Muscle cells and plain old "white" fat cells can be coaxed into becoming brown fat cells by treating them with a certain protein, according to a new study.
Brown fat cells burn energy, rather than store it, and the findings could lead to treatments based on using this protein to create more brown fat within people who are genetically predisposed to becoming obese, the researchers said.
"This was really exciting to show that we could induce these cells and increase the amount or activity of brown fat cells," said study researcher Yu-Hua Tseng, an assistant professor of medicine at Harvard Medical School. Though the study was mainly conducted in mice, and much work needs to be done before treatments for humans might come of it, she said, "This could be a way to fight obesity."
Tseng and her colleagues found that up to 95 percent of the cells they isolated from skeletal muscle or from white fat — all specifically chosen because they bore a special marker on their membrane — could be induced to begin the process of turning into brown fat cells.
"Recently, people have started to think that brown fat is more similar to muscle than to white fat," Tseng told MyHealthNewsDaily. But the ways that cells change from one type to another over time are complex processes, she said, and not well understood.
The new study revealed that some cells found within skeletal muscle tissue cannot develop into muscle cells. Instead, these cells could develop into brown fat cells.
The researchers removed white fat and muscle tissue from mice, and then isolated the cells they believed could become brown fat cells. When they exposed these cells, growing in lab dishes, to a protein called BMP-7, the cells began to look and act like brown fat cells.
Further, when they injected these cells back into the mice, they found the cells survived and the number of brown fat cells within the mice increased.
A similar experiment with human cells, which did not involve the step of injecting the cells back into people, also showed the muscle and white fat cells could turn into brown fat cells in lab dishes.
A 2007 study in the journal Proceedings of the National Academy of Sciences showed that, of two genetically-similar types of mice — one of which was prone to becoming obese and the other of which was resistant to becoming obese — the obesity-resistant mice had "islands" of brown fat cells nestled within their skeletal muscle, Tseng said.
"This could very, very likely contribute to the obesity-resistance of these mice," she said.
Previous work by Tseng, published in 2008 in the journal Nature, showed that mice injected with BMP-7 had more brown fat than mice not injected with it.
The researchers also observed that a diabetes drug rosiglitazone could act synergistically with BMP-7, and increase the number of cells induced to become brown fat. The drug is used to treat people with Type 1 diabetes, Tseng said, and is known to promote the development of both brown and white fat.
"As an obesity researcher, I think, for most people, to lose weight you have to exercise," Tseng said. "But for some people genetically-predisposed to obesity, or for who being overweight has caused severe metabolic disorders, this could help them make more brown fat and burn more energy."
The study is published today in the journal Proceedings of the National Academy of Sciences.
Pass it on: Researchers made brown fat cells from muscle cells, and may one day use this strategy as a way to treat obesity.