TAR-DNA binding protein of 43 kDa (TDP-43) is the major component protein of ubiquitin-positive inclusions observed in brains of patients with frontotemporal lobar degeneration (FTLD-TDP) and amyotrophic lateral sclerosis (ALS). Here we report a seed-dependent TDP-43 aggregation model using detergent-insoluble TDP-43 prepared from diseased brains and the characterization of Prion-like properties of insoluble TDP-43.
When insoluble TDP-43 from ALS or FTLD-TDP brains was introduced into SH-SY5Y cells expressing TDP-43, round inclusions composed of phosphorylated and ubiquitinated TDP-43 were observed. Biochemical fractionation revealed the presence of Sarkosyl-insoluble TDP-43 detectable with anti-phospho TDP-43 antibody. We found that the heat treatment of insoluble TDP-43 impaired its ability to seed for aggregation, while it functioned as seeds even after the protease treatment with Proteinase K. Insoluble fraction from cells harboring TDP-43 aggregates also triggered intracellular TDP-43 aggregation. Furthermore, phosphorylated TDP-43 aggregates were shown to propagate from cell to cell via exosome. These results indicates that TDP-43 aggregates have surprising properties similar to those of pathogenic prion protein.
This unique seeding model reproduces characteristic features of affected neurons in brains with TDP-43 proteinopathy, and is expected to be useful for screening of drug candidates for treatment or prevention of these diseases.