The aging factor EPS8 induces disease-related protein aggregation through RAC signaling hyperactivation.

Aging is a major risk factor for neurodegenerative diseases associated with protein aggregation, including Huntington's disease and amyotrophic lateral sclerosis (ALS). Although these diseases involve different aggregation-prone proteins, their common late onset suggests a link to converging changes resulting from aging. In this study, we found that age-associated hyperactivation of EPS8/RAC signaling in Caenorhabditis elegans promotes the pathological aggregation of Huntington's disease-related polyglutamine repeats and ALS-associated mutant FUS and TDP-43 variants. Conversely, knockdown of eps-8 or RAC orthologs prevents protein aggregation and subsequent deficits in neuronal function during aging. Similarly, inhibiting EPS8 signaling reduces protein aggregation and neurodegeneration in human cell models. We further identify the deubiquitinating enzyme USP4 as a regulator of EPS8 ubiquitination and degradation in both worms and human cells. Notably, reducing USP-4 upregulation during aging prevents EPS-8 accumulation, extends longevity and attenuates disease-related changes. Our findings suggest that targeting EPS8 and its regulatory mechanisms could provide therapeutic strategies for age-related diseases.