Identification and characteristics of extracellular vesicles from bovine blastocysts produced in vitro

Extracellular vesicles and its advances in female reproduction

Intercellular communication is an essential mechanism for development and maintenance of multicellular organisms. Extracellular vesicles (EVs) were recently described as new players in the intercellular communication. EVs are double-membrane vesicles secreted by cells and are classified according to their biosynthesis, protein markers and morphology. These extracellular vesicles contain bioactive materials such as miRNA, mRNA, protein and lipids. These characteristics permit their involvement in different biological processes. Reproductive physiology is complex and involves constant communication between cells. Different laboratories have described the presence of EVs secreted by ovarian follicular cells, oviductal cells, in vitro produced embryos and by the endometrium, suggesting that EVs are involved in the development of gametes and embryos, in animals and humans. Therefore, is important to understand physiological mechanisms and contributions of EVs in female reproduction in order to develop new tools to improve in vivo reproductive events and assisted reproductive techniques (ARTs). This review will provide the current knowledge related to EVs in female reproductive tissues and their role in ARTs.

The Separation and Characterization of Extracellular Vesicles from Medium Conditioned by Bovine Embryos

Extracellular vesicles (EVs) have been identified as one of the communication mechanisms amongst embryos. They are secreted into the embryo culture medium and, as such, represent a source of novel biomarkers for identifying the quality of cells and embryos. However, only small amounts of embryo-conditioned medium are available, which represents a challenge for EV enrichment. Our aim is to assess the suitability of different EV separation methods to retrieve EVs with high specificity and sufficient efficiency. Bovine embryo-conditioned medium was subjected to differential ultracentrifugation (DU), OptiPrep^TM density gradient (ODG) centrifugation, and size exclusion chromatography. Separated EVs were characterized by complementary characterization methods, including Western blot, electron microscopy, and nanoparticle tracking analysis, to assess the efficiency and specificity. OptiPrep^TM density gradient centrifugation outperformed DU and SEC in terms of specificity by substantial removal of contaminating proteins such as ribonucleoprotein complexes (Argonaute-2 (AGO-2)) and lipoproteins (ApoA-I) from bovine embryo-derived EVs (density: 1.02–1.04, 1.20–1.23 g/mL, respectively). In conclusion, ODG centrifugation is the preferred method for identifying EV-enriched components and for improving our understanding of EV function in embryo quality and development.

Individually cultured bovine embryos produce extracellular vesicles that have the potential to be used as non-invasive embryo quality markers

Extracellular vesicles (EVs) are membrane-bound biological nanoparticles (NPs) and have gained wide attention as potential biomarkers. We aimed to isolate and characterize EVs from media conditioned by individually cultured preimplantation bovine embryos and to assess their relationship with embryo quality. Presumptive zygotes were cultured individually in 60 μl droplets of culture media, and 50 μl of media were collected from the droplets either on day 2, 5 or 8 post-fertilization. After sampling, the embryo cultures were continued in the remaining media until day 8, and the embryo development was evaluated at day 2 (cleavage), day 5 (morula stage) and day 8 (blastocyst stage). EVs were isolated using qEVsingle® columns and characterized. Based on EV Array, EVs isolated from embryo conditioned media were strongly positive for EV-markers CD9 and CD81 and weakly positive for CD63 and Alix among others. They had a cup-like shape typical to EVs as analyzed by transmission electron microscopy and spherical shape in scanning electron microscopy, and hence regarded as EVs. However, the NPs isolated from control media were negative for EV markers. Based on nanoparticle tracking analysis, at day 2, the mean concentration of EVs isolated from media conditioned by embryos that degenerated after cleaving (8.25 × 10⁸/ml) was higher compared to that of embryos that prospectively developed to blastocysts (5.86 × 10⁸/ml, p < 0.05). Moreover, at day 8, the concentration of EVs isolated from media conditioned by degenerating embryos (7.17 × 10⁸/ml) was higher compared to that of blastocysts (5.68 × 10⁸/ml, p < 0.05). Furthermore, at day 8, the mean diameter of EVs isolated from media conditioned by degenerating embryos (153.7 nm) was smaller than EVs from media conditioned by blastocysts (163.5 nm, p < 0.05). In conclusion, individually cultured preimplantation bovine embryos secrete EVs in the culture media and their concentration and size are influenced by embryo quality and may indicate their prospective development potential.

Identification and Characterization of Extracellular Vesicles and Its DNA Cargo Secreted During Murine Embryo Development

Extracellular vesicles (EVs) are known to transport DNA, but their implications in embryonic implantation are unknown. The aim of this study was to investigate EVs production and secretion by preimplantation embryos and assess their DNA cargo. Murine oocytes and embryos were obtained from six- to eight-week-old females, cultured until E4.5 and analyzed using transmission electron microscopy to examine EVs production. EVs were isolated from E4.5-day conditioned media and quantified by nanoparticle tracking analysis, characterized by immunogold, and their DNA cargo sequenced. Multivesicular bodies were observed in murine oocytes and preimplantation embryos together with the secretion of EVs to the blastocoel cavity and blastocyst spent medium. Embryo-derived EVs showed variable electron-densities and sizes (20–500 nm) and total concentrations of 1.74 × 10⁷ ± 2.60 × 10⁶ particles/mL. Embryo secreted EVs were positive for CD63 and ARF6. DNA cargo sequencing demonstrated no differences in DNA between apoptotic bodies or smaller EVs, although they showed significant gene enrichment compared to control medium. The analysis of sequences uniquely mapping the murine genome revealed that DNA contained in EVs showed higher representation of embryo genome than vesicle-free DNA. Murine blastocysts secrete EVs containing genome-wide sequences of DNA to the medium, reinforcing the relevance of studying these vesicles and their cargo in the preimplantation moment, where secreted DNA may help the assessment of the embryo previous to implantation.

Extracellular Vesicles Mediated Early Embryo-Maternal Interactions

Embryo-maternal crosstalk is an important event that involves many biological processes, which must occur perfectly for pregnancy success. This complex communication starts from the zygote stage within the oviduct and continues in the uterus up to the end of pregnancy. Small extracellular vesicles (EVs) are part of this communication and carry bioactive molecules such as proteins, lipids, mRNA, and miRNA. Small EVs are present in the oviductal and uterine fluid and have important functions during fertilization and early embryonic development. Embryonic cells are able to uptake oviductal and endometrium-derived small EVs. Conversely, embryo-derived EVs might modulate oviductal and uterine function. In this review, our aim is to demonstrate the role of extracellular vesicles modulating embryo-maternal interactions during early pregnancy.

Challenges in studying preimplantation embryo-maternal interaction in cattle

A comprehensive understanding of the complex embryo-maternal interactions during the preimplantation period requires the analysis of the very early stages of pregnancy encompassing early embryonic development, maternal recognition and the events leading to implantation. Despite the fact that embryo development until blastocyst stage is somewhat autonomous (i.e., does not require contact with the maternal reproductive tract and can be successfully recapitulated in vitro), many studies on ruminant embryo production have focused on the fundamental question of why: (i) only 30%-40% of immature oocytes develop to the blastocyst stage and (ii) the quality of such blastocysts continually lags behind that of blastocysts produced in vivo. Clear evidence indicates that in vitro culture conditions are far from optimal with deficiencies being manifested in short- and long-term effects on the embryo. Thus, enhanced knowledge of mechanisms controlling embryo-maternal interactions would allow the design of novel strategies to improve in vitro embryo conditions and reproductive outcomes in cattle.

Oxygen tension modulates extracellular vesicles and its miRNA contents in bovine embryo culture medium

The biotechnology for in vitro embryo production is becoming increasingly popular, being applied to humans and domestic animals. Embryo development can be achieved with either 20% or 5% oxygen tension. The extracellular vesicles (EVs) are secreted by different cell types and carry bioactive materials. Our objective was to determine the secretion pattern and micro RNA (miRNA) contents of EVs released in the bovine embryo culture environment-embryo and cumulus cell monolayer-on Days 3 and 7 of in vitro culture under two different oxygen tensions: High (20%) and low (5%). The EVs were isolated from the medium and analyzed to determine size, concentration, and miRNA levels. EVs concentration in low oxygen tension increased on Day 3 and decreased on Day 7. Additionally, altered EV miRNAs derived from the embryo-cumulus culture medium were predicted to regulate survival and proliferation-related pathways on Days 3 and 7. Moreover, miR-210 levels decreased in EVs isolated from the culture medium under high oxygen tension suggesting that this miRNA can be used as a marker for normoxia since it is associated with low oxygen tension. In summary, this study provides knowledge of the oxygen tension effects on EVs release and content, and potentially, on cell-to-cell communication during in vitro bovine embryo production.

Ultrastructural identification of CD9 positive extracellular vesicles released from human embryos and transported through the zona pellucida

Extracellular vesicles (EVs) are highly specific and multi-purpose vesicular structures that are released by various cell and tissue types in the body. However, the secretion of EVs from mammalian embryos, especially human, has not been well characterized. Thus, the aim of this study was to 1) identify EVs in human preimplantation embryos at different stages of their development using scanning and electron microscopy, and 2) investigate whether EVs can cross the zona pellucida (ZP) and be released from human embryos cultured in vitro. Human oocytes, zygotes, cleavage embryos and blastocysts donated for research were labeled with the tetraspanin EV marker CD9 and analyzed by scanning and transmission electron microscopy. Embryo culture conditioned media collected 3- and 5-days post fertilization were examined for the presence of EVs using electron microscopy. We detected numerous CD9 positive vesicles released from all embryos examined. They were observed on the surface of the plasma membrane, within the perivitelline space as well as throughout the zona pellucida. Interestingly, EVs were not seen in the ZP of all mature metaphase II oocytes, however, were detected just after fertilization in the ZP of zygotes and embryos. Electron microscopy using negative staining, and nanoparticle tracking analysis (NTA) of embryo conditioned culture media also showed the presence of vesicles of various sizes, which were round shaped, and had a lipid bilayer. Their size ranged from 30 to 500 nm, consistent with the sizes of exosomes and microvesicles. In conclusion, the results of the study provide evidence that human preimplantation embryos at all developmental stages secrete EVs into the perivitelline space, which then traverse through the ZP, and are then released into the surrounding culture medium. Abbreviations: EVs: extracellular vesicles; ZP: zona pellucida; CD9, CD63, and CD81: tetraspanin EV markers; NTA: nanoparticle tracking analysis; ESCRT: endosomal sorting complexes required for transport; SEM: scanning electron microscopy; TEM: transmission electron microscopy; TE: trophectoderm; ICM: inner cell mass; PVS: perivitelline space; MI: metaphase I; MII: metaphase II; GV: germinal vesicle; MVs/EXs: microvesicles/exosomes; hCG: human chorionic gonadotrophin; GnRH: gonadogrophin releasing hormone; ICSI: intracytoplasmic sperm injection; SPS: serum protein substitute; 1PN: one pronuclear zygote; 3PN: tri-pronuclear zygote; IgG: immunoglobulin G; PBS: phosphate buffer saline; ETHO: ethanol; ESED: Environmental Secondary Electron Detector; BSA: bovine serum albumin.

Embryonic extracellular vesicles as informers to the immune cells at the maternal-fetal interface

Extracellular vesicle (EV) exchange is emerging as a novel method of communication at the maternal-fetal interface. The presence of the EVs has been demonstrated in the preimplantation embryo culture medium from different species, such as bovines, porcines and humans. Preimplantation embryo-derived EVs have been shown to carry molecules potentially able to modulate the local endometrial immune system. The non-classical major histocompatibility complex (MHC) class I molecule human leucocyte antigen (HLA)-G, the immunomodulatory molecule progesterone-induced blocking factor and some regulatory miRNAs species are contained in embryo-derived EV cargo. The implanted syncytiotrophoblasts are also well known to secrete EVs, with microvesicles exerting a mainly proinflammatory effect while exosomes in general mediate local immunotolerance. This review focuses on the current knowledge on the potential role of EVs released by the embryo in the first weeks of pregnancy on the maternal immune cells. Collectively, the data warrant further exploration of the dialogue between the mother and the embryo via EVs.

Extracellular vesicle mediated embryo-endometrial cross talk during implantation and in pregnancy

Extracellular vesicles are lipoproteinaceous membrane-enclosed nanometer-sized structures produced by cells and are thought to mediate cellular communications. Loaded with a specific set of miRNA and protein depending on their tissue of origin, these extracellular vesicles modulate diverse set of biological processes in their target tissues. In recent years, data has gathered on the roles of extracellular vesicles in embryo implantation and pregnancy. Embryo, oviduct, endometrial epithelium and stroma/decidua derived vesicles interact with trophoblast cells and promote their growth and differentiation to aid in embryo implantation. The placental vesicles are detected in maternal circulation that aids in feto-maternal immune tolerance, their levels vary in women with pregnancy-related complications like preeclampsia. Beyond the host, the microbes in the genital tract are also reported to produce extracellular vesicles which are thought to be responsible for inflammation and preterm births. This review focuses on the extracellular vesicular trafficking involved in success of pregnancy.

Effect of BMP15 and/or AMH during in vitro maturation of oocytes from involuntarily culled dairy cows

The high metabolic activity to which the dairy cattle are exposed to maintain milk production altered steroid metabolism that affects reproductive physiology and reduce oocyte competence. Our aims were (a) to characterize the competence of immature oocytes collected from dairy cattle based on the expression of genes in cumulus cells (CCs) and (b) to improve oocyte competence to support preimplantation embryo development by the supplementation of maturation medium with bone morphogenetic protein 15 (BMP15) and/or anti-mullerian hormone (AMH). Oocyte donors were identified at the moment of ovary collection and grouped by involuntarily culled dairy cows (Holstein breed) or beef cattle. The embryo development speed to blastocyst of the cull dairy cattle versus beef cattle (control group) was lower. Besides, <10% of oocytes (with CC biopsies) derived from dairy cattle were able to develop to the blastocyst stage. In addition, a higher level of expression and a positive correlation were observed in the expression of most of the genes evaluated (LUM, KRT18, KRT8, CLIC3, BMPR1B, and SLC38A3) in the cumulus-oocyte complexes that produced blastocysts versus those which did not develop correctly (arrested development). Further, use of BMP15 in the maturation of oocytes from dairy cattle seems to increase competence, modulating the expression of OCT4, SOX2, CDX2, GATA6, and TP1 in resulting blastocysts.

Isolation and Characterization of Functionally Active Extracellular Vesicles from Culture Medium Conditioned by Bovine Embryos In Vitro

Extracellular vesicles (EVs) play a possible role in cell–cell communication and are found in various body fluids and cell conditioned culture media. The aim of this study was to isolate and characterize EVs in culture medium conditioned by bovine embryos in group and to verify if these EVs are functionally active. Initially, ultracentrifuged bovine serum albumin (BSA) containing medium was selected as suitable EV-free embryo culture medium. Next, EVs were isolated from embryo conditioned culture medium by OptiPrep^TM density gradient ultracentrifugation. Isolated EVs were characterized by nanoparticle tracking analysis, western blotting, transmission, and immunoelectron microscopy. Bovine embryo-derived EVs were sizing between 25–230 nm with an average concentration of 236.5 ± 1.27 × 10⁸ particles/mL. Moreover, PKH67 EV pre-labeling showed that embryo-secreted EVs were uptaken by zona-intact bovine embryos. Since BSA did not appear to be a contaminating EV source in culture medium, EV functionality was tested in BSA containing medium. Individual embryo culture in BSA medium enriched with EVs derived from conditioned embryo culture medium showed significantly higher blastocyst rates at day 7 and 8 together with a significantly lower apoptotic cell ratio. In conclusion, our study shows that EVs play an important role in inter embryo communication during bovine embryo culture in group.

The Role of Extracellular Vesicles and PIBF in Embryo-Maternal Immune-Interactions

Pregnancy represents a unique immunological situation. Though paternal antigens expressed by the conceptus are recognized by the immune system of the mother, the immune response does not harm the fetus. Progesterone and a progesterone induced protein; PIBF are important players in re-adjusting the functioning of the maternal immune system during pregnancy. PIBF expressed by peripheral pregnancy lymphocytes, and other cell types, participates in the feto-maternal communication, partly, by mediating the immunological actions of progesterone. Several splice variants of PIBF were identified with different physiological activity. The full length 90 kD PIBF protein plays a role in cell cycle regulation, while shorter splice variants are secreted and act as cytokines. Aberrant production of PIBF isoforms lead to the loss of immune-regulatory functions, resulting in and pregnancy failure. By up regulating Th2 type cytokine production and by down-regulating NK activity, PIBF contributes to the altered attitude of the maternal immune system. Normal pregnancy is characterized by a Th2-dominant cytokine balance, which is partly due to the action of the smaller PIBF isoforms. These bind to a novel form of the IL-4 receptor, and induce increased production of IL-3, IL-4, and IL-10. The communication between the conceptus and the mother is established via extracellular vesicles (EVs). Pre-implantation embryos produce EVs both in vitro, and in vivo. PIBF transported by the EVs from the embryo to maternal lymphocytes induces increased IL-10 production by the latter, this way contributing to the Th2 dominant immune responses described during pregnancy.

Symposium review: Embryo survival-A genomic perspective of the other side of fertility

The majority of embryonic loss in cattle occurs within the first 3 to 4 wk of pregnancy, and there are currently no accurate predictors of pregnancy outcome. Existing embryo quality assessment methods include morphological evaluation and embryo biopsy. These methods are not accurate and carry some health risks to the developing embryo, respectively. Therefore, there is need to identify noninvasive biomarkers such as microRNA that can predict embryo quality and pregnancy outcome. Furthermore, researchers need a better understanding of the dynamic interaction between the mother and the embryo. The transcriptome of the uterus shows plasticity that depends on the embryo type so that the expression level of some genes for in vivo embryos would be different from that of in vitro-produced embryos. Similarly, the embryonic transcriptome and epigenome change in response to different environmental factors such as stress, diet, disease, and physiological status of the mother. This embryo-mother crosstalk could be better understood by investigating the molecular signaling that occurs at different stages of embryonic development. Although transcriptomics is a useful tool to assess the roles of genes and pathways in embryo quality and maternal receptivity, it does not provide the exact functions of these genes, and it shows correlation rather than causality. Therefore, an in-depth functional genomic analysis is needed for better understanding of the molecular mechanisms controlling embryo development. In this review, we discuss recent genomic technologies such as RNA interference, gapmer technology, and genome editing techniques used in humans and livestock to elucidate the molecular mechanisms of genes affecting embryo development.

Murine embryos exposed to human endometrial MSCs-derived extracellular vesicles exhibit higher VEGF/PDGF AA release, increased blastomere count and hatching rates

Endometrial Mesenchymal Stromal Cells (endMSCs) are multipotent cells with immunomodulatory and pro-regenerative activity which is mainly mediated by a paracrine effect. The exosomes released by MSCs have become a promising therapeutic tool for the treatment of immune-mediated diseases. More specifically, extracellular vesicles derived from endMSCs (EV-endMSCs) have demonstrated a cardioprotective effect through the release of anti-apoptotic and pro-angiogenic factors. Here we hypothesize that EV-endMSCs may be used as a co-adjuvant to improve in vitro fertilization outcomes and embryo quality. Firstly, endMSCs and EV-endMSCs were isolated and phenotypically characterized for in vitro assays. Then, in vitro studies were performed on murine embryos co-cultured with EV-endMSCs at different concentrations. Our results firstly demonstrated a significant increase on the total blastomere count of expanded murine blastocysts. Moreover, EV-endMSCs triggered the release of pro-angiogenic molecules from embryos demonstrating an EV-endMSCs concentration-dependent increase of VEGF and PDGF-AA. The release of VEGF and PDGF-AA by the embryos may indicate that the beneficial effect of EV-endMSCs could be mediating not only an increase in the blastocyst’s total cell number, but also may promote endometrial angiogenesis, vascularization, differentiation and tissue remodeling. In summary, these results could be relevant for assisted reproduction being the first report describing the beneficial effect of human EV-endMSCs on embryo development.

PIBF+ extracellular vesicles from mouse embryos affect IL-10 production by CD8+ cells

Earlier evidence suggests, that the embryo signals to the maternal immune system. Extracellular vesicles (EVs) are produced by all types of cells, and because they transport different kinds of molecules from one cell to the other, they can be considered as means of intercellular communication. The aim of this work was to test, whether the embryo is able to produce sufficient amounts of EVs to alter the function of peripheral lymphocytes. Embryo-derived EVs were identified by their Annexin V biding capacity, and sensitivity to Triton X dependent lysis, using flow cytometry. Transmission electron microscopy was used to detect EVs at the implantation site. Progesterone-induced blocking factor (PIBF) expression in embryo-derived EVs was demonstrated with immuno-electron microscopy. The % of IL-10 + murine lymphocytes was determined by flow cytometry. EVs were present in embryo culture media, but not in empty media. Mouse embryo-derived EVs adhere to the surface of both CD4+ and CD8+ murine peripheral T lymphocytes, partly, via phosphatidylserine binding. The number of IL-10+ murine peripheral CD8+ cells increases in the presence of embryo-derived EVS, and this effect is counteracted by pre-treatment of EVs with an anti-PIBF antibody, suggesting that the embryo communicates with the maternal immune system via EVs.

MicroRNAs: tiny molecules with a significant role in mammalian follicular and oocyte development

The genetic regulation of female fertility (follicular development, oocyte maturation and early preimplantation embryo development) involves the spatio-temporal regulation of those genes that play key roles in various stages of the female reproductive axis. MicroRNAs (miRNAs), a class of small non-coding RNAs, are known to regulate the expression of a large proportion of such genes. In recent decades, multiple studies have aimed to determine the roles of these non-coding RNAs in mammalian follicular development, oocyte growth and embryo development. These studies have applied a variety of approaches, including conditional knockout of miRNA biogenesis genes, high-throughput sequencing technologies for pattern recognition in miRNA expression and loss- and gain-of-function of miRNAs in various animal models. In addition to the cellular miRNAs, a large variety of RNAs are found in circulation, being coupled with extracellular vesicles, proteins and lipids. Because of their potential as diagnostic markers for abnormal physiologies, there is increasing interest in the identification of extracellular miRNAs in various biological fluids and spent in vitro culture media. This review focuses on studies addressing the expression and potential role of cellular and extracellular miRNAs in mammalian follicular cell physiology and subsequent ovarian functionality and oocyte maturation.