Selected Amino Acids Promote Mouse Pre-implantation Embryo Development in a Growth Factor-Like Manner

Testicular Toxicity in Rats Exposed to AlCl3: a Proteomics Study

Aluminum contamination is a growing environmental and public health concern, and aluminum testicular toxicity has been reported in male rats; however, the underlying mechanisms of this toxicity are unclear. The objective of this study was to investigate the effects of exposure to aluminum chloride (AlCl3) on alterations in the levels of sex hormones (testosterone [T], luteinizing hormone [LH], and follicle-stimulating hormone [FSH]) and testicular damage. Additionally, the mechanisms of toxicity in the testes of AlCl3-exposed rats were analyzed by proteomics. Three different concentrations of AlCl3 were administered to rats. The results demonstrated a decrease in T, LH, and FSH levels with increasing concentrations of AlCl3 exposure. HE staining results revealed that the spermatogenic cells in the AlCl3-exposed rats were widened, disorganized, or absent, with increased severe tissue destruction at higher concentrations of AlCl3 exposure. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses revealed that differentially expressed proteins (DEPs) after AlCl3 exposure were primarily associated with various metabolic processes, sperm fibrous sheath, calcium-dependent protein binding, oxidative phosphorylation, and ribosomes. Subsequently, DEPs from each group were subjected to protein-protein interaction (PPI) analysis followed by the screening of interactional key DEPs. Western blot experiments validated the proteomics data, revealing the downregulation of sperm-related DEPs (AKAP4, ODF1, and OAZ3) and upregulation of regulatory ribosome-associated protein (UBA52) and mitochondrial ribosomal protein (MRPL32). These findings provide a basis for studying the mechanism of testicular toxicity due to AlCl3 exposure.

Arginine with leucine drives reactive oxygen species-mediated integrin α5β1 expression and promotes implantation in mouse blastocysts

The implantation rate of in vitro fertilization (IVF)-derived blastocysts after embryo transfer remains low, suggesting that the inadequate expression of specific proteins in culture-induced IVF-derived blastocysts contributes to low implantation rates. Therefore, treatment with appropriate regulation may improve the blastocyst implantation ability. This study demonstrated that the combination of l-arginine (Arg) and l-leucine (Leu) exerts distinct effects on IVF-derived mouse blastocysts. Arg with Leu promotes blastocyst implantation, whereas Arg alone decreases the blastocyst ability. Integrin α5β1 expression was increased in blastocysts treated with Arg and Leu. Arg with Leu also increased reactive oxygen species (ROS) levels and showed a positive correlation with integrin α5β1. Ascorbic acid, an antioxidant, decreased ROS and integrin α5β1 levels, which were elevated by Arg with Leu. Meanwhile, the mitochondrial membrane potential (ΔΨm) in blastocysts did not differ between treatments. Glutathione peroxidase (GPx) is involved in ROS scavenging using glutathione (GSH) as a reductant. Arg with Leu decreased GPx4 and GSH levels in blastocysts, and blastocysts with higher ROS levels had lower GPx4 and GSH levels. In contrast, Arg alone increased the percentage of caspase-positive cells, indicating that Arg alone, which attenuated implantation ability, was associated with apoptosis. This study revealed that elevated ROS levels induced by Arg with Leu stimulated integrin α5β1 expression, thereby enhancing implantation capacity. Our results also suggest that ROS were not due to increased production by oxidative phosphorylation, but rather to a reduction in ROS degradation due to diminished GPx4 and GSH levels.

Osmolar Modulation Drives Reversible Cell Cycle Exit and Human Pluripotent Cell Differentiation via NF-κВ and WNT Signaling

Terminally differentiated cells are commonly regarded as the most stable cell state in adult organisms, characterized by growth arrest while fulfilling their specialized functions. A better understanding of the mechanisms involved in promoting cell cycle exit will improve the ability to differentiate pluripotent cells into mature tissues for both pharmacological and therapeutic use. Here, it demonstrates that a hyperosmolar environment enforces a protective p53-independent quiescent state in immature hepatoma cells and in pluripotent stem cell-derived models of human hepatocytes and endothelial cells. Prolonged culture in hyperosmolar conditions stimulates changes in gene expression promoting functional cell maturation. Interestingly, hyperosmolar conditions do not only trigger growth arrest and cellular maturation but are also necessary to maintain this maturated state, as switching back to plasma osmolarity reverses the changes in expression of maturation and proliferative markers. Transcriptome analysis revealed sequential stages of osmolarity-regulated growth arrest followed by cell maturation, mediated by activation of NF-κВ, and repression of WNT signaling, respectively. This study reveals that a modulated increase in osmolarity serves as a biochemical signal to promote long-term growth arrest and cellular maturation into different lineages, providing a practical method to generate differentiated hiPSCs that resemble their mature counterpart more closely.

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.

Signalling pathway crosstalk stimulated by L-proline drives mouse embryonic stem cells to primitive-ectoderm-like cells

The amino acid L-proline exhibits growth factor-like properties during development - from improving blastocyst development to driving neurogenesis in vitro. Addition of 400 μM L-proline to self-renewal medium drives naïve mouse embryonic stem cells (ESCs) to early primitive ectoderm-like (EPL) cells - a transcriptionally distinct primed or partially primed pluripotent state. EPL cells retain expression of pluripotency genes, upregulate primitive ectoderm markers, undergo a morphological change and have increased cell number. These changes are facilitated by a complex signalling network hinging on the Mapk, Fgfr, Pi3k and mTor pathways. Here, we use a factorial experimental design coupled with statistical modelling to understand which signalling pathways are involved in the transition between ESCs and EPL cells, and how they underpin changes in morphology, cell number, apoptosis, proliferation and gene expression. This approach reveals pathways which work antagonistically or synergistically. Most properties were affected by more than one inhibitor, and each inhibitor blocked specific aspects of the naïve-to-primed transition. These mechanisms underpin progression of stem cells across the in vitro pluripotency continuum and serve as a model for pre-, peri- and post-implantation embryogenesis.

Metabolomic Profiling of Female Mink Serum during Early to Mid-Pregnancy to Reveal Metabolite Changes

Mink embryos enter a period of diapause after the embryo develops into the blastocyst, and its reactivation is mainly caused by an increase in polyamine. The specific process of embryo diapause regulation and reactivation remains largely unexamined. This study aimed to identify changes in metabolites in the early pregnancy of mink by comparing and analyzing in serum metabolites up to twenty-nine days after mating. Blood samples were taken on the first day of mating, once a week until the fifth week. Metabolomic profiles of the serum samples taken during this period were analyzed by ultra-performance liquid chromatography/mass spectrometry. Multivariate statistical analyses identified differential metabolite expression at different time points in both positive and negative ion modes. The levels of dopamine, tyramine, L-phenylalanine, L-tyrosine, tyrosine, L-kynurenine, L-lysine, L-arginine, D-ornithine, and leucine changed significantly. These metabolites may be associated with the process of embryo diapause and subsequent reactivation.

Molecular and Clinical Advances in Understanding Early Embryo Development

The articles in this Special Issue address a wide variety of topics concerning molecular and clinical advances in understanding early embryo development [...].

Glutamine, proline, and isoleucine support maturation and fertilisation of bovine oocytes

Successful in-vitro production of bovine embryos relies on meiotic maturation of oocytes in vitro (IVM) before they can be fertilised. High levels of IVM are currently achieved using a complex medium that contains all 20 common amino acids, namely TCM199, but can also be achieved using a simple inorganic salt solution containing non-essential amino acids, proline, and glutamine. Further simplification of the amino acid content of medium used for IVM could lead to a more defined medium that provides reproducible IVM. The aim of this study was, therefore, to determine the minimal amino acid requirements for bovine oocyte nuclear maturation, as measured by progression to metaphase II (MII) of meiosis. Supplementation of a simple medium composed of inorganic salts (M1 medium) with multiple amino-acid combinations showed that M1 containing glutamine, proline, and isoleucine resulted in nuclear maturation comparable to that of TCM199 (57.4 ± 3.4% vs 67% ± 1.7%, respectively) but was reduced when cystine (Cys2) to that seen with M1 alone (38.0 ± 2.2%). Viability of oocytes matured in this simplified medium was equal to those matured in TCM199 since the same proportion of zygotes with 2 pronuclei were observed following fertilisation in medium containing no amino acids (33.9 ± 6.5% vs 33.3 ± 3.6%, respectively). Addition of glutamine, proline and isoleucine to fertilisation medium also increased the proportion of zygotes but did not increase blastocyst development rates. Thus, a defined medium containing only glutamine, proline and isoleucine is sufficient for oocyte maturation and successful fertilisation.

Stage-Specific L-Proline Uptake by Amino Acid Transporter Slc6a19/B0AT1 Is Required for Optimal Preimplantation Embryo Development in Mice

L-proline (Pro) has previously been shown to support normal development of mouse embryos. Recently we have shown that Pro improves subsequent embryo development when added to fertilisation medium during in vitro fertilisation of mouse oocytes. The mechanisms by which Pro improves embryo development are still being elucidated but likely involve signalling pathways that have been observed in Pro-mediated differentiation of mouse embryonic stem cells. In this study, we show that B⁰AT1, a neutral amino acid transporter that accepts Pro, is expressed in mouse preimplantation embryos, along with the accessory protein ACE2. B⁰AT1 knockout (Slc6a19^-/-) mice have decreased fertility, in terms of litter size and preimplantation embryo development in vitro. In embryos from wild-type (WT) mice, excess unlabelled Pro inhibited radiolabelled Pro uptake in oocytes and 4-8-cell stage embryos. Radiolabelled Pro uptake was reduced in 4-8-cell stage embryos, but not in oocytes, from Slc6a19^-/- mice compared to those from WT mice. Other B⁰AT1 substrates, such as alanine and leucine, reduced uptake of Pro in WT but not in B⁰AT1 knockout embryos. Addition of Pro to culture medium improved embryo development. In WT embryos, Pro increased development to the cavitation stage (on day 4); whereas in B⁰AT1 knockout embryos Pro improved development to the 5-8-cell (day 3) and blastocyst stages (day 6) but not at cavitation (day 4), suggesting B⁰AT1 is the main contributor to Pro uptake on day 4 of development. Our results highlight transporter redundancy in the preimplantation embryo.

Insulin-like Growth Factor Binding Protein 3 Increases Mouse Preimplantation Embryo Cleavage Rate by Activation of IGF1R and EGFR Independent of IGF1 Signalling

The viability of embryos cultured in vitro is poor compared to those that develop in vivo. The lack of maternally derived growth factors in vitro may contribute to this problem. Insulin-like growth factor binding protein 3 (IGFBP3) is one such growth factor that has been identified in the maternal reproductive system. This study examined the role of autocrine and exogenous IGFBP3 in mouse preimplantation embryos. Embryos expressed IGFBP3 across all stages of preimplantation development, and addition of exogenous IGFBP3 to embryo culture media increased the rate of development to the 2-, 4-, 5-, and 8-cell stages. Addition of inhibitors of the IGF1 and EGF receptors prevented this IGFBP3-mediated improvement in developmental rate, but the effect was not cumulative, indicating that both receptors are transactivated downstream of IGFBP3 as part of the same signalling pathway. Acute exposure to IGFBP3 increased phosphorylation of Akt and rps6 in 4-8 cell embryos, suggesting activation of the PI3-kinase/Akt pathway downstream of the IGF1 and EGFR receptors to promote cell proliferation and survival. In conclusion, addition of IGFBP3 to embryo culture media increases early cleavage rates independent of IGF1 signalling and therefore, IGFBP3 addition to IVF culture media should be considered.

Leucine and Arginine Availability Modulate Mouse Embryonic Stem Cell Proliferation and Metabolism

Amino acids are crucial nutrients involved in several cellular and physiological processes, including fertilization and early embryo development. In particular, Leucine and Arginine have been shown to stimulate implantation, as lack of both in a blastocyst culture system is able to induce a dormant state in embryos. The aim of this work was to evaluate the effects of Leucine and Arginine withdrawal on pluripotent mouse embryonic stem cell status, notably, their growth, self-renewal, as well as glycolytic and oxidative metabolism. Our results show that the absence of both Leucine and Arginine does not affect mouse embryonic stem cell pluripotency, while reducing cell proliferation through cell-cycle arrest. Importantly, these effects are not related to Leukemia Inhibitory Factor (LIF) and are reversible when both amino acids are reconstituted in the culture media. Moreover, a lack of these amino acids is related to a reduction in glycolytic and oxidative metabolism and decreased protein translation in mouse embryonic stem cells (mESCs), while maintaining their pluripotent status.

Glutamate can act as a signaling molecule in mouse preimplantation embryos

Free amino acids are present in the natural environment of the preimplantation embryo, and their availability can influence early embryo development. Glutamic acid is one of the amino acids with highest concentrations in female reproductive fluids, and we investigated whether glutamic acid/glutamate can affect preimplantation embryo development by acting through cell membrane receptors. Using RT-PCR, we detected 15 ionotropic glutamate receptor transcripts and 8 metabotropic glutamate receptor transcripts in mouse ovulated oocytes and/or in vivo developed blastocysts. Using immunohistochemistry, we detected expression of two AMPA receptor subunits, three kainate receptor subunits and member 5 metabotropic glutamate receptor protein in blastocysts. Extracellular concentrations of glutamic acid starting at 5 mM impaired mouse blastocyst development, and this fact may be of great practical importance since glutamic acid and its salts (mainly monosodium glutamate) are widely used as food additives. Experiments with glutamate receptor agonists (in combination with gene expression analysis) revealed that specific AMPA receptors (formed from GRIA3 and/or GRIA4 subunits), kainate receptors (formed from GRIK 3 and GRIK 4 or GRIK 5 subunits) and GRM5 glutamate receptor were involved in this effect. The glutamic acid-induced effects were prevented or reduced by pre-treatment of blastocysts with AMPA, kainate and GRM5 receptor antagonists, further confirming the involvement of these receptor types. Our results show that glutamic acid can act as a signaling molecule in preimplantation embryos, exerting its effects through activation of cell membrane receptors.

L-Proline Supplementation Drives Self-Renewing Mouse Embryonic Stem Cells to a Partially Primed Pluripotent State: The Early Primitive Ectoderm-Like Cell

Mouse embryonic stem cells (mESCs) can be grown under a variety of culture conditions as discrete cell states along the pluripotency continuum, ranging from the least mature "ground state" to being "primed" to differentiate. Cells along this continuum are demarcated by differences in gene expression, X chromosome inactivation, ability to form chimeras and epigenetic marks. We have developed a protocol to differentiate "naïve" mESCs to a "partially primed" state by adding the amino acid L-proline to self-renewal medium. These cells express the primitive ectoderm markers Dnmt3b and Fgf5, and are thus called early primitive ectoderm-like (EPL) cells. In addition to changes in gene expression, these cells undergo a morphological change to flattened, dispersed colonies, have an increased proliferation rate, and a predisposition to neural fate. EPL cells can be used to study the cell states along the pluripotency continuum, peri-implantation embryogenesis, and as a starting point for efficient neuronal differentiation.

Epigenetic Modifications at the Center of the Barker Hypothesis and Their Transgenerational Implications

Embryo/fetal nutrition and the environment in the reproductive tract influence the subsequent risk of developing adult diseases and disorders, as formulated in the Barker hypothesis. Metabolic syndrome, obesity, heart disease, and hypertension in adulthood have all been linked to unwanted epigenetic programing in embryos and fetuses. Multiple studies support the conclusion that environmental challenges, such as a maternal low-protein diet, can change one-carbon amino acid metabolism and, thus, alter histone and DNA epigenetic modifications. Since histones influence gene expression and the program of embryo development, these epigenetic changes likely contribute to the risk of adult disease onset not just in the directly affected offspring, but for multiple generations to come. In this paper, we hypothesize that the effects of parental nutritional status on fetal epigenetic programming are transgenerational and warrant further investigation. Numerous studies supporting this hypothesis are reviewed, and potential research techniques to study these transgenerational epigenetic effects are offered.

Amino Acid Transport and Metabolism Regulate Early Embryo Development: Species Differences, Clinical Significance, and Evolutionary Implications

In this review we discuss the beneficial effects of amino acid transport and metabolism on pre- and peri-implantation embryo development, and we consider how disturbances in these processes lead to undesirable health outcomes in adults. Proline, glutamine, glycine, and methionine transport each foster cleavage-stage development, whereas leucine uptake by blastocysts via transport system B^0,+ promotes the development of trophoblast motility and the penetration of the uterine epithelium in mammalian species exhibiting invasive implantation. (Amino acid transport systems and transporters, such as B^0,+, are often oddly named. The reader is urged to focus on the transporters’ functions, not their names.) B^0,+ also accumulates leucine and other amino acids in oocytes of species with noninvasive implantation, thus helping them to produce proteins to support later development. This difference in the timing of the expression of system B^0,+ is termed heterochrony—a process employed in evolution. Disturbances in leucine uptake via system B^0,+ in blastocysts appear to alter the subsequent development of embryos, fetuses, and placentae, with undesirable consequences for offspring. These consequences may include greater adiposity, cardiovascular dysfunction, hypertension, neural abnormalities, and altered bone growth in adults. Similarly, alterations in amino acid transport and metabolism in pluripotent cells in the blastocyst inner cell mass likely lead to epigenetic DNA and histone modifications that produce unwanted transgenerational health outcomes. Such outcomes might be avoided if we learn more about the mechanisms of these effects.

Redox Regulation and Oxidative Stress in Mammalian Oocytes and Embryos Developed In Vivo and In Vitro

Oocytes and preimplantation embryos require careful regulation of the redox environment for optimal development both in vivo and in vitro. Reactive oxygen species (ROS) are generated throughout development as a result of cellular metabolism and enzyme reactions. ROS production can result in (i) oxidative eustress, where ROS are helpful signalling molecules with beneficial physiological functions and where the redox state of the cell is maintained within homeostatic range by a closely coupled system of antioxidants and antioxidant enzymes, or (ii) oxidative distress, where excess ROS are deleterious and impair normal cellular function. in vitro culture of embryos exacerbates ROS production due to a range of issues including culture-medium composition and laboratory culture conditions. This increase in ROS can be detrimental not only to assisted reproductive success rates but can also result in epigenetic and genetic changes in the embryo, resulting in transgenerational effects. This review examines the effects of oxidative stress in the oocyte and preimplantation embryo in both the in vivo and in vitro environment, identifies mechanisms responsible for oxidative stress in the oocyte/embryo in culture and approaches to reduce these problems, and briefly examines the potential impacts on future generations.

The Multifaceted Roles of Proline in Cell Behavior

Herein, we review the multifaceted roles of proline in cell biology. This peculiar cyclic imino acid is: (i) A main precursor of extracellular collagens (the most abundant human proteins), antimicrobial peptides (involved in innate immunity), salivary proteins (astringency, teeth health) and cornifins (skin permeability); (ii) an energy source for pathogenic bacteria, protozoan parasites, and metastatic cancer cells, which engage in extracellular-protein degradation to invade their host; (iii) an antistress molecule (an osmolyte and chemical chaperone) helpful against various potential harms (UV radiation, drought/salinity, heavy metals, reactive oxygen species); (iv) a neural metabotoxin associated with schizophrenia; (v) a modulator of cell signaling pathways such as the amino acid stress response and extracellular signal-related kinase pathway; (vi) an epigenetic modifier able to promote DNA and histone hypermethylation; (vii) an inducer of proliferation of stem and tumor cells; and (viii) a modulator of cell morphology and migration/invasiveness. We highlight how proline metabolism impacts beneficial tissue regeneration, but also contributes to the progression of devastating pathologies such as fibrosis and metastatic cancer.

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.

Different response of embryos originating from control and obese mice to insulin in vitro

The aim of the present work was to investigate the impact of maternal obesity on DNA methylation in ovulated oocytes, and to compare the response of in vitro-developing preimplantation embryos originating from control and obese mice to insulin. An intergenerational, diet-induced obesity model was used to produce outbred mice with an increased body weight and body fat. Two-cell and eight-cell embryos recovered from obese and control mice were cultured in a medium supplemented with 1 or 10 ng/ml insulin until blastocyst formation. In the derived blastocysts, cell proliferation, differentiation, and death rates were determined. The results of immunochemical visualization of 5-methylcytosine indicated a slightly higher DNA methylation in ovulated metaphase II oocytes recovered from obese females; however, the difference between groups did not reach statistical significance. Expanded blastocysts developed from embryos provided by control dams showed increased mean cell numbers (two and eight-cell embryos exposed to 10 ng/ml), an increased inner-cell-mass/trophectoderm ratio (two-cell embryos exposed to 1 ng/ml and eight-cell embryos exposed to 10 ng/ml), and a reduced level of apoptosis (two and eight-cell embryos exposed to 10 ng/ml). In contrast, embryos originating from obese mice were significantly less sensitive to insulin; indeed, no difference was recorded in any tested variable between the embryos exposed to insulin and those cultured in insulin-free medium. Real-time RT-PCR analysis showed a significant increase in the amount of insulin receptor transcripts in blastocysts recovered from obese dams. These results suggest that maternal obesity might modulate the mitogenic and antiapoptotic responses of preimplantation embryos to insulin.

Perspective: One-Cell and Cleavage-Stage Mouse Embryos Thrive in Hyperosmotic Oviductal Fluid Through Expression of a Glycine Neurotransmitter Transporter and a Glycine-Gated Chloride Channel: Clinical and Transgenerational Implications

The osmolality of mouse oviductal fluid ranges from about 300 mOsmol/kg in the ampulla 0–3 h post coitus (h p.c.) to more than 350 mOsmol/kg in the isthmus 34–36 h p.c. Thus, it has been surprising to find that development of one-cell and cleavage-stage mouse embryos arrests in vitro in media exceeding 300 mOsmol/kg, and they develop best in unphysiological, hypotonic media. The glycine concentration in oviductal fluid can, however, rescue development in hypertonic media, so physiological conditions in vivo and in vitro likely work together to foster embryo well-being. Glycine acts on one-cell and cleavage-stage mouse embryos through the glycine-gated chloride channel, GLRA4, and uptake via the glycine neurotransmitter transporter, GLYT1. Since these processes lead to further signaling in neurons, the presence and function of such signaling in preimplantation embryos also should be investigated. The more we know about the interactions of physiological processes and conditions in vivo, the better we would be able to reproduce them in vitro. Such improvements in assisted reproductive technology (ART) could improve patient outcomes for IVF and potentially help prevent unwanted developmental abnormalities in early embryos, which might include undesirable epigenetic DNA and histone modifications. These epigenetic modifications may lead to transgenerational adult disorders such as metabolic syndrome and related conditions.

Non-Invasive Human Embryo Metabolic Assessment as a Developmental Criterion

The selection of a highly-viable single embryo in assisted reproductive technology requires an acceptable predictive method in order to reduce the multiple pregnancy rate and increase the success rate. In this study, the metabolomic profiling of growing and impaired embryos was assessed on the fifth day of fertilization using capillary electrophoresis in order to find a relationship between the profiling and embryo development, and then to provide a mechanistic insight into the appearance/depletion of the metabolites. This unique qualitative technique exhibited the appearance of most non-essential amino acids and lactate, and depleting the serine, alanyl-glutamine and pyruvate in such a manner that the embryos impaired in their development secreted a considerably higher level of lactate and consumed a significantly higher amount of alanyl-glutamine. The different significant ratios of metabolomic depletion/appearance between the embryos confirm their potential for the improvement of the prospective selection of the developed single embryos, and also suggest the fact that pyruvate and alanyl-glutamine are the most critical ATP suppliers on the fifth day of blastocyst development.

mTORC1/2 signaling is downregulated by amino acid-free culture of mouse preimplantation embryos and is only partially restored by amino acid readdition

Development of the mammalian preimplantation embryo is influenced by autocrine/paracrine factors and the availability of nutrients. Deficiencies of these during in vitro culture reduce the success of assisted reproductive technologies. The mechanistic target of rapamycin complex 1 (mTORC1) pathway integrates external and internal signals, including those by amino acids (AAs), to promote normal preimplantation development. For this reason, AAs are often included in embryo culture media. In this study, we examined how withdrawal and addition of AAs to culture media modulate mTORC1 pathway activity compared with its activity in mouse embryos developed in vivo. Phosphorylation of signaling components downstream of mTORC1, namely, p70 ribosomal protein S6 kinase (p70S6K), ribosomal protein S6, and 4E binding protein 1 (4E-BP1), and that of protein kinase B (Akt), which lies upstream of mTORC1, changed significantly across stages of embryos developed in vivo. For freshly isolated blastocysts placed in vitro, the absence of AAs in the culture medium, even for a few hours, decreased mTORC1 signaling, which could only be partially restored by their addition. Long-term culture of early embryos to blastocysts in the absence of AAs decreased mTORC1 signaling to a greater extent and again this could only be partially restored by their inclusion. This failure to fully restore is probably due to decreased phosphatidylinositol 3-kinase (PI3K)/Akt/mTORC2 signaling in culture, as indicated by decreased P-Akt^S473. mTORC2 lies upstream of mTORC1 and is insensitive to AAs, and its reduced activity probably results from loss of maternal/autocrine factors. These data highlight reduced mTORC1/2 signaling activity correlating with compromised development in vitro and show that the addition of AAs can only partially offset these effects.