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Multimodal information processing in neurons.

Advances in neuroscience research have led to substantial expansion and even revision of many concepts of neuronal structure and function. The essence of this progress is contained in the knowledge that there are multiple modes of information processing in neurons and even subneuronal elements such as the dendrite. The challenge and opportunity of the new findings lies in understanding how the various modes are integrated in complex brain function. Progress in this area should offer new insights into the pathophysiology of neurological disease.

Action Potentials

A specialized information center. The clinical neurology information center.

The history, philosophy, and methodology of a unique specialized medical information center are reported. The Clinical Neurology Information Center is an educational information service (giving its audience information which can be the basis for formulating their own questions) rather than an instructional information service (giving information in reply to questions). Clinical, as well as basic neuroscience, information is culled by professional neurologists from 855 medical periodicals. The essence of each article is summarized in a single sentence ("terse conclusions") or a bibliographic reference only is given; this material is published every two weeks in the Concise Clinical Neurology Review (CCNR). The format of the CCNR is such that the reader should be able to scan a very large amount of current literature by investing only twenty to thirty minutes every two weeks. The values of this system as well as some of its problems are discussed.

Abstracting and Indexing

A cellular approach to neurological disease.

This presentation is necessarily an overview of the work in our laboratories. We have chosen to study oligodendroglia and myelin first, because we have specific markers we can use, and we can focus on specific disease entities. However, the same strategy can be applied to neurons and neuronal diseases. Despite major advances in the neurosciences, many questions remain unanswered. In general there has been a predictable sequence in our progress in understanding the nature of neurological disorders. Early studies focused on a clinical description of the disease. Next the pathology was described, and attempts were made to correlate these findings with the clinical symptoms. Now that we are able to isolate some of the cells involved in specific diseases (see Table I) we can begin to investigate the normal metabolism of these cells, study their components, and follow any changes that take place under different pathological conditions. Thus, we have shown that it is possible to study and perphaps eventually provide therapy for certain disorders, such as multiple sclerosis, without knowning that delineation of events in the normal cell is an essential step in unraveling the mysteries of neurological disease.

Animals

Combined somatic mutation and transcriptome analysis reveals region-specific differences in clonal architecture in human cortex.

The human cerebral cortex is specialized into regions, but little is known about how human cellular lineages shape cortical regional variation and neuronal cell-type distribution during development. Here, we map single-cell lineages of human cortical regions and neuronal subtypes using >1,000 somatic single-nucleotide variants (sSNVs) identified from deep bulk whole-genome sequencing and analyzed over 25 regions and >72,000 single cells. In the fronto-parietal cortex, sSNVs are rarely restricted, marking neuron-generating clones that disperse into neighboring regions. In contrast, the primary visual cortex harbors 30%-70% more sSNVs than the neighboring secondary visual cortex. Clones at this border exhibit more restricted dispersion, suggesting late developmental lineage segregation. Single-nucleus sSNV and whole-transcriptome analysis reveal glutamatergic neuron clones with modest regional restrictions that share low-mosaic sSNVs with some GABAergic neurons, suggesting a recent dorsal cortical progenitor. Our analysis reveals human-specific cortical lineage patterns, regional differences in clonal patterns, and late divergence of some glutamatergic/GABAergic lineages.

Humans

Phospho-proteome profiling in human neurons reveals targets of TBK1 in ALS/FTD-associated autophagy networks.

Loss-of-function variants in TBK1, encoding a protein kinase, are strongly associated with familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, how haploinsufficiency for TBK1 leads to age-related neurodegeneration remains unresolved. Here, we utilize sets of isogenic induced pluripotent stem cells (iPSCs) with loss of TBK1 or loss of optineurin (OPTN) for quantitative global proteomics and phospho-proteomics in both stem cells and excitatory neurons. We found that TBK1 sustains the abundance and phosphorylation of its interacting adapter proteins, AZI2/NAP1, TANK, and TBKBP1/SINTBAD. Moreover, TBK1 regulates the phosphorylation of endo-lysosomal proteins, such as GABARAPL2, the late-endosome GTPase RAB7A, and selective autophagy cargo receptor proteins-including novel phospho-sites in p62/SQSTM1-in neurons. Finally, we provide a census of the phospho-proteome in nascent human neurons for further studies. Overall, TBK1 serves as a point of convergence in ALS/FTD-linked endo-lysosomal networks that act in a cell-autonomous manner to maintain protein homeostasis in neurons.

Humans

Ketogenic diet dampens excitatory neurotransmission by shrinking synaptic vesicle pools.

Ketogenic diet (KD) is used for the treatment of drug-resistant childhood epilepsy and has been proposed to improve outcomes in neurodegenerative diseases. However, the mechanisms by which KD alters brain circuitry remain unclear. Here, we investigated the impact of KD on hippocampal function through integrative analysis of gene expression and neurotransmission. We found that KD induces extensive transcriptional reprogramming, including altered expression of numerous synaptic genes. Proteomic and genomic profiling revealed significant changes in histone modifications, particularly at promoters of KD-regulated genes. Electrophysiological recordings showed that KD reduces excitatory synaptic gain and short-term plasticity at CA3-CA1 synapses, dampening the summation of excitatory inputs and enhancing the summation of inhibitory inputs. These functional changes were driven, in part, by a reduction in the readily releasable vesicle pool at excitatory synapses under KD. Together, our findings demonstrate that KD drives transcriptional remodeling of hippocampal circuits, leading to synaptic adaptations that may underlie its anti-epileptic and neuroprotective effects.

Animals

Locus coeruleus activation transforms cortical taste representations.

Noradrenergic neurons in the locus coeruleus (LC) shape sensory processing, yet how LC activity influences population taste coding remains unclear. Using optogenetic LC activation with miniscope imaging in the gustatory cortex (GC), we examined LC modulation of multiple taste attributes. Phasic LC activation strengthens correlations between neuronal responses and palatability and expands the dynamic range of stimulus representations along a palatability axis. This expansion is driven by an aversive shift in the representations of all tastants except sucrose, the most palatable stimulus. For mixture ratio and concentration, phasic activation expands and rotates attribute axes, potentially reflecting dependencies between these attributes and palatability. These transformations likely arise from multiplicative gain modulation and more flexible tuning changes. Tonic LC activation affects fewer neurons and does not expand attribute axes. Together, the findings show that LC activation reorganizes GC population geometry in a pattern-dependent manner, linking neuromodulation with feeding behavior and affective processing.

CP: neuroscience

SIMS: A deep-learning label transfer tool for single-cell RNA sequencing analysis.

Cell atlases serve as vital references for automating cell labeling in new samples, yet existing classification algorithms struggle with accuracy. Here we introduce SIMS (scalable, interpretable machine learning for single cell), a low-code data-efficient pipeline for single-cell RNA classification. We benchmark SIMS against datasets from different tissues and species. We demonstrate SIMS's efficacy in classifying cells in the brain, achieving high accuracy even with small training sets (<3,500 cells) and across different samples. SIMS accurately predicts neuronal subtypes in the developing brain, shedding light on genetic changes during neuronal differentiation and postmitotic fate refinement. Finally, we apply SIMS to single-cell RNA datasets of cortical organoids to predict cell identities and uncover genetic variations between cell lines. SIMS identifies cell-line differences and misannotated cell lineages in human cortical organoids derived from different pluripotent stem cell lines. Altogether, we show that SIMS is a versatile and robust tool for cell-type classification from single-cell datasets.

Single-Cell Analysis

Regulators of interferon-responsive microglia uncovered by Genome-wide CRISPRi screening.

Microglia dynamically support brain health through the induction of specialized activation states in response to injury or disease. Activation of the interferon-responsive microglia (IRM) state has been identified across neurodevelopmental windows, age-related cognitive decline, and neurodegenerative diseases. Functionally, IRM have been linked to synaptic pruning, dead cell removal, and neuroinflammation, making this state critical to brain homeostasis. While the functional importance of this state is becoming increasingly clear, our understanding of the regulatory networks that govern IRM induction remain incomplete. To systematically identify genetic regulators of the IRM state, we conducted a genome-wide CRISPR interference screen in human iPSC-derived microglia using IFIT1 as a representative IRM marker. We identified 772 genes that modulate IRM, including canonical type I interferon signaling genes (IFNAR2, TYK2, STAT1/2, USP18) and newly described regulators. We uncovered a non-canonical role for the CCR4-NOT transcription complex subunit 10, CNOT10, in IRM activation. This work provides a comprehensive resource that can be applied to dissect the functions of interferon-responsive microglia and highlights both established and novel targets for modulating microglial interferon signaling in health and disease.

Computational biology and bioinformatics

Blood-based biomarkers of Alzheimer's disease and neurodegeneration in an indigenous African cohort using both Simoa and NULISA platforms.

In low- and middle-income countries, Alzheimer's disease (AD) constitutes a growing public health burden. However, AD biomarkers research remains underrepresented in African populations. This study assesses core biomarkers of AD and their relevance in the African context as potential aid in clinical diagnosis. Nigerian older adults from VALIANT cohort (n&#x2009;=&#x2009;967) underwent biomarker quantification in plasma (p-tau217, GFAP, NfL, A&#x3b2;42 and A&#x3b2;40) employing both the Single Molecule Assay (Simoa, Quanterix) and Nucleic acid-Linked Immuno-Sandwich Assay (NULISA, Alamar). Biomarkers were associated with disease severity in clinical-diagnostic and clinical-biological groups, with stepwise increases of p-tau217, NfL and GFAP from cognitively unimpaired to dementia (p&#x2009;<&#x2009;0.05). Results were consistent across platforms. Comparison between sexes showed higher biomarker levels in male participants across diagnostic groups. A significant effect of apoE-E4 proteotype on p-tau217 levels, after adjusting for age and sex was identified. These findings support the application of plasma AD biomarkers in the African context and the relevance of further AD biomarker research in diverse populations.

Biomarkers

Unraveling Neuronal Identities Using SIMS: A Deep Learning Label Transfer Tool for Single-Cell RNA Sequencing Analysis.

Large single-cell RNA datasets have contributed to unprecedented biological insight. Often, these take the form of cell atlases and serve as a reference for automating cell labeling of newly sequenced samples. Yet, classification algorithms have lacked the capacity to accurately annotate cells, particularly in complex datasets. Here we present SIMS (Scalable, Interpretable Machine Learning for Single-Cell), an end-to-end data-efficient machine learning pipeline for discrete classification of single-cell data that can be applied to new datasets with minimal coding. We benchmarked SIMS against common single-cell label transfer tools and demonstrated that it performs as well or better than state of the art algorithms. We then use SIMS to classify cells in one of the most complex tissues: the brain. We show that SIMS classifies cells of the adult cerebral cortex and hippocampus at a remarkably high accuracy. This accuracy is maintained in trans-sample label transfers of the adult human cerebral cortex. We then apply SIMS to classify cells in the developing brain and demonstrate a high level of accuracy at predicting neuronal subtypes, even in periods of fate refinement, shedding light on genetic changes affecting specific cell types across development. Finally, we apply SIMS to single cell datasets of cortical organoids to predict cell identities and unveil genetic variations between cell lines. SIMS identifies cell-line differences and misannotated cell lineages in human cortical organoids derived from different pluripotent stem cell lines. When cell types are obscured by stress signals, label transfer from primary tissue improves the accuracy of cortical organoid annotations, serving as a reliable ground truth. Altogether, we show that SIMS is a versatile and robust tool for cell-type classification from single-cell datasets.

Brain organoids

The cellular associates of late life changes in white matter microstructure.

The microstructural architecture of white matter supporting information flow across local circuits and large-scale networks changes throughout the lifespan. However, the genetic and cellular factors underlying age-related variations in white matter microstructure have yet to be established. Here, we examined the genetic associates of individual differences in diffusion-based measures of white matter in a population-based cohort (N=29,862) from the UK Biobank. Estimates of heritability from Genome-Wide Association Study (GWAS) data revealed that genetic factors are linked to population variability in 96.1% of 432 tract microstructural measures. The presence of shared genetic influences was observed to be greater within, relative to between, broad tract classes (commissural, association, projection, and complex cerebellar). Age associations with microstructural changes were estimated across diffusivity measures, with association class tracts showing the greatest vulnerability to age-related decline in older adults. Analyses of imputed cellular associates of age-related changes in white matter revealed a preferential relationship with cell gene markers of oligodendrocytes and other glial cell types, with sparse relationships observed for inhibitory and excitatory cells. These data indicate that white matter tract microstructure is shaped by genetic factors and suggest a role for glial cell-related transcripts in late-life changes in the structural wiring properties of the human brain.

Aging

Transcriptional signature of induced neurons differentiates virologically suppressed people with HIV from people without HIV.

Neurocognitive impairment is a prevalent comorbidity in virologically suppressed people living with HIV (PLWH), yet the underlying mechanisms remain elusive and treatments lacking. We explored use of participant-derived directly induced neurons (iNs) to model neuronal biology and injury in PLWH. iNs retain age- and disease-related donor features, providing unique opportunities to reveal important aspects of neurological disorders. We obtained primary dermal fibroblasts from 6 virologically suppressed PLWH and 7 matched people without HIV (PWOH). iNs were generated using transcription factors NGN2 and ASCL1 and validated by immunocytochemistry, single-cell RNA-Seq, and electrophysiological recordings. Transcriptomic aging analyses confirmed retention of donor age-related signatures. Bulk RNA-Seq identified 29 significantly differentially expressed genes between PLWH and PWOH iNs. Of these, 16 were downregulated and 13 upregulated in PLWH iNs. Protein-protein interaction network mapping indicated iNs from PLWH exhibited differences in extracellular matrix organization and synaptic transmission. IFI27 was upregulated in PLWH iNs, complementing independent postmortem studies demonstrating elevated IFI27 expression in PLWH-derived brain tissue. FOXL2NB-FOXL2-LINC01391 expression was reduced in PLWH iNs and negatively correlated with neurocognitive impairment. Thus, we identified an iN gene signature of HIV revealing mechanisms of neurocognitive impairment in PLWH.

Humans

Structural and functional gastrointestinal abnormalities in ACTA2 R179H mice modeling multisystemic smooth muscle dysfunction syndrome.

Multisystemic smooth muscle dysfunction syndrome (MSMDS) is a rare disorder caused by ACTA2 mutations, including the R179H variant, which alters actin filament stability and dynamics and smooth muscle contractility. Cardiovascular complications dominate its clinical presentation, but gastrointestinal (GI) dysfunction significantly affects quality of life. To investigate the structural, functional, and cellular basis of gut dysmotility in MSMDS, we reviewed clinical data from 24 patients with MSMDS and studied the ACTA2 R179H mouse model. Patients exhibited severe gut dysmotility, with 75% requiring medication for chronic constipation. ACTA2 mutant mice displayed cecal and colonic dilatation, reduced intestinal length, and disrupted colonic migrating motor complexes. Delayed whole-gut transit and impaired contractile responses to electrical and pharmacological stimulation were observed. Transcriptomic analysis revealed significant actin cytoskeleton-related gene changes in smooth muscle cells, and immune profiling identified increased lymphocytic infiltration. Despite functional abnormalities, there were no obvious changes in the enteric nervous system. These findings establish ACTA2 mice as a robust model for studying GI pathology in MSMDS, elucidating the role of smooth muscle dysfunction in gut dysmotility. This model provides a foundation for developing targeted therapies aimed at restoring intestinal motility by directly addressing actin cytoskeletal disruptions in smooth muscle cells.

Animals

Sex-specific disruptions in PKC&#x3b3; signaling in a mouse model of spinocerebellar ataxia type 14.

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disease caused by mutations in the gene encoding protein kinase C &#x3b3; (PKC&#x3b3;), a Ca2+- and diacylglycerol-dependent Ser/Thr kinase dominantly expressed in cerebellar Purkinje cells. These mutations impair autoinhibitory constraints to increase the basal activity of the kinase, resulting in deficits in the cerebellum that are not observed upon simple deletion of the gene, and severe ataxia. To better understand the impact of aberrant PKC&#x3b3; signaling in disease pathology, we developed a knockin murine model of the SCA14 mutation &#x394;F48 in PKC&#x3b3;. This fully penetrant mutation is severe in humans and is mechanistically informative, as it has high basal activity but is unresponsive to agonist stimulation. Genetic, behavioral, and molecular testing revealed that &#x394;F48 PKC&#x3b3; mice have ataxia-related phenotypes and an altered cerebellar phosphoproteome driven primarily by enhanced Ca2+/calmodulin-dependent kinase 2 signaling, effects that were more severe in male mice. Analysis of existing human data revealed that SCA14 has a significantly earlier age of onset for males compared with females. Data from this clinically relevant mutation suggested that enhanced basal activity of PKC&#x3b3; is sufficient to cause ataxia and that treatment strategies to modulate aberrant PKC&#x3b3; may be particularly beneficial in males.

Animals

FGF13 is not secreted from mouse neurons.

FGF13, a noncanonical fibroblast growth factor (FGF) and member of the fibroblast growth factor homologous factor (FHF) subset, lacks a signal sequence and was previously reported to remain intracellular, where it regulates voltage-gated sodium channels (VGSCs) at least in part through direct interaction with the cytoplasmic C-terminus of VGSCs. Recent reports suggest FGF13 is secreted and regulates neuronal VGSCs through interactions with extracellular domains of integral plasma membrane proteins, yet supportive data are limited. Using rigorous positive and negative controls, we show that transfected FGF13 is not secreted from cultured cells in a heterologous expression system, nor is endogenous FGF13 secreted from cultured neurons. Furthermore, using multiple unbiased screens including proximity labeling proteomics, our results suggest FGF13 remains within membranes and is unavailable to interact directly with extracellular protein domains.

Animals

A dual-reporter mouse for therapeutic discovery in Angelman syndrome.

Angelman syndrome is a neurodevelopmental disorder caused by loss of the maternal UBE3A allele, the sole source of UBE3A in mature neurons owing to epigenetic silencing of the paternal allele. Although emerging therapies are being developed to restore UBE3A expression by activating the dormant paternal UBE3A allele, existing mouse models for such preclinical studies have limited throughput and utility, creating bottlenecks for both in vitro therapeutic screening and in vivo characterization. To address this, we developed the Ube3a-INSG dual-reporter knockin mouse, in which an IRES-Nanoluciferase-T2A-Sun1-sfGFP (INSG) cassette was inserted downstream of the endogenous Ube3a stop codon. The INSG model preserves UBE3A protein levels and function while enabling 2 complementary allele-specific readouts: Sun1-sfGFP and Nanoluciferase. We show that Sun1-sfGFP, a nuclear envelope-localized reporter, enables single-cell fluorescence analysis, whole-brain light-sheet imaging, and nuclear quantification by flow cytometry. Further, Nanoluciferase supports high-throughput luminescence assays for sensitive pharmacological profiling in cultured neurons and noninvasive in vivo bioluminescence imaging for pharmacodynamic assessment. By combining scalable screening, cellular analysis, and real-time in vivo monitoring in a single model, the Ube3a-INSG dual-reporter mouse provides a powerful platform to accelerate therapeutic development centered on UBE3A.

Animals