Microglia innately develop within cerebral organoids

Human Cerebral Organoids and Fetal Brain Tissue Share Proteomic Similarities

The limited access to functional human brain tissue has led to the development of stem cell-based alternative models. The differentiation of human pluripotent stem cells into cerebral organoids with self-organized architecture has created novel opportunities to study the early stages of the human cerebral formation. Here we applied state-of-the-art label-free shotgun proteomics to compare the proteome of stem cell-derived cerebral organoids to the human fetal brain. We identified 3,073 proteins associated with different developmental stages, from neural progenitors to neurons, astrocytes, or oligodendrocytes. The major protein groups are associated with neurogenesis, axon guidance, synaptogenesis, and cortical brain development. Glial cell proteins related to cell growth and maintenance, energy metabolism, cell communication, and signaling were also described. Our data support the variety of cells and neural network functional pathways observed within cell-derived cerebral organoids, confirming their usefulness as an alternative model. The characterization of brain organoid proteome is key to explore, in a dish, atypical and disrupted processes during brain development or neurodevelopmental, neurodegenerative, and neuropsychiatric diseases.

Microglial NLRP3 inflammasome activation in multiple sclerosis

Multiple sclerosis (MS) is a chronic, autoimmune and neuroinflammatory disease of the central nervous system (CNS) mediated by autoreactive T cells directed against myelin antigens. Although the crucial role of adaptive immunity is well established in MS, the contribution of innate immunity has only recently been appreciated. Microglia are the main innate immune cells of the CNS. Similar to other myeloid cells, microglia recognize both exogenous and host-derived endogenous danger signals through pattern recognition receptors (PRRs) localized on their cell surface such as Toll Like receptor 4, or in the cytosol such as NLRP3. The second one is the sensor protein of the multi-molecular NLRP3 inflammasome complex in activated microglia that promotes the maturation and secretion of proinflammatory cytokines, interleukin-1β and interleukin-18. Overactivation of microglia and aberrant activation of the NLRP3 inflammasome have been implicated in the pathogenesis of MS. Indeed, experimental data, together with post-mortem and clinical studies have revealed an increased expression of NLRP3 inflammasome complex elements in microglia and other immune cells. In this review, we focus on microglial NLRP3 inflammasome activation in MS. First, we overview the basic knowledge about MS, microglia and the NLRP3 inflammasome. Then, we summarize studies about microglial NLRP3 inflammasome activation in MS and its animal models. We also highlight experimental therapeutic approaches that target different steps of NLRP inflammasome activation. Finally, we discuss future research avenues and new methods in this rapidly evolving area.

Back to the origins: Human brain organoids to investigate neurodegeneration

Neurodegenerative disorders represent a high burden in terms of individual, social and economical resources. No ultimate therapy has been established so far; human brain morphology and development can not be entirely reproduced by animal models, and genomic, metabolic and biochemical differences might contribute to a limited predictive power for human translation. Thus, the development of human brain organoid models holds a wide potential to investigate the range of physiological and pathological features that characterise the early onset of the degeneration. Moreover, central nervous system development has gained a crucial role in the study of the pathogenesis of neurodegenerative disorders. Premature alterations during brain maturation have been related to late disease manifestations; genetic mutations responsible for neurodegeneration have been found in genes highly expressed during neural development. Elucidating the mechanisms triggering neuronal susceptibility to degeneration is crucial for pathogenetic studies and therapeutic discoveries. In the present work, we provide an overview on the current applications of human brain organoids towards studies of neurodegenerative diseases, with a survey on the recent discoveries and a closing discussion on the present challenges and future perspectives.

Neuronal maturation reduces the type I IFN response to orthobunyavirus infection and leads to increased apoptosis of human neurons

BACKGROUND

La Crosse virus (LACV) is the leading cause of pediatric arboviral encephalitis in the USA. LACV encephalitis can result in learning and memory deficits, which may be due to infection and apoptosis of neurons in the brain. Despite neurons being the primary cell infected in the brain by LACV, little is known about neuronal responses to infection.

METHODS

Human cerebral organoids (COs), which contain a spectrum of developing neurons, were used to examine neuronal responses to LACV. Plaque assay and quantitative reverse transcription (qRT) PCR were used to determine the susceptibility of COs to LACV infection. Immunohistochemistry, flow cytometry, and single-cell transcriptomics were used to determine specific neuronal subpopulation responses to the virus.

RESULTS

Overall, LACV readily infected COs causing reduced cell viability and increased apoptosis. However, it was determined that neurons at different stages of development had distinct responses to LACV. Both neural progenitors and committed neurons were infected with LACV, however, committed neurons underwent apoptosis at a higher rate. Transcriptomic analysis showed that committed neurons expressed fewer interferon (IFN)-stimulated genes (ISGs) and genes involved IFN signaling in response to infection compared to neural progenitors. Furthermore, induction of interferon signaling in LACV-infected COs by application of recombinant IFN enhanced cell viability.

CONCLUSIONS

These findings indicate that neuronal maturation increases the susceptibility of neurons to LACV-induced apoptosis. This susceptibility is likely due, at least in part, to mature neurons being less responsive to virus-induced IFN as evidenced by their poor ISG response to LACV. Furthermore, exogenous administration of recombinant IFN to LACV COs rescued cellular viability suggesting that increased IFN signaling is overall protective in this complex neural tissue. Together these findings indicate that induction of IFN signaling in developing neurons is an important deciding factor in virus-induced cell death.

iPSCs-Based Neural 3D Systems: A Multidimensional Approach for Disease Modeling and Drug Discovery

Induced pluripotent stem cells (iPSCs)-based two-dimensional (2D) protocols have offered invaluable insights into the pathophysiology of neurological diseases. However, these systems are unable to reproduce complex cytoarchitectural features, cell-cell and tissue-tissue interactions like their in vivo counterpart. Three-dimensional (3D)-based culture protocols, though in their infancy, have offered new insights into modeling human diseases. Human neural organoids try to recapitulate the cellular diversity of complex tissues and can be generated from iPSCs to model the pathophysiology of a wide spectrum of pathologies. The engraftment of iPSCs into mice models and the improvement of differentiation protocols towards 3D cultures has enabled the generation of more complex multicellular systems. Consequently, models of neuropsychiatric disorders, infectious diseases, brain cancer and cerebral hypoxic injury can now be investigated from new perspectives. In this review, we consider the advancements made in modeling neuropsychiatric and neurological diseases with iPSC-derived organoids and their potential use to develop new drugs.

Modeling Brain Somatic Mosaicism With Cerebral Organoids, Including a Note on Mutant Microglia

The brain is a genomic mosaic. Cell-to-cell genomic differences, which are the result of somatic mutations during development and aging, contribute to cellular diversity in the nervous system. This genomic diversity has important implications for nervous system development, function, and disease. Brain somatic mosaicism might contribute to individualized behavioral phenotypes and has been associated with several neuropsychiatric and neurodegenerative disorders. Therefore, understanding the causes and consequences of somatic mosaicism in neural circuits is of great interest. Recent advances in 3D cell culture technology have provided new means to study human organ development and various human pathologies in vitro. Cerebral organoids ("mini-brains") are pluripotent stem cell-derived 3D culture systems that recapitulate, to some extent, the developmental processes and organization of the developing human brain. Here, I discuss the application of these neural organoids for modeling brain somatic mosaicism in a lab dish. Special emphasis is given to the potential role of microglial mutations in the pathogenesis of neurodegenerative diseases.

Developmental analyses of mouse embryos and adults using a non-overlapping tracing system for all three germ layers

Genetic lineage-tracing techniques are powerful tools for studying specific cell populations in development and pathogenesis. Previous techniques have mainly involved systems for tracing a single gene, which are limited in their ability to facilitate direct comparisons of the contributions of different cell lineages. We have developed a new combinatorial system for tracing all three germ layers using self-cleaving 2A peptides and multiple site-specific recombinases (SSRs). In the resulting TRiCK (TRiple Coloured germ layer Knock-in) mice, the three germ layers are conditionally and simultaneously labelled with distinct fluorescent proteins via embryogenesis. We show that previously reported ectopic expressions of lineage markers are the outcome of secondary gene expression. The results presented here also indicate that the commitment of caudal axial stem cells to neural or mesodermal fate proceeds without lineage fluctuations, contrary to the notion of their bi-potency. Moreover, we developed IMES, an optimized tissue clearing method that is highly compatible with a variety of fluorescent proteins and immunostaining, and the combined use of TRiCK mice and IMES can facilitate comprehensive analyses of dynamic contributions of all three germ layers.

Opportunities in precision psychiatry using PET neuroimaging in psychosis

With the movement toward precision medicine in healthcare, recent studies of individuals with psychosis have begun to explore positron emission tomography (PET) as a tool to test for biochemical signatures that may distinguish subtypes of psychosis that guide subtype-specific therapeutic interventions. This review presents selected PET findings that exemplify early promise in using molecular imaging to predict treatment response, provide rationale for new therapeutic targets, and monitor target engagement in biomarker-defined subtypes of psychosis. PET data, among other data types, may prove useful in the scientific pursuit of identifying precision strategies to improve clinical outcomes for individuals with psychosis.

Generation of complex human organoid models including vascular networks by incorporation of mesodermal progenitor cells

Organoids derived from human pluripotent stem cells are interesting models to study mechanisms of morphogenesis and promising platforms for disease modeling and drug screening. However, they mostly remain incomplete as they lack stroma, tissue resident immune cells and in particular vasculature, which create important niches during development and disease. We propose, that the directed incorporation of mesodermal progenitor cells (MPCs) into organoids will overcome the aforementioned limitations. In order to demonstrate the feasibility of the method, we generated complex human tumor as well as neural organoids. We show that the formed blood vessels display a hierarchic organization and mural cells are assembled into the vessel wall. Moreover, we demonstrate a typical blood vessel ultrastructure including endothelial cell-cell junctions, a basement membrane as well as luminal caveolae and microvesicles. We observe a high plasticity in the endothelial network, which expands, while the organoids grow and is responsive to anti-angiogenic compounds and pro-angiogenic conditions such as hypoxia. We show that vessels within tumor organoids connect to host vessels following transplantation. Remarkably, MPCs also deliver Iba1⁺ cells that infiltrate the neural tissue in a microglia-like manner.

Cien Años de Microglía: Milestones in a Century of Microglial Research

The year 2019 marks the 100-year anniversary of the discovery of microglia by Pío del Río-Hortega. We will recount the state of neuroscience research at the beginning of the 20th century and the heated scientific dispute regarding microglial identity. We will then walk through some of the milestones of microglial research in the decades since then. In the last 20 years, the field has grown exponentially. Researchers have shown that microglia are unlike any other resident macrophages: they have a unique origin and distinguishing features. Microglia are extraordinarily motile cells and constantly survey their environment, interacting with neurons, astrocytes, oligodendrocytes, neural stem cells, and infiltrating immune cells. We finally highlight some open questions for future research regarding microglia's identity, population dynamics, and dual (beneficial and detrimental) role in pathology.

Probing disrupted neurodevelopment in autism using human stem cell-derived neurons and organoids: An outlook into future diagnostics and drug development

Autism spectrum disorders (ASDs) represent a spectrum of neurodevelopmental disorders characterized by impaired social interaction, repetitive or restrictive behaviors, and problems with speech. According to a recent report by the Centers for Disease Control and Prevention, one in 68 children in the US is diagnosed with ASDs. Although ASD-related diagnostics and the knowledge of ASD-associated genetic abnormalities have improved in recent years, our understanding of the cellular and molecular pathways disrupted in ASD remains very limited. As a result, no specific therapies or medications are available for individuals with ASDs. In this review, we describe the neurodevelopmental processes that are likely affected in the brains of individuals with ASDs and discuss how patient-specific stem cell-derived neurons and organoids can be used for investigating these processes at the cellular and molecular levels. Finally, we propose a discovery pipeline to be used in the future for identifying the cellular and molecular deficits and developing novel personalized therapies for individuals with idiopathic ASDs.

Past, Present, and Future of Brain Organoid Technology

Brain organoids are an exciting new technology with the potential to significantly change our understanding of the development and disorders of the human brain. With step-by-step differentiation protocols, three-dimensional neural tissues are self-organized from pluripotent stem cells, and recapitulate the major millstones of human brain development in vitro. Recent studies have shown that brain organoids can mimic the spatiotemporal dynamicity of neurogenesis, the formation of regional neural circuitry, and the integration of glial cells into a neural network. This suggests that brain organoids could serve as a representative model system to study the human brain. In this review, we will overview the development of brain organoid technology, its current progress and applications, and future prospects of this technology.

Brain Organoids as Tools for Modeling Human Neurodevelopmental Disorders

Brain organoids recapitulate in vitro the specific stages of in vivo human brain development, thus offering an innovative tool by which to model human neurodevelopmental disease. We review here how brain organoids have been used to study neurodevelopmental disease and consider their potential for both technological advancement and therapeutic development.

Functionalization of Brain Region-specific Spheroids with Isogenic Microglia-like Cells

Current brain spheroids or organoids derived from human induced pluripotent stem cells (hiPSCs) still lack a microglia component, the resident immune cells in the brain. The objective of this study is to engineer brain region-specific organoids from hiPSCs incorporated with isogenic microglia-like cells in order to enhance immune function. In this study, microglia-like cells were derived from hiPSCs using a simplified protocol with stage-wise growth factor induction, which expressed several phenotypic markers, including CD11b, IBA-1, CX3CR1, and P2RY12, and phagocytosed micron-size super-paramagnetic iron oxides. The derived cells were able to upregulate pro-inflammatory gene (TNF-α) and secrete anti-inflammatory cytokines (i.e., VEGF, TGF-β1, and PGE2) when stimulated with amyloid β42 oligomers, lipopolysaccharides, or dexamethasone. The derived isogenic dorsal cortical (higher expression of TBR1 and PAX6) and ventral (higher expression of NKX2.1 and PROX1) spheroids/organoids displayed action potentials and synaptic activities. Co-culturing the microglia-like cells (MG) with the dorsal (D) or ventral (V) organoids showed differential migration ability, intracellular Ca2+ signaling, and the response to pro-inflammatory stimuli (V-MG group had higher TNF-α and TREM2 expression). Transcriptome analysis exhibited 37 microglia-related genes that were differentially expressed in MG and D-MG groups. In addition, the hybrid D-MG spheroids exhibited higher levels of immunoreceptor genes in activating members, but the MG group contained higher levels for most of genes in inhibitory members (except SIGLEC5 and CD200). This study should advance our understanding of the microglia function in brain-like tissue and establish a transformative approach to modulate cellular microenvironment toward the goal of treating various neurological disorders.

Tissue Response to Neural Implants: The Use of Model Systems Toward New Design Solutions of Implantable Microelectrodes

The development of implantable neuroelectrodes is advancing rapidly as these tools are becoming increasingly ubiquitous in clinical practice, especially for the treatment of traumatic and neurodegenerative disorders. Electrodes have been exploited in a wide number of neural interface devices, such as deep brain stimulation, which is one of the most successful therapies with proven efficacy in the treatment of diseases like Parkinson or epilepsy. However, one of the main caveats related to the clinical application of electrodes is the nervous tissue response at the injury site, characterized by a cascade of inflammatory events, which culminate in chronic inflammation, and, in turn, result in the failure of the implant over extended periods of time. To overcome current limitations of the most widespread macroelectrode based systems, new design strategies and the development of innovative materials with superior biocompatibility characteristics are currently being investigated. This review describes the current state of the art of in vitro, ex vivo, and in vivo models available for the study of neural tissue response to implantable microelectrodes. We particularly highlight new models with increased complexity that closely mimic in vivo scenarios and that can serve as promising alternatives to animal studies for investigation of microelectrodes in neural tissues. Additionally, we also express our view on the impact of the progress in the field of neural tissue engineering on neural implant research.

All Together Now: Modeling the Interaction of Neural With Non-neural Systems Using Organoid Models

The complex development of the human nervous system has been traditionally studied using a combination of animal models, human post-mortem brain tissue, and human genetics studies. However, there has been a lack of experimental human cellular models that would allow for a more precise elucidation of the intricate dynamics of early human brain development. The development of stem cell technologies, both embryonic and induced pluripotent stem cells (iPSCs), has given neuroscientists access to the previously inaccessible early stages of human brain development. In particular, the recent development of three-dimensional culturing methodologies provides a platform to study the differentiation of stem cells in both normal development and disease states in a more in vivo like context. Three-dimensional neural models or cerebral organoids possess an innate advantage over two-dimensional neural cultures as they can recapitulate tissue organization and cell type diversity that resemble the developing brain. Brain organoids also provide the exciting opportunity to model the integration of different brain regions in vitro. Furthermore, recent advances in the differentiation of non-neuronal tissue from stem cells provides the opportunity to study the interaction between the developing nervous system and other non-neuronal systems that impact neuronal function. In this review, we discuss the potential and limitations of the organoid system to study in vitro neurological diseases that arise in the neuroendocrine and the enteric nervous system or from interactions with the immune system.

Sporadic Creutzfeldt-Jakob disease prion infection of human cerebral organoids

For the transmissible, neurogenerative family of prion diseases, few human models of infection exist and none represent structured neuronal tissue. Human cerebral organoids are self-organizing, three-dimensional brain tissues that can be grown from induced pluripotent stem cells. Organoids can model aspects of neurodegeneration in Alzheimer's Disease and Down's Syndrome, reproducing tau hyperphosphorylation and amyloid plaque pathology. To determine whether organoids could be used to reproduce human prion infection and pathogenesis, we inoculated organoids with two sporadic Creutzfeldt-Jakob Disease prion subtypes. Organoids showed uptake, followed by clearance, of the infectious inoculum. Subsequent re-emergence of prion self-seeding activity indicated de novo propagation. Organoid health assays, prion titer, prion protein electrophoretic mobility and immunohistochemistry demonstrated inoculum-specific differences. Our study shows, for the first time, that cerebral organoids can model aspects of human prion disease and thus offer a powerful system for investigating different human prion subtype pathologies and testing putative therapeutics.

Organoids by design

Organoids are multicellular structures that can be derived from adult organs or pluripotent stem cells. Early versions of organoids range from simple epithelial structures to complex, disorganized tissues with large cellular diversity. The current challenge is to engineer cellular complexity into organoids in a controlled manner that results in organized assembly and acquisition of tissue function. These efforts have relied on studies of organ assembly during embryonic development and have resulted in the development of organoids with multilayer tissue complexity and higher-order functions. We discuss how the next generation of organoids can be designed by means of an engineering-based narrative design to control patterning, assembly, morphogenesis, growth, and function.

Microglia in Alzheimer's Disease: Exploring How Genetics and Phenotype Influence Risk

Research into the function of microglia has dramatically accelerated during the last few years, largely due to recent genetic findings implicating microglia in virtually every neurodegenerative disorder. In Alzheimer's disease (AD), a majority of risk loci discovered through genome-wide association studies were found in or near genes expressed most highly in microglia leading to the hypothesis that microglia play a much larger role in disease progression than previously thought. From this body of work produced in the last several years, we find that almost every function of microglia has been proposed to influence the progression of AD from altered phagocytosis and synaptic pruning to cytokine secretion and changes in trophic support. By studying key Alzheimer's risk genes such as TREM2, CD33, ABCA7, and MS4A6A, we will be able to distinguish true disease-modulatory pathways from the full range of microglial-related functions. To successfully carry out these experiments, more advanced microglial models are needed. Microglia are quite sensitive to their local environment, suggesting the need to more fully recapitulate an in vivo environment to study this highly plastic cell type. Likely only by combining the above approaches will the field fully elucidate the molecular pathways that regulate microglia and influence neurodegeneration, in turn uncovering potential new targets for future therapeutic development.

MicroRNA-124 regulates the expression of p62/p38 and promotes autophagy in the inflammatory pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor and nonmotor symptoms due to the selective loss of midbrain dopaminergic neurons. The evidence for a chronic inflammatory reaction mediated by microglial cells in the brain is particularly strong in PD. In our previous study, we have shown that brain-specific microRNA-124 (miR-124) is significantly down-regulated in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD and that it can also inhibit neuroinflammation during the development of PD. However, further investigation is required to understand whether the abnormal expression of miR-124 regulates microglial activation. In this study, we found that the expression of sequestosome 1 (p62) and phospho-p38 mitogen-activated protein kinases (p-p38) showed a significant increase in LPS-treated immortalized murine microglial cell line BV2 cells in an MPTP-induced mouse model of PD. Knockdown of p62 could suppress the secretion of proinflammatory cytokines and p-p38 of microglia. Besides, inhibition of p38 suppressed the secretion of proinflammatory cytokines and promoted autophagy in BV2 cells. Moreover, our study is the first to identify a unique role of miR-124 in mediating the microglial inflammatory response by targeting p62 and p38 in PD. In the microglial culture supernatant transfer model, the knockdown of p62 in BV2 cells prevented apoptosis and death of human neuroblastoma cell lines SH-SY5Y (SH-SY5Y) cells following microglia activation. In addition, the exogenous delivery of miR-124 could suppress p62 and p-p38 expression and could also attenuate the activation of microglia in the substantia nigra par compacta of MPTP-treated mice. Taken together, our data suggest that miR-124 could inhibit neuroinflammation during the development of PD by targeting p62, p38, and autophagy, indicating that miR-124 could be a potential therapeutic target for regulating the inflammatory response in PD.-Yao, L., Zhu, Z., Wu, J., Zhang, Y., Zhang, H., Sun, X., Qian, C., Wang, B., Xie, L., Zhang, S., Lu, G. MicroRNA-124 regulates the expression of p62/p38 and promotes autophagy in the inflammatory pathogenesis of Parkinson's disease.

Minocycline mitigates the effect of neonatal hypoxic insult on human brain organoids

Neonatal hypoxic injury (NHI) is a devastating cause of disease that affects >60% of babies born with a very low birth weight, resulting in significant morbidity and mortality, including life-long neurological consequences such as seizures, cerebral palsy, and intellectual disability. Hypoxic injury results in increased neuronal death, which disrupts normal brain development. Although animal model systems have been useful to study the effects of NHI, they do not fully represent the uniqueness and complexities of the human brain. To better understand the effects of hypoxia on human brain development, we have generated a brain organoid protocol and evaluated these cells over the course of 6 months. As anticipated, the expression of a forebrain marker, FOXG1, increased and then remained expressed over time, while there was a transition in the expression of the deep-layer (TBR1) and upper-layer (SATB2) cortical markers. In addition, ventral genes (Eng1 and Nkx2.1) as well as markers of specialized nonneuronal cells (Olig2 and GFAP) also increased at later time points. We next tested the development of our in vitro cerebral organoid model at different oxygen concentrations and found that hypoxia repressed gene markers for forebrain, oligodendrocytes, glial cells, and cortical layers, as well as genes important for the migration of cortical neurons. In contrast, ventral markers were either unaffected or even increased in expression with hypoxic insult. Interestingly, the negative effect of hypoxia on the dorsal brain genes as well as oligodendrocytes, and neuronal progenitors could be mitigated by the use of minocycline, an FDA-approved small molecule. Taken together, we have generated a unique and relevant in vitro human brain model system to study diseases such as NHI as well as their potential treatments. Using this system, we have shown the efficacy of minocycline for human NHI.

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.

Concise Review: Modeling Neurodegenerative Diseases with Human Pluripotent Stem Cell-Derived Microglia

Inflammation of the brain and the consequential immunological responses play pivotal roles in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and frontotemporal dementia (FTD). Microglia, the resident macrophage cells of the brain, have also emerged as key players in neuroinflammation. As primary human microglia from living subjects are normally not accessible to researchers, there is a pressing need for an alternative source of authentic human microglia which allows modeling of neurodegeneration in vitro. Several protocols for induced pluripotent stem cell (iPSC)‐derived microglia have recently been developed and provide unlimited access to patient‐derived material. In this present study, we give an overview of iPSC‐derived microglia models in monoculture and coculture systems, their advantages and limitations, and how they have already been used for disease phenotyping. Furthermore, we outline some of the gene engineering tools to generate isogenic controls, the creation of gene knockout iPSC lines, as well as covering reporter cell lines, which could help to elucidate complex cell interaction mechanisms in the microglia/neuron coculture system, for example, microglia‐induced synapse loss. Finally, we deliberate on how said cocultures could aid in personalized drug screening to identify patient‐specific therapies against neurodegeneration. stem cells2019;37:724–730

Modeling Human Brain Circuitry Using Pluripotent Stem Cell Platforms

Neural circuits are the underlying functional units of the human brain that govern complex behavior and higher-order cognitive processes. Disruptions in neural circuit development have been implicated in the pathogenesis of multiple neurodevelopmental disorders such as autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and schizophrenia. Until recently, major efforts utilizing neurological disease modeling platforms based on human induced pluripotent stem cells (hiPSCs), investigated disease phenotypes primarily at the single cell level. However, recent advances in brain organoid systems, microfluidic devices, and advanced optical and electrical interfaces, now allow more complex hiPSC-based systems to model neuronal connectivity and investigate the specific brain circuitry implicated in neurodevelopmental disorders. Here we review emerging research advances in studying brain circuitry using in vitro and in vivo disease modeling platforms including microfluidic devices, enhanced functional recording interfaces, and brain organoid systems. Research efforts in these areas have already yielded critical insights into pathophysiological mechanisms and will continue to stimulate innovation in this promising area of translational research.

Neuronal migration in the CNS during development and disease: insights from in vivo and in vitro models

Neuronal migration is a fundamental process that governs embryonic brain development. As such, mutations that affect essential neuronal migration processes lead to severe brain malformations, which can cause complex and heterogeneous developmental and neuronal migration disorders. Our fragmented knowledge about the aetiology of these disorders raises numerous issues. However, many of these can now be addressed through studies of in vivo and in vitro models that attempt to recapitulate human-specific mechanisms of cortical development. In this Review, we discuss the advantages and limitations of these model systems and suggest that a complementary approach, using combinations of in vivo and in vitro models, will broaden our knowledge of the molecular and cellular mechanisms that underlie defective neuronal positioning in the human cerebral cortex.

Modeling Psychiatric Diseases with Induced Pluripotent Stem Cells

Neuropsychiatric disorders are a heterogeneous group of disorders that are challenging to model and treat, due to their underlying complex genetic architecture and clinical variability. Presently, increasingly more studies are making use of induced pluripotent stem cell (iPSC)-derived neurons, reprogrammed from patient somatic cells, to model neuropsychiatric disorders. iPSC-derived neurons offer the possibility to recapitulate relevant disease biology in the context of the individual patient genetic background. In addition to disease modeling, iPSC-derived neurons offer unprecedented opportunities in drug screening. In this chapter, the current status of iPSC disease modeling for neuropsychiatric disorders is presented. Both 2D and 3D disease modeling approaches are discussed as well as the generation of different neuronal cell types that are relevant for studying neuropsychiatric disorders. Moreover, the advantages and limitations are highlighted in addition to the future perspectives of using iPSC-derived neurons in the uncovering of robust cellular phenotypes that consecutively have the potential to lead to clinical developments.

The Dynamic Partnership of Polycomb and Trithorax in Brain Development and Diseases

Epigenetic mechanisms, including DNA and histone modifications, are pivotal for normal brain development and functions by modulating spatial and temporal gene expression. Dysregulation of the epigenetic machinery can serve as a causal role in numerous brain disorders. Proper mammalian brain development and functions depend on the precise expression of neuronal-specific genes, transcription factors and epigenetic modifications. Antagonistic polycomb and trithorax proteins form multimeric complexes and play important roles in these processes by epigenetically controlling gene repression or activation through various molecular mechanisms. Aberrant expression or disruption of either protein group can contribute to neurodegenerative diseases. This review focus on the current progress of Polycomb and Trithorax complexes in brain development and disease, and provides a future outlook of the field.