Project Summary/Abstract: Understanding the aggregation of the β-amyloid peptide (Aβ) to form toxic oligomers is fundamental to understanding the molecular basis of Alzheimer’s disease (AD). Despite decades of research, the structures of Aβ oligomers remain a mystery, constituting a significant gap in understanding AD. This proposal seeks to address this knowledge gap through the structural, biophysical, and biological profiling of a diverse group of Aβ oligomer models and correlation of these models with biogenic Aβ oligomers. My laboratory has developed an approach for create structurally defined Aβ oligomer models composed of peptide fragments from Aβ constrained into a β-hairpin. The X-ray crystallographic structures of these Aβ β- hairpin peptides reveal the structures of oligomers that the peptides can form and key intermolecular contacts that the peptides make in the oligomeric state. These contacts reveal sites that can be crosslinked to create covalently stabilized Aβ oligomer models that mimic the crystallographic oligomers. Studying the crosslinked oligomers then allows detailed correlation between oligomer structure and biophysical and biological properties. We will characterize how our Aβ oligomer models interact with and affect neurons, microglia, and astrocytes, to provide detailed insights into how our Aβ oligomer models impact different brain cell types and thus help shed light on the relationship between Aβ oligomer structure and cellular events that occur in AD. We will use fluorescence microscopy and fluorescence-assisted cell sorting (FACS) to visualize and quantify the interactions and uptake of our Aβ oligomer models with neurons, microglia, and astrocytes. We will evaluate downstream biochemical and cellular effects elicited by Aβ oligomer models in neurons, microglia, and astrocytes and evaluate how treatment affects apoptosis, necrosis, calcium homeostasis, endoplasmic reticulum stress, oxidative stress, neurite length, tau phosphorylation and aggregation, and proinflammatory responses in microglia and astrocytes. To elucidate the relationship between the structures of our Aβ oligomer models and biogenic Aβ oligomers, we will generate polyclonal antibodies against each Aβ oligomer model and then examine the immunoreactivity of these antibodies with brain protein extract and brain slices from 5XFAD mice. We will discover new Aβ oligomer models, by creating new Aβ β-hairpin peptides that contain more of the Aβ peptide sequence and alternate β-strand alignments. We will create new crosslinked Aβ oligomer models by identifying key contacts in existing and newly discovered Aβ oligomer models and then engineering in disulfide bonds to stabilize the oligomers. To characterize the structures and oligomerization properties of the new Aβ oligomer models that we generate, we will use X-ray crystallography and a variety of other biophysical experiments, including CD spectroscopy, SDS-PAGE, size exclusion chromatography (SEC), ana...