Lysosomal escape and TMEM106B fibrillar core determine TDP-43 seeding outcomes.

Frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP) shows striking clinical and neuropathological heterogeneity, yet a systematic analysis of subtype-specific features and inter-patient variability was missing. We treated human neurons and neuron-like cells with 30 postmortem brain samples and quantified neoaggregate formation, loss of function and changes in the TDP-43 interactome to define determinants of seeding outcomes. Potent FTLD-TDP-A seeds drove a progressive collapse of physiological TDP-43 interactions accompanied by functional loss. Beyond the burden of pathological TDP-43, we identified the fibrillar core of the lysosomal protein TMEM106B as a critical pro-seeding factor. Transient lysosomal injury markedly enhanced neoaggregation and loss of function, likely by promoting fibril interactions with native TDP-43. Our work establishes a mechanistic link between TMEM106B and TDP-43 aggregation, identifies lysosomal escape as a key driver of pathology and introduces the strongest model yet for seeded TDP-43 aggregation and loss of function, to enable discovery of disease modifiers.