A synthetic heparinoid blocks Tau aggregate cell uptake and amplification

Tau aggregation underlies neurodegeneration in Alzheimer's disease and related tauopathies. We and others have proposed that transcellular propagation of pathology is mediated by Tau prions, which are ordered protein assemblies that faithfully replicate in vivo and cause specific biological effects. The prion model predicts the release of aggregates from a first-order cell and subsequent uptake into a second-order cell. The assemblies then serve as templates for their own replication, a process termed "seeding." We have previously observed that heparan sulfate proteoglycans on the cell surface mediate the cellular uptake of Tau aggregates. This interaction is blocked by heparin, a sulfated glycosaminoglycan. Indeed, heparin-like molecules, or heparinoids, have previously been proposed as a treatment for PrP prion disorders. However, heparin is not ideal for managing chronic neurodegeneration, because it is difficult to synthesize in defined sizes, may have poor brain penetration because of its negative charge, and is a powerful anticoagulant. Therefore, we sought to generate an oligosaccharide that would bind Tau and block its cellular uptake and seeding, without exhibiting anticoagulation activity. We created a compound, SN7-13, from pentasaccharide units and tested it in a range of assays that measured direct binding of Tau to glycosaminoglycans and inhibition of Tau uptake and seeding in cells. SN7-13 does not inhibit coagulation, binds Tau with low nanomolar affinity, and inhibits cellular Tau aggregate propagation similarly to standard porcine heparin. This synthetic heparinoid could facilitate the development of agents to treat tauopathy.