Many lines of evidence suggest that beta-amyloid peptides cause neuronal damage and affect fundamental memory processes early in the course of Alzheimer's disease (AD). Two membrane-associated enzymes, namely betasecretase (BACEl) and gamma-secretase are responsible for beta-amyloid production. Understanding the details regarding the cellular and molecular mechanisms involved in beta-amyloid production in neurons is a topic of central importance in molecular AD research. Many investigators have studied the membrane transport of amyloid precursor protein in cultured cell lines and neurons in order to ascertain where in neurons this protein is processed by BACEl and gamma-secretase. There is a general agreement in the field that amyloid precursor protein is transported along the nerve fibers (called axons) and is proteolytically converted into beta-amyloid near axon terminals, termed presynaptic sites. BACEl has been found in neuronal dendrites and axons (the two types of neuronal projections). How BACE1 is transported in axons is not clearly understood. Recent findings from our lab suggest that BACEl is transported in membrane organelles called recycling endosomes in neurons cultured from embryonic mouse hippocampus. Moreover, we found evidence for a highly polarized transport of BACEl from the cell surface of dendrites towards axons (a process termed transcytosis). The goal of this proposal is to characterize the functional significance of polarized BACE1 transport in neurons. Specifically, we propose to interfere with BACEl transcytosis in cultured hippocampal neurons and in brains of transgenic mice to test our hypothesis that this process contributes to neuronal beta-amyloid production and deposition.
Our proposal is timely, unique and highly innovative because BACEl transcytosis in recycling endosomes has never been described. Our proposal is also highly significant because we employ both in vitro and in vivo models to investigate the molecular and cellular mechanisms involved in neuronal BACE1 trafficking that is functionally important for Af3production. This is a novel and exciting area of research, and we feel that our investigation will uncover significant insights on cellular and molecular mechanisms that are relevant to AD pathogenesis.