Metabolism of the viable mammalian embryo: quietness revisited

Lipotoxicity and Oocyte Quality in Mammals: Pathogenesis, Consequences, and Reversibility

Metabolic stress conditions are often characterized by upregulated lipolysis and subsequently increased serum free fatty acid (FFA) concentrations, leading to the uptake of FFAs by non-adipose tissues and impairment of their function. This phenomenon is known as lipotoxicity. The increased serum FFA concentrations are reflected in the ovarian follicular fluid, which can have harmful effects on oocyte development. Several studies using in vitro and in vivo mammalian models showed that altered oocyte metabolism, increased oxidative stress, and mitochondrial dysfunction are crucial mechanisms underlying this detrimental impact. Ultimately, this can impair offspring health through the persistence of defective mitochondria in the embryo, hampering epigenetic reprogramming and early development. In vitro and in vivo treatments to enhance oocyte mitochondrial function are increasingly being developed. This can help to improve pregnancy rates and safeguard offspring health in metabolically compromised individuals.

Heat shock on bovine embryos from day 2.5-3 selects the most competent for progression to the blastocyst stage

Heat shock can impair embryo formation, while growth factors, such as colony-stimulating factor 2 (CSF2), modulate embryonic development. This study evaluated the effect of heat shock between days 2.5 and 3, as well as the impact of CSF2 at day 5 on bovine embryos cultured in a serum-free in vitro medium. The focus was on blastocyst development, the number of blastomeres, DNA fragmentation (TUNEL-positive cells), and mitochondrial activity. Heat shock reduced the proportion of cleaved embryos that developed into blastocysts (P = 0.0603). The resultant blastocysts exhibited a reduced number and proportion of TUNEL-positive cells in the trophectoderm (P = 0.0270 and P = 0.0240, respectively) and in the entire embryo (P = 0.0029 and P = 0.0031, respectively). Additionally, mitochondrial activity was lower in blastocysts derived from heat-shocked embryos (P = 0.0150) and further reduced in embryos exposed to both heat shock and CSF2 (P = 0.0415). In conclusion, the exposure of cleaved embryos to heat shock reduced their development to the blastocyst stage. However, the resulting blastocysts showed decreased DNA fragmentation and mitochondrial activity.

Bovine embryo production in vitro: evolution of culture media and commercial perspectives

In vitro produced embryos exhibit lower viability compared to their in vivo counterparts. Mammalian preimplantation embryos have the ability to reach the blastocyst stage in diverse culture media, showcasing considerable metabolic adaptability, which complicates the identification of optimal developmental conditions. Despite embryos successfully progressing to the blastocyst stage, adaptation to suboptimal culture environments may jeopardize blastocyst viability, cryotolerance, and implantation potential. Enhancing our capacity to support preimplantation embryonic development in vitro requires a deeper understanding of fundamental embryo physiology, including preferred metabolic substrates and pathways utilized by high-quality embryos. Armed with this knowledge, it becomes achievable to optimize culture conditions to support normal, in vivo-like embryo physiology, mitigate adaptive stress, and enhance viability. The objective of this review is to summarize the evolution of culture media for bovine embryos, highlighting significant milestones and remaining challenges.

Transcription factor-based transdifferentiation of human embryonic to trophoblast stem cells

During the first week of development, human embryos form a blastocyst composed of an inner cell mass and trophectoderm (TE) cells, the latter of which are progenitors of placental trophoblast. Here, we investigated the expression of transcripts in the human TE from early to late blastocyst stages. We identified enrichment of the transcription factors GATA2, GATA3, TFAP2C and KLF5 and characterised their protein expression dynamics across TE development. By inducible overexpression and mRNA transfection, we determined that these factors, together with MYC, are sufficient to establish induced trophoblast stem cells (iTSCs) from primed human embryonic stem cells. These iTSCs self-renew and recapitulate morphological characteristics, gene expression profiles, and directed differentiation potential, similar to existing human TSCs. Systematic omission of each, or combinations of factors, revealed the crucial importance of GATA2 and GATA3 for iTSC transdifferentiation. Altogether, these findings provide insights into the transcription factor network that may be operational in the human TE and broaden the methods for establishing cellular models of early human placental progenitor cells, which may be useful in the future to model placental-associated diseases.

Quantitative Proteomics and Metabolomics of Culture Medium from Single Human Embryo Reveal Embryo Quality-Related Multiomics Biomarkers

An effective tool to assess embryo quality in the assisted reproduction clinical practice will enhance successful implantation rates and mitigate high risks of multiple pregnancies. Potential biomarkers secreted into culture medium (CM) during embryo development enable rapid and noninvasive methods of assessing embryo quality. However, small volumes, low biomolecule concentrations, and impurity interference collectively preclude the identification of quality-related biomarkers in single blastocyst CM. Here, we developed a noninvasive trace multiomics approach to screen for potential markers in individual human blastocyst CM. We collected 84 CM samples and divided them into high-quality (HQ) and low-quality (LQ) groups. We evaluated the differentially expressed proteins (DEPs) and metabolites (DEMs) in HQ and LQ CM. A total of 504 proteins and 189 metabolites were detected in individual blastocyst CM. Moreover, 9 DEPs and 32 DEMs were identified in different quality embryo CM. We also categorized HQ embryos into positive implantation (PI) and negative implantation (NI) groups based on ultrasound findings on day 28. We identified 41 DEPs and 4 DEMs associated with clinical implantation outcomes in morphologically HQ embryos using a multiomics analysis approach. This study provides a noninvasive multiomics analysis technique and identifies potential biomarkers for clinical embryo developmental quality assessment.

Antioxidant Response of Maternal and Fetal Rat Liver to Selenium Nanoparticle Supplementation Compared to Sodium Selenite: Sex Differences between Fetuses

To compare the effects of organic selenium nanoparticles (SeNPs, Se0) and inorganic sodium selenite (NaSe, Na2SeO3, Se4+) on the antioxidant response in maternal and fetal rat liver, pregnant females were treated with two forms of selenium (Se) at equivalent doses during gestation (0.5 mg SeNPs or 0.5 mg NaSe/kg body weight/day). Structural parameters of the liver of gravid females and their fetuses were examined in a sex-specific manner. The oxidative stress parameters superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), glutathione S-transferase (GST), total glutathione (GSH) and sulfhydryl groups (SH) were established. In addition, the Se concentration was determined in the blood, liver, urine and feces of the gravid females and in the liver of the fetuses. The structure of the liver of gravid females remained histologically the same after supplementation with both forms of Se, while the oxidative stress in the liver was significantly lower after the use of SeNPs compared to NaSe. Immaturity of fetal antioxidant defenses and sex specificity were demonstrated. This study provides a detailed insight into the differences in the bioavailability of the nano form of Se compared to sodium selenite in the livers of pregnant females and fetuses.

Effect of time post warming to embryo transfer on human blastocyst metabolism and pregnancy outcome

PURPOSE

This study is aiming to test whether variation in post warming culture time impacts blastocyst metabolism or pregnancy outcome.

METHODS

In this single center retrospective cohort study, outcomes of 11,520 single frozen embryo transfer (FET) cycles were analyzed from January 2015 to December 2020. Patient treatments included both natural and programmed cycles. Time categories were determined using the time between blastocyst warming and embryo transfer: 0 (0- <1h), 1 (1-<2h), 2 (2-<3h), 3(3-<4h), 4 (4-<5), 5 (5-<6), 6 (6-<7) and 7 (7-8h). Non-invasive metabolic imaging of discarded human blastocysts for up to 10h was also performed using Fluorescence lifetime imaging microscopy (FLIM) to examine for metabolic perturbations during culture.

RESULTS

The mean age of patients across all time categories were comparable (35.6 ± 3.9). Live birth rates (38-52%) and miscarriage rate (5-11%) were not statistically different across post-warming culture time. When assessing pregnancy outcomes based on the use of PGT-A, miscarriage and live birth rates were not statistically different across culture hours in both PGT-A and non-PGT cycles. Further metabolic analysis of blastocysts for the duration of 10h of culture post warming, revealed minimal metabolic changes of embryos in culture.

CONCLUSION

Overall, our results show that differences in the time of post warming culture have no significant impact on miscarriage or live birth rate for frozen embryo transfers. This information can be beneficial for clinical practices with either minimal staffing or a high number of patient cases.

Impact of preovulatory follicle maturity on oocyte metabolism and embryo development

Improved oocyte competence for embryo development and pregnancy was observed following ovulation of preovulatory follicles with greater physiological maturity, as indicated by estradiol production, prior to the gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) surge. It was hypothesized that follicular fluid from preovulatory follicles of greater maturity better supports the maturing oocyte's metabolic requirements and improves embryo development. The objective was to determine if differences in preovulatory follicular fluid due to follicle maturity influence oocyte metabolism during in vitro maturation (IVM) and affect embryo development. Bovine preovulatory follicular fluid was collected 18 h after a GnRH-induced LH surge. Serum estradiol concentration at GnRH administration categorized follicles as greater or lesser maturity. Immature bovine oocytes were submitted to 24 h IVM in medium supplemented with 20% follicular fluid from preovulatory follicles of greater or lesser maturity. Embryo development was recorded. Oocyte maturation media and media conditioned by developing embryos were submitted for metabolomics. A randomized block design was utilized to determine differences in embryo development and media metabolites (P ≤ 0.05). Blastocysts from oocytes matured in greater vs. lesser maturity follicular fluid had a more moderate rate of development (P = 0.01). At the conclusion of 24 h IVM, abundance of 66 metabolites differed between greater and lesser follicle maturity treatments. Nine metabolites differed in media conditioned by developing embryos. Metabolome results suggest improved amino acid, purine, and glucose metabolism, followed by a more efficient rate of embryo development, in oocytes matured in greater vs lesser maturity follicular fluid.

Dynamics of Mitochondrial DNA Copy Number and Membrane Potential in Mouse Pre-Implantation Embryos: Responses to Diverse Types of Oxidative Stress

Mitochondria undergo a myriad of changes during pre-implantation embryo development, including shifts in activity levels and mitochondrial DNA (mtDNA) replication. However, how these distinct aspects of mitochondrial function are linked and their responsiveness to diverse stressors is not well understood. Here, we show that mtDNA content increased between 8-cell embryos and the blastocyst stage, with similar copy numbers per cell in the inner cell mass (ICM) and trophectoderm (TE). In contrast, mitochondrial membrane potential (MMP) was higher in TE than ICM. Culture in ambient oxygen (20% O2) altered both aspects of mitochondrial function: the mtDNA copy number was upregulated in ICM, while MMP was diminished in TE. Embryos cultured in 20% O2 also exhibited delayed development kinetics, impaired implantation, and reduced mtDNA levels in E18 fetal liver. A model of oocyte mitochondrial stress using rotenone showed only a modest effect on on-time development and did not alter the mtDNA copy number in ICM; however, following embryo transfer, mtDNA was higher in the fetal heart. Lastly, endogenous mitochondrial dysfunction, induced by maternal age and obesity, altered the blastocyst mtDNA copy number, but not within the ICM. These results demonstrate that mitochondrial activity and mtDNA content exhibit cell-specific changes and are differentially responsive to diverse types of oxidative stress during pre-implantation embryogenesis.

Heat shock interferes with the amino acid metabolism of bovine cumulus-oocyte complexes in vitro: a multistep analysis

By affecting the ovarian pool of follicles and their enclosed oocytes, heat stress has an impact on dairy cow fertility. This study aimed to determine how heat shock (HS) during in vitro maturation affected the ability of the bovine cumulus-oocyte complexes (COCs) to develop, as well as their metabolism of amino acids (AAs). In this study, COCs were in vitro matured for 23 h at 38.5 °C (control; n = 322), 39.5 °C (mild HS (MHS); n = 290), or 40.5 °C (severe HS (SHS); n = 245). In comparison to the control group, the MHS and SHS groups significantly decreased the percentage of metaphase-II oocytes, as well as cumulus cell expansion and viability. The SHS decreased the rates of cleavage and blastocyst formation in comparison to the control and MHS. Compared to the control and MHS-COCs, the SHS-COCs produced significantly more phenylalanine, threonine, valine, arginine, alanine, glutamic acid, and citrulline while depleting less leucine, glutamine, and serine. Data showed that SHS-COCs had the highest appearance and turnover of all AAs and essential AAs. Heat shock was positively correlated with the appearance of glutamic acid, glutamine, isoleucine, alanine, serine, valine, phenylalanine, and asparagine. Network analysis identified the relationship between HS and alanine or glutamic acid, as well as the relationship between blastocyst and cleavage rates and ornithine. The findings imply that SHS may have an impact on the quality and metabolism of AAs in COCs. Moreover, the use of a multistep analysis could simply identify the AAs most closely linked to HS and the developmental competence of bovine COCs.

An Overview of Reactive Oxygen Species Damage Occurring during In Vitro Bovine Oocyte and Embryo Development and the Efficacy of Antioxidant Use to Limit These Adverse Effects

The in vitro production (IVP) of bovine embryos has gained popularity worldwide and in recent years and its use for producing embryos from genetically elite heifers and cows has surpassed the use of conventional superovulation-based embryo production schemes. There are, however, several issues with the IVP of embryos that remain unresolved. One limitation of special concern is the low efficiency of the IVP of embryos. Exposure to reactive oxygen species (ROS) is one reason why the production of embryos with IVP is diminished. These highly reactive molecules are generated in small amounts through normal cellular metabolism, but their abundances increase in embryo culture because of oocyte and embryo exposure to temperature fluctuations, light exposure, pH changes, atmospheric oxygen tension, suboptimal culture media formulations, and cryopreservation. When uncontrolled, ROS produce detrimental effects on the structure and function of genomic and mitochondrial DNA, alter DNA methylation, increase lipid membrane damage, and modify protein activity. Several intrinsic enzymatic pathways control ROS abundance and damage, and antioxidants react with and reduce the reactive potential of ROS. This review will focus on exploring the efficiency of supplementing several of these antioxidant molecules on oocyte maturation, sperm viability, fertilization, and embryo culture.

Proline and Proline Analogues Improve Development of Mouse Preimplantation Embryos by Protecting Them against Oxidative Stress

The culture of embryos in the non-essential amino acid L-proline (Pro) or its analogues pipecolic acid (PA) and L-4-thiazolidine carboxylic acid (L4T) improves embryo development, increasing the percentage that develop to the blastocyst stage and hatch. Staining of 2-cell and 4-cell embryos with tetramethylrhodamine methyl ester and 2',7'-dichlorofluorescein diacetate showed that the culture of embryos in the presence of Pro, or either of these analogues, reduced mitochondrial activity and reactive oxygen species (ROS), respectively, indicating potential mechanisms by which embryo development is improved. Inhibition of the Pro metabolism enzyme, proline oxidase, by tetrahydro-2-furoic-acid prevented these reductions and concomitantly prevented the improved development. The ways in which Pro, PA and L4T reduce mitochondrial activity and ROS appear to differ, despite their structural similarity. Specifically, the results are consistent with Pro reducing ROS by reducing mitochondrial activity while PA and L4T may be acting as ROS scavengers. All three may work to reduce ROS by contributing to the GSH pool. Overall, our results indicate that reduction in mitochondrial activity and oxidative stress are potential mechanisms by which Pro and its analogues act to improve pre-implantation embryo development.

The Task Matters: A Comprehensive Review and Proposed Literature Score of the Effects of Chemical and Physical Parameters on Embryo Developmental Competence

To explore the effects of chemical and physical parameters on embryo developmental competence, we conducted a systematic search on PubMed for peer-reviewed original papers using specific keywords and medical subject heading terms. Studies of interest were selected from an initial cohort of 4141 potentially relevant records retrieved. The most relevant publications were critically evaluated to identify the effect of these parameters on embryo development. Moreover, we generated a literature score (LS) using the following procedure: (i) the number of studies favoring a reference group was expressed as a fraction of all analyzed papers; (ii) the obtained fraction was multiplied by 10 and converted into a decimal number. We identified and discussed six parameters (oxygen, temperature, humidity, oil overlay, light, pH). Moreover, we generated a LS according to five different comparisons (37 °C vs. <37 °C; 5% vs. 20% oxygen; 5-2% vs. 5% oxygen; humidity conditions vs. dry conditions; light exposure vs. reduced/protected light exposure). Only two comparisons (37 °C vs. <37 °C and 5% vs. 20% oxygen) yielded a medium-high LS (8.3 and 7, respectively), suggesting a prevalence of studies in favor of the reference group (37 °C and 5% oxygen). In summary, this review and LS methodology offer semi-quantitative information on studies investigating the effects of chemical and physical parameters on embryo developmental competence.

Effects of lactate, super-GDF9, and low oxygen tension during bi-phasic in vitro maturation on the bioenergetic profiles of mouse cumulus-oocyte complex†

In vitro maturation (IVM) is an alternative assisted reproductive technology with reduced hormone-related side effects and treatment burden compared to conventional IVF. Capacitation (CAPA)-IVM is a bi-phasic IVM system with improved clinical outcomes compared to standard monophasic IVM. Yet, CAPA-IVM efficiency compared to conventional IVF is still suboptimal in terms of producing utilizable blastocysts. Previously, we have shown that CAPA-IVM leads to a precocious increase in cumulus cell (CC) glycolytic activity during cytoplasmic maturation. In the current study, considering the fundamental importance of CCs for oocyte maturation and cumulus-oocyte complex (COC) microenvironment, we further analyzed the bioenergetic profiles of maturing CAPA-IVM COCs. Through a multi-step approach, we (i) explored mitochondrial function of the in vivo and CAPA-IVM matured COCs through real-time metabolic analysis with Seahorse analyzer, and to improve COC metabolism (ii) supplemented the culture media with lactate and/or super-GDF9 (an engineered form of growth differentiation factor 9) and (iii) reduced culture oxygen tension. Our results indicated that the pre-IVM step is delicate and prone to culture-related disruptions. Lactate and/or super-GDF9 supplementations failed to eliminate pre-IVM-induced stress on COC glucose metabolism and mitochondrial respiration. However, when performing pre-IVM culture under 5% oxygen tension, CAPA-IVM COCs showed similar bioenergetic profiles compared to in vivo matured counterparts. This is the first study providing real-time metabolic analysis of the COCs from a bi-phasic IVM system. The currently used analytical approach provides the quantitative measures and the rational basis to further improve IVM culture requirements.

Mitochondrial dysfunction in the offspring of obese mothers and it's transmission through damaged oocyte mitochondria: Integration of mechanisms

In vivo and in vitro studies demonstrate that mitochondria in the oocyte, are susceptible to damage by suboptimal pre/pregnancy conditions, such as obesity. These suboptimal conditions have been shown to induce mitochondrial dysfunction (MD) in multiple tissues of the offspring, suggesting that mitochondria of oocytes that pass from mother to offspring, can carry information that can programme mitochondrial and metabolic dysfunction of the next generation. They also suggest that transmission of MD could increase the risk of obesity and other metabolic diseases in the population inter- and trans-generationally. In this review, we examined whether MD observed in offspring tissues of high energetic demand, is the result of the transmission of damaged mitochondria from the oocytes of obese mothers to the offspring. The contribution of genome-independent mechanisms (namely mitophagy) in this transmission were also explored. Finally, potential interventions aimed at improving oocyte/embryo health were investigated, to see if they may provide an opportunity to halter the generational effects of MD.

Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis

BACKGROUND

A normal chromosomal constitution defined through PGT-A assessing all chromosomes on trophectoderm (TE) biopsies represents the strongest predictor of embryo implantation. Yet, its positive predictive value is not higher than 50-60%. This gap of knowledge on the causes of euploid blastocysts' reproductive failure is known as 'the black box of implantation'.

OBJECTIVE AND RATIONALE

Several embryonic, maternal, paternal, clinical, and IVF laboratory features were scrutinized for their putative association with reproductive success or implantation failure of euploid blastocysts.

SEARCH METHODS

A systematic bibliographical search was conducted without temporal limits up to August 2021. The keywords were '(blastocyst OR day5 embryo OR day6 embryo OR day7 embryo) AND (euploid OR chromosomally normal OR preimplantation genetic testing) AND (implantation OR implantation failure OR miscarriage OR abortion OR live birth OR biochemical pregnancy OR recurrent implantation failure)'. Overall, 1608 items were identified and screened. We included all prospective or retrospective clinical studies and randomized-controlled-trials (RCTs) that assessed any feature associated with live-birth rates (LBR) and/or miscarriage rates (MR) among non-mosaic euploid blastocyst transfer after TE biopsy and PGT-A. In total, 41 reviews and 372 papers were selected, clustered according to a common focus, and thoroughly reviewed. The PRISMA guideline was followed, the PICO model was adopted, and ROBINS-I and ROB 2.0 scoring were used to assess putative bias. Bias across studies regarding the LBR was also assessed using visual inspection of funnel plots and the trim and fill method. Categorical data were combined with a pooled-OR. The random-effect model was used to conduct the meta-analysis. Between-study heterogeneity was addressed using I2. Whenever not suitable for the meta-analysis, the included studies were simply described for their results. The study protocol was registered at http://www.crd.york.ac.uk/PROSPERO/ (registration number CRD42021275329).

OUTCOMES

We included 372 original papers (335 retrospective studies, 30 prospective studies and 7 RCTs) and 41 reviews. However, most of the studies were retrospective, or characterized by small sample sizes, thus prone to bias, which reduces the quality of the evidence to low or very low. Reduced inner cell mass (7 studies, OR: 0.37, 95% CI: 0.27-0.52, I2 = 53%), or TE quality (9 studies, OR: 0.53, 95% CI: 0.43-0.67, I2 = 70%), overall blastocyst quality worse than Gardner's BB-grade (8 studies, OR: 0.40, 95% CI: 0.24-0.67, I2 = 83%), developmental delay (18 studies, OR: 0.56, 95% CI: 0.49-0.63, I2 = 47%), and (by qualitative analysis) some morphodynamic abnormalities pinpointed through time-lapse microscopy (abnormal cleavage patterns, spontaneous blastocyst collapse, longer time of morula formation I, time of blastulation (tB), and duration of blastulation) were all associated with poorer reproductive outcomes. Slightly lower LBR, even in the context of PGT-A, was reported among women ≥38 years (7 studies, OR: 0.87, 95% CI: 0.75-1.00, I2 = 31%), while obesity was associated with both lower LBR (2 studies, OR: 0.66, 95% CI: 0.55-0.79, I2 = 0%) and higher MR (2 studies, OR: 1.8, 95% CI: 1.08-2.99, I2 = 52%). The experience of previous repeated implantation failures (RIF) was also associated with lower LBR (3 studies, OR: 0.72, 95% CI: 0.55-0.93, I2 = 0%). By qualitative analysis, among hormonal assessments, only abnormal progesterone levels prior to transfer were associated with LBR and MR after PGT-A. Among the clinical protocols used, vitrified-warmed embryo transfer was more effective than fresh transfer (2 studies, OR: 1.56, 95% CI: 1.05-2.33, I2 = 23%) after PGT-A. Lastly, multiple vitrification-warming cycles (2 studies, OR: 0.41, 95% CI: 0.22-0.77, I2 = 50%) or (by qualitative analysis) a high number of cells biopsied may slightly reduce the LBR, while simultaneous zona-pellucida opening and TE biopsy allowed better results than the Day 3 hatching-based protocol (3 studies, OR: 1.41, 95% CI: 1.18-1.69, I2 = 0%).

WIDER IMPLICATIONS

Embryo selection aims at shortening the time-to-pregnancy, while minimizing the reproductive risks. Knowing which features are associated with the reproductive competence of euploid blastocysts is therefore critical to define, implement, and validate safer and more efficient clinical workflows. Future research should be directed towards: (i) systematic investigations of the mechanisms involved in reproductive aging beyond de novo chromosomal abnormalities, and how lifestyle and nutrition may accelerate or exacerbate their consequences; (ii) improved evaluation of the uterine and blastocyst-endometrial dialogue, both of which represent black boxes themselves; (iii) standardization/automation of embryo assessment and IVF protocols; (iv) additional invasive or preferably non-invasive tools for embryo selection. Only by filling these gaps we may finally crack the riddle behind 'the black box of implantation'.

The embryo non-invasive pre-implantation diagnosis era: how far are we?

Advancements in assisted reproduction (AR) methodologies have allowed significant improvements in live birth rates of women who otherwise would not be able to conceive. One of the tools that allowed this improvement is the possibility of embryo selection based on genetic status, performed via preimplantation genetic testing (PGT). Even though the widespread use of PGT from TE biopsy helped to decrease the interval from the beginning of the AR intervention to pregnancy, especially in older patients, in AR, there are still many concerns about the application of this invasive methodology in all cycles. Therefore, recently, researchers started to study the use of cell free DNA (cfDNA) released by the blastocyst in its culture medium to perform PGT, in a method called non-invasive PGT (niPGT). The development of a niPGT would bring the diagnostics power of conventional PGT, but with the advantage of being potentially less harmful to the embryo. Its implementation in clinical practice, however, is under heavy discussion since there are many unknowns about the technique, such as the origin of the cfDNA or if this genetic material is a true representative of the actual ploidy status of the embryo. Available data indicates that there is high correspondence between results observed in TE biopsies and the ones observed from cfDNA, but these results are still contradictory and highly debatable. In the present review, the advantages and disadvantages of niPGT are presented and discussed in relation to tradition TE biopsy-based PGT. Furthermore, there are also presented some other possible non-invasive tools that could be applied in the selection of the best embryo, such as quantification of other molecules as quality biomarkers, or the use artificial intelligence (AI) to identify the best embryos based on morphological and/or morphokitetic parameters.

Long-Term Effects of ART on the Health of the Offspring

Assisted reproductive technologies (ART) significantly increase the chance of successful pregnancy and live birth in infertile couples. The different procedures for ART, including in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), intrauterine insemination (IUI), and gamete intrafallopian tube transfer (GIFT), are widely used to overcome infertility-related problems. In spite of its inarguable usefulness, concerns about the health consequences of ART-conceived babies have been raised. There are reports about the association of ART with birth defects and health complications, e.g., malignancies, high blood pressure, generalized vascular functional disorders, asthma and metabolic disorders in later life. It has been suggested that hormonal treatment of the mother, and the artificial environment during the manipulation of gametes and embryos may cause genomic and epigenetic alterations and subsequent complications in the health status of ART-conceived babies. In the current study, we aimed to review the possible long-term consequences of different ART procedures on the subsequent health status of ART-conceived offspring, considering the confounding factors that might account for/contribute to the long-term consequences.

Metabolism-epigenetic interactions on in vitro produced embryos

Metabolism and epigenetics, which reciprocally regulate each other in different cell types, are fundamental aspects of cellular adaptation to the environment. Evidence in cancer and stem cells has shown that the metabolic status modifies the epigenome while epigenetic mechanisms regulate the expression of genes involved in metabolic processes, thereby altering the metabolome. This crosstalk occurs as many metabolites serve as substrates or cofactors of chromatin-modifying enzymes. If we consider the intense metabolic dynamic and the epigenetic remodelling of the embryo, the comprehension of these regulatory networks will be important not only for understanding early embryonic development, but also to determine in vitro culture conditions that support embryo development and may insert positive regulatory marks that may persist until adult life. In this review, we focus on how metabolism may affect epigenetic reprogramming of the early stages of development, in particular acetylation and methylation of histone and DNA. We also present other metabolic modifications in bovine embryos, such as lactylation, highlighting the promising epigenetic and metabolic targets to improve conditions for in vitro embryo development.

The Effects of BSA-Stabilized Selenium Nanoparticles and Sodium Selenite Supplementation on the Structure, Oxidative Stress Parameters and Selenium Redox Biology in Rat Placenta

The chemical element selenium (Se) is a nonmetal that is in trace amounts indispensable for normal cellular functioning. During pregnancy, a low Se status can increase the risk of oxidative stress. However, elevated concentrations of Se in the body can also cause oxidative stress. This study aimed to compare the effects of BSA-stabilized Se nanoparticles (SeNPs, Se0) (BSA-bovine serum albumin) and inorganic sodium selenite (NaSe, Se+4) supplementation on the histological structure of the placenta, oxidative stress parameters and the total placental Se concentration of Wistar rats during pregnancy. Pregnant females were randomized into four groups: (i) intact controls; (ii) controls that were dosed by daily oral gavage with 8.6% bovine serum albumin (BSA) and 0.125 M vit C; (iii) the SeNP group that was administered 0.5 mg of SeNPs stabilized with 8.6% BSA and 0.125 M vit C/kg bw/day by oral gavage dosing; (iv) the NaSe group, gavage dosed with 0.5 mg Na2SeO3/kg bw/day. The treatment of pregnant females started on gestational day one, lasted until day 20, and on day 21 of gestation, the fetuses with the placenta were removed from the uterus. Our findings show that the mode of action of equivalent concentrations of Se in SeNPs and NaSe depended on its redox state and chemical structure. Administration of SeNPs (Se0) increased fetal lethality and induced changes in the antioxidative defense parameters in the placenta. The accumulation of Se in the placenta was highest in SeNP-treated animals. All obtained data indicate an increased bioavailability of Se in its organic nano form and Se0 redox state in comparison to its inorganic sodium selenite form and Se+4 redox state.

Pre-Treatment Physical Activity Could Positively Influence Pregnancy Rates in IVF despite the Induced Oxidative Stress: A Cohort Study on Salivary 8-Hydroxy-2'-deoxyguanosine

(1) Background: This study was designed to define whether pretreatment habitual physical activity (PA)-induced oxidative stress (OS) influences outcome measures by using 8-hydroxy-2′-deoxyguanosine (8-OHdG) in saliva samples of patients undergoing in vitro fertilization (IVF). (2) Method: In this cohort study, samples were obtained from 26 patients (age: 34.6 ± 5.5 years, BMI: 25.3 ± 5.1, infertility: 51.0 ± 28.7 months) before the treatment and a follow-up of outcome measures of IVF/ICSI. The 8-OHdG was evaluated by Abcam’s ELISA (ab201734), PA patterns by GPAQ-H and ActiGraph GT3X; (3) Results: The number of matured oocytes was positively influenced by the GPAQ-H recreation MET (R2 = 0.367, F = 10.994, p = 0.004; β = 0.005, p = 0.004, B Constant = 4.604) and a positive significant relationship (R2 = 0.757, F = 17.692, p < 0.001, B Constant = 1.342) was found with GPAQ-H recreational PA MET (β = 0.004, p < 0.001), and Grade 1 embryos and higher very vigorous activity (GT3X) were accompanied (R2 = 0.958, F = 408.479, p < 0.001) by higher ß-hCG levels (β = 63.703, p ≤ 0.001). Unanticipated positive correlation between 8-OHdG and ß-hCG level (R = 0.467, p = 0.028) was noticed, and there were significant differences in 8-OHdG in biochemical pregnancies (pregnant: 54.82 ± 35.56 ng/mL, non-pregnant: 30.06 ± 10.40 ng/mL, p = 0.022) as well. (4) Conclusions: Pretreatment PA could positively influence reproductive performance in IVF/ICSI despite the induced OS. However, a more sensitive biomarker and the recommended amount of activity should be further investigated.

Maladaptation to the transition period and consequences on fertility of dairy cows

After parturition, dairy cows undergo a plethora of metabolic, inflammatory, and immunologic changes to adapt to the onset of lactation. These changes are mainly due to the homeorhetic shift to support milk production when nutrient demand exceeds dietary intake, resulting in a state of negative energy balance. Negative energy balance in postpartum dairy cows is characterized by upregulated adipose tissue modelling, insulin resistance, and systemic inflammation. However, half of the postpartum cows fail to adapt to these changes and develop one or more types of clinical and subclinical disease within 5 weeks after calving, and this is escorted by impaired reproductive performance in the same lactation. Maladaptation to the transition period exerts molecular and structural changes in the follicular and reproductive tract fluids, the microenvironment in which oocyte maturation, fertilization, and embryo development occur. Although the negative effects of transition diseases on fertility are well-known, the involved pathways are only partially understood. This review reconstructs the mechanism of maladaptation to lactation in the transition period, explores their key (patho)physiological effects on reproductive organs, and briefly describes potential carryover effects on fertility in the same lactation.

The Quiet Embryo Hypothesis: 20 years on

This article revisits the hypothesis, proposed in 2002, that the successful development of oocytes and preimplantation mammalian embryos is associated with a metabolism which is “quiet” rather than “active”, within limits which had yet to be defined. A distinction was drawn between Functional Quietness, Loss of quietness in response to stress and Inter-individual differences in embryo metabolism and here we document applications of the hypothesis to other areas of reproductive biology. In order to encompass the requirement for “limits” and replace the simple distinction between “quiet” and “active”, evidence is presented which led to a re-working of the hypothesis by proposing the existence of an optimal range of metabolic activity, termed a “Goldilocks zone”, within which oocytes and embryos with maximum developmental potential will be located. General and specific mechanisms which may underlie the Goldilocks phenomenon are proposed and the added value that may be derived by expressing data on individual embryos as distributions rather than mean values is emphasised especially in the context of the response of early embryos to stress and to the concept of the Developmental Origins of Health and Disease. The article concludes with a cautionary note that being “quietly efficient” may not always ensure optimal embryo survival.

The effects of temperature variation treatments on embryonic development: a mouse study

Since the development of ART, embryos have been cultured at 37 °C in an attempt to mimic the in vivo conditions and the average body temperature of an adult. However, a gradient of temperatures within the reproductive tract has been demonstrated in humans and several other mammalian species. Therefore, the aim of this study was to evaluate the effects of temperature variation treatments on mouse embryo quality through morphokinetic events, blastocyst morphology, the relative gene expression of Igf2, Bax, Bcl2 and Apaf1 and the metabolomics of individual culture media. Study groups consisted of 2 circadian treatments, T1 with embryos being cultured at 37 °C during the day and 35.5 °C during the night, T2 with 38.5 °C during the day and 37 °C during the night and a control group with constant 37 °C. Our main findings are that the lower-temperature group (T1) showed a consistent negative effect on mouse embryo development with “slow” cleaving embryos, poor-quality blastocysts, a higher expression of the apoptotic gene Apaf1, and a significantly different set of amino acids representing a more stressed metabolism. On the other hand, our higher-temperature group (T2) showed similar results to the control group, with no adverse effects on blastocyst viability.

Capillary electrophoresis-mass spectrometry as a tool for the noninvasive target metabolomic analysis of underivatized amino acids for evaluating embryo viability in assisted reproduction

Monitoring metabolite uptake and excretion in the culture medium is a noninvasive technique that is used for the metabolic study of cleaving embryos after in vitro fertilization. Low sample consumption, the versatility of the detection, and optimal sensitivity and selectivity are essential elements for extracellular metabolome analyses, and can be conveniently achieved by combining CE with mass spectrometric detection. This paper reports a method for amino acid determination in a limited volume sample (8 μL) of spent culture media collected after the cultivation of in vitro fertilized embryos. Special attention was focused on the sample preparation procedure. The sample was processed with acetonitrile, which facilitates online sample preconcentration via field-amplified sample stacking, and undesired sample evaporation was significantly reduced by the simultaneous addition of dimethyl sulfoxide. Key parameters that affected electrophoretic separation and mass spectrometric detection were investigated, including the type of buffers and organic solvent, optimization of their concentrations, and finally the settings for their ionization. The separation and quantification of 19 amino acids were achieved using 15% acetic acid as the background electrolyte with a sheath liquid consisting of an equimolar mixture of methanol and water. The applicability of the optimized system was demonstrated by determining the amino acid profile in 40 samples of spent cultivation medium in this pilot study. This developed method also has great potential for amino acid analyses in minute sample volumes of other biological matrices.

Probing morphological, genetic and metabolomic changes of in vitro embryo development in a microfluidic device

Assisted reproduction technologies for clinical and research purposes rely on a brief in vitro embryo culture which, despite decades of progress, remain suboptimal in comparison to the physiological environment. One promising tool to improve this technique is the development of bespoke microfluidic chambers. Here we present and validate a new microfluidic device in polydimethylsiloxane (PDMS) for the culture of early mouse embryos. Device material and design resulted embryo compatible and elicit minimal stress. Blastocyst formation, hatching, attachment and outgrowth formation on fibronectin-coated devices were similar to traditional microdrop methods. Total blastocyst cell number and allocation to the trophectoderm and inner cell mass lineages were unaffected. The devices were designed for culture of 10-12 embryos. Development rates, mitochondrial polarization and metabolic turnover of key energy substrates glucose, pyruvate and lactate were consistent with groups of 10 embryos in microdrop controls. Increasing group size to 40 embryos per device was associated with increased variation in development rates and altered metabolism. Device culture did not perturb blastocyst gene expression but did elicit changes in embryo metabolome, which can be ascribed to substrate leaching from PDMS and warrant further investigation.

Amino Acids and the Early Mammalian Embryo: Origin, Fate, Function and Life-Long Legacy

Amino acids are now recognised as having multiple cellular functions in addition to their traditional role as constituents of proteins. This is well-illustrated in the early mammalian embryo where amino acids are now known to be involved in intermediary metabolism, as energy substrates, in signal transduction, osmoregulation and as intermediaries in numerous pathways which involve nitrogen metabolism, e.g., the biosynthesis of purines, pyrimidines, creatine and glutathione. The amino acid derivative S-adenosylmethionine has emerged as a universal methylating agent with a fundamental role in epigenetic regulation. Amino acids are now added routinely to preimplantation embryo culture media. This review examines the routes by which amino acids are supplied to the early embryo, focusing on the role of the oviduct epithelium, followed by an outline of their general fate and function within the embryo. Functions specific to individual amino acids are then considered. The importance of amino acids during the preimplantation period for maternal health and that of the conceptus long term, which has come from the developmental origins of health and disease concept of David Barker, is discussed and the review concludes by considering the potential utility of amino acid profiles as diagnostic of embryo health.

Less is more: Reduced nutrient concentration during in vitro culture improves embryo production rates and morphophysiology of bovine embryos

Reproducing the environment to which the embryo is naturally exposed may be an alternative to improve viability of embryos produced in vitro. In the first part of this work, we describe a novel culture media, namely Embryonic Culture Supplementation (ECS100). The composition of this media was based on the contents of carbohydrates and amino acids found in oviductal and uterine fluids. Because it was a new formulation, we investigated the performance of ECS100 in comparison with conventionally used SOFaa, and possible benefits to embryo development. Embryo production rates (cleavage, morula and blastocyst conversion, blastocyst and hatching rates) and morphophysiological parameters (total cell number, cell allocation, Mitochondrial membrane potential (MMP), Reactive Oxygen Species (ROS), NADH, FAD⁺ and ATP content) were similar between ECS100 and SOFaa. Next, we tested if a reduction of ECS100 concentration could positively contribute to embryo viability by resembling the more dynamic availability of nutrients that reach the embryos in vivo. Therefore, embryos were cultured in ECS100 or in its serial dilution (ECS75, 50 and 25). Despite the fact that the lowest concentration (ECS25) still supported blastocyst formation, halving the concentration of metabolites (ECS50) actually improved embryo production rates. Thus, embryos produced in ECS100 or ECS50 were submitted to further analyses on Days 4 and 7. Embryos cultured in ECS50 presented better developmental rates and morphophysiological profile than embryos cultured in ECS100. Additionally, physiological traits (MMP, ROS and NADH levels) of embryos cultured in ECS50 presented the expected pattern for embryos produced in vivo. In conclusion, we presented a novel, more personalized and effective culture media for bovine IVP embryos. And although the ECS media formulation was based on the contents of female reproductive fluids, it is worth mentioning that adaptations must be specifically directed for in vitro conditions rather than reproduced exactly from in vivo state.

Analysis of the uterine lumen in fertility-classified heifers: I. Glucose, prostaglandins, and lipids†

Survival and growth of the bovine conceptus (embryo and associated extraembryonic membranes) are dependent on endometrial secretions or histotroph found in the uterine lumen. Previously, serial embryo transfer was used to classify heifers as high fertile (HF), subfertile (SF), or infertile (IF). Here, we investigated specific histotroph components [glucose, prostaglandins (PGs), and lipids] in the uterine lumen of day 17 pregnant and open fertility-classified heifers. Concentrations of glucose in the uterine lumen were increased by pregnancy but did not differ among fertility-classified heifers. Differences in expression of genes encoding glucose transporters and involved with glycolysis and gluconeogenesis were observed between conceptuses collected from HF and SF heifers. In the uterine lumen, PGE2 and PGF2α were increased by pregnancy, and HF heifers had higher concentrations of PGE2, PGF2α, and 6-keto-PFG1α than SF heifers. Differences were found in expression of genes regulating PG signaling, arachidonic acid metabolism, and peroxisome proliferator-activated receptor signaling among conceptuses and endometrium from fertility-classified heifers. Lipidomics was conducted exclusively in samples from HF heifers, and phosphatidylcholine was the main lipid class that increased in the uterine lumen by pregnancy. Expression of several lipid metabolism genes differed between HF and SF conceptuses, and a number of fatty acids were differentially abundant in the uterine lumen of pregnant HF and SF heifers. These results support the ideas that uterine luminal histotroph impacts conceptus survival and programs its development and is a facet of dysregulated conceptus-endometrial interactions that result in loss of the conceptus in SF cattle during the implantation period of pregnancy establishment.

In Vitro Fertilisation of Mouse Oocytes in L-Proline and L-Pipecolic Acid Improves Subsequent Development

Exposure of oocytes to specific amino acids during in vitro fertilisation (IVF) improves preimplantation embryo development. Embryos fertilised in medium with proline and its homologue pipecolic acid showed increased blastocyst formation and inner cell mass cell numbers compared to embryos fertilised in medium containing no amino acids, betaine, glycine, or histidine. The beneficial effect of proline was prevented by the addition of excess betaine, glycine, and histidine, indicating competitive inhibition of transport-mediated uptake. Expression of transporters of proline in oocytes was investigated by measuring the rate of uptake of radiolabelled proline in the presence of unlabelled amino acids. Three transporters were identified, one that was sodium-dependent, PROT (SLC6A7), and two others that were sodium-independent, PAT1 (SLC36A1) and PAT2 (SLC36A2). Immunofluorescent staining showed localisation of PROT in intracellular vesicles and limited expression in the plasma membrane, while PAT1 and PAT2 were both expressed in the plasma membrane. Proline and pipecolic acid reduced mitochondrial activity and reactive oxygen species in oocytes, and this may be responsible for their beneficial effect. Overall, our results indicate the importance of inclusion of specific amino acids in IVF medium and that consideration should be given to whether the addition of multiple amino acids prevents the action of beneficial amino acids.

Metabolomic Analysis Evidences That Uterine Epithelial Cells Enhance Blastocyst Development in a Microfluidic Device

Here we report the use of a microfluidic system to assess the differential metabolomics of murine embryos cultured with endometrial cells-conditioned media (CM). Groups of 10, 1-cell murine B6C3F1 × B6D2F1 embryos were cultured in the microfluidic device. To produce CM, mouse uterine epithelial cells were cultured in potassium simplex optimized medium (KSOM) for 24 h. Media samples were collected from devices after 5 days of culture with KSOM (control) and CM, analyzed by reverse phase liquid chromatography and untargeted positive ion mode mass spectrometry analysis. Blastocyst rates were significantly higher (p < 0.05) in CM (71.8%) compared to control media (54.6%). We observed significant upregulation of 341 compounds and downregulation of 214 compounds in spent media from CM devices when compared to control. Out of these, 353 compounds were identified showing a significant increased abundance of metabolites involved in key metabolic pathways (e.g., arginine, proline and pyrimidine metabolism) in the CM group, suggesting a beneficial effect of CM on embryo development. The metabolomic study carried out in a microfluidic environment confirms our hypothesis on the potential of uterine epithelial cells to enhance blastocyst development. Further investigations are required to highlight specific pathways involved in embryo development and implantation.

Ultrastructure of mitochondria of human oocytes in different clinical conditions during assisted reproduction

Infertility affects around 8% of couples with a slight change in percentage in the last years. Despite the significant efforts made in Assisted Reproductive Technologies (ARTs) in handling this disorder, oocyte quality remains a crucial factor for a positive outcome. A better understanding of the dynamics underlying oocyte maturation, fertilization, and embryo development remains one of the main areas for progress in the ARTs field. Mitochondria are believed to play an essential role in these processes. Mitochondria have a crucial part in producing energy for oocyte maturation and embryo development throughout precise cellular functions comprising Ca²⁺ homeostasis regulation, glycolysis, amino acid and fatty acid metabolism, and regulation of apoptosis. Recent studies suggest that mitochondrial structure, content, and function may be related to oocyte competence, embryo viability, and implantation success during ARTs. Their defects could lead to low fertilization rates and embryonic development failure. This review aimed to provide an overview of the available literature data surrounding the correlation between changes at ultrastructural level of mitochondria or correlated-mitochondrial aggregates and oocyte quality and ARTs treatments. Our reported data demonstrated that oocyte mitochondrial ultrastructural alterations could be partial or complete recovery during the early embryo stages. However, these changes could persist as quiescent during the pre-implantation embryo development, causing abnormalities that become evident only during fetal and postnatal life. These factors led to consider the mitochondria as a crucial marker of oocyte and embryo quality, as well as a strategic target for further prospective therapeutical approaches.

Metabolomics analysis of follicular fluid coupled with oocyte aspiration reveals importance of glucocorticoids in primate periovulatory follicle competency

Gonadotropin administration during infertility treatment stimulates the growth and development of multiple ovarian follicles, yielding heterogeneous oocytes with variable capacity for fertilization, cleavage, and blastocyst formation. To determine how the intrafollicular environment affects oocyte competency, 74 individual rhesus macaque follicles were aspirated and the corresponding oocytes classified as failed to cleave, cleaved but arrested prior to blastulation, or those that formed blastocysts following in vitro fertilization. Metabolomics analysis of the follicular fluid (FF) identified 60 unique metabolites that were significantly different between embryo classifications, of which a notable increase in the intrafollicular ratio of cortisol to cortisone was observed in the blastocyst group. Immunolocalization of the glucocorticoid receptor (GR, NR3C1) revealed translocation from the cytoplasm to nucleus with oocyte maturation in vitro and, correlation to intrafollicular expression of the 11-hydroxy steroid dehydrogenases that interconvert these glucocorticoids was detected upon an ovulatory stimulus in vivo. While NR3C1 knockdown in oocytes had no effect on their maturation or fertilization, expansion of the associated cumulus granulosa cells was inhibited. Our findings indicate an important role for NR3C1 in the regulation of follicular processes via paracrine signaling. Further studies are required to define the means through which the FF cortisol:cortisone ratio determines oocyte competency.

Mitochondrial DNA Copy Number in Human Blastocyst: A Novel Biomarker for the Prediction of Implantation Potential

The relationship between mitochondrial DNA (mtDNA) copy number and the outcome of embryo transfer is under debate. Our aim was to explore the relationship between mtDNA copy number in human blastocysts and embryonic development to determine whether mtDNA represents a novel biomarker for the prediction of implantation potential. A total of 246 blastocysts were analyzed by next-generation sequencing. There was no correlation between mtDNA copy number and maternal age in all blastocyst groups and euploid blastocyst groups. Additionally, the mtDNA copy number was not significantly higher in aneuploid blastocysts. Subsequently, no relationship was observed between mtDNA copy number and blastocyst quality. The assessment of clinical pregnancy outcome after the transfer of euploid blastocysts to the uterus indicated that the mtDNA copy number was significantly lower in the clinical pregnancy group than in those who failed implantation. The cut-off value of mtDNA copy number was 320.5, which was a highly predictive value. Blastocysts with an increased mtDNA copy number had lower implantation potential, and mtDNA copy number was largely equal in terms of maternal age, chromosome ploidy, and quality of blastocysts.

Does blastocyst mitochondrial DNA content affect miscarriage rate in patients undergoing single euploid frozen embryo transfer?

PURPOSE

To determine whether the blastocyst mitochondrial DNA (mtDNA) content is related to the miscarriage rate in patients undergoing single euploid frozen embryo transfer (SEFET).

METHODS

A total of 355 single euploid frozen embryo transfer cycles were studied retrospectively between April 2017 and December 2018. A trophectoderm biopsy was performed on day 5/6 blastocysts. Post next-generation sequencing (NGS), the mtDNA content was calculated as the ratio of mitochondrial DNA over nuclear DNA, and the association between blastocyst mtDNA content and miscarriage rate was evaluated.

RESULT(S)

Three hundred fifty-five euploid blastocysts were selected for SEFET in 314 patients with an average age of 33.7 ± 5.6 years; 255 were biopsied on day 5 (71.8%) and 100 on day 6 (28.2%). Frozen embryo transfer (FET) was performed either in a hormone replacement therapy (HRT) cycle (71.8%; n = 255) or in a natural cycle (NC) (28.2%; n = 100). A pregnancy rate of 66.2% (235/355) was obtained with clinical pregnancy and miscarriage rates of 52.4% (n = 186) and 5.6% (n = 20), respectively. There was no significant difference neither between the blastocyst mtDNA content of pregnant and nonpregnant patients (27.7 ± 9.2 vs. 29.4 ± 8.6, P = 0.095) nor between patients with a clinical pregnancy and miscarriage (30.5 ± 9.3 vs. 27.3 ± 9.2, P = 0.136). Multivariate logistic regression analysis showed the same nonsignificant relationship, except for the miscarriage rate and BMI (OR 1.149, 95% CI 1.03-1.28; P = 0.012).

CONCLUSION(S)

Mitochondrial DNA content is unable to predict the miscarriage of implanted human euploid blastocysts.

Coculture of porcine luteal cells during in vitro porcine oocyte maturation affects blastocyst gene expression and developmental potential

Oocyte maturation in culture is still the weakest part of in vitro fertilization (IVF) and coculture with somatic cells may be an alternative to improve suboptimal culture conditions, especially in the pig in which maturation takes more than 44 h. In the present study, we investigated the effect of a coculture system of porcine luteal cells (PLC) during in vitro maturation (IVM) on embryo development and gene expression. Cumulus-oocyte complexes were matured in vitro in TCM-199 with human menopausal gonadotrophin (control) and in coculture with PLC. IVF was performed with frozen-thawed boar semen in Tris-buffered medium. Presumptive zygotes were cultured in PZM for 7 days. The coculture with PLC significantly increased blastocysts rates. Gene expression changes were measured with a porcine embryo-specific microarray and confirmed by RT-qPCR. The global transcription pattern of embryos developing after PLC coculture exhibited overall downregulation of gene expression. Following global gene expression pattern analysis, genes associated with lipid metabolism, mitochondrial function, endoplasmic reticulum stress, and apoptosis were found downregulated, and genes associated with cell cycle and proliferation were found upregulated in the PLC coculture. Canonical pathway analysis by Ingenuity Pathway revealed that differential expression transcripts were associated with the sirtuin signaling pathway, oxidative phosphorylation pathway, cytokines and ephrin receptor signaling. To conclude, the coculture system of PLC during IVM has a lasting effect on the embryo until the blastocyst stage, modifying gene expression, with a positive effect on embryo development. Our model could be an alternative to replace the conventional maturation medium with gonadotrophins with higher rates of embryo development, a key issue in porcine in vitro embryo production.

Extracellular vesicles and domestic animal reproduction

Embryo implantation is a complex process in which significant changes occur continually in both the corpora lutea and in the endometrium of females and which varies depending on the embryonic, pre-implantation, or fetal stages. However, at all stages, correct maternal-embryonic communication is essential. In the last few years, a new intercellular communication tool, mediated by extracellular vesicles (EVs), has emerged. Many authors agree on the relevant role of EVs in correct communication between the mother and the embryo, as a fundamental system for the pregnancy to reach term and embryonic development to occur correctly. This review analyzes current information on known EVs, their main functions, and their role in implantation and embryonic development in domestic animals.

Comparison of Anti-Oxidative Effect of Human Adipose- and Amniotic Membrane-Derived Mesenchymal Stem Cell Conditioned Medium on Mouse Preimplantation Embryo Development

Oxidative stress is a major cause of damage to the quantity and quality of embryos produced in vitro. Antioxidants are usually supplemented to protect embryos from the suboptimal in vitro culture (IVC) environment. Amniotic membrane-derived mesenchymal stem cells (AMSC) have emerged as a promising regenerative therapy, and their paracrine factors with anti-oxidative effects are present in AMSC conditioned medium (CM). We examined the anti-oxidative potential of human AMSC-CM treatment during IVC on mouse preimplantation embryo development and antioxidant gene expression in the forkhead box O (FoxO) pathway. AMSC-CM (10%) was optimal for overall preimplantation embryo developmental processes and upregulated the expression of FoxOs and their downstream antioxidants in blastocysts (BL). Subsequently, compared to adipose-derived mesenchymal stem cell (ASC)-CM, AMSC-CM enhanced antioxidant gene expression and intracellular GSH levels in the BL. Total antioxidant capacity and SOD activity were greater in AMSC-CM than in ASC-CM. Furthermore, SOD and catalase were more active in culture medium supplemented with AMSC-CM than in ASC-CM. Lastly, the anti-apoptotic effect of AMSC-CM was observed with the regulation of apoptosis-related genes and mitochondrial membrane potential in BL. In conclusion, the present study established AMSC-CM treatment at an optimal concentration as a novel antioxidant intervention for assisted reproduction.

Development of Decellularized Oviductal Hydrogels as a Support for Rabbit Embryo Culture

The oviducts (fallopian tubes in mammals) function as the site of fertilization and provide necessary support for early embryonic development, mainly via embryonic exposure to the tubal microenvironment. The main objective of this study was to create an oviduct-specific extracellular matrix (oviECM) hydrogel rich in bioactive components that mimics the native environment, thus optimizing the developmental trajectories of cultured embryos. Rabbit oviducts were decellularized through SDS treatment and enzymatic digestion, and the acellular tissue was converted into oviductal pre-gel extracellular matrix (ECM) solutions. Incubation of these solutions at 37 °C resulted in stable hydrogels with a fibrous structure based on scanning electron microscopy. Histological staining, DNA quantification and colorimetric assays confirmed that the decellularized tissue and hydrogels contained no cellular or nuclear components but retained important components of the ECM, e.g. hyaluronic acid, glycoproteins and collagens. To evaluate the ability of oviECM hydrogels to maintain early embryonic development, two-cell rabbit embryos were cultured on oviECM-coated surfaces and compared to those cultured with standard techniques. Embryo development was similar in both conditions, with 95.9% and 98% of the embryos reaching the late morula/early blastocyst stage by 48 h under standard culture and oviECM conditions, respectively. Metabolomic analysis of culture media in the presence or absence of embryos, however, revealed that the oviECM coating may include signalling molecules and release compounds beneficial to embryo metabolism.

Glucose metabolism characterization during mouse in vitro maturation identifies alterations in cumulus cells†

In vitro maturation (IVM) is an assisted reproduction technique with reduced hormone-related side-effects. Several attempts to implement IVM in routine practice have failed, primarily due to its relatively low efficiency compared with conventional in vitro fertilization (IVF). Recently, capacitation (CAPA)-IVM-a novel two-step IVM method-has improved the embryology outcomes through synchronizing the oocyte nuclear and cytoplasmic maturation. However, the efficiency gap between CAPA-IVM and conventional IVF is still noticeable especially in the numerical production of good quality embryos. Considering the importance of glucose for oocyte competence, its metabolization is studied within both in vivo and CAPA-IVM matured mouse cumulus-oocyte-complexes (COCs) through direct measurements in both cellular compartments, from transcriptional and translational perspectives, to reveal metabolic shortcomings within the CAPA-IVM COCs. These results confirmed that within in vivo COC, cumulus cells (CCs) are highly glycolytic, whereas oocytes, with low glycolytic activity, are deviating their glucose towards pentose phosphate pathway. No significant differences were observed in the CAPA-IVM oocytes compared with their in vivo counterparts. However, their CCs exhibited a precocious increase of glycolytic activity during the pre-maturation culture step and activity was decreased during the IVM step. Here, specific alterations in mouse COC glucose metabolism due to CAPA-IVM culture were characterized using direct measurements for the first time. Present data show that, while CAPA-IVM CCs are able to utilize glucose, their ability to support oocytes during final maturation is impaired. Future CAPA-IVM optimization strategies could focus on adjusting culture media energy substrate concentrations and/or implementing co-culture strategies.

Altered embryotrophic capacities of the bovine oviduct under elevated free fatty acid conditions: an in vitro embryo--oviduct co-culture model

Maternal metabolic stress conditions are of growing importance in both human and dairy cattle settings as they can have significant repercussions on fertility. Upregulated lipolysis is a common trait associated with metabolic disorders and results in systemically elevated concentrations of non-esterified fatty acids (NEFAs). The effects of high NEFA concentrations on the follicular environment, oocyte and embryo development is well documented. However, knowledge on the effects of NEFAs within the oviduct, representing the initial embryonic growth environment, is currently lacking. Therefore, the experiments outlined here were designed to obtain fundamental insights into both the direct and indirect interactions between NEFAs, bovine oviductal cells and developing zygotes. Hence, zygotes were co-cultured with NEFA-pre-exposed bovine oviductal cells or subjected to simultaneous NEFA exposure during the co-culture period. The outcome parameters assessed were embryo development with cleavage (48h post insemination (pi)), morula (120-126h pi) and blastocyst (192h pi) rates, as well as morula intracellular lipid content and blastocyst quality using Bodipy and differential staining respectively. Our data suggest a direct embryotoxicity of NEFAs as well as impaired embryo development through a reduced oviductal ability to support and protect early embryo development.

The Impact of Unbalanced Maternal Nutritional Intakes on Oocyte Mitochondrial Activity: Implications for Reproductive Function

Accumulating evidence on the effect of nutrition on reproduction is emerging from both animal and human studies. A healthy dietary pattern and nutrient supplementation, especially during the peri-conceptional period, might be helpful to achieve a live birth, although the mechanisms implicated are not fully understood. The endocrine system and the ooplasmic organelles apparatus, in particular the mitochondria, are clearly key elements during oogenesis and subsequent embryo development, and their proper functioning is associated with nutrition, even beyond maternal aging. Several studies in animal models have reported various adverse effects on mitochondria caused by unbalanced dietary intakes such as high fat diet, high fat high sugar diet, and low protein diet. The alterations produced might include mitochondrial intracellular distribution, content, structure, biogenesis, and functioning. This review summarizes the key role of mitochondria in female reproduction and the effects of different dietary macronutrient compositions on oocyte mitochondrial activity with their possible short-, medium-, and long-term effects.

Identifying biomarkers for predicting successful embryo implantation: applying single to multi-OMICs to improve reproductive outcomes

BACKGROUND

Successful embryo implantation is a complex process that requires the coordination of a series of events, involving both the embryo and the maternal endometrium. Key to this process is the intricate cascade of molecular mechanisms regulated by endocrine, paracrine and autocrine modulators of embryonic and maternal origin. Despite significant progress in ART, implantation failure still affects numerous infertile couples worldwide and fewer than 10% of embryos successfully implant. Improved selection of both the viable embryos and the optimal endometrial phenotype for transfer remains crucial to enhancing implantation chances. However, both classical morphological embryo selection and new strategies incorporated into clinical practice, such as embryonic genetic analysis, morphokinetics or ultrasound endometrial dating, remain insufficient to predict successful implantation. Additionally, no techniques are widely applied to analyse molecular signals involved in the embryo-uterine interaction. More reliable biological markers to predict embryo and uterine reproductive competence are needed to improve pregnancy outcomes. Recent years have seen a trend towards 'omics' methods, which enable the assessment of complete endometrial and embryonic molecular profiles during implantation. Omics have advanced our knowledge of the implantation process, identifying potential but rarely implemented biomarkers of successful implantation.

OBJECTIVE AND RATIONALE

Differences between the findings of published omics studies, and perhaps because embryonic and endometrial molecular signatures were often not investigated jointly, have prevented firm conclusions being reached. A timely review summarizing omics studies on the molecular determinants of human implantation in both the embryo and the endometrium will help facilitate integrative and reliable omics approaches to enhance ART outcomes.

SEARCH METHODS

In order to provide a comprehensive review of the literature published up to September 2019, Medline databases were searched using keywords pertaining to omics, including 'transcriptome', 'proteome', 'secretome', 'metabolome' and 'expression profiles', combined with terms related to implantation, such as 'endometrial receptivity', 'embryo viability' and 'embryo implantation'. No language restrictions were imposed. References from articles were also used for additional literature.

OUTCOMES

Here we provide a complete summary of the major achievements in human implantation research supplied by omics approaches, highlighting their potential to improve reproductive outcomes while fully elucidating the implantation mechanism. The review highlights the existence of discrepancies among the postulated biomarkers from studies on embryo viability or endometrial receptivity, even using the same omic analysis.

WIDER IMPLICATIONS

Despite the huge amount of biomarker information provided by omics, we still do not have enough evidence to link data from all omics with an implantation outcome. However, in the foreseeable future, application of minimally or non-invasive omics tools, together with a more integrative interpretation of uniformly collected data, will help to overcome the difficulties for clinical implementation of omics tools. Omics assays of the embryo and endometrium are being proposed or already being used as diagnostic tools for personalised single-embryo transfer in the most favourable endometrial environment, avoiding the risk of multiple pregnancies and ensuring better pregnancy rates.

Equine blastocyst production under different incubation temperatures and different CO2 concentrations during early cleavage

Some basic parameters for equine invitro embryo production have not yet been established, including the optimum temperature for maturation and embryo culture, and the optimum CO2 concentration and pH during early embryo development. To explore this, we first performed cultures in incubators set at 37.2°C, 37.7°C or 38.2°C. At these temperatures, the corresponding maturation rates were 33%, 38% and 42%; cleavage rates were 84%, 86% and 88%; and blastocyst rates were 35%, 44% and 44% per injected oocyte. These rates did not differ significantly (P>0.2). We then evaluated three different CO2 concentrations (6%, 6.5% or 7% CO2) in 5% O2 for culture over Days 0-5 after intracytoplasmic sperm injection, using a commercial human embryo medium with added serum, at 38.2°C. The pH values of these media were 7.36, 7.33 and 7.29 respectively. In the presence of 6%, 6.5% or 7% CO2, cleavage rates were 68%, 80% and 70% respectively, and blastocyst rates per injected oocyte were 42%, 54% and 27% respectively. The blastocyst rate for the 7% CO2 treatment was significantly lower than that for the 6.5% CO2 treatment (P<0.05). We conclude that equine invitro embryo production is equally effective within the range of 37.2-38.2°C, but that equine early cleavage stage development is sensitive to small changes in CO2 atmosphere and/or medium pH.

The dynamics between in vitro culture and metabolism: embryonic adaptation to environmental changes

Previous studies have discussed the importance of an optimal range of metabolic activity during preimplantation development. To avoid factors than can trigger an undesirable trajectory, it is important to learn how nutrients and metabolites interact to help launching the correct developmental program of the embryo, and how much the in vitro culture system can impair this process. Here, using the bovine model, we describe a factorial experimental design used to investigate the biochemical and molecular signature of embryos in response to different combinations of morphological features—i.e. speed of development—and external stimuli during in vitro culture—i.e. different oxygen tensions and glucose supplementation. Our analyses demonstrate that the embryos present heterogeneous metabolic responses depending on early morphological phenotypes and the composition of their surroundings. However, despite the contribution of each single stimulus for the embryo phenotype, oxygen tension is determinant for such differences. The lower oxygen environment boosts the metabolism of embryos with faster kinetics, in particular those cultured in lower glucose concentrations.

Inhibiting diacylglycerol acyltransferase-1 reduces lipid biosynthesis in bovine blastocysts produced in vitro

Diacylglycerol acyltransferase-1 (DGAT1) is one of the DGAT enzymes that catalyzes the final step in the synthesis of triacylglycerol, which is a major component of the lipid droplets in embryos. Intracellular lipids accumulated in embryos produced in vitro have been associated with reduced cryotolerance and quality. The objective of the present study was to investigate the influence of DGAT1 inhibition on embryo development, quality, and post-vitrification survival, in addition to expression profiles of selected lipid metabolism-regulating and oxidative stress genes. Bovine cumulus-oocyte complexes were matured and fertilized in vitro and were cultured in synthetic oviduct fluid (SOF) supplemented with 5% fetal calf serum (FCS) alone (Control) or with 1, 5, 10 or 50 μM DGAT1 inhibitor (A922500®; D1, D5, D10, and D50, respectively) or 0.1% dimethyl sulfoxide (CDMSO: vehicle for DGAT1 inhibitor dilution) from 54 h post-insemination until Day 8 post insemination. No differences were found in blastocyst yield on days 7 and 8 in Control, CDMSO, D10, and D50 groups. Embryos cultured with 10 or 50 μM DGAT1 inhibitor had greater mitochondrial activity (P < 0.01), and increased number of cells (P < 0.05), while the cytoplasmic lipid content was reduced (P < 0.01), the latter associated with altered expression profiles of selected genes regulating lipid metabolism or genes related with oxidative stress (transcript abundance increased for SLC2A1 and SLC2A5 and decreased for DGAT1 and GPX1). Importantly, the survival rate of blastocysts produced with 10 μM DGAT1 was higher than that of Control, CDMSO and D50 groups at 72 h after vitrification and warming (73.8 vs 57.1, 55.9 and 56.1%, respectively, P < 0.001). In conclusion, inhibition of DGAT1 synthesis in bovine embryos produced in vitro abrogates the negative effect of FCS by decreasing their lipid content, increasing mitochondria activity and improving embryo cryotolerance, as well as favoring the expression of lipid metabolism regulating and oxidative stress-related transcripts.

Repeated hyperstimulation affects the ultrastructure of mouse fallopian tube epithelium

Controlled ovarian hyperstimulation (COH) is routinary used in assisted reproductive technologies (ARTs) to increase the yields of mature oocytes. The possibility that patients with a history of failures or poor-responders may develop side-effects following these treatments is still debated. Epidemiological studies reported controversial results about pregnancy outcome and the risk of developing gynecological cancers. By using a mouse model, here we compared the ultrastructural features of fallopian tubes (FTs) obtained from mice undergoing or not (control, CTR) four (4R) and eight (8R) rounds of gonadotropin stimulation. Although the morphological characteristics of oviductal layers seemed unaffected by repeated treatments, dose-response ultrastructural alterations in the ampulla appeared in the 4R group and even more in the 8R group. The targets were oviductal ciliated (CCs) and non-ciliated (NCCs) cells, which showed damaged mitochondria and glycogen accumulations in the cytoplasm. The drastic reduction of CCs, evident after 4R, was supported by the absence of cilia. After 8R, glycogen granules were significantly reduced and massive degeneration of mitochondria, which appeared swollen and/or vacuolated, occurred in NCCs. Moreover, disintegrated mitochondria were found at the periphery of mitophagic vacuoles with evident signs of cristolysis. The morphometric analysis evidenced a significant increase in the density and frequency of damaged mitochondria after 4R and 8R. The absence of cilia, necessary to sustain oviductal transport of oocytes, spermatozoa and embryos, may originate from either mitochondrial dysfunction or glycogen consumption. These results suggest that repeated COH treatments could induce alterations impairing fertilization and embryo transport toward the uterus.

Butaphosphan Effects on Glucose Metabolism Involve Insulin Signaling and Depends on Nutritional Plan

Butaphosphan is an organic phosphorus compound used in several species for the prevention of rapid catabolic states, however, the mechanism of action remains unclear. This study aimed at determining the effects of butaphosphan on energy metabolism of mice receiving a normal or hypercaloric diet (HCD) and submitted or not to food restriction. Two experiments were conducted: (1) during nine weeks, animals were fed with HCD (n = 28) ad libitum, and at the 10th week, were submitted to food restriction and received butaphosphan (n = 14) or saline injections (n = 14) (twice a day, for seven days) and; (2) during nine weeks, animals were fed with a control diet (n = 14) or HCD (n = 14) ad libitum, and at the 10th week, all animals were submitted to food restriction and received butaphosphan or saline injections (twice a day, for seven days). In food restriction, butaphosphan preserved epididymal white adipose tissue (WAT) mass, increased glucose, NEFA, and the HOMA index. In mice fed HCD and submitted to food restriction, the butaphosphan preserved epididymal WAT mass. Control diet influences on PI3K, GCK, and Irs1 mRNA expression. In conclusion, butaphosphan increased blood glucose and reduced fat mobilization in overweight mice submitted to caloric restriction, and these effects are influenced by diet.