Elucidation of Molecular Mechanisms of Lipid-Altered Cytotoxicity of TDP-43 Fibrils

Progressive aggregation of TAR DNA-binding protein 43 (TDP-43) is a hallmark of numerous neurodegenerative diseases, including amyotrophic lateral sclerosis, frontotemporal dementia, Alzheimer's disease, and limbic predominant age-related TDP-43 encephalopathy (LATE). This highly conserved nuclear RNA/DNA-binding protein is involved in the regulation of RNA processing. The C-terminal domain (CTD) of TDP-43 plays a key role in protein solubility, cellular localization, and protein-protein interactions. CTD is rich in glycine, glutamine, and asparagine, which facilitate TDP-43 aggregation into amyloid oligomers and fibrils observed in the brain. In this study, we examine the role of lipid bilayers in the aggregation properties of the CTD of TDP-43. We found that lipid bilayers composed of anionic phosphatidylserine and cardiolipin accelerated TDP-43 aggregation. Although lipids did not alter the secondary structure, they altered the cytotoxicity that TDP-43 fibrils exerted to rat dopaminergic cells. Using molecular methods, we showed that TDP-43 fibrils damage cell endosomes. This causes aggregate leakage into the cytosol, where TDP-43 fibrils impair cell autophagy, simultaneously triggering a severe unfolded protein response in the endoplasmic reticulum. Our results indicate that TDP-43 aggregation may be linked to pathological changes in the lipid profiles of neurons.