"Good" fat may be new weapon in obesity fight

CHICAGO (Reuters) - A new understanding of the origins of brown fat cells -- the "good" kind of fat that burns energy and keeps us warm -- may lead to new treatments for obesity, two research teams reported on Wednesday.

Researchers at the Dana-Farber Cancer Institute in Boston said they used a single molecular switch to turn immature muscle cells into brown fat cells in the lab, suggesting that brown fat may be more akin to muscle cells than conventional white fat cells.

A second team from the Joslin Diabetes Center in Boston, found a protein important for bone growth helped promote the development of brown fat tissue in mice.

Both teams, reporting in the journal Nature, said their new findings lend understanding about the origins of brown fat, which releases energy, in contrast to conventional white fat, which stores energy.

A person who is obese has large stores of white fat, and researchers think if they can coax the body into making more calorie-burning brown fat, this might help people obese people lose weight.

Dana-Farber's Bruce Spiegelman, who worked on the research, said in a telephone interview that researchers have been trying to find the genes that turn brown fat cells on.

Spiegelman said his team previously found that PRDM16, a kind of genetic switch called a gene transcription factor, appears to regulate the development of brown fat cells.

"What we show in this paper is kind of a big shock. We show that brown fat is derived from a muscle-like cell, and that brown fat and white fat are completely different," he said.

When Spiegelman's team removed PRDM16 from immature brown fat cells in the lab, something strange happened.

"The dish filled up with muscle," Spiegelman said. "What it means is that muscle cells are precursor cells to brown fat cells."

Previously, his team also showed that PRDM16 could turn conventional white fat cells into brown fat cells, but Spiegelman thinks in living creatures, the muscle cell is a natural cell type that gives rise to brown fat cells.

His team is now looking for a drug that could chemically stimulate PRDM16 to make more brown fat cells, which would shift the metabolism into more of a fat-burning mode.

In a separate finding, a team led by Yu-Hua Tseng of the Joslin Diabetes Center found the protein BMP-7, known for inducing bone growth, can also promote the development of brown fat cells.

When Tseng's team delivered this protein into mice through a virus, the mice made more brown fat tissue.

And they found mice that developed extra brown fat tissue gained less weight than other mice, suggesting a potential use in weight loss.

The researchers were also able to get mice to develop extra brown fat cells by pre-treating immature brown fat cells with BMP-7 and transplanting them into the mice.

"We hope this study can be translated into applications to help treat or prevent obesity," Tseng said in a statement.

(Editing by Cynthia Osterman)