A recently released study from Maria Blasco and her team of researchers at the Spanish National Cancer Research Center (CNIO) shows that the rate of telomere shortening is strongly correlated with the maximum lifespan of animal species.
Telomeres, which are simply repeating segments of DNA on the ends of our chromosomes, serve two critical functions: They protect the ends of our chromosomes, preventing genetic damage, and they serve as a clock, limiting the number of times that our cells can divide. This limit, known as the Hayflick limit, serves as a basic defense against cancer. However, telomere attrition is a primary hallmark of aging and leads to cellular senescence and other age-related disorders.
Shortening rate, not initial length
In studying nine different species of birds and mammals, including human beings, the researchers found a very strong, but not perfect, correlation between longevity and the rate of telomere shortening (rather than initial length as was once believed). For example, humans, whose telomeres degrade at 70 base pairs per year, live roughly 40 times longer than mice, whose telomeres degrade at 7,000 base pairs per year. The researchers also note that other studies have shown the link between critically short telomeres and genetic damage, and they mentioned that oxidative stress has also been shown to shorten telomeres.
Telomere shortening to a critical length can trigger aging and shorter life spans in mice and humans by a mechanism that involves induction of a persistent DNA damage response at chromosome ends and loss of cellular viability. However, whether telomere length is a universal determinant of species longevity is not known. To determine whether telomere shortening can be a single parameter to predict species longevities, here we measured in parallel the telomere length of a wide variety of species (birds and mammals) with very different life spans and body sizes, including mouse (Mus musculus), goat (Capra hircus), Audouin’s gull (Larus audouinii), reindeer (Rangifer tarandus), griffon vulture (Gyps fulvus), bottlenose dolphin (Tursiops truncatus), American flamingo (Phoenicopterus ruber), and Sumatran elephant (Elephas maximus sumatranus). We found that the telomere shortening rate, but not the initial telomere length alone, is a powerful predictor of species life span. These results support the notion that critical telomere shortening and the consequent onset of telomeric DNA damage and cellular senescence are a general determinant of species life span.
While telomeres are not the end-all, be-all of the many causes of aging, this study shows that the two are strongly linked, and there is a significant relationship between mortality and telomere shortening. While it is fortunate that the telomeres of human beings shorten more slowly than those of other species, critically short telomeres are still dangerous; telomerase-based therapies, if they can ameliorate the damaging effects of these shortened telomeres, may demonstrate clinical effectiveness against age-related diseases.