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The microtubule associated protein, tau, is implicated in a multitude of neurodegenerative disorders that are collectively termed as tauopathies. These disorders are characterized by the presence of tau aggregates within the brain of afflicted individuals. Mutations within the MAPT gene that encodes the tau protein form the genetic backdrop for familial forms of tauopathies, such as frontotemporal dementia (FTD), but the molecular consequences of such alterations and their pathological effects are unclear. We sought to investigate the conformational properties of the aggregates of three tau mutants: A152T, P301L, and R406W, all implicated within FTD, and compare them to those of the native form (WT-Tau 2N4R). Our immunochemical analysis reveals that mutants and WT tau oligomers exhibit similar affinity for conformation-specific antibodies but have distinct morphology and secondary structure. Additionally, these oligomers possess different dye-binding properties and varying sensitivity to proteolytic processing. These results point to conformational variety among them. We then tested the ability of the mutant oligomers to cross-seed the aggregation of WT tau monomer. Using similar array of experiments, we found that cross-seeding with mutant aggregates leads to the formation of conformationally unique WT oligomers. The results discussed in this paper provide a novel perspective on the structural properties of oligomeric forms of WT tau 2N4R and its mutant, along with shedding some light on their cross-seeding behavior.
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Tauopatías , Proteínas tau , Proteínas tau/química , Proteínas tau/genética , Proteínas tau/metabolismo , Humanos , Tauopatías/genética , Tauopatías/metabolismo , Mutación , Conformación Proteica , Multimerización de Proteína , Demencia Frontotemporal/genética , Demencia Frontotemporal/metabolismoRESUMEN
Pathological tau aggregates cause cognitive decline in neurodegenerative tauopathies, including Alzheimer's disease (AD). These aggregates are prevalent within intracellular compartments. Current tau immunotherapies have shown limited efficacy in clearing intracellular tau aggregates and improving cognition in clinical trials. In this study, we developed toxic tau conformation-specific monoclonal antibody-2 (TTCM2), which selectively recognized pathological tau aggregates in brain tissues from patients with AD, dementia with Lewy bodies (DLB), and progressive supranuclear palsy (PSP). TTCM2 potently inhibited tau-seeding activity, an essential mechanism underlying tauopathy progression. To effectively target intracellular tau aggregates and ensure rapid delivery to the brain, TTCM2 was loaded in micelles (TTCM2-ms) and administered through the intranasal route. We found that intranasally administered TTCM2-ms efficiently entered the brain in hTau-tauopathy mice, targeting pathological tau in intracellular compartments. Moreover, a single intranasal dose of TTCM2-ms effectively cleared pathological tau, elevated synaptic proteins, and improved cognitive functions in aged tauopathy mice. Mechanistic studies revealed that TTCM2-ms cleared intracellular, synaptic, and seed-competent tau aggregates through tripartite motif-containing 21 (TRIM21), an intracellular antibody receptor and E3 ubiquitin ligase known to facilitate proteasomal degradation of cytosolic antibody-bound proteins. TRIM21 was found to be essential for TTCM2-ms-mediated clearance of tau pathology. Our study collectively provides evidence of the effectiveness of nasal tau immunotherapy in targeting and clearing intracellular tau pathology through TRIM21 and enhancing cognition in aged tauopathy mice. This study could be valuable in designing effective tau immunotherapies for AD and other tauopathies.
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Cognición , Tauopatías , Proteínas tau , Animales , Humanos , Ratones , Administración Intranasal , Envejecimiento/patología , Anticuerpos Monoclonales/farmacología , Encéfalo/patología , Encéfalo/metabolismo , Modelos Animales de Enfermedad , Inmunoterapia/métodos , Ratones Transgénicos , Agregado de Proteínas/efectos de los fármacos , Proteínas tau/metabolismo , Tauopatías/inmunología , Tauopatías/metabolismo , Tauopatías/patología , Tauopatías/terapiaRESUMEN
This study investigates various pathological tau isoforms in the retina of individuals with early and advanced Alzheimer's disease (AD), exploring their connection with disease status. Retinal cross-sections from predefined superior-temporal and inferior-temporal subregions and corresponding brains from neuropathologically confirmed AD patients with a clinical diagnosis of either mild cognitive impairment (MCI) or dementia (n = 45) were compared with retinas from age- and sex-matched individuals with normal cognition (n = 30) and non-AD dementia (n = 4). Retinal tau isoforms, including tau tangles, paired helical filament of tau (PHF-tau), oligomeric-tau (Oligo-tau), hyperphosphorylated-tau (p-tau), and citrullinated-tau (Cit-tau), were stereologically analyzed by immunohistochemistry and Nanostring GeoMx digital spatial profiling, and correlated with clinical and neuropathological outcomes. Our data indicated significant increases in various AD-related pretangle tau isoforms, especially p-tau (AT8, 2.9-fold, pS396-tau, 2.6-fold), Cit-tau at arginine residue 209 (CitR209-tau; 4.1-fold), and Oligo-tau (T22+, 9.2-fold), as well as pretangle and mature tau tangle forms like MC-1-positive (1.8-fold) and PHF-tau (2.3-fold), in AD compared to control retinas. MCI retinas also exhibited substantial increases in Oligo-tau (5.2-fold), CitR209-tau (3.5-fold), and pS396-tau (2.2-fold). Nanostring GeoMx analysis confirmed elevated retinal p-tau at epitopes: Ser214 (2.3-fold), Ser396 (2.6-fold), Ser404 (2.4-fold), and Thr231 (1.8-fold), particularly in MCI patients. Strong associations were found between retinal tau isoforms versus brain pathology and cognitive status: a) retinal Oligo-tau vs. Braak stage, neurofibrillary tangles (NFTs), and CDR cognitive scores (ρ = 0.63-0.71), b) retinal PHF-tau vs. neuropil threads (NTs) and ABC scores (ρ = 0.69-0.71), and c) retinal pS396-tau vs. NTs, NFTs, and ABC scores (ρ = 0.67-0.74). Notably, retinal Oligo-tau strongly correlated with retinal Aß42 and arterial Aß40 forms (r = 0.76-0.86). Overall, this study identifies and quantifies diverse retinal tau isoforms in MCI and AD patients, underscoring their link to brain pathology and cognition. These findings advocate for further exploration of retinal tauopathy biomarkers to facilitate AD detection and monitoring via noninvasive retinal imaging.
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Enfermedad de Alzheimer , Isoformas de Proteínas , Retina , Proteínas tau , Humanos , Proteínas tau/metabolismo , Masculino , Femenino , Anciano , Enfermedad de Alzheimer/patología , Enfermedad de Alzheimer/metabolismo , Retina/patología , Retina/metabolismo , Anciano de 80 o más Años , Disfunción Cognitiva/patología , Disfunción Cognitiva/metabolismo , Persona de Mediana Edad , Ovillos Neurofibrilares/patología , Ovillos Neurofibrilares/metabolismo , Encéfalo/patología , Encéfalo/metabolismoRESUMEN
BACKGROUND: Tau post-translational modifications (PTMs) result in the gradual build-up of abnormal tau and neuronal degeneration in tauopathies, encompassing variants of frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). Tau proteolytically cleaved by active caspases, including caspase-6, may be neurotoxic and prone to self-aggregation. Also, our recent findings show that caspase-6 truncated tau represents a frequent and understudied aspect of tau pathology in AD in addition to phospho-tau pathology. In AD and Pick's disease, a large percentage of caspase-6 associated cleaved-tau positive neurons lack phospho-tau, suggesting that many vulnerable neurons to tau pathology go undetected when using conventional phospho-tau antibodies and possibly will not respond to phospho-tau based therapies. Therefore, therapeutic strategies against caspase cleaved-tau pathology could be necessary to modulate the extent of tau abnormalities in AD and other tauopathies. METHODS: To understand the timing and progression of caspase activation, tau cleavage, and neuronal death, we created two mAbs targeting caspase-6 tau cleavage sites and probed postmortem brain tissue from an individual with FTLD due to the V337M MAPT mutation. We then assessed tau cleavage and apoptotic stress response in cortical neurons derived from induced pluripotent stem cells (iPSCs) carrying the FTD-related V337M MAPT mutation. Finally, we evaluated the neuroprotective effects of caspase inhibitors in these iPSC-derived neurons. RESULTS: FTLD V337M MAPT postmortem brain showed positivity for both cleaved tau mAbs and active caspase-6. Relative to isogenic wild-type MAPT controls, V337M MAPT neurons cultured for 3 months post-differentiation showed a time-dependent increase in pathogenic tau in the form of caspase-cleaved tau, phospho-tau, and higher levels of tau oligomers. Accumulation of toxic tau species in V337M MAPT neurons was correlated with increased vulnerability to pro-apoptotic stress. Notably, this mutation-associated cell death was pharmacologically rescued by the inhibition of effector caspases. CONCLUSIONS: Our results suggest an upstream, time-dependent accumulation of caspase-6 cleaved tau in V337M MAPT neurons promoting neurotoxicity. These processes can be reversed by caspase inhibition. These results underscore the potential of developing caspase-6 inhibitors as therapeutic agents for FTLD and other tauopathies. Additionally, they highlight the promise of using caspase-cleaved tau as biomarkers for these conditions.
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Alzheimer's disease and other tauopathies are characterized by the misfolding and aggregation of the tau protein into oligomeric and fibrillar structures. Antibodies against tau play an increasingly important role in studying these neurodegenerative diseases and the generation of tools to diagnose and treat them. The development of antibodies that recognize tau protein aggregates, however, is hindered by complex immunization and antibody selection strategies and limitations to antigen presentation. Here, we have taken a facile approach to identify single-domain antibodies, or nanobodies, that bind to many forms of tau by screening a synthetic yeast surface display nanobody library against monomeric tau and creating multivalent versions of our lead nanobody, MT3.1, to increase its avidity for tau aggregates. We demonstrate that MT3.1 binds to tau monomer, oligomers, and fibrils, as well as pathogenic tau from a tauopathy mouse model, despite being identified through screens against monomeric tau. Through epitope mapping, we discovered binding epitopes of MT3.1 contain the key motif VQIXXK which drives tau aggregation. We show that our bivalent and tetravalent versions of MT3.1 have greatly improved binding ability to tau oligomers and fibrils compared to monovalent MT3.1. Our results demonstrate the utility of our nanobody screening and multivalent design approach in developing nanobodies that bind amyloidogenic protein aggregates. This approach can be extended to the generation of multivalent nanobodies that target other amyloid proteins and has the potential to advance the research and treatment of neurodegenerative diseases.
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Type 2 diabetes (T2D) is a common forerunner of neurodegeneration and dementia, including Alzheimer's Disease (AD), yet the underlying mechanisms remain unresolved. Individuals of Mexican descent living in South Texas have increased prevalence of comorbid T2D and early onset AD, despite low incidence of the predisposing APOE-e4 variant and an absence of the phenotype among relatives residing in Mexico - suggesting a role for environmental factors in coincident T2D and AD susceptibility. Here, in a small clinical trial, we show dysbiosis of the human gut microbiome could contribute to neuroinflammation and risk for AD in this population. Divergent Gastrointestinal Symptom Rating Scale (GSRS) responses, despite no differences in expressed dietary preferences, provided the first evidence for altered gut microbial ecology among T2D subjects (sT2D) versus population-matched healthy controls (HC). Metataxonomic 16S rRNA sequencing of participant stool revealed a decrease in alpha diversity of sT2D versus HC gut communities and identified BMI as a driver of gut community structure. Linear discriminant analysis effect size (LEfSe) identified a significant decrease in the relative abundance of the short-chain fatty acid-producing taxa Lachnospiraceae, Faecalibacterium, and Alistipes and an increase in pathobionts Escherichia-Shigella, Enterobacter, and Clostridia innocuum among sT2D gut microbiota, as well as differentially abundant gene and metabolic pathways. These results suggest characterization of the gut microbiome of individuals with T2D could identify key actors among "disease state" microbiota which may increase risk for or accelerate the onset of neurodegeneration. Furthermore, they identify candidate microbiome-targeted approaches for prevention and treatment of neuroinflammation in AD.
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The pathological misfolding and aggregation of the microtubule associated protein tau (MAPT), a full length Tau2N4R with 441aa, is considered the principal disease relevant constituent in tauopathies including Alzheimer's disease (AD) with an imbalanced ratio in 3R/4R isoforms. The exact cellular fluid composition, properties, and changes that coincide with tau misfolding, seed formation, and propagation events remain obscure. The proteostasis network, along with the associated osmolytes, is responsible for maintaining the presence of tau in its native structure or dealing with misfolding. In this study, for the first time, the roles of natural brain osmolytes are being investigated for their potential effects on regulating the conformational stability of the tau monomer (tauM) and its propensity to aggregate or disaggregate. Herein, the effects of physiological osmolytes myo-inositol, taurine, trimethyl amine oxide (TMAO), betaine, sorbitol, glycerophosphocholine (GPC), and citrulline on tau's aggregation state were investigated. The overall results indicate the ability of sorbitol and GPC to maintain the monomeric form and prevent aggregation of tau, whereas myo-inositol, taurine, TMAO, betaine, and citrulline promote tau aggregation to different degrees, as revealed by protein morphology in atomic force microscopy images. Biochemical and biophysical methods also revealed that tau proteins adopt different conformations under the influence of these osmolytes. TauM in the presence of all osmolytes expressed no toxicity when tested by a lactate dehydrogenase assay. Investigating the conformational stability of tau in the presence of osmolytes may provide a better understanding of the complex nature of tau aggregation in AD and the protective and/or chaotropic nature of osmolytes.
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Enfermedad de Alzheimer , Metilaminas , Proteínas tau , Humanos , Proteínas tau/metabolismo , Betaína , Citrulina , Enfermedad de Alzheimer/tratamiento farmacológico , Enfermedad de Alzheimer/metabolismo , Taurina/farmacología , Inositol/metabolismo , Sorbitol/metabolismoRESUMEN
Aggregation of α-synuclein into oligomers and fibrils is associated with numerous neurodegenerative diseases such as Parkinson's disease (PD). Although the identity of the pathogenic species formed during the aggregation process is still under active debate, mounting evidence suggests that small oligomeric species rather than fibrillar aggregates are real toxic species. Isolation and characterization of small oligomers is essential to developing therapeutic strategies to prevent oligomer formation. Preparation of misfolded oligomeric species for biophysical characterization is, however, a great challenge due to their heterogenous, transient nature. Here we report the preparation of toxic and non-toxic α-synuclein oligomeric species formed at different pH values in the presence of lipid vesicles that mimic mitochondria membranes containing cardiolipin. Biophysical characterization of the lipid-induced α-synuclein oligomeric assemblies revealed that α-synuclein oligomers formed at pH 7.4 have higher surface hydrophobicity than the aggregates formed at pH 6.0. In addition, the high-pH oligomers were shown to exhibit higher toxicity than the low-pH aggregates. Structural, dynamic properties of the oligomers were also investigated by using circular dichroism (CD) and NMR spectroscopy. Our CD analyses revealed that the two oligomeric species have distinct molecular conformations, and 2D 1H/15N HSQC NMR experiments suggested that the high-pH oligomers have more extended dynamic regions than the low-pH aggregates. The distinct structural and dynamic properties of the oligomers might be associated with their different cytotoxic properties.
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Tau oligomers have been shown to be the main toxic tau species in several neurodegenerative disorders. To study tau oligomers, we have developed reagents and established methods for the reliable preparation, isolation, and detection of tau oligomers as well as their seeding and propagation both in vitro and in vivo. Detailed below are methods for isolation of tau oligomers from brain tissues and detection of tau oligomers using tau oligomer-specific antibodies by biochemical, immunohistochemical, and biophysical methods. Further, methods for evaluating the biological activity of the tau oligomers including their effects on synaptic function, seeding, and propagation in cell models and in vivo are also described.
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Enfermedad de Alzheimer , Proteínas tau , Humanos , Proteínas tau/química , Anticuerpos , BiofisicaRESUMEN
Importance: This study identifies and quantifies diverse pathological tau isoforms in the retina of both early and advanced-stage Alzheimer's disease (AD) and determines their relationship with disease status. Objective: A case-control study was conducted to investigate the accumulation of retinal neurofibrillary tangles (NFTs), paired helical filament (PHF)-tau, oligomeric tau (oligo-tau), hyperphosphorylated tau (p-tau), and citrullinated tau (Cit-tau) in relation to the respective brain pathology and cognitive dysfunction in mild cognitively impaired (MCI) and AD dementia patients versus normal cognition (NC) controls. Design setting and participants: Eyes and brains from donors diagnosed with AD, MCI (due to AD), and NC were collected (n=75 in total), along with clinical and neuropathological data. Brain and retinal cross-sections-in predefined superior-temporal and inferior-temporal (ST/IT) subregions-were subjected to histopathology analysis or Nanostring GeoMx digital spatial profiling. Main outcomes and measure: Retinal burden of NFTs (pretangles and mature tangles), PHF-tau, p-tau, oligo-tau, and Cit-tau was assessed in MCI and AD versus NC retinas. Pairwise correlations revealed associations between retinal and brain parameters and cognitive status. Results: Increased retinal NFTs (1.8-fold, p=0.0494), PHF-tau (2.3-fold, p<0.0001), oligo-tau (9.1-fold, p<0.0001), CitR 209 -tau (4.3-fold, p<0.0001), pSer202/Thr205-tau (AT8; 4.1-fold, p<0.0001), and pSer396-tau (2.8-fold, p=0.0015) were detected in AD patients. Retinas from MCI patients showed significant increases in NFTs (2.0-fold, p=0.0444), CitR 209 -tau (3.5-fold, p=0.0201), pSer396-tau (2.6-fold, p=0.0409), and, moreover, oligo-tau (5.8-fold, p=0.0045). Nanostring GeoMx quantification demonstrated upregulated retinal p-tau levels in MCI patients at phosphorylation sites of Ser214 (2.3-fold, p=0.0060), Ser396 (1.8-fold, p=0.0052), Ser404 (2.4-fold, p=0.0018), and Thr231 (3.3-fold, p=0.0028). Strong correlations were found between retinal tau forms to paired-brain pathology and cognitive status: a) retinal oligo-tau vs. Braak stage (r=0.60, P=0.0002), b) retinal PHF-tau vs. ABC average score (r=0.64, P=0.0043), c) retinal pSer396-tau vs. brain NFTs (r=0.68, P<0.0001), and d) retinal pSer202/Thr205-tau vs. MMSE scores (r= -0.77, P=0.0089). Conclusions and Relevance: This study reveals increases in immature and mature retinal tau isoforms in MCI and AD patients, highlighting their relationship with brain pathology and cognition. The data provide strong incentive to further explore retinal tauopathy markers that may be useful for early detection and monitoring of AD staging through noninvasive retinal imaging.
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Hexanucleotide repeat expansion in C9orf72 is one of the most common causes of amyotrophic lateral sclerosis and frontotemporal dementia. The hexanucleotide expansion, formed by GGGGCC (G4C2) repeats, leads to the production of five dipeptide protein repeats (DPRs) via repeat-associated non-AUG translation. Among the five dipeptide repeats, Gly-Arg, Pro-Arg, and Gly-Ala form neuronal inclusions that contain aggregates of the peptides. Several studies have attempted to model DPR-associated toxicity using various repeat lengths, which suggests a unique conformation that is cytotoxic and is independent of the repeat length. However, the structural characteristics of DPR aggregates have yet to be determined. Increasing evidence suggests that soluble species, such as oligomers, are the main cause of toxicity in proteinopathies, such as Alzheimer's and Parkinson's disease. To investigate the ability of DPRs to aggregate and form toxic oligomers, we adopted a reductionist approach using small dipeptide repeats of 3, 6, and 12. This study shows that DPRs, particularly glycine-arginine and proline-arginine, form oligomers that exhibit distinct dye-binding properties and morphologies. Importantly, we also identified toxic DPR oligomers in amyotrophic lateral sclerosis and frontotemporal dementia postmortem brains that are morphologically similar to those generated recombinantly. This study demonstrates that, similar to soluble oligomers formed by various amyloid proteins, DPR oligomers are toxic, independent of their repeat length.
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Esclerosis Amiotrófica Lateral , Demencia Frontotemporal , Humanos , Demencia Frontotemporal/genética , Esclerosis Amiotrófica Lateral/genética , Esclerosis Amiotrófica Lateral/metabolismo , Proteína C9orf72/genética , Proteína C9orf72/metabolismo , Expansión de las Repeticiones de ADN , Dipéptidos/química , Arginina , Proteínas Amiloidogénicas , GlicinaRESUMEN
Aging, tau pathology, and chronic inflammation in the brain play crucial roles in synaptic loss, neurodegeneration, and cognitive decline in tauopathies, including Alzheimer's disease. Senescent cells accumulate in the aging brain, accelerate the aging process, and promote tauopathy progression through their abnormal inflammatory secretome known as the senescence-associated secretory phenotype (SASP). Tau oligomers (TauO)-the most neurotoxic tau species-are known to induce senescence and the SASP, which subsequently promote neuropathology, inflammation, oxidative stress, synaptic dysfunction, neuronal death, and cognitive dysfunction. TauO, brain inflammation, and senescence are associated with heterogeneity in tauopathy progression and cognitive decline. However, the underlying mechanisms driving the disease heterogeneity remain largely unknown, impeding the development of therapies for tauopathies. Based on clinical and preclinical evidence, this review highlights the critical role of TauO and senescence in neurodegeneration. We discuss key knowledge gaps and potential strategies for targeting senescence and TauO to treat tauopathies. HIGHLIGHTS: Senescence, oligomeric Tau (TauO), and brain inflammation accelerate the aging process and promote the progression of tauopathies, including Alzheimer's disease. We discuss their role in contributing to heterogeneity in tauopathy and cognitive decline. We highlight strategies to target senescence and TauO to treat tauopathies while addressing key knowledge gaps.
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Enfermedad de Alzheimer , Disfunción Cognitiva , Encefalitis , Tauopatías , Humanos , Enfermedad de Alzheimer/patología , Proteínas tau/metabolismo , Tauopatías/patología , Encéfalo/patología , Encefalitis/complicaciones , Encefalitis/patología , Disfunción Cognitiva/patología , InflamaciónRESUMEN
The misfolding and aggregation of the tau protein into neurofibrillary tangles constitutes a central feature of tauopathies. Traumatic brain injury (TBI) has emerged as a potential risk factor, triggering the onset and progression of tauopathies. Our previous research revealed distinct polymorphisms in soluble tau oligomers originating from single versus repetitive mild TBIs. However, the mechanisms orchestrating the dissemination of TBI brain-derived tau polymorphs (TBI-BDTPs) remain elusive. In this study, we explored whether TBI-BDTPs could initiate pathological tau formation, leading to distinct pathogenic trajectories. Wild-type mice were exposed to TBI-BDTPs from sham, single-blast (SB), or repeated-blast (RB) conditions, and their memory function was assessed through behavioral assays at 2- and 8-month post-injection. Our findings revealed that RB-BDTPs induced cognitive and motor deficits, concurrently fostering the emergence of toxic tau aggregates within the injected hippocampus. Strikingly, this tau pathology propagated to cortical layers, intensifying over time. Importantly, RB-BDTP-exposed animals displayed heightened glial cell activation, NLRP3 inflammasome formation, and increased TBI biomarkers, particularly triggering the aggregation of S100B, which is indicative of a neuroinflammatory response. Collectively, our results shed light on the intricate mechanisms underlying TBI-BDTP-induced tau pathology and its association with neuroinflammatory processes. This investigation enhances our understanding of tauopathies and their interplay with neurodegenerative and inflammatory pathways following traumatic brain injury.
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Lesiones Traumáticas del Encéfalo , Tauopatías , Ratones , Animales , Proteínas tau/metabolismo , Lesiones Traumáticas del Encéfalo/complicaciones , Tauopatías/metabolismo , Ovillos Neurofibrilares/metabolismo , Inflamación/complicaciones , Modelos Animales de EnfermedadRESUMEN
Before the controversial approval of humanized monoclonal antibody lecanemab, which binds to the soluble amyloid-ß protofibrils, all the treatments available earlier, for Alzheimer's disease (AD) were symptomatic. The researchers are still struggling to find a breakthrough in AD therapeutic medicine, which is partially attributable to lack in understanding of the structural information associated with the intrinsically disordered proteins and amyloids. One of the major challenges in this area of research is to understand the structural diversity of intrinsically disordered proteins under in vitro conditions. Therefore, in this review, we have summarized the in vitro applications of biophysical methods, which are aimed to shed some light on the heterogeneity, pathogenicity, structures and mechanisms of the intrinsically disordered protein aggregates associated with proteinopathies including AD. This review will also rationalize some of the strategies in modulating disease-relevant pathogenic protein entities by small molecules using structural biology approaches and biophysical characterization. We have also highlighted tools and techniques to simulate the in vivo conditions for native and cytotoxic tau/amyloids assemblies, urge new chemical approaches to replicate tau/amyloids assemblies similar to those in vivo conditions, in addition to designing novel potential drugs.
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The ß-sheet-rich amyloid core is the defining feature of protein aggregates associated with neurodegenerative disorders. Recent investigations have revealed that there exist multiple examples of the same protein, with the same sequence, forming a variety of amyloid cores with distinct structural characteristics. These structural variants, termed as polymorphs, are hypothesized to influence the pathological profile and the progression of different neurodegenerative diseases, giving rise to unique phenotypic differences. Thus, identifying the origin and properties of these structural variants remain a focus of studies, as a preliminary step in the development of therapeutic strategies. Here, we review the potential role of the flanking regions of amyloid cores in inducing polymorphism. These regions, adjacent to the amyloid cores, show a preponderance for being structurally disordered, imbuing them with functional promiscuity. The dynamic nature of the flanking regions can then manifest in the form of conformational polymorphism of the aggregates. We take a closer look at the sequences flanking the amyloid cores, followed by a review of the polymorphic aggregates of the well-characterized proteins amyloid-ß, α-synuclein, Tau, and TDP-43. We also consider different factors that can potentially influence aggregate structure and how these regions can be viewed as novel targets for therapeutic strategies by utilizing their unique structural properties.
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Amiloide , alfa-Sinucleína/metabolismo , Amiloide/química , Amiloide/genética , Amiloide/metabolismo , Péptidos beta-Amiloides/química , Agregado de Proteínas , Conformación Proteica en Lámina beta , HumanosRESUMEN
Tau protein blood levels dependent on its distribution to peripheral organs and possible elimination from the body. Thus, the peripheral distribution of CSF-derived tau protein was explored, especially since there is a transition to blood-based biomarkers and the emerging idea that tau pathology may spread beyond brain. Near infrared fluorescence (NIRF) was mainly used to analyze tau (tau-NIRF) distribution after its intracisternal or intravenous injection. There was a striking uptake of blood- or CSF-derived tau-NIRF protein by the skeletal structures, liver, small intestine (duodenum), gall bladder, kidneys, urinary bladder, lymph nodes, heart, and spleen. In aging and in older APP/PS1 mice, tau uptake in regions, such as the brain, liver, and skeleton, was increased. In bone (femur) injected tau protein was associated with integrin-binding sialoprotein (IBSP), a major non-collagenous glycoprotein that is associated with mineralization. Tau-NIRF was cleared slowly from CSF via mainly across the cribriform plate, and cervical lymph nodes. In brain, some of the CSF injected tau protein was associated with NeuN-positive and PDGFRý-positive cells, which may explain its retention. The presence of tau in the bladders suggested excretion routes of tau. CSF anti-tau antibody increased CSF tau clearance, while blood anti-tau antibody decreased tau accumulation in the femur but not in liver, kidney, and spleen. Thus, the data show a body-wide distribution and retention of CSF-derived tau protein, which increased with aging and in older APP/PS1 mice. Further work is needed to elucidate the relevance of tau accumulation in each organ to tauopathy.
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Vascular mechanisms of Alzheimer's disease (AD) may constitute a therapeutically addressable biological pathway underlying dementia. We previously demonstrated that soluble pathogenic forms of tau (tau oligomers) accumulate in brain microvasculature of AD and other tauopathies, including prominently in microvascular endothelial cells. Here we show that soluble pathogenic tau accumulates in brain microvascular endothelial cells of P301S(PS19) mice modeling tauopathy and drives AD-like brain microvascular deficits. Microvascular impairments in P301S(PS19) mice were partially negated by selective removal of pathogenic soluble tau aggregates from brain. We found that similar to trans-neuronal transmission of pathogenic forms of tau, soluble tau aggregates are internalized by brain microvascular endothelial cells in a heparin-sensitive manner and induce microtubule destabilization, block endothelial nitric oxide synthase (eNOS) activation, and potently induce endothelial cell senescence that was recapitulated in vivo in microvasculature of P301S(PS19) mice. Our studies suggest that soluble pathogenic tau aggregates mediate AD-like brain microvascular deficits in a mouse model of tauopathy, which may arise from endothelial cell senescence and eNOS dysfunction triggered by internalization of soluble tau aggregates.
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Enfermedad de Alzheimer , Tauopatías , Ratones , Animales , Proteínas tau/genética , Proteínas tau/metabolismo , Células Endoteliales/metabolismo , Tauopatías/metabolismo , Enfermedad de Alzheimer/metabolismo , Encéfalo/metabolismo , Modelos Animales de Enfermedad , Senescencia Celular , Ratones TransgénicosRESUMEN
BACKGROUND: Amyloid plaques and neurofibrillary tangles, the molecular lesions that characterize Alzheimer's disease (AD) and other forms of dementia, are emerging as determinants of proteinopathies 'beyond the brain'. This study aims to establish tau's putative pathophysiological mechanistic roles and potential future therapeutic targeting of tau in heart failure (HF). METHODS AND RESULTS: A mouse model of tauopathy and human myocardial and brain tissue from patients with HF, AD, and controls was employed in this study. Tau protein expression was examined together with its distribution, and in vitro tau-related pathophysiological mechanisms were identified using a variety of biochemical, imaging, and functional approaches. A novel tau-targeting immunotherapy was tested to explore tau-targeted therapeutic potential in HF. Tau is expressed in normal and diseased human hearts, in contradistinction to the current oft-cited observation that tau is expressed specifically in the brain. Notably, the main cardiac isoform is high-molecular-weight (HMW) tau (also known as big tau), and hyperphosphorylated tau segregates in aggregates in HF and AD hearts. As previously described for amyloid-beta, the tauopathy phenotype in human myocardium is of diastolic dysfunction. Perturbation in the tubulin code, specifically a loss of tyrosinated microtubules, emerged as a potential mechanism of myocardial tauopathy. Monoclonal anti-tau antibody therapy improved myocardial function and clearance of toxic aggregates in mice, supporting tau as a potential target for novel HF immunotherapy. CONCLUSION: The study presents new mechanistic evidence and potential treatment for the brain-heart tauopathy axis in myocardial and brain degenerative diseases and ageing.
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Enfermedad de Alzheimer , Tauopatías , Humanos , Ratones , Animales , Proteínas tau/química , Proteínas tau/genética , Proteínas tau/metabolismo , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Tauopatías/metabolismo , Tauopatías/patología , Microtúbulos/metabolismo , Microtúbulos/patología , Miocardio/patologíaRESUMEN
The pathological hallmark of many neurodegenerative diseases is the accumulation of characteristic proteinaceous aggregates. Parkinson's disease and dementia with Lewy bodies can be characterized as synucleinopathies due to the abnormal accumulation of the protein alpha-synuclein (α-Syn). Studies have shown amyloidogenic proteins such as α-Syn and tau can exist as polymorphic aggregates, a theory widely studied mostly in their fibrillar morphology. It is now well understood that an intermediate state of aggregates, oligomers, are the most toxic species. We have shown α-Syn, when modified by different physiological inducers, result in distinct oligomeric conformations of α-Syn. Polymorphic α-Syn oligomers exhibit distinct properties such as aggregate size, conformation, and differentially interact with tau. In this study, we confirm α-Syn oligomeric polymorphs furthermore using in-house novel α-Syn toxic conformation monoclonal antibodies (SynTCs). It is unclear the biological relevance of α-Syn oligomeric polymorphisms. Utilizing a combination of biochemical, biophysical, and cell-based assays, we characterize α-Syn oligomeric polymorphs. We found α-Syn oligomeric polymorphs exhibit distinct immunoreactivity and SynTCs exhibit differential selectivity and binding affinity for α-Syn species. Isothermal titration calorimetry experiments suggest distinct α-Syn:SynTC binding enthalpies in a species-specific manner. Additionally, we found SynTCs differentially reduce α-Syn oligomeric polymorph-mediated neurotoxicity and propagation in primary cortical neurons in a polymorph-specific manner. These studies demonstrate the biological significance of polymorphic α-Syn oligomers along with the importance of polymorph-specific antibodies that target toxic α-Syn aggregates. Monoclonal antibodies that can target the conformational heterogeneity of α-Syn oligomeric species and reduce their mediated toxicity have promising immunotherapeutic potential.