Glucocorticoid-Induced Obesity Develops Independently of UCP1

Summary: An excess of glucocorticoids leads to the development of obesity in both mice and humans, but the mechanism for this is unknown. Here, we determine the extent to which decreased BAT thermogenic capacity (as a result of glucocorticoid treatment) contributes to the development of obesity. Contrary to previous suggestions, we show that only in mice housed at thermoneutrality (30°C) does corticosterone treatment reduce total BAT UCP1 protein. This reduction is reflected in reduced brown adipocyte cellular and mitochondrial UCP1-dependent respiration. However, glucocorticoid-induced obesity develops to the same extent in animals housed at 21°C and 30°C, whereas total BAT UCP1 protein levels differ 100-fold between the two groups. In corticosterone-treated wild-type and UCP1 knockout mice housed at 30°C, obesity also develops to the same extent. Thus, our results demonstrate that the development of glucocorticoid-induced obesity is not caused by a decreased UCP1-dependent thermogenic capacity. : Glucocorticoid treatment induces obesity, and reduced brown fat thermogenesis has been suggested to be the cause. However, Luijten et al. show here that this is not the case, nor is it fully explainable by overeating. Thus, glucocorticoids channel food energy into lipid storage through a currently unexplained pathway. Keywords: uncoupling protein 1, corticosterone, obesity, thermogenesis, energy balance, brown adipose tissue, thermoneutrality, cold exposur