Scientists have found a protein that can promote the burning of body fat – a discovery that could lead to new ways to tackle obesity.Mice injected with a protein called BMP7 increased their production of "good" brown fat cells, while keeping their levels of the normal white fat cells constant.
Fat is a crucial part of the body's regulation of metabolism and body temperature. There are two types of fat cell with different functions: the well-known white fat cells, which store energy and contribute to obesity, and lesser-known brown fat cells that burn calories to generate body heat.
Though people are born with a good supply of brown fat cells, these are usually lost after infancy. Reintroducing brown fat could therefore increase the amount of energy a person burns.
In their experiments, Yu-Hua Tseng's team at the Joslin Diabetes Centre at Harvard Medical School looked at the factors that determine the amounts of different types of fat cell in the body. They identified a protein called BMP7 which promotes the creation of brown fat. Without it, the amount of brown fat in mice ran low.
When the protein was administered artificially, it boosted the amount of brown fat and left the white fat unchanged. The results are published today in Nature.
"As we learn more about the controls of brown fat development, medical interventions to increase energy expenditure by brown fat inducing agents, such as BMP7, may provide hope to these individuals in losing weight and preventing the metabolic disorders associated with obesity," said Tseng.
A separate study led by Bruce Spiegelman at the Dana-Farber Cancer Institute in Massachusetts found that brown fat cells can be made from the same precursor tissue that normally produces muscle cells.
Spiegelman found that a molecular switch called PRDM16 regulates the creation of brown fat from immature muscle cells. Turning off the switch in the lab converted brown fat in mice into muscle cells.
Both studies are published in this week's issue of the journal Nature.
"Brown fat can increase energy expenditure and protect against obesity," Spiegelman writes. "The epidemic of obesity, closely associated with increases in diabetes, hypertension, hyperlipidemia, cancer and other disorders, has propelled a major interest in adipose cells and tissues."
The next step, he says, is to find specific drugs and techniques that could help the body make more brown fat cells or else genetically engineer white fat cells to turn brown.
In an accompanying commentary in Nature, Barbara Cannon and Jan Nedergaard, both biologists at Stockholm University, said: "Insights into the developmental origin of brown fat cells are of particular interest because of the ability of these cells to burn fat. But, as is often the case in science, new questions follow new insights."
They add that a thorough understanding the function and creation of brown fat cells could take us closer to the "ultimate goal of promoting the brown fat lineage as a potential way of counteracting obesity."
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