Exploring the role of phase separation in <scp>TDP</scp> ‐43 pathogenesis with <scp>ArtiTDP43</scp>

TDP-43 is a nuclear RNA-binding protein implicated in neurodegenerative diseases such as ALS and FTLD, where it becomes mislocalized to the cytoplasm and forms pathological aggregates. These aggregates are thought to arise through liquid-liquid phase separation, a process by which proteins form dynamic, membrane-less condensates that can mature into solid structures. To better understand this process, the authors developed ArtiTDP43, a chemically controllable system that enables reversible formation of TDP-43 condensates in cells. Using this tool, they showed that TDP-43 forms different structures depending on its concentration: small liquid-like puncta, intermediate condensates associated with stress granules, and large solid aggregates resembling disease pathology. These transitions are reversible at early stages but become irreversible as aggregates solidify. The study by Combe et al. demonstrates that increasing cytoplasmic TDP-43 concentration drives a liquid-to-solid transition, while oxidative stress accelerates this process and promotes pathological features such as phosphorylation and p62 recruitment. Importantly, formation of cytoplasmic aggregates leads to depletion of nuclear TDP-43 and increased cell death, indicating toxicity. Overall, the findings establish a mechanistic link between phase separation, aggregation, and cytotoxicity in TDP-43 proteinopathies. ArtiTDP43 provides a powerful tool to study early disease mechanisms and explore therapeutic strategies aimed at preventing pathological aggregation or maintaining normal TDP-43 dynamics.