Eating grapefruit, climbing stairs, counting carbs--you've tried everything to shed the extra pounds. But still that stubborn paunch persists. Researchers might be one step closer to a solution for this persistent fat. They have found a way to turn ordinary skin cells into a type of fat that burns rather than stores calories. These cells might one day be used to help curb our rapidly expanding waistlines.
When most people think of body fat, they picture the whitish goo in love handles and saddlebags. These white fat cells store energy. Brown fat cells, on the other hand, burn energy and release heat. Scientists have known for decades that newborns and other baby animals have brown fat deposits that help them keep warm. Earlier this year, researchers discovered that adults possess functional brown fat too. Because brown fat burns calories, scientists have been searching for a way to harness it to fight obesity and obesity-related diabetes.
Bruce Spiegelman, a cell biologist at Harvard University, and colleagues took an important step in this direction last year when they published research suggesting that brown fat arises from muscle precursors. A key protein called PRDM16 appears to be involved in the transformation. When the researchers prompted muscle cells to manufacture PRDM16, they became brown fat cells. The process worked in reverse as well: Blocking expression of PRDM16 in brown fat cells led to the creation of muscle cells.
Now the researchers have more information about how the transformation works. In their latest paper, which appears online today in Nature, Spiegelman and colleagues report that a partner protein called C/EBP-beta binds to PRDM16. "With those two factors, you can go away from muscle and convert connective tissue cells to brown fat, too," Spiegelman says. Indeed, when the researchers engineered connective tissue cells from mouse and human skin to produce PRDM16 and C/EBP-beta, they became fully functional brown fat. Moreover, after the team injected the cells into mice, they behaved like brown fat, sopping up glucose.
Spiegelman's team has yet to show that the cells spur mice to shed weight--that's one of the next steps. But if further research pans out, a physician might one day be able to collect a patient's skin cells, turn them into brown fat cells, and then inject those fat cells back into the patient to promote weight loss.
Leslie Kozak, a molecular geneticist at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, calls the experiment "elegant," but he says that "the application is really a long way off--if ever." He points out that natural brown fat cells can turn on and off. The cells Spiegelman and colleagues produced, in contrast, seemed to be constantly producing heat. So one concern is that if enough synthetic cells were transplanted into a person to spark weight loss, fever might result. "Chronic fever would not be a good thing at all," says Kozak.
Other hurdles remain, such as determining the proper dose of brown fat cells. For now, says Clay Semenkovich, an endocrinologist at Washington University in St. Louis, Missouri, the idea remains an "exciting fantasy."
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