Researchers Make Energy-Burning Fat

Could injections of brown fat treat obesity?

Emily Singerarchive page

July 29, 2009

Researchers have developed a recipe for making brown fat, an energy-burning type of fat found mostly in infants and hibernating animals, and discovered that when injected into mice, it caused the cells to develop into brown fat tissue that burned excess energy. However, it’s not yet clear whether the fat transplant can prevent these animals from gaining weight when on a high-calorie diet. The research was reported online today in the journal Nature.

This is a microscope image of brown fat (e-BAT, or engineered
Brown Adipose Tissue) created by adding a key control switch
to skin cells of mice. Presence of green-stained objects
(droplets of oil stored in the cell) confirms the skin cells have
been converted to brown fat-producing cells. Blue objects are
cell nuclei.
Credit: Shingo Kajimura, Ph.D., Dana-Farber Cancer Institute

White fat–the culprit behind beer bellies and dimpled thighs–stores excess energy from a person’s diet. High levels of white fat, especially around the abdomen, can increase the risk for heart disease and diabetes. The primary role of brown fat, in contrast, is to generate heat, protecting newborns from the cold, for example. Scientists previously thought that only young animals had significant amounts of this tissue, but recent research using positron-emission tomography has shown that adults have a surprising amount of brown fat around the neck and chest. Because these cells burn calories, scientists have been searching for ways to turn up their activity as a potential treatment for obesity.

In the recent study, Bruce Spiegelman and colleagues at the Dana Farber Cancer Institute identified two proteins that work together to trigger development of brown fat. When researchers engineered genes for these two proteins into both mouse and human skin cells, the cells developed into brown fat.

According to a press release from Dana Farber:

The scientists then transplanted these synthetic brown fat precursors, known as eBAT (engineered [brown adipose tissue]), into adult mice to augment their innate stores of brown fat. Tests showed that the brown fat transplants were burning caloric energy at a high rate – energy that otherwise would have been stored as fat in white adipose tissue.
“Since brown fat cells have very high capacity to dissipate excess energy and counteract obesity, eBAT has a very high potential for treating obesity,” said Shingo Kajimura, PhD, lead author of the paper. “We are currently working on this.”
… The experiments did not test whether the extra brown fat actually protected the mice from becoming obese.