SUMMARY The goal of this project is to understand how protein quality control mechanisms in adult stem cells and their progeny are regulated during aging, with the objective to restore the functionality of old cells. Preservation of a pristine proteome is emerging as a critical mechanism for maintaining cellular function throughout life. Disruption in the machinery that maintains protein quality control leads to protein aggregation diseases and accelerated aging in invertebrate models. However, how cell types with different roles regulate protein homeostasis during long periods of time remains unexplored, particularly in mammals. The adult brain offers a unique paradigm for understanding protein quality control mechanisms in cell types with different functions. It contains reservoirs of quiescent neural stem cells (NSCs) that can activate and in turn generate differentiated cells with specialized function – neurons, astrocytes, and oligodendrocytes. During aging, the ability of NSCs to exit quiescence and their ability to produce new neurons both decline dramatically yet this deterioration is not inexorable and can be reversed by environmental interventions, including diet. However, the mechanisms that can regulate NSC function are largely unknown. We recently embarked on a systematic characterization of protein aggregates and proteostasis mechanisms in young NSCs and their progeny. Excitingly, we find that quiescent NSCs contain large protein aggregates that are present undegraded in large lysosomes. Nutrient deprivation can clear protein aggregates and enhance their ability to activate, a process that is dramatically affected by aging. Interestingly, our RNA- seq profiling from young and also mice reveal that quiescent NSCs from old mice exhibit a large degree of transcriptome-wide change with age. The central hypothesis of this Project is that the protein quality control mechanisms differ in cell types with distinct functions, which could underlie their different degree of deterioration with age and could be used for specifically ameliorating old cells. To test this idea, we propose the following experiments: 1. To understand how protein aggregates and protein quality control mechanisms are influenced by increasing age and by rejuvenating strategies 2. To specifically modulate proteostasis mechanisms to ameliorate function in old NSCs and their differentiated progeny 3. To determine the composition of protein aggregates and generate new aggregate reporters in NSCs and their progeny Completion of these Aims will provide unique mechanistic insights into the regulation of protein aggregates and their alteration during aging in regenerative cells and their differentiated progeny. This st...