Aging is inevitable. With time, cells lose their ability to regenerate and tissues and organs succumb to wear and tear. Behind the stiff joints and wrinkles are changes accumulating in genes involved with DNA replication and transcription that disrupt cell proliferation and eventually lead to senescence, wherein cells stop actively dividing, or apoptosis, programmed cell death. Current theory links aging to an organism's lifespan and life history. Short-lived species that tend to reproduce early and rapidly are thought to not invest the resources and energy into cellular maintenance and repair and thus age quickly, while the aging process may be more gradual in species with longer lifespans and later reproductive maturity. Andrea Bodnar and James Coffman set out to document contrasting aging phenomena in sea urchins with vastly different lifespans in a recent study published in Aging Cell (15, 778–787; 2016).

Lifespans in sea urchins can vary greatly by species, with some surviving only a few short years while others are capable of living for decades with negligible senescence—growing, reproducing, and regenerating to the very end. Bodnar and Coffman were interested in three species: the short-lived Lytechinus variegatus, the middle-aged Strongylocentrotus purpuratus, and the centenarian Mesocentrotus franciscanus. Dividing each of their subject species into “young” and “old” groups, they tested the expression of genes involved in cell proliferation, telomere maintenance, and multipotency in several different tissue types. They also studied the urchins' ability to regrow their spines and tube feet. By any measure, the youth showed no major advantages over their elders, regardless of species. As Coffman explained in a press release, “...aging is not inevitable: sea urchins don't appear to age, even when they are short-lived. Because these findings were unexpected in light of the prevailing theories about the evolution of aging, we may have to rethink theories on why aging occurs.”

Credit: Jillian Suzanne, Getty

Although one might be hard-pressed to find similarities between an urchin and a human, they actually share a closer phylogenetic relationship than humans and other kinds of invertebrates. The genes analyzed in this study are either conserved in humans or similar in function. Urchin embryos have long been used to study life at the earliest developmental stages but adults are now becoming models for understanding life's progression to the end. Understanding how sea urchins are able to avoid the ravages of time may inform the evolutionary theory of aging as well as the underlying process in humans and other vertebrates.