Role of the N-Terminal Hydrophilic Region of Amyloid Beta Peptide in Amyloidogenesis, Membrane Interaction and Toxicity Associated with Alzheimer’s Disease

Alzheimer’s disease (AD) is a deleterious neurodegenerative disease caused in major part by the aberrant processing and accumulation of amyloid beta peptides. In this dissertation, we systematically investigated the role of N-terminal region (NTR) residues of amyloid (1-40) (Aβ40) peptide in amyloidogenesis, lipid bilayer membrane interaction and damage, as well as neurotoxicity. Herein, we investigated the role of NTR residues on the aggregation and amyloid fibril formation process, to gain understanding on the electrostatic and hydrophobic constituents of the mechanism. This was achieved by substituting specific charged residues located in the NTR of Aβ40 and investigating their effects through a variety of techniques. We also investigated the role of NTR charged residues in their interaction with supported phospholipid bilayer membranes through the use of Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring to gain insight on the mechanistic details of the interaction. To further understand the implications of substituting charged NTR residues on membrane interaction, pore formation and damage, we utilized a carboxyfluorescein dye leakage assay to quantify the membrane damage caused by Aβ40 and the NTR mutants. We also performed neurotoxicity assay with SH-SY5Y neuroblastoma cells to shed light on the effects of NTR substitutions on cellular toxicity. Finally, we synthesized a polymer, trimethyl chitosan (TMC), and utilized it as a polyelectrolyte monitor of electrostatic interactions occurring between TMC and the NTR of Aβ40. Our results demonstrate that the NTR charged residues of Aβ40 contribute significantly to the aggregation process, amyloidogenesis, and phospholipid membrane interaction and perturbation by means of electrostatic, thermodynamic and hydrophobic forces.