Ion channels and ionotropic receptors in human embryonic stem cell derived neural progenitors

Roles of TRPM channels in glioma

Gliomas are the most common type of primary brain tumor. Despite advances in treatment, it remains one of the most aggressive and deadly tumor of the central nervous system (CNS). Gliomas are characterized by high malignancy, heterogeneity, invasiveness, and high resistance to radiotherapy and chemotherapy. It is urgent to find potential new molecular targets for glioma. The TRPM channels consist of TRPM1-TPRM8 and play a role in many cellular functions, including proliferation, migration, invasion, angiogenesis, etc. More and more studies have shown that TRPM channels can be used as new therapeutic targets for glioma. In this review, we first introduce the structure, activation patterns, and physiological functions of TRPM channels. Additionally, the pathological mechanism of glioma mediated by TRPM2, 3, 7, and 8 and the related signaling pathways are described. Finally, we discuss the therapeutic potential of targeting TRPM for glioma.

Impaired T3 uptake and action in MCT8-deficient cerebral organoids underlie Allan-Herndon-Dudley syndrome

Patients with mutations in the thyroid hormone (TH) cell transporter monocarboxylate transporter 8 (MCT8) gene develop severe neuropsychomotor retardation known as Allan-Herndon-Dudley syndrome (AHDS). It is assumed that this is caused by a reduction in TH signaling in the developing brain during both intrauterine and postnatal developmental stages, and treatment remains understandably challenging. Given species differences in brain TH transporters and the limitations of studies in mice, we generated cerebral organoids (COs) using human induced pluripotent stem cells (iPSCs) from MCT8-deficient patients. MCT8-deficient COs exhibited (i) altered early neurodevelopment, resulting in smaller neural rosettes with thinner cortical units, (ii) impaired triiodothyronine (T3) transport in developing neural cells, as assessed through deiodinase-3-mediated T3 catabolism, (iii) reduced expression of genes involved in cerebral cortex development, and (iv) reduced T3 inducibility of TH-regulated genes. In contrast, the TH analogs 3,5-diiodothyropropionic acid and 3,3',5-triiodothyroacetic acid triggered normal responses (induction/repression of T3-responsive genes) in MCT8-deficient COs, constituting proof of concept that lack of T3 transport underlies the pathophysiology of AHDS and demonstrating the clinical potential for TH analogs to be used in treating patients with AHDS. MCT8-deficient COs represent a species-specific relevant preclinical model that can be utilized to screen drugs with potential benefits as personalized therapeutics for patients with AHDS.

PLPPR4 haploinsufficiency causes neurodevelopmental disorders by disrupting synaptic plasticity via mTOR signalling

Phospholipid phosphatase related 4 (PLPPR4), a neuron-specific membrane protein located at the postsynaptic density of glutamatergic synapses, is a putative regulator of neuronal plasticity. However, PLPPR4 dysfunction has not been linked to genetic disorders. In this study, we report three unrelated patients with intellectual disability (ID) or autism spectrum disorder (ASD) who harbour a de novo heterozygous copy number loss of PLPPR4 in 1p21.2p21.3, a heterozygous nonsense mutation in PLPPR4 (NM_014839, c.4C > T, p.Gln2*) and a homozygous splice mutation in PLPPR4 (NM_014839: c.408 + 2 T > C), respectively. Bionano single-molecule optical mapping confirmed PLPPR4 deletion contains no additional pathogenic genes. Our results suggested that the loss of function of PLPPR4 is associated with neurodevelopmental disorders. To test the pathogenesis of PLPPR4, peripheral blood mononuclear cells obtained from the patient with heterozygous deletion of PLPPR4 were induced to specific iPSCs (CHWi001-A) and then differentiated into neurons. The neurons carrying the deletion of PLPPR4 displayed the reduced density of dendritic protrusions, shorter neurites and reduced axon length, suggesting the causal role of PLPPR4 in neurodevelopmental disorders. As the mTOR signalling pathway was essential for regulating the axon maturation and function, we found that mTOR signalling was inhibited with a higher level of p-AKT, p-mTOR and p-ERK1/2, decreased p-PI3K in PLPPR4-iPSCs neurons. Additionally, we found silencing PLPPR4 disturbed the mTOR signalling pathway. Our results suggested PLPPR4 modulates neurodevelopment by affecting the plasticity of neurons via the mTOR signalling pathway.

FOXP1 orchestrates neurogenesis in human cortical basal radial glial cells

During cortical development, human basal radial glial cells (bRGCs) are highly capable of sustained self-renewal and neurogenesis. Selective pressures on this cell type may have contributed to the evolution of the human neocortex, leading to an increase in cortical size. bRGCs have enriched expression for Forkhead Box P1 (FOXP1), a transcription factor implicated in neurodevelopmental disorders (NDDs) such as autism spectrum disorder. However, the cell type-specific roles of FOXP1 in bRGCs during cortical development remain unexplored. Here, we examine the requirement for FOXP1 gene expression regulation underlying the production of bRGCs using human brain organoids. We examine a developmental time point when FOXP1 expression is highest in the cortical progenitors, and the bRGCs, in particular, begin to actively produce neurons. With the loss of FOXP1, we show a reduction in the number of bRGCs, as well as reduced proliferation and differentiation of the remaining bRGCs, all of which lead to reduced numbers of excitatory cortical neurons over time. Using single-nuclei RNA sequencing and cell trajectory analysis, we uncover a role for FOXP1 in directing cortical progenitor proliferation and differentiation by regulating key signaling pathways related to neurogenesis and NDDs. Together, these results demonstrate that FOXP1 regulates human-specific features in early cortical development.

P2 receptor-mediated signaling in the physiological and pathological brain: From development to aging and disease

The purinergic pathway mediates both pro-inflammatory and anti-inflammatory responses, whereas the breakdown of adenosine triphosphate (ATP) is in a critical equilibrium. Under physiological conditions, extracellular ATP is maintained at a nanomolar concentration. Whether released into the medium following tissue damage, inflammation, or hypoxia, ATP is considered a clear indicator of cell damage and a marker of pathological conditions. In this overview, we provide an update on the participation of P2 receptor-mediated purinergic signaling in normal and pathological brain development, with special emphasis on neurodevelopmental psychiatric disorders. Since purinergic signaling is ubiquitous, it is not surprising that it plays a prominent role in developmental processes and pathological alterations. The main aim of this review is to conceptualize the time-dependent dynamic changes in the participation of different players in the purinome in shaping the normal and aberrant developmental patterns and diseases of the central nervous system over one's lifespan.

Screening Biophysical Sensors and Neurite Outgrowth Actuators in Human Induced-Pluripotent-Stem-Cell-Derived Neurons

All living cells maintain a charge distribution across their cell membrane (membrane potential) by carefully controlled ion fluxes. These bioelectric signals regulate cell behavior (such as migration, proliferation, differentiation) as well as higher-level tissue and organ patterning. Thus, voltage gradients represent an important parameter for diagnostics as well as a promising target for therapeutic interventions in birth defects, injury, and cancer. However, despite much progress in cell and molecular biology, little is known about bioelectric states in human stem cells. Here, we present simple methods to simultaneously track ion dynamics, membrane voltage, cell morphology, and cell activity (pH and ROS), using fluorescent reporter dyes in living human neurons derived from induced neural stem cells (hiNSC). We developed and tested functional protocols for manipulating ion fluxes, membrane potential, and cell activity, and tracking neural responses to injury and reinnervation in vitro. Finally, using morphology sensor, we tested and quantified the ability of physiological actuators (neurotransmitters and pH) to manipulate nerve repair and reinnervation. These methods are not specific to a particular cell type and should be broadly applicable to the study of bioelectrical controls across a wide range of combinations of models and endpoints.

Gold Nanostrip Array-Mediated Wireless Electrical Stimulation for Accelerating Functional Neuronal Differentiation

Neural stem cell (NSC)-based therapy holds great promise for the treatment of neurodegenerative diseases. Presently, however, it is hindered by poor functional neuronal differentiation. Electrical stimulation is considered one of the most effective ways to promote neuronal differentiation of NSCs. In addition to surgically implanted electrodes, traditional electrical stimulation includes wires connected to the external power supply, and an additional surgery is required to remove the electrodes or wires following stimulation, which may cause secondary injuries and infections. Herein, a novel method is reported for generation of wireless electrical signals on an Au nanostrip array by leveraging the effect of electromagnetic induction under a rotating magnetic field. The intensity of the generated electrical signals depends on the rotation speed and magnetic field strength. The Au nanostrip array-mediated electric stimulation promotes NSC differentiation into mature neurons within 5 days, at the mRNA, protein, and function levels. The rate of differentiation is faster by at least 5 days than that in cells without treatment. The Au nanostrip array-based wireless device also accelerates neuronal differentiation of NSCs in vivo. The novel method to accelerate the neuronal differentiation of NSCs has the advantages of wireless, timely, localized and precise controllability, and noninvasive power supplementation.

Downregulation of neurodevelopmental gene expression in iPSC-derived cerebral organoids upon infection by human cytomegalovirus

Human cytomegalovirus (HCMV) is a betaherpesvirus that can cause severe birth defects including vision and hearing loss, microcephaly, and seizures. Currently, no approved treatment options exist for in utero infections. Here, we aimed to determine the impact of HCMV infection on the transcriptome of developing neurons in an organoid model system. Cell populations isolated from organoids based on a marker for infection and transcriptomes were defined. We uncovered downregulation in key cortical, neurodevelopmental, and functional gene pathways which occurred regardless of the degree of infection. To test the contributions of specific HCMV immediate early proteins known to disrupt neural differentiation, we infected NPCs using a recombinant virus harboring a destabilization domain. Despite suppressing their expression, HCMV-mediated transcriptional downregulation still occurred. Together, our studies have revealed that HCMV infection causes a profound downregulation of neurodevelopmental genes and suggest a role for other viral factors in this process.

Progenitor cells from brown adipose tissue undergo neurogenic differentiation

Multipotent cells derived from white adipose tissue have been shown to differentiate into multiple lineages including neurogenic lineages. However, the high innervation of brown adipose tissue by the sympathetic nervous system suggest it might be a better source of neural precursor cells. To investigate potential differences between white and brown progenitors, we cultured white and brown dedifferentiated fat (wDFAT and brDFAT) cells from mouse and human adipose tissue and compared marker expression of neural precursors, and neuronal and glial cells, using fluorescence-activated cell sorting, bright-field imaging, immunofluorescence, and RNA analysis by qPCR. The results showed that both wDFAT and brDFAT cells had the capacity to generate neuronal and glial-like cells under neurogenic conditions. However, the brDFAT cells exhibited enhanced propensity for neurogenic differentiation. The neurogenic cells were at least in part derived from Adiponectin-expressing cells. TdTomato-expressing cells derived from Adiponectin (Adipoq) Cre ^ERT2 -tdTomato ^flox/flox mice gave rise to individual cells and cell clusters with neurogenic characteristics. Moreover, human brDFAT cells demonstrated a similar ability to undergo neurogenic differentiation after treatment with neurogenic medium, as assessed by immunofluorescence and qPCR. Together, our results support that brDFAT cells have ability to undergo neurogenic differentiation.

Glutamatergic Neurons Differentiated from Embryonic Stem Cells: An Investigation of Differentiation and Associated Diseases

Neurons that have been derived from various types of stem cells have recently undergone significant study due to their potential for use in various aspects of biomedicine. In particular, glutamatergic neurons differentiated from embryonic stem cells (ESCs) potentially have many applications in both basic research and regenerative medicine. This review summarized the literatures published thus far and focused on two areas related to these applications. Firstly, these neurons can be used to investigate neuronal signal transduction during differentiation and this means that the genes/proteins/markers involved in this process can be identified. In this way, the dynamic spatial and temporal changes associated with neuronal morphology can be investigated relatively easily. Such an in vitro system can also be used to study how neurons during neurogenesis integrate into normal tissue. At the same time, the integration, regulation and functions of extracellular matrix secretion, various molecular interactions, various ion channels, the neuronal microenvironment, etc., can be easily traced. Secondly, the disease-related aspects of ESC-derived glutamatergic neurons can also be studied and then applied therapeutically. In the future, greater efforts are needed to explore how ESC-differentiated glutamatergic neurons can be used as a neuronal model for the study of Alzheimer’s disease (AD) mechanistically, to identify possible therapeutic strategies for treating AD, including tissue replacement, and to screen for drugs that can be used to treat AD patients. With all of the modern technology that is available, translational medicine should begin to benefit patients soon.

Anchoring a dynamic in vitro model of human neuronal differentiation to key processes of early brain development in vivo

We characterize temporal pathway dynamics of differentiation in an in vitro neurotoxicity model with the aim of informing design and interpretation of toxicological assays. Human neural progenitor cells (hNPCs) were cultured in differentiation conditions up to 21 days. Genes significantly changed through time were identified and grouped according to temporal dynamics. Quantitative pathway analysis identified gene ontology (GO) terms enriched among significantly changed genes and provided a temporal roadmap of pathway trends in vitro. Gene expression in hNPCs was compared with publicly available gene expression data from developing human brain tissue in vivo. Quantitative pathway analysis of significantly changed genes and targeted analysis of specific pathways of interest identified concordance between in vivo and in vitro expression associated with proliferation, migration, differentiation, synapse formation, and neurotransmission. Our analysis anchors gene expression patterns in vitro to sensitive windows of in vivo development, helping to define appropriate applications of the model.

Expression and Functional Properties of NMDA and GABAA Receptors during Differentiation of Human Induced Pluripotent Stem Cells into Ventral Mesencephalic Neurons

Ionotropic glutamate and GABA receptors regulate the differentiation and determine the functional properties of mature neurons. Both insufficient and excessive activity of these neurotransmission systems are associated with various nervous system diseases. Our knowledge regarding the expression profiles of these receptors and the mechanisms of their regulation during the differentiation of specialized human neuron subtypes is limited. Here the expression profiles of the NMDA and GABA_A receptor subunits were explored during in vitro differentiation of human induced pluripotent stem cells (iPSCs) into ventral mesencephalic neurons. The correlation between the neuronal maturation and the expression dynamics of these genes was investigated, and the functional activity of these receptors was assessed by calcium imaging. The role of NMDA and GABA_A receptors in neurite outgrowth and the development of spontaneous activity was analyzed using the viral transduction of neural progenitors with the reporter genes TagGFP and TagRFP. The data indicate that agonists of the investigated receptors can be employed for optimization of existing protocols for neural differentiation of iPSCs, in particular for acceleration of neuronal maturation.

Purinergic receptors in neurogenic processes

Neurogenesis is a process of generating functional neurons, which occurs during embryonic and adult stages in mammals. While neurogenesis during development phase is characterized by intensive proliferation activity in all regions of the brain to form the architecture and neural function of the nervous system, adult neurogenesis occurs with less intensity in two brain regions and is involved in the maintenance of neurogenic niches, local repair, memory and cognitive functions in the hippocampus. Taking such differences into account, the understanding of molecular mechanisms involved in cell differentiation in developmental stages and maintenance of the nervous system is an important research target. Although embryonic and adult neurogenesis presents several differences, signaling through purinergic receptors participates in this process throughout life. For instance, while embryonic neurogenesis involves P2X7 receptor down-regulation and calcium waves triggered by P2Y1 receptor stimulation, adult neurogenesis may be enhanced by increased activity of A_2A and P2Y1 receptors and impaired by A₁, P2Y13 and P2X7 receptor stimulation.

Propofol Regulates Neural Stem Cell Proliferation and Differentiation via Calmodulin-Dependent Protein Kinase II/AMPK/ATF5 Signaling Axis

BACKGROUND

Propofol can cause degeneration of developing brain cells and subsequent long-term learning or memory impairment. However, at the early stage of embryonic development, the molecular mechanism of propofol-induced inhibition in neural stem cells (NSCs) neurogenesis is still unclear. The aim of this study was to determine the role of propofol in NSCs neurogenesis and, more importantly, to explore the underlying mechanism.

METHODS

First, a single intraperitoneal injection of propofol was performed in pregnant mice, and 6 hours after administration of propofol, the hippocampus RNA and the protein of the embryos' brains was extracted to analyze the expression of neuron-specific markers. Second, the primary NSCs were isolated from the hippocampus of mouse embryonic brain and then treated with propofol for cell viability, immunostaining, and transwell assays; more importantly, we performed RNA sequencing (RNA-seq) and q-reverse transcription polymerase chain reaction assays to identify genes regulated by propofol; the Western blot, small interfering RNA (SiRNA), and luciferase reporter assays were used to study the effects of propofol on calmodulin-dependent protein kinase (CaMk) II/5' adenosine monophosphate-activated protein kinase (AMPK)/activating transcription factor 5 (ATF5) signaling pathway.

RESULTS

Our results indicated that propofol treatment could inhibit the proliferation, migration, and differentiation of NSCs. The results of RNA-seq assays showed that propofol treatment resulted in downregulation of a group of Ca-dependent genes. The following mechanism studies showed that propofol regulates the proliferation, differentiation, and migration of NSCs through the CaMkII/phosphorylation of serine at amino acid position 485 (pS485)/AMPK/ATF5 signaling pathway.

CONCLUSIONS

The results from study demonstrated that propofol inhibits the proliferation, differentiation, and migration of NSCs, and these effects are partially mediated by CaMkII/pS485/AMPK/ATF5 signaling pathway.

Strain-Dependent Consequences of Zika Virus Infection and Differential Impact on Neural Development

Maternal infection with Zika virus (ZIKV) during pregnancy can result in neonatal abnormalities, including neurological dysfunction and microcephaly. Experimental models of congenital Zika syndrome identified neural progenitor cells as a target of viral infection. Neural progenitor cells are responsible for populating the developing central nervous system with neurons and glia. Neural progenitor dysfunction can lead to severe birth defects, namely, lissencephaly, microcephaly, and cognitive deficits. For this study, the consequences of ZIKV infection in human pluripotent stem cell-derived neural progenitor (hNP) cells and neurons were evaluated. ZIKV isolates from Asian and African lineages displayed lineage-specific replication kinetics, cytopathic effects, and impacts on hNP function and neuronal differentiation. The currently circulating ZIKV isolates exhibit a unique profile of virulence, cytopathic effect, and impaired cellular functions that likely contribute to the pathological mechanism of congenital Zika syndrome. The authors found that infection with Asian-lineage ZIKV isolates impaired the proliferation and migration of hNP cells, and neuron maturation. In contrast, the African-lineage infections resulted in abrupt and extensive cell death. This work furthers the understanding of ZIKV-induced brain pathology.

Human-Derived Neurons and Neural Progenitor Cells in High Content Imaging Applications

Due to advances in the fields of stem cell biology and cellular engineering, a variety of commercially available human-derived neurons and neural progenitor cells (NPCs) are now available for use in research applications, including small molecule efficacy or toxicity screening. The use of human-derived neural cells is anticipated to address some of the uncertainties associated with the use of nonhuman culture models or transformed cell lines derived from human tissues. Many of the human-derived neurons and NPCs currently available from commercial sources recapitulate critical process of nervous system development including NPC proliferation, neurite outgrowth, synaptogenesis, and calcium signaling, each of which can be evaluated using high content image analysis (HCA). Human-derived neurons and NPCs are also amenable to culture in multiwell plate formats and thus may be adapted for use in HCA-based screening applications. This article reviews various types of HCA-based assays that have been used in conjunction with human-derived neurons and NPC cultures. This article also highlights instances where lower throughput analysis of neurodevelopmental processes has been performed and which demonstrate a potential for adaptation to higher-throughout imaging methods. Finally, a generic protocol for evaluating neurite outgrowth in human-derived neurons using a combination of immunocytochemistry and HCA is presented. The information provided in this article is intended to serve as a resource for cell model and assay selection for those interested in evaluating neurodevelopmental processes in human-derived cells.

Fingolimod induces neuronal-specific gene expression with potential neuroprotective outcomes in maturing neuronal progenitor cells exposed to HIV

Fingolimod (FTY720), a structural analogue of sphingosine, targets sphingosine-1-phosphate receptor signaling and is currently an immunomodulatory therapy for multiple sclerosis. Fingolimod accesses the central nervous system (CNS) where its active metabolite, fingolimod phosphate (FTY720-P), has pleotropic neuroprotective effects in an inflammatory microenvironment. To investigate potential neuronal-specific mechanisms of fingolimod neuroprotection, we cultured the human neuronal progenitor cell line, hNP1, in differentiation medium supplemented with HIV- or Mock-infected supernatants, with or without FTY720-P. Gene expression was investigated using microarray and functional genomics. FTY720-P treatment increased differentially expressed (DE) neuronal genes by 33% in HIV-exposed and 40% in Mock-exposed cultures. FTY720-P treatment broadened the functional profile of DE genes in HIV-exposed versus Mock-exposed neurons, including not only immune responses but also transcriptional regulation and cell differentiation, among others. FTY720-P treatment downregulated the gene for follistatin, the antagonist of activin signaling, in all culture conditions. FTY720-P treatment differentially affected both glycolysis-related and immune response genes in Mock- or HIV-exposed cultures, significantly upregulating 11 glycolysis-related genes in HIV-exposed neurons. FTY720-P treatment also differentially upregulated genes related to innate immune responses and antigen presentation in Mock-exposed and more so in HIV-exposed neurons. However, in HIV-exposed neurons, FTY720-P depressed the magnitude of differential expression in almost half the genes, suggesting an anti-inflammatory potential. Moreover, in HIV-exposed neurons, FTY720-P reduced expression of the amyloid precursor protein (APP) gene, resulting in reduced expression of the APP protein. This study provides new evidence that fingolimod alters neuronal gene expression in inflammatory, viral-infected microenvironments, with the potential for neuroprotective effects.

Apolipoprotein E4 Suppresses Neuronal-Specific Gene Expression in Maturing Neuronal Progenitor Cells Exposed to HIV

The apolipoprotein ε4 gene allele and the apolipoprotein E4 protein (ApoE4) are important host susceptibility factors linked to neurocognitive disorders associated with HIV infection or Alzheimer’s disease. Our previous studies showed differential effects of the two most common human ApoE genotypes, APOE3/3 and APOE3/4, on gene expression by differentiating human neuroepithelial progenitor cells continuously exposed to HIV. To investigate the effects of ApoE3 versus ApoE4 isoforms specifically on maturing neurons, we adapted a human neuronal progenitor cell line, hNP1, with ApoE genotype APOE3/3. Differentiating hNP1 cells were exposed for 16 days to HIV- or mock-infected supernatants and to added recombinant ApoE isoforms rApoE3 or rApoE4 to modulate the ApoE phenotype of the cells. Gene expression was investigated using microarray and functional genomics analyses. Added rApoE3 differentially affected 36 genes. Added rApoE4 differentially affected 85 genes; 41 of which were differentially expressed only in HIV or mock-supernatant treated cells, and 80% of which were downregulated. Genes differentially downregulated only by rApoE4 represented multiple neuronal functions related to neurogenesis. Approximately five times more genes were differentially enriched by rApoE4 versus rApoE3 in the Gene Ontology (GO) cellular process analysis, with 4 orders of magnitude greater significance. Half of the top 10 GO processes affected by rApoE4 treatment were neurogenesis-related. The largest differences in gene expression between the two isoforms were observed within the HIV-exposed cultures, suggesting that HIV exposure magnifies ApoE4’s suppressive effect on neuronal gene expression. This study provides evidence for neuronal-specific responses to ApoE4 that could affect neurogenesis and neuronal survival.

High content imaging quantification of multiple in vitro human neurogenesis events after neurotoxin exposure

Background

Our objective was to test neural active compounds in a human developmental neurotoxicity (DNT) model that represents neural tube stages of vulnerability. Previously we showed that 14 days in vitro (DIV 14) was sufficient to generate cryopreserved neuronal cells for post thaw neurite recovery assays. However, short exposure and assessment may not detect toxicants that affect an early neurogenesis continuum, from a mitotic human neural progenitor (hNP) cell population through the course of neurite outgrowth in differentiating neurons. Therefore, we continuously exposed differentiating hNP cells from DIV 0 through DIV 14 to known toxicants and endocrine active compounds in order to assess at DIV 14 effects of these compounds in a human DNT maturation model for neurogenesis.

Methods

The Human DNT continuum (DIV 0 to DIV 14) was determined using immunocytochemistry for SOX1+ (proliferating hNP) and HuC/D+ (post mitotic neurons). The cumulative effects of five compounds was observed on neurite outgrowth in (βIII-tubulin+) and (HuC/D+) cells using high content imaging. All data were analyzed using a one-way ANOVA with a significance threshold of p < 0.05.

Results

During maturation in vitro, the neural cultures transitioned from uniform hNP cells (DIV 0) to predominantly mature post mitotic neuronal neurons (HuC/D+, 65%; DIV14) but also maintained a smaller population of hNP cells (SOX1+). Using this DNT maturation model system, Bis-1, testosterone, and β-estradiol inhibited neuronal maturation at micromolar levels but were unaffected by acetaminophen. β-estradiol also disrupted neurite extension at 10 μM. Treating cells in this window with Bisphenol A (BPA) significantly inhibited neurite outgrowth and branching in these continuum cultures but only at the highest concentrations tested (10 μM).

Conclusions

Cumulative effects of neurotoxicant exposure during a maturation continuum altered human neurogenesis at lower exposure levels than observed in acute exposure of static cryopreserved neurite recovery neurons cultures. Unlike prior acute studies, β-estradiol was highly toxic when present throughout the continuum and cytotoxicity was manifested starting early in the continuum via a non-estrogen receptor α (ER α) mechanism. Therefore, the effect of neural developmental neurotoxins can and should be determined during the dynamic process of human neural maturation.

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-016-0107-4) contains supplementary material, which is available to authorized users.

One-Step Seeding of Neural Stem Cells with Vitronectin-Supplemented Medium for High-Throughput Screening Assays

Human neuronal cells differentiated from induced pluripotent cells have emerged as a new model system for the study of disease pathophysiology and evaluation of drug efficacy. Differentiated neuronal cells are more similar in genetics and biological content to human brain cells than other animal disease models. However, culture of neuronal cells in assay plates requires a labor-intensive procedure of plate precoating, hampering its applications in high-throughput screening (HTS). We developed a simplified method with one-step seeding of neural stem cells in assay plates by supplementing the medium with a recombinant human vitronectin (VTN), thus avoiding plate precoating. Robust results were obtained from cell viability, calcium response, and neurite outgrowth assays using this new method. Our data demonstrate that this approach greatly simplifies high-throughput assays using neuronal cells differentiated from human stem cells for translational research.

Regulation of adult neural progenitor cell functions by purinergic signaling

Extracellular purines are signaling molecules in the neurogenic niches of the brain and spinal cord, where they activate cell surface purinoceptors at embryonic neural stem cells (NSCs) and adult neural progenitor cells (NPCs). Although mRNA and protein are expressed at NSCs/NPCs for almost all subtypes of the nucleotide-sensitive P2X/P2Y, and the nucleoside-sensitive adenosine receptors, only a few of those have acquired functional significance. ATP is sequentially degraded by ecto-nucleotidases to ADP, AMP, and adenosine with agonistic properties for distinct receptor-classes. Nucleotides/nucleosides facilitate or inhibit NSC/NPC proliferation, migration and differentiation. The most ubiquitous effect of all agonists (especially of ATP and ADP) appears to be the facilitation of cell proliferation, usually through P2Y1Rs and sometimes through P2X7Rs. However, usually P2X7R activation causes necrosis/apoptosis of NPCs. Differentiation can be initiated by P2Y2R-activation or P2X7R-blockade. A key element in the transduction mechanism of either receptor is the increase of the intracellular free Ca²⁺ concentration, which may arise due to its release from intracellular storage sites (G protein-coupling; P2Y) or due to its passage through the receptor-channel itself from the extracellular space (ATP-gated ion channel; P2X). Further research is needed to clarify how purinergic signaling controls NSC/NPC fate and how the balance between the quiescent and activated states is established with fine and dynamic regulation. GLIA 2017;65:213-230.

Differential epigenetic effects of chlorpyrifos and arsenic in proliferating and differentiating human neural progenitor cells

Understanding the underlying temporal and mechanistic responses to neurotoxicant exposures during sensitive periods of neuronal development are critical for assessing the impact of these exposures on developmental processes. To investigate the importance of timing of neurotoxicant exposure for perturbation of epigenetic regulation, we exposed human neuronal progenitor cells (hNPCs) to chlorpyrifos (CP) and sodium arsenite (As; positive control) during proliferation and differentiation. CP or As treatment effects on hNPCs morphology, cell viability, and changes in protein expression levels of neural differentiation and cell stress markers, and histone H3 modifications were examined. Cell viability, proliferation/differentiation status, and epigenetic results suggest that hNPCs cultures respond to CP and As treatment with different degrees of sensitivity. Histone modifications, as measured by changes in histone H3 phosphorylation, acetylation and methylation, varied for each toxicant and growth condition, suggesting that differentiation status can influence the epigenetic effects of CP and As exposures.

Tracking and Quantification of Magnetically Labeled Stem Cells using Magnetic Resonance Imaging

Stem cell based therapies have critical impacts on treatments and cures of diseases such as neurodegenerative or cardiovascular disease. In vivo tracking of stem cells labeled with magnetic contrast agents is of particular interest and importance as it allows for monitoring of the cells' bio-distribution, viability, and physiological responses. Herein, recent advances are introduced in tracking and quantification of super-paramagnetic iron oxide (SPIO) nanoparticles-labeled cells with magnetic resonance imaging, a noninvasive approach that can longitudinally monitor transplanted cells. This is followed by recent translational research on human stem cells that are dual-labeled with green fluorescence protein (GFP) and SPIO nanoparticles, then transplanted and tracked in a chicken embryo model. Cell labeling efficiency, viability, and cell differentiation are also presented.

Purinergic receptors in embryonic and adult neurogenesis

ATP (adenosine 5'-triphosphate), one of the most ancient neurotransmitters, exerts essential functions in the brain, including neurotransmission and modulation of synaptic activity. Moreover, this nucleotide has been attributed with trophic properties and experimental evidence points to the participation of ATP-activated P2X and P2Y purinergic receptors in embryonic brain development as well as in adult neurogenesis for maintenance of normal brain functions and neuroregeneration upon brain injury. We discuss here the available data on purinergic P2 receptor expression and function during brain development and in the neurogenic zones of the adult brain, as well as the insights based on the use of in vitro stem cell cultures. While several P2 receptor subtypes were shown to be expressed during in vitro and in vivo neurogenesis, specific functions have been proposed for P2Y1, P2Y2 metabotropic as well as P2X2 ionotropic receptors to promote neurogenesis. Further, the P2X7 receptor is suggested to function in the maintenance of pools of neural stem and progenitor cells through induction of proliferation or cell death, depending on the microenvironment. Pathophysiological actions have been proposed for this receptor in worsening damage in brain disease. The P2X7 receptor and possibly additional P2 receptor subtypes have been implicated in pathophysiology of neurological diseases including Parkinson's disease, Alzheimer's disease and epilepsy. New strategies in cell therapy could involve modulation of purinergic signaling, either in the achievement of more effective protocols to obtain viable and homogeneous cell populations or in the process of functional engraftment of transplanted cells into the damaged brain. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

High-content high-throughput assays for characterizing the viability and morphology of human iPSC-derived neuronal cultures

Abstract Development of quantitative high-throughput in vitro assays that enable assessment of viability and morphological changes in neuronal cells is an active area of investigation in drug discovery and environmental chemical safety assessment. High-content imaging is an emerging and efficient tool for generating multidimensional quantitative cellular readouts; in addition, human induced pluripotent stem cell (iPSC)-derived neurons are a promising in vitro model system that emulates both the functionality and behavior of mature neurons, and they are available in quantities sufficient for screening workflows. The goal of this study was to develop high-content imaging and analysis methods to assess multiple phenotypes in human iPSC-derived neuronal cells. Specifically, we optimized cell culture, staining, and imaging protocols in a 384-well assay format and improved laboratory workflow by designing a one-step procedure to reduce assay time and minimize cell disturbance. Phenotypic readouts include quantitative characterization of neurite outgrowth and branching, cell number and viability, as well as measures of adverse effects on mitochondrial integrity and membrane potential. To verify the robustness of the workflow, we tested a series of compounds that are established toxicants. We report concentration-response effects of selected test compounds on human iPSC-derived neuronal cells and illustrate how the proposed methods may be used for high-content high-throughput compound toxicity screening and safety evaluation of drugs and environmental chemicals.

Effects of ATP and NGF on Proliferation and Migration of Neural Precursor Cells

Purinergic receptors belong to the most ancient neurotransmitter system. While their relevance in neurotransmission is well characterized, it has become clear that they have many other cellular functions. During development, they participate in regulation of proliferation and differentiation of stem cells. Here, we used rat embryonic telencephalon neurosphere cultures to detect purinergic P2 receptor subtype expression and possible synergistic actions of these receptors with NGF. Neurospheres proliferate in the presence of EGF and FGF-2; however, upon depletion of these growth factors, they migrate and differentiate into neurons and glial phenotypes. Expression patterns of P2X and P2Y receptors changed along neural differentiation. Gene expression of P2X2-7 and P2Y1,2,4,6,12,14 receptors was confirmed in undifferentiated and neural-differentiated neurospheres, with an up-regulation of P2X2 and P2X6 subtypes, together with a down-regulation of P2X4, P2X7 and P2Y subtypes upon induction to differentiation. BrdU-labeling and subsequent flow cytometry analysis was used to measure cell proliferation, which was increased by chronic exposure to NGF and increasing concentrations of ATP, in line with the expression levels of PCNA. Furthermore, a synergistic effect on proliferation was observed in conditions of co-incubation with ATP and NGF. While ATP and NGF independently promoted neural migration, no inter-relation between these factors was detected for this cellular process. As conclusion, an unknown synergism of ATP and NGF in proliferation is described. Future efforts may elucidate the underlying mechanisms of the interrelationship of ATP and NGF during neurogenesis.

Cellular responses to Sindbis virus infection of neural progenitors derived from human embryonic stem cells

Background

Sindbis virus (SINV) causes age-dependent encephalitis in mice, and therefore serves as a model to study viral encephalitis. SINV is used as a vector for the delivery of genes into selected neural stem cell lines; however, the toxicity and side effects of this vector have rarely been discussed. In this context, we investigated the cellular responses of human embryonic stem cell (hESCs) derived neural progenitors (hNPCs) to SINV infection by assessing susceptibility of the cells to SINV infection, analyzing the effect of infection on cell proliferation and cell death, and examining the impact of SINV infection on hNPCs markers of stemness.

Findings

We found that hNPCs are highly susceptible to SINV infection. Upon infection, the viruses induced apoptosis to hNPCs while not affecting the expression of cell proliferation markers. Lastly, SINV infections result in significant changes in the expression of key regulators of hNPCs’ plasticity and homeostasis.

Conclusion

The robust and versatile signaling, proliferation, and other cell responses of hESCs-derived hNPCs to virus infection demonstrated that it is a good model to study the pathogenesis of viral-induced neurodevelopmental and degenerative diseases. On the other hand, the toxicity of SINV to hNPCs cells cannot be ignored, and therefore extra care should be taken when using SINV as a vector to deliver genes into human stem cell lines.

Label-free characterization of emerging human neuronal networks

The emergent self-organization of a neuronal network in a developing nervous system is the result of a remarkably orchestrated process involving a multitude of chemical, mechanical and electrical signals. Little is known about the dynamic behavior of a developing network (especially in a human model) primarily due to a lack of practical and non-invasive methods to measure and quantify the process. Here we demonstrate that by using a novel optical interferometric technique, we can non-invasively measure several fundamental properties of neural networks from the sub-cellular to the cell population level. We applied this method to quantify network formation in human stem cell derived neurons and show for the first time, correlations between trends in the growth, transport, and spatial organization of such a system. Quantifying the fundamental behavior of such cell lines without compromising their viability may provide an important new tool in future longitudinal studies.

Plasticity of calcium signaling cascades in human embryonic stem cell-derived neural precursors

Human embryonic stem cell-derived neural precursors (hESC NPs) are considered to be a promising tool for cell-based therapy in central nervous system injuries and neurodegenerative diseases. The Ca(2+) ion is an important intracellular messenger essential for the regulation of various cellular functions. We investigated the role and physiology of Ca(2+) signaling to characterize the functional properties of CCTL14 hESC NPs during long-term maintenance in culture (in vitro). We analyzed changes in cytoplasmic Ca(2+) concentration ([Ca(2+)]i) evoked by high K(+), adenosine-5'-triphosphate (ATP), glutamate, γ-aminobutyric acid (GABA), and caffeine in correlation with the expression of various neuronal markers in different passages (P6 through P10) during the course of hESC differentiation. We found that only differentiated NPs from P7 exhibited significant and specific [Ca(2+)]i responses to various stimuli. About 31% of neuronal-like P7 NPs exhibited spontaneous [Ca(2+)]i oscillations. Pharmacological and immunocytochemical assays revealed that P7 NPs express L- and P/Q-type Ca(2+) channels, P2X2, P2X3, P2X7, and P2Y purinoreceptors, glutamate receptors, and ryanodine (RyR1 and RyR3) receptors. The ATP- and glutamate-induced [Ca(2+)]i responses were concentration-dependent. Higher glutamate concentrations (over 100 μM) caused cell death. Responses to ATP were observed in the presence or in the absence of extracellular Ca(2+). These results emphasize the notion that with time in culture, these cells attain a transient period of operative Ca(2+) signaling that is predictive of their ability to act as stem elements.

Inhibition of DNA methyltransferases and histone deacetylases induces astrocytic differentiation of neural progenitors

Understanding how to specify rapid differentiation of human neural progenitor towards enriched non-transformed human astrocyte progenitors will provide a critical cell source to further our understanding of how astrocytes play a pivotal role in neural function and development. Human neural progenitors derived from pluripotent embryonic stem cells and propagated in adherent serum-free cultures provide a fate restricted renewable source for quick production of neural cells; however, such cells are highly refractive to astrocytogenesis and show a strong neurogenic bias, similar to neural progenitors from the early embryonic central nervous system (CNS). We found that several astrocytic genes are hypermethylated in such progenitors potentially preventing generation of astrocytes and leading to the proneuronal fate of these progenitors. However, epigenetic modification by Azacytidine (Aza-C) and Trichostatin A (TSA), with concomitant signaling from BMP2 and LIF in neural progenitor cultures shifts this bias, leading to expression of astrocytic markers as early as 5days of differentiation, with near complete suppression of neuronal differentiation. The resultant cells express major astrocytic markers, are amenable to co-culture with neurons, can be propagated as astrocyte progenitors and are cryopreservable. Although previous reports have generated astrocytes from pluripotent cells, the differentiation required extensive culture or selection based on cell surface antigens. The development of a label free and rapid differentiation process will expedite future derivation of astrocytes from various sources pluripotent cells including, but not limited to, human astrocytes associated with various neurological diseases.

Neurotrophic effects of leukemia inhibitory factor on neural cells derived from human embryonic stem cells

Various growth factor cocktails have been used to proliferate and then differentiate human neural progenitor (NP) cells derived from embryonic stem cells (ESC) for in vitro and in vivo studies. However, the cytokine leukemia inhibitory factor (LIF) has been largely overlooked. Here, we demonstrate that LIF significantly enhanced in vitro survival and promoted differentiation of human ESC-derived NP cells. In NP cells, as well as NP-derived neurons, LIF reduced caspase-mediated apoptosis and reduced both spontaneous and H2O2-induced reactive oxygen species in culture. In vitro, NP cell proliferation and the yield of differentiated neurons were significantly higher in the presence of LIF. In NP cells, LIF enhanced cMyc phosphorylation, commonly associated with self-renewal/proliferation. Also, in differentiating NP cells LIF activated the phosphoinositide 3-kinase and signal transducer and activator of transcription 3 pathways, associated with cell survival and reduced apoptosis. When differentiated in LIF+ media, neurite outgrowth and ERK1/2 phosphorylation were potentiated together with increased expression of gp130, a component of the LIF receptor complex. NP cells, pretreated in vitro with LIF, were effective in reducing infarct volume in a model of focal ischemic stroke but LIF did not lead to significantly improved initial NP cell survival over nontreated NP cells. Our results show that LIF signaling significantly promotes human NP cell proliferation, survival, and differentiation in vitro. Activated LIF signaling should be considered in cell culture expansion systems for future human NP cell-based therapeutic transplant studies.

Promoted neuronal differentiation after activation of alpha4/beta2 nicotinic acetylcholine receptors in undifferentiated neural progenitors

BACKGROUND

Neural progenitor is a generic term used for undifferentiated cell populations of neural stem, neuronal progenitor and glial progenitor cells with abilities for proliferation and differentiation. We have shown functional expression of ionotropic N-methyl-D-aspartate (NMDA) and gamma-aminobutyrate type-A receptors endowed to positively and negatively regulate subsequent neuronal differentiation in undifferentiated neural progenitors, respectively. In this study, we attempted to evaluate the possible functional expression of nicotinic acetylcholine receptor (nAChR) by undifferentiated neural progenitors prepared from neocortex of embryonic rodent brains.

METHODOLOGY/PRINCIPAL FINDINGS

Reverse transcription polymerase chain reaction analysis revealed mRNA expression of particular nAChR subunits in undifferentiated rat and mouse progenitors prepared before and after the culture with epidermal growth factor under floating conditions. Sustained exposure to nicotine significantly inhibited the formation of neurospheres composed of clustered proliferating cells and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction activity at a concentration range of 1 µM to 1 mM without affecting cell survival. In these rodent progenitors previously exposed to nicotine, marked promotion was invariably seen for subsequent differentiation into cells immunoreactive for a neuronal marker protein following the culture of dispersed cells under adherent conditions. Both effects of nicotine were significantly prevented by the heteromeric α4β2 nAChR subtype antagonists dihydro-β-erythroidine and 4-(5-ethoxy-3-pyridinyl)-N-methyl-(3E)-3-buten-1-amine, but not by the homomeric α7 nAChR subtype antagonist methyllycaconitine, in murine progenitors. Sustained exposure to nicotine preferentially increased the expression of Math1 among different basic helix-loop-helix proneural genes examined. In undifferentiated progenitors from embryonic mice defective of NMDA receptor subunit-1, nicotine was still effective in significantly inhibiting the proliferation.

CONCLUSIONS/SIGNIFICANCE

Functional α4β2 nAChR subtype would be constitutively expressed to play a role in the mechanism underlying the determination of proliferation and subsequent differentiation fate into a neuronal lineage in association with preferential promotion of Math1 expression in undifferentiated neural progenitors of developing rodent neocortex independently of NMDA receptor activation.