The role of extracellular vesicles in the removal of aggregated TDP-43 responsible for ALS/FTD diseases

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are two related neurodegenerative diseases, with a continuous clinical spectrum. A common feature between the two diseases is the abnormal cytoplasmic localization and the aggregation of the TAR DNA binding protein 43 (TDP-43), in affected cells (i.e both upper and lower motoneurons for ALS and neurons of the frontal and temporal lobes, for FTD). Pathological TDP-43 aggregates are mainly composed by its C-terminal fragments of 35 kDa (TDP-35) and 25 kDa (TDP-25), as a result of caspase 3-dependent cleavage. These species are highly aggregation-prone and are thought to be neurotoxic. Thus, the removal of TDP-35 or TDP-25 fragments is protective for cells. The clearance of aberrantly folded or misfolded proteins is mediated by the intracellular protein quality control (PQC) system, composed by chaperone/co-chaperone proteins, the ubiquitin proteasome system and the autophagy. Recent data underlined that also the extracellular secretory pathway, mainly represented by exosomes (EXOs) and microvesicles (MVs), might be involved in misfolded proteins clearance from affected cells. We investigated the role of both EXOs and MVs in the secretion of TDP-43 and its C-terminal fragments, in the motoneuronal NSC34 cell model. Using an ultracentrifugation approach, we separated larger (MVs) from smaller (EXOs) vesicles. The vesicles were analysed by i) the NanoSight, Nanoparticle Tracking Analysis, to establish the size and the count, ii) western blot analysis, to characterize the protein content. Our preliminary results show that all TDP-43 species are secreted in EVs, mainly in MVs. Very interestingly, we found that some PQC-components, involved in TDP-43s clearance, are present in EVs, suggesting an interplay between PQC and EVs. GRANTS: Fondazione Cariplo, Italy (n. 2017_0747); Università degli Studi di Milano e piano di sviluppo UNIMI - linea B.