Directed differentiation of forebrain GABA interneurons from human pluripotent stem cells

An update on stem cell biology and engineering for brain development

Two recent technologies, induced-pluripotent stem cells (iPSCs) and direct somatic reprogramming, have shown enormous potential for cell-based therapies against intractable diseases such as those that affect the central nervous system. Already, methods that generate most major cell types of the human brain exist. Whether the cell types are directly reprogrammed from human somatic cells or differentiated from an iPSC intermediate, the overview presented here demonstrates how these protocols vary greatly in their efficiencies, purity and maturation of the resulting cells. Possible solutions including micro-RNA switch technologies that purify target cell types are also outlined. Further, an update on the transition from 2D to 3D cultures and current organoid (mini-brain) cultures are reviewed to give the stem cell and developmental engineering communities an up-to-date account of the progress and future perspectives for modeling of central nervous system disease and brain development in vitro.

Fused cerebral organoids model interactions between brain regions

Human brain development involves complex interactions between different areas, including long distance neuronal migration or formation of major axonal tracts. 3D cerebral organoids allow the growth of diverse brain regions in vitro, but the random arrangement of regional identities limits the reliable analysis of complex phenotypes. Here, we describe a co-culture method combining various brain regions of choice within one organoid tissue. By fusing organoids specified toward dorsal and ventral forebrain, we generate a dorsal-ventral axis. Using fluorescent reporters, we demonstrate robust directional GABAergic interneuron migration from ventral into dorsal forebrain. We describe methodology for time-lapse imaging of human interneuron migration that is inhibited by the CXCR4 antagonist AMD3100. Our results demonstrate that cerebral organoid fusion cultures can model complex interactions between different brain regions. Combined with reprogramming technology, fusions offer the possibility to analyze complex neurodevelopmental defects using cells from neurological disease patients, and to test potential therapeutic compounds.

Three-dimensional tissues using human pluripotent stem cell spheroids as biofabrication building blocks

A recently emerged approach for tissue engineering is to biofabricate tissues using cellular spheroids as building blocks. Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs), can be cultured to generate large numbers of cells and can presumably be differentiated into all the cell types of the human body in vitro, thus are an ideal cell source for biofabrication. We previously developed a hydrogel-based cell culture system that can economically produce large numbers of hPSC spheroids. With hPSCs and this culture system, there are two potential methods to biofabricate a desired tissue. In Method 1, hPSC spheroids are first utilized to biofabricate an hPSC tissue that is subsequently differentiated into the desired tissue. In Method 2, hPSC spheroids are first converted into tissue spheroids in the hydrogel-based culture system and the tissue spheroids are then utilized to biofabricate the desired tissue. In this paper, we systematically measured the fusion rates of hPSC spheroids without and with differentiation toward cortical and midbrain dopaminergic neurons and found spheroids' fusion rates dropped sharply as differentiation progressed. We found Method 1 was appropriate for biofabricating neural tissues.

Direct comparison of distinct naive pluripotent states in human embryonic stem cells

Until recently, human embryonic stem cells (hESCs) were shown to exist in a state of primed pluripotency, while mouse embryonic stem cells (mESCs) display a naive or primed pluripotent state. Here we show the rapid conversion of in-house-derived primed hESCs on mouse embryonic feeder layer (MEF) to a naive state within 5–6 days in naive conversion media (NCM-MEF), 6–10 days in naive human stem cell media (NHSM-MEF) and 14–20 days using the reverse-toggle protocol (RT-MEF). We further observe enhanced unbiased lineage-specific differentiation potential of naive hESCs converted in NCM-MEF, however, all naive hESCs fail to differentiate towards functional cell types. RNA-seq analysis reveals a divergent role of PI3K/AKT/mTORC signalling, specifically of the mTORC2 subunit, in the different naive hESCs. Overall, we demonstrate a direct evaluation of several naive culture conditions performed in the same laboratory, thereby contributing to an unbiased, more in-depth understanding of different naive hESCs.

Human embryonic stem cells (hESCs) in culture display a state of primed pluripotency, but recent protocols have been developed that enable hESCs to adopt a naive-like pluripotent state. Here the authors perform a side-by-side comparison of methods used to culture naive hESCs and confirm the role of PI3K/AKT/mTORC signalling in facilitating the induction of naive pluripotency.

Formyl peptide receptors promotes neural differentiation in mouse neural stem cells by ROS generation and regulation of PI3K-AKT signaling

This study aimed to determine whether formyl peptide receptors (FPRs) regulated the differentiation of neural stem cells (NSCs). FPRs promote the migration of NSCs both in vitro and in vivo. However, the role of FPRs during differentiation of NSCs is unknown. Analysis by Western blot showed significantly increased expression of FPR1 and FPR2 during differentiation of NSCs. The activation of FPRs promotes NSCs to differentiate into neurons with more primary neurites and branch points and longer neurites per cell. Meanwhile, this activation also inhibits the differentiation of NSC into astrocytes. This bidirectional effect can be inhibited by the FPRs-specific inhibitor. Moreover, it was found that the activation of FPRs increased the generation of reactive oxygen species (ROS) and phosphorylation of AKT in the NSCs, while N-acetylcysteine and LY294002 inhibited the FPRs-stimulated increase in ROS generation and AKT phosphorylation, and blocked the FPRs-stimulated neural differentiation into neurons. Therefore, FPRs-stimulated neural differentiation was mediated via ROS and PI3K-AKT signaling pathways. Collectively, the present findings provided a novel insight into the functional role of FPRs in neurogenesis, with important implications for its potential use as a candidate for treating brain or spinal cord injury.

Modeling neurodevelopmental and psychiatric diseases with human iPSCs

Neurodevelopmental and psychiatric disorders, including autism spectrum disorder and schizophrenia, are complex and heterogeneous disorders that affect a large portion of the world's population. While the causes are still poorly understood, currently available treatments are limited; the development of rational therapeutics based on an understanding of the etiology and pathogenesis of the disease is imperative. The breakthrough technology of deriving induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells of healthy subjects or patients, offers an unprecedented opportunity to recapitulate both normal and pathological development of human tissue, thereby opening up a new avenue for disease modeling and drug development in a more genetically tractable and disease-relevant system. Here, I review the recent progress in the use of human iPSCs for modeling neurodevelopmental and psychiatric disorders and developing novel therapeutic strategies, and discuss challenges in this rapidly moving field. © 2017 Wiley Periodicals, Inc.

An Integrated Miniature Bioprocessing for Personalized Human Induced Pluripotent Stem Cell Expansion and Differentiation into Neural Stem Cells

Human induced pluripotent stem cells (iPSCs) are ideal cell sources for personalized cell therapies since they can be expanded to generate large numbers of cells and differentiated into presumably all the cell types of the human body in vitro. In addition, patient specific iPSC-derived cells induce minimal or no immune response in vivo. However, with current cell culture technologies and bioprocessing, the cost for biomanufacturing clinical-grade patient specific iPSCs and their derivatives are very high and not affordable for majority of patients. In this paper, we explored the use of closed and miniature cell culture device for biomanufacturing patient specific neural stem cells (NSCs) from iPSCs. We demonstrated that, with the assist of a thermoreversible hydrogel scaffold, the bioprocessing including iPSC expansion, iPSC differentiation into NSCs, the subsequent depletion of undifferentiated iPSCs from the NSCs, and concentrating and transporting the purified NSCs to the surgery room, could be integrated and completed within two closed 15 ml conical tubes.

Gene-environment interactions in cortical interneuron development and dysfunction: A review of preclinical studies

Cortical interneurons (cINs) are a diverse group of locally projecting neurons essential to the organization and regulation of neural networks. Though they comprise only ∼20% of neurons in the neocortex, their dynamic modulation of cortical activity is requisite for normal cognition and underlies multiple aspects of learning and memory. While displaying significant morphological, molecular, and electrophysiological variability, cINs collectively function to maintain the excitatory-inhibitory balance in the cortex by dampening hyperexcitability and synchronizing activity of projection neurons, primarily through use of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Disruption of the excitatory-inhibitory balance is a common pathophysiological feature of multiple seizure and neuropsychiatric disorders, including epilepsy, schizophrenia, and autism. While most studies have focused on genetic disruption of cIN development in these conditions, emerging evidence indicates that cIN development is exquisitely sensitive to teratogenic disruption. Here, we review key aspects of cIN development, including specification, migration, and integration into neural circuits. Additionally, we examine the mechanisms by which prenatal exposure to common chemical and environmental agents disrupt these events in preclinical models. Understanding how genetic and environmental factors interact to disrupt cIN development and function has tremendous potential to advance prevention and treatment of prevalent seizure and neuropsychiatric illnesses.

Targeting the hedgehog signaling pathway for cardiac repair and regeneration

The hedgehog (Hh) signaling pathway is involved in the angiogenesis and development of the coronary vasculature in the embryonic heart. Recently, the Hh signal pathway has emerged as an important regulator that can increase cardiomyocyte proliferation, inhibit cardiomyocyte death and apoptosis, recruit endothelial progenitor cell (EPCs) into sites of myocardial ischemia, and direct stem cells to differentiate into cardiac muscle lineage. Experimental studies have tried to target the Hh signaling pathway for cardiac repair and regeneration. The purpose of this review is to discuss the role of the Hh signal pathway in cardiac repair and regeneration as well as the current strategies targeting the Hh signaling pathway and its potential in heart diseases.

Rapamycin regulates autophagy and cell adhesion in induced pluripotent stem cells

BACKGROUND

Cellular reprogramming is a stressful process, which requires cells to engulf somatic features and produce and maintain stemness machineries. Autophagy is a process to degrade unwanted proteins and is required for the derivation of induced pluripotent stem cells (iPSCs). However, the role of autophagy during iPSC maintenance remains undefined.

METHODS

Human iPSCs were investigated by microscopy, immunofluorescence, and immunoblotting to detect autophagy machinery. Cells were treated with rapamycin to activate autophagy and with bafilomycin to block autophagy during iPSC maintenance. High concentrations of rapamycin treatment unexpectedly resulted in spontaneous formation of round floating spheres of uniform size, which were analyzed for differentiation into three germ layers. Mass spectrometry was deployed to reveal altered protein expression and pathways associated with rapamycin treatment.

RESULTS

We demonstrate that human iPSCs express high basal levels of autophagy, including key components of APMKα, ULK1/2, BECLIN-1, ATG13, ATG101, ATG12, ATG3, ATG5, and LC3B. Block of autophagy by bafilomycin induces iPSC death and rapamycin attenuates the bafilomycin effect. Rapamycin treatment upregulates autophagy in iPSCs in a dose/time-dependent manner. High concentration of rapamycin reduces NANOG expression and induces spontaneous formation of round and uniformly sized embryoid bodies (EBs) with accelerated differentiation into three germ layers. Mass spectrometry analysis identifies actin cytoskeleton and adherens junctions as the major targets of rapamycin in mediating iPSC detachment and differentiation.

CONCLUSIONS

High levels of basal autophagy activity are present during iPSC derivation and maintenance. Rapamycin alters expression of actin cytoskeleton and adherens junctions, induces uniform EB formation, and accelerates differentiation. IPSCs are sensitive to enzyme dissociation and require a lengthy differentiation time. The shape and size of EBs also play a role in the heterogeneity of end cell products. This research therefore highlights the potential of rapamycin in producing uniform EBs and in shortening iPSC differentiation duration.

Stem cell-derived astrocytes: are they physiologically credible?

Astrocytes are now increasingly acknowledged as having fundamental and sophisticated roles in brain function and dysfunction. Unravelling the complex mechanisms that underlie human brain astrocyte-neuron interactions is therefore an essential step on the way to understanding how the brain operates. Insights into astrocyte function to date have almost exclusively been derived from studies conducted using murine or rodent models. Whilst these have led to significant discoveries, preliminary work with human astrocytes has revealed a hitherto unknown range of astrocyte types with potentially greater functional complexity and increased neuronal interaction with respect to animal astrocytes. It is becoming apparent, therefore, that many important functions of astrocytes will only be discovered by direct physiological interrogation of human astrocytes. Recent advancements in the field of stem cell biology have provided a source of human-based models. These will provide a platform to facilitate our understanding of normal astrocyte functions as well as their role in CNS pathology. A number of recent studies have demonstrated that stem cell-derived astrocytes exhibit a range of properties, suggesting that they may be functionally equivalent to their in vivo counterparts. Further validation against in vivo models will ultimately confirm the future utility of these stem cell-based approaches in fulfilling the need for human-based cellular models for basic and clinical research. In this review we discuss the roles of astrocytes in the brain and highlight the extent to which human stem cell-derived astrocytes have demonstrated functional activities that are equivalent to those observed in vivo.

Using Induced Pluripotent Stem Cells to Investigate Complex Genetic Psychiatric Disorders

PURPOSE OF REVIEW

Induced pluripotent stem cells (iPSCs) can be generated from human patient tissue samples, differentiated into any somatic cell type, and studied under controlled culture conditions. We review how iPSCs are used to investigate genetic factors and biological mechanisms underlying psychiatric disorders, and considerations for synthesizing data across studies.

RECENT FINDINGS

Results from patient specific-iPSC studies often reveal cellular phenotypes consistent with postmortem and brain imaging studies. Unpredicted findings illustrate the power of iPSCs as a discovery tool, but may also be attributable to limitations in modeling dynamic neural networks or difficulty in identifying the most affected neural subtype or developmental stage.

SUMMARY

Technological advances in differentiation protocols and organoid generation will enhance our ability to model the salient pathology underlying psychiatric disorders using iPSCs. The field will also benefit from context-driven interpretations of iPSC studies that recognize all potential sources of variability, including differences in patient symptomatology, genetic risk factors and affected cellular subtype.

Time-Course Gene Expression Profiling Reveals a Novel Role of Non-Canonical WNT Signaling During Neural Induction

The process of neuroepithelial differentiation from human pluripotent stem cells (PSCs) resembles in vivo neuroectoderm induction in the temporal course, morphogenesis, and biochemical changes. This in vitro model is therefore well-suited to reveal previously unknown molecular mechanisms underlying neural induction in humans. By transcriptome analysis of cells along PSC differentiation to early neuroepithelia at day 6 and definitive neuroepithelia at day 10, we found downregulation of genes that are associated with TGF-β and canonical WNT/β-CATENIN signaling, confirming the roles of classical signaling in human neural induction. Interestingly, WNT/Ca²⁺ signaling was upregulated. Pharmacological inhibition of the downstream effector of WNT/Ca²⁺ pathway, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), led to an inhibition of the neural marker PAX6 and upregulation of epidermal marker K18, suggesting that Ca²⁺/CaMKII signaling promotes neural induction by preventing the alternative epidermal fate. In addition, our analyses revealed known and novel expression patterns of genes that are involved in DNA methylation, histone modification, as well as epithelial-mesenchymal transition, highlighting potential roles of those genes and signaling pathways during neural differentiation.

Neural Stem Cell or Human Induced Pluripotent Stem Cell-Derived GABA-ergic Progenitor Cell Grafting in an Animal Model of Chronic Temporal Lobe Epilepsy

Grafting of neural stem cells (NSCs) or GABA-ergic progenitor cells (GPCs) into the hippocampus could offer an alternative therapy to hippocampal resection in patients with drug-resistant chronic epilepsy, which afflicts >30% of temporal lobe epilepsy (TLE) cases. Multipotent, self-renewing NSCs could be expanded from multiple regions of the developing and adult brain, human embryonic stem cells (hESCs), and human induced pluripotent stem cells (hiPSCs). On the other hand, GPCs could be generated from the medial and lateral ganglionic eminences of the embryonic brain and from hESCs and hiPSCs. To provide comprehensive methodologies involved in testing the efficacy of transplantation of NSCs and GPCs in a rat model of chronic TLE, NSCs derived from the rat medial ganglionic eminence (MGE) and MGE-like GPCs derived from hiPSCs are taken as examples in this unit. The topics comprise description of the required materials, reagents and equipment, methods for obtaining rat MGE-NSCs and hiPSC-derived MGE-like GPCs in culture, generation of chronically epileptic rats, intrahippocampal grafting procedure, post-grafting evaluation of the effects of grafts on spontaneous recurrent seizures and cognitive and mood impairments, analyses of the yield and the fate of graft-derived cells, and the effects of grafts on the host hippocampus. © 2016 by John Wiley & Sons, Inc.

Direct Induction and Functional Maturation of Forebrain GABAergic Neurons from Human Pluripotent Stem Cells

Gamma-aminobutyric acid (GABA)-releasing interneurons play an important modulatory role in the cortex and have been implicated in multiple neurological disorders. Patient-derived interneurons could provide a foundation for studying the pathogenesis of these diseases as well as for identifying potential therapeutic targets. Here, we identified a set of genetic factors that could robustly induce human pluripotent stem cells (hPSCs) into GABAergic neurons (iGNs) with high efficiency. We demonstrated that the human iGNs express neurochemical markers and exhibit mature electrophysiological properties within 6-8 weeks. Furthermore, in vitro, iGNs could form functional synapses with other iGNs or with human-induced glutamatergic neurons (iENs). Upon transplantation into immunodeficient mice, human iGNs underwent synaptic maturation and integration into host neural circuits. Taken together, our rapid and highly efficient single-step protocol to generate iGNs may be useful to both mechanistic and translational studies of human interneurons.

Single-Cell Detection of Secreted Aβ and sAPPα from Human IPSC-Derived Neurons and Astrocytes

Secreted factors play a central role in normal and pathological processes in every tissue in the body. The brain is composed of a highly complex milieu of different cell types and few methods exist that can identify which individual cells in a complex mixture are secreting specific analytes. By identifying which cells are responsible, we can better understand neural physiology and pathophysiology, more readily identify the underlying pathways responsible for analyte production, and ultimately use this information to guide the development of novel therapeutic strategies that target the cell types of relevance. We present here a method for detecting analytes secreted from single human induced pluripotent stem cell (iPSC)-derived neural cells and have applied the method to measure amyloid β (Aβ) and soluble amyloid precursor protein-alpha (sAPPα), analytes central to Alzheimer's disease pathogenesis. Through these studies, we have uncovered the dynamic range of secretion profiles of these analytes from single iPSC-derived neuronal and glial cells and have molecularly characterized subpopulations of these cells through immunostaining and gene expression analyses. In examining Aβ and sAPPα secretion from single cells, we were able to identify previously unappreciated complexities in the biology of APP cleavage that could not otherwise have been found by studying averaged responses over pools of cells. This technique can be readily adapted to the detection of other analytes secreted by neural cells, which would have the potential to open new perspectives into human CNS development and dysfunction.

SIGNIFICANCE STATEMENT

We have established a technology that, for the first time, detects secreted analytes from single human neurons and astrocytes. We examine secretion of the Alzheimer's disease-relevant factors amyloid β (Aβ) and soluble amyloid precursor protein-alpha (sAPPα) and present novel findings that could not have been observed without a single-cell analytical platform. First, we identify a previously unappreciated subpopulation that secretes high levels of Aβ in the absence of detectable sAPPα. Further, we show that multiple cell types secrete high levels of Aβ and sAPPα, but cells expressing GABAergic neuronal markers are overrepresented. Finally, we show that astrocytes are competent to secrete high levels of Aβ and therefore may be a significant contributor to Aβ accumulation in the brain.

Modeling Alzheimer's disease with human induced pluripotent stem (iPS) cells

In the last decade, induced pluripotent stem (iPS) cells have revolutionized the utility of human in vitro models of neurological disease. The iPS-derived and differentiated cells allow researchers to study the impact of a distinct cell type in health and disease as well as performing therapeutic drug screens on a human genetic background. In particular, clinical trials for Alzheimer's disease (AD) have been failing. Two of the potential reasons are first, the species gap involved in proceeding from initial discoveries in rodent models to human studies, and second, an unsatisfying patient stratification, meaning subgrouping patients based on the disease severity due to the lack of phenotypic and genetic markers. iPS cells overcome this obstacles and will improve our understanding of disease subtypes in AD. They allow researchers conducting in depth characterization of neural cells from both familial and sporadic AD patients as well as preclinical screens on human cells. In this review, we briefly outline the status quo of iPS cell research in neurological diseases along with the general advantages and pitfalls of these models. We summarize how genome-editing techniques such as CRISPR/Cas9 will allow researchers to reduce the problem of genomic variability inherent to human studies, followed by recent iPS cell studies relevant to AD. We then focus on current techniques for the differentiation of iPS cells into neural cell types that are relevant to AD research. Finally, we discuss how the generation of three-dimensional cell culture systems will be important for understanding AD phenotypes in a complex cellular milieu, and how both two- and three-dimensional iPS cell models can provide platforms for drug discovery and translational studies into the treatment of AD.

Formylpeptide Receptors Promote the Migration and Differentiation of Rat Neural Stem Cells

Neural stem cells (NSCs) bear characteristics for proliferation, migration and differentiation into three main neural cell type(s): neurons, astrocytes and/or oligodendrocytes. Formylpeptide receptors (Fprs), belonging to the family of G protein-coupled chemoattractant receptors, have been detected on neurons in the central nervous system (CNS). Here, we report that Fpr1 and Fpr2 are expressed on NSCs as detected with immunohistochemistry, RT-PCR and WB assays. In addition, Fpr1 and Fpr2 promoted NSC migration through F-actin polymerization and skewed NSC differentiation to neurons. Our study demonstrates a unique role of Fpr1 and Fpr2 in NSCs and opens a novel window for cell replacement therapies for brain and spinal cord injury.

Using Patient-Derived Induced Pluripotent Stem Cells to Model and Treat Epilepsies

Human induced pluripotent stem cells (iPSCs) are transforming the fields of disease modeling and precision therapy. For the treatment of neurological disorders, iPSCs introduce the possibility for targeted cell-based therapies by deriving patient-specific neural tissue in vitro that may ultimately be used for transplantation. We review iPSC technologies and their applications that have already advanced our understanding of neurological disorders, focusing on the epilepsies. We also discuss the application of powerful new tools such as genome editing and multi-well, multi-electrode array recording platforms to iPSC disease modeling and therapy development for the epilepsies. Despite some limitations, the field of iPSCs is evolving rapidly and is quickly becoming vital for understanding mechanisms of genetic epilepsies and for future patient-specific therapeutic applications.

Estrogen Receptor-α in the Medial Amygdala Prevents Stress-Induced Elevations in Blood Pressure in Females

Psychological stress contributes to the development of hypertension in humans. The ovarian hormone, estrogen, has been shown to prevent stress-induced pressor responses in females by unknown mechanisms. Here, we showed that the antihypertensive effects of estrogen during stress were blunted in female mice lacking estrogen receptor-α in the brain medial amygdala. Deletion of estrogen receptor-α in medial amygdala neurons also resulted in increased excitability of these neurons, associated with elevated ionotropic glutamate receptor expression. We further demonstrated that selective activation of medial amygdala neurons mimicked effects of stress to increase blood pressure in mice. Together, our results support a model where estrogen acts on estrogen receptor-α expressed by medial amygdala neurons to prevent stress-induced activation of these neurons, and therefore prevents pressor responses to stress.

Engineering human cells and tissues through pluripotent stem cells

The utility of human pluripotent stem cells (hPSCs) depends on their ability to produce functional cells and tissues of the body. Two strategies have been developed: directed differentiation of enriched populations of cells that match a regional and functional profile and spontaneous generation of three-dimensional organoids that resemble tissues in the body. Genomic editing of hPSCs and their differentiated cells broadens the use of the hPSC paradigm in studying human cellular function and disease as well as developing therapeutics.

Visualizing estrogen receptor-α-expressing neurons using a new ERα-ZsGreen reporter mouse line

BACKGROUND

A variety of biological functions of estrogens, including regulation of energy metabolism, are mediated by neurons expressing estrogen receptor-α (ERα) in the brain. However, complex intracellular processes in these ERα-expressing neurons are difficult to unravel, due to the lack of strategy to visualize ERα-expressing neurons, especially in unfixed brain tissues.

RESULTS AND CONCLUSIONS

Here we generated a novel ERα-ZsGreen reporter mouse line in which expression of a green fluorescent reporter protein, ZsGreen, is driven by a 241kb ERα gene promoter. We validated that ZsGreen is highly colocalized with endogenous ERα in the brain. Native ZsGreen signals were visualized in unfixed brain tissue, and were used to assist single cell collection and electrophysiological recordings. Finally, we demonstrated that this ERα-ZsGreen mouse allele can be used in combination with other genetic reporter alleles to allow experiments in highly selective neural populations.

Directed differentiation of basal forebrain cholinergic neurons from human pluripotent stem cells

BACKGROUND

Basal forebrain cholinergic neurons (BFCNs) play critical roles in learning, memory and cognition. Dysfunction or degeneration of BFCNs may connect to neuropathology, such as Alzheimer's disease, Down's syndrome and dementia. Generation of functional BFCNs may contribute to the studies of cell-based therapy and pathogenesis that is related to learning and memory deficits.

NEW METHOD

Here we describe a detail method for robust generation of BFCNs from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). In this method, BFCN progenitors are patterned from hESC or hiPSC-derived primitive neuroepithelial cells, with the treatment of sonic hedgehog (SHH) or combination with its agonist Purmorphamine, and by co-culturing with human astrocytes.

RESULTS

At day 20, ∼90% hPSC-derived progenitors expressed NKX2.1, which is a transcriptional marker for MGE. Moreover, around 40% of NKX2.1+ cells co-expressed OLIG2 and ∼15% of NKX2.1+ cells co-expressed ISLET1, which are ventral markers. At day 35, ∼40% neurons robustly express ChAT, most of which are co-labeled with NKX2.1, ISLET1 and FOXG1, indicating the basal forebrain-like identity. At day 45, these neurons express mature neuronal markers MAP2, Synapsin, and VAChT.

COMPARISON WITH EXISTING METHOD(S)

In this method, undefined conditions including genetic modification or cell-sorting are avoided. As a choice, feeder free conditions are used to avoid ingredients of animal origin. Moreover, Purmorphamine can be substituted for SHH to induce ventral progenitors effectively and economically.

CONCLUSION

We provide an efficient method to generate BFCNs from multiple hPSC lines, which offers the potential application for disease modeling and pharmacological studies.

Concise Review: Progress and Challenges in Using Human Stem Cells for Biological and Therapeutics Discovery: Neuropsychiatric Disorders

In facing the daunting challenge of using human embryonic and induced pluripotent stem cells to study complex neural circuit disorders such as schizophrenia, mood and anxiety disorders, and autism spectrum disorders, a 2012 National Institute of Mental Health workshop produced a set of recommendations to advance basic research and engage industry in cell-based studies of neuropsychiatric disorders. This review describes progress in meeting these recommendations, including the development of novel tools, strides in recapitulating relevant cell and tissue types, insights into the genetic basis of these disorders that permit integration of risk-associated gene regulatory networks with cell/circuit phenotypes, and promising findings of patient-control differences using cell-based assays. However, numerous challenges are still being addressed, requiring further technological development, approaches to resolve disease heterogeneity, and collaborative structures for investigators of different disciplines. Additionally, since data obtained so far is on small sample sizes, replication in larger sample sets is needed. A number of individual success stories point to a path forward in developing assays to translate discovery science to therapeutics development.

Human dermal fibroblasts in psychiatry research

In order to decipher the disease etiology, progression and treatment of multifactorial human brain diseases we utilize a host of different experimental models. Recently, patient-derived human dermal fibroblast (HDF) cultures have re-emerged as promising in vitro functional system for examining various cellular, molecular, metabolic and (patho)physiological states and traits of psychiatric disorders. HDF studies serve as a powerful complement to postmortem and animal studies, and often appear to be informative about the altered homeostasis in neural tissue. Studies of HDFs from patients with schizophrenia (SZ), depression, bipolar disorder (BD), autism, attention deficit and hyperactivity disorder and other psychiatric disorders have significantly advanced our understanding of these devastating diseases. These reports unequivocally prove that signal transduction, redox homeostasis, circadian rhythms and gene*environment (G*E) interactions are all amenable for assessment by the HDF model. Furthermore, the reported findings suggest that this underutilized patient biomaterial, combined with modern molecular biology techniques, may have both diagnostic and prognostic value, including prediction of response to therapeutic agents.

Model systems for studying cellular mechanisms of SCN1A-related epilepsy

Mutations in SCN1A, the gene encoding voltage-gated sodium channel NaV1.1, cause a spectrum of epilepsy disorders that range from genetic epilepsy with febrile seizures plus to catastrophic disorders such as Dravet syndrome. To date, more than 1,250 mutations in SCN1A have been linked to epilepsy. Distinct effects of individual SCN1A mutations on neuronal function are likely to contribute to variation in disease severity and response to treatment in patients. Several model systems have been used to explore seizure genesis in SCN1A epilepsies. In this article we review what has been learned about cellular mechanisms and potential new therapies from these model systems, with a particular emphasis on the novel model system of knock in Drosophila and a look toward the future with expanded use of patient-specific induced pluripotent stem cell-derived neurons.

Modeling psychiatric disorders with patient-derived iPSCs

Psychiatric disorders are heterogeneous disorders characterized by complex genetics, variable symptomatology, and anatomically distributed pathology, all of which present challenges for effective treatment. Current treatments are often blunt tools used to ameliorate the most severe symptoms, often at the risk of disrupting functional neural systems, thus there is a pressing need to develop rational therapeutics. Induced pluripotent stem cells (iPSCs) reprogrammed from patient somatic cells offer an unprecedented opportunity to recapitulate both normal and pathologic human tissue and organ development, and provides new approaches for understanding disease mechanisms and for drug discovery with higher predictability of their effects in humans. Here we review recent progress and challenges in using human iPSCs for modeling neuropsychiatric disorders and developing novel therapeutic strategies.

Current methods and challenges in the comprehensive characterization of human pluripotent stem cells

Pluripotent stem cells (PSCs) are powerful tools for basic scientific research and promising agents for drug discovery and regenerative medicine. Technological advances have made it increasingly easy to generate PSCs but the various lines generated may differ in their characteristics based on their origin, derivation, number of passages, and culture conditions. In order to confirm the pluripotency, quality, identity, and safety of pluripotent cell lines as they are derived and maintained, it is critical to perform a panel of characterization assays. Functional pluripotency is determined using tests that rely on the expression of specific markers in the undifferentiated and differentiated states; tests for quality, identity and safety are less specialized. This article provides a comprehensive review of current practices in PSC characterization and explores challenges in the field, from the selection of markers to the development of simple and scalable methods. It also delves into emerging trends like the adoption of alternative assays that could be used to supplement or replace traditional methods, specifically the use of in silico assays for determining pluripotency.

Is this a brain which I see before me? Modeling human neural development with pluripotent stem cells

The human brain is arguably the most complex structure among living organisms. However, the specific mechanisms leading to this complexity remain incompletely understood, primarily because of the poor experimental accessibility of the human embryonic brain. Over recent years, technologies based on pluripotent stem cells (PSCs) have been developed to generate neural cells of various types. While the translational potential of PSC technologies for disease modeling and/or cell replacement therapies is usually put forward as a rationale for their utility, they are also opening novel windows for direct observation and experimentation of the basic mechanisms of human brain development. PSC-based studies have revealed that a number of cardinal features of neural ontogenesis are remarkably conserved in human models, which can be studied in a reductionist fashion. They have also revealed species-specific features, which constitute attractive lines of investigation to elucidate the mechanisms underlying the development of the human brain, and its link with evolution.

Gene Expression Studies on Human Trisomy 21 iPSCs and Neurons: Towards Mechanisms Underlying Down's Syndrome and Early Alzheimer's Disease-Like Pathologies

The cause of Alzheimer disease (AD) is not well understood and there is no cure. Our ability to understand the early events in the course of AD is severely limited by the difficulty of identifying individuals who are in the early, preclinical stage of this disease. Most individuals with Down's syndrome (DS, trisomy 21) will predictably develop AD and that they will do so at a young age makes them an ideal population in which to study the early stages of AD. Several recent studies have exploited induced pluripotent stem cells (iPSCs) generated from individuals with familial AD, spontaneous AD and DS to attempt to identify early events and discover novel biomarkers of disease progression in AD. Here, we summarize the progress and limitations of these iPSC studies with a focus on iPSC-derived neurons. Further, we outline the methodology and results for comparing gene expression between AD and DS iPSC-derived neurons. We highlight differences and commonalities in these data that may implicate underlying genes and pathways that are causative for AD.

Apolipoprotein A-IV Inhibits AgRP/NPY Neurons and Activates Pro-Opiomelanocortin Neurons in the Arcuate Nucleus

BACKGROUND/AIMS

Apolipoprotein A-IV (apoA-IV) in the brain potently suppresses food intake. However, the mechanisms underlying its anorexigenic effects remain to be identified.

METHODS

We first examined the effects of apoA-IV on cellular activities in hypothalamic neurons that co-express agouti-related peptide (AgRP) and neuropeptide Y (NPY) and in neurons that express pro-opiomelanocortin (POMC). We then compared anorexigenic effects of apoA-IV in wild-type mice and in mutant mice lacking melanocortin 4 receptors (MC4Rs; the receptors of AgRP and the POMC gene product). Finally, we examined expression of apoA-IV in mouse hypothalamus and quantified its protein levels at fed versus fasted states.

RESULTS

We demonstrate that apoA-IV inhibited the firing rate of AgRP/NPY neurons. The decreased firing was associated with hyperpolarized membrane potential and decreased miniature excitatory postsynaptic current. We further used c-fos immunoreactivity to show that intracerebroventricular (i.c.v.) injections of apoA-IV abolished the fasting-induced activation of AgRP/NPY neurons in mice. Further, we found that apoA-IV depolarized POMC neurons and increased their firing rate. In addition, genetic deletion of MC4Rs blocked anorexigenic effects of i.c.v. apoA-IV. Finally, we detected endogenous apoA-IV in multiple neural populations in the mouse hypothalamus, including AgRP/NPY neurons, and food deprivation suppressed hypothalamic apoA-IV protein levels.

CONCLUSION

Our findings support a model where central apoA-IV inhibits AgRP/NPY neurons and activates POMC neurons to activate MC4Rs, which in turn suppresses food intake.

GABA-ergic cell therapy for epilepsy: Advances, limitations and challenges

Diminution in the number of gamma-amino butyric acid positive (GABA-ergic) interneurons and their axon terminals, and/or alterations in functional inhibition are conspicuous brain alterations believed to contribute to the persistence of seizures in acquired epilepsies such as temporal lobe epilepsy. This has steered a perception that replacement of lost GABA-ergic interneurons would improve inhibitory synaptic neurotransmission in the epileptic brain region and thereby reduce the occurrence of seizures. Indeed, studies using animal prototypes have reported that grafting of GABA-ergic progenitors derived from multiple sources into epileptic regions can reduce seizures. This review deliberates recent advances, limitations and challenges concerning the development of GABA-ergic cell therapy for epilepsy. The efficacy and limitations of grafts of primary GABA-ergic progenitors from the embryonic lateral ganglionic eminence and medial ganglionic eminence (MGE), neural stem/progenitor cells expanded from MGE, and MGE-like progenitors generated from human pluripotent stem cells for alleviating seizures and co-morbidities of epilepsy are conferred. Additional studies required for possible clinical application of GABA-ergic cell therapy for epilepsy are also summarized.

A Dishful of a Troubled Mind: Induced Pluripotent Stem Cells in Psychiatric Research

Neuronal differentiation of induced pluripotent stem cells and direct reprogramming represent powerful methods for modeling the development of neurons in vitro. Moreover, this approach is also a means for comparing various cellular phenotypes between cell lines originating from healthy and diseased individuals or isogenic cell lines engineered to differ at only one or a few genomic loci. Despite methodological constraints and initial skepticism regarding this approach, the field is expanding at a fast pace. The improvements include the development of new differentiation protocols resulting in selected neuronal populations (e.g., dopaminergic, GABAergic, hippocampal, and cortical), the widespread use of genome editing methods, and single-cell techniques. A major challenge awaiting in vitro disease modeling is the integration of clinical data in the models, by selection of well characterized clinical populations. Ideally, these models will also demonstrate how different diagnostic categories share overlapping molecular disease mechanisms, but also have unique characteristics. In this review we evaluate studies with regard to the described developments, to demonstrate how differentiation of induced pluripotent stem cells and direct reprogramming can contribute to psychiatry.

Efficient generation of region-specific forebrain neurons from human pluripotent stem cells under highly defined condition

Human pluripotent stem cells (hPSCs) have potential to differentiate to unlimited number of neural cells, which provide powerful tools for neural regeneration. To date, most reported protocols were established with an animal feeder system. However, cells derived on this system are inappropriate for the translation to clinical applications because of the introduction of xenogenetic factors. In this study, we provided an optimized paradigm to generate region-specific forebrain neurons from hPSCs under a defined system. We assessed five conditions and found that a vitronectin-coated substrate was the most efficient method to differentiate hPSCs to neurons and astrocytes. More importantly, by applying different doses of purmorphamine, a small-molecule agonist of sonic hedgehog signaling, hPSCs were differentiated to different region-specific forebrain neuron subtypes, including glutamatergic neurons, striatal medium spiny neurons, and GABA interneurons. Our study offers a highly defined system without exogenetic factors to produce human neurons and astrocytes for translational medical studies, including cell therapy and stem cell-based drug discovery.

Urine-derived induced pluripotent stem cells as a modeling tool for paroxysmal kinesigenic dyskinesia

Paroxysmal kinesigenic dyskinesia (PKD) is a monogenic movement disorder with autosomal dominant inheritance. We previously identified the proline-rich transmembrane protein 2 (PRRT2) as a causative gene of PKD. However, the pathogenesis of PKD remains largely unknown so far. In addition, applicable modeling tools to investigate the underlying mechanisms of PKD are still lacking. The combination of disease-specific human induced pluripotent stem cells (iPSCs) and directed cell differentiation offers an ideal platform for disease modeling. In this study, we generated two iPSC lines from the renal epithelial cells of one PKD patient with the hotspot c.649dupC mutation (PKD-iPSCs). These cell lines were positive for alkaline phosphatase Nanog, Tra-1-80, Tra-1-60, SSEA-3 and SSEA-4. Teratomas with three blastoderms including ectoderm, mesoderm, and endoderm were obtained two months after injection of PKD-iPSCs into NOD/SCID mice. The expression of PRRT2 mRNA was decreased in PKD-iPSCs compared with that of the control iPSCs. Furthermore, PKD-iPSCs possessed the differentiation potential of functional glutamatergic, dopaminergic and motor neurons in vitro. Electrophysiological examinations revealed that the current densities of fast activated and deactivated sodium channels as well as voltage gated potassium channels were not different between the neurons from PKD-iPSCs and control iPSCs. Thus, PKD-iPSCs are a feasible modeling tool to investigate the pathogenic mechanisms of PKD.

Summary: This is the first report of urinary cell-induced pluripotent stem cells being used as resources for investigation of the pathological mechanisms of paroxysmal kinesigenic dyskinesia.

Human pluripotent stem cell models of Fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and autism. The causal mutation in FXS is a trinucleotide CGG repeat expansion in the FMR1 gene that leads to human specific epigenetic silencing and loss of Fragile X Mental Retardation Protein (FMRP) expression. Human pluripotent stem cells (PSCs), including human embryonic stem cells (ESCs) and particularly induced PSCs (iPSCs), offer a model system to reveal cellular and molecular events underlying human neuronal development and function in FXS. Human FXS PSCs have been established and have provided insight into the epigenetic silencing of the FMR1 gene as well as aspects of neuronal development.

Rapid generation of sub-type, region-specific neurons and neural networks from human pluripotent stem cell-derived neurospheres

Stem cell-based neuronal differentiation has provided a unique opportunity for disease modeling and regenerative medicine. Neurospheres are the most commonly used neuroprogenitors for neuronal differentiation, but they often clump in culture, which has always represented a challenge for neurodifferentiation. In this study, we report a novel method and defined culture conditions for generating sub-type or region-specific neurons from human embryonic and induced pluripotent stem cells derived neurosphere without any genetic manipulation. Round and bright-edged neurospheres were generated in a supplemented knockout serum replacement medium (SKSRM) with 10% CO2, which doubled the expression of the NESTIN, PAX6 and FOXG1 genes compared with those cultured with 5% CO2. Furthermore, an additional step (AdSTEP) was introduced to fragment the neurospheres and facilitate the formation of a neuroepithelial-type monolayer that we termed the "neurosphederm". The large neural tube-type rosette (NTTR) structure formed from the neurosphederm, and the NTTR expressed higher levels of the PAX6, SOX2 and NESTIN genes compared with the neuroectoderm-derived neuroprogenitors. Different layers of cortical, pyramidal, GABAergic, glutamatergic, cholinergic neurons appeared within 27 days using the neurosphederm, which is a shorter period than in traditional neurodifferentiation-protocols (42-60 days). With additional supplements and timeline dopaminergic and Purkinje neurons were also generated in culture too. Furthermore, our in vivo results indicated that the fragmented neurospheres facilitated significantly better neurogenesis in severe combined immunodeficiency (SCID) mouse brains compared with the non-fragmented neurospheres. Therefore, this neurosphere-based neurodifferentiation protocol is a valuable tool for studies of neurodifferentiation, neuronal transplantation and high throughput screening assays.

Modeling Huntington׳s disease with patient-derived neurons

Huntington׳s Disease (HD) is a fatal neurodegenerative disorder caused by expanded polyglutamine repeats in the Huntingtin (HTT) gene. While the gene was identified over two decades ago, it remains poorly understood why mutant HTT (mtHTT) is initially toxic to striatal medium spiny neurons (MSNs). Models of HD using non-neuronal human patient cells and rodents exhibit some characteristic HD phenotypes. While these current models have contributed to the field, they are limited in disease manifestation and may vary in their response to treatments. As such, human HD patient MSNs for disease modeling could greatly expand the current understanding of HD and facilitate the search for a successful treatment. It is now possible to use pluripotent stem cells, which can generate any tissue type in the body, to study and potentially treat HD. This review covers disease modeling in vitro and, via chimeric animal generation, in vivo using human HD patient MSNs differentiated from embryonic stem cells or induced pluripotent stem cells. This includes an overview of the differentiation of pluripotent cells into MSNs, the established phenotypes found in cell-based models and transplantation studies using these cells. This review not only outlines the advancements in the rapidly progressing field of HD modeling using neurons derived from human pluripotent cells, but also it highlights several remaining controversial issues such as the 'ideal' series of pluripotent lines, the optimal cell types to use and the study of a primarily adult-onset disease in a developmental model. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Potential of GABA-ergic cell therapy for schizophrenia, neuropathic pain, and Alzheimer's and Parkinson's diseases

Several neurological and psychiatric disorders present hyperexcitability of neurons in specific regions of the brain or spinal cord, partly because of some loss and/or dysfunction of gamma-amino butyric acid positive (GABA-ergic) inhibitory interneurons. Strategies that enhance inhibitory neurotransmission in the affected brain regions may therefore ease several or most deficits linked to these disorders. This perception has incited a huge interest in testing the efficacy of GABA-ergic interneuron cell grafting into regions of the brain or spinal cord exhibiting hyperexcitability, dearth of GABA-ergic interneurons or impaired inhibitory neurotransmission, using preclinical models of neurological and psychiatric disorders. Interneuron progenitors from the embryonic ventral telencephalon capable of differentiating into diverse subclasses of interneurons have particularly received much consideration because of their ability for dispersion, migration and integration with the host neural circuitry after grafting. The goal of this review is to discuss the premise, scope and advancement of GABA-ergic cell therapy for easing neurological deficits in preclinical models of schizophrenia, chronic neuropathic pain, Alzheimer's disease and Parkinson's disease. As grafting studies in these prototypes have so far utilized either primary cells from the embryonic medial and lateral ganglionic eminences or neural progenitor cells expanded from these eminences as donor material, the proficiency of these cell types is highlighted. Moreover, future studies that are essential prior to considering the possible clinical application of these cells for the above neurological conditions are proposed. Particularly, the need for grafting studies utilizing medial ganglionic eminence-like progenitors generated from human pluripotent stem cells via directed differentiation approaches or somatic cells through direct reprogramming methods are emphasized. This article is part of a Special Issue entitled SI: PSC and the brain.

Utilizing induced pluripotent stem cells (iPSCs) to understand the actions of estrogens in human neurons

This article is part of a Special Issue "Estradiol and Cognition". Over recent years tremendous progress has been made towards understanding the molecular and cellular mechanism by which estrogens exert enhancing effects on cognition, and how they act as a neuroprotective or neurotrophic agent in disease. Currently, much of this work has been carried out in animal models with only a limited number of studies using native human tissue or cells. Recent advances in stem cell technology now make it possible to reprogram somatic cells from humans into induced pluripotent stem cells (iPSCs), which can subsequently be differentiated into neurons of specific lineages. Importantly, the reprogramming of cells allows for the generation of iPSCs that retain the genetic "makeup" of the donor. Therefore, it is possible to generate iPSC-derived neurons from patients diagnosed with specific diseases, that harbor the complex genetic background associated with the disorder. Here, we review the iPSC technology and how it's currently being used to model neural development and neurological diseases. Furthermore, we explore whether this cellular system could be used to understand the role of estrogens in human neurons, and present preliminary data in support of this. We further suggest that the use of iPSC technology offers a novel system to not only further understand estrogens' effects in human cells, but also to investigate the mechanism by which estrogens are beneficial in disease. Developing a greater understanding of these mechanisms in native human cells will also aid in the development of safer and more effective estrogen-based therapeutics.

Mesencephalic GABA neuronal development: no more on the other side of oblivion

Midbrain GABA neurons, endowed with multiple morphological, physiological and molecular characteristics as well as projection patterns are key players interacting with diverse regions of the brain and capable of modulating several aspects of behavior. The diversity of these GABA neuronal populations based on their location and function in the dorsal, medial or ventral midbrain has challenged efforts to rapidly uncover their developmental regulation. Here we review recent developments that are beginning to illuminate transcriptional control of GABA neurons in the embryonic midbrain (mesencephalon) and discuss its implications for understanding and treatment of neurological and psychiatric illnesses.

Building blocks of the cerebral cortex: from development to the dish

Since Ramon y Cajal's examination of the cellular makeup of the cerebral cortex, it has been appreciated that this tissue exhibits some of the greatest degrees of cellular heterogeneity in the entire nervous system. This intricate structure emerges during a well-choreographed developmental process. Here, we review current classifications of the cellular constituents of the cerebral cortex and examine how these building blocks are forged during development. We also look at how basic developmental features underlying cortex formation in vivo have been applied to protocols aimed at generating cortical tissue in vitro.

Human pluripotent stem cells as tools for neurodegenerative and neurodevelopmental disease modeling and drug discovery

INTRODUCTION

Although intensive efforts have been made, effective treatments for neurodegenerative and neurodevelopmental diseases have not been yet discovered. Possible reasons for this include the lack of appropriate disease models of human neurons and a limited understanding of the etiological and neurobiological mechanisms. Recent advances in pluripotent stem cell (PSC) research have now opened the path to the generation of induced pluripotent stem cells (iPSCs) starting from somatic cells, thus offering an unlimited source of patient-specific disease-relevant neuronal cells.

AREAS COVERED

In this review, the authors focus on the use of human PSC-derived cells in modeling neurological disorders and discovering of new drugs and provide their expert perspectives on the field.

EXPERT OPINION

The advent of human iPSC-based disease models has fuelled renewed enthusiasm and enormous expectations for insights of disease mechanisms and identification of more disease-relevant and novel molecular targets. Human PSCs offer a unique tool that is being profitably exploited for high-throughput screening (HTS) platforms. This process can lead to the identification and optimization of molecules/drugs and thus move forward new pharmacological therapies for a wide range of neurodegenerative and neurodevelopmental conditions. It is predicted that improvements in the production of mature neuronal subtypes, from patient-specific human-induced pluripotent stem cells and their adaptation to culture, to HTS platforms will allow the increased exploitation of human pluripotent stem cells in drug discovery programs.

Neuronal medium that supports basic synaptic functions and activity of human neurons in vitro

Human cell reprogramming technologies offer access to live human neurons from patients and provide a new alternative for modeling neurological disorders in vitro. Neural electrical activity is the essence of nervous system function in vivo. Therefore, we examined neuronal activity in media widely used to culture neurons. We found that classic basal media, as well as serum, impair action potential generation and synaptic communication. To overcome this problem, we designed a new neuronal medium (BrainPhys basal + serum-free supplements) in which we adjusted the concentrations of inorganic salts, neuroactive amino acids, and energetic substrates. We then tested that this medium adequately supports neuronal activity and survival of human neurons in culture. Long-term exposure to this physiological medium also improved the proportion of neurons that were synaptically active. The medium was designed to culture human neurons but also proved adequate for rodent neurons. The improvement in BrainPhys basal medium to support neurophysiological activity is an important step toward reducing the gap between brain physiological conditions in vivo and neuronal models in vitro.

Advances in reprogramming-based study of neurologic disorders

The technology to convert adult human non-neural cells into neural lineages, through induced pluripotent stem cells (iPSCs), somatic cell nuclear transfer, and direct lineage reprogramming or transdifferentiation has progressed tremendously in recent years. Reprogramming-based approaches aimed at manipulating cellular identity have enormous potential for disease modeling, high-throughput drug screening, cell therapy, and personalized medicine. Human iPSC (hiPSC)-based cellular disease models have provided proof of principle evidence of the validity of this system. However, several challenges remain before patient-specific neurons produced by reprogramming can provide reliable insights into disease mechanisms or be efficiently applied to drug discovery and transplantation therapy. This review will first discuss limitations of currently available reprogramming-based methods in faithfully and reproducibly recapitulating disease pathology. Specifically, we will address issues such as culture heterogeneity, interline and inter-individual variability, and limitations of two-dimensional differentiation paradigms. Second, we will assess recent progress and the future prospects of reprogramming-based neurologic disease modeling. This includes three-dimensional disease modeling, advances in reprogramming technology, prescreening of hiPSCs and creating isogenic disease models using gene editing.