Tau mislocalization to dendritic spines mediates synaptic dysfunction independently of neurodegeneration

Differential roles of human tau isoforms in the modulation of inflammation and development of neuropathology

Alzheimer's disease (AD) is the most common tauopathy characterized by progressive accumulation of Aß and tau neuropathology. Tau is expressed in two major isoforms containing either 3 or 4C-terminal repeats, 3R and 4R. Despite tau isoforms occurring in roughly equimolar ratios in AD, the majority of research focus in developed mouse and in vitro models focus only on 4Rtau. To generate a more complete model of AD tauopathy and understand specific tau isoform-mediated neuropathology and neurodegeneration, we generated a transgenic mouse line expressing both 3Rtau and 4Rtau and determined how this impacted the timing and severity of neuropathological and behavioral changes.

METHODS

3Rtau-tg and 4Rtau-tg mice were crossed to generate 3R/4Rtau-tg bigenic mice. At 3, 6, and 9 months of age, mice were assessed for behavior, neuropathology and RNA expression.

RESULTS

3R/4Rtau bigenic mice expressed increased tau and phosphorylated tau in the hippocampus and cortex compared to single (3R or 4R) transgenic cohorts as early as 3-months of age and this was accompanied with increased astrogliosis and microglial activation. Bigenic mice had significantly greater behavioral deficits compared to either single transgenic littermates in spatial learning and memory as well as nest building, indicative of depression and/or cognitive deficits.

CONCLUSION

This new mouse model of tauopathy more completely recapitulates the pattern, severity and accumulation of tau and associated neuropathology and behavioral changes observed in human tauopathies such as AD. 3R/4Rtau-tg bigenic mice should supplant existing single transgenic tau models for general validation of therapeutic targets and investigations of novel therapies on tauopathy endpoints.

Are we missing a trick by not exploiting fruit flies in inflammation-led drug discovery for neurodegeneration?

INTRODUCTION

Alzheimer's disease (AD) remains a formidable challenge in neurodegeneration research, with limited therapeutic options despite decades of study. While Drosophila melanogaster has been instrumental in in modeling AD related Tau and amyloid beta toxicity, inflammation, a key driver of AD pathology, remains unexplored in fly models. Given the evolutionary conservation of innate immune pathways between flies and mammals, drosophila presents a powerful yet underutilized tool for inflammation led drug discovery in AD.

AREAS COVERED

This perspective highlights the relevance of Drosophila in studying neuroinflammatory processes, including microglial-like glial activation, systemic inflammation and gut-brain axis interactions. It further explores how fly models can be leveraged to screen anti-inflammatory compounds and dissect immune related genetic factors implicated in AD.

EXPERT OPINION

By integrating immune modulation in Drosophila-based drug discovery pipeline we can accelerate the identification of novel therapeutic strategies. Fully exploiting the potential of Drosophila in inflammation led drug screening may usher in a new era of AD therapeutics, bridging gaps between fundamental research and translational medicine.

Elevated TGF-β1 impairs synaptic and cognitive function through activation of Smad2/3-Sp1 pathway in AngII-related hypertension

Vascular dementia (VaD) is characterized by cognitive decline due to reduced cerebral blood flow, although its molecular mechanisms remain unclear. This study shows that angiotensin II (AngII) elevates blood pressure, reduces hippocampal blood flow, and impairs synaptic and cognitive function, which correlates with increased TGF-β1 levels. Overexpressing TGF-β1 in rats induces similar deficits, while its downregulation partially mitigates these effects, with the exception of hypoperfusion. Phosphorylation of Smad2/3, downstream of TGF-β1, is elevated in AngII-treated rats and TGF-β1-exposed neurons, and inhibiting Smad2/3 activation prevents synaptic damage. Additionally, phosphorylated Smad2/3 interacts more with the transcription factor Sp1 in hippocampal neurons of AngII-treated rats. Overexpression of Sp1 worsens synaptic and cognitive function, whereas Sp1 knockdown improves TGF-β1-induced impairments. These findings highlight TGF-β1 as a key mediator of AngII-induced cognitive deficits, beyond hypoperfusion, suggesting that targeting the TGF-β1/Smad2/3/Sp1 axis may offer therapeutic benefits for hypertension-related synaptic and cognitive dysfunction.

Chuanxiong-Danggui herb pair alleviated cognitive deficits of APP/PS1 mice by promoting mitophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Disruption of receptor-mediated mitophagy contributes to neuronal damage in Alzheimer's disease (AD). Chuanxiong-Danggui herb pair (CDHP) is classic herbal pair applied to treating neurodegenerative diseases including AD, Amyotrophic Lateral Sclerosis, Parkinson's disease. Though studies have demonstrated the neuroprotective effects of CDHP, the underlying mechanisms by which CDHP attenuates neuronal impairment of AD remains to be elucidated.

AIM OF THE STUDY

The objective of this work was to investigate the anti-AD mechanism of CDHP in APP/PS1 mice.

MATERIALS AND METHODS

Behavioral assessments were conducted on C57BL/6J and APP/PS1 mice following CDHP treatment, alongside an evaluation of neuronal morphology in the hippocampal region. In vitro, HT-22 cells were induced by Aβ25-35 before being treated with CDHP. The mechanisms of CDHP were investigated using transmission electron microscopy, Golgi staining, immunofluorescence, and Western blot analysis.

RESULTS

Results from the passive avoidance test and the Morris water maze (MWM) indicated that CDHP significantly mitigated cognitive deficits of APP/PS1 mice, accompanied by a reduction of pathological damage in the CA1 and CA3 regions of hippocampus. Further testing found that a significant reduction in dendritic spines density was rescued by CDHP. Synaptophysin (SYN) and postsynaptic density protein 95 (PSD-95) were elevated in the CDHP group, while β-amyloid (Aβ) plaques deposition was significantly reduced. Simultaneously, CDHP markedly inhibited neuronal apoptosis through a decrease of the levels of Cleaved Caspase-12 and enhanced expression of Bcl-2/Bax, both in vivo and in vitro. Additionally, CDHP improved mitochondrial morphology and function in the AD model by decreasing abnormal mitochondria and increasing the expression of COXIV. Transmission electron microscopy (TEM) revealed that clear mitophagy-autophagosomes were nearly absent in APP/PS1 mice, while the expression of p62 and LC3B were elevated following CDHP treatment. Furthermore, CDHP increased the expression of the FUNDC1 and PGAM5 in APP/PS1 mice and AD-like cell models.

CONCLUSION

These findings suggest that CDHP mitigated cognitive dysfunction in APP/PS1 mice by enhancing mitophagy to reduce neuronal injury.

Ultrasmall Nanoparticles Mitigate Tau Hyperphosphorylation to Restore Synaptic Integrity and Boost Cognitive Function in Alzheimer's Disease

Tau hyperphosphorylation represents a critical pathological hallmark of Alzheimer's disease (AD), a prevalent neurodegenerative disorder characterized by progressive cognitive decline. The ubiquitin-specific proteases 14 (USP14) impairs proteasomal function and accelerates hyperphosphorylated Tau accumulation, making it an attractive therapeutic target for modulating the ubiquitin-proteasome pathway in AD treatment. In this study, it is reported that wogonoside-functionalized ultrasmall Cu2-xSe nanoparticles (CSPW NPs) significantly reduce hyperphosphorylated Tau accumulation and alleviate AD symptoms. The therapeutic mechanism involves activation of the ubiquitin-proteasome pathway through USP14 inhibition by CSPW NPs, thereby preventing hyperphosphorylated Tau accumulation. Furthermore, after cell membrane coating (CSPW@CM NPs), these nanoparticles efficiently cross the blood-brain barrier with focused ultrasound assistance and accumulate in the brain to target neurons. Within neurons, they inhibit USP14, reduce phosphorylated Tau deposition, enhance microtubule stability, mitigate synaptic loss, restore synaptic integrity, and ultimately alleviate cognitive dysfunction in AD mice. The findings highlight the substantial potential of USP14 modulation for mitigating Tau hyperphosphorylation in the treatment of AD and related tauopathies.

Systematic Review and Network Meta-Analysis of Retinal Imaging Biomarkers in Neurodegenerative Diseases: Correlation with Brain Changes

INTRODUCTION

The retina and brain share a common embryonic origin and neural composition. Both undergo structural, vascular, and physiological changes in neurodegenerative diseases (NDs). This Systematic and network meta-analysis (NMA) aims to identify retinal-brain biomarkers across the spectrum of NDs.

METHODS

We conducted an NMA using random-effects models to assess retinal layer thickness changes in Alzheimer's disease (AD) and mild cognitive impairment (MCI). Data from 225 AD patients, 97 MCI patients, and 345 cognitively normal (CN) individuals, published between 2016 and 2023, were analyzed. Brain imaging findings were also evaluated for comparison.

RESULTS

Compared to controls, the MCI group exhibited significant thinning in the inferior and superior peripapillary retinal nerve fiber layer (pRNFL) and inner macular thickness. Specifically, reductions were observed in Right Eye Inferior pRNFL (SMD = -21.5306), Right Eye Superior pRNFL (SMD = -11.5011), Left Eye Inferior pRNFL (SMD = -27.6244), Left Eye Superior pRNFL (SMD = -9.8137), and Inner Macular Thickness (SMD = -4.8791). When comparing AD to MCI, Right Eye Nasal pRNFL (SMD = 5.95), Left Eye Superior pRNFL (SMD = -9.1786), and Outer Macular Thickness (SMD = -4.1046) were significantly thinner in AD. No significant differences were found between AD and CN in most retinal regions.

CONCLUSION

Thinning of the superior and inferior pRNFL and inner macular layer may serve as early biomarkers of MCI. In AD, retinal layer thinning is accompanied by hippocampal, entorhinal cortex, and temporal lobe atrophy, with macular volume (EZ-RPE) correlating with total brain volume.

PRMT3-Mediated H4R3me2a Promotes Primary Age-Related Tauopathy by Driving Tau Hyperphosphorylation in Neuron

Primary age-related tauopathy (PART) and Alzheimer's disease (AD) both exhibit 3R/4R hyperphosphorylated tau-positive neurofibrillary tangles (NFTs) within the hippocampal-entorhinal system. Notably, PART patients show a higher degree of tau hyperphosphorylation in the entorhinal cortex (EC) than AD, yet the molecular mechanisms driving Aβ-independent tau hyperphosphorylation in PART remain poorly understood. Herein, through transcriptomic profiling of postmortem EC tissues and in vitro and in vivo functional validation, the present study identifies protein arginine methyltransferase 3 (PRMT3) as a critical driver of tau hyperphosphorylation. Mechanistically, PRMT3-mediated tau hyperphosphorylation is dependent on asymmetric dimethylation of histone H4 at arginine 3 (H4R3me2a), which upregulates miR-448. Elevated miR-448 specifically targets and suppresses IGF1R, leading to downstream GSK3β activation and subsequent tau hyperphosphorylation through PI3K/AKT/GSK3β signaling. Treatment with SGC707, a selective PRMT3 inhibitor, effectively reduces tau hyperphosphorylation and demonstrates therapeutic promise for PART and potentially other tauopathies. Collectively, this study defines the PRMT3/H4R3me2a/miR-448 axis as a critical regulatory pathway in tau hyperphosphorylation within PART, underscoring the potential of PRMT3 inhibition as a targeted therapeutic strategy for tauopathies.

Diverse influences on tau aggregation and implications for disease progression

Tau is an intrinsically disordered protein that accumulates in fibrillar aggregates in neurodegenerative diseases. The misfolding of tau can be understood as an equilibrium between different states and their propensity to form higher-order fibers, which is affected by several factors. First, modulation of the biochemical state of tau due to ionic conditions, post-translational modifications, cofactors, and interacting molecules or assemblies can affect the formation and structure of tau fibrils. Second, cellular processes impact tau aggregation through modulating stability, clearance, disaggregation, and transport. Third, through interactions with glial cells, the neuronal microenvironment can affect intraneuronal conditions with impacts on tau fibrilization and toxicity. Importantly, tau fibrils propagate through the brain via a "prion-like" manner, contributing to disease progression. This review highlights the biochemical and cellular pathways that modulate tau aggregation and discusses implications for pathobiology and tau-directed therapeutic approaches.

RILP cleavage links an inflammatory state to enhanced tau propagation in a cell culture model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by the progressive spread of tau pathology throughout the brain. Inflammation has been demonstrated to be present in the disease state as well as changes in endocytic trafficking. Here we identify the Rab7 effector RILP, a protein at the intersection of inflammatory states and endocytic trafficking, as a novel player in tau propagation. We show that RILP is cleaved in AD brain and this cleavage correlates to increases in hyperphosphorylated tau. Cleavage can be induced in both BE(2) neuron-like cells as well as a microglia cell line when they are treated with the inflammatory mediators lipopolysaccharide (LPS) and ATP. This inflammatory state also enhances tau propagation between BE(2) cells, an effect that is mitigated by overexpressing a noncleavable RILP. Furthermore, microglial cells contribute to intercellular tau propagation through both the release of inflammation-associated factors and the direct uptake and secretion of tau, potentially via extracellular vesicles (EVs). In HMC3 microglial cells, RILP cleavage led to impaired tau degradation, increasing intracellular tau accumulation. Additionally, the RILP cleavage status influences EV secretion in microglia. These findings suggest that RILP cleavage alters the endocytic trafficking of tau causing increased cell-cell propagation in a cell-culture model of AD.

Alzheimer's Disease and Frontotemporal Dementia: A Review of Pathophysiology and Therapeutic Approaches

Alzheimer's disease (AD) is a devastating form of dementia, with the number of affected individuals rising sharply. The main hallmarks of the disease include amyloid-beta plaque deposits and neurofibrillary tangles consisting of hyperphosphorylated tau protein, besides other pathological features that contribute to the disease's complexity. The causes of sporadic AD are multifactorial and mostly age-related and involve risk factors such as diabetes and cardiovascular or cerebrovascular disorders. Frontotemporal dementia (FTD) is another type of dementia characterized by a spectrum of behaviors, memory, and motor abnormalities and associated with abnormal depositions of protein aggregation, including tau protein. Currently approved medications are symptomatic, and no disease-modifying therapy is available to halt the disease progression. Therefore, the development of multi-targeted therapeutic approaches could hold promise for the treatment of AD and other neurodegenerative disorders, including tauopathies. In this article, we will discuss the pathophysiology of AD and FTD, the proposed hypotheses, and current therapeutic approaches, highlighting the development of novel drug candidates and the progress of clinical trials in this field of research.

Loss of excitatory inputs and decreased tonic and evoked activity of locus coeruleus neurons in aged P301S mice

Tau pathology in the locus coeruleus (LC) is associated with several neurodegenerative conditions including Alzheimer's disease and frontotemporal dementia. Phosphorylated tau accumulates in the LC and results in inflammation, synaptic loss, and eventually cell death as the disease progresses. Loss of LC neurons and noradrenergic innervation is thought to contribute to the symptoms of cognitive decline later in disease. While loss and degeneration of LC neurons has been well studied, less is known about changes in LC physiology at advanced stages of tau pathology that precedes neurodegeneration. In this study, we investigated the ex vivo electrophysiological properties of LC neurons in male and female mice from the P301S mouse model of tauopathy at 9 months of age, a time-point when significant tau accumulation, cell death, and cognitive impairments are observed. We found a reduction in excitatory inputs and changes in excitatory post-synaptic current kinetics in male and female P301S. There was also a decrease in spontaneous discharge of LC neurons and an increase in AP threshold in P301S mice of both sexes. Finally, we observed a decrease in excitability and increase in rheobase current in P301S mice. Despite the decrease in LC activity in ex vivo slices, we did not identify differences in total tissue norepinephrine (NE) or NE metabolites in prefrontal cortex or hippocampus. Together these findings demonstrate reductions in the activity and excitability of LC neurons at late stages of tau accumulation. However, compensatory mechanisms may maintain normal NE levels in LC projection regions in vivo.

Prediction of longitudinal synaptic loss in Alzheimer's disease using tau PET and plasma biomarkers

INTRODUCTION

We investigated the associations of longitudinal synaptic loss and cognitive decline with tau burden and plasma biomarkers in Alzheimer's disease (AD).

METHODS

Twenty cognitively impaired (CI) individuals and 16 healthy controls (HC) underwent cognitive and plasma biomarker assessments, amyloid positron emission tomography (PET), tau PET, and synaptic density PET; after 1 year, tau and synaptic density PET were repeated. The relationships among tau burden, plasma biomarkers, synaptic density, and cognition were investigated.

RESULTS

The CI group had more longitudinal synapse loss and tau deposition than HCs. Longitudinal synaptic loss was positively associated with longitudinal cognitive decline, negatively with longitudinal tau deposition. Plasma glial fibrillary acidic protein (GFAP) mediates the relationship between longitudinal tau deposition and longitudinal synaptic loss. Tau burden, plasma phosphorylated tau181, and GFAP could predict longitudinal synaptic loss and cognitive decline.

CONCLUSIONS

The CI group had more longitudinal synapse loss and tau burden increases than HCs. Tau pathology and plasma GFAP could predict longitudinal synapse loss and cognitive decline.

HIGHLIGHTS

Cognitively impaired individuals had more longitudinal synapse loss in the medial temporal lobe, and increased tau burden in the widespread neocortex than healthy controls. The longitudinal change of synaptic density was negatively associated with the longitudinal change of tau burden, and positively associated with longitudinal cognitive decline. Plasma glial fibrillary acidic protein (GFAP) mediates the relationship between longitudinal tau deposition and longitudinal synaptic loss. Tau burden, plasma phosphorylated tau181, and GFAP could predict longitudinal synaptic loss and cognitive decline.

The Unified Theory of Neurodegeneration Pathogenesis Based on Axon Deamidation

Until now, neurodegenerative diseases like Alzheimer's and Parkinson's have been studied separately in biochemistry and therapeutic drug development, and no causal link has ever been established between them. This study has developed a Unified Theory, which establishes that the regulation of axon and dendrite-specific 4E-BP2 deamidation rates controls the occurrence and progression of neurodegenerative diseases. This is based on identifying axon-specific 4E-BP2 deamidation as a universal denominator for the biochemical processes of deamidation, translational control, oxidative stress, and neurodegeneration. This was achieved by conducting a thorough and critical review of 224 scientific publications regarding (a) deamidation, (b) translational control in protein synthesis initiation, (c) neurodegeneration and (d) oxidative stress, and by applying my discovery of the fundamental neurobiological mechanism behind neuron-specific 4E-BP2 deamidation to practical applications in medicine. Based on this newly developed Unified Theory and my critical review of the scientific literature, I also designed three biochemical flowsheets of (1) in-vivo deamidation, (2) protein synthesis initiation and translational control, and (3) 4E-BP2 deamidation as a control system of the four biochemical processes. The Unified Theory of Neurodegeneration Pathogenesis based on axon deamidation, developed in this work, paves the way to controlling the occurrence and progression of neurodegenerative diseases such as Alzheimer's and Parkinson's through a unique, neuron-specific regulatory system that is 4E-BP2 deamidation, caused by the proteasome-poor environment in neuronal projections, consisting mainly of axons.

Early signs of neuron autonomous and non-autonomous hyperexcitability in locus coeruleus noradrenergic neurons of a mouse model of tauopathy and Alzheimer's disease

AIM

The locus coeruleus (LC) is one of the earliest brain regions affected by phosphorylated tau (p-tau) in Alzheimer's disease (AD). Using the P301S mouse model, we investigated the temporal progression of tau pathology and its functional consequences.

METHODS

Immunohistochemistry was used to assess p-tau deposition in LC noradrenergic neurons at 2-3 and 5-6 months. Electrophysiological recordings evaluated neuronal hyperexcitability, measuring membrane potential, rheobase, and spontaneous action potential (AP) frequency in P301S and wild-type (WT) mice. Fast-scan cyclic voltammetry (FSCV) was used to measure norepinephrine (NE) release. GABA(A) receptor subunit expression was analyzed via immunoblotting.

RESULTS

P-tau was detected in LC neurons as early as 2-3 months, with a rostral-to-caudal gradient, and by 5-6 months, nearly all LC neurons exhibited p-tau immunoreactivity. P301S neurons showed hyperexcitability, characterized by depolarized membrane potentials, a more negative rheobase, and increased spontaneous AP frequency. Synaptic blockade elicited a reduced increase in AP frequency, suggesting diminished inhibitory tone. GABA(A) α2 subunit expression significantly declined with age in P301S mice, whereas α3 remained unchanged. FSCV showed significantly elevated NE release in P301S mice at 3 and 6 months compared to WT.

CONCLUSION

The findings highlight early LC dysfunction in tauopathies, characterized by increased excitability, reduced inhibitory tone, and exaggerated NE release. This hyperactivity may contribute to excitotoxicity and downstream dysfunction in LC-regulated brain regions. Targeting LC hyperactivity and restoring inhibitory signaling could be promising therapeutic strategies for mitigating AD progression.

Detecting the Undetectable: Advances in Methods for Identifying Small Tau Aggregates in Neurodegenerative Diseases

Tau, a microtubule-associated protein, plays a critical role in maintaining neuronal structure and function. However, in neurodegenerative diseases such as Alzheimer's disease and other tauopathies, tau misfolds and aggregates into oligomers and fibrils, leading to neuronal damage. Tau oligomers are increasingly recognised as the most neurotoxic species, inducing synaptic dysfunction and contributing to disease progression. Detecting these early-stage aggregates is challenging due to their low concentration and high heterogeneity in biological samples. Traditional methods such as immunostaining and enzyme-linked immunosorbent assay (ELISA) lack the sensitivity and specificity to reliably detect small tau aggregates. Advanced single-molecule approaches, including single-molecule fluorescence resonance energy transfer (smFRET) and single-molecule pull-down (SiMPull), offer improved sensitivity for studying tau aggregation at the molecular level. These emerging tools provide critical insights into tau pathology, enabling earlier detection and characterisation of disease-relevant aggregates, thereby offering potential for the development of targeted therapies and diagnostic approaches for tauopathies.

Targeted protein degradation with bifunctional molecules as a novel therapeutic modality for Alzheimer's disease & beyond

Alzheimer's disease (AD) is associated with memory and cognitive impairment caused by progressive degeneration of neurons. The events leading to neuronal death are associated with the accumulation of aggregating proteins in neurons and glia of the affected brain regions, in particular extracellular deposition of amyloid plaques and intracellular formation of tau neurofibrillary tangles. Moreover, the accumulation of pathological tau proteoforms in the brain concurring with disease progression is a key feature of multiple neurodegenerative diseases, called tauopathies, like frontotemporal dementia (FTD) where autosomal dominant mutations in the tau encoding MAPT gene provide clear evidence of a causal role for tau dysfunction. Observations from disease models, post-mortem histology, and clinical evidence have demonstrated that pathological tau undergoes abnormal post-translational modifications, misfolding, oligomerization, changes in solubility, mislocalization, and intercellular spreading. Despite extensive research, there are few disease-modifying or preventative therapeutics for AD and none for other tauopathies. Challenges faced in tauopathy drug development include an insufficient understanding of pathogenic mechanisms of tau proteoforms, limited specificity of agents tested, and inadequate levels of brain exposure, altogether underscoring the need for innovative therapeutic modalities. In recent years, the development of experimental therapeutic modalities, such as targeted protein degradation (TPD) strategies, has shown significant and promising potential to promote the degradation of disease-causing proteins, thereby reducing accumulation and aggregation. Here, we review all modalities of TPD that have been developed to target tau in the context of AD and FTD, as well as other approaches that with innovation could be adapted for tau-specific TPD.

Review on pathogenesis and treatment of Alzheimer's disease

The rising incidence of Alzheimer's disease (AD) and the associated economic impacts has prompted a global focus in the field. In recent years, there has been a growing understanding of the pathogenic mechanisms of AD, including the aggregation of β-amyloid, hyperphosphorylated tau, and neuroinflammation. These processes collectively lead to neurodegeneration and cognitive decline, which ultimately results in the loss of autonomy in patients. Currently, there are three main types of AD treatments: clinical tools, pharmacological treatment, and material interventions. This review provides a comprehensive analysis of the underlying etiology and pathogenesis of AD, as well as an overview of the current prevalence of AD treatments. We believe this article can help deepen our understanding of the AD mechanism, and facilitate the clinical translation of scientific research or therapies, to address this global problem of AD.

Ser14-phosphorylated Rpn6 Limits Proteostasis Impairment and Pathology in Both Brain and Heart of Tauopathy Mice

Alzheimer's disease (AD) patients often display neurobehavioral and cardiac impairments, but the underlying factors remain unclear. Ser14 phosphorylation in RPN6 (p-S14-RPN6) mediates the activation of 26S proteasomes by protein kinase A (PKA). Proteasome priming is implicated in protection by cAMP-PKA against AD, but this remains to be established. Hence, this study was conducted to interrogate homeostatic p-S14-RPN6 in AD. The recently validated Rpn6 S14A knock-in (S14A) mice were crossbred with the PS19 tauopathy mice (RRID: IMSR_JAX:008169). The resultant wild type (WT), PS19, and PS19::S14A littermates were compared. Expedited declines in cognitive and motor functions as indicated respectively by significant decreases in object recognition and discrimination indexes and rotarod time were observed in PS19::S14A mice vs. PS19 mice, which is associated with more pronounced synaptic losses, microglial activation, and gliosis in the hippocampus. Compared with WT and PS19 mice, PS19::S14A mice showed exacerbated cardiac malfunction, cardiac hypertrophic responses and fibrosis, and greater increases of total and hyperphosphorylated tau proteins and ubiquitin conjugates in both hippocampi and hearts. These findings demonstrate that genetic blockade of p-S14-RPN6 exacerbates tauopathy in both the brain and heart, which for the first time establishes that homeostatic p-S14-RPN6 promotes proteostasis and protects against pathogenesis in AD.

GSK-3β dysregulation in aging: Implications for tau pathology and Alzheimer's disease progression

The role of glycogen synthase kinase-3β (GSK-3β) in the pathogenesis of Alzheimer's disease (AD) is critical for linking amyloid-beta (Aβ) and Tau pathology. The activity of GSK-3β is dysregulated in the regulation of Tau hyperphosphorylation, formation of neurofibrillary tangles (NFTs), and production of Aβ by modulating amyloid precursor protein (APP) processing. This review discusses the mechanisms controlling GSK-3β dysregulation in aging and its influence on AD progression, focusing on the role of neuroinflammation, oxidative stress, and defective signaling pathways, including PI3K/Akt and Wnt. Critical analysis is presented for therapeutic strategies targeting GSK-3β using natural compounds (e.g., curcumin, geniposide) and emerging approaches such as TREM2 modulation and miRNA therapies. In preclinical models, these interventions promise to reduce Tau hyperphosphorylation and Aβ burden, along with associated neurodegeneration. Nevertheless, achieving selective GSK-3β inhibition and optimizing drug delivery are still critical barriers to clinical translation. This review underscores the central role of GSK-3β in AD pathogenesis to highlight its potential as a multifaceted therapeutic target of an innovative strategy for treating this complex neurodegenerative disease.

The interplay between age at menopause and synaptic integrity on Alzheimer's disease risk in women

Menopause is a major biological transition that may influence women's late-life brain health. Earlier estrogen depletion-via earlier menopause-has been associated with increased risk for Alzheimer's disease (AD). Synaptic dysfunction also incites and exacerbates AD progression. We investigated whether age at menopause and synaptic health together influence AD neuropathology and cognitive trajectories using clinical and autopsy data from 268 female decedents in the Rush Memory and Aging Project. We observed significant interactions between age at menopause and synaptic integrity on cognitive decline and tau tangles, such that earlier menopause strengthened the associations of reduced synaptic integrity with faster cognitive decline and elevated tau. Exploratory analyses showed that these relationships were attenuated in women who took menopausal hormone therapy. These findings suggest that midlife endocrine processes or their sequalae may influence synaptic vulnerability to AD. Interventions addressing both hormonal factors and synaptic health could enhance resilience to dementia in women.

Intra-axonal Nanomagnetic Forces Differentially Impact hTau40 Transport Dynamics in Primary Cortical and Hippocampal Neurons

A crucial aspect of neural engineering is the ability to manipulate proteins that are substantially involved in axonal outgrowth and maintenance. Previous work in this field has shown that applying low-magnitude (piconewton) forces to early stage neurons can result in altered distributions of critical structural proteins, such as the microtubule-associated protein Tau. Uncovering the mechanisms of Tau redistribution could provide a tool for manipulating dysregulated forms of the protein. This study examined how the transport of Tau responded to intra-axonal nanomagnetic forces (NMFs) in primary cortical and hippocampal neurons. High magnification, live cell fluorescent imaging was employed to visualize the transport of both full-length human Tau (hTau40) and amine-terminated, starch-coated fluorescent magnetic nanoparticles (afMNPs) to observe how these cell-internal forces could impact the transport of hTau40 within the axon. Here, we found that afMNPs acted by pulling on hTau40 puncta under NMF application, especially within cortical cells, where afMNPs were more likely to be found within the axon. Forces greater than 1 pN enabled differentiated transport speeds and displacement of hTau40 based on relative force direction. This data indicates that NMF can be utilized to engineer hTau40 transport, even in cells at later stages of maturation.

Ligature-induced periodontitis in a transgenic mouse model of Alzheimer's disease dysregulates neuroinflammation, exacerbates cognitive impairment, and accelerates amyloid pathology

A growing body of literature has identified periodontal disease among the modifiable risk factors for Alzheimer's disease (AD), but the mechanisms underlying this relationship is unknown. This study investigated this relationship using a ligature-induced preclinical periodontitis (Pd) model in non-transgenic (non-Tg) and 3xTg-AD mice. We found that ligature placement caused significant alveolar bone loss, with 3xTg-AD mice exhibiting exacerbated bone loss, suggesting AD-related genetic risk may amplify disease progression. Pd induced robust local inflammatory gene expression in both genotypes, but 3xTg-AD mice indicated a dysregulated immune response. Cognitive deficits were observed only in Pd-afflicted 3xTg-AD mice, specifically in hippocampus-mediated spatial memory and perirhinal cortex-mediated object recognition memory, while non-Tg mice remained unaffected. Neuroinflammatory responses varied by brain region, with the hippocampus and prefrontal cortex (PFC) showing the most pronounced changes. In these regions, 3xTg-AD mice exhibited significantly altered cytokine gene expression compared to non-Tg mice, particularly at later time points. Synaptic markers revealed vulnerabilities in 3xTg-AD mice, including reduced baseline Syp expression and dysregulated Synpo post-ligature. Pd transiently reduced glutamate receptor gene expression in both genotypes, with non-Tg mice showing persistent changes, potentially linked to preserved memory. Pd also accelerated amyloid-β (Aβ) deposition and sustained neurodegeneration in 3xTg-AD mice. Overall, this study shows that combining Pd and AD-related genetic risk exacerbates inflammation, cognitive impairment, synaptic dysfunction, Aβ pathology, and neurodegeneration. Neither insult alone was sufficient to produce these effects, highlighting the synergistic impact. These findings emphasize the need to explore anti-inflammatory interventions and downstream mechanisms to mitigate the confluence of these diseases.

Locus coeruleus vulnerability to tau hyperphosphorylation in a rat model

Post-mortem investigations indicate that the locus coeruleus (LC) is the initial site of hyperphosphorylated pretangle tau, a precursor to neurofibrillary tangles (NFTs) found in Alzheimer's disease (AD). The presence of pretangle tau and NFTs correlates with AD progression and symptomatology. LC neuron integrity and quantity are linked to cognitive performance, with degeneration strongly associated with AD. Despite their importance, the mechanisms of pretangle tau-induced LC degeneration are unclear. This study examined the transcriptomic and mitochondrial profiles of LC noradrenergic neurons after transduction with pseudophosphorylated human tau. Tau hyperphosphorylation increased the somatic expression of the L-type calcium channel (LTCC), impaired mitochondrial health, and led to deficits in spatial and olfactory learning. Sex-dependent alterations in gene expression were observed in rats transduced with pretangle tau. Chronic LTCC blockade prevented behavioral deficits and altered mitochondrial mRNA expression, suggesting a potential link between LTCC hyperactivity and mitochondrial dysfunction. Our research provides insights into the consequences of tau pathology in the originating structure of AD.

Pathological tau alters head direction signaling and induces spatial disorientation

Spatial disorientation, an early symptom of dementia, is emerging as an early and reliable cognitive biomarker predicting future memory problems associated with Alzheimer's disease, but the underlying neural mechanisms have yet to be fully defined. The anterodorsal thalamic nucleus (ADn) exhibits early and selective vulnerability to pathological misfolded forms of tau, a major hallmark of Alzheimer's disease and ageing. The ADn contains a high density of head direction (HD) cells, which contribute to spatial navigation and orientation. Hence, their disruption may contribute to spatial disorientation. To test this, we virally expressed human mutant tau (htau) in the ADn of adult mice. HD-tau mice were defined by phosphorylated and oligomeric forms of htau in ADn somata and in axon terminals in postsynaptic target regions. Compared to controls, HD-tau mice exhibited increased looping behavior during spatial learning, and made a greater number of head turns during memory recall, indicative of spatial disorientation. Using in vivo extracellular recordings, we identified htau-expressing ADn cells and found a lower proportion of HD cells in the ADn from HD-tau mice, along with reduced directionality and altered burst firing. These findings provide evidence that expression of pathological human tau can alter HD signaling, leading to impairments in spatial orientation.

A Massively Parallel CRISPR-Based Screening Platform for Modifiers of Neuronal Activity

Understanding the complex interplay between gene expression and neuronal activity is crucial for unraveling the molecular mechanisms underlying cognitive function and neurological disorders. Here, we developed pooled screens for neuronal activity, using CRISPR interference (CRISPRi) and the fluorescent calcium integrator CaMPARI2. Using this screening method, we evaluated 1343 genes for their effect on excitability in human iPSC-derived neurons, revealing potential links to neurodegenerative and neurodevelopmental disorders. These genes include known regulators of neuronal excitability, such as TARPs and ion channels, as well as genes associated with autism spectrum disorder and Alzheimer's disease not previously described to affect neuronal excitability. This CRISPRi-based screening platform offers a versatile tool to uncover molecular mechanisms controlling neuronal activity in health and disease.

In vivo hyperphosphorylation of tau is associated with synaptic loss and behavioral abnormalities in the absence of tau seeds

Tau pathology is a hallmark of several neurodegenerative diseases, including frontotemporal dementia and Alzheimer's disease. However, the sequence of events and the form of tau that confers toxicity are still unclear, due in large part to the lack of physiological models of tauopathy initiation and progression in which to test hypotheses. We have developed a series of targeted mice expressing frontotemporal-dementia-causing mutations in the humanized MAPT gene to investigate the earliest stages of tauopathy. MAPTInt10+3G>A and MAPTS305N;Int10+3G>A lines show abundant hyperphosphorylated tau in the hippocampus and entorhinal cortex, but they do not develop seed-competent fibrillar structures. Accumulation of hyperphosphorylated tau was accompanied by neurite degeneration, loss of viable synapses and indicators of behavioral abnormalities. Our results demonstrate that neuronal toxicity can occur in the absence of fibrillar, higher-order structures and that tau hyperphosphorylation is probably involved in the earliest etiological events in tauopathies showing isoform ratio imbalance.

Lactylation of tau in human Alzheimer's disease brains

INTRODUCTION

Aggregation of hyperphosphorylated tau (tauopathy) is associated with cognitive impairment in patients with Alzheimer's disease (AD). In AD, a metabolic shift due to the Warburg effect results in increased lactate production. Lactate can induce a post-translational modification (PTM) on proteins that conjugates lactyl groups to lysine (K) residues, which is known as lactylation.

METHODS

We analyzed lactylation of tau in control and AD brain tissue and conducted cell-based assays. In addition, we used in vitro assays to determine whether p300 catalyzed tau lactylation.

RESULTS

Quantitative proteomics detected that tau lactylation was elevated in AD brains, with K residue at position 331 (K331) being a prominent site. Lactate induced tau lactylation, which increased tau phosphorylation and cleavage and reduced ubiquitination. Inhibition of lactate production lowered tau lactylation; p300 catalyzed tau lactylation.

DISCUSSION

Our findings suggest that tau lactylation links metabolic dysregulation with tauopathy and could serve as a novel diagnostic and therapeutic target.

HIGHLIGHTS

Elevated tau lactylation, particularly at K331, is evident in in human AD brain samples. Lactate induces tau lactylation, enhancing phosphorylation and cleavage while inhibiting ubiquitination. The acetyl-transferase p300 catalyzes tau lactylation, with K331 being the most prominent site.

Longitudinal synaptic loss versus tau Braak staging in amnestic mild cognitive impairment

INTRODUCTION

The longitudinal progression of synaptic loss in Alzheimer's disease (AD) and how it is affected by tau pathology remains poorly understood.

METHODS

Thirty patients with amnestic mild cognitive impairment (aMCI) and 26 healthy controls underwent cognitive evaluations and tau, synaptic vesicle protein 2A (SV2A), and amyloid positron emission tomography. Twenty-one aMCI underwent 2-year follow-up (FU) investigations.

RESULTS

Tau levels in aMCI increased longitudinally in Braak regions III through VI but not in Braak regions I and II. SV2A decreased longitudinally in all Braak regions in aMCI. Baseline tau was negatively associated with longitudinal SV2A loss in early Braak regions and with SV2A at FU across regions. Baseline tau and longitudinal change in SV2A were associated with longitudinal cognitive decline.

DISCUSSION

Tau accumulation reaches a plateau in early Braak regions already in the aMCI stage of AD. In early Braak regions, the association between baseline tau and longitudinal SV2A loss might reflect synaptic dysfunction caused by tau pathology.

HIGHLIGHTS

Tau accumulation reached a plateau in early Braak regions in amnestic mild cognitive impairment (aMCI) patients. aMCI patients show widespread longitudinal decrease in synaptic vesicle protein 2A (SV2A) over 2 years. Baseline tau was predictive for longitudinal SV2A loss. The tau-SV2A relation showed individual variability and was negative across patients. Baseline tau and longitudinal SV2A change were associated with change in cognition.

Synaptic vulnerability to amyloid-β and tau pathologies differentially disrupts emotional and memory neural circuits

Alzheimer's disease (AD) is characterized by memory loss and neuropsychiatric symptoms associated with cerebral amyloid-β (Aβ) and tau pathologies, but whether and how these factors differentially disrupt neural circuits remains unclear. Here, we investigated the vulnerability of memory and emotional circuits to Aβ and tau pathologies in mice expressing mutant human amyloid precursor protein (APP), Tau or both APP/Tau in excitatory neurons. APP/Tau mice develop age- and sex-dependent Aβ and phosphorylated tau pathologies, the latter exacerbated at early stages, in vulnerable brain regions. Early memory deficits were associated with hippocampal tau pathology in Tau and APP/Tau mice, whereas anxiety and fear appeared linked to intracellular Aβ in the basolateral amygdala (BLA) of APP and APP/Tau mice. Transcriptome hippocampal profiling revealed gene changes affecting myelination and RNA processing in Tau mice, and inflammation and synaptic-related pathways in APP/Tau mice at 6 months. At 9 months, we detected common and region-specific changes in astrocytic, microglia and 63 AD-associated genes in the hippocampus and BLA of APP/Tau mice. Spatial learning deficits were associated with synaptic tau accumulation and synapse disruption in the hippocampus of Tau and APP/Tau mice, whereas emotional disturbances were linked to Aβ pathology but not synaptic tau in the BLA. Interestingly, Aβ and tau exhibited synergistic detrimental effects in long-term potentiation (LTP) in the hippocampus but they counteract with each other to mitigate LTP impairments in the amygdala. These findings indicate that Aβ and tau pathologies cause region-specific effects and synergize to induce synaptic dysfunction and immune responses, contributing to the differing vulnerability of memory and emotional neural circuits in AD.

Anti-herpetic tau preserves neurons via the cGAS-STING-TBK1 pathway in Alzheimer's disease

Alzheimer's disease (AD) diagnosis relies on the presence of extracellular β-amyloid (Aβ) and intracellular hyperphosphorylated tau (p-tau). Emerging evidence suggests a potential link between AD pathologies and infectious agents, with herpes simplex virus 1 (HSV-1) being a leading candidate. Our investigation, using metagenomics, mass spectrometry, western blotting, and decrowding expansion pathology, detects HSV-1-associated proteins in human brain samples. Expression of the herpesvirus protein ICP27 increases with AD severity and strongly colocalizes with p-tau but not with Aβ. Modeling in human brain organoids shows that HSV-1 infection elevates tau phosphorylation. Notably, p-tau reduces ICP27 expression and markedly decreases post-infection neuronal death from 64% to 7%. This modeling prompts investigation into the cGAS-STING-TBK1 pathway products, nuclear factor (NF)-κB and IRF-3, which colocalizes with ICP27 and p-tau in AD. Furthermore, experimental activation of STING enhances tau phosphorylation, while TBK1 inhibition prevents it. Together, these findings suggest that tau phosphorylation acts as an innate immune response in AD, driven by cGAS-STING.

Loss of excitatory inputs and decreased tonic and evoked activity of locus coeruleus neurons in aged P301S mice

Tau pathology in the locus coeruleus (LC) is associated with several neurodegenerative conditions including Alzheimer's disease and frontotemporal dementia. Phosphorylated tau accumulates in the LC and results in inflammation, synaptic loss, and eventually cell death as the disease progresses. Loss of LC neurons and noradrenergic innervation is thought to contribute to the symptoms of cognitive decline later in disease. While loss and degeneration of LC neurons has been well studied, less is known about changes in LC physiology at advanced stages of tau pathology that precedes neurodegeneration. In this study, we investigated the ex vivo electrophysiological properties of LC neurons in male and female mice from the P301S mouse model of tauopathy at 9 months of age, a time-point when significant tau accumulation, cell death, and cognitive impairments are observed. We found a reduction in excitatory inputs and changes in excitatory post-synaptic current kinetics in male and female P301S. There was also a decrease in spontaneous discharge of LC neurons and an increase in AP threshold in P301S mice of both sexes. Finally, we observed a decrease in excitability and increase in rheobase current in P301S mice. Despite the decrease in LC activity in slice, we did not identify differences in total tissue norepinephrine (NE) or NE metabolites in prefrontal cortex or hippocampus. Together these findings demonstrate reductions in the activity and excitability of LC neurons at late stages of tau accumulation. However, compensatory mechanisms may maintain normal NE levels in LC projection regions in vivo.

The Role of Oligodendrocyte Lineage Cells in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a central nervous system degenerative disease with a stealthy onset and a progressive course characterized by memory loss, cognitive dysfunction, and abnormal psychological and behavioral symptoms. However, the pathogenesis of AD remains elusive. An increasing number of studies have shown that oligodendrocyte progenitor cells (OPCs) and oligodendroglial lineage cells (OLGs), especially OPCs and mature oligodendrocytes (OLGs), which are derived from OPCs, play important roles in the pathogenesis of AD. OLGs function mainly by myelinating axons, transmitting electrical signals, and regulating neural development. In addition to myelin, OPCs and OLGs can also participate in AD pathogenesis in other ways. This review summarizes the mechanisms by which OPCs and OLGs affect myelin formation, oxidative stress, neuroinflammation, the blood-brain barrier, synaptic function, and amyloid-beta protein and further elucidates the mechanisms by which oligodendrocyte lineage cells participate in AD pathogenesis and treatment, which is highly important for clarifying the pathogenesis of AD, clinical treatment, and prevention.

Fyn Kinase in Alzheimer's Disease: Unraveling Molecular Mechanisms and Therapeutic Implications

Alzheimer's disease, characterized by the accumulation of abnormal protein aggregates and neuronal damage in the brain, leads to a gradual decline in cognitive function and memory. As a complex neurodegenerative disorder, it involves disruptions in various biochemical pathways and neurotransmitter systems, contributing to the progressive loss of neurons and synaptic connections. The complexity of Alzheimer's signaling pathways complicates treatment, presenting a formidable challenge in the quest for effective therapeutic interventions. A member of the Src family of kinases (SFKs), Fyn, is a type of non-receptor tyrosine kinase that has been linked to multiple essential CNS processes, such as myelination and synaptic transmission. Fyn is an appealing target for AD treatments because it is uniquely linked to the two major pathologies in AD by its interaction with tau, in addition to being activated by amyloid-beta (Aβ) through PrPC. Fyn mediates neurotoxicity and synaptic impairments caused by Aβ and is involved in regulating the process of Aβ synthesis.Additionally, the tau protein's tyrosine phosphorylation is induced by Fyn. Fyn is also a challenging target because of its widespread body expression and strong homology with other kinases of the Src family, which could cause unintentional off-target effects. This review emphasizes signaling pathways mediated by Fyn that govern neuronal development and plasticity while also summarizing the most noteworthy recent research relevant to Fyn kinase's function in the brain. Additionally, the therapeutic inhibition of Fyn kinase has been discussed, with a focus on the Fyn kinase inhibitors that are in clinical trials, which presents a fascinating opportunity for targeting Fyn kinase in the creation of possible therapeutic approaches for the management of Alzheimer's disease.

Mitochondrial bioenergetics stimulates autophagy for pathological MAPT/Tau clearance in tauopathy neurons

Hyperphosphorylation and aggregation of MAPT (microtubule-associated protein tau) is a pathogenic hallmark of tauopathies and a defining feature of Alzheimer disease (AD). Pathological MAPT/tau is targeted by macroautophagy/autophagy for clearance after being sequestered within autophagosomes, but autophagy dysfunction is indicated in tauopathy. While mitochondrial bioenergetic deficits have been shown to precede MAPT/tau pathology in tauopathy brains, it is unclear whether energy metabolism deficiency is involved in the pathogenesis of autophagy defects. Here, we reveal that stimulation of anaplerotic metabolism restores defective oxidative phosphorylation (OXPHOS) in tauopathy neurons which, strikingly, leads to pronounced MAPT/tau clearance by boosting autophagy functionality through enhancements of mitochondrial biosynthesis and supply of phosphatidylethanolamine for autophagosome biogenesis. Furthermore, early anaplerotic stimulation of OXPHOS elevates autophagy activity and attenuates MAPT/tau pathology, thereby counteracting memory impairment in tauopathy mice. Taken together, our study sheds light on a pivotal role of mitochondrial bioenergetic deficiency in tauopathy-related autophagy defects and suggests a new therapeutic strategy to prevent the buildup of pathological MAPT/tau in AD and other tauopathy diseases.Abbreviation: AA: antimycin A; AD, Alzheimer disease; ATP, adenosine triphosphate; AV, autophagosome/autophagic vacuole; AZ, active zone; Baf-A1: bafilomycin A1; CHX, cycloheximide; COX, cytochrome c oxidase; DIV, days in vitro; DRG, dorsal root ganglion; ETN, ethanolamine; FRET, Förster/fluorescence resonance energy transfer; FTD, frontotemporal dementia; Gln, glutamine; HA: hydroxylamine; HsMAPT/Tau, human MAPT; IMM, inner mitochondrial membrane; LAMP1, lysosomal-associated membrane protein 1; LIs, lysosomal inhibitors; MDAV, mitochondria-derived autophagic vacuole; MmMAPT/Tau, murine MAPT; NFT, neurofibrillary tangle; OCR, oxygen consumption rate; Omy: oligomycin; OXPHOS, oxidative phosphorylation; PPARGC1A/PGC-1alpha: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PE, phosphatidylethanolamine; phospho-MAPT/tau, hyperphosphorylated MAPT; PS, phosphatidylserine; PISD, phosphatidylserine decarboxylase;SQSTM1/p62, sequestosome 1; STX1, syntaxin 1; SYP, synaptophysin; Tg, transgenic; TCA, tricarboxylic acid; TEM, transmission electron microscopy.

Light-Inducible Deformation of Mitochondria in Live Cells

Mitochondria are dynamic organelles with constantly changing morphologies. Despite recent reports indicating that mechanical cues modulate mitochondrial morphologies and functions, there is a lack of methods that can exclusively and precisely exert mechanical forces to and deform mitochondria in live cells. Therefore, how mitochondria sense and respond to mechanical forces remains largely elusive. Optogenetic methods open up new venues for remote and precise manipulation of intracellular activities using light, providing an unprecedented opportunity to establish targeted mechano-stimulation toward mitochondria. This chapter describes the development of a novel optogenetic approach to optically mechanostimulate and induce the deformation of mitochondria. In this approach, light-gated protein-protein heterodimerization recruits force-generating molecular motors to the outer mitochondrial membrane, enabling direct exertion of mechanical force on mitochondria. Details for the design, application, and experimental procedures are laid out in this chapter. This method presents a mitochondria-specific mechano-stimulator for studying the correlation between mitochondrial morphology and functions as well as mitochondrial mechanobiology.

Advancing Alzheimer's Disease Modelling by Developing a Refined Biomimetic Brain Microenvironment for Facilitating High-Throughput Screening of Pharmacological Treatment Strategies

Alzheimer's disease (AD) poses a significant worldwide health challenge, requiring novel approaches for improved models and treatment development. This comprehensive review emphasises the systematic development and improvement of a biomimetic brain environment to address the shortcomings of existing AD models and enhance the efficiency of screening potential drug treatments. We identify drawbacks in traditional models and emphasise the necessity for more physiologically accurate systems through an in-depth analysis of current literature. This review aims to study the development of an advanced AD model that accurately replicates key AD pathophysiological aspects using cutting-edge biomaterials and microenvironment design. Incorporating biomolecular elements like Tau proteins and beta-amyloid (Aβ) plaques improve the accuracy of illustrating disease mechanisms. The expected results involve creating a solid foundation for high-throughput screening with enhanced scalability, translational significance, and the possibility of speeding up drug discovery. Thus, this review fills the gaps in AD modelling and shows potential for creating precise and efficient drug treatments for AD.

Development of MAPT S305 mutation human iPSC lines exhibiting elevated 4R tau expression and functional alterations in neurons and astrocytes

Due to the importance of 4R tau (with four microtubule-binding-repeat domains) in the pathogenicity of primary tauopathies, it has been challenging to model these diseases in induced pluripotent stem cell (iPSC)-derived neurons, which express very low levels of 4R tau. To address this, we have developed a panel of isogenic iPSC lines carrying MAPT splice-site mutations, S305S, S305I, or S305N, derived from four different donors. All mutations significantly increase 4R tau expression in iPSC neurons and astrocytes. Functional analyses of S305 mutant neurons reveal shared disruption in synaptic signaling and maturity but divergent effects on mitochondrial bioenergetics. In iPSC astrocytes, S305 mutations promote internalization of exogenous tau that may be a precursor to glial pathology. These lines recapitulate previously characterized tauopathy-relevant phenotypes and highlight functional differences between the wild-type 4R and the mutant 4R proteins in both neurons and astrocytes. As such, these lines enable a more complete understanding of pathogenic mechanisms underlying 4R tauopathies across different cell types.

Regulation of presynaptic homeostatic plasticity by glial signalling in Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia among the elderly, affects numerous individuals worldwide. Despite advances in understanding the molecular underpinnings of AD pathology, effective treatments to prevent or cure the disease remain elusive. AD is characterized not only by pathological hallmarks such as amyloid plaques and neurofibrillary tangles but also by impairments in synaptic physiology, circuit activity and cognitive function. Synaptic homeostatic plasticity plays a vital role in maintaining the stability of synaptic and neural functions amid genetic and environmental disturbances. A key component of this regulation is presynaptic homeostatic potentiation, where increased presynaptic neurotransmitter release compensates for reduced postsynaptic glutamate receptor functionality, thereby stabilizing neuronal excitability. The role of presynaptic homeostatic plasticity in synapse stabilization in AD, however, remains unclear. Moreover, recent advances in transcriptomics have illuminated the complex roles of glial cells in regulating synaptic function in ageing brains and in the progression of neurodegenerative diseases. Yet, the impact of AD-related abnormalities in glial signalling on synaptic homeostatic plasticity has not been fully delineated. This review discusses recent findings on how glial dysregulation in AD affects presynaptic homeostatic plasticity. There is increasing evidence that disrupted glial signalling, particularly through aberrant histone acetylation and transcriptomic changes in glia, compromises this plasticity in AD. Notably, the sphingosine signalling pathway has been identified as being protective in stabilizing synaptic physiology through epigenetic and homeostatic mechanisms, presenting potential therapeutic targets for treating neurodegenerative disorders.

Dihydroartemisinin promotes tau O-GlcNAcylation and improves cognitive function in hTau transgenic mice

Tauopathy is a collective term for several neurodegenerative diseases characterized by the intracellular accumulation of hyperphosphorylated microtubule-associated protein Tau (P-tau). Our recent report has revealed the neuroprotective effect of dihydroartemisinin (DHA) on mice overexpressing human Tau (hTau) in the hippocampus by enhancing O-linked-N-Acetylglucosaminylation (O-GlcNAcylation) modification. However, whether DHA can improve synaptic and cognitive function in hTau transgenic mice by specifically promoting Tau O-GlcNAcylation is still unclear. Here, we introduced hTau transgenic mice, a more optimal tauopathy model, to study the effect of DHA on Tau O-GlcNAcylation. We reported that DHA treatment alleviated the deficits of hippocampal CA1 LTP and spatial learning and memory in the Barnes maze and context fear conditioning tests in hTau transgenic mice. Mechanically, we revealed that DHA exerted a significant protective effect by upregulating Tau O-GlcNAcylation and attenuating Tau hyperphosphorylation. Through molecular docking, we found a stable binding between DHA and O-GlcNAc transferase (OGT). We further reported that DHA treatment had no effect on the expression of OGT, but it promoted OGT nuclear export, thereby enhancing OGT-mediated Tau O-GlcNAcylation. Taken together, these results indicate that DHA exerts neuroprotective effect by promoting cytoplasmic translocation of OGT and rebuilding the balance of Tau O-GlcNAcylation/phosphorylation, enhancing O-GlcNAcylation of Tau, suggesting that DHA may be a potential therapeutic agent against tauopathy.

Super-Resolved Protein Imaging Using Bifunctional Light-Up Aptamers

Efficient labeling methods for protein visualization with minimal tag size and appropriate photophysical properties are required for single-molecule localization microscopy (SMLM), providing insights into the organization and interactions of biomolecules in cells at the molecular level. Among the fluorescent light-up aptamers (FLAPs) originally developed for RNA imaging, RhoBAST stands out due to its remarkable brightness, photostability, fluorogenicity, and rapid exchange kinetics, enabling super-resolved imaging with high localization precision. Here, we expand the applicability of RhoBAST to protein imaging by fusing it to protein-binding aptamers. The versatility of such bifunctional aptamers is demonstrated by employing a variety of protein-binding aptamers and different FLAPs. Moreover, fusing RhoBAST with the GFP-binding aptamer AP3 facilitates high- and super-resolution imaging of GFP-tagged proteins, which is particularly valuable in view of the widespread availability of plasmids and stable cell lines expressing proteins fused to GFP. The bifunctional aptamers compare favorably with standard antibody-based immunofluorescence protocols, as they are 7-fold smaller than antibody conjugates and exhibit higher bleaching-resistance. We demonstrate the effectiveness of our approach in super-resolution microscopy in secondary mammalian cell lines and primary neurons by RhoBAST-PAINT, an SMLM protein imaging technique that leverages the transient binding of the fluorogenic rhodamine dye SpyRho to RhoBAST.

Transmissible long-term neuroprotective and pro-cognitive effects of 1-42 beta-amyloid with A2T icelandic mutation in an Alzheimer's disease mouse model

The amyloid cascade hypothesis assumes that the development of Alzheimer's disease (AD) is driven by a self-perpetuating cycle, in which β-amyloid (Aβ) accumulation leads to Tau pathology and neuronal damages. A particular mutation (A673T) of the amyloid precursor protein (APP) was identified among Icelandic population. It provides a protective effect against Alzheimer- and age-related cognitive decline. This APP mutation leads to the reduced production of Aβ with A2T (position in peptide sequence) change (Aβice). In addition, Aβice has the capacity to form protective heterodimers in association with wild-type Aβ. Despite the emerging interest in Aβice during the last decade, the impact of Aβice on events associated with the amyloid cascade has never been reported. First, the effects of Aβice were evaluated in vitro by electrophysiology on hippocampal slices and by studying synapse morphology in cortical neurons. We showed that Aβice protects against endogenous Aβ-mediated synaptotoxicity. Second, as several studies have outlined that a single intracerebral administration of Aβ can worsen Aβ deposition and cognitive functions several months after the inoculation, we evaluated in vivo the long-term effects of a single inoculation of Aβice or Aβ-wild-type (Aβwt) in the hippocampus of transgenic mice (APPswe/PS1dE9) over-expressing Aβ1-42 peptide. Interestingly, we found that the single intra-hippocampal inoculation of Aβice to mice rescued synaptic density and spatial memory losses four months post-inoculation, compared with Aβwt inoculation. Although Aβ load was not modulated by Aβice infusion, the amount of Tau-positive neuritic plaques was significantly reduced. Finally, a lower phagocytosis by microglia of post-synaptic compounds was detected in Aβice-inoculated animals, which can partly explain the increased density of synapses in the Aβice animals. Thus, a single event as Aβice inoculation can improve the fate of AD-associated pathology and phenotype in mice several months after the event. These results open unexpected fields to develop innovative therapeutic strategies against AD.

Targeting Protein Misfolding and Aggregation as a Therapeutic Perspective in Neurodegenerative Disorders

The abnormal deposition and intercellular propagation of disease-specific protein play a central role in the pathogenesis of many neurodegenerative disorders. Recent studies share the common observation that the formation of protein oligomers and subsequent pathological filaments is an essential step for the disease. Synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB) or multiple system atrophy (MSA) are neurodegenerative diseases characterized by the aggregation of the α-synucleinprotein in neurons and/or in oligodendrocytes (glial cytoplasmic inclusions), neuronal loss, and astrogliosis. A similar mechanism of protein Tau-dependent neurodegeneration is a major feature of tauopathies, represented by Alzheimer's disease (AD), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PD). The specific inhibition of the protein misfolding and their interneuronal spreading represents a promising therapeutic strategy against both disease pathology and progression. The most recent research focuses on finding potential applications targeting the pathological forms of proteins responsible for neurodegeneration. This review highlights the mechanisms relevant to protein-dependent neurodegeneration based on the most common disorders and describes current therapeutic approaches targeting protein misfolding and aggregation.

AMPA receptors in Alzheimer disease: Pathological changes and potential therapeutic targets

Alzheimer disease (AD) is a prevalent neurodegenerative disorder that affects synapses and leads to progressive cognitive decline. The role of N-methyl-D-aspartic acid (NMDA) receptors in the pathogenesis of AD is well-established as they contribute to excitotoxicity and neurodegeneration in the pathological process of extrasynaptic glutamate concentration. However, the therapeutic potential of the NMDA receptor antagonist memantine in rescuing synaptic damage is limited. Research indicates that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors also play a significant role in AD. Abnormal transcription, expression, and localization of AMPA receptors lead to synaptic dysfunction and damage, contributing to early cognitive impairment in AD patients. Understanding the impact of AMPA receptors on AD pathogenesis and exploring the potential for the development of AMPA receptor-targeting drugs are crucial. This review aims to consolidate recent research findings on AMPA receptors in AD, elucidate the current state of AMPA receptor research and lay the foundation for future basic research and drug development.

Cellular and pathological functions of tau

Tau protein is involved in various cellular processes, including having a canonical role in binding and stabilization of microtubules in neurons. Tauopathies are neurodegenerative diseases marked by the abnormal accumulation of tau protein aggregates in neurons, as seen, for example, in conditions such as frontotemporal dementia and Alzheimer disease. Mutations in tau coding regions or that disrupt tau mRNA splicing, tau post-translational modifications and cellular stress factors (such as oxidative stress and inflammation) increase the tendency of tau to aggregate and interfere with its clearance. Pathological tau is strongly implicated in the progression of neurodegenerative diseases, and the propagation of tau aggregates is associated with disease severity. Recent technological advancements, including cryo-electron microscopy and disease models derived from human induced pluripotent stem cells, have increased our understanding of tau-related pathology in neurodegenerative conditions. Substantial progress has been made in deciphering tau aggregate structures and the molecular mechanisms that underlie protein aggregation and toxicity. In this Review, we discuss recent insights into the diverse cellular functions of tau and the pathology of tau inclusions and explore the potential for therapeutic interventions.

Neurosteroids Alter p-ERK Levels and Tau Distribution, Restraining the Effects of High Extracellular Calcium

Neurosteroids are undeniably regarded as neuroprotective mediators, regulating brain function by rapid non-genomic actions involving interference with microtubules. Conversely, hyperphosphorylated Tau is considered responsible for the onset of a plethora of neurodegenerative diseases, as it dissociates from microtubules, leading to their destabilization, thus impairing synaptic vesicle transport and neurotransmission. Consequently, we aimed to investigate the effects of neurosteroids, specifically allopregnanolone (Allo) and dehydroepiandrosterone (DHEA), on the levels of total and phosphorylated at Serine 404 Tau (p-Tau) in C57BL/6 mice brain slices. In total tissue extracts, we found that neurosteroids elevated both total and p-Tau levels without significantly altering the p-Tau/Tau ratio. In addition, the levels of several enzymes implicated in Tau phosphorylation did not display significant differences between conditions, suggesting that neurosteroids influence Tau distribution rather than its phosphorylation. Hence, we subsequently examined the mitochondria-enriched subcellular fraction where, again, both p-Tau and total Tau levels were increased in the presence of neurosteroids. These effects seem actin-dependent, as disrupting actin polymerization by cytochalasin B preserved Tau levels. Furthermore, co-incubation with high [Ca2+] and neurosteroids mitigated the effects of Ca2+ overload, pointing to cytoskeletal remodeling as a potential mechanism underlying neurosteroid-induced neuroprotection.

Arc mediates intercellular tau transmission via extracellular vesicles

Intracellular neurofibrillary tangles that consist of misfolded tau protein1 cause neurodegeneration in Alzheimer's disease (AD) and frontotemporal dementia (FTD). Tau pathology spreads cell-to-cell2 but the exact mechanisms of tau release and intercellular transmission remain poorly defined. Tau is released from neurons as free protein or in extracellular vesicles (EVs)3-5 but the role of these different release mechanisms in intercellular tau transmission is unclear. Here, we show that the neuronal gene Arc is critical for packaging tau into EVs. Brain EVs purified from human tau (hTau) transgenic rTg4510 mice (rTgWT) contain high levels of hTau that are capable of seeding tau pathology. In contrast, EVs purified from rTgWT crossed with Arc knock-out mice (rTgArc KO) have significantly less hTau and cannot seed tau aggregation. Arc facilitates the release of hTau in EVs produced via the I-BAR protein IRSp53, but not free tau. Arc protein directly binds hTau to form a fuzzy complex that we identified in both mouse and human brain tissue. We find that pathological intracellular hTau accumulates in neurons in rTgArc KO mice, which correlates with accelerated neuron loss in the hippocampus. Finally, we find that intercellular tau transmission is significantly abrogated in Arc KO mice. We conclude that Arc-dependent release of tau in EVs plays a significant role in intracellular tau elimination and intercellular tau transmission.

HSV-1 infection induces phosphorylated tau propagation among neurons via extracellular vesicles

Extracellular vesicles (EV), key players in cell-to-cell communication, may contribute to disease propagation in several neurodegenerative diseases, including Alzheimer's disease (AD), by favoring the dissemination of neurotoxic proteins within the brain. Interestingly, growing evidence supports the role of herpes simplex virus type 1 (HSV-1) infection in the pathogenesis of AD. Here, we investigated whether HSV-1 infection could promote the spread of phosphorylated tau (ptau) among neurons via EV. We analyzed the ptau species that were secreted via EV following HSV-1 infection in neuroblastoma cells and primary neurons, focusing particularly on T205, T181, and T217, the phosphorylation sites mainly associated with AD. Moreover, by overexpressing human tau tagged with GFP (htauGFP), we found that recipient tau knockout (KO) neurons uptook EV that are loaded with HSV-1-induced phtauGFP. Finally, we exploited an in vivo model of acute infection and assessed that cerebral HSV-1 infection promotes the release of ptau via EV in the brain of infected mice. Overall, our data suggest that, following HSV-1 infection, EV play a role in tau spreading within the brain, thus contributing to neurodegeneration.IMPORTANCEHerpes simplex virus type 1 (HSV-1) infection that reaches the brain has been repeatedly linked with the appearance of the pathognomonic markers of Alzheimer's disease (AD), including accumulation of amyloid beta and hyperphosphorylated tau proteins, and cognitive deficits. AD is a multifactorial neurodegenerative disease representing the most common form of dementia in the elderly, and no cure is currently available, thus prompting additional investigation on potential risk factors and pathological mechanisms. Here, we demonstrate that the virus exploits the extracellular vesicles (EV) to disseminate phosphorylated tau (ptau) among brain cells. Importantly, we provide evidence that the HSV-1-induced EV-bearing ptau can be undertaken by recipient neurons, thus likely contributing to misfolding and aggregation of native tau, as reported for other AD models. Hence, our data highlight a novel mechanism exploited by HSV-1 to propagate tau-related damage in the brain.

Altered Protein Palmitoylation as Disease Mechanism in Neurodegenerative Disorders

Palmitoylation, a lipid-based posttranslational protein modification, plays a crucial role in regulating various aspects of neuronal function through altering protein membrane-targeting, stabilities, and protein-protein interaction profiles. Disruption of palmitoylation has recently garnered attention as disease mechanism in neurodegeneration. Many proteins implicated in neurodegenerative diseases and associated neuronal dysfunction, including but not limited to amyloid precursor protein, β-secretase (BACE1), postsynaptic density protein 95, Fyn, synaptotagmin-11, mutant huntingtin, and mutant superoxide dismutase 1, undergo palmitoylation, and recent evidence suggests that altered palmitoylation contributes to the pathological characteristics of these proteins and associated disruption of cellular processes. In addition, dysfunction of enzymes that catalyze palmitoylation and depalmitoylation has been connected to the development of neurological disorders. This review highlights some of the latest advances in our understanding of palmitoylation regulation in neurodegenerative diseases and explores potential therapeutic implications.

AAV8-P301L tau expression confers age-related disruptions in sleep quantity and timing

Sleep timing and quantity disturbances persist in tauopathy patients. This has been studied in transgenic models of primary tau neuropathology using traditional electroencephalograms (EEGs) and more recently, the PiezoSleep Mouse Behavioral Tracking System. Here, we generated a primary tauopathy model using an intracerebroventricular injection of human mutant hSyn-P301L-tau, using adeno-associated virus of serotype 8 (AAV8). We discovered distinctions in sleep architecture with altered quantity and timing in AAV8-P301L tau expressing mice of both sexes using the noninvasive PiezoSleep System. The AAV8-P301L tau mice exhibit striking age-related increases in sleep duration specifically at the active phase onset, suggesting a critical and sensitive time-of-day for tauopathy related sleep disturbances to occur. Since our findings show sleep behavior changes at specific transitional periods of the day, tau neuropathology may impact normal diurnal variation in biological processes, which should be explored using the AAV8-P301L tauopathy model.

A small molecule p38α MAPK inhibitor, MW150, attenuates behavioral deficits and neuronal dysfunction in a mouse model of mixed amyloid and vascular pathologies

Background

Inhibition of p38 alpha mitogen activated protein kinase (p38α) has shown great promise as a treatment for Alzheimer's disease (AD) in preclinical tests. However, previous preclinical studies were performed in "pure" models of AD pathology. A vast majority of AD patients have comorbid dementia-contributing pathologies, particularly some form of vascular damage. The present study therefore aimed to test the potential of p38α inhibition to address dysfunction in the context of comorbid amyloid and vascular pathologies.

Methods

An amyloid overexpressing mouse strain (5xFAD) was placed on an 8-week long diet to induce the hyperhomocysteinemia (HHcy) model of small vessel disease. Mice were treated with the brain-penetrant small molecule p38α inhibitor MW150 for the duration of the HHcy diet, and subsequently underwent behavioral, neuroimaging, electrophysiological, or biochemical/immunohistochemical analyses.

Results

MW150 successfully reduced behavioral impairment in the Morris Water Maze, corresponding with attenuation of synaptic loss, reduction in tau phosphorylation, and a partial normalization of electrophysiological parameters. No effect of MW150 was observed on the amyloid, vascular, or neuroinflammatory endpoints measured.

Conclusions

This study provides proof-of-principle that the inhibition of p38α is able to provide benefit even in the context of mixed pathological contributions to cognitive impairment. Interestingly, the benefit was mediated primarily via rescue of neuronal function without any direct effects on the primary pathologies. These data suggest a potential use for p38 inhibitors in the preservation of cognition across contexts, and in particular AD, either alone or as an adjunct to other AD therapies (i.e. anti-amyloid approaches). Future studies to delineate the precise neuronal pathways implicated in the benefit may help define other specific comorbid conditions amenable to this type of approach or suggest future refinement in pharmacological targeting.