Dissertation

Intracellular trafficking of the Alzheimer β-amyloid precursor protein regulates β-amyloid peptide generation

Greenfield, Jeffrey Peter

1999

Overview

Alzheimer's disease (AD) is a progressive brain disorder that results in the gradual irreversible loss of memory, personality changes and a decline in thinking abilities. These mental losses are directly attributable to the death of neurons and the breakdown of the connections between them caused by two abnormal structures found in the AD brain: amyloid plaques and neurofibrilary tangles. Amyloid plaques are formed from the inappropriate accumulation of pathogenic β-amyloid (Aβ) peptides, the end products of a series of proteolytic cleavages of the β-amyloid precursor protein (βAPP). The doctoral research summarized in this dissertation examines the connection between the intracellular trafficking of βAPP, and βAPP's proteolysis to Aβ. The first chapter describes a series of experiments which directly address the great degree of heterogeneity in βAPP metabolism and Aβ generation. The results presented define the precise intracellular compartments within which varied Aβ peptides are generated, and the compartments from which they are secreted. In addition, we delineate several novel populations of Aβ peptides based upon biochemical parameters such as the optimal pH at which they are generated and their solubility. The following chapter links the generation of Aβ with the intracellular trafficking of βAPP using one principal assay, the cell-free reconstitution of βAPP trafficking. This assay allowed us to demonstrate how diverse molecules and drugs can influence the intracellular generation of Aβ, simply by regulating the rate of βAPP secretion from specific organelles within the secretory pathway. The final chapter extends the results of the previous two chapters, in which the experiments were performed in mammalian cells, to a novel system, the eukaryotic, but unicellular organism, Saccharomyces cerevisiae. The demonstration that budding yeast expressing βAPP can generated authentic Aβ peptides, suggests that these simple genetically manipulatable cells can provide a system within which the elusive proteolytic enzymes which generate Aβ can be discovered. Taken together, the results presented in this thesis indicate that βAPP trafficking and Aβ generation are inextricably intertwined. The hope is that by understanding the regulation of βAPP trafficking, we will one day soon be able to suggest therapeutically relevant targets for intervention in Aβ generation, which might delay or prevent the onset of this tragic disease.

• Publisher: ProQuest Dissertations & Theses
• Subject: Neurology / Neurosciences
• ISBN: 0493324895, 9780493324890