Human Brain Tissue Research Articles

Rapid, scalable assay of amylin‐β amyloid co‐aggregation in brain tissue and blood

AbstractBackgroundIslet amyloid polypeptide (amylin) secreted from the pancreas crosses the blood brain barrier into the brain parenchyma and interacts with Alzheimer’s disease (AD) associated cerebral β‐amyloid (Aβ) plaques, which are found in both sporadic and early‐onset familial AD. Immunoprecipitated amylin from human AD brain tissue analyzed by Western blot using an anti‐Aβ antibody detects Aβ immunoreactivity, which indicates that the amylin and Aβ peptides aggregate in the brains of humans with AD, forming amylin‐Aβ hetero‐oligomers that are sodium dodecyl sulfate (SDS)‐soluble. We report the development of an ELISA to detect amylin‐Aβ hetero‐oligomers in brain tissue and blood.MethodThe amylin‐Aβ ELISA relies on a monoclonal anti‐Aβ middomain antibody (detection) and a polyclonal anti‐amylin antibody (capture) designed to recognize an epitope that is distinct from the high affinity amylin‐Aβ binding sites. We screened temporal cortex homogenates obtained from 13 cognitively unaffected (CU) humans and 47 persons with sporadic AD (sAD) for amylin‐Aβ hetero‐oligomers. Individuals were of similar age (sAD, 85.65 ± 7.04 years vs. CU, 87.22 ± 7.30 years; p = 0.482). Brain tissue amylin and Aβ concentrations were measured using conventional ELISAs. Amylin‐Aβ oligomer levels were also measured in whole blood lysates from APP/PS1 rats and APP/PS1 rats expressing amyloid forming amylin in the pancreas (APP/PS1/HIP rats; all rats age‐matched, 16‐months).ResultThe brains of most AD patients had detectable amylin‐Aβ hetero‐oligomer concentrations, whereas about half of those CU had brain tissue amylin‐Aβ hetero‐oligomers below the detection limit (0.02 ng/mg total protein; one‐way ANOVA, P < 0.0001). Amylin‐Aβ hetero‐oligomers were more common in brains with frequent neuritic plaques (CERAD C). Higher brain tissue amylin‐Aβ hetero‐oligomer levels were associated with greater brain tissue amylin concentrations (r = 0.38; P < 0.05). There was no correlation between cerebral amylin‐Aβ hetero‐oligomer accumulation and age in the analysis of samples from sAD and CU groups (r = ‐0.22; P > 0.05). Levels of amylin‐Aβ hetero‐oligomers in whole blood lysates obtained from APP/PS1/HIP rats were higher than those from APP/PS1 littermates (P < 0.05).ConclusionStudies are needed to determine the extent to which amylin‐Aβ hetero‐oligomerization can be detected in human blood.

Glial changes are associated with cerebrovascular integrity in hyperhomocysteinemia‐induced VCID in mouse and human brain

AbstractBackgroundWith the aged population estimated to double by 2050 and the rate of dementia expected to triple, it is critical to identify treatments for dementia. One of the leading causes of dementia is vascular contributions to cognitive impairment and dementia (VCID), and is frequently found co‐morbidly with Alzheimer’s disease, the other leading cause of dementia. A modifiable risk factor for VCID is hyperhomocysteinemia (HHcy), which is defined as elevated levels of plasma homocysteine (a non‐protein‐forming amino acid), and most late‐life HHcy is caused by impaired B vitamin absorption. Although HHcy is a risk factor for VCID, the mechanism through which it induces cognitive impairment remains unclear.MethodWe used human and mouse brain tissue to determine glial and vascular changes associated with HHcy. Wild‐type (C57Bl6J) mice were placed on a HHcy or control diet for 6, 10, 14, or 18 weeks. Using qPCR, we investigated pro‐ and anti‐inflammatory cytokines. We also determined changes in microglia (IBA‐1) and identified the number of microhemorrhages and cognitive changes. In humans, we identified 31 autopsied research volunteers with antemortem homocysteine levels; 13 cases had normal plasma homocysteine levels (<14µmol/L) and 18 had high plasma homocysteine levels (>14µmol/L). We determined whether the level of plasma homocysteine was associated with microglia (IBA‐1) and astrocytes (GFAP) as well as microhemorrhages and atherosclerosis severity in the frontal and occipital cortices. Both gene expression and protein inflammatory markers were measured to determine associations with plasma homocysteine.ResultIn our mouse model of HHcy, we identified a time course of glial changes that first begins with an increase in pro‐inflammatory cytokines and increases in microglial staining at 6 weeks on diet. This is followed by cognitive changes at 10 weeks on diet. Finally, at 14 weeks on diet, we see significant cognitive deficits due to HHcy. In human tissue, HHcy was associated with more microglia but fewer astrocytes, a significant decrease in inflammation and increased microhemorrhages in the frontal cortex.ConclusionTaken together, this data shows that in both mouse and human tissue, HHcy induces significant glial and vascular pathology that could be driven by inflammatory effects.

Genetic overlap between cortical brain morphometry and frontotemporal dementia risk

AbstractBackgroundFrontotemporal dementia (FTD) has a complex genetic aetiology, where the precise mechanisms underlying the selective vulnerability of brain regions remain unknown.MethodWe leveraged summary‐based data from genome‐wide association studies (GWASs) and performed LD‐score regression to estimate pairwise genetic correlations between FTD risk and cortical brain imaging. Then, we isolate specific genomic loci with a shared aetiology between FTD and brain structure. We also performed functional annotation, summary‐based‐data Mendelian randomisation for eQTL using human peripheral blood and brain tissue data and evaluated the gene expression in mice targeted brain regions to better understand the dynamics of the FTD candidate genes.ResultPairwise genetic correlation estimates between FTD and brain morphology measures were high but not statistically significant. We identified five brain regions with a strong genetic correlation (rg > 0.45) with FTD risk. Functional annotation identified eight protein‐coding genes. Building upon these findings, we show in a mouse model of FTD that cortical NSF expression decreases with age.ConclusionOur results highlight the molecular and genetic overlap between brain morphology and higher risk for FTD, specifically for the right inferior parietal surface area and right medial orbitofrontal cortical thickness. In addition, our findings implicate NSF gene expression in the aetiology of FTD.

Rapid, scalable assay of amylin‐β amyloid co‐aggregation in brain tissue and blood

AbstractBackgroundIslet amyloid polypeptide (amylin) secreted from the pancreas crosses the blood brain barrier into the brain parenchyma and interacts with Alzheimer’s disease (AD) associated cerebral ß‐amyloid (Aß) plaques, which are found in both sporadic and early‐onset familial AD. Immunoprecipitated amylin from human AD brain tissue analyzed by Western blot using an anti‐Aß antibody detects Aß immunoreactivity, which indicates that the amylin and Aß peptides aggregate in the brains of humans with AD, forming amylin‐Aß hetero‐oligomers that are sodium dodecyl sulfate (SDS)‐soluble. We report the development of an ELISA to detect amylin‐Aß hetero‐oligomers in brain tissue and blood.MethodThe amylin‐Aß ELISA relies on a monoclonal anti‐Aß middomain antibody (detection) and a polyclonal anti‐amylin antibody (capture) designed to recognize an epitope that is distinct from the high affinity amylin‐Aß binding sites. We screened temporal cortex homogenates obtained from 13 cognitively unaffected (CU) humans and 47 persons with sporadic AD (sAD) for amylin‐Aß hetero‐oligomers. Individuals were of similar age (sAD, 85.65 ± 7.04 years vs. CU, 87.22 ± 7.30 years; p = 0.482). Brain tissue amylin and Aß concentrations were measured using conventional ELISAs. Amylin‐Aß oligomer levels were also measured in whole blood lysates from APP/PS1 rats and APP/PS1 rats expressing amyloid forming amylin in the pancreas (APP/PS1/HIP rats; all rats age‐matched, 16‐months).ResultThe brains of most AD patients had detectable amylin‐Aß hetero‐oligomer concentrations, whereas about half of those CU had brain tissue amylin‐Aß hetero‐oligomers below the detection limit (0.02 ng/mg total protein; one‐way ANOVA, P < 0.0001). Amylin‐Aß hetero‐oligomers were more common in brains with frequent neuritic plaques (CERAD C). Higher brain tissue amylin‐Aß hetero‐oligomer levels were associated with greater brain tissue amylin concentrations (r = 0.38; P < 0.05). There was no correlation between cerebral amylin‐Aß hetero‐oligomer accumulation and age in the analysis of samples from sAD and CU groups (r = ‐0.22; P > 0.05). Levels of amylin‐Aß hetero‐oligomers in whole blood lysates obtained from APP/PS1/HIP rats were higher than those from APP/PS1 littermates (P < 0.05).ConclusionStudies are needed to determine the extent to which amylin‐Aß hetero‐oligomerization can be detected in human blood.

An optimized integrated functional genomics toolkit identifies novel role of SORL1 in microglia

AbstractBackgroundRecent genome wide association studies implicated microglia in the pathophysiology of neurodegeneration; however, the translation of these genetic discoveries is hindered by the current lack of a robust human microglia in vitro model system and standardized protocols for functional genomics assessment. Though microglia differentiated from human induced pluripotent stem cells (iMG) could be a promising cellular model, the available differentiation protocols are variable, lengthy and give inefficient, mixed yields, limiting our ability to utilize modern gene editing tools (e.g., CRISPR‐Cas9) in this model for elucidating the functional consequences of disease relevant genes and variants.MethodsIn order to streamline microglia functional genomics, we optimized a highly efficient protocol to differentiate human induced pluripotent stem cells into iMG in two easy steps, offering a significant improvement in purity and time requirement for iMG production. We validated this iMG model system in a robust way through a comprehensive single cell RNA‐sequencing (scRNA‐Seq) study, mass spectrometry‐based proteomics and microglial functional assays. In addition, the iMG differentiation protocol includes sequential iMG harvesting and cell freezing steps, that will allow the researchers to scale up the production of iMG for high‐throughput assays. Furthermore, the toolkit also includes a drug inducible CRISPR‐ON/OFF approach in our newly established microglia model system that enables the investigation of gene function in a temporal fashion. All the data generated as part of the comprehensive validation is publicly available in the form of a searchable online platform (https://jasonchungngo.shinyapps.io/IPSC-derived-Microglia/).ResultsWe used this newly developed integrated microglia functional genomics toolkit, along with human primary microglia freshly purified from dorsolateral prefrontal cortex (DLPFC), to investigate the thus far unidentified role of SORL1, an AD associated gene, in microglia. By combining state‐of‐the art (e.g. single cell RNA‐Seq, proteomics and focused CRISPR‐Cas9 screen) and standard (immunohistochemistry on postmortem human aged brain tissues) approaches we established the molecular mechanisms by which SORL1 shapes the functional phenotypes of human microglia. Most interestingly, we have found divergent roles for SORL1 in microglia when compared to neurons.ConclusionsOur findings highlight the importance of cell type specific functional genomics of susceptibility genes in AD.

RNA‐Binding Proteins Musashi and Tau Aggresome in Alzheimer’s disease

AbstractBackgroundTauopathies, such as Alzheimer’s disease (AD), are characterized by the accumulation of toxic tau oligomers in the brain and accumulation of proteinaceous inclusions stored in cellular structures called aggresomes. Recent studies suggest that AD also exhibits pathology related to RNA binding proteins (RBPs), including Musashi proteins. Our lab has previously discovered that Musashi 1 (MSI1) and Musashi 2 (MSI2) aggregate in human AD brains and we have also visualized co‐localization with tau oligomers, suggesting toxic direct crosstalk between tau and MSI proteins. With this discovery and the growing evidence indicating MSI proteins as contributors to AD pathology, through their loss of functions it is crucial to elucidate how the interactions between misfolded tau and MSI influence tau aggregation and perhaps formation of cellular aggresomes.MethodIn this study, we characterize which tau oligomeric species, including phosphorylated and ubiquitinated ones, interact with MSI within the human AD brain (Braak Stage V‐VI). We investigate the deposition and cellular location of MSI and tau aggregates in AD and age‐matched control human cortical brain tissues by biochemical, immunohistochemistry and co‐immunofluorescence assays. Using high‐resolution microscopy and imaging analysis we measured the differences in size and morphology of MSI/tau co‐aggregates.ResultInvestigation of these co‐aggregates showed specific accumulation in neurons as well as in glial cells (astrocytes and microglia). We performed biochemical assays using commercial and in‐house antibodies to qualitatively investigate MSI1, MSI2, and tau across in AD brains. Co‐IF was performed to investigate the spatial and quantitative distribution of MSI1, MSI2, and tau aggregates. MSI/tau aggregate morphological characterization was conducted to profile their size and shape in AD cortices.ConclusionFor the first time, we show that the presence and quantity of tau oligomeric species and MSI co‐aggregates vary across the AD brains, showing inter‐subjects’ variability in size and deposition density. We also identify that tau conformers with MSI1 and MSI2 form different co‐aggregates in size and morphology quantifying their colocalization in high‐resolution 3D imaging. Further investigations are warranted to determine the temporal and regional distribution of these tau species in association with MSI proteins as well as the mechanisms underlying their aggregation.

Effects of cholesterol depletion, pro‐inflammatory cytokines and the apolipoprotein E isoforms on ABCA7 protein levels in human neural cell lines and brain tissue

AbstractBackgroundStrong evidence from diverse sources points to adenosine triphosphate‐binding cassette transporter subfamily A member 7 (ABCA7) as a major risk factor in Alzheimer’s disease (AD). However, the mode of its involvement with the disease and many aspects of its function are understood incompletely.MethodHuman microglia cells C20 and HMC3 and neuronal cells SK‐N‐SH were either depleted in cholesterol using methyl‐β‐cyclodextrin and/or rosuvastatin or treated with pro‐inflammatory cytokines IL‐1β, IL‐6 or TNFα, and ABCA7 protein levels in these cells were then assessed using a validated monoclonal antibody. ABCA7 levels were also assessed using the antibody in the parietal cortex from 170 donors, who were genotyped for the APOE isoforms.ResultLarge (∼75%) reductions in intracellular cholesterol and saturating amounts of pro‐inflammatory cytokines IL‐1β and TNFα reduced ABCA7 protein by, respectively, 36.8±9.1% (mean±standard deviation, two‐tailed t test p = 0.0002, n = 4), 53.0±22.6% (p = 0.002, n = 4) and 59.2±8.0% (p = 0.0006, n = 4) in C20 cells and by similar percentages in HMC3 cells. Similarly severe cholesterol depletion had no effect on ABCA7 and IL‐1β and TNFα moderately increased ABCA7 amounts in SK‐N‐SH cells. IL‐6 had no effect on ABCA7 expression in any cell line. IL‐1β and TNFα significantly cross‐induced each other’s secretion in C20 cells. We have previously shown that ABCA7 protein levels drop suddenly during AD pathogenesis between Braak and Braak stages I and II in the human brain. Among the individuals without AD pathology or with Braak stage I pathology, ABCA7 levels were lower in APOE4 carriers without reaching statistical significance (0.74, 0.35‐2.51 vs 1.5, 0.30‐3.16 ABCA7/GAPDH ratios; median, 25%‐75% interval; Mann‐Whitney p = 0.44, n = 68 vs 14); among the individuals with Braak stages II‐V, ABCA7 was also lower in APOE4 carriers (0.21, 0.07‐1.07 vs 0.55, 0.11‐1.35; Mann‐Whitney p = 0.18, n = 53 vs 35). The comparison groups were matched for age, sex and PMI.ConclusionThe effect of cholesterol depletion on ABCA7 expression is tissue specific. ABCA7 functions are homeostatic and not compatible with inflammation in microglia. If APOE4 has an effect on ABCA7 levels, it is smaller than the reduction in ABCA7 between Braak stages I and II. These findings improve our understanding of ABCA7 pathophysiology.

Disordered ganglioside localization in the Alzheimer’s disease brain

AbstractBackgroundAlzheimer’s disease (AD) is a progressive dementia that impairs memory and cognition. Gangliosides are glycosphingolipids enriched within the central nervous system and known to alter the secondary structure of amyloid beta deposits, a hallmark of AD (Choo‐Smith et al., 1997). The ganglioside GM1 is known to exert neuroprotective properties and was proposed as a therapeutic for AD (Svennerholm, 1994). In support of this, intraventricular administration of GM1 decreased amyloid beta deposits and provided clinical benefit (Augustinsson et al., 1997). Pre‐clinical work has since demonstrated a shift from complex GM1 species to simple GM2 and GM3 is linked to neurodegenerative pathogenesis (Wang & Whitehead, 2020). However, the ganglioside GM1 also converts amyloid beta to a toxic form with beta sheet structure (Yamamoto et al., 2007), and acts as a seed for amyloid beta fibrillogenesis (Yanagisawa et al., 1995). It is possible that different GM1 subtypes may be responsible for varying affects. Understanding the profile of GM1 subtypes in the AD brain may be a key step in capitalizing on its therapeutic potential. We investigate the ratio between 18 and 20 carbon subtypes of GM1 and simple ganglioside species in post‐mortem human AD brain tissue and non‐AD controls. Brain regions interrogated include the entorhinal cortex, basal forebrain, anterior commissure and hippocampus.MethodNeuroanatomical regions of interest (ROIs) were blocked from neuropathologically confirmed AD and non‐AD brains and stored in 10% formalin. Samples were prepared for matrix assisted laser desorption ionization imagining mass spectrometry (MALDI‐IMS) (Caughlin et al., 2017). MALDI‐IMS was performed in reflectron negative mode. Matching ROIs in AD and non‐AD samples (n = 5) were selected using TissueView software. Mass spectra were normalized by area under curve and peaks corresponding to gangliosides were statistically analyzed.ResultNon‐AD brains demonstrated distinct d20:1/d18:1 ratios of both simple and complex gangliosides between different brain regions. This expression profile was lost in the AD brain samples. Additionally, a significant decrease in this ratio was observed in AD compared to non‐AD samples in several brain regions.ConclusionGanglioside dysregulation and a decrease in the d20:1/d18:1 ratios in multiple brain regions are critical pathological biomarkers of AD.

CD147 associates cerebrovascular lesion with Aβ pathology in Alzheimer’s disease

AbstractBackgroundCerebrovascular abnormality is recognized as a major contributor to Alzheimer’s disease (AD). However, how cerebrovascular damage accelerates Aβ production/deposition remains poorly defined. CD147, a transmembrane molecule mainly expressed in cerebral small vessels, modulates γ secretase function and Aβ production in vitro. The present study was to study whether CD147 associated cerebrovascular damage with the Aβ pathology in autopsied human brains with AD, and whether CD147 in the CSF was related with CSF Aβ AD patients from China Aging and Neurodegenerative Initiative (CANDI) cohort.MethodAmounts of soluble CD147, membrane CD147 / Claudin‐5 / CD31 and insoluble Aβ43 /42 /40 from autopsied human brain tissue samples were assessed by ELISA, Luminex and MSD, respectively. In CANDI cohort, CSF Aβ40 and 42, CSF CD147, CSF Aβ43, and CSFAβ38 were measure with Simoa, Luminex, ELISA, and MSD, respectively. Linear regression models were used to evaluate the associations between CSF CD147 with cognitive decline (MMSE and cortical thickness), GFAP, NFL, Aβ burden (18F‐Flobetapir), and Aβ isoforms (Aβ43/42/40/38).ResultIn autopsied human AD brains, the lower soluble/membrane CD147 ratio was significantly associated with worse BBB integrity (lower Claudin‐5/CD31 ratio) and with higher levels of insoluble Aβ43 and Aβ42. In the CANDI cohort, lower CSF CD147 in AD patients was also significantly associated with higher level of Aβ burden. Interestingly, CSF CD147 show a stronger association with shorter Aβ isoforms (Aβ38 ≈ Aβ40 > Aβ42 > Aβ43). Decreasing CSF CD147 was significantly linked to worse cognitive function (MMSE and cortical thickness) and with higher levels of CSF GFAP and NFL. White matter hyperintensity was negatively significantly associated with CSF CD147.ConclusionCerebrovascular damage may impair the release of CD147 from vessels, thereby further exacerbate Aβ pathology via shifting the production of Aβ from longer to shorter isoforms. The findings suggest that soluble CD147 links cerebrovascular damage and Aβ pathology and cerebrovascular CD147 could be a potential therapeutic target for AD.

Explainable AI and its instantiation in Computational Pathology for a better understanding of Alzheimer’s disease

AbstractBackgroundEXplainable Artificial Intelligence (XAI) has an essential role to accelerate the AI adoption by empowering biomedical experts and catalyzing modern research through the emergence of a new generation of virtual actors, enabling traceable knowledge‐based quantification, as a guided qualification support. XAI instantiation is shown through our study, hypothesizing that rapid Alzheimer’s Disease (rAD) brains display subtle histological changes that would be undercovered by high‐throughput automated microscopic analysis. We study the topography and morphology of tau lesions’ aggregates to better understand the morphological substratum of Alzheimer’s Disease (AD) heterogeneity.MethodTo address this question at a large scale, we designed, tested and implemented a software for automatic segmentation, annotation and quantitation of brain lesions in histopathological whole slide images (WSI). A dataset of 15 whole slide images of postmortem human brain tissue is used in this study. These are fully annotated by neuropathologists yielding a set of more than 30,000 annotated plaques and tangle objects. A deep learning pipeline consisting of an attention‐UNet model with explainability features is trained for segmentation of tau aggregates in WSIs. The attention maps corresponding to segmentation predictions from the model are used by pathologists as a comparable reference to assist their decision making process.ResultThe DL‐based WSI analysis framework allows detecting a majority of the tau aggregates and refining tau aggregate boundaries with higher accuracy compared to manual annotations. Besides, with such a DL model based tau identification, the pathologist needs to annotate only a few samples for the DL model training. Overall, DL assisted analysis of tau aggregates could ease the effort of pathologists and facilitate analysis of hundreds of WSIs which are vital in AD research areas such as identifying different AD forms and AD patient stratification.ConclusionXAI is not only providing traceability by opening the way to an effective adoption, but also allows optimizing the ML/DL design, by keeping high performances. The green footprint is, therefore, considered, as well as the GDPR (European General Data Protection Regulation), towards Responsible Artificial Intelligence.

Exploratory analysis of 3000 proteins in postmortem human brain tissue lysates using proximity extension assay

Exploratory analysis of 3000 proteins in postmortem human brain tissue lysates using proximity extension assay

Towards the Biomechanics of Alzheimer’s Disease: Computational Models

AbstractBackgroundPhysical changes in the brain microenvironment are highly associated with changes in mechanosensitivity of neuronal cells and mechanical properties of brain tissue. The progression of amyloid plaques and neurofibrillary tangles in the brain network significantly affects brain microstructure in Alzheimer’s disease (AD). To better understand the underlying mechanisms of AD, it is crucial to explore the effect of neuropathologies that cause brain tissue softening.MethodWe propose a microstructural model of brain white matter characterized by axons embedded in an extracellular matrix (ECM). The microscale is described by a representative volume element and includes features such as mechanical properties of axons and ECM, distribution of axon diameters, and axon tortuosity from experimental observations. The aim of this work is to investigate how the presence of β‐amyloid as hard senile plaques in the ECM and neurofibrillary tangles leads to softer mechanical properties of the brain during AD. The model is validated by simulating healthy brain tissue and comparing the homogenized response with existing experimental data.ResultPreliminary analyses to validate the model have shown tissue behavior similar to that seen in the mechanical experiments. In the case of AD, as expected, changes in the mechanical properties of the ECM due to the presence of hard senile plaques, demyelination due to the detachment of hyperphosphorylated tau proteins and neuronal death significantly affect the material properties at the macroscale.ConclusionThe combination of computational mechanical models with experimental observations opens a window to assess the structure‐function relationship of brain tissues in neuropathological disorders, which may be particularly useful to precisely design biomarkers for early detection or more informed therapeutic strategies.References• Schäfer, J. Weickenmeier, and E. Kuhl, “The interplay of biochemical and biomechanical degeneration in Alzheimer’s disease”, Comput. Methods Appl. Mech. Eng., vol. 352, pp. 369‐388, 2019.• M. Hall, E. Moeendarbary, and G.K. Sheridan, “Mechanobiology of the brain in ageing and Alzheimer’s disease”, Eur. J. Neurosci., pp. 1‐28, 2020.• Budday, G. Sommer, C. Birkl, C. Langkammer, J. Haybaeck, J. Kohnert, M. Bauer, F. Paulsen, P. Steinmann, E. Kuhl, G.A. Holzapfel, “Mechanical characterization of human brain tissue”, Acta Biomater., pp. 319‐340, 2017.

Blood‐brain barrier neuropathology in individuals with Down syndrome and Alzheimer’s disease

AbstractBackgroundIndividuals with Down syndrome (DS) are the largest population at genetic risk of developing early‐onset Alzheimer’s disease (AD). Throughout their lifespan, individuals with DS develop the spectrum of AD neuropathology. By 40 years of age, mature amyloid beta plaques and tau neurofibrillary tangles are present in DS brains, followed by the development of AD dementia. Despite having a low frequency of vascular risk factors (i.e., hypertension, atherosclerosis), individuals with DS display significant cerebrovascular pathology, including cerebral amyloid angiopathy, increased white matter hyperintensities, microbleeds, microinfarcts, and enlarged perivascular spaces. Such pathological changes suggest that the blood‐brain barrier (BBB) undergoes neuropathological alterations and may be associated with the development of AD pathology, in DS. Nevertheless, BBB integrity has not been studied in DS. Our main objective is to investigate BBB pathology in the brains of people with DS and AD (DSAD).MethodPost‐mortem brain tissue was obtained from the ABC‐DS study, NIH Neurobiobank, and BrightFocus Foundation. BBB components (basement membrane, endothelial cells, pericyte cell number) and BBB leakage were assessed by free‐floating immunohistochemistry in human brain tissue sections from the occipital cortex of individuals with DSAD (49‐55 years old), and their age‐matched neurotypical controls (48‐57 years old). Brain sections were digitized, and BBB components and vessel morphology were quantified using ImageJ.ResultOur preliminary data suggest that, compared to age‐matched controls, adults with DSAD have a lower number of pericytes and lower Collagen‐IV load. A proportion of DSAD cases also had lower endothelial cell coverage and shorter blood vessels. Moreover, fibrinogen leakage was observed in the brain parenchyma of DSAD brains. Interestingly, some individuals with DSAD displayed no BBB pathological changes.ConclusionIndividuals with DS have pathological alterations in the BBB. However, some people with DSAD may be resilient to such changes. Studies are ongoing to determine if BBB changes in DS are associated with the development and progression of AD neuropathology.

Neuronal populations in the inferior temporal gyrus with truncated tau inclusions occur as early as those with hyperphosphorylated tau inclusions in Alzheimer’s disease, however they do not completely overlap

AbstractBackgroundAlzheimer’s disease (AD) features stereotypical spread of hyperphosphorylated tau (p‐tau) and beta‐amyloid. Although other pathological tau posttranslational modifications (PTMs) have been described in AD, a prevalent disease model preconizes that other tau PTMs always overlap with p‐tau, making the latter an excellent marker of tau pathology burden. We recently showed in experimental studies that truncated tau (tr‐tau), a pathological tau PTM generated via cleavage by active caspases, is as common as p‐tau in neurons at late AD stages; however, only about 40% of tr‐tau positive neurons also show p‐tau positivity. This makes tr‐tau a potential marker of AD previously invisible at neuropathological investigation or a potential target of diagnostic tool development. We sought to determine how early in AD tr‐tau is detected compared to p‐tau and to what degree tr‐tau and p‐tau neuronal populations overlap at early AD stages.MethodsWe used multiplex immunofluorescence to probe tr‐tau (D13, D402, D418, TauC3) and p‐tau (PHF1) species in the same tissue slides of postmortem human brain tissue of healthy controls and subjects at progressive AD stages. We quantified neuronal tau pathology and colocalization in digital images of inferior temporal gyrus (ITG) as representative of an area involved in p‐tau pathology in intermediate stages.ResultsOur preliminary analysis included 14 cases (4 controls, 10 AD) from all Braak stages (1:1:2:3:3:2:2 for Braak 0 through 6). Of the cases used in the study, 71% were male and the mean (SD) age of death was 82.3 (10.9). As expected, p‐tau was detected from Braak 4; however, we detected tr‐tau species from Braak 3 (Fig. 1). Both p‐tau and tr‐tau burden increased with Braak stage (Fig. 2). The overlap between tr‐tau and p‐tau positive neuron populations was 30.8% at Braak 4 (Fig. 3A) and increased to 54.6% at Braak 6 (Fig. 3B).ConclusionNeuronal tr‐tau deposits develop in AD as early as p‐tau pathology. Even in earlier stages, the % of overlapping is moderate. This corroborates tr‐tau as a potential biomarker of tau pathology in AD not covered by p‐tau screening. We are currently finalizing analysis of a much larger cohort including other brain regions.

18F]MK6240 and [18F]PI2620 autoradiography on postmortem human brain tissue in AD

AbstractBackgroundTo compare the post mortem uptake of [18F]MK6240 and [18F]PI2620 in the brain hemisphere, of A‐T‐ (CN) and A+T+ tissueMethodAutoradiography (ARG) imaging using [18F]MK6240 and [18F]PI2620 was used to assess uptake of CN and AD tissues. One study used sections of whole‐hemisphere of one CN tissue and one AD tissue. The uptake value of [18F]MK6240 was calculated from a regions of interest (ROI) drawn manually from the area of cortex gray matter (GM), cortex white matter (WM), and background (BG).Other study was 24 tissues from the prefrontal cortex (Pfc) (12CN, 12AD), hippocampus (Hip) (12 CN, 12 AD) and cerebellum (Cer) (12 CN, 12 AD) were evaluated with [18F]MK6240, and [18F]PI2620. The uptake value of [18F]MK6240 and [18F]PI2620 was calculated from ROI drawn manually from the area of pfc GM, hip GM and cer GM.ResultThe ARG showed greater [18F]MK6240 uptake in AD than in CN tissue. There were significant differences between CN and AD tissue in terms of cortex gray GM distribution and cortex WM, but no significant differences in BG. These results also, there is no correlation between the specific activity of [18F]MK6240 and the uptake value in CN and AD tissues. In a second experiment, based on our findings there was a significant difference between CN and AD groups when assessed by [18F]MK6240 as well as [18F]PI2620 in the pfc_GM and hip_GM. Furthermore, we found no difference between AD and CN tissues when assessed by [18F]MK6240 and [18F]PI2620 in cerebellum GM. Ratio values Pfc/Cer and Hip/Cer assessed by [18F]MK6240 as well as there were significant differences between CN and AD. [18F]MK6240 and [18F]PI2620 were highly correlated in AD but not in CN brain tissues.ConclusionWe also found that [18F]PI2620 and [18F]MK6240 have similar brain uptake in post‐mortem tissue.

Distinct CSF biomarker‐associated DNA methylation in Alzheimer’s disease and cognitively normal subjects

AbstractBackgroundGrowing evidence has demonstrated that DNA methylation (DNAm) plays an important role in Alzheimer’s disease and that DNAm differences can be detected in the blood of AD subjects. Because access to human brain tissues is primarily limited to postmortem samples, most studies have correlated blood DNAm with clinical diagnosis of AD in living individuals. However, as the pathophysiological process of AD can begin many years before the onset of clinical symptoms, there is often disagreement between neuropathology in the brain and clinical phenotypes. Thus, the association of blood DNAm with changes in AD neuropathology, rather than with clinical data, would provide more relevant information on AD pathogenesis.MethodCSF biomarkers are well‐established AD endophenotypes and correlate significantly with neuropathology scores measured on postmortem brain samples. In this study, we performed a comprehensive analysis to identify blood DNA methylation associated with CSF pathological biomarkers for AD in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohort. Our study included matched samples of whole blood DNA methylation, CSF Aβ42, phosphorylated tau181 (pTau181), and total tau (tTau) biomarkers data, measured on the same subjects and at the same clinical visits from a total of 202 subjects (123 cognitively normal, 79 AD cases).ResultWe identified a number of novel associations between blood DNAm and CSF Aβ42, pTau181, and total tau biomarkers, demonstrating that changes in various pathological processes in the CSF are also reflected in the blood epigenome. Overall, the CSF biomarker‐associated DNAm is relatively distinct in cognitively normal (CN) and AD subjects, highlighting the importance of analyzing omics data measured on cognitively normal subjects (which includes preclinical AD subjects) to identify diagnostic biomarkers, and considering disease stages in the development and testing of AD treatment strategies. Moreover, our pathway analysis of CSF biomarker associated‐DNAm from CN subjects revealed that biological processes associated with early brain impairment relevant to AD are marked by DNAm in the blood.ConclusionOur study provides a valuable resource for future mechanistic and biomarker studies of DNAm in AD.

INPP5D regulates inflammasome activation in human microglia

Microglia and neuroinflammation play an important role in the development and progression of Alzheimer’s disease (AD). Inositol polyphosphate-5-phosphatase D (INPP5D/SHIP1) is a myeloid-expressed gene genetically-associated with AD. Through unbiased analyses of RNA and protein profiles in INPP5D-disrupted iPSC-derived human microglia, we find that reduction in INPP5D activity is associated with molecular profiles consistent with disrupted autophagy and inflammasome activation. These findings are validated through targeted pharmacological experiments which demonstrate that reduced INPP5D activity induces the formation of the NLRP3 inflammasome, cleavage of CASP1, and secretion of IL-1β and IL-18. Further, in-depth analyses of human brain tissue across hundreds of individuals using a multi-analytic approach provides evidence that a reduction in function of INPP5D in microglia results in inflammasome activation in AD. These findings provide insights into the molecular mechanisms underlying microglia-mediated processes in AD and highlight the inflammasome as a potential therapeutic target for modulating INPP5D-mediated vulnerability to AD.

Three-dimensional visualization and analysis of dendritic spines in human brain tissue.

We developed a simple yet powerful technique to visualize neuronal morphology in human brain tissues. By ballistically shooting DiI (1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate)-coated tungsten particles to randomly label neurons, then clearing tissues with OPTIClear, we demonstrated the tracing of branched dendritic trees and spines in three dimensions. High-resolution imaging revealed dendrites up to 300μm long and spine necks down to 200nm across. Quantitative analyses of 1304 dendritic spines showed no decrease in spine density with imaging depth, indicating excellent clearing and tracing. Segmentation and modeling of dendritic spines enabled morphological characterization. This technique enables assumption-free, high-resolution and cost-efficient visualization of neuronal morphology in human tissues. Combined with immunohistochemistry and electron microscopy, it could provide new perspectives for studying human neuroanatomy and pathology.

Liquid Biopsy in Alzheimer's Disease Patients Reveals Epigenetic Changes in the PRLHR Gene.

In recent years, new DNA methylation variants have been reported in genes biologically relevant to Alzheimer's disease (AD) in human brain tissue. However, this AD-specific epigenetic information remains brain-locked and unreachable during patients' lifetimes. In a previous methylome performed in the hippocampus of 26 AD patients and 12 controls, we found higher methylation levels in AD patients in the promoter region of PRLHR, a gene involved in energy balance regulation. Our aim was to further characterize PRLHR's role in AD and to evaluate if the liquid biopsy technique would provide life access to this brain information in a non-invasive way. First, we extended the methylation mapping of PRLHR and validated previous methylome results via bisulfite cloning sequencing. Next, we observed a positive correlation between PRLHR methylation levels and AD-related neuropathological changes and a decreased expression of PRLHR in AD hippocampus. Then, we managed to replicate the hippocampal methylation differences in plasma cfDNA from an additional cohort of 35 AD patients and 35 controls. The isolation of cfDNA from the plasma of AD patients may constitute a source of potential epigenetic biomarkers to aid AD clinical management.

Modular Splicing Is Linked to Evolution in the Synapse-Specificity Molecule Kirrel3.

Kirrel3 is a cell-adhesion molecule that instructs the formation of specific synapses during brain development in mouse and Kirrel3 variants may be risk factors for autism and intellectual disabilities in humans. Kirrel3 is predicted to undergo alternative splicing but brain isoforms have not been studied. Here, we present the first in-depth characterization of Kirrel3 isoform diversity in brain using targeted, long-read mRNA sequencing of mouse hippocampus. We identified 19 isoforms with predicted transmembrane and secreted forms and show that even rare isoforms generate detectable protein in the brain. We also analyzed publicly-available long-read mRNA databases from human brain tissue and found 11 Kirrel3 isoforms that, similar to mouse, encode transmembrane and secreted forms. In mice and humans, Kirrel3 diversity arises from alternative, independent use of protein-domain coding exons and alternative early translation-stop signals. Intriguingly, the alternatively spliced exons appear at branch points in the chordate phylogenetic tree, including one exon only found in humans and their closest living relatives, the great apes. Together, these results validate a simple pipeline for analyzing isoform diversity in genes with low expression and suggest that Kirrel3 function is fine-tuned by alternative splicing and may play a role in brain evolution.