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Talukdar S, Bhatnagar S, Dridi S, Hillgartner FB. Chenodeoxycholic acid suppresses the activation of acetyl-coenzyme A carboxylase-alpha gene transcription by the liver X receptor agonist T0-901317. J Lipid Res 2007; 48:2647-63. [PMID: 17823458 DOI: 10.1194/jlr.m700189-jlr200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The therapeutic utility of liver X receptor (LXR) agonists in treating atherosclerosis is limited by an undesired accumulation of triglycerides in the blood and liver. This effect is caused by an increase in the transcription of genes involved in fatty acid synthesis. Here, we show that the primary bile acid, chenodeoxycholic acid (CDCA), antagonizes the stimulatory effect of the synthetic LXR agonist, T0-901317, on the expression of acetyl-coenzyme A carboxylase-alpha (ACCalpha) and other lipogenic enzymes in chick embryo hepatocyte cultures. CDCA inhibits T0-901317-induced ACCalpha transcription by suppressing the enhancer activity of a LXR response unit (-101 to -71 bp) that binds LXR and sterol-regulatory element binding protein-1 (SREBP-1). We also demonstrate that CDCA decreases the expression of SREBP-1 in the nucleus and the acetylation of histone H3 and H4 at the ACCalpha LXR response unit. The CDCA-mediated reduction in ACCalpha expression is associated with a decrease in the expression of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) and small heterodimer partner and an increase in the expression of fibroblast growth factor-19 (FGF-19). Ectopic expression of FGF-19 decreases T0-901317-induced ACCalpha expression. Inhibition of p38 mitogen-activated protein kinase (MAPK) and/or extracellular signal-regulated kinase (ERK) suppresses the effects of CDCA on the expression of ACCalpha, SREBP-1, PGC-1alpha, and FGF-19. These results demonstrate that CDCA inhibits T0-901317-induced ACCalpha transcription by suppressing the activity of LXR and SREBP-1. We postulate that p38 MAPK, ERK, PGC-1alpha, and FGF-19 are components of the signaling pathway(s) mediating the regulation of ACCalpha gene transcription by CDCA.
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Affiliation(s)
- Saswata Talukdar
- Department of Biochemistry, School of Medicine, West Virginia University, Morgantown, WV 26506, USA
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202
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Commerford SR, Vargas L, Dorfman SE, Mitro N, Rocheford EC, Mak PA, Li X, Kennedy P, Mullarkey TL, Saez E. Dissection of the insulin-sensitizing effect of liver X receptor ligands. Mol Endocrinol 2007; 21:3002-12. [PMID: 17717069 DOI: 10.1210/me.2007-0156] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The liver X receptors (LXRalpha and beta) are nuclear receptors that coordinate carbohydrate and lipid metabolism. Treatment of insulin-resistant mice with synthetic LXR ligands enhances glucose tolerance, inducing changes in gene expression expected to decrease hepatic gluconeogenesis (via indirect suppression of gluconeogenic enzymes) and increase peripheral glucose disposal (via direct up-regulation of glut4 in fat). To evaluate the relative contribution of each of these effects on whole-body insulin sensitivity, we performed hyperinsulinemic-euglycemic clamps in high-fat-fed insulin-resistant rats treated with an LXR agonist or a peroxisome proliferator-activated receptor gamma ligand. Both groups showed significant improvement in insulin action. Interestingly, rats treated with LXR ligand had lower body weight and smaller fat cells than controls. Insulin-stimulated suppression of the rate of glucose appearance (Ra) was pronounced in LXR-treated rats, but treatment failed to enhance peripheral glucose uptake (R'g), despite increased expression of glut4 in epididymal fat. To ascertain whether LXR ligands suppress hepatic gluconeogenesis directly, mice lacking LXRalpha (the primary isotype in liver) were treated with LXR ligand, and gluconeogenic gene expression was assessed. LXR activation decreased expression of gluconeogenic genes in wild-type and LXRbeta null mice, but failed to do so in animals lacking LXRalpha. Our observations indicate that despite inducing suggestive gene expression changes in adipose tissue in this model of diet-induced insulin resistance, the antidiabetic effect of LXR ligands is primarily due to effects in the liver that appear to require LXRalpha. These findings have important implications for clinical development of LXR agonists as insulin sensitizers.
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Affiliation(s)
- S Renee Commerford
- The Genomics Institute of the Novartis Research Foundation, San Diego, California 92121, USA
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203
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Gene expression of transporters and phase I/II metabolic enzymes in murine small intestine during fasting. BMC Genomics 2007; 8:267. [PMID: 17683626 PMCID: PMC1971072 DOI: 10.1186/1471-2164-8-267] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2007] [Accepted: 08/07/2007] [Indexed: 12/30/2022] Open
Abstract
Background Fasting has dramatic effects on small intestinal transport function. However, little is known on expression of intestinal transport and phase I/II metabolism genes during fasting and the role the fatty acid-activated transcription factor PPARα may play herein. We therefore investigated the effects of fasting on expression of these genes using Affymetrix GeneChip MOE430A arrays and quantitative RT-PCR. Results After 24 hours of fasting, expression levels of 33 of the 253 analyzed transporter and phase I/II metabolism genes were changed. Upregulated genes were involved in transport of energy-yielding molecules in processes such as glycogenolysis (G6pt1) and mitochondrial and peroxisomal oxidation of fatty acids (Cact, Mrs3/4, Fatp2, Cyp4a10, Cyp4b1). Other induced genes were responsible for the inactivation of the neurotransmitter serotonin (Sert, Sult1d1, Dtd, Papst2), formation of eicosanoids (Cyp2j6, Cyp4a10, Cyp4b1), or for secretion of cholesterol (Abca1 and Abcg8). Cyp3a11, typically known because of its drug metabolizing capacity, was also increased. Fasting had no pronounced effect on expression of phase II metabolic enzymes, except for glutathione S-transferases which were down-regulated. Time course studies revealed that some genes were acutely regulated, whereas expression of other genes was only affected after prolonged fasting. Finally, we identified 8 genes that were PPARα-dependently upregulated upon fasting. Conclusion We have characterized the response to fasting on expression of transporters and phase I/II metabolic enzymes in murine small intestine. Differentially expressed genes are involved in a variety of processes, which functionally can be summarized as a) increased oxidation of fat and xenobiotics, b) increased cholesterol secretion, c) increased susceptibility to electrophilic stressors, and d) reduced intestinal motility. This knowledge increases our understanding of gut physiology, and may be of relevance for e.g. pre-surgery regimen of patients.
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204
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Abstract
Aberrant cholesterol metabolism has been implicated in Alzheimer disease (AD) and other neurological disorders. Oxysterols and other cholesterol oxidation products are effective ligands of liver X activated receptor (LXR) nuclear receptors, major regulators of genes subserving cholesterol homeostasis. LXR receptors act as molecular sensors of cellular cholesterol concentrations and effectors of tissue cholesterol reduction. Following their interaction with oxysterols, activation of LXRs induces the expression of ATP-binding cassette, sub-family A member 1, a pivotal modulator of cholesterol efflux. The relative solubility of oxysterols facilitates lipid flux among brain compartments and egress across the blood-brain barrier. Oxysterol-mediated LXR activation induces local apoE biosynthesis (predominantly in astrocytes) further enhancing cholesterol re-distribution and removal. Activated LXRs invoke additional neuroprotective mechanisms, including induction of genes governing bile acid synthesis (sterol elimination pathway), apolipoprotein elaboration, and amyloid precursor protein processing. The latter translates into attenuated beta-amyloid production that may ameliorate amyloidogenic neurotoxicity in AD brain. Stress-induced up-regulation of the heme-degrading enzyme, heme oxygenase-1 in AD-affected astroglia may impact central lipid homeostasis by promoting the oxidation of cholesterol to a host of oxysterol intermediates. Synthetic oxysterol-mimetic drugs that activate LXR receptors within the CNS may provide novel therapeutics for management of AD and other neurological afflictions characterized by deranged tissue cholesterol homeostasis.
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Affiliation(s)
- Jacob Vaya
- The Laboratory of Natural Medicinal Compounds, Migal-Galilee Technology Center, Kiryat-Shmona, and Tel Hai Academic College, IsraelDepartment of Neurology and Neurosurgery, McGill University, Montreal, Quebec, CanadaCentre for Neurotranslational Research, Lady Davis Institute for Medical Research, SMBD Jewish General Hospital, Montreal, Quebec, Canada
| | - Hyman M Schipper
- The Laboratory of Natural Medicinal Compounds, Migal-Galilee Technology Center, Kiryat-Shmona, and Tel Hai Academic College, IsraelDepartment of Neurology and Neurosurgery, McGill University, Montreal, Quebec, CanadaCentre for Neurotranslational Research, Lady Davis Institute for Medical Research, SMBD Jewish General Hospital, Montreal, Quebec, Canada
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205
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Chuu CP, Kokontis JM, Hiipakka RA, Liao S. Modulation of liver X receptor signaling as novel therapy for prostate cancer. J Biomed Sci 2007; 14:543-53. [PMID: 17372849 DOI: 10.1007/s11373-007-9160-8] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Accepted: 02/26/2007] [Indexed: 10/23/2022] Open
Abstract
Liver X receptors (LXRs) are important regulators of cholesterol, fatty acid, and glucose homeostasis. LXR agonists are effective for treatment of murine models of atherosclerosis, diabetes, and Alzheimer's disease. Recently we observed that LXR agonists suppressed proliferation of prostate and breast cancer cells in vitro and treatment of mice with the LXR agonist T0901317 suppressed the growth of prostate tumor xenografts. LXR agonists appear to cause G1 cell cycle arrest in cells by reducing expression of Skp2 and inducing the accumulation of p27(Kip). T0901317 induced expression of ATP-binding cassette transporter A1 (ABCA1) and delayed the progression of androgen-dependent human prostate tumor xenografts towards androgen-independency in mice. Phytosterols, the plant equivalent of mammalian cholesterol, have recently been shown to be agonists for LXRs. beta-Sitosterol and campesterol, the two most common phytosterols, suppressed proliferation of prostate and breast cancer cells. The anticancer activity of phytosterols may be due to LXR signaling. This review examines the potential use of LXR signaling as a therapeutic target in prostate and other cancers.
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Affiliation(s)
- Chih-Pin Chuu
- The Ben May Department for Cancer Research, The University of Chicago, 929 East 57th Street, CIS W325F, Chicago, IL 60637, USA
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206
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Moore DD, Kato S, Xie W, Mangelsdorf DJ, Schmidt DR, Xiao R, Kliewer SA. International Union of Pharmacology. LXII. The NR1H and NR1I receptors: constitutive androstane receptor, pregnene X receptor, farnesoid X receptor alpha, farnesoid X receptor beta, liver X receptor alpha, liver X receptor beta, and vitamin D receptor. Pharmacol Rev 2007; 58:742-59. [PMID: 17132852 DOI: 10.1124/pr.58.4.6] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The nuclear receptors of the NR1H and NR1I subgroups include the constitutive androstane receptor, pregnane X receptor, farnesoid X receptors, liver X receptors, and vitamin D receptor. The newly emerging functions of these related receptors are under the control of metabolic pathways, including metabolism of xenobiotics, bile acids, cholesterol, and calcium. This review summarizes results of structural, pharmacologic, and genetic studies of these receptors.
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Affiliation(s)
- David D Moore
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
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207
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Cummins CL, Mangelsdorf DJ. Liver X receptors and cholesterol homoeostasis: spotlight on the adrenal gland. Biochem Soc Trans 2007; 34:1110-3. [PMID: 17073762 DOI: 10.1042/bst0341110] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The LXRs (liver X receptors) (LXRalpha and LXRbeta) are nuclear hormone receptors that are activated by oxysterols, endogenous oxidative metabolites of cholesterol. These receptors regulate an integrated network of genes that control whole body cholesterol and lipid homoeostasis. A brief overview of the mechanism of this regulation by LXRs in the liver, macrophage and intestine will be outlined, followed by data from our recent work demonstrating that LXRalpha is crucial in maintaining adrenal cholesterol homoeostasis. In the adrenal gland, oxysterols are formed as intermediates in the conversion of cholesterol into steroid hormones and can act as endogenous activators of LXR. We have found using both gain- and loss-of-function models that LXR acts to maintain free cholesterol below toxic levels in the adrenal gland, through the co-ordinated regulation of genes involved in cholesterol efflux [ABCA1 (ATP-binding-cassette transporter A1)], storage (sterol-regulatory-element-binding protein-1c and apolipoprotein E) and metabolism to steroid hormones (steroidogenic acute regulatory protein). Furthermore, we show that under chronic dietary stress, the adrenal glands of LXR-null mice (and not wild-type mice) accumulate free cholesterol. These results support the role of LXR as a global regulator of cholesterol homoeostasis, where LXR provides a safety valve to limit free cholesterol in tissues experiencing high cholesterol flux.
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Affiliation(s)
- C L Cummins
- Howard Hughes Medical Institute, Department of Pharmacology, University of Texas Southwestern Medical Center, 6001 Forest Park, Dallas, TX 75390-9050, USA.
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208
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Yamamoto T, Shimano H, Inoue N, Nakagawa Y, Matsuzaka T, Takahashi A, Yahagi N, Sone H, Suzuki H, Toyoshima H, Yamada N. Protein kinase A suppresses sterol regulatory element-binding protein-1C expression via phosphorylation of liver X receptor in the liver. J Biol Chem 2007; 282:11687-95. [PMID: 17296605 DOI: 10.1074/jbc.m611911200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sterol regulatory element-binding protein (SREBP)-1c is a transcription factor that controls synthesis of fatty acids and triglycerides in the liver and is highly regulated by nutrition and hormones. In the current studies we show that protein kinase A (PKA), a mediator of glucagon/cAMP, a fasting signaling, suppresses SREBP-1c by modulating the activity of liver X receptor alpha (LXRalpha), a dominant activator of SREBP-1c expression. Activation of PKA repressed LXR-induced SREBP-1c expression both in rat primary hepatocytes and mouse livers. Promoter analyses revealed that the LXRalpha-binding site in the SREBP-1c promoter is responsible for PKA inhibitory effect on SREBP-1c transcription. In vitro and in vivo PKA directly phosphorylated LXRalpha, and the two consensus PKA target sites (195, 196 serines and 290, 291 serines) in its ligand binding/heterodimerization domain were crucial for the inhibition of LXR signaling. PKA phosphorylation of LXRalpha caused impaired DNA binding activity by preventing LXRalpha/RXR dimerization and decreased its transcription activity by inhibiting recruitment of coactivator SCR-1 and enhancing recruitment of corepressor NcoR1. These results indicate that LXRalpha is regulated not only by oxysterol derivatives but also by PKA-mediated phosphorylation, which suggests that nutritional regulation of SREBP-1c and lipogenesis could be regulated at least partially through modulation of LXR.
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Affiliation(s)
- Takashi Yamamoto
- Department of Internal Medicine, Metabolism and Endocrinology, Graduate School of Comprehensive Human Sciences and Center for Tsukuba Advanced Research Alliance, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan
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209
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Prüfer K, Boudreaux J. Nuclear localization of liver X receptor α and β is differentially regulated. J Cell Biochem 2007; 100:69-85. [PMID: 16888799 DOI: 10.1002/jcb.21006] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Activity of nuclear receptors is regulated by their nuclear localization. Liver X receptors (LXR) alpha and beta are nuclear receptors that regulate transcription of genes for cholesterol metabolism, cholesterol transport, and lipogenesis. While LXR alpha and beta are very similar in structure and exhibit similar ligand binding properties, their physiological roles are quite different. Since the LXRs fall into a class of receptors that move between the nucleus and cytoplasm, experiments were conducted to determine whether LXR alpha and LXR beta show differences in their nuclear localization pattern. To determine the location of each receptor, cell lines stably expressing yellow fluorescent protein (YFP) chimeras with either LXR alpha or LXR beta were examined. Retention in the nucleus of the chimeric proteins in the presence or absence of ligands was assessed using fluorescence microscopy coupled with digitonin permeabilization assays. Surprisingly, differences were found between LXR alpha and LXR beta. Whereas unliganded LXR alpha was retained in the nucleus, unliganded LXR beta was partially exported. Mutations were then introduced into putative nuclear localization sequences (NLS) to determine which sequences are important for nuclear localization and function. Mutation in one such sequence abolished nuclear localization of LXR alpha, whereas the analogous change in LXR beta had a much less dramatic effect. Mutations in analogous putative NLS also differentially affected transcriptional activation by LXR alpha and LXR beta. These data demonstrate for the first time that nuclear retention and localization as well as function of LXR alpha and LXR beta are differentially regulated.
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Affiliation(s)
- Kirsten Prüfer
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, USA.
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210
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Nilsson M, Stulnig TM, Lin CY, Yeo AL, Nowotny P, Liu ET, Steffensen KR. Liver X receptors regulate adrenal steroidogenesis and hypothalamic-pituitary-adrenal feedback. Mol Endocrinol 2006; 21:126-37. [PMID: 16973760 DOI: 10.1210/me.2006-0187] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The nuclear hormone receptors liver X receptor alpha (LXRalpha) (NR1H3) and LXRbeta (NR1H2) are established regulators of cholesterol, lipid, and glucose metabolism and are attractive drug targets for the treatment of diabetes and cardiovascular disease. Adrenal steroid hormones including glucocorticoids and mineralocorticoids are known to interfere with glucose metabolism, insulin signaling, and blood pressure regulation. Here we present genome-wide expression profiles of LXR-responsive genes in both the adrenal and the pituitary gland. LXR activation in cultured adrenal cells inhibited expression of multiple steroidogenic genes and consequently decreased adrenal steroid hormone production. In addition, LXR agonist treatment elevated ACTH mRNA expression and hormone secretion from pituitary cells both in vitro and in vivo. Reduced expression of the glucocortioid-activating enzyme 11beta-hydroxysteroid dehydrogenase 1 in pituitary cells upon LXR activation suggests blunting of the negative feedback of glucocorticoids by LXRs. In conclusion, LXRs independently interfere with the hypothalamic-pituitary-adrenal axis regulation at the level of the pituitary and the adrenal gland.
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Affiliation(s)
- Maria Nilsson
- Department of Biosciences and Nutrition, Karolinska Institutet, S-14157 Huddinge, Sweden
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211
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Schuster GU, Johansson L, Kietz S, Stulnig TM, Parini P, Gustafsson JA. Improved metabolic control by depletion of Liver X Receptors in mice. Biochem Biophys Res Commun 2006; 348:176-82. [PMID: 16876124 DOI: 10.1016/j.bbrc.2006.07.044] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2006] [Accepted: 07/10/2006] [Indexed: 10/24/2022]
Abstract
Liver X Receptors (LXRs) coordinate the regulation of lipid and carbohydrate metabolism and insulin signaling. LXR-ligands lower plasma glucose in hyperglycemic rodents and have consequently been proposed as anti-diabetic agents. We investigated the metabolic effects induced by high carbohydrate diet in LXRalpha(-/-)beta(-/-) mice. Irrespective of diets, LXRalpha(-/-)beta(-/-) mice had reduced fatty acid, insulin, and C-peptide plasma levels than wild-type controls, suggesting a lower insulin production. High carbohydrate diet decreased the plasma glucose levels and the homeostasis model assessment (HOMA)-index in LXRalpha(-/-)beta(-/-) mice and increased hepatic triglyceride content and mRNA levels of lipogenic genes in wild-type and LXRalpha(-/-)beta(-/-) mice, proportionally. In wild-type mice high carbohydrate diet was associated with induced expression of LXR (1.5-fold), despite unchanged SREBP-1c expression. LXRalpha(-/-)beta(-/-) mice responded to this diet by induction of SREBP-1c. Our study suggests that in LXRalpha(-/-)beta(-/-) mice, glucose utilization seems to be privileged possibly due to reduced circulating free fatty acid levels.
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Affiliation(s)
- Gertrud U Schuster
- Department of Biosciences and Nutrition, Karolinska University Hospital, Novum, Karolinska Institutet, S-141 57 Huddinge, Sweden.
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212
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Talukdar S, Hillgartner FB. The mechanism mediating the activation of acetyl-coenzyme A carboxylase-alpha gene transcription by the liver X receptor agonist T0-901317. J Lipid Res 2006; 47:2451-61. [PMID: 16931873 DOI: 10.1194/jlr.m600276-jlr200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In birds and mammals, agonists of the liver X receptor (LXR) increase the expression of enzymes that make up the fatty acid synthesis pathway. Here, we investigate the mechanism by which the synthetic LXR agonist, T0-901317, increases the transcription of the acetyl-coenzyme A carboxylase-alpha (ACC alpha) gene in chick embryo hepatocyte cultures. Transfection analyses demonstrate that activation of ACC alpha transcription by T0-901317 is mediated by a cis-acting regulatory unit (-101 to -71 bp) that is composed of a liver X receptor response element (LXRE) and a sterol-regulatory element (SRE). The SRE enhances the ability of the LXRE to activate ACC alpha transcription in the presence of T0-901317. Treating hepatocytes with T0-901317 increases the concentration of mature sterol-regulatory element binding protein-1 (SREBP-1) in the nucleus and the acetylation of histone H3 and histone H4 at the ACC alpha LXR response unit. These results indicate that T0-901317 increases hepatic ACC alpha transcription by directly activating LXR*retinoid X receptor (RXR) heterodimers and by increasing the activity of an accessory transcription factor (SREBP-1) that enhances ligand induced-LXR*RXR activity.
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Affiliation(s)
- Saswata Talukdar
- Department of Biochemistry and Molecular Pharmacology, School of Medicine, West Virginia University, Morgantown, WV 26506, USA
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213
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Steffensen KR, Robertson K, Gustafsson JA, Andersen CY. Reduced fertility and inability of oocytes to resume meiosis in mice deficient of the Lxr genes. Mol Cell Endocrinol 2006; 256:9-16. [PMID: 16895745 DOI: 10.1016/j.mce.2006.03.044] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/16/2006] [Indexed: 10/24/2022]
Abstract
Cholesterol precursors act as activators of the nuclear hormone receptor, liver X receptor (LXR). One of these LXR-activating ligands is meiosis activating sterol (MAS), which also induces resumption of meiosis in oocytes from mice in vitro. Whether LXR participates in the regulation of oocyte maturation and whether the expression of either one of the two paralogues of LXR (alpha and beta) affect fertility of mice has, however, not yet been clarified. Female mice lacking Lxra, Lxrb or both genes (Lxra(-/-), Lxrb(-/-) and Lxrab(-/-), respectively) conceive less frequently and have significantly fewer pups per litter as compared to wild type mice. Both Lxra and Lxrb mRNA were found to be expressed in mouse oocytes. The relative expression of, in particular, Lxrb was almost two orders of magnitude higher than in liver, brain and testis. A water-soluble LXR agonist caused naked oocytes, but not cumulus enclosed oocytes (CEO), from wild type mice to resume meiosis significantly more often than control oocytes. Follicle stimulating hormone (FSH) is a potent stimulator of meiosis in CEO from wild type mice, but was without effect in mice lacking both Lxr genes. Zymosterol, a MAS active substance, induced resumption of meiosis in oocytes from Lxrab(-/-) mice, but significantly less effectively than in oocytes from wild type mice. Taken together, LXRs seem to affect ovarian function, suggesting specific roles of cholesterol precursors in regulation of female reproduction.
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Affiliation(s)
- Knut R Steffensen
- Department of Biosciences and Nutrition at NOVUM, Karolinska Institutet, Sweden
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214
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Robertson KM, Norgård M, Windahl SH, Hultenby K, Ohlsson C, Andersson G, Gustafsson JA. Cholesterol-sensing receptors, liver X receptor alpha and beta, have novel and distinct roles in osteoclast differentiation and activation. J Bone Miner Res 2006; 21:1276-87. [PMID: 16869726 DOI: 10.1359/jbmr.060503] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
UNLABELLED The liver X receptor (alpha,beta) is responsible for regulating cholesterol homeostasis in cells. However, our studies using the LXRalpha-/-, LXRbeta-/-, and LXRalpha-/-beta-/- mice show that both LXRalpha and beta are also important for bone turnover, mainly by regulating osteoclast differentiation/activity. INTRODUCTION The liver X receptors (alpha,beta) are primarily responsible for regulating cholesterol homeostasis within cells and the whole body. However, as recent studies show that the role for this receptor is expanding, we studied whether the LXRs could be implicated in bone homeostasis and development. MATERIALS AND METHODS pQCT was performed on both male and female LXRalpha-/-, LXRbeta-/-, LXRalpha-/-beta-/-, and WT mice at 4 months and 1 year of age. Four-month-old female mice were additionally analyzed with reference to qPCR, immunohistochemistry, histomorphometry, transmission electron microscopy, and serum bone turnover markers. RESULTS At the mRNA level, LXRbeta was more highly expressed than LXRalpha in both whole long bones and differentiating osteoblast-like MC3T3-E1 and osteoclast-like RAW 264.7 cells. Four-month-old female LXRalpha-/- mice had a significant increase in BMD because of an increase in all cortical parameters. No difference was seen regarding trabecular BMD. Quantitative histomorphometry showed that these mice had significantly more endosteal osteoclasts in the cortical bone; however, these cells appeared less active than normal cells as suggested by a significant reduction in serum levels of cross-linked carboxyterminal telopeptides of type I collagen (CTX) and a reduction in bone TRACP activity. Conversely, the female LXRbeta-/- mice exhibited no change in BMD, presumably because a significant decline in the number of the trabecular osteoclasts was compensated for by an increase in the expression of the osteoclast markers cathepsin K and TRACP. These mice also had a significant decrease in serum CTX, suggesting decreased bone resorption; however, in addition presented with an increase in the expression of osteoblast associated genes, bone formation markers, and serum leptin levels. CONCLUSIONS Our findings show that both LXRs influence cellular function within the bone, with LXRalpha having an impact on osteoclast activity, primarily in cortical bone, whereas LXRbeta modulates trabecular bone turnover.
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215
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Wang YY, Dahle MK, Agren J, Myhre AE, Reinholt FP, Foster SJ, Collins JL, Thiemermann C, Aasen AO, Wang JE. Activation of the liver X receptor protects against hepatic injury in endotoxemia by suppressing Kupffer cell activation. Shock 2006; 25:141-6. [PMID: 16525352 DOI: 10.1097/01.shk.0000191377.78144.d9] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Recent reports have demonstrated that liver X receptors (LXRs) of the nuclear receptor family have anti-inflammatory effects on macrophages. Here we examine whether activation of LXR by the synthetic agonist GW3965 can ameliorate the liver injury/dysfunction caused by endotoxins in the rat. Male Wistar rats received GW3965 (0.3 mg/kg) or vehicle (50% dimethyl sulfoxide) 30 min before coadministration of lipopolysaccharide (LPS, 5 mg/kg i.v.) and peptidoglycan (1 mg/kg i.v.). Treatment with GW3965 attenuated the increase in the plasma levels of alanine aminotransferase and bilirubin (markers of liver injury/dysfunction) as well as the focal hepatocyte necrosis (histology) caused by coadministration of LPS and peptidoglycan. This protective effect of GW3965 treatment was associated with reduced infiltration of mast cells in the liver (histopathology) and reduced gene expression of the chemokines eotaxins 1 and 2, whereas MIP-2 mRNA levels were not affected. Plasma levels of tumor necrosis factor alpha and prostaglandin E2 were significantly attenuated by GW3965, whereas plasma interleukins 6 and 10 were not altered. High expression of LXRalpha mRNA was observed in Kupffer cell cultures, suggesting that Kupffer cells are targets of GW3965. Subsequent in vitro studies in Kupffer cells demonstrated that exposure to GW3965 attenuated the LPS-induced release of tumor necrosis factor alpha and prostaglandin E2 in a dose-dependent manner. In conclusion, this study demonstrates that activation of LXR by GW3965 protects against liver injury and dysfunction in a rat model of endotoxemia, in part by exerting an anti-inflammatory effect on Kupffer cells.
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Affiliation(s)
- Yun Yong Wang
- University of Oslo, Faculty Division Rikshospitalet, Institute for Surgical Research, Sognsvannsveien 20, 0027 Oslo, Norway
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Quinet EM, Savio DA, Halpern AR, Chen L, Schuster GU, Gustafsson JA, Basso MD, Nambi P. Liver X receptor (LXR)-beta regulation in LXRalpha-deficient mice: implications for therapeutic targeting. Mol Pharmacol 2006; 70:1340-9. [PMID: 16825483 DOI: 10.1124/mol.106.022608] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The nuclear receptors liver X receptor (LXR) LXRalpha and LXRbeta are differentially expressed ligand-activated transcription factors that induce genes controlling cholesterol homeostasis and lipogenesis. Synthetic ligands for both receptor subtypes activate ATP binding cassette transporter A1 (ABCA1)-mediated cholesterol metabolism, increase reverse cholesterol transport, and provide atheroprotection in mice. However, these ligands may also increase hepatic triglyceride (TG) synthesis via a sterol response element binding protein 1c (SREBP-1c)-dependent mechanism through a process reportedly regulated by LXRalpha. We studied pan-LXRalpha/beta agonists in LXRalpha knockout mice to assess the contribution of LXRbeta to the regulation of selected target genes. In vitro dose-response studies with macrophages from LXRalpha-/- and beta-/- mice confirm an equivalent role for LXRalpha and LXRbeta in the regulation of ABCA1 and SREBP-1c gene expression. Cholesterol-efflux studies verify that LXRbeta can drive apoA1-dependent cholesterol mobilization from macrophages. The in vivo role of LXRbeta in liver was further evaluated by treating LXRalpha-/- mice with a pan-LXRalpha/beta agonist. High-density lipoprotein (HDL) cholesterol increased without significant changes in plasma TG or very low density lipoprotein. Analysis of hepatic gene expression consistently revealed less activation of ABCA1 and SREBP-1c genes in the liver of LXRalpha null animals than in treated wild-type controls. In addition, hepatic CYP7A1 and several genes involved in fatty acid/TG biosynthesis were not induced. In peripheral tissues from these LXRalpha-null mice, LXRbeta activation increases ABCA1 and SREBP-1c gene expression in a parallel manner. However, putative elevation of SREBP-1c activity in these tissues did not cause hypertriglyceridemia. In summary, selective LXRbeta activation is expected to stimulate ABCA1 gene expression in macrophages, contribute to favorable HDL increases, but circumvent hepatic LXRalpha-dominated lipogenesis.
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Affiliation(s)
- Elaine M Quinet
- Department of Cardiovascular/Metabolic Diseases, Wyeth Research, 500 Arcola Road, RN2229, Collegeville, PA 19426, USA.
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217
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Mauldin JP, Srinivasan S, Mulya A, Gebre A, Parks JS, Daugherty A, Hedrick CC. Reduction in ABCG1 in Type 2 diabetic mice increases macrophage foam cell formation. J Biol Chem 2006; 281:21216-21224. [PMID: 16723355 DOI: 10.1074/jbc.m510952200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Atherosclerosis development is accelerated severalfold in patients with Type 2 diabetes. In the initial stages of disease, monocytes transmigrate into the subendothelial space and differentiate into foam cells. Scavenger receptors and ATP binding cassette (ABC) Transporters play an important role in foam cell formation as they regulate the influx and efflux of oxidized lipids. Here, we show that peritoneal macrophages isolated from Type 2 diabetic db/db mice have decreased expression of the ABC transporter ABCG1 and increased expression of the scavenger receptor CD36. We found a 2-fold increase in accumulation of esterified cholesterol in diabetic db/db macrophages compared with wild-type control macrophages. Diabetic db/db macrophages also had impaired cholesterol efflux to high density lipoprotein but not to lipid-free apo A-I, suggesting that the increased esterified cholesterol in diabetic db/db macrophages was due to a selective loss of ABCG1-mediated efflux to high density lipoprotein. Additionally, we were able to confirm down-regulation of ABCG1 using C57BL/6J peritoneal macrophages cultured in elevated glucose in vitro (25 mM glucose for 7 days), suggesting that ABCG1 expression in diabetic macrophages is regulated by chronic exposure to elevated glucose. Diabetic KK(ay) mice were also studied and were found to have decreased ABCG1 expression without an increase in CD36. These observations demonstrate that ABCG1 plays a major role in macrophage cholesterol efflux and that decreased ABCG1 function can facilitate foam cell formation in Type 2 diabetic mice.
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Affiliation(s)
- Jeremy P Mauldin
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908; Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia 22908
| | - Suseela Srinivasan
- Division of Endocrinology & Metabolism, University of Virginia, Charlottesville, Virginia 22908; Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia 22908
| | - Anny Mulya
- Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27106
| | - Abraham Gebre
- Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27106
| | - John S Parks
- Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27106
| | - Alan Daugherty
- Gill Heart Institute, Division of Cardiovascular Medicine, University of Kentucky, Lexington, Kentucky 40506
| | - Catherine C Hedrick
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908; Division of Endocrinology & Metabolism, University of Virginia, Charlottesville, Virginia 22908; Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia 22908.
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218
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Abstract
Dyslipidemia is the sine qua non of atherosclerosis, but it is also strongly associated with the metabolic syndrome, obesity, diabetes, and fatty liver disease. The molecular basis for future therapies requires understanding the pivotal role of nuclear hormone receptors in lipid and inflammatory homeostasis. This review summarizes evidence that the liver X receptor (LXR) and peroxisome proliferator-activated receptor (PPAR) are key transcriptional regulators in lipid metabolism. Additionally, their effects on glucose homeostasis and inflammation make LXR and PPAR signaling networks attractive molecular targets for managing lipid-related diseases.
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Affiliation(s)
- Simon W Beaven
- Department of Medicine, Division of Digestive Diseases, Howard Hughes Medical Institute, University of California, Los Angeles, California 90095-1662, USA.
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219
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Zelcer N, Tontonoz P. Liver X receptors as integrators of metabolic and inflammatory signaling. J Clin Invest 2006; 116:607-14. [PMID: 16511593 PMCID: PMC1386115 DOI: 10.1172/jci27883] [Citation(s) in RCA: 754] [Impact Index Per Article: 41.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The liver X receptors (LXRs) are nuclear receptors that play central roles in the transcriptional control of lipid metabolism. LXRs function as nuclear cholesterol sensors that are activated in response to elevated intracellular cholesterol levels in multiple cell types. Once activated, LXRs induce the expression of an array of genes involved in cholesterol absorption, efflux, transport, and excretion. In addition to their function in lipid metabolism, LXRs have also been found to modulate immune and inflammatory responses in macrophages. Synthetic LXR agonists promote cholesterol efflux and inhibit inflammation in vivo and inhibit the development of atherosclerosis in animal models. The ability of LXRs to integrate metabolic and inflammatory signaling makes them particularly attractive targets for intervention in human metabolic disease.
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Affiliation(s)
- Noam Zelcer
- Howard Hughes Medical Institute, Department of Pathology and Laboratory Medicine, UCLA, Los Angeles, California 90055-1662, USA
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220
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Steffensen KR, Gustafsson JÅ. Liver X receptors: new drug targets to treat Type 2 diabetes? ACTA ACUST UNITED AC 2006. [DOI: 10.2217/17460875.1.2.181] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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221
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Kishimoto M, Fujiki R, Takezawa S, Sasaki Y, Nakamura T, Yamaoka K, Kitagawa H, Kato S. Nuclear receptor mediated gene regulation through chromatin remodeling and histone modifications. Endocr J 2006; 53:157-72. [PMID: 16618973 DOI: 10.1507/endocrj.53.157] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Nuclear steroid/thyroid vitamin A/D receptor genes form a gene superfamily and encode DNA-binding transcription factors that control the transcription of target genes in a ligand-dependent manner. It has become clear that chromatin remodeling and the modification of histones, the main components of chromatin, play crucial roles in gene transcription, and many distinct classes of NR-interacting co-regulators have been identified that perform significant roles in gene transcription. Since NR dysfunction can lead to the onset or progression of endocrine disease, elucidation of the mechanisms of gene regulation mediated by NRs, as well as the identification and characterization of co-regulator complexes (especially chromatin remodeling and histone-modifying complexes), is essential not only for better understanding of NR ligand function, but also for pathophysiological studies and the development of therapeutic interventions in humans.
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Affiliation(s)
- Masahiko Kishimoto
- Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan
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222
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Parini P, Johansson L, Bröijersén A, Angelin B, Rudling M. Lipoprotein profiles in plasma and interstitial fluid analyzed with an automated gel-filtration system. Eur J Clin Invest 2006; 36:98-104. [PMID: 16436091 DOI: 10.1111/j.1365-2362.2006.01597.x] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
BACKGROUND High-quality methods for lipoprotein characterization are warranted in studies on various metabolic diseases. MATERIALS AND METHODS An automated system for size-exclusion chromatography (SEC) of lipoproteins using commercially available components is described. Cholesterol or triglyceride content in separated lipoproteins from plasma and interstitial fluid (IF) was continuously determined on-line using microlitre sample volumes. RESULTS The lipoprotein assay showed a good concordance with the classic ultra-centrifugation/precipitation technique using fresh or frozen samples. Determination of lipoproteins in IF obtained from vacuum-induced skin blisters from 18 healthy subjects revealed that very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol levels were 18%, 19% and 25%, respectively, of concomitant plasma concentrations. The size-exclusion chromatography (SEC) system also allows for triglyceride determination on-line and it could be shown that the system is advantageous for an accurate determination of triglycerides in conditions when there are high levels of glycerol, e.g. in mice and in patients with hyperglycerolaemia (pseudo-hypertriglyceridaemia). CONCLUSIONS The described system should be of value in studies where detailed lipoprotein analysis is warranted and particularly when significant sample series with small volumes are available. Our data also suggest that there is a 4-5.5-fold concentration gradient between plasma and IF for the three major plasma lipoproteins.
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Affiliation(s)
- P Parini
- Center for Nutrition and Toxicology, Karolinska Institute at Karolinska University Hospital, Stockholm, Sweden
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223
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Zanotti I, Potì F, Favari E, Steffensen KR, Gustafsson JA, Bernini F. Pitavastatin effect on ATP binding cassette A1-mediated lipid efflux from macrophages: evidence for liver X receptor (LXR)-dependent and LXR-independent mechanisms of activation by cAMP. J Pharmacol Exp Ther 2006; 317:395-401. [PMID: 16415093 DOI: 10.1124/jpet.105.093930] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The promotion of lipid efflux from macrophages is an important ATP binding cassette A1 (ABCA1)-mediated antiatherosclerotic mechanism that prevents peripheral tissues from foam cell accumulation. Statins exert beneficial antiatherosclerotic effects on cardiovascular disease correlated to the cholesterol-lowering properties and the pleiotropic activities. In this work, we investigated the ability of statins to modulate ABCA1-mediated lipid efflux from macrophages, where the protein expression was differently induced. Pitavastatin (0.1-10 microM) and compactin (10 microM) reduced both cholesterol and phospholipid efflux up to 60% from macrophages expressing ABCA1 upon treatment with 8-(4-chlorophenylthio)-cyclic AMP (cpt-cAMP), and this was secondary to a reduction of ABCA1 mRNA and protein content. Conversely, statins did not affect ABCA1 activity when the protein was up-regulated by 22-hydroxycholesterol/9-cis-retinoic acid or through cholesterol loading. Statin inhibition of lipid efflux induced by cpt-cAMP was reversed in the presence of mevalonate, 22-hydroxycholesterol, and cholesterol but not geranyl geraniol. In macrophages obtained from liver X receptor (LXR)-deficient mice, cpt-cAMP still promoted cholesterol efflux, but pitavastatin did not exert any effect. The present work shows that statins may inhibit ABCA1-mediated lipid efflux in macrophages only when ABCA1 protein expression is induced by cpt-cAMP and provides evidence that cAMP may activate ABCA1 independently of an increase of intracellular sterol synthesis but through at least two pathways: one independent of LXR and one involving an intracellular sterol(s) acting as LXR ligand(s). In addition, the lack of inhibitory effect on lipid efflux in cholesterol-loaded macrophages is likely to exclude a potential negative pleiotropic effect by statins.
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Affiliation(s)
- Ilaria Zanotti
- Department of Pharmacological and Biological Sciences and Applied Chemistries, School of Pharmacy, University of Parma, Italy
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224
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Naik SU, Wang X, Da Silva JS, Jaye M, Macphee CH, Reilly MP, Billheimer JT, Rothblat GH, Rader DJ. Pharmacological activation of liver X receptors promotes reverse cholesterol transport in vivo. Circulation 2005; 113:90-7. [PMID: 16365197 DOI: 10.1161/circulationaha.105.560177] [Citation(s) in RCA: 285] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
BACKGROUND Liver X receptors (LXRs) are ligand-activated transcription factors involved in the control of lipid metabolism and inflammation. Synthetic LXR agonists have been shown to inhibit the progression of atherosclerosis in mice, but the mechanism is uncertain. LXR agonism upregulates the genes encoding ATP binding cassette transporters A1 (ABCA1) and G1 (ABCG1) in macrophages, thus promoting efflux of cholesterol; it also upregulates liver and intestinal ABCG5 and ABCG8, helping to promote biliary and fecal excretion of cholesterol. Thus, LXR agonism may inhibit atherosclerosis through promotion of reverse cholesterol transport (RCT) in vivo, but this has not been proven. We previously described an in vivo method to trace the movement of cholesterol from 3H-cholesterol-labeled J774 macrophages into plasma, into liver, and ultimately into the bile and feces as free cholesterol or bile acids. In the present study we used this approach to test the hypothesis that administration of the synthetic LXR agonist GW3965 would increase the rate of macrophage RCT in vivo. METHODS AND RESULTS Three different mouse models-wild-type C57BL/6 mice, LDLR/apobec-1 double knockout mice, and human apolipoprotein (apo)B/cholesteryl ester transfer protein (CETP) double transgenic mice-were treated with either vehicle or GW3965. Mice were injected intraperitoneally with 3H-cholesterol-labeled and cholesterol-loaded macrophages and monitored for the appearance of 3H-tracer in plasma, liver, and feces. Administration of GW3965 significantly increased the levels of 3H-tracer in plasma and feces in all 3 mouse models. CONCLUSIONS These results demonstrate that administration of the LXR agonist GW3965 increases the rate of RCT from macrophages to feces in vivo.
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Affiliation(s)
- Snehal U Naik
- Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
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225
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Lund EG, Peterson LB, Adams AD, Lam MHN, Burton CA, Chin J, Guo Q, Huang S, Latham M, Lopez JC, Menke JG, Milot DP, Mitnaul LJ, Rex-Rabe SE, Rosa RL, Tian JY, Wright SD, Sparrow CP. Different roles of liver X receptor alpha and beta in lipid metabolism: effects of an alpha-selective and a dual agonist in mice deficient in each subtype. Biochem Pharmacol 2005; 71:453-63. [PMID: 16325781 DOI: 10.1016/j.bcp.2005.11.004] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Revised: 11/02/2005] [Accepted: 11/02/2005] [Indexed: 12/20/2022]
Abstract
Liver X receptor (LXR) alpha and LXRbeta are closely related nuclear receptors that respond to elevated levels of intracellular cholesterol by enhancing transcription of genes that control cholesterol efflux and fatty acid biosynthesis. The consequences of inactivation of either LXR isoform have been thoroughly studied, as have the effects of simultaneous activation of both LXRalpha and LXRbeta by synthetic compounds. We here describe the effects of selective activation of LXRalpha or LXRbeta on lipid metabolism. This was accomplished by treating mice genetically deficient in either LXRalpha or LXRbeta with an agonist with equal potency for both isoforms (Compound B) or a synthetic agonist selective for LXRalpha (Compound A). We also determined the effect of these agonists on gene expression and cholesterol efflux in peritoneal macrophages derived from wild-type and knockout mice. Both compounds raised HDL-cholesterol and increased liver triglycerides in wild-type mice; in contrast, in mice deficient in LXRalpha, Compound B increased HDL-cholesterol but did not cause hepatic steatosis. Compound B induced ATP-binding cassette transporter (ABC) A1 expression and stimulated cholesterol efflux in macrophages from both LXRalpha and LXRbeta-deficient mice. Our data lend further experimental support to the hypothesis that LXRbeta-selective agonists may raise HDL-cholesterol and stimulate macrophage cholesterol efflux without causing liver triglyceride accumulation.
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MESH Headings
- 8-Bromo Cyclic Adenosine Monophosphate/pharmacology
- ATP Binding Cassette Transporter 1
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Administration, Oral
- Animals
- Cholesterol/metabolism
- Cholesterol, HDL/blood
- Cholesterol, HDL/metabolism
- Cyclic AMP/pharmacology
- DNA-Binding Proteins/agonists
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/physiology
- Dose-Response Relationship, Drug
- Gene Expression Regulation/drug effects
- Isoxazoles/pharmacology
- Lipid Metabolism/physiology
- Liver/drug effects
- Liver/metabolism
- Liver X Receptors
- Macrophages, Peritoneal/drug effects
- Macrophages, Peritoneal/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Molecular Structure
- Orphan Nuclear Receptors
- Phenylurea Compounds/pharmacology
- Protein Isoforms/agonists
- Protein Isoforms/genetics
- Protein Isoforms/physiology
- Pyrazines/pharmacology
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Sterol Regulatory Element Binding Protein 1/genetics
- Sterol Regulatory Element Binding Protein 1/metabolism
- Triglycerides/blood
- Triglycerides/metabolism
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Affiliation(s)
- Erik G Lund
- Department of Cardiovascular Diseases, Merck Research Laboratories, Merck & Co., Inc., RY80W-250, P.O. Box 2000, Rahway, NJ 07065, United States.
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226
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Hu T, Foxworthy P, Siesky A, Ficorilli JV, Gao H, Li S, Christe M, Ryan T, Cao G, Eacho P, Michael MD, Michael LF. Hepatic peroxisomal fatty acid beta-oxidation is regulated by liver X receptor alpha. Endocrinology 2005; 146:5380-7. [PMID: 16123164 DOI: 10.1210/en.2005-0591] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Peroxisomes are the exclusive site for the beta-oxidation of very-long-chain fatty acids of more than 20 carbons in length (VLCFAs). Although the bulk of dietary long-chain fatty acids are oxidized in the mitochondria, VLCFAs cannot be catabolized in mitochondria and must be shortened first by peroxisomal beta-oxidation. The regulation of peroxisomal, mitochondrial, and microsomal fatty acid oxidation systems in liver is mediated principally by peroxisome proliferator-activated receptor alpha (PPARalpha). In this study we provide evidence that the liver X receptor (LXR) regulates the expression of the genetic program for peroxisomal beta-oxidation in liver. The genes encoding the three enzymes of the classic peroxisomal beta-oxidation cycle, acyl-coenzyme A (acyl-CoA) oxidase, enoyl-CoA hydratase/L-3-hydroxyacyl-CoA dehydrogenase, and 3-ketoacyl-CoA thiolase, are activated by the LXR ligand, T0901317. Accordingly, administration of T0901317 in mice promoted a dose-dependent and greater than 2-fold increase in the rate of peroxisomal beta-oxidation in the liver. The LXR effect is independent of PPARalpha, because T0901317-induced peroxisomal beta-oxidation in the liver of PPARalpha-null mice. Interestingly, T0901317-induced peroxisomal beta-oxidation is dependent on the LXRalpha isoform, but not the LXRbeta isoform. We propose that induction of peroxisomal beta-oxidation by LXR agonists may serve as a counterregulatory mechanism for responding to the hypertriglyceridemia and liver steatosis that is promoted by potent LXR agonists in vivo; however, additional studies are warranted.
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Affiliation(s)
- Tonghuan Hu
- Lilly Research Laboratories, Department of Cardiovascular Research, Eli Lilly & Co., Indianapolis, Indiana 46285, USA
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227
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Tamehiro N, Sato Y, Suzuki T, Hashimoto T, Asakawa Y, Yokoyama S, Kawanishi T, Ohno Y, Inoue K, Nagao T, Nishimaki-Mogami T. Riccardin C: a natural product that functions as a liver X receptor (LXR)alpha agonist and an LXRbeta antagonist. FEBS Lett 2005; 579:5299-304. [PMID: 16182288 DOI: 10.1016/j.febslet.2005.08.054] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2005] [Revised: 08/25/2005] [Accepted: 08/25/2005] [Indexed: 11/23/2022]
Abstract
Liver X receptors (LXRs) alpha and beta share considerable sequence homology and several functions, respond to the same endogenous and synthetic ligands, and play critical roles in maintaining lipid homeostasis. In this study, liverwort-derived riccardin C (RC) and F (RF) were identified as an LXRalpha agonist/LXRbeta antagonist and an LXRalpha antagonist, respectively. RC and RF bound to LXRs, but had different abilities to recruit a coactivator and thereby induce transactivation. Despite its unique subtype-selective activity, RC enhanced ABCA1 and ABCG1 expression and cellular cholesterol efflux in THP-1 cells. RC may provide a novel tool for identifying subtype-function and drug development.
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228
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Huang THW, Razmovski-Naumovski V, Salam NK, Duke RK, Tran VH, Duke CC, Roufogalis BD. A novel LXR-α activator identified from the natural product Gynostemma pentaphyllum. Biochem Pharmacol 2005; 70:1298-308. [PMID: 16154115 DOI: 10.1016/j.bcp.2005.07.033] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2005] [Revised: 07/27/2005] [Accepted: 07/28/2005] [Indexed: 11/24/2022]
Abstract
Liver X receptors (LXR) play an important role in cholesterol homeostasis by serving as regulatory sensors of cholesterol levels in tissues. The present study reports a novel LXR-alpha activator, (20S)-2alpha, 3beta, 12beta, 24(S)-pentahydroxydammar-25-ene 20-O-beta-d-glucopyranoside (TR1), a dammarane-type gynosaponin, isolated from the herbal medicine, Gynostemma pentaphyllum. Gynosaponin TR1 demonstrated greater selectivity toward activation of the LXR-alpha isoform than LXR-beta in HEK293 cells. TR1 selectively enhanced LXR-mediated transcriptional activation and protein expression of ABCA1 and apoE gene expression and secretion in THP-1-derived macrophages. The selectivity of TR1 for LXR-alpha was consistent with ligand docking studies, which showed favourable interaction of TR1 in the LXR-alpha-binding domain, whereas the presence of the sugar substituent interfered with binding to the LXR-beta site. Findings from the present study may provide insight into the development of pharmaceutical agents for treating atherosclerosis.
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Affiliation(s)
- Tom Hsun-Wei Huang
- Pharmaceutical Chemistry, Herbal Medicines Research and Education Centre, Faculty of Pharmacy, A15, S322, University of Sydney, NSW 2006, Australia
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229
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Adighibe O, Arepalli S, Duckworth J, Hardy J, Wavrant-De Vrièze F. Genetic variability at the LXR gene (NR1H2) may contribute to the risk of Alzheimer's disease. Neurobiol Aging 2005; 27:1431-4. [PMID: 16207502 DOI: 10.1016/j.neurobiolaging.2005.08.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2005] [Revised: 08/03/2005] [Accepted: 08/26/2005] [Indexed: 10/25/2022]
Abstract
We have initiated a systematic analysis of the role of cholesterol metabolizing genes as risk factors for Alzheimer's disease pathogenesis. As part of this analysis, we have assessed the NR1H2 gene on chromosome 19 and report here a modest association with the locus in sibpairs with late onset disease.
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Affiliation(s)
- Omanma Adighibe
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Porter Neuroscience Building, 35 Convent Drive, Bethesda, MD 20892 3707, USA
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230
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Morello F, de Boer RA, Steffensen KR, Gnecchi M, Chisholm JW, Boomsma F, Anderson LM, Lawn RM, Gustafsson JA, Lopez-Ilasaca M, Pratt RE, Dzau VJ. Liver X receptors alpha and beta regulate renin expression in vivo. J Clin Invest 2005; 115:1913-22. [PMID: 16007255 PMCID: PMC1159146 DOI: 10.1172/jci24594] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2005] [Accepted: 05/10/2005] [Indexed: 12/21/2022] Open
Abstract
The renin-angiotensin-aldosterone system controls blood pressure and salt-volume homeostasis. Renin, which is the first enzymatic step of the cascade, is critically regulated at the transcriptional level. In the present study, we investigated the role of liver X receptor alpha (LXR(alpha)) and LXR(beta) in the regulation of renin. In vitro, both LXRs could bind to a noncanonical responsive element in the renin promoter and regulated renin transcription. While LXR(alpha) functioned as a cAMP-activated factor, LXR(beta) was inversely affected by cAMP. In vivo, LXRs colocalized in juxtaglomerular cells, in which LXR(alpha) was specifically enriched, and interacted with the renin promoter. In mouse models, renin-angiotensin activation was associated with increased binding of LXR(alpha) to the responsive element. Moreover, acute administration of LXR agonists was followed by upregulation of renin transcription. In LXR(alpha) mice, the elevation of renin triggered by adrenergic stimulation was abolished. Untreated LXR(beta) mice exhibited reduced kidney renin mRNA levels compared with controls. LXR(alpha)LXR(beta) mice showed a combined phenotype of lower basal renin and blunted adrenergic response. In conclusion, we show herein that LXR(alpha) and LXR(beta) regulate renin expression in vivo by directly interacting with the renin promoter and that the cAMP/LXR(alpha) signaling pathway is required for the adrenergic control of the renin-angiotensin system.
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231
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Johansson L, Rudling M, Scanlan TS, Lundåsen T, Webb P, Baxter J, Angelin B, Parini P. Selective thyroid receptor modulation by GC-1 reduces serum lipids and stimulates steps of reverse cholesterol transport in euthyroid mice. Proc Natl Acad Sci U S A 2005; 102:10297-302. [PMID: 16006512 PMCID: PMC1177400 DOI: 10.1073/pnas.0504379102] [Citation(s) in RCA: 150] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Thyroid hormones [predominantly 3,5,3'-triiodo-L-thyronine (T3)] regulate cholesterol and lipoprotein metabolism, but cardiac effects restrict their use as hypolipidemic drugs. T3 binds to thyroid hormone receptors (TRs) alpha and beta. TRbeta is the predominant isoform in liver, whereas T3 effects on heart rate are mediated mostly by TRalpha. Drugs that target TRbeta or exhibit tissue-selective uptake may improve plasma lipid levels while sparing the heart. Here, we asked how the TRbeta- and liver uptake-selective agonist GC-1 influences cholesterol and triglyceride metabolism in euthyroid mice. GC-1 treatment reduced serum cholesterol levels by 25% and serum triglycerides by 75% in chow-fed mice and also attenuated diet-induced hypercholesterolemia. GC-1 reduced plasma high-density lipoprotein cholesterol levels; increased expression of the hepatic high-density lipoprotein receptor, SR-BI; stimulated activity of cholesterol 7alpha-hydroxylase; and increased fecal excretion of bile acids. Collectively, these results suggest that GC-1 stimulates important steps in reverse cholesterol transport. Use of TRbeta and uptake selective agonists such as GC-1 should be further explored as a strategy to improve lipid metabolism in dyslipoproteinemia.
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Affiliation(s)
- Lisen Johansson
- Metabolism Unit, Center for Metabolism and Endocrinology, Department of Medicine, and Molecular Nutrition Unit, Center for Nutrition and Toxicology, NOVUM, Karolinska Institute at Karolinska University Hospital-Huddinge, SE-141 86 Stockholm, Sweden
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232
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Groot PHE, Pearce NJ, Yates JW, Stocker C, Sauermelch C, Doe CP, Willette RN, Olzinski A, Peters T, d'Epagnier D, Morasco KO, Krawiec JA, Webb CL, Aravindhan K, Jucker B, Burgert M, Ma C, Marino JP, Collins JL, Macphee CH, Thompson SK, Jaye M. Synthetic LXR agonists increase LDL in CETP species. J Lipid Res 2005; 46:2182-91. [PMID: 16024916 DOI: 10.1194/jlr.m500116-jlr200] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Liver X receptor (LXR) nuclear receptors regulate the expression of genes involved in whole body cholesterol trafficking, including absorption, excretion, catabolism, and cellular efflux, and possess both anti-inflammatory and antidiabetic actions. Accordingly, LXR is considered an appealing drug target for multiple indications. Synthetic LXR agonists demonstrated inhibition of atherosclerosis progression in murine genetic models; however, these and other studies indicated that their major undesired side effect is an increase of plasma and hepatic triglycerides. A significant impediment to extrapolating results with LXR agonists from mouse to humans is the absence in mice of cholesteryl ester transfer protein, a known LXR target gene, and the upregulation in mice but not humans of cholesterol 7alpha-hydroxylase. To better predict the human response to LXR agonism, two synthetic LXR agonists were examined in hamsters and cynomolgus monkeys. In contrast to previously published results in mice, neither LXR agonist increased HDL-cholesterol in hamsters, and similar results were obtained in cynomolgus monkeys. Importantly, in both species, LXR agonists increased LDL-cholesterol, an unfavorable effect not apparent from earlier murine studies. These results reveal additional problems associated with current synthetic LXR agonists and emphasize the importance of profiling compounds in preclinical species with a more human-like LXR response and lipoprotein metabolism.
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Affiliation(s)
- Pieter H E Groot
- Cardiovascular Center for Excellence in Drug Discovery, GlaxoSmithKline, King of Prussia, PA 19406-0939, USA
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233
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Robertson KM, Schuster GU, Steffensen KR, Hovatta O, Meaney S, Hultenby K, Johansson LC, Svechnikov K, Söder O, Gustafsson JA. The liver X receptor-{beta} is essential for maintaining cholesterol homeostasis in the testis. Endocrinology 2005; 146:2519-30. [PMID: 15761042 DOI: 10.1210/en.2004-1413] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The liver X receptor (LXR)alpha and -beta has been found to play a central role in maintaining cellular cholesterol homeostasis. In this study we comprehensively investigated the effect of deleting LXRalpha and -beta on testicular morphology and function. In the absence of LXRbeta, excessive cholesterol accumulated in the Sertoli cells from 2.5 months, resulting in severe cellular disruption and dysregulation of spermatogenesis by 10 months of age. This correlated with gene expression analyses that clearly indicated that LXRbeta was the dominant transcript in the testis Although the LXRalpha(-/-) testis was normal, the LXRalpha(-/-)beta(-/-) testis presented with a more severe phenotype than the LXRbeta(-/-) mice, and males were infertile by 4 months of age, indicating LXRalpha may partially rescue the testicular phenotype. Although Leydig cells did not accumulate excessive cholesterol, declining serum and intratesticular androgen levels with age suggested that these cells were in fact less functional. Treatment of a Sertoli cell line with the LXR agonist T0901317 led to increased expression of known LXR target genes like ATP binding cassette-G1 and sterol regulatory binding protein-1c; similar results were observed in wild-type testis after in vivo administration, suggesting the LXR is functioning in the same way as in other tissues. Ordinarily increased levels of cholesterol activate intracellular sensors to decrease these levels; however, the increasing amount of cholesterol in the Sertoli cells indicates improper control of cholesterol metabolism when LXRbeta is absent. Although the precise molecular mechanism at this time remains unclear, our study highlights the crucial role for LXRbeta in retaining cholesterol homeostasis in Sertoli cells.
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Affiliation(s)
- Kirsten M Robertson
- Karolinska Institutet, Department of Biosciences at Novum, Huddinge 14157, Sweden.
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234
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Gerin I, Dolinsky VW, Shackman JG, Kennedy RT, Chiang SH, Burant CF, Steffensen KR, Gustafsson JA, MacDougald OA. LXRβ Is Required for Adipocyte Growth, Glucose Homeostasis, and β Cell Function. J Biol Chem 2005; 280:23024-31. [PMID: 15831500 DOI: 10.1074/jbc.m412564200] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Liver X receptors (LXR) alpha and beta are nuclear oxysterol receptors with established roles in cholesterol, lipid, and carbohydrate metabolism. Although LXRs have been extensively studied in liver and macrophages, the importance for development and metabolism of other tissues and cell types is not as well characterized. We demonstrate here that although LXRalpha and LXRbeta are not required for adipocyte development per se, LXRbeta is required for the increase in adipocyte size that normally occurs with aging and diet-induced obesity. Similar food intake and oxygen consumption in LXRbeta-/- mice suggests that reduced storage of lipid in adipose tissue is not due to altered energy balance. Despite reduced amounts of adipose tissue, LXRbeta-/- mice on a chow diet have insulin sensitivity and levels of adipocyte hormones similar to wild type mice. However, these mice are glucose-intolerant due to impaired glucose-induced insulin secretion. Lipid droplets in pancreatic islets may result from accumulation of cholesterol esters as analysis of islet gene expression reveals that LXRbeta is required for expression of the cholesterol transporters, ABCA1 and ABCG1. Our data establish novel roles for LXRbeta in adipocyte growth, glucose homeostasis, and beta cell function.
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Affiliation(s)
- Isabelle Gerin
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, 48109, USA
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235
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Gnerre C, Schuster GU, Roth A, Handschin C, Johansson L, Looser R, Parini P, Podvinec M, Robertsson K, Gustafsson JA, Meyer UA. LXR deficiency and cholesterol feeding affect the expression and phenobarbital-mediated induction of cytochromes P450 in mouse liver. J Lipid Res 2005; 46:1633-42. [PMID: 15930522 DOI: 10.1194/jlr.m400453-jlr200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Metabolic transformation by the superfamily of cytochromes P450 (CYPs) plays an important role in the detoxification of xenobiotics such as drugs, environmental pollutants, and food additives. Endogenous substrates of CYPs include fatty acids, sterols, steroids, and bile acids. Induction of CYPs via transcriptional activation by substrates and other xenobiotics is an important adaptive mechanism that increases the organism's defense capability against toxicity. Numerous in vivo and in vitro data have highlighted the concept that the molecular mechanism of hepatic drug induction is linked to endogenous regulatory pathways. In particular, in vitro data suggest that oxysterols via the liver X receptor (LXR) inhibit phenobarbital (PB)-mediated induction of CYPs. To study the link between LXR, cholesterol homeostasis, and drug induction in vivo, we designed experiments in wild-type, LXRalpha-, LXRbeta-, and LXRalpha/beta-deficient mice. Our data expose differential regulatory patterns for Cyp2b10 and Cyp3a11 dependent on the expression of LXR isoforms and on challenge of cholesterol homeostasis by excess dietary cholesterol. Our results suggest that, in the mouse, liver cholesterol status significantly alters the pattern of expression of Cyp3a11, whereas the absence of LXR leads to an increase in PB-mediated activation of Cyp2b10.
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Affiliation(s)
- Carmela Gnerre
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, CH-4056 Basel, Switzerland
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236
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Affiliation(s)
- Vassilios Papadopoulos
- Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, 3900 Reservoir Road Northwest, Washington, DC 20057, USA.
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237
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238
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Abstract
Cholesterol is essential for all mammalian cells. Cellular cholesterol requirements are met through de novo synthesis and uptake of plasma lipoproteins, homeostatic responses that are transcriptionally regulated by the sterol regulatory element-binding proteins (SREBPs). To prevent cytotoxicity attributable to accumulation of excess cholesterol, liver X receptors (LXRs) and the farnesoid X receptor (FXR), together with other members of the nuclear receptor superfamily, promote the storage, transport, and catabolism of sterols and their metabolites. Members of this metabolic nuclear receptor family include receptors for oxysterols (LXRs), bile acids (CAR, FXR, and PXR), and fatty acids (PPARs). Through coordinated regulation of transcriptional programs, these nuclear receptors regulate key aspects of cellular and whole-body sterol homeostasis, including cholesterol absorption, lipoprotein synthesis and remodeling, lipoprotein uptake by peripheral tissues, reverse cholesterol transport, and bile acid synthesis and absorption. This review focuses on the nuclear receptors that are central to the lipid metabolic signaling cascades, communication between lipid metabolites and their receptors, and the role of nuclear receptors in orchestrating the complex transcriptional programs that govern cholesterol and bile acid metabolism.
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Affiliation(s)
- Daniel S Ory
- Center for Cardiovascular Research, Department of Internal Medicine, Washington University School of Medicine, Box 8086, 660 S Euclid Ave, St Louis, MO 63110, USA.
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239
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Granlund L, Larsen LN, Nebb HI, Pedersen JI. Effects of structural changes of fatty acids on lipid accumulation in adipocytes and primary hepatocytes. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1687:23-30. [PMID: 15708350 DOI: 10.1016/j.bbalip.2004.11.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2004] [Revised: 11/02/2004] [Accepted: 11/03/2004] [Indexed: 11/17/2022]
Abstract
Conjugated linoleic acids (CLAs), tetradecylthioacetic acid (TTA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are all shown to differently affect lipid homeostasis. Additionally, previous studies have shown that introducing a methyl group in the molecule potentiates the hypolipidemic effect of EPA. The objective of this study was to determine how cis9,trans11 CLA, trans10,cis12 CLA, TTA, EPA and DHA affect lipid accumulation in 3T3-L1 adipocytes and in cultured primary rat hepatocytes, and to what extent changes in cis/trans configuration or introducing a methyl group in the molecules influence their way of affecting lipid accumulation in these cells. Our results show that trans10,cis12 CLA is highly specific in preventing lipid accumulation in adipocytes, and that small structural changes in the molecule (changing to trans/trans or introducing an alpha-methyl group) totally abolish this effect and up-regulate the expression levels of adipogenic marker genes towards control levels. Furthermore, all the fatty acids increased hepatic lipid accumulation, whereas the lipid content was normalized after adding an alpha-methyl group into the molecules. Taken together, our data demonstrate that the various fatty acids are highly specialized molecules, and that small structural changes markedly alter their way of affecting lipid accumulation in adipocytes and hepatocytes.
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Affiliation(s)
- Linda Granlund
- Institute of Basic Medical Sciences, Department of Nutrition, University of Oslo, P.O.B. 1046 Blindern, 0316 Oslo, Norway
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240
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Kase ET, Wensaas AJ, Aas V, Højlund K, Levin K, Thoresen GH, Beck-Nielsen H, Rustan AC, Gaster M. Skeletal muscle lipid accumulation in type 2 diabetes may involve the liver X receptor pathway. Diabetes 2005; 54:1108-15. [PMID: 15793250 DOI: 10.2337/diabetes.54.4.1108] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Liver X receptors (LXRs) are important regulators of cholesterol and lipid metabolism and are also involved in glucose metabolism. However, the functional role of LXRs in human skeletal muscle is at present unknown. This study demonstrates that chronic ligand activation of LXRs by a synthetic LXR agonist increases the uptake, distribution into complex cellular lipids, and oxidation of palmitate as well as the uptake and oxidation of glucose in cultured human skeletal muscle cells. Furthermore, the effect of the LXR agonist was additive to acute effects of insulin on palmitate uptake and metabolism. Consistently, activation of LXRs induced the expression of relevant genes: fatty acid translocase (CD36/FAT), glucose transporters (GLUT1 and -4), sterol regulatory element-binding protein-1c, peroxisome proliferator-activated receptor-gamma, carnitine palmitoyltransferase-1, and uncoupling protein 2 and 3. Interestingly, in response to activation of LXRs, myotubes from patients with type 2 diabetes showed an elevated uptake and incorporation of palmitate into complex lipids but an absence of palmitate oxidation to CO(2). These results provide evidence for a functional role of LXRs in both lipid and glucose metabolism and energy uncoupling in human myotubes. Furthermore, these data suggest that increased intramyocellular lipid content in type 2 diabetic patients may involve an altered response to activation of components in the LXR pathway.
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Affiliation(s)
- Eili T Kase
- Department of Pharmacology, School of Pharmacy, University of Oslo, P.O. Box 1068, Blindern, N-0316 Oslo, Norway
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241
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Toresson G, Schuster GU, Steffensen KR, Bengtsson M, Ljunggren J, Dahlman-Wright K, Gustafsson JA. Purification of functional full-length liver X receptor beta produced in Escherichia coli. Protein Expr Purif 2005; 35:190-8. [PMID: 15135392 DOI: 10.1016/j.pep.2004.01.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2003] [Revised: 12/18/2003] [Indexed: 11/30/2022]
Abstract
Liver X receptor beta (LXRbeta) is a ligand dependent transcription factor that is a member of the nuclear receptor superfamily. LXRbeta and its isoform LXRalpha have recently been recognized as important regulators of lipid homeostasis in vertebrates. N-terminally hexahistidine-tagged rat LXRbeta was expressed in Escherichia coli as a full-length protein and purified in two chromatographic steps, immobilized metal affinity chromatography and gel filtration. From 10g of bacterial cells, 2.5mg of protein was recovered. The purified LXRbeta is functional with respect to ligand-, DNA-, and coactivator-binding. The synthetic ligand T0901317 bound to LXRbeta with high affinity yielding a K(d) of 2.7nM. Specific interaction with DR4 response elements, in the presence of RXR, was demonstrated with electrophoretic mobility shift assay. Furthermore, surface plasmon resonance analysis of LXRbeta binding to coactivator peptides revealed a ligand dependent interaction with the C-terminal nuclear receptor binding site of the coactivator RAP250. The purified LXRbeta constitutes an important tool for further functional and structural studies.
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Affiliation(s)
- Gudrun Toresson
- Department of Biosciences, Novum, Karolinska Institute, Huddinge SE-14157, Sweden.
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242
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Linsel-Nitschke P, Tall AR. HDL as a target in the treatment of atherosclerotic cardiovascular disease. Nat Rev Drug Discov 2005; 4:193-205. [PMID: 15738977 DOI: 10.1038/nrd1658] [Citation(s) in RCA: 339] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Lipid abnormalities are among the key risk factors for cardiovascular disease. Indeed, lipid-modifying drugs - in particular, the statins, which primarily lower plasma levels of low-density lipoprotein (LDL) cholesterol - considerably reduce the risk of cardiovascular events, leading to their widespread use. Nevertheless, it seems that there might be limits to the degree of benefit that can be achieved by lowering LDL-cholesterol levels alone, which has led to increased interest in targeting other lipid-related risk factors for cardiovascular disease, such as low levels of high-density lipoprotein (HDL) cholesterol. In this article, we first consider the mechanisms that underlie the protective effect of HDL cholesterol, and then discuss several strategies that have recently emerged to increase levels of HDL cholesterol to treat cardiovascular disease, including nuclear receptor modulation, inhibition of cholesteryl ester transfer protein and infusion of apolipoprotein/phospholipid complexes.
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Affiliation(s)
- Patrick Linsel-Nitschke
- Division of Molecular Medicine, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10027, USA.
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243
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Andersson S, Gustafsson N, Warner M, Gustafsson JA. Inactivation of liver X receptor beta leads to adult-onset motor neuron degeneration in male mice. Proc Natl Acad Sci U S A 2005; 102:3857-62. [PMID: 15738425 PMCID: PMC553330 DOI: 10.1073/pnas.0500634102] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Male mice with inactivated liver X receptor (LXR) beta suffer from adult-onset motor neuron degeneration. By 7 months of age, motor coordination is impaired, and this condition is associated with lipid accumulation and loss of motor neurons in the spinal cord, together with axonal atrophy and astrogliosis. Several of these features are reminiscent of the neuropathological signs of chronic motor neuron disease such as amyotrophic lateral sclerosis. Because the LXRs are important for cholesterol and lipid metabolism, we speculate that absence of LXRbeta leads to pathological accumulation of sterols and lipids that may themselves be neurotoxic or may modulate intracellular pathways and thereby predispose motor neurons to degeneration.
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Affiliation(s)
- Sandra Andersson
- Department of Medical Nutrition, Karolinska Institute, Novum, 141 86 Huddinge, Sweden
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244
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Makishima M. Nuclear receptors as targets for drug development: regulation of cholesterol and bile acid metabolism by nuclear receptors. J Pharmacol Sci 2005; 97:177-83. [PMID: 15725701 DOI: 10.1254/jphs.fmj04008x4] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Nuclear receptors are ligand-dependent transcription factors that recently have been shown to play important roles in the metabolism of cholesterol and bile acids. Cholesterol homeostasis is maintained by de novo synthesis, absorption from diet, catabolism to bile acids and other steroids, and excretion into bile. Dysregulation of this mechanism leads to atherosclerosis and its life-threatening coronary and cerebrovascular sequelae. Conversion of cholesterol to bile acids in the liver is positively regulated by liver X receptor (LXR) alpha, a nuclear receptor for oxysterols. LXRalpha and LXRbeta, a second oxysterol receptor, regulate intestinal absorption and biliary excretion of cholesterol by inducing target gene expression. LXRs stimulate reverse cholesterol transport from peripheral tissues and exhibit antiatherogenic activity. Farnesoid X receptor (FXR), a bile acid receptor, represses bile acid synthesis and import in hepatocytes, stimulates bile acid export from cells, and protects hepatocytes from bile acid toxicity. Pregnane X receptor (PXR) and vitamin D receptor (VDR) respond to secondary bile acids and induce their catabolism. Thus, nuclear receptors play important roles in regulation of cholesterol and bile acid metabolism.
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Affiliation(s)
- Makoto Makishima
- Department of Biochemistry, Nihon University School of Medicine, Tokyo, Japan.
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245
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Castrillo A, Tontonoz P. Nuclear receptors in macrophage biology: at the crossroads of lipid metabolism and inflammation. Annu Rev Cell Dev Biol 2005; 20:455-80. [PMID: 15473848 DOI: 10.1146/annurev.cellbio.20.012103.134432] [Citation(s) in RCA: 232] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Macrophages are essential modulators of lipid metabolism and the innate immune system. Lipid and inflammatory pathways induced in activated macrophages are central to the pathogenesis of human diseases including atherosclerosis. Recent work has shown that expression of genes involved in lipid uptake and cholesterol efflux in macrophages is controlled by peroxisome proliferator-activated receptors (PPARs) and liver X receptors (LXRs). Other studies have implicated these same receptors in the modulation of macrophage inflammatory gene expression. Together, these observations position PPARs and LXRs at the crossroads of lipid metabolism and inflammation and suggest that these receptors may serve to integrate these pathways in the control of macrophage gene expression. In this review, we summarize recent work that has advanced our understanding of the roles of PPARs and LXRs in macrophage biology and discuss the implication of these results for cardiovascular physiology and disease.
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Affiliation(s)
- Antonio Castrillo
- Howard Hughes Medical Institute, and Department of Pathology and Laboratory Medicine, University of California-Los Angeles, Los Angeles, CA 90095, USA.
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246
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Kennedy MA, Barrera GC, Nakamura K, Baldán A, Tarr P, Fishbein MC, Frank J, Francone OL, Edwards PA. ABCG1 has a critical role in mediating cholesterol efflux to HDL and preventing cellular lipid accumulation. Cell Metab 2005; 1:121-31. [PMID: 16054053 DOI: 10.1016/j.cmet.2005.01.002] [Citation(s) in RCA: 651] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2004] [Revised: 11/19/2004] [Accepted: 01/11/2005] [Indexed: 01/19/2023]
Abstract
Here we demonstrate that the ABC transporter ABCG1 plays a critical role in lipid homeostasis by controlling both tissue lipid levels and the efflux of cellular cholesterol to HDL. Targeted disruption of Abcg1 in mice has no effect on plasma lipids but results in massive accumulation of both neutral lipids and phospholipids in hepatocytes and in macrophages within multiple tissues following administration of a high-fat and -cholesterol diet. In contrast, overexpression of human ABCG1 protects murine tissues from dietary fat-induced lipid accumulation. Finally, we show that cholesterol efflux to HDL specifically requires ABCG1, whereas efflux to apoA1 requires ABCA1. These studies identify Abcg1 as a key gene involved in both cholesterol efflux to HDL and in tissue lipid homeostasis.
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Affiliation(s)
- Matthew A Kennedy
- Department of Biological Chemistry, CHS 33-257, David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, California 90095, USA
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247
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Annicotte JS, Schoonjans K, Auwerx J. Expression of the liver X receptor alpha and beta in embryonic and adult mice. ACTA ACUST UNITED AC 2004; 277:312-6. [PMID: 15052659 DOI: 10.1002/ar.a.20015] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We characterized the expression pattern of the nuclear receptors liver X receptor (LXR) alpha and beta during mouse embryonic development and in adulthood by in situ hybridization experiments. LXRalpha and LXRbeta are detected in the liver starting at 11.5 days postcoitum. Later, LXRalpha expression remains high in organs involved in lipid homeostasis, such as liver, intestine, and brown adipose tissue, whereas LXRbeta is more ubiquitously expressed and enriched in tissues of neuronal and endocrine origin.
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Affiliation(s)
- Jean-Sébastien Annicotte
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut National de la Santé et de la Recherche Médicale, Université Louis Pasteur, Illkirch, France
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248
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Mascrez B, Ghyselinck NB, Watanabe M, Annicotte JS, Chambon P, Auwerx J, Mark M. Ligand-dependent contribution of RXRbeta to cholesterol homeostasis in Sertoli cells. EMBO Rep 2004; 5:285-90. [PMID: 14993927 PMCID: PMC1299005 DOI: 10.1038/sj.embor.7400094] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Revised: 12/02/2003] [Accepted: 01/08/2004] [Indexed: 11/08/2022] Open
Abstract
We show that mice expressing retinoid X receptor beta (RXRbeta) impaired in its transcriptional activation function AF-2 (Rxrb(af20) mutation) do not display the spermatid release defects observed in RXRbeta-null mutants, indicating that the role of RXRbeta in spermatid release is ligand-independent. In contrast, like RXRbeta-null mutants, Rxrb(af20) mice accumulate cholesteryl esters in Sertoli cells (SCs) due to reduced ABCA1 transporter-mediated cholesterol efflux. We provide genetic and molecular evidence that cholesterol homeostasis in SCs does not require PPARalpha and beta, but depends upon the TIF2 coactivator and RXRbeta/LXRbeta heterodimers, in which RXRbeta AF-2 is transcriptionally active. Our results also indicate that RXRbeta may be activated by a ligand distinct from 9-cis retinoic acid.
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Affiliation(s)
- Bénédicte Mascrez
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
- These authors contributed equally to this work
| | - Norbert B Ghyselinck
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
- These authors contributed equally to this work
| | - Mitsuhiro Watanabe
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
| | - Jean-Sébastien Annicotte
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
| | - Pierre Chambon
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
| | - Johan Auwerx
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
| | - Manuel Mark
- Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut Clinique de la Souris (ICS), CNRS/INSERM/ULP, Collège de France, BP10142, 67404 Illkirch Cedex, CU de Strasbourg, France
- Tel: +33 388 655 636; Fax: +33 388 653 201; E-mail:
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Davies JD, Carpenter KLH, Challis IR, Figg NL, McNair R, Proudfoot D, Weissberg PL, Shanahan CM. Adipocytic differentiation and liver x receptor pathways regulate the accumulation of triacylglycerols in human vascular smooth muscle cells. J Biol Chem 2004; 280:3911-9. [PMID: 15548517 DOI: 10.1074/jbc.m410075200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipid accumulation by vascular smooth muscle cells (VSMC) is a feature of atherosclerotic plaques. In this study we describe two mechanisms whereby human VSMC foam cell formation is driven by de novo synthesis of fatty acids leading to triacylglycerol accumulation in intracellular vacuoles, a process distinct from serum lipoprotein uptake. VSMC cultured in adipogenic differentiation medium accumulated lipids and were induced to express the adipocyte marker genes adipsin, adipocyte fatty acid-binding protein, C/EBPalpha, PPARgamma, and leptin. However, complete adipocyte differentiation was not observed as numerous genes present in mature adipocytes were not detected, and the phenotype was reversible. The rate of lipid accumulation was not affected by PPARgamma agonists, but screening for the effects of other nuclear receptor agonists showed that activation of the liver X receptors (LXR) dramatically promoted lipid accumulation in VSMC. Both LXRalpha and LXRbeta were present in VSMC, and their activation with TO901317 resulted in induction of the lipogenic genes fatty acid synthetase, sterol regulatory element binding protein (SREBP1c), and stearoyl-CoA desaturase. 27-Hydroxycholesterol, an abundant oxysterol synthesized by VSMC acted as an LXR antagonist and, therefore, may have a protective role in preventing foam cell formation. Immunohistochemistry showed that VSMC within atherosclerotic plaques express adipogenic and lipogenic markers, suggesting these pathways are present in vivo. Moreover, the development of an adipogenic phenotype in VSMC is consistent with their known phenotypic plasticity and may contribute to their dysfunction in atherosclerotic plaques and, thus, impinge on plaque growth and stability.
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Affiliation(s)
- John D Davies
- Department of Medicine, University of Cambridge, ACCI, Box 110, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2QQ, United Kingdom.
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Abstract
Diets rich in omega-3 polyunsaturated fatty acids (n-3 PUFAs), such as alpha-linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid, are associated with decreased incidence and severity of coronary heart disease. Similarly, conjugated linoleic acids (CLAs), which are found in meat and dairy products, have beneficial effects against atherosclerosis, diabetes, and obesity. The effects of n3-PUFAs and CLAs are in contrast to fatty acids with virtually identical structures, such as linoleic acid and arachidonic acid (ie, n-6 PUFAs). This article discusses the possibility that cognate receptors exist for fatty acids or their metabolites that are able to regulate gene expression and coordinately affect metabolic or signaling pathways associated with coronary heart disease. Three nuclear receptors are emphasized as fatty acid receptors that respond to dietary and endogenous ligands: peroxisome proliferator activated receptors, retinoid X receptors, and liver X receptors.
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Affiliation(s)
- John P Vanden Heuvel
- Department of Veterinary Sciences and Center for Molecular Toxicology and Carcinogenesis, Pennsylvania State University, University Park, PA 16802, USA.
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