Modulation of regulatory factors involved in cholesterol metabolism in response to feeding of pravastatin- or cholesterol-supplemented diet in chickens

mRNA transcripts encoding multiple proteins from the cholesterol biosynthetic and uptake pathways in livers are controlled by sterol regulatory element binding protein-2 (SREBP-2), a membrane-bound mammalian transcription factor. The aims of the present study were to investigate whether SREBP-2 responds to plasma cholesterol levels and modulates expression of factors involved in the cholesterol metabolism of chickens. Supplementing the diets of chickens with 0.1% pravastatin, a drug used to control hypercholesterolemia, decreased plasma LDL-cholesterol concentrations. It also increased levels of the nuclear forms of SREBP-2 and increased gene expression of 3-hydroxy-3- methylglutaryl CoA reductase (HMGR) and low-density lipoprotein receptor (LDLr) in livers, relative to a control group. In contrast, feeding of 3% cholesterol-supplemented diet increased plasma total- and LDL-cholesterol concentrations but decreased levels of nuclear forms of SREBP-2 and reduced gene expression of HMGR and LDLr. However, the LDL-binding activities of chicken liver membranes were not affected by plasma cholesterol concentrations or by hepatic levels of the nuclear form of SREBP-2. LDL-binding proteins were detected as bands of 90 and 515 kDa on a ligand blot and the intensity of these bands was unaffected by pravastatin and cholesterol supplementation. These findings suggest that the cholesterol biosynthetic pathway is regulated by the nuclear form of SREBP-2 in chickens as well as in mammals, but that there may be species-specific differences in the regulatory mechanisms of hepatic cholesterol uptake.