Neurodegenerative Disease-Associated TDP-43 Fragments Are Extracellularly Secreted with CASA Complex Proteins

Abstract

Extracellular vesicles (EVs) play a central role in neurodegenerative diseases (NDs) since they may either spread the pathology or contribute to the intracellular protein quality control (PQC) system for the cellular clearance of NDs-associated proteins. Here, we investigated the crosstalk between large (LVs) and small (SVs) EVs and PQC in the disposal of TDP-43 and its FTLD and ALS-associated C-terminal fragments (TDP-35 and TDP-25). By taking advantage of neuronal cells (NSC-34 cells), we demonstrated that both EVs types, but particularly LVs, contained TDP-43, TDP-35 and TDP-25. When the PQC system was inhibited, as it occurs in NDs, we found that TDP-35 and TDP-25 secretion via EVs increased. In line with this observation, we specifically detected TDP-35 in EVs derived from plasma of FTLD patients. Moreover, we demonstrated that both neuronal and plasma-derived EVs transported components of the chaperone-assisted selective autophagy (CASA) complex (HSP70, BAG3 and HSPB8). Neuronal EVs also contained the autophagy-related MAP1LC3B-II protein. Notably, we found that, under PQC inhibition, HSPB8, BAG3 and MAP1LC3B-II secretion paralleled that of TDP-43 species. Taken together, our data highlight the role of EVs, particularly of LVs, in the disposal of disease-associated TDP-43 species, and suggest a possible new role for the CASA complex in NDs.

International Society for Extracellular Vesicles workshop. QuantitatEVs: Multiscale analyses, from bulk to single extracellular vesicle

“…Dr. D'Agostino showed that a DNA base‐excision repair protein, that is, APE1, modulates the secretion of EV‐RNA (Mangiapane et al., 2021), providing evidence that a functional base‐excision repair protein is delivered through exosomes in response to genotoxic stresses. Dr. Elena Casarotto used microRNA analysis to investigate whether and how the protein quality control system (PQC) can affect not only the secretion of proteins into large and small EVs (Casarotto et al., 2022), but also the EV microRNA content, especially in the context of neurodegenerative diseases, where the PQC is usually impaired.…”

The chaperone-assisted selective autophagy complex dynamics and dysfunctions

“…The CASA complex may utilize alternative pathways for substrates disposal, which are based on CASA complex secretion into the extracellular environment [ 135 ]. It has been postulated that CASA complex secretion into extracellular vesicles might represent an alternative attempt of cells to clear proteotoxic and aggregating substrates when the intracellular degradative pathways are impaired [ 136 ]. In support of this notion, the toxic fragments of TARDBP/TDP-43 (TAR DNA binding protein) associated with amyotrophic lateral sclerosis (ALS) have been detected in extracellular vesicles containing CASA complex members and their secretion increased upon combined UPS and autophagy blockage [ 136 ].…”

Attenuation of amyotrophic lateral sclerosis via stem cell and extracellular vesicle therapy: An updated review

“…TDP-43 has a prionlike structure at its C-terminal domain that enables it to propagate to cultured cells in an EV-mediated mechanism. 9,10,49 Further evidence of the role of EVs in TDP-43 propagation revealed the ability of extracellular exosomes with TDP-43 aggregates to transmit intercellularly and exhibit seeding properties. 50 EVs may also contribute to the propagation of nucleic acids and neuroinflammation.…”

“…Given that TDP‐43 aggregates are found in damaged cells of ALS patients, elucidating the mechanism of accumulation is paramount. TDP‐43 has a prion‐like structure at its C‐terminal domain that enables it to propagate to cultured cells in an EV‐mediated mechanism 9,10,49 . Further evidence of the role of EVs in TDP‐43 propagation revealed the ability of extracellular exosomes with TDP‐43 aggregates to transmit intercellularly and exhibit seeding properties 50 …”