Constructing and deconstructing stem cell models of neurological disease

Exploiting urine-derived induced pluripotent stem cells for advancing precision medicine in cell therapy, disease modeling, and drug testing

The field of regenerative medicine has witnessed remarkable advancements with the emergence of induced pluripotent stem cells (iPSCs) derived from a variety of sources. Among these, urine-derived induced pluripotent stem cells (u-iPSCs) have garnered substantial attention due to their non-invasive and patient-friendly acquisition method. This review manuscript delves into the potential and application of u-iPSCs in advancing precision medicine, particularly in the realms of drug testing, disease modeling, and cell therapy. U-iPSCs are generated through the reprogramming of somatic cells found in urine samples, offering a unique and renewable source of patient-specific pluripotent cells. Their utility in drug testing has revolutionized the pharmaceutical industry by providing personalized platforms for drug screening, toxicity assessment, and efficacy evaluation. The availability of u-iPSCs with diverse genetic backgrounds facilitates the development of tailored therapeutic approaches, minimizing adverse effects and optimizing treatment outcomes. Furthermore, u-iPSCs have demonstrated remarkable efficacy in disease modeling, allowing researchers to recapitulate patient-specific pathologies in vitro. This not only enhances our understanding of disease mechanisms but also serves as a valuable tool for drug discovery and development. In addition, u-iPSC-based disease models offer a platform for studying rare and genetically complex diseases, often underserved by traditional research methods. The versatility of u-iPSCs extends to cell therapy applications, where they hold immense promise for regenerative medicine. Their potential to differentiate into various cell types, including neurons, cardiomyocytes, and hepatocytes, enables the development of patient-specific cell replacement therapies. This personalized approach can revolutionize the treatment of degenerative diseases, organ failure, and tissue damage by minimizing immune rejection and optimizing therapeutic outcomes. However, several challenges and considerations, such as standardization of reprogramming protocols, genomic stability, and scalability, must be addressed to fully exploit u-iPSCs' potential in precision medicine. In conclusion, this review underscores the transformative impact of u-iPSCs on advancing precision medicine and highlights the future prospects and challenges in harnessing this innovative technology for improved healthcare outcomes.

Efficient generation of lower induced motor neurons by coupling Ngn2 expression with developmental cues

Human pluripotent stem cells (hPSCs) are a powerful tool for disease modeling of hard-to-access tissues (such as the brain). Current protocols either direct neuronal differentiation with small molecules or use transcription-factor-mediated programming. In this study, we couple overexpression of transcription factor Neurogenin2 (Ngn2) with small molecule patterning to differentiate hPSCs into lower induced motor neurons (liMoNes/liMNs). This approach induces canonical MN markers including MN-specific Hb9/MNX1 in more than 95% of cells. liMNs resemble bona fide hPSC-derived MN, exhibit spontaneous electrical activity, express synaptic markers, and can contact muscle cells in vitro. Pooled, multiplexed single-cell RNA sequencing on 50 hPSC lines reveals reproducible populations of distinct subtypes of cervical and brachial MNs that resemble their in vivo, embryonic counterparts. Combining small molecule patterning with Ngn2 overexpression facilitates high-yield, reproducible production of disease-relevant MN subtypes, which is fundamental in propelling our knowledge of MN biology and its disruption in disease.

Oxidative Stress in Tauopathies: From Cause to Therapy

Oxidative stress (OS) is the result of an imbalance between the production of reactive oxygen species (ROS) and the antioxidant capacity of cells. Due to its high oxygen demand, the human brain is highly susceptible to OS and, thus, it is not a surprise that OS has emerged as an essential component of the pathophysiology of several neurodegenerative diseases, including tauopathies. Tauopathies are a heterogeneous group of age-related neurodegenerative disorders characterized by the deposition of abnormal tau protein in the affected neurons. With the worldwide population aging, the prevalence of tauopathies is increasing, but effective therapies have not yet been developed. Since OS seems to play a key role in tauopathies, it has been proposed that the use of antioxidants might be beneficial for tau-related neurodegenerative diseases. Although antioxidant therapies looked promising in preclinical studies performed in cellular and animal models, the antioxidant clinical trials performed in tauopathy patients have been disappointing. To develop effective antioxidant therapies, the molecular mechanisms underlying OS in tauopathies should be completely understood. Here, we review the link between OS and tauopathies, emphasizing the causes of OS in these diseases and the role of OS in tau pathogenesis. We also summarize the antioxidant therapies proposed as a potential treatment for tauopathies and discuss why they have not been completely translated to clinical trials. This review aims to provide an integrated perspective of the role of OS and antioxidant therapies in tauopathies. In doing so, we hope to enable a more comprehensive understanding of OS in tauopathies that will positively impact future studies.

Peripheral inflammation and neurodegeneration; a potential for therapeutic intervention in Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS)

Background

Degeneration of the central nervous system (CNS), also known as neurodegeneration, describes an age-associated progressive loss of the structure and function of neuronal materials, leading to functional and mental impairments.

Main body

Neuroinflammation contributes to the continuous worsening of neurodegenerative states which are characterised by functional and mental impairments due to the progressive loss of the structure and function of neuronal materials. Some of the most common neurodegenerative diseases include Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS). Whilst neuroinflammation is a key contributor to the progression of such disease states, it is not the single cause as there are multiple factors which contribute. Theoretically, non-steroidal anti-inflammatory drugs (NSAIDs) have potential to target neuroinflammation to reduce the severity of disease states. Whilst some animal models investigating the effects of NSAIDs on the risk of neurodegenerative diseases have shown a beneficial effect, this is not always the case and a large number of clinical trials have not shown the same finding.

Conclusion

Further investigation using more advanced research methods is required to better understand neuroinflammatory pathways and understand if there is still a potential window for NSAID efficacy.

Neurodegenerative brain models vs. cell replacement or restoration therapy: A review on promises and pitfalls

Disease models have proven useful tools for gaining deeper mechanistic insights into neurodegenerative diseases. In this context, stem cell technology is effective, especially induced pluripotent stem cell (iPSC)-derived brain organoids and cell replacement/restoration which can be used for personalized medicine, allowing physicians to test the efficacy of drugs in vitro before delivering them to patients, enabling more precise and personalized treatment. Nonetheless, it offers the potential to minimize (or even eliminate) the use of animals, provides important clues for disease processes, and accelerates therapeutic strategies. Perhaps in the not-too-distant future, organoid models of the human brain will be able to link blood-brain barrier cultures with other liver cultures, simulating blood flow across organs and as a method of testing medicines, giving crucial pharmacokinetics and pharmacodynamics data. Simultaneously, stem cell interventions for cell replacements or restoration therapy would enable us to realize efficacious and realistic therapeutic options for Neurodegenerative diseases.

Cellular functions of the protein kinase ATM and their relevance to human disease

The protein kinase ataxia telangiectasia mutated (ATM) is a master regulator of double-strand DNA break (DSB) signalling and stress responses. For three decades, ATM has been investigated extensively to elucidate its roles in the DNA damage response (DDR) and in the pathogenesis of ataxia telangiectasia (A-T), a human neurodegenerative disease caused by loss of ATM. Although hundreds of proteins have been identified as ATM phosphorylation targets and many important roles for this kinase have been identified, it is still unclear how ATM deficiency leads to the early-onset cerebellar degeneration that is common in all individuals with A-T. Recent studies suggest the existence of links between ATM deficiency and other cerebellum-specific neurological disorders, as well as the existence of broader similarities with more common neurodegenerative disorders. In this Review, we discuss recent structural insights into ATM regulation, and possible aetiologies of A-T phenotypes, including reactive oxygen species, mitochondrial dysfunction, alterations in transcription, R-loop metabolism and alternative splicing, defects in cellular proteostasis and metabolism, and potential pathogenic roles for hyper-poly(ADP-ribosyl)ation.

Nanomedicine against Alzheimer's and Parkinson's Disease

Alzheimer's and Parkinson's are the two most rampant neurodegenerative disorders worldwide. Existing treatments have a limited effect on the pathophysiology but are unable to fully arrest the progression of the disease. This is due to the inability of these therapeutic molecules to efficiently cross the blood-brain barrier. We discuss how nanotechnology has enabled researchers to develop novel and efficient nano-therapeutics against these diseases. The development of nanotized drug delivery systems has permitted an efficient, site-targeted, and controlled release of drugs in the brain, thereby presenting a revolutionary therapeutic approach. Nanoparticles are also being thoroughly studied and exploited for their role in the efficient and precise diagnosis of neurodegenerative conditions. We summarize the role of different nano-carriers and RNAi-conjugated nanoparticle-based therapeutics for their efficacy in pre-clinical studies. We also discuss the challenges underlying the use of nanomedicine with a focus on their route of administration, concentration, metabolism, and any toxic effects for successful therapeutics in these diseases.

Growing Glia: Cultivating Human Stem Cell Models of Gliogenesis in Health and Disease

Glia are present in all organisms with a central nervous system but considerably differ in their diversity, functions, and numbers. Coordinated efforts across many model systems have contributed to our understanding of glial-glial and neuron-glial interactions during nervous system development and disease, but human glia exhibit prominent species-specific attributes. Limited access to primary samples at critical developmental timepoints constrains our ability to assess glial contributions in human tissues. This challenge has been addressed throughout the past decade via advancements in human stem cell differentiation protocols that now offer the ability to model human astrocytes, oligodendrocytes, and microglia. Here, we review the use of novel 2D cell culture protocols, 3D organoid models, and bioengineered systems derived from human stem cells to study human glial development and the role of glia in neurodevelopmental disorders.

Neural Differentiation of Mouse Embryonic Stem Cells-An in vitro Approach to Profile DNA Methylation of Reprogramming Factor Sox2-SRR2

Sox2 is one of the core transcription factors maintaining the embryonic stem cells (ES) pluripotency and, also indispensable for cellular reprogramming. However, limited data is available about the DNA methylation of pluripotency genes during lineage-specific differentiations. This study investigated the DNA methylation of Sox2 regulatory region 2 (SRR2) during directed differentiation of mouse ES into neural lineage. ES cells were first grown to form embryoid bodies in suspension which were then dissociated, and cultured in defined medium to promote neural differentiation. Typical neuronal morphology together with the up-regulation of Pax6, neuroepithelial stem cell intermediate filament and β-tubulin III and, down-regulation of pluripotency genes Oct4, Nanog and Sox2 showed the existence of neural phenotype in cells undergoing differentiation. Three CpGs in the core enhancer region of neural-specific SRR2 were individually investigated by direct DNA sequencing post-bisulfite treatment and, found to be unmethylated in differentiated cells at time-points chosen for analysis. This analysis does not limit the possibility of methylation at other CpG sites than those profiled here and/or transient methylation. Hence, similar analyses exploring the DNA methylation at other regions of the Sox2 gene could unravel the onset and transitions of epigenetic signatures influencing the outcome of differentiation pathways and neural development. The data presented here shows that in vitro neural differentiation of embryonic stem cells can be employed to study and characterize molecular regulatory mechanisms governing neurogenesis by applying diverse pharmacological and toxicological agents.

Genome editing of hPSCs: Recent progress in hPSC-based disease modeling for understanding disease mechanisms

Generation of proper models for studying human genetic diseases has been hindered until recently by the scarcity of primary cell samples from genetic disease patients and inefficient genetic modification tools. However, recent advances in clustered, regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology and human induced pluripotent stem cells (hiPSCs) have provided an opportunity to explore the function of pathogenic variants and obtain gene-corrected cells for autologous cell therapy. In this chapter, we address recent applications of CRISPR/Cas9 to hiPSCs in genetic diseases, including neurodegenerative, cardiovascular, and rare diseases.

Generation of Functional Human 3D Cortico-Motor Assembloids

Neurons in the cerebral cortex connect through descending pathways to hindbrain and spinal cord to activate muscle and generate movement. Although components of this pathway have been previously generated and studied in vitro, the assembly of this multi-synaptic circuit has not yet been achieved with human cells. Here, we derive organoids resembling the cerebral cortex or the hindbrain/spinal cord and assemble them with human skeletal muscle spheroids to generate 3D cortico-motor assembloids. Using rabies tracing, calcium imaging, and patch-clamp recordings, we show that corticofugal neurons project and connect with spinal spheroids, while spinal-derived motor neurons connect with muscle. Glutamate uncaging or optogenetic stimulation of cortical spheroids triggers robust contraction of 3D muscle, and assembloids are morphologically and functionally intact for up to 10 weeks post-fusion. Together, this system highlights the remarkable self-assembly capacity of 3D cultures to form functional circuits that could be used to understand development and disease.

CRISPR-based functional genomics for neurological disease

Neurodegenerative, neurodevelopmental and neuropsychiatric disorders are among the greatest public health challenges, as many lack disease-modifying treatments. A major reason for the absence of effective therapies is our limited understanding of the causative molecular and cellular mechanisms. Genome-wide association studies are providing a growing catalogue of disease-associated genetic variants, and the next challenge is to elucidate how these variants cause disease and to translate this understanding into therapies. This Review describes how new CRISPR-based functional genomics approaches can uncover disease mechanisms and therapeutic targets in neurological diseases. The bacterial CRISPR system can be used in experimental disease models to edit genomes and to control gene expression levels through CRISPR interference (CRISPRi) and CRISPR activation (CRISPRa). These genetic perturbations can be implemented in massively parallel genetic screens to evaluate the functional consequences for human cells. CRISPR screens are particularly powerful in combination with induced pluripotent stem cell technology, which enables the derivation of differentiated cell types, such as neurons and glia, and brain organoids from cells obtained from patients. Modelling of disease-associated changes in gene expression via CRISPRi and CRISPRa can pinpoint causal changes. In addition, genetic modifier screens can be used to elucidate disease mechanisms and causal determinants of cell type-selective vulnerability and to identify therapeutic targets.

The frontiers of sequencing in undiagnosed neurodevelopmental diseases

Characterized by impairments in brain and central nervous system development, neurodevelopmental diseases causes are highly heterogeneous. Although many of these diseases are individually rare, collectively more than 3% of the children are reported to be affected with a type of neurodevelopmental diseases worldwide, and many remain undiagnosed even with current genomic tools. Identifying the genetic causes of these diseases allows better clinical management and expands our understanding of human neurodevelopment. Over the past decade, expansion of genomic sequencing and some methodologic improvements have improved molecular diagnostic yield as well as the discovery of novel genetic causes for wide spectrum of neurodevelopmental diseases. Here we review the current diagnostic workflow and propose ways of improving the diagnostic yield.

Deconstructing and reconstructing the human brain with regionally specified brain organoids

Brain organoids, three-dimensional neural cultures recapitulating the spatiotemporal organization and function of the brain in a dish, offer unique opportunities for investigating the human brain development and diseases. To model distinct parts of the brain, various region-specific human brain organoids have been developed. In this article, we review current approaches to produce human region-specific brain organoids, developed through the endeavor of many researchers. We highlight the applications of human region-specific brain organoids, especially in reconstructing regional interactions in the brain through organoid fusion. We also outline the existing challenges to drive forward further the brain organoid technology and its applications for future studies.

Modeling Brain Disorders Using Induced Pluripotent Stem Cells

Brain disorders, from neurodegenerative to psychiatric disorders, are among the most challenging conditions to study because of the intricate nature of the human brain and the limitations of existing model systems in recapitulating all these intricacies. However, innovations in stem cell technologies now allow us to reprogram patient somatic cells to induced pluripotent stem cells (iPSCs), which can then be differentiated to disease-relevant neural and glial cells. iPSCs are a valuable tool to model brain disorders, as they can be derived from patients with known symptom histories, genetics, and drug-response profiles. Here, we discuss the premise and validity of the iPSC-based in vitro model system and highlight key findings from the most commonly studied neurodegenerative and psychiatric disorders.

Deciphering the Proteome Dynamics during Development of Neurons Derived from Induced Pluripotent Stem Cells

Neuronal development is a complex multistep process that shapes neurons by progressing though several typical stages, including axon outgrowth, dendrite formation, and synaptogenesis. Knowledge of the mechanisms of neuronal development is mostly derived from the study of animal models. Advances in stem cell technology now enable us to generate neurons from human induced pluripotent stem cells (iPSCs). Here we provide a mass spectrometry-based quantitative proteomic signature of human iPSC-derived neurons, i.e., iPSC-derived induced glutamatergic neurons and iPSC-derived motor neurons, throughout neuronal differentiation. Tandem mass tag 10-plex labeling was carried out to perform proteomic profiling of cells at different time points. Our analysis reveals significant expression changes (FDR < 0.001) of several key proteins during the differentiation process, e.g., proteins involved in the Wnt and Notch signaling pathways. Overall, our data provide a rich resource of information on protein expression during human iPSC neuron differentiation.

Defects in Axonal Transport in Inherited Neuropathies

Axonal transport is a highly complex process essential for sustaining proper neuronal functioning. Disturbances can result in an altered neuronal homeostasis, aggregation of cargoes, and ultimately a dying-back degeneration of neurons. The impact of dysfunction in axonal transport is shown by genetic defects in key proteins causing a broad spectrum of neurodegenerative diseases, including inherited peripheral neuropathies. In this review, we provide an overview of the cytoskeletal components, molecular motors and adaptor proteins involved in axonal transport mechanisms and their implication in neuronal functioning. In addition, we discuss the involvement of axonal transport dysfunction in neurodegenerative diseases with a particular focus on inherited peripheral neuropathies. Lastly, we address some recent scientific advances most notably in therapeutic strategies employed in the area of axonal transport, patient-derived iPSC models, in vivo animal models, antisense-oligonucleotide treatments, and novel chemical compounds.

In vitro models of HIV-1 infection of the Central Nervous System

Neurocognitive disorders associated with HIV-1 infection affect more than half of persons living with HIV (PLWH) under retroviral therapy. Understanding the molecular mechanisms and the complex cellular network communication underlying neurological dysfunction is critical for the development of an effective therapy. As with other neurological disorders, challenges to studying HIV infection of the brain include limited access to clinical samples and proper reproducibility of the complexity of brain networks in cellular and animal models. This review focuses on cellular models used to investigate various aspects of neurological dysfunction associated with HIV infection.

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.

Modern approaches for modelling dystonia and Huntington's disease in vitro and in vivo

Dystonia associated with Huntington's disease, Parkinson's disease or other neurodegenerative diseases substantially affects patients' quality of life and is a major health problem worldwide. The above-mentioned diseases are characterized by neurodegeneration accompanied by motor and cognitive impairment and often have complex aetiology. A frequent feature of these conditions is the abnormal accumulation of protein aggregates within specific neuronal populations in the affected brain regions. Familial neurodegenerative diseases are associated with a number of genetic mutations. Identification of these mutations allowed creation of modern model systems for studying neurodegeneration, either in cultured cells or in model animals. Animal models, especially mouse models, have contributed considerably to improving our understanding of the pathophysiology of neurodegenerative diseases. These models have allowed study of the pathogenic mechanisms and development of new disease-modifying strategies and therapeutic approaches. However, due to the complex nature of these pathologies and the irreversible damage that they cause to the neural tissue, effective therapies against neurodegeneration remain to be elaborated. In this review, we provide an overview of cellular and animal models developed for studying neurodegenerative diseases, including Huntington's disease and dystonia of different origins.

ALS-implicated protein TDP-43 sustains levels of STMN2, a mediator of motor neuron growth and repair

The findings that amyotrophic lateral sclerosis (ALS) patients almost universally display pathological mislocalization of the RNA-binding protein TDP-43 and that mutations in its gene cause familial ALS have nominated altered RNA metabolism as a disease mechanism. However, the RNAs regulated by TDP-43 in motor neurons and their connection to neuropathy remain to be identified. Here we report transcripts whose abundances in human motor neurons are sensitive to TDP-43 depletion. Notably, expression of STMN2, which encodes a microtubule regulator, declined after TDP-43 knockdown and TDP-43 mislocalization as well as in patient-specific motor neurons and postmortem patient spinal cord. STMN2 loss upon reduced TDP-43 function was due to altered splicing, which is functionally important, as we show STMN2 is necessary for normal axonal outgrowth and regeneration. Notably, post-translational stabilization of STMN2 rescued neurite outgrowth and axon regeneration deficits induced by TDP-43 depletion. We propose that restoring STMN2 expression warrants examination as a therapeutic strategy for ALS.

Past, Present, and Future of Neuronal Models In Vitro

Over the past century, robust methods were developed that enable the isolation, culture, and dynamic observation of mammalian neuronal networks in vitro. But even if neuronal culture cannot yet fully recapitulate the normal brain, the knowledge that has been acquired from these surrogate in vitro models is invaluable. Indeed, neuronal culture has continued to propel basic neuroscience research, proving that in vitro systems have legitimacy when it comes to studying either the healthy or diseased human brain. Furthermore, scientific advancement typically parallels technical refinements in the field. A pertinent example is that a collective drive in the field of neuroscience to better understand the development, organization, and emergent properties of neuronal networks is being facilitated by progressive advances in micro-electrode array (MEA) technology. In this chapter, we briefly review the emergence of neuronal cell culture as a technique, the current trends in human stem cell-based modeling, and the technologies used to monitor neuronal communication. We conclude by highlighting future prospects that are evolving specifically out of the combination of human neuronal models and MEA technology.

Comparative genomic analysis of embryonic, lineage-converted and stem cell-derived motor neurons

Advances in stem cell science allow the production of different cell types in vitro either through the recapitulation of developmental processes, often termed 'directed differentiation', or the forced expression of lineage-specific transcription factors. Although cells produced by both approaches are increasingly used in translational applications, their quantitative similarity to their primary counterparts remains largely unresolved. To investigate the similarity between in vitro-derived and primary cell types, we harvested and purified mouse spinal motor neurons and compared them with motor neurons produced by transcription factor-mediated lineage conversion of fibroblasts or directed differentiation of pluripotent stem cells. To enable unbiased analysis of these motor neuron types and their cells of origin, we then subjected them to whole transcriptome and DNA methylome analysis by RNA sequencing (RNA-seq) and reduced representation bisulfite sequencing (RRBS). Despite major differences in methodology, lineage conversion and directed differentiation both produce cells that closely approximate the primary motor neuron state. However, we identify differences in Fas signaling, the Hox code and synaptic gene expression between lineage-converted and directed differentiation motor neurons that affect their utility in translational studies.

Identification of protein kinase inhibitors to reprogram breast cancer cells

Direct reversion of cancers into normal-like tissues is an ideal strategy for cancer treatment. Recent reports have showed that defined transcription factors can induce reprogramming of cancer cells into pluripotent stem cells, supporting this notion. Here, we have developed a reprogramming method that uses a conceptually unique strategy for breast cancer cell treatment. We have screened a kinase inhibitor library and found that Rho-associated protein kinase (ROCK) and mammalian target of rapamycin (mTOR) kinase inhibitors can substitute for all transcription factors to be sufficient to reprogram breast cancer cells into progenitor cells. Furthermore, ROCK–mTOR inhibitors could reprogram breast cancer cells to another terminal lineage-adipogenic cells. Genome-wide transcriptional analysis shows that the induced fat-like cells have a profile different from breast cancer cells and similar to that of normal adipocytes. In vitro and in vivo tumorigenesis assays have shown that induced fat-like cells lose proliferation and tumorigenicity. Moreover, reprogramming treatment with ROCK–mTOR inhibitors prevents breast cancer local recurrence in mice. Currently, ROCK–mTOR inhibitors are already used as antitumor drugs in patients, thus, this reprogramming strategy has significant potential to move rapidly toward clinical trials for breast cancer treatment.

Reprogramming glioblastoma multiforme cells into neurons by protein kinase inhibitors

Background

Reprogramming of cancers into normal-like tissues is an innovative strategy for cancer treatment. Recent reports demonstrate that defined factors can reprogram cancer cells into pluripotent stem cells. Glioblastoma multiforme (GBM) is the most common and aggressive malignant brain tumor in humans. Despite multimodal therapy, the outcome for patients with GBM is still poor. Therefore, developing novel therapeutic strategy is a critical requirement.

Methods

We have developed a novel reprogramming method that uses a conceptually unique strategy for GBM treatment. We screened a kinase inhibitor library to find which candidate inhibitors under reprogramming condition can reprogram GBM cells into neurons. The induced neurons are identified whether functional and loss of tumorigenicity.

Results

We have found that mTOR and ROCK kinase inhibitors are sufficient to reprogram GBM cells into neural-like cells and “normal” neurons. The induced neurons expressed neuron-specific proteins, generated action potentials and neurotransmitter receptor-mediated currents. Genome-wide transcriptional analysis showed that the induced neurons had a profile different from GBM cells and were similar to that of control neurons induced by established methods. In vitro and in vivo tumorigenesis assays showed that induced neurons lost their proliferation ability and tumorigenicity. Moreover, reprogramming treatment with ROCK-mTOR inhibitors prevented GBM local recurrence in mice.

Conclusion

This study indicates that ROCK and mTOR inhibitors-based reprogramming treatment prevents GBM local recurrence. Currently ROCK-mTOR inhibitors are used as anti-tumor drugs in patients, so this reprogramming strategy has significant potential to move rapidly toward clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0857-5) contains supplementary material, which is available to authorized users.

Cells of Matter-In Vitro Models for Myotonic Dystrophy

Myotonic dystrophy type 1 (DM1 also known as Steinert disease) is a multisystemic disorder mainly characterized by myotonia, progressive muscle weakness and wasting, cognitive impairments, and cardiac defects. This autosomal dominant disease is caused by the expression of nuclear retained RNAs containing pathologic expanded CUG repeats that alter the function of RNA-binding proteins in a tissue-specific manner, leading ultimately to neuromuscular dysfunction and clinical symptoms. Although considerable knowledge has been gathered on myotonic dystrophy since its first description, the development of novel relevant disease models remains of high importance to investigate pathophysiologic mechanisms and to assess new therapeutic approaches. In addition to animal models, in vitro cell cultures provide a unique resource for both fundamental and translational research. This review discusses how cellular models broke ground to decipher molecular basis of DM1 and describes currently available cell models, ranging from exogenous expression of the CTG tracts to variable patients' derived cells.

All-Optical Electrophysiology for High-Throughput Functional Characterization of a Human iPSC-Derived Motor Neuron Model of ALS

Human induced pluripotent stem cell (iPSC)-derived neurons are an attractive substrate for modeling disease, yet the heterogeneity of these cultures presents a challenge for functional characterization by manual patch-clamp electrophysiology. Here, we describe an optimized all-optical electrophysiology, “Optopatch,” pipeline for high-throughput functional characterization of human iPSC-derived neuronal cultures. We demonstrate the method in a human iPSC-derived motor neuron (iPSC-MN) model of amyotrophic lateral sclerosis (ALS). In a comparison of iPSC-MNs with an ALS-causing mutation (SOD1 A4V) with their genome-corrected controls, the mutants showed elevated spike rates under weak or no stimulus and greater likelihood of entering depolarization block under strong optogenetic stimulus. We compared these results with numerical simulations of simple conductance-based neuronal models and with literature results in this and other iPSC-based models of ALS. Our data and simulations suggest that deficits in slowly activating potassium channels may underlie the changes in electrophysiology in the SOD1 A4V mutation.

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All-optical electrophysiology enables high-throughput assays in hiPSC-derived neurons

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Neurons derived from ALS patients fire differently from genome-corrected controls

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A deficit in the Kv7 potassium current can explain the difference in firing

Neural Stem Cell Dysfunction in Human Brain Disorders

Neural stem cells (NSCs) give rise to the entire nervous system. Animal models suggest that defects in NSC proliferation and differentiation contribute to several brain disorders (e.g., microcephaly, macrocephaly, autism, schizophrenia, and Huntington's disease). However, animal models of such diseases do not fully recapitulate all disease-related phenotypes because of substantial differences in brain development between rodents and humans. Therefore, additional human-based evidence is required to understand the mechanisms that are involved in the development of neurological diseases that result from human NSC (hNSC) dysfunction. Human-induced pluripotent stem cells provide a new model to investigate the contribution of hNSCs to various neurological pathologies. In this chapter, we review the role of hNSCs in both neurodevelopment- and neurodegeneration-related human brain pathologies, with an emphasis on recent evidence that has been obtained using embryonic stem cell- or induced pluripotent stem cell-derived hNSCs and progenitors.

Large-Scale Production of Mature Neurons from Human Pluripotent Stem Cells in a Three-Dimensional Suspension Culture System

Human pluripotent stem cells (hPSCs) offer a renewable source of cells that can be expanded indefinitely and differentiated into virtually any type of cell in the human body, including neurons. This opens up unprecedented possibilities to study neuronal cell and developmental biology and cellular pathology of the nervous system, provides a platform for the screening of chemical libraries that affect these processes, and offers a potential source of transplantable cells for regenerative approaches to neurological disease. However, defining protocols that permit a large number and high yield of neurons has proved difficult. We present differentiation protocols for the generation of distinct subtypes of neurons in a highly reproducible manner, with minimal experiment-to-experiment variation. These neurons form synapses with neighboring cells, exhibit spontaneous electrical activity, and respond appropriately to depolarization. hPSC-derived neurons exhibit a high degree of maturation and survive in culture for up to 4-5 months, even without astrocyte feeder layers.

All-Optical Electrophysiology for Disease Modeling and Pharmacological Characterization of Neurons

A key challenge for establishing a phenotypic screen for neuronal excitability is measurement of membrane potential changes with high throughput and accuracy. Most approaches for probing excitability rely on low-throughput, invasive methods or lack cell-specific information. These limitations stimulated the development of novel strategies for characterizing the electrical properties of cultured neurons. Among these was the development of optogenetic technologies (Optopatch) that allow for stimulation and recording of membrane voltage signals from cultured neurons with single-cell sensitivity and millisecond temporal resolution. Neuronal activity is elicited using blue light activation of the channelrhodopsin variant 'CheRiff'. Action potentials and synaptic signals are measured with 'QuasAr', a rapid and sensitive voltage-indicating protein with near-infrared fluorescence that scales proportionately with transmembrane potential. This integrated technology of optical stimulation and recording of electrical signals enables investigation of neuronal electrical function with unprecedented scale and precision. © 2017 by John Wiley & Sons, Inc.

Neurodegenerative disease: models, mechanisms, and a new hope

Neurodegeneration is a feature of many debilitating, incurable diseases that are rapidly rising in prevalence, such as Parkinson's disease. There is an urgent need to develop new and more effective therapeutic strategies to combat these devastating diseases. Models - from cell-based systems, to unicellular organisms, to complex animals - have proven to be a useful tool to help the research community shed light on the mechanisms underlying neurodegenerative diseases, and these advances have now begun to provide promising therapeutic avenues. In this themed issue of Disease Models & Mechanisms, a special collection of articles focused on neurodegenerative diseases is introduced. The collection includes original research articles that provide new insights into the complex pathophysiology of such diseases, revealing candidate biomarkers or therapeutic targets. Some of the articles describe a new disease model that enables deeper exploration of key mechanisms. We also present a series of reviews that highlight some of the recent translational advances made in studies of neurodegenerative diseases. In this Editorial, we summarize the articles featured in this collection, emphasizing the impact that model-based studies have made in this exciting area of research.

Human induced pluripotent stem cells for modelling neurodevelopmental disorders

We currently have a poor understanding of the pathogenesis of neurodevelopmental disorders, owing to the fact that postmortem and imaging studies can only measure the postnatal status quo and offer little insight into the processes that give rise to the observed outcomes. Human induced pluripotent stem cells (hiPSCs) should, in principle, prove powerful for elucidating the pathways that give rise to neurodevelopmental disorders. hiPSCs are embryonic-stem-cell-like cells that can be derived from somatic cells. They retain the unique genetic signature of the individual from whom they were derived, and thus enable researchers to recapitulate that individual's idiosyncratic neural development in a dish. In the case of individuals with disease, we can re-enact the disease-altered trajectory of brain development and examine how and why phenotypic and molecular abnormalities arise in these diseased brains. Here, we review hiPSC biology and possible experimental designs when using hiPSCs to model disease. We then discuss existing hiPSC models of neurodevelopmental disorders. Our hope is that, as some studies have already shown, hiPSCs will illuminate the pathophysiology of developmental disorders of the CNS and lead to therapeutic options for the millions that are affected by these conditions.

TBR1 regulates autism risk genes in the developing neocortex

Exome sequencing studies have identified multiple genes harboring de novo loss-of-function (LoF) variants in individuals with autism spectrum disorders (ASD), including TBR1, a master regulator of cortical development. We performed ChIP-seq for TBR1 during mouse cortical neurogenesis and show that TBR1-bound regions are enriched adjacent to ASD genes. ASD genes were also enriched among genes that are differentially expressed in Tbr1 knockouts, which together with the ChIP-seq data, suggests direct transcriptional regulation. Of the nine ASD genes examined, seven were misexpressed in the cortices of Tbr1 knockout mice, including six with increased expression in the deep cortical layers. ASD genes with adjacent cortical TBR1 ChIP-seq peaks also showed unusually low levels of LoF mutations in a reference human population and among Icelanders. We then leveraged TBR1 binding to identify an appealing subset of candidate ASD genes. Our findings highlight a TBR1-regulated network of ASD genes in the developing neocortex that are relatively intolerant to LoF mutations, indicating that these genes may play critical roles in normal cortical development.

[Neuronal cells derived from induced pluripotent stem cells to model motoneuron diseases]

Among motor neuron diseases, spinal muscular atrophy type 1 and amyotrophic lateral sclerosis are very aggressive diseases with no cure. With the breakthrough of human induced pluripotent stem cells, iPS, researchers have now at their disposal a powerful tool to generate human motor neurons in culture and study the pathological defects in patient cells. In this review, we will see which tools for the study of patients motoneurons were developed from iPS cells and the different cellular models that were generated. We will also see how these models were validated and current research to identify new therapeutic leads.

The Human Model: Changing Focus on Autism Research

The lack of live human brain cells for research has slowed progress toward understanding the mechanisms underlying autism spectrum disorders. A human model using reprogrammed patient somatic cells offers an attractive alternative, as it captures a patient's genome in relevant cell types. Despite the current limitations, the disease-in-a-dish approach allows for progressive time course analyses of target cells, offering a unique opportunity to investigate the cellular and molecular alterations before symptomatic onset. Understanding the current drawbacks of this model is essential for the correct data interpretation and extrapolation of conclusions applicable to the human brain. Innovative strategies for collecting biological material and clinical information from large patient cohorts are important for increasing the statistical power that will allow for the extraction of information from the noise resulting from the variability introduced by reprogramming and differentiation methods. Working with large patient cohorts is also important for understanding how brain cells derived from diverse human genetic backgrounds respond to specific drugs, creating the possibility of personalized medicine for autism spectrum disorders.

Induced Pluripotent Stem Cell Therapies for Cervical Spinal Cord Injury

Cervical-level injuries account for the majority of presented spinal cord injuries (SCIs) to date. Despite the increase in survival rates due to emergency medicine improvements, overall quality of life remains poor, with patients facing variable deficits in respiratory and motor function. Therapies aiming to ameliorate symptoms and restore function, even partially, are urgently needed. Current therapeutic avenues in SCI seek to increase regenerative capacities through trophic and immunomodulatory factors, provide scaffolding to bridge the lesion site and promote regeneration of native axons, and to replace SCI-lost neurons and glia via intraspinal transplantation. Induced pluripotent stem cells (iPSCs) are a clinically viable means to accomplish this; they have no major ethical barriers, sources can be patient-matched and collected using non-invasive methods. In addition, the patient’s own cells can be used to establish a starter population capable of producing multiple cell types. To date, there is only a limited pool of research examining iPSC-derived transplants in SCI—even less research that is specific to cervical injury. The purpose of the review herein is to explore both preclinical and clinical recent advances in iPSC therapies with a detailed focus on cervical spinal cord injury.

Quo vadis motor neuron disease?

Motor neuron disease (MND), also known as amyotrophic lateral sclerosis, is a relentlessly progressive neurodegenerative condition that is invariably fatal, usually within 3 to 5 years of diagnosis. The aetio-pathogenesis of MND remains unresolved and no effective treatments exist. The only Food and Drug Administration approved disease modifying therapy is riluzole, a glutamate antagonist, which prolongs survival by up to 3 mo. Current management is largely symptomatic/supportive. There is therefore a desperate and unmet clinical need for discovery of disease mechanisms to guide novel therapeutic strategy. In this review, we start by introducing the organizational anatomy of the motor system, before providing a clinical overview of its dysfunction specifically in MND. We then summarize insights gained from pathological, genetic and animal models and conclude by speculating on optimal strategies to drive the step change in discovery, which is so desperately needed in this arena.

Neural Conversion and Patterning of Human Pluripotent Stem Cells: A Developmental Perspective

Since the reprogramming of adult human terminally differentiated somatic cells into induced pluripotent stem cells (hiPSCs) became a reality in 2007, only eight years have passed. Yet over this relatively short period, myriad experiments have revolutionized previous stem cell dogmata. The tremendous promise of hiPSC technology for regenerative medicine has fuelled rising expectations from both the public and scientific communities alike. In order to effectively harness hiPSCs to uncover fundamental mechanisms of disease, it is imperative to first understand the developmental neurobiology underpinning their lineage restriction choices in order to predictably manipulate cell fate to desired derivatives. Significant progress in developmental biology provides an invaluable resource for rationalising directed differentiation of hiPSCs to cellular derivatives of the nervous system. In this paper we begin by reviewing core developmental concepts underlying neural induction in order to provide context for how such insights have guided reductionist in vitro models of neural conversion from hiPSCs. We then discuss early factors relevant in neural patterning, again drawing upon crucial knowledge gained from developmental neurobiological studies. We conclude by discussing open questions relating to these concepts and how their resolution might serve to strengthen the promise of pluripotent stem cells in regenerative medicine.

5-HT2 receptors mediate functional modulation of GABAa receptors and inhibitory synaptic transmissions in human iPS-derived neurons

Neural progenitors differentiated from induced pluripotent stem cells (iPS) hold potentials for treating neurological diseases. Serotonin has potent effects on neuronal functions through multiple receptors, underlying a variety of neural disorders. Glutamate and GABA receptors have been proven functional in neurons differentiated from iPS, however, little is known about 5-HT receptor-mediated modulation in such neuronal networks. In the present study, human iPS were differentiated into cells possessing featured physiological properties of cortical neurons. Whole-cell patch-clamp recording was used to examine the involvement of 5-HT₂ receptors in functional modulation of GABAergic synaptic transmission. We found that serotonin and DOI (a selective agonist of 5-HT_2A/C receptor) reversibly reduced GABA-activated currents, and this 5-HT_2A/C receptor mediated inhibition required G protein, PLC, PKC, and Ca²⁺ signaling. Serotonin increased the frequency of miniature inhibitory postsynaptic currents (mIPSCs), which could be mimicked by α-methylserotonin, a 5-HT₂ receptor agonist. In contrast, DOI reduced both frequency and amplitude of mIPSCs. These findings suggested that in iPS-derived human neurons serotonin postsynaptically reduced GABAa receptor function through 5-HT_2A/C receptors, but presynaptically other 5-HT₂ receptors counteracted the action of 5-HT_2A/C receptors. Functional expression of serotonin receptors in human iPS-derived neurons provides a pre-requisite for their normal behaviors after grafting.

Neural Stem Cells (NSCs) and Proteomics

Neural stem cells (NSCs) can self-renew and give rise to the major cell types of the CNS. Studies of NSCs include the investigation of primary, CNS-derived cells as well as animal and human embryonic stem cell (ESC)-derived and induced pluripotent stem cell (iPSC)-derived sources. NSCs provide a means with which to study normal neural development, neurodegeneration, and neurological disease and are clinically relevant sources for cellular repair to the damaged and diseased CNS. Proteomics studies of NSCs have the potential to delineate molecules and pathways critical for NSC biology and the means by which NSCs can participate in neural repair. In this review, we provide a background to NSC biology, including the means to obtain them and the caveats to these processes. We then focus on advances in the proteomic interrogation of NSCs. This includes the analysis of posttranslational modifications (PTMs); approaches to analyzing different proteomic compartments, such the secretome; as well as approaches to analyzing temporal differences in the proteome to elucidate mechanisms of differentiation. We also discuss some of the methods that will undoubtedly be useful in the investigation of NSCs but which have not yet been applied to the field. While many proteomics studies of NSCs have largely catalogued the proteome or posttranslational modifications of specific cellular states, without delving into specific functions, some have led to understandings of functional processes or identified markers that could not have been identified via other means. Many challenges remain in the field, including the precise identification and standardization of NSCs used for proteomic analyses, as well as how to translate fundamental proteomics studies to functional biology. The next level of investigation will require interdisciplinary approaches, combining the skills of those interested in the biochemistry of proteomics with those interested in modulating NSC function.

Modeling ALS and FTD with iPSC-derived neurons

Recent advances in genetics and neuropathology support the idea that amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia (FTD) are two ends of a disease spectrum. Although several animal models have been developed to investigate the pathogenesis and disease progression in ALS and FTD, there are significant limitations that hamper our ability to connect these models with the neurodegenerative processes in human diseases. With the technical breakthrough in reprogramming biology, it is now possible to generate patient-specific induced pluripotent stem cells (iPSCs) and disease-relevant neuron subtypes. This review provides a comprehensive summary of studies that use iPSC-derived neurons to model ALS and FTD. We discuss the unique capabilities of iPSC-derived neurons that capture some key features of ALS and FTD, and underscore their potential roles in drug discovery. There are, however, several critical caveats that require improvements before iPSC-derived neurons can become highly effective disease models. This article is part of a Special Issue entitled SI: Exploiting human neurons.

FTD/ALS-associated poly(GR) protein impairs the Notch pathway and is recruited by poly(GA) into cytoplasmic inclusions

C9ORF72 repeat expansion is the most common genetic mutation in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Abnormal dipeptide repeat proteins (DPRs) generated from repeat-associated non-AUG (RAN) translation of repeat-containing RNAs are thought to be pathogenic; however, the mechanisms are unknown. Here we report that (GR)₈₀ and (PR)₈₀ are toxic in neuronal and non-neuronal cells in Drosophila. In contrast to reported shorter poly(GR) forms, (GR)₈₀ is mostly localized throughout the cytosol without detectable accumulation in the nucleolus, accompanied by suppression of Notch signaling and cell loss in the wing. Some Notch target genes are also downregulated in brains and iPSC-derived cortical neurons of C9ORF72 patients. Increased Notch expression largely suppressed (GR)₈₀-induced cell loss in the wing. When co-expressed in Drosophila, HeLa cells, or human neurons, (GA)₈₀ recruited (GR)₈₀ into cytoplasmic inclusions, partially decreasing the toxicity of (GR)₈₀ and restoring Notch signaling in Drosophila. Thus, different DPRs have opposing roles in cell loss and we identify the Notch pathway as one of the receptor signaling pathways that might be compromised in C9ORF72 FTD/ALS.

Understanding the molecular basis of autism in a dish using hiPSCs-derived neurons from ASD patients

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by deficits in social cognition, language development, and repetitive/restricted behaviors. Due to the complexity and heterogeneity of ASD and lack of a proper human cellular model system, the pathophysiological mechanism of ASD during the developmental process is largely unknown. However, recent progress in induced pluripotent stem cell (iPSC) technology as well as in vitro neural differentiation techniques have allowed us to functionally characterize neurons and analyze cortical development during neural differentiation. These technical advances will increase our understanding of the pathogenic mechanisms of heterogeneous ASD and help identify molecular biomarkers for patient stratification as well as personalized medicine. In this review, we summarize our current knowledge of iPSC generation, differentiation of specific neuronal subtypes from iPSCs, and phenotypic characterizations of human ASD patient-derived iPSC models. Finally, we discuss the current limitations of iPSC technology and future directions of ASD pathophysiology studies using iPSCs.

GGGGCC repeat expansion in C9orf72 compromises nucleocytoplasmic transport

The GGGGCC (G4C2) repeat expansion in a noncoding region of C9orf72 is the most common cause of sporadic and familial forms of amyotrophic lateral sclerosis and frontotemporal dementia. The basis for pathogenesis is unknown. To elucidate the consequences of G4C2 repeat expansion in a tractable genetic system, we generated transgenic fly lines expressing 8, 28 or 58 G4C2-repeat-containing transcripts that do not have a translation start site (AUG) but contain an open-reading frame for green fluorescent protein to detect repeat-associated non-AUG (RAN) translation. We show that these transgenic animals display dosage-dependent, repeat-length-dependent degeneration in neuronal tissues and RAN translation of dipeptide repeat (DPR) proteins, as observed in patients with C9orf72-related disease. This model was used in a large-scale, unbiased genetic screen, ultimately leading to the identification of 18 genetic modifiers that encode components of the nuclear pore complex (NPC), as well as the machinery that coordinates the export of nuclear RNA and the import of nuclear proteins. Consistent with these results, we found morphological abnormalities in the architecture of the nuclear envelope in cells expressing expanded G4C2 repeats in vitro and in vivo. Moreover, we identified a substantial defect in RNA export resulting in retention of RNA in the nuclei of Drosophila cells expressing expanded G4C2 repeats and also in mammalian cells, including aged induced pluripotent stem-cell-derived neurons from patients with C9orf72-related disease. These studies show that a primary consequence of G4C2 repeat expansion is the compromise of nucleocytoplasmic transport through the nuclear pore, revealing a novel mechanism of neurodegeneration.

Human Neuropsychiatric Disease Modeling using Conditional Deletion Reveals Synaptic Transmission Defects Caused by Heterozygous Mutations in NRXN1

Heterozygous mutations of the NRXN1 gene, which encodes the presynaptic cell-adhesion molecule neurexin-1, were repeatedly associated with autism and schizophrenia. However, diverse clinical presentations of NRXN1 mutations in patients raise the question of whether heterozygous NRXN1 mutations alone directly impair synaptic function. To address this question under conditions that precisely control for genetic background, we generated human ESCs with different heterozygous conditional NRXN1 mutations and analyzed two different types of isogenic control and NRXN1 mutant neurons derived from these ESCs. Both heterozygous NRXN1 mutations selectively impaired neurotransmitter release in human neurons without changing neuronal differentiation or synapse formation. Moreover, both NRXN1 mutations increased the levels of CASK, a critical synaptic scaffolding protein that binds to neurexin-1. Our results show that, unexpectedly, heterozygous inactivation of NRXN1 directly impairs synaptic function in human neurons, and they illustrate the value of this conditional deletion approach for studying the functional effects of disease-associated mutations.

Impact of prenatal environmental stress on cortical development

Prenatal exposure of the developing brain to various types of environmental stress increases susceptibility to neuropsychiatric disorders such as autism, attention deficit hyperactivity disorder and schizophrenia. Given that even subtle perturbations by prenatal environmental stress in the cerebral cortex impair the cognitive and memory functions, this review focuses on underlying molecular mechanisms of pathological cortical development. We especially highlight recent works that utilized animal exposure models, human specimens or/and induced Pluripotent Stem (iPS) cells to demonstrate: (1) molecular mechanisms shared by various types of environmental stressors, (2) the mechanisms by which the affected extracortical tissues indirectly impact the cortical development and function, and (3) interaction between prenatal environmental stress and the genetic predisposition of neuropsychiatric disorders. Finally, we discuss current challenges for achieving a comprehensive understanding of the role of environmentally disturbed molecular expressions in cortical maldevelopment, knowledge of which may eventually facilitate discovery of interventions for prenatal environment-linked neuropsychiatric disorders.