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Vitali C, Bajaj A, Nguyen C, Schnall J, Chen J, Stylianou K, Rader DJ, Cuchel M. A systematic review of the natural history and biomarkers of primary Lecithin:Cholesterol Acyltransferase (LCAT) deficiency. J Lipid Res 2022; 63:100169. [PMID: 35065092 PMCID: PMC8953693 DOI: 10.1016/j.jlr.2022.100169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 12/16/2021] [Accepted: 12/28/2021] [Indexed: 10/31/2022] Open
Abstract
Syndromes associated with LCAT deficiency, a rare autosomal recessive condition, include fish-eye disease (FED) and familial LCAT deficiency (FLD). FLD is more severe and characterized by early and progressive chronic kidney disease (CKD). No treatment is currently available for FLD, but novel therapeutics are under development. Furthermore, although biomarkers of LCAT deficiency have been identified, their suitability to monitor disease progression and therapeutic efficacy is unclear, as little data exist on the rate of progression of renal disease. Here, we systematically review observational studies of FLD, FED, and heterozygous subjects, which summarize available evidence on the natural history and biomarkers of LCAT deficiency, in order to guide the development of novel therapeutics. We identified 146 FLD and 53 FED patients from 219 publications, showing that both syndromes are characterized by early corneal opacity and markedly reduced HDL-C levels. Proteinuria/hematuria were the first signs of renal impairment in FLD, followed by rapid decline of renal function. Furthermore, LCAT activity toward endogenous substrates and the percentage of circulating esterified cholesterol (EC%) were the best discriminators between these two syndromes. In FLD, higher levels of total, non-HDL, and unesterified cholesterol were associated with severe CKD. We reveal a nonlinear association between LCAT activity and EC% levels, in which subnormal levels of LCAT activity were associated with normal EC%. This review provides the first step toward the identification of disease biomarkers to be used in clinical trials and suggests that restoring LCAT activity to subnormal levels may be sufficient to prevent renal disease progression.
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Fountoulakis N, Lioudaki E, Lygerou D, Dermitzaki EK, Papakitsou I, Kounali V, Holleboom AG, Stratigis S, Belogianni C, Syngelaki P, Stratakis S, Evangeliou A, Gakiopoulou H, Kuivenhoven JA, Wevers R, Dafnis E, Stylianou K. The P274S Mutation of Lecithin-Cholesterol Acyltransferase (LCAT) and Its Clinical Manifestations in a Large Kindred. Am J Kidney Dis 2019; 74:510-522. [PMID: 31103331 DOI: 10.1053/j.ajkd.2019.03.422] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2018] [Accepted: 03/02/2019] [Indexed: 12/25/2022]
Abstract
RATIONALE & OBJECTIVE Lecithin-cholesterol acyltransferase (LCAT) catalyzes the maturation of high-density lipoprotein. Homozygosity for loss-of-function mutations causes familial LCAT deficiency (FLD), characterized by corneal opacities, anemia, and renal involvement. This study sought to characterize kidney biopsy findings and clinical outcomes in a family with FLD. STUDY DESIGN Prospective observational study. SETTING & PARTICIPANTS 2 (related) index patients with clinically apparent FLD were initially identified. 110 of 122 family members who consented to genetic analysis were also studied. PREDICTORS Demographic and laboratory parameters (including lipid profiles and LCAT activity) and full sequence analysis of the LCAT gene. Kidney histologic examination was performed with samples from 6 participants. OUTCOMES Cardiovascular and renal events during a median follow-up of 12 years. Estimation of annual rate of decline in glomerular filtration rate. ANALYTICAL APPROACH Analysis of variance, linear regression analysis, and Fine-Gray competing-risk survival analysis. RESULTS 9 homozygous, 57 heterozygous, and 44 unaffected family members were identified. In all affected individuals, full sequence analysis of the LCAT gene revealed a mutation (c.820C>T) predicted to cause a proline to serine substitution at amino acid 274 (P274S). Homozygosity caused a complete loss of LCAT activity. Kidney biopsy findings demonstrated lipid deposition causing glomerular basement membrane thickening, mesangial expansion, and "foam-cell" infiltration of kidney tissue. Tubular atrophy, glomerular sclerosis, and complement fixation were associated with worse kidney outcomes. Estimated glomerular filtration rate deteriorated among homozygous family members at an average annual rate of 3.56 mL/min/1.73 m2. The incidence of cardiovascular and renal complications was higher among homozygous family members compared with heterozygous and unaffected members. Mild thrombocytopenia was a common finding among homozygous participants. LIMITATIONS The presence of cardiovascular disease was mainly based on medical history. CONCLUSIONS The P274S LCAT mutation was found to cause FLD with renal involvement. Tubular atrophy, glomerular sclerosis, and complement fixation were associated with a worse renal prognosis.
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Affiliation(s)
| | - Eirini Lioudaki
- Nephrology Department, Heraklion University Hospital, Crete, Greece
| | - Dimitra Lygerou
- Nephrology Department, Heraklion University Hospital, Crete, Greece
| | | | | | - Vasiliki Kounali
- Nephrology Department, Heraklion University Hospital, Crete, Greece
| | - Adriaan G Holleboom
- Department of Vascular Medicine, Academic Medical Center, Amsterdam, the Netherlands
| | - Spyros Stratigis
- Nephrology Department, Heraklion University Hospital, Crete, Greece
| | | | | | | | - Athanasios Evangeliou
- Papageorgiou General Hospital, Department of Pediatrics IV, Aristotle University of Thessaloniki, Thessalonika
| | - Hariklia Gakiopoulou
- Pathology Department, National and Kapodistrian University of Athens, Athens, Greece
| | | | - Ron Wevers
- Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Eugene Dafnis
- Nephrology Department, Heraklion University Hospital, Crete, Greece
| | - Kostas Stylianou
- Nephrology Department, Heraklion University Hospital, Crete, Greece.
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Korber M, Klein I, Daum G. Steryl ester synthesis, storage and hydrolysis: A contribution to sterol homeostasis. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:1534-1545. [DOI: 10.1016/j.bbalip.2017.09.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 08/25/2017] [Accepted: 09/05/2017] [Indexed: 02/01/2023]
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Manthei KA, Ahn J, Glukhova A, Yuan W, Larkin C, Manett TD, Chang L, Shayman JA, Axley MJ, Schwendeman A, Tesmer JJG. A retractable lid in lecithin:cholesterol acyltransferase provides a structural mechanism for activation by apolipoprotein A-I. J Biol Chem 2017; 292:20313-20327. [PMID: 29030428 DOI: 10.1074/jbc.m117.802736] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2017] [Revised: 09/15/2017] [Indexed: 12/12/2022] Open
Abstract
Lecithin:cholesterol acyltransferase (LCAT) plays a key role in reverse cholesterol transport by transferring an acyl group from phosphatidylcholine to cholesterol, promoting the maturation of high-density lipoproteins (HDL) from discoidal to spherical particles. LCAT is activated through an unknown mechanism by apolipoprotein A-I (apoA-I) and other mimetic peptides that form a belt around HDL. Here, we report the crystal structure of LCAT with an extended lid that blocks access to the active site, consistent with an inactive conformation. Residues Thr-123 and Phe-382 in the catalytic domain form a latch-like interaction with hydrophobic residues in the lid. Because these residues are mutated in genetic disease, lid displacement was hypothesized to be an important feature of apoA-I activation. Functional studies of site-directed mutants revealed that loss of latch interactions or the entire lid enhanced activity against soluble ester substrates, and hydrogen-deuterium exchange (HDX) mass spectrometry revealed that the LCAT lid is extremely dynamic in solution. Upon addition of a covalent inhibitor that mimics one of the reaction intermediates, there is an overall decrease in HDX in the lid and adjacent regions of the protein, consistent with ordering. These data suggest a model wherein the active site of LCAT is shielded from soluble substrates by a dynamic lid until it interacts with HDL to allow transesterification to proceed.
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Affiliation(s)
- Kelly A Manthei
- Life Sciences Institute and the Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Joomi Ahn
- MedImmune, Gaithersburg, Maryland 20878
| | - Alisa Glukhova
- Life Sciences Institute and the Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Wenmin Yuan
- Department of Pharmaceutical Sciences and Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109
| | | | - Taylor D Manett
- Life Sciences Institute and the Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Louise Chang
- Life Sciences Institute and the Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - James A Shayman
- Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109
| | | | - Anna Schwendeman
- Department of Pharmaceutical Sciences and Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109
| | - John J G Tesmer
- Life Sciences Institute and the Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109.
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Fotakis P, Kuivenhoven JA, Dafnis E, Kardassis D, Zannis VI. The Effect of Natural LCAT Mutations on the Biogenesis of HDL. Biochemistry 2015; 54:3348-59. [PMID: 25948084 DOI: 10.1021/acs.biochem.5b00180] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have investigated how the natural LCAT[T147I] and LCAT[P274S] mutations affect the pathway of biogenesis of HDL. Gene transfer of WT LCAT in LCAT(-/-) mice increased 11.8-fold the plasma cholesterol, whereas the LCAT[T147I] and LCAT[P274S] mutants caused a 5.2- and 2.9-fold increase, respectively. The LCAT[P274S] and the WT LCAT caused a monophasic distribution of cholesterol in the HDL region, whereas the LCAT[T147I] caused a biphasic distribution of cholesterol in the LDL and HDL region. Fractionation of plasma showed that the expression of WT LCAT increased plasma apoE and apoA-IV levels and shifted the distribution of apoA-I to lower densities. The LCAT[T147I] and LCAT[P274S] mutants restored partially apoA-I in the HDL3 fraction and LCAT[T147I] increased apoE in the VLD/IDL/LDL fractions. The in vivo functionality of LCAT was further assessed based on is its ability to correct the aberrant HDL phenotype that was caused by the apoA-I[L159R]FIN mutation. Co-infection of apoA-I(-/-) mice with this apoA-I mutant and either of the two mutant LCAT forms restored only partially the HDL biogenesis defect that was caused by the apoA-I[L159R]FIN and generated a distinct aberrant HDL phenotype.
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Affiliation(s)
- Panagiotis Fotakis
- †Molecular Genetics, Boston University School of Medicine, 700 Albany Street, W509, Boston, Massachusetts 02118-2394, United States.,‡Department of Biochemistry, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology of Hellas, GR-74100 Heraklion, Greece
| | - Jan Albert Kuivenhoven
- §Department of Pediatrics, Section Molecular Genetics, Groningen, University of Groningen, University Medical Center Groningen, 9700 Groningen, The Netherlands
| | - Eugene Dafnis
- ∥Department of Nephrology, University of Crete Medical School, GR-74100 Heraklion, Greece
| | - Dimitris Kardassis
- ‡Department of Biochemistry, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology of Hellas, GR-74100 Heraklion, Greece
| | - Vassilis I Zannis
- †Molecular Genetics, Boston University School of Medicine, 700 Albany Street, W509, Boston, Massachusetts 02118-2394, United States
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Affiliation(s)
- Federico Oldoni
- From the Departments of Molecular Genetics (F.O., J.A.K.) and Genetics (R.J.S.), University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Richard J. Sinke
- From the Departments of Molecular Genetics (F.O., J.A.K.) and Genetics (R.J.S.), University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Jan Albert Kuivenhoven
- From the Departments of Molecular Genetics (F.O., J.A.K.) and Genetics (R.J.S.), University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
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Kunnen S, Van Eck M. Lecithin:cholesterol acyltransferase: old friend or foe in atherosclerosis? J Lipid Res 2012; 53:1783-99. [PMID: 22566575 PMCID: PMC3413220 DOI: 10.1194/jlr.r024513] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Revised: 04/23/2012] [Indexed: 11/20/2022] Open
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme that catalyzes the esterification of free cholesterol in plasma lipoproteins and plays a critical role in high-density lipoprotein (HDL) metabolism. Deficiency leads to accumulation of nascent preβ-HDL due to impaired maturation of HDL particles, whereas enhanced expression is associated with the formation of large, apoE-rich HDL(1) particles. In addition to its function in HDL metabolism, LCAT was believed to be an important driving force behind macrophage reverse cholesterol transport (RCT) and, therefore, has been a subject of great interest in cardiovascular research since its discovery in 1962. Although half a century has passed, the importance of LCAT for atheroprotection is still under intense debate. This review provides a comprehensive overview of the insights that have been gained in the past 50 years on the biochemistry of LCAT, the role of LCAT in lipoprotein metabolism and the pathogenesis of atherosclerosis in animal models, and its impact on cardiovascular disease in humans.
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Affiliation(s)
- Sandra Kunnen
- Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands
| | - Miranda Van Eck
- Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands
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The role of lecithin:cholesterol acyltransferase in the modulation of cardiometabolic risks - a clinical update and emerging insights from animal models. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:654-9. [PMID: 22326749 DOI: 10.1016/j.bbalip.2011.12.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2011] [Revised: 12/20/2011] [Accepted: 12/22/2011] [Indexed: 11/22/2022]
Abstract
Lecithin cholesterol acyltransferase (LCAT) is the key enzyme in mediating the esterification of cholesterol on circulating lipoproteins. It has long been suggested that LCAT plays a crucial role in reverse cholesterol transport, a process depicting the removal of cellular cholesterol through efflux to high density lipoproteins (HDL) and its delivery to the liver for eventual excretion from the body. Although loss-of-function LCAT mutations invariably result in profound HDL deficiency, the role of LCAT in atherogenesis continues to be clouded with controversy. Increasing number of large scale, population-based studies failed to detect an elevated cardiac risk with reduced blood levels of LCAT, suggesting that reduced LCAT activity may not be a risk factor nor a therapeutic target. More recent studies in human LCAT gene mutation carriers tend to suggest that atherogenicity in LCAT deficiency may be dependent on the nature of the mutations, providing plausible explanations for the otherwise contradictory findings. Genetic models of LCAT excess or deficiency yielded mixed findings. Despite its known profound effects on HDL and triglyceride metabolism, the role of LCAT in metabolic disorders, including obesity and diabetes, has not received much attention. Recent studies in LCAT deficient mouse models suggest that absence of LCAT may protect against insulin resistance, diabetes and obesity. Coordinated modulation of a number of anti-obesity and insulin sensitizing pathways has been implicated. Further studies to explore the role of LCAT in the modulation of cardiometabolic disorders and the underlying mechanisms are warranted.
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Holleboom AG, Kuivenhoven JA, Peelman F, Schimmel AW, Peter J, Defesche JC, Kastelein JJP, Hovingh GK, Stroes ES, Motazacker MM. High prevalence of mutations in LCAT in patients with low HDL cholesterol levels in The Netherlands: identification and characterization of eight novel mutations. Hum Mutat 2011; 32:1290-8. [PMID: 21901787 DOI: 10.1002/humu.21578] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Accepted: 07/04/2011] [Indexed: 12/13/2022]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is crucial to the maturation of high-density lipoprotein (HDL). Homozygosity for LCAT mutations underlies rare disorders characterized by HDL-cholesterol (HDL-c) deficiency while heterozygotes have half normal HDL-c levels. We studied the prevalence of LCAT mutations in referred patients with low HDL-c to better understand the molecular basis of low HDL-c in our patients. LCAT was sequenced in 98 patients referred for HDL-c <5th percentile and in four patients referred for low HDL-c and corneal opacities. LCAT mutations were highly prevalent: in 28 of the 98 participants (29%), heterozygosity for nonsynonymous mutations was identified while 18 patients carried the same mutation (p.T147I). The four patients with corneal opacity were compound heterozygotes. All previously identified mutations are documented to cause loss of catalytic activity. Nine novel mutations-c.402G>T (p.E134D), c.403T>A (p.Y135N), c.964C>T (p.R322C), c.296G>C (p.W99S), c.736G>T (p.V246F), c.802C>T (p.R268C), c.945G>A (p.W315X), c.1012C>T (p.L338F), and c.1039C>T (p.R347C)--were shown to be functional through in vitro characterization. The effect of several mutations on the core protein structure was studied by a three-dimensional (3D) model. Unlike previous reports, functional mutations in LCAT were found in 29% of patients with low HDL-c, thus constituting a common cause of low HDL-c in referred patients in The Netherlands.
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Affiliation(s)
- Adriaan G Holleboom
- Department of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands
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Holleboom AG, Kuivenhoven JA, van Olden CC, Peter J, Schimmel AW, Levels JH, Valentijn RM, Vos P, Defesche JC, Kastelein JJP, Hovingh GK, Stroes ESG, Hollak CEM. Proteinuria in early childhood due to familial LCAT deficiency caused by loss of a disulfide bond in lecithin:cholesterol acyl transferase. Atherosclerosis 2011; 216:161-5. [PMID: 21315357 DOI: 10.1016/j.atherosclerosis.2011.01.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2010] [Revised: 01/06/2011] [Accepted: 01/07/2011] [Indexed: 11/30/2022]
Abstract
INTRODUCTION Familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is a rare recessive disorder of cholesterol metabolism characterized by the absence of high density lipoprotein (HDL) and the triad of corneal opacification, hemolytic anemia and glomerulopathy. PATIENTS We here report on FLD in three siblings of a kindred of Moroccan descent with HDL deficiency. In all cases (17, 12 and 3 years of age) corneal opacification and proteinuria were observed. In the 17-year-old female proband, anemia with target cells was observed. RESULTS Homozygosity for a mutation in LCAT resulted in the exchange of cysteine to tyrosine at position 337, disrupting the second disulfide bond in LCAT. LCAT protein and activity were undetectable in the patients' plasma and in media of COS7 cells transfected with an expression vector with mutant LCAT cDNA. Upon treatment with an ACE inhibitor and a thiazide diuretic, proteinuria in the proband decreased from 6g to 2g/24h. CONCLUSION This is the first report that FLD can cause nephropathy at a very early age.
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Affiliation(s)
- A G Holleboom
- Department of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands.
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Rousset X, Vaisman B, Amar M, Sethi AA, Remaley AT. Lecithin: cholesterol acyltransferase--from biochemistry to role in cardiovascular disease. Curr Opin Endocrinol Diabetes Obes 2009; 16:163-71. [PMID: 19306528 PMCID: PMC2910390 DOI: 10.1097/med.0b013e328329233b] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PURPOSE OF REVIEW We discuss the latest findings on the biochemistry of lecithin : cholesterol acyltransferase (LCAT), the effect of LCAT on atherosclerosis, clinical features of LCAT deficiency, and the impact of LCAT on cardiovascular disease from human studies. RECENT FINDINGS Although there has been much recent progress in the biochemistry of LCAT and its effect on high-density lipoprotein metabolism, its role in the pathogenesis of atherosclerosis is still not fully understood. Studies from various animal models have revealed a complex interaction between LCAT and atherosclerosis that may be modified by diet and by other proteins that modify lipoproteins. Furthermore, the ability of LCAT to lower apoB appears to be the best way to predict its effect on atherosclerosis in animal models. Recent studies on patients with LCAT deficiency have shown a modest but significant increase in incidence of cardiovascular disease consistent with a beneficial effect of LCAT on atherosclerosis. The role of LCAT in the general population, however, has not revealed a consistent association with cardiovascular disease. SUMMARY Recent research findings from animal and human studies have revealed a potential beneficial role of LCAT in reducing atherosclerosis but additional studies are necessary to better establish the linkage between LCAT and cardiovascular disease.
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Affiliation(s)
- Xavier Rousset
- National Institutes of Health, National Heart, Lung and Blood Institute, Pulmonary and Vascular Medicine Branch, Lipoprotein Metabolism Section, Bethesda, MD. 20814
| | - Boris Vaisman
- National Institutes of Health, National Heart, Lung and Blood Institute, Pulmonary and Vascular Medicine Branch, Lipoprotein Metabolism Section, Bethesda, MD. 20814
| | - Marcelo Amar
- National Institutes of Health, National Heart, Lung and Blood Institute, Pulmonary and Vascular Medicine Branch, Lipoprotein Metabolism Section, Bethesda, MD. 20814
| | - Amar A. Sethi
- National Institutes of Health, National Heart, Lung and Blood Institute, Pulmonary and Vascular Medicine Branch, Lipoprotein Metabolism Section, Bethesda, MD. 20814
| | - Alan T. Remaley
- National Institutes of Health, National Heart, Lung and Blood Institute, Pulmonary and Vascular Medicine Branch, Lipoprotein Metabolism Section, Bethesda, MD. 20814
- To whom correspondence should be addressed: National Institutes of Health, National Heart, Lung and Blood Institute, Pulmonary and Vascular Medicine Branch, Lipoprotein Metabolism Section, 10 Center Dr. Bldg. 10/2C-433, Bethesda, MD. 20814, , 301-402-9796
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Hirsch-Reinshagen V, Donkin J, Stukas S, Chan J, Wilkinson A, Fan J, Parks JS, Kuivenhoven JA, Lütjohann D, Pritchard H, Wellington CL. LCAT synthesized by primary astrocytes esterifies cholesterol on glia-derived lipoproteins. J Lipid Res 2008; 50:885-93. [PMID: 19065001 DOI: 10.1194/jlr.m800584-jlr200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipid trafficking in the brain is essential for the maintenance and repair of neuronal membranes, especially after neurotoxic insults. However, brain lipid metabolism is not completely understood. In plasma, LCAT catalyses the esterification of free cholesterol on circulating lipoproteins, a key step in the maturation of HDL. Brain lipoproteins are apolipoprotein E (apoE)-containing, HDL-like particles secreted initially as lipid-poor discs by glial cells. LCAT is synthesized within the brain, suggesting that it may play a key role in the maturation of these lipoproteins. Here we demonstrate that astrocytes are the primary producers of brain LCAT. This LCAT esterifies free cholesterol on nascent apoE-containing lipopoproteins secreted from glia. ApoE is the major LCAT activator in glia-conditioned media (GCM), and both the cholesterol transporter ABCA1 and apoE are required to generate glial LCAT substrate particles. LCAT deficiency leads to the appearance of abnormal approximately 8 nm particles in GCM, and exogenous LCAT restores the lipoprotein particle distribution to the wild-type (WT) pattern. In vivo, complete LCAT deficiency results in a dramatic increase in apoE-HDL and reduced apolipoprotein A-I (apoA-I)-HDL in murine cerebrospinal fluid (CSF). These data show that brain LCAT esterifies cholesterol on glial-derived apoE-lipoproteins, and influences CSF apoE and apoA-I levels.
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Reshetnyak Y, Tchedre KT, Nair MP, Pritchard PH, Lacko AG. Structural differences between wild-type and fish eye disease mutant of lecithin:cholesterol acyltransferase. J Biomol Struct Dyn 2006; 24:75-82. [PMID: 16780378 DOI: 10.1080/07391102.2006.10507101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Fluorescence spectroscopy has been used to investigate the conformational changes that occur upon binding of wild type (WT) and mutant (Thr123Ile) lecithin:cholesterol acyltransferase (LCAT) to the potential substrates (dioleoyl-phosphatidyl choline [DOPC] and high density lipoprotein [HDL]). For a detailed analysis of structural differences between WT and mutant LCAT, we performed decompositional analysis of a set of tryptophan fluorescence spectra, measured at increasing concentrations of external quenchers (acrylamide and KI). The data obtained show that Thr123Ile mutation in LCAT leads to a conformation that is likely to be more rigid (less mobile/flexible) than that of the WT protein with a redistribution of charged residues around exposed tryptophan fluorophores. We propose that the redistribution of charged residues in mutant LCAT may be a major factor responsible for the dramatically reduced activity of the enzyme with HDL and reconstituted high density lipoprotein (rHDL).
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Affiliation(s)
- Yana Reshetnyak
- Department of Physics, University of Rhode Island, Kingston, Rhode Island 02881, USA.
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Lane SB, Tchedre KT, Nair MP, Thigpen AE, Lacko AG. Characterization of lecithin:cholesterol acyltransferase expressed in a human lung cell line. Protein Expr Purif 2005; 36:157-64. [PMID: 15249036 DOI: 10.1016/j.pep.2004.03.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2003] [Revised: 01/09/2004] [Indexed: 11/19/2022]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme for the transfer of mammalian cholesterol from peripheral tissues to the liver. In patients deficient in LCAT, serum cholesterol levels rise and can lead to corneal opacity, proteinuria, anemia, and kidney failure. As early as 1968, relatively low volume transfusion of normal plasma was shown to temporarily correct the abnormal lipoprotein profiles in LCAT-deficient patients. However, despite the cloning, study, and extensive expression of LCAT in mammalian cell lines, there is still no viable, clinical therapy for LCAT deficiency. The current study was initiated to provide a source of recombinant human LCAT for enzyme replacement therapy. Accordingly, human LCAT has been cloned and expressed for the first time in a human cell line. The recombinant LCAT secreted by these cells was purified by phenyl-Sepharose chromatography, analyzed to determine the nature of its glycosylation, and tested for its enzymatic properties. The activity and basic kinetic parameters for the enzyme were determined using both a fluorescent water-soluble substrate and a macromolecular (proteoliposome) substrate. The enzymatic properties and the carbohydrate components of the recombinant LCAT were all sufficiently similar to those of the circulating human plasma enzyme, suggesting that this source of LCAT may be appropriate for use in some form of enzyme replacement therapy.
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Zhu X, Herzenberg AM, Eskandarian M, Maguire GF, Scholey JW, Connelly PW, Ng DS. A novel in vivo lecithin-cholesterol acyltransferase (LCAT)-deficient mouse expressing predominantly LpX is associated with spontaneous glomerulopathy. THE AMERICAN JOURNAL OF PATHOLOGY 2004; 165:1269-78. [PMID: 15466392 PMCID: PMC3118835 DOI: 10.1016/s0002-9440(10)63386-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Complete lecithin cholesterol acyltransferase (LCAT) deficiency is a rare genetic cause of extreme reduction in high density lipoproteins and there is a high prevalence of chronic renal dysfunction that may progress to renal failure. Previous in vitro studies suggest the vesicular lipoprotein X (LpX) particles commonly seen in LCAT-deficient plasmas may be causative. To test this hypothesis, we have generated a novel murine model that selectively accumulate LpX in the circulation by cross breeding the sterol regulatory element binding protein (SREBP) 1a transgenic mice (S+) with the LCAT knockout (lcat-/-) mice. Fast protein liquid chromatography fractionation of pooled plasma lipids revealed that virtually all cholesterol is concentrated in the very low density lipoprotein (VLDL)-sized fractions. These fractions are enriched in free cholesterol and phospholipid but extremely poor in triglyceride. Electron microscopy of the d <1.063 g/ml fraction of the S+lcat-/- mice revealed abnormal large vesicular particles, suggestive of LpX. The S+lcat-/- mice developed glomerular lesions spontaneously evident at 6 months with glomerular and tubulointerstitial lipid-deposits. Immunohistochemical staining with RhoA showed marked positive focal staining in glomeruli in the S+lcat-/- mice and undetectable in the S+/lcat+/+ control. By 10 months of age, the kidneys showed progressive glomerular injury including segmental foam cell infiltrates, mesangial expansion, and hyalinosis. Renal abnormalities are very similar to those seen in human LCAT deficiency. We conclude that the selective high-level accumulation of plasma LpX in the S+lcat-/- mice is strongly associated with a spontaneous glomerulopathy, providing in vivo evidence that LpX contributes to the LCAT deficiency-related nephropathy.
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Affiliation(s)
- Xianghong Zhu
- Department of Medicine, St. Michael's Hospital West Annex 2-015, 38 Shuter Street, Toronto, Ontario M5B 1A6 Canada
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16
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Peelman F, Verschelde JL, Vanloo B, Ampe C, Labeur C, Tavernier J, Vandekerckhove J, Rosseneu M. Effects of natural mutations in lecithin:cholesterol acyltransferase on the enzyme structure and activity. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33339-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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17
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Adimoolam S, Jin L, Grabbe E, Shieh JJ, Jonas A. Structural and functional properties of two mutants of lecithin-cholesterol acyltransferase (T123I and N228K). J Biol Chem 1998; 273:32561-7. [PMID: 9829992 DOI: 10.1074/jbc.273.49.32561] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two naturally occurring mutants of human lecithin-cholesterol acyltransferase (LCAT), T123I and N228K, were expressed in COS-1 and Chinese hamster ovary cells, overproduced, and purified to homogeneity in order to study the structural and functional defects that lead to the LCAT deficiency phenotypes of these mutations. The mutants were expressed and secreted by transfected cells normally and had molecular weights and levels of glycosylation similar to wild type LCAT. The purified proteins (>98% purity) had almost indistinguishable structures and stabilities as determined by CD and fluorescence spectroscopy. Enzymatic activities and kinetic analysis of the pure enzyme forms showed that wild type LCAT and both mutants were reactive with the water-soluble substrate, p-nitrophenyl butyrate, indicating the presence of an intact core active site and catalytic triad. Both the T123I and N228K mutants had markedly depressed reactivity with reconstituted HDL (rHDL), but T123I retained activity with low density lipoprotein. To determine whether defective binding to rHDL was responsible for the low activity of both mutants with rHDL, the equilibrium binding constants were measured directly with isothermal titration calorimetry and surface plasmon resonance (SPR) methods. The results indicated that the affinities of the mutants for rHDL were only about 2-fold lower than the affinity of wild type LCAT (Kd = 2.3 x 10(-7) M). Together, the activity and equilibrium binding results suggest that the T123I mutant is defective in activation by apolipoprotein A-I, and the N228K mutant has impaired binding of lipid substrate to the active site. In addition, the kinetic binding rate constants determined by the SPR method indicate that normal LCAT dissociates from rHDL, on average, after one catalytic cycle.
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Affiliation(s)
- S Adimoolam
- Department of Biochemistry, University of Illinois College of Medicine at Urbana-Champaign, Urbana, Illinois 61801, USA
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18
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Lacko AG, Reason AJ, Nuckolls C, Kudchodkar BJ, Nair MP, Sundarrajan G, Pritchard PH, Morris HR, Dell A. Characterization of recombinant human plasma lecithin: cholesterol acyltransferase (LCAT): N-linked carbohydrate structures and catalytic properties. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32568-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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19
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Li M, Kuivenhoven JA, Ayyobi AF, Pritchard PH. T-->G or T-->A mutation introduced in the branchpoint consensus sequence of intron 4 of lecithin:cholesterol acyltransferase (LCAT) gene: intron retention causing LCAT deficiency. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1391:256-64. [PMID: 9555046 DOI: 10.1016/s0005-2760(97)00198-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Previous mutations associated with lecithin:cholesteryl acyltransferase (LCAT) deficiency syndromes have been identified in the coding regions of the LCAT gene. However, recently, an intron mutation was found in a family in which three sisters presented with fish-eye disease (FED). The probands were shown to be heterozygotes for a mutation in intron 4. The respective T-->C nucleotide substitution, 22 bases upstream of the 3'-splice site, causes a null allele as the result of complete intron retention. Since the natural mutation occurs in a putative branchpoint consensus sequence of the intron, it was hypothesized that the point mutation may disrupt the splicing of the pre-mRNA. To further study the functional significance of the above thymine residue in the branchpoint sequence, we introduced other nucleotides at this position, i.e., LCAT Int-4 MUT-1 (T-->G) and LCAT Int-4 MUT-2 (T-->A). After stable transfection of the mutated pNUT-LCAT minigenes into BHK cells, we could detect neither LCAT activity nor LCAT protein in the culture medium of the pNUT-LCAT Int-4 MUT-1 and pNUT-LCAT Int-4 MUT-2 cell lines, as was previously described for the natural mutation. To determine the effects of the introduced mutations on pre-mRNA splicing, total RNA from transfected BHK cells was used for RT-PCR analysis. All BHK cell lines were shown to transcribe the integrated LCAT minigenes. However, the sizes of these LCAT messengers indicated that intron 4 was retained in the pNUT-LCAT Int-4 MUT-1 and pNUT-LCAT Int-4 MUT-2 cell lines. Subsequent sequence analysis of the RT-PCR products demonstrated that the unspliced intronic sequences contained the introduced mutations. In conclusion, the observed retention of intron 4 of the LCAT gene is the result of the specific loss of a thymine residue two bases upstream of the branchpoint adenosine residue in the putative branchpoint consensus sequence. The results confirm that a single base change in the branchpoint consensus sequence of an intron can cause human disease although this sequence is poorly conserved in mammals.
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Affiliation(s)
- M Li
- Atherosclerosis Specialty Laboratory, Department of Pathology and Laboratory Medicine, St. Paul's Hospital and University of British Columbia, 1081 Burrard Street, Vancouver, British Columbia, Canada
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20
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Brousseau ME, Santamarina-Fojo S, Vaisman BL, Applebaum-Bowden D, Bérard AM, Talley GD, Brewer HB, Hoeg JM. Overexpression of human lecithin:cholesterol acyltransferase in cholesterol-fed rabbits: LDL metabolism and HDL metabolism are affected in a gene dose-dependent manner. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)30038-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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21
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Lynn EG, O K. Role of lipoprotein-X in foam cell formation and rat mesangial cell proliferation. Clin Exp Pharmacol Physiol 1997; 24:973-5. [PMID: 9406668 DOI: 10.1111/j.1440-1681.1997.tb02731.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
1. In the present study, the effect of reconstituted lipoprotein-X (rLp-X) on lipid accumulation and foam cell formation in rat peritoneal macrophages was evaluated. Furthermore, the combined effect of rLp-X and macrophages on mesangial cell proliferation was examined. 2. Incubation of macrophages with rLp-X (177 and 387 nmol unesterified cholesterol (FC)/mL) resulted in an increase of cellular cholesterol (162%) and cholesteryl esters (223 to 245%) relative to control. 3. Oil Red O staining of macrophages treated with rLp-X revealed the presence of foam cells. 4. In conclusion, rLp-X had no effect on the proliferation of mesangial cells incubated in macrophage-conditioned medium.
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Affiliation(s)
- E G Lynn
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada
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22
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Blanco-Vaca F, Qu SJ, Fiol C, Fan HZ, Pao Q, Marzal-Casacuberta A, Albers JJ, Hurtado I, Gracia V, Pintó X, Martí T, Pownall HJ. Molecular basis of fish-eye disease in a patient from Spain. Characterization of a novel mutation in the LCAT gene and lipid analysis of the cornea. Arterioscler Thromb Vasc Biol 1997; 17:1382-91. [PMID: 9261271 DOI: 10.1161/01.atv.17.7.1382] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The genetic and biochemical basis of fish-eye disease (FED) was investigated in a 63-year-old female proband with low plasma HDL cholesterol. Analyses of corneal and plasma lipids of the proband were consistent with impaired lecithin:cholesterol acyltransferase (LCAT) activity. Free cholesterol and phospholipid levels were elevated relative to control values, whereas cholesteryl ester levels were greatly reduced. Fatty acid compositions of corneal lipids from the proband and control subjects differ from the respective fatty acid compositions of their plasma lipids. This suggests that the metabolic pathways and acyl chain specificities for phospholipid, cholesteryl ester, and triglyceride metabolism within the cornea are distinct from those of plasma. Sequencing of the LCAT gene from the proband revealed a novel mutation at nucleotide 399, corresponding to an Arg99-->Cys substitution. Secretion of LCAT (Arg99-->Cys) by transfected COS-6 cells was approximately 50% of that of the wild type, but its specific activity against reassembled HDL was 93% lower than that of wild-type LCAT. The specific activities of wild-type and LCAT (Arg99-->Cys) against LDL were reduced similarly, suggesting that the appearance of the FED phenotype does not require enhanced activity against LDL. Our data support the hypothesis that FED is a partial LCAT deficiency in which poor esterification in specific types of HDL particles may contribute to the appearance of the corneal opacities.
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Affiliation(s)
- F Blanco-Vaca
- Department of Medicine, Baylor College of Medicine and Methodist Hospital, Houston, Tex. 77030, USA.
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23
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Catalytically inactive lecithin: cholesterol acyltransferase (LCAT) caused by a Gly 30 to Ser mutation in a family with LCAT deficiency. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)37266-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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24
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Lee YP, Adimoolam S, Liu M, Subbaiah PV, Glenn K, Jonas A. Analysis of human lecithin-cholesterol acyltransferase activity by carboxyl-terminal truncation. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1344:250-61. [PMID: 9059515 DOI: 10.1016/s0005-2760(96)00149-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Lecithin-cholesterol acyltransferase (LCAT) is a key enzyme in reverse cholesterol transport and catalyzes the esterification of cholesterol in human plasma. Human LCAT is a glycosylated protein, containing 416 amino acids and a proline-rich region at the C-terminus. To address the function of the C-terminal region of LCAT as well as that of the proline-rich region, we constructed and expressed LCAT mutants with C-terminal truncations at different positions. The expression of wild-type LCAT in COS-1 cells resulted in an enzymatically active protein that was secreted by the cells. The mutants lacking the proline-rich region at the C-terminus were expressed and secreted at levels comparable to those of wild-type (approximately 50% of wild-type concentrations in cell media). The proline-deletion mutants were similar to wild-type LCAT in terms of phospholipase or transferase activities with various interfacial substrates, including reconstituted HDL, proteoliposomes, LDL, and micelles of platelet activating factor. Thus, the binding of LCAT to the diverse interfaces is not affected by the removal of its C-terminal region. Also, the activation by apolipoproteins and access of water-insoluble substrates to the active site are not significantly affected by the deletion of the proline-rich region. However, deletions of the proline-rich region, including the five amino acids nearest to the C-terminus, resulted in approximately an 8-fold increase in the specific activity of LCAT towards the water-soluble substrate, p-nitrophenylbutyrate. This suggests that the C-terminal proline-rich region may interfere with the access of this water-soluble substrate to the active site of LCAT, and may form part of a protective covering of the active site of LCAT while in solution. Further deletions at the C-terminus, beyond the proline-rich region, impaired the secretion of the enzyme, implying that this region may play a critical role in either the secretion or folding of LCAT in COS-1 cells.
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Affiliation(s)
- Y P Lee
- Department of Biochemistry, College of Medicine, University of Illinois at Urbana-Champaign 61801, USA
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25
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Kuivenhoven JA, Pritchard H, Hill J, Frohlich J, Assmann G, Kastelein J. The molecular pathology of lecithin:cholesterol acyltransferase (LCAT) deficiency syndromes. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)37433-2] [Citation(s) in RCA: 124] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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26
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Kuivenhoven JA, Stalenhoef AF, Hill JS, Demacker PN, Errami A, Kastelein JJ, Pritchard PH. Two novel molecular defects in the LCAT gene are associated with fish eye disease. Arterioscler Thromb Vasc Biol 1996; 16:294-303. [PMID: 8620346 DOI: 10.1161/01.atv.16.2.294] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A 53-year-old man with a severely reduced HDL cholesterol level, dense corneal opacities, normal renal function, and premature coronary artery disease was investigated together with 16 members of his family. The proband was diagnosed with fish eye disease. As in previously reported patients with fish eye disease, the endogenous plasma cholesterol esterification rate was near normal, yet lecithin:cholesterol acyltransferase (LCAT) activity was almost absent when measured with exogenous HDL analogues used as substrate. Direct sequencing of the LCAT gene revealed two novel missense mutations in exon 1 and exon 4, resulting in the substitution of Pro10 with Gln (P10Q) and Arg135 with Gln (R135Q), respectively. Both missense mutations were located on different alleles. Genetic analysis by polymerase chain reaction revealed 4 carriers of the P10Q and 3 carriers of the R135Q defect. Functional assessment of both missense mutations revealed that when exogenous HDL analogues were used as substrate, the specific activity of rLCAT p10Q was 18% of wild type (WT); however, when LDL was used as substrate, the activity was 146% of WT. By contrast, rLCATR135Q was inactive against both substrates. Thus, we conclude that the LCATR135D mutation is causative for complete LCAT deficiency and that the clinical phenotype of fish eye disease seen in this patient is due to the Pro10 mutation. The presence of premature coronary artery disease in the absence of other risk factors in this new case of fish eye disease raises questions regarding the risk of atherosclerosis, which has previously been reported to be nonexistent.
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Affiliation(s)
- J A Kuivenhoven
- Department of Hemostasis, Thrombosis, Atherosclerosis and Inflammation Research, University of Amsterdam, The Netherlands
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27
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Qu SJ, Fan HZ, Blanco-Vaca F, Pownall HJ. In vitro expression of natural mutants of human lecithin:cholesterol acyltransferase. J Lipid Res 1995. [DOI: 10.1016/s0022-2275(20)39854-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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28
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Klein HG, Duverger N, Albers JJ, Marcovina S, Brewer HB, Santamarina-Fojo S. In vitro expression of structural defects in the lecithin-cholesterol acyltransferase gene. J Biol Chem 1995; 270:9443-7. [PMID: 7721870 DOI: 10.1074/jbc.270.16.9443] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Classic LCAT deficiency (CLD) and fish eye disease (FED) are two clinically distinct syndromes, associated with defects in the lecithin-cholesterol acyltransferase (LCAT) gene resulting in total (CLD) or partial (FED) enzyme deficiency. In order to investigate the underlying molecular mechanisms that lead to different phenotypic expression in CLD and FED, LCAT mutants associated with either CLD (LCAT147, LCAT156, and LCAT228) or FED (LCAT10, LCAT123, LCAT158, LCAT293, LCAT300, and LCAT347) were expressed in vitro in human embryonic kidney 293 cells and characterized with respect to LCAT expression and enzyme activity. Evaluation of mutant LCAT gene transcription by Northern blot analysis demonstrated LCAT mRNA of normal size and concentration. Although all constructs gave rise to similar intracellular LCAT mass, the amount of enzyme present in the media for LCAT147, LCAT156, and LCAT300 was reduced to less than 10% of normal, suggesting that these mutations disrupted LCAT secretion. Western blot analysis of cell culture media containing wild type or mutant LCAT demonstrated the presence of a single normal-sized band of 67 kDa. The ability of the different enzymes to esterify free cholesterol in high density lipoprotein-like proteoliposomes (alpha-LCAT-specific activity) was reduced to less than 5% of normal for CLD mutants LCAT147 and LCAT228 and FED mutants LCAT10, LCAT123, LCAT293, and LCAT347, whereas that of LCAT156, LCAT158, and LCAT300 ranged from 45 to 110% of control. Although most FED mutant LCAT enzymes retained the ability to esterify free cholesterol present in alpha- and beta-lipoproteins of heat-inactivated plasma, esterification was undetectable in all CLD mutants (LCAT147, LCAT156, and LCAT228). In contrast, all mutant enzymes retained the ability to hydrolyze the water soluble, short-chained fatty acid substrate p-nitrophenolbutyrate. In summary, our studies establish the functional significance of nine LCAT gene defects associated with either FED or CLD. Characterization of the expressed LCAT mutants identified multiple, overlapping functional abnormalities that include defects in secretion and/or disruption of enzymic activity. All nine LCAT mutants retained the ability to hydrolyze the water-soluble PNPB substrate, indicating intact hydrolytic function. Based on these studies we propose that mutations in LCAT residues 147, 156, 228 (CLD) and 10, 123, 158, 293, 300, and 347 (FED) do not disrupt the functional domain mediating LCAT phospholipase activity, but alter structural domains involved in lipid binding or transesterification.
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Affiliation(s)
- H G Klein
- Molecular Disease Branch, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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29
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O K, Hill JS, Pritchard PH. Role of N-linked glycosylation of lecithin:cholesterol acyltransferase in lipoprotein substrate specificity. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1254:193-7. [PMID: 7827124 DOI: 10.1016/0005-2760(94)00183-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Lecithin:cholesterol acyltransferase (LCAT) is responsible for the formation of cholesteryl ester in plasma. LCAT is a glycoprotein which has a carbohydrate content estimated to be approx. 25% of its total mass. Previous studies of recombinant LCAT have characterized the function of the four N-linked glycosylation sites of LCAT with respect to reconstituted HDL analogue substrates. In order to investigate the relationship between N-linked glycosylation and the ability of LCAT to esterify cholesterol in native plasma lipoproteins, we have expressed a series of mutant LCAT cDNAs in which each of the four glycosylation consensus sequences was eliminated individually. All mutant LCAT proteins were secreted by stably transfected baby hamster kidney cells. The ability of mutant LCATs to esterify cholesterol in purified native lipoproteins indicated that the elimination of the carbohydrate chain at position 20 of recombinant LCAT was associated with a lower activity than the wild type enzyme when HDL was used as a substrate, but no inhibitory effect was observed when LDL was used as a substrate. A mutant enzyme with a substitution of Asn-84-->Gln or Asn-272-->Gln displayed a decreased ability to esterify cholesterol in either HDL or LDL. In contrast, the loss of a carbohydrate chain at position 384 was associated with an increase in enzyme activity for both HDL (1.5-fold) and LDL (2.5-fold) substrates. Kinetic analysis of these recombinant enzymes indicated that the apparent Km values for cholesterol in either HDL or LDL were not affected, but that the differences in activities were due to changes in the apparent Vmax. Heat inactivation studies were performed to assess the role of specific carbohydrate groups in enzyme stability. Loss of a carbohydrate chain at position 20, 272 or 384 decreased thermostability of LCAT whereas a mutation at position 84 did not affect thermostability. These results suggest that individual carbohydrate chains confer specific structural and functional properties to LCAT.
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Affiliation(s)
- K O
- Department of Pathology, University of British Columbia, Vancouver, Canada
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Subbaiah PV, Liu M, Senz J, Wang X, Pritchard PH. Substrate and positional specificities of human and mouse lecithin-cholesterol acyltransferases. Studies with wild type recombinant and chimeric enzymes expressed in vitro. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1215:150-6. [PMID: 7947997 DOI: 10.1016/0005-2760(94)90104-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Human lecithin-cholesterol acyltransferase (LCAT) preferentially attacks sn-1 position of 16:0-20:4 phosphatidylcholine (PC), producing more 16:0 cholesteryl ester (CE) than 20:4 CE. In contrast, rat and mouse LCATs produce mostly 20:4 CE from the same PC. To understand the structural basis for this difference in positional specificity, we studied the specificities of recombinant mouse and human LCATs and several chimeric constructs of the two. The rLCATs retained the substrate and positional specificities of the plasma enzymes when expressed in COS-1 cells. Human and mouse LCAT cDNAs were each cleaved into three fragments, recombined in various combinations, and the chimeric products were analyzed for their specificities. When the N-terminal, or (and) C-terminal segments of human LCAT were replaced by the corresponding mouse LCAT segments, the chimeric products exhibited the specificity of intact human enzyme. However, when the middle segment, containing the residues 130-306 was replaced by the corresponding mouse LCAT segment, the enzyme exhibited the specificity of mouse LCAT. Similarly, the mouse rLCAT exhibited the specificity of human enzyme when its central segment, but not its N-terminal or C-terminal segment was replaced by the corresponding segment from human LCAT. These results show that the substrate and positional specificities of LCAT are controlled by the central domain of LCAT protein, corresponding to the amino acid residues 130-306.
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Affiliation(s)
- P V Subbaiah
- Department of Medicine, Rush Medical College, Chicago, IL 60612
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Hill JS, O K, Wang X, Pritchard PH. Lecithin:cholesterol acyltransferase deficiency: identification of a causative gene mutation and a co-inherited protein polymorphism. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1181:321-3. [PMID: 8318557 DOI: 10.1016/0925-4439(93)90039-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We have recreated and expressed two known natural mutations within the LCAT gene which were reported on both alleles in a single case of familial LCAT deficiency. We demonstrate that the Ala-93-->Thr mutation is responsible for the biochemical defect while the Arg-158-->Cys mutation is a co-inherited natural polymorphism of LCAT which results in normal enzyme function.
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Affiliation(s)
- J S Hill
- University Hospital Lipid Research Group, Department of Pathology, University of British Columbia, Vancouver, Canada
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