When tau stalls the lysosome: decoupling trafficking and degradation in autophagy

Tauopathies are characterized by the accumulation of misfolded tau and lysosomal dysfunction, yet whether defects in the autophagy-lysosome pathway are causal or secondary remains unclear. Recent work using human iPSC-derived neurons harboring the MAPT p.R406W mutation demonstrates that pathogenic tau is sufficient to disrupt lysosomal function upstream of tau accumulation. Tau species are differentially processed within lysosomes, with phosphorylated tau retained at the lysosomal membrane, consistent with a barrier to efficient cargo processing. Importantly, pharmacologic activation of autophagy restores degradative capacity and reduces tau burden without rescuing lysosomal motility, suggesting that trafficking and degradation represent separable axes of lysosomal biology. These findings position tau as an active disruptor of proteostasis and define a degradative bottleneck that shares features with lysosomal storage disorders. Together, this work reframes autophagy dysfunction in tauopathy as a modular defect with distinct therapeutic entry points.