Human Alzheimer's Disease Brain Research Articles

Microglial Expression of the Wnt Signaling Modulator DKK2 Differs between Human Alzheimer's Disease Brains and Mouse Neurodegeneration Models.

Wnt signaling is crucial for synapse and cognitive function. Indeed, deficient Wnt signaling is causally related to increased expression of DKK1, an endogenous negative Wnt regulator, and synapse loss, both of which likely contribute to cognitive decline in Alzheimer's disease (AD). Increasingly, AD research efforts have probed the neuroinflammatory role of microglia, the resident immune cells of the CNS, which have furthermore been shown to be modulated by Wnt signaling. The DKK1 homolog DKK2 has been previously identified as an activated response and/or disease-associated microglia (DAM/ARM) gene in a mouse model of AD. Here, we performed a detailed analysis of DKK2 in mouse models of neurodegeneration, and in human AD brain. In APP/PS1 and APPNL-G-F AD mouse model brains as well as in SOD1G93A ALS mouse model spinal cords, but not in control littermates, we demonstrated significant microgliosis and microglial Dkk2 mRNA upregulation in a disease-stage-dependent manner. In the AD models, these DAM/ARM Dkk2+ microglia preferentially accumulated close to βAmyloid plaques. Furthermore, recombinant DKK2 treatment of rat hippocampal primary neurons blocked WNT7a-induced dendritic spine and synapse formation, indicative of an anti-synaptic effect similar to that of DKK1. In stark contrast, no such microglial DKK2 upregulation was detected in the postmortem human frontal cortex from individuals diagnosed with AD or pathologic aging. In summary, the difference in microglial expression of the DAM/ARM gene DKK2 between mouse models and human AD brain highlights the increasingly recognized limitations of using mouse models to recapitulate facets of human neurodegenerative disease.

Systemic Inflammation Causes Microglial Dysfunction With a Vascular AD phenotype

BackgroundStudies in rodents and humans have indicated that inflammation outside CNS (systemic inflammation) affects brain homeostasis contributing to neurodevelopmental disorders. Itis becoming increasingly evident that such early insults may also belinked to neurodegenerative diseases like late-onset Alzheimer's disease (AD). Importantly, lifestyle and stress, such as viral or bacterial infection causing chronic inflammation, may contribute to neurodegenerative dementia. Systemic inflammatory response triggers a cascade of neuroinflammatory responses, altering brain transcriptome, cell death characteristic of AD, and vascular dementia. Our study aimed to assess the temporal evolution of the pathological impact of systemic inflammation evoked by prenatal and early postnatal peripheral exposure of viral mimetic Polyinosinic:polycytidylic acid (PolyI:C) and compare the hippocampal transcriptomic changes with the profiles of human post-mortem AD and vascular dementia brain specimens. MethodsWe have engineered the PolyI:C sterile infection model in wildtype C57BL6 mice to achieve chronic low-grade systemic inflammation. We have conducted a cross-sectional analysis of aging PolyI:C and Saline control mice (3 months, 6 months, 9 months, and 16 months), taking the hippocampus as a reference brain region, and compared the brain aging phenotype to AD progression in humans with mild AD, severe AD, and Controls (CTL), in parallel to Vascular dementia (VaD) patients’ specimens. ResultsWe found that PolyI:C mice display both peripheral and central inflammation with a peak at 6 months, associated with memory deficits. The hippocampus is characterized by a pronounced and progressive tauopathy. In PolyI:C brains, microglia undergo aging-dependent morphological shifts progressively adopting a phagocytic phenotype. Transcriptomic analysis reveals a profound change in gene expression throughout aging, with a peak in differential expression at 9 months. We show that the proinflammatory marker Lcn2 is one of the genes with the strongest upregulation in PolyI:C mice upon aging. Validation in brains from patients with increasing severity of AD and VaD shows the reproducibility of some gene targets in vascular dementia specimens as compared to AD ones. ConclusionsThe PolyI:C model of sterile infection demonstrates that peripheral chronic inflammation causes progressive tau hyperphosphorylation, changes in microglia morphology, astrogliosis and gene reprogramming reflecting increased neuroinflammation, vascular remodeling, and the loss of neuronal functionality seen to some extent in human AD and Vascular dementia suggesting early immune insults could be crucial in neurodegenerative diseases.

Mechanistic insight into female predominance in Alzheimer's disease based on aberrant protein S-nitrosylation of C3.

Protein S-nitros(yl)ation (SNO) is a posttranslational modification involved in diverse processes in health and disease and can contribute to synaptic damage in Alzheimer's disease (AD). To identify SNO proteins in AD brains, we used triaryl phosphine (SNOTRAP) combined with mass spectrometry (MS). We detected 1449 SNO proteins with 2809 SNO sites, representing a wide range of S-nitrosylated proteins in 40 postmortem AD and non-AD human brains from patients of both sexes. Integrative protein ranking revealed the top 10 increased SNO proteins, including complement component 3 (C3), p62 (SQSTM1), and phospholipase D3. Increased levels of S-nitrosylated C3 were present in female over male AD brains. Mechanistically, we show that formation of SNO-C3 is dependent on falling β-estradiol levels, leading to increased synaptic phagocytosis and thus synapse loss and consequent cognitive decline. Collectively, we demonstrate robust alterations in the S-nitrosoproteome that contribute to AD pathogenesis in a sex-dependent manner.

Insights into the Mixture of Aβ24 and Aβ42 Peptides from Atomistic Simulations

Amyloid-β (Aβ) oligomers play a central role in Alzheimer's disease (AD). Plaques of AD patients consist of Aβ40 and Aβ42 peptides and truncated Aβ peptides. The Aβ24 peptide, identified in human AD brains, was found to impair Aβ42 clearance through the brain-blood barrier. The Aβ24 peptide was also shown to reduce Aβ42 aggregation kinetics in pure buffer, but the underlying mechanism is unknown at atomistic level. In this study, we explored the conformational ensemble of the equimolar mixture of Aβ24 and Aβ42 by replica exchange molecular dynamics simulations and compared it to our previous results on the pure Aβ42 dimer. Our simulations demonstrate that the truncation at residue 24 changes the secondary, tertiary, and quaternary structures of the dimer, offering an explanation of the slower aggregation kinetics of the mixture.

Consistency of Graph Theoretical Measurements of Alzheimer's Disease Fiber Density Connectomes Across Multiple Parcellation Scales.

Graph theoretical measures have frequently been used to study disrupted connectivity in Alzheimer's disease human brain connectomes. However, prior studies have noted that differences in graph creation methods are confounding factors that may alter the topological observations found in these measures. In this study, we conduct a novel investigation regarding the effect of parcellation scale on graph theoretical measures computed for fiber density networks derived from diffusion tensor imaging. We computed 4 network-wide graph theoretical measures of average clustering coefficient, transitivity, characteristic path length, and global efficiency, and we tested whether these measures are able to consistently identify group differences among healthy control (HC), mild cognitive impairment (MCI), and AD groups in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort across 5 scales of the Lausanne parcellation. We found that the segregative measure of transtivity offered the greatest consistency across scales in distinguishing between healthy and diseased groups, while the other measures were impacted by the selection of scale to varying degrees. Global efficiency was the second most consistent measure that we tested, where the measure could distinguish between HC and MCI in all 5 scales and between HC and AD in 3 out of 5 scales. Characteristic path length was highly sensitive to the variation in scale, corroborating previous findings, and could not identify group differences in many of the scales. Average clustering coefficient was also greatly impacted by scale, as it consistently failed to identify group differences in the higher resolution parcellations. From these results, we conclude that many graph theoretical measures are sensitive to the selection of parcellation scale, and further development in methodology is needed to offer a more robust characterization of AD's relationship with disrupted connectivity.

Initial Correlation Analysis of Diffusion Basis Spectrum Imaging of Alzheimer's Brain and Quantitative Histology

AbstractBackgroundDiffusion Basis Spectrum Imaging (DBSI), a novel MR imaging method, can be utilized as a biomarker in Alzheimer's disease (AD) staging and progression. By distinguishing diffusion effects from other concomitant disorders like axonal injury/loss and demyelination, it is capable of specifically evaluating cellularity and edema in AD brains. To test the hypothesis that DBSI cell fraction and mean cell apparent diffusion coefficient (ADC) correlate with measures of cell density and neuroinflammation, we employed high‐resolution ex vivo DBSI sequences and quantitative digital histology on post‐mortem human AD brain tissue.MethodA 15 × 20 × 6 mm3 sample of middle frontal gyrus (coronal plane) from a formalin‐fixed post‐mortem human AD brain (Knight ADRC) was incubated in phosphate‐buffered saline for 48 hours and then imaged with a Varian 11.7T MRI, using 2D spin‐echo sequence with 20‐direction diffusion encoding (max b = 3900 s/mm2, voxel = 0.25 × 0.25 × 1 mm). After MRI, it was precisely bisected along the plane of imaging, and processed into paraffin. Slide‐mounted 6 µm histologic sections were stained with H&E and DAB immunohistochemistry (IBA‐1 antibody, hematoxylin counterstain) and digitized (20× magnification, Hamamatsu NanoZoomer). Maps of nuclei and microglia density were computed by segmenting nuclei and microglia respectively using Orbit Image Analysis and in‐house MATLAB programs. These histology maps were registered and downsampled to the corresponding DBSI maps. We generated cell fraction maps and mean cell ADC maps from MR images using in‐house DBSI software by computing the fraction and mean ADC of restricted isotropic diffusion (0 – 0.4 ×10‐3 mm2/s in each image voxel, respectively.ResultAmong 71 evenly spaced regions of interest (ROIs, 2 × 2 mm2) drawn across the entire specimen, the mean DBSI cell fraction correlated with nuclei density (R = 0.74, P < 0.001). Additionally, among 42 ROIs drawn in the white matter region, the mean cell ADC in each ROI correlated with microglia density (R = 0.54, P < 0.001).ConclusionOur findings demonstrated the feasibility of DBSI technique in ex vivo AD brain, which could improve our understanding of neuroinflammation in AD pathogenesis, early diagnostics and new disease‐modifying therapies targeting the immune response.

Withdrawn: Glycine transporter 1 (GlyT1) is a novel therapeutic target for Alzheimer’s disease

Withdrawal: Miran Yoo, Seong Muk Kim, Juho Lee, Hye‐Ju Kim, Seong Jeong Park “Glycine transporter 1 (GlyT1) is a novel therapeutic target for Alzheimer's disease” Alzheimer's & Dementia, Volume 18, Supplemental Issue 10.The above abstract, published online on 20th December 2022, on Wiley Online Library (https://alz‐journals.onlinelibrary.wiley.com/doi/abs/10.1002/alz.064468) has been withdrawn by agreement between the authors, the Senior Director of Scientific Programs and Outreach, Claire Sexton, the Director of Scientific Programs at the Alzheimer's Association, Ozama Ismail, and John Wiley & Sons Inc. The abstract has been withdrawn at the authors’ request because the authors did not have Amyloid Solution's authorization to publish the information contained in it.

TMEM176B regulates phagosome maturation of glial cells and its increased activity contributes to the therapy of Alzheimer’s disease

AbstractBackgroundGiven recent interest in using amyloid b (Aβ)‐targeted antibodies as a therapy for patients with Alzheimer’s disease (AD), removal of Aβ by phagocytosis likely protective early in AD. Impaired phagocytic function of glial cells surrounding Aβ plaques during later stages in AD likely contributes to worsened disease outcomes, therefore enhancing phagocytic activity of glial cells could be a potent strategy for AD therapy.MethodChanges in TMEM176B expression according to the progression of AD pathology was assessed by measuring TMEM176B protein in human AD brain lysates and TMEM176B transcripts in Ab‐treated primary rat astrocytes. The roles of TMEM176B in phagosome maturation of glial cells was investigated by measuring Rab5, Rab7, LAMP1, LAMP2, cathepsin D, and LC3B in presence of Aβ. Intracellular pH of glial cells was detected using fluorescent dye‐based pHrodo Red AM intracellular pH indicator (Invitrogen, Carlsbad, CA). In 5xFAD and 3xTg AD mice model, therapeutic effects of AAV‐TMEM176B was examined. AAV (adenovirus‐associated virus)‐TMEM176B (1 – 2×1010 GC) was intracerebroventricularly injected, and Aβ plaque and p‐tau in brains were assessed 3 months later. Behavioral studies such as Y‐maze, Morris water maze, and novel‐object‐recognition were conducted to exam the effect of TMEM176B overexpression in alleviation of cognition decline.ResultIn human AD brains, Tmem176B expression was increased in moderate AD (Braak III‐IV) was decreased in severe AD (Braak V‐VI). TMEM176B was upregulated by acute Aβ treatment in primary rat astrocytes, and was gradually downregulated concomitantly with impairment of Aβ phagocytosis activity by chronic exposure to Aβ. The TMEM176B agonistic compound augmented phagosome maturation and phagosomal acidification, which led to increased Aβ phagocytosis and lysosomal degradation. Studies confirmed that intracerebroventrical administration of AAV carrying TMEM176B in AD mice results in enhanced glial phagocytosis followed by lowered Aβ burden in brain. Moreover, overexpression of TMEM176B by AAV injection significantly improved cognition impairment of AD mice.ConclusionData from these studies suggest that TMEM176B plays a direct and critical role in phagolysosmal function of glial cells and AD pathogenesis and highlight this ion channel as a potential therapeutic target for treating AD.

MiR-191-5p Attenuates Tau Phosphorylation, Aβ Generation, and Neuronal Cell Death by Regulating Death-Associated Protein Kinase 1.

Dysregulation of microRNAs has been implicated in diverse diseases, including Alzheimer's disease (AD). MiR-191-5p in plasma/serum has been identified as a novel and promising noninvasive diagnostic biomarker for AD. However, whether miR-191-5p is involved in AD pathogenesis is largely unknown, and its levels in human AD brains are undetermined. Herein, we demonstrated that miR-191-5p downregulated tau phosphorylation at multiple AD-related sites and promoted neurite outgrowth using immunoblotting, immunofluorescence, and neurite outgrowth assays. Moreover, immunoblotting and enzyme-linked immunosorbent assays indicated that miR-191-5p decreased amyloid precursor protein phosphorylation levels and beta-amyloid (Aβ) generation. Furthermore, miR-191-5p reduced ceramide-induced neuronal cell death analyzed by trypan blue staining, the in situ cell death detection kit, and Annexin V-FITC/PI flow cytometry. Next, we verified that death-associated protein kinase 1 (DAPK1) was a direct target of miR-191-5p through the dual luciferase reporter assay and confirmed that the effects of miR-191-5p were antagonized by restoration of DAPK1 expression. Finally, the hippocampal miR-191-5p level was found to be decreased in humans with AD compared with controls and was inversely correlated with the DAPK1 expression level. Collectively, these findings suggest that miR-191-5p might exert inhibitory effects on tau phosphorylation, Aβ secretion, and neuronal cell death by directly targeting DAPK1, providing an attractive therapeutic option for AD.

Extracellular Tau Oligomers Rapidly Induce Nuclear Invagination in Neurons

AbstractBackgroundNeuronal nuclei are normally spheroidal with a smoothly contoured surface. In Alzheimer’s disease (AD) and other tauopathies, however, neuronal nuclei often develop deep invaginations that include the nuclear lamina, a meshwork of intermediate filaments on the inner face of the inner nuclear membrane. The lamina is involved in numerous nuclear activities that might be adversely affected by invagination, including chromatin organization, nucleocytoplasmic trafficking of macromolecules, cell cycle regulation and apoptosis. Previous work showed that in vivo expression of pathogenically mutated human tau in Drosophila melanogaster neurons causes nuclear lamina invagination and that invaginated neuronal nuclei are found in human AD brain (Frost, et al. 2016. Current Biology 26; 129‐136). In light of this background we sought to shed further light on the mechanism of pathological nuclear invagination in mammalian neurons.MethodLamina invagination was assessed by immunofluorescence microscopy in human and mouse brain tissue, and in cultured mouse neurons using an antibody against lamin B1, a major subunit protein of the nuclear lamina. To ensure thorough neuroanatomical coverage in mouse brain, we stained lateral, medial, and middle sections from each brain, and imaged across the cortical region. To seek stimuli that would cause neuronal nuclear invagination, cultured mouse neurons were exposed to extracellular tau oligomers (xcTauOs).ResultWe detected nuclear invagination in neurons in brains of AD patients and CVN (APPSwDI;NOS2−/−) mice, in the latter of which nuclear invagination in cortical neurons was more frequent than in age‐matched wild type control neurons. In cultured mouse neurons, lamina invagination was induced by xcTauOs within one hour of exposure. This effect of xcTauOs was found to depend on intracellular tau, because nuclear invagination was not detected in neurons derived from tau knockout mice unless they expressed human tau by lentiviral transduction.ConclusionOur data confirm that nuclear invagination is common in both naturally occurring human AD and a transgenic mouse model of AD, and implicate xcTauOs as likely triggers of this phenomenon by a mechanism that also requires intracellular tau.

Cellular senescence profiling reveals distinct sub‐types of neurofibrillary tangle bearing neurons.

AbstractBackgroundNeurons with tau‐containing neurofibrillary tangles (NFTs) closely correlate with Alzheimer’s disease (AD) progression and severity. Our prior work determined that NFT‐bearing neurons undergo a change in cell fate consistent with cellular senescence. The goal of this project was to determine whether senescent NFT‐bearing neurons differ from quiescent NFT‐bearing neurons.MethodPostmortem human AD brains were analyzed using GeoMx (NanoString, Inc) digital spatial profiling (DSP). Region of interest (ROI) selection included the presence or absence of neuronally expressed AT8 (phosphorylated tau, NFTs) and/or p19 (senescence). NFTs with or without p19 expression were compared to healthy neurons from the same cases. The expression of 86 proteins associated with neuropathology, inflammation, autophagy and cell typing was determined for each ROI and immediate environment (Fig. 1a‐b).ResultNFT‐bearing neurons with p19 (senescent) were significantly different than NFT‐bearing neurons without p19 (quiescent). Senescent NFT‐bearing neurons appeared similar to neurons without tau pathology. In contrast quiescent NFT‐bearing neurons displayed signs of crisis (i.e. apoptosis). Additionally, we revealed significant differences in tau phosphorylation at multiple epitopes between the two classes of NFT‐bearing neurons (Fig. 1c‐h).ConclusionThese data indicate the presence of distinct NFT‐bearing neuron subtypes in AD. Our ongoing studies are investigating (i) whether senescent or quiescent NFTs are more closely associated with pathogenesis, (ii) the transition between neuronal quiescence to senescence and (iii) which tau species contribute to this cell fate decision (self‐sacrificing versus disease propagating). More broadly, these results will provide a better understanding of distinct tau species in neurodegeneration which is critically important to clinical studies that are increasingly relying on tau biomarkers to predict disease onset, progression and target engagement in clinical trials.

Transcriptomic profiling of myeloid cells in Alzheimer’s Disease brain illustrates heterogeneity of microglia endolysosomal subtypes

AbstractBackgroundMicroglia‐mediated neuroinflammation contributes to disease progression in Alzheimer’s Disease (AD). Microglia demonstrate heterogeneous states with proposed beneficial, harmful, and disease‐specific subtypes. Defining the spectrum of microglia phenotypes is crucially important to the design of neuroinflammation‐modulating therapies.MethodWe performed single‐nucleus RNA‐seq on over 120,000 microglia nuclei isolated from dorsolateral prefrontal cortices collected from 12 AD and 10 controls. Nuclei were sorted for PU.1 expression using fluorescence activated nucleus sorting.ResultsWe detected several microglia clusters that expressed features of “activation” as well as three previously unrecognized microglia transcriptomic subpopulations. These newly described subpopulations are defined by predominant endolysosomal gene expression patterns heterogeneous for metabolic and inflammatory signatures. One endolysosomal subtype is more abundant in AD individuals and uniquely enriched for transcripts involved in nucleic acid detection and interferon signaling. This population is distinct from a classic inflammatory subpopulation also present in our cohort, which upregulates NFKB, TLR and interferon related pathways but does not share the endolysosomal signature. Network analysis revealed subtype specific enrichment of IRF3 and IRF5 regulomes. AD individuals also exhibited increased expression of unfolded protein response and inflammatory genes in homeostatic microglia subpopulations.ConclusionWe demonstrate significant heterogeneity in human brain microglia subtypes including identifying multiple endolysosomal subpopulations. Like neuroinflammation, alterations in the endolysosomal system have been identified as a key component of AD pathology; however, how endolysosomal dysfunction contributes to AD progression remains unresolved. Our study is the first to identify a subpopulation of microglia in human AD brain correlating endolysosomal activity and interferon pathway induction supporting a relationship between these two pathways in AD pathogenesis. These results highlight the heterogenous nature of the microglia response to AD pathology and inform efforts to target specific subtypes of microglia in the development of novel AD therapies.

Multi-fluorine labeled indanone derivatives as potential MRI imaging probes for β-Amyloid plaques.

In order to realize the early diagnosis of Alzheimer's disease (AD), we designed and synthesized a series of multi-fluorine labeled indanone derivatives based on indanone which could target β-amyloid (Aβ). Through the in vitro staining experiment and affinity experiment, we selected 7d out, and then evaluated it through other in vivo and in vitro experiments. The staining of AD human brain adjacent sections revealed that compound 7d could bind to Aβ plaques with high affinity. In the in vitro binding assay, 7d showed a balanced affinity with Aβ1-40 (Kd = 367 ± 13) and Aβ1-42 (Kd = 384 ± 56). Also, 7d exhibited a low toxicity (LD50 > 50 mg/kg) and an excellent ability to pass through the blood-brain barrier (Log p = 3.87). The biodistribution experiment in mice showed that 7d reached the highest brain uptake after 1 h of tail vein injection and cleared after 24 h. A low concentration of 7d (1.875 mg/ml) showed a strong imaging ability (19F-weighted mode), and the imaging capability increased with the increasing of concentration. All the results showed that 7d could provide a feasible solution for the early diagnosis of AD under non-radioactive condition.

Use of Affinity Purification-Mass Spectrometry to Identify Phosphorylated Tau Interactors in Alzheimer's Disease.

Phosphorylated tau is the main protein present in neurofibrillary tangles, the presence of which is a key neuropathological hallmark of Alzheimer's disease (AD). The toxic effects of phosphorylated tau are likely mediated by interacting proteins; however, methods to identify these interacting proteins comprehensively in human brain tissue are limited. Here, we describe a method that enables the efficient identification of hundreds of proteins that interact with phosphorylated tau (pTau), using affinity purification-mass spectrometry (AP-MS) on human, fresh-frozen brain tissue from donors with AD. Tissue is homogenized using a gentle technique that preserves protein-protein interactions, and co-immunoprecipitation of pTau and its interacting proteins is performed using the PHF1 antibody. The resulting protein interactors are then identified using label-free quantitative liquid chromatography-mass spectrometry (LC-MS)/MS. The Significance Analysis of INTeractome (SAINT) algorithm is used to determine which proteins significantly interact with pTau. This approach enables the detection of an abundance of all 6 isoforms of tau, 23 phosphorylated residues on tau, and 125 significant pTau protein interactors, in human AD brain tissue.

Suppression of Wnt/β-Catenin Signaling Is Associated with Downregulation of Wnt1, PORCN, and Rspo2 in Alzheimer's Disease.

Wnt and R-spondin (Rspo) proteins are two major types of endogenous Wnt/β-catenin signaling agonists. While Wnt/β-catenin signaling is greatly diminished in Alzheimer's disease (AD), it remains to be elucidated whether the inhibition of this pathway is associated with dysregulation of Wnt and Rspo proteins. By analyzing temporal cortex RNA-seq data of the human postmortem brain samples, we found that WNT1 and RRPO2 were significantly downregulated in human AD brains. In addition, the expression of Wnt acyltransferase porcupine (PORCN), which is essential for Wnt maturation and secretion, was greatly deceased in these human AD brains. Interestingly, the lowest levels of WNT1, PORCN, and RSPO2 expression were found in human AD brains carrying two copies of APOE4 allele, the strongest genetic risk factor of late-onset AD. Importantly, there were positive correlations among the levels of WNT1, PORCN, and RSPO2 expression in human AD brains. Supporting observations in humans, Wnt1, PORCN, and Rspo2 were downregulated and Wnt/β-catenin signaling was diminished in the 5xFAD amyloid model mice. In human APOE-targeted replacement mice, downregulation of WNT1, PORCN, and RSPO2 expression was positively associated with aging and APOE4 genotype. Finally, WNT1 and PORCN expression and Wnt/β-catenin signaling were inhibited in human APOE4 iPSC-derived astrocytes when compared to the isogenic APOE3 iPSC-derived astrocytes. Altogether, our findings suggest that the dysregulations of Wnt1, PORCN, and Rspo2 could be coordinated together to diminish Wnt/β-catenin signaling in aging- and APOE4-dependent manners in the AD brain.

Correlative Chemical Imaging Identifies Amyloid Peptide Signatures of Neuritic Plaques and Dystrophy in Human Sporadic Alzheimer's Disease.

Objective: Alzheimer's disease (AD) is the most common neurodegenerative disease. The predominantly sporadic form of AD is age-related, but the underlying pathogenic mechanisms remain not fully understood. Current efforts to combat the disease focus on the main pathological hallmarks, in particular beta-amyloid (Aβ) plaque pathology. According to the amyloid cascade hypothesis, Aβ is the critical early initiator of AD pathogenesis. Plaque pathology is very heterogeneous, where a subset of plaques, neuritic plaques (NPs), are considered most neurotoxic rendering their in-depth characterization essential to understand Aβ pathogenicity. Methods: To delineate the chemical traits specific to NP types, we investigated senile Aβ pathology in the postmortem, human sporadic AD brain using advanced correlative biochemical imaging based on immunofluorescence (IF) microscopy and mass spectrometry imaging (MSI). Results: Immunostaining-guided MSI identified distinct Aβ signatures of NPs characterized by increased Aβ1-42(ox) and Aβ2-42. Moreover, correlation with a marker of dystrophy (reticulon 3 [RTN3]) identified key Aβ species that both delineate NPs and display association with neuritic dystrophy. Conclusion: Together, these correlative imaging data shed light on the complex biochemical architecture of NPs and associated dystrophic neurites. These in turn are obvious targets for disease-modifying treatment strategies, as well as novel biomarkers of Aβ pathogenicity.

X-linked ubiquitin-specific peptidase 11 increases tauopathy vulnerability in women.

Although women experience significantly higher tau burden and increased risk for Alzheimer's disease (AD) than men, the underlying mechanism for this vulnerability has not been explained. Here, we demonstrate through invitro and invivo models, as well as human AD brain tissue, that X-linked ubiquitin specific peptidase 11 (USP11) augments pathological tau aggregation via tau deubiquitination initiated at lysine-281. Removal of ubiquitin provides access for enzymatic tau acetylation at lysines 281 and 274. USP11 escapes complete X-inactivation, and female mice and people both exhibit higher USP11 levels than males. Genetic elimination of usp11 in a tauopathy mouse model preferentially protects females from acetylated tau accumulation, tau pathology, and cognitive impairment. USP11 levels also strongly associate positively with tau pathology in females but not males. Thus, inhibiting USP11-mediated tau deubiquitination may provide an effective therapeutic opportunity to protect women from increased vulnerability to AD and other tauopathies.

A CHCHD6–APP axis connects amyloid and mitochondrial pathology in Alzheimer’s disease

The mechanistic relationship between amyloid-beta precursor protein (APP) processing and mitochondrial dysfunction in Alzheimer’s disease (AD) has long eluded the field. Here, we report that coiled-coil-helix-coiled-coil-helix domain containing 6 (CHCHD6), a core protein of the mammalian mitochondrial contact site and cristae organizing system, mechanistically connects these AD features through a circular feedback loop that lowers CHCHD6 and raises APP processing. In cellular and animal AD models and human AD brains, the APP intracellular domain fragment inhibits CHCHD6 transcription by binding its promoter. CHCHD6 and APP bind and stabilize one another. Reduced CHCHD6 enhances APP accumulation on mitochondria-associated ER membranes and accelerates APP processing, and induces mitochondrial dysfunction and neuronal cholesterol accumulation, promoting amyloid pathology. Compensation for CHCHD6 loss in an AD mouse model reduces AD-associated neuropathology and cognitive impairment. Thus, CHCHD6 connects APP processing and mitochondrial dysfunction in AD. This provides a potential new therapeutic target for patients.

Identification and Quantitation of Novel ABI3 Isoforms Relative to Alzheimer's Disease Genetics and Neuropathology.

Elucidating the actions of genetic polymorphisms associated with the risk of Alzheimer’s disease (AD) may provide novel insights into underlying mechanisms. Two polymorphisms have implicated ABI3 as a modulator of AD risk. Here, we sought to identify ABI3 isoforms expressed in human AD and non-AD brain, quantify the more abundant isoforms as a function of AD genetics and neuropathology, and provide an initial in vitro characterization of the proteins produced by these novel isoforms. We report that ABI3 expression is increased with AD neuropathology but not associated with AD genetics. Single-cell RNAseq of APP/PS1 mice showed that Abi3 is primarily expressed by microglia, including disease-associated microglia. In human brain, several novel ABI3 isoforms were identified, including isoforms with partial or complete loss of exon 6. Expression of these isoforms correlated tightly with total ABI3 expression but were not influenced by AD genetics. Lastly, we performed an initial characterization of these isoforms in transfected cells and found that, while full-length ABI3 was expressed in a dispersed punctate fashion within the cytosol, isoforms lacking most or all of exon six tended to form extensive protein aggregates. In summary, ABI3 expression is restricted to microglia, is increased with Alzheimer’s neuropathology, and includes several isoforms that display a variable tendency to aggregate when expressed in vitro.

Modeling the early stages of Alzheimer’s disease by administering intracerebroventricular injections of human native Aβ oligomers to rats

Alzheimer’s disease (AD) is a progressive and irreversible neurodegenerative disease characterized by the accumulation of aggregated amyloid beta (Aβ) and hyperphosphorylated tau along with a slow decline in cognitive functions. Unlike advanced AD, the initial steps of AD pathophysiology have been poorly investigated, partially due to limited availability of animal models focused on the early, plaque-free stages of the disease. The aim of this study was to evaluate the early behavioral, anatomical and molecular alterations in wild-type rats following intracerebroventricular injections of human Aβ oligomers (AβOs). Bioactive human AD and nondemented control brain tissue extracts were characterized using ELISA and proteomics approaches. Following a bilateral infusion, rats underwent behavioral testing, including the elevated plus maze, social recognition test, Morris water maze and Y-maze within 6 weeks postinjection. An analysis of brain structure was performed with manganese-enhanced MRI. Collected brain tissues were analyzed using stereology, immunohistochemistry, ELISA and qPCR. No sensorimotor deficits affecting motor performance on different maze tasks were observed, nor was spatial memory disturbed in AD rats. In contrast, a significant impairment of social memory became evident at 21 days postinjection. This deficit was associated with a significantly decreased volume of the lateral entorhinal cortex and a tendency toward a decrease in the total brain volume. Significant increase of cleaved caspase-3-positive cells, microglial activation and proinflammatory responses accompanied by altered expression of synaptic markers were observed in the hippocampus of AD rats with immunohistochemical and qPCR approaches at 6 weeks postinjection. Our data suggest that the social memory impairment observed in AβO-injected rats might be determined by neuroinflammatory responses and synaptopathy. An infusion of native oligomeric Aβ in the rat brain represents a feasible tool to model early plaque-free events associated with AD.