The role of tau in neurodegeneration

Molecular Dynamics Simulation Study of the Self-Assembly of Tau-Derived PHF6 and Its Inhibition by Oleuropein Aglycone from Extra Virgin Olive Oil

Alzheimer's disease (AD) and other taupathies are neurodegenerative disorders associated with the amyloid deposition of the Tau protein in the brain. This amyloid formation may be inhibited by small molecules, which is recognized as one of the best therapeutic strategies to stop the progression of the disease. This work focuses on the small nucleating segment, hexapeptide-paired helical filament 6 (PHF6), responsible for Tau aggregation. Using computational modeling and classical molecular dynamics simulations, we show that PHF6 monomers collapse in water to form β-sheet rich structures, and the main olive oil polyphenol oleuropein aglycone (OleA) prevents peptide aggregation significantly. We gradually increase the ratio of the PHF6-OleA from 1:1 to 1:3 and find that for the 1:1 ratio, the peptide monomers are prone to form aggregated structures, while for the 1:2 ratio, the formation of the extended β-sheet structure is significantly less. For a 1:3 ratio of protein/OleA, the peptide residues are sufficiently crowded by OleA molecules through hydrogen bonding, hydrophobic interactions, and π-π stacking; hence, the peptide chains prefer to exist in a monomeric random coil conformation.

The novel anti-fibrillary effects of volatile compounds α-asarone and β-caryophyllene on tau protein: Towards promising therapeutic agents for Alzheimer's disease

The abnormal deposition of tau protein is one of the critical causes of tauopathies including Alzheimer's disease (AD). In recent years, there has been great interest in the use of essential oils and volatile compounds in aromatherapy for treating AD, since volatile compounds can directly reach the brain through intranasal administration. The volatile compounds α-asarone (ASA) and β-caryophyllene (BCP) have revealed various important neuroprotective properties, useful in treating AD. In this study, the volatile compounds ASA and BCP were assessed for their effectiveness in preventing tau fibrillation, disassembly of pre-formed tau fibrils, and disaggregation of tau aggregates. SDS-PAGE and AFM analyses revealed that ASA and BCP inhibited tau fibrillation/aggregation and decreased the mean size of tau oligomers. Tau samples treated with ASA and BCP, showed a reduction in ThT and ANS fluorescence intensities, and a decrease in the β-sheet content. Additionally, ASA and BCP disassembled the pre-formed tau fibrils to the granular and linear oligomeric intermediates. Treatment of neuroblastoma SH-SY5Y cells with tau samples treated with ASA and BCP, revealed protective effects as shown by reduced toxicity of the cells, due to the inhibition of tau fibrillation/aggregation. Overall, ASA and BCP appeared to be promising therapeutic candidates for AD.

Current biomarkers and treatment strategies in Alzheimer disease: An overview and future perspectives

Alzheimer's disease (AD), a progressive degenerative disorder first identified by Alois Alzheimer in 1907, poses a significant public health challenge. Despite its prevalence and impact, there is currently no definitive ante mortem diagnosis for AD pathogenesis. By 2050, the United States may face a staggering 13.8 million AD patients. This review provides a concise summary of current AD biomarkers, available treatments, and potential future therapeutic approaches. The review begins by outlining existing drug targets and mechanisms in AD, along with a discussion of current treatment options. We explore various approaches targeting Amyloid β (Aβ), Tau Protein aggregation, Tau Kinases, Glycogen Synthase kinase-3β, CDK-5 inhibitors, Heat Shock Proteins (HSP), oxidative stress, inflammation, metals, Apolipoprotein E (ApoE) modulators, and Notch signaling. Additionally, we examine the historical use of Estradiol (E2) as an AD therapy, as well as the outcomes of Randomized Controlled Trials (RCTs) that evaluated antioxidants (e.g., vitamin E) and omega-3 polyunsaturated fatty acids as alternative treatment options. Notably, positive effects of docosahexaenoic acid nutriment in older adults with cognitive impairment or AD are highlighted. Furthermore, this review offers insights into ongoing clinical trials and potential therapies, shedding light on the dynamic research landscape in AD treatment.

Drug repurposing for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are neuronal problems that include the brain and spinal cord and result in loss of sensory and motor dysfunction. Common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple Sclerosis (MS), and Amyotrophic Lateral Sclerosis (ALS) etc. The occurrence of these diseases increases with age and is one of the challenging problems among elderly people. Though, several scientific research has demonstrated the key pathologies associated with NDDs still the underlying mechanisms and molecular details are not well understood and need to be explored and this poses a lack of effective treatments for NDDs. Several lines of evidence have shown that NDDs have a high prevalence and affect more than a billion individuals globally but still, researchers need to work forward in identifying the best therapeutic target for NDDs. Thus, several researchers are working in the directions to find potential therapeutic targets to alter the disease pathology and treat the diseases. Several steps have been taken to identify the early detection of the disease and drug repurposing for effective treatment of NDDs. Moreover, it is logical that current medications are being evaluated for their efficacy in treating such disorders; therefore, drug repurposing would be an efficient, safe, and cost-effective way in finding out better medication. In the current manuscript we discussed the utilization of drugs that have been repurposed for the treatment of AD, PD, HD, MS, and ALS.

Blood biomarkers of neurodegeneration associate differently with amyloid deposition, medial temporal atrophy, and cerebrovascular changes in APOE ε4-enriched cognitively unimpaired elderly

BACKGROUND

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β (Aβ) plaques, neurofibrillary tau tangles, and neurodegeneration in the brain parenchyma. Here, we aimed to (i) assess differences in blood and imaging biomarkers used to evaluate neurodegeneration among cognitively unimpaired APOE ε4 homozygotes, heterozygotes, and non-carriers with varying risk for sporadic AD, and (ii) to determine how different cerebral pathologies (i.e., Aβ deposition, medial temporal atrophy, and cerebrovascular pathology) contribute to blood biomarker concentrations in this sample.

METHODS

Sixty APOE ε4 homozygotes (n = 19), heterozygotes (n = 21), and non-carriers (n = 20) ranging from 60 to 75 years, were recruited in collaboration with Auria biobank (Turku, Finland). Participants underwent Aβ-PET ([11C]PiB), structural brain MRI including T1-weighted and T2-FLAIR sequences, and blood sampling for measuring serum neurofilament light chain (NfL), plasma total tau (t-tau), plasma N-terminal tau fragments (NTA-tau) and plasma glial fibrillary acidic protein (GFAP). [11C]PiB standardized uptake value ratio was calculated for regions typical for Aβ accumulation in AD. MRI images were analysed for regional volumes, atrophy scores, and volumes of white matter hyperintensities. Differences in biomarker levels and associations between blood and imaging biomarkers were tested using uni- and multivariable linear models (unadjusted and adjusted for age and sex).

RESULTS

Serum NfL concentration was increased in APOE ε4 homozygotes compared with non-carriers (mean 21.4 pg/ml (SD 9.5) vs. 15.5 pg/ml (3.8), p = 0.013), whereas other blood biomarkers did not differ between the groups (p > 0.077 for all). From imaging biomarkers, hippocampal volume was significantly decreased in APOE ε4 homozygotes compared with non-carriers (6.71 ml (0.86) vs. 7.2 ml (0.7), p = 0.029). In the whole sample, blood biomarker levels were differently predicted by the three measured cerebral pathologies; serum NfL concentration was associated with cerebrovascular pathology and medial temporal atrophy, while plasma NTA-tau associated with medial temporal atrophy. Plasma GFAP showed significant association with both medial temporal atrophy and Aβ pathology. Plasma t-tau concentration did not associate with any of the measured pathologies.

CONCLUSIONS

Only increased serum NfL concentrations and decreased hippocampal volume was observed in cognitively unimpaired APOEε4 homozygotes compared to non-carriers. In the whole population the concentrations of blood biomarkers were affected in distinct ways by different pathologies.

Towards Early Diagnosis and Screening of Alzheimer's Disease Using Frequency Locked Whispering Gallery Mode Microtoroid Biosensors

Alzheimer's disease (AD) is a progressive form of dementia affecting almost 55 million people worldwide. It is characterized by the abnormal deposition of amyloid plaques and neurofibrillary tangles within the brain, leading to a pathological cascade of neuron degeneration and death as well as memory loss and cognitive decline. Amyloid beta (Aβ) is an AD biomarker present in cerebrospinal fluid and blood serum and correlates with the presence of amyloid plaques and tau tangles in the brain. Measuring the levels of Aβ can help with early diagnosis of AD, which is key for studying novel AD drugs and delaying the symptoms of dementia. However, this goal is difficult to achieve due to the low levels of AD biomarkers in biofluids. Here we demonstrate for the first time the use of FLOWER (frequency locked optical whispering evanescent resonator) for quantifying the levels of post-mortem cerebrospinal fluid (CSF) Aβ42 in clinicopathologically classified control, mild cognitive impairment (MCI), and AD participants. FLOWER is capable of measuring CSF Aβ42 (area under curve, AUC = 0.92) with higher diagnostic performance than standard ELISA (AUC = 0.82) and was also able to distinguish between control and MCI samples. Our results demonstrate the capability of FLOWER for screening CSF samples for early diagnosis of Alzheimer's pathology.

P-tau217 correlates with neurodegeneration in Alzheimer's disease, and targeting p-tau217 with immunotherapy ameliorates murine tauopathy

Neuronal loss is the central issue in Alzheimer's disease (AD), yet no treatment developed so far can halt AD-associated neurodegeneration. Here, we developed a monoclonal antibody (mAb2A7) against 217 site-phosphorylated human tau (p-tau217) and observed that p-tau217 levels positively correlated with brain atrophy and cognitive impairment in AD patients. Intranasal administration efficiently delivered mAb2A7 into male PS19 tauopathic mouse brain with target engagement and reduced tau pathology/aggregation with little effect on total soluble tau. Further, mAb2A7 treatment blocked apoptosis-associated neuronal loss and brain atrophy, reversed cognitive deficits, and improved motor function in male tauopathic mice. Proteomic analysis revealed that mAb2A7 treatment reversed alterations mainly in proteins associated with synaptic functions observed in murine tauopathy and AD brain. An antibody (13G4) targeting total tau also attenuated tau-associated pathology and neurodegeneration but impaired the motor function of male tauopathic mice. These results implicate p-tau217 as a potential therapeutic target for AD-associated neurodegeneration.

Human iPSC 4R tauopathy model uncovers modifiers of tau propagation

Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to a lack of appropriate human models. Here, we engineered human induced pluripotent stem cell (hiPSC)-derived neuronal lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes including shared transcriptomic signatures, autophagic body accumulation, and reduced neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of seeding-induced Tau propagation, including retromer VPS29 and genes in the UFMylation cascade. In progressive supranuclear palsy (PSP) and Alzheimer's Disease (AD) brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade in vitro and in vivo suppressed seeding-induced Tau propagation. This model provides a robust platform to identify novel therapeutic strategies for 4R tauopathy.

Sensor-integrated brain-on-a-chip platforms: Improving the predictive validity in neurodegenerative research

Affecting millions of individuals worldwide, neurodegenerative diseases (NDDs) pose a significant and growing health concern in people over the age of 60 years. Contributing to this trend are the steady increase in the aging population coupled with a persistent lack of disease-altering treatment strategies targeting NDDs. The absence of efficient therapeutics can be attributed to high failure rates in clinical trials and the ineptness of animal models in preceding preclinical studies. To that end, in recent years, significant research effort has been dedicated to the development of human cell-based preclinical disease models characterized by a higher degree of predictive validity. However, a key requirement of any in vitro model constitutes the precise knowledge and replication of the target tissues' (patho-)physiological microenvironment. Herein, microphysiological systems have demonstrated superiority over conventional static 2D/3D in vitro cell culture systems, as they allow for the emulation and continuous monitoring of the onset, progression, and remission of disease-associated phenotypes. This review provides an overview of recent advances in the field of NDD research using organ-on-a-chip platforms. Specific focus is directed toward non-invasive sensing strategies encompassing electrical, electrochemical, and optical sensors. Additionally, promising on- and integrable off-chip sensing strategies targeting key analytes in NDDs will be presented and discussed in detail.

Amyloid-β and Phosphorylated Tau are the Key Biomarkers and Predictors of Alzheimer's Disease

Alzheimer's disease (AD) is a age-related neurodegenerative disease and is a major public health concern both in Texas, US and Worldwide. This neurodegenerative disease is mainly characterized by amyloid-beta (Aβ) and phosphorylated Tau (p-Tau) accumulation in the brains of patients with AD and increasing evidence suggests that these are key biomarkers in AD. Both Aβ and p-tau can be detected through various imaging techniques (such as positron emission tomography, PET) and cerebrospinal fluid (CSF) analysis. The presence of these biomarkers in individuals, who are asymptomatic or have mild cognitive impairment can indicate an increased risk of developing AD in the future. Furthermore, the combination of Aβ and p-tau biomarkers is often used for more accurate diagnosis and prediction of AD progression. Along with AD being a neurodegenerative disease, it is associated with other chronic conditions such as cardiovascular disease, obesity, depression, and diabetes because studies have shown that these comorbid conditions make people more vulnerable to AD. In the first part of this review, we discuss that biofluid-based biomarkers such as Aβ, p-Tau in cerebrospinal fluid (CSF) and Aβ & p-Tau in plasma could be used as an alternative sensitive technique to diagnose AD. In the second part, we discuss the underlying molecular mechanisms of chronic conditions linked with AD and how they affect the patients in clinical care.

Mitochondrial Permeability Transition, Cell Death and Neurodegeneration

Neurodegenerative diseases are chronic conditions occurring when neurons die in specific brain regions that lead to loss of movement or cognitive functions. Despite the progress in understanding the mechanisms of this pathology, currently no cure exists to treat these types of diseases: for some of them the only help is alleviating the associated symptoms. Mitochondrial dysfunction has been shown to be involved in the pathogenesis of most the neurodegenerative disorders. The fast and transient permeability of mitochondria (the mitochondrial permeability transition, mPT) has been shown to be an initial step in the mechanism of apoptotic and necrotic cell death, which acts as a regulator of tissue regeneration for postmitotic neurons as it leads to the irreparable loss of cells and cell function. In this study, we review the role of the mitochondrial permeability transition in neuronal death in major neurodegenerative diseases, covering the inductors of mPTP opening in neurons, including the major ones-free radicals and calcium-and we discuss perspectives and difficulties in the development of a neuroprotective strategy based on the inhibition of mPTP in neurodegenerative disorders.

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

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

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.

Tau and delirium superimposed on dementia: A case report

We present a case involving a 60-year-old man with subacute delirium characterized by challenging attention shifts and obstinate behavior, contrasting with his usual mild-mannered personality. The patient developed pneumonia and a urinary tract infection following the onset of subacute delirium. Despite exhaustive investigations, the cause remained elusive until cerebrospinal fluid analysis revealed Tau positivity. Our overview suggests neurodegenerative diseases as the primary cause, rather than infectious or autoimmune factors. The case underscores a significant association between Tau and delirium superimposed on dementia, offering guidance to clinicians managing such patients.

Association of APOE gene with longitudinal changes of CSF amyloid beta and tau levels in Alzheimer's disease: racial differences

BACKGROUND

The Apolipoprotein E (APOE) ε4 allele is a risk factor for late-onset Alzheimer's disease (AD). However, no investigation has focused on racial differences in the longitudinal effect of APOE genotypes on CSF amyloid beta (Aβ42) and tau levels in AD.

METHODS

This study used data from the Alzheimer's Disease Neuroimaging Initiative (ADNI): 222 participants with AD, 264 with cognitive normal (CN), and 692 with mild cognitive impairment (MCI) at baseline and two years follow-up. We used a linear mixed model to investigate the effect of APOE-ε4-genotypes on longitudinal changes in the amyloid beta and tau levels.

RESULTS

Individuals with 1 or 2 APOE ε4 alleles revealed significantly higher t-Tau and p-Tau, but lower amyloid beta Aβ42 compared with individuals without APOE ε4 alleles. Significantly higher levels of log-t-Tau, log-p-Tau, and low levels of log-Aβ42 were observed in the subjects with older age, being female, and the two diagnostic groups (AD and MCI). The higher p-Tau and Aβ42 values are associated with poor Mini-Mental State Examination (MMSE) performance. Non-Hispanic Africa American (AA) and Hispanic participants were associated with decreased log-t-Tau levels (β =  - 0.154, p = 0.0112; β =  - 0.207, and p = 0.0016, respectively) as compared to those observed in Whites. Furthermore, Hispanic participants were associated with a decreased log-p-Tau level (β =  - 0.224, p = 0.0023) compared to those observed in Whites. There were no differences in Aβ42 level for non-Hispanic AA and Hispanic participants compared with White participants.

CONCLUSION

Our study, for the first time, showed that the APOE ε4 allele was associated with these biomarkers, however with differing degrees among racial groups.

Recent Aspects of Periodontitis and Alzheimer's Disease-A Narrative Review

Periodontitis is an inflammatory condition affecting the supporting structures of the teeth. Periodontal conditions may increase the susceptibility of individuals to various systemic illnesses, including Alzheimer's disease. Alzheimer's disease is a neurodegenerative condition characterized by a gradual onset and progressive deterioration, making it the primary cause of dementia, although the exact cause of the disease remains elusive. Both Alzheimer's disease and periodontitis share risk factors and clinical studies comparing the associations and occurrence of periodontitis among individuals with Alzheimer's disease have suggested a potential correlation between these conditions. Brains of individuals with Alzheimer's disease have substantiated the existence of microorganisms related to periodontitis, especially Porphyromonas gingivalis, which produces neurotoxic gingipains and may present the capability to breach the blood-brain barrier. Treponema denticola may induce tau hyperphosphorylation and lead to neuronal apoptosis. Lipopolysaccharides-components of bacterial cell membranes and mediators of inflammation-also have an impact on brain function. Further research could unveil therapeutic approaches targeting periodontal pathogens to potentially alleviate AD progression.

Mitochondrial bioenergetics stimulates autophagy for pathological tau clearance in tauopathy neurons

Hyperphosphorylation and aggregation of microtubule-associated tau is a pathogenic hallmark of tauopathies and a defining feature of Alzheimer's disease (AD). Pathological tau is targeted by autophagy for clearance, but autophagy dysfunction is indicated in tauopathy. While mitochondrial bioenergetic failure has been shown to precede the development of tau pathology, it is unclear whether energy metabolism deficiency is involved in tauopathy-related autophagy defects. Here, we reveal that stimulation of anaplerotic metabolism restores defective oxidative phosphorylation (OXPHOS) in tauopathy which, strikingly, leads to enhanced autophagy and pronounced tau clearance. OXPHOS-induced autophagy is attributed to increased ATP-dependent phosphatidylethanolamine biosynthesis in mitochondria. Excitingly, early bioenergetic stimulation boosts autophagy activity and reduces tau pathology, thereby counteracting memory impairment in tauopathy mice. Taken together, our study sheds light on a pivotal role of bioenergetic dysfunction in tauopathy-linked autophagy defects and suggests a new therapeutic strategy to prevent toxic tau buildup in AD and other tauopathies.

New horizons in the diagnosis and management of Alzheimer's Disease in older adults

Alzheimer's Disease (ad) is the most common cause of dementia, and in addition to cognitive decline, it directly contributes to physical frailty, falls, incontinence, institutionalisation and polypharmacy in older adults. Increasing availability of clinically validated biomarkers including cerebrospinal fluid and positron emission tomography to assess both amyloid and tau pathology has led to a reconceptualisation of ad as a clinical-biological diagnosis, rather than one based purely on clinical phenotype. However, co-pathology is frequent in older adults which influence the accuracy of biomarker interpretation. Importantly, some older adults with positive amyloid or tau pathological biomarkers may never experience cognitive impairment or dementia. These strides towards achieving an accurate clinical-biological diagnosis are occurring alongside recent positive phase 3 trial results reporting statistically significant effects of anti-amyloid Disease-Modifying Therapies (DMTs) on disease severity in early ad. However, the real-world clinical benefit of these DMTs is not clear and concerns remain regarding how trial results will translate to real-world clinical populations, potential adverse effects (including amyloid-related imaging abnormalities), which can be severe and healthcare systems readiness to afford and deliver potential DMTs to appropriate populations. Here, we review recent advances in both clinical-biological diagnostic classification and future treatment in older adults living with ad. Advocating for access to both more accurate clinical-biological diagnosis and potential DMTs must be done so in a holistic and gerontologically attuned fashion, with geriatricians advocating for enhanced multi-component and multi-disciplinary care for all older adults with ad. This includes those across the ad severity spectrum including older adults potentially ineligible for emerging DMTs.

Reinstated Activity of Human Tau-induced Enhanced Insulin Signaling Restricts Disease Pathogenesis by Regulating the Functioning of Kinases/Phosphatases and Tau Hyperphosphorylation in Drosophila

Tauopathies such as Alzheimer's disease (AD), Frontotemporal dementia, and parkinsonism linked to chromosome 17 (FTDP-17), etc. are characterized by tau hyperphosphorylation and distinguished accumulation of paired helical filaments (PHFs)/or neurofibrillary tangles (NFTs) in a specific-neuronal subset of the brain. Among different reported risk factors, type 2 diabetes (T2D) has gained attention due to its correlation with tau pathogenesis. However, mechanistic details and the precise contribution of insulin pathway in tau etiology is still debatable. We demonstrate that expression of human tau causes overactivation of insulin pathway in Drosophila disease models. We subsequently noted that tissue-specific downregulation of insulin signaling or even exclusive reduction of its growth-promoting sub-branch effectively reinstates the overactivated insulin signaling pathway in human tau expressing cells, which in turn restricts pathogenic tau hyperphosphorylation and aggregate formation. It was further noted that restored tau phosphorylation was achieved due to a reestablished balance between the levels of different kinase(s) (GSK3β and ERK/P38 MAP kinase) and phosphatase (PP2A). Taken together, our study demonstrates a precise involvement of the insulin pathway and associated molecular events in the pathogenesis of human tauopathies in Drosophila, which will be immensely helpful in developing novel therapeutic options against these devastating human brain disorders. Moreover, our study reveals an interesting link between tau etiology and aberrant insulin signaling, which is a characteristic feature of Type 2 Diabetes.

Environmental aluminum oxide inducing neurodegeneration in human neurovascular unit with immunity

Aluminum oxide nanoparticle (AlNP), a ubiquitous neurotoxin highly enriched in air pollution, is often produced as an inevitable byproduct in the manufacturing of industrial products such as cosmetics and metal materials. Meanwhile, ALNP has emerged as a significant public health concern due to its potential association with neurological diseases. However, the studies about the neurotoxic effects of AlNP are limited, partially due to the lack of physiologically relevant human neurovascular unit with innate immunity (hNVUI). Here, we employed our AlNP-treated hNVUI model to investigate the underlying mechanism of AlNP-driven neurodegeneration. First, we validated the penetration of AlNP across a blood-brain barrier (BBB) compartment and found AlNP-derived endothelial cellular senescence through the p16 and p53/p21 pathways. Our study showed that BBB-penetrating AlNP promoted reactive astrocytes, which produced a significant level of reactive oxygen species (ROS). The astrocytic neurotoxic factors caused neuronal damage, including the synaptic impairment, the accumulation of phosphoric-tau proteins, and even neuronal death. Our study suggests that AlNP could be a potential environmental risk factor of neurological disorders mediated by neuroinflammation.

Caspase-3 cleaved tau impairs mitochondrial function through the opening of the mitochondrial permeability transition pore

Mitochondrial dysfunction is a significant factor in the development of Alzheimer's disease (AD). Previous studies have demonstrated that the expression of tau cleaved at Asp421 by caspase-3 leads to mitochondrial abnormalities and bioenergetic impairment. However, the underlying mechanism behind these alterations and their impact on neuronal function remains unknown. To investigate the mechanism behind mitochondrial dysfunction caused by this tau form, we used transient transfection and pharmacological approaches in immortalized cortical neurons and mouse primary hippocampal neurons. We assessed mitochondrial morphology and bioenergetics function after expression of full-length tau and caspase-3-cleaved tau. We also evaluated the mitochondrial permeability transition pore (mPTP) opening and its conformation as a possible mechanism to explain mitochondrial impairment induced by caspase-3 cleaved tau. Our studies showed that pharmacological inhibition of mPTP by cyclosporine A (CsA) prevented all mitochondrial length and bioenergetics abnormalities in neuronal cells expressing caspase-3 cleaved tau. Neuronal cells expressing caspase-3-cleaved tau showed sustained mPTP opening which is mostly dependent on cyclophilin D (CypD) protein expression. Moreover, the impairment of mitochondrial length and bioenergetics induced by caspase-3-cleaved tau were prevented in hippocampal neurons obtained from CypD knock-out mice. Interestingly, previous studies using these mice showed a prevention of mPTP opening and a reduction of mitochondrial failure and neurodegeneration induced by AD. Therefore, our findings showed that caspase-3-cleaved tau negatively impacts mitochondrial bioenergetics through mPTP activation, highlighting the importance of this channel and its regulatory protein, CypD, in the neuronal damage induced by tau pathology in AD.

Tridimensional Structural Analysis of Tau Isoforms Generated by Intronic Retention

Background

Tauopathies are a subset of neurodegenerative diseases characterized by abnormal tau inclusions. Recently, we have discovered a new, human specific, tau isoform termed W-tau that originates by intron 12 retention. Our preliminary data suggests this newly discovered W-tau isoform might prevent aberrant aggregation of other tau isoforms but is significantly downregulated in tauopathies such as Alzheimer's disease.

Objective

To accurately predict, examine, and understand tau protein structure and the conformational basis for the neuroprotective role of W-tau.

Methods

A tridimensional deep learning-based approach and in vitro polymerization assay was included to accurately predict, analyze, and understand tau protein structure and the conformational basis for the neuroprotective role of W-tau.

Results

Our findings demonstrate: a) the predicted protein tridimensionality structure of the tau isoforms raised by intron retention and their comparison with the other tau isoforms; b) the interaction of W-tau peptide (from W-tau isoform) with other tau isoforms; c) the effect of W-tau peptide in the polymerization of those tau isoforms.

Conclusions

This study supports the importance of the structure-function relationship on the neuroprotective behavior of W-tau inhibiting tau fibrillization in vitro.

Diligent Design Enables Antibody-ASO Conjugates with Optimal Pharmacokinetic Properties

Antisense-oligonucleotides (ASOs) are a promising drug modality for the treatment of neurological disorders, but the currently established route of administration via intrathecal delivery is a major limitation to its broader clinical application. An attractive alternative is the conjugation of the ASO to an antibody that facilitates access to the central nervous system (CNS) after peripheral application and target engagement at the blood-brain barrier, followed by transcytosis. Here, we show that the diligent conjugate design of Brainshuttle-ASO conjugates is the key to generating promising delivery vehicles and thereby establishing design principles to create optimized molecules with drug-like properties. An innovative site-specific transglutaminase-based conjugation technology was chosen and optimized in a stepwise process to identify the best-suited conjugation site, tags, reaction conditions, and linker design. The overall conjugation performance was found to be specifically governed by the choice of buffer conditions and the structure of the linker. The combination of the peptide tags YRYRQ and RYESK was chosen, showing high conjugation fidelity. Elaborate conjugate analysis revealed that one leading differentiating factor was hydrophobicity. The increase of hydrophobicity by the ASO payload could be mitigated by the appropriate choice of conjugation site and the heavy chain position 297 proved to be the most optimal. Evaluating the properties of the linker suggested a short bicyclo[6.1.0]nonyne (BCN) unit as best suited with regards to conjugation performance and potency. Promising in vitro activity and in vivo pharmacokinetic behavior of optimized Brainshuttle-ASO conjugates, based on a microtubule-associated protein tau (MAPT) targeting oligonucleotide, suggest that such designs have the potential to serve as a blueprint for peripherally delivered ASO-based drugs for the CNS in the future.

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

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

Inhibition of Sirt2 Decreases ApoE Secretion in Astrocytes and Microglial Cells

Amyloid-β (Aβ) accumulation caused by an imbalance of the production and clearance of Aβ in the brain is associated with the development of Alzheimer's disease (ad). Apolipoprotein E (ApoE) (the strongest genetic risk factor) enhances Aβ clearance, preventing Aβ deposition. Sirtuin 2 (Sirt2) is an NAD+-dependent histone deacetylase and its inhibition has been reported to ameliorate memory impairment in ad-like model mice. However, the role of Sirt2 in ApoE secretion is unknown. Here, we found that inhibition of Sirt2 activity in primary cultured astrocytes and BV2 cells decreased ApoE secretion, resulting in the accumulation of intracellular ApoE and inhibiting extracellular Aβ degradation. However, the reduction of Sirt2 protein level by Sirt2 siRNA decreased ApoE protein level, which ultimately reduces ApoE secretion. In addition, the knockdown of Sirt2 in the HEK293-APP cells also decreased levels of intracellular ApoE leading to reduction of its secretion, which is accompanied by increased Aβ levels without altering APP and APP processing enzymes. Our findings provide a novel role of Sirt2 in ApoE secretion.

Effect of arctigenin on neurological diseases: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Arctium lappa L. is a common specie of Asteraceae. Its main active ingredient, Arctigenin (AG), in mature seeds exerts pharmacological effects on the Central Nervous System (CNS).

AIM OF THE STUDY

To review studies on the specific effects of the AG mechanism on various CNS diseases and elucidate signal transduction mechanisms and their pharmacological actions.

MATERIALS AND METHODS

This investigation reviewed the essential role of AG in treating neurological disorders. Basic information on Arctium lappa L. was retrieved from the Pharmacopoeia of the People's Republic of China. The related articles from 1981 to 2022 on the network database (including CNKI, PubMed, and Wan Fang and so on) were reviewed using AG and CNS diseases-related terms such as Arctigenin and Epilepsy.

RESULTS

It was confirmed that AG has a therapeutic effect on Alzheimer's disease, Glioma, infectious CNS diseases (such as Toxoplasma and Japanese Encephalitis Virus), Parkinson's disease, Epilepsy, etc. In these diseases, related experiments such as a Western blot analysis revealed that AG could alter the content of some key factors (such as the reduction of Aβ in Alzheimer's disease). However, in-vivo AG's metabolic process and possible metabolites are still undetermined.

CONCLUSION

Based on this review, the existing pharmacological research has indeed made objective progress to elucidate how AG prevents and treats CNS diseases, especially senile degenerative disease such as Alzheimer's diseases. It was revealed that AG could be used as a potential nervous system drug as it has a wide range of effects in theory with markedly high application value, especially in the elder group. However, the existing studies are limited to in-vitro experiments; therefore, little is known about how AG metabolizes and functions in-vivo, limiting its clinical application and requiring further research.

Mammalian Models in Alzheimer's Research: An Update

A form of dementia distinct from healthy cognitive aging, Alzheimer's disease (AD) is a complex multi-stage disease that currently afflicts over 50 million people worldwide. Unfortunately, previous therapeutic strategies developed from murine models emulating different aspects of AD pathogenesis were limited. Consequently, researchers are now developing models that express several aspects of pathogenesis that better reflect the clinical situation in humans. As such, this review seeks to provide insight regarding current applications of mammalian models in AD research by addressing recent developments and characterizations of prominent transgenic models and their contributions to pathogenesis as well as discuss the advantages, limitations, and application of emerging models that better capture genetic heterogeneity and mixed pathologies observed in the clinical situation.

TAUCON and TAUCOM: A novel biosensor based on fluorescence resonance energy transfer for detecting tau hyperphosphorylation-associated cellular pathologies

Tauopathies are neurodegenerative diseases characterized by abnormal conformational changes in tau protein. Early hyperphosphorylation-induced conformational changes are considered a hallmark of tauopathy, but real-time tracking methods are lacking. Here, we present two novel fluorescence resonance energy transfer (FRET)-based tau biosensors that detect such changes with high spatiotemporal resolution at the single-cell level. The TAUCON biosensor measures instantaneous conformational changes in hyperphosphorylated tau within 20 min, while the TAUCOM biosensor detects changes in the paper-clip structure of microtubule-associated tau. Our biosensors provide faster and more precise detection than conventional methods and can serve as valuable tools for investigating the initial causes, mechanisms, progression, and treatment of tauopathies.

Self-Aggregating Tau Fragments Recapitulate Pathologic Phenotypes and Neurotoxicity of Alzheimer's Disease in Mice

In tauopathy conditions, such as Alzheimer's disease (AD), highly soluble and natively unfolded tau polymerizes into an insoluble filament; however, the mechanistic details of this process remain unclear. In the brains of AD patients, only a minor segment of tau forms β-helix-stacked protofilaments, while its flanking regions form disordered fuzzy coats. Here, it is demonstrated that the tau AD nucleation core (tau-AC) sufficiently induced self-aggregation and recruited full-length tau to filaments. Unexpectedly, phospho-mimetic forms of tau-AC (at Ser324 or Ser356) show markedly reduced oligomerization and seeding propensities. Biophysical analysis reveal that the N-terminus of tau-AC facilitates the fibrillization kinetics as a nucleation motif, which becomes sterically shielded through phosphorylation-induced conformational changes in tau-AC. Tau-AC oligomers are efficiently internalized into cells via endocytosis and induced endogenous tau aggregation. In primary hippocampal neurons, tau-AC impaired axon initial segment plasticity upon chronic depolarization and is mislocalized to the somatodendritic compartments. Furthermore, it is observed significantly impaired memory retrieval in mice intrahippocampally injected with tau-AC fibrils, which corresponds to the neuropathological staining and neuronal loss in the brain. These findings identify tau-AC species as a key neuropathological driver in AD, suggesting novel strategies for therapeutic intervention.

Post-synthesis of a titanium-rich magnetic COF nanocomposite with flexible branched polymers for efficient enrichment of phosphopeptides from human saliva and serum

A Ti4+-functionalized magnetic covalent organic framework material with flexible branched polymers (mCOF@ε-PL@THBA-Ti4+) built via an immobilized metal ion affinity chromatography (IMAC) enrichment strategy was proposed through post-synthesis modification. Hydrophilic ε-poly-L-lysine (ε-PL) rich in amino active groups was first introduced in the fabrication of the phosphopeptide enrichment material to increase the hydrophilicity while providing more functional modification pathways of the material. 2,3,4-Trihydroxy-benzaldehyde (THBA) provides abundant binding sites for the immobilization of numerous Ti4+, which is advantageous for the subsequent efficient phosphopeptide enrichment. The magnetic nanocomposite exhibited outstanding performance of phosphopeptide enrichment with good selectivity (1 : 5000), a low detection limit (2 fmol), and relatively high loading capacity (66.7 mg g-1). What's more, after treatment with mCOF@ε-PL@THBA-Ti4+, 16 endogenous phosphopeptides from fresh saliva of healthy people were recognized by MALDI-TOF MS, and 50 phosphopeptides belonging to 35 phosphoproteins from the serum of uremia patients were detected by nano-LC-MS/MS. Proteomics data analysis for the differential protein selection between uremia and normal controls was conducted using R software, and four down-regulated and three up-regulated proteins were obtained. The results suggested that the prepared material has potential applications in biomarker discovery.

Exploring the role of COX-2 in Alzheimer's disease: Potential therapeutic implications of COX-2 inhibitors

This review highlights the potential role of cyclooxygenase-2 enzyme (COX-2) in the pathogenesis of Alzheimer's disease (AD) and the potential therapeutic use of non-steroidal anti-inflammatory drugs (NSAIDs) in the management of AD. In addition to COX-2 enzymes role in inflammation, the formation of amyloid plaques and neurofibrillary tangles in the brain, the review emphasizes that COXs-2 have a crucial role in normal synaptic activity and plasticity, and have a relationship with acetylcholine, tau protein, and beta-amyloid (Aβ) which are the main causes of Alzheimer's disease. Furthermore, the review points out that COX-2 enzymes have a relationship with kinase enzymes, including Cyclin Dependent Kinase 5 (CDK5) and Glycogen Synthase Kinase 3β (GSK3β), which are known to play a role in tau phosphorylation and are strongly associated with Alzheimer's disease. Therefore, the use of drugs like NSAIDs may be a hopeful approach for managing AD. However, results from studies examining the effectiveness of NSAIDs in treating AD have been mixed and further research is needed to fully understand the mechanisms by which COX-2 and NSAIDs may be involved in the development and progression of AD and to identify new therapeutic strategies.

Blood-Based Biomarkers in the Diagnosis of Chronic Traumatic Encephalopathy: Research to Date and Future Directions

Chronic Traumatic Encephalopathy (CTE) is a neurodegenerative disease consistently associated with repetitive traumatic brain injuries (TBIs), which makes multiple professions, such as contact sports athletes and the military, especially susceptible to its onset. There are currently no approved biomarkers to diagnose CTE, thus it can only be confirmed through a post-mortem brain autopsy. Several imaging and cerebrospinal fluid biomarkers have shown promise in the diagnosis. However, blood-based biomarkers can be more easily obtained and quantified, increasing their clinical feasibility and potential for prophylactic use. This article aimed to comprehensively review the studies into potential blood-based biomarkers of CTE, discussing common themes and limitations, as well as suggesting future research directions. While the interest in blood-based biomarkers of CTE has recently increased, the research is still in its early stages. The main issue for many proposed biomarkers is their lack of selectivity for CTE. However, several molecules, such as different phosphorylated tau isoforms, were able to discern CTE from different neurodegenerative diseases. Further, the results from studies on exosomal biomarkers suggest that exosomes are a promising source of biomarkers, reflective of the internal environment of the brain. Nonetheless, more longitudinal studies combining imaging, neurobehavioral, and biochemical approaches are warranted to establish robust biomarkers for CTE.

Human iPSC 4R tauopathy model uncovers modifiers of tau propagation

Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to lack of appropriate human models. Current human induced pluripotent stem cell (hiPSC)-derived neurons express very low levels of 4-repeat (4R)-tau isoforms that are normally expressed in adult brain. Here, we engineered new iPSC lines to express 4R-tau and 4R-tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes, including shared transcriptomic signatures, autophagic body accumulation, and impaired neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of Tau-seeding-induced Tau propagation, including retromer VPS29 and the UFMylation cascade as top modifiers. In AD brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade suppressed seeding-induced Tau propagation. This model provides a powerful platform to identify novel therapeutic strategies for 4R tauopathy.

Age-dependent increase in tau phosphorylation at serine 396 in Huntington's disease pre-frontal cortex

Background

To date, it is still controversial whether tau phosphorylation plays a role in Huntington's disease (HD), as previous studies demonstrated either no alterations or increases in phosphorylated tau (pTau) in HD post-mortem brain and mouse models.

Objectives

The goal of this study was to determine whether total tau and pTau levels are altered in HD.

Methods

Immunohistochemistry, cellular fractionations, and western blots were used to measure tau and pTau levels in a large cohort of HD and control post-mortem prefrontal cortex (PFC). Furthermore, western blots were performed to assess tau, and pTau levels in HD and control isogenic embryonic stem cell (ESC)-derived cortical neurons and neuronal stem cells (NSCs). Similarly, western blots were used to assess tau and pTau in Htt Q111 and transgenic R6/2 mice. Lastly, total tau levels were assessed in HD and healthy control plasma using Quanterix Simoa assay.

Results

Our results revealed that, while there was no difference in tau or pTau levels in HD PFC compared to controls, tau phosphorylated at S396 levels were increased in PFC samples from HD patients 60 years or older at time of death. Additionally, tau and pTau levels were not changed in HD ESC-derived cortical neurons and NSCs. Similarly, tau or pTau levels were not altered in Htt Q111 and transgenic R6/2 mice compared to wild-type littermates. Lastly, tau levels were not changed in plasma from a small cohort of HD patients compared to controls.

Conclusion

Together these findings demonstrate that pTau-S396 levels increase significantly with age in HD PFC.

Role of microbial dysbiosis in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly and detected during the advanced stages where the chances of reversal are minimum. The gut-brain axis mediates a bidirectional communication between the gut and brain, which is dependent on bacterial products such as short chain fatty acids (SCFA) and neurotransmitters. Accumulating lines of evidence suggests that AD is associated with significant alteration in the composition of gut microbiota. Furthermore, transfer of gut microbiota from healthy individuals to patients can reshape the gut microbiota structure and thus holds the potential to be exploited for the treatment of various neurodegenerative disease. Moreover, AD-associated gut dysbiosis can be partially reversed by using probiotics, prebiotics, natural compounds and dietary modifications, but need further validations. Reversal of AD associated gut dysbiosis alleviate AD-associated pathological feature and therefore can be explored as a therapeutic approach in the future. The current review article will describe various studies suggesting that AD dysbiosis occurs with AD and highlights the causal role by focussing on the interventions that hold the potential to reverse the gut dysbiosis partially.

Insights from Drosophila on Aβ- and tau-induced mitochondrial dysfunction: mechanisms and tools

Alzheimer's disease (AD) is the most prevalent neurodegenerative dementia in older adults worldwide. Sadly, there are no disease-modifying therapies available for treatment due to the multifactorial complexity of the disease. AD is pathologically characterized by extracellular deposition of amyloid beta (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. Increasing evidence suggest that Aβ also accumulates intracellularly, which may contribute to the pathological mitochondrial dysfunction observed in AD. According with the mitochondrial cascade hypothesis, mitochondrial dysfunction precedes clinical decline and thus targeting mitochondria may result in new therapeutic strategies. Unfortunately, the precise mechanisms connecting mitochondrial dysfunction with AD are largely unknown. In this review, we will discuss how the fruit fly Drosophila melanogaster is contributing to answer mechanistic questions in the field, from mitochondrial oxidative stress and calcium dysregulation to mitophagy and mitochondrial fusion and fission. In particular, we will highlight specific mitochondrial insults caused by Aβ and tau in transgenic flies and will also discuss a variety of genetic tools and sensors available to study mitochondrial biology in this flexible organism. Areas of opportunity and future directions will be also considered.

Insulin and Disorders of Behavioural Flexibility

Behavioural inflexibility is a symptom of neuropsychiatric and neurodegenerative disorders such as Obsessive-Compulsive Disorder, Autism Spectrum Disorder and Alzheimer's Disease, encompassing the maintenance of a behaviour even when no longer appropriate. Recent evidence suggests that insulin signalling has roles apart from its regulation of peripheral metabolism and mediates behaviourally-relevant central nervous system (CNS) functions including behavioural flexibility. Indeed, insulin resistance is reported to generate anxious, perseverative phenotypes in animal models, with the Type 2 diabetes medication metformin proving to be beneficial for disorders including Alzheimer's Disease. Structural and functional neuroimaging studies of Type 2 diabetes patients have highlighted aberrant connectivity in regions governing salience detection, attention, inhibition and memory. As currently available therapeutic strategies feature high rates of resistance, there is an urgent need to better understand the complex aetiology of behaviour and develop improved therapeutics. In this review, we explore the circuitry underlying behavioural flexibility, changes in Type 2 diabetes, the role of insulin in CNS outcomes and mechanisms of insulin involvement across disorders of behavioural inflexibility.

Spermidine Rescues Bioenergetic and Mitophagy Deficits Induced by Disease-Associated Tau Protein

Abnormal tau build-up is a hallmark of Alzheimer’s disease (AD) and more than 20 other serious neurodegenerative diseases. Mitochondria are paramount organelles playing a predominant role in cellular bioenergetics, namely by providing the main source of cellular energy via adenosine triphosphate generation. Abnormal tau impairs almost every aspect of mitochondrial function, from mitochondrial respiration to mitophagy. The aim of our study was to investigate the effects of spermidine, a polyamine which exerts neuroprotective effects, on mitochondrial function in a cellular model of tauopathy. Recent evidence identified autophagy as the main mechanism of action of spermidine on life-span prolongation and neuroprotection, but the effects of spermidine on abnormal tau-induced mitochondrial dysfunction have not yet been investigated. We used SH-SY5Y cells stably expressing a mutant form of human tau protein (P301L tau mutation) or cells expressing the empty vector (control cells). We showed that spermidine improved mitochondrial respiration, mitochondrial membrane potential as well as adenosine triphosphate (ATP) production in both control and P301L tau-expressing cells. We also showed that spermidine decreased the level of free radicals, increased autophagy and restored P301L tau-induced impairments in mitophagy. Overall, our findings suggest that spermidine supplementation might represent an attractive therapeutic approach to prevent/counteract tau-related mitochondrial impairments.

DJ-1 Molecular Chaperone Activity Depresses Tau Aggregation Propensity through Interaction with Monomers

Tau aggregate-bearing lesions are pathological markers and potential mediators of tauopathic neurodegenerative diseases, including Alzheimer's disease. The molecular chaperone DJ-1 colocalizes with tau pathology in these disorders, but it has been unclear what functional link exists between them. In this study, we examined the consequences of tau/DJ-1 interaction as isolated proteins in vitro. When added to full-length 2N4R tau under aggregation-promoting conditions, DJ-1 inhibited both the rate and extent of filament formation in a concentration-dependent manner. Inhibitory activity was low affinity, did not require ATP, and was not affected by substituting oxidation incompetent missense mutation C106A for wild-type DJ-1. In contrast, missense mutations previously linked to familial Parkinson's disease and loss of α-synuclein chaperone activity, M26I and E64D, displayed diminished tau chaperone activity relative to wild-type DJ-1. Although DJ-1 directly bound the isolated microtubule-binding repeat region of tau protein, exposure of preformed tau seeds to DJ-1 did not diminish seeding activity in a biosensor cell model. These data reveal DJ-1 to be a holdase chaperone capable of engaging tau as a client in addition to α-synuclein. Our findings support a role for DJ-1 as part of an endogenous defense against the aggregation of these intrinsically disordered proteins.

Nature's Toolbox Against Tau Aggregation: An Updated Review of Current Research

Tau aggregation is a hallmark of several neurodegenerative disorders, such as Alzheimer's disease (AD), frontotemporal dementia, and progressive supranuclear palsy. Hyperphosphorylated tau is believed to contribute to the degeneration of neurons and the development of these complex diseases. Therefore, one potential treatment for these illnesses is to prevent or counteract tau aggregation. In recent years, interest has been increasing in developing nature-derived tau aggregation inhibitors as a potential treatment for neurodegenerative disorders. Researchers have become increasingly interested in natural compounds with multifunctional features, such as flavonoids, alkaloids, resveratrol, and curcumin, since these molecules can interact simultaneously with the various targets of AD. Recent studies have demonstrated that several natural compounds can inhibit tau aggregation and promote the disassembly of pre-formed tau aggregates. Nature-derived tau aggregation inhibitors hold promise as a potential treatment for neurodegenerative disorders. However, it is important to note that more research is needed to fully understand the mechanisms by which these compounds exert their effects and their safety and efficacy in preclinical and clinical studies. Nature-derived inhibitors of tau aggregation are a promising new direction in the research of neurodegenerative complexities. This review focuses on the natural products that have proven to be a rich supply for inhibitors in tau aggregation and their uses in neurodegenerative complexities, including AD.

Extensive accumulation of misfolded protein aggregates during natural aging and senescence

Accumulation of misfolded protein aggregates is a hallmark event in many age-related protein misfolding disorders, including some of the most prevalent and insidious neurodegenerative diseases. Misfolded protein aggregates produce progressive cell damage, organ dysfunction, and clinical changes, which are common also in natural aging. Thus, we hypothesized that aging is associated to the widespread and progressive misfolding and aggregation of many proteins in various tissues. In this study, we analyzed whether proteins misfold, aggregate, and accumulate during normal aging in three different biological systems, namely senescent cells, Caenorhabditis elegans, and mouse tissues collected at different times from youth to old age. Our results show a significant accumulation of misfolded protein aggregates in aged samples as compared to young materials. Indeed, aged samples have between 1.3 and 2.5-fold (depending on the biological system) higher amount of insoluble proteins than young samples. These insoluble proteins exhibit the typical characteristics of disease-associated aggregates, including insolubility in detergents, protease resistance, and staining with amyloid-binding dye as well as accumulation in aggresomes. We identified the main proteins accumulating in the aging brain using proteomic studies. These results show that the aged brain contain large amounts of misfolded and likely non-functional species of many proteins, whose soluble versions participate in cellular pathways that play fundamental roles in preserving basic functions, such as protein quality control, synapsis, and metabolism. Our findings reveal a putative role for protein misfolding and aggregation in aging.

Using ΔK280 TauRD Folding Reporter Cells to Screen TRKB Agonists as Alzheimer's Disease Treatment Strategy

Misfolded aggregation of the hyperphosphorylated microtubule binding protein Tau in the brain is a pathological hallmark of Alzheimer's disease (AD). Tau aggregation downregulates brain-derived neurotrophic factor (BDNF)/tropomycin receptor kinase B (TRKB) signaling and leads to neurotoxicity. Therefore, enhancement of BDNF/TRKB signaling could be a strategy to alleviate Tau neurotoxicity. In this study, eight compounds were evaluated for the potential of inhibiting Tau misfolding in human neuroblastoma SH-SY5Y cells expressing the pro-aggregator Tau folding reporter (ΔK280 Tau_RD-DsRed). Among them, coumarin derivative ZN-015 and quinoline derivatives VB-030 and VB-037 displayed chemical chaperone activity to reduce ΔK280 Tau_RD aggregation and promote neurite outgrowth. Studies of TRKB signaling revealed that ZN-015, VB-030 and VB-037 treatments significantly increased phosphorylation of TRKB and downstream Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), extracellular signal-regulated kinase 1/2 (ERK) and AKT serine/threonine kinase (AKT), to activate ribosomal S6 kinase (RSK) and cAMP response element-binding protein (CREB). Subsequently, p-CREB enhanced the transcription of pro-survival BDNF and BCL2 apoptosis regulator (BCL2), accompanied with reduced expression of anti-survival BCL2-associated X protein (BAX) in ΔK280 Tau_RD-DsRed-expressing cells. The neurite outgrowth promotion effect of ZN-015, VB-030 and VB-037 was counteracted by a RNA interference-mediated knockdown of TRKB, suggesting the role of these compounds acting as TRKB agonists. Tryptophan fluorescence quenching analysis showed that ZN-015, VB-030 and VB-037 interacted directly with a Pichia pastoris-expressed TRKB extracellular domain, indirectly supporting the role through TRKB signaling. The results of up-regulation in TRKB signaling open up the therapeutic potentials of ZN-015, VB-030 and VB-037 for AD.

Age-Dependent Increase in Tau Phosphorylation at Serine 396 in Huntington's Disease Prefrontal Cortex

BACKGROUND

To date, it is still controversial whether tau phosphorylation plays a role in Huntington's disease (HD), as previous studies demonstrated either no alterations or increases in phosphorylated tau (pTau) in HD postmortem brain and mouse models.

OBJECTIVE

The goal of this study was to determine whether total tau and pTau levels are altered in HD.

METHODS

Immunohistochemistry, cellular fractionations, and western blots were used to measure total tau and pTau levels in a large cohort of HD and control postmortem prefrontal cortex (PFC). Furthermore, western blots were performed to assess tau, and pTau levels in HD and control isogenic embryonic stem cell (ESC)-derived cortical neurons and neuronal stem cells (NSCs). Similarly, western blots were used to assess tau and pTau levels in HttQ111 and transgenic R6/2 mice. Lastly, total tau levels were assessed in HD and healthy control plasma using Quanterix Simoa assay.

RESULTS

Our results revealed that, while there was no difference in total tau or pTau levels in HD PFC compared to controls, the levels of tau phosphorylated at S396 were increased in PFC samples from HD patients 60 years or older at time of death. Additionally, tau and pTau levels were not changed in HD ESC-derived cortical neurons and NSCs. Similarly, total tau or pTau levels were not altered in HttQ111 and transgenic R6/2 mice compared to wild-type littermates. Lastly, tau levels were not changed in plasma from a small cohort of HD patients compared to controls.

CONCLUSIONS

Together these findings demonstrate that pTau-S396 levels increase significantly with age in HD PFC.

Mechanistic and therapeutic implications of EphA-4 receptor tyrosine kinase in the pathogenesis of Alzheimer's disease

Erythropoietin-producing hepatoma (Eph) receptors belong to a family of tyrosine kinase receptors that plays a pivotal role in the development of the brain. Eph can be divided broadly into two groups, namely, EphA and EphB, comprising nine and five members, respectively. In recent years, the role of EphA-4 has become increasingly apparent in the onset of Alzheimer's disease (AD). Emerging evidence suggests that EphA-4 results in synaptic dysfunction, which in turn promotes the progression of AD. Moreover, pharmacological or genetic ablation of EphA-4 in the murine model of AD can alleviate the symptoms. The current review summarizes different pathways by which EphA-4 can influence pathogenesis. Since, majority of the studies had reported the protective effect of EphA-4 inhibition during AD, designing therapeutics based on decreasing its enzymatic activity might be necessary for introducing the novel interventions. Therefore, the review described peptide and nanobodies inhibitors of EphA-4 that exhibit the potential to modulate EphA-4 and could be used as lead molecules for the targeted therapy of AD.

Mechanistic and therapeutic role of Drp1 in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, has emerged as the most common form of dementia in the elderly. Two major pathological hallmarks have been identified for AD: extracellular amyloid plaques and intracellular neurofibrillary tangles (NFT). Recently, dynamin-related protein 1 (Drp1) was recognized to contribute significantly towards the pathogenesis of AD. Drp1 is primarily located in the cytosol, from where it translocates to the mitochondrial outer membrane and drives the mitochondrial fission via GTP hydrolysis. Drp1 interacts with Aβ and phosphorylated tau, leading to excessive mitochondrial fragmentation, which in turn results in synaptic dysfunction, neuronal damage and cognitive decline. Several studies suggest an increase in the level of Drp1 in the post-mortem brain specimen collected from the AD patients and murine models of AD. Interestingly, heterozygous deletion of Drp1 in the transgenic murine model of AD ameliorates the mitochondrial dysfunction, improving learning and memory. The current review article discusses the possible mechanistic pathways by which Drp1 can influence the pathogenesis of AD. Besides, it will describe various inhibitors for Drp1 and their potential role as therapeutics for AD in the future.

Role of proline-rich tyrosine kinase 2 (Pyk2) in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is the most common form of dementia in the elderly. Two major pathological hallmarks have been identified for AD: extracellular amyloid plaques and intracellular neurofibrillary tangles (NFT). Recently, proline-rich tyrosine kinase 2 (Pyk2), which belongs to the focal adhesion kinase (FAK) non-receptor tyrosine kinase family, was recognized to contribute significantly towards the pathogenesis of AD. Pyk2 can influence the formation of amyloid plaques as well as NFTs. The kinase can directly phosphorylate tau, which is a significant component of NFTs and enhances tau pathology. Several competitive inhibitors have been developed for Pyk2, tested in several cancer models, as Pyk2 is known to be overexpressed under those conditions. The current review article discusses the possible mechanistic pathways by which Pyk2 can influence the pathogenesis of AD. Besides, it describes various inhibitors for Pyk2 and their potential role as therapeutics for AD in the future.

Longitudinal characterization of retinal vasculature alterations with optical coherence tomography angiography in a mouse model of tauopathy

Tauopathies are a family of neurodegenerative diseases which predominately afflict the rapidly growing aging population suffering from various brain disorders including Alzheimer's disease, frontotemporal dementia with parkinsonism-17 and Pick disease. As the only visually accessible region of the central nervous system, in recent years, the retina has attracted extensive attention for its potential as a target for visualizing and quantifying emerging biomarkers of neurodegenerative diseases. Our previous study has found that retinal vascular inflammation and leakage occur at the very early stage of tauopathic mouse model. Here, we aimed to non-invasively visualize age-dependent alterations of retinal vasculature assessing the potential for using changes in retinal vasculature as the biomarker for the early diagnosis of tauopathy. Optical coherence tomography angiography (OCTA), a non-invasive depth-resolved high-resolution imaging technique was used to visualize and quantify tauopathy-induced alterations of retinal vasculature in P301S transgenic mice overexpressing the P301S mutant form of human tau and age-matched wild type littermate mice at 3, 6 and 10 months of age. We observed significant alterations of vascular features in the intermediate capillary plexus (ICP) and deep capillary plexus (DCP) but not in the superficial vascular complex (SVC) of P301S mice at early stages of tauopathy. With aging, alterations of vascular features in P301S mice became more prominent in all three vascular plexuses. Staining of retinal vasculature in flatmounts and trypsin digests of P301S mice at 10 months of age revealed decreased vessel density and increased acellular capillary formation, indicating that vascular degeneration also occurs during tauopathy. Overall, our results demonstrate that the changes in retinal vascular features accelerate during the progression of tauopathy. Vessels in the ICP and DCP may be more susceptible to tauopathy than vessels in the SVC. Since changes in retinal vasculature often precede tau pathology in the brain, non-invasive identification of retinal vascular alterations with OCTA may be a useful biomarker for the early diagnosis of tauopathy and monitoring its progression.

SYK coordinates neuroprotective microglial responses in neurodegenerative disease

Recent studies have begun to reveal critical roles for the brain's professional phagocytes, microglia, and their receptors in the control of neurotoxic amyloid beta (Aβ) and myelin debris accumulation in neurodegenerative disease. However, the critical intracellular molecules that orchestrate neuroprotective functions of microglia remain poorly understood. In our studies, we find that targeted deletion of SYK in microglia leads to exacerbated Aβ deposition, aggravated neuropathology, and cognitive defects in the 5xFAD mouse model of Alzheimer's disease (AD). Disruption of SYK signaling in this AD model was further shown to impede the development of disease-associated microglia (DAM), alter AKT/GSK3β-signaling, and restrict Aβ phagocytosis by microglia. Conversely, receptor-mediated activation of SYK limits Aβ load. We also found that SYK critically regulates microglial phagocytosis and DAM acquisition in demyelinating disease. Collectively, these results broaden our understanding of the key innate immune signaling molecules that instruct beneficial microglial functions in response to neurotoxic material.

Phosphorylated Tau in Alzheimer's Disease and Other Tauopathies

Alzheimer's disease (AD) is the leading cause of dementia in elderly people. Amyloid beta (Aβ) deposits and neurofibrillary tangles are the major pathological features in an Alzheimer's brain. These proteins are highly expressed in nerve cells and found in most tissues. Tau primarily provides stabilization to microtubules in the part of axons and dendrites. However, tau in a pathological state becomes hyperphosphorylated, causing tau dysfunction and leading to synaptic impairment and degeneration of neurons. This article presents a summary of the role of tau, phosphorylated tau (p-tau) in AD, and other tauopathies. Tauopathies, including Pick's disease, frontotemporal dementia, corticobasal degeneration, Alzheimer's disease, argyrophilic grain disease, progressive supranuclear palsy, and Huntington's disease, are the result of misprocessing and accumulation of tau within the neuronal and glial cells. This article also focuses on current research on the post-translational modifications and genetics of tau, tau pathology, the role of tau in tauopathies and the development of new drugs targeting p-tau, and the therapeutics for treating and possibly preventing tauopathies.