Human embryonic stem cell-derived motor neurons expressing SOD1 mutants exhibit typical signs of motor neuron degeneration linked to ALS

Patient-Specific iPSCs-Based Models of Neurodegenerative Diseases: Focus on Aberrant Calcium Signaling

The development of cell reprogramming technologies became a breakthrough in the creation of new models of human diseases, including neurodegenerative pathologies. The iPSCs-based models allow for the studying of both hereditary and sporadic cases of pathologies and produce deep insight into the molecular mechanisms underlying neurodegeneration. The use of the cells most vulnerable to a particular pathology makes it possible to identify specific pathological mechanisms and greatly facilitates the task of selecting the most effective drugs. To date, a large number of studies on patient-specific models of neurodegenerative diseases has been accumulated. In this review, we focused on the alterations of such a ubiquitous and important intracellular regulatory pathway as calcium signaling. Here, we reviewed and analyzed the data obtained from iPSCs-based models of different neurodegenerative disorders that demonstrated aberrant calcium signaling.

Neural induction: Historical views and application to pluripotent stem cells

Embryonic stem (ES) cells are a useful experimental material to recapitulate the differentiation steps of early embryos, which are usually invisible and inaccessible from outside of the body, especially in mammals. ES cells have greatly facilitated the analyses of gene expression profiles and cell characteristics. In addition, understanding the mechanisms during neural differentiation is important for clinical purposes, such as developing new therapeutic methods or regenerative medicine. As neurons have very limited regenerative ability, neurodegenerative diseases are usually intractable, and patients suffer from the disease throughout their lifetimes. The functional cells generated from ES cells in vitro could replace degenerative areas by transplantation. In this review, we will first demonstrate the historical views and widely accepted concepts regarding the molecular mechanisms of neural induction and positional information to produce the specific types of neurons in model animals. Next, we will describe how these concepts have recently been applied to the research in the establishment of the methodology of neural differentiation from mammalian ES cells. Finally, we will focus on examples of the applications of differentiation systems to clinical purposes. Overall, the discussion will focus on how historical developmental studies are applied to state-of-the-art stem cell research.

ALS-Linked SOD1 Mutants Enhance Neurite Outgrowth and Branching in Adult Motor Neurons

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease characterized by motor neuron cell death. However, not all motor neurons are equally susceptible. Most of what we know about the surviving motor neurons comes from gene expression profiling; less is known about their functional traits. We found that resistant motor neurons cultured from SOD1 ALS mouse models have enhanced axonal outgrowth and dendritic branching. They also have an increase in the number and size of actin-based structures like growth cones and filopodia. These phenotypes occur in cells cultured from presymptomatic mice and mutant SOD1 models that do not develop ALS but not in embryonic motor neurons. Enhanced outgrowth and upregulation of filopodia can be induced in wild-type adult cells by expressing mutant SOD1. These results demonstrate that mutant SOD1 can enhance the regenerative capability of ALS-resistant motor neurons. Capitalizing on this mechanism could lead to new therapeutic strategies.

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Motor neurons from end-stage SOD1 ALS mice have enhanced neurite outgrowth/branching

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Increased outgrowth occurs only in adult neurons and is independent of ALS symptoms

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SOD1^G93A adult motor neurons have larger growth cones and more axonal filopodia

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Acute SOD1^G93A expression upregulates outgrowth in wild-type adult motor neurons

Advances in Patient-Specific Induced Pluripotent Stem Cells Shed Light on Drug Discovery for Amyotrophic Lateral Sclerosis

Induced pluripotent stem cells (iPSCs), which are generated through reprogramming adult somatic cells by expressing specific transcription factors, can differentiate into derivatives of the three embryonic germ layers and accelerate rapid advances in stem cell research. Neurological diseases such as amyotrophic lateral sclerosis (ALS) have benefited enormously from iPSC technology. This approach can be particularly important for creating iPSCs from patients with familial or sporadic forms of ALS. Motor neurons differentiated from the ALS-patient-derived iPSC can help to determine the relationship between cellular phenotype and genotype. Patient-derived iPSCs facilitate the development of new drugs and/or drug screening for ALS treatment and allow the exploration of the possible mechanism of ALS disease. In this article, we reviewed ALS-patient-specific iPSCs with various genetic mutations, progress in drug development for ALS disease, functional assays showing the differentiation of iPSCs into mature motor neurons, and promising biomarkers in ALS patients for the evaluation of drug candidates.

Representing Diversity in the Dish: Using Patient-Derived in Vitro Models to Recreate the Heterogeneity of Neurological Disease

Neurological diseases, including dementias such as Alzheimer's disease (AD) and fronto-temporal dementia (FTD) and degenerative motor neuron diseases such as amyotrophic lateral sclerosis (ALS), are responsible for an increasing fraction of worldwide fatalities. Researching these heterogeneous diseases requires models that endogenously express the full array of genetic and epigenetic factors which may influence disease development in both familial and sporadic patients. Here, we discuss the two primary methods of developing patient-derived neurons and glia to model neurodegenerative disease: reprogramming somatic cells into induced pluripotent stem cells (iPSCs), which are differentiated into neurons or glial cells, or directly converting (DC) somatic cells into neurons (iNeurons) or glial cells. Distinct differentiation techniques for both models result in a variety of neuronal and glial cell types, which have been successful in displaying unique hallmarks of a variety of neurological diseases. Yield, length of differentiation, ease of genetic manipulation, expression of cell-specific markers, and recapitulation of disease pathogenesis are presented as determining factors in how these methods may be used separately or together to ascertain mechanisms of disease and identify therapeutics for distinct patient populations or for specific individuals in personalized medicine projects.

Evaluation of Holistic Treatment for ALS Reveals Possible Mechanism and Therapeutic Potential

There has been a tremendous amount of research into the causes of Amyotrophic Lateral Sclerosis (ALS), but yet very few treatment options beyond amelioration of symptoms. A holistic approach has shown anecdotal evidence of slowing disease progression and this treatment, known as the Deanna protocol (DP), postulates that ALS is a metabolic disease caused by glutamate that induces toxicity. In this study, glutamate exposure to human motoneurons was investigated and found not to significantly affect cell viability or electrophysiological properties. However, varicosities were observed in axons suggestive of transport impairment that was dose dependent for glutamate exposure. Surprisingly, a subset of the components of the DP eliminated these varicosities. To verify this finding a human SOD1 patient-derived iPSC line was examined and significant numbers of varicosities were present without glutamate treatment, compared to the iPSC control, indicating the possibility of a common mechanism despite different origins for the varicosities. Importantly, the DP ameliorated these varicosities by over 70% in the patient derived cells as well. These results are consistent with much of the literature on ALS and give hope for treatment not only for arresting disease progression using compounds considered safe but also the potential for restoration of function.

Simple Derivation of Spinal Motor Neurons from ESCs/iPSCs Using Sendai Virus Vectors

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal degenerative disorder of motor neurons (MNs). Embryonic stem cells (ESCs)/induced pluripotent stem cells (iPSCs) now help us to understand the pathomechanisms of ALS via disease modeling. Various methods to differentiate ESCs/iPSCs into MNs by the addition of signaling molecules have been reported. However, classical methods require multiple steps, and newer simple methods using the transduction of transcription factors run the risk of genomic integration of the vector genes. Heterogeneity of the expression levels of the transcription factors also remains an issue. Here we describe a novel approach for differentiating human and mouse ESCs/iPSCs into MNs using a single Sendai virus vector encoding three transcription factors, LIM/homeobox protein 3, neurogenin 2, and islet-1, which are integration free. This single-vector method, generating HB9-positive cells on day 2 from human iPSCs, increases the ratio of MNs to neurons compared to the use of three separate Sendai virus vectors. In addition, the MNs derived via this method from iPSCs of ALS patients and model mice display disease phenotypes. This simple approach significantly reduces the efforts required to generate MNs, and it provides a useful tool for disease modeling.

New In Vitro Models to Study Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a complex multifactorial disorder, characterized by motor neuron loss with involvement of several other cell types, including astrocytes, oligodendrocytes and microglia. Studies in vivo and in in vitro models have highlighted that the contribution of non-neuronal cells to the disease is a primary event and ALS pathogenesis is driven by both cell-autonomous and non-cell autonomous mechanisms. The advancements in genetics and in vitro modeling of the past 10 years have dramatically changed the way we investigate the pathogenic mechanisms involved in ALS. The identification of mutations in transactive response DNA-binding protein gene (TARDBP), fused in sarcoma (FUS) and, more recently, a GGGGCC-hexanucleotide repeat expansion in chromosome 9 open reading frame 72 (C9ORF72) and their link with familial ALS have provided new avenues of investigation and hypotheses on the pathophysiology of this devastating disease. In the same years, from 2007 to present, in vitro technologies to model neurological disorders have also undergone impressive developments. The advent of induced pluripotent stem cells (iPSCs) gave the field of ALS the opportunity to finally model in vitro not only familial, but also the larger part of ALS cases affected by sporadic disease. Since 2008, when the first human iPS-derived motor neurons from patients were cultured in a petri dish, several different techniques have been developed to produce iPSC lines through genetic reprogramming and multiple direct conversion methods have been optimised. In this review, we will give an overview of how human in vitro models have been used so far, what discoveries they have led to since 2007, and how the recent advances in technology combined with the genetic discoveries, have tremendously widened the horizon of ALS research.

Motor neurons derived from ALS-related mouse iPS cells recapitulate pathological features of ALS

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive neurodegenerative disease characterized by the loss of motor neurons in the spinal cord and brain. Mutations in Cu/Zn superoxide dismutase 1 (SOD1) are known to induce ALS. Although many research models have been developed, the exact pathological mechanism of ALS remains unknown. The recently developed induced pluripotent stem (iPS) cell technology is expected to illuminate the pathological mechanisms and new means of treatment for neurodegenerative diseases. To determine the pathological mechanism of ALS, we generated mouse iPS (miPS) cells from experimental ALS transgenic mice and control mice and characterized the cells using molecular biological methods. The generated miPS cells expressed many pluripotent genes and differentiated into three germ layers in vitro and in vivo. Motor neurons derived from ALS-related miPS cells recapitulated the pathological features of ALS. The ALS-model motor neurons showed SOD1 aggregates, as well as decreased cell survival rate and neurite length compared with wild-type motor neurons. Our study will be helpful in revealing the mechanism of motor neuronal cell death in ALS.

rAAV Gene Therapy in a Canavan's Disease Mouse Model Reveals Immune Impairments and an Extended Pathology Beyond the Central Nervous System

Aspartoacylase (AspA) gene mutations cause the pediatric lethal neurodegenerative Canavan disease (CD). There is emerging promise of successful gene therapy for CD using recombinant adeno-associated viruses (rAAVs). Here, we report an intracerebroventricularly delivered AspA gene therapy regime using three serotypes of rAAVs at a 20-fold reduced dose than previously described in AspA(-/-) mice, a bona-fide mouse model of CD. Interestingly, central nervous system (CNS)-restricted therapy prolonged survival over systemic therapy in CD mice but failed to sustain motor functions seen in systemically treated mice. Importantly, we reveal through histological and functional examination of untreated CD mice that AspA deficiency in peripheral tissues causes morphological and functional abnormalities in this heretofore CNS-defined disorder. We demonstrate for the first time that AspA deficiency, possibly through excessive N-acetyl aspartic acid accumulation, elicits both a peripheral and CNS immune response in CD mice. Our data establish a role for peripheral tissues in CD pathology and serve to aid the development of more efficacious and sustained gene therapy for this disease.

Reverse engineering human neurodegenerative disease using pluripotent stem cell technology

With the technology of reprogramming somatic cells by introducing defined transcription factors that enables the generation of "induced pluripotent stem cells (iPSCs)" with pluripotency comparable to that of embryonic stem cells (ESCs), it has become possible to use this technology to produce various cells and tissues that have been difficult to obtain from living bodies. This advancement is bringing forth rapid progress in iPSC-based disease modeling, drug screening, and regenerative medicine. More and more studies have demonstrated that phenotypes of adult-onset neurodegenerative disorders could be rather faithfully recapitulated in iPSC-derived neural cell cultures. Moreover, despite the adult-onset nature of the diseases, pathogenic phenotypes and cellular abnormalities often exist in early developmental stages, providing new "windows of opportunity" for understanding mechanisms underlying neurodegenerative disorders and for discovering new medicines. The cell reprogramming technology enables a reverse engineering approach for modeling the cellular degenerative phenotypes of a wide range of human disorders. An excellent example is the study of the human neurodegenerative disease amyotrophic lateral sclerosis (ALS) using iPSCs. ALS is a progressive neurodegenerative disease characterized by the loss of upper and lower motor neurons (MNs), culminating in muscle wasting and death from respiratory failure. The iPSC approach provides innovative cell culture platforms to serve as ALS patient-derived model systems. Researchers have converted iPSCs derived from ALS patients into MNs and various types of glial cells, all of which are involved in ALS, to study the disease. The iPSC technology could be used to determine the role of specific genetic factors to track down what's wrong in the neurodegenerative disease process in the "disease-in-a-dish" model. Meanwhile, parallel experiments of targeting the same specific genes in human ESCs could also be performed to control and to complement the iPSC-based approach for ALS disease modeling studies. Much knowledge has been generated from the study of both ALS iPSCs and ESCs. As these methods have advantages and disadvantages that should be balanced on experimental design in order for them to complement one another, combining the diverse methods would help build an expanded knowledge of ALS pathophysiology. The goals are to reverse engineer the human disease using ESCs and iPSCs, generate lineage reporter lines and in vitro disease models, target disease related genes, in order to better understand the molecular and cellular mechanisms of differentiation regulation along neural (neuronal versus glial) lineages, to unravel the pathogenesis of the neurodegenerative disease, and to provide appropriate cell sources for replacement therapy. This article is part of a Special Issue entitled SI: PSC and the brain.

Enrichment of human embryonic stem cell derived motor neuron cultures using arabinofuranosyl cytidine

ABSTRACT 

Aim: Human embryonic stem cell (hESC)-derived motor neurons (MNs) can model neurodegenerative diseases, in other words, for the development of cell-based drug screening assays. However, efficient MN generation is challenging and high level of contamination of undifferentiated cells remains a significant problem when culturing hESC-derived MNs. We describe a protocol for the removal of undifferentiated cells using the DNA synthesis inhibitor arabinofuranosyl cytidine (Ara-C). Materials & methods: hESC-MNs were treated with Ara-C after the last step of differentiation. FACS analysis and fluorescence microscopy were used to identify and quantify MNs. Results: HB9/ChAT-positive live mature MNs were enriched 3.9-times in Ara-C-treated cultures when compared with untreated cells. The Ara-C-treated MNs are electrophysiologically functional and discharge action potentials. Conclusion: Ara-C selection of MNs can be combined with stem cell differentiation protocols to enrich MNs in culture.

Hippo/YAP-mediated rigidity-dependent motor neuron differentiation of human pluripotent stem cells

Our understanding of the intrinsic mechanosensitive properties of human pluripotent stem cells (hPSCs), in particular the effects that the physical microenvironment has on their differentiation, remains elusive. Here, we show that neural induction and caudalization of hPSCs can be accelerated by using a synthetic microengineered substrate system consisting of poly(dimethylsiloxane) micropost arrays (PMAs) with tunable mechanical rigidities. The purity and yield of functional motor neurons derived from hPSCs within 23 days of culture using soft PMAs were improved more than fourfold and tenfold, respectively, compared with coverslips or rigid PMAs. Mechanistic studies revealed a multi-targeted mechanotransductive process involving Smad phosphorylation and nucleocytoplasmic shuttling, regulated by rigidity-dependent Hippo/YAP activities and actomyosin cytoskeleton integrity and contractility. Our findings suggest that substrate rigidity is an important biophysical cue influencing neural induction and subtype specification, and that microengineered substrates can thus serve as a promising platform for large-scale culture of hPSCs.

Retrograde labeling, transduction, and genetic targeting allow cellular analysis of corticospinal motor neurons: implications in health and disease

Corticospinal motor neurons (CSMN) have a unique ability to receive, integrate, translate, and transmit the cerebral cortex's input toward spinal cord targets and therefore act as a “spokesperson” for the initiation and modulation of voluntary movements that require cortical input. CSMN degeneration has an immense impact on motor neuron circuitry and is one of the underlying causes of numerous neurodegenerative diseases, such as primary lateral sclerosis (PLS), hereditary spastic paraplegia (HSP), and amyotrophic lateral sclerosis (ALS). In addition, CSMN death results in long-term paralysis in spinal cord injury patients. Detailed cellular analyses are crucial to gain a better understanding of the pathologies underlying CSMN degeneration. However, visualizing and identifying these vulnerable neuron populations in the complex and heterogeneous environment of the cerebral cortex have proved challenging. Here, we will review recent developments and current applications of novel strategies that reveal the cellular and molecular basis of CSMN health and vulnerability. Such studies hold promise for building long-term effective treatment solutions in the near future.

Disease modeling and drug screening for neurological diseases using human induced pluripotent stem cells

With the general decline of pharmaceutical research productivity, there are concerns that many components of the drug discovery process need to be redesigned and optimized. For example, the human immortalized cell lines or animal primary cells commonly used in traditional drug screening may not faithfully recapitulate the pathological mechanisms of human diseases, leading to biases in assays, targets, or compounds that do not effectively address disease mechanisms. Recent advances in stem cell research, especially in the development of induced pluripotent stem cell (iPSC) technology, provide a new paradigm for drug screening by permitting the use of human cells with the same genetic makeup as the patients without the typical quantity constraints associated with patient primary cells. In this article, we will review the progress made to date on cellular disease models using human stem cells, with a focus on patient-specific iPSCs for neurological diseases. We will discuss the key challenges and the factors that associated with the success of using stem cell models for drug discovery through examples from monogenic diseases, diseases with various known genetic components, and complex diseases caused by a combination of genetic, environmental and other factors.

Derivation and expansion using only small molecules of human neural progenitors for neurodegenerative disease modeling

Phenotypic drug discovery requires billions of cells for high-throughput screening (HTS) campaigns. Because up to several million different small molecules will be tested in a single HTS campaign, even small variability within the cell populations for screening could easily invalidate an entire campaign. Neurodegenerative assays are particularly challenging because neurons are post-mitotic and cannot be expanded for implementation in HTS. Therefore, HTS for neuroprotective compounds requires a cell type that is robustly expandable and able to differentiate into all of the neuronal subtypes involved in disease pathogenesis. Here, we report the derivation and propagation using only small molecules of human neural progenitor cells (small molecule neural precursor cells; smNPCs). smNPCs are robust, exhibit immortal expansion, and do not require cumbersome manual culture and selection steps. We demonstrate that smNPCs have the potential to clonally and efficiently differentiate into neural tube lineages, including motor neurons (MNs) and midbrain dopaminergic neurons (mDANs) as well as neural crest lineages, including peripheral neurons and mesenchymal cells. These properties are so far only matched by pluripotent stem cells. Finally, to demonstrate the usefulness of smNPCs we show that mDANs differentiated from smNPCs with LRRK2 G2019S are more susceptible to apoptosis in the presence of oxidative stress compared to wild-type. Therefore, smNPCs are a powerful biological tool with properties that are optimal for large-scale disease modeling, phenotypic screening, and studies of early human development.

Recapitulation of spinal motor neuron-specific disease phenotypes in a human cell model of spinal muscular atrophy

Establishing human cell models of spinal muscular atrophy (SMA) to mimic motor neuron-specific phenotypes holds the key to understanding the pathogenesis of this devastating disease. Here, we developed a closely representative cell model of SMA by knocking down the disease-determining gene, survival motor neuron (SMN), in human embryonic stem cells (hESCs). Our study with this cell model demonstrated that knocking down of SMN does not interfere with neural induction or the initial specification of spinal motor neurons. Notably, the axonal outgrowth of spinal motor neurons was significantly impaired and these disease-mimicking neurons subsequently degenerated. Furthermore, these disease phenotypes were caused by SMN-full length (SMN-FL) but not SMN-Δ7 (lacking exon 7) knockdown, and were specific to spinal motor neurons. Restoring the expression of SMN-FL completely ameliorated all of the disease phenotypes, including specific axonal defects and motor neuron loss. Finally, knockdown of SMN-FL led to excessive mitochondrial oxidative stress in human motor neuron progenitors. The involvement of oxidative stress in the degeneration of spinal motor neurons in the SMA cell model was further confirmed by the administration of N-acetylcysteine, a potent antioxidant, which prevented disease-related apoptosis and subsequent motor neuron death. Thus, we report here the successful establishment of an hESC-based SMA model, which exhibits disease gene isoform specificity, cell type specificity, and phenotype reversibility. Our model provides a unique paradigm for studying how motor neurons specifically degenerate and highlights the potential importance of antioxidants for the treatment of SMA.

Amyotrophic lateral sclerosis model derived from human embryonic stem cells overexpressing mutant superoxide dismutase 1

The generation of amyotrophic lateral sclerosis (ALS) disease models is an important subject for investigating disease mechanisms and pharmaceutical applications. In transgenic mice, expression of a mutant form of superoxide dismutase 1 (SOD1) can lead to the development of ALS that closely mimics the familial type of ALS (FALS). Although SOD1 mutant mice show phenotypes similar to FALS, dissimilar drug responses and size differences limit their usefulness to study the disease mechanism(s) and identify potential therapeutic compounds. Development of an in vitro model system for ALS is expected to help in obtaining novel insights into disease mechanisms and discovery of therapeutics. We report the establishment of an in vitro FALS model from human embryonic stem cells overexpressing either a wild-type (WT) or a mutant SOD1 (G93A) gene and the evaluation of the phenotypes and survival of the spinal motor neurons (sMNs), which are the neurons affected in ALS patients. The in vitro FALS model that we developed mimics the in vivo human ALS disease in terms of the following: (a) selective degeneration of sMNs expressing the G93A SOD1 but not those expressing the WT gene; (b) susceptibility of G93A SOD1-derived sMNs to form ubiquitinated inclusions; (c) astrocyte-derived factor(s) in the selective degeneration of G93A SOD1 sMNs; and (d) cell-autonomous, as well as non-cell-autonomous, dependent sMN degeneration. Thus, this model is expected to help unravel the disease mechanisms involved in the development of FALS and also lead to potential drug discoveries based on the prevention of neurodegeneration.

Functional neuromuscular junctions formed by embryonic stem cell-derived motor neurons

A key objective of stem cell biology is to create physiologically relevant cells suitable for modeling disease pathologies in vitro. Much progress towards this goal has been made in the area of motor neuron (MN) disease through the development of methods to direct spinal MN formation from both embryonic and induced pluripotent stem cells. Previous studies have characterized these neurons with respect to their molecular and intrinsic functional properties. However, the synaptic activity of stem cell-derived MNs remains less well defined. In this study, we report the development of low-density co-culture conditions that encourage the formation of active neuromuscular synapses between stem cell-derived MNs and muscle cells in vitro. Fluorescence microscopy reveals the expression of numerous synaptic proteins at these contacts, while dual patch clamp recording detects both spontaneous and multi-quantal evoked synaptic responses similar to those observed in vivo. Together, these findings demonstrate that stem cell-derived MNs innervate muscle cells in a functionally relevant manner. This dual recording approach further offers a sensitive and quantitative assay platform to probe disorders of synaptic dysfunction associated with MN disease.

Superoxide dismutase 1 encoding mutations linked to ALS adopts a spectrum of misfolded states

Background

Mutations in superoxide dismutase 1 (SOD1), which are one cause of familial amyotrophic lateral sclerosis (fALS), induce misfolding and aggregation of the protein. Misfolding can be detected by the binding of antibodies raised against peptide epitopes that are normally buried in the native conformation, shifts in solubility in non-ionic detergents, and the formation of macromolecular inclusions. In the present study, we investigate the relationship between detergent-insoluble and sedimentable forms of mutant SOD1, forms of mutant SOD1 with aberrantly accessible epitopes, and mutant protein in inclusions with the goal of defining the spectrum of misfolded states that mutant SOD1 can adopt.

Results

Using combined approaches in cultured cell models, we demonstrate that a substantial fraction of mutant SOD1 adopts a non-native conformation that remains soluble and freely mobile. We also show that mutant SOD1 can produce multimeric assemblies of which some are insoluble in detergent and large enough to sediment by ultracentrifugation and some are large enough to detect visually. Three conformationally restricted antibodies were found to be useful in discriminating mal-folded forms of mutant SOD1. An antibody termed C4F6 displays properties consistent with recognition of soluble, freely mobile, mal-folded mutant SOD1. An antibody termed SEDI, which recognizes C-terminal residues, detects larger inclusion structures as well as soluble misfolded entities. An antibody termed hSOD1, which recognizes aa 24-36, detects an epitope shared by soluble non-natively folded WT and mutant SOD1. This epitope becomes inaccessible in aggregates of mutant SOD1.

Conclusions

Our studies demonstrate how different methods of detecting misfolding and aggregation of mutant SOD1 reveal different forms of aberrantly folded protein. Immunological and biochemical methods can be used in combination to detect soluble and insoluble misfolded forms of mutant SOD1. Our findings support the view that mutant SOD1 can adopt multiple misfolded conformations with the potential that different structural variants mediate different aspects of fALS.

Neuromuscular junction formation between human stem cell-derived motoneurons and human skeletal muscle in a defined system

Functional in vitro models composed of human cells will constitute an important platform in the next generation of system biology and drug discovery. This study reports a novel human-based in vitro Neuromuscular Junction (NMJ) system developed in a defined serum-free medium and on a patternable non-biological surface. The motoneurons and skeletal muscles were derived from fetal spinal stem cells and skeletal muscle stem cells. The motoneurons and skeletal myotubes were completely differentiated in the co-culture based on morphological analysis and electrophysiology. NMJ formation was demonstrated by phase contrast microscopy, immunocytochemistry and the observation of motoneuron-induced muscle contractions utilizing time-lapse recordings and their subsequent quenching by d-Tubocurarine. Generally, functional human based systems would eliminate the issue of species variability during the drug development process and its derivation from stem cells bypasses the restrictions inherent with utilization of primary human tissue. This defined human-based NMJ system is one of the first steps in creating functional in vitro systems and will play an important role in understanding NMJ development, in developing high information content drug screens and as test beds in preclinical studies for spinal or muscular diseases/injuries such as muscular dystrophy, Amyotrophic lateral sclerosis and spinal cord repair.

Constructing and deconstructing stem cell models of neurological disease

Among the disciplines of medicine, the study of neurological disorders is particularly challenging. The fundamental inaccessibility of the human neural types affected by disease prevents their isolation for in vitro studies of degenerative mechanisms or for drug screening efforts. However, the ability to reprogram readily accessible tissue from patients into pluripotent stem (iPS) cells may now provide a general solution to this shortage of human neurons. Gradually improving methods for directing the differentiation of patient-specific stem cells has enabled the production of several neural cell types affected by disease. Furthermore, initial studies with stem cell lines derived from individuals with pediatric, monogenic disorders have validated the stem cell approach to disease modeling, allowing relevant neural phenotypes to be observed and studied. Whether iPS cell-derived neurons will always faithfully recapitulate the same degenerative processes observed in patients and serve as platforms for drug discovery relevant to common late-onset diseases remains to be determined.

Primary cells and stem cells in drug discovery: emerging tools for high-throughput screening

Many drug discovery screening programs employ immortalized cells, recombinantly engineered to express a defined molecular target. Several technologies are now emerging that render it feasible to employ more physiologically, and clinically relevant, cell phenotypes. Consequently, numerous approaches use primary cells, which retain many functions seen in vivo, as well as endogenously expressing the target of interest. Furthermore, stem cells, of either embryonic or adult origin, as well as those derived from differentiated cells, are now finding a place in drug discovery. Collectively, these cells are expanding the utility of authentic human cells, either as screening tools or as therapeutics, as well as providing cells derived directly from patients. Nonetheless, the growing use of phenotypically relevant cells (including primary cells or stem cells) is not without technical difficulties, particularly when their envisioned use lies in high-throughput screening (HTS) protocols. In particular, the limited availability of homogeneous primary or stem cell populations for HTS mandates that novel technologies be developed to accelerate their adoption. These technologies include detection of responses with very few cells as well as protocols to generate cell lines in abundant, homogeneous populations. In parallel, the growing use of changes in cell phenotype as the assay readout is driving greater use of high-throughput imaging techniques in screening. Taken together, the greater availability of novel primary and stem cell phenotypes as well as new detection technologies is heralding a new era of cellular screening. This convergence offers unique opportunities to identify drug candidates for disorders at which few therapeutics are presently available.

Human motor neuron generation from embryonic stem cells and induced pluripotent stem cells

Motor neuron diseases (MNDs) are a group of neurological disorders that selectively affect motor neurons. There are currently no cures or efficacious treatments for these diseases. In recent years, significant developments in stem cell research have been applied to MNDs, particularly regarding neuroprotection and cell replacement. However, a consistent source of motor neurons for cell replacement is required. Human embryonic stem cells (hESCs) could provide an inexhaustible supply of differentiated cell types, including motor neurons that could be used for MND therapies. Recently, it has been demonstrated that induced pluripotent stem (iPS) cells may serve as an alternative source of motor neurons, since they share ES characteristics, self-renewal, and the potential to differentiate into any somatic cell type. In this review, we discuss several reproducible methods by which hESCs or iPS cells are efficiently isolated and differentiated into functional motor neurons, and possible clinical applications.

Amyotrophic lateral sclerosis: applications of stem cells - an update

Neurodegenerative diseases are a growing public health challenge, and amyotrophic lateral sclerosis (ALS) remains a fatal incurable disease. The advent of stem cell therapy has opened new horizons for both researchers and ALS patients, desperately looking for a treatment. ALS must be considered a systemic disease affecting many cell phenotypes besides motor neurons, even outside the central nervous system. Cell replacement therapy needs to address the specific neurobiological issues of ALS to safely and efficiently reach clinical settings. Moreover, the enormous potential of induced pluripotent cells directly derived from patients for modeling and understanding the pathological mechanisms, in correlation with the discoveries of new genes and animal models, provides new opportunities that need to be integrated with previously described transplantation strategies. Finally, a careful evaluation of preclinical data in conjunction with wary patient choice in clinical trials needs to be established in order to generate meaningful results.

Stem Cells for the Treatment of Neurodegenerative Diseases

Neurodegenerative diseases are characterized by neurodegenerative changes or apoptosis of neurons involved in networks, leading to permanent paralysis and loss of sensation below the site of the injury. Cell replacement therapy has provided the basis for the development of potentially powerful new therapeutic strategies for a broad spectrum of human neurological diseases. In recent years, neurons and glial cells have successfully been generated from stem cells, and extensive efforts by investigators to develop stem cell-based brain transplantation therapies have been carried out. We review here notable previously published experimental and preclinical studies involving stem cell-based cell for neurodegenerative diseases and discuss the future prospects for stem cell therapy of neurological disorders in the clinical setting. Steady and solid progress in stem cell research in both basic and preclinical settings should support the hope for development of stem cell-based cell therapies for neurological diseases.

Pluripotent stem cells in neurodegenerative and neurodevelopmental diseases

Most of our current knowledge about cellular phenotypes in neurodevelopmental and neurodegenerative diseases in humans was gathered from studies in postmortem brain tissues. These samples often represent the end-stage of the disease and therefore are not always a fair representation of how the disease developed. Moreover, under these circumstances, the pathology observed could be a secondary effect rather than the authentic disease cellular phenotype. Likewise, the rodent models available do not always recapitulate the pathology from human diseases. In this review, we will examine recent literature on the use of induced pluripotent stem cells to model neurodegenerative and neurodevelopmental diseases. We highlight the characteristics of diseases like spinal muscular atrophy and familial dysautonomia that allowed partial modeling of the disease phenotype. We review human stem cell literature on common neurodegenerative late-onset diseases such as Parkinson's disease and amyotrophic lateral sclerosis where patients' cells have been successfully reprogrammed but a disease phenotype has not yet been described. So far, the technique is of great interest for early onset monogenetic neurodevelopmental diseases. We speculate about potential further experimental requirements and settings for reprogrammed neurons for in vitro disease modeling and drug discovery.

Developmental regulation of human embryonic stem cell-derived neurons by calcium entry via transient receptor potential channels

Spontaneous calcium (Ca(2+)) transients in the developing nervous system can affect proliferation, migration, neuronal subtype specification, and neurite outgrowth. Here, we show that telencephalic human neuroepithelia (hNE) and postmitotic neurons (PMNs) generated from embryonic stem cells display robust Ca(2+) transients. Unlike previous reports in animal models, transients occurred by a Gd(3+)/La(3+)-sensitive, but thapsigargin- and Cd(2+)-insensitive, mechanism, strongly suggestive of a role for transient receptor potential (Trp) channels. Furthermore, Ca(2+) transients in PMNs exhibited an additional sensitivity to the canonical Trp (TrpC) antagonist SKF96365 and shRNA-mediated knockdown of the TrpC1 subunit. Functionally, inhibition of Ca(2+) transients in dividing hNE cells led to a significant reduction in proliferation, whereas either pharmacological inhibition or shRNA-mediated knockdown of the TrpC1 and TrpC4 subunits significantly reduced neurite extension in PMNs. Primary neurons cultured from fetal human cortex displayed nearly identical Ca(2+) transients and pharmacological sensitivities to Trp channel antagonists. Together these data suggest that Trp channels present a novel mechanism for controlling Ca(2+) transients in human neurons and may offer a target for regulating proliferation and neurite outgrowth when engineering cells for therapeutic transplantation.

Highly efficient differentiation and enrichment of spinal motor neurons derived from human and monkey embryonic stem cells

Background

There are no cures or efficacious treatments for severe motor neuron diseases. It is extremely difficult to obtain naïve spinal motor neurons (sMNs) from human tissues for research due to both technical and ethical reasons. Human embryonic stem cells (hESCs) are alternative sources. Several methods for MN differentiation have been reported. However, efficient production of naïve sMNs and culture cost were not taken into consideration in most of the methods.

Methods/Principal Findings

We aimed to establish protocols for efficient production and enrichment of sMNs derived from pluripotent stem cells. Nestin+ neural stem cell (NSC) clusters were induced by Noggin or a small molecule inhibitor of BMP signaling. After dissociation of NSC clusters, neurospheres were formed in a floating culture containing FGF2. The number of NSCs in neurospheres could be expanded more than 30-fold via several passages. More than 33% of HB9+ sMN progenitor cells were observed after differentiation of dissociated neurospheres by all-trans retinoic acid (ATRA) and a Shh agonist for another week on monolayer culture. HB9+ sMN progenitor cells were enriched by gradient centrifugation up to 80% purity. These HB9+ cells differentiated into electrophysiologically functional cells and formed synapses with myotubes during a few weeks after ATRA/SAG treatment.

Conclusions and Significance

The series of procedures we established here, namely neural induction, NSC expansion, sMN differentiation and sMN purification, can provide large quantities of naïve sMNs derived from human and monkey pluripotent stem cells. Using small molecule reagents, reduction of culture cost could be achieved.