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Scientists create 'endurance' mouse

May lead to wonder drug for distance athletes

Scientists create 'endurance' mouse

By Kate Tobin
CNN Sci-Tech

BOSTON, Massachusetts (CNN) -- Mighty Mouse lives, and the "new age" version is downright buff.

Researchers say they have created a transgenic mouse with muscles like a marathoner, capable of enduring rigorous exercise for extended periods of time.

While so far the research has only been conducted on mice, scientists say they expect the techniques they've developed to treat the mouse muscle will also work on humans. Doctors say the discovery may one day lead to new treatments for people who are bedridden or have degenerative muscle disease, and could prove to be a wonder drug for endurance athletes like long distance runners or cross country skiers.

Bruce Spiegelman and colleagues at the Dana-Farber Cancer Institute identified a biochemical called PGC-1 that operates as a molecular switch, converting so-called "fast-twitch" muscle, which is strong but tires quickly, into high-endurance "slow-twitch" muscle.

"PGC-1 appears to be the switch, or a major component of it, that enables your body's muscles to adjust to the demands being put on them," said Spiegelman. "Understanding how this system works could make it possible to develop a drug to manipulate this system."

Muscle is made up of a combination of different types of fibers. Endurance athletes train long and hard to build up slow-twitch muscle fibers, called Type I fibers, which are long and lean and can keep pumping for long periods of aerobic exercise. Sprinters or weightlifters, on the other hand, have muscle rich in fast-twitch, Type II fibers. These muscles are bulkier and stronger but tire quickly.

Further studies

To create the endurance mouse, Spiegelman's group bioengineered PGC-1 into mouse muscle tissue. They expected that it would promote the development of cellular power plants called mitochondria, which fuel the growth and development of slow-twitch muscle fiber. But they were surprised to find that PGC-1 appeared to be converting Type II fast-twitch fibers into Type I slow-twitch fibers.

The muscle itself actually changed color, taking on a reddish hue characteristic of oxygen-rich tissue. Further, in an endurance test at a Texas laboratory, the bioengineered muscle turned out to contract efficiently two and a half times longer than regular muscle.

Spiegelman cautions that there is still five to 10 years of work to be done before PGC-1 based treatments will be available.

The research is published in this week's edition of the journal Nature.


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