aging: genes vs. the environment
As far as we know, every living on our planet has something in common besides the same nucleotides and amino acids. Aging. When scientists started deciphering genomes and what specific genes did, the idea was that aging came from a preprogrammed set of genetic instructions and death was triggered by some sort of kill switch. But there was a problem with that idea. It turns out that while genes do play some role in the aging process, they don’t necessarily control it every step of the way. Instead, the current thinking is that aging is an accumulation of physical wear and tear on the body. Stanford biologist Stuart Kim disagrees and he thinks an experiment on which he worked could show that aging is actually just a bizarre accident of evolution.
By tracking gene expression in fast aging worms frequently used for this sort of research, he found that with age, increasing amounts of transcription factor elt-3 turned hundreds of genes on and off. By themselves, the changes in gene expression with age don’t necessarily prove they’re responsible for the aging process. And this is why typical environmental stresses were inflicted on the worms. They were blasted with with heat and radiation, infected with diseases and bombarded by free radicals, long cited as a major culprit in aging and the cause for a huge marketing boom in vitamins and foods rich with anti-oxidants. But oddly, all that stress didn’t seem to affect the level of elt-3 buildup. The conclusion of the team? The worms’ genetic pathways drift as the organism gets older and that drift has to be the main cause of the aging process.
According to Kim, as organisms evolved, they lived long enough to reproduce and keep their species alive for as long as possible which is why natural selection wouldn’t necessarily favor animals with mutations that would somehow lessen this genetic drift. So does this mean that the wear and tear theory will be shown the door and we’ll start trying to find the genetic drift responsible for aging in humans? Probably not. It seems that Kim isn’t sure whether the same kind of drift would happen in humans and this research focuses so narrowly on gene expression and environmental stress, it looks like he forgot about other factors in aging. In the article linked above, he’s quoted as saying the following about lifespans…
“Everyone has assumed we age by rust, But then how do you explain animals that don’t age?”
Some tortoises lay eggs at the age of 100, he points out. There are whales that live to be 200, and clams that make it past 400. The chemistry of the wear-and-tear process, including damage from oxygen free-radicals, should be the same in all cells, which makes it hard to explain why species have dramatically different life spans.
If an organism has a limited lifespan, be it 200 years for turtles or 5,000 years for some pines, then it actually does age and die. Despite having the same building blocks, living things have a great deal of variety and the difference in metabolism, reproduction cycles, and sensitivity and exposure to environmental damage would produce radically different lifespans. Aging is a very complex process with many variables. The same species of nematodes often used for aging research seems to show lots of different ways to slow aging and a variety of mechanisms active in the aging process. While the study itself seems very interesting, we need to confirm that there aren’t any other factors involved with how living things deal with stress and whether the findings in these nematodes can be scaled up to larger and more complex organisms.
See: Budovskaya, Y., et al. (2008). An elt-3/elt-5/elt-6 GATA Transcription Circuit Guides Aging in C. elegans Cell, 134 (2), 291–303 DOI: 10.1016/j.cell.2008.05.044