The genes encoding the amyloid beta protein precursor (APP) and presenilins 1 and 2 (PS1 and PS2) have been shown to harbor autosomal dominant gene defects in approximately 50 % of early-onset (<60 years) cases of familial Alzheimer's disease (FAD) tested. Recently Dr. Steve Younkin, in collaboration with this and other laboratories found PS2 and PS1 FAD mutations to be associated with elevated amounts of Abeta42 in the plasma and fibroblasts of carriers as well as in cells and transgenic mice overexpressing mutant PS1. These data suggest that PS1 and PS2 gene defects steer APP metabolism toward a pathway leading to the increased production of Abeta42. The P.I. and his collaborators have recently observed two additional molecular consequences of presenilin FAD mutation. First, they observed that overexpression of wild-type or mutant PS1 or PS2 leads to increased cell death and enhanced sensitivity to apoptotic stimuli. Second, they discovered that a PS2 FAD mutation associated with increased Abeta42, also causes PS2 proteolytic by-products to hyper-accumulate in a pre-Golgi intracellular compartment of the cell. Based on the findings described above, the goal of this proposal is to generate first order information regarding the mechanism of PS1-associated cell death and the potential role of PS1 in apoptosis. To this end, the P.I. proposes to expand upon his preliminary findings showing that prolonged expression of PS1 leads to enhanced sensitivity to cytotoxic and apoptotic stimuli. He will also explore whether cell death induced by PS1 requires elevated production of Abeta42 and APP expression and test whether PS1 mutations lead to altered maturation, processing, and/or subcellular distribution of APP. Finally, PS1-expressing cells will be examined for changes in the trafficking, degradation/aggregation, and processing of PS1 in the ER-Golgi. Throughout these studies, correlations will be sought between the rate of cell death/enhanced sensitivity to cytotoxic stimuli and changes in the post-translational processing and subcellular localization of APP and PS1 in a variety of stably-transfected and inducible wild-type and mutant PS1 cell lines as well as in primary neurons prepared from the brains of wild-type and mutant PS1 transgenic mice.
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