PROJECT SUMMARY/ABSTRACT Nucleo-cytoplasmic partitioning of proteins is an emerging intracellular process with crucial roles in Alzheimer’s disease and aging. Karyopherins mediate proper partitioning by transporting proteins across the nuclear pore. Pharmacological modulation of karyopherins provides a new approach for therapies against Alzheimer’s disease. Recent studies in model organisms and mammalian cells have uncovered that several neurodegenerative diseases display dysfunctional nucleo-cytoplasmic protein partitioning. We have reported that the conserved karyopherin XPO1 accelerates aging by promoting the nuclear export of longevity-associated transcription factors, thereby preventing the maintenance of proteostatic mechanisms. Specifically, we showed that inhibiting XPO1 leads to lifespan extensions and results in enhanced proteostasis across phyla, in part via the autophagy- lysosomal pathway. Levels of XPO1 are reduced in long-lived animals and our recent data suggest that XPO1-mediated lifespan modulation relies on fundamental changes in transcriptome and proteome partitioning as well as nucleoli re-organization, which results in altered ribosomal biogenesis. Thus, we hypothesize that XPO1 coordinately modulates the nucleo-cytoplasmic partitioning of proteins and nucleoli formation, thereby regulating compartment-specific protein functions, ribosomal biogenesis, active mRNA translation and consequently lifespan. To address this hypothesis, we propose to conduct a global characterization of protein partitioning and specification and its impact on proteostasis and aging. We will combine cutting- edge genetics and biochemical approaches in C. elegans and mammalian cells to characterize the nucleo-cytoplasmic partitioning of proteins during aging (Aim 1) and, ultimately, to uncover new modulators of nucleolar function with potential benefits against Alzheimer’s disease (Aim 2). These proposed studies are significant as they address an important question in aging related to the role and regulation of nucleo-cytoplasmic partitioning and nucleoli function during organism aging. Our approaches are innovative since we utilize C. elegans and mammalian cells in parallel to quickly identify specific protein translation and partitioning of proteins with roles in aging and to uncover pharmacological strategies to modulate nucleolar and ribosomal dynamics and preventing Alzheimer’s disease.