TDP-43 Aggregation: The Healthy-Toxic Balance of the Prion-Like Domain.

TAR DNA-binding protein 43 (TDP-43) is a ubiquitously expressed RNA-binding protein that plays essential roles in RNA metabolism, including transcription, splicing, transport, and stability. Pathological TDP-43 aggregates have become a defining hallmark of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and a large subset of frontotemporal lobar degeneration (FTLD). In the last decade, increasing evidence has challenged the initial thought of TDP-43 condensates as a purely pathological event, highlighting instead the physiological relevance of reversible self-association, polymerization and liquid-liquid phase separation (LLPS) in regulating TDP-43 functions. In this review, we provide an integrated overview of the structural determinants governing TDP-43 two-faced polymerization, with a particular focus on the prion-like domain and its parallelism with prion proteins. Indeed, while physiological assemblies support normal RNA processing, the dysregulation of LLPS by either disease-associated mutations, altered RNA-binding, aberrant post-translational modifications, or proteolytic cleavage can promote the transition toward irreversible, pathogenic aggregates. Finally, we summarize strategies aimed at eliminating TDP-43 aggregates or modulating its phase-separation behavior. Altogether, this review frames TDP-43 polymerization in both healthy and pathological conditions, offering a prion-like centered view of TDP-43 proteinopathies.