Present state and future perspectives of using pluripotent stem cells in toxicology research

Profiling transcriptomic responses of human stem cell-derived medium spiny neuron-like cells to exogenous phasic and tonic neurotransmitters

Transcriptomic responses to neurotransmitters contribute to the complex processes driving memory and addiction. Advances in both measurement methods and experimental models continue to improve our understanding of this regulatory layer. Here we focus on the experimental potential of stem cell derived neurons, currently the only ethical model that can be used in reductionist and experimentally perturbable studies of human cells. Prior work has focused on generating distinct cell types from human stem cells, and has also shown their utility in modeling development and cellular phenotypes related to neurodegeneration. Here we seek an understanding of how stem cell derived neural cultures respond to perturbations experienced during development and disease progression. This work profiles transcriptomic responses of human medium spiny neuron-like cells with three specific goals. We first characterize transcriptomic responses to dopamine and dopamine receptor agonists and antagonists presented in dosing patterns mimicking acute, chronic, and withdrawal regimens. We also assess transcriptomic responses to low and persistent tonic levels of dopamine, acetylcholine, and glutamate to better mimic the in vivo environment. Finally, we identify similar and distinct responses between hMSN-like cells derived from H9 and H1 stem cell lines, providing some context for the extent of variability these types of systems will likely pose for experimentalists. The results here suggest future optimizations of human stem cell derived neurons to increase their in vivo relevance and the biological insights that can be garnered from these models.

Heart in a dish - choosing the right in vitro model

The heart is the first functional organ established during embryogenesis. Investigating heart development and disease is a fascinating and crucial field of research because cardiovascular diseases remain the leading cause of morbidity and mortality worldwide. Therefore, there is great interest in establishing in vitro models for recapitulating both physiological and pathological aspects of human heart development, tissue function and malfunction. Derived from pluripotent stem cells, a large variety of three-dimensional cardiac in vitro models have been introduced in recent years. In this At a Glance article, we discuss the available methods to generate such models, grouped according to the following classification: cardiac organoids, cardiac microtissues and engineered cardiac tissues. For these models, we provide a systematic overview of their applications for disease modeling and therapeutic development, as well as their advantages and limitations to assist scientists in choosing the most suitable model for their research purpose.

"Cutting the Mustard" with Induced Pluripotent Stem Cells: An Overview and Applications in Healthcare Paradigm

Treatment of numerous ailments has been made accessible by the advent of genetic engineering, where the self-renewal property has unfolded the mysteries of regeneration, i.e., stem cells. This is narrowed down to pluripotency, the cell property of differentiating into other adult cells. The generation of induced pluripotent stem cells (iPSCs) was a major breakthrough in 2006, which was generated by a cocktail of 4 Yamanaka Factors, following which significant advancements have been reported in medical science and therapeutics. The iPSCs are reprogrammed from somatic cells, and the fascinating results focused on developing authentic techniques for their generation via molecular reprogramming mechanisms, with a plethora of molecules, like NANOG, miRNAs, and DNA modifying agents, etc. The iPSCs have exhibited reliable results in assessing the etiology and molecular mechanisms of diseases, followed by the development of possible treatments and the elimination of risks of immune rejection. The authors formulate a comprehensive review to develop a clear understanding of iPSC generation, their advantages and limitations, with potential challenges associated with their medical utility. In addition, a wide compendium of applications of iPSCs in regenerative medicine and disease modeling has been discussed, alongside bioengineering technologies for iPSC reprogramming, expansion, isolation, and differentiation. The manuscript aims to provide a holistic picture of the booming advancement of iPSC therapy, to attract the attention of global researchers, to investigate this versatile approach in treatment of multiple disorders, subsequently overcoming the challenges, in order to effectively expand its therapeutic window.

Perfluorinated Iodine Alkanes Promoted Neural Differentiation of mESCs by Targeting miRNA-34a-5p in Notch-Hes Signaling

The neurodevelopmental process is highly vulnerable to environmental stress from exposure to endocrine-disrupting chemicals. Perfluorinated iodine alkanes (PFIs) possess estrogenic activities, while their potential neurodevelopmental toxicity remains blurry. In the present study, the effects of two PFIs, including dodecafluoro-1,6-diiodohexane (PFHxDI) and tridecafluorohexyl iodide (PFHxI), were investigated in the neural differentiation of the mouse embryonic stem cells (mESCs). Without influencing the cytobiological process of the mESCs, PFIs interfered the triploblastic development by increasing ectodermal differentiation, thus promoting subsequent neurogenesis. The temporal regulation of PFIs in Notch-Hes signaling through the targeting of mmu-miRNA-34a-5p provided a substantial explanation for the underlying mechanism of PFI-promoted mESC commitment to the neural lineage. The findings herein provided new knowledge on the potential neurodevelopmental toxicities of PFIs, which would help advance the health risk assessment of these kinds of emerging chemicals.

Human Umbilical Cord Mesenchymal Stem Cell-Based in vitro Model for Neurotoxicity Testing

Neurotoxicity (NT) testing for regulatory purposes is based on in vivo animal testing. There is general consensus, however, about the need for the development of alternative methodologies to allow researchers to more rapidly and cost effectively screen large numbers of chemicals for their potential to cause NT, or to investigate their mode of action. In vitro assays are considered an important source of information for making regulatory decisions, and human cell-based systems are recommended as one of the most relevant models in toxicity testing, to reduce uncertainty in the extrapolation of results from animal-based models. Human neuronal models range from various neuroblastoma cell lines to stem cell-derived systems, including those derived from mesenchymal stem/stromal cells (hMSC). hMSCs exhibit numerous advantages, including the fact that they can be obtained in high yield from healthy human adult tissues, can be cultured with a minimal laboratory setup and without genetic manipulations, are able of continuous and repeated self-renewal, are nontumorigenic, and can form large populations of stably differentiated cells representative of different tissues, including neuronal cells. hMSCs derived from human umbilical cord (hUC) in particular possess several prominent advantages, including a painless, non-invasive, and ethically acceptable collection procedure, simple and convenient preparation, and high proliferation capacity. In addition, hMSCs can be efficiently differentiated into neuron-like cells (hNLCs), which can then be used for the assessment of neuronal toxicity of potential neurotoxic compounds in humans. Here, we describe a step-by-step procedure to use hMSCs from the umbilical cord for in vitro neurotoxicity testing. First, we describe how to isolate, amplify, and store hMSCs derived from the umbilical cord. We then outline the steps to transdifferentiate these cells into hNLCs, and then use the hNLCs for neurotoxicity testing by employing multiple common cytotoxicity assays after treatment with test compounds. The approach follows the most updated guidance on using human cell-based systems. These protocols will allow investigators to implement an alternative system for obtaining primary NLCs of human origin, and support advancement in neurotoxicity research. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Isolation and maintenance of human mesenchymal stem/stromal cells (hMSCs) obtained from the umbilical cord lining membrane Basic Protocol 2: Transdifferentiation of hMSCs into neuron-like cells (hNLCs) and basic neurotoxicity assessment.

Scientific Validation of Human Neurosphere Assays for Developmental Neurotoxicity Evaluation

There is a call for a paradigm shift in developmental neurotoxicity (DNT) evaluation, which demands the implementation of faster, more cost-efficient, and human-relevant test systems than current in vivo guideline studies. Under the umbrella of the Organisation for Economic Co-operation and Development (OECD), a guidance document is currently being prepared that instructs on the regulatory use of a DNT in vitro battery (DNT IVB) for fit-for-purpose applications. One crucial issue for OECD application of methods is validation, which for new approach methods (NAMs) requires novel approaches. Here, mechanistic information previously identified in vivo, as well as reported neurodevelopmental adversities in response to disturbances on the cellular and tissue level, are of central importance. In this study, we scientifically validate the Neurosphere Assay, which is based on human primary neural progenitor cells (hNPCs) and an integral part of the DNT IVB. It assesses neurodevelopmental key events (KEs) like NPC proliferation (NPC1ab), radial glia cell migration (NPC2a), neuronal differentiation (NPC3), neurite outgrowth (NPC4), oligodendrocyte differentiation (NPC5), and thyroid hormone-dependent oligodendrocyte maturation (NPC6). In addition, we extend our work from the hNPCs to human induced pluripotent stem cell-derived NPCs (hiNPCs) for the NPC proliferation (iNPC1ab) and radial glia assays (iNPC2a). The validation process we report for the endpoints studied with the Neurosphere Assays is based on 1) describing the relevance of the respective endpoints for brain development, 2) the confirmation of the cell type-specific morphologies observed in vitro, 3) expressions of cell type-specific markers consistent with those morphologies, 4) appropriate anticipated responses to physiological pertinent signaling stimuli and 5) alterations in specific in vitro endpoints upon challenges with confirmed DNT compounds. With these strong mechanistic underpinnings, we posit that the Neurosphere Assay as an integral part of the DNT in vitro screening battery is well poised for DNT evaluation for regulatory purposes.

Applications of 3D Bioprinting Technology in Induced Pluripotent Stem Cells-Based Tissue Engineering

Induced pluripotent stem cells (iPSCs) are essentially produced by the genetic reprogramming of adult cells. Moreover, iPSC technology prevents the genetic manipulation of embryos. Hence, with the ensured element of safety, they rarely cause ethical concerns when utilized in tissue engineering. Several cumulative outcomes have demonstrated the functional superiority and potency of iPSCs in advanced regenerative medicine. Recently, an emerging trend in 3D bioprinting technology has been a more comprehensive approach to iPSC-based tissue engineering. The principal aim of this review is to provide an understanding of the applications of 3D bioprinting in iPSC-based tissue engineering. This review discusses the generation of iPSCs based on their distinct purpose, divided into two categories: (1) undifferentiated iPSCs applied with 3D bioprinting; (2) differentiated iPSCs applied with 3D bioprinting. Their significant potential is analyzed. Lastly, various applications for engineering tissues and organs have been introduced and discussed in detail.

Embryoid Bodies-Based Multilineage Differentiation of Human Embryonic Stem Cells Grown on Feeder-Free Conditions

Human embryonic stem cells (hESCs) can differentiate into any cell lineage (pluripotency potential) derived from the three germ layers: ectoderm, mesoderm, and endoderm. Pluripotency is usually demonstrated in vitro by spontaneous differentiation of hESCs grown on a monolayer of feeder-cells using an embryoid bodies (EBs)-based method. However, currently hESCs are grown mostly using fully defined media in the absence of a feeder layer. Here we describe a EBs-based protocol that allows multilineage differentiation of hESCs and human induced pluripotent stem cells (hiPSCs) grown on feeder-free conditions.

Biofabricated 3D in vitro model of fibrosis-induced abnormal hepatoblast/biliary progenitors' expansion of the developing liver

Congenital disorders of the biliary tract are the primary reason for pediatric liver failure and ultimately for pediatric liver transplant needs. Not all causes of these disorders are well understood, but it is known that liver fibrosis occurs in many of those afflicted. The goal of this study is to develop a simple yet robust model that recapitulates physico-mechanical and cellular aspects of fibrosis mediated via hepatic stellate cells (HSCs) and their effects on biliary progenitor cells. Liver organoids were fabricated by embedding various HSCs, with distinctive abilities to generate mild to severe fibrotic environments, together with undifferentiated liver progenitor cell line, HepaRG, within a collagen I hydrogel. The fibrotic state of each organoid was characterized by examination of extracellular matrix (ECM) remodeling through quantitative image analysis, rheometry, and qPCR. In tandem, the phenotype of the liver progenitor cell and cluster formation was assessed through histology. Activated HSCs (aHSCs) created a more severe fibrotic state, exemplified by a more highly contracted and rigid ECM, as well higher relative expression of TGF-β, TIMP-1, LOXL2, and COL1A2 as compared to immortalized HSCs (LX-2). Within the more severe fibrotic environment, generated by the aHSCs, higher Notch signaling was associated with an expansion of CK19+ cells as well as the formation of larger, more densely populated cell biliary like-clusters as compared to mild and non-fibrotic controls. The expansion of CK19+ cells, coupled with a severely fibrotic environment, are phenomena found within patients suffering from a variety of congenital liver disorders of the biliary tract. Thus, the model presented here can be utilized as a novel in vitro testing platform to test drugs and identify new targets that could benefit pediatric patients that suffer from the biliary dysgenesis associated with a multitude of congenital liver diseases.

Human iPSCs and Genome Editing Technologies for Precision Cardiovascular Tissue Engineering

Induced pluripotent stem cells (iPSCs) originate from the reprogramming of adult somatic cells using four Yamanaka transcription factors. Since their discovery, the stem cell (SC) field achieved significant milestones and opened several gateways in the area of disease modeling, drug discovery, and regenerative medicine. In parallel, the emergence of clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR-Cas9) revolutionized the field of genome engineering, allowing the generation of genetically modified cell lines and achieving a precise genome recombination or random insertions/deletions, usefully translated for wider applications. Cardiovascular diseases represent a constantly increasing societal concern, with limited understanding of the underlying cellular and molecular mechanisms. The ability of iPSCs to differentiate into multiple cell types combined with CRISPR-Cas9 technology could enable the systematic investigation of pathophysiological mechanisms or drug screening for potential therapeutics. Furthermore, these technologies can provide a cellular platform for cardiovascular tissue engineering (TE) approaches by modulating the expression or inhibition of targeted proteins, thereby creating the possibility to engineer new cell lines and/or fine-tune biomimetic scaffolds. This review will focus on the application of iPSCs, CRISPR-Cas9, and a combination thereof to the field of cardiovascular TE. In particular, the clinical translatability of such technologies will be discussed ranging from disease modeling to drug screening and TE applications.

Current EU regulatory requirements for the assessment of chemicals and cosmetic products: challenges and opportunities for introducing new approach methodologies

The EU Directive 2010/63/EU   on the protection of animals used for scientific purposes and other EU regulations, such as REACH and the Cosmetic Products Regulation advocate for a change in the way toxicity testing is conducted. Whilst the Cosmetic Products Regulation bans animal testing altogether, REACH aims for a progressive shift from in vivo testing towards quantitative in vitro and computational approaches. Several endpoints can already be addressed using non-animal approaches including skin corrosion and irritation, serious eye damage and irritation, skin sensitisation, and mutagenicity and genotoxicity. However, for systemic effects such as acute toxicity, repeated dose toxicity and reproductive and developmental toxicity, evaluation of chemicals under REACH still heavily relies on animal tests. Here we summarise current EU regulatory requirements for the human health assessment of chemicals under REACH and the Cosmetic Products Regulation, considering the more critical endpoints and identifying the main challenges in introducing alternative methods into regulatory testing practice. This supports a recent initiative taken by the International Cooperation on Alternative Test Methods (ICATM) to summarise current regulatory requirements specific for the assessment of chemicals and cosmetic products for several human health-related endpoints, with the aim of comparing different jurisdictions and coordinating the promotion and ultimately the implementation of non-animal approaches worldwide. Recent initiatives undertaken at European level to promote the 3Rs and the use of alternative methods in current regulatory practice are also discussed.

Gene Regulatory Network Analysis and Engineering Directs Development and Vascularization of Multilineage Human Liver Organoids

Pluripotent stem cell (PSC)-derived organoids have emerged as novel multicellular models of human tissue development but display immature phenotypes, aberrant tissue fates, and a limited subset of cells. Here, we demonstrate that integrated analysis and engineering of gene regulatory networks (GRNs) in PSC-derived multilineage human liver organoids direct maturation and vascular morphogenesis in vitro. Overexpression of PROX1 and ATF5, combined with targeted CRISPR-based transcriptional activation of endogenous CYP3A4, reprograms tissue GRNs and improves native liver functions, such as FXR signaling, CYP3A4 enzymatic activity, and stromal cell reactivity. The engineered tissues possess superior liver identity when compared with other PSC-derived liver organoids and show the presence of hepatocyte, biliary, endothelial, and stellate-like cell populations in single-cell RNA-seq analysis. Finally, they show hepatic functions when studied in vivo. Collectively, our approach provides an experimental framework to direct organogenesis in vitro by systematically probing molecular pathways and transcriptional networks that promote tissue development.

Alteration of gene expression profile in mouse embryonic stem cells and neural differentiation deficits by ethephon

Ethephon, a member of the organophosphorus compounds, is one of the most widely used plant growth regulators for artificial ripening. Although million pounds of this chemical is being used annually, the knowledge regarding its molecular toxicity is yet not sufficient. The purpose of this study was to evaluate the potential developmental toxicity of ethephon using embryonic stem cell model. The mouse embryonic stem cells (mESCs) were exposed to various concentrations of ethephon and the viability, cell cycle alteration and changes in the gene expression profile were evaluated using high-throughput RNA sequencing. Further, the effect of ethephon on neural differentiation potential was examined. The results showed that ethephon at noncytotoxic doses induced cell cycle arrest in mESCs. Gene ontology enrichment analysis showed that terms related to cell fate and organismal development, including neuron fate commitment, embryo development and cardiac cell differentiation, were markedly enriched in ethephon-treated cells. Neural induction of mESCs in the presence of ethephon was inhibited and the expression of neural genes was decreased in differentiated cells. Results obtained from this work clearly demonstrate that ethephon affects the gene expression profile of undifferentiated mESCs and prevents neural differentiation. Therefore, more caution against the frequent application of ethephon is advised.

The role of teratogens in neural crest development

The neural crest (NC), discovered by Wilhelm His 150 years ago, gives rise to a multipotent migratory embryonic cell population that generates a remarkably diverse and important array of cell types during the development of the vertebrate embryo. These cells originate in the neural plate border (NPB), which is the ectoderm between the neural plate and the epidermis. They give rise to the neurons and glia of the peripheral nervous system, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies are a class of congenital diseases resulting from the abnormal induction, specification, migration, differentiation or death of NC cells (NCCs) during embryonic development and have an important medical and societal impact. In general, congenital defects affect an appreciable percentage of newborns worldwide. Some of these defects are caused by teratogens, which are agents that negatively impact the formation of tissues and organs during development. In this review, we will discuss the teratogens linked to the development of many birth defects, with a strong focus on those that specifically affect the development of the NC, thereby producing neurocristopathies. Although increasing attention is being paid to the effect of teratogens on embryonic development in general, there is a strong need to critically evaluate the specific role of these agents in NC development. Therefore, increased understanding of the role of these factors in NC development will contribute to the planning of strategies aimed at the prevention and treatment of human neurocristopathies, whose etiology was previously not considered.

The role of metabolism in the developmental toxicity of polycyclic aromatic hydrocarbon-containing extracts of petroleum substances

In vitro assays presently used for prenatal developmental toxicity (PDT) testing only assess the embryotoxic potential of parent substances and not that of potentially embryotoxic metabolites. Here we combined a biotransformation system, using hamster liver microsomes, with the ES‐D3 cell differentiation assay of the embryonic stem cell test (EST) to compare the in vitro PDT potency of two 5‐ring polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene (BaP) and dibenz[a,h]anthracene (DBA), and dimethyl sulfoxide extracts from five PAH‐containing petroleum substances (PS) and a gas‐to‐liquid base oil (GTLb), with and without bioactivation. In the absence of bioactivation, DBA, but not BaP, inhibited the differentiation of ES‐D3 cells into beating cardiomyocytes in a concentration‐dependent manner. Upon bioactivation, BaP induced in vitro PDT, while its major metabolite 3‐hydroxybenzo[a]pyrene was shown to be active in the EST as well. This means BaP needs biotransformation to exert its embryotoxic effects. GTLb extracts tested negative in the EST, with and without bioactivation. The PS‐induced PDT in the EST was not substantially changed following bioactivation, implying that metabolism may not play a crucial role for the PS extracts under study to exert the in vitro PDT effects. Altogether, these results indicate that although some PAH require bioactivation to induce PDT, some do not and this latter appears to hold for the (majority of) the PS constituents responsible for the in vitro PDT of these complex substances.

The present study combines a biotransformation system, using hamster liver microsomes, with the embryonic stem cell test to compare the in vitro prenatal developmental toxicity potency of two 5‐ring polycyclic aromatic hydrocarbons, benzo[a]pyrene and dibenz[a,h]anthracene, and dimethyl sulfoxide extracts from five PAH‐containing petroleum substances and a gas‐to‐liquid base oil, with and without bioactivation.

In vitro toxicity screening of magnetite nanoparticles by applying mesenchymal stem cells derived from human umbilical cord lining

Despite the growing interest in nanoparticles (NPs), their toxicity has not yet been defined and the development of new strategies and predictive models are required. Human stem cells (SCs) offer a promising and innovative cell-based model. Among SCs, mesenchymal SCs (MSCs) derived from cord lining membrane (CL) may represent a new species-specific tool for establishing efficient platforms for primary screening and toxicity/safety testing of NPs. Superparamagnetic iron oxide NPs, including magnetite (Fe₃ O₄ NPs), have aroused great public health and scientific concerns despite their extensive uses. In this study, CL-MSCs were characterized and applied for in vitro toxicity screening of Fe₃ O₄ NPs. Cytotoxicity, internalization/uptake, differentiation and proliferative capacity were evaluated after exposure to different Fe₃ O₄ NP concentrations. Data were compared with those obtained from bone marrow (BM)-MSCs. We observed, at early passages (P3), that: (1) cytotoxicity occurred at 10 μg/mL in CL-MSCs and 100 μg/mL in BM-MSCs (no differences in toxicity, between CL- and BM-MSCs, were observed at higher dosage, 100-300 μg/mL); (2) cell density decrease and monolayer features loss were affected at ≥50 μg/mL in CL-MSCs only; and (3) NP uptake was concentration-dependent in both MSCs. After 100 μg/mL Fe₃ O₄ NP exposures, the capacity of proliferation was decreased (P5-P9) in CL-MSCs without morphology alteration. Moreover, a progressive decrease of intracellular Fe₃ O₄ NPs was observed over culture time. Antigen surface expression and multilineage differentiation were not influenced. These findings suggest that CL-MSCs could be used as a reliable cell-based model for Fe₃ O₄ NP toxicity screening evaluation and support the use of this approach for improving the confidence degree on the safety of NPs to predict health outcomes.

In vitro investigation of the effects of boron nitride nanotubes and curcumin on DNA damage

BACKROUND

Stem cells provide an opportunity to analyse the effects of xenobiotic on cell viability, differentiation and cell functions. Evaluation of the possible cytotoxic and DNA damaging effects on bone marrow CD34+ stem cells is important for their ability to differentiate into blood cells, and also for bone marrow diseases therapy. Boron nitride nanotubes and curcumin are potential nanoformulation agents that can be used together in the treatment of cancer or bone marrow diseases. Therefore, it is important to evaluate their possible effects on different cell lines.

OBJECTIVES

In this study, it was aimed to evaluate the cytotoxic and DNA damaging effects of boron nitride nanotubes which are commonly used in pyroelectric, piezoelectric and optical applications, but there is not enough information about its biocompatibility. Also, it was intended to research the effects of curcumin being used frequently in treatment processes for antioxidant properties.

METHODS

The possible cytotoxic and DNA damaging effects of boron nitride nanotubes and curcumin on CD34+ cells, HeLa and V79 cells were evaluated by MTT assay and Comet assay, respectively.

RESULTS AND CONCLUSION

Boron nitride nanotubes and curcumin had cytotoxic effects and cause DNA damage on CD34+ cells, HeLa and V79 cells at several concentrations, probably because of increased ROS level. However, there were not concentration - dependent effect and there were controversial toxicity results of the studied cell lines. Its mechanism needs to be enlightened by further analysis for potential targeted drug development. Graphical abstract.

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.

Human-induced pluripotent stems cells as a model to dissect the selective neurotoxicity of methylmercury

Methylmercury (MeHg) is a potent neurotoxicant affecting both the developing and mature central nervous system (CNS) with apparent indiscriminate disruption of multiple homeostatic pathways. However, genetic and environmental modifiers contribute significant variability to neurotoxicity associated with human exposures. MeHg displays developmental stage and neural lineage selective neurotoxicity. To identify mechanistic-based neuroprotective strategies to mitigate human MeHg exposure risk, it will be critical to improve our understanding of the basis of MeHg neurotoxicity and of this selective neurotoxicity. Here, we propose that human-based pluripotent stem cell cellular approaches may enable mechanistic insight into genetic pathways that modify sensitivity of specific neural lineages to MeHg-induced neurotoxicity. Such studies are crucial for the development of novel disease modifying strategies impinging on MeHg exposure vulnerability.

Disruption of mesoderm formation during cardiac differentiation due to developmental exposure to 13-cis-retinoic acid

13-cis-retinoic acid (isotretinoin, INN) is an oral pharmaceutical drug used for the treatment of skin acne, and is also a known teratogen. In this study, the molecular mechanisms underlying INN-induced developmental toxicity during early cardiac differentiation were investigated using both human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs). Pre-exposure of hiPSCs and hESCs to a sublethal concentration of INN did not influence cell proliferation and pluripotency. However, mesodermal differentiation was disrupted when INN was included in the medium during differentiation. Transcriptomic profiling by RNA-seq revealed that INN exposure leads to aberrant expression of genes involved in several signaling pathways that control early mesoderm differentiation, such as TGF-beta signaling. In addition, genome-wide chromatin accessibility profiling by ATAC-seq suggested that INN-exposure leads to enhanced DNA-binding of specific transcription factors (TFs), including HNF1B, SOX10 and NFIC, often in close spatial proximity to genes that are dysregulated in response to INN treatment. Altogether, these results identify potential molecular mechanisms underlying INN-induced perturbation during mesodermal differentiation in the context of cardiac development. This study further highlights the utility of human stem cells as an alternative system for investigating congenital diseases of newborns that arise as a result of maternal drug exposure during pregnancy.

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.

Ten years of progress and promise of induced pluripotent stem cells: historical origins, characteristics, mechanisms, limitations, and potential applications

The discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka in 2006 was heralded as a major breakthrough of the decade in stem cell research. The ability to reprogram human somatic cells to a pluripotent embryonic stem cell-like state through the ectopic expression of a combination of embryonic transcription factors was greeted with great excitement by scientists and bioethicists. The reprogramming technology offers the opportunity to generate patient-specific stem cells for modeling human diseases, drug development and screening, and individualized regenerative cell therapy. However, fundamental questions have been raised regarding the molecular mechanism of iPSCs generation, a process still poorly understood by scientists. The efficiency of reprogramming of iPSCs remains low due to the effect of various barriers to reprogramming. There is also the risk of chromosomal instability and oncogenic transformation associated with the use of viral vectors, such as retrovirus and lentivirus, which deliver the reprogramming transcription factors by integration in the host cell genome. These challenges can hinder the therapeutic prospects and promise of iPSCs and their clinical applications. Consequently, extensive studies have been done to elucidate the molecular mechanism of reprogramming and novel strategies have been identified which help to improve the efficiency of reprogramming methods and overcome the safety concerns linked with iPSC generation. Distinct barriers and enhancers of reprogramming have been elucidated, and non-integrating reprogramming methods have been reported. Here, we summarize the progress and the recent advances that have been made over the last 10 years in the iPSC field, with emphasis on the molecular mechanism of reprogramming, strategies to improve the efficiency of reprogramming, characteristics and limitations of iPSCs, and the progress made in the applications of iPSCs in the field of disease modelling, drug discovery and regenerative medicine. Additionally, this study appraises the role of genomic editing technology in the generation of healthy iPSCs.

Phthalazinone Pyrazole Enhances the Hepatic Functions of Human Embryonic Stem Cell-Derived Hepatocyte-Like Cells via Suppression of the Epithelial-Mesenchymal Transition

During liver development, nonpolarized hepatic progenitor cells differentiate into mature hepatocytes with distinct polarity. This polarity is essential for maintaining the intrinsic properties of hepatocytes. The balance between the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) plays a decisive role in differentiation of polarized hepatocytes. In this study, we found that phthalazinone pyrazole (PP), a selective inhibitor of Aurora-A kinase (Aurora-A), suppressed the EMT during the differentiation of hepatocyte-like cells (HLCs) from human embryonic stem cells. The differentiated HLCs treated with PP at the hepatoblast stage showed enhanced hepatic morphology and functions, particularly with regard to the expression of drug metabolizing enzymes. Moreover, we found that these effects were mediated though suppression of the AKT pathway, which is involved in induction of the EMT, and upregulation of hepatocyte nuclear factor 4α expression rather than Aurora-A inhibition. In conclusion, these findings provided insights into the regulatory role of the EMT on in vitro hepatic maturation, suggesting that inhibition of the EMT may drive transformation of hepatoblast cells into mature and polarized HLCs.

Studying the Toxic Effects of Some Biologically Active Peptides on the Model of Mouse Embryonic Stem Cells

We studied the effects of peptide drugs (HLDF-6, PGP, RPGP, and PGLP) and peptide pharmaceutical products (Semax, Selank, and thyroliberin) on proliferation and survival of mouse embryonic stem cells and their derivatives. Differentiation of mouse embryonic stem cells into neuronal precursors was evaluated. PGP and PGLP in concentrations of 10 and 0.1 μM, respectively, had little, but significant inhibitory effect on proliferative activity of cells. These peptides in concentrations of 10 and 0.1 μM, respectively, and Semax (10 and 0.1 μM) significantly increased the survival rate of mouse embryonic stem cells (serum deprivation). Moreover, study peptides had little effect on the formation of neuronal precursors from mouse embryonic stem cells. HLDF-6, Selank, and thyroliberin produced an insignificant effect on the differentiation of these cells into mature neurons. Analysis of differentiation of embryonic stem cells into GABA⁺ neurons showed that Selank, thyroliberin (100 μM), and NGF (100 ng/ml) decrease the ratio of these cells by 61, 58, and 87%, respectively, in comparison with the control. Our results indicate that these peptide compounds do not produce toxic effect during the embryonic and fetal period of life.

Towards a New Paradigm in Nano-Genotoxicology: Facing Complexity of Nanomaterials' Cellular Interactions and Effects

Changes in paradigm contribute to advances in research. The current paradigms for the evaluation of toxicity of chemicals refer to linear or curvilinear dose-response curves with or without threshold and to surface-dependent induction of oxidative damage for particles. The unique physicochemical properties and biological/genotoxic activity of engineered nanomaterials (NMs) require the development of a new paradigm. Because of their unusual dosimetry and their multiple interactions at NM level (agglomeration/aggregation) and at different cellular and extracellular levels, NMs are likely to have complex modes of action (multiple hits at multiple targets) leading to complex thresholded-non-thresholded dose-response curves. Understanding their cellular targets and their modes of action will contribute to the production of safe-by-design NMs. An integrative, cell-by-cell approach for genotoxic effects should be applied to tackle this emerging paradigm in nano-genotoxicology.

17β-Oestradiol promotes differentiation of human embryonic stem cells into dopamine neurons via cross-talk between insulin-like growth factors-1 and oestrogen receptor β

Human embryonic stem cells (hESCs) can self‐renew and differentiate into all cell lineages. E2 is known to exhibit positive effects on embryo development. Although the importance of E2 in many physiological processes has been reported, to date few researchers have investigated the effects of E2 on hESCs differentiation. We studied the effects of E2 on dopamine (DA) neuron induction of hESCs and its related signalling pathways using the three‐stage protocol. In our study, 0.1 μM E2 were applied to hESCs‐derived human embryoid bodies (hEBs) and effects of E2 on neural cells differentiation were investigated. Protein and mRNA level assay indicated that E2 up‐regulated the expression of insulin‐like growth factors (IGF)‐1, ectoderm, neural precursor cells (NPC) and DA neuron markers, respectively. The population of hESC‐derived NPCs and DA neurons was increased to 92% and 93% to that of DMSO group, respectively. Furthermore, yield of DA neuron‐secreted tyrosine hydroxylase (TH) and dopamine was also increased. E2‐caused promotion was relieved in single inhibitor (ICI or JB1) group partly, and E2 effects were repressed more stronger in inhibitors combination (ICI plus JB1) group than in single inhibitor group at hEBs, hNPCs and hDA neurons stages. Owing to oestrogen receptors regulate multiple brain functions, when single or two inhibitors were used to treat neural differentiation stage, we found that oestrogen receptor (ER)β but not ERα is strongly repressed at the hNPCs and hDA neurons stage. These findings, for the first time, demonstrate the molecular cascade and related cell biology events involved in E2‐improved hNPC and hDA neuron differentiation through cross‐talk between IGF‐1 and ERβ in vitro.

Clinical potentials of human pluripotent stem cells

Aging, injuries, and diseases can be considered as the result of malfunctioning or damaged cells. Regenerative medicine aims to restore tissue homeostasis by repairing or replacing cells, tissues, or damaged organs, by linking and combining different disciplines including engineering, technology, biology, and medicine. To pursue these goals, the discipline is taking advantage of pluripotent stem cells (PSCs), a peculiar type of cell possessing the ability to differentiate into every cell type of the body. Human PSCs can be isolated from the blastocysts and maintained in culture indefinitely, giving rise to the so-called embryonic stem cells (ESCs). However, since 2006, it is possible to restore in an adult cell a pluripotent ESC-like condition by forcing the expression of four transcription factors with the rejuvenating reprogramming technology invented by Yamanaka. Then the two types of PSC can be differentiated, using standardized protocols, towards the cell type necessary for the regeneration. Although the use of these derivatives for therapeutic transplantation is still in the preliminary phase of safety and efficacy studies, a lot of efforts are presently taking place to discover the biological mechanisms underlying genetic pathologies, by differentiating induced PSCs derived from patients, and new therapies by challenging PSC-derived cells in drug screening.

Concise Review: Liver Regenerative Medicine: From Hepatocyte Transplantation to Bioartificial Livers and Bioengineered Grafts

Donor organ shortage is the main limitation to liver transplantation as a treatment for end-stage liver disease and acute liver failure. Liver regenerative medicine may in the future offer an alternative form of therapy for these diseases, be it through cell transplantation, bioartificial liver (BAL) devices, or bioengineered whole organ liver transplantation. All three strategies have shown promising results in the past decade. However, before they are incorporated into widespread clinical practice, the ideal cell type for each treatment modality must be found, and an adequate amount of metabolically active, functional cells must be able to be produced. Research is ongoing in hepatocyte expansion techniques, use of xenogeneic cells, and differentiation of stem cell-derived hepatocyte-like cells (HLCs). HLCs are a few steps away from clinical application, but may be very useful in individualized drug development and toxicity testing, as well as disease modeling. Finally, safety concerns including tumorigenicity and xenozoonosis must also be addressed before cell transplantation, BAL devices, and bioengineered livers occupy their clinical niche. This review aims to highlight the most recent advances and provide an updated view of the current state of affairs in the field of liver regenerative medicine. Stem Cells 2017;35:42-50.

In vitro acute and developmental neurotoxicity screening: an overview of cellular platforms and high-throughput technical possibilities

Neurotoxicity and developmental neurotoxicity are important issues of chemical hazard assessment. Since the interpretation of animal data and their extrapolation to man is challenging, and the amount of substances with information gaps exceeds present animal testing capacities, there is a big demand for in vitro tests to provide initial information and to prioritize for further evaluation. During the last decade, many in vitro tests emerged. These are based on animal cells, human tumour cell lines, primary cells, immortalized cell lines, embryonic stem cells, or induced pluripotent stem cells. They differ in their read-outs and range from simple viability assays to complex functional endpoints such as neural crest cell migration. Monitoring of toxicological effects on differentiation often requires multiomics approaches, while the acute disturbance of neuronal functions may be analysed by assessing electrophysiological features. Extrapolation from in vitro data to humans requires a deep understanding of the test system biology, of the endpoints used, and of the applicability domains of the tests. Moreover, it is important that these be combined in the right way to assess toxicity. Therefore, knowledge on the advantages and disadvantages of all cellular platforms, endpoints, and analytical methods is essential when establishing in vitro test systems for different aspects of neurotoxicity. The elements of a test, and their evaluation, are discussed here in the context of comprehensive prediction of potential hazardous effects of a compound. We summarize the main cellular characteristics underlying neurotoxicity, present an overview of cellular platforms and read-out combinations assessing distinct parts of acute and developmental neurotoxicology, and highlight especially the use of stem cell-based test systems to close gaps in the available battery of tests.

Xeno-sensing activity of the aryl hydrocarbon receptor in human pluripotent stem cell-derived hepatocyte-like cells

Although hepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) are considered a promising model for predicting hepatotoxicity, their application has been restricted because of the low activity of drug metabolizing enzymes (DMEs). Here we found that the low expression of xenobiotic receptors (constitutive androstane receptor, CAR; and pregnane X receptor, PXR) contributes to the low activity of DMEs in hPSC-HLCs. Most CAR- and PXR-regulated DMEs and transporters were transcriptionally down-regulated in hPSC-HLC. Transcriptional expression of CAR and PXR was highly repressed in hPSC-HLCs, whereas mRNA levels of aryl hydrocarbon receptor (AHR) were comparable to those of adult liver. Furthermore, ligand-induced transcriptional activation was observed only at AHR in hPSC-HLCs. Bisulfite sequencing analysis demonstrated that promoter hypermethylation of CAR and PXR was associated with diminished transcriptional activity in hPSC-HLCs. Treatment with AHR-selective ligands increased the transcription of AHR-dependent target genes by direct AHR-DNA binding at the xenobiotic response element. In addition, an antagonist of AHR significantly inhibited AHR-dependent target gene expression. Thus, AHR may function intrinsically as a xenosensor as well as a ligand-dependent transcription factor in hPSC-HLCs. Our results indicate that hPSC-HLCs can be used to screen toxic substances related to AHR signaling and to identify potential AHR-targeted therapeutics.

Toxicity testing and drug screening using iPSC-derived hepatocytes, cardiomyocytes, and neural cells

Unexpected toxicity in areas such as cardiotoxicity, hepatotoxicity, and neurotoxicity is a serious complication of clinical therapy and one of the key causes for failure of promising drug candidates in development. Animal studies have been widely used for toxicology research to provide preclinical security evaluation of various therapeutic agents under development. Species differences in drug penetration of the blood-brain barrier, drug metabolism, and related toxicity contribute to failure of drug trials from animal models to human. The existing system for drug discovery has relied on immortalized cell lines, animal models of human disease, and clinical trials in humans. Moreover, drug candidates that are passed as being safe in the preclinical stage often show toxic effects during the clinical stage. Only around 16% drugs are approved for human use. Research on induced pluripotent stem cells (iPSCs) promises to enhance drug discovery and development by providing simple, reproducible, and economically effective tools for drug toxicity screening under development and, on the other hand, for studying the disease mechanism and pathways. In this review, we provide an overview of basic information about iPSCs, and discuss efforts aimed at the use of iPSC-derived hepatocytes, cardiomyocytes, and neural cells in drug discovery and toxicity testing.

Carbon nanoparticle induced cytotoxicity in human mesenchymal stem cells through upregulation of TNF3, NFKBIA and BCL2L1 genes

Carbon based nanomaterials, including carbon nanotubes, graphene, nanodiamond and carbon nanoparticles, have emerged as potential candidates for a wide variety of applications because of their unusual electrical, mechanical, thermal and optical properties. However, our understanding of how increased usage of carbon based nanomaterials could lead to harmful effects in humans and other biological systems is inadequate. Our present investigation is focused on the cellular toxicity of carbon nanoparticles (CNPs) on human mesenchymal stem cells (hMSCs). Following exposure to CNPs, cell viability, nuclear morphological changes, apoptosis and cell cycle progression were monitored. Furthermore, the expression of genes involved in both cell death (e.g., P53, TNF3, CDKN1A, TNFRSF1A, TNFSF10, NFKBIA, BCL2L1) and cell cycle regulation (e.g., PCNA, EGR1, E2F1, CCNG1, CCND1, CCNC, CYCD3) were assessed using qPCR. Our results indicated that CNPs reduce cell viability and cause chromatin condensation and DNA fragmentation. Cell cycle analysis indicated that CNPs affect the cell cycle progression. However, the gene expression measurements confirmed that CNPs significantly upregulated the P53, TNF3, CDKNIA, and NFKBIA genes and downregulated the EGR1 gene in hMSCs. Our findings suggest that CNPs reduce cell viability by disrupting the expression of cell death genes in human mesenchymal stem cell (hMSC). The results of this investigation revealed that CNPs exhibited moderate toxicity on hMSCs.

Ionizing Radiation Impacts on Cardiac Differentiation of Mouse Embryonic Stem Cells

Little is known about the effects of ionizing radiation on the earliest stages of embryonic development although it is well recognized that ionizing radiation is a natural part of our environment and further exposure may occur due to medical applications. The current study addresses this issue using D3 mouse embryonic stem cells as a model system. Cells were irradiated with either X-rays or carbon ions representing sparsely and densely ionizing radiation and their effect on the differentiation of D3 cells into spontaneously contracting cardiomyocytes through embryoid body (EB) formation was measured. This study is the first to demonstrate that ionizing radiation impairs the formation of beating cardiomyocytes with carbon ions being more detrimental than X-rays. However, after prolonged culture time, the number of beating EBs derived from carbon ion irradiated cells almost reached control levels indicating that the surviving cells are still capable of developing along the cardiac lineage although with considerable delay. Reduced EB size, failure to downregulate pluripotency markers, and impaired expression of cardiac markers were identified as the cause of compromised cardiomyocyte formation. Dysregulation of cardiac differentiation was accompanied by alterations in the expression of endodermal and ectodermal markers that were more severe after carbon ion irradiation than after exposure to X-rays. In conclusion, our data show that carbon ion irradiation profoundly affects differentiation and thus may pose a higher risk to the early embryo than X-rays.

Integrative analysis of genes and miRNA alterations in human embryonic stem cells-derived neural cells after exposure to silver nanoparticles

Given the rapid growth of engineered and customer products made of silver nanoparticles (Ag NPs), understanding their biological and toxicological effects on humans is critically important. The molecular developmental neurotoxic effects associated with exposure to Ag NPs were analyzed at the physiological and molecular levels, using an alternative cell model: human embryonic stem cell (hESC)-derived neural stem/progenitor cells (NPCs). In this study, the cytotoxic effects of Ag NPs (10-200μg/ml) were examined in these hESC-derived NPCs, which have a capacity for neurogenesis in vitro, at 6 and 24h. The results showed that Ag NPs evoked significant toxicity in hESC-derived NPCs at 24h in a dose-dependent manner. In addition, Ag NPs induced cell cycle arrest and apoptosis following a significant increase in oxidative stress in these cells. To further clarify the molecular mechanisms of the toxicological effects of Ag NPs at the transcriptional and post-transcriptional levels, the global expression profiles of genes and miRNAs were analyzed in hESC-derived NPCs after Ag NP exposure. The results showed that Ag NPs induced oxidative stress and dysfunctional neurogenesis at the molecular level in hESC-derived NPCs. Based on this hESC-derived neural cell model, these findings have increased our understanding of the molecular events underlying developmental neurotoxicity induced by Ag NPs in humans.

Assessment of Bisphenol A (BPA) neurotoxicity in vitro with mouse embryonic stem cells

The adverse effects of environmental pollution on our well-being have been intensively studied with many in vitro and in vivo systems. In our group, we focus on stem cell toxicology due to the multitude of embryonic stem cell (ESC) properties which can be exerted in toxicity assays. In fact, ESCs can differentiate in culture to mimic embryonic development in vivo, or specifically to virtually any kind of somatic cells. Here, we used the toxicant Bisphenol A (BPA), a chemical known as a hazard to infants and children, and showed that our stem cell toxicology system was able to efficiently recapitulate most of the toxic effects of BPA previously detected by in vitro system or animal tests. More precisely, we demonstrated that BPA affected the proper specification of germ layers during our in vitro mimicking of the embryonic development, as well as the establishment of neural ectoderm and neural progenitor cells.

Neural Differentiation of Human Pluripotent Stem Cells for Nontherapeutic Applications: Toxicology, Pharmacology, and In Vitro Disease Modeling

Human pluripotent stem cells (hPSCs) derived from either blastocyst stage embryos (hESCs) or reprogrammed somatic cells (iPSCs) can provide an abundant source of human neuronal lineages that were previously sourced from human cadavers, abortuses, and discarded surgical waste. In addition to the well-known potential therapeutic application of these cells in regenerative medicine, these are also various promising nontherapeutic applications in toxicological and pharmacological screening of neuroactive compounds, as well as for in vitro modeling of neurodegenerative and neurodevelopmental disorders. Compared to alternative research models based on laboratory animals and immortalized cancer-derived human neural cell lines, neuronal cells differentiated from hPSCs possess the advantages of species specificity together with genetic and physiological normality, which could more closely recapitulate in vivo conditions within the human central nervous system. This review critically examines the various potential nontherapeutic applications of hPSC-derived neuronal lineages and gives a brief overview of differentiation protocols utilized to generate these cells from hESCs and iPSCs.

B-cell receptor-associated protein 31 regulates human embryonic stem cell adhesion, stemness, and survival via control of epithelial cell adhesion molecule

B-Cell receptor-associated protein 31 (BAP31) regulates the export of secreted membrane proteins from the endoplasmic reticulum (ER) to the downstream secretory pathway. Previously, we generated a monoclonal antibody 297-D4 against the surface molecule on undifferentiated human embryonic stem cells (hESCs). Here, we found that 297-D4 antigen was localized to pluripotent hESCs and downregulated during early differentiation of hESCs and identified that the antigen target of 297-D4 was BAP31 on the hESC-surface. To investigate the functional role of BAP31 in hESCs, BAP31 expression was knocked down by small interfering RNA. BAP31 depletion impaired hESC self-renewal and pluripotency and drove hESC differentiation into multicell lineages. BAP31 depletion hindered hESC proliferation by arresting cell cycle at G0/G1 phase and inducing caspase-independent cell death. Interestingly, BAP31 depletion reduced hESC adhesion to extracellular matrix (ECM). Analysis of cell surface molecules showed decreased expression of epithelial cell adhesion molecule (EpCAM) in BAP31-depleted hESCs, while ectopic expression of BAP31 elevated the expression of EpCAM. EpCAM depletion also reduced hESC adhesion to ECM, arrested cell cycle at G0/G1 phase and induced cell death, producing similar effects to those of BAP31 depletion. BAP31 and EpCAM were physically associated and colocalized at the ER and cell surface. Both BAP31 and EpCAM depletion decreased cyclin D1 and E expression and suppressed PI3K/Akt signaling, suggesting that BAP31 regulates hESC stemness and survival via control of EpCAM expression. These findings provide, for the first time, mechanistic insights into how BAP31 regulates hESC stemness and survival via control of EpCAM expression.

A method for human teratogen detection by geometrically confined cell differentiation and migration

Unintended exposure to teratogenic compounds can lead to various birth defects; however current animal-based testing is limited by time, cost and high inter-species variability. Here, we developed a human-relevant in vitro model, which recapitulated two cellular events characteristic of embryogenesis, to identify potentially teratogenic compounds. We spatially directed mesoendoderm differentiation, epithelial-mesenchymal transition and the ensuing cell migration in micropatterned human pluripotent stem cell (hPSC) colonies to collectively form an annular mesoendoderm pattern. Teratogens could disrupt the two cellular processes to alter the morphology of the mesoendoderm pattern. Image processing and statistical algorithms were developed to quantify and classify the compounds' teratogenic potential. We not only could measure dose-dependent effects but also correctly classify species-specific drug (Thalidomide) and false negative drug (D-penicillamine) in the conventional mouse embryonic stem cell test. This model offers a scalable screening platform to mitigate the risks of teratogen exposures in human.

Stem cell-derived liver cells for drug testing and disease modeling

Differences between animals and humans in liver pathways now necessitate the use of in vitro models of the human liver for several applications such as drug screening. However, isolated primary human hepatocytes (PHHs) are a limited resource for building such models given shortages of donor organs. In contrast, human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) can be propagated nearly indefinitely and differentiated into hepatocyte-like cells in vitro using soluble factors inspired from liver development. Additionally, iPSCs can be generated from patients with specific genetic backgrounds to study genotype-phenotype relationships. While current protocols to differentiate hESCs and iPSCs into human hepatocyte-like cells (hESC-HHs and iPSC-HHs) still need improvement to yield cells functionally similar to the adult liver, proof-of-concept studies have already shown utility of these cells in drug development and modeling liver diseases such as α1-antitrypsin deficiency, hepatitis B/C viral infections, and malaria. Here, we present an overview of hESC-HH and iPSC-HH culture platforms that have been utilized for the aforementioned applications. We also discuss the use of semiconductor-driven microfabrication tools to precisely control the microenvironment around these cells to enable higher and longer-term liver functions in vitro. Finally, we discuss areas for improvement in creating next generation stem cell-derived liver models. In the future, stem cell-derived hepatocyte-like cells could provide a sustainable cell source for high-throughput drug screening, enabling better mechanistic understanding of human liver diseases for the development of more efficacious and safer therapeutics, and personalized cell-based therapies in the clinic.

Induced pluripotent stem cells: applications in regenerative medicine, disease modeling, and drug discovery

Recent progresses in the field of Induced Pluripotent Stem Cells (iPSCs) have opened up many gateways for the research in therapeutics. iPSCs are the cells which are reprogrammed from somatic cells using different transcription factors. iPSCs possess unique properties of self renewal and differentiation to many types of cell lineage. Hence could replace the use of embryonic stem cells (ESC), and may overcome the various ethical issues regarding the use of embryos in research and clinics. Overwhelming responses prompted worldwide by a large number of researchers about the use of iPSCs evoked a large number of peple to establish more authentic methods for iPSC generation. This would require understanding the underlying mechanism in a detailed manner. There have been a large number of reports showing potential role of different molecules as putative regulators of iPSC generating methods. The molecular mechanisms that play role in reprogramming to generate iPSCs from different types of somatic cell sources involves a plethora of molecules including miRNAs, DNA modifying agents (viz. DNA methyl transferases), NANOG, etc. While promising a number of important roles in various clinical/research studies, iPSCs could also be of great use in studying molecular mechanism of many diseases. There are various diseases that have been modeled by uing iPSCs for better understanding of their etiology which maybe further utilized for developing putative treatments for these diseases. In addition, iPSCs are used for the production of patient-specific cells which can be transplanted to the site of injury or the site of tissue degeneration due to various disease conditions. The use of iPSCs may eliminate the chances of immune rejection as patient specific cells may be used for transplantation in various engraftment processes. Moreover, iPSC technology has been employed in various diseases for disease modeling and gene therapy. The technique offers benefits over other similar techniques such as animal models. Many toxic compounds (different chemical compounds, pharmaceutical drugs, other hazardous chemicals, or environmental conditions) which are encountered by humans and newly designed drugs may be evaluated for toxicity and effects by using iPSCs. Thus, the applications of iPSCs in regenerative medicine, disease modeling, and drug discovery are enormous and should be explored in a more comprehensive manner.