Nucleolar stress caused by arginine-rich peptides triggers a ribosomopathy and accelerates ageing in mice
Nucleolar stress (NS) has been associated to several age-related diseases such as cancer or neurodegeneration. To investigate the mechanisms of toxicity triggered by NS, we here used (PR)n arginine-rich peptides that are found in patients of some neurodegenerative diseases. Although these peptides accumulate at nucleoli and generate NS, how this translates into cellular toxicity is poorly understood. We here reveal that whereas (PR)n expression leads to an overall decrease in protein abundance, this occurs concomitant with an accumulation of free ribosomal (r) proteins in the cytoplasm, a hallmark of ribosomopathies. Conversely, cells with acquired resistance to (PR)n peptides present global downregulation of r-proteins and low levels of mTOR signaling. In mice, systemic expression of (PR)97 drives widespread NS and accelerated ageing, which is associated to an increased expression of r-proteins and mTOR hyperactivation. Furthermore, the reduced lifespan of (PR)97-expressing mice was alleviated by the mTOR inhibitor rapamycin. Importantly, we show that the generalised accumulation of free r-proteins is a common outcome in response to chemical or genetic perturbations that trigger NS, such as Actinomycin D, TIF-IA depletion, or the expression of mutant HMGB1 variants recently associated to rare human diseases. Together, our study presents in vivo evidence supporting the role of NS as a driver of ageing, and provides a general framework to explain the toxicity caused by NS in mammalian cells.