More stressed out with age? Check your RNA granule aggregation

Low complexity (LC) prion-like domains are over-represented among RNA-binding proteins (RBPs) and contribute to the dynamic nature of RNA granules. Importantly, several neurodegenerative diseases are characterized by cytoplasmic "solid" aggregates formed by mainly nuclear RBPs harboring LC prion-like domains. Although RBP aggregation in disease has been extensively characterized, it remains unknown how the process of aging disturbs RBP dynamics. Our recent study revealed that RNA granule components including 2 key stress granule RBPs with LC prion-like domains, PAB-1 and TIAR-2, aggregate in aged Caenorhabditis elegans in the absence of disease. Here we present new evidence showing that sustained stress granule formation triggers RBP aggregation. In addition, we demonstrate that mild chronic stress during aging promotes mislocalization of nuclear RBPs. We discuss the consequences of aberrant interactions between age-related RBP aggregation and disease-associated RBP aggregation. In particular, we show that FUST-1 and PAB-1 co-localize in aberrant cytoplasmic accumulations. Significantly, long-lived animals with reduced insulin/IGF-1 signaling abrogate stress granule RBP aggregation through activation of the transcription factors HSF-1 and DAF-16. We evaluate the different mechanisms that could maintain dynamic stress granules. Together these findings highlight how changes with age could contribute to pathogenesis in neurodegenerative diseases and disruption of RNA homeostasis.