Investigating the binding of high molecular weight tau to LRP1

Abstract Background The spread of neurofibrillary tangle (NFT) pathology across the brain is a hallmark of Alzheimer’s disease (AD) and is thought to be driven by the cell‐to‐cell transport of seed competent tau protein. LRP1 is a receptor for tau that mediates tau uptake, degradation, and seeding of intracellular tau aggregation. We previously found that LRP1 binds recombinantly produced 2N4R tau with high affinity, and that phosphorylation on tau reduces its affinity for LRP1. However, it is unknown if LRP1 interacts with the soluble HMW forms of tau that drive tau seeding, and here we investigate LRP1 binding to HMW phospho‐mimetic tau or HMW tau isolated from AD patient brains. Method We recombinantly produced tau containing mutations to mimic phosphorylation patterns of high‐molecular weight (D20Q3) or low molecular weight (D8Q2) tau found in AD brains. Next, we measured their ability to bind purified LRP1 binding via surface plasmon resonance (SPR) and determined the ability of LRP1 expressed in cells to mediate 125 I‐labeled tau internalization. We also investigate the binding of HMW pathogenic forms of tau as well as LMW forms of tau isolated by size exclusion chromatography from AD patient brain extracts to LRP1 using a novel SPR capture assay. Result We found that D20Q3 and D8Q2 tau bind LRP1 much weaker (Kd = 1249nM & Kd = 388nM, respectively) than unmodified 2N4R tau (Kd = 20nM). 125 I‐labeled tau uptake assays indicate reduced uptake for both D20Q3 and D8Q2 tau compared to 2N4R tau. Finally, preliminary results demonstrate that LRP1 is able to bind pathogenic forms of HMW tau isolated from AD patient brains, although there appears to be variability from different patients and LRP1 may bind HMW tau weaker than LMW tau. Studies are underway to determine the affinity of these forms for LRP1. Conclusion Our results demonstrate that LRP1 binds pathogenic forms of tau, with significant variation seen between patients. Future studies will investigate if the affinity of these forms correlate with their ability to promote tau seeding.