(138a) Engineering Approaches to Understanding the Role of Tau in Neurodegeneration

Tauopathies comprise a major class of neurodegenerative diseases that are characterized by intracellular accumulations of the microtubule-associated protein tau with the most common tauopathy being Alzheimer’s disease. Currently, 5.7 million people in America are suffering from Alzheimer’s disease, and that number is expected to increase to 14 million over the next 20 years. Despite intense research and the best efforts in the scientific community, our fundamental understanding of disease progression is lacking. The brains of AD patients typically show a distribution of extracellular amyloid plaques, composed of Ab and neurofibrillary tangles, composed of postranslationally-modified and abnormally aggregated tau protein.

The mechanism underlying the initial conversion and spread of pathological tau aggregates remains unknown. Recent work suggests that tau species can be released into the extracellular space and be subsequently endocytosed via negatively-charged heparan sulfate proteoglycans (HSPGs) available on the cell surface. Based on previous reports, we hypothesized that hyperphosphorylated tau monomer would be endocytosed at a faster rate compared to non-phosphorylated monomer. To test this, we expressed monomeric tau in both states recombinantly and purified for testing in cell culture. Surprisingly, phosphorylated tau was endocytosed at the same rate as compared to non-phosphorylated protein across all cell lines tested. Using live-cell confocal microscopy and flow cytometry, we show here that soluble 0N4R monomer can be rapidly endocytosed by multiple cell types and that this uptake is independent of phosphorylation state. Furthermore, we demonstrate that heparan sulfate proteoglycans (HSPGs) enhance, but are not necessary, for cellular endocytosis of both phosphorylated and non-phosphorylated tau.