Tiny Roundworm's Telomeres Help Scientists To Tease Apart Different Types Of Aging

Researchers at Salk Institute for Biological Studies demonstrate forthe first time that the roundworm Caenorhabditis elegans succumbs tothe trials of old age although its telomeres are still long, and moveswith a youthful spring in its crawl despite short telomeres, theyreport in PLoS Genetics, available online now.

In the past, preventing telomere shortening has often been portrayed asthe key to preventing aging and living longer. In their study, Salkscientists Jan Karlseder, an assistant professor in the RegulatoryBiology Laboratory, and Andrew Dillin, an assistant professor in theMolecular and Cell Biology Laboratory, provide a much more nuanced viewof telomeres and the process of cellular and organismal aging.

"Some long-lived species like humans have telomeres that aremuch shorter than the telomeres in species like mice, which live only afew years. Nobody yet knows why. But now we have conclusive evidencethat telomeres alone do not dictate aging and lifespan," saysKarlseder.

Each time a cell divides, its telomeres get shorter, a processcalled replicative or cellular aging. Some have likened thisprogressive erosion of telomeres to a genetic biological clock thatwinds down over time, leading to a gradual decline in our mental andphysical prowess. Yet, C. elegans, a tiny creature, which spends thebetter part of its adult life without a single dividing cell in itsbody, still shows signs of old age and eventually dies, raisingintriguing questions.

Are telomeres in non-dividing cells eroding slowly over time? If so,will worms with longer telomeres live longer? If not, how do worm cellsand by extension non-dividing human cells, such as nerve cells, keeptrack of their biological age? To answer these vexing questions,Karlseder, who is interested in telomeres, teamed up with Dillin, whostudies lifespan and aging in C. elegans.

Researchers use this 1 millimeter-long soil roundworm that feeds onbacteria mainly because it is simple, easy to grow in bulk populations,and is quite convenient for genetic analysis.

When these scientists began their work almost nothing was known aboutworm telomeres. "We had to start at the very beginning. But now we knowthat C. elegans is the perfect model organism to study telomere biologysince their regulation is similar to human telomeres," says firstauthor Marcela Raices, a post-doctoral researcher in Karlseder's lab.

Many cells in our body keep dividing throughout life (e.g., those thatline our digestive tract, blood, and immune cells) because they must bereplaced over time. When these cells' telomeres reach a criticallyshort length, however, they can no longer replicate. The cell'sstructure and function begin to fail as it enters this state of growtharrest, called replicative senescence.

"But even in very old people, blood cells, which divide continuously,don't have critically short