Musculature: marathon mouse

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Musculature: marathon mouse
Musculature: marathon mouse

Marathonmaus - modern doped

Athletes train hard to become fast and enduring. A modern doping method helped a few little mice to improve their running performance.


Muscle is not just muscle. Depending on the requirement, the individual muscles specialize in tenacious endurance work or in fast, short exercises of strength and are structured accordingly. For example, those muscles that mainly have to perform lengthy holding work contain muscle fibers of the so-called type I and type IIa. These fiber types are packed with mitochondria, which provide the muscle with ample energy through an oxygen-consuming process. They are therefore optimal for long-lasting work and only tire slowly.

Muscles, on the other hand, which are primarily used for rapid, powerful movement, are packed with Type IIb fibers, which contain little mitochondria and derive energy from anaerobic glycolysis, predominantly without oxygen consumption. They are best suited for short, sudden contractions and tire quickly.

No muscle consists exclusively of one fiber type, and the two fiber types can be converted into one another with appropriate training.

There is also another type of fiber in the muscle that combines the properties of the other muscle fibers: the type IIx fibers. Very little is known about this type of fiber, since it occurs only in small quantities and therefore eludes research. Apparently, like the slow Type I fibers, it gains energy aerobically, but it performs like the fast Type IIb fibers and can be converted into IIa fibers. Zoltan Arany and his research group led by Bruce Spiegelman from Harvard Medical School have now shed a little more light on this type of fiber.

The scientists were interested in the role played by a specific transcriptional coactivator, PGC-1beta, in converting muscle fibers into a different fiber type. Such coactivators control the activity of genes via an indirect interaction with other proteins. For example, the coactivator PGC-1alpha is important for the conversion from fast to slow muscle fiber type - but it is not the sole responsible factor. Arany and colleagues now wanted to find out whether PGC-1beta is also involved.

To do this, the researchers developed genetically modified mice whose muscles contained significantly more of the coactivator PGC-1beta than normal. The muscles of the transgenic mice were equipped with significantly more mitochondria than unmodified control mice and were therefore significantly redder. The fiber composition of the muscles was also changed: they consisted of only a few type I, type IIa and type IIb fibers and had all the more type IIx fibers. The genetic manipulation had drastically increased the amount of this actually rare type of fiber and thereby changed the muscle structure significantly.

Since the mice now had so many muscle fibers that generate their energy oxidatively, these rodents should be extremely enduring, the scientists suspected. The running wheel test confirmed the assumption: the little animals endured an average of 32.5 minutes of continuous running - this corresponds to a running distance of 746 meters - before they were at the end of their strength; unmodified mice, on the other hand, collapsed after just 26 minutes and only 516 meters of running distance.

"We have shown that an increased amount of oxidative IIx fibers increases athletic performance in mice," says Arany. This turned normal rodents into marathon mice, which easily cover longer distances than the unmanipulated animals without any special training.

"We have shown that increased levels of oxidative IIx fibers increase athletic performance in mice "

(Zoltan Arany) From these observations, the scientists hope to find new therapeutic approaches for people whose muscles are wasting away due to paralysis, being bedridden or being ill. But many a sports doctor will follow these results and other developments based on them with alert eyes, as they promise a significant increase in performance - which could easily evade doping controls if gene doping should one day be suitable for humans.

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