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

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 beta-amyloid (Abeta) peptides, the end products of a series of proteolytic cleavages of the beta-amyloid precursor protein (betaAPP).;Taken together, the results presented in this thesis indicate that betaAPP trafficking and Abeta generation are inextricably intertwined. The hope is that by understanding the regulation of betaAPP trafficking, we will one day soon be able to suggest therapeutically relevant targets for intervention in Abeta generation, which might delay or prevent the onset of this tragic disease.;The doctoral research summarized in this dissertation examines the connection between the intracellular trafficking of betaAPP, and betaAPP's proteolysis to Abeta. The first chapter describes a series of experiments which directly address the great degree of heterogeneity in betaAPP metabolism and Abeta generation. The results presented define the precise intracellular compartments within which varied Abeta peptides are generated, and the compartments from which they are secreted. In addition, we delineate several novel populations of Abeta 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 Abeta with the intracellular trafficking of betaAPP using one principal assay, the cell-free reconstitution of betaAPP trafficking. This assay allowed us to demonstrate how diverse molecules and drugs can influence the intracellular generation of Abeta, simply by regulating the rate of betaAPP 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 betaAPP can generated authentic Abeta peptides, suggests that these simple genetically manipulatable cells can provide a system within which the elusive proteolytic enzymes which generate Abeta can be discovered.