iPSC Models Research Articles

Undergraduate Political Science Curriculum of International Islamic University Malaysia (IIUM)

Uplifting human moral values, social commitment and integrated personality is the core aim of education in addition to prepare graduates with professional skills and disciplinary knowledge. On that focus, the study developed the Integrated Political Science Curriculum Framework (IPSC) followed by mainly three approaches of educational research: philosophical, historical, and curriculum criticism. The IPSC model accommodated the courses on core disciplinary and faculty required courses, revealed knowledge, and generic skills. The proposed model was in response to growing scholastic debate on educational dualism and crisis of western education, devoid of moral and religious essence. The study mainly adopts library research and document analysis: previous curriculum models and university education frameworks, official documents, etc. In this article, the successful application of IPSC in the IIUM political science curriculum is rightly exemplified and indicates the relevancy of this in the multicultural society like Malaysia, Indonesia and Bangladesh.

Mitochondrial dysfunction of induced pluripotent stem cells-based neurodegenerative disease modeling and therapeutic strategy.

Neurodegenerative diseases (NDDs) are disorders in which neurons are lost owing to various factors, resulting in a series of dysfunctions. Their rising prevalence and irreversibility have brought physical pain to patients and economic pressure to both individuals and society. However, the pathogenesis of NDDs has not yet been fully elucidated, hampering the use of precise medication. Induced pluripotent stem cell (IPSC) modeling provides a new method for drug discovery, and exploring the early pathological mechanisms including mitochondrial dysfunction, which is not only an early but a prominent pathological feature of NDDs. In this review, we summarize the iPSC modeling approach of Alzheimer's disease, Parkinson's disease, and Amyotrophic lateral sclerosis, as well as outline typical mitochondrial dysfunction and recapitulate corresponding therapeutic strategies.

IPSC-Derived Neurons from Patients with POLG Mutations Exhibit Decreased Mitochondrial Content and Dendrite Simplification

Mutations in POLG, the gene encoding the catalytic subunit of DNA polymerase gamma, result in clinical syndromes characterized by mitochondrial DNA (mtDNA) depletion in affected tissues with variable organ involvement. The brain is one of the most affected organs, and symptoms include intractable seizures, developmental delay, dementia, and ataxia. Patient-derived induced pluripotent stem cells (iPSCs) provide opportunities to explore mechanisms in affected cell types and potential therapeutic strategies. Fibroblasts from two patients were reprogrammed to create new iPSC models of POLG-related mitochondrial diseases. Compared with iPSC-derived control neurons, mtDNA depletion was observed upon differentiation of the POLG-mutated lines to cortical neurons. POLG-mutated neurons exhibited neurite simplification with decreased mitochondrial content, abnormal mitochondrial structure and function, and increased cell death. Expression of the mitochondrial kinase PTEN-induced kinase 1 (PINK1) mRNA was decreased in patient neurons. Overexpression of PINK1 increased mitochondrial content and ATP:ADP ratios in neurites, decreasing cell death and rescuing neuritic complexity. These data indicate an intersection of polymerase gamma and PINK1 pathways that may offer a novel therapeutic option for patients affected by this spectrum of disorders.

Patient-Derived iPSCs Faithfully Represent the Genetic Diversity and Cellular Architecture of Human Acute Myeloid Leukemia

The reprogramming of malignant cells to pluripotency has presented considerable challenges, hindering the application of induced pluripotent stem cell (iPSC) modeling technology to human leukemia. In addition, how well iPSC-derived cells resemble their primary counterparts is currently largely unknown. We developed a reprogramming method tailored to human malignancies, "Complete Capture of Mutational Burden" (CCoMB), that combines comprehensive genetic characterization of the starting sample and inference of its clonal architecture with large-scale screening of clonally reprogrammed colonies. Using this method we were able to generate a panel of iPSC lines for the modeling of human acute myeloid leukemia (AML) representing all major genetic groups of AML. Specifically, we derived iPSC lines from 15 patients representing all major genetic groups of AML - PML-RARA; chromatin-spliceosome; TP53-mutated/aneuploidy; AML1-ETO, MLL-rearranged; NPM1-mutated and others - collectively capturing 21 distinct genotypes and 24 driver genetic lesions (mutations, translocations, deletions). Matched normal iPSCs were derived from 7 of these patients. Reprogramming to iPSCs captured both preleukemic (CH/initiating mutation only) and fully leukemic clones (baring the full set of patient mutations). In almost all cases, reprogramming informed reconstruction of the evolutionary hierarchy of the AML, with unexpected hierarchies unveiled in 4 of the cases. These AML-iPSCs retain genetic fidelity and, upon in vitro hematopoietic differentiation, produce hematopoietic cells with hallmark phenotypic leukemic features, including serial engraftment of a lethal myeloid leukemia into immunocompromised mice and extended self-renewal in vitro. Transplantation of cells derived from iPSCs representing two distinct AML clones from each of 3 patients revealed that these mimic the clonal dynamics in the patients, with more advanced clones showing increased representation in the xenografts, compared to the earlier clones. To compare the iPSC-derived to the primary leukemias, we performed single-cell transcriptomics analyses in patient-matched iPSC-derived and primary leukemic cells from 3 patients, both ex vivo/in vitro and after transplantation into NSGS mice. Clustering analyses identified cell types corresponding to primitive hematopoietic stem cell (HSC)/ multipotent progenitor (MPP), hematopoietic progenitor cells (HPCs) and more mature myelomonocytic lineage cells in all samples from all patients, at varying frequencies. Leukemias derived through in vitro differentiation from iPSC lines exhibited both similarities, as well as differences, in their cellular composition and transcriptome, compared to the patient-matched ex vivo leukemias. However, upon transplantation of the same leukemias into NSG-3GS mice, iPSC-derived xenografts were strikingly similar to the patient-derived xenografts. iPSC-derived leukemic cells exhibited a more stem/progenitor cell phenotype in vitro, with progressive maturation along the myeloid lineage upon primary and, even more, upon secondary transplantation, mimicking primary xenografts. In summary, our results reveal very few true biological barriers to the reprogramming of AML cells (with NPM1 mutations the most notable) and show that AML-iPSC-derived leukemias faithfully mimic the primary patient leukemias upon xenotransplantation. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Duplication Versus Deletion Through the Lens of 15q13.3: Clinical and Research Implications of Studying Copy Number Variants Associated with Neuropsychiatric Disorders in Induced Pluripotent Stem Cell-Derived Neurons.

Copy number variants (CNVs), involving duplication or deletion of susceptible intervals of the human genome, underlie a range of neurodevelopmental and neuropsychiatric disorders. As accessible in vivo animal models of these disorders often cannot be generated, induced pluripotent stem cell (iPSC) models derived from patients carrying these CNVs can reveal alterations of brain development and neuronal function that contribute to these disorders. CNVs involving deletion versus duplication of a particular genomic interval often result both in distinct clinical phenotypes and in differential phenotypic penetrance. This review initially focuses on CNVs at 15q13.3, which contribute to autism spectrum disorder, attention deficit/hyperactivity disorder, and schizophrenia. Like most CNVs, deletions at 15q13.3 usually cause severe clinical phenotypes, while duplications instead result in highly variable penetrance, with some carriers exhibiting no clinical phenotype. Here, we describe cellular and molecular phenotypes seen in iPSC-derived neuronal models of 15q13.3 duplication and deletion, which may contribute both to the differential clinical consequences and phenotypic penetrance. We then relate this work to many other CNVs involving both duplication and deletion, summarizing findings from iPSC studies and their relationship to clinical phenotype. Together, this work highlights how CNVs involving duplication versus deletion can differentially alter neural development and function to contribute to neuropsychiatric disorders. iPSC-derived neuronal models of these disorders can be used both to understand the underlying neurodevelopmental alterations and to develop pharmacological or molecular approaches for phenotypic rescue that may suggest leads for patient intervention. Top: Deletion versus duplication of the same genomic interval results in different clinical phenotypes and degrees of phenotypic penetrance. Example findings schematized. Bottom: iPSC-derived neurons from individuals with these CNVs involving deletion versus duplication likewise often differential phenotypes (increases or decreases) in the categories shown. Figure created with BioRender.com.

Abstract 12541: Development of a Transgenic Rabbit Model of Dravet Syndrome

Introduction: Sudden Unexpected Death in Epilepsy (SUDEP) is a leading cause of death in patients with epilepsy. While SUDEP mechanisms are not understood, there is evidence to implicate autonomic dysfunction and cardiac arrhythmias. Loss-of-function variants in SCN1A are linked to Dravet syndrome (DS). Importantly, SCN1A is expressed in both heart and brain in humans and rodents. Studies on Scn1a+/- DS mice and induced pluripotent stem cell (iPSC)-derived cardiac myocytes from DS patients show altered cardiac electrophysiology that serves as substrates for arrhythmias. However, no mouse or iPSC model can completely replicate the human DS phenotype. Hypothesis: Cardiac arrhythmias contribute to the mechanisms of SUDEP in a rabbit model of DS. Methods: We generate a New Zealand White (NZW) rabbit Scn1a deletion model using CRISPR-Cas9 gene editing. Rabbits were tested using video EEG/ECG telemetry as well as surface ECG under anesthesia. Optical mapping studies were performed in isolated hearts and patch clamp electrophysiology was performed in acutely isolated cardiac myocytes. Results: NZW Scn1a-/- kits died by postnatal day (P) 7-9 and showed bradycardia, long QT intervals, and AP prolongation. Cardiac myocytes isolated from NZW Scn1a+/- kits showed increased late sodium current compared to WT. We did not observe behavioral seizures or arrhythmias in NZW Scn1a+/- rabbits, which live normal life spans and breed normally. These data suggested, like mouse models, that the DS rabbit phenotype may be background strain dependent. To test this hypothesis, we crossed Scn1a+/- NZW rabbits to the Dutch Belted (DB) strain. We found that F1:NZW x DB Scn1a+/- rabbits have spontaneous seizures as well as pre- and post-ictal cardiac arrhythmia as assessed by video/EEG/ECG telemetry. Approximately 22% of the kits undergo premature death. Severe seizures are observed in adult animals, but to date no adults have died during seizures. Conclusions: F1:NZW x DB Scn1a+/- rabbits model DS in terms of seizures and SUDEP and are an optimal model to investigate neuro-cardiac mechanisms of SUDEP as well as to develop novel therapeutics for DS. To our knowledge, this is the first transgenic large animal model of a developmental and epileptic encephalopathy

ZEB2 haploinsufficient Mowat-Wilson syndrome induced pluripotent stem cells show disrupted GABAergic transcriptional regulation and function.

Mowat-Wilson syndrome (MWS) is a severe neurodevelopmental disorder caused by heterozygous variants in the gene encoding transcription factor ZEB2. Affected individuals present with structural brain abnormalities, speech delay and epilepsy. In mice, conditional loss of Zeb2 causes hippocampal degeneration, altered migration and differentiation of GABAergic interneurons, a heterogeneous population of mainly inhibitory neurons of importance for maintaining normal excitability. To get insights into GABAergic development and function in MWS we investigated ZEB2 haploinsufficient induced pluripotent stem cells (iPSC) of MWS subjects together with iPSC of healthy donors. Analysis of RNA-sequencing data at two time points of GABAergic development revealed an attenuated interneuronal identity in MWS subject derived iPSC with enrichment of differentially expressed genes required for transcriptional regulation, cell fate transition and forebrain patterning. The ZEB2 haploinsufficient neural stem cells (NSCs) showed downregulation of genes required for ventral telencephalon specification, such as FOXG1, accompanied by an impaired migratory capacity. Further differentiation into GABAergic interneuronal cells uncovered upregulation of transcription factors promoting pallial and excitatory neurons whereas cortical markers were downregulated. The differentially expressed genes formed a neural protein-protein network with extensive connections to well-established epilepsy genes. Analysis of electrophysiological properties in ZEB2 haploinsufficient GABAergic cells revealed overt perturbations manifested as impaired firing of repeated action potentials. Our iPSC model of ZEB2 haploinsufficient GABAergic development thus uncovers a dysregulated gene network leading to immature interneurons with mixed identity and altered electrophysiological properties, suggesting mechanisms contributing to the neuropathogenesis and seizures in MWS.

Clinical Trial-Ready Patient Cohorts for Multiple System Atrophy: Coupling Biospecimen and iPSC Banking to Longitudinal Deep-Phenotyping

Multiple system atrophy (MSA) is a fatal neurodegenerative disease of unknown etiology characterized by widespread aggregation of the protein alpha-synuclein in neurons and glia. Its orphan status, biological relationship to Parkinson’s disease (PD), and rapid progression have sparked interest in drug development. One significant obstacle to therapeutics is disease heterogeneity. Here, we share our process of developing a clinical trial-ready cohort of MSA patients (69 patients in 2 years) within an outpatient clinical setting, and recruiting 20 of these patients into a longitudinal “n-of-few” clinical trial paradigm. First, we deeply phenotype our patients with clinical scales (UMSARS, BARS, MoCA, NMSS, and UPSIT) and tests designed to establish early differential diagnosis (including volumetric MRI, FDG-PET, MIBG scan, polysomnography, genetic testing, autonomic function tests, skin biopsy) or disease activity (PBR06-TSPO). Second, we longitudinally collect biospecimens (blood, CSF, stool) and clinical, biometric, and imaging data to generate antecedent disease-progression scores. Third, in our Mass General Brigham SCiN study (stem cells in neurodegeneration), we generate induced pluripotent stem cell (iPSC) models from our patients, matched to biospecimens, including postmortem brain. We present 38 iPSC lines derived from MSA patients and relevant disease controls (spinocerebellar ataxia and PD, including alpha-synuclein triplication cases), 22 matched to whole-genome sequenced postmortem brain. iPSC models may facilitate matching patients to appropriate therapies, particularly in heterogeneous diseases for which patient-specific biology may elude animal models. We anticipate that deeply phenotyped and genotyped patient cohorts matched to cellular models will increase the likelihood of success in clinical trials for MSA.

Generation and validation of an iPSC line (BBANTWi008-A) from a Loeys-Dietz Syndrome type 3 patient

Loeys-Dietz Syndrome (LDS) is an autosomal dominant connective tissue disorder. The major hallmark of LDS is thoracic aortic aneurysm and dissection (TAAD). We generated an induced pluripotent stem cell (iPSC) line of a severely affected LDS patient carrying a pathogenic SMAD3 p.Arg287Gln variant. Peripheral blood mononuclear cells were reprogrammed using non-integrating Sendai viral vectors. The autonomous pluripotency state of the resulting iPSC model was proven by the presence of pluripotency markers, trilineage differentiation potential and absence of the Sendai vector backbone. This iPSC line can be used to study and/or therapeutically target the cellular pathomechanisms of SMAD3-related LDS.

Modelling urea cycle disorders using iPSCs.

The urea cycle is a liver-based pathway enabling disposal of nitrogen waste. Urea cycle disorders (UCDs) are inherited metabolic diseases caused by deficiency of enzymes or transporters involved in the urea cycle and have a prevalence of 1:35,000 live births. Patients present recurrent acute hyperammonaemia, which causes high rate of death and neurological sequelae. Long-term therapy relies on a protein-restricted diet and ammonia scavenger drugs. Currently, liver transplantation is the only cure. Hence, high unmet needs require the identification of effective methods to model these diseases to generate innovative therapeutics. Advances in both induced pluripotent stem cells (iPSCs) and genome editing technologies have provided an invaluable opportunity to model patient-specific phenotypes in vitro by creating patients’ avatar models, to investigate the pathophysiology, uncover novel therapeutic targets and provide a platform for drug discovery. This review summarises the progress made thus far in generating 2- and 3-dimensional iPSCs models for UCDs, the challenges encountered and how iPSCs offer future avenues for innovation in developing the next-generation of therapies for UCDs.

Myogenesis defects in a patient-derived iPSC model of hereditary GNE myopathy

Hereditary muscle diseases are disabling disorders lacking effective treatments. UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) myopathy (GNEM) is an autosomal recessive distal myopathy with rimmed vacuoles typically manifesting in late adolescence/early adulthood. GNE encodes the rate-limiting enzyme in sialic acid biosynthesis, which is necessary for the proper function of numerous biological processes. Outside of the causative gene, very little is known about the mechanisms contributing to the development of GNE myopathy. In the present study, we aimed to address this knowledge gap by querying the underlying mechanisms of GNE myopathy using a patient-derived induced pluripotent stem-cell (iPSC) model. Control and patient-specific iPSCs were differentiated down a skeletal muscle lineage, whereby patient-derived GNEM iPSC clones were able to recapitulate key characteristics of the human pathology and further demonstrated defects in myogenic progression. Single-cell RNA sequencing time course studies revealed clear differences between control and GNEM iPSC-derived muscle precursor cells (iMPCs), while pathway studies implicated altered stress and autophagy signaling in GNEM iMPCs. Treatment of GNEM patient-derived iMPCs with an autophagy activator improved myogenic differentiation. In summary, we report an in vitro, iPSC-based model of GNE myopathy and implicate defective myogenesis as a contributing mechanism to the etiology of GNE myopathy.

Investigating Peripheral Regional Anesthesia Using Induced Pluripotent Stem Cell Technology: Exploring Novel Terrain.

Investigating Peripheral Regional Anesthesia Using Induced Pluripotent Stem Cell Technology: Exploring Novel Terrain.

Assessing the consistency of iPSC and animal models in cystic fibrosis modelling: A meta-analysis.

IntroductionCystic fibrosis (CF) is a hereditary autosomal recessive disorder caused by a range of mutations in the CF Transmembrane Conductance Regulator (CFTR) gene. This gene encodes the CFTR protein, which acts as a chloride channel activated by cyclic AMP (cAMP). This meta-analysis aimed to compare the responsiveness of induced pluripotent stem cells (iPSCs) to cAMP analogues to that of commonly used animal models.MethodsDatabases searched included PubMed, Scopus, and Medline from inception to January 2020. A total of 8 and 3 studies, respectively, for animal models and iPSCs, were analyzed. Studies were extracted for investigating cAMP-stimulated anion transport by measuring the short circuit current (Isc) of chloride channels in different animal models and iPSC systems We utilized an inverse variance heterogeneity model for synthesis.ResultsOur analysis showed considerable heterogeneity in the mean Isc value in both animal models and iPSCs studies (compared to their WT counterparts), and both suffer from variable responsiveness based on the nature of the underlying model. There was no clear advantage of one over the other.ConclusionsStudies on both animal and iPSCs models generated considerable heterogeneity. Given the potential of iPSC-derived models to study different diseases, we recommend paying more attention to developing reproducible models of iPSC as it has potential if adequately developed.

Aberrant Splicing of INS Impairs Beta-Cell Differentiation and Proliferation by ER Stress in the Isogenic iPSC Model of Neonatal Diabetes.

One of the causes of diabetes in infants is the defect of the insulin gene (INS). Gene mutations can lead to proinsulin misfolding, an increased endoplasmic reticulum (ER) stress and possible beta-cell apoptosis. In humans, the mechanisms underlying beta-cell failure remain unclear. We generated induced pluripotent stem cells (iPSCs) from a patient diagnosed with neonatal diabetes mellitus carrying the INS mutation in the 2nd intron (c.188-31G>A) and engineered isogenic CRISPR/Cas9 mutation-corrected cell lines. Differentiation into beta-like cells demonstrated that mutation led to the emergence of an ectopic splice site within the INS and appearance of the abnormal RNA transcript. Isogenic iPSC lines differentiated into beta-like cells showed a clear difference in formation of organoids at pancreatic progenitor stage of differentiation. Moreover, MIN6 insulinoma cell line expressing mutated cDNA demonstrated significant decrease in proliferation capacity and activation of ER stress and unfolded protein response (UPR)-associated genes. These findings shed light on the mechanism underlying the pathogenesis of monogenic diabetes.

TPC2 rescues lysosomal storage in mucolipidosis type IV, Niemann–Pick type C1, and Batten disease

Lysosomes are cell organelles that degrade macromolecules to recycle their components. If lysosomal degradative function is impaired, e.g., due to mutations in lysosomal enzymes or membrane proteins, lysosomal storage diseases (LSDs) can develop. LSDs manifest often with neurodegenerative symptoms, typically starting in early childhood, and going along with a strongly reduced life expectancy and quality of life. We show here that small molecule activation of the Ca2+‐permeable endolysosomal two‐pore channel 2 (TPC2) results in an amelioration of cellular phenotypes associated with LSDs such as cholesterol or lipofuscin accumulation, or the formation of abnormal vacuoles seen by electron microscopy. Rescue effects by TPC2 activation, which promotes lysosomal exocytosis and autophagy, were assessed in mucolipidosis type IV (MLIV), Niemann–Pick type C1, and Batten disease patient fibroblasts, and in neurons derived from newly generated isogenic human iPSC models for MLIV and Batten disease. For in vivo proof of concept, we tested TPC2 activation in the MLIV mouse model. In sum, our data suggest that TPC2 is a promising target for the treatment of different types of LSDs, both in vitro and in‐vivo.

Developing Bottom-Up Induced Pluripotent Stem Cell Derived Solid Tumor Models Using Precision Genome Editing Technologies.

Advances in genome and tissue engineering have spurred significant progress and opportunity for innovation in cancer modeling. Human induced pluripotent stem cells (iPSCs) are an established and powerful tool to study cellular processes in the context of disease-specific genetic backgrounds; however, their application to cancer has been limited by the resistance of many transformed cells to undergo successful reprogramming. Here, we review the status of human iPSC modeling of solid tumors in the context of genetic engineering, including how base and prime editing can be incorporated into "bottom-up" cancer modeling, a term we coined for iPSC-based cancer models using genetic engineering to induce transformation. This approach circumvents the need to reprogram cancer cells while allowing for dissection of the genetic mechanisms underlying transformation, progression, and metastasis with a high degree of precision and control. We also discuss the strengths and limitations of respective engineering approaches and outline experimental considerations for establishing future models.

Metabolic rescue ameliorates mitochondrial encephalo-cardiomyopathy in murine and human iPSC models of Leigh syndrome.

BackgroundMice with deletion of complex I subunit Ndufs4 develop mitochondrial encephalomyopathy resembling Leigh syndrome (LS). The metabolic derangement and underlying mechanisms of cardio‐encephalomyopathy in LS remains incompletely understood.MethodsWe performed echocardiography, electrophysiology, confocal microscopy, metabolic and molecular/morphometric analysis of the mice lacking Ndufs4. HEK293 cells, human iPS cells‐derived cardiomyocytes and neurons were used to determine the mechanistic role of mitochondrial complex I deficiency.ResultsLS mice develop severe cardiac bradyarrhythmia and diastolic dysfunction. Human‐induced pluripotent stem cell‐derived cardiomyocytes (iPS‐CMs) with Ndufs4 deletion recapitulate LS cardiomyopathy. Mechanistically, we demonstrate a direct link between complex I deficiency, decreased intracellular (nicotinamide adenine dinucleotide) NAD+/NADH and bradyarrhythmia, mediated by hyperacetylation of the cardiac sodium channel NaV1.5, particularly at K1479 site. Neuronal apoptosis in the cerebellar and midbrain regions in LS mice was associated with hyperacetylation of p53 and activation of microglia. Targeted metabolomics revealed increases in several amino acids and citric acid cycle intermediates, likely due to impairment of NAD+‐dependent dehydrogenases, and a substantial decrease in reduced Glutathione (GSH). Metabolic rescue by nicotinamide riboside (NR) supplementation increased intracellular NAD+/ NADH, restored metabolic derangement, reversed protein hyperacetylation through NAD+‐dependent Sirtuin deacetylase, and ameliorated cardiomyopathic phenotypes, concomitant with improvement of NaV1.5 current and SERCA2a function measured by Ca2+‐transients. NR also attenuated neuronal apoptosis and microglial activation in the LS brain and human iPS‐derived neurons with Ndufs4 deletion.ConclusionsOur study reveals direct mechanistic explanations of the observed cardiac bradyarrhythmia, diastolic dysfunction and neuronal apoptosis in mouse and human induced pluripotent stem cells (iPSC) models of LS.

Probing the molecular and cellular pathological mechanisms of schizophrenia using human induced pluripotent stem cell models.

With recent advancements in psychiatric genomics, as a field, "stem cell-based disease modelers" were given the exciting yet daunting task of translating the extensive list of disease-associated risks into biologically and clinically relevant information in order to deliver therapeutically meaningful leads and insights. Despite their limitations, human induced pluripotent stem cell (iPSCs) based models have greatly aided our understanding of the molecular and cellular mechanisms underlying the complex etiology of brain disorders including schizophrenia (SCZ). In this review, we summarize the major findings from studies in the past decade which utilized iPSC models to investigate cell type-specific phenotypes relevant to idiopathic SCZ and disease penetrant alleles. Across cell type differences, several biological themes emerged, serving as potential neurodevelopmental mechanisms of SCZ, including oxidative stress and mitochondrial dysfunction, depletion of progenitor pools and insufficient differentiation potential of these progenitors, and structural and functional deficits of neurons and other supporting cells. Here, we discuss both the recent progress as well as challenges and improvements needed for future studies utilizing iPSCs as a model for SCZ and other neuropsychiatric disorders.

Type-I-interferon signaling drives microglial dysfunction and senescence in human iPSC models of Down syndrome and Alzheimer's disease.

Microglia are critical in brain development and Alzheimer's disease (AD) etiology. Down syndrome (DS) is the most common genetic developmental disorder and risk factor for AD. Surprisingly, little information is available on the impact of trisomy of human chromosome 21 (Hsa21) on microglial functions during DS brain development and in AD in DS. Using induced pluripotent stem cell (iPSC)-based organoid and chimeric mouse models, we report that DS microglia exhibit an enhanced synaptic pruning function, which alters neuronal synaptic functions. In response to human brain tissue-derived pathological tau, DS microglia undergo cellular senescence and exhibit elevated type-I-interferon signaling. Mechanistically, knockdown of Hsa21-encoded type I interferon receptors, IFNARs, rescues the DS microglial phenotypes both during brain development and in response to pathological tau. Our findings provide invivo evidence that human microglia respond to pathological tau by exhibiting dystrophic phenotypes. Targeting IFNARs may improve DS microglial functions and prevent senescence.

Brain microvascular endothelial cell dysfunction in an isogenic juvenile iPSC model of Huntington’s disease

Huntington’s disease (HD) is an inherited neurodegenerative disease caused by expansion of cytosine–adenine–guanine (CAG) repeats in the huntingtin gene, which leads to neuronal loss and decline in cognitive and motor function. Increasing evidence suggests that blood–brain barrier (BBB) dysfunction may contribute to progression of the disease. Studies in animal models, in vitro models, and post-mortem tissue find that disease progression is associated with increased microvascular density, altered cerebral blood flow, and loss of paracellular and transcellular barrier function. Here, we report on changes in BBB phenotype due to expansion of CAG repeats using an isogenic pair of induced pluripotent stem cells (iPSCs) differentiated into brain microvascular endothelial-like cells (iBMECs). We show that CAG expansion associated with juvenile HD alters the trajectory of iBMEC differentiation, producing cells with ~ two-fold lower percentage of adherent endothelial cells. CAG expansion is associated with diminished transendothelial electrical resistance and reduced tight junction protein expression, but no significant changes in paracellular permeability. While mutant huntingtin protein (mHTT) aggregates were not observed in HD iBMECs, widespread transcriptional dysregulation was observed in iBMECs compared to iPSCs. In addition, CAG expansion in iBMECs results in distinct responses to pathological and therapeutic perturbations including angiogenic factors, oxidative stress, and osmotic stress. In a tissue-engineered BBB model, iBMECs show subtle changes in phenotype, including differences in cell turnover and immune cell adhesion. Our results further support that CAG expansion in BMECs contributes to BBB dysfunction during HD.