Citations

AbstractBackgroundBlood‐based biomarkers of amyloid and neurodegeneration are increasingly used in clinical trials and entering clinical use. Differentially mapping the plasma markers to post‐mortem neuropathology in a community‐based sample is critical for interpretation.MethodWe identified 64 Mayo Clinic Study of Aging (MCSA) participants with antemortem plasma markers (Aβ42, Aβ40, NfL, T‐tau, Aβ42/40 ratio) measured on the Quanterix Simoa HD‐1 analyzer and with postmortem neuropathologic assessments of Alzheimer’s pathology (Braak tangle stage, Thal phase, neuritic plaque burden) and cerebrovascular pathology (Strozyk scale focused on macrovascular brain changes and Kalaria scale focused on detailed micro‐ and macro‐ vascular brain changes). Weighted linear regression models with adjustment for time between plasma markers and death were conducted with exact permutation tests to evaluate the relationships between antemortem plasma and postmortem neuropathology markers.ResultHigher plasma NfL levels and Aβ42/40 ratio were associated with both cerebrovascular neuropathologic scales (p<0.05) but were not associated with Braak neurofibrillary tangle stage, neuritic plaque score, or Thal stage (p>0.5). Plasma T‐tau was not associated with any pathological assessment. Plasma Aβ42/40 and NfL explained up to 18% of the variability in cerebrovascular neuropathologic scales.ConclusionIn this community sample of participants predominantly without dementia, plasma markers for amyloid (Aβ42/40) and neurodegeneration (NfL) were associated with cerebrovascular neuropathology at autopsy. NfL is a non‐specific marker of brain injury, therefore, its association with cerebrovascular neuropathology was in the expected direction. The association between greater cerebrovascular neuropathology and elevated Aβ42/40 requires further investigation. These findings provide evidence that cerebrovascular disease may significantly influence levels of plasma biomarkers proposed for Alzheimer’s disease. This information will be important to consider for accurate clinical interpretation of the proposed biomarkers.

AbstractBackgroundThe coarse‐grained plaque (CGP) is a divergent plaque‐type recently described in Alzheimer’s disease (AD)1. In the current study, we studied the CGPs distribution over the brain, and its association with APOE, p‐tau, and neuroinflammation.MethodThe cohort (N = 60) was selected from the Mayo Clinic brain bank in Jacksonville, USA. Brain tissue from the frontal ‐, parietal ‐, temporal cortex, and the hippocampus was immunohistochemically stained for Aβ (6F/3D), p‐tau (AT8), CD68, and GFAP. The CGP and classic cored plaque (CCP) were scored as previously described1. Total plaque burden was expressed as the sum of all cortical regions.ResultThe CGP was predominantly located in the neocortex and present in ∼60% of AD cases, who were younger at onset (p<0.05) and had a lower brain weight (p<0.05) than CGP negative cases. When stratified for APOE Ɛ4+ and Ɛ4‐, CGP burden was only in Ɛ4+ positively correlated with p‐tau, Aβ, and GFAP burden in the frontal and parietal cortex (Table 1). CGP burden was not correlated with CD68. The CCP was negatively correlated with p‐tau, and not with GFAP, Aβ or CD68 (Table 1). In APOE Ɛ4+ cases, the burden of CGPs was negatively correlated with the burden of CCPs (Fig.1).ConclusionThe neocortical CGP is correlated with increased p‐tau burden and astrogliosis in APOE Ɛ4+. The CGP is inversely correlated with the common CCP, suggesting an opposite effect of Aβ‐induced tau‐toxicity for the CGP versus the CCP. 1Boon et al., Acta Neuropathologica, 2020

AbstractBackgroundWe previously demonstrated that Alzheimer’s disease (AD) patients ≥70 y/o tend to have smaller medial temporal volumes in the presence of relatively less medial temporal 18F‐flortaucipir‐PET uptake compared to young AD patients. TAR DNA‐binding protein 43 (TDP‐43) is frequently found in the brains of AD patients and is associated with old age and medial temporal atrophy. In this study, we aimed to determine whether TDP‐43 could be contributing to the mismatch between medial temporal volumes and flortaucipir‐PET uptake in older AD patients.MethodWe identified 77 participants (median age at death 79 years [range: 51‐99]) who had been enrolled into the Mayo Clinic Alzheimer’s Disease Research Center or Neurodegenerative Research Group (NRG), had undergone flortaucipir‐PET and volumetric MRI scans close to death, and autopsy confirmed AD neuropathological changes, as well as TDP‐43 assessments. Grey matter volumes and flortaucipir standard uptake value ratios (SUVRs) were calculated for hippocampus, amygdala, entorhinal, inferior temporal, and midfrontal cortices. We used bivariate‐response linear regression modelling, adjusting for Braak neurofibrillary tangle stage, to estimate the effect of TDP‐43 and age on gray matter volume and flortaucipir uptake, and tested whether TDP‐43 effect sizes varied according to age.ResultAfter accounting for Braak stage, older individuals tended to have significantly lower flortaucipir uptake across regions and lower hippocampal and entorhinal cortex (ERC) volumes. TDP‐43 was associated with reduced hippocampus and ERC volumes but was unrelated to flortaucipir SUVRs (Figure 1). Notably, the TDP‐43 effect size for the hippocampus and ERC was largely consistent across age, i.e., at any age, TDP‐43‐positive participants had significantly smaller hippocampal (∼12% decrease) and ERC (13% decrease) volumes than TDP‐43‐negative participants. However, at older ages, the mean volumes in the whole cohort and, more evidently, in those with dementia moved closer towards the mean of those with TDP‐43 (Figure 1), likely attributable to the increasing frequency of TDP‐43 with age.ConclusionTDP‐43 is a major contributor to the mismatch between flortaucipir uptake and medial temporal lobe volumes in older AD patients where lower medial temporal regional volumes are observed in the presence of less flortaucipir uptake.

AbstractBackgroundTDP‐43 is a nuclear RNA‐binding protein involved in various neurodegenerative diseases, including Alzheimer’s Disease (AD), and normal aging. It strongly affects cognition and memory loss in AD. Concomitant TDP‐43 pathology increases the likelihood of being cognitively impaired at death.MethodMayo Clinic has amassed a large database with 1072 study participants with known TDP‐43 pathology status, who were prospectively recruited and followed in the Mayo Clinic Alzheimer’s Disease Research Center, Mayo Clinic Study of Aging, and Neurodegenerative Research Group. All underwent neurologic, genetic, and neuropathologic evaluations. Amygdala sections immunostained with antibodies against TDP‐43 were screened for TDP‐43‐immunoreactive inclusions and successively staged using the Josephs staging scheme. The frequency of TDP‐43 pathology by age at death was estimated using logistic regression with age modelled using a restricted cubic spline. Models were fit for all cases including the subset of 581 cases with dementia.ResultOur cohort was predominantly White (99%) with median age at death of 87 years (IQR: 80‐92) and relatively even sex distribution (52% female). About 55% had Braak stage V‐VI and 61% had Thal amyloid phase ≥3. Fifty‐two percent met criteria for intermediate‐high probability AD. TDP‐43‐immunoreactivity (TDP‐43+) was detected in 44% with median TDP‐43 stage of 3 (IQR: 1‐5), and in 54% with a median stage of 3 (IQR: 2‐5) in those with dementia. TDP‐43+ frequency increased approximately linearly with age at death. At 70 years at death, an estimated 30% (95% CI: 25–35) of the cohort was TDP‐43+ versus 33% (CI: 27–40) of those with dementia. By 90 years at death, 49% (CI: 45–52) of the overall cohort and 68% (CI:62‐73) of those with dementia were TDP‐43+.ConclusionThe results from our large cohort confirm that TDP‐43 pathology frequency increases in elderly White study participants with age of death, independent of cognitive status. Furthermore, TDP‐43 pathology frequency increases to a greater degree with age in those with dementia. Given the clear links between TDP‐43 and impaired cognition, the contribution of TDP‐43 to an individual’s cognitive impairment is likely to increase with age; a dynamic with significant public health consequences given our aging population.

AbstractBackgroundMost series exploring the causes of rapidly progressive dementia (RPD) rely on clinical diagnoses, with limited pathological confirmation. This approach may underestimate the contributions of Alzheimer disease and related dementias to RPD, recognizing challenges associated with extrapolating clinical phenotypes to neuropathological diagnoses. A clearer understanding of the neuropathological causes of RPD is needed to inform the diagnosis and treatment of patients. To meet this need, we determined the neuropathological causes of RPD within the Mayo Clinic neurodegenerative brain bank.MethodPatients with disease duration <4.0 years (symptom‐onset to death due to dementia) were identified within the Mayo Clinic neurodegenerative brain bank (1998‐2020). Available clinical records were reviewed, and details extracted including demographics, family history, dominant symptoms/signs at onset, and common comorbidities (depression, psychoses, sleep disturbance). Neuropathological diagnoses were assigned following standard protocols.Result310/8586 (3.6%) cases met RPD criteria. Relative to typically progressive cases, prion disease most commonly presented as RPD (74%, 32/43), followed by progressive supranuclear palsy/corticobasal degeneration (PSP/CBD: 7.5%, 142/1894), other frontotemporal lobar degeneration (FTLD: 5.7%, 32/561), Lewy body disease (LBD: 4.1%, 49/1202), and Alzheimer disease (AD: 1.8%, 48/2687). Average age‐at‐symptom onset was 69.5±10.4 years. Patients with rapidly progressive AD were older than others (p<0.01), except LBD. Patients with FTLD were younger than others (p<0.05), except prion disease. Average disease duration was 2.9±1.0 years: prion diseases had the most rapid disease course (1.6±1.3 years). Comorbid cerebrovascular disease (25.5%), and clinically symptomatic depression (41.3%), psychoses (37.1%) and sleep disturbances (39.4%) were common across groups. Only psychosis was associated with shorter disease duration (β=‐0.31 years, CI95% [‐0.53, ‐0.082]; controlling for age‐at‐symptom onset).ConclusionRapidly progressive neurodegenerative diseases accounted for 3.6% of cases in this neurodegenerative brain bank. Although prion disease commonly presented as RPD, atypical presentations of more prevalent neurodegenerative diseases accounted for most cases. Atypical (rapidly progressive) variants of typical neurodegenerative diseases warrant consideration in clinical practice.

AbstractBackgroundNeurofibrillary tangles are dynamic entities with a lifespan encompassing three maturity levels: intracellular pretangles, intracellular mature tangles, and extracellular ghost tangles. Proteins are suggested to be differentially expressed throughout the tangle lifespan; however, past studies may be limited by spatial expression or number of proteins investigated. We sought to assess differences in protein expression across the tangle lifespan using GeoMxTM Digital Spatial Profiler (DSP) by NanoString, a new technology allowing for spatially derived multiplex investigation.MethodWe used DSP to measure protein expression in hippocampi from Alzheimer’s disease (n=6) and nondemented controls (n=2) using the “Human Neural Cell Profiling Core” and “Alzheimer’s Pathology” module. Regions of interest (ROIs) were classified by the major tangle maturity level recognized by a primary fluorescent conjugated tau antibody. Protein expression was normalized to the geomean of the three housekeeping genes. The tau‐positive segment was specifically analyzed for comparisons. ANOVA was used for group‐wise comparisons and t‐test using the Benjamini‐Yekutieli adjustment for multiple tests was used for pair‐wise comparisons.ResultAs expected, cytoskeletal (e.g., MAP2, Tau) and neuronal (e.g., NeuN) markers generally decreased through the neurofibrillary tangle lifespan (Figure). Markers profiled as neurodegenerative (e.g., amyloid‐β1‐42, APOE, APP) generally increased through tangle maturity levels, except for TDP‐43 which decreased. Interestingly, there was no significant difference in ubiquitin expression. Astrocytic GFAP and S100B expression was significantly increased through each maturity level. Expression of microglial‐specific markers P2RY12 and TMEM119 was significantly elevated in ghost tangles compared to mature tangles. Additional microglial/macrophage markers including Iba‐1 and CD68 were generally increased as neurofibrillary tangles matured. Interestingly, APOE expression remained low in pretangles and mature tangles before dramatically increasing in ghost tangles (Figure).ConclusionOur findings suggest that proteins are differentially expressed throughout the tangle lifespan and the majority followed a monotonically directed pattern. Non‐monotonically directed protein patterns may reflect the death of the neuron during the ghost tangle maturity level. Future studies will test the hypothesis that the microenvironment of the hippocampus is altered with increasing vulnerability to tangle pathology.

AbstractBackgroundCognitive resilience, the discrepancy observed in individuals with high Alzheimer’s disease (AD) neuropathology and near‐normal cognition, is a growing area of study, wherein multiple factors are responsible. Currently, the role of the microglial activation in cognitive resilience is unknown. Herein described is a case report characterizing the amyloid responsive microglia (ARM) in an 88‐year‐old male decedent homozygous for APOE E4, clinically cognitively intact, and found to have AD neuropathologic change (ADNC) upon autopsy.MethodThe participant was enrolled in the Mayo Clinic Study of Aging (MCSA) and continuously followed for 14 years from 73‐ to 87‐years‐old, wherein serial MRI and clinical assessments were obtained. An autopsy was performed upon death, and routine neuropathologic sections were taken. Formalin‐fixed, paraffin‐embedded sections were stained with H&E, and single immunohistochemistry was performed using antibodies against tau (AT8), beta‐amyloid (6F3D), alpha‐synuclein (LB509), TDP‐43 (pS409/410), and CD163 (10D6). Digital image analysis was performed on dorsolateral prefrontal cortex sections scanned at 40x (Leica GT450). ARM (CD163% area) and beta‐amyloid (% area) measurements were obtained using QuPath threshold classifiers. Descriptive statistics were performed (Graphpad).ResultThe decedent was an 88‐year‐old male, homozygous for APOE E4, with a history of three cardiovascular and metabolic conditions, and lifelong smoking. His MMSE (average 28/30) and global cognition (average ‐0.51) were relatively stable (Figure 1), with no clinical concerns for cognitive impairment. Cortical thickness was normal (temporal meta‐ROI>3 mm) on four serial MRIs. The participant reported high cognitive, physical activities, and education‐occupation scores (upper quartile for the 70+ population). Neuropathologic evaluation was notable for severe cerebral amyloid angiopathy, high ADNC (A3B3C3), and remote microinfarcts. CD163‐positive ARM were observed in the neocortices and perivascular spaces, and the ARM:beta‐amyloid ratio was 0.26 (Figure 1). This ARM:beta‐amyloid ratio trended upwards (>90th percentile) compared to APOE E4/E4‐matched‐ and age‐matched controls provided from the University of Pennsylvania.ConclusionThis case report demonstrates a cognitively resilient individual with an elevated ARM:amyloid ratio. Conversely, lower ARM ratios were observed in a cognitively impaired cohort, raising the possibility ARM may associate with cognition. ARM may represent a protective and phagocytic population, and further studies correlating microglia, cognition, and putative mechanism are required.

AbstractBackgroundAlzheimer's disease (AD) and related neurodegenerative diseases are characterized by the accumulation of abnormal protein aggregates. A defining hallmark of AD is the formation of neurofibrillary tangles (NFTs) by aggregation of the microtubule‐associated protein tau into pathological oligomers and fibrils. Although NFTs are believed to play a pivotal role in the disease process, we have a poor understanding of how their formation, toxicity, and spread across brain regions is regulated. Recent data suggest that the seeding behavior of tau is governed by patterns of posttranslational modifications and varying filament structures. Understanding how tau‐associated proteins regulate the oligomerization, pathological accumulation, and seeding of tau in affected neurons and glia is of critical importance for therapy development.MethodTo profile the interactome of tau aggregates, we have established proximity‐dependent biotin‐identification (BioID) as a novel method to identify the composition and proximal molecular environment of insoluble protein aggregates in the context of living brain cells and tissue. Using an in vitro and ex vivo model approach coupled with mass spectrometry, we are generating datasets containing top identified proteins, stratified based on significance and molecular pathway. Once we validate their co‐localization with NFTs in the context of human AD pathology, functional characterization of putative modifiers will be performed to assess their impact on tau‐aggregate and toxicity.ResultTo determine the physiological and aggregate specific interacting partners of tau, we are comparing wild type tau (TauWT) with mutant tau (Tau3xMUT) carrying three tauopathy‐associated mutations (A152T/P301L/S320F) that form hyper‐phosphorylated and thioflavin S‐positive aggregates even in the absence of seeding. The proteomic analysis from our pilot study revealed that significantly changed proteins included candidates involved in RNA processing, as well as protein ubiquitination and proteasome degradation.ConclusionThis study provides novel insights into cellular pathways and molecular mechanisms of neurodegeneration, by identifying in the context of living neurons and brain tissue different functional classes of tau‐associated proteins with relevance for AD pathophysiology. These are expected to include proteins that may mediate the toxic effect of NFTs, facilitate the formation or degradation of pathological tau aggregates, and catalyze posttranslational modifications of tau oligomers and associated proteins.

AbstractBackgroundAlzheimer’s disease (AD) is a progressive neurodegenerative disorder neuropathologically characterized by amyloid‐β (Aβ) plaques and tau neurofibrillary tangles often measured by Thal phase and Braak stage, respectively. Frequently, Aβ also deposits in the brain vasculature with severity categorized by a cerebral amyloid angiopathy (CAA) score. Assessment of these and related endophenotypes can reveal biological insights into the phenotypic variability in AD. We hypothesize that, amongst AD patients, severity of neuropathology and brain levels of AD‐related proteins are influenced by variation in DNA methylation (DNAm), the identification of which may uncover biological pathways for AD pathogenesis. To test this, we performed epigenome‐wide association studies (EWAS) using DNAm from the temporal cortex (TCX) and cerebellum (CER) with AD‐related neuropathology measures (Braak, Thal, and CAA) and brain levels of five proteins (apoE, Aβ40, Aβ42, tau, and p‐tau).MethodsDNAm from autopsy‐confirmed AD cases available through the Mayo Clinic Brain Bank was measured by reduced representation bisulfite sequencing (RRBS) from 471 brain samples, 200 of which had both TCX and CER measures. Bisulfite converted reads were sequenced on the Illumina High Seq4000 and quality filtered. Neuropathology scoring was performed by an experienced neuropathologist. TCX levels of five AD‐related proteins from three fractions (buffer‐soluble, detergent‐soluble, and insoluble) were measured by ELISA (Liu et al. 2020). Individual CpG methylation ratios were tested for association with each neuropathological and biochemical measure using the R package CpGassoc.ResultsWe identified multiple epigenome‐wide significant CpGs unique to each AD‐related measure. Comparisons between the TCX and CER revealed region specific CpG associations. The effects of sex, age at death, APOE genotype, and presence of genetic variants for each significant CpG association were also identified.ConclusionsAlthough all neuropathological and biochemical measures tested reflect core AD pathologies, our results demonstrate unique associations of epigenetic factors with these individual phenotypes, suggesting that their variability may be governed by distinct epigenetic processes. Discovery of DNAm changes that underlie specific neuropathological or biochemical outcomes can enhance our understanding of AD pathophysiology and may lead to the identification of novel gene or pathway targets for the different facets of this complex condition.

AbstractBackgroundProgressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by cell‐type‐specific tau lesions in neurons and glia. Using bulk brain RNAseq, we previously identified PSP‐associated genes and co‐expression networks that are enriched with cell‐type marker genes. We extended our work to identify cell‐type‐specific expression perturbations in PSP using a systems approach and in vivo validations in a model system.MethodSingle‐nucleus RNAseq (snRNAseq) was performed using 33 frozen brain temporal cortex (TCX) samples from PSP and control brains. After quality control (QC), integration, and clustering of nuclei, each cluster was annotated for its cell type. We identified differentially expressed genes (DEG) in PSP and further investigated them using an independent bulk RNAseq dataset comprising 408 PSP and control TCX samples for replication and assessing co‐expression patterns. Top DEGs were identified and then validated using external bulk RNAseq datasets from a tau transgenic mouse model. Further, the ability of the validated DEGs to rescue tau‐mediated cellular toxicity was evaluated in a tau transgenic Drosophila model.ResultAfter QC, 30 clusters comprised of 27,284 nuclei were obtained, encompassing two neuronal and six glial cell types. DEGs of each cluster revealed cell‐type‐specific PSP associations. Notably, many of the up‐regulated DEGs in the astroglial clusters were members of the bulk RNAseq co‐expression modules that were also up‐regulated in PSP and enriched with astrocytic markers. There were also consistent findings for the up‐regulated DEGs in the endothelial and microglial clusters, and for down‐regulated DEGs in the oligodendroglial clusters. Subsequently, we prioritized 240 DEGs with congruent cell‐type‐specific perturbations in snRNAseq and bulk RNAseq and validated 29 of those using transgenic mouse model data. Lastly, a significant number of the up‐regulated glial genes, when knocked down in a tau transgenic Drosophila model, led to reduced tau‐mediated cellular toxicity, suggesting novel potential therapeutic avenues.ConclusionPSP brains demonstrated robust cell‐type‐specific gene expression perturbations in the glial cells populations that were validated across different datasets. Importantly, inhibiting the up‐regulated expression perturbations rescued tau‐mediated toxicity in a Drosophila model. Our findings highlight the cell‐type‐specific transcriptome changes in PSP and provide potential therapeutic options for primary tauopathies.