Molecular characterization and expression of angiopoietin-like protein 3 in the chicken, Gallus gallus

Angiopoietin-like protein 3 (ANGPTL3) is a 70 kDa secretory glycoprotein, which has been identified as a plasma triacylglycerol (TG)-increasing factor in KK/San mice. In this study, we have characterized the expression profile and activity of ANGPTL3 in the chicken, Gallus gallus. This is the first report of this protein in a pre-mammalian species and reveals novel details about the molecular structure of, and specific features of the expression of, important molecules in lipid metabolism. Recombinant chicken ANGPTL3 inhibited chicken lipoprotein lipase activity in vitro and increased plasma TG concentrations in vivo. Chicken ANGPTL3 mRNA expression was detected only in the liver. ANGPTL3 mRNA expression was significantly higher in mature (i.e. egg producing) chickens than in immature chickens. However, this increase was not associated with estradiol, although estradiol does enhance triacylglycerol and very low density lipoprotein secretion by the chicken liver. Changes in chicken ANGPTL3 mRNA expression with nutritional state were examined. ANGPLT3 expression was affected by certain nutritional treatments, i.e. fasting and re-feeding, and ANGPTL3 gene expression in the livers of chickens fed a cholesterol-supplemented diet was lower than that in the livers of chickens fed a control diet. The present study is the first to molecularly characterize and analyze the gene expression of ANGPTL3, and suggests that in avian species ANGPTL3 plays a key role in lipid delivery to the yolk.