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Bond LM, Ibrahim A, Lai ZW, Walzem RL, Bronson RT, Ilkayeva OR, Walther TC, Farese RV. Fitm2 is required for ER homeostasis and normal function of murine liver. J Biol Chem 2023; 299:103022. [PMID: 36805337 PMCID: PMC10027564 DOI: 10.1016/j.jbc.2023.103022] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 01/25/2023] [Accepted: 01/30/2023] [Indexed: 02/17/2023] Open
Abstract
The endoplasmic reticulum (ER)-resident protein fat storage-inducing transmembrane protein 2 (FIT2) catalyzes acyl-CoA cleavage in vitro and is required for ER homeostasis and normal lipid storage in cells. The gene encoding FIT2 is essential for the viability of mice and worms. Whether FIT2 acts as an acyl-CoA diphosphatase in vivo and how this activity affects the liver, where the protein was discovered, are unknown. Here, we report that hepatocyte-specific Fitm2 knockout (FIT2-LKO) mice fed a chow diet exhibited elevated acyl-CoA levels, ER stress, and signs of liver injury. These mice also had more triglycerides in their livers than control littermates due, in part, to impaired secretion of triglyceride-rich lipoproteins and reduced capacity for fatty acid oxidation. We found that challenging FIT2-LKO mice with a high-fat diet worsened hepatic ER stress and liver injury but unexpectedly reversed the steatosis phenotype, similar to what is observed in FIT2-deficient cells loaded with fatty acids. Our findings support the model that FIT2 acts as an acyl-CoA diphosphatase in vivo and is crucial for normal hepatocyte function and ER homeostasis in the murine liver.
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Affiliation(s)
- Laura M Bond
- Department of Molecular Metabolism, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA; Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA
| | - Ayon Ibrahim
- Department of Molecular Metabolism, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA; Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA
| | - Zon W Lai
- Department of Molecular Metabolism, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA; Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA; Harvard T.H. Chan Advanced Multi-omics Platform, Department of Molecular Metabolism, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, USA
| | - Rosemary L Walzem
- Department of Poultry Science and Graduate Faculty of Nutrition, Kleberg Animal & Food Science Center, Texas A&M University, College Station, Texas, USA
| | - Roderick T Bronson
- Rodent Histopathology Core, Harvard Medical School, Boston, Massachusetts, USA
| | - Olga R Ilkayeva
- Division of Endocrinology, Metabolism, and Nutrition, Department of Medicine, Duke Molecular Physiology Institute, Sarah W. Stedman Nutrition and Metabolism Center, Duke University School of Medicine, Durham, North Carolina, USA
| | - Tobias C Walther
- Department of Molecular Metabolism, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA; Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA; Harvard T.H. Chan Advanced Multi-omics Platform, Department of Molecular Metabolism, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, USA; Cell Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, New York, USA; Broad Institute of Harvard and MIT, Cambridge, Massachusetts, USA; Howard Hughes Medical Institute, Boston, Massachusetts, USA.
| | - Robert V Farese
- Department of Molecular Metabolism, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA; Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA; Cell Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, New York, USA; Broad Institute of Harvard and MIT, Cambridge, Massachusetts, USA.
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Oh M, Ha DI, Son C, Kang JG, Hwang H, Moon SB, Kim M, Nam J, Kim JS, Song SY, Kim YS, Park S, Yoo JS, Ko JH, Park K. Defect in cytosolic Neu2 sialidase abrogates lipid metabolism and impairs muscle function in vivo. Sci Rep 2022; 12:3216. [PMID: 35217678 PMCID: PMC8881595 DOI: 10.1038/s41598-022-07033-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 01/27/2022] [Indexed: 12/25/2022] Open
Abstract
Sialic acid (SA) is present in glycoconjugates and important in cell–cell recognition, cell adhesion, and cell growth and as a receptor. Among the four mammalian sialidases, cytosolic NEU2 has a pivotal role in muscle and neuronal differentiation in vitro. However, its biological functions in vivo remain unclear due to its very low expression in humans. However, the presence of cytoplasmic glycoproteins, gangliosides, and lectins involved in cellular metabolism and glycan recognition has suggested the functional importance of cytosolic Neu2 sialidases. We generated a Neu2 knockout mouse model via CRISPR/Cas9-mediated genome engineering and analyzed the offspring littermates at different ages to investigate the in vivo function of cytosolic Neu2 sialidase. Surprisingly, knocking out the Neu2 gene in vivo abrogated overall lipid metabolism, impairing motor function and leading to diabetes. Consistent with these results, Neu2 knockout led to alterations in sialylated glycoproteins involved in lipid metabolism and muscle function, as shown by glycoproteomics analysis.
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Affiliation(s)
- Mijung Oh
- Medical Research Institute, Sungkyunkwan University School of Medicine, Suwon, 16419, Republic of Korea
| | - Dae-In Ha
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea
| | - Chaeyeon Son
- Medical Research Institute, Sungkyunkwan University School of Medicine, Suwon, 16419, Republic of Korea
| | - Jeong Gu Kang
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea
| | - Heeyoun Hwang
- Research Center for Bioconvergence Analysis, Korea Basic Science Institute, Cheongju, 28119, Republic of Korea
| | - Su Bin Moon
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea
| | - Minjeong Kim
- Department of Pathology and Translational Genomics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, 06351, Republic of Korea
| | - Jihae Nam
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea.,Department of Bio-Molecular Science, KRIBB School of Bioscience, Korea University of Science and Technology (UST), Daejeon, Republic of Korea
| | - Jung Soo Kim
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea
| | - Sang Yong Song
- Department of Pathology and Translational Genomics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, 06351, Republic of Korea
| | - Yong-Sam Kim
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea
| | - Sangwoo Park
- Research Center for Bioconvergence Analysis, Korea Basic Science Institute, Cheongju, 28119, Republic of Korea
| | - Jong Shin Yoo
- Research Center for Bioconvergence Analysis, Korea Basic Science Institute, Cheongju, 28119, Republic of Korea
| | - Jeong-Heon Ko
- Genome Editing Research Center, Korea Research Institute of Bioscience and Biotechnology, 34141, Daejeon, Republic of Korea. .,Department of Bio-Molecular Science, KRIBB School of Bioscience, Korea University of Science and Technology (UST), Daejeon, Republic of Korea.
| | - Kyoungsook Park
- Medical Research Institute, Sungkyunkwan University School of Medicine, Suwon, 16419, Republic of Korea.
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3
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Xu J, Donepudi AC, More VR, Kulkarni SR, Li L, Guo L, Yan B, Chatterjee T, Weintraub N, Slitt AL. Deficiency in Nrf2 transcription factor decreases adipose tissue mass and hepatic lipid accumulation in leptin-deficient mice. Obesity (Silver Spring) 2015; 23:335-44. [PMID: 25451536 PMCID: PMC4310781 DOI: 10.1002/oby.20929] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 09/19/2014] [Indexed: 12/12/2022]
Abstract
OBJECTIVE To evaluate whether Nrf2 deficiency impacts insulin resistance and lipid accumulation in liver and white adipose tissue. METHODS Lep(ob/ob) mice (OB) with targeted Nrf2 deletion (OB-Nrf2KO) were generated. Pathogenesis of obesity and type 2 diabetes was measured in C57BL/6J, Nrf2KO, OB, and OB-Nrf2KO mice. Hepatic lipid content, lipid clearance, and very low-density lipoprotein (VLDL) secretion were determined between OB and OB-Nrf2KO mice. RESULTS OB-Nrf2KO mice exhibited decreased white adipose tissue mass and decreased adipogenic and lipogenic gene expression compared with OB mice. Nrf2 deficiency prolonged hyperglycemia in response to glucose challenge, which was paralleled by reduced insulin-stimulated Akt phosphorylation. In OB mice, Nrf2 deficiency decreased hepatic lipid accumulation, decreased peroxisome proliferator-activated receptor γ expression and nicotinamide adenine dinucleotide phosphate (NADPH) content, and enhanced VLDL secretion. However, this observation was opposite in lean mice. Additionally, OB-Nrf2KO mice exhibited increased plasma triglyceride content, decreased HDL-cholesterol content, and enhanced apolipoprotein B expression, suggesting Nrf2 deficiency caused dyslipidemia in these mice. CONCLUSIONS Nrf2 deficiency in Lep(ob/ob) mice reduced white adipose tissue mass and prevented hepatic lipid accumulation but induced insulin resistance and dyslipidemia. This study indicates a dual role of Nrf2 during metabolic dysregulation-increasing lipid accumulation in liver and white adipose tissue but preventing lipid accumulation in obese mice.
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Affiliation(s)
- Jialin Xu
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
- Institute of Biochemistry and Molecular Biology, College of Life and Health Sciences, Northeastern University, Shenyang, P. R. China, 110819
| | - Ajay C. Donepudi
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
| | - Vijay R. More
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
| | - Supriya R. Kulkarni
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
| | - Liya Li
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
- Institute of Microbial Pharmaceuticals, College of Life and Health Sciences, Northeastern University, Shenyang, P. R. China, 110819
| | - Liangran Guo
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
| | - Bingfang Yan
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
| | - Tapan Chatterjee
- College of Medicine, University of Cincinnati, Cincinnati, OH 45221
| | - Neal Weintraub
- College of Medicine, University of Cincinnati, Cincinnati, OH 45221
| | - Angela L. Slitt
- Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881
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5
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Lee MY, Park SJ, Park K, Kim KS, Lee H, Hahn SK. Target-specific gene silencing of layer-by-layer assembled gold-cysteamine/siRNA/PEI/HA nanocomplex. ACS Nano 2011; 5:6138-6147. [PMID: 21739990 DOI: 10.1021/nn2017793] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Target-specific intracellular delivery of small interfering RNA (siRNA) is regarded as one of the most important technologies for the development of siRNA therapeutics. In this work, a cysteamine modified gold nanoparticles (AuCM)/siRNA/polyethyleneimine (PEI)/hyaluronic acid (HA) complex was successfully developed using a layer-by-layer method for target-specific intracellular delivery of siRNA by HA receptor mediated endocytosis. Atomic force microscopic and zeta potential analyses confirmed the formation of a AuCM/siRNA/PEI/HA complex having a particle size of ca. 37.3 nm and a negative surface charge of ca. -12 mV. With a negligible cytotoxicity, AuCM/siRNA/PEI/HA complex showed an excellent target-specific gene silencing efficiency of ca. 70% in the presence of 50 vol % serum, which was statistically much higher than that of siRNA/Lipofectamine 2000 complex. In the competitive binding tests with free HA, dark-field bioimaging and inductively coupled plasma-atomic emission spectroscopy confirmed the target-specific intracellular delivery of AuCM/siRNA/PEI/HA complex to B16F1 cells with HA receptors. Moreover, the systemic delivery of AuCM/siRNA/PEI/HA complex using apolipoprotein B (ApoB) siRNA as a model drug resulted in a significantly reduced ApoB mRNA level in the liver tissue. Taken together, AuCM/siRNA/PEI/HA complex was thought to be developed as target-specific siRNA therapeutics for the systemic treatment of various liver diseases.
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Affiliation(s)
- Min-Young Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk 790-784, Korea
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6
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Xu C, Haiyan Z, Hua Z, Jianhong Z, Pin D. Effect of Curcuma kwangsiensis polysaccharides on blood lipid profiles and oxidative stress in high-fat rats. Int J Biol Macromol 2009; 44:138-42. [DOI: 10.1016/j.ijbiomac.2008.11.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2008] [Revised: 11/05/2008] [Accepted: 11/10/2008] [Indexed: 10/21/2022]
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7
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Minehira K, Young SG, Villanueva CJ, Yetukuri L, Oresic M, Hellerstein MK, Farese RV, Horton JD, Preitner F, Thorens B, Tappy L. Blocking VLDL secretion causes hepatic steatosis but does not affect peripheral lipid stores or insulin sensitivity in mice. J Lipid Res 2008; 49:2038-44. [PMID: 18515909 DOI: 10.1194/jlr.m800248-jlr200] [Citation(s) in RCA: 128] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The liver secretes triglyceride-rich VLDLs, and the triglycerides in these particles are taken up by peripheral tissues, mainly heart, skeletal muscle, and adipose tissue. Blocking hepatic VLDL secretion interferes with the delivery of liver-derived triglycerides to peripheral tissues and results in an accumulation of triglycerides in the liver. However, it is unclear how interfering with hepatic triglyceride secretion affects adiposity, muscle triglyceride stores, and insulin sensitivity. To explore these issues, we examined mice that cannot secrete VLDL [due to the absence of microsomal triglyceride transfer protein (Mttp) in the liver]. These mice exhibit markedly reduced levels of apolipoprotein B-100 in the plasma, along with reduced levels of triglycerides in the plasma. Despite the low plasma triglyceride levels, triglyceride levels in skeletal muscle were unaffected. Adiposity and adipose tissue triglyceride synthesis rates were also normal, and body weight curves were unaffected. Even though the blockade of VLDL secretion caused hepatic steatosis accompanied by increased ceramides and diacylglycerols in the liver, the mice exhibited normal glucose tolerance and were sensitive to insulin at the whole-body level, as judged by hyperinsulinemic euglycemic clamp studies. Normal hepatic glucose production and insulin signaling were also maintained in the fatty liver induced by Mttp deletion. Thus, blocking VLDL secretion causes hepatic steatosis without insulin resistance, and there is little effect on muscle triglyceride stores or adiposity.
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Affiliation(s)
- Kaori Minehira
- Gladstone Institute of Cardiovascular Disease, University of California-San Francisco, CA 94158, USA.
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8
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Yang Q, Li Y. Roles of PPARs on regulating myocardial energy and lipid homeostasis. J Mol Med (Berl) 2007; 85:697-706. [PMID: 17356846 DOI: 10.1007/s00109-007-0170-9] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 01/19/2007] [Accepted: 02/23/2007] [Indexed: 12/13/2022]
Abstract
Myocardial energy and lipid homeostasis is crucial for normal cardiac structure and function. Either shortage of energy or excessive lipid accumulation in the heart leads to cardiac disorders. Peroxisome proliferator-activated receptors (PPARalpha, -beta/delta and -gamma), members of the nuclear receptor transcription factor superfamily, play important roles in regulating lipid metabolic genes. All three PPAR subtypes are expressed in cardiomyocytes. PPARalpha has been shown to control transcriptional expression of key enzymes that are involved in fatty acid (FA) uptake and oxidation, triglyceride synthesis, mitochondrial respiration uncoupling, and glucose metabolism. Similarly, PPARbeta/delta is a transcriptional regulator of FA uptake and oxidation, mitochondrial respiration uncoupling, and glucose metabolism. On the other hand, the role of PPARgamma on transcriptional regulation of FA metabolism in the heart remains obscure. Therefore, both PPARalpha and PPARbeta/delta are important transcriptional regulators of myocardial energy and lipid homeostasis. Moreover, it appears that the heart needs to have two PPAR subtypes with seemingly overlapping functions in maintaining myocardial lipid and energy homeostasis. Further studies on the potential distinctive roles of each PPAR subtype in the heart should provide new therapeutic targets for treating heart disease.
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Affiliation(s)
- Qinglin Yang
- Cardiovascular Research Institute, Morehouse School of Medicine, 720 Westview Dr SW, Atlanta, GA 30310, USA.
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9
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Abstract
The transfer of large DNA fragments to the mouse genome in the form of bacterial, yeast or phage artificial chromosomes is an important process in the definition of transcription units, the modeling of inherited disease states, the dissection of candidate regions identified by linkage analysis and the construction of in vivo reporter genes. However, as with small recombinant transgenes, the transferred sequences are usually integrated randomly often with accompanying genomic alterations and variable expression of the introduced genes due to the site of integration and/or copy number. Therefore, alternative methods of integrating large genomic transgenes into the genome have been developed to avoid the variables associated with random integration. This review encourages the reader to imagine the large variety of applications where artificial chromosome transgenes can facilitate in vivo and ex vivo studies in the mouse and provides a context for making the necessary decisions regarding the specifics of experimental design.
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Affiliation(s)
- Jason D Heaney
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, 500 University Drive, Hershey, PA 17033-0850, USA
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10
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Minehira-Castelli K, Leonard SW, Walker QM, Traber MG, Young SG. Absence of VLDL secretion does not affect alpha-tocopherol content in peripheral tissues. J Lipid Res 2006; 47:1733-8. [PMID: 16710047 DOI: 10.1194/jlr.m600125-jlr200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
alpha-Tocopherol is a lipid-soluble antioxidant that helps to prevent oxidative damage to cellular lipids. alpha-Tocopherol is absorbed by the intestine and is taken up and retained by the liver; it is widely presumed that alpha-tocopherol is then delivered to peripheral tissues by the secretion of VLDL. To determine whether VLDL secretion is truly important for the delivery of alpha-tocopherol to peripheral tissues, we examined alpha-tocopherol metabolism in mice that lack microsomal triglyceride transfer protein (Mttp) expression in the liver and therefore cannot secrete VLDL (Mttp(Delta/Delta) mice). Mttp(Delta/Delta) mice have low plasma lipid levels and increased stores of lipids in the liver. Similarly, alpha-tocopherol levels in the plasma were lower in Mttp(Delta/Delta) mice than in controls, whereas hepatic alpha-tocopherol stores were higher. However, alpha-tocopherol levels in the peripheral tissues of Mttp(Delta/Delta) mice were nearly identical to those of control mice, suggesting that VLDL secretion is not critical for the delivery of alpha-tocopherol to peripheral tissues. When fed a diet containing deuterated alpha-tocopherol, Mttp(Delta/Delta) and control mice had similar incorporation of deuterated alpha-tocopherol into plasma and various peripheral tissues. We conclude that the absence of VLDL secretion has little effect on the stores of alpha-tocopherol in peripheral tissues, at least in the mouse.
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Affiliation(s)
- Kaori Minehira-Castelli
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, 94158, USA
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11
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Hinsdale ME, Maeda N. Complex control of mouse apolipoprotein B gene expression revealed by targeted duplication. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1734:178-89. [PMID: 15904874 DOI: 10.1016/j.bbalip.2005.03.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Revised: 02/28/2005] [Accepted: 03/01/2005] [Indexed: 10/25/2022]
Abstract
An elevated plasma level of apolipoprotein B-containing lipoproteins is a risk factor for atherosclerotic cardiovascular disease. Subtle genetic abnormalities in gene expression including an increased expression of the APOB gene may play an important role in determining overall risk. In an attempt to increase mouse Apob expression, we used gene targeting and duplicated approximately 65 kb of genomic DNA containing the Apob locus in its natural genomic position in mice. While we successfully generated mice carrying the Apob gene duplication, the amount of the total Apob mRNA was not increased in their liver. In the intestine, total Apob mRNA was reduced to half of the wild-type mice. Plasma lipids in the Apob duplication mice were not altered. Expression analyses showed that the proximal Apob gene in the duplicated locus was preferentially expressed in both tissues suggesting a limitation of tissue-specific enhancer function. The previously characterized distant intestinal control element was not duplicated, explaining the unequal ratio of intestinal Apob expression. While the existence of an additional liver-specific enhancer element is unknown, our findings suggest the presence of an additional enhancer outside the duplicated region, and that Apob gene expression is more complicated than previously thought.
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Affiliation(s)
- Myron E Hinsdale
- Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525, USA.
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12
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O'Brien KD, McDonald TO, Kunjathoor V, Eng K, Knopp EA, Lewis K, Lopez R, Kirk EA, Chait A, Wight TN, deBeer FC, LeBoeuf RC. Serum Amyloid A and Lipoprotein Retention in Murine Models of Atherosclerosis. Arterioscler Thromb Vasc Biol 2005; 25:785-90. [PMID: 15692094 DOI: 10.1161/01.atv.0000158383.65277.2b] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Objective—
Elevated serum amyloid A (SAA) levels are associated with increased cardiovascular risk in humans. Because SAA associates primarily with lipoproteins in plasma and has proteoglycan binding domains, we postulated that SAA might mediate lipoprotein retention on atherosclerotic extracellular matrix.
Methods and Results—
Immunohistochemistry was performed for SAA, apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), and perlecan on proximal aortic lesions from chow-fed low-density lipoprotein receptor (LDLR)
−/−
and apoE
−/−
mice euthanized at 10, 50, and 70 weeks. SAA was detected on atherosclerotic lesion extracellular matrix at all time points in both strains. SAA area correlated highly with lesion areas (apoE
−/−
,
r
=0.76; LDLR
−/−
,
r
=0.86), apoA-I areas (apoE
−/−
,
r
=0.88; LDLR
−/−
,
r
=0.80), apoB areas (apoE
−/−
,
r
=0.74; LDLR
−/−
,
r
=0.89), and perlecan areas (apoE
−/−
,
r
=0.83; LDLR
−/−
,
r
=0.79) (all
P
<0.0001). In vitro, SAA enrichment increased high-density lipoprotein (HDL) binding to heparan sulfate proteoglycans, and immunoprecipitation experiments using plasma from apoE
−/−
and LDLR
−/−
mice demonstrated that SAA was present on both apoA-I–containing and apoB-containing lipoproteins.
Conclusions—
In chow-fed apoE
−/−
and LDLR
−/−
mice, SAA is deposited in murine atherosclerosis at all stages of lesion development, and SAA immunoreactive area correlates highly with lesion area, apoA-I area, apoB area, and perlecan area. These findings are consistent with a possible role for SAA-mediated lipoprotein retention in atherosclerosis.
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Affiliation(s)
- Kevin D O'Brien
- Division of Cardiology, University of Washington, Seattle, WA 98195-6422, USA.
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Abstract
OBJECTIVE Increased expression of human hepatic lipase (HL) or a catalytically inactive (ci) HL clears plasma cholesterol in mice deficient in low-density lipoprotein receptors (LDLr) and murine HL. We hypothesized that increased expression of both HL and ciHL reduces atherosclerosis in these mice. METHODS AND RESULTS Mice deficient in both LDLr and murine HL, alone or transgenically expressing similar levels of either human HL or ciHL, were fed a high-fat, cholesterol-enriched "Western" diet for 3 months to accelerate the development of atherosclerosis. Levels of plasma lipids, insulin, glucose, and liver enzymes were measured monthly, and aortic atherosclerosis was quantitated after 3 months. Plasma insulin, glucose, and liver enzyme levels did not differ significantly from controls. After 3 months, expression of HL reduced plasma cholesterol by 55% to 65% and reduced atherosclerosis by 40%. Surprisingly, expression of ciHL did not reduce plasma cholesterol or atherosclerosis. CONCLUSIONS High levels of HL, but not ciHL, delay the development of atherosclerosis in mice deficient in LDLr and mHL. These studies demonstrate that high levels of catalytically active human hepatic lipase (HL) reduce atherosclerosis, whereas high levels of a catalytically inactive HL do not affect atherosclerosis in mice genetically deficient in low-density lipoprotein receptor and mouse HL.
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Affiliation(s)
- Helén L Dichek
- Department of Pediatrics, Box 356320, University of Washington, 1959 NE Pacific Street, Seattle WA 98195, USA.
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Dichek HL, Qian K, Agrawal N. The bridging function of hepatic lipase clears plasma cholesterol in LDL receptor-deficient “apoB-48-only” and “apoB-100-only” mice. J Lipid Res 2004; 45:551-60. [PMID: 14679168 DOI: 10.1194/jlr.m300459-jlr200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hepatic lipase clears plasma cholesterol by lipolytic and nonlipolytic processing of lipoproteins. We hypothesized that the nonlipolytic processing (known as the bridging function) clears cholesterol by removing apoB-48- and apoB-100-containing lipoproteins by whole particle uptake. To test our hypotheses, we expressed catalytically inactive human HL (ciHL) in LDL receptor deficient "apoB-48-only" and "apoB-100-only" mice. Expression of ciHL in "apoB-48-only" mice reduced cholesterol by reducing LDL-C (by 54%, 46 +/- 6 vs. 19 +/- 8 mg/dl, P < 0.001). ApoB-48 was similarly reduced (by 60%). The similar reductions in LDL-C and apoB-48 indicate cholesterol removal by whole particle uptake. Expression of ciHL in "apoB-100-only" mice reduced cholesterol by reducing IDL-C (by 37%, 61 +/- 19 vs. 38 +/- 12 mg/dl, P < 0.003). Apo-B100 was also reduced (by 27%). The contribution of nutritional influences was examined with a high-fat diet challenge in the "apoB-100-only" background. On the high fat diet, ciHL reduced IDL-C (by 30%, 355 +/- 72 vs. 257 +/- 64 mg/dl, P < 0.04) but did not reduce apoB-100. The reduction in IDL-C in excess of apoB-100 suggests removal either by selective cholesteryl ester uptake, or by selective removal of larger, cholesteryl ester-enriched particles. Our results demonstrate that the bridging function removes apoB-48- and apoB-100-containing lipoproteins by whole particle uptake and other mechanisms.
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Affiliation(s)
- Helén L Dichek
- Department of Pediatrics, University of Washington, Seattle, WA 98195, USA.
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Abstract
BACKGROUND We evaluated the role of aldosterone as a mediator of renal inflammation and fibrosis in a rat model of aldosterone/salt hypertension using the selective aldosterone blocker, eplerenone. METHODS Unnephrectomized, Sprague-Dawley rats were given 1% NaCl (salt) to drink and randomized to receive treatment for 28 days: vehicle infusion (control); 0.75 microg/hour aldosterone subcutaneous infusion; or aldosterone infusion + 100 mg/kg/day oral dose of eplerenone. Blood pressure and urinary albumin were measured and kidneys were evaluated histologically. Renal injury, inflammation, and fibrosis were assessed by immunohistochemistry, in situ hybridization, and reverse transcription-polymerase chain reaction (RT-PCR). RESULTS Aldosterone/salt induced severe hypertension compared to controls (220 +/- 4 mm Hg vs. 131 +/- 4 mm Hg, P < 0.05), which was partially attenuated by eplerenone (179 +/- 4 mm Hg, P < 0.05). In aldosterone/salt treated rats, renal histopathologic evaluation revealed severe vascular and glomerular sclerosis, fibrinoid necrosis and thrombosis, interstitial leukocyte infiltration, and tubular damage and regeneration. Aldosterone/salt increased circulating osteopontin (925.0 +/- 80.2 ng/mL vs. 53.6 +/- 6.3 ng/mL) and albuminuria (75.8 +/- 10.9 mg/24 hours vs. 13.2 +/- 3.0 mg/24 hours) compared to controls and increased expression of proinflammatory molecules. Treatment with eplerenone reduced systemic osteopontin (58.3 +/- 4.2 ng/mL), albuminuria (41.5 +/- 7.2 mg/24 hours), and proinflammatory gene expression: osteopontin (OPN), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), and interleukin-1beta (IL-1beta). CONCLUSION These findings indicate that aldosterone/salt-induced renal injury and fibrosis has inflammatory components involving macrophage infiltration and cytokine up-regulation. Attenuation of renal damage and inflammation by eplerenone supports the protective effects of aldosterone blockade in hypertensive renal disease.
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Affiliation(s)
- Eileen R Blasi
- Pharmacia Corporation, Cardiovascular and Metabolic Diseases, Global Medical Affairs, and Global Toxicology, St. Louis, Missouri 63167, USA
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16
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Lieu HD, Withycombe SK, Walker Q, Rong JX, Walzem RL, Wong JS, Hamilton RL, Fisher EA, Young SG. Eliminating atherogenesis in mice by switching off hepatic lipoprotein secretion. Circulation 2003; 107:1315-21. [PMID: 12628954 DOI: 10.1161/01.cir.0000054781.50889.0c] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND LDL receptor-deficient "apolipoprotein (apo)-B100-only" mice (Ldlr-/-Apob100/100 have elevated LDL cholesterol levels on a chow diet and develop severe aortic atherosclerosis. We hypothesized that both the hypercholesterolemia and the susceptibility to atherosclerosis could be eliminated by switching off hepatic lipoprotein production. METHODS AND RESULTS We bred Ldlr-/-Apob100/100 mice that were homozygous for a conditional allele for Mttp (the gene for microsomal triglyceride transfer protein) and the inducible Mx1-Cre transgene. In these animals, which we called "Reversa mice," the hypercholesterolemia could be reversed, without modifying the diet or initiating a hypolipidemic drug, by the transient induction of Cre expression in the liver. After Cre induction, hepatic Mttp expression was virtually eliminated (as judged by quantitative real-time PCR), hepatic lipoprotein secretion was abolished (as judged by electron microscopy), and LDLs were virtually eliminated from the plasma. Intestinal lipoprotein production was unaffected. In mice fed a chow diet, Cre induction reduced plasma cholesterol levels from 233.9+/-46.0 to 37.2+/-6.5 mg/dL. In mice fed a high-fat diet, cholesterol levels fell from 525.7+/-32.2 to 100.6+/-14.3 mg/dL. The elimination of hepatic lipoprotein production completely prevented both the development of atherosclerosis and the changes in gene expression that accompany atherogenesis. CONCLUSIONS We developed mice in which hypercholesterolemia can be reversed with a genetic switch. These mice will be useful for understanding gene-expression changes that accompany the reversal of hypercholesterolemia and atherosclerosis.
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Affiliation(s)
- Hsiao D Lieu
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94141-9100, USA.
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17
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Wang X, Chauhan V, Nguyen AT, Schultz J, Davignon J, Young SG, Boren J, Innerarity TL, Rutai H, Milne RW. Immunochemical evidence that human apoB differs when expressed in rodent versus human cells. J Lipid Res 2003; 44:547-53. [PMID: 12562832 DOI: 10.1194/jlr.m200413-jlr200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
LDL from human apolipoprotein B-100 (apoB-100) transgenic (HuBTg+/+) mice contains more triglyceride than LDL from normolipidemic subjects. To obtain novel monoclonal antibody (MAb) probes of apoB conformation, we generated hybridomas from HuBTg+/+ that had been immunized with LDL isolated from human plasma. One apoE-specific and four anti-apoB-100-specific hybridomas were identified. Two MAbs, 2E1 and 3D11, recognized an epitope in the amino-terminal 689 residues of apoB in native apoB-containing lipoproteins (LpBs) from human plasma or from the supernatant of human hepatoma HepG2 cells, but did not react with LpB from HuBTg+/+ mice or LpB secreted by human apoB-100-transfected rat McArdle 7777 hepatoma cells. 2E1 reacted weakly and 3D11 reacted strongly with apoB from HuBTg+/+ mice after SDS-PAGE. The lack of expression of the 2E1 and 3D11 epitopes on native LpB from HuBTg+/+ mice did not solely reflect the abnormal lipid composition of murine LpB. Both epitopes were detected in all human plasma samples tested and in all human plasma LpB classes. Therefore, human apoB expressed by rodent hepatocytes or hepatoma cells appears to adopt a different conformation or undergoes different posttranslational modification than apoB expressed in human hepatocytes or hepatoma cells.
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Affiliation(s)
- Xingyu Wang
- Lipoprotein and Atherosclerosis Research Group and the Department of Pathology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada
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18
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Willner EL, Tow B, Buhman KK, Wilson M, Sanan DA, Rudel LL, Farese RV. Deficiency of acyl CoA:cholesterol acyltransferase 2 prevents atherosclerosis in apolipoprotein E-deficient mice. Proc Natl Acad Sci U S A 2003; 100:1262-7. [PMID: 12538880 PMCID: PMC298761 DOI: 10.1073/pnas.0336398100] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2002] [Indexed: 01/20/2023] Open
Abstract
Deficiency of acyl CoA:cholesterol acyltransferase 2 (ACAT2) in mice results in a reduction in cholesterol ester synthesis in the small intestine and liver, which in turn limits intestinal cholesterol absorption, hepatic cholesterol gallstone formation, and the accumulation of cholesterol esters in the plasma lipoproteins. Here we examined the contribution of ACAT2-derived cholesterol esters to atherosclerosis by crossing ACAT2-deficient (ACAT2(-/-)) mice with apolipoprotein (apo) E-deficient (ApoE(-/-)) mice, an atherosclerosis-susceptible strain that has impaired apoE-mediated clearance of apoB-containing lipoproteins. ACAT2(-/-) ApoE(-/-) mice and ACAT2(+/+) ApoE(-/-) (control) mice had similar elevations of plasma apoB and total plasma lipids; however, the lipid cores of the apoB-containing lipoproteins in ACAT2(-/-) ApoE(-/-) mice contained primarily triglycerides rather than cholesterol esters. At 30 wk of age, only the control mice had significant atherosclerosis, which was nearly absent in ACAT2(-/-) ApoE(-/-) mice. ACAT2 deficiency in the apoE-deficient background also led to a compensatory increase in the activity of lecithincholesterol acyltransferase, the major plasma cholesterol esterification enzyme, which increased high-density lipoprotein cholesterol esters. Our results demonstrate the crucial role of ACAT2-derived cholesterol esters in the development of atherosclerosis in mice and suggest that triglyceride-rich apoB-containing lipoproteins are not as atherogenic as those containing cholesterol esters. Our results also support the rationale of pharmacological inhibition of ACAT2 as a therapy for atherosclerosis.
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Affiliation(s)
- Emily L Willner
- Gladstone Institute of Cardiovascular Disease, P. O. Box 419100, San Francisco, CA 94141-9100, USA
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19
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Heyen JRR, Blasi ER, Nikula K, Rocha R, Daust HA, Frierdich G, Van Vleet JF, De Ciechi P, McMahon EG, Rudolph AE. Structural, functional, and molecular characterization of the SHHF model of heart failure. Am J Physiol Heart Circ Physiol 2002; 283:H1775-84. [PMID: 12384454 DOI: 10.1152/ajpheart.00305.2002] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Heart failure is a complex multifactorial disease resulting in a myriad of progressive changes at the molecular, cellular, and physiological level. To better understand the mechanisms associated with the development of congestive heart failure, a comprehensive examination of the aging lean male spontaneously hypertensive, heart failure-prone rat (SHHF) was conducted. Myocardial function and structural integrity progressively diminished as evidenced by decreased ejection fraction and increased left ventricular volume measured using echocardiography. Functional and structural changes were accompanied by elevations in circulating inflammatory markers, including tumor necrosis factor-alpha (TNF-alpha), IL-6, and TNF receptors type 1 and 2. Increased systemic inflammatory marker levels were consistent with age-dependent changes in the expression pattern of genes that contribute to stress, inflammation, and the extracellular matrix in SHHF animals analyzed from age 4 to 18 mo. In summary, the SHHF rat shares many hallmark features of the human disease state and represents a key experimental model for the dissection of complex human heart failure pathophysiology.
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Affiliation(s)
- Jonathan R R Heyen
- Pharmacia Corporation, 800 N. Lindbergh Boulevard, St. Louis, MO 63167, USA.
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Singh K, Batuman OA, Akman HO, Kedees MH, Vakil V, Hussain MM. Differential, tissue-specific, transcriptional regulation of apolipoprotein B secretion by transforming growth factor beta. J Biol Chem 2002; 277:39515-24. [PMID: 12177061 DOI: 10.1074/jbc.m205513200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Apolipoprotein B (apoB) is required for the assembly and secretion of triglyceride-rich lipoproteins. ApoB synthesis is constitutive, and post-translational mechanisms modulate its secretion. Transforming growth factor beta (TGF-beta) increased apoB secretion in both differentiated and nondifferentiated Caco-2 cells and decreased secretion in HepG2 cells without affecting apolipoprotein A-I secretion. TGF-beta altered apoB secretion by changing steady-state mRNA levels and protein synthesis. Expression of SMAD3 and SMAD4 differentially regulated apoB secretion in these cells. Thus, SMADs mediate dissimilar secretion of apoB in both the cell lines by affecting gene transcription. We identified a 485-bp element, 55 kb upstream of the apob gene that contains a SMAD binding motif. This motif increased the expression of chloramphenicol acetyltransferase in Caco-2 cells treated with TGF-beta or transfected with SMADs. Hence, TGF-beta activates SMADs that bind to the 485-bp intestinal enhancer element in the apob gene and increase its transcription and secretion in Caco-2 cells. This is the first example showing differential transcriptional regulation of the apob gene by cytokines and dissimilar regulation of one gene in two different cell lines by TGF-beta. In this regulation, the presence of cytokine-responsive motif in the tissue-specific enhancer element confers cell-specific response.
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Affiliation(s)
- Karnail Singh
- Department of Anatomy and Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York 11203, USA
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21
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Abstract
Intestinal reabsorption of bile salts plays a crucial role in human health and disease. This process is primarily localized to the terminal ileum and is mediated by a 48-kd sodium-dependent bile acid cotransporter (SLC10A2 = ASBT). ASBT is also expressed in renal tubule cells, cholangiocytes, and the gallbladder. Exon skipping leads to a truncated version of ASBT, which sorts to the basolateral surface and mediates efflux of bile salts. Inherited mutation of ASBT leads to congenital diarrhea secondary to bile acid malabsorption. Partial inhibition of ASBT may be useful in the treatment of hypercholesterolemia and intrahepatic cholestasis. During normal development in the rat ileum, ASBT undergoes a biphasic pattern of expression with a prenatal onset, postnatal repression, and reinduction at the time of weaning. The bile acid responsiveness of the ASBT gene is not clear and may be dependent on both the experimental model used and the species being investigated. Future studies of the transcriptional and posttranscriptional regulation of the ASBT gene and analysis of ASBT knockout mice will provide further insight into the biology, physiology, and pathophysiology of intestinal bile acid transport.
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Affiliation(s)
- B L Shneider
- Mount Sinai Medical Center, New York, NY 10029, USA
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22
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Abstract
Apolipoprotein (apo)B circulates in two distinct forms, apoB100 and apoB48. Human liver secretes apoB100, the product of a large mRNA encoding 4536 residues. The small intestine of all mammals secretes apoB48, which arises following C-to-U deamination of a single cytidine base in the nuclear apoB transcript, introducing a translational stop codon. This process, referred to as apoB RNA editing, operates through a multicomponent enzyme complex that contains a single catalytic subunit, apobec-1, in addition to other protein factors that have yet to be cloned. ApoB RNA editing also exhibits stringent cis-acting requirements that include both structural and sequence-specific elements-specifically efficiency elements that flank the minimal cassette, an AU-rich RNA context, and an 11-nucleotide mooring sequence-located in proximity to a suitably positioned (usually upstream) cytidine. C-to-U RNA editing may become unconstrained under circumstances where apobec-1 is overexpressed, in which case multiple cytidines in apoB RNA, as well as in other transcripts, undergo C-to-U editing. ApoB RNA editing is eliminated following targeting of apobec-1, establishing that there is no genetic redundancy in this function. Under physiological circumstances, apoB RNA editing exhibits developmental, hormonal, and nutritional regulation, in some cases related to transcriptional regulation of apobec-1 mRNA. ApoB and the microsomal triglyceride transfer protein (MTP) are essential for the assembly and secretion of apoB-containing lipoproteins. MTP functions by transferring lipid to apoB during its translation and by transporting triglycerides into the endoplasmic reticulum to form apoB-free lipid droplets. These droplets fuse with nascent apoB-containing particles to form mature, very low-density lipoproteins or chylomicrons. In cultured hepatic cells, lipid availability dictates the rate of apoB production. Unlipidated or underlipidated forms of apoB are subjected to presecretory degradation, a process mediated by retrograde transport from the lumen of the endoplasmic reticulum to the cytosol, coupled with multiubquitination and proteasomal degradation. Although control of lipid secretion in vivo is primarily achieved at the level of lipoprotein particle size, regulation of apoB production by presecretory degradation may be relevant in some dyslipidemic states.
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Affiliation(s)
- N O Davidson
- Departments of Medicine and Molecular Biology and Pharmacology, Washington University Medical School, St. Louis, Missouri 63110, USA.
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23
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Véniant MM, Sullivan MA, Kim SK, Ambroziak P, Chu A, Wilson MD, Hellerstein MK, Rudel LL, Walzem RL, Young SG. Defining the atherogenicity of large and small lipoproteins containing apolipoprotein B100. J Clin Invest 2000; 106:1501-10. [PMID: 11120757 PMCID: PMC387257 DOI: 10.1172/jci10695] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Apo-E-deficient apo-B100-only mice (APOE:(-/-)APOB:(100/100)) and LDL receptor-deficient apo-B100-only mice (LDLR:(-/-)APOB:(100/100)) have similar total plasma cholesterol levels, but nearly all of the plasma cholesterol in the former animals is packaged in VLDL particles, whereas, in the latter, plasma cholesterol is found in smaller LDL particles. We compared the apo-B100-containing lipoprotein populations in these mice to determine their relation to susceptibility to atherosclerosis. The median size of the apo-B100-containing lipoprotein particles in APOE:(-/-)APOB:(100/100) plasma was 53.4 nm versus only 22.1 nm in LDLR:(-/-)APOB:(100/100) plasma. The plasma levels of apo-B100 were three- to fourfold higher in LDLR:(-/-)APOB:(100/100) mice than in APOE:(-/-)APOB:(100/100) mice. After 40 weeks on a chow diet, the LDLR:(-/-)APOB:(100/100) mice had more extensive atherosclerotic lesions than APOE:(-/-)APOB:(100/100) mice. The aortic DNA synthesis rate and the aortic free and esterified cholesterol contents were also higher in the LDLR:(-/-)APOB:(100/100) mice. These findings challenge the notion that all non-HDL lipoproteins are equally atherogenic and suggest that at a given cholesterol level, large numbers of small apo-B100-containing lipoproteins are more atherogenic than lower numbers of large apo-B100-containing lipoproteins.
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Affiliation(s)
- M M Véniant
- Gladstone Institute of Cardiovascular Disease, Cardiovascular Research Institute, University of California, San Francisco, California, USA.
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24
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Buhman KK, Accad M, Novak S, Choi RS, Wong JS, Hamilton RL, Turley S, Farese RV. Resistance to diet-induced hypercholesterolemia and gallstone formation in ACAT2-deficient mice. Nat Med 2000; 6:1341-7. [PMID: 11100118 DOI: 10.1038/82153] [Citation(s) in RCA: 264] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The importance of cholesterol ester synthesis by acyl CoA:cholesterol acyltransferase (ACAT) enzymes in intestinal and hepatic cholesterol metabolism has been unclear. We now demonstrate that ACAT2 is the major ACAT in mouse small intestine and liver, and suggest that ACAT2 deficiency has profound effects on cholesterol metabolism in mice fed a cholesterol-rich diet, including complete resistance to diet-induced hypercholesterolemia and cholesterol gallstone formation. The underlying mechanism involves the lack of cholesterol ester synthesis in the intestine and a resultant reduced capacity to absorb cholesterol. Our results indicate that ACAT2 has an important role in the response to dietary cholesterol, and suggest that ACAT2 inhibition may be a useful strategy for treating hypercholesterolemia or cholesterol gallstones.
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Affiliation(s)
- K K Buhman
- Gladstone Institute of Cardiovascular Disease, P.O. Box 419100, San Francisco, California 94141-9100, USA
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25
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Cheesman EJ, Sharp RJ, Zlot CH, Liu CY, Taylor S, Marcovina SM, Young SG, McCormick SP. An analysis of the interaction between mouse apolipoprotein B100 and apolipoprotein(a). J Biol Chem 2000; 275:28195-200. [PMID: 10837476 DOI: 10.1074/jbc.m002772200] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The assembly of lipoprotein(a) (Lp(a)) involves an initial noncovalent interaction between apolipoprotein (apo) B100 and apo(a), followed by the formation of a disulfide bond between apoB100 cysteine 4326 and apo(a) cysteine 4057. The structural features of apoB100 that are required for its noncovalent interaction with apo(a) have not been fully defined. To analyze that initial interaction, we tested whether apo(a) could bind noncovalently to two apoB proteins that lack cysteine 4326: mouse apoB100 and human apoB100-C4326G. Our experiments demonstrated that both mouse apoB and the human apoB100-C4326G bind noncovalently to apo(a). We next sought to gain insights into the apoB amino acid sequences required for the interaction between apoB100 and apo(a). Previous studies of truncated human apoB proteins indicated that the carboxyl terminus of human apoB100 (amino acids 4330-4397) is important for Lp(a) assembly. To determine whether the carboxyl terminus of mouse apoB100 can interact with apo(a), transgenic mice were produced with a mutant human apoB gene construct in which human apoB100 amino acids 4279-4536 were replaced with the corresponding mouse apoB100 sequences and tyrosine 4326 was changed to a cysteine. The mutant apoB100 bound to apo(a) and formed bona fide disulfide-linked Lp(a), but Lp(a) assembly was less efficient than with wild-type human apoB100. The fact that Lp(a) assembly was less efficient with the mouse apoB sequences provides additional support for the notion that sequences in the carboxyl terminus of apoB100 are important for Lp(a) assembly.
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Affiliation(s)
- E J Cheesman
- Biochemistry Department, University of Otago, Dunedin 9001, New Zealand
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26
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Abstract
Large insert genomic clones are useful for generating transgenic animals, particularly when specific mutations are introduced. To facilitate manipulation of large genomic sequences, we developed a method of converting Escherichia coli P1 artificial chromosomes (PACs) into yeast artificial chromosomes (YACs). A shuttle vector, pMAX-121, was generated that contains elements needed to generate a YAC (cen4, ars, ura3, his, and two telomere segments) along with approximately 1.3 kb of sequence homologous to P1 and PAC vector sequences. Cotransformation of yeast with the target PAC or P1 clone and pMAX-121 results in two homologous recombination events. The first, between the target clone and pMAX-121, results in a circular molecule. The second is an intramolecular recombination event between the two pMAX-121 telomere sequences, resulting in a linear molecule. The resulting YAC is stably maintained in yeast and can be further modified using homologous recombination. The method was used to convert a 201-kb PAC containing the human tau gene into a stable linear YAC. A second vector, pLys2-neo, was developed to retrofit the YAC with the yeast lys2 gene, a selectable marker replacing the yeast ura3 gene, and a Pgk-neo cassette that confers G418 resistance to mammalian cells. The resulting YAC can be used for generating transgenic animals and stably transfected cell lines. Also, the lys2 marker facilitates introduction of mutations by homologous recombination.
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Affiliation(s)
- P Poorkaj
- Geriatric Research Education Clinical Center, Seattle, Washington 98108, USA.
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27
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Ebara T, Conde K, Kako Y, Liu Y, Xu Y, Ramakrishnan R, Goldberg IJ, Shachter NS. Delayed catabolism of apoB-48 lipoproteins due to decreased heparan sulfate proteoglycan production in diabetic mice. J Clin Invest 2000; 105:1807-18. [PMID: 10862796 PMCID: PMC378502 DOI: 10.1172/jci8283] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We used wild-type (WT) mice and mice engineered to express either apoB-100 only (B100 mice) or apoB-48 only (B48 mice) to examine the effects of streptozotocin-induced diabetes (DM) on apoB-100- and apoB-48-containing lipoproteins. Plasma lipids increased with DM in WT mice, and fat tolerance was markedly impaired. Lipoprotein profiles showed increased levels and cholesterol enrichment of VLDL in diabetic B48 mice but not in B100 mice. C apolipoproteins, in particular apoC-I in VLDL, were increased. To investigate the basis of the increase in apoB-48 lipoproteins in streptozotocin-treated animals, we characterized several parameters of lipoprotein metabolism. Triglyceride and apoB production rates were normal, as were plasma lipase activity, VLDL glycosaminoglycan binding, and VLDL lipolysis. However, beta-VLDL clearance decreased due to decreased trapping by the liver. Whereas LRP activity was normal, livers from treated mice incorporated significantly less sulfate into heparan sulfate proteoglycans (HSPG) than did controls. Hepatoma (HepG2) cells and endothelial cells cultured in high glucose also showed decreased sulfate and glucosamine incorporation into HSPG. Western blots of livers from diabetic mice showed a decrease in the HSPG core protein, perlecan. Delayed clearance of postprandial apoB-48-containing lipoproteins in DM appears to be due to decreased hepatic perlecan HSPG.
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Affiliation(s)
- T Ebara
- Division of Preventive Medicine and Nutrition, Department of Medicine, College of Physicians and Surgeons of Columbia University, 630 West 168th Street, New York, New York, USA
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28
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van 't Hooft FM, Jormsjö S, Lundahl B, Tornvall P, Eriksson P, Hamsten A. A functional polymorphism in the apolipoprotein B promoter that influences the level of plasma low density lipoprotein. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33415-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Liao W, Kobayashi K, Chan L. Adenovirus-mediated overexpression of microsomal triglyceride transfer protein (MTP): mechanistic studies on the role of MTP in apolipoprotein B-100 biogenesis. Biochemistry 1999; 38:7532-44. [PMID: 10360951 DOI: 10.1021/bi9904196] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The intracellular concentration of the microsomal triglyceride transfer protein large subunit (lMTP), the abetalipoproteinemia gene product, is tightly controlled. To date, attempts at overexpressinglMTP in vivo or in vitro have been unsuccessful. We successfully overexpressed lMTP in HepG2 cells using an adenoviral vector containing an lMTP cDNA, AdMTP. AdMTP-transduced HepG2 cells overexpressed MTP activity. They secreted increased amounts of apoB-100 lipoproteins with LDL and HDL density into the medium. lMTP overexpression alone minimally changed the density profile of apoB-containing lipoproteins, but addition of oleic acid shifted the profile toward lower densities. Oleic acid had a greater stimulatory effect on apoB-100 secretion in control HepG2 cells than in AdMTP-transduced cells, because (i) adenoviral transduction per se suppressed protein synthesis, affecting apoB-100 and albumin equally, and (ii) adenoviral transduction partially attenuated the increase in triglyceride synthesis in response to oleic acid supplementation. AdMTP treatment greatly diminished the intracellular degradation of apoB-100, but in comparison with recombinant virus containing luciferase cDNA (AdLuc), it caused no change in its biosynthetic rate. It greatly reduced, but did not eliminate, its proteasomal degradation. Our study constitutes the initial demonstration that adenovirus-mediated transfer of lMTP markedly stimulates MTP expression which in turn stimulates apoB-100 production. The mechanism involves a downregulation of ubiquitin-proteasome-mediated degradation without any change in synthetic rate.
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Affiliation(s)
- W Liao
- Department of Medicine, Baylor College of Medicine, Texas Medical Center, Houston 77030, USA
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31
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Raabe M, Véniant MM, Sullivan MA, Zlot CH, Björkegren J, Nielsen LB, Wong JS, Hamilton RL, Young SG. Analysis of the role of microsomal triglyceride transfer protein in the liver of tissue-specific knockout mice. J Clin Invest 1999; 103:1287-98. [PMID: 10225972 PMCID: PMC408359 DOI: 10.1172/jci6576] [Citation(s) in RCA: 336] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
A deficiency in microsomal triglyceride transfer protein (MTP) causes the human lipoprotein deficiency syndrome abetalipoproteinemia. However, the role of MTP in the assembly and secretion of VLDL in the liver is not precisely understood. It is not clear, for instance, whether MTP is required to move the bulk of triglycerides into the lumen of the endoplasmic reticulum (ER) during the assembly of VLDL particles. To define MTP's role in hepatic lipoprotein assembly, we recently knocked out the mouse MTP gene (Mttp). Unfortunately, achieving our objective was thwarted by a lethal embryonic phenotype. In this study, we produced mice harboring a "floxed" Mttp allele and then used Cre-mediated recombination to generate liver-specific Mttp knockout mice. Inactivating the Mttp gene in the liver caused a striking reduction in VLDL triglycerides and large reductions in both VLDL/LDL and HDL cholesterol levels. The Mttp inactivation lowered apo B-100 levels in the plasma by >95% but reduced plasma apo B-48 levels by only approximately 20%. Histologic studies in liver-specific knockout mice revealed moderate hepatic steatosis. Ultrastructural studies of wild-type mouse livers revealed numerous VLDL-sized lipid-staining particles within membrane-bound compartments of the secretory pathway (ER and Golgi apparatus) and few cytosolic lipid droplets. In contrast, VLDL-sized lipid-staining particles were not observed in MTP-deficient hepatocytes, either in the ER or in the Golgi apparatus, and there were numerous cytosolic fat droplets. We conclude that MTP is essential for transferring the bulk of triglycerides into the lumen of the ER for VLDL assembly and is required for the secretion of apo B-100 from the liver.
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Affiliation(s)
- M Raabe
- Gladstone Institute of Cardiovascular Disease, San Francisco, California 94141-9100, USA
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Zlot CH, Flynn LM, Véniant MM, Kim E, Raabe M, McCormick SP, Ambroziak P, McEvoy LM, Young SG. Generation of monoclonal antibodies specific for mouse apolipoprotein B-100 in apolipoprotein B-48-only mice. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33341-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Kim E, Ambroziak P, Véniant MM, Hamilton RL, Young SG. A gene-targeted mouse model for familial hypobetalipoproteinemia. Low levels of apolipoprotein B mRNA in association with a nonsense mutation in exon 26 of the apolipoprotein B gene. J Biol Chem 1998; 273:33977-84. [PMID: 9852051 DOI: 10.1074/jbc.273.51.33977] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Familial hypobetalipoproteinemia, a syndrome characterized by abnormally low plasma levels of low density lipoprotein cholesterol, is caused by mutations in the apolipoprotein (apo) B gene that interfere with the synthesis of a full-length apoB100. In many cases of familial hypobetalipoproteinemia, nonsense or frameshift mutations result in the synthesis of a truncated apoB protein. To understand why these mutations result in low plasma cholesterol levels, we used gene targeting in mouse embryonic stem cells to introduce a nonsense mutation (N1785Stop) into exon 26 of the mouse Apob gene. The sole product of this mutant Apob allele was a truncated apoB, apoB39. Mice homozygous for this "apoB39-only" (Apob39) allele had low plasma levels of apoB39 and markedly reduced plasma levels of very low density lipoprotein and low density lipoprotein cholesterol when fed a high fat diet. Analysis of liver and intestinal RNA from heterozygous apoB39-only mice revealed that the Apob39 mRNA levels were 60-70% lower than those from the wild-type allele. Interestingly, apoB39 was not cleared as rapidly from the plasma as apoB48. The apoB39-only mice provide new insights into the mechanisms of familial hypobetalipoproteinemia and the structural features of apoB that are important for lipoprotein metabolism.
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Affiliation(s)
- E Kim
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94141-9100, USA
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34
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Nielsen LB, Kahn D, Duell T, Weier HU, Taylor S, Young SG. Apolipoprotein B gene expression in a series of human apolipoprotein B transgenic mice generated with recA-assisted restriction endonuclease cleavage-modified bacterial artificial chromosomes. An intestine-specific enhancer element is located between 54 and 62 kilobases 5' to the structural gene. J Biol Chem 1998; 273:21800-7. [PMID: 9705318 DOI: 10.1074/jbc.273.34.21800] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Prior studies have established that the expression of the human apolipoprotein B (apoB) gene in the intestine is dependent on DNA sequences located a great distance from the structural gene. To identify the location of those sequences, we used recA-assisted restriction endonuclease (RARE) cleavage to truncate the 5'- or 3'-flanking sequences from a 145-kilobase (kb) bacterial artificial chromosome spanning the entire human apoB gene. Seven RARE cleavage- modified bacterial artificial chromosomes with different lengths of flanking sequences were used to generate transgenic mice. An analysis of those mice revealed that as little as 1.5 kb of 3' sequences or 5 kb of 5' sequences were sufficient to confer apoB expression in the liver. In contrast, apoB gene expression in the intestine required DNA sequences 54-62 kb 5' to the structural gene. Those sequences retained their ability to direct apoB expression in the intestine when they were moved closer to the gene. These studies demonstrate that the intestinal expression of the apoB gene is dependent on DNA sequences located an extraordinary distance from the structural gene and that the RARE cleavage/transgenic expression strategy is a powerful approach for analyzing distant gene-regulatory sequences.
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Affiliation(s)
- L B Nielsen
- Gladstone Institute of Cardiovascular Disease, San Francisco, California 94141-9100, USA
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35
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Hamilton RL, Wong JS, Cham CM, Nielsen LB, Young SG. Chylomicron-sized lipid particles are formed in the setting of apolipoprotein B deficiency. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32183-0] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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36
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Raabe M, Flynn LM, Zlot CH, Wong JS, Véniant MM, Hamilton RL, Young SG. Knockout of the abetalipoproteinemia gene in mice: reduced lipoprotein secretion in heterozygotes and embryonic lethality in homozygotes. Proc Natl Acad Sci U S A 1998; 95:8686-91. [PMID: 9671739 PMCID: PMC21137 DOI: 10.1073/pnas.95.15.8686] [Citation(s) in RCA: 198] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Abetalipoproteinemia, an inherited human disease characterized by a near-complete absence of the apolipoprotein (apo) B-containing lipoproteins in the plasma, is caused by mutations in the gene for microsomal triglyceride transfer protein (MTP). We used gene targeting to knock out the mouse MTP gene (Mttp). In heterozygous knockout mice (Mttp+/- ), the MTP mRNA, protein, and activity levels were reduced by 50%, in both liver and intestine. Compared with control mice (Mttp+/+), chow-fed Mttp+/- mice had reduced plasma levels of low-density lipoprotein cholesterol and had a 28% reduction in plasma apoB100 levels. On a high-fat diet, the Mttp+/- mice exhibited a marked reduction in total plasma cholesterol levels, compared with those in Mttp+/+ mice. Both the livers of adult Mttp+/- mice and the visceral endoderm of the yolk sacs from Mttp+/- embryos manifested an accumulation of cytosolic fat. All homozygous embryos (Mttp-/-) died during embryonic development. In the visceral endoderm of Mttp-/- yolk sacs, lipoprotein synthesis was virtually absent, and there was a marked accumulation of cytosolic fat droplets. In summary, half-normal MTP levels do not support normal levels of lipoprotein synthesis and secretion, and a complete deficiency of MTP causes lethal developmental abnormalities, perhaps because of an impaired capacity of the yolk sac to export lipids to the developing embryo.
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Affiliation(s)
- M Raabe
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94141-9100, USA.
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38
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Nielsen LB, Véniant M, Borén J, Raabe M, Wong JS, Tam C, Flynn L, Vanni-Reyes T, Gunn MD, Goldberg IJ, Hamilton RL, Young SG. Genes for apolipoprotein B and microsomal triglyceride transfer protein are expressed in the heart: evidence that the heart has the capacity to synthesize and secrete lipoproteins. Circulation 1998; 98:13-6. [PMID: 9665054 DOI: 10.1161/01.cir.98.1.13] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Expression of both the apolipoprotein B (apoB) gene and the microsomal triglyceride transfer protein (MTP) gene is required for the assembly and secretion of triglyceride-rich lipoproteins in the liver and intestine. Both genes have been assumed to be silent in the heart. METHODS AND RESULTS Northern blot and RNase protection analyses showed that the apoB and MTP genes were expressed in the hearts of mice and humans. In situ hybridization studies revealed that the apoB mRNA was produced in cardiac myocytes. Electron microscopy of human cardiac myocytes revealed lipid-staining particles of relatively small diameter (approximately 250 A) within the Golgi apparatus. CONCLUSIONS These studies strongly suggest that the heart synthesizes and secretes apoB-containing lipoproteins.
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Affiliation(s)
- L B Nielsen
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco 94141-9100, USA
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39
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Jamil H, Chu CH, Dickson JK, Chen Y, Yan M, Biller SA, Gregg RE, Wetterau JR, Gordon DA. Evidence that microsomal triglyceride transfer protein is limiting in the production of apolipoprotein B-containing lipoproteins in hepatic cells. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32526-8] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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40
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Borén J, Olin K, Lee I, Chait A, Wight TN, Innerarity TL. Identification of the principal proteoglycan-binding site in LDL. A single-point mutation in apo-B100 severely affects proteoglycan interaction without affecting LDL receptor binding. J Clin Invest 1998; 101:2658-64. [PMID: 9637699 PMCID: PMC508856 DOI: 10.1172/jci2265] [Citation(s) in RCA: 205] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The subendothelial retention of LDLs through their interaction with proteoglycans has been proposed to be a key process in the pathogenesis of atherosclerosis. In vitro studies have identified eight clusters of basic amino acids in delipidated apo-B100, the protein moiety of LDL, that bind the negatively charged proteoglycans. To determine which of these sites is functional on the surface of LDL particles, we analyzed the proteoglycan-binding activity of recombinant human LDL isolated from transgenic mice. Substitution of neutral amino acids for the basic amino acids residues in site B (residues 3359-3369) abolished both the receptor-binding and the proteoglycan-binding activities of the recombinant LDL. Chemical modification of the remaining basic residues caused only a marginal further reduction in proteoglycan binding, indicating that site B is the primary proteoglycan-binding site of LDL. Although site B was essential for normal receptor-binding and proteoglycan-binding activities, these activities could be separated in recombinant LDL containing single-point mutation. Recombinant LDL with a K3363E mutation, in which a glutamic acid had been inserted into the basic cluster RKR in site B, had normal receptor binding but interacted defectively with proteoglycans; in contrast, another mutant LDL, R3500Q, displayed defective receptor binding but interacted normally with proteoglycans. LDL with normal receptor-binding activity but with severely impaired proteoglycan binding will be a unique resource for analyzing the importance of LDL- proteoglycan interaction in atherogenesis. If the subendothelial retention of LDL by proteoglycans is the initial event in early atherosclerosis, then LDL with defective proteoglycan binding may have little or no atherogenic potential.
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Affiliation(s)
- J Borén
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94141-9100, USA.
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41
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Abstract
Extensive manipulation of the apolipoprotein B gene in yeast and bacterial artificial chromosome clones and subsequent expression of these clones in transgenic mice have provided fresh insights into several aspects of apolipoprotein B biology, including the identification of sequences important for lipoprotein (a) assembly, the demonstration that intestinal expression of apolipoprotein B is controlled by DNA sequences > 50 kb from the gene, and the extraordinary finding that apolipoprotein B is expressed in the heart.
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Affiliation(s)
- S P McCormick
- Biochemistry Department, University of Otago, Dunedin, New Zealand.
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Ihara Y, Yoshimura M, Miyoshi E, Nishikawa A, Sultan AS, Toyosawa S, Ohnishi A, Suzuki M, Yamamura K, Ijuhin N, Taniguchi N. Ectopic expression of N-acetylglucosaminyltransferase III in transgenic hepatocytes disrupts apolipoprotein B secretion and induces aberrant cellular morphology with lipid storage. Proc Natl Acad Sci U S A 1998; 95:2526-30. [PMID: 9482919 PMCID: PMC19400 DOI: 10.1073/pnas.95.5.2526] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
N-Acetylglucosaminyltransferase III (GnT-III) produces "bisecting-GlcNAc" and regulates the branching of N-glycans. GnT-III activity is elevated during hepatocarcinogenesis, which is in contrast to the undetectable level found in normal hepatocytes. To determine the biological significance of GnT-III in hepatocytes, transgenic mice that specifically express GnT-III in the liver were established and characterized. The transgenic hepatocytes had a swollen oval-like morphology, with many lipid droplets. Apolipoprotein B, which contained increased level of bisecting-GlcNAc accumulated in the transgenic hepatocytes. In the transgenic serum, triglycerides, the beta- and pre-beta-lipoprotein fractions, and apolipoprotein B100 were significantly decreased, compared with levels in nontransgenic serum. These abnormal phenotypes were more prominent in the mice with more copies of the transgene and a resulting high GnT-III activity. We demonstrate that aberrant glycosylation, as the direct result of the formation of bisecting-GlcNAc, disrupts the function of apolipoprotein B, leading to the generation of fatty liver. This observation suggests a novel mechanism for the pathogenesis of fatty liver.
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Affiliation(s)
- Y Ihara
- Department of Biochemistry, Osaka University Medical School, 2-2 Yamadaoka, 1-8 Yamadaoka, Suita, Osaka 565, Japan
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44
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Boren J, Lee I, Zhu W, Arnold K, Taylor S, Innerarity TL. Identification of the low density lipoprotein receptor-binding site in apolipoprotein B100 and the modulation of its binding activity by the carboxyl terminus in familial defective apo-B100. J Clin Invest 1998; 101:1084-93. [PMID: 9486979 PMCID: PMC508660 DOI: 10.1172/jci1847] [Citation(s) in RCA: 165] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Familial defective apolipoprotein B100 (FDB) is caused by a mutation of apo-B100 (R3500Q) that disrupts the receptor binding of low density lipoproteins (LDL), which leads to hypercholesterolemia and premature atherosclerosis. In this study, mutant forms of human apo-B were expressed in transgenic mice, and the resulting human recombinant LDL were purified and tested for their receptor-binding activity. Site-directed mutagenesis and other evidence indicated that Site B (amino acids 3,359-3,369) binds to the LDL receptor and that arginine-3,500 is not directly involved in receptor binding. The carboxyl-terminal 20% of apo-B100 is necessary for the R3500Q mutation to disrupt receptor binding, since removal of the carboxyl terminus in FDB LDL results in normal receptor-binding activity. Similarly, removal of the carboxyl terminus of apo-B100 on receptor-inactive VLDL dramatically increases apo-B-mediated receptor-binding activity. We propose that the carboxyl terminus normally functions to inhibit the interaction of apo-B100 VLDL with the LDL receptor, but after the conversion of triglyceride-rich VLDL to smaller cholesterol-rich LDL, arginine-3,500 interacts with the carboxyl terminus, permitting normal interaction between LDL and its receptor. Moreover, the loss of arginine at this site destabilizes this interaction, resulting in receptor-binding defective LDL.
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MESH Headings
- Animals
- Anura
- Apolipoproteins B/genetics
- Apolipoproteins B/immunology
- Apolipoproteins B/metabolism
- Arginine/metabolism
- Base Sequence
- Cells, Cultured
- Chickens
- Cloning, Molecular
- DNA Primers/genetics
- Gene Expression
- Humans
- Hyperlipoproteinemia Type II/genetics
- Hyperlipoproteinemia Type II/metabolism
- Immunoassay
- Lipoproteins, LDL/blood
- Lipoproteins, LDL/isolation & purification
- Lipoproteins, LDL/metabolism
- Lipoproteins, VLDL/metabolism
- Mice
- Mice, Transgenic
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Plasmids
- Rabbits
- Receptors, LDL/metabolism
- Recombinant Proteins/immunology
- Recombinant Proteins/isolation & purification
- Recombinant Proteins/metabolism
- Recombination, Genetic
- Sequence Alignment
- Sequence Analysis
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Affiliation(s)
- J Boren
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94141-9100, USA.
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45
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Dichek HL, Brecht W, Fan J, Ji ZS, McCormick SP, Akeefe H, Conzo L, Sanan DA, Weisgraber KH, Young SG, Taylor JM, Mahley RW. Overexpression of hepatic lipase in transgenic mice decreases apolipoprotein B-containing and high density lipoproteins. Evidence that hepatic lipase acts as a ligand for lipoprotein uptake. J Biol Chem 1998; 273:1896-903. [PMID: 9442022 DOI: 10.1074/jbc.273.4.1896] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
To determine the mechanisms by which human hepatic lipase (HL) contributes to the metabolism of apolipoprotein (apo) B-containing lipoproteins and high density lipoproteins (HDL) in vivo, we developed and characterized HL transgenic mice. HL was localized by immunohistochemistry to the liver and to the adrenal cortex. In hemizygous (hHLTg+/0) and homozygous (hHLTg+/+) mice, postheparin plasma HL activity increased by 25- and 50-fold and plasma cholesterol levels decreased by 80% and 85%, respectively. In mice fed a high fat, high cholesterol diet to increase endogenous apoB-containing lipoproteins, plasma cholesterol decreased 33% (hHLTg+/0) and 75% (hHLTg+/+). Both apoB-containing remnant lipoproteins and HDL were reduced. To extend this observation, the HL transgene was expressed in human apoB transgenic (huBTg) and apoE-deficient (apoE-/-) mice, both of which have high plasma levels of apoB-containing lipoproteins. (Note that the huBTg mice that were used in these studies were all hemizygous for the human apoB gene.) In both the huBTg,hHLTg+/0 mice and the apoE-/-,hHLTg+/0 mice, plasma cholesterol decreased by 50%. This decrease was reflected in both the apoB-containing and the HDL fractions. To determine if HL catalytic activity is required for these decreases, we expressed catalytically inactive HL (HL-CAT) in apoE-/- mice. The postheparin plasma HL activities were similar in the apoE-/- and the apoE-/-,HL-CAT+/0 mice, reflecting the activity of the endogenous mouse HL and confirming that the HL-CAT was catalytically inactive. However, the postheparin plasma HL activity was 20-fold higher in the apoE-/-,hHLTg+/0 mice, indicating expression of the active human HL. Immunoblotting demonstrated high levels of human HL in postheparin plasma of both apoE-/-,hHLTg+/0 and apoE-/-,HL-CAT+/0 mice. Plasma cholesterol and apoB-containing lipoprotein levels were approximately 60% lower in apoE-/-,HL-CAT+/0 mice than in apoE-/- mice. However, the HDL were only minimally reduced. Thus, the catalytic activity of HL is critical for its effects on HDL but not for its effects on apoB-containing lipoproteins. These results provide evidence that HL can act as a ligand to remove apoB-containing lipoproteins from plasma.
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Affiliation(s)
- H L Dichek
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco 94141-9100, USA
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46
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Nielsen LB, McCormick SP, Pierotti V, Tam C, Gunn MD, Shizuya H, Young SG. Human apolipoprotein B transgenic mice generated with 207- and 145-kilobase pair bacterial artificial chromosomes. Evidence that a distant 5'-element confers appropriate transgene expression in the intestine. J Biol Chem 1997; 272:29752-8. [PMID: 9368045 DOI: 10.1074/jbc.272.47.29752] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We reported previously that approximately 80-kilobase pair (kb) P1 bacteriophage clones spanning either the human or mouse apoB gene (clones p158 and p649, respectively) confer apoB expression in the liver of transgenic mice, but not in the intestine. We hypothesized that the absence of intestinal expression was due to the fact that these clones lacked a distant DNA element controlling intestinal expression. To test this possibility, transgenic mice were generated with 145- and 207-kb bacterial artificial chromosomes (BACs) that contained the human apoB gene and more extensive 5'- and 3'-flanking sequences. RNase protection, in situ hybridization, immunohistochemical, and genetic complementation studies revealed that the BAC transgenic mice manifested appropriate apoB gene expression in both the intestine and the liver, indicating that both BACs contained the distant intestinal element. To determine whether the regulatory element was located 5' or 3' to the apoB gene, transgenic mice were generated by co-microinjecting embryos with p158 and either the 5'- or 3'-sequences from the 145-kb BAC. Analysis of these mice indicated that the apoB gene's intestinal element is located 5' to the structural gene. Cumulatively, the transgenic mouse studies suggest that the intestinal element is located between -33 and -70 kb 5' to the apoB gene.
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Affiliation(s)
- L B Nielsen
- Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94141-9100, USA.
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47
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Véniant MM, Pierotti V, Newland D, Cham CM, Sanan DA, Walzem RL, Young SG. Susceptibility to atherosclerosis in mice expressing exclusively apolipoprotein B48 or apolipoprotein B100. J Clin Invest 1997; 100:180-8. [PMID: 9202070 PMCID: PMC508178 DOI: 10.1172/jci119511] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
All classes of lipoproteins considered to be atherogenic contain apo-B100 or apo-B48. However, there is a distinct paucity of data regarding whether lipoproteins containing apo-B48 or apo-B100 differ in their intrinsic ability to promote the development of atherosclerosis. To address this issue, we compared the extent of atherosclerosis in three groups of animals: apo-E-deficient mice (apo-B+/+apo-E-/-) and apo-E-deficient mice that synthesize exclusively either apo-B48 (apo-B48/48apo-E-/-) or apo-B100 (apo-B100/100apo-E-/-). Mice (n = 25 in each group) were fed a chow diet for 200 days, and plasma lipid levels were assessed throughout the study. Compared with the levels in apo-B+/+apo-E-/- mice, the total plasma cholesterol levels were higher in the apo-B48/48apo-E-/- mice and were lower in the apo-B100/100apo-E-/- mice. However, the ranges of cholesterol levels in the three groups overlapped. Compared with those in the apo-B+/+apo-E-/- mice, atherosclerotic lesions were more extensive in the apo-B48/48apo-E-/- mice and less extensive in the apo-B100/100apo-E-/- mice. Once again, however, there was overlap among the three groups. The extent of atherosclerosis in each group of mice correlated significantly with plasma cholesterol levels. In mice from different groups that had similar cholesterol levels, the extent of atherosclerosis was quite similar. Thus, susceptibility to atherosclerosis was dependent on total cholesterol levels. Whether mice synthesized apo-B48 or apo-B100 did not appear to have an independent effect on susceptibility to atherosclerosis.
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Affiliation(s)
- M M Véniant
- Gladstone Institute of Cardiovascular Disease, San Francisco, California 94141-9100, USA.
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48
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Albers JJ, Tu AY, Paigen B, Chen H, Cheung MC, Marcovina SM. Transgenic mice expressing human phospholipid transfer protein have increased HDL/non-HDL cholesterol ratio. Int J Clin Lab Res 1996; 26:262-7. [PMID: 9007618 DOI: 10.1007/bf02602960] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The role of plasma phospholipid transfer protein (PLTP) in lipoprotein metabolism is poorly understood. In vitro studies suggest that PLTP influences HDL size and composition and transfers phospholipids among lipoproteins. To provide an in vivo model for studies of PLTP physiology, transgenic mice that express human PLTP were generated. Human PLTP transcripts were detected in total RNA from adipose tissue, lung, heart, and spleen of the two distinct lines (A and C) of transgenic mice. Despite minimal expression of human PLTP in the liver of these transgenic mice and similar plasma phospholipid transfer activity in transgenic and non-transgenic mice (19.1 +/- 3.1 vs 18.9 +/- 2.7 mumol/ml/h), differences in lipoprotein levels were observed between transgenic and control mice receiving the same chow diet. Male transgenic mice of line C had significantly higher HDL cholesterol than control mice (76.4 +/- 4.6 vs 71.9 +/- 7.0 mg/dl, p < 0.05) and the male transgenic mice of lines A and C had a significantly lower non-HDL cholesterol (15.1 +/- 4.1 and 15.6 +/- 4.7 vs 20.9 +/- 5.5 mg/dl, P < 0.01 and P < 0.02) and a significantly higher HDL cholesterol/non-HDL cholesterol ratio than the control mice (5.3 +/- 1.3 and 5.5 +/- 2.2 vs 3.9 +/- 1.9 mg/dl, P < 0.01 and P < 0.02). Female mice from transgenic line C had higher HDL cholesterol than control mice (64.6 +/- 4.8 vs 57.4 +/- 5.1 mg/dl, P < 0.01) while female mice from line A tended to have higher HDL cholesterol/non-HDL cholesterol ratio than control mice (5.5 +/- 3.7 vs 3.8 +/- 1.4). These observations suggest that expression of PLTP in peripheral tissues play an important role in lipoprotein metabolism. Expression of human PLTP produced a more favorable lipoprotein profile and thus, enhanced expression of PLTP could potentially retard atherosclerosis.
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Affiliation(s)
- J J Albers
- Department of Medicine, University of Washington, Seattle 98103-9103 USA
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49
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Abstract
The B apolipoproteins, apo-B48 and apo-B100, are key proteins in mammalian lipoprotein metabolism and are components of all classes of lipoproteins considered to be atherogenic. Our laboratory has generated an array of genetically modified mice for studying apo-B biology. Using gene targeting in mouse embryonic stem cells, we have generated apo-B-deficient mice. Heterozygotes had low plasma levels of apo-B and cholesterol; homozygotes died early in embryonic development, most likely because the absence of lipoprotein secretion by the yolk sac interfered with the delivery of lipid nutrients to the developing embryo. We have also generated human apo-B transgenic mice with an 80-kb genomic DNA fragment spanning the entire human apo-B gene; those mice had markedly increased plasma levels of low density lipoprotein cholesterol and exhibited increased susceptibility to atherosclerosis. The human apo-B transgenic mice have also yielded insights regarding the regulation of apo-B expression in different tissues. Although the 80-kb transgene contained nearly 20 kb of 5' and 3' flanking sequences and was expressed at high levels in the liver, no transgene expression was detectable in the intestine. Subsequent transgenic mouse studies have demonstrated that the expression of the apo-B gene in the intestine is controlled by DNA sequences that are very distant from the structural gene. Transgenic mice have also proved useful for studying apo-B structure/function relationships. By expressing mutant forms of human apo B in transgenic mice, we have examined the structural features of the apo-B molecule that are required for lipoprotein (a) formation. We have demonstrated that the carboxyl terminal cystine residue of apo-B100, cysteine-4326, is required for apo-B100's disulfide linkage with apo(a) to form lipoprotein (a). Finally, we have used gene targeting techniques to generate mice that synthesize exclusively apo-B48 (apo B48-only mice) and mice that synthesize exclusively apo-B100 (apo-B100 only mice): These mice have helped to clarify the unique metabolic roles of the two apo-B proteins.
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Affiliation(s)
- S G Young
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94141-9100, USA
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