TDP-43 loss of cellular function through aggregation requires additional structural determinants beyond its C-terminal Q/N prion-like domain

TDP-43 aggregates are the neurohistological landmark of diseases like amyotrophic lateral sclerosis and frontotemporal dementia. Their role in the pathogenesis of these conditions is not yet clear mainly due to the lack of proper models of aggregation that may allow the study of the mechanism of formation, their interactions with other cellular components and their effect on the cell metabolism. In this work, we have used tandem repeats of the prion like Q/N-rich region of TAR DNA-binding protein (TDP-43) fused to additional TDP-43 protein sequences to trigger aggregate formation in neuronal and non-neuronal cell lines. At the functional level, these aggregates are able to sequester endogenous TDP-43 depleting its nuclear levels and inducing loss of function at the pre-mRNA splicing level. No apparent direct cellular toxicity of the aggregates seems to be present beyond the lack of functional TDP-43. To our knowledge, this is the only system that achieves full functional TDP 43 depletion with effects similar to RNAi depletion or gene deletion. As a result, this model will prove useful to investigate the loss-of-function effects mediated by TDP-43 aggregation within cells without affecting the expression of the endogenous gene. We have identified the N-terminus sequence of TDP-43 as the domain that enhances its interaction with the aggregates and its insolubilization. These data show for the first time that cellular TDP-43 aggregation can lead to total loss of function and to defective splicing of TDP-43-dependent splicing events in endogenous genes.