Expression of the chicken peroxisome proliferator-activated receptor-γ gene is influenced by aging, nutrition, and agonist administration

Peroxisome proliferatior-activated receptor-gamma (PPARgamma) is a transcription factor that modulates lipid and glucose metabolism in mammals. The aim of the present study was to investigate whether chicken PPARgamma is expressed in tissues in a similar manner to mammalian PPAR and whether it is involved in the regulation of lipid metabolism, particularly in the regulation of fat accumulation in adipose tissue and ovaries. In 30-wk-old chickens, PPARgamma mRNA was detected in most tissues that were examined. Of those tissues expressing chicken PPARgamma mRNA, the lowest expression levels were found in adipose tissue, the tissue that in mammals was shown to express the highest levels of PPARgamma mRNA. Chicken PPARgamma mRNA expression in abdominal adipose tissue tended to increase with age, as shown by higher expression levels at 6 wk than at 1 and 2 wk of age. With regard to nutritional modulation, PPARgamma mRNA levels in abdominal adipose tissue were significantly higher in wbroiler chickens fed for 7 d a diet containing 8% safflower oil (18:2-rich) or linseed oil (18:3-rich) compared with chickens fed a diet containing olive oil (18:1-rich). In contrast, feeding a 3% cholesterol-supplemented diet for 7 d resulted in no changes to adipose PPARgamma mRNA expression. In broiler chickens orally administered troglitazone, a PPARgamma ligand, abdominal fat pad weight and PPARgamma and lipoprotein lipase (LPL) mRNA levels were significantly increased relative to those of control chickens. Levels of PPARgamma mRNA in liver, skeletal muscle, and ovaries were increased with the onset of egg laying, whereas in adipose tissue the level of PPARgamma mRNA was decreased. These findings suggest that PPARgamma plays an important role in the regulation of fat deposition and egg production and the characteristic pattern of PPARgamma mRNA expression may be indicative of specific differences in the lipid and glucose metabolism of chickens compared with mammals.