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- Islam, Md Tohidul, 1982-
(författare)
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Mechanistic and morphological studies of Aβ amyloid formation using surface plasmon resonance
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) is the most common form of dementia and apart from the individual suffering AD also causes a large economic burden for society. AD is associated with progressive neurodegeneration and atrophy of the brain. Extracellular fibrillar assemblies of the amyloid-β peptide (Aβ) in the brain represent a clinical hallmark of AD and these are today considered to be the initial cause of the disease. The tissue-damaging properties of Aβ assemblies are, however, linked to their structures. Aβ represents a spectrum of peptides between 38-43 residues that can adopt several structures that differ both concerning their morphology and pathological properties. The mechanisms by which Aβ self-assembles, the binding strength of these structures to Aβ monomers, as well as the cross-interaction between different Aβ variants are today not fully understood. Aβ amyloid formation follows a nucleation-dependent mechanism which implies that a kinetically unfavorable nucleus must form before the formation of an amyloid fibril. The elongation of the fibril then proceeds via a template-dependent mechanism where monomeric peptides are incorporated in a highly ordered manner. Using SPR the template-dependent mode of elongation can be selectively monitored. Here, we have used the technique to probe the binding strength of Aβ fibrils and in paper 1 the role of pH and the intrinsic histidines in the Aβ sequence were investigated. The result shows that the histidines do not contribute to the previously observed increase in fibrillar strength at low pH. In paper 2 we analyzed the cross-templation between the in vivo most common variants of Aβ, represented by Aβ1-40 and Aβ1-42. Within this work, we revealed two intrinsic mechanisms preventing Aβ to adopt the structure of the significantly more pathogenic Aβ1-42 variant. In paper 3 we characterized the effect of apolipoprotein E (ApoE) on Aβ amyloid formation. ApoE is today the strongest genetic linker to the development of AD and a well-known binding partner to Aβ fibrils in vivo. Using SPR we can here show that ApoE can prevent Aβ fibril elongation. Although ApoE effectively impairs fibril formation, preventing elongation may result in alternative assemblies with higher cytotoxic properties which hence may explain its pathological effect. In paper 4 we have linked SPR to scanning electron microscopy (SEM). The work presents a novel and generic approach to simultaneously monitor the kinetic properties of amyloid formation, the binding of ligands, and its morphology. We have here specifically probed the binding properties of ApoE to Aβ fibrils, and in combination with immunogold staining technique revealed its binding pattern. Taken together this work pioneers the use of SPR as a powerful technique to elucidate Aβ amyloid formation and the complex enigma of factors causing AD.
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| 2. |
- Islam, Tohidul, 1982, et al.
(författare)
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Novel ultrasensitive immunoassay for the selective quantification of tau oligomers and related soluble aggregates
- 2024
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Ingår i: ALZHEIMERS & DEMENTIA. - 1552-5260 .- 1552-5279.
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTIONTau aggregation into paired helical filaments and neurofibrillary tangles is characteristic of Alzheimer's disease (AD) and related disorders. However, biochemical assays for the quantification of soluble, earlier-stage tau aggregates are lacking. We describe an immunoassay that is selective for tau oligomers and related soluble aggregates over monomers.METHODSA homogeneous (single-antibody) immunoassay was developed using a novel anti-tau monoclonal antibody and validated with recombinant and brain tissue-derived tau.RESULTSThe assay signals were concentration dependent for recombinant tau aggregates in solution but not monomers, and recognized peptides within, but not outside, the aggregation-prone microtubule binding region. The signals in inferior and middle frontal cortical tissue homogenates increased with neuropathologically determined Braak staging, and were higher in insoluble than soluble homogenized brain fractions. Autopsy-verified AD gave stronger signals than other neurodegenerative diseases.DISCUSSIONThe quantitative oligomer/soluble aggregate-specific assay can identify soluble tau aggregates, including oligomers, from monomers in human and in vitro biospecimens.Highlights The aggregation of tau to form fibrils and neurofibrillary tangles is a key feature of Alzheimer's disease. However, biochemical assays for the quantification of oligomers/soluble aggregated forms of tau are lacking. We developed a new assay that preferentially binds to soluble tau aggregates, including oligomers and fibrils, versus monomers. The assay signal increased corresponding to the total protein content, Braak staging, and insolubility of the sequentially homogenized brain tissue fractions in an autopsy-verified cohort. The assay recognized tau peptides containing the microtubule binding region but not those covering the N- or C-terminal regions only.
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