Insights into Energy-Burning Fat Cells

NIH | APRIL 18, 2015

Humans have 2 main types of fat: white and brown. White fat, which tends to be located under the skin and around internal organs, stores excess calories. Too much white fat, a characteristic of obesity, increases the risk of several metabolic disorders.

Researchers have identified a specific type of fat cell, known as beige, that has some characteristics of brown fat. Beige fat cells appear in white fat in response to specific triggers such as cold.

Since beige and brown fat cells are able to burn calories, they could potentially serve as targets for therapies to try to reduce obesity and its associated disorders. Brown fat, however, can be difficult to find in adult humans, and its origin isn’t clear.

A team of researchers led by Dr. Shingo Kajimura at the University of California, San Francisco, set out to determine the nature of brown and beige fat from adult humans, and to better characterize it at a cellular level.

The group obtained cells from biopsies from the shoulder area of 2 normal weight adults and grew them in culture dishes. They then identified specific populations of cells with a protein marker of brown fat cells known as uncoupling protein 1 (UCP1).

The scientists surveyed genes that were active in the human fat cells and found that they were similar to those active in mouse beige fat cells, but not in mouse brown fat cells. Novel genes whose expression marked human beige cells included KCNK3 and MTUS1. Analysis of these 2 genes in mice revealed that they were required for beige fat cells to become brown fat cells and to burn energy to create heat.

The group plans to use the beige fat cells to screen different molecules to determine how to stimulate the heat-producing activity of human brown fat.

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