In this project we will use in vitro strategies to examine our hypothesis that the progressive nature of AD results in the neuropathological changes characteristic of end-stage AD because some earlier, unknown effector initiates a series of neurodegenerative events (i.e., a cascade), that includes activation of microglia with synthesis and release of interleukin-1 (IL-1) at or above a threshold level necessary to: i) activate astrocytes with overexpression and release of S100beta, which stimulates growth of neurites and increases in intracellular calcium, ii) induce excessive synthesis and processing of beta-amyloid precursor protein (beta-APP), and thereby iii) directly or indirectly cause neurodegenerative changes, including dystrophic neurite outgrowth, extracellular beta-amyloid deposition, and increases in calcium-dependent neuronal cell functions that culminate in neuronal dysfunction and death. Potential consequences of IL-1-based actions in vivo, especially cell death and P-amyloid deposits, could propagate activation of microglia and, in so doing, induce chronic overexpression of IL-1 thus self- propagation of our proposed neurodegenerative cascade. Examination of the cellular and molecular events hypothesized in this neurodegenerative cascade are less accessible in human and animal studies than in vitro experiments. In our experiments, we will i) establish threshold levels necessary for induction of IL-1- and S100beta-based actions, ii) determine the importance of the absolute level vs the duration of exposure to IL-1 and S100beta, iii) evaluate potential interactions of IL-1 and S100beta on cellular and molecular events, and iv) assess the pluripotency of IL-1 as reflected in direct changes in neurons and astrocytes and indirect changes in either neurons, as a result of IL-1-induced activation of astrocytes and overexpression of S100beta, or in astrocytes as a result of IL-1-induced overexpression of beta-APP and other as-yet-unrecognized events or molecules in neurons. In addition to providing more direct study of our hypothesis of the involvement of a self-propagating cascade in the progression of neuropathological changes in AD, treatments to block the effects of IL-1 in vitro may lead to new therapeutic strategies.
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