PROJECT SUMMARY/ABSTRACT Alzheimer’s disease (AD) is a multifactorial and complex neurodegenerative disorder that involves numerous genetic, epigenetic and environmental factors. Advances in genomics have identified new genes and rare variants that are associated with AD. However, the molecular mechanisms of how these factors contribute to AD pathogenesis are largely undefined. In collaboration with the CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology) consortium, we recently identified a rare missense variant in TM2D3 that is associated with a significant increase in the risk of late-onset AD (LOAD). Furthermore, a recent study by an independent group reported that another rare missense variant was found in a patient with early-onset AD. Although the function of this gene has not been explored in vertebrates in vivo, our experiments using fruit flies, Drosophila melanogaster, suggests that this gene is a potential regulator of a key enzyme that process APP, a precursor protein that produces neurotoxic Ab42 peptides that contribute to AD. In this proposal, we elucidate the molecular function of TM2D3 and its related family members (TM2D1/2) to understand their role in APP processing and AD pathogenesis using Drosophila. Flies are excellent model organisms to genetically dissect molecular mechanisms of neurodegeneration. Moreover, since APP is processed by the same set of enzymes that activate Notch, a pathway affected in TM2D3 mutant flies, rich research infrastructure for Notch signaling studies in Drosophila greatly facilitates the mechanistic study of this protein in vivo. By combining genetic, cell biological, biochemical, electrophysiological and behavioral methodologies, we will uncover how TM2D3 and its relatives modulate proteolysis of membrane proteins to understand how rare missense variants in this gene affects the risk of LOAD and EOAD in humans. Such understanding will provide novel insights into AD pathogenesis and will deliver a new framework to understand how genetic risk factors of AD may impinge on a common molecular pathway to facilitate disease expression and progression.