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Cholesterol dysregulation in APOE4 astrocytes promotes α-synuclein pathology in miBrains.

The pathological hallmarks of neurodegeneration are the aberrant post-translational modification and aggregation of proteins. Genetic factors, like APOE4, increase the prevalence and severity of tau, amyloid, and α-synuclein pathologies. However, the human brain is largely inaccessible during this process, limiting mechanistic understanding. Here, we developed an iPSC-based 3D model that integrates neurons, glia, myelin, and cerebrovascular cells into a human brain-like tissue ("miBrain"). Single-nucleus RNA sequencing of miBrains confirmed the presence of diverse cell populations and revealed transcriptional responses to α-synuclein pathology. Like the human brain, pathogenic α-synuclein is increased in APOE4/4 miBrains. Combinatorial experiments revealed that endolysosomal dysfunction caused by cholesterol accumulation in APOE4/4 astrocytes impairs the degradation of soluble α-synuclein leading to a pathogenic transformation that seeds α-synuclein inclusions in neurons. Collectively, this study establishes a robust model for investigating protein inclusions in human iPSC-derived brain tissue and highlights the role of astrocytes and cholesterol in APOE4-mediated pathologies.

alpha-Synuclein

Fetal signatures in the 3D genome of iPSC-derived neurons and their implications for disease modeling.

Induced pluripotent stem cells (iPSCs) have revolutionized neuroscience, providing an approach to generate patient-specific neurons for modeling of neurological diseases. However, it remains unclear how closely iPSC-derived neurons replicate the chromatin architecture of authentic brain neurons. Here, we uniformly processed newly generated Hi-C data from iPSC-derived neurons and neurons isolated from the human postmortem brain, together with previously published data sets comprising 228 human and 89 mouse Hi-C and snm3C-seq samples from different cell subtypes. These data were merged into 96 high-coverage contact maps used to examine chromatin features ranging from chromatin compartments and topologically associating domains (TADs) to chromatin loops, Polycomb-mediated contacts, and frequently interacting regions (FIREs). We find that iPSC-derived neurons largely retain the chromatin state of undifferentiated cells and resemble fetal rather than mature neurons. iPSC-derived neurons exhibit unusually strong compartmentalization, an enrichment of developmental genes at TAD borders, and a marked reduction of long-range repressive Polycomb-mediated contacts that typically silence early fetal programs. Although immature, iPSC-derived neurons offer advantages for modeling interactions between disease-associated SNPs and target genes, as many psychiatric disorders have neurodevelopmental origins. Integrating iPSC-derived and postmortem neuronal data sets therefore provides complementary insights into the chromatin landscape underlying disease-associated interactions. Our study offers a valuable Hi-C resource for the community and provides a detailed comparison of chromatin architecture throughout neuronal maturation, underscoring its importance for validating neuronal models and providing a robust framework for future studies.

Journal Article

A novel iPSC model of Bryant-Li-Bhoj neurodevelopmental/neurodegenerative syndrome demonstrates the role of histone H3.3 in chromatin dynamics, neuronal differentiation, and maturation.

BACKGROUND: Bryant-Li-Bhoj neurodevelopmental syndrome (BLBS) is neurogenetic disorder caused by variants in H3-3A and H3-3B, the two genes that encode histone H3.3. Ninety-nine percent of individuals with BLBS show developmental delay/intellectual disability, but the mechanism by which variants in H3.3 result in these phenotypes is not yet understood, limiting the therapeutic interventions available to individuals living with BLBS. METHODS: Here, we investigate how one BLBS-causative variant, H3-3B p.Leu48Arg (L48R), affects neurodevelopment using an induced pluripotent stem cell model differentiated to 2D neural progenitor cells (NPCs), 2D forebrain neurons (FBNs), and 3D dorsal forebrain organoids (DFBOs). We employ a multi-omic approach in the 2D models to quantify the resulting changes in gene expression and chromatin accessibility. We used immunofluorescence (IF) staining to define the identities of cells in the 3D DFBOs and whole-cell patch clamp to investigate the electrophysiological properties of neurons in DFBOs. RESULTS: In the 2D systems, we found dysregulated gene expression and chromatin accessibility affecting neuronal fate, adhesion, neurotransmission, and excitatory/inhibitory balance. Immunofluorescence of DFBOs corroborated altered proportions of radial glia and mature neuronal populations. Patch clamp recordings revealed decreased electrical activity in neurons from L48R DFBOs compared to control DFBOs. CONCLUSIONS: These data provide the first mechanistic insights into the pathogenesis of BLBS from a human-derived model of neurodevelopment, which suggest that H3.3 L48R increases H3-3B expression, resulting in the hyper-deposition of H3.3 into the nucleosome, which underlies changes in gene expression and chromatin accessibility. Functionally, this causes dysregulation of cell adhesion, neurotransmission, and the balance between excitatory and inhibitory signaling. These results are a crucial step towards preclinical development and testing of targeted therapies for this and related disorders.

Histones

Mapping key mitochondrial genes in Alzheimer's disease through human tissue and iPSC derived neurons.

Alzheimer's disease (AD) is a progressive neurodegenerative condition that has become a global health challenge due to an aging world population and no available effective treatment. Mitochondrial dysfunction plays a crucial role in the development of AD due to its critical role in neuronal survival and function. However, the specific mitochondrial genes and pathways involved in AD pathogenesis remain poorly defined. In this study, we incorporated seven AD human postmortem and three AD iPSC-derived neurons (iNs) gene expression datasets to identify mitochondria-related Differentially Expressed Genes (mitoDEGs) between AD and control. The Gene Ontology (GO) analysis is conducted to investigate the AD biological mechanisms, and a random forest model is developed to assess how well the key mitoDEGs differentiate AD and control groups. Through our analysis, we identified fourteen key mitochondria related genes that show significant dysregulation in both postmortem brain tissues and iNs derived from AD patients. These genes have strong connections to oxidative stress, indicating mitochondrial dysfunction plays a crucial role in Alzheimer's disease pathology. Our study identified the key genes and pathways as promising targets for future research and therapeutic interventions, highlighting the importance of mitigating oxidative stress and restoring mitochondrial function in AD.

Humans

Telomeric DNA damage response mediates neurotoxicity of Aβ42 oligomers in Alzheimer's disease.

Ageing is the major risk factor for Alzheimer's disease (AD), the most common neurodegenerative disorder. DNA damage is a hallmark of ageing, particularly when occurring at telomeres, genomic regions vulnerable to oxidative damage and often challenging for the cell to repair. Here, we show that brains of 3xTg-AD mice, an established AD model characterized by amyloid-β (Aβ)-induced pathology, exhibit increased activation of DNA damage response (DDR) pathways at telomeres. Exposure of mouse primary hippocampal neurons to 42-residue Aβ (Aβ42) oligomers, a significant pathogenetic contributor to AD, triggers telomeric DDR by increasing the levels of reactive oxygen species caused by calcium imbalance. Antisense oligonucleotides targeting non-coding RNAs generated at damaged telomeres in vivo (in 3xTg-AD mice) and in vitro reduce neurotoxicity in iPSC-derived human cortical neurons and mouse primary neurons while inhibiting Aβ42-induced telomeric DDR, and restore transcriptional pathways altered by Aβ and found dysregulated in AD patients. These results unveil an unexpected role of telomeric DNA damage responses in Alzheimer's disease pathogenesis, and suggest a novel target for the development of RNA-based therapies.

Alzheimer Disease

CRISPRi screens in human iPSC-derived astrocytes elucidate regulators of distinct inflammatory reactive states.

Astrocytes become reactive in response to insults to the central nervous system by adopting context-specific cellular signatures and outputs, but a systematic understanding of the underlying molecular mechanisms is lacking. In this study, we developed CRISPR interference screening in human induced pluripotent stem cell-derived astrocytes coupled to single-cell transcriptomics to systematically interrogate cytokine-induced inflammatory astrocyte reactivity. We found that autocrine-paracrine IL-6 and interferon signaling downstream of canonical NF-κB activation drove two distinct inflammatory reactive signatures, one promoted by STAT3 and the other inhibited by STAT3. These signatures overlapped with those observed in other experimental contexts, including mouse models, and their markers were upregulated in human brains in Alzheimer's disease and hypoxic-ischemic encephalopathy. Furthermore, we validated that markers of these signatures were regulated by STAT3 in vivo using a mouse model of neuroinflammation. These results and the platform that we established have the potential to guide the development of therapeutics to selectively modulate different aspects of inflammatory astrocyte reactivity.

Humans