Extracellular vesicles and their role in TDP-43 proteinopathies

Introduction and objectives: Amyotrophic Lateral Sclerosis (ALS) and frontotemporal dementia (FTD) are two neurodegenerative diseases. 98% of ALS cases and the majority of Tau-negative FTD cases are characterized by the presence of abnormal cytoplasmic inclusions of TAR DNA binding protein 43 (TDP-43) in affected cells (Feneberg et al., 2018). In these aggregates, together with the full-length TDP-43 are often present two TDP-43 C-terminal fragments of 35 and 25KDa, resulting from the caspase 3-dependent cleavage of TDP-43 (Neumann et al., 2006). The main mechanism responsible for the clearance of these neurotoxic inclusions is the protein quality control (PQC) system (Cristofani et al., 2019). However, also the secretory pathway, composed by spherical extracellular vesicles (EVs), classified mainly in small (MVs) and large (EXOs) vesicles, on the basis of their biogenesis, size and surface markers, contributes to it (Iguchi et al., 2016). Our first objective is to evaluate if the TDPs species are preferentially secreted in MVs or in EXOs. Our second objective is to evaluate if exists a possible correlation between PQC and EVs. Results: We separated MVs and EXOs from neuronal cells using an ultracentrifugation method and analyzed them, for their size, number and morphology through the Nanoparticle Tracking Analysis and the transmission electron microscopy. Then, we evaluated EVs protein content through western blot analysis. Our results confirmed that all TDPs species are secreted in EVs; moreover, we demonstrated that insoluble TDPs species are secreted preferentially in MVs. In addition, we found that important PQC-components are secreted in EVs. Conclusions: The secretion of TDPs species through MVs and EXOs may have a protective role for the affected cells but it may also contribute to the prion-like distribution of toxic proteins. While, the presence of some members of the PQC in EVs, suggests a possible interplay between PQC and EVs. Research Area: Disorders of the nervous system GRANTS: Fondazione Cariplo, Italy (n. 2017_0747); PRIN_2017