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Petkevicius K, Palmgren H, Glover MS, Ahnmark A, Andréasson AC, Madeyski-Bengtson K, Kawana H, Allman EL, Kaper D, Uhrbom M, Andersson L, Aasehaug L, Forsström J, Wallin S, Ahlstedt I, Leke R, Karlsson D, González-King H, Löfgren L, Nilsson R, Pellegrini G, Kono N, Aoki J, Hess S, Sienski G, Pilon M, Bohlooly-Y M, Maresca M, Peng XR. TLCD1 and TLCD2 regulate cellular phosphatidylethanolamine composition and promote the progression of non-alcoholic steatohepatitis. Nat Commun 2022; 13:6020. [PMID: 36241646 PMCID: PMC9568529 DOI: 10.1038/s41467-022-33735-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 09/29/2022] [Indexed: 11/29/2022] Open
Abstract
The fatty acid composition of phosphatidylethanolamine (PE) determines cellular metabolism, oxidative stress, and inflammation. However, our understanding of how cells regulate PE composition is limited. Here, we identify a genetic locus on mouse chromosome 11, containing two poorly characterized genes Tlcd1 and Tlcd2, that strongly influences PE composition. We generated Tlcd1/2 double-knockout (DKO) mice and found that they have reduced levels of hepatic monounsaturated fatty acid (MUFA)-containing PE species. Mechanistically, TLCD1/2 proteins act cell intrinsically to promote the incorporation of MUFAs into PEs. Furthermore, TLCD1/2 interact with the mitochondria in an evolutionarily conserved manner and regulate mitochondrial PE composition. Lastly, we demonstrate the biological relevance of our findings in dietary models of metabolic disease, where Tlcd1/2 DKO mice display attenuated development of non-alcoholic steatohepatitis compared to controls. Overall, we identify TLCD1/2 proteins as key regulators of cellular PE composition, with our findings having broad implications in understanding and treating disease. The regulation of cellular phosphatidylethanolamine (PE) acyl chain composition is poorly understood. Here, the authors show that TLCD1 and TLCD2 proteins mediate the formation of monounsaturated fatty acid-containing PE species and promote the progression of non-alcoholic steatohepatitis.
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Affiliation(s)
- Kasparas Petkevicius
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden. .,Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden.
| | - Henrik Palmgren
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden.,Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Matthew S Glover
- Dynamic Omics, Centre for Genomics Research, Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gaithersburg, MD, USA
| | - Andrea Ahnmark
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Anne-Christine Andréasson
- Bioscience Cardiovascular, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | | | - Hiroki Kawana
- Department of Health Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan.,Advanced Research & Development Programs for Medical Innovation (AMED-LEAP), Tokyo, Japan
| | - Erik L Allman
- Dynamic Omics, Centre for Genomics Research, Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gaithersburg, MD, USA
| | - Delaney Kaper
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Martin Uhrbom
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Liselotte Andersson
- Clinical Pharmacology and Safety Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Leif Aasehaug
- Bioscience Cardiovascular, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Johan Forsström
- Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Simonetta Wallin
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Ingela Ahlstedt
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Renata Leke
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Daniel Karlsson
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Hernán González-King
- Bioscience Cardiovascular, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Lars Löfgren
- Translational Science and Experimental Medicine, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Ralf Nilsson
- Translational Science and Experimental Medicine, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Giovanni Pellegrini
- Clinical Pharmacology and Safety Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Nozomu Kono
- Department of Health Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Junken Aoki
- Department of Health Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan.,Advanced Research & Development Programs for Medical Innovation (AMED-LEAP), Tokyo, Japan
| | - Sonja Hess
- Dynamic Omics, Centre for Genomics Research, Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gaithersburg, MD, USA
| | - Grzegorz Sienski
- Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Marc Pilon
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | | | - Marcello Maresca
- Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Xiao-Rong Peng
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
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Maraninchi M, Calabrese A, Nogueira JP, Castinetti F, Mancini J, Mourre F, Piétri L, Bénamo E, Albarel F, Morange I, Dupont-Roussel J, Nicolay A, Brue T, Béliard S, Valéro R. Role of growth hormone in hepatic and intestinal triglyceride-rich lipoprotein metabolism. J Clin Lipidol 2021; 15:712-723. [PMID: 34462238 DOI: 10.1016/j.jacl.2021.08.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 07/23/2021] [Accepted: 08/09/2021] [Indexed: 11/16/2022]
Abstract
BACKGROUND Elevated plasma concentrations of hepatic- and intestinally-derived triglyceride-rich lipoproteins (TRL) are implicated in the pathogenesis of atherosclerotic cardiovascular disease and all-cause mortality. Excess of TRL is the driving cause of atherogenic dyslipidemia commonly occurring in insulin-resistant individuals such as patients with obesity, type 2 diabetes and metabolic syndrome. Interestingly, growth hormone (GH)-deficient individuals display similar atherogenic dyslipidemia, suggesting an important role of GH and GH deficiency in the regulation of TRL metabolism. OBJECTIVE We aimed to examine the direct and/or indirect role of GH on TRL metabolism. METHODS We investigated the effect on fasting and postprandial hepatic-TRL and intestinal-TRL metabolism of short-term (one month) withdrawal of GH in 10 GH-deficient adults. RESULTS After GH withdrawal, we found a reduction in fasting plasma TRL concentration (significant decrease in TRL-TG, TRL-cholesterol, TRL-apoB-100, TRL-apoC-III and TRL-apoC-II) but not in postprandial TRL response. This reduction was due to fewer fasting TRL particles without a change in TG per particle and was not accompanied by a change in postprandial TRL-apoB-48 response. Individual reductions in TRL correlated strongly with increases in insulin sensitivity and decreases in TRL-apoC-III. CONCLUSION In this relatively short term 'loss of function' human experimental model, we have shown an unanticipated reduction of hepatic-TRL particles despite increase in total body fat mass and reduction in lean mass. These findings contrast with the atherogenic dyslipidemia previously described in chronic GH deficient states, providing a new perspective for the role of GH in lipoprotein metabolism.
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Affiliation(s)
- Marie Maraninchi
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France
| | - Anastasia Calabrese
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France
| | - Juan-Patricio Nogueira
- Docencia e Investigacion, Hospital Central de Formosa, Salta 555, Formosa CP 3600, Argentina; Facultad de Ciencias de la Salud, Universidad Nacional de Formosa, Gutnisky 3200, Formosa CP 3600, Argentina
| | - Frédéric Castinetti
- INSERM, U1251, Marseille Medical Genetics (MMG), Faculté des Sciences médicales et paramédicales, France and AP-HM, Department of Endocrinology, Hôpital de la Conception, Centre de Référence des Maladies Rares de l'hypophyse HYPO, Institut Marseille Maladies Rares (MarMaRa), Aix-Marseille Univ, Marseille 13005, France
| | - Julien Mancini
- INSERM, IRD, UMR1252, SESSTIM, Aix-Marseille Univ, Marseille F-13273, France; APHM, Timone Hospital, Public Health Department (BIOSTIC), Marseille, F-13385, France
| | - Florian Mourre
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France
| | - Léa Piétri
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France
| | - Eric Bénamo
- Department of Endocrinology and Metabolic Diseases, Hospital d'Avignon Henri Duffaut, 205 rue Raoul Follereau, Avignon 84000, France
| | - Frédérique Albarel
- INSERM, U1251, Marseille Medical Genetics (MMG), Faculté des Sciences médicales et paramédicales, France and AP-HM, Department of Endocrinology, Hôpital de la Conception, Centre de Référence des Maladies Rares de l'hypophyse HYPO, Institut Marseille Maladies Rares (MarMaRa), Aix-Marseille Univ, Marseille 13005, France
| | - Isabelle Morange
- INSERM, U1251, Marseille Medical Genetics (MMG), Faculté des Sciences médicales et paramédicales, France and AP-HM, Department of Endocrinology, Hôpital de la Conception, Centre de Référence des Maladies Rares de l'hypophyse HYPO, Institut Marseille Maladies Rares (MarMaRa), Aix-Marseille Univ, Marseille 13005, France
| | - Jeanine Dupont-Roussel
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France
| | - Alain Nicolay
- APHM, Laboratory of Endocrine Biochemistry, La Conception Hospital, Marseille, France
| | - Thierry Brue
- INSERM, U1251, Marseille Medical Genetics (MMG), Faculté des Sciences médicales et paramédicales, France and AP-HM, Department of Endocrinology, Hôpital de la Conception, Centre de Référence des Maladies Rares de l'hypophyse HYPO, Institut Marseille Maladies Rares (MarMaRa), Aix-Marseille Univ, Marseille 13005, France
| | - Sophie Béliard
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France
| | - René Valéro
- Aix Marseille Univ, APHM, INSERM, INRAE, C2VN, University Hospital La Conception, Department of Nutrition, Metabolic Diseases and Endocrinology, 147 boulevard Baille, Marseille 13005, France.
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Placental secretion of apolipoprotein A1 and E: the anti-atherogenic impact of the placenta. Sci Rep 2019; 9:6225. [PMID: 30996342 PMCID: PMC6470155 DOI: 10.1038/s41598-019-42522-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Accepted: 04/01/2019] [Indexed: 12/12/2022] Open
Abstract
High levels of atherogenic lipids in pregnancy are associated with health complications for the mother, the fetus and the newborn. As endocrine secretory tissue, the human placenta releases apolipoproteins (apos), particularly apoA1 and apoE. However, the magnitude and the directionality of the apo secretions remain unknown. We aimed to 1) determine the amount and orientation (apical-maternal versus basal-fetal) of placentally secreted apoA1 and apoE using human perfused placenta and primary trophoblast cell (PTC) culture, 2) compare apoA1 and apoE secretions of PTC with that of hepatocytes and 3) associate the obtained results with human blood levels by determining apoA1 and apoE concentrations in maternal and fetal serum samples. In perfused placenta and serum samples, apoA1 and apoE concentrations were significantly higher at the maternal compared to the fetal side. For apoE a similar trend was found in PTC. For apoA1, the secretion to the apical side declined over time while release to the basal side was stable resulting in significantly different apoA1 concentrations between both sides. Unexpectedly, PTC secreted significantly higher amounts of apoA1 and apoE compared to hepatocytes. Our data indicate that the placenta may play an important role in maternal and fetal cholesterol homeostasis via secretion of anti-atherogenic apos.
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Liu HH, Li JJ. Aging and dyslipidemia: a review of potential mechanisms. Ageing Res Rev 2015; 19:43-52. [PMID: 25500366 DOI: 10.1016/j.arr.2014.12.001] [Citation(s) in RCA: 150] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 11/25/2014] [Accepted: 12/01/2014] [Indexed: 01/02/2023]
Abstract
Elderly adults constitute a rapidly growing part of the global population, thus resulting in an increase in morbidity and mortality related to cardiovascular disease (CVD), which remains the major cause of death in elderly population, including men and women. Dyslipidemia is a well-established risk factor for CVD and is estimated to account for more than half of the worldwide cases of coronary artery disease (CAD). Many studies have shown a strong correlation between serum cholesterol levels and risk of developing CAD. In this paper, we review the changes of plasma lipids that occur in men and women during aging and the potential mechanisms of age-related disorders of lipoprotein metabolism covering humans and/or animals, in which changes of the liver sinusoidal endothelium, postprandial lipemia, insulin resistance induced by free fatty acid (FFA), growth hormone (GH), androgen (only for men) and expression and activity of peroxisome proliferator-activated receptor α (PPARα) are mainly focused.
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Abstract
RNA editing is a process through which the nucleotide sequence specified in the genomic template is modified to produce a different nucleotide sequence in the transcript. RNA editing is an important mechanism of genetic regulation that amplifies genetic plasticity by allowing the production of alternative protein products from a single gene. There are two generic classes of RNA editing in nuclei, involving enzymatic deamination of either C-to-U or A-to-I nucleotides. The best characterized example of C-to-U RNA editing is that of apolipoprotein B (apoB), which is mediated by a holoenzyme that contains a minimal core composed of an RNA-specific cytidine deaminase apobec-1, and its cofactor apobec-1 complementation factor (ACF). C-to-U editing of apoB RNA generates two different isoforms--apoB100 and apoB48--from a single transcript. Both are important regulators of lipid transport and metabolism, and are functionally distinct. C-to-U apoB RNA editing is regulated by a range of factors including developmental, nutritional, environmental, and metabolic stimuli. Rodent models have provided a tractable system in which to study the effects of such stimuli on lipid metabolism. In addition, both transgenic and gene knockout experiments have provided important insights into gain and loss of function approaches for studying C-to-U RNA editing in a murine background.
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Affiliation(s)
- Soo-Jin Cho
- Division of Gastroenterology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
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Edvardsson U, Ljungberg A, Lindén D, William-Olsson L, Peilot-Sjögren H, Ahnmark A, Oscarsson J. PPARalpha activation increases triglyceride mass and adipose differentiation-related protein in hepatocytes. J Lipid Res 2005; 47:329-40. [PMID: 16282640 DOI: 10.1194/jlr.m500203-jlr200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adipose differentiation-related protein (ADRP) is a lipid droplet-associated protein that is expressed in various tissues. In mice treated with the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist Wy14,643 (Wy), hepatic mRNA and protein levels of ADRP as well as hepatic triglyceride content increased. Also in primary mouse hepatocytes, Wy increased ADRP expression and intracellular triglyceride mass. The triglyceride mass increased in spite of unchanged triglyceride biosynthesis and increased palmitic acid oxidation. However, Wy incubation decreased the secretion of newly synthesized triglycerides, whereas apolipoprotein B secretion increased. Thus, decreased availability of triglycerides for VLDL assembly could help to explain the cellular accumulation of triglycerides after Wy treatment. We hypothesized that this effect could be mediated by increased ADRP expression. Similar to PPARalpha activation, adenovirus-mediated ADRP overexpression in mouse hepatocytes enhanced cellular triglyceride mass and decreased the secretion of newly synthesized triglycerides. In ADRP-overexpressing cells, Wy incubation resulted in a further decrease in triglyceride secretion. This effect of Wy was not attributable to decreased cellular triglycerides after increased fatty acid oxidation because the triglyceride mass in Wy-treated ADRP-overexpressing cells was unchanged. In summary, PPARalpha activation prevents the availability of triglycerides for VLDL assembly and increases hepatic triglyceride content in part by increasing the expression of ADRP.
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Affiliation(s)
- Ulrika Edvardsson
- Wallenberg Laboratory for Cardiovascular Research, Sahlgrenska University Hospital, Göteborg, Sweden.
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7
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Matasconi M, Parini P, Angelin B, Rudling M. Pituitary control of cholesterol metabolism in normal and LDL receptor knock-out mice: Effects of hypophysectomy and growth hormone treatment. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1736:221-7. [PMID: 16185916 DOI: 10.1016/j.bbalip.2005.08.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Revised: 08/11/2005] [Accepted: 08/11/2005] [Indexed: 11/17/2022]
Abstract
The pituitary is important in the control of lipid metabolism and studies of hypophysectomized (Hx) rats have shown strong effects of growth hormone (GH) on bile acid synthesis, hepatic LDL receptor (LDLR) expression and on the sensitivity to dietary cholesterol. It is unclear if mice may be used in such studies. The aim of the current study was to evaluate if Hx mice may be used to further explore how GH modulates cholesterol and bile acid metabolism, and to define the importance of the LDLR in this regulation by studying LDLR-deficient mice (LDLRko). Experiments on three mouse strains showed that, following Hx, HDL were reduced and LDL increased. Cholesterol/fat feeding of Hx mice increased serum cholesterol levels 2- to 3-fold. Serum triglycerides were reduced 50% in Hx mice; a further 30% reduction was seen after dietary cholesterol/fat. A serum marker for CYP7A1-mediated bile acid synthesis (C4) increased 2-fold in intact mice on cholesterol/fat diet. In Hx mice C4 levels were reduced by 50% as compared to intact controls, but were unexpectedly increased to levels seen in normal mice upon cholesterol/fat feeding. Hx of LDLRko mice moderately increased LDL-cholesterol and reduced triglycerides and GH treatment attenuated these effects; serum C4 levels were increased by GH treatment in all groups. In conclusion, mice can be used to explore the role of the pituitary in lipid metabolism. CYP7A1 is generally reduced in Hx mice but has a normal stimulatory response following dietary cholesterol suggesting that faulty regulation of CYP7A1 is not important for the reduced resistance to dietary cholesterol in Hx mice. Further, the LDLR is only to a minor part involved in the pituitary regulation of serum cholesterol in mice.
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Affiliation(s)
- Manuela Matasconi
- Metabolism Unit, Center for Metabolism and Endocrinology, Department of Medicine and Molecular Nutrition Unit, Center for Nutrition and Toxicology, NOVUM, Karolinska Institute, M63, Karolinska University Hospital, Huddinge, S-141 86 Stockholm, Sweden
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8
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Stillemark-Billton P, Beck C, Borén J, Olofsson SO. Relation of the size and intracellular sorting of apoB to the formation of VLDL 1 and VLDL 2. J Lipid Res 2005; 46:104-14. [PMID: 15520448 DOI: 10.1194/jlr.m400296-jlr200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this study, we tested the hypothesis that two separate pathways, the two-step process and an apolipoprotein B (apoB) size-dependent lipidation process, give rise to different lipoproteins. Expression of apoB-100 and C-terminally truncated forms of apoB-100 in McA-RH7777 cells demonstrated that VLDL particles can be assembled by apoB size-dependent linear lipidation, resulting in particles whose density is inversely related to the size of apoB. This lipidation results in a LDL-VLDL 2 particle containing apoB-100. VLDL 1 is assembled by the two-step process by apoB-48 and larger forms of apoB but not to any significant amount by apoB-41. The major amount of intracellular apoB-80 and apoB-100 banded with a mean density of 1.10 g/ml. Its formation was dependent on the sequence between apoB-72 and apoB-90. This dense particle, which is retained in the cell, possibly by chaperones or association with the microsomal membrane, is a precursor of secreted VLDL 1. The intracellular LDL-VLDL 2 particles formed during size-dependent lipidation appear to be the precursors of intracellular VLDL 1. We propose that the dense apoB-100 intracellular particle is converted to LDL-VLDL 2 by size-dependent lipidation. LDL-VLDL 2 is secreted or converted to VLDL 1 by the uptake of the major amount of triglycerides.
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Affiliation(s)
- Pia Stillemark-Billton
- Department of Medical Biochemistry and the Wallenberg Laboratory for Cardiovascular Research, University of Göteborg, Göteborg, Sweden
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Améen C, Edvardsson U, Ljungberg A, Asp L, Akerblad P, Tuneld A, Olofsson SO, Lindén D, Oscarsson J. Activation of peroxisome proliferator-activated receptor alpha increases the expression and activity of microsomal triglyceride transfer protein in the liver. J Biol Chem 2004; 280:1224-9. [PMID: 15537571 DOI: 10.1074/jbc.m412107200] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Microsomal triglyceride transfer protein (MTP) is rate-limiting in the assembly and secretion of lipoproteins containing apolipoprotein (apo) B. Previously we demonstrated that Wy 14,643 (Wy), a peroxisome proliferator-activated receptor (PPAR) alpha agonist, increases apoB-100 secretion despite decreased triglyceride synthesis. In this study, we sought to determine whether PPARalpha activation increases MTP expression and activity. Treatment with Wy increased hepatic MTP expression and activity in rats and mice and increased MTP expression in primary cultures of rat and mouse hepatocytes. Addition of actinomycin D blocked this increase and the MTP promoter (-136 to +67) containing a conserved DR1 element was activated by Wy, showing that PPARalpha activates transcription of the gene. Wy did not affect MTP expression in the intestine or in cultured hepatocytes from PPARalpha-null mice. A retinoid X receptor agonist (9-cis-retinoic acid), but not a PPARgamma agonist (rosiglitazone), increased MTP mRNA expression in cultured hepatocytes from both wild type and PPARalpha-null mice. In rat hepatocytes incubated with Wy, MTP mRNA levels increased between 6 and 24 h, and MTP protein expression and apoB-100 secretion increased between 24 and 72 h. In conclusion, PPARalpha activation stimulates hepatic MTP expression via increased transcription of the Mtp gene. This effect is paralleled by a change in apoB-100 secretion, indicating that the effect of Wy on apoB-100 secretion is mediated by increased expression of MTP.
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Affiliation(s)
- Caroline Améen
- Wallenberg Laboratory for Cardiovascular Research, Sahlgrenska University Hospital, S-41345 Göteborg, Sweden
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10
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Colao A, Ferone D, Marzullo P, Lombardi G. Systemic complications of acromegaly: epidemiology, pathogenesis, and management. Endocr Rev 2004; 25:102-52. [PMID: 14769829 DOI: 10.1210/er.2002-0022] [Citation(s) in RCA: 787] [Impact Index Per Article: 39.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This review focuses on the systemic complications of acromegaly. Mortality in this disease is increased mostly because of cardiovascular and respiratory diseases, although currently neoplastic complications have been questioned as a relevant cause of increased risk of death. Biventricular hypertrophy, occurring independently of hypertension and metabolic complications, is the most frequent cardiac complication. Diastolic and systolic dysfunction develops along with disease duration; and other cardiac disorders, such as arrhythmias, valve disease, hypertension, atherosclerosis, and endothelial dysfunction, are also common in acromegaly. Control of acromegaly by surgery or pharmacotherapy, especially somatostatin analogs, improves cardiovascular morbidity. Respiratory disorders, sleep apnea, and ventilatory dysfunction are also important contributors in increasing mortality and are advantageously benefitted by controlling GH and IGF-I hypersecretion. An increased risk of colonic polyps, which more frequently recur in patients not controlled after treatment, has been reported by several independent investigations, although malignancies in other organs have also been described, but less convincingly than at the gastrointestinal level. Finally, the most important cause of morbidity and functional disability of the disease is arthropathy, which can be reversed at an initial stage, but not if the disease is left untreated for several years.
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Affiliation(s)
- Annamaria Colao
- Department of Molecular and Clinical Endocrinology and Oncology, Federico II University of Naples, 80131 Naples, Italy.
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11
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Lind S, Rudling M, Ericsson S, Olivecrona H, Eriksson M, Borgström B, Eggertsen G, Berglund L, Angelin B. Growth Hormone Induces Low-Density Lipoprotein Clearance but not Bile Acid Synthesis in Humans. Arterioscler Thromb Vasc Biol 2004; 24:349-56. [PMID: 14656733 DOI: 10.1161/01.atv.0000110657.67317.90] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Growth hormone (GH) induces hepatic low-density lipoprotein (LDL) receptors and lowers plasma cholesterol. We characterized the influence of GH treatment on plasma LDL clearance in normal humans and investigated the relative role of LDL receptor (LDLR) activity and stimulation of bile acid synthesis in subjects with different LDLR expression. METHODS AND RESULTS Plasma clearance of autologous 125I-LDL was measured before and during 3 weeks of treatment with GH (0.1 IU/kg per day) in 9 healthy young males. Plasma LDL cholesterol was reduced by 13% and the fractional catabolic rate of LDL increased by 27%. More marked changes were seen in a patient with hypopituitarism substituted with GH (0.07 IU/kg per day) for 3 months. In a second study, GH dose-dependently reduced LDL cholesterol and increased Lp(a) levels in 3 groups of males: younger and elderly healthy subjects and heterozygous familial hypercholesterolemia (FH). No effect on bile acid synthesis measured by the plasma marker 7alpha-hydroxy-4-cholesten-3-one was observed. In an LDLR-deficient FH homozygote, LDL cholesterol was not affected by GH. CONCLUSIONS GH treatment reduces plasma LDL cholesterol by inducing LDL clearance. In humans, LDLR expression is a prerequisite for this effect, whereas it is not related to stimulation of bile acid synthesis.
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Affiliation(s)
- Suzanne Lind
- Metabolism Unit, Center for Metabolism and Endocrinology, Department of Medicine, Novum, Sweden
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Améen C, Oscarsson J. Sex difference in hepatic microsomal triglyceride transfer protein expression is determined by the growth hormone secretory pattern in the rat. Endocrinology 2003; 144:3914-21. [PMID: 12933665 DOI: 10.1210/en.2003-0518] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Microsomal triglyceride transfer protein (MTP) is essential and rate limiting for the assembly and secretion of apoB-containing lipoproteins. The aim of this study was to investigate whether gender and GH influence hepatic MTP expression. We used intact, gonadectomized, or hypophysectomized (Hx) adult Sprague Dawley rats. Gonadal steroids and insulin were given as a daily sc injection for 7 d. GH was given for 7 d either as a continuous infusion or as two daily injections (2 x GH) to mimic the feminine and masculine GH secretory patterns, respectively. MTP mRNA and MTP and protein disulfide isomerase protein expression was measured. MTP mRNA, and protein expression was higher in females than in males. Gonadectomy abolished the sex difference, and treatment with gonadal steroids restored the sex difference in MTP mRNA levels. MTP mRNA expression was not influenced in either sex by 2 wk of cholesterol (1% wt/wt) feeding. Hx decreased MTP mRNA in females but not in males. A continuous GH infusion increased MTP mRNA and protein expression in intact males but not in females. A continuous GH infusion to Hx females normalized MTP mRNA and protein expression, but 2 x GH had no effect. Also, insulin treatment had no effect. In summary, MTP expression is sex differentiated and regulated by the sexually dimorphic secretory pattern of GH at the level of mRNA. These results are important for the understanding of the effects of gender and GH in the regulation of very low-density lipoprotein assembly and secretion.
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Affiliation(s)
- Caroline Améen
- Department of Physiology and Pharmacology and Wallenberg Laboratory for Cardiovascular Research, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
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13
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Patterson AP, Chen Z, Rubin DC, Moucadel V, Iovanna JL, Brewer HB, Eggerman TL. Developmental regulation of apolipoprotein B mRNA editing is an autonomous function of small intestine involving homeobox gene Cdx1. J Biol Chem 2003; 278:7600-6. [PMID: 12493769 DOI: 10.1074/jbc.m201601200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Apolipoprotein B mRNA editing is developmentally regulated in the human and rodent small intestine, changing from <1% at day 14 to approximately 90% by day 20 in the rat fetus. This regulation is coincident with the developmental formation of the crypt-to-villus axis functional unit, a continuous and rapidly renewing system involving cell generation, migration, and differentiation. Utilizing small intestine isografts implanted into the subcutaneous tissue of adult recipients, apolipoprotein B mRNA editing was developmentally up-regulated, parallel to that seen with an intact control. In contrast, apoB mRNA expression remains nearly constant in the isograft, unlike the normal intact small intestine. Immunohistochemical analyses demonstrated that apoB-48 protein existed predominantly in well differentiated enterocytes along the villus surface whereas apoB-100 was in the lamina propria and crypts. ApoB mRNA editing levels were very low in the crypt-like rat intestinal cell line, IEC-6 ( approximately 0.3%), but very high in well differentiated enterocytes ( approximately 91.5%). The expression of homeobox gene Cdx1 increased 18-fold in small intestine in vivo during the same time course when apoB mRNA editing increased from approximately 2 to approximately 90%. The overexpression of Cdx1 in IEC-6 cells increased apoB mRNA editing over 10-fold compared with the vector control. This increase was associated with a significant increase of activating factor ACF, a component of the apoB mRNA editing complex. Taken together, these data suggest that the developmental regulation of apoB mRNA editing is an autonomous cytodifferentiation function of small intestine for which homeobox gene Cdx1 may play an important role.
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Affiliation(s)
- Amy P Patterson
- NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
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14
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Persson AI, Aberg ND, Oscarsson J, Isaksson OGP, Rönnbäck L, Frick F, Sonesson C, Eriksson PS. Expression of delta opioid receptor mRNA and protein in the rat cerebral cortex and cerebellum is decreased by growth hormone. J Neurosci Res 2003; 71:496-503. [PMID: 12548705 DOI: 10.1002/jnr.10515] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Hormones released from the pituitary have been shown to regulate the expression of different proteins in the central nervous system. We wanted to examine whether peripheral administration of bovine growth hormone (bGH) regulates the expression of delta-opioid receptor (DOR) in the cerebral cortex and cerebellum. Expression of the DOR protein was quantified using Western blot densitometry. DOR mRNA was quantified with a solution hybridization RNase protection assay. Hypophysectomized (Hx) and untreated normal female rats were included in the study. All Hx rats were hormonally treated with cortisol (400 microg/kg/day) and L-thyroxine (10 microg/kg/day) for 19 days. Hypophysectomy resulted in a threefold increase in cerebral cortex and a twofold increase in cerebellum of the DOR protein compared with normal rats. One subgroup of Hx rats received bGH (1 mg/kg body weight) as a daily subcutaneous injection for 19 days. This treatment normalized the levels of DOR protein in the cerebral cortex and cerebellum. Immunohistochemical experiments showed that GH decreased DOR expression especially in layers II-VI in cerebral cortex and in stratum moleculare in cerebellum. Quantification of DOR mRNA by solution hybridization RNase protection assay corresponded to the DOR protein measurements. We conclude that the expression of DORs in cerebral cortex and cerebellum is regulated by GH.
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Affiliation(s)
- Anders I Persson
- Institute of Clinical Neuroscience, Göteborg University, Göteborg, Sweden
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15
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Jalouli M, Carlsson L, Améen C, Lindén D, Ljungberg A, Michalik L, Edén S, Wahli W, Oscarsson J. Sex difference in hepatic peroxisome proliferator-activated receptor alpha expression: influence of pituitary and gonadal hormones. Endocrinology 2003; 144:101-9. [PMID: 12488335 DOI: 10.1210/en.2002-220630] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Peroxisome proliferator-activated receptor (PPAR) alpha is a nuclear receptor that is mainly expressed in tissues with a high degree of fatty acid oxidation such as liver, heart, and skeletal muscle. Unsaturated fatty acids, their derivatives, and fibrates activate PPARalpha. Male rats are more responsive to fibrates than female rats. We therefore wanted to investigate if there is a sex difference in PPARalpha expression. Male rats had higher levels of hepatic PPARalpha mRNA and protein than female rats. Fasting increased hepatic PPARalpha mRNA levels to a similar degree in both sexes. Gonadectomy of male rats decreased PPARalpha mRNA expression to similar levels as in intact and gonadectomized female rats. Hypophysectomy increased hepatic PPARalpha mRNA and protein levels. The increase in PPARalpha mRNA after hypophysectomy was more pronounced in females than in males. GH treatment decreased PPARalpha mRNA and protein levels, but the sex-differentiated secretory pattern of GH does not determine the sex-differentiated expression of PPARalpha. The expression of PPARalpha mRNA in heart or soleus muscle was not influenced by gender, gonadectomy, hypophysectomy, or GH treatment. In summary, pituitary-dependent hormones specifically regulate hepatic PPARalpha expression. Sex hormones regulate the sex difference in hepatic PPARalpha levels, but not via the sexually dimorphic GH secretory pattern.
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Affiliation(s)
- Masoumeh Jalouli
- Department of Physiology and Pharmacology, Göteborg University, Göteborg S-405 30, Sweden
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16
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Frick F, Lindén D, Améen C, Edén S, Mode A, Oscarsson J. Interaction between growth hormone and insulin in the regulation of lipoprotein metabolism in the rat. Am J Physiol Endocrinol Metab 2002; 283:E1023-31. [PMID: 12376331 DOI: 10.1152/ajpendo.00260.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The importance of insulin for the in vivo effects of growth hormone (GH) on lipid and lipoprotein metabolism was investigated by examining the effects of GH treatment of hypophysectomized (Hx) female rats with and without concomitant insulin treatment. Hypophysectomy-induced changes of HDL, apolipoprotein (apo)E, LDL, and apoB levels were normalized by GH treatment but not affected by insulin treatment. The hepatic triglyceride secretion rate was lower in Hx rats than in normal rats and increased by GH treatment. This effect of GH was blunted by insulin treatment. The triglyceride content in the liver changed in parallel with the changes in triglyceride secretion rate, indicating that the effect of the hormones on triglyceride secretion was dependent on changed availability of triglycerides for VLDL assembly. GH and insulin independently increased editing of apoB mRNA, but the effects were not additive. The expression of fatty-acid synthase (FAS), stearoyl-CoA desaturase-1 (SCD-1), and sterol regulatory element-binding protein-1c (SREBP-1c) was increased by GH treatment. Insulin and GH had no additive effects on these genes; instead, insulin blunted the effect of GH on SREBP-1c mRNA. In contrast to the liver, adipose tissue expression of SREBP-1c, FAS, or SCD-1 mRNA was not influenced by GH. In conclusion, the increased hepatic expression of lipogenic enzymes after GH treatment may be explained by increased expression of SREBP-1c. Insulin does not mediate the effects of GH but inhibits the stimulatory effect of GH on hepatic SREBP-1c expression and triglyceride secretion rate.
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Affiliation(s)
- Fredrik Frick
- Department of Physiology, Göteborg University, S-405 30 Göteborg, Sweden
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17
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Frick F, Bohlooly-Y M, Lindén D, Olsson B, Törnell J, Edén S, Oscarsson J. Long-term growth hormone excess induces marked alterations in lipoprotein metabolism in mice. Am J Physiol Endocrinol Metab 2001; 281:E1230-9. [PMID: 11701438 DOI: 10.1152/ajpendo.2001.281.6.e1230] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of long-term chronic growth hormone (GH) excess on lipid and lipoprotein metabolism were investigated in 8-mo-old bovine GH (bGH)-transgenic mice. Total body weight, serum cholesterol, insulin-like growth factor-I, and insulin levels were higher, whereas serum levels of glucose, free fatty acids, and triglycerides were lower in transgenic mice. Very low-density lipoprotein (VLDL) cholesterol levels were lower, and low-density lipoprotein (LDL) cholesterol levels were higher, in transgenic mice irrespective of gender, whereas only transgenic male mice had higher high-density lipoprotein cholesterol levels. Total serum apolipoprotein B (apoB) levels were not affected, but the amount of apoB in the LDL fraction was higher in transgenic mice. Hepatic LDL receptor expression was unchanged, whereas apoB mRNA editing and hepatic triglyceride secretion rate were reduced in bGH-transgenic male mice. Both lipoprotein lipase activity in adipose and heart tissue and beta-adrenergic-stimulated lipolysis were increased in transgenic male mice. The relative weight of adipose tissue was lower in transgenic mice, whereas hepatic triglyceride content was unchanged. Fat feeding of the mice equalized serum triglycerides and free fatty acids in bGH-transgenic and control mice. In summary, long-term GH excess is associated with marked alterations in lipid and lipoprotein metabolism, indicating decreased production and increased degradation of VLDL and preferential flux of fatty acids to muscle tissues.
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Affiliation(s)
- F Frick
- Department of Physiology, Göteborg University, 405 30 Goteborg, Sweden.
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18
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Lindén D, Alsterholm M, Wennbo H, Oscarsson J. PPARα deficiency increases secretion and serum levels of apolipoprotein B-containing lipoproteins. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31509-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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19
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Carlsson L, Lindén D, Jalouli M, Oscarsson J. Effects of fatty acids and growth hormone on liver fatty acid binding protein and PPARalpha in rat liver. Am J Physiol Endocrinol Metab 2001; 281:E772-81. [PMID: 11551854 DOI: 10.1152/ajpendo.2001.281.4.e772] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aim of this study was to investigate the interaction between long-chain fatty acids (LCFA) and growth hormone (GH) in the regulation of liver fatty acid binding protein (LFABP) and peroxisome proliferator-activated receptor-alpha (PPARalpha). Cultured rat hepatocytes were given oleic acid (OA; 500 microM) and GH (100 ng/ml) for 3 days. LFABP mRNA increased 3.6-fold by GH and 5.7-fold by OA, and combined incubation with GH and OA increased LFABP mRNA 17.6-fold. PPARalpha mRNA was decreased 50% by GH, but OA had no effect. Hypophysectomized (Hx) female rats were treated with L-thyroxine, cortisol, GH, and dietary fat for 7 days. PPARalpha mRNA levels were three- to fourfold higher in Hx than in normal female rats. GH decreased PPARalpha mRNA 50% in Hx rats. Dietary triglycerides (10% corn oil) increased LFABP mRNA and cytosolic LFABP about twofold but had no effect on PPARalpha mRNA in Hx rats. GH and dietary triglycerides had an additive effect on LFABP expression. Dietary triglycerides increased mitochondrial hydroxymethylglutaryl-CoA synthase mRNA only in the presence of GH. The diet increased serum triglycerides in Hx rats, and GH treatment prevented this increase. Addition of cholesterol to the diet did not influence LFABP levels but mitigated increased hepatic triglyceride content. In summary, these studies show that GH regulates LFABP expression independently of PPARalpha. Moreover, GH has different effects on PPARalpha-responsive genes and does not counteract the effect of LCFA on the expression of these gene products.
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MESH Headings
- Animals
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Cells, Cultured
- Cholesterol, Dietary/pharmacology
- Corn Oil/pharmacology
- Cytosol/metabolism
- DNA-Binding Proteins/genetics
- Dietary Fats/pharmacology
- Fatty Acid-Binding Protein 7
- Fatty Acid-Binding Proteins
- Fatty Acids/metabolism
- Fatty Acids, Nonesterified/pharmacology
- Female
- Gene Expression Regulation/drug effects
- Gene Expression Regulation/physiology
- Growth Hormone/pharmacology
- Hepatocytes/drug effects
- Hepatocytes/metabolism
- Hydrocortisone/pharmacology
- Hydroxymethylglutaryl-CoA Synthase/genetics
- Hypophysectomy
- Liver/drug effects
- Liver/metabolism
- Mitochondria, Liver/enzymology
- Neoplasm Proteins
- Nerve Tissue Proteins
- Oleic Acid/pharmacology
- RNA, Messenger/genetics
- Rats
- Rats, Sprague-Dawley
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Reference Values
- Thyroxine/pharmacology
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Transcription, Genetic/drug effects
- Transcription, Genetic/physiology
- Triglycerides/blood
- Triglycerides/pharmacology
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Affiliation(s)
- L Carlsson
- Department of Physiology, Göteborg University, S-405 30 Goteborg, Sweden
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20
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Chen Z, Eggerman TL, Patterson AP. Phosphorylation is a regulatory mechanism in apolipoprotein B mRNA editing. Biochem J 2001; 357:661-72. [PMID: 11463337 PMCID: PMC1221996 DOI: 10.1042/0264-6021:3570661] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The editing of apolipoprotein B (apoB) mRNA is under tissue-specific, developmental and metabolic regulation. We found that multiple protein kinase inhibitors or activators increased apoB mRNA editing up to 2.5-fold in Caco-2 cells and 3-8-fold in McA7777 and FAO rat cells respectively. The phosphorylation-agent-induced modulation is independent of the apolipoprotein B editing catalytic subunit 1 (APOBEC-1) and of apoB mRNA expression levels, indicating the involvement of a protein modification, such as phosphorylation, regulating the cellular editing of apoB mRNA. Transient expression of protein kinase C-θ more than doubled apoB mRNA editing in FAO cells. Chronic exposure to ethanol, a treatment known to increase the expression of protein kinases and to change protein phosphorylation status, increased apoB mRNA editing in FAO cells up to 2.5-fold without increasing the mRNA abundance of APOBEC-1. The elimination of potential phosphorylation sites 47 and 72 of human APOBEC-1 decreased its activity to approx. one-eighth of control levels by a Ser(47)-->Ala mutation, but more than doubled the activity by a Ser(72)-->Ala mutation. The activity modulation was reversed by a Ser-->Asp mutation at sites 47 and 72, which introduced a phosphorylation-like carbonic acid group. Both human APOBEC-1 dephosphorylated by alkaline phosphase and the Ser(47,72)-to-alanine double mutant protein demonstrated a shifted isoelectric focusing pattern compared with the wild type, indicating phosphorylation at these sites. Taken together, these results suggest that phosphorylation might be an important mechanism in the regulation of apoB mRNA editing.
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Affiliation(s)
- Z Chen
- National Heart, Lung and Blood Institute, National Institutes of Health, 6000 Executive Boulevard, Suite 302, Bethesda, MD 20892, USA
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21
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Oscarsson J, Gardmo C, Edén S, Mode A. Pulsatile growth hormone secretion decreases S-adenosylmethionine synthetase in rat liver. Am J Physiol Endocrinol Metab 2001; 280:E280-6. [PMID: 11158931 DOI: 10.1152/ajpendo.2001.280.2.e280] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
S-adenosylmethionine synthetase (AdoMet synthetase) is responsible for the synthesis of the major methyl donor S-adenosylmethionine. The AdoMet synthetase gene was identified by subtractive suppressive hybridization as being expressed at higher levels in the liver of rats continuously exposed to growth hormone (GH) than in rats intermittently exposed to the hormone. Further studies on the regulation of AdoMet synthetase showed that the activity and mRNA levels were higher in female than in male rats. Hypophysectomy increased AdoMet synthetase mRNA in both male and female rats. Combined thyroxine and cortisol treatment of hypophysectomized rats had no effect on AdoMet synthetase mRNA levels. Two daily injections of GH for 7 days, mimicking the male secretory pattern of GH, decreased AdoMet synthetase activity and mRNA levels. A continuous infusion of GH, mimicking the female secretory pattern of GH, had small or no effects on AdoMet synthetase activity and decreased the mRNA levels to a lesser degree than two daily injections. It is concluded that the lower AdoMet synthetase activity in male rats is due to an inhibitory effect of the male characteristic pulsatile secretory pattern of GH on AdoMet synthetase mRNA expression.
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Affiliation(s)
- J Oscarsson
- Department of Physiology, Endocrinology Unit, Göteborg University, Box 434, S-405 30 Göteborg, Sweden.
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22
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Lindén D, Sjöberg A, Asp L, Carlsson L, Oscarsson J. Direct effects of growth hormone on production and secretion of apolipoprotein B from rat hepatocytes. Am J Physiol Endocrinol Metab 2000; 279:E1335-46. [PMID: 11093922 DOI: 10.1152/ajpendo.2000.279.6.e1335] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aim of this study was to investigate the direct effects of growth hormone (GH) on production and secretion of apolipoprotein B (apoB)-containing lipoproteins from hepatocytes. Bovine GH (5-500 ng/ml) was given for 1 or 3 days to rat hepatocytes cultured on laminin-rich matrigel in serum-free medium. The effects of GH were compared with those of 3 nM insulin and 500 microM oleic acid. GH increased the editing of apoB mRNA, and the proportion of newly synthesized apoB-48 (of total apoB) in the cells and secreted into the medium changed in parallel. GH increased total secretion of apoB-48 (+30%) and apoB-48 in very low density lipoproteins (VLDL) more than twofold. Total apoB-100 secretion decreased 63%, but apoB-100-VLDL secretion was unaffected by GH. Pulse-chase studies indicated that GH increased intracellular early degradation of apoB-100 but not apoB-48. GH had no effect on apoB mRNA or LDL receptor mRNA levels. The triglyceride synthesis, the mass of triglycerides in the cells, and the VLDL fraction of the medium increased after GH incubation. Three days of insulin incubation had effects similar to those of GH. Combined incubation with oleic acid and GH had additive effects on apoB mRNA editing and apoB-48-VLDL secretion. In summary, GH has direct effects on production and secretion of apoB-containing lipoproteins, which may add to the effects of hyperinsulinemia and increased flux of fatty acids to the liver during GH treatment in vivo.
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Affiliation(s)
- D Lindén
- Department of Physiology, Goteborg University, S-405 30 Goteborg, Sweden
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23
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Chen Z, Eggerman TL, Potosky D, Arborati M, Patterson AP. Calcium increases apolipoprotein B mRNA editing. Biochem Biophys Res Commun 2000; 277:221-7. [PMID: 11027667 DOI: 10.1006/bbrc.2000.3668] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ApoB-100 and apoB-48 are major components of chylomicrons, very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL). The two proteins are generated from a single apoB mRNA by apoB mRNA editing which induces an in-frame stop codon in apoB mRNA. Apolipoprotein B (apoB) mRNA editing is an important determinant of the proportion of full-length (apoB-100) and truncated (apoB-48) proteins in total apoB metabolism. Calcium is involved in the regulation of secretion and synthesis of VLDL and apoB. In this paper, we demonstrate for the first time that the amount of edited apoB mRNA in the cultured cells Caco-2 and McA7777 is markedly increased by calcium. Increasing extracellular calcium concentration, calcium ionophore (A23187 and ionomycin) treatment, and depleting calcium stores and raising cytoplasmic calcium concentration by thapsigargin increase apoB mRNA editing up to threefold in a dose dependent manner. Calcium has no direct stimulative effect on apoB mRNA editing in an in vitro editing system. The editing increase by extracellular calcium is not related to alterations of APOBEC-1 mRNA expression. These data suggest that calcium is not only involved in the regulation of apolipoprotein metabolism but also apoB mRNA editing.
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Affiliation(s)
- Z Chen
- National Heart, Lung and Blood Institute, Bethesda, Maryland, 20892, USA
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24
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Maldonado Castro GF, Escobar-Morreale HF, Ortega H, Gómez-Coronado D, Balsa Barro JA, Varela C, Lasunción MA. Effects of normalization of GH hypersecretion on lipoprotein(a) and other lipoprotein serum levels in acromegaly. Clin Endocrinol (Oxf) 2000; 53:313-9. [PMID: 10971448 DOI: 10.1046/j.1365-2265.2000.01092.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND & AIMS Lipoprotein(a) has been recognized as an important risk factor for cardiovascular disease. Lipoprotein(a) has been found to be elevated in sera of acromegalic patients, possibly contributing to the increased incidence of coronary heart disease found in these patients. In the present study we sought to determine the effects of GH hormonal status on lipoprotein(a) and other lipid parameters, including lipoprotein lipase (LPL) activity. DESIGN Cross-sectional study. PATIENTS Twenty acromegalic patients, with either active (n = 12) or controlled (n = 8) acromegaly, were studied. Twenty-nine healthy subjects served as control group for serum lipid measurements. MEASUREMENTS Serum GH, IGF-1, IGF binding protein-3 (IGFBP-3) and insulin levels were measured in patients. Insulin resistance was measured by the homeostatic model assessment (HOMA). Plasma total cholesterol, triglycerides, HDL-lipids, apolipoproteins A-I and B, lipoprotein(a) and lipoprotein lipase activity were also measured. RESULTS The highest lipoprotein(a) levels were observed in patients with active acromegaly, followed by patients with controlled acromegaly, whose lipoprotein(a) concentrations were still significantly higher than those of the control group (means +/- SEM: active acromegaly, 0.67+/-0.13 g/l; controlled acromegaly, 0.41+/-0.12 g/l; controls 0.17+/-0.02 g/l; P<0.05). There were no differences in other lipid and lipoprotein values among the groups. In patients, significant correlations were observed between lipoprotein(a) and basal GH levels (r = 0.56, P<0.02), mean GH levels (r = 0.48, P<0.05) and with insulin resistance estimated by HOMA (r = 0.62, P<0.01). No correlations were found between lipoprotein(a) and IGF-1 or IGFBP-3 levels. CONCLUSIONS Our present results demonstrate that both active acromegalic patients and those with controlled disease have elevated serum lipoprotein(a) concentrations. The findings might suggest that the present biochemical criteria for cure of acromegaly are not strict enough to result in the normalization of all the undesirable metabolic changes found in this disease, and also that significant cardiovascular risk may persist despite successful treatment of acromegaly.
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25
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Levy E, Beaulieu JF, Delvin E, Seidman E, Yotov W, Basque JR, Ménard D. Human crypt intestinal epithelial cells are capable of lipid production, apolipoprotein synthesis, and lipoprotein assembly. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32069-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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26
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Svensson J, Jansson JO, Ottosson M, Johannsson G, Taskinen MR, Wiklund O, Bengtsson BA. Treatment of obese subjects with the oral growth hormone secretagogue MK-677 affects serum concentrations of several lipoproteins, but not lipoprotein(a). J Clin Endocrinol Metab 1999; 84:2028-33. [PMID: 10372705 DOI: 10.1210/jcem.84.6.5799] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Obesity is associated with blunted GH secretion and an unfavorable lipoprotein pattern. The objective of this study was to investigate the effects of treatment with the oral GH secretagogue MK-677 on lipoproteins in otherwise healthy obese males. The study was randomized, double blind, and parallel. Twenty-four obese males, aged 18-50 yr, with body mass index greater than 30 kg/m2 and waist/hip ratio above 0.95 were treated with 25 mg MK-677 (n = 12) or placebo (n = 12) daily for 8 weeks. MK-677 treatment did not significantly change serum lipoprotein(a) [Lp(a)] levels. Serum apolipoprotein A-I and E (apoA-I and apoE) were increased at 2 weeks (P < 0.001 and P < 0.01 vs. placebo, respectively), but were not changed at study end. Serum total cholesterol and low density lipoprotein (LDL) cholesterol (LDL-C) levels were not significantly changed by MK-677 treatment. Serum high density lipoprotein (HDL) cholesterol (HDL-C) was increased at 2 weeks of MK-677 treatment (P < 0.01 vs. placebo), but not at 8 weeks. The LDL-C/HDL-C ratio was reduced after 8 weeks of MK-677 treatment (P < 0.05 vs. placebo). Mean LDL particle diameter was decreased at 2 weeks (P < 0.05 vs. placebo), but was unchanged compared with baseline values at 8 weeks (P = NS vs. placebo). The level of serum triglycerides was increased at 2 (P < 0.05 vs. placebo), but not at 8, weeks. Lipoprotein lipase activity in abdominal and gluteal sc adipose tissue was not affected by active treatment. In conclusion, treatment with the oral GH secretagogue MK-677 affected circulating lipoproteins. The effects on serum apoA-1, apoE, triglycerides, and mean LDL particle diameter were transient. At study end, the LDL-C/HDL-C ratio was decreased. MK-677 treatment did not significantly affect serum Lp(a) concentrations at the present dose and administration protocol.
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Affiliation(s)
- J Svensson
- Research Center for Endocrinology and Metabolism, Sahlgrenska University Hospital, Göteborg, Sweden
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27
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Parini P, Angelin B, Rudling M. Cholesterol and lipoprotein metabolism in aging: reversal of hypercholesterolemia by growth hormone treatment in old rats. Arterioscler Thromb Vasc Biol 1999; 19:832-9. [PMID: 10195906 DOI: 10.1161/01.atv.19.4.832] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Plasma cholesterol levels increase with age, as does the incidence of coronary heart disease. The mechanisms responsible for the age-related hypercholesterolemia are not well understood. An interesting hypothesis suggests that the relative deficiency in growth hormone (GH), which occurs with aging, contributes to the development of the age-related hypercholesterolemia, because GH has beneficial effects on cholesterol metabolism. In the present work, we tested this hypothesis by the administration of GH to normal rats of varying ages. Plasma lipids and hepatic cholesterol metabolism were characterized in 2-, 12-, and 18-month-old male Sprague-Dawley rats. In 2-month-old rats, GH specifically stimulated the hepatic low density lipoprotein (LDL) receptor expression in a dose-dependent way, both at the protein level and at the mRNA level. Concomitantly, plasma cholesterol increased by approximately 30% within the large high density lipoprotein and LDL fractions. In 12-month-old animals, cholesterol 7alpha-hydroxylase (C7alphaOH) activity was reduced, whereas hepatic LDL receptors and plasma total cholesterol were unchanged. GH treatment (1 mg. kg-1. d-1) normalized the activity of C7alphaOH and had effects on plasma cholesterol and LDL receptors similar to those seen in 2-month-old animals. In 18-month-old rats, plasma cholesterol was increased 2-fold, whereas hepatic LDL receptor expression and C7alphaOH activity were similar to those of the 12-month-old animals. Infusion of GH to 18-month-old rats had similar effects on hepatic C7alphaOH and LDL receptors as seen in 12-month-old rats. However, GH treatment strongly reduced the hypercholesterolemia in 18-month-old animals. We conclude that the age-dependent increase of plasma cholesterol in rats can be reversed by the administration of GH, presumably through the pleiotropic effects of this hormone on lipoprotein metabolism.
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Affiliation(s)
- P Parini
- Metabolism Unit, Center for Metabolism and Endocrinology, Department of Medicine, Karolinska Institute at Huddinge University Hospital, Huddinge, Sweden
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Rudling M, Parini P, Angelin B. Effects of growth hormone on hepatic cholesterol metabolism. Lessons from studies in rats and humans. Growth Horm IGF Res 1999; 9 Suppl A:1-7. [PMID: 10429873 DOI: 10.1016/s1096-6374(99)80002-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- M Rudling
- Department of Medicine, Karolinska Institute, Huddinge University Hospital, Sweden.
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29
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Greeve J, Axelos D, Welker S, Schipper M, Greten H. Distinct promoters induce APOBEC-1 expression in rat liver and intestine. Arterioscler Thromb Vasc Biol 1998; 18:1079-92. [PMID: 9672068 DOI: 10.1161/01.atv.18.7.1079] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The expression of apolipoprotein (apo) B can be modulated by mRNA editing, a unique posttranscriptional base change in the apo B mRNA. Apo B-48, the translation product of edited apo B mRNA, is not a precursor of the atherogenic low density lipoproteins and lipoprotein(a). In humans and various other mammals, the apo B mRNA is edited in the intestine but not in the liver, which exclusively secretes apo B-100-containing lipoproteins as precursors for low density lipoprotein formation. In species such as the rat, mouse, dog, and horse, apo B mRNA is also edited in the liver, resulting in low plasma levels of low density lipoprotein. Editing of the apo B mRNA is mediated by the apo B mRNA-editing enzyme complex, of which the catalytic subunit APOBEC-1 is not expressed in the liver of species without hepatic editing. To understand the molecular basis for liver-specific expression of APOBEC-1 and the editing of hepatic apo B mRNA, the expression pattern and genomic organization of the rat APOBEC-1 gene have been characterized. The rat APOBEC-1 gene contains 6 exons and 2 promoters with distinct activities. The expression of APOBEC-1 in the rat liver is the result of a promoter located upstream, with tissue-specific exon use and alternate splicing within the 5'-untranslated region of APOBEC-1 mRNA encoded by exon 2. In addition to the liver, this promoter also induces APOBEC-1 expression in the spleen, lung, kidney, heart, and skeletal muscle. The promoter located downstream belongs to a new class of TATA-less promoters and is responsible for the abundant expression of APOBEC-1 in the intestine. Mapping of the transcriptional start sites and deletion analysis of the promoter regions by using luciferase as the reporter gene have defined the regulatory elements of both promoters. The downstream, intestine-specific promoter contains a negative regulatory element between -1100 and -500, which appears to restrict its activity to the intestine. The upstream, liver-specific promoter of the rat APOBEC-1 gene induces APOBEC-1 expression and editing of apo B mRNA in human hepatoma HuH-7 and Hep G2 cells. Understanding the molecular basis for the liver-specific expression of APOBEC-1 in the rat promises new strategies to induce APOBEC-1 expression in the human liver for the reduction of atherogenic lipoprotein levels by hepatic apo B mRNA editing.
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Affiliation(s)
- J Greeve
- Medizinische Kernklinik und Poliklinik, Universitäts-Krankenhaus Eppendorf, Hamburg, Germany
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30
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Carlsson L, Nilsson I, Oscarsson J. Hormonal regulation of liver fatty acid-binding protein in vivo and in vitro: effects of growth hormone and insulin. Endocrinology 1998; 139:2699-709. [PMID: 9607775 DOI: 10.1210/endo.139.6.6041] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Liver fatty acid-binding protein (LFABP) is an abundant protein in hepatocytes that binds most of the long chain fatty acids present in the cytosol. It is suggested to be of importance for fatty acid uptake and utilization in the hepatocyte. In the present study, the effects of bovine GH (bGH) and other hormones on the expression of LFABP and its messenger RNA (mRNA) were studied in hypophysectomized rats and in vitro using primary cultures of rat hepatocytes. One injection of bGH increased LFABP mRNA levels about 5-fold after 6 h, but there was no effect of this treatment on LFABP levels. However, 7 days of bGH treatment increased both LFABP mRNA and LFABP protein levels 2- to 5-fold. Female rats had higher levels of LFABP than male rats. Hypophysectomy of female rats, but not that of male rats, decreased LFABP levels markedly. Treatment of hypophysectomized rats with bGH for 7 days as two daily injections or as a continuous infusion increased LFABP levels to a similar degree. This finding indicates that the sex difference in the expression of LFABP is not regulated by the sexually dimorphic secretory pattern of GH. Neither insulin nor insulin-like growth factor I treatment of hypophysectomized rats for 6-7 days had any effect on LFABP mRNA or LFABP levels. In vitro, bGH dose-dependently increased the expression of LFABP mRNA, but only in the presence of insulin. Insulin alone had a marked dose-dependent effect on LFABP mRNA levels and was of importance for maintaining the expression of LFABP mRNA during the culture. Incubation with bGH increased LFABP mRNA levels within 3 h. GH had no effect on LFABP mRNA levels in the presence of actinomycin D, indicating a transcriptional effect of GH. Incubation with glucagon in vitro decreased LFABP mRNA levels markedly, indicating that glucagon, in contrast to GH, has an effect opposite that of insulin on LFABP mRNA expression. It is concluded that GH is an important regulator of LFABP in vivo and in vitro. In contrast to the effect of GH on insulin-like growth factor I mRNA, the presence of insulin was a prerequisite for the effect of GH on LFABP mRNA expression in vitro. The results emphasize the role of GH in the regulation of hepatic fatty acid metabolism.
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Affiliation(s)
- L Carlsson
- Department of Physiology, Göteborg University, Sweden
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31
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Ceda GP, Dall'Aglio E, Magnacavallo A, Vargas N, Fontana V, Maggio M, Valenti G, Lee PD, Hintz RL, Hoffman AR. The insulin-like growth factor axis and plasma lipid levels in the elderly. J Clin Endocrinol Metab 1998; 83:499-502. [PMID: 9467564 DOI: 10.1210/jcem.83.2.4548] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The activity of the hypothalamic-GH-insulin-like growth factor (IGF) network declines with age. It has recently been shown that increased cardiovascular mortality occurs in adults with GH deficiency. As hypercholesterolemia is common in GH-deficient adults, and because there is experimental evidence that GH may play a role in regulating plasma cholesterol, we decided to investigate the activity of the GH-IGF axis in an elderly population by measuring serum IGF-I, IGF-II, and IGF-binding protein-3 (IGFBP-3) levels and to study their relationship with blood lipid levels. One hundred and thirty-two elderly subjects, 52 men and 80 women, were studied (age range, 60-91 yr). Men had significantly lower levels of IGFBP-3, high density lipoprotein cholesterol (HDL-C) and apoprotein A1 (ApoA1) compared to the women, whereas IGF-I and IGF-II were only slightly lower. Using linear regression analysis, we observed an inverse relationship of age with IGF-I (r = -0.35; P < 0.001), IGF-II (r = 0.40; P < 0.001), IGFBP-3 (r = 0.52; P < 0.001), body mass index, and lipid levels. Univariate regression analysis showed a strong and positive correlation of both IGF-I and IGFBP-3 with HDL-C and ApoA1. Partial correlation analysis, after adjustment for age and body mass index, showed that IGFBP-3 and IGF-II were still significantly and positively related to HDL-C and ApoA1. Furthermore, a strong association was documented among IGF-I, IGF-II, and IGFBP-3. These data demonstrate that even in an elderly population, further aging is accompanied by a progressive decline in circulating IGF-I, IGF-II, and IGFBP-3, suggesting a continuing diminution of the GH-IGF axis throughout aging. Moreover, the strong correlation between HDL-C and an index of GH secretion, such as IGFBP-3, suggests that GH might play an important role in lipid metabolism in healthy elderly subjects.
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Affiliation(s)
- G P Ceda
- Cattedra di Geriatria, Università di Parma, Italy
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32
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Rudling M, Parini P, Angelin B. Growth hormone and bile acid synthesis. Key role for the activity of hepatic microsomal cholesterol 7alpha-hydroxylase in the rat. J Clin Invest 1997; 99:2239-45. [PMID: 9151797 PMCID: PMC508055 DOI: 10.1172/jci119398] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Growth hormone (GH) has an important role in the regulation of hepatic LDL receptor expression and plasma lipoprotein levels. This investigation was undertaken to characterize the effects of GH on hepatic cholesterol and bile acid metabolism in the rat. In hypophysectomized (Hx) rats, the activities of the rate-limiting enzymes in cholesterol and bile acid biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) and cholesterol 7alpha-hydroxylase (C7alphaOH), were reduced by 71 and 64%, respectively. HMG CoA reductase mRNA levels were reduced by 37%, whereas C7alphaOH mRNA was increased by 81%. LDL receptor expression was reduced by 18% in Hx rats, without any change in the LDL receptor mRNA levels. Although the normal diurnal variation of C7alphaOH activity was preserved in Hx rats, the activity of C7alphaOH was much reduced both at midday and midnight. Total hepatic cholesterol was increased by 14% in Hx animals whereas microsomal cholesterol was unchanged. The rate of cholesterol esterification was enhanced (by 38%) in liver microsomes from Hx rats. Stepwise hormonal substitution of Hx rats showed that GH, but not thyroid hormone or cortisone, was essential to normalize the enzymatic activity of C7alphaOH. GH also normalized the altered plasma lipoprotein pattern in Hx rats, and increased the fecal output of bile acids. The latter effect was particularly evident when GH was combined with cortisone and thyroid hormone. Also in normal rats, GH stimulated C7alphaOH activity. In conclusion, GH has an essential role to maintain a normal enzymatic activity of C7alphaOH, and this, at least in part, explains the effects of GH on hepatic cholesterol metabolism. GH is also of critical importance to normalize the altered plasma lipoprotein pattern in Hx rats.
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Affiliation(s)
- M Rudling
- Department of Medicine, Karolinska Institute at Huddinge University Hospital, Sweden.
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33
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Lorentz A, Plonné D, Schulze HP, Dargel R. Dexamethasone enhanced by insulin, but not by thyroid hormones stimulates apolipoprotein B mRNA editing in cultured rat hepatocytes depending on the developmental stage. FEBS Lett 1996; 391:57-60. [PMID: 8706930 DOI: 10.1016/0014-5793(96)00706-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The increase of hepatic apolipoprotein B (apoB) mRNA editing during rat development was not affected by hypothyroidism. Furthermore, the addition of 3,3',5'-triiodothyronine (T3) to cultured hepatocytes taken from fetal, neonatal and adult rats had no effect on apoB mRNA editing. In contrast, dexamethasone markedly stimulated apoB mRNA editing in hepatocytes taken from neonates. This effect was enhanced by the addition of insulin. For the first time our data provide evidence that glucocorticoids together with insulin are important for the regulation of apoB mRNA editing during postnatal development, whereas thyroid hormones are not critical for this process.
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Affiliation(s)
- A Lorentz
- Department of Medicine, Friedrich-Schiller University, Jena, Germany
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34
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Innerarity TL, Borén J, Yamanaka S, Olofsson SO. Biosynthesis of apolipoprotein B48-containing lipoproteins. Regulation by novel post-transcriptional mechanisms. J Biol Chem 1996; 271:2353-6. [PMID: 8576187 DOI: 10.1074/jbc.271.5.2353] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Affiliation(s)
- T L Innerarity
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94141-9100, USA
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35
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Mode of growth hormone administration influences triacylglycerol synthesis and assembly of apolipoprotein B-containing lipoproteins in cultured rat hepatocytes. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)37615-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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36
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Rudling M, Olivecrona H, Eggertsen G, Angelin B. Regulation of rat hepatic low density lipoprotein receptors. In vivo stimulation by growth hormone is not mediated by insulin-like growth factor I. J Clin Invest 1996; 97:292-9. [PMID: 8567947 PMCID: PMC507017 DOI: 10.1172/jci118415] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Growth hormone (GH) has an important role in the regulation of hepatic LDL receptor expression and plasma lipoprotein levels. This investigation was undertaken to evaluate if these effects of GH on hepatic LDL receptors are direct or mediated by insulin-like growth factor I (IGF-I). Two models were studied in which substitution with GH is important for the regulation of hepatic LDL receptors: hypophysectomized rats receiving high-dose ethynylestradiol or challenge with dietary cholesterol. The hypophysectomized rats were hormonally substituted by infusion with dexamethasone and L-thyroxine, and either GH or IGF-I. In both models, GH was essential for maintaining normal expression of LDL receptors. In contrast, despite fully normalized plasma levels, IGF-I did not support the expression of hepatic LDL receptors. Analysis of plasma lipoproteins revealed that substitution with GH, but not with IGF-I, reduced LDL and intermediate density lipoproteins. In addition, determination of hepatic mRNA levels for apo B-100 and apo B-48 indicated that GH may be more effective than IGF-I in the promotion of apo B mRNA editing. In conclusion, GH has specific effects on hepatic LDL receptor expression and plasma lipoprotein levels that are not mediated by IGF-I.
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Affiliation(s)
- M Rudling
- Department of Medicine, Novum, Karolinska Institute at Huddinge University Hospital, Sweden
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37
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Wang CN, McLeod RS, Yao Z, Brindley DN. Effects of dexamethasone on the synthesis, degradation, and secretion of apolipoprotein B in cultured rat hepatocytes. Arterioscler Thromb Vasc Biol 1995; 15:1481-91. [PMID: 7670964 DOI: 10.1161/01.atv.15.9.1481] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Oversecretion of apoB and decreased removal of apoB-containing lipoproteins by the liver results in hyperapobetalipoproteinemia, which is a risk factor for atherosclerosis. We investigated how dexamethasone, a synthetic glucocorticoid, affects the synthesis, degradation, and secretion of apoB-100 and apoB-48. Primary rat hepatocytes were incubated with dexamethasone for 16 hours. Incorporation of [35S]methionine into apoB-48 and apoB-100 was increased by 36% and 50%, respectively, with 10 nmol/L dexamethasone, despite a 28% decrease of incorporation into total cell proteins. However, Northern blot analysis revealed that dexamethasone (1 to 1000 nmol/L) did not significantly alter the steady-state concentrations of apoB mRNA, suggesting that the net increase in apoB synthesis may involve increased translational efficiency. The intracellular retention and the rate and efficiency of apoB secretion were determined by pulse-chase experiments in which the hepatocytes were labeled with [35S]methionine for 10 minutes or 1 hour, and the disappearance of labeled apoB from the cells and its accumulation in the medium were monitored. Degradation of labeled apoB-100 after a 3-hour chase in both protocols was decreased from about 50% to 30%, whereas degradation of apoB-48 was decreased from 30% to 10% to 20% by treatment with 10 or 100 nmol/L dexamethasone. Additionally, the half-life of decay (time required for 50% of labeled cell apoB-100 to disappear from the peak of radioactivity following a 10-minute pulse) was increased by treatment with 10 nmol/L dexamethasone from 77 to 112 minutes, and the value for apoB-48 increased from 145 to 250 minutes. Treatment with 100 nmol/L dexamethasone also stimulated secretion of 35S-labeled apoB-100 and apoB-48 by twofold and 1.5-fold, respectively. The increased secretion of apoB-100 and apoB-48 after dexamethasone treatment was confirmed by immunoblot analysis for apoB mass, and the effect was relatively specific since albumin secretion was not significantly changed. We conclude that glucocorticoids promote the secretion of hepatic apoB-containing lipoproteins by increasing the net synthesis of apoB-100 and apoB-48 and by decreasing the intracellular degradation of newly synthesized apoB. An increased action of glucocorticoids coupled with a decreased ability of insulin to suppress these effects in insulin resistance can lead to hyperapobetalipoproteinemia and an increased risk of atherosclerosis.
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Affiliation(s)
- C N Wang
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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38
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Hansen PS, Kassem M, Brixen K, Klausen IC, Mosekilde L, Faergeman O. Effect of short-term treatment with recombinant human growth hormone on lipids and lipoproteins in women and men without growth hormone disturbances. Metabolism 1995; 44:725-9. [PMID: 7783656 DOI: 10.1016/0026-0495(95)90184-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The effect of recombinant human growth hormone (rHGH) on cholesterol, high- and low-density lipoprotein (HDL and LDL) cholesterol, triglycerides (TG), apolipoprotein (apo) B, apo A-I, and lipoprotein(a) [Lp(a)] was studied in 40 postmenopausal women treated with 0.05, 0.1, or 0.2 IU/kg/d rHGH or placebo for 7 days. Cholesterol, LDL cholesterol, and HDL cholesterol decreased in a dose-dependent manner (P = .001, P = .001, and P = .003, respectively), whereas apo B decreased insignificantly (P = .15). Apo A-I decreased significantly only among women treated with rHGH at a dose of 0.1 IU/kg/d (P = .03). When all rHGH-treated women were grouped together, Lp(a) increased (P = .001). We also studied 20 young men treated with either 0.2 IU/kg/d rHGH or placebo. As in women, cholesterol and apo B decreased P = .005 and P = .02, respectively), whereas Lp(a) increased (P = .05). There was no detectable effect of rHGH on TG concentrations in men. As in women, there was no significant effect of 0.2 IU/kg/d rHGH on apo A-I concentrations. All lipid and lipoprotein measures reached pretreatment levels during the first week after treatment was stopped, except Lp(a), which remained elevated 2 weeks after rHGH cessation.
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Affiliation(s)
- P S Hansen
- Department of Internal Medicine and Cardiology A, Aarhus University Hospital, Denmark
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39
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Borén J, Rustaeus S, Olofsson SO. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47328-0] [Citation(s) in RCA: 176] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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40
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Thorngate FE, Raghow R, Wilcox HG, Werner CS, Heimberg M, Elam MB. Insulin promotes the biosynthesis and secretion of apolipoprotein B-48 by altering apolipoprotein B mRNA editing. Proc Natl Acad Sci U S A 1994; 91:5392-6. [PMID: 8202496 PMCID: PMC44001 DOI: 10.1073/pnas.91.12.5392] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Long-term insulin treatment selectively stimulates secretion of the truncated form of apolipoprotein B (apoB), apoB-48, from primary rat hepatocytes in culture. Chronic treatment with insulin at 400 ng/ml causes a 3-fold increase in total apoB secretion, with apoB-48 making up about 75% of that increase. apo-B-48 is the protein product generated by translation of full-length apoB mRNA which has been modified by a posttranscriptional editing mechanism. Editing changes codon 2153 in the middle of the apoB-100 coding region from CAA, coding for glutamine, to UAA, a translation stop signal. We therefore examined the effect of insulin treatment on the ratio of edited to nonedited apoB mRNA in RNA isolated from primary rat hepatocyte cultures. There was a dramatic shift in the ratio of edited versus nonedited forms of apoB mRNA, from about 1:1 in untreated cells to 7:1 in insulin-treated cells. Insulin exerted a dose-dependent effect on apoB secretion and apoB mRNA editing over the range of insulin concentrations studied (0.4-400 ng/ml). In contrast, oleic acid, which also increased apoB (B-48 and B-100) secretion, had no significant effect on the ratio of apoB-48 to apoB-100 particles secreted and no effect on the proportion of edited apoB mRNA. Neither insulin nor oleic acid affects total apoB mRNA levels as assayed by Northern blot analysis. These data strongly suggest that insulin stimulates biosynthesis and secretion of apoB-48 in rat hepatocytes by regulating the proportion of edited apoB mRNA.
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Affiliation(s)
- F E Thorngate
- Department of Pharmacology, University of Tennessee, Memphis 38163
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41
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Borén J, Rustaeus S, Wettesten M, Andersson M, Wiklund A, Olofsson SO. Influence of triacylglycerol biosynthesis rate on the assembly of apoB-100-containing lipoproteins in Hep G2 cells. ARTERIOSCLEROSIS AND THROMBOSIS : A JOURNAL OF VASCULAR BIOLOGY 1993; 13:1743-54. [PMID: 8241094 DOI: 10.1161/01.atv.13.12.1743] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Apolipoprotein B-100 (apoB-100) appears in three forms in the endoplasmic reticulum of Hep G2 cells: (1) tightly bound to the membrane, ie, not extractable by sodium carbonate. This form is glycosylated but protease sensitive when present in intact microsomes, suggesting that it is only partially translocated to the microsomal lumen; (2) extractable by sodium carbonate and present on low-density lipoprotein-very-low-density lipoprotein (LDL-VLDL)-like particles. This form is glycosylated and secreted into the medium; and (3) extractable by sodium carbonate but having a higher density than the LDL-VLDL-like particles. This form, referred to as Fraction I, is glycosylated and protected against proteases when present in intact microsomal vesicles, indicating that it is completely translocated to the luminal side of the microsomal membrane. Fraction I is not secreted into the medium, but it disappears with time from the cell, suggesting that it is degraded. Oleic acid induced a 2.7-fold increase in the rate of the biosynthesis of triacylglycerol but not of phosphatidylcholine in Hep G2 cells. Incubation of the cells with oleic acid had no significant effect on the rate of initiation of the apoB-100-containing lipoproteins, nor did it influence the amount of apoB-100 that was associated with the membrane or the turnover of apoB-100 in the membrane. Instead, it increased the proportion of the nascent apoB polypeptides on initiated lipoproteins that was converted into full-length apoB-100 on LDL-VLDL-like particles, giving rise to an increased amount of these particles in the lumen of the secretory pathway. Pulse-chase experiments showed that incubation with oleic acid gave rise to an increased formation of LDL-VLDL-like particles on behalf of the formation of Fraction I. This effect of oleic acid could partially explain the protective effect of the fatty acid on apoB-100, preventing it from undergoing posttranslational degradation.
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Affiliation(s)
- J Borén
- Department of Medical Biochemistry, University of Göteborg, Sweden
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42
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Rudling M, Angelin B. Loss of resistance to dietary cholesterol in the rat after hypophysectomy: importance of the presence of growth hormone for hepatic low density lipoprotein-receptor expression. Proc Natl Acad Sci U S A 1993; 90:8851-5. [PMID: 8415619 PMCID: PMC47458 DOI: 10.1073/pnas.90.19.8851] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
This investigation was undertaken to determine the role of pituitary function and, in particular, the possible influence of growth hormone (GH) on hepatic low density lipoprotein (LDL)-receptor expression in response to dietary cholesterol. Feeding normal rats with 2% cholesterol for 5 or 6 days did not alter LDL-receptor numbers, LDL-receptor mRNA levels, or plasma cholesterol, although hepatic cholesterol increased 5-fold. When hypophysectomized rats received the same diet, the LDL-receptor number and its mRNA levels were reduced by 75%, plasma cholesterol increased 6-fold, and hepatic cholesterol increased 12-fold. Stepwise hormonal substitution of cholesterol-fed, hypophysectomized rats revealed that substitution with GH was important to restore hepatic LDL-receptor number and mRNA levels. The presence of GH was also important to reduce the hypercholesterolemia in cholesterol-fed hypophysectomized rats. We conclude that the presence of GH is important for hepatic LDL-receptor expression, both at the protein and the mRNA level. The resistance to suppression of rat hepatic LDL receptors by dietary cholesterol depends, at least in part, on the presence of GH.
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Affiliation(s)
- M Rudling
- Department of Medicine, Karolinska Institute, Huddinge University Hospital, Sweden
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43
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Greeve J, Altkemper I, Dieterich JH, Greten H, Windler E. Apolipoprotein B mRNA editing in 12 different mammalian species: hepatic expression is reflected in low concentrations of apoB-containing plasma lipoproteins. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)36966-2] [Citation(s) in RCA: 195] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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