The roles of inflammasome-dependent cytokines on neuronal excitability in Alzheimer's disease

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Alzheimer’s disease (AD) is a devastating neurodegenerative disorder leading to profound cognitive decline. Coupled with the well-described behavioral manifestations, epileptic seizures are frequently observed in AD patients. Importantly, AD patients have a 2- to 6-fold increased risk of developing the seizures compared with age-matched controls. Furthermore, a longitudinal study suggests that ~ 2/3s of AD patients will develop seizures during the course of their illness and that seizures adversely effect disease progression. Recent evidence suggests an association of inflammation and epilepsy, although it remains unclear to what degree inflammation causes seizure susceptibility in AD. This research proposal focuses on this critical question. We previously discovered that β 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 into each of three unique NLRP3 inflammasome knockouts (KOs) and observed that these mice were completely protected from numerous AD features including learning/memory deficits. NLRP3 inflammasomes regulate the expression of IL-1β and IL18, which are highly pro-inflammatory cytokines. The elevated expression of IL-1β in AD and in vitro cultured cell studies suggest that microglial-derived IL-1β causes detrimental over-excitation in neurons, leading to seizures and neuronal cell death. However, our knowledge of the association of IL18 with AD is far more limited. We have generated IL-18KO/APP/PS1 mice and discovered that these mice developed a lethal seizure disorder, which was completely reversed by levetiracetam therapy. This is highly relevant to the AD patients having increased incidence of seizures. In Aim 1, we will first perform electrophysiological recordings to determine the degree to which synaptic function is altered in IL18KO/APP/PS1 mice. Next, we will determine whether levetiracetam rescues abnormal IL-18KO/APP/PS1 phenotypes at the level of synapses. Lastly, we will determine the cell-types that express IL-1β and IL18 and their cognate receptors in the AD brain. This Aim will determine, i) how the lack of IL18 causes seizures in the IL18KO/APP/PS1 mice and ii) the cell types that activate interleukin signaling during AD progression. In Aim2, we will perform immunoblotting, immunohistochemical, electrophysiological and behavioral tests to address the roles of IL-1β in AD-associated epileptogenesis by knocking out IL-1β in AD mouse models. This Aim will elucidate how IL-1β contributes to AD-related seizures in the AD models. Successful completion of the proposed studies will identify novel targets for the development of drugs to ameliorate or prevent the effects of seizure disorders in human AD.