Solubility of the amyloidogenic core of tau in CSF.

Abstract

Do the extrinsic factors in cerebral spinal fluid (CSF) from patients suffering from Alzheimer's disease (AD) affect the solubility of tau differently than that of healthy individuals? A method utilizing 3H-labeled tau to quantify the monomer concentration after separation from amyloid fibrils at equilibrium has been established. This is a functional platform on which the effects of extrinsic factors on solubility can be investigated. This method can address questions like how the solubility of tau is affected by the components present in CSF and could elucidate important fundamental aspects of amyloid formation. Determining how much of something you can dissolve in solution can be straightforward: simply keep on adding more of your solute until it starts to precipitate. Proteins on the other hand can often be dissolved above their thermodynamic equilibrium and remain metastable for long periods of time. One way to overcome these energy barriers is to start with high concentration supersaturated solutions of monomers, allow the system enough time to nucleate, elongate and reach equilibrium. Then quantify the amount of monomer left in the solution after separation from the insoluble fibrils. This approach has been successfully adopted in the lab for the Aβ40 peptide. Full-length isoforms of tau are notoriously soluble and require negatively charged inducers to aggregate in vitro. We have overcome the need of inducers by using only the amyloidogenic core of tau, found in ex vivo tangles from patients suffering from AD with Cryo-EM. We have shown that this fragment, spanning amino acids 304-380C322S, aggregates reproducibly through a secondary nucleation dependent manner without the need of inducers. With this model of tau, we aim to investigate the effect of extrinsic factors on solubility.