This challenge targets the hypothesis: **Inhibiting Heparan Sulfate Proteoglycan Receptor-Mediated Neuronal Tau Uptake** **Hypothesis Summary:** **Molecular Mechanism and Rationale** The pathological spread of tau protein aggregates represents a central mechanism underlying the progression of Alzheimer's disease and related tauopathies. Recent advances have elucidated the critical role of heparan sulfate proteoglycans (HSPGs) in facilitating the uptake of extracellular tau species by neurons, establishing these cell surface receptors as compelling therapeutic targets. The molecular mechanism centers on the interaction between pathologic **Falsifiable Predictions:** 1. Pharmacological modulation of SULF1/SULF2 will alter neuroscience markers in validated models by ≥20% 2. Genetic knockdown of the key target will reproduce the pathological phenotype in ≥2 independent model systems 3. Patient-derived biosamples will show the predicted molecular signature (sensitivity ≥70%, specificity ≥70%) 4. Mechanistic intervention at the proposed node will rescue neuronal viability in vitro by ≥30% **Bounty Tier:** $127,220 USD (composite score 0.772) **Challenge Type:** Open — any team may submit experimental evidence supporting or refuting this hypothesis **Success Criteria:** Peer-reviewed evidence demonstrating mechanistic validation of ≥2 of the 4 predictions, with independent replication.