201
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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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Buono C, Li Y, Waldo SW, Kruth HS. Liver X receptors inhibit human monocyte-derived macrophage foam cell formation by inhibiting fluid-phase pinocytosis of LDL. J Lipid Res 2007; 48:2411-8. [PMID: 17693624 DOI: 10.1194/jlr.m700170-jlr200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Liver X receptors (LXRs) are ligand-activated transcription factors involved in the control of lipid metabolism and inflammation. Several studies have recently shown that LXRs promote reverse cholesterol transport and inhibit atherosclerosis. Our study investigated whether LXRs affect macrophage uptake of LDL by human monocyte-derived macrophages. We have previously shown that human monocytes differentiated into macrophages with macrophage-colony-stimulating factor (M-CSF) constitutively take up large amounts of native LDL by receptor-independent, fluid-phase pinocytosis. In the research reported here, human monocytes were differentiated to macrophages in the presence of M-CSF with or without the LXR agonists T0901317 or 22(R)-hydroxycholesterol. Then, macrophages were incubated with native (125)I-LDL to determine LDL uptake. T0901317 and 22(R)-hydroxycholesterol inhibited (125)I-LDL uptake by 68 +/- 1% and 69 +/- 2%, respectively, and decreased pinocytotic vacuoles in the macrophages. (125)I-BSA uptake, a measure of fluid-phase pinocytosis, and (125)I-LDL uptake were the same, and T0901317 treatment inhibited uptake of both to the same degree. T0901317 did not affect receptor-mediated uptake of acetylated LDL, showing that the LXR effect is specific for fluid-phase pinocytosis of lipoproteins. Our results show that LXRs downregulate macrophage pinocytosis of LDL. The findings reveal an additional new mechanism by which LXR agonists may inhibit macrophage cholesterol accumulation and atherosclerosis, namely, by inhibiting macrophage uptake of LDL.
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Affiliation(s)
- Chiara Buono
- Section of Experimental Atherosclerosis, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD 20892-1422, USA
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203
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Zadelaar S, Kleemann R, Verschuren L, de Vries-Van der Weij J, van der Hoorn J, Princen HM, Kooistra T. Mouse models for atherosclerosis and pharmaceutical modifiers. Arterioscler Thromb Vasc Biol 2007; 27:1706-21. [PMID: 17541027 DOI: 10.1161/atvbaha.107.142570] [Citation(s) in RCA: 405] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Atherosclerosis is a multifactorial highly-complex disease with numerous etiologies that work synergistically to promote lesion development. The ability to develop preventive and ameliorative treatments will depend on animal models that mimic the human subject metabolically and pathophysiologically and will develop lesions comparable to those in humans. The mouse is the most useful, economic, and valid model for studying atherosclerosis and exploring effective therapeutic approaches. Among the most widely used mouse models for atherosclerosis are apolipoprotein E-deficient (ApoE-/-) and LDL receptor-deficient (LDLr-/-) mice. An up-and-coming model is the ApoE*3Leiden (E3L) transgenic mouse. Here, we review studies that have explored how and to what extent these mice respond to compounds directed at treatment of the risk factors hypercholesterolemia, hypertriglyceridemia, hypertension, and inflammation. An important outcome of this survey is that the different models used may differ markedly from one another in their response to a specific experimental manipulation. The choice of a model is therefore of critical importance and should take into account the risk factor to be studied and the working spectrum of the compounds tested.
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Affiliation(s)
- Susanne Zadelaar
- TNO Quality of Life, Gaubius Laboratory, Department of Biosciences, P.O. Box 2215, 2301 CE Leiden, The Netherlands
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204
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Dai X, Ou X, Hao X, Cao D, Tang Y, Hu Y, Li X, Tang C. Effect of T0901317 on Hepatic Proinflammatory Gene Expression in ApoE−/− Mice Fed a High-fat/high-cholesterol Diet. Inflammation 2007; 30:105-17. [PMID: 17516158 DOI: 10.1007/s10753-007-9026-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2007] [Accepted: 05/01/2007] [Indexed: 01/20/2023]
Abstract
OBJECTIVE In present study, we employed cDNA-based microarray technique to investigate the effect of a synthetic LXR ligand T0901317 on hepatic gene expression of proinflammatory cytokines in apolipoprotein E knockout mice fed an atherogenic diet. METHODS AND RESULTS Male 8-week-old apoE-/- mice were randomly divided into four groups, baseline group, vehicle group, prevention group and treatment group. All of the mice were fed a high-fat/high-cholesterol diet with or without LXR agonist T0901317 for 8 or 14 weeks. Gene array analysis found 17 atherosclerosis-related genes with a 2- to 8-fold difference in expression level between vehicle-treated group and T0901317-treated group. It induced mRNA expression of proinflammatory cytokine tumor necrosis factor (TNF), but inhibited gene expression of several other proinflammatory cytokines including interleukin (IL)-1alpha, IL-6, and IL-7 in the liver. C-reactive protein, TNF, matrix metalloproteinase-9, IL-1alpha, IL-6, and IL-7 were verified by real-time quantitative PCR. Next, enzyme-linked immunosorbent assay analyses showed up-regulation of TNFalpha levels and down-regulation of IL-alpha, IL-6, IL-7 levels in plasma sample. CONCLUSION The synthetic LXR agonist T0901317 has paradoxical roles in hepatic gene expression of proinflammatory cytokines in apoE-/- mice.
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Affiliation(s)
- Xiaoyan Dai
- Institute of Cardiovascular Research, Nanhua University, Hengyang, Hunan 421001, China
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205
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Wong J, Quinn CM, Gelissen IC, Jessup W, Brown AJ. The effect of statins on ABCA1 and ABCG1 expression in human macrophages is influenced by cellular cholesterol levels and extent of differentiation. Atherosclerosis 2007; 196:180-189. [PMID: 17466310 DOI: 10.1016/j.atherosclerosis.2007.03.030] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2007] [Revised: 03/15/2007] [Accepted: 03/23/2007] [Indexed: 12/27/2022]
Abstract
The ATP-binding cassette transporters, ABCA1 and ABCG1, are LXR-target genes that participate in the removal of cholesterol from lipid-laden macrophages, a crucial anti-atherogenic mechanism. Statins are currently the most efficacious therapy for the treatment of hypercholesterolemia and cardiovascular disease. We and others have shown that statins decrease ABCA1 and ABCG1 expression as well as cholesterol efflux from human macrophages. However, other studies have reported that statins produce no change, or even a modest increase in these variables. In an attempt to reconcile these conflicting reports, we investigated how the effect of statins on transcription of ABCA1 and ABCG1 is modulated by cellular cholesterol status and the extent of macrophage differentiation. We showed that supplementing human macrophages with cholesterol reversed the statin-mediated down-regulation of ABC transporter expression whereas depletion of cellular cholesterol tended to accentuate the statin effect. Down-regulation of ABC transporter expression was more pronounced with increased macrophage differentiation status and already evident at statin concentrations equivalent to those present in plasma. Addition of LXR agonists, which are currently on trial as anti-atherogenic agents, reversed the effects on ABC transporter expression while PPAR alpha and PPAR gamma agonists did not. The significance of these results in light of current and future combination therapies is discussed.
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Affiliation(s)
- Jenny Wong
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney 2052, Australia
| | - Carmel M Quinn
- Centre for Vascular Research, The University of New South Wales and Department of Haematology, Prince of Wales Hospital, Sydney, Australia
| | - Ingrid C Gelissen
- Centre for Vascular Research, The University of New South Wales and Department of Haematology, Prince of Wales Hospital, Sydney, Australia
| | - Wendy Jessup
- Centre for Vascular Research, The University of New South Wales and Department of Haematology, Prince of Wales Hospital, Sydney, Australia
| | - Andrew J Brown
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney 2052, Australia.
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206
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Chuu CP, Chen RY, Hiipakka RA, Kokontis JM, Warner KV, Xiang J, Liao S. The liver X receptor agonist T0901317 acts as androgen receptor antagonist in human prostate cancer cells. Biochem Biophys Res Commun 2007; 357:341-6. [PMID: 17416342 PMCID: PMC2693411 DOI: 10.1016/j.bbrc.2007.03.116] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Accepted: 03/13/2007] [Indexed: 11/21/2022]
Abstract
T0901317 is a potent non-steroidal synthetic liver X receptor (LXR) agonist. T0901317 blocked androgenic stimulation of the proliferation of androgen-dependent LNCaP 104-S cells and androgenic suppression of the proliferation of androgen-independent LNCaP 104-R2 cells, inhibited the transcriptional activation of an androgen-dependent reporter gene by androgen, and suppressed gene and protein expression of prostate specific antigen (PSA), a target gene of androgen receptor (AR) without affecting gene and protein expression of AR. T0901317 also inhibited binding of a radiolabeled androgen to AR, but inhibition was much weaker compared to the effect of the antiandrogens, bicalutamide and hydroxyflutamide. The LXR agonist T0901317, therefore, acts as an antiandrogen in human prostate cancer cells.
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Affiliation(s)
- Chih-pin Chuu
- The Ben May Department for Cancer Research, The University of Chicago, CIS W325F, 929 E. 57th St., Chicago, Illinois 60637, USA
| | - Rou-Yu Chen
- Department of Biological, Chemical, and Physical Science, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL 60616
| | - Richard A. Hiipakka
- The Ben May Department for Cancer Research, The University of Chicago, CIS W325F, 929 E. 57th St., Chicago, Illinois 60637, USA
| | - John M. Kokontis
- The Ben May Department for Cancer Research, The University of Chicago, CIS W325F, 929 E. 57th St., Chicago, Illinois 60637, USA
| | - Karen V. Warner
- The Ben May Department for Cancer Research, The University of Chicago, CIS W325F, 929 E. 57th St., Chicago, Illinois 60637, USA
| | - Jialing Xiang
- Department of Biological, Chemical, and Physical Science, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL 60616
| | - Shutsung Liao
- The Ben May Department for Cancer Research, The University of Chicago, CIS W325F, 929 E. 57th St., Chicago, Illinois 60637, USA
- Correspondence author: Fax. +1 773 702 6260; Tel. +1 773 702 6999, E-mail address:
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207
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Beyea MM, Heslop CL, Sawyez CG, Edwards JY, Markle JG, Hegele RA, Huff MW. Selective Up-regulation of LXR-regulated Genes ABCA1, ABCG1, and APOE in Macrophages through Increased Endogenous Synthesis of 24(S),25-Epoxycholesterol. J Biol Chem 2007; 282:5207-16. [PMID: 17186944 DOI: 10.1074/jbc.m611063200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Liver X receptor (LXR) activation represents a mechanism to prevent macrophage foam cell formation. Previously, we demonstrated that partial inhibition of oxidosqualene:lanosterol cyclase (OSC) stimulated synthesis of the LXR agonist 24(S),25-epoxycholesterol (24(S),25-epoxy) and enhanced ABCA1-mediated cholesterol efflux. In contrast to a synthetic, nonsteroidal LXR activator, TO-901317, triglyceride accumulation was not observed. In the present study, we determined whether endogenous 24(S),25-epoxy synthesis selectively enhanced expression of macrophage LXR-regulated cholesterol efflux genes but not genes that regulate fatty acid metabolism. THP-1 human macrophages incubated with the OSC inhibitor (OSCi) RO0714565 (15 nM) significantly reduced cholesterol synthesis and maximized synthesis of 24(S),25-epoxy. Endogenous 24(S),25-epoxy increased ABCA1, ABCG1, and APOE mRNA abundance and consequently increased cholesterol efflux to apoAI. In contrast, OSCi had no effect on LXR-regulated genes LPL (lipoprotein lipase) and FAS (fatty acid synthase). TO-901317 (>or=10 nM) significantly enhanced expression of all genes examined. OSCi and TO-901317 increased the mRNA and precursor form of SREBP-1c, a major regulator of fatty acid and triglyceride synthesis. However, conversion of the precursor to the active form (nSREBP-1c) was blocked by OSCi-induced 24(S),25-epoxy but not by TO-901317 (>or=10 nm), which instead markedly increased nSREBP-1c. Disruption of nSREBP-1c formation by 24(S),25-epoxy accounted for diminished FAS and LPL expression. In summary, endogenous synthesis of 24(S),25-epoxy selectively up-regulates expression of macrophage LXR-regulated cholesterol efflux genes without stimulating genes linked to fatty acid and triglyceride synthesis.
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Affiliation(s)
- Michael M Beyea
- Robarts Research Institute Vascular Biology Group, Department of Biochemistry, University of Western, London, Ontario, Canada
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208
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Rader DJ. Molecular regulation of HDL metabolism and function: implications for novel therapies. J Clin Invest 2007; 116:3090-100. [PMID: 17143322 PMCID: PMC1679714 DOI: 10.1172/jci30163] [Citation(s) in RCA: 415] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
HDL metabolism represents a major target for the development of therapies intended to reduce the risk of atherosclerotic cardiovascular disease. HDL metabolism is complex and involves dissociation of HDL apolipoprotein and HDL cholesterol metabolism. Advances in our understanding of the molecular regulation of HDL metabolism, macrophage cholesterol efflux, and HDL function will lead to a variety of novel therapeutics.
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Affiliation(s)
- Daniel J Rader
- Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6160, USA.
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209
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Luoma PV. Cytochrome P450--physiological key factor against cholesterol accumulation and the atherosclerotic vascular process. Ann Med 2007; 39:359-70. [PMID: 17701478 DOI: 10.1080/07853890701379767] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
In the early 1960s liver cytochrome P450 (P450) was known as an enzyme in drug metabolism. By the late 1970s, P450 induction was associated with elevation of plasma high-density lipoprotein cholesterol and apolipoprotein AI indicating a reduced risk of atherosclerotic disease. Later on, 57 human P450 genes have been identified. One P450 enzyme participates in cholesterol synthesis, and several others catabolize it to oxysterols and other metabolites. Oxysterols are physiological ligands specific for liver X receptors (LXRs) in the activation of ATP-binding cassette (ABC) transporter and other cholesterol-lowering genes. Elevation of cholesterol leads to an endogenous induction of P450 and consequently to enhanced generation of oxysterols and activation of genes coding proteins which efflux cholesterol out of cells, transport it to the liver, catabolize and excrete cholesterol into bile, and prevent absorption of cholesterol in the intestine in the processes that maintain cellular cholesterol homeostasis and protect arteries from atherosclerosis. Peroxisome proliferator-activated receptors (PPARs) co-operate with LXRs and ABC transporters in cholesterol regulation. Secretion of oxysterol is a direct pathway for cellular cholesterol elimination. Several compounds induce P450 and other genes regulating cholesterol balance and prevent or regress atherosclerosis, whereas inhibition of P450 blocks oxidative reactions, promotes cholesterol accumulation, and enhances the atherosclerotic vascular process.
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Affiliation(s)
- Pauli V Luoma
- Institute of Biomedicine, Pharmacology, University of Helsinki, Finland.
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210
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Blaschke F, Takata Y, Caglayan E, Collins A, Tontonoz P, Hsueh WA, Tangirala RK. A nuclear receptor corepressor-dependent pathway mediates suppression of cytokine-induced C-reactive protein gene expression by liver X receptor. Circ Res 2006; 99:e88-99. [PMID: 17110595 DOI: 10.1161/01.res.0000252878.34269.06] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
C-reactive protein (CRP), the prototypical human acute phase protein, is an independent risk predictor of future cardiovascular events, both in healthy individuals and in patients with known cardiovascular disease. In addition, previous studies indicate that CRP might have direct proatherogenic properties. Ligand activation of the liver X receptor (LXR), a member of the nuclear hormone receptor superfamily, inhibits inflammatory gene expression in macrophages and attenuates the development of atherosclerosis in various animal models. We demonstrate herein that 2 synthetic LXR ligands, T0901317 and GW3965, inhibit interleukin-1beta/interleukin-6-induced CRP mRNA and protein expression in human hepatocytes. Knockdown of LXRalpha/beta by short interfering RNAs completely abolished the inhibitory effect of the LXR agonist T0901317 on cytokine-induced CRP gene transcription. Transient transfection experiments with 5'-deletion CRP promoter constructs identified a region from -125 to -256 relative to the initiation site that mediated the inhibitory effect of LXR ligands on CRP gene transcription. Depletion of the nuclear receptor corepressor by specific short interfering RNA increased cytokine-inducible CRP mRNA expression and promoter activity and reversed LXR ligand-mediated repression of CRP gene transcription. Chromatin immunoprecipitation assays indicated that nuclear receptor corepressor is present on the endogenous CRP promoter under basal conditions. Cytokine-induced clearance of nuclear receptor corepressor complexes was inhibited by LXR ligand treatment, maintaining the CRP gene in a repressed state. Finally, treatment of C57Bl6/J mice with LXR ligands attenuated lipopolysaccharide-induced mouse CRP and serum amyloid P component gene expression in the liver, whereas no effect was observed in LXRalphabeta knockout mice. Our observations identify a novel mechanism of inflammatory gene regulation by LXR ligands. Thus, inhibition of CRP expression by LXR agonists may provide a promising approach to impact initiation and progression of atherosclerosis.
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MESH Headings
- Acute-Phase Reaction/metabolism
- Acute-Phase Reaction/physiopathology
- Animals
- Benzoates/pharmacology
- Benzylamines/pharmacology
- C-Reactive Protein/genetics
- C-Reactive Protein/metabolism
- Carcinoma, Hepatocellular
- Cell Line, Tumor
- DNA-Binding Proteins/agonists
- DNA-Binding Proteins/metabolism
- Gene Expression/drug effects
- Gene Expression/physiology
- Hepatocytes/cytology
- Hepatocytes/physiology
- Humans
- Hydrocarbons, Fluorinated
- Interleukin-1beta/pharmacology
- Interleukin-6/pharmacology
- Ligands
- Liver Neoplasms
- Liver X Receptors
- Male
- Mice
- Mice, Inbred C57BL
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- Nuclear Receptor Co-Repressor 1
- Orphan Nuclear Receptors
- Promoter Regions, Genetic/physiology
- RNA, Small Interfering
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/metabolism
- Repressor Proteins/genetics
- Repressor Proteins/metabolism
- Signal Transduction/drug effects
- Signal Transduction/physiology
- Sulfonamides/pharmacology
- Transcription, Genetic/drug effects
- Transcription, Genetic/physiology
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Affiliation(s)
- Florian Blaschke
- Division of Endocrinology, Diabetes and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
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211
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Kruit JK, Groen AK, van Berkel TJ, Kuipers F. Emerging roles of the intestine in control of cholesterol metabolism. World J Gastroenterol 2006; 12:6429-39. [PMID: 17072974 PMCID: PMC4100631 DOI: 10.3748/wjg.v12.i40.6429] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The liver is considered the major “control center” for maintenance of whole body cholesterol homeostasis. This organ is the main site for de novo cholesterol synthesis, clears cholesterol-containing chylomicron remnants and low density lipoprotein particles from plasma and is the major contributor to high density lipoprotein (HDL; good cholesterol) formation. The liver has a central position in the classical definition of the reverse cholesterol transport pathway by taking up periphery-derived cholesterol from lipoprotein particles followed by conversion into bile acids or its direct secretion into bile for eventual removal via the feces. During the past couple of years, however, an additional important role of the intestine in maintenance of cholesterol homeostasis and regulation of plasma cholesterol levels has become apparent. Firstly, molecular mechanisms of cholesterol absorption have been elucidated and novel pharmacological compounds have been identified that interfere with the process and positively impact plasma cholesterol levels. Secondly, it is now evident that the intestine itself contributes to fecal neutral sterol loss as a cholesterol-secreting organ. Finally, very recent work has unequivocally demonstrated that the intestine contributes significantly to plasma HDL cholesterol levels. Thus, the intestine is a potential target for novel anti-atherosclerotic treatment strategies that, in addition to interference with cholesterol absorption, modulate direct cholesterol excretion and plasma HDL cholesterol levels.
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Affiliation(s)
- Janine-K Kruit
- Department of Pediatrics, Center for Liver, Digestive, and Metabolic Diseases, University Medical Center Groningen, Groningen, The Netherlands
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212
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Chu K, Miyazaki M, Man WC, Ntambi JM. Stearoyl-coenzyme A desaturase 1 deficiency protects against hypertriglyceridemia and increases plasma high-density lipoprotein cholesterol induced by liver X receptor activation. Mol Cell Biol 2006; 26:6786-98. [PMID: 16943421 PMCID: PMC1592860 DOI: 10.1128/mcb.00077-06] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Stearoyl-coenzyme A desaturase (SCD) is the rate-limiting enzyme necessary for the biosynthesis of monounsaturated fatty acids. In this study, we investigated the regulation of mouse SCD1 by liver X receptor (LXR) and its role in plasma lipoprotein metabolism upon LXR activation. In vivo, the SCD1 gene remained induced upon LXR activation in the absence of sterol regulatory element-binding protein 1c (SREBP-1c), a known transcriptional regulator of SCD1. Serial deletion and point mutation analyses in reporter gene assays, as well as a gel mobility shift assay, identified an LXR response element in the mouse SCD1 promoter. In addition, SCD1 deficiency prevented the hypertriglyceridemic effect and reduced hepatic triglyceride accumulation associated with LXR activation despite induced hepatic expression of SREBP-1c protein and several SREBP1c and LXR target genes involved in lipoprotein metabolism. Unlike wild-type mice, SCD1-deficient mice failed to elevate the hepatic triglyceride monounsaturated acid (MUFA)/saturated fatty acid (SFA) ratio despite induction of the SCD2 gene. Together, these findings suggest that SCD1 plays a pivotal role in the regulation of hepatic and plasma triglyceride accumulation, possibly by modulating the MUFA-to-SFA ratio. In addition, SCD1 deficiency also increased plasma high-density lipoprotein cholesterol levels induced by LXR activation.
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Affiliation(s)
- Kiki Chu
- Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA
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213
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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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214
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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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215
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Kim KH, Choi SH, Lee TS, Oh WK, Kim DS, Kim JB. Selective LXRalpha inhibitory effects observed in plant extracts of MEH184 (Parthenocissua tricuspidata) and MEH185 (Euscaphis japonica). Biochem Biophys Res Commun 2006; 349:513-8. [PMID: 16949052 DOI: 10.1016/j.bbrc.2006.08.092] [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: 08/01/2006] [Accepted: 08/11/2006] [Indexed: 11/21/2022]
Abstract
Liver X receptors (LXRs) are nuclear hormone receptors that behave as lipid sensors of cellular cholesterol and fatty acid. Although LXR activation can alleviate hypercholesterolemia by inducing cholesterol efflux, it also results in undesirable effects of fatty acid synthesis, resulting in hepatic steatosis and hyperlipidemia. Therefore, it is critical to identify LXRalpha inhibitory agents that would repress fatty acid synthesis and hepatic lipid accumulation. In current study, screening of plant extracts used for traditional oriental medicine resulted in the identification of two candidates demonstrating selective LXRalpha inhibitory activity. These were whole leaf methanol extracts of Parthenocissua tricuspidata (MEH184) and Euscaphis japonica (MEH185). Both MEH184 and MEH185 decreased transcriptional activity of LXRalpha and the expression of LXRalpha target genes, such as FAS and ADD1/SREBP1c. Additionally, MEH184 and MEH184 significantly reduced lipogenesis and adipocyte differentiation. Together, the data imply that MEH184 and MEH185 possess selective antagonistic properties on LXRalpha to downregulate lipogenesis.
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Affiliation(s)
- Kang Ho Kim
- Department of Biological Sciences, Research Center for Functional Cellulomics, Seoul National University, Seoul 151-742, Republic of Korea
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216
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Panday N, Benz J, Blum-Kaelin D, Bourgeaux V, Dehmlow H, Hartman P, Kuhn B, Ratni H, Warot X, Wright MB. Synthesis and evaluation of anilinohexafluoroisopropanols as activators/modulators of LXRalpha and beta. Bioorg Med Chem Lett 2006; 16:5231-7. [PMID: 16876993 DOI: 10.1016/j.bmcl.2006.06.081] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2006] [Revised: 06/27/2006] [Accepted: 06/28/2006] [Indexed: 11/25/2022]
Abstract
A series of branched and unbranched anilinohexafluoroisopropanols related to the known sulfonamide T0901317 were prepared and evaluated as activators/modulators of both LXRalpha and LXRbeta. A structure-activity relationship was established and compounds with high potency on both the receptors were identified. Many compounds showed a tendency toward selectivity for LXRbeta versus LXRalpha. Several analogues were evaluated for effects on plasma lipoprotein levels in mice. A few of these significantly raised HDL-cholesterol levels in plasma but showed markedly different effects on liver triglyceride content, suggesting that this series may yield candidates with improved efficacy/safety profiles compared to existing molecules.
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Affiliation(s)
- Narendra Panday
- F. Hoffmann-La Roche Ltd., Pharmaceuticals Division, Preclinical Research, CH-4070 Basel, Switzerland.
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217
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Terasaka N, Miyazaki A, Kasanuki N, Ito K, Ubukata N, Koieyama T, Kitayama K, Tanimoto T, Maeda N, Inaba T. ACAT inhibitor pactimibe sulfate (CS-505) reduces and stabilizes atherosclerotic lesions by cholesterol-lowering and direct effects in apolipoprotein E-deficient mice. Atherosclerosis 2006; 190:239-47. [PMID: 16626720 DOI: 10.1016/j.atherosclerosis.2006.03.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Revised: 02/20/2006] [Accepted: 03/06/2006] [Indexed: 10/24/2022]
Abstract
The objective of the present study was to determine whether a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, pactimibe sulfate (CS-505), could reduce atherosclerotic lesions beyond and independent of the reduction achieved by cholesterol lowering alone from two different types of lesions. (1) Early lesion model. Twelve-week-old apolipoprotein E (apoE)(-/-) mice were treated with 0.03 or 0.1% (w/w) CS-505, 0.1 or 0.3% avasimibe (CI-1011), or 3% cholestyramine for 12 weeks. Each treatment significantly reduced plasma cholesterol by a similar degree (43-48%). The antiatherosclerotic activity of 0.1% CS-505, however, was more efficacious than the effects of the other treatments (90% versus 40-50%). (2) Advanced lesion model. Twenty-four-week-old apoE(-/-) mice were treated with 0.03 or 0.1% CS-505 or 0.1% CI-1011 for 12 weeks. CS-505 at 0.1% revealed enhanced lesion reduction compared with 0.1% CI-1011 (77% versus 54%), whereas the plasma cholesterol-lowering effect of 0.1% CS-505 was almost the same as that of 0.1% CI-1011. Furthermore, immunohistochemical analysis demonstrated that CS-505 significantly reduced the number of macrophages and expression of matrix metalloproteinase (MMP)-2, MMP-9, and MMP-13. These data indicate that CS-505 can reduce and stabilize atherosclerotic lesions. This antiatherosclerotic activity is exerted via both cholesterol lowering and direct ACAT inhibition in plaque macrophages.
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Affiliation(s)
- Naoki Terasaka
- Pharmacology and Molecular Biology Research Laboratories, Sankyo Co Ltd, 1-2-58 Hiromachi, Tokyo, Japan.
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218
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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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219
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Affiliation(s)
- Danielle Duffy
- Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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220
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Barish GD. Peroxisome proliferator-activated receptors and liver X receptors in atherosclerosis and immunity. J Nutr 2006; 136:690-4. [PMID: 16484544 DOI: 10.1093/jn/136.3.690] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Atherosclerosis is a primary cause of death in the United States, and the current obesity epidemic threatens to exacerbate its morbidity and mortality worldwide. Despite important cardiovascular treatment advances over the past few decades, new approaches are needed to curb dangerous health trends. Nuclear receptors are a superfamily of ligand-activated transcription factors. The discovery of subfamilies known as peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) as lipid-sensors that regulate lipid and glucose metabolism as well as inflammation offers new targets for nutritional and pharmacologic treatment of cardiovascular disease.
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Affiliation(s)
- Grant D Barish
- Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
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221
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Schmidt RJ, Ficorilli JV, Zhang Y, Bramlett KS, Beyer TP, Borchert K, Dowless MS, Houck KA, Burris TP, Eacho PI, Liang G, Guo LW, Wilson WK, Michael LF, Cao G. A 15-ketosterol is a liver X receptor ligand that suppresses sterol-responsive element binding protein-2 activity. J Lipid Res 2006; 47:1037-44. [PMID: 16415294 DOI: 10.1194/jlr.m500526-jlr200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hypercholesterolemia is a major risk factor for coronary artery disease. Oxysterols are known to inhibit cholesterol biosynthesis and have been explored as potential antihypercholesterolemic agents. The ability of 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one (15-ketosterol) to lower non-HDL cholesterol has been demonstrated in rodent and primate models, but the mechanisms of action remain poorly understood. Here we show in a coactivator recruitment assay and cotransfection assays that the 15-ketosterol is a partial agonist for liver X receptor-alpha and -beta (LXRalpha and LXRbeta). The binding affinity for the LXRs was comparable to those of native oxysterols. In a macrophage cell line of human origin, the 15-ketosterol elevated ATP binding cassette transporter ABCA1 mRNA in a concentration-dependent fashion with a potency similar to those of other oxysterols. We further found that in human embryonic kidney HEK 293 cells, the 15-ketosterol suppressed sterol-responsive element binding protein processing activity and thus inhibited mRNA expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, LDL receptor, and PCSK9. Our data thus provide a molecular basis for the hypocholesterolemic activity of the 15-ketosterol and further suggest its potential antiatherosclerotic benefit as an LXR agonist.
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Affiliation(s)
- Robert J Schmidt
- Lilly Research Laboratories, Eli Lilly & Company, Indianapolis, IN 46285, USA
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222
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Albers M, Blume B, Schlueter T, Wright MB, Kober I, Kremoser C, Deuschle U, Koegl M. A novel principle for partial agonism of liver X receptor ligands. Competitive recruitment of activators and repressors. J Biol Chem 2005; 281:4920-30. [PMID: 16354658 DOI: 10.1074/jbc.m510101200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Partial, selective activation of nuclear receptors is a central issue in molecular endocrinology but only partly understood. Using LXRs as an example, we show here that purely agonistic ligands can be clearly and quantitatively differentiated from partial agonists by the cofactor interactions they induce. Although a pure agonist induces a conformation that is incompatible with the binding of repressors, partial agonists such as GW3965 induce a state where the interaction not only with coactivators, but also corepressors is clearly enhanced over the unliganded state. The activities of the natural ligand 22(R)-hydroxycholesterol and of a novel quinazolinone ligand, LN6500 can be further differentiated from GW3965 and T0901317 by their weaker induction of coactivator binding. Using biochemical and cell-based assays, we show that the natural ligand of LXR is a comparably weak partial agonist. As predicted, we find that a change in the coactivator to corepressor ratio in the cell will affect NCoR recruiting compounds more dramatically than NCoR-dissociating compounds. Our data show how competitive binding of coactivators and corepressors can explain the tissue-specific behavior of partial agonists and open up new routes to a rational design of partial agonists for LXRs.
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Affiliation(s)
- Michael Albers
- PheneX Pharmaceuticals AG, 67056 Ludwigshafen, Germany and Department of Vascular and Metabolic Diseases, F. Hoffmann-La Roche AG, 4070 Basel, Switzerland
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223
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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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224
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Grefhorst A, van Dijk TH, Hammer A, van der Sluijs FH, Havinga R, Havekes LM, Romijn JA, Groot PH, Reijngoud DJ, Kuipers F. Differential effects of pharmacological liver X receptor activation on hepatic and peripheral insulin sensitivity in lean and ob/ob mice. Am J Physiol Endocrinol Metab 2005; 289:E829-38. [PMID: 15941783 DOI: 10.1152/ajpendo.00165.2005] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Liver X receptor (LXR) agonists have been proposed to act as anti-diabetic drugs. However, pharmacological LXR activation leads to severe hepatic steatosis, a condition usually associated with insulin resistance and type 2 diabetes mellitus. To address this apparent contradiction, lean and ob/ob mice were treated with the LXR agonist GW-3965 for 10 days. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp studies. Hepatic glucose production (HGP) and metabolic clearance rate (MCR) of glucose were determined with stable isotope techniques. Blood glucose and hepatic and whole body insulin sensitivity remained unaffected upon treatment in lean mice, despite increased hepatic triglyceride contents (61.7 +/- 7.2 vs. 12.1 +/- 2.0 nmol/mg liver, P < 0.05). In ob/ob mice, LXR activation resulted in lower blood glucose levels and significantly improved whole body insulin sensitivity. GW-3965 treatment did not affect HGP under normo- and hyperinsulinemic conditions, despite increased hepatic triglyceride contents (221 +/- 13 vs. 176 +/- 19 nmol/mg liver, P < 0.05). Clamped MCR increased upon GW-3965 treatment (18.2 +/- 1.0 vs. 14.3 +/- 1.4 ml x kg(-1) x min(-1), P = 0.05). LXR activation increased white adipose tissue mRNA levels of Glut4, Acc1 and Fasin ob/ob mice only. In conclusion, LXR-induced blood glucose lowering in ob/ob mice was attributable to increased peripheral glucose uptake and metabolism, physiologically reflected in a slightly improved insulin sensitivity. Remarkably, steatosis associated with LXR activation did not affect hepatic insulin sensitivity.
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Affiliation(s)
- Aldo Grefhorst
- Center for Liver, Digestive, and Metabolic Diseases, Laboratory of Pediatrics, Rm. Y2117, CMC IV, Univ. Medical Center Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands.
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225
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Graham TL, Mookherjee C, Suckling KE, Palmer CNA, Patel L. The PPARdelta agonist GW0742X reduces atherosclerosis in LDLR(-/-) mice. Atherosclerosis 2005; 181:29-37. [PMID: 15939051 DOI: 10.1016/j.atherosclerosis.2004.12.028] [Citation(s) in RCA: 164] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2004] [Revised: 11/19/2004] [Accepted: 12/03/2004] [Indexed: 01/22/2023]
Abstract
Several lines of evidence suggest a biological role for peroxisome proliferator-activated receptor (PPARdelta) in the pathogenesis of atherosclerosis. Administration of synthetic PPARdelta agonists to obese rhesus monkeys elevates serum high-density lipoprotein (HDL) cholesterol as a result of increased reverse cholesterol transport whilst in vitro studies have suggested a role for PPARdelta in lipid uptake into macrophages. Recent studies have found that PPARdelta depletion from macrophages in LDL receptor (LDLR(-/-)) mice decreases lesion area via modulation of the inflammatory status of the macrophage, an effect also seen on pharmacological activation of PPARdelta in vitro. We demonstrate here that the PPARdelta agonist, GW0742X has potent anti-atherogenic activity in the LDLR(-/-) mouse, decreasing lesion area by up to 50%. Administration of GW0742X had no effect on total cholesterol, HDL or LDL cholesterol and modest effects on very low-density lipoprotein (VLDL). Treatment with GW0742X resulted in decreased expression of monocyte chemoattractant protein 1 (MCP-1) and intracellular adhesion moleculae 1 (ICAM-1) in the aortae of treated mice. In addition, GW0742X decreased tumour necrosis factor-alpha (TNFalpha) expression in peritoneal macrophages, aortae and adipose tissue in comparison with control animals. Changes in gene expression were reflected in decreased plasma levels of MCP-1. These observations support an atheroprotective effect of PPARdelta agonists in vivo.
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Affiliation(s)
- Tracey L Graham
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Scotland, UK
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226
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Takata Y, Chu V, Collins AR, Lyon CJ, Wang W, Blaschke F, Bruemmer D, Caglayan E, Daley W, Higaki J, Fishbein MC, Tangirala RK, Law RE, Hsueh WA. Transcriptional repression of ATP-binding cassette transporter A1 gene in macrophages: a novel atherosclerotic effect of angiotensin II. Circ Res 2005; 97:e88-96. [PMID: 16224068 DOI: 10.1161/01.res.0000190400.46267.7e] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Angiotensin II (Ang II) is a powerful accelerator of atherosclerosis. Herein, we describe a novel transcription mechanism through which Ang II inhibits macrophage expression of the ATP-binding cassette transporter A1 (ABCA1), a key regulator of reverse cholesterol transport. We demonstrate that chronic Ang II infusion substantially promotes macrophage infiltration, foam cell formation, and atherosclerosis in low-density lipoprotein receptor-deficient mice and significantly reduces ABCA1 expression in peripheral macrophages. Administration of the Ang II type 1 receptor blocker valsartan inhibited Ang II-induced ABCA1 mRNA repression, macrophage cholesterol accumulation, and atherosclerosis. Ang II treatment reduced ABCA1 promoter activity of in vitro cultured mouse peritoneal macrophages, inducing fos-related antigen 2 (Fra2) protein binding to an ABCA1 promoter E-box motif, a site known to negatively regulate macrophage ABCA1 transcription. Valsartan pretreatment blocked Fra2 binding to the ABCA1 promoter, and Fra2 small interfering RNA pretreatment attenuated Ang II-mediated ABCA1 transcriptional inhibition, confirming the role of Fra2 in this process. This new evidence suggests that Ang II, a well-known proinflammatory and pro-oxidative factor, alters macrophage cholesterol homeostasis by repressing ABCA1 to promote foam cell formation and atherosclerosis.
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Affiliation(s)
- Yasunori Takata
- Division of Endocrinology, Diabetes, and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
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227
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Bradley MN, Tontonoz P. Lesion macrophages are a key target for the antiatherogenic effects of LXR agonists. Arterioscler Thromb Vasc Biol 2005; 25:10-1. [PMID: 15626767 DOI: 10.1161/01.atv.0000152727.69018.61] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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228
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Abstract
Macrophages play essential roles in infection and resolution of inflammation. This review summarizes recent findings that suggest a relevant role for the nuclear receptor liver X receptor (LXR) in the evolution of immune responses. By exerting both positive and negative regulation of specific macrophage gene expression networks, LXRs display anti-inflammatory activities and promote macrophage survival in bacterial infection settings. Agonists that activate the LXR pathway may be used to enhance innate immunity to highly virulent pathogens that otherwise induce macrophage apoptosis as a means to subvert host immune defense.
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Affiliation(s)
- Annabel F Valledor
- Macrophage Biology Unit, Parc Científic de Barcelona-Institut Recerca Biomèdica de Barcelona, Josep Samitier 1-5, 08028 Barcelona, Spain.
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229
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Jaye MC, Krawiec JA, Campobasso N, Smallwood A, Qiu C, Lu Q, Kerrigan JJ, De Los Frailes Alvaro M, Laffitte B, Liu WS, Marino JP, Meyer CR, Nichols JA, Parks DJ, Perez P, Sarov-Blat L, Seepersaud SD, Steplewski KM, Thompson SK, Wang P, Watson MA, Webb CL, Haigh D, Caravella JA, Macphee CH, Willson TM, Collins JL. Discovery of Substituted Maleimides as Liver X Receptor Agonists and Determination of a Ligand-Bound Crystal Structure. J Med Chem 2005; 48:5419-22. [PMID: 16107141 DOI: 10.1021/jm050532w] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Substituted 3-(phenylamino)-1H-pyrrole-2,5-diones were identified from a high throughput screen as inducers of human ATP binding cassette transporter A1 expression. Mechanism of action studies led to the identification of GSK3987 as an LXR ligand. GSK3987 recruits the steroid receptor coactivator-1 to human LXRalpha and LXRbeta with EC(50)s of 40 nM, profiles as an LXR agonist in functional assays, and activates LXR though a mechanism that is similar to first generation LXR agonists.
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Affiliation(s)
- Michael C Jaye
- GlaxoSmithKline Research and Development, Research Triangle Park, North Carolina 27709, USA
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230
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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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231
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232
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Lehrke M, Lebherz C, Millington SC, Guan HP, Millar J, Rader DJ, Wilson JM, Lazar MA. Diet-dependent cardiovascular lipid metabolism controlled by hepatic LXRalpha. Cell Metab 2005; 1:297-308. [PMID: 16054077 DOI: 10.1016/j.cmet.2005.04.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Revised: 04/01/2005] [Accepted: 04/19/2005] [Indexed: 10/25/2022]
Abstract
The high-cholesterol/high-fat Western diet has abetted an epidemic of atherosclerotic cardiovascular disease, the leading cause of death in industrialized nations. Liver X receptors (LXRs) are oxysterol sensors that are required for normal cholesterol and triglyceride homeostasis, yet synthetic LXR agonists produce undesirable hypertriglyceridemia. Here we report a previously unrecognized role for hepatic LXRalpha in the links between diet, serum lipids, and atherosclerosis. A modest increase in hepatic LXRalpha worsened serum lipid profiles in LDL-receptor null mice fed normal chow but had the opposite effect on lipids and afforded strong protection against atherosclerosis on a Western diet. The beneficial effect of hepatic LXRalpha was abrogated by a synthetic LXR agonist, which activated SREBP-1c and its target genes. Thus, the interplay between diet and hepatic LXRalpha is a critical determinant of serum lipid profiles and cardiovascular risk, and selective modulation of LXR target genes in liver can ameliorate hyperlipidemia and cardiovascular disease.
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Affiliation(s)
- Michael Lehrke
- Division of Endocrinology, Diabetes, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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233
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Terasaka N, Hiroshima A, Ariga A, Honzumi S, Koieyama T, Inaba T, Fujiwara T. Liver X receptor agonists inhibit tissue factor expression in macrophages. FEBS J 2005; 272:1546-56. [PMID: 15752369 DOI: 10.1111/j.1742-4658.2005.04599.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Exposure of blood to tissue factor (TF) rapidly initiates the coagulation serine protease cascades. TF is expressed by macrophages and other types of cell within atherosclerotic lesions and plays an important role in thrombus formation after plaque rupture. Macrophage TF expression is induced by pro-inflammatory stimuli including lipopolysaccharide (LPS), interleukin-1beta and tumor necrosis factor-alpha. Here we demonstrate that activation of liver X receptors (LXRs) LXRalpha and LXRbeta suppresses TF expression. Treatment of mouse peritoneal macrophages with synthetic LXR agonist T0901317 or GW3965 reduced TF expression induced by pro-inflammatory stimuli. LXR agonists also suppressed TF expression and its activity in human monocytes. Human and mouse TF promoters contain binding sites for the transcription factors AP-1, NFkappaB, Egr-1 and Sp1, but no LXR-binding sites could be found. Cotransfection assays with LXR and TF promoter constructs in RAW 264.7 cells revealed that LXR agonists suppressed LPS-induced TF promoter activity. Analysis of TF promoter also showed that inhibition of TF promoter activity by LXR was at least in part through inhibition of the NFkappaB signaling pathway. In addition, in vivo, LXR agonists reduced TF expression within aortic lesions in an atherosclerosis mouse model as well as in kidney and lung in mice stimulated with LPS. These findings indicate that activation of LXR results in reduction of TF expression, which may influence atherothrombosis in patients with vascular disease.
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Affiliation(s)
- Naoki Terasaka
- Pharmacology and Molecular Biology Research Laboratories, Sankyo Co. Ltd, Tokyo, Japan.
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234
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Fukuchi J, Song C, Dai Q, Hiipakka RA, Liao S. 5beta-Cholane activators of the farnesol X receptor. J Steroid Biochem Mol Biol 2005; 94:311-8. [PMID: 15857750 DOI: 10.1016/j.jsbmb.2004.11.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2004] [Accepted: 11/29/2004] [Indexed: 11/24/2022]
Abstract
The farnesoid X receptor (FXR) is activated by bile acids, natural agonists for this nuclear receptor. FXR-target genes play important roles in cholesterol and lipid metabolism. We have found that a series of 5beta-cholanic acid derivatives, even though without a hydroxyl group or any other substituent on the steroidal rings, can activate FXR more potently than hydroxylated bile acids in a reporter gene assay. The most potent compound among these derivatives, N-methyl-5beta-glycocholanic acid (NMGCA), induces the formation of receptor/coactivator complex in a gel-shift assay and also increases the expression of FXR target genes in human hepatoma HepG2 cells. Furthermore, in rats, NMGCA causes hypolipidemic effects as well as induction of the FXR target genes in liver. Our results suggest that NMGCA and its derivatives are important FXR activators in the study of the physiological functions of FXR and are potentially useful as pharmaceutical agents for treatment of cholesterol and lipid-related diseases.
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Affiliation(s)
- Junichi Fukuchi
- Ben May Institute for Cancer Research, Department of Biochemistry and Molecular Biology, The University of Chicago, IL 60637, USA
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235
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Bennett DJ, Cooke AJ, Edwards AS, Moir E, Ray PC. Liver X receptor agonists as a treatment for atherosclerosis. Expert Opin Ther Pat 2005. [DOI: 10.1517/13543776.14.7.967] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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236
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Levin N, Bischoff ED, Daige CL, Thomas D, Vu CT, Heyman RA, Tangirala RK, Schulman IG. Macrophage Liver X Receptor Is Required for Antiatherogenic Activity of LXR Agonists. Arterioscler Thromb Vasc Biol 2005; 25:135-42. [PMID: 15539622 DOI: 10.1161/01.atv.0000150044.84012.68] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Objective—
Complications of atherosclerotic cardiovascular disease due to elevated blood cholesterol levels are the major cause of death in the Western world. The liver X receptors, LXRα and LXRβ (LXRs), are ligand-dependent transcription factors that act as cholesterol sensors and coordinately control transcription of genes involved in cholesterol and lipid homeostasis as well as macrophage inflammatory gene expression. LXRs regulate cholesterol balance through activation of ATP-binding cassette transporters that promote cholesterol transport and excretion from the liver, intestine, and macrophage. Although LXR agonists are known to delay progression of atherosclerosis in mouse models, their ability to abrogate preexisting cardiovascular disease by inducing regression and stabilization of established atherosclerotic lesions has not been addressed.
Methods and Results—
We demonstrate that LXR agonist treatment increases ATP-binding cassette transporter expression within preexisting atherosclerotic lesions, resulting in regression of these lesions as well as remodeling from vulnerable to stable lesions and a reduction in macrophage content. Further, using macrophage-selective LXR-deficient mice created by bone marrow transplantation, we provide the first evidence that macrophage LXR expression is necessary for the atheroprotective actions of an LXR agonist.
Conclusions—
These data substantiate that drugs targeting macrophage LXR activity may offer therapeutic benefit in the treatment of atherosclerotic cardiovascular disease.
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Affiliation(s)
- Nancy Levin
- X-Ceptor Therapeutics Inc, San Diego, Calif 92121, USA
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237
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Watanabe Y, Jiang S, Takabe W, Ohashi R, Tanaka T, Uchiyama Y, Katsumi K, Iwanari H, Noguchi N, Naito M, Hamakubo T, Kodama T. Expression of the LXRalpha protein in human atherosclerotic lesions. Arterioscler Thromb Vasc Biol 2004; 25:622-7. [PMID: 15625283 DOI: 10.1161/01.atv.0000154489.53077.4e] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Liver X-activated receptor alpha (LXRalpha) regulates multiple genes controlling cholesterol metabolism and transport. To clarify its role in atherogenesis, we established a monoclonal antibody recognizing native human LXRalpha protein and studied the expression pattern in human atherosclerotic lesions. METHODS AND RESULTS A novel monoclonal antibody PPZ0412 was raised against the ligand-binding domain of LXRalpha, which can be used for immunostaining of human LXRalpha protein. LXRalpha protein was detected in the nucleus of macrophages in the liver, spleen, or lung and also in hepatocytes and adipocytes. In atherosclerotic lesions, the LXRalpha protein was detected in macrophages positive for scavenger receptor class A and/or CD68. CONCLUSIONS In the human body, the LXRalpha protein is highly expressed in macrophage lineage cells and foam cells in atherosclerotic lesions and is identified as a target for intervention in atherosclerotic disease.
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Affiliation(s)
- Yuichiro Watanabe
- Department of Systems Biology and Medicine, Research Center for Advanced Science and Technology, the University of Tokyo, Japan
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238
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Abstract
LXRs are members of the nuclear receptor superfamily and function as master regulators of cholesterol metabolism. In the macrophage, they control cholesterol efflux and inhibit the transcription factor NF-kappaB-mediated proinflammatory responses. In this issue of Cell, discover surprising, protective functions for LXRalpha in innate immunity.
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Affiliation(s)
- Grant D Barish
- Howard Hughes Medical Institute, Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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239
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Blaschke F, Leppanen O, Takata Y, Caglayan E, Liu J, Fishbein MC, Kappert K, Nakayama KI, Collins AR, Fleck E, Hsueh WA, Law RE, Bruemmer D. Liver X receptor agonists suppress vascular smooth muscle cell proliferation and inhibit neointima formation in balloon-injured rat carotid arteries. Circ Res 2004; 95:e110-23. [PMID: 15539633 DOI: 10.1161/01.res.0000150368.56660.4f] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The liver X receptors alpha and beta (LXRalpha and LXRbeta) are important regulators of cholesterol homeostasis in liver and macrophages. Synthetic LXR ligands prevent the development of atherosclerosis in murine models; however, the potential functional relevance of LXRs in vascular smooth muscle cells (VSMCs) has not been investigated. In the present study, we demonstrate that LXRs are expressed and functional in primary human coronary artery VSMCs (CASMCs). LXR ligands inhibited mitogen-induced VSMC proliferation and G1-->S phase progression of the cell cycle. Inhibition of G1 exit by LXR ligands was accompanied by a dose-dependent inhibition of retinoblastoma protein (Rb) phosphorylation, which functions as the key switch for G1-->S cell cycle progression. LXR ligands suppressed mitogen-induced degradation of the cyclin-dependent kinase inhibitor p27Kip1, attenuated cyclin D1 and cyclin A expression, and inhibited the expression of S phase-regulatory minichromosome maintenance protein 6. Stabilization of p27kip1 by LXR ligands was mediated by supressing the transcriptional activation of the S phase kinase-associated protein 2 (Skp2), an F-box protein that targets p27Kip1 for degradation. Inhibition of Rb phosphorylation and G1-->S cell cycle progression by LXR ligands was reversed in VSMCs overexpressing Skp2, indicating that Skp2 as an upstream regulator of p27Kip1 degradation plays a central role in LXR ligand-mediated inhibition of VSMC proliferation. Furthermore, adenovirus-mediated overexpression of the S phase transcription factor E2F, which is released after Rb phosphorylation, reversed the inhibitory effect of LXR ligands on VSMC proliferation and S phase gene expression, suggesting that the primary mechanisms by which LXR ligands inhibit VSMC proliferation occur upstream of Rb phosphorylation. Finally, neointima formation in a model of rat carotid artery balloon injury was significantly attenuated after treatment with the LXR ligand T1317 compared with vehicle-treated animals. These data demonstrate that LXR ligands inhibit VSMC proliferation and neointima formation after balloon injury and suggest that LXR ligands may constitute a novel therapy for proliferative vascular diseases. The full text of this article is available online at http://circres.ahajournals.org.
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MESH Headings
- Animals
- Anticholesteremic Agents/pharmacology
- Benzoates/pharmacology
- Benzylamines/pharmacology
- Carotid Artery Injuries/pathology
- Cell Cycle/drug effects
- Cell Cycle Proteins/biosynthesis
- Cell Cycle Proteins/genetics
- Cell Cycle Proteins/metabolism
- Cell Division/drug effects
- Cells, Cultured/drug effects
- Cells, Cultured/metabolism
- Coronary Vessels/cytology
- Cyclin-Dependent Kinase Inhibitor p27
- DNA-Binding Proteins/agonists
- DNA-Binding Proteins/physiology
- G1 Phase/drug effects
- Gene Expression Regulation/drug effects
- Humans
- Hydrocarbons, Fluorinated
- Hyperplasia
- Insulin/pharmacology
- Ligands
- Liver X Receptors
- Minichromosome Maintenance Complex Component 6
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Orphan Nuclear Receptors
- Phosphorylation/drug effects
- Platelet-Derived Growth Factor/pharmacology
- Protein Processing, Post-Translational/drug effects
- Rats
- Rats, Sprague-Dawley
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/physiology
- Recombinant Fusion Proteins/physiology
- Retinoblastoma Protein/metabolism
- S-Phase Kinase-Associated Proteins/biosynthesis
- S-Phase Kinase-Associated Proteins/genetics
- S-Phase Kinase-Associated Proteins/physiology
- Sulfonamides
- Transfection
- Tumor Suppressor Proteins/metabolism
- Tunica Intima/drug effects
- Tunica Intima/pathology
- Tunica Media/drug effects
- Tunica Media/pathology
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Affiliation(s)
- Florian Blaschke
- Division of Endocrinology, Diabetes, and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, USA
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240
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Fukuchi J, Kokontis JM, Hiipakka RA, Chuu CP, Liao S. Antiproliferative Effect of Liver X Receptor Agonists on LNCaP Human Prostate Cancer Cells. Cancer Res 2004; 64:7686-9. [PMID: 15520170 DOI: 10.1158/0008-5472.can-04-2332] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Liver X receptors function as central transcriptional regulators for lipid homeostasis, for which agonists have been developed as potential drugs for treatment of cardiovascular diseases and metabolic syndromes. Because dysregulation of lipid metabolism has been implicated in sex hormone-dependent cancers, we investigated the effect of liver X receptor agonists on prostate and breast cancer cell proliferation. Treatment of human prostate cancer LNCaP cell lines with the synthetic liver X receptor agonist T0901317 decreased the percentage of S-phase cells in a dose-dependent manner and increased the expression of cyclin-dependent kinase inhibitor p27(Kip-1) (p27). Knockdown of p27 by RNA interference blocks T0901317-induced growth inhibition, suggesting that p27 expression plays a crucial role in this signaling. Liver X receptor agonists also inhibited the proliferation of other prostate and breast cancer cell lines. The level of liver X receptor alpha expression correlated directly with sensitivity to growth inhibition by liver X receptor agonists. Retroviral expression of liver X receptor alpha in human breast cancer MDA-MB435S cells, which express low levels of endogenous liver X receptors and are insensitive to T0901317, sensitized these cells to T0901317. Consistent with our observations in LNCaP cells, T0901317 induces dramatic up-regulation of p27 in liver X receptor alpha-overexpressing MDA-MB435S cells. Furthermore, oral administration of T0901317 inhibited the growth of LNCaP tumors in athymic nude mice. Based on these results, modulation of the liver X receptor signaling pathway is a new target for controlling tumor cell proliferation; therefore, liver X receptor agonists may have utility as antitumorigenic agents.
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Affiliation(s)
- Junichi Fukuchi
- The Ben May Institute for Cancer Research and The Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA
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241
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Stein Y, Stein O, Dabach Y, Halperin G, Ben-Naim M. LXR activation and cholesterol efflux from a lipoprotein depot in vivo. Biochim Biophys Acta Mol Cell Biol Lipids 2004; 1686:24-9. [PMID: 15522819 DOI: 10.1016/j.bbalip.2004.08.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2004] [Revised: 07/20/2004] [Accepted: 08/03/2004] [Indexed: 12/19/2022]
Abstract
Activation of LXR in cultured cells results in enhancement of cholesterol efflux to apo Al. To study cholesterol efflux, in vivo cationized LDL was injected into the rectus femoris muscle of mice to create a lipoprotein depot. LXR ligand TO901317, 10 mg/kg, was given by gavage for 8 days, starting 4 days after injection of the lipoprotein. The rate of cholesterol efflux from the depot was compared in treated and control mice. Administration of the ligand resulted in a 70% increase in plasma cholesterol and 40% in phospholipids, but HDL-cholesterol and HDL-phospholipids increased by 43% and 24% only. Efflux of the injected cholesterol from the lipoprotein depot of treated mice was not enhanced but even somewhat delayed. This impairment was unexpected and its cause could be multifactorial. A plausible explanation seems that induced hypercholesterolemia, and a decrease in HDL-cholesterol to total cholesterol ratio, delayed the clearance.
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Affiliation(s)
- Yechezkiel Stein
- Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem 91 120, Israel.
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242
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Jakel H, Nowak M, Moitrot E, Dehondt H, Hum DW, Pennacchio LA, Fruchart-Najib J, Fruchart JC. The Liver X Receptor Ligand T0901317 Down-regulates APOA5 Gene Expression through Activation of SREBP-1c. J Biol Chem 2004; 279:45462-9. [PMID: 15317819 DOI: 10.1074/jbc.m404744200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Alterations in the expression of the recently discovered apolipoprotein A5 gene strongly affect plasma triglyceride levels. In this study, we investigated the contribution of APOA5 to the liver X receptor (LXR) ligand-mediated effect on plasma triglyceride levels. Following treatment with the LXR ligand T0901317, we found that APOA5 mRNA levels were decreased in hepatoma cell lines. The observation that no down-regulation of APOA5 promoter activity was obtained by LXR-retinoid X receptor (RXR) co-transfection prompted us to explore the possible involvement of the known LXR target gene SREBP-1c (sterol regulatory element-binding protein 1c). In fact, we found that co-transfection with the active form of SREBP-1c down-regulated APOA5 promoter activity in a dose-dependent manner. We then scanned the human APOA5 promoter sequence and identified two putative E-box elements that were able to bind specifically SREBP-1c in gel-shift assays and were shown to be functional by mutation analysis. Subsequent suppression of SREBP-1 mRNA through small interfering RNA interference abolished the decrease of APOA5 mRNA in response to T0901317. Finally, administration of T0901317 to hAPOA5 transgenic mice revealed a significant decrease of APOA5 mRNA in liver tissue and circulating apolipoprotein AV protein in plasma, confirming that the described down-regulation also occurs in vivo. Taken together, our results demonstrate that APOA5 gene expression is regulated by the LXR ligand T0901317 in a negative manner through SREBP-1c. These findings may provide a new mechanism responsible for the elevation of plasma triglyceride levels by LXR ligands and support the development of selective LXR agonists, not affecting SREBP-1c, as beneficial modulators of lipid metabolism.
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Affiliation(s)
- Heidelinde Jakel
- Département d'Athérosclérose, UR545 INSERM, Institut Pasteur de Lille and Faculté de Pharmacie de Lille, 1 rue du Pr. Calmette BP 245, 59019 Lille Cedex, France, Genfit SA, Loos F-59120, France
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243
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Miao B, Zondlo S, Gibbs S, Cromley D, Hosagrahara VP, Kirchgessner TG, Billheimer J, Mukherjee R. Raising HDL cholesterol without inducing hepatic steatosis and hypertriglyceridemia by a selective LXR modulator. J Lipid Res 2004; 45:1410-7. [PMID: 15145986 DOI: 10.1194/jlr.m300450-jlr200] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Liver X receptors (LXRs) are ligand-activated transcription factors that belong to the nuclear receptor superfamily. LXRs activate transcription of a spectrum of genes that regulate reverse cholesterol transport, including the ATP binding cassette transporter A1 (ABCA1), and raise HDL cholesterol (HDL-C) levels. However, LXR agonists also induce genes that stimulate lipogenesis, including the sterol response element binding protein (SREBP1-c) and fatty acid synthetase (FAS). The induction of these genes in the liver cause increased hepatic triglyceride synthesis, hypertriglyceridemia, and hepatic steatosis. As LXR response elements have been identified in these promoters, it is not clear if these two processes can be separated. Herein, we demonstrate that plasma HDL-C elevation and intestinal ABCA1 induction can occur with relatively little induction of FAS and SREBP1-c in mouse liver via a selective LXR modulator GW3965. This is in contrast to the strong induction of hepatic lipogenic genes by the well-characterized LXR agonist T0901317 (T317). Consistent with the in vivo results, GW3965 is a very weak LXR activator compared with T317 in human hepatoma cells. GW3965-liganded LXR recruits selected coactivators less effectively than T317 and may explain in part the tissue selective gene induction. This demonstration that tissue and gene selective modulation is possible with selective LXR modulators has positive implications for the development of this class of antiatherosclerotic agents.
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Affiliation(s)
- Bowman Miao
- Cardiovascular Biology, Bristol-Myers Squibb Company, Experimental Station, Wilmington, DE 19880, USA
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244
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Abstract
Atherosclerosis is the leading cause of mortality in the Western world, and new therapeutics to target the metabolic and inflammatory factors that underlie its pathogenesis are needed. Peroxisome proliferator-activated receptors and liver X receptors are lipid-activated nuclear receptors that regulate systemic glucose and lipid metabolism, and modulate inflammation within the vascular wall. New understanding of their functions in physiology and the development of high-affinity synthetic ligands highlight their potential as targets for the treatment of cardiovascular disease.
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Affiliation(s)
- Grant D Barish
- Howard Hughes Medical Institute, Gene Expression Laboratory, The Salk Institute for Biological Studies, PO Box 85800, San Diego, CA 92186-5800, USA
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245
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Tailleux A, Torpier G, Mezdour H, Fruchart JC, Staels B, Fiévet C. Murine models to investigate pharmacological compounds acting as ligands of PPARs in dyslipidemia and atherosclerosis. Trends Pharmacol Sci 2004; 24:530-4. [PMID: 14559405 DOI: 10.1016/j.tips.2003.08.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Anne Tailleux
- Unité de Recherche INSERM 545, Département d'Athérosclérose, Institut Pasteur de Lille, France
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246
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Abstract
Macrophages play diverse roles in host defense and in maintenance of homeostasis. Based on their ability to promote inflammatory responses, inappropriate macrophage function also contributes to numerous pathological processes, including atherosclerosis, rheumatoid arthritis and inflammatory bowel disease. Members of the nuclear receptor superfamily of ligand-dependent transcriptions factors have emerged as key regulators of inflammation and lipid homeostasis in macrophages. These include the glucocorticoid receptor (GR), which inhibits inflammatory programs of gene expression in response to natural corticosteroids and synthetic anti-inflammatory ligands such as dexamethasone. Also, in response to endogenous eicosanoids and oxysterols, respectively, peroxisome proliferator-activated receptors (PPARs) and liver X receptors (LXRs) regulate transcriptional programs involved in inflammatory responses and lipid homeostasis. Identification of their mechanisms of action should help guide the development of new therapeutic agents useful in the treatment of diseases in which macrophages play critical pathogenic roles.
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Affiliation(s)
- Annabel F Valledor
- Department of Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0651, USA
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247
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Ricote M, Valledor AF, Glass CK. Decoding Transcriptional Programs Regulated by PPARs and LXRs in the Macrophage. Arterioscler Thromb Vasc Biol 2004; 24:230-9. [PMID: 14592855 DOI: 10.1161/01.atv.0000103951.67680.b1] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Macrophages play essential roles in immunity and homeostasis. As professional scavengers, macrophages phagocytose microbes and apoptotic and necrotic cells and take up modified lipoprotein particles. These functions require tightly regulated mechanisms for the processing and disposal of cellular lipids. Under pathological conditions, arterial wall macrophages become foam cells by accumulating large amounts of cholesterol, contributing to the development of atherosclerosis. Peroxisome proliferator–activated receptors (PPARs) and liver X receptors (LXRs) are members of the nuclear receptor superfamily of transcription factors that have emerged as key regulators of macrophage homeostasis. PPARs and LXRs control transcriptional programs involved in processes of lipid uptake and efflux, lipogenesis, and lipoprotein metabolism. In addition, PPARs and LXRs negatively regulate transcriptional programs involved in the development of inflammatory responses. This review summarizes recent efforts to decode the differential and overlapping roles of PPARs and LXRs in the context of macrophage lipid homeostasis and the control of inflammation.
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Affiliation(s)
- Mercedes Ricote
- Department of Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, Calif 92093-0651, USA
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248
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Hoerer S, Schmid A, Heckel A, Budzinski RM, Nar H. Crystal structure of the human liver X receptor beta ligand-binding domain in complex with a synthetic agonist. J Mol Biol 2004; 334:853-61. [PMID: 14643652 DOI: 10.1016/j.jmb.2003.10.033] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
LXRbeta belongs to the nuclear hormone receptor superfamily of ligand-activated transcription factors. Its natural ligands are supposed to be oxidised derivatives of cholesterol. Stimulation of LXRbeta by agonists activates a number of genes that are involved in the regulation of lipid metabolism and cholesterol efflux from cells. Therefore, LXRbeta may represent a novel therapeutic target for the treatment of dyslipidemia and atherosclerosis.Here, we report the X-ray crystal structure of the LXRbeta ligand-binding domain in complex with a synthetic agonist, T-0901317. This compound occupies the ligand-binding pocket of the receptor, forms numerous lipophilic contacts with the protein and one crucial hydrogen bond to His435 and stabilises the agonist conformation of the receptor ligand-binding domain. The recruitment of the AF2-region of the protein is not achieved via direct polar interactions of the ligand with protein side-chains of this helical segment, but rather via few hydrophobic contacts and probably more importantly via indirect effects involving the pre-orientation of side-chains that surround the ligand-binding pocket and form the interface to the AF2-helix. On the basis of these results we propose a binding mode and a mechanism of action for the putative natural ligands, oxidised derivatives of cholesterol.
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Affiliation(s)
- Stefan Hoerer
- Department of Lead Discovery, Boehringer Ingelheim Pharma GmbH & Co. KG, Birkendorfer Strasse 65, D-88397 Biberach/Riss, Germany
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249
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Chinetti G, Zawadski C, Fruchart JC, Staels B. Expression of adiponectin receptors in human macrophages and regulation by agonists of the nuclear receptors PPARα, PPARγ, and LXR. Biochem Biophys Res Commun 2004; 314:151-8. [PMID: 14715259 DOI: 10.1016/j.bbrc.2003.12.058] [Citation(s) in RCA: 193] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors expressed in macrophages where they control cholesterol homeostasis and inflammation. In an attempt to identify new PPARalpha and PPARgamma target genes in macrophages, a DNA array-based global gene expression profiling experiment was performed on human primary macrophages treated with specific PPARalpha and PPARgamma agonists. Surprisingly, AdipoR2, one of the two recently identified receptors for adiponectin, an adipocyte-specific secreted hormone with anti-diabetic and anti-atherogenic activities, was found to be induced by both PPARalpha and PPARgamma. AdipoR2 induction by PPARalpha and PPARgamma in primary and THP-1 macrophages was confirmed by Q-PCR analysis. Interestingly, treatment with a synthetic LXR agonist induced the expression of both AdipoR1 and AdipoR2. Furthermore, co-incubation with a PPARalpha ligand and adiponectin resulted in an additive effect on the reduction of macrophage cholesteryl ester content. Finally, AdipoR1 and AdipoR2 are both present in human atherosclerotic lesions. Moreover, AdipoR1 is more abundant than AdipoR2 in monocytes and its expression decreases upon differentiation into macrophages, whereas AdipoR2 remains constant. In conclusion, AdipoR1 and AdipoR2 are expressed in human atherosclerotic lesions and macrophages and can be modulated by PPAR and LXR ligands, thus identifying a mechanism of crosstalk between adiponectin and these nuclear receptor signaling pathways.
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Affiliation(s)
- G Chinetti
- UR 545 INSERM, Institut Pasteur de Lille and Université de Lille 2, Lille, France
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250
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Abstract
Oxidized derivatives of cholesterol have been investigated actively for decades in the context of the oxidative hypothesis of atherosclerosis. Oxysterols arise in our tissues as a result of enzymatic or non-enzymatic oxidation reactions and are also obtained from dietary sources. Even though these compounds are found enriched in the atherosclerotic lesions in arterial walls, the plasma concentrations of oxysterols cannot, in the light of current knowledge, be regarded as a risk factor for atherosclerotic disease. However, oxysterols may still have important local effects in the arterial wall as factors that regulate the cellular lipid homeostasis and possibly the maturation of the lesions. Work during the past few years has revealed that oxysterols have a potential as signaling molecules that may play important roles in lipid metabolism, especially the reverse cholesterol transport process. This finding has recently moved oxysterols and the protein mediators of their biological effects, liver X receptors and cytosolic oxysterol binding proteins, into the center stage of atherosclerosis research.
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Affiliation(s)
- Vesa M Olkkonen
- Department of Molecular Medicine, National Public Health Institute, Helsinki, Finland
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