Hepatic Hepatocyte Nuclear Factor 4α Is Essential for Maintaining Triglyceride and Cholesterol Homeostasis

Abstract

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...

Transcriptome meta-analysis of three follicular compartments and its correlation with ovarian follicle maturity and oocyte developmental competence in cows

“…This gene is expressed in liver, adipose, pancreatic, and intestinal tissues and is an important metabolic regulator involved in gluconeogenesis (23), lipid metabolism (34), and inflammation (4). Although we could not detect HNF4A transcripts in granulosa cells using qRT-PCR, we did confirm the abundance of HNF4A downstream targets (TTR and PPL), which suggests that this transcription factor has an active role in ovarian follicle differentiation.…”

“…It is therefore plausible that HNF4A, which interacts with several genes involved in lipid metabolism and homoeostasis (34), is involved in the regulation of follicle metabolic activities. Hnf4␣ knockout is lethal in mice (14), and conditional knockout in hepatic cells has been shown to depress genes involved in lipogenesis (Srebf1, Acc, Fas, Dgat2), de novo cholesterol biosynthesis (Hmgcr, Hmgcs), cholesterol esterification (Acat2), and fatty acid uptake (CD36) (34). The corresponding bovine genes had similar expression patterns in the present study.…”

Aldo-keto reductase 1B7 is a target gene of FXR and regulates lipid and glucose homeostasis

“…Plasma lipid levels were determined using kits from Wako Chemicals. Plasma lipoprotein profi le was analyzed by fast protein liquid chromatography (FPLC) as described ( 18 ).…”

“…On day 6, these mice were fasted overnight, followed by intravenous injection of Tyloxapol (500 mg/kg). Blood was taken at indicated time points, and plasma triglyceride levels were determined ( 18 ).…”

“…Results were normalized to 36b4 mRNA. The primer sequences for qRT-PCR were described previously ( 17,18 ), except for Akr1b7 (forward primer, 5 ′ -AAGCG-GGAGGATCTCTTCAT-3 ′ and reverse primer, 5 ′ -TCAGAT-CCGAGAGGGTGTTC-3 ′ ).…”