Strain-specific clearance of seed-dependent tau aggregation by lithium-induced autophagy

Different conformational strains of tau have been implicated in the clinicopathological heterogeneity of tauopathies. In this study, we hypothesized that distinct strains are degraded in a different manner. Lithium, a drug for bipolar disorder, had previously been reported to reduce aggregation-prone protein content by promoting autophagy. Here, we assessed the effects of lithium on tau aggregates using different tauopathy brain seeds. SH-SY5Y cells were transfected with C-terminal tau fragment Tau-CTF24 (residues 243-441), and Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) brain seeds were introduced. After 48-h lithium treatment, sarkosyl-insoluble fractions were prepared. Lithium treatment was found to reduce the amount of insoluble tau and p62, and increase LC3-II levels along with the number of autophagic vacuoles in AD-seeded cells. The effects were lower in case of CBD seeds, and comparable between PSP and AD seeds. An inhibitor of myo-inositol monophosphatase (IMPase) also demonstrated similar effects. Overall, the study suggested that aggregated tau protein is degraded by lithium-induced autophagy, influencing IMPase in a strain-specific manner.