Tau-induced neurodegeneration: mechanisms and targets

Mitophagy in Alzheimer's Disease: A Bibliometric Analysis from 2007 to 2022

Background

The investigation of mitophagy in Alzheimer's disease (AD) remains relatively underexplored in bibliometric analysis.

Objective

To delve into the progress of mitophagy, offering a comprehensive overview of research trends and frontiers for researchers.

Methods

Basic bibliometric information, targets, and target-drug-clinical trial-disease extracted from publications identified in the Web of Science Core Collection from 2007 to 2022 were assessed using bibliometric software.

Results

The study encompassed 5,146 publications, displaying a consistent 16-year upward trajectory. The United States emerged as the foremost contributor in publications, with the Journal of Alzheimer's Disease being the most prolific journal. P. Hemachandra Reddy, George Perry, and Xiongwei Zhu are the top 3 most prolific authors. PINK1 and Parkin exhibited an upward trend in the last 6 years. Keywords (e.g., insulin, aging, epilepsy, tauopathy, and mitochondrial quality control) have recently emerged as focal points of interest within the past 3 years. "Mitochondrial dysfunction" is among the top terms in disease clustering. The top 10 drugs/molecules (e.g., curcumin, insulin, and melatonin) were summarized, accompanied by their clinical trials and related targets.

Conclusions

This study presents a comprehensive overview of the mitophagy research landscape in AD over the past 16 years, underscoring mitophagy as an emerging molecular mechanism and a crucial focal point for potential drug in AD. This study pioneers the inclusion of targets and their correlations with drugs, clinical trials, and diseases in bibliometric analysis, providing valuable insights and inspiration for scholars and readers of JADR interested in understanding the potential mechanisms and clinical trials in AD.

Cadmium-promoted thyroid hormones disruption mediates ROS, inflammation, Aβ and Tau proteins production, gliosis, spongiosis and neurodegeneration in rat basal forebrain

Cadmium (Cd) produces cognition decline following single and repeated treatment, although the complete mechanisms are still unrevealed. Basal forebrain (BF) cholinergic neurons innervate the cortex and hippocampus, regulating cognition. Cd single and repeated exposure induced BF cholinergic neuronal loss, partly through thyroid hormones (THs) disruption, which may cause the cognition decline observed following Cd exposure. However, the mechanisms through which THs disruption mediate this effect remain unknown. To research the possible mechanisms through which Cd-induced THs deficiency may mediate BF neurodegeneration, Wistar male rats were treated with Cd for 1- (1 mg/kg) or 28-days (0.1 mg/kg) with or without triiodothyronine (T3, 40 μg/kg/day). Cd exposure promoted neurodegeneration, spongiosis, gliosis and several mechanisms related to these alterations (increased H₂0₂, malondialdehyde, TNF-α, IL-1β, IL-6, BACE1, Aβ and phosphorylated-Tau levels, and decreased phosphorylated-AKT and phosphorylated-GSK-3β levels). T3 supplementation partially reversed the effects observed. Our results show that Cd induces several mechanisms that may be responsible for the neurodegeneration, spongiosis and gliosis observed in the rats' BF, which are partially mediated by a reduction in THs levels. These data may help to explain the mechanisms through which Cd induces BF neurodegeneration, possibly leading to the cognitive decline observed, providing new therapeutic tools to prevent and treat these damages.

Deregulated Transcription and Proteostasis in Adult mapt Knockout Mouse

Transcriptomics and phosphoproteomics were carried out in the cerebral cortex of B6.Cg-Mapttm1(EGFP)Klt (tau knockout: tau-KO) and wild-type (WT) 12 month-old mice to learn about the effects of tau ablation. Compared with WT mice, tau-KO mice displayed reduced anxiety-like behavior and lower fear expression induced by aversive conditioning, whereas recognition memory remained unaltered. Cortical transcriptomic analysis revealed 69 downregulated and 105 upregulated genes in tau-KO mice, corresponding to synaptic structures, neuron cytoskeleton and transport, and extracellular matrix components. RT-qPCR validated increased mRNA levels of col6a4, gabrq, gad1, grm5, grip2, map2, rab8a, tubb3, wnt16, and an absence of map1a in tau-KO mice compared with WT mice. A few proteins were assessed with Western blotting to compare mRNA expression with corresponding protein levels. Map1a mRNA and protein levels decreased. However, β-tubulin III and GAD1 protein levels were reduced in tau-KO mice. Cortical phosphoproteomics revealed 121 hypophosphorylated and 98 hyperphosphorylated proteins in tau-KO mice. Deregulated phosphoproteins were categorized into cytoskeletal (n = 45) and membrane proteins, including proteins of the synapses and vesicles, myelin proteins, and proteins linked to membrane transport and ion channels (n = 84), proteins related to DNA and RNA metabolism (n = 36), proteins connected to the ubiquitin-proteasome system (UPS) (n = 7), proteins with kinase or phosphatase activity (n = 21), and 22 other proteins related to variegated pathways such as metabolic pathways, growth factors, or mitochondrial function or structure. The present observations reveal a complex altered brain transcriptome and phosphoproteome in tau-KO mice with only mild behavioral alterations.

Binding Parameters of [11C]MPC-6827, a Microtubule-Imaging PET Radiopharmaceutical in Rodents

Impairment and/or destabilization of neuronal microtubules (MTs) resulting from hyper-phosphorylation of the tau proteins is implicated in many pathologies, including Alzheimer's disease (AD), Parkinson's disease and other neurological disorders. Increasing scientific evidence indicates that MT-stabilizing agents protect against the deleterious effects of neurodegeneration in treating AD. To quantify these protective benefits, we developed the first brain-penetrant PET radiopharmaceutical, [11C]MPC-6827, for in vivo quantification of MTs in rodent and nonhuman primate models of AD. Mechanistic insights revealed from recently reported studies confirm the radiopharmaceutical's high selectivity for destabilized MTs. To further translate it to clinical settings, its metabolic stability and pharmacokinetic parameters must be determined. Here, we report in vivo plasma and brain metabolism studies establishing the radiopharmaceutical-binding constants of [11C]MPC-6827. Binding constants were extrapolated from autoradiography experiments; pretreatment with a nonradioactive MPC-6827 decreased the brain uptake >70%. It exhibited ideal binding characteristics (typical of a CNS radiopharmaceutical) including LogP (2.9), Kd (15.59 nM), and Bmax (11.86 fmol/mg). Most important, [11C]MPC-6827 showed high serum and metabolic stability (>95%) in rat plasma and brain samples.

Optimal anti-amyloid-beta therapy for Alzheimer’s disease via a personalized mathematical model

With the recent approval by the FDA of the first disease-modifying drug for Alzheimer’s Disease (AD), personalized medicine will be increasingly important for appropriate management and counseling of patients with AD and those at risk. The growing availability of clinical biomarker data and data-driven computational modeling techniques provide an opportunity for new approaches to individualized AD therapeutic planning. In this paper, we develop a new mathematical model, based on AD cognitive, cerebrospinal fluid (CSF) and MRI biomarkers, to provide a personalized optimal treatment plan for individuals. This model is parameterized by biomarker data from the AD Neuroimaging Initiative (ADNI) cohort, a large multi-institutional database monitoring the natural history of subjects with AD and mild cognitive impairment (MCI). Optimal control theory is used to incorporate time-varying treatment controls and side-effects into the model, based on recent clinical trial data, to provide a personalized treatment regimen with anti-amyloid-beta therapy. In-silico treatment studies were conducted on the approved treatment, aducanumab, as well as on another promising anti-amyloid-beta therapy under evaluation, donanemab. Clinical trial simulations were conducted over both short-term (78 weeks) and long-term (10 years) periods with low-dose (6 mg/kg) and high-dose (10 mg/kg) regimens for aducanumab, and a single-dose regimen (1400 mg) for donanemab. Results confirm those of actual clinical trials showing a large and sustained effect of both aducanumab and donanemab on amyloid beta clearance. The effect on slowing cognitive decline was modest for both treatments, but greater for donanemab. This optimal treatment computational modeling framework can be applied to other single and combination treatments for both prediction and optimization, as well as incorporate new clinical trial data as it becomes available.

Although personalized therapy will likely play a major role in the appropriate management and counseling of patients with AD in the future, there are currently no clinically utilized markers that can easily distinguish among the different clinical trajectories of individual patients, nor provide personalized treatment plans. The mathematical model developed in this paper, based on current theories of AD pathophysiology, enables prediction of disease trajectory under a natural history scenario in individual patients with a clinical diagnosis of AD or late MCI (L-MCI) using current clinically validated biomarkers. This analytical approach also provides an in-silico method to simulate and optimize treatment at an individual level, thereby accelerating the development of personalized treatments. By accessing longitudinal biomarker data from the ADNI database, we validate our computational modeling approach to identify patient-specific disease trajectories and optimize individual treatments for two anti-amyloid-beta therapies, aducanumab and donanemab, in proof-of-principle clinical trial simulations. Simulation results show that, with the optimization, the effect on slowing cognitive decline is greater for doneneumab than aducanumab for a 10-year treatment regimen, although the effect on amyloid beta clearance is similar for both drugs.

Investigation of the role of prolines 232/233 in RTPPK motif in tau protein aggregation: An in vitro study

Disease-related tau protein in Alzheimer's disease is hyperphosphorylated and aggregates into neurofibrillary tangles. The cis-proline isomer of the pSer/Thr-Pro sequence has been proposed to act as a precursor of aggregation ('Cistauosis' hypothesis), but this aggregation scheme is not yet entirely accepted. Hence to investigate isomer-specific-aggregation of tau, proline residues at the RTPPK motif were replaced by alanine residues (with permanent trans configuration) employing genetic engineering methods. RTPAK, RTAPK, and RTAAK mutant variants of tau were generated, and their in vitro aggregation propensity was investigated using multi-spectroscopic techniques. Besides, the cell toxicity of oligomers/fibrils was analyzed and compared to those of the wild-type (WT) tau. Analyses of mutant variants have shown to be in agreement (to some degree) to the theory of the 'cistauosis' hypothesis. The results showed that the trans isomer in the 232-rd residue (P232A mutant rather than P233A) had reduced aggregation propensity. However, this study did not illustrate any statistically significant difference between the wild and the mutant protein aggregations concerning cell toxicity.

New insights into the role and mechanisms of ginsenoside Rg1 in the management of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disorder in the elderly characterized by memory loss and cognitive dysfunction. The pathogenesis of AD is complex. One-targeted anti-AD drugs usually fail to delay AD progression. Traditional Chinese medicine records have documented the use of the roots of Panax ginseng (ginseng roots) and its prescriptions to treat dementia. Ginsenoside Rg1, the main ginsenoside component of ginseng roots, exhibits a certain therapeutic effect in the abovementioned diseases, suggesting its potential in the management of AD. Therefore, we combed the pathogenesis of AD and currently used anti-AD drugs, and reviewed the availability, pharmacokinetics, and pharmaceutic studies of ginsenoside Rg1. This review summarizes the therapeutic effects and mechanisms of ginsenoside Rg1 and its deglycosylated derivatives in AD in vivo and in vitro. The main mechanisms include improvement in Aβ and Tau pathologies, regulation of synaptic function and intestinal microflora, and reduction of inflammation, oxidative stress, and apoptosis. The underlying mechanisms mainly involve the regulation of PKC, MAPK, PI3K/Akt, CDK5, GSK-3β, BDNF/TrkB, PKA/CREB, FGF2/Akt, p21WAF1/CIP1, NF-κB, NLRP1, TLR3, and TLR4 signaling pathways. As the effects and underlying mechanisms of ginsenoside Rg1 on AD have not been systematically reviewed, we have provided a comprehensive review and shed light on the future directions in the utilization of ginsenoside Rg1 and ginseng roots as well as the development of anti-AD drugs.

Research trends of the neuroimaging in aphasia: A bibliometric analysis and visualization analysis from 2004 to 2021

Objectives

To review the current research status of the neuroimaging of aphasia, and reveal the hotspots and frontiers of research in this field.

Methods

We searched articles related to the neuroimaging research on aphasia since Web of Science (WOS) database construction and extracted the data. CiteSpace and VOSviewer were used for the country/institution analysis, journal analysis, discipline analysis, burst keyword analysis and cited-reference cluster analysis.

Results

Of the studies retrieved from WOS, 2922 studies that related to the neuroimaging of aphasia were screened and finally included 2799 articles for research. The United States of America and University of California San Francisco were the main countries and institutions in this field. Brain had the highest impact factor in both published and cited journals. Through the discipline and topic analysis of this field, the most common category was Neurosciences and Neurology. The keyword with the strongest citation strength was “functional connectivity,” and the recent burst keywords were “functional connectivity” and “network.” The co-citation network showed seven clusters greater than 100. Among the top 5 clusters, the most recently formed cluster, Cluster #2 (progressive supranuclear palsy), had an average year of 2017. The literature in the top 5 clusters mainly focused on 3 aspects, specifically, the discovery of language processing models, injury and recovery mechanisms of post-stroke aphasia (PSA), and diagnosis of primary progressive aphasia (PPA) variants.

Conclusion

The results of this bibliometric study revealed the following three research hotspots in the neuroimaging of aphasia: clarifying the connotation of the most recognized language processing model, the dual-stream model, exploring the injury mechanism based on the dual-stream model and the recovery mechanism involving the left and right hemispheres of PSA, and determining the diagnostic criteria for PPA variants. A major research trend is to combine new neuroimaging technology, such as PET tracer technology, to realize the visual presentation of disease-specific proteins to improve the pathological diagnostic criteria of PPA variants. Accordingly, a visualized analysis of literature that uses CiteSpace provides a more rapid, repeatable and flexible method, which is more conducive to capturing research hotspots and emerging trends.

Insulin Deficiency Increases Sirt2 Level in Streptozotocin-Treated Alzheimer's Disease-Like Mouse Model: Increased Sirt2 Induces Tau Phosphorylation Through ERK Activation

Accumulating evidence suggests that insulin deficiency is a risk factor for Alzheimer’s disease (AD); however, the underlying molecular mechanisms are not completely understood. Here, we investigated the effects of insulin deficiency on AD-like pathologies using an insulin-deficient amyloid-β (Aβ) precursor protein (APP) transgenic mouse model (Tg2576 mice). Female Tg2576 mice were injected intraperitoneally with streptozotocin (STZ) to induce insulin deficiency, and their body weights, serum glucose levels, and serum insulin levels were evaluated. STZ-treated mice showed exacerbated Aβ accumulation, tau hyperphosphorylation, glial activation, neuroinflammation, and increased Sirt2 protein levels in the brain, as determined by two-dimensional gel electrophoresis (2-DE) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS) and Western blotting. Furthermore, our in vitro experiments revealed that insulin depletion or interleukin-6 treatment increased Sirt2 protein levels in both Neuro2a and Neuro2a-P301L cells. The overexpression of Sirt2 in these cells induced tau hyperphosphorylation through extracellular signal-regulated kinase (ERK) activation. Conversely, Sirt2 knockdown reversed tau hyperphosphorylation in these cells. We showed for the first time that Sirt2 is upregulated in the brains of STZ-treated Tg2576 mice and is involved in tau phosphorylation through ERK activation. Our findings suggest that Sirt2 is a promising therapeutic target for the treatment of AD.

Tau protein quantification in skin biopsies differentiates tauopathies from alpha-synucleinopathies

Abnormal accumulation of microtubule-associated protein tau (τ) is a characteristic feature of atypical parkinsonisms with tauopathies such as Progressive Supranuclear Palsy (PSP) and Corticobasal Degeneration (CBD). However, pathological τ has also been observed in α-synucleinopathies like Parkinson's Disease (PD) and Multiple System Atrophy (MSA). Based on the involvement of peripheral nervous system in several neurodegenerative diseases, we characterized and compared τ expression in skin biopsies of patients clinically diagnosed with PD, MSA, PSP, CBD, and in healthy control subjects. In all groups, τ protein was detected along both somatosensory and autonomic nerve fibers in the epidermis and dermis by immunofluorescence. We found by western blot the presence of mainly two different bands at 55 and 70 KDa, co-migrating with 0N4R/1N3R and 2N4R isoforms, respectively. At the RNA level, the main transcript variants were 2N and 4R, and both resulted more expressed in PSP/CBD by real-time PCR. ELISA assay demonstrated significantly higher levels of total τ protein in skin lysates of PSP/CBD compared to the other groups. Multivariate regression analysis and ROC curves analysis of τ amount at both sites showed a clinical association with tauopathies diagnosis and high diagnostic value for PSP/CBD vs. PD (sensitivity 90%, specificity 69%) and PSP/CBD vs. MSA (sensitivity 90%, specificity 86%). τ protein increase correlated with cognitive impairment in PSP/CBD. This study is a comprehensive characterization of τ in the human cutaneous peripheral nervous system in physiologic and pathologic conditions. The differential expression of τ, both at transcript and protein levels, suggests that skin biopsy, an easily accessible and minimally invasive exam, can help in discriminating among different neurodegenerative diseases.

The Role of Post-Translational Modifications on the Structure and Function of Tau Protein

Involving addition of chemical groups or protein units to specific residues of the target protein, post-translational modifications (PTMs) alter the charge, hydrophobicity, and conformation of a protein, which in tune influences protein function, protein - protein interaction, and protein aggregation. While the occurrence of PTMs is dynamic and subject to regulations, conformational disorder of the target protein facilitates PTMs. The microtubule-associated protein tau is a typical intrinsically disordered protein that undergoes a variety of PTMs including phosphorylation, acetylation, ubiquitination, methylation, and oxidation. Accumulated evidence shows that these PTMs play a critical role in regulating tau-microtubule interaction, tau localization, tau degradation and aggregation, and reinforces the correlation between tau PTMs and pathogenesis of neurodegenerative disease. Here, we review tau PTMs with an emphasis on their influence on tau structure. With available biophysical characterization results, we describe how PTMs induce conformational changes in tau monomer and regulate tau aggregation. Compared to functional analysis of tau PTMs, biophysical characterization of tau PTMs is lagging. While it is challenging, characterizing the specific effects of PTMs on tau conformation and interaction is indispensable to unravel the tau PTM code.

Epigenetics of Neurotrauma

Epigenetic changes have been linked to a host of disease states. Besides the physiological function of epigenetic changes in regulating cellular function, recent data indicates that key changes in epigenetic activity also play an important pathophysiologic role following neurotrauma specifically. Such manifestations occur through the activation or silencing of different genes. Histone methylation has emerged as a critical component of this process and can be selectively modulated after injury. Pre-clinical studies have resulted in key discoveries regarding specific methylation sites of interest. This focused review highlights some of these early findings and their relationship to clinical outcomes. These findings suggest areas of future investigation and discovery in the quest to develop ideal biomarkers and methods to utilize them in developing therapeutic interventions.

The Clinical Significance of Cerebrospinal Fluid Reticulon 4 (RTN4) Levels in the Differential Diagnosis of Neurodegenerative Diseases

Neurodegenerative diseases (NDs) belong to the top global causes of mortality. Diagnostic approaches to improve early diagnosis and differentiation of these diseases are constantly being sought. Therefore, we aimed to assess the cerebrospinal fluid (CSF) concentrations of Reticulon 4 (RTN4) in patients with neurodegenerative diseases and evaluate the potential clinical usefulness of this protein. RTNs are transmembrane proteins mediating neuroanatomical plasticity and functional recovery after central nervous system injury or diseases. According to our best knowledge, this is the first investigation providing the data concerning the dynamic of CSF RTN4 protein levels in patients with different NDs. Methods: Overall, 77 newly diagnosed patients with neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and multiple sclerosis (MS), as well as 21 controls, were enrolled in the study. The CSF concentrations of tested proteins were assessed using immunological assays. Results: We revealed significantly higher CSF RTN4A levels in patients with AD, PD, and MS in comparison to the controls. Moreover, the comparative analysis of RTN4 concentration between different neurodegenerative diseases revealed the highest concentration of RTN4A in AD patients and a statistically significant difference between AD vs. PD, and AD vs. MS groups. The increased CSF level of the protein correlated with Tau, and pTau181 proteins in AD as well as in PD patients. Conclusions: Our study presents a previously not identified clinical utility of RTN4 in the differential diagnosis of neurodegenerative diseases.

The Structure Biology of Tau and Clue for Aggregation Inhibitor Design

Tau is a microtubule-associated protein that is mainly expressed in central and peripheral nerve systems. Tau binds to tubulin and regulates assembly and stabilization of microtubule, thus playing a critical role in neuron morphology, axon development and navigation. Tau is highly stable under normal conditions; however, there are several factors that can induce or promote aggregation of tau, forming neurofibrillary tangles. Neurofibrillary tangles are toxic to neurons, which may be related to a series of neurodegenerative diseases including Alzheimer's disease. Thus, tau is widely accepted as an important therapeutic target for neurodegenerative diseases. While the monomeric structure of tau is highly disordered, the aggregate structure of tau is formed by closed packing of β-stands. Studies on the structure of tau and the structural transition mechanism provide valuable information on the occurrence, development, and therapy of tauopathies. In this review, we summarize recent progress on the structural investigation of tau and based on which we discuss aggregation inhibitor design.

Epibrassinolide prevents tau hyperphosphorylation via GSK3β inhibition in vitro and improves Caenorhabditis elegans lifespan and motor deficits in combination with roscovitine

Glycogen synthase kinase 3β (GSK3β) is considered an important element of glycogen metabolism; however, it has many other regulatory roles. Changes in the GSK3β signaling mechanism have been associated with various disorders, such as Alzheimer's disease (AD), type II diabetes, and cancer. Although the effects of GSK3β inhibitors on reducing the pathological effects of AD have been described, an effective inhibitor has not yet been developed. Epibrassinolide (EBR), a brassinosteroid (BR), is structurally similar to mammalian steroid hormones. Our studies have shown that EBR has an inhibitory effect on GSK3β in different cell lines. Roscovitine (ROSC), a cyclin-dependent kinase (CDK) inhibitor, has also been identified as a potential GSK3 inhibitor. Within the scope of this study, we propose that EBR and/or ROSC might have mechanistic action in AD models. To test this hypothesis, we used in vitro models and Caenorhabditis elegans (C. elegans) AD strains. Finally, EBR treatment successfully protected cells from apoptosis and increased the inhibitory phosphorylation of GSK3β. In addition, EBR and/or ROSC treatment had a positive effect on the survival rates of C. elegans strains. More interestingly, the paralysis phenotype of the C. elegans AD model due to Aβ42 toxicity was prevented by EBR and/or ROSC. Our findings suggest that EBR and ROSC administration have neuroprotective effects on both in vitro and C. elegans models via inhibitory GSK3β phosphorylation at Ser9.

Antisense Oligonucleotide-Mediated Reduction of HDAC6 Does Not Reduce Tau Pathology in P301S Tau Transgenic Mice

Acetylation of tau protein is dysregulated in Alzheimer's Disease (AD). It has been proposed that acetylation of specific sites in the KXGS motif of tau can regulate phosphorylation of nearby residues and reduce the propensity of tau to aggregate. Histone deacetylase 6 (HDAC6) is a cytoplasmic enzyme involved in deacetylation of multiple targets, including tau, and it has been suggested that inhibition of HDAC6 would increase tau acetylation at the KXGS motifs and thus may present a viable therapeutic approach to treat AD. To directly test the contribution of HDAC6 to tau pathology, we intracerebroventricularly injected an antisense oligonucleotide (ASO) directed against HDAC6 mRNA into brains of P301S tau mice (PS19 model), which resulted in a 70% knockdown of HDAC6 protein in the brain. Despite a robust decrease in levels of HDAC6, no increase in tau acetylation was observed. Additionally, no change of tau phosphorylation or tau aggregation was detected upon the knockdown of HDAC6. We conclude that HDAC6 does not impact tau pathology in PS19 mice.

Impact of Tau on Neurovascular Pathology in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most prevalent cause of dementia. The main cerebral histological hallmarks are represented by parenchymal insoluble deposits of amyloid beta (Aβ plaques) and neurofibrillary tangles (NFT), intracellular filamentous inclusions of tau, a microtubule-associated protein. It is well-established that cerebrovascular dysfunction is an early feature of AD pathology, but the detrimental mechanisms leading to blood vessel impairment and the associated neurovascular deregulation are not fully understood. In 90% of AD cases, Aβ deposition around the brain vasculature, known as cerebral amyloid angiopathy (CAA), alters blood brain barrier (BBB) essential functions. While the effects of vascular Aβ accumulation are better documented, the scientific community has only recently started to consider the impact of tau on neurovascular pathology in AD. Emerging compelling evidence points to transmission of neuronal tau to different brain cells, including astrocytes, as well as to the release of tau into brain interstitial fluids, which may lead to perivascular neurofibrillar tau accumulation and toxicity, affecting vessel architecture, cerebral blood flow (CBF), and vascular permeability. BBB integrity and functionality may therefore be impacted by pathological tau, consequentially accelerating the progression of the disease. Tau aggregates have also been shown to induce mitochondrial damage: it is known that tau impairs mitochondrial localization, distribution and dynamics, alters ATP and reactive oxygen species production, and compromises oxidative phosphorylation systems. In light of this previous knowledge, we postulate that tau can initiate neurovascular pathology in AD through mitochondrial dysregulation. In this review, we will explore the literature investigating tau pathology contribution to the malfunction of the brain vasculature and neurovascular unit, and its association with mitochondrial alterations and caspase activation, in cellular, animal, and human studies of AD and tauopathies.

Relationship Between Oxidative Stress, Tau Level and Antioxidant Mechanisms of the KEAP-1/NRF-2/HO-1 in Children with Hydrocephalus

BACKGROUND

Hydrocephalus is a complex neurologic disorder which has a widespread impact on the central nervous system, and a multifactor disease which effect the CSF dynamics and causes severe neurological impairments in children. The pathophysiology of hydrocephalus is not fully understood. However, increasing evidence suggests that oxidative stress may be an important factor in the pathogenesis of hydrocephalus.

OBJECTIVE

The purpose of this study is to investigate the relationship of KEAP-1/NRF-2/HO-1 pathway, one of the main regulators of the antioxidant system in the hydrocephalus pathology, on oxidative stress and tau protein level.

METHODS

The study included 32 patients with hydrocephalus and 32 healthy controls. KEAP-1, NRF-2, HO-1, TAU, and MPO levels are measured using ELISA method TAS, TOS, Total THIOL colorimetric method.

RESULTS

KEAP-1, TAS, Total THIOL levels were found significantly low in the hydrocephalus group compared to the control group. Nevertheless, it is identified in the hydrocephalus group that the NRF-2, HO-1, TAU, MPO, TOS, and OSI levels were significantly elevated.

CONCLUSION

In conclusion, although KEAP-1/NRF-2/HO-1 pathway is activated in patients with hydrocephalus, it is identified that the antioxidant defense system is insufficient, and ultimately leads to elevated oxidative stress. The elevation in the tau level may be an indicator of oxidative stress induced neurodegenerative damage.

The Crosstalk Between Pathological Tau Phosphorylation and Mitochondrial Dysfunction as a Key to Understanding and Treating Alzheimer's Disease

Alzheimer's disease (AD) is the most common progressive neurodegenerative disorder. A defining hallmark of the AD brain is the presence of intraneuronal neurofibrillary tangles (NFTs) which are made up of abnormally modified tau, with aberrant phosphorylation being the most studied posttranslational modification (PTM). Although the accumulation of tau as NFTs is an invariant feature of the AD brain, it has become evident that these insoluble aggregates are likely not the primary pathogenic form of tau, rather soluble forms of tau with abnormal PTMs are the mediators of toxicity. The most prevalent PTM on tau is phosphorylation, with the abnormal modification of specific residues on tau playing a key role in its toxicity. Even though it is widely accepted that tau with aberrant PTMs facilitates neurodegeneration, the precise cellular mechanisms remain unknown. Nonetheless, there is an evolving conceptual framework that an important contributing factor may be selective pathological tau species compromising mitochondrial biology. Understanding the mechanisms by which tau with site-specific PTM impacts mitochondria is crucial for understanding the role tau plays in AD. Here, we provide a brief introduction to tau and its phosphorylation and function in a physiological context, followed by a discussion of the impact of soluble phosphorylated tau species on neuronal processes in general and mitochondria more specifically. We also discuss how therapeutic strategies that attenuate pathological tau species in combination with treatments that improve mitochondrial biology could be a potential therapeutic avenue to mitigate disease progression in AD and other tauopathies.

Tau Protein and Its Role in Blood-Brain Barrier Dysfunction

The blood-brain barrier (BBB) plays a crucial role in maintaining the specialized microenvironment of the central nervous system (CNS). In aging, the stability of the BBB declines and the permeability increases. The list of CNS pathologies involving BBB dysfunction is growing. The opening of the BBB and subsequent infiltration of serum components to the brain can lead to a host of processes resulting in progressive synaptic, neuronal dysfunction, and detrimental neuroinflammatory changes. Such processes have been implicated in different diseases, including vascular dementia, stroke, Alzheimer's disease (AD), Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, hypoxia, ischemia, and diabetes mellitus. The BBB damage is also observed in tauopathies that lack amyloid-β overproduction, suggesting a role for tau in BBB damage. Tauopathies represent a heterogeneous group of around 20 different neurodegenerative diseases characterized by abnormal deposition of the MAPT in cells of the nervous system. Neuropathology of tauopathies is defined as intracellular accumulation of neurofibrillary tangles (NFTs) consisting of aggregated hyper- and abnormal phosphorylation of tau protein and neuroinflammation. Disruption of the BBB found in tauopathies is driven by chronic neuroinflammation. Production of pro-inflammatory signaling molecules such as cytokines, chemokines, and adhesion molecules by glial cells, neurons, and endothelial cells determine the integrity of the BBB and migration of immune cells into the brain. The inflammatory processes promote structural changes in capillaries such as fragmentation, thickening, atrophy of pericytes, accumulation of laminin in the basement membrane, and increased permeability of blood vessels to plasma proteins. Here, we summarize the knowledge about the role of tau protein in BBB structural and functional changes.

Understanding the Pathophysiological Actions of Tau Oligomers: A Critical Review of Current Electrophysiological Approaches

Tau is a predominantly neuronal protein that is normally bound to microtubules, where it acts to modulate neuronal and axonal stability. In humans, pathological forms of tau are implicated in a range of diseases that are collectively known as tauopathies. Kinases and phosphatases are responsible for maintaining the correct balance of tau phosphorylation to enable axons to be both stable and labile enough to function properly. In the early stages of tauopathies, this balance is interrupted leading to dissociation of tau from microtubules. This leaves microtubules prone to damage and phosphorylated tau prone to aggregation. Initially, phosphorylated tau forms oligomers, then fibrils, and ultimately neurofibrillary tangles (NFTs). It is widely accepted that the initial soluble oligomeric forms of tau are probably the most pathologically relevant species but there is relatively little quantitative information to explain exactly what their toxic effects are at the individual neuron level. Electrophysiology provides a valuable tool to help uncover the mechanisms of action of tau oligomers on synaptic transmission within single neurons. Understanding the concentration-, time-, and neuronal compartment-dependent actions of soluble tau oligomers on neuronal and synaptic properties are essential to understanding how best to counteract its effects and to develop effective treatment strategies. Here, we briefly discuss the standard approaches used to elucidate these actions, focusing on the advantages and shortcomings of the experimental procedures. Subsequently, we will describe a new approach that addresses specific challenges with the current methods, thus allowing real-time toxicity evaluation at the single-neuron level.

Reduced TUBA1A Tubulin Causes Defects in Trafficking and Impaired Adult Motor Behavior

Newly born neurons express high levels of TUBA1A α-tubulin to assemble microtubules for neurite extension and to provide tracks for intracellular transport. In the adult brain, Tuba1a expression decreases dramatically. A mouse that harbors a loss-of-function mutation in the gene encoding TUBA1A (Tuba1a^ND/+) allows us to ask whether TUBA1A is important for the function of mature neurons. α-Tubulin levels are about half of wild type in juvenile Tuba1a^ND/+ brains, but are close to normal in older animals. In postnatal day (P)0 cultured neurons, reduced TUBA1A allows for assembly of less microtubules in axons resulting in more pausing during organelle trafficking. While Tuba1a^ND/+ mouse behavior is indistinguishable from wild-type siblings at weaning, Tuba1a^ND/+ mice develop adult-onset ataxia. Neurons important for motor function in Tuba1a^ND/+ remain indistinguishable from wild-type with respect to morphology and number and display no evidence of axon degeneration. Tuba1a^ND/+ neuromuscular junction (NMJ) synapses are the same size as wild-type before the onset of ataxia, but are reduced in size in older animals. Together, these data indicate that the TUBA1A-rich microtubule tracks that are assembled during development are essential for mature neuron function and maintenance of synapses over time.

Tau Related Pathways as a Connecting Link between Epilepsy and Alzheimer's Disease

Emerging findings point toward an important interconnection between epilepsy and Alzheimer's disease (AD) pathogenesis. Patients with epilepsy (PWE) commonly exhibit cognitive impairment similar to AD patients, who in turn are at a higher risk of developing epilepsy compared to age-matched controls. To date, no disease-modifying treatment strategy is available for either epilepsy or AD, reflecting an immediate need for exploring common molecular targets, which can delineate a possible mechanistic link between epilepsy and AD. This review attempts to disentangle the interconnectivity between epilepsy and AD pathogenesis via the crucial contribution of Tau protein. Tau protein is a microtubule-associated protein (MAP) that has been implicated in the pathophysiology of both epilepsy and AD. Hyperphosphorylation of Tau contributes to the different forms of human epilepsy and inhibition of the same exerted seizure inhibitions and altered disease progression in a range of animal models. Moreover, Tau-protein-mediated therapy has demonstrated promising outcomes in experimental models of AD. In this review, we discuss how Tau-related mechanisms might present a link between the cause of seizures in epilepsy and cognitive disruption in AD. Untangling this interconnection might be instrumental in designing novel therapies that can minimize epileptic seizures and cognitive deficits in patients with epilepsy and AD.

Nuclear Tau, p53 and Pin1 Regulate PARN-Mediated Deadenylation and Gene Expression

While nuclear tau plays a role in DNA damage response (DDR) and chromosome relaxation, the mechanisms behind these functions are not fully understood. Here, we show that tau forms complex(es) with factors involved in nuclear mRNA processing such as tumor suppressor p53 and poly(A)-specific ribonuclease (PARN) deadenylase. Tau induces PARN activity in different cellular models during DDR, and this activation is further increased by p53 and inhibited by tau phosphorylation at residues implicated in neurological disorders. Tau's binding factor Pin1, a mitotic regulator overexpressed in cancer and depleted in Alzheimer's disease (AD), also plays a role in the activation of nuclear deadenylation. Tau, Pin1 and PARN target the expression of mRNAs deregulated in AD and/or cancer. Our findings identify novel biological roles of tau and toxic effects of hyperphosphorylated-tau. We propose a model in which factors involved in cancer and AD regulate gene expression by interactions with the mRNA processing machinery, affecting the transcriptome and suggesting insights into alternative mechanisms for the initiation and/or developments of these diseases.

Insight into the Structure of the "Unstructured" Tau Protein

Combining structural proteomics experimental data with computational methods is a powerful tool for protein structure prediction. Here, we apply a recently developed approach for de novo protein structure determination based on the incorporation of short-distance crosslinking data as constraints in discrete molecular dynamics simulations (CL-DMD), for the determination of the conformational ensemble of tau protein in solution. The predicted structures were in agreement with surface modification and long-distance crosslinking data. Tau in solution was found as an ensemble of rather compact globular conformations with distinct topology, inter-residue contacts, and a number of transient secondary-structure elements. Regions important for pathological aggregation consistently were found to contain β strands. The determined structures are compatible with the tau protein in solution being a molten globule at near-ground state with persistent residual structural features which we were able to capture by CL-DMD. The predicted structure may facilitate an understanding of the misfolding and oligomerization pathways of the tau protein.

Normal and Pathological Tau Uptake Mediated by M1/M3 Muscarinic Receptors Promotes Opposite Neuronal Changes

The microtubule associated protein tau is mainly found in the cell’s cytosol but recently it was also shown in the extracellular space. In neurodegenerative diseases, like Alzheimer’s disease (AD), pathological tau spreads from neuron to neuron enhancing neurodegeneration. Here, we show that HEK293 cells and neurons in culture uptake extracellular normal and pathological Tau. Muscarinic receptor antagonists atropine and pirenzepine block 80% this uptake. CHO cells do not express these receptors therefore cannot uptake tau, unless transfected with M1 and/or M3 receptor. These results strongly suggest that muscarinic receptors mediate this process. Uptake of normal tau in neurons enhances neuronal process formation but a pseudophosphorylated form of tau (pathological human tau, PH-Tau) disrupts them and accumulates in the somatodendritic compartment. AD hyperphosphorylated tau (AD P-Tau) has similar effects as PH-Tau on cultured neurons. Addition of either PH-Tau or AD P-tau to neuronal cultures induced microglial activation. In conclusion, uptake of extracellular tau is mediated by muscarinic receptors with opposite effects: normal tau stabilizes neurites; whereas pathological tau disrupts this process leading to neurodegeneration.

Level of education mitigates the impact of tau pathology on neuronal function

PURPOSE

Using PET imaging in a group of patients with Alzheimer's disease (AD), we investigated whether level of education, a proxy for resilience, mitigates the harmful impact of tau pathology on neuronal function.

METHODS

We included 38 patients with mild-to-moderate AD (mean age 67 ± 7 years, mean MMSE score 24 ± 4, mean years of education 14 ± 4; 20 men, 18 women) in whom a [¹⁸F]AV-1451 scan (a measure of tau pathology) and an [¹⁸F]FDG scan (a measure of neuronal function) were available. The preprocessed PET scans were z-transformed using templates for [¹⁸F]AV-1451 and [¹⁸F]FDG from healthy controls, and subsequently thresholded at a z-score of ≥3.0, representing an one-tailed p value of 0.001. Next, three volumes were computed in each patient: the tau-specific volume (tau pathology without neuronal dysfunction), the FDG-specific volume (neuronal dysfunction without tau pathology), and the overlap volume (tau pathology and neuronal dysfunction). Mean z-scores and volumes were extracted and used as dependent variables in regression analysis with years of education as predictor, and age and MMSE score as covariates.

RESULTS

Years of education were positively associated with tau-specific volume (β = 0.362, p = 0.022), suggesting a lower impact of tau pathology on neuronal function in patients with higher levels of education. Concomitantly, level of education was positively related to tau burden in the overlap volume (β = 0.303, p = 0.036) implying that with higher levels of education more tau pathology is necessary to induce neuronal dysfunction.

CONCLUSION

In patients with higher levels of education, tau pathology is less paralleled by regional and remote neuronal dysfunction. The data suggest that early life-time factors such as level of education support resilience mechanisms, which ameliorate AD-related effects later in life.

The impact of curcumin and its modified formulations on Alzheimer's disease

Alzheimer's disease (AD) is a major health problem worldwide, with no effective treatment approach. Curcumin is the main ingredient of turmeric traditionally used in Asian medicine. Several experimental studies have indicated the protective effect of curcumin and its novel formulations in AD. Curcumin has antioxidant, anti-inflammatory and neurotrophic activities, proposing a strong potential to prevent neurodegenerative diseases. However, there are no sufficient clinical trials to confirm curcumin use in AD patients. Low bioavailability following oral administration of curcumin limits its usage in human. The present study was designed to gather the effects of curcumin and its modified formulations in human and experimental models of AD.

The Link Between Tau and Insulin Signaling: Implications for Alzheimer's Disease and Other Tauopathies

The microtubule-associated protein tau (MAPT) is mainly identified as a tubulin binding protein essential for microtubule dynamics and assembly and for neurite outgrowth. However, several other possible functions for Tau remains to be investigated. Insulin signaling is important for synaptic plasticity and memory formation and therefore is essential for proper brain function. Tau has recently been characterized as an important regulator of insulin signaling, with evidence linking Tau to brain and peripheral insulin resistance and beta cell dysfunction. In line with this notion, the hypothesis of Tau pathology as a key trigger of impaired insulin sensitivity and secretion has emerged. Conversely, insulin resistance can also favor Tau dysfunction, resulting in a vicious cycle of these events. In this review article, we discuss recent evidence linking Tau pathology, insulin resistance and insulin deficiency. We further highlight the deleterious consequences of Tau pathology-induced insulin resistance to the brain and/or peripheral tissues, suggesting that these are key events mediating cognitive decline in Alzheimer’s disease (AD) and other tauopathies.

Tau protein function: The mechanical exploration of axonal transport disorder caused by persistent pressure in dorsal root ganglia

Objective

We analyzed the function of Tau protein to explore the underlying mechanism of axonal transport disorder caused by persistent pressure in the dorsal root ganglia (DRG).

Methods

Wistar rats were divided into the sham operated group, the control group and the experimental group. The Wistar rat model of continuous compression of DRG was used for further investigation. DRG neurons were extracted and cultured, and the protein content was detected using bicinchoninic acid method. Western blotting and immunofluorescence assays were performed to detect the protein content. Intraperitoneal injection of lithium chloride was performed for interaction with Tau. The results were then analyzed statistically.

Results

After 2 weeks of sustained pressure, the expression level of Tau₃₉₆ increased by 33%, while Tau₄₀₄ increased by 25% in the DRG of the experimental group (p < 0.05). The expression level of PSD‐95 in the DRG decreased by 15% (p < 0.05), while the expression of vGluT1, vGluT3 and vAchT decreased significantly in the DRG of the experimental group (p < 0.05). There was no significant difference in the expression of vGluT2 and vGAT among the three groups (p > 0.05). After intervention with lithium chloride, the expression of phosphorylated Tau at the above sites decreased in varying degrees compared with the model group. The expression level of Tau₄₀₄ was reduced by 55%, and that of Tau₁₉₉ by 60% in the DRG of the experimental group.

Conclusion

Chronic compression of DRG and hypoxia caused phosphorylation of Tau in axons and inhibition of PSD‐95, and the function of the synaptic glutamic acid vesicle is defective in the synapse. This process is crucial in the development and progression of axonal transport dysfunction induced by chronic DRG compression, and phosphorylation of Tau plays a substantial role in this process.

Proteomics Analysis Reveals the Implications of Cytoskeleton and Mitochondria in the Response of the Rat Brain to Starvation

Long-term starvation provokes a metabolic response in the brain to adapt to the lack of nutrient intake and to maintain the physiology of this organ. Here, we study the changes in the global proteomic profile of the rat brain after a seven-day period of food deprivation, to further our understanding of the biochemical and cellular mechanisms underlying the situations without food. We have used two-dimensional electrophoresis followed by mass spectrometry (2D-MS) in order to identify proteins differentially expressed during prolonged food deprivation. After the comparison of the protein profiles, 22 brain proteins were found with altered expression. Analysis by peptide mass fingerprinting and MS/MS (matrix-assisted laser desorption-ionization-time of flight mass spectrometer, MALDI-TOF/TOF) enabled the identification of 14 proteins differentially expressed that were divided into 3 categories: (1) energy catabolism and mitochondrial proteins; (2) chaperone proteins; and (3) cytoskeleton, exocytosis, and calcium. Changes in the expression of six proteins, identified by the 2D-MS proteomics procedure, were corroborated by a nanoliquid chromatography-mass spectrometry proteomics procedure (nLC-MS). Our results show that long-term starvation compromises essential functions of the brain related with energetic metabolism, synapsis, and the transmission of nervous impulse.

Acetylation as a major determinant to microtubule-dependent autophagy: Relevance to Alzheimer's and Parkinson disease pathology

Protein post-translational modifications (PTMs) that potentiate protein aggregation have been implicated in several neurological disorders, including Alzheimer's (AD) and Parkinson's disease (PD). In fact, Tau and alpha-synuclein (ASYN) undergo several PTMs potentiating their aggregation and neurotoxicity. Recent data posits a role for acetylation in Tau and ASYN aggregation. Herein we aimed to clarify the role of Sirtuin-2 (SIRT2) and HDAC6 tubulin deacetylases as well as p300 acetyltransferase in AD and PD neurodegeneration. We used transmitochondrial cybrids that recapitulate pathogenic alterations observed in sporadic PD and AD patient brains and ASYN and Tau cellular models. We confirmed that Tau protein and ASYN are microtubules (MTs)-associated proteins (MAPs). Moreover, our results suggest that α-tubulin acetylation induced by SIRT2 inhibition is functionally associated with the improvement of MT dynamic determined by decreased Tau phosphorylation and by increased Tau/tubulin and ASYN/tubulin binding. Our data provide a strong evidence for a functional role of tubulin and MAPs acetylation on autophagic vesicular traffic and cargo clearance. Additionally, we showed that an accumulation of ASYN oligomers imbalance mitochondrial dynamics, which further compromise autophagy. We also demonstrated that an increase in Tau acetylation is associated with Tau phosphorylation. We found that p300, HDAC6 and SIRT2 influences Tau phosphorylation and autophagic flux in AD. In addition, we demonstrated that p300 and HDAC6 modulate Tau and Tubulin acetylation. Overall, our data disclose the role of Tau and ASYN modifications through acetylation in AD and PD pathology, respectively. Moreover, this study indicates that MTs can be a promising therapeutic target in the field of neurodegenerative disorders in which intracellular transport is altered.

Hyperphosphorylation of Tau Associates With Changes in Its Function Beyond Microtubule Stability

Tau is a neuronal microtubule associated protein whose main biological functions are to promote microtubule self-assembly by tubulin and to stabilize those already formed. Tau also plays an important role as an axonal microtubule protein. Tau is an amazing protein that plays a key role in cognitive processes, however, deposits of abnormal forms of tau are associated with several neurodegenerative diseases, including Alzheimer disease (AD), the most prevalent, and Chronic Traumatic Encephalopathy (CTE) and Traumatic Brain Injury (TBI), the most recently associated to abnormal tau. Tau post-translational modifications (PTMs) are responsible for its gain of toxic function. Alonso et al. (1996) were the first to show that the pathological tau isolated from AD brains has prion-like properties and can transfer its toxic function to the normal molecule. Furthermore, we reported that the pathological changes are associated with tau phosphorylation at Ser199 and 262 and Thr212 and 231. This pathological version of tau induces subcellular mislocalization in cultured cells and neurons, and translocates into the nucleus or accumulated in the perinuclear region of cells. We have generated a transgenic mouse model that expresses pathological human tau (PH-Tau) in neurons at two different concentrations (4% and 14% of the total endogenous tau). In this model, PH-Tau causes cognitive decline by at least two different mechanisms: one that involves the cytoskeleton with axonal disruption (at high concentration), and another in which the apparent neuronal morphology is not grossly affected, but the synaptic terminals are altered (at lower concentration). We will discuss the putative involvement of tau in proteostasis under these conditions. Understanding tau’s biological activity on and off the microtubules will help shed light to the mechanism of neurodegeneration and of normal neuronal function.

Therapeutic Strategies for Restoring Tau Homeostasis

Normal tau homeostasis is achieved when the synthesis, processing, and degradation of the protein is balanced. Together, the pathways that regulate tau homeostasis ensure that the protein is at the proper levels and that its posttranslational modifications and subcellular localization are appropriately controlled. These pathways include the enzymes responsible for posttranslational modifications, those systems that regulate mRNA splicing, and the molecular chaperones that control tau turnover and its binding to microtubules. In tauopathies, this delicate balance is disturbed. Tau becomes abnormally modified by posttranslational modification, it loses affinity for microtubules, and it accumulates in proteotoxic aggregates. How and why does this imbalance occur? In this review, we discuss how molecular chaperones and other components of the protein homeostasis (e.g., proteostasis) network normally govern tau quality control. We also discuss how aging might reduce the capacity of these systems and how tau mutations might further affect this balance. Finally, we discuss how small-molecule inhibitors are being used to probe and perturb the tau quality-control systems, playing a particularly prominent role in revealing the logic of tau homeostasis. As such, there is now interest in developing these chemical probes into therapeutics, with the goal of restoring normal tau homeostasis to treat disease.

Quantification of Tau Load in Alzheimer's Disease Clinical Trials Using Positron Emission Tomography

Alzheimer's disease is a neurodegenerative condition that is neuropathologically characterized by the presence of amyloid-β plaques and neurofibrillary tangles consisting of tau. Recently, several positron emission tomography (PET) tracers have been developed that yielded promising initial results. In this chapter, we discuss how tau PET can be used in the context in clinical trials. We argue that simplified reference tissue models based on dynamic data acquisition are most suitable for accurately measuring changes in tau pathology in trials tailored to reduce cerebral tau load. Therefore, we discuss the importance of tracer kinetic modeling and describe in detail how a reliable measurement of specific binding can be obtained.

Use of curcumin in diagnosis, prevention, and treatment of Alzheimer's disease

This review summarizes and describes the use of curcumin in diagnosis, prevention, and treatment of Alzheimer's disease. For diagnosis of Alzheimer's disease, amyloid-β and highly phosphorylated tau protein are the major biomarkers. Curcumin was developed as an early diagnostic probe based on its natural fluorescence and high binding affinity to amyloid-β. Because of its multi-target effects, curcumin has protective and preventive effects on many chronic diseases such as cerebrovascular disease, hypertension, and hyperlipidemia. For prevention and treatment of Alzheimer's disease, curcumin has been shown to effectively maintain the normal structure and function of cerebral vessels, mitochondria, and synapses, reduce risk factors for a variety of chronic diseases, and decrease the risk of Alzheimer's disease. The effect of curcumin on Alzheimer's disease involves multiple signaling pathways: anti-amyloid and metal iron chelating properties, antioxidation and anti-inflammatory activities. Indeed, there is a scientific basis for the rational application of curcumin in prevention and treatment of Alzheimer's disease.

Region-Specific Association of Subjective Cognitive Decline With Tauopathy Independent of Global β-Amyloid Burden

Importance

The ability to explore associations between reports of subjective cognitive decline (SCD) and biomarkers of early Alzheimer disease (AD) pathophysiologic processes (accumulation of neocortical β-amyloid [Aβ] and tau) provides an important opportunity to understand the basis of SCD and AD risk.

Objective

To examine associations between SCD and global Aβ and tau burdens in regions of interest in clinically healthy older adults.

Design, Setting, and Participants

This imaging substudy of the Harvard Aging Brain Study included 133 clinically healthy older participants (Clinical Dementia Rating Scale global scores of 0) participating in the Harvard Aging Brain Study who underwent cross-sectional flortaucipir F 18 (previously known as AV 1451, T807) positron emission tomography (FTP-PET) imaging for tau and Pittsburgh compound B carbon 11-labeled PET (PiB-PET) imaging for Aβ. The following 2 regions for tau burden were identified: the entorhinal cortex, which exhibits early signs of tauopathy, and the inferior temporal region, which is more closely associated with AD-related pathologic mechanisms. Data were collected from June 11, 2012, through April 7, 2016.

Main Outcomes and Measures

Subjective cognitive decline was measured using a previously published method of z-transforming subscales from the Memory Functioning Questionnaire, the Everyday Cognition battery, and a 7-item questionnaire. The Aβ level was measured according to a summary distribution volume ratio of frontal, lateral temporal and parietal, and retrosplenial PiB-PET tracer uptake. The FTP-PET measures were computed as standardized uptake value ratios. Linear regression models focused on main and interactive effects of Aβ, entorhinal cortical, and inferior temporal tau on SCD, controlling for age, sex, educational attainment, and Geriatric Depression Scale score.

Results

Of the 133 participants, 75 (56.3%) were women and 58 (43.6%) were men; mean (SD) age was 76 (6.9) years (range, 55-90 years). Thirty-nine participants (29.3%) exhibited a high Aβ burden. Greater SCD was associated with increasing entorhinal cortical tau burden (β = 0.35; 95% CI, 0.19-.52; P < .001) and Aβ burden (β = 0.24; 95% CI, 0.08-.40; P = .005), but not inferior temporal tau burden (β = 0.10; 95% CI, -0.08 to 0.28; P = .27). This association between entorhinal cortical tau burden and SCD was largely unchanged after accounting for Aβ burden (β = 0.36; 95% CI, 0.15-.58; P = .001), and no interaction influenced SCD (β = -0.36; 95% CI, -0.34 to 0.09; P = .25). An exploratory post hoc whole-brain analysis also indicated that SCD was predominantly associated with greater tau burden in the entorhinal cortex.

Conclusions and Relevance

Subjective cognitive decline is indicative of accumulation of early tauopathy in the medial temporal lobe, specifically in the entorhinal cortex, and to a lesser extent, elevated global levels of Aβ. Our findings suggest multiple underlying pathways that motivate SCD that do not necessarily interact to influence SCD endorsement. As such, multiple biological factors must be considered when assessing SCD in clinically healthy older adults.

Overexpression of U1 snRNA induces decrease of U1 spliceosome function associated with Alzheimer's disease

We recently reported that presenilin-1 (PS1) induced an increase of U1 snRNA expression accompanied with the change of amyloid precursor protein expression, β-amyloid level and cell death. In the present study, our data showed that both overexpression and knockdown of U1 snRNA could cause the loss in the function of U1 snRNA and resulted in PCPA as well as the same downstream phenomena including the expression changes of genes specific to AD, tau hyperphosphorylation on the site of Thr212, the decrease of acetylated α-tubulin, the reduction of cell viability and upregulation of RIPK1, RIPK3 and caspase8. These findings not only helped researchers better understand the functions of U1 snRNA, but also paved the way to reveal the mechanisms of AD from a different point of view and may find a new therapeutic target for the disease.

Amyloidogenesis of Tau protein

The role of microtubule-associated protein Tau in neurodegeneration has been extensively investigated since the discovery of Tau amyloid aggregates in the brains of patients with Alzheimer's disease (AD). The process of formation of amyloid fibrils is known as amyloidogenesis and attracts much attention as a potential target in the prevention and treatment of neurodegenerative conditions linked to protein aggregation. Cerebral deposition of amyloid aggregates of Tau is observed not only in AD but also in numerous other tauopathies and prion diseases. Amyloidogenesis of intrinsically unstructured monomers of Tau can be triggered by mutations in the Tau gene, post-translational modifications, or interactions with polyanionic molecules and aggregation-prone proteins/peptides. The self-assembly of amyloid fibrils of Tau shares a number of characteristic features with amyloidogenesis of other proteins involved in neurodegenerative diseases. For example, in vitro experiments have demonstrated that the nucleation phase, which is the rate-limiting stage of Tau amyloidogenesis, is shortened in the presence of fragmented preformed Tau fibrils acting as aggregation templates ("seeds"). Accordingly, Tau aggregates released by tauopathy-affected neurons can spread the neurodegenerative process in the brain through a prion-like mechanism, originally described for the pathogenic form of prion protein. Moreover, Tau has been shown to form amyloid strains-structurally diverse self-propagating aggregates of potentially various pathological effects, resembling in this respect prion strains. Here, we review the current literature on Tau aggregation and discuss mechanisms of propagation of Tau amyloid in the light of the prion-like paradigm.

Protein arginylation targets alpha synuclein, facilitates normal brain health, and prevents neurodegeneration

Alpha synuclein (α-syn) is a central player in neurodegeneration, but the mechanisms triggering its pathology are not fully understood. Here we found that α-syn is a highly efficient substrate for arginyltransferase ATE1 and is arginylated in vivo by a novel mid-chain mechanism that targets the acidic side chains of E46 and E83. Lack of arginylation leads to increased α-syn aggregation and causes the formation of larger pathological aggregates in neurons, accompanied by impairments in its ability to be cleared via normal degradation pathways. In the mouse brain, lack of arginylation leads to an increase in α-syn’s insoluble fraction, accompanied by behavioral changes characteristic for neurodegenerative pathology. Our data show that lack of arginylation in the brain leads to neurodegeneration, and suggests that α-syn arginylation can be a previously unknown factor that facilitates normal α-syn folding and function in vivo.

Inhibition of peptide aggregation by means of enzymatic phosphorylation

As is the case in numerous natural processes, enzymatic phosphorylation can be used in the laboratory to influence the conformational populations of proteins. In nature, this information is used for signal transduction or energy transfer, but has also been shown to play an important role in many diseases like tauopathies or diabetes. With the goal of determining the effect of phosphorylation on amyloid fibril formation, we designed a model peptide which combines structural characteristics of α-helical coiled-coils and β-sheets in one sequence. This peptide undergoes a conformational transition from soluble structures into insoluble amyloid fibrils over time and under physiological conditions and contains a recognition motif for PKA (cAMP-dependent protein kinase) that enables enzymatic phosphorylation. We have analyzed the pathway of amyloid formation and the influence of enzymatic phosphorylation on the different states along the conformational transition from random-coil to β-sheet-rich oligomers to protofilaments and on to insoluble amyloid fibrils, and we found a remarkable directing effect from β-sheet-rich structures to unfolded structures in the initial growth phase, in which small oligomers and protofilaments prevail if the peptide is phosphorylated.

Overexpression of Tau Rescues Nogo-66-Induced Neurite Outgrowth Inhibition In Vitro

Nogo-66 plays a central role in the myelin-mediated inhibition of neurite outgrowth. Tau is a microtubule-associated protein involved in microtubule assembly and stabilization. It remains unverified whether tau interacts directly with growth factor receptors, or engages in cross-talk with regeneration inhibitors like Nogo-66. Here, we report that plasmid overexpression of tau significantly elevated the protein levels of total tau, phosphorylated tau, and microtubule-affinity regulating kinase (MARK). Nogo-66 transiently elevated the total tau protein level and persistently reduced the level of p-S262 tau (tau phosphorylated at serine 262), whereas it had little influence on the level of p-T205 tau (tau phosphorylated at threonine 205). Nogo-66 significantly decreased the protein level of MARK. Hymenialdisine, an inhibitor of MARK, significantly reduced the level of p-S262 tau. Overexpression of tau rescued the Nogo-66-induced inhibition of neurite outgrowth in neuroblastoma 2a (N2a) cells and primary cortical neurons. However, concomitant inhibition of MARK abolished the rescue of neurite outgrowth by tau in N2a cells. We conclude that dephosphorylation of tau at S262 is able to regulate Nogo-66 signaling, and that overexpression of tau can rescue the Nogo-66-induced inhibition of neurite outgrowth in vitro.

Tau PET patterns mirror clinical and neuroanatomical variability in Alzheimer's disease

SEE SARAZIN ET AL DOI101093/BRAIN/AWW041 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: The advent of the positron emission tomography tracer (18)F-AV1451 provides the unique opportunity to visualize the regional distribution of tau pathology in the living human brain. In this study, we tested the hypothesis that tau pathology is closely linked to symptomatology and patterns of glucose hypometabolism in Alzheimer's disease, in contrast to the more diffuse distribution of amyloid-β pathology. We included 20 patients meeting criteria for probable Alzheimer's disease dementia or mild cognitive impairment due to Alzheimer's disease, presenting with a variety of clinical phenotypes, and 15 amyloid-β-negative cognitively normal individuals, who underwent (18)F-AV1451 (tau), (11)C-PiB (amyloid-β) and (18)F-FDG (glucose metabolism) positron emission tomography, apolipoprotein E (APOE) genotyping and neuropsychological testing. Voxel-wise contrasts against controls (at P < 0.05 family-wise error corrected) showed that (18)F-AV1451 and (18)F-FDG patterns in patients with posterior cortical atrophy ('visual variant of Alzheimer's disease', n = 7) specifically targeted the clinically affected posterior brain regions, while (11)C-PiB bound diffusely throughout the neocortex. Patients with an amnestic-predominant presentation (n = 5) showed highest (18)F-AV1451 retention in medial temporal and lateral temporoparietal regions. Patients with logopenic variant primary progressive aphasia ('language variant of Alzheimer's disease', n = 5) demonstrated asymmetric left greater than right hemisphere (18)F-AV1451 uptake in three of five patients. Across 30 FreeSurfer-defined regions of interest in 16 Alzheimer's disease patients with all three positron emission tomography scans available, there was a strong negative association between (18)F-AV1451 and (18)F-FDG uptake (Pearson's r = -0.49 ± 0.07, P < 0.001) and less pronounced positive associations between (11)C-PiB and (18)F-FDG (Pearson's r = 0.16 ± 0.09, P < 0.001) and (18)F-AV1451 and (11)C-PiB (Pearson's r = 0.18 ± 0.09, P < 0.001). Voxel-wise linear regressions thresholded at P < 0.05 (uncorrected) showed that, across all patients, younger age was associated with greater (18)F-AV1451 uptake in wide regions of the neocortex, while older age was associated with increased (18)F-AV1451 in the medial temporal lobe. APOE ϵ4 carriers showed greater temporal and parietal (18)F-AV1451 uptake than non-carriers. Finally, worse performance on domain-specific neuropsychological tests was associated with greater (18)F-AV1451 uptake in key regions implicated in memory (medial temporal lobes), visuospatial function (occipital, right temporoparietal cortex) and language (left > right temporoparietal cortex). In conclusion, tau imaging-contrary to amyloid-β imaging-shows a strong regional association with clinical and anatomical heterogeneity in Alzheimer's disease. Although preliminary, these results are consistent with and expand upon findings from post-mortem, animal and cerebrospinal fluid studies, and suggest that the pathological aggregation of tau is closely linked to patterns of neurodegeneration and clinical manifestations of Alzheimer's disease.