Exploring the role of senescent pericyte in the oral cancer microenvironment

Cancer is often defined as a disease of ageing. Genotoxic stimuli to which we are exposed as we age contribute to the accumulation of DNA damage and other events associated with cellular ageing. The pro-survival, and anti-neoplastic, response to this damage is known as senescence. In recent years it has become apparent that senescent cells residing in the tumour microenvironment (TME) can promote tumour progression and metastasis. Pericytes are perivascular cells which act in coordination with endothelial cells to regulate blood vessel formation and integrity. Several studies have linked irregular tumour angiogenesis to senescent endothelial cells; little is known, however, of the ability of pericytes to senesce, how senescent pericytes may influence angiogenesis or crosstalk with other cells of TME and potentially influence cancer progression. Therefore, this project aims to characterise pericyte senescent phenotype and investigate the crosstalk of senescent pericytes with oral cancer cells. Here, the capacity of pericytes to undergo senescence in response to genotoxic damage and ageing was assessed. In addition, the ability of pericytes to release extracellular vesicles (EV) was characterised, and the influence of senescence on EV release analysed. Furthermore, the effect of inducing senescence on the communication between pericytes and cancer cells was assessed in vitro. Primary human pericytes were treated with H₂O₂, an oxidative stimulus known to induce senescence in other cell types, and cellular and secreted markers of senescence assessed at different time intervals following treatment. The data generated in this study indicates pericytes demonstrate some features of senescence in response to genotoxic stimulus, such as increased endosomal beta-galactosidase activity, and elevated expression of p16INK4a protein and SASP (senescence-associated secretory phenotype) factors. This was supported by transcriptomic analysis, which revealed increased expression of genes known to be associated with senescence such as IL6 and CYFIP2 and SESN2. It also shows that pericytes produce particles with characteristics typical of those described for EV, and that the release of EV is increased by induction of senescence. Functional analysis showed that senescent pericytes conditioned media inhibited OSCC proliferation and invasion but induced migration. In summary, this study provides evidence that human pericytes are able to develop a senescent phenotype and associated transcriptome, and suggests that OSCC respond to SASPs released by senescent pericytes, indicating that senescent pericytes could provide a promising target for therapeutic agent.