Accessing the human trophoblast stem cell state from pluripotent and somatic cells

Transcriptome comparisons of trophoblasts from regenerative cell models with peri-implantation human embryos†

Mechanisms controlling trophoblast (TB) proliferation and differentiation during embryo implantation are poorly understood. Human trophoblast stem cells (TSC) and BMP4/A83-01/PD173074-treated pluripotent stem cell-derived trophoblast cells (BAP) are two widely employed, contemporary models to study TB development and function, but how faithfully they mimic early TB cells has not been fully examined. We evaluated the transcriptomes of TB cells from BAP and TSC and directly compared them with those from peri-implantation human embryos during extended embryo culture (EEC) between embryonic days 8 to 12. The BAP and TSC grouped closely with TB cells from EEC within each TB sublineage following dimensional analysis and unsupervised hierarchical clustering. However, subtle differences in transcriptional programs existed within each TB sublineage. We also validated the presence of six genes in peri-implantation human embryos by immunolocalization. Our analysis reveals that both BAP and TSC models have features of peri-implantation TB s, while maintaining minor transcriptomic differences, and thus serve as valuable tools for studying implantation in lieu of human embryos.

Highly efficient generation of self-renewing trophoblast from human pluripotent stem cells

Human pluripotent stem cells (hPSCs) represent a powerful model system to study early developmental processes. However, lineage specification into trophectoderm (TE) and trophoblast (TB) differentiation remains poorly understood, and access to well-characterized placental cells for biomedical research is limited, largely depending on fetal tissues or cancer cell lines. Here, we developed novel strategies enabling highly efficient TE specification that generates cytotrophoblast (CTB) and multinucleated syncytiotrophoblast (STB), followed by the establishment of trophoblast stem cells (TSCs) capable of differentiating into extravillous trophoblast (EVT) and STB after long-term expansion. We confirmed stepwise and controlled induction of lineage- and cell-type-specific genes consistent with developmental biology principles and benchmarked typical features of placental cells using morphological, biochemical, genomics, epigenomics, and single-cell analyses. Charting a well-defined roadmap from hPSCs to distinct placental phenotypes provides invaluable opportunities for studying early human development, infertility, and pregnancy-associated diseases.

Fetus Exposure to Drugs and Chemicals: A Holistic Overview on the Assessment of Their Transport and Metabolism across the Human Placental Barrier

BACKGROUND

The placenta exerts a crucial role in fetus growth and development during gestation, protecting the fetus from maternal drugs and chemical exposure. However, diverse drugs and chemicals (xenobiotics) can penetrate the maternal placental barrier, leading to deleterious, adverse effects concerning fetus health. Moreover, placental enzymes can metabolize drugs and chemicals into more toxic compounds for the fetus. Thus, evaluating the molecular mechanisms through which drugs and chemicals transfer and undergo metabolism across the placental barrier is of vital importance. In this aspect, this comprehensive literature review aims to provide a holistic approach by critically summarizing and scrutinizing the potential molecular processes and mechanisms governing drugs and chemical transfer and metabolism across the placental barrier, which may lead to fetotoxicity effects, as well as analyzing the currently available experimental methodologies used to assess xenobiotics placental transfer and metabolism.

METHODS

A comprehensive and in-depth literature review was conducted in the most accurate scientific databases such as PubMed, Scopus, and Web of Science by using relevant and effective keywords related to xenobiotic placental transfer and metabolism, retrieving 8830 published articles until 5 February 2024. After applying several strict exclusion and inclusion criteria, a final number of 148 relevant published articles were included.

RESULTS

During pregnancy, several drugs and chemicals can be transferred from the mother to the fetus across the placental barrier by either passive diffusion or through placental transporters, resulting in fetus exposure and potential fetotoxicity effects. Some drugs and chemicals also appear to be metabolized across the placental barrier, leading to more toxic products for both the mother and the fetus. At present, there is increasing research development of diverse experimental methodologies to determine the potential molecular processes and mechanisms of drug and chemical placental transfer and metabolism. All the currently available methodologies have specific strengths and limitations, highlighting the strong demand to utilize an efficient combination of them to obtain reliable evidence concerning drug and chemical transfer and metabolism across the placental barrier. To derive the most consistent and safe evidence, in vitro studies, ex vivo perfusion methods, and in vivo animal and human studies can be applied together with the final aim to minimize potential fetotoxicity effects.

CONCLUSIONS

Research is being increasingly carried out to obtain an accurate and safe evaluation of drug and chemical transport and metabolism across the placental barrier, applying a combination of advanced techniques to avoid potential fetotoxic effects. The improvement of the currently available techniques and the development of novel experimental protocols and methodologies are of major importance to protect both the mother and the fetus from xenobiotic exposure, as well as to minimize potential fetotoxicity effects.

Multiple factors to assist human-derived induced pluripotent stem cells to efficiently differentiate into midbrain dopaminergic neurons

Midbrain dopaminergic neurons play an important role in the etiology of neurodevelopmental and neurodegenerative diseases. They also represent a potential source of transplanted cells for therapeutic applications. In vitro differentiation of functional midbrain dopaminergic neurons provides an accessible platform to study midbrain neuronal dysfunction and can be used to examine obstacles to dopaminergic neuronal development. Emerging evidence and impressive advances in human induced pluripotent stem cells, with tuned neural induction and differentiation protocols, makes the production of induced pluripotent stem cell-derived dopaminergic neurons feasible. Using SB431542 and dorsomorphin dual inhibitor in an induced pluripotent stem cell-derived neural induction protocol, we obtained multiple subtypes of neurons, including 20% tyrosine hydroxylase-positive dopaminergic neurons. To obtain more dopaminergic neurons, we next added sonic hedgehog (SHH) and fibroblast growth factor 8 (FGF8) on day 8 of induction. This increased the proportion of dopaminergic neurons, up to 75% tyrosine hydroxylase-positive neurons, with 15% tyrosine hydroxylase and forkhead box protein A2 (FOXA2) co-expressing neurons. We further optimized the induction protocol by applying the small molecule inhibitor, CHIR99021 (CHIR).This helped facilitate the generation of midbrain dopaminergic neurons, and we obtained 31-74% midbrain dopaminergic neurons based on tyrosine hydroxylase and FOXA2 staining. Thus, we have established three induction protocols for dopaminergic neurons. Based on tyrosine hydroxylase and FOXA2 immunostaining analysis, the CHIR, SHH, and FGF8 combined protocol produces a much higher proportion of midbrain dopaminergic neurons, which could be an ideal resource for tackling midbrain-related diseases.

Complex regulatory networks influence pluripotent cell state transitions in human iPSCs

Stem cells exist in vitro in a spectrum of interconvertible pluripotent states. Analyzing hundreds of hiPSCs derived from different individuals, we show the proportions of these pluripotent states vary considerably across lines. We discover 13 gene network modules (GNMs) and 13 regulatory network modules (RNMs), which are highly correlated with each other suggesting that the coordinated co-accessibility of regulatory elements in the RNMs likely underlie the coordinated expression of genes in the GNMs. Epigenetic analyses reveal that regulatory networks underlying self-renewal and pluripotency are more complex than previously realized. Genetic analyses identify thousands of regulatory variants that overlapped predicted transcription factor binding sites and are associated with chromatin accessibility in the hiPSCs. We show that the master regulator of pluripotency, the NANOG-OCT4 Complex, and its associated network are significantly enriched for regulatory variants with large effects, suggesting that they play a role in the varying cellular proportions of pluripotency states between hiPSCs. Our work bins tens of thousands of regulatory elements in hiPSCs into discrete regulatory networks, shows that pluripotency and self-renewal processes have a surprising level of regulatory complexity, and suggests that genetic factors may contribute to cell state transitions in human iPSC lines.

Analysis of regulatory network modules in hundreds of human stem cell lines reveals complex epigenetic and genetic factors contribute to pluripotency state differences between subpopulations

Stem cells exist in vitro in a spectrum of interconvertible pluripotent states. Analyzing hundreds of hiPSCs derived from different individuals, we show the proportions of these pluripotent states vary considerably across lines. We discovered 13 gene network modules (GNMs) and 13 regulatory network modules (RNMs), which were highly correlated with each other suggesting that the coordinated co-accessibility of regulatory elements in the RNMs likely underlied the coordinated expression of genes in the GNMs. Epigenetic analyses revealed that regulatory networks underlying self-renewal and pluripotency have a surprising level of complexity. Genetic analyses identified thousands of regulatory variants that overlapped predicted transcription factor binding sites and were associated with chromatin accessibility in the hiPSCs. We show that the master regulator of pluripotency, the NANOG-OCT4 Complex, and its associated network were significantly enriched for regulatory variants with large effects, suggesting that they may play a role in the varying cellular proportions of pluripotency states between hiPSCs. Our work captures the coordinated activity of tens of thousands of regulatory elements in hiPSCs and bins these elements into discrete functionally characterized regulatory networks, shows that regulatory elements in pluripotency networks harbor variants with large effects, and provides a rich resource for future pluripotent stem cell research.

3D-cultured blastoids model human embryogenesis from pre-implantation to early gastrulation stages

Naive human pluripotent stem cells have the remarkable ability to self-organize into blastocyst-like structures ("blastoids") that model lineage segregation in the pre-implantation embryo. However, the extent to which blastoids can recapitulate the defining features of human post-implantation development remains unexplored. Here, we report that blastoids cultured on thick three-dimensional (3D) extracellular matrices capture hallmarks of early post-implantation development, including epiblast lumenogenesis, rapid expansion and diversification of trophoblast lineages, and robust invasion of extravillous trophoblast cells by day 14. Extended blastoid culture results in the localized activation of primitive streak marker TBXT and the emergence of embryonic germ layers by day 21. We also show that the modulation of WNT signaling alters the balance between epiblast and trophoblast fates in post-implantation blastoids. This work demonstrates that 3D-cultured blastoids offer a continuous and integrated in vitro model system of human embryonic and extraembryonic development from pre-implantation to early gastrulation stages.

Generating Functional Multicellular Organoids from Human Placenta Villi

The interaction between trophoblasts, stroma cells, and immune cells at the maternal-fetal interface constitutes the functional units of the placenta, which is crucial for successful pregnancy outcomes. However, the investigation of this intricate interplay is restricted due to the absence of efficient experimental models. To address this challenge, a robust, reliable methodology for generating placenta villi organoids (PVOs) from early, late, or diseased pregnancies using air-liquid surface culture is developed. PVOs contain cytotrophoblasts that can self-renew and differentiate directly, along with stromal elements that retain native immune cells. Analysis of scRNA sequencing and WES data reveals that PVOs faithfully recapitulate the cellular components and genetic alterations of the corresponding source tissue. Additionally, PVOs derived from patients with preeclampsia exhibit specific pathological features such as inflammation, antiangiogenic imbalance, and decreased syncytin expression. The PVO-based propagation of primary placenta villi should enable a deeper investigation of placenta development and exploration of the underlying pathogenesis and therapeutics of placenta-originated diseases.