Solid-phase self-assembly of amyloid peptides and its cytotoxicity to cells

Abstract

Self-assembly is a process through which small building blocks spontaneously form ordered structures. In nature, self-assembly is one of major routes for organizing essential biological materials such as lipid bilayers, DNAs, proteins, and many supramolecular structures. Amyloids are self-assembled materials closely associated with various neurodegenerative diseases. Numerous studies indicate a central role of amyloidogenic proteins in the pathogenesis of neurodegenerative diseases. However, few studies have investigated the underlying mechanism of amyloid fibril formation and amyloid-mediated neuronal cell death. In this thesis study, prion fragment and β-amyloid peptides were studied as model amyloidogenic peptides using a solid surface-based self-assembly system. According to the results, the self-assembly of the peptides into amyloid fibrils was highly accelerated on the solid surface than in solution. Amyloid-like properties of fibrils self-assembled on the solid surface were confirmed by multiple analyses with circular dichroism and amyloid-specific dyes such as Congo red and thioflavin T. The fibril formation of prion peptides was substantially affected by incubation temperature and pre-formed fibrils disassembled after additional heat treatment at 100 ℃. Cellular response against β-amyloid fibrils was also explored. Neuronal cells grew atop β-amyloid fibril surfaces, creating physical contacts between the cells and the fibrils. Cell viability was differentially affected when grown atop monomeric, oligomeric, or fibrillar Aβ. The mode of cell death by Aβ fibrils was confirmed to be apoptotic rather than necrotic, implying that cells undergo suicide by just contact with Aβ fibrils. Our further observation of elevated activities of caspase-3 enzyme in the cells grown in contact with Aβ fibrils indicated the occurrence of apoptosis through a caspase-3 dependent way.