Conceptus implantation and placentation: molecules related to epithelial-mesenchymal transition, lymphocyte homing, endogenous retroviruses, and exosomes

Global analyses and potential effects of extracellular vesicles on the establishment of conceptus implantation during the peri-implantation period

Intrauterine extracellular vesicles (EVs) are involved in establishing proper conceptus-endometrial communication, which is essential for conceptus implantation and subsequent successful placentation. Despite several studies on intrauterine EVs, the composition and quantitative changes in conceptus and endometrial EVs, as well as the effects of intrauterine EVs on endometrial epithelial cells (EECs) during the peri-implantation period, have not been well characterized. To elucidate global changes in proteins in EVs extracted from uterine flushings (UFs) during the pre-implantation (P17), just-implantation (P20), and post-implantation (P22) periods, the datasets of the proteome iTRAQ analysis were compared among P17, P20, and P22 EVs. These analyses revealed that the composition and function of proteins in the EVs changed dramatically during peri-implantation in cattle. Notably, intrauterine P17 EVs affected the high expression of "Developmental Biology" and "morphogenesis of an endothelium" compared with those in P20 and P22 EVs. Furthermore, P20 EVs had the functions of the high expression of "mitochondrial calcium ion homeostasis" and "Viral mRNA Translation" compared with those in P17 EVs. Transcripts extracted from EECs treated with P17, P20, or P22 EVs were subjected to RNA-seq analysis. These analyses identified 60 transcripts in EECs commonly induced by intrauterine EVs recovered from P17, P20, and P22, a large number of which were associated with "type I interferon signaling pathway". Collectively, these findings reveal the presence and multiple functions of EVs that are potentially implicated in facilitating conceptus implantation into the uterine epithelium during the peri-implantation period.

The Extracellular Vesicles Proteome of Endometrial Cells Simulating the Receptive Menstrual Phase Differs from That of Endometrial Cells Simulating the Non-Receptive Menstrual Phase

Successful embryo implantation into a receptive endometrium requires mutual endometrial-embryo communication. Recently, the function of extracellular vehicles (EVs) in cell-to-cell interaction in embryo-maternal interactions has been investigated. We explored isolated endometrial-derived EVs, using RL95-2 cells as a model of a receptive endometrium, influenced by the menstrual cycle hormones estrogen (E2; proliferative phase), progesterone (P4; secretory phase), and estrogen plus progesterone (E2P4; the receptive phase). EV sized particles were isolated by differential centrifugation and size exclusion chromatography. Nanoparticle tracking analysis was used to examine the different concentrations and sizes of particles and EV proteomic analysis was performed using shotgun label-free mass spectrometry. Our results showed that although endometrial derived EVs were secreted in numbers independent of hormonal stimulation, EV sizes were statistically modified by it. Proteomics analysis showed that hormone treatment changes affect the endometrial EV's proteome, with proteins enhanced within the EV E2P4 group shown to be involved in different processes, such as embryo implantation, endometrial receptivity, and embryo development, supporting the concept of a communication system between the embryo and the maternal endometrium via EVs.

TNF-α Regulated Endometrial Stroma Secretome Promotes Trophoblast Invasion

Successful implantation requires the coordinated migration and invasion of trophoblast cells from out of the blastocyst and into the endometrium. This process relies on signals produced by cells in the maternal endometrium. However, the relative contribution of stroma cells remains unclear. The study of human implantation has major technical limitations, therefore the need of in vitro models to elucidate the molecular mechanisms. Using a recently described 3D in vitro models we evaluated the interaction between trophoblasts and human endometrial stroma cells (hESC), we assessed the process of trophoblast migration and invasion in the presence of stroma derived factors. We demonstrate that hESC promotes trophoblast invasion through the generation of an inflammatory environment modulated by TNF-α. We also show the role of stromal derived IL-17 as a promoter of trophoblast migration through the induction of essential genes that confer invasive capacity to cells of the trophectoderm. In conclusion, we describe the characterization of a cellular inflammatory network that may be important for blastocyst implantation. Our findings provide a new insight into the complexity of the implantation process and reveal the importance of inflammation for embryo implantation.

The effect of bta-miR-26b in intrauterine extracellular vesicles on maternal immune system during the implantation period

Extracellular vesicles (EVs) in utero play a role in cellular interactions between endometrium-conceptuses (embryo plus extraembryonic membranes) during peri-implantation periods. However, how intrauterine EVs function on endometrium have not been well characterized. In our previous study, bta-miR-98 found in intrauterine EVs from uterine flushing fluids (UFs) on pregnant day 20 (a half day after initial conceptus attachment, P20) could regulate the maternal immune system and collaborate with other miRNAs and/or components of EVs for conceptus implantation. We, therefore, hypothesized that in addition to bta-miR-98, other miRNAs present in bovine intrauterine EVs may regulate the maternal immune system in the endometrial epithelium. A global analysis of differentially expressed proteins between EVs from P17 and P20 UFs revealed that components of intrauterine P20 EVs had the effect on the down-regulation of "neutrophil activation involved in immune response" and "neutrophil mediated immunity". In silico analyses predicted bta-miR-26b as one of potential miRNA to regulate maternal immune system. In our cell culture experiments, bta-miR-26b negatively regulated several immune system-related genes PSMC6, CD40, and IER3 in bovine endometrial epithelial cells. Our findings revealed that intrauterine EV-derived bta-miR-26b contributes to the down-regulation of the maternal immune system, allowing conceptus implantation to the uterine endometrium. Furthermore, our results suggest that intrauterine EVs extracted from P20 UFs could regulate neutrophils, the first line of immunological defense, to modulate endometrial immune and inflammatory responses for implanting conceptuses.

Conceptus metabolomic profiling reveals stage-specific phenotypes leading up to pregnancy recognition in cattle†

Reproductive efficiency in livestock is a major driver of sustainable food production. The poorly understood process of ruminant conceptus elongation (a) prerequisites maternal pregnancy recognition, (b) is essential to successful pregnancy establishment, and (c) coincides with a period of significant conceptus mortality. Conceptuses at five key developmental stages between Days 8-16 were recovered and cultured in vitro for 6 h prior to conditioned media analysis by untargeted ultrahigh-performance liquid chromatography tandem mass spectroscopy. This global temporal biochemical interrogation of the ex situ bovine conceptus unearths two antithetical stage-specific metabolic phenotypes during tubular (metabolically retentive) vs. filamentous (secretory) development. Moreover, the retentive conceptus phenotype on Day 14 coincides with an established period of elevated metabolic density in the uterine fluid of heifers with high systemic progesterone-a model of accelerated conceptus elongation. These data, combined, suggest a metabolic mechanism underpinning conceptus elongation, thereby enhancing our understanding of the biochemical reciprocity of maternal-conceptus communication, prior to maternal pregnancy recognition.

The supression of DOCK family members by their specific inhibitors induces the cell fusion of human trophoblastic cells

PURPOSE

Among the members of the DOCK family, DOCK1-5 function as guanine-nucleotide exchange factors for small GTPase Rac1, which regulates the actin cytoskeleton. It has been reported that in model organisms the Dock-Rac axis is required for myoblast fusion. We examined the role of DOCK1-5 in trophoblast fusion herein.

METHODS

We used a quantitative polymerase chain reaction (qPCR) to examine the mRNA expressions of DOCK1-5 and differentiation-related genes, i.e., fusogenic genes, in human trophoblastic cell lines, BeWo and JEG-3. We treated BeWo cells with TBOPP and C21 to inhibit DOCK1 and DOCK5. Cell dynamics and cell fusion were assessed by live imaging and immunostaining. The signaling pathways induced by DOCK1/5 inhibition were examined by western blotting.

RESULTS

DOCK1 and DOCK5 were expressed in BeWo cells. The inhibition of DOCK1 or DOCK5 did not prevent the cell fusion induced by forskolin (a common reagent for cell fusion); it induced cell fusion. DOCK1 inhibition induced cell death, as did forskolin. DOCK1 and DOCK5 inhibition for 24 and 48 h increased the expression of the genes ASCT2 and SYNCYTIN2, which code responsive proteins of trophoblast cell fusion, respectively.

CONCLUSION

DOCK1 and DOCK5 inhibition participates in BeWo cell fusion, probably via pathways independent from forskolin-mediated pathways.

Promoting Roles of Embryonic Signals in Embryo Implantation and Placentation in Cooperation with Endocrine and Immune Systems

Embryo implantation in the uterus is an essential process for successful pregnancy in mammals. In general, the endocrine system induces sufficient embryo receptivity in the endometrium, where adhesion-promoting molecules increase and adhesion-inhibitory molecules decrease. Although the precise mechanisms remain unknown, it is widely accepted that maternal–embryo communications, including embryonic signals, improve the receptive ability of the sex steroid hormone-primed endometrium. The embryo may utilize repulsive forces produced by an Eph–ephrin system for its timely attachment to and subsequent invasion through the endometrial epithelial layer. Importantly, the embryonic signals are considered to act on maternal immune cells to induce immune tolerance. They also elicit local inflammation that promotes endometrial differentiation and maternal tissue remodeling during embryo implantation and placentation. Additional clarification of the immune control mechanisms by embryonic signals, such as human chorionic gonadotropin, pre-implantation factor, zona pellucida degradation products, and laeverin, will aid in the further development of immunotherapy to minimize implantation failure in the future.

Effects of miR-98 in intrauterine extracellular vesicles on maternal immune regulation during the peri-implantation period in cattle

Evidence accumulated suggests that extracellular vesicles (EVs) present in uterine lumen play a role in conceptus-endometrial cell interactions during peri-implantation periods. However, how intrauterine EVs function on endometrium have not been well characterized. To study how intrauterine EVs affect endometrial milieu in cattle, bovine endometrial epithelial cells (EECs) were treated with EVs isolated from uterine flushing fluids (UFs) on day 17 or 20 pregnancy (P17, P20, respectively; conceptus implantation to endometrium begins on days 19–19.5). RNA extracted from EECs were then subjected to RNA sequence analysis. The analysis revealed that transcripts related to immune system were down-regulated in EECs treated with EVs on P20 compared with those on P17. To investigate whether microRNAs (miRNAs) in EVs regulate maternal immune system in the endometrium during the peri-implantation, microRNA sequence and in silico analyses were performed, identifying bta-miR-98 in EVs as a potential miRNA to regulate maternal immune system. Furthermore, the treatment of EECs with bta-miR-98 negatively regulated several immune system-related genes, CTSC, IL6, CASP4 and IKBKE, in EECs. These results suggest that EVs containing bta-miR-98 is a regulator of maternal immune system, possibly allowing the conceptus attachment to the endometrial epithelium during the peri-implantation period.

Review: Eicosanoids in preterm labor and delivery: Potential roles of exosomes in eicosanoid functions

Preterm delivery is a major obstetric health problem contributing to poor neonatal outcome including low birth weight, respiratory distress syndrome, gastrointestinal, immunologic, central nervous system, hearing, and vision problems. Worldwide, approximately 15 million babies are born prematurely each year. The critical question which remains is how to identify women destined to deliver preterm from those who will achieve a term delivery. Prostaglandins, in all mammals, are important in the parturient process. Increased intrauterine prostaglandin production is associated with labor and in fact prostaglandin E₂ (PGE₂) or analogs are widely used clinically for cervical ripening and labor induction. Measurements of circulating eicosanoids have been problematic because of the rapid and major clearance by the lungs and then kidneys resulting in very low concentrations in plasma. Moreover, since eicosanoids are produced by all mammalian tissues, the sources of the measured eicosanoids are unknown. Our understanding of how cells communicate has undergone a paradigm shift with the recognition of the role of exosomes in intercellular signaling. Recent publications have identified enzymes and products of arachidonic acid metabolism (eicosanoids) within exosomes. This review will explore the potential roles of exosomes in eicosanoid functions that are critical in preterm labor and delivery.