Controlling the Regional Identity of hPSC-Derived Neurons to Uncover Neuronal Subtype Specificity of Neurological Disease Phenotypes

Changes in metabolite profiles in the cerebrospinal fluid and in human neuronal cells upon tick-borne encephalitis virus infection

BACKGROUND

Tick-borne encephalitis virus (TBEV) is a significant threat to human health. The virus causes potentially fatal disease of the central nervous system (CNS), for which no treatments are available. TBEV infected individuals display a wide spectrum of neuronal disease, the determinants of which are undefined. Changes to host metabolism and virus-induced immunity have been postulated to contribute to the neuronal damage observed in infected individuals. In this study, we evaluated the cytokine, chemokine, and metabolic alterations in the cerebrospinal fluid (CSF) of symptomatic patients infected with TBEV presenting with meningitis or encephalitis. Our aim was to investigate the host immune and metabolic responses associated with specific TBEV infectious outcomes.

METHODS

CSF samples of patients with meningitis (n = 27) or encephalitis (n = 25) were obtained upon consent from individuals hospitalised with confirmed TBEV infection in Brno. CSF from uninfected control patients was also collected for comparison (n = 12). A multiplex bead-based system was used to measure the levels of pro-inflammatory cytokines and chemokines. Untargeted metabolomics followed by bioinformatics and integrative omics were used to profile the levels of metabolites in the CSF. Human motor neurons (hMNs) were differentiated from induced pluripotent stem cells (iPSCs) and infected with the highly pathogenic TBEV-Hypr strain to profile the role(s) of identified metabolites during the virus lifecycle. Virus infection was quantified via plaque assay.

RESULTS

Significant differences in proinflammatory cytokines (IFN-α2, TSLP, IL-1α, IL-1β, GM-CSF, IL-12p40, IL-15, and IL-18) and chemokines (IL-8, CCL20, and CXCL11) were detected between neurological-TBEV and control patients. A total of 32 CSF metabolites differed in TBE patients with meningitis and encephalitis. CSF S-Adenosylmethionine (SAM), Fructose 1,6-bisphosphate (FBP1) and Phosphoenolpyruvic acid (PEP) levels were 2.4-fold (range ≥ 2.3-≥3.2) higher in encephalitis patients compared to the meningitis group. CSF urocanic acid levels were significantly lower in patients with encephalitis compared to those with meningitis (p = 0.012209). Follow-up analyses showed fluctuations in the levels of O-phosphoethanolamine, succinic acid, and L-proline in the encephalitis group, and pyruvic acid in the meningitis group. TBEV-infection of hMNs increased the production of SAM, FBP1 and PEP in a time-dependent manner. Depletion of the metabolites with characterised pharmacological inhibitors led to a concentration-dependent attenuation of virus growth, validating the identified changes as key mediators of TBEV infection.

CONCLUSIONS

Our findings reveal that the neurological disease outcome of TBEV infection is associated with specific and dynamic metabolic signatures in the cerebrospinal fluid. We describe a new in vitro model for in-depth studies of TBEV-induced neuropathogenesis, in which the depletion of identified metabolites limits virus infection. Collectively, this reveals new biomarkers that can differentiate and predict TBEV-associated neurological disease. Additionally, we have identified novel therapeutic targets with the potential to significantly improve patient outcomes and deepen our understanding of TBEV pathogenesis.

Traumatic Brain Injury: Novel Experimental Approaches and Treatment Possibilities

Traumatic brain injury (TBI) remains a critical global health issue with limited effective treatments. Traditional care of TBI patients focuses on stabilization and symptom management without regenerating damaged brain tissue. In this review, we analyze the current state of treatment of TBI, with focus on novel therapeutic approaches aimed at reducing secondary brain injury and promoting recovery. There are few innovative strategies that break away from the traditional, biological target-focused treatment approaches. Precision medicine includes personalized treatments based on biomarkers, genetics, advanced imaging, and artificial intelligence tools for prognosis and monitoring. Stem cell therapies are used to repair tissue, regulate immune responses, and support neural regeneration, with ongoing development in gene-enhanced approaches. Nanomedicine uses nanomaterials for targeted drug delivery, neuroprotection, and diagnostics by crossing the blood-brain barrier. Brain-machine interfaces enable brain-device communication to restore lost motor or neurological functions, while virtual rehabilitation and neuromodulation use virtual and augmented reality as well as brain stimulation techniques to improve rehabilitation outcomes. While these approaches show great potential, most are still in development and require more clinical testing to confirm safety and effectiveness. The future of TBI therapy looks promising, with innovative strategies likely to transform care.

NEUROD1 efficiently converts peripheral blood cells into neurons with partial reprogramming by pluripotency factors

The direct reprogramming of cells has tremendous potential in in vitro neurological studies. Previous attempts to convert blood cells into induced neurons have presented several challenges, necessitating a less invasive, efficient, rapid, and convenient approach. The current study introduces an optimized method for converting somatic cells into neurons using a nonsurgical approach that employs peripheral blood cells as an alternative source to fibroblasts. We have demonstrated the efficacy of a unique combination of transcription factors, including NEUROD1, and four Yamanaka reprogramming factors (OCT3/4, SOX2, KLF4, and c-MYC), in generating glutamatergic neurons within 3 wk. This approach, which requires only five pivotal factors (NEUROD1, OCT3/4, SOX2, KLF4, and c-MYC), has the potential to create functional neurons and circumvents the need for induced pluripotent stem cell (iPSC) intermediates, as evidenced by single-cell RNA sequencing and whole-genome bisulfite sequencing, along with lineage-tracing experiments using Cre-LoxP system. While fibroblasts have been widely used for neuronal reprogramming, our findings suggest that peripheral blood cells offer a potential alternative, particularly in contexts where minimally invasive sampling and procedures convenient for patients are emphasized. This method provides a rapid strategy for modeling neuronal diseases and contributes to advancements in drug discovery and personalized medicine.

α-Synuclein Pathology Spreads in a Midbrain-Hindbrain Assembloid Model

Understanding the progression of α-synuclein pathology in neurodegenerative diseases such as Parkinson's disease (PD) is a longstanding challenge. Here, a novel midbrain-hindbrain-assembloid model that recapitulates the spread of α-synuclein pathology observed in PD patients, akin to Braak's hypothesis, is presented. Initially, the presence α-synuclein pathology is demonstrated in the hindbrain organoids. Subsequently, sophisticated tissue engineering methods are employed to create midbrain-hindbrain assembloids. These assembloids allow investigation and description of the spreading of α-synuclein pathology, as it progresses from the hindbrain components to the midbrain regions within the integrated structure. It is observed that an increase in α-synuclein in the hindbrain can induce transfer of the pathology into the healthy midbrain, as well as cause changes at the synapse level. The presented model constitutes a robust in vitro platform for investigating the mechanisms underlying α-synuclein spreading and disease progression, and holding potential for the screening of prospective therapeutics targeting the pathological propagation in PD and related synucleinopathies.

Patient-derived induced pluripotent stem cells: Tools to advance the understanding and drug discovery in Major Depressive Disorder

Major Depressive Disorder (MDD) is a pleomorphic disease with substantial patterns of symptoms and severity with mensurable deficits in several associated domains. The broad spectrum of phenotypes observed in patients diagnosed with depressive disorders is the reflection of a very complex disease where clusters of biological and external factors (e.g., response/processing of life events, intrapsychic factors) converge and mediate pathogenesis, clinical presentation/phenotypes and trajectory. Patient-derived induced pluripotent stem cells (iPSCs) enable their differentiation into specialised cell types in the central nervous system to explore the pathophysiological substrates of MDD. These models may complement animal models to advance drug discovery and identify therapeutic approaches, such as cell therapy, drug repurposing, and elucidation of drug metabolism, toxicity, and mechanisms of action at the molecular/cellular level, to pave the way for precision psychiatry. Despite the remarkable scientific and clinical progress made over the last few decades, the disease is still poorly understood, the incidence and prevalence continue to increase, and more research is needed to meet clinical demands. This review aims to summarise and provide a critical overview of the research conducted thus far using patient-derived iPSCs for the modelling of psychiatric disorders, with a particular emphasis on MDD.

Recent advances and applications of human brain models

Recent advances in human pluripotent stem cell (hPSC) technologies have prompted the emergence of new research fields and applications for human neurons and brain organoids. Brain organoids have gained attention as an in vitro model system that recapitulates the higher structure, cellular diversity and function of the brain to explore brain development, disease modeling, drug screening, and regenerative medicine. This progress has been accelerated by abundant interactions of brain organoid technology with various research fields. A cross-disciplinary approach with human brain organoid technology offers a higher-ordered advance for more accurately understanding the human brain. In this review, we summarize the status of neural induction in two- and three-dimensional culture systems from hPSCs and the modeling of neurodegenerative diseases using brain organoids. We also highlight the latest bioengineered technologies for the assembly of spatially higher-ordered neural tissues and prospects of brain organoid technology toward the understanding of the potential and abilities of the human brain.

Reduced ER-mitochondrial contact sites and mitochondrial Ca2+ flux in PRKN-mutant patient tyrosine hydroxylase reporter iPSC lines

Endoplasmic reticulum-mitochondrial contact sites (ERMCS) play an important role in mitochondrial dynamics, calcium signaling, and autophagy. Disruption of the ERMCS has been linked to several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). However, the etiological role of ERMCS in these diseases remains unclear. We previously established tyrosine hydroxylase reporter (TH-GFP) iPSC lines from a PD patient with a PRKN mutation to perform correlative light-electron microscopy (CLEM) analysis and live cell imaging in GFP-expressing dopaminergic neurons. Here, we analyzed ERMCS in GFP-expressing PRKN-mutant dopaminergic neurons from patients using CLEM and a proximity ligation assay (PLA). The PLA showed that the ERMCS were significantly reduced in PRKN-mutant patient dopaminergic neurons compared to the control under normal conditions. The reduction of the ERMCS in PRKN-mutant patient dopaminergic neurons was further enhanced by treatment with a mitochondrial uncoupler. In addition, mitochondrial calcium imaging showed that mitochondrial Ca2+ flux was significantly reduced in PRKN-mutant patient dopaminergic neurons compared to the control. These results suggest a defect in calcium flux from ER to mitochondria is due to the decreased ERMCS in PRKN-mutant patient dopaminergic neurons. Our study of ERMCS using TH-GFP iPSC lines would contribute to further understanding of the mechanisms of dopaminergic neuron degeneration in patients with PRKN mutations.

A defined method for differentiating human iPSCs into midbrain dopaminergic progenitors that safely restore motor deficits in Parkinson's disease

Background

Parkinson's disease (PD) is a progressive neurodegenerative condition that primarily affects motor functions; it is caused by the loss of midbrain dopaminergic (mDA) neurons. The therapeutic effects of transplanting human-induced pluripotent stem cell (iPSC)-derived mDA neural progenitor cells in animal PD models are known and are being evaluated in an ongoing clinical trial. However, However, improvements in the safety and efficiency of differentiation-inducing methods are crucial for providing a larger scale of cell therapy studies. This study aimed to investigate the usefulness of dopaminergic progenitor cells derived from human iPSCs by our previously reported method, which promotes differentiation and neuronal maturation by treating iPSCs with three inhibitors at the start of induction.

Methods

Healthy subject-derived iPS cells were induced into mDA progenitor cells by the CTraS-mediated method we previously reported, and their proprieties and dopaminergic differentiation efficiency were examined in vitro. Then, the induced mDA progenitors were transplanted into 6-hydroxydopamine-lesioned PD model mice, and their efficacy in improving motor function, cell viability, and differentiation ability in vivo was evaluated for 16 weeks.

Results

Approximately ≥80% of cells induced by this method without sorting expressed mDA progenitor markers and differentiated primarily into A9 dopaminergic neurons in vitro. After transplantation in 6-hydroxydopamine-lesioned PD model mice, more than 90% of the engrafted cells differentiated into the lineage of mDA neurons, and approximately 15% developed into mature mDA neurons without tumour formation. The grafted PD model mice also demonstrated significantly improved motor functions.

Conclusion

This study suggests that the differentiation protocol for the preparation of mDA progenitors is a promising option for cell therapy in patients with PD.

Neuroprotective Effects of Genome-Edited Human iPS Cell-Derived Neural Stem/Progenitor Cells on Traumatic Brain Injury

Despite developing neurosurgical procedures, few treatment options have achieved functional recovery from traumatic brain injury (TBI). Neural stem/progenitor cells (NS/PCs) may produce a long-term effect on neurological recovery. Although induced pluripotent stem cells (iPSCs) can overcome ethical and practical issues of human embryonic or fetal-derived tissues in clinical applications, the tumorigenicity of iPSC-derived populations remains an obstacle to their safe use in regenerative medicine. We herein established a novel treatment strategy for TBI using iPSCs expressing the enzyme-prodrug gene yeast cytosine deaminase-uracil phosphoribosyl transferase (yCD-UPRT). NS/PCs derived from human iPSCs displayed stable and high transgene expression of yCD-UPRT following CRISPR/Cas9-mediated genome editing. In vivo bioluminescent imaging and histopathological analysis demonstrated that NS/PCs concentrated around the damaged cortex of the TBI mouse model. During the subacute phase, performances in both beam walking test and accelerating rotarod test were significantly improved in the treatment group transplanted with genome-edited iPSC-derived NS/PCs compared with the control group. The injury area visualized by extravasation of Evans blue was smaller in the treatment group compared with the control group, suggesting the prevention of secondary brain injury. During the chronic phase, cerebral atrophy and ventricle enlargement were significantly less evident in the treatment group. Furthermore, after 5-fluorocytosine (5-FC) administration, 5-fluorouracil converted from 5-FC selectively eliminated undifferentiated NS/PCs while preserving the adjacent neuronal structures. NS/PCs expressing yCD-UPRT can be applied for safe regenerative medicine without the concern for tumorigenesis.

Mesenchymal properties of iPSC-derived neural progenitors that generate undesired grafts after transplantation

Although neural stem/progenitor cells derived from human induced pluripotent stem cells (hiPSC-NS/PCs) are expected to be a cell source for cell-based therapy, tumorigenesis of hiPSC-NS/PCs is a potential problem for clinical applications. Therefore, to understand the mechanisms of tumorigenicity in NS/PCs, we clarified the cell populations of NS/PCs. We established single cell-derived NS/PC clones (scNS/PCs) from hiPSC-NS/PCs that generated undesired grafts. Additionally, we performed bioassays on scNS/PCs, which classified cell types within parental hiPSC-NS/PCs. Interestingly, we found unique subsets of scNS/PCs, which exhibited the transcriptome signature of mesenchymal lineages. Furthermore, these scNS/PCs expressed both neural (PSA-NCAM) and mesenchymal (CD73 and CD105) markers, and had an osteogenic differentiation capacity. Notably, eliminating CD73⁺ CD105⁺ cells from among parental hiPSC-NS/PCs ensured the quality of hiPSC-NS/PCs. Taken together, the existence of unexpected cell populations among NS/PCs may explain their tumorigenicity leading to potential safety issues of hiPSC-NS/PCs for future regenerative medicine.

Rapid and Robust Multi-Phenotypic Assay System for ALS Using Human iPS Cells with Mutations in Causative Genes

Amyotrophic lateral sclerosis (ALS) is a major life-threatening disease caused by motor neuron degeneration. More effective treatments through drug discovery are urgently needed. Here, we established an effective high-throughput screening system using induced pluripotent stem cells (iPSCs). Using a Tet-On-dependent transcription factor expression system carried on the PiggyBac vector, motor neurons were efficiently and rapidly generated from iPSCs by a single-step induction method. Induced iPSC transcripts displayed characteristics similar to those of spinal cord neurons. iPSC-generated motor neurons carried a mutation in fused in sarcoma (FUS) and superoxide dismutase 1 (SOD1) genes and had abnormal protein accumulation corresponding to each mutation. Calcium imaging and multiple electrode array (MEA) recordings demonstrated that ALS neurons were abnormally hyperexcitable. Noticeably, protein accumulation and hyperexcitability were ameliorated by treatment with rapamycin (mTOR inhibitor) and retigabine (Kv7 channel activator), respectively. Furthermore, rapamycin suppressed ALS neuronal death and hyperexcitability, suggesting that protein aggregate clearance through the activation of autophagy effectively normalized activity and improved neuronal survival. Our culture system reproduced several ALS phenotypes, including protein accumulation, hyperexcitability, and neuronal death. This rapid and robust phenotypic screening system will likely facilitate the discovery of novel ALS therapeutics and stratified and personalized medicine for sporadic motor neuron diseases.

Role of Oligodendrocyte Lineage Cells in Multiple System Atrophy

Multiple system atrophy (MSA) is a debilitating movement disorder with unknown etiology. Patients present characteristic parkinsonism and/or cerebellar dysfunction in the clinical phase, resulting from progressive deterioration in the nigrostriatal and olivopontocerebellar regions. MSA patients have a prodromal phase subsequent to the insidious onset of neuropathology. Therefore, understanding the early pathological events is important in determining the pathogenesis, which will assist with developing disease-modifying therapy. Although the definite diagnosis of MSA relies on the positive post-mortem finding of oligodendroglial inclusions composed of α-synuclein, only recently has MSA been verified as an oligodendrogliopathy with secondary neuronal degeneration. We review up-to-date knowledge of human oligodendrocyte lineage cells and their association with α-synuclein, and discuss the postulated mechanisms of how oligodendrogliopathy develops, oligodendrocyte progenitor cells as the potential origins of the toxic seeds of α-synuclein, and the possible networks through which oligodendrogliopathy induces neuronal loss. Our insights will shed new light on the research directions for future MSA studies.

Using Human iPSC-Derived Peripheral Nervous System Disease Models for Drug Discovery

Induced pluripotent stem cells (IPSCs), with their remarkable ability to differentiate into various cell types, including peripheral nervous system cells such as neurons and glial cells, offer an excellent platform for in vitro disease modeling. These iPSC-derived disease models have proven valuable in drug discovery, as they provide more precise simulations of a patient's disease state and allow for the assessment of potential therapeutic effectiveness and safety.

Generation of four iPSC lines from a family harboring a 1p36-35 haplotype linked with bipolar disorder and recurrent depressive disorder: Three-generation patients and a healthy sibling

Induced pluripotent stem cells (iPSCs) obtained from genetically characterized patients benefit the biological study of bipolar disorder (BD). Here, we present iPSC lines from three-generation patients with BD and recurrent depressive disorder (RDD) and a healthy control sibling in a family. All patients shared the specified haplotype in the 1p36-35, previously reported as the susceptibility locus of mood disorders. iPSCs were generated with the reprogramming factors OTC3/4, l-MYC, LIN28, SOX2, KLF4, and p53 shRNA through non-integrated episomal vectors. All iPSC lines strongly expressed pluripotency markers and proved the ability to differentiate into three germ lineages in vitro.

iPSCs in Neurodegenerative Disorders: A Unique Platform for Clinical Research and Personalized Medicine

In the past, several animal disease models were developed to study the molecular mechanism of neurological diseases and discover new therapies, but the lack of equivalent animal models has minimized the success rate. A number of critical issues remain unresolved, such as high costs for developing animal models, ethical issues, and lack of resemblance with human disease. Due to poor initial screening and assessment of the molecules, more than 90% of drugs fail during the final step of the human clinical trial. To overcome these limitations, a new approach has been developed based on induced pluripotent stem cells (iPSCs). The discovery of iPSCs has provided a new roadmap for clinical translation research and regeneration therapy. In this article, we discuss the potential role of patient-derived iPSCs in neurological diseases and their contribution to scientific and clinical research for developing disease models and for developing a roadmap for future medicine. The contribution of humaniPSCs in the most common neurodegenerative diseases (e.g., Parkinson’s disease and Alzheimer’s disease, diabetic neuropathy, stroke, and spinal cord injury) were examined and ranked as per their published literature on PUBMED. We have observed that Parkinson’s disease scored highest, followed by Alzheimer’s disease. Furthermore, we also explored recent advancements in the field of personalized medicine, such as the patient-on-a-chip concept, where iPSCs can be grown on 3D matrices inside microfluidic devices to create an in vitro disease model for personalized medicine.

Pathogenic Mutation of TDP-43 Impairs RNA Processing in a Cell Type-Specific Manner: Implications for the Pathogenesis of ALS/FTLD

Transactivating response element DNA-binding protein of 43 kDa (TDP-43), which is encoded by the TARDBP gene, is an RNA-binding protein with fundamental RNA processing activities, and its loss-of-function (LOF) has a central role in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). TARDBP mutations are postulated to inactivate TDP-43 functions, leading to impaired RNA processing. However, it has not been fully examined how mutant TDP-43 affects global RNA regulation, especially in human cell models. Here, we examined global RNA processing in forebrain cortical neurons derived from human induced pluripotent stem cells (iPSCs) with a pathogenic TARDBP mutation encoding the TDP-43K263E protein. In neurons expressing mutant TDP-43, we detected disrupted RNA regulation, including global changes in gene expression, missplicing, and aberrant polyadenylation, all of which were highly similar to those induced by TDP-43 knock-down. This mutation-induced TDP-43 LOF was not because of the cytoplasmic mislocalization of TDP-43. Intriguingly, in nonneuronal cells, including iPSCs and neural progenitor cells (NPCs), we did not observe impairments in RNA processing, thus indicating that the K263E mutation results in neuron-specific LOF of TDP-43. This study characterizes global RNA processing impairments induced by mutant TDP-43 and reveals the unprecedented cell type specificity of TDP-43 LOF in ALS/FTLD pathogenesis.

iPSC-based disease modeling and drug discovery in cardinal neurodegenerative disorders

It has been 15 years since the birth of human induced pluripotent stem cell (iPSC) technology in 2007, and the scope of its application has been expanding. In addition to the development of cell therapies using iPSC-derived cells, pathological analyses using disease-specific iPSCs and clinical trials to confirm the safety and efficacy of drugs developed using iPSCs are progressing. With the innovation of related technologies, iPSC applications are about to enter a new stage. This review outlines advances in iPSC modeling and therapeutic development for cardinal neurodegenerative diseases, such as amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease.

Methods to Induce Small-Scale Differentiation of iPS Cells into Dopaminergic Neurons and to Detect Disease Phenotypes

Disease-specific induced pluripotent stem (iPS) cells are useful tools to analyze the pathology of neurodegenerative diseases. In this chapter, we describe a procedure to efficiently induce small-scale differentiation of patient iPS cells into midbrain dopaminergic neurons to detect cell death and mitochondrial clearance by using immunostaining. A combination of our method described here and an image analysis system, such as the IN Cell Analyzer, will enable the quantitative assessment of cell vulnerability and mitochondrial quality control abnormalities in cells derived from patients with Parkinson's disease; this set-up might be used to perform drug screening.

Making neurons, made easy: The use of Neurogenin-2 in neuronal differentiation

Directed neuronal differentiation of human pluripotent stem cells (hPSCs), neural progenitors, or fibroblasts using transcription factors has allowed for the rapid and highly reproducible differentiation of mature and functional neurons. Exogenous expression of the transcription factor Neurogenin-2 (NGN2) has been widely used to generate different populations of neurons, which have been used in neurodevelopment studies, disease modeling, drug screening, and neuronal replacement therapies. Could NGN2 be a “one-glove-fits-all” approach for neuronal differentiations? This review summarizes the cellular roles of NGN2 and describes the applications and limitations of using NGN2 for the rapid and directed differentiation of neurons.

Modeling schizophrenia with iPS cell technology and disease mouse models

Induced pluripotent stem cell (iPSC) technology, which enables the direct analysis of neuronal cells with the same genetic background as patients, has recently garnered significant attention in schizophrenia research. This technology is important because it enables a comprehensive interpretation using mice and human clinical research and cross-species verification. Here I review recent advances in modeling schizophrenia using iPSC technology, alongside the utility of disease mouse models.

In vitro monitoring of HTR2A-positive neurons derived from human-induced pluripotent stem cells

The serotonin 5-HT_2A receptor (5-HT_2AR) has been receiving increasing attention because its genetic variants have been associated with a variety of neurological diseases. To elucidate the pathogenesis of the neurological diseases associated with 5-HT_2AR gene (HTR2A) variants, we have previously established a protocol to induce HTR2A-expressing neurons from human-induced pluripotent stem cells (hiPSCs). Here, we investigated the maturation stages and electrophysiological properties of HTR2A-positive neurons induced from hiPSCs and constructed an HTR2A promoter-specific reporter lentivirus to label the neurons. We found that neuronal maturity increased over time and that HTR2A expression was induced at the late stage of neuronal maturation. Furthermore, we demonstrated successful labelling of the HTR2A-positive neurons, which had fluorescence and generated repetitive action potentials in response to depolarizing currents and an inward current during the application of TCB-2, a selective agonist of 5-HT_2ARs, respectively. These results indicated that our in vitro model mimicked the in vivo dynamics of 5-HT_2AR. Therefore, in vitro monitoring of the function of HTR2A-positive neurons induced from hiPSCs could help elucidate the pathophysiological mechanisms of neurological diseases associated with genetic variations of the HTR2A gene.

[Pharmacological studies using iPSC-derived neurons from patients with schizophrenia]

Schizophrenia is characterized by positive symptoms, negative symptoms and cognitive dysfunction. Although the abnormal neuronal development, impaired synaptic functions and impaired neural circuit functions are suggested to be the causes of psychiatric disorders, the molecular and cellular etiology of schizophrenia remains largely unclear. iPS-related technologies can be powerful for not only understanding the molecular and cellular etiology of schizophrenia but also drug discovery research. In 2011, the first iPS cells derived from patients with schizophrenia harboring a DISC1 mutation were generated. Subsequently, many iPS cells from patients with schizophrenia were established for understanding the molecular and cellular disease phenotypes of the differentiated neuronal cells. For replicating disease phenotypes with iPSC-derived neuronal cells, it is important to develop the differentiation strategies for generating cell-type specific cultures of various types of neurons, astrocytes and oligodendrocytes. Especially, scalable cultures of iPSC-derived neuronal cells are valuable platforms for drug discovery research. In this review, the focus has been made on the iPSC differentiation technology, pharmacological and drug discovery studies with iPSC-derived neurons from patients with schizophrenia. Continued advancement of the iPSC-related technologies and research will help the success in central nervous system drug discovery and development.

Cerebellar Differentiation from Human Stem Cells Through Retinoid, Wnt, and Sonic Hedgehog Pathways

Differentiating cerebellar organoids can be challenging due to complex cell organization and structure in the cerebellum. Different approaches were investigated to recapitulate differentiation process of the cerebellum from human-induced pluripotent stem cells (hiPSCs) without high efficiency. This study was carried out to test the hypothesis that the combination of different signaling factors including retinoic acid (RA), Wnt activator, and sonic hedgehog (SHH) activator promotes the cerebellar differentiation of hiPSCs. Wnt, RA, and SHH pathways were activated by CHIR99021 (CHIR), RA, and purmorphamine (PMR), respectively. Different combinations of the morphogens (RA/CHIR, RA/PMR, CHIR/PMR, and RA/CHIR/PMR) were utilized, and the spheroids (day 35) were characterized for the markers of three cerebellum layers (the molecular layer, the Purkinje cell layer, and the granule cell layer). Of all the combinations tested, RA/CHIR/PMR promoted both the Purkinje cell layer and the granule cell layer differentiation. The cells also exhibited electrophysiological characteristics using whole-cell patch clamp recording, especially demonstrating Purkinje cell electrophysiology. This study should advance the understanding of different signaling pathways during cerebellar development to engineer cerebellum organoids for drug screening and disease modeling. Impact statement This study investigated the synergistic effects of retinoic acid, Wnt activator, and sonic hedgehog activator on cerebellar patterning of human-induced pluripotent stem cell (hiPSC) spheroids and organoids. The results indicate that the combination promotes the differentiation of the Purkinje cell layer and the granule cell layer. The cells also exhibit electrophysiological characteristics using whole-cell patch clamp recording, especially demonstrating Purkinje cell electrophysiology. The findings are significant for understanding the biochemical signaling of three-dimensional microenvironment on neural patterning of hiPSCs for applications in organoid engineering, disease modeling, and drug screening.

Amyloid β (Aβ) ELISA of Human iPSC-Derived Neuronal Cultures

Amyloid β (Aβ) peptides are the main component of the characteristic insoluble deposits in brain parenchyma and small blood vessels in the patients afflicted with Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). These small peptides are attributed to the pathogenesis of both AD and CAA, suggesting an important index for disease stage and progression. In the brain tissue, Aβs are released mainly from neuronal cells into extracellular space. Here, we describe a step-by-step protocol to measure Aβs secreted from human pluripotent stem cell-derived neuronal cells.

Identification of hub molecules of FUS-ALS by Bayesian gene regulatory network analysis of iPSC model: iBRN

Fused in sarcoma/translated in liposarcoma (FUS) is a causative gene of amyotrophic lateral sclerosis (ALS). Mutated FUS causes accumulation of DNA damage and cytosolic stress granule (SG) formation, thereby motor neuron (MN) death. However, key molecular aetiology remains unclear. Here, we applied a novel platform technology, iBRN, "Non- biased" Bayesian gene regulatory network analysis based on induced pluripotent stem cell (iPSC)-derived cell model, to elucidate the molecular aetiology using transcriptome of iPSC-derived MNs harboring FUS^H517D. iBRN revealed "hub molecules", which strongly influenced transcriptome network, such as miR-125b-5p-TIMELESS axis and PRKDC for the molecular aetiology. Next, we confirmed miR-125b-5p-TIMELESS axis in FUS^H517D MNs such that miR-125b-5p regulated several DNA repair-related genes including TIMELESS. In addition, we validated both introduction of miR-125b-5p and knocking down of TIMELESS caused DNA damage in the cell culture model. Furthermore, PRKDC was strongly associated with FUS mis-localization into SGs by DNA damage under impaired DNA-PK activity. Collectively, our iBRN strategy provides the first compelling evidence to elucidate molecular aetiology in neurodegenerative diseases.

Using organoids to study human brain development and evolution

Recent advances in methods for making cerebral organoids have opened a window of opportunity to directly study human brain development and disease, countering limitations inherent in non-human-based approaches. Whether freely patterned, guided into a region-specific fate or fused into assembloids, organoids have successfully recapitulated key features of in vivo neurodevelopment, allowing its examination from early to late stages. Although organoids have enormous potential, their effective use relies on understanding the extent of their limitations in accurately reproducing specific processes and components in the developing human brain. Here we review the potential of cerebral organoids to model and study human brain development and evolution and discuss the progress and current challenges in their use for reproducing specific human neurodevelopmental processes.

Establishment of an in vitro model for analyzing mitochondrial ultrastructure in PRKN-mutated patient iPSC-derived dopaminergic neurons

Mitochondrial structural changes are associated with the regulation of mitochondrial function, apoptosis, and neurodegenerative diseases. PRKN is known to be involved with various mechanisms of mitochondrial quality control including mitochondrial structural changes. Parkinson's disease (PD) with PRKN mutations is characterized by the preferential degeneration of dopaminergic neurons in the substantia nigra pars compacta, which has been suggested to result from the accumulation of damaged mitochondria. However, ultrastructural changes of mitochondria specifically in dopaminergic neurons derived from iPSC have rarely been analyzed. The main reason for this would be that the dopaminergic neurons cannot be distinguished directly among a mixture of iPSC-derived differentiated cells under electron microscopy. To selectively label dopaminergic neurons and analyze mitochondrial morphology at the ultrastructural level, we generated control and PRKN-mutated patient tyrosine hydroxylase reporter (TH-GFP) induced pluripotent stem cell (iPSC) lines. Correlative light-electron microscopy analysis and live cell imaging of GFP-expressing dopaminergic neurons indicated that iPSC-derived dopaminergic neurons had smaller and less functional mitochondria than those in non-dopaminergic neurons. Furthermore, the formation of spheroid-shaped mitochondria, which was induced in control dopaminergic neurons by a mitochondrial uncoupler, was inhibited in the PRKN-mutated dopaminergic neurons. These results indicate that our established TH-GFP iPSC lines are useful for characterizing mitochondrial morphology, such as spheroid-shaped mitochondria, in dopaminergic neurons among a mixture of various cell types. Our in vitro model would provide insights into the vulnerability of dopaminergic neurons and the processes leading to the preferential loss of dopaminergic neurons in patients with PRKN mutations.

Flexible and Accurate Substrate Processing with Distinct Presenilin/γ-Secretases in Human Cortical Neurons

Mutations in the presenilin genes (PS1, PS2) have been linked to the majority of familial Alzheimer’s disease (AD). Although great efforts have been made to investigate pathogenic PS mutations, which ultimately cause an increase in the toxic form of β-amyloid (Aβ), the intrinsic physiological functions of PS in human neurons remain to be determined. In this study, to investigate the physiological roles of PS in human neurons, we generated PS1 conditional knock-out (KO) induced pluripotent stem cells (iPSCs), in which PS1 can be selectively abrogated under Cre transduction with or without additional PS2 KO. We showed that iPSC-derived neural progenitor cells (NPCs) do not confer a maintenance ability in the absence of both PS1 and PS2, showing the essential role of PS in Notch signaling. We then generated PS-null human cortical neurons, where PS1 was intact until full neuronal differentiation occurred. Aβ40 production was reduced exclusively in human PS1/PS2-null neurons along with a concomitant accumulation of amyloid β precursor protein (APP)-C-terminal fragments CTFs, whereas Aβ42 was decreased in neurons devoid of PS2. Unlike previous studies in mice, in which APP cleavage is largely attributable to PS1, γ-secretase activity seemed to be comparable between PS1 and PS2. In contrast, cleavage of another substrate, N-cadherin, was impaired only in neurons devoid of PS1. Moreover, PS2/γ-secretase exists largely in late endosomes/lysosomes, as measured by specific antibody against the γ-secretase complex, in which Aβ42 species are supposedly produced. Using this novel stem cell-based platform, we assessed important physiological PS1/PS2 functions in mature human neurons, the dysfunction of which could underlie AD pathogenesis.

Understanding axial progenitor biology in vivo and in vitro

The generation of the components that make up the embryonic body axis, such as the spinal cord and vertebral column, takes place in an anterior-to-posterior (head-to-tail) direction. This process is driven by the coordinated production of various cell types from a pool of posteriorly-located axial progenitors. Here, we review the key features of this process and the biology of axial progenitors, including neuromesodermal progenitors, the common precursors of the spinal cord and trunk musculature. We discuss recent developments in the in vitro production of axial progenitors and their potential implications in disease modelling and regenerative medicine.

Generation of region-specific and high-purity neurons from human feeder-free iPSCs

Human induced pluripotent stem cells (iPSCs) have great potential to elucidate the molecular pathogenesis of neurological/psychiatric diseases. In particular, neurological/psychiatric diseases often display brain region-specific symptoms, and the technology for generating region-specific neural cells from iPSCs has been established for detailed modeling of neurological/psychiatric disease phenotypes in vitro. On the other hand, recent advances in culturing human iPSCs without feeder cells have enabled highly efficient and reproducible neural induction. However, conventional regional control technologies have mainly been developed based on on-feeder iPSCs, and these methods are difficult to apply to feeder-free (ff) iPSC cultures. In this study, we established a novel culture system to generate region-specific neural cells from human ff-iPSCs. This system is the best optimized approach for feeder-free iPSC culture and generates specific neuronal subtypes with high purity and functionality, including forebrain cortical neurons, forebrain interneurons, midbrain dopaminergic neurons, and spinal motor neurons. In addition, the temporal patterning of cortical neuron layer specification in the forebrain was reproduced in our culture system, which enables the generation of layer-specific cortical neurons. Neuronal activity was demonstrated in the present culture system by using multiple electrode array and calcium imaging. Collectively, our ff-iPSC-based culture system would provide a desirable platform for modeling various types of neurological/psychiatric disease phenotypes.

Differentiation of Midbrain Dopaminergic Neurons from Human iPS Cells

Human-induced pluripotent stem (iPS) cells provide a powerful means for analyzing disease mechanisms and drug screening, especially for neurological diseases, considering the difficulty to obtain live pathological tissue. The midbrain dopaminergic neurons of the substantia nigra are mainly affected in Parkinson's disease, but it is impossible to obtain and analyze viable dopaminergic neurons from live patients. This problem can be overcome by the induction of dopaminergic neurons from human iPS cells. Here, we describe an efficient method for differentiating human iPS cells into midbrain dopaminergic neurons. This protocol holds merit for obtaining a deeper understanding of the disease and for developing novel treatments.

Modeling neurodevelopment in a dish with pluripotent stem cells

Pluripotent stem cells (PSCs) can differentiate into all cell types in the body, and their differentiation procedures recapitulate the developmental processes of embryogenesis. Focusing on neurodevelopment, we describe here the application of knowledge gained from embryology to the neural induction of PSCs. Furthermore, PSC-based neural modeling provides novel insights into neurodevelopmental processes. In particular, human PSC cultures are a powerful tool for the study of human-specific neurodevelopmental processes and could even enable the elucidation of the mechanisms of human brain evolution. We also discuss challenges and potential future directions in further improving PSC-based neural modeling.

Astrocytes and microglia in neurodegenerative diseases: Lessons from human in vitro models

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Astrocytes and microglia key fulfil homeostatic and immune functions in the CNS.

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Dysfunction of these cell types is implicated in neurodegenerative diseases.

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Understanding cellular autonomy and early pathogenic changes is a key goal.

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New human iPSC models will inform on disease mechanisms and therapy development.

Both astrocytes and microglia fulfil homeostatic and immune functions in the healthy CNS. Dysfunction of these cell types have been implicated in the pathomechanisms of several neurodegenerative diseases. Understanding the cellular autonomy and early pathological changes in these cell types may inform drug screening and therapy development. While animal models and post-mortem tissue have been invaluable in understanding disease processes, the advent of human in vitro models provides a unique insight into disease biology as a manipulable model system obtained directly from patients. Here, we discuss the different human in vitro models of astrocytes and microglia and outline the phenotypes that have been recapitulated in these systems.

Recent progress in translational engineered in vitro models of the central nervous system

The complexity of the human brain poses a substantial challenge for the development of models of the CNS. Current animal models lack many essential human characteristics (in addition to raising operational challenges and ethical concerns), and conventional in vitro models, in turn, are limited in their capacity to provide information regarding many functional and systemic responses. Indeed, these challenges may underlie the notoriously low success rates of CNS drug development efforts. During the past 5 years, there has been a leap in the complexity and functionality of in vitro systems of the CNS, which have the potential to overcome many of the limitations of traditional model systems. The availability of human-derived induced pluripotent stem cell technology has further increased the translational potential of these systems. Yet, the adoption of state-of-the-art in vitro platforms within the CNS research community is limited. This may be attributable to the high costs or the immaturity of the systems. Nevertheless, the costs of fabrication have decreased, and there are tremendous ongoing efforts to improve the quality of cell differentiation. Herein, we aim to raise awareness of the capabilities and accessibility of advanced in vitro CNS technologies. We provide an overview of some of the main recent developments (since 2015) in in vitro CNS models. In particular, we focus on engineered in vitro models based on cell culture systems combined with microfluidic platforms (e.g. 'organ-on-a-chip' systems). We delve into the fundamental principles underlying these systems and review several applications of these platforms for the study of the CNS in health and disease. Our discussion further addresses the challenges that hinder the implementation of advanced in vitro platforms in personalized medicine or in large-scale industrial settings, and outlines the existing differentiation protocols and industrial cell sources. We conclude by providing practical guidelines for laboratories that are considering adopting organ-on-a-chip technologies.

A robust culture system to generate neural progenitors with gliogenic competence from clinically relevant induced pluripotent stem cells for treatment of spinal cord injury

Cell-based therapy targeting spinal cord injury (SCI) is an attractive approach to promote functional recovery by replacing damaged tissue. We and other groups have reported the effectiveness of transplanting neural stem/progenitor cells (NS/PCs) derived from human induced pluripotent stem cells (hiPSCs) in SCI animal models for neuronal replacement. Glial replacement is an additional approach for tissue repair; however, the lack of robust procedures to drive iPSCs into NS/PCs which can produce glial cells has hindered the development of glial cell transplantation for the restoration of neuronal functions after SCI. Here, we established a method to generate NS/PCs with gliogenic competence (gNS/PCs) optimized for clinical relevance and utilized them as a source of therapeutic NS/PCs for SCI. We could successfully generate gNS/PCs from clinically relevant hiPSCs, which efficiently produced astrocytes and oligodendrocytes in vitro. We also performed comparison between gNS/PCs and neurogenic NS/PCs based on single cell RNA-seq analysis and found that gNS/PCs were distinguished by expression of several transcription factors including HEY2 and NFIB. After gNS/PC transplantation, the graft did not exhibit tumor-like tissue formation, indicating the safety of them as a source of cell therapy. Importantly, the gNS/PCs triggered functional recovery in an SCI animal model, with remyelination of demyelinated axons and improved motor function. Given the inherent safety of gNS/PCs and favorable outcomes observed after their transplantation, cell-based medicine using the gNS/PCs-induction procedure described here together with clinically relevant iPSCs is realistic and would be beneficial for SCI patients.

SOX1 Is Required for the Specification of Rostral Hindbrain Neural Progenitor Cells from Human Embryonic Stem Cells

Region-specific neural progenitor cells (NPCs) can be generated from human embryonic stem cells (hESCs) by modulating signaling pathways. However, how intrinsic transcriptional factors contribute to the neural regionalization is not well characterized. Here, we generate region-specific NPCs from hESCs and find that SOX1 is highly expressed in NPCs with the rostral hindbrain identity. Moreover, we find that OTX2 inhibits SOX1 expression, displaying exclusive expression between the two factors. Furthermore, SOX1 knockout (KO) leads to the upregulation of midbrain genes and downregulation of rostral hindbrain genes, indicating that SOX1 is required for specification of rostral hindbrain NPCs. Our SOX1 chromatin immunoprecipitation sequencing analysis reveals that SOX1 binds to the distal region of GBX2 to activate its expression. Overexpression of GBX2 largely abrogates SOX1-KO-induced aberrant gene expression. Taken together, this study uncovers previously unappreciated role of SOX1 in early neural regionalization and provides new information for the precise control of the OTX2/GBX2 interface.

Cell therapy for spinal cord injury by using human iPSC-derived region-specific neural progenitor cells

The transplantation of neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (iPSCs) has beneficial effects on spinal cord injury (SCI). However, while there are many subtypes of NPCs with different regional identities, the subtype of iPSC-derived NPCs that is most appropriate for cell therapy for SCI has not been identified. Here, we generated forebrain- and spinal cord-type NPCs from human iPSCs and grafted them onto the injured spinal cord in mice. These two types of NPCs retained their regional identities after transplantation and exhibited different graft-host interconnection properties. NPCs with spinal cord regional identity but not those with forebrain identity resulted in functional improvement in SCI mice, especially in those with mild-to-moderate lesions. This study highlights the importance of the regional identity of human iPSC-derived NPCs used in cell therapy for SCI.

Variants in saposin D domain of prosaposin gene linked to Parkinson's disease

Recently, the genetic variability in lysosomal storage disorders has been implicated in the pathogenesis of Parkinson's disease. Here, we found that variants in prosaposin (PSAP), a rare causative gene of various types of lysosomal storage disorders, are linked to Parkinson's disease. Genetic mutation screening revealed three pathogenic mutations in the saposin D domain of PSAP from three families with autosomal dominant Parkinson's disease. Whole-exome sequencing revealed no other variants in previously identified Parkinson's disease-causing or lysosomal storage disorder-causing genes. A case-control association study found two variants in the intronic regions of the PSAP saposin D domain (rs4747203 and rs885828) in sporadic Parkinson's disease had significantly higher allele frequencies in a combined cohort of Japan and Taiwan. We found the abnormal accumulation of autophagic vacuoles, impaired autophagic flux, altered intracellular localization of prosaposin, and an aggregation of α-synuclein in patient-derived skin fibroblasts or induced pluripotent stem cell-derived dopaminergic neurons. In mice, a Psap saposin D mutation caused progressive motor decline and dopaminergic neurodegeneration. Our data provide novel genetic evidence for the involvement of the PSAP saposin D domain in Parkinson's disease.

Robust detection of undifferentiated iPSC among differentiated cells

Recent progress in human induced pluripotent stem cells (iPSC) technologies suggest that iPSC application in regenerative medicine is a closer reality. Numerous challenges prevent iPSC application in the development of numerous tissues and for the treatment of various diseases. A key concern in therapeutic applications is the safety of the cell products to be transplanted into patients. Here, we present novel method for detecting residual undifferentiated iPSCs amongst directed differentiated cells of all three germ lineages. Marker genes, which are expressed specifically and highly in undifferentiated iPSC, were selected from single cell RNA sequence data to perform robust and sensitive detection of residual undifferentiated cells in differentiated cell products. ESRG (Embryonic Stem Cell Related), CNMD (Chondromodulin), and SFRP2 (Secreted Frizzled Related Protein 2) were well-correlated with the actual amounts of residual undifferentiated cells and could be used to detect residual cells in a highly sensitive manner using qPCR. In addition, such markers could be used to detect residual undifferentiated cells from various differentiated cells, including hepatic cells and pancreatic cells for the endodermal lineage, endothelial cells and mesenchymal cells for the mesodermal lineage, and neural cells for the ectodermal lineage. Our method facilitates robust validation and could enhance the safety of the cell products through the exclusion of undifferentiated iPSC.

Neuronal Reprogramming for Tissue Repair and Neuroregeneration

Stem cell and cell reprogramming technology represent a rapidly growing field in regenerative medicine. A number of novel neural reprogramming methods have been established, using pluripotent stem cells (PSCs) or direct reprogramming, to efficiently derive specific neuronal cell types for therapeutic applications. Both in vitro and in vivo cellular reprogramming provide diverse therapeutic pathways for modeling neurological diseases and injury repair. In particular, the retina has emerged as a promising target for clinical application of regenerative medicine. Herein, we review the potential of neuronal reprogramming to develop regenerative strategy, with a particular focus on treating retinal degenerative diseases and discuss future directions and challenges in the field.

Identifying Therapeutic Agents for Amelioration of Mitochondrial Clearance Disorder in Neurons of Familial Parkinson Disease

Parkinson disease (PD) is a neurodegenerative disorder caused by the progressive loss of midbrain dopaminergic neurons, and mitochondrial dysfunction is involved in its pathogenesis. This study aimed to establish an imaging-based, semi-automatic, high-throughput system for the quantitative detection of disease-specific phenotypes in dopaminergic neurons from induced pluripotent stem cells (iPSCs) derived from patients with familial PD having Parkin or PINK1 mutations, which exhibit abnormal mitochondrial homeostasis. The proposed system recapitulates the deficiency of mitochondrial clearance, ROS accumulation, and increasing apoptosis in these familial PD-derived neurons. We screened 320 compounds for their ability to ameliorate multiple phenotypes and identified four candidate drugs. Some of these drugs improved the locomotion defects and reduced ATP production caused by PINK1 inactivation in Drosophila and were effective for idiopathic PD-derived neurons with impaired mitochondrial clearance. Our findings suggest that the proposed high-throughput system has potential for identifying effective drugs for familial and idiopathic PD.

miRNA-Based Rapid Differentiation of Purified Neurons from hPSCs Advancestowards Quick Screening for Neuronal Disease Phenotypes In Vitro

Obtaining differentiated cells with high physiological functions by an efficient, but simple and rapid differentiation method is crucial for modeling neuronal diseases in vitro using human pluripotent stem cells (hPSCs). Currently, methods involving the transient expression of one or a couple of transcription factors have been established as techniques for inducing neuronal differentiation in a rapid, single step. It has also been reported that microRNAs can function as reprogramming effectors for directly reprogramming human dermal fibroblasts to neurons. In this study, we tested the effect of adding neuronal microRNAs, miRNA-9/9*, and miR-124 (miR-9/9*-124), for the neuronal induction method of hPSCs using Tet-On-driven expression of the Neurogenin2 gene (Ngn2), a proneural factor. While it has been established that Ngn2 can facilitate differentiation from pluripotent stem cells into neurons with high purity due to its neurogenic effect, a long or indefinite time is required for neuronal maturation with Ngn2 misexpression alone. With the present method, the cells maintained a high neuronal differentiation rate while exhibiting increased gene expression of neuronal maturation markers, spontaneous calcium oscillation, and high electrical activity with network bursts as assessed by a multipoint electrode system. Moreover, when applying this method to iPSCs from Alzheimer's disease (AD) patients with presenilin-1 (PS1) or presenilin-2 (PS2) mutations, cellular phenotypes such as increased amount of extracellular secretion of amyloid β42, abnormal oxygen consumption, and increased reactive oxygen species in the cells were observed in a shorter culture period than those previously reported. Therefore, it is strongly anticipated that the induction method combining Ngn2 and miR-9/9*-124 will enable more rapid and simple screening for various types of neuronal disease phenotypes and promote drug discovery.

SOX21 Ensures Rostral Forebrain Identity by Suppression of WNT8B during Neural Regionalization of Human Embryonic Stem Cells

The generation of brain region-specific progenitors from human embryonic stem cells (hESCs) is critical for their application. However, transcriptional regulation of neural regionalization in humans is poorly understood. Here, we applied a rostrocaudal patterning system from hESCs to dissect global transcriptional networks controlling early neural regionalization. We found that SOX21 is required for rostral forebrain fate specification. SOX21 knockout led to activation of Wnt signaling, resulting in caudalization of regional identity of rostral forebrain neural progenitor cells. Moreover, we identified WNT8B as a SOX21 direct target. Deletion of WNT8B or inhibition of Wnt signaling in SOX21 knockout neural progenitor cells restored rostral forebrain identity. Furthermore, SOX21 interacted with β-catenin, interfering with the binding of TCF4/β-catenin complex to the WNT8B enhancer. Collectively, these results unveil the unknown role of SOX21 and shed light on how a transcriptional factor modulates early neural regionalization through crosstalk with a key component of Wnt signaling.

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The transcriptomic analysis of rostrocaudal patterning of hESC-derived NPCs

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SOX21 KO leads to caudalized regional identity in rostral forebrain progenitors

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SOX21 represses Wnt signaling to ensure the rostral forebrain identity

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WNT8B is a major downstream target of SOX21

In Vitro Modeling of the Bipolar Disorder and Schizophrenia Using Patient-Derived Induced Pluripotent Stem Cells with Copy Number Variations of PCDH15 and RELN

Bipolar disorder (BP) and schizophrenia (SCZ) are major psychiatric disorders, but the molecular mechanisms underlying the complicated pathologies of these disorders remain unclear. It is difficult to establish adequate in vitro models for pathological analysis because of the heterogeneity of these disorders. In the present study, to recapitulate the pathologies of these disorders in vitro, we established in vitro models by differentiating mature neurons from human induced pluripotent stem cells (hiPSCs) derived from BP and SCZ patient with contributive copy number variations, as follows: two BP patients with PCDH15 deletion and one SCZ patient with RELN deletion. Glutamatergic neurons and GABAergic neurons were induced from hiPSCs under optimized conditions. Both types of induced neurons from both hiPSCs exhibited similar phenotypes of MAP2 (microtubule-associated protein 2)-positive dendrite shortening and decreasing synapse numbers. Additionally, we analyzed isogenic PCDH15- or RELN-deleted cells. The dendrite and synapse phenotypes of isogenic neurons were partially similar to those of patient-derived neurons. These results suggest that the observed phenotypes are general phenotypes of psychiatric disorders, and our in vitro models using hiPSC-based technology may be suitable for analysis of the pathologies of psychiatric disorders.

A combinational treatment of carotenoids decreases Aβ secretion in human neurons via β-secretase inhibition

Alzheimer's disease (AD) is the most common cause of dementia and is characterized neuropathologically by the presence of amyloid plaques and neurofibrillary tangles. Amyloid-β (Aβ) peptides, major components of amyloid plaques and crucial pathogenic molecules in terms of the amyloid hypothesis, are derived from successive proteolytic processing of amyloid-β precursor protein (APP). In this study, we established a human neuronal culture system using induced pluripotent stem cells (iPSCs) to evaluate the possible effects of natural compounds on the amyloid phenotype. Unexpectedly, we found that combinational treatment of carotenoids, but not docosahexaenoic acid, significantly decreased Aβ secretion from iPSC-derived human cortical neurons. Importantly, the effects of the carotenoids resulted from specific inhibition of BACE1 activity and not from expression changes in APP or BACE1. Therefore, these results indicate a novel beneficial function of carotenoids in the anti-amyloidogenic processing of APP. Collectively, this study will shed light on neuronal protection by a novel mechanism during the pathogenesis of AD.

Evaluating the efficacy of small molecules for neural differentiation of common marmoset ESCs and iPSCs

The common marmoset (marmoset; Callithrix jacchus) harbors various desired features as a non-human primate (NHP) model for neuroscience research. Recently, efforts have been made to induce neural cells in vitro from marmoset pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), which are characterized by their capacity to differentiate into all cell types from the three germ layers. Successful generation of marmoset neural cells is not only invaluable for understanding neural development and for modeling neurodegenerative and psychiatric disorders, but is also necessary for the phenotypic screening of genetically-modified marmosets. However, differences in the differentiation propensity among PSC lines hamper the applicability and the reproducibility of differentiation methods. To overcome this limitation, we evaluated the efficacy of small molecules for neural differentiation of marmoset ESCs (cjESCs) and iPSCs using multiple differentiation methods. By immunochemical and transcriptomic analyses, we confirmed that our methods using the small molecules are efficient for various differentiation protocols by either enhancing the yield of a mixture of neural cells including both neurons and glial cells, or a pure population of neurons. Collectively, our findings optimized in vitro neural differentiation methods for marmoset PSCs, which would ultimately help enhance the utility of the animal model in neuroscience.

Induced pluripotent stem cells in multiple system atrophy: recent developments and scientific challenges

Multiple system atrophy (MSA) is a rare and fatal neurodegenerative disease, with no known genetic cause to date. Oligodendroglial α-synuclein accumulation, neuroinflammation, and early myelin dysfunction are hallmark features of the disease and have been modeled in part in various preclinical models of MSA, yet the pathophysiology of MSA remains elusive. Here, we review the role and scientific challenges of induced pluripotent stem cells in the detection of novel biomarkers and druggable targets in MSA.