201
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Abstract
Orphan nuclear receptors of the peroxisome proliferator activated receptor (PPAR) and liver X receptor (LXR) subfamilies have been shown to play critical roles in both local and systemic lipid metabolism. The PPARs control fatty acid metabolism in various cell types, including adipocytes, liver, and macrophages. The LXRs have been implicated in the regulation of cholesterol metabolism in the liver, intestines, and macrophages. The importance of these receptors in physiologic lipid metabolism suggests that they may influence the development of metabolic disorders such as obesity, diabetes, and atherosclerosis. Furthermore, the ability of these receptors to be modulated pharmacologically makes them attractive therapeutic targets. This review focuses on the role of PPAR and LXR signaling pathways in macrophage lipid metabolism and the potential of these pathways to modulate the development of atherosclerosis.
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Affiliation(s)
- Bryan A Laffitte
- Howard Hughes Medical Institute, UCLA School of Medicine, Box 951662, Los Angeles, CA 90095-1662, USA
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202
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Abstract
During the past year studies with mouse models have significantly clarified our understanding of atherosclerosis. Noteworthy achievements include: the discovery of a number of novel genes and pathways; new evidence emphasizing the role of lymphocytes in atherogenesis; the development of mouse models exhibiting advanced lesions with evidence of thrombosis; and new results indicating an anti-atherogenic effect of testosterone.
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Affiliation(s)
- Sonal S Sheth
- Department of Human Genetics, UCLA School of Medicine, Los Angeles, California 90095, USA
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203
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Akiyama TE, Sakai S, Lambert G, Nicol CJ, Matsusue K, Pimprale S, Lee YH, Ricote M, Glass CK, Brewer HB, Gonzalez FJ. Conditional disruption of the peroxisome proliferator-activated receptor gamma gene in mice results in lowered expression of ABCA1, ABCG1, and apoE in macrophages and reduced cholesterol efflux. Mol Cell Biol 2002; 22:2607-19. [PMID: 11909955 PMCID: PMC133709 DOI: 10.1128/mcb.22.8.2607-2619.2002] [Citation(s) in RCA: 311] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Disruption of the peroxisome proliferator-activated receptor gamma (PPAR gamma) gene causes embryonic lethality due to placental dysfunction. To circumvent this, a PPAR gamma conditional gene knockout mouse was produced by using the Cre-loxP system. The targeted allele, containing loxP sites flanking exon 2 of the PPAR gamma gene, was crossed into a transgenic mouse line expressing Cre recombinase under the control of the alpha/beta interferon-inducible (MX) promoter. Induction of the MX promoter by pIpC resulted in nearly complete deletion of the targeted exon, a corresponding loss of full-length PPAR gamma mRNA transcript and protein, and marked reductions in basal and troglitazone-stimulated expression of the genes encoding lipoprotein lipase, CD36, LXR alpha, and ABCG1 in thioglycolate-elicited peritoneal macrophages. Reductions in the basal levels of apolipoprotein E (apoE) mRNA in macrophages and apoE protein in total plasma and high-density lipoprotein (HDL) were also observed in pIpC-treated PPAR gamma-MXCre(+) mice. Basal cholesterol efflux from cholesterol-loaded macrophages to HDL was significantly reduced after disruption of the PPAR gamma gene. Troglitazone selectively inhibited ABCA1 expression (while rosiglitazone, ciglitazone, and pioglitazone had little effect) and cholesterol efflux in both PPAR gamma-deficient and control macrophages, indicating that this drug can exert paradoxical effects on cholesterol homeostasis that are independent of PPAR gamma. Together, these data indicate that PPAR gamma plays a critical role in the regulation of cholesterol homeostasis by controlling the expression of a network of genes that mediate cholesterol efflux from cells and its transport in plasma.
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MESH Headings
- ATP Binding Cassette Transporter 1
- ATP Binding Cassette Transporter, Subfamily G, Member 1
- ATP-Binding Cassette Transporters/genetics
- Alleles
- Animals
- Apolipoproteins E/genetics
- Biological Transport, Active
- Cholesterol/metabolism
- Exons
- Female
- Gene Expression/drug effects
- Gene Targeting
- Integrases/genetics
- Lipoprotein Lipase/genetics
- Macrophages/drug effects
- Macrophages/metabolism
- Mice
- Mice, Knockout
- Mice, Transgenic
- Poly I-C/pharmacology
- Pregnancy
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/deficiency
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Sequence Deletion
- Transcription Factors/deficiency
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Viral Proteins/genetics
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Affiliation(s)
- Taro E Akiyama
- Laboratory of Metabolism, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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204
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Lin G. Insights of high-density lipoprotein apolipoprotein-mediated lipid efflux from cells. Biochem Biophys Res Commun 2002; 291:727-31. [PMID: 11866424 DOI: 10.1006/bbrc.2002.6505] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
High-density lipoprotein (HDL) protects against cardiovascular diseases by removal of excess lipids from cells. HDL apolipoprotein-mediated lipid efflux involves multiple cellular proteins to remove both cholesterol and phospholipids that are otherwise stored in the cells. This article reviews recent progress in the understanding of receptors, signal mediators, Golgi and vesicle transport related to the pathway and proposes a model of HDL apolipoprotein receptor-mediated exocytosis of cellular cholesterol. Such an exocytotic pathway could provide the most effective mechanism to remove excess cellular lipids and prevent atherogenesis.
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Affiliation(s)
- Guorong Lin
- Department of Pathology, University of Washington, Seattle, Washington 98195-7470, USA.
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205
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Schild RL, Schaiff WT, Carlson MG, Cronbach EJ, Nelson DM, Sadovsky Y. The activity of PPAR gamma in primary human trophoblasts is enhanced by oxidized lipids. J Clin Endocrinol Metab 2002; 87:1105-10. [PMID: 11889173 DOI: 10.1210/jcem.87.3.8284] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The ligand-dependent nuclear receptor PPAR gamma plays an important role in murine and human trophoblast differentiation. Oxidized lipids, which are implicated in the pathophysiology of placental dysfunction, have recently been identified as ligands for PPAR gamma. We therefore hypothesized that oxidized lipids activate PPAR gamma in human trophoblasts and influence placental function. To test our hypothesis, we examined the effect of 9S-hydroxy-10E,12Z-octadecadienoic acid (9-HODE), 13S-hydroxy-9Z,11E-octadecadienoic acid (13-HODE), and 15S-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (15-HETE) on PPAR gamma activity in cultured term human trophoblasts. Our results demonstrate that these lipids stimulate PPAR gamma activity and that the AF-2 fragment, which harbors the ligand-binding domain of PPAR gamma, mediates this effect. Furthermore, we assessed the consequences of PPAR gamma activation by the oxidized lipids, and we found that these lipids stimulate human CG production, a measure of trophoblast differentiation. In contrast, the expression of syncytin, a marker for syncytium formation as well as the expression of the cell cycle modulators cyclin E and p27 are unchanged by the oxidized lipids. We concluded that 9-HODE, 13-HODE, and 15-HETE activate PPAR gamma in primary human trophoblasts. These PPAR gamma ligands may play a role in placental differentiation, yet they are unlikely to contribute to trophoblast dysfunction.
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Affiliation(s)
- Ralf L Schild
- Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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206
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Abstract
Coronary artery disease is the leading cause of death in much of the western world. Atherosclerotic plaques in the coronary arteries contribute to luminal obstruction leading to myocardial ischemia; however, abrupt coronary artery occlusion most frequently results from superimposition of a thrombus on a disrupted plaque, leading to the most serious clinical manifestations of coronary artery disease, ie, unstable angina, acute myocardial infarction, and sudden death. Plaque that have undergone disruption and, by inference, plaques at risk for disruption (vulnerable plaques), tend to demonstrate outward vessel remodeling, contain a large lipid core, thinned out fibrous cap, reduced collagen content, and increased inflammatory cell infiltration. Plaque stabilization through change in plaque composition may be responsible for reduced frequency of acute vaso-occlusive events observed with lipid and other risk-factor modifying interventions.
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Affiliation(s)
- Prediman K Shah
- Division of Cardiology and Atherosclerosis Research Center, Burns and Allen Research Institute, and Department of Medicine, Cedars Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048, USA
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207
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Kwak BR, Myit S, Mulhaupt F, Veillard N, Rufer N, Roosnek E, Mach F. PPARgamma but not PPARalpha ligands are potent repressors of major histocompatibility complex class II induction in atheroma-associated cells. Circ Res 2002; 90:356-62. [PMID: 11861426 DOI: 10.1161/hh0302.104924] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Peroxisome proliferator-activated receptors (PPARs) are essential in glucose and lipid metabolism and are implicated in metabolic disorders predisposing to atherosclerosis, such as diabetes and dyslipidemia. Conversely, antidiabetic glitazones and hypolipidemic fibrate drugs, known as PPARgamma and PPARalpha ligands, respectively, reduce the process of atherosclerotic lesion formation, which involves chronic immunoinflammatory processes. Major histocompatibility complex class II (MHC-II) molecules, expressed on the surface of specialized cells, are directly involved in the activation of T lymphocytes and in the control of the immune response. Interestingly, expression of MHC-II has recently been observed in atherosclerotic plaques, and it can be induced by the proinflammatory cytokine interferon-gamma (IFN-gamma) in vascular cells. To explore a possible role for PPAR ligands in the regulation of the immune response, we investigated whether PPAR activation affects MHC-II expression in atheroma-associated cells. In the present study, we demonstrate that PPARgamma but not PPARalpha ligands act as inhibitors of IFN-gamma-induced MHC-II expression and thus as repressors of MHC-II-mediated T-cell activation. All different types of PPARgamma ligands tested inhibit MHC-II. This effect of PPARgamma ligands is due to a specific inhibition of promoter IV of CIITA and does not concern constitutive expression of MHC-II. Thus, the beneficial effects of antidiabetic PPARgamma activators on atherosclerotic plaque development may be partly explained by their repression of MHC-II expression and subsequent inhibition of T-lymphocyte activation.
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Affiliation(s)
- Brenda R Kwak
- Division of Cardiology, Department of Medicine, University Hospital, Geneva Medical School, Foundation for Medical Research, Geneva, Switzerland
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208
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Landis MS, Patel HV, Capone JP. Oxysterol activators of liver X receptor and 9-cis-retinoic acid promote sequential steps in the synthesis and secretion of tumor necrosis factor-alpha from human monocytes. J Biol Chem 2002; 277:4713-21. [PMID: 11741944 DOI: 10.1074/jbc.m108807200] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Liver X receptor alpha (LXRalpha), is a nuclear hormone receptor that is activated by oxysterols and plays a crucial role in regulating cholesterol and lipid metabolism in liver and cholesterol efflux from lipid-loaded macrophages. Here we show that treatment of human peripheral blood monocytes or monocytic THP-1 cells with the LXR ligand 22(R)-hydroxycholesterol (22(R)-HC), in combination with 9-cis-retinoic acid (9cRA), a ligand for the LXR heterodimerization partner retinoid X receptor (RXR), results in the specific induction of the potent pro-apoptotic and pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Promoter analysis, inhibitor studies, and order-of-addition experiments demonstrated that TNF-alpha induction by 22(R)-HC and 9cRA occurs by a novel two-step process. The initial step involves 22(R)-HC-dependent induction of TNF-alpha mRNA, and intracellular accumulation of TNF-alpha protein, mediated by binding of LXRalpha/RXRalpha to an LXR response element at position -879 of the TNF-alpha promoter. Subsequent cell release of TNF-alpha protein occurs via a separable 9cRA-dependent, LXRalpha-independent step that requires de novo transcription and protein synthesis. Our findings reveal a potentially new dimension of the physiological role of LXRalpha and identify a unique multistep pathway of TNF-alpha production that may be of consequence to the normal function of LXR in monocyte/macrophages and in disease conditions such as atherosclerosis.
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Affiliation(s)
- Mark S Landis
- Department of Biochemistry, Faculty of Health Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada
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209
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Stein O, Ben-Naim M, Dabach Y, Hollander G, Stein Y. Macrophage cholesterol efflux to free apoprotein A-I in C3H and C57BL/6 mice. Biochem Biophys Res Commun 2002; 290:1376-81. [PMID: 11820773 DOI: 10.1006/bbrc.2002.6358] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cholesterol efflux from peritoneal macrophages of mice C57BL/6 susceptible and C3H resistant to atherosclerosis was compared, using apoprotein A-I as acceptor. The elicited macrophages were labeled with 3H-cholesterol and cholesterol enriched by incubation for 24 h with acetylated LDL. After incubation for 6 or 24 h, 3H-cholesterol efflux to free apoA-I (10 microg/ml) was significantly higher with macrophages derived from C3H mice compared to C57BL/6 mice. The cells were also pretreated with 0.3-0.45 mM cyclic AMP, 10 microM 9-cis-retinoic acid or 10 microM 22(R)-hydroxycholesterol, RXR and LXR ligands. Treatment with cyclic AMP, RXR, or LXR ligands, resulted in enhancement of 3H-cholesterol efflux in both strains. Under all conditions, 3H-cholesterol efflux was significantly higher in C3H compared to C57BL/6 macrophages. In conclusion, the higher cholesterol efflux from C3H macrophages could contribute toward the resistance of this strain to diet-induced atherosclerosis despite hypercholesterolemia.
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Affiliation(s)
- Olga Stein
- Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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210
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Lin G, Bornfeldt KE. Cyclic AMP-specific phosphodiesterase 4 inhibitors promote ABCA1 expression and cholesterol efflux. Biochem Biophys Res Commun 2002; 290:663-9. [PMID: 11785950 DOI: 10.1006/bbrc.2001.6259] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
ATP cassette binding protein 1 (ABCA1) controls the apolipoprotein-mediated cholesterol efflux pathway and determines plasma HDL levels. Although cAMP is known to promote ABCA1 expression and cholesterol efflux from cells, it has not been determined whether cyclic nucleotide phosphodiesterase (PDE) isoforms regulate this pathway. We show that rolipram and cilomilast, inhibitors of cAMP-specific PDE4, increase apolipoprotein A-I (apoA-I)-mediated cholesterol efflux up to 80 and 140% in human THP-1 and mouse J774.A1 macrophages, respectively, concomitant with an elevation of cAMP levels. The EC(50) value was estimated to be 1 to 2 microM for both inhibitors. Rolipram and cilomilast also increase ABCA1 protein expression in THP-1 and J774.A1 macrophages. Thus, PDE4 inhibitors cause parallel increases in cAMP levels, ABCA1 expression and apoA-I-mediated cholesterol efflux. PDE4 inhibitors may provide a novel strategy for the treatment of cardiovascular disease by mobilizing cholesterol from atherosclerotic lesions.
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Affiliation(s)
- Guorong Lin
- Department of Pathology, University of Washington School of Medicine, Seattle, Washington 98195-7470, USA
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211
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Besnard S, Silvestre JS, Duriez M, Bakouche J, Lemaigre-Dubreuil Y, Mariani J, Levy BI, Tedgui A. Increased ischemia-induced angiogenesis in the staggerer mouse, a mutant of the nuclear receptor Roralpha. Circ Res 2001; 89:1209-15. [PMID: 11739287 DOI: 10.1161/hh2401.101755] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ror alpha is an orphan nuclear receptor. In homozygous staggerer mutant mice (Ror alpha(sg/sg)), a deletion within the Ror alpha gene leads to an overexpression of inflammatory cytokines. Because inflammation and hypoxia are 2 key stimuli of ischemia-induced angiogenesis, we studied the role of Ror alpha in this setting. Ischemia was induced by ligation of the right femoral artery in C57BL/6 Ror alpha(+/+) and Ror alpha(sg/sg) mice. After 3 and 28 days, angiogenesis was evaluated by microangiography, measurement of capillary density using immunohistochemistry (anti-CD31), and measurement of blood flow by laser Doppler imaging. At day 3, angiographic score and blood flow were similar in Ror alpha(sg/sg) mice and in Ror alpha(+/+) littermates. Conversely, at day 28, Ror alpha(sg/sg) mice showed a significant 2-fold increase in angiographic score and a 3-fold increase in capillary density within the ischemic hindlimb compared with control. Functionally, this coincided with a significant rise in leg perfusion in Ror alpha(sg/sg) mice (0.83+/-0.05 for ischemic/nonischemic leg perfusion ratio) compared with Ror(+/+) mice (0.66+/-0.04, P<0.05). In addition, more extensive angiogenesis in Ror alpha(sg/sg) mice correlated with an increased expression of eNOS protein by 83+/-12% and 71+/-24% at 3 and 28 days, respectively (P<0.05), whereas the level of the antiangiogenic cytokine IL-12 was significantly reduced by 38+/-10% at day 28 (P<0.05). Conversely, no changes in VEGF expression were observed. Our study identifies for the first time a new role for Ror alpha as a potent negative regulator of ischemia-induced angiogenesis.
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MESH Headings
- Animals
- Arterioles/cytology
- Blood Flow Velocity/physiology
- Blotting, Western
- Capillaries/cytology
- Endothelial Growth Factors/metabolism
- Femoral Artery/physiology
- Hindlimb/blood supply
- Interleukin-12/metabolism
- Ischemia/metabolism
- Laser-Doppler Flowmetry
- Ligation
- Lymphokines/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Neurologic Mutants
- Microcirculation/physiology
- Muscle, Skeletal/blood supply
- Muscle, Skeletal/cytology
- Muscle, Skeletal/metabolism
- Neovascularization, Physiologic/physiology
- Nitric Oxide Synthase/metabolism
- Nitric Oxide Synthase Type II
- Nitric Oxide Synthase Type III
- Nuclear Receptor Subfamily 1, Group F, Member 1
- Platelet Endothelial Cell Adhesion Molecule-1/metabolism
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/deficiency
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Regional Blood Flow/physiology
- Trans-Activators/deficiency
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Vascular Endothelial Growth Factor A
- Vascular Endothelial Growth Factors
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Affiliation(s)
- S Besnard
- INSERM U541, Hôpital Lariboisière, and IFR Circulation-Paris 7, Université Paris 7-Denis Diderot, France
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212
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Zhang Y, Repa JJ, Gauthier K, Mangelsdorf DJ. Regulation of lipoprotein lipase by the oxysterol receptors, LXRalpha and LXRbeta. J Biol Chem 2001; 276:43018-24. [PMID: 11562371 DOI: 10.1074/jbc.m107823200] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipoprotein lipase (LPL) is a key enzyme for lipoprotein metabolism and is responsible for hydrolysis of triglycerides in circulating lipoproteins, releasing free fatty acids to peripheral tissues. In liver, LPL is also believed to promote uptake of high density lipoprotein (HDL)-cholesterol and thereby facilitate reverse cholesterol transport. In this study we show that the Lpl gene is a direct target of the oxysterol liver X receptor, LXRalpha. Mice fed diets containing high cholesterol or an LXR-selective agonist exhibited a significant increase in LPL expression in the liver and macrophages, but not in other tissues (e.g. adipose and muscle). Studies in Lxr-deficient mice confirmed that this response was dependent more on the presence of LXRalpha than LXRbeta. Analysis of the Lpl gene revealed the presence of a functional DR4 LXR response element in the intronic region between exons 1 and 2. This response element directly binds rexinoid receptor (RXR)/LXR heterodimers and is sufficient for rexinoid- and LXR agonist-induced transcription of the Lpl gene. Together, these studies further distinguish the roles of LXRalpha and beta and support a growing body of evidence that LXRs function as key regulators of lipid metabolism and are anti-atherogenic.
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MESH Headings
- Adipose Tissue/metabolism
- Animals
- Base Sequence
- Biological Transport
- Blotting, Northern
- Cell Adhesion
- Cell Line
- Cells, Cultured
- Cholesterol/metabolism
- Cholesterol/pharmacology
- DNA-Binding Proteins
- Diet
- Diet, Atherogenic
- Dimerization
- Exons
- Gene Expression Regulation, Enzymologic
- Humans
- Introns
- Lipid Metabolism
- Lipoprotein Lipase/genetics
- Lipoprotein Lipase/metabolism
- Liver/enzymology
- Liver/metabolism
- Liver X Receptors
- Macrophages/enzymology
- Macrophages/metabolism
- Male
- Mice
- Molecular Sequence Data
- Orphan Nuclear Receptors
- Plasmids/metabolism
- Promoter Regions, Genetic
- Protein Binding
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/chemistry
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Retinoic Acid/agonists
- Receptors, Retinoic Acid/chemistry
- Receptors, Retinoic Acid/metabolism
- Receptors, Thyroid Hormone/agonists
- Receptors, Thyroid Hormone/chemistry
- Receptors, Thyroid Hormone/metabolism
- Time Factors
- Transcriptional Activation
- Transfection
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Affiliation(s)
- Y Zhang
- Department of Pharmacology and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9050, USA
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213
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Shah PK, Kaul S, Nilsson J, Cercek B. Exploiting the vascular protective effects of high-density lipoprotein and its apolipoproteins: an idea whose time for testing is coming, part II. Circulation 2001; 104:2498-502. [PMID: 11705831 DOI: 10.1161/hc4501.098468] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- P K Shah
- Atherosclerosis Research Center, Division of Cardiology and Burns and Allen research Institute, Department of Medicine, Cedars Sinai Medical Center and UCLA School of Medicine, Los Angeles, California, USA.
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214
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Abstract
An elevated low-density lipoprotein (LDL) cholesterol level is a strong predictor of coronary heart disease (CHD) risk. Over the past seven years, equally strong evidence has accumulated that lowering LDL cholesterol with HMG-CoA reductase inhibitors or statins reduces CHD risk and there is now widespread use of these agents for the primary and secondary prevention of CHD. Treatment issues remain regarding the appropriate degree of LDL cholesterol reduction and whether, in people with very high levels, it would be preferable to achieve the LDL cholesterol goal with a powerful statin alone or combined with an agent that lowers LDL cholesterol by a different mechanism. The main focus in the development of novel agents is the patient with low high-density lipoprotein (HDL) cholesterol, usually associated with hypertriglyceridaemia. Already prevalent as a risk factor for CHD, this abnormality has been linked with insulin resistance, which is likely to increase greatly over the next decade, along with increasing obesity and diabetes. Agents that have potent HDL cholesterol raising capacity include cholesteryl ester transfer protein (CETP) inhibitors, retinoid X receptor (RXR) selective agonists, specific peroxisome proliferator-activated receptor (PPAR) agonists and oestrogen-like compounds. Another area of development involves agents that will lower both cholesterol and triglyceride levels, such as partial inhibitors of microsomal triglyceride transfer protein (MTP) and perhaps squalene synthase inhibitors and agonists of AMP kinase. Future emphasis will be on correcting all lipid abnormalities for the prevention of CHD, not just lowering LDL cholesterol.
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Affiliation(s)
- J D Best
- University of Melbourne, Department of Medicine, St Vincent's Hospital Melbourne, Victoria 3065, Australia.
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215
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Tall AR, Wang N, Mucksavage P. Is it time to modify the reverse cholesterol transport model? J Clin Invest 2001; 108:1273-5. [PMID: 11696569 PMCID: PMC209451 DOI: 10.1172/jci14342] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Affiliation(s)
- A R Tall
- Columbia University, Department of Medicine, Division of Molecular Medicine, New York, New York 10032, USA.
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216
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Tall AR, Wang N, Mucksavage P. Is it time to modify the reverse cholesterol transport model? J Clin Invest 2001. [DOI: 10.1172/jci200114342] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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217
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Chen J, Streb JW, Maltby KM, Kitchen CM, Miano JM. Cloning of a novel retinoid-inducible serine carboxypeptidase from vascular smooth muscle cells. J Biol Chem 2001; 276:34175-81. [PMID: 11447226 DOI: 10.1074/jbc.m104162200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Retinoids block smooth muscle cell (SMC) proliferation and attenuate neointimal formation after vascular injury, presumably through retinoid receptor-mediated changes in gene expression. To identify target genes in SMC whose encoded proteins could contribute to such favorable biological effects, we performed a subtractive screen for retinoid-inducible genes in cultured SMC. Here, we report on the cloning and initial characterization of a novel retinoid-inducible serine carboxypeptidase (RISC). Expression of RISC is low in cultured SMC but progressively increases over a 5-day time-course treatment with all-trans-retinoic acid. A near full-length rat RISC cDNA was cloned and found to have a 452-amino acid open reading frame containing an amino-terminal signal sequence, followed by several conserved domains comprising the catalytic triad common to members of the serine carboxypeptidase family. In vitro transcription and translation experiments showed that the rat RISC cDNA generates an approximately 51-kDa protein. Confocal immunofluorescence microscopy of COS-7 cells transiently transfected with a RISC-His tag plasmid revealed cytosolic localization of the fusion protein. Western blotting studies using conditioned medium from transfected COS-7 cells suggest that RISC is a secreted protein. Tissue Northern blotting studies demonstrated robust expression of RISC in rat aorta, bladder, and kidney with much lower levels in all other tissues analyzed; high level RISC expression was also observed in human kidney. In situ hybridization verified the localization of RISC to medial SMC of the adult rat aorta. Interestingly, expression in kidney was restricted to proximal convoluted tubules; little or no expression was observed in glomerular cells, distal convoluted and collecting tubules, or medullary cells. Radiation hybrid mapping studies placed the rat RISC locus on chromosome 10q. These studies reveal a novel retinoid-inducible protease whose activity may be involved in vascular wall and kidney homeostasis.
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MESH Headings
- Amino Acid Sequence
- Animals
- Aorta/metabolism
- Base Sequence
- Blotting, Northern
- Blotting, Western
- COS Cells
- Carboxy-Lyases/chemistry
- Carboxy-Lyases/genetics
- Carboxypeptidases/biosynthesis
- Carboxypeptidases/chemistry
- Carboxypeptidases/genetics
- Cells, Cultured
- Chromosome Mapping
- Cloning, Molecular
- DNA, Complementary/metabolism
- In Situ Hybridization
- Kidney/metabolism
- Male
- Microscopy, Confocal
- Microscopy, Fluorescence
- Molecular Sequence Data
- Muscle, Smooth, Vascular/metabolism
- Nucleic Acid Hybridization
- Open Reading Frames
- Phenotype
- Plasmids/metabolism
- Protein Biosynthesis
- RNA, Messenger/metabolism
- Radiation Hybrid Mapping
- Rats
- Rats, Sprague-Dawley
- Recombinant Fusion Proteins/metabolism
- Sequence Homology, Amino Acid
- Time Factors
- Tissue Distribution
- Transcription, Genetic
- Transfection
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Affiliation(s)
- J Chen
- Center for Cardiovascular Research, University of Rochester Medical Center, Rochester, New York 14642, USA
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Zhou XD, Zhou WS. A new highly stereoselective synthesis of cerebrosterol, an agonist of the nuclear receptor LXRs. Tetrahedron 2001. [DOI: 10.1016/s0040-4020(01)00812-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Abstract
Recently, a number of nuclear receptors have been identified as key regulators of cholesterol homeostasis. Two of these, liver X receptor alpha (LXRalpha) (NR1H3) [1] and ubiquitous receptor (UR) (NR1H2) [1], appear to be involved in cholesterol reverse transport and disposal. LXRalpha null gene mice fail to adapt metabolically to high-cholesterol diets. We have recently shown that some 6alpha-hydroxylated bile acid analogs are selective activators of LXRalpha. In this report, we show that these orally administered LXRalpha agonists have an overall hypolipidemic effect in hypercholesterolemic rats, mice and hamsters, which indicates that in these animal models, endogenous LXRalpha agonist is a limiting factor for induction of cholesterol disposal. Furthermore, in animals, these 6alpha-hydroxylated bile acid analogs exhibit a unique pharmacokinetic profile and do not increase the serum triglyceride level; therefore, they may represent a novel class of therapeutic agents for cholesterol management.
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Affiliation(s)
- C Song
- The Ben May Institute for Cancer Research, Department of Biochemistry and Molecular Biology, the Tang Center for Herbal Medicine Research, 5841 South Maryland Avenue, , Chicago, Illinois 60637, USA
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