The white adipose organ is composed of both subcutaneous and several intra-abdominal depots. Excess abdominal adiposity is a major risk factor for metabolic disease in rodents and humans, while expansion of subcutaneous fat does not carry the same risks. Brown adipose produces heat as a defense against hypothermia and obesity, and the appearance of brown-like adipocytes within white adipose tissue depots is associated with improved metabolic phenotypes. Thus, understanding the differences in cell biology and function of these different adipose cell types and depots may be critical to the development of new therapies for metabolic disease. Here, we found that Prdm16, a brown adipose determination factor, is selectively expressed in subcutaneous white adipocytes relative to other white fat depots in mice. Transgenic expression of Prdm16 in fat tissue robustly induced the development of brown-like adipocytes in subcutaneous, but not epididymal, adipose depots. Prdm16 transgenic mice displayed increased energy expenditure, limited weight gain, and improved glucose tolerance in response to a high-fat diet. shRNA-mediated depletion of Prdm16 in isolated subcutaneous adipocytes caused a sharp decrease in the expression of thermogenic genes and a reduction in uncoupled cellular respiration. Finally, Prdm16 haploinsufficiency reduced the brown fat phenotype in white adipose tissue stimulated by β-adrenergic agonists. These results demonstrate that Prdm16 is a cell-autonomous determinant of a brown fat-like gene program and thermogenesis in subcutaneous adipose tissues.
IntroductionThe rise in the incidence of obesity has driven a public health crisis because excess adiposity predisposes to cardiovascular disease, type 2 diabetes, hypertension, stroke, and many cancers (1, 2). Since weight gain is almost always caused by chronic energy imbalance, nonsurgical therapy for obesity must reduce energy intake and/or increase energy expenditure.There are 2 major types of adipose tissues in mammals, white and brown. White adipose tissue (WAT) is highly adapted to store excess energy in the form of triglycerides. Conversely, brown adipose tissue (BAT) oxidizes chemical energy to produce heat as a defense against hypothermia and obesity. WAT develops in distinct intra-abdominal depots and in the subcutaneous layer (between the fascia and muscle). The accumulation of intra-abdominal, visceral WAT, rather than total adiposity, is most strongly correlated with elevated risk for metabolic dysfunction and cardiovascular disease (3-8). By contrast, expansion of subcutaneous WAT, even in the setting of obesity, has been suggested to promote insulin sensitivity in rodents and humans (9)(10)(11)(12)(13)(14). Implantation of subcutaneous WAT, but not visceral WAT, into the abdominal cavity of mice improves whole-body metabolism (15, 16). Moreover, subcutaneous and visceral WAT express unique gene signatures (17). These data suggest that some of the distinct metabolic effects of subcutaneous and visceral WAT are cell autonomous. However, the ...