Role of amyloid precursor protein and amyloid-beta in Alzheimer's disease: Modulation of APP processing detection of Abeta oligomers, and their role in the pathogenesis and treatment of AD.

摘要

Amyloid beta (Abeta) is an amyloidogenic peptide that forms senile plaques, a pathological hallmark found in the brains of Alzheimer's disease (AD). Abeta is generated from proteolytic cleavages of Amyloid Precursor Protein (APP) by beta- and gamma-secretase. Alternatively, APP can be cleaved within Abeta domain by alpha-secretase, precluding the formation of the neurotoxic protein. One of the enzymes that consist of alpha-secretase pool for APP, tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE), is also responsible for the secretion of TNF-alpha, a proinflammatory cytokine that is implicated in the pathogenesis of AD. The dual role of TACE as an APP and a TNF-alpha processing enzyme may confound the use of TACE inhibitors for AD in suppressing excessive TNF-alpha-mediated inflammatory reactions, should it result in an unwanted increase in the amyloidogenic cleavage of APP. The first half of this dissertation is driven by the hypothesis that a specific inhibitor of TACE can effectively block TACE activity without affecting Abeta production. In this study, we tested effects of a novel TACE inhibitor, BMS-561392, on Abeta production and APP processing in vitro and in vivo, and examined our theory that expression level of APP is not a rate-limiting factor in alpha- and beta-cleavage reactions. Abeta peptides can also aggregate into small oligomers, acutely synaptotoxic species responsible for synaptic malfunction in AD. Despite the important role Abeta oligomers may play in the disease, developing a sensitive and reliable assay that can quantify Abeta oligomers has remained elusive until recently. In the second study of this dissertation, we developed a highly specific oligomeric Abeta enzyme-linked immunosorbent assay (ELISA) with picomolar sensitivity. Because Abeta oligomers have the same sequence with its monomeric form, we relied on the previously characterized Nab61 antibody that recognizes a conformational epitopes of oligomeric Abeta structures. We utilized the novel assay to detect and quantify Abeta oligomers in brain extracts and cerebrospinal fluid (CSF) from AD patients and animal models. These studies have yielded novel insights into the dynamics between APP processing, inflammation, and Abeta oligomers in AD brains and lay the groundwork for developing effective and specific treatments against AD.