Biology subjects

Ramakers, M.

Publications and source records attributed to Ramakers, M..

5 recordsLinked to original sources

bioRxiv2025

Phagocytes as Plaque Catalysts: Human Macrophages Actively Generate Pathogenic Aβ42 Fibrils with Seeding and Cross-Seeding Potency

The prevailing view frames microglia and macrophages as guardians against amyloid beta (A{beta}) accumulation in Alzheimers disease (AD). Here, we overturn this paradigm by demonstrating that human phagocytic cells--including differentiated THP-1 macrophages and iPSC-derived microglia--are not merely passive responders but active producers of extracellular, seeding-competent A{beta}42 fibrils, the amyloid species most strongly linked to parenchymal plaque formation and neurodegeneration. These cell-generated aggregates differ structurally and functionally from synthetic fibrils, exhibiting heightened seeding activity and the ability to cross-seed tau aggregation, a key driver of AD progression. Notably, A{beta}42 fibril formation in this system requires active cellular processes and is exacerbated by loss of TREM2, a major AD risk gene. Transcriptomic profiling reveals an early inflammatory response resembling microglial states observed in human AD models, positioning this system as a tractable, human-relevant platform to dissect the interplay between A{beta} aggregation, innate immunity, and genetic susceptibility. Our findings suggest that macrophages and microglia play a dual role in AD, acting both as responders and inadvertent catalysts of pathogenic amyloid formation, with implications for early therapeutic intervention. Significance StatementHow amyloid plaques emerge and spread in Alzheimers disease remains a critical unanswered question. Here, we show that human immune cells--including brain-resident microglia--can actively generate A{beta}42 fibrils, the form of amyloid most strongly linked to neurodegeneration. These cell-produced fibrils not only seed further amyloid buildup but also trigger tau aggregation, a key event in disease progression. We further demonstrate that genetic risk factors like TREM2 amplify this process. Our findings reveal a direct link between immune cell activity, genetic susceptibility, and the earliest stages of Alzheimers pathology, offering new insights into disease mechanisms and potential intervention points.

biochemistry↗

bioRxiv2022

Tau amyloid polymorphism is shaped by local structural propensities of its protein sequence

Different tauopathies are characterized by specific amyloid filament folds that are conserved between patients. Disease-specific tau filament folds probably reflect the specific pathological contexts leading to their formation including isoforms or post-translational modifications. Little is known, however, as to whether and how intrinsic conformational tendencies of the tau sequence itself contribute to its polymorphism. Using cryo-EM structure determination we find that a short amyloidogenic C-terminal peptide consisting of residues 350-362 of the tau repeat domain adopts the same polymorphic conformations in isolation as it does in the context of major disease-associated protofilament folds. Biophysical characterisation and molecular modelling show that the amyloid conformations adopted by this peptide constitute core structural motifs stabilizing distinct disease-associated tau filament folds. In accordance this segment also contributes to the efficient propagation of human AD tau seeds in tau reporter cells while it is irrelevant to heparin-induced recombinant seeds. Our findings suggest that tau 350-362 is key to the propagation of disease-associated tau polymorphs and that the conformational preferences of this segment predispose to the topological diversity observed in tau filament folds.

biophysics↗

bioRxiv2021

Mapping the sequence specificity of heterotypic amyloid interactions enables the identification of aggregation modifiers

Heterotypic amyloid interactions between related protein sequences have been observed in functional and disease amyloids. While sequence homology seems to favour heterotypic amyloid interactions, we have no systematic understanding of the structural rules determining such interactions nor whether they inhibit or facilitate amyloid assembly. Using structure-based thermodynamic calculations and extensive experimental validation, we performed a comprehensive exploration of the defining role of sequence promiscuity in amyloid interactions. Using this knowledge, we demonstrate, using tau as a model system, that predicted cross-interactions driven by sequence homology indeed can modify nucleation, fibril morphology, kinetic assembly and cellular spreading of aggregates. We also find that these heterotypic amyloid interactions can result in the mis-localisation of brain-expressed protein sequences with prevalent activities in neurodegenerative disorders. Our findings suggest a structural mechanism by which the proteomic background can modulate the aggregation propensity of amyloidogenic proteins and discuss how such sequence-specific proteostatic perturbations could contribute to the selective cellular susceptibility of amyloid disease progression.

biophysics↗

bioRxiv2021

Heterotypic Aβ interactions facilitate amyloid assembly and modify amyloid structure

It is still unclear why pathological amyloid deposition initiates in specific brain regions, nor why specific cells or tissues are more susceptible than others. Amyloid deposition is determined by the self-assembly of short protein segments called aggregation-prone regions (APRs) that favour cross-{beta} structure. Here we investigated whether A{beta} amyloid assembly can be modified by heterotypic interactions between A{beta} APRs and short homologous segments in otherwise unrelated human proteins. We identified heterotypic interactions that accelerate A{beta} assembly, modify fibril morphology and affect its pattern of deposition in vitro. Moreover, we found that co-expression of these proteins in an A{beta} reporter cell line promotes A{beta} amyloid aggregation. Importantly, reanalysis of proteomics data of A{beta} plaques from AD patients revealed an enrichment in proteins that share homologous sequences to the A{beta} APRs, suggesting heterotypic amyloid interactions may occur in patients. Strikingly, we did not find such a bias in plaques from overexpression models in mouse. Based on these data, we propose that heterotypic APR interactions may play a hitherto unrealised role in amyloid-deposition diseases.

neuroscience↗

bioRxiv2020

The tumor suppressor protein PTEN undergoes amyloid-like aggregation in tumor cells.

Protein aggregation is an underappreciated mechanism that may contribute to the loss- and oncogenic-gain-of-function of mutant tumor suppressors such as p53 and axin. In the present study, we describe amyloid-like aggregation behaviour of the second most frequently mutated tumor suppressor in human cancer, PTEN. In silico analysis revealed a particularly high aggregation vulnerability for this protein, which was corroborated by in vitro aggregation assays. In cultured tumor cells, we found that under stress conditions, PTEN readily undergoes amyloid-like aggregation as a result of mutation. However, we also show that severe dysregulation of protein homeostasis may lead to aggregation of wild-type PTEN. These observations were supported by a small survey of patient-derived uterine tumor tissues, which found that more than 25% of tumors analyzed displayed wild-type PTEN aggregation. Finally, in an exploratory clinical study we found that PTEN aggregation status was correlated with a decline in clinical outcome. Our findings establish that the tumor suppressor PTEN is highly aggregation-prone and our work suggests that protein aggregation might be an underestimated but prevalent component of cancer cell biology.

cancer biology↗