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In situ studies of aggregation dynamics and structure of Alzheimer amyloid fibrils using customized AFM methods
2003 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

One of the hallmarks of Alzheimer’s disease is the formation of amyloid plaques in the human brain, mostly consisting of aggregates of the amyloid beta peptides (Aß). The peptides are generated from secretase cleavages of the larger transmembrane amyloid precursor protein (APP). In this work, the aggregational behaviour of two different types of Aß peptides have been investigated and compared, the normal Aß(1-40) wild type, and the rare Aß(1- 40) with the “arctic” mutation. The latter is a special mutation found in a few families in the northern Sweden, leading to an early onset Alzheimer’s disease, exhibiting a clear inheritance pattern. The unique capabilities of an Atomic Force Microscope (AFM) were used, to directly, in situ, monitor the peptide aggregation process in a physiologically relevant buffer. A commercially available Nanoscope II AFM (Digital Instruments/Veeco) was modified with a customized “add-on” tapping mode system to provide high- resolution topographical imaging even of soft biological samples. This setup was successfully applied to study the peptide aggregation. From a general point of view, the results points out a more “aggressive” aggregational behaviour for the Aß(1-40) arctic mutant than the normal wild type peptide. Studies on peptide concentration dependence on aggregation reveal that the arctic mutant forms aggregates and fibrils, at much lower concentrations than for the wild type peptide. In a time perspective, the aggregation process occurs more rapidly for the arctic mutant. At the same concentrations, ordered structures were observed already after 48 hours and fibrils after three days for arctic mutant incubated at 50 µM in TRIS- buffer solution (pH 7.4). Whereas for wild type, incubated at the same conditions, similar structures appeared only after 168 hours. Moreover, the arctic mutant exhibits a large variety of different morphologies, both coiled and non-coiled fibril structures were observed. In this thesis, seven distinct morphologies have been identified and classified into different types. Furthermore, small spherical intermediates denoted spherical bodies, were detected during the aggregation process. These structures are believed to be of particular importance, as in their link to neurotoxicity. Also, time-lapse AFM imaging has been successfully applied to observe the real time aggregation process, revealing important information about the aggregation dynamics and morphology changes during the assembly of amyloid fibrils. Our results contribute to a better understanding of the complex aggregation process and its link to neurotoxic action in Alzheimer’s disease. Hence, they may facilitate drug development for the treatment of AD.

Place, publisher, year, edition, pages
Keyword [en]
Technology, biofysik, in situ, Alzheimer, Alzheimer's disease, AFM, atomic force microscope, aggregation, fibrils, structure, amyloid beta peptides, arctic mutant, wild type, polymorphism, morphology
Keyword [sv]
URN: urn:nbn:se:ltu:diva-52289ISRN: LTU-EX--03/193--SELocal ID: 969a035e-84d8-43fc-b885-f79ed3abb534OAI: diva2:1025659
Subject / course
Student thesis, at least 30 credits
Educational program
Engineering Physics, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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