A Modified Murine Embryonic Stem Cell Test for Evaluating the Teratogenic Effects of Drugs on Early Embryogenesis

Neural crest related gene transcript regulation by valproic acid analogues in the cardiac embryonic stem cell test

In vivo, neural crest (NC) cells contribute critically to heart formation. The embryonic stem cells in the cardiac Embryonic Stem cell Test (ESTc) differentiate into a heterogeneous cell population including non-cardiomyocyte cells. The use of molecular biomarkers from different mechanistic pathways can refine quantitative embryotoxicity assessment. Gene expression levels representing different signalling pathways that could relate to beating cardiomyocyte formation were analysed at different time-points. Immunocytochemistry showed NC cells were present in the ESTc and RT-qPCR showed upregulation of NC related gene expression levels in a time-dependent manner. NC related genes were sensitive to VPA and its analogues 2-ethylhexanoic acid (EHA) and 2-ethylhexanol (EHOL) and indicated VPA as the most potent one. STITCH ('search tool for interactions of chemicals') analysis showed relationships between the examined signalling pathways and suggested additional candidate marker genes. Biomarkers from dedicated mechanistic pathways, e.g. NC differentiation, provide promising tools for monitoring specific effects in ESTc.

An engineered mouse embryonic stem cell model with survivin as a molecular marker and EGFP as the reporter for high throughput screening of embryotoxic chemicals in vitro

Embryonic stem cell test (EST) is the only generally accepted in vitro method for assessing embryotoxicity without animal sacrifice. However, the implementation and application of EST for regulatory embryotoxicity screening are impeded by its technical complexity, long testing period, and limited endpoint data. In this study, a high throughput embryotoxicity screening based on mouse embryonic stem cells (mESCs) expressing enhanced green fluorescent protein (EGFP) driven by a human survivin promoter and a human cytomegalovirus promoter, respectively, was developed. These EGFP expressing mESCs were cultured in three-dimensional (3D) fibrous scaffolds in microbioreactors on a multiwell plate with EGFP fluorescence signals as cell responses to chemicals monitored noninvasively in a high throughput manner. Nine chemicals with known developmental toxicity were used to validate the survivin-based embryotoxicity assay, which showed that strongly embryotoxic compounds such as 5-fluorouracil, retinoic acid, and methotrexate downregulated survivin expression by more than 50% in 3 days, while weakly embryotoxic compounds such as boric acid, methoxyacetic acid, and tetracyclin showed modest downregulation effect and nonembryotoxic saccharin, penicillin G, and acrylamide had negligible downregulation effect on survivin expression, confirming that survivin can be used as a molecular endpoint for high throughput screening of embryotoxicants. The potential developmental toxicity of three Chinese herbal medicines were also evaluated using this assay, demonstrating its application in in vitro developmental toxicity test for drug safety assessment.

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.

Editor's Highlight: Development of Novel Neural Embryonic Stem CellTests for High-Throughput Screening of Embryotoxic Chemicals

There is a great demand for appropriate alternative methods to rapidly evaluate the developmental and reproductive toxicity of a wide variety of chemicals. We used the differentiation of mouse embryonic stem cells (mESCs) into cardiomyocytes as a basis for establishing a rapid and highly reproducible invitro embryotoxicity test known as the Hand1-Luc Embryonic Stem Cell Test (Hand1-Luc EST). In this study, we developed novel neural-Luc ESTs using two marker genes for neural development, tubulin beta-3 (Tubb3) and Reelin (Reln), and evaluated the capacity of these tests to predict developmental toxicity. In addition, we tested whether an integrated approach (a combination of neural-Luc ESTs and the Hand1-Luc EST) improved developmental toxicant detection. To perform our neural-Luc ESTs, we needed to generate stable transgenic mESCs with individual promoters linked to the luciferase gene, and to establish that similar changes in promoter activities and mRNA expression levels occur during neural differentiation. Based on the concentration-response curves of 15 developmental toxicants and 17 non-developmental toxic chemicals, we derived a prediction formula and assessed the capacity of this formula to predict developmental toxicity. Although both were highly sensitive and specific for predicting developmental toxicity, neural-Luc ESTs had similar predictive capacities. In contrast, neural-Luc ESTs and Hand1-Luc EST had significantly different predictive powers. As expected, the combination of these ESTs increased the sensitivity of developmental toxicant detection. These results demonstrate the convenience and the usefulness of this combination of ESTs as an alternative assay system for future toxicological and mechanistic studies of developmental toxicity.

YAP determines the cell fate of injured mouse hepatocytes in vivo

The presence of senescent, transformed or damaged cells can impair tissue function or lead to tumorigenesis; therefore, organisms have evolved quality control mechanisms to eliminate them. Here, we show that YAP activation induced by inactivation of the Hippo pathway specifically in damaged hepatocytes promotes their selective elimination by using in vivo mosaic analysis in mouse liver. These damaged hepatocytes migrate into the hepatic sinusoids, undergo apoptosis and are engulfed by Kupffer cells. In contrast, YAP activation in undamaged hepatocytes leads to proliferation. Cellular stresses such as ethanol that damage both liver sinusoidal endothelial cells and hepatocytes switch cell fate from proliferation to migration/apoptosis in the presence of activated YAP. This involves the activation of CDC42 and Rac that regulate cell migration. Thus, we suggest that YAP acts as a stress sensor that induces elimination of injured cells to maintain tissue and organ homeostasis.

Senescent and injured cells affect tissue functions and can drive tumorigenesis. Thus, efficient elimination of these cells is pivotal for tissue integrity. Here Miyamura et al. show that YAP acts as a cellular stress sensor and promotes the elimination of damaged cells to maintain tissue homeostasis.

The mevalonate pathway regulates primitive streak formation via protein farnesylation

The primitive streak in peri-implantation embryos forms the mesoderm and endoderm and controls cell differentiation. The metabolic cues regulating primitive streak formation remain largely unknown. Here we utilised a mouse embryonic stem (ES) cell differentiation system and a library of well-characterised drugs to identify these metabolic factors. We found that statins, which inhibit the mevalonate metabolic pathway, suppressed primitive streak formation in vitro and in vivo. Using metabolomics and pharmacologic approaches we identified the downstream signalling pathway of mevalonate and revealed that primitive streak formation requires protein farnesylation but not cholesterol synthesis. A tagging-via-substrate approach revealed that nuclear lamin B1 and small G proteins were farnesylated in embryoid bodies and important for primitive streak gene expression. In conclusion, protein farnesylation driven by the mevalonate pathway is a metabolic cue essential for primitive streak formation.