Dynamic proteomic profiles of in vivo- and in vitro-produced mouse postimplantation extraembryonic tissues and placentas

Trophectoderm biopsy of blastocysts following IVF and embryo culture increases epigenetic dysregulation in a mouse model

STUDY QUESTION

Does trophectoderm biopsy (TEBx) of blastocysts for preimplantation genetic testing in the clinic affect normal placental and embryo development and offspring metabolic outcomes in a mouse model?

SUMMARY ANSWER

TEBx impacts placental and embryonic health during early development, with some alterations resolving and others worsening later in development and triggering metabolic changes in adult offspring.

WHAT IS KNOWN ALREADY

Previous studies have not assessed the epigenetic and morphological impacts of TEBx either in human populations or in animal models.

STUDY DESIGN, SIZE, DURATION

We employed a mouse model to identify the effects of TEBx during IVF. Three groups were assessed: naturally conceived (Naturals), IVF, and IVF + TEBx, at two developmental timepoints: embryonic day (E)12.5 (n = 40/Naturals, n = 36/IVF, and n = 36/IVF + TEBx) and E18.5 (n = 42/Naturals, n = 30/IVF, and n = 35/IVF + TEBx). Additionally, to mimic clinical practice, we assessed a fourth group: IVF + TEBx + Vitrification (Vit) at E12.5 (n = 29) that combines TEBx and vitrification. To assess the effect of TEBx in offspring health, we characterized a 12-week-old cohort (n = 24/Naturals, n = 25/IVF and n = 25/IVF + TEBx).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Our mouse model used CF-1 females as egg donors and SJL/B6 males as sperm donors. IVF, TEBx, and vitrification were performed using standardized methods. Placenta morphology was evaluated by hematoxylin-eosin staining, in situ hybridization using Tpbpa as a junctional zone marker and immunohistochemistry using CD34 fetal endothelial cell markers. For molecular analysis of placentas and embryos, DNA methylation was analyzed using pyrosequencing, luminometric methylation assay, and chip array technology. Expression patterns were ascertained by RNA sequencing. Triglycerides, total cholesterol, high-, low-, and very low-density lipoprotein, insulin, and glucose were determined in the 12-week-old cohort using commercially available kits.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed that at E12.5, IVF + TEBx had a worse outcome in terms of changes in DNA methylation and differential gene expression in placentas and whole embryos compared with IVF alone and compared with Naturals. These changes were reflected in alterations in placental morphology and blood vessel density. At E18.5, early molecular changes in fetuses were maintained or exacerbated. With respect to placentas, the molecular and morphological changes, although different compared to Naturals, were equivalent to the IVF group, except for changes in blood vessel density, which persisted. Of note is that most differences were sex specific. We conclude that TEBx has more detrimental effects in mid-gestation placental and embryonic tissues, with alterations in embryonic tissues persisting or worsening in later developmental stages compared to IVF alone, and the addition of vitrification after TEBx results in more pronounced and potentially detrimental epigenetic effects: these changes are significantly different compared to Naturals. Finally, we observed that 12-week IVF + TEBx offspring, regardless of sex, showed higher glucose, insulin, triglycerides, lower total cholesterol, and lower high-density lipoprotein compared to IVF and Naturals, with only males having higher body weight compared to IVF and Naturals. Our findings in a mouse model additionally support the need for more studies to assess the impact of new procedures in ART to ensure healthy pregnancies and offspring outcomes.

LARGE SCALE DATA

Data reported in this work have been deposited in the NCBI Gene Expression Omnibus under accession number GSE225318.

LIMITATIONS, REASONS FOR CAUTION

This study was performed using a mouse model that mimics many clinical IVF procedures and outcomes observed in humans, where studies on early embryos are not possible.

WIDER IMPLICATIONS OF THE FINDINGS

This study highlights the importance of assaying new procedures used in ART to assess their impact on placenta and embryo development, and offspring metabolic outcomes.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by a National Centers for Translational Research in Reproduction and Infertility grant P50 HD068157-06A1 (M.S.B., C.C., M.M.), Ruth L. Kirschstein National Service Award Individual Postdoctoral Fellowship F32 HD107914 (E.A.R.-C.) and F32 HD089623 (L.A.V.), and National Institutes of Health Training program in Cell and Molecular Biology T32 GM007229 (C.N.H.). No conflict of interest.

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.

Comparative Proteomic and Phospho-proteomic Analysis of Mouse Placentas Generated via In Vivo and In Vitro Fertilization

Offspring conceived by assisted reproductive technologies (ART) have increased risk of suffering from gestational complications, and placental dysfunction is related with the adverse outcomes. Studies have revealed that abnormal or adaptive changes can occur in ART placentas, but the potential reasons are not fully understood. Hereby, we tried to use proteomics and phospho-proteomics to find the underlying mechanisms responsible for the changes of ART placentas. Liquid chromatography-tandem mass spectrometry was utilized to perform proteome and phospho-proteome detection on mouse placentas. The differential expressed proteins (DEPs) or phospho-proteins (DEPPs) were analyzed based on subcellular localization, functional classification, and enrichment. Western blot was used to verify the DEPs (Afadin, ZO-1, Ace2, Agt, Slc7a5, and Slc38a10) and measure mTOR signaling activities (mTOR, Rps6, and 4Ebp1). The data showed that 161 DEPs and 304 DEPPs were found in proteome and phospho-proteome, respectively. Multiple biological processes were enriched based on those DEPs and DEPPs, and renin-angiotensin system, cell junction, and PI3K-Akt pathway were investigated. By protein expression identification, two key proteins associated with renin-angiotensin system (Ace2 and Agt) were down-regulated, and the levels of Afadin and ZO-1 (related with cell junction) as well as Slc38a10 were increased in IVF placentas. In addition, mTOR downstream activities were increased as shown by p-Rps6 and p-4Ebp1 in IVF placentas. In conclusion, IVF leads to the changes of cell junction, renin-angiotensin system, amino acid transport, and increased mTOR signaling in mouse placentas, which may be associated with the altered structure and function of IVF placentas.

Protocol for Increasing the Sensitivity of MS-Based Protein Detection in Human Chorionic Villi

An important step in the proteomic analysis of missing proteins is the use of a wide range of tissues, optimal extraction, and the processing of protein material in order to ensure the highest sensitivity in downstream protein detection. This work describes a purification protocol for identifying low-abundance proteins in human chorionic villi using the proposed “1DE-gel concentration” method. This involves the removal of SDS in a short electrophoresis run in a stacking gel without protein separation. Following the in-gel digestion of the obtained holistic single protein band, we used the peptide mixture for further LC–MS/MS analysis. Statistically significant results were derived from six datasets, containing three treatments, each from two tissue sources (elective or missed abortions). The 1DE-gel concentration increased the coverage of the chorionic villus proteome. Our approach allowed the identification of 15 low-abundance proteins, of which some had not been previously detected via the mass spectrometry of trophoblasts. In the post hoc data analysis, we found a dubious or uncertain protein (PSG7) encoded on human chromosome 19 according to neXtProt. A proteomic sample preparation workflow with the 1DE-gel concentration can be used as a prospective tool for uncovering the low-abundance part of the human proteome.

Placental Abnormalities are Associated With Specific Windows of Embryo Culture in a Mouse Model

Assisted Reproductive Technologies (ART) employ gamete/embryo handling and culture in vitro to produce offspring. ART pregnancies have an increased risk of low birth weight, abnormal placentation, pregnancy complications, and imprinting disorders. Embryo culture induces low birth weight, abnormal placental morphology, and lower levels of DNA methylation in placentas in a mouse model of ART. Whether preimplantation embryos at specific stages of development are more susceptible to these perturbations remains unresolved. Accordingly, we performed embryo culture for several discrete periods of preimplantation development and following embryo transfer, assessed fetal and placental outcomes at term. We observed a reduction in fetal:placental ratio associated with two distinct windows of preimplantation embryo development, one prior to the morula stage and the other from the morula to blastocyst stage, whereas placental morphological abnormalities and reduced imprinting control region methylation were only associated with culture prior to the morula stage. Extended culture to the blastocyst stage also induces additional placental DNA methylation changes compared to embryos transferred at the morula stage, and female concepti exhibited a higher loss of DNA methylation than males. By identifying specific developmental windows of susceptibility, this study provides a framework to optimize further culture conditions to minimize risks associated with ART pregnancies.

N6-Methyladenosine Modifications in the Female Reproductive System: Roles in Gonad Development and Diseases

N6-methyladenosine (m⁶A) is the most prevalent chemical modification in eukaryotic messenger RNAs. By participating in various RNA-related bioprocesses including RNA decay, splicing, transport and translation, m⁶A serves as a pivotal regulator of RNA fate and plays an irreplaceable role in cellular activities. The m⁶A modifications of transcripts are coordinately regulated by methyltransferase “writers” and demethylase “erasers”, and produce variable effects via different m⁶A reading protein “readers”. There is emerging evidence that m⁶A modifications play a critical role in a variety of physiological and pathological processes in the female reproductive system, subsequently affecting female fertility. Here, we introduce recent advances in research on m⁶A regulators and their functions, then highlight the role of m⁶A in gonad development and female reproductive diseases, as well as the underlying mechanisms driving these processes.

A proteomic atlas of ligand-receptor interactions at the ovine maternal-fetal interface reveals the role of histone lactylation in uterine remodeling

Well-orchestrated maternal–fetal cross talk occurs via secreted ligands, interacting receptors, and coupled intracellular pathways between the conceptus and endometrium and is essential for successful embryo implantation. However, previous studies mostly focus on either the conceptus or the endometrium in isolation. The lack of integrated analysis impedes our understanding of early maternal–fetal cross talk. Herein, focusing on ligand–receptor complexes and coupled pathways at the maternal–fetal interface in sheep, we provide the first comprehensive proteomic map of ligand–receptor pathway cascades essential for embryo implantation. We demonstrate that these cascades are associated with cell adhesion and invasion, redox homeostasis, and the immune response. Candidate interactions and their physiological roles were further validated by functional experiments. We reveal the physical interaction of albumin and claudin 4 and their roles in facilitating embryo attachment to endometrium. We also demonstrate a novel function of enhanced conceptus glycolysis in remodeling uterine receptivity by inducing endometrial histone lactylation, a newly identified histone modification. Results from in vitro and in vivo models supported the essential role of lactate in inducing endometrial H3K18 lactylation and in regulating redox homeostasis and apoptotic balance to ensure successful implantation. By reconstructing a map of potential ligand–receptor pathway cascades at the maternal–fetal interface, our study presents new concepts for understanding molecular and cellular mechanisms that fine-tune conceptus–endometrium cross talk during implantation. This provides more direct and accurate insights for developing potential clinical intervention strategies to improve pregnancy outcomes following both natural and assisted conception.

Sex-specific effects of in vitro fertilization on adult metabolic outcomes and hepatic transcriptome and proteome in mouse

Although in vitro fertilization (IVF) is associated with adverse perinatal outcomes, there is increasing concern about the long-term and sex-specific health implications. Augmenting our IVF mouse model to longitudinally investigate metabolic outcomes in offspring from optimal neonatal litter sizes, we found sex-specific metabolic outcomes in IVF offspring. IVF-conceived females had higher body weight and cholesterol levels compared to naturally conceived females, whereas IVF-conceived males had higher levels of triglycerides and insulin, and increased body fat composition. Through adult liver transcriptomics and proteomics, we identified sexually dimorphic dysregulation of the sterol regulatory element-binding protein (SREBP) pathways that are associated with the sex-specific phenotypes. We also found that global loss of DNA methylation in placenta was linked to higher cholesterol levels in IVF-conceived females. Our findings indicate that IVF procedures have long-lasting sex-specific effects on metabolic health of offspring and lay the foundation to utilize the placenta as a predictor of long-term outcomes.

[ALKBH5 suppresses migration and invasion of human trophoblast cells by inhibiting epithelial-mesenchymal transition]

OBJECTIVE

To investigate the effects of ALKBH5 on migration, invasion and epithelial-mesenchymal transition (EMT) of human trophoblast cells.

METHODS

The expression plasmid of ALKBH5 or a negative control plasmid (ALKBH5-NC) was transfected in human trophoblast HTR-8 /SVneo cells, and the expressions of ALKBH5 mRNA and protein were detected by qRT-PCR and Western blotting. Transwell assay was used to assess the changes in migration and invasion abilities of the trophoblast cells after the transfection. Western blotting was performed to detect the expressions of EMT-related proteins in the cells including vimentin, fibronectin, E-cadherin, N-cadherin, MMP9 and MMP2.

RESULTS

ALKBH5 mRNA and protein expressions were significantly higher in ALKBH5 group than in the control group (P < 0.05). Over-expression of ALKBH5 significantly attenuated migration and invasion abilities of HTR-8/Svneo cells (P < 0.05). Compared with the control cells, the cells overexpressing ALKBH5 showed an up-regulated expression of E-cadherin and down-regulated expressions of vimentin, fibronectin, N-cadherin, MMP9 and MMP2 (P < 0.05).

CONCLUSIONS

ALKBH5 is involved in the pathogenesis of preeclampsia by inhibiting EMT of trophoblast cells and hence reducing their migration and invasion abilities.

Repression of FGF signaling is responsible for Dnmt3b inhibition and impaired de novo DNA methylation during early development of in vitro fertilized embryos

Well-orchestrated epigenetic modifications during early development are essential for embryonic survival and postnatal growth. Erroneous epigenetic modifications due to environmental perturbations such as manipulation and culture of embryos during in vitro fertilization (IVF) are linked to various short- or long-term consequences. Among these, DNA methylation defects are of great concern. Despite the critical role of DNA methylation in determining embryonic development potential, the mechanisms underlying IVF-associated DNA methylation defects, however, remains largely elusive. We reported herein that repression of fibroblast growth factor (FGF) signaling as the main reason for IVF-associated DNA methylation defects. Comparative methylome analysis by postimplantation stage suggested that IVF mouse embryos undergo impaired de novo DNA methylation during implantation stage. Further analyses indicated that Dnmt3b, the main de novo DNA methyltransferase, was consistently inhibited during the transition from the blastocyst to postimplantation stage (Embryonic day 7.5, E7.5). Using blastocysts and embryonic stem cells (ESCs) as the model, we showed repression of FGF signaling is responsible for Dnmt3b inhibition and global hypomethylation during early development, and MEK/ERK-SP1 pathway plays an essential mediating role in FGF signaling-induced transcriptional activation of Dnmt3b. Supplementation of FGF2, which was exclusively produced in the maternal oviduct, into embryo culture medium significantly rescued Dnmt3b inhibition. Our study, using mouse embryos as the model, not only identifies FGF signaling as the main target for correcting IVF-associated epigenetic errors, but also highlights the importance of oviductal paracrine factors in supporting early embryonic development and improving in vitro culture system.

Assisted reproductive technologies induce temporally specific placental defects and the preeclampsia risk marker sFLT1 in mouse

Although widely used, assisted reproductive technologies (ARTs) are associated with adverse perinatal outcomes. To elucidate their underlying causes, we have conducted a longitudinal analysis of placental development and fetal growth using a mouse model to investigate the effects of individual ART procedures: hormone stimulation, in vitro fertilization (IVF), embryo culture and embryo transfer. We demonstrate that transfer of blastocysts naturally conceived without hormone stimulation and developed in vivo prior to transfer can impair early placentation and fetal growth, but this effect normalizes by term. In contrast, embryos cultured in vitro before transfer do not exhibit this compensation but rather display placental overgrowth, reduced fetal weight, reduced placental DNA methylation and increased levels of sFLT1, an anti-angiogenic protein implicated in causing the maternal symptoms of preeclampsia in humans. Increases in sFLT1 observed in this study suggest that IVF procedures could increase the risk for preeclampsia. Moreover, our results indicate that embryo culture is the major factor contributing to most placental abnormalities and should therefore be targeted for optimization.

The proteome of IVF-induced aberrant embryo-maternal crosstalk by implantation stage in ewes

Background

Implantation failure limits the success of in vitro fertilization and embryo transfer (IVF-ET). Well-organized embryo-maternal crosstalk is essential for successful implantation. Previous studies mainly focused on the aberrant development of in vitro fertilized (IVF) embryos. In contrast, the mechanism of IVF-induced aberrant embryo-maternal crosstalk is not well defined.

Results

In the present study, using ewes as the model, we profiled the proteome that features aberrant IVF embryo-maternal crosstalk following IVF-ET. By comparing in vivo (IVO) and IVF conceptuses, as well as matched endometrial caruncular (C) and intercaruncular (IC) areas, we filtered out 207, 295, and 403 differentially expressed proteins (DEPs) in each comparison. Proteome functional analysis showed that the IVF conceptuses were characterized by the increased abundance of energy metabolism and proliferation-related proteins, and the decreased abundance of methyl metabolism-related proteins. In addition, IVF endometrial C areas showed the decreased abundance of endometrial remodeling and redox homeostasis-related proteins; while IC areas displayed the aberrant abundance of protein homeostasis and extracellular matrix (ECM) interaction-related proteins. Based on these observations, we propose a model depicting the disrupted embryo-maternal crosstalk following IVF-ET: Aberrant energy metabolism and redox homeostasis of IVF embryos, might lead to an aberrant endometrial response to conceptus-derived pregnancy signals, thus impairing maternal receptivity. In turn, the suboptimal uterine environment might stimulate a compensation effect of the IVF conceptuses, which was revealed as enhanced energy metabolism and over-proliferation.

Conclusion

Systematic proteomic profiling provides insights to understand the mechanisms that underlie the aberrant IVF embryo-maternal crosstalk. This might be helpful to develop practical strategies to prevent implantation failure following IVF-ET.

Epitranscriptomic profiling in human placenta: N6-methyladenosine modification at the 5'-untranslated region is related to fetal growth and preeclampsia

Intracellular mRNA levels are not always proportional to their respective protein levels, especially in the placenta. This discrepancy may be attributed to various factors including post‐transcriptional regulation, such as mRNA methylation (N6‐methyladenosine: m⁶A). Here, we conducted a comprehensive m⁶A analysis of human placental tissue from neonates with various birth weights to clarify the involvement of m⁶A in placental biology. The augmented m⁶A levels at the 5′‐untranslated region (UTR) in mRNAs of small‐for‐date placenta samples were dominant compared to reduction of m⁶A levels, whereas a decrease in m⁶A in the vicinity of stop codons was common in heavy‐for‐date placenta samples. Notably, most of these genes showed similar expression levels between the different birth weight categories. In particular, preeclampsia placenta samples showed consistently upregulated SMPD1 protein levels and increased m⁶A at 5′‐UTR but did not show increased mRNA levels. Mutagenesis of adenosines at 5′‐UTR of SMPD1 mRNAs actually decreased protein levels in luciferase assay. Collectively, our findings suggest that m⁶A both at the 5′‐UTR and in the vicinity of stop codon in placental mRNA may play important roles in fetal growth and disease.

Comparative Analysis of the Transcriptome and Proteome during Mouse Placental Development

The condition of the placenta is a determinant of the short- and long-term health of the mother and the fetus. However, critical processes occurring in early placental development, such as trophoblast invasion and establishment of placental metabolism, remain poorly understood. To gain a better understanding of the genes involved in regulating these processes, we utilized a multiomics approach, incorporating transcriptome, proteome, and phosphoproteome data generated from mouse placental tissue collected at two critical developmental time points. We found that incorporating information from both the transcriptome and proteome identifies genes associated with time point-specific biological processes, unlike using the proteome alone. We further inferred genes upregulated on the basis of the proteome data but not the transcriptome data at each time point, leading us to identify 27 genes that we predict to have a role in trophoblast migration or placental metabolism. Finally, using the phosphoproteome data set, we discovered novel phosphosites that may play crucial roles in the regulation of placental transcription factors. By generating the largest proteome and phosphoproteome data sets in the developing placenta, and integrating transcriptome analysis, we uncovered novel aspects of placental gene regulation.

Gender proteomics II. Which proteins in sexual organs

In continuity with the review dealing with differences by gender in non-sexual organs [1], this review collects data on the proteomes of the sexual organs as involved in human reproduction, under both physiological and pathological conditions. It also collects data on the tissue structures and biological fluids typical of pregnancy, such as placenta and amniotic fluid, as well as what may be tested on preimplantation embryos during medically assisted reproduction. The review includes as well mention to all fluids and secretions connected with sex organs and/or reproduction, including sperm and milk, to exemplify two distinctive items in male and female physiology.

SIGNIFICANCE

The causes of infertility are only incompletely understood; the same holds for the causes, and even the early markers, of the most frequent complications of pregnancy. To these established medical challenges, present day practice adds new issues connected with medically assisted reproduction. Omics approaches, including proteomics, are building the database for basic knowledge to possibly translate into clinical testing and eventually into medical routine in this critical branch of health care.

High-resolution profiles of gene expression and DNA methylation highlight mitochondrial modifications during early embryonic development

Well-organized mitochondrial functions and dynamics are critical for early embryonic development and are operated via a large number of mitochondria-related genes (MtGs) encoded by both the nuclear and the mitochondrial genome. However, the mechanisms underlying mitochondrial modifications during the critical window between blastocyst implantation and postimplantation organogenesis are poorly understood. Herein, we performed high-resolution dynamic profiling of MtGs to acquire a more detailed understanding of mitochondrial modifications during early development. Our data suggest that the resumption of mitochondrial mass growth is not only facilitated by increased mitochondrial biogenesis and mitochondrial DNA (mtDNA) replication, but also by the appropriate balance between mitochondrial fission and fusion. In addition, increased levels of reactive oxygen species (ROS) resulting from enhanced mitochondrial functions may be the critical inducer for activating the glutathione (GSH)-based stress response system in early embryos. The appropriate balance between the mitochondrial stress response and apoptosis appears to be significant for cell differentiation and early organogenesis. Furthermore, we found that most MtGs undergo de novo promoter methylation, which may have functional consequences on mitochondrial functions and dynamics during early development. We also report that mtDNA methylation can be observed as early as soon after implantation. DNMT1, the predominant enzyme for maintaining DNA methylation, localized to the mitochondria and bound to mtDNA by the implantation stage. Our study provides a new insight into the involvement of mitochondria in early mammalian embryogenesis. We also propose that the epigenetic modifications during early development are significant for modulating mitochondrial functions and dynamics.

Cobalamin supplementation during in vitro maturation improves developmental competence of sheep oocytes

Pregnancies obtained by Assisted Reproductive Technologies are at higher risk of miscarriage than those obtained naturally. Previously, we reported impaired placental vascular development of in vitro produced (IVP) sheep embryos and defective DNA methylation in the placentae of those embryos. One reason behind these observed defects may be an impaired One Carbon Metabolism (OCM) The present study was performed to test the hypothesis that Cobalamin (Vitamin B12, an important OCM co-factor) supplementation during IVM corrects DNA methylation of IVP embryos and, consequently, ameliorates placental vasculogenesis. To this aim, embryos derived from oocytes matured with Cobalamin (B12 group) or without (negative control group, -CTR) were transferred to synchronized recipient sheep. At day 20 of pregnancy, collected embryos were morphologically evaluated while placentae were subjected to qPCR and histological analysis. The positive control group (+CTR) consisted of conceptuses obtained from naturally mated sheep. Results showed an increased fertilization rate in the B12 group vs -CTR (69.56% vs 57.91% respectively, P = 0.006) not associated with quantitative improvement in blastocyst and/or implantation rate (44.32% vs 36.67% respectively, P > 0.05). Moreover, Cobalamin supplementation during oocyte IVM ameliorated resulting conceptuses quality, in terms of placental vascularization (vessels' maturity and vasculogenetic factors' expression). The expression of DNA methyltransferases (DNMT1, DNMT3A and DNMT3B) was also improved in placentae from the B12 group. In conclusion, Cobalamin supplementation during oocyte IVM improves IVP embryo quality. These results suggest that Cobalamin should be included in standard IVM media.

Morphologic and molecular changes in the placenta: what we can learn from environmental exposures

In mammals, the extraembryonic tissues, which include the placenta, are crucial for embryonic development and growth. Because the placenta is no longer needed for postnatal life, however, it has been relatively understudied as a tissue of interest in biomedical research. Recently, increased efforts have been placed on understanding the placenta and how it may play a key role in human health and disease. In this review, we discuss two very different types of environmental exposures: assisted reproductive technologies and in utero exposure to endocrine-disrupting chemicals. We summarize the current literature on their effects on placental development in both rodent and human, and comment on the potential use of placental biomarkers as predictors of offspring health outcomes.

Evidence of Placental Autophagy during Early Pregnancy after Transfer of In Vitro Produced (IVP) Sheep Embryos

Pregnancies obtained by Assisted Reproductive Technologies (ART) are associated with limited maternal nutrient uptake. Our previous studies shown that in vitro culture of sheep embryos is associated with vascularization defects in their placentae and consequent reduction of embryo growth. Autophagy is a pro-survival cellular mechanism triggered by nutrient insufficiency. Therefore, the goal of our present study was to determine if autophagy is involved in early placental development after transfer of in vitro produced (IVP) embryos. To do this, placentae obtained following transfer of IVP sheep embryos were compared with placentae obtained after natural mating (control-CTR). The placentae were collected on day 20 post-fertilization and post-mating, respectively, and were analyzed using molecular (qPCR), ultrastructural and histological/immunological approaches. Our results show drastically increased autophagy in IVP placentae: high levels of expression (p<0.05) of canonical markers of cellular autophagy and a high proportion of autophagic cells (35.08%; p<0.001) were observed. We conclude that high autophagic activity in IVP placentae can be a successful temporary counterbalance to the retarded vasculogenesis and the reduction of foetal growth observed in pregnancies after transfer of IVP embryos.

Dynamic integrated analysis of DNA methylation and gene expression profiles in in vivo and in vitro fertilized mouse post-implantation extraembryonic and placental tissues

STUDY HYPOTHESIS

How does in vitro fertilization (IVF) alter promoter DNA methylation patterns and its subsequent effects on gene expression profiles during placentation in mice?

STUDY FINDING

IVF-induced alterations in promoter DNA methylation might have functional consequences in a number of biological processes and functions during IVF placentation, including actin cytoskeleton organization, hematopoiesis, vasculogenesis, energy metabolism and nutrient transport.

WHAT IS KNOWN ALREADY

During post-implantation embryonic development, both embryonic and extraembryonic tissues undergo de novo DNA methylation, thereby establishing a global DNA methylation pattern, and influencing gene expression profiles. Embryonic and placental tissues of IVF conceptuses can have aberrant morphology and functions, resulting in adverse pregnancy outcomes such as pregnancy loss, low birthweight, and long-term health effects. To date, the IVF-induced global profiling of DNA methylation alterations, and their functional consequences on aberrant gene expression profiles in IVF placentas have not been systematically studied.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Institute for Cancer Research mice (6 week-old females and 8-9 week-old males) were used to generate in vivo fertilization (IVO) and IVF blastocysts. After either IVO and development (IVO group as control) or in vitro fertilization and culture (IVF group), blastocysts were collected and transferred to pseudo-pregnant recipient mice. Extraembryonic (ectoplacental cone and extraembryonic ectoderm) and placental tissues from both groups were sampled at embryonic day (E) 7.5 (IVO, n = 822; IVF, n = 795) and E10.5 (IVO, n = 324; IVF, n = 278), respectively. The collected extraembryonic (E7.5) and placental tissues (E10.5) were then used for high-throughput RNA sequencing (RNA-seq) and methylated DNA immunoprecipitation sequencing (MeDIP-seq). The main dysfunctions indicated by bioinformatic analyses were further validated using molecular detection, and morphometric and phenotypic analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

Dynamic functional profiling of high-throughput data, together with molecular detection, and morphometric and phenotypic analyses, showed that differentially expressed genes dysregulated by DNA methylation were functionally involved in: (i) actin cytoskeleton disorganization in IVF extraembryonic tissues, which may impair allantois or chorion formation, and chorioallantoic fusion; (ii) disturbed hematopoiesis and vasculogenesis, which may lead to abnormal placenta labyrinth formation and thereby impairing nutrition transport in IVF placentas; (iii) dysregulated energy and amino acid metabolism, which may cause placental dysfunctions, leading to delayed embryonic development or even lethality; (iv) disrupted genetic information processing, which can further influence gene transcriptional and translational processes.

LIMITATIONS, REASONS FOR CAUTION

Findings in mouse placental tissues may not be fully representative of human placentas. Further studies are necessary to confirm these findings and determine their clinical significance.

WIDER IMPLICATIONS OF THE FINDINGS

Our study is the first to provide the genome-wide analysis of gene expression dysregulation caused by DNA methylation during IVF placentation. Systematic understanding of the molecular mechanisms implicated in IVF placentation can be useful for the improvement of existing assisted conception systems to prevent these IVF-associated safety concerns.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by grants from the National Natural Science Foundation of China (No. 31472092), and the National High-Tech R&D Program (Nos. 2011|AA100303, 2013AA102506). There was no conflict of interest.

Characterization and comparative analyses of transcriptomes for in vivo and in vitro produced peri-implantation conceptuses and endometria from sheep

An increasing number of reports indicate that in vitro fertilization (IVF) is highly associated with long‑term side effects on embryonic and postnatal development, and can sometimes result in embryonic implant failure. While high‑throughput gene expression analysis has been used to explore the mechanisms underlying IVF-induced side effects on embryonic development, little is known about the effects of IVF on conceptus–endometrial interactions during the peri-implantation period. Using sheep as a model, we performed a comparative transcriptome analysis between in vivo (IVO; in vivo fertilized followed by further development in the uterus) and in vitro produced (IVP; IVF with further culture in the incubator) conceptuses, and the caruncular and intercaruncular areas of the ovine endometrium. We identified several genes that were differentially expressed between the IVO and IVP groups on day 17, when adhesion between the trophoblast and the uterine luminal epithelium begins in sheep. By performing Gene Ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, we found that, in the conceptus, differentially expressed genes (DEGs) were associated mainly with functions relating to cell binding and the cell cycle. In the endometrial caruncular area, DEGs were involved in cell adhesion/migration and apoptosis, and in the intercaruncular area, they were significantly enriched in pathways of signal transduction and transport. Thus, these DEGs are potential candidates for further exploring the mechanism underlying IVF/IVP-induced embryonic implant failure that occurs due to a loss of interaction between the conceptus and endometrium during the peri-implantation period.

In vitro fertilization (IVF) in mammals: epigenetic and developmental alterations. Scientific and bioethical implications for IVF in humans

The advent of in vitro fertilization (IVF) in animals and humans implies an extraordinary change in the environment where the beginning of a new organism takes place. In mammals fertilization occurs in the maternal oviduct, where there are unique conditions for guaranteeing the encounter of the gametes and the first stages of development of the embryo and thus its future. During this period a major epigenetic reprogramming takes place that is crucial for the normal fate of the embryo. This epigenetic reprogramming is very vulnerable to changes in environmental conditions such as the ones implied in IVF, including in vitro culture, nutrition, light, temperature, oxygen tension, embryo-maternal signaling, and the general absence of protection against foreign elements that could affect the stability of this process. The objective of this review is to update the impact of the various conditions inherent in the use of IVF on the epigenetic profile and outcomes of mammalian embryos, including superovulation, IVF technique, embryo culture and manipulation and absence of embryo-maternal signaling. It also covers the possible transgenerational inheritance of the epigenetic alterations associated with assisted reproductive technologies (ART), including its phenotypic consequences as is in the case of the large offspring syndrome (LOS). Finally, the important scientific and bioethical implications of the results found in animals are discussed in terms of the ART in humans.

The cumulative effect of assisted reproduction procedures on placental development and epigenetic perturbations in a mouse model

Assisted reproductive technologies (ART) are associated with several complications including low birth weight, abnormal placentation and increased risk for rare imprinting disorders. Indeed, experimental studies demonstrate ART procedures independent of existing infertility induce epigenetic perturbations in the embryo and extraembryonic tissues. To test the hypothesis that these epigenetic perturbations persist and result in adverse outcomes at term, we assessed placental morphology and methylation profiles in E18.5 mouse concepti generated by in vitro fertilization (IVF) in two different genetic backgrounds. We also examined embryo transfer (ET) and superovulation procedures to ascertain if they contribute to developmental and epigenetic effects. Increased placental weight and reduced fetal-to-placental weight ratio were observed in all ART groups when compared with naturally conceived controls, demonstrating that non-surgical embryo transfer alone can impact placental development. Furthermore, superovulation further induced overgrowth of the placental junctional zone. Embryo transfer and superovulation defects were limited to these morphological changes, as we did not observe any differences in epigenetic profiles. IVF placentae, however, displayed hypomethylation of imprinting control regions of select imprinted genes and a global reduction in DNA methylation levels. Although we did not detect significant differences in DNA methylation in fetal brain or liver samples, rare IVF concepti displayed very low methylation and abnormal gene expression from the normally repressed allele. Our findings suggest that individual ART procedures cumulatively increase placental morphological abnormalities and epigenetic perturbations, potentially causing adverse neonatal and long-term health outcomes in offspring.

Dynamic comparisons of high-resolution expression profiles highlighting mitochondria-related genes between in vivo and in vitro fertilized early mouse embryos

STUDY QUESTION

Does in vitro fertilization (IVF) induce comprehensive and consistent changes in gene expression associated with mitochondrial biogenesis and function in mouse embryos from the pre- to post-implantation stage?

SUMMARY ANSWER

IVF-induced consistent mitochondrial dysfunction in early mouse embryos by altering the expression of a number of mitochondria-related genes.

WHAT IS KNOWN ALREADY

Although IVF is generally safe and successful for the treatment of human infertility, there is increasing evidence that those conceived by IVF suffer increased health risks. The mitochondrion is a multifunctional organelle that plays a crucial role in early development. We hypothesized that mitochondrial dysfunction is associated with increased IVF-induced embryonic defects and risks in offspring.

STUDY DESIGN, SIZE, DURATION

After either IVF and development (IVO groups as control) or IVF and culture (IVF groups), blastocysts were collected and transferred to pseudo-pregnant recipient mice. Both IVO and IVF embryos were sampled at E3.5, E7.5 and E10.5, and the expression profiles of mitochondria-related genes from the pre- to post-implantation stage were compared.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ICR mice (5- to 6-week-old males and 8- to 9-week-old females) were used to generate IVO and IVF blastocysts. Embryo day (E) 3.5 blastocysts were transferred to pseudo-pregnant recipient mice. Both IVO and IVF embryos were sampled at E3.5, E7.5 and E10.5 for generating transcriptome data. Mitochondria-related genes were filtered for dynamic functional profiling. Mitochondrial dysfunctions indicated by bioinformatic analysis were further validated using cytological and molecular detection, morphometric and phenotypic analysis and integrated analysis with other high-throughput data.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 806, 795 and 753 mitochondria-related genes were significantly (P < 0.05) dysregulated in IVF embryos at E3.5, E7.5 and E10.5, respectively. Dynamic functional profiling, together with cytological and molecular investigations, indicated that IVF-induced mitochondrial dysfunctions mainly included: (i) inhibited mitochondrial biogenesis and impaired maintenance of DNA methylation of mitochondria-related genes during the post-implantation stage; (ii) dysregulated glutathione/glutathione peroxidase (GSH/Gpx) system and increased mitochondria-mediated apoptosis; (iii) disturbed mitochondrial β-oxidation, oxidative phosphorylation and amino acid metabolism; and (iv) disrupted mitochondrial transmembrane transport and membrane organization. We also demonstrated that some mitochondrial dysfunctions in IVF embryos, including impaired mitochondrial biogenesis, dysregulated GSH homeostasis and reactive oxygen species-induced apoptosis, can be rescued by treatment with melatonin, a mitochondria-targeted antioxidant, during in vitro culture.

LIMITATIONS, REASONS FOR CAUTION

Findings in mouse embryos and fetuses may not be fully transferable to humans. Further studies are needed to confirm these findings and to determine their clinical significance better.

WIDER IMPLICATIONS OF THE FINDINGS

The present study provides a new insight in understanding the mechanism of IVF-induced aberrations during embryonic development and the increased health risks in the offspring. In addition, we highlighted the possibility of improving existing IVF systems by modulating mitochondrial functions.