The long-range goal of this research is to develop tools for reducing production of beta-amyloid, which is a neurotoxic peptide that is thought to play a key role in causing Alzheimer's disease. The two homologous proteins presenilin 1 and 2 (PS1 and PS2) appear to play an important role in the generation of beta- amyloid from its parent protein, amyloid precursor protein. Using fibroblasts lacking PS1, we have observed that elimination of PS1 interferes with amyloid precursor protein processing and reduces production of beta-amyloid. This suggests that inhibitors of PS1 might also reduce beta-amyloid production. Over-expression of PS2 (as well as PS1) is able to restore processing of amyloid precursor protein in fibroblasts lacking PS1, which suggests that PS2 also participates in the metabolism of amyloid precursor protein and production of beta-amyloid. In this proposal we will investigate the hypothesis that specific domains of PS1 and PS2 regulate the metabolism of amyloid precursor protein and production of beta-amyloid. In addition, we will investigate whether the same presenilin domains that are required in the metabolism of amyloid precursor protein also necessary for other activities associated with presenilins, such as the regulation of apoptosis, glycogen synthase kinase 3 and -catenin activity. We will perform our studies in neurons, which are important generators of beta-amyloid in the brain. In the first aim we will investigate whether PS1 regulates amyloid precursor protein metabolism in cortical neurons. In the second aim we will investigate whether PS2 regulates amyloid precursor protein metabolism in cortical neurons lacking PS1. In the third aim, we will determine whether mutation or deletion of specific protein domains in PS1 and PS2, generates a modified presenilin that inhibits amyloid precursor protein processing and reduces beta-amyloid production. Our studies of amyloid precursor protein processing in neurons lacking PS1 or PS2 will serve as models for identifying inhibitory presenilin constructs. Identification of mutant forms of presenilin that inhibit beta- amyloid production could lead to novel strategies for therapeutic intervention in Alzheimer's disease.