ERRγ is essential for maintaining brown fat's function
Fat tissue in our bodies possesses multiple functions. There are mainly two types of fat tissue in our bodies: white fat and brown fat. White fat serves as heat insulation, mechanical cushion, and a source of energy. If an individual accumulates too much white fat, he/she may have obesity and increased risk of other relevant diseases. For this reason, white fat is also referred to as 'bad fat'. In contrast, brown fat is believed to be 'good fat', because this type of fat tissue burns calories to make heat and helps the body respond to cold. Brown fat is prevalent in infants but less abundant in adults.
Scientists from Salk Institute for Biological Studies in the USA recently identify the estrogen-related receptor gamma (ERRγ)
as a critical factor for maintaining brown fat identity. ERRγ is a nuclear receptor that belongs to the subfamily of estrogen-related receptors. Other members of this receptor family include ERRα and ERRβ. ERRγ is known to play a role in different tissues including muscle and the pancreas. Moreover, ERRγ is highly expressed in brown fat. But its role in brown fat has not been fully understood. The Salk study now provides insights into this question.
Previous studies have shown that brown fat has a different gene expression signature compared with white fat. Brown fat cells express high levels of genes involved in fatty acid oxidation and thermogenesis, and are rich in mitochondria (the energy factories of cells). In this work, Salk scientists discovered that ERRγ is constitutively expressed in brown fat cells but not in white fat cells and that ERRγ drives a transcriptional network of thermogenic genes in the basal state.
In mice that lacked ERRγ, brown fat cells were similar to white fat cells. Further, these animals were unable to maintain their body temperature, and this inability severely compromised their survival under cold conditions.
Taken together, these data reveal that ERRγ helps maintains the identity of brown fat. More specifically, ERRγ serves as a key factor in maintaining the gene expression signature, morphology, and physiological function of brown fat.
The study extends our understanding of brown fat biology and would have implications for the development of drugs that treat obesity and related disorders. But many questions regarding ERRγ's role still remain, for instance, whether expressing ERRγ in white fat could change its identity and function.
The full paper (ERRγ Preserves Brown Fat Innate Thermogenic Activity) is published in this week's issue of the journal Cell Reports.
Other research institutions involved in the study include the University of California in the USA, école Polytechnique Fédérale de Lausanne in Switzerland, and the University of Sydney in Australia.