

Vertical transmission of maternal DNA through extracellular vesicles associates with altered embryo bioenergetics during the periconception period

The transmission of DNA through extracellular vesicles (EVs) represents a novel genetic material transfer mechanism that may impact genome evolution and tumorigenesis. We aimed to investigate the potential for vertical DNA transmission within maternal endometrial EVs to the pre-implantation embryo and describe any effect on embryo bioenergetics. We discovered that the human endometrium secretes all three general subtypes of EV - apoptotic bodies (ABs), microvesicles (MVs), and exosomes (EXOs) - into the human endometrial fluid (EF) within the uterine cavity. EVs become uniformly secreted into the EF during the menstrual cycle, with the proportion of different EV populations remaining constant; however, MVs contain significantly higher levels of mitochondrial (mt)DNA than ABs or EXOs. During the window of implantation, MVs contain an eleven-fold higher level of mtDNA when compared to cells-of-origin within the receptive endometrium, which possesses a lower mtDNA content and displays the upregulated expression of mitophagy-related genes. Furthermore, we demonstrate the internalization of EV-derived nuclear-encoded (n)DNA/mtDNA by trophoblast cells of murine embryos, which associates with a reduction in mitochondrial respiration and ATP production. These findings suggest that the maternal endometrium suffers a reduction in mtDNA content during the preconceptional period, that nDNA/mtDNA become packaged into secreted EVs that the embryo uptakes, and that the transfer of DNA to the embryo within EVs occurs alongside the modulation of bioenergetics during implantation.

Effect of food supplementation on in vitro embryo production and growth performance in prepubertal Nelore heifers

In vitro embryos production from prepubertal heifers can help contribute to breeding programs; however, strategies are necessary to increase their embryo production. The aim of this study was to investigate the effects of two nutritional plans on oocyte recovery, embryo production and growth performance of prepubertal Nelore heifers. Thirty-four Nelore heifers with age of 6.5 months were divided into two feeding treatments (NP1 and NP2). The NP1 diets served as the control and NP2 diets were formulated to contain an average of 1.22-fold more energy than NP1. After 3 months of supplementation, the animals underwent follicular aspiration (ovum pick-up, OPU) every 21 d for 3 months and embryos were produced in vitro. Wither height, chest depth, body weight and subcutaneous fat of animals were measured. The number of retrieved and viable oocytes per OPU were 1.49-fold and 1.42-fold greater in NP2 heifers (p = 0.018 and p = 0.049, respectively) than those in NP1 heifers. Heifers administered NP2 produced 29.7% blastocysts, a percentage higher than NP1 animals that produced 24.40% embryos (p < 0.05). Consequently, females in the NP2 treatment showed improved body development. These results indicate a positive effect of a higher energy diet on assisted reproduction and body development in prepubertal heifers.

Incorporation of L-Carnitine in the OvSynch protocol enhances the morphometrical and hemodynamic parameters of the ovarian structures and uterus in ewes under summer climatic conditions

Heat stress negatively impacts the reproductive performance of sheep including the efficiency of estrous synchronization regimens. This study aimed to investigate the potential effects of L-Carnitine (LC) administration on the efficacy of the OvSynch protocol in ewes under summer climatic conditions. Ewes were synchronized for estrus using the OvSynch protocol and a dose of LC (20 mg/kg body weight) was intravenously (IV) administered on the same day of PGF2α injection to one group (n = 8; LC group), while other ewes (n = 8; control group) received the same protocol without LC. Ultrasonographic evaluation (including B-mode, color, and pulsed Doppler) was used to assess the morphometrical and hemodynamic parameters of ovarian structures [number, size, and blood flow of follicles (GFs) and corpora lutea (CLs)] and uterus during the estrous phase (Day 0), and on Day 8 post ovulation (luteal phase). Uterine artery blood flow (MUA) was assessed by measuring the resistive index (RI) and pulsatility index (PI) at both stages. The serum samples were collected to measure the concentrations of estradiol (E2), progesterone (P4), and total antioxidant capacity (TAC) using commercial kits. Results revealed a significant (P<0.05) increase in the colored pixel area of GFs and uterus in the LC group (392.84 ± 31.86 and 712.50 ± 46.88, respectively) compared to the control one (226.25 ± 17.74 and 322 ± 18.78, respectively) during Day 0. Circulating E2 and TAC levels were significantly (P<0.05) higher in the LC-treated ewes (31.45 ± 1.53 pg/ml and 1.80 ± 0.13 mM/L, respectively) compared to those in the control ewes (21.20 ± 1.30 pg/ml and 0.98 ± 0.09 mM/L, respectively) during Day 0. Moreover, LC improved the colored pixel area of CLs (2038.14 ± 102.94 versus 1098 ± 82.39) and uterus (256.38 ± 39.28 versus 121.75 ± 11.36) and circulating P4 (2.99 ± 0.26 ng/ml versus1.67 ± 0.15 ng/ml) on Day 8. Values of RI of MUA were significantly lower in the LC group compared to the control one on Day 0 and Day 8 (0.48 ± 0.03 versus 0.72 ± 0.03 and 0.58 ± 0.03 versus 0.78 ± 0.02, respectively). In conclusion, LC incorporation in the OvSynch protocol enhanced the morphometrical and hemodynamic parameters of the ovarian structures and the uterus concomitantly with improvements in the TAC, E2, and P4 concentrations in ewes under hot summer conditions.

Zinc-nanoparticles alleviate the ovarian damage induced by bacterial lipopolysaccharide (LPS) in pregnant rats and their fetuses

Lipopolysaccharide (LPS) is an endotoxin derived from the cell wall of Gram-negative bacteria. LPS exposure during early gestation is associated with adverse effects on the placenta as well as on developmental outcomes, including embryonic resorption, fetal death, congenital teratogenesis, and fetal growth retardation. This work aimed to explore the adverse effects of LPS injected at an early stage of gestation on the gonads of pregnant rats and the ovaries of their pups and the role of zinc nanoparticles (Zn-NPs) against these adverse effects. Twenty-four pregnant rats were used in this study. They were divided at gestation day 4 into four groups (n = 6): control, Zn-NPs (20 mg/kg orally from gestation day E14 till the end of weaning), LPS (50 µg/kg at gestation days E7 and E9), and LPS + Zn-NPs group. The body weight and placenta weight were recorded at gestational day 16. At postnatal day 21 (weaning), the mothers rats and their offspring were sacrificed and immediately dissected to remove the ovaries and uteri from the mothers and the ovaries from their offspring for subsequent biochemical, histological, and immunohistochemical investigations. The obtained results revealed that LPS exposure during early gestation caused severe histopathological alterations in the placenta, uterus, and ovaries of mothers, as well as in the ovaries of their pups. Also, the uterine and ovarian sections displayed a positive reaction for caspase-3 antibody and a negative reaction for Bcl-2 antibody, which reflects the apoptotic effect of LPS. Additionally, remarkable reductions in the levels of antioxidants (superoxide dismutase and catalase) and significant increases in malondialdehyde (MDA) levels were recorded in the serum of LPS-treated mothers and in the ovarian tissues of their offspring. Further biochemical analysis of the ovarian tissues from LPS-maternally treated offspring showed a significant increase in the levels of caspase-3, TNF-α, and TGF-β1, but a significant decrease in the level of IGF-1. On the other hand, treatment of mothers with Zn-NPs from day 14 of gestation until the weaning day (21st day postnatal) successfully ameliorated most of the deleterious histopathological, immunohistochemical, and biochemical changes induced by LPS.

In vitro and in vivo embryo production efficiency in Flemish and Holstein donor females

The aim of this study was to compare embryo production efficiency in Flemish and Holstein donor females using ovum pick-up and in vitro fertilization (OPU-IVF) or in vivo production (superovulation; SOV) procedures. The study was conducted using a split-plot design, with eight Flemish and eight Holstein non-lactating cycling females. Females were subjected to ten weekly OPU/IVF sessions and/or two SOV/embryo collections sessions at a 63-day interval, for a total of 160 OPU-IVF and 32 SOV sessions. Mean numbers of follicles and corpora lutea, and cumulus-oocyte complex (COC) recovery rates were similar between breeds after the OPU and SOV sessions. However, Flemish donors yielded better quality grade II COCs (301, 41.9%) than Holstein females (609, and 202, 33.1%). Also, cleavage and blastocyst rates, and the total number and the mean number of viable embryos obtained after OPU-IVF were higher in Flemish (49.6% and 11.8%, and 63 and 11.8 per donor, respectively) than in Holstein (32.8% and 7.2%, and 34 and 7.2 per donor, respectively) females. Flemish females were also more efficient in yielding viable embryos after SOV (111, 7.3 per donor) than Holstein (48, 3.3 per donor) females. Overall, Flemish donor females had better responses to OPU-IVF or SOV procedures than Holstein counterparts. Irrespective of the breeds, SOV procedures were more efficient than OPU-IVF in yielding more viable embryos, under the conditions of this study. Both reproductive procedures were useful tools for the genetic conservation of the Flemish cattle breed in Southern Brazil.

Aging and oocyte competence: A molecular cell perspective

Follicular microenvironment is paramount in the acquisition of oocyte competence, which is dependent on two interconnected and interdependent processes: nuclear and cytoplasmic maturation. Extensive research conducted in human and model systems has provided evidence that those processes are disturbed with female aging. In fact, advanced maternal age (AMA) is associated with a lower chance of pregnancy and live birth, explained by the age-related decline in oocyte quality/competence. This decline has largely been attributed to mitochondria, essential for oocyte maturation, fertilization, and embryo development; with mitochondrial dysfunction leading to oxidative stress, responsible for nuclear and mitochondrial damage, suboptimal intracellular energy levels, calcium disturbance, and meiotic spindle alterations, that may result in oocyte aneuploidy. Nuclear-related mechanisms that justify increased oocyte aneuploidy include deoxyribonucleic acid (DNA) damage, loss of chromosomal cohesion, spindle assembly checkpoint dysfunction, meiotic recombination errors, and telomere attrition. On the other hand, age-dependent cytoplasmic maturation failure is related to mitochondrial dysfunction, altered mitochondrial biogenesis, altered mitochondrial morphology, distribution, activity, and dynamics, dysmorphic smooth endoplasmic reticulum and calcium disturbance, and alterations in the cytoskeleton. Furthermore, reproductive somatic cells also experience the effects of aging, including mitochondrial dysfunction and DNA damage, compromising the crosstalk between granulosa/cumulus cells and oocytes, also affected by a loss of gap junctions. Old oocytes seem therefore to mature in an altered microenvironment, with changes in metabolites, ribonucleic acid (RNA), proteins, and lipids. Overall, understanding the mechanisms implicated in the loss of oocyte quality will allow the establishment of emerging biomarkers and potential therapeutic anti-aging strategies. This article is categorized under: Reproductive System Diseases > Molecular and Cellular Physiology.

Detrimental effects of vitrification on integrin genes (α9 and β1) and in vitro fertilization in mouse oocytes

OBJECTIVE

Integrins are known as key molecules that importantly involve in fertilization. This study aimed to evaluate effects of vitrification on fertilization rate and expression of integrin genes, α9 and β1, on mice oocytes in GV and MІІ stages.

MATERIALS AND METHODS

From the ovarian tissue and fallopian tube of NMRI mice, germinal vesicle (GV, n = 200) and metaphase II (MII, n = 200) oocytes were obtained. Then, oocytes were distributed into 4 groups including non-vitrified GV, non-vitrified MII, vitrified GV, and vitrified MII. Cryotop method was used for vitrification and oocytes (for 4 weeks) were kept in liquid nitrogen. After that, by using an inverted microscope, the rate of survived oocytes was assessed. Also, in vitro fertilization (IVF) for oocytes, obtained from in vitro maturated MII and mice ovaries (ovulated MII), was done to assess embryos at differenced stages (2-cells, morula, and hatched). Finally, RT-qPCR was performed to investigate the mRNA expression of integrin genes (α9 and β1).

RESULTS

After vitrification, the rate of survived oocytes, 68.65%for GV and 65.07% % for MII, did not show a remarkable difference related to non-vitrified groups, while the fertilization rate in vitrified groups remarkably decrease compared to non-vitrified groups (p < 0.05). Also, the expression of α9 and β1 genes was significantly altered in vitrified groups when compared to non-vitrified groups (p < 0.05). There was no significant difference in embryo developmental rates for non-vitrified and vitrified groups.

CONCLUSION

Cryotop method for vitrification caused an alternation in oocyte quality by reducing fertilization rate and integrin gene expression.

Seasonal variations in the metabolomic profile of the ovarian follicle components in Italian Mediterranean Buffaloes

The aim of this work was to evaluate the seasonal effect on the metabolomic profile of the ovarian follicle in Italian Mediterranean buffalo to unravel the causes of the reduced competence during the non-breeding season (NBS). Samples of follicular fluid, follicular cells, cumulus cells and oocytes were collected from abattoir-derived ovaries during breeding season (BS) and NBS and analyzed by 1H Nuclear Magnetic Resonance. The Orthogonal Projections to Latent Structures of the Discriminant Analysis showed clear separation into seasonal classes and Variable Importance in Projection method identified differentially abundant metabolites between seasons. Seasonal differences were recorded in metabolite content in all analyzed components suggesting that the decreased oocyte competence during NBS may be linked to alteration of several metabolic pathways. The pathway enrichment analysis revealed that differences in the metabolites between the seasons were linked to glutathione, energy generating and amino acid metabolism and phospholipid biosynthesis. The current work allows the identification of potential positive competence markers in the follicular fluid as glutathione, glutamate, lactate and choline, and negative markers like leucine, isoleucine and β-hydroxybutyrate. These results form a major basis to develop potential strategies to optimize the follicular environment and the IVM medium to improve the competence of oocytes during the NBS.

Micro-vibration results in vitro-derived bovine blastocysts with greater cryotolerance, epigenetic abnormalities, and a massive transcriptional change

Much effort has been employed to improve the quality of embryos obtained by in vitro production (IVP) given the relevance of this technology to current livestock systems. In this context, dynamic IVP systems have proved beneficial to the embryo once they mimic fluid flows and mechanical forces resulting from the movement of ciliated cells and muscle contraction in the reproductive tract. In the present study, we sought to confirm these initial findings as well as assess potential molecular consequences to the embryo by applying micro-vibration (45 Hz for 5 s once per 60 min) during both oocyte maturation and embryo culture in cattle. As a result, micro-vibration led to lower incidence of apoptosis in blastocysts following vitrification-thawing. Further analyses revealed epigenetic and transcriptional changes in blastocysts derived from the micro-vibration treatment, with a total of 502 differentially expressed genes. Enrichment analyses linked differentially expressed genes to 'Oxidative phosphorylation', 'Cytokine-cytokine receptor interaction', and 'Signaling pathways regulating pluripotency of stem cells'. Yet, a meta-analysis indicated that the transcriptional changes induced by micro-vibration were not toward that of in vivo-derived embryos. In conclusion, micro-vibration increases the cryoresistance of bovine embryos, but caution should be taken given the unclear consequences of epigenetic and transcriptional abnormalities induced by the treatment.

Persistent organic pollutants affect steroidogenic and apoptotic activities in granulosa cells and reactive oxygen species concentrations in oocytes in the mouse

CONTEXT

The destruction of granulosa cells (GCs), the main functional cell type in the ovary, prevents steroid hormone production, which in turn may damage oocytes, resulting in ovarian failure. The accumulation of a number of persistent organic pollutants (POPs) in the ovarian follicular fluid (FF) has been documented, which raises serious questions regarding their impact on female fertility.

AIMS

We aimed to determine whether a mixture of POPs reflecting the profile found in FF influences mouse GCs or oocyte function and viability.

METHODS

A mixture of POPs, comprising perfluorooctanoate, perfluorooctane sulfonate, 2,2-dichlorodiphenyldichloroethylene, polychlorinated biphenyl 153, and hexachlorobenzene, was used. In addition to using the exact concentration of POPs previously measured in human FF, we tested two other mixtures, one with10-fold lower and another with 10-fold higher concentrations of each POP.

KEY RESULTS

Steroidogenesis was disrupted in GCs by the POP mixture, as demonstrated by lower oestradiol and progesterone secretion and greater lipid droplet accumulation. Furthermore, the POP mixture reduced GC viability and increased apoptosis, assessed using caspase-3 activity. The POP mixture significantly increased the number of oocytes that successfully progressed to the second meiotic metaphase and the oocyte reactive oxygen species (ROS) concentration.

CONCLUSIONS

Thus, a mixture of POPs that are typically present in human FF has detrimental effects on ovarian function: it reduces the viability of GCs, and increases the oocyte concentrations of ROS.

IMPLICATIONS

These results indicate that chronic exposure to POPs adversely affects female reproductive health.

Multidrug resistance transporter-1 dysfunction perturbs meiosis and Ca2+ homeostasis in oocytes

In brief

Oocyte quality remains the most important and unsolved issue in reproduction. Our data show that multidrug resistance transporters and oocyte mitochondria are involved in determining oocyte quality in a mouse model.

Abstract

Multidrug resistance transporter-1 (MDR-1) is a transmembrane ATP-dependent effluxer present in organs that transport a variety of xenobiotics and by-products. Previous findings by our group demonstrated that this transporter is also present in the oocyte mitochondrial membrane and that its mutation led to abnormal mitochondrial homeostasis. Considering the importance of these organelles in the female gamete, we assessed the impact of MDR-1 dysfunction on mouse oocyte quality, with a particular focus on the meiotic spindle organization, aneuploidies, Ca2+ homeostasis, ATP production and mtDNA mutations. Our results demonstrate that young Mdr1a mutant mice produce oocytes characterized by lower quality, with a significant delay in the germinal vesicle to germinal vesicle breakdown transition, an increased percentage of symmetric divisions, chromosome misalignments and a severely altered meiotic spindle shape compared to the wild types. Mutant oocytes exhibit 7000 more SNPs in the exomic DNA and twice the amount of mitochondrial DNA (mtDNA) SNPs compared to the wild-type ones. Ca2+ analysis revealed the inability of MDR-1 mutant oocytes to manage Ca2+ storage content and oscillations in response to several stimuli, and ATP quantification shows that mutant oocytes trend toward lower ATP levels compared to wild types. Finally, 1-year-old mutant ovaries express a lower amount of SIRT1, SIRT3, SIRT5, SIRT6 and SIRT7 compared to wild-type levels. These results together emphasize the importance of MDR-1 in mitochondrial physiology and highlight the influence of MDR-1 on oocyte quality and ovarian aging.

Mitochondrial function of human embryo: Decline in their quality with maternal aging

Background

Female fertility declines with age, due to increased chromosomal aneuploidy and possible reduced mitochondrial function in the embryo.

Methods

This review outlines how mitochondrial function in human embryos, as predicted from oxygen consumption rate (OCR) measurements, changes in preimplantation stage, and what factors, particularly maternal age, affect mitochondrial function in embryos.

Main findings

The structure of the mitochondrial inner membrane and its respiratory function developed with embryo development, while the copy number of mitochondrial DNA per specimen was transiently reduced compared with that of the oocyte. The undifferentiated state of the inner cell mass cells appears to be associated with a low OCR. In contrast, the copy number of mitochondrial DNA increased in trophoblast cells and mitochondrial aerobic metabolism increased.The OCRs at morulae stage decreased with maternal age, but there was no relationship between maternal age and the copy number of mitochondrial DNA at any stages. The higher oxygen spent at the morula stage; the shorter time was needed for development to the mid-stage blastocyst.

Conclusions

The mitochondrial respiratory function of human embryos developed along with embryonic growth. Mitochondrial function at morula stage declined with their maternal age and reduced mitochondrial function decreased the rate of development from morula to blastocyst.

Metabolic enhancement of the one carbon metabolism (OCM) in bovine oocytes IVM increases the blastocyst rate: evidences for a OCM checkpoint

The one carbon metabolism (OCM) has a primary role in the process of oocyte maturation. In this study bovine oocytes were cultured for 24 h, up to MII stage, with standard medium supplemented or not with 8 metabolic enhancers of the OCM and the MII and blastocyst rate were compared. Additional analyses were performed on matured oocytes, cumulus cells, zygotes and blastocysts. The OCM supplementation increased the blastocyst rate derived from in vitro fertilization. The mitochondrial mass and DNMT3a protein expression were increased whereas DNA fragmentation decreased in matured oocytes. DNA methylation in female pronucleus of zygotes was increased. The supplementation did not directly affect the redox balance as ROS and GSH in matured oocytes and homocysteine in the spent medium were unchanged. The supplementation of the oocytes with metabolic enhancers of the OCM may increase the yield from the culture, likely due to improved DNA methylation and epigenetic programming. The lack of effects on MII rate with huge differences appearing at the blastocyst stage suggest the existence of a OCM metabolic check point that hampers oocytes progression to blastocyst post-fertilization, if they were not properly primed at the time of maturation.

β-Mercaptoethanol in culture medium improves cryotolerance of in vitro-produced bovine embryos

The objective of this study was to investigate the effects of adding β-mercaptoethanol (βME) to culture medium of bovine in vitro-produced (IVP) embryos prior to or after vitrification on embryo development and cryotolerance. In Experiment I, Day-7 IVP blastocysts were vitrified and, after warming, cultured in medium containing 0, 50 or 100 μM βME for 72 h. Embryos cultured in 100 μM βME attained higher hatching rates (66.7%) than those culture in 0 (47.7%) and 50 (52.4%) μM βME. In Experiment II, IVP embryos were in vitro-cultured (IVC) to the blastocyst stage in 0 (control) or 100 μM βME, followed by vitrification. After warming, embryos were cultured for 72 h (post-warming culture, PWC) in 0 (control) or 100 μM βME, in a 2 × 2 factorial design: (i) CTRL-CTRL, control IVC and control PWC; (ii) CTRL-βME, control IVC and βME-supplemented PWC; (iii) βME-CTRL, βME-supplemented IVC and control PWC; or (iv) βME-βME, βME-supplemented IVC and βME-supplemented PWC. βME during IVC reduced embryo development (28.0% vs. 43.8%) but, following vitrification, higher re-expansion rates were seen in βME-CTRL (84.0%) and βME-βME (87.5%) than in CTRL-CTRL (71.0%) and CTRL-βME (73.1%). Hatching rates were higher in CTRL-βME (58.1%) and βME-βME (63.8%) than in CTRL-CTRL (36.6%) and βME-CTRL (42.0%). Total cell number in hatched blastocysts was higher in βME-βME (181.2 ± 7.4 cells) than CTRL-CTRL (139.0 ± 9.9 cells). Adding βME to the IVC medium reduced development but increased cryotolerance, whereas adding βME to the PWC medium improved embryo survival, hatching rates, and total cell numbers.

The Clinical Application of Growth Hormone and Its Biological and Molecular Mechanisms in Assisted Reproduction

Growth hormone (GH) has been used as a co-gonadotrophin in assisted reproduction, particularly in poor ovarian responders. The application of GH has been alleged to activate primordial follicles and improve oocyte quality, embryo quality, and steroidogenesis. However, the effects of GH on the live birth rate among women is controversial. Additionally, although the basic biological mechanisms that lead to the above clinical differences have been investigated, they are not yet well understood. The actions of GH are mediated by GH receptors (GHRs) or insulin-like growth factors (IGFs). GH regulates the vital signal transduction pathways that are involved in primordial follicular activation, steroidogenesis, and oocyte maturation. However, the therapeutic windows and duration of GH administration during assisted reproductive technology require further investigation. The review aimed to clarify the role of GH in human fertility from a molecular and biological point of view to provide evidence for proper GH administration.

Effect of Moringa oleifera seed extract on antimicrobial activity and in vitro fertilization ability of cryopreserved ram semen

Cryopreservation has adverse effects on the post-thaw sperm quality due to oxidative stress and the presence of bacteria. To minimize such effects, plant extracts have been included in the composition of the semen diluents. The objective of the present study was to evaluate the antimicrobial and antioxidant effects of Moringa oleifera seed extract (MOSE) on cryopreserved ram semen, as well as its impact on in vitro fertilization. Semen from six hair rams was treated with five treatments before cryopreservation: Control (without any antibiotic), Standard (conventional antibiotic), 1.0, 10.0, and 50.0 mg/mL of MOSE. Post-thawing sperm characteristics were evaluated by the computer-assisted semen analysis. Antimicrobial activity was assessed by counting colony-forming units (CFU) and the antioxidant capacity by the ferric reducing antioxidant power method. A heterologous in vitro fertilization technique was implemented to measure the fertilization rate. Progressive and rapid motility, membrane and acrosome integrity, and active mitochondria were higher (p < 0.05) in the 10.0 mg/mL treatment compared to Standard after thawing. All M. oleifera treatments showed inhibition of CFU. The antioxidant capacity of M. oleifera seed extract was higher in the 10.0 and 50.0 mg/mL treatments. Fertilization rate (cleavage percentage) was higher (p < 0.05) in the 10.0 mg/mL (82.9±10.0) and Control (82.5±9.9) treatments compared to Standard (73.7±9.1). The addition of 10.0 mg/mL of MOSE to ram semen inhibits the development of microorganisms and improves sperm characteristics and the in vitro fertility of the semen.

Dynamics of the Reproductive Changes and Acquisition of Oocyte Competence in Nelore (Bos taurus indicus) Calves during the Early and Intermediate Prepubertal Periods

The purpose of this study was to characterize the reproductive physiology, oocyte competence, and chromatin compaction in Nelore calves in the early-prepubertal period (EPP) and the intermediate-prepubertal period (IPP). Calves aged 2-5 (EPP) and 8-11 months old (IPP) were assigned to Trial 1 (morpho-physiological-endocrine evaluations, n = 8) or Trial 2 (oocyte donors, n = 8) vs. the respective control groups of cows (n = 8, each). All morphological endpoints, except the antral follicle count, increased from the EPP to the IPP. The EPP LH-FSH plasma concentrations were similar to cows, whereas LH was lower and FSH was higher in the IPP than in cows. . Cows produced more Grade I (12.9% vs. 4.1% and 1.7%) and fewer Grade III COC (30.1% vs. 44.5% and 49.0%) than the EPP and IPP calves, respectively. The IPP calves' oocyte diameter was similar to those from cows but greater than those from EPP females (124.8 ± 8.5 and 126.0 ± 7.5 μm vs. 121.3 ± 7.5 μm, respectively). The expression of the chromatin compaction-related gene HDAC3 was downregulated in calves. The proportion of the blastocyst rate to the controls was lower in EPP than in IPP calves (43.7% vs. 78.7%, respectively). Progressive oocyte competence was found during the prepubertal period, which can help to decide whether to recover oocytes from calves.

Cytoplasmic streaming induced by intracytoplasmic spindle translocation contributes to developmental competence through mitochondrial distribution in mouse oocytes

OBJECTIVE

To evaluate the developmental competency of mouse metaphase II oocytes and the pattern of mitochondrial positioning through cytoplasmic streaming in mouse metaphase II oocytes.

DESIGN

We observed cytoplasmic streaming as movement indicated by fluorescently stained mitochondria using a newly developed method in which the spindle is translocated to the opposite site of the oocyte. This method is termed as intracytoplasmic spindle translocation (ICST).

SETTING

University research laboratory.

ANIMALS

Female B6D2F1 mice.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Fresh oocytes, postovulatory-aged oocytes, and oocytes treated with cytochalasin B were classified based on the presence of cytoplasmic streaming induced by ICST. The pattern of redistributed mitochondria and developmental competence caused by parthenogenetic activation were evaluated in oocytes with or without cytoplasmic streaming.

RESULT(S)

Induced cytoplasmic streaming occurred in 84% of the fresh oocytes but not in the postovulatory-aged oocytes and the oocytes treated with cytochalasin B. Abnormal mitochondrial aggregation was observed in oocytes in which cytoplasmic streaming was not induced. Furthermore, the developmental competence was significantly lower in oocytes without cytoplasmic streaming.

CONCLUSION(S)

Cytoplasmic streaming induced by ICST contributes to developmental competence through the redistribution of mitochondria and may be a valuable criterion for predicting early developmental competence in mouse oocytes.

Optical imaging detects metabolic signatures associated with oocyte quality

Oocyte developmental potential is intimately linked to metabolism. Existing approaches to measure metabolism in the cumulus oocyte complex (COC) do not provide information on the separate cumulus and oocyte compartments. Development of an assay that achieves this may lead to an accurate diagnostic for oocyte quality. Optical imaging of the autofluorescent cofactors NAD(P)H and FAD provides a spatially resolved indicator of metabolism via the optical redox ratio ($\mathrm{FAD}/\left[\mathrm{NAD}\left(\mathrm{P}\right)\mathrm{H}+\mathrm{FAD}\right]$). This may provide an assessment of oocyte quality. Here, we determined whether the optical redox ratio is a robust methodology for measuring metabolism in the cumulus and oocyte compartments compared with oxygen consumption in the whole COC. We also determined whether optical imaging could detect metabolic differences associated with poor oocyte quality (etomoxir-treated). We used confocal microscopy to measure NAD(P)H and FAD, and extracellular flux to measure oxygen consumption. We found that the optical redox ratio was an accurate reflection of metabolism in the oocyte compartment when compared with oxygen consumption (whole COC). Etomoxir-treated COCs showed significantly lower levels of NAD(P)H and FAD compared to control. While confocal imaging demonstrated the premise, we validated this approach using hyperspectral imaging, which is clinically compatible due to its low energy dose. This confirmed lower NAD(P)H and FAD in etomoxir-treated COCs. When comparing imaged vs non-imaged COCs, subsequent preimplantation development and post-transfer viability were comparable. Collectively, these results demonstrate that label-free optical imaging of metabolic cofactors is a safe and sensitive assay for measuring metabolism and has potential to assess oocyte developmental competence.

Preovulatory serum estradiol concentration is positively associated with oocyte ATP and follicular fluid metabolite abundance in lactating beef cattle

Cattle induced to ovulate a small, physiologically immature preovulatory follicle had reduced oocyte developmental competence that resulted in decreased embryo cleavage and day 7 embryo quality compared with animals induced to ovulate a more advanced follicle. RNA-sequencing was performed on oocytes and their corresponding cumulus cells approximately 23 h after gonadotropin-releasing hormone (GnRH) administration to induce the preovulatory gonadotropin surge suggested reduced capacity for glucose metabolism and oxidative phosphorylation in the cumulus cells and oocytes from follicles ≤11.7 mm, respectively. We hypothesized that induced ovulation of a small, physiologically immature preovulatory follicle results in a suboptimal follicular microenvironment and reduced oocyte metabolic capacity. We performed a study with the objective to determine the impact of preovulatory follicle diameter and serum estradiol concentration at GnRH administration on oocyte metabolic competence and follicular fluid metabolome profiles. We synchronized the development of a preovulatory follicle and collected the follicle contents via transvaginal aspiration approximately 19 h after GnRH administration in lactating beef cows (n = 319). We determined ATP levels and mitochondrial DNA (mtDNA) copy number in 110 oocytes and performed ultra-high-performance liquid chromatography–high resolution mass spectrometry metabolomic studies on 45 follicular fluid samples. Intraoocyte ATP and the amount of ATP produced per mtDNA copy number were associated with serum estradiol concentration at GnRH and time from GnRH administration to follicle aspiration (P < 0.05). mtDNA copy number was not related to follicle diameter at GnRH, serum estradiol concentration at GnRH, or any potential covariates (P > 0.10). We detected 90 metabolites in the aspirated follicular fluid. We identified 22 metabolites associated with serum estradiol concentration at GnRH and 63 metabolites associated with follicular fluid progesterone concentration at the time of follicle aspiration (FDR < 0.10). Pathway enrichment analysis of significant metabolites suggested altered proteinogenesis, citric acid cycle, and pyrimidine metabolism in follicles of reduced estrogenic capacity pre-gonadotropin surge or reduced progesterone production by the time of follicle aspiration.

Altered microfilament dynamics contribute to the formation of diploid metaphase spindles in porcine oocytes which fail to reach the metaphase-II stage during in vitro maturation

Premature meiotic arrest during in vitro maturation (IVM) of porcine oocytes after germinal vesicle breakdown is associated with microfilament degradation. We aimed to clarify (1) if such arrest occurs at the metaphase-I (MI) stage or the oocyte progresses to a so-called diploid metaphase-II (MII) stage and (2) if microfilament degradation is the cause or result of the meiotic arrest. The number and morphology of chromosomes in oocytes showing premature meiotic arrest at 44 h IVM (38 monovalents) was similar to those cultured in the presence of the actin polymerization-inhibitor cytochalasin-B, but different from those of MI-stage (19 bivalents), and MII-stage oocytes (19 monovalents) at 33 and 44 h of IVM, respectively. Immunostaining revealed similar frequencies of microfilament degradation in prematurely arrested and cytochalasin-B-treated oocytes (58.7% and 57.2%, respectively), which were higher (P < 0.05) than those in MI- and MII-stage oocytes (10.6% and 6.8%, respectively). Induction of MI-arrest by nocodazole did not affect microfilament morphology. ATP and mRNA levels of microfilament-related genes in oocytes were similar among all groups. These results suggest that altered microfilament dynamics contribute to the formation of diploid metaphase spindles in oocytes, which fail to reach the MII stage. However, the cause of microfilament degeneration remains unclear.

Mitofusins: from mitochondria to fertility

Germ cell formation and embryonic development require ATP synthesized by mitochondria. The dynamic system of the mitochondria, and in particular, the fusion of mitochondria, are essential for the generation of energy. Mitofusin1 and mitofusin2, the homologues of Fuzzy onions in yeast and Drosophila, are critical regulators of mitochondrial fusion in mammalian cells. Since their discovery mitofusins (Mfns) have been the source of significant interest as key influencers of mitochondrial dynamics, including membrane fusion, mitochondrial distribution, and the interaction with other organelles. Emerging evidence has revealed significant insight into the role of Mfns in germ cell formation and embryonic development, as well as the high incidence of reproductive diseases such as asthenospermia, polycystic ovary syndrome, and gestational diabetes mellitus. Here, we describe the key mechanisms of Mfns in mitochondrial dynamics, focusing particularly on the role of Mfns in the regulation of mammalian fertility, including spermatogenesis, oocyte maturation, and embryonic development. We also highlight the role of Mfns in certain diseases associated with the reproductive system and their potential as therapeutic targets.

Concurrent Measurement of Mitochondrial DNA Copy Number and ATP Concentration in Single Bovine Oocytes

To sustain energy-demanding developmental processes, oocytes must accumulate adequate stores of metabolic substrates and mitochondrial numbers prior to the initiation of maturation. In the past, researchers have utilized pooled samples to study oocyte metabolism, and studies that related multiple metabolic outcomes in single oocytes, such as ATP concentration and mitochondrial DNA copy number, were not possible. Such scenarios decreased sensitivity to intraoocyte metabolic relationships and made it difficult to obtain adequate sample numbers during studies with limited oocyte availability. Therefore, we developed and validated procedures to measure both mitochondrial DNA (mtDNA) copy number and ATP quantity in single oocytes. Validation of our procedures revealed that we could successfully divide oocyte lysates into quarters and measure consistent results from each of the aliquots for both ATP and mtDNA copy number. Coefficient of variation between the values retrieved for mtDNA copy number and ATP quantity quadruplicates were 4.72 ± 0.98 and 1.61 ± 1.19, respectively. We then utilized our methodology to concurrently measure mtDNA copy number and ATP quantity in germinal vesicle (GV) and metaphase two (MII) stage oocytes. Our methods revealed a significant increase in ATP levels (GV = 628.02 ± 199.53 pg, MII = 1326.24 ± 199.86 pg, p < 0.001) and mtDNA copy number (GV = 490,799.4 ± 544,745.9 copies, MII = 1,087,126.9 ± 902,202.8 copies, p = 0.035) in MII compared to GV stage oocytes. This finding is consistent with published literature and provides further validation of the accuracy of our methods. The ability to produce consistent readings and expected results from aliquots of the lysate from a single oocyte reveals the sensitivity and feasibility of using this method.

Uncovering the important role of mitochondrial dynamics in oogenesis: impact on fertility and metabolic disorder transmission

Oocyte health is tightly tied to mitochondria given their role in energy production, metabolite supply, calcium (Ca2+) buffering, and cell death regulation, among others. In turn, mitochondrial function strongly relies on these organelle dynamics once cyclic events of fusion and fission (division) are required for mitochondrial turnover, positioning, content homogenization, metabolic flexibility, interaction with subcellular compartments, etc. Importantly, during oogenesis, mitochondria change their architecture from an "orthodox" elongated shape characterized by the presence of numerous transversely oriented cristae to a round-to-oval morphology containing arched and concentrically arranged cristae. This, along with evidence showing that mitochondrial function is kept quiescent during most part of oocyte development, suggests an important role of mitochondrial dynamics in oogenesis. To investigate this, recent works have downregulated/upregulated in oocytes the expression of key effectors of mitochondrial dynamics, including mitofusins 1 (MFN1) and 2 (MFN2) and the dynamin-related protein 1 (DRP1). As a result, both MFN1 and DRP1 were found to be essential to oogenesis and fertility, while MFN2 deletion led to offspring with increased weight gain and glucose intolerance. Curiously, neither MFN1/MFN2 deficiency nor DRP1 overexpression enhanced mitochondrial fragmentation, indicating that mitochondrial size is strictly regulated in oocytes. Therefore, the present work seeks to discuss the role of mitochondria in supporting oogenesis as well as recent findings connecting defective mitochondrial dynamics in oocytes with infertility and transmission of metabolic disorders.

Paraquat exposure impairs porcine oocyte meiotic maturation

Paraquat (PQ) is a heterocyclic pesticide that not only damages the testicular development and reduces the quality of semen, but also disturbs the secretion of hormones in the reproductive system. However, the effects of PQ on oocyte maturation and its toxic mechanism have not been yet fully clarified. Here we showed that PQ exposure could have toxic effects on porcine oocyte maturation. PQ exposure with 100 μM inhibited cumulus cell expansion and significantly reduced the rate of first polar body extrusion during oocyte maturation. PQ-exposed oocytes could not develop to the 2-cell and blastocyst stage. PQ exposure with 100 μM significantly increased abnormal spindle rate (65.2% ± 1.0%) and misaligned chromosome rate (63.2% ± 3.4%) compared to the control group (38.3% ± 1.0% and 38.4% ± 1.0%, respectively; P < 0.05). F-actin also exhibited reduced distribution in PQ-exposed oocytes (10.3% ± 1.0%) compared to the control group (14.4% ± 1.0%, P < 0.05). In addition, PQ exposure reduced the active mitochondria levels, but apparently increased the reactive oxygen species (ROS), rH2AX, and LC3 (autophagy marker) levels. qPCR analyses showed that PQ exposure caused the aberrant expression of genes associated with cumulus cell expansion, but did not affect the expression of apoptosis-related genes. Taken together, these results indicate that PQ exposure impaired oocyte nuclear and cytoplasmic maturation probably through oxidative stress.

Effect of docosahexaenoic acid on in vitro growth of bovine oocytes

PURPOSE

The present study investigated the effects of docosahexaenoic acid (DHA) on the growth of bovine oocytes.

METHODS

Oocytes and granulosa cell complexes (OGCs) were collected from early antral follicles (0.4-0.7 mm) on the surface of ovaries harvested from a slaughterhouse. The OGCs were cultured with 0, 1, and 10 μmol/L docosahexanoic acid (DHA) for 16 days.

RESULTS

Antrum formation of the OGCs and the number of granulosa cells (GCs) surrounding the oocytes were comparable among groups, whereas supplementation of 0.1 μmol/L of DHA significantly improved oocyte growth. Oocytes grown with DHA had a higher fertilization rate, acetylation levels of H4K12, and ATP contents, as well as a lower lipid content compared with those grown without DHA. In addition, GCs surrounding OGCs grown with DHA had low lipid content compared with vehicle counterparts. Furthermore, when GCs were cultured in vitro, DHA increased ATP production, mitochondrial membrane potential, and reduced lipid content and levels of reactive oxygen species. RNA-seq of GCs revealed that DHA increased CPT1A expression levels and affect genes associated with focal adhesion, oxidative phosphorylation, and PI3K-AKT etc.

CONCLUSION

The results suggest that DHA supplementation affects granulosa cell characteristics and supports oocyte growth in vitro.

Mitochondrial content, activity, and morphology in prepubertal and adult human ovaries

PURPOSE

To investigate whether mitochondrial content, activity, and morphology differ in prepubertal versus adult ovarian follicles.

METHODS

Ovarian tissue was collected from 7 prepubertal girls (age 1-10 years) and 6 adult women (age 20-35 years). Primordial and primary follicles were isolated from frozen-thawed prepubertal and adult ovarian tissue and their viability was assessed. Mitochondrial content was investigated by TOMM20 immunostaining of prepubertal and adult ovarian tissue, while mitochondrial activity in isolated follicles was analyzed by MitoTracker CM-H2XRos and JC-1. Frozen-thawed ovarian tissue from the same patients was also evaluated by transmission electron microscopy to examine mitochondrial morphology.

RESULTS

Higher TOMM20 staining was detected in prepubertal follicles compared to their adult counterparts, indicating the presence of more mitochondria in prepubertal follicles. Analysis of mitochondrial activity by MitoTracker showed higher fluorescence intensity in prepubertal follicles, suggesting that follicles in this group are more active than adult follicles. JC-1 analysis did not reveal any statistically significant difference in the inactive/active ratio between the two groups. Moreover, ultrastructural analysis by TEM detected morphological differences in the shape and cristae of prepubertal mitochondria, probably suggesting a mechanism of response to autophagy.

CONCLUSION

Differences in the number, activity, and morphology of mitochondria were reported, suggesting that consequential modifications might occur during puberty, which could be the window of opportunity required by mitochondria to undergo changes needed to reach maturity, and hence the capacity for ovulation and fertilization.

In vitro maturation using an agarose matrix with incorporated extracellular matrix proteins improves porcine oocyte developmental competence by enhancing cytoplasmic maturation

Here, we present a novel in vitro maturation (IVM) system comprising an agarose matrix supplemented with extracellular matrix (ECM) proteins for enhanced maturation of immature oocytes within cumulus-oocyte complexes (COCs) derived from porcine medium antral follicles (MAFs). Immunocytochemical analyses of integrin subunit α₂ , α₅ , α₆ , β₁ , and β₄ expression suggested that integrin α₂ β₁ , α₅ β₁ , α₆ β₁ , and α₆ β₄ play pivotal roles in IVM of porcine immature oocytes. Combinatorial supplementation of fibronectin interacting with integrin α₅ β₁ , collagen interacting with integrin α₂ β₁ , and laminin interacting with integrin α₆ β₁ and α₆ β₄ to the agarose matrix had no significant effect on nuclear maturation. However, the number of parthenogenetic embryos that developed into blastocysts increased when oocytes were matured using agarose IVM matrices supplemented with fibronectin, collagen, or laminin. Furthermore, significant increases in cytoplasmic maturation-related parameters (BMP15 level, cumulus cell expansion score, intra-oocyte ATP level, and index of cortical granule distribution) were observed in COCs matured in vitro using ECM protein-incorporated agarose matrices. Our data suggest that mature porcine oocytes with enhanced developmental competence and high-quality cytoplasm can be generated via IVM using agarose matrices supplemented with fibronectin, collagen, or laminin.

A Nuclear and Cytoplasmic Characterization of Bovine Oocytes Reveals That Cysteamine Partially Rescues the Embryo Development in a Model of Low Ovarian Reserve

Simple Summary

Women’s reproductive performance starts declining in the mid-30s, and by age 40–45, the possibility of becoming pregnant becomes very small. Reproductive aging is a physiological process of fertility decline characterized by a decrease in quality and stockpile of eggs (also called ovarian reserve) in most mammals. However, young individuals too can show an accelerated reproductive aging that similarly results in a low ovarian reserve and hypofertility. This syndrome, called premature ovarian failure (POF), is becoming a relevant problem due to the general tendency to postpone the first pregnancy. In this study, we used bovine ovaries that were classified in two categories, according to the number of follicles visible on the ovarian surface, and analyzed some parameters of egg maturation. We observed that eggs from the ‘aging-like’ ovaries carry several defects that impair maturation. However, one of the parameters was improved upon supplementation with a scavenger of free radicals, providing a proof of concept that in-depth knowledge of the cellular mechanisms is essential to find solutions to everyday-life problems.

Abstract

Decreased oocyte quality is a major determinant of age-associated fertility decline. Similarly, individuals affected by early ovarian aging carry low-quality oocytes. Using an established bovine model of early ovarian aging, we investigated key features of ‘quality’ oocyte maturation, associated with the onset of egg aneuploidy and reproductive aging, such as histone modifications, mitochondria distribution and activity, reduced glutathione (GSH) content, and gap junction functionality. Bovine ovaries were classified according to the antral follicle count (AFC), and the retrieved oocytes were processed immediately or matured in vitro. We observed alterations in several cellular processes, suggesting a multifactorial etiology of the reduced oocyte quality. Furthermore, we performed a rescue experiment for one of the parameters considered. By adding cysteamine to the maturation medium, we experimentally increased the free radical scavenger ability of the ‘low competence’ oocytes and obtained a higher embryo development. Our findings show that adopting culture conditions that counteract the free radicals has a positive impact on the quality of ‘compromised’ oocytes. Specifically, cysteamine treatment seems to be a promising option for treating aging-related deficiencies in embryo development.

Differential Transcript Profiles in Cumulus-Oocyte Complexes Originating from Pre-Ovulatory Follicles of Varied Physiological Maturity in Beef Cows

Small dominant follicle diameter at induced ovulation, but not at spontaneous ovulation, decreased pregnancy rate, fertilization rate, and day seven embryo quality in beef cows. We hypothesized that the physiological status of the follicle at GnRH-induced ovulation has a direct effect on the transcriptome of the Cumulus-Oocyte complex, thereby affecting oocyte competence and subsequent embryo development. The objective of this study was to determine if the transcriptome of oocytes and associated cumulus cells (CC) differed among small (≤11.7 mm) and large follicles (≥12.7 mm) exposed to a GnRH-induced gonadotropin surge and follicles (11.7–14.0 mm) exposed to an endogenous gonadotropin surge (spontaneous follicles). RNA sequencing data, from pools of four oocytes or their corresponding CC, revealed 69, 94, and 83 differentially expressed gene transcripts (DEG) among oocyte pools from small versus large, small versus spontaneous, and large versus spontaneous follicle classifications, respectively. An additional 128, 98, and 80 DEG were identified among small versus large, small versus spontaneous, and large versus spontaneous follicle CC pools, respectively. The biological pathway “oxidative phosphorylation” was significantly enriched with DEG from small versus spontaneous follicle oocyte pools (FDR < 0.01); whereas the glycolytic pathway was significantly enriched with DEG from CC pools obtained from large versus small follicles (FDR < 0.01). These findings collectively suggest that altered carbohydrate metabolism within the Cumulus-Oocyte complex likely contributes to the decreased competency of oocytes from small pre-ovulatory follicles exposed to an exogenous GnRH-induced gonadotropin surge.

Effect of different cryopreservation extenders added with antioxidants on semen quality and in vitro embryo production efficiency in cattle

To evaluate the addition of antioxidants in extenders on post-thaw bovine semen quality and in vitro embryo production efficiency. Six semen samples were collected from five Holstein bulls. In the experiment I, the samples were diluted with AndroMed® and Bovimix® and added antioxidants glutathione (1.5 and 2.5 mM) and melatonin (0.5 and 1.0 mM). In the experiment II, the best treatments obtained in experiment I were used for in vitro fecundation. Glutathione did not improve sperm viability. Melatonin had a negative effect on semen characteristics. Andromed® showed better results in sperm kinetics parameters. Bovimix® was more efficient in maintaining cell integrity parameters. Significant correlation was found between sperm kinetics parameters and between cell integrity parameters. For in vitro embryo production, after oocyte selection, maturation, fertilization and cultivation were performed using the four treatments previously evaluated. Andromed® was more efficient in the cleavage rate, no effect of the addition of glutathione. However, the addition of 2.5 mM glutathione in the Bovimix® improved the cleavage rate. There was a significant moderate correlation between cleavage rate and sperm kinetic characteristics. Glutathione did not improve sperm viability. Melatonin reduced the maintenance of sperm characteristics. Andromed® was more efficient in in vitro embryo production and no effect of glutathione was found in this extender. Addition of 2.5 mM glutathione in the Bovimix® extender provided a higher cleavage rate.

Transcriptome profiles of pre-pubertal and adult in vitro matured ovine oocytes obtained from FSH-stimulated animals

Pre-pubertal females produce more oocytes than adult individuals, but the ability of oocytes to undergo embryonic development and produce viable offspring is less in pre-pubertal animals than in adult animals. Oocyte quality is associated with abnormal gene expression. To date, the transcriptome profiles of 1-month-old lamb oocytes after in vitro maturation (IVM) are poorly reported. This study aimed to identify differentially expressed genes (DEGs) in lamb oocytes with varying competencies, affecting oocyte competence. Using RNA sequencing (RNA developmental -seq) technology, the transcriptome profiles of 1-month-old lamb oocytes after IVM were assessed, and oocytes from adult sheep large follicles were used as controls. We found 11 up-regulated and 39 down-regulated DEGs in lamb oocytes. Gene Ontology analysis of DEGs showed that molecular functions were clustered in catalytic and binding activities, while biological processes were clustered in metabolic process, cellular process, single-organism process and biological regulation. Kyoto Encyclopedia of Genes and Genomes analysis showed that the DEGs were involved in oxidative phosphorylation, transforming growth factor-beta signalling pathway, or DNA replication. In lamb MII oocytes, down-regulation of oxidative phosphorylation genes (ATP5E, NDUFA7 and COX6C), thiol protease inhibitor (CSTB) and 26S proteasome component (SHFM1) and up-regulation of CUL1, MARCH7 and TRIM17 might cause low competence of lamb embryos. In conclusion, this study provided detailed information on mRNA transcriptomes in lamb oocytes after IVM, which offers insights into the reduced developmental potential of lamb oocytes.

Effect of maternal aging and vitrification on mitochondrial DNA copy number in embryos and spent culture medium

Maternal aging and vitrification affect mitochondrial quality and quantity in embryos. The present study investigated the effects of maternal aging on mitochondrial DNA (mtDNA) copy number in embryos, and the amount of cell-free mtDNA (cf-mtDNA) in spent culture medium (SCM) of embryos. Moreover, we examined the effects of vitrification on mtDNA copy number in embryos of young and aged cows, and on cf-mtDNA abundance in SCM. Oocytes collected from ovaries of young (20-40 months old) and aged cows (> 140 months old) were used to produce early stage embryos (8-12 cell-stage, 48 h after insemination). These embryos were individually cultured for 5 days, and mtDNA copy number in blastocysts and cf-mtDNA content in SCM, were evaluated by real-time PCR. At 48 h post-insemination, mtDNA copy number in embryos was greater for young cows compared with that of aged cows, whereas no significant difference was observed in cf-mtDNA in the SCM. Next, we addressed whether zona pellucida (ZP) may mask the difference in cf-mtDNA content in SCM. Using ZP-free embryos, we found significantly greater cf-mtDNA content in the SCM of blastocysts derived from aged cows. Furthermore, when embryos were vitrified and warmed, mtDNA copy number in blastocysts derived from young cows was lower, whereas cf-mtDNA content in SCM was greater than in those derived from aged cows. In conclusion, maternal aging affects mitochondrial kinetics and copy number in embryos following vitrification.