Gamma entrainment using audiovisual stimuli alleviates chemobrain pathology and cognitive impairment induced by chemotherapy in mice.

Patients with cancer undergoing chemotherapy frequently experience a neurological condition known as chemotherapy-related cognitive impairment, or "chemobrain," which can persist for the remainder of their lives. Despite the growing prevalence of chemobrain, both its underlying mechanisms and treatment strategies remain poorly understood. Recent findings suggest that chemobrain shares several characteristics with neurodegenerative diseases, including chronic neuroinflammation, DNA damage, and synaptic loss. We investigated whether a noninvasive sensory stimulation treatment we term gamma entrainment using sensory stimuli (GENUS), which has been shown to alleviate aberrant immune and synaptic pathologies in mouse models of neurodegeneration, could also mitigate chemobrain phenotypes in mice administered a chemotherapeutic drug. When administered concurrently with the chemotherapeutic agent cisplatin, GENUS alleviated cisplatin-induced brain pathology, promoted oligodendrocyte survival, and improved cognitive function in a mouse model of chemobrain. These effects persisted for up to 105 days after GENUS treatment, suggesting the potential for long-lasting benefits. However, when administered to mice 90 days after chemotherapy, GENUS treatment only provided limited benefits, indicating that it was most effective when used to prevent the progression of chemobrain pathology. Furthermore, we demonstrated that the effects of GENUS in mice were not limited to cisplatin-induced chemobrain but also extended to methotrexate-induced chemobrain. Collectively, these findings suggest that GENUS may represent a versatile approach for treating chemobrain induced by different chemotherapy agents.

Lateral mammillary body neurons in mouse brain are disproportionately vulnerable in Alzheimer's disease.

The neural circuits governing the induction and progression of neurodegeneration and memory impairment in Alzheimer's disease (AD) are incompletely understood. The mammillary body (MB), a subcortical node of the medial limbic circuit, is one of the first brain regions to exhibit amyloid deposition in the 5xFAD mouse model of AD. Amyloid burden in the MB correlates with pathological diagnosis of AD in human postmortem brain tissue. Whether and how MB neuronal circuitry contributes to neurodegeneration and memory deficits in AD are unknown. Using 5xFAD mice and postmortem MB samples from individuals with varying degrees of AD pathology, we identified two neuronal cell types in the MB harboring distinct electrophysiological properties and long-range projections: lateral neurons and medial neurons. lateral MB neurons harbored aberrant hyperactivity and exhibited early neurodegeneration in 5xFAD mice compared with lateral MB neurons in wild-type littermates. Inducing hyperactivity in lateral MB neurons in wild-type mice impaired performance on memory tasks, whereas attenuating aberrant hyperactivity in lateral MB neurons ameliorated memory deficits in 5xFAD mice. Our findings suggest that neurodegeneration may be a result of genetically distinct, projection-specific cellular dysfunction and that dysregulated lateral MB neurons may be causally linked to memory deficits in AD.

Down-syndrome-induced senescence disrupts the nuclear architecture of neural progenitors.

Down syndrome (DS) is a genetic disorder driven by the triplication of chromosome 21 (T21) and characterized by a wide range of neurodevelopmental and physical disabilities. Transcriptomic analysis of tissue samples from individuals with DS has revealed that T21 induces a genome-wide transcriptional disruption. However, the consequences of T21 on the nuclear architecture and its interplay with the transcriptome remain unknown. In this study, we find that unlike human induced pluripotent stem cells (iPSCs), iPSC-derived neural progenitor cells (NPCs) exhibit genome-wide "chromosomal introversion," disruption of lamina-associated domains, and global chromatin accessibility changes in response to T21, consistent with the transcriptional and nuclear architecture changes characteristic of senescent cells. Treatment of T21-harboring NPCs with senolytic drugs alleviates the transcriptional, molecular, and cellular dysfunctions associated with DS. Our findings provide a mechanistic link between T21 and global transcriptional disruption and indicate that senescence-associated phenotypes may play a key role in the neurodevelopmental pathogenesis of DS.

MEF2 is a key regulator of cognitive potential and confers resilience to neurodegeneration.

Recent increases in human longevity have been accompanied by a rise in the incidence of dementia, highlighting the need to preserve cognitive function in an aging population. A small percentage of individuals with pathological hallmarks of neurodegenerative disease are able to maintain normal cognition. Although the molecular mechanisms that govern this neuroprotection remain unknown, individuals that exhibit cognitive resilience (CgR) represent a unique source of therapeutic insight. For both humans and animal models, living in an enriched, cognitively stimulating environment is the most effective known inducer of CgR. To understand potential drivers of this phenomenon, we began by profiling the molecular changes that arise from environmental enrichment in mice, which led to the identification of MEF2 transcription factors (TFs). We next turned to repositories of human clinical and brain transcriptomic data, where we found that the MEF2 transcriptional network was overrepresented among genes that are most predictive of end-stage cognition. Through single-nucleus RNA sequencing of cortical tissue from resilient and nonresilient individuals, we further confirmed up-regulation of MEF2C in resilient individuals to a subpopulation of excitatory neurons. Last, to determine the causal impact of MEF2 on cognition in the context of neurodegeneration, we overexpressed Mef2a/c in the PS19 mouse model of tauopathy and found that this was sufficient to improve cognitive flexibility and reduce hyperexcitability. Overall, our findings reveal a previously unappreciated role for MEF2 TFs in promoting CgR, highlighting their potential as biomarkers or therapeutic targets for neurodegeneration and healthy aging.

3D mapping reveals network-specific amyloid progression and subcortical susceptibility in mice.

Alzheimer's disease (AD) is a progressive, neurodegenerative dementia with no cure. Prominent hypotheses suggest accumulation of beta-amyloid (Aß) contributes to neurodegeneration and memory loss, however identifying brain regions with early susceptibility to Aß remains elusive. Using SWITCH to immunolabel intact brain, we created a spatiotemporal map of Aß deposition in the 5XFAD mouse. We report that subcortical memory structures show primary susceptibility to Aß and that aggregates develop in increasingly complex networks with age. The densest early Aß occurs in the mammillary body, septum, and subiculum- core regions of the Papez memory circuit. Previously, early mammillary body dysfunction in AD had not been established. We also show that Aß in the mammillary body correlates with neuronal hyper-excitability and that modulation using a pharmacogenetic approach reduces Aß deposition. Our data demonstrate large-tissue volume processing techniques can enhance biological discovery and suggest that subcortical susceptibility may underlie early brain alterations in AD.

Author Correction: Single-cell transcriptomic analysis of Alzheimer's disease.

Change history: In this Article, the Acknowledgements section should have included that the work was supported in part by the Cure Alzheimer's Fund (CAF), and the final NIH grant acknowledged should have been 'U01MH119509' instead of 'RF1AG054012'. In Supplementary Table 2, the column labels 'early.pathology.mean' and 'late.pathology.mean' were reversed in each worksheet (that is, columns Y and Z). These errors have been corrected online.

Single-cell transcriptomic analysis of Alzheimer's disease.

Alzheimer's disease is a pervasive neurodegenerative disorder, the molecular complexity of which remains poorly understood. Here, we analysed 80,660 single-nucleus transcriptomes from the prefrontal cortex of 48 individuals with varying degrees of Alzheimer's disease pathology. Across six major brain cell types, we identified transcriptionally distinct subpopulations, including those associated with pathology and characterized by regulators of myelination, inflammation, and neuron survival. The strongest disease-associated changes appeared early in pathological progression and were highly cell-type specific, whereas genes upregulated at late stages were common across cell types and primarily involved in the global stress response. Notably, we found that female cells were overrepresented in disease-associated subpopulations, and that transcriptional responses were substantially different between sexes in several cell types, including oligodendrocytes. Overall, myelination-related processes were recurrently perturbed in multiple cell types, suggesting that myelination has a key role in Alzheimer's disease pathophysiology. Our single-cell transcriptomic resource provides a blueprint for interrogating the molecular and cellular basis of Alzheimer's disease.

Multi-sensory Gamma Stimulation Ameliorates Alzheimer's-Associated Pathology and Improves Cognition.

We previously reported that inducing gamma oscillations with a non-invasive light flicker (gamma entrainment using sensory stimulus or GENUS) impacted pathology in the visual cortex of Alzheimer's disease mouse models. Here, we designed auditory tone stimulation that drove gamma frequency neural activity in auditory cortex (AC) and hippocampal CA1. Seven days of auditory GENUS improved spatial and recognition memory and reduced amyloid in AC and hippocampus of 5XFAD mice. Changes in activation responses were evident in microglia, astrocytes, and vasculature. Auditory GENUS also reduced phosphorylated tau in the P301S tauopathy model. Furthermore, combined auditory and visual GENUS, but not either alone, produced microglial-clustering responses, and decreased amyloid in medial prefrontal cortex. Whole brain analysis using SHIELD revealed widespread reduction of amyloid plaques throughout neocortex after multi-sensory GENUS. Thus, GENUS can be achieved through multiple sensory modalities with wide-ranging effects across multiple brain areas to improve cognitive function.

Noninvasive 40-Hz light flicker to recruit microglia and reduce amyloid beta load.

Microglia, the primary immune cells of the brain, play a key role in pathological and normal brain function. Growing efforts aim to reveal how these cells may be harnessed to treat both neurodegenerative diseases such as Alzheimer's and developmental disorders such as schizophrenia and autism. We recently showed that using noninvasive exposure to 40-Hz white-light (4,000 K) flicker to drive 40-Hz neural activity transforms microglia into an engulfing state and reduces amyloid beta, a peptide thought to initiate neurotoxic events in Alzheimer's disease (AD). This article describes how to construct an LED-based light-flicker apparatus, expose animals to 40-Hz flicker and control conditions, and perform downstream assays to study the effects of these stimuli. Light flicker is simple, faster to implement, and noninvasive, as compared with driving 40-Hz activity using optogenetics; however, it does not target specific cell types, as is achievable with optogenetics. This noninvasive approach to driving 40-Hz neural activity should enable further research into the interactions between neural activity, molecular pathology, and the brain's immune system. Construction of the light-flicker system requires ~1 d and some electronics experience or available guidance. The flicker manipulation and assessment can be completed in a few days, depending on the experimental design.

Author Correction: Gamma frequency entrainment attenuates amyloid load and modifies microglia.

Change history: In this Article, Extended Data Fig. 8 and Extended Data Table 1 contained errors, which have been corrected online.

APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer's Disease Phenotypes in Human iPSC-Derived Brain Cell Types.

The apolipoprotein E4 (APOE4) variant is the single greatest genetic risk factor for sporadic Alzheimer's disease (sAD). However, the cell-type-specific functions of APOE4 in relation to AD pathology remain understudied. Here, we utilize CRISPR/Cas9 and induced pluripotent stem cells (iPSCs) to examine APOE4 effects on human brain cell types. Transcriptional profiling identified hundreds of differentially expressed genes in each cell type, with the most affected involving synaptic function (neurons), lipid metabolism (astrocytes), and immune response (microglia-like cells). APOE4 neurons exhibited increased synapse number and elevated Aß42 secretion relative to isogenic APOE3 cells while APOE4 astrocytes displayed impaired Aß uptake and cholesterol accumulation. Notably, APOE4 microglia-like cells exhibited altered morphologies, which correlated with reduced Aß phagocytosis. Consistently, converting APOE4 to APOE3 in brain cell types from sAD iPSCs was sufficient to attenuate multiple AD-related pathologies. Our study establishes a reference for human cell-type-specific changes associated with the APOE4 variant. VIDEO ABSTRACT.

Gamma frequency entrainment attenuates amyloid load and modifies microglia.

Changes in gamma oscillations (20-50 Hz) have been observed in several neurological disorders. However, the relationship between gamma oscillations and cellular pathologies is unclear. Here we show reduced, behaviourally driven gamma oscillations before the onset of plaque formation or cognitive decline in a mouse model of Alzheimer's disease. Optogenetically driving fast-spiking parvalbumin-positive (FS-PV)-interneurons at gamma (40 Hz), but not other frequencies, reduces levels of amyloid-ß (Aß)1-40 and Aß 1-42 isoforms. Gene expression profiling revealed induction of genes associated with morphological transformation of microglia, and histological analysis confirmed increased microglia co-localization with Aß. Subsequently, we designed a non-invasive 40 Hz light-flickering regime that reduced Aß1-40 and Aß1-42 levels in the visual cortex of pre-depositing mice and mitigated plaque load in aged, depositing mice. Our findings uncover a previously unappreciated function of gamma rhythms in recruiting both neuronal and glial responses to attenuate Alzheimer's-disease-associated pathology.

Self-Organizing 3D Human Neural Tissue Derived from Induced Pluripotent Stem Cells Recapitulate Alzheimer's Disease Phenotypes.

The dismal success rate of clinical trials for Alzheimer's disease (AD) motivates us to develop model systems of AD pathology that have higher predictive validity. The advent of induced pluripotent stem cells (iPSCs) allows us to model pathology and study disease mechanisms directly in human neural cells from healthy individual as well as AD patients. However, two-dimensional culture systems do not recapitulate the complexity of neural tissue, and phenotypes such as extracellular protein aggregation are difficult to observe. We report brain organoids that use pluripotent stem cells derived from AD patients and recapitulate AD-like pathologies such as amyloid aggregation, hyperphosphorylated tau protein, and endosome abnormalities. These pathologies are observed in an age-dependent manner in organoids derived from multiple familial AD (fAD) patients harboring amyloid precursor protein (APP) duplication or presenilin1 (PSEN1) mutation, compared to controls. The incidence of AD pathology was consistent amongst several fAD lines, which carried different mutations. Although these are complex assemblies of neural tissue, they are also highly amenable to experimental manipulation. We find that treatment of patient-derived organoids with ß- and γ-secretase inhibitors significantly reduces amyloid and tau pathology. Moreover, these results show the potential of this model system to greatly increase the translatability of pre-clinical drug discovery in AD.