Project DetailsA hallmark of Alzheimer's disease (AD) is the presence of deposits called amyloid plaques in the brain. These plaques are mostly composed of a peptide called amyloid-beta. Recent research indicates that soluble clusters of Abeta, called oligomers, are perhaps the primary cause of AD. We are trying to determine the chemical structure of these oligomers and, in particular, whether the structure contains a feature called a cross-link. This is a challenging goal, as the amount of these oligomers in the brain is too low for conventional chemical analyses. To our knowledge, no other researchers have tried to address this question in a technically rigorous manner. Our project could have significant therapeutic benefits. Diagnostic tests could be designed to specifically quantify cross-linked oligomers in cerebrospinal fluid and correlate their levels with cognitive deficits in elderly individuals. Other tests of the neurotoxicity of these oligomers could be conducted by chemical synthesis of their precise structures and evaluation their toxicity in cellular and intact animal assays. Such synthetic peptides could even be investigated as possible vaccines. However, before we can determine whether cross-linked oligomers are enriched in individuals with AD, we must first develop the analytical techniques required for sensitive oligomer detection. This developmental effort is best directed at synthetic Abeta oligomers that are prepared and chemically cross-linked in our laboratory. Our grant proposal has three aims. In Aim 1 we will prepare stable oligomers of Abeta by chemical cross-linking in vitro and isolate individual oligomers. In Aim 2 we will evaluate and then establish procedures to detect covalently cross-linked Abeta oligomers and identify sites of cross-linking by two mass spectrometry techniques. In Aim 3 we will apply our optimized techniques to determine the structure and amounts of Abeta oligomers that can be isolated from AD brain tissue.