Rapid Generation of Ventral Spinal Cord-like Astrocytes from Human iPSCs for Modeling Non-Cell Autonomous Mechanisms of Lower Motor Neuron Disease

Lycium barbarum oligosaccharide-derived carbon quantum dots inhibit glial scar formation while promoting neuronal differentiation of neural stem cells

Overexpression of glial fibrillary acidic protein (GFAP) in activated astrocytes following spinal cord injury is closely associated with glial scar formation, which harms axonal regrowth. In this study, we prepared ultrasmall cationic carbon quantum dots (CQDs) via one-step hydrothermal carbonization. Lycium barbarum oligosaccharides were used as the carbon source for the first time, and polyetherimide (PEI) and ethylenediamine (ED) were used as cationic reagents. Interestingly, the resultant CQDs show the bioactivity of specifically inhibiting GFAP protein expression, while promoting neuronal marker expression in neural stem cells (NSCs). Furthermore, CQDs together with NSCs can remarkably improve the motor activity of animals after implantation into the transection lesion of the rat spinal cord. Histological analysis confirmed that CQDs can enhance neuronal differentiation of NSCs while inhibiting glial scar formation in vivo. Altogether, this study represents the first report of producing CQDs from oligosaccharides and investigating their impact on NSCs differentiation, thus providing a paradigm for exploring the bioactivity of quantum dots.

Early nuclear phenotypes and reactive transformation in human iPSC-derived astrocytes from ALS patients with SOD1 mutations

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the progressive death of motor neurons (MNs). Glial cells play roles in MN degeneration in ALS. More specifically, astrocytes with mutations in the ALS-associated gene Cu/Zn superoxide dismutase 1 (SOD1) promote MN death. The mechanisms by which SOD1-mutated astrocytes reduce MN survival are incompletely understood. To characterize the impact of SOD1 mutations on astrocyte physiology, we generated astrocytes from human induced pluripotent stem cell (iPSC) derived from ALS patients carrying SOD1 mutations, together with control isogenic iPSCs. We report that astrocytes harboring SOD1(A4V) and SOD1(D90A) mutations exhibit molecular and morphological changes indicative of reactive astrogliosis when compared to isogenic astrocytes. We show further that a number of nuclear phenotypes precede, or coincide with, reactive transformation. These include increased nuclear oxidative stress and DNA damage, and accumulation of the SOD1 protein in the nucleus. These findings reveal early cell-autonomous phenotypes in SOD1-mutated astrocytes that may contribute to the acquisition of a reactive phenotype involved in alterations of astrocyte-MN communication in ALS.

CelltypeR: A flow cytometry pipeline to characterize single cells from brain organoids

Motivated by the cellular heterogeneity in complex tissues, particularly in brain and induced pluripotent stem cell (iPSC)-derived brain models, we developed a complete workflow to reproducibly characterize cell types in complex tissues. Our approach combines a flow cytometry (FC) antibody panel with our computational pipeline CelltypeR, enabling dataset aligning, unsupervised clustering optimization, cell type annotating, and statistical comparisons. Applied to human iPSC derived midbrain organoids, it successfully identified the major brain cell types. We performed fluorescence-activated cell sorting of CelltypeR-defined astrocytes, radial glia, and neurons, exploring transcriptional states by single-cell RNA sequencing. Among the sorted neurons, we identified subgroups of dopamine neurons: one reminiscent of substantia nigra cells most vulnerable in Parkinson's disease. Finally, we used our workflow to track cell types across a time course of organoid differentiation. Overall, our adaptable analysis framework provides a generalizable method for reproducibly identifying cell types across FC datasets in complex tissues.

The use of a SOX10 reporter toward ameliorating oligodendrocyte lineage differentiation from human induced pluripotent stem cells

Oligodendrocytes (OLs) are key players in the central nervous system, critical for the formation and maintenance of the myelin sheaths insulating axons, ensuring efficient neuronal communication. In the last decade, the use of human induced pluripotent stem cells (iPSCs) has become essential for recapitulating and understanding the differentiation and role of OLs in vitro. Current methods include overexpression of transcription factors for rapid OL generation, neglecting the complexity of OL lineage development. Alternatively, growth factor-based protocols offer physiological relevance but struggle with efficiency and cell heterogeneity. To address these issues, we created a novel SOX10-P2A-mOrange iPSC reporter line to track and purify oligodendrocyte precursor cells. Using this reporter cell line, we analyzed an existing differentiation protocol and shed light on the origin of glial cell heterogeneity. Additionally, we have modified the differentiation protocol, toward enhancing reproducibility, efficiency, and terminal maturity. Our approach not only advances OL biology but also holds promise to accelerate research and translational work with iPSC-derived OLs.

Neural lineage differentiation of human pluripotent stem cells: Advances in disease modeling

Brain diseases affect 1 in 6 people worldwide. These diseases range from acute neurological conditions such as stroke to chronic neurodegenerative disorders such as Alzheimer’s disease. Recent advancements in tissue-engineered brain disease models have overcome many of the different shortcomings associated with the various animal models, tissue culture models, and epidemiologic patient data that are commonly used to study brain disease. One innovative method by which to model human neurological disease is via the directed differentiation of human pluripotent stem cells (hPSCs) to neural lineages including neurons, astrocytes, and oligodendrocytes. Three-dimensional models such as brain organoids have also been derived from hPSCs, offering more physiological relevance due to their incorporation of various cell types. As such, brain organoids can better model the pathophysiology of neural diseases observed in patients. In this review, we will emphasize recent developments in hPSC-based tissue culture models of neurological disorders and how they are being used to create neural disease models.

Comparing the Characteristics of Microglia Preparations Generated Using Different Human iPSC-Based Differentiation Methods to Model Neurodegenerative Diseases

As the resident immune cells of the healthy nervous system, homeostatic microglia can rapidly become activated in response to injury/disease. Dysregulated microglia activation is a hallmark of nervous system disorders including neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. The elucidation of the biological and pathological roles of microglia has recently benefitted from the development of microglia-like cells using human induced pluripotent stem cell (iPSC)-based approaches. The success of iPSC-derived microglia preparations as a disease-relevant model system depends on their representation of the in vivo spatial and temporal heterogeneity of microglia under pathological conditions. Little is currently known about the potential of human iPSC-derived microglia generated using different methods for the study of neurodegenerative diseases. We compared the transcriptomes of human iPSC-derived microglia generated using two frequently used in vitro differentiation methods to determine whether separate strategies can generate microglia with distinct transcriptional signatures in vitro. We show that microglia derived using different differentiation methods display distinct maturation characteristics after equivalent times in culture. We also reveal that iPSC-derived microglia preparations generated using these two methods are composed of different subpopulations with transcriptomic signatures resembling those of in vivo regionally distinct microglia subtypes, specifically white-matter and gray-matter microglia. These findings highlight the need to better characterize the subtype composition of each microglia preparation prior to its use to model neurodegenerative diseases.