Biophysical regulation of nucleolar structure and function in cellular senescence and ageing

As tissues in the body age, they progressively accumulate dysfunctional senescent cells, which are unable to proliferate and contribute to the age-related decline in tissue health. Senescent cells are characterised by numerous biochemical and structural changes, including remodelling of DNA and nucleoli within the nucleus. As the nucleoli are central hubs for production of ribosomes and the regulation of protein synthesis, disruption of their normal structure and function during senescence could contribute to cell and tissue ageing.

Recent studies by our team and others have also shown that physical interactions between the nucleoli and surrounding DNA control the structure of nucleoli and the cell's ability to synthesise ribosomes and protein. We therefore propose that during senescence cells undergo dramatic changes in their physical and mechanical properties, which regulate the structure and function of the nucleoli and contribute to age-related defects in cell and tissue health.

In this project we plan to investigate how the physical properties of the cell and nucleoli become altered during senescence and how structural changes in the nucleoli impact on cell metabolism and tissue ageing. We will focus on the skin as a model system and employ state-of-the-art biophysical tools to characterise the mechanical properties of healthy and senescent skin cells. In addition, we will use molecular profiling methods to determine the corresponding changes in gene expression and protein synthesis. We will then construct 3D synthetic skin models with healthy and senescent cells and investigate how the physical properties of the nucleoli influence the function of these tissue models. Finally, we will compare these findings and responses to those of skin samples obtained from young and old donors.

Together, these studies will define for the first time the biophysical changes that occur within the nucleus of senescent cells and the impact on the essential functions of the nucleolus. The findings will shed new light on the fundamental process of cellular senescence and ageing, and the work will open up new opportunities for promoting healthy ageing.

Nucleoli are large biomolecular condensates that form through a liquid-liquid phase separation process and are responsible for the regulation ribosomal RNA transcription and ribogenesis. Recent studies by our team have shown that nucleolar structure and function not only depend on mechanical cues from the extracellular matrix, but also the intrinsic biophysical properties of the chromatin. In addition, we observe dramatic changes in nucleolar structure following the induction of replicative or premature senescence. We therefore hypothesise that during senescence cells undergo defined changes in their mechanical and biophysical properties, which alter the structure and function of the nucleoli and contribute to the ageing phenotype.

To explore this hypothesis, the proposed interdisciplinary project aims to determine the fundamental biophysical mechanisms that define nucleolar structure and function in proliferative and senescent cells. We will employ a range of biophysical tools and computational methods to characterise the biophysical properties of the nucleus, chromatin, and nucleoli in response to distinct triggers of senescence and to dissect the mechanical mechanisms that regulate these responses. To understand the biological context and impact of nucleolar remodelling in senescence, we will also profile to corresponding changes in the transcriptome and translatome using RNA-sequencing and ribosome foot printing methods. Finally, we will assess the contribution to tissue ageing through the analysis of engineered 3D skin equivalent models and skin samples from young and old donors. Together, these studies will provide new and significant insights into the biophysics of nucleolar remodelling during cellular senescence and will lead to major advances in our overall understanding of human ageing.