This LEAD proposal will enable an interdisciplinary group of four investigators who have collaborated productively on macromolecular studies of Alzheimer's disease (AD) to expand their work into new aspects of the protein chemistry and molecular biology of regionally selective cellular dysfunction in AD brain. We will use biochemical, cell biological and molecular genetic techniques to elucidate further the complex age-related alterations of certain normal gene products (viz., the cytoskeletal protein, tau, and the precursor of the beta-amyloid protein (beta- AP) that invariably accompany progressive neuronal dysfunction in AD. Our experiments are based on specific hypotheses (described herein) about the origin of neuritic plaques and the reorganization of the neuronal cytoskeleton in AD. They seek answers to questions arising directly from recent progress in AD research. (1) How does the beta-AP precursor, whose gene is not known to be altered in AD and whose mRNAs are widely expressed in neural and non-neural tissues, undergo selective processing into amyloidogenic fragments only in certain brain regions, especially cortex and its microvasculature? (2) Whatever the mechanism of local amyloid formation, does the beta-AP itself (or associated macromolecules) exert any toxic and/or trophic effects on cortical cells, or is it inert? Can such effects be detected and studied in an in vitro or in vivo model? (3) In view of the widespread neuritic and perikaryal accumulation of altered, aggregated tau protein in AD, can we build on our recent progress in sequencing full-length cDNAs for both mouse and human tau to determine which epitopes of tau are deposited in AD, which kinases phosphorylate normal or AD tau at these epitopes and whether the critical microtubule binding domain is incorporated into PHF and thus dysfunctional in AD? Our experiments include: (a) detection of brain-region-specific fragments of the amyloid precursor that precede the formation of the final beta-AP subunit and a search for local proteases and their inhibitors that could effect this progressive processing; (b) a dynamic study of the assembly properties of fetal, adult and AD microtubule-associated proteins; and (c) analyses of the effects of beta-AP or adherent proteins on cortical neurons in vitro (humans) and in vivo (primates and rodents). We believe our new research program as well as our prior productivity and strong commitment to molecular research on AD will allow us to use the singular opportunities provided by the LEAD Award to full advantage.