Telomeres and longevity

the basic elements of telomere biology are very similar across many taxa [1], there is diversity among species, and among tissues, in telomere dynamics. Not surprisingly, given that species differ in many other relevant aspects of their biology, including the pattern of activity of the telomere-restoring enzyme telomerase simple comparisons of average telomere length across species do not map directly onto interspecific variation in maximum lifespan [2-4]. In relatively long-lived species, telomerase is downregulated in most somatic cells, thought to have evolved as a mechanism to counteract an increased risk of tumour formation, particularly in endotherms [1]. One potential cost of this is that tissue renewal capacity is limited, resulting in somatic deterioration with age. However, within a given long-lived species, there is good reason to predict that variation in average telomere length in somatic cells will be related to potential lifespan. Examining this link is fraught with difficulties, not least of which is that studies covering the entire lifespan of a cohort of long lived animals take a very long time. Circumventing this by looking at telomere length and subsequent survival in individuals that are already old omits all the individuals who died early in life (and who may have had the shortest telomeres). The alternative approach of comparing average telomere length in a cross sectional sample of individuals of different ages suffers from a related bias; mean telomere length could actually appear to increase with age if individuals with short telomeres die and so drop out of the sample. Furthermore, since telomere length is a dynamic character, if it is predictive of lifespan, we also need to know at what life history stage the relationship is strongest. Longitudinal studies are therefore essential. We recently examined the relationship between telomere length and longevity in a longitudinal study of a small songbird, the zebra finch Taeniopygia guttata [5]. Longevity is a feature of avian life histories [6]. Like long lived mammals, zebra finches have low telomerase activity in somatic tissues [7]. We measured telomere length from 25 days of age onwards in a cohort of birds and recorded their natural lifespan, which varied from less than one to almost nine years. We found that there was indeed a highly significant relationship between lifespan and telomere length. Editorial Importantly, it was telomere length in early life that was most predictive of lifespan. Because the longer lived individuals had relatively long telomeres …