Image: Birgit Ritschka
For decades, scientists had ignored senescent cells—which are trapped in a long-term state of cell cycle arrest—dismissing them as artifacts of cell culture with no significance inside living organisms. But in recent years, Kirkland and other researchers have established senescence as an important physiological process that appears to play seemingly opposing roles in vivo. On the one hand, senescent cells are thought to mediate tissue development when they form in the embryo, and also to promote tissue regeneration and wound repair in later life. However, as these zombie cells accumulate with age, they can ooze inflammatory proteins believed to cause tissue dysfunction and to push neighboring cells into senescence. Indeed, animal studies have suggested that destroying senescent cells can slow down age-related physical decline and boost overall health, and many researchers who study aging now regard senescence as a driver of the physical decline characteristic of old age and a contributor to a range of age-related diseases.