Biology subjects

Vassar, R.

Publications and source records attributed to Vassar, R..

10 recordsLinked to original sources

bioRxiv2026

Neuronal overexpression of Nrf2 reduces dystrophic neurites in 5XFAD Alzheimer's disease model mice

BackgroundThe hallmark lesions of the Alzheimers disease (AD) brain are amyloid plaques consisting of the {beta}-amyloid protein and neurofibrillary tangles comprised of hyperphosphorylated, aggregated tau protein, which both cause neuronal dysfunction and loss. One goal of neuroprotective therapies is to maintain normal neuronal function and survival in the presence of toxic pathologies such as plaques and tangles. A potential neuroprotective target is nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor, which regulates the expression of many antioxidant and detoxification genes. Nrf2 mRNA is decreased in AD brains, and deletion of the Nrf2 gene causes increased BACE1 and A{beta} production and worsened cognitive deficits in amyloid pathology mouse models. Overexpression of Nrf2 in astrocytes has been shown to be protective against neurodegeneration, but the role of Nrf2 is neurons is unclear. MethodsWe overexpressed Nrf2 from birth in neurons of 5XFAD amyloid pathology model mice using AAV8, hypothesizing that neuronal Nrf2 overexpression decreases cortical neuron loss and reduces plaque load by decreasing BACE1 levels. We quantified protein levels by immunoblot and neuropathology by immunofluorescent staining, using two-way ANOVA to measure differences between genotypes and AAV treatments. To assess genetic changes, we performed bulk mRNA seq. ResultsWhile neuronal overexpression of Nrf2 in 5XFAD mice did not prevent neuronal loss as measured by NeuN labeling, decrease neuroinflammation by Iba1 or GFAP labeling, or reduce amyloid load by A{beta} antibody or methoxy-XO4 staining, we show that increased Nrf2 expression reduces BACE1 protein levels, especially in swollen axonal dystrophic neurites around amyloid plaques. Other proteins that accumulate in dystrophic neurites were also reduced, indicating decreased dystrophic neurites overall. Immunoblot analysis suggested increased autophagy was unlikely to play a role, while bulk mRNA sequencing indicated changes in lipid metabolism and microtubule stability may have contributed to reduced dystrophic neurite formation. ConclusionsDystrophic neurites impair action potential conductance and contribute to tau seeding and spreading. Their reduction by neuronal Nrf2 overexpression may protect neurons against these pathologic changes. Further study of the mechanisms by which Nrf2 reduces dystrophic neurites may lead to therapeutic strategies that can limit neuritic damage caused by cerebral amyloid accumulation.

neuroscience↗

bioRxiv2025

Influenza A infection accelerates disease-associated microglia formation during physiological aging

Severe pneumonia is associated with an increased risk of cognitive decline and dementia, particularly in the elderly. Changes in microglia, the most abundant immune cell population in the brain, are also associated with cognitive decline and dementia, including the emergence of a transcriptional cell state referred to as disease-associated microglia (DAM). We sought to test the hypothesis that non-neuroinvasive influenza A virus (IAV) pneumonia results in transcriptional responses in brain microglia that drive premature expansion of DAM. Using bulk and single-cell RNA-sequencing, metabolomics, and spatial transcriptomics, we profiled neuroimmune populations in young, middle-aged, and old male mice during IAV infection and recovery. We observed an increased abundance of DAM, interferon-responsive microglia (IRM), CD4+ T cells, and CD8+ T cells in white matter regions beginning in middle age and persisting in old animals, irrespective of IAV infection. DAM exhibited a metabolic shift toward aerobic glycolysis with disrupted TCA cycling, citrulline depletion, and an elevated itaconate/-ketoglutarate ratio. Spatial transcriptomic profiling of the human middle frontal gyrus (MFG) in normal agers, SuperAgers, and patients with dementia revealed an analogous accumulation of DAM and CD8+ T cells in white matter. IAV pneumonia induced a transient immunosenescent-like response in microglia, marked by glucocorticoid-responsive gene expression and Ccnd3 upregulation. In response to IAV pneumonia, DAM expanded in middle-aged mice, whereas old mice were elevated at baseline and were largely unaffected by IAV infection. The age-related expansion of DAM was unaffected by pharmacological depletion and repopulation of microglia with a CSF1R antagonist or genetic gain or loss of function of the phagocytic receptor MERTK, suggesting the DAM phenotype is driven by the CNS microenvironment, rather than cell-intrinsic mechanisms. Our findings suggest that IAV pneumonia induces an acute immunosenescence response in microglia and accelerates the age-dependent expansion of DAM in white matter.

neuroscience↗

bioRxiv2024

Levetiracetam prevents Aβ42 production through SV2a-dependent modulation of App processing in Alzheimer's disease models

In Alzheimers disease (AD), amyloid-beta (A{beta}) peptides are produced by proteolytic cleavage of the amyloid precursor protein (APP), which can occur during synaptic vesicle (SV) cycling at presynapses. Precisely how amyloidogenic APP processing may impair presynaptic proteostasis and how to therapeutically target this process remains poorly understood. Using App knock-in mouse models of early A{beta} pathology, we found proteins with hampered degradation accumulate at presynaptic sites. At this mild pathological stage, amyloidogenic processing leads to accumulation of A{beta}42 inside SVs. To explore if targeting SVs modulates A{beta} accumulation, we investigated levetiracetam (Lev), a SV-binding small molecule drug that has shown promise in mitigating AD-related pathologies despite its mechanism of action being unclear. We discovered Lev reduces A{beta}42 levels by decreasing amyloidogenic processing of APP in a SV2a-dependent manner. Lev corrects SV protein levels and cycling, which results in increased surface localization of APP, where it favors processing via the non-amyloidogenic pathway. Using metabolic stable isotopes and mass spectrometry we confirmed that Lev prevents the production of A{beta}42 in vivo. In transgenic mice with aggressive pathology, electrophysiological and immunofluorescent microscopy analyses revealed that Lev treatment reduces SV cycling and minimizes synapse loss. Finally, we found that human Down syndrome brains with early A{beta} pathology, have elevated levels of presynaptic proteins, confirming a comparable presynaptic deficit in human brains. Taken together, we report a mechanism that highlights the therapeutic potential of Lev to modify the early stages of AD and represent a promising strategy to prevent A{beta}42 pathology before irreversible damage occurs. One Sentence SummaryWe discovered that the SV-binding drug levetiracetam prevents A{beta}42 production by modulating SV cycling which alters APP localization and thus proteolytic processing, highlighting its therapeutic potential for AD.

neuroscience↗

bioRxiv2024

Selective suppression of oligodendrocyte-derived amyloid beta rescues neuronal dysfunction in Alzheimer's Disease

Reduction of amyloid beta (A{beta}) has been shown to be effective in treating Alzheimers Disease (AD), but the underlying assumption that neurons are the main source of pathogenic A{beta} is untested. Here we challenge this prevailing belief by demonstrating that oligodendrocytes are an important source of A{beta}, and play a key role in promoting abnormal neuronal hyperactivity in AD. We show that selectively suppressing oligodendrocyte A{beta} production improves AD brain pathology and restores neuronal function in vivo. Our findings suggest that targeting oligodendrocyte A{beta} production could be a promising therapeutic strategy for treating AD.

neuroscience↗

bioRxiv2024

ACE1 knockout in neurons selectively dysregulates the hippocampal renin angiotensin system and causes vascular loss

Angiotensin I converting enzyme (ACE1) maintains blood pressure homeostasis by converting angiotensin I (angI) into angiotensin II (angII) in the renin-angiotensin system (RAS). ACE1 is expressed in the brain, where an intrinsic RAS regulates complex cognitive functions including learning and memory. ACE1 has been implicated in neurodegenerative disorders including Alzheimers disease (AD) and Parkinsons disease (PD), but the mechanisms remain incompletely understood. Here, we performed single-nucleus RNA sequencing to characterize the expression RAS genes in the hippocampus and discovered that Ace is mostly expressed in CA region excitatory neurons. To gain a deeper understanding of the function of neuronal ACE1, we generated ACE1 conditional knockout (cKO) mice lacking ACE1 expression specifically in hippocampal and cortical excitatory neurons. Interestingly, ACE1 cKO mice exhibited hippocampus-dependent memory impairment in the Morris water maze, y-maze, and fear conditioning tests, but exhibited normal motor skills in rotarod. Total ACE1 level was significantly reduced in the cortex and hippocampus of ACE1 cKO mice showing that excitatory neurons are the predominant cell type expressing ACE1 in the forebrain. Despite similar reductions in total ACE1 level in both the hippocampus and cortex, the RAS pathway was dysregulated in the hippocampus only. Importantly, ACE cKO mice exhibited exacerbated age-related capillary loss selectively in the hippocampus. Here, we show selective vulnerability of the hippocampal microvasculature and RAS pathway to neuronal ACE1 knockout. Our results provide important insights into the function of ACE1 in the brain and demonstrate a connection between neuronal ACE and cerebrovascular function in the hippocampus.

neuroscience↗

bioRxiv2024

Cellular heterogeneity in the developing forebrain masks transcriptional outcomes and principles of Evf2 enhancer lncRNA-Dlx5/6UCE-gene guidance

During mouse embryonic brain development, the Evf2 ultraconserved enhancer (UCE) lncRNA guides the Dlx5/6UCE to [~]129 sites across chr6. However, previous work identified only 4 transcriptionally regulated targets associated with Evf2-Dlx5/6UCE enhancer-gene guided sites (EGGs), raising questions about the significance of the majority of Evf2-EGGs. Here, single cell transcriptomics (scRNAseq) shows that Evf2-EGGs on chr6 coincide with subpopulation-specific Evf2 transcriptional targets, revealing far greater alignment between EGGs and transcriptional targets than previously reported. Surprisingly, subpopulation-specific Evf2 regulated gene networks in embryonic progenitors predict adult synaptic and seizure defects. Evf2 regulation of EGGs to gene bodies (GB, Dlx5/6UCE locations within {+/-}5kb of the target gene) divides chr6 into short-range (<10Mb distant), highly activated genes, and long/super-long-range (10-129Mb), moderately repressed genes. Clustering of Evf2 transcriptionally regulated chr6 targets in populations where Evf2 is first activated supports that Evf2-EGG transcriptional effects can occur from EGG shifts as far as 3Mb, uncoupling enhancer shift distance and transcriptional direction from transcriptional outcome. Evf2 RNA binding sites (RBSs) divide chr6 into 4 major regions, consistent with a role for RBS chromosomal spacing in long-and super-long-range EGG selectivity. Surprisingly, 95% of 147 RBSs genome-wide potentially form inter-chromosomal DNA loops. Evf2-regulated combinatorial recruitment of Evf2-ribonucleoproteins at EGGs and RBSs, together with effects on homeodomain transcription factor DNA motif recognition, support a novel model of lncRNA directed multi-modal EGG selectivity during intra- and inter-chromosomal gene regulation.

molecular biology↗

bioRxiv2023

Oligodendrocytes and neurons contribute to amyloid-β deposition in Alzheimer's disease

In Alzheimers disease (AD), amyloid-{beta} (A{beta}) is thought to be of neuronal origin. However, in single-cell RNAseq datasets from mouse and human, we found transcripts of amyloid precursor protein (APP) and the amyloidogenic-processing machinery equally abundant in oligodendrocytes (OLs). By cell-type-specific deletion of Bace1 in a humanized knock-in AD model, APPNLGF, we demonstrate that almost a third of cortical A{beta} deposited in plaques is derived from OLs. However, excitatory projection neurons must provide a threshold level of A{beta} production for plaque deposition to occur and for oligodendroglial A{beta} to co-aggregate. Indeed, very few plaques are deposited in the absence of neuronally-derived A{beta}, although soluble A{beta} species are readily detected, especially in subcortical white matter. Our data identify OLs as a source of A{beta} in vivo and further underscore a non-linear relationship between cellular A{beta} production and resulting plaque formation. Ultimately, our observations are relevant for therapeutic strategies aimed at disease prevention in AD.

neuroscience↗

bioRxiv2023

Amyloid fibril proteomics of AD brains reveals modifiers of aggregation and toxicity

BackgroundThe accumulation of amyloid beta (A{beta}) peptides in fibrils is prerequisite for Alzheimers disease (AD). Our understanding of the proteins that promote A{beta} fibril formation and mediate neurotoxicity has been limited due to technical challenges in isolating pure amyloid fibrils from brain extracts. MethodsTo investigate how amyloid fibrils form and cause neurotoxicity in AD brain, we developed a robust biochemical strategy. We benchmarked the success of our purifications using electron microscopy, amyloid dyes, and a large panel of A{beta} immunoassays. Tandem mass-spectrometry based proteomic analysis workflows provided quantitative measures of the amyloid fibril proteome. These methods allowed us to compare amyloid fibril composition from human AD brains, three amyloid mouse models, transgenic A{beta}42 flies, and A{beta}42 seeded cultured neurons. ResultsAmyloid fibrils are primarily composed by A{beta}42 and unexpectedly harbor A{beta}38 but generally lack A{beta}40 peptides. Multidimensional quantitative proteomics allowed us to redefine the fibril proteome by identifying 17 new amyloid-associated proteins. Notably, we confirmed 126 previously reported plaque-associated proteins. We validated a panel of these proteins as bona fide amyloid-interacting proteins using antibodies and orthogonal proteomic analysis. One metal-binding chaperone metallothionein-3 is tightly associated with amyloid fibrils and modulates fibril formation in vitro. Lastly, we used a transgenic A{beta}42 fly model to test if knock down or over-expression of fibril-interacting gene homologues modifies neurotoxicity. Eight RNAi lines suppressed and 11 enhanced A{beta}42 toxicity. ConclusionsThese discoveries and subsequent confirmation indicate that fibril-associated proteins play a key role in amyloid formation and AD pathology.

neuroscience↗

bioRxiv2022

Death induced by survival gene elimination (DISE) contributes to neurotoxicity in Alzheimer's disease

Alzheimers disease (AD) is characterized by progressive neurodegeneration, but the specific events that cause cell death remain poorly understood. Death Induced by Survival gene Elimination (DISE) is a cell death mechanism mediated by short (s) RNAs acting through the RNA induced silencing complex (RISC). DISE is thus a form of RNA interference, in which G-rich 6mer seed sequences in the sRNAs (position 2-7) target hundreds of C-rich 6mer seed matches in genes essential for cell survival, resulting in the activation of cell death pathways. Here, using Argonaute precipitation and RNAseq (Ago-RP-Seq), we analyze RISC-bound sRNAs to quantify 6mer seed toxicity in several model systems. In mouse AD models and aging brain, in induced pluripotent stem cell-derived neurons from AD patients, and in cells exposed to A{beta}42 oligomers, RISC-bound sRNAs show a shift to more toxic 6mer seeds compared to controls. In contrast, in brains of "SuperAgers", humans over age 80 who have superior memory performance, RISC-bound sRNAs are shifted to more nontoxic 6mer seeds. Cells depleted of nontoxic sRNAs are sensitized to A{beta}42-induced cell death, and reintroducing nontoxic RNAs is protective. Altogether, the correlation between DISE and A{beta}42 toxicity suggests that increasing the levels of nontoxic miRNAs in the brain or blocking the activity of toxic RISC-bound sRNAs could ameliorate neurodegeneration.

neuroscience↗

bioRxiv2019

Astrocyte senescence in an Alzheimer’s disease mouse model is mediated by TGF-β1 and results in neurotoxicity

Alterations in astrocyte function such as a pro-inflammatory phenotype are associated with Alzheimers disease (AD). We had shown impairments in the ability of aged astrocytes isolated from 5xFAD mice to clear and uptake amyloid-{beta} (A{beta}) as well as to support neuronal growth. Senescent cells accumulate with age and exhibit a senescence-associated secretory phenotype, which includes secretion of pro-inflammatory cytokines. In this study, we predicted that with age, astrocytes in 5xFAD mice would exhibit a cellular senescence phenotype that could promote neurodegeneration. We found an age-dependent increase in senescent astrocytes adjacent to A{beta} plaques in 5xFAD mice. Inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells reduced interelukin-6 secretion by senescent astrocytes and resulted in improved neuronal support. Moreover, senescent astrocytes exhibited an increase in the induction of the TGF-{beta}1-SMAD2/3 pathway, and inhibition of this pathway resulted in a reduction of cellular senescence. We also discovered that soluble A{beta}42 induced astrocyte senescence in young naive mice in a SMAD2/3-dependent manner. Our results suggest an important role of astrocyte senescence in AD and its role in mediating the neurotoxicity properties of astrocytes in AD and related neurodegenerative diseases.

neuroscience↗