Longevity and Telomeres - Planet Earth Online

DNA, life's genetic code, can be found tightly packaged inside chromosomes.  And at the end of these chromosomes are specialised bits of DNA called telomeres - which are often associated with ageing.

Birds are known for their long lives.  Petrels, for instance, can live up to 40 or 50 years. But by studying Australian zebra finches, whose average life expectancy is around five years, researchers can examine the relationship between telomeres and longevity.

Planet Earth podcast presenter Sue Nelson met up with Pat Monaghan, professor of animal ecology at the University of Glasgow to find out more - as Pat studies the length of these telomeres in birds.

Pat -   You can think of the telomeres as a bit like the little plastic caps that you get on the ends of shoelaces.  Also if you were to tie your shoelaces in the dark you can feel the plastic caps.  Now, these telomeres do the same kind of job inside a cell.  They identify the chromosome ends and they also protect the DNA from a number of processes that cause the ends to, in effect, fray, if you like.

Sue -    Apart from the protection aspect of what they do they're often associated with aging though as well, why?

Pat -   Yes they are and one of the reasons is that every time a cell divides the telomere gets a little bit shorter.  Eventually it will get so short that it doesn't work anymore, then the whole genome becomes unstable and the cell doesn't function anymore, and it enters a state of what's called replicative senescence.  That just means it can't divide anymore, sometimes the cell dies, sometimes it stays there but it's not quite working in the same way, so the loss of telomeres is associated with an age related decline in tissue function.

Sue -   Pat examines what factors are involved in the loss of telomeres, be it environment or stresses such as a change in the availability of food for zebra finches. She also led a UK team that tracked a group of these birds measuring their telomere length from when they were young until died of natural causes.  And earlier this year they discovered a correlation between length of telomeres and the longevity of a bird.

Pat -   The best predictor of lifespan was that very first measurement of telomere length in early life.

Sue -   Is this also as a result of when environment kicks in and when these other external stresses possibly affect your lifestyle in much the way with human beings as well?

Pat -   Yes, there is a lot of work on telomeres in human beings and I am afraid that almost all the things that we know are bad for us are also bad for telomere length, so smoking and stress are associated with reduced telomere length.  However, when it comes to early life telomere lengths we still don't really know to what extent growth conditions are influencing telomere loss or whether the variation that we see is largely a consequence of inherited factors.

Sue -   So, work is ongoing then with a whole range of factors?

Pat -   Yes, we're doing a number of different projects looking at different environmental conditions in the wild; animals born in different years, in different situations, in different brood sizes.  Then also we're looking within individual changes using the zebra finch.

Sue -   There were a lot of suggestions when your research came out of the possible connection to human ageing and it almost being that in this case when it comes to how long we live size of telomeres does matter.

Pat -   One of the really interesting things though is that animals can restore telomere length.  Now, in normal body cells that is a very risky thing to do because if you keep restoring telomeres you run the risk that a cell can divide uncontrollably and of course that happens during cancer.  It is thought that one of the reasons we don't have, for example, in human body cells, we don't have telomerase usually active, it's a protective process, it keeps a check on cell division.  However, in some much shorter lived animals they do have telomerase active in their tissues.  So, yes, the basic processes are relevant to humans.

People haven't done the kinds of studies that we have done in the zebra finch in humans that's to say tracking telomere length in the same individuals from early in life until they die.  The question about should we all run along and get our telomeres measured and say, that predicts how long I'm going to live; telomeres aren't everything there are other things that go on. 

So it's a very active area of biology but I wouldn't waste your money on running out and getting your telomere length measured because it's only going to make you either happy or miserable but it scientifically isn't going to tell you exactly how long you're going to live.