Tau-mediated neurodegeneration in Alzheimer's disease and related disorders

Development of dietary small molecules as multi-targeting treatment strategies for Alzheimer's disease

Cognitive dysfunction can occur both in normal aging and age-related neurological disorders, such as mild cognitive impairment and Alzheimer's disease (AD). These disorders have few treatment options due to side effects and limited efficacy. New approaches to slow cognitive decline are urgently needed. Dietary interventions (nutraceuticals) have received considerable attention because they exhibit strong neuroprotective properties and may help prevent or minimize AD symptoms. Biological aging is driven by a series of interrelated mechanisms, including oxidative stress, neuroinflammation, neuronal apoptosis, and autophagy, which function through various signaling pathways. Recent clinical and preclinical studies have shown that dietary small molecules derived from natural sources, including flavonoids, carotenoids, and polyphenolic acids, can modulate oxidative damage, cognitive impairments, mitochondrial dysfunction, neuroinflammation, neuronal apoptosis, autophagy dysregulation, and gut microbiota dysbiosis. This paper reviews research on different dietary small molecules and their bioactive constituents in the treatment of AD. Additionally, the chemical structure, effective dose, and specific molecular mechanisms of action are comprehensively explored. This paper also discusses the advantages of using nanotechnology-based drug delivery, which significantly enhances oral bioavailability, safety, and therapeutic effect, and lowers the risk of adverse effects. These agents have considerable potential as novel and safe therapeutic agents that can prevent and combat age-related AD.

Biphasic modulation of tau liquid-liquid phase separation by polyphenols

Molecular tools that modulate tau liquid-liquid phase separation (LLPS) promise to treat tauopathies. We screened a set of polyphenols and demonstrated concentration-dependent biphasic modulation of tau LLPS by gallic acid (GA), showcasing its ability to expedite the liquid-to-gel transition in tau condensates and effectively impede the formation of deleterious fibrillar aggregates.

Distinct plasma phosphorylated-tau proteins profiling for the differential diagnosis of mild cognitive impairment and Alzheimer's disease by plasmonic asymmetric nanobridge-based biosensor

The differential diagnosis between mild cognitive impairment (MCI) and Alzheimer's disease (AD) has been highly demanded for its effectiveness in preventing and contributing to early diagnosis of AD. To this end, we developed a single plasmonic asymmetric nanobridge (PAN)-based biosensor to differentially diagnose MCI and AD by quantitative profiling of phosphorylated tau proteins (p-tau) in clinical plasma samples, which revealed a significant correlation with AD development and progression. The PAN was designed to have a conductive junction and asymmetric structure, which was unable to be synthesized by the traditional thermodynamical methods. For its unique morphological characteristics, PAN features high electromagnetic field enhancement, enabling the biosensor to achieve high sensitivity, with a limit of detection in the attomolar regime for quantitative analysis of p-tau. By introducing support vector machine (SVM)-based machine learning algorithm, the improved diagnostic system was achieved for prediction of healthy controls, MCI, and AD groups with an accuracy of 94.47 % by detecting various p-tau species levels in human plasma. Thus, our proposed PAN-based plasmonic biosensor has a powerful potential in clinical utility for predicting the onset of AD progression in the asymptomatic phase.

Multi-pathological contributions toward atrophy patterns in the Alzheimer's disease continuum

Introduction

Heterogeneity in downstream atrophy in Alzheimer's disease (AD) is predominantly investigated in relation to pathological hallmarks (Aβ, tau) and co-pathologies (cerebrovascular burden) independently. However, the proportional contribution of each pathology in determining atrophy pattern remains unclear. We assessed heterogeneity in atrophy using two recently conceptualized dimensions: typicality (typical AD atrophy at the center and deviant atypical atrophy on either extreme including limbic predominant to hippocampal sparing patterns) and severity (overall neurodegeneration spanning minimal atrophy to diffuse typical AD atrophy) in relation to Aβ, tau, and cerebrovascular burden.

Methods

We included 149 Aβ + individuals on the AD continuum (cognitively normal, prodromal AD, AD dementia) and 163 Aβ- cognitively normal individuals from the ADNI. We modeled heterogeneity in MRI-based atrophy with continuous-scales of typicality (ratio of hippocampus to cortical volume) and severity (total gray matter volume). Partial correlation models investigated the association of typicality/severity with (a) Aβ (global Aβ PET centiloid), tau (global tau PET SUVR), cerebrovascular (total white matter hypointensity volume) burden (b) four cognitive domains (memory, executive function, language, visuospatial composites). Using multiple regression, we assessed the association of each pathological burden and typicality/severity with cognition.

Results

(a) In the AD continuum, typicality (r = -0.31, p < 0.001) and severity (r = -0.37, p < 0.001) were associated with tau burden after controlling for Aβ, cerebrovascular burden and age. Findings imply greater tau pathology in limbic predominant atrophy and diffuse atrophy. (b) Typicality was associated with memory (r = 0.49, p < 0.001) and language scores (r = 0.19, p = 0.02). Severity was associated with memory (r = 0.26, p < 0.001), executive function (r = 0.24, p = 0.003) and language scores (r = 0.29, p < 0.001). Findings imply better cognitive performance in hippocampal sparing and minimal atrophy patterns. Beyond typicality/severity, tau burden but not Aβ and cerebrovascular burden explained cognition.

Conclusion

In the AD continuum, atrophy-based severity was more strongly associated with tau burden than typicality after accounting for Aβ and cerebrovascular burden. Cognitive performance in memory, executive function and language domains was explained by typicality and/or severity and additionally tau pathology. Typicality and severity may differentially reflect burden arising from tau pathology but not Aβ or cerebrovascular pathologies which need to be accounted for when investigating AD heterogeneity.

Effect of Natural Osmolytes on Recombinant Tau Monomer: Propensity of Oligomerization and Aggregation

The pathological misfolding and aggregation of the microtubule associated protein tau (MAPT), a full length Tau2N4R with 441aa, is considered the principal disease relevant constituent in tauopathies including Alzheimer's disease (AD) with an imbalanced ratio in 3R/4R isoforms. The exact cellular fluid composition, properties, and changes that coincide with tau misfolding, seed formation, and propagation events remain obscure. The proteostasis network, along with the associated osmolytes, is responsible for maintaining the presence of tau in its native structure or dealing with misfolding. In this study, for the first time, the roles of natural brain osmolytes are being investigated for their potential effects on regulating the conformational stability of the tau monomer (tauM) and its propensity to aggregate or disaggregate. Herein, the effects of physiological osmolytes myo-inositol, taurine, trimethyl amine oxide (TMAO), betaine, sorbitol, glycerophosphocholine (GPC), and citrulline on tau's aggregation state were investigated. The overall results indicate the ability of sorbitol and GPC to maintain the monomeric form and prevent aggregation of tau, whereas myo-inositol, taurine, TMAO, betaine, and citrulline promote tau aggregation to different degrees, as revealed by protein morphology in atomic force microscopy images. Biochemical and biophysical methods also revealed that tau proteins adopt different conformations under the influence of these osmolytes. TauM in the presence of all osmolytes expressed no toxicity when tested by a lactate dehydrogenase assay. Investigating the conformational stability of tau in the presence of osmolytes may provide a better understanding of the complex nature of tau aggregation in AD and the protective and/or chaotropic nature of osmolytes.

The role of the Pin1-cis P-tau axis in the development and treatment of vascular contribution to cognitive impairment and dementia and preeclampsia

Tauopathies are neurodegenerative diseases characterized by deposits of abnormal Tau protein in the brain. Conventional tauopathies are often defined by a limited number of Tau epitopes, notably neurofibrillary tangles, but emerging evidence suggests structural heterogeneity among tauopathies. The prolyl isomerase Pin1 isomerizes cis P-tau to inhibit the development of oligomers, tangles and neurodegeneration in multiple neurodegenerative diseases such as Alzheimer's disease, traumatic brain injury, vascular contribution to cognitive impairment and dementia (VCID) and preeclampsia (PE). Thus, cis P-tau has emerged as an early etiological driver, blood marker and therapeutic target for multiple neurodegenerative diseases, with clinical trials ongoing. The discovery of cis P-tau and other tau pathologies in VCID and PE calls attention for simplistic classification of tauopathy in neurodegenerative diseases. These recent advances have revealed the exciting novel role of the Pin1-cis P-tau axis in the development and treatment of vascular contribution to cognitive impairment and dementia and preeclampsia.

Korean red ginseng polysaccharide as a potential therapeutic agent targeting tau pathology in Alzheimer's disease

Tau is a microtubule-associated protein that plays a critical role in the stabilization and modulation of neuronal axons. Tau pathology is stronger associated with cognitive decline in patients with Alzheimer's disease (AD) than amyloid beta (Aβ) pathology. Hence, tau targeting is a promising approach for the treatment of AD. Previous studies have demonstrated that the non-saponin fraction with rich polysaccharide (NFP) from Korean red ginseng (KRG) can modulate tau aggregation and exert a therapeutic effect on AD. Therefore, we investigated the efficacy of NFP isolated from KRG on tau pathology in experimental models of AD. Our results showed that NFP from KRG ameliorated deposition and hyperphosphorylation of tau in the brain of 3xTg mice. Moreover, NFP from KRG modulated the aggregation and dissociation of tau K18 in vitro. We demonstrated the alleviatory effects of NFP from KRG on hyperphosphorylated tau and tau kinase in okadaic acid-treated HT22 cells. Furthermore, NFP from KRG mitigated Aβ deposition, neurodegeneration, and neuroinflammation in 3xTg mice. We revealed the neuroprotective effects of NFP from KRG on tau-induced neuronal loss in HT22 cells. Our results indicate that NFP extracted from KRG is a novel therapeutic agent for the treatment of AD associated with 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

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.

Microtubule-affinity regulating kinase family members distinctively affect tau phosphorylation and promote its toxicity in a Drosophila model

Accumulation of abnormally phosphorylated tau and its aggregation constitute a significant hallmark of Alzheimer's disease (AD). Tau phosphorylation at Ser262 and Ser356 in the KXGS motifs of microtubule-binding repeats plays a critical role in its physiological function and AD disease progression. Major tau kinases to phosphorylate tau at Ser262 and Ser356 belong to the Microtubule Affinity Regulating Kinase family (MARK1-4), which are considered one of the major contributors to tau abnormalities in AD. However, whether and how each member affects tau toxicity in vivo is unclear. We used transgenic Drosophila as a model to compare the effect on tau-induced neurodegeneration among MARKs in vivo. MARK4 specifically promotes tau accumulation and Ser396 phosphorylation, which yields more tau toxicity than was caused by other MARKs. Interestingly, MARK1, 2, and 4 increased tau phosphorylation at Ser262 and Ser356, but only MARK4 caused tau accumulation, indicating that these sites alone did not cause pathological tau accumulation. Our results revealed MARKs are different in their effect on tau toxicity, and also in tau phosphorylation at pathological sites other than Ser262 and Ser356. Understanding the implementation of each MARK into neurodegenerative disease helps to develop more target and safety therapies to overcome AD and related tauopathies.

Cyclization Scaffolding for Improved Vaccine Immunogen Stability: Application to Tau Protein in Alzheimer's Disease

Effective scaffolding of immunogens is crucial for generating conformationally selective antibodies through active immunization, particularly in the treatment of protein misfolding diseases such as Alzheimer's and Parkinson's disease. Previous computational work has revealed that a disorder-prone region of the tau protein, when in a stacked form, is predicted to structurally resemble a small, soluble protofibril, having conformational properties similar to those of experimental in vitro tau oligomers. Such an oligomeric structural mimic has the potential to serve as a vaccine immunogen design for Alzheimer's disease. In this study, we developed a cyclization scaffolding method in Rosetta, in which multiple cyclic peptides are stacked into a protofibril. Cyclization results in significant stabilization of protofibril-like structures by constraining the conformational space. Applying this method to the disorder-prone region of the tau fibril, we evaluated the metastability of the cyclized tau immunogen using molecular dynamics simulations, and we identified sequences of two cyclic constructs having high metastability in the protofibril. We then assessed their thermodynamic stability by computing the free energy required to separate a distal chain from the rest of the stacked structure. Our computational results, based on molecular dynamics simulations and free energy calculations, demonstrate that two cyclized constructs, cyclo-(VKSEKLDFKDRVQSKIFyN) and cyclo-(VKSEKLDFKDRVQSKIYvG) (lowercase letters indicate d-form amino acids), possess significantly increased thermodynamic stability in the protofibril over an uncyclized linear construct VKSEKLDFKDRVQSKI. The cyclization scaffolding approach proposed here holds promise as a means to effectively design immunogens for protein misfolding diseases, particularly those involving liposome-conjugated peptide constructs.

Structures of AT8 and PHF1 phosphomimetic tau: Insights into the posttranslational modification code of tau aggregation

The microtubule-associated protein tau aggregates into amyloid fibrils in Alzheimer's disease and other neurodegenerative diseases. In these tauopathies, tau is hyperphosphorylated, suggesting that this posttranslational modification (PTM) may induce tau aggregation. Tau is also phosphorylated in normal developing brains. To investigate how tau phosphorylation induces amyloid fibrils, here we report the atomic structures of two phosphomimetic full-length tau fibrils assembled without anionic cofactors. We mutated key Ser and Thr residues to Glu in two regions of the protein. One construct contains three Glu mutations at the epitope of the anti-phospho-tau antibody AT8 (AT8-3E tau), whereas the other construct contains four Glu mutations at the epitope of the antibody PHF1 (PHF1-4E tau). Solid-state NMR data show that both phosphomimetic tau mutants form homogeneous fibrils with a single set of chemical shifts. The AT8-3E tau rigid core extends from the R3 repeat to the C terminus, whereas the PHF1-4E tau rigid core spans R2, R3, and R4 repeats. Cryoelectron microscopy data show that AT8-3E tau forms a triangular multi-layered core, whereas PHF1-4E tau forms a triple-stranded core. Interestingly, a construct combining all seven Glu mutations exhibits the same conformation as PHF1-4E tau. Scalar-coupled NMR data additionally reveal the dynamics and shape of the fuzzy coat surrounding the rigid cores. These results demonstrate that specific PTMs induce structurally specific tau aggregates, and the phosphorylation code of tau contains redundancy.

Establishment of a high-content imaging assay for tau aggregation in hiPSC-derived neurons differentiated from two protocols to routinely evaluate compounds and genetic perturbations

Aberrant protein aggregation is a pathological cellular hallmark of many neurodegenerative diseases, such as Alzheimer's disease (AD) and frontotemporal dementia (FTD), where the tau protein is aggregating, forming neurofibrillary tangles (NFTs), and propagating from neuron to neuron. These processes have been linked to disease progression and a decline in cognitive function. Various therapeutic approaches aim at the prevention or reduction of tau aggregates in neurons. Human induced pluripotent stem cells (hiPSCs) are a very valuable tool in neuroscience discovery, as they offer access to potentially unlimited amounts of cell types that are affected in disease, including cortical neurons, for in vitro studies. We have generated an in vitro model for tau aggregation that uses hiPSC - derived neurons expressing an aggregation prone, fluorescently tagged version of the human tau protein after lentiviral transduction. Upon addition of tau seeds in the form of recombinant sonicated paired helical filaments (sPHFs), the neurons show robust, disease-like aggregation of the tau protein. The model was developed as a plate-based high content screening assay coupled with an image analysis algorithm to evaluate the impact of small molecules or genetic perturbations on tau. We show that the assay can be used to evaluate small molecules or screen targeted compound libraries. Using siRNA-based gene knockdown, genes of interest can be evaluated, and we could show that a targeted gene library can be screened, by screening nearly 100 deubiquitinating enzymes (DUBs) in that assay. The assay uses an imaging-based readout, a relatively short timeline, quantifies the extent of tau aggregation, and also allows the assessment of cell viability. Furthermore, it can be easily adapted to different hiPSC lines or neuronal subtypes. Taken together, this complex and highly relevant approach can be routinely applied on a weekly basis in the screening funnels of several projects and generates data with a turnaround time of approximately five weeks.

Systematic characterization of protein structural features of alternative splicing isoforms using AlphaFold 2

Alternative splicing is an important cellular process in eukaryotes, altering pre-mRNA to yield multiple protein isoforms from a single gene. However, our understanding of the impact of alternative splicing events on protein structures is currently constrained by a lack of sufficient protein structural data. To address this limitation, we employed AlphaFold 2, a cutting-edge protein structure prediction tool, to conduct a comprehensive analysis of alternative splicing for approximately 3,000 human genes, providing valuable insights into its impact on the protein structural. Our investigation employed state of the art high-performance computing infrastructure to systematically characterize structural features in alternatively spliced regions and identified changes in protein structure following alternative splicing events. Notably, we found that alternative splicing tends to alter the structure of residues primarily located in coils and beta-sheets. Our research highlighted a significant enrichment of loops and highly exposed residues within human alternatively spliced regions. Specifically, our examination of the Septin-9 protein revealed potential associations between loops and alternative splicing, providing insights into its evolutionary role. Furthermore, our analysis uncovered two missense mutations in the Tau protein that could influence alternative splicing, potentially contributing to the pathogenesis of Alzheimer's disease. In summary, our work, through a thorough statistical analysis of extensive protein structural data, sheds new light on the intricate relationship between alternative splicing, evolution, and human disease.

Tau-S214 Phosphorylation Inhibits Fyn Kinase Interaction and Increases the Decay Time of NMDAR-mediated Current

Fyn kinase SH3 domain interaction with PXXP motif in the Tau protein is implicated in AD pathology and is central to NMDAR function. Among seven PXXP motifs localized in proline-rich domain of Tau protein, tandem 5th and 6th PXXP motifs are critical to Fyn-SH3 domain interaction. Here, we report the crystal structure of Fyn-SH3 -Tau (207-221) peptide consisting of 5th and 6th PXXP motif complex to 1.01 Å resolution. Among five AD-specific phosphorylation sites encompassing the 5th and 6th PXXP motifs, only S214 residue showed interaction with SH3 domain. Biophysical studies showed that Tau (207-221) with S214-phosphorylation (pS214) inhibits its interaction with Fyn-SH3 domain. The individual administration of Tau (207-221) with/without pS214 peptides to a single neuron increased the decay time of evoked NMDA current response. Recordings of spontaneous NMDA EPSCs at +40 mV indicate an increase in frequency and amplitude of events for the Tau (207-221) peptide. Conversely, the Tau (207-221) with pS214 peptide exhibited a noteworthy amplitude increase alongside a prolonged decay time. These outcomes underscore the distinctive modalities of action associated with each peptide in the study. Overall, this study provides insights into how Tau (207-221) with/without pS214 affects the molecular framework of NMDAR signaling, indicating its involvement in Tau-related pathogenesis.

Pathology steered stratification network for subtype identification in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a heterogeneous, multifactorial neurodegenerative disorder characterized by three neurobiological factors beta-amyloid, pathologic tau, and neurodegeneration. There are no effective treatments for AD at a late stage, urging for early detection and prevention. However, existing statistical inference approaches in neuroimaging studies of AD subtype identification do not take into account the pathological domain knowledge, which could lead to ill-posed results that are sometimes inconsistent with the essential neurological principles.

PURPOSE

Integrating systems biology modeling with machine learning, the study aims to assist clinical AD prognosis by providing a subpopulation classification in accordance with essential biological principles, neurological patterns, and cognitive symptoms.

METHODS

We propose a novel pathology steered stratification network (PSSN) that incorporates established domain knowledge in AD pathology through a reaction-diffusion model, where we consider non-linear interactions between major biomarkers and diffusion along the brain structural network. Trained on longitudinal multimodal neuroimaging data, the biological model predicts long-term evolution trajectories that capture individual characteristic progression pattern, filling in the gaps between sparse imaging data available. A deep predictive neural network is then built to exploit spatiotemporal dynamics, link neurological examinations with clinical profiles, and generate subtype assignment probability on an individual basis. We further identify an evolutionary disease graph to quantify subtype transition probabilities through extensive simulations.

RESULTS

Our stratification achieves superior performance in both inter-cluster heterogeneity and intra-cluster homogeneity of various clinical scores. Applying our approach to enriched samples of aging populations, we identify six subtypes spanning AD spectrum, where each subtype exhibits a distinctive biomarker pattern that is consistent with its clinical outcome.

CONCLUSIONS

The proposed PSSN (i) reduces neuroimage data to low-dimensional feature vectors, (ii) combines AT[N]-Net based on real pathological pathways, (iii) predicts long-term biomarker trajectories, and (iv) stratifies subjects into fine-grained subtypes with distinct neurological underpinnings. PSSN provides insights into pre-symptomatic diagnosis and practical guidance on clinical treatments, which may be further generalized to other neurodegenerative diseases.

C9orf72-associated dipeptide protein repeats form A11-positive oligomers in amyotrophic lateral sclerosis and frontotemporal dementia

Hexanucleotide repeat expansion in C9orf72 is one of the most common causes of amyotrophic lateral sclerosis and frontotemporal dementia. The hexanucleotide expansion, formed by GGGGCC (G4C2) repeats, leads to the production of five dipeptide protein repeats (DPRs) via repeat-associated non-AUG translation. Among the five dipeptide repeats, Gly-Arg, Pro-Arg, and Gly-Ala form neuronal inclusions that contain aggregates of the peptides. Several studies have attempted to model DPR-associated toxicity using various repeat lengths, which suggests a unique conformation that is cytotoxic and is independent of the repeat length. However, the structural characteristics of DPR aggregates have yet to be determined. Increasing evidence suggests that soluble species, such as oligomers, are the main cause of toxicity in proteinopathies, such as Alzheimer's and Parkinson's disease. To investigate the ability of DPRs to aggregate and form toxic oligomers, we adopted a reductionist approach using small dipeptide repeats of 3, 6, and 12. This study shows that DPRs, particularly glycine-arginine and proline-arginine, form oligomers that exhibit distinct dye-binding properties and morphologies. Importantly, we also identified toxic DPR oligomers in amyotrophic lateral sclerosis and frontotemporal dementia postmortem brains that are morphologically similar to those generated recombinantly. This study demonstrates that, similar to soluble oligomers formed by various amyloid proteins, DPR oligomers are toxic, independent of their repeat length.

Liquid-liquid phase separation in Alzheimer's disease

The pathological aggregation and misfolding of tau and amyloid-β play a key role in Alzheimer's disease (AD). However, the underlying pathological mechanisms remain unclear. Emerging evidences indicate that liquid-liquid phase separation (LLPS) has great impacts on regulating human health and diseases, especially neurodegenerative diseases. A series of studies have revealed the significance of LLPS in AD. In this review, we summarize the latest progress of LLPS in AD, focusing on the impact of metal ions, small-molecule inhibitors, and proteinaceous partners on tau LLPS and aggregation, as well as toxic oligomerization, the role of LLPS on amyloid-β (Aβ) aggregation, and the cross-interactions between amyloidogenic proteins in AD. Eventually, the fundamental methods and techniques used in LLPS study are introduced. We expect to present readers a deeper understanding of the relationship between LLPS and AD.

Molecular mechanisms involved in the destabilization of two types of R3-R4 tau fibrils associated with chronic traumatic encephalopathy by Fisetin

Chronic traumatic encephalopathy is a neurodegenerative tauopathy pathologically characterized by fibrillary tau aggregates in the depth of sulci. Clearing fibrous tau aggregates is considered a promising strategy in the treatment of CTE. Fisetin (FS), a natural polyphenolic small molecule, was confirmed to disassociate the tau filaments in vitro. However, the molecular mechanisms of FS in destabilizing the CTE-related R3-R4 tau fibrils remain largely unknown. In this study, we compared the atomic-level structural differences of the two types of CTE-related R3-R4 tau fibrils and explored the influence and molecular mechanisms of FS on the two types of fibrils by conducting multiple molecular dynamics (MD) simulations. The results reveal that the type 1 fibril displays higher structural stability than the type 2 fibril, with a lower root-mean-square-fluctuation value and higher β-sheet structure probability. FS can destabilize both types of fibrils by decreasing the β-sheet structure content, interrupting the mainchain H-bond network, and increasing the solvent accessible surface area and β7-β8 angle of the fibrils. H-bonding, π-π stacking and cation-π are the common interactions driving FS molecules binding on the two types of fibrils, while the hydrophobic interaction occurs only in the type 2 fibril. Due to the relatively short simulation time, our study captures the early molecular mechanisms. However, it does provide beneficial information for the design of drugs to prevent or treat CTE.

p-tau Ser356 is associated with Alzheimer's disease pathology and is lowered in brain slice cultures using the NUAK inhibitor WZ4003

Tau hyperphosphorylation and aggregation is a common feature of many dementia-causing neurodegenerative diseases. Tau can be phosphorylated at up to 85 different sites, and there is increasing interest in whether tau phosphorylation at specific epitopes, by specific kinases, plays an important role in disease progression. The AMP-activated protein kinase (AMPK)-related enzyme NUAK1 has been identified as a potential mediator of tau pathology, whereby NUAK1-mediated phosphorylation of tau at Ser356 prevents the degradation of tau by the proteasome, further exacerbating tau hyperphosphorylation and accumulation. This study provides a detailed characterisation of the association of p-tau Ser356 with progression of Alzheimer's disease pathology, identifying a Braak stage-dependent increase in p-tau Ser356 protein levels and an almost ubiquitous presence in neurofibrillary tangles. We also demonstrate, using sub-diffraction-limit resolution array tomography imaging, that p-tau Ser356 co-localises with synapses in AD postmortem brain tissue, increasing evidence that this form of tau may play important roles in AD progression. To assess the potential impacts of pharmacological NUAK inhibition in an ex vivo system that retains multiple cell types and brain-relevant neuronal architecture, we treated postnatal mouse organotypic brain slice cultures from wildtype or APP/PS1 littermates with the commercially available NUAK1/2 inhibitor WZ4003. Whilst there were no genotype-specific effects, we found that WZ4003 results in a culture-phase-dependent loss of total tau and p-tau Ser356, which corresponds with a reduction in neuronal and synaptic proteins. By contrast, application of WZ4003 to live human brain slice cultures results in a specific lowering of p-tau Ser356, alongside increased neuronal tubulin protein. This work identifies differential responses of postnatal mouse organotypic brain slice cultures and adult human brain slice cultures to NUAK1 inhibition that will be important to consider in future work developing tau-targeting therapeutics for human disease.

Pre-clinical Evidence-based Neuroprotective Potential of Naringin against Alzheimer's Disease-like Pathology: A Comprehensive Review

Neurodegenerative disorders (NDs) are a group of progressive, chronic, and disabling disorders that are highly prevalent and the incidence is on a constant rise globally. Alzheimer's disease (AD), one of the most common neurodegenerative disorders is hallmarked by cognitive impairment, amyloid-β (Aβ) deposition, hyperphosphorylation of tau protein, cholinergic dysfunction, mitochondrial toxicity, and neurodegeneration. Available therapeutic agents only provide symptomatic relief and their use are limited due to serious side effects. Recent research has recognized flavonoids as potential multi-target biomolecules that can reduce the pathogenesis of AD. Naringin, a natural citrus flavonoid has been traditionally used to treat various NDs including AD, and has gained special attention because exhibits a neuroprotective effect by affecting numerous signaling pathways with minimum adverse effects. Naringin reduces deposition of Aβ, hyperphosphorylation of tau protein, cholinergic dysfunction, oxidative stress burden, mitochondrial toxicity, the activity of glutamate receptors, and apoptosis of the neuronal cells. Additionally, it reduces the expression of phosphorylated-P38/P38 and the NF-κB signaling pathway, showing that a wide range of molecular targets is involved in naringin's neuroprotective action. The present study describes the possible pharmacological targets, signaling pathways, and molecular mechanisms of naringin involved in neuroprotection against AD-like pathology. Based on the above pre-clinical reports it can be concluded that naringin could be an alternative therapeutic agent for the management of AD-like manifestation. Thus, there is a strong recommendation to perform more preclinical and clinical studies to develop naringin as a novel molecule that could be a multi-target drug to counteract AD.

Associations of Multimorbidity with Cerebrospinal Fluid Biomarkers for Neurodegenerative Disorders in Early Parkinson's Disease: A Crosssectional and Longitudinal Study

OBJECT

The study aims to determine whether multimorbidity status is associated with cerebrospinal fluid (CSF) biomarkers for neurodegenerative disorders.

METHODS

A total of 827 patients were enrolled from the Parkinson's Progression Markers Initiative (PPMI) database, including 638 patients with early-stage Parkinson's disease (PD) and 189 healthy controls (HCs). Multimorbidity status was evaluated based on the count of long-term conditions (LTCs) and the multimorbidity pattern. Using linear regression models, cross-sectional and longitudinal analyses were conducted to assess the associations of multimorbidity status with CSF biomarkers for neurodegenerative disorders, including α-synuclein (αSyn), amyloid-β42 (Aβ42), total tau (t-tau), phosphorylated tau (p-tau), glial fibrillary acidic protein (GFAP), and neurofilament light chain protein (NfL).

RESULTS

At baseline, the CSF t-tau (p = 0.010), p-tau (p = 0.034), and NfL (p = 0.049) levels showed significant differences across the three categories of LTC counts. In the longitudinal analysis, the presence of LTCs was associated with lower Aβ42 (β < -0.001, p = 0.020), and higher t-tau (β = 0.007, p = 0.026), GFAP (β = 0.013, p = 0.022) and NfL (β = 0.020, p = 0.012); Participants with tumor/musculoskeletal/mental disorders showed higher CSF levels of t-tau (β = 0.016, p = 0.011) and p-tau (β = 0.032, p = 0.044) than those without multimorbidity.

CONCLUSION

Multimorbidity, especially severe multimorbidity and the pattern of mental/musculoskeletal/ tumor disorders, was associated with CSF biomarkers for neurodegenerative disorders in early-stage PD patients, suggesting that multimorbidity might play a crucial role in aggravating neuronal damage in neurodegenerative diseases.

"Cyclophilin A" Enzymatic Effect on the Aggregation Behavior of 1N4R Tau Protein: An Overlooked Crucial Determinant that should be Re-considered in Alzheimer's Disease Pathogenesis

BACKGROUND

Neurodegenerative disorders like Alzheimer's disease (AD) involve the abnormal aggregation of tau protein, which forms toxic oligomers and amyloid deposits. The structure of tau protein is influenced by the conformational states of distinct proline residues, which are regulated by peptidyl-prolyl isomerases (PPIases). However, there has been no research on the impact of human cyclophilin A (CypA) as a PPIase on (non-phosphorylated) tau protein aggregation.

METHODS

On the basis of these explanations, we used various spectroscopic techniques to explore the effects of CypA on tau protein aggregation behavior.

RESULTS

We demonstrated the role of the isomerization activity of CypA in promoting the formation of tau protein amyloid fibrils with well-defined and highly ordered cross-β structures. According to the "cistauosis hypothesis," CypA's ability to enhance tau protein fibril formation in AD is attributed to the isomerization of specific proline residues from the trans to cis configuration. To corroborate this theory, we conducted refolding experiments using lysozyme as a model protein. The presence of CypA increased lysozyme aggregation and impeded its refolding process. It is known that proper refolding of lysozyme relies on the correct (trans) isomerization of two critical proline residues.

CONCLUSION

Thus, our findings confirmed that CypA induces the trans-to-cis isomerization of specific proline residues, ultimately leading to increased aggregation. Overall, this study highlights the emerging role of isomerization in tau protein pathogenesis in AD.

Multi-Target-Directed Cinnamic Acid Hybrids Targeting Alzheimer's Disease

Progressive cognitive decline in Alzheimer's disease (AD) is a growing challenge. Present therapies are based on acetylcholinesterase inhibition providing only temporary relief. Promising alternatives include butyrylcholinesterase (BuChE) inhibitors, multi-target ligands (MTDLs) that address the multi-factorial nature of AD, and compounds that target oxidative stress and inflammation. Cinnamate derivatives, known for their neuroprotective properties, show potential when combined with established AD agents, demonstrating improved efficacy. They are being positioned as potential AD therapeutic leads due to their ability to inhibit Aβ accumulation and provide neuroprotection. This article highlights the remarkable potential of cinnamic acid as a basic structure that is easily adaptable and combinable to different active groups in the struggle against Alzheimer's disease. Compounds with a methoxy substitution at the para-position of cinnamic acid display increased efficacy, whereas electron-withdrawing groups are generally more effective. The effect of the molecular volume is worthy of further investigation.

Effect and Mechanism of Rapamycin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic Review and Meta-analysis of Preclinical Studies

Background

Alzheimer's disease (AD), the most common form of dementia, remains long-term and challenging to diagnose. Furthermore, there is currently no medication to completely cure AD patients. Rapamycin has been clinically demonstrated to postpone the aging process in mice and improve learning and memory abilities in animal models of AD. Therefore, rapamycin has the potential to be significant in the discovery and development of drugs for AD patients.

Objective

The main objective of this systematic review and meta-analysis was to investigate the effects and mechanisms of rapamycin on animal models of AD by examining behavioral indicators and pathological features.

Methods

Six databases were searched and 4,277 articles were retrieved. In conclusion, 13 studies were included according to predefined criteria. Three authors independently judged the selected literature and methodological quality. Use of subgroup analyses to explore potential mechanistic effects of rapamycin interventions: animal models of AD, specific types of transgenic animal models, dosage, and periodicity of administration.

Results

The results of Morris Water Maze (MWM) behavioral test showed that escape latency was shortened by 15.60 seconds with rapamycin therapy, indicating that learning ability was enhanced in AD mice; and the number of traversed platforms was increased by 1.53 times, indicating that the improved memory ability significantly corrected the memory deficits.

CONCLUSIONS

Rapamycin therapy reduced age-related plaque deposition by decreasing AβPP production and down-regulating β-secretase and γ-secretase activities, furthermore increased amyloid-β clearance by promoting autophagy, as well as reduced tau hyperphosphorylation by up-regulating insulin-degrading enzyme levels.

Neuronanomedicine for Alzheimer's and Parkinson's disease: Current progress and a guide to improve clinical translation

Neuronanomedicine is an emerging multidisciplinary field that aims to create innovative nanotechnologies to treat major neurodegenerative disorders, such as Alzheimer's (AD) and Parkinson's disease (PD). A key component of neuronanomedicine are nanoparticles, which can improve drug properties and demonstrate enhanced safety and delivery across the blood-brain barrier, a major improvement on existing therapeutic approaches. In this review, we critically analyze the latest nanoparticle-based strategies to modify underlying disease pathology to slow or halt AD/PD progression. We find that a major roadblock for neuronanomedicine translation to date is a poor understanding of how nanoparticles interact with biological systems (i.e., bio-nano interactions), which is partly due to inconsistent reporting in published works. Accordingly, this review makes a set of specific recommendations to help guide researchers to harness the unique properties of nanoparticles and thus realise breakthrough treatments for AD/PD.

The HSP40 family chaperone isoform DNAJB6b prevents neuronal cells from tau aggregation

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disorder with clinical presentations of progressive cognitive and memory deterioration. The pathologic hallmarks of AD include tau neurofibrillary tangles and amyloid plaque depositions in the hippocampus and associated neocortex. The neuronal aggregated tau observed in AD cells suggests that the protein folding problem is a major cause of AD. J-domain-containing proteins (JDPs) are the largest family of cochaperones, which play a vital role in specifying and directing HSP70 chaperone functions. JDPs bind substrates and deliver them to HSP70. The association of JDP and HSP70 opens the substrate-binding domain of HSP70 to help the loading of the clients. However, in the initial HSP70 cycle, which JDP delivers tau to the HSP70 system in neuronal cells remains unclear.

RESULTS

We screened the requirement of a diverse panel of JDPs for preventing tau aggregation in the human neuroblastoma cell line SH-SY5Y by a filter retardation method. Interestingly, knockdown of DNAJB6, one of the JDPs, displayed tau aggregation and overexpression of DNAJB6b, one of the isoforms generated from the DNAJB6 gene by alternative splicing, reduced tau aggregation. Further, the tau bimolecular fluorescence complementation assay confirmed the DNAJB6b-dependent tau clearance. The co-immunoprecipitation and the proximity ligation assay demonstrated the protein-protein interaction between tau and the chaperone-cochaperone complex. The J-domain of DNAJB6b was critical for preventing tau aggregation. Moreover, reduced DNAJB6 expression and increased tau aggregation were detected in an age-dependent manner in immunohistochemical analysis of the hippocampus tissues of a mouse model of tau pathology.

CONCLUSIONS

In summary, downregulation of DNAJB6b increases the insoluble form of tau, while overexpression of DNAJB6b reduces tau aggregation. Moreover, DNAJB6b associates with tau. Therefore, this study reveals that DNAJB6b is a direct sensor for its client tau in the HSP70 folding system in neuronal cells, thus helping to prevent AD.

Site-Specific Ubiquitination of Tau Amyloids Promoted by the E3 Ligase CHIP

Post-translational modifications of Tau are emerging as key players in determining the onset and progression of different tauopathies such as Alzheimer's disease, and are recognized to mediate the structural diversity of the disease-specific Tau amyloids. Here we show that the E3 ligase CHIP catalyzes the site-specific ubiquitination of Tau filaments both in vitro and in cellular models, proving that also Tau amyloid aggregates are direct substrate of PTMs. Transmission electron microscopy and mass spectrometry analysis on ubiquitin-modified Tau amyloids revealed that the conformation of the filaments restricts CHIP-mediated ubiquitination to specific positions of the repeat domain, while only minor alterations in the structure of the fibril core were inferred using seeding experiments in vitro and in a cell-based tauopathy model. Overexpression of CHIP significantly increased the ubiquitination of exogenous PHF, proving that the ligase can interact and modify Tau aggregates also in a complex cellular environment.

Brain-derived neurotrophic factor interplay with oxidative stress: neuropathology approach in potential biomarker of Alzheimer's disease

The aging population poses a serious challenge concerning an increased prevalence of Alzheimer's disease (AD) and its impact on global burden, morbidity, and mortality. Oxidative stress, as a molecular hallmark that causes susceptibility in AD, interplays to other AD-related neuropathology cascades and decreases the expression of central and circulation brain-derived neurotrophic factor (BDNF), an essential neurotrophin that serves as nerve development and survival, and synaptic plasticity in AD. By its significant correlation with the molecular and clinical progression of AD, BDNF can potentially be used as an objectively accurate biomarker for AD diagnosis and progressivity follow-up in future clinical practice. This comprehensive review highlights the oxidative stress interplay with BDNF in AD neuropathology and its potential use as an AD biomarker.

Second Wave, Late-Stage Neuroinflammation in Cleared Brains of Aged 5xFAD Alzheimer's Mice Detected by Macrolaser Light Sheet Microscopy Imaging

This study leverages the innovative imaging capabilities of macrolaser light-sheet microscopy to elucidate the 3D spatial visualization of AD-associated neuropathologic networks in the transparent brains of 44-week-old 5xFAD mice. Brain samples from ten AD and seven control mice were prepared through a hydrophilic tissue-clearing pipeline and immunostained with thioflavin S (β-amyloid), anti-CD11b antibody (microglia), and anti-ACSA-2 antibody (astrocytes). The 5xFAD group exhibited significantly higher average total surface volumes of β-amyloid accumulation than the control group (AD, 898,634,368 µm3 [383,355,488-1,324,986,752]; control, 33,320,178 µm3 [11,156,785-65,390,988], p = 0.0006). Within the AD group, there was significant interindividual and interindividual variability concerning the number and surface volume of individual amyloid particles throughout the entire brain. In the context of neuroinflammation, the 5xFAD group showed significantly higher average total surface volumes of anti-ACSA-2-labeled astrocytes (AD, 59,064,360 µm3 [27,815,500-222,619,280]; control, 20,272,722 µm3 [9,317,288-27,223,352], p = 0.0047) and anti-CD11b labeled microglia (AD, 51,210,100 µm3 [15,309,118-135,532,144]; control, 23,461,593 µm3 [14,499,170-27,924,110], p = 0.0162) than the control group. Contrary to the long-standing finding that early-stage neuroinflammation precedes the subsequent later-stage of neurodegeneration, our data reveal that the second wave, late-stage active neuroinflammation persists in the aged AD brains, even as they continue to show signs of ongoing neurodegeneration and significant amyloid accumulation.

Batokine in Central Nervous System Diseases

Brown adipose tissue (BAT) is a special type of fat tissue in mammals and is also a key endocrine organ in the human body. Batokine, the endocrine effector of BAT, plays a neuroprotective role and improves the prognosis by exerting anti-apoptotic and anti-inflammatory effects, as well as by improving vascular endothelial function and other mechanisms in nerve injury diseases. The present article briefly reviewed several types of batokines related to central nervous system (CNS) diseases. Following this, the potential therapeutic value and future research direction of batokines for CNS diseases were chiefly discussed from the aspects of protective mechanism and signaling pathway.

Identification of tau-tubulin kinase 1 inhibitors by microfluidics-based mobility shift assay from a kinase inhibitor library

Tau tubulin kinase 1 (TTBK1) is a serine/threonine/tyrosine kinase that phosphorylates multiple residues in tau protein. Hyperphosphorylated tau is the main cause of tauopathy, such as Alzheimer's disease (AD). Therefore, preventing tau phosphorylation by inhibiting TTBK1 has been proposed as a therapeutic strategy for AD. However, few substrates of TTBK1 are reported for a biochemical assay and few inhibitors targeting TTBK1 have been reported so far. In this study, we identified a fluorescein amidite (FAM)-labeled peptide 15 from a small peptide library as the optimal peptide substrate for human TTBK1 (hTTBK1). We then developed and validated a microfluidics-based mobility shift assay (MMSA) with peptide 15. We further confirmed that peptide 15 could also be used in the ADP-Glo kinase assay. The established MMSA was applied for screening of a 427-compound kinase inhibitor library, yielding five compounds with IC50s of several micro molars against hTTBK1. Among them, three compounds, AZD5363, A-674,563 and GSK690693 inhibited hTTBK1 in an ATP competitive manner and molecular docking simulations revealed that they enter the ATP pocket and form one or two hydrogen bonds to the hinge region with hTTBK1. Another hit compound, piceatannol, showed non-ATP competitive inhibitory effect on hTTBK1 and may serve as a starting point to develop highly selective hTTBK1 inhibitors. Altogether, this study provided a new in vitro platform for the development of novel hTTBK1 inhibitors that might have potential applications in AD prevention.

Alzheimer's disease brain-derived extracellular vesicles reveal altered synapse-related proteome and induce cognitive impairment in mice

INTRODUCTION

Extracellular vesicles (EVs) have been implicated in the spread of neuropathology in Alzheimer's disease (AD), but their involvement in behavioral outcomes linked to AD remains to be determined.

METHODS

EVs isolated from post mortem brain tissue from control, AD, or frontotemporal dementia (FTD) donors, as well as from APP/PS1 mice, were injected into the hippocampi of wild-type (WT) or a humanized Tau mouse model (hTau/mTauKO). Memory tests were carried out. Differentially expressed proteins in EVs were assessed by proteomics.

RESULTS

Both AD-EVs and APP/PS1-EVs trigger memory impairment in WT mice. We further demonstrate that AD-EVs and FTD-EVs carry Tau protein, present altered protein composition associated with synapse regulation and transmission, and trigger memory impairment in hTau/mTauKO mice.

DISCUSSION

Results demonstrate that AD-EVs and FTD-EVs have negative impacts on memory in mice and suggest that, in addition to spreading pathology, EVs may contribute to memory impairment in AD and FTD.

HIGHLIGHTS

Aβ was detected in EVs from post mortem AD brain tissue and APP/PS1 mice. Tau was enriched in EVs from post mortem AD, PSP and FTD brain tissue. AD-derived EVs and APP/PS1-EVs induce cognitive impairment in wild-type (WT) mice. AD- and FTD-derived EVs induce cognitive impairment in humanized Tau mice. Proteomics findings associate EVs with synapse dysregulation in tauopathies.

Recent advancement in therapeutic strategies for Alzheimer's disease: Insights from clinical trials

Alzheimer's disease (AD) is the most prevalent form of dementia, characterized by the presence of plaques of amyloid beta and Tau proteins. There is currently no permanent cure for AD; the only medications approved by the FDA for mild to moderate AD are cholinesterase inhibitors, NMDA receptor antagonists, and immunotherapies against core pathophysiology, that provide temporary relief only. Researchers worldwide have made significant attempts to find new targets and develop innovative therapeutic molecules to treat AD. The FDA-approved drugs are palliative and couldn't restore the damaged neuron cells of AD. Stem cells have self-differentiation properties, making them prospective therapeutics to treat AD. The promising results in pre-clinical studies of stem cell therapy for AD seek attention worldwide. Various stem cells, mainly mesenchymal stem cells, are currently in different phases of clinical trials and need more advancements to take this therapy to the translational level. Here, we review research from the past decade that has identified several hypotheses related to AD pathology. Moreover, this article also focuses on the recent advancement in therapeutic strategies for AD treatment including immunotherapy and stem cell therapy detailing the clinical trials that are currently undergoing development.

Beyond uniformity: Exploring the heterogeneous and dynamic nature of the microtubule lattice

A fair amount of research on microtubules since their discovery in 1963 has focused on their dynamic tips. In contrast, the microtubule lattice was long believed to be highly regular and static, and consequently received far less attention. Yet, as it turned out, the microtubule lattice is neither as regular, nor as static as previously believed: structural studies uncovered the remarkable wealth of different conformations the lattice can accommodate. In the last decade, the microtubule lattice was shown to be labile and to spontaneously undergo renovation, a phenomenon that is intimately linked to structural defects and was called "microtubule self-repair". Following this breakthrough discovery, further recent research provided a deeper understanding of the lattice self-repair mechanism, which we review here. Instrumental to these discoveries were in vitro microtubule reconstitution assays, in which microtubules are grown from the minimal components required for their dynamics. In this review, we propose a shift from the term "lattice self-repair" to "lattice dynamics", since this phenomenon is an inherent property of microtubules and can happen without microtubule damage. We focus on how in vitro microtubule reconstitution assays helped us learn (1) which types of structural variations microtubules display, (2) how these structural variations influence lattice dynamics and microtubule damage caused by mechanical stress, (3) how lattice dynamics impact tip dynamics, and (4) how microtubule-associated proteins (MAPs) can play a role in structuring the lattice. Finally, we discuss the unanswered questions about lattice dynamics and how technical advances will help us tackle these questions.

Mapping the configurational landscape and aggregation phase behavior of the tau protein fragment PHF6

The PHF6 (Val-Gln-Ile-Val-Tyr-Lys) motif, found in all isoforms of the microtubule-associated protein tau, forms an integral part of ordered cores of amyloid fibrils formed in tauopathies and is thought to play a fundamental role in tau aggregation. Because PHF6 as an isolated hexapeptide assembles into ordered fibrils on its own, it is investigated as a minimal model for insight into the initial stages of aggregation of larger tau fragments. Even for this small peptide, however, the large length and time scales associated with fibrillization pose challenges for simulation studies of its dynamic assembly, equilibrium configurational landscape, and phase behavior. Here, we develop an accurate, bottom-up coarse-grained model of PHF6 for large-scale simulations of its aggregation, which we use to uncover molecular interactions and thermodynamic driving forces governing its assembly. The model, not trained on any explicit information about fibrillar structure, predicts coexistence of formed fibrils with monomers in solution, and we calculate a putative equilibrium phase diagram in concentration-temperature space. We also characterize the configurational and free energetic landscape of PHF6 oligomers. Importantly, we demonstrate with a model of heparin that this widely studied cofactor enhances the aggregation propensity of PHF6 by ordering monomers during nucleation and remaining associated with growing fibrils, consistent with experimentally characterized heparin-tau interactions. Overall, this effort provides detailed molecular insight into PHF6 aggregation thermodynamics and pathways and, furthermore, demonstrates the potential of modern multiscale modeling techniques to produce predictive models of amyloidogenic peptides simultaneously capturing sequence-specific effects and emergent aggregate structures.

Emerging evidence for dysregulated proteome cargoes of tau-propagating extracellular vesicles driven by familial mutations of tau and presenilin

Tau propagation, pathogenesis, and neurotoxicity are hallmarks of neurodegenerative diseases that result in cognitive impairment. Tau accumulates in Alzheimer's disease (AD), frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), chronic traumatic encephalopathy (CTE), progressive supranuclear palsy, and related tauopathies. Knowledge of the mechanisms for tau propagation in neurodegeneration is necessary for understanding the development of dementia. Exosomes, known as extracellular vesicles (EVs), have emerged as participants in promoting tau propagation. Recent findings show that EVs generated by neurons expressing familial mutations of tauopathies of FTDP-17 (P301L and V337M) (mTau) and presenilin (A246E) (mPS1) in AD induce tau propagation and accumulation after injection into rodent brain. To gain knowledge of the proteome cargoes of the mTau and mPS1 EVs that promote tau pathogenesis, this review compares the proteomes of these EVs, which results in important new questions concerning EV mechanisms of tau pathogenesis. Proteomics data show that EVs produced by mTau- and mPS1-expressing iPSC neurons share proteins involved in exocytosis and vesicle secretion and, notably, these EVs also possess differences in protein components of vesicle-mediated transport, extracellular functions, and cell adhesion. It will be important for future studies to gain an understanding of the breadth of familial genetic mutations of tau, presenilin, and other genes in promoting EV initiation of tau propagation and pathogenesis. Furthermore, elucidation of EV cargo components that mediate tau propagation will have potential as biomarkers and therapeutic strategies to ameliorate dementia of tauopathies.

Astaxanthin enhances autophagy, amyloid beta clearance and exerts anti-inflammatory effects in in vitro models of Alzheimer's disease-related blood brain barrier dysfunction and inflammation

Defective degradation and clearance of amyloid-β as well as inflammation per se are crucial players in the pathology of Alzheimer's disease (AD). A defective transport across the blood-brain barrier is causative for amyloid-β (Aβ) accumulation in the brain, provoking amyloid plaque formation. Using primary porcine brain capillary endothelial cells and murine organotypic hippocampal slice cultures as in vitro models of AD, we investigated the effects of the antioxidant astaxanthin (ASX) on Aβ clearance and neuroinflammation. We report that ASX enhanced the clearance of misfolded proteins in primary porcine brain capillary endothelial cells by inducing autophagy and altered the Aβ processing pathway. We observed a reduction in the expression levels of intracellular and secreted amyloid precursor protein/Aβ accompanied by an increase in ABC transporters ABCA1, ABCG1 as well as low density lipoprotein receptor-related protein 1 mRNA levels. Furthermore, ASX treatment increased autophagic flux as evidenced by increased lipidation of LC3B-II as well as reduced protein expression of phosphorylated S6 ribosomal protein and mTOR. In LPS-stimulated brain slices, ASX exerted anti-inflammatory effects by reducing the secretion of inflammatory cytokines while shifting microglia polarization from M1 to M2 phenotype. Our data suggest ASX as potential therapeutic compound ameliorating AD-related blood brain barrier impairment and inflammation.

Potential Implications of miRNAs in the Pathogenesis, Diagnosis, and Therapeutics of Alzheimer's Disease

Alzheimer's disease (AD) is a complex multifactorial disorder that poses a substantial burden on patients, caregivers, and society. Considering the increased aging population and life expectancy, the incidence of AD will continue to rise in the following decades. However, the molecular pathogenesis of AD remains controversial, superior blood-based biomarker candidates for early diagnosis are still lacking, and effective therapeutics to halt or slow disease progression are urgently needed. As powerful genetic regulators, microRNAs (miRNAs) are receiving increasing attention due to their implications in the initiation, development, and theranostics of various diseases, including AD. In this review, we summarize miRNAs that directly target microtubule-associated protein tau (MAPT), amyloid precursor protein (APP), and β-site APP-cleaving enzyme 1 (BACE1) transcripts and regulate the alternative splicing of tau and APP. We also discuss related kinases, such as glycogen synthase kinase (GSK)-3β, cyclin-dependent kinase 5 (CDK5), and death-associated protein kinase 1 (DAPK1), as well as apolipoprotein E, that are directly targeted by miRNAs to control tau phosphorylation and amyloidogenic APP processing leading to Aβ pathologies. Moreover, there is evidence of miRNA-mediated modulation of inflammation. Furthermore, circulating miRNAs in the serum or plasma of AD patients as noninvasive biomarkers with diagnostic potential are reviewed. In addition, miRNA-based therapeutics optimized with nanocarriers or exosomes as potential options for AD treatment are discussed.

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.

Characterization of Traumatic Brain Injury in a Gyrencephalic Ferret Model Using the Novel Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA)

Traumatic brain injury (TBI) results from mechanical force to the brain and leads to a series of biochemical responses that further damage neurons and supporting cells. Clinically, most TBIs result from an impact to the intact skull, making closed head TBI pre-clinical models highly relevant. However, most of these closed head TBI models use lissencephalic rodents, which may not transduce biomechanical load in the same manner as gyrencephalic humans. To address this translational gap, this study aimed to characterize acute axonal injury and microglial responses in ferrets-the smallest gyrencephalic mammal. Injury was induced in male ferrets (Mustela furo; 1.20-1.51 kg; 6-9 months old) with the novel Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA) model. Animals were randomly allocated to either sham (n = 4), a 22J (joules) impact (n = 4), or a 27J impact (n = 4). Axonal injury was examined histologically with amyloid precursor protein (APP), neurofilament M (RMO 14.9) (RMO-14), and phosphorylated tau (AT180) and the microglial response with ionized calcium-binding adaptor molecule 1 at 24 h post-injury in gray and white matter regions. Graded axonal injury was observed with modest increases in APP and RMO-14 immunoreactivity in the 22J TBI group, mostly within the corpus callosum and fornix and more extensive diffuse axonal injury encompassing gray matter structures like the thalamus and hypothalamus in the 27J group. Accompanying microglial activation was only observed in the 27J group, most prominently within the white matter tracts in response to the larger amounts of axonal injury. The 27J, but not the 22J, group showed an increase in AT180 within the base of the sulci post-injury. This could suggest that the strain may be highest in this region, demonstrating the different responses in gyrencephalic compared to lissencephalic brains. The CHIMERA model in ferrets mimic many of the histopathological features of human closed head TBI acutely and provides a promising model to investigate the pathophysiology of TBI.

The role of TREM2 in Alzheimer's disease: from the perspective of Tau

Triggering receptor expressed on myeloid cells 2 (TREM2), a pattern recognition receptor abundantly expressed on microglia, has been identified as one of the risk factors for Alzheimer's disease (AD). Several studies have already demonstrated the relationship between TREM2 and Tau. TREM2 mutations and altered expression play an important role in Tau phosphorylation. Furthermore, the level of Tau phosphorylation is correlated with soluble TREM2 (sTREM2). However, in different stages of AD, TREM2 seems to have varying effects on Tau pathology. The explicit interaction between TREM2 and Tau, as well as how they affect AD pathology, remains unclear, and there is much evidence to the contrary that requires rational interpretation. Reviewing the dual roles of TREM2 in AD will help identify a more appropriate development strategy for targeting TREM2 to treat AD. Therefore, this review focuses on the interplay between Tau and TREM2 in relation to AD.

Molecular rules governing the structural polymorphism of amyloid fibrils in neurodegenerative diseases

Amyloid fibrils are hallmarks of various neurodegenerative diseases. The structural polymorphism of amyloid fibrils holds significant pathological importance in diseases. This review aims to provide an in-depth overview on the complexity of amyloid fibrils' structural polymorphism and its implications in disease pathogenesis. We firstly decipher the molecular rules governing the structural polymorphism of amyloid fibrils. We then discuss pivotal factors that contribute to the assortment of fibril structural polymorphs, including post-translational modifications (PTMs), disease mutations, and interacting molecules, and elucidate the structural basis of how these determinants influence amyloid fibril polymorphism. Furthermore, we underscore the need for a comprehensive understanding of the relationship between diverse fibril polymorphs and pathological activities, as well as their potential roles in therapeutic applications.

Poly (ADP-ribose) polymerase 1 and neurodegenerative diseases: Past, present, and future

Poly (ADP-ribose) polymerase 1 (PARP1) is a first responder that recognizes DNA damage and facilitates its repair. Neurodegenerative diseases, characterized by progressive neuron loss driven by various risk factors, including DNA damage, have increasingly shed light on the pivotal involvement of PARP1. During the early phases of neurodegenerative diseases, PARP1 experiences controlled activation to swiftly address mild DNA damage, thereby contributing to maintain brain homeostasis. However, in late stages, exacerbated PARP1 activation precipitated by severe DNA damage exacerbates the disease condition. Consequently, inhibition of PARP1 overactivation emerges as a promising therapeutic approach for neurodegenerative diseases. In this review, we comprehensively synthesize and explore the multifaceted role of PARP1 in neurodegenerative diseases, with a particular emphasis on its over-activation in the aggregation of misfolded proteins, dysfunction of the autophagy-lysosome pathway, mitochondrial dysfunction, neuroinflammation, and blood-brain barrier (BBB) injury. Additionally, we encapsulate the therapeutic applications and limitations intrinsic of PARP1 inhibitors, mainly including limited specificity, intricate pathway dynamics, constrained clinical translation, and the heterogeneity of patient cohorts. We also explore and discuss the potential synergistic implementation of these inhibitors alongside other agents targeting DNA damage cascades within neurodegenerative diseases. Simultaneously, we propose several recommendations for the utilization of PARP1 inhibitors within the realm of neurodegenerative disorders, encompassing factors like the disease-specific roles of PARP1, combinatorial therapeutic strategies, and personalized medical interventions. Lastly, the encompassing review presents a forward-looking perspective along with strategic recommendations that could guide future research endeavors in this field.

Effects of anti-tau immunotherapy on reactive microgliosis, cerebral endotheliopathy, and cognitive function in an experimental model of cerebral malaria

Cerebral malaria (CM), a potentially fatal encephalopathy caused primarily by infection with Plasmodium falciparum, results in long-term adverse neuro-psychiatric sequelae. Neural cell injury contributes to the neurological deficits observed in CM. Abnormal regulation of tau, an axonal protein pathologically associated with the formation of neurofibrillary lesions in neurodegenerative diseases, has been linked to inflammation and cerebral microvascular compromise and has been reported in human and experimental CM (ECM). Immunotherapy with a monoclonal antibody to pathological tau (PHF-1 mAB) in experimental models of neurodegenerative diseases has been reported to mitigate cognitive decline. We investigated whether immunotherapy with PHF-1 mAB prevented cerebral endotheliopathy, neural cell injury, and neuroinflammation during ECM. Using C57BL/6 mice infected with either Plasmodium berghei ANKA (PbA), which causes ECM, Plasmodium berghei NK65 (PbN), which causes severe malaria, but not ECM, or uninfected mice (Un), we demonstrated that when compared to PbN infection or uninfected mice, PbA infection resulted in significant memory impairment at 6 days post-infection, in association with abnormal tau phosphorylation at Ser202 /Thr205 (pSer202 /Thr205 ) and Ser396-404 (pSer396-404 ) in mouse brains. ECM also resulted in significantly higher expression of inflammatory markers, in microvascular congestion, and glial cell activation. Treatment with PHF-1 mAB prevented PbA-induced cognitive impairment and was associated with significantly less vascular congestion, neuroinflammation, and neural cell activation in mice with ECM. These findings suggest that abnormal regulation of tau protein contributes to cerebral vasculopathy and is critical in the pathogenesis of neural cell injury during CM. Tau-targeted therapies may ameliorate the neural cell damage and subsequent neurocognitive impairment that occur during disease.

Identification of Aggregation Mechanism of Acetylated PHF6* and PHF6 Tau Peptides Based on Molecular Dynamics Simulations and Markov State Modeling

The microtubule-associated protein tau (MAPT) has a critical role in the development and preservation of the nervous system. However, tau's dysfunction and accumulation in the human brain can lead to several neurodegenerative diseases, such as Alzheimer's disease, Down's syndrome, and frontotemporal dementia. The microtubule binding (MTB) domain plays a significant, important role in determining the tau's pathophysiology, as the core of paired helical filaments PHF6* (275VQIINK280) and PHF6 (306VQIVYK311) of R2 and R3 repeat units, respectively, are formed in this region, which promotes tau aggregation. Post-translational modifications, and in particular lysine acetylation at K280 of PHF6* and K311 of PHF6, have been previously established to promote tau misfolding and aggregation. However, the exact aggregation mechanism is not known. In this study, we established an atomic-level nucleation-extension mechanism of the separated aggregation of acetylated PHF6* and PHF6 hexapeptides, respectively, of tau. We show that the acetylation of the lysine residues promotes the formation of β-sheet enriched high-ordered oligomers. The Markov state model analysis of ac-PHF6* and ac-PHF6 aggregation revealed the formation of an antiparallel dimer nucleus which could be extended from both sides in a parallel manner to form mixed-oriented and high-ordered oligomers. Our study describes the detailed mechanism for acetylation-driven tau aggregation, which provides valuable insights into the effect of post-translation modification in altering the pathophysiology of tau hexapeptides.

APOE4-promoted gliosis and degeneration in tauopathy are ameliorated by pharmacological inhibition of HMGB1 release

Apolipoprotein E4 (APOE4) is an important driver of Tau pathology, gliosis, and degeneration in Alzheimer's disease (AD). Still, the mechanisms underlying these APOE4-driven pathological effects remain elusive. Here, we report in a tauopathy mouse model that APOE4 promoted the nucleocytoplasmic translocation and release of high-mobility group box 1 (HMGB1) from hippocampal neurons, which correlated with the severity of hippocampal microgliosis and degeneration. Injection of HMGB1 into the hippocampus of young APOE4-tauopathy mice induced considerable and persistent gliosis. Selective removal of neuronal APOE4 reduced HMGB1 translocation and release. Treatment of APOE4-tauopathy mice with HMGB1 inhibitors effectively blocked the intraneuronal translocation and release of HMGB1 and ameliorated the development of APOE4-driven gliosis, Tau pathology, neurodegeneration, and myelin deficits. Single-nucleus RNA sequencing revealed that treatment with HMGB1 inhibitors diminished disease-associated and enriched disease-protective subpopulations of neurons, microglia, and astrocytes in APOE4-tauopathy mice. Thus, HMGB1 inhibitors represent a promising approach for treating APOE4-related AD.

Unveiling the Molecular Footprint: Proteome-Based Biomarkers for Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive decline and memory loss. Early and accurate diagnosis of AD is crucial for implementing timely interventions and developing effective therapeutic strategies. Proteome-based biomarkers have emerged as promising tools for AD diagnosis and prognosis due to their ability to reflect disease-specific molecular alterations. There is of great significance for biomarkers in AD diagnosis and management. It emphasizes the limitations of existing diagnostic approaches and the need for reliable and accessible biomarkers. Proteomics, a field that comprehensively analyzes the entire protein complement of cells, tissues, or bio fluids, is presented as a powerful tool for identifying AD biomarkers. There is a diverse range of proteomic approaches employed in AD research, including mass spectrometry, two-dimensional gel electrophoresis, and protein microarrays. The challenges associated with identifying reliable biomarkers, such as sample heterogeneity and the dynamic nature of the disease. There are well-known proteins implicated in AD pathogenesis, such as amyloid-beta peptides, tau protein, Apo lipoprotein E, and clusterin, as well as inflammatory markers and complement proteins. Validation and clinical utility of proteome-based biomarkers are addressing the challenges involved in validation studies and the diagnostic accuracy of these biomarkers. There is great potential in monitoring disease progression and response to treatment, thereby aiding in personalized medicine approaches for AD patients. There is a great role for bioinformatics and data analysis in proteomics for AD biomarker research and the importance of data preprocessing, statistical analysis, pathway analysis, and integration of multi-omics data for a comprehensive understanding of AD pathophysiology. In conclusion, proteome-based biomarkers hold great promise in the field of AD research. They provide valuable insights into disease mechanisms, aid in early diagnosis, and facilitate personalized treatment strategies. However, further research and validation studies are necessary to harness the full potential of proteome-based biomarkers in clinical practice.

Neuronal loss and inflammation preceding fibrillary tau pathology in a rat model with early human-like tauopathy

In tauopathies such as Alzheimer's disease (AD) and frontotemporal dementia (FTD), the microtubule associated protein tau undergoes conformational and posttranslational modifications in a gradual, staged pathological process. While brain atrophy and cognitive decline are well-established in the advanced stages of tauopathy, it is unclear how the early pathological processes manifest prior to extensive neurodegeneration. For these studies we have applied a transgenic rat model of human-like tauopathy in its heterozygous form, named McGill-R955-hTau. The goal of the present study was to investigate whether lifelong accumulation of mutated human tau could reveal the earliest tau pathological processes in a context of advanced aging, and, at stages before the overt aggregated or fibrillary tau deposition. We characterized the phenotype of heterozygous R955-hTau rats at three endpoints, 10, 18 and 24-26 months of age, focusing on markers of cognitive capabilities, progressive tau pathology, neuronal health, neuroinflammation and brain ultrastructural integrity, using immunohistochemistry and electron microscopy. Heterozygous R955-hTau transgenic rats feature a modest, life-long accumulation of mutated human tau that led to tau hyperphosphorylation and produced deficits in learning and memory tasks after 24 months of age. Such impairments coincided with more extensive tau hyperphosphorylation in the brain at residues pThr231 and with evidence of oligomerization. Importantly, aged R955-hTau rats presented evidence of neuroinflammation, detriments to myelin morphology and detectable hippocampal neuronal loss in the absence of overt neurofibrillary lesions and brain atrophy. The slow-progressing tauopathy of R955-hTau rats should allow to better delineate the temporal progression of tau pathological events and therefore to distinguish early indicators of tauopathy as having the capability to induce degenerative events in the aged CNS.

Optogenetics in Alzheimer's Disease: Focus on Astrocytes

Alzheimer's disease (AD) is the most common form of dementia, resulting in disability and mortality. The global incidence of AD is consistently surging. Although numerous therapeutic agents with promising potential have been developed, none have successfully treated AD to date. Consequently, the pursuit of novel methodologies to address neurodegenerative processes in AD remains a paramount endeavor. A particularly promising avenue in this search is optogenetics, enabling the manipulation of neuronal activity. In recent years, research attention has pivoted from neurons to glial cells. This review aims to consider the potential of the optogenetic correction of astrocyte metabolism as a promising strategy for correcting AD-related disorders. The initial segment of the review centers on the role of astrocytes in the genesis of neurodegeneration. Astrocytes have been implicated in several pathological processes associated with AD, encompassing the clearance of β-amyloid, neuroinflammation, excitotoxicity, oxidative stress, and lipid metabolism (along with a critical role in apolipoprotein E function). The effect of astrocyte-neuronal interactions will also be scrutinized. Furthermore, the review delves into a number of studies indicating that changes in cellular calcium (Ca2+) signaling are one of the causes of neurodegeneration. The review's latter section presents insights into the application of various optogenetic tools to manipulate astrocytic function as a means to counteract neurodegenerative changes.