Developmental regulation and modulation of apoptotic genes expression in sheep oocytes and embryos cultured in vitro with L-carnitine

Carnitines as Mitochondrial Modulators of Oocyte and Embryo Bioenergetics

Recently, the importance of bioenergetics in the reproductive process has emerged. For its energetic demand, the oocyte relies on numerous mitochondria, whose activity increases during embryo development under a fine regulation to limit ROS production. Healthy oocyte mitochondria require a balance of pyruvate and fatty acid oxidation. Transport of activated fatty acids into mitochondria requires carnitine. In this regard, the interest in the role of carnitines as mitochondrial modulators in oocyte and embryos is increasing. Carnitine pool includes the un-esterified l-carnitine (LC) and carnitine esters, such as acetyl-l-carnitine (ALC) and propionyl-l-carnitine (PLC). In this review, carnitine medium supplementation for counteracting energetic and redox unbalance during in vitro culture and cryopreservation is reported. Although most studies have focused on LC, there is new evidence that the addition of ALC and/or PLC may boost LC effects. Pathways activated by carnitines include antiapoptotic, antiglycative, antioxidant, and antiinflammatory signaling. Nevertheless, the potential of carnitine to improve energetic metabolism and oocyte and embryo competence remains poorly investigated. The importance of carnitine as a mitochondrial modulator may suggest that this molecule may exert a beneficial role in ovarian disfunctions associated with metabolic and mitochondrial alterations, including PCOS and reproductive aging.

In vitro production of desired sex ovine embryos modulating polarity of oocytes for sex-specific sperm binding during fertilization

The present study aimed to modulate the oxidative status-mediated polarity of the oocytes for sex-specific sperm fertilization to generate desired sex embryos. In vitro embryos were produced at different oxidative status, varying O₂ concentrations, and without/with l-carnitine in maturation and culture media. The majority of the embryos produced at high oxidative stress were males whereas; low oxidative status favoured female embryos production. Low O₂ doubled the proportion of female embryos (10.59 vs 21.95%); however, l-carnitine supplementation in media increased approximately seven-folds of the female embryos (12.26 vs. 77.62%) production. Oocytes matured at high oxidative status were in the repolarized state favouring positively charged Y sperm fertilization to produce significantly more male embryos. Low oxidative status favoured negatively charged X sperm fertilization to the oocytes in the depolarized state to produce more female embryos. Intracellular ROS was significantly low in female embryos than in males; however, female embryos were more stressful than males. The study concluded that the oxidative status-mediated alteration in pH of the medium to modulate the intracellular positive ions is the main critical factor to influence the sex of embryos through sex-specific sperms fertilization to the oocytes as per their polarity.

The role of L-carnitine in bovine embryo metabolism. A review of the effect of supplementation with a metabolic modulator on in vitro embryo production

Early embryo development is driven first by the maternal RNAs and proteins accumulated during the oocyte's cytoplasmic maturation and then after the embryo genome activation. In mammalian cells, ATP generation occurs via oxidative pathways or by glycolysis, whereas in embryonic stem cells, the consumption of glucose, pyruvate, lipids, and amino acids results in ATP synthesis. Although the bovine embryo has energy reserves in glycogen and lipids, the glycogen concentration is deficient. Conversely, lipids represent the most abundant energy reservoir of bovine embryos, where lipid droplets-containing triacylglycerols are the main fatty acid stores. Oocytes of many mammalian species contain comparatively high amounts of lipids stored as droplets in the ooplasm. L-carnitine has been described as a cofactor that facilitates the mobilization of fatty acids present in the oocyte's cytoplasm into the mitochondria to facilitate β-oxidation processes. However, the L-carnitine effects by addition to media in the in vitro produced embryos on the quality are highly disputed and contradictory by different researchers. This review's objective was to explore the effect that the addition of L-carnitine on culture media could have on the overall bovine embryo production in vitro, from the oocyte metabolism to the modulation of gene expression in the developing embryos.

Beneficial Effects of L-Carnitine Supplementation during IVM of Canine Oocytes on Their Nuclear Maturation and Development In Vitro

Simple Summary

In vitro production of canine embryos is a technique that can be used as a model to conserve endangered species and to establish efficient breeding systems for domestic dogs. However, compared with other species, the success rates of in vitro embryo production (IVEP) in dogs are low. L-Carnitine (LC) is a small water-soluble molecule; it plays an essential role in fatty acid metabolism and acts as a potent antioxidant. Various studies have reported the beneficial impacts of LC on IVEP in many mammalian species other than dogs. Therefore, these experiments investigated the effects of LC supplementation during in vitro maturation (IVM) on canine oocytes maturation, fertilization, and development in vitro. We show that the supplementation of IVM media with LC has positive impacts on oocyte maturation, fertilization, and preimplantation embryo development rates. We also demonstrate that 0.6 mg/mL LC is the most beneficial concentration to be used. It resulted in significantly higher maturation, fertilization, and embryo developmental rates than the control and other LC concentrations. These outcomes are essential for refining the IVM conditions that can advance the efficiency of assisted reproductive technologies (ARTs) in dogs.

Abstract

This study aimed to investigate the effect of L-Carnitine (LC) supplementation during in vitro maturation (IVM) of canine oocytes on nuclear maturation, fertilization status, and preimplantation development. Cumulus–oocyte complexes (COCs) collected from the ovaries of ovariohysterectomized female dogs were matured in vitro for 72 h in a TCM-199 medium supplemented with (0.1, 0.3, 0.6, 1.0, or 2.0 mg/mL) or without (0.0 mg/mL) LC. Matured oocytes were fertilized in vitro with frozen–thawed spermatozoa, and zygotes were cultured in a SOF medium for 7 days. IVM rates were higher (p ≤ 0.05) in 0.3 and 0.6 mg/mL LC supplemented groups than in the control (0.0 mg/mL LC) and other LC groups. Fertilization (18 h postinsemination (pi)) and cleavage (2–16-cell stage at day 3 pi) rates were higher (p ≤ 0.05) in the 0.6 mg/mL LC group than in the control and 0.1, 1.0, and 2 mg/mL LC supplemented groups. Interestingly, 4.5% of fertilized oocytes developed to morula (day 5 pi) in the 0.6 mg/mL LC group, which was higher (p ≤ 0.05) than those developed in the 0.3 mg/mL group (1.0%). No cleaved embryos developed to morula in other groups. In conclusion, LC supplementation at 0.6 mg/mL during IVM of canine oocytes improved their maturation, fertilization, and preimplantation embryo development rates following IVF and in vitro culture (IVC).

In vitro production of small ruminant embryos: latest improvements and further research

This review presents the latest advances in and main obstacles to the application of invitro embryo production (IVEP) systems in small ruminants. This biotechnology is an extremely important tool for genetic improvement for livestock and is essential for the establishment of other biotechnologies, such as cloning and transgenesis. At present, the IVEP market is almost non-existent for small ruminants, in contrast with the trends observed in cattle. This is probably related to the lower added value of small ruminants, lower commercial demand and fewer qualified professionals interested in this area. Moreover, there are fewer research groups working on small ruminant IVEP than those working with cattle and pigs. The heterogeneity of oocytes collected from growing follicles in live females or from ovaries collected from abattoirs remains a challenge for IVEP dissemination in goats and sheep. Of note, although the logistics of oocyte collection from live small ruminant females are more complex than in the bovine, in general the IVEP outcomes, in terms of blastocyst production, are similar. We anticipate that after appropriate training and repeatable results, the commercial demand for small ruminant invitro -produced embryos may increase.

Actinomycin D causes oocyte maturation failure by inhibiting chromosome separation and spindle assembly†

Actinomycin D (ActD) has been considered as one of the most effective and safe chemotherapeutic medications for treating a number of cancers. Although ActD has been used in the treatment of gynecological tumors and pediatric tumors for more than 50 years, the toxic effects of ActD on mammalian oocytes remain unknown. In this study, the influence of ActD on mouse and human oocyte maturation and the possible mechanisms were investigated. Notably, ActD inhibited oocyte maturation and arrested oocytes at the metaphase I (MI) stage in a dose-dependent manner. In addition, ActD arrested oocyte maturation when the oocytes were treated at different successive stages, including the germinal vesicle (GV), germinal vesicle breakdown, and MI stages. In ActD-treated oocytes, disordered chromosome condensation and irregular spindle assembly occurred, resulting in incomplete chromosome segregation and oocytes arresting at the MI phase; these results possibly occurred because ActD triggered the formation of reactive oxygen species, resulting in DNA damage and decreased ATP in mouse GV oocytes. Besides, in vivo treatment with ActD also inhibited mouse oocyte maturation. Similar effects were seen in human oocytes. Collectively, our results indicated that ActD exposure disrupted oocyte maturation by increasing DNA damage, which is a finding that might help with optimizing future methods for female fertility preservation before undergoing chemotherapy.

l-Carnitine Supplementation during In Vitro Maturation and In Vitro Culture Does not Affect the Survival Rates after Vitrification and Warming but Alters Inf-T and ptgs2 Gene Expression

l-carnitine is a potent antioxidant used for in vitro culture systems. Controversial results have been reported using l-carnitine in culture medium at different stages of in vitro bovine embryo production. Cumulus-oocyte complexes (n = 843) were in vitro-fertilized and cultured and added (treatment group) or not added (control group) with l-carnitine. At day three of culture, each group was subdivided into two subgroups receiving no l-carnitine (group 1), 3.8 mM l-carnitine added during in vitro maturation (group 2), 1.5 mM added during the in vitro culture (group 3), and 3.8 mM and 1.5 mM added during the maturation and culture, respectively (group 4). At day 8, blastocyst embryos were examined for mitochondrial activity, the presence of lipid droplets, total cell number, gene expression, and cryotolerance by vitrification. The data were analyzed with a one-way analysis of variance. l-carnitine added in the late in vitro culture significantly reduced mitochondrial activity and lipid content, and upregulated ifn-τ and ptgs2 gene expression compared to controls (p < 0.05). l-carnitine supplementation did not significantly affect the embryo rate production or survival rate after vitrification and warming (p > 0.05). l-carnitine supplementation significantly improved embryo potential to develop viable pregnancies in agreement with a study reporting improved pregnancy rates.

Sexing of pre-implantation ovine embryos through polymerase chain reaction-based amplification of GAPDH, SRY and AMEL genes

The ability to identify the sex of embryo and control of sex ratio has a great commercial importance to livestock industry. Prediction of embryonic sex could be useful in the management decisions of sex selection in breeding programs. Several methods have been attempted to determine the sex but the polymerase chain reaction (PCR)-based sexing method is generally favoured, as it is cost effective, simple and reliable. The aim of the present study was to identify sex of sheep embryos produced in vitro through amplification of glyceraldehyde 3-phosphate dehydrogenase (GAPDH), sex-determining region Y (SRY) and amelogenin genes present in genomic DNA (gDNA) of embryos through PCR. To avoid false interpretation of the result by no amplification of SRY in female embryos, a duplex PCR was approached to amplify combinedly SRY and GAPDH genes. Sex-specific blood was used in PCR as positive control. In vitro sheep embryos were produced as per standardized protocol of laboratory. Sexing of sex-specific blood and in vitro produced embryos were approached though PCR to amplify the respective genes using gDNA present in the sample without its traditional isolation. The accuracy of sex prediction for embryos was 100% by this procedure.

Interaction of apoptosis and pluripotency related transcripts for developmental potential of ovine embryos produced in vitro at different oxygen concentrations

The present study in sheep model was to find out the interaction of apoptotic transcripts, that is, Bcl2, Bax, Casp3, PCNA and p53 and pluripotency related transcripts, that is, Sox2, Nanog and Oct4 in ovine embryos produced in vitro at different O₂ concentrations (20% and 5% O₂) to compare their developmental potential. Oxygen concentrations did not influence the maturation and cleavage rate but the percentage of morula and blastocysts was significantly more at 5% as compared to 20% O₂. A significant upregulated expression of Bcl2 and PCNA genes and significantly downregulated expression of Casp3 and p53 were observed in the blastocysts at 5% than those at 20% O₂. The expression of Bax was not influenced by the O₂ concentration. Among the pluripotency related transcripts, the expression of Oct4 was significantly upregulated and the expression of Sox2 and Nanog was significantly downregulated in embryos at 5% than at 20% O₂. The study concluded that the embryos produced in vitro at low O₂ (5%) concentration regulate the expression of developmental genes related to apoptosis and pluripotency to improve the developmental potential of embryos as compared to high O₂ (20%) concentration.

Low oxygen tension activates glucose metabolism, improves antioxidant capacity and augment developmental potential of ovine embryos in vitro

Context Oxygen (O2) is one of the most powerful regulators of embryo function. Nevertheless, most in vitro embryo production studies do not consider O2 as a determining factor. Aim The present study was designed to assess the effect of different O2 (5 and 20%) concentrations on the developmental ability and expression of genes related to cellular antioxidant functions and glucose metabolism in the in vitro produced ovine embryos. Methods In vitro sheep embryos were produced at different O2 (5 and 20%) concentrations as per the laboratory protocol. Developmental stages of embryos at different O2 concentrations were compared. Messenger RNA abundance of antioxidant and glucose metabolism genes in embryos produced at different O2 concentrations were compared. Key results No significant (P &lt; 0.05) effect of different O2 concentrations on oocyte maturation and cleavage rate was observed. In contrast, significantly (P &lt; 0.05) more number of morula and blastocysts were observed at 5 compared with 20%O2. The expression level of the genes related to antioxidant functions (GPX, SOD1, SOD2 and CAT) and glucose metabolism (G6PD and HPRT) were found significantly (P &lt; 0.05) greater in the embryos generated with 5 compared with 20% O2. In contrast, the expression of GAPDH did not differ significantly (P &lt; 0.05) between the groups. Conclusions Ovine embryos at 5%O2 generated low ROS and synthesised more GSH due to the activation of G6PD and GPX that in turn increased the antioxidant capability and developmental potential of the embryos. Implications Embryos at higher O2 concentration (20%) generated more reactive oxygen species (ROS) that caused oxidative damage to the embryos and in turn reduced their developmental ability and alter gene expression.

l-Ergothioneine improves the developmental potential of in vitro sheep embryos without influencing OCTN1-mediated cross-membrane transcript expression

The objective of the study was to investigate the effect of l-ergothioneine (l-erg) (5 mM or 10 mM) supplementation in maturation medium on the developmental potential and OCTN1-dependant l-erg-mediated (10 mM) change in mRNA abundance of apoptotic (Bcl2, Bax, Casp3 and PCNA) and antioxidant (GPx, SOD1, SOD2 and CAT) genes in sheep oocytes and developmental stages of embryos produced in vitro. Oocytes matured with l-erg (10 mM) reduced their embryo toxicity by decreasing intracellular ROS and increasing intracellular GSH in matured oocytes that in turn improved developmental potential, resulting in significantly (P < 0.05) higher percentages of cleavage (53.72% vs 38.86, 46.56%), morulae (34.36% vs 20.62, 25.84%) and blastocysts (14.83% vs 6.98, 9.26%) compared with other lower concentrations (0 mM and 5 mM) of l-erg without change in maturation rate. l-Erg (10 mM) treatment did not influence the mRNA abundance of the majority of apoptotic and antioxidant genes studied in the matured oocytes and developmental stages of embryo. A gene expression study found that the SLC22A4 gene that encodes OCTN1, an integral membrane protein and specific transporter of l-erg was not expressed in oocytes and developmental stages of embryos. Therefore it was concluded from the study that although there was improvement in the developmental potential of sheep embryos by l-erg supplementation in maturation medium, there was no change in the expression of the majority of the genes studied due to the absence of the SLC22A4 gene in oocytes and embryos that encode OCTN1, which is responsible for transportation of l-erg across the membrane to alter gene expression.