Generation of Human Neurons and Oligodendrocytes from Pluripotent Stem Cells for Modeling Neuron-Oligodendrocyte Interactions

Utilizing hiPSC-derived oligodendrocytes to study myelin pathophysiology in neuropsychiatric and neurodegenerative disorders

Oligodendrocytes play a crucial role in our central nervous system (CNS) by myelinating axons for faster action potential conduction, protecting axons from degeneration, structuring the position of ion channels, and providing nutrients to neurons. Oligodendrocyte dysfunction and/or dysmyelination can contribute to a range of neurodegenerative diseases and neuropsychiatric disorders such as Multiple Sclerosis (MS), Leukodystrophy (LD), Schizophrenia (SCZ), and Autism Spectrum Disorder (ASD). Common characteristics identified across these disorders were either an inability of oligodendrocytes to remyelinate after degeneration or defects in oligodendrocyte development and maturation. Unfortunately, the causal mechanisms of oligodendrocyte dysfunction are still uncertain, and therapeutic targets remain elusive. Many studies rely on the use of animal models to identify the molecular and cellular mechanisms behind these disorders, however, such studies face species-specific challenges and therefore lack translatability. The use of human induced pluripotent stem cells (hiPSCs) to model neurological diseases is becoming a powerful new tool, improving our understanding of pathophysiology and capacity to explore therapeutic targets. Here, we focus on the application of hiPSC-derived oligodendrocyte model systems to model disorders caused by oligodendrocyte dysregulation.

Characterizing the Neuron-Glial Interactions by the Co-cultures of Human iPSC-Derived Oligodendroglia and Neurons

Induced pluripotent stem cell (iPSC) techniques have had considerable breakthroughs in modeling human neurological diseases. Multiple protocols inducing neurons, astrocytes, microglia, oligodendrocytes, and endothelial cells have been well-established thus far. However, these protocols have limitations, including the long time period to get cells of interest or the challenge of culturing more than one cell type simultaneously. Protocols for handling multiple cell types within a shorter time period are still being established. Here we describe a simple and reliable co-culture system to study interactions between neurons and oligodendrocyte precursor cells (OPC) in health and in disease.

Generation of Oligodendrocytes from Human Pluripotent and Embryonic Stem Cells

Oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes (OLs) can be generated using human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs). By manipulating culture conditions, pluripotent cell types are serially guided through intermediary cell types, developing first into neural progenitor cells (NPCs) then OPCs before maturing as CNS-specific OLs. This procedure is conducted under adherent, feeder-free conditions to derive mature OLs in as few as 28 days.

Modeling Cellular Crosstalk of Neuroinflammation Axis by Tri-cultures of iPSC-Derived Human Microglia, Astrocytes, and Neurons

Neuroinflammation is a common early pathological feature in many neurodegenerative disorders, including Alzheimer's disease (AD), which has been heavily implicated as a causative factor in disease pathology. However, the role neuroinflammation and inflammatory cells, including microglia and astrocytes, play in AD development and progression has not been fully defined. To try to better understand and study this neuroinflammatory role in AD pathogenesis, researchers use a variety of model systems, particularly in vivo animal models. Despite their usefulness, these models do come with a variety of limitations due to the inherent complexity of the brain and the human-specific nature of AD. Here, we describe a reductionist approach at modeling neuroinflammation by utilizing an in vitro tri-culture system of neurons, astrocytes, and microglia induced from human pluripotent stem cells. This tri-culture model is a powerful tool to dissect intercellular interactions that can facilitate future studies on neuroinflammation, particularly in the context of neurodegeneration and AD.

Potential role of chitinase-3-like protein 1 (CHI3L1/YKL-40) in neurodegeneration and Alzheimer's disease

Chitinase-3-like protein 1 (CHI3L1/YKL-40) has long been known as a biomarker for early detection of neuroinflammation and disease diagnosis of Alzheimer's disease (AD). In the brain, CHI3L1 is primarily provided by astrocytes and heralds the reactive, neurotoxic state triggered by inflammation and other stress signals. However, how CHI3L1 acts in neuroinflammation or how it contributes to AD and relevant neurodegenerative conditions remains unknown. In peripheral tissues, our group and others have uncovered that CHI3L1 is a master regulator for a wide range of injury and repair events, including the innate immunity pathway that resembles the neuroinflammation process governed by microglia and astrocytes. Based on assessment of current knowledge regarding CHI3L1 biology, we hypothesize that CHI3L1 functions as a signaling molecule mediating distinct neuroinflammatory responses in brain cells and misfunctions to precipitate neurodegeneration. We also recommend future research directions to validate such assertions for better understanding of disease mechanisms.

Novel Tools and Investigative Approaches for the Study of Oligodendrocyte Precursor Cells (NG2-Glia) in CNS Development and Disease

Oligodendrocyte progenitor cells (OPCs), also referred to as NG2-glia, are the most proliferative cell type in the adult central nervous system. While the primary role of OPCs is to serve as progenitors for oligodendrocytes, in recent years, it has become increasingly clear that OPCs fulfil a number of other functions. Indeed, independent of their role as stem cells, it is evident that OPCs can regulate the metabolic environment, directly interact with and modulate neuronal function, maintain the blood brain barrier (BBB) and regulate inflammation. In this review article, we discuss the state-of-the-art tools and investigative approaches being used to characterize the biology and function of OPCs. From functional genetic investigation to single cell sequencing and from lineage tracing to functional imaging, we discuss the important discoveries uncovered by these techniques, such as functional and spatial OPC heterogeneity, novel OPC marker genes, the interaction of OPCs with other cells types, and how OPCs integrate and respond to signals from neighboring cells. Finally, we review the use of in vitro assay to assess OPC functions. These methodologies promise to lead to ever greater understanding of this enigmatic cell type, which in turn will shed light on the pathogenesis and potential treatment strategies for a number of diseases, such as multiple sclerosis (MS) and gliomas.

Utilising Induced Pluripotent Stem Cells in Neurodegenerative Disease Research: Focus on Glia

Induced pluripotent stem cells (iPSCs) are a self-renewable pool of cells derived from an organism's somatic cells. These can then be programmed to other cell types, including neurons. Use of iPSCs in research has been two-fold as they have been used for human disease modelling as well as for the possibility to generate new therapies. Particularly in complex human diseases, such as neurodegenerative diseases, iPSCs can give advantages over traditional animal models in that they more accurately represent the human genome. Additionally, patient-derived cells can be modified using gene editing technology and further transplanted to the brain. Glial cells have recently become important avenues of research in the field of neurodegenerative diseases, for example, in Alzheimer's disease and Parkinson's disease. This review focuses on using glial cells (astrocytes, microglia, and oligodendrocytes) derived from human iPSCs in order to give a better understanding of how these cells contribute to neurodegenerative disease pathology. Using glia iPSCs in in vitro cell culture, cerebral organoids, and intracranial transplantation may give us future insight into both more accurate models and disease-modifying therapies.