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Gorshkova IN, Meyers NL, Herscovitz H, Mei X, Atkinson D. Human apoA-I[Lys107del] mutation affects lipid surface behavior of apoA-I and its ability to form large nascent HDL. J Lipid Res 2022; 64:100319. [PMID: 36525992 PMCID: PMC9926306 DOI: 10.1016/j.jlr.2022.100319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 11/18/2022] [Accepted: 12/05/2022] [Indexed: 12/15/2022] Open
Abstract
Population studies have found that a natural human apoA-I variant, apoA-I[K107del], is strongly associated with low HDL-C but normal plasma apoA-I levels. We aimed to reveal properties of this variant that contribute to its unusual phenotype associated with atherosclerosis. Our oil-drop tensiometry studies revealed that compared to WT, recombinant apoA-I[K107del] adsorbed to surfaces of POPC-coated triolein drops at faster rates, remodeled the surfaces to a greater extent, and was ejected from the surfaces at higher surface pressures on compression of the lipid drops. These properties may drive increased binding of apoA-I[K107del] to and its better retention on large triglyceride-rich lipoproteins, thereby increasing the variant's content on these lipoproteins. While K107del did not affect apoA-I capacity to promote ABCA1-mediated cholesterol efflux from J774 cells, it impaired the biogenesis of large nascent HDL particles resulting in the formation of predominantly smaller nascent HDL. Size-exclusion chromatography of spontaneously reconstituted 1,2-dimyristoylphosphatidylcholine-apoA-I complexes showed that apoA-I[K107del] had a hampered ability to form larger complexes but formed efficiently smaller-sized complexes. CD analysis revealed a reduced ability of apoA-I[K107del] to increase α-helical structure on binding to 1,2-dimyristoylphosphatidylcholine or in the presence of trifluoroethanol. This property may hinder the formation of large apoA-I[K107del]-containing discoidal and spherical HDL but not smaller HDL. Both factors, the increased content of apoA-I[K107del] on triglyceride-rich lipoproteins and the impaired ability of the variant to stabilize large HDL particles resulting in reduced lipid:protein ratios in HDL, may contribute to normal plasma apoA-I levels along with low HDL-C and increased risk for CVD.
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2
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Lee CK, Liao CW, Meng SW, Wu WK, Chiang JY, Wu MS. Lipids and Lipoproteins in Health and Disease: Focus on Targeting Atherosclerosis. Biomedicines 2021; 9:biomedicines9080985. [PMID: 34440189 PMCID: PMC8393881 DOI: 10.3390/biomedicines9080985] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 08/01/2021] [Accepted: 08/04/2021] [Indexed: 12/15/2022] Open
Abstract
Despite advances in pharmacotherapy, intervention devices and techniques, residual cardiovascular risks still cause a large burden on public health. Whilst most guidelines encourage achieving target levels of specific lipids and lipoproteins to reduce these risks, increasing evidence has shown that molecular modification of these lipoproteins also has a critical impact on their atherogenicity. Modification of low-density lipoprotein (LDL) by oxidation, glycation, peroxidation, apolipoprotein C-III adhesion, and the small dense subtype largely augment its atherogenicity. Post-translational modification by oxidation, carbamylation, glycation, and imbalance of molecular components can reduce the capacity of high-density lipoprotein (HDL) for reverse cholesterol transport. Elevated levels of triglycerides (TGs), apolipoprotein C-III and lipoprotein(a), and a decreased level of apolipoprotein A-I are closely associated with atherosclerotic cardiovascular disease. Pharmacotherapies aimed at reducing TGs, lipoprotein(a), and apolipoprotein C-III, and enhancing apolipoprotein A-1 are undergoing trials, and promising preliminary results have been reported. In this review, we aim to update the evidence on modifications of major lipid and lipoprotein components, including LDL, HDL, TG, apolipoprotein, and lipoprotein(a). We also discuss examples of translating findings from basic research to potential therapeutic targets for drug development.
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Affiliation(s)
- Chih-Kuo Lee
- College of Medicine, National Taiwan University, Taipei 100, Taiwan; (C.-K.L.); (C.-W.L.); (S.-W.M.); (W.-K.W.)
- Department of Internal Medicine, National Taiwan University Hospital Hsin-Chu Branch, Hsin-Chu 300, Taiwan
- Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, Taipei 100, Taiwan
| | - Che-Wei Liao
- College of Medicine, National Taiwan University, Taipei 100, Taiwan; (C.-K.L.); (C.-W.L.); (S.-W.M.); (W.-K.W.)
- Department of Internal Medicine, National Taiwan University Cancer Center, Taipei 106, Taiwan
| | - Shih-Wei Meng
- College of Medicine, National Taiwan University, Taipei 100, Taiwan; (C.-K.L.); (C.-W.L.); (S.-W.M.); (W.-K.W.)
- Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital Hsin-Chu Branch, Hsin-Chu 300, Taiwan
| | - Wei-Kai Wu
- College of Medicine, National Taiwan University, Taipei 100, Taiwan; (C.-K.L.); (C.-W.L.); (S.-W.M.); (W.-K.W.)
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei 100, Taiwan
| | - Jiun-Yang Chiang
- College of Medicine, National Taiwan University, Taipei 100, Taiwan; (C.-K.L.); (C.-W.L.); (S.-W.M.); (W.-K.W.)
- Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, Taipei 100, Taiwan
- Division of Cardiology, Department of Internal Medicine and Cardiovascular Center, National Taiwan University Hospital, Taipei 100, Taiwan
- Correspondence: (J.-Y.C.); (M.-S.W.)
| | - Ming-Shiang Wu
- College of Medicine, National Taiwan University, Taipei 100, Taiwan; (C.-K.L.); (C.-W.L.); (S.-W.M.); (W.-K.W.)
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei 100, Taiwan
- Correspondence: (J.-Y.C.); (M.-S.W.)
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3
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Gkolfinopoulou C, Soukou F, Dafnis I, Kellici TF, Sanoudou D, Mavromoustakos T, Stratikos E, Chroni A. Structure-function analysis of naturally occurring apolipoprotein A-I L144R, A164S and L178P mutants provides insight on their role on HDL levels and cardiovascular risk. Cell Mol Life Sci 2021; 78:1523-1544. [PMID: 32666307 PMCID: PMC11072781 DOI: 10.1007/s00018-020-03583-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 06/03/2020] [Accepted: 06/22/2020] [Indexed: 01/04/2023]
Abstract
Naturally occurring point mutations in apolipoprotein A-I (apoA-I), the major protein component of high-density lipoprotein (HDL), may affect plasma HDL-cholesterol levels and cardiovascular risk. Here, we evaluated the effect of human apoA-I mutations L144R (associated with low HDL-cholesterol), L178P (associated with low HDL-cholesterol and increased cardiovascular risk) and A164S (associated with increased cardiovascular risk and mortality without low HDL-cholesterol) on the structural integrity and functions of lipid-free and lipoprotein-associated apoA-I in an effort to explain the phenotypes of subjects carrying these mutations. All three mutants, in lipid-free form, presented structural and thermodynamic aberrations, with apoA-I[L178P] presenting the greatest thermodynamic destabilization. Additionally, apoA-I[L178P] displayed reduced ABCA1-mediated cholesterol efflux capacity. When in reconstituted HDL (rHDL), apoA-I[L144R] and apoA-I[L178P] were more thermodynamically destabilized compared to wild-type apoA-I, both displayed reduced SR-BI-mediated cholesterol efflux capacity and apoA-I[L144R] showed severe LCAT activation defect. ApoA-I[A164S] was thermodynamically unaffected when in rHDL, but exhibited a series of functional defects. Specifically, it had reduced ABCG1-mediated cholesterol and 7-ketocholesterol efflux capacity, failed to reduce ROS formation in endothelial cells and had reduced capacity to induce endothelial cell migration. Mechanistically, the latter was due to decreased capacity of rHDL-apoA-I[A164S] to activate Akt kinase possibly by interacting with endothelial LOX-1 receptor. The impaired capacity of rHDL-apoA-I[A164S] to preserve endothelial function may be related to the increased cardiovascular risk for this mutation. Overall, our structure-function analysis of L144R, A164S and L178P apoA-I mutants provides insights on how HDL-cholesterol levels and/or atheroprotective properties of apoA-I/HDL are impaired in carriers of these mutations.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily G, Member 1/genetics
- ATP Binding Cassette Transporter, Subfamily G, Member 1/metabolism
- Apolipoprotein A-I/genetics
- Apolipoprotein A-I/metabolism
- Apolipoprotein A-I/ultrastructure
- Cardiovascular Diseases/genetics
- Cardiovascular Diseases/pathology
- Cell Movement/genetics
- Cholesterol, HDL/genetics
- Cholesterol, HDL/metabolism
- Cholesterol, HDL/ultrastructure
- Endothelial Cells/metabolism
- Endothelial Cells/pathology
- Heart Disease Risk Factors
- Humans
- Ketocholesterols/genetics
- Ketocholesterols/metabolism
- Lipoproteins, HDL/genetics
- Lipoproteins, HDL/metabolism
- Lipoproteins, HDL/ultrastructure
- Mutant Proteins/genetics
- Mutant Proteins/metabolism
- Mutant Proteins/ultrastructure
- Mutation/genetics
- Scavenger Receptors, Class E/genetics
- Scavenger Receptors, Class E/metabolism
- Structure-Activity Relationship
- Thermodynamics
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Affiliation(s)
- Christina Gkolfinopoulou
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, 15341, Athens, Greece
| | - Faye Soukou
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, 15341, Athens, Greece
| | - Ioannis Dafnis
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, 15341, Athens, Greece
| | - Tahsin F Kellici
- Laboratory of Organic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimioupolis Zografou, Athens, Greece
| | - Despina Sanoudou
- 4th Department of Internal Medicine, Clinical Genomics and Pharmacogenomics Unit, 'Attikon' Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece
- Molecular Biology Division, Biomedical Research Foundation of the Academy of Athens, Athens, Greece
- Center for New Biotechnologies and Precision Medicine, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Thomas Mavromoustakos
- Laboratory of Organic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimioupolis Zografou, Athens, Greece
| | - Efstratios Stratikos
- Protein Chemistry Laboratory, Institute of Nuclear and Radiological Sciences and Technology, Energy and Safety, National Center for Scientific Research "Demokritos", Agia Paraskevi, Athens, Greece
| | - Angeliki Chroni
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, 15341, Athens, Greece.
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Koike T, Koike Y, Yang D, Guo Y, Rom O, Song J, Xu J, Chen Y, Wang Y, Zhu T, Garcia-Barrio MT, Fan J, Chen YE, Zhang J. Human apolipoprotein A-II reduces atherosclerosis in knock-in rabbits. Atherosclerosis 2021; 316:32-40. [PMID: 33296791 PMCID: PMC7770079 DOI: 10.1016/j.atherosclerosis.2020.11.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 11/19/2020] [Accepted: 11/26/2020] [Indexed: 11/23/2022]
Abstract
BACKGROUND AND AIMS Apolipoprotein A-II (apoAII) is the second major apolipoprotein of the high-density lipoprotein (HDL) particle, after apoAI. Unlike apoAI, the biological and physiological functions of apoAII are unclear. We aimed to gain insight into the specific roles of apoAII in lipoprotein metabolism and atherosclerosis using a novel rabbit model. METHODS Wild-type (WT) rabbits are naturally deficient in apoAII, thus their HDL contains only apoAI. Using TALEN technology, we replaced the endogenous apoAI in rabbits through knock-in (KI) of human apoAII. The newly generated apoAII KI rabbits were used to study the specific function of apoAII, independent of apoAI. RESULTS ApoAII KI rabbits expressed exclusively apoAII without apoAI, as confirmed by RT-PCR and Western blotting. On a standard diet, the KI rabbits exhibited lower plasma triglycerides (TG, 52%, p < 0.01) due to accelerated clearance of TG-rich particles and higher lipoprotein lipase activity than the WT littermates. ApoAII KI rabbits also had higher plasma HDL-C (28%, p < 0.05) and their HDL was rich in apoE, apoAIV, and apoAV. When fed a cholesterol-rich diet for 16 weeks, apoAII KI rabbits were resistant to diet-induced hypertriglyceridemia and developed significantly less aortic atherosclerosis compared to WT rabbits. HDL isolated from rabbits with apoAII KI had similar cholesterol efflux capacity and anti-inflammatory effects as HDL isolated from the WT rabbits. CONCLUSIONS ApoAII KI rabbits developed less atherosclerosis than WT rabbits, possibly through increased plasma HDL-C, reduced TG and atherogenic lipoproteins. These results suggest that apoAII may serve as a potential target for the treatment of atherosclerosis.
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Affiliation(s)
- Tomonari Koike
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Yamanashi, Japan
| | - Yui Koike
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Dongshan Yang
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Yanhong Guo
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Oren Rom
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Jun Song
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Jie Xu
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Yajie Chen
- Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Yamanashi, Japan
| | - Yanli Wang
- Department of Pathology, Xi'an Medical University, Xi'an, China
| | - Tianqing Zhu
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Minerva T Garcia-Barrio
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Jianglin Fan
- Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Yamanashi, Japan.
| | - Y Eugene Chen
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA.
| | - Jifeng Zhang
- Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI, USA.
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5
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Gkolfinopoulou C, Bourtsala A, Chroni A. Structural and functional basis for increased HDL-cholesterol levels due to the naturally occurring V19L mutation in human apolipoprotein A-I. Biochim Biophys Acta Mol Cell Biol Lipids 2019; 1865:158593. [PMID: 31863971 DOI: 10.1016/j.bbalip.2019.158593] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 12/09/2019] [Accepted: 12/16/2019] [Indexed: 11/26/2022]
Abstract
Several hereditary point mutations in human apolipoprotein A-I (apoA-I) have been associated with low HDL-cholesterol levels and/or increased coronary artery disease (CAD) risk. However, one apoA-I mutation, the V19L, recently identified in Icelanders, has been associated with increased HDL-cholesterol levels and decreased CAD risk. In an effort to gain mechanistic insight linking the presence of this mutation in apoA-I with the increase of HDL-cholesterol levels we evaluated the effect of V19L mutation on the conformational integrity and functional properties of apoA-I in lipid-free and lipidated form. ApoA-I[V19L] was found to be thermodynamically destabilized in lipid-free form and displays an increased capacity to associate with phospholipids compared to WT apoA-I. When associated to reconstituted HDL (rHDL), apoA-I[V19L] was more thermodynamically stabilized than WT apoA-I. ApoA-I[V19L] displayed normal capacity to promote ABCA1-mediated cholesterol efflux and to activate the enzyme LCAT, in lipid-free and rHDL-associated forms, respectively. Additionally, rHDL-associated apoA-I[V19L] showed normal capacity to promote ABCG1-mediated cholesterol efflux, but 45% increased capacity to promote SR-BI-mediated cholesterol efflux, while the SR-BI-mediated HDL-lipid uptake was normal. Overall, our findings show that the apoA-I V19L mutation does not affect the first steps of HDL biogenesis pathway. However, the increased capacity of apoA-I[V19L] to associate with phospholipids, in combination with the enhanced thermodynamic stability of lipoprotein-associated apoA-I[V19L] and increased capacity of apoA-I[V19L]-containing lipoprotein particles to accept additional cholesterol by SR-BI could account for the increased HDL-cholesterol levels observed in human carriers of the mutation.
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Affiliation(s)
- Christina Gkolfinopoulou
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, Athens, Greece
| | - Angeliki Bourtsala
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, Athens, Greece
| | - Angeliki Chroni
- Institute of Biosciences and Applications, National Center for Scientific Research "Demokritos", Agia Paraskevi, Athens, Greece.
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6
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Cooke AL, Morris J, Melchior JT, Street SE, Jerome WG, Huang R, Herr AB, Smith LE, Segrest JP, Remaley AT, Shah AS, Thompson TB, Davidson WS. A thumbwheel mechanism for APOA1 activation of LCAT activity in HDL. J Lipid Res 2018; 59:1244-1255. [PMID: 29773713 DOI: 10.1194/jlr.m085332] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Revised: 05/08/2018] [Indexed: 01/28/2023] Open
Abstract
APOA1 is the most abundant protein in HDL. It modulates interactions that affect HDL's cardioprotective functions, in part via its activation of the enzyme, LCAT. On nascent discoidal HDL, APOA1 comprises 10 α-helical repeats arranged in an anti-parallel stacked-ring structure that encapsulates a lipid bilayer. Previous chemical cross-linking studies suggested that these APOA1 rings can adopt at least two different orientations, or registries, with respect to each other; however, the functional impact of these structural changes is unknown. Here, we placed cysteine residues at locations predicted to form disulfide bonds in each orientation and then measured APOA1's ability to adopt the two registries during HDL particle formation. We found that most APOA1 oriented with the fifth helix of one molecule across from fifth helix of the other (5/5 helical registry), but a fraction adopted a 5/2 registry. Engineered HDLs that were locked in 5/5 or 5/2 registries by disulfide bonds equally promoted cholesterol efflux from macrophages, indicating functional particles. However, unlike the 5/5 registry or the WT, the 5/2 registry impaired LCAT cholesteryl esterification activity (P < 0.001), despite LCAT binding equally to all particles. Chemical cross-linking studies suggest that full LCAT activity requires a hybrid epitope composed of helices 5-7 on one APOA1 molecule and helices 3-4 on the other. Thus, APOA1 may use a reciprocating thumbwheel-like mechanism to activate HDL-remodeling proteins.
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Affiliation(s)
- Allison L Cooke
- Departments of Pathology and Laboratory Medicine University of Cincinnati, Cincinnati, OH 45237
| | - Jamie Morris
- Departments of Pathology and Laboratory Medicine University of Cincinnati, Cincinnati, OH 45237
| | - John T Melchior
- Departments of Pathology and Laboratory Medicine University of Cincinnati, Cincinnati, OH 45237
| | - Scott E Street
- Departments of Pathology and Laboratory Medicine University of Cincinnati, Cincinnati, OH 45237
| | - W Gray Jerome
- Departments of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Rong Huang
- Departments of Pathology and Laboratory Medicine University of Cincinnati, Cincinnati, OH 45237
| | - Andrew B Herr
- Division of Immunobiology and Center for Systems Immunology Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229
| | - Loren E Smith
- Anesthesiology, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Jere P Segrest
- Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Alan T Remaley
- Lipoprotein Metabolism Section, Cardiovascular-Pulmonary Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - Amy S Shah
- Division of Endocrinology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229
| | - Thomas B Thompson
- Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, OH 45237
| | - W Sean Davidson
- Departments of Pathology and Laboratory Medicine University of Cincinnati, Cincinnati, OH 45237
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7
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Gorshkova IN, Mei X, Atkinson D. Arginine 123 of apolipoprotein A-I is essential for lecithin:cholesterol acyltransferase activity. J Lipid Res 2017; 59:348-356. [PMID: 29208698 DOI: 10.1194/jlr.m080986] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 11/29/2017] [Indexed: 01/10/2023] Open
Abstract
ApoA-I activates LCAT that converts lipoprotein cholesterol to cholesteryl ester (CE). Molecular dynamic simulations suggested earlier that helices 5 of two antiparallel apoA-I molecules on discoidal HDL form an amphipathic tunnel for migration of acyl chains and unesterified cholesterol to the active sites of LCAT. Our recent crystal structure of Δ(185-243)apoA-I showed the tunnel formed by helices 5/5, with two positively charged residues arginine 123 positioned at the edge of the hydrophobic tunnel. We hypothesized that these uniquely positioned residues Arg123 are poised for interaction with fatty acids produced by LCAT hydrolysis of the sn-2 chains of phosphatidylcholine, thus positioning the fatty acids for esterification to cholesterol. To test the importance of Arg123 for LCAT phospholipid hydrolysis and CE formation, we generated apoA-I[R123A] and apoA-I[R123E] mutants and made discoidal HDL with the mutants and WT apoA-I. Neither mutation of Arg123 changed the particle composition or size, or the protein conformation or stability. However, both mutations of Arg123 significantly reduced LCAT catalytic efficiency and the apparent Vmax for CE formation without affecting LCAT phospholipid hydrolysis. A control mutation, apoA-I[R131A], did not affect LCAT phospholipid hydrolysis or CE formation. These data suggest that Arg123 of apoA-I on discoidal HDL participates in LCAT-mediated cholesterol esterification.
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Affiliation(s)
- Irina N Gorshkova
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - Xiaohu Mei
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - David Atkinson
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
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8
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Zannis VI, Su S, Fotakis P. Role of apolipoproteins, ABCA1 and LCAT in the biogenesis of normal and aberrant high density lipoproteins. J Biomed Res 2017; 31:471. [PMID: 29109329 PMCID: PMC6307667 DOI: 10.7555/jbr.31.20160082] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 08/30/2016] [Indexed: 12/28/2022] Open
Abstract
In this review, we focus on the pathway of biogenesis of HDL, the essential role of apoA-I, ATP binding cassette transporter A1 (ABCA1), and lecithin: cholesterol acyltransferase (LCAT) in the formation of plasma HDL; the generation of aberrant forms of HDL containing mutant apoA-I forms and the role of apoA-IV and apoE in the formation of distinct HDL subpopulations. The biogenesis of HDL requires functional interactions of the ABCA1 with apoA-I (and to a lesser extent with apoE and apoA-IV) and subsequent interactions of the nascent HDL species thus formed with LCAT. Mutations in apoA-I, ABCA1 and LCAT either prevent or impair the formation of HDL and may also affect the functionality of the HDL species formed. Emphasis is placed on three categories of apoA-I mutations. The first category describes a unique bio-engineered apoA-I mutation that disrupts interactions between apoA-I and ABCA1 and generates aberrant preβ HDL subpopulations that cannot be converted efficiently to α subpopulations by LCAT. The second category describes natural and bio-engineered apoA-I mutations that generate preβ and small size α4 HDL subpopulations, and are associated with low plasma HDL levels. These phenotypes can be corrected by excess LCAT. The third category describes bio-engineered apoA-I mutations that induce hypertriglyceridemia that can be corrected by excess lipoprotein lipase and also have defective maturation of HDL. The HDL phenotypes described here may serve in the future for diagnosis, prognoses and potential treatment of abnormalities that affect the biogenesis and functionality of HDL.
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Affiliation(s)
- Vassilis I. Zannis
- . Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, USA
- . Department University of Crete, School of Medicine, Heraklion, Crete, Greece
| | - Shi Su
- . Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, USA
| | - Panagiotis Fotakis
- . Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, USA
- . Department University of Crete, School of Medicine, Heraklion, Crete, Greece
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9
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Zvintzou E, Lhomme M, Chasapi S, Filou S, Theodoropoulos V, Xapapadaki E, Kontush A, Spyroulias G, Tellis CC, Tselepis AD, Constantinou C, Kypreos KE. Pleiotropic effects of apolipoprotein C3 on HDL functionality and adipose tissue metabolic activity. J Lipid Res 2017; 58:1869-1883. [PMID: 28701354 DOI: 10.1194/jlr.m077925] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 06/29/2017] [Indexed: 12/28/2022] Open
Abstract
APOC3 is produced mainly by the liver and intestine and approximately half of plasma APOC3 associates with HDL. Though it was believed that APOC3 associates with HDL by simple binding to preexisting particles, recent data support that biogenesis of APOC3-containing HDL (APOC3-HDL) requires Abca1. Moreover, APOC3-HDL contributes to plasma triglyceride homeostasis by preventing APOC3 association with triglyceride-rich lipoproteins. Interestingly, APOC3-HDL also shows positive correlation with the morbidly obese phenotype. However, the roles of APOC3 in HDL functionality and adipose tissue metabolic activity remain unknown. Therefore, here we investigated the direct effects of APOC3 expression on HDL structure and function, as well as white adipose tissue (WAT) and brown adipose tissue (BAT) metabolic activity. C57BL/6 mice were infected with an adenovirus expressing human APOC3 or a recombinant attenuated control adenovirus expressing green fluorescent protein and blood and tissue samples were collected at 5 days postinfection. HDL was then analyzed for its apolipoprotein and lipid composition and particle functionality. Additionally, purified mitochondria from BAT and WAT were analyzed for uncoupling protein 1, cytochrome c (Cytc), and Cytc oxidase subunit 4 protein levels as an indirect measure of their metabolic activity. Serum metabolomic analysis was performed by NMR. Combined, our data show that APOC3 modulates HDL structure and function, while it selectively promotes BAT metabolic activation.
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Affiliation(s)
- Evangelia Zvintzou
- Pharmacology Department, University of Patras Medical School, Rio Achaias TK 26500, Greece
| | - Marie Lhomme
- ICANalytics and INSERM UMR_S 1166, ICAN, 75013 Paris, France
| | - Stella Chasapi
- Department of Pharmacy, University of Patras, 26504 Patras, Greece
| | - Serafoula Filou
- Pharmacology Department, University of Patras Medical School, Rio Achaias TK 26500, Greece
| | | | - Eva Xapapadaki
- Pharmacology Department, University of Patras Medical School, Rio Achaias TK 26500, Greece
| | - Anatol Kontush
- Faculté de Médecine Pitié-Salpêtrière, ICAN, 75013 Paris, France
| | | | - Constantinos C Tellis
- Laboratory of Biochemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
| | - Alexandros D Tselepis
- Laboratory of Biochemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
| | - Caterina Constantinou
- Pharmacology Department, University of Patras Medical School, Rio Achaias TK 26500, Greece
| | - Kyriakos E Kypreos
- Pharmacology Department, University of Patras Medical School, Rio Achaias TK 26500, Greece
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10
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Oda MN. Lipid-free apoA-I structure - Origins of model diversity. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:221-233. [PMID: 27890580 DOI: 10.1016/j.bbalip.2016.11.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 10/20/2016] [Accepted: 11/20/2016] [Indexed: 01/22/2023]
Abstract
Apolipoprotein A-I (apoA-I) is a prominent member of the exchangeable apolipoprotein class of proteins, capable of transitioning between lipid-bound and lipid-free states. It is the primary structural and functional protein of high density lipoprotein (HDL). Lipid-free apoA-I is critical to de novo HDL formation as it is the preferred substrate of the lipid transporter, ATP Binding Cassette Transporter A1 (ABCA1) Remaley et al. (2001) [1]. Lipid-free apoA-I is an important element in reverse cholesterol transport and comprehension of its structure is a core issue in our understanding of cholesterol metabolism. However, lipid-free apoA-I is highly conformationally dynamic making it a challenging subject for structural analysis. Over the past 20years there have been significant advances in overcoming the dynamic nature of lipid-free apoA-I, which have resulted in a multitude of proposed conformational models.
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Affiliation(s)
- Michael N Oda
- Children's Hospital Oakland Research Institute, Oakland, CA 94609, United States.
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11
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Filou S, Lhomme M, Karavia EA, Kalogeropoulou C, Theodoropoulos V, Zvintzou E, Sakellaropoulos GC, Petropoulou PI, Constantinou C, Kontush A, Kypreos KE. Distinct Roles of Apolipoproteins A1 and E in the Modulation of High-Density Lipoprotein Composition and Function. Biochemistry 2016; 55:3752-62. [PMID: 27332083 DOI: 10.1021/acs.biochem.6b00389] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In addition to high-density lipoprotein cholesterol (HDL-C) levels, HDL quality also appears to be very important for atheroprotection. Analysis of various clinical paradigms suggests that the lipid and apolipoprotein composition of HDL defines its size, shape, and functions and may determine its beneficial effects on human health. Previously, we reported that like apolipoprotein A-I (Apoa1), apolipoprotein E (Apoe) is also capable of promoting the de novo biogenesis of HDL with the participation of ATP binding cassette A lipid transporter member 1 (Abca1) and plasma enzyme lecithin:cholesterol acyltransferase (Lcat), in a manner independent of a functional Apoa1. Here, we performed a comparative analysis of the functions of these HDL subpopulations. Specifically, Apoe and Apoa1 double-deficient (Apoe(-/-) × Apoa1(-/-)) mice were infected with APOA1- or APOE3-expressing adenoviruses, and APOA1-containing HDL (APOA1-HDL) and APOE3-containing HDL (APOE3-HDL), respectively, were isolated and analyzed by biochemical and physicochemical methods. Western blot and lipidomic analyses indicated significant differences in the apolipoprotein and lipid composition of the two HDL species. Moreover APOE3-HDL presented a markedly reduced antioxidant potential and Abcg1-mediated cholesterol efflux capacity. Surprisingly, APOE3-HDL but not APOA1-HDL attenuated LPS-induced production of TNFα in RAW264.7 cells, suggesting that the anti-inflammatory effects of APOA1 are dependent on APOE expression. Taken together, our data indicate that APOA1 and APOE3 recruit different apolipoproteins and lipids on the HDL particle, leading to structurally and functionally distinct HDL subpopulations. The distinct role of these two apolipoproteins in the modulation of HDL functionality may pave the way toward the development of novel pharmaceuticals that aim to improve HDL functionality.
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Affiliation(s)
- Serafoula Filou
- Department of Pharmacology, University of Patras Medical School , Rio Achaias, TK 26500, Greece
| | - Marie Lhomme
- ICANalytics, ICAN , 83 Bd de l'hopital, 75013 Paris, France
| | - Eleni A Karavia
- Department of Pharmacology, University of Patras Medical School , Rio Achaias, TK 26500, Greece
| | | | - Vassilis Theodoropoulos
- Department of Pharmacology, University of Patras Medical School , Rio Achaias, TK 26500, Greece
| | - Evangelia Zvintzou
- Department of Pharmacology, University of Patras Medical School , Rio Achaias, TK 26500, Greece
| | - George C Sakellaropoulos
- Department of Medical Physics, University of Patras Medical School , Rio Achaias, TK 26500, Greece
| | | | - Caterina Constantinou
- Department of Pharmacology, University of Patras Medical School , Rio Achaias, TK 26500, Greece
| | - Anatol Kontush
- INSERM UMR_S 1166-ICAN , Faculté de Médecine Pitié-Salpêtrière, 91 Bd de l'Hôpital, 75013 Paris, France
| | - Kyriakos E Kypreos
- Department of Pharmacology, University of Patras Medical School , Rio Achaias, TK 26500, Greece
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12
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Impact of phosphatidylcholine liposomes on the compositional changes of VLDL during lipoprotein lipase (LPL)-mediated lipolysis. Chem Phys Lipids 2016; 195:63-70. [DOI: 10.1016/j.chemphyslip.2015.12.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Revised: 12/18/2015] [Accepted: 12/31/2015] [Indexed: 12/31/2022]
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13
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Song P, Kwon Y, Yea K, Moon HY, Yoon JH, Ghim J, Hyun H, Kim D, Koh A, Berggren PO, Suh PG, Ryu SH. Apolipoprotein a1 increases mitochondrial biogenesis through AMP-activated protein kinase. Cell Signal 2015; 27:1873-81. [DOI: 10.1016/j.cellsig.2015.05.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Accepted: 05/07/2015] [Indexed: 10/23/2022]
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14
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Mei X, Atkinson D. Lipid-free Apolipoprotein A-I Structure: Insights into HDL Formation and Atherosclerosis Development. Arch Med Res 2015; 46:351-60. [PMID: 26048453 DOI: 10.1016/j.arcmed.2015.05.012] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 05/27/2015] [Indexed: 12/22/2022]
Abstract
Apolipoprotein A-I is the major protein in high-density lipoprotein (HDL) and plays an important role during the process of reverse cholesterol transport (RCT). Knowledge of the high-resolution structure of full-length apoA-I is vital for a molecular understanding of the function of HDL at the various steps of the RCT pathway. Due to the flexible nature of apoA-I and aggregation properties, the structure of full-length lipid-free apoA-I has evaded description for over three decades. Sequence analysis of apoA-I suggested that the amphipathic α-helix is the structural motif of exchangeable apolipoprotein, and NMR, X-ray and MD simulation studies have confirmed this. Different laboratories have used different methods to probe the secondary structure distribution and organization of both the lipid-free and lipid-bound apoA-I structure. Mutation analysis, synthetic peptide models, surface chemistry and crystal structures have converged on the lipid-free apoA-I domain structure and function: the N-terminal domain [1-184] forms a helix bundle while the C-terminal domain [185-243] mostly lacks defined structure and is responsible for initiating lipid-binding, aggregation and is also involved in cholesterol efflux. The first 43 residues of apoA-I are essential to stabilize the lipid-free structure. In addition, the crystal structure of C-terminally truncated apoA-I suggests a monomer-dimer conversation mechanism mediated through helix 5 reorganization and dimerization during the formation of HDL. Based on previous research, we have proposed a structural model for full-length monomeric apoA-I in solution and updated the HDL formation mechanism through three states. Mapping the known natural mutations on the full-length monomeric apoA-I model provides insight into atherosclerosis development through disruption of the N-terminal helix bundle or deletion of the C-terminal lipid-binding domain.
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Affiliation(s)
- Xiaohu Mei
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - David Atkinson
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA.
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15
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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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16
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Tiniakou I, Drakos E, Sinatkas V, Van Eck M, Zannis VI, Boumpas D, Verginis P, Kardassis D. High-density lipoprotein attenuates Th1 and th17 autoimmune responses by modulating dendritic cell maturation and function. THE JOURNAL OF IMMUNOLOGY 2015; 194:4676-87. [PMID: 25870241 DOI: 10.4049/jimmunol.1402870] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 03/16/2015] [Indexed: 12/11/2022]
Abstract
Aberrant levels and function of the potent anti-inflammatory high-density lipoprotein (HDL) and accelerated atherosclerosis have been reported in patients with autoimmune inflammatory diseases. Whether HDL affects the development of an autoimmune response remains elusive. In this study, we used apolipoprotein A-I-deficient (apoA-I(-/-)) mice, characterized by diminished circulating HDL levels, to delineate the role of HDL in autoimmunity. ApoA-I(-/-) mice exhibited increased severity of Ag-induced arthritis compared with wild-type mice, and this was associated with elevated Th1 and Th17 cell reactivity in the draining lymph nodes. Furthermore, reconstituted HDL (rHDL) attenuated IFN-γ and IL-17 secretion by Ag-specific T cells upon stimulation of draining lymph nodes in vitro. The suppressive effects of rHDL were mediated through modulation of dendritic cell (DC) function. Specifically, rHDL-treated DCs demonstrated an immature phenotype characterized by downregulated costimulatory molecules, the release of low amounts of proinflammatory cytokines, and failure to promote T cell proliferation in vitro. The mechanism of action involved the inhibition of NF-κB nuclear translocation and the decrease of Myd88 mRNA levels by rHDL. Finally, modulation of DC function by rHDL was critically dependent on the presence of scavenger receptor class B type I and ATP Binding Cassette Transporter A1, but not the ATP Binding Cassette Transporter G1. These findings reveal a novel role of HDL in the regulation of adaptive inflammatory responses through suppression of DC function that could be exploited therapeutically in autoimmune inflammatory diseases.
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Affiliation(s)
- Ioanna Tiniakou
- Laboratory of Biochemistry, Department of Basic Sciences, University of Crete Medical School, 71003 Heraklion, Crete, Greece; Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, 70013 Heraklion, Crete, Greece
| | - Elias Drakos
- Department of Pathology, University of Crete Medical School, 71003 Heraklion, Crete, Greece
| | - Vaios Sinatkas
- Department of Pathology, University of Crete Medical School, 71003 Heraklion, Crete, Greece
| | - Miranda Van Eck
- Division of Biopharmaceutics, Leiden Academic Centre for Drug Research, 2333 Leiden, the Netherlands
| | - Vassilis I Zannis
- Laboratory of Biochemistry, Department of Basic Sciences, University of Crete Medical School, 71003 Heraklion, Crete, Greece; Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118; and
| | - Dimitrios Boumpas
- Biomedical Research Foundation, Academy of Athens, 11527 Athens, Greece
| | | | - Dimitris Kardassis
- Laboratory of Biochemistry, Department of Basic Sciences, University of Crete Medical School, 71003 Heraklion, Crete, Greece; Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, 70013 Heraklion, Crete, Greece;
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17
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Zannis VI, Fotakis P, Koukos G, Kardassis D, Ehnholm C, Jauhiainen M, Chroni A. HDL biogenesis, remodeling, and catabolism. Handb Exp Pharmacol 2015; 224:53-111. [PMID: 25522986 DOI: 10.1007/978-3-319-09665-0_2] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In this chapter, we review how HDL is generated, remodeled, and catabolized in plasma. We describe key features of the proteins that participate in these processes, emphasizing how mutations in apolipoprotein A-I (apoA-I) and the other proteins affect HDL metabolism. The biogenesis of HDL initially requires functional interaction of apoA-I with the ATP-binding cassette transporter A1 (ABCA1) and subsequently interactions of the lipidated apoA-I forms with lecithin/cholesterol acyltransferase (LCAT). Mutations in these proteins either prevent or impair the formation and possibly the functionality of HDL. Remodeling and catabolism of HDL is the result of interactions of HDL with cell receptors and other membrane and plasma proteins including hepatic lipase (HL), endothelial lipase (EL), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP), apolipoprotein M (apoM), scavenger receptor class B type I (SR-BI), ATP-binding cassette transporter G1 (ABCG1), the F1 subunit of ATPase (Ecto F1-ATPase), and the cubulin/megalin receptor. Similarly to apoA-I, apolipoprotein E and apolipoprotein A-IV were shown to form discrete HDL particles containing these apolipoproteins which may have important but still unexplored functions. Furthermore, several plasma proteins were found associated with HDL and may modulate its biological functions. The effect of these proteins on the functionality of HDL is the topic of ongoing research.
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Affiliation(s)
- Vassilis I Zannis
- Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA, 02118, USA,
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18
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Gorshkova IN, Mei X, Atkinson D. Binding of human apoA-I[K107del] variant to TG-rich particles: implications for mechanisms underlying hypertriglyceridemia. J Lipid Res 2014; 55:1876-85. [PMID: 24919401 DOI: 10.1194/jlr.m047241] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We found earlier that apoA-I variants that induced hypertriglyceridemia (HTG) in mice had increased affinity to TG-rich lipoproteins and thereby impaired their catabolism. Here, we tested whether a naturally occurring human apoA-I mutation, Lys107del, associated with HTG also promotes apoA-I binding to TG-rich particles. We expressed apoA-I[Lys107del] variant in Escherichia coli, studied its binding to TG-rich emulsion particles, and performed a physicochemical characterization of the protein. Compared with WT apoA-I, apoA-I[Lys107del] showed enhanced binding to TG-rich particles, lower stability, and greater exposure of hydrophobic surfaces. The crystal structure of truncated, Δ(185-243), apoA-I suggests that deletion of Lys107 disrupts helix registration and disturbs a stabilizing salt bridge network in the N-terminal helical bundle. To elucidate the structural changes responsible for the altered function of apoA-I[Lys107del], we studied another mutant, apoA-I [Lys107Ala]. Our findings suggest that the registry shift and ensuing disruption of the inter-helical salt bridges in apoA-I[Lys107del] result in destabilization of the helical bundle structure and greater exposure of hydrophobic surfaces. We conclude that the structural changes in the apoA-I[Lys107del] variant facilitate its binding to TG-rich lipoproteins and thus, may reduce their lipolysis and contribute to the development of HTG in carriers of the mutation.
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Affiliation(s)
- Irina N Gorshkova
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118 Department of Medicine, Boston University School of Medicine, Boston, MA 02118
| | - Xiaohu Mei
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - David Atkinson
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
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19
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Kuivenhoven JA, Hegele RA. Mining the genome for lipid genes. Biochim Biophys Acta Mol Basis Dis 2014; 1842:1993-2009. [PMID: 24798233 DOI: 10.1016/j.bbadis.2014.04.028] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 04/22/2014] [Accepted: 04/27/2014] [Indexed: 12/12/2022]
Abstract
Mining of the genome for lipid genes has since the early 1970s helped to shape our understanding of how triglycerides are packaged (in chylomicrons), repackaged (in very low density lipoproteins; VLDL), and hydrolyzed, and also how remnant and low-density lipoproteins (LDL) are cleared from the circulation. Gene discoveries have also provided insights into high-density lipoprotein (HDL) biogenesis and remodeling. Interestingly, at least half of these key molecular genetic studies were initiated with the benefit of prior knowledge of relevant proteins. In addition, multiple important findings originated from studies in mouse, and from other types of non-genetic approaches. Although it appears by now that the main lipid pathways have been uncovered, and that only modulators or adaptor proteins such as those encoded by LDLRAP1, APOA5, ANGPLT3/4, and PCSK9 are currently being discovered, genome wide association studies (GWAS) in particular have implicated many new loci based on statistical analyses; these may prove to have equally large impacts on lipoprotein traits as gene products that are already known. On the other hand, since 2004 - and particularly since 2010 when massively parallel sequencing has become de rigeur - no major new insights into genes governing lipid metabolism have been reported. This is probably because the etiologies of true Mendelian lipid disorders with overt clinical complications have been largely resolved. In the meantime, it has become clear that proving the importance of new candidate genes is challenging. This could be due to very low frequencies of large impact variants in the population. It must further be emphasized that functional genetic studies, while necessary, are often difficult to accomplish, making it hazardous to upgrade a variant that is simply associated to being definitively causative. Also, it is clear that applying a monogenic approach to dissect complex lipid traits that are mostly of polygenic origin is the wrong way to proceed. The hope is that large-scale data acquisition combined with sophisticated computerized analyses will help to prioritize and select the most promising candidate genes for future research. We suggest that at this point in time, investment in sequence technology driven candidate gene discovery could be recalibrated by refocusing efforts on direct functional analysis of the genes that have already been discovered. This article is part of a Special Issue entitled: From Genome to Function.
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Affiliation(s)
- Jan Albert Kuivenhoven
- University of Groningen, University Medical Center Groningen, Department of Pediatrics, Section Molecular Genetics, Antonius Deusinglaan 1, 9713GZ Groningen, The Netherlands
| | - Robert A Hegele
- Blackburn Cardiovascular Genetics Laboratory, Robarts Research Institute, 4288A-1151 Richmond Street North, London, ON N6A 5B7, Canada
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20
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Fotakis P, Tiniakou I, Kateifides AK, Gkolfinopoulou C, Chroni A, Stratikos E, Zannis VI, Kardassis D. Significance of the hydrophobic residues 225-230 of apoA-I for the biogenesis of HDL. J Lipid Res 2013; 54:3293-302. [PMID: 24123812 DOI: 10.1194/jlr.m043489] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We studied the significance of four hydrophobic residues within the 225-230 region of apoA-I on its structure and functions and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of an apoA-I[F225A/V227A/F229A/L230A] mutant in apoA-I⁻/⁻ mice decreased plasma cholesterol, HDL cholesterol, and apoA-I levels. When expressed in apoA-I⁻/⁻ × apoE⁻/⁻ mice, approximately 40% of the mutant apoA-I as well as mouse apoA-IV and apoB-48 appeared in the VLDL/IDL/LDL. In both mouse models, the apoA-I mutant generated small spherical particles of pre-β- and α4-HDL mobility. Coexpression of the apoA-I mutant and LCAT increased and shifted the-HDL cholesterol peak toward lower densities, created normal αHDL subpopulations, and generated spherical-HDL particles. Biophysical analyses suggested that the apoA-I[225-230] mutations led to a more compact folding that may limit the conformational flexibility of the protein. The mutations also reduced the ability of apoA-I to promote ABCA1-mediated cholesterol efflux and to activate LCAT to 31% and 66%, respectively, of the WT control. Overall, the apoA-I[225-230] mutations inhibited the biogenesis of-HDL and led to the accumulation of immature pre-β- and α4-HDL particles, a phenotype that could be corrected by administration of LCAT.
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Affiliation(s)
- Panagiotis Fotakis
- Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118
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21
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Oda MN, Budamagunta MS, Geier EG, Chandradas SH, Shao B, Heinecke JW, Voss JC, Cavigiolio G. Conservation of apolipoprotein A-I's central domain structural elements upon lipid association on different high-density lipoprotein subclasses. Biochemistry 2013; 52:6766-78. [PMID: 23984834 DOI: 10.1021/bi4007012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The antiatherogenic properties of apolipoprotein A-I (apoA-I) are derived, in part, from lipidation-state-dependent structural elements that manifest at different stages of apoA-I's progression from lipid-free protein to spherical high-density lipoprotein (HDL). Previously, we reported the structure of apoA-I's N-terminus on reconstituted HDLs (rHDLs) of different sizes. We have now investigated at the single-residue level the conformational adaptations of three regions in the central domain of apoA-I (residues 119-124, 139-144, and 164-170) upon apoA-I lipid binding and HDL formation. An important function associated with these residues of apoA-I is the activation of lecithin:cholesterol acyltransferase (LCAT), the enzyme responsible for catalyzing HDL maturation. Structural examination was performed by site-directed tryptophan fluorescence and spin-label electron paramagnetic resonance spectroscopies for both the lipid-free protein and rHDL particles 7.8, 8.4, and 9.6 nm in diameter. The two methods provide complementary information about residue side chain mobility and molecular accessibility, as well as the polarity of the local environment at the targeted positions. The modulation of these biophysical parameters yielded new insight into the importance of structural elements in the central domain of apoA-I. In particular, we determined that the loosely lipid-associated structure of residues 134-145 is conserved in all rHDL particles. Truncation of this region completely abolished LCAT activation but did not significantly affect rHDL size, reaffirming the important role of this structural element in HDL function.
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Affiliation(s)
- Michael N Oda
- Children's Hospital Oakland Research Institute , Oakland, California 94609, United States
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22
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Fotakis P, Kateifides AK, Gkolfinopoulou C, Georgiadou D, Beck M, Gründler K, Chroni A, Stratikos E, Kardassis D, Zannis VI. Role of the hydrophobic and charged residues in the 218-226 region of apoA-I in the biogenesis of HDL. J Lipid Res 2013; 54:3281-92. [PMID: 23990662 DOI: 10.1194/jlr.m038356] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We investigated the significance of hydrophobic and charged residues 218-226 on the structure and functions of apoA-I and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of apoA-I[L218A/L219A/V221A/L222A] in apoA-I⁻/⁻ mice decreased plasma cholesterol and apoA-I levels to 15% of wild-type (WT) control mice and generated pre-β- and α4-HDL particles. In apoA-I⁻/⁻ × apoE⁻/⁻ mice, the same mutant formed few discoidal and pre-β-HDL particles that could not be converted to mature α-HDL particles by excess LCAT. Expression of the apoA-I[E223A/K226A] mutant in apoA-I⁻/⁻ mice caused lesser but discrete alterations in the HDL phenotype. The apoA-I[218-222] and apoA-I[E223A/K226A] mutants had 20% and normal capacity, respectively, to promote ABCA1-mediated cholesterol efflux. Both mutants had ∼65% of normal capacity to activate LCAT in vitro. Biophysical analyses suggested that both mutants affected in a distinct manner the structural integrity and plasticity of apoA-I that is necessary for normal functions. We conclude that the alteration of the hydrophobic 218-222 residues of apoA-I disrupts apoA-I/ABCA1 interactions and promotes the generation of defective pre-β particles that fail to mature into α-HDL subpopulations, thus resulting in low plasma apoA-I and HDL. Alterations of the charged 223, 226 residues caused milder but discrete changes in HDL phenotype.
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Affiliation(s)
- Panagiotis Fotakis
- Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118
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23
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Daniil G, Zannis VI, Chroni A. Effect of apoA-I Mutations in the Capacity of Reconstituted HDL to Promote ABCG1-Mediated Cholesterol Efflux. PLoS One 2013; 8:e67993. [PMID: 23826352 PMCID: PMC3694867 DOI: 10.1371/journal.pone.0067993] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 05/23/2013] [Indexed: 12/29/2022] Open
Abstract
ATP binding cassette transporter G1 (ABCG1) mediates the cholesterol transport from cells to high-density lipoprotein (HDL), but the role of apolipoprotein A-I (apoA-I), the main protein constituent of HDL, in this process is not clear. To address this, we measured cholesterol efflux from HEK293 cells or J774 mouse macrophages overexpressing ABCG1 using as acceptors reconstituted HDL (rHDL) containing wild-type or various mutant apoA-I forms. It was found that ABCG1-mediated cholesterol efflux was severely reduced (by 89%) when using rHDL containing the carboxyl-terminal deletion mutant apoA-I[Δ(185–243)]. ABCG1-mediated cholesterol efflux was not affected or moderately decreased by rHDL containing amino-terminal deletion mutants and several mid-region deletion or point apoA-I mutants, and was restored to 69–99% of control by double deletion mutants apoA-I[Δ(1–41)Δ(185–243)] and apoA-I[Δ(1–59)Δ(185–243)]. These findings suggest that the central helices alone of apoA-I associated to rHDL can promote ABCG1-mediated cholesterol efflux. Further analysis showed that rHDL containing the carboxyl-terminal deletion mutant apoA-I[Δ(185–243)] only slightly reduced (by 22%) the ABCG1-mediated efflux of 7-ketocholesterol, indicating that depending on the sterol type, structural changes in rHDL-associated apoA-I affect differently the ABCG1-mediated efflux of cholesterol and 7-ketocholesterol. Overall, our findings demonstrate that rHDL-associated apoA-I structural changes affect the capacity of rHDL to accept cellular cholesterol by an ABCG1-mediated process. The structure-function relationship seen here between rHDL-associated apoA-I mutants and ABCG1-mediated cholesterol efflux closely resembles that seen before in lipid-free apoA-I mutants and ABCA1-dependent cholesterol efflux, suggesting that both processes depend on the same structural determinants of apoA-I.
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Affiliation(s)
- Georgios Daniil
- Institute of Biosciences and Applications, National Center for Scientific Research “Demokritos”, Agia Paraskevi, Athens, Greece
| | - Vassilis I. Zannis
- Molecular Genetics, Departments of Medicine and Biochemistry, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts, United States of America
| | - Angeliki Chroni
- Institute of Biosciences and Applications, National Center for Scientific Research “Demokritos”, Agia Paraskevi, Athens, Greece
- * E-mail:
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Sequence-specific apolipoprotein A-I effects on lecithin:cholesterol acyltransferase activity. Mol Cell Biochem 2013; 378:283-90. [DOI: 10.1007/s11010-013-1619-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 03/02/2013] [Indexed: 01/08/2023]
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Karavia EA, Papachristou DJ, Liopeta K, Triantaphyllidou IE, Dimitrakopoulos O, Kypreos KE. Apolipoprotein A-I modulates processes associated with diet-induced nonalcoholic fatty liver disease in mice. Mol Med 2012; 18:901-12. [PMID: 22576368 DOI: 10.2119/molmed.2012.00113] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 05/04/2012] [Indexed: 12/13/2022] Open
Abstract
Apolipoprotein A-I (apoA-I) is the main protein of high-density lipoprotein (HDL). We investigated the involvement of apoA-I in diet-induced accumulation of triglycerides in hepatocytes and its potential role in the treatment of nonalcoholic fatty liver disease (NAFLD). ApoA-I-deficient (apoA-I(-/-)) mice showed increased diet-induced hepatic triglyceride deposition and disturbed hepatic histology while they exhibited reduced glucose tolerance and insulin sensitivity. Quantification of FASN (fatty acid synthase) [corrected], DGAT-1 (diacylglycerol O-acyltransferase 1), and PPARγ (peroxisome proliferator-activated receptor γ) mRNA expression suggested that the increased hepatic triglyceride content of the apoA-I(-/-) mice was not due to de novo synthesis of triglycerides. Similarly, metabolic profiling did not reveal differences in the energy expenditure between the two mouse groups. However, apoA-I(-/-) mice exhibited enhanced intestinal absorption of dietary triglycerides (3.6 ± 0.5 mg/dL/min for apoA-I(-/-) versus 2.0 ± 0.7 mg/dL/min for C57BL/6 mice, P < 0.05), accelerated clearance of postprandial triglycerides and a reduced rate of hepatic very low density lipoprotein (VLDL) triglyceride secretion (9.8 ± 1.1 mg/dL/min for apoA-I(-/-) versus 12.5 ± 1.3 mg/dL/min for C57BL/6 mice, P < 0.05). In agreement with these findings, adenovirus-mediated gene transfer of apoA-I(Milano) in apoA-I(-/-) mice fed a Western-type diet for 12 wks resulted in a significant reduction in hepatic triglyceride content and an improvement of hepatic histology and architecture. Our data extend the current knowledge on the functions of apoA-I, indicating that in addition to its well-established properties in atheroprotection, it is also an important modulator of processes associated with diet-induced hepatic lipid deposition and NAFLD development in mice. Our findings raise the interesting possibility that expression of therapeutic forms of apoA-I by gene therapy approaches may have a beneficial effect on NAFLD.
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Affiliation(s)
- Eleni A Karavia
- Pharmacology Laboratory, Department of Medicine, University of Patras Medical School, Rio, Greece
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26
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Mei X, Atkinson D. Crystal structure of C-terminal truncated apolipoprotein A-I reveals the assembly of high density lipoprotein (HDL) by dimerization. J Biol Chem 2011; 286:38570-38582. [PMID: 21914797 DOI: 10.1074/jbc.m111.260422] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Apolipoprotein A-I (apoA-I) plays important structural and functional roles in plasma high density lipoprotein (HDL) that is responsible for reverse cholesterol transport. However, a molecular understanding of HDL assembly and function remains enigmatic. The 2.2-Å crystal structure of Δ(185-243)apoA-I reported here shows that it forms a half-circle dimer. The backbone of the dimer consists of two elongated antiparallel proline-kinked helices (five AB tandem repeats). The N-terminal domain of each molecule forms a four-helix bundle with the helical C-terminal region of the symmetry-related partner. The central region forms a flexible domain with two antiparallel helices connecting the bundles at each end. The two-domain dimer structure based on helical repeats suggests the role of apoA-I in the formation of discoidal HDL particles. Furthermore, the structure suggests the possible interaction with lecithin-cholesterol acyltransferase and may shed light on the molecular details of the effect of the Milano, Paris, and Fin mutations.
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Affiliation(s)
- Xiaohu Mei
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118
| | - David Atkinson
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118.
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Abstract
INTRODUCTION. We have studied the functions of truncated apoE4 forms in vitro and in vivo in order to identify the domains of apoE4 required for the biogenesis of apoE-containing high-density lipoprotein (HDL). RESULTS. We have found that apoE4-185, -202, -229, or -259 could promote ATP-binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux in vitro, although less efficiently than Full-length apoE4, and had diminished capacity to activate lecithin cholesterol acyltransferase (LCAT). Formation of HDL in vivo was assessed by various methods following gene transfer in apolipoprotein A-I(-/-) × apoE(-/-) mice. Fast protein liquid chromatography of plasma showed that the truncated apoE forms, except apoE4-185, generated an apoE-containing HDL peak. Two-dimensional gel electrophoresis of plasma and electron microscopy showed that truncated apoE forms generated distinct HDL subpopulations and formed discoidal HDL particles which could be converted to spherical by co-administration of truncated apoE4-202 and LCAT. CONCLUSION. Overall, the in-vivo and in-vitro data are consistent and indicate that apoE4-185 is the shortest truncated form that supports formation of discoidal apoE4-containing HDL particles.
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Affiliation(s)
- Alexander M Vezeridis
- Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, USA
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Kateifides AK, Gorshkova IN, Duka A, Chroni A, Kardassis D, Zannis VI. Alteration of negatively charged residues in the 89 to 99 domain of apoA-I affects lipid homeostasis and maturation of HDL. J Lipid Res 2011; 52:1363-72. [PMID: 21504968 DOI: 10.1194/jlr.m012989] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this study, we investigated the role of positively and negatively charged amino acids within the 89-99 region of apolipoprotein A-I (apoA-I), which are highly conserved in mammals, on plasma lipid homeostasis and the biogenesis of HDL. We previously showed that deletion of the 89-99 region of apoA-I increased plasma cholesterol and phospholipids, but it did not affect plasma triglycerides. Functional studies using adenovirus-mediated gene transfer of two apoA-I mutants in apoA-I-deficient mice showed that apoA-I[D89A/E91A/E92A] increased plasma cholesterol and caused severe hypertriglyceridemia. HDL levels were reduced, and approximately 40% of the apoA-I was distributed in VLDL/IDL. The HDL consisted of mostly spherical and a few discoidal particles and contained preβ1 and α4-HDL subpopulations. The lipid, lipoprotein, and HDL profiles generated by the apoA-I[K94A/K96A] mutant were similar to those of wild-type (WT) apoA-I. Coexpression of apoA-I[D89A/E91A/E92A] and human lipoprotein lipase abolished hypertriglyceridemia, restored in part the α1,2,3,4 HDL subpopulations, and redistributed apoA-I in the HDL2/HDL3 regions, but it did not prevent the formation of discoidal HDL particles. Physicochemical studies showed that the apoA-I[D89A/E91A/E92A] mutant had reduced α-helical content and effective enthalpy of thermal denaturation, increased exposure of hydrophobic surfaces, and increased affinity for triglyceride-rich emulsions. We conclude that residues D89, E91, and E92 of apoA-I are important for plasma cholesterol and triglyceride homeostasis as well as for the maturation of HDL.
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Gorshkova IN, Atkinson D. Enhanced binding of apolipoprotein A-I variants associated with hypertriglyceridemia to triglyceride-rich particles. Biochemistry 2011; 50:2040-7. [PMID: 21288012 PMCID: PMC6128146 DOI: 10.1021/bi200158b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hypertriglyceridemia (HTG) is a common lipid abnormality in humans. However, its etiology remains largely unknown. It was shown that severe HTG can be induced in mice by overexpression of wild-type (WT) apolipoprotein E (apoE) or specific apoA-I mutants. Certain mutations in apoE4 were found to affect plasma triglyceride (TG) levels in mice overexpressing the protein. HTG appeared to positively correlate with the ability of the apoE4 variants to bind to TG-rich particles, protein destabilization, and the exposure of protein hydrophobic surface in solution. Here, we propose that the apoA-I mutations that cause HTG may also lead to changes in the conformation and stability that promote binding of apoA-I to TG-rich lipoproteins. To test this hypothesis, we studied binding to TG-rich emulsion and biophysical properties of the apoA-I mutants that induce HTG, apoA-I[E110A/E111A] and apoA-I[Δ(61-78)], and compared them to those of WT apoA-I and another apoA-I mutant, apoA-I[Δ(89-99)], that does not induce HTG but causes hypercholesterolemia in mice. We found that the apoA-I[E110A/E111A] and apoA-I[Δ(61-78)] mutations lead to enhanced binding of apoA-I to TG-rich particles, destabilization, and greater exposure of the hydrophobic surface of the protein. The apoA-I[Δ(89-99)] mutant did not show enhanced binding to the emulsion or a more exposed hydrophobic surface. Thus, like apoE4, the apoA-I variants that cause HTG in mice have the altered conformation and stability that facilitate their binding to TG-rich lipoproteins and thereby may lead to the reduced level of lipolysis of these lipoproteins. While many factors may be involved in induction of HTG, we suggest that an increased level of association of destabilized loosely folded apolipoproteins with TG-rich lipoproteins may contribute to some cases of HTG in humans.
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Affiliation(s)
- Irina N Gorshkova
- Department of Physiology and Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, Massachusetts 02118, United States.
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30
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Abstract
Schizophrenia is one of the most severe psychiatric disorders affecting 1% of the world population. There is yet no empirical method to validate the diagnosis of the disease. The identification of an underlying molecular alteration could lead to an improved disease understanding and may yield an objective panel of biomarkers to aid in the diagnosis of this devastating disease. Presented is the largest reported liquid chromatography-mass spectrometry-based proteomic profiling study investigating serum samples taken from first-onset drug-naive patients compared with samples collected from healthy volunteers. The results of this large-scale study are presented along with enzyme-linked immunosorbent assay-based validation data.
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31
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Allahverdian S, Francis GA. Cholesterol Homeostasis and High-Density Lipoprotein Formation in Arterial Smooth Muscle Cells. Trends Cardiovasc Med 2010; 20:96-102. [DOI: 10.1016/j.tcm.2010.09.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/31/2010] [Indexed: 01/24/2023]
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Jones MK, Catte A, Li L, Segrest JP. Dynamics of activation of lecithin:cholesterol acyltransferase by apolipoprotein A-I. Biochemistry 2009; 48:11196-210. [PMID: 19860440 DOI: 10.1021/bi901242k] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The product of transesterification of phospholipid acyl chains and unesterified cholesterol (UC) by the enzyme lecithin:cholesterol acyltransferase (LCAT) is cholesteryl ester (CE). Activation of LCAT by apolipoprotein (apo) A-I on nascent (discoidal) high-density lipoproteins (HDL) is essential for formation of mature (spheroidal) HDL during the antiatherogenic process of reverse cholesterol transport. Here we report all-atom and coarse-grained (CG) molecular dynamics (MD) simulations of HDL particles that have major implications for mechanisms of LCAT activation. Both the all-atom and CG simulations provide support for a model in which the helix 5/5 domains of apoA-I create an amphipathic "presentation tunnel" that exposes methyl ends of acyl chains at the bilayer center to solvent. Further, CG simulations show that UC also becomes inserted with high efficiency into the amphipathic presentation tunnel with its hydroxyl moiety (UC-OH) exposed to solvent; these results are consistent with trajectory analyses of the all-atom simulations showing that UC is being concentrated in the vicinity of the presentation tunnel. Finally, consistent with known product inhibition of CE-rich HDL by CE, CG simulations of CE-rich spheroidal HDL indicate partial blockage of the amphipathic presentation tunnel by CE. These results lead us to propose the following working hypothesis. After attachment of LCAT to discoidal HDL, the helix 5/5 domains in apoA-I form amphipathic presentation tunnels for migration of hydrophobic acyl chains and amphipathic UC from the bilayer to the phospholipase A2-like and esterification active sites of LCAT, respectively. This hypothesis is currently being tested by site-directed mutagenesis.
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Affiliation(s)
- Martin K Jones
- Department of Medicine and Atherosclerosis Research Unit, University ofAlabama, Birmingham, Alabama 35294, USA
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33
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Gorshkova IN, Kypreos KE, Gantz DL, Zannis VI, Atkinson D. Biophysical properties of apolipoprotein E4 variants: implications in molecular mechanisms of correction of hypertriglyceridemia. Biochemistry 2009; 47:12644-54. [PMID: 18959431 DOI: 10.1021/bi8015857] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In humans and animal models, high plasma concentrations of apolipoprotein (apo) E are associated with hypertriglyceridemia. It has been shown that overexpression of human wild-type (WT) apoE4 in apoE-deficient mice induces hypertriglyceridemia. In contrast, overexpression of an apoE4 variant, apoE4-mut1 (apoE4(L261A, W264A, F265A, L268A, V269A)), does not induce hypertriglyceridemia and corrects hypercholesterolemia. Furthermore, overexpression of another variant, apoE4-mut2 (apoE4(W276A, L279A, V280A, V283A)), induces mild hypertriglyceridemia and does not correct hypercholesterolemia. To better understand how these mutations improve the function of apoE4, we investigated the conformation and stability of apoE4-mut1 and apoE4-mut2 and their binding to dimyristoyl phosphatidylcholine (DMPC) vesicles and to triglyceride (TG)-rich emulsion particles. We found that the mutations introduced in apoE4-mut1 lead to a more stable and compactly folded conformation of apoE4. These structural changes are associated with a slower rate of solubilization of DMPC vesicles by apoE4-mut1 and reduced binding of the protein to emulsion particles compared with WT apoE4. Under conditions of apoE4 overexpression, the reduced binding of apoE4-mut1 to TG-rich lipoprotein particles may facilitate the lipolysis of these particles and may alter the conformation of the lipoprotein-bound apoE in a way that favors the efficient clearance of the lipoprotein remnants. Mutations introduced in apoE4-mut2 result in smaller structural alterations compared with those observed in apoE4-mut1. The slightly altered structural properties of apoE4-mut2 are associated with slightly reduced binding of this protein to TG-rich lipoprotein particles and milder hypertriglyceridemia as compared with WT apoE4.
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Affiliation(s)
- Irina N Gorshkova
- Department of Physiology and Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, Massachusetts 02118, USA.
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34
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Kypreos KE. ABCA1 Promotes the de Novo Biogenesis of Apolipoprotein CIII-Containing HDL Particles in Vivo and Modulates the Severity of Apolipoprotein CIII-Induced Hypertriglyceridemia. Biochemistry 2008; 47:10491-502. [DOI: 10.1021/bi801249c] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kyriakos E. Kypreos
- Department of Medicine, Pharmacology Unit, University of Patras Medical School, Rio, TK 26500, Greece
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35
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Stavrakoudis A. Molecular dynamics simulations of an apoliprotein A–I derived peptide in explicit water. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.07.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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36
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Boucher JG, Nguyen T, Sparks DL. Lipoprotein electrostatic properties regulate hepatic lipase association and activity. Biochem Cell Biol 2008; 85:696-708. [PMID: 18059528 DOI: 10.1139/o07-137] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The effect of lipoprotein electrostatic properties on the catalytic regulation of hepatic lipase (HL) was investigated. Enrichment of serum or very low density lipoprotein (VLDL) with oleic acid increased lipoprotein negative charge and stimulated lipid hydrolysis by HL. Similarly, enrichment of serum or isolated lipoproteins with the anionic phospholipids phosphatidylinositol (PI), phosphatidic acid, or phosphatidylserine also increased lipoprotein negative charge and stimulated hydrolysis by HL. Anionic lipids had a small effect on phospholipid hydrolysis, but significantly stimulated triacylglyceride (TG) hydrolysis. High density lipoprotein (HDL) charge appears to have a specific effect on lipolysis. Enrichment of HDL with PI significantly stimulated VLDL-TG hydrolysis by HL. To determine whether HDL charge affects the association of HL with HDL and VLDL, HL-lipoprotein interactions were probed immunochemically. Under normal circumstances, HL associates with HDL particles, and only small amounts bind to VLDL. PI enrichment of HDL blocked the binding of HL with HDL. These data indicate that increasing the negative charge of HDL stimulates VLDL-TG hydrolysis by reducing the association of HL with HDL. Therefore, HDL controls the hydrolysis of VLDL by affecting the interlipoprotein association of HL. Lipoprotein electrostatic properties regulate lipase association and are an important regulator of the binding and activity of lipolytic enzymes.
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Affiliation(s)
- Jonathan G Boucher
- Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, 40 Ruskin Street H452, Ottawa, Ontario, Canada
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37
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Zannis VI, Koukos G, Drosatos K, Vezeridis A, Zanni EE, Kypreos KE, Chroni A. Discrete roles of apoA-I and apoE in the biogenesis of HDL species: lessons learned from gene transfer studies in different mouse models. Ann Med 2008; 40 Suppl 1:14-28. [PMID: 18246469 DOI: 10.1080/07853890701687219] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Using adenovirus-mediated gene transfer in apolipoprotein A-I (apoA-I)-deficient mice, we have established that apoA-I mutations inhibit discrete steps in a pathway that leads to the biogenesis and remodeling of high-density lipoprotein (HDL). To this point, five discrete categories of apoA-I mutants have been characterized that may affect the interactions of apoA-I with ATP-binding cassette superfamily A, member 1 (ABCA1) or lecithin:cholesterol acyl transferase (LCAT) or may influence the plasma phospholipid transfer protein activity or may cause various forms of dyslipidemia. Biogenesis of HDL is not a unique property of apoA-I. Using adenovirus-mediated gene transfer of apoE in apoA-I- or ABCA1-deficient mice, we have established that apolipoprotein E (apoE) also participates in a novel pathway of biogenesis of apoE-containing HDL particles. This process requires the functions of the ABCA1 lipid transporter and LCAT, and it is promoted by substitution of hydrophobic residues in the 261 to 269 region of apoE by Ala. The apoE-containing HDL particles formed in the circulation may have atheroprotective properties. ApoE-containing HDL may also have important biological functions in the brain that confer protection from Alzheimer's disease.
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Affiliation(s)
- Vassilis I Zannis
- Molecular Genetics, Whitaker Cardiovascular Institute, Departments of Medicine and Biochemistry, Boston University School of Medicine, Boston, MA 02118-2394, USA.
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Koukos G, Chroni A, Duka A, Kardassis D, Zannis V. Naturally occurring and bioengineered apoA-I mutations that inhibit the conversion of discoidal to spherical HDL: the abnormal HDL phenotypes can be corrected by treatment with LCAT. Biochem J 2007; 406:167-74. [PMID: 17506726 PMCID: PMC1948983 DOI: 10.1042/bj20070296] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
In the present study we have used adenovirus-mediated gene transfer of apoA-I (apolipoprotein A-I) mutants in apoA-I-/- mice to investigate how structural mutations in apoA-I affect the biogenesis and the plasma levels of HDL (high-density lipoprotein). The natural mutants apoA-I(R151C)Paris, apoA-I(R160L)Oslo and the bioengineered mutant apoA-I(R149A) were secreted efficiently from cells in culture. Their capacity to activate LCAT (lecithin:cholesterol acyltransferase) in vitro was greatly reduced, and their ability to promote ABCA1 (ATP-binding cassette transporter A1)-mediated cholesterol efflux was similar to that of WT (wild-type) apoA-I. Gene transfer of the three mutants in apoA-I-/- mice generated aberrant HDL phenotypes. The total plasma cholesterol of mice expressing the apoA-I(R160L)Oslo, apoA-I(R149A) and apoA-I(R151C)Paris mutants was reduced by 78, 59 and 61% and the apoA-I levels were reduced by 68, 64 and 55% respectively, as compared with mice expressing the WT apoA-I. The CE (cholesteryl ester)/TC (total cholesterol) ratio of HDL was decreased and the apoA-I was distributed in the HDL3 region. apoA-I(R160L)Oslo and apoA-I(R149A) promoted the formation of prebeta1 and alpha4-HDL subpopulations and gave a mixture of discoidal and spherical particles. apoA-I(R151C)Paris generated subpopulations of different sizes that migrate between prebeta and alpha-HDL and formed mostly spherical and a few discoidal particles. Simultaneous treatment of mice with adenovirus expressing any of the three mutants and human LCAT normalized plasma apoA-I, HDL cholesterol levels and the CE/TC ratio. It also led to the formation of spherical HDL particles consisting mostly of alpha-HDL subpopulations of larger size. The correction of the aberrant HDL phenotypes by treatment with LCAT suggests a potential therapeutic intervention for HDL abnormalities that result from specific mutations in apoA-I.
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Affiliation(s)
- Georgios Koukos
- *Molecular Genetics, Departmental of Medicine and Biochemistry, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, U.S.A
- †Department of Basic Sciences, University of Crete Medical School, Heraklion, GR-71110, Greece
| | - Angeliki Chroni
- ‡Institute of Biology, National Center for Scientific Research ‘Demokritos’, 15310 Agia Paraskevi, Athens, Greece
| | - Adelina Duka
- *Molecular Genetics, Departmental of Medicine and Biochemistry, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, U.S.A
| | - Dimitris Kardassis
- ‡Institute of Biology, National Center for Scientific Research ‘Demokritos’, 15310 Agia Paraskevi, Athens, Greece
- §Institute of Molecular Biology and Biotechnology, FORTH (Foundation for Research and Technology-Hellas), Heraklion, Crete, Greece
| | - Vassilis I. Zannis
- *Molecular Genetics, Departmental of Medicine and Biochemistry, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA 02118, U.S.A
- ‡Institute of Biology, National Center for Scientific Research ‘Demokritos’, 15310 Agia Paraskevi, Athens, Greece
- To whom correspondence should be addressed (email )
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Drosatos K, Kypreos KE, Zannis VI. Residues Leu261, Trp264, and Phe265 account for apolipoprotein E-induced dyslipidemia and affect the formation of apolipoprotein E-containing high-density lipoprotein. Biochemistry 2007; 46:9645-53. [PMID: 17655277 PMCID: PMC2736595 DOI: 10.1021/bi700232g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Overexpression of apolipoprotein E (apoE) induces hypertriglyceridemia in apoE-deficient mice, which is abrogated by deletion of the carboxy-terminal segment of residues 260-299. We have used adenovirus-mediated gene transfer in apoE-/- and apoA-I-/- mice to test the effect of three sets of apoE mutations within the region of residues 261-265 on the induction of hypertriglyceridemia, the esterification of cholesterol of very low-density lipoprotein (VLDL) and high-density lipoprotein (HDL), and the formation of spherical or discoidal apoE-containing HDL. A single-amino acid substitution (apoE4[Phe265Ala]) induced hypertriglyceridemia in apoE-/- or apoA-I-/- mice, promoted the accumulation of free cholesterol in the very low-density lipoprotein (VLDL) and HDL region, and decreased HDL cholesterol levels. A double substitution (apoE4[Leu261Ala/Trp264Ala]) induced milder hypertriglyceridemia and increased HDL cholesterol levels. A triple substitution (apoE4[Leu261Ala/Trp264Ala/Phe265Ala] or apoE2[Leu261Ala/Trp264Ala/Phe265Ala]) did not induce hypertriglyceridemia and increased greatly the HDL cholesterol levels. Electron microscopy (EM) analysis of the HDL fractions showed that apoE4[Leu261Ala/Trp264Ala/Phe265Ala] and apoE2[Leu261Ala/Trp264Ala/Phe265Ala] contained spherical HDL, apoE4[Leu261Ala/Trp264Ala] contained mostly spherical and few discoidal HDL particles, and apoE4[Phe265Ala] contained discoidal HDL. We conclude that residues Leu261, Trp264, and Phe265 play an important role in apoE-induced hypertriglyceridemia, the accumulation of free cholesterol in VLDL and HDL, and the formation of discoidal HDL. Substitution of these residues with Ala improves the apoE functions by preventing hypertriglyceridemia and promoting formation of spherical apoE-containing HDL.
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Affiliation(s)
- Konstantinos Drosatos
- Molecular Genetics, Departments of Medicine and Biochemistry, Whitaker CardioVascular Institute, Boston UniVersity School of Medicine, Boston, Massachusetts 02118
- Department of Basic Sciences, UniVersity of Crete Medical School, Heraklion GR-71110, Greece
| | - Kyriakos E. Kypreos
- Molecular Genetics, Departments of Medicine and Biochemistry, Whitaker CardioVascular Institute, Boston UniVersity School of Medicine, Boston, Massachusetts 02118
| | - Vassilis I. Zannis
- Molecular Genetics, Departments of Medicine and Biochemistry, Whitaker CardioVascular Institute, Boston UniVersity School of Medicine, Boston, Massachusetts 02118
- Department of Basic Sciences, UniVersity of Crete Medical School, Heraklion GR-71110, Greece
- To whom correspondence should be addressed: 700 Albany St., W509, Boston, MA 02118-2394. Fax: (617) 638–5141. Telephone: (617) 638-5085. E-mail:
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Chroni A, Koukos G, Duka A, Zannis VI. The carboxy-terminal region of apoA-I is required for the ABCA1-dependent formation of alpha-HDL but not prebeta-HDL particles in vivo. Biochemistry 2007; 46:5697-708. [PMID: 17447731 PMCID: PMC2528067 DOI: 10.1021/bi602354t] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
ATP-binding cassette transporter A-1 (ABCA1)-mediated lipid efflux to lipid-poor apolipoprotein A-I (apoA-I) results in the gradual lipidation of apoA-I. This leads to the formation of discoidal high-density lipoproteins (HDL), which are subsequently converted to spherical HDL by the action of lecithin:cholesterol acyltransferase (LCAT). We have investigated the effect of point mutations and deletions in the carboxy-terminal region of apoA-I on the biogenesis of HDL using adenovirus-mediated gene transfer in apoA-I-deficient mice. It was found that the plasma HDL levels were greatly reduced in mice expressing the carboxy-terminal deletion mutants apoA-I[Delta(185-243)] and apoA-I[Delta(220-243)], shown previously to diminish the ABCA1-mediated lipid efflux. The HDL levels were normal in mice expressing the WT apoA-I, the apoA-I[Delta(232-243)] deletion mutant, or the apoA-I[E191A/H193A/K195A] point mutant, which promote normal ABCA1-mediated lipid efflux. Electron microscopy and two-dimensional gel electrophoresis showed that the apoA-I[Delta(185-243)] and apoA-I[Delta(220-243)] mutants formed mainly prebeta-HDL particles and few spherical particles enriched in apoE, while WT apoA-I, apoA-I[Delta(232-243)], and apoA-I[E191A/H193A/K195A] formed spherical alpha-HDL particles. The findings establish that (a) deletions that eliminate the 220-231 region of apoA-I prevent the synthesis of alpha-HDL but allow the synthesis of prebeta-HDL particles in vivo, (b) the amino-terminal segment 1-184 of apoA-I can promote synthesis of prebeta-HDL-type particles in an ABCA1-independent process, and (c) the charged residues in the 191-195 region of apoA-I do not influence the biogenesis of HDL.
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Affiliation(s)
- Angeliki Chroni
- Institute of Biology, National Center for Scientific Research Demokritos, Agia Paraskevi, Athens 15310, Greece.
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Zhang B, Katafuchi R, Arishima H, Matsunaga A, Rye KA, Saku K. Effects of atorvastatin and apoA-I/phosphatidylcholine discs on triglyceride-rich lipoprotein subfractions as characterized by capillary isotachophoresis. Clin Chim Acta 2006; 373:55-61. [PMID: 16806136 DOI: 10.1016/j.cca.2006.04.026] [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: 11/01/2005] [Revised: 04/27/2006] [Accepted: 04/30/2006] [Indexed: 12/31/2022]
Abstract
BACKGROUND The present study examined the effects of atorvastatin and the in vitro effect of apolipoprotein (apo) A-I/phosphatidylcholine (POPC) discs on charge-based triglyceride-rich lipoprotein (TRL) subfractions in a patient with type III hyperlipoproteinemia (HLP) and the apoE2/2 phenotype. METHODS Charge-based lipoprotein subfractions were characterized by capillary isotachophoresis (cITP). cITP analysis was performed using plasma that had been prestained with a lipophilic dye on a Beckman P/ACE MDQ system. RESULTS Treatment with atorvastatin for 4 weeks markedly decreased the slow (s)-migrating TRL subfraction and both fast- and slow-migrating low-density lipoprotein (LDL) subfractions, but did not affect the fast (f)-migrating TRL subfraction in this patient. ApoA-I/POPC discs consisted of two major charge-based subfractions that had the mobility of cITP fTRL and sTRL. Incubation of plasma from this patient in the presence of apoA-I/POPC discs caused not only a reduction in cITP fast- and intermediate-migrating HDL and an increase in cITP sHDL but also a reduction in fTRL and sTRL and an increase in sLDL. CONCLUSION Atorvastatin and apoA-I/POPC discs decreased cITP TRL subfractions in a complementary manner, suggesting that the combination of apoA-I/POPC discs and atorvastatin could be a promising therapeutic approach for hypertriglyceridemia.
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Affiliation(s)
- Bo Zhang
- Department of Cardiology, Fukuoka University School of Medicine, 7-45-1 Nanakuma Jonan-ku, Fukuoka 814-0180, Japan
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Gorshkova IN, Liu T, Kan HY, Chroni A, Zannis VI, Atkinson D. Structure and stability of apolipoprotein a-I in solution and in discoidal high-density lipoprotein probed by double charge ablation and deletion mutation. Biochemistry 2006; 45:1242-54. [PMID: 16430220 PMCID: PMC2532493 DOI: 10.1021/bi051669r] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
To identify residues and segments in the central region of apolipoprotein A-I (apoA-I) that are important for the protein structure and stability, we studied the effects of four double charge ablations, D102A/D103A, E110A/E111A, R116V/K118A, and R160V/H162A, and two deletion mutations, Delta(61-78) and Delta(121-142), on the conformation and stability of apoA-I in the lipid-free state and in reconstituted discoidal phospholipid-cholesterol-apoA-I particles (rHDL). The findings suggest that D102/D103 and E110/E111 located in helix 4 and segment(s) between residues 61 and 78 are involved in maintenance of the conformation and stability of apoA-I in both the lipid-free state and in rHDL. R116/K118 located in helix 4 are essential for the conformation and stabilization of apoA-I in rHDL but not vital for the lipid-free state of the protein. The R160V/H162A substitutions in helix 6 lead to a less compact tertiary structure of lipid-free apoA-I without notable effects on the lipid-free or lipid-bound secondary conformation, suggesting involvement of R160/H162 in important interhelical interactions. The results on the Delta(121-142) mutant, together with our earlier findings, suggest disordered structure of a major segment between residues 121 and 143, likely including residues 131-143, in lipid-free apoA-I. Our findings provide the first experimental evidence for stabilization of rHDL by specific electrostatic interhelical interactions, in agreement with the double belt model. The effects of alterations in the conformation and stability of the apoA-I mutants on in vitro and in vivo functions of apoA-I and lipid homeostasis are discussed.
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Affiliation(s)
- Irina N Gorshkova
- Department of Physiology and Biophysics, Boston University School of Medicine, 715 Albany Street, Boston, Massachusetts 02118, USA.
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Zannis VI, Chroni A, Krieger M. Role of apoA-I, ABCA1, LCAT, and SR-BI in the biogenesis of HDL. J Mol Med (Berl) 2006; 84:276-94. [PMID: 16501936 DOI: 10.1007/s00109-005-0030-4] [Citation(s) in RCA: 282] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Accepted: 11/21/2005] [Indexed: 12/12/2022]
Abstract
The concentration, composition, shape, and size of plasma high-density lipoprotein (HDL) are determined by numerous proteins that influence its biogenesis, remodeling, and catabolism. The discoveries of the HDL receptor (scavenger receptor class B type I, SR-BI) and the ABCA1 (ATP-binding cassette transporter A1) lipid transporter provided two missing links that were necessary to understand the biogenesis and some of the functions of HDL. Existing data indicate that functional interactions between apoA-I and ABCA1 are necessary for the initial lipidation of apoA-I. Through a series of intermediate steps, lipidated apoA-I proceeds to form discoidal HDL particles that can be converted to spherical particles by the action of lecithin:cholesterol acyltransferase (LCAT). Discoidal and spherical HDL can interact functionally with SR-BI and these interactions lead to selective lipid uptake and net efflux of cholesterol and thus remodel HDL. Defective apoA-I/ABCA1 interactions prevent lipidation of apoA-I that is necessary for the formation of HDL particles. In the same way, specific mutations in apoA-I or LCAT prevent the conversion of discoidal to spherical HDL particles. The interactions of lipid-bound apoA-I with SR-BI are affected in vitro by specific mutations in apoA-I or SR-BI. Furthermore, deficiency of SR-BI affects the lipid and apolipoprotein composition of HDL and is associated with increased susceptibility to atherosclerosis. Here we review the current status of the pathway of HDL biogenesis and mutations in apoA-I, ABCA1, and SR-BI that disrupt different steps of the pathway and may lead to dyslipidemia and atherosclerosis in mouse models. The phenotypes generated in experimental mouse models for apoA-I, ABCA1, LCAT, SR-BI, and other proteins of the HDL pathway may facilitate early diagnosis of similar phenotypes in the human population and provide guidance for proper treatment.
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Affiliation(s)
- Vassilis I Zannis
- Molecular Genetics, Whitaker Cardiovascular Institute and Department of Biochemistry, Boston University School of Medicine, MA 02118, USA.
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Abstract
PURPOSE OF REVIEW This review highlights recent advances in structural studies of exchangeable human apolipoproteins and the insights they provide into lipoprotein action in cardiovascular and amyloid diseases. RECENT FINDINGS The high-resolution X-ray crystal structure of free apoA-II reveals a parallel helical array that may represent other lipid-poor apolipoproteins, and the structure in complex with detergent substantiates the belt model for the protein arrangement on lipoproteins. Nuclear magnetic resonance structures of apolipoprotein-detergent complexes show a repertoire of curved helical conformations, suggesting multiple helical arrangements on the lipid. Low-resolution spectroscopic analyses, interface studies and molecular modeling provide new insights into the 'hinge-domain' mechanism of apolipoprotein adaptation at variable lipoprotein surfaces. A kinetic mechanism for lipoprotein stabilization is proposed. SUMMARY Cumulative evidence supports the belt model that provides a general structural basis for understanding the molecular mechanisms of functional apolipoprotein reactions, such as binding to lipoprotein receptors, lipid transporters, and the activation of lipophilic enzymes. However, the detailed protein and lipid conformations on lipoproteins and the underlying molecular interactions are unclear. New insights will hopefully emerge once the first detailed lipoprotein structure is solved.
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Affiliation(s)
- Olga Gursky
- Department of Physiology and Biophysics, Boston University School of Medicine, W329, Boston, Massachusetts 02118, USA.
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