Co-localization of tau and TDP-43 after extracellular vesicle delivery to cells

Perturbations in the metabolism of microtubule-associated protein tau (tau) underlie the pathology of a broad array of dementias, including chronic traumatic encephalopathy, amyotrophic lateral sclerosis (ALS) with cognitive impairment (ALSci) and approximately half of the dementias associated with frontotemporal lobar degeneration. We recently observed significantly increased hippocampal tau pathology in rats injected with pseudophosphorylated human tau (2N4R tau^T175D) co-expressing an ALS-associated TAR DNA-binding protein 43 (TDP-43) mutant (TDP-43^M337V) when compared to wild-type rats. To understand this mechanism, we examined whether the extracellular vesicles (EVs) derived from wild-type TDP-43 (wtTDP-43) or tau-expressing cells could transfer expression of these proteins to recipient cells, and whether co-localization of these proteins occurs. mCherry-wtTDP-43 or EGFP-tau constructs were expressed in HEK293 or SH-SY5Y cells. The secretome and EV fractions contained wtTDP-43 or 2N4R tau protein and RNA, and could transfer proteins into nontransfected cells. Co-localization was also detected in the cytosol of recipient cells. In silico modeling of tau and TDP-43 interactions suggests hydrogen bonding underlies this interaction. These studies further our understanding of the interaction between tau and TDP-43 by demonstrating their ability to co-aggregate and in providing a mechanism by which cell-cell transfer of either protein via extracellular vesicles can lead to these synergistic interactions.