SAN ANTONIO — The human body contains more than one type of fat — some better for you than others.
Storing too much unhealthy white fat (which also goes by the fancier name of white adipose tissue) is connected with obesity and diabetes. But researchers from the University of Texas Health Science Center at San Antonio published a study this month in the journal Cell Metabolism about their discovery in mice of a protein that acts as an on-off switch to control the conversion of white fat into a faster-burning type.
“We know that if we want to keep our body lean, we have to get rid of extra nutrients in the body, which means burning more energy,” said Feng Liu, a UTHSC pharmacology professor and senior author of the study, in a written statement.
The protein — called Grb10 — could be a target for scientists to develop drugs to fight obesity and diabetes in humans.
People who think about adipose tissues usually distinguish between two types — white and brown, Liu said. The white version functions mainly to store what we've eaten for later use.
Brown adipose tissue, on the other hand, primarily functions to release energy by converting it to heat. It is stored in smaller droplets and gets its color because the droplets are filled with iron-rich mitochondria.
In the past, scientists thought brown fat was present in the bodies of babies and in rodents but not in adult humans. However, researchers have since discovered small deposits on adults' chests, said co-author Lily Dong, a UTHSC cellular and structural biology professor.
They also found a subset of cells, primarily among white adipose tissue under the skin, that could be induced to act more like brown adipose tissue in its capacity to expend energy. Liu called them “beige” cells.
Liu and his co-authors discovered a naturally occurring feedback mechanism within a molecular pathway called mTORC1, which can become overactivated by consuming too much food. When mTORC1 becomes overactivated in various tissues, it's been linked to increased obesity, shortened lifespan and increased cancer rates.
When the researchers removed the Grb10 protein from the fat tissues of mice, they found that the mice became obese. They had discovered that the Grb10 protein is the mTORC1 pathway's on-off switch, which would have normally played an important role in the “beigeing” process.
“Understanding how beigeing is controlled is so very important, because if we can improve energy expenditure, we can reduce obesity,” Liu said.
Now the researchers say they are working on a new study to engineer an animal that would over-express this protein in adipose tissue to see if, when fed a high-fat diet, the animal would be able to maintain its weight.
Liu said that, by identifying the Grb10 protein as a target for potential drug development for humans, scientists may be able to “either increase the level of the protein or increase the activity of the protein,” which would be beneficial for fighting obesity and cancer and increasing longevity.
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