This competing renewal application will extend the applicant's studies on the relationship of the alpha-2- macroglobulin receptor/low density lipoprotein receptor related protein (LRP) to Alzheimer's disease (AD). LRP, a large multifunctional receptor with multiple ligand binding domains, is the major neuronal receptor for apolipoprotein E (apoE), alpha-2 macroglobulin (a2M), and the KPI containing forms of the amyloid precursor protein (APP), all implicated in the pathophysiology of AD by both biochemical and genetic evidence. Our overarching hypothesis is that A6 deposition is central to AD, and that LRP is in a critical position to influence the balance of ABgeneration and clearance. Both apoE and a2M form stable complexes with AB. Aim 1 tests the hypothesis that apoE/AB and a2M/AB complexes are cleared, and that this clearance is via LRP. We will determine the specific domains on LRP which mediate these processes. Aim 2 explores our recent observation that LRP binds and internalizes full length APP, and that blockingthis endocytic process decreases AB generation and secretion. The discovery that the LRP intracellulardomain binds the adapter protein Fe65, a protein which is known to form a complex with the intracellular domain of APP, also implicates APP-LRP complex formation as being important in APP trafficking and potentially AB generation. We have also found that LRP undergoes PKC-mediated serine phosphorylation, and will test the hypotheses that this affects LRP trafficking, or LRP interactions with Fe65 or APP. Aim 3 tests the hypothesis,based on new preliminary data, that LRP may serve a role both as an endocytic receptor and as a novel type of signalingreceptor in neurons. We have observed that activated a2M induces a RAP blockable, calcium response in neurons (but not nonneuronal cells), and will characterize this calcium response. Ligand competent A2M also induces an increase in LRP amount and cell surface LRP;our working hypothesis is that the amount of cell surface LRP is regulated in part by this calcium response. The proposed studies will continue a highly productive and long standing collaboration among investigators at the Massachusetts General Hospital and the American Red Cross in order to pursue new exciting leads which impact our understandingof pathophysiologicmechanismsin AD, and which will lead toadditional insight in the neurobiology of LRP. PERFORMANCE SIIE:(S) (organization, city, state) Massachusetts General Hospital, Boston, MA American Red Cross, Rockville,MD KEY PEIRSONNEL. See instructions on Page 11. Use continuation pages as needed to provide the required information Name Organization Bradley T. Hyman,M.D., Ph.D. G. William Rebeck, Ph.D. Zhihua Qiu, Ph.D. Dudley Strickland, Ph.D. Sripriya Ranganathan PhD Brian Bacskai PhD - Suzanne Guenette PhD Karen Hsiao, MD- Massachusetts General Hospital Massachusetts General Hospital Massachusetts General Hospital American Red Cross American Red Cross Massachusetts General Hospital Massachusetts General Hospital Univ of Minnesota in the format shown below. Role on Project Principal Investigator Co-Investigator Fellow Co-Investigator Fellow Collaborator Collaborator Collaborator CC ^fP Principal Investigator/Program Directo^^frHyman, Bradley T _ Type the lame of the principal investigator/program director at the top of each printedpageand each continuation page. (For type specifications, see instructions on pagee.) RESEARCH GRANT TABLE OF CONTENTS Page Numbers Face Page .......................................................................................................................................................................................................................... Description,