Contact PD/PI: Rossoll, Wilfried PROJECT SUMMARY/ABSTRACT The goal of this project is to capture the molecular complexity of pathological tau-associated proteomes in the brain of Alzheimer’s disease (AD) and related tauopathy patients, in order to gain a thorough mechanistic understanding of their role in the pathophysiology of these dementias. Recent studies suggest a correlation of characteristic temporal and topographic patterns of microtubule- associated protein tau (MAPT) aggregates with the observed clinical phenotype and progression of AD. Although neurofibrillary tangles (NFTs) and other forms of phospho-tau aggregates are believed to play a pivotal role in the disease process, we have a poor understanding of the composition and molecular environment of these insoluble aggregates, and how their formation, toxicity, and spread across specific brain regions is regulated. Greater understanding of the phospho-tau interactome in AD and primary tauopathies, and how these proteins regulate the oligomerization, pathological accumulation, and seeding of tau in affected neurons and glia is of critical importance for the identification of novel therapeutic targets. As a limitation of current technologies, the in-depth characterization of NFTs and other neuropathologic inclusions has historically been difficult to address, since these aggregates are detergent-insoluble, and thus refractory to classical affinity purification methods. To address this limitation, we have established a novel method for the proximity-labeling, purification and identification of pathological phospho-tau associated proteins from fixed human tissue followed by quantitative proteomics analysis. We hypothesize that the molecular environment and differential accumulation of pathological tau aggregates contributes to etiology of AD and related tauopathies. We propose to use the latest cutting-edge technologies to profile the phospho-tau associated proteome across different patient cohorts and disease stages, to decipher molecular signaling networks in disease development, and to functionally validate novel therapeutic targets in mouse models and human organoid systems. Our three specific aims are: (i) to compare tau pathology-associated proteomes across common tauopathies via proximity proteomics of phospho-tau inclusions in the brain of AD and primary tauopathy patients, (ii) to establish spatiotemporal patterns of tau pathology-associated proteomes specific for disease stages in brain regions, and brain resilience in AD patient cohorts, and (iii) to determine the functional role of tau pathology-associated proteins in neurodegenerative processes through target validation in AD-related tauopathy mouse models and human brain organoids. Successful completion of this project will result in the identification of novel molecular components regulating tauopathy-specific disease pathways during the pathogenesis of AD and related dementias, which may provide new therapeutic strategies for effective treatment of these devastating disorders. Project Summary/Abstract Page 6

Contact PD/PI: Rossoll, Wilfried PROJECT NARRATIVE Alzheimer’s disease (AD) is the most common form of dementia and a leading cause of death in the United States. We propose to use the latest technologies to determine the molecular composition of disease- causing tau protein aggregates in human AD and other tauopathy patient brain tissue. Potential modifiers of the disease process will be further investigated using mouse models and advanced cell culture models of AD. Project Narrative Page 7