Hepatic Nuclear Factor 4α Research Articles

Essential fatty acids in early life: structural and functional role.

Essential fatty acids (EFA) are structural components of all tissues and are indispensable for cell membrane synthesis; the brain, retina and other neural tissues are particularly rich in long-chain polyunsaturated fatty acids (LCPUFA). These fatty acids serve as specific precursors for eicosanoids that regulate numerous cell and organ functions. Results from animal and recent human studies support the essential nature of n-3 EFA in addition to the well-established role of n-6 EFA for human subjects, particularly in early life. The most significant effects relate to neural development and maturation of sensory systems. Recent studies using stable-isotope-labelled tracers demonstrate that even preterm infants are able to form arachidonic acid (AA) and docosahexaenoic acid (DHA), but that synthesis is extremely low. Intracellular fatty acids or their metabolites regulate transcriptional activation of gene expression during adipocyte differentiation, and retinal and nervous system development. Regulation of gene expression by LCPUFA occurs at the transcriptional level and is mediated by nuclear transcription factors activated by fatty acids. These nuclear receptors are part of the steroid hormone receptor family. Two types of polyunsaturated fatty acid responsive transcription factors have been characterized, the peroxisome proliferator-activated receptor (PPAR) and the hepatic nuclear factor 4alpha. DHA also has significant effects on photoreceptor membranes involved in the signal transduction process, rhodopsin activation, and rod and cone development. Comprehensive clinical studies have shown that dietary supplementation with marine oil or single-cell oils, sources of LCPUFA, results in increased blood levels of DHA and AA, as well as an associated improvement in visual function in formula-fed premature infants to match that of human milk-fed infant. Recent clinical trials convincingly support LCPUFA supplementation of preterm infant formulations and possibly term formula to mimic human milk composition.

Pterin-4α-carbinolamine dehydratase in rat brain: I. Patterns of co-localization with tyrosine hydroxylase

The bifunctional protein, PCD/DCoH, is both a pterin-4α-carbinolamine dehydratase (PCD) and a dimerization cofactor of the hepatic nuclear factor 1α (DCoH). In association with brain tyrosine hydroxylase (TH), which is required for dopamine synthesis, PCD catalyses dehydration and thus recycling of the cofactor tetrahydrobiopterin (BH 4). PCD immunoreactivity in the catecholaminergic system of the rat brain was studied using a rabbit polyclonal antibody. Double immunofluorescence was performed to establish intracellular co-localization with TH. PCD immunoreactivity was found to be high and consistently present in all the neuron groups expressing TH. More than 90% of the TH+ cells were also expressing PCD. The highest co-expression (99–100% of TH+ cells) was observed in pontine catecholaminergic cell groups including locus coeruleus. Lower co-expression was observed in substantia nigra (17% of TH+ cells without PCD) and particularly in arcuate nucleus (41% of TH+ cells without PCD). Our results argue in favor of a generalized recycling of BH 4 in catecholaminergic neurons except when the neuron terminal field is located outside the blood–brain barrier. The respective roles of synthesis and recycling of BH 4 in the control of TH activity are discussed.

Down-regulation of the rat hepatic sterol 27-hydroxylase: gene by bile acids in transfected primary hepatocytes: possible role of hepatic nuclear factor 1α

In vitro and in vivo studies have shown that the sterol 27-hydroxylase (CYP27) gene is transcriptionally repressed by hydrophobic bile acids. The molecular mechanism(s) of repression of CYP27 by bile acids is unknown. To identify the bile acid responsive element (BARE) and transcription factor(s) that mediate the repression of CYP27 by bile acids, constructs of the CYP27 5′-flanking DNA were linked to either the CAT or luciferase reporter gene and transiently transfected into primary rat hepatocytes. Taurocholate (TCA), taurodeoxycholate (TDCA) and taurochenodeoxycholate (TCDCA) significantly reduced CAT activities of the −840/+23, −329/+23, and −195/+23 mCAT constructs. A −76/+23 construct showed no regulation by bile acids. When a DNA fragment (−110/−86) from this region was cloned in front of an SV 40 promoter it showed down-regulation by TDCA. ‘Super’-electrophoretic mobility shift assays (EMSA) indicated that both HNF1α and C/EBP bind to the −110 to −86 bp DNA fragment. Recombinant rat HNF1α and C/EBPα competitively bound to this DNA fragment. ‘Super’-EMSA showed that TDCA addition to hepatocytes in culture decreased HNF1α, but not C/EBP, binding to the −110/−86 bp DNA fragment. A four base pair substitution mutation (−103 to −99) in this sequence eliminated TCA and TDCA regulation of the (−840/+23) construct. The substitution mutation also eliminated (>95%) HNF1α, but not C/EBP, binding to this DNA fragment. We conclude that bile acids repress CYP27 transcription through a putative BARE located between −110 and −86 bp of the CYP27 promoter. The data suggest that bile acids repress CYP27 transcriptional activity by decreasing HNF1α binding to the CYP27 promoter.

Fatty acyl-CoA thioesters are ligands of hepatic nuclear factor-4alpha.

Dietary fatty acids specifically modulate the onset and progression of various diseases, including cancer, atherogenesis, hyperlipidaemia, insulin resistances and hypertension, as well as blood coagulability and fibrinolytic defects; their effects depend on their chain length and degree of saturation. Hepatocyte nuclear factor-4alpha (HNF-4alpha) is an orphan transcription factor of the superfamily of nuclear receptors and controls the expression of genes that govern the pathogenesis and course of some of these diseases. Here we show that long-chain fatty acids directly modulate the transcriptional activity of HNF-4alpha by binding as their acyl-CoA thioesters to the ligand-binding domain of HNF-4alpha. This binding may shift the oligomeric-dimeric equilibrium of HNF-4alpha or may modulate the affinity of HNF-4alpha for its cognate promoter element, resulting in either activation or inhibition of HNF-4alpha transcriptional activity as a function of chain length and the degree of saturation of the fatty acyl-CoA ligands. In addition to their roles as substrates to yield energy, as an energy store, or as constituents of membrane phospholipids, dietary fatty acids may affect the course of a disease by modulating the expression of HNF-4alpha-controlled genes.

Hepatic nuclear factor 1 alpha (HNF-1 alpha) is expressed in the oviduct of hens and interacts with regulatory elements of the lysozyme gene.

HNF-1 alpha is a nuclear transcriptional regulatory protein required for the expression of a variety of liver-specific genes. This factor was previously considered liver-specific but later shown to be expressed also in a few other mammalian tissues. Here we report on the occurrence of HNF-1 alpha in the avian oviduct. This finding is of particular interest because HNF-1 alpha is not expressed in female reproductive organs of mammals. The avian oviduct is the site of assembly for the avian egg and the site of tissue-specific synthesis of the major egg white proteins, such as lysozyme. We also demonstrate that the chicken lysozyme gene contains HNF-1 recognition sites within two of its important upstream regulatory elements. The presence of HNF-1 recognition elements in functionally significant regulatory sites of the lysozyme gene and high levels of HNF-1 alpha in the oviduct is a strong indication for the involvement of HNF-1 alpha in the control of the lysozyme gene and possibly other egg white protein genes in the chicken oviduct. Apparently, HNF-1 alpha performs functions in the avian oviduct that were lost upon development from birds to mammals.