Translational Neurodegeneration

Extracellular amyloid plaques, the pathognomonic hallmark of Alzheimers Disease (AD), are also observed in cognitively unimpaired subjects in the preclinical stages. Progressive accumulation of fibrillar amyloid-{beta} (A{beta}) as plaques and perivascular deposits occur two decades prior to clinical onset, making A{beta} a long-lived peptide. To characterize the amyloid plaques biochemically, both the A{beta}-load as well the post-translational modifications (PTMs) could serve as markers for distinguishing the pre-clinical stage compared to later prodromal and clinical stages of AD. Recently, we described the presence of extensive isomerization of the A{beta} N-terminus in AD post-mortem brains that are significantly increased compared to the age-matched non-AD control brains with A{beta} aggregates in the frontal cortex. In this report, we used targeted mass spectrometry to conduct a quantitative analysis of the most common PTMs associated with A{beta}; pyroglutamation, citrullination, N-terminal truncation (A{beta}4-x), C-terminal truncation (A{beta}42 and A{beta}40), and isomerization of aspartic acid residues (Asp-1 and Asp-7) in postmortem human brain tissue from pathologically negative (no A{beta} plaques) controls, controls with A{beta} plaques, Parkinsons disease (PD) with and without A{beta} accumulation/plaques and symptomatic AD. The AD cases contained statistically significant amounts of Asp-1and Asp-7 isomerized A{beta}1-15 ([~] 90 %) compared to controls (preclinical AD) and PD brains with fibrillar A{beta} aggregates/deposits. We find that ratio of isomerized N-terminus A{beta} (A{beta}1-15) species in the brain detergent soluble pool differentiates older fibrillar A{beta} deposits in symptomatic AD brain compared to A{beta} deposits detected in preclinical AD and PD. Citrullinated A{beta}3pglu-15 was increased only in symptomatic AD, highlighting this A{beta} PTM is a unique feature of parenchymal plaques in advanced AD. Our results have implications for early therapeutic targeting of these modified species as well potential for better biofluid biomarker development for drug efficacy monitoring.

Proteomic studies of human Alzheimers disease brain tissue have exceptional potential to identify protein changes that drive disease and to identify new drug targets. Here, we detail a combined analysis of 38 published Alzheimers disease proteomic studies, generating a comprehensive map of protein changes in human brain tissue across thirteen brain regions, three disease stages (preclinical Alzheimers disease, mild cognitive impairment, advanced Alzheimers disease), and proteins enriched in amyloid plaques, neurofibrillary tangles, and cerebral amyloid angiopathy. Our dataset is compiled into a user-friendly, searchable database called NeuroPro. Our combined analysis included 18,119 reported protein differences in human Alzheimers disease brain tissue, which mapped to 5,311 total altered proteins. Proteomic studies were remarkably consistent. 848 proteins were consistently altered in [≥]5 studies, many of which are understudied in the Alzheimers field. Comparison of protein changes in early-stage and advanced Alzheimers disease revealed significant synapse, vesicle, and lysosomal changes early in disease, but widespread mitochondrial changes only in advanced Alzheimers disease. Comparison of vulnerable and resistant brain regions suggested that protein changes in resistant regions in advanced Alzheimers disease are similar to those in vulnerable regions in early-stage Alzheimers disease, indicating a temporal progression of protein dysfunction during Alzheimers disease advancement. We conclude that NeuroPro is a powerful new resource that provides new insights into human Alzheimers disease brain protein changes and highlights novel proteins of particular interest that may mechanistically drive Alzheimers disease.

BackgroundThiamine diphosphate (TDP) reduction plays an important role in cerebral glucose hypometabolism, the neurodegenerative indicator, in Alzheimers disease (AD). The mechanism underlying TDP reduction remains elusive. Thus, it is critical to define the mechanism and its effect on neurodegeneration, the pathological basis of the disease occurrence and progression. MethodsThe mRNA levels of all known genes associated with thiamine metabolism, including thiamine pyrophosphokinase (TPK), Solute Carrier Family 19 Member 2 (SLC19A2), SLC19A3, and SLC25A19, in brain samples of patients with AD and other neurodegenerative disorders in multiple independent datasets were analyzed. TPK protein levels were further examined in the brain tissues of AD patients and control subjects. A mouse model with conditional knockout (cKO) of TPK gene in the excitatory neurons of adult brain was established. ResultsThe brain TPK mRNA level was markedly lower in AD patients, but not in other neurodegenerative disorders. The brain TPK protein level was also significantly decreased in AD patients. TPK gene knockout in the mice caused cerebral glucose hypometabolism, {beta}-amyloid deposition, Tau hyperphosphorylation, neuroinflammation, and neuronal loss and brain atrophy. Cross-species correlation analysis revealed the similar changes of gene profiling between the cKO mice and AD patients. ConclusionsThe deficiency of brain TPK, a key enzyme for TDP synthesis, is specific to AD. The cKO mice show AD-associated phenotypes and could serve as a new mouse model for AD studies. Our study provides a novel insight into the critical role of TPK in AD pathogenesis and its potential for the disease treatment.

AD presents with severe neurodegeneration which leads to cognitive deficits and dementia. Identifying the molecular signals that attenuate neurodegeneration in AD may be exploited as therapeutic targets. This study revealed that transgenic AD mice (PSAPP) exhibit decreased caveolin-1 (Cav-1), a membrane/lipid raft (MLR) scaffolding protein that organizes synaptic signaling components. Subcellularly, Cav-1 and full length (fl)-TrkB were significantly decreased in MLRs. We thus developed an in vivo gene therapy that re-expresses neuronal-targeted Cav-1 using the synapsin promoter (SynCav1). While AD mice showed significant learning and memory deficits at 9 and 11 months, AD mice that received hippocampal SynCav1 (AD-SynCav1) maintained normal learning and memory at 9 and 11 months respectively. Furthermore, AD-SynCav1 mice showed preserved hippocampal MLR-localized fl-TrkB, synaptic ultrastructure, dendritic arborization and axonal myelin content, all of which occurred independent of reducing amyloid deposit and astrogliosis. Thus, SynCav1 demonstrates translational potential to treat AD by delaying neurodegeneration. SummaryTransgenic PSAPP mice exhibit decreased hippocampal expression of the membrane lipid raft (MLR) scaffolding protein caveolin-1. Synapsin-promoted re-expression of Cav-1 (termed SynCav1) mitigated neuropathology and cognitive deficits. SynCav1 gene therapy has the potential to treat AD and other forms of neurodegeneration.

Familial Alzheimers disease (AD) involving known AD causing genes accounts for a small fraction of cases, the vast majority are sporadic. Neuroinflammation, secondary to viral infection, has been suggested as an initiating or accelerating factor. In this work we tested the hypothesis that SARS-CoV-2 (SCV2) viral infection accelerates the development of AD pathology in mouse models of AD. We profiled transcriptomic changes using transgenic APP/PSEN1 and P301S mouse models that develop AD pathology and k18hACE2 mice that express the humanized ACE2 receptor used by SCV2 to enter cells. This study identified the interferon and chemokine responses constituting key shared pathways between SCV2 infection and the development of AD pathology. Two transgenic mouse models of AD: APP/PSEN1 (develops amyloid pathology) and 3xTg AD (develops both amyloid and tau pathology) were crossed with k18-hACE2 mice to generate hybrid hACE2-3xTg and hACE2-APP/PSEN1 mice. Neuroinflammation and amyloid deposition in the brain of infected mice were imaged in vivo using molecular MRI (mMRI) probes and confirmed postmortem by histopathology. Results show that 11-14-month-old SCV2 infected hACE2-3xTg mice exhibit neuroinflammation 10 days post infection and 4-5-month-old hACE2-APP/PS1 hybrid mice develop amyloid deposits, while age-matched uninfected mice exhibit neither phenotype. This suggests that SCV2 infection could induce or accelerate AD when risk factors are present.

Alzheimers Disease (AD) is distinguished by the presence of two key pathological features: amyloid plaques, accumulations of proteolytic products of Amyloid Precursor Protein, and neurofibrillary tangles (NFTs), intracellular aggregations of microtubule-associated protein tau. NFTs first appear in particular entorhinal cortex (EC) neurons (called pre-alpha neurons) in asymptomatic patients, then continue to spread through other connected brain regions as the disease progresses. This stereotypical progression of tauopathy through synaptically connected brain regions (i.e. Braak stages) not only suggests that the tauopathy in AD spreads transsynaptically, it also raises the question whether particular neuronal subtypes and/or brain regions are especially prone to tauopathy. We explored this question by overexpressing wildtype human tau protein (hTau) in a variety of entorhinal and neocortical neuronal subtypes. We then compared the tendencies of different neuronal cell types to develop different pathological tau species over time and found that tau pathology does indeed develop at markedly different rates in different neuronal subtypes. Perhaps unsurprisingly, the EC is particularly prone, with the likely rat cognates of the pre-alpha neurons (ECLII fan cells) among the first to express pathological tau label. Fan cells were not, however, the neurons with the greatest vulnerability to generate pathological tau species: subsets of ECLIII neurons were found to express disproportional amounts of pathological tau. This is of particular interest given that the next structures to develop AD-related tauopathy after the EC in patients are CA1 hippocampus and subiculum, where ECLIII neurons project, rather than the dentate gyrus and CA3, where ECLII fan cells project. These results demonstrate differential susceptibility of different neuronal subtypes to pathological tau species and suggest distinct roles for different entorhinal neuronal subtypes in the propagation of the tauopathy underlying AD-related neurodegeneration.

Sleep disturbances are prevalent in Alzheimers disease (AD) and Progressive Supranuclear Palsy (PSP), often exacerbating disease progression. Understanding the neuropathological basis of these disturbances is essential for identifying potential therapeutic targets. This study investigates the intermediate nucleus (IntN) of the human hypothalamus--a key sleep-regulating region analogous to the rodent ventrolateral preoptic area (VLPO)--to assess neuronal loss and tau pathology in AD and PSP. Using postmortem brain tissue, we applied unbiased stereology to quantify galanin-expressing neurons and phosphorylated tau (p-tau) accumulation. Among 26 cases analyzed, both AD and PSP exhibited significant neuronal loss in the IntN, with PSP showing the most pronounced reduction (84.9% fewer neurons than healthy controls [HC]). In AD, neuronal loss correlated with Braak staging, with late-stage AD cases (Braak 5-6) demonstrating a 76.9% reduction in galanin-expressing neurons compared to HC, while non-galanin neurons exhibited a more moderate decline (45.7%). In PSP, extensive neuronal loss precluded a clear assessment of p-tau burden. These findings suggest a differential neuronal vulnerability to tau pathology across diseases, aligning with distinct sleep disturbances observed in each condition. PSP, characterized by severe insomnia despite preserved wake-promoting neurons, may be explained by the near-total loss of NREM sleep-regulating neurons. In contrast, AD exhibits a progressive decline in both wake- and sleep-promoting neurons, contributing to excessive daytime sleepiness and sleep fragmentation. This study provides critical insights into the selective neuronal vulnerabilities underlying sleep dysfunction in tauopathies, emphasizing the need for targeted interventions to mitigate sleep disturbances in these disorders.

We report consistent increases in phosphoglycerate dehydrogenase (PHGDH) expression in mouse models of Alzheimers disease (AD) (3xTg-AD) and related tauopathy (PS19), particularly in hippocampal astrocytes. Human single-cell RNA-sequencing data reveal a sequential increase of PHGDH expression in people with no, early, and late AD pathology, which is corroborated by protein mass spectrometry and immunohistochemical analyses of three independent cohorts. A sequential increase of PHGDH expression also correlates with increasing clinical AD symptoms and worsening cognitive decline in patients. The consistent increase of PHGDH expression in six AD cohorts (Mayo, ROSMAP, Mount Sinai, Baltimore, Amsterdam, and UCSD/UCI) corroborates with the recent report of PHGDH extracellular RNA in blood plasma as a candidate biomarker for early diagnosis of AD and offers a caution to the suggested use of L-serine as a potential therapy of AD.

Substantia nigra pars compacta dopamine neuron loss and Lewy pathology, aggregates of -synuclein, characterize Parkinsons disease and Dementia with Lewy Bodies. Lewy pathology localizes to cortical neurons, and is found as Lewy neurites in the striatum, but its effects on excitatory synaptic function are just beginning to be understood. Corticostriatal projections regulate motor and cognitive behaviors impaired in these disorders. Here, -synuclein aggregation was induced in mouse M2 cortex, a vulnerable region in human disease. Early after initiation, aggregates localized to corticostriatal vesicular glutamate transporter 1 (vGLUT1)-positive terminals, with sparing of spiny projection neuron (SPN) soma, and dopamine terminals and neurons. Corticostriatal presynaptic aggregates significantly impaired glutamatergic transmission, without overt cortical neuron loss, and were associated with decreased synaptic density and volume. Thus, formation of presynaptic -synuclein aggregates impairs corticostriatal function without degeneration of cortical neurons or striatal dopamine terminals, suggesting pathologic -synuclein is sufficient for synaptic loss. Our findings also point to early synaptic dysfunction as a therapeutic target in Lewy body diseases.

Background and Hypothesis: Alzheimers disease with psychosis (AD+P) is a subgroup of AD patients with more rapid cognitive deterioration. While our previous study showed that AD+P is associated with loss of prefrontal cortex postsynaptic density (PSD) proteins, identifying proteins in the broader cellular environment that influence PSD loss addresses a critical knowledge gap about synaptic dysfunction mechanisms in early disease stages. Study Design: We conducted a proteomic analysis comparing prefrontal grey matter cortex tissue homogenates from elderly normal controls (n=18), individuals with AD+P (n=61), and individuals with AD-P (n=48), all with Braak stages 3-5. Study Results: AD+P showed the most pronounced alterations relative to controls (178 proteins with q<0.05), although alterations in AD-P and AD+P relative to controls were highly similar (R{superscript 2}=0.965, p<0.001). Weighted-gene correlation network analysis (WGCNA) identified four modules significantly associated with disease status comparing AD subjects to controls, but none differed significantly between AD+P and AD-P. We identified 15 proteins significantly correlated with PSD yield across all samples, including ENPP6, linked to AD+P by GWAS. Additionally, PSD yield-associated proteins showed minimal overlap with altered AD proteins (1 of 137). WGCNA revealed one module significantly correlated with PSD yield across all samples, enriched for inflammatory terms. Conclusions: Our findings suggest a model in which AD+P arises from the combination of quantitative alterations within a shared AD proteome profile and a superimposed set of protein alterations correlated with PSD yield that are largely independent of the shared AD proteome, conferring distinct mechanisms of synaptic vulnerability and psychosis risk.

Synaptic dysfunction is an early hallmark of Alzheimers disease, characterized by the disruption of synaptic transmission and plasticity. Central to these processes is endosomal trafficking, mediated by the retromer complex, which orchestrates the movement of vesicle contents for recycling to the plasma membrane, return to the Golgi, or degradation. Variants of VPS35, the cargo recognition component of the retromer complex, have been linked to neurodegenerative diseases, including Parkinsons disease (PARK17, D620N mutation) and Alzheimers disease (L625P mutation). While substantial research has focused on Parkinsons, the role of VPS35 in Alzheimers has been less explored. This study investigates the acute neuroprotective effects of retromer-stabilizing compounds in the 5xFAD mouse model of Alzheimers. Our results reveal that stabilization of the retromer complex not only mitigates pathogenic A{beta} production mechanisms but also compensates for early synaptic dysfunction and microglial activation. Specifically, we observed significant modulation of genes involved in long-term potentiation and a reduction in abnormal retromer-associated cargos. These findings highlight the potential of retromer stabilisation as atherapeutic strategy to address fundamental pathological pathological processes in Alzheimers disease.

According to the prevalent Amyloid Hypothesis, the underlying cause for neurodegeneration in Alzheimer Disease (AD) is attributed to the accumulation of misfolded Amyloid {beta} and tau protein in the form of extracellular sticky plaques and neurofibrillary tangles respectively. These protein accumulations are thought to be caused by impaired waste removal. In an alternative hypothesis, we have proposed the existence of an extensive glial canal system that is likely formed by myelinated aquaporin-4 (AQP4)-expressing tanycytes and removes cellular waste from the hippocampal formation. Here, we demonstrate that tanycyte-derived waste-internalizing receptacles are immunoreactive for A{beta} and emanate from specialized nucleus-like organelles in the following referred to as tanysomes. Utilizing RNA-scope in situ hybridization, we demonstrate that these receptacle-forming tanysomes express RNA for AQP4 and the A{beta}-related genes, amyloid precursor protein, and presenilin 1. These findings suggest that A{beta} is likely synthesized where receptacle formation is observed and that A{beta} may play an important structural role in receptacle formation. In AD-affected hippocampus excessive amounts of A{beta}-immunoreactive waste receptacles emerge from tanysomes and have the appearance of plaques in A{beta}-immunolabeled hippocampus. Moreover, we demonstrate that the same receptacle-forming organelles exhibit strong immunolabeling for hyperphosphorylated tau protein in AD-affected tissue. We postulate that both proteins may play important structural roles in waste uptake and that hypertrophic swelling of impaired tanycytes in AD-affected brain may be due to obstructions of this extensive interconnected glial canal system.

Millions of people suffer worldwide from neurodegenerative diseases ranging from rapidly progressing and fatal motor neuron diseases like Amyotrophic Lateral Sclerosis (ALS) to more chronic illnesses such as frontotemporal dementia (FTD) and Alzheimers disease (AD). A growing number of studies have implicated neuroinflammation as a key and causative phenomenon and an important target for novel therapeutics for these diseases. Neuroinflammation is characterized by reactive glial cells that produce pro-inflammatory neurotoxic cytokines. Our previous studies have shown a brain-penetrant Nanoligomer cocktail (NI112) inhibiting the neuroinflammation mediators nuclear factor kappa-light-chain-enhancer of activated B cells (NF-{kappa}B) and NOD-like receptor family, pyrin domain containing 3 (NLRP3) is a safe, targeted, and effective neurotherapeutic drug. Here, we show that a four-week NI112 treatment is therapeutic using: 1) an ALS-FTD 3D human motor neuron organoid model of tar DNA binding protein 43 (TDP-43, a key contributor to ALS pathology) overexpression (knock-in); 2) an AD model of APOE4/APOE4 (AD risk allele) double mutation in human neurons comprising a 3D human prefrontal cortex (PFC) organoid; and 3) multiple in vivo (mouse models) of the same/related conditions. In 3D organoids made from healthy motor neurons (HMN negative control) and TDP-43 overexpressing (or ALS organoids), we monitored the mean firing rate using calcium signaling as a functional output, while measuring TDP-43 and other key neurodegeneration biomarkers. After 4 weeks, we observed a massive improvement in the mean firing rate of NI112-treated ALS organoids compared to untreated ALS organoids, which was more comparable to healthy HMN organoids. Similarly, we found a significant decrease in neurodegeneration markers like amyloid beta 42 (A{beta}42) in NI112-treated AD organoids compared to untreated AD organoids (A{beta}42 comparable to healthy PFC organoids). In the mouse ALS (SOD1-G93A) model, we observed behavioral improvements and restoration of motor function (e.g., grip strength) in NI112-treated mice, and in mouse AD model mice (radiation-induced accelerated neuropathology in APP/PS1, and rTg4510 phospho-tau), we observed improved cognition. In both models, we also found an accompanying reduction in neuroinflammation and reduced neuropathology. These results show the promise for further testing and development of neuroinflammation-targeting Nanoligomers to benefit patients suffering from debilitating neurodegenerative diseases like ALS, FTD, and AD.

Analyzing Alzheimers disease (AD) pathology within anatomical subregions is a significant challenge, often carried out by pathologists using a standardized, semi-quantitative approach. To augment traditional methods, a high-throughput, high-resolution pipeline was created to classify the distribution of AD pathology within hippocampal subregions. USC ADRC post-mortem tissue sections from 51 patients were stained with 4G8 for amyloid, Gallyas for neurofibrillary tangles (NFTs) and Iba1 for microglia. Machine learning (ML) techniques were utilized to identify and classify amyloid pathology (dense, diffuse and APP (amyloid precursor protein)), NFTs, neuritic plaques and microglia. These classifications were overlaid within manually segmented regions (aligned with the Allen Human Brain Atlas) to create detailed pathology maps. Cases were separated into low, intermediate, or high AD stages. Further data extraction enabled quantification of plaque size and pathology density alongside ApoE genotype, sex, and cognitive status. Our findings revealed that the increase in pathology burden across AD stages was driven mainly by diffuse amyloid. The pre and para-subiculum had the highest levels of diffuse amyloid while NFTs were highest in the A36 region in high AD cases. Moreover, different pathology types had distinct trajectories across disease stages. In a subset of AD cases, microglia were elevated in intermediate and high compared to low AD. Microglia also correlated with amyloid pathology in the Dentate Gyrus. The size of dense plaques, which may represent microglial function, was lower in ApoE4 carriers. In addition, individuals with memory impairment had higher levels of both dense and diffuse amyloid. Taken together, our findings integrating ML classification approaches with anatomical segmentation maps provide new insights on the complexity of disease pathology in AD progression. Specifically, we identified diffuse amyloid pathology as being a major driver of AD in our cohort, regions of interest and microglial responses that might advance AD diagnosis and treatment.

Alzheimers disease (AD) is defined by the accumulation of neurofibrillary tangles containing hyperphosphorylated Tau and plaques containing Amyloid-{beta} (A{beta}). The aggregation of these two proteins is considered central to the disease. The lack of animal models that can recapitulate A{beta} and tau pathologies without overexpressing these proteins has hindered AD research. Accelerating pathology by inoculating A{beta} and tau seeds has helped to understand their prion-like propagation in the brain. Previous studies failed to characterise both A{beta} and tau pathologies in vivo upon inoculating AD brain homogenates. Here we present a longitudinal and systematic study; we inoculated the AppNL-F/NL-F knockin mice, which express humanised A{beta} and murine wild-type tau, with extracts from diseased human brains to analyse the contribution of A{beta} and tau assemblies to AD pathogenesis. We found that mice inoculated with AD brain extracts evinced early and prominent amyloid deposition, while those injected with control brain extracts or vehicle did not. Parenchymal and vascular amyloid accumulated in the same brain regions affected in control-inoculated AppNL-F/NL-F mice. However, the extent of vascular amyloid far exceeded that seen in AppNL-F/NL-Fmice injected with control brain extracts, and parenchymal deposits extended to a previously untargeted brain region - the cerebellum. An end-point titration of an AD brain homogenate in AppNL-F/NL-F mice demonstrated that human A{beta} seeds can be titrated in a prion-like fashion, which is useful for sample comparison, diagnostic and risk studies. Notably, the inoculation of AppNL-F/NL-F mice with AD brain homogenate induced intense tau phosphorylation, and provides more detailed context for the inoculation of AppNL-F/NL-F mice with human samples to study temporal and mechanistic relationships between A{beta} and tau pathology, vascular amyloid deposition and bioactivity of A{beta} seeds.

Herpes Simplex virus type 1 (HSV-1) is a highly prevalent neurotropic virus from the alphaherpesviruses family. In recent years, a growing body of research has focused on the potential role of HSV-1 infections and recurrent reactivations in the pathophysiology of Alzheimers disease (AD). In particular, it has been hypothesized that HSV-1 could initiate or amplify the formation of neuropathological lesions characteristic of AD. To explore further this hypothesis, we adopted an integrated approach aiming at deciphering the impact of HSV-1 infection on AD molecular markers (A{beta} and Tau pathologies) and combining experimental animal models of in vivo infection, postmortem neuropathological analysis of AD brains, as well as in-vivo clinical analysis in AD patients. In animal models of peripheral (labial) infection with HSV-1 virus, we analyzed viral dissemination from peripheral tissues to the CNS, and the associated neuropathological consequences. Histological and molecular analyses revealed the occurrence of viral material (RNA, proteins) in the brainstem, the primary site of viral neuroinvasion, and in more anterior regions of the brain. Viral signatures were accompanied by early abnormal deposits of A{beta} peptides and accumulation of phosphoTau (pTau) proteins in various brain areas. Neuropathological examination of AD/control participants also underlined the presence of HSV-1 DNA in the human brainstem (pons) that was always associated with local A{beta}/Tau aggregates. Finally, in AD patients, associations were found between HSV-1 seropositivity and neuropathological lesion burden (region-specific Tau and A{beta} deposition detected by neuroimaging). Taken together, these data provide new evidence in favor of the involvement of HSV-1 in the pathophysiology of AD, stressing a possible causal link between HSV-1 infection, neuroinvasion and AD neuropathological hallmarks (A{beta} lesions and tauopathy).

One of the neuropathological hallmarks of Alzheimers disease (AD) is the accumulation of amyloid-{beta} (A{beta}) plaques, which is preceded by intraneuronal build-up of toxic, aggregated A{beta} during disease progression. A{beta} plaques are first deposited in the neocortex before appearing in the medial temporal lobe, and tau pathology with subsequent neurodegeneration in the latter anatomical region causes early memory impairments in patients. Current research suggests that early intraneuronal A{beta} build-up may begin in superficial layers of lateral entorhinal cortex (LEC). To examine whether manipulation of neuronal activity of LEC layer II neurons affected intraneuronal A{beta} levels in LEC and in downstream perforant path terminals in the hippocampus (HPC), we used a chemogenetic approach to selectively and chronically silence superficial LEC neurons in young and aged 3xTg AD mice and monitored its effect on intraneuronal A{beta} levels in LEC and HPC. Chronic chemogenetic silencing of LEC neurons led to reduced early intraneuronal A{beta} in LEC and in projection terminals in the HPC, compared with controls. Early intraneuronal A{beta} levels in the downstream HPC correlated with activity levels in superficial layers of LEC, with the subiculum being the earliest subregion involved, and our findings give evidence to early AD neuropathology originating in select neuronal populations.

The accumulation of tau tangles and A{beta} plaques are prominent neuropathologies that characterize Alzheimers disease (AD) and Down Syndrome (DS). Continuous developments of PET tracers as biomarkers can be supported by autoradiography to validate effectiveness and accuracy of binding properties that elucidate the pathophysiology of DSAD and AD. This in vitro comparative study evaluates [125I]IPPI binding to tau and [125I]IBETA binding to A{beta} plaques in the frontal cortex (FCX) and temporal cortex (TCX) of postmortem human brain slices of AD (n=5), DSAD (n=5), and cognitively normal (CN) (n=5) cases. With anti-tau and anti-A{beta} immunostains confirming the presence of tau and A{beta} plaques, [125I]IPPI and [125I]IBETA binding in autoradiographic images were significantly higher in DSAD and AD gray matter (GM) compared to CN. When comparing DSAD with AD, FCX and TCX GM binding was similar throughout DSAD and AD except in FCX GM where there was 48% more [125I]IPPI binding in DSAD than AD. In vitro drug inhibition studies revealed that [125I]IPPI binding was significantly inhibited with increasing harmine concentrations (IC50=115{+/-}40 nM) in DSAD FCX and TCX but KuFal194 minimally inhibited [125I]IPPI binding in the same cases. The GM/white matter ratios for DSAD ([125I]IPPI=4.1, [125I]IBETA=2.9) and AD ([125I]IPPI=4.2, [125I]IBETA=2.6) were significantly greater than CN ([125I]IPPI=1.3, [125I]IBETA=1.2). A positive correlation between [125I]IPPI and [125I]IBETA binding suggests a synergistic relationship between tau and A{beta} plaque in DSAD and AD pathology. This study demonstrates that [125I]IPPI and [125I]IBETA may serve as novel radiotracers in both DSAD and AD to continue diagnostic investigations in vivo.

Structured AbstractINTRODUCTION Tau pathology typically occurs in Alzheime[r]s disease (AD), however is also frequently present in Parkinso[n]s disease dementia (PDD) and Dementia with Lewy Bodies (DLB), yet its disease-specific signature is unclear. METHODSFive tau, amyloid-{beta}, -synuclein and neuronal markers were analysed across hippocampal subfields in non-demented controls (CTLs), AD, PDD and DLB using multiplex immunohistochemistry, single-tangle classification and confocal imaging. RESULTSAT8, pTau217, and GT38 were predominatly detected in AD, while pS422 was enriched in PDD and pS396 showed a region- and disease-specific pattern. DLB resembled AD in subregional tau distribution. Tau marker correlation were different comparing AD, PDD and CTL. Single-tangle analyses revealed disease-specific immunophenotypes but conserved mature intra-tangle epitope organisation. Distinct tau signatures were associated with inhibitory interneuron vulnerability, while regional tau co-occurrence with amyloid-{beta} and -synuclein remained conserved. DISCUSSIONDisease-specific tau signatures vary across hippocampal subregions and neuronal populations, implicating the contribution of regional and cell-specific factors beyond pathology burden.

Overproduction or suppression of certain microRNAs (miRNAs) in Alzheimers disease (AD) brains promote alterations in tau proteostasis and neurodegeneration. However, the mechanisms governing how specific miRNAs are dysregulated in AD brains are still under investigation. Epitranscriptomic regulation adds a layer of post-transcriptional control to brain function during development and adulthood. NOP2/Sun RNA methyltransferase 2 (NSun2) is one of the few known brain-enriched methyltransferases able to modify mammalian non-coding RNAs and loss of function autosomal-recessive mutations in NSUN2 have been associated with neurological abnormalities in humans. Here, we provide evidence that NSun2 is expressed in adult human neurons in the hippocampal formation and prefrontal cortex. When we evaluated NSun2 protein expression in post-mortem brain tissue from AD patients we find is dysregulated which was also found in mice and human cellular AD models. To probe these observed alterations were unique to AD we further evaluated brain tissue from other tauopathies, observing NSun2 protein levels were similar between cases and controls. In a well-established Drosophila melanogaster model of tau-induced toxicity we investigated the pathological role of NSun2 observing that reduction of NSun2 protein levels exacerbated tau toxicity, while overexpression of NSun2 partially abrogated the toxic effects. We further show using human induced pluripotent stem cell (iPSC) derived neuronal cultures that NSun2 deficiency results in tau hyperphosphorylation and we found in primary hippocampal neuronal cultures NSun2 levels decrease in response to amyloid-beta oligomers (A{beta}O). Furthermore, in mice, we observed that NSun2 deficiency promotes aberrant levels of m6A methylated miR-125b and tau hyperphosphorylation. Altogether, our study supports that neuronal NSun2 deficiency in AD promotes neurodegeneration by altering tau phosphorylation and tau toxicity through an epitranscriptomic regulatory mechanism and highlights a novel avenue for therapeutic targeting.