| With more than 20 million cases worldwide, Alzheimer's disease (AD) is now the most common neurodegenerative disease. The two defining features of this disease are extracellular plaques and intracellular neurofibrillary tangles. The plaques are composed primarily of amyloid-beta (Abeta), an aberrant cleavage product of amyloid precursor protein (APP). The neurofibrillary tangles (NFTs) are composed of hyperphosphorylated, aggregated tau protein.;Genetic studies have shown that Abeta and tau are intimately linked in the neuronal cell death pathway leading to neurodegenerative diseases like Alzheimer's. It has been shown that tau action lies downstream of Abeta and is required for Abeta-mediated cell death; however, the mechanistic link and the actual cause of cell death are not well understood. In this dissertation, I hypothesized that Abeta oligomers induce specific 'pathological' changes in tau degradation and phosphorylation that play key roles in mediating cell death.;I have used embryonic rat hippocampal neuronal culture treated with oligomeric Abeta peptide as a model system. Key observations are that Abeta treatment resulted in tau cleavage/degradation within 10 minutes, and by 4 hours, about 80% of the tau was degraded. After 8 hours of Abeta-treatment, there was no full-length tau remaining. As visualized on 2D western blots, Abeta induced an acidic shift (in a subset of the tau) that is consistent with phosphorylation.;The addition of phosphorylation causes a decrease in pH, which is not resolved in one dimension; therefore, to obtain better resolution for our study, I used both one and two-dimensional (2D) gels to characterize Abeta-induced acidic shifts using total tau and site-specific, phosphorylation-specific tau antibodies.;Using tau antibodies specific for phosphorylation at sites T217, T231, S235, and S413, I detected high molecular weight species that are present in normal, untreated neurons, and these high molecular weight tau species are not resistant to Abeta-induced degradation. Overall, there were no pronounced Abeta-induced effects on tau phosphorylation at the sites studied.;The current paradigm views Abeta-mediated tau phosphorylation at specific sites as a key element in tau-mediated cell death. Taken together, my data suggests that some aspects of this paradigm require revisiting. |
