Targeted autophagic clearance of Tau protects against Alzheimer's disease through amelioration of Tau-mediated lysosomal stress.

Background

Lysosomal dysfunction could be an underlying cause of Alzheimer's disease, with Tau oligomer being an important inducer or amplifier of lysosomal stress associated with the disease. Tau oligomer is a well-known substrate of autophagy, and selective degradation of Tau with Tau-specific autophagy degrader might be feasible.

Methods

Tau-specific autophagic degraders were synthesized by combining leucomethylene blue, linkers and a lysosomal degradation tag (Autac). Tau clearance and changes of Tau-mediated lysosomal stress by these degraders were studied in vitro. In vivo effects of a Tau-specific degrader were investigated employing a combined Tau/Aβ mutant mouse model characterized by an accelerated onset of neurological deficits. Human relevance was investigated using induced pluripotent stem cell (iPSC)-derived neuronal cells from an Alzheimer's disease patient.

Results

Among Tau-specific Autac degraders, TauAutac-3 (TA-3) efficiently degraded Tau oligomer and monomer, an effect inhibited by bafilomycin A1, suggesting lysosomal Tau degradation. TA-3 treatment induced LC3, K63, OPTN or NDP52 puncta, which was partially colocalized with Tau oligomer. Signs of lysosomal stress, such as galectin-3 puncta, pHluorin fluorescence, altered lysosomal pH and CHMP2B recruitment, induced by Tau expression were reversed by TA-3. Autophagy impairment by Tau expression in vitro, likely due to lysosomal stress, was also reversed by TA-3. In vivo, TA-3 administration markedly reduced the accumulation of both Tau and Aβ in 6xTg mice, which was associated with amelioration of Tau-mediated lysosomal stress and autophagy impairment. Neuroinflammation characterized by increased numbers of GFAP+ glial cells and Iba1+ microglial cells, was also reduced following TA-3 administration. TA-3 remarkably improved neurologic deficits in 6xTg mice, such as impaired memory and reduced exploratory behavior. TA-3 reduced Tau and phospho-Tau accumulation in iPSC-derived neuronal cells from an Alzheimer's disease patient.

Conclusion

These results suggest that Tau-specific autophagic (Autac) degraders could serve as novel therapeutic agents for Alzheimer's disease through reduction of Tau-mediated lysosomal stress.