Sphingolipid imbalance aggravates fibrillar Tau-induced endomembrane rigidification and rupture

Abstract

Numerous studies have implicated endolysosomal dysfunction in Alzheimer's disease (AD) and related tauopathies. However, the mechanisms driving these disturbances remain poorly understood. Using C. elegans, we recently identified genes involved in sphingolipid metabolism as crucial for the maintenance of endolysosomal integrity. Abnormal sphingolipid metabolism is increasingly reported in AD, but its impact on Tau pathology remains unclear. Here, we investigated the role of sphingolipid metabolism in endolysosomal membrane homeostasis and its effect on Tau aggregation and toxicity in C. elegans and human cell culture models. Fluorescence recovery after photobleaching (FRAP) analysis and C-Laurdan dye imaging revealed that silencing of sphingolipid metabolism genes reduced the fluidity of endolysosomal vesicle membranes, and increased their susceptibility to rupture. The accumulation of aggregated Tau in endolysosomal vesicles further exacerbated endomembrane rigidification and damage. Moreover, enhanced membrane rigidity facilitated seeded Tau aggregation in a biosensor cell line. Restoring membrane fluidity by supplementation with the polyunsaturated omega-3 fatty acid alpha-linoleic acid suppressed endomembrane rupture and seeded Tau aggregation in cell models and neurotoxicity in C. elegans. This study provides mechanistic insights into how impaired sphingolipid homeostasis leads to endolysosomal membrane damage and how this might contribute to the progression of tau pathology.