It’s a truism that exercise helps with stress. But have you ever wondered… why? Could it be your DNA? A gang of swimming rats takes the plunge to find out.
The holiday season should be re-named the “stressed out of my mind” season.
Going to the mall, fighting the crowds, mailing holiday greeting cards in time, avoiding eating a ridiculous amount of ridiculously bad food -– insert fruit cake joke here -– all add to the stress.
So what’s the first thing you stop doing when you’re stressed and don’t have time? Well, exercise of course.
With this week’s review I hope to convince you to keep exercising through your stress, and describe how exercise can alter your DNA.
Before I dive into the study, though, here’s a crash course in DNA to help you understand the study.
A brief molecular biology interlude
Thanks to a rash of crime dramas, investigative reports, the OJ Simpson trial, and hopefully your high school biology class, DNA has become a part of our collective knowledge. Great!
I think it’s fantastic, but there is much more to DNA than just DNA.
What do I mean? Have you ever wondered how all your DNA gets packed into you?
Probably not, but just think about how difficult it is to squish all that DNA into you and more importantly… does that matter to you?
Miles and miles of DNA
Let me explain the problem.
Each cell in your body has about 3 metres (some estimates are as low as 1.3 metre) of DNA. Now that might not seem like a lot, but consider this the average human cell is 10 µm (or 10-5m) in diameter. (In case your math isn’t good, that’s very, very, very small.)
While thinking in terms of cells and micrometres may be too abstract, how about thinking about all the DNA in your body?
You have between 50-75 trillion cells in your body. Now imagine squeezing 150 x 1012 metres of DNA (50 x 1012 cells x 3 metres of DNA/cell) into your body. Just for reference, the sun is 1.5×1011 metres from the earth.
This may help you understand the problem of packaging DNA into your body.
DNÄ storage solutions
Since a clever worldwide Swedish furniture company has yet to come up with an ingenious DNÄ storage device, our cells had to organize their DNA on their own. They came up with histones.
Histones are four proteins grouped together that wrap around DNA kinda like thread wraps around a spool.
DNA and histone together is called chromatin . If you take a look at figure 1 you can see how your DNA wraps around a bunch of histones that coil (condense) the DNA into what looks like a knitted jumpsuit gone awry (a chromosome).I’m sure by now you’re wondering why I’ve brought up the storage problems faced by your cells – really, as long as it all fits in there, does it matter?
I bring it up because histones don’t just pack your DNA into small and convenient packages. They also control your DNA.
Histones are one of DNA’s gatekeepers. They control whether genes in your DNA get produced (transcribed and translated) into proteins.
If your DNA is tightly wrapped around a histone, then your cell’s protein making machinery (transcriptional machinery) can’t physically get to the DNA, and so no protein is made.
A famous muscle molecular biology experiment converted connective tissue cells (fibroblasts) into muscle cells (myoblasts) by using a chemical (5-azacytidine) to release the DNA from its histones . Once released from its histones, a specific gene, MyoD (MyoA thru MyoC turned out to be dead ends) could convert fibroblasts to muscle cells.
One reason that exercise can affect so many things in your body is that exercise can loosen DNA from histones.
We know that regular exercise can decrease depression and stress, and improve sleep by changing brain chemistry.
The study in this week’s review looks at two things:
- how regular exercise changes histone-DNA tightness
- whether that’s why exercise helps with stress.
Collins A, Hill LE, Chandramohan Y, Whitcomb D, Droste SK, Reul JM. Exercise improves cognitive responses to psychological stress through enhancement of epigenetic mechanisms and gene expression in the dentate gyrus. PLoS One. 2009;4(1):e4330.
In this study the scientists had no choice but to use animals (rats) for two main reasons. First, they needed protein samples from brains; and second, the animals had to undergo a fair bit of psychological stress.
For four weeks, the exercise group of rats got free access to a gym. OK, not a real gym with a juice bar and towel service and stuff. It was a running wheel.
But the rats put in a much better performance than the average person with a treadmill in their living room — these rats rat 4-7 km a night!
Control rats got to hang out on the couch and watch TV.
The scientists stressed the rats psychologically by putting them in a new environment or by making them swim.
Just like your cat or dog, putting the rats in a new home stresses them. The longer it takes for the rats to settle down, the more stressed they are. Thus, scientists can measure rat stress levels by observing how long it takes for the rats to chill out.
Stress number two was swimming. Though rats can swim, they aren’t fond of it. Putting them in water causes them stress and struggling is an indication of stress.
I know this sounds harsh, but the rats didn’t drown — they just wanted out of the water.
Checking histone “tightness”
Testing brain samples (using immunohistochemistry) the scientist figured out how tightly the rats’ DNA was wrapped around histones.
For those interested, testing was immunhistochemical staining for phosphorylation of Ser10 and acetylation of Lys14 in histone H3 of neurons from the dentate gyrus level.
More exercise equals less stress
Exercise helped the rats deal with stress. Exercised rats didn’t run around their new home as much or with as much panic — to anthropomorphise them just a bit — compared to the non-exercise control rats.
Exercise rats were less stressed after swimming too. They were more mellow, based on less struggling, compared to the control rats.
More exercise equals looser DNA
Counting how many neurons from the memory centre (dentate gyrus) were positive for loose DNA (phosphorylated and acetylated histone H3) it turned out the exercising rats had more loose DNA.
That means that it’s easier to make new proteins that help resist stress.
The conclusion is pretty straightforward: exercise helps rats deal with stress and it isn’t a big leap to say the same happens with people.
For me, the more interesting part was that the area of the brain responsible for memory was able to make more protein after exercising, because of changes in histones.
The chain of events goes like this: exercise alters your DNA by modifying histones; modified histones means more access for your transcriptional machinery to your DNA. Once the transcriptional machinery can get at the DNA, it can make changes.
Why the memory centre of the brain? The scientist figure it’s because somehow, remembering what happened in the past during a stressful event is helpful the next time it happens. Perhaps the unknown is more stressful than the actual event.
Exercise changes a lot of different things in your body, from metabolism to how happy you feel.
Molecularly, exercise alters your DNA by changing how it’s packed. Less packing means more access to your DNA for your protein-making machinery. More access to DNA means more proteins to respond to stress.
So, go for a workout before you tackle that mall or family dinner.
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