[Show abstract][Hide abstract] ABSTRACT: With an excessive postprandial accumulation of intestine-derived, triglyceride-rich lipoproteins being a risk factor of cardiovascular diseases, it is essential to characterize the mechanisms controlling the intestinal absorption of dietary lipids. Our aim was to investigate the role of the transcription factor hepatocyte nuclear factor (HNF)-4α in this process. We used transgenic mice with a specific and inducible intestinal knockout of Hnf-4α gene. One hour after a lipid bolus, in the presence of the lipase inhibitor tyloxapol, lower amounts of triglycerides were found in both plasma and intestinal epithelium of the intestine-specific Hnf-4α knockout (Hnf-4α(intΔ)) mice compared with the Hnf-4α(loxP/loxP) control mice. These discrepancies were due to a net decrease of the intestinal uptake of fatty acid in Hnf-4α(intΔ) mice compared with Hnf-4α(loxP/loxP) mice, as assessed by the amount of radioactivity that was recovered in intestine and plasma after gavage with labeled triolein or oleic acid, or in intestinal epithelial cells isolated from jejunum after a supply of labeled oleic acid-containing micelles. This decreased fatty acid uptake was associated with significant lower levels of the fatty acid transport protein-4 mRNA and protein along the intestinal tract and with a lower acyl-CoA synthetase activity in Hnf-4α(intΔ) mice compared with the control mice. We conclude that the transcription factor HNF-4α is a key factor of the intestinal absorption of dietary lipids, which controls this process as early as in the initial step of fatty acid uptake by enterocytes.
Preview · Article · Mar 2012 · AJP Gastrointestinal and Liver Physiology
[Show abstract][Hide abstract] ABSTRACT: Hepatocyte nuclear factor 4α (HNF-4α) is a transcription factor which is highly expressed in the intestinal epithelium from
duodenum to colon and from crypt to villus. The homeostasis of this constantly renewing epithelium relies on an integrated
control of proliferation, differentiation, and apoptosis, as well as on the functional architecture of the epithelial cells.
In order to determine the consequences of HNF-4α loss in the adult intestinal epithelium, we used a tamoxifen-inducible Cre-loxP
system to inactivate the Hnf-4a gene. In the intestines of adult mice, loss of HNF-4α led to an increased proliferation in crypts and to an increased expression
of several genes controlled by the Wnt/β-catenin system. This control of the Wnt/β-catenin signaling pathway by HNF-4α was
confirmed in vitro. Cell lineage was affected, as indicated by an increased number of goblet cells and an impairment of enterocyte
and enteroendocrine cell maturation. In the absence of HNF-4α, cell-cell junctions were destabilized and paracellular intestinal
permeability increased. Our results showed that HNF-4α modulates Wnt/β-catenin signaling and controls intestinal epithelium
homeostasis, cell function, and cell architecture. This study indicates that HNF-4α regulates the intestinal balance between
proliferation and differentiation, and we hypothesize that it might act as a tumor suppressor.
Full-text · Article · Oct 2009 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: Hepatic nuclear factor-4 (HNF-4) is a transcription factor and a member of the large family of nuclear receptors. It was first cloned from liver but is expressed also in kidney, pancreas and intestine. Three genes encoding three isoforms have been identified, HNF- 4α and γ, in mammals, drosophila and xenopus and HNF-4β, exclusively in xenopus. HNF-4α is the best studied isoform, especially in liver. Such studies put HNF-4α at the crossroads between architecture and function of epithelia, as it induces expression of cell/cell junction proteins while it also controls glucido-lipidic metabolism and drug metabolizing enzyme genes. Furthermore, mutations in the HNF-4α gene lead to a metabolic disease in humans, Maturity Onset Diabetes of the Young-1 (MODY-1). The existence of a “true ligand” is not clearly established but a “structural” fatty acid is present in the ligand binding pocket of HNF-4α and γ. Consequently, activity of HNF-4 can be modulated by the interaction with co-regulators or by post-translational modifications. Then, HNF-4 is a potential direct or indirect target for pharmacologic drugs, with a special interest for the intestinal epithelium which is the primary site of metabolic control, due to its roles in nutrient absorption and in sensing energy. The patents related to the HNF-4α gene are also discussed in this article.
Full-text · Article · May 2007 · Recent Patents on Endocrine Metabolic & Immune Drug Discovery
[Show abstract][Hide abstract] ABSTRACT: We have generated transgenic mouse lines expressing exclusively a human INS transgene on an Ins1/Ins2 double knockout (mIKO) background. The transgene expression was driven by either a 4000 bp or a 353 bp promoter. These transgenic lines, designated mIKO:INS4000 and mIKO:INS353, were viable and fertile. Determination of the amounts of insulin transcripts and total pancreatic insulin content revealed relative insulin underproduction in both lines, from birth to adulthood. Total pancreatic insulin stores in mIKO:INS4000 and mIKO:INS353 mice represented only about 50% and 27%, respectively, as compared to wild-type mice. Morphometric analysis of pancreas did not show any compensatory beta-cell hyperplasia. The majority of animals in both lines remained normoglycemic throughout their lives. Nevertheless, glucose tolerance tests revealed glucose intolerance in nearly half of mIKO:INS4000 male mice, likely due to impaired insulin secretion detected in those animals. In addition, a small fraction (2-4%) of male mice in both lines spontaneously developed diabetes with very distinct pathophysiological features. Diabetes was never seen in female animals. The diabetes developed by mIKO:INS353 mice was rapidly lethal, accompanied by a dramatic depletion of pancreatic insulin stores whereas the mIKO:INS4000 diabetic animals could live for several months. This suggests a possible link between the structure of the human INS gene promoter and the type of diabetes developed in these lines.
No preview · Article · Feb 2007 · Frontiers in Bioscience
[Show abstract][Hide abstract] ABSTRACT: Insulin receptor (IR)-deficient mice develop severe diabetes mellitus, diabetic ketoacidosis (DKA) and liver steatosis and die within 1 week after birth. We examined in this work whether the metabolic phenotype of IR(-/-) mutants could be improved by transgenic complementation with IR selectively in the liver. We first generated transgenic mice expressing a human DNA complementary to RNA encoding a truncated constitutively activated form of IR (IRdelta) under the control of liver-specific phenylalanine hydroxylase (PAH) gene promoter. These mice presented more pronounced fasting hypoglycemia and showed slightly improved glucose tolerance as compared to controls. The transgenic mice were crossed with IR(+/-) mutants to generate IR(-/-) mice carrying the PAH-IRDelta transgene. Although such mutants developed glycosuria, DKA was delayed by more than 1 week and survival was prolonged to 8-20 days in approximately 10% of mice. In these partially rescued pups, serum glucose and triglyceride levels were lowered, hepatic glycogen stores were reconstituted and liver steatosis was absent as compared with pups which developed strong DKA and died earlier. Thus, lack of insulin action in the liver is responsible in large part for the metabolic disorders seen in IR(+/-) mice. This study should stimulate interest in therapeutic strategies aimed at improving hepatic function in diabetes.
[Show abstract][Hide abstract] ABSTRACT: Transgenic and gene targeting approaches have now been applied to a number of genes in order to investigate the metabolic disorders that would result by manipulating insulin action or pancreatic beta-cell function in the mouse. The availability of such mutant mice will allow in the future to develop animal models in which the pathophysiologies resulting from polygenic defects might be reconstituted and studied in detail. Such animal models hopefully will lead to better understanding of complex polygenic diseases such as non-insulin-dependent diabetes mellitus (NIDDM).
No preview · Article · Jun 1998 · Molecular and Cellular Biochemistry
[Show abstract][Hide abstract] ABSTRACT: Transgenic and gene targeting approaches have now been applied to a number of genes in order to investigate the metabolic disorders that would result by manipulating insulin action or pancreatic -cell function in the mouse. The availability of such mutant mice will allow in the future to develop animal models in which the pathophysiologies resulting from polygenic defects might be reconstituted and studied in detail. Such animal models hopefully will lead to better understanding of complex polygenic diseases such as non-insulin-dependent diabetes mellitus (NIDDM).
No preview · Article · Apr 1998 · Molecular and Cellular Biochemistry