PPARβ/δ is probably the less characterized isoform of the PPAR family. It is expressed in a large array of tissues, including central nervous system, liver, adipose tissue, muscles, and the gastrointestinal tract. In skeletal and cardiac muscle PPARβ/δ is expressed at much higher levels than PPARα and PPARγ [74, 75]. Recent studies suggest that, in the adult, PPARβ/δ plays important roles in maintaining the glucose-lipid homeostasis by stimulating fatty acid oxidation and uncoupling of the respiratory chain in the muscle, by inhibiting glucose and VLDL secretion from the liver, by stimulating the cholesterol efflux increasing circulating HDL levels; moreover PPARβ/δ is also implicated in the regulation of the inflammatory activity of macrophages (for recent reviews on the metabolic action of PPARβ/δ see [76, 77]).
