Extracellular Citrate as a Novel Biomarker of Senescence; Insights from Metabolomic Pro ling

Abstract

Senescent cells play an important role in normal biological processes such as wound healing and cancer prevention. If not eff ectively cleared by the immune system however, senescent cells can accumulate and have been linked to negative events; most notably fibrosis and ageing. To understand more about the molecular mechanisms underpinning senescence as well as the e ects senescent cells have on surrounding cells, the organism as a whole and why some cells evade the immune system, it is necessary to study and manipulate senescent cells in vitro and in vivo. In order to do this, accurate identi fication of senescent cells is required, something which can currently only be achieved by staining for multiple markers, a process that requires invasive tissue sampling when using in vivo models, and is a limitation in human studies in particular. A secreted biomarker that is detectable in bio-fluids such as blood would facilitate more informative human and animal studies. In this thesis un-targeted metabolomic screens were performed using fibroblasts from multiple tissue types and two well characterised models of senescence: replicative senescence and irreparable DNA double strand break induced senescence. Controls for transient growth arrest and repairable DNA damage were also included and all groups were compared to young dividing cells. These investigations not only give insight into the metabolic changes occurring in senescence but also provided candidate biomarkers that were then more closely studied using targeted techniques. Extracellular citrate was identified ed as the most robust candidate, and its regulation was investigated at the molecular level. The work presented in this thesis represents a novel contribution to the field of senescence both in terms of the metabolic pro les of senescent and quiescent fi broblasts and the strong candidate biomarker, citrate, which has the potential to broaden studies of senescence in humans in vivo