271 Ribosome heterogeneity by rRNA methylation in skin cell senescence

The accumulation of senescent cells is associated with several age-related pathologies and represents a primary driver of skin aging. Senescence cells cause tissue damage by secreting a mix of pro-inflammatory cytokines and extracellular matrix remodeling factors. This study aims to elucidate how ribosomes and protein translation change in cellular senescence. Particularly we focus on alterations of the methylation patterns of ribosomal RNA. We exposed human dermal fibroblasts to doxorubicin to induce cellular senescence and tested if specific methylations of ribosomal RNA contribute to the senescent phenotype. We also measured total protein synthesis by OPP incorporation and specific translation of senescence-associated mRNAs by polysome profiling. Global protein synthesis, ribosome biogenesis, and nucleolar size surprisingly increased in senescent compared to contact-inhibited quiescent cells. Furthermore, several differentially methylated sites, either hyper- or hypo-modified, were present in the rRNA of senescent and quiescent compared to proliferating cells. Methylation levels showed a correlation with the expression of snoRNAs installing these modifications. By inhibiting specific snoRNAs, we confirmed the causality of these modifications for either promoting or inhibiting cell proliferation. Our combined data suggest that even subtle modifications of the ribosomal RNA might have profound and precise effects on cellular physiology and contribute to the heterogeneity of ribosomes. Ribosomal RNA modifications and translation might provide future targets for the selective elimination of senescent cells or blocking their harmful secretome.