Potential for Host Cytotoxicity from Microbially-derived Abeta Oligomers

Alzheimer’s disease (AD) is the most common form of dementia in the elderly afflicting over 20 million people worldwide. Two decades of findings from cell biology, genetic, neuropathological, biochemical and animal studies overwhelmingly point to the β-amyloid peptide (Aβ) as the key protein in the disease’s pathology (see review by Hardy and Selkoe, 20001). Aβ appears to be a soluble component of normal brain. However, in AD brain the peptide accumulates as β-amyloid, an insoluble semi-crystalline deposit that is the hallmark of the disease pathology. The most pathologically important forms of Aβ appear to be oligomers that are intermediates between insoluble β-amyloid and normal soluble monomeric species. Mounting evidence suggests that these soluble, low molecular weight oligomeric forms of Aβ are the critical cytotoxic species mediating neuronal death in AD. Of particular interest are soluble cross-linked β-amyloid protein species (CAPS) containing between 2 and 12 cross-linked Aβ subunits. CAPS, particularly dimeric2,3 forms, are highly neurotoxic. CAPS are also abundant in vivo with dimeric species alone comprising as much as 40% of the total Aβ pool in late stage AD brain. While the mechanism of Aβ cytotoxicity remains contentious, evidence is accumulating that membrane permiabilization plays a key role in the pathological activity of the peptide. In this study we propose to focus on role of Aβ oligomerization in the Aβ-mediated disruption of lipid bilayers.

The planned experiments will use many of the methods and techniques we have
developed in our previous CAF-funded project. Experiments will test our own CAPS
preparations as well as material from collaborators, including the “prion”-like Aβ oligomers generated in Dr Charles Glabe’s laboratory at the University of California-Irvine. Immunochemical, chromatographic and electron microscopic techniques will be used to characterize Aβ oligomers. Characterization experiments will include immuno studies using conformation-dependent antibodies developed by Dr. Glabe’s laboratory. Antimicrobial activities will be tested using published assays previously employed in our study that identified Aβ as an AMP.