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

Single cell multiome analysis of the bovine placenta identifies gene regulatory networks in trophoblast differentiation†

A central determinant of successful reproduction is pregnancy establishment and maintenance that relies on proper development of the conceptus (embryo/fetus and associated extraembryonic membranes including the placenta). Pregnancy loss in cattle can be caused by inadequate development and differentiation of the placenta. However, the cellular and molecular mechanisms regulating bovine placenta development and, particularly, trophoblast differentiation are not well understood. Recent single-cell RNA-seq analyses revealed dynamic changes in cell populations and gene expression patterns during bovine placental development. Here, the chromatin accessibility landscape across diverse cell populations was determined in the developing (Day 40) and mature (Day 170) bovine placenta using the 10X Genomics multiome (snRNA-seq and snATAC-seq) platform. Analyses revealed distinct trophoblast, mesenchyme, endothelial, immune, and epithelial cell populations characterized by unique gene expression and chromatin accessibility signatures. ATAC-seq peaks defined open chromatin regions, facilitating the identification of transcription factor binding sites and candidate gene regulatory networks involved with trophoblast differentiation. Several transcription factors, known for their involvement in trophoblast differentiation in other mammalian species, were identified as candidate regulators of uninucleate to binucleate trophoblast differentiation. This study adds to our foundational understanding of gene regulation and expression in the placenta, offering insights into the mechanisms governing pregnancy loss in cattle.

Chromosomal instability in human trophoblast stem cells and placentas

The human placenta, a unique tumor-like organ, is thought to exhibit rare aneuploidy associated with adverse pregnancy outcomes. Discrepancies in reported aneuploidy prevalence in placentas stem from limitations in modeling and detection methods. Here, we use isogenic trophoblast stem cells (TSCs) derived from both naïve and primed human pluripotent stem cells (hPSCs) to reveal the spontaneous occurrence of aneuploidy, suggesting chromosomal instability (CIN) as an inherent feature of the trophoblast lineage. We identify potential pathways contributing to the occurrence and tolerance of CIN, such as autophagy, which may support the survival of aneuploid cells. Despite extensive chromosomal abnormalities, TSCs maintain their proliferative and differentiation capacities. These findings are further validated in placentas, where we observe a high prevalence of heterogeneous aneuploidy across trophoblasts, particularly in invasive extravillous trophoblasts. Our study challenges the traditional view of aneuploidy in the placenta and provides insights into the implications of CIN in placental function.

Single-nucleus transcriptional profiling of the placenta reveals the syncytiotrophoblast stress response to COVID-19

BACKGROUND

COVID-19 in pregnancy is associated with placental immune activation, inflammation, and vascular malperfusion, but its impact on syncytiotrophoblast biology and function is unclear.

OBJECTIVE

This study aimed to determine the effects of maternal COVID-19 on placental syncytiotrophoblasts using single-nucleus transcriptional profiling and to compare placental stress responses in COVID-19 and preeclampsia.

STUDY DESIGN

For transcriptional characterization of syncytiotrophoblasts, we used the single-nucleus RNA sequencing platform, single-cell combinatorial indexing RNA sequencing (sci-RNA-seq3), to profile placental villi and fetal membranes from unvaccinated patients with symptomatic COVID-19 at birth (n = 4), gestational age-matched controls (n = 4), and a case of critical COVID-19 in the second trimester with delivery at term (n = 1). Clustering of nuclei and differential gene expression analysis was performed in Seurat. Gene ontology analysis was conducted using Enrichr. High-confidence transcriptional target analysis was used to identify key transcription factor nodes governing the syncytiotrophoblast response to maternal SARS-CoV-2 infection. Bioinformatic approaches were further used to compare the COVID-19 dataset to published preeclampsia gene signatures. Tissue analysis, including immunofluorescence, was conducted to validate the transcriptional data and to compare COVID-19 and preeclampsia placental histology for an expanded cohort of placentas: controls (n = 6), asymptomatic COVID-19 (n = 3), symptomatic COVID-19 (n = 5), and preeclampsia with severe features (n = 7).

RESULTS

The analyzed dataset comprised 15 cell clusters and 47,889 nuclei. We identified 3 clusters of syncytiotrophoblasts representing fusing and mature nuclei with overlapping but distinct transcriptional responses to COVID-19. Bioinformatic analyses indicated that COVID-19 is associated with the following alterations in syncytiotrophoblasts: (1) endoplasmic reticulum stress and activation of stress signaling pathways, including the unfolded protein response and integrated stress response; (2) regulation of gene expression by CCAAT/enhancer-binding protein beta (CEBPB), a master transcription factor of the syncytiotrophoblast lineage; and (3) upregulation of preeclampsia-associated genes. Using complementary methods, we confirmed increased levels of stress response proteins (eg, BiP, G3BP1) in syncytiotrophoblasts, unfolded protein response signaling (spliced XBP1 mRNA), and CEBPB activation (phosphorylation) in COVID-19. Increased cytotrophoblast proliferation (Ki-67) was also detected in COVID-19, consistent with a trophoblast response to injury. Markers of stress detected in preeclampsia demonstrated similarities in the placental stress phenotype of COVID-19 and preeclampsia.

CONCLUSION

Maternal COVID-19 is associated with syncytiotrophoblast endoplasmic reticulum stress and activation of the syncytiotrophoblast lineage transcription factor, CEBPB. Similarities between syncytiotrophoblast stress in COVID-19 and preeclampsia provide insights into their clinical association.

Development of apical out trophoblast stem cell derived organoids to model early human pregnancy

The development of trophoblast organoids has enabled investigation of placental physiology, disease, and early maternal-fetal interactions during a previously restricted stage of pregnancy. A key shortcoming in existing trophoblast organoid methodologies is the non-physiologic position of the syncytiotrophoblast (STB) within the inner portion of the organoid, which neither recapitulates in vivo placental villous morphology nor allows for facile modeling of STB exposure to the endometrium or the contents of the intervillous space. Here, we have successfully established apical-out human trophoblast stem cells (hTSC)-sourced organoids with STB forming on the surface of the organoid. These organoids can also be induced to give rise to the extravillous trophoblast (EVT) lineage, which invades into an extracellular matrix-based hydrogel. Compared to previous methods, our organoids more closely mimic developing human placental architecture, offering a novel platform to study normal and abnormal placental development and to model exposures to pharmaceuticals, pathogens, and environmental factors.

Ethical considerations for advancing research using organoid models derived from the placenta

BACKGROUND

The advent of organoid culture systems has revolutionized our ability to model and study complex tissues in vitro. The placenta is one of the last human organs to have a functional organoid model developed: trophoblast organoids. These 3-dimensional structures, derived from placental tissue, offer researchers a valuable tool for studying previously inaccessible processes that occur within the womb and play a significant role in determining the health of the offspring. While primarily used for research, trophoblast organoids hold promise for clinical applications, including prenatal diagnostics and therapeutic interventions, both of which may have commercial interest. However, to ensure that research with organoid models derived from the placenta is conducted responsibly, the relevant ethics of these models need to be addressed.

OBJECTIVE AND RATIONALE

Ethical considerations related to organoid models derived from the placenta, such as trophoblast organoids are important but remain unexplored in literature. Therefore, the goal of this review is to explore the ethical considerations related to trophoblast organoids.

SEARCH METHODS

Since there is no ethical research specifically addressing organoid models of the placenta to date, we have based our findings on discussions related to other organoid models and research involving fetal tissue, placenta, or umbilical cord blood. We employed a scoping review method to search PubMed, Embase, Medline (all), Bioethics Research Library, and Google Scholar for research articles, books, or other correspondence on ethical issues regarding these indicated topics, with no date limits.

OUTCOMES

Ethical considerations related to trophoblast organoids can be divided into three distinct categories. First, there is a need to assess the moral value of trophoblast organoids, including their potential relational and symbolic dimensions. Second, it is important to understand ethical issues associated with ownership and commercialization of trophoblast organoids. Last, there are considerations related to appropriate informed consent procedures. It is worth noting that these three categories are interconnected, with the second and third being largely dependent on the moral value attributed to trophoblast organoids. Future research should assess the perspectives of various stakeholders, including parents who may donate placental tissue for organoid research.

WIDER IMPLICATIONS

This review offers valuable insights into the ethical landscape surrounding the derivation of tissues or products from pregnancies, and their further application, highlighting areas that require attention and discussion within both the scientific community and the broader society.

REGISTRATION NUMBER

N/A.

Human placental models for studying viral infections

Viral infections during pregnancy represent a major threat to maternal, fetal, and neonatal health outcome, with a high risk of vertical transmission. It is therefore crucial to understand the mechanisms underlying the interaction between viruses and placenta, which ensures communication between maternal and fetal compartments throughout pregnancy. Human placental models, both in vitro and ex vivo, enable to dissect in detail these interactions. By studying in detail viral entry, replication, and immune responses within the placenta, they represent ideal tools for analyzing the effects of various viruses on pregnancy outcomes. In addition, these models serve as platforms for evaluating diagnostic and therapeutic approaches to protect pregnant women and their babies from viral infections. This review examines recent advances, the main advantages and limitations of different human placental models and discusses their potential to improve our understanding of virus-placenta interactions, thereby contributing to improved maternal and fetal health.

The modeling of human implantation and early placentation: achievements and perspectives

BACKGROUND

Successful implantation is a critical step for embryo survival. The major losses in natural and assisted human reproduction appeared to occur during the peri-implantation period. Because of ethical constraints, the fascinating maternal-fetal crosstalk during human implantation is difficult to study and thus, the possibility for clinical intervention is still limited.

OBJECTIVE AND RATIONALE

This review highlights some features of human implantation as a unique, ineffective and difficult-to-model process and summarizes the pros and cons of the most used in vivo, ex vivo and in vitro models. We point out the variety of cell line-derived models and how these data are corroborated by well-defined primary cells of the same nature. Important aspects related to the handling, standardization, validation, and modus operandi of the advanced 3D in vitro models are widely discussed. Special attention is paid to blastocyst-like models recapitulating the hybrid phenotype and HLA profile of extravillous trophoblasts, which are a unique yet poorly understood population with a major role in the successful implantation and immune mother-embryo recognition. Despite raising new ethical dilemmas, extended embryo cultures and synthetic embryo models are also in the scope of our review.

SEARCH METHODS

We searched the electronic database PubMed from inception until March 2024 by using a multi-stage search strategy of MeSH terms and keywords. In addition, we conducted a forward and backward reference search of authors mentioned in selected articles.

OUTCOMES

Primates and rodents are valuable in vivo models for human implantation research. However, the deep interstitial, glandular, and endovascular invasion accompanied by a range of human-specific factors responsible for the survival of the fetus determines the uniqueness of the human implantation and limits the cross-species extrapolation of the data. The ex vivo models are short-term cultures, not relevant to the period of implantation, and difficult to standardize. Moreover, the access to tissues from elective terminations of pregnancy raises ethical and legal concerns. Easy-to-culture cancer cell lines have many limitations such as being prone to spontaneous transformation and lacking decent tissue characteristics. The replacement of the original human explants, primary cells or cancer cell lines with cultures of immortalized cell lines with preserved stem cell characteristics appears to be superior for in vitro modeling of human implantation and early placentation. Remarkable advances in our understanding of the peri-implantation stages have also been made by advanced three dimensional (3D) models i.e. spheroids, organoids, and assembloids, as placental and endometrial surrogates. Much work remains to be done for the optimization and standardization of these integrated and complex models. The inclusion of immune components in these models would be an asset to delineate mechanisms of immune tolerance. Stem cell-based embryo-like models and surplus IVF embryos for research bring intriguing possibilities and are thought to be the trend for the next decade for in vitro modeling of human implantation and early embryogenesis. Along with this research, new ethical dilemmas such as the moral status of the human embryo and the potential exploitation of women consenting to donate their spare embryos have emerged. The careful appraisal and development of national legal and ethical frameworks are crucial for better regulation of studies using human embryos and embryoids to reach the potential benefits for human reproduction.

WIDER IMPLICATIONS

We believe that our data provide a systematization of the available information on the modeling of human implantation and early placentation and will facilitate further research in this field. A strict classification of the advanced 3D models with their pros, cons, applicability, and availability would help improve the research quality to provide reliable outputs.

Ectopic expression of DNMT3L in human trophoblast stem cells restores features of the placental methylome

The placental DNA methylation landscape is unique, with widespread partially methylated domains (PMDs). The placental "methylome" is conserved across mammals, a shared feature of many cancers, and extensively studied for links with pregnancy complications. Human trophoblast stem cells (hTSCs) offer exciting potential for functional studies to better understand this epigenetic feature; however, whether the hTSC epigenome recapitulates primary trophoblast remains unclear. We find that hTSCs exhibit an atypical methylome compared with trophectoderm and 1st trimester cytotrophoblast. Regardless of cell origin, oxygen levels, or culture conditions, hTSCs show localized DNA methylation within transcribed gene bodies and a complete loss of PMDs. Unlike early human trophoblasts, hTSCs display a notable absence of DNMT3L expression, which is necessary for PMD establishment in mouse trophoblasts. Remarkably, we demonstrate that ectopic expression of DNMT3L in hTSCs restores placental PMDs, supporting a conserved role for DNMT3L in de novo methylation in trophoblast development in human embryogenesis.

A transcriptomic comparison of in vitro models of the human placenta

INTRODUCTION

Selecting an in vitro culture model of the human placenta is challenging due to representation of different trophoblast cell types with distinct biological roles and limited comparative studies that define key characteristics of these models. The aim of this research was to compare the transcriptomes of common in vitro models of the human placenta compared to bulk human placental tissue.

METHODS

We performed differential gene expression analysis on publicly available transcriptomic data from 7 in vitro models of the human placenta (HTR-8/SVneo, BeWo, JEG-3, JAR, Primary Trophoblasts, Villous Explants, and Trophoblast Stem Cells) and compared to bulk placental tissue from 2 cohort studies (CANDLE and GAPPS) or individual trophoblast cell types derived from bulk placental tissue.

RESULTS

All in vitro placental models had a substantial number of differentially expressed genes (DEGs, FDR<0.01) compared to the CANDLE and GAPPS placentas (Average DEGs = 10,624), and the individual trophoblast cell types (Average DEGs = 5413), indicating that there are vast differences in gene expression. Hierarchical clustering identified 54 gene clusters with distinct expression profiles across placental models, with 23 clusters enriched for specific KEGG pathways. Placental cell lines were classified by fetal sex based on expression of Y-chromosome genes that identified HTR-8/SVneo cells as female origin, while JEG-3, JAR, and BeWo cells are of male origin.

DISCUSSION

None of the models were a close approximation of the human bulk placental transcriptome, highlighting the challenges with model selection. To enable appropriate model selection, we adapted our data into a web application: "Comparative Transcriptomic Placental Model Atlas (CTPMA)".

A comprehensive human embryo reference tool using single-cell RNA-sequencing data

Stem cell-based embryo models offer unprecedented experimental tools for studying early human development. The usefulness of embryo models hinges on their molecular, cellular and structural fidelities to their in vivo counterparts. To authenticate human embryo models, single-cell RNA sequencing has been utilized for unbiased transcriptional profiling. However, an organized and integrated human single-cell RNA-sequencing dataset, serving as a universal reference for benchmarking human embryo models, remains unavailable. Here we developed such a reference through the integration of six published human datasets covering development from the zygote to the gastrula. Lineage annotations are contrasted and validated with available human and nonhuman primate datasets. Using stabilized Uniform Manifold Approximation and Projection, we constructed an early embryogenesis prediction tool, where query datasets can be projected on the reference and annotated with predicted cell identities. Using this reference tool, we examined published human embryo models, highlighting the risk of misannotation when relevant references are not utilized for benchmarking and authentication.

Generation of Bona Fide Human Induced Trophoblast Stem Cells by Direct Reprogramming of Term Umbilical Cord Cells

Placentation disorders, including severe preeclampsia and fetal growth restriction, have their origins in early pregnancy, whereas symptoms typically present later on. To investigate the pathogenesis of these diseases, there is a need for a reliable in vitro model system of early placenta development with known pregnancy outcomes. Therefore, we optimized the generation of human induced trophoblast stem cells (iTSCs) from term umbilical cord, enabling non-invasive collection of patient-derived material immediately after birth. Using a direct reprogramming approach previously described for dermal fibroblasts, we investigated the effects of three supplements (A-485, BMP4, and EPZ-6438) to assess their potential to enhance iTSC induction. The generated iTSCs fulfilled the criteria for bona fide first-trimester trophoblasts and exhibited key functional capacities, including long-term self-renewal, differentiation into hormone-producing syncytiotrophoblasts and invasive extravillous trophoblasts, and the formation of organoids. Furthermore, transcriptomic analysis revealed high similarity between the generated iTSCs and trophoblast stem cells derived from first-trimester placental tissue. The supplements did not improve the generation of iTSCs. In conclusion, we successfully generated bona fide iTSCs from term umbilical cord using a direct reprogramming approach, providing a robust and clinically relevant model to study early placentation mechanisms in patient-derived trophoblasts.

Autophagy in reproduction and pregnancy-associated diseases

As advantageous as sexual reproduction is during progeny generation, it is also an expensive and treacherous reproductive strategy. The viviparous eukaryote has evolved to survive stress before, during, and after pregnancy. An important and conserved intracellular pathway for the control of metabolic stress is autophagy. The autophagy process occurs in multiple stages through the coordinated action of autophagy-related genes. This review summarizes the evidence that autophagy is an integral component of reproduction. Additionally, we discuss emerging in vitro techniques that will enable cellular and molecular studies of autophagy and its associated pathways in reproduction. Finally, we discuss the role of autophagy in the pathogenesis and progression of several pregnancy-related disorders such as preterm birth, preeclampsia, and intra-uterine growth restriction, and its potential as a therapeutic target.

Emerging models of human and non-human primate placental development - Centre for Trophoblast Research 17th annual meeting 2024

The 17th annual meeting of the Centre for Trophoblast Research (CTR) took place at the University of Cambridge, UK, on 1-2 July 2024. This year's meeting provided an opportunity to reflect on the significant advancements made recently in modelling the human placenta in vitro. The meeting featured 12 invited speakers and attracted 260 participants from 25 countries. Many of the speakers were leading figures who have developed methods to derive human trophoblast stem cells or organoids from first trimester and term placentas, and from pluripotent stem cells. Accompanying the invited presentations were flash talks selected from the abstract submissions and poster presentations. The meeting concluded with a stimulating panel discussion to evaluate the current human trophoblast models. This Meeting Review aims to capture the spirit of the event and highlight the key themes and take-home messages that emerged.

Teratogenic parasites: disease mechanisms and emerging study models

Congenital infections are a leading preventable cause of pregnancy complications impacting both mother and fetus. Although advancements have been made in understanding various congenital infections, the mechanisms of parasitic infections during pregnancy remain poorly understood. This review covers the global incidence of three parasites capable of congenital transmission - Trypanosoma cruzi, Plasmodium spp., and Toxoplasma gondii - and the state of research into their transplacental transmission strategies. We highlight technological advancements in placental modeling that offer opportunities to reveal how parasites cause gestational pathology. Additionally, we discuss the likelihood that selective adaptation contributed to the evolution of mechanisms that facilitate placental infection. These insights provide a foundation for understanding the progression and pathology of congenital parasitic diseases and identifying future research directions.

Pluripotent stem cell-derived organoids: A brief history of curiosity-led discoveries

Organoids are quickly becoming an accepted model for understanding human biology and disease. Pluripotent stem cells (PSC) provide a starting point for many organs and enable modeling of the embryonic development and maturation of such organs. The foundation of PSC-derived organoids can be found in elegant developmental studies demonstrating the remarkable ability of immature cells to undergo histogenesis even when taken out of the embryo context. PSC-organoids are an evolution of earlier methods such as embryoid bodies, taken to a new level with finer control and in some cases going beyond tissue histogenesis to organ-like morphogenesis. But many of the discoveries that led to organoids were not necessarily planned, but rather the result of inquisitive minds with freedom to explore. Protecting such curiosity-led research through flexible funding will be important going forward if we are to see further ground-breaking discoveries.

Beyond 2D: Novel biomaterial approaches for modeling the placenta

This review considers fully three-dimensional biomaterial environments of varying complexity as these pertain to research on the placenta. The developments in placental cell sources are first considered, along with the corresponding maternal cells with which the trophoblast interact. We consider biomaterial sources, including hybrid and composite biomaterials. Properties and characterization of biomaterials are discussed in the context of material design for specific placental applications. The development of increasingly complicated three-dimensional structures includes examples of advanced fabrication methods such as microfluidic device fabrication and 3D bioprinting, as utilized in a placenta context. The review finishes with a discussion of the potential for in vitro, three-dimensional placenta research to address health disparities and sexual dimorphism, especially in light of the exciting recent changes in the regulatory environment for in vitro devices.

Early human development and stem cell-based human embryo models

The use of stem cells to model the early human embryo promises to transform our understanding of developmental biology and human reproduction. In this review, we present our current knowledge of the first 2 weeks of human embryo development. We first focus on the distinct cell lineages of the embryo and the derivation of stem cell lines. We then discuss the intercellular crosstalk that guides early embryo development and how this crosstalk is recapitulated in vitro to generate stem cell-based embryo models. We highlight advances in this fast-developing field, discuss current limitations, and provide a vision for the future.

SARS-CoV-2 ORF3a Protein Impairs Syncytiotrophoblast Maturation, Alters ZO-1 Localization, and Shifts Autophagic Pathways in Trophoblast Cells and 3D Organoids

SARS-CoV-2 infection poses a significant risk to placental physiology, but its impact on placental homeostasis is not well understood. We and others have previously shown that SARS-CoV-2 can colonize maternal and fetal placental cells, yet the specific mechanisms remain unclear. In this study, we investigate ORF3a, a key accessory protein of SARS-CoV-2 that exhibits continuous mutations. Our findings reveal that ORF3a is present in placental tissue from pregnant women infected with SARS-CoV-2 and disrupts autophagic flux in placental cell lines and 3D stem-cell-derived trophoblast organoids (SC-TOs), impairing syncytiotrophoblast differentiation and trophoblast invasion. This disruption leads to protein aggregation in cytotrophoblasts (CTB) and activates secretory autophagy, increasing CD63+ extracellular vesicle secretion, along with ORF3a itself. ORF3a also compromises CTB barrier integrity by disrupting tight junctions via interaction with ZO-1, mediated by its PDZ-binding motif, SVPL. Co-localization of ORF3a and ZO-1 in SARS-CoV-2-infected human placental tissue supports our in vitro findings. Deleting the PDZ binding motif in the ORF3a protein (ORF3a-noPBM mutant) restored proper ZO-1 localization at the cell junctions in an autophagy-independent manner. Lastly, we demonstrate that constitutive ORF3a expression induces SC-TOs to transition towards a secretory autophagy pathway likely via the PBM motif, as the ORF3a-NoPBM mutants showed a significant lack of CD63 expression. This study demonstrates the functional impact of ORF3a on placental autophagy and reveals a new mechanism for the activation of secretory autophagy, which may lead to increased extracellular vesicle secretion. These findings provide a foundation for exploring therapeutic approaches targeting ORF3a, specifically focusing on its PBM region to block its interactions with host cellular proteins and limiting placental impact.

Fetal MAVS and type I IFN signaling pathways control ZIKV infection in the placenta and maternal decidua

The contribution of placental immune responses to congenital Zika virus (ZIKV) syndrome remains poorly understood. Here, we leveraged a mouse model of ZIKV infection to identify mechanisms of innate immune restriction exclusively in the fetal compartment of the placenta. ZIKV principally infected mononuclear trophoblasts in the junctional zone, which was limited by mitochondrial antiviral-signaling protein (MAVS) and type I interferon (IFN) signaling mechanisms. Single nuclear RNA sequencing revealed MAVS-dependent expression of IFN-stimulated genes (ISGs) in spongiotrophoblasts but not in other placental cells that use alternate pathways to induce ISGs. ZIKV infection of Ifnar1-/- or Mavs-/- placentas was associated with greater infection of the adjacent immunocompetent decidua, and heterozygous Mavs+/- or Ifnar1+/- dams carrying immunodeficient fetuses sustained greater maternal viremia and tissue infection than dams carrying wild-type fetuses. Thus, MAVS-IFN signaling in the fetus restricts ZIKV infection in junctional zone trophoblasts, which modulates dissemination and outcome for both the fetus and the pregnant mother.

Long-term culture and passaging of term trophoblast for the investigation of syncytiotrophoblast function

Recent advances in the use of trophoblast stem cells and organoid models have markedly enhanced our understanding of placental development and function. These models offer significant improvements over previous systems due to their extended viability in culture and capacity to replicate various trophoblast functions, such as extravillous trophoblast invasion, syncytialisation and 3D architecture. Initially, the generation of trophoblast organoids was confined to first trimester placental tissue; however, it was recently reported that term placentae can also serve as a source of trophoblast stem cells. Here, we report that both 2D proliferative cytotrophoblasts and 3D trophoblast organoids can be effectively derived from cryopreserved term cytotrophoblasts isolated by the 'Kliman' method of sequential trypsin digestion and Percoll density gradient centrifugation, when cultured in specialised medium. This was confirmed by the expression of characteristic trophoblast markers including cytokeratin-7, E-cadherin, and human chorionic gonadotropin beta (β-hCG). The proliferative cytotrophoblasts were induced to differentiate to syncytiotrophoblasts, marked by elevated β-hCG expression, reduced Ki67-positive nuclei, and a fused syncytial phenotype. The protocol described here enables the application of organoid models and in vitro functional studies to stored cytotrophoblast samples for the study of placental function from unique patient cohorts. Moreover, the utilization of term placental sources may alleviate ethical concerns with using cells from pregnancy terminations, thus expanding access for a broader research community.

Placental Origins of Preeclampsia: Insights from Multi-Omic Studies

Preeclampsia (PE) is a major cause of maternal and neonatal morbidity and mortality worldwide, with the placenta playing a central role in disease pathophysiology. This review synthesizes recent advancements in understanding the molecular mechanisms underlying PE, focusing on placental genes, proteins, and genetic variants identified through multi-omic approaches. Transcriptomic studies in bulk placental tissue have identified many dysregulated genes in the PE placenta, including the PE signature gene, Fms-like tyrosine kinase 1 (FLT1). Emerging single-cell level transcriptomic data have revealed key cell types and molecular signatures implicated in placental dysfunction and PE. However, the considerable variability among studies underscores the need for standardized methodologies and larger sample sizes to enhance the reproducibility of results. Proteomic profiling of PE placentas has identified numerous PE-associated proteins, offering insights into potential biomarkers and pathways implicated in PE pathogenesis. Despite significant progress, challenges such as inconsistencies in study findings and lack of validation persist. Recent fetal genome-wide association studies have identified multiple genetic loci associated with PE, with ongoing efforts to elucidate their impact on placental gene expression and function. Future directions include the integration of multi-omic data, validation of findings in diverse PE populations and clinical subtypes, and the development of analytical approaches and experimental models to study the complex interplay of placental and maternal factors in PE etiology. These insights hold promise for improving risk prediction, diagnosis, and management of PE, ultimately reducing its burden on maternal and neonatal health.

Rapid retinoic acid-induced trophoblast cell model from human induced pluripotent stem cells

A limited number of accessible and representative models of human trophoblast cells currently exist for the study of placentation. Current stem cell models involve either a transition through a naïve stem cell state or precise dynamic control of multiple growth factors and small-molecule cues. Here, we demonstrated that a simple five-day treatment of human induced pluripotent stem cells with two small molecules, retinoic acid (RA) and Wnt agonist CHIR 99021 (CHIR), resulted in rapid, synergistic upregulation of CDX2. Transcriptomic analysis of RA + CHIR-treated cells showed high similarity to primary trophectoderm cells. Multipotency was verified via further differentiation towards cells with syncytiotrophoblast or extravillous trophoblast features. RA + CHIR-treated cells were also assessed for the established criteria defining a trophoblast cell model, and they possess all the features necessary to be considered valid. Collectively, our data demonstrate a facile, scalable method for generating functional trophoblast-like cells in vitro to better understand the placenta.

Microfluidic chips in female reproduction: a systematic review of status, advances, and challenges

The female reproductive system is essential to women's health, human reproduction and societal well-being. However, the clinical translation of traditional research models is restricted due to the uncertain effects and low efficiency. Emerging evidence shows that microfluidic chips provide valuable platforms for studying the female reproductive system, while no paper has ever comprehensively discussed the topic. Here, a total of 161 studies out of 14,669 records are identified in PubMed, Scopus, Web of Science, ScienceDirect and IEEE Xplore databases. Among these, 61 studies focus on oocytes, which further involves culture, cell surgeries (oocyte separation, rotation, enucleation, and denudation), evaluation and cryopreservation. Forty studies investigate embryo manipulation via microfluidic chips, covering in vitro fertilization, cryopreservation and functional evaluation. Forty-six studies reconstitute both the physiological and pathological statuses of in vivo organs, mostly involved in placenta and fetal membrane research. Fourteen studies perform drug screening and toxicity testing. In this review, we summarize the current application of microfluidic chips in studying the female reproductive system, the advancements in materials and methods, and discuss the future challenges. The present evidence suggests that microfluidic chips-assisted reproductive system reconstruction is promising and more studies are urgently needed.

Novel high throughput screen reports that benzo(a)pyrene overrides mouse trophoblast stem cell multipotency, inducing SAPK activity, HAND1 and differentiated trophoblast giant cells

INTRODUCTION

Cultured mouse trophoblast stem cells (mTSC) maintain proliferation/normal stemness (NS) under FGF4, which when removed, causes normal differentiation (ND). Hypoxic, or hyperosmotic stress forces trophoblast giant cells (TGC) differentiate. Hypoxic, hyperosmotic, and genotoxic benzo(a)pyrene (BaP), which is found in tobacco smoke, force down-regulation of inhibitor of differentiation (Id)2, enabling TGC differentiation. Hypoxic and hyperosmotic stress induce TGC by SAPK-dependent HAND1 increase. Here we test whether BaP forces mTSC-to-TGC while inducing SAPK and HAND1.

METHODS

Hand1 and SAPK activity were assayed by immunoblot, mTSC-to-TGC growth and differentiation were assayed at Tfinal after 72hr exposure of BaP, NS, ND, Retinoic acid (RA), or sorbitol. Nuclear-stained cells were micrographed automatically by a live imager, and assayed by ImageJ/FIJI, Biotek Gen 5, AIVIA proprietary artificial intelligence (AI) software or open source, CellPose artificial intelligence/AI software.

RESULTS

BaP (0.05-1μM) activated SAPK and HAND1 without diminishing growth. TSC-to-TGC differentiation was assayed with increasingly accuracy for 2-4 N cycling nuclei and >4 N differentiating TGC nuclei, using ImageJ/FIJI, Gen 5, AIVIA, or CellPose AI software. The AIVIA and Cellpose AI software matches human accuracy. The lowest BaP effects on SAPK activation/HAND1 increase are >10-fold more sensitive than similar effects for mESC. RA induces 44-47% 1st lineage TGC differentiation, but the same RA dose induces only 1% 1st lineage mESC differentiation.

DISCUSSION

First, these pilot data suggest that mTSC can be used in high throughput screens (HTS) to predict toxicant exposures that force TGC differentiation. Second, mTSC differentiated more cells than mESC for similar stress exposures, Third, open source AI can replace human micrograph quantitation and enable a miscarriage-predicting HTS.

TGFβ signalling: a nexus between inflammation, placental health and preeclampsia throughout pregnancy

BACKGROUND

The placenta is a unique and pivotal organ in reproduction, controlling crucial growth and cell differentiation processes that ensure a successful pregnancy. Placental development is a tightly regulated and dynamic process, in which the transforming growth factor beta (TGFβ) superfamily plays a central role. This family of pleiotropic growth factors is heavily involved in regulating various aspects of reproductive biology, particularly in trophoblast differentiation during the first trimester of pregnancy. TGFβ signalling precisely regulates trophoblast invasion and the cell transition from cytotrophoblasts to extravillous trophoblasts, which is an epithelial-to-mesenchymal transition-like process. Later in pregnancy, TGFβ signalling ensures proper vascularization and angiogenesis in placental endothelial cells. Beyond its role in trophoblasts and endothelial cells, TGFβ signalling contributes to the polarization and function of placental and decidual macrophages by promoting maternal tolerance of the semi-allogeneic foetus. Disturbances in early placental development have been associated with several pregnancy complications, including preeclampsia (PE) which is one of the severe complications. Emerging evidence suggests that TGFβ is involved in the pathogenesis of PE, thereby offering a potential target for intervention in the human placenta.

OBJECTIVE AND RATIONALE

This comprehensive review aims to explore and elucidate the roles of the major members of the TGFβ superfamily, including TGFβs, bone morphogenetic proteins (BMPs), activins, inhibins, nodals, and growth differentiation factors (GDFs), in the context of placental development and function. The review focusses on their interactions within the major cell types of the placenta, namely trophoblasts, endothelial cells, and immune cells, in both normal pregnancies and pregnancies complicated by PE throughout pregnancy.

SEARCH METHODS

A literature search was carried out using PubMed and Google Scholar, searching terms: 'TGF signalling preeclampsia', 'pregnancy TGF signalling', 'preeclampsia tgfβ', 'preeclampsia bmp', 'preeclampsia gdf', 'preeclampsia activin', 'endoglin preeclampsia', 'endoglin pregnancy', 'tgfβ signalling pregnancy', 'bmp signalling pregnancy', 'gdf signalling pregnancy', 'activin signalling pregnancy', 'Hofbauer cell tgfβ signalling', 'placental macrophages tgfβ', 'endothelial cells tgfβ', 'endothelium tgfβ signalling', 'trophoblast invasion tgfβ signalling', 'trophoblast invasion Smad', 'trophoblast invasion bmp', 'trophoblast invasion tgfβ', 'tgfβ preeclampsia', 'tgfβ placental development', 'TGFβ placental function', 'endothelial dysfunction preeclampsia tgfβ signalling', 'vascular remodelling placenta TGFβ', 'inflammation pregnancy tgfβ', 'immune response pregnancy tgfβ', 'immune tolerance pregnancy tgfβ', 'TGFβ pregnancy NK cells', 'bmp pregnancy NK cells', 'bmp pregnancy tregs', 'tgfβ pregnancy tregs', 'TGFβ placenta NK cells', 'TGFβ placenta tregs', 'NK cells preeclampsia', 'Tregs preeclampsia'. Only articles published in English until 2023 were used.

OUTCOMES

A comprehensive understanding of TGFβ signalling and its role in regulating interconnected cell functions of the main placental cell types provides valuable insights into the processes essential for successful placental development and growth of the foetus during pregnancy. By orchestrating trophoblast invasion, vascularization, immune tolerance, and tissue remodelling, TGFβ ligands contribute to the proper functioning of a healthy maternal-foetal interface. However, dysregulation of TGFβ signalling has been implicated in the pathogenesis of PE, where the shallow trophoblast invasion, defective vascular remodelling, decreased uteroplacental perfusion, and endothelial cell and immune dysfunction observed in PE, are all affected by an altered TGFβ signalling.

WIDER IMPLICATIONS

The dysregulation of TGFβ signalling in PE has important implications for research and clinical practice. Further investigation is required to understand the underlying mechanisms, including the role of different ligands and their regulation under pathophysiological conditions, in order to discover new therapeutic targets. Distinguishing between clinically manifested subtypes of PE and studying TGFβ signalling in different placental cell types holistically is an important first step. To put this knowledge into practice, pre-clinical animal models combined with new technologies are needed. This may also lead to improved human research models and identify potential therapeutic targets, ultimately improving outcomes for affected pregnancies and reducing the burden of PE.

Transcriptomic comparison of in vitro models of the human placenta

Studying the human placenta through in vitro cell culture methods is necessary due to limited access and amenability of human placental tissue to certain experimental methods as well as distinct anatomical and physiological differences between animal and human placentas. Selecting an in vitro culture model of the human placenta is challenging due to representation of different trophoblast cell types with distinct biological roles and limited comparative studies that define key characteristics of these models. Therefore, the aim of this research was to create a comprehensive transcriptomic comparison of common in vitro models of the human placenta compared to bulk placental tissue from the CANDLE and GAPPS cohorts (N=1083). We performed differential gene expression analysis on publicly available RNA sequencing data from 6 common in vitro models of the human placenta (HTR-8/SVneo, BeWo, JEG-3, JAR, Primary Trophoblasts, and Villous Explants) and compared to CANDLE and GAPPS bulk placental tissue or cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast cell types derived from bulk placental tissue. All in vitro placental models had a substantial number of differentially expressed genes (DEGs, FDR<0.01) compared to the CANDLE and GAPPS placentas (Average DEGs=10,873), and the individual trophoblast cell types (Average DEGs=5,346), indicating that there are vast differences in gene expression compared to bulk and cell-type specific human placental tissue. Hierarchical clustering identified 53 gene clusters with distinct expression profiles across placental models, with 22 clusters enriched for specific KEGG pathways, 7 clusters enriched for high-expression placental genes, and 7 clusters enriched for absorption, distribution, metabolism, and excretion genes. In vitro placental models were classified by fetal sex based on expression of Y-chromosome genes that identified HTR-8/SVneo cells as being of female origin, while JEG-3, JAR, and BeWo cells are of male origin. Overall, none of the models were a close approximation of the transcriptome of bulk human placental tissue, highlighting the challenges with model selection. To enable researchers to select appropriate models, we have compiled data on differential gene expression, clustering, and fetal sex into an accessible web application: "Comparative Transcriptomic Placental Model Atlas (CTPMA)" which can be utilized by researchers to make informed decisions about their selection of in vitro placental models.

The reprotoxic adverse side effects of neurogenic and neuroprotective drugs: current use of human organoid modeling as a potential alternative to preclinical models

The management of neurological disorders heavily relies on neurotherapeutic drugs, but notable concerns exist regarding their possible negative effects on reproductive health. Traditional preclinical models often fail to accurately predict reprotoxicity, highlighting the need for more physiologically relevant systems. Organoid models represent a promising approach for concurrently studying neurotoxicity and reprotoxicity, providing insights into the complex interplay between neurotherapeutic drugs and reproductive systems. Herein, we have examined the molecular mechanisms underlying neurotherapeutic drug-induced reprotoxicity and discussed experimental findings from case studies. Additionally, we explore the utility of organoid models in elucidating the reproductive complications of neurodrug exposure. Have discussed the principles of organoid models, highlighting their ability to recapitulate neurodevelopmental processes and simulate drug-induced toxicity in a controlled environment. Challenges and future perspectives in the field have been addressed with a focus on advancing organoid technologies to improve reprotoxicity assessment and enhance drug safety screening. This review underscores the importance of organoid models in unraveling the complex relationship between neurotherapeutic drugs and reproductive health.

A prospects tool in virus research: Analyzing the applications of organoids in virus studies

Organoids have emerged as a powerful tool for understanding the biology of the respiratory, digestive, nervous as well as urinary system, investigating infections, and developing new therapies. This article reviews recent progress in the development of organoid and advancements in virus research. The potential applications of these models in studying virul infections, pathogenesis, and antiviral drug discovery are discussed.

Unraveling hallmark suitability for staging pre- and post-implantation stem cell models

The advent of novel 2D and 3D models for human development, including trophoblast stem cells and blastoids, has expanded opportunities for investigating early developmental events, gradually illuminating the enigmatic realm of human development. While these innovations have ushered in new prospects, it has become essential to establish well-defined benchmarks for the cell sources of these models. We aimed to propose a comprehensive characterization of pluripotent and trophoblastic stem cell models by employing a combination of transcriptomic, proteomic, epigenetic, and metabolic approaches. Our findings reveal that extended pluripotent stem cells share many characteristics with primed pluripotent stem cells, with the exception of metabolic activity. Furthermore, our research demonstrates that DNA hypomethylation and high metabolic activity define trophoblast stem cells. These results underscore the necessity of considering multiple hallmarks of pluripotency rather than relying on a single criterion. Multiplying hallmarks alleviate stage-matching bias.

Engineered 3D Hydrogel Matrices to Modulate Trophoblast Stem Cell-Derived Placental Organoid Phenotype

Placental organoid models are a promising platform to study human placental development and function. Organoid systems typically use naturally derived hydrogel extracellular matrices (ECM), resulting in batch-to-batch variability that limits experimental reproducibility. As an alternative, synthetic ECM-mimicking hydrogel matrices offer greater consistency and control over environmental cues. Here, we generated trophoblast stem cell-derived placental organoids using poly(ethylene glycol) (PEG) hydrogels with tunable degradability and placenta-derived ECM cues to evaluate trophoblast differentiation relative to Matrigel and two-dimensional (2D) culture controls. Our data demonstrate that PEG hydrogels support trophoblast viability and metabolic function comparable to gold standard Matrigel. Additionally, phenotypic characterization via proteomic analysis revealed that PEG and Matrigel matrices drive syncytiotrophoblast and extravillous trophoblast-dominant placental organoid phenotypes, respectively. Further, three-dimensional (3D) environments promoted greater integrin expression and ECM production than 2D culture. This study demonstrates that engineered 3D culture environments can be used to reliably generate placental organoids and guide trophoblast differentiation.

Acute response to pathogens in the early human placenta at single-cell resolution

The placenta is a selective maternal-fetal barrier that provides nourishment and protection from infections. However, certain pathogens can attach to and even cross the placenta, causing pregnancy complications with potential lifelong impacts on the child's health. Here, we profiled at the single-cell level the placental responses to three pathogens associated with intrauterine complications-Plasmodium falciparum, Listeria monocytogenes, and Toxoplasma gondii. We found that upon exposure to the pathogens, all placental lineages trigger inflammatory responses that may compromise placental function. Additionally, we characterized the responses of fetal macrophages known as Hofbauer cells (HBCs) to each pathogen and propose that they are the probable niche for T. gondii. Finally, we revealed how P. falciparum adapts to the placental microenvironment by modulating protein export into the host erythrocyte and nutrient uptake pathways. Altogether, we have defined the cellular networks and signaling pathways mediating acute placental inflammatory responses that could contribute to pregnancy complications.

Why study human embryo development?

Understanding the processes and mechanisms underlying early human embryo development has become an increasingly active and important area of research. It has potential for insights into important clinical issues such as early pregnancy loss, origins of congenital anomalies and developmental origins of adult disease, as well as fundamental insights into human biology. Improved culture systems for preimplantation embryos, combined with the new tools of single cell genomics and live imaging, are providing new insights into the similarities and differences between human and mouse development. However, access to human embryo material is still restricted and extended culture of early embryos has regulatory and ethical concerns. Stem cell-derived models of different phases of human development can potentially overcome these limitations and provide a scalable source of material to explore the early postimplantation stages of human development. To date, such models are clearly incomplete replicas of normal development but future technological improvements can be envisaged. The ethical and regulatory environment for such studies remains to be fully resolved.

The chicken chorioallantoic membrane assay revisited - A face-lifted approach for new perspectives in placenta research

The study of very early human placentation is largely limited due to ethical restrictions on the use of embryonic tissue and the fact that the placental anatomy of common laboratory animal models varies considerably from that of humans. In recent years several promising models, including trophoblast stem cell-derived organoids, have been developed that have also proven useful for the study of important trophoblast differentiation processes. However, the consideration of maternal blood flow in trophoblast invasion models currently appears to be limited to animal models. An almost forgotten model to study the invasive behavior of trophoblasts is to culture them in vitro on the chicken chorioallantoic membrane (CAM), showing an extraembryonic vascular network in its mesenchymal stroma that is continuously perfused by the chicken embryonic blood circulation. Here, we present an extension of the previously described ex ovo CAM assay and describe the use of cavity-bearing trophoblast spheroids obtained from the first trimester cell line ACH-3P. We demonstrate how spheroids penetrated the CAM and that erosion of CAM vessels by trophoblasts led to filling of the spheroid cavities with chicken blood, mimicking initial steps of intervillous space blood perfusion. Moreover, we prove that this model is useful for state-of-the-art techniques including immunofluorescence and in situ padlock probe hybridization, making it a versatile tool to study aspects of trophoblast invasion in presence of blood flow.

Human trophoblast stem cells restrict human cytomegalovirus replication

Placental infection plays a central role in the pathogenesis of congenital human cytomegalovirus (HCMV) infections and is a cause of fetal growth restriction and pregnancy loss. HCMV can replicate in some trophoblast cell types, but it remains unclear how the virus evades antiviral immunity in the placenta and how infection compromises placental development and function. Human trophoblast stem cells (TSCs) can be differentiated into extravillous trophoblasts (EVTs), syncytiotrophoblasts (STBs), and organoids, and this study assessed the utility of TSCs as a model of HCMV infection in the first-trimester placenta. HCMV was found to non-productively infect TSCs, EVTs, and STBs. Immunofluorescence assays and flow cytometry experiments further revealed that infected TSCs frequently only express immediate early viral gene products. Similarly, RNA sequencing found that viral gene expression in TSCs does not follow the kinetic patterns observed during lytic infection in fibroblasts. Canonical antiviral responses were largely not observed in HCMV-infected TSCs and TSC-derived trophoblasts. Rather, infection dysregulated factors involved in cell identity, differentiation, and Wingless/Integrated signaling. Thus, while HCMV does not replicate in TSCs, infection may perturb trophoblast differentiation in ways that could interfere with placental function.

IMPORTANCE

Placental infection plays a central role in human cytomegalovirus (HCMV) pathogenesis during pregnancy, but the species specificity of HCMV and the limited availability and lifespan of primary trophoblasts have been persistent barriers to understanding how infection impacts this vital organ. Human trophoblast stem cells (TSCs) represent a new approach to modeling viral infection early in placental development. This study reveals that TSCs, like other stem cell types, restrict HCMV replication. However, infection perturbs the expression of genes involved in differentiation and cell fate determination, pointing to a mechanism by which HCMV could cause placental injury.

DUSP22 Ameliorates Endothelial-to-Mesenchymal Transition in HUVECs through Smad2/3 and MAPK Signaling Pathways

Endothelial-to-mesenchymal transition (EndMT) is the process by which endothelial cells lose their endothelial properties and acquire mesenchymal characteristics. Dual-specific protein phosphatase 22 (DUSP22) inactivates various protein kinases and transcription factors by dephosphorylating serine/threonine residues: hence, it plays a key role in many diseases. The aim of this study was to explore the functional role of DUSP22 in EndMT. In the transforming growth factor-β-induced EndMT model in human umbilical vein endothelial cells (HUVECs), we observed a downregulation of DUSP22 expression. This DUSP22 deficiency could aggravate EndMT. Conversely, the overexpression of DUSP22 could ameliorate EndMT. We used signaling pathway inhibitors to verify our results and found that DUSP22 could regulate EndMT through the smad2/3 and the mitogen-activated protein kinase (MAPK) signaling pathways. In summary, DUSP22 ameliorates EndMT in HUVECs in vitro through the smad2/3 and MAPK signaling pathways.

Unraveling the molecular mechanisms driving enhanced invasion capability of extravillous trophoblast cells: a comprehensive review

Precise extravillous trophoblast (EVT) invasion is crucial for successful placentation and pregnancy. This review focuses on elucidating the mechanisms that promote heightened EVT invasion. We comprehensively summarize the pivotal roles of hormones, angiogenesis, hypoxia, stress, the extracellular matrix microenvironment, epithelial-to-mesenchymal transition (EMT), immunity, inflammation, programmed cell death, epigenetic modifications, and microbiota in facilitating EVT invasion. The molecular mechanisms underlying enhanced EVT invasion may provide valuable insights into potential pathogenic mechanisms associated with diseases characterized by excessive invasion, such as the placenta accreta spectrum (PAS), thereby offering novel perspectives for managing pregnancy complications related to deficient EVT invasion.

The GATA transcriptional program dictates cell fate equilibrium to establish the maternal-fetal exchange interface and fetal development

The placenta establishes a maternal-fetal exchange interface to transport nutrients and gases between the mother and the fetus. Establishment of this exchange interface relies on the development of multinucleated syncytiotrophoblasts (SynT) from trophoblast progenitors, and defect in SynT development often leads to pregnancy failure and impaired embryonic development. Here, we show that mouse embryos with conditional deletion of transcription factors GATA2 and GATA3 in labyrinth trophoblast progenitors (LaTPs) have underdeveloped placenta and die by ~embryonic day 9.5. Single-cell RNA sequencing analysis revealed excessive accumulation of multipotent LaTPs upon conditional deletion of GATA factors. The GATA factor-deleted multipotent progenitors were unable to differentiate into matured SynTs. We also show that the GATA factor-mediated priming of trophoblast progenitors for SynT differentiation is a conserved event during human placentation. Loss of either GATA2 or GATA3 in cytotrophoblast-derived human trophoblast stem cells (human TSCs) drastically inhibits SynT differentiation potential. Identification of GATA2 and GATA3 target genes along with comparative bioinformatics analyses revealed that GATA factors directly regulate hundreds of common genes in human TSCs, including genes that are essential for SynT development and implicated in preeclampsia and fetal growth retardation. Thus, our study uncovers a conserved molecular mechanism, in which coordinated function of GATA2 and GATA3 promotes trophoblast progenitor-to-SynT commitment, ensuring establishment of the maternal-fetal exchange interface.

Controlling placental spheroid growth and phenotype using engineered synthetic hydrogel matrices

The human placenta is a complex organ comprised of multiple trophoblast subtypes, and inadequate models to study the human placenta in vitro limit the current understanding of human placental behavior and development. Common in vitro placental models rely on two-dimensional culture of cell lines and primary cells, which do not replicate the native tissue microenvironment, or poorly defined three-dimensional hydrogel matrices such as Matrigel™ that provide limited environmental control and suffer from high batch-to-batch variability. Here, we employ a highly defined, synthetic poly(ethylene glycol)-based hydrogel system with tunable degradability and presentation of extracellular matrix-derived adhesive ligands native to the placenta microenvironment to generate placental spheroids. We evaluate the capacity of a hydrogel library to support the viability, function, and phenotypic protein expression of three human trophoblast cell lines modeling varied trophoblast phenotypes and find that degradable synthetic hydrogels support the greatest degree of placental spheroid viability, proliferation, and function relative to standard Matrigel controls. Finally, we show that trophoblast culture conditions modulate cell functional phenotype as measured by proteomics analysis and functional secretion assays. Engineering precise control of placental spheroid development in vitro may provide an important new tool for the study of early placental behavior and development.

Trophoblast stem cell-based organoid models of the human placental barrier

Human placental villi have essential roles in producing hormones, mediating nutrient and waste exchange, and protecting the fetus from exposure to xenobiotics. Human trophoblast organoids that recapitulate the structure of villi could provide an important in vitro tool to understand placental development and the transplacental passage of xenobiotics. However, such organoids do not currently exist. Here we describe the generation of trophoblast organoids using human trophoblast stem (TS) cells. Following treatment with three kinds of culture medium, TS cells form spherical organoids with a single outer layer of syncytiotrophoblast (ST) cells that display a barrier function. Furthermore, we develop a column-type ST barrier model based on the culture condition of the trophoblast organoids. The bottom membrane of the column is almost entirely covered with syndecan 1-positive ST cells. The barrier integrity and maturation levels of the model are confirmed by measuring transepithelial/transendothelial electrical resistance (TEER) and the amount of human chorionic gonadotropin. Further analysis reveals that the model can be used to derive the apparent permeability coefficients of model compounds. In addition to providing a suite of tools for the study of placental development, our trophoblast models allow the evaluation of compound transfer and toxicity, which will facilitate drug development.

Single-nucleus multi-omic profiling of human placental syncytiotrophoblasts identifies cellular trajectories during pregnancy

The human placenta has a vital role in ensuring a successful pregnancy. Despite the growing body of knowledge about its cellular compositions and functions, there has been limited research on the heterogeneity of the billions of nuclei within the syncytiotrophoblast (STB), a multinucleated entity primarily responsible for placental function. Here we conducted integrated single-nucleus RNA sequencing and single-nucleus ATAC sequencing analyses of human placentas from early and late pregnancy. Our findings demonstrate the dynamic heterogeneity and developmental trajectories of STB nuclei and their correspondence with human trophoblast stem cell (hTSC)-derived STB. Furthermore, we identified transcription factors associated with diverse STB nuclear lineages through their gene regulatory networks and experimentally confirmed their function in hTSC and trophoblast organoid-derived STBs. Together, our data provide insights into the heterogeneity of human STB and represent a valuable resource for interpreting associated pregnancy complications.

VGLL1 cooperates with TEAD4 to control human trophectoderm lineage specification

In contrast to rodents, the mechanisms underlying human trophectoderm and early placenta specification are understudied due to ethical barriers and the scarcity of embryos. Recent reports have shown that human pluripotent stem cells (PSCs) can differentiate into trophectoderm (TE)-like cells (TELCs) and trophoblast stem cells (TSCs), offering a valuable in vitro model to study early placenta specification. Here, we demonstrate that the VGLL1 (vestigial-like family member 1), which is highly expressed during human and non-human primate TE specification in vivo but is negligibly expressed in mouse, is a critical regulator of cell fate determination and self-renewal in human TELCs and TSCs derived from naïve PSCs. Mechanistically, VGLL1 partners with the transcription factor TEAD4 (TEA domain transcription factor 4) to regulate chromatin accessibility at target gene loci through histone acetylation and acts in cooperation with GATA3 and TFAP2C. Our work is relevant to understand primate early embryogenesis and how it differs from other mammalian species.

Generation of 3D Trophoblast Organoids from Human Naïve Pluripotent Stem Cells

The human placenta is a transient organ that functions to support the needs of the fetus throughout gestation. Trophoblasts are the major epithelial cells found within the placenta and comprise a variety of distinct cell types with specialized roles in fetal-maternal communication. Our understanding of human trophoblast development remains limited due to ethical and legal restrictions on accessing first-trimester placental tissues, as well as the inability of common animal models to replicate primate placental development. It is therefore important to advance in vitro models of human trophoblast development as a basis for studying pregnancy-associated complications and diseases. In this chapter, we describe a protocol for generating 3D trophoblast organoids from naïve human pluripotent stem cells (hPSCs). The resulting stem-cell-derived trophoblast organoids (SC-TOs) contain distinct cytotrophoblast (CTB), syncytiotrophoblast (STB), and extravillous trophoblast (EVT) cell types, which closely correspond to trophoblast identities in the human post-implantation embryo. We discuss methods for characterizing SC-TOs by immunofluorescence, flow cytometry, mRNA and microRNA expression profiling, and placental hormone secretion. Furthermore, SC-TOs can undergo differentiation into specialized 3D EVT organoids, which display robust invasion when co-cultured with human endometrial cells. Thus, the protocol described herein offers an accessible 3D model system of human placental development and trophoblast invasion.

Induction of Human Extraembryonic Mesoderm Cells from Naive Pluripotent Stem Cells

The human extraembryonic mesoderm (EXM) is an important tissue in the postimplantation embryo which is specified before gastrulation in primates but not in rodents. EXM is mesenchymal and plays an important role in embryogenesis, including early erythropoiesis, and provides mechanical support to the developing embryo. Recently, it has been shown that self-renewing extraembryonic mesoderm cells (EXMCs) can be modeled in vitro by using human naive pluripotent stem cells. Here, we present a detailed step-by-step protocol to induce EXMCs from naive pluripotent stem cells in vitro.

Human Trophoblast Stem Cells Restrict Human Cytomegalovirus Replication

Placental infection plays a central role in the pathogenesis of congenital human cytomegalovirus (HCMV) infections and is a cause of fetal growth restriction and pregnancy loss. HCMV can replicate in some trophoblast cell types, but it remains unclear how the virus evades antiviral immunity in the placenta and how infection compromises placental development and function. Human trophoblast stem cells (TSCs) can be differentiated into extravillous trophoblasts (EVTs), syncytiotrophoblasts (STBs), and organoids, and this study assessed the utility of TSCs as a model of HCMV infection in the first trimester placenta. HCMV was found to non-productively infect TSCs, EVTs, and STBs. Immunofluorescence assays and flow cytometry experiments further revealed that infected TSCs frequently only express immediate early viral gene products. Similarly, RNA-sequencing found that viral gene expression in TSCs does not follow the kinetic patterns observed during lytic infection in fibroblasts. Canonical antiviral responses were largely not observed in HCMV-infected TSCs and TSC-derived trophoblasts. Rather, infection dysregulated factors involved in cell identity, differentiation, and WNT signaling. Thus, while HCMV does not replicate in TSCs, infection may perturb trophoblast differentiation in ways that could interfere with placental function.

Importance

Placental infection plays a central role in HCMV pathogenesis during pregnancy, but the species-specificity of HCMV and the limited availability and lifespan of primary trophoblasts have been persistent barriers to understanding how infection impacts this vital organ. Human TSCs represent a new approach to modeling viral infection early in placental development. This study reveals that TSCs, like other stem cell types, restrict HCMV replication. However, infection perturbs the expression of genes involved in differentiation and cell fate determination, pointing to a mechanism by which HCMV could cause placental injury.

Human fetal tissue is critical for biomedical research

Human fetal tissue and cells derived from fetal tissue are crucial for biomedical research. Fetal tissues and cells are used to study both normal development and developmental disorders. They are broadly applied in vaccine development and production. Further, research using cells from fetal tissue is instrumental for studying many infectious diseases, including a broad range of viruses. These widespread applications underscore the value of fetal tissue research and reflect an important point: cells derived from fetal tissues have capabilities that cells from other sources do not. In many cases, increased functionality of cells derived from fetal tissues arises from increased proliferative capacity, ability to survive in culture, and developmental potential that is attenuated in adult tissues. This review highlights important, representative applications of fetal tissue for science and medicine.

Modeling the Progression of Placental Transport from Early- to Late-Stage Pregnancy by Tuning Trophoblast Differentiation and Vascularization

The early-stage placental barrier is characterized by a lack of fetal circulation and by a thick trophoblastic barrier, whereas the later-stage placenta consists of vascularized chorionic villi encased in a thin, differentiated trophoblast layer, ideal for nutrient transport. In this work, predictive models of early- and late-stage placental transport are created using blastocyst-derived placental stem cells (PSCs) by modulating PSC differentiation and model vascularization. PSC differentiation results in a thinner, fused trophoblast layer, as well as an increase in human chorionic gonadotropin secretion, barrier permeability, and secretion of certain inflammatory cytokines, which are consistent with in vivo findings. Further, gene expression confirms this shift toward a differentiated trophoblast subtype. Vascularization results in a molecule type- and size-dependent change in dextran and insulin permeability. These results demonstrate that trophoblast differentiation and vascularization have critical effects on placental barrier permeability and that this model can be used as a predictive measure to assess fetal toxicity of xenobiotic substances at different stages of pregnancy.

Using human pluripotent stem cells to dissect trophoblast development

In 2021, we showed that naive human pluripotent stem cells (PSCs) can differentiate into trophoblasts via trophectoderm (TE)-like cells. Since TE is a pre-implantation stage of trophoblasts constituting blastocysts, naive human PSCs are an invaluable tool for understanding the entire process of trophoblast development. It has been reported for many years that primed human PSCs can also differentiate into the trophoblast lineage. The in vitro differentiation of naive and primed human PSCs hints at the possibility that human pre- and even post-implantation epiblasts retain the differentiation potential into the trophoblast lineages in vivo. Here, we review the in vitro specification of trophoblasts from human PSCs. Moreover, we discuss the different trophoblast differentiation pathways from naive and primed PSCs.

Exploring maternal-fetal interface with in vitro placental and trophoblastic models

The placenta, being a temporary organ, plays a crucial role in facilitating the exchange of nutrients and gases between the mother and the fetus during pregnancy. Any abnormalities in the development of this vital organ not only lead to various pregnancy-related disorders that can result in fetal injury or death, but also have long-term effects on maternal health. In vitro models have been employed to study the physiological features and molecular regulatory mechanisms of placental development, aiming to gain a detailed understanding of the pathogenesis of pregnancy-related diseases. Among these models, trophoblast stem cell culture and organoids show great promise. In this review, we provide a comprehensive overview of the current mature trophoblast stem cell models and emerging organoid models, while also discussing other models in a systematic manner. We believe that this knowledge will be valuable in guiding further exploration of the complex maternal-fetal interface.

A comprehensive review of human trophoblast fusion models: recent developments and challenges

As an essential component of the maternal-fetal interface, the placental syncytiotrophoblast layer contributes to a successful pregnancy by secreting hormones necessary for pregnancy, transporting nutrients, mediating gas exchange, balancing immune tolerance, and resisting pathogen infection. Notably, the deficiency in mononuclear trophoblast cells fusing into multinucleated syncytiotrophoblast has been linked to adverse pregnancy outcomes, such as preeclampsia, fetal growth restriction, preterm birth, and stillbirth. Despite the availability of many models for the study of trophoblast fusion, there exists a notable disparity from the ideal model, limiting the deeper exploration into the placental development. Here, we reviewed the existing models employed for the investigation of human trophoblast fusion from several aspects, including the development history, latest progress, advantages, disadvantages, scope of application, and challenges. The literature searched covers the monolayer cell lines, primary human trophoblast, placental explants, human trophoblast stem cells, human pluripotent stem cells, three-dimensional cell spheres, organoids, and placenta-on-a-chip from 1938 to 2023. These diverse models have significantly enhanced our comprehension of placental development regulation and the underlying mechanisms of placental-related disorders. Through this review, our objective is to provide readers with a thorough understanding of the existing trophoblast fusion models, making it easier to select most suitable models to address specific experimental requirements or scientific inquiries. Establishment and application of the existing human placental trophoblast fusion models.

Development of properly-polarized trophoblast stem cell-derived organoids to model early human pregnancy

The development of human trophoblast stem cells (hTSC) and stem cell-derived trophoblast organoids has enabled investigation of placental physiology and disease and early maternal-fetal interactions during a stage of human pregnancy that previously had been severely restricted. A key shortcoming in existing trophoblast organoid methodologies is the non-physiologic position of the syncytiotrophoblast (STB) within the inner portion of the organoid, which neither recapitulates placental villous morphology in vivo nor allows for facile modeling of STB exposure to the endometrium or the contents of the intervillous space. Here we have successfully established properly-polarized human trophoblast stem cell (hTSC)-sourced organoids with STB forming on the surface of the organoid. These organoids can also be induced to give rise to the extravillous trophoblast (EVT) lineage with HLA-G + migratory cells that invade into an extracellular matrix-based hydrogel. Compared to previous hTSC organoid methods, organoids created by this method more closely mimic the architecture of the developing human placenta and provide a novel platform to study normal and abnormal human placental development and to model exposures to pharmaceuticals, pathogens and environmental insults.

Motivation

Human placental organoids have been generated to mimic physiological cell-cell interactions. However, those published models derived from human trophoblast stem cells (hTSCs) or placental villi display a non-physiologic "inside-out" morphology. In vivo , the placental villi have an outer layer of syncytialized cells that are in direct contact with maternal blood, acting as a conduit for gas and nutrient exchange, and an inner layer of progenitor, single cytotrophoblast cells that fuse to create the syncytiotrophoblast layer. Existing "inside-out" models put the cytotrophoblast cells in contact with culture media and substrate, making physiologic interactions between syncytiotrophoblast and other cells/tissues and normal and pathogenic exposures coming from maternal blood difficult to model. The goal of this study was to develop an hTSC-derived 3-D human trophoblast organoid model that positions the syncytiotrophoblast layer on the outside of the multicellular organoid.

Graphical abstract