5-fold, but only 1.6-fold in Cyp7a1-tg mice. In fatty acid synthesis pathway, a FXR target gene fatty acid synthase (FAS) was strongly induced, but the rate-limiting enzyme acetyl-CoA carboxylase (ACC) was induced only 90% in Cyp7a1-tg mice versus WT mice. However, microarray analysis did not indicate differential expression of any fatty acid synthesis genes, and IPA did not identify fatty acid metabolism as a top regulated pathway. Interestingly, mRNA levels of CD36, a major hepatic fatty selleckchem acid transporter, were reduced in Cyp7a1-tg. Peroxisome proliferator-activated
receptor gamma (PPARγ), involved in the induction of hepatic fatty acid synthesis, was markedly reduced in both chow- and WD-fed Cyp7a1-tg mice. Liver pyruvate kinase (L-PK) and carbohydrate
response element-binding protein (ChREBP), involved in lipogenesis, were increased in chow-fed, but Selleck MK2206 decreased in WD-fed, Cyp7a1-tg mice, compared to respective WT mice. These data suggest that reduced free fatty transport to hepatocytes and fatty acid synthesis in hepatocytes may prevent hepatic steatosis in Cyp7a1-tg mice. Given that induction of hepatic bile acid synthesis in Cyp7a1-tg mice is associated with increased expression of cholesterologenic and lipogenic genes, we injected 14C-labeled sodium acetate to chow-fed WT and Cyp7a1-tg mice to study hepatic fatty acid and cholesterol synthesis rate. As estimated by pmole of 14C-acetate incorporated into fatty acids and sterols, Fig.
1A shows that acetyl-CoA was mainly used for fatty acid synthesis in WT liver. Interestingly, cholesterol synthesis rate was increased ∼12-fold, whereas fatty acid synthesis rate was decreased ∼60% in Cyp7a1-tg mice, resulting in approximately equal incorporation of 14C-acetate into cholesterol and fatty acids. During the postprandial state, acetyl-CoA derived from glycolysis is used for both lipogenesis and cholesterologenesis. Induction this website of cholesterol synthesis provides cholesterol substrate to stimulate CYP7A1 activity and bile acid synthesis and, subsequently, stimulates fecal excretion of cholesterol and bile acids. To test the potential contribution of this route to hepatic lipid metabolism, we administered 14C-glucose to mice and measured 14C radioactivity in fecal neutral and acidic sterols. Figure 1B shows that fecal 14C radioactivity in neutral, acidic, and total sterols was markedly and rapidly increased in day 1 in Cyp7a1-tg mice, compared to WT mice. Fecal samples from Cyp7a1-tg mice contained significantly higher 14C radioactivity, accounting for ∼15% of 14C-glucose administered, compared to WT mice feces, which contained only ∼2% of 14C-glucose administered. In addition, the majority of fecal 14C radioactivity was recovered as neutral sterols. Fecal acidic sterols (bile acids) were increased 2-fold in Cyp7a1-tg mice.