Brown fat: the next weapon against obesity?

Researchers in the US and Canada have identified the factors that regulate the formation of two distinct types of fat — brown and white — which could lead to new therapies to tackle obesity.

Love or hate it, fat is essential for maintaining our energy balance and helping to regulate body temperature. White fat acts as an energy store whereas brown fat helps burn calories to generate body heat, which can increase energy expenditure and reduce weight gain.

Now the results of two related studies, published as separate papers in Nature this week, show that the origin and destiny of brown fat cells is different to white fat cells, despite similarities in appearance. In fact, brown fat cells share a developmental pathway with muscle cells.

Bruce Spiegelman of the Harvard Medical School in Boston, Massachusetts, and colleagues showed that brown and white fat cells develop from distinct cell types in the early embryo and, by tracking the fate of these cells, observed the common developmental pathway of muscle and brown fat cells. They also identified PRDM16 as the transcriptional factor that regulates the switch between muscle and fat; in its absence brown fat precursor cells become muscle, but in excess these cells become brown, but not white, fat.

Yu-Hua Tseng, also of the Harvard Medical School, and colleagues identified bone morphogenetic protein 7 (BMP7) as the factor that uniquely promotes brown fat development. They showed that in mouse embryos lacking BMP7, stocks of brown fat run low. Mouse embryos with an excess of BMP7, however, exhibit a marked increase in brown fat whereas the amount of white fat remains normal.

Commenting in a related ‘News and Views’ article, Barbara Cannon and Jan Nedergaard of Stockholm University in Sweden note that: “Determining how brown fat cells form is … of broad interest, because mimicking this process could have potential use as a treatment for obesity.”