The Role of APP-metabolites on Extracellular Vesicle Cargo and Function

Alzheimer’s Disease (AD) is the most common form of dementia in the elderly. AD brains are characterized by senile plaques composed of amyloid beta (Aβ) and intracellular tangles composed of tau. Mutations in the Amyloid Precursor Protein (APP), the protein from which Aβ is derived, cause AD, but the precise function of APP in the brain is unclear. APP undergoes complex metabolism, and its metabolites are secreted by cells in extracellular vesicles (EVs). To study the function of APP-containing EVs, we isolated App- EVs from rat primary neuronal conditioned media and proteomic analysis identified the Valosin-containing protein (Vcp) as molecular cargo. Vcp is a segregase/molecular unfoldase, a known tau-interacting protein, and a protein mutated in AD related dementias (ADRDs). In this application, we hypothesize that AD and ADRD causing mutations alter the abundance and composition of App-EVs and that this affects the target and function of App-EVs. To test this, we have proposed three aims. The first aim will investigate the molecular mechanism of App-related cargo loading into EVs. The second aim will test the effect that App-EV biogenesis has on a rat model of tau pathology, as tau is a substrate for Vcp. The third aim will test the effect of App-EVs on Vcp mutation-induced pathology. The proposed aims will leverage the Tambini lab’s significant expertise in the generation, validation and use of AD rat knock-in models and the optimization of techniques for pure App- EV isolation to address fundamental questions about the function of APP.