Trophoblast organoids as a model for maternal-fetal interactions during human placentation

Immunity at maternal-fetal interface: KIR/HLA (Allo)recognition

Both KIR and HLA are the most variable gene families in the human genome. The recognition of the semi-allogeneic embryo-derived trophoblasts by maternal decidual NK (dNK) cells is essential for the establishment of the functional placenta. This recognition is based on the KIR-HLA interactions and trophoblast expresses a specific HLA profile that constitutes classical polymorphic HLA-C and non-classical oligomorphic HLA-E, HLA-F, and HLA-G molecules. This review highlights some features of the KIR/HLA-C (allo)recognition by decidual NK (dNK) cells as a main immune cell population specifically enriched at maternal-fetal interface during human early pregnancy. How KIR/HLA-C axis operates in pregnancy disorders and in the context of transplacental infections is discussed as well. We summarized old and new data on dNK-cell functional plasticity, their selective expression of KIR and fetal maternal/paternal HLA-C haplotypes present. Results showed that KIR-HLA-C combinations and the corresponding axis operate differently in each pregnancy, determined by the variability of both maternal KIR haplotypes and fetus' maternal/paternal HLA-C allotype combinations. Moreover, the maturation of NK cells strongly depends on if or not HLA allotypes for certain KIR are present. We suggest that the unique KIR/HLA combinations reached in each pregnancy (normal and pathological) should be studied according to well-defined guidelines and unified methodologies to have comparable results ease to interpret and use in clinics.

Primary Trophoblast Cultures: Characterization of HLA Profiles and Immune Cell Interactions

Introduction

Trophoblasts are essential in fetal-maternal interaction during pregnancy. The goal was to study HLA profiles of primary trophoblasts derived from placentas, and to investigate their usefulness in studying interaction with immune cells.

Methods

After enzymatic digestion of first-trimester placental tissue from seven donors (6-9 weeks gestation) and trophoblast enrichment we cultured cytotrophoblasts (CTB) in stem cell medium. CTB were differentiated into EVT in a Matrigel-containing medium. A subset of CTB/EVT was profiled for microRNA levels. Expression of classical HLA molecules and of HLA-G was studied by flow cytometry, qPCR, and ELISA. Secondary trophoblast cell lines JAR and JEG-3 were studied as controls. Lymphocytes were investigated during co-culturing with EVT.

Results

The trophoblasts could be easily maintained for several passages, upregulated classical trophoblast markers (GATA3, TFAP2C, chromosome-19 microRNAs), and upon differentiation to EVT they were selective in expressing HLA-C. EVT showed increasing expression of total HLA-G, an increasing proportion of HLA-G1 over G2- and G3 isoforms, and elevated excretion of soluble HLA-G. These features were distinct from those of the secondary trophoblast cell lines. TNF-α and IL-8 represented the most abundantly secreted cytokines by CTB, but their levels were minimal in EVT cultures. As proof of principle, we showed that EVT affect lymphocytes in three-day co-cultures (n=4) by decreasing activation marker HLA-DR.

Conclusion

We verified the possibility culturing trophoblasts from first-term placentas, and their capability of differentiating to HLA-G expressing EVT. This culture model better represents the in-vivo situation than previously studied secondary trophoblast cell lines and enables mechanistic studies of fetal-maternal interactions.

Mapping Human Reproduction with Single-Cell Genomics

The trillions of cells in the human body develop as a result of the fusion of two extremely specialized cells: an oocyte and a sperm. This process is essential for the continuation of our species, as it ensures that parental genetic information is mixed and passed on from generation to generation. In addition to producing oocytes, the female reproductive system must provide the environment for the appropriate development of the fetus until birth. New genomic and computational tools offer unique opportunities to study the tight spatiotemporal regulatory mechanisms that are required for the cycle of human reproduction. This review explores how single-cell technologies have been used to build cellular atlases of the human reproductive system across the life span and how these maps have proven useful to better understand reproductive pathologies and dissect the heterogeneity of in vitro model systems. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The Role of Endometrial Stem/Progenitor Cells in Recurrent Reproductive Failure

Recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL), collectively referred to as recurrent reproductive failure (RRF), are both challenging conditions with many unanswered questions relating to causes and management options. Both conditions are proposed to be related to an aberrant endometrial microenvironment, with different proposed aetiologies related to a restrictive or permissive endometrium for an invading embryo. The impressive regenerative capacity of the human endometrium has been well-established and has led to the isolation and characterisation of several subtypes of endometrial stem/progenitor cells (eSPCs). eSPCs are known to be involved in the pathogenesis of endometrium-related disorders (such as endometriosis) and have been proposed to be implicated in the pathogenesis of RRF. This review appraises the current knowledge of eSPCs, and their involvement in RRF, highlighting the considerable unknown aspects in this field, and providing avenues for future research to facilitate much-needed advances in the diagnosis and management of millions of women suffering with RRF.

Establishment of a non‐integrated induced pluripotent stem cell line derived from human chorionic villi cells

Background

Few studies have investigated the generation of induced pluripotent stem cells (iPSCs) derived from human primary chorionic villi (CV) cells. The present study aimed to explore an optimal electroporation (EP) condition for generating non‐integrated iPSCs from CV cells (CV‐iPSCs).

Methods

The EGFP plasmid was transfected into CV cells under different EP conditions to evaluate cell adherence and the rate of EGFP positive cells. Subsequently, CV cells were transfected with the pEP4‐E02S‐ET2K and pCEP4‐miR‐302–367 plasmids under optimal EP conditions. Finally, CV‐iPSC pluripotency, karyotype analysis, and differentiation ability were investigated.

Results

Following EP for 48 h under different conditions, different confluency, and transfection efficiency were observed in CV cells. Higher cell density was observed in CV cells exposed to 200 V for 100 s, while higher transfection efficiency was obtained in cells electroporated at a pulse of 300 V for 300 s. To generate typical primitive iPSCs, CV cells were transfected with pEP4‐E02S‐ET2K and pCEP4‐miR‐302–367 plasmids using EP and were then cultured in induction medium for 20 days under selected conditions. Subsequently, monoclonal iPSCs were isolated and were evaluated pluripotency with AP positive staining, the expression of OCT4, SOX2, and NANOG in vitro and the formation of three germ layer teratomas in vivo.

Conclusion

CV‐iPSCs were successfully established under the conditions of 100 μl shock cup and EP pulse of 200 V for 300 s for two times. This may provide a novel strategy for investigating the pathogenesis of several diseases and gene therapy.

Stem-cell-derived trophoblast organoids model human placental development and susceptibility to emerging pathogens

Trophoblast organoids derived from placental villi provide a 3D model system of human placental development, but access to first-trimester tissues is limited. Here, we report that trophoblast stem cells isolated from naive human pluripotent stem cells (hPSCs) can efficiently self-organize into 3D stem-cell-derived trophoblast organoids (SC-TOs) with a villous architecture similar to primary trophoblast organoids. Single-cell transcriptome analysis reveals the presence of distinct cytotrophoblast and syncytiotrophoblast clusters and a small cluster of extravillous trophoblasts, which closely correspond to trophoblast identities in the post-implantation embryo. These organoid cultures display clonal X chromosome inactivation patterns previously described in the human placenta. We further demonstrate that SC-TOs exhibit selective vulnerability to emerging pathogens (SARS-CoV-2 and Zika virus), which correlates with expression levels of their respective entry factors. The generation of trophoblast organoids from naive hPSCs provides an accessible 3D model system of the developing placenta and its susceptibility to emerging pathogens.

Screening of Organophosphate Flame Retardants with Placentation-Disrupting Effects in Human Trophoblast Organoid Model and Characterization of Adverse Pregnancy Outcomes in Mice

BACKGROUND

Abnormal placental development may result in adverse pregnancy outcomes and metabolic diseases in adulthood; however, it remains unknown whether and how xenobiotics affect human placentation.

OBJECTIVES

This study aimed to screen and identify placentation-disrupting chemicals in commonly used organophosphate flame retardants (OPFRs) and, if identified, to investigate potential adverse effects on placentation in relation to adverse pregnancy outcomes and metabolic disorder in offspring in mice.

METHODS

We devised a high-throughput immunofluorescence screening assay based on human trophoblast organoids and used it to screen OPFRs that inhibit the proliferation of organoids. One identified chemical was assessed for its effects on placentation by evaluating villous cytotrophoblasts, syncytiotrophoblasts, and extravillous trophoblasts using immunofluorescence and a mitochondrial stress test after 2 d of exposure. A 10-d exposure study was further performed to observe the dynamic effect of the OPFR on the structure of the organoids. RNA-sequencing and western blotting experiments were performed to explore the associated pathways, and a potential binding protein was identified by immunoprecipitation and in vitro kinase activity assays. Animal studies were performed to determine whether the findings in organoids could be replicated in mice and to observe adverse pregnancy outcomes.

RESULTS

The proliferation of organoids exposed to three aryl-OPFRs was significantly lower than the proliferation of control organoids. Further analysis demonstrated that one such chemical, 2-ethylhexyl-diphenyl phosphate (EHDPP), disrupted placentation in organoids. Mechanistically, EHDPP interfered with insulin-like growth factor 1 receptor (IGF1R) to inhibit aerobic respiration. Mice exposed to EHDPP at a physiological human concentrations exhibited immature and mature placental disorders, which correlated with fetal growth restriction, implantation failure, stillbirth, and impaired glucose tolerance.

CONCLUSIONS

The human trophoblast organoid model showed that the commonly used OPFRs disrupted placentation via IGF1R, indicating that its use may contribute to adverse pregnancy outcomes and metabolic disorders in offspring. https://doi.org/10.1289/EHP10273.

Current understanding in deciphering trophoblast cell differentiation during human placentation

The placenta is a unique organ that forms during gestation and supports fetus survival and communication with the mother. However, of such an arguably essential organ for a successful pregnancy, our knowledge is limited. New progress has been made for human placenta study in recent years. We herein summarize the current understanding of human placental trophoblast differentiation and the molecules that govern trophoblast cell lineage specification. More importantly, the powerful tools for placental studies are also explained, such as human trophoblast stem cells (hTSCs), 3-dimensional (3D) trophoblast organoids, engineering-based placental devices, and single-cell RNA sequencing (sc-RNAseq). These advances have brought us new insights into placental development and provided multiple investigation strategies for deciphering molecular mechanisms.

Chronic Inflammatory Placental Disorders Associated With Recurrent Adverse Pregnancy Outcome

Chronic inflammatory placental disorders are a group of rare but devastating gestational syndromes associated with adverse pregnancy outcome. This review focuses on three related conditions: villitis of unknown etiology (VUE), chronic histiocytic intervillositis (CHI) and massive perivillous fibrin deposition (MPFD). The hallmark of these disorders is infiltration of the placental architecture by maternal immune cells and disruption of the intervillous space, where gas exchange between the mother and fetus occurs. Currently, they can only be detected through histopathological examination of the placenta after a pregnancy has ended. All three are associated with a significant risk of recurrence in subsequent pregnancies. Villitis of unknown etiology is characterised by a destructive infiltrate of maternal CD8+ T lymphocytes invading into the chorionic villi, combined with activation of fetal villous macrophages. The diagnosis can only be made when an infectious aetiology has been excluded. VUE becomes more common as pregnancy progresses and is frequently seen with normal pregnancy outcome. However, severe early-onset villitis is usually associated with fetal growth restriction and recurrent pregnancy loss. Chronic histiocytic intervillositis is characterised by excessive accumulation of maternal CD68+ histiocytes in the intervillous space. It is associated with a wide spectrum of adverse pregnancy outcomes including high rates of first-trimester miscarriage, severe fetal growth restriction and late intrauterine fetal death. Intervillous histiocytes can also accumulate due to infection, including SARS-CoV-2, although this infection-induced intervillositis does not appear to recur. As with VUE, the diagnosis of CHI requires exclusion of an infectious cause. Women with recurrent CHI and their families are predisposed to autoimmune diseases, suggesting CHI may have an alloimmune pathology. This observation has driven attempts to prevent CHI with a wide range of maternal immunosuppression. Massive perivillous fibrin deposition is diagnosed when >25% of the intervillous space is occupied by fibrin, and is associated with fetal growth restriction and late intrauterine fetal death. Although not an inflammatory disorder per se, MPFD is frequently seen in association with both VUE and CHI. This review summarises current understanding of the prevalence, diagnostic features, clinical consequences, immune pathology and potential prophylaxis against recurrence in these three chronic inflammatory placental syndromes.

Placental Models for Evaluation of Nanocarriers as Drug Delivery Systems for Pregnancy Associated Disorders

Pregnancy-associated disorders affect around 20% of pregnancies each year around the world. The risk associated with pregnancy therapeutic management categorizes pregnant women as "drug orphan" patients. In the last few decades, nanocarriers have demonstrated relevant properties for controlled drug delivery, which have been studied for pregnancy-associated disorders. To develop new drug dosage forms it is mandatory to have access to the right evaluation models to ensure their usage safety and efficacy. This review exposes the various placental-based models suitable for nanocarrier evaluation for pregnancy-associated therapies. We first review the current knowledge about nanocarriers as drug delivery systems and how placenta can be used as an evaluation model. Models are divided into three categories: in vivo, in vitro, and ex vivo placental models. We then examine the recent studies using those models to evaluate nanocarriers behavior towards the placental barrier and which information can be gathered from these results. Finally, we propose a flow chart on the usage and the combination of models regarding the nanocarriers and nanoparticles studied and the intended therapeutic strategy.

In Vitro Model of Human Trophoblast in Early Placentation

The complex process of placental implantation and development affects trophoblast progenitors and uterine cells through the regulation of transcription factors, cytokines, adhesion receptors and their ligands. Differentiation of trophoblast precursors in the trophectoderm of early ontogenesis, caused by the transcription factors, such as CDX2, TEAD4, Eomes and GATA3, leads to the formation of cytotrophoblast and syncytiotrophoblast populations. The molecular mechanisms involved in placental formation inside the human body along with the specification and differentiation of trophoblast cell lines are, mostly due to the lack of suitable cell models, not sufficiently elucidated. This review is an evaluation of current technologies, which are used to study the behavior of human trophoblasts and other placental cells, as well as their ability to represent physiological conditions both in vivo and in vitro. An in vitro 3D model with a characteristic phenotype is of great benefit for the study of placental physiology. At the same time, it provides great support for future modeling of placental disease.

Human organoid models to study SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is one of the deadliest pandemics in history. SARS-CoV-2 not only infects the respiratory tract, but also causes damage to many organs. Organoids, which can self-renew and recapitulate the various physiology of different organs, serve as powerful platforms to model COVID-19. In this Perspective, we overview the current effort to apply both human pluripotent stem cell-derived organoids and adult organoids to study SARS-CoV-2 tropism, host response and immune cell-mediated host damage, and perform drug discovery and vaccine development. We summarize the technologies used in organoid-based COVID-19 research, discuss the remaining challenges and provide future perspectives in the application of organoid models to study SARS-CoV-2 and future emerging viruses.

Modeling Innate Antiviral Immunity in Physiological Context

An effective innate antiviral response is critical for the mitigation of severe disease and host survival following infection. In vivo, the innate antiviral response is triggered by cells that detect the invading pathogen and then communicate through autocrine and paracrine signaling to stimulate the expression of genes that inhibit viral replication, curtail cell proliferation, or modulate the immune response. In other words, the innate antiviral response is complex and dynamic. Notably, in the laboratory, culturing viruses and assaying viral life cycles frequently utilizes cells that are derived from tissues other than those that support viral replication during natural infection, while the study of viral pathogenesis often employs animal models. In recapitulating the human antiviral response, it is important to consider that variation in the expression and function of innate immune sensors and antiviral effectors exists across species, cell types, and cell differentiation states, as well as when cells are placed in different contexts. Thus, to gain novel insight into the dynamics of the host response and how specific sensors and effectors impact infection kinetics by a particular virus, the model system must be selected carefully. In this review, we briefly introduce key signaling pathways involved in the innate antiviral response and highlight how these differ between systems. We then review the application of tissue-engineered or 3D models for studying the antiviral response, and suggest how these in vitro culture systems could be further utilized to assay physiologically-relevant host responses and reveal novel insight into virus-host interactions.

Renalase and its receptor, PMCA4b, are expressed in the placenta throughout the human gestation

Placental function requires organized growth, transmission of nutrients, and an anti-inflammatory milieu between the maternal and fetal interface, but placental factors important for its function remain unclear. Renalase is a pro-survival, anti-inflammatory flavoprotein found to be critical in other tissues. We examined the potential role of renalase in placental development. PCR, bulk RNA sequencing, immunohistochemistry, and immunofluorescence for renalase and its binding partners, PMCA4b and PZP, were performed on human placental tissue from second-trimester and full-term placentas separated into decidua, placental villi and chorionic plates. Quantification of immunohistochemistry was used to localize renalase across time course from 17 weeks to term. Endogenous production of renalase was examined in placental tissue and organoids. Renalase and its receptor PMCA4b transcripts and proteins were present in all layers of the placenta. Estimated RNLS protein levels did not change with gestation in the decidual samples. However, placental villi contained more renalase immunoreactive cells in fetal than full-term placental samples. RNLS co-labeled with markers for Hofbauer cells and trophoblasts within the placental villi. Endogenous production of RNLS, PMCA4b, and PZP by trophoblasts was validated in placental organoids. Renalase is endogenously expressed throughout placental tissue and specifically within Hofbauer cells and trophoblasts, suggesting a potential role for renalase in placental development and function. Future studies should assess renalase's role in normal and diseased human placenta.

The Roles of Extracellular Vesicles and Organoid Models in Female Reproductive Physiology

Culture model systems that can recapitulate the anatomy and physiology of reproductive organs, such as three-dimensional (3D) organoid culture systems, limit the cost and welfare concerns associated with a research animal colony and provide alternative approaches to study specific processes in humans and animals. These 3D models facilitate a greater understanding of the physiological role of individual cell types and their interactions than can be accomplished with traditional monolayer culture systems. Furthermore, 3D culture systems allow for the examination of specific cellular, molecular, or hormonal interactions, without confounding factors that occur with in vivo models, and provide a powerful approach to study physiological and pathological reproductive conditions. The goal of this paper is to review and compare organoid culture systems to other in vitro cell culture models, currently used to study female reproductive physiology, with an emphasis on the role of extracellular vesicle interactions. The critical role of extracellular vesicles for intercellular communication in physiological processes, including reproduction, has been well documented, and an overview of the roles of extracellular vesicles in organoid systems will be provided. Finally, we will propose future directions for understanding the role of extracellular vesicles in normal and pathological conditions of reproductive organs, utilizing 3D organoid culture systems.

UHRF1 shapes both the trophoblast invasion and decidual macrophage differentiation in early pregnancy

Trophoblasts play critical roles in establishment and maintenance of a normal pregnancy. Their dysfunction in early pregnancy is closely related to pregnancy-related diseases, including recurrent pregnancy loss (RPL). Epigenetic modifications dynamically change during pregnancy; however, the role of the epigenetic modifier UHRF1 in trophoblast regulation remains unknown. This is the first study to show that UHRF1 expression was localized in the cytoplasm of cytotrophoblasts, syncytiotrophoblasts, and villi columns, and decreased in the villi of patients with RPL. The invasion and cell viability in a UHRF1 knockdown trophoblast cell line were significantly decreased. In addition, the mRNA expression profiles of Swan71 cells were partially altered by UHRF1 knockdown. The altered immune-related genes were screened out and the pro-inflammatory TH1-type chemokine/cytokines CXCL2 and IL-1β were identified as the most promising targets of UHRF1 in the trophoblasts, which were significantly increased in the UHRF1 knockdown Swan71 cells, villi, and serum from patients with RPL. The macrophages treated with the supernatants of UHRF1 knockdown Swan71 cells were polarized to the M1 phenotype and secreted high levels of pro-inflammatory cytokines, which might be driven by the activated MyD88/NF-κB signaling pathway and mediated by the increased expression of CXCR2 and IL-1R1 (CXCL2 and IL-1β receptors, respectively). In addition, the supernatants of UHRF1 knockdown Swan71 cells showed stronger chemotaxis to macrophages than those from the controls. Our findings highlight the previously unknown roles of UHRF1 as one of the key regulators on the trophoblasts and their cross-talk with local immune cells, and demonstrate a potential approach for RPL intervention.

Does LIN28B gene dysregulation make women more likely to abort?

Background

LIN28B plays an important role in early embryonic development, but its role in villous trophoblast implantation and differentiation remains unknown. This study aims to verify the role of LIN28B in trophoblastic villous tissue and cells from women with URSA (unexplained recurrent spontaneous abortion) and artificial termination of pregnancy (negative control, NC).

Methods

The LIN28B gene and its protein expression level were detected with real-time quantitative PCR, Western immunoblotting analysis, and immunocytochemistry. The gene was also overexpressed in chorionic villous cell lines (HTR-8/SVneo and BeWo) to examine its effect on trophoblast function.

Results

The expression of LIN28B mRNA and protein of URSA villi was lower than that in the NC group. At the cellular level, overexpression of LIN28B enhanced cellular migration, and invasion, and inhibited apoptosis. LIN28B may inhibit apoptosis by promoting Akt phosphorylation and by inhibiting Bad phosphorylation and Bcl-2 expression. In addition, LIN28B inhibited cell fusion and reduced cellular syncytia.

Conclusions

LIN28B can inhibit cell invasion and migration in vitro and promote apoptosis and fusion. The low expression of LIN28B in URSA villous trophoblast cells may be one of the causes of abortion. The role of LIN28B in villous trophoblasts needs further study.

Lay summary

Propagation of offspring is of great significance to the continuation of the human race. However, continuous pregnancy is more difficult for some women, especially women who have multiple miscarriages. One important contributor is the cessation of development caused by genetic factors of the embryo, but there are still many unknown reasons. We investigated the LIN28B gene which is a possible pathogenic factor in the placenta. We collected 25 cases of abortion in the experimental group (unexplained recurrent abortion group) and 25 in the control group (artificial termination of pregnancy group): on average at 7–8 weeks of pregnancy. We tested the function of lin28b in these samples and verified its function in cell lines. LIN28B plays an important role in maintaining early pregnancy by promoting the invasion of villous cells, inhibiting apoptosis and fusion, and the reduction of LIN28B expression may lead to the occurrence of early miscarriage.

Organoids to model the endometrium: implantation and beyond

Despite advances in assisted reproductive techniques in the 4 decades since the first human birth after in vitro fertilisation, 1–2% of couples experience recurrent implantation failure, and some will never achieve a successful pregnancy even in the absence of a confirmed dysfunction. Furthermore, 1–2% of couples who do conceive, either naturally or with assistance, will experience recurrent early loss of karyotypically normal pregnancies. In both cases, embryo-endometrial interaction is a clear candidate for exploration. The impossibility of studying implantation processes within the human body has necessitated the use of animal models and cell culture approaches. Recent advances in 3-dimensional modelling techniques, namely the advent of organoids, present an exciting opportunity to elucidate the unanswerable within human reproduction. In this review, we will explore the ontogeny of implantation modelling and propose a roadmap to application and discovery.

Infections at the maternal-fetal interface: an overview of pathogenesis and defence

Infections are a major threat to human reproductive health, and infections in pregnancy can cause prematurity or stillbirth, or can be vertically transmitted to the fetus leading to congenital infection and severe disease. The acronym 'TORCH' (Toxoplasma gondii, other, rubella virus, cytomegalovirus, herpes simplex virus) refers to pathogens directly associated with the development of congenital disease and includes diverse bacteria, viruses and parasites. The placenta restricts vertical transmission during pregnancy and has evolved robust mechanisms of microbial defence. However, microorganisms that cause congenital disease have likely evolved diverse mechanisms to bypass these defences. In this Review, we discuss how TORCH pathogens access the intra-amniotic space and overcome the placental defences that protect against microbial vertical transmission.

Innate immune defenses at the maternal-fetal interface

The human maternal-fetal interface is an immunologically complex environment that must balance the divergent demands of tolerance towards the developing fetus with anti-pathogen defense. The innate immune responses at the maternal-fetal interface that function in anti-microbial defense have been understudied to-date and how 'TORCH' pathogens evade maternal innate immunity to infect the fetus remains poorly understood. Herein, we discuss how newly described decidual innate lymphoid cells and maternal placenta-associated macrophage subsets may be involved in anti-pathogen defense. Moreover, we outline recent advances in our understanding of how placental trophoblasts and fetal-derived macrophages (Hofbauer cells) function in anti-microbial defense. In summary, we highlight current gaps in knowledge and describe novel experimental models of the human decidua and placenta that are poised to advance our knowledge of innate immune defenses at the maternal-fetal interface.

Placental energy metabolism in health and disease-significance of development and implications for preeclampsia

The placenta is a highly metabolically active organ fulfilling the bioenergetic and biosynthetic needs to support its own rapid growth and that of the fetus. Placental metabolic dysfunction is a common occurrence in preeclampsia although its causal relationship to the pathophysiology is unclear. At the outset, this may simply be seen as an "engine out of fuel." However, placental metabolism plays a vital role beyond energy production and is linked to physiological and developmental processes. In this review, we discuss the metabolic basis for placental dysfunction and propose that the alterations in energy metabolism may explain many of the placental phenotypes of preeclampsia such as reduced placental and fetal growth, redox imbalance, oxidative stress, altered epigenetic and gene expression profiles, and the functional consequences of these aberrations. We propose that placental metabolic reprogramming reflects the dynamic physiological state allowing the tissue to adapt to developmental changes and respond to preeclampsia stress, whereas the inability to reprogram placental metabolism may result in severe preeclampsia phenotypes. Finally, we discuss common tested and novel therapeutic strategies for treating placental dysfunction in preeclampsia and their impact on placental energy metabolism as possible explanations into their potential benefits or harm.

Emerging Progress in Nausea and Vomiting of Pregnancy and Hyperemesis Gravidarum: Challenges and Opportunities

Nausea and vomiting of pregnancy (NVP) is a common condition that affects up to 70% of pregnant women. Hyperemesis gravidarum (HG) is considered the serious form of NVP, which is reported in 0.3–10.8% of pregnant women. NVP has a relatively benign course, but HG can be linked with some poor maternal, fetal, and offspring outcomes. The exact causes of NVP and HG are unknown, but various factors have been hypothesized to be associated with pathogenesis. With the advance of precision medicine and molecular biology, some genetic factors such as growth/differentiation factor 15 (GDF15) have become therapeutic targets. In our review, we summarize the historical hypotheses of the pathogenesis of NVP and HG including hormonal factors, Helicobacter pylori, gastrointestinal dysmotility, placenta-related factors, psychosocial factors, and new factors identified by genetics. We also highlight some approaches to the management of NVP and HG, including pharmacological treatment, complementary treatment, and some supporting treatments. Looking to the future, progress in understanding NVP and HG may reduce the adverse outcomes and improve the maternal quality of life during pregnancy.

The Future of 3D Brain Cultures in Developmental Neurotoxicity Testing

Human brain is undoubtedly the most complex organ in the body. Thus, it is difficult to develop adequate and at the same time human relevant test systems and models to cover the aspects of brain homeostasis and even more challenging to address brain development. Animal tests for Developmental Neurotoxicity (DNT) have been devised, but because of complex underlying mechanisms of neural development, and interspecies differences, there are many limitations of animal-based approaches. The high costs, high number of animals used per test and technical difficulties of these tests are prohibitive for routine DNT chemical screening. Therefore, many potential DNT chemicals remain unidentified. New approach methodologies (NAMs) are needed to change this. Experts in the field have recommended the use of a battery of human in vitro tests to be used for the initial prioritization of high-risk environmental chemicals for DNT testing. Microphysiological systems (MPS) of the brain mimic the in vivo counterpart in terms of cellular composition, recapitulation of regional architecture and functionality. These systems amendable to use in a DNT test battery with promising features such as (i) complexity, (ii) closer recapitulation of in vivo response and (iii) possibility to multiplex many assays in one test system, which can increase throughput and predictivity for human health. The resent progress in 3D brain MPS research, advantages, limitations and future perspectives are discussed in this review.

The impact of bisphenol a (BPA) on the placenta

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) that is used in a wide-variety of plastic and common house-hold items. Therefore, there is potential continual exposure to this compound. BPA exposure has been linked to certain placenta-associated obstetric complications such as preeclampsia, fetal growth restriction, miscarriage, and preterm birth. However, how BPA exposure results in these disorders remains uncertain. Hence, we have herein summarized the reported impact of BPA on the morphology and metabolic state of the placenta and have proposed mechanisms by which BPA affects placentation, potentially leading to obstetric complications. Current findings suggest that BPA induces pathological changes in the placenta and disrupts its metabolic activities. Based on exposure concentrations, BPA can elicit apoptotic or anti-apoptotic signals in the trophoblasts; and can exaggerate trophoblast fusion while inhibiting trophoblast migration and invasion to affect pregnancy. Accordingly, the usage of BPA products by pregnant women should be minimized and less harmful alternative chemicals should be explored and employed where possible.

Establishment of Trophoblast-Like Tissue Model from Human Pluripotent Stem Cells in Three-Dimensional Culture System

The placenta has a lifelong impact on the health of both the mother and fetus. Despite its significance, human early placental development is poorly understood due to the limited models. The models that can reflect the key features of early human placental development, especially at early gestation, are still lacking. Here, the authors report the generation of trophoblast-like tissue model from human pluripotent stem cells (hPSCs) in three-dimensional (3D) cultures. hPSCs efficiently self-organize into blastocoel-like cavities under defined conditions, which produce different trophoblast subtypes, including cytotrophoblasts (CTBs), syncytiotrophoblasts (STBs), and invasive extravillous trophoblasts (EVTs). The 3D cultures can exhibit microvilli structure and secrete human placenta-specific hormone. Single-cell RNA sequencing analysis further identifies the presence of major cell types of trophoblast-like tissue as existing in vivo. The results reveal the feasibility to establish 3D trophoblast-like tissue model from hPSCs in vitro, which is not obtained by monolayer culture. This new model system can not only facilitate to dissect the underlying mechanisms of early human placental development, but also imply its potential for study in developmental biology and gestational disorders.

The effect of ethanol and nicotine on ER stress in human placental villous explants

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Nicotine increased the GRP78/BiP protein in first trimester and term placental villous explants.

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Nicotine can cause endoplasmic reticulum stress in human placenta.

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Placental villous explants can be isolated from first trimester and term placenta to compare responses to toxic compounds.

Pregnant mothers continue smoking and drinking during pregnancy. To clarify the mechanisms of nicotine and ethanol toxicity during development, we have examined their effects on endoplasmic reticulum (ER) stress in human first trimester and term placental explants. First trimester and term human placental explants were treated with ethanol (2 ‰) or nicotine (15 µM), or their combination. The ER stress markers glucose regulated protein 78 (GRP78/BiP) and inositol requiring enzyme 1 α (IRE1α) were analyzed by immunoblotting. A statistically significant increase (p < 0.05) of GRP78/BiP by nicotine was noted in first trimester placental explants at 48 h, and in term placental explants at 24 h. Ethanol did not change protein expression of GRP78/BiP in either first trimester or term placental explants. IRE1α increased, although not statistically significantly, by all treatments in both first trimester and term placental explants. Thus, regardless of the known structural and functional differences in early and late placenta, both responded very similarly to the toxic compounds studied. These data support our earlier results in BeWo cells (Repo et al., 2014) implicating that nicotine induces ER stress in human placenta and may interfere with placental functions potentially disrupting fetal growth and development.

Exogenous melatonin protects preimplantation embryo development from decabromodiphenyl ethane-induced circadian rhythm disorder and endogenous melatonin reduction

Decabromodiphenyl ethane (DBDPE) is a novel flame retardant that is widely used in plastics, electronic products, building materials and textiles. Our previous studies have revealed the oocyte toxicity of DBDPE, but the effect of DBDPE on preimplantation embryo development has not been reported. Here, we investigated whether and how DBDPE exposure affects preimplantation embryo development. Adult female mice were orally exposed to DBDPE (0, 5, 50, 500 μg/kg bw/day) for 14 days. First, we found that after DBDPE exposure, mice showed obvious circadian rhythm disorder. Moreover, the development of preimplantation embryos was inhibited in DBDPE-exposed mice after pregnancy. Then, we further explored and revealed that DBDPE exposure reduced the endogenous melatonin (MLT) level during pregnancy, thereby inhibiting the development of preimplantation embryos. Furthermore, we discovered that exogenous MLT supplementation (15 mg/kg bw/day) rescued the inhibition of preimplantation embryo development induced by DBDPE, and a mechanistic study demonstrated that exogenous MLT inhibited the overexpression of ROS and DNA methylation at the 5-position of cytosine (5-mC) in DBDPE-exposed preimplantation embryos. Simultaneously, MLT ameliorated the DBDPE-induced mitochondrial dysfunction by increasing the mitochondrial membrane potential (MMP), ATP, and Trp1 expression. Additionally, MLT restored DBDPE-induced changes in zona pellucida (ZP) hardness and trophectoderm (TE) cortical tension. Finally, the protective effect of MLT on embryos ameliorated the adverse reproductive outcomes (dead fetus, fetus with abnormal liver, fetal weight loss) induced by DBDPE. Collectively, DBDPE induced preimplantation embryo damage leading to adverse reproductive outcomes, and MLT has emerged as a potential tool to rescue adverse reproductive outcomes induced by DBDPE.

Human blastoids model blastocyst development and implantation

One week after fertilization, human embryos implant into the uterus. This event requires the embryo to form a blastocyst consisting of a sphere encircling a cavity lodging the embryo proper. Stem cells can form a blastocyst model that we called a blastoid¹. Here we show that naive human pluripotent stem cells cultured in PXGL medium² and triply inhibited for the Hippo, TGF-β and ERK pathways efficiently (with more than 70% efficiency) form blastoids generating blastocyst-stage analogues of the three founding lineages (more than 97% trophectoderm, epiblast and primitive endoderm) according to the sequence and timing of blastocyst development. Blastoids spontaneously form the first axis, and we observe that the epiblast induces the local maturation of the polar trophectoderm, thereby endowing blastoids with the capacity to directionally attach to hormonally stimulated endometrial cells, as during implantation. Thus, we propose that such a human blastoid is a faithful, scalable and ethical model for investigating human implantation and development^3,4.

Regionally distinct trophoblast regulate barrier function and invasion in the human placenta

The human placenta contains two specialized regions: the villous chorion where gases and nutrients are exchanged between maternal and fetal blood, and the smooth chorion (SC) which surrounds more than 70% of the developing fetus but whose cellular composition and function is poorly understood. Here, we use single cell RNA-sequencing to compare the cell types and molecular programs between these two regions in the second trimester human placenta. Each region consists of progenitor cytotrophoblasts (CTBs) and extravillous trophoblasts (EVTs) with similar gene expression programs. While CTBs in the villous chorion differentiate into syncytiotrophoblasts, they take an alternative trajectory in the SC producing a previously unknown CTB population which we term SC-specific CTBs (SC-CTBs). Marked by expression of region-specific cytokeratins, the SC-CTBs form a stratified epithelium above a basal layer of progenitor CTBs. They express epidermal and metabolic transcriptional programs consistent with a primary role in defense against physical stress and pathogens. Additionally, we show that SC-CTBs closely associate with EVTs and secrete factors that inhibit the migration of the EVTs. This restriction of EVT migration is in striking contrast to the villous region where EVTs migrate away from the chorion and invade deeply into the decidua. Together, these findings greatly expand our understanding of CTB differentiation in these distinct regions of the human placenta. This knowledge has broad implications for studies of the development, functions, and diseases of the human placenta.

Cell trajectory modeling identifies a primitive trophoblast state defined by BCAM enrichment

In early placental development, progenitor cytotrophoblasts (CTB) differentiate along one of two cellular trajectories: the villous or extravillous pathways. CTB committed to the villous pathway fuse with neighboring CTB to form the outer multinucleated syncytiotrophoblast (SCT), whereas CTB committed to the extravillous pathway differentiate into invasive extravillous trophoblasts (EVT). Unfortunately, little is known about the processes controlling human CTB progenitor maintenance and differentiation. To address this, we established a single cell RNA sequencing (scRNA-seq) dataset from first trimester placentas to identify cell states important in trophoblast progenitor establishment, renewal and differentiation. Multiple distinct trophoblast states were identified, representing progenitor CTB, column CTB, SCT precursors and EVT. Lineage trajectory analysis identified a progenitor origin that was reproduced in human trophoblast stem cell organoids. Heightened expression of basal cell adhesion molecule (BCAM) defined this primitive state, where BCAM enrichment or gene silencing resulted in enhanced or diminished organoid growth, respectively. Together, this work describes at high-resolution trophoblast heterogeneity within the first trimester, resolves gene networks within human CTB progenitors and identifies BCAM as a primitive progenitor marker and possible regulator.

WNT and NOTCH signaling in human trophoblast development and differentiation

Correct development of the human placenta and its differentiated epithelial cells, syncytial trophoblasts (STBs) and extravillous trophoblasts (EVTs), is crucial for a successful pregnancy outcome. STBs develop by cell fusion of mononuclear cytotrophoblasts (CTBs) in placental floating villi, whereas migratory EVTs originate from specialized villi anchoring to the maternal decidua. Defects in trophoblast differentiation have been associated with severe pregnancy disorders such as early-onset preeclampsia and fetal growth restriction. However, the evolutionary pathways underlying normal and adverse placentation are poorly understood. Herein, we discuss Wingless (WNT) and NOTCH signaling, two pathways that play pivotal roles in human placenta and trophoblast development. Whereas WNT is necessary for expansion of trophoblast progenitors and stem cells, NOTCH1 is required for proliferation and survival of EVT precursors. Differentiation of the latter is orchestrated by a switch in NOTCH receptor expression as well as by changes in WNT ligands and their downstream effectors.

Joan Hunt Senior award lecture: New tools to shed light on the 'black box' of pregnancy

Correct establishment of the placenta is critical to the success of a pregnancy, but many of the key events take place during or shortly after implantation and are inaccessible for study. This inaccessibility, coupled with the lack of a suitable preclinical animal model, means that knowledge of human early placental development and function is extremely limited. Hence, the first trimester is often referred to as the 'black box' of pregnancy. However, recent advances in the derivation of trophoblast stem cells and organoid cultures of the trophoblast and endometrium are opening new opportunities for basic and translational research, providing for the first time cells that faithfully replicate their tissue of origin and proliferate and differentiate in culture in a stable and reproducible manner. These cells are valuable new tools for investigating cell-lineage differentiation and maternal-fetal interactions, but become even more powerful when combined with advances in bioengineering, microfabrication and microfluidic technologies. Assembloids of the endometrium comprising various cell types as model systems to investigate events at implantation, and placentas-on-a-chip for the study of nutrient transfer or drug screening are just two examples. This is a rapidly advancing field that may usher in more personalised approaches to infertility and pregnancy complications. Many of the developments are still at the proof-of-principle phase, but with continued refinement they are likely to shed important light on events that are fundamental to our reproduction as individuals and as a species, yet for ethical reasons are hidden from view.

Role of GRK2 in Trophoblast Necroptosis and Spiral Artery Remodeling: Implications for Preeclampsia Pathogenesis

Impaired invasion of extravillous trophoblasts and severe oxidative stress manifest the poor placentation in preeclampsia, which is life-threatening and more than a hypertensive disease of pregnancy. Previous studies have reported that G protein-coupled receptor kinases (GRKs) play a key role in initiating hypertension and hypertensive renal damage, yet little evidence so far suggests a link between GRKs and preeclampsia-related hypertension. Here, we demonstrate GRK2 expression is significantly downregulated (P < 0.0001) in preeclamptic placentae compared to normotensive controls. Knockdown or inhibition of GRK2 in placentae caused insufficient arterial remodeling and elevated trophoblast necroptosis in vivo. These further induced preeclampsia-like phenotype in mice: hypertension, proteinuria, and elevated pro-angiogenic cytokines. By human extra-villous invasive trophoblast cell line (HTR8/SVneo cells), we revealed the knockdown or inhibition of GRK2 triggered excessive death with typical necroptotic characteristics: nuclear envelope rupture and the activation of RIPK1, RIPK3, and MLKL. Necrostatin-1, an inhibitor of RIPK1, is able to restore the survival of trophoblasts. Together, our findings demonstrated that insufficient GRK2 activity compromises spiral artery remodeling and initiates necrotic events in placentae, thereby leading to preeclampsia. These findings advance our understanding of GRK2 in the pathogenesis of preeclampsia and could shed light on a potential treatment for preeclampsia.

From stem cells to spiral arteries: A journey through early placental development

Early placental development lays the foundation of a healthy pregnancy, and numerous tightly regulated processes must occur for the placenta to meet the increasing nutrient and oxygen exchange requirements of the growing fetus later in gestation. Inadequacies in early placental development can result in disorders such as fetal growth restriction that do not present clinically until the second half of gestation. Indeed, growth restricted placentae exhibit impaired placental development and function, including reduced overall placental size, decreased branching of villi and the blood vessels within them, altered trophoblast function, and impaired uterine vascular remodelling, which together combine to reduce placental exchange capacity. This review explores the importance of early placental development across multiple anatomical aspects of placentation, from the stem cells and lineage hierarchies from which villous core cells and trophoblasts arise, through extravillous trophoblast invasion and spiral artery remodelling, and finally remodelling of the larger uterine vessels.

Maternal, Decidual, and Neonatal Lymphocyte Composition Is Affected in Pregnant Kidney Transplant Recipients

Pregnancy after renal transplantation is associated with an increased risk of complications. While a delicately balanced uterine immune system is essential for a successful pregnancy, little is known about the uterine immune environment of pregnant kidney transplant recipients. Moreover, children born to kidney transplant recipients are exposed in utero to immunosuppressive drugs, with possible consequences for neonatal outcomes. Here, we defined the effects of kidney transplantation on the immune cell composition during pregnancy with a cohort of kidney transplant recipients as well as healthy controls with uncomplicated pregnancies. Maternal immune cells from peripheral blood were collected during pregnancy as well as from decidua and cord blood obtained after delivery. Multiparameter flow cytometry was used to identify and characterize populations of cells. While systemic immune cell frequencies were altered in kidney transplant patients, immune cell dynamics over the course of pregnancy were largely similar to healthy women. In the decidua of women with a kidney transplant, we observed a decreased frequency of HLA-DR⁺ Treg, particularly in those treated with tacrolimus versus those that were treated with azathioprine next to tacrolimus, or with azathioprine alone. In addition, both the innate and adaptive neonatal immune system of children born to kidney transplant recipients was significantly altered compared to neonates born from uncomplicated pregnancies. Overall, our findings indicate a significant and distinct impact on the maternal systemic, uterine, and neonatal immune cell composition in pregnant kidney transplant recipients, which could have important consequences for the incidence of pregnancy complications, treatment decisions, and the offspring's health.

Evaluation of growth, viability, and structural integrity of equine endometrial organoids following cryopreservation

Reproductive diseases in mares are a significant cause of subfertility and profound economic loss in the equine industry. Utilizing a 3D in vitro cell culture system that recapitulates the in vivo physiology will reduce time, cost, and welfare concerns associated with in vivo reproductive research in mares. If this 3D model is combined with effective cryopreservation, reproductive research on mares can occur year-round, which is not currently possible in this seasonal species. Endometrial organoids, 3D in vitro cell clusters that exhibit in vivo uterine physiology, have been established in mice, women, and mares. Here we report the first comprehensive assessment of cryopreservation of endometrial organoids in the domestic mare. Organoid growth rate was not affected by the type of freezing media. However, growth rate varied among non-cryopreserved controls, organoids cryopreserved at passage 0 (P0), and organoids cryopreserved at passage 3 (P3). Additionally, there was no difference in organoid viability among freezing media or freezing timepoint (passages). Furthermore, fresh and frozen-thawed organoids displayed positive immunohistochemical staining for ZO-1, which is a marker for intercellular tight junctions, and for periodic acid-Schiff staining as marker for organoid function through mucin production. Results demonstrate that equine endometrial organoids can be cryopreserved with 10% dimethyl sulfoxide with minimal detrimental effects while maintaining intercellular tight junctions (ZO-1) and secretory function. Availability of cryopreserved endometrial organoids may permit expanded research on uterine pathologies that negatively affect mare fertility and improve efficiency, reduce cost, and minimize animal welfare concerns associated with in vivo research in the domestic mare.

On Placental Toxicology Studies and Cerium Dioxide Nanoparticles

The human placenta is a transient organ essential for pregnancy maintenance, fetal development and growth. It has several functions, including that of a selective barrier against pathogens and xenobiotics from maternal blood. However, some pollutants can accumulate in the placenta or pass through with possible repercussions on pregnancy outcomes. Cerium dioxide nanoparticles (CeO₂ NPs), also termed nanoceria, are an emerging pollutant whose impact on pregnancy is starting to be defined. CeO₂ NPs are already used in different fields for industrial and commercial applications and have even been proposed for some biomedical applications. Since 2010, nanoceria have been subject to priority monitoring by the Organization for Economic Co-operation and Development in order to assess their toxicity. This review aims to summarize the current methods and models used for toxicology studies on the placental barrier, from the basic ones to the very latest, as well as to overview the most recent knowledge of the impact of CeO₂ NPs on human health, and more specifically during the sensitive window of pregnancy. Further research is needed to highlight the relationship between environmental exposure to CeO₂ and placental dysfunction with its implications for pregnancy outcome.

Malaria in Pregnancy: From Placental Infection to Its Abnormal Development and Damage

Malaria remains a global health burden with Plasmodium falciparum accounting for the highest mortality and morbidity. Malaria in pregnancy can lead to the development of placental malaria, where P. falciparum-infected erythrocytes adhere to placental receptors, triggering placental inflammation and subsequent damage, causing harm to both mother and her infant. Histopathological studies of P. falciparum-infected placentas revealed various placental abnormalities such as excessive perivillous fibrinoid deposits, breakdown of syncytiotrophoblast integrity, trophoblast basal lamina thickening, increased syncytial knotting, and accumulation of mononuclear immune cells within intervillous spaces. These events in turn, are likely to impair placental development and function, ultimately causing placental insufficiency, intrauterine growth restriction, preterm delivery and low birth weight. Hence, a better understanding of the mechanisms behind placental alterations and damage during placental malaria is needed for the design of effective interventions. In this review, using evidence from human studies and murine models, an integrated view on the potential mechanisms underlying placental pathologies in malaria in pregnancy is provided. The molecular, immunological and metabolic changes in infected placentas that reflect their responses to the parasitic infection and injury are discussed. Finally, potential models that can be used by researchers to improve our understanding on the pathogenesis of malaria in pregnancy and placental pathologies are presented.

Comparison of Maternal Serum Levels and Placental mRNA Levels of Dickkopf-1 in Preeclamptic and Normal Pregnant Women at Delivery

Background Preeclampsia remains a major cause of perinatal and maternal mortality and morbidity worldwide. Wnt/β-catenin signaling is known to be critically involved in placenta development processes. Dickkopf-1 (DKK1) is a key regulator of this transduction pathway. The aim of this study is to compare maternal serum DKK1 levels and placental mRNA levels of DKK1 and β-catenin in preeclamptic and normal pregnant women at delivery.

Methods The present study included 30 women with preeclampsia and 30 women with normal pregnancy. Maternal serum DKK1 levels were measured by ELISA. Placental mRNA levels of DKK1 and β-catenin were detected using RT-PCR.

Results Decreased maternal serum DKK1 levels were associated with worse maternal and fetal complications including HELLP syndrome, determination of one or more pathological symptom and IUGR diagnosis. No significant difference in maternal serum DKK1 levels was reported between preeclamptic women and women with normal pregnancy. Placental mRNA DKK1 levels were lower in preeclamptic women compared with normal pregnant women. Placental mRNA β-catenin levels showed no significant difference between two groups.

Conclusions Our findings reported the aberrant placental mRNA DKK1 levels in patients with preeclampsia. In addition, worse preeclampsia features were associated with decreased maternal serum DKK1 levels. Hence, aberrant Wnt/β-catenin signaling might present a plausible mechanism in preeclampsia pathogenicity. Dysregulated expression of DKK1 at gene level in the placenta but not at protein level in the maternal serum might confirm the notion that preeclampsia is a type of placenta-derived disease.

Vascular Dysfunction in Preeclampsia

Preeclampsia is a life-threatening pregnancy-associated cardiovascular disorder characterized by hypertension and proteinuria at 20 weeks of gestation. Though its exact underlying cause is not precisely defined and likely heterogenous, a plethora of research indicates that in some women with preeclampsia, both maternal and placental vascular dysfunction plays a role in the pathogenesis and can persist into the postpartum period. Potential abnormalities include impaired placentation, incomplete spiral artery remodeling, and endothelial damage, which are further propagated by immune factors, mitochondrial stress, and an imbalance of pro- and antiangiogenic substances. While the field has progressed, current gaps in knowledge include detailed initial molecular mechanisms and effective treatment options. Newfound evidence indicates that vasopressin is an early mediator and biomarker of the disorder, and promising future therapeutic avenues include mitigating mitochondrial dysfunction, excess oxidative stress, and the resulting inflammatory state. In this review, we provide a detailed overview of vascular defects present during preeclampsia and connect well-established notions to newer discoveries at the molecular, cellular, and whole-organism levels.

Transposable elements shape the evolution of mammalian development

Transposable elements (TEs) promote genetic innovation but also threaten genome stability. Despite multiple layers of host defence, TEs actively shape mammalian-specific developmental processes, particularly during pre-implantation and extra-embryonic development and at the maternal-fetal interface. Here, we review how TEs influence mammalian genomes both directly by providing the raw material for genetic change and indirectly via co-evolving TE-binding Krüppel-associated box zinc finger proteins (KRAB-ZFPs). Throughout mammalian evolution, individual activities of ancient TEs were co-opted to enable invasive placentation that characterizes live-born mammals. By contrast, the widespread activity of evolutionarily young TEs may reflect an ongoing co-evolution that continues to impact mammalian development.

Characterization of primary models of human trophoblast

Two recently developed models, trophoblast organoids and trophoblast stem cells (TSCs), are useful tools to further the understanding of human placental development. Both differentiate from villous cytotrophoblast (VCT) to either extravillous trophoblast (EVT) or syncytiotrophoblast (SCT). Here, we compare the transcriptomes and miRNA profiles of these models to identify which trophoblast they resemble in vivo. Our findings indicate that TSCs do not readily undergo SCT differentiation and closely resemble cells at the base of the cell columns from where EVT derives. In contrast, organoids are similar to VCT and undergo spontaneous SCT differentiation. A defining feature of human trophoblast is that VCT and SCT are human leukocyte antigen (HLA) null, whereas EVT expresses HLA-C, -G and -E molecules. We find that trophoblast organoids retain these in vivo characteristics. In contrast, TSCs express classical HLA-A and HLA-B molecules, and maintain their expression after EVT differentiation, with upregulation of HLA-G. Furthermore, HLA expression in TSCs differs when grown in 3D rather than in 2D, suggesting that mechanical cues are important. Our results can be used to select the most suitable model for the study of trophoblast development, function and pathology.

Summary: Characterization of trophoblast organoids and trophoblast stem cells as exciting models of human placentation enables the selection of the most suitable system to address specific research questions.

Super Enhancer Profiles Identify Key Cell Identity Genes During Differentiation From Embryonic Stem Cells to Trophoblast Stem Cells Super Enhencers in Trophoblast Differentiation

Trophoblast stem cells (TSCs) are derived from blastocysts and the extra-embryonic ectoderm (ExE) of post-implantation embryos and play a significant role in fetal development, but the roles that TSCs play in the earlier status of fetal diseases need further exploration. Super enhancers (SEs) are dense clusters of stitched enhancers that control cell identity determination and disease development and may participate in TSC differentiation. We identified key cell identity genes regulated by TSC-SEs via integrated analysis of H3K27ac and H3K4me1 chromatin immunoprecipitation sequencing (ChIP-seq), RNA-sequencing (RNA-seq) and ATAC-sequencing (ATAC-seq) data. The identified key TSC identity genes regulated by SEs, such as epidermal growth factor receptor (EGFR), integrin β5 (ITGB5) and Paxillin (Pxn), were significantly upregulated during TSC differentiation, and the transcription network mediated by TSC-SEs enriched in terms like focal adhesion and actin cytoskeleton regulation related to differentiation of TSCs. Additionally, the increased chromatin accessibility of the key cell identity genes verified by ATAC-seq further demonstrated the regulatory effect of TSC-SEs on TSC lineage commitment. Our results illustrated the significant roles of the TSC-SE-regulated network in TSC differentiation, and identified key TSC identity genes EGFR, ITGB5 and Pxn, providing novel insight into TSC differentiation and lays the foundation for future studies on embryo implantation and related diseases.

Whole transcriptome analysis of trophoblasts under hypoxia

INTRODUCTION

A physiological hypoxia environment exists at maternal-fetal interface during early pregnancy. In addition, there is a pathological hypoxic microenvironment in patients with preeclampsia. Therefore, investigating the hypoxic adaptation and the effects of hypoxia on trophoblasts transcriptome is helpful to better understand the function and regulatory mechanism of trophoblasts at the maternal-fetal interface.

METHODS

Trophoblast cell line HTR-8/SVneo was cultured under normoxia and hypoxia for 24 h, the full transcriptome was analyzed via RNA-Seq. GO and KEGG enrichment were performed on differentially expressed mRNA, adjacent genes of differentially expressed lncRNA, host genes of differentially expressed circRNA and target genes of differential expressed miRNA.

RESULTS

The results showed that hypoxia differentially regulated 373 mRNAs, 334 lncRNAs, 71 circRNAs and 33 miRNAs. GO and KEGG enrichment showed that hypoxia negatively regulated TLR3 and PI3K-Akt signaling pathways. Consistently, we found hypoxia significantly inhibited TLR3 agonist-induced cytokines expression and the phosphorylation of Akt and mTOR.

DISCUSSION

Our study obtained the full transcriptome data and potential regulatory network of trophoblasts under hypoxia, providing supportive data for revealing the function of trophoblasts.