Familial Alzheimer’s disease modelling using induced pluripotent stem cell technology

Brain-derived neurotrophic factor increases cell number of neural progenitor cells derived from human induced pluripotent stem cells

Background

Several pieces of evidence from in vitro studies showed that brain-derived neurotrophic factor (BDNF) promotes proliferation and differentiation of neural stem/progenitor cells (NSCs) into neurons. Moreover, the JAK2 pathway was proposed to be associated with mouse NSC proliferation. BDNF could activate the STAT-3 pathway and induce proliferation in mouse NSCs. However, its effects on proliferation are not fully understood and JAK/STAT pathway was proposed to play a role in this activity.

Methods

In the present study, the effects of BDNF on cell proliferation and neurite outgrowth of Alzheimer’s disease (AD) induced pluripotent stem cells (iPSCs)-derived human neural progenitor cells (hNPCs) were examined. Moreover, a specific signal transduction pathway important in cell proliferation was investigated using a JAK2 inhibitor (AG490) to clarify the role of that pathway.

Results

The proliferative effect of BDNF was remarkably observed as an increase in Ki-67 positive cells. The cell number of hNPCs was significantly increased after BDNF treatment represented by cellular metabolic activity of the cells measured by MTT assay. This noticeable effect was statistically shown at 20 ng/ml of BDNF treatment. BDNF, however, did not promote neurite outgrowth but increased neuronal cell number. It was found that AG490 suppressed hNPCs proliferation. However, this inhibitor partially decreased BDNF-induced hNPCs proliferation. These results demonstrated the potential role of BDNF for the amelioration of AD through the increase of AD-derived hNPCs number.

Presence of a mutation in PSEN1 or PSEN2 gene is associated with an impaired brain endothelial cell phenotype in vitro

Background

Alzheimer’s disease (AD) is the most common form of neurodegenerative disease. It is an irreversible condition marked by irreversible cognitive loss, commonly attributed to the loss of hippocampal neurons due to the formation of senile plaques and neurofibrillary tangles. Although the sporadic form is the most prevalent, the presence of familial form (involving several genes such as APP, PSEN1, and PSEN2) of the disease is commonly used as a model for understanding the pathophysiology of the disease. The aim of this study is to investigate the effect of a mutation on PSEN1 and PSEN2 genes on the BBB function using induced pluripotent stem cells (iPSCs).

Methods

iPSC lines from patients suffering from a familial form of Alzheimer’s disease and harboring mutations in PSEN1 or PSEN2 were used in this study and compared to a control iPSC line. Cells were differentiated into brain microvascular endothelial cells (BMECs) following established differentiation protocols. Barrier function was assessed by measuring TEER and fluorescein permeability, drug transporter activity was assessed by uptake assay, glucose uptake and metabolism assessed by cell flux analyzer, mitochondrial potential by JC-1, and lysosomal acidification by acridine orange.

Results

iPSC-derived BMECs from the FAD patient presenting a mutation in the PSEN1 gene showed impaired barrier function compared to the FAD patient harboring a mutation in PSEN2 and to the control group. Such impaired barrier function correlated with poor tight junction complexes and reduced drug efflux pump activity. In addition, both PSEN1 and PSEN2-BMECs displayed reduced bioenergetics, lysosomal acidification, autophagy, while showing an increase in radical oxygen species (ROS) production. Finally, PSEN1- and PSEN2-BMECs showed an elevated secretion of Aβ1–40 peptides compared to control-BMECs.

Conclusions

Our study reports that iPSC-derived BMECs obtained from FAD patients showed impaired barrier properties and BMEC metabolism. In particular, mutation in the PSEN1 gene was associated with a more detrimental phenotype than mutation in PSEN2, as noted by a reduced barrier function, reduced drug efflux pump activity, and diminished glucose metabolism. Therefore, assessing the contribution of genetic mutations associated with Alzheimer’s disease will allow us to better understand the contribution of the BBB in dementia, but also other neurodegenerative diseases.

A Three-Dimensional Alzheimer's Disease Cell Culture Model Using iPSC-Derived Neurons Carrying A246E Mutation in PSEN1

Alzheimer's disease (AD) is a chronic brain disorder characterized by progressive intellectual decline and memory and neuronal loss, caused mainly by extracellular deposition of amyloid-β (Aβ) and intracellular accumulation of hyperphosphorylated tau protein, primarily in areas implicated in memory and learning as prefrontal cortex and hippocampus. There are two forms of AD, a late-onset form that affects people over 65 years old, and the early-onset form, which is hereditable and affect people at early ages ~45 years. To date, there is no cure for the disease; consequently, it is essential to develop new tools for the study of processes implicated in the disease. Currently, in vitro AD three-dimensional (3D) models using induced pluripotent stem cells (iPSC)-derived neurons have broadened the horizon for in vitro disease modeling and gained interest for mechanistic studies and preclinical drug discovery due to their potential advantages in providing a better physiologically relevant information and more predictive data for in vivo tests. Therefore, this study aimed to establish a 3D cell culture model of AD in vitro using iPSCs carrying the A246E mutation. We generated human iPSCs from fibroblasts from a patient with AD harboring the A246E mutation in the PSEN1 gene. Cell reprogramming was performed using lentiviral vectors with Yamanaka's factors (OSKM: Oct4, Sox2, Klf4, and c-Myc). The resulting iPSCs expressed pluripotency genes (such as Nanog and Oct4), alkaline phosphatase activity, and pluripotency stem cell marker expression, such as OCT4, SOX2, TRA-1-60, and SSEA4. iPSCs exhibited the ability to differentiate into neuronal lineage in a 3D environment through dual SMAD inhibition as confirmed by Nestin, MAP2, and Tuj1 neural marker expression. These iPSC-derived neurons harbored Aβ oligomers confirmed by Western Blot (WB) and immunostaining. With human iPSC-derived neurons able to produce Aβ oligomers, we established a novel human hydrogel-based 3D cell culture model that recapitulates Aβ aggregation without the need for mutation induction or synthetic Aβ exposure. This model will allow the study of processes implicated in disease spread throughout the brain, the screening of molecules or compounds with therapeutic potential, and the development of personalized therapeutic strategies.

In vitro Models of Neurodegenerative Diseases

Neurodegenerative diseases are progressive degenerative conditions characterized by the functional deterioration and ultimate loss of neurons. These incurable and debilitating diseases affect millions of people worldwide, and therefore represent a major global health challenge with severe implications for individuals and society. Recently, several neuroprotective drugs have failed in human clinical trials despite promising pre-clinical data, suggesting that conventional cell cultures and animal models cannot precisely replicate human pathophysiology. To bridge the gap between animal and human studies, three-dimensional cell culture models have been developed from human or animal cells, allowing the effects of new therapies to be predicted more accurately by closely replicating some aspects of the brain environment, mimicking neuronal and glial cell interactions, and incorporating the effects of blood flow. In this review, we discuss the relative merits of different cerebral models, from traditional cell cultures to the latest high-throughput three-dimensional systems. We discuss their advantages and disadvantages as well as their potential to investigate the complex mechanisms of human neurodegenerative diseases. We focus on in vitro models of the most frequent age-related neurodegenerative disorders, such as Parkinson’s disease, Alzheimer’s disease and prion disease, and on multiple sclerosis, a chronic inflammatory neurodegenerative disease affecting young adults.

Pathological manifestation of the induced pluripotent stem cell-derived cortical neurons from an early-onset Alzheimer's disease patient carrying a presenilin-1 mutation (S170F)

Objectives

Alzheimer's disease (AD) is the most common neurodegenerative disease which is characterized by the formation of amyloid beta (Aβ) plaques and neurofibrillary tangles. These abnormal proteins induce disturbance in mitochondrial dynamics and defect in autophagy system. Since presenilin‐1 (PS1) is a core component in γ‐secretase complex, the mutations of PS1 gene cause the interference of γ‐secretase activity and lead to the increased Aβ₄₂ secretion. We aimed to characterize the patient‐specific induced pluripotent stem cell (iPSC) line carrying PS1‐S170F mutation. Furthermore, we tested whether disease‐modifying drug can reduce AD pathology in the AD iPSC‐derived neurons.

Materials and methods

Mononuclear cells (MNCs) were isolated freshly from the peripheral blood of an autosomal dominant AD (ADAD) patient carrying presenilin‐1 (PS1) mutation (Ser170Phe; PS1‐S170F) and a cognitively normal control. We generated induced pluripotent stem cell (iPSC) lines, which were differentiated into functional cortical neurons. Then, we measured the markers indicative of AD pathogenesis using immunocytochemistry and Western blot. We also investigated the mitochondrial dynamics in the AD iPSC‐derived neurons using Mito‐tracker.

Results

We observed that both extracellular and intracellular Aβ levels were dramatically increased in the PS1‐S170F iPSC‐derived neurons, compared with the control iPSC‐derived neurons. Furthermore, PS1‐S170F iPSC‐derived neurons showed high expression levels of p‐Tau, which were detected both in the soma and neurites. The mitochondrial velocity in the PS1‐S170F iPSC‐derived neurons was much reduced, compared with that of the control. We also found a significant decrease of fusion‐related protein Mfn1 (membrane proteins mitofusin 1) and an increase of fission‐related protein DRP1 (dynamin‐related protein 1) in the PS1‐S170F iPSC‐derived neurons. We further observed the defects of autophagy‐related clearance in the PS1‐S170F iPSC‐derived neurons. Finally, we demonstrated the levels of Aβ and p‐Tau can be dramatically reduced by the treatment of LY‐2886721, a BACE1 inhibitor.

Conclusions

Taken together, we have established and characterized the pathological features of an AD patient carrying PS1‐S170F mutation using iPSC technology, which will be the first case on this mutation and this iPSC line will serve as a useful resource for studying AD pathogenesis and drug screening in the future.

The First Generation of iPSC Line from a Korean Alzheimer's Disease Patient Carrying APP-V715M Mutation Exhibits a Distinct Mitochondrial Dysfunction

Alzheimer's Disease (AD) is a progressive neurodegenerative disease, which is pathologically defined by the accumulation of amyloid plaques and hyper-phosphorylated tau aggregates in the brain. Mitochondrial dysfunction is also a prominent feature in AD, and the extracellular Aβ and phosphorylated tau result in the impaired mitochondrial dynamics. In this study, we generated an induced pluripotent stem cell (iPSC) line from an AD patient with amyloid precursor protein (APP) mutation (Val715Met; APP-V715M) for the first time. We demonstrated that both extracellular and intracellular levels of Aβ were dramatically increased in the APP-V715M iPSC-derived neurons. Furthermore, the APP-V715M iPSC-derived neurons exhibited high expression levels of phosphorylated tau (AT8), which was also detected in the soma and neurites by immunocytochemistry. We next investigated mitochondrial dynamics in the iPSC-derived neurons using Mito-tracker, which showed a significant decrease of anterograde and retrograde velocity in the APP-V715M iPSC-derived neurons. We also found that as the Aβ and tau pathology accumulates, fusion-related protein Mfn1 was decreased, whereas fission-related protein DRP1 was increased in the APP-V715M iPSC-derived neurons, compared with the control group. Taken together, we established the first iPSC line derived from an AD patient carrying APP-V715M mutation and showed that this iPSC-derived neurons exhibited typical AD pathological features, including a distinct mitochondrial dysfunction.

Neurological diseases at the blood-brain barrier: Stemming new scientific paradigms using patient-derived induced pluripotent cells

The blood-brain barrier (BBB) is a component of the neurovascular unit formed by specialized brain microvascular endothelial cells (BMECs) surrounded by a specific basement membrane interacting with astrocytes, neurons, and pericytes. The BBB plays an essential function in the maintenance of brain homeostasis, by providing a physical and chemical barrier against pathogens and xenobiotics. Although the disruption of the BBB occurs with several neurological disorders, the scarcity of patient material source and lack of reliability of current in vitro models hindered our ability to model the BBB during such neurological conditions. The development of novel in vitro models based on patient-derived stem cells opened new venues in modeling the human BBB in vitro, by being more accurate than existing in vitro models, but also bringing such models closer to the in vivo setting. In addition, patient-derived models of the BBB opens the avenue to address the contribution of genetic factors commonly associated with certain neurological diseases on the BBB pathophysiology. This review provides a comprehensive understanding of the BBB, the current development of stem cell-based models in the field, the current challenges and limitations of such models.

Pathological human astroglia in Alzheimer's disease: opening new horizons with stem cell technology

Pathological remodeling, degeneration and reactivity of astrocytes are fundamental astrogliopathies contributing to all neurological diseases. In neurodegenerative disorders (including Alzheimer's disease [AD]) astroglia undergo complex changes that range from atrophy with loss of function to accumulation of reactive cells around disease-specific lesions (senile plaques in the case of AD). The cellular pathology of astroglia in the context of human AD remains enigmatic; mainly because of the severe limitations of animal models, which, although reproducing some pathological features of the disease, do not mimic its progression in full. Human-induced pluripotent stem cells technology creates a novel and potentially revolutionizing platform for studying fundamental mechanisms of the disease and for screening to identify new therapeutic compounds.

Stem Cell Technology for (Epi)genetic Brain Disorders

Despite the enormous efforts of the scientific community over the years, effective therapeutics for many (epi)genetic brain disorders remain unidentified. The common and persistent failures to translate preclinical findings into clinical success are partially attributed to the limited efficiency of current disease models. Although animal and cellular models have substantially improved our knowledge of the pathological processes involved in these disorders, human brain research has generally been hampered by a lack of satisfactory humanized model systems. This, together with our incomplete knowledge of the multifactorial causes in the majority of these disorders, as well as a thorough understanding of associated (epi)genetic alterations, has been impeding progress in gaining more mechanistic insights from translational studies. Over the last years, however, stem cell technology has been offering an alternative approach to study and treat human brain disorders. Owing to this technology, we are now able to obtain a theoretically inexhaustible source of human neural cells and precursors in vitro that offer a platform for disease modeling and the establishment of therapeutic interventions. In addition to the potential to increase our general understanding of how (epi)genetic alterations contribute to the pathology of brain disorders, stem cells and derivatives allow for high-throughput drugs and toxicity testing, and provide a cell source for transplant therapies in regenerative medicine. In the current chapter, we will demonstrate the validity of human stem cell-based models and address the utility of other stem cell-based applications for several human brain disorders with multifactorial and (epi)genetic bases, including Parkinson's disease (PD), Alzheimer's disease (AD), fragile X syndrome (FXS), Angelman syndrome (AS), Prader-Willi syndrome (PWS), and Rett syndrome (RTT).

Aberrant iPSC-derived human astrocytes in Alzheimer's disease

The pathological potential of human astroglia in Alzheimer's disease (AD) was analysed in vitro using induced pluripotent stem cell (iPSC) technology. Here, we report development of a human iPSC-derived astrocyte model created from healthy individuals and patients with either early-onset familial AD (FAD) or the late-onset sporadic form of AD (SAD). Our chemically defined and highly efficient model provides >95% homogeneous populations of human astrocytes within 30 days of differentiation from cortical neural progenitor cells (NPCs). All astrocytes expressed functional markers including glial fibrillary acidic protein (GFAP), excitatory amino acid transporter-1 (EAAT1), S100B and glutamine synthetase (GS) comparable to that of adult astrocytes in vivo. However, induced astrocytes derived from both SAD and FAD patients exhibit a pronounced pathological phenotype, with a significantly less complex morphological appearance, overall atrophic profiles and abnormal localisation of key functional astroglial markers. Furthermore, NPCs derived from identical patients did not show any differences, therefore, validating that remodelled astroglia are not as a result of defective neural intermediates. This work not only presents a novel model to study the mechanisms of human astrocytes in vitro, but also provides an ideal platform for further interrogation of early astroglial cell autonomous events in AD and the possibility of identification of novel therapeutic targets for the treatment of AD.

3D culture models of Alzheimer's disease: a road map to a "cure-in-a-dish"

Alzheimer's disease (AD) transgenic mice have been used as a standard AD model for basic mechanistic studies and drug discovery. These mouse models showed symbolic AD pathologies including β-amyloid (Aβ) plaques, gliosis and memory deficits but failed to fully recapitulate AD pathogenic cascades including robust phospho tau (p-tau) accumulation, clear neurofibrillary tangles (NFTs) and neurodegeneration, solely driven by familial AD (FAD) mutation(s). Recent advances in human stem cell and three-dimensional (3D) culture technologies made it possible to generate novel 3D neural cell culture models that recapitulate AD pathologies including robust Aβ deposition and Aβ-driven NFT-like tau pathology. These new 3D human cell culture models of AD hold a promise for a novel platform that can be used for mechanism studies in human brain-like environment and high-throughput drug screening (HTS). In this review, we will summarize the current progress in recapitulating AD pathogenic cascades in human neural cell culture models using AD patient-derived induced pluripotent stem cells (iPSCs) or genetically modified human stem cell lines. We will also explain how new 3D culture technologies were applied to accelerate Aβ and p-tau pathologies in human neural cell cultures, as compared the standard two-dimensional (2D) culture conditions. Finally, we will discuss a potential impact of the human 3D human neural cell culture models on the AD drug-development process. These revolutionary 3D culture models of AD will contribute to accelerate the discovery of novel AD drugs.

Alzheimer's in 3D culture: challenges and perspectives

Alzheimer's disease (AD) is the most common cause of dementia, and there is currently no cure. The "β-amyloid cascade hypothesis" of AD is the basis of current understanding of AD pathogenesis and drug discovery. However, no AD models have fully validated this hypothesis. We recently developed a human stem cell culture model of AD by cultivating genetically modified human neural stem cells in a three-dimensional (3D) cell culture system. These cells were able to recapitulate key events of AD pathology including β-amyloid plaques and neurofibrillary tangles. In this review, we will discuss the progress and current limitations of AD mouse models and human stem cell models as well as explore the breakthroughs of 3D cell culture systems. We will also share our perspective on the potential of dish models of neurodegenerative diseases for studying pathogenic cascades and therapeutic drug discovery.

Generation of induced pluripotent stem cells from renal tubular cells of a patient with Alport syndrome

Alport syndrome (AS) is a hereditary disease that leads to kidney failure and is caused by mutations in the COL4A3, COL4A4, and COL4A5 genes that lead to the absence of collagen α3α4α5 (IV) networks in the mature kidney glomerular basement membrane. Approximately 80% of AS is X-linked because of mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen. To investigate the pathogenesis of AS at the genetic level, we generated induced pluripotent stem cells (iPSCs) from renal tubular cells of a patient with AS. The successful iPSC generation laid the foundation to master the repair of the COL4A5 gene and to evaluate the differentiation of iPSC into Sertoli cells and the accompanying epigenetic changes at each stage. The generation of iPSCs from AS patients not only confirms that iPSCs could be generated from renal tubular cells, but also provides a novel type of genetic therapy for AS patients. In this study, we generated iPSCs from renal tubular cells via ectopic expression of four transcription factors (Oct4, Sox2, c-myc, and Klf4). According to the human embryonic stem cell (hESC) charter, iPSC formation was confirmed by comparatively analyzing hESC markers via colony morphology, immunohistochemistry, qRT-PCR, flow cytometry, gene expression profiling of the three germ layers, and karyotyping. Our results demonstrated that iPSCs were similar to hESCs with regard to morphology, proliferation, hESC-specific surface marker expression, and differentiation into the cell types of the three germ layers. The efficient generation of iPSCs from the renal tubular cells of an AS patient would provide a novel model to investigate the mechanisms underlying AS and to develop new treatments for AS.

The potential of induced pluripotent stem cells in models of neurological disorders: implications on future therapy

There is an urgent need for new and advanced approaches to modeling the pathological mechanisms of complex human neurological disorders. This is underscored by the decline in pharmaceutical research and development efficiency resulting in a relative decrease in new drug launches in the last several decades. Induced pluripotent stem cells represent a new tool to overcome many of the shortcomings of conventional methods, enabling live human neural cell modeling of complex conditions relating to aberrant neurodevelopment, such as schizophrenia, epilepsy and autism as well as age-associated neurodegeneration. This review considers the current status of induced pluripotent stem cell-based modeling of neurological disorders, canvassing proven and putative advantages, current constraints, and future prospects of next-generation culture systems for biomedical research and translation.

Recapitulating amyloid β and tau pathology in human neural cell culture models: clinical implications

The "amyloid β hypothesis" of Alzheimer's disease (AD) has been the reigning hypothesis explaining pathogenic mechanisms of AD over the last two decades. However, this hypothesis has not been fully validated in animal models, and several major unresolved issues remain. We recently developed a human neural cell culture model of AD based on a three-dimensional (3D) cell culture system. This unique, cellular model recapitulates key events of the AD pathogenic cascade, including β-amyloid plaques and neurofibrillary tangles. Our 3D human neural cell culture model system provides a premise for a new generation of cellular AD models that can serve as a novel platform for studying pathogenic mechanisms and for high-throughput drug screening in a human brain-like environment.

Cellular reprogramming for understanding and treating human disease

In the last two decades we have witnessed a paradigm shift in our understanding of cells so radical that it has rewritten the rules of biology. The study of cellular reprogramming has gone from little more than a hypothesis, to applied bioengineering, with the creation of a variety of important cell types. By way of metaphor, we can compare the discovery of reprogramming with the archeological discovery of the Rosetta stone. This stone slab made possible the initial decipherment of Egyptian hieroglyphics because it allowed us to see this language in a way that was previously impossible. We propose that cellular reprogramming will have an equally profound impact on understanding and curing human disease, because it allows us to perceive and study molecular biological processes such as differentiation, epigenetics, and chromatin in ways that were likewise previously impossible. Stem cells could be called “cellular Rosetta stones” because they allow also us to perceive the connections between development, disease, cancer, aging, and regeneration in novel ways. Here we present a comprehensive historical review of stem cells and cellular reprogramming, and illustrate the developing synergy between many previously unconnected fields. We show how stem cells can be used to create in vitro models of human disease and provide examples of how reprogramming is being used to study and treat such diverse diseases as cancer, aging, and accelerated aging syndromes, infectious diseases such as AIDS, and epigenetic diseases such as polycystic ovary syndrome. While the technology of reprogramming is being developed and refined there have also been significant ongoing developments in other complementary technologies such as gene editing, progenitor cell production, and tissue engineering. These technologies are the foundations of what is becoming a fully-functional field of regenerative medicine and are converging to a point that will allow us to treat almost any disease.

Concise review: modeling central nervous system diseases using induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) offer an opportunity to delve into the mechanisms underlying development while also affording the potential to take advantage of a number of naturally occurring mutations that contribute to either disease susceptibility or resistance. Just as with any new field, several models of screening are being explored, and innovators are working on the most efficient methods to overcome the inherent limitations of primary cell screens using iPSCs. In the present review, we provide a background regarding why iPSCs represent a paradigm shift for central nervous system (CNS) disease modeling. We describe the efforts in the field to develop more biologically relevant CNS disease models, which should provide screening assays useful for the pharmaceutical industry. We also provide some examples of successful uses for iPSC-based screens and suggest that additional development could revolutionize the field of drug discovery. The development and implementation of these advanced iPSC-based screens will create a more efficient disease-specific process underpinned by the biological mechanism in a patient- and disease-specific manner rather than by trial-and-error. Moreover, with careful and strategic planning, shared resources can be developed that will enable exponential advances in the field. This will undoubtedly lead to more sensitive and accurate screens for early diagnosis and allow the identification of patient-specific therapies, thus, paving the way to personalized medicine.