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Mapping cell-type- and age-dependent neuronal vulnerability through genome-wide in vivo CRISPRi screens in the mouse brain.

Current brain atlases are largely descriptive, cataloging correlative molecular snapshots such as gene expression signatures yet offering limited functional insight. Here, we develop a scalable, cell-type-resolved in vivo CRISPR interference (CRISPRi) platform enabling systematic gene function profiling in the mouse brain. Through genome-wide screens across four neuronal populations at three time points spanning youth to aging, we identify neuronal essential genes missed in vitro and define a consensus set of 269 neuronal core essential genes. The data reveal cell-type-specific genetic vulnerabilities, including divergent dependencies validated for exosome component 9 (Exosc9) and osteopetrosis-associated transmembrane protein 1 (Ostm1) between excitatory and inhibitory neurons. We uncover aging-specific dependencies enriched in mitochondrial and translational pathways, aligning with transcriptional changes in the aging human brain. Finally, we establish the CRISPRinvivo data portal as a community resource for in vivo screening. Altogether, this work provides a broadly applicable platform for in vivo functional genomics and a framework for building comprehensive gene-function brain atlases.

brain aging

Effects of cortical ablation on the neurotoxicity and receptor binding of kainic acid in striatum.

Lesions of the cerebral cortex alter striatal neuronal vulnerability to locally injected kainic acid. Whereas extensive lesions involving the frontal-parietal-occipital cortex are most effective, lesions limited to the frontal or to the dorsal-lateral parietal cortex offer partial protection. The extensive cortical lesions are associated with selective, marked reductions in the presynaptic markers for glutamatergic afferents in striatum. The protective effects of decortication appear between 6 and 24 hours after the lesion and are maintained up to 30 days after decortication. Whereas decortication results in only a transient reduction of specific receptor binding of [3H]kainic acid to striatal membranes, lesion of striatal intrinsic neurons with kainic acid causes a delayed but marked reduction in specific binding of the ligand. Coadministration of L-glutamic acid (1 mumole) with kainic acid (9 nmoles) partially restores the neurotoxic action of kainic acid in the decorticate striatum; GABA, alanine, and proline (1 mumole) are ineffective with regard to restoring kainate's toxicity for striatal GABAergic neurons. These results suggest that afferent input exerts a permissive effect on the neurotoxic action of kainic acid and that neurotoxicity may involve a cooperative interaction between kainic acid at specific receptors on vulnerable neurons and synaptically released endogenous neurotransmitters, in particular L-glutamic acid.

Animals

RNA dysregulation as a determinant of aging and neurodegenerative vulnerability.

In the nervous system, aging causes deterioration of cellular and molecular processes that are associated with declines in cognition, sensory perception, and motor coordination. Aging is also the strongest risk factor for neurodegenerative disease, yet the mechanisms by which aging predisposes neurons to dysfunction remain incompletely understood. While genomic instability, proteostasis decline, mitochondrial dysfunction, and chronic inflammation have dominated prevailing models, recent evidence highlights RNA dysregulation as a central component of age-associated decline. In this review, we summarize recent findings suggesting that aging progressively erodes RNA regulatory fidelity through alterations in RNA-binding protein abundance, localization, biophysical behavior, and RNA interactions. We argue that age-dependent RNA dysregulation represents an important mechanism that converges with genetic risk to drive neuronal vulnerability and neurodegeneration.

RNA dysregulation

An animal model for Huntington's disease.

In review is concerned with research done on an animal model for the hereditary neuropsychiatric disorder, Huntington's disease (HD). The neuropathology of HD involves primarily a selective degeneration of neurons with cell bodies in the striatum. Injection of kainic acid, a potent neuroexcitant structurally related to glutamic acid, into the rat striatum causes a selective neuronal degeneration resembling that of HD. Striatal cholinergic and GABAergic neurons, including their terminal projections in the substantia nigra, are affected by kainate; dopaminergic axons innervating the striatum as well as corticofugal fibers passing through the region are spared. The striatal kainate lesion has aided in the characterization of the neuronal circuitry in the nigrostriatal axis including the neuronal localization of dopamine-sensitive adenylate cyclase, neuroleptic binding sites, and GABA receptors. Studies in vivo and in vitro with kainate and its analogues suggest that the potent neurotoxicity of kainate involves a cooperative interaction between synaptically released glutamate and injected kainate on vulnerable neurons; prior destruction of cortico-striatal glutamatergic afferents attenuates kainate's neurotoxicity. The kainate model has been used to test drugs that may be of therapeutic benefit for HD. A better understanding of the mechanism of neurotoxicity of kainate may shed light on the cause of neuronal degeneration in HD.

Animals

CHCHD10 Mitigates Alzheimer's Disease-Related Phenotypes in Association With Epigenetic Remodeling in Directly Reprogrammed Neurons.

Mitochondrial dysfunction and chromatin dysregulation are interconnected contributors to neuronal vulnerability in Alzheimer's disease (AD), yet the molecular mechanisms linking these processes remain poorly understood. CHCHD10, a mitochondrial intermembrane space protein, has been implicated in neurodegenerative disorders, but its role in AD has not been defined. Here, we identify CHCHD10 as a previously unrecognized modulator of neuronal epigenomic stability in AD. Using direct fibroblast-to-neuron reprogramming, which preserves patient-specific epigenetic signatures, we show that AD neurons recapitulate genome-wide hypomethylation patterns observed in postmortem AD cortex. CHCHD10 expression is significantly reduced in AD neurons and across multiple human brain datasets, including single-cell and bulk RNA sequencing, proteomics, and human cortical tissue analyses. Restoration of CHCHD10 in AD neurons reduces amyloid-β and insoluble tau accumulation while reversing AD-associated differentially methylated regions across CpG islands, promoters, and regulatory elements. CHCHD10-responsive methylation changes overlap with those observed in human AD brain regions and colocalize with significant AD loci and cortex-specific eQTL loci, including MAPT and ABCA7. Finally, we identify KATNAL2 as a CHCHD10-responsive effector whose loss enhances tau phosphorylation and seeding, whereas its restoration mitigates tau pathology. Together, these findings support a CHCHD10-associated neuroprotective pathway linking mitochondrial dysfunction, epigenomic instability, and tau pathology in AD.

Humans

m6A-Mediated epitranscriptomic control of mitochondrial dysfunction in neurodegeneration.

Mitochondrial dysfunction is a common pathology of neurodegenerative diseases, which contributes to neuronal vulnerability via excessive oxidative stress, impaired bioenergetics, and dysregulated apoptosis. Emerging studies highlighted the critical role of epitranscriptomic RNA modifications, particularly N6-methyladenosine (m6A), in mitochondrial gene expression regulation and cellular stress responses. m6A modifications are installed by methyltransferases ("writers," METTL3/METTL14), recognized by reader proteins (YTH domain family proteins, IGF2BPs), and removed by demethylases ("erasers," FTO, ALKBH5), collectively orchestrating mRNA splicing, localization, stability, and translation. Recent evidence demonstrates that m6A modifications modulate both nuclear-encoded and mitochondrially encoded transcripts and regulate key mitochondrial processes, including fission/fusion dynamics, oxidative phosphorylation, mitophagy, and apoptosis. Dysregulation of m6A machinery disrupts mitochondrial homeostasis, exacerbates oxidative stress and neuroinflammation, and promotes neuronal loss. Importantly, pharmacological or genetic modulation of m6A regulators can restore mitochondrial function, inhibit caspase activation, and dampen pro-inflammatory signaling, underscoring their therapeutic potential. This review consolidates current insights into mitochondrial epitranscriptomics, emphasizing how m6A modifications act as central regulators of mitochondrial stress responses and neurodegeneration.

Humans

Interspecies Organoids Reveal Human-Specific Molecular Features of Dopaminergic Neuron Development and Vulnerability.

The disproportionate expansion of telencephalic structures during human evolution involved tradeoffs that imposed greater connectivity and metabolic demands on midbrain dopaminergic neurons. Despite the central role of dopaminergic neurons in human-enriched disorders, molecular specializations associated with human-specific features and vulnerabilities of the dopaminergic system remain unexplored. Here, we establish a phylogeny-in-a-dish approach to examine gene regulatory evolution by differentiating pools of human, chimpanzee, orangutan, and macaque pluripotent stem cells into ventral midbrain organoids capable of forming long-range projections, spontaneous activity, and dopamine release. We identify human-specific gene expression changes related to axonal transport of mitochondria and reactive oxygen species buffering and candidate cis- and trans-regulatory mechanisms underlying gene expression divergence. Our findings are consistent with a model of evolved neuroprotection in response to tradeoffs related to brain expansion and could contribute to the discovery of therapeutic targets and strategies for treating disorders involving the dopaminergic system.

Brain evolution

Distinct Behavioral Profiles and Neuronal Correlates of Heroin Vulnerability Versus Resiliency in a Multi-Symptomatic Model of Heroin Use Disorder in Rats.

OBJECTIVE: The behavioral and diagnostic heterogeneity within the opioid use disorder (OUD) diagnosis is not readily captured in current animal models, limiting the translational relevance of the mechanistic research that is conducted in experimental animals. The authors hypothesized that a nonlinear clustering of OUD-like behavioral traits would capture population heterogeneity and yield subpopulations of OUD vulnerable rats with distinct behavioral and neurocircuit profiles. METHODS: Over 900 male and female heterogeneous stock rats, a line capturing genetic and behavioral heterogeneity present in humans, were assessed for several measures of heroin use and rewarded and non-rewarded seeking behaviors. A nonlinear stochastic block model clustering analysis was used to assign rats to OUD vulnerable, intermediate, and resilient clusters. Additional behavioral tests and circuit analyses using c-fos protein activation were conducted on the vulnerable and resilient subpopulations. RESULTS: OUD vulnerable rats exhibited greater heroin taking and seeking behaviors relative to those in the intermediate and resilient clusters. Akin to human OUD diagnosis, further vulnerable rat subclustering revealed subpopulations with different combinations of behavioral traits, including sex differences. Lastly, heroin cue-induced neuronal patterns of circuit activation differed between resilient and vulnerable phenotypes. Behavioral sex differences were recapitulated in patterns of circuitry activation, including preferential engagement of extended amygdala stress circuitry in males and cortico-striatal drug cue-seeking circuitry in females. CONCLUSION: Using a nonlinear clustering approach in rats, the analysis captured behavioral diagnostic heterogeneity reflective of human OUD diagnosis. OUD vulnerability and resiliency were associated with distinct neuronal activation patterns, posing this approach as a translational tool in assessing neurobiological mechanisms underpinning OUD.

Animals

Hypothesis-free evaluation of circulating metabolome provides cell-specific insights regarding the role of energy substrate availability in amyotrophic lateral sclerosis.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with limited therapeutic options. The circulating metabolome comprises small molecules present in plasma/serum which are the intermediates and end-products of cellular metabolism, and is linked to ALS pathogenesis. METHODS: We conducted hypothesis-free two-sample Mendelian randomisation (MR) analysis of the concentration of 575 plasma/serum metabolites, to determine which are causally linked to risk of ALS. Significant metabolites were validated in an independent GWAS of plasma/serum metabolite concentrations and evaluated for sex-specific effects. Correlations between directly measured patient biofluid metabolite concentrations and ALS risk/severity were examined in 94 ALS patients and 40 controls. We experimentally assessed metabolic function in a murine neurons and human astrocytes carrying an ALS-associated G4C2-repeat expansion within C9orf72. RESULTS: MR causally associated five metabolites with ALS risk after multiple-testing correction. Higher serum concentration of glycoprotein acetyls (P&#x2009;=&#x2009;9.7e&#x2009;-&#x2009;9, &#x3b2;&#x2009;=&#x2009;0.21) and the peptide DSGEGDFXAEGGGVR (P&#x2009;=&#x2009;8.0e&#x2009;-&#x2009;6, &#x3b2;&#x2009;=&#x2009;0.22) was associated with increased ALS risk, whereas higher plasma concentration of phenylalanylserine, isobutyrylcarnitine, and acetylcarnitine was protective (P&#x2009;<&#x2009;5e&#x2009;-&#x2009;5, &#x3b2;&#x2009;= -&#x2009;0.29 to&#x2009;-&#x2009;0.72). DSGEGDFXAEGGGVR has been linked to glucose metabolism but we have used genetic fine-mapping to link DSGEGDFXAEGGGVR, neuronal glucose uptake through GLUT3, and ALS risk. Direct measurement of metabolite concentrations in patient biofluids revealed elevated acetylcarnitine levels in patients with ALS, which were associated with delayed symptom onset (Cox regression, P&#x2009;=&#x2009;0.02, HR&#x2009;=&#x2009;0.4). Similarly, lactate is elevated in ALS patient CSF (ANOVA, P&#x2009;=&#x2009;1.3e&#x2009;-&#x2009;3) and in patients with longer survival time (Cox regression, P&#x2009;=&#x2009;0.03, HR&#x2009;=&#x2009;0.3). Plasma fructose is elevated in ALS patients with shorter survival time (Cox regression, P&#x2009;=&#x2009;0.02, HR&#x2009;=&#x2009;1.1). In vitro, neurons and astrocytes carrying an ALS-associated G4C2-repeat expansion within C9orf72 demonstrated reduced metabolic flexibility. CONCLUSIONS: We provide evidence that impaired energy substrate availability contributes to ALS risk and severity. CNS cell types differ in their use of energy substrates and therefore we postulate the relative importance of different cell types for different stages of disease. Our findings support further investigation of metabolic interventions to treat or prevent ALS.

Amyotrophic Lateral Sclerosis

Acute dendrotoxic changes in the hippocampus of kainate treated rats.

Kainic acid (KA), a potent neuroexcitatory and neurotoxic analog of glutamate (Glu), induces a widespread pattern of brain damage when administered subcutaneously to adult rats. The hippocampus is among the brain regions most consistently and severely damaged. Here we describe acute swelling of certain spines and branchlets of dendrites as the first detectable sign of KA neurotoxic changes in the hippocampus. These swellings conform to a laminar pattern suggesting selective toxic interaction of KA at specific levels of the dendritic trees of hippocampal pyramidal and dentate granule neurons. The frequency and severity of involvement of each type of hippocampal neuron at each level of its dendritic tree was roughly estimated and neuronal types were ranked from the most to least extensively involved (CA3 greater than CA4 greater than CA1 greater than CA2 greater than dentate granules). The same rank order has been described for the vulnerability of these neurons to acute destruction following intraventricular KA administration. Because the pattern of dendritic dilatations observed corresponds well with the pattern of termination of putative glutamergic inputs to the hippocampus, we interpret the findings as being consistent with the hypothesis that the toxic effects of KA are mediated through glutamergic excitatory receptors. We propose that the sensitivity of a given neuron to the neurodestructive action of KA may be determined by the percentage of its dendritic surface occupied by Glu receptors. We suspect that most, if not all, hippocampal neurons receive some glutamergic input and, therefore, are sensitive to KA. That CA3 pyramids are substantially more sensitive than dentate granules may signify that the former receive many more Glu terminals than the latter, an assumption quite consistent with our observation that focal dendritic swellings were both more densely and more widely distributed over the dendritic surfaces of the former than the latter.

Animals

Ontogenetic development of kainate neurotoxicity: correlates with glutamatergic innervation.

Stereotaxic injection of kainic acid into the striatum of adult rats causes degeneration of neurons intrinsic to the striatum but spares axons of passage and of termination of extrinsic neurons. Neurochemical and histologic studies demonstrate that striatal neurons are almost insensitive to kainate at 7 days after birth and that their vulnerability increases with age; by 3 weeks after birth, striatal injection of kainate produces a lesion comparable to that of the adult. The intensity and duration of the acute behavioral response to kainate also increases with age. The maturational increase in striatal neuronal sensitivity to kainate correlates with the development of glutamatergic innervation to the striatum, as measured by [3H]glutamate uptake by synaptosomes, and with the development of a postsynaptic, high-affinity receptor site for kainate. These ontogenetic studies provide additional evidence that kainate's neurotoxicity is a receptor-mediated event related to glutamatergic innervation of vulnerable neurons.

Animals

Reversible exacerbation of parkinsonism during epirubicin-cyclophosphamide chemotherapy in a patient with PTEN hamartoma tumor syndrome and young-onset Parkinson's disease.

BACKGROUND: PTEN hamartoma tumor syndrome (PHTS), caused by germline loss-of-function variants in PTEN, typically manifests as macrocephaly, neurodevelopmental disorders, and cancer susceptibility. Parkinson's disease has not been recognized as part of its known neurological spectrum. METHODS: We describe the clinical course of a patient with a germline PTEN nonsense variant (p.Arg130Ter) who developed young-onset Parkinson's disease before being diagnosed with bilateral breast cancer. RESULTS: The patient developed asymmetric, levodopa-responsive parkinsonism at 35&#xa0;years of age, with reduced bilateral striatal dopamine transporter uptake. During two cycles of epirubicin-cyclophosphamide chemotherapy, her previously well-controlled parkinsonism showed reproducible and severe exacerbations. Symptoms began several days after chemotherapy, reached their maximum severity approximately one week after treatment, and resolved completely within approximately two weeks without modification of her antiparkinsonian medications. No dehydration, electrolyte disturbance, infection, or exposure to dopamine-receptor antagonists was identified. The chemotherapy regimen was discontinued after the second episode because of the reproducible temporal association. CONCLUSIONS: This case demonstrates reproducible, fully reversible exacerbations of parkinsonism during epirubicin-cyclophosphamide chemotherapy in a patient with PHTS and young-onset Parkinson's disease. These episodes may reflect transient vulnerability of dopaminergic neurons to chemotherapy-related systemic stress, although the causal role of PTEN haploinsufficiency remains uncertain.

Humans

Single-cell transcriptomic atlas of Alzheimer's disease middle temporal gyrus reveals region, cell type and sex specificity of gene expression with novel genetic risk for MERTK in female.

Alzheimer's disease, the most common age-related neurodegenerative disease, is closely associated with both amyloid-&#xdf; plaque and neuroinflammation. Two thirds of Alzheimer's disease patients are females and they have a higher disease risk. Moreover, women with Alzheimer's disease have more extensive brain histological changes than men along with more severe cognitive symptoms and neurodegeneration. To identify how sex difference induces structural brain changes, we performed unbiased massively parallel single nucleus RNA sequencing on Alzheimer's disease and control brains focusing on the middle temporal gyrus, a brain region strongly affected by the disease but not previously studied with these methods. We identified a subpopulation of selectively vulnerable layer 2/3 excitatory neurons that that were RORB-negative and CDH9-expressing. This vulnerability differs from that reported for other brain regions, but there was no detectable difference between male and female patterns in middle temporal gyrus samples. Disease-associated, but sex-independent, reactive astrocyte signatures were also present. In clear contrast, the microglia signatures of diseased brains differed between males and females. Combining single cell transcriptomic data with results from genome-wide association studies (GWAS), we identified MERTK genetic variation as a risk factor for Alzheimer's disease selectively in females. Taken together, our single cell dataset revealed a unique cellular-level view of sex-specific transcriptional changes in Alzheimer's disease, illuminating GWAS identification of sex-specific Alzheimer's risk genes. These data serve as a rich resource for interrogation of the molecular and cellular basis of Alzheimer's disease.

Journal Article

Heterozygous knockout of Synaptotagmin13 phenocopies ALS features and TP53 activation in human motor neurons.

Spinal motor neurons (MNs) represent a highly vulnerable cellular population, which is affected in fatal neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). In this study, we show that the heterozygous loss of SYT13 is sufficient to trigger a neurodegenerative phenotype resembling those observed in ALS and SMA. SYT13+/- hiPSC-derived MNs displayed a progressive manifestation of typical neurodegenerative hallmarks such as loss of synaptic contacts and accumulation of aberrant aggregates. Moreover, analysis of the SYT13+/- transcriptome revealed a significant impairment in biological mechanisms involved in motoneuron specification and spinal cord differentiation. This transcriptional portrait also strikingly correlated with ALS signatures, displaying a significant convergence toward the expression of pro-apoptotic and pro-inflammatory genes, which are controlled by the transcription factor TP53. Our data show for the first time that the heterozygous loss of a single member of the synaptotagmin family, SYT13, is sufficient to trigger a series of abnormal alterations leading to MN sufferance, thus revealing novel insights into the selective vulnerability of this cell population.

Humans

The Long Haul: Microtubule Motors as the Essential Supply Line for Neuronal Longevity.

The extreme morphology and polarised architecture of neurons require the highly sophisticated microtubule transport system for both construction and lifelong survival. Genomic evidence from an expanding landscape of human mutations supports the essential role of the microtubule transport machinery. During neurodevelopment, mutations disrupt the proliferation and migration of neuronal precursors, as well as the initial establishment of polarity. In the mature nervous system, the reliance on microtubule transport shifts to the long-term maintenance of axon integrity and synaptic proteostasis. Across the motor proteins responsible for long distance transport in neurons, mutations highlight a specific vulnerability of long axons to transport failure in Hereditary Spastic Paraplegia (HSP), Charcot Marie Tooth disease Type 2 (CMT2), Spinal Muscular Atrophy (SMA), Perry Syndrome, and Amyotrophic Lateral Sclerosis (ALS) amongst others. Due to the role of microtubule motors in development and maintenance, there is frequently a phenotypic spectrum within a single gene of the microtubule transport system. For example, mutations in dynein motors are linked both to malformations of cortical development and specific motor neuron loss in SMA-LED (Spinal Muscular Atrophy with Lower Extremity Predominance). By synthesising genetic evidence, this review illustrates how specific molecular failures, ranging from motor-domain kinetics to cargo binding, can inform our understanding of neuronal homeostasis. Ultimately, we argue that microtubule transport is not merely a cellular utility, but a key determinant of neuronal longevity.

Humans

Psychoses precipitated by psychotomimetic drugs. A follow-up study.

Fifteen patients who developed prolonged psychotic reactions following psychotomimetic drug use (probably primarily LSD) were followed up 1.9 to 5.8 years later. Two patients had committed suicide. Approximately half of the patients had a relatively good outcome and half did poorly. Aspects of the initial clinical picture that correlated with outcome measures are discussed. The possibility is considered that vulnerability to a prolonged psychotic reaction following psychotomimetic drug use may be related to a genetic vulnerability to illnesses in the manic-depressive/schizo-affective spectrum. In some instances this vulnerability may implicate central serotonergic neuronal systems.

Adolescent

Transcriptomic landscape of microglia in mouse models of social dysfunction and oxytocin-mediated recovery.

Atypical sociability is a hallmark of neurodevelopmental disorders arising from genetic susceptibility and prenatal environmental perturbations that can affect diverse brain cell types. Using single-cell transcriptomics, we previously identified selective vulnerability of parvocellular oxytocin (OT) neurons in the paraventricular hypothalamus (PVH) following embryonic exposure to valproic acid (VPA), a teratogen that induces social deficits. Neonatal chemogenetic activation of OT neurons rescued these behavioral abnormalities and partially restored dysregulated gene expression. However, the effects of VPA exposure and OT neuron stimulation on non-neuronal PVH cells remained unclear. Here, we show that VPA induces transcriptional abnormalities in PVH microglia. Spatial transcriptomics revealed altered distributions of PVH microglial subtypes. Notably, neonatal OT neuron stimulation reversed a subset of VPA-induced microglial gene downregulation, while pharmacological manipulation of microglia normalized aberrant OT gene expression in putative parvocellular OT neurons. These findings support bidirectional OT neuron-microglia interactions that may underlie social dysfunction following embryonic VPA exposure.

autism spectrum disorder