Ganglioside sialylation modulates tau internalization and pathology spread

Gangliosides serve as receptors for proteins, bacteria, and viruses, with sialylation at the termini of their glycan chains playing a crucial role in ligand recognition and endocytosis. The internalization of proteopathic tau aggregates by neurons is integral to the propagation of tau pathology in Alzheimer's disease (AD). However, the influence of gangliosides and their sialylation modifications on the uptake of proteopathic tau aggregates and the subsequent impact on AD pathology remains unclear. This study investigates the roles of the four mammalian sialidases (Neu1-Neu4) in modulating tau aggregation in cellular models. Our findings demonstrate that Neu3 significantly inhibits tau aggregation induced by proteopathic tau derived from the brains of AD patients (AD P-tau). Overexpressing Neu3 or administering ganglioside GM1, which results from Neu3-catalyzed removal of one sialic acid from GD1a, in the mouse model decreases the GD1a/GM1 ratio in mouse brain, effectively blocks the spread of tau pathology and improves recognition in AD P-tau-injected mice. Both Neu3 and GM1 reduce the internalization of tau aggregates, while GD1a enhances tau uptake, showing a positive correlation with the level of internalized tau. Moreover, the internalization of tau mediated by GD1a dependent on low-density lipoprotein receptor-related protein 1 (LRP1) and compensates for heparin-inhibited tau uptake. In vitro assays demonstrate that GD1a exhibits a higher binding avidity for tau filaments than GM1. These findings indicate that GD1a may directly bind to tau aggregates via the sialic acid moiety, facilitating LRP1-mediated tau uptake. This study proposes a novel mechanism for tau internalization and posits that reducing ganglioside sialylation may be a promising strategy for hindering the spread of tau pathology in AD.