Intra-condensate demixing of TDP-43 inside stress granules generates pathological aggregates

Abstract

SUMMARYCytosolic aggregation of the nuclear protein TDP-43 is associated with many neurodegenerative diseases, but the triggers for TDP-43 aggregation are still debated. Here, we demonstrate that TDP-43 aggregation requires a double event. One is up-concentration in stress granules beyond a threshold, and the other is oxidative stress. These two events collectively induce intra-condensate demixing, giving rise to a dynamic TDP-43 enriched phase within stress granules, which subsequently transitions into pathological aggregates. Mechanistically, intra-condensate demixing is triggered by local unfolding of the RRM1 domain for intermolecular disulfide bond formation and by increased hydrophobic patch interactions in the C-terminal domain. By engineering TDP-43 variants resistant to intra-condensate demixing, we successfully eliminate pathological TDP-43 aggregates in cells. We conclude that up-concentration inside condensates and simultaneous exposure to environmental stress could be a general pathway for protein aggregation, with intra-condensate demixing constituting a key intermediate step.

A hydrophobic core stabilizes the residual structure in the RRM2 intermediate state of the ALS-linked protein TDP-43

“…First, partial unfolding of RRM2 impacts RNA binding, shifting the localization from nuclear to cytoplasmic (35)(36)(37). Second, increased concentration of TDP-43 in the cytoplasm may affect stress granule formation and the formation of insoluble aggregates (38). Finally, exposure of hydrophobic residues in the RRM2 intermediate may also affect interactions with chaperones such as with HSP70 (39), altering overall protein homeostasis (40).…”

Effects of charge asymmetry on the liquid–liquid phase separation of polyampholytes and their condensate properties

“…The coarse-grained models have demonstrated good agreement with experimental results in predicting the phase separation of disordered proteins as well as the macroscopic properties of condensed phases. [26][27][28] Each amino acid is represented by one coarse-grained bead in implicit solvent. The coarse-grained beads are connected by harmonic bonds.…”