Distinct glycosaminoglycan chain length and sulfation patterns required for cellular uptake of Tau, Aβ, and α-Synuclein
Transcellular propagation of aggregate \"seeds\" has been proposed to mediate progression of neurodegenerative diseases in tauopathies and -synucleinopathies. We have previously determined that tau and -synuclein aggregates bind heparan sulfate proteoglycans (HSPGs) on the cell surface. This mediates uptake and intracellular seeding. The specificity and mode of binding to HSPGs has been unknown. We used modified heparins to determine the size and sulfation requirements of glycosaminoglycan (GAGs) binding to aggregates in biochemical and cell uptake and seeding assays. Aggregates of tau require a precise GAG architecture with defined sulfate moieties in the N- and 6-O-positions, whereas -synuclein and A{beta} rely slightly more on overall charge on the GAGs. To determine the genetic requirements for aggregate uptake, we individually knocked out the major genes of the HSPG synthesis pathway using CRISPR/Cas9 in HEK293T cells. Knockout of EXT1, EXT2 and EXTL3, N-sulfotransferase (NDST1), and 6-O-sulfotransferase (HS6ST2) significantly reduced tau uptake. -Synuclein was not sensitive to HS6ST2 knockout. Good correlation between pharmacologic and genetic manipulation of GAG binding by tau and -synuclein indicates specificity that may help elucidate a path to mechanism-based inhibition of transcellular propagation of pathology.