A Human Neuronal Cell Model of Endogenous TDP-43 A315T Reveals Altered Protein Dynamics and Disease-Relevant Cellular Dysfunction

TAR DNA-binding protein 43 (TDP-43) aggregation is the defining pathological hallmark of nearly all cases of amyotrophic lateral sclerosis (ALS), yet physiologically relevant human models that faithfully recapitulate disease-associated TDP-43 proteinopathy and dysfunction remain limited. To cover this gap, we generated a novel human-based model of cortical neurons carrying the endogenous ALS-linked TDP-43 A315T mutation together with an in-frame Dendra2 fluorescent reporter, enabling temporal and spatial monitoring of the protein. Neurons expressing TDP-43 A315T exhibited progressive neurite degeneration, altered neuronal activity, and impaired mitochondrial respiration, recapitulating several ALS-associated phenotypes. Our model also displays autophagy-dependent accumulation of cytoplasmic aggregates of mutant TDP-43 without overt loss of nuclear function, maintaining normal processing of canonical cryptic exon targets. In contrast, experimental induction of TDP-43 nuclear exclusion readily triggered cryptic exon incorporation, demonstrating that the model faithfully reproduces loss-of-function phenotypes under stress conditions. In line with perturbed protein solubility, mutant TDP-43 neurons show increased stress granule (SG) formation at baseline and under an oxidative stress condition. Finally, treatment with the RNA chaperone Clip34 significantly reduced TDP-43 aggregation under both basal and oxidative stress conditions as well as its localization to SGs. Taken together, these findings establish a physiologically relevant human model that separates early TDP-43 toxic gain-of-function from basal loss-of-function while providing a robust platform for investigating TDP-43 biology and accelerating therapeutic discovery in ALS.