355 Heterogenous Ribosomes in Human Dermal Fibroblast Senescence

Researchers previously regarded ribosomes as static and identical molecular machines within cells. In recent years the discovery of heterogeneous ribosomes challenged this simplified view. Heterogeneous ribosomes may differ in rRNA, ribosomal protein composition, or differential modifications of ribosomal proteins or rRNA. However, the functional consequences of these structural specializations are still poorly understood. The presence of senescent cells in vivo is associated with several age-related changes. Using human dermal fibroblasts (HDFs) as a model, we found increased global protein synthesis, ribosome biogenesis, and nucleolar size in senescent cells. As the underlying mechanisms of these effects are still unknown, we explored if specific methylations of the ribose backbone contribute to the senescent phenotype. We quantified methylation levels across all positions of rRNA. Thereby, we identified several differentially methylated sites in senescent compared to proliferating and quiescent cells. We identified several positions to be hypo- or hyper-methylated in quiescent and senescent cells compared to proliferating cells. Methylation levels showed a correlation with the expression of snoRNAs mediating these modifications. Importantly, inhibition of single snoRNAs specifically either promoted or inhibited 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.