U.S. Department of Health and Human Services

New Insight into Adult Human Brown Fat Identity

Scientists have shown that adult human brown fat may actually be “beige” fat—a distinct tissue that burns energy and could serve as a potential target for novel therapies for obesity. The human body has been thought to possess two kinds of fat cells: white fat cells, which store fat molecules; and brown fat cells, found most abundantly in infants, which burn calories and generate heat. However, in mice, for many years scientists have observed, embedded in white fat, a third type of fat cell—now called “beige” fat—that shares characteristics of both brown and white fat. While it was clear that beige fat cells resemble brown fat in appearance and function, little was known about their properties, development, and activity. In a recent study, researchers developed methods to isolate and characterize beige fat cells from certain areas of mouse white fat tissue (subcutaneous white fat), and found that they exhibit unique properties, as well as some characteristics of classical brown fat cells. By isolating these cells, the scientists could then carefully define the set of genes that were turned on specifically in beige fat. The scientists also isolated cells that have the potential to become beige fat—cells called “precursors.” They showed that these beige fat precursors were responsive to the hormone irisin, which is known to convert white fat tissue to a more brown fat-like identity. The researchers then utilized their new knowledge from mice to better characterize adult human brown fat deposits, and found that the fat cells within more closely resembled beige fat than they did classical brown fat cells. This greater understanding of beige cell properties may lead to the development of potential therapies for obesity through the activation of energy-burning adult human beige fat tissue.

Wu J, Boström P, Sparks LM, et al. Beige adipocytes are a distinct type of thermogenic fat cell in mouse and human. Cell 150: 366-376, 2012.