Biology subjects

Diamond, M. I.

Publications and source records attributed to Diamond, M. I..

32 records · Page 2Linked to original sources

bioRxiv2022

Network of hotspot interactions cluster tau amyloid folds

Cryogenic electron microscopy has revealed unprecedented molecular insight into the conformation of {beta}-sheet-rich protein amyloids linked to neurodegenerative diseases. It remains unknown how a protein can adopt a diversity of folds and form multiple distinct fibrillar structures. Here we develop an in silico alanine scan method to estimate the relative energetic contribution of each amino acid in an amyloid assembly. We apply our method to twenty-seven ex vivo and in vitro fibril structural polymorphs of the microtubule-associated protein tau. We uncover networks of energetically important interactions involving amyloid-forming motifs that stabilize the different fibril folds. We test our predictions in cellular and in vitro aggregation assays. Using a machine learning approach, we classify the structures based on residue energetics to identify distinguishing and unifying features. Our energetic profiling suggests that minimal sequence elements that control the stability of tau fibrils, allowing future design of protein sequences that fold into unique structures.

neuroscience↗

bioRxiv2022

Tau seeds translocate across the cell membrane to initiate aggregation

Neurodegenerative tauopathies, including Alzheimers disease and related disorders, are caused by intracellular aggregation of tau protein in ordered assemblies. Experimental evidence suggests that tau assemblies propagate pathology across brain networks. Tau seeds enter cells through endocytosis but must access the cytoplasm to serve as templates for their own replication. The mechanism by which this occurs is unknown. To study tau uptake, we began with a whole-genome CRISPR knockout screen, which indicated a requirement vacuolar H+ ATPase (v-ATPase) components. Treatment with Bafilomycin A1, an inhibitor of the v-ATPase, also reduced tau entry. We next tested direct modifiers of endolysosomal trafficking. Dominant-negative Rab5a expression uniquely decreased tau uptake, as did temporary cold temperature during tau exposure, consistent with a primary role of endocytosis in tau uptake. However, despite reducing tau uptake, these interventions all paradoxically increased intracellular seeding. Consequently, we generated giant plasma membrane vesicles (GPMVs), which cannot undergo endocytosis, and observed that tau fibrils and monomer translocated into the vesicles, in addition to TAT peptide, whereas transferrin and albumin did not. In every case, tau required binding to heparan sulfate proteoglycans (HSPGs) for cell uptake, seeding, or GPMV entry. These findings are most consistent with direct translocation of tau seeds across the lipid bilayer, a novel mechanism of entry into the cytoplasm.

cell biology↗

bioRxiv2022

The AAA+ chaperone VCP disaggregates Tau fibrils and generates aggregate seeds

Amyloid-like aggregates of the microtubule-associated protein Tau are associated with several neurodegenerative disorders including Alzheimers disease. The existence of cellular machinery for the removal of such aggregates has remained unclear, as specialized disaggregase chaperones are thought to be absent in mammalian cells. Here we show in cell culture and in neurons that the AAA+ chaperone VCP is recruited to ubiquitylated Tau fibrils, resulting in their efficient disaggregation. Aggregate clearance depends on the functional cooperation of VCP with Hsp70 and the ubiquitin-proteasome machinery. Inhibition of VCP activity stabilizes large Tau aggregates, and is accompanied by a reduction in the amount of Tau species competent of prion- like aggregate seeding in recipient cells. Thus, disaggregation by VCP generates seeding-active Tau as byproduct. These findings identify VCP as a core component of the machinery for the removal of neurodegenerative disease aggregates and suggest that its activity can be associated with enhanced aggregate spreading in tauopathies.

cell biology↗

bioRxiv2022

Tau seeding without tauopathy

Neurodegenerative tauopathies such as Alzheimers disease (AD) are caused by brain accumulation of tau assemblies. Evidence suggests tau functions as a prion, and cells and animals efficiently propagate unique tau assemblies. This suggests a dedicated cellular replication machinery, with normal physiologic function for tau seeds. Consequently, we hypothesized that healthy control brains would have seeding activity. We recently developed a novel monoclonal antibody (MD3.1) specific for tau seeds. We used this antibody to immunopurify tau from the parietal and cerebellar cortices of 19 healthy subjects ranging 19-65 years. We detected seeding in the parietal cortex, but not in the cerebellum, or in wild-type or human tau knockin mice, suggesting that cellular/genetic context dictates development of seed-competent tau. Seeding did not correlate with subject age or brain tau levels. Dot blot analyses revealed no AT8 immunoreactivity above background levels in parietal and cerebellar extracts and <1/100 of that present in AD. Based on binding to a panel of antibodies, the conformational characteristics of control seeds differed from AD, suggesting a unique underlying assembly, or structural ensemble. Taus ability to adopt self-replicating conformations under non-pathogenic conditions may reflect normal function that goes awry in disease states.

neuroscience↗

bioRxiv2022

RNA induces unique tau strains and stabilizes Alzheimer disease seeds

Tau aggregation causes neurodegenerative tauopathies, and trans-cellular propagation of tau assemblies of unique structure, i.e. strains, may underlie the diversity of these disorders. Polyanions have been reported to induce tau aggregation in vitro, but the precise trigger to convert tau from an inert to a seed-competent form in disease states is unknown. RNA triggers tau fibril formation in vitro and has been observed in association with neurofibrillary tangles in human brain. We tested whether RNA exerts sequence-specific effects on tau assembly and strain formation. Three RNA homopolymers, polyA, polyU, and polyC all bound tau, but only polyA triggered seed and fibril formation. PolyA:tau seeds and fibrils were sensitive to RNase. The origin of RNA influenced the ability of tau to adopt a structure that would form stable strains. Human RNA potently induced tau seed formation and created tau conformations that preferentially formed stable strains in a HEK293T cell model, whereas other inducers produced strains that sectored. Finally, we found that soluble, but not insoluble, seeds from Alzheimers disease (AD) brain were sensitive to RNase. Thus, RNA specifically induces stable tau strains, and may trigger the formation of dominant pathological assemblies that propagate in AD, and possibly other tauopathies.

biochemistry↗

bioRxiv2022

Dual fates of exogenous tau seeds: lysosomal clearance vs. cytoplasmic amplification

Tau assembly propagation from the extracellular to intracellular space of a cell may underlie neurodegenerative tauopathies. The first step involves tau binding to heparan sulfate proteoglycans on the cell surface, followed by macropinocytosis. Pathological tau assemblies are thought to exit the vesicular compartment as "seeds" for replication in the cytoplasm. Tau uptake is highly efficient, but only [~]1-10% of cells that take up aggregates exhibit seeding. To investigate the basis for this observation, we used fluorescently tagged full-length (FL) tau fibrils added to native U2OS cells, and "biosensor" cells expressing FL tau or repeat domain fused to mClover (Clo). FL tau-Clo bound tubulin, but seeds triggered its aggregation in multiple locations simultaneously in the cytoplasm, generally independent of visible exogenous aggregates. Most exogenous tau trafficked to the lysosome, but imaging revealed a small percentage that slowly and steadily accumulated in the cytosol. Intracellular expression of Gal3-mRuby, which binds intravesicular galactosides and forms puncta upon vesicle rupture, revealed no evidence of vesicle damage following tau exposure. In fact, most seeded cells had no evidence of lysosome rupture. However, live cell imaging indicated that cells with pre-existing Gal3-positive puncta exhibited seeding at a slightly higher rate than the general population, indicating a potential role for vesicle instability as a predisposing factor. Clearance of tau seeds occurred rapidly in both vesicular and cytosolic fractions. Bafilomycin inhibited vesicular clearance, whereas MG132 inhibited cytosolic clearance. Tau seeds that enter the cell thus have at least two fates: lysosomal clearance that degrades most tau, and entry into the cytosol, where seeds replicate, and are cleared by the proteasome.

cell biology↗

bioRxiv2022

Seed-competent tau monomer initiates pathology in PS19 tauopathy mice

Tau aggregation into ordered assemblies causes myriad neurodegenerative tauopathies. We previously reported that tau monomer exists in either inert (Mi) or seed-competent (Ms) conformational ensembles, and that Ms encodes strains, which are biologically active, self-propagating assemblies. We have previously isolated Ms from tauopathy brains, but it is unknown if disease begins with Ms formation followed by fibril assembly, or if Ms derives from fibrils and is an epiphenomenon. Consequently, we studied a tauopathy mouse model (PS19) that expresses full-length human (1N4R) tau containing a disease-associated mutation (P301S). Using tau repeat domain biosensor cells, we detected insoluble tau seeding activity at 2 months. We found insoluble tau protein assemblies by immunoblot at 3 months. We next immunopurified monomer from mice aged 1-6 weeks using size exclusion chromatography. We detected soluble seeding activity at 4 weeks, before insoluble material or larger assemblies, with assemblies ranging from n=1-3 tau units. By 5 and 6 weeks, large soluble assemblies had formed. This indicated the first detectable pathological forms of tau were Ms. We next tested for post-translational modifications of tau monomer from 1-6 weeks. We detected no phosphorylation unique to Ms in PS19 or Alzheimers disease brain. We conclude that tauopathy begins with formation of Ms monomer, whose activity is phosphorylation-independent. Ms self-assembles to form oligomers before it forms insoluble fibrils. The conversion of tau monomer from Mi to Ms thus constitutes the first detectable step in the initiation of tauopathy in this mouse model, with obvious implications for origins of disease in humans.

neuroscience↗

bioRxiv2019

Alzheimers Disease risk modifier genes do not impact tau aggregate uptake, seeding or maintenance in cell models

Alzheimers disease (AD) afflicts millions of people worldwide, and is caused by accumulated amyloid beta and tau pathology. Progression of tau pathology in AD may utilize prion mechanisms of propagation in which pathological tau aggregates released from one cell are taken up by neighboring or connected cells and act as templates for their own replication, a process termed \"seeding.\" In cultured cells we have modeled various aspects of pathological tau propagation, including uptake of aggregates, induced (naked) seeding by exogenous aggregates, seeding caused by Lipofectamine-mediated delivery to the cell interior, and chronic maintenance of aggregates in cells through mother-to-daughter transmission. The factors that regulate these processes are not well understood, and we hypothesized that AD risk modifier genes might play a role. We identified 22 genes strongly linked to AD via meta-analysis of genome-wide association studies (GWAS). We used CRISPR/Cas-9 to individually knock out each in gene in HEK293T cells, and verified disruption using genomic sequencing. We then tested the effect of gene knockout in tau aggregate uptake, naked and Lipofectamine-mediated seeding, and aggregate maintenance in cultured cell lines. GWAS gene knockouts had no effect on these models of tau pathology. With obvious caveats due to the model systems used, these results imply that these 22 AD risk modifier genes do not directly modulate tau uptake, seeding, or aggregate maintenance.

molecular biology↗

bioRxiv2019

Site-specific hyperphosphorylation of tau inhibits its fibrillization in vitro, blocks its seeding capacity in cells, and disrupts its microtubule binding; Implications for the native state stabilization of tau

The consistent observation of aggregated phosopho-tau in the pathology of Alzheimers disease and other tauopathies has contributed to the emergence of a model where hyperphosphorylation of tau causes its disassociation from microtubules and subsequent pathological polymerization. However, the large number of possible phosphorylation sites in tau and lack of robust methods that enable the preparation of homogeneously phosphorylated tau species have made it difficult to validate this model. Herein, we applied a total chemical synthetic approach to site-specifically phosphorylate single (pS356) or multiple (pS356/pS262 and pS356/pS262/pS258) residues within the microtubule binding repeat domain (MTBD) of tau and show that hyperphosphorylation within the microtubule MTBD inhibits K18 tau 1) aggregation in vitro; 2) its seeding activity in cells, and 3) its ability to promote microtubule polymerization. The inhibition increased with the number of phosphorylated sites, with phosphorylation at S262 having the strongest effect. On the basis of these findings, we propose that targeting the kinases that regulate phosphorylation at these sites could provide a viable strategy to stabilize the native state of tau and inhibit its aggregation. Taken together, our results argue against the pathogenic hyperphosphorylation hypothesis and underscore the critical importance of revisiting the role of site-specific hyperphosphorylation of tau in regulating its function in health and disease.\n\nO_FIG O_LINKSMALLFIG WIDTH=159 HEIGHT=200 SRC=\"FIGDIR/small/772046v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (48K):\norg.highwire.dtl.DTLVardef@1328421org.highwire.dtl.DTLVardef@1809f73org.highwire.dtl.DTLVardef@16459a4org.highwire.dtl.DTLVardef@1393751_HPS_FORMAT_FIGEXP M_FIG Table of content C_FIG

neuroscience↗

bioRxiv2018

Native tau structure is disrupted by disease-associated mutations that promote aggregation

Tauopathies are neurodegenerative diseases characterized by intracellular amyloid deposits of tau protein. Missense mutations in the tau gene (MAPT) correlate with aggregation propensity and cause dominantly inherited tauopathies, but their biophysical mechanism driving amyloid formation is poorly understood. Many disease-associated mutations localize within taus repeat domain at inter-repeat interfaces proximal to amyloidogenic sequences, such as 306VQIVYK311. Using cross-linking mass spectrometry, intramolecular FRET, recombinant protein and synthetic peptide systems, in silico modeling, and cell models, we conclude that the aggregation prone 306VQIVYK311 motif forms metastable compact structures with the upstream sequence that modulates aggregation propensity. Disease-associated mutations, isomerization of a critical proline, or alternative splicing are all sufficient to destabilize this local structure and trigger spontaneous aggregation. These findings provide a biophysical framework to explain the basis of early conformational changes that may underlie genetic and sporadic tau pathogenesis.

biophysics↗

bioRxiv2018

Tau monomer encodes strains

Tauopathies have diverse presentation, progression, and neuropathology. They are linked to tau prion strains, self-replicating assemblies of unique quaternary conformation. Strains can be propagated indefinitely in cultured cells, and induce unique patterns of transmissible neuropathology upon inoculation into mice. Aggregates from a single strain reproduce only that strain upon re-inoculation into cells or mice. DS9 and DS10 cell lines propagate distinct synthetic strains. Surprisingly, DS9 monomer inoculated into naive cells encoded an identical \"sub-strain,\" whereas DS10 monomer encoded multiple sub-strains. Sub-strains produced distinct pathology upon inoculation into a tauopathy mouse model (PS19). Brain-derived tau monomer from an Alzheimers brain encoded a single strain. Monomer from a corticobasal degeneration brain encoded three sub-strains in which monomer from each encoded all three upon re-inoculation into cells. Tau monomer thus adopts multiple, stable seed-competent conformations, each of which encodes a limited number of strains. This provides insights into the origins of distinct tauopathies.

biochemistry↗

bioRxiv2018

Tau seeding activity anticipates phospho-tau pathology in Alzheimer’s disease

Alzheimers disease (AD) is characterized by accumulation of tau neurofibrillary tangles (NFTs) and, according to the prion model, transcellular propagation of pathological \"seeds\" may underlie its progression. Staging of NFT pathology with phospho-tau antibody is useful to classify AD and primary age-related tauopathy (PART) cases. The locus coeruleus (LC) shows the earliest phospho-tau signal, whereas other studies suggest that pathology begins in the transentorhinal/entorhinal cortices (TRE/EC). The relationship of tau seeding activity, phospho-tau pathology, and progression of neurodegeneration remains obscure. Consequently, we employed an established cellular biosensor assay to quantify tau seeding activity in fixed human tissue, in parallel with AT8 phospho-tau staining of immediately adjacent sections. We studied four brain regions from each of n=247 individuals across a range of disease stages. We detected the earliest and most robust seeding activity in the TRE/EC. The LC did not uniformly exhibit seeding activity until later NFT stages. We also detected seeding activity in the first temporal gyrus and visual cortex at stages before NFTs and/or AT8-immunopositivity were detectable. AD and putative PART cases exhibited similar patterns of seeding activity that anticipated histopathology across all NFT stages. Our findings are consistent with the prion model and suggest that pathological seeding activity begins in the TRE/EC rather than in the LC, and may offer an important addition to classical histopathology.

neuroscience↗

bioRxiv2017

Distinct glycosaminoglycan chain length and sulfation patterns required for cellular uptake of Tau, Aβ, and α-Synuclein

Transcellular propagation of aggregate \"seeds\" has been proposed to mediate progression of neurodegenerative diseases in tauopathies and -synucleinopathies. We have previously determined that tau and -synuclein aggregates bind heparan sulfate proteoglycans (HSPGs) on the cell surface. This mediates uptake and intracellular seeding. The specificity and mode of binding to HSPGs has been unknown. We used modified heparins to determine the size and sulfation requirements of glycosaminoglycan (GAGs) binding to aggregates in biochemical and cell uptake and seeding assays. Aggregates of tau require a precise GAG architecture with defined sulfate moieties in the N- and 6-O-positions, whereas -synuclein and A{beta} rely slightly more on overall charge on the GAGs. To determine the genetic requirements for aggregate uptake, we individually knocked out the major genes of the HSPG synthesis pathway using CRISPR/Cas9 in HEK293T cells. Knockout of EXT1, EXT2 and EXTL3, N-sulfotransferase (NDST1), and 6-O-sulfotransferase (HS6ST2) significantly reduced tau uptake. -Synuclein was not sensitive to HS6ST2 knockout. Good correlation between pharmacologic and genetic manipulation of GAG binding by tau and -synuclein indicates specificity that may help elucidate a path to mechanism-based inhibition of transcellular propagation of pathology.

neuroscience↗

bioRxiv2017

Inert and seed-competent tau monomers elucidate the structural origins of aggregation

Tauopathies feature progressive accumulation of tau amyloids. Pathology may begin when these amplify from a protein template, or seed, whose structure is unknown. We have purified and characterized distinct forms of tau monomer--inert (Mi) and seed-competent (Ms). Recombinant Ms triggered intracellular tau aggregation, induced tau fibrillization in vitro, and self-assembled. Ms from Alzheimers disease also seeded aggregation and self-assembled in vitro to form seed-competent multimers. We used crosslinking with mass spectrometry to probe structural differences in Mi vs. Ms. Crosslinks informed models of local peptide structure within the repeat domain which suggest relative inaccessibility of residues that drive aggregation (VQIINK/VQIVYK) in Mi, and exposure in Ms. Limited proteolysis supported this idea. Although tau monomer has been considered to be natively unstructured, our findings belie this assumption and suggest that initiation of pathological aggregation could begin with conversion of tau monomer from an inert to a seed-competent form.

neuroscience↗