Neuroinflammation in Cholesterol-Induced AD Pathogenesis

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Alzheimer's disease (AD), a progressive neurodegenerative condition, is the most prevalent form of dementia in the elderly. The pathology is characterized by an accumulation of amyloid beta (Ap), the product of amyloid precursor protein (APR). The amyloid cascade hypothesis proposes that Ap oligomers cause neuronal injury both directly and indirectly via an activation of microglia and their production of neurotoxic molecules. Recent findings (genetic, experimental, and epidemiological) suggest a link between abnormal cholesterol metabolism and the pathogenesis of AD. The project tests the hypothesis that failure of cholesterol homeostasis facilitates an exacerbated neuroinflammatory response in association with increased Ap generation that, in turn, leads to neurodegeneration characteristic of AD. The studies willuse: high fat/cholesterol diet fed hypercholesterolemic, low density lipoprotein receptor knockout (LDLR-/-) mice, a mouse strain expressing the wild type human APR (akin to sporadic AD), as well as the cross between the two. The specific objectives of the project are as follows: * Determine neuroinflammatory changes in brain regions of high cholesterol-fed LDLR-/-, wtAPP and wtAPP/LDLR-/- mice by immunohistochemical detection of activated microglia and cerebrovascular cells in relation to amyloid levels and synaptotoxicity (i.e., loss of synaptophysin-immunoreactivity). Inflammatory mediators (i.e., cytokines, pro-oxidant enzymes), Ap peptides, and proteins involved in cholesterol homeostasis (i.e., ApoE, ABCA1) will be quantified by biochemical and immunochemical techniques. 4 Determine the nature and role of pro- and anti-inflammatory stimuli relevant to impaired brain chol- esterol metabolism using cell culture models. Cultures of glia and glial-neuronal co-cultures will be used to investigate the effects of oxidized lipoproteins and ApoE isoforms (in the presence or absence of Ap) on glial inflammatory response (i.e., production of mediators) and on neuronal APR processing. Also, the anti- inflammatory and anti-amyloidogenic effects of oxysterol ligands of a nuclear receptor, i.e., Liver X Receptor (LXR) will be examined and the mechanisms explored. *Test the therapeutic potential of a synthetic LXR ligand (T0901317) with both cholesterol lowering and anti-inflammatory properties, and minocycline, a tetracycline derivative known to suppress microglial activa- tion, by examining neuropathological (i.e., Ap peptide levels and synaptotoxicity) and behavioral changes (8- arm water maze performance) in parallel to attenuated neuroinflammation in hypercholesterolemic mice. The outcome of these studies should have implications for developing novel and effective anti- inflammatory treatments for AD.