This is the first time that PGC-1 has been completely removed from muscle tissue, providing researchers with a new model to unravel the protein's role in muscle development, exercise and metabolism. So what happens to mice with muscles short on PGC-1? Their mitochondria - the part of the cell that converts fuel into energy - can't function properly, so cells have to work harder to stay vigorous. This extra effort rapidly depletes carbohydrate fuel stores, leading to premature fatigue. In short, PGC-1 is necessary for exercise, but not normal muscle development and activity.

But these mice held another surprise. PGC-1-deficient couch potato mice were not obese and still respond normally to insulin - meaning they are not at risk for developing diabetes despite their sedentary lifestyles and mitochondrial problems. This was unexpected because many scientists believe that dysfunctional mitochondria trigger a cascade of insulin resistance and diabetes. This study dispels that notion, instead suggesting that perhaps malfunctioning mitochondria are a result of diabetes, rather than a cause.

"Lo and behold, even though these animals couldn't run, they showed no evidence of insulin resistance," Dr. Kelly said. "We are now investigating what happens when we boost PGC-1 activity intermittently, as normally occurs when a person exercises."

Source: Sanford-Burnham Medical Research Institute