Saturday, July 6, 2013

Fat Cells React To Cold Temperatures By Burning Calories For Heat, New Research Suggests

Transforming fat cells into calorie-burning machines may sound like the ultimate form of weight control, but the idea is not as far-fetched as it sounds. Unexpectedly, some fat cells directly sense dropping temperatures and release their energy as heat, according to a new study; that ability might be harnessed to treat obesity and diabetes, researchers suggest.
Fat is known to help protect animals from the cold—and not only by acting as insulation. In the early 1990s, scientists studying mice discovered that cold temperatures trigger certain fat cells, called brown adipose tissue, to release stored energy in the form of heat—to burn calories, in other words. Researchers have always assumed this mechanism was an indirect response to the physiological stress of cold temperatures, explains cell biologist Bruce Spiegelman of Harvard Medical School, Boston. The activation of brown fat seems to start with sensory neurons throughout the body informing the brain of a drop in temperature. In response the brain sends out norepinephrine, the chief chemical messenger of the sympathetic nervous system, which mobilizes the body to cope with many situations. In experimental animals, stimulating norepinephrine receptors triggered brown adipose tissue to release its energy and generate heat, while animals bred to be missing these receptors were unable to mount the same fat cell response.
People also have brown adipose tissue that generates heat when the body is cold. And unlike white fat, which builds up around the abdomen and contributes to many disorders including heart disease and diabetes, this brown fat is found in higher proportions in leaner people and seems to actively protect against diabetes.
In brown fat, the heat-generating process depends on a protein called UCP1; the protein is also thought to be central in brown fat's ability to prevent diabetes. Researchers are now exploring ways of activating this molecular pathway. But in trying to figure out exactly how fat cells respond to the body being cold, Spiegelman and colleagues discovered that plain old "white" fat cells have a few surprises left. In a study appearing online today in the Proceedings of the National Academy of Sciences, the researchers exposed various kinds of fat cells to cold temperatures directly. "We were a little surprised that no one had tried this before," Spiegelman says.
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