Assessment and Comparison of Early Developmental Toxicity of Six Per- and Polyfluoroalkyl Substances with Human Embryonic Stem Cell Models

Per- and polyfluoroalkyl substances (PFAS) are extensively utilized in varieties of products and tend to accumulate in the human body including umbilical cord blood and embryos/fetuses. In this study, we conducted an assessment and comparison of the potential early developmental toxicity of perfluorooctanoic acid (PFOA), undecafluorohexanoic acid (PFHxA), heptafluorobutyric acid, perfluorooctanesulfonate (PFOS), perfluorohexanesulfonate, and perfluorobutyric acid at noncytotoxic concentrations relevant to human exposure using models based on human embryonic stem cells in both three-dimensional embryoid body (EB) and monolayer differentiation configurations. All six compounds influenced the determination of cell fate by disrupting the expression of associated markers in both models and, in some instances, even led to alterations in the formation of cystic EBs. The expression of cilia-related gene IFT122 was significantly inhibited. Additionally, PFOS and PFOA inhibited ciliogenesis, while PFOA specifically reduced the cilia length. Transcriptome analysis revealed that PFOS altered 1054 genes and disrupted crucial signaling pathways such as WNT and TGF-β, which play integral roles in cilia transduction and are critical for early embryonic development. These results provide precise and comprehensive insights into the potential adverse health effects of these six PFAS compounds directly concerning early human embryonic development.

Stem cell modeling of nervous system tumors

Nervous system tumors, particularly brain tumors, represent the most common tumors in children and one of the most lethal tumors in adults. Despite decades of research, there are few effective therapies for these cancers. Although human nervous system tumor cells and genetically engineered mouse models have served as excellent platforms for drug discovery and preclinical testing, they have limitations with respect to accurately recapitulating important aspects of the pathobiology of spontaneously arising human tumors. For this reason, attention has turned to the deployment of human stem cell engineering involving human embryonic or induced pluripotent stem cells, in which genetic alterations associated with nervous system cancers can be introduced. These stem cells can be used to create self-assembling three-dimensional cerebral organoids that preserve key features of the developing human brain. Moreover, stem cell-engineered lines are amenable to xenotransplantation into mice as a platform to investigate the tumor cell of origin, discover cancer evolutionary trajectories and identify therapeutic vulnerabilities. In this article, we review the current state of human stem cell models of nervous system tumors, discuss their advantages and disadvantages, and provide consensus recommendations for future research.

POZ/BTB and AT hook containing zinc finger 1 (PATZ1) suppresses differentiation and regulates metabolism in human embryonic stem cells

Human embryonic stem cells (hESCs) can proliferate infinitely (self-renewal) and give rise to almost all types of somatic cells (pluripotency). Hence, understanding the molecular mechanism of pluripotency regulation is important for applications of hESCs in regenerative medicine. Here we report that PATZ1 is a key factor that regulates pluripotency and metabolism in hESCs. We found that depletion of PATZ1 is associated with rapid downregulation of master pluripotency genes and prominent deceleration of cell growth. We also revealed that PATZ1 regulates hESC pluripotency though binding the regulatory regions of OCT4 and NANOG. In addition, we demonstrated PATZ1 is a key node in the OCT4/NANOG transcriptional network. We further revealed that PATZ1 is essential for cell growth in hESCs. Importantly, we discovered that depletion of PATZ1 drives hESCs to exploit glycolysis which energetically compensates for the mitochondrial dysfunction. Overall, our study establishes the fundamental role of PATZ1 in regulating pluripotency in hESCs. Moreover, PATZ1 is essential for maintaining a steady metabolic homeostasis to refine the stemness of hESCs.

TGFβ3, dibutyryl cAMP and a notch inhibitor modulate phenotype late in stem cell-derived dopaminergic neuron maturation

The generation of midbrain dopaminergic neurons (mDAs) from pluripotent stem cells (hPSC) holds much promise for both disease modelling studies and as a cell therapy for Parkinson's disease (PD). Generally, dopaminergic neuron differentiation paradigms rely on inhibition of smad signalling for neural induction followed by hedgehog signalling and an elevation of β-catenin to drive dopaminergic differentiation. Post-patterning, differentiating dopaminergic neuron cultures are permitted time for maturation after which the success of these differentiation paradigms is usually defined by expression of tyrosine hydroxylase (TH), the rate limiting enzyme in the synthesis of dopamine. However, during maturation, culture media is often supplemented with additives to promote neuron survival and or promote cell differentiation. These additives include dibutyryl cyclic adenosine monophosphate (dbcAMP), transforming growth factor β3 (TGFβ3) and or the γ-secretase inhibitor (DAPT). While these factors are routinely added to cultures, their impact upon pluripotent stem cell-derived mDA phenotype is largely unclear. In this study, we differentiate pluripotent stem cells toward a dopaminergic phenotype and investigate how the omission of dbcAMP, TGFβ3 or DAPT, late in maturation, affects the regulation of multiple dopaminergic neuron phenotype markers. We now show that the removal of dbcAMP or TGFβ3 significantly and distinctly impacts multiple markers of the mDA phenotype (FOXA2, EN1, EN2, FOXA2, SOX6), while commonly increasing both MSX2 and NEUROD1 and reducing expression of both tyrosine hydroxylase and WNT5A. Removing DAPT significantly impacted MSX2, OTX2, EN1, and KCNJ6. In the absence of any stressful stimuli, we suggest that these culture additives should be viewed as mDA phenotype-modifying, rather than neuroprotective. We also suggest that their addition to cultures is likely to confound the interpretation of both transplantation and disease modelling studies.

Co-grafts of Human Embryonic Stem Cell Derived Retina Organoids and Retinal Pigment Epithelium for Retinal Reconstruction in Immunodeficient Retinal Degenerate Royal College of Surgeons Rats

End-stage age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are two major retinal degenerative (RD) conditions that result in irreversible vision loss. Permanent eye damage can also occur in battlefields or due to accidents. This suggests there is an unmet need for developing effective strategies for treating permanent retinal damages. In previous studies, co-grafted sheets of fetal retina with its retinal pigment epithelium (RPE) have demonstrated vision improvement in rat retinal disease models and in patients, but this has not yet been attempted with stem-cell derived tissue. Here we demonstrate a cellular therapy for irreversible retinal eye injuries using a "total retina patch" consisting of retinal photoreceptor progenitor sheets and healthy RPE cells on an artificial Bruch's membrane (BM). For this, retina organoids (ROs) (cultured in suspension) and polarized RPE sheets (cultured on an ultrathin parylene substrate) were made into a co-graft using bio-adhesives [gelatin, growth factor-reduced matrigel, and medium viscosity (MVG) alginate]. In vivo transplantation experiments were conducted in immunodeficient Royal College of Surgeons (RCS) rats at advanced stages of retinal degeneration. Structural reconstruction of the severely damaged retina was observed based on histological assessments and optical coherence tomography (OCT) imaging. Visual functional assessments were conducted by optokinetic behavioral testing and superior colliculus electrophysiology. Long-term survival of the co-graft in the rat subretinal space and improvement in visual function were observed. Immunohistochemistry showed that co-grafts grew, generated new photoreceptors and developed neuronal processes that were integrated into the host retina. This novel approach can be considered as a new therapy for complete replacement of a degenerated retina.

Uncovering the Metabolic and Stress Responses of Human Embryonic Stem Cells to FTH1 Gene Silencing

Embryonic stem cells (ESCs) are pluripotent cells with indefinite self-renewal ability and differentiation properties. To function properly and maintain genomic stability, ESCs need to be endowed with an efficient repair system as well as effective redox homeostasis. In this study, we investigated different aspects involved in ESCs' response to iron accumulation following stable knockdown of the ferritin heavy chain (FTH1) gene, which encodes for a major iron storage protein with ferroxidase activity. Experimental findings highlight unexpected and, to a certain extent, paradoxical results. If on one hand FTH1 silencing does not correlate with increased ROS production nor with changes in the redox status, strengthening the concept that hESCs are extremely resistant and, to a certain extent, even refractory to intracellular iron imbalance, on the other, the differentiation potential of hESCs seems to be affected and apoptosis is observed. Interestingly, we found that FTH1 silencing is accompanied by a significant activation of the nuclear factor (erythroid-derived-2)-like 2 (Nrf2) signaling pathway and pentose phosphate pathway (PPP), which crosstalk in driving hESCs antioxidant cascade events. These findings shed new light on how hESCs perform under oxidative stress, dissecting the molecular mechanisms through which Nrf2, in combination with PPP, counteracts oxidative injury triggered by FTH1 knockdown.

The Developmental & Molecular Requirements for Ensuring that Human Pluripotent Stem Cell-Derived Hair Follicle Bulge Stem Cells Have Acquired Competence for Hair Follicle Generation Following Transplantation

When using human induced pluripotent stem cells (hiPSCs) to achieve hair follicle (HF) replacement, we found it best to emulate the earliest fundamental developmental processes of gastrulation, ectodermal lineage commitment, and dermogenesis. Viewing hiPSCs as a model of the epiblast, we exploited insights from mapping the dynamic up- and down-regulation of the developmental molecules that determine HF lineage in order to ascertain the precise differentiation stage and molecular requirements for grafting HF-generating progenitors. To yield an integrin-dependent lineage like the HF in vivo, we show that hiPSC derivatives should co-express, just prior to transplantation, the following combination of markers: integrins α6 and β1 and the glycoprotein CD200 on their surface; and, intracellularly, the epithelial marker keratin 18 and the hair follicle bulge stem cell (HFBSC)-defining molecules transcription factor P63 and the keratins 15 and 19. If the degree of trichogenic responsiveness indicated by the presence of these molecules is not achieved (they peak on Days 11-18 of the protocol), HF generation is not possible. Conversely, if differentiation of the cells is allowed to proceed beyond the transient intermediate progenitor state represented by the HFBSC, and instead cascades to their becoming keratin 14⁺ keratin 5⁺ CD200^– keratinocytes (Day 25), HF generation is equally impossible. We make the developmental case for transplanting at Day 16-18 of differentiation—the point at which the hiPSCs have lost pluripotency, have attained optimal expression of HFBSC markers, have not yet experienced downregulation of key integrins and surface glycoproteins, have not yet started expressing keratinocyte-associated molecules, and have sufficient proliferative capacity to allow a well-populated graft. This panel of markers may be used for isolating (by cytometry) HF-generating derivatives away from cell types unsuited for this therapy as well as for identifying trichogenic drugs.

Activin A-derived human embryonic stem cells show increased competence to differentiate into primordial germ cell-like cells

Protocols for specifying human primordial germ cell‐like cells (hPGCLCs) from human embryonic stem cells (hESCs) remain hindered by differences between hESC lines, their derivation methods, and maintenance culture conditions. This poses significant challenges for establishing reproducible in vitro models of human gametogenesis. Here, we investigated the influence of activin A (ActA) during derivation and maintenance on the propensity of hESCs to differentiate into PGCLCs. We show that continuous ActA supplementation during hESC derivation (from blastocyst until the formation of the post‐inner cell mass intermediate [PICMI]) and supplementation (from the first passage of the PICMI onwards) is beneficial to differentiate hESCs to PGCLCs subsequently. Moreover, comparing isogenic primed and naïve states prior to differentiation, we showed that conversion of hESCs to the 4i‐state improves differentiation to (TNAP [tissue nonspecific alkaline phosphatase]+/PDPN [podoplanin]+) PGCLCs. Those PGCLCs expressed several germ cell markers, including TFAP2C (transcription factor AP‐2 gamma), SOX17 (SRY‐box transcription factor 17), and NANOS3 (nanos C2HC‐type zinc finger 3), and markers associated with germ cell migration, CXCR4 (C‐X‐C motif chemokine receptor 4), LAMA4 (laminin subunit alpha 4), ITGA6 (integrin subunit alpha 6), and CDH4 (cadherin 4), suggesting that the large numbers of PGCLCs obtained may be suitable to differentiate further into more mature germ cells. Finally, hESCs derived in the presence of ActA showed higher competence to differentiate to hPGCLC, in particular if transiently converted to the 4i‐state. Our work provides insights into the differences in differentiation propensity of hESCs and delivers an optimized protocol to support efficient human germ cell derivation.

Comprehensive proteogenomic analysis of human embryonic and induced pluripotent stem cells

Although the concepts of somatic cell reprogramming and human‐induced pluripotent stem cells (hiPSCs) generation have undergone several analyses to validate the usefulness of these cells in research and clinic, it remains still controversial whether the hiPSCs are equivalent to human embryonic stem cells (hESCs), pointing to the need of further characterization for a more comprehensive understanding of pluripotency. Most of the experimental evidence comes from the transcriptome analysis, while a little is available on protein data, and even less is known about the post‐translational modifications. Here, we report a combined strategy of mass spectrometry and gene expression profiling for proteogenomic analysis of reprogrammed and embryonic stem cells. The data obtained through this integrated, multi‐“omics” approach indicate that a small, but still significant, number of distinct pathways is enriched in reprogrammed versus embryonic stem cells, supporting the view that pluripotency is an extremely complex, multifaceted phenomenon, with peculiarities that are characteristic of each cell type.

DICER1 Is Essential for Self-Renewal of Human Embryonic Stem Cells

MicroRNAs (miRNAs) are the effectors of a conserved gene-silencing system with broad roles in post-transcriptional regulation. Due to functional overlaps, assigning specific functions to individual miRNAs has been challenging. DICER1 cleaves pre-miRNA hairpins into mature miRNAs, and previously Dicer1 knockout mouse embryonic stem cells have been generated to study miRNA function in early mouse development. Here we report an essential requirement of DICER1 for the self-renewal of human embryonic stem cells (hESCs). Utilizing a conditional knockout approach, we found that DICER1 deletion led to increased death receptor-mediated apoptosis and failure of hESC self-renewal. We further devised a targeted miRNA screening strategy and uncovered essential pro-survival roles of members of the mir-302-367 and mir-371-373 clusters that bear the seed sequence AAGUGC. This platform is uniquely suitable for dissecting the roles of individual miRNAs in hESC self-renewal and differentiation, which may help us better understand the early development of human embryos.

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Conditional DICER1 knockouts enable the study of its essential requirement in hESCs

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DICER1 deletion leads to increased extrinsic (receptor-mediated) apoptosis

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miRNAs rescue the DICER1 knockout apoptotic phenotype

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This work provides a platform for interrogating miRNA function in hESCs

OCIAD1 Controls Electron Transport Chain Complex I Activity to Regulate Energy Metabolism in Human Pluripotent Stem Cells

Pluripotent stem cells (PSCs) derive energy predominantly from glycolysis and not the energy-efficient oxidative phosphorylation (OXPHOS). Differentiation is initiated with energy metabolic shift from glycolysis to OXPHOS. We investigated the role of mitochondrial energy metabolism in human PSCs using molecular, biochemical, genetic, and pharmacological approaches. We show that the carcinoma protein OCIAD1 interacts with and regulates mitochondrial complex I activity. Energy metabolic assays on live pluripotent cells showed that OCIAD1-depleted cells have increased OXPHOS and may be poised for differentiation. OCIAD1 maintains human embryonic stem cells, and its depletion by CRISPR/Cas9-mediated knockout leads to rapid and increased differentiation upon induction, whereas OCIAD1 overexpression has the opposite effect. Pharmacological alteration of complex I activity was able to rescue the defects of OCIAD1 modulation. Thus, hPSCs can exist in energy metabolic substates. OCIAD1 provides a target to screen for additional modulators of mitochondrial activity to promote transient multipotent precursor expansion or enhance differentiation.

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OCIAD1 regulates energy metabolism in human pluripotent stem cells

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OCIAD1 interacts with electron transport chain proteins and downregulates OXPHOS

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OCIAD1 regulates complex I activity and early mesodermal progenitor formation

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Pharmacological increase in complex I activity enhances stem cell differentiation

Direct Conversion of Human Pluripotent Stem Cells to Osteoblasts With a Small Molecule

Human pluripotent stem cells (hPSCs), which exhibit unlimited self-renewal ability and can differentiate into all cell types in the human body, are a promising cell source for cell-based therapies and regenerative medicine. Small molecules hold great potential in the derivation of tissue-specific cells from hPSCs owing to their cost-effectiveness and scalability. Here, we describe a protocol for deriving osteoblasts from hPSCs by using a single, natural small molecule: adenosine. This simple and effective experimental protocol allows one to obtain large numbers of osteoblasts or osteoprogenitor cells, with the ability to form functional bone tissues, from hPSCs, including human embryonic stem cells and induced pluripotent stem cells. This protocol could potentially enable studies of tissue regeneration and skeletal diseases. © 2018 by John Wiley & Sons, Inc.

Disruption of cardiogenesis in human embryonic stem cells exposed to trichloroethylene

Trichloroethylene (TCE) is ubiquitous in our living environment, and prenatal exposure to TCE is reported to cause congenital heart disease in humans. Although multiple studies have been performed using animal models, they have limited value in predicting effects on humans due to the unknown species-specific toxicological effects. To test whether exposure to low doses of TCE induces developmental toxicity in humans, we investigated the effect of TCE on human embryonic stem cells (hESCs) and cardiomyocytes (derived from the hESCs). In the current study, hESCs cardiac differentiation was achieved by using differentiation medium consisting of StemPro-34. We examined the effects of TCE on cell viability by cell growth assay and cardiac inhibition by analysis of spontaneously beating cluster. The expression levels of genes associated with cardiac differentiation and Ca²⁺ channel pathways were measured by immunofluorescence and qPCR. The overall data indicated the following: (1) significant cardiac inhibition, which was characterized by decreased beating clusters and beating rates, following treatment with low doses of TCE; (2) significant up-regulation of the Nkx2.5/Hand1 gene in cardiac progenitors and down regulation of the Mhc-7/cTnT gene in cardiac cells; and (3) significant interference with Ca²⁺ channel pathways in cardiomyocytes, which contributes to the adverse effect of TCE on cardiac differentiation during early embryo development. Our results confirmed the involvement of Ca²⁺ turnover network in TCE cardiotoxicity as reported in animal models, while the inhibition effect of TCE on the transition of cardiac progenitors to cardiomyocytes is unique to hESCs, indicating a species-specific effect of TCE on heart development. This study provides new insight into TCE biology in humans, which may help explain the development of congenital heart defects after TCE exposure. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1372-1380, 2016.

Quercetin induced ROS production triggers mitochondrial cell death of human embryonic stem cells

Small molecules to selectively induce cell death of undifferentiated human pluripotent stem cells (hPSCs) have been developed with the aim of lowering the risk of teratoma formation during hPSC-based cell therapy. In this context, we have reported that Quercetin (QC) induces cell death selectively in hESCs via p53 mitochondrial localization. However, the detailed molecular mechanism by which hESCs undergo selective cell death induced by QC remains unclear. Herein, we demonstrate that mitochondrial reactive oxygen species (ROS), strongly induced by QC in human embryonic stem cells (hESCs) but not in human dermal fibroblasts (hDFs), were responsible for QC-mediated hESC's cell death. Increased p53 protein stability and subsequent mitochondrial localization by QC treatment triggered mitochondrial cell death only in hESCs. Of interest, peptidylprolyl isomerase D [PPID, also called cyclophilin D (CypD)], which functions in mitochondrial permeability transition and mitochondrial cell death, was highly expressed in hESCs. Inhibition of CypD by cyclosporine A (CsA) clearly inhibited the QC-mediated loss of mitochondrial membrane potential and mitochondrial cell death. These results suggest that p53 and CypD in the mitochondria are critical for the QC-mediated induction of cell death in hESCs.

The safety of human pluripotent stem cells in clinical treatment

Human pluripotent stem cells (hPSCs) have practically unlimited proliferation potential and a capability to differentiate into any cell type in the human body. Since the first derivation in 1998, they have been an attractive source of cells for regenerative medicine. Numerous ethical, technological, and regulatory complications have been hampering hPSC use in clinical applications. Human embryonic stem cells (ESCs), parthenogenetic human ESCs, human nuclear transfer ESCs, and induced pluripotent stem cells are four types of hPSCs that are different in many clinically relevant features such as propensity to epigenetic abnormalities, generation methods, and ability for development of autologous cell lines. Propensity to genetic mutations and tumorigenicity are common features of all pluripotent cells that complicate hPSC-based therapies. Several recent advances in methods of derivation, culturing, and monitoring of hPSCs have addressed many ethical concerns and technological challenges in development of clinical-grade hPSC lines. Generation of banks of such lines may be useful to minimize immune rejection of hPSC-derived allografts. In this review, we discuss different sources of hPSCs available at the moment, various safety risks associated with them, and possible solutions for successful use of hPSCs in the clinic. We also discuss ongoing clinical trials of hPSC-based treatments.