A perspective on stem cell modeling of amyotrophic lateral sclerosis

Human Induced Pluripotent Stem Cells: Directed Differentiation Methods and Applications in Brain Diseases

Human induced pluripotent stem cells (hiPSCs), similar to embryonic stem cells, are a class of pluripotent stem cells with the potential to differentiate into various kinds of cells. Because the application of hiPSCs obtained by reprogramming patients' somatic cells in the treatment of brain diseases bypasses the ethical constraints on the use of embryonic stem cells and mitigates immune rejection, hiPSCs have profound clinical application prospects. In this review, we first summarized the differentiation methods of hiPSCs into different kinds of neurons, and secondly discussed the application of hiPSCs in several brain disease models, so as to provide a reference for the future application of hiPSCs in the studies and treatment of brain diseases.

Emerging hiPSC Models for Drug Discovery in Neurodegenerative Diseases

Neurodegenerative diseases affect millions of people worldwide and are characterized by the chronic and progressive deterioration of neural function. Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), represent a huge social and economic burden due to increasing prevalence in our aging society, severity of symptoms, and lack of effective disease-modifying therapies. This lack of effective treatments is partly due to a lack of reliable models. Modeling neurodegenerative diseases is difficult because of poor access to human samples (restricted in general to postmortem tissue) and limited knowledge of disease mechanisms in a human context. Animal models play an instrumental role in understanding these diseases but fail to comprehensively represent the full extent of disease due to critical differences between humans and other mammals. The advent of human-induced pluripotent stem cell (hiPSC) technology presents an advantageous system that complements animal models of neurodegenerative diseases. Coupled with advances in gene-editing technologies, hiPSC-derived neural cells from patients and healthy donors now allow disease modeling using human samples that can be used for drug discovery.

Human Pluripotent Stem Cells in Neurodegenerative Diseases: Potentials, Advances and Limitations

Neurodegenerative diseases are progressive and uncontrolled gradual loss of motor neurons function or death of neuron cells in the central nervous system (CNS) and the mechanisms underlying their progressive nature remain elusive. There is urgent need to investigate therapeutic strategies and novel treatments for neural regeneration in disorders like Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Currently, the development and identification of pluripotent stem cells enabling the acquisition of a large number of neural cells in order to improve cell recovery after neurodegenerative disorders. Pluripotent stem cells which consist of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are characterized by their ability to indefinitely self-renew and the capacity to differentiate into different types of cells. The first human ESC lines were established from donated human embryos; while, because of a limited supply of donor embryos, human ESCs derivation remains ethically and politically controversial. Hence, hiPSCs-based therapies have been shown as an effective replacement for human ESCs without embryo destruction. Compared to the invasive methods for derivation of human ESCs, human iPSCs has opened possible to reprogram patient-specific cells by defined factors and with minimally invasive procedures. Human pluripotent stem cells are a good source for cell-based research, cell replacement therapies and disease modeling. To date, hundreds of human ESC and human iPSC lines have been generated with the aim of treating various neurodegenerative diseases. In this review, we have highlighted the recent potentials, advances, and limitations of human pluripotent stem cells for the treatment of neurodegenerative disorders.

Revised Airlie House consensus guidelines for design and implementation of ALS clinical trials

OBJECTIVE

To revise the 1999 Airlie House consensus guidelines for the design and implementation of preclinical therapeutic studies and clinical trials in amyotrophic lateral sclerosis (ALS).

METHODS

A consensus committee comprising 140 key members of the international ALS community (ALS researchers, clinicians, patient representatives, research funding representatives, industry, and regulatory agencies) addressed 9 areas of need within ALS research: (1) preclinical studies; (2) biological and phenotypic heterogeneity; (3) outcome measures; (4) disease-modifying and symptomatic interventions; (5) recruitment and retention; (6) biomarkers; (7) clinical trial phases; (8) beyond traditional trial designs; and (9) statistical considerations. Assigned to 1 of 8 sections, committee members generated a draft set of guidelines based on a "background" of developing a (pre)clinical question and a "rationale" outlining the evidence and expert opinion. Following a 2-day, face-to-face workshop at the Airlie House Conference Center, a modified Delphi process was used to develop draft consensus research guidelines, which were subsequently reviewed and modified based on comments from the public. Statistical experts drafted a separate document of statistical considerations (section 9).

RESULTS

In this report, we summarize 112 guidelines and their associated backgrounds and rationales. The full list of guidelines, the statistical considerations, and a glossary of terms can be found in data available from Dryad (appendices e-3-e-5, doi.org/10.5061/dryad.32q9q5d). The authors prioritized 15 guidelines with the greatest potential to improve ALS clinical research.

CONCLUSION

The revised Airlie House ALS Clinical Trials Consensus Guidelines should serve to improve clinical trial design and accelerate the development of effective treatments for patients with ALS.

Aggregated SOD1 causes selective death of cultured human motor neurons

Most human neurodegenerative diseases share a phenotype of neuronal protein aggregation. In Amyotrophic Lateral Sclerosis (ALS), the abundant protein superoxide dismutase (SOD1) or the TAR-DNA binding protein TDP-43 can aggregate in motor neurons. Recently, numerous studies have highlighted the ability of aggregates to spread from neuron to neuron in a prion-like fashion. These studies have typically focused on the use of neuron-like cell lines or neurons that are not normally affected by the specific aggregated protein being studied. Here, we have investigated the uptake of pre-formed SOD1 aggregates by cultures containing pluripotent stem cell-derived human motor neurons. We found that all cells take up aggregates by a process resembling fluid-phase endocytosis, just as found in earlier studies. However, motor neurons, despite taking up smaller amounts of SOD1, were much more vulnerable to the accumulating aggregates. Thus, the propagation of disease pathology depends less on selective uptake than on selective response to intracellular aggregates. We further demonstrate that anti-SOD1 antibodies, being considered as ALS therapeutics, can act by blocking the uptake of SOD1, but also by blocking the toxic effects of intracellular SOD1. This work demonstrates the importance of using disease relevant cells even in studying phenomena such as aggregate propagation.

Fine-Tuning ER Stress Signal Transducers to Treat Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motoneurons and paralysis. The mechanisms underlying neuronal degeneration in ALS are starting to be elucidated, highlighting disturbances in motoneuron proteostasis. Endoplasmic reticulum (ER) stress has emerged as an early pathogenic event underlying motoneuron vulnerability and denervation in ALS. Maintenance of ER proteostasis is controlled by a dynamic signaling network known as the unfolded protein response (UPR). Inositol-requiring enzyme 1 (IRE1) is an ER-located kinase and endoribonuclease that operates as a major ER stress transducer, mediating the establishment of adaptive and pro-apoptotic programs. Here we discuss current evidence supporting the role of ER stress in motoneuron demise in ALS and build the rational to target IRE1 to ameliorate neurodegeneration.

Myogenic differentiation of VCP disease-induced pluripotent stem cells: A novel platform for drug discovery

Valosin Containing Protein (VCP) disease is an autosomal dominant multisystem proteinopathy caused by mutations in the VCP gene, and is primarily associated with progressive muscle weakness, including atrophy of the pelvic and shoulder girdle muscles. Currently, no treatments are available and cardiac and respiratory failures can lead to mortality at an early age. VCP is an AAA ATPase multifunction complex protein and mutations in the VCP gene resulting in disrupted autophagic clearance. Due to the rarity of the disease, the myopathic nature of the disorder, ethical and practical considerations, VCP disease muscle biopsies are difficult to obtain. Thus, disease-specific human induced pluripotent stem cells (hiPSCs) now provide a valuable resource for the research owing to their renewable and pluripotent nature. In the present study, we report the differentiation and characterization of a VCP disease-specific hiPSCs into precursors expressing myogenic markers including desmin, myogenic factor 5 (MYF5), myosin and heavy chain 2 (MYH2). VCP disease phenotype is characterized by high expression of TAR DNA Binding Protein-43 (TDP-43), ubiquitin (Ub), Light Chain 3-I/II protein (LC3-I/II), and p62/SQSTM1 (p62) protein indicating disruption of the autophagy cascade. Treatment of hiPSC precursors with autophagy stimulators Rapamycin, Perifosine, or AT101 showed reduction in VCP pathology markers TDP-43, LC3-I/II and p62/SQSTM1. Conversely, autophagy inhibitors chloroquine had no beneficial effect, and Spautin-1 or MHY1485 had modest effects. Our results illustrate that hiPSC technology provide a useful platform for a rapid drug discovery and hence constitutes a bridge between clinical and bench research in VCP and related diseases.

Proteasome impairment in neural cells derived from HMSN-P patient iPSCs

Hereditary motor and sensory neuropathy with proximal dominant involvement (HMSN-P) is caused by a heterozygous mutation (P285L) in Tropomyosin-receptor kinase Fused Gene (TFG), histopathologically characterized by progressive spinal motor neuron loss with TFG cytosolic aggregates. Although the TFG protein, found as a type of fusion oncoprotein, is known to facilitate vesicle transport from endoplasmic reticulum (ER) to Golgi apparatus at ER exit site, it is unclear how mutant TFG causes motor neuron degeneration. Here we generated induced pluripotent stem cells (iPSCs) from HMSN-P patients, and differentiated the iPSCs into neural cells with spinal motor neurons (iPS-MNs). We found that HMSN-P patient iPS-MNs exhibited ubiquitin proteasome system (UPS) impairment, and HMSN-P patient iPS-MNs were vulnerable to UPS inhibitory stress. Gene correction of the mutation in TFG using the CRISPR-Cas9 system reverted the cellular phenotypes of HMSN-P patient iPS-MNs. Collectively, these results suggest that our cellular model with defects in cellular integrity including UPS impairments may lead to identification of pathomechanisms and a therapeutic target for HMSN-P.

A new hERG allosteric modulator rescues genetic and drug-induced long-QT syndrome phenotypes in cardiomyocytes from isogenic pairs of patient induced pluripotent stem cells

Long-QT syndrome (LQTS) is an arrhythmogenic disorder characterised by prolongation of the QT interval in the electrocardiogram, which can lead to sudden cardiac death. Pharmacological treatments are far from optimal for congenital forms of LQTS, while the acquired form, often triggered by drugs that (sometimes inadvertently) target the cardiac hERG channel, is still a challenge in drug development because of cardiotoxicity. Current experimental models in vitro fall short in predicting proarrhythmic properties of new drugs in humans. Here, we leveraged a series of isogenically matched, diseased and genetically engineered, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from patients to test a novel hERG allosteric modulator for treating congenital LQTS, drug-induced LQTS or a combination of the two. By slowing IK r deactivation and positively shifting IK r inactivation, the small molecule LUF7346 effectively rescued all of these conditions, demonstrating in a human system that allosteric modulation of hERG may be useful as an approach to treat inherited and drug-induced LQTS Furthermore, our study provides experimental support of the value of isogenic pairs of patient hiPSC-CMs as platforms for testing drug sensitivities and performing safety pharmacology.

Differential neuronal vulnerability identifies IGF-2 as a protective factor in ALS

The fatal disease amyotrophic lateral sclerosis (ALS) is characterized by the loss of somatic motor neurons leading to muscle wasting and paralysis. However, motor neurons in the oculomotor nucleus, controlling eye movement, are for unknown reasons spared. We found that insulin-like growth factor 2 (IGF-2) was maintained in oculomotor neurons in ALS and thus could play a role in oculomotor resistance in this disease. We also showed that IGF-1 receptor (IGF-1R), which mediates survival pathways upon IGF binding, was highly expressed in oculomotor neurons and on extraocular muscle endplate. The addition of IGF-2 induced Akt phosphorylation, glycogen synthase kinase-3β phosphorylation and β-catenin levels while protecting ALS patient motor neurons. IGF-2 also rescued motor neurons derived from spinal muscular atrophy (SMA) patients from degeneration. Finally, AAV9::IGF-2 delivery to muscles of SOD1^G93A ALS mice extended life-span by 10%, while preserving motor neurons and inducing motor axon regeneration. Thus, our studies demonstrate that oculomotor-specific expression can be utilized to identify candidates that protect vulnerable motor neurons from degeneration.