Brown Adipose Tissue PPARγ Is Required for the Insulin-Sensitizing Action of Thiazolidinediones

Brown adipose tissue (BAT) plays a critical role in metabolic homeostasis. BAT dysfunction is associated with the development of obesity through an imbalance between energy expenditure and energy intake. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is the master regulator of adipogenesis. However, the roles of PPARγ and thiazolidinediones (TZDs) in the regulation of BAT metabolism remain unclear. TZDs, which are selective PPARγ activators, improve systemic insulin resistance in animals and humans. In the present study, we generated brown adipocyte-specific PPARγ-deficient mice (BATγKO) to examine the in vivo roles of PPARγ and TZDs in BAT metabolism. In electron microscopic examinations, brown adipocyte-specific PPARγ deletion promoted severe whitening of brown fat and morphological alteration of mitochondria. Brown adipocyte-specific PPARγ deletion also reduced mRNA expression of BATselective genes. Although there was no difference in energy expenditure between control and BATγKO mice in calorimetry, norepinephrine-induced thermogenesis was impaired in BATγKO mice. Moreover, pioglitazone treatment improved diet-induced insulin resistance in the control mice but not in the BATγKO mice. These findings suggest that BAT PPARγ is necessary for the maintenance of brown adipocyte function and for the insulin-sensitizing action of TZDs.