Tissue-specific knockout defines peroxisome proliferator-activated receptor gamma function in muscle and liver

Although the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed mostly in adipose tissue, it also occurs in skeletal muscle and liver. Mice lacking a functional PPARgamma gene, specifically in muscle, showed increased adiposity with reduced caloric intake, resulting from shunting of lipid to the liver. This result suggested a function for muscle PPARgamma in the up-regulation of muscle lipid metabolism. A study in lipoatrophic mice--that were also defective in the liver PPARgamma gene--suggested that liver PPARgamma functions in the uptake and clearance of fat in that organ. However, PPARgamma in liver has an antidiabetic role, whereas muscle PPARgamma was found to have no part in opposing diabetes.