Validation of a mouse 3D gastruloid-based embryotoxicity assay in reference to the ICH S5(R3) guideline chemical exposure list

There is growing interest in establishing alternative methods in place of conventional animal tests to assess the developmental and reproductive toxicity (DART) of chemicals. Gastruloids are 3D aggregates of pluripotent stem cells that spontaneously exhibit axial elongation morphogenesis similar to gastrulation. They have been explored as in vitro embryogenesis models for developmental and toxicological studies. Here, a mouse gastruloid-based assay was validated for DART assessment in accordance with the ICH S5(R3) guideline, which provides the plasma concentration data of various reference drugs in rodents, specifically Cmax and AUC for NOAEL and LOAEL. First, adverse effect concentrations of the reference drugs and their known metabolites on gastruloid development were determined based on morphological impact, namely reduced growth or aberrant elongation. Then, the NOAEL to LOAEL concentration range obtained from the gastruloid assay was compared with that in rodents to examine similarities in sensitivity between the in vitro and in vivo assays for each chemical. For 18 out of the 24 reference drugs that have both NOAEL and LOAEL information in rodents, the sensitivity of the gastruloid assay was comparable to the in vivo assay within an 8-fold concentration margin. For 7 out of the 8 additional reference drugs that have only NOAEL or LOAEL information in rodents, the gastruloid assay was in line with the in vivo data. Altogether, these results support the effectiveness of the gastruloid assay, which may be exploited as a non-animal alternative method for DART assessment.

Developmental toxicity of remdesivir, an anti-COVID-19 drug, is implicated by in vitro assays using morphogenetic embryoid bodies of mouse and human pluripotent stem cells

BACKGROUND

Remdesivir is an antiviral drug approved for the treatment of COVID-19, whose developmental toxicity remains unclear. More information about the safety of remdesivir is urgently needed for people of childbearing potential, who are affected by the ongoing pandemic. Morphogenetic embryoid bodies (MEBs) are three-dimensional (3D) aggregates of pluripotent stem cells that recapitulate embryonic body patterning in vitro, and have been used as effective embryo models to detect the developmental toxicity of chemical exposures specifically and sensitively.

METHODS

MEBs were generated from mouse P19C5 and human H9 pluripotent stem cells, and used to examine the effects of remdesivir. The morphological effects were assessed by analyzing the morphometric parameters of MEBs after exposure to varying concentrations of remdesivir. The molecular impact of remdesivir was evaluated by measuring the transcript levels of developmental regulator genes.

RESULTS

The mouse MEB morphogenesis was impaired by remdesivir at 1-8 μM. Remdesivir affected MEBs in a manner dependent on metabolic conversion, and its potency was higher than GS-441524 and GS-621763, presumptive anti-COVID-19 drugs that act similarly to remdesivir. The expressions of developmental regulator genes, particularly those involved in axial and somite patterning, were dysregulated by remdesivir. The early stage of MEB development was more vulnerable to remdesivir exposure than the later stage. The morphogenesis and gene expression profiles of human MEBs were also impaired by remdesivir at 1-8 μM.

CONCLUSIONS

Remdesivir impaired mouse and human MEBs at concentrations that are comparable to the therapeutic plasma levels in humans, urging further investigation into the potential impact of remdesivir on developing embryos.

Toward better assessments of developmental toxicity using stem cell-based in vitro embryogenesis models

In the past few decades, pluripotent stem cells have been explored as nonanimal alternatives to assess the developmental toxicity of chemicals. To date, numerous versions of stem cell-based assays have been reported that are allegedly effective. Nonetheless, none of the assays has become the gold standard in developmental toxicity assessment. Why? This article discusses several issues in the hope of facilitating the refinement of stem cell assays and their acceptance as the cornerstone in predictive developmental toxicology. Each stem cell assay is built on a limited representation of embryogenesis, so that multiple assays are needed to detect the diverse effects of various chemicals. To validate and compare the strengths and weaknesses of individual assays, standardized lists of reference chemicals should be established. Reference lists should consist of exposures defined by toxicokinetic data, namely maternal plasma concentrations that cause embryonic death or malformations, and also by the effects on the molecular machineries that control embryogenesis. Although not entirely replacing human or animal tests, carefully selected stem cell assays should serve as practical and ethical alternatives to proactively identify chemical exposures that disturb embryogenesis. To achieve this goal, unprecedented levels of coordination and conviction are required among research and regulatory communities.

Archetypal Architecture Construction, Patterning, and Scaling Invariance in a 3D Embryoid Body Differentiation Model

Self-organized patterning and architecture construction studying is a priority goal for fundamental developmental and stem cell biology. To study the spatiotemporal patterning of pluripotent stem cells of different origins, we developed a three-dimensional embryoid body (EB) differentiation model quantifying volumetric parameters and investigated how the EB architecture formation, patterning, and scaling depend on the proliferation, cavitation, and differentiation dynamics, external environmental factors, and cell numbers. We identified three similar spatiotemporal patterns in the EB architectures, regardless of cell origin, which constitute the EB archetype and mimick the pre-gastrulation embryonic patterns. We found that the EB patterning depends strongly on cellular positional information, culture media factor/morphogen content, and free diffusion from the external environment and between EB cell layers. However, the EB archetype formation is independent of the EB size and initial cell numbers forming EBs; therefore, it is capable of scaling invariance and patterning regulation. Our findings indicate that the underlying principles of reaction-diffusion and positional information concepts can serve as the basis for EB architecture construction, patterning, and scaling. Thus, the 3D EB differentiation model represents a highly reproducible and reliable platform for experimental and theoretical research on developmental and stem cell biology issues.

A novel human stem cell-based biomarker assay for in vitro assessment of developmental toxicity

BACKGROUND

Testing for developmental toxicity according to the current regulatory guidelines requires large numbers of animals, making these tests very resource intensive, time-consuming, and ethically debatable. Over the past decades, several alternative in vitro assays have been developed, but these often suffered from low predictability and the inability to provide a mechanistic understanding of developmental toxicity.

METHODS

To identify embryotoxic compounds, we developed a human induced pluripotent stem cells (hiPSCs)-based biomarker assay. The assay is based on the differentiation of hiPSCs into functional cardiomyocytes and hepatocytes. Proper stem cell differentiation is investigated by morphological profiling and assessment of time-dependent expression patterns of cell-specific biomarkers. In this system, a decrease in the expression of the biomarker genes and morphology disruption of the differentiated cells following compound treatment indicated teratogenicity.

RESULTS

The hiPSCs-based biomarker assay was validated with 21 well-established in vivo animal teratogenic and non-teratogenic compounds during cardiomyocyte and hepatocyte differentiation. The in vivo teratogenic compounds (e.g., thalidomide and valproic acid) markedly disrupted morphology, functionality, and the expression pattern of the biomarker genes in either one or both cell types. Non-teratogenic chemicals generally had no effect on the morphology of differentiated cells, nor on the expression of the biomarker genes. Compared to the in vivo classification, the assay achieved high accuracy (91%), sensitivity (91%), and specificity (90%).

CONCLUSION

The assay, which we named ReproTracker®, is a state-of-the-art in vitro method that can identify the teratogenicity potential of new pharmaceuticals and chemicals and signify the outcome of in vivo test systems.

Thin fluorinated polymer film microcavity arrays for 3D cell culture and label-free automated feature extraction

There is an increasing need for automated label-free morphometric analysis using brightfield microscopy images of 3D cell culture systems. This requires automated feature detection which can be achieved by improving the image contrast, e.g. by reducing the refractive index mismatch in the light path. Here, a novel microcavity platform fabricated using microthermoforming of thin fluorinated ethylene-propylene (FEP) films which match the refractive index of cell culture medium and provide a homogenous background signal intensity is described. FEP is chemically inert, mechanically stable and has been used as a substrate for light sheet microscopy. The microcavities promote formation of mouse embryonic stem cell (mESC) aggregates, which show axial elongation and germ layer specification similar to embryonic development. A label-free feature extraction pipeline based on a machine-learning plugin for FIJI is used to extract morphometric features from time-lapse imaging in a highly robust and reproducible manner. Lastly, the pipeline is utilized for testing the effect of the drug Latrunculin A on the mESC aggregates, highlighting the platform's potential for high-content screening (HCS) in drug discovery. This new microengineered tool is an important step towards label-free imaging of free-floating stem cell aggregates and paves the way for high-content drug testing and translational studies.

High Content Image Analysis of Spatiotemporal Proliferation and Differentiation Patterns in 3D Embryoid Body Differentiation Model

The 3D embryoid body (EB) differentiation model is a promising tool for fundamental cell biology and drug discovery studies assessing the compound effects on mammalian and human development. This 3D cell model allows for analyzing spatiotemporal changes during morphogenesis and differentiation. A combination of confocal microscopy with high content image analysis (HCIA) can significantly improve the study of spatiotemporal patterns of early embryonic lineages and compound efficacy and toxicity testing by enhancing the identification and quantification of various cell types. HCIA can be used to assess the EB architecture through quantitative and qualitative characteristics, such as viability and apoptosis, identification, localization, ratio and timing for various types of early embryonic cells, dimensions of compartments of proliferating and differentiating cells, changes in the size and shape of EBs, and translocation of individual cells and cell layers. This chapter describes a comprehensive framework for HCIA for 3D EB differentiation model that allows investigators to analyze EB growth, differentiation, and morphogenetic dynamics.

Comparative assessment of toxic responses in 3D embryoid body differentiation model and mouse early embryos treated with 5-hydroxytryptophan

Pluripotent stem cells recapitulate in vitro the early developmental stages and are considered promising cell models for predictive developmental toxicity studies. To investigate the consistency between adverse drug effects on early development and the early stages of embryonic stem cell differentiation in three-dimensional (3D) in vitro culture, the toxic responses to 5-hydroxytryptophan (5-HTP; 0.5-2 mM) were evaluated in early mouse embryos and the embryoid body (EB) differentiation model. 3D architectures, developmental and differentiation dynamics and the cell death rates were analyzed in early mouse embryos (E2.5-E5.5) and EBs at 1 and 6 days of differentiation using a combination of confocal immunofluorescence microscopy with high content imaging analysis and quantitative gene expression analysis. Comparative analysis of toxic responses in early embryos and EBs revealed a similar dose- and stage-dependent decrease in the 5-HTP toxic effects during development and differentiation. The integral toxic responses in the early embryos and EBs were significantly dependent on their 3D architecture and cellular composition. Treatment with 5-HTP (1 mM and above) induced developmental arrest, growth inhibition, and increased cell death in the early embryos without the trophoblasts (E2.5) and those with impaired trophoblasts and in early EBs, whereas later embryos and EBs were more resistant due to the protection of the extraembryonic tissues. This study demonstrates that the EB differentiation model is a relevant 3D-model of early mammalian development and can be useful for the predictive evaluation of toxic and teratogenic effects in embryos at the preimplantation and early post-implantation developmental stages.

Methoxyacetic acid inhibits histone deacetylase and impairs axial elongation morphogenesis of mouse gastruloids in a retinoic acid signaling-dependent manner

BACKGROUND

Teratogenic potential has been linked to various industrial compounds. Methoxyacetic acid (MAA) is a primary metabolite of the widely used organic solvent and plasticizer, methoxyethanol and dimethoxyethyl phthalate, respectively. Studies using model animals have shown that MAA acts as the proximate teratogen that causes various malformations in developing embryos. Nonetheless, the molecular mechanisms by which MAA exerts its teratogenic effects are not fully understood.

METHODS

Gastruloids of mouse P19C5 pluripotent stem cells, which recapitulate axial elongation morphogenesis of gastrulation-stage embryos, were explored as an in vitro model to investigate the teratogenic action of MAA. Morphometric parameters of gastruloids were measured to evaluate the morphogenetic effect, and transcript levels of various developmental regulator genes were examined to assess the impact on gene expression patterns. The effects of MAA on the level of retinoic acid (RA) signaling and histone deacetylase activity were also measured.

RESULTS

MAA reduced axial elongation of gastruloids at concentrations comparable to the teratogenic plasma level (5 mM) in vivo. MAA at 4 mM significantly altered the expression profiles of developmental regulator genes. In particular, it upregulated the RA signaling target genes. The concomitant suppression of RA signaling using a pharmacological agent alleviated the morphogenetic effect of MAA. MAA at 4 mM also significantly reduced the activity of purified histone deacetylase protein.

CONCLUSIONS

MAA impaired axial elongation morphogenesis in a RA signaling-dependent manner in mouse gastruloids, possibly through the inhibition of histone deacetylase.

Exposure-based assessment of chemical teratogenicity using morphogenetic aggregates of human embryonic stem cells

Pluripotent stem cells recapitulate many aspects of embryogenesis in vitro. Here, we established a novel culture system to differentiate human embryonic stem cell aggregates (HESCA), and evaluated its utility for teratogenicity assessment. Culture of HESCA with modulators of developmental signals induced morphogenetic and molecular changes associated with differentiation of the paraxial mesoderm and neuroectoderm. To examine impact of teratogenic exposures on HESCA differentiation, 18 compounds were tested, for which adequate information on in vivo plasma concentrations is available. HESCA treated with each compound were examined for gross morphology and transcript levels of 15 embryogenesis regulator genes. Significant alterations in the transcript levels were observed for 94% (15/16) of the teratogenic exposures within 5-fold margin, whereas no alteration was observed for 92% (11/12) of the non-teratogenic exposures. Our study demonstrates that transcriptional changes in HESCA serve as predictive indicator of teratogenicity in a manner comparable to in vivo exposure levels.

Prenatal toxicity of the environmental pollutants on neuronal and cardiac development derived from embryonic stem cells

Pesticides, antibiotics, and industrial excipients are widely used in agriculture, medicine, and chemical industry, respectively. They often end up in the environment, not only being not easily decomposed but also being accumulated. Moreover, they may cause serious toxic problems such as reproductive and developmental defects, immunological toxicity, and carcinogenesis. Hence, they are called environmental pollutants. It is known that the environmental pollutants easily enter the body through various channels such as respiration, ingestion of food, and skin contact etc. in everyday life. If they enter the mother through the placenta, they can cause the disturbance in embryo development as well as malfunction of organs after birth because early prenatal developmental process is highly sensitive to toxic chemicals and stress. Embryonic stem cells (ESCs) that consist of inner cell mass of blastocyst differentiate into distinct cell lineages via three germ layers such as the ectoderm, mesoderm, and endoderm due to their pluripotency. The differentiation process initiated from ESCs reflects dynamic nature of embryonic development. Therefore, ESCs have been used as a useful tool to investigate early developmental toxicities of a variety of stress. Based on relatively recent scientific results, this review would address toxicity of a few chemical substances that have been widely used as pesticide, antibiotics, and industrial excipient on ESCs based-prenatal developmental process. This review further suggests how they act on the viability of ESCs and/or early stages of cardiac and neuronal development derived from ESCs as well as on expression of pluripotency and/or differentiation markers through diverse mechanisms.

Fluoxetine Inhibits Canonical Wnt Signaling to Impair Embryoid Body Morphogenesis: Potential Teratogenic Mechanisms of a Commonly Used Antidepressant

Fluoxetine is one of the most commonly prescribed antidepressants in the selective serotonin reuptake inhibitor (SSRI) class. Epidemiologic studies have suggested a link between maternal fluoxetine use during pregnancy and an increased incidence of birth defects. However, the mechanisms by which fluoxetine adversely impacts embryonic developments are unknown. Here, we used the mouse P19C5 embryoid body (EB) as a 3D morphogenesis model to investigate the developmental toxicity of fluoxetine. Morphological and molecular changes in P19C5 EBs replicate the processes of axial elongation and patterning seen in early embryos, and these changes are specifically and sensitively altered by exposure to developmental toxicants. Treatment with fluoxetine, or its major metabolite, norfluoxetine, adversely affected EB morphogenesis at concentrations of 6 µM and above. Treatment with other serotonin reuptake inhibitors or serotonin itself did not impair EB morphogenesis, suggesting that the adverse effects of fluoxetine are independent of serotonin signaling. Gene expression analyses showed that various key developmental regulators were affected by fluoxetine, particularly those involved in mesodermal differentiation. Reporter assays demonstrated that fluoxetine inhibited canonical Wnt signaling, and that the pharmacologic activation of canonical Wnt signaling partially alleviated the morphogenetic effects of fluoxetine. Fluoxetine also exhibited cytostatic effects independently of inhibition of the serotonin transporter or canonical Wnt signaling. These results suggest that the SSRI-independent actions of fluoxetine, namely inhibition of canonical Wnt signaling and reduction of cellular proliferation, are largely responsible for the observed adverse morphogenetic impacts. This study provides mechanistic insight for further investigations on the teratogenicity of fluoxetine.

Embryoid body test with morphological and molecular endpoints implicates potential developmental toxicity of trans-resveratrol

Developmental toxicity of compounds, which women of reproductive age are exposed to, should be assessed to minimize the incidence of miscarriage and birth defects. The present study examined the potential developmental toxicity of resveratrol, a dietary supplement widely marketed with various health claims, using the P19C5 embryoid body (EB) morphogenesis assay, which evaluates adverse effects of chemical exposures on tissue growth and axial elongation. Resveratrol (trans isoform) impaired morphogenesis at 4 μM and higher, creating smaller and rounder EBs, whereas cis isoform, and glucuronated and sulfonated metabolites did not. Trans-resveratrol also altered expression levels of developmental regulator genes involved in embryonic patterning, such as Wnt3a, Tbx6, and Cyp26a1. To investigate the mechanisms of trans-resveratrol action, the roles of estrogen receptor, sirtuin 1 (SIRT1), and DNA replication in EB morphogenesis were examined. Neither activators of estrogen receptors (diethylstilbestrol [18 μM] and raloxifene [8 μM]) nor activator of SIRT1 (SRT1720 [2.4-3.2 μM]) caused morphological and molecular alterations that are comparable to trans-resveratrol (10 μM). By contrast, a reduction in the DNA replication rate with aphidicolin (0.4 μM) or hydroxyurea (40 μM) created smaller and rounder EBs and altered the expression levels of Wnt3a, Tbx6, and Cyp26a1 in a manner similar to trans-resveratrol. Consistently, trans-resveratrol significantly reduced the rate of EdU incorporation in P19C5 cells. These results suggest that a reduction in the DNA replication rate is one of the mechanisms by which trans-resveratrol impacts EB development. This study provides mechanistic insight for further investigations on the developmental toxicity of trans-resveratrol.

Droplet microarray: miniaturized platform for rapid formation and high-throughput screening of embryoid bodies

Stem cells are influenced by various factors present in their in vivo microenvironment, such as interactions with neighboring cells, the extracellular matrix or soluble molecules. This demonstrates the high complexity of the in vivo microenvironment. Hence, many advances have been made in developing 3D screening models mimicking this complexity and the in vivo-like state in order to ensure more biomedically relevant investigations in drug discovery. In the field of stem cell research embryoid bodies are often used as relevant 3D systems. Embryoid bodies are embryonic stem cell aggregates that recapitulate the early embryonic development and that can differentiate into derivatives of the three germ layers. Embryoid bodies enable the investigation of processes underlying embryonic development, tissue generation and identification of drugs with developmental toxicity. The ability to perform high-throughput screenings using embryoid bodies could be extremely important to accelerate the progress in the field of stem cell research and embryonic development. To date, there are no simple methods to create high-density microarrays of embryoid bodies that further enable their high-throughput screening important for biomedical research. Here we demonstrate a new method that enables formation and high-throughput screening of embryoid bodies in arrays of defined, separated microdroplets. Using the superhydrophobic-hydrophilic micropattern of the droplet microarray, we demonstrate rapid and facile one-step formation of a dense array of multiple droplets containing homogeneous, single embryoid bodies. Thorough characterization of the influence of the initial cell number on embryoid body size, roundness and distribution was performed. We applied the embryoid body microarray to screen 774 FDA-approved compounds, identifying compounds with developmental toxicity such as mycophenolate mofetil or embryonic lethality such as eptifibatide. This work demonstrates the potential of the droplet microarray for the rapid formation of high-density microarrays of single embryoid bodies and their high-throughput drug screenings.

Exposure-Based Validation of an In Vitro Gastrulation Model for Developmental Toxicity Assays

Establishment of effective non-animal alternatives for developmental toxicity screening assays is desirable to ensure maternal and fetal health outcomes. Validation of such assays requires a comparison between the in vitro responses to chemical exposures and the in vivo impacts of the corresponding compounds at equivalent concentrations. Here, we investigated how the P19C5 gastrulation model responds to 24 compounds at specific concentrations, some of which are categorized as positive exposures based on previously observed detrimental effects on development in vivo, whereas others are categorized as negative exposures due to lack of effects in vivo. The P19C5 gastrulation model consists of in vitro morphogenesis of mouse stem cells aggregated into embryoid bodies (EBs), which recapitulates growth and axial elongation of early embryos during four days of three-dimensional culture. Adverse impacts of chemical exposures were defined as: death, impaired growth, and altered axial elongation of EBs. Ten out of 17 positive exposures caused adverse impacts on EBs. In contrast, only three out of 17 negative exposures adversely affected EBs, although two of the three diminished viability of somatic cell lines (NIH/3T3, HEK293, and JEG3), suggesting general cytotoxicity. Overall, the study showed that 24 out of 34 exposures impacted EB development in a manner concordant with the in vivo developmental effects. Validation of other alternative assays using the same set of chemical exposures will provide information on the strengths and weaknesses of each assay, and should help determine the most effective ensemble of assays to detect a wide range of developmentally toxic exposures.

Developmental toxicity assessment of common excipients using a stem cell-based in vitro morphogenesis model

Various chemical compounds can inflict developmental toxicity when sufficiently high concentrations are exposed to embryos at the critical stages of development. Excipients, such as coloring agents and preservatives, are pharmacologically inactive ingredients that are included in various medications, foods, and cosmetics. However, concentrations that may adversely affect embryo development are largely unknown for most excipients. Here, the lowest observed adverse effect level (LOAEL) to inflict developmental toxicity was assessed for three coloring agents (allura red, brilliant blue, and tartrazine) and three preservatives (butylated hydroxyanisole, metabisulfite, and methylparaben). Adverse impact of a compound exposure was determined using the stem cell-based in vitro morphogenesis model, in which three-dimensional cell aggregates, or embryoid bodies (EBs), recapitulate embryonic processes of body axis elongation and patterning. LOAEL to impair EB morphogenesis was 200 μM for methylparaben, 400 μM for butylated hydroxyanisole, 600 μM for allura red and brilliant blue, and 1000 μM for metabisulfite. Gene expression analyses of excipient-treated EBs revealed that butylated hydroxyanisole and methylparaben significantly altered profiles of developmental regulators involved in axial elongation and patterning of the body. The present study may provide a novel in vitro approach to investigate potential developmental toxicity of common excipients with mechanistic insights.

In Vitro Micropatterned Human Pluripotent Stem Cell Test (µP-hPST) for Morphometric-Based Teratogen Screening

Exposure to teratogenic chemicals during pregnancy may cause severe birth defects. Due to high inter-species variation of drug responses as well as financial and ethical burdens, despite the widely use of in vivo animal tests, it’s crucial to develop highly predictive human pluripotent stem cell (hPSC)-based in vitro assays to identify potential teratogens. Previously we have shown that the morphological disruption of mesoendoderm patterns formed by geometrically-confined cell differentiation and migration using hPSCs could potentially serve as a sensitive morphological marker in teratogen detection. Here, a micropatterned human pluripotent stem cell test (µP-hPST) assay was developed using 30 pharmaceutical compounds. A simplified morphometric readout was developed to quantify the mesoendoderm pattern changes and a two-step classification rule was generated to identify teratogens. The optimized µP-hPST could classify the 30 compounds with 97% accuracy, 100% specificity and 93% sensitivity. Compared with metabolic biomarker-based hPSC assay by Stemina, the µP-hPST could successfully identify misclassified drugs Bosentan, Diphenylhydantoin and Lovastatin, and show a higher accuracy and sensitivity. This scalable µP-hPST may serve as either an independent assay or a complement assay for existing assays to reduce animal use, accelerate early discovery-phase drug screening and help general chemical screening of human teratogens.

Miniaturized platform for high-throughput screening of stem cells

Over the past decades stem cells have gained great interest in clinical research, tissue engineering and regenerative medicine, due to their ability of self-renewal and potential to differentiate into the various cell types of the organism. The long-term maintenance of these unique properties and the control of stem cell differentiation in vitro, however, remains challenging, thus limiting their applicability in these fields. High-throughput screening (HTS) of stem cells is widely used by the researchers in order to gain more insight in the underlying mechanisms of stem cell fate as well as identifying compounds and factors maintaining stemness. However, limited availability and expandability of stem cells restricts the use of microtiter plates for HTS of stem cells emitting the urge for miniaturized platforms. This review highlights recent advances in the development of miniaturized platforms for HTS of stem cells and presents novel designs of miniaturized HTS systems.

Adverse effect of valproic acid on an in vitro gastrulation model entails activation of retinoic acid signaling

Valproic acid (VPA), an antiepileptic drug, is a teratogen that causes neural tube and axial skeletal defects, although the mechanisms are not fully understood. We previously established a gastrulation model using mouse P19C5 stem cell embryoid bodies (EBs), which exhibits axial patterning and elongation morphogenesis in vitro. Here, we investigated the effects of VPA on the EB axial morphogenesis to gain insights into its teratogenic mechanisms. Axial elongation and patterning of EBs were inhibited by VPA at therapeutic concentrations. VPA elevated expression levels of various developmental regulators, including Cdx1 and Hoxa1, known transcriptional targets of retinoic acid (RA) signaling. Co-treatment of EBs with VPA and BMS493, an RA receptor antagonist, partially rescued axial elongation as well as gene expression profiles. These results suggest that VPA requires active RA signaling to interfere with EB morphogenesis.

High-Dose Fluoride Impairs the Properties of Human Embryonic Stem Cells via JNK Signaling

Fluoride is a ubiquitous natural substance that is often used in dental products to prevent dental caries. The biphasic actions of fluoride imply that excessive systemic exposure to fluoride can cause harmful effects on embryonic development in both animal models and humans. However, insufficient information is available on the effects of fluoride on human embryonic stem cells (hESCs), which is a novel in vitro humanized model for analyzing the embryotoxicities of chemical compounds. Therefore, we investigated the effects of sodium fluoride (NaF) on the proliferation, differentiation and viability of H9 hESCs. For the first time, we showed that 1 mM NaF did not significantly affect the proliferation of hESCs but did disturb the gene expression patterns of hESCs during embryoid body (EB) differentiation. Higher doses of NaF (2 mM and above) markedly decreased the viability and proliferation of hESCs. The mode and underlying mechanism of high-dose NaF-induced cell death were further investigated by assessing the sub-cellular morphology, mitochondrial membrane potential (MMP), caspase activities, cellular reactive oxygen species (ROS) levels and activation of mitogen-activated protein kinases (MAPKs). High-dose NaF caused the death of hESCs via apoptosis in a caspase-mediated but ROS-independent pathway, coupled with an increase in the phospho-c-Jun N-terminal kinase (p-JNK) levels. Pretreatment with a p-JNK-specific inhibitor (SP600125) could effectively protect hESCs from NaF-induced cell death in a concentration- and time-dependent manner. These findings suggest that NaF might interfere with early human embryogenesis by disturbing the specification of the three germ layers as well as osteogenic lineage commitment and that high-dose NaF could cause apoptosis through a JNK-dependent pathway in hESCs.

Cord Blood Cells for Developmental Toxicology and Environmental Health

The Tox21 program initiated a shift in toxicology toward in vitro testing with a focus on the biological mechanisms responsible for toxicological response. We discuss the applications of these initiatives to developmental toxicology. Specifically, we briefly review current approaches that are widely used in developmental toxicology to demonstrate the gap in relevance to human populations. An important aspect of human relevance is the wide variability of cellular responses to toxicants. We discuss how this gap can be addressed by using cells isolated from umbilical cord blood, an entirely non-invasive source of fetal/newborn cells. Extension of toxicological testing to collections of human fetal/newborn cells would be useful for better understanding the effect of toxicants on fetal development in human populations. By presenting this perspective, we aim to initiate a discussion about the use of cord blood donor-specific cells to capture the variability of cellular toxicological responses during this vulnerable stage of human development.