Disruption of the sterol 27-hydroxylase gene in mice results in hepatomegaly and hypertriglyceridemia - Reversal by cholic acid feeding

Sterol 27-hydroxylase (CYP27) participates in the conversion of cholesterol to bile acids, We examined lipid metabolism in mice lacking the Cyp27 gene . On normal rodent chow, Cyp27(-/-) mice have 40% larger livers, 45% larger adrenals, a-fold higher hepatic and plasma triacylglycerol concentrations, a 70% higher rate of hepatic fatty acid synthesis, and a 70% increase in t he ratio of oleic to stearic acid in the liver versus Cyp27(+/+) controls, In Cyp27(-/-) mice, cholesterol 7 alpha -hydroxylase activity is increased B-fold, but bile acid synthesis and pool size are 47 and 27%, respectively, of those in Cyp27(+/+) mice, Intestinal cholesterol, absorption decreases from 54 to 4% in knockout mice, while fecal neutral sterol excretion increa ses 2.5-fold, A compensatory 2.5-fold increase in whole body cholesterol sy nthesis occurs in Cyp27(-/-) mice, principally in liver, adrenal, small int estine, lung, and spleen. The mRNA for the cholesterogenic transcription fa ctor sterol regulatory element-binding protein-2 (SREBP-2) and mRNAs for SR EBP-2-regulated cholesterol biosynthetic genes are elevated in livers of mu tant mice. In addition, the mRNAs encoding the lipogenic transcription fact or SREBP-1 and SREBP-1-regulated monounsaturated fatty acid biosynthetic en zymes are also increased. Hepatic synthesis of fatty acids and accumulation of triacylglycerols increases in Cyp27-/- mice and is associated with hype rtriglyceridemia. Cholic acid feeding reverses hepatomegaly and hypertrigly ceridemia but not adrenomegaly in Cyp27(-/-) mice, These studies confirm th e importance of CYP27 in bile acid synthesis and they reveal an unexpected function of the enzyme in triacylglycerol metabolism.