The peroxisome proliferator-activated receptor alpha (PPARalpha) regulates bile acid biosynthesis

Fibrates are a group of hypolipidemic agents that efficiently lower serum triglyceride levels by affecting the expression of many genes involved in lipid metabolism. These effects are exerted via the peroxisome proliferator-activated receptor alpha (PPARalpha). In addition, fibrates also lower serum cholesterol levels, suggesting a possible link between the PPARalpha and cholesterol metabolism. Bile acid formation represents an important pathway for elimination of cholesterol, and the sterol 12alpha-hydroxylase is a branch-point enzyme in the bile acid biosynthetic pathway, which determines the ratio of cholic acid to chenodeoxycholic acid. Treatment of mice for 1 week with the peroxisome proliferator WY-14,643 or fasting for 24 h both induced the sterol 12alpha-hydroxylase mRNA in liver. Using the PPARalpha knockout mouse model, we show that the induction by both treatments was dependent on the PPARalpha. A reporter plasmid containing a putative peroxisome proliferator-response element (PPRE) identified in the rat sterol 12alpha-hydroxylase promoter region was activated by treatment with WY-14,643 in HepG2 cells, being dependent on co-transfection with a PPARalpha expression plasmid. The rat 12alpha-hydroxylase PPRE bound in vitro translated PPARalpha and retinoid X receptor alpha, albeit weakly, in electrophoretic mobility shift assay. Treatment of wild-type mice with WY-14,643 for 1 week resulted in an increased relative amount of cholic acid, an effect that was abolished in the PPARalpha null mice, verifying the functionality of the PPRE in vivo.