Biology subjects

Bekier, M.

Publications and source records attributed to Bekier, M..

5 recordsLinked to original sources

bioRxiv2024

Molecular Visualization of Neuronal TDP43 Pathology In Situ

Nuclear exclusion and cytoplasmic accumulation of the RNA-binding protein TDP43 are characteristic of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Despite this, the origin and ultrastructure of cytosolic TDP43 deposits remain unknown. Accumulating evidence suggests that abnormal RNA homeostasis can drive pathological TDP43 mislocalization, thereby enhancing RNA misprocessing due to the loss of nuclear TDP43, and engendering a cycle that ultimately leads to cell death. Here, we demonstrate that the addition of small monovalent oligonucleotides successfully recapitulates pathological TDP43 mislocalization and aggregation, aberrant splicing, and degeneration in iPSC-derived neurons (iNeurons). By employing a tailored multimodal in situ cryo-correlative light and electron microscopy pipeline, we examine the localization and aggregation of TDP43 in near-native conditions. We discover that mislocalized TDP43 accumulates and forms ordered fibrils within autophagosomes and lysosomes in iNeurons, as well as in ALS/FTLD patient tissue. We provide the first high-resolution snapshots of TDP43 aggregates in situ, delivering an unprecedented view of the earliest pathogenic events underlying ALS, FTLD, and related TDP43 proteinopathies.

neuroscience↗

bioRxiv2024

TDP43 autoregulation gives rise to shortened isoforms that are tightly controlled by both transcriptional and post-translational mechanisms

The nuclear RNA-binding protein TDP43 is integrally involved in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Previous studies uncovered N-terminal TDP43 isoforms that are predominantly cytosolic in localization, highly prone to aggregation, and enriched in susceptible spinal motor neurons. In healthy cells, however, these shortened (s)TDP43 isoforms are difficult to detect in comparison to full-length (fl)TDP43, raising questions regarding their origin and selective regulation. Here, we show that sTDP43 is created as a byproduct of TDP43 autoregulation and cleared by nonsense mediated RNA decay (NMD). The sTDP43-encoding transcripts that escape NMD can lead to toxicity but are rapidly degraded post-translationally. Circumventing these regulatory mechanisms by overexpressing sTDP43 results in neurodegeneration in vitro and in vivo via N-terminal oligomerization and impairment of flTDP43 splicing activity, in addition to RNA binding-dependent gain-of-function toxicity. Collectively, these studies highlight endogenous mechanisms that tightly regulate sTDP43 expression and provide insight into the consequences of aberrant sTDP43 accumulation in disease.

neuroscience↗

bioRxiv2022

RNA methylation influences TDP43 binding and disease pathogenesis in models of amyotrophic lateral sclerosis and frontotemporal dementia

Methylation of RNA at the N6 position of adenosine (m6A) is one of the most common RNA modifications, impacting RNA stability as well as its transport and translation. Previous studies uncovered RNA destabilization in models of amyotrophic lateral sclerosis (ALS), in association with accumulation of the RNA-binding protein TDP43, which is itself mislocalized from the nucleus in >95% of those with ALS. Here, we show that TDP43 recognizes m6A-modified RNA, and that RNA methylation is critical for both TDP43 binding and autoregulation. We also observed extensive hypermethylation of coding and non-coding transcripts in ALS spinal cord, many of which overlap with methylated TDP43 target RNAs. Emphasizing the importance of m6A for TDP43 binding and function, we identified several m6A factors that enhance or suppress TDP43-mediated toxicity via a single-cell CRISPR/Cas9 candidate-based screen in primary neurons. The most promising genetic modifier among these--the canonical m6A reader YTHDF2-- accumulated within spinal motor neurons in ALS postmortem sections, and its knockdown prolonged the survival of human neurons carrying ALS-associated mutations. Collectively, these data show that m6A modifications modulate RNA binding by TDP43, and that m6A is pivotal for TDP43-related neurodegeneration in ALS.

neuroscience↗

bioRxiv2019

Apolipoprotein A-I Mimetic 4F Peptide Generates Amyloid Cytotoxins by Forming Hetero-oligomers with β-amyloid

Apolipoproteins are involved in pathological conditions of Alzheimers disease (AD), truncated apolipoprotein fragments and {beta}-amyloid (A{beta}) peptides coexist as neurotoxic heteromers within the plaques. Therefore, it is important to investigate these complexes at the molecular level to better understand their properties and roles in the pathology of AD. Here, we present a mechanistic insight into such heteromerization using a structurally homologue apolipoprotein fragment of apoA-I (4F) complexed with A{beta}(M1-42) and characterize their toxicity. The 4F peptide slows down the aggregation kinetics of A{beta}(M1-42) by constraining its structural plasticity. NMR and CD experiments identified 4F-A{beta}(M1-42) heteromers as being comprised of unstructured A{beta}(M1-42) and helical 4F. A uniform {approx}2-fold reduction in A{beta}42 15N/1H NMR signal intensities with no observable chemical shift perturbation indicated the formation of a large complex, which was further confirmed by diffusion NMR experiments. Microsecond scale atomistic molecular dynamics simulations showed that 4F interaction with A{beta}(M1-42) is electrostatically driven and induces unfolding of A{beta}(M1-42). Neurotoxicity profiling of A{beta}(M1-42) complexed with 4F confirms a significant reduction in cell-viability and neurite growth. The molecular architecture of heteromerization between 4F and A{beta}(M1-42) discovered in this study provides evidence towards our understanding of the role of apolipoproteins or their truncated fragments in exacerbating AD pathology.

biophysics↗

bioRxiv2018

Alzheimer’s Amyloid-Beta Intermediates Generated by Polymer-Nanodiscs

Polymethacrylate-copolymer (PMA) encased lipid-nanodiscs (~10 nm) and macro-nanodiscs (>15 nm) are used to study A{beta}1-40 aggregation. We demonstrate that PMA-nanodiscs form a ternary association with A{beta} and regulate its aggregation kinetics by trapping intermediates. Results demonstrating reduced neurotoxicity of nanodisc-bound A{beta} oligomers are also reported.

biophysics↗