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Elijah IE, Børsheim E, Maybauer DM, Finnerty CC, Herndon DN, Maybauer MO. Role of the PPAR-α agonist fenofibrate in severe pediatric burn. Burns 2012; 38:481-6. [PMID: 22226866 DOI: 10.1016/j.burns.2011.12.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2011] [Accepted: 12/10/2011] [Indexed: 12/13/2022]
Abstract
Fenofibrate is a peroxisome proliferator activated receptor alpha agonist that contains both pro and anti-inflammatory properties, and has been used in the treatment of dyslipidemia and diabetes for decades. Its receptors are expressed in the liver, skeletal muscle, cardiac, enteric, and renal cells, which allow it to provide systemic regulation of lipoprotein metabolism, fatty acid oxidation, and fatty acid transport. Hyperglycemia is a common complication found in the burn population because hepatic glucose production and catecholamine-mediated hepatic glycogenolysis are augmented. Insulin resistance occurs often in these patients and is associated with poor outcomes. In the pediatric burn population, fenofibrate has been found to ameliorate or decrease the number of hypoglycemic episodes when compared to management with insulin alone. Its mechanism of action is thought to involve an improvement in insulin signaling in skeletal muscle, as well as improvements in mitochondrial function, glucose oxidation, and insulin sensitivity. The long term use of fenofibrate in severely burned patients may improve hyperglycemia and insulin resistance, as well as improve wound healing, and reduce apoptosis, and oxidative stress.
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Affiliation(s)
- Itoro E Elijah
- Department of Surgery, The University of Texas Medical Branch and Shriners Burns Hospital for Children at Galveston, TX 77555-0591, USA
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Jelen S, Wacker S, Aponte-Santamaría C, Skott M, Rojek A, Johanson U, Kjellbom P, Nielsen S, de Groot BL, Rützler M. Aquaporin-9 protein is the primary route of hepatocyte glycerol uptake for glycerol gluconeogenesis in mice. J Biol Chem 2011; 286:44319-25. [PMID: 22081610 DOI: 10.1074/jbc.m111.297002] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It has been hypothesized that aquaporin-9 (AQP9) is part of the unknown route of hepatocyte glycerol uptake. In a previous study, leptin receptor-deficient wild-type mice became diabetic and suffered from fasting hyperglycemia whereas isogenic AQP9(-/-) knock-out mice remained normoglycemic. The reason for this improvement in AQP9(-/-) mice was not established before. Here, we show increased glucose output (by 123% ± 36% S.E.) in primary hepatocyte culture when 0.5 mM extracellular glycerol was added. This increase depended on AQP9 because it was absent in AQP9(-/-) cells. Likewise, the increase was abolished by 25 μM HTS13286 (IC(50) ~ 2 μM), a novel AQP9 inhibitor, which we identified in a small molecule library screen. Similarly, AQP9 deletion or chemical inhibition eliminated glycerol-enhanced glucose output in perfused liver preparations. The following control experiments suggested inhibitor specificity to AQP9: (i) HTS13286 affected solute permeability in cell lines expressing AQP9, but not in cell lines expressing AQPs 3, 7, or 8. (ii) HTS13286 did not influence lactate- and pyruvate-dependent hepatocyte glucose output. (iii) HTS13286 did not affect glycerol kinase activity. Our experiments establish AQP9 as the primary route of hepatocyte glycerol uptake for gluconeogenesis and thereby explain the previously observed, alleviated diabetes in leptin receptor-deficient AQP9(-/-) mice.
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Affiliation(s)
- Sabina Jelen
- From the Water and Salt Research Center, Department of Biomedicine, Aarhus University, Wilhelm Meyers Allè, DK-8000 Aarhus C, Denmark
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Eslam M, Khattab MA, Harrison SA. Peroxisome proliferator-activated receptors and hepatitis C virus. Therap Adv Gastroenterol 2011; 4:419-31. [PMID: 22043232 PMCID: PMC3187680 DOI: 10.1177/1756283x11405251] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The prevalence of type 2 diabetes mellitus and insulin resistance are higher among people chronically infected with hepatitis C (CHC) when compared with the general population and people with other causes of chronic liver disease. Both insulin resistance and diabetes are associated with adverse outcomes across all stages of CHC, including the liver transplant population. CHC is also associated with the development of hepatic steatosis, a common histological feature present in approximately 55% (32-81%) of cases. There is a complex interrelationship between insulin resistance and hepatic steatosis and both are postulated to aggravate each other. The peroxisome proliferator-activated receptors (PPARs) are nuclear factors involved in the regulation of glucose, lipid homeostasis, inflammatory response, cell differentiation, and cell cycle. The relationship between hepatitis C virus replication and PPARs has been the focus of recent study. Given the availability of potent agonists, PPARs may represent a novel pharmacological target in the treatment of CHC.
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Affiliation(s)
- M. Eslam
- Department of Internal Medicine, Minia University, Minia, Egypt
| | - M. A. Khattab
- Department of Internal Medicine, Minia University, Minia, Egypt
| | - S. A. Harrison
- Division of Gastroenterology and Hepatology, Department of Medicine, Brooke Army Medical Center, 3851 Roger Brooke Drive, Fort Sam Houston, TX 78234, USA
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Fan Y, Guo Y, Hamblin M, Chang L, Zhang J, Chen YE. Inhibition of gluconeogenic genes by calcium-regulated heat-stable protein 1 via repression of peroxisome proliferator-activated receptor α. J Biol Chem 2011; 286:40584-94. [PMID: 21990353 DOI: 10.1074/jbc.m111.232918] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Gluconeogenesis contributes to insulin resistance in type 1 and type 2 diabetes, but its regulation and the underlying molecular mechanisms remain unclear. Recently, calcium-regulated heat-stable protein 1 (CARHSP1) was identified as a biomarker for diabetic complications. In this study, we investigated the role of CARHSP1 in hepatic gluconeogenesis. We assessed the regulation of hepatic CARHSP1 expression under conditions of fasting and refeeding. Adenovirus-mediated CARHSP1 overexpression and siRNA-mediated knockdown experiments were performed to characterize the role of CARHSP1 in the regulation of gluconeogenic gene expression. Here, we document for the first time that CARHSP1 is regulated by nutrient status in the liver and functions at the transcriptional level to negatively regulate gluconeogenic genes, including the glucose-6-phosphatase catalytic subunit (G6Pc) and phosphoenolpyruvate carboxykinase 1 (PEPCK1). In addition, we found that CARHSP1 can physically interact with peroxisome proliferator-activated receptor-α (PPARα) and inhibit its transcriptional activity. Both pharmacological and genetic ablations of PPARα attenuate the inhibitory effect of CARHSP1 on gluconeogenic gene expression in hepatocytes. Our data suggest that CARHSP1 inhibits hepatic gluconeogenic gene expression via repression of PPARα and that CARHSP1 may be a molecular target for the treatment of diabetes.
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Affiliation(s)
- Yanbo Fan
- Cardiovascular Center, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA
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Consequences of PPAR(α) Invalidation on Glutathione Synthesis: Interactions with Dietary Fatty Acids. PPAR Res 2011; 2011:256186. [PMID: 21915176 PMCID: PMC3171156 DOI: 10.1155/2011/256186] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 06/26/2011] [Accepted: 07/11/2011] [Indexed: 02/07/2023] Open
Abstract
Glutathione (GSH) derives from cysteine and plays a key role in redox status. GSH synthesis is determined mainly by cysteine availability and γ-glutamate cysteine ligase (γGCL) activity. Because PPARα activation is known to control the metabolism of certain amino acids, GSH synthesis from cysteine and related metabolisms were explored in wild-type (WT) and PPARα-null (KO) mice, fed diets containing either saturated (COCO diet) or 18 : 3 n-3, LIN diet. In mice fed the COCO diet, but not in those fed the LIN diet, PPARα deficiency enhanced hepatic GSH content and γGCL activity, superoxide dismutase 2 mRNA levels, and plasma uric acid concentration, suggesting an oxidative stress. In addition, in WT mice, the LIN diet increased the hepatic GSH pool, without effect on γGCL activity, or change in target gene expression, which rules out a direct effect of PPARα. This suggests that dietary 18 : 3 n-3 may regulate GSH metabolism and thus mitigate the deleterious effects of PPARα deficiency on redox status, without direct PPARα activation.
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Comprehensive analysis of PPARalpha-dependent regulation of hepatic lipid metabolism by expression profiling. PPAR Res 2011; 2007:26839. [PMID: 18288265 PMCID: PMC2233741 DOI: 10.1155/2007/26839] [Citation(s) in RCA: 162] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2007] [Accepted: 07/25/2007] [Indexed: 01/30/2023] Open
Abstract
PPARα is a ligand-activated transcription factor involved in the regulation of nutrient metabolism and inflammation. Although much is already known about the function of PPARα in hepatic lipid metabolism, many PPARα-dependent pathways and genes have yet to be discovered. In order to obtain an overview of PPARα-regulated genes relevant to lipid metabolism, and to probe for novel candidate PPARα target genes, livers from several animal studies in which PPARα was activated and/or disabled were analyzed by Affymetrix GeneChips. Numerous novel PPARα-regulated genes relevant to lipid metabolism were identified. Out of this set of genes, eight genes were singled out for study of PPARα-dependent regulation in mouse liver and in mouse, rat, and human primary hepatocytes, including thioredoxin interacting protein (Txnip), electron-transferring-flavoprotein β polypeptide (Etfb), electron-transferring-flavoprotein dehydrogenase (Etfdh), phosphatidylcholine transfer protein (Pctp), endothelial lipase (EL, Lipg), adipose triglyceride lipase (Pnpla2), hormone-sensitive lipase (HSL, Lipe), and monoglyceride lipase (Mgll). Using an in silico screening approach, one or more PPAR response elements (PPREs) were identified in each of these genes. Regulation of Pnpla2, Lipe, and Mgll, which are involved in triglyceride hydrolysis, was studied under conditions of elevated hepatic lipids. In wild-type mice fed a high fat diet, the decrease in hepatic lipids following treatment with the PPARα agonist Wy14643 was paralleled by significant up-regulation of Pnpla2, Lipe, and Mgll, suggesting that induction of triglyceride hydrolysis may contribute to the anti-steatotic role of PPARα. Our study illustrates the power of transcriptional profiling to uncover novel PPARα-regulated genes and pathways in liver.
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Stienstra R, Duval C, Müller M, Kersten S. PPARs, Obesity, and Inflammation. PPAR Res 2011; 2007:95974. [PMID: 17389767 PMCID: PMC1783744 DOI: 10.1155/2007/95974] [Citation(s) in RCA: 188] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2006] [Revised: 11/13/2006] [Accepted: 11/13/2006] [Indexed: 01/12/2023] Open
Abstract
The worldwide prevalence of obesity and related metabolic disorders is rising rapidly, increasing the burden on our healthcare system. Obesity is often accompanied by excess fat storage in tissues other than adipose tissue, including liver and skeletal muscle, which may lead to local insulin resistance and may stimulate inflammation, as in steatohepatitis. In addition, obesity changes the morphology and composition of adipose tissue, leading to changes in protein production and secretion. Some of these secreted proteins, including several proinflammatory mediators, may be produced by macrophages resident in the adipose tissue. The changes in inflammatory status of adipose tissue and liver with obesity feed a growing recognition that obesity represents a state of chronic low-level inflammation. Various molecular mechanisms have been implicated in obesity-induced inflammation, some of which are modulated by the peroxisome proliferator-activated receptors (PPARs). PPARs are ligand-activated transcription factors involved in the regulation of numerous biological processes, including lipid and glucose metabolism, and overall energy homeostasis. Importantly, PPARs also modulate the inflammatory response, which makes them an interesting therapeutic target to mitigate obesity-induced inflammation and its consequences. This review will address the role of PPARs in obesity-induced inflammation specifically in adipose tissue, liver, and the vascular wall.
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Affiliation(s)
- Rinke Stienstra
- Nutrition, Metabolism and Genomics Group and Nutrigenomics Consortium, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands
| | - Caroline Duval
- Nutrition, Metabolism and Genomics Group and Nutrigenomics Consortium, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands
| | - Michael Müller
- Nutrition, Metabolism and Genomics Group and Nutrigenomics Consortium, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands
| | - Sander Kersten
- Nutrition, Metabolism and Genomics Group and Nutrigenomics Consortium, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands
- *Sander Kersten:
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58
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The Role of PPAR Ligands in Controlling Growth-Related Gene Expression and their Interaction with Lipoperoxidation Products. PPAR Res 2011; 2008:524671. [PMID: 18615196 PMCID: PMC2443425 DOI: 10.1155/2008/524671] [Citation(s) in RCA: 203] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2008] [Accepted: 06/05/2008] [Indexed: 11/18/2022] Open
Abstract
Peroxisome proliferators-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. The three PPAR isoforms (α, γ and β/δ) have been found to play a pleiotropic role in cell fat metabolism. Furthermore, in recent years, evidence has been found regarding the antiproliferative, proapoptotic, and differentiation-promoting activities displayed by PPAR ligands, particularly by PPARγ ligands. PPAR ligands affect the expression of different growth-related genes through both PPAR-dependent and PPAR-independent mechanisms. Moreover, an interaction between PPAR ligands and other molecules which strengthen the effects of PPAR ligands has been described. Here we review the action of PPAR on the control of gene expression with particular regard to the effect of PPAR ligands on the expression of genes involved in the regulation of cell-cycle, differentiation, and apoptosis. Moreover, the interaction between PPAR ligands and 4-hydroxynonenal (HNE), the major product of the lipid peroxidation, has been reviewed.
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59
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Chamouton J, Hansmannel F, Bonzo JA, Clémencet MC, Chevillard G, Battle M, Martin P, Pineau T, Duncan S, Gonzalez FJ, Latruffe N, Mandard S, Nicolas-Francès V. The Peroxisomal 3-keto-acyl-CoA thiolase B Gene Expression Is under the Dual Control of PPARα and HNF4α in the Liver. PPAR Res 2011; 2010:352957. [PMID: 21437216 PMCID: PMC3061263 DOI: 10.1155/2010/352957] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Revised: 12/01/2010] [Accepted: 12/09/2010] [Indexed: 01/10/2023] Open
Abstract
PPARα and HNF4α are nuclear receptors that control gene transcription by direct binding to specific nucleotide sequences. Using transgenic mice deficient for either PPARα or HNF4α, we show that the expression of the peroxisomal 3-keto-acyl-CoA thiolase B (Thb) is under the dependence of these two transcription factors. Transactivation and gel shift experiments identified a novel PPAR response element within intron 3 of the Thb gene, by which PPARα but not HNF4α transactivates. Intriguingly, we found that HNF4α enhanced PPARα/RXRα transactivation from TB PPRE3 in a DNA-binding independent manner. Coimmunoprecipitation assays supported the hypothesis that HNF4α was physically interacting with RXRα. RT-PCR performed with RNA from liver-specific HNF4α-null mice confirmed the involvement of HNF4α in the PPARα-regulated induction of Thb by Wy14,643. Overall, we conclude that HNF4α enhances the PPARα-mediated activation of Thb gene expression in part through interaction with the obligate PPARα partner, RXRα.
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Affiliation(s)
- J. Chamouton
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
| | - F. Hansmannel
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
- INSERM U744, Laboratoire d'Épidémiologie et Santé Publique, Institut Pasteur de Lille, 1 Rue du Professeur Calmette, BP 245, 59019 Lille Cedex, France
| | - J. A. Bonzo
- Laboratory of Metabolism, Division of Basic Sciences, National Cancer Institute, Bethesda, MD 20892, USA
| | - M. C. Clémencet
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
| | - G. Chevillard
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
- Lady Davis Institute for Medical Research, McGill University, 3755 Côte Ste. Catherine Road, Montreal, QC, Canada H3T 1E2
| | - M. Battle
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226-0509, USA
| | - P. Martin
- Laboratoire de Pharmacologie et Toxicologie, UR66, INRA, 31931, Toulouse, France
| | - T. Pineau
- Laboratoire de Pharmacologie et Toxicologie, UR66, INRA, 31931, Toulouse, France
| | - S. Duncan
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226-0509, USA
| | - F. J. Gonzalez
- Laboratory of Metabolism, Division of Basic Sciences, National Cancer Institute, Bethesda, MD 20892, USA
| | - N. Latruffe
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
| | - S. Mandard
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
| | - V. Nicolas-Francès
- Centre de Recherche, INSERM U866, LBMN 6, Boulevard Gabriel, 21000 Dijon, France
- Laboratoire de Biochimie Métabolique et Nutritionnelle (LBMN), Faculté des Sciences Gabriel, Université de Bourgogne, 21000 Dijon, France
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60
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Goto T, Lee JY, Teraminami A, Kim YI, Hirai S, Uemura T, Inoue H, Takahashi N, Kawada T. Activation of peroxisome proliferator-activated receptor-alpha stimulates both differentiation and fatty acid oxidation in adipocytes. J Lipid Res 2011; 52:873-84. [PMID: 21324916 PMCID: PMC3073464 DOI: 10.1194/jlr.m011320] [Citation(s) in RCA: 161] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Peroxisome proliferator-activated receptor-α (PPARα) is a dietary lipid sensor, whose activation results in hypolipidemic effects. In this study, we investigated whether PPARα activation affects energy metabolism in white adipose tissue (WAT). Activation of PPARα by its agonist (bezafibrate) markedly reduced adiposity in KK mice fed a high-fat diet. In 3T3-L1 adipocytes, addition of GW7647, a highly specific PPARα agonist, during adipocyte differentiation enhanced glycerol-3-phosphate dehydrogenase activity, insulin-stimulated glucose uptake, and adipogenic gene expression. However, triglyceride accumulation was not increased by PPARα activation. PPARα activation induced expression of target genes involved in FA oxidation and stimulated FA oxidation. In WAT of KK mice treated with bezafibrate, both adipogenic and FA oxidation-related genes were significantly upregulated. These changes in mRNA expression were not observed in PPARα-deficient mice. Bezafibrate treatment enhanced FA oxidation in isolated adipocytes, suppressing adipocyte hypertrophy. Chromatin immunoprecipitation (ChIP) assay revealed that PPARα was recruited to promoter regions of both adipogenic and FA oxidation-related genes in the presence of GW7647 in 3T3-L1 adipocytes. These findings indicate that the activation of PPARα affects energy metabolism in adipocytes, and PPARα activation in WAT may contribute to the clinical effects of fibrate drugs.
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Affiliation(s)
- Tsuyoshi Goto
- Laboratory of Molecular Function of Food, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Uji, Kyoto, Japan
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61
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Potter JJ, Koteish A, Hamilton J, Liu X, Liu K, Agre P, Mezey E. Effects of acetaldehyde on hepatocyte glycerol uptake and cell size: implication of aquaporin 9. Alcohol Clin Exp Res 2011; 35:939-45. [PMID: 21294757 DOI: 10.1111/j.1530-0277.2010.01424.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND The effects of ethanol and acetaldehyde on uptake of glycerol and on cell size of hepatocytes and a role Aquaporin 9 (AQP9), a glycerol transport channel, were evaluated. METHODS The studies were done in primary rat and mouse hepatocytes. The uptake of [(14) C] glycerol was determined with hepatocytes in suspension. For determination of cell size, rat hepatocytes on coated dishes were incubated with a lipophilic fluorochrome that is incorporated into the cell membrane and examined by confocal microscopy. A three-dimensional z scan of the cell was performed, and the middle slice of the z scan was used for area measurements. RESULTS Acute exposure to acetaldehyde, but not to ethanol, causes a rapid increase in the uptake of glycerol and an increase in hepatocyte size, which was inhibited by HgCl(2) , an inhibitor of aquaporins. This was not observed in hepatocytes from AQP9 knockout mice, nor observed by direct application of acetaldehyde to AQP9 expressed in Xenopus Laevis oocytes. Prolonged 24-hour exposure to either acetaldehyde or ethanol did not result in an increase in glycerol uptake by rat hepatocytes. Acetaldehyde decreased AQP9 mRNA and AQP9 protein, while ethanol decreased AQP9 mRNA but not AQP9 protein. Ethanol, but not acetaldehyde, increased the activities of glycerol kinase and phosphoenolpyruvate carboxykinase. CONCLUSIONS The acute effects of acetaldehyde, while mediated by AQP9, are probably influenced by binding of acetaldehyde to hepatocyte membranes and changes in cell permeability. The effects of ethanol in enhancing glucose kinase, and phosphoenolpyruvate carboxykinase leading to increased formation of glycerol-3-phosphate most likely contribute to alcoholic fatty liver.
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Affiliation(s)
- James J Potter
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195, USA
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62
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Poplawski MM, Mastaitis JW, Mobbs CV. Naloxone, but not valsartan, preserves responses to hypoglycemia after antecedent hypoglycemia: role of metabolic reprogramming in counterregulatory failure. Diabetes 2011; 60:39-46. [PMID: 20811039 PMCID: PMC3012195 DOI: 10.2337/db10-0326] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
OBJECTIVE Hypoglycemia-associated autonomic failure (HAAF) constitutes one of the main clinical obstacles to optimum treatment of type 1 diabetes. Neurons in the ventromedial hypothalamus are thought to mediate counterregulatory responses to hypoglycemia. We have previously hypothesized that hypoglycemia-induced hypothalamic angiotensin might contribute to HAAF, suggesting that the angiotensin blocker valsartan might prevent HAAF. On the other hand, clinical studies have demonstrated that the opioid receptor blocker naloxone ameliorates HAAF. The goal of this study was to generate novel hypothalamic markers of hypoglycemia and use them to assess mechanisms mediating HAAF and its reversal. RESEARCH DESIGN AND METHODS Quantitative PCR was used to validate a novel panel of hypothalamic genes regulated by hypoglycemia. Mice were exposed to one or five episodes of insulin-induced hypoglycemia, with or without concurrent exposure to valsartan or naloxone. Corticosterone, glucagon, epinephrine, and hypothalamic gene expression were assessed after the final episode of hypoglycemia. RESULTS A subset of hypothalamic genes regulated acutely by hypoglycemia failed to respond after repetitive hypoglycemia. Responsiveness of a subset of these genes was preserved by naloxone but not valsartan. Notably, hypothalamic expression of four genes, including pyruvate dehydrogenase kinase 4 and glycerol 3-phosphate dehydrogenase 1, was acutely induced by a single episode of hypoglycemia, but not after antecedent hypoglycemia; naloxone treatment prevented this failure. Similarly, carnitine palmitoyltransferase-1 was inhibited after repetitive hypoglycemia, and this inhibition was prevented by naloxone. Repetitive hypoglycemia also caused a loss of hypoglycemia-induced elevation of glucocorticoid secretion, a failure prevented by naloxone but not valsartan. CONCLUSIONS Based on these observations we speculate that acute hypoglycemia induces reprogramming of hypothalamic metabolism away from glycolysis toward β-oxidation, HAAF is associated with a reversal of this reprogramming, and naloxone preserves some responses to hypoglycemia by preventing this reversal.
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Affiliation(s)
- Michal M. Poplawski
- Fishberg Center for Neurobiology, Mount Sinai School of Medicine, New York, New York
| | - Jason W. Mastaitis
- Department of Internal Medicine, The Anlyan Center, Yale University School of Medicine, New Haven, Connecticut
| | - Charles V. Mobbs
- Fishberg Center for Neurobiology, Mount Sinai School of Medicine, New York, New York
- Corresponding author: Charles V. Mobbs,
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63
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Im SS, Kim MY, Kwon SK, Kim TH, Bae JS, Kim H, Kim KS, Oh GT, Ahn YH. Peroxisome proliferator-activated receptor {alpha} is responsible for the up-regulation of hepatic glucose-6-phosphatase gene expression in fasting and db/db Mice. J Biol Chem 2010; 286:1157-64. [PMID: 21081500 DOI: 10.1074/jbc.m110.157875] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Glucose-6-phosphatase (G6Pase) is a key enzyme that is responsible for the production of glucose in the liver during fasting or in type 2 diabetes mellitus (T2DM). During fasting or in T2DM, peroxisome proliferator-activated receptor α (PPARα) is activated, which may contribute to increased hepatic glucose output. However, the mechanism by which PPARα up-regulates hepatic G6Pase gene expression in these states is not well understood. We evaluated the mechanism by which PPARα up-regulates hepatic G6Pase gene expression in fasting and T2DM states. In PPARα-null mice, both hepatic G6Pase and phosphoenolpyruvate carboxykinase levels were not increased in the fasting state. Moreover, treatment of primary cultured hepatocytes with Wy14,643 or fenofibrate increased the G6Pase mRNA level. In addition, we have localized and characterized a PPAR-responsive element in the promoter region of the G6Pase gene. Chromatin immunoprecipitation (ChIP) assay revealed that PPARα binding to the putative PPAR-responsive element of the G6Pase promoter was increased in fasted wild-type mice and db/db mice. These results indicate that PPARα is responsible for glucose production through the up-regulation of hepatic G6Pase gene expression during fasting or T2DM animal models.
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Affiliation(s)
- Seung-Soon Im
- Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea
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Park UH, Yoon SK, Park T, Kim EJ, Um SJ. Additional sex comb-like (ASXL) proteins 1 and 2 play opposite roles in adipogenesis via reciprocal regulation of peroxisome proliferator-activated receptor {gamma}. J Biol Chem 2010; 286:1354-63. [PMID: 21047783 DOI: 10.1074/jbc.m110.177816] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Our previous studies have suggested that the mammalian additional sex comb-like 1 protein functions as a coactivator or repressor of retinoic acid receptors in a cell-specific manner. Here, we investigated the roles of additional sex comb-like 1 proteins in regulating peroxisome proliferator-activated receptors (PPARs). In pulldown assays in vitro and in immunoprecipitation assays in vivo, ASXL1 and its paralog, ASXL2, interacted with PPARα and PPARγ. In 3T3-L1 preadipocyte cells, overexpression of ASXL1 inhibited the induction of PPARγ activity by rosiglitazone, as shown by transcription assays, and completely suppressed adipogenesis, as shown by Oil Red O staining. In contrast, overexpression of ASXL2 greatly enhanced rosiglitazone-induced PPARγ activity and enhanced adipogenesis. Deletion of the heterochromatin protein 1 (HP1)-binding domain from ASXL1 caused the mutant protein to enhance adipogenesis similarly to ASXL2, indicating that HP1 binding is required for the adipogenesis-suppressing activity of ASXL1. Adipocyte differentiation was associated with a gradual decrease in ASXL1 expression but did not affect ASXL2 expression. Knockdown of ASXL1 and ASXL2 had reciprocal effects on adipogenesis. In chromatin immunoprecipitation assays in 3T3-L1 cells, ASXL1 occupied the promoter of the PPARγ target gene aP2 together with HP1α and Lys-9-methylated histone H3, whereas ASXL2 occupied the aP2 promoter together with histone-lysine N-methyltransferase MLL1 and Lys-9-acetylated and Lys-4-methylated H3 histones. Finally, microarray analysis demonstrated that ASXL1 represses, whereas ASXL2 increases, the expression of adipogenic genes, most of which are PPARγ targets. These results suggest that members of the additional sex comb-like family provide complex regulation of adipogenesis via differential modulation of PPARγ activity.
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Affiliation(s)
- Ui-Hyun Park
- Department of Bioscience and Biotechnology, BK21 Graduate Program, Sejong University, 98 Kunja-dong, Kwangjin-gu, Seoul 143-747, Korea
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65
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Atshaves B, Martin G, Hostetler H, McIntosh A, Kier A, Schroeder F. Liver fatty acid-binding protein and obesity. J Nutr Biochem 2010; 21:1015-32. [PMID: 20537520 PMCID: PMC2939181 DOI: 10.1016/j.jnutbio.2010.01.005] [Citation(s) in RCA: 162] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Revised: 01/11/2010] [Accepted: 01/12/2010] [Indexed: 12/17/2022]
Abstract
While low levels of unesterified long chain fatty acids (LCFAs) are normal metabolic intermediates of dietary and endogenous fat, LCFAs are also potent regulators of key receptors/enzymes and at high levels become toxic detergents within the cell. Elevated levels of LCFAs are associated with diabetes, obesity and metabolic syndrome. Consequently, mammals evolved fatty acid-binding proteins (FABPs) that bind/sequester these potentially toxic free fatty acids in the cytosol and present them for rapid removal in oxidative (mitochondria, peroxisomes) or storage (endoplasmic reticulum, lipid droplets) organelles. Mammals have a large (15-member) family of FABPs with multiple members occurring within a single cell type. The first described FABP, liver-FABP (L-FABP or FABP1), is expressed in very high levels (2-5% of cytosolic protein) in liver as well as in intestine and kidney. Since L-FABP facilitates uptake and metabolism of LCFAs in vitro and in cultured cells, it was expected that abnormal function or loss of L-FABP would reduce hepatic LCFA uptake/oxidation and thereby increase LCFAs available for oxidation in muscle and/or storage in adipose. This prediction was confirmed in vitro with isolated liver slices and cultured primary hepatocytes from L-FABP gene-ablated mice. Despite unaltered food consumption when fed a control diet ad libitum, the L-FABP null mice exhibited age- and sex-dependent weight gain and increased fat tissue mass. The obese phenotype was exacerbated in L-FABP null mice pair fed a high-fat diet. Taken together with other findings, these data suggest that L-FABP could have an important role in preventing age- or diet-induced obesity.
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Affiliation(s)
- B.P. Atshaves
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843-4466
| | - G.G. Martin
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843-4466
| | - H.A. Hostetler
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843-4466
| | - A.L. McIntosh
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843-4466
| | - A.B. Kier
- Department of Pathobiology, Texas A&M University, TVMC, College Station, TX 77843-4467
| | - F. Schroeder
- Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station, TX 77843-4466
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Abstract
Tight control of storage and synthesis of glucose during nutritional transitions is essential to maintain blood glucose levels, a process in which the liver has a central role. PPARα is the master regulator of lipid metabolism during fasting, but evidence is emerging for a role of PPARα in balancing glucose homeostasis as well. By using PPARα ligands and PPARα(-/-) mice, several crucial genes were shown to be regulated by PPARα in a direct or indirect way. We here review recent evidence that PPARα contributes to the adaptation of hepatic carbohydrate metabolism during the fed-to-fasted or fasted-to-fed transition in rodents.
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67
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Rakhshandehroo M, Knoch B, Müller M, Kersten S. Peroxisome proliferator-activated receptor alpha target genes. PPAR Res 2010; 2010:612089. [PMID: 20936127 PMCID: PMC2948931 DOI: 10.1155/2010/612089] [Citation(s) in RCA: 532] [Impact Index Per Article: 38.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Accepted: 08/09/2010] [Indexed: 12/11/2022] Open
Abstract
The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor involved in the regulation of a variety of processes, ranging from inflammation and immunity to nutrient metabolism and energy homeostasis. PPARα serves as a molecular target for hypolipidemic fibrates drugs which bind the receptor with high affinity. Furthermore, PPARα binds and is activated by numerous fatty acids and fatty acid-derived compounds. PPARα governs biological processes by altering the expression of a large number of target genes. Accordingly, the specific role of PPARα is directly related to the biological function of its target genes. Here, we present an overview of the involvement of PPARα in lipid metabolism and other pathways through a detailed analysis of the different known or putative PPARα target genes. The emphasis is on gene regulation by PPARα in liver although many of the results likely apply to other organs and tissues as well.
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Affiliation(s)
- Maryam Rakhshandehroo
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
| | - Bianca Knoch
- Food, Metabolism & Microbiology, Food & Textiles Group, AgResearch, Palmerston North 4442, New Zealand
- Institute of Food, Nutrition & Human Health, Massey University, Tennent Drive, Palmerston North 4442, New Zealand
| | - Michael Müller
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
| | - Sander Kersten
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
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Gustavsson C, Yassin K, Wahlström E, Cheung L, Lindberg J, Brismar K, Ostenson CG, Norstedt G, Tollet-Egnell P. Sex-different hepaticglycogen content and glucose output in rats. BMC BIOCHEMISTRY 2010; 11:38. [PMID: 20863371 PMCID: PMC2955586 DOI: 10.1186/1471-2091-11-38] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Accepted: 09/23/2010] [Indexed: 02/08/2023]
Abstract
Background Genes involved in hepatic metabolism have a sex-different expression in rodents. To test whether male and female rat livers differ regarding lipid and carbohydrate metabolism, whole-genome transcript profiles were generated and these were complemented by measurements of hepatic lipid and glycogen content, fatty acid (FA) oxidation rates and hepatic glucose output (HGO). The latter was determined in perfusates from in situ perfusion of male and female rat livers. These perfusates were also analysed using nuclear magnetic resonance (NMR) spectroscopy to identify putative sex-differences in other liver-derived metabolites. Effects of insulin were monitored by analysis of Akt-phosphorylation, gene expression and HGO after s.c. insulin injections. Results Out of approximately 3 500 gene products being detected in liver, 11% were significantly higher in females, and 11% were higher in males. Many transcripts for the production of triglycerides (TG), cholesterol and VLDL particles were female-predominant, whereas genes for FA oxidation, gluconeogenesis and glycogen synthesis were male-predominant. Sex-differences in mRNA levels related to metabolism were more pronounced during mild starvation (12 h fasting), as compared to the postabsorptive state (4 h fasting). No sex-differences were observed regarding hepatic TG content, FA oxidation rates or blood levels of ketone bodies or glucose. However, males had higher hepatic glycogen content and higher HGO, as well as higher ratios of insulin to glucagon levels. Based on NMR spectroscopy, liver-derived lactate was also higher in males. HGO was inhibited by insulin in parallel with increased phosphorylation of Akt, without any sex-differences in insulin sensitivity. However, the degree of Thr172-phosphorylated AMP kinase (AMPK) was higher in females, indicating a higher degree of AMPK-dependent actions. Conclusions Taken together, males had higher ratios of insulin to glucagon levels, higher levels of glycogen, lower degree of AMPK phosphorylation, higher expression of gluconeogenic genes and higher hepatic glucose output. Possibly these sex-differences reflect a higher ability for the healthy male rat liver to respond to increased energy demands.
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69
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Abstract
PPARα is one of three members of the soluble nuclear receptor family called peroxisome proliferator-activated receptor (PPAR). It is a sensor for changes in levels of fatty acids and their derivatives that responds to ligand binding with PPAR target gene transcription, inasmuch as it can influence physiological homeostasis, including lipid and carbohydrate metabolism in various tissues. In this paper we summarize the involvement of PPARα in the metabolically active tissues liver and skeletal muscle and provide an overview of the risks and benefits of ligand activation of PPARα, with particular consideration to interspecies differences.
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70
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Warrier M, Hinds TD, Ledford KJ, Cash HA, Patel PR, Bowman TA, Stechschulte LA, Yong W, Shou W, Najjar SM, Sanchez ER. Susceptibility to diet-induced hepatic steatosis and glucocorticoid resistance in FK506-binding protein 52-deficient mice. Endocrinology 2010; 151:3225-36. [PMID: 20427484 PMCID: PMC2903936 DOI: 10.1210/en.2009-1158] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Although FK506-binding protein 52 (FKBP52) is an established positive regulator of glucocorticoid receptor (GR) activity, an in vivo role for FKBP52 in glucocorticoid control of metabolism has not been reported. To address this question, FKBP52(+/-) mice were placed on a high-fat (HF) diet known to induce obesity, hepatic steatosis, and insulin resistance. Tissue profiling of wild-type mice showed high levels of FKBP52 in the liver but little to no expression in muscle or adipose tissue, predicting a restricted pattern of FKBP52 effects on metabolism. In response to HF, FKBP52(+/-) mice demonstrated a susceptibility to hyperglycemia and hyperinsulinemia that correlated with reduced insulin clearance and reduced expression of hepatic CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1), a mediator of clearance. Livers of HF-fed mutant mice had high lipid content and elevated expression of lipogenic genes (peroxisome proliferator-activated receptor gamma, fatty acid synthase, and sterol regulatory element-binding protein 1c) and inflammatory markers (TNFalpha). Interestingly, mutant mice under HF showed elevated serum corticosterone, but their steatotic livers had reduced expression of gluconeogenic genes (phosphoenolpyruvate carboxy kinase, glucose 6 phosphatase, and pyruvate dehydrogenase kinase 4), whereas muscle and adipose expressed normal to elevated levels of glucocorticoid markers. These data suggest a state of glucocorticoid resistance arising from liver-specific loss of GR activity. Consistent with this hypothesis, reduced expression of gluconeogenic genes and CEACAM1 was observed in dexamethasone-treated FKBP52-deficient mouse embryonic fibroblast cells. We propose a model in which FKBP52 loss reduces GR control of gluconeogenesis, predisposing the liver to steatosis under HF-diet conditions attributable to a shunting of metabolism from glucose production to lipogenesis.
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Affiliation(s)
- Manya Warrier
- Center for Diabetes and Endocrine Research, Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, OH 43614-5804, USA
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71
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Sriram G, Parr LS, Rahib L, Liao JC, Dipple KM. Moonlighting function of glycerol kinase causes systems-level changes in rat hepatoma cells. Metab Eng 2010; 12:332-40. [PMID: 20399282 DOI: 10.1016/j.ymben.2010.04.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Revised: 04/08/2010] [Accepted: 04/12/2010] [Indexed: 10/19/2022]
Abstract
Glycerol kinase (GK) is an enzyme with diverse (moonlighting) cellular functions. GK overexpression affects central metabolic fluxes substantially; therefore, to elucidate the mechanism underlying these changes, we employed a systems-level evaluation of GK overexpression in H4IIE rat hepatoma cells. Microarray analysis revealed altered expression of genes in metabolism (central carbon and lipid), which correlated with previous flux analysis, and of genes regulated by the glucocorticoid receptor (GR). Oil Red O staining showed that GK overexpression leads to increased fat storage in H4IIE cells. Network component analysis revealed that activities of peroxisome proliferator-activated receptor alpha, GR, and seven other transcription factors were altered by GK overexpression. The increased activity of GR was experimentally verified by quantitative RT-PCR of GR-responsive genes in the presence and absence of the glucocorticoid agonist, dexamethasone. This systems biology approach further emphasizes GK's essential role in central and lipid metabolism and experimentally verifies GK's alternative (moonlighting) function of affecting GR transcription factor activity.
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Affiliation(s)
- Ganesh Sriram
- Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-7088, USA
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72
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Cavalieri D, Calura E, Romualdi C, Marchi E, Radonjic M, Van Ommen B, Müller M. Filling gaps in PPAR-alpha signaling through comparative nutrigenomics analysis. BMC Genomics 2009; 10:596. [PMID: 20003344 PMCID: PMC2801700 DOI: 10.1186/1471-2164-10-596] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Accepted: 12/11/2009] [Indexed: 12/28/2022] Open
Abstract
Background The application of high-throughput genomic tools in nutrition research is a widespread practice. However, it is becoming increasingly clear that the outcome of individual expression studies is insufficient for the comprehensive understanding of such a complex field. Currently, the availability of the large amounts of expression data in public repositories has opened up new challenges on microarray data analyses. We have focused on PPARα, a ligand-activated transcription factor functioning as fatty acid sensor controlling the gene expression regulation of a large set of genes in various metabolic organs such as liver, small intestine or heart. The function of PPARα is strictly connected to the function of its target genes and, although many of these have already been identified, major elements of its physiological function remain to be uncovered. To further investigate the function of PPARα, we have applied a cross-species meta-analysis approach to integrate sixteen microarray datasets studying high fat diet and PPARα signal perturbations in different organisms. Results We identified 164 genes (MDEGs) that were differentially expressed in a constant way in response to a high fat diet or to perturbations in PPARs signalling. In particular, we found five genes in yeast which were highly conserved and homologous of PPARα targets in mammals, potential candidates to be used as models for the equivalent mammalian genes. Moreover, a screening of the MDEGs for all known transcription factor binding sites and the comparison with a human genome-wide screening of Peroxisome Proliferating Response Elements (PPRE), enabled us to identify, 20 new potential candidate genes that show, both binding site, both change in expression in the condition studied. Lastly, we found a non random localization of the differentially expressed genes in the genome. Conclusion The results presented are potentially of great interest to resume the currently available expression data, exploiting the power of in silico analysis filtered by evolutionary conservation. The analysis enabled us to indicate potential gene candidates that could fill in the gaps with regards to the signalling of PPARα and, moreover, the non-random localization of the differentially expressed genes in the genome, suggest that epigenetic mechanisms are of importance in the regulation of the transcription operated by PPARα.
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Affiliation(s)
- Duccio Cavalieri
- Department of Pharmacology, University of Firenze, Firenze, Italy.
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73
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Oosterveer MH, Grefhorst A, van Dijk TH, Havinga R, Staels B, Kuipers F, Groen AK, Reijngoud DJ. Fenofibrate simultaneously induces hepatic fatty acid oxidation, synthesis, and elongation in mice. J Biol Chem 2009; 284:34036-44. [PMID: 19801551 DOI: 10.1074/jbc.m109.051052] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A growing body of evidence indicates that peroxisome proliferator-activated receptor alpha (PPARalpha) not merely serves as a transcriptional regulator of fatty acid catabolism but also exerts a much broader role in hepatic lipid metabolism. We determined adaptations in hepatic lipid metabolism and related aspects of carbohydrate metabolism upon treatment of C57Bl/6 mice with the PPARalpha agonist fenofibrate. Stable isotope procedures were applied to assess hepatic fatty acid synthesis, fatty acid elongation, and carbohydrate metabolism. Fenofibrate treatment strongly induced hepatic de novo lipogenesis and chain elongation (+/-300, 150, and 600% for C16:0, C18:0, and C18:1 synthesis, respectively) in parallel with an increased expression of lipogenic genes. The lipogenic induction in fenofibrate-treated mice was found to depend on sterol regulatory element-binding protein 1c (SREBP-1c) but not carbohydrate response element-binding protein (ChREBP). Fenofibrate treatment resulted in a reduced contribution of glycolysis to acetyl-CoA production, whereas the cycling of glucose 6-phosphate through the pentose phosphate pathway presumably was enhanced. Altogether, our data indicate that beta-oxidation and lipogenesis are induced simultaneously upon fenofibrate treatment. These observations may reflect a physiological mechanism by which PPARalpha and SREBP-1c collectively ensure proper handling of fatty acids to protect the liver against cytotoxic damage.
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Affiliation(s)
- Maaike H Oosterveer
- Department of Pediatrics, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands.
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74
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Rakhshandehroo M, Hooiveld G, Müller M, Kersten S. Comparative analysis of gene regulation by the transcription factor PPARalpha between mouse and human. PLoS One 2009; 4:e6796. [PMID: 19710929 PMCID: PMC2729378 DOI: 10.1371/journal.pone.0006796] [Citation(s) in RCA: 226] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Accepted: 07/15/2009] [Indexed: 12/18/2022] Open
Abstract
Background Studies in mice have shown that PPARα is an important regulator of hepatic lipid metabolism and the acute phase response. However, little information is available on the role of PPARα in human liver. Here we set out to compare the function of PPARα in mouse and human hepatocytes via analysis of target gene regulation. Methodology/Principal Findings Primary hepatocytes from 6 human and 6 mouse donors were treated with PPARα agonist Wy14643 and gene expression profiling was performed using Affymetrix GeneChips followed by a systems biology analysis. Baseline PPARα expression was similar in human and mouse hepatocytes. Depending on species and time of exposure, Wy14643 significantly induced the expression of 362–672 genes. Surprisingly minor overlap was observed between the Wy14643-regulated genes from mouse and human, although more substantial overlap was observed at the pathway level. Xenobiotics metabolism and apolipoprotein synthesis were specifically regulated by PPARα in human hepatocytes, whereas glycolysis-gluconeogenesis was regulated specifically in mouse hepatocytes. Most of the genes commonly regulated in mouse and human were involved in lipid metabolism and many represented known PPARα targets, including CPT1A, HMGCS2, FABP1, ACSL1, and ADFP. Several genes were identified that were specifically induced by PPARα in human (MBL2, ALAS1, CYP1A1, TSKU) or mouse (Fbp2, lgals4, Cd36, Ucp2, Pxmp4). Furthermore, several putative novel PPARα targets were identified that were commonly regulated in both species, including CREB3L3, KLF10, KLF11 and MAP3K8. Conclusions/Significance Our results suggest that PPARα activation has a major impact on gene regulation in human hepatocytes. Importantly, the role of PPARα as master regulator of hepatic lipid metabolism is generally well-conserved between mouse and human. Overall, however, PPARα regulates a mostly divergent set of genes in mouse and human hepatocytes.
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Affiliation(s)
- Maryam Rakhshandehroo
- Nutrigenomics Consortium, Top Institute (TI) Food and Nutrition, Wageningen, the Netherlands
- Nutrition, Metabolism and Genomics group, Division of Human Nutrition, Wageningen University, Wageningen, the Netherlands
| | - Guido Hooiveld
- Nutrigenomics Consortium, Top Institute (TI) Food and Nutrition, Wageningen, the Netherlands
- Nutrition, Metabolism and Genomics group, Division of Human Nutrition, Wageningen University, Wageningen, the Netherlands
| | - Michael Müller
- Nutrigenomics Consortium, Top Institute (TI) Food and Nutrition, Wageningen, the Netherlands
- Nutrition, Metabolism and Genomics group, Division of Human Nutrition, Wageningen University, Wageningen, the Netherlands
| | - Sander Kersten
- Nutrigenomics Consortium, Top Institute (TI) Food and Nutrition, Wageningen, the Netherlands
- Nutrition, Metabolism and Genomics group, Division of Human Nutrition, Wageningen University, Wageningen, the Netherlands
- * E-mail:
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75
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Dean JT, Tran L, Beaven S, Tontonoz P, Reue K, Dipple KM, Liao JC. Resistance to diet-induced obesity in mice with synthetic glyoxylate shunt. Cell Metab 2009; 9:525-36. [PMID: 19490907 PMCID: PMC4277884 DOI: 10.1016/j.cmet.2009.04.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2009] [Revised: 03/17/2009] [Accepted: 04/23/2009] [Indexed: 10/20/2022]
Abstract
Given the success in engineering synthetic phenotypes in microbes and mammalian cells, constructing non-native pathways in mammals has become increasingly attractive for understanding and identifying potential targets for treating metabolic disorders. Here, we introduced the glyoxylate shunt into mouse liver to investigate mammalian fatty acid metabolism. Mice expressing the shunt showed resistance to diet-induced obesity on a high-fat diet despite similar food consumption. This was accompanied by a decrease in total fat mass, circulating leptin levels, plasma triglyceride concentration, and a signaling metabolite in liver, malonyl-CoA, that inhibits fatty acid degradation. Contrary to plants and bacteria, in which the glyoxylate shunt prevents the complete oxidation of fatty acids, this pathway when introduced in mice increases fatty acid oxidation such that resistance to diet-induced obesity develops. This work suggests that using non-native pathways in higher organisms to explore and modulate metabolism may be a useful approach.
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Affiliation(s)
- Jason T Dean
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, CA 90095, USA
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76
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McIntosh AL, Atshaves BP, Hostetler HA, Huang H, Davis J, Lyuksyutova OI, Landrock D, Kier AB, Schroeder F. Liver type fatty acid binding protein (L-FABP) gene ablation reduces nuclear ligand distribution and peroxisome proliferator-activated receptor-alpha activity in cultured primary hepatocytes. Arch Biochem Biophys 2009; 485:160-73. [PMID: 19285478 DOI: 10.1016/j.abb.2009.03.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 03/03/2009] [Accepted: 03/05/2009] [Indexed: 11/29/2022]
Abstract
The effect of liver type fatty acid binding protein (L-FABP) gene ablation on the uptake and distribution of long chain fatty acids (LCFA) to the nucleus by real-time laser scanning confocal imaging and peroxisome proliferator-activated receptor-alpha (PPARalpha) activity was examined in cultured primary hepatocytes from livers wild-type L-FABP+/+ and gene ablated L-FABP-/- mice. Cultured primary hepatocytes from livers of L-FABP-/- mice exhibited: (i) reduced oxidation of palmitic acid, a common dietary long chain fatty acid (LCFA); (ii) reduced expression of fatty acid oxidative enzymes-proteins transcriptionally regulated by PPARalpha; (iii) reduced palmitic acid-induced PPARalpha co-immunoprecipitation with coactivator SRC-1 concomitant with increased PPARalpha co-immunoprecipitation with coinhibitor N-CoR; (iv) reduced palmitic acid-induced PPARalpha. Diminished PPARalpha activation in L-FABP null hepatocytes was associated with lower uptake of common dietary LCFA (palmitic acid as well as its fluorescent derivative BODIPY FL C(16)), reduced level of total unesterified LCFA, and real-time redistribution of BODIPY FL C(16) from the central nucleoplasm to the nuclear envelope. Taken together, these studies support the hypothesis that L-FABP may facilitate ligand (LCFA)-activated PPARalpha transcriptional activity at least in part by increasing total LCFA ligand available to PPARalpha for inducing PPARalpha-mediated transcription of proteins involved in LCFA metabolism.
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Affiliation(s)
- Avery L McIntosh
- Department of Physiology and Pharmacology, TVMC College Station, TX 77843-4466, USA
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Fan W, Imamura T, Sonoda N, Sears DD, Patsouris D, Kim JJ, Olefsky JM. FOXO1 transrepresses peroxisome proliferator-activated receptor gamma transactivation, coordinating an insulin-induced feed-forward response in adipocytes. J Biol Chem 2009; 284:12188-97. [PMID: 19246449 DOI: 10.1074/jbc.m808915200] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The transcriptional factor FoxO1 plays an important role in metabolic homeostasis. Herein we identify a novel transrepressional function that converts FoxO1 from an activator of transcription to a promoter-specific repressor of peroxisome proliferator-activated receptor gamma (PPARgamma) target genes that regulate adipocyte biology. FoxO1 transrepresses PPARgamma via direct protein-protein interactions; it is recruited to PPAR response elements (PPRE) on PPARgamma target genes by PPARgamma bound to PPRE and interferes with promoter DNA occupancy of the receptor. The FoxO1 transrepressional function, which is independent and dissectible from the transactivational effects, does not require a functional FoxO1 DNA binding domain, but dose require an evolutionally conserved 31 amino acids LXXLL-containing domain. Insulin induces FoxO1 phosphorylation and nuclear exportation, which prevents FoxO1-PPARgamma interactions and rescues transrepression. Adipocytes from insulin resistant mice show reduced phosphorylation and increased nuclear accumulation of FoxO1, which is coupled to lowered expression of endogenous PPARgamma target genes. Thus the innate FoxO1 transrepression function enables insulin to augment PPARgamma activity, which in turn leads to insulin sensitization, and this feed-forward cycle represents positive reinforcing connections between insulin and PPARgamma signaling.
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Affiliation(s)
- Wuqiang Fan
- Division of Endocrinology-Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California 92093, USA
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Nielsen R, Pedersen TA, Hagenbeek D, Moulos P, Siersbaek R, Megens E, Denissov S, Børgesen M, Francoijs KJ, Mandrup S, Stunnenberg HG. Genome-wide profiling of PPARgamma:RXR and RNA polymerase II occupancy reveals temporal activation of distinct metabolic pathways and changes in RXR dimer composition during adipogenesis. Genes Dev 2009; 22:2953-67. [PMID: 18981474 DOI: 10.1101/gad.501108] [Citation(s) in RCA: 424] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is a key regulator of adipocyte differentiation in vivo and ex vivo and has been shown to control the expression of several adipocyte-specific genes. In this study, we used chromatin immunoprecipitation combined with deep sequencing to generate genome-wide maps of PPARgamma and retinoid X receptor (RXR)-binding sites, and RNA polymerase II (RNAPII) occupancy at very high resolution throughout adipocyte differentiation of 3T3-L1 cells. We identify >5000 high-confidence shared PPARgamma:RXR-binding sites in adipocytes and show that during early stages of differentiation, many of these are preoccupied by non-PPARgamma RXR-heterodimers. Different temporal and compositional patterns of occupancy are observed. In addition, we detect co-occupancy with members of the C/EBP family. Analysis of RNAPII occupancy uncovers distinct clusters of similarly regulated genes of different biological processes. PPARgamma:RXR binding is associated with the majority of induced genes, and sites are particularly abundant in the vicinity of genes involved in lipid and glucose metabolism. Our analyses represent the first genome-wide map of PPARgamma:RXR target sites and changes in RNAPII occupancy throughout adipocyte differentiation and indicate that a hitherto unrecognized high number of adipocyte genes of distinctly regulated pathways are directly activated by PPARgamma:RXR.
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Affiliation(s)
- Ronni Nielsen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
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79
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Kley S, Hoenig M, Glushka J, Jin ES, Burgess SC, Waldron M, Jordan ET, Prestegard JH, Ferguson DC, Wu S, Olson DE. The impact of obesity, sex, and diet on hepatic glucose production in cats. Am J Physiol Regul Integr Comp Physiol 2009; 296:R936-43. [PMID: 19193946 DOI: 10.1152/ajpregu.90771.2008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Obesity is a risk factor for type 2 diabetes in cats. The risk of developing diabetes is severalfold greater for male cats than for females, even after having been neutered early in life. The purpose of this study was to investigate the role of different metabolic pathways in the regulation of endogenous glucose production (EGP) during the fasted state considering these risk factors. A triple tracer protocol using (2)H(2)O, [U-(13)C(3)]propionate, and [3,4-(13)C(2)]glucose was applied in overnight-fasted cats (12 lean and 12 obese; equal sex distribution) fed three different diets. Compared with lean cats, obese cats had higher insulin (P < 0.001) but similar blood glucose concentrations. EGP was lower in obese cats (P < 0.001) due to lower glycogenolysis and gluconeogenesis (GNG; P < 0.03). Insulin, body mass index, and girth correlated negatively with EGP (P < 0.003). Female obese cats had approximately 1.5 times higher fluxes through phosphoenolpyruvate carboxykinase (P < 0.02) and citrate synthase (P < 0.05) than male obese cats. However, GNG was not higher because pyruvate cycling was increased 1.5-fold (P < 0.03). These results support the notion that fasted obese cats have lower hepatic EGP compared with lean cats and are still capable of maintaining fasting euglycemia, despite the well-documented existence of peripheral insulin resistance in obese cats. Our data further suggest that sex-related differences exist in the regulation of hepatic glucose metabolism in obese cats, suggesting that pyruvate cycling acts as a controlling mechanism to modulate EGP. Increased pyruvate cycling could therefore be an important factor in modulating the diabetes risk in female cats.
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Affiliation(s)
- Saskia Kley
- College of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA
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80
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Mfsd2a encodes a novel major facilitator superfamily domain-containing protein highly induced in brown adipose tissue during fasting and adaptive thermogenesis. Biochem J 2009; 416:347-55. [PMID: 18694395 DOI: 10.1042/bj20080165] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
This study describes the identification of Mfsd2a (major facilitator superfamily domain-containing protein 2a), a novel mammalian major facilitator superfamily domain-containing protein, and an additional closely related protein, Mfsd2b. Most intron/exon junctions are conserved between the two genes, suggesting that they are derived from a common ancestor. Mfsd2a and Mfsd2b share a 12 transmembrane alpha-helical domain structure that bears greatest similarity to that of the bacterial Na(+)/melibiose symporters. Confocal microscopy demonstrated that Mfsd2a localizes to the endoplasmic reticulum. Mfsd2a is expressed in many tissues and is highly induced in liver and BAT (brown adipose tissue) during fasting. Mfsd2a displays an oscillatory expression profile in BAT and liver, consistent with a circadian rhythm. Although the basal level of Mfsd2a expression is relatively low in mouse BAT, it is greatly induced during cold-induced thermogenesis and after treatment with betaAR (beta-adrenergic receptor) agonists. This induction is totally abolished in beta-less (betaAR-deficient) mice. These findings indicate that Mfsd2a is greatly up-regulated in BAT during thermogenesis and that its induction is controlled by the betaAR signalling pathway. The observed induction of Mfsd2a expression in cultured BAT cells by dibutyryl-cAMP is in agreement with this conclusion. The present study suggests that Mfsd2a plays a role in adaptive thermogenesis.
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81
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Enzymes of glycerol and glyceraldehyde metabolism in mouse liver: effects of caloric restriction and age on activities. Biosci Rep 2008; 28:107-15. [PMID: 18429748 DOI: 10.1042/bsr20080015] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The influence of caloric restriction on hepatic glyceraldehyde- and glycerol-metabolizing enzyme activities of young and old mice were studied. Glycerol kinase and cytoplasmic glycerol-3-phosphate dehydrogenase activities were increased in both young and old CR (calorie-restricted) mice when compared with controls, whereas triokinase increased only in old CR mice. Aldehyde dehydrogenase and aldehyde reductase activities in both young and old CR mice were unchanged by caloric restriction. Mitochondrial glycerol-3-phosphate dehydrogenase showed a trend towards an increased activity in old CR mice, whereas a trend towards a decreased activity in alcohol dehydrogenase was observed in both young and old CR mice. Serum glycerol levels decreased in young and old CR mice. Therefore increases in glycerol kinase and glycerol-3-phosphate dehydrogenase were associated with a decrease in fasting blood glycerol levels in CR animals. A prominent role for triokinase in glyceraldehyde metabolism with CR was also observed. The results indicate that long-term caloric restriction induces sustained increases in the capacity for gluconeogenesis from glycerol.
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82
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Grabacka M, Placha W, Urbanska K, Laidler P, Płonka PM, Reiss K. PPAR gamma regulates MITF and beta-catenin expression and promotes a differentiated phenotype in mouse melanoma S91. Pigment Cell Melanoma Res 2008; 21:388-96. [PMID: 18444964 DOI: 10.1111/j.1755-148x.2008.00460.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Melanoma represents one of the most rapidly metastasizing, hence deadly tumors due to its high proliferation rate and invasiveness, characteristics of undifferentiated embryonic tissues. Given the absence of effective therapy for metastatic melanoma, understanding more fully the molecular mechanisms underlying melanocyte differentiation may provide opportunities for novel therapeutic intervention. Here we show that in mouse melanoma S91 cells activation of the peroxisome proliferator activated receptor (PPAR) gamma induces events resembling differentiation, such as growth arrest accompanied by apoptosis, spindle morphology and enhanced tyrosinase expression. These events are preceded by an initial transient increase in expression from the Microphthalmia-associated transcription factor gene, (MITF) promoter, whereas exposure to a PPAR gamma ligand- ciglitazone that exceeds 8 h, causes a gradual decrease of MITF, until by 48 h MITF expression is substantially reduced. Beta-catenin, an MITF transcriptional activator, shows a similar pattern of decline during ciglitazone treatment, consistent with previous reports that activated PPAR gamma inhibits the Wnt/beta-catenin pathway through induction of beta-catenin proteasomal degradation. We suggest that the PPAR gamma-mediated beta-catenin down-regulation is likely to be responsible for changes in MITF levels. The data suggest that PPAR gamma, besides its well-established role in mesenchymal cell differentiation towards adipocytes, might regulate differentiation in the melanocytic lineage.
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Affiliation(s)
- Maja Grabacka
- Department of Food Biotechnology, Faculty of Food Technology, Agricultural University of Krakow, Krakow, Poland.
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83
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Heinäniemi M, Uski JO, Degenhardt T, Carlberg C. Meta-analysis of primary target genes of peroxisome proliferator-activated receptors. Genome Biol 2008; 8:R147. [PMID: 17650321 PMCID: PMC2323243 DOI: 10.1186/gb-2007-8-7-r147] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2007] [Revised: 07/02/2007] [Accepted: 07/25/2007] [Indexed: 12/20/2022] Open
Abstract
A combined experimental and in silico approach identifies Peroxisome Proliferator Activated Receptor (PPAR) binding sites and six novel target genes in the human genome. Background Peroxisome proliferator-activated receptors (PPARs) are known for their critical role in the development of diseases, such as obesity, cardiovascular disease, type 2 diabetes and cancer. Here, an in silico screening method is presented, which incorporates experiment- and informatics-derived evidence, such as DNA-binding data of PPAR subtypes to a panel of PPAR response elements (PPREs), PPRE location relative to the transcription start site (TSS) and PPRE conservation across multiple species, for more reliable prediction of PPREs. Results In vitro binding and in vivo functionality evidence agrees with in silico predictions, validating the approach. The experimental analysis of 30 putative PPREs in eight validated PPAR target genes indicates that each gene contains at least one functional, strong PPRE that occurs without positional bias relative to the TSS. An extended analysis of the cross-species conservation of PPREs reveals limited conservation of PPRE patterns, although PPAR target genes typically contain strong or multiple medium strength PPREs. Human chromosome 19 was screened using this method, with validation of six novel PPAR target genes. Conclusion An in silico screening approach is presented, which allows increased sensitivity of PPAR binding site and target gene detection.
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Affiliation(s)
- Merja Heinäniemi
- Department of Biochemistry, University of Kuopio, FIN-70211 Kuopio, Finland
- Life Sciences Research Unit, University of Luxembourg, L-1511 Luxembourg
| | - J Oskari Uski
- Department of Biochemistry, University of Kuopio, FIN-70211 Kuopio, Finland
| | - Tatjana Degenhardt
- Department of Biochemistry, University of Kuopio, FIN-70211 Kuopio, Finland
| | - Carsten Carlberg
- Department of Biochemistry, University of Kuopio, FIN-70211 Kuopio, Finland
- Life Sciences Research Unit, University of Luxembourg, L-1511 Luxembourg
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84
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Sriram G, Rahib L, He JS, Campos AE, Parr LS, Liao JC, Dipple KM. Global metabolic effects of glycerol kinase overexpression in rat hepatoma cells. Mol Genet Metab 2008; 93:145-59. [PMID: 18029214 PMCID: PMC2702542 DOI: 10.1016/j.ymgme.2007.09.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2007] [Accepted: 09/10/2007] [Indexed: 10/22/2022]
Abstract
Glycerol kinase has several diverse activities in mammalian cells. Glycerol kinase deficiency is a complex, single-gene, inborn error of metabolism wherein no genotype-phenotype correlation has been established. Since glycerol kinase has been suggested to exhibit additional activities than glycerol phosphorylation, expression level perturbation in this enzyme may affect cellular physiology globally. To investigate this possibility, we conducted metabolic investigations of wild-type and two glycerol kinase-overexpressing H4IIE rat hepatoma cell lines constructed in this study. The glycerol kinase-overexpressing cell lines exhibited a significantly higher consumption of carbon sources per cell, suggesting excess carbon expenditure. Furthermore, we quantified intracellular metabolic fluxes by employing stable isotope 13C labeling with a mathematically designed substrate mixture, gas chromatography-mass spectrometry, and comprehensive isotopomer balancing. This flux analysis revealed that the pentose phosphate pathway flux in the glycerol kinase-overexpressing cell lines was 2-fold higher than that in the wild-type, in addition to subtler flux changes in other pathways of carbohydrate metabolism. Furthermore, the activity and transcript level of the lipogenic enzyme glucose-6-phosphate dehydrogenase, the rate-limiting enzyme of the pentose phosphate pathway, were also about 2-fold higher than that of the wild-type; these data corroborate the flux analysis results. This study shows that glycerol kinase affects carbon metabolism globally, possibly through its additional functions, and highlights glycerol kinase's multifaceted role in cellular physiology.
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Affiliation(s)
- Ganesh Sriram
- Department of Human Genetics, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California
| | - Lola Rahib
- Biomedical Engineering Interdepartmental Program, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, California
| | - Jian-Sen He
- Department of Human Genetics, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California
| | - Allison E. Campos
- Department of Human Genetics, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California
| | - Lilly S. Parr
- Department of Human Genetics, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California
| | - James C. Liao
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California
- Biomedical Engineering Interdepartmental Program, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, California
| | - Katrina M. Dipple
- Department of Human Genetics, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California
- Biomedical Engineering Interdepartmental Program, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, California
- Department of Pediatrics, David Geffen School of Medicine at UCLA, and Mattel Children’s Hospital at UCLA, University of California, Los Angeles, California
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85
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Abstract
BACKGROUND/AIMS Recent evidence has implicated the involvement of aquaporins (AQPs) in cellular functions that are unrelated to transepithelial water transport. Although AQPs are expressed in the gastrointestinal tract, their importance has so far been unclear. AQP3 is a water/glycerol transporter expressed at the basolateral membrane of colonic epithelial cells. The aim of this study was to investigate the involvement of AQP3 in enterocyte proliferation using mouse models of inflammatory bowel disease. METHODS Expression and function of AQP3 in mouse colonic epithelium were established. Colitis was induced in wild-type and AQP3 null mice by oral dextran sulphate administration or intracolonic acetic acid administration. Outcome measures included clinical disease severity, survival, pathology and cellular responses. Some mice were administered glycerol to test whether disease progression could be altered. RESULTS AQP3 null mice given dextran sulphate developed severe colitis after 3 days, with colonic haemorrhage, marked epithelial cell loss and death. Wild-type mice, which had comparable initial colonic damage as assessed by cell apoptosis, developed remarkably less severe colitis, surviving to >8 days. Cell proliferation was greatly reduced in AQP3 null mice. Oral glycerol administration significantly improved survival and reduced the severity of colitis in AQP3 null mice. Survival was also reduced in AQP3 null mice in the acetic acid model. CONCLUSIONS The results implicate a novel role for AQP3 in enterocyte proliferation that is probably related to its glycerol-transporting function. AQP3 is thus a potential target for therapy of intestinal diseases associated with enterocyte destruction.
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Affiliation(s)
- Jay R Thiagarajah
- Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, CA 94143-0521, USA
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86
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Mandard S, Stienstra R, Escher P, Tan NS, Kim I, Gonzalez FJ, Wahli W, Desvergne B, Müller M, Kersten S. Glycogen synthase 2 is a novel target gene of peroxisome proliferator-activated receptors. Cell Mol Life Sci 2007; 64:1145-57. [PMID: 17437057 PMCID: PMC2771145 DOI: 10.1007/s00018-007-7006-1] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Glycogen synthase 2 (Gys-2) is the ratelimiting enzyme in the storage of glycogen in liver and adipose tissue, yet little is known about regulation of Gys-2 transcription. The peroxisome proliferator-activated receptors (PPARs) are transcription factors involved in the regulation of lipid and glucose metabolism and might be hypothesized to govern glycogen synthesis as well. Here, we show that Gys-2 is a direct target gene of PPARalpha, PPARbeta/delta and PPARgamma. Expression of Gys-2 is significantly reduced in adipose tissue of PPARalpha-/-, PPARbeta/delta-/- and PPARgamma+/- mice. Furthermore, synthetic PPARbeta/delta, and gamma agonists markedly up-regulate Gys-2 mRNA and protein expression in mouse 3T3-L1 adipocytes. In liver, PPARalpha deletion leads to decreased glycogen levels in the refed state, which is paralleled by decreased expression of Gys-2 in fasted and refed state. Two putative PPAR response elements (PPREs) were identified in the mouse Gys-2 gene: one in the upstream promoter (DR-1prom) and one in intron 1 (DR-1int). It is shown that DR-1int is the response element for PPARs, while DR-1prom is the response element for Hepatic Nuclear Factor 4 alpha (HNF4alpha). In adipose tissue, which does not express HNF4alpha, DR-1prom is occupied by PPARbeta/delta and PPARgamma, yet binding does not translate into transcriptional activation of Gys-2. Overall, we conclude that mouse Gys-2 is a novel PPAR target gene and that transactivation by PPARs and HNF4alpha is mediated by two distinct response elements.
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Affiliation(s)
- S. Mandard
- Nutrition, Metabolism and Genomics group and Nutrigenomics Consortium, Division of Human Nutrition, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands
- INSERM UMR 866 (Lipides, Nutrition et Cancer, équipe Biochimie Métabolique et Nutritionnelle), Faculté des Sciences Gabriel, Université de Bourgogne, 6 Bd Gabriel, 21000 Dijon, France
| | - R. Stienstra
- Nutrition, Metabolism and Genomics group and Nutrigenomics Consortium, Division of Human Nutrition, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands
| | - P. Escher
- Institute of Physiology, Pharmazentrum, University of Basel, Basel, Switzerland
| | - N. S. Tan
- Center for Integrative Genomics, Université de Lausanne, Lausanne, Switzerland
| | - I. Kim
- Laboratory of Metabolism, Division of Basic Sciences, National Cancer Institute, Bethesda, MD 20892 USA
| | - F. J. Gonzalez
- Laboratory of Metabolism, Division of Basic Sciences, National Cancer Institute, Bethesda, MD 20892 USA
| | - W. Wahli
- Center for Integrative Genomics, Université de Lausanne, Lausanne, Switzerland
| | - B. Desvergne
- Center for Integrative Genomics, Université de Lausanne, Lausanne, Switzerland
| | - M. Müller
- Nutrition, Metabolism and Genomics group and Nutrigenomics Consortium, Division of Human Nutrition, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands
| | - S. Kersten
- Nutrition, Metabolism and Genomics group and Nutrigenomics Consortium, Division of Human Nutrition, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands
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87
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Bernal-Mizrachi C, Xiaozhong L, Yin L, Knutsen RH, Howard MJ, Arends JJA, DeSantis P, Coleman T, Semenkovich CF. An afferent vagal nerve pathway links hepatic PPARalpha activation to glucocorticoid-induced insulin resistance and hypertension. Cell Metab 2007; 5:91-102. [PMID: 17276352 PMCID: PMC1899170 DOI: 10.1016/j.cmet.2006.12.010] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2005] [Revised: 08/23/2006] [Accepted: 12/20/2006] [Indexed: 11/19/2022]
Abstract
Glucocorticoid excess causes insulin resistance and hypertension. Hepatic expression of PPARalpha (Ppara) is required for glucocorticoid-induced insulin resistance. Here we demonstrate that afferent fibers of the vagus nerve interface with hepatic Ppara expression to disrupt blood pressure and glucose homeostasis in response to glucocorticoids. Selective hepatic vagotomy decreased hyperglycemia, hyperinsulinemia, hepatic insulin resistance, Ppara expression, and phosphoenolpyruvate carboxykinase (PEPCK) enzyme activity in dexamethasone-treated Ppara(+/+) mice. Selective vagotomy also decreased blood pressure, adrenergic tone, renin activity, and urinary sodium retention in these mice. Hepatic reconstitution of Ppara in nondiabetic, normotensive dexamethasone-treated PPARalpha null mice increased glucose, insulin, hepatic PEPCK enzyme activity, blood pressure, and renin activity in sham-operated animals but not hepatic-vagotomized animals. Disruption of vagal afferent fibers by chemical or surgical means prevented glucocorticoid-induced metabolic derangements. We conclude that a dynamic interaction between hepatic Ppara expression and a vagal afferent pathway is essential for glucocorticoid induction of diabetes and hypertension.
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Affiliation(s)
- Carlos Bernal-Mizrachi
- Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Liu Xiaozhong
- Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Li Yin
- Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Russell H. Knutsen
- Department of Cell Biology and Physiology, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Michael J. Howard
- Department of Neurology, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Joop J. A. Arends
- Department of Neurology, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Pascual DeSantis
- Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Trey Coleman
- Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
| | - Clay F. Semenkovich
- Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
- Department of Cell Biology and Physiology, Washington University School of Medicine, Campus Box 8127, 660 South Euclid Avenue, St. Louis, MO 63110
- *Correspondence: , Phone 314-362-4454, Fax 314-362-7641
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88
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Lefebvre P, Chinetti G, Fruchart JC, Staels B. Sorting out the roles of PPAR alpha in energy metabolism and vascular homeostasis. J Clin Invest 2006; 116:571-80. [PMID: 16511589 PMCID: PMC1386122 DOI: 10.1172/jci27989] [Citation(s) in RCA: 699] [Impact Index Per Article: 38.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
PPARalpha is a nuclear receptor that regulates liver and skeletal muscle lipid metabolism as well as glucose homeostasis. Acting as a molecular sensor of endogenous fatty acids (FAs) and their derivatives, this ligand-activated transcription factor regulates the expression of genes encoding enzymes and transport proteins controlling lipid homeostasis, thereby stimulating FA oxidation and improving lipoprotein metabolism. PPARalpha also exerts pleiotropic antiinflammatory and antiproliferative effects and prevents the proatherogenic effects of cholesterol accumulation in macrophages by stimulating cholesterol efflux. Cellular and animal models of PPARalpha help explain the clinical actions of fibrates, synthetic PPARalpha agonists used to treat dyslipidemia and reduce cardiovascular disease and its complications in patients with the metabolic syndrome. Although these preclinical studies cannot predict all of the effects of PPARalpha in humans, recent findings have revealed potential adverse effects of PPARalpha action, underlining the need for further study. This Review will focus on the mechanisms of action of PPARalpha in metabolic diseases and their associated vascular pathologies.
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Affiliation(s)
- Philippe Lefebvre
- Département d'Athérosclérose, Institut Pasteur de Lille, INSERM U545, and Université de Lille 2, Lille, France
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89
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Zandbergen F, Mandard S, Escher P, Tan N, Patsouris D, Jatkoe T, Rojas-Caro S, Madore S, Wahli W, Tafuri S, Müller M, Kersten S. The G0/G1 switch gene 2 is a novel PPAR target gene. Biochem J 2006; 392:313-24. [PMID: 16086669 PMCID: PMC1316267 DOI: 10.1042/bj20050636] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
PPARs (peroxisome-proliferator-activated receptors) alpha, beta/delta and gamma are a group of transcription factors that are involved in numerous processes, including lipid metabolism and adipogenesis. By comparing liver mRNAs of wild-type and PPARalpha-null mice using microarrays, a novel putative target gene of PPARalpha, G0S2 (G0/G1 switch gene 2), was identified. Hepatic expression of G0S2 was up-regulated by fasting and by the PPARalpha agonist Wy14643 in a PPARalpha-dependent manner. Surprisingly, the G0S2 mRNA level was highest in brown and white adipose tissue and was greatly up-regulated during mouse 3T3-L1 and human SGBS (Simpson-Golabi-Behmel syndrome) adipogenesis. Transactivation, gel shift and chromatin immunoprecipitation assays indicated that G0S2 is a direct PPARgamma and probable PPARalpha target gene with a functional PPRE (PPAR-responsive element) in its promoter. Up-regulation of G0S2 mRNA seemed to be specific for adipogenesis, and was not observed during osteogenesis or myogenesis. In 3T3-L1 fibroblasts, expression of G0S2 was associated with growth arrest, which is required for 3T3-L1 adipogenesis. Together, these data indicate that G0S2 is a novel target gene of PPARs that may be involved in adipocyte differentiation.
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Affiliation(s)
- Fokko Zandbergen
- *Nutrition, Metabolism and Genomics Group, Wageningen University, 6700 EV, Wageningen, The Netherlands
| | - Stéphane Mandard
- *Nutrition, Metabolism and Genomics Group, Wageningen University, 6700 EV, Wageningen, The Netherlands
| | - Pascal Escher
- †Institute of Physiology, Pharmazentrum, University of Basel, Basel, CH-4056, Switzerland
- §Pfizer Global Research & Development, Ann Arbor Laboratories, Molecular Sciences, 2800 Plymouth Road, Ann Arbor, MI 48105, U.S.A
| | - Nguan Soon Tan
- ‡Center for Integrative Genomics, University of Lausanne, Lausanne, CH-1015, Switzerland
| | - David Patsouris
- *Nutrition, Metabolism and Genomics Group, Wageningen University, 6700 EV, Wageningen, The Netherlands
| | - Tim Jatkoe
- §Pfizer Global Research & Development, Ann Arbor Laboratories, Molecular Sciences, 2800 Plymouth Road, Ann Arbor, MI 48105, U.S.A
| | - Sandra Rojas-Caro
- §Pfizer Global Research & Development, Ann Arbor Laboratories, Molecular Sciences, 2800 Plymouth Road, Ann Arbor, MI 48105, U.S.A
| | - Steve Madore
- §Pfizer Global Research & Development, Ann Arbor Laboratories, Molecular Sciences, 2800 Plymouth Road, Ann Arbor, MI 48105, U.S.A
| | - Walter Wahli
- ‡Center for Integrative Genomics, University of Lausanne, Lausanne, CH-1015, Switzerland
| | - Sherrie Tafuri
- §Pfizer Global Research & Development, Ann Arbor Laboratories, Molecular Sciences, 2800 Plymouth Road, Ann Arbor, MI 48105, U.S.A
| | - Michael Müller
- *Nutrition, Metabolism and Genomics Group, Wageningen University, 6700 EV, Wageningen, The Netherlands
| | - Sander Kersten
- *Nutrition, Metabolism and Genomics Group, Wageningen University, 6700 EV, Wageningen, The Netherlands
- To whom correspondence should be addressed (email )
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90
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Abstract
Fibrates are a widely used class of hypolipidemic drugs. The effects of fibrates are mediated through the activation of the transcription factor peroxisome proliferator-activated receptor a (PPARa). Fibrates act to modulate the transcription of genes that encode proteins controlling lipid transport and metabolism. Fibrates also exert pleiotropic anti-inflammatory effects by down regulating expression of genes encoding inflammatory cytokines and acute phase response proteins. These combined actions translate into clinical benefit as demonstrated by the reduction in cardiovascular morbidity and mortality in primary and secondary intervention trials.
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91
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Tachibana K, Kobayashi Y, Tanaka T, Tagami M, Sugiyama A, Katayama T, Ueda C, Yamasaki D, Ishimoto K, Sumitomo M, Uchiyama Y, Kohro T, Sakai J, Hamakubo T, Kodama T, Doi T. Gene expression profiling of potential peroxisome proliferator-activated receptor (PPAR) target genes in human hepatoblastoma cell lines inducibly expressing different PPAR isoforms. NUCLEAR RECEPTOR 2005; 3:3. [PMID: 16197558 PMCID: PMC1262764 DOI: 10.1186/1478-1336-3-3] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/24/2005] [Accepted: 10/03/2005] [Indexed: 11/10/2022]
Abstract
BACKGROUND Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors and commonly play an important role in the regulation of lipid homeostasis. To identify human PPARs-responsive genes, we established tetracycline-regulated human hepatoblastoma cell lines that can be induced to express each human PPAR and investigated the gene expression profiles of these cells. RESULTS The expression of each introduced PPAR gene was investigated using the various concentrations of doxycycline in the culture media. We found that the expression of each PPAR subtype was tightly controlled by the concentration of doxycycline in these established cell lines. DNA microarray analyses using these cell lines were performed with or without adding each subtype ligand and provided much important information on the PPAR target genes involved in lipid metabolism, transport, storage and other activities. Interestingly, it was noted that while ligand-activated PPARdelta induced target gene expression, unliganded PPARdelta repressed these genes. The real-time RT-PCR was used to verify the altered expression of selected genes by PPARs and we found that these genes were induced to express in the same pattern as detected in the microarray analyses. Furthermore, we analysed the 5'-flanking region of the human adipose differentiation-related protein (adrp) gene that responded to all subtypes of PPARs. From the detailed analyses by reporter assays, the EMSAs, and ChIP assays, we determined the functional PPRE of the human adrp gene. CONCLUSION The results suggest that these cell lines are important tools used to identify the human PPARs-responsive genes.
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Affiliation(s)
- Keisuke Tachibana
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Yumi Kobayashi
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Toshiya Tanaka
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
| | - Masayuki Tagami
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Akira Sugiyama
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
- Perseus Proteomics Inc, Tokyo, Japan
| | - Tatsuya Katayama
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Chihiro Ueda
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Daisuke Yamasaki
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Kenji Ishimoto
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Mikako Sumitomo
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Yasutoshi Uchiyama
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
- Perseus Proteomics Inc, Tokyo, Japan
| | - Takahide Kohro
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
| | - Juro Sakai
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
| | - Takao Hamakubo
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
| | - Tatsuhiko Kodama
- Laboratory for System Biology and Medicine, The Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan
| | - Takefumi Doi
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
- Graduate School of Medicine, Osaka University, Osaka, Japan
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92
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Chui PC, Guan HP, Lehrke M, Lazar MA. PPARgamma regulates adipocyte cholesterol metabolism via oxidized LDL receptor 1. J Clin Invest 2005; 115:2244-56. [PMID: 16007265 PMCID: PMC1172230 DOI: 10.1172/jci24130] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Accepted: 05/17/2005] [Indexed: 01/21/2023] Open
Abstract
In addition to its role in energy storage, adipose tissue also accumulates cholesterol. Concentrations of cholesterol and triglycerides are strongly correlated in the adipocyte, but little is known about mechanisms regulating cholesterol metabolism in fat cells. Here we report that antidiabetic thiazolidinediones (TZDs) and other ligands for the nuclear receptor PPARgamma dramatically upregulate oxidized LDL receptor 1 (OLR1) in adipocytes by facilitating the exchange of coactivators for corepressors on the OLR1 gene in cultured mouse adipocytes. TZDs markedly stimulate the uptake of oxidized LDL (oxLDL) into adipocytes, and this requires OLR1. Increased OLR1 expression, resulting either from TZD treatment or adenoviral gene delivery, significantly augments adipocyte cholesterol content and enhances fatty acid uptake. OLR1 expression in white adipose tissue is increased in obesity and is further induced by PPARgamma ligand treatment in vivo. Serum oxLDL levels are decreased in both lean and obese diabetic animals treated with TZDs. These data identify OLR1 as a novel PPARgamma target gene in adipocytes. While the physiological role of adipose tissue in cholesterol and oxLDL metabolism remains to be established, the induction of OLR1 is a potential means by which PPARgamma ligands regulate lipid metabolism and insulin sensitivity in adipocytes.
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Affiliation(s)
- Patricia C Chui
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, and The Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6149, USA
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93
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Guan HP, Ishizuka T, Chui PC, Lehrke M, Lazar MA. Corepressors selectively control the transcriptional activity of PPARgamma in adipocytes. Genes Dev 2005; 19:453-61. [PMID: 15681609 PMCID: PMC548946 DOI: 10.1101/gad.1263305] [Citation(s) in RCA: 238] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Peroxisome proliferator-activated receptor gamma (PPARgamma) is the master regulator of adipogenesis as well as the target of thiazolidinedione (TZD) antidiabetic drugs. Many PPARgamma target genes are induced during adipogenesis, but others, such as glycerol kinase (GyK), are expressed at low levels in adipocytes and dramatically up-regulated by TZDs. Here, we have explored the mechanism whereby an exogenous PPARgamma ligand is selectively required for adipocyte gene expression. The GyK gene contains a functional PPARgamma-response element to which endogenous PPARgamma is recruited in adipocytes. However, unlike the classic PPARgamma-target gene aP2, which is constitutively associated with coactivators, the GyK gene is targeted by nuclear receptor corepressors in adipocytes. TZDs trigger the dismissal of corepressor histone deacetylase (HDAC) complexes and the recruitment of coactivators to the GyK gene. TZDs also induce PPARgamma-Coactivator 1alpha (PGC-1alpha), whose recruitment to the GyK gene is sufficient to release the corepressors. Thus, selective modulation of adipocyte PPARgamma target genes by TZDs involves the dissociation of corepressors by direct and indirect mechanisms.
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Affiliation(s)
- Hong-Ping Guan
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, The Penn Diabetes Center, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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