PROJECT SUMMARY/ABSTRACT Neuroinflammation is an important component of Alzheimer's disease (AD). However, the molecular mechanism by which inflammation modulates AD progression is not defined. We discovered that beta-amyloid 1-42 activates NLRP3 inflammasomes and that AD patients uniformly have evidence of activated inflammasomes in their brains. To test the role of NLRP3 inflammasomes in AD, we bred APP/PS1 mice (an amyloid-based murine model of AD) into NLRP3, ASC, or caspase-1 KOs (the three proteins comprising the NLRP3 inflammasome) and observed that these mice were completely protected from numerous AD features including learning/memory deficits and abnormalities in long-term potentiation. NLRP3 inflammasomes regulate the expression of IL-1beta and IL-18, two highly proinflammatory cytokines abundantly produced in microglial cells; in addition, astrocytes are strong expresses of pro-IL-18. IL-1beta is abundant in microglial cells on the periphery of amyloid plaques and can cause fever, a strong acute phase response, sepsis syndrome, and pyroptotic cell death. IL-18 is a member of the IL1 superfamily. Unlike IL- 1beta, IL-18 does not activate NF-kappaB or have pyrogenic activity. It is unknown if IL-1beta or IL-18 reduction was responsible for the protective phenotype in inflammasome-deficient APP/PS1 mice. We generated IL-18KO/APP/PS1 mice and, surprisingly, these mice developed a lethal seizure disorder, which was completely reversed by levetiracetam therapy. This is highly relevant as epidemiologic studies suggest that almost two-thirds of AD patients have seizures at some point during the course of their disease. In Aim 1, we will examine the role of inflammasome-dependent pyroptosis in microglial cells in the pathogenesis of AD using transgenic mice in which the inflammasome has been specifically deleted from microglial cells on an APP/PS1 background. We will also test APP/PS1 mice deficient for Gasdermin D (a caspase-1 substrate and the final effector molecule of pyroptosis). In Aim 2, we will examine if IL-18 counterbalances the proepileptic effects of IL-1beta in AD-related seizures. We will use a genetic approach (deleting IL-18 in other AD mouse models) as well as a pharmacological approach (an IL-1beta loss-of-function approach) in IL-18KO/APP/PS1 mice and assess animals for seizures. In Aim 3, we will determine the role of IL-18 in reducing neuronal network activity and modulating synaptic transmission. We will identify the types of synapses that are dysregulated in IL-18KO/APP/PS1 mice by performing morphological and electrophysiological studies as well as biochemical analysis using immunohistochemistry. We will specifically examine the role of microglial IL-18 using a floxed IL-18 transgenic mouse line. Successful completion of these Aims will elucidate the role of inflammasome-generated cytokines in AD, and could result in novel translational approaches designed to specifically halt the inflammation that drives AD, as well ...