Prolonged dietary treatment with conjugated linoleic acid stimulates porcine muscle peroxisome proliferator activated receptor γ and glutamine-fructose aminotransferase gene expression in vivo

Peroxisome proliferator activated receptors (PPARs) represent a family of DNA binding proteins that are activated by a variety of dietary and endogenous fatty acids. The PPAR proteins are expressed throughout the body and are the target of a variety of lipidaemic and insulin sensitizing drugs. Conjugated linoleic acid (CLA) is a collective name for octadecadienoic acid isomers with conjugated double bonds, which can also act as ligands for some of the PPAR family. To gain better understanding of the long-term effects of PPAR activation, CLA was fed at 11 g/kg of feed for 45 days to castrated male pigs (barrows). These barrows had a significant repartitioning of subcutaneous fat to lean tissue in the carcass: fat was reduced by 9.2% and lean muscle was increased by 3.5%, but intramuscular fat content was also increased by 14% (P<0.05). PPARgamma, glutamine-fructose aminotransferase (GFAT), adipocyte fatty acid binding protein (AFABP), but not PPARalpha mRNA levels were significantly increased (P<0.05) in the CLA-fed pigs. The increased expression of PPAR7 and AFABP indicates that CLA induced the development of preadipocytes from stromal-vascular (s-v) stem cells to promote intramuscular fat content. The increase in the expression of GFAT mRNA indicates that the glucose supply of the muscle cells had been increased with the CLA diet, possibly sparing intramuscular fatty acid reserves.