Glycerol-3-phosphate dehydrogenase is induced by glucocorticoids in hepatocytes and hepatoma cells in vitro

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

Vitamin A decreases pre-receptor amplification of glucocorticoids in obesity: study on the effect of vitamin A on 11beta-hydroxysteroid dehydrogenase type 1 activity in liver and visceral fat of WNIN/Ob obese rats

BACKGROUND

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) catalyzes the conversion of inactive glucocorticoids to active glucocorticoids and its inhibition ameliorates obesity and metabolic syndrome. So far, no studies have reported the effect of dietary vitamin A on 11β-HSD1 activity in visceral fat and liver under normal and obese conditions. Here, we studied the effect of chronic feeding of vitamin A-enriched diet (129 mg/kg diet) on 11β-HSD1 activity in liver and visceral fat of WNIN/Ob lean and obese rats.

METHODS

Male, 5-month-old, lean and obese rats of WNIN/Ob strain (n = 16 for each phenotype) were divided into two subgroups consisting of 8 rats of each phenotype. Control groups received stock diet containing 2.6 mg vitamin A/kg diet, where as experimental groups received diet containing 129 mg vitamin A/Kg diet for 20 weeks. Food and water were provided ad libitum. At the end of the experiment, tissues were collected and 11β-HSD1 activity was assayed in liver and visceral fat.

RESULTS

Vitamin A supplementation significantly decreased body weight, visceral fat mass and 11β-HSD1 activity in visceral fat of WNIN/Ob obese rats. Hepatic 11β-HSD1 activity and gene expression were significantly reduced by vitamin A supplementation in both the phenotypes. CCAAT/enhancer binding protein α (C/EBPα), the main transcription factor essential for the expression of 11β-HSD1, decreased in liver of vitamin A fed-obese rats, but not in lean rats. Liver × receptor α (LXRα), a nuclear transcription factor which is known to downregulate 11β-HSD1 gene expression was significantly increased by vitamin A supplementation in both the phenotypes.

CONCLUSIONS

This study suggests that chronic consumption of vitamin A-enriched diet decreases 11β-HSD1 activity in liver and visceral fat of WNIN/Ob obese rats. Decreased 11β-HSD1 activity by vitamin A may result in decreased levels of active glucocorticoids in adipose tissue and possibly contribute to visceral fat loss in these obese rats. Studying the role of various nutrients on the regulation of 11β-HSD1 activity and expression will help in the evolving of dietary approaches to treat obesity and insulin resistance.

Low temperature directly activates the initial glycerol antifreeze response in isolated rainbow smelt (Osmerus mordax) liver cells

Rainbow smelt ( Osmerus mordax) accumulate high levels of glycerol in winter that serve as an antifreeze. Liver glycogen is a source of glycerol during the early stages of glycerol accumulation, whereas dietary glucose and amino acids are essential to maintain rates of glycerol synthesis. We presently report rates of glycerol and glucose production by isolated hepatocytes. Cells from fish held at 0.4 to –1.5°C and incubated at 0.4°C were metabolically quiescent with negligible rates of glycerol or glucose production. Hepatocytes isolated from fish maintained at 8°C and incubated at 8°C produced glucose but not glycerol. Glycerol production was activated in cells isolated from 8°C fish and incubated at 0.4°C without substrate or when glucose, aspartate, or pyruvate was available in the medium. Incubation at 0.4°C without substrate resulted in similar molar rates of glucose and glycerol production in concert with glycogen mobilization. Glycogenolysis and glycerol production were associated with increases in total in vitro activities of glycogen phosphorylase and glycerol-3-phosphate dehydrogenase. Maximal in vitro activities of hexokinase and glucokinase were not influenced by temperature, but high activities of a low- Kmhexokinase may serve to redirect glycogen-derived glucose to glycolysis as opposed to releasing it from the cells. Rates of glycerol production were not enhanced in cells from fish held at 8°C and incubated at 0.4°C with adrenergic or glucocorticoid stimulation. As such, low temperature alone is sufficient to activate the glycerol production mechanism and results in a shift from glucose to a mix of glucose and glycerol production.

Analysis of aldosterone-induced differential receptor-independent protein patterns using 2D-electrophoresis and mass spectrometry

In the human body the mineralocorticoid aldosterone is responsible for maintaining water and electrolyte homeostasis and therefore controlling blood pressure. In addition, aldosterone has recently been associated with severe heart failure. Besides receptor-dependent action, the damaging effects of aldosterone may also be partly mediated through non-genomic mechanisms. The present study focuses on the mineralocorticoid receptor-independent action of aldosterone at the protein level. We chose the fission yeast Schizosaccharomyces pombe as a model organism, since this yeast does not contain nuclear steroid receptors, but many genes and regulatory mechanisms that are close to those of mammals. Using 2D-electrophoresis we identified for the first time protein spots affected by aldosterone in a nuclear receptor-free system. Mass spectrometry analysis using MALDI-TOF MS and nanoLC-MS/MS approaches allowed the unambiguous identification of 11 proteins that showed increased or decreased levels, which may represent newly identified players and pathways of aldosterone-induced action. Two proteins with a connection to osmotic regulation (NAD-dependent malic enzyme and glycerol-3-phosphate-dehydrogenase), as well as two proteins involved in the overall organization of the cytoskeleton, vip1 and glyceraldehyde-3-phosphate dehydrogenase, which was also found to be specifically affected by aldosterone in human HCT116 cells, are discussed.

Metabolic flux analysis of hepatocyte function in hormone- and amino acid-supplemented plasma

Understanding the metabolic and regulatory pathways of hepatocytes is important for biotechnological applications involving liver cells. Previous attempts to culture hepatocytes in plasma yielded poor functional results. Recently we reported that hormone (insulin and hydrocortisone) and amino acid supplementation reduces intracellular lipid accumulation and restores liver-specific function in hepatocytes exposed to heparinized human plasma. In the current study, we performed metabolic flux analysis (MFA) using a simplified metabolic network model of cultured hepatocytes to quantitively estimate the changes in lipid metabolism and relevant intracellular pathways in response to hormone and amino acid supplementation. The model accounts for the majority of central carbon and nitrogen metabolism, and assumes pseudo-steady-state with no metabolic futile cycles. We found that beta-oxidation and tricarboxylic acid (TCA) cycle fluxes were upregulated by both hormone and amino acid supplementation, thus enhancing the rate of lipid oxidation. Concomitantly, hormone and amino acid supplementation increased gluconeogenic fluxes. This, together with an increased rate of glucose clearance, caused an increase in predicted glycogen synthesis. Urea synthesis was primarily derived from ammonia and aspartate generated through transamination reactions, while exogenous ammonia removal accounted for only 3-6% of the urea nitrogen. Amino acid supplementation increased the endogenous synthesis of oxaloacetate, and in turn that of aspartate, a necessary substrate for the urea cycle. These findings from MFA provide cues as to which genes/pathways relevant to fatty acid oxidation, urea production, and gluconeogenesis may be upregulated by plasma supplementation, and are consistent with current knowledge of hepatic amino acid metabolism, which provides further credence to this approach for evaluating the metabolic state of hepatocytes under various environmental conditions.

Regulatory effect of various steroid hormones on the incorporation and metabolism of [14C]stearate in rat hepatoma cells in culture

We have examined the incorporation and metabolism of [14C] stearic acid within the total lipids of HTC rat-hepatoma cells in suspension culture in presence and in absence of steroidal hormone stimulation. Both, glucocorticoids (dexamethasone, cortisol and corticosterone) and mineralocorticoids (deoxycorticosterone and aldosterone) as well as the estrogen beta-estradiol and the androgen testosterone enhanced the extent of delta 9 desaturation to oleic acid of the saturated precursors, whereas only the two mineralocorticoids affected the incorporation rate of the exogenous acid into total cellular lipids, thus promoting a little stimulation. Furthermore, all the hormones tested increased the radiolabelling of the total cellular phospholipids except deoxycorticosterone and testosterone, the former having no effect and the latter exerting a moderate inhibition. On the other hand, the incorporation of 14C into neutral lipids was stimulated by testosterone, in contrast to the inhibition of this parameter observed exclusively with either the mineralocorticoids or the estrogen. Within the phospholipid subclasses, the radiolabelling of phosphatidylcholine was augmented by means of all the steroids tested save deoxycorticosterone and testosterone, whereas phosphatidylethanolamine exhibited a decrease only in the presence of testosterone. In a similar fashion, within the neutral lipids, the predominating triglyceride fraction was preferentially labelled--at the expense of other subclasses of lesser abundance--upon treatment with the steroids except aldosterone, which exerted no effect. The results obtained were correlated with those changes observed in the mass distribution of the different lipid subclasses either with or without prior hormonal stimulation.

Simultaneous expression of salivary and pancreatic amylase genes in cultured mouse hepatoma cells

The tissue-specific expression of two types of mouse amylase genes does not overlap in vivo; the Amy-1 locus is transcribed in the parotid gland and the liver, while expression of Amy-2 is limited to the pancreas. We identified a mouse hepatoma cell line, Hepa 1-6, in which both amylase genes can be simultaneously expressed. Amy-1 is constitutively active in these cells and is inducible by dexamethasone at the level of mRNA. We demonstrated that the liver-specific promoter of Amy-1 is utilized by the dexamethasone-treated hepatoma cells, and that glucocorticoid consensus sequences are present upstream of this promoter. Amy-2 is not detectable constitutively, but can be activated if the cells are cultured in serum-free medium containing dexamethasone. Expression of Amy-2 in a nonpancreatic cell type has not previously been observed. We speculate that induction of Amy-1 and activation of Amy-2 may involve different regulatory mechanisms. Hepa 1-6 cells provide an experimental system for molecular analysis of these events.

Simultaneous expression of salivary and pancreatic amylase genes in cultured mouse hepatoma cells

The tissue-specific expression of two types of mouse amylase genes does not overlap in vivo; the Amy-1 locus is transcribed in the parotid gland and the liver, while expression of Amy-2 is limited to the pancreas. We identified a mouse hepatoma cell line, Hepa 1-6, in which both amylase genes can be simultaneously expressed. Amy-1 is constitutively active in these cells and is inducible by dexamethasone at the level of mRNA. We demonstrated that the liver-specific promoter of Amy-1 is utilized by the dexamethasone-treated hepatoma cells, and that glucocorticoid consensus sequences are present upstream of this promoter. Amy-2 is not detectable constitutively, but can be activated if the cells are cultured in serum-free medium containing dexamethasone. Expression of Amy-2 in a nonpancreatic cell type has not previously been observed. We speculate that induction of Amy-1 and activation of Amy-2 may involve different regulatory mechanisms. Hepa 1-6 cells provide an experimental system for molecular analysis of these events.

Synergistic enzyme induction by glucocorticoids and cyclic AMP observed in glioma x hepatoma cell hybrids but not in their parents

Enzyme induction by hydrocortisone (HC) and dibutyryl cyclic AMP (dbcAMP) was studied in C6 rat glioma cells, FU5AH rat hepatoma cells, and five C6 x FU5AH hybrids. Hormone responsive enzymes from both parental lines were studied, including: tyrosine aminotransferase (TAT), alanine aminotransferase (AAT), glycerol phosphate dehydrogenase (GPDH), lactate dehydrogenase (LDH), and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP). There was no overall dominance of one parental phenotype over the other in expression of uninduced or induced enzyme activity after fusion, and the hybrids possessed some enzymatic properties characteristic of both parents. GPDH was induced by dbcAMP in all five hybrids, and TAT was induced by dbcAMP in four of the hybrids, although neither of these enzymes were induced by dbcAMP in the parents. Furthermore, synergistic induction of these enzymes by HC and dbcAMP was observed in the hybrids but not in the parents. These hybrids provide a model system to study hormone interaction in enzyme induction.

Adrenalectomy of rats results in hypomyelination of the central nervous system

The effect of adrenalectomy on CNS myelin accumulation was investigated to determine whether glucocorticoids play a role in regulating myelination. When 14-day-old rats were adrenalectomized and sacrificed 7-8 days later, the amount of bulk-isolated myelin in whole brain, as expressed per gram wet weight of brain or per milligram DNA-phosphate, was reduced to about 75% that of sham-operated controls. Both brain weight and DNA content were unchanged by adrenalectomy. Examination of individual brain regions also revealed decreased amounts of myelin in adrenalectomized animals. Brain glycerol 3-phosphate dehydrogenase specific activity was reduced in adrenalectomized animals to 40-60% that of controls, and serum corticosterone levels were less than 0.6% of control levels. The amount of cerebral myelin in animals adrenalectomized on day 21 and sacrificed 9 days later was not significantly reduced. This suggests a possible role of glucocorticoids during the early period of rapid myelination.

Regulation by glucocorticoids of rat-liver phenylalanine hydroxylase in vivo

Phenylalanine hydroxylase, a liver-associated enzyme, is induced markedly by glucocorticoids in two permanent rat-hepatoma cell lines. In order to gain evidence that this phenomenon also occurs in vivo, we examined the effect of adrenalectomy and/or hormone supplementation on the levels of phenylalanine hydroxylase in the livers of adult rats: glucocorticoid administration increases, and adrenal ablation reduces, the activity of the hepatic enzyme, and the diminution occurring in the latter instance is entirely prevented by concurrent hormone replacement. These results thus corroborate earlier findings from a single experiment and are consistent with the hypothesis that adrenal corticosteroid hormones participate in modulating phenylalanine-hydroxylase levels within the diploid hepatocyte.