MAPT and neurodegenerative disease: Therefore, our work reveals a role for the permeabilization of endosomal membranes in the induction of tau aggregation induced by exosomes, and underscores the importance of the integrity of endosomal membranes in the trans-cellular invasion by aggregated proteins that are resistant to lysosomal degradation, a mechanism that appears to be shared by multiple neurodegenerative diseases.