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

Unveiling the regulatory role of miRNAs in stroke pathophysiology and diagnosis

Stroke, a major global cause of mortality, leads to a range of problems for those who survive. Besides its brutal events, stroke also tends to have a characteristic of recurrence, making it a complex disease involving intricate regulatory networks. One of the major cellular regulators is the non-coding RNAs (ncRNA), specifically microRNAs (miRNAs), thus the possible functions of miRNAs in the pathogenesis of stroke are discussed as well as the possibility of using miRNA-based therapeutic approaches. Firstly, the molecular mechanisms by which miRNAs regulate vital physiological processes, including synaptic plasticity, oxidative stress, apoptosis, and the integrity of the blood-brain barrier (BBB) are reviewed. The miRNA indirectly impacts stroke outcomes by regulating BBB function and angiogenesis through the targeting of transcription factors and angiogenic factors. In addition, the tendency for some miRNAs to be upregulated in response to hypoxia, which is a prevalent phenomenon in stroke and various neurological disorders, highlights the possibility that it controls hypoxia-inducible factor (HIF) signaling and angiogenesis, thereby influencing the integrity of the BBB as examples of the discussed mechanisms. Furthermore, this review explores the potential therapeutic targets that miRNAs may offer for stroke recovery and highlights their promising capacity to alleviate post-stroke complications. This review provides researchers and clinicians with valuable resources since it attempts to decipher the complex network of miRNA-mediated mechanisms in stroke. Additionally, the review addresses the interplay between miRNAs and stroke risk factors as well as clinical applications of miRNAs as diagnostic and prognostic markers.

Exploring the promising potential of induced pluripotent stem cells in cancer research and therapy

The advent of iPSCs has brought about a significant transformation in stem cell research, opening up promising avenues for advancing cancer treatment. The formation of cancer is a multifaceted process influenced by genetic, epigenetic, and environmental factors. iPSCs offer a distinctive platform for investigating the origin of cancer, paving the way for novel approaches to cancer treatment, drug testing, and tailored medical interventions. This review article will provide an overview of the science behind iPSCs, the current limitations and challenges in iPSC-based cancer therapy, the ethical and social implications, and the comparative analysis with other stem cell types for cancer treatment. The article will also discuss the applications of iPSCs in tumorigenesis, the future of iPSCs in tumorigenesis research, and highlight successful case studies utilizing iPSCs in tumorigenesis research. The conclusion will summarize the advancements made in iPSC-based tumorigenesis research and the importance of continued investment in iPSC research to unlock the full potential of these cells.

Engineering circuits of human iPSC-derived neurons and rat primary glia

Novel in vitro platforms based on human neurons are needed to improve early drug testing and address the stalling drug discovery in neurological disorders. Topologically controlled circuits of human induced pluripotent stem cell (iPSC)-derived neurons have the potential to become such a testing system. In this work, we build in vitro co-cultured circuits of human iPSC-derived neurons and rat primary glial cells using microfabricated polydimethylsiloxane (PDMS) structures on microelectrode arrays (MEAs). Our PDMS microstructures are designed in the shape of a stomach, which guides axons in one direction and thereby facilitates the unidirectional flow of information. Such circuits are created by seeding either dissociated cells or pre-aggregated spheroids at different neuron-to-glia ratios. Furthermore, an antifouling coating is developed to prevent axonal overgrowth in undesired locations of the microstructure. We assess the electrophysiological properties of different types of circuits over more than 50 days, including their stimulation-induced neural activity. Finally, we demonstrate the inhibitory effect of magnesium chloride on the electrical activity of our iPSC circuits as a proof-of-concept for screening of neuroactive compounds.

Mitochondrial genome mutations and neuronal dysfunction of induced pluripotent stem cells derived from patients with Alzheimer's disease

OBJECTIVES

Patient-derived induced pluripotent stem cells (iPSCs) are materials that can be used for autologous stem cell therapy. We screened mtDNA mutations in iPSCs and iPSC-derived neuronal cells from patients with Alzheimer's disease (AD). Also, we investigated whether the mutations could affect mitochondrial function and deposition of β-amyloid (Aβ) in differentiated neuronal cells.

MATERIALS AND METHODS

mtDNA mutations were measured and compared among iPSCs and iPSC-derived neuronal cells. The selected iPSCs carrying mtDNA mutations were subcloned, and then their growth rate and neuronal differentiation pattern were analyzed. The differentiated cells were measured for mitochondrial respiration and membrane potential, as well as deposition of Aβ.

RESULTS

Most iPSCs from subjects with AD harbored ≥1 mtDNA mutations, and the number of mutations was significantly higher than that from umbilical cord blood. About 35% and 40% of mutations in iPSCs were shared with isogenic iPSCs and their differentiated neuronal precursor cells, respectively, with similar or different heteroplasmy. Furthermore, the mutations in clonal iPSCs were stable during extended culture and neuronal differentiation. Finally, mtDNA mutations could induce a growth advantage with higher viability and proliferation, lower mitochondrial respiration and membrane potential, as well as increased Aβ deposition.

CONCLUSION

This study demonstrates that mtDNA mutations in patients with AD could lead to mitochondrial dysfunction and accelerated Aβ deposition. Therefore, early screening for mtDNA mutations in iPSC lines would be essential for developing autologous cell therapy or drug screening for patients with AD.

Hepatocyte-like cells differentiated from methylmalonic aciduria cblB type induced pluripotent stem cells: A platform for the evaluation of pharmacochaperoning

Methylmalonic aciduria cblB type (MMA cblB type, MMAB OMIM #251110), caused by a deficiency in the enzyme ATP:cob(I)alamin adenosyltransferase (ATR, E.C_2. 5.1.17), is a severe metabolic disorder with a poor prognosis despite treatment. We recently described the potential therapeutic use of pharmacological chaperones (PCs) after increasing the residual activity of ATR in patient-derived fibroblasts. The present work reports the successful generation of hepatocyte-like cells (HLCs) differentiated from two healthy and two MMAB induced pluripotent stem cell (iPSC) lines, and the use of this platform for testing the effects of PCs. The MMAB cells produced little ATR, showed reduced residual ATR activity, and had higher concentrations of methylmalonic acid compared to healthy HLCs. Differential proteome analysis revealed the two MMAB HCLs to show reproducible differentiation, but this was not so for the healthy HLCs. Interestingly, PC treatment in combination with vitamin B₁₂ increased the amount of ATR available, and subsequently ATR activity, in both MMAB HLCs. More importantly, the treatment significantly reduced the methylmalonic acid content of both. In summary, the HLC model would appear to be an excellent candidate for the pharmacological testing of the described PCs, for analyzing the effects of new drugs, and investigating the repurposing of older drugs, before testing in animal models.

Multidisciplinary Effort to Drive Precision-Medicine for the Future

In the past one or two decades, countries across the world have successively implemented different precision medicine (PM) programs, and also cooperated to implement international PM programs. We are now in the era of PM. Singapore's National Precision Medicine (NPM) program, initiated in 2017, is now entering its second phase to generate a large genomic database for Asians. The National University of Singapore (NUS) also launched its own PM translational research program (TRP) in 2021, aimed at consolidating multidisciplinary expertise within the Yong Loo Lin School of Medicine to develop collaborative projects that can help to identify and validate novel therapeutic targets for the realization of PM. To achieve this, appropriate data collection, data processing, and results interpretation must be taken into consideration. There may be some difficulties during these processes, but with the improvement of relevant rules and the continuous development of omics-based technologies, we will be able to solve these problems, eventually achieving precise prediction, diagnosis, treatment, or even prevention of diseases.

Ultrasound and Transcriptomics Identify a Differential Impact of Cisplatin and Histone Deacetylation on Tumor Structure and Microenvironment in a Patient-Derived In Vivo Model of Gastric Cancer

The reasons behind the poor efficacy of transition metal-based chemotherapies (e.g., cisplatin) or targeted therapies (e.g., histone deacetylase inhibitors, HDACi) on gastric cancer (GC) remain elusive and recent studies suggested that the tumor microenvironment could contribute to the resistance. Hence, our objective was to gain information on the impact of cisplatin and the pan-HDACi SAHA (suberanilohydroxamic acid) on the tumor substructure and microenvironment of GC, by establishing patient-derived xenografts of GC and a combination of ultrasound, immunohistochemistry, and transcriptomics to analyze. The tumors responded partially to SAHA and cisplatin. An ultrasound gave more accurate tumor measures than a caliper. Importantly, an ultrasound allowed a noninvasive real-time access to the tumor substructure, showing differences between cisplatin and SAHA. These differences were confirmed by immunohistochemistry and transcriptomic analyses of the tumor microenvironment, identifying specific cell type signatures and transcription factor activation. For instance, cisplatin induced an "epithelial cell like" signature while SAHA favored a "mesenchymal cell like" one. Altogether, an ultrasound allowed a precise follow-up of the tumor progression while enabling a noninvasive real-time access to the tumor substructure. Combined with transcriptomics, our results underline the different intra-tumoral structural changes caused by both drugs that impact differently on the tumor microenvironment.

Neuroprotective gain of Apelin/APJ system

Apelin is an endogenous ligand of G protein-coupled receptor APJ. In recent years, many studies have shown that the apelin/APJ system has neuroprotective properties, such as anti-inflammatory, anti-oxidative stress, anti-apoptosis, and regulating autophagy, blocking excitatory toxicity. Apelin/APJ system has been proven to play a role in various neurological diseases and may be a promising therapeutic target for nervous system diseases. In this paper, the neuroprotective properties of the apelin/APJ system and its role in neurologic disorders are reviewed. Further understanding of the pathophysiological effect and mechanism of the apelin/APJ system in the nervous system will help develop new therapeutic interventions for various neurological diseases.

Longitudinal Characterization of Transcriptomic, Functional, and Morphological Features in Human iPSC-Derived Neurons and Their Application to Investigate Translational Progranulin Disease Biology

The disease biology of frontotemporal lobe dementia (FTD) is complex and not fully understood, with limited translational value appreciated from animal models to date. Human cellular systems that can recapitulate phenotypic features of disease offer promise as translational tools to not only increase our understanding of disease processes but also increase the probability of success of translating novel treatment options to patients. However not all researchers may necessarily have access to well-characterized induced pluripotent stem cell (iPSC)-derived human neurons. As an example, we therefore comprehensively profiled phenotypic features over time in one commercially-available IPSC-derived human neuron cell line. This included systems-level assessments of neurite outgrowth dynamics, neuronal network function, and genome-wide gene expression. By investigating progranulin biology as an example we then demonstrated the utility of these cells as a tool to investigate human disease biology. For example, by using the siRNA-mediated knockdown of the progranulin (GRN) gene, we demonstrated the establishment of an isogenic human cellular model to facilitate translational FTD research. We reproduced findings from rodent neurons by demonstrating that recombinant progranulin (rPGRN) mediated neuroprotection. Contrary to previous rodent data, in our human cellular models, growth factor treatment showed no consistent sensitivity to modulate neurite outgrowth dynamics. Our study further provides the first evidence that rRPGRN modulated neuronal firing and synchrony in human neurons. Taken together, our datasets are a valuable systems-level resource demonstrating the utility of the tested commercially-available human iPSC neurons for investigating basic human neurobiology, translational neuroscience, and drug discovery applications in neurodegenerative and other CNS diseases.

Nontraditional systems in aging research: an update

Research on the evolutionary and mechanistic aspects of aging and longevity has a reductionist nature, as the majority of knowledge originates from experiments on a relatively small number of systems and species. Good examples are the studies on the cellular, molecular, and genetic attributes of aging (senescence) that are primarily based on a narrow group of somatic cells, especially fibroblasts. Research on aging and/or longevity at the organismal level is dominated, in turn, by experiments on Drosophila melanogaster, worms (Caenorhabditis elegans), yeast (Saccharomyces cerevisiae), and higher organisms such as mice and humans. Other systems of aging, though numerous, constitute the minority. In this review, we collected and discussed a plethora of up-to-date findings about studies of aging, longevity, and sometimes even immortality in several valuable but less frequently used systems, including bacteria (Caulobacter crescentus, Escherichia coli), invertebrates (Turritopsis dohrnii, Hydra sp., Arctica islandica), fishes (Nothobranchius sp., Greenland shark), reptiles (giant tortoise), mammals (blind mole rats, naked mole rats, bats, elephants, killer whale), and even 3D organoids, to prove that they offer biogerontologists as much as the more conventional tools. At the same time, the diversified knowledge gained owing to research on those species may help to reconsider aging from a broader perspective, which should translate into a better understanding of this tremendously complex and clearly system-specific phenomenon.

Three-dimensional differentiation of human pluripotent stem cell-derived neural precursor cells using tailored porous polymer scaffolds

This study investigates the utility of a tailored poly(ethylene glycol) diacrylate-crosslinked porous polymeric tissue engineering scaffold, with mechanical properties specifically optimised to be comparable to that of mammalian brain tissue for 3D human neural cell culture. Results obtained here demonstrate the attachment, proliferation and terminal differentiation of both human induced pluripotent stem cell- and embryonic stem cell-derived neural precursor cells (hPSC-NPCs) throughout the interconnected porous network within laminin-coated scaffolds. Phenotypic data and functional analyses are presented demonstrating that this material supports terminal in vitro neural differentiation of hPSC-NPCs to a mixed population of viable neuronal and glial cells for periods of up to 49 days. This is evidenced by the upregulation of TUBB3, MAP2, SYP and GFAP gene expression, as well as the presence of the proteins βIII-TUBULIN, NEUN, MAP2 and GFAP. Functional maturity of neural cells following 49 days 3D differentiation culture was tested via measurement of intracellular calcium. These analyses revealed spontaneously active, synchronous and rhythmic calcium flux, as well as response to the neurotransmitter glutamate. This tailored construct has potential application as an improved in vitro human neurogenesis model with utility in platform drug discovery programs. STATEMENT OF SIGNIFICANCE: The interconnected porosity of polyHIPE scaffolds exhibits the ability to support three-dimensional neural cell network formation due to limited resistance to cellular migration and re-organisation. The previously developed scaffold material displays mechanical properties similar to that of the mammalian brain. This research also employs the utility of pluripotent stem cell-derived neural cells which are of greater clinical relevance than primary neural cell lines. This scaffold material has future potential in better mimicking three-dimensional neural networks found in the human brain and may result in improved in vitro models for disease modelling and drug screening applications.

A transient reporter for editing enrichment (TREE) in human cells

Current approaches to identify cell populations that have been modified with deaminase base editing technologies are inefficient and rely on downstream sequencing techniques. In this study, we utilized a blue fluorescent protein (BFP) that converts to green fluorescent protein (GFP) upon a C-to-T substitution as an assay to report directly on base editing activity within a cell. Using this assay, we optimize various base editing transfection parameters and delivery strategies. Moreover, we utilize this assay in conjunction with flow cytometry to develop a transient reporter for editing enrichment (TREE) to efficiently purify base-edited cell populations. Compared to conventional cell enrichment strategies that employ reporters of transfection (RoT), TREE significantly improved the editing efficiency at multiple independent loci, with efficiencies approaching 80%. We also employed the BFP-to-GFP conversion assay to optimize base editor vector design in human pluripotent stem cells (hPSCs), a cell type that is resistant to genome editing and in which modification via base editors has not been previously reported. At last, using these optimized vectors in the context of TREE allowed for the highly efficient editing of hPSCs. We envision TREE as a readily adoptable method to facilitate base editing applications in synthetic biology, disease modeling, and regenerative medicine.

A Simple Procedure for Creating Scalable Phenotypic Screening Assays in Human Neurons

Neurons created from human induced pluripotent stem cells (hiPSCs) provide the capability of identifying biological mechanisms that underlie brain disorders. IPSC-derived human neurons, or iNs, hold promise for advancing precision medicine through drug screening, though it remains unclear to what extent iNs can support early-stage drug discovery efforts in industrial-scale screening centers. Despite several reported approaches to generate iNs from iPSCs, each suffer from technological limitations that challenge their scalability and reproducibility, both requirements for successful screening assays. We addressed these challenges by initially removing the roadblocks related to scaling of iNs for high throughput screening (HTS)-ready assays. We accomplished this by simplifying the production and plating of iNs and adapting them to a freezer-ready format. We then tested the performance of freezer-ready iNs in an HTS-amenable phenotypic assay that measured neurite outgrowth. This assay successfully identified small molecule inhibitors of neurite outgrowth. Importantly, we provide evidence that this scalable iN-based assay was both robust and highly reproducible across different laboratories. These streamlined approaches are compatible with any iPSC line that can produce iNs. Thus, our findings indicate that current methods for producing iPSCs are appropriate for large-scale drug-discovery campaigns (i.e. >10e5 compounds) that read out simple neuronal phenotypes. However, due to the inherent limitations of currently available iN differentiation protocols, technological advances are required to achieve similar scalability for screens that require more complex phenotypes related to neuronal function.

The Use of Pluripotent Stem Cell-Derived Organoids to Study Extracellular Matrix Development during Neural Degeneration

The mechanism that causes the Alzheimer's disease (AD) pathologies, including amyloid plaque, neurofibrillary tangles, and neuron death, is not well understood due to the lack of robust study models for human brain. Three-dimensional organoid systems based on human pluripotent stem cells (hPSCs) have shown a promising potential to model neurodegenerative diseases, including AD. These systems, in combination with engineering tools, allow in vitro generation of brain-like tissues that recapitulate complex cell-cell and cell-extracellular matrix (ECM) interactions. Brain ECMs play important roles in neural differentiation, proliferation, neuronal network, and AD progression. In this contribution related to brain ECMs, recent advances in modeling AD pathology and progression based on hPSC-derived neural cells, tissues, and brain organoids were reviewed and summarized. In addition, the roles of ECMs in neural differentiation of hPSCs and the influences of heparan sulfate proteoglycans, chondroitin sulfate proteoglycans, and hyaluronic acid on the progression of neurodegeneration were discussed. The advantages that use stem cell-based organoids to study neural degeneration and to investigate the effects of ECM development on the disease progression were highlighted. The contents of this article are significant for understanding cell-matrix interactions in stem cell microenvironment for treating neural degeneration.

A SMN2 Splicing Modifier Rescues the Disease Phenotypes in an In Vitro Human Spinal Muscular Atrophy Model

Spinal muscular atrophy (SMA) is caused by the mutation or deletion of the survival motor neuron 1 (SMN1) gene. Only ∼10% of the products of SMN2, a paralogue of SMN1, are functional full-length SMN (SMN-FL) proteins, whereas SMN2 primarily produces alternatively spliced transcripts lacking exon 7. Reduced SMN protein levels in SMA patients lead to progressive degeneration of spinal motor neurons (MNs). In this study, we report an advanced platform based on an SMN2 splicing-targeting approach for SMA drug screening and validation using an SMN2 splicing reporter cell line and an in vitro human SMA model through induced pluripotent stem cell (iPSC) technology. Through drug screening using a robust cell-based luciferase assay to quantitatively measure SMN2 splicing, the small-molecule candidate compound rigosertib was identified as an SMN2 splicing modulator that led to enhanced SMN protein expression. The therapeutic potential of the candidate compound was validated in MN progenitors differentiated from SMA patient-derived iPSCs (SMA iPSC-pMNs) as an in vitro human SMA model, which recapitulated the biochemical and molecular phenotypes of SMA, including lower levels of SMN-FL transcripts and protein, enhanced cell death, and reduced neurite length. The candidate compound exerted strong splicing correction activity for SMN2 and potently alleviated the disease-related phenotypes of SMA iPSC-pMNs by modulating various cellular and molecular abnormalities. Our combined screening platform representing a pMN model of human SMA provides an efficient and reliable drug screening system and is a promising resource for drug evaluation and the exploration of drug modes of action.

Stem cells technology: a powerful tool behind new brain treatments

Stem cell research has recently become a hot research topic in biomedical research due to the foreseen unlimited potential of stem cells in tissue engineering and regenerative medicine. For many years, medicine has been facing intense challenges, such as an insufficient number of organ donations that is preventing clinicians to fulfill the increasing needs. To try and overcome this regrettable matter, research has been aiming at developing strategies to facilitate the in vitro culture and study of stem cells as a tool for tissue regeneration. Meanwhile, new developments in the microfluidics technology brought forward emerging cell culture applications that are currently allowing for a better chemical and physical control of cellular microenvironment. This review presents the latest developments in stem cell research that brought new therapies to the clinics and how the convergence of the microfluidics technology with stem cell research can have positive outcomes on the fields of regenerative medicine and high-throughput screening. These advances will bring new translational solutions for drug discovery and will upgrade in vitro cell culture to a new level of accuracy and performance. We hope this review will provide new insights into the understanding of new brain treatments from the perspective of stem cell technology especially regarding regenerative medicine and tissue engineering.

Neuroprotective Role of Agmatine in Neurological Diseases

Background:

Neurological diseases have always been one of the leading cause of mobility and mortality world-widely. However, it is still lacking efficient agents. Agmatine, an endogenous polyamine, exerts its diverse biological characteristics and therapeutic potential in varied aspects.

Methods:

This review would focus on the neuroprotective actions of agmatine and its potential mechanisms in the setting of neurological diseases.

Results:

Numerous studies had demonstrated the neuroprotective effect of agmatine in varied types of neurological diseases, including acute attack (stroke and trauma brain injury) and chronic neurodegenerative diseases (Parkinson's disease, Alz-heimer’s disease). The potential mechanism of agmatine induced neuroprotection includes anti-oxidation, anti-apoptosis, anti-inflammation, brain blood barrier (BBB) protection and brain edema prevention.

Conclusions:

The safety and low incidence of adverse effects indicate the vast potential therapeutic value of agmatine in the treatment of neurological diseases. However, most of the available studies relate to the agmatine are conducted in experi-mental models, more clinical trials are needed before the agmatine could be extensively clinically used

The Roles of MicroRNAs in Stroke: Possible Therapeutic Targets

Stroke is one of the most devastating diseases worldwide. In recent years, a great number of studies have focused on the effects of microRNAs (miRNAs) on stroke and the results demonstrated that the expressions of miRNAs are associated with the prognosis of stroke. In the present study, we review relevant articles regarding miRNAs and stroke and will explain the complex link between both. The miRNAs participate extensively in the pathophysiology following the stroke, including apoptosis, neuroinflammation, oxidative stress, blood–brain barrier (BBB) disruption and brain edema. The information about the stroke–miRNA system may be helpful for therapeutic and diagnostic methods in stroke treatment.

The GluN2B subunit represents a major functional determinant of NMDA receptors in human induced pluripotent stem cell-derived cortical neurons

Abnormal signaling pathways mediated by N-methyl-d-aspartate receptors (NMDARs) have been implicated in the pathogenesis of various CNS disorders and have been long considered as promising points of therapeutic intervention. However, few efforts have been previously described concerning evaluation of therapeutic modulators of NMDARs and their downstream pathways in human neurons with endogenous expression of NMDARs. In the present study, we assessed expression, functionality, and subunit composition of endogenous NMDARs in human induced pluripotent stem cell (hiPSC)-derived cortical neurons (iCell Neurons and iCell GlutaNeurons). We initially confirmed the expected pharmacological response of iCell Neurons and iCell GlutaNeurons to NMDA by patch-clamp recordings. Subsequent pharmacological interrogation using GluN2 subunit-selective antagonists revealed the predominance of GluN2B in both iCell Neurons and iCell GlutaNeurons. This observation was also supported by qRT-PCR and Western blot analyses of GluN2 subunit expression as well as pharmacological experiments using positive allosteric modulators with distinct GluN2 subunit selectivity. We conclude that iCell Neurons and iCell GlutaNeurons express functional GluN2B-containing NMDARs and could serve as a valuable system for development and validation of GluN2B-modulating pharmaceutical agents.

Neuroprotective Effects of Stem Cells in Ischemic Stroke

Ischemic stroke, the most common subtype of stroke, has been one of the leading causes of mobility and mortality worldwide. However, it is still lacking of efficient agents. Stem cell therapy, with its vigorous advantages, has attracted researchers around the world. Numerous experimental researches in animal models of stroke have demonstrated the promising efficacy in treating ischemic stroke. The underlying mechanism involved antiapoptosis, anti-inflammation, promotion of angiogenesis and neurogenesis, formation of new neural cells and neuronal circuitry, antioxidation, and blood-brain barrier (BBB) protection. This review would focus on the types and neuroprotective actions of stem cells and its potential mechanisms for ischemic stroke.

Induced pluripotent stem cell: A headway in reprogramming with promising approach in regenerative biology

Since the embryonic stem cells have knocked the doorsteps, they have proved themselves in the field of science, research, and medicines, but the hovered restrictions confine their application in human welfare. Alternate approaches used to reprogram the cells to the pluripotent state were not up to par, but the innovation of induced pluripotent stem cells (iPSCs) paved a new hope for the researchers. Soon after the discovery, iPSCs technology is undergoing renaissance day by day, i.e., from the use of genetic material to recombinant proteins and now only chemicals are employed to convert somatic cells to iPSCs. Thus, this technique is moving straightforward and productive at an astonishing pace. Here, we provide a brief introduction to iPSCs, the mechanism and methods for their generation, their prevailing and prospective applications and the future opportunities that can be expected from them.

Scaffolds for 3D in vitro culture of neural lineage cells

Understanding how neurodegenerative disorders develop is not only a key challenge for researchers but also for the wider society, given the rapidly aging populations in developed countries. Advances in this field require new tools with which to recreate neural tissue in vitro and produce realistic disease models. This in turn requires robust and reliable systems for performing 3D in vitro culture of neural lineage cells. This review provides a state of the art update on three-dimensional culture systems for in vitro development of neural tissue, employing a wide range of scaffold types including hydrogels, solid porous polymers, fibrous materials and decellularised tissues as well as microfluidic devices and lab-on-a-chip systems. To provide some context with in vivo development of the central nervous system (CNS), we also provide a brief overview of the neural stem cell niche, neural development and neural differentiation in vitro. We conclude with a discussion of future directions for this exciting and important field of biomaterials research.

STATEMENT OF SIGNIFICANCE

Neurodegenerative diseases, including dementia, Parkinson's and Alzheimer's diseases and motor neuron diseases, are a major societal challenge for aging populations. Understanding these conditions and developing therapies against them will require the development of new physical models of healthy and diseased neural tissue. Cellular models resembling neural tissue can be cultured in the laboratory with the help of 3D scaffolds - materials that allow the organization of neural cells into tissue-like structures. This review presents recent work on the development of different types of scaffolds for the 3D culture of neural lineage cells and the generation of functioning neural-like tissue. These in vitro culture systems are enabling the development of new approaches for modelling and tackling diseases of the brain and CNS.

Novel therapeutic approaches: Rett syndrome and human induced pluripotent stem cell technology

Recent advances in induced pluripotent stem cell (iPSC) technology target screening and discovering of therapeutic agents for the possible cure of human diseases. Human induced pluripotent stem cells (hiPSC) are the right kind of platform for testing potency of specific active compounds. Ayurveda, the Indian traditional system of medicine developed between 2,500 and 500 BC, is a science involving the intelligent formulations of herbs and minerals. It can serve as a "goldmine" for novel neuroprotective agents used for centuries to treat neurological disorders. This review discusses limitations in screening drugs for neurological disorders and the advantages offered by hiPSC integrated with Indian traditional system of medicine. We begin by describing the current state of hiPSC technology in research on Rett syndrome (RTT) followed by the current controversies in RTT research combined with the emergence of patient-specific hiPSC that indicate an urgent need for researchers to understand the etiology and drug mechanism. We conclude by offering recommendations to reinforce the screening of active compounds present in the ayurvedic medicines using the human induced pluripotent neural model system for research involving drug discovery for RTT. This integrative approach will fill the current knowledge gap in the traditional medicines and drug discovery.

Glia-neuron interactions in neurological diseases: Testing non-cell autonomy in a dish

For the past century, research on neurological disorders has largely focused on the most prominently affected cell types - the neurons. However, with increasing knowledge of the diverse physiological functions of glial cells, their impact on these diseases has become more evident. Thus, many conditions appear to have more complex origins than initially thought. Since neurological pathologies are often sporadic with unknown etiology, animal models are difficult to create and might only reflect a small portion of patients in which a mutation in a gene has been identified. Therefore, reliable in vitro systems to studying these disorders are urgently needed. They might be a pre-requisite for improving our understanding of the disease mechanisms as well as for the development of potential new therapies. In this review, we will briefly summarize the function of different glial cell types in the healthy central nervous system (CNS) and outline their implication in the development or progression of neurological conditions. We will then describe different types of culture systems to model non-cell autonomous interactions in vitro and evaluate advantages and disadvantages. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Multi-target therapeutics for neuropsychiatric and neurodegenerative disorders

Historically, neuropsychiatric and neurodegenerative disease treatments focused on the 'magic bullet' concept; however multi-targeted strategies are increasingly attractive gauging from the escalating research in this area. Because these diseases are typically co-morbid, multi-targeted drugs capable of interacting with multiple targets will expand treatment to the co-morbid disease condition. Despite their theoretical efficacy, there are significant impediments to clinical success (e.g., difficulty titrating individual aspects of the drug and inconclusive pathophysiological mechanisms). The new and revised diagnostic frameworks along with studies detailing the endophenotypic characteristics of the diseases promise to provide the foundation for the circumvention of these impediments. This review serves to evaluate the various marketed and nonmarketed multi-targeted drugs with particular emphasis on their design strategy.

High-throughput platforms for the screening of new therapeutic targets for neurodegenerative diseases

Despite the recent progress in the understanding of neurodegenerative disorders, a lack of solid fundamental knowledge on the etiology of many of the major neurodegenerative diseases has made it difficult to obtain effective therapies to treat these conditions. Scientists have been looking to carry out more-human-relevant studies, with strong statistical power, to overcome the limitations of preclinical animal models that have contributed to the failure of numerous therapeutics in clinical trials. Here, we identify currently existing platforms to mimic central nervous system tissues, healthy and diseased, mainly focusing on cell-based platforms and discussing their strengths and limitations in the context of the high-throughput screening of new therapeutic targets and drugs.

Wnt-YAP interactions in the neural fate of human pluripotent stem cells and the implications for neural organoid formation

Human pluripotent stem cells (hPSCs) have shown the ability to self-organize into different types of neural organoids (e.g., whole brain organoids, cortical spheroids, midbrain organoids etc.) recently. The extrinsic and intrinsic signaling elicited by Wnt pathway, Hippo/Yes-associated protein (YAP) pathway, and extracellular microenvironment plays a critical role in brain tissue morphogenesis. This article highlights recent advances in neural tissue patterning from hPSCs, in particular the role of Wnt pathway and YAP activity in this process. Understanding the Wnt-YAP interactions should provide us the guidance to predict and modulate brain-like tissue structure through the regulation of extracellular microenvironment of hPSCs.

Human Induced Pluripotent Stem Cell Derived Neuronal Cells Cultured on Chemically-Defined Hydrogels for Sensitive In Vitro Detection of Botulinum Neurotoxin

Botulinum neurotoxin (BoNT) detection provides a useful model for validating cell-based neurotoxicity screening approaches, as sensitivity is dependent on functionally competent neurons and clear quantitative endpoints are available for correlating results to approved animal testing protocols. Here, human induced pluripotent stem cell (iPSC)-derived neuronal cells were cultured on chemically-defined poly(ethylene glycol) (PEG) hydrogels formed by "thiol-ene" photopolymerization and tested as a cell-based neurotoxicity assay by determining sensitivity to active BoNT/A1. BoNT/A1 sensitivity was comparable to the approved in vivo mouse bioassay for human iPSC-derived neurons and neural stem cells (iPSC-NSCs) cultured on PEG hydrogels or treated tissue culture polystyrene (TCP) surfaces. However, maximum sensitivity for BoNT detection was achieved two weeks earlier for iPSC-NSCs that were differentiated and matured on PEG hydrogels compared to TCP. Therefore, chemically-defined synthetic hydrogels offer benefits over standard platforms when optimizing culture conditions for cell-based screening and achieve sensitivities comparable to an approved animal testing protocol.

Directed cardiomyogenesis of human pluripotent stem cells by modulating Wnt/β-catenin and BMP signalling with small molecules

Cardiomyocytes derived from human pluripotent stem cells (PSCs) are a potential cell source for regenerative medicine, disease modelling and drug development. However, current approaches for in vitro cardiac differentiation of human PSCs are often time-consuming, heavily depend on expensive growth factors and involve the tedious formation of embryonic bodies whose signalling pathways are difficult to precisely modulate due to their complex microenvironments. In the present study, we report a new small molecule-based differentiation approach, which significantly promoted contracting cardiomyocytes in human PSCs in a monolayer format in as little as 7 days, in contrast with most traditional differentiation methods that usually take up to 3 weeks for cardiomyogenesis. This approach consists in activation of the Wnt/β-catenin signalling at day 0-1 with small molecule CHIR99021 (CH) followed by inhibition of bone morphogenetic protein (BMP) signalling at day 1-4 with DMH1 [termed as CH(0-1)/DMH1(1-4) treatment], a selective small molecule BMP inhibitor reported by us previously. Our study further demonstrated that the CH(0-1)/DMH1(1-4) treatment significantly promotes cardiac formation via mesoderm and mesoderm-derived cardiac progenitor cells without impacts on either endoderm or ectoderm differentiation of human PSCs. This rapid, efficient and inexpensive small molecule-based cardiomyogenic method may potentially harness the use of human PSCs in regenerative medicine as well as other applications.

Applications of iPSCs in Cancer Research

Induced pluripotent stem cells (iPSCs) derived from reprogrammed somatic cells are emerging as one of the most versatile tools in biomedical research and pharmacological studies. Oncogenic transformation and somatic cell reprogramming are multistep processes that share some common features, and iPSCs generated from cancerous cells can help us better understand the molecular mechanisms underlying the initiation and progression of human cancers and overcome them. Aside from the mechanistic modeling of human tumorigenesis, immediate applications of this technology in cancer research include high-throughput drug screening, toxicological testing, early biomarker identification, and bioengineering of replacement tissues. Here, we review the current advances in generating iPSCs from cancer cell lines and patient-derived primary cancer tissues, and discuss their potential applications.

Derivation of Canine Induced Pluripotent Stem Cells

Dogs and humans have many inherited genetic diseases in common and conditions that are increasingly prevalent in humans also occur naturally in dogs. The use of dogs for the experimental and clinical testing of stem cell and regenerative medicine products would benefit canine health and welfare and provide relevant animal models for the translation of therapies to the human field. Induced pluripotent stem cells (iPSCs) have the capacity to turn into all cells of the body and therefore have the potential to provide cells for therapeutic use and for disease modelling. The objective of this study was to derive and characterize iPSCs from karyotypically abnormal adult canine cells. Aneuploid adipose-derived mesenchymal stromal cells (AdMSCs) from an adult female Weimeraner were re-programmed into iPSCs via overexpression of four human pluripotency factors (Oct 4, Sox2, Klf4 and c-myc) using retroviral vectors. The iPSCs showed similarity to human ESCs with regard to morphology, pluripotency marker expression and the ability to differentiate into derivatives of all three germ layers in vitro (endoderm, ectoderm and mesoderm). The iPSCs also demonstrated silencing of the viral transgenes and re-activation of the silent X chromosome, suggesting full reprogramming had occurred. The levels of aneuploidy observed in the AdMSCs were maintained in the iPSCs. This finding demonstrates the potential for generating canine induced pluripotent stem cells for use as disease models in addition to regenerative medicine and pharmaceutical testing.

High-Throughput Screening Using iPSC-Derived Neuronal Progenitors to Identify Compounds Counteracting Epigenetic Gene Silencing in Fragile X Syndrome

Fragile X syndrome (FXS) is the most common form of inherited mental retardation, and it is caused in most of cases by epigenetic silencing of the Fmr1 gene. Today, no specific therapy exists for FXS, and current treatments are only directed to improve behavioral symptoms. Neuronal progenitors derived from FXS patient induced pluripotent stem cells (iPSCs) represent a unique model to study the disease and develop assays for large-scale drug discovery screens since they conserve the Fmr1 gene silenced within the disease context. We have established a high-content imaging assay to run a large-scale phenotypic screen aimed to identify compounds that reactivate the silenced Fmr1 gene. A set of 50,000 compounds was tested, including modulators of several epigenetic targets. We describe an integrated drug discovery model comprising iPSC generation, culture scale-up, and quality control and screening with a very sensitive high-content imaging assay assisted by single-cell image analysis and multiparametric data analysis based on machine learning algorithms. The screening identified several compounds that induced a weak expression of fragile X mental retardation protein (FMRP) and thus sets the basis for further large-scale screens to find candidate drugs or targets tackling the underlying mechanism of FXS with potential for therapeutic intervention.

Scalable 96-well Plate Based iPSC Culture and Production Using a Robotic Liquid Handling System

Continued advancement in pluripotent stem cell culture is closing the gap between bench and bedside for using these cells in regenerative medicine, drug discovery and safety testing. In order to produce stem cell derived biopharmaceutics and cells for tissue engineering and transplantation, a cost-effective cell-manufacturing technology is essential. Maintenance of pluripotency and stable performance of cells in downstream applications (e.g., cell differentiation) over time is paramount to large scale cell production. Yet that can be difficult to achieve especially if cells are cultured manually where the operator can introduce significant variability as well as be prohibitively expensive to scale-up. To enable high-throughput, large-scale stem cell production and remove operator influence novel stem cell culture protocols using a bench-top multi-channel liquid handling robot were developed that require minimal technician involvement or experience. With these protocols human induced pluripotent stem cells (iPSCs) were cultured in feeder-free conditions directly from a frozen stock and maintained in 96-well plates. Depending on cell line and desired scale-up rate, the operator can easily determine when to passage based on a series of images showing the optimal colony densities for splitting. Then the necessary reagents are prepared to perform a colony split to new plates without a centrifugation step. After 20 passages (~3 months), two iPSC lines maintained stable karyotypes, expressed stem cell markers, and differentiated into cardiomyocytes with high efficiency. The system can perform subsequent high-throughput screening of new differentiation protocols or genetic manipulation designed for 96-well plates. This technology will reduce the labor and technical burden to produce large numbers of identical stem cells for a myriad of applications.

Pancreatic Islet-Like Three-Dimensional Aggregates Derived From Human Embryonic Stem Cells Ameliorate Hyperglycemia in Streptozotocin-Induced Diabetic Mice

We previously reported the in vitro differentiation of human embryonic stem cells (hESCs) into pancreatic endoderm. Here we demonstrate that islet-like three-dimensional (3D) aggregates can be derived from the pancreatic endoderm by optimizing our previous protocol. Sequential treatment with Wnt3a, activin A, and noggin induced a transient upregulation of T and MixL1, followed by increased expression of endodermal genes, including FOXA2, SOX17, and CXCR4. Subsequent treatment with retinoic acid highly upregulated PDX1 expression. We also show that inhibition of sonic hedgehog signaling by bFGF/activin βB and cotreatment with VEGF and FGF7 produced many 3D cellular clusters that express both SOX17 and PDX1. We found for the first time that proteoglycans and vimentin(+) mesenchymal cells were mainly localized in hESC-derived PDX1(+) clusters. Importantly, treatment with chlorate, an inhibitor of proteoglycan sulfation, together with inhibition of Notch signaling significantly increased the expression of Neurog3 and NeuroD1, promoting a transition from PDX1(+) progenitor cells toward mature pancreatic endocrine cells. Purified dithizone(+) 3D aggregates generated by our refined protocol produced pancreatic hormones and released insulin in response to both glucose and pharmacological drugs in vitro. Furthermore, the islet-like 3D aggregates decreased blood glucose levels and continued to exhibit pancreatic features after transplantation into diabetic mice. Generation of islet-like 3D cell aggregates from human pluripotent stem cells may overcome the shortage of cadaveric donor islets for future cases of clinical islet transplantation.

Human pluripotent stem cells on artificial microenvironments: a high content perspective

Self-renewing stem cell populations are increasingly considered as resources for cell therapy and tools for drug discovery. Human pluripotent stem (hPS) cells in particular offer a virtually unlimited reservoir of homogeneous cells and can be differentiated toward diverse lineages. Many diseases show impairment in self-renewal or differentiation, abnormal lineage choice or other aberrant cell behavior in response to chemical or physical cues. To investigate these responses, there is a growing interest in the development of specific assays using hPS cells, artificial microenvironments and high content analysis. Several hurdles need to be overcome that can be grouped into three areas: (i) availability of robust, homogeneous, and consistent cell populations as a starting point; (ii) appropriate understanding and use of chemical and physical microenvironments; (iii) development of assays that dissect the complexity of cell populations in tissues while mirroring specific aspects of their behavior. Here we review recent progress in the culture of hPS cells and we detail the importance of the environment surrounding the cells with a focus on synthetic material and suitable high content analysis approaches. The technologies described, if properly combined, have the potential to create a paradigm shift in the way diseases are modeled and drug discovery is performed.

iPS cells: a game changer for future medicine

The induced pluripotent stem cell (iPSC) technology is instrumental in advancing the fields of disease modeling and cell transplantation. We herein discuss the various issues regarding disease modeling and cell transplantation presented in previous reports, and also describe new iPSC-based medicine including iPSC clinical trials. In such trials, iPSCs from patients can be used to predict drug responders/non-responders by analyzing the efficacy of the drug on iPSC-derived cells. They could also be used to stratify patients after actual clinical trials, including those with sporadic diseases, based on the drug responsiveness of each patient in the clinical trials. iPSC-derived cells can be used for the identification of response markers, leading to increased success rates in such trials. Since iPSCs can be used in micromedicine for drug discovery, and in macromedicine for actual clinical trials, their use would tightly connect both micro- and macromedicine. The use of iPSCs in disease modeling, cell transplantation, and clinical trials could therefore lead to significant changes in the future of medicine.

Neural differentiation from pluripotent stem cells: The role of natural and synthetic extracellular matrix

Neural cells differentiated from pluripotent stem cells (PSCs), including both embryonic stem cells and induced pluripotent stem cells, provide a powerful tool for drug screening, disease modeling and regenerative medicine. High-purity oligodendrocyte progenitor cells (OPCs) and neural progenitor cells (NPCs) have been derived from PSCs recently due to the advancements in understanding the developmental signaling pathways. Extracellular matrices (ECM) have been shown to play important roles in regulating the survival, proliferation, and differentiation of neural cells. To improve the function and maturation of the derived neural cells from PSCs, understanding the effects of ECM over the course of neural differentiation of PSCs is critical. During neural differentiation of PSCs, the cells are sensitive to the properties of natural or synthetic ECMs, including biochemical composition, biomechanical properties, and structural/topographical features. This review summarizes recent advances in neural differentiation of human PSCs into OPCs and NPCs, focusing on the role of ECM in modulating the composition and function of the differentiated cells. Especially, the importance of using three-dimensional ECM scaffolds to simulate the in vivo microenvironment for neural differentiation of PSCs is highlighted. Future perspectives including the immediate applications of PSC-derived neural cells in drug screening and disease modeling are also discussed.

Phenotypic screens targeting neurodegenerative diseases

Neurodegenerative diseases affect millions of people worldwide, and the incidences increase as the population ages. Disease-modifying therapy that prevents or slows disease progression is still lacking, making neurodegenerative diseases an area of high unmet medical need. Target-based drug discovery for disease-modifying agents has been ongoing for many years, without much success due to incomplete understanding of the molecular mechanisms underlying neurodegeneration. Phenotypic screening, starting with a disease-relevant phenotype to screen for compounds that change the outcome of biological pathways rather than activities at certain specific targets, offers an alternative approach to find small molecules or targets that modulate the key characteristics of neurodegeneration. Phenotypic screens that focus on amelioration of disease-specific toxins, protection of neurons from degeneration, or promotion of neuroregeneration could be potential fertile grounds for discovering therapeutic agents for neurodegenerative diseases. In this review, we will summarize the progress of compound screening using these phenotypic-based strategies for this area, with a highlight on unique considerations for disease models, assays, and screening methodologies. We will further provide our perspectives on how best to use phenotypic screening to develop drug leads for neurodegenerative diseases.