Scientists Cut Through the Secrets of Fat

A scissors-like enzyme gives fat cells the room they need to grow

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By Randy Dotinga
HealthDay Reporter

THURSDAY, May 4, 2006 (HealthDay News) -- Why is fat so fattening?

Scientists think they've uncovered part of the answer in an enzyme that allows fat cells to cut through surrounding tissue and balloon in size.

The research is preliminary and only in mice, so it's not clear if the enzyme would work the same way in humans. But if it does, the findings could open the door to new and better obesity treatments.

"We really don't know if the enzyme is critical in human obesity, but there's a very strong possibility," said study author Dr. Tae-Hwa Chun, a research investigator of molecular medicine and genetics at the University of Michigan.

While it doesn't have the greatest reputation today, fat is actually crucial to the life of many animals, including humans, because it is an efficient means of storing food energy. Unfortunately, too much fat can also lead to a variety of health woes.

Chun and colleagues stumbled upon their findings while studying how a specific enzyme affects blood vessel formation. They genetically engineered mice to not have the enzyme and discovered something unusual: all the mice were skinny.

The researchers report their findings in the May 5 issue of Cell.

According to Chun, the enzyme -- called membrane-anchored metalloproteinase (MT1-MMP) -- appears to act as a kind of scissors, cutting through a web of collagen fibers that surround certain fat cells. As a result, fat cells can "expand or migrate out into that space," he explained.

In mice lacking the enzyme, fat cells took up just 5 percent of the space they would have normally, he said.

The raises the possibility that inhibiting MT1-MMP could help zap away 95 percent of fat deposits in humans. However, Chun cautioned that tests in people are still years away, and there aren't currently any drugs out there that block the enzyme.

It's also not clear what "thinner" fat cells might mean for the body's metabolism, Chun said. His team noted that the genetically engineered mice produced only a slight amount of a crucial hormone called leptin -- a major player in how the body processes fuel.

Future tests will examine what happens when levels of MT1-MMP are reduced, but not eliminated, in mice, Chun said.

More information

Which U.S. states are fattest? The U.S. Centers for Disease Control & Prevention have the answer.

SOURCES: Tae-Hwa Chun, M.D., Ph.D., research investigator, molecular medicine and genetics, department of internal medicine, University of Michigan, Ann Arbor; May 5, 2006, Cell

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