Alzheimer's Disease Neuropathology Research Articles

Mapping enhancer and chromatin accessibility landscapes charts the regulatory network of Alzheimer's disease

BackgroundEnhancers are regulatory elements that target and modulate gene expression and play a role in human health and disease. However, the roles of enhancer regulatory circuit abnormalities driven by epigenetic alterations in Alzheimer's disease (AD) are unclear. MethodsIn this study, a multiomic integrative analysis was performed to map enhancer and chromatin accessibility landscapes and identify regulatory network abnormalities in AD. We identified differentially methylated enhancers and constructed regulatory networks across brain regions using AD brain tissue samples. Through the integration of snATAC-seq and snRNA-seq datasets, we mapped enhancers with DNA methylation alterations (DMA) and chromatin accessibility landscapes. Core regulatory triplets that contributed to AD neuropathology in specific cell types were further prioritized. ResultsWe revealed widespread DNA methylation alterations (DMA) in the enhancers of AD patients across different brain regions. In addition, the genome-wide transcription factor (TF) binding profiles showed that enhancers with DMA are pervasively regulated by TFs. The TF-enhancer-gene regulatory network analysis identified core regulatory triplets that are associated with brain and immune cell proportions and play important roles in AD pathogenesis. Enhancer regulatory circuits with DMA exhibited distinct chromatin accessibility patterns, which were further characterized at single-cell resolutions. ConclusionsOur study comprehensively investigated DNA methylation-mediated regulatory circuit abnormalities and provided novel insights into the potential pathogenesis of AD.

Association between anxiety symptoms and Alzheimer’s disease biomarkers in cognitively healthy adults: A systematic review and meta‐analysis

AbstractBackgroundAnxiety has been identified as both a risk factor and prodromal symptom for Alzheimer’s disease (AD) and related dementias, however, the underlying neurobiological correlates remain unknown. The aim of this systematic review and meta‐analysis was to examine the association between anxiety symptoms and two defining markers of AD neuropathology: amyloid‐beta (Aβ) and tau.MethodSystematic literature searches were conducted across 5 databases. Studies investigating the relationship between anxiety and AD neuropathology (i.e., Aβ and/or tau) in cognitively healthy adults were eligible. Where possible, effect sizes were combined across studies, for Aβ and tau separately, using random‐effects meta‐analyses. Sensitivity analyses were performed to assess whether results differed according to anxiety type (i.e., state and trait) and biomarker assessment modality (i.e., positron emission tomography and cerebrospinal fluid). Between‐study heterogeneity was quantified using I 2 with 95% confidence intervals (CI), publication bias evaluated by examining funnel plots, and risk of bias assessed via the National Heart, Lung, and Blood Institute Quality Assessment Tool.ResultTwenty‐seven studies reporting data from 14 unique cohorts met eligibility criteria (Figure‐1). All studies received a quality rating of either ‘good’ (k = 15) or ‘fair’ (k = 12). Random‐effects meta‐analyses revealed no associations between self‐reported anxiety symptoms and either Aβ (13 studies, N = 5141; Fisher’s z = 0.02, 95% CI ‐0.01–0.05, p = 0.194 [Figure‐2]) or tau (4 studies, N = 1126; Fisher’s z = 0.04, 95% CI ‐0.02–0.09, p = 0.235 [Figure‐3]). There was no evidence of publication bias and heterogeneity was low (I 2 = 0.0%). Results remained substantively unchanged across sensitivity analyses assessing the effects of anxiety type and biomarker assessment modality.ConclusionIn cognitively healthy adults, meta‐analytic syntheses revealed no associations between anxiety symptoms and either Aβ or tau. There is a critical need, however, for larger studies with follow‐up periods to examine the effect of anxiety symptom onset, severity, and chronicity on AD neuropathology. An association between anxiety and dementia‐related neurobiological correlates is also likely complex, underpinned by multiple factors, and not restricted to AD neuropathology. Further research investigating other potential neurobiological correlates is crucial to advance understanding of the relationship between anxiety and dementia.

Clinical Manifestations.

Depression is increasingly recognized as a modulator of dementia risk and course, and is associated with multiple etiologies of cognitive decline. While it has been studied in clinically diagnosed cohorts, which may suffer from diagnostic error, there is less information in neuropathologically-defined subjects. We sought to define the depression prevalence and sex difference at mild cognitive impairment (MCI) and mild dementia in an autopsy-confirmed cohort of Alzheimer's disease (AD) and vascular neuropathology. Retrospective data was gathered from the National Alzheimer's Coordinating Center database on autopsy-confirmed cases of primary Alzheimer's disease (AD) and vascular neuropathology. Prevalence of depression was measured by the Geriatric Depression Scale score > = 5 during any visits at MCI (n = 364 AD cases, n = 51 vascular cases) and mild dementia (n = 557 AD cases, n = 24 vascular cases). We excluded those without pathology report, sex data or GDS results. Groups were compared via the chi-squared test. Depression prevalence was equal in MCI from AD and vascular neuropathology (27% in each, p = 0.9974). At mild dementia, depression was significantly more prevalent in vascular neuropathology compared to AD (37% versus 20%, p = 0.0363). In AD, at MCI there was no sex difference in depression prevalence (male 28% versus female 27%, p = 0.7560) but at mild dementia there was a female predominance (male 16% versus female 25%, p = 0.0075). In contrast, with vascular neuropathology, at MCI there was a trend for female predominance (male 21% versus female 33%, p = 0.3181) and no sex difference at mild dementia (male 38% versus female 36%, p = 0.9158). These results demonstrate that the prevalence of depression in cognitive disorders is driven by etiology, stage, and sex, which promotes further mechanistic studies on the interaction of these factors. Moreover, this illustrates the importance of depression screening in dementia, especially in females and those with suspected vascular etiology.

Examining sex differences in Alzheimer Disease neuropathology in Down Syndrome

AbstractBackgroundPeople with Down syndrome (DS) have a higher risk of developing Alzheimer disease (AD), due to an extra copy of the amyloid precursor protein (APP) gene on chromosome 21. Overexpression of APP is associated with increased production of amyloid beta (Aβ) in DS, and contributes to early onset of AD. Some studies suggest women with DS are at a higher risk for AD, while others find the opposite. Sex differences may be mediated by estrogen, which is critically involved in neuronal survival and modulation. We hypothesized that lower levels of ERα protein would correlate with increasing AD pathology in DS.MethodWe examined 35 brains (frontal and occipital cortices) of people with DS and DS with AD. Serial sections were immunostained for phosphorylated tau (pTau ‐AT8) and Aβ (6E10) along with ERα and quantified using QuPath. Spearman rank correlations using log transformed % load data were calculated, Kruskal‐Wallis was used to compare men and women.ResultNo significant differences in protein levels of ERα, Aβ, or tau were observed when comparing men and women with DS. However, we found higher levels of ERα protein were associated with higher levels of Aβ in the gray matter of the occipital cortex (R = 0.7078; p = 0.0005) in all cases. This positive correlation was driven primarily by women. Females with DS showed a significant positive association with Aβ and ERα (R = 0.93; p = 0.00012) whereas men showed a weaker trend (R = 0.62; p = 0.057). In contrast, no significant associations between ERα, Aβ or pTau were observed in the frontal cortex. PTau measures in the occipital cortex in women with DS were positively associated with ERα (R = 0.61; p = 0.055), whereas men with DS showed a slight negative, though not significant association (R = ‐0.29; p = 0.41). There was no such trend in the frontal cortex.ConclusionThese results suggest ERα, in contrast to our original hypothesis, may be increasing in response to AD pathology to preserve neuronal health in the occipital cortex. Lack of similar positive associations in the frontal cortex may be related to AD progression, with the occipital cortex being affected later in disease, giving us the opportunity to observe increased ERα.

History of infections is associated with smaller hippocampal volume in older women

AbstractBackgroundAccumulating evidence suggests that infections can play a major role in Alzheimer’s disease (AD), however, mechanism is unclear as multiple pathways may be involved. One possibility is that infections might contribute to AD directly by promoting neuronal death and neurodegeneration.MethodWe investigated the relationship between history of infectious diseases (a potential AD risk factor) and brain hippocampal volume, HV (a biomarker of neurodegeneration and AD neuropathology) in a subsample of the UK Biobank participants with respective information. Infectious disease diagnoses were based on ICD‐10 codes. The left/right HV was measured by the MRI. Analysis of variance (ANOVA) and Welch Two Sample t‐test were used to examine the statistical significance.ResultThe HV was significantly lower in older women (age 65+) with prior history of infections, compared to the same age women without such history (p‐value = 0.014 and 0.029, for the left and right HV, respectively). The effect size increased with age, and this increase was faster for the right vs. left HV. The difference in HV between male subjects with and without history of infections was not statistically significant.ConclusionIn this study, prior infections were significantly associated with the lower left/right HV in women aged 65+, which supports the role of infectious diseases in neurodegeneration and preclinical AD pathology in females. The effect size increased with age, in line with the increase in brain vulnerability to stressors due to aging. The faster increase for the right vs. left HV might indicate that females’ verbal memory declines faster with age compared to visual‐spatial memory, following the exposure to infectious disease, which deserves further investigation. The observed sex differences may reflect a higher vulnerability of the female brain to infection‐related factors, which in turn might contribute to the higher risk of AD in women compared to men.

Neuronal hyperexcitability in AD

AbstractBackgroundBecause neuronal and network deficits are the imperative immediate consequences of pathological changes of disease mechanisms, neurophysiological manifestations associated with Aβ and tau are uniquely positioned to demonstrate the abnormal homeostatic and maladaptive circuit alterations and the dynamic integrated effects of underlying genetics and neuropathological changes in Alzheimer’s disease (AD). Importantly, network dysfunction manifesting as abnormal hyper‐ as well as hypo‐active oscillatory brain rhythms is detectable even during the prodromal phase of disease. Here we leveraged the higher spatial and precise temporal resolution of Magnetoencephalography (MEG) to define frequency‐specific and region‐dependent patterns of oscillatory deficits in AD patients, and to demonstrate the earliest neurophysiological abnormalities associated with AD neuropathology and their mechanistic relationships to network hyperexcitability.MethodWe studied the resting brain oscillations in individuals with AD‐spectrum (n = 88) and age‐matched controls (n = 70) using MEG. In addition, subsets of participants were evaluated with positron emission tomography (PET) with Aβ and tau specific tracers and fluid biomarker including plasma P‐tau181 and Neuro‐Filament‐Light (NFL). We used statistical mixed models to investigate the associations between neural oscillations and pathology. We used a linear Neural‐Mass‐Model (NMM) in combination with empirical MEG spectra to derive the excitatory‐to‐inhibitory activity within neuronal subpopulations in AD patients. Based on standard neurophysiological monitoring we determined clinical evidence of hyperexcitability as AD with and without epileptiform activity (AD‐EPI+; AD‐EPI‐).ResultWhile increase and decrease of oscillatory activity are distinctly associated Aβ and tau, respectively, the characteristic frequency‐specific manifestation in AD was increased spectral signature within delta‐theta (2‐7Hz) and reduced spectral signature within alpha (8‐12Hz). Earliest spectral changes were detected in Aβ+ cognitively unimpaired and the increased spectral signature associated with Aβ was replicated in identical associations with plasma p‐tau181. The presence of APO‐E4 allele strengthened these associations. NMM demonstrated greater excitatory‐inhibitory‐activity in AD‐EPI+ vs. AD‐EPI‐ while these were specifically correlated with the reduced alpha spectrum which was more profound in AD‐EPI+ as well as uniquely associated with increased tau depositions.ConclusionOur results provide critical insights about potential mechanistic links between abnormal neural oscillations and cellular correlates of impaired excitatory and inhibitory synaptic functions associated with tau and Aβ, in patients with AD.

Signatures of abnormal deviations in excitation‐inhibition balance for amyloid positive individuals

AbstractBackgroundDysfunctional excitation‐inhibition balance (EIB) is hypothesized to precede cognitive impairment in Alzheimer’s disease (AD); however, overlapping neuropathology (like amyloid plaques) can develop in cognitively normal (CN) and impaired (CI) individuals. We investigate EIB trajectories for individuals with significant amyloid (Aβ+).MethodMultimodal imaging was used to construct hybrid resting‐state structural connectomes (Fortel, Igor, et al. Network Neuroscience 6.2 (2022): 420‐444.), computing whole‐brain EIB based on 105 ROIs. This cohort (N = 185, 94 Female) aged 55‐90 (μ FEMALES = 74.9, and μ MALES 73) was limited to Aβ+ individuals with APOE genotyping (ε3/ε3, ε3/ε4, ε4/ε4); grouped further by clinical dementia rating (CDR), with CDR > 0 indicating CI. Imaging, Aβ+ classifications, CDR, and APOE were obtained from OASIS‐3: Longitudinal Multimodal Neuroimaging: Principal Investigators: T. Benzinger, D. Marcus, J. Morris; NIH P30 AG066444, P50 AG00561, P30 NS09857781, P01 AG026276, P01 AG003991, R01 AG043434, UL1 TR000448, R01 EB009352. AV‐45 doses were provided by Avid Radiopharmaceuticals, a wholly owned subsidiary of Eli Lilly.ResultResults presented in Figure 1 suggest whole‐brain EIB in both CN sexes with Aβ+ decreases with increasing age (APOE‐ε4 agnostic). However, sex differences are highlighted with CI; regression analyses produce a marginally significant 4‐way interaction of age, sex, cognitive status, and APOE (P = 0.085, β = ‐0.013). Partial correlation of EIB with age, controlling for sex, APOE and cognitive status is also significant (P = 0.016, r = ‐0.18). Results indicate sex‐mediated EIB differences in individuals with CI, dominated by APOE‐ε4 in women rather than amyloid.ConclusionWe’ve demonstrated EIB deviations in cognitively impaired men and women that may be associated with AD neuropathology. Our findings are consistent with known AD sex differences and suggest novel multimodal connectomics may capture subtle disruptions in brain dynamics that traditional methods may not. Figure. 1. Whole‐brain excitation‐Inhibition balance (EIB) trajectories for amyloid positive (Aβ+) men and women. The cognitively normal (CN) group (rows A‐B) suggests no sex differences in EIB trajectories with age, while the cognitively impaired (CI) group (rows C‐D) begins to reveal distinct patterns of dysfunction (more significantly in women with APOE‐ε4). Note a value of 0.5 indicates perfect balance.

Single‐cell Transcriptomes Reveal Cell‐type Specific Roles of VEGF Family Genes in the Pathogenesis of Alzheimer’s Disease

AbstractBackgroundThe role of the vascular endothelial growth factors (VEGFs) in the pathogenesis of Alzheimer’s disease (AD) has been recently described, including notable changes along the VEGFB/FLT1 signaling pathway. Yet, cell‐specific alterations are not well characterized. To disentangle VEGFs’ cell‐specific effect on AD‐related traits, we performed association analyses of mRNA expression from 10 VEGF genes with cognitive performance and AD pathology in eight brain cell types using a large single nucleus RNA sequencing dataset from human brain.MethodThis project utilized recently published single‐cell transcriptomes derived from dorsolateral prefrontal cortex tissues of 424 donors collected at Rush Alzheimer’s Disease Center. Processed single cell RNA sequencing data were acquired from AD Knowledge Portal (syn2580853). Mean age at death was 89 years, 68% were females, and 37% were AD cases. Negative binomial lognormal mixed models implemented in the NEBULA R package were used to detect differential expression between AD cases and cognitively normal controls, and to analyze the associations with immunohistochemical amyloid and tangles, and finally to assess cross‐sectional and longitudinal global cognitive scores. Correction for multiple comparisons was completed using the false discovery rate procedure (Pfdr<0.05).ResultPrefrontal cortical FLT1 expression was upregulated in AD participants compared to cognitively normal controls in both endothelial (endo) and microglial (micro) cells. Higher micro‐FLT1, endo‐FLT4, and oligodendrocyte (oligo) VEGFB expression was associated with greater β‐amyloid burden in AD samples, whereas higher VEGFB expression in inhibitory neurons was associated with lower β‐amyloid burden. Higher expression of micro‐FLT1 and oligo‐VEGFB associated with worse cognitive trajectories. Higher micro‐ and endo‐ expression of FLT1 associated with lower cognition scores at the last clinic visit before death. Lastly, higher astrocyte‐expressed NRP1 was associated with lower tangle burden.ConclusionConsistent with our previously reported bulk tissue results, prefrontal cortical expression of FLT1 and FLT4 were associated with global cognition, longitudinal cognitive trajectories, and AD neuropathology, and these associations appear to be limited to endothelial and microglial cells. In contrast, VEGFB expression seems to have opposite effects on amyloid burden depending on the cell types, suggesting its more dynamic role in AD physiopathology.

Phosphorylated tau in the Down syndrome brain: Age related increases and comparison to late‐onset Alzheimer’s Disease

AbstractBackgroundIndividuals with Down Syndrome (DS) have an increased risk of developing Alzheimer’s Disease (AD) with nearly all individuals exhibiting neuropathological changes in the brain by age 40 years, and with a mean diagnosis of dementia by age ∼55 years. The purpose of this postmortem study was to characterize the age‐associated burden of several tau phosphorylation epitopes, including threonine (pT) 181, 217, and 231 by immunohistochemistry in the frontal cortex. We hypothesized that cerebral pT burden would increase with age in DS but not in controls and be higher in DS with AD neuropathology (DSAD) compared to late‐onset AD (LOAD).MethodWe examined 117 brains from: controls (non‐DS n = 53; ages 1‐91), DS without AD (n = 13; ages 1‐48), DSAD (n = 31; age 43‐68), and LOAD (n = 20; ages 63‐96). Serial sections from the frontal cortex were cut at 30µm and immunostained for phosphorylated tau pT181, pT217 and pT231. Whole slide images were digitized and analyzed by Aperio ImageScope software. The % area for each type of tau was quantified using positive pixel counts. Spearman rank correlations on log‐transformed data were used to test for positive age associations and t‐test was used to compare pT between DSAD and LOAD.ResultIn control cases, there was a positive correlation of age with pT181 (r = 0.47 p<0.001) but not with pT217 or pT231. In DS cases across the lifespan (DS and DSAD combined) displayed a positive correlation of age with pT181 (r = 0.70 p<.001), pT217 (r = 0.70 p<.001), and pT231 (r = 0.42 p = 0.005). DSAD cases had significantly higher pT181, pT217 and pT231 (p<.001) than late‐onset AD and control cases.ConclusionThese results suggest that tau phosphorylation for these epitopes is more positively correlated with age in people with DS than people without DS. Although pT181 increased with age in both cohorts, pT217 and pT231 showed a positive correlation with age in people with DS but not controls. Fluid biomarker studies focused on pTau in longitudinal cohorts of people with DS with subsequent brain donation will help reveal the link between peripheral and central pTau levels.

Alterations of Astrocytic Aquaporin 4 expression and distribution in Down Syndrome with Alzheimer’s Disease onset

AbstractBackgroundAstrocytic Aquaporin 4 (AQP4) is a water channel that is typically expressed in astrocytic endfeet, associated with the blood brain barrier (BBB). This association is thought to facilitate the removal of waste products (e.g. beta amyloid (Aβ)) via the ‘glymphatic system’. With Aβ plaque deposition in Alzheimer’s Disease (AD), AQP4 becomes dysregulated observed as a shift in distribution from astrocytic endfeet to astrocytic processes, resulting in inefficient Aβ removal. Here, AQP4 expression and distribution within astrocytes was characterized via immunohistochemistry in human brain tissue from people with Down Syndrome without AD (DS) and with AD (DSAD). We hypothesized that AQP4 protein level would be higher and distributed along astrocytic processes as opposed to the BBB in DSAD relative to DS.MethodAQP4 was evaluated by immunohistochemistry and quantified using QuPath (% loads, positive pixel count) for both frontal (FC) and occipital cortex (OC) in the following groups: DS (n = 17, age range = 0‐51) and DSAD (n = 20, age range = 46‐70). In addition, AQP4 distribution was classified by a blinded observer who annotated distinct AQP4 positive astrocytic morphologies, listed as follows: In WM, ‘Star,’ ‘Webbed,’ and ‘Stippled,’ and in GM, ‘Bushy,’ ‘Branched,’ ‘Globular,’ ‘Endfoot/Vascular Associated.’ResultWe show that AQP4 protein staining was higher in GM DS with AD neuropathology than in DS without AD neuropathology for both FC and OC (FC p = 0.0007; OC p = 0.0034). In addition, we observed a shift from ‘star’ shaped distribution within DS astrocytes to more ‘webbed’ and ‘stippled’ shapes in DSAD; this was not observed in OC. We found a shift in GM morphologies from ‘bushy’ morphology of AQP4 immunostaining in DS to more ‘Branched and Globular’ shapes in DSAD in OC whereas there is a shift from a ‘Bushy’ morphology in DS to more ‘Endfoot/Vascular Associated’ morphologies in the DSAD FC.ConclusionAQP4 expression is higher in DSAD than DS and appears to show a spectrum of astrocyte morphologies with distinct patterns based upon spatial location (FC/OC and GM/WM). Taken together, AQP4 dysfunction and shift to abnormal spatial location may reduce Aβ clearance through the glymphatic system, leading to enhanced plaque formation in DSAD.

Region‐Specific Associations of Human Astrocytic Endfoot Genes with Alzheimer’s Disease Neuropathology and Cognitive Decline

AbstractBackgroundWe completed a well‐powered bulk transcriptomic analysis of the astrocytic water channel aquaporin‐4 (AQP4) and related glymphatic molecules and discovered significant associations with Alzheimer’s disease (AD) neuropathological and cognitive outcomes. Genes included AQP4 and dystrophin‐associated complex components, namely DMD, DTNA, DAG1, and SNTA1, which encode proteins responsible for anchoring the AQP4 channel to the astrocytic endfoot membrane.MethodLeveraging regional brain RNA sequencing from the ROS/MAP dataset (Table 1), we determined the effects of transcript‐level variation on neuropathological outcomes at autopsy and longitudinal cognition using multiple linear regression models and mixed effects models, respectively. Discrete brain regions included: the dorsolateral prefrontal cortex (DLPFC, N = 921), caudate nucleus (CN, N = 705), and posterior cingulate cortex (PCC, N = 516). Square‐root transformed neuropathological measures of amyloid and tau burden at autopsy were quantified using immunohistochemistry. Cognitive performance was assessed longitudinally with global cognition calculated as a composite score derived from 19 neuropsychological tests. All model covariates included age at death, sex, educational attainment, and post‐mortem interval. Longitudinal models also included latency to death and the fixed and random effect of interval between current and last visit.ResultHigher AQP4 expression in the DLPFC related to higher amyloid pathology (β = 0.21, P.fdr = 0.04). Similarly, higher DTNA expression was associated with higher tau burden (βDLPFC = 0.36, P.fdrDLPFC = 0.008) and a faster rate of cognitive decline (βDLPFC = ‐0.036, P.fdrDLPFC = 0.0004; βPCC = ‐0.037, P.fdrPCC = 0.02). Higher SNTA1 in the CN related to a faster rate of cognitive decline (β = ‐0.038, P.fdr = 0.03). A summary of significant associations is presented in Table 2 and select plots are provided in Figure 2. AQP4, DTNA, and SNTA1 showed comparable associations with clinical AD in independent datasets within the AMP‐AD project (https://agora.adknowledgeportal.org/).ConclusionOur results indicate that gene expression at the AQP4‐dystrophin axis relates to both AD neuropathology and cognition, particularly in the prefrontal cortex. Future analyses will incorporate single‐nucleus measures of gene expression and cell‐type deconvolution to clarify cell‐type specific contributions in this pathway. Together, these results highlight a set of genes relevant to glymphatic function that should be prioritized for future mechanistic studies.

Glia response on Amyloid plaque microenvironment protects against pathological tau conversion in Alzheimer’s disease resilience

AbstractBackgroundAymptomatic Alzheimer’s disease (AsymAD) subjects have an intrinsic capacity to tolerate the presence of Aβ‐plaques and neurofibrillary tangles (NFTs) without developing cognitive impairment. In contrast to typical demented Alzheimer’s disease (AD) brains, AsymAD brains show distinct neuroinflammatory response and less accumulation of soluble pathological tau species at synaptic levels. The link between these observations and AD neuropathology is not fully understood, but increasing evidence suggests that the local plaque microenvironment plays a key role in the Aβ plaque‐associated tau pathogenesis. In this work we aim to identify the main molecular contributors of resiliency against amyloid and tau aggregation in AsymAD brains.MethodWe conducted a detailed histological and biochemical analysis using postmortem brain cortex samples from age‐matched controls (N = 21), demented AD (N = 22), and AsymAD subjects (N = 30). In fixed brain tissue, we performed the GeoMx whole spatial transcriptome atlas to compare the Aβ‐plaque microenvironment in AsymAD versus typical demented AD cases.ResultThere was no difference observed in the overall amyloid plaque burden between AsymAD and demented AD brains. However, immunofluorescence analyses indicates that AsymAD cases have the capability to form a glial barrier surrounding filamentous plaques, thereby avoiding the pathological conversion of tau. This observation is supported by biochemical analysis, which reveals that AsymAD cases have lower levels of high molecular weight tau and less seeding activity in soluble fractions. Using spatial whole transcriptomics to further characterize the plaque niche, we found an enrichment of migration signaling and autophagy in the AsymAD plaque niche, but not in AD. We are currently investigating the significance of these two molecular pathways in the Aβ plaque‐associated tau pathogenesis.ConclusionOur study provides new insights into the mechanism of Alzheimer’s disease resilience focus in the local Aβ plaque‐associated tau pathogenesis and potentials therapeutic approach to cognitive deterioration

Ante‐mortem magnetic resonance imaging grey‐white matter contrast regional signatures of Alzheimer’s disease neuropathology

AbstractBackgroundGrey matter (GM), white matter (WM) contrast (GWC) in T1‐weighted MRI has been shown to decrease with age in healthy populations and cognitive impairment in clinical Alzheimer’s Disease (AD). However, the neuropathological determinants of this signal remain unknown. Here, we aimed to study whether GWC is associated with AD neuropathology and longitudinal hippocampal atrophy.Method157 patients with neuropathological, clinical data and ante‐mortem MRI were selected from the National Alzheimer’s Coordinating Center database. Cortical volume and GWC (WM/GM intensity) in T1/MRI were obtained with Freesurfer 6.0. Hippocampal volume was divided into anterior, intermediate and posterior regions using a lab‐based algorithm. Correlational analysis was conducted for GWC with age, and GWC residuals after linear regression with age for volume, BRAAK stage (neurofibrillary tangles), CERAD score (neuritic plaque density) and Cognitive Dementia Rating Sum‐of‐Boxes (CDR‐SB). APOE genotypes were compared using one‐way‐ANOVA.ResultGWC was negatively correlated with age in widespread brain areas (p < 0.05, FDR), but only the entorhinal cortex showed a positive correlation between volume and GWC. There were no significant correlations between GWC and BRAAK stage, CERAD score, CDR‐SB or differences according to APOE genotype. Entorhinal GWC correlated positively only with the posterior hippocampal volume in BRAAK III‐IV.ConclusionGWC is highly modulated by age, but not by classical AD neuropathology, APOE genotype or dementia severity in this cohort. Entorhinal GWC correlates with entorhinal and posterior hippocampal volume, suggesting it might reflect an early pathophysiological process distinct from classical AD neuropathology.

Isoform characterisation & splicing signatures of AD‐risk genes using long‐read sequencing

AbstractBackgroundAn increasing number of studies implicate a role for alternative splicing in development and neuropathology of Alzheimer’s disease (AD). However, it has been historically challenging to characterise splicing events, due to the inherent limitations of traditional RNA‐sequencing (RNA‐Seq) to capture full‐length transcripts critical for transcriptome assembly. In this study, we use two complementary targeted long‐read sequencing approaches, Pacific Biosciences (PacBio) isoform sequencing (Iso‐Seq) and Oxford Nanopore Technologies (ONT) nanopore cDNA sequencing, to profile the cortex of a mouse model of tau pathology (rTg4510) with ultra‐deep sequencing of a panel of 20 genes robustly implicated in AD.MethodTargeted PacBio Iso‐Seq and targeted ONT profiling were performed on RNA isolated from 24 female rTg4510 transgenic and wild‐type mice, aged 2, 4, 6 and 8 months. Following successful enrichment for target genes using custom‐designed probes (IDT), library preparation were performed for subsequent sequencing on Sequel and MinION. The panel of genes selected for enrichment included genes (i.e. App, Mapt, Snca) and dementia risk genes identified from GWAS analyses. Raw sequence data was processed using a customised bioinformatics, and full‐length reads were merged and annotated with our developed custom scripts (FICLE).ResultWe identify thousands of novel transcripts across the panel of 20 AD‐ and dementia‐associated genes. We reveal unprecedented diversity of alternatively‐spliced isoforms with widespread usage of alternative novel 5’ and 3’ splice sites. We further robust transcriptional and splicing differences in these AD‐risk genes associated with the development of tau pathology. Among these changes, we observed global up‐regulation of Trem2‐associated isoforms and isoform switches in Bin1, further supporting a role for the dysregulation of the immune response in the development of AD pathology.ConclusionThis represents the first study to comprehensively assess variable AS associated with the development of tau pathology using both PacBio Iso‐Seq and ONT nanopore sequencing. Our analyses confirm the importance of alternative RNA splicing in AD and identify evidence of differential transcript usage, even in the absence of gene‐level expression alterations. Further work will be undertaken to validate and functionally characterise these novel isoforms, and to extend these analyses to human post‐mortem AD brain samples.

The decline of quantitative EEG goes along with neuropathology in Alzheimer’s Disease

AbstractBackgroundFew studies investigate the correlation between the quantitative EEG (QEEG) and the neuropathological picture. The purpose of this study is to explore how QEEG can recognize the type and extent of neuropathological changes.MethodThe EEG traces and brains belonging to 14 donors of the Abbiategrasso Brain Bank were analyzed. The subjects suffered from neurocognitive disorders due to AD, LBD or AD/vascular lesions (mixed dementia‐MD), with different stages of clinical and neuropathological severity. Clinical and neuropathological characterization was performed according to our protocol; biochemical measurements to determine the amount of proteinopathies are in runtime on frozen samples. QEEG analysis considered the relative power distribution (RPD) of the frequency bands (β, α, θ, δ) and the peak frequency (PF), i.e. the most represented frequency considering all the leads. The PF was measured every 2 seconds for 200‐400 samples, and then averaged. The Kruskall‐Wallis test was used for the comparison between groups.ResultThe clinical diagnosis included: 2 MCI, 4 AD, 6 MD, and 2 LBD. The neuropathological definite diagnosis demonstrated frequent co‐pathologies, and some discrepancies compared to the clinical diagnosis. The neuropathological characterization identified 2 cases with low AD pathology (corresponding to the 2 MCI), 8 cases with intermediate or high AD pathology (4 MD with concomitant cerebrovascular disease), and 4 cases with prevalent LBD pathology. Considering both clinical and neuropathological diagnoses, the comparison between groups revealed no significant differences in QEEG parameters. Nonetheless, a trend emerges towards a lower β‐RPD and a higher θ‐RPD in cases with prevalent LBD pathology. Grouping based on the severity of AD pathology (2 low, 4 intermediate, 4 high) demonstrated significant differences depending upon the neuropathological scoring with a progressive decrease of α‐RPD (p = 0.029) and PF (p = 0.019), and an increase of δ‐RPD (p = 0.020).ConclusionRPD and PF show low discriminatory capacity on etiology. Nonetheless, the presence of LBD seems to boost the EEG slowing. The PF slowing down parallels the increase of AD pathology, representing an indicator for the degenerative load. PF is a simple QEEG parameter, easily obtainable through standard digital EEG; it can be useful for monitoring neurodegenerative burden and disease evolution.

Interhemispheric EEG Coincidence during REM sleep correlates with mild cognitive impairment

AbstractBackgroundThere exists a bidirectional relationship between sleep disruption and neuropathology in Alzheimer’s disease (AD). Interhemispheric EEG coincidence during sleep polysomnography (PSG) may reflect coordination of brain networks. While several EEG features of non‐REM (NREM) sleep, such as slow wave activity, are associated with proteins and measures related to AD pathogenesis, less is known about EEG features of rapid eye‐movement (REM) sleep in AD. We assessed EEG features across hemispheres during REM, NREM, and wake states, comparing participants with mild cognitive impairment to cognitively‐normal participants.MethodEEG was collected during an attended overnight polysomnogram from the Biomarkers of Alzheimer’s Disease in Sleep and EEG (BASE) cohort (n = 87, average age 70.7 ± 4.6 years), 19 of whom had Clinical Dementia Rating (CDR) of 0.5, considered Mild Cognitive Impairment (MCI) and the rest healthy controls (HC). A custom low frequency (0.5 – 8Hz) EEG oscillatory peak detector was implemented in MATLAB across six EEG leads (F3, F4, C3, C4, O1, and O2). Interhemispheric EEG coincidence between lead pairs was calculated as the number of mini‐epochs with oscillatory peaks in both leads divided by the number of mini‐epochs with a peak in either or both leads.ResultNeither sleep macro‐architecture (total time in any stage of sleep, wake after sleep onset, number of awakenings and sleep efficiency) nor spectral power density in delta or theta frequency bands differed between HC and MCI groups. Interhemispheric EEG coincidence was reduced during REM sleep in F3‐F4 (Frontal), C3‐C4 (Central) and O1‐O2 (Occipital) lead pairs in the MCI group compared to HC, all regions p<0.0001. REM F3‐F4 coincidence was negatively correlated with nighttime awakenings (r ‐0.4, p<0.0001). Performance on the Word‐Pair Task, which measures memory, was correlated with REM F3‐F4, C3‐C4, and O1‐O2 coincidence (r0.29 p0.009; r0.27 p0.01; r0.25 p0.03, respectively).ConclusionA novel neurophysiological marker of interhemispheric EEG coincidence, specific to lower frequency spectra during REM sleep, differentiates MCI from HC and correlates to memory performance. Interhemispheric EEG coincidence may reflect coordination of brain networks during REM and may be sensitive to changes in cognitive status that would otherwise go undetected by traditional analyses of sleep macro‐architecture.

Neuropathological characterization of PiB binding in postmortem striatum in Down syndrome

AbstractBackgroundAmyloid‐beta plaques form in the brain throughout life in people with Down syndrome (DS) and are one of the hallmarks of Alzheimer disease (AD) neuropathology. The regional progression of amyloid buildup in DS is similar to that of late onset AD (LOAD) in the neurotypical population. The development of positron emission tomography (PET) ligands like Pittsburgh Compound B (PiB) has allowed researchers and clinicians to visualize and track amyloid accumulation in the brain throughout life. Using this technology, a unique pattern emerges in people with DS, where the earliest and strongest PiB PET retention is in the striatum, unlike LOAD but similar to autosomal dominant AD. Frontal cortex PiB PET retention is similar in all groups. We used a fluorescent derivative of PiB, cyano‐PiB (CN‐PiB), to investigate PiB labeling postmortem in DS striatum. We hypothesized that striatal CN‐PiB load increases with age and is greater than in the frontal cortex, similar to observations from PiB PET studies of adults with DS.MethodWe conducted CN‐PiB labeling in postmortem striatum and frontal cortex from 44 cases with DS ages ranging from 42 to 70 years (25F/19M, mean PMI 7.4 hours). Whole slide imaging and automated image analysis were used to derive individual plaque‐level information regarding load, size, and distribution of CN‐PiB+ plaques in DS with age.ResultCN‐PiB labeled plaques in both the striatum and frontal cortex were also positive for amyloid‐beta antibodies targeting epitopes 1‐16, 17‐24, and x‐42. Preliminary data suggest that striatal CN‐PiB load (median = 2.3%) is not higher compared to the frontal cortex in DS (median = 10%). Striatal CN‐PiB load did not change with age from 42 to 70 years, suggesting an early saturation (IQR = 3.5%).ConclusionCN‐PiB labeled amyloid‐beta plaque load in the striatum in DS is comparable to conventional neuropathologic analysis and does not differ from frontal cortical load. Other aspects of PiB‐binding or pathologies may contribute to the early and prominent striatal PiB PET retention reported in DS. It will be important in future studies to include younger cases with DS.

The cytoskeletal protein Plectin regulates Tau‐induced neurotoxicity in Alzheimer’s Disease

AbstractBackgroundThe genetic causes for most cases of Alzheimer’s disease (AD) and the underlying biology of pathogenesis remain unknown. Recent large scale proteomics studies on AD patient brains have identified novel protein networks and targets that are highly correlated with AD diagnosis and neuropathology. The most significantly AD‐correlated protein network identified contains the cytoskeletal protein Plectin (PLEC) as a network hub. PLEC functions to crosslink different cytoskeletal components and plays a role in axonal transport of synaptic proteins. Considering that microtubule associated protein‐Tau (MAPT) dysfunction is an AD hallmark, we hypothesize that PLEC dysfunction increases AD susceptibility by disrupting cytoskeletal homeostasis and synaptic function.MethodUtilizing a combination of genetic and proteomic analyses, we validate Plectin as a potential AD risk factor. We assessed the role of PLEC in Tau‐induced neurotoxicity in the animal model Drosophila melanogaster and human neuronal cell culture. Furthermore, we have also elucidated PLEC mutant neurodegenerative phenotypes independent of Tau overexpression in the fly. Immunoprecipitation‐mass spectrometry (IP‐MS) analysis was performed to define a Drosophila Plectin protein‐protein interaction network in adult brains. This network will serve as the basis for cross‐species analysis of protein networks.ResultThe Drosophila homolog of Plectin (dPLEC) is ubiquitously expressed within the adult brain with strong enrichment in neuronal rich tissues. Using Drosophila models of human tauopathy, dPLEC regulates age dependent Tau‐induced neurotoxicity and locomotor dysfunction. Plus, altering levels dPLEC regulates Tau‐phosphorylation in both adult Drosophila brains and human neurons. In the absence of Tau overexpression, dPLEC functions in light‐induced neuronal transmission confirming its role in normal neuronal function. Continued mechanistic analysis in both Drosophila and human neuronal cultures will determine PLEC’s role in AD neuropathogenesis and elucidate the underlying role of the cytoskeleton in AD susceptibility. To that end, we generated an endogenous GFP‐tagged dPLEC (dPLEC‐GFP) and performed immunoprecipitation‐mass spectrometry (IP‐MS) analysis to identify dPLEC protein interactors. Several cytoskeletal and synaptic proteins were identified and are currently being tested for their role in Tau‐induced neurodegeneration and synaptic dysfunction.ConclusionWe functionally validate the AD target PLEC as a regulator of Tau‐induced neurodegeneration and identify PLEC as a regulator of Tau dynamics and neuronal function.

Anabolic Androgenic Steroid predisposes to the neuropathology of Alzheimer’s disease: insights from Animal model

AbstractBackgroundAnabolic androgenic steroids (AASs) are synthetic derivatives of testosterone use for body enhancement by athletes and its use has been abused over the years. Various studies have reported the harmful potential of AAS use, however, there is need to document its possibility as a risk factor in neuropathology of dementia. This study is to demonstrate potential of AAS as a risk factor in Alzheimer’s disease (AD) pathology by demonstrating changes in the neuro‐morphology, astrocytic proliferation and neurofibrillary tangle formation in animal model.MethodTwenty (20) adult male Wistar rats used were divided into four groups (A‐D), treated as follows, Control (A), Olive oil as vehicle (B), oral 120mg/kg of AAS for 21days (C), and 7 days withdrawal group following 120mg/kg/ 21days of AAS intake (D). Serum was assayed for lipid peroxidation marker Malondialdehyde (MDA) and antioxidant enzyme ‐superoxide Dismutase (SOD). The prefrontal cortices were processed and stained for Nissl (chromatophilic) bodies, astrocytes immunohistochemistry and Bielschowsky stain for neurofibrillary tangles.ResultAAS treated group has characteristic pathology of AD demonstrated by the presence of necrosis, chromatolysis, marked astrocytic proliferation and presence of neurofibrillary tangles using Bielschowsky stain along with an increase in MDA and decline in endogenous SOD activities as compared with the control and olive oil treated groups. The withdrawal group (D) had a notable or mild restoration of the neurons demonstrated by presence of few necrotic neurons, reduced reactive astrocytes (astrogliosis) proliferation, decline in MDA with an increase in SOD when compared to the AAS treated group.ConclusionAAS has the potential to predispose individual to the neuropathology of AD characterized by neurodegeneration, astrogliosis, neurofibrillary tangles even in the presence of endogenous antioxidant enzyme, however, upon discontinuation endogenous antioxidant enzyme level increases enabling neuro repair via mobbing off free radicals generated by AAS.

TREM2 Agonism Affects Human Microglia Response in the Presence of Amyloid Pathology In Vivo

AbstractBackgroundPharmacological activation of TREM2 represents a novel therapeutic approach to slow Alzheimer´s disease (AD) progression. Mutations in microglial gene, TREM2, confers increased risk to developing late‐onset AD. Moreover, animal studies demonstrate the loss‐of‐of function variants or complete absence of Trem2 aggravates amyloid pathology. Genetic ablation of TREM2 function has been shown to lock microglia in a homeostatic state, preventing a switch to the disease‐associated state supporting the phagocytic clearance of misfolded proteins and cellular debris. Due to low gene sequence and protein structure homology between mouse and human TREM2, as well as phenotypical disparities between mouse and human microglia, monitoring the impact of TREM2 activation in vivo requires humanized animal models.MethodHere we studied the impact of TREM2 agonism on xenografted human microglia in a mouse model of amyloid pathology. We systematically treated 7‐month‐old transgenic AppNL‐G‐F mice transplanted with human embryonic‐stem‐cell‐derived microglia with TREM2 small molecule agonists. Human microglia were sorted from the brain and subsequently assessed using multi‐omics technologies.ResultThe activation of TREM2 lead to increased expression of cytokines and chemokines in xenografted human microglia in the presence of amyloid pathology in AppNL‐G‐F, but not in wild‐type mice. Other changes in the transcriptome profile indicated shifts in microglia populations in TREM2‐agonist‐treated AppNL‐G‐F mice. These effects were observed at exposures consistent with activation of TREM2 in vitro assessed by pSYK and sTREM2 levels.ConclusionAll together, we show the human microglia xenograft mouse model is a valuable tool to study the impact of pharmacological TREM2 activation in the presence of AD neuropathology.