Abstract This proposal leverages a new interdisciplinary collaboration between Drs. Guoyan Zhao and Erik Musiek to define the transcriptional control of astrocyte identities, reactivities, and their roles in in Alzheimer disease (AD) and Parkinson disease (PD) pathogenesis. AD and PD are heterogeneous, multifactorial disease that selectively affects certain regions of the brain. Astrocytes are a major glial cell type in the central nervous system that play critical roles in neural circuit function and brain homeostasis. Accumulating evidence supports astrocyte as a major contributor of the neurodegenerative processes in AD and AD Related Dementias (AD/ADRD). In our recently published work, we identified three evolutionarily conserved astrocyte subpopulations which had unique marker gene expressions shared by the corresponding populations across multiple brain regions and different disease conditions. However, astrocytes do exhibit regional differences and transcriptomic changes in disease conditions linked to amyloid pathology, tauopathy, neuronal death, and neurodegenerative diseases, suggesting that astrocytes may contribute to regional differences in disease susceptibility. From this work, we have identified ten candidate TFs that exhibited regional differential expression patterns in human astrocytes whose expressions were dysregulated in disease conditions. Furthermore, these TFs are either known AD risk genes or have known functions in regulating cell activation or inflammatory response in cell types other than astrocyte. In this proposal, we will use our established in vitro and in vivo mouse experimental systems and the cutting-edge technologies of spatial transcriptomics and scRNA-seq to systematically evaluate each candidate TF in regulating astrocyte property and AD/PD pathogenesis. In Aim 1, we will perform in vitro experimental investigation of candidate TFs in regulating astrocyte property and neurodegenerative disease pathogenesis. We will manipulate candidate TF expression in primary murine astrocyte-enriched cultures properties of astrocyte with and without TF manipulation, astrocyte cultures to sustain growth of mouse cortical and human astrocytes cell line assess the including morphological changes, the ability of neurons, cytokine/chemokine expression, and and phagocytosis capability. In Aim 2 we will perform MERSCOPE spatial transcriptomic analysis to assess region- specific expression of candidate TFs. In Aim 3 we will perform in vivo gene knock-down and overexpression analyses to assess the function of candidate TFs in regulating astrocyte reactivity, neurodegenerative disease pathology, and the impact on other cell types. If funded and successfully implemented this proposal will provide validated TFs that regulate astrocyte activation and/or AD/PD pathology relevant to human disease pathogenesis. These TFs are excellent candidate targets for the development of effective AD or PD treatment strategies.