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Research

Calorie-burning “Beige Fat” Identified

7.12.12

Bruce Spiegelman

Bruce Spiegelman

Photograph by Sam Ogden/Dana-Farber Cancer Institute

“White fat” cells store excess calories; “brown fat” cells, found primarily in infants, burn energy. Now a team of scientists at Dana-Farber Cancer Institute (DFCI), led by Korsmeyer professor of cell biology and medicine Bruce Spiegelman, has identified “beige fat,” another energy-burning but genetically distinct fat cell in adult humans that may have therapeutic potential in the fight against obesity and diseases such as diabetes. The team’s report was published online today by Cell, in advance of the journal’s July 20 print issue.

Beige fat cells are found in scattered pea-sized deposits beneath the skin near the collarbone and along the spine in human adults, according to the DFCI press release. A 2008 paper from Spiegleman’s lab proposed the existence of this third type of fat, but the Dana-Farber team is the first to locate deposits and determine their unique genetic profile. The team issuing the new paper—led by first author Jun Wu, instructor in cell biology, with Spiegelman as senior author—also discovered that the beige fat cells are specifically targeted by the hormone irisin, which muscle cells express during exercise. Irisin not only turns on the genetic machinery that converts white fat into brown fat, but also improves glucose tolerance and leads to weight loss in obese, prediabetic mice.

In previous research, Spiegelman found that brown fat cells are born from stem cell precursors that also produce muscle cells. Beige fat, instead, forms within deposits of white fat cells from beige cell precursors. But both brown and beige fat cells contain mitochondria, energy-burning organelles that contain iron and cause the cells’ distinct color. A key difference is that

brown fat cells express high levels of UCP1—a protein required by mitochondria to burn calories and generate heat—while beige cells normally express low levels of it. Beige cells can, however, turn on high levels of UCP1 in response to cold or certain hormones like irisin, enabling beige fat to burn calories nearly as effectively as brown fat.

Ember Therapeutics, a biotech company founded by Spiegelman, plans to develop irisin as a therapy for obesity and diabetes, under license from Dana-Farber. “Going forward,” Spiegelman said, “what you want to study for potential therapies are the beige fat cells in these ‘hotspots’ we’re all walking around with.”

For further details on beige fat, read the Dana-Farber press release. The paper’s authors include researchers from Maastricht University Medical Center in the Netherlands, Göteborg University in Sweden, and the University of Turku in Finland; their research was supported in part by grants from the National Institute of Health and the American Heart Association.

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