February 2, 2012
Telomeres and Longevity in Zebra Finches
A telomere is like an aglet. Aglets are those plastic or metal tubular thingies at the end of your shoe laces that keep the end of the shoelace from becoming frayed and facilitate inserting the lace into the eyelet. A telomere is a sequence of base pairs at the end of a chromosome. A chromosome zips apart during cell division so that it can be replicated, and a small number of base pairs typically get lost during replication. This is because the molecular machinery that duplicates the chromosome can’t read through to the end of the strand, so it just skips the last bit. Any meaningful genetic information at the end of the chromosome would be lost or garbled. A nice long telomere at the end of the chromosome allows for multiple duplications without the loss of meaningful information, but over time even the telomere may be lost through attrition, and further replication of that chromosome would be a problem.
There is a system, using the enzyme “telomerase,” that adds base pairs to the telomeres, but there tends to be an imbalance between adding new base pairs by telomerase and losing the base pairs during replication, so in a given individual, new copies of chromosomes may eventually start to have less information than they are supposed to, which leads to cell death or worse—it is thought that this can be a cause of cancer in some cases. Shorter telomeres may mean a shorter lifespan, and longer telomeres a longer lifespan, for a cell line, or more interestingly, for an individual.
That is all pretty well established science, but the numerical details have been somewhat lacking. There has not been a study of a reasonably large sample of organisms in which telomere length was measured early in life, then lifespan measured in each organism, to verify if there is an association between telomere length and how long an individual lives. Until now.
A Zebra Finch. Photograph by Flickr user pixelblume.
A team of researchers from the University of Glasgow and the University of Exeter at Cornwall have just published an article in PNAS called “Telomere length in early life predicts lifespan.” The paper looks at 99 zebra finches in which telomere length was measured on the 25th day of life, and lifespan was measured by keeping the birds in a controlled captive environment until they died. Lifespan for these birds ranged from less than one year to almost 9 years. One can imagine the researchers waiting around for that last bird to die so they could submit the paper.
Telomere length early in life correlated strongly with lifespan of the birds, though there was enough variation in the outcome to suggest that multiple other factors are involved. The researchers conclude that “[a]lthough reduced telomere length has been associated with a number of degenerative diseases in humans, there has been increasing interest in their role in the aging process in otherwise normal individuals. The results of this study clearly show that telomere length early in life is predictive of longevity.”
At this point you are probably wondering if it is possible to add to our existing telomeres and possibly increase lifespan. It is possible that this could actually work, through gene therapy. This has been done in lab mice and other test animals. It is also possible, however, that long telomeres or telomeres lengthened artificially can cause an increased risk of cancer (for as yet unknown reasons). Also, it is not universally true that telomere length decreases during lifespan; in some organisms is seems to increase. One thing can be said about telomere biology at this point: There are many unknowns. Don’t be surprised to hear more interesting research about them over coming months and years.
Heidinger, B., Blount, J., Boner, W., Griffiths, K., Metcalfe, N., & Monaghan, P. (2012). Telomere length in early life predicts lifespan Proceedings of the National Academy of Sciences, 109 (5), 1743-1748 DOI: 10.1073/pnas.1113306109
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Lengthening of telomeres has not been shown to increase cancers and in fact the reverse is true in normal cells. We get cancers basically when we are old and the telomeres are short. Cancers cells do lengthen their telomeres to survive and thrive, but those are not normal cells and are already cancer cells.
To learn more you might want to check out Dr Ed Park MD MPH on youtube.
MadMax:
… and, somatic cell lines that are cancerous ten to get more rapidly shortening telomeres. And yes, the link between cancer and shortened telomeres is the main link.
Your point about telomere shortness and cancer is, of course, the whole point of the research; I mention the link between longer telomeres and/or increased telomerase activation and cancer for completeness. It has not been demonstrated and how this would work is unclear, but I refer you to Weinstein and Ciszek, (2002) if you want to know more about that. It probably isn’t of any great importance, but it does bring up the basic question: Why aren’t all telomeres very very long?
The cancer causing explanation (just noted) is one possibility, another is energy use (longer telomeres = more energy used) and a third is that there is simply not selection against short telomeres or effecasious telomerase activity in lineages of short lived organisms, and thus some long lived organisms that evolved from short lived ones (like us) are unlucky (phylogenetic constraints can be a drag).
See Dan Eisenberg’s paper “An evolutionary review of human telomere biology” (American journal of human bilogy) from 2010 for a great overview of these questions.
Wow you did quit a research there. It’s almost hard to believe that those researchers have waited for 9 years for the zebra finches to die before they could submit a paper about it.