TITLE: Targeting P2RX7 Signaling as a Treatment for ADRD ABSTRACT Recent work indicates neuroinflammation is a key driver of cellular dysfunction in Alzheimer’s disease and related dementias (ADRD), where purinergic receptors play a key role. These receptors are cell surface plasma membrane proteins that communicate between neuronal and glia cells, and are sub-divided into G-coupled protein and ligand-gated ion channel receptors, and are evoked by extracellular adenosine 5′-triphosphate (eATP). Subtype-7 P2X receptors (P2X7R), which are expressed on microglia, astrocytes, oligodendrocytes, and hippocampal neurons, are considered “silent” due to inactivity; however, release of eATP, or downregulation of ectonucleosidases CD39 and CD73, results in beneficial channel opening to ions, mobilizing microglia to the site of injury for phagocytosis. Sustained activation of P2X7R via eATP results in Ca2+ overload, NLRP3 activation, superoxide formation, conversion and release of IL1β and IL18 cytokines, recruitment of pannexin-1 pores, auto- induction, NFkB transcription, caspases activation, and cell death of surrounding microglia and neurons. Provided this, P2X7R has been implicated in ADRD and neurodegenerative diseases. The majority of this work have been conducted with mice which retain the P451L loss-of-function mutation, which significantly reduces the affinity for eATP. Moreover, models retaining this SNP show limited human relevant neurodegeneration with age, and work has solely focused on amyloid clearance. Moving beyond amyloid, we will test the hypothesis that P2X7 receptors play a central role in neuroinflammation, and that inhibiting this pathway will prevent neurodegeneration through the use of genetically diverse mouse strains which retain functional P2X7R. In Aim 1, we will characterize WSB.APP/PS1 and CAST.APP/PS1 mice (Aim 1.1), and then determine whether temporally controlled genetic global ablation of P2X7R leads to prevention of neurodegeneration in our mouse models (Aim 1.2). Cohorts will be assessed at 4, 8, and 14 mos, where neuroinflammation (microglial and astroglial), synaptic density, and neuronal health will be assessed via translationally relevant PET/CT imaging. In addition, short term memory will be measured via the spatial novel recognition task (Aim 1.3). Blood and tissue will be collected for biochemical, immunopathology, and molecular analyses (Aim 1.4). To understand the spatial and temporal role of P2X7R signaling, select brain regions determined by PET/CT will be subjected to MALDI- IMS for differential protein expression (Aim 1.5). In Aim 2, we will determine a safe and effective dosing strategy for GSK1482160, a selective and potent P2X7R allosteric antagonist, in WSB.APP/PS1 and CAST.APP/PS1 at 14 mos via PK/PD modeling (Aim 2.1). We will then titrate GSK1482160 (0, 0.4, 4, 40 mg/kg) as a tool compound to specifically inhibit P2X7R activity, and assess its impact on neurodegeneration via PET/CT and behavior (Aims ...