ABSTRACT
Antisense oligonucleotides (ASOs) are promising therapeutics for treating various neurological disorders. However, ASOs are unable to readily cross the mammalian blood-brain barrier (BBB) and therefore need to be delivered intrathecally to the central nervous system (CNS). Here, we engineered a human transferrin receptor 1 (TfR1) binding molecule, the oligonucleotide transport vehicle (OTV), to transport a tool ASO across the BBB in human TfR knockin (TfRmu/hu KI) mice and nonhuman primates. Intravenous injection and systemic delivery of OTV to TfRmu/hu KI mice resulted in sustained knockdown of the ASO target RNA, Malat1, across multiple mouse CNS regions and cell types, including endothelial cells, neurons, astrocytes, microglia, and oligodendrocytes. In addition, systemic delivery of OTV enabled Malat1 RNA knockdown in mouse quadriceps and cardiac muscles, which are difficult to target with oligonucleotides alone. Systemically delivered OTV enabled a more uniform ASO biodistribution profile in the CNS of TfRmu/hu KI mice and greater knockdown of Malat1 RNA compared with a bivalent, high-affinity TfR antibody. In cynomolgus macaques, an OTV directed against MALAT1 displayed robust ASO delivery to the primate CNS and enabled more uniform biodistribution and RNA target knockdown compared with intrathecal dosing of the same unconjugated ASO. Our data support systemically delivered OTV as a potential platform for delivering therapeutic ASOs across the BBB.
Subject(s)
Blood-Brain Barrier , Oligonucleotides, Antisense , RNA, Long Noncoding , Receptors, Transferrin , Animals , Oligonucleotides, Antisense/pharmacokinetics , Oligonucleotides, Antisense/administration & dosage , Blood-Brain Barrier/metabolism , Receptors, Transferrin/metabolism , Humans , RNA, Long Noncoding/metabolism , RNA, Long Noncoding/genetics , Mice , Biological Transport , Macaca fascicularis , Gene Knockdown Techniques , Tissue DistributionABSTRACT
Progranulin (PGRN) haploinsufficiency is a major risk factor for frontotemporal lobar degeneration with TAR DNA-binding protein 43 (TDP-43) pathology (FTLD-GRN). Multiple therapeutic strategies are in clinical development to restore PGRN in the CNS, including gene therapy. However, a limitation of current gene therapy approaches aimed to alleviate FTLD-associated pathologies may be their inefficient brain exposure and biodistribution. We therefore developed an adeno-associated virus (AAV) targeting the liver (L) to achieve sustained peripheral expression of a transferrin receptor (TfR) binding, brain-penetrant (b) PGRN variant [AAV(L):bPGRN] in two mouse models of FTLD-GRN, namely, Grn knockout and GrnxTmem106b double knockout mice. This therapeutic strategy avoids potential safety and biodistribution issues of CNS-administered AAVs and maintains sustained concentrations of PGRN in the brain after a single dose. AAV(L):bPGRN treatment reduced several FTLD-GRN-associated pathologies including severe motor function deficits, aberrant TDP-43 phosphorylation, dysfunctional protein degradation, lipid metabolism, gliosis, and neurodegeneration in the brain. The potential translatability of our findings was tested in an in vitro model using cocultured human induced pluripotent stem cell (hiPSC)-derived microglia lacking PGRN and TMEM106B and wild-type hiPSC-derived neurons. As in mice, aberrant TDP-43, lysosomal dysfunction, and neuronal loss were ameliorated after treatment with exogenous TfR-binding protein transport vehicle fused to PGRN (PTV:PGRN). Together, our studies suggest that peripherally administered brain-penetrant PGRN replacement strategies ameliorate FTLD-GRN relevant phenotypes including TDP-43 pathology, neurodegeneration, and behavioral deficits. Our data provide preclinical proof of concept for the use of this AAV platform for treatment of FTLD-GRN and potentially other CNS disorders.
Subject(s)
Brain , Dependovirus , Disease Models, Animal , Frontotemporal Lobar Degeneration , Mice, Knockout , Progranulins , Animals , Humans , Mice , Brain/metabolism , Brain/pathology , Dependovirus/metabolism , DNA-Binding Proteins/metabolism , DNA-Binding Proteins/genetics , Frontotemporal Lobar Degeneration/metabolism , Frontotemporal Lobar Degeneration/pathology , Genetic Therapy , Phosphorylation , Progranulins/metabolism , Progranulins/genetics , Receptors, Transferrin/metabolismABSTRACT
Plant-associated microbes play vital roles in promoting plant growth and health, with plants secreting root exudates into the rhizosphere to attract beneficial microbes. Exudate composition defines the nature of microbial recruitment, with different plant species attracting distinct microbiota to enable optimal adaptation to the soil environment. To more closely examine the relationship between plant genotype and microbial recruitment, we analysed the rhizosphere microbiomes of landrace (Chevallier) and modern (NFC Tipple) barley (Hordeum vulgare) cultivars. Distinct differences were observed between the plant-associated microbiomes of the 2 cultivars, with the plant-growth promoting rhizobacterial genus Pseudomonas substantially more abundant in the Tipple rhizosphere. Striking differences were also observed between the phenotypes of recruited Pseudomonas populations, alongside distinct genotypic clustering by cultivar. Cultivar-driven Pseudomonas selection was driven by root exudate composition, with the greater abundance of hexose sugars secreted from Tipple roots attracting microbes better adapted to growth on these metabolites and vice versa. Cultivar-driven selection also operates at the molecular level, with both gene expression and the abundance of ecologically relevant loci differing between Tipple and Chevallier Pseudomonas isolates. Finally, cultivar-driven selection is important for plant health, with both cultivars showing a distinct preference for microbes selected by their genetic siblings in rhizosphere transplantation assays.
Subject(s)
Genotype , Hordeum , Microbiota , Plant Roots , Pseudomonas , Rhizosphere , Hordeum/microbiology , Hordeum/genetics , Hordeum/metabolism , Plant Roots/microbiology , Plant Roots/metabolism , Microbiota/physiology , Microbiota/genetics , Pseudomonas/genetics , Pseudomonas/metabolism , Pseudomonas/physiology , Soil Microbiology , Plant Exudates/metabolismABSTRACT
AIMS: socNAMs provides a comprehensive and comparative dataset for researchers to identify how students' recent migration and their school setting relates to their social wellbeing, particularly regarding their feelings of loneliness. Results: This study design article delineates a quantitative cross-sectional research study (socNAMs) which successfully developed three questionnaires that were administered with unique and hard to reach populations, newly-arrived adolescent migrants (NAMs) and school staff offering reception education in Flanders, Belgium. METHODS: At the individual level, socNAMs collected information on: (1) socio-demographic variables of NAMs; (2) migration and family context; (3) social relationships; (4) school experiences; (5) self-perceived wellbeing (physical and social); and (6) experiences with discrimination. The questionnaire developed for NAMs is available in 16 languages. To gain a further understanding of the impact of the school environment on NAMs, socNAMs collected contextual information primarily concerning school social capital by including data collected from teachers and reception-class coordinators. The final sample included 1379 NAMs, 50 teachers and 26 reception-class coordinators, from 35 schools offering reception education. CONCLUSIONS: In this article, we present the rationale for this study, the methodology of sampling and recruitment, the development and content of the questionnaires, some preliminary descriptive results and the strengths and limitations of the study. Future empirical studies will address the research aims outlined in this protocol paper. In addition, we highlight the opportunities that the dataset provides for advancing research regarding the social wellbeing of NAMs in varying school and national contexts.
ABSTRACT
Loss-of-function heterozygous mutations in GRN, the gene encoding progranulin (PGRN), were identified in patients with frontotemporal lobar degeneration (FTLD) almost two decades ago and are generally linked to reduced PGRN protein expression levels. Although initial characterization of PGRN function primarily focused on its role in extracellular signaling as a secreted protein, more recent studies revealed critical roles of PGRN in regulating lysosome function, including proteolysis and lipid degradation, consistent with its lysosomal localization. Emerging from these studies is the notion that PGRN regulates glucocerebrosidase activity via direct chaperone activities and via interaction with prosaposin (i.e., a key regulator of lysosomal sphingolipid-metabolizing enzymes), as well as with the anionic phospholipid bis(monoacylglycero)phosphate. This emerging lysosomal biology of PGRN identified novel and promising opportunities in therapeutic discovery as well as biomarker development.
Subject(s)
Frontotemporal Dementia , Frontotemporal Lobar Degeneration , Humans , Progranulins/genetics , Progranulins/metabolism , Frontotemporal Dementia/genetics , Frontotemporal Dementia/metabolism , Intercellular Signaling Peptides and Proteins/metabolism , Frontotemporal Lobar Degeneration/genetics , Frontotemporal Lobar Degeneration/metabolism , Lysosomes/metabolismABSTRACT
BACKGROUND: Genetic mutations underlying familial Alzheimer's disease (AD) were identified decades ago, but the field is still in search of transformative therapies for patients. While mouse models based on overexpression of mutated transgenes have yielded key insights in mechanisms of disease, those models are subject to artifacts, including random genetic integration of the transgene, ectopic expression and non-physiological protein levels. The genetic engineering of novel mouse models using knock-in approaches addresses some of those limitations. With mounting evidence of the role played by microglia in AD, high-dimensional approaches to phenotype microglia in those models are critical to refine our understanding of the immune response in the brain. METHODS: We engineered a novel App knock-in mouse model (AppSAA) using homologous recombination to introduce three disease-causing coding mutations (Swedish, Arctic and Austrian) to the mouse App gene. Amyloid-ß pathology, neurodegeneration, glial responses, brain metabolism and behavioral phenotypes were characterized in heterozygous and homozygous AppSAA mice at different ages in brain and/ or biofluids. Wild type littermate mice were used as experimental controls. We used in situ imaging technologies to define the whole-brain distribution of amyloid plaques and compare it to other AD mouse models and human brain pathology. To further explore the microglial response to AD relevant pathology, we isolated microglia with fibrillar Aß content from the brain and performed transcriptomics and metabolomics analyses and in vivo brain imaging to measure energy metabolism and microglial response. Finally, we also characterized the mice in various behavioral assays. RESULTS: Leveraging multi-omics approaches, we discovered profound alteration of diverse lipids and metabolites as well as an exacerbated disease-associated transcriptomic response in microglia with high intracellular Aß content. The AppSAA knock-in mouse model recapitulates key pathological features of AD such as a progressive accumulation of parenchymal amyloid plaques and vascular amyloid deposits, altered astroglial and microglial responses and elevation of CSF markers of neurodegeneration. Those observations were associated with increased TSPO and FDG-PET brain signals and a hyperactivity phenotype as the animals aged. DISCUSSION: Our findings demonstrate that fibrillar Aß in microglia is associated with lipid dyshomeostasis consistent with lysosomal dysfunction and foam cell phenotypes as well as profound immuno-metabolic perturbations, opening new avenues to further investigate metabolic pathways at play in microglia responding to AD-relevant pathogenesis. The in-depth characterization of pathological hallmarks of AD in this novel and open-access mouse model should serve as a resource for the scientific community to investigate disease-relevant biology.
Subject(s)
Alzheimer Disease , Amyloid beta-Protein Precursor , Alzheimer Disease/genetics , Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Amyloid beta-Protein Precursor/genetics , Amyloid beta-Protein Precursor/metabolism , Amyloidosis/metabolism , Animals , Brain/metabolism , Disease Models, Animal , Mice , Mice, Transgenic , Microglia/metabolism , Plaque, Amyloid/pathology , Receptors, GABA/metabolismABSTRACT
Transposable elements comprise almost half of the mammalian genome. A growing body of evidence suggests that transposable element dysregulation accompanies brain aging and neurodegenerative disorders, and that transposable element activation is neurotoxic. Recent studies have identified links between pathogenic forms of tau, a protein that accumulates in Alzheimer's disease and related "tauopathies," and transposable element-induced neurotoxicity. Starting with transcriptomic analyses, we find that age- and tau-induced transposable element activation occurs in the mouse brain. Among transposable elements that are activated at the RNA level in the context of brain aging and tauopathy, we find that the endogenous retrovirus (ERV) class of retrotransposons is particularly enriched. We show that protein encoded by Intracisternal A-particle, a highly active mouse ERV, is elevated in brains of tau transgenic mice. Using two complementary approaches, we find that brains of tau transgenic mice contain increased DNA copy number of transposable elements, raising the possibility that these elements actively retrotranspose in the context of tauopathy. Taken together, our study lays the groundwork for future mechanistic studies focused on transposable element regulation in the aging mouse brain and in mouse models of tauopathy and provides support for ongoing therapeutic efforts targeting transposable element activation in patients with Alzheimer's disease.
Subject(s)
DNA Transposable Elements , tau Proteins , Aging/genetics , Animals , Brain/metabolism , DNA Transposable Elements/genetics , Disease Models, Animal , Humans , Mammals/genetics , Mammals/metabolism , Mice , Mice, Transgenic , tau Proteins/genetics , tau Proteins/metabolismABSTRACT
Studies supporting a strong association between tau deposition and neuronal loss, neurodegeneration, and cognitive decline have heightened the allure of tau and tau-related mechanisms as therapeutic targets. In February 2020, leading tau experts from around the world convened for the first-ever Tau2020 Global Conference in Washington, DC, co-organized and cosponsored by the Rainwater Charitable Foundation, the Alzheimer's Association, and CurePSP. Representing academia, industry, government, and the philanthropic sector, presenters and attendees discussed recent advances and current directions in tau research. The meeting provided a unique opportunity to move tau research forward by fostering global partnerships among academia, industry, and other stakeholders and by providing support for new drug discovery programs, groundbreaking research, and emerging tau researchers. The meeting also provided an opportunity for experts to present critical research-advancing tools and insights that are now rapidly accelerating the pace of tau research.
Subject(s)
Alzheimer Disease , Cognitive Dysfunction , Biomarkers , Drug Discovery , Humans , tau ProteinsABSTRACT
Both the replication of protein aggregates and their spreading throughout the brain are implicated in the progression of Alzheimer's disease (AD). However, the rates of these processes are unknown and the identity of the rate-determining process in humans has therefore remained elusive. By bringing together chemical kinetics with measurements of tau seeds and aggregates across brain regions, we can quantify their replication rate in human brains. Notably, we obtain comparable rates in several different datasets, with five different methods of tau quantification, from postmortem seed amplification assays to tau PET studies in living individuals. Our results suggest that from Braak stage III onward, local replication, rather than spreading between brain regions, is the main process controlling the overall rate of accumulation of tau in neocortical regions. The number of seeds doubles only every â¼5 years. Thus, limiting local replication likely constitutes the most promising strategy to control tau accumulation during AD.
ABSTRACT
Neuronal tau reduction confers resilience against ß-amyloid and tau-related neurotoxicity in vitro and in vivo. Here, we introduce a novel translational approach to lower expression of the tau gene MAPT at the transcriptional level using gene-silencing zinc finger protein transcription factors (ZFP-TFs). Following a single administration of adeno-associated virus (AAV), either locally into the hippocampus or intravenously to enable whole-brain transduction, we selectively reduced tau messenger RNA and protein by 50 to 80% out to 11 months, the longest time point studied. Sustained tau lowering was achieved without detectable off-target effects, overt histopathological changes, or molecular alterations. Tau reduction with AAV ZFP-TFs was able to rescue neuronal damage around amyloid plaques in a mouse model of Alzheimer's disease (APP/PS1 line). The highly specific, durable, and controlled knockdown of endogenous tau makes AAV-delivered ZFP-TFs a promising approach for the treatment of tau-related human brain diseases.
Subject(s)
Alzheimer Disease , Transcription Factors , Alzheimer Disease/genetics , Alzheimer Disease/pathology , Alzheimer Disease/therapy , Amyloid beta-Peptides/metabolism , Animals , Brain/metabolism , Dependovirus/genetics , Dependovirus/metabolism , Disease Models, Animal , Mice , Plaque, Amyloid/pathology , Transcription Factors/genetics , Transcription Factors/metabolism , Zinc Fingers/genetics , tau Proteins/genetics , tau Proteins/metabolismABSTRACT
Effective delivery of protein therapeutics to the central nervous system (CNS) has been greatly restricted by the blood-brain barrier (BBB). We describe the development of a BBB transport vehicle (TV) comprising an engineered Fc fragment that exploits receptor-mediated transcytosis for CNS delivery of biotherapeutics by binding a highly expressed brain endothelial cell target. TVs were engineered using directed evolution to bind the apical domain of the human transferrin receptor (hTfR) without the use of amino acid insertions, deletions, or unnatural appendages. A crystal structure of the TV-TfR complex revealed the TV binding site to be away from transferrin and FcRn binding sites, which was further confirmed experimentally in vitro and in vivo. Recombinant expression of TVs fused to anti-ß-secretase (BACE1) Fabs yielded antibody transport vehicle (ATV) molecules with native immunoglobulin G (IgG) structure and stability. Peripheral administration of anti-BACE1 ATVs to hTfR-engineered mice and cynomolgus monkeys resulted in substantially improved CNS uptake and sustained pharmacodynamic responses. The TV platform readily accommodates numerous additional configurations, including bispecific antibodies and protein fusions, yielding a highly modular CNS delivery platform.
Subject(s)
Amyloid Precursor Protein Secretases , Blood-Brain Barrier , Amyloid Precursor Protein Secretases/metabolism , Animals , Aspartic Acid Endopeptidases/metabolism , Blood-Brain Barrier/metabolism , Brain/metabolism , Haplorhini/metabolism , Immunoglobulin Fc Fragments , Mice , Receptors, Transferrin/metabolismABSTRACT
BACKGROUND: Aggression against GPs has increased in the past decade. Depending on experience, interpretation, and personality, the interpretation of aggressive patient behaviour will differ among doctors. AIM: To investigate how often GPs experience aggression in a 1-year time span and what the relationship is between the GP's personality (based on the 'Big Five' personality traits) and the reporting of aggression. Secondly, to investigate how personality is related to feeling safe. DESIGN & SETTING: Flemish (Belgian Federal State) GPs were questioned in a cross-sectional design by online survey. GPs were recruited and questioned in their professional environment. METHOD: Outcome measures were the 'Big Five' personality traits ('reserved' versus 'outgoing', 'compassionate' versus 'challenging', 'efficient' versus 'careless', 'confident' versus 'nervous', and 'cautious' versus 'innovative', based on Cattel's 'Big Five' model of personality), the type of aggression, the reporting of aggression, and feeling safe. RESULTS: Both (n = 247) male and female doctors considered physical contact and verbal intimidation as aggression. Female doctors were more likely to consider sexual harassment as aggression. The majority of GPs were confronted with verbal aggression. More than half considered physical aggression as the most threatening. GPs with 'reserved' and 'careless' personality types were more likely to experience aggression. GPs with 'innovative', 'challenging', or 'confident' personality types were also at increased risk, but to a lesser extent than those with 'reserved' and 'careless' personalities. GPs with 'efficient' and 'innovative' personalities were more likely to report incidents. Male GPs and those with 'efficient' personalities felt safer. GPs with 'confident' and 'cautious' personalities were more likely to feel unsafe. CONCLUSION: The results of this study might help future interventions and support strategies (designed to prevent aggressive incidents or help GPs cope with them) to target the vulnerable groups. Further research should therefore explore the results of these data in depth and on a larger sample size.
ABSTRACT
BACKGROUND: Misfolding of microtubule-associated protein tau (MAPT) within neurons into neurofibrillary tangles is an important pathological feature of Alzheimer's disease (AD). Tau pathology correlates with cognitive decline in AD and follows a stereotypical anatomical course; several recent studies indicate that tau pathology spreads inter-neuronally via misfolded tau "seeds." Previous research has focused on neurons as the source of these tau seeds. However, recent studies as well as the data contained herein suggest that microglia, the resident immune cells of the central nervous system, play a direct role in the spread of tau pathology. METHODS: Primary adult microglia were isolated from human AD cases and the rTg4510 tauopathy mouse model and used for analysis of gene expression, tau protein by Simoa technology, and quantification of tau seeding using a highly sensitive fluorescence resonance energy transfer (FRET) biosensing cell line for tau seeding and aggregation. RESULTS: Here, we show that microglia isolated from both human tauopathy and AD cases and the rTg4510 tauopathy mouse model stably contain tau seeds, despite not synthesizing any tau. Microglia releases these tau seeds in vitro into their conditioned media (CM). This suggests that microglia have taken up tau but are incapable of entirely neutralizing its seeding activity. Indeed, when in vitro microglia are given media containing tau seeds, they reduce (but do not eliminate) tau seeding. When microglia are treated with inflammagens such as lipopolysaccharide (LPS), interleukin-1ß (IL1ß), tumor necrosis factor α (TNFα), or amyloid-ß, their ability to reduce tau seeding is unchanged and these factors do not induce seeding activity on their own. CONCLUSIONS: Overall, these data suggest that microglia have a complex role: they are capable of taking up and breaking down seed competent tau, but do so inefficiently and could therefore potentially play a role in the spread of tau pathology.
Subject(s)
Alzheimer Disease/pathology , Brain/pathology , Gene Expression Regulation/genetics , Microglia/metabolism , tau Proteins/metabolism , Amyloid beta-Peptides/metabolism , Amyloid beta-Protein Precursor/genetics , Animals , Calcium-Binding Proteins/metabolism , Cells, Cultured , Culture Media, Conditioned/pharmacology , Cytokines/metabolism , Disease Models, Animal , Humans , Mice , Mice, Inbred C57BL , Mice, Transgenic , Microfilament Proteins/metabolism , Mutation/genetics , Neurofibrillary Tangles , Neurons/metabolism , tau Proteins/geneticsABSTRACT
Tau is the major constituent of neurofibrillary tangles in Alzheimer's disease (AD), but the mechanism underlying tau-associated neural damage remains unclear. Here, we show that tau can directly interact with nucleoporins of the nuclear pore complex (NPC) and affect their structural and functional integrity. Pathological tau impairs nuclear import and export in tau-overexpressing transgenic mice and in human AD brain tissue. Furthermore, the nucleoporin Nup98 accumulates in the cell bodies of some tangle-bearing neurons and can facilitate tau aggregation in vitro. These data support the hypothesis that tau can directly interact with NPC components, leading to their mislocalization and consequent disruption of NPC function. This raises the possibility that NPC dysfunction contributes to tau-induced neurotoxicity in AD and tauopathies.
Subject(s)
Alzheimer Disease/metabolism , Cell Nucleus/metabolism , Cytoplasm/metabolism , tau Proteins/metabolism , Active Transport, Cell Nucleus/physiology , Alzheimer Disease/genetics , Alzheimer Disease/pathology , Animals , Cell Nucleus/pathology , Cytoplasm/pathology , Female , Humans , Male , Mice , Mice, TransgenicABSTRACT
Several studies have now supported the use of a tau lowering agent as a possible therapy in the treatment of tauopathy disorders, including Alzheimer's disease. In human Alzheimer's disease, however, concurrent amyloid-ß deposition appears to synergize and accelerate tau pathological changes. Thus far, tau reduction strategies that have been tested in vivo have been examined in the setting of tau pathology without confounding amyloid-ß deposition. To determine whether reducing total human tau expression in a transgenic model where there is concurrent amyloid-ß plaque formation can still reduce tau pathology and protect against neuronal loss, we have taken advantage of the regulatable tau transgene in APP/PS1 × rTg4510 mice. These mice develop both neurofibrillary tangles as well as amyloid-ß plaques throughout the cortex and hippocampus. By suppressing human tau expression for 6 months in the APP/PS1 × rTg4510 mice using doxycycline, AT8 tau pathology, bioactivity, and astrogliosis were reduced, though importantly to a lesser extent than lowering tau in the rTg4510 alone mice. Based on non-denaturing gels and proteinase K digestions, the remaining tau aggregates in the presence of amyloid-ß exhibit a longer-lived aggregate conformation. Nonetheless, lowering the expression of the human tau transgene was sufficient to equally ameliorate thioflavin-S positive tangles and prevent neuronal loss equally well in both the APP/PS1 × rTg4510 mice and the rTg4510 cohort. Together, these results suggest that, although amyloid-ß stabilizes tau aggregates, lowering total tau levels is still an effective strategy for the treatment of tau pathology and neuronal loss even in the presence of amyloid-ß deposition.
Subject(s)
Plaque, Amyloid/pathology , Tauopathies/metabolism , tau Proteins/metabolism , Alzheimer Disease/pathology , Amyloid beta-Peptides/metabolism , Amyloid beta-Protein Precursor/metabolism , Animals , Disease Models, Animal , Hippocampus/metabolism , Humans , Mice , Mice, Transgenic , Neurofibrillary Tangles/pathology , Neurons/metabolism , Phosphorylation , Plaque, Amyloid/metabolism , Presenilin-1/metabolismABSTRACT
Alzheimer's disease (AD) is defined by the presence of intraneuronal neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau aggregates as well as extracellular amyloid-beta plaques. The presence and spread of tau pathology through the brain is classified by Braak stages and thought to correlate with the progression of AD. Several in vitro and in vivo studies have examined the ability of tau pathology to move from one neuron to the next, suggesting a "prion-like" spread of tau aggregates may be an underlying cause of Braak tau staging in AD. Using the HEK293 TauRD-P301S-CFP/YFP expressing biosensor cells as a highly sensitive and specific tool to identify the presence of seed competent aggregated tau in brain lysate-i.e., tau aggregates that are capable of recruiting and misfolding monomeric tau-, we detected substantial tau seeding levels in the entorhinal cortex from human cases with only very rare NFTs, suggesting that soluble tau aggregates can exist prior to the development of overt tau pathology. We next looked at tau seeding levels in human brains of varying Braak stages along six regions of the Braak Tau Pathway. Tau seeding levels were detected not only in the brain regions impacted by pathology, but also in the subsequent non-pathology containing region along the Braak pathway. These data imply that pathogenic tau aggregates precede overt tau pathology in a manner that is consistent with transneuronal spread of tau aggregates. We then detected tau seeding in frontal white matter tracts and the optic nerve, two brain regions comprised of axons that contain little to no neuronal cell bodies, implying that tau aggregates can indeed traverse along axons. Finally, we isolated cytosolic and synaptosome fractions along the Braak Tau Pathway from brains of varying Braak stages. Phosphorylated and seed competent tau was significantly enriched in the synaptic fraction of brain regions that did not have extensive cellular tau pathology, further suggesting that aggregated tau seeds move through the human brain along synaptically connected neurons. Together, these data provide further evidence that the spread of tau aggregates through the human brain along synaptically connected networks results in the pathogenesis of human Alzheimer's disease.
ABSTRACT
In contrast to the idea that tau phosphorylation is toxic, Ittner et al. (2016) recently showed that specific tau phosphorylation is neuroprotective, phenocopying tau ablation (DeVos et al., 2017), thus highlighting the complex tau biology that underlies neurotoxicity and neuroprotection.
Subject(s)
Amyloid beta-Peptides , tau Proteins , Alzheimer Disease , Neuroprotection , PhosphorylationABSTRACT
Amyloid plaques and neurofibrillary tangles co-occur in Alzheimer disease, but with different topological and temporal patterns. Whether these two lesions are independent or pathobiologically related is uncertain. For example, amyloid deposition in the neocortex precedes the spread of tau neurofibrillary tangles from the limbic areas to the cortex. We examined the aggregation properties of tau isolated from human cases with early tau pathology (Braak II) with and without plaques. Using a well-established HEK cell biosensor assay, we show that tau from cases with plaques has an enhanced ability to induce tau aggregates compared to tau from cases without plaques. To further explore this effect, we combined mice carrying the APP/PS1 transgene array that develop plaques with rTg4510 mice carrying the P301L mutant human tau transgene that develop extensive tau pathology with age. The resulting APP/PS1-rTg4510 mice had a threefold increase in tau seeding activity over the rTg4510 strain, without change in tau production or extracellular release. Surprisingly, this effect was observed before overt amyloid deposition. The enhancement of tau aggregation was also apparent by an increase in histological measures of tau pathology in young APP/PS1-rTg4510 mice and an increase in high-molecular-weight tau. Overall, these data provide evidence that amyloid ß acts to enhance tau pathology by increasing the formation of tau species capable of seeding new aggregates.
Subject(s)
Alzheimer Disease/pathology , Amyloid beta-Peptides/metabolism , Neurofibrillary Tangles/pathology , Plaque, Amyloid/pathology , tau Proteins/metabolism , Aged , Aged, 80 and over , Alzheimer Disease/metabolism , Amyloid beta-Peptides/genetics , Animals , Disease Models, Animal , Female , Humans , Male , Mice , Mice, Transgenic , Middle Aged , Neocortex/metabolism , Neocortex/pathology , Neurofibrillary Tangles/metabolism , Phosphorylation , Plaque, Amyloid/metabolism , Protein Aggregation, Pathological , tau Proteins/geneticsABSTRACT
The spread of neurofibrillary tangle (NFT) pathology through the human brain is a hallmark of Alzheimer's disease (AD), which is thought to be caused by the propagation of "seeding" competent soluble misfolded tau. "TauC3", a C-terminally truncated form of tau that is generated by caspase-3 cleavage at D421, has previously been observed in NFTs and has been implicated in tau toxicity. Here we show that TauC3 is found in the seeding competent high molecular weight (HMW) protein fraction of human AD brain. Using a specific TauC3 antibody, we were able to substantially block the HMW tau seeding activity of human AD brain extracts in an in vitro tau seeding FRET assay. We propose that TauC3 could contribute to the templated tau misfolding that leads to NFT spread in AD brains.