Cellular senescence— defined as a process of stable cell-cycle arrest—was first identified as a biological state that marked the end of a cell’s replicative life (Hayflick, 1965). In the investigations that followed, senescence was established as a component of disease states {e.g. DNA damage} (Kuilman et al., 2010), and was correlated with aging-associated disorders (Keyes et al., 2005; Baker ...