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Conlon DM, Schneider CV, Ko YA, Rodrigues A, Guo K, Hand NJ, Rader DJ. Sortilin restricts secretion of apolipoprotein B-100 by hepatocytes under stressed but not basal conditions. J Clin Invest 2022; 132:144334. [PMID: 35113816 PMCID: PMC8920325 DOI: 10.1172/jci144334] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 02/02/2022] [Indexed: 12/02/2022] Open
Abstract
Genetic variants at the SORT1 locus in humans, which cause increased SORT1 expression in the liver, are significantly associated with reduced plasma levels of LDL cholesterol and apolipoprotein B (apoB). However, the role of hepatic sortilin remains controversial, as genetic deletion of sortilin in mice has resulted in variable and conflicting effects on apoB secretion. Here, we found that Sort1-KO mice on a chow diet and several Sort1-deficient hepatocyte lines displayed no difference in apoB secretion. When these models were challenged with high-fat diet or ER stress, the loss of Sort1 expression resulted in a significant increase in apoB-100 secretion. Sort1-overexpression studies yielded reciprocal results. Importantly, carriers of SORT1 variant with diabetes had larger decreases in plasma apoB, TG, and VLDL and LDL particle number as compared with people without diabetes with the same variants. We conclude that, under basal nonstressed conditions, loss of sortilin has little effect on hepatocyte apoB secretion, whereas, in the setting of lipid loading or ER stress, sortilin deficiency leads to increased apoB secretion. These results are consistent with the directionality of effect in human genetics studies and suggest that, under stress conditions, hepatic sortilin directs apoB toward lysosomal degradation rather than secretion, potentially serving as a quality control step in the apoB secretion pathway in hepatocytes.
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Affiliation(s)
- Donna M Conlon
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Carolin V Schneider
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Yi-An Ko
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Amrith Rodrigues
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Kathy Guo
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Nicholas J Hand
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Daniel J Rader
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
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2
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Vilar-Gomez E, Gawrieh S, Liang T, McIntyre AD, Hegele RA, Chalasani N. Interrogation of selected genes influencing serum LDL-Cholesterol levels in patients with well characterized NAFLD. J Clin Lipidol 2021; 15:275-291. [PMID: 33454241 PMCID: PMC8187295 DOI: 10.1016/j.jacl.2020.12.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Revised: 12/07/2020] [Accepted: 12/23/2020] [Indexed: 12/28/2022]
Abstract
BACKGROUND The clinical significance of rare mutations in LDL metabolism genes on nonalcoholic fatty liver disease (NAFLD) severity is not well understood. OBJECTIVE To examine the significance of mutations in LDL metabolism genes including apolipoprotein B (APOB), proprotein convertase subtilisin kexin 9 (PCSK9) and LDL receptor (LDLR) in patients with NAFLD. METHODS Patients with biopsy-confirmed NAFLD from the NASH Clinical Research Network studies were stratified into 3 groups of LDL-C (≤50 mg/dL, 130-150 mg/dL, ≥ 190 mg/dL) and then 120 (40 per group) were randomly selected from the strata. We examined the presence of mutations on LDL genes and analyzed its association with selected NAFLD-related features. Multivariable analyses were adjusted for age, race, gender and use of statins. RESULTS Among 40 patients with LDL-C ≤ 50 mg/dL, 7 (18%) patients had heterozygous variants in APOB and 2 had heterozygous variants in PCSK9 (5%). We also found heterozygous mutations in 3 (8%) patients with LDL-C ≥ 190 mg/dL; 2 and 1 located in LDLR and APOE genes, respectively. Compared to wild-type controls with LDL-C ≤ 50, APOB carriers displayed higher levels of alanine aminotransferase (85.86 ± 35.14 U/L vs 45.61 ± 20.84 U/L, Adj. P = 0.002) and steatosis >66% (57% vs 24%, Adj. P = 0.050). These associations remained statistically significant after excluding statin users. Other histological features of NAFLD severity were not different between wild-type controls and APOB mutation carriers. CONCLUSION Mutations in the APOB gene are common among NAFLD patients with very low LDL-C and may be associated with increased aminotransferase levels and steatosis severity.
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Affiliation(s)
- Eduardo Vilar-Gomez
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Samer Gawrieh
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Tiebing Liang
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Adam D McIntyre
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Robert A Hegele
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Department of Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Naga Chalasani
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
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3
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Payolla TB, Teixeira CJ, Sato FT, Murata GM, Zonta GA, Sodré FS, Campos CV, Mesquita FN, Anhê GF, Bordin S. In Utero Dexamethasone Exposure Exacerbates Hepatic Steatosis in Rats That Consume Fructose During Adulthood. Nutrients 2019; 11:nu11092114. [PMID: 31491968 PMCID: PMC6770256 DOI: 10.3390/nu11092114] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 08/10/2019] [Accepted: 08/21/2019] [Indexed: 12/12/2022] Open
Abstract
Distinct environmental insults might interact with fructose consumption and contribute to the development of metabolic disorders. To address whether in utero glucocorticoid exposure and fructose intake modulate metabolic responses, adult female Wistar rats were exposed to dexamethasone (DEX) during pregnancy, and the offspring were administered fructose at a later time. Briefly, dams received DEX during the third period of pregnancy, while control dams remained untreated. Offspring born to control and DEX-treated mothers were defined as CTL-off and DEX-off, respectively, while untreated animals were designated CTL-off-CTL and DEX-off-CTL. CLT-off and DEX-off treated with 10% fructose in the drinking water for 8 weeks are referred to as CTL-off-FRU and DEX-off-FRU. We found that fructose promoted glucose intolerance and whole-body gluconeogenesis in both CTL-off-FRU and DEX-off-FRU animals. On the other hand, hepatic lipid accumulation was significantly stimulated in DEX-off-FRU rats when compared to the CTL-off-FRU group. The DEX-off-FRU group also displayed impaired very-low-density lipoprotein (VLDL) production and reduced hepatic expression of apoB, mttp, and sec22b. DEX-off-FRU has lower hepatic levels of autophagy markers. Taken together, our results support the unprecedented notion that in utero glucocorticoid exposure exacerbates hepatic steatosis caused by fructose consumption later in life.
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Affiliation(s)
- Tanyara B Payolla
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil
| | - Caio J Teixeira
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas, Sao Paulo 13083-887, Brazil
| | - Fabio T Sato
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil
| | - Gilson M Murata
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil
| | - Gizela A Zonta
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil
| | - Frhancielly S Sodré
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil
| | - Carolina V Campos
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil
| | - Filiphe N Mesquita
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas, Sao Paulo 13083-887, Brazil
| | - Gabriel F Anhê
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas, Sao Paulo 13083-887, Brazil
| | - Silvana Bordin
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil.
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4
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Hartz J, Hegele RA, Wilson DP. Low LDL cholesterol—Friend or foe? J Clin Lipidol 2019; 13:367-373. [DOI: 10.1016/j.jacl.2019.05.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Revised: 05/09/2019] [Accepted: 05/10/2019] [Indexed: 01/19/2023]
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5
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Vicente JM, Teixeira CJ, Santos-Silva JC, de Souza DN, Tobar N, Furtuoso FS, Adabo IG, Sodré FS, Murata G, Bordin S, Anhê GF. The absence of lactation after pregnancy induces long-term lipid accumulation in maternal liver of mice. Life Sci 2019; 217:261-270. [DOI: 10.1016/j.lfs.2018.12.026] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Revised: 12/11/2018] [Accepted: 12/14/2018] [Indexed: 01/17/2023]
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6
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Levy E. Insights from human congenital disorders of intestinal lipid metabolism. J Lipid Res 2014; 56:945-62. [PMID: 25387865 DOI: 10.1194/jlr.r052415] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Indexed: 12/24/2022] Open
Abstract
The intestine must challenge the profuse daily flux of dietary fat that serves as a vital source of energy and as an essential component of cell membranes. The fat absorption process takes place in a series of orderly and interrelated steps, including the uptake and translocation of lipolytic products from the brush border membrane to the endoplasmic reticulum, lipid esterification, Apo synthesis, and ultimately the packaging of lipid and Apo components into chylomicrons (CMs). Deciphering inherited disorders of intracellular CM elaboration afforded new insight into the key functions of crucial intracellular proteins, such as Apo B, microsomal TG transfer protein, and Sar1b GTPase, the defects of which lead to hypobetalipoproteinemia, abetalipoproteinemia, and CM retention disease, respectively. These "experiments of nature" are characterized by fat malabsorption, steatorrhea, failure to thrive, low plasma levels of TGs and cholesterol, and deficiency of liposoluble vitamins and essential FAs. After summarizing and discussing the functions and regulation of these proteins for reader's comprehension, the current review focuses on their specific roles in malabsorptions and dyslipidemia-related intestinal fat hyperabsorption while dissecting the spectrum of clinical manifestations and managements. The influence of newly discovered proteins (proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 protein) on fat absorption has also been provided. Finally, it is stressed how the overexpression or polymorphism status of the critical intracellular proteins promotes dyslipidemia and cardiometabolic disorders.
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Affiliation(s)
- Emile Levy
- Research Centre, CHU Sainte-Justine and Department of Nutrition, Université de Montréal, Montreal, Quebec H3T 1C5, Canada
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7
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Katsanos CS. Clinical considerations and mechanistic determinants of postprandial lipemia in older adults. Adv Nutr 2014; 5:226-34. [PMID: 24829469 PMCID: PMC4013175 DOI: 10.3945/an.113.004903] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The typical diet of individuals in Western societies results in metabolic responses associated with fed-state fat metabolism for most of the daily life of the individual. This fat metabolism is characterized specifically by an increase in the concentration of plasma lipids, primarily triglycerides. Increased postprandial lipemia, which is typically observed in older individuals (i.e., >65 y old), has now emerged as an important correlate of cardiovascular disease risk. An understanding of the mechanisms contributing to the increased postprandial lipemia in older individuals becomes, therefore, of particular clinical importance in any effort to explain and address the well-documented increase in cardiovascular disease risk as individuals age. Current evidence points to an increase in the accumulation of ingested lipid in lipoprotein particles of hepatic origin, together with an overall accumulation of lipid in these lipoproteins during the postprandial period, as primary contributors to the postprandial lipemia in older persons. When this evidence is considered together with the evidence suggesting large atherogenic potential of lipoproteins of hepatic origin, this can, at least in part, explain the increased risk of cardiovascular disease in older individuals. Understanding changes in the metabolism of ingested fat in the immediate postprandial period with advancing age, and how lifestyle interventions such as diet and physical exercise can ameliorate the increase in postprandial lipemia in older individuals, is important in order to address the increased cardiovascular disease risk in this particularly affected and growing segment of the population.
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8
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Hesse D, Radloff K, Jaschke A, Lagerpusch M, Chung B, Tailleux A, Staels B, Schürmann A. Hepatic trans-Golgi action coordinated by the GTPase ARFRP1 is crucial for lipoprotein lipidation and assembly. J Lipid Res 2013; 55:41-52. [PMID: 24186947 DOI: 10.1194/jlr.m040089] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The liver is a major organ in whole body lipid metabolism and malfunctioning can lead to various diseases including dyslipidemia, fatty liver disease, and type 2 diabetes. Triglycerides and cholesteryl esters are packed in the liver as very low density lipoproteins (VLDLs). Generation of these lipoproteins is initiated in the endoplasmic reticulum and further maturation likely occurs in the Golgi. ADP-ribosylation factor-related protein 1 (ARFRP1) is a small trans-Golgi-associated guanosine triphosphatase (GTPase) that regulates protein sorting and is required for chylomicron lipidation and assembly in the intestine. Here we show that the hepatocyte-specific deletion of Arfrp1 (Arfrp1(liv-/-)) results in impaired VLDL lipidation leading to reduced plasma triglyceride levels in the fasted state as well as after inhibition of lipoprotein lipase activity by Triton WR-1339. In addition, the concentration of ApoC3 that comprises 40% of protein mass of secreted VLDLs is markedly reduced in the plasma of Arfrp1(liv-/-) mice but accumulates in the liver accompanied by elevated triglycerides. Fractionation of Arfrp1(liv-/-) liver homogenates reveals more ApoB48 and a lower concentration of triglycerides in the Golgi compartments than in the corresponding fractions from control livers. In conclusion, ARFRP1 and the Golgi apparatus play an important role in lipoprotein maturation in the liver by influencing lipidation and assembly of proteins to the lipid particles.
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Affiliation(s)
- Deike Hesse
- Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, D-14558 Nuthetal, Germany
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9
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Lam MCW, Singham J, Hegele RA, Riazy M, Hiob MA, Francis G, Steinbrecher UP. Familial hypobetalipoproteinemia-induced nonalcoholic steatohepatitis. Case Rep Gastroenterol 2012; 6:429-37. [PMID: 22855658 PMCID: PMC3398101 DOI: 10.1159/000339761] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Familial hypobetalipoproteinemia (FHBL) is a rare genetic disorder of lipid metabolism that is associated with abnormally low serum levels of low-density lipoprotein (LDL) cholesterol and apolipoprotein B. It is an autosomal co-dominant disorder, and depending on zygosity, the clinical manifestations may vary from none to neurological, endocrine, hematological or liver dysfunction. Nonalcoholic fatty liver disease is common in persons with FHBL, however progression to nonalcoholic steatohepatitis is unusual. We describe here a patient with a novel APOB mutation, V703I, which appears to contribute to the severity of the FHBL phenotype. He had liver enzyme abnormalities, increased echogenicity of the liver consistent with steatosis, very low LDL cholesterol at 0.24 mmol/l (normal 1.8–3.5 mmol/l) and an extremely low apolipoprotein B level of 0.16 g/l (normal 0.6–1.2 g/l). APOB gene sequencing revealed him to be a compound heterozygote with two mutations (R463W and V703I). APOB R463W has previously been reported to cause FHBL. Genetic sequencing of his first-degree relatives identified the APOB V703I mutation in his normolipidemic brother and father and the APOB R463W mutation in his mother and sister, both of whom have very low LDL cholesterol levels. These results suggest that the APOB V703I mutation alone does not cause the FHBL phenotype. However, it is possible that it has a contributory role to a more aggressive phenotype in the presence of APOB R463W.
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Affiliation(s)
- Mindy C W Lam
- Divisions of Gastroenterology, University of British Columbia, Vancouver, B.C
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10
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11
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Chen Z, Norris JY, Finck BN. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) stimulates VLDL assembly through activation of cell death-inducing DFFA-like effector B (CideB). J Biol Chem 2010; 285:25996-6004. [PMID: 20551328 DOI: 10.1074/jbc.m110.141598] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Abnormalities in very low density lipoprotein (VLDL) assembly and secretion impact intrahepatic lipid homeostasis, plasma lipoprotein profile, and energy metabolism of distal peripheral tissues. We have evaluated the role of the transcriptional coactivator, the peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), in VLDL assembly and secretion. PGC-1alpha overexpression in HepG2 cells led to diminished rates of triglyceride (TG) synthesis but strongly stimulated VLDL-TG secretion, markedly increasing the efficiency of secretion of newly synthesized TG. PGC-1alpha overexpression increased the rate of secretion of apoB100 and promoted secretion of larger, less dense VLDL particles. PGC-1alpha overexpression in intact mouse liver also stimulated rates of VLDL TG secretion and attenuated hepatic TG accumulation resulting from high fat diet feeding. To determine the molecular mechanisms mediating the effect of PGC-1alpha on VLDL assembly, we evaluated the expression of several candidate mediators known to be involved in VLDL assembly or hepatic lipid homeostasis. Cell death-inducing DFFA-like effector B (CideB) expression was greatly induced by PGC-1alpha, and siRNA against CideB reversed the effects of PGC-1alpha on the secretion of TG and VLDL-sized particles by HepG2 cells, indicating that CideB is a critical mediator of stimulatory effects of PGC-1alpha on VLDL secretion. Collectively, these data suggest that PGC-1alpha plays an important role in partitioning cytoplasmic TG toward the VLDL secretory compartments and promoting VLDL secretion via transcriptional induction of CideB.
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Affiliation(s)
- Zhouji Chen
- Division of Geriatrics and Nutritional Science, Department of Medicine, Washington University School of Medicine, St Louis, Missouri 63110, USA.
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12
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Hooper AJ, van Bockxmeer FM, Burnett JR. Monogenic Hypocholesterolaemic Lipid Disorders and Apolipoprotein B Metabolism. Crit Rev Clin Lab Sci 2008; 42:515-45. [PMID: 16390683 DOI: 10.1080/10408360500295113] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The study of apolipoprotein (apo) B metabolism is central to our understanding of human lipoprotein metabolism. Moreover, the assembly and secretion of apoB-containing lipoproteins is a complex process. Increased plasma concentrations of apoB-containing lipoproteins are an important risk factor for the development of atherosclerotic coronary heart disease. In contrast, decreased levels of, but not the absence of, these apoB-containing lipoproteins is associated with resistance to atherosclerosis and potential long life. The study of inherited monogenic dyslipidaemias has been an effective means to elucidate key metabolic steps and biologically relevant mechanisms. Naturally occurring gene mutations in affected families have been useful in identifying important domains of apoB and microsomal triglyceride transfer protein (MTP) governing the metabolism of apoB-containing lipoproteins. Truncation-causing mutations in the APOB gene cause familial hypobetalipoproteinaemia, whereas mutations in MTP result in abetalipoproteinaemia; both rare conditions are characterised by marked hypocholesterolaemia. The purpose of this review is to examine the role of apoB in lipoprotein metabolism and to explore the key biochemical, clinical, metabolic and genetic features of the monogenic hypocholesterolaemic lipid disorders affecting apoB metabolism.
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Affiliation(s)
- Amanda J Hooper
- School of Surgery and Pathology, University of Western Australia, Crawley, Australia
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13
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Chen Z, Newberry EP, Norris JY, Xie Y, Luo J, Kennedy SM, Davidson NO. ApoB100 is required for increased VLDL-triglyceride secretion by microsomal triglyceride transfer protein in ob/ob mice. J Lipid Res 2008; 49:2013-22. [PMID: 18519977 DOI: 10.1194/jlr.m800240-jlr200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Microsomal triglyceride transfer protein (Mttp) is a key player in the assembly and secretion of hepatic very low density lipoproteins (VLDL). Here we determined the effects of Mttp overexpression on hepatic triglyceride (TG) and VLDL secretion in leptin-deficient (ob/ob) mice, specifically in relation to apolipoproteinB (apoB) isoforms. We crossed Apobec1(-/-) mice with congenic ob/ob mice to generate apoB100-only ob/ob mice (A-ob/ob). The obesity phenotype in both genotypes was similar, but A-ob/ob mice had greater hepatic TG content. Administration of recombinant adenovirus expressing murine Mttp cDNA (Ad-mMTP) increased hepatic Mttp content and activity and increased hepatic VLDL-TG secretion in A-ob/ob mice. However, despite equivalent overexpression of Mttp, there was no change in VLDL-TG secretion in ob/ob mice in a wild-type Apobec1 background. Metabolic labeling studies in primary hepatocytes from A-ob/ob mice demonstrated that Ad-mMTP increased triglyceride secretion without changing the synthesis and secretion of apoB100, suggesting greater incorporation of TG into existing VLDL particles rather than increased particle number. Ad-mMTP administration failed to increase hepatic VLDL secretion in lean Apobec1(-/-) mice or controls. By contrast, VLDL secretion increased and hepatic TG content decreased following Ad-mMTP administration to human APOB transgenic mice crossed into the Apobec1(-/-) line. These findings demonstrate that Ad-mMTP increases murine hepatic VLDL-TG secretion only in the apoB100 background, and even then only in situations with either increased hepatic TG accumulation or increased apoB100 expression.
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Affiliation(s)
- Zhouji Chen
- Center for Human Nutrition, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
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14
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Degrace P, Demizieux L, Du ZY, Gresti J, Caverot L, Djaouti L, Jourdan T, Moindrot B, Guilland JC, Hocquette JF, Clouet P. Regulation of Lipid Flux between Liver and Adipose Tissue during Transient Hepatic Steatosis in Carnitine-depleted Rats. J Biol Chem 2007; 282:20816-26. [PMID: 17496329 DOI: 10.1074/jbc.m611391200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rats with carnitine deficiency due to trimethylhydrazinium propionate (mildronate) administered at 80 mg/100 g body weight per day for 10 days developed liver steatosis only upon fasting. This study aimed to determine whether the transient steatosis resulted from triglyceride accumulation due to the amount of fatty acids preserved through impaired fatty acid oxidation and/or from up-regulation of lipid exchange between liver and adipose tissue. In liver, mildronate decreased the carnitine content by approximately 13-fold and, in fasted rats, lowered the palmitate oxidation rate by 50% in the perfused organ, increased 9-fold the triglyceride content, and doubled the hepatic very low density lipoprotein secretion rate. Concomitantly, triglyceridemia was 13-fold greater than in controls. Hepatic carnitine palmitoyltransferase I activity and palmitate oxidation capacities measured in vitro were increased after treatment. Gene expression of hepatic proteins involved in fatty acid oxidation, triglyceride formation, and lipid uptake were all increased and were associated with increased hepatic free fatty acid content in treated rats. In periepididymal adipose tissue, mildronate markedly increased lipoprotein lipase and hormone-sensitive lipase activities in fed and fasted rats, respectively. On refeeding, carnitine-depleted rats exhibited a rapid decrease in blood triglycerides and free fatty acids, then after approximately 2 h, a marked drop of liver triglycerides and a progressive decrease in liver free fatty acids. Data show that up-regulation of liver activities, peripheral lipolysis, and lipoprotein lipase activity were likely essential factors for excess fat deposit and release alternately occurring in liver and adipose tissue of carnitine-depleted rats during the fed/fasted transition.
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Affiliation(s)
- Pascal Degrace
- UMR 866 INSERM-UB, Equipe Physiopathologie des dyslipidémies, Faculté des Sciences, 21000 Dijon, France
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15
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Blanco-Rodríguez M, Muñoz-Calvo MT, Martos-Moreno GA, Abad-Pérez E, Argente-Oliver J. [Familial hypobetalipoproteinemia secondary to a mutation in the apolipoprotein B gene]. An Pediatr (Barc) 2007; 66:535-7. [PMID: 17517208 DOI: 10.1157/13102518] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Familial hypobetalipoproteinemia (FHB) is a rare genetically heterogeneous disorder provoking abnormally low serum levels of apoprotein (apo) B, total cholesterol, and low-density lipoprotein (LDL-C). Patients carrying heterozygous mutations in the APOB (2p24) gene are usually asymptomatic, but homozygous mutations cause clinical disturbances as a result of intestinal fat malabsorption and fat-soluble vitamin deficiency. We present an asymptomatic boy, aged 8 years and 7 months, with low serum levels of apo-B, total cholesterol, triglyceride, LDL-C and very low-density lipoprotein (VLDL-C), as well as vitamin E deficiency. Three asymptomatic relatives also exhibited low apo-B, total cholesterol and LDL-C levels. The APOB (2p24) gene was fully sequenced, demonstrating a heterozygous mutation in exon 26 (G --> T) in all four members of this family. Familial genetic studies in FHB could be useful in the early detection and treatment of homozygous carriers.
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Affiliation(s)
- M Blanco-Rodríguez
- Servicio de Endocrinología, Departamento de Pediatría, Hospital Infantil Universitario Niño Jesús, Universidad Autónoma de Madrid, Spain
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16
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Bock HH, Herz J, May P. Conditional animal models for the study of lipid metabolism and lipid disorders. Handb Exp Pharmacol 2007:407-39. [PMID: 17203665 DOI: 10.1007/978-3-540-35109-2_17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The advent of technologies that allow conditional mutagenesis has revolutionized our ability to explore gene functions and to establish animal models of human diseases. Both aspects have proven to be of particular importance in the study of lipid-related disorders. Classical approaches to gene inactivation by conventional gene targeting strategies have been successfully applied to generate animal models like the LDL receptor- and the apolipoprotein E-knockout mice, which are still widely used to study diverse aspects of atherosclerosis, lipid transport, and neurodegenerative disease. In many cases, however, simply inactivating the gene of interest has resulted in early lethal or complex phenotypes which are difficult to interpret. In recent years, additional tools have therefore been developed that allow the spatiotemporally controlled manipulation of the genome, as described in detail in Part I of this volume. Our aim is to provide an exemplary survey of the application of different conditional mutagenesis techniques in lipid research in order to illustrate their potential to unravel physiological functions of a broad range of genes involved in lipid homeostasis.
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Affiliation(s)
- H H Bock
- Zentrum für Neurowissenschaften, Universität Freiburg, Albertstrasse 23, 79104 Freiburg, Germany.
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Sankatsing RR, Fouchier SW, de Haan S, Hutten BA, de Groot E, Kastelein JJP, Stroes ESG. Hepatic and cardiovascular consequences of familial hypobetalipoproteinemia. Arterioscler Thromb Vasc Biol 2005; 25:1979-84. [PMID: 16002743 DOI: 10.1161/01.atv.0000176191.64314.07] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Individuals with familial hypobetalipoproteinemia (FHBL) have been reported to be prone to fatty liver disease (FLD). Conversely, the profound reduction of low-density lipoprotein (LDL) cholesterol in this disorder might decrease cardiovascular risk. In the present study, we assessed hepatic steatosis as well as noninvasive surrogate markers for cardiovascular disease (CVD) in subjects with FHBL and in matched controls. METHODS AND RESULTS Hepatic steatosis was assessed by abdominal ultrasonography. Carotid intima-media thickness (IMT) and distal common carotid arterial wall stiffness as surrogate markers for CVD risk were measured using high-resolution B-mode ultrasonography. Whereas transaminase levels were only modestly elevated, both prevalence (54% versus 29%; P=0.01) and severity of steatosis were significantly higher in FHBL individuals compared with controls. Despite similar IMT measurements, arterial stiffness was significantly lower in FHBL (P=0.04) compared with controls. Additionally, the increase in arterial stiffness as seen in the presence of traditional risk factors was attenuated, suggesting that very low levels of apoB-containing lipoproteins can negate the adverse effects of other risk factors on the vasculature. CONCLUSIONS FHBL is characterized by an increased prevalence and severity of fatty liver disease. The observed decreased level of arterial wall stiffness, most pronounced in the presence of nonlipid risk factors, is indicative of cardiovascular protection in these subjects.
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Affiliation(s)
- Raaj R Sankatsing
- Department of Vascular Medicine, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
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Lin X, Yue P, Xie Y, Davidson NO, Sakata N, Ostlund RE, Chen Z, Schonfeld G. Reduced intestinal fat absorptive capacity but enhanced susceptibility to diet-induced fatty liver in mice heterozygous for ApoB38.9 truncation. Am J Physiol Gastrointest Liver Physiol 2005; 289:G146-52. [PMID: 15790761 DOI: 10.1152/ajpgi.00309.2004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Fatty liver is prevalent in apolipoprotein B (apoB)-defective familial hypobetalipoproteinemia (FHBL). Similar to humans, mouse models of FHBL produced by gene targeting (apob(+/38.9)) manifest low plasma cholesterol and increased hepatic triglycerides (TG) even on a chow diet due to impaired hepatic VLDL-TG secretive capacity. Because apoB truncations shorter than apoB48 are expressed in the intestine, we examined whether FHBL mice may have limited capacity for intestinal dietary TG absorption. In addition, we investigated whether FHBL mice are more susceptible to diet-induced hepatic TG accumulation. Fat absorption capacity was impaired in apoB38.9 mice in a gene dose-dependent manner. Relative fractional fat absorption coefficients for apob(+/+), apob(+/38.9), and apob(38.9/38.9) were 1.00, 0.96, and 0.71, respectively. To raise hepatic TG, we fed high-fat (HF) and low-fat (LF) pellets. Hepatic TG level was observed in rank order: HF > LF > chow. On both LF and HF, liver TG level was higher in the apob(+/38.9) than in apob(+/+). Hepatic TG secretion remained impaired in the apob(+/38.9) on the HF diet. Thus the FHBL mice are more susceptible to diet-induced fatty liver despite relatively reduced intestinal TG absorption capacity on a HF diet.
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Affiliation(s)
- Xiaobo Lin
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Yue P, Isley WL, Harris WS, Rosipal S, Akin CD, Schonfeld G. Genetic variants of ApoE account for variability of plasma low-density lipoprotein and apolipoprotein B levels in FHBL. Atherosclerosis 2005; 178:107-13. [PMID: 15585207 DOI: 10.1016/j.atherosclerosis.2004.06.020] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2003] [Revised: 06/16/2004] [Accepted: 06/28/2004] [Indexed: 10/26/2022]
Abstract
We report two novel APOB mutations causing short apolipoprotein B (apoB) truncations undetectable in plasma and familial hypobetalipoproteinemia (FHBL). In Family 56, a 5 bp deletion in APOB exon 7 (870_874del5) causes a frame shift, converting tyrosine to a stop codon (Y220X) and producing an apoB-5 truncation. In Family 59, a point mutation (1941G>T) in APOB exon 13 converts glutamic acid to stop codon (E578X), specifying apoB-13. A recurrent mutation in exon 26 (4432delT) produces apoB-30.9 in Family 58. In some members of these families, we observed that plasma low-density lipoprotein (LDL) cholesterol and apoB levels were unusually low even for subjects heterozygous for FHBL. To ascertain whether genetic variations in apolipoprotein E (apoE) would explain some of the variations of apoB and LDL cholesterol levels, apoE genotypes were assessed in affected subjects from a total of eight FHBL families with short apoB truncations. Heterozygous FHBL with the epsilon3/epsilon4 genotype had 10-1 5mg/dL higher plasma LDL cholesterol and apoB levels compared to subjects with the epsilon2/epsilon3 and epsilon3/epsilon3 genotypes. The apoE genotype has been reported to account for approximately 10% of the variation of LDL cholesterol in the general population. It accounted for 15-60% of the variability of plasma LDL cholesterol or apoB levels in our FHBL subjects. The physiologic bases for the greater effects of apoE in FHBL remain to be determined.
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Affiliation(s)
- Pin Yue
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University, School of Medicine, St. Louis, MO 63110, USA
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Abstract
AbstractBackground: Plasma lipoproteins are important determinants of atherosclerosis. Apolipoprotein (apo) B is a large, amphipathic glycoprotein that plays a central role in human lipoprotein metabolism. Two forms of apoB are produced from the APOB gene by a unique posttranscriptional editing process: apoB-48, which is required for chylomicron production in the small intestine, and apoB-100, required for VLDL production in the liver. In addition to being the essential structural component of VLDL, apoB-100 is the ligand for LDL-receptor-mediated endocytosis of LDL particles.Content: The study of monogenic dyslipidemias has revealed important aspects of metabolic pathways. In this review, we discuss the regulation of apoB metabolism and examine how APOB gene defects can lead to both hypo- and hypercholesterolemia. The key clinical, metabolic, and genetic features of familial hypobetalipoproteinemia and familial ligand-defective apoB-100 are described.Summary: Missense mutations in the LDL-receptor-binding domain of apoB cause familial ligand-defective apoB-100, characterized by hypercholesterolemia and premature coronary artery disease. Other mutations in APOB can cause familial hypobetalipoproteinemia, characterized by hypocholesterolemia and resistance to atherosclerosis. These naturally occurring mutations reveal key domains in apoB and demonstrate how monogenic dyslipidemias can provide insight into biologically important mechanisms.
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Affiliation(s)
- Amanda J Whitfield
- School of Surgery and Pathology, University of Western Australia, Crawley
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Garbow JR, Lin X, Sakata N, Chen Z, Koh D, Schonfeld G. In vivo MRS measurement of liver lipid levels in mice. J Lipid Res 2004; 45:1364-71. [PMID: 15102892 DOI: 10.1194/jlr.d400001-jlr200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A magnetic resonance spectroscopy (MRS) procedure for in vivo measurement of lipid levels in mouse liver is described and validated. The method uses respiratory-gated, localized spectroscopy to collect proton spectra from voxels within the mouse liver. Bayesian probability theory analysis of these spectra allows the relative intensities of the lipid and water resonances within the liver to be accurately measured. All spectral data were corrected for measured spin-spin relaxation. A total of 48 mice were used in this study, including wild-type mice and two different transgenic mouse strains. Different groups of these mice were fed high-fat or low-fat diets or liquid diets with and without the addition of alcohol. Proton spectra were collected at baseline and, subsequently, every 4 weeks for up to 16 weeks. Immediately after the last MRS measurement, mice were killed and their livers analyzed for triglyceride level by conventional wet-chemistry methods. The excellent correlation between in vivo MRS and ex vivo wet-chemistry determinations of liver lipids validates the MRS method. These results clearly demonstrate that in vivo MRS will be an extremely valuable technique for longitudinal studies aimed at providing important insights into the genetic, environmental, and dietary factors affecting fat deposition and accumulation within the mouse liver.
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Affiliation(s)
- J R Garbow
- Department of Chemistry and Alvin J Siteman Cancer Center, Washington University, St. Louis, MO 63130, USA.
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