Dysregulation of the Progranulin-driven Autophagy-lysosomal Pathway Mediates Secretion of the Nuclear Protein TDP-43

by Selleckchem | Dec 27 2023

The cytoplasmic accumulation of the nuclear protein TDP-43 has been linked to the progression of amyotrophic lateral sclerosis and frontotemporal lobar degeneration (FTLD). TDP-43 secreted into the extracellular space has been suggested to contribute to the cell-to-cell spread of the cytoplasmic accumulation of TDP-43 throughout the brain; however, the underlying mechanisms remain unknown. We herein demonstrated that the secretion of TDP-43 was stimulated by the inhibition of the autophagy-lysosomal pathway driven by progranulin (PGRN), a causal protein of FTLD. Among modulators of autophagy, only vacuolar-ATPase inhibitors, such as bafilomycin A1 (Baf), increased the levels of the full-length and cleaved forms of TDP-43 and the autophagosome marker LC3-II in extracellular vesicle fractions prepared from the culture media of HeLa, SH-SY5Y or NSC-34 cells, whereas vacuolin-1, MG132, chloroquine, rapamycin, and serum starvation did not. The C-terminal fragment of TDP-43 was required for Baf-induced TDP-43 secretion. The Baf treatment induced the translocation of the aggregate-prone GFP-tagged C-terminal fragment of TDP-43 and mCherry-tagged LC3 to the plasma membrane. The Baf-induced secretion of TDP-43 was attenuated in autophagy-deficient ATG16L1 knockout HeLa cells. The knockdown of PGRN induced the secretion of cleaved TDP-43 in an autophagy-dependent manner in HeLa cells. The knockout of PGRN in MEFs increased the secretion of the cleaved forms of TDP-43 and LC3-II. The treatment inducing TDP-43 secretion increased the nuclear translocation of GFP-tagged TFEB, a master regulator of the autophagy-lysosomal pathway in SH-SY5Y cells. These results suggest that the secretion of TDP-43 is promoted by dysregulation of the PGRN-driven autophagy-lysosomal pathway.

Comments:

This text discusses a study on the mechanisms behind the spread of TDP-43, a protein associated with conditions like amyotrophic lateral sclerosis and frontotemporal lobar degeneration, within the brain. It suggests that the inhibition of the autophagy-lysosomal pathway, which is regulated by progranulin (PGRN), leads to the secretion of TDP-43 into the extracellular space. This secretion seems to involve vacuolar-ATPase inhibitors like bafilomycin A1 (Baf) rather than other autophagy modulators.

The study observed that Baf treatment increased the levels of both full-length and cleaved forms of TDP-43 and the autophagosome marker LC3-II in extracellular vesicle fractions in various cell types. Specifically, the C-terminal fragment of TDP-43 was found to be crucial for this secretion induced by Baf. Additionally, the study showed that Baf treatment led to the translocation of the aggregate-prone C-terminal fragment of TDP-43 and LC3 to the plasma membrane.

Autophagy-deficient cells showed a decrease in Baf-induced TDP-43 secretion, indicating the role of autophagy in this process. Knockdown of PGRN induced TDP-43 secretion in an autophagy-dependent manner. Moreover, the knockout of PGRN increased the secretion of cleaved forms of TDP-43 and LC3-II. The study also found that treatments inducing TDP-43 secretion increased the nuclear translocation of TFEB, a master regulator of the autophagy-lysosomal pathway.

Overall, the findings suggest a link between dysregulation of the PGRN-driven autophagy-lysosomal pathway and the promotion of TDP-43 secretion, potentially contributing to the spread of TDP-43 associated with neurodegenerative diseases.