Possible Mechanisms of Tau Spread and Toxicity in Alzheimer's Disease

Inflammasome links traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease

Traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease are three distinct neurological disorders that share common pathophysiological mechanisms involving neuroinflammation. One sequela of neuroinflammation includes the pathologic hyperphosphorylation of tau protein, an endogenous microtubule-associated protein that protects the integrity of neuronal cytoskeletons. Tau hyperphosphorylation results in protein misfolding and subsequent accumulation of tau tangles forming neurotoxic aggregates. These misfolded proteins are characteristic of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease and can lead to downstream neuroinflammatory processes, including assembly and activation of the inflammasome complex. Inflammasomes refer to a family of multimeric protein units that, upon activation, release a cascade of signaling molecules resulting in caspase-induced cell death and inflammation mediated by the release of interleukin-1β cytokine. One specific inflammasome, the NOD-like receptor protein 3, has been proposed to be a key regulator of tau phosphorylation where it has been shown that prolonged NOD-like receptor protein 3 activation acts as a causal factor in pathological tau accumulation and spreading. This review begins by describing the epidemiology and pathophysiology of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease. Next, we highlight neuroinflammation as an overriding theme and discuss the role of the NOD-like receptor protein 3 inflammasome in the formation of tau deposits and how such tauopathic entities spread throughout the brain. We then propose a novel framework linking traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease as inflammasome-dependent pathologies that exist along a temporal continuum. Finally, we discuss potential therapeutic targets that may intercept this pathway and ultimately minimize long-term neurological decline.

Amyloid-β oligomers increase the binding and internalization of tau oligomers in human synapses

In Alzheimer's disease (AD), the propagation and spreading of CNS tau pathology closely correlates with cognitive decline, positioning tau as an attractive therapeutic target. Amyloid beta (Aβ) has been strongly implicated in driving tau spread, whereas primary tauopathies such as primary age-related tauopathy (PART)-which lack Aβ pathology-exhibit limited tau spread and minimal-to-no cognitive decline. Emerging evidence converges on a trans-synaptic mechanism of tau spread, facilitated by the transfer of misfolded tau aggregates (e.g. soluble oligomers). However, it is unclear whether Aβ oligomers modulate the binding and internalization of tau oligomers in human synapses. Our translationally focused paradigms utilize post-mortem brain specimens from Control, PART, and AD patients. Synaptosomes isolated from the temporal cortex of all three groups were incubated with preformed recombinant tauO (rtauO), ± preformed recombinant AβO (rAβO), and oligomer binding/internalization was quantified via flow cytometry following proteinase K (PK) digestion of surface-bound oligomers. TauO-synapse interactions were visualized using EM immunogold. Brain-derived tau oligomers (BDTO) from AD and PART PBS-soluble hippocampal fractions were co-immunoprecipitated and analyzed via mass spectrometry to compare synaptic tauO interactomes in primary and secondary tauopathies, thereby inferring the role of Aβ. AD synaptosomes, enriched in endogenous Aβ pathology, exhibited increased rtauO internalization compared to PART synaptosomes. This observation was mirrored in Control synaptosomes, where recombinant rAβO significantly increased rtauO binding and internalization. PK pre-treatment abolished this effect, implicating synaptic membrane proteins in AβO-mediated tauO internalization. While both PART and AD BDTO were broadly enriched in synaptic proteins, AD BDTO exhibited differential enrichment of endocytic proteins across pre- and post-synaptic compartments, whereas PART BDTO showed no significant synaptic enrichment. This study demonstrates that Aβ oligomers enhance tau oligomer binding and drive its internalization through synaptic membrane proteins. These findings offer novel mechanistic insights underlying pathological tau spreading directly within human synapses and emphasize the therapeutic potential of targeting Aβ-tau interactions.

Effects of All-Atom and Coarse-Grained Molecular Mechanics Force Fields on Amyloid Peptide Assembly: The Case of a Tau K18 Monomer

To propose new mechanism-based therapeutics for Alzheimer's disease (AD), it is crucial to study the kinetics and oligomerization/aggregation mechanisms of the hallmark tau proteins, which have various isoforms and are intrinsically disordered. In this study, multiple all-atom (AA) and coarse-grained (CG) force fields (FFs) have been benchmarked on molecular dynamics (MD) simulations of K18 tau (M243-E372), which is a truncated form (130 residues) of full-length tau (441 residues). FF19SB is first excluded because the dynamics are too slow, and the conformations are too stable. All other benchmarked AAFFs (Charmm36m, FF14SB, Gromos54A7, and OPLS-AA) and CGFFs (Martini3 and Sirah2.0) exhibit a trend of shrinking K18 tau into compact structures with the radius of gyration (ROG) around 2.0 nm, which is much smaller than the experimental value of 3.8 nm, within 200 ns of AA-MD or 2000 ns of CG-MD. Gromos54A7, OPLS-AA, and Martini3 shrink much faster than the other FFs. To perform meaningful postanalysis of various properties, we propose a strategy of selecting snapshots with 2.5 < ROG < 4.5 nm, instead of using all sampled snapshots. The calculated chemical shifts of all C, CA, and CB atoms have very good and close root-mean-square error (RMSE) values, while Charmm36m and Sirah2.0 exhibit better chemical shifts of N than other FFs. Comparing the calculated distributions of the distance between the CA atoms of CYS291 and CYS322 with the results of the FRET experiment demonstrates that Charmm36m is a perfect match with the experiment while other FFs exhibit limitations. In summary, Charmm36m is recommended as the best AAFF, and Sirah2.0 is recommended as an excellent CGFF for simulating tau K18.

Tau Protein and Tauopathies: Exploring Tau Protein-Protein and Microtubule Interactions, Cross-Interactions and Therapeutic Strategies

Tau, a microtubule-associated protein (MAP), is essential to maintaining neuronal stability and function in the healthy brain. However, aberrant modifications and pathological aggregations of Tau are implicated in various neurodegenerative disorders, collectively known as tauopathies. The most common Tauopathy is Alzheimer's Disease (AD) counting nowadays more than 60 million patients worldwide. This comprehensive review delves into the multifaceted realm of Tau protein, puzzling out its intricate involvement in both physiological and pathological roles. Emphasis is put on Tau Protein-Protein Interactions (PPIs), depicting its interaction with tubulin, microtubules and its cross-interaction with other proteins such as Aβ1-42, α-synuclein, and the chaperone machinery. In the realm of therapeutic strategies, an overview of diverse possibilities is presented with their relative clinical progresses. The focus is mostly addressed to Tau protein aggregation inhibitors including recent small molecules, short peptides and peptidomimetics with specific focus on compounds that showed a double anti aggregative activity on both Tau protein and Aβ amyloid peptide. This review amalgamates current knowledge on Tau protein and evolving therapeutic strategies, providing a comprehensive resource for researchers seeking to deepen their understanding of the Tau protein and for scientists involved in the development of new peptide-based anti-aggregative Tau compounds.

Photobiomodulation as a Potential Treatment for Alzheimer's Disease: A Review Paper

BACKGROUND

Alzheimer's disease (AD), the most prevalent form of dementia, is a leading neurodegenerative disorder currently affecting approximately 55 million individuals globally, a number projected to escalate to 139 million by 2050. Despite extensive research spanning several decades, the cure for AD remains at a developing stage. The only existing therapeutic options are limited to symptom management, and are often accompanied by adverse side effects. The pathological features of AD, including the accumulation of beta-amyloid plaques and tau protein tangles, result in progressive neuronal death, synaptic loss, and brain atrophy, leading to significant cognitive decline and a marked reduction in quality of life.

OBJECTIVE

In light of the shortcomings of existing pharmacological interventions, this review explores the potential of photobiomodulation (PBM) as a non-invasive therapeutic option for AD. PBM employs infrared light to facilitate cellular repair and regeneration, focusing on addressing the disease's underlying biomechanical mechanisms.

METHOD

This paper presents a comprehensive introduction to the mechanisms of PBM and an analysis of preclinical studies evaluating its impact on cellular health, cognitive function, and disease progression in AD.The review provides a comprehensive overview of the various wavelengths and application methods, evaluating their efficacy in mitigating AD-related symptoms.

CONCLUSIONS

The findings underscore the significant potential of PBM as a safe and effective alternative treatment for Alzheimer's disease, emphasizing the necessity for further research and clinical trials to establish its therapeutic efficacy conclusively.

Brain Microvascular Pericyte Pathology Linking Alzheimer's Disease to Diabetes

The brain microvasculature, which delivers oxygen and nutrients and forms a critical barrier protecting the central nervous system via capillaries, is deleteriously affected by both Alzheimer's disease (AD) and type 2 diabetes (T2D). T2D patients have an increased risk of developing AD, suggesting potentially related microvascular pathological mechanisms. Pericytes are an ideal cell type to study for functional links between AD and T2D. These specialized capillary-enwrapping cells regulate capillary density, lumen diameter, and blood flow. Pericytes also maintain endothelial tight junctions to ensure blood-brain barrier integrity, modulation of immune cell extravasation, and clearance of toxins. Changes in these phenomena have been observed in both AD and T2D, implicating "pericyte pathology" as a common feature of AD and T2D. This review examines the mechanisms of AD and T2D from the perspective of the brain microvasculature, highlighting how pericyte pathology contributes to both diseases. Our review identifies voids in understanding how AD and T2D negatively impact the brain microvasculature and suggests future studies to examine the intersections of these diseases.

A Drosophila model for mechanistic investigation of tau protein spread

Brain protein aggregates are a hallmark of neurodegenerative disease. Previous work indicates that specific protein components of these aggregates are toxic, including tau (encoded by MAPT) in Alzheimer's disease and related tauopathies. Increasing evidence also indicates that these toxic proteins traffic between cells in a prion-like fashion, thereby spreading pathology from one brain region to another. However, the mechanisms involved in trafficking are poorly understood. We therefore developed a transgenic Drosophila model to facilitate rapid evaluation of candidate tau trafficking modifiers. Our model uses the bipartite Q system to drive co-expression of tau and GFP in the fly eye. We found age-dependent spread of tau into the brain, represented by detection of tau, but not of GFP. We also found that tau trafficking was attenuated upon inhibition of the endocytic factor dynamin (encoded by shi) or knockdown of glycogen synthase kinase-3β (GSK-3β, encoded by sgg). Further work revealed that dynamin promoted tau uptake in recipient tissues, whereas GSK-3β appeared to promote tau spread via direct phosphorylation of tau. Our robust and flexible system will promote the identification of tau-trafficking components involved in the pathogenesis of neurodegenerative diseases.

Complement receptor 4 mediates the clearance of extracellular tau fibrils by microglia

Tauopathies exhibit a characteristic accumulation of misfolded tau aggregates in the brain. Tau pathology shows disease-specific spatiotemporal propagation through intercellular transmission, which is closely correlated with the progression of clinical manifestations. Therefore, identifying molecular mechanisms that prevent tau propagation is critical for developing therapeutic strategies for tauopathies. The various innate immune receptors, such as complement receptor 3 (CR3) and complement receptor 4 (CR4), have been reported to play a critical role in the clearance of various extracellular toxic molecules by microglia. However, their role in tau clearance has not been studied yet. In the present study, we investigated the role of CR3 and CR4 in regulating extracellular tau clearance. We found that CR4 selectively binds to tau fibrils but not to tau monomers, whereas CR3 does not bind to either of them. Inhibiting CR4, but not CR3, significantly reduces the uptake of tau fibrils by BV2 cells and primary microglia. By contrast, inhibiting CR4 has no effect on the uptake of tau monomers by BV2 cells. Furthermore, inhibiting CR4 suppresses the clearance of extracellular tau fibrils, leading to more seed-competent tau fibrils remaining in the extracellular space relative to control samples. We also provide evidence that the expression of CR4 is upregulated in the brains of human Alzheimer's disease patients and the PS19 mouse model of tauopathy. Taken together, our data strongly support that CR4 is a previously undescribed receptor for the clearance of tau fibrils in microglia and may represent a novel therapeutic target for tauopathy.

Protein modification in neurodegenerative diseases

Posttranslational modifications play a crucial role in governing cellular functions and protein behavior. Researchers have implicated dysregulated posttranslational modifications in protein misfolding, which results in cytotoxicity, particularly in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease. These aberrant posttranslational modifications cause proteins to gather in certain parts of the brain that are linked to the development of the diseases. This leads to neuronal dysfunction and the start of neurodegenerative disease symptoms. Cognitive decline and neurological impairments commonly manifest in neurodegenerative disease patients, underscoring the urgency of comprehending the posttranslational modifications' impact on protein function for targeted therapeutic interventions. This review elucidates the critical link between neurodegenerative diseases and specific posttranslational modifications, focusing on Tau, APP, α-synuclein, Huntingtin protein, Parkin, DJ-1, and Drp1. By delineating the prominent aberrant posttranslational modifications within Alzheimer disease, Parkinson disease, and Huntington disease, the review underscores the significance of understanding the interplay among these modifications. Emphasizing 10 key abnormal posttranslational modifications, this study aims to provide a comprehensive framework for investigating neurodegenerative diseases holistically. The insights presented herein shed light on potential therapeutic avenues aimed at modulating posttranslational modifications to mitigate protein aggregation and retard neurodegenerative disease progression.

Tau, RNA, and RNA-Binding Proteins: Complex Interactions in Health and Neurodegenerative Diseases

The tau protein is a key contributor to multiple neurodegenerative diseases. The pathology of tau is thought to be related to tau's propensity to form self-templating fibrillar structures that allow tau fibers to propagate in the brain by prion-like mechanisms. Unresolved issues with respect to tau pathology are how the normal function of tau and its misregulation contribute to disease, how cofactors and cellular organelles influence the initiation and propagation of tau fibers, and determining the mechanism of tau toxicity. Herein, we review the connection between tau and degenerative diseases, the basis for tau fibrilization, and how that process interacts with cellular molecules and organelles. One emerging theme is that tau interacts with RNA and RNA-binding proteins, normally and in pathologic aggregates, which may provide insight into alterations in RNA regulation observed in disease.

Transcriptomics analysis reveals potential regulatory role of nSMase2 (Smpd3) in nervous system development and function of middle-aged mouse brains

Neutral sphingomyelinase-2 (nSMase2), gene name sphingomyelin phosphodiesterase-3 (Smpd3), is a key regulatory enzyme responsible for generating the sphingolipid ceramide. The function of nSMase2 in the brain is still controversial. To better understand the functional roles of nSMase2 in the aging mouse brain, we applied RNA-seq analysis, which identified a total of 1462 differentially abundant mRNAs between +/fro and fro/fro, of which 891 were increased and 571 were decreased in nSMase2-deficient mouse brains. The most strongly enriched GO and KEGG annotation terms among transcripts increased in fro/fro mice included synaptogenesis, synapse development, synaptic signaling, axon development, and axonogenesis. Among decreased transcripts, enriched annotations included ribosome assembly and mitochondrial protein complex functions. KEGG analysis of decreased transcripts also revealed overrepresentation of annotations for Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington disease (HD). Ingenuity Pathway Analysis (IPA) tools predicted lower susceptibility to these neurodegenerative disorders, as well as predictions agreeing with stronger synaptic function, learning, and memory in fro/fro mice. The IPA tools identified signaling proteins, epigenetic regulators, and microRNAs as likely upstream regulators of the broader set of genes encoding the affected transcripts. It also revealed 16 gene networks, each linked to biological processes identified as overrepresented annotations among the affected transcripts by multiple analysis methods. Therefore, the analysis of these RNA-seq data indicates that nSMase2 impacts synaptic function and neural development, and may contribute to the onset and development of neurodegenerative diseases in middle-aged mice.

Identification of retinal oligomeric, citrullinated, and other tau isoforms in early and advanced AD and relations to disease status

This study investigates various pathological tau isoforms in the retina of individuals with early and advanced Alzheimer's disease (AD), exploring their connection with disease status. Retinal cross-sections from predefined superior-temporal and inferior-temporal subregions and corresponding brains from neuropathologically confirmed AD patients with a clinical diagnosis of either mild cognitive impairment (MCI) or dementia (n = 45) were compared with retinas from age- and sex-matched individuals with normal cognition (n = 30) and non-AD dementia (n = 4). Retinal tau isoforms, including tau tangles, paired helical filament of tau (PHF-tau), oligomeric-tau (Oligo-tau), hyperphosphorylated-tau (p-tau), and citrullinated-tau (Cit-tau), were stereologically analyzed by immunohistochemistry and Nanostring GeoMx digital spatial profiling, and correlated with clinical and neuropathological outcomes. Our data indicated significant increases in various AD-related pretangle tau isoforms, especially p-tau (AT8, 2.9-fold, pS396-tau, 2.6-fold), Cit-tau at arginine residue 209 (CitR209-tau; 4.1-fold), and Oligo-tau (T22+, 9.2-fold), as well as pretangle and mature tau tangle forms like MC-1-positive (1.8-fold) and PHF-tau (2.3-fold), in AD compared to control retinas. MCI retinas also exhibited substantial increases in Oligo-tau (5.2-fold), CitR209-tau (3.5-fold), and pS396-tau (2.2-fold). Nanostring GeoMx analysis confirmed elevated retinal p-tau at epitopes: Ser214 (2.3-fold), Ser396 (2.6-fold), Ser404 (2.4-fold), and Thr231 (1.8-fold), particularly in MCI patients. Strong associations were found between retinal tau isoforms versus brain pathology and cognitive status: a) retinal Oligo-tau vs. Braak stage, neurofibrillary tangles (NFTs), and CDR cognitive scores (ρ = 0.63-0.71), b) retinal PHF-tau vs. neuropil threads (NTs) and ABC scores (ρ = 0.69-0.71), and c) retinal pS396-tau vs. NTs, NFTs, and ABC scores (ρ = 0.67-0.74). Notably, retinal Oligo-tau strongly correlated with retinal Aβ42 and arterial Aβ40 forms (r = 0.76-0.86). Overall, this study identifies and quantifies diverse retinal tau isoforms in MCI and AD patients, underscoring their link to brain pathology and cognition. These findings advocate for further exploration of retinal tauopathy biomarkers to facilitate AD detection and monitoring via noninvasive retinal imaging.

Particulate matter constituents trigger the formation of extracellular amyloid β and Tau -containing plaques and neurite shortening in vitro

Air pollution is an environmental factor associated with an increased risk of neurodegenerative diseases, such as Alzheimer's and Parkinson's, characterized by decreased cognitive abilities and memory. The limited models of sporadic Alzheimer's disease fail to replicate all pathological hallmarks of the disease, making it challenging to uncover potential environmental causes. Environmentally driven models of Alzheimer's disease are thus timely and necessary. We used live-cell confocal fluorescent imaging combined with high-resolution stimulated emission depletion (STED) microscopy to follow the response of retinoic acid-differentiated human neuroblastoma SH-SY5Y cells to nanomaterial exposure. Here, we report that exposure of the cells to some particulate matter constituents reproduces a neurodegenerative phenotype, including extracellular amyloid beta-containing plaques and decreased neurite length. Consistent with the existing in vivo research, we observed detrimental effects, specifically a substantial reduction in neurite length and formation of amyloid beta plaques, after exposure to iron oxide and diesel exhaust particles. Conversely, after exposure to engineered cerium oxide nanoparticles, the lengths of neurites were maintained, and almost no extracellular amyloid beta plaques were formed. Although the exact mechanism behind this effect remains to be explained, the retinoic acid differentiated SH-SY5Y cell in vitro model could serve as an alternative, environmentally driven model of neurodegenerative diseases, including Alzheimer's disease.

New insights into the therapeutic approaches for the treatment of tauopathies

Tauopathies are a group of neurological disorders, including Alzheimer's disease and frontotemporal dementia, which involve progressive neurodegeneration, cognitive deficits, and aberrant tau protein accumulation. The development of tauopathies cannot currently be stopped or slowed down by treatment measures. Given the significant contribution of tau burden in primary tauopathies and the strong association between pathogenic tau accumulation and cognitive deficits, there has been a lot of interest in creating therapies that can alleviate tau pathology and render neuroprotective effects. Recently, small molecules, immunotherapies, and gene therapy have been used to reduce the pathological tau burden and prevent neurodegeneration in animal models of tauopathies. However, the major pitfall of the current therapeutic approach is the difficulty of drugs and gene-targeting modalities to cross the blood-brain barrier and their unintended side effects. In this review, the current therapeutic strategies used for tauopathies including the use of oligonucleotide-based gene therapy approaches that have shown a promising result for the treatment of tauopathies and Alzheimer's disease in preclinical animal models, have been discussed.

Deconstructing pathological tau by biological process in early stages of Alzheimer disease: a method for quantifying tau spatial spread in neuroimaging

BACKGROUND

Neuroimaging studies often quantify tau burden in standardized brain regions to assess Alzheimer disease (AD) progression. However, this method ignores another key biological process in which tau spreads to additional brain regions. We have developed a metric for calculating the extent tau pathology has spread throughout the brain and evaluate the relationship between this metric and tau burden across early stages of AD.

METHODS

445 cross-sectional participants (aged ≥ 50) who had MRI, amyloid PET, tau PET, and clinical testing were separated into disease-stage groups based on amyloid positivity and cognitive status (older cognitively normal control, preclinical AD, and symptomatic AD). Tau burden and tau spatial spread were calculated for all participants.

FINDINGS

We found both tau metrics significantly elevated across increasing disease stages (p < 0.0001) and as a function of increasing amyloid burden for participants with preclinical (p < 0.0001, p = 0.0056) and symptomatic (p = 0.010, p = 0.0021) AD. An interaction was found between tau burden and tau spatial spread when predicting amyloid burden (p = 0.00013). Analyses of slope between tau metrics demonstrated more spread than burden in preclinical AD (β = 0.59), but then tau burden elevated relative to spread (β = 0.42) once participants had symptomatic AD, when the tau metrics became highly correlated (R = 0.83).

INTERPRETATION

Tau burden and tau spatial spread are both strong biomarkers for early AD but provide unique information, particularly at the preclinical stage. Tau spatial spread may demonstrate earlier changes than tau burden which could have broad impact in clinical trial design.

FUNDING

This research was supported by the Knight Alzheimer Disease Research Center (Knight ADRC, NIH grants P30AG066444, P01AG026276, P01AG003991), Dominantly Inherited Alzheimer Network (DIAN, NIH grants U01AG042791, U19AG03243808, R01AG052550-01A1, R01AG05255003), and the Barnes-Jewish Hospital Foundation Willman Scholar Fund.

A Drosophila model for mechanistic investigation of tau protein spread

Brain protein aggregates are a hallmark of neurodegenerative disease. Previous work indicates that specific protein components of these aggregates are toxic, including tau in Alzheimer's disease and related tauopathies. Increasing evidence also indicates that these toxic proteins traffic between cells in a prion-like fashion, thereby spreading pathology from one brain region to another. However, the mechanisms involved in trafficking are poorly understood. We therefore developed a transgenic Drosophila model to facilitate rapid evaluation of candidate tau trafficking modifiers. Our model uses the bipartite Q system to drive co-expression of tau and GFP in the fly eye. We find age-dependent tau spread into the brain, represented by detection of tau, but not GFP in the brain. We also found that tau trafficking was attenuated upon inhibition of the endocytic factor dynamin or the kinase glycogen synthase kinase-3β ( GSK-3β ). Further work revealed that dynamin promotes tau uptake in recipient tissues, whereas GSK-3β appears to promote tau spread via direct phosphorylation of tau. Our robust and flexible system will promote the identification of tau trafficking components involved in the pathogenesis of neurodegenerative diseases.

SUMMARY STATEMENT

The trafficking of toxic proteins in neurodegenerative disease is well-known but poorly understood. Our model will allow rapid and new insight into molecular mechanisms underlying this process.

Assessment of Efficacy and Safety of Zagotenemab: Results From PERISCOPE-ALZ, a Phase 2 Study in Early Symptomatic Alzheimer Disease

BACKGROUND AND OBJECTIVES

Zagotenemab (LY3303560), a monoclonal antibody that preferentially targets misfolded, extracellular, aggregated tau, was assessed in the PERISCOPE-ALZ phase 2 study to determine its ability to slow cognitive and functional decline relative to placebo in early symptomatic Alzheimer disease (AD).

METHODS

Participants were enrolled across 56 sites in North America and Japan. Key eligibility criteria included age of 60-85 years, Mini-Mental State Examination score of 20-28, and intermediate levels of brain tau on PET imaging. In this double-blind study, participants were equally randomized to 1,400 mg or 5,600 mg of zagotenemab, or placebo (IV infusion every 4 weeks for 100 weeks). The primary outcome was change on the Integrated AD Rating Scale (iADRS) assessed by a Bayesian Disease Progression model. Secondary measures include mixed model repeated measures analysis of additional cognitive and functional endpoints as well as biomarkers of AD pathology.

RESULTS

A total of 360 participants (mean age = 75.4 years; female = 52.8%) were randomized, and 218 completed the treatment period. Demographics and baseline characteristics were reasonably balanced among arms. The mean disease progression ratio (proportional decline in the treated vs placebo group) with 95% credible intervals for the iADRS was 1.10 (0.959-1.265) for the zagotenemab low-dose group and 1.05 (0.907-1.209) for the high-dose, where a ratio less than 1 favors the treatment group. Secondary clinical endpoint measures failed to show a drug-placebo difference in favor of zagotenemab. No treatment effect was demonstrated by flortaucipir PET, volumetric MRI, or neurofilament light chain (NfL) analyses. A dose-related increase in plasma phosphorylated tau181 and total tau was demonstrated. Zagotenemab treatment groups reported a higher incidence of adverse events (AEs) (85.1%) compared with the placebo group (74.6%). This difference was not attributable to any specific AE or category of AEs.

DISCUSSION

In participants with early symptomatic AD, zagotenemab failed to achieve significant slowing of clinical disease progression compared with placebo. Imaging biomarker and plasma NfL findings did not show evidence of pharmacodynamic activity or disease modification.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov: NCT03518073.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that for patients with early symptomatic AD, zagotenemab does not slow clinical disease progression.

Identification of retinal tau oligomers, citrullinated tau, and other tau isoforms in early and advanced AD and relations to disease status

Importance

This study identifies and quantifies diverse pathological tau isoforms in the retina of both early and advanced-stage Alzheimer's disease (AD) and determines their relationship with disease status.

Objective

A case-control study was conducted to investigate the accumulation of retinal neurofibrillary tangles (NFTs), paired helical filament (PHF)-tau, oligomeric tau (oligo-tau), hyperphosphorylated tau (p-tau), and citrullinated tau (Cit-tau) in relation to the respective brain pathology and cognitive dysfunction in mild cognitively impaired (MCI) and AD dementia patients versus normal cognition (NC) controls.

Design setting and participants

Eyes and brains from donors diagnosed with AD, MCI (due to AD), and NC were collected (n=75 in total), along with clinical and neuropathological data. Brain and retinal cross-sections-in predefined superior-temporal and inferior-temporal (ST/IT) subregions-were subjected to histopathology analysis or Nanostring GeoMx digital spatial profiling.

Main outcomes and measure

Retinal burden of NFTs (pretangles and mature tangles), PHF-tau, p-tau, oligo-tau, and Cit-tau was assessed in MCI and AD versus NC retinas. Pairwise correlations revealed associations between retinal and brain parameters and cognitive status.

Results

Increased retinal NFTs (1.8-fold, p=0.0494), PHF-tau (2.3-fold, p<0.0001), oligo-tau (9.1-fold, p<0.0001), CitR 209 -tau (4.3-fold, p<0.0001), pSer202/Thr205-tau (AT8; 4.1-fold, p<0.0001), and pSer396-tau (2.8-fold, p=0.0015) were detected in AD patients. Retinas from MCI patients showed significant increases in NFTs (2.0-fold, p=0.0444), CitR 209 -tau (3.5-fold, p=0.0201), pSer396-tau (2.6-fold, p=0.0409), and, moreover, oligo-tau (5.8-fold, p=0.0045). Nanostring GeoMx quantification demonstrated upregulated retinal p-tau levels in MCI patients at phosphorylation sites of Ser214 (2.3-fold, p=0.0060), Ser396 (1.8-fold, p=0.0052), Ser404 (2.4-fold, p=0.0018), and Thr231 (3.3-fold, p=0.0028). Strong correlations were found between retinal tau forms to paired-brain pathology and cognitive status: a) retinal oligo-tau vs. Braak stage (r=0.60, P=0.0002), b) retinal PHF-tau vs. ABC average score (r=0.64, P=0.0043), c) retinal pSer396-tau vs. brain NFTs (r=0.68, P<0.0001), and d) retinal pSer202/Thr205-tau vs. MMSE scores (r= -0.77, P=0.0089).

Conclusions and Relevance

This study reveals increases in immature and mature retinal tau isoforms in MCI and AD patients, highlighting their relationship with brain pathology and cognition. The data provide strong incentive to further explore retinal tauopathy markers that may be useful for early detection and monitoring of AD staging through noninvasive retinal imaging.

Extra-Virgin Olive Oil in Alzheimer's Disease: A Comprehensive Review of Cellular, Animal, and Clinical Studies

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by several pathological hallmarks, including the deposition of amyloid-β (Aβ) plaques, neurofibrillary tangles, blood-brain barrier (BBB) dysfunction, increased oxidative stress, and neuroinflammation. Current treatment options include monoclonal antibody drugs, acetylcholinesterase, and n-methyl-d-aspartate (NMDA) antagonists. Although those treatments provide some improvements in patients' quality of life, they fail to prevent or cure AD. Current research aims to identify novel targets and tools for AD prevention and modification. In this context, several studies showed the beneficial effect of the Mediterranean diet in the prevention and treatment of AD. One integral component of the Mediterranean diet is olive oil and extra-virgin olive oil (EVOO), which is high in phenolic compounds. EVOO and other olive-related phenolic compounds have been shown to reduce the risk of developing mild cognitive impairment (MCI) and AD. In this review, we discuss the mechanisms by which EVOO and phenolic compounds exert neuroprotective effects, including modulation of AD pathologies and promotion of cognitive health. Findings indicate that EVOO and its phenolic constituents influence key pathological processes of AD, such as Aβ aggregation, tau phosphorylation, and neuroinflammation, while also enhancing BBB integrity and reducing oxidative stress. The human studies cited reveal a consistent trend where the consumption of olive oil is associated with cognitive benefits and a decreased risk of AD and related dementias. In conclusion, EVOO and its phenolic compounds hold promising potential for the prevention and treatment of AD, representing a significant shift towards more effective strategies against this complex neurodegenerative disorder.

Early Diagnosis of Neurodegenerative Diseases: What Has Been Undertaken to Promote the Transition from PET to Fluorescence Tracers

Alzheimer's Disease (AD) and Parkinson's Disease (PD) represent two among the most frequent neurodegenerative diseases worldwide. A common hallmark of these pathologies is the misfolding and consequent aggregation of amyloid proteins into soluble oligomers and insoluble β-sheet-rich fibrils, which ultimately lead to neurotoxicity and cell death. After a hundred years of research on the subject, this is the only reliable histopathological feature in our hands. Since AD and PD are diagnosed only once neuronal death and the first symptoms have appeared, the early detection of these diseases is currently impossible. At present, there is no effective drug available, and patients are left with symptomatic and inconclusive therapies. Several reasons could be associated with the lack of effective therapeutic treatments. One of the most important factors is the lack of selective probes capable of detecting, as early as possible, the most toxic amyloid species involved in the onset of these pathologies. In this regard, chemical probes able to detect and distinguish among different amyloid aggregates are urgently needed. In this article, we will review and put into perspective results from ex vivo and in vivo studies performed on compounds specifically interacting with such early species. Following a general overview on the three different amyloid proteins leading to insoluble β-sheet-rich amyloid deposits (amyloid β1-42 peptide, Tau, and α-synuclein), a list of the advantages and disadvantages of the approaches employed to date is discussed, with particular attention paid to the translation of fluorescence imaging into clinical applications. Furthermore, we also discuss how the progress achieved in detecting the amyloids of one neurodegenerative disease could be leveraged for research into another amyloidosis. As evidenced by a critical analysis of the state of the art, substantial work still needs to be conducted. Indeed, the early diagnosis of neurodegenerative diseases is a priority, and we believe that this review could be a useful tool for better investigating this field.

Antiepileptic Drugs as Potential Dementia Prophylactics Following Traumatic Brain Injury

Seizures and other forms of neurovolatility are emerging as druggable prodromal mechanisms that link traumatic brain injury (TBI) to the progression of later dementias. TBI neurotrauma has both acute and long-term impacts on health, and TBI is a leading risk factor for dementias, including chronic traumatic encephalopathy and Alzheimer's disease. Treatment of TBI already considers acute management of posttraumatic seizures and epilepsy, and impressive efforts have optimized regimens of antiepileptic drugs (AEDs) toward that goal. Here we consider that expanding these management strategies could determine which AED regimens best prevent dementia progression in TBI patients. Challenges with this prophylactic strategy include the potential consequences of prolonged AED treatment and that a large subset of patients are refractory to available AEDs. Addressing these challenges is warranted because the management of seizure activity following TBI offers a rare opportunity to prevent the onset or progression of devastating dementias.

Alzheimer's Disease Immunotherapy: Current Strategies and Future Prospects

Alzheimer's disease (AD) is an extremely complex and heterogeneous pathology influenced by many factors contributing to its onset and progression, including aging, amyloid-beta (Aβ) plaques, tau fibril accumulation, inflammation, etc. Despite promising advances in drug development, there is no cure for AD. Although there have been substantial advancements in understanding the pathogenesis of AD, there have been over 200 unsuccessful clinical trials in the past decade. In recent years, immunotherapies have been at the forefront of these efforts. Immunotherapy alludes to the immunological field that strives to identify disease treatments via the enhancement, suppression, or induction of immune responses. Interestingly, immunotherapy in AD is a relatively new approach for non-infectious disease. At present, antibody therapy (passive immunotherapy) that targets anti-Aβ aimed to prevent the fibrillization of Aβ peptides and disrupt pre-existing fibrils is a predominant AD immunotherapy due to the continuous failure of active immunotherapy for AD. The most rational and safe strategies will be those targeting the toxic molecule without triggering an abnormal immune response, offering therapeutic advantages, thus making clinical trial design more efficient. This review offers a concise overview of immunotherapeutic strategies, including active and passive immunotherapy for AD. Our review encompasses approved methods and those presently under investigation in clinical trials, while elucidating the recent challenges, complications, successes, and potential treatments. Thus, immunotherapies targeting Aβ throughout the disease progression using a mutant oligomer-Aβ stimulated dendritic cell vaccine may offer a promising therapy in AD.

Nuclear face of Tau: an inside player in neurodegeneration

Tau (Tubulin associated unit) protein is a major hallmark of Alzheimer's disease (AD) and tauopathies. Tau is predominantly an axonal protein with a crucial role in the stabilization and dynamics of the microtubules. Since the discovery of Tau protein in 1975, research efforts were concentrated on the pathophysiological role of Tau protein in the context of the microtubules. Although, for more than three decades, different localizations of Tau protein have been discovered e.g., in the nuclear compartments. Discovery of the role of Tau protein in various cellular compartments especially in the nucleus opens up a new fold of complexity in tauopathies. Data from cellular models, animal models, and the human brain indicate that nuclear Tau is crucial for genome stability and to cope with cellular distress. Moreover, it's nature of nuclear translocation, its interactions with the nuclear DNA/RNA and proteins suggest it could play multiple roles in the nucleus. To comprehend Tau pathophysiology and efficient Tau-based therapies, there is an urgent need to understand whole repertoire of Tau species (nuclear and cytoplasmic) and their functional relevance. To complete the map of Tau repertoire, understanding of various species of Tau in the nucleus and cytoplasm, identification if specific transcripts of Tau, isoforms and post-translational modifications could foretell Tau's localizations and functions, and how they are modified in neurodegenerative diseases like AD, is urgently required. In this review, we explore the nuclear face of Tau protein, its nuclear localizations and functions and its linkage with Alzheimer's disease.

Untangling Tau: Molecular Insights into Neuroinflammation, Pathophysiology, and Emerging Immunotherapies

Neuroinflammation, a core pathological feature observed in several neurodegenerative diseases, including Alzheimer's disease (AD), is rapidly gaining attention as a target in understanding the molecular underpinnings of these disorders. Glial cells, endothelial cells, peripheral immune cells, and astrocytes produce a variety of pro-inflammatory mediators that exacerbate the disease progression. Additionally, microglial cells play a complex role in AD, facilitating the clearance of pathological amyloid-beta peptide (Aβ) plaques and aggregates of the tau protein. Tau proteins, traditionally associated with microtubule stabilization, have come under intense scrutiny for their perturbed roles in neurodegenerative conditions. In this narrative review, we focus on recent advances from molecular insights that have revealed aberrant tau post-translational modifications, such as phosphorylation and acetylation, serving as pathological hallmarks. These modifications also trigger the activation of CNS-resident immune cells, such as microglia and astrocytes substantially contributing to neuroinflammation. This intricate relationship between tau pathologies and neuroinflammation fosters a cascading impact on neural pathophysiology. Furthermore, understanding the molecular mechanisms underpinning tau's influence on neuroinflammation presents a frontier for the development of innovative immunotherapies. Neurodegenerative diseases have been relatively intractable to conventional pharmacology using small molecules. We further comprehensively document the many alternative approaches using immunotherapy targeting tau pathological epitopes and structures with a wide array of antibodies. Clinical trials are discussed using these therapeutic approaches, which have both promising and disappointing outcomes. Future directions for tau immunotherapies may include combining treatments with Aβ immunotherapy, which may result in more significant clinical outcomes for neurodegenerative diseases.

Nanoparticles loaded with natural medicines for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that disrupts cognitive function and severely affects the quality of life. Existing drugs only improve cognitive function and provide temporary relief of symptoms but do not stop or delay disease progression. Recently, natural medicines, especially Chinese herbal medicines, have gained attention in the treatment of AD due to their antioxidant, anti-inflammatory, and neuroprotective effects. However, conventional oral dosage forms lack brain specificity and have side effects that lead to poor patient compliance. Utilizing nanomedicine is a promising approach to improve brain specificity, bioavailability, and patient compliance. This review evaluates recent advances in the treatment of AD with nanoparticles containing various natural medicines. This review highlights that nanoparticles containing natural medicines are a promising strategy for the treatment of AD. It is believed that this technology can be translated into the clinic, thereby providing opportunities for AD patients to participate in social activities.

Safety, Tolerability, and Pharmacokinetics of Zagotenemab in Participants with Symptomatic Alzheimer's Disease: A Phase I Clinical Trial

Background

Zagotenemab (LY3303560), a monoclonal antibody, preferentially binds to extracellular, misfolded, aggregated tau that has been implicated in Alzheimer's disease (AD).

Objective

The goal of this study was to assess the safety and pharmacokinetics of multiple doses of zagotenemab in participants with AD.

Methods

This was a Phase Ib, multi-site, participant- and investigator-blind, placebo-controlled, parallel-group study in participants with mild cognitive impairment due to AD or mild to moderate AD. After screening, participants were randomized to zagotenemab 70 mg, 210 mg, or placebo every 4 weeks for up to 49 weeks and were followed up for 16 weeks.

Results

A total of 13 males and 9 females, aged 59 to 84 years, were dosed. No deaths occurred during this study. A total of 4 serious adverse events occurred in 2 participants who then discontinued the study. The most commonly reported (3 or more participants) treatment-emergent adverse events were sinus bradycardia, headache, fall, and bronchitis. The pharmacokinetics profile showed generally linear exposures across the dose range studied with a clearance of ~8 mL/h. The half-life of zagotenemab in serum was ~20 days. A dose-dependent increase in plasma tau was observed. No other significant pharmacodynamic differences were observed due to low dose levels and limited treatment duration.

Conclusions

No dose-limiting adverse events were observed with zagotenemab treatment. Pharmacokinetics of zagotenemab were typical for a monoclonal antibody. Meaningful pharmacodynamic differences were not observed.Clinicaltrials.gov: NCT03019536.

A New Perspective for the Treatment of Alzheimer's Disease: Exosome-like Liposomes to Deliver Natural Compounds and RNA Therapies

With the increment of the aging population in recent years, neurodegenerative diseases exert a major global disease burden, essentially as a result of the lack of treatments that stop the disease progression. Alzheimer's Disease (AD) is an example of a neurodegenerative disease that affects millions of people globally, with no effective treatment. Natural compounds have emerged as a viable therapy to fill a huge gap in AD management, and in recent years, mostly fueled by the COVID-19 pandemic, RNA-based therapeutics have become a hot topic in the treatment of several diseases. Treatments of AD face significant limitations due to the complex and interconnected pathways that lead to their hallmarks and also due to the necessity to cross the blood-brain barrier. Nanotechnology has contributed to surpassing this bottleneck in the treatment of AD by promoting safe and enhanced drug delivery to the brain. In particular, exosome-like nanoparticles, a hybrid delivery system combining exosomes and liposomes' advantageous features, are demonstrating great potential in the treatment of central nervous system diseases.

Aging, NRF2, and TAU: A Perfect Match for Neurodegeneration?

Although the trigger for the neurodegenerative disease process is unknown, the relevance of aging stands out as a major risk for the development of neurodegeneration. In this review, we highlighted the relationship between the different cellular mechanisms that occur as a consequence of aging and transcription factor nuclear factor erythroid-2-related factor 2 (NRF2) and the connection with the TAU protein. We focused on the relevance of NRF2 in the main processes involved in neurodegeneration and associated with aging, such as genomic instability, protein degradation systems (proteasomes/autophagy), cellular senescence, and stem cell exhaustion, as well as inflammation. We also analyzed the effect of aging on TAU protein levels and its aggregation and spread process. Finally, we investigated the interconnection between NRF2 and TAU and the relevance of alterations in the NRF2 signaling pathway in both primary and secondary tauopathies. All these points highlight NRF2 as a possible therapeutic target for tauopathies.

Apitherapy in Post-Ischemic Brain Neurodegeneration of Alzheimer's Disease Proteinopathy: Focus on Honey and Its Flavonoids and Phenolic Acids

Neurodegeneration of the brain after ischemia is a major cause of severe, long-term disability, dementia, and mortality, which is a global problem. These phenomena are attributed to excitotoxicity, changes in the blood-brain barrier, neuroinflammation, oxidative stress, vasoconstriction, cerebral amyloid angiopathy, amyloid plaques, neurofibrillary tangles, and ultimately neuronal death. In addition, genetic factors such as post-ischemic changes in genetic programming in the expression of amyloid protein precursor, β-secretase, presenilin-1 and -2, and tau protein play an important role in the irreversible progression of post-ischemic neurodegeneration. Since current treatment is aimed at preventing symptoms such as dementia and disability, the search for causative therapy that would be helpful in preventing and treating post-ischemic neurodegeneration of Alzheimer's disease proteinopathy is ongoing. Numerous studies have shown that the high contents of flavonoids and phenolic acids in honey have antioxidant, anti-inflammatory, anti-apoptotic, anti-amyloid, anti-tau protein, anticholinesterase, serotonergic, and AMPAK activities, influencing signal transmission and neuroprotective effects. Notably, in many preclinical studies, flavonoids and phenolic acids, the main components of honey, were also effective when administered after ischemia, suggesting their possible use in promoting recovery in stroke patients. This review provides new insight into honey's potential to prevent brain ischemia as well as to ameliorate damage in advanced post-ischemic brain neurodegeneration.

The Adult Neurogenesis Theory of Alzheimer's Disease

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

MAPT allele and haplotype frequencies in Nigerian Africans: population distribution and association with Parkinson's disease risk and age at onset

BACKGROUND

The microtubule-associated protein tau ( MAPT ) gene is critical because of its putative role in the causal pathway of neurodegenerative diseases including Parkinson's disease (PD). However, there is a lack of clarity regarding the link between the main H1 haplotype and risk of PD. Inconsistencies in reported association may be driven by genetic variability in the populations studied to date. Data on MAPT haplotype frequencies in the general population and association studies exploring the role of MAPT haplotypes in conferring PD risk in black Africans are lacking.

OBJECTIVES

To determine the frequencies of MAPT haplotypes and explore the role of the H1 haplotype as a risk factor for PD risk and age at onset in Nigerian Africans.

METHODS

The haplotype and genotype frequencies of MAPT rs1052553 were analysed using PCR-based KASP™ in 907 individuals with PD and 1,022 age-matched neurologically normal controls from the Nigeria Parkinson's Disease Research (NPDR) network cohort. Clinical data related to PD included age at study, age at onset, and disease duration.

RESULTS

The frequency of the main MAPT H1 haplotype in this cohort was 98.7% in individuals with PD, and 99.1% in healthy controls (p=0.19). The H2 haplotype was present in 41/1929 (2.1%) of the cohort (PD - 1.3%; Controls - 0.9%; p=0.24). The most frequent MAPT genotype was H1H1 (PD - 97.5%, controls - 98.2%). The H1 haplotype was not associated with PD risk after accounting for gender and age at onset (Odds ratio for H1/H1 vs H1/H2 and H2/H2: 0.68 (95% CI:0.39-1.28); p=0.23).

CONCLUSIONS

Our findings support previous studies that report a low frequency of the MAPT H2 haplotype in black ancestry Africans, but document its occurrence in the Nigerian population (2.1%). In this cohort of black Africans with PD, the MAPT H1 haplotype was not associated with an increased risk or age at onset of PD.

Alzheimer's Disease and Alzheimer's Disease-Related Dementias in African Americans: Focus on Caregivers

Alzheimer's disease (AD) and Alzheimer's Disease-Related Dementias (ADRD) are chronic illnesses that are highly prevalent in African Americans (AA). AD and ADRD are caused by multiple factors, such as genetic mutations, modifiable and non-modifiable risk factors, and lifestyle. Histopathological, morphological, and cellular studies revealed how multiple cellular changes are implicated in AD and ADRD, including synaptic damage, inflammatory responses, hormonal imbalance, mitochondrial abnormalities, and neuronal loss, in addition to the accumulation of amyloid beta and phosphorylated tau in the brain. The contributions of race, ethnicity, location and socioeconomic status all have a significant impact on the care and support services available to dementia patients. Furthermore, disparities in health care are entangled with social, economic, and environmental variables that perpetuate disadvantages among different groups, particularly African Americans. As such, it remains important to understand how various racial and ethnic groups perceive, access, and experience health care. Considering that the mounting data shows AA may be more susceptible to AD than white people, the demographic transition creates significant hurdles in providing adequate care from family caregivers. Furthermore, there is growing recognition that AD and ADRD pose a significant stress on AA caregivers compared to white people. In this review, we examine the current literature on racial disparities in AD and ADRD, particularly concerning AA caregivers.

TGF-β1 signalling in Alzheimer's pathology and cytoskeletal reorganization: a specialized Tau perspective

Microtubule-associated protein, Tau has been implicated in Alzheimer's disease for its detachment from microtubules and formation of insoluble intracellular aggregates within the neurons. Recent findings have suggested the expulsion of Tau seeds in the extracellular domain and their prion-like propagation between neurons. Transforming Growth Factor-β1 (TGF-β1) is a ubiquitously occurring cytokine reported to carry out immunomodulation and neuroprotection in the brain. TGF-β-mediated regulation occurs at the level of neuronal survival and differentiation, glial activation (astrocyte and microglia), amyloid production-distribution-clearance and neurofibrillary tangle formation, all of which contributes to Alzheimer's pathophysiology. Its role in the reorganization of cytoskeletal architecture and remodelling of extracellular matrix to facilitate cellular migration has been well-documented. Microglia are the resident immune sentinels of the brain responsible for surveying the local microenvironment, migrating towards the beacon of pertinent damage and phagocytosing the cellular debris or patho-protein deposits at the site of insult. Channelizing microglia to target extracellular Tau could be a good strategy to combat the prion-like transmission and seeding problem in Alzheimer's disease. The current review focuses on reaffirming the role of TGF-β1 signalling in Alzheimer's pathology and cytoskeletal reorganization and considers utilizing the approach of TGF-β-triggered microglia-mediated targeting of extracellular patho-protein, Tau, as a possible potential strategy to combat Alzheimer's disease.

New Pathways Identify Novel Drug Targets for the Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable, progressive neurodegenerative disorder. AD is a complex and multifactorial disease that is responsible for 60-80% of dementia cases. Aging, genetic factors, and epigenetic changes are the main risk factors for AD. Two aggregation-prone proteins play a decisive role in AD pathogenesis: β-amyloid (Aβ) and hyperphosphorylated tau (pTau). Both of them form deposits and diffusible toxic aggregates in the brain. These proteins are the biomarkers of AD. Different hypotheses have tried to explain AD pathogenesis and served as platforms for AD drug research. Experiments demonstrated that both Aβ and pTau might start neurodegenerative processes and are necessary for cognitive decline. The two pathologies act in synergy. Inhibition of the formation of toxic Aβ and pTau aggregates has been an old drug target. Recently, successful Aβ clearance by monoclonal antibodies has raised new hopes for AD treatments if the disease is detected at early stages. More recently, novel targets, e.g., improvements in amyloid clearance from the brain, application of small heat shock proteins (Hsps), modulation of chronic neuroinflammation by different receptor ligands, modulation of microglial phagocytosis, and increase in myelination have been revealed in AD research.

Linking Diabetes to Alzheimer's Disease: Potential Roles of Glucose Metabolism and Alpha-Glucosidase

Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) are more prevalent with ageing and cause a substantial global socio-economic burden. The biology of these two conditions is well elaborated, but whether AD and type 2 DM arise from coincidental roots in ageing or are linked by pathophysiological mechanisms remains unclear. Research findings involving animal models have identified mechanisms shared by both AD and type 2 DM. Deposition of β-amyloid peptides and formation of intracellular neurofibrillary tangles are pathological hallmarks of AD. Type 2 DM, on the other hand, is a metabolic disorder characterised by hyperglycaemia and insulin resistance. Several studies show that improving type 2 DM can delay or prevent the development of AD, and hence, prevention and control of type 2 DM may reduce the risk of AD later in life. Alpha-glucosidase is an enzyme that is commonly associated with hyperglycaemia in type 2 DM. However, it is uncertain if this enzyme may play a role in the progression of AD. This review explores the experimental evidence that depicts the relationship between dysregulation of glucose metabolism and AD. We also delineate the links between alpha-glucosidase and AD and the potential role of alpha-glucosidase inhibitors in treating AD.

Critical appraisal on mitochondrial dysfunction in Alzheimer's disease

It is widely recognized that Alzheimer's disease (AD) is a common type of progressive neurodegenerative disorder that results in cognitive impairment over time. Approximately 152 million cases of AD are predicted to be reported by 2050. Amyloid plaques and tau proteins are two major hallmarks of AD which can be seen under electron microscope. Mitochondria plays a vital role in the pathogenesis of AD and mitochondria disruption leads to mitochondrial DNA (mtDNA) dysfunction, alteration of mitochondria dependent Ca2+ homeostasis, copper dysfunction, immune cell dysfunction, etc. In this review, we try to cover all the mechanisms related with mitochondrial dysfunction and mitochondrial pathogenesis that may help us to better understand AD as well as open a new era for therapeutic target of AD and treat this progressive disease.

Linking the Amyloid, Tau, and Mitochondrial Hypotheses of Alzheimer's Disease and Identifying Promising Drug Targets

Damage or loss of brain cells and impaired neurochemistry, neurogenesis, and synaptic and nonsynaptic plasticity of the brain lead to dementia in neurodegenerative diseases, such as Alzheimer's disease (AD). Injury to synapses and neurons and accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles are considered the main morphological and neuropathological features of AD. Age, genetic and epigenetic factors, environmental stressors, and lifestyle contribute to the risk of AD onset and progression. These risk factors are associated with structural and functional changes in the brain, leading to cognitive decline. Biomarkers of AD reflect or cause specific changes in brain function, especially changes in pathways associated with neurotransmission, neuroinflammation, bioenergetics, apoptosis, and oxidative and nitrosative stress. Even in the initial stages, AD is associated with Aβ neurotoxicity, mitochondrial dysfunction, and tau neurotoxicity. The integrative amyloid-tau-mitochondrial hypothesis assumes that the primary cause of AD is the neurotoxicity of Aβ oligomers and tau oligomers, mitochondrial dysfunction, and their mutual synergy. For the development of new efficient AD drugs, targeting the elimination of neurotoxicity, mutual potentiation of effects, and unwanted protein interactions of risk factors and biomarkers (mainly Aβ oligomers, tau oligomers, and mitochondrial dysfunction) in the early stage of the disease seems promising.

Towards a Mechanistic Model of Tau-Mediated Pathology in Tauopathies: What Can We Learn from Cell-Based In Vitro Assays?

Tauopathies are a group of neurodegenerative diseases characterized by the hyperphosphorylation and deposition of tau proteins in the brain. In Alzheimer’s disease, and other related tauopathies, the pattern of tau deposition follows a stereotypical progression between anatomically connected brain regions. Increasing evidence suggests that tau behaves in a “prion-like” manner, and that seeding and spreading of pathological tau drive progressive neurodegeneration. Although several advances have been made in recent years, the exact cellular and molecular mechanisms involved remain largely unknown. Since there are no effective therapies for any tauopathy, there is a growing need for reliable experimental models that would provide us with better knowledge and understanding of their etiology and identify novel molecular targets. In this review, we will summarize the development of cellular models for modeling tau pathology. We will discuss their different applications and contributions to our current understanding of the “prion-like” nature of pathological tau.

Probiotics: Protecting Our Health from the Gut

The gut microbiota (GM) comprises billions of microorganisms in the human gastrointestinal tract. This microbial community exerts numerous physiological functions. Prominent among these functions is the effect on host immunity through the uptake of nutrients that strengthen intestinal cells and cells involved in the immune response. The physiological functions of the GM are not limited to the gut, but bidirectional interactions between the gut microbiota and various extraintestinal organs have been identified. These interactions have been termed interorganic axes by several authors, among which the gut-brain, gut-skin, gut-lung, gut-heart, and gut-metabolism axes stand out. It has been shown that an organism is healthy or in homeostasis when the GM is in balance. However, altered GM or dysbiosis represents a critical factor in the pathogenesis of many local and systemic diseases. Therefore, probiotics intervene in this context, which, according to various published studies, allows balance to be maintained in the GM, leading to an individual's good health.

CX3CR1 deficiency aggravates amyloid driven neuronal pathology and cognitive decline in Alzheimer's disease

BACKGROUND

Despite its identification as a key checkpoint regulator of microglial activation in Alzheimer's disease, the overarching role of CX3CR1 signaling in modulating mechanisms of Aβ driven neurodegeneration, including accumulation of hyperphosphorylated tau is not well understood.

METHODOLOGY

Accumulation of soluble and insoluble Aβ species, microglial activation, synaptic dysregulation, and neurodegeneration is investigated in 4- and 6-month old 5xFAD;Cx3cr1+/+ and 5xFAD;Cx3cr1-/- mice using immunohistochemistry, western blotting, transcriptomic and quantitative real time PCR analyses of purified microglia. Flow cytometry based, in-vivo Aβ uptake assays are used for characterization of the effects of CX3CR1-signaling on microglial phagocytosis and lysosomal acidification as indicators of clearance of methoxy-X-04+ fibrillar Aβ. Lastly, we use Y-maze testing to analyze the effects of Cx3cr1 deficiency on working memory.

RESULTS

Disease progression in 5xFAD;Cx3cr1-/- mice is characterized by increased deposition of filamentous plaques that display defective microglial plaque engagement. Microglial Aβ phagocytosis and lysosomal acidification in 5xFAD;Cx3cr1-/- mice is impaired in-vivo. Interestingly, Cx3cr1 deficiency results in heighted accumulation of neurotoxic, oligomeric Aβ, along with severe neuritic dystrophy, preferential loss of post-synaptic densities, exacerbated tau pathology, neuronal loss and cognitive impairment. Transcriptomic analyses using cortical RNA, coupled with qRT-PCR using purified microglia from 6 month-old mice indicate dysregulated TGFβ-signaling and heightened ROS metabolism in 5xFAD;Cx3cr1-/- mice. Lastly, microglia in 6 month-old 5xFAD;Cx3cr1-/- mice express a 'degenerative' phenotype characterized by increased levels of Ccl2, Ccl5, Il-1β, Pten and Cybb along with reduced Tnf, Il-6 and Tgfβ1 mRNA.

CONCLUSIONS

Cx3cr1 deficiency impairs microglial uptake and degradation of fibrillar Aβ, thereby triggering increased accumulation of neurotoxic Aβ species. Furthermore, loss of Cx3cr1 results in microglial dysfunction typified by dampened TGFβ-signaling, increased oxidative stress responses and dysregulated pro-inflammatory activation. Our results indicate that Aβ-driven microglial dysfunction in Cx3cr1-/- mice aggravates tau hyperphosphorylation, neurodegeneration, synaptic dysregulation and impairs working memory.

The function of gut microbiota in immune-related neurological disorders: a review

This review provides an overview of the importance of microbiota in the regulation of gut–brain communication in immune-related neurological disorders. The gastrointestinal (GI) tract hosts a diverse abundance of microbiota, referred to as gut microbiota. The gut microbiota plays a role in the maintenance of GI tract homeostasis and is likely to have multiple effects on brain development and function. The bidirectional communication between the gut microbiota and the brain is termed the microbiota–gut–brain axis. This communication between the intestine and the brain appears to affect human health and behavior, as certain animal studies have demonstrated the association between alterations in the gut microbiota and neurological disorders. Most insights about the microbiota–gut–brain axis come from germ-free animal models, which reveal the importance of gut microbiota in neural function. To date, many studies have observed the impact of the gut microbiota in patients with neurological disorders. Although many studies have investigated the microbiota–gut–brain axis, there are still limitations in translating this research to humans given the complexities of the relationship between the gut microbiota and the brain. In this review, we discuss emerging evidence of how the microbiota–gut–brain axis regulates brain development and function through biological networks, as well as the possible contribution of the microbiota–gut–brain axis in immune-related neurological disorders.

The Role of Extracellular Matrix Components in the Spreading of Pathological Protein Aggregates

Several neurodegenerative diseases are characterized by the accumulation of aggregated misfolded proteins. These pathological agents have been suggested to propagate in the brain via mechanisms similar to that observed for the prion protein, where a misfolded variant is transferred from an affected brain region to a healthy one, thereby inducing the misfolding and/or aggregation of correctly folded copies. This process has been characterized for several proteins, such as α-synuclein, tau, amyloid beta (Aβ) and less extensively for huntingtin and TDP-43. α-synuclein, tau, TDP-43 and huntingtin are intracellular proteins, and their aggregates are located in the cytosol or nucleus of neurons. They have been shown to spread between cells and this event occurs, at least partially, via secretion of these protein aggregates in the extracellular space followed by re-uptake. Conversely, Aβ aggregates are found mainly extracellularly, and their spreading occurs in the extracellular space between brain regions. Due to the inherent nature of their spreading modalities, these proteins are exposed to components of the extracellular matrix (ECM), including glycans, proteases and core matrix proteins. These ECM components can interact with or process pathological misfolded proteins, potentially changing their properties and thus regulating their spreading capabilities. Here, we present an overview of the documented roles of ECM components in the spreading of pathological protein aggregates in neurodegenerative diseases with the objective of identifying the current gaps in knowledge and stimulating further research in the field. This could potentially lead to the identification of druggable targets to slow down the spreading and/or progression of these pathologies.

A Tau Pathogenesis-Based Network Pharmacology Approach for Exploring the Protections of Chuanxiong Rhizoma in Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common cause of neurodegenerative dementia and one of the top medical concerns worldwide. Currently, the approved drugs to treat AD are effective only in treating the symptoms, but do not cure or prevent AD. Although the exact causes of AD are not understood, it is recognized that tau aggregation in neurons plays a key role. Chuanxiong Rhizoma (CR) has been widely reported as effective for brain diseases such as dementia. Thus, we explored the protections of CR in AD by a tau pathogenesis–based network pharmacology approach. According to ultra-HPLC with triple quadrupole mass spectrometry data and Lipinski’s rule of five, 18 bioactive phytochemicals of CR were screened out. They were shown corresponding to 127 tau pathogenesis–related targets, among which VEGFA, IL1B, CTNNB1, JUN, ESR1, STAT3, APP, BCL2L1, PTGS2, and PPARG were identified as the core ones. We further analyzed the specific actions of CR-active phytochemicals on tau pathogenesis from the aspects of tau aggregation and tau-mediated toxicities. It was shown that neocnidilide, ferulic acid, coniferyl ferulate, levistilide A, Z-ligustilide, butylidenephthalide, and caffeic acid can be effective in reversing tau hyperphosphorylation. Neocnidilide, senkyunolide A, butylphthalide, butylidenephthalide, Z-ligustilide, and L-tryptophan may be effective in promoting lysosome-associated degradation of tau, and levistilide A, neocnidilide, ferulic acid, L-tryptophan, senkyunolide A, Z-ligustilide, and butylidenephthalide may antagonize tau-mediated impairments of intracellular transport, axon and synaptic damages, and neuron death (especially apoptosis). The present study suggests that acting on tau aggregation and tau-mediated toxicities is part of the therapeutic mechanism of CR against AD.

Bezafibrate Exerts Neuroprotective Effects in a Rat Model of Sporadic Alzheimer’s Disease

Bezafibrate, a pan-peroxisome proliferator-activated receptor (PPAR) agonist, reportedly attenuated tau pathology in a transgenic mouse model of primary tauopathy. Since tau pathology is a neuropathological hallmark of Alzheimer’s disease (AD), bezafibrate may be a potential drug for the treatment of AD. However, no study has investigated its effects in AD models. Thus, we aimed to evaluate whether bezafibrate has neuroprotective effects in a sporadic AD model induced by streptozotocin (STZ) intracerebroventricular (ICV) injection. Rats were administered STZ-ICV (3 mg/kg) followed by bezafibrate (50 mg/kg/day, intraperitoneal) for 4 weeks. Behavior tests and positron emission tomography (PET) were performed to evaluate longitudinal changes in cognitive function, tau pathology, and cerebral glucose metabolism. Immunofluorescence staining was performed to assess neuronal survival and microglial accumulation. STZ-ICV administration induced significant cognitive impairment and substantial neuronal loss, tau pathology, glucose hypometabolism, and microgliosis in the cortex and hippocampus, while bezafibrate effectively attenuated these abnormalities. This study demonstrated that bezafibrate has long-lasting neuroprotective effects in a sporadic AD model. Our data indicate that the neuroprotective effects of bezafibrate might be associated with its ability to ameliorate tau pathology, brain glucose hypometabolism, and neuroinflammation. These findings suggest that bezafibrate is a potential multi-target drug candidate for the treatment of AD.

Revisiting the grammar of Tau aggregation and pathology formation: how new insights from brain pathology are shaping how we study and target Tauopathies

Converging evidence continues to point towards Tau aggregation and pathology formation as central events in the pathogenesis of Alzheimer's disease and other Tauopathies. Despite significant advances in understanding the morphological and structural properties of Tau fibrils, many fundamental questions remain about what causes Tau to aggregate in the first place. The exact roles of cofactors, Tau post-translational modifications, and Tau interactome in regulating Tau aggregation, pathology formation, and toxicity remain unknown. Recent studies have put the spotlight on the wide gap between the complexity of Tau structures, aggregation, and pathology formation in the brain and the simplicity of experimental approaches used for modeling these processes in research laboratories. Embracing and deconstructing this complexity is an essential first step to understanding the role of Tau in health and disease. To help deconstruct this complexity and understand its implication for the development of effective Tau targeting diagnostics and therapies, we firstly review how our understanding of Tau aggregation and pathology formation has evolved over the past few decades. Secondly, we present an analysis of new findings and insights from recent studies illustrating the biochemical, structural, and functional heterogeneity of Tau aggregates. Thirdly, we discuss the importance of adopting new experimental approaches that embrace the complexity of Tau aggregation and pathology as an important first step towards developing mechanism- and structure-based therapies that account for the pathological and clinical heterogeneity of Alzheimer's disease and Tauopathies. We believe that this is essential to develop effective diagnostics and therapies to treat these devastating diseases.

Altered protein secretion in Batten disease

The neuronal ceroid lipofuscinoses (NCLs), collectively known as Batten disease, are a group of neurological diseases that affect all ages and ethnicities worldwide. There are 13 different subtypes of NCL, each caused by a mutation in a distinct gene. The NCLs are characterized by the accumulation of undigestible lipids and proteins in various cell types. This leads to progressive neurodegeneration and clinical symptoms including vision loss, progressive motor and cognitive decline, seizures, and premature death. These diseases have commonly been characterized by lysosomal defects leading to the accumulation of undigestible material but further research on the NCLs suggests that altered protein secretion may also play an important role. This has been strengthened by recent work in biomedical model organisms, including Dictyostelium discoideum, mice, and sheep. Research in D. discoideum has reported the extracellular localization of some NCL-related proteins and the effects of NCL-related gene loss on protein secretion during unicellular growth and multicellular development. Aberrant protein secretion has also been observed in mammalian models of NCL, which has allowed examination of patient-derived cerebrospinal fluid and urine for potential diagnostic and prognostic biomarkers. Accumulated evidence links seven of the 13 known NCL-related genes to protein secretion, suggesting that altered secretion is a common hallmark of multiple NCL subtypes. This Review highlights the impact of altered protein secretion in the NCLs, identifies potential biomarkers of interest and suggests that future work in this area can provide new therapeutic insight.

Summary: This Review discusses work in different model systems and humans, examining the impact of altered protein secretion in the neuronal ceroid lipofuscinoses group of diseases to provide novel therapeutic insights.

Inflammatory Cascade in Alzheimer's Disease Pathogenesis: A Review of Experimental Findings

Alzheimer’s disease (AD) is the leading cause of dementia worldwide. Most AD patients develop the disease in late life, named late onset AD (LOAD). Currently, the most recognized explanation for AD pathology is the amyloid cascade hypothesis. It is assumed that amyloid beta (Aβ) aggregation and deposition are critical pathogenic processes in AD, leading to the formation of amyloid plaques, as well as neurofibrillary tangles, neuronal cell death, synaptic degeneration, and dementia. In LOAD, the causes of Aβ accumulation and neuronal loss are not completely clear. Importantly, the blood–brain barrier (BBB) disruption seems to present an essential role in the induction of neuroinflammation and consequent AD development. In addition, we propose that the systemic inflammation triggered by conditions like metabolic diseases or infections are causative factors of BBB disruption, coexistent inflammatory cascade and, ultimately, the neurodegeneration observed in AD. In this regard, the use of anti-inflammatory molecules could be an interesting strategy to treat, delay or even halt AD onset and progression. Herein, we review the inflammatory cascade and underlying mechanisms involved in AD pathogenesis and revise the anti-inflammatory effects of compounds as emerging therapeutic drugs against AD.