Biology subjects

Meisl, G.

Publications and source records attributed to Meisl, G..

At least 19 recordsLinked to original sources

bioRxiv2026

Two functionally distinct amyloid-β intermediates link aggregation pathways to pathology in Alzheimer's disease

Neurotoxic intermediates formed during amyloid-{beta}(A{beta}) aggregation are thought to drive Alzheimer's disease, yet their rarity and transient nature have obscured their identity and formation pathways in the human brain. Here, we combine super-resolution microscopy and single-molecule functional imaging with kinetic modelling to classify A{beta} intermediates according to their membrane-disrupting activity and connect their damaging effects to the aggregation pathways that generate them. Applying this framework to recombinant A{beta}42, an Alzheimer's knock-in mouse model and human Alzheimer's brain tissue, we find two functionally distinct intermediate populations present across all systems. They form through separate aggregation routes and differ in their neurotoxicity, abundance and susceptibility to inhibition. Both damage neurons and glia, but only one converts into plaques. Suppressing these intermediates pharmacologically in mice reduces plaque burden, attenuates astrogliosis and improves cognition. Our findings connect model systems with human pathology and identify intermediate formation pathways as actionable therapeutic targets across protein-misfolding disorders.

biophysics↗

bioRxiv2026

Potent substoichiometric inhibition of alpha-synuclein aggregation by de novo oligomer-binding proteins

The intrinsically disordered, non-amyloid-{beta} component domain of -synuclein (Syn) drives aggregation in Parkinson's disease but lacks a stable epitope for structure-based drug design. We used deep learning-based protein design to generate de novo binders capturing this region in a {beta}-strand conformation. Three designs bound Syn with nanomolar affinities, with solution NMR spectroscopy supporting the intended fold. All three suppressed fibril formation at substoichiometric ratios, and fitting of aggregation kinetics resolved the microscopic steps inhibited by each. Notably, one binder preferentially engaged oligomers and inhibited secondary nucleation, both closely linked to toxicity. In cells, all three suppressed seeded Syn assembly, with the oligomer binder being the most effective. Together, these findings establish a set of molecules that target distinct aggregation intermediates and mechanistically reshape Syn assembly.

biophysics↗

bioRxiv2026

Tau aggregate replication occurs at the pre-synapse of cultured human neurons and increases with application of TNFa

Tau aggregation at synapses is a key process driving Alzheimers disease but the mechanism(s) that cause this have not been established. We used a model system of forward-programming induced glutamatergic neurons (iNeurons) with three independent cell lines treated with TNF[a]. Using aggregate-specific SIMOA, STED microscopy, and SynPull to detect nanoscopic tau aggregates in bulk samples and at individual synapses, we found that TNF[a]-driven tau aggregation occurs preferentially at the pre-synapse, forming predominantly non-fibrillar aggregates that are larger than ones in the extra- and post-synaptic regions. Using mathematical models of aggregate formation, we fitted the frequency of AT8-positive tau aggregates in synaptosomes, which showed that aggregate replication is the dominant process and is much faster than de-novo aggregate formation, leading to rapid local amplification once one aggregate is formed. Our results provide direct evidence for tau aggregate replication at the pre-synapse, linking inflammation induced tau aggregation with synaptic pathology. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=134 SRC="FIGDIR/small/728997v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@169dacorg.highwire.dtl.DTLVardef@c9894corg.highwire.dtl.DTLVardef@1551253org.highwire.dtl.DTLVardef@260ae7_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Tau catalyzes amyloid-β aggregation in a fold-dependent manner

Interactions between amyloidogenic proteins are emerging as critical drivers of neurodegenerative diseases, yet the molecular mechanisms remain poorly understood. In Alzheimers disease (AD) and chronic traumatic encephalopathy (CTE), co-deposition of tau and amyloid-{beta} (A{beta}) leads to accelerated disease progression. Here, we investigated the direct interaction between A{beta} and tau, combining in vitro reconstruction, computational modeling, and in vivo models. We show that tau aggregates with AD paired helical filament (PHF) and CTE folds catalyze the primary nucleation of A{beta}42 in a fold-specific manner, through an enzyme-like kinetic with recognition mechanisms. CTE fibrils exhibit the highest catalytic activity, also constraining A{beta}42 polymorphism. PHF and CTE tau fibrils increase A{beta}42 toxicity in SH-SY5Y neuroblastoma cells and transgenic Caenorhabditis elegans. Catalytic heterotypic interactions between amyloidogenic proteins offer new insights into the pathological mechanisms of multiple proteinopathies. The mechanisms described here may guide the structure-based design of new therapeutic agents targeting specific amyloidogenic interactions.

biochemistry↗

bioRxiv2025

Rare bioactive tau oligomers from Alzheimer brain support both templated misfolding and fibril formation

In Alzheimers disease, both classical neurofibrillary tangles, and diffusible, aqueous soluble (High Molecular Weight, or HMW) species are able to support templated misfolding. How these tau proteoforms relate is uncertain. Using sequential size exclusion and anion exchange chromatography, we fractionated the HMW tau population and found both seed competent, and seed not competent proteoforms. Super resolution, atomic force, and immunogold electron microscopy confirmed that the size and conformation of both bioactive and non-bioactive tau proteoforms are similar, with dimers, trimers, and tetramers predominating. The presence of surface phosphorylation correlates with seeding capacity. Bioactive tau at fMol concentrations can induce seeding in a reporter cell. The soluble bioactive species support aggregation of a truncated repeat domain tau construct into thioflavin T positive fibrils and retain seeding activity over serial amplification in vitro and in cellulo, whereas non-bioactive oligomeric species do not. Together, these findings indicate that oligomeric assembly is required but not sufficient for seeding; instead, specific biochemical attributes of a rare oligomeric tau subset confer self-propagating, prion-like templated misfolding.

neuroscience↗

bioRxiv2025

Early synaptic pathology is associated with small tau aggregates in Alzheimer's disease

Alzheimers disease (AD) is phenotypically characterised by progressive memory loss, which involves tau aggregation and synaptic pathology. Here we characterised the tau aggregates in individual synaptosomes from AD cases and controls measuring their number and size using single molecule fluorescence microscopy. A total of 7,888 synaptosomes from pre-frontal cortex samples were studied, showing the presence of AT8-positive tau aggregates in a small fraction of synaptosomes ([~]3%) from control brains, reaching [~]20% by Braak stage 6 with more larger aggregates. We then investigated the multi-phosphorylation of synaptic tau aggregates for AT8 and T181 and quantified the co-localisation of phosphatidylserine and CD47, synaptic "eat me" and "dont eat me" signals respectively, along with synaptogyrin-3, which contributes to tau mediated synaptic dysfunction. T181, phosphatidylserine, and synaptogyrin-3 co-localisation with AT8-positive tau were increased during stage 3 and CD47 was decreased, indicating early synaptic pathology is associated with the formation of small tau aggregates, contributing to microglia-driven synaptic loss.

neuroscience↗

bioRxiv2025

Super-resolution microscopy of alpha-synuclein aggregates in brain samples indicates a subset of cells have disrupted protein homeostasis

Nanoscopic aggregates of alpha-synuclein have been observed in Parkinsons disease (PD). However, the processes that occur in-vivo leading to the formation of these small aggregates are not well understood. We used ultra-sensitive single-molecule methods including SIMOA and super-resolution microscopy to quantify and characterise alpha-synuclein aggregates harvested from human brain samples alongside the Line 61 mouse model using different tissue processing methods. While aggregate numbers did not differ between PD and control samples, larger aggregates were detected in PD brain samples. Moreover, different sub-populations of aggregates were obtained by different extraction methods, with diffusible and membrane-bound aggregates producing a more pronounced difference between disease and control samples. Our data suggests that alpha-synuclein aggregates slowly in the brain, leading to formation of larger aggregates in a sub-set of cells.

neuroscience↗

bioRxiv2025

Neurodegeneration emerges at a cellular tipping point between protein accumulation and removal.

Protein aggregates are a pathological hallmark across neurodegenerative diseases. Yet, the disconnect between molecular-level aggregation and the emergence of disease severely limits mechanistic understanding of neurodegeneration. Here, we bridge this disconnect by showing that a cellular tipping point emerges as a universal feature across diseases from the competition between aggregate accumulation and removal. We map the resulting cellular phase transition with our high-throughput live-cell assay, measuring the tipping point that separates healthy cells from those with large aggregate loads. Using super-resolution imaging of brain tissue from Alzheimers and Parkinsons disease, we quantify how the balance of accumulation and removal is shifted in disease. We validate our framework by predicting how designed aggregation inhibitors shift the tipping point to restore cellular homeostasis. Our results provide a mechanistic framework connecting molecular-level aggregation to disease, paving the way for a quantitative, unified understanding of neurodegeneration and enabling predictions of therapeutic efficacy.

neuroscience↗

bioRxiv2025

Direct, high-throughput linking of single cell imaging and gene expression

Understanding sequence-phenotype relationships in biology requires large-scale datasets that provide one-to-one mapping of sequence to phenotype. Here, we address this challenge by introducing multimodal droplet barcoding, enabling individual microfluidic droplets to be tracked across both optical and sequencing measurements. We demonstrate the power of this approach through multimodal single-cell analysis. We pair imaging with gene expression profiling of individual cells, identifying genes that correlate with phenotypic features.

genomics↗

bioRxiv2025

Small tau aggregates exhibit disease-specific molecular profiles across tauopathies

Tauopathies are neurodegenerative diseases marked by pathological tau aggregation. While disease-specific folds of insoluble tau filaments have been established, it remains unclear whether the smaller, earlier species also differ across tauopathies. Here, we characterise these small tau aggregates from post-mortem brain of individuals with Alzheimers disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration, Picks disease, and healthy controls. Using two complementary single-molecule assays, we confirm that small tau aggregates vary in abundance, morphology, and post-translational modifications. AD features specific long, fibrillar-shaped aggregates enriched in phospho-epitopes, while PSP aggregates are shorter, round, and selectively phosphorylated at serine-356, a site we identify as correlating with markers of inflammation and apoptosis. Aggregate properties co-vary with cellular stress signatures and align with disease-specific seeding profiles, suggesting distinct pathological mechanisms. These findings suggest that small tau aggregates are not a shared intermediate, but instead encode disease-specific mechanisms, with potential as both biomarkers and therapeutic targets. Key pointsSmall tau aggregates show disease-specific signatures across tauopathies, differing in abundance, morphology, and post-translational modifications. Tau aggregates in AD show enhanced phosphorylation density and structural heterogeneity, including a distinct population of long fibrillar species detectable in the soluble fraction. Alzheimers disease is characterised by specific long, fibrillar-shaped tau aggregates enriched in disease-relevant phospho-epitopes. PSP features round pSer356-positive aggregates that correlate with apoptotic and inflammatory markers, suggesting a distinct mechanism of toxicity. Isoform-specific biosensor assays reveal divergent seeding behaviour: CBD shows strong 4R seeding, while PSP lacks seeding activity. Features of small aggregates co-vary with distinct patterns of gliosis and cell stress, suggesting disease-specific mechanisms of tau-mediated toxicity.

neuroscience↗

bioRxiv2025

Structural defects in amyloid-β fibrils drive secondary nucleation

The nucleation of amyloid fibrils from monomeric protein, catalyzed by the surface of existing fibrils, is an important driver of many disorders such as Alzheimers and Parkinsons diseases. The structural basis of this secondary nucleation process, however, is poorly understood. Here, we ask whether secondary nucleation sites are found predominantly at rare growth defects: defects in the fibril core structure generated during their original assembly. We first demonstrate using the specific inhibitor of secondary nucleation, Brichos, that secondary nucleation sites on Alzheimers disease-associated fibrils composed of A{beta}40 and A{beta}42 peptides are rare compared to the number of protein molecules they contain. We then grow A{beta}40 fibrils under conditions designed to eliminate most growth defects while leaving the regular fibril morphology unchanged, and confirm the latter using cryo-electron microscopy. We measure both the ability of these annealed fibrils to promote secondary nucleation and the stoichiometry of their secondary nucleation sites, finding that both are greatly reduced as predicted. Re-analysis of published data for other proteins suggests that fibril growth defects that expose monomer planes or other structural units may also drive secondary nucleation generally, across most or all amyloids. These findings could unlock structure-based drug design of therapeutics that aim to halt amyloid disorders by inhibiting secondary nucleation sites.

biophysics↗

bioRxiv2024

Global kinetic model of lipid-induced alpha-synuclein aggregation and its inhibition by small molecules

The aggregation of -synuclein into amyloid fibrils is a hallmark of Parkinsons disease. This process has been shown to directly involve interactions between proteins and lipid surfaces when the latter are present. Despite this importance, the molecular mechanisms of lipid-induced amyloid aggregation have remained largely elusive. Here, we present a global kinetic model to describe lipid-induced amyloid aggregation of -synuclein. Using this framework we find that -synuclein fibrils form via a two-step primary nucleation mechanism and that lipid molecules are directly involved in both the nucleation and fibril elongation steps, giving rise to lipid-protein coaggregates. To illustrate the applicability of this kinetic approach to drug discovery, we identify the mechanism of action of squalamine, a known inhibitor of -synuclein aggregation, finding that this small molecule reduces the rate of lipid-dependent primary nucleation. Our work will likely guide the rational design of -synuclein aggregation inhibitors. Significance StatementAmyloid aggregation is a hallmark of a diverse range of diseases including Parkinsons Disease, where the protein -synuclein is a major con-stituent of proteinaceous deposits found in patients. It is well established that interactions between -synuclein and lipids modulate aggregation. However, the molecular mechanisms driving this lipid-induced aggregation have remained largely elusive, which has frustrated so far the discovery of drugs that prevent lipid-induced aggregation. In this work, we present the first global kinetic model describing lipid-induced aggregation and by integrating this theoretical framework with in vitro experimental data of lipid-induced -synuclein aggregation, we reveal the role of lipid membranes in the aggregation process and uncover the mechanism by which small molecule inhibitors interfere with this process.

biophysics↗

bioRxiv2024

SynPull: a novel method for studying neurodegeneration-related aggregates in synaptosomes using super-resolution microscopy

Synaptic dysfunction is one of the primary hallmarks of both Alzheimers and Parkinsons disease, leading to cognitive and behavioural decline. While alpha-synuclein, beta-amyloid, and tau are involved in the physiological functioning of synapses, their pathological aggregation has been linked to synaptic dysfunction. However, the methodology for studying the small (sub-diffraction limit) and soluble aggregates -often called oligomers, formed by these proteins is limited. Here we describe SynPull, a novel method combining single-molecule pulldown, super-resolution microscopy, and advanced computational analyses, in order to reliably study the quantity and morphology of the oligomeric alpha-synuclein, beta-amyloid, and AT8-positive tau aggregates in synaptosomes harvested from post-mortem human brain samples and mouse models. Using SynPull, we show that AT8-positive tau is the predominant aggregate type in AD, with significantly more aggregates compared to the control samples, yet the aggregate size does not differ between disease and control samples. Meanwhile, the relatively smaller amount of alpha-synuclein and beta-amyloid aggregates found in the synapses are larger than the extra-synaptic ones. Collectively, these results show the utility of SynPull to study pathological aggregates in dementia, which can help further understand the disease mechanisms causing synaptic dysfunction. O_FIG O_LINKSMALLFIG WIDTH=140 HEIGHT=200 SRC="FIGDIR/small/609517v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@d53d06org.highwire.dtl.DTLVardef@1995971org.highwire.dtl.DTLVardef@bf3edaorg.highwire.dtl.DTLVardef@1b75ca5_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract.C_FLOATNO Human post-mortem orbitofrontal cortex samples from subjects with neuropathological diagnosis of Alzheimers and Parkinsons disease, as well as age-matched controls cut into [~]300 mg sections, and MI2, APPNL-G-F, P301S, and C57Bl/6J mouse brains were first homogenised in synaptosome buffer using a Dounce homogeniser and then filtered and centrifuged to separate nuclei and organelles from the synaptic fragments. Then, the isolated synaptosomes were incubated on the SiMPull surface with anti-neurexin antibody overnight, followed by fixation and permeabilisation. Imaging antibodies against beta-amyloid, alpha-synuclein, and AT8-positive tau were added to the samples and dSTORM imaging was performed to super-resolve the aggregates. C_FIG

neuroscience↗

bioRxiv2023

Microfluidic antibody profiling after repeated SARS-CoV-2 vaccination links antibody affinity and concentration to impaired immunity and variant escape in patients on anti-CD-20 therapy

BackgroundPatients with autoimmune/inflammatory conditions on anti-CD20 therapies, such as Rituximab, have suboptimal humoral responses to vaccination and are vulnerable to poorer clinical outcomes following SARS-CoV-2 infection. We aimed to examine how the fundamental parameters of antibody responses, namely affinity and concentration, shape the quality of humoral immunity after vaccination in these patients. MethodsWe performed in depth antibody characterisation in sera collected four to six weeks after each of three vaccine doses to wild-type (WT) SARS-CoV-2 in Rituximab-treated primary vasculitis patients (n=14) using Luminex and pseudovirus neutralisation assays, whereas a novel microfluidic-based immunoassay was used to quantify polyclonal antibody affinity and concentration against both WT and Omicron (B.1.1.529) variants. Comparative antibody profiling was performed at equivalent time points in healthy individuals after three antigenic exposures to WT SARS-CoV-2 (one infection and two vaccinations; n=15) and in convalescent patients after WT SARS-CoV-2 infection (n=30). ResultsRituximab-treated patients had lower antibody levels and neutralisation titres against both WT and Omicron SARS-CoV-2 variants compared to healthy individuals. Neutralisation capacity was weaker against Omicron versus WT both in Rituximab-treated patients and in healthy individuals. In the Rituximab cohort, this was driven by lower antibody affinity against Omicron versus WT (median [range] KD: 21.6 [9.7-38.8] nM vs 4.6 [2.3-44.8] nM, p=0.0004). By contrast, healthy individuals with hybrid immunity produced a broader antibody response, a subset of which recognised Omicron with higher affinity than antibodies in Rituximab-treated patients (median [range] KD: 1.05 [0.45-1.84] nM vs 20.25 [13.2-38.8] nM, p=0.0002), underpinning the stronger serum neutralisation capacity against Omicron in the former group. Rituximab-treated patients had similar anti-WT antibody levels and neutralisation titres to unvaccinated convalescent individuals, despite two more exposures to SARS-CoV-2 antigen. Temporal profiling of the antibody response showed evidence of affinity maturation in healthy convalescent patients after a single SARS-CoV-2 infection which was not observed in Rituximab-treated patients, despite repeated vaccination. DiscussionOur results enrich previous observations of impaired humoral immune responses to SARS-CoV-2 in Rituximab-treated patients and highlight the significance of quantitative assessment of serum antibody affinity and concentration in monitoring anti-viral immunity, viral escape, and the evolution of the humoral response.

immunology↗

bioRxiv2023

Molecular mechanism of α-synuclein aggregation on lipid membranes revealed.

The central hallmark of Parkinsons disease pathology is the aggregation of the -synuclein protein, which, in its healthy form, is associated with lipid membranes. Purified monomeric -synuclein is relatively stable in vitro, but its aggregation can be triggered by the presence of lipid vesicles. Despite this central importance of lipids in the context of -synuclein aggregation, their mechanistic role in this process has not been established to date. Here, we use chemical kinetics to develop a detailed mechanistic model that is able to globally describe the aggregation behaviour of -synuclein in the presence of DMPS lipid vesicles, across a range of lipid and protein concentrations. Through the application of our kinetic model to experimental data, we find that the reaction is a co-aggregation process involving both protein and lipids and that lipids promote aggregation predominantly by enabling the elongation process. Moreover, we find that the initial formation of aggregates, via primary nucleation, takes place not on the surface of lipid vesicles but at the interfaces present in vitro. Our model will enable mechanistic insights, also in other lipid-protein co-aggregation systems, which will be crucial in the rational design of drugs that inhibit aggregate formation and act at the key points in the -synuclein aggregation cascade.

biophysics↗

bioRxiv2023

Self-replication of Abeta42 aggregates occurs on small and isolated fibril sites

Self-replication of amyloid fibrils via secondary nucleation is an intriguing physicochemical phenomenon in which existing fibrils catalyse the formation of their own copies. The molecular events behind this fibril surface-mediated process remain largely inaccessible to current structural and imaging techniques. Using statistical mechanics, computer modelling, and chemical kinetics, we show that the catalytic structure of the fibril surface can be inferred from the aggregation behaviour in the presence and absence of a fibril-binding inhibitor. We apply our approach to the case of Alzheimers A{beta}42 amyloid fibrils formed in the presence of proSP-C Brichos inhibitors. We find that self-replication of A{beta}42 fibrils occurs on small catalytic sites on the fibril surface, which are far apart from each other, and each of which can be covered by a single Brichos inhibitor.

biophysics↗

bioRxiv2023

α-Synuclein oligomers form by secondary nucleation

Oligomeric species arising during aggregation of -synuclein are proposed to be a major source of toxicity in Parkinsons disease, and thus a major potential drug target. However, their mechanism of formation and role in aggregation are largely unresolved. Here we first show that, at physiological pH, -synuclein aggregates by secondary nucleation, rather than fragmentation, and that this process is enhanced by agitation. Moreover, using a combination of single molecule and bulk level techniques, we identify secondary nucleation on the surfaces of existing fibrils, rather than formation directly from monomers, as the dominant source of oligomers. Our results highlight secondary nucleation as not only the key source of oligomers, but also the main mechanism of aggregate formation, and show that these processes take place under physiologically relevant conditions.

biophysics↗

bioRxiv2023

Design of amyloidogenic peptide traps

Segments of proteins with {beta}-strand propensity can self associate to form amyloid fibrils associated with many diseases. These regions often adopt alternative structures in their folded states, or are intrinsically disordered in solution, making it difficult to generate binders or inhibitors with existing strategies. Here we describe a general approach to bind such segments in {beta}-strand and {beta}-hairpin conformations using de novo designed scaffolds that contain deep peptide binding clefts flanked by {beta}-strands that form hydrogen bonds to the peptide upon binding. The designs bind their cognate peptides in vitro with nanomolar affinities and in mammalian cells. The crystal structure of a designed protein-peptide complex is close to the design model, and NMR characterization reveals how the peptide binding cleft is protected in the apo state. We use the approach to design binders to segments of the amyloid forming proteins Transthyretin, Tau, Serum amyloid A1 and A{beta}42. The A{beta} binders block assembly of A{beta} fibrils as effectively as the most potent of the clinically tested antibodies to date.

synthetic biology↗