Without a gene called IL-15Rα, mice can run in their exercise wheels for hours every night. Going nowhere still, but doing it with the fortitude of a marathon runner.
Previous studies have hinted that IL-15Rα might be important for muscle strength and contraction, but the gene has never been studied in a live animal.
So a team led by Tejvir Khurana of the University of Pennsylvania genetically engineered mice who lack IL-15Rα. And these mighty modified mice ran 6 times farther than normal mice each night, according to the sensors on their wheels.
After dissecting the mice’s muscles, the researchers found that they sported:
- Increased numbers of mitochondria, the energy-generating power plants of our cells.
- And more muscle fibers, which indicates that they tired less easily.
- And when stimulated with electricity, the muscles contracted for longer than normal, taking longer to use up their energy stores.
Mice, like humans, have two types of muscles. ScienceNOW explains:
Fast-twitch muscles, such as the muscles in our fingers, allow more precise movements but tire faster, whereas slow-twitch muscles, like those in our back, are more resistant to fatigue but don't allow such precise movements. Removing the IL-15Rα gene, Khurana says, coaxed the mice's fast-twitch leg muscles to turn into slow-twitch muscles.
To study whether the gene affects human endurance, the team worked with Australian researchers to look at genetic samples from Olympians and other world-class athletes.
They found that certain variants of the IL-15Rα gene were more common in long-distance cyclists and rowers than they were in sprinters – suggesting that the most successful endurance athletes might have a variant that gives their muscles extra endurance.
The work raises the possibility that drugs blocking IL-15Rα could one day enhance endurance.
The study was published this week in The Journal of Clinical Investigation.
Image by KevinMcCarthyPhoto via Flickr