Gel‐like inclusions of C‐terminal fragments of TDP‐43 sequester stalled proteasomes in neurons

Henrick Riemenschneider , Qiang Guo , Jakob Bader , Frédéric Frottin (1) , Daniel Farny , Gernot Kleinberger , Christian Haass , Matthias Mann , F Ulrich Hartl , Wolfgang Baumeister , Mark S Hipp , Felix Meissner , Rubén Fernández‐busnadiego , Dieter Edbauer

1 I2BC - Institut de Biologie Intégrative de la Cellule

Aggregation of the multifunctional RNA-binding protein TDP-43 defines large subgroups of amyotrophic lateral sclerosis and frontotemporal dementia and correlates with neurodegeneration in both diseases. In disease, characteristic C-terminal fragments of ~25 kDa ("TDP-25") accumulate in cytoplasmic inclusions. Here, we analyze gain-of-function mechanisms of TDP-25 combining cryo-electron tomography, proteomics, and functional assays. In neurons, cytoplasmic TDP-25 inclusions are amorphous, and photobleaching experiments reveal gel-like biophysical properties that are less dynamic than nuclear TDP-43. Compared with full-length TDP-43, the TDP-25 interactome is depleted of low-complexity domain proteins. TDP-25 inclusions are enriched in 26S proteasomes adopting exclusively substrate-processing conformations, suggesting that inclusions sequester proteasomes, which are largely stalled and no longer undergo the cyclic conformational changes required for proteolytic activity. Reporter assays confirm that TDP-25 impairs proteostasis, and this inhibitory function is enhanced by ALScausing TDP-43 mutations. These findings support a pathophysiological relevance of proteasome dysfunction in ALS/FTD.

Mots clés: ALS; neurodegeneration; phase separation; proteasome; TDP-43

Domaines: Sciences du Vivant [q-bio]

Henrick Riemenschneider, Qiang Guo, Jakob Bader, Frédéric Frottin, Daniel Farny, et al.. Gel‐like inclusions of C‐terminal fragments of TDP‐43 sequester stalled proteasomes in neurons. EMBO Reports, 2022, 23, ⟨10.15252/embr.202153890⟩. ⟨hal-03851291⟩