Cross-seeding by prion protein inactivates TDP-43.

A common pathological denominator of various neurodegenerative diseases is the accumulation of protein aggregates. Neurotoxic effects are caused by a loss of the physiological activity of the aggregating protein and/or a gain of toxic function of the misfolded protein conformers. In transmissible spongiform encephalopathies or prion diseases, neurodegeneration is caused by aberrantly folded isoforms of the prion protein (PrP). However, it is poorly understood how pathogenic PrP conformers interfere with neuronal viability. Employing in vitro approaches, cell culture, animal models and patients' brain samples, we show that misfolded PrP can induce aggregation and inactivation of TAR DNA-binding protein-43 (TDP-43). Purified PrP aggregates interact with TDP-43 in vitro and in cells and induce the conversion of soluble TDP-43 into non-dynamic protein assemblies. Similarly, mislocalized PrP conformers in the cytosol bind to and sequester TDP-43 in cytosolic aggregates. As a consequence, TDP-43-dependent splicing activity in the nucleus is significantly decreased, leading to altered protein expression in cells with cytosolic PrP aggregates. Finally, we present evidence for cytosolic TDP-43 aggregates in neurons of transgenic flies expressing mammalian PrP and Creutzfeldt-Jakob disease patients. Our study identified a novel mechanism of how aberrant PrP conformers impair physiological pathways by cross-seeding.