Scientists discover protein that acts as on; off switch for fat

WASHINGTON In America's endless search for a magic pill to shrinkthe waistline, researchers have found a "fat switch"-a protein thatcauses developing cells to become either muscle or fat.

But unfortunately, the "fat switch" protein does not offer thepromise of an eternally slim body, say University of Michigan MedicalSchool researchers.

"If you could see my midriff, you would know that breaks myheart," says Ormond A. MacDougald, one of the scientists.

In a study appearing today in the journal Science, co-authorsMacDougald and Sarah E. Ross report that a protein called Wnt 10bacts as a molecular switch to determine which developing cells becomefat and which become muscle.

MacDougald said that fat and muscle cells evolve from what arecalled precursor cells. The ultimate destiny in the body of some ofthese precursor cells is determined by a family of 18 proteins calledWnts.

MacDougald and Ross found that one of these proteins, Wnt 10b,appears to regulate production of muscle cells. When Wnt 10b linkswith certain precursor cells, they develop into muscle. But when theWnt protein is missing, the same cells will turn into fat.

In effect, said MacDougald, Wnt 10b acts as "a molecular switch toturn on either fat or muscle."

MacDougald said the action of the Wnt protein is local, affectingonly a few cells in its vicinity. It does not work like a hormonethat travels through the blood stream and affects billions of cells.

As a result, he said, Wnt 10b is unlikely to be developed into ananti-fat pill.

"Our findings will be important in learning how obesity develops,but the Wnt protein will not be a target for an anti-obesity drug,"MacDougald said.

Instead, he predicted that the best target for a magic slimnesspill would be one that controls appetite-not one that controls howthe body makes fat or muscle.