The aggregation of the protein tau occurs in a range of neurodegenerative diseases, including Alzheimer’s Disease1. The presence of tau aggregates, also known as neurofibrillary tangles (NFTs), is correlated with disease symptoms and clinical severity in patients2. In addition to tau pathology, the ability of innate immune cells in the brain, particularly microglia and astrocytes, to mediate neuroinflammation has been implicated as a significant contributor to Alzheimer’s Disease pathogenesis. Unfortunately, a detailed understanding of how tau aggregation is spurred in the central nervous system (CNS) and how this influences neuroimmune pathways has remained unclear. In the completed K99 phase, we discovered a cellular receptor for tau uptake, LRP1, and developed expertise in single-cell RNA sequencing methods. In the R00 phase, we will expand on the knowledge gained in the K99 mentored phase and focus the research on questions related to microglial tau regulation and cellular influences on tau’s physical state. In the first half of this proposal we will examine the molecular pathways that define microglial recognition of tau and decipher which genes are most critical for this process. In the second half we will leverage our functional genomics expertise to understand pathways critical for de novo aggregation of tau. The novel experimental methods and comprehensive analyses outlined herein will develop our understanding of pathogenic tau regulation. Further, with this mechanistic insight we will be able to envision novel therapeutic strategies for diseases such as Alzheimer’s Disease. Mandelkow, E. M. & Mandelkow, E. Biochemistry and cell biology of tau protein in neurofibrillary degeneration. Cold Spring Harb Perspect Med 2, a006247, doi:10.1101/cshperspect.a006247 (2012). Haroutunian, V., Davies, P., Vianna, C., Buxbaum, J. D. & Purohit, D. P. Tau protein abnormalities associated with the progression of alzheimer disease type dementia. Neurobiol Aging 28, 1-7, doi:10.1016/j.neurobiolaging.2005.11.001 (2007).