EZ spheres: a stable and expandable culture system for the generation of pre-rosette multipotent stem cells from human ESCs and iPSCs

Systemic HER3 ligand-mimicking nanobioparticles enter the brain and reduce intracranial tumour growth

Crossing the blood-brain barrier (BBB) and reaching intracranial tumours is a clinical challenge for current targeted interventions including antibody-based therapies, contributing to poor patient outcomes. Increased cell surface density of human epidermal growth factor receptor 3 (HER3) is associated with a growing number of metastatic tumour types and is observed on tumour cells that acquire resistance to a growing number of clinical targeted therapies. Here we describe the evaluation of HER3-homing nanobiological particles (nanobioparticles (NBPs)) on such tumours in preclinical models and our discovery that systemic NBPs could be found in the brain even in the absence of such tumours. Our subsequent studies described here show that HER3 is prominently associated with both mouse and human brain endothelium and with extravasation of systemic NBPs in mice and in human-derived BBB chips in contrast to non-targeted agents. In mice, systemically delivered NBPs carrying tumoricidal agents reduced the growth of intracranial triple-negative breast cancer cells, which also express HER3, with improved therapeutic profile compared to current therapies and compared to agents using traditional BBB transport routes. As HER3 associates with a growing number of metastatic tumours, the NBPs described here may offer targeted efficacy especially when such tumours localize to the brain.

Injured inflammatory environment overrides the TET2 shaped epigenetic landscape of pluripotent stem cell derived human neural stem cells

Spinal cord injury creates an inflammatory microenvironment that regulates the capacity of transplanted human Neural Stem Cells (hNSC) to migrate, differentiate, and repair injury. Despite similarities in gene expression and markers detected by immunostaining, hNSC populations exhibit heterogeneous therapeutic potential. This heterogeneity derives in part from the epigenetic landscape in the hNSC genome, specifically methylation (5mC) and hydroxymethylation (5hmC) state, which may affect the response of transplanted hNSC in the injury microenvironment and thereby modulate repair capacity. We demonstrate a significant up-regulation of methylcytosine dioxygenase 2 gene (TET2) expression in undifferentiated hNSC derived from human embryonic stem cells (hES-NSC), and report that this is associated with hES-NSC competence for differentiation marker expression. TET2 protein catalyzes active demethylation and TET2 upregulation could be a signature of pluripotent exit, while shaping the epigenetic landscape in hES-NSC. We determine that the inflammatory environment overrides epigenetic programming in vitro and in vivo by directly modulating TET2 expression levels in hES-NSC to change cell fate. We also report the effect of cell fate and microenvironment on differential methylation 5mC/5hmC balance. Understanding how the activity of epigenetic modifiers changes within the transplantation niche in vivo is crucial for assessment of hES-NSC behavior for potential clinical applications.

Cellular and transcriptomic changes by the supplementation of aged rat serum in human pluripotent stem cell-derived myogenic progenitors

Introduction

The changing composition of non-cell autonomous circulating factors in blood as humans age is believed to play a role in muscle mass and strength loss. The mechanisms through which these circulating factors act in age-related skeletal muscle changes is not fully understood. In this study, we used human myogenic progenitors derived from human pluripotent stem cells to study non-cell autonomous roles of circulating factors during the process of myogenic differentiation.

Methods

Myogenic progenitors from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) were supplemented with serum samples from aged or young Fischer 344 × Brown Norway F1-hybrid rats. The effect of aged or young serum supplementation on myogenic progenitor proliferation, myotube formation capacity, differentiation, and early transcriptomic profiles were analyzed.

Results

We found that aged rat serum supplementation significantly reduced cell proliferation and increased cell death in both ESC- and iPSC-derived myogenic progenitors. Next, we found that the supplementation of aged rat serum inhibited myotube formation and maturation during terminal differentiation from progenitors to skeletal myocytes when compared to the cells treated with young adult rat serum. Lastly, we identified that gene expression profiles were affected following serum supplementation in culture.

Discussion

Together, aged serum supplementation caused cellular and transcriptomic changes in human myogenic progenitors. The current data from our in vitro model possibly simulate non-cell autonomous contributions of blood composition to age-related processes in human skeletal muscle.

Human iPSC-derived neural progenitor cells secreting GDNF provide protection in rodent models of ALS and retinal degeneration

Human induced pluripotent stem cells (iPSCs) are a renewable cell source that can be differentiated into neural progenitor cells (iNPCs) and transduced with glial cell line-derived neurotrophic factor (iNPC-GDNFs). The goal of the current study is to characterize iNPC-GDNFs and test their therapeutic potential and safety. Single-nuclei RNA-seq show iNPC-GDNFs express NPC markers. iNPC-GDNFs delivered into the subretinal space of the Royal College of Surgeons rodent model of retinal degeneration preserve photoreceptors and visual function. Additionally, iNPC-GDNF transplants in the spinal cord of SOD1G93A amyotrophic lateral sclerosis (ALS) rats preserve motor neurons. Finally, iNPC-GDNF transplants in the spinal cord of athymic nude rats survive and produce GDNF for 9 months, with no signs of tumor formation or continual cell proliferation. iNPC-GDNFs survive long-term, are safe, and provide neuroprotection in models of both retinal degeneration and ALS, indicating their potential as a combined cell and gene therapy for various neurodegenerative diseases.

Tetracycline-Inducible and Reversible Stable Gene Expression in Human iPSC-Derived Neural Progenitors and in the Postnatal Mouse Brain

Our group has developed several approaches for stable, non-viral integration of inducible transgenic elements into the genome of mammalian cells. Specifically, a piggyBac tetracycline-inducible genetic element of interest (pB-tet-GOI) plasmid system allows for stable piggyBac transposition-mediated integration into cells, identification of cells that have been transfected using a fluorescent nuclear reporter, and robust transgene activation or suppression upon the addition of doxycycline (dox) to the cell culture or the diet of the animal. Furthermore, the addition of luciferase downstream of the target gene allows for quantitative assessment of gene activity in a non-invasive manner. More recently, we have developed a transgenic system as an alternative to piggyBac called mosaic analysis by dual recombinase-mediated cassette exchange (MADR), as well as additional in vitro transfection techniques and in vivo dox chow applications. The protocols herein provide instructions for the use of this system in cell lines and in the neonatal mouse brain. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Cloning of respective genetic element of interest (GOI) into response plasmid Basic Protocol 2: In vitro nucleofection of iPSC-derived human/mouse neural progenitor cells and subsequent derivation of stable inducible cell lines Alternate Protocol: In vitro electroporation of iPSC-derived human/mouse neural progenitor cells Support Protocol: Recovery stage after in vitro transfection Basic Protocol 3: Adding doxycycline to cells to induce/reverse GOI Basic Protocol 4: Assessing gene expression in vitro by non-invasive bioluminescence imaging of luciferase activity.

Diminished motor neuron activity driven by abnormal astrocytic EAAT1 glutamate transporter activity in spinal muscular atrophy is not fully restored after lentiviral SMN delivery

Spinal muscular atrophy (SMA) is characterized by the loss of the lower spinal motor neurons due to survival motor neuron (SMN) deficiency. The motor neuron cell autonomous and non-cell autonomous disease mechanisms driving early glutamatergic dysfunction, a therapeutically targetable phenotype prior to motor neuron cell loss, remain unclear. Using microelectrode array analysis, we demonstrate that the secretome and cell surface proteins needed for proper synaptic modulation are likely disrupted in human SMA astrocytes and lead to diminished motor neuron activity. While healthy astrocyte conditioned media did not improve SMA motor neuron activity, SMA motor neurons robustly responded to healthy astrocyte neuromodulation in direct contact cultures. This suggests an important role of astrocyte synaptic-associated plasma membrane proteins and contact-mediated cellular interactions for proper motor neuron function in SMA. Specifically, we identified a significant reduction of the glutamate Na⁺ dependent excitatory amino acid transporter EAAT1 within human SMA astrocytes and SMA lumbar spinal cord tissue. The selective inhibition of EAAT1 in healthy co-cultures phenocopied the diminished neural activity observed in SMA astrocyte co-cultures. Caveolin-1, an SMN-interacting protein previously associated with local translation at the plasma membrane, was abnormally elevated in human SMA astrocytes. Although lentiviral SMN delivery to SMA astrocytes partially rescued EAAT1 expression, limited activity of healthy motor neurons was still observed in SMN-transduced SMA astrocyte co-cultures. Together, these data highlight the detrimental impact of astrocyte-mediated disease mechanisms on motor neuron function in SMA and that SMN delivery may be insufficient to fully restore astrocyte function at the synapse.

NeuroLINCS Proteomics: Defining human-derived iPSC proteomes and protein signatures of pluripotency

The National Institute of Health (NIH) Library of integrated network-based cellular signatures (LINCS) program is premised on the generation of a publicly available data resource of cell-based biochemical responses or "signatures" to genetic or environmental perturbations. NeuroLINCS uses human inducible pluripotent stem cells (hiPSCs), derived from patients and healthy controls, and differentiated into motor neuron cell cultures. This multi-laboratory effort strives to establish i) robust multi-omic workflows for hiPSC and differentiated neuronal cultures, ii) public annotated data sets and iii) relevant and targetable biological pathways of spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS). Here, we focus on the proteomics and the quality of the developed workflow of hiPSC lines from 6 individuals, though epigenomics and transcriptomics data are also publicly available. Known and commonly used markers representing 73 proteins were reproducibly quantified with consistent expression levels across all hiPSC lines. Data quality assessments, data levels and metadata of all 6 genetically diverse human iPSCs analysed by DIA-MS are parsable and available as a high-quality resource to the public.

Sphere-Based Expansion of Myogenic Progenitors from Human Pluripotent Stem Cells

The protocol presented here is to derive, maintain, and differentiate human pluripotent stem cells into skeletal muscle progenitor/stem cells (myogenic progenitors) using a sphere-based culture approach. This sphere-based culture is an attractive method for maintaining progenitor cells due to their longevity and the presence of cell-cell interactions and molecules. Large numbers of cells can be expanded in culture using this method, which represents a valuable source for cell-based tissue modeling and regenerative medicine.

Suspension culture in a rotating bioreactor for efficient generation of human intestinal organoids

Human intestinal organoids (HIOs) derived from human pluripotent stem cells (hPSCs) hold great promise for translational medical applications. A common method to obtain HIOs has been to harvest floating hindgut spheroids arising from hPSCs. As this technique is elegant but burdensome due to the complex protocol and line-to-line variability, a more feasible method is desired. Here, we establish a robust differentiation method into suspension-cultured HIOs (s-HIOs) by seeding dissociated cells on a spheroid-forming plate. This protocol realizes the reliable generation of size-controllable spheroids. Under optimized conditions in a rotating bioreactor, the generated spheroids quickly grow and mature into large s-HIOs with supporting mesenchyme. Upon mesenteric transplantation, s-HIOs further mature and develop complex tissue architecture in vivo. This method demonstrates that intestinal tissue can be generated from iPSC-derived HIOs via suspension induction and bioreactor maturation, establishing a reliable culture platform with wide applications in regenerative medicine.

Organ-On-A-Chip Models of the Blood-Brain Barrier: Recent Advances and Future Prospects

The human brain and central nervous system (CNS) present unique challenges in drug development for neurological diseases. One major obstacle is the blood-brain barrier (BBB), which hampers the effective delivery of therapeutic molecules into the brain while protecting it from blood-born neurotoxic substances and maintaining CNS homeostasis. For BBB research, traditional in vitro models rely upon Petri dishes or Transwell systems. However, these static models lack essential microenvironmental factors such as shear stress and proper cell-cell interactions. To this end, organ-on-a-chip (OoC) technology has emerged as a new in vitro modeling approach to better recapitulate the highly dynamic in vivo human brain microenvironment so-called the neural vascular unit (NVU). Such BBB-on-a-chip models have made substantial progress over the last decade, and concurrently there has been increasing interest in modeling various neurological diseases such as Alzheimer's disease and Parkinson's disease using OoC technology. In addition, with recent advances in other scientific technologies, several new opportunities to improve the BBB-on-a-chip platform via multidisciplinary approaches are available. In this review, an overview of the NVU and OoC technology is provided, recent progress and applications of BBB-on-a-chip for personalized medicine and drug discovery are discussed, and current challenges and future directions are delineated.

Bilirubin-Induced Neurological Damage: Current and Emerging iPSC-Derived Brain Organoid Models

Bilirubin-induced neurological damage (BIND) has been a subject of studies for decades, yet the molecular mechanisms at the core of this damage remain largely unknown. Throughout the years, many in vivo chronic bilirubin encephalopathy models, such as the Gunn rat and transgenic mice, have further elucidated the molecular basis of bilirubin neurotoxicity as well as the correlations between high levels of unconjugated bilirubin (UCB) and brain damage. Regardless of being invaluable, these models cannot accurately recapitulate the human brain and liver system; therefore, establishing a physiologically recapitulating in vitro model has become a prerequisite to unveil the breadth of complexities that accompany the detrimental effects of UCB on the liver and developing human brain. Stem-cell-derived 3D brain organoid models offer a promising platform as they bear more resemblance to the human brain system compared to existing models. This review provides an explicit picture of the current state of the art, advancements, and challenges faced by the various models as well as the possibilities of using stem-cell-derived 3D organoids as an efficient tool to be included in research, drug screening, and therapeutic strategies for future clinical applications.

Ferritin-mediated iron detoxification promotes hypothermia survival in Caenorhabditis elegans and murine neurons

How animals rewire cellular programs to survive cold is a fascinating problem with potential biomedical implications, ranging from emergency medicine to space travel. Studying a hibernation-like response in the free-living nematode Caenorhabditis elegans, we uncovered a regulatory axis that enhances the natural resistance of nematodes to severe cold. This axis involves conserved transcription factors, DAF-16/FoxO and PQM-1, which jointly promote cold survival by upregulating FTN-1, a protein related to mammalian ferritin heavy chain (FTH1). Moreover, we show that inducing expression of FTH1 also promotes cold survival of mammalian neurons, a cell type particularly sensitive to deterioration in hypothermia. Our findings in both animals and cells suggest that FTN-1/FTH1 facilitates cold survival by detoxifying ROS-generating iron species. We finally show that mimicking the effects of FTN-1/FTH1 with drugs protects neurons from cold-induced degeneration, opening a potential avenue to improved treatments of hypothermia.

Strategies to improve cold resistance are of potential biomedical interest. Here the authors demonstrate that ferritin-mediated detoxification of iron, preventing the generation of reactive oxygen species, promotes cold survival in both Caenorhabditis elegans and cultured mammalian neurons.

Nitric Oxide Attenuates Human Cytomegalovirus Infection yet Disrupts Neural Cell Differentiation and Tissue Organization

Human cytomegalovirus (HCMV) is a prevalent betaherpesvirus that is asymptomatic in healthy individuals but can cause serious disease in immunocompromised patients. HCMV is also the leading cause of virus-mediated birth defects. Many of these defects manifest within the central nervous system and include microcephaly, sensorineural hearing loss, and cognitive developmental delays. Nitric oxide is a critical effector molecule produced as a component of the innate immune response during infection. Congenitally infected fetal brains show regions of brain damage, including necrotic foci with infiltrating macrophages and microglia, cell types that produce nitric oxide during infection. Using a 3-dimensional cortical organoid model, we demonstrate that nitric oxide inhibits HCMV spread and simultaneously disrupts neural rosette structures, resulting in tissue disorganization. Nitric oxide also attenuates HCMV replication in 2-dimensional cultures of neural progenitor cells (NPCs), a prominent cell type in cortical organoids that differentiate into neurons and glial cells. The multipotency factor SOX2 was decreased during nitric oxide exposure, suggesting that early neural differentiation is affected. Nitric oxide also reduced maximal mitochondrial respiration in both uninfected and infected NPCs. We determined that this reduction likely influences neural differentiation, as neurons (Tuj1⁺ GFAP^- Nestin^-) and glial populations (Tuj1^- GFAP⁺ Nestin^-) were reduced following differentiation. Our studies indicate a prominent, immunopathogenic role of nitric oxide in promoting developmental defects within the brain despite its antiviral activity during congenital HCMV infection. IMPORTANCE Human cytomegalovirus (HCMV) is the leading cause of virus-mediated congenital birth defects. Congenitally infected infants can have a variety of symptoms manifesting within the central nervous system. The use of 3-dimensional (3-D) cortical organoids to model infection of the fetal brain has advanced the current understanding of development and allowed broader investigation of the mechanisms behind disease. However, the impact of the innate immune molecule nitric oxide during HCMV infection has not been explored in neural cells or cortical 3-D models. Here, we investigated the effect of nitric oxide on cortical development during HCMV infection. We demonstrate that nitric oxide plays an antiviral role during infection yet results in disorganized cortical tissue. Nitric oxide contributes to differentiation defects of neuron and glial cells from neural progenitor cells despite inhibiting viral replication. Our results indicate that immunopathogenic consequences of nitric oxide during congenital infection promote developmental defects that undermine its antiviral activity.

Downregulation of neurodevelopmental gene expression in iPSC-derived cerebral organoids upon infection by human cytomegalovirus

Human cytomegalovirus (HCMV) is a betaherpesvirus that can cause severe birth defects including vision and hearing loss, microcephaly, and seizures. Currently, no approved treatment options exist for in utero infections. Here, we aimed to determine the impact of HCMV infection on the transcriptome of developing neurons in an organoid model system. Cell populations isolated from organoids based on a marker for infection and transcriptomes were defined. We uncovered downregulation in key cortical, neurodevelopmental, and functional gene pathways which occurred regardless of the degree of infection. To test the contributions of specific HCMV immediate early proteins known to disrupt neural differentiation, we infected NPCs using a recombinant virus harboring a destabilization domain. Despite suppressing their expression, HCMV-mediated transcriptional downregulation still occurred. Together, our studies have revealed that HCMV infection causes a profound downregulation of neurodevelopmental genes and suggest a role for other viral factors in this process.

Cell Surface Proteins for Enrichment and In Vitro Characterization of Human Pluripotent Stem Cell-Derived Myogenic Progenitors

Human myogenic progenitors can be derived from pluripotent stem cells (PSCs) for use in modeling natural and pathological myogenesis, as well as treating muscle diseases. Transgene-free methods of deriving myogenic progenitors from different PSC lines often produce mixed populations that are heterogeneous in myogenic differentiation potential, yet detailed and accurate characterization of human PSC-derived myogenic progenitors remains elusive in the field. The isolation and purification of human PSC-derived myogenic progenitors is thus an important methodological consideration when we investigate the properties and behaviors of these cells in culture. We previously reported a transgene-free, serum-free floating sphere culture method for the derivation of myogenic progenitors from human PSCs. In this study, we first performed comprehensive cell surface protein profiling of the sphere culture cells through the screening of 255 antibodies. Next, we used magnetic activated cell sorting and enriched the cells according to the expression of specific surface markers. The ability of muscle differentiation in the resulting cells was characterized by immunofluorescent labeling and quantification of positively stained cells. Our results revealed that myotube-forming cells resided in the differentiated cultures of CD29+, CD56+, CD271+, and CD15– fractions, while thick and multinucleated myotubes were identified in the differentiated cultures from CD9+ and CD146+ fractions. We found that PAX7 localization to the nucleus correlates with myotube-forming ability in these sorted populations. We also demonstrated that cells in unsorted, CD271+, and CD15– fractions responded differently to cryopreservation and prolonged culture expansion. Lastly, we showed that CD271 expression is essential for terminal differentiation of human PSC-derived myogenic progenitors. Taken together, these cell surface proteins are not only useful markers to identify unique cellular populations in human PSC-derived myogenic progenitors but also functionally important molecules that can provide valuable insight into human myogenesis.

Immortalized striatal precursor neurons from Huntington's disease patient-derived iPS cells as a platform for target identification and screening for experimental therapeutics

We have previously established induced pluripotent stem cell (iPSC) models of Huntington's disease (HD), demonstrating CAG-repeat-expansion-dependent cell biological changes and toxicity. However, the current differentiation protocols are cumbersome and time consuming, making preparation of large quantities of cells for biochemical or screening assays difficult. Here, we report the generation of immortalized striatal precursor neurons (ISPNs) with normal (33) and expanded (180) CAG repeats from HD iPSCs, differentiated to a phenotype resembling medium spiny neurons (MSN), as a proof of principle for a more tractable patient-derived cell model. For immortalization, we used co-expression of the enzymatic component of telomerase hTERT and conditional expression of c-Myc. ISPNs can be propagated as stable adherent cell lines, and rapidly differentiated into highly homogeneous MSN-like cultures within 2 weeks, as demonstrated by immunocytochemical criteria. Differentiated ISPNs recapitulate major HD-related phenotypes of the parental iPSC model, including brain-derived neurotrophic factor (BDNF)-withdrawal-induced cell death that can be rescued by small molecules previously validated in the parental iPSC model. Proteome and RNA-seq analyses demonstrate separation of HD versus control samples by principal component analysis. We identified several networks, pathways, and upstream regulators, also found altered in HD iPSCs, other HD models, and HD patient samples. HD ISPN lines may be useful for studying HD-related cellular pathogenesis, and for use as a platform for HD target identification and screening experimental therapeutics. The described approach for generation of ISPNs from differentiated patient-derived iPSCs could be applied to a larger allelic series of HD cell lines, and to comparable modeling of other genetic disorders.

Bioinspired 3D Culture in Nanoliter Hyaluronic Acid-Rich Core-Shell Hydrogel Microcapsules Isolates Highly Pluripotent Human iPSCs

Human induced pluripotent stem cells (iPSCs) are ideal for developing personalized medicine. However, the spontaneous differentiation of human iPSCs under conventional 2D and 3D cultures results in significant heterogeneity and compromised quality. Therefore, a method for effectively isolating and expanding high-quality human iPSCs is critically needed. Here, a biomimetic microencapsulation approach for isolating and culturing high-quality human iPSCs is reported. This is inspired by the natural proliferation and development of blastomeres into early blastocyst where the early embryonic stem cells-containing core is enclosed in a semipermeable hydrogel shell known as the zona pellucida (Zona). Blastomere cluster-like human iPSC clusters are encapsulated in a miniaturized (≈10 nanoliter) hyaluronic acid (HA)-rich core of microcapsules with a semipermeable Zona-like hydrogel shell and subsequently cultured to form pluripotent human iPSC spheroids with significantly improved quality. This is indicated by their high expression of pluripotency markers and highly efficient 3D cardiac differentiation. In particular, HA is found to be crucial for isolating the high-quality human iPSCs with the biomimetic core-shell microencapsulation culture. Interestingly, the isolated human iPSCs can maintain high pluripotency even after being cultured again in 2D. These discoveries and the bioinspired culture method may be valuable to facilitate the human iPSC-based personalized medicine.

Chitosan 3D cell culture system promotes naïve-like features of human induced pluripotent stem cells: A novel tool to sustain pluripotency and facilitate differentiation

A simplified and cost-effective culture system for maintaining the pluripotency of human induced pluripotent stem cells (hiPSCs) is crucial for stem cell applications. Although recombinant protein-based feeder-free hiPSC culture systems have been developed, their manufacturing processes are expensive and complicated, which hinders hiPSC technology progress. Chitosan, a versatile biocompatible polysaccharide, has been reported as a biomaterial for three-dimensional (3D) cell culture system that promotes the physiological activities of mesenchymal stem cells and cancer cells. In the current study, we demonstrated that chitosan membranes sustained proliferation and pluripotency of hiPSCs in long-term culture (up to 365 days). Moreover, using vitronectin as the comparison group, the pluripotency of hiPSCs grown on the membranes was altered into a naïve-like state, which, for pluripotent stem cells, is an earlier developmental stage with higher stemness. On the chitosan membranes, hiPSCs self-assembled into 3D spheroids with an average diameter of ~100 μm. These hiPSC spheroids could be directly differentiated into lineage-specific cells from the three germ layers with 3D structures. Collectively, chitosan membranes not only promoted the naïve pluripotent features of hiPSCs but also provided a novel 3D differentiation platform. This convenient biomaterial-based culture system may enable the effective expansion and accessibility of hiPSCs for regenerative medicine, disease modeling, and drug screening.

Generation of Neural Progenitor Cells From Canine Induced Pluripotent Stem Cells and Preliminary Safety Test in Dogs With Spontaneous Spinal Cord Injuries

Advances in stem cell technology, including the use of induced pluripotent stem cells (iPSC) to produce neurons and glial cells, offer new hope for patients with neurological disease and injuries. Pet dogs with spinal cord injuries provide an important spontaneous animal model for evaluating new approaches to stem cell therapy. Therefore, studies were conducted to identify optimal conditions for generating neural progenitor cells (NPC) from canine induced pluripotent stem cells (iPSC) for preliminary evaluation in animals with spinal cord injury. We found that canine NPC could be induced to differentiate into mature neural cells, including glia and neurons. In addition, canine NPC did not form teratomas when injected in NOD/SCID mice. In a pilot study, two dogs with chronic spinal cord injury underwent fluoroscopically guided intrathecal injections of canine NPC. In follow-up MRI evaluations, tumor formation was not observed at the injection sites. However, none of the animals experienced meaningful clinical or electrophysiological improvement following NPC injections. These studies provide evidence that canine iPSC can be used to generate NPC for evaluation in cellular therapy of chronic spinal cord injury in the dog spontaneous injury model. Further refinements in the cell implantation procedure are likely required to enhance stem cell treatment efficacy.

The Interaction of Aging and Cellular Stress Contributes to Pathogenesis in Mouse and Human Huntington Disease Neurons

Huntington disease (HD) is a fatal, inherited neurodegenerative disorder caused by a mutation in the huntingtin (HTT) gene. While mutant HTT is present ubiquitously throughout life, HD onset typically occurs in mid-life. Oxidative damage accumulates in the aging brain and is a feature of HD. We sought to interrogate the roles and interaction of age and oxidative stress in HD using primary Hu97/18 mouse neurons, neurons differentiated from HD patient induced pluripotent stem cells (iPSCs), and the brains of HD mice. We find that primary neurons must be matured in culture for canonical stress responses to occur. Furthermore, when aging is accelerated in mature HD neurons, mutant HTT accumulates and sensitivity to oxidative stress is selectively enhanced. Furthermore, we observe HD-specific phenotypes in neurons and mouse brains that have undergone accelerated aging, including a selective increase in DNA damage. These findings suggest a role for aging in HD pathogenesis and an interaction between the biological age of HD neurons and sensitivity to exogenous stress.

Human iPSC-Derived Blood-Brain Barrier Chips Enable Disease Modeling and Personalized Medicine Applications

The blood-brain barrier (BBB) tightly regulates the entry of solutes from blood into the brain and is disrupted in several neurological diseases. Using Organ-Chip technology, we created an entirely human BBB-Chip with induced pluripotent stem cell (iPSC)-derived brain microvascular endothelial-like cells (iBMECs), astrocytes, and neurons. The iBMECs formed a tight monolayer that expressed markers specific to brain vasculature. The BBB-Chip exhibited physiologically relevant transendothelial electrical resistance and accurately predicted blood-to-brain permeability of pharmacologics. Upon perfusing the vascular lumen with whole blood, the microengineered capillary wall protected neural cells from plasma-induced toxicity. Patient-derived iPSCs from individuals with neurological diseases predicted disease-specific lack of transporters and disruption of barrier integrity. By combining Organ-Chip technology and human iPSC-derived tissue, we have created a neurovascular unit that recapitulates complex BBB functions, provides a platform for modeling inheritable neurological disorders, and advances drug screening, as well as personalized medicine.

Genetic predispositions of Parkinson's disease revealed in patient-derived brain cells

Parkinson's disease (PD) is the second most prevalent neurological disorder and has been the focus of intense investigations to understand its etiology and progression, but it still lacks a cure. Modeling diseases of the central nervous system in vitro with human induced pluripotent stem cells (hiPSC) is still in its infancy but has the potential to expedite the discovery and validation of new treatments. Here, we discuss the interplay between genetic predispositions and midbrain neuronal impairments in people living with PD. We first summarize the prevalence of causal Parkinson's genes and risk factors reported in 74 epidemiological and genomic studies. We then present a meta-analysis of 385 hiPSC-derived neuronal lines from 67 recent independent original research articles, which point towards specific impairments in neurons from Parkinson's patients, within the context of genetic predispositions. Despite the heterogeneous nature of the disease, current iPSC models reveal converging molecular pathways underlying neurodegeneration in a range of familial and sporadic forms of Parkinson's disease. Altogether, consolidating our understanding of robust cellular phenotypes across genetic cohorts of Parkinson's patients may guide future personalized drug screens in preclinical research.

Rac1 Activity Is Modulated by Huntingtin and Dysregulated in Models of Huntington's Disease

Background:

Previous studies suggest that Huntingtin, the protein mutated in Huntington’s disease (HD), is required for actin based changes in cell morphology, and undergoes stimulus induced targeting to plasma membranes where it interacts with phospholipids involved in cell signaling. The small GTPase Rac1 is a downstream target of growth factor stimulation and PI 3-kinase activity and is critical for actin dependent membrane remodeling.

Objective:

To determine if Rac1 activity is impaired in HD or regulated by normal Huntingtin.

Methods:

Analyses were performed in differentiated control and HD human stem cells and HD Q140/Q140 knock-in mice. Biochemical methods included SDS-PAGE, western blot, immunoprecipitation, affinity chromatography, and ELISA based Rac activity assays.

Results:

Basal Rac1 activity increased following depletion of Huntingtin with Huntingtin specific siRNA in human primary fibroblasts and in human control neuron cultures. Human cells (fibroblasts, neural stem cells, and neurons) with the HD mutation failed to increase Rac1 activity in response to growth factors. Rac1 activity levels were elevated in striatum of 1.5-month-old HD Q140/Q140 mice and in primary embryonic cortical neurons from HD mice. Affinity chromatography analysis of striatal lysates showed that Huntingtin is in a complex with Rac1, p85α subunit of PI 3-kinase, and the actin bundling protein α-actinin and interacts preferentially with the GTP bound form of Rac1. The HD mutation reduced Huntingtin interaction with p85α.

Conclusions:

These findings suggest that Huntingtin regulates Rac1 activity as part of a coordinated response to growth factor signaling and this function is impaired early in HD.

Human Stem Cell-derived Aggregates of Forebrain Astroglia Respond to Amyloid Beta Oligomers

Astrocytes are vital components in neuronal circuitry and there is increasing evidence linking the dysfunction of these cells to a number of central nervous system diseases. Studying the role of these cells in human brain function in the past has been difficult due to limited access to the human brain. In this study, human induced pluripotent stem cells were differentiated into astrospheres using a hybrid plating method, with or without dual SMAD inhibition. The derived cells were assessed for astrocytic markers, brain regional identity, phagocytosis, calcium-transient signaling, reactive oxygen species production, and immune response. Neural degeneration was modeled by stimulation with amyloid-β (Aβ) 42 oligomers. Finally, co-culture was performed for the derived astrospheres with isogenic neurospheres. Results indicate that the derived astroglial cells express astrocyte markers with forebrain dorsal cortical identity, secrete extracellular matrix, and are capable of phagocytosing iron oxide particles and responding to Aβ42 stimulation (higher oxidative stress, higher TNF-α, and IL-6 expression). RNA-sequencing results reveal the distinct transcriptome of the derived cells responding to Aβ42 stimulation for astrocyte markers, chemokines, and brain regional identity. Co-culture experiments show the synaptic activities of neurons and the enhanced neural protection ability of the astroglial cells. This study provides knowledge about the roles of brain astroglial cells, heterotypic cell-cell interactions, and the formation of engineered neuronal synapses in vitro. The implications lie in neurological disease modeling, drug screening, and studying progression of neural degeneration and the role of stem cell microenvironment. Impact Statement Human pluripotent stem cell-derived astrocytes are a powerful tool for disease modeling and drug screening. However, the properties regarding brain regional identity and the immune response to neural degeneration stimulus have not been well characterized. Results of this study indicate that the derived astroglial cells express astrocyte markers with forebrain dorsal cortical identity, secrete extracellular matrix (ECM), and are capable of phagocytosing iron oxide particles and responding to amyloid-β oligomers, showing the distinct transcriptome in astrocyte markers, chemokines, and brain regional identity. This study provides knowledge about the roles of brain astroglial cells, heterotypic cell-cell interactions, and engineering neural tissues in vitro.

Modeling Polyglutamine Expansion Diseases with Induced Pluripotent Stem Cells

Polyglutamine expansion disorders, which include Huntington's disease, have expanded CAG repeats that result in polyglutamine expansions in affected proteins. How this specific feature leads to distinct neuropathies in 11 different diseases is a fascinating area of investigation. Most proteins affected by polyglutamine expansions are ubiquitously expressed, yet their mechanisms of selective neurotoxicity are unknown. Induced pluripotent stem cells have emerged as a valuable tool to model diseases, understand molecular mechanisms, and generate relevant human neural and glia subtypes, cocultures, and organoids. Ideally, this tool will generate specific neuronal populations that faithfully recapitulate specific polyglutamine expansion disorder phenotypes and mimic the selective vulnerability of a given disease. Here, we review how induced pluripotent technology is used to understand the effects of the disease-causing polyglutamine protein on cell function, identify new therapeutic targets, and determine how polyglutamine expansion affects human neurodevelopment and disease. We will discuss ongoing challenges and limitations in our use of induced pluripotent stem cells to model polyglutamine expansion diseases.

C9ORF72-related cellular pathology in skeletal myocytes derived from ALS-patient induced pluripotent stem cells

Amyotrophic lateral sclerosis (ALS) is a late-onset neuromuscular disease with no cure and limited treatment options. Patients experience a gradual paralysis leading to death from respiratory complications on average only 2-5 years after diagnosis. There is increasing evidence that skeletal muscle is affected early in the disease process, yet the pathological processes occurring in the skeletal muscle of ALS patients are still mostly unknown. Specifically, the most common genetic cause of ALS, a hexanucleotide repeat expansion in the C9ORF72 gene, has yet to be fully characterized in the context of skeletal muscle. In this study, we used the protocol previously developed in our lab to differentiate skeletal myocytes from induced pluripotent stem cells (iPSCs) of C9ORF72 ALS (C9-ALS) patients in order to create an in vitro disease model of C9-ALS skeletal muscle pathology. Of the three C9ORF72 mutation hallmarks, we did not see any evidence of haploinsufficiency, but we did detect RNA foci and dipeptide repeat (DPR) proteins. Additional abnormalities included changes in the expression of mitochondrial genes and a susceptibility to oxidative stress, indicating that mitochondrial dysfunction may be a critical feature of C9-ALS skeletal muscle pathology. Finally, the C9-ALS myocytes had increased expression and aggregation of TDP-43. Together, these data show that skeletal muscle cells experience pathological changes due to the C9ORF72 mutation. Our in vitro model could facilitate further study of cellular and molecular pathology in ALS skeletal muscle in order to discover new therapeutic targets against this devastating disease.

This article has an associated First Person interview with the first author of the paper.

Summary: Evidence of protein aggregation and mitochondrial dysfunction were found in skeletal myocytes differentiated from ALS-patient induced pluripotent stem cells with the C9ORF72 mutation.

Human Cytomegalovirus Disruption of Calcium Signaling in Neural Progenitor Cells and Organoids

The herpesvirus human cytomegalovirus (HCMV) is a leading cause of congenital birth defects. Infection can result in infants born with a variety of symptoms, including hepatosplenomegaly, microcephaly, and developmental disabilities. Microcephaly is associated with disruptions in the neural progenitor cell (NPC) population. Here, we defined the impact of HCMV infection on neural tissue development and calcium regulation, a critical activity in neural development. Regulation of intracellular calcium involves purinergic receptors and voltage-gated calcium channels (VGCC). HCMV infection compromised the ability of both pathways in NPCs as well as fibroblasts to respond to stimulation. We observed significant drops in basal calcium levels in infected NPCs which were accompanied by loss in VGCC activity and purinergic receptor responses. However, uninfected cells in the population retained responsiveness. Addition of the HCMV inhibitor maribavir reduced viral spread but failed to restore activity in infected cells. To study neural development, we infected three-dimensional cortical organoids with HCMV. Infection spread to a subset of cells over time and disrupted organoid structure, with alterations in developmental and neural layering markers. Organoid-derived infected neurons and astrocytes were unable to respond to stimulation whereas uninfected cells retained nearly normal responses. Maribavir partially restored structural features, including neural rosette formation, and dampened the impact of infection on neural cellular function. Using a tissue model system, we have demonstrated that HCMV alters cortical neural layering and disrupts calcium regulation in infected cells.IMPORTANCE Human cytomegalovirus (HCMV) replicates in several cell types throughout the body, causing disease in the absence of an effective immune response. Studies on HCMV require cultured human cells and tissues due to species specificity. In these studies, we investigated the impact of infection on developing three-dimensional cortical organoid tissues, with specific emphasis on cell-type-dependent calcium signaling. Calcium signaling is an essential function during neural differentiation and cortical development. We observed that HCMV infects and spreads within these tissues, ultimately disrupting cortical structure. Infected cells exhibited depleted calcium stores and loss of ATP- and KCl-stimulated calcium signaling while uninfected cells in the population maintained nearly normal responses. Some protection was provided by the viral inhibitor maribavir. Overall, our studies provide new insights into the impact of HCMV on cortical tissue development and function.

An isogenic neurovascular unit model comprised of human induced pluripotent stem cell-derived brain microvascular endothelial cells, pericytes, astrocytes, and neurons

Background

Brain microvascular endothelial cells (BMECs) astrocytes, neurons, and pericytes form the neurovascular unit (NVU). Interactions with NVU cells endow BMECs with extremely tight barriers via the expression of tight junction proteins, a host of active efflux and nutrient transporters, and reduced transcellular transport. To recreate the BMEC-enhancing functions of NVU cells, we combined BMECs, astrocytes, neurons, and brain pericyte-like cells.

Methods

BMECs, neurons, astrocytes, and brain like pericytes were differentiated from human induced pluripotent stem cells (iPSCs) and placed in a Transwell-type NVU model. BMECs were placed in co-culture with neurons, astrocytes, and/or pericytes alone or in varying combinations and critical barrier properties were monitored.

Results

Co-culture with pericytes followed by a mixture of neurons and astrocytes (1:3) induced the greatest barrier tightening in BMECs, supported by a significant increase in junctional localization of occludin. BMECs also expressed active P-glycoprotein (PGP) efflux transporters under baseline BMEC monoculture conditions and continued to express baseline active PGP efflux transporters regardless of co-culture conditions. Finally, brain-like pericyte co-culture significantly reduced the rate of non-specific transcytosis across BMECs.

Conclusions

Importantly, each cell type in the NVU model was differentiated from the same donor iPSC source, yielding an isogenic model that could prove enabling for enhanced personalized modeling of the NVU in human health and disease.

Huntington's Disease Patient-Derived Astrocytes Display Electrophysiological Impairments and Reduced Neuronal Support

In Huntington’s disease (HD), while the ubiquitously expressed mutant Huntingtin (mtHTT) protein primarily compromises striatal and cortical neurons, glia also undergo disease-contributing alterations. Existing HD models using human induced pluripotent stem cells (iPSCs) have not extensively characterized the role of mtHTT in patient-derived astrocytes. Here physiologically mature astrocytes are generated from HD patient iPSCs. These human astrocytes exhibit hallmark HD phenotypes that occur in mouse models, including impaired inward rectifying K⁺ currents, lengthened spontaneous Ca²⁺ waves and reduced cell membrane capacitance. HD astrocytes in co-culture provided reduced support for the maturation of iPSC-derived neurons. In addition, neurons exposed to chronic glutamate stimulation are not protected by HD astrocytes. This iPSC-based HD model demonstrates the critical effects of mtHTT on human astrocytes, which not only broadens the understanding of disease susceptibility beyond cortical and striatal neurons but also increases potential drug targets.

Studying Heterotypic Cell⁻Cell Interactions in the Human Brain Using Pluripotent Stem Cell Models for Neurodegeneration

Human cerebral organoids derived from induced pluripotent stem cells (iPSCs) provide novel tools for recapitulating the cytoarchitecture of the human brain and for studying biological mechanisms of neurological disorders. However, the heterotypic interactions of neurovascular units, composed of neurons, pericytes (i.e., the tissue resident mesenchymal stromal cells), astrocytes, and brain microvascular endothelial cells, in brain-like tissues are less investigated. In addition, most cortical organoids lack a microglia component, the resident immune cells in the brain. Impairment of the blood-brain barrier caused by improper crosstalk between neural cells and vascular cells is associated with many neurodegenerative disorders. Mesenchymal stem cells (MSCs), with a phenotype overlapping with pericytes, have promotion effects on neurogenesis and angiogenesis, which are mainly attributed to secreted growth factors and extracellular matrices. As the innate macrophages of the central nervous system, microglia regulate neuronal activities and promote neuronal differentiation by secreting neurotrophic factors and pro-/anti-inflammatory molecules. Neuronal-microglia interactions mediated by chemokines signaling can be modulated in vitro for recapitulating microglial activities during neurodegenerative disease progression. In this review, we discussed the cellular interactions and the physiological roles of neural cells with other cell types including endothelial cells and microglia based on iPSC models. The therapeutic roles of MSCs in treating neural degeneration and pathological roles of microglia in neurodegenerative disease progression were also discussed.

Studying Human Neurological Disorders Using Induced Pluripotent Stem Cells: From 2D Monolayer to 3D Organoid and Blood Brain Barrier Models

Neurological disorders have emerged as a predominant healthcare concern in recent years due to their severe consequences on quality of life and prevalence throughout the world. Understanding the underlying mechanisms of these diseases and the interactions between different brain cell types is essential for the development of new therapeutics. Induced pluripotent stem cells (iPSCs) are invaluable tools for neurological disease modeling, as they have unlimited self-renewal and differentiation capacity. Mounting evidence shows: (i) various brain cells can be generated from iPSCs in two-dimensional (2D) monolayer cultures; and (ii) further advances in 3D culture systems have led to the differentiation of iPSCs into organoids with multiple brain cell types and specific brain regions. These 3D organoids have gained widespread attention as in vitro tools to recapitulate complex features of the brain, and (iii) complex interactions between iPSC-derived brain cell types can recapitulate physiological and pathological conditions of blood-brain barrier (BBB). As iPSCs can be generated from diverse patient populations, researchers have effectively applied 2D, 3D, and BBB models to recapitulate genetically complex neurological disorders and reveal novel insights into molecular and genetic mechanisms of neurological disorders. In this review, we describe recent progress in the generation of 2D, 3D, and BBB models from iPSCs and further discuss their limitations, advantages, and future ventures. This review also covers the current status of applications of 2D, 3D, and BBB models in drug screening, precision medicine, and modeling a wide range of neurological diseases (e.g., neurodegenerative diseases, neurodevelopmental disorders, brain injury, and neuropsychiatric disorders). © 2019 American Physiological Society. Compr Physiol 9:565-611, 2019.

Induced Pluripotent Stem Cells (iPSCs) in Developmental Toxicology

The discovery of induced pluripotent stem cells (iPSCs) by Dr. Shinya Yamanaka and his team has opened up many avenues of research. This includes medical initiatives such as the Precision Medicine and Personalized Medicine initiatives to use patient-specific stem cells to guide medical professionals on the base courses of treatment for various disorders based on the patient's own genetic background, i.e., targeting the best treatment for the individual patient. However iPSC technology has greater potential than disease modeling and regenerative medicine therapies. In this chapter, we will outline how to culture and maintain human iPSCs, differentiate human iPSCs into neurons, and discuss how iPSCs can be utilized for developmental toxicology studies. Furthermore, this chapter will highlight a burgeoning field using iPSCs to examine personalized exposure risks.

A multiple-funnels cell culture insert for the scale-up production of uniform cell spheroids

Introduction

Formation of cell spheres is an important procedure in biomedical research. A large number of high-quality cell spheres of uniform size and shape are required for basic studies and therapeutic applications. Conventional approaches, including the hanging drop method and suspension culture, are used for cell sphere production. However, these methods are time consuming, cell spheres cannot be harvested easily, and it is difficult to control the size and geometry of cell spheres. To resolve these problems, a novel multiple-funnel cell culture insert was designed for size controlling, easy harvesting, and scale-up production of cell spheres.

Methods

The culture substrate has 680 micro-funnels with a 1-mm width top, 0.89 mm depth, and 0.5 mm square bottom. Mouse embryonic stem cells were used to test the newly developed device. The seeded embryonic stem cells settled at the downward medium surface toward the bottom opening and aggregated as embryoid bodies (EBs). For cell sphere harvest, the bottom of the culture insert was put in contact with the medium surface in another culture dish, and the medium in the device flowed down with cell spheres by hydrostatic pressure.

Results

Compact cell spheres with uniform size and shape were collected easily. The diameter of the spheres could be controlled by adjusting the seeding cell density. Spontaneous neural differentiation (nestin and Tju1) and retinoic acid-induced endodermal differentiation (Pdx-1 and insulin I) were improved in the EBs produced using the new insert compared to those in EBs produced by suspension culture.

Conclusions

This novel cell culture insert shall improve future studies of cell spheres and benefit clinical applications of cell therapy.

SRCP1 Conveys Resistance to Polyglutamine Aggregation

The polyglutamine (polyQ) diseases are a group of nine neurodegenerative diseases caused by the expansion of a polyQ tract that results in protein aggregation. Unlike other model organisms, Dictyostelium discoideum is a proteostatic outlier, naturally encoding long polyQ tracts yet resistant to polyQ aggregation. Here we identify serine-rich chaperone protein 1 (SRCP1) as a molecular chaperone that is necessary and sufficient to suppress polyQ aggregation. SRCP1 inhibits aggregation of polyQ-expanded proteins, allowing for their degradation via the proteasome, where SRCP1 is also degraded. SRCP1's C-terminal domain is essential for its activity in cells, and peptides that mimic this domain suppress polyQ aggregation in vitro. Together our results identify a novel type of molecular chaperone and reveal how nature has dealt with the problem of polyQ aggregation.

Inducible Expression of GDNF in Transplanted iPSC-Derived Neural Progenitor Cells

Trophic factor delivery to the brain using stem cell-derived neural progenitors is a powerful way to bypass the blood-brain barrier. Protection of diseased neurons using this technology is a promising therapy for neurodegenerative diseases. Glial cell line-derived neurotrophic factor (GDNF) has provided benefits to Parkinsonian patients and is being used in a clinical trial for amyotrophic lateral sclerosis. However, chronic trophic factor delivery prohibits dose adjustment or cessation if side effects develop. To address this, we engineered a doxycycline-regulated vector, allowing inducible and reversible expression of a therapeutic molecule. Human induced pluripotent stem cell (iPSC)-derived neural progenitors were stably transfected with the vector and transplanted into the adult mouse brain. Doxycycline can penetrate the graft, with addition and withdrawal providing inducible and reversible GDNF expression in vivo, over multiple cycles. Our findings provide proof of concept for combining gene and stem cell therapy for effective modulation of ectopic protein expression in transplanted cells.

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Created plasmid with tetracycline transactivator along with dual reporters and GDNF

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Efficient, stable transduction of human iPSC-derived neural progenitor cells

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Inducible and reversible in vivo expression of GDNF, reporter protein, and luciferase

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Promising stem cell and gene therapy strategy for neurodegenerative diseases

Huntington's Disease iPSC-Derived Brain Microvascular Endothelial Cells Reveal WNT-Mediated Angiogenic and Blood-Brain Barrier Deficits

Brain microvascular endothelial cells (BMECs) are an essential component of the blood-brain barrier (BBB) that shields the brain against toxins and immune cells. While BBB dysfunction exists in neurological disorders, including Huntington’s disease (HD), it is not known if BMECs themselves are functionally compromised to promote BBB dysfunction. Further, the underlying mechanisms of BBB dysfunction remain elusive given limitations with mouse models and post-mortem tissue to identify primary deficits. We undertook a transcriptome and functional analysis of human induced pluripotent stem cell (iPSC)-derived BMECs (iBMEC) from HD patients or unaffected controls. We demonstrate that HD iBMECs have intrinsic abnormalities in angiogenesis and barrier properties, as well as in signaling pathways governing these processes. Thus, our findings provide an iPSC-derived BBB model for a neurodegenerative disease and demonstrate autonomous neurovascular deficits that may underlie HD pathology with implications for therapeutics and drug delivery.

Self-oligomerization regulates stability of survival motor neuron protein isoforms by sequestering an SCFSlmb degron

Spinal muscular atrophy (SMA) is caused by homozygous mutations in human SMN1 Expression of a duplicate gene (SMN2) primarily results in skipping of exon 7 and production of an unstable protein isoform, SMNΔ7. Although SMN2 exon skipping is the principal contributor to SMA severity, mechanisms governing stability of survival motor neuron (SMN) isoforms are poorly understood. We used a Drosophila model system and label-free proteomics to identify the SCFSlmb ubiquitin E3 ligase complex as a novel SMN binding partner. SCFSlmb interacts with a phosphor degron embedded within the human and fruitfly SMN YG-box oligomerization domains. Substitution of a conserved serine (S270A) interferes with SCFSlmb binding and stabilizes SMNΔ7. SMA-causing missense mutations that block multimerization of full-length SMN are also stabilized in the degron mutant background. Overexpression of SMNΔ7S270A, but not wild-type (WT) SMNΔ7, provides a protective effect in SMA model mice and human motor neuron cell culture systems. Our findings support a model wherein the degron is exposed when SMN is monomeric and sequestered when SMN forms higher-order multimers.

Astrocyte-produced miR-146a as a mediator of motor neuron loss in spinal muscular atrophy

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is caused by the loss of the survival motor neuron-1 (SMN1) gene, which leads to motor neuron loss, muscle atrophy, respiratory distress, and death. Motor neurons exhibit the most profound loss, but the mechanisms underlying disease pathogenesis are not fully understood. Recent evidence suggests that motor neuron extrinsic influences, such as those arising from astrocytes, contribute to motor neuron malfunction and loss. Here we investigated both loss-of-function and toxic gain-of-function astrocyte mechanisms that could play a role in SMA pathology. We had previously found that glial derived neurotrophic factor (GDNF) is reduced in SMA astrocytes. However, reduced GDNF expression does not play a major role in SMA pathology as viral-mediated GDNF re-expression did not improve astrocyte function or motor neuron loss. In contrast, we found that SMA astrocytes increased microRNA (miR) production and secretion compared to control astrocytes, suggesting potential toxic gain-of-function properties. Specifically, we found that miR-146a was significantly upregulated in SMA induced pluripotent stem cell (iPSC)-derived astrocytes and SMNΔ7 mouse spinal cord. Moreover, increased miR-146a was sufficient to induce motor neuron loss in vitro, whereas miR-146a inhibition prevented SMA astrocyte-induced motor neuron loss. Together, these data indicate that altered astrocyte production of miR-146a may be a contributing factor in astrocyte-mediated SMA pathology.

Engineering the human blood-brain barrier in vitro

The blood-brain barrier (BBB) is the interface between the vasculature and the brain, regulating molecular and cellular transport into the brain. Endothelial cells (ECs) that form the capillary walls constitute the physical barrier but are dependent on interactions with other cell types. In vitro models are widely used in BBB research for mechanistic studies and drug screening. Current models have both biological and technical limitations. Here we review recent advances in stem cell engineering that have been utilized to create innovative platforms to replicate key features of the BBB. The development of human in vitro models is envisioned to enable new mechanistic investigations of BBB transport in central nervous system diseases.

Decreased Sirtuin Deacetylase Activity in LRRK2 G2019S iPSC-Derived Dopaminergic Neurons

Mitochondrial changes have long been implicated in the pathogenesis of Parkinson's disease (PD). The glycine to serine mutation (G2019S) in leucine-rich repeat kinase 2 (LRRK2) is the most common genetic cause for PD and has been shown to impair mitochondrial function and morphology in multiple model systems. We analyzed mitochondrial function in LRRK2 G2019S induced pluripotent stem cell (iPSC)-derived neurons to determine whether the G2019S mutation elicits similar mitochondrial deficits among central and peripheral nervous system neuron subtypes. LRRK2 G2019S iPSC-derived dopaminergic neuron cultures displayed unique abnormalities in mitochondrial distribution and trafficking, which corresponded to reduced sirtuin deacetylase activity and nicotinamide adenine dinucleotide levels despite increased sirtuin levels. These data indicate that mitochondrial deficits in the context of LRRK2 G2019S are not a global phenomenon and point to distinct sirtuin and bioenergetic deficiencies intrinsic to dopaminergic neurons, which may underlie dopaminergic neuron loss in PD.

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LRRK2 G2019S iPSC-derived dopaminergic neurons have unique mitochondrial defects

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LRRK2 G2019S dopaminergic neurons have increased sirtuin levels but reduced activity

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LRRK2 G2019S dopaminergic neurons have reduced NAD⁺ levels compared with other neurons

Directed differentiation of human pluripotent stem cells to blood-brain barrier endothelial cells

The blood-brain barrier (BBB) is composed of specialized endothelial cells that are critical to neurological health. A key tool for understanding human BBB development and its role in neurological disease is a reliable and scalable source of functional brain microvascular endothelial cells (BMECs). Human pluripotent stem cells (hPSCs) can theoretically generate unlimited quantities of any cell lineage in vitro, including BMECs, for disease modeling, drug screening, and cell-based therapies. We demonstrate a facile, chemically defined method to differentiate hPSCs to BMECs in a developmentally relevant progression via small-molecule activation of key signaling pathways. hPSCs are first induced to mesoderm commitment by activating canonical Wnt signaling. Next, these mesoderm precursors progress to endothelial progenitors, and treatment with retinoic acid leads to acquisition of BBB-specific markers and phenotypes. hPSC-derived BMECs generated via this protocol exhibit endothelial properties, including tube formation and low-density lipoprotein uptake, as well as efflux transporter activities characteristic of BMECs. Notably, these cells exhibit high transendothelial electrical resistance above 3000 ohm·cm2. These hPSC-derived BMECs serve as a robust human in vitro BBB model that can be used to study brain disease and inform therapeutic development.

Optimization of trans-Splicing for Huntington's Disease RNA Therapy

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by a polyglutamine (polyQ) expansion in exon 1 of the Huntingtin (HTT) gene. We have previously demonstrated that spliceosome-mediated trans-splicing is a viable molecular strategy to specifically reduce and repair mutant HTT (mtHTT). Here, the targeted tethering efficacy of the pre-mRNA trans-splicing modules (PTM) in HTT was optimized. Various PTMs that targeted the 3′ end of HTT intron 1 or the intron 1 branch point were shown trans-splice into an HTT mini-gene, as well as the endogenous HTT pre-mRNA. PTMs that specifically target the endogenous intron 1 branch point increased the trans-splicing efficacy from 1–5 to 10–15%. Furthermore, lentiviral expression of PTMs in a human HD patient iPSC-derived neural culture significantly reversed two previously established polyQ-length dependent phenotypes. These results suggest that pre-mRNA repair of mtHTT could hold therapeutic benefit and it demonstrates an alternative platform to correct the mRNA product produced by the mtHTT allele in the context of HD.

The Generation of Mouse and Human Huntington Disease iPS Cells Suitable for In vitro Studies on Huntingtin Function

Huntington disease (HD) is an incurable neurodegenerative disorder caused by expansion of CAG repeats in huntingtin (HTT) gene, resulting in expanded polyglutamine tract in HTT protein. Although, HD has its common onset in adulthood, subtle symptoms in patients may occur decades before diagnosis, and molecular and cellular changes begin much earlier, even in cells that are not yet lineage committed such as stem cells. Studies in induced pluripotent stem cell (iPSC) HD models have demonstrated that multiple molecular processes are altered by the mutant HTT protein and suggested its silencing as a promising therapeutic strategy. Therefore, we aimed to generate HD iPS cells with stable silencing of HTT and further to investigate the effects of HTT knock-down on deregulations of signaling pathways e.g., p53 downregulation, present in cells already in pluripotent state. We designed a gene silencing strategy based on RNAi cassette in piggyBAC vector for constant shRNA expression. Using such system we delivered and tested several shRNA targeting huntingtin in mouse HD YAC128 iPSC and human HD109, HD71, and Control iPSC. The most effective shRNA (shHTT2) reagent stably silenced HTT in all HD iPS cells and remained active upon differentiation to neural stem cells (NSC). When investigating the effects of HTT silencing on signaling pathways, we found that in mouse HD iPSC lines expressing shRNA the level of mutant HTT inversely correlated with p53 levels, resulting in p53 level normalization upon silencing of mutant HTT. We also found that p53 deregulation continues into the NSC developmental stage and it was reversed upon HTT silencing. In addition, we observed subtle effects of silencing on proteins of Wnt/β-catenin and ERK1/2 signaling pathways. In summary, we successfully created the first mouse and human shRNA-expressing HD iPS cells with stable and continuous HTT silencing. Moreover, we demonstrated reversal of HD p53 phenotype in mouse HD iPSC, therefore, the stable knockdown of HTT is well-suited for investigation on HD cellular pathways, and is potentially useful as a stand-alone therapy or component of cell therapy. In addition, the total HTT knock-down in our human cells has further implications for mutant allele selective approach in iPSC.

Survival of iPSC-derived grafts within the striatum of immunodeficient mice: Importance of developmental stage of both transplant and host recipient

Degeneration of the striatum can occur in multiple disorders with devastating consequences for the patients. Infantile infections with streptococcus, measles, or herpes can cause striatal necrosis associated with dystonia or dyskinesia; and in patients with Huntington's disease the striatum undergoes massive degeneration, leading to behavioral, psychological and movement issues, ultimately resulting in death. Currently, only supportive therapies are available for striatal degeneration. Clinical trials have shown some efficacy using transplantation of fetal-derived primary striatal progenitors. Large banks of fetal progenitors that give rise to medium spiny neurons (MSNs), the primary neuron of the striatum, are needed to make transplantation therapy a reality. However, fetal tissue is of limited supply, has ethical concerns, and is at risk of graft immunorejection. An alternative potential source of MSNs is induced pluripotent stem cells (iPSCs), adult somatic tissues reprogrammed back to a stem cell fate. Multiple publications have demonstrated the ability to differentiate striatal MSNs from iPSCs. Previous publications have demonstrated that the efficacy of fetal progenitor transplants is critically dependent upon the age of the donor embryo/fetus as well as the age of the transplant recipient. With the advent of iPSC technology, a question that remains unanswered concerns the graft's "age," which is crucial since transplanting pluripotent cells has an inherent risk of over proliferation and teratoma formation. Therefore, in order to also determine the effect of transplant recipient age on the graft, iPSCs were differentiated to three stages along a striatal differentiation paradigm and transplanted into the striatum of both neonatal and adult immunodeficient mice. This study demonstrated that increased murine transplant-recipient age (adult vs neonate) resulted in decreased graft survival and volume/rostro-caudal spread after six weeks in vivo, regardless of "age" of the cells transplanted. Importantly, this study implicates that the in vivo setting may provide a better neurogenic niche for iPSC-based modeling as compared to the in vitro setting. Together, these results recapitulate findings from fetal striatal progenitor transplantation studies and further demonstrate the influence of the host environment on cellular survival and maturation.

Modeling Psychomotor Retardation using iPSCs from MCT8-Deficient Patients Indicates a Prominent Role for the Blood-Brain Barrier

Inactivating mutations in the thyroid hormone (TH) transporter Monocarboxylate transporter 8 (MCT8) cause severe psychomotor retardation in children. Animal models do not reflect the biology of the human disease. Using patient-specific induced pluripotent stem cells (iPSCs), we generated MCT8-deficient neural cells that showed normal TH-dependent neuronal properties and maturation. However, the blood-brain barrier (BBB) controls TH entry into the brain, and reduced TH availability to neural cells could instead underlie the diseased phenotype. To test potential BBB involvement, we generated an iPSC-based BBB model of MCT8 deficiency, and we found that MCT8 was necessary for polarized influx of the active form of TH across the BBB. We also found that a candidate drug did not appreciably cross the mutant BBB. Our results therefore clarify the underlying physiological basis of this disorder, and they suggest that circumventing the diseased BBB to deliver active TH to the brain could be a viable therapeutic strategy.

Tetracycline-Inducible and Reversible Stable Gene Expression in Human iPSC-Derived Neural Progenitors and in the Postnatal Mouse Brain

The pB-tet-GOI plasmid system allows for stable piggyBac transposition-mediated integration into cells, a fluorescent nuclear reporter to identify cells that have been transfected, and robust transgene activation or suppression upon the addition of dox to the cell culture or diet of the animal. Furthermore, the addition of luciferase downstream of the target gene allows for quantitative assessment of gene activity in a non-invasive manner. The protocols herein provide instructions for the use of this system in cell lines and in the neonatal mouse brain. Specifically, a detailed protocol is provided to illustrate: (1) cloning of the respective GOI (genetic element(s) of interest); (2) nucleofection of the plasmid system into human induced pluripotent stem cell (iPSC)-derived neural progenitors; (3) dox-induced activation in vitro or in vivo; and (4) non-invasive assessment of gene activity in vivo by bioluminescence imaging. © 2017 by John Wiley & Sons, Inc.

Developmental alterations in Huntington's disease neural cells and pharmacological rescue in cells and mice

Neural cultures derived from Huntington's disease (HD) patient-derived induced pluripotent stem cells were used for 'omics' analyses to identify mechanisms underlying neurodegeneration. RNA-seq analysis identified genes in glutamate and GABA signaling, axonal guidance and calcium influx whose expression was decreased in HD cultures. One-third of gene changes were in pathways regulating neuronal development and maturation. When mapped to stages of mouse striatal development, the profiles aligned with earlier embryonic stages of neuronal differentiation. We observed a strong correlation between HD-related histone marks, gene expression and unique peak profiles associated with dysregulated genes, suggesting a coordinated epigenetic program. Treatment with isoxazole-9, which targets key dysregulated pathways, led to amelioration of expanded polyglutamine repeat-associated phenotypes in neural cells and of cognitive impairment and synaptic pathology in HD model R6/2 mice. These data suggest that mutant huntingtin impairs neurodevelopmental pathways that could disrupt synaptic homeostasis and increase vulnerability to the pathologic consequence of expanded polyglutamine repeats over time.

Huntington's Disease: Calcium Dyshomeostasis and Pathology Models

Huntington's disease (HD) is a severe inherited neurodegenerative disorder characterized by motor dysfunction, cognitive decline, and mental impairment. At the molecular level, HD is caused by a mutation in the first exon of the gene encoding the huntingtin protein. The mutation results in an expanded polyglutamine tract at the N-terminus of the huntingtin protein, causing the neurodegenerative pathology. Calcium dyshomeostasis is believed to be one of the main causes of the disease, which underlies the great interest in the problem among experts in molecular physiology. Recent studies have focused on the development of animal and insect HD models, as well as patient-specific induced pluripotent stem cells (HD-iPSCs), to simulate the disease's progression. Despite a sesquicentennial history of HD studies, the issues of diagnosis and manifestation of the disease have remained topical. The present review addresses these issues.

An isogenic blood-brain barrier model comprising brain endothelial cells, astrocytes, and neurons derived from human induced pluripotent stem cells

The blood-brain barrier (BBB) is critical in maintaining a physical and metabolic barrier between the blood and the brain. The BBB consists of brain microvascular endothelial cells (BMECs) that line the brain vasculature and combine with astrocytes, neurons and pericytes to form the neurovascular unit. We hypothesized that astrocytes and neurons generated from human-induced pluripotent stem cells (iPSCs) could induce BBB phenotypes in iPSC-derived BMECs, creating a robust multicellular human BBB model. To this end, iPSCs were used to form neural progenitor-like EZ-spheres, which were in turn differentiated to neurons and astrocytes, enabling facile neural cell generation. The iPSC-derived astrocytes and neurons induced barrier tightening in primary rat BMECs indicating their BBB inductive capacity. When co-cultured with human iPSC-derived BMECs, the iPSC-derived neurons and astrocytes significantly elevated trans-endothelial electrical resistance, reduced passive permeability, and improved tight junction continuity in the BMEC cell population, while p-glycoprotein efflux transporter activity was unchanged. A physiologically relevant neural cell mixture of one neuron: three astrocytes yielded optimal BMEC induction properties. Finally, an isogenic multicellular BBB model was successfully demonstrated employing BMECs, astrocytes, and neurons from the same donor iPSC source. It is anticipated that such an isogenic facsimile of the human BBB could have applications in furthering understanding the cellular interplay of the neurovascular unit in both healthy and diseased humans. Read the Editorial Highlight for this article on page 843.

Ex vivo gene therapy for the treatment of neurological disorders

Ex vivo gene therapy involves the genetic modification of cells outside of the body to produce therapeutic factors and their subsequent transplantation back into patients. Various cell types can be genetically engineered. However, with the explosion in stem cell technologies, neural stem/progenitor cells and mesenchymal stem cells are most often used. The synergy between the effect of the new cell and the additional engineered properties can often provide significant benefits to neurodegenerative changes in the brain. In this review, we cover both preclinical animal studies and clinical human trials that have used ex vivo gene therapy to treat neurological disorders with a focus on Parkinson's disease, Huntington's disease, Alzheimer's disease, ALS, and stroke. We highlight some of the major advances in this field including new autologous sources of pluripotent stem cells, safer ways to introduce therapeutic transgenes, and various methods of gene regulation. We also address some of the remaining hurdles including tunable gene regulation, in vivo cell tracking, and rigorous experimental design. Overall, given the current outcomes from researchers and clinical trials, along with exciting new developments in ex vivo gene and cell therapy, we anticipate that successful treatments for neurological diseases will arise in the near future.