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Cell by Date

20 Jan

By Tiffany Taylor

It has recently been reported that one in six people in the UK today will live to see their 100th birthday. Interestingly, there was quite a loud outcry from the public who voiced their fears over reaching such a grand old age, but what do we really understand about ageing? In this article I will look at ageing from the genetic, cellular and multicellular level to find out what we know, what we don’t, and whether there’s anything we can do about it.

Growing old is one of life’s inevitabilities and we can see the symptoms of ageing all around us, in the colour of our hair, the texture of our skin, and the functionality of our mind… “What was I saying? Oh yes!” Despite its omnipresence, ageing remains one of science’s great mysteries – why do we age? Is our degenerative destiny mapped out from birth in our DNA? We all know ‘those’ stories of heavy smokers who lived to be a hundred and marathon runners who dropped dead at fifty. Or is it an effect of environment? A morbid summation of the general stresses and strains our body is exposed to during a lifetime which ultimately equals our expiration date. The truth is it is likely to be a combination of the two, but to what extent? And is the science out there which could let us stay forever young?

Geriatric Genes and Senior Cells

Evidence shows there is a heritable component of life span. “So, does this mean it’s all in our genes?” The short answer is, no. If it were “all in our genes” we would expect genetically identical individuals to die at approximately the same time. In humans, scientists have found identical twins to have very different life spans, and studies looking at large groups of animals with identical genetic backgrounds – such as honey bees – found huge variability in longevity. “So, does that mean there are no genes which determine ageing, and it’s all about lifestyle?” Well, again the answer is no. In recent years, many genes have been identified which contribute to an animal’s lifespan, however, further research found the actual contribution of these genes to the realised lifespan of the individual appeared to be very variable. Interestingly, the one result the scientists can agree on is the effect of food. Way back in 1934 Clive McCay and Mary Crowell from Cornell University found underfeeding (without malnutrition) increased a rodent’s lifespan by as much as 50%, and this result has been replicated many times since. However, more than 70 years later the “hows and whys” behind the mechanisms underlying this phenomena are still unknown – so don’t beat yourself up about that festive overindulgence.

“Ok, so the detail’s from the genetics seem to be a bit sketchy. But, what can we see in the ageing cell? How are the cells in someone who is old different from those in someone who is young?”

It was Peter Medwar who put forward the idea that overtime DNA would get worn out and damaged, a lot like the human body. He said that the probability of mutation accumulation (mistakes in the genetic code) increases over a longer period of time, and it is this deterioration of code that influences the ageing process. The genome – or the DNA that makes up your genes – is the recipe for all the proteins in your body. Proteins are like the cogs in a machine – they must be exactly the right shape and size to do their job. If they’re just a fraction off then the mechanism fails, and the machine starts to slow down as efficiency is reduced. There is evidence that such mistakes in protein production are involved in age-related degenerative diseases such as cataracts, Alzheimer’s disease and Parkinson’s disease.

“Ok, now we’re getting somewhere. But how does the body get rid of these old cells which are rusting up the cogs?” All cells come with a built in ticking time bomb in their DNA in a region called the telomere. The telomere gets shorter with every cell division, and when the code runs out, the cell has two options, either it will go into a suspended state called “senescence”, or it will initiate a “self-destruct mode” whereby intracellular proteins are released which destroys the cell. When this system breaks the cell becomes immortal, and will continue to replicate beyond its expiration date – this is how tumours arise. It is predicted that 85% of tumours are caused by a mutation in the telomere.

The Fountain of Eternal Youth

There is a multi-billion dollar cosmetic industry dedicated to anti-ageing products. Potions and lotions which promise your Grandmother the face of a teenager, and your mother a booty like Beyoncè.  The unfortunate truth is, most are just re-packaged moisturisers – but science is making some major leaps forward in masking, and even reversing the effects of ageing.

A team of scientists from Harvard Medical School have managed to reverse the effects of ageing resulting in worn out old wrinkly rodents being rejuvenated into versions of their younger selves. They did this by breeding genetically engineered mice that were unable to produce the enzyme which caused the telomere to shorten during cell division – called telomerase. Mice without this enzyme aged prematurely, however, when the mice were given an injection to reactivate the telomerase enzyme, the signs of ageing were reversed. It is currently under further investigation as to whether this procedure actually increases longevity, but it might help improve the quality of life of individuals showing signs of age related degenerative diseases. This study is still in its early days and not yet safe for human testing, but it is certainly an important discovery into the secrets of the ageing body.

Who Wants to Live Forever?

There are some scientists that believe they will ‘cure’ ageing, allowing us to live… indefinitely. But, is that a good idea? For many, growing old gracefully isn’t an option– just take a look at the profits made by the anti-ageing cosmetic companies. It seems likely that within the next few decades the science behind ageing will take huge leaps forward, to places we find hard to contemplate. There will undoubtedly be companies looking to make some cash, and people willing to put some pretty toxic stuff into their bodies to cover the signs of ageing. I’m reminded of the dark comedy “Death Becomes Her” where two ladies who learn the secret of eternal youth end up, literally, in pieces. Research which carries with it such ethical responsibility is always tricky, but I do not believe in the stifling of knowledge due to fear of the unknown – just in its careful and responsible monitoring and application. However, it’s easy to get up on my high horse when I’m twenty five and the science isn’t there yet – but could I honestly say no? If fifty years from now someone offered me a magic potion which would literally take decades off, allow me to go running again, travel the world, see my great grand-children grow up, would I walk away? … Ask me in fifty years.

Sources

One in six people in the UK today will live to 100, study says; Reported in the Guardian by David Batty, 30 December 2010

Jaskelioff, M. et al. Telomerase reactivation reverses tissue degeneration in aged telomerase-deficient mice. Nature 469 (7328), 102.

Kirkwood, T. B. L. Understanding the Odd Science of Aging. Cell 120 (4), 437 (2005).

McCay, C. M. & Crowell, M. F. Prolonging the Life Span. The Scientific Monthly 39 (5), 405 (1934).

Harvard scientists reverse the ageing process in mice – now for humans; Reported in the Guardian by Ian Sample, 28 November 2010

Vijg, J. & Campisi, J. Puzzles, promises and a cure for ageing. Nature 454 (7208), 1065 (2008).

 
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Posted by on January 20, 2011 in Biology, Genetics, Human Biology

 

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