PROJECT SUMMARY Mitochondrial dysfunction and protein misfolding are central pathological processes in aging and aging- associated neurodegenerative diseases including Alzheimer’s disease (AD) and frontotemporal dementia (FTD), but the relationship between these processes is poorly understood, as are the mechanisms by which they lead eventually to cell death. Although mitochondrial dysfunction occurs in AD, little is understood about the consequences of this mitochondrial failure or how it contributes to neurodegeneration, especially its impact on protein misfolding. To gain insight into how mitochondria impact protein misfolding, we used innovative high throughput CRISPR-based screens to identify critical roles for the mitochondrial respiratory chain as well as genes that regulate ATP and reactive oxygen species (ROS) levels in the regulation of tau misfolding. In this proposal, we will test our central hypothesis that in AD, age-associated mitochondrial dysfunction impairs tau homeostasis, and that increasing ATP and decreasing ROS can decrease tau misfolding and cell death. The overall objectives of our proposed study are to determine how mitochondrial respiratory chain dysfunction regulates tau aggregation, and define the most robust mechanisms to prevent tau-induced neurodegeneration. We will accomplish these objectives in two specific aims. (1) We will use pharmacologic inhibitors and gene knockdown with assays of energy levels and oxidative stress to gain insight into the consequences of mitochondrial perturbation. We will also use transcriptomics to identify broad mechanisms by which metabolic dysfunction promotes tau misfolding in human neurons. (2) We will determine how increasing energy or decreasing ROS can decrease protein misfolding and enhance neuronal survival in models of AD. Overall, these studies will yield new information about the causal relationships between metabolic failure and protein aggregation in AD, and begin to reveal new therapeutic strategies to target metabolic dysfunction in AD.