For a long time, the ribosome has been regarded as a static machine and all ribosomes within a cell were assumed to be identical. This simplified view has been challenged in recent years, when the existence of heterogeneous ribosome populations was reported and evidence for “specialized” ribosomes emerged. 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.

Presence of senescent cells in vivo is associated with several age-related changes in the skin and other organs. Using human dermal fibroblasts (HDFs) as a model, we have established protocols to induce and confirm the senescent state of cells in vitro. So far, our data indicates increased global protein synthesis 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.

By Ribometh-seq we quantified methylation levels across all positions of rRNA which were previously reported to be modified. Thereby, we identified several differentially methylated sites in senescent compared to proliferating and quiescent cells. For most of the sites, almost complete methylation was detected in all three cellular states. However, we also identified several positions to be hypo- or hyper-methylated in quiescent and senescent cells in comparison to proliferating cells. Methylation levels were highly correlated with expression of snoRNAs mediating these modifications. Currently we are testing functional consequences of depletion of these differently regulated snoRNA on cellular physiology and ribosome function.

Taken together, our data suggest that even subtitle modifications of the ribosomal RNA might have profound and very specific effects on cellular physiology and contribute to the specialization of ribosomes.

Specialized ribosomes in human dermal fibroblast senescence