Friday, March 9, 2012

Science Friday: Exercise changes gene expression

Although all your cells have all your genes wrapped up in their DNA, not all those genes are expressed. Heart cells don’t express genes specific to your liver, for example. The genes which aren’t expressed are turned off by being kept tightly wound up, like thread wrapped around a spool, so that proteins and various cellular machinery can’t get to them. To get them turned on, they need to be unraveled from the spool. One thing that keeps them wrapped up is a process called DNA methylation, which is basically the addition of a small group of atoms (a chemical “tag”) that puts a lock on the spool. Removing the methylation allows the DNA to unwind and proteins to interact with it (eventually creating more proteins, the worker bees of the cell.)

These chemical tags are epigenetic changes.  Epigenetic changes are not something you are born with (like your DNA is) but are modified during your life, perhaps because of some external influence. In a new study, one of these external influences seems to be exercise.

Juleen Zierath’s group at the Karolinska Institute in Stockholm took muscle biopsies from the quadriceps of adults and found that methylation was decreased after exercise (biking.) In particular, the methylation of genes known to play a role in fat and carbohydrate metabolism (including PGC-1 alpha, which we have heard about before) was decreased (meaning these genes were turned on.) They also compared low-intensity exercise to more strenuous exercise and found the decrease in methylation only after a hard effort. Interestingly, they found that this was caused by contraction of the muscles themselves (not messages from the rest of the body) by isolating a piece of muscle from a mouse and making it contract in a petri dish. Even cut off from the rest of the body, the methylation still decreased. Finally, they used yet another system (muscle cells grown in the lab) to test the effects of caffeine. Caffeine causes calcium to be released from intracellular organelles and they hypothesized that calcium release might be causing the demethylation. Their findings supported that idea, as caffeine also demethylated the genes in question. The authors are quick to note in various press releases that that does NOT mean caffeine has the same effects as exercise. Bathing your muscles in the same amount of caffeine the cells got would mean 50-100 cups of coffee/day—close to the lethal dose. It has already been shown that caffeine may be beneficial to endurance athletes, but for other reasons, which is certainly verified by anyone trying to squeeze in a workout before the sun comes up.

One important thing to note: a lot of the press regarding this paper claims that this means exercise changes your genes. That isn't the case. Your genes are something you inherit from your parents and aren't changeable. Epigenetics don’t change the actual genetic code, just the expression of those genes. Although this group plans to test if epigenetic changes are heritable and can be passed on to your children, as far as this study is concerned, the changes discussed are transient.

Note: This research was presented on the real Science Friday! I listened to it while doing my own experiments with cells in culture.

Dream big,

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