Postmortem Alzheimer's Disease Brain Research Articles

Unsaturated Fatty Acids Are Decreased in Aβ Plaques in Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-beta (Aβ) plaques in the brain, contributing to neurodegeneration. This study investigates lipid alterations within these plaques using a novel, label-free, multimodal approach. Combining infrared (IR) imaging, machine learning, laser microdissection (LMD), and flow injection analysis mass spectrometry (FIA-MS), we provide the first comprehensive lipidomic analysis of chemically unaltered Aβ plaques in post-mortem human AD brain tissue. IR imaging revealed decreased lipid unsaturation within plaques, evidenced by a reduction in the alkene (=C-H) stretching vibration band. The high spatial resolution of IR imaging, coupled with machine learning-based plaque detection, enabled precise and label-free extraction of plaques via LMD. Subsequent FIA-MS analysis confirmed a significant increase in short-chain saturated lipids and a concomitant decrease in long-chain unsaturated lipids within plaques compared to the surrounding tissue. These findings highlight a substantial depletion of unsaturated fatty acids (UFAs) in Aβ plaques, suggesting a pivotal role for lipid dysregulation and oxidative stress in AD pathology. This study advances our understanding of the molecular landscape of Aβ plaques and underscores the potential of lipid-based therapeutic strategies in AD.

Cross-disease modeling of peripheral blood identifies biomarkers of type 2 diabetes predictive of Alzheimer's disease.

Type 2 diabetes (T2D) is a significant risk factor for Alzheimer's disease (AD). Despite multiple studies reporting this connection, the mechanism by which T2D exacerbates AD is poorly understood. It is challenging to design studies that address co-occurring and comorbid diseases, limiting the number of existing evidence bases. To address this challenge, we expanded the applications of a computational framework called Translatable Components Regression (TransComp-R), initially designed for cross-species translation modeling, to perform cross-disease modeling to identify biological programs of T2D that may exacerbate AD pathology. Using TransComp-R, we combined peripheral blood-derived T2D and AD human transcriptomic data to identify T2D principal components predictive of AD status. Our model revealed genes enriched for biological pathways associated with inflammation, metabolism, and signaling pathways from T2D principal components predictive of AD. The same T2D PC predictive of AD outcomes unveiled sex-based differences across the AD datasets. We performed a gene expression correlational analysis to identify therapeutic hypotheses tailored to the T2D-AD axis. We identified six T2D and two dementia medications that induced gene expression profiles associated with a non-T2D or non-AD state. Finally, we assessed our blood-based T2DxAD biomarker signature in post-mortem human AD and control brain gene expression data from the hippocampus, entorhinal cortex, superior frontal gyrus, and postcentral gyrus. Using partial least squares discriminant analysis, we identified a subset of genes from our cross-disease blood-based biomarker panel that significantly separated AD and control brain samples. Our methodological advance in cross-disease modeling identified biological programs in T2D that may predict the future onset of AD in this population. This, paired with our therapeutic gene expression correlational analysis, also revealed alogliptin, a T2D medication that may help prevent the onset of AD in T2D patients.

Hyperactive neuronal networks facilitate tau spread in an Alzheimer's disease mouse model.

Pathological tau spreads throughout the brain along neuronal connections in Alzheimer's disease (AD), but the mechanisms that underlie this process are poorly understood. Given the high incidence and deleterious consequences of epileptiform activity in AD, we hypothesized neuronal hyperactivity and seizures are key factors in tau spread. To examine these interactions, we created a novel mouse model involving the cross of targeted recombination in active populations (TRAP) mice and the 5 times familial AD (5XFAD; 5X-TRAP) model allowing for the permanent fluorescent labelling of neuronal activity. To establish a causal role of seizures in tau spread, we seeded mice with human AD brain-derived tau lysate and induced seizures with pentylenetetrazol (PTZ) kindling. Comprehensive brain mapping of tau pathology and neuronal activity revealed that basal hyperactivity in 5X-TRAP mice was associated with increased tau spread, which was exacerbated by seizure induction through activated networks and correlated with memory deficits. Computational modeling revealed that anterograde tau spread was elevated in 5X-TRAP mice and that regional neuronal activity was predictive of tau spread to that brain region. On a cellular level, we found that in both saline and PTZ-treated 5X-TRAP mice, hyperactive neurons disproportionately contributed to the spread of tau. Further, we found that Synaptogyrin-3, a synaptic vesicle protein that interacts with tau, was increased following PTZ kindling in 5X-TRAP mice, possibly indicative of a synaptic mechanism underlying seizure-exacerbated tau spread. Importantly, postmortem AD brain tissue from patients with a history of seizures showed increased tau pathology in patterns indicative of increased spread and increased Synaptogyrin-3 levels compared to those without seizures. Overall, our study identifies neuronal hyperactivity and seizures as key factors underlying the pathobiological and cognitive progression of AD. Therapies targeting these factors should be tested clinically to slow tau spread and AD progression.

Role of PIM Kinase Inhibitor in the Treatment of Alzheimer's Disease.

Alzheimer's disease (AD), a neurodegenerative disorder, is the most prevalent form of senile dementia, causing progressive deterioration of cognition, behavior, and rational skills. Neuropathologically, AD is characterized by two hallmark proteinaceous aggregates: amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) formed of hyperphosphorylated tau. A significant study has been done to understand how Aβ and/or tau accumulation can alter signaling pathways that affect neuronal function. A conserved protein kinase known as the mammalian target of rapamycin (mTOR) is essential for maintaining the proper balance between protein synthesis and degradation. Overwhelming evidence shows mTOR signaling's primary role in age-dependent cognitive decline and the pathogenesis of AD. Postmortem human AD brains consistently show an upregulation of mTOR signaling. Confocal microscopy findings demonstrated a direct connection between mTOR and intraneuronal Aβ42 through molecular processes of PRAS40 phosphorylation. By attaching to the mTORC1 complex, PRAS40 inhibits the activity of mTOR. Furthermore, inhibiting PRAS40 phosphorylation can stop the Aβ-mediated increase in mTOR activity, indicating that the accumulation of Aβ may aid in PRAS40 phosphorylation. Physiologically, PRAS40 is phosphorylated by PIM1 which is a serine/threonine kinase of proto-oncogene PIM kinase family. Pharmacological inhibition of PIM1 activity prevents the Aβ-induced mTOR hyperactivity in vivo by blocking PRAS40 phosphorylation and restores cognitive impairments by enhancing proteasome function. Recently identified small-molecule PIM1 inhibitors have been developed as potential therapeutic to reduce AD-neuropathology. This comprehensive study aims to address the activity of PIM1 inhibitor that has been tested for the treatment of AD, in addition to the pharmacological and structural aspects of PIM1.

Single cell nuclei transcriptomics of human brains identify a role for homeostatic microglia in cellular senescence in Alzheimer’s disease

AbstractBackgroundCellular senescence is a hallmark of aging and has been implicated in several neurodegenerative diseases including Alzheimer’s disease (AD). Senescence cells undergo changes in gene expression and metabolism and can exhibit a so‐called “senescence‐associated secretory phenotype” (SASP) characterized by increased secretion of pro‐inflammatory molecules and factors which can damage nearby cells, contributing to AD pathology progression.MethodIn this study, we determined mechanisms of cellular senescence using human postmortem brain samples, cellular models, and APOE4 animal models. Bulk (n = 632) and single‐cell nuclei transcriptomic profiling (n = 427) of the human dorsolateral prefrontal cortex (DLPFC) from the Religious Order Study/Memory Aging Project (ROSMAP). Lipidomic profiling was performed on a subset of 200 brains from the midfrontal cortex of ROS.ResultOur findings revealed upregulation of cellular senescence signatures in postmortem AD brain tissues across different cell types in comparison with controls. We identified a strong correlation between SASP and arachidonic acid (AA) metabolism (P<0.001) in bulk RNA. In single cell nuclei transcriptomics, AA Activation was strongly correlated with P2RY12 (homeostatic) microglia (P<0.0001), and was associated with worse performance on all cognitive domains (p<0.001) and AD neuropathology (P<0.001) as shown in the figure. Lipidomic analysis of postmortem brain tissues confirmed activation of AA derived eicosanoids. Pathway analysis implicated the activation of calcium dependent phospholipase A2 (cPLA2). Inhibiting cPLA2 by treatment with ASB14780 reduced senescence‐associated eicosanoids in APOE4 mouse models.ConclusionThis work implicates the sustained activation of homeostatic microglia as an underlying mechanism of cellular senescence in the AD brain.

Tau Accumulation Induces Microglial State Alterations in Alzheimer's Disease Model Mice.

Unique microglial states have been identified in Alzheimer's disease (AD) model mice and postmortem AD brains. Although it has been well documented that amyloid-β accumulation induces the alteration of microglial states, the relationship between tau pathology and microglial states remains incompletely understood because of a lack of suitable AD models. In the present study, we generated a novel AD model mouse by the intracerebral administration of tau purified from human brains with primary age-related tauopathy into App knock-in mice with humanized tau. Immunohistochemical analyses revealed that Dectin-1-positive disease-associated microglia were increased in the AD model mice after tau accumulation in the brain. We then performed single-nucleus RNA sequencing on the AD model mice to evaluate the differences in microglial states with and without tau propagation and accumulation. By taking advantage of spatial transcriptomics and existing single-cell RNA sequencing datasets, we showed for the first time that tau propagation and accumulation induce a disease-associated microglial phenotype at the expense of an age-related nonhomeostatic counterpart (namely, white matter-associated microglia) in an AD model mouse brain. Future work using spatial transcriptomics at single-cell resolution will pave the way for a more appropriate interpretation of microglial alterations in response to tau pathology in the AD brain.

Post-Translational Modifications Control Phase Transitions of Tau.

The self-assembly of Tau into filaments, which mirror the structures observed in Alzheimer's disease (AD) brains, raises questions about the role of AD-specific post-translational modifications (PTMs) in the formation of paired helical filaments (PHFs). To investigate this, we developed a synthetic approach to produce Tau(291-391) featuring N-acetyllysine, phosphoserine, phosphotyrosine, and N-glycosylation at positions commonly modified in post-mortem AD brains. Using various electron and optical microscopy techniques, we discovered that these modifications generally hinder the in vitro assembly of Tau into PHFs. Interestingly, while acetylation's effect on Tau assembly displayed variability, either promoting or inhibiting phase transitions in cofactor-free aggregation, heparin-induced aggregation, and RNA-mediated liquid-liquid phase separation (LLPS), phosphorylation uniformly mitigated these processes. Our observations suggest that PTMs, particularly those situated outside the rigid core, are pivotal in the nucleation of PHFs. Moreover, with heparin-induced aggregation leading to the formation of heterogeneous aggregates, most AD-specific PTMs appeared to decelerate aggregation. The impact of acetylation on RNA-induced LLPS was notably site-dependent, whereas phosphorylation consistently reduced LLPS across all proteoforms examined. These insights underscore the complex interplay between site-specific PTMs and environmental factors in modulating Tau aggregation kinetics, highlighting the role of PTMs located outside the ordered filament core in driving the self-assembly.

Integrative pathway analysis across humans and 3D cellular models identifies the p38 MAPK-MK2 axis as a therapeutic target for Alzheimer's disease.

Alzheimer's disease (AD) presents a complex pathological landscape, posing challenges to current therapeutic strategies that primarily target amyloid-β (Aβ). Using a novel integrative pathway activity analysis (IPAA), we identified 83 dysregulated pathways common between both post-mortem AD brains and three-dimensional AD cellular models showing robust Aβ42 accumulation. p38 mitogen-activated protein kinase (MAPK) was the most upregulated common pathway. Active p38 MAPK levels increased in the cellular models, human brains, and 5XFAD mice and selectively localized to presynaptic dystrophic neurites. Unbiased phosphoproteomics confirmed increased phosphorylation of p38 MAPK substrates. Downstream activation of MAPK-activated protein kinase 2 (MK2) plays a crucial role in Aβ42-p38 MAPK-mediated tau pathology. Therapeutic targeting of the p38 MAPK-MK2 axis with selective inhibitors significantly reduced Aβ42-driven tau pathology and neuronal loss. IPAA prioritizes the best models to derisk target-drug discovery by integrating human tissue gene expression with functional readouts from cellular models, enabling the identification and validation of high-confidence AD therapeutic targets.

Transcriptomic alterations in APP/PS1 mice astrocytes lead to early postnatal axon initial segment structural changes

Alzheimer´s disease (AD) is characterized by neuronal function loss and degeneration. The integrity of the axon initial segment (AIS) is essential to maintain neuronal function and output. AIS alterations are detected in human post-mortem AD brains and mice models, as well as, neurodevelopmental and mental disorders. However, the mechanisms leading to AIS deregulation in AD and the extrinsic glial origin are elusive. We studied early postnatal differences in AIS cellular/molecular mechanisms in wild-type or APP/PS1 mice and combined neuron-astrocyte co-cultures. We observed AIS integrity alterations, reduced ankyrinG expression and shortening, in APP/PS1 mice from P21 and loss of AIS integrity at 21 DIV in wild-type and APP/PS1 neurons in the presence of APP/PS1 astrocytes. AnkyrinG decrease is due to mRNAs and protein reduction of retinoic acid synthesis enzymes Rdh1 and Aldh1b1, as well as ADNP (Activity-dependent neuroprotective protein) in APP/PS1 astrocytes. This effect was mimicked by wild-type astrocytes expressing ADNP shRNA. In the presence of APP/PS1 astrocytes, wild-type neurons AIS is recovered by inhibition of retinoic acid degradation, and Adnp-derived NAP peptide (NAPVSIPQ) addition or P2X7 receptor inhibition, both regulated by retinoic acid levels. Moreover, P2X7 inhibitor treatment for 2 months impaired AIS disruption in APP/PS1 mice. Our findings extend current knowledge on AIS regulation, providing data to support the role of astrocytes in early postnatal AIS modulation. In conclusion, AD onset may be related to very early glial cell alterations that induce AIS and neuronal function changes, opening new therapeutic approaches to detect and avoid neuronal function loss.

TRPC3 suppression ameliorates synaptic dysfunctions and memory deficits in Alzheimer's disease.

Transient receptor potential canonical (TRPC) channels are widely expressed in the brain; however, their precise roles in neurodegeneration, such as Alzheimer's disease (AD) remain elusive. Bioinformatic analysis of the published single-cell RNA-seq data collected from AD patient cohorts indicates that the Trpc3 gene is uniquely upregulated in excitatory neurons. TRPC3 expression is also upregulated in post-mortem AD brains, and in both acute and chronic mouse models of AD. Functional screening of TRPC3 antagonists resulted in a lead inhibitor JW-65, which completely rescued Aβ-induced neurotoxicity, impaired synaptic plasticity (e.g., LTP), and learning memory in acute and chronic experimental AD models. In cultured rat hippocampal neurons, we found that treatment with soluble β-amyloid oligomers (AβOs) induces rapid and sustained upregulation of the TRPC3 expression selectively in excitatory neurons. This aberrantly upregulated TRPC3 contributes to AβOs-induced Ca 2+ overload through the calcium entry and store-release mechanisms. The neuroprotective action of JW-65 is primarily mediated via restoring AβOs-impaired Ca 2+ /calmodulin-mediated signaling pathways, including calmodulin kinases CaMKII/IV and calcineurin (CaN). The synaptic protective mechanism via TRPC3 inhibition was further supported by hippocampal RNA-seq data from the symptomatic 5xFAD mice after chronic treatment with JW-65. Overall, these findings not only validate TRPC3 as a novel therapeutic target for treating synaptic dysfunction of AD but most importantly, disclose a distinct role of upregulated TRPC3 in AD pathogenesis in mediating Ca 2+ dyshomeostasis.

A Holistic Analysis of Alzheimer’s Disease-Associated lncRNA Communities Reveals Enhanced lncRNA-miRNA-RBP Regulatory Triad Formation Within Functionally Segregated Clusters

Recent studies on the regulatory networks implicated in Alzheimer’s disease (AD) evince long non-coding RNAs (lncRNAs) as crucial regulatory players, albeit a poor understanding of the mechanism. Analyzing differential gene expression in the RNA-seq data from the post-mortem AD brain hippocampus, we categorized a list of AD-dysregulated lncRNA transcripts into functionally similar communities based on their k-mer profiles. Using machine-learning-based algorithms, their subcellular localizations were mapped. We further explored the functional relevance of each community through AD-dysregulated miRNA, RNA-binding protein (RBP) interactors, and pathway enrichment analyses. Further investigation of the miRNA–lncRNA and RBP–lncRNA networks from each community revealed the top RBPs, miRNAs, and lncRNAs for each cluster. The experimental validation community yielded ELAVL4 and miR-16-5p as the predominant RBP and miRNA, respectively. Five lncRNAs emerged as the top-ranking candidates from the RBP/miRNA-lncRNA networks. Further analyses of these networks revealed the presence of multiple regulatory triads where the RBP–lncRNA interactions could be augmented by the enhanced miRNA–lncRNA interactions. Our results advance the understanding of the mechanism of lncRNA-mediated AD regulation through their interacting partners and demonstrate how these functionally segregated but overlapping regulatory networks can modulate the disease holistically.Graphical

Modeling APOE ε4 familial Alzheimer's disease in directly converted 3D brain organoids.

Brain organoids have become a valuable tool for studying human brain development, disease modeling, and drug testing. However, generating brain organoids with mature neurons is time-intensive and often incomplete, limiting their utility in studying age-related neurodegenerative diseases such as Alzheimer's disease (AD). Here, we report the generation of 3D brain organoids from human fibroblasts through direct reprogramming, with simplicity, efficiency, and reduced variability. We also demonstrate that induced brain organoids from APOE ε4 AD patient fibroblasts capture some disease-specific features and pathologies associated with APOE ε4 AD. Moreover, APOE ε4-induced brain organoids with mutant APP overexpression faithfully recapitulate the acceleration of AD-related pathologies, providing a more physiologically relevant and patient-specific model of familial AD. Importantly, transcriptome analysis reveals that gene sets specific to APOE ε4 patient-induced brain organoids are highly similar to those of APOE ε4 post-mortem AD brains. Overall, induced brain organoids from direct reprogramming offer a promising approach for more efficient and controlled studies of neurodegenerative disease modeling.

18F]Flotaza for Aβ Plaque Diagnostic Imaging: Evaluation in Postmortem Human Alzheimer's Disease Brain Hippocampus and PET/CT Imaging in 5xFAD Transgenic Mice.

The diagnostic value of imaging Aβ plaques in Alzheimer's disease (AD) has accelerated the development of fluorine-18 labeled radiotracers with a longer half-life for easier translation to clinical use. We have developed [18F]flotaza, which shows high binding to Aβ plaques in postmortem human AD brain slices with low white matter binding. We report the binding of [18F]flotaza in postmortem AD hippocampus compared to cognitively normal (CN) brains and the evaluation of [18F]flotaza in transgenic 5xFAD mice expressing Aβ plaques. [18F]Flotaza binding was assessed in well-characterized human postmortem brain tissue sections consisting of HP CA1-subiculum (HP CA1-SUB) regions in AD (n = 28; 13 male and 15 female) and CN subjects (n = 32; 16 male and 16 female). Adjacent slices were immunostained with anti-Aβ and analyzed using QuPath. In vitro and in vivo [18F]flotaza PET/CT studies were carried out in 5xFAD mice. Post-mortem human brain slices from all AD subjects were positively IHC stained with anti-Aβ. High [18F]flotaza binding was measured in the HP CA1-SUB grey matter (GM) regions compared to white matter (WM) of AD subjects with GM/WM > 100 in some subjects. The majority of CN subjects had no decipherable binding. Male AD exhibited greater WM than AD females (AD WM♂/WM♀ > 5; p < 0.001) but no difference amongst CN WM. In vitro studies in 5xFAD mice brain slices exhibited high binding [18F]flotaza ratios (>50 versus cerebellum) in the cortex, HP, and thalamus. In vivo, PET [18F]flotaza exhibited binding to Aβ plaques in 5xFAD mice with SUVR~1.4. [18F]Flotaza is a new Aβ plaque PET imaging agent that exhibited high binding to Aβ plaques in postmortem human AD. Along with the promising results in 5xFAD mice, the translation of [18F]flotaza to human PET studies may be worthwhile.

Development of a New Positron Emission Tomography Imaging Radioligand Targeting RIPK1 in the Brain and Characterization in Alzheimer's Disease.

Targeting receptor-interacting protein kinase 1 (RIPK1) has emerged as a promising therapeutic stratagem for neurodegenerative disorders, particularly Alzheimer's disease (AD). A positron emission tomography (PET) probe enabling brain RIPK1 imaging can provide a powerful tool to unveil the neuropathology associated with RIPK1. Herein, the development of a new PET radioligand, [11C]CNY-10 is reported, which may enable brain RIPK1 imaging. [11C]CNY-10 is radiosynthesized with a high radiochemical yield (41.8%) and molar activity (305 GBq/µmol). [11C]CNY-10 is characterized by PET imaging in rodents and a non-human primate, demonstrating good brain penetration, binding specificity, and a suitable clearance kinetic profile. It is performed autoradiography of[11C]CNY-10 in human AD and healthy control postmortem brain tissues, which shows strong radiosignal in AD brains higher than healthy controls. Subsequently, it is conducted further characterization of RIPK1 in AD using [11C]CNY-10-based PET studies in combination with immunohistochemistry leveraging the 5xFAD mouse model. It is found that AD mice revealed RIPK1 brain signal significantly higher than WT control mice and that RIPK1 is closely related to amyloid plaques in the brain. The studies enable further translational studies of [11C]CNY-10 for AD and potentially other RIPK1-related human studies.

Virus-like particle (VLP)-based vaccine targeting tau phosphorylated at Ser396/Ser404 (PHF1) site outperforms phosphorylated S199/S202 (AT8) site in reducing tau pathology and restoring cognitive deficits in the rTg4510 mouse model of tauopathy.

Tauopathies, including Alzheimer's disease (AD) and Frontotemporal Dementia (FTD), are histopathologically defined by the aggregation of hyperphosphorylated pathological tau (pTau) as neurofibrillary tangles in the brain. Site-specific phosphorylation of tau occurs early in the disease process and correlates with progressive cognitive decline, thus serving as targetable pathological epitopes for immunotherapeutic development. Previously, we developed a vaccine (Qβ-pT181) displaying phosphorylated Thr181 tau peptides on the surface of a Qβ bacteriophage virus-like particle (VLP) that induced robust antibody responses, cleared pathological tau, and rescued memory deficits in a transgenic mouse model of tauopathy. Here we report the characterization and comparison of two additional Qβ VLP-based vaccines targeting the dual phosphorylation sites Ser199/Ser202 (Qβ-AT8) and Ser396/Ser404 (Qβ-PHF1). Both Qβ-AT8 and Qβ-PHF1 vaccines elicited high-titer antibody responses against their pTau epitopes. However, only Qβ-PHF1 rescued cognitive deficits, reduced soluble and insoluble pathological tau, and reactive microgliosis in a 4-month rTg4510 model of FTD. Both sera from Qβ-AT8 and Qβ-PHF1 vaccinated mice were specifically reactive to tau pathology in human AD post-mortem brain sections. These studies further support the use of VLP-based immunotherapies to target pTau in AD and related tauopathies and provide potential insight into the clinical efficacy of various pTau epitopes in the development of immunotherapeutics.

Involvement of Endolysosomes and Aurora Kinase A in the Regulation of Amyloid β Protein Levels in Neurons.

Aurora kinase A (AURKA) is a serine/threonine-protein kinase that regulates microtubule organization during neuron migration and neurite formation. Decreased activity of AURKA was found in Alzheimer's disease (AD) brain samples, but little is known about the role of AURKA in AD pathogenesis. Here, we demonstrate that AURKA is expressed in primary cultured rat neurons, neurons from adult mouse brains, and neurons in postmortem human AD brains. AURKA phosphorylation, which positively correlates with its activity, is reduced in human AD brains. In SH-SY5Y cells, pharmacological activation of AURKA increased AURKA phosphorylation, acidified endolysosomes, decreased the activity of amyloid beta protein (Aβ) generating enzyme β-site amyloid precursor protein cleaving enzyme (BACE-1), increased the activity of the Aβ degrading enzyme cathepsin D, and decreased the intracellular and secreted levels of Aβ. Conversely, pharmacological inhibition of AURKA decreased AURKA phosphorylation, de-acidified endolysosomes, decreased the activity of cathepsin D, and increased intracellular and secreted levels of Aβ. Thus, reduced AURKA activity in AD may contribute to the development of intraneuronal accumulations of Aβ and extracellular amyloid plaque formation.

Co-registration of MALDI-MSI and histology demonstrates gangliosides co-localize with amyloid beta plaques in Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurological condition characterized by impaired cognitive function and behavioral alterations. While AD research historically centered around mis-folded proteins, advances in mass spectrometry techniques have triggered increased exploration of the AD lipidome with lipid dysregulation emerging as a critical player in AD pathogenesis. Gangliosides are a class of glycosphingolipids enriched within the central nervous system. Previous work has suggested a shift in a-series gangliosides from complex (GM1) to simple (GM2 and GM3) species may be related to the development of neurodegenerative disease. In addition, complex gangliosides with 20 carbon sphingosine chains have been shown to increase in the aging brain. In this study, we utilized matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) to interrogate the in situ relationship of a-series gangliosides with either 18 or 20 carbon sphingosine chains (d18:1 or d20:1, respectively) in the post-mortem human AD brain. Here, we expanded upon previous literature and demonstrated a significant decrease in the GM1 d20:1 to GM1 d18:1 ratio in regions of the dentate gyrus and entorhinal cortex in AD relative to control brain tissue. Then, we demonstrated that the MALDI-MSI profile of GM3 co-localizes with histologically confirmed amyloid beta (Aβ) plaques and found a significant increase in both GM1 and GM3 in proximity to Aβ plaques. Collectively, this study demonstrates a perturbation of the ganglioside profile in AD, and validates a pipeline for MALDI-MSI and classic histological staining in the same tissue sections. This demonstrates feasibility for integrating untargeted mass spectrometry imaging approaches into a digital pathology framework.

Distinct patterns of plaque and microglia glycosylation in Alzheimer's disease.

Glycosylation is the most common form of post-translational modification in the brain. Aberrant glycosylation has been observed in cerebrospinal fluid and brain tissue of Alzheimer's disease (AD) cases, including dysregulation of terminal sialic acid (SA) modifications. While alterations in sialylation have been identified in AD, the localization of SA modifications on cellular or aggregate-associated glycans is largely unknown because of limited spatial resolution of commonly utilized methods. The present study aims to overcome these limitations with novel combinations of histologic techniques to characterize the sialylation landscape of O- and N-linked glycans in autopsy-confirmed AD post-mortem brain tissue. Sialylated glycans facilitate important cellular functions including cell-to-cell interaction, cell migration, cell adhesion, immune regulation, and membrane excitability. Previous studies have not investigated both N- and O-linked sialylated glycans in neurodegeneration. In this study, the location and distribution of sialylated glycans were evaluated in three brain regions (frontal cortex, hippocampus, and cerebellum) from 10 AD cases using quantitative digital pathology techniques. Notably, we found significantly greater N-sialylation of the Aβ plaque microenvironment compared with O-sialylation. Plaque-associated microglia displayed the most intense N-sialylation proximal to plaque pathology. Further analyses revealed distinct differences in the levels of N- and O-sialylation between cored and diffuse Aβ plaque morphologies. Interestingly, phosphorylated tau pathology led to a slight increase in N-sialylation and no influence of O-sialylation in these AD brains. Confirming our previous observations in mice with novel histologic approach, these findings support microglia sialylation appears to have a relationship with AD protein aggregates while providing potential targets for therapeutic strategies.

Probing Alzheimer's pathology: Exploring the next generation of FDDNP analogues for amyloid β detection

Fluorescent probes are a powerful tool for imaging amyloid β (Aβ) plaques, the hallmark of Alzheimer’s disease (AD). Herein, we report the synthesis and comprehensive characterization of 21 novel probes as well as their optical properties and binding affinities to Aβ fibrils. One of these dyes, 1Ae, exhibited several improvements over FDDNP, an established biomarker for Aβ- and Tau-aggregates. First, 1Ae had large Stokes shifts (138–213 nm) in various solvents, thereby reducing self-absorption. With a high quantum yield ratio (φ(dichloromethane/methanol) = 104), 1Ae also ensures minimal background emission in aqueous environments and high sensitivity. In addition, compound 1Ae exhibited low micromolar binding affinity to Aβ fibrils in vitro (Kd = 1.603 µM), while increasing fluorescence emission (106-fold) compared to emission in buffer alone. Importantly, the selective binding of 1Ae to Aβ1–42 fibrils was confirmed by an in cellulo assay, supported by ex vivo fluorescence microscopy of 1Ae on postmortem AD brain sections, allowing unequivocal identification of Aβ plaques. The intermolecular interactions of fluorophores with Aβ were elucidated by docking studies and molecular dynamics simulations. Density functional theory calculations revealed the unique photophysics of these rod-shaped fluorophores, with a twisted intramolecular charge transfer (TICT) excited state. These results provide valuable insights into the future application of such probes as potential diagnostic tools for AD in vitro and ex vivo such as determination of Aβ1–42 in cerebrospinal fluid or blood.

Role of Neurocellular Endoplasmic Reticulum Stress Response in Alzheimer's Disease and Related Dementias Risk.

Currently, more than 55 million people around the world suffer from dementia, and Alzheimer's Disease and Related Dementias (ADRD) accounts for nearly 60-70% of all those cases. The spread of Alzheimer's Disease (AD) pathology and progressive neurodegeneration in the hippocampus and cerebral cortex is strongly correlated with cognitive decline in AD patients; however, the molecular underpinning of ADRD's causality is still unclear. Studies of postmortem AD brains and animal models of AD suggest that elevated endoplasmic reticulum (ER) stress may have a role in ADRD pathology through altered neurocellular homeostasis in brain regions associated with learning and memory. To study the ER stress-associated neurocellular response and its effects on neurocellular homeostasis and neurogenesis, we modeled an ER stress challenge using thapsigargin (TG), a specific inhibitor of sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), in the induced pluripotent stem cell (iPSC)-derived neural stem cells (NSCs) of two individuals from our Mexican American Family Study (MAFS). High-content screening and transcriptomic analysis of the control and ER stress-challenged NSCs showed that the NSCs' ER stress response resulted in a significant decline in NSC self-renewal and an increase in apoptosis and cellular oxidative stress. A total of 2300 genes were significantly (moderated t statistics FDR-corrected p-value ≤ 0.05 and fold change absolute ≥ 2.0) differentially expressed (DE). The pathway enrichment and gene network analysis of DE genes suggests that all three unfolded protein response (UPR) pathways, protein kinase RNA-like ER kinase (PERK), activating transcription factor-6 (ATF-6), and inositol-requiring enzyme-1 (IRE1), were significantly activated and cooperatively regulated the NSCs' transcriptional response to ER stress. Our results show that IRE1/X-box binding protein 1 (XBP1) mediated transcriptional regulation of the E2F transcription factor 1 (E2F1) gene, and its downstream targets have a dominant role in inducing G1/S-phase cell cycle arrest in ER stress-challenged NSCs. The ER stress-challenged NSCs also showed the activation of C/EBP homologous protein (CHOP)-mediated apoptosis and the dysregulation of synaptic plasticity and neurotransmitter homeostasis-associated genes. Overall, our results suggest that the ER stress-associated attenuation of NSC self-renewal, increased apoptosis, and dysregulated synaptic plasticity and neurotransmitter homeostasis plausibly play a role in the causation of ADRD.