Synaptic Contacts Enhance Cell-to-Cell Tau Pathology Propagation

Exploring the Mechanisms and Therapeutic Approaches of Mitochondrial Dysfunction in Alzheimer's Disease: An Educational Literature Review

Alzheimer's disease (AD) presents a significant challenge to global health. It is characterized by progressive cognitive deterioration and increased rates of morbidity and mortality among older adults. Among the various pathophysiologies of AD, mitochondrial dysfunction, encompassing conditions such as increased reactive oxygen production, dysregulated calcium homeostasis, and impaired mitochondrial dynamics, plays a pivotal role. This review comprehensively investigates the mechanisms of mitochondrial dysfunction in AD, focusing on aspects such as glucose metabolism impairment, mitochondrial bioenergetics, calcium signaling, protein tau and amyloid-beta-associated synapse dysfunction, mitophagy, aging, inflammation, mitochondrial DNA, mitochondria-localized microRNAs, genetics, hormones, and the electron transport chain and Krebs cycle. While lecanemab is the only FDA-approved medication to treat AD, we explore various therapeutic modalities for mitigating mitochondrial dysfunction in AD, including antioxidant drugs, antidiabetic agents, acetylcholinesterase inhibitors (FDA-approved to manage symptoms), nutritional supplements, natural products, phenylpropanoids, vaccines, exercise, and other potential treatments.

hiPSC-neurons recapitulate the subtype-specific cell intrinsic nature of susceptibility to neurodegenerative disease-relevant aggregation

Alzheimer's disease (AD) is characterized by the accumulation and spread of Tau intraneuronal inclusions throughout most of the telencephalon, leaving hindbrain regions like the cerebellum and spinal cord largely spared. These neuropathological observations, along with the identification of specific vulnerable sub-populations from AD brain-derived single nuclei transcriptomics, suggest that a subset of brain regions and neuronal subtypes possess a selective vulnerability to Tau pathology. Given the inability to culture neurons from patient brains, a disease-relevant in vitro model which recapitulates these features would serve as a critical tool to validate modulators of vulnerability and resilience. Using our recently established platform for inducing endogenous Tau aggregation in human induced pluripotent stem cell (hiPSC)-derived cortical excitatory neurons via application of AD brain-derived exogenous Tau aggregates, we explored whether Tau aggregates preferentially induce aggregation in specific neuronal subtypes. We compared Tau seeding in hiPSC-derived neuron subtypes representing regional identities across the forebrain, midbrain, and hindbrain. Higher susceptibility (i.e. more Tau aggregation) was consistently observed among cortical neuron subtypes, with CTIP2-positive, somatostatin (SST)-positive cortical inhibitory neurons showing the greatest aggregation levels across hiPSC lines from multiple donors. hiPSC-neurons also delineated between the disease-specific vulnerabilities of different protein aggregates, as α-synuclein preformed fibrils showed an increased propensity to induce aggregates in midbrain dopaminergic (mDA)-like neurons, mimicking Parkinson's disease (PD)-specific susceptibility. Aggregate uptake and degradation rates were insufficient to explain differential susceptibility. The absence of a consistent transcriptional response following aggregate seeding further indicated that intrinsic neuronal subtype-specific properties could drive susceptibility. The present data provides evidence that hiPSC-neurons exhibit features of selective neuronal vulnerability which manifest in a cell autonomous manner, suggesting that mining intrinsic (or basal) transcriptomic signatures of more vulnerable compared to more resilient hiPSC-neurons could uncover the molecular underpinnings of differential susceptibility to protein aggregation found in a variety of neurodegenerative diseases.

Multimodal spatial gradients to explain regional susceptibility to fibrillar tau in Alzheimer's disease

INTRODUCTION

In Alzheimer's disease (AD), fibrillar tau gradually progresses from initial seed to larger brain area. However, those brain properties underlying the region-dependent susceptibility to tau accumulation remain unclear.

METHODS

We constructed multimodal spatial gradients to characterize molecular properties and connectomic architecture. A predictive model for regional tau deposition was developed by integrating embeddings in the principal gradients of global connectome gradients with gene expression, neurotransmitters, myelin, and amyloid-beta. The model was trained on amyloid-beta-positive participants from Alzheimer's Disease Neuroimaging Initiative (ADNI) and externally validated in independent datasets.

RESULTS

The combination of gradients explained up to 77.7% of cross-sectional and 77.3% of longitudinal inter-regional variance of tau deposition. Gene set enrichment analysis of a major gene expression gradient points to synaptic transmission to confer increased susceptibility to tau.

DISCUSSION

Our findings reveal a spatially heterogeneous molecular landscape shaping regional susceptibility to tau deposition, presenting a powerful system-level explanatory model of tau pathology in AD.

HIGHLIGHTS

Spatial gradients of fundamental molecular brain properties associated with tau pathology. The explanatory power showed high consistency across studies. Genetic analyses suggested that synapse expression plays a vital role in tau accumulation.

Dysregulated calcium signaling in the aged macaque entorhinal cortex associated with tau hyperphosphorylation

Introduction

Tau pathology in sporadic Alzheimer's disease (AD) follows a distinct pattern, beginning in the entorhinal cortex (ERC) and spreading to interconnected brain regions. Early-stage tau pathology, characterized by soluble phosphorylated tau, is difficult to study in human brains post-mortem due to rapid dephosphorylation.

Methods

Rhesus macaques, which naturally develop age-related tau pathology resembling human AD, provide an ideal model for investigating early tau etiology. This study examines the molecular processes underlying tau pathology in the macaque ERC, focusing on calcium and inflammatory signaling pathways using biochemical and immunohistochemistry.

Results

Our findings reveal an age-related decrease in PDE4 phosphodiesterase that hydrolyzes cAMP and increases in calpain-2 and glutamate carboxypeptidase II that occur in parallel with early-stage tau hyperphosphorylation at multiple epitopes (pS214-tau, pT181-tau, pT217-tau).

Discussion

These findings suggest that dysregulated calcium signaling in ERC, beginning in middle-age, may prime tau for hyperphosphorylation, potentially driving the early stages of AD, advancing our understanding of how ERC vulnerabilities contribute to neurodegeneration in AD.

Microfluidic tools to model, monitor, and modulate the gut-brain axis

The gut-brain axis (GBA) connects the gastrointestinal tract and the central nervous system (CNS) via the peripheral nervous system and humoral (e.g., circulatory and lymphatic system) routes. The GBA comprises a sophisticated interaction between various mammalian cells, gut microbiota, and systemic factors. This interaction shapes homeostatic and pathophysiological processes and plays an important role in the etiology of many disorders including neuropsychiatric conditions. However, studying the underlying processes of GBA in vivo, where numerous confounding factors exist, is challenging. Furthermore, conventional in vitro models fall short of capturing the GBA anatomy and physiology. Microfluidic platforms with integrated sensors and actuators are uniquely positioned to enhance in vitro models by representing the anatomical layout of cells and allowing to monitor and modulate the biological processes with high spatiotemporal resolution. Here, we first briefly describe microfluidic technologies and their utility in modeling the CNS, vagus nerve, gut epithelial barrier, blood-brain barrier, and their interactions. We then discuss the challenges and opportunities for each model, including the use of induced pluripotent stem cells and incorporation of sensors and actuator modalities to enhance the capabilities of these models. We conclude by envisioning research directions that can help in making the microfluidics-based GBA models better-suited to provide mechanistic insight into pathophysiological processes and screening therapeutics.

Molecular mechanisms and pathological implications of unconventional protein secretion in human disease: from cellular stress to therapeutic targeting

Unconventional protein secretion (UcPS) encompasses diverse non-canonical cellular export mechanisms that operate independently of the classical secretory pathway, representing a crucial cellular response to various physiological and pathological conditions. This comprehensive review synthesizes current understanding of UcPS mechanisms, particularly focusing on their roles in disease pathogenesis and progression. Recent advances in proteomics and cellular biology have revealed that UcPS facilitates the secretion of various biomedically significant proteins, including inflammatory mediators, growth factors, and disease-associated proteins, through multiple pathways such as membrane translocation, secretory lysosomes, and membrane-bound organelles. Notably, dysregulation of UcPS mechanisms has been implicated in various pathological conditions, including chronic inflammation, neurodegenerative disorders, and malignant transformation. We critically evaluate the molecular machinery governing UcPS, its regulation under cellular stress, and its contribution to disease mechanisms. Furthermore, we examine emerging therapeutic strategies targeting UcPS pathways, highlighting both opportunities and challenges in developing novel interventional approaches.

Tau pathology is associated with postsynaptic metabotropic glutamate receptor 5 (mGluR5) in early Alzheimer's disease in a sex-specific manner

INTRODUCTION

To investigate the associations of metabotropic glutamate receptor 5 (mGluR5) with tau deposition and cognitive ability in patients with early Alzheimer's disease (AD).

METHODS

Twenty-six cognitively impaired (CI) and 14 cognitively unimpaired (CU) individuals underwent mGluR5 positron emission tomography (PET) ([18F]PSS232), amyloid PET ([18F]florbetapir), and tau PET ([18F]MK6240), and neuropsychological assessment. The relationships among mGluR5 availability, tau deposition, and neuropsychological assessment were analyzed using Spearman's correlation and mediation analyses.

RESULTS

CI patients had lower mGluR5 in the hippocampus than CU (standardized uptake value ratio [SUVr]: 2.03 ± 0.25 vs 1.79 ± 0.17, p = 0.003). Hippocampal mGluR5 was negatively associated with hippocampal tau deposition (r = -.46, p = 0.003) and positively associated with cognitive performance, but only in women. Hippocampal tau deposition mediated the effect of mGluR5 on cognitive performance.

DISCUSSION

Reduced hippocampal mGluR5 is negatively related with tau deposition in most cortical regions and positively associated with cognitive performance, making it a promising biomarker for AD diagnosis and therapy.

HIGHLIGHTS

Cognitively impaired (CI) patients exhibited lower metabotropic glutamate receptor 5 (mGluR5) availability in the hippocampus than cognitively unimpaired (CU) subjects. Hippocampal mGluR5 availability was negatively associated with tau deposition in widespread cortex. Hippocampal mGluR5 availability was positively associated with cognitive performance. The close association of mGluR5 with tau and cognition performance exists only in females. Tau pathology mediated the relationship between mGluR5 availability and cognition.

The etiology and prevention of early-stage tau pathology in higher cortical circuits: Insights from aging rhesus macaques

Aging rhesus macaques provide a unique model for learning how age and inflammation drive early-stage pathology in sporadic Alzheimer's disease, and for testing potential therapeutics. Unlike mice, aging macaques have extensive association cortices and inflammatory signaling similar to humans, are apolipoprotein E ε4 homozygotes, and naturally develop tau and amyloid pathology with marked cognitive deficits. Importantly, monkeys provide the unique opportunity to study early-stage, soluble hyperphosphorylated tau (p-tau), including p-tau217. As soluble p-tau is rapidly dephosphorylated post mortem, it is not captured in human brains except with biopsy material. However, new macaque data show that soluble p-tau is toxic to neurons and capable of seeding across cortical circuits. Extensive evidence indicates that age-related inflammatory signaling contributes to calcium dysregulation, which drives tau hyperphosphorylation and amyloid beta generation. Pharmacological studies in aged macaques suggest that inhibiting inflammation and restoring calcium regulation can reduce tau hyperphosphorylation with minimal side effects, appropriate for potential preventive therapeutics. HIGHLIGHTS: Aging monkeys provide a unique window into early stage, soluble phosphorylated tau (p-tau). Inflammation with advancing age leads to calcium dysregulation, p-tau, and amyloid beta (Aβ). Macaque research shows p-tau undergoes transsynaptic seeding early in the cortex. p-tau traps amyloid precursor protein-containing endosomes, which may increase Aβ and drive vicious cycles. Restoring calcium regulation in cortex reduced p-tau217 levels in aged macaques.

Amyloid-β and tau deposition in traumatic brain injury: a study of Vietnam War veterans

Traumatic brain injury is widely viewed as a risk factor for dementia, but the biological mechanisms underlying this association are still unclear. In previous studies, traumatic brain injury has been associated with the hallmark pathologies of Alzheimer's disease, i.e. amyloid-β plaques and neurofibrillary tangles comprised of hyperphosphorylated tau. Depending on the type and location of trauma, traumatic brain injury can induce spatially heterogeneous brain lesions that may pre-dispose for the development of Alzheimer's disease pathology in aging. Therefore, we hypothesized that a history of traumatic brain injury may be related to spatially heterogeneous amyloid-β and tau pathology patterns that deviate from the stereotypical temporo-parietal patterns in Alzheimer's disease. To test this, we included 103 Vietnam War veterans of whom 65 had experienced traumatic brain injury (n = 40, 38.8% mild; n = 25, 24.3% moderate/severe). Most individuals had a history of 1 (n = 35, 53.8%) or 2 (n = 15, 23.1%) traumatic brain injury events. We included the group without a history of traumatic brain injury (n = 38, 36.9%) as controls. The majority was cognitively normal (n = 80, 77.7%), while a subset had mild cognitive impairment (n = 23, 22.3%). All participants underwent [18F]florbetapir/Amyvid amyloid-β PET and [18F]flortaucipir/Tauvid tau-PET 39.63 ± 18.39 years after their last traumatic brain injury event. We found no differences in global amyloid-β and tau-PET levels between groups, suggesting that a history of traumatic brain injury does not pre-dispose to accumulate amyloid-β or tau pathology in general. However, we found that traumatic brain injury was associated with altered spatial patterns of amyloid-β and tau, with relatively greater deposition in fronto-parietal brain regions. These regions are prone to damage in traumatic brain injury, while they are typically only affected in later stages of Alzheimer's disease. Moreover, in our traumatic brain injury groups, the association between amyloid-β and tau was reduced in Alzheimer-typical temporal regions but increased in frontal regions that are commonly associated with traumatic brain injury. Altogether, while acknowledging the relatively small sample size and generally low levels of Alzheimer's disease pathology in this sample, our findings suggest that traumatic brain injury induces spatial patterns of amyloid-β and tau that differ from patterns observed in typical Alzheimer's disease. Furthermore, traumatic brain injury may be associated with a de-coupling of amyloid-β and tau in regions vulnerable in Alzheimer's disease. These findings indicate that focal brain damage in early/mid-life may change neurodegenerative trajectories in late-life.

Unknown roles of tau pathology in neurological disorders. Challenges and new perspectives

Aging presents progressive changes that increase the susceptibility of the central nervous system (CNS) to suffer neurological disorders (NDs). Several studies have reported that an aged brain suffering from NDs shows the presence of pathological forms of tau protein, a microtubule accessory protein (MAP) critical for neuronal function. In this context, accumulative evidence has shown a pivotal contribution of pathological forms of tau to Alzheimer's disease (AD) and tauopathies. However, current investigations have implicated tau toxicity in other NDs that affect the central nervous system (CNS), including Parkinson's disease (PD), Huntington's disease (HD), Traumatic brain injury (TBI), Multiple sclerosis (MS), and Amyotrophic lateral sclerosis (ALS). These diseases are long-term acquired, affecting essential functions such as motor movement, cognition, hearing, and vision. Previous evidence indicated that toxic forms of tau do not have a critical contribution to the genesis or progression of these diseases. However, recent studies have shown that these tau forms contribute to neuronal dysfunction, inflammation, oxidative damage, and mitochondrial impairment events that contribute to the pathogenesis of these NDs. Recent studies have suggested that these neuropathologies could be associated with a prion-like behavior of tau, which induces a pathological dissemination of these toxic protein forms to different brain areas. Moreover, it has been suggested that this toxic propagation of tau from neurons into neighboring cells impairs the function of glial cells, oligodendrocytes, and endothelial cells by affecting metabolic function and mitochondrial health and inducing oxidative damage by tau pathology. Therefore, in this review, we will discuss current evidence demonstrating the critical role of toxic tau forms on NDs not related to AD and how its propagation and induced-bioenergetics failure may contribute to the pathogenic mechanism present in these NDs.

pTau pathology in the retina of TAU58 mice: association with ganglion cell degeneration and implications on seeding and propagation of pTau from human brain lysates

The accumulation of abnormal phosphorylated Tau protein (pTau) in neurons of the brain is a pathological hallmark of Alzheimer's disease (AD). PTau pathology also occurs in the retina of AD cases. Accordingly, questions arise whether retinal pTau can act as a potential seed for inducing cerebral pTau pathology and whether retinal pTau pathology causes degeneration of retinal neurons. To address these questions, we (1) characterized pTau pathology in the retina of TAU58 mice, (2) determined the impact of pTau pathology on retinal ganglion cell density, and (3) used this mouse model to test whether brain lysates from AD and/or non-AD control cases induce seeding in the retina and/or propagation into the brain. TAU58 mice developed retinal pTau pathology at 6 months of age, increasing in severity and extent with age. TAU58 mice showed reduced retinal ganglion cell density compared to wild-type mice, which declined with age and pTau pathology progression. Brain lysates from non-AD Braak neurofibrillary tangle (NFT) stage I controls increased retinal pTau pathology after subretinal injection compared to phosphate-buffered saline (PBS) but did not accelerate pTau pathology in the brain. In contrast, subretinally injected AD brain lysates accelerated pTau pathology in the retina and the contralateral superior colliculus. Subretinal injection of AD brain lysates, but not of non-AD brain, induced in this context a neuroinflammatory response in the retina and in the contralateral primary visual cortex. These results lead to the following conclusions: (1) Brain lysates from AD and non-AD sources can accelerate tauopathy within the retina. (2) The anterograde propagation of pTau pathology from the retina to the brain can be triggered by subretinal injections of AD brain lysates. (3) Such subretinal injections also provoke a neuroinflammatory response in both the retina and the visual cortex. (4) The accumulation of retinal pTau is associated with the degeneration of the involved ganglion cells, indicating that retinal tauopathy might contribute to vision impairment in the elderly and underscore the retina's potential role in spreading tau pathology to the brain.

Dysregulated calcium signaling in the aged macaque entorhinal cortex associated with tau hyperphosphorylation

Tau pathology in sporadic Alzheimer's disease (AD) follows a distinct pattern, beginning in the entorhinal cortex (ERC) and spreading to interconnected brain regions. Early-stage tau pathology, characterized by soluble phosphorylated tau, is difficult to study in human brains post-mortem due to rapid dephosphorylation. Rhesus macaques, which naturally develop age-related tau pathology resembling human AD, provide an ideal model for investigating early tau etiology. This study examines the molecular processes underlying tau pathology in the macaque ERC, focusing on calcium and inflammatory signaling pathways. Our findings reveal age-related decreases in PDE4 phosphodiesterases that hydrolyze cAMP and increases in calpain-2 and GCPII that occur in parallel with early-stage tau hyperphosphorylation at multiple epitopes (pS214-tau, pT181-tau, pT217-tau). These findings suggest that dysregulated calcium signaling in ERC, beginning in middle-age, primes tau for hyperphosphorylation, potentially driving the early stages of AD, advancing our understanding of how ERC vulnerabilities contribute to neurodegeneration in AD.

Amygdala-predominant α-synuclein pathology is associated with exacerbated hippocampal neuron loss in Alzheimer's disease

Misfolded α-synuclein protein accumulates in 43-63% of individuals with symptomatic Alzheimer's disease. Two main patterns of comorbid α-synuclein pathology have been identified: caudo-rostral and amygdala-predominant. α-Synuclein aggregates have been shown to interact with the transactive response DNA-binding protein 43 (TDP-43) and abnormally phosphorylated tau protein. All these proteins accumulate in the amygdala, which is anatomically connected with the hippocampus. However, the specific role of amygdala-predominant α-synuclein pathology in the progression of Alzheimer's disease and hippocampal degeneration remains unclear. In this cross-sectional study, we analysed 291 autopsy brains from both demented and non-demented elderly individuals neuropathologically. Neuronal density in the CA1 region of the hippocampus was assessed for all cases. We semiquantitatively evaluated α-synuclein pathology severity across seven brain regions and calculated a ratio of limbic to brainstem α-synuclein pathology severity, which was used to stratify the cases into two distinct spreading patterns. In the 99 symptomatic Alzheimer's disease cases, we assessed severity of limbic-predominant age-related TDP-43 neuropathological changes and CA1 phosphorylated tau density. We performed triple fluorescence staining of medial temporal lobe samples with antibodies against phosphorylated TDP-43, α-synuclein and phosphorylated tau. Finally, we employed path analysis to determine the association network of various parameters of limbic pathology in Alzheimer's disease cases and CA1 neuronal density. We identified an association between the amygdala-predominant αSyn pathology pattern and decreased neuronal density in the CA1 region. We found that Alzheimer's disease cases with an amygdala-predominant α-synuclein pattern exhibited the highest TDP-43 severity and prevalence of TDP-43 inclusions in the dentate gyrus among all groups, while those with the caudo-rostral pattern had the lowest severity of Alzheimer's disease neuropathological changes. We observed colocalization of TDP-43, aggregated α-synuclein and hyperphosphorylated tau in cytoplasmic inclusions within hippocampal and amygdala neurons of Alzheimer's disease cases. Path analysis modelling suggests that the relationship between amygdala-predominant α-synuclein pathology and CA1 neuron loss is partially mediated by hippocampal tau and TDP-43 aggregates. Our findings suggest that Alzheimer's disease cases with amygdala-predominant α-synuclein pathology may constitute a distinct group with more severe hippocampal damage, a higher TDP-43 burden and potential interactions among α-synuclein, TDP-43 and hyperphosphorylated tau.

Inducing aggresome and stable tau aggregation in Neuro2a cells with an optogenetic tool

Tauopathy is a spectrum of diseases characterized by fibrillary tau aggregate formation in neurons and glial cells in the brain. Tau aggregation originates in the brainstem and entorhinal cortex and then spreads throughout the brain in Alzheimer's disease (AD), which is the most prevalent type of tauopathy. Understanding the mechanism by which locally developed tau pathology propagates throughout the brain is crucial for comprehending AD pathogenesis. Therefore, a novel model of tau pathology that artificially induces tau aggregation in targeted cells at specific times is essential. This study describes a novel optogenetic module, OptoTau, which is a human tau with the P301L mutation fused with a photosensitive protein CRY2olig, inducing various forms of tau according to the temporal pattern of blue light illumination pattern. Continuous blue light illumination for 12 h to Neuro2a cells that stably express OptoTau (OptoTauKI cells) formed clusters along microtubules, many of which eventually accumulated in aggresomes. Conversely, methanol-resistant tau aggregation was formed when alternating light exposure and darkness in 30-min cycles for 8 sets per day were repeated over 8 days. Methanol-resistant tau was induced more rapidly by repeating 5-min illumination followed by 25-min darkness over 24 h. These results indicate that OptoTau induced various tau aggregation stages based on the temporal pattern of blue light exposure. Thus, this technique exhibits potential as a novel approach to developing specific tau aggregation in targeted cells at desired time points.

Potential Mechanisms of Tunneling Nanotube Formation and Their Role in Pathology Spread in Alzheimer's Disease and Other Proteinopathies

Alzheimer's disease (AD) is the most common type of dementia worldwide. The etiopathogenesis of this disease remains unknown. Currently, several hypotheses attempt to explain its cause, with the most well-studied being the cholinergic, beta-amyloid (Aβ), and Tau hypotheses. Lately, there has been increasing interest in the role of immunological factors and other proteins such as alpha-synuclein (α-syn) and transactive response DNA-binding protein of 43 kDa (TDP-43). Recent studies emphasize the role of tunneling nanotubes (TNTs) in the spread of pathological proteins within the brains of AD patients. TNTs are small membrane protrusions composed of F-actin that connect non-adjacent cells. Conditions such as pathogen infections, oxidative stress, inflammation, and misfolded protein accumulation lead to the formation of TNTs. These structures have been shown to transport pathological proteins such as Aβ, Tau, α-syn, and TDP-43 between central nervous system (CNS) cells, as confirmed by in vitro studies. Besides their role in spreading pathology, TNTs may also have protective functions. Neurons burdened with α-syn can transfer protein aggregates to glial cells and receive healthy mitochondria, thereby reducing cellular stress associated with α-syn accumulation. Current AD treatments focus on alleviating symptoms, and clinical trials with Aβ-lowering drugs have proven ineffective. Therefore, intensifying research on TNTs could bring scientists closer to a better understanding of AD and the development of effective therapies.

Chronic Neuronal Hyperexcitation Exacerbates Tau Propagation in a Mouse Model of Tauopathy

The intracerebral spread of tau is a critical mechanism associated with functional decline in Alzheimer's disease (AD) and other tauopathies. Recently, a hypothesis has emerged suggesting that tau propagation is linked to functional neuronal connections, specifically driven by neuronal hyperactivity. However, experimental validation of this hypothesis remains limited. In this study, we investigated how tau propagation from the entorhinal cortex to the hippocampus, the neuronal circuit most susceptible to tau pathology in AD, is affected by the selective stimulation of neuronal activity along this circuit. Using a mouse model of seed-induced propagation combined with optogenetics, we found that the chronic stimulation of this neuronal connection over a 4-week period resulted in a significant increase in insoluble tau accumulation in both the entorhinal cortex and hippocampus. Importantly, the ratio of tau accumulation in the hippocampus relative to that in the entorhinal cortex, serving as an indicator of transcellular spreading, was significantly higher in mice subjected to chronic stimulation. These results support the notion that abnormal neuronal activity promotes tau propagation, thereby implicating it in the progression of tauopathy.

Synaptopathy: presynaptic convergence in frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia and amyotrophic lateral sclerosis are common forms of neurodegenerative disease that share overlapping genetics and pathologies. Crucially, no significantly disease-modifying treatments are available for either disease. Identifying the earliest changes that initiate neuronal dysfunction is important for designing effective intervention therapeutics. The genes mutated in genetic forms of frontotemporal dementia and amyotrophic lateral sclerosis have diverse cellular functions, and multiple disease mechanisms have been proposed for both. Identification of a convergent disease mechanism in frontotemporal dementia and amyotrophic lateral sclerosis would focus research for a targetable pathway, which could potentially effectively treat all forms of frontotemporal dementia and amyotrophic lateral sclerosis (both familial and sporadic). Synaptopathies are diseases resulting from physiological dysfunction of synapses, and define the earliest stages in multiple neuronal diseases, with synapse loss a key feature in dementia. At the presynapse, the process of synaptic vesicle recruitment, fusion and recycling is necessary for activity-dependent neurotransmitter release. The unique distal location of the presynaptic terminal means the tight spatio-temporal control of presynaptic homeostasis is dependent on efficient local protein translation and degradation. Recently, numerous publications have shown that mutations associated with frontotemporal dementia and amyotrophic lateral sclerosis present with synaptopathy characterized by presynaptic dysfunction. This review will describe the complex local signalling and membrane trafficking events that occur at the presynapse to facilitate neurotransmission and will summarize recent publications linking frontotemporal dementia/amyotrophic lateral sclerosis genetic mutations to presynaptic function. This evidence indicates that presynaptic synaptopathy is an early and convergent event in frontotemporal dementia and amyotrophic lateral sclerosis and illustrates the need for further research in this area, to identify potential therapeutic targets with the ability to impact this convergent pathomechanism.

A genome-wide association study reveals a polygenic architecture of speech-in-noise deficits in individuals with self-reported normal hearing

Speech-in-noise (SIN) perception is a primary complaint of individuals with audiometric hearing loss. SIN performance varies drastically, even among individuals with normal hearing. The present genome-wide association study (GWAS) investigated the genetic basis of SIN deficits in individuals with self-reported normal hearing in quiet situations. GWAS was performed on 279,911 individuals from the UB Biobank cohort, with 58,847 reporting SIN deficits despite reporting normal hearing in quiet. GWAS identified 996 single nucleotide polymorphisms (SNPs), achieving significance (p < 5*10-8) across four genomic loci. 720 SNPs across 21 loci achieved suggestive significance (p < 10-6). GWAS signals were enriched in brain tissues, such as the anterior cingulate cortex, dorsolateral prefrontal cortex, entorhinal cortex, frontal cortex, hippocampus, and inferior temporal cortex. Cochlear cell types revealed no significant association with SIN deficits. SIN deficits were associated with various health traits, including neuropsychiatric, sensory, cognitive, metabolic, cardiovascular, and inflammatory conditions. A replication analysis was conducted on 242 healthy young adults. Self-reported speech perception, hearing thresholds (0.25-16 kHz), and distortion product otoacoustic emissions (1-16 kHz) were utilized for the replication analysis. 73 SNPs were replicated with a self-reported speech perception measure. 211 SNPs were replicated with at least one and 66 with at least two audiological measures. 12 SNPs near or within MAPT, GRM3, and HLA-DQA1 were replicated for all audiological measures. The present study highlighted a polygenic architecture underlying SIN deficits in individuals with self-reported normal hearing.

Tau accumulation is associated with dopamine deficiency in vivo in four-repeat tauopathies

PURPOSE

We hypothesized that severe tau burden in brain regions involved in direct or indirect pathways of the basal ganglia correlate with more severe striatal dopamine deficiency in four-repeat (4R) tauopathies. Therefore, we correlated [18F]PI-2620 tau-positron-emission-tomography (PET) imaging with [123I]-Ioflupane single-photon-emission-computed tomography (SPECT) for dopamine transporter (DaT) availability.

METHODS

Thirty-eight patients with clinically diagnosed 4R-tauopathies (21 male; 69.0 ± 8.5 years) and 15 patients with clinically diagnosed α-synucleinopathies (8 male; 66.1 ± 10.3 years) who underwent [18F]PI-2620 tau-PET and DaT-SPECT imaging with a time gap of 3 ± 5 months were evaluated. Regional Tau-PET signals and DaT availability as well as their principal components were correlated in patients with 4R-tauopathies and α-synucleinopathies. Both biomarkers and the residuals of their association were correlated with clinical severity scores in 4R-tauopathies.

RESULTS

In patients with 4R-tauopathies, [18F]PI-2620 binding in basal ganglia and midbrain regions was negatively associated with striatal DaT availability (i.e. globus pallidus internus and putamen (β =  - 0.464, p = 0.006, Durbin-Watson statistics = 1.824) in a multiple regression model. Contrarily, [18F]PI-2620 binding in the dentate nucleus showed no significant regression factor with DaT availability in the striatum (β = 0.078, p = 0.662, Durbin-Watson statistics = 1.686). Patients with α-synucleinopathies did not indicate any regional associations between [18F]PI-2620-binding and DaT availability. Higher DaT-SPECT binding relative to tau burden was associated with better clinical performance (β =  - 0.522, p = 0.011, Durbin-Watson statistics = 2.663) in patients with 4R-tauopathies.

CONCLUSION

Tau burden in brain regions involved in dopaminergic pathways is associated with aggravated dopaminergic dysfunction in patients with clinically diagnosed primary tauopathies. The ability to sustain dopamine transmission despite tau accumulation may preserve motor function.

The Enigma of Tau Protein Aggregation: Mechanistic Insights and Future Challenges

Tau protein misfolding and aggregation are pathological hallmarks of Alzheimer's disease and over twenty neurodegenerative disorders. However, the molecular mechanisms of tau aggregation in vivo remain incompletely understood. There are two types of tau aggregates in the brain: soluble aggregates (oligomers and protofibrils) and insoluble filaments (fibrils). Compared to filamentous aggregates, soluble aggregates are more toxic and exhibit prion-like transmission, providing seeds for templated misfolding. Curiously, in its native state, tau is a highly soluble, heat-stable protein that does not form fibrils by itself, not even when hyperphosphorylated. In vitro studies have found that negatively charged molecules such as heparin, RNA, or arachidonic acid are generally required to induce tau aggregation. Two recent breakthroughs have provided new insights into tau aggregation mechanisms. First, as an intrinsically disordered protein, tau is found to undergo liquid-liquid phase separation (LLPS) both in vitro and inside cells. Second, cryo-electron microscopy has revealed diverse fibrillar tau conformations associated with different neurodegenerative disorders. Nonetheless, only the fibrillar core is structurally resolved, and the remainder of the protein appears as a "fuzzy coat". From this review, it appears that further studies are required (1) to clarify the role of LLPS in tau aggregation; (2) to unveil the structural features of soluble tau aggregates; (3) to understand the involvement of fuzzy coat regions in oligomer and fibril formation.

Customized Intranasal Hydrogel Delivering Methylene Blue Ameliorates Cognitive Dysfunction against Alzheimer's Disease

The accumulation of hyperphosphorylated tau protein aggregates is a key pathogenic event in Alzheimer's disease (AD) and induces mitochondrial dysfunction and reactive oxygen species overproduction. However, the treatment of AD remains challenging owning to the hindrance caused by the blood-brain barrier (BBB) and the complex pathology of AD. Nasal delivery represents an effective means of circumventing the BBB and delivering drugs to the brain. In this study, black phosphorus (BP) is used as a drug carrier, as well as an antioxidant, and loaded with a tau aggregation inhibitor, methylene blue (MB), to obtain BP-MB. For intranasal (IN) delivery, a thermosensitive hydrogel is fabricated by cross-linking carboxymethyl chitosan and aldehyde Pluronic F127 (F127-CHO) micelles. The BP-MB nanocomposite is incorporated into the hydrogel to obtain BP-MB@Gel. BP-MB@Gel could be injected intranasally, providing high nasal mucosal retention and controlled drug release. After IN administration, BP-MB is continuously released and delivered to the brain, exerting synergistic therapeutic effects by suppressing tau neuropathology, restoring mitochondrial function, and alleviating neuroinflammation, thus inducing cognitive improvements in mouse models of AD. These findings highlight a potential strategy for brain-targeted drug delivery in the management of the complex pathologies of AD.

Glymphatic inhibition exacerbates tau propagation in an Alzheimer's disease model

BACKGROUND

The aggregation and spread of misfolded amyloid structured proteins, such as tau and α-synuclein, are key pathological features associated with neurodegenerative disorders, including Alzheimer's and Parkinson's disease. These proteins possess a prion-like property, enabling their transmission from cell to cell leading to propagation throughout the central and peripheral nervous systems. While the mechanisms underlying their intracellular spread are still being elucidated, targeting the extracellular space has emerged as a potential therapeutic approach. The glymphatic system, a brain-wide pathway responsible for clearing extracellular metabolic waste from the central nervous system, has gained attention as a promising target for removing these toxic proteins.

METHODS

In this study, we investigated the impact of long-term modulation of glymphatic function on tau aggregation and spread by chronically treating a mouse model of tau propagation with a pharmacological inhibitor of AQP4, TGN-020. Thy1-hTau.P301S mice were intracerebrally inoculated with tau into the hippocampus and overlying cortex, and subsequently treated with TGN-020 (3 doses/week, 50 mg/kg TGN-020, i.p.) for 10-weeks. During this time, animal memory was studied using cognitive behavioural tasks, and structural MR images were acquired of the brain in vivo prior to brain extraction for immunohistochemical characterisation.

RESULTS

Our findings demonstrate increased tau aggregation in the brain and transhemispheric propagation in the hippocampus following the inhibition of glymphatic clearance. Moreover, disruption of the glymphatic system aggravated recognition memory in tau inoculated mice and exacerbated regional changes in brain volume detected in the model. When initiation of drug treatment was delayed for several weeks post-inoculation, the alterations were attenuated.

CONCLUSIONS

These results indicate that by modulating AQP4 function and, consequently, glymphatic clearance, it is possible to modify the propagation and pathological impact of tau in the brain, particularly during the initial stages of the disease. These findings highlight the critical role of the glymphatic system in preserving healthy brain homeostasis and offer valuable insights into the therapeutic implications of targeting this system for managing neurodegenerative diseases characterized by protein aggregation and spread.

Nanoscale imaging of pT217-tau in aged rhesus macaque entorhinal and dorsolateral prefrontal cortex: Evidence of interneuronal trafficking and early-stage neurodegeneration

INTRODUCTION

Tau phosphorylated at threonine-217 (pT217-tau) is a novel fluid-based biomarker that predicts onset of Alzheimer's disease (AD) symptoms, but little is known about how pT217-tau arises in the brain, as soluble pT217-tau is dephosphorylated post mortem in humans.

METHODS

We used multilabel immunofluorescence and immunoelectron microscopy to examine the subcellular localization of early-stage pT217-tau in entorhinal and prefrontal cortices of aged macaques with naturally occurring tau pathology and assayed pT217-tau levels in plasma.

RESULTS

pT217-tau was aggregated on microtubules within dendrites exhibiting early signs of degeneration, including autophagic vacuoles. It was also seen trafficking between excitatory neurons within synapses on spines, where it was exposed to the extracellular space, and thus accessible to cerebrospinal fluid (CSF)/blood. Plasma pT217-tau levels increased across the age span and thus can serve as a biomarker in macaques.

DISCUSSION

These data help to explain why pT217-tau predicts degeneration in AD and how it gains access to CSF and plasma to serve as a fluid biomarker.

Neuropathogenesis-on-chips for neurodegenerative diseases

Developing diagnostics and treatments for neurodegenerative diseases (NDs) is challenging due to multifactorial pathogenesis that progresses gradually. Advanced in vitro systems that recapitulate patient-like pathophysiology are emerging as alternatives to conventional animal-based models. In this review, we explore the interconnected pathogenic features of different types of ND, discuss the general strategy to modelling NDs using a microfluidic chip, and introduce the organoid-on-a-chip as the next advanced relevant model. Lastly, we overview how these models are being applied in academic and industrial drug development. The integration of microfluidic chips, stem cells, and biotechnological devices promises to provide valuable insights for biomedical research and developing diagnostic and therapeutic solutions for NDs.

Combined Connectomics, MAPT Gene Expression, and Amyloid Deposition to Explain Regional Tau Deposition in Alzheimer Disease

OBJECTIVE

We aimed to test whether region-specific factors, including spatial expression patterns of the tau-encoding gene MAPT and regional levels of amyloid positron emission tomography (PET), enhance connectivity-based modeling of the spatial variability in tau-PET deposition in the Alzheimer disease (AD) spectrum.

METHODS

We included 685 participants (395 amyloid-positive participants within AD spectrum and 290 amyloid-negative controls) with tau-PET and amyloid-PET from 3 studies (Alzheimer's Disease Neuroimaging Initiative, 18 F-AV-1451-A05, and BioFINDER-1). Resting-state functional magnetic resonance imaging was obtained in healthy controls (n = 1,000) from the Human Connectome Project, and MAPT gene expression from the Allen Human Brain Atlas. Based on a brain-parcellation atlas superimposed onto all modalities, we obtained region of interest (ROI)-to-ROI functional connectivity, ROI-level PET values, and MAPT gene expression. In stepwise regression analyses, we tested connectivity, MAPT gene expression, and amyloid-PET as predictors of group-averaged and individual tau-PET ROI values in amyloid-positive participants.

RESULTS

Connectivity alone explained 21.8 to 39.2% (range across 3 studies) of the variance in tau-PET ROI values averaged across amyloid-positive participants. Stepwise addition of MAPT gene expression and amyloid-PET increased the proportion of explained variance to 30.2 to 46.0% and 45.0 to 49.9%, respectively. Similarly, for the prediction of patient-level tau-PET ROI values, combining all 3 predictors significantly improved the variability explained (mean adjusted R2 range across studies = 0.118-0.148, 0.156-0.196, and 0.251-0.333 for connectivity alone, connectivity plus MAPT expression, and all 3 modalities combined, respectively).

INTERPRETATION

Across 3 study samples, combining the functional connectome and molecular properties substantially enhanced the explanatory power compared to single modalities, providing a valuable tool to explain regional susceptibility to tau deposition in AD. ANN NEUROL 2024;95:274-287.

Exploring Alzheimer's disease: a comprehensive brain connectome-based survey

Dementia is an escalating global health challenge, with Alzheimer's disease (AD) at its forefront. Substantial evidence highlights the accumulation of AD-related pathological proteins in specific brain regions and their subsequent dissemination throughout the broader area along the brain network, leading to disruptions in both individual brain regions and their interconnections. Although a comprehensive understanding of the neurodegeneration-brain network link is lacking, it is undeniable that brain networks play a pivotal role in the development and progression of AD. To thoroughly elucidate the intricate network of elements and connections constituting the human brain, the concept of the brain connectome was introduced. Research based on the connectome holds immense potential for revealing the mechanisms underlying disease development, and it has become a prominent topic that has attracted the attention of numerous researchers. In this review, we aim to systematically summarize studies on brain networks within the context of AD, critically analyze the strengths and weaknesses of existing methodologies, and offer novel perspectives and insights, intending to serve as inspiration for future research.

Transmission-selective muscle pathology induced by the active propagation of mutant huntingtin across the human neuromuscular synapse

Neuron-to-neuron transmission of aggregation-prone, misfolded proteins may potentially explain the spatiotemporal accumulation of pathological lesions in the brains of patients with neurodegenerative protein-misfolding diseases (PMDs). However, little is known about protein transmission from the central nervous system to the periphery, or how this propagation contributes to PMD pathology. To deepen our understanding of these processes, we established two functional neuromuscular systems derived from human iPSCs. One was suitable for long-term high-throughput live-cell imaging and the other was adapted to a microfluidic system assuring that connectivity between motor neurons and muscle cells was restricted to the neuromuscular junction. We show that the Huntington's disease (HD)-associated mutant HTT exon 1 protein (mHTTEx1) is transmitted from neurons to muscle cells across the human neuromuscular junction. We found that transmission is an active and dynamic process that starts before aggregate formation and is regulated by synaptic activity. We further found that transmitted mHTTEx1 causes HD-relevant pathology at both molecular and functional levels in human muscle cells, even in the presence of the ubiquitous expression of mHTTEx1. In conclusion, we have uncovered a causal link between mHTTEx1 synaptic transmission and HD pathology, highlighting the therapeutic potential of blocking toxic protein transmission in PMDs.

Astrocyte-Neuron Interactions in Alzheimer's Disease

Besides its two defining misfolded proteinopathies-Aβ plaques and tau neurofibrillary tangles-Alzheimer's disease (AD) is an exemplar of a neurodegenerative disease with prominent reactive astrogliosis, defined as the set of morphological, molecular, and functional changes that astrocytes suffer as the result of a toxic exposure. Reactive astrocytes can be observed in the vicinity of plaques and tangles, and the relationship between astrocytes and these AD neuropathological lesions is bidirectional so that each AD neuropathological hallmark causes specific changes in astrocytes, and astrocytes modulate the severity of each neuropathological feature in a specific manner. Here, we will review both how astrocytes change as a result of their chronic exposure to AD neuropathology and how those astrocytic changes impact each AD neuropathological feature. We will emphasize the repercussions that AD-associated reactive astrogliosis has for the astrocyte-neuron interaction and highlight areas of uncertainty and priorities for future research.

Differentiation of Neurons, Astrocytes, Oligodendrocytes and Microglia From Human Induced Pluripotent Stem Cells to Form Neural Tissue-On-Chip: A Neuroinflammation Model to Evaluate the Therapeutic Potential of Extracellular Vesicles Derived from Mesenchymal Stem Cells

Advances in stem cell (SC) technology allow the generation of cellular models that recapitulate the histological, molecular and physiological properties of humanized in vitro three dimensional (3D) models, as well as production of cell-derived therapeutics such as extracellular vesicles (EVs). Improvements in organ-on-chip platforms and human induced pluripotent stem cells (hiPSCs) derived neural/glial cells provide unprecedented systems for studying 3D personalized neural tissue modeling with easy setup and fast output. Here, we highlight the key points in differentiation procedures for neurons, astrocytes, oligodendrocytes and microglia from single origin hiPSCs. Additionally, we present a well-defined humanized neural tissue-on-chip model composed of differentiated cells with the same genetic backgrounds, as well as the therapeutic potential of bone marrow mesenchymal stem cells (BMSCs)-derived extracellular vesicles to propose a novel treatment for neuroinflammation derived diseases. Around 100 nm CD9 + EVs promote a more anti-inflammatory and pro-remodeling of cell-cell interaction cytokine responses on tumor necrosis factor-α (TNF-α) induced neuroinflammation in neural tissue-on-chip model which is ideal for modeling authentic neural-glial patho-physiology.

Localization of PDE4D, HCN1 channels, and mGluR3 in rhesus macaque entorhinal cortex may confer vulnerability in Alzheimer's disease

Alzheimer's disease cortical tau pathology initiates in the layer II cell clusters of entorhinal cortex, but it is not known why these specific neurons are so vulnerable. Aging macaques exhibit the same qualitative pattern of tau pathology as humans, including initial pathology in layer II entorhinal cortex clusters, and thus can inform etiological factors driving selective vulnerability. Macaque data have already shown that susceptible neurons in dorsolateral prefrontal cortex express a "signature of flexibility" near glutamate synapses on spines, where cAMP-PKA magnification of calcium signaling opens nearby potassium and hyperpolarization-activated cyclic nucleotide-gated channels to dynamically alter synapse strength. This process is regulated by PDE4A/D, mGluR3, and calbindin, to prevent toxic calcium actions; regulatory actions that are lost with age/inflammation, leading to tau phosphorylation. The current study examined whether a similar "signature of flexibility" expresses in layer II entorhinal cortex, investigating the localization of PDE4D, mGluR3, and HCN1 channels. Results showed a similar pattern to dorsolateral prefrontal cortex, with PDE4D and mGluR3 positioned to regulate internal calcium release near glutamate synapses, and HCN1 channels concentrated on spines. As layer II entorhinal cortex stellate cells do not express calbindin, even when young, they may be particularly vulnerable to magnified calcium actions and ensuing tau pathology.

Nanoscale imaging of pT217-tau in aged rhesus macaque entorhinal and dorsolateral prefrontal cortex: Evidence of interneuronal trafficking and early-stage neurodegeneration

INTRODUCTION

pT217-tau is a novel fluid-based biomarker that predicts onset of Alzheimer's disease (AD) symptoms, but little is known about how pT217-tau arises in brain, as soluble pT217-tau is dephosphorylated postmortem in humans.

METHODS

We utilized multi-label immunofluorescence and immunoelectron-microscopy to examine the subcellular localization of early-stage pT217-tau in entorhinal and prefrontal cortices of aged macaques with naturally-occurring tau pathology and assayed pT217-tau levels in plasma.

RESULTS

pT217-tau was aggregated on microtubules within dendrites exhibiting early signs of degeneration, including autophagic vacuoles. It was also seen trafficking between excitatory neurons within synapses on spines, where it was exposed to the extracellular space, and thus accessible to CSF/blood. Plasma pT217-tau levels increased across the age-span and thus can serve as a biomarker in macaques.

DISCUSSION

These data help to explain why pT217-tau predicts degeneration in AD and how it gains access to CSF and plasma to serve as a fluid biomarker.

Aggregation, Transmission, and Toxicity of the Microtubule-Associated Protein Tau: A Complex Comprehension

The microtubule-associated protein tau is an intrinsically disordered protein containing a few short and transient secondary structures. Tau physiologically associates with microtubules (MTs) for its stabilization and detaches from MTs to regulate its dynamics. Under pathological conditions, tau is abnormally modified, detaches from MTs, and forms protein aggregates in neuronal and glial cells. Tau protein aggregates can be found in a number of devastating neurodegenerative diseases known as "tauopathies", such as Alzheimer's disease (AD), frontotemporal dementia (FTD), corticobasal degeneration (CBD), etc. However, it is still unclear how the tau protein is compacted into ordered protein aggregates, and the toxicity of the aggregates is still debated. Fortunately, there has been considerable progress in the study of tau in recent years, particularly in the understanding of the intercellular transmission of pathological tau species, the structure of tau aggregates, and the conformational change events in the tau polymerization process. In this review, we summarize the concepts of tau protein aggregation and discuss the views on tau protein transmission and toxicity.

Tau protein spreads through functionally connected neurons in Alzheimer's disease: a combined MEG/PET study

Recent studies on Alzheimer's disease (AD) suggest that tau proteins spread through the brain following neuronal connections. Several mechanisms could be involved in this process: spreading between brain regions that interact strongly (functional connectivity); through the pattern of anatomical connections (structural connectivity); or simple diffusion. Using magnetoencephalography (MEG), we investigated which spreading pathways influence tau protein spreading by modelling the tau propagation process using an epidemic spreading model. We compared the modelled tau depositions with 18F-flortaucipir PET binding potentials at several stages of the AD continuum. In this cross-sectional study, we analysed source-reconstructed MEG data and dynamic 100-min 18F-flortaucipir PET from 57 subjects positive for amyloid-β pathology [preclinical AD (n = 16), mild cognitive impairment (MCI) due to AD (n = 16) and AD dementia (n = 25)]. Cognitively healthy subjects without amyloid-β pathology were included as controls (n = 25). Tau propagation was modelled as an epidemic process (susceptible-infected model) on MEG-based functional networks [in alpha (8-13 Hz) and beta (13-30 Hz) bands], a structural or diffusion network, starting from the middle and inferior temporal lobe. The group-level network of the control group was used as input for the model to predict tau deposition in three stages of the AD continuum. To assess performance, model output was compared to the group-specific tau deposition patterns as measured with 18F-flortaucipir PET. We repeated the analysis by using networks of the preceding disease stage and/or using regions with most observed tau deposition during the preceding stage as seeds. In the preclinical AD stage, the functional networks predicted most of the modelled tau-PET binding potential, with best correlations between model and tau-PET [corrected amplitude envelope correlation (AEC-c) alpha C = 0.584; AEC-c beta C = 0.569], followed by the structural network (C = 0.451) and simple diffusion (C = 0.451). Prediction accuracy declined for the MCI and AD dementia stages, although the correlation between modelled tau and tau-PET binding remained highest for the functional networks (C = 0.384; C = 0.376). Replacing the control-network with the network from the preceding disease stage and/or alternative seeds improved prediction accuracy in MCI but not in the dementia stage. These results suggest that in addition to structural connections, functional connections play an important role in tau spread, and highlight that neuronal dynamics play a key role in promoting this pathological process. Aberrant neuronal communication patterns should be taken into account when identifying targets for future therapy. Our results also suggest that this process is more important in earlier disease stages (preclinical AD/MCI); possibly, in later stages, other processes may be influential.

A Human Neuron/Astrocyte Co-culture to Model Seeded and Spontaneous Intraneuronal Tau Aggregation

Communication and contact between neurons and astrocytes is important for proper brain physiology. How neuron/astrocyte crosstalk is affected by intraneuronal tau aggregation in neurodegenerative tauopathies is largely elusive. Human induced pluripotent stem cell (iPSC)-derived neurons provide the opportunity to model tau pathology in a translationally relevant in vitro context. However, current iPSC models inefficiently develop tau aggregates, and co-culture models of tau pathology have thus far utilized rodent astrocytes. In this article, we describe the co-culture of human iPSC-derived neurons with primary human astrocytes in a 96-well format compatible with high-content microscopy. By lentiviral overexpression of different mutated tau variants, this protocol can be flexibly adapted for the efficient induction of seeded or spontaneous tau aggregation. We used this novel co-culture model to identify cell type-specific disease mechanisms and to provide proof of concept for intervention by antisense therapy. These results show that this human co-culture model provides a highly translational tool for target discovery and drug development for human tauopathies. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Human neuron/astrocyte co-culture for seeded and spontaneous intraneuronal tau aggregation Support Protocol 1: Human induced pluripotent stem cell culture Support Protocol 2: Human primary astrocyte culture.

Connectome-based modelling of neurodegenerative diseases: towards precision medicine and mechanistic insight

Neurodegenerative diseases are the most common cause of dementia. Although their underlying molecular pathologies have been identified, there is substantial heterogeneity in the patterns of progressive brain alterations across and within these diseases. Recent advances in neuroimaging methods have revealed that pathological proteins accumulate along specific macroscale brain networks, implicating the network architecture of the brain in the system-level pathophysiology of neurodegenerative diseases. However, the extent to which 'network-based neurodegeneration' applies across the wide range of neurodegenerative disorders remains unclear. Here, we discuss the state-of-the-art of neuroimaging-based connectomics for the mapping and prediction of neurodegenerative processes. We review findings supporting brain networks as passive conduits through which pathological proteins spread. As an alternative view, we also discuss complementary work suggesting that network alterations actively modulate the spreading of pathological proteins between connected brain regions. We conclude this Perspective by proposing an integrative framework in which connectome-based models can be advanced along three dimensions of innovation: incorporating parameters that modulate propagation behaviour on the basis of measurable biological features; building patient-tailored models that use individual-level information and allowing model parameters to interact dynamically over time. We discuss promises and pitfalls of these strategies for improving disease insights and moving towards precision medicine.

Microglial-Targeted nSMase2 Inhibitor Fails to Reduce Tau Propagation in PS19 Mice

The progression of Alzheimer's disease (AD) correlates with the propagation of hyperphosphorylated tau (pTau) from the entorhinal cortex to the hippocampus and neocortex. Neutral sphingomyelinase2 (nSMase2) is critical in the biosynthesis of extracellular vesicles (EVs), which play a role in pTau propagation. We recently conjugated DPTIP, a potent nSMase2 inhibitor, to hydroxyl-PAMAM-dendrimer nanoparticles that can improve brain delivery. We showed that dendrimer-conjugated DPTIP (D-DPTIP) robustly inhibited the spread of pTau in an AAV-pTau propagation model. To further evaluate its efficacy, we tested D-DPTIP in the PS19 transgenic mouse model. Unexpectantly, D-DPTIP showed no beneficial effect. To understand this discrepancy, we assessed D-DPTIP's brain localization. Using immunofluorescence and fluorescence-activated cell-sorting, D-DPTIP was found to be primarily internalized by microglia, where it selectively inhibited microglial nSMase2 activity with no effect on other cell types. Furthermore, D-DPTIP inhibited microglia-derived EV release into plasma without affecting other brain-derived EVs. We hypothesize that microglial targeting allowed D-DPTIP to inhibit tau propagation in the AAV-hTau model, where microglial EVs play a central role in propagation. However, in PS19 mice, where tau propagation is independent of microglial EVs, it had a limited effect. Our findings confirm microglial targeting with hydroxyl-PAMAM dendrimers and highlight the importance of understanding cell-specific mechanisms when designing targeted AD therapies.

Association of Novelty-Related Locus Coeruleus Function With Entorhinal Tau Deposition and Memory Decline in Preclinical Alzheimer Disease

BACKGROUND AND OBJECTIVES

The predictable Braak staging scheme suggests that cortical tau progression may be related to synaptically connected neurons. Animal and human neuroimaging studies demonstrated that changes in neuronal activity contribute to tau spreading. Whether similar mechanisms explain tau progression from the locus coeruleus (LC), a tiny noradrenergic brainstem nucleus involved in novelty, learning, and memory and among the earliest regions to accumulate tau, has not yet been established. We aimed to investigate whether novelty-related LC activity was associated with the accumulation of cortical tau and its implications for cognitive decline.

METHODS

We combined functional MRI data of a novel vs repeated face-name learning paradigm, [18F]-FTP-PET, [11C]-PiB-PET, and longitudinal cognitive data from 92 well-characterized older individuals in the Harvard Aging Brain Study. We related novelty vs repetition LC activity to cortical tau deposition and to longitudinal decline in memory, executive function, and the Preclinical Alzheimer Disease Cognitive Composite (version 5; PACC5). Structural equation modeling was used to examine whether entorhinal cortical (EC) tau mediated the relationship between LC activity and cognitive decline and whether this depended on beta-amyloid deposition.

RESULTS

The participants' average age at baseline was 69.67 ± 10.14 years. Fifty-one participants were female. Ninety-one participants were cognitively normal (CDR global = 0), and one participant had mild cognitive impairment (CDR global = 0.5) at baseline. Lower novelty-related LC activity was specifically related to greater tau deposition in the medial-lateral temporal cortex and steeper memory decline. LC activity during novelty vs repetition was not related to executive dysfunction or decline on the PACC5. The relationship between LC activity and memory decline was partially mediated by EC tau, particularly in individuals with elevated beta-amyloid deposition.

DISCUSSION

Our results suggested that lower novelty-related LC activity is associated with the emergence of EC tau and that the downstream effects of this LC-EC pathway on memory decline also require the presence of elevated beta-amyloid. Longitudinal studies are required to investigate whether optimal LC activity has the potential to delay tau spread and memory decline, which may have implications for designing targeted interventions promoting resilience.

Evolving prion-like tau conformers differentially alter postsynaptic proteins in neurons inoculated with distinct isolates of Alzheimer's disease tau

OBJECTIVES

Although accumulation of misfolded tau species has been shown to predict cognitive decline in patients with Alzheimer's disease (AD) and other tauopathies but with the remarkable diversity of clinical manifestations, neuropathology profiles, and time courses of disease progression remaining unexplained by current genetic data. We considered the diversity of misfolded tau conformers present in individual AD cases as an underlying driver of the phenotypic variations of AD and progressive loss of synapses.

METHODS

To model the mechanism of tau propagation and synaptic toxicity of distinct tau conformers, we inoculated wild-type primary mouse neurons with structurally characterized Sarkosyl-insoluble tau isolates from the frontal cortex of six AD cases and monitored the impact for fourteen days. We analyzed the accumulation rate, tau isoform ratio, and conformational characteristics of de novo-induced tau aggregates with conformationally sensitive immunoassays, and the dynamics of synapse formation, maintenance, and their loss using a panel of pre-and post-synaptic markers.

RESULTS

At the same concentrations of tau, the different AD tau isolates induced accumulation of misfolded predominantly 4-repeat tau aggregates at different rates in mature neurons, and demonstrated distinct conformational characteristics corresponding to the original AD brain tau. The time-course of the formation of misfolded tau aggregates and colocalization correlated with significant loss of synapses in tau-inoculated cell cultures and the reduction of synaptic connections implicated the disruption of postsynaptic compartment as an early event.

CONCLUSIONS

The data obtained with mature neurons expressing physiological levels and adult isoforms of tau protein demonstrate markedly different time courses of endogenous tau misfolding and differential patterns of post-synaptic alterations. These and previous biophysical data argue for an ensemble of various misfolded tau aggregates in individual AD brains and template propagation of their homologous conformations in neurons with different rates and primarily postsynaptic interactors. Modeling tau aggregation in mature differentiated neurons provides a platform for investigating divergent molecular mechanisms of tau strain propagation and for identifying common structural features of misfolded tau and critical interactors for new therapeutic targets and approaches in AD.

Global brain activity and its coupling with cerebrospinal fluid flow is related to tau pathology

Amyloid-β (Aβ) and tau deposition constitute Alzheimer's disease (AD) neuropathology. Cortical tau deposits first in the entorhinal cortex and hippocampus and then propagates to neocortex in an Aβ-dependent manner. Tau also tends to accumulate earlier in higher-order association cortex than in lower-order primary sensory-motor cortex. While previous research has examined the production and spread of tau, little attention has been paid to its clearance. Low-frequency (<0.1 Hz) global brain activity during the resting state is coupled with cerebrospinal fluid (CSF) flow and potentially reflects glymphatic clearance. Here we report that tau deposition in subjects with evaluated Aβ, accompanied by cortical thinning and cognitive decline, is strongly associated with decreased coupling between CSF flow and global brain activity. Substantial modulation of global brain activity is also manifested as propagating waves of brain activation between higher- and lower-order regions, resembling tau spreading. Together, the findings suggest an important role of resting-state global brain activity in AD tau pathology.

Training-induced circuit-specific excitatory synaptogenesis in mice is required for effort control

Synaptogenesis is essential for circuit development; however, it is unknown whether it is critical for the establishment and performance of goal-directed voluntary behaviors. Here, we show that operant conditioning via lever-press for food reward training in mice induces excitatory synapse formation onto a subset of anterior cingulate cortex neurons projecting to the dorsomedial striatum (ACC→DMS). Training-induced synaptogenesis is controlled by the Gabapentin/Thrombospondin receptor α2δ-1, which is an essential neuronal protein for proper intracortical excitatory synaptogenesis. Using germline and conditional knockout mice, we found that deletion of α2δ-1 in the adult ACC→DMS circuit diminishes training-induced excitatory synaptogenesis. Surprisingly, this manipulation does not impact learning but results in a significant increase in effort exertion without affecting sensitivity to reward value or changing contingencies. Bidirectional optogenetic manipulation of ACC→DMS neurons rescues or phenocopies the behaviors of the α2δ-1 cKO mice, highlighting the importance of synaptogenesis within this cortico-striatal circuit in regulating effort exertion.

Interrogating the Etiology of Sporadic Alzheimer's Disease Using Aging Rhesus Macaques: Cellular, Molecular, and Cortical Circuitry Perspectives

Aging is the most significant risk factor for neurodegenerative disorders such as Alzheimer's disease (AD) associated with profound socioeconomic and personal costs. Consequently, there is an urgent need for animal models that recapitulate the age-related spatial and temporal complexity and patterns of pathology identical to human AD. Our research in aging nonhuman primate models involving rhesus macaques has revealed naturally occurring amyloid and tau pathology, including the formation of amyloid plaques and neurofibrillary tangles comprising hyperphosphorylated tau. Moreover, rhesus macaques exhibit synaptic dysfunction in association cortices and cognitive impairments with advancing age, and thus can be used to interrogate the etiological mechanisms that generate neuropathological cascades in sporadic AD. Particularly, unique molecular mechanisms (eg, feedforward cyclic adenosine 3',5'-monophosphate [cAMP]-Protein kinase A (PKA)-calcium signaling) in the newly evolved primate dorsolateral prefrontal cortex are critical for persistent firing required for subserving higher-order cognition. For example, dendritic spines in primate dorsolateral prefrontal cortex contain a specialized repertoire of proteins to magnify feedforward cAMP-PKA-calcium signaling such as N-methyl-d-aspartic acid receptors and calcium channels on the smooth endoplasmic reticulum (eg, ryanodine receptors). This process is constrained by phosphodiesterases (eg, PDE4) that hydrolyze cAMP and calcium-buffering proteins (eg, calbindin) in the cytosol. However, genetic predispositions and age-related insults exacerbate feedforward cAMP-Protein kinase A-calcium signaling pathways that induce a myriad of downstream effects, including the opening of K+ channels to weaken network connectivity, calcium-mediated dysregulation of mitochondria, and activation of inflammatory cascades to eliminate synapses, thereby increasing susceptibility to atrophy. Therefore, aging rhesus macaques provide an invaluable model to explore novel therapeutic strategies in sporadic AD.

Tau seeding and spreading in vivo is supported by both AD-derived fibrillar and oligomeric tau

Insoluble fibrillar tau, the primary constituent of neurofibrillary tangles, has traditionally been thought to be the biologically active, toxic form of tau mediating neurodegeneration in Alzheimer's disease. More recent studies have implicated soluble oligomeric tau species, referred to as high molecular weight (HMW), due to their properties on size-exclusion chromatography, in tau propagation across neural systems. These two forms of tau have never been directly compared. We prepared sarkosyl-insoluble and HMW tau from the frontal cortex of Alzheimer patients and compared their properties using a variety of biophysical and bioactivity assays. Sarkosyl-insoluble fibrillar tau comprises abundant paired-helical filaments (PHF) as quantified by electron microscopy (EM) and is more resistant to proteinase K, compared to HMW tau, which is mostly in an oligomeric form. Sarkosyl-insoluble and HMW tau are nearly equivalent in potency in HEK cell bioactivity assay for seeding aggregates, and their injection reveals similar local uptake into hippocampal neurons in PS19 Tau transgenic mice. However, the HMW preparation appears to be far more potent in inducing a glial response including Clec7a-positive rod microglia in the absence of neurodegeneration or synapse loss and promotes more rapid propagation of misfolded tau to distal, anatomically connected regions, such as entorhinal and perirhinal cortices. These data suggest that soluble HMW tau has similar properties to fibrillar sarkosyl-insoluble tau with regard to tau seeding potential, but may be equal or even more bioactive with respect to propagation across neural systems and activation of glial responses, both relevant to tau-related Alzheimer phenotypes.

Tau and neuroinflammation in Alzheimer's disease: interplay mechanisms and clinical translation

Alzheimer's Disease (AD) contributes to most cases of dementia. Its prominent neuropathological features are the extracellular neuritic plaques and intercellular neurofibrillary tangles composed of aggregated β-amyloid (Aβ) and hyperphosphorylated tau protein, respectively. In the past few decades, disease-modifying therapy targeting Aβ has been the focus of AD drug development. Even though it is encouraging that two of these drugs have recently received accelerated US Food and Drug Administration approval for AD treatment, their efficacy or long-term safety is controversial. Tau has received increasing attention as a potential therapeutic target, since evidence indicates that tau pathology is more associated with cognitive dysfunction. Moreover, inflammation, especially neuroinflammation, accompanies AD pathological processes and is also linked to cognitive deficits. Accumulating evidence indicates that inflammation has a complex and tight interplay with tau pathology. Here, we review recent evidence on the interaction between tau pathology, focusing on tau post-translational modification and dissemination, and neuroinflammatory responses, including glial cell activation and inflammatory signaling pathways. Then, we summarize the latest clinical trials targeting tau and neuroinflammation. Sustained and increased inflammatory responses in glial cells and neurons are pivotal cellular drivers and regulators of the exacerbation of tau pathology, which further contributes to its worsening by aggravating inflammatory responses. Unraveling the precise mechanisms underlying the relationship between tau pathology and neuroinflammation will provide new insights into the discovery and clinical translation of therapeutic targets for AD and other tau-related diseases (tauopathies). Targeting multiple pathologies and precision therapy strategies will be the crucial direction for developing drugs for AD and other tauopathies.

Implication of tau propagation on neurodegeneration in Alzheimer's disease

Propagation of tau fibrils correlate closely with neurodegeneration and memory deficits seen during the progression of Alzheimer's disease (AD). Although it is not well-established what drives or attenuates tau spreading, new studies on human brain using positron emission tomography (PET) have shed light on how tau phosphorylation, genetic factors, and the initial epicenter of tau accumulation influence tau accumulation and propagation throughout the brain. Here, we review the latest PET studies performed across the entire AD continuum looking at the impact of amyloid load on tau pathology. We also explore the effects of structural, functional, and proximity connectivity on tau spreading in a stereotypical manner in the brain of AD patients. Since tau propagation can be quite heterogenous between individuals, we then consider how the speed and pattern of propagation are influenced by the starting localization of tau accumulation in connected brain regions. We provide an overview of some genetic variants that were shown to accelerate or slow down tau spreading. Finally, we discuss how phosphorylation of certain tau epitopes affect the spreading of tau fibrils. Since tau pathology is an early event in AD pathogenesis and is one of the best predictors of neurodegeneration and memory impairments, understanding the process by which tau spread from one brain region to another could pave the way to novel therapeutic avenues that are efficient during the early stages of the disease, before neurodegeneration induces permanent brain damage and severe memory loss.

A luminescence-based reporter to study tau secretion reveals overlapping mechanisms for the release of healthy and pathological tau

In Alzheimer's disease, tau pathology is thought to spread via a prion-like manner along connected neuronal networks. For this to occur, the usually cytosolic tau protein must be secreted via an unconventional mechanism prior to uptake into the connected neuron. While secretion of healthy and pathological tau has been documented, it remains under-investigated whether this occurs via overlapping or distinct processes. Here, we established a sensitive bioluminescence-based assay to assess mechanisms underlying the secretion of pseudohyperphosphorylated and wild-type tau in cultured murine hippocampal neurons. We found that under basal conditions, both wild-type and mutant tau are secreted, with mutant tau being more robustly secreted. Pharmacological stimulation of neuronal activity led to a modest increase of wild-type and mutant tau secretion, whereas inhibition of activity had no effect. Interestingly, inhibition of heparin sulfate proteoglycan (HSPG) biosynthesis drastically decreased secretion of both wild-type and mutant tau without affecting cell viability. This shows that native and pathological tau share release mechanisms; both activity-dependent and non-activity-dependent secretion of tau is facilitated by HSPGs.

Tau-targeting antisense oligonucleotide MAPTRx in mild Alzheimer's disease: a phase 1b, randomized, placebo-controlled trial

Tau plays a key role in Alzheimer's disease (AD) pathophysiology, and accumulating evidence suggests that lowering tau may reduce this pathology. We sought to inhibit MAPT expression with a tau-targeting antisense oligonucleotide (MAPTRx) and reduce tau levels in patients with mild AD. A randomized, double-blind, placebo-controlled, multiple-ascending dose phase 1b trial evaluated the safety, pharmacokinetics and target engagement of MAPTRx. Four ascending dose cohorts were enrolled sequentially and randomized 3:1 to intrathecal bolus administrations of MAPTRx or placebo every 4 or 12 weeks during the 13-week treatment period, followed by a 23 week post-treatment period. The primary endpoint was safety. The secondary endpoint was MAPTRx pharmacokinetics in cerebrospinal fluid (CSF). The prespecified key exploratory outcome was CSF total-tau protein concentration. Forty-six patients enrolled in the trial, of whom 34 were randomized to MAPTRx and 12 to placebo. Adverse events were reported in 94% of MAPTRx-treated patients and 75% of placebo-treated patients; all were mild or moderate. No serious adverse events were reported in MAPTRx-treated patients. Dose-dependent reduction in the CSF total-tau concentration was observed with greater than 50% mean reduction from baseline at 24 weeks post-last dose in the 60 mg (four doses) and 115 mg (two doses) MAPTRx groups. Clinicaltrials.gov registration number: NCT03186989 .

The Adult Neurogenesis Theory of Alzheimer's Disease

Alzheimer's disease starts in neural stem cells (NSCs) in the niches of adult neurogenesis. All primary factors responsible for pathological tau hyperphosphorylation are inherent to adult neurogenesis and migration. However, when amyloid pathology is present, it strongly amplifies tau pathogenesis. Indeed, the progressive accumulation of extracellular amyloid-β deposits in the brain triggers a state of chronic inflammation by microglia. Microglial activation has a significant pro-neurogenic effect that fosters the process of adult neurogenesis and supports neuronal migration. Unfortunately, this "reactive" pro-neurogenic activity ultimately perturbs homeostatic equilibrium in the niches of adult neurogenesis by amplifying tau pathogenesis in AD. This scenario involves NSCs in the subgranular zone of the hippocampal dentate gyrus in late-onset AD (LOAD) and NSCs in the ventricular-subventricular zone along the lateral ventricles in early-onset AD (EOAD), including familial AD (FAD). Neuroblasts carrying the initial seed of tau pathology travel throughout the brain via neuronal migration driven by complex signals and convey the disease from the niches of adult neurogenesis to near (LOAD) or distant (EOAD) brain regions. In these locations, or in close proximity, a focus of degeneration begins to develop. Then, tau pathology spreads from the initial foci to large neuronal networks along neural connections through neuron-to-neuron transmission.

Microfluidic 'brain-on chip' systems to supplement neurological practice: development, applications and considerations

Among the greatest general challenges in bioengineering is to mimic human physiology. Advanced efforts in tissue engineering have led to sophisticated 'brain-on-chip' (BoC) microfluidic devices that can mimic structural and functional aspects of brain tissue. BoC may be used to understand the biochemical pathways of neurolgical pathologies and assess promising therapeutic agents for facilitating regenerative medicine. We evaluated the potential of microfluidic BoC devices in various neurological pathologies, such as Alzheimer's, glioblastoma, traumatic brain injury, stroke and epilepsy. We also discuss the principles, limitations and future considerations of BoC technology. Results suggest that BoC models can help understand complex neurological pathologies and augment drug testing efforts for regenerative applications. However, implementing organ-on-chip technology to clinical practice has some practical limitations that warrant greater attention to improve large-scale applicability. Nevertheless, they remain to be versatile and powerful tools that can broaden our understanding of pathophysiological and therapeutic uncertainties to neurological diseases.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

Mechanism of action deconvolution of the small-molecule pathological tau aggregation inhibitor Anle138b

BACKGROUND

A key histopathological hallmark of Alzheimer's disease (AD) is the presence of neurofibrillary tangles of aggregated microtubule-associated protein tau in neurons. Anle138b is a small molecule which has previously shown efficacy in mice in reducing tau aggregates and rescuing AD disease phenotypes.

METHODS

In this work, we employed bioinformatics analysis-including pathway enrichment and causal reasoning-of an in vitro tauopathy model. The model consisted of cultured rat cortical neurons either unseeded or seeded with tau aggregates derived from human AD patients, both of which were treated with Anle138b to generate hypotheses for its mode of action. In parallel, we used a collection of human target prediction models to predict direct targets of Anle138b based on its chemical structure.

RESULTS

Combining the different approaches, we found evidence supporting the hypothesis that the action of Anle138b involves several processes which are key to AD progression, including cholesterol homeostasis and neuroinflammation. On the pathway level, we found significantly enriched pathways related to these two processes including those entitled "Superpathway of cholesterol biosynthesis" and "Granulocyte adhesion and diapedesis". With causal reasoning, we inferred differential activity of SREBF1/2 (involved in cholesterol regulation) and mediators of the inflammatory response such as NFKB1 and RELA. Notably, our findings were also observed in Anle138b-treated unseeded neurons, meaning that the inferred processes are independent of tau pathology and thus represent the direct action of the compound in the cellular system. Through structure-based ligand-target prediction, we predicted the intracellular cholesterol carrier NPC1 as well as NF-κB subunits as potential targets of Anle138b, with structurally similar compounds in the model training set known to target the same proteins.

CONCLUSIONS

This study has generated feasible hypotheses for the potential mechanism of action of Anle138b, which will enable the development of future molecular interventions aiming to reduce tau pathology in AD patients.