Objective-Loss-of-function mutations in human hepatocyte nuclear factor 4␣ (HNF4␣) are associated with maturity-onset diabetes of the young and lipid disorders. However, the mechanisms underlying the lipid disorders are poorly understood. In this study, we determined the effect of acute loss or augmentation of hepatic HNF4␣ function on lipid homeostasis. Methods and Results-We generated an adenovirus expressing LacZ (Ad-shLacZ) or short hairpin RNA of Hnf4␣ (Ad-shHnf4␣). Tail vain injection of C57BL/6J mice with Ad-shHnf4␣ reduced hepatic Hnf4␣ expression and resulted in striking phenotypes, including the development of fatty liver and a Ͼ80% decrease in plasma levels of triglycerides, total cholesterol, and high-density lipoprotein cholesterol. These latter changes were associated with reduced hepatic lipogenesis and impaired very-low-density lipoprotein secretion. Deficiency in hepatic Hnf4␣ did not affect intestinal cholesterol absorption despite decreased expression of genes involved in bile acid synthesis. Consistent with the loss-of-function data, overexpression of Hnf4␣ induced numerous genes involved in lipid metabolism in isolated primary hepatocytes. Interestingly, many of these HNF4␣-regulated genes were not induced in wild-type mice that overexpressed hepatic Hnf4␣. Because of selective gene regulation, mice overexpressing hepatic Hnf4␣ had unchanged plasma triglyceride levels and decreased plasma cholesterol levels. Conclusion-Loss of hepatic HNF4␣ results in severe lipid disorder as a result of dysregulation of multiple genes involved in lipid metabolism. In contrast, augmentation of hepatic HNF4␣ activity lowers plasma cholesterol levels but has no effect on plasma triglyceride levels because of selective gene regulation. N uclear receptors are ligand-activated transcription factors that regulate diverse physiological processes such as reproduction, development and metabolism. Hepatocyte nuclear factor 4␣ (HNF4␣, NR2A1) is a member of the nuclear receptor superfamily. It is highly expressed in the liver, with lower levels in the kidney, intestine, and pancreatic ␤ cells. 1,2 Like other members of the nuclear receptor superfamily, HNF4␣ has a highly conserved DNA-binding domain and a variable ligand-binding domain. However, HNF4␣ is known to be constitutively active. Structural analysis of the ligand-binding domain of HNF4␣ indicates the C14 to C18 long-chain fatty acids are tightly bound to the hydrophobic pocket 3,4 and cannot be dissociated from the receptor under nondenaturing conditions. 4 Recent data also show that linoleic acid selectively occupies the binding pocket of ligand-binding domain but does not affect the transcriptional activity of HNF4␣. 5 Together, these data indicate that under normal conditions, HNF4␣ activity is not affected by fatty acids, the endogenous ligands for HNF4␣.Loss-of-function mutations in human HNF4␣ are associated with maturity-onset diabetes of the young (MODY1), 6 characterized by autosomal dominant inheritance, early-onset diabetes, and pancreatic ␤-cell dys...

Non-alcoholic fatty liver disease (NAFLD) is one of the major health concerns worldwide. Farnesoid X receptor (FXR) is considered a therapeutic target for treatment of NAFLD. However, the mechanism by which activation of FXR lowers hepatic triglyceride (TG) levels remains unknown. Here we investigated the role of hepatic carboxylesterase 1 (CES1) in regulating both normal and FXR-controlled lipid homeostasis. Over-expression of hepatic CES1 lowered hepatic TG and plasma glucose levels in both wild-type and diabetic mice. In contrast, knockdown of hepatic CES1 increased hepatic TG and plasma cholesterol levels. These effects likely resulted from the TG hydrolase activity of CES1, with subsequent changes in fatty acid oxidation and/or de novo lipogenesis. Activation of FXR induced hepatic CES1, and reduced the levels of hepatic and plasma TG as well as plasma cholesterol in a CES1-dependent manner. Therefore, hepatic CES1 plays a critical role in regulating both lipid and carbohydrate metabolism and FXR-controlled lipid homeostasis.

Background:The hormone FGF21 is a potent regulator of carbohydrate and lipid metabolism and a promising drug for treating metabolic syndrome. Results: Farnesoid X receptor (FXR) agonists and FGF19 induce hepatic FGF21 secretion via a transcriptional mechanism and posttranscriptional mechanism, respectively. Conclusion: Activation of the FXR pathway stimulates FGF21 expression and secretion. Significance: Activation of FXR is a potential approach to enhance endogenous FGF21 production and reverse metabolic syndrome.