1
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Strickland MR, Rau MJ, Summers B, Basore K, Wulf J, Jiang H, Chen Y, Ulrich JD, Randolph GJ, Zhang R, Fitzpatrick JAJ, Cashikar AG, Holtzman DM. Apolipoprotein E secreted by astrocytes forms antiparallel dimers in discoidal lipoproteins. Neuron 2024; 112:1100-1109.e5. [PMID: 38266643 PMCID: PMC10994765 DOI: 10.1016/j.neuron.2023.12.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 11/24/2023] [Accepted: 12/22/2023] [Indexed: 01/26/2024]
Abstract
The Apolipoprotein E gene (APOE) is of great interest due to its role as a risk factor for late-onset Alzheimer's disease. ApoE is secreted by astrocytes in the central nervous system in high-density lipoprotein (HDL)-like lipoproteins. Structural models of lipidated ApoE of high resolution could aid in a mechanistic understanding of how ApoE functions in health and disease. Using monoclonal Fab and F(ab')2 fragments, we characterize the structure of lipidated ApoE on astrocyte-secreted lipoproteins. Our results provide support for the "double-belt" model of ApoE in nascent discoidal HDL-like lipoproteins, where two ApoE proteins wrap around the nanodisc in an antiparallel conformation. We further show that lipidated, recombinant ApoE accurately models astrocyte-secreted ApoE lipoproteins. Cryogenic electron microscopy of recombinant lipidated ApoE further supports ApoE adopting antiparallel dimers in nascent discoidal lipoproteins.
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Affiliation(s)
| | - Michael J Rau
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Brock Summers
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Katherine Basore
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - John Wulf
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Hong Jiang
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Yun Chen
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Department of Pathology and Immunology, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Jason D Ulrich
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Hope Center for Neurological Disorders, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Knight Alzheimer's Disease Research Center, 4488 Forest Park Ave., St. Louis, MO 63108, USA
| | - Gwendalyn J Randolph
- Department of Pathology and Immunology, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Rui Zhang
- Department of Biochemistry and Molecular Biophysics, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - James A J Fitzpatrick
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Anil G Cashikar
- Hope Center for Neurological Disorders, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Department of Psychiatry, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Taylor Family institute for Innovative Psychiatric Research, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - David M Holtzman
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Hope Center for Neurological Disorders, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Knight Alzheimer's Disease Research Center, 4488 Forest Park Ave., St. Louis, MO 63108, USA.
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2
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Ohgita T, Sakai K, Fukui N, Namba N, Nakano M, Kiguchi Y, Morita I, Oyama H, Yamaki K, Nagao K, Kobayashi N, Saito H. Generation of novel anti-apoE monoclonal antibodies that selectively recognize apoE isoforms. FEBS Lett 2024; 598:902-914. [PMID: 38529702 DOI: 10.1002/1873-3468.14858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 12/21/2023] [Accepted: 12/22/2023] [Indexed: 03/27/2024]
Abstract
Apolipoprotein E (apoE) is a regulator of lipid metabolism, cholesterol transport, and the clearance and aggregation of amyloid β in the brain. The three human apoE isoforms apoE2, apoE3, and apoE4 only differ in one or two residues. Nevertheless, the functions highly depend on the isoform types and lipidated states. Here, we generated novel anti-apoE monoclonal antibodies (mAbs) and obtained an apoE4-selective mAb whose epitope is within residues 110-117. ELISA and bio-layer interferometry measurements demonstrated that the dissociation constants of mAbs are within the nanomolar range. Using the generated antibodies, we successfully constructed sandwich ELISA systems, which can detect all apoE isoforms or selectively detect apoE4. These results suggest the usability of the generated anti-apoE mAbs for selective detection of apoE isoforms.
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Affiliation(s)
- Takashi Ohgita
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
- Center for Instrumental Analysis, Kyoto Pharmaceutical University, Japan
| | - Koto Sakai
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
| | - Nodoka Fukui
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
| | - Norihiro Namba
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
| | - Miyu Nakano
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
| | - Yuki Kiguchi
- Laboratory of Bioanalytical Chemistry, Kobe Pharmaceutical University, Japan
| | - Izumi Morita
- Laboratory of Bioanalytical Chemistry, Kobe Pharmaceutical University, Japan
| | - Hiroyuki Oyama
- Laboratory of Bioanalytical Chemistry, Kobe Pharmaceutical University, Japan
| | - Kouya Yamaki
- Laboratory of Pharmacology, Kobe Pharmaceutical University, Japan
| | - Kohjiro Nagao
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
| | - Norihiro Kobayashi
- Laboratory of Bioanalytical Chemistry, Kobe Pharmaceutical University, Japan
| | - Hiroyuki Saito
- Laboratory of Biophysical Chemistry, Kyoto Pharmaceutical University, Japan
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3
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Lewkowicz E, Nakamura MN, Rynkiewicz MJ, Gursky O. Molecular modeling of apoE in complexes with Alzheimer's amyloid-β fibrils from human brain suggests a structural basis for apolipoprotein co-deposition with amyloids. Cell Mol Life Sci 2023; 80:376. [PMID: 38010414 PMCID: PMC11061799 DOI: 10.1007/s00018-023-05026-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 10/06/2023] [Accepted: 10/30/2023] [Indexed: 11/29/2023]
Abstract
Apolipoproteins co-deposit with amyloids, yet apolipoprotein-amyloid interactions are enigmatic. To understand how apoE interacts with Alzheimer's amyloid-β (Aβ) peptide in fibrillary deposits, the NMR structure of full-length human apoE was docked to four structures of patient-derived Aβ1-40 and Aβ1-42 fibrils determined previously using cryo-electron microscopy or solid-state NMR. Similar docking was done using the NMR structure of human apoC-III. In all complexes, conformational changes in apolipoproteins were required to expose large hydrophobic faces of their amphipathic α-helices for sub-stoichiometric binding to hydrophobic surfaces on sides or ends of fibrils. Basic residues flanking the hydrophobic helical faces in apolipoproteins interacted favorably with acidic residue ladders in some amyloid polymorphs. Molecular dynamics simulations of selected apoE-fibril complexes confirmed their stability. Amyloid binding via cryptic sites, which became available upon opening of flexibly linked apolipoprotein α-helices, resembled apolipoprotein-lipid binding. This mechanism probably extends to other apolipoprotein-amyloid interactions. Apolipoprotein binding alongside fibrils could interfere with fibril fragmentation and secondary nucleation, while binding at the fibril ends could halt amyloid elongation and dissolution in a polymorph-specific manner. The proposed mechanism is supported by extensive prior experimental evidence and helps reconcile disparate reports on apoE's role in Aβ aggregation. Furthermore, apoE domain opening and direct interaction of Arg/Cys158 with amyloid potentially contributes to isoform-specific effects in Alzheimer's disease. In summary, current modeling supported by prior experimental studies suggests similar mechanisms for apolipoprotein-amyloid and apolipoprotein-lipid interactions; explains why apolipoproteins co-deposit with amyloids; and helps reconcile conflicting reports on the chaperone-like apoE action in Aβ aggregation.
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Affiliation(s)
- Emily Lewkowicz
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisian School of Medicine, W302, 700 Albany Street, Boston, MA, 02118, USA
| | - Mari N Nakamura
- Undergraduate program, Department of Chemistry and Biochemistry, Middlebury College, 14 Old Chapel Rd, Middlebury, VT, 05753, USA
| | - Michael J Rynkiewicz
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisian School of Medicine, W302, 700 Albany Street, Boston, MA, 02118, USA
| | - Olga Gursky
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisian School of Medicine, W302, 700 Albany Street, Boston, MA, 02118, USA.
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4
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Lewkowicz E, Nakamura MN, Rynkiewicz MJ, Gursky O. Molecular modeling of apoE in complexes with Alzheimer's amyloid-β fibrils from human brain suggests a structural basis for apolipoprotein co-deposition with amyloids. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.04.551703. [PMID: 37577501 PMCID: PMC10418262 DOI: 10.1101/2023.08.04.551703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Apolipoproteins co-deposit with amyloids, yet apolipoprotein-amyloid interactions are enigmatic. To understand how apoE interacts with Alzheimer's amyloid-β (Aβ) peptide in fibrillary deposits, the NMR structure of full-length human apoE was docked to four structures of patient-derived Aβ1-40 and Aβ1-42 fibrils determined previously using cryo-electron microscopy or solid-state NMR. Similar docking was done using the NMR structure of human apoC-III. In all complexes, conformational changes in apolipoproteins were required to expose large hydrophobic faces of their amphipathic α-helices for sub-stoichiometric binding to hydrophobic surfaces on sides or ends of fibrils. Basic residues flanking the hydrophobic helical faces in apolipoproteins interacted favorably with acidic residue ladders in some amyloid polymorphs. Molecular dynamics simulations of selected apoE-fibril complexes confirmed their stability. Amyloid binding via cryptic sites, which became available upon opening of flexibly linked apolipoprotein α-helices, resembled apolipoprotein-lipid binding. This mechanism probably extends to other apolipoprotein-amyloid interactions. Apolipoprotein binding alongside fibrils could interfere with fibril fragmentation and secondary nucleation, while binding at the fibril ends could halt amyloid elongation and dissolution in a polymorph-specific manner. The proposed mechanism is supported by extensive prior experimental evidence and helps reconcile disparate reports on apoE's role in Aβ aggregation. Furthermore, apoE domain opening and direct interaction of Arg/Cys158 with amyloid potentially contributes to isoform-specific effects in Alzheimer's disease. In summary, current modeling supported by prior experimental studies suggests similar mechanisms for apolipoprotein-amyloid and apolipoprotein-lipid interactions; explains why apolipoproteins co-deposit with amyloids; and helps reconcile conflicting reports on the chaperone-like apoE action in Aβ aggregation.
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Affiliation(s)
- Emily Lewkowicz
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisian School of Medicine, W302, 700 Albany Street, Boston, MA, 02118, United States
| | - Mari N. Nakamura
- Undergraduate program, Department of Chemistry, Middlebury College, 14 Old Chapel Rd, Middlebury, VT 05753VT United States
| | - Michael J. Rynkiewicz
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisian School of Medicine, W302, 700 Albany Street, Boston, MA, 02118, United States
| | - Olga Gursky
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisian School of Medicine, W302, 700 Albany Street, Boston, MA, 02118, United States
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5
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Mustafa AI, Shams GM, Fawzy EM, Alhusseini NF, Khashaba RA, El-Shimi OS. Apolipoprotein E Gene Polymorphism, Serum Lipids, and Risk of Superficial Fungal Infections in Egyptian Patients - A Preliminary Case-Controlled Study. Indian J Dermatol 2023; 68:233. [PMID: 37275815 PMCID: PMC10239005 DOI: 10.4103/ijd.ijd_1001_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023] Open
Abstract
Background Apolipoprotein E (APOE) gene isoforms have been found to affect the risk of superficial fungal infections (SFIs). However, the data only cover a few ethnicities. Aims The present work intended to investigate the association of APOE gene polymorphism and serum lipids with the susceptibility of SFIs among a group of Egyptian patients. Materials and Methods Standard laboratory methods were used to estimate the serum lipid profile, and polymerase chain reaction-restriction fragment length polymorphism was used to detect APOE gene polymorphism in deoxyribonucleic acid extracted from 150 SFI patients and an equal number of apparently healthy matched controls. Results Serum total cholesterol, triglycerides, and low-density lipoprotein cholesterol were significantly higher in the studied patients than in controls. The APOE gene ε2, ε4 alleles, and ε3/4 and ε3/2 genotypes were significantly distributed in the patients than in the controls. APOE ε3/3 genotype was predominant in dermatophytosis and tinea versicolour patients, and ε3/4 genotype was predominant in candidiasis. Conclusions ApoE alleles ε2 and ε4, and genotypes ε2/3 and ε3/4 are linked to SFI and may be risk factors, whereas allele ε3 and genotype ε3/3 may be protective for SFI in the Egyptian population studied. The lipid profile results suggest that hyperlipidemia may provide evidence for SFI pathogenesis. However; further large-scale studies are still needed to validate our results.
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Affiliation(s)
- Amany I Mustafa
- From the Departments of Dermatology, Venereology and Andrology, Faculty of Medicine, Benha University, Benha, Egypt
| | - Ghada M Shams
- From the Departments of Dermatology, Venereology and Andrology, Faculty of Medicine, Benha University, Benha, Egypt
| | - Eman M Fawzy
- Department of Laboratory Medicine, Mansoura Fever Hospital, Mansoura, Egypt
| | - Naglaa F Alhusseini
- Medical Biochemistry and Molecular Biology, Faculty of Medicine, Benha University, Benha, Egypt
| | - Rana A Khashaba
- Clinical and Chemical Pathology, Faculty of Medicine, Benha University, Benha, Egypt
| | - Ola S El-Shimi
- Clinical and Chemical Pathology, Faculty of Medicine, Benha University, Benha, Egypt
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6
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Apolipoprotein E4 has extensive conformational heterogeneity in lipid-free and lipid-bound forms. Proc Natl Acad Sci U S A 2023; 120:e2215371120. [PMID: 36749730 PMCID: PMC9963066 DOI: 10.1073/pnas.2215371120] [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] [Indexed: 02/08/2023] Open
Abstract
The ε4-allele variant of apolipoprotein E (ApoE4) is the strongest genetic risk factor for Alzheimer's disease, although it only differs from its neutral counterpart ApoE3 by a single amino acid substitution. While ApoE4 influences the formation of plaques and neurofibrillary tangles, the structural determinants of pathogenicity remain undetermined due to limited structural information. Previous studies have led to conflicting models of the C-terminal region positioning with respect to the N-terminal domain across isoforms largely because the data are potentially confounded by the presence of heterogeneous oligomers. Here, we apply a combination of single-molecule spectroscopy and molecular dynamics simulations to construct an atomically detailed model of monomeric ApoE4 and probe the effect of lipid association. Importantly, our approach overcomes previous limitations by allowing us to work at picomolar concentrations where only the monomer is present. Our data reveal that ApoE4 is far more disordered and extended than previously thought and retains significant conformational heterogeneity after binding lipids. Comparing the proximity of the N- and C-terminal domains across the three major isoforms (ApoE4, ApoE3, and ApoE2) suggests that all maintain heterogeneous conformations in their monomeric form, with ApoE2 adopting a slightly more compact ensemble. Overall, these data provide a foundation for understanding how ApoE4 differs from nonpathogenic and protective variants of the protein.
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7
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Gharibyan AL, Wasana Jayaweera S, Lehmann M, Anan I, Olofsson A. Endogenous Human Proteins Interfering with Amyloid Formation. Biomolecules 2022; 12:biom12030446. [PMID: 35327638 PMCID: PMC8946693 DOI: 10.3390/biom12030446] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/08/2022] [Accepted: 03/11/2022] [Indexed: 01/09/2023] Open
Abstract
Amyloid formation is a pathological process associated with a wide range of degenerative disorders, including Alzheimer’s disease, Parkinson’s disease, and diabetes mellitus type 2. During disease progression, abnormal accumulation and deposition of proteinaceous material are accompanied by tissue degradation, inflammation, and dysfunction. Agents that can interfere with the process of amyloid formation or target already formed amyloid assemblies are consequently of therapeutic interest. In this context, a few endogenous proteins have been associated with an anti-amyloidogenic activity. Here, we review the properties of transthyretin, apolipoprotein E, clusterin, and BRICHOS protein domain which all effectively interfere with amyloid in vitro, as well as displaying a clinical impact in humans or animal models. Their involvement in the amyloid formation process is discussed, which may aid and inspire new strategies for therapeutic interventions.
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Affiliation(s)
- Anna L. Gharibyan
- Department of Clinical Microbiology, Umeå University, 901 87 Umeå, Sweden;
- Correspondence: (A.L.G.); (A.O.)
| | | | - Manuela Lehmann
- Department of Public Health and Clinical Medicine, Umeå University, 901 87 Umeå, Sweden; (M.L.); (I.A.)
| | - Intissar Anan
- Department of Public Health and Clinical Medicine, Umeå University, 901 87 Umeå, Sweden; (M.L.); (I.A.)
| | - Anders Olofsson
- Department of Clinical Microbiology, Umeå University, 901 87 Umeå, Sweden;
- Correspondence: (A.L.G.); (A.O.)
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8
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Waldie S, Sebastiani F, Moulin M, Del Giudice R, Paracini N, Roosen-Runge F, Gerelli Y, Prevost S, Voss JC, Darwish TA, Yepuri N, Pichler H, Maric S, Forsyth VT, Haertlein M, Cárdenas M. ApoE and ApoE Nascent-Like HDL Particles at Model Cellular Membranes: Effect of Protein Isoform and Membrane Composition. Front Chem 2021; 9:630152. [PMID: 33996741 PMCID: PMC8117676 DOI: 10.3389/fchem.2021.630152] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 03/30/2021] [Indexed: 11/13/2022] Open
Abstract
Apolipoprotein E (ApoE), an important mediator of lipid transportation in plasma and the nervous system, plays a large role in diseases such as atherosclerosis and Alzheimer's. The major allele variants ApoE3 and ApoE4 differ only by one amino acid. However, this difference has major consequences for the physiological behaviour of each variant. In this paper, we follow (i) the initial interaction of lipid-free ApoE variants with model membranes as a function of lipid saturation, (ii) the formation of reconstituted High-Density Lipoprotein-like particles (rHDL) and their structural characterisation, and (iii) the rHDL ability to exchange lipids with model membranes made of saturated lipids in the presence and absence of cholesterol [1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) with and without 20 mol% cholesterol]. Our neutron reflection results demonstrate that the protein variants interact differently with the model membranes, adopting different protein conformations. Moreover, the ApoE3 structure at the model membrane is sensitive to the level of lipid unsaturation. Small-angle neutron scattering shows that the ApoE containing lipid particles form elliptical disc-like structures, similar in shape but larger than nascent or discoidal HDL based on Apolipoprotein A1 (ApoA1). Neutron reflection shows that ApoE-rHDL do not remove cholesterol but rather exchange saturated lipids, as occurs in the brain. In contrast, ApoA1-containing particles remove and exchange lipids to a greater extent as occurs elsewhere in the body.
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Affiliation(s)
- Sarah Waldie
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden.,Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France
| | - Federica Sebastiani
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Martine Moulin
- Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France
| | - Rita Del Giudice
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Nicolò Paracini
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Felix Roosen-Runge
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Yuri Gerelli
- Institut Laue-Langevin, Grenoble, France.,Department of Life and Environmental Sciences, Marche Polytechnic University, Ancona, Italy
| | | | - John C Voss
- Department of Biochemistry and Molecular Medicine, University of California, Davis, Davis, CA, United States
| | - Tamim A Darwish
- National Deuteration Facility, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Nageshwar Yepuri
- National Deuteration Facility, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Harald Pichler
- Austrian Centre of Industrial Biotechnology, Graz, Austria.,Graz University of Technology, Institute of Molecular Biotechnology, NAWI Graz, BioTechMed Graz, Graz, Austria
| | | | - V Trevor Forsyth
- Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France.,Faculty of Natural Sciences, Keele University, Staffordshire, United Kingdom
| | - Michael Haertlein
- Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France
| | - Marité Cárdenas
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
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9
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Chen Y, Strickland MR, Soranno A, Holtzman DM. Apolipoprotein E: Structural Insights and Links to Alzheimer Disease Pathogenesis. Neuron 2020; 109:205-221. [PMID: 33176118 DOI: 10.1016/j.neuron.2020.10.008] [Citation(s) in RCA: 136] [Impact Index Per Article: 34.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 10/05/2020] [Accepted: 10/06/2020] [Indexed: 01/02/2023]
Abstract
Apolipoprotein E (ApoE) is of great interest due to its role as a cholesterol/lipid transporter in the central nervous system (CNS) and as the most influential genetic risk factor for Alzheimer disease (AD). Work over the last four decades has given us important insights into the structure of ApoE and how this might impact the neuropathology and pathogenesis of AD. In this review, we highlight the history and progress in the structural and molecular understanding of ApoE and discuss how these studies on ApoE have illuminated the physiology of ApoE, receptor binding, and interaction with amyloid-β (Aβ). We also identify future areas of study needed to advance our understanding of how ApoE influences neurodegeneration.
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Affiliation(s)
- Yun Chen
- Department of Neurology, Washington University in St. Louis, St. Louis, MO, USA; Hope Center for Neurological Disorders, Washington University in St. Louis, St. Louis, MO, USA; Knight Alzheimer's Disease Research Center, Washington University in St. Louis, St. Louis, MO, USA; The Division of Biology and Biomedical Sciences, Washington University in St. Louis, St. Louis, MO, USA; Department of Pathology and Immunology, Washington University in St. Louis, St. Louis, MO, USA
| | - Michael R Strickland
- Department of Neurology, Washington University in St. Louis, St. Louis, MO, USA; Hope Center for Neurological Disorders, Washington University in St. Louis, St. Louis, MO, USA; Knight Alzheimer's Disease Research Center, Washington University in St. Louis, St. Louis, MO, USA; The Division of Biology and Biomedical Sciences, Washington University in St. Louis, St. Louis, MO, USA
| | - Andrea Soranno
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, MO, USA; Center for Science & Engineering of Living Systems, Washington University in St. Louis, St. Louis, MO, USA
| | - David M Holtzman
- Department of Neurology, Washington University in St. Louis, St. Louis, MO, USA; Center for Science & Engineering of Living Systems, Washington University in St. Louis, St. Louis, MO, USA; Knight Alzheimer's Disease Research Center, Washington University in St. Louis, St. Louis, MO, USA.
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10
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Henry N, Krammer EM, Stengel F, Adams Q, Van Liefferinge F, Hubin E, Chaves R, Efremov R, Aebersold R, Vandenbussche G, Prévost M, Raussens V, Deroo S. Lipidated apolipoprotein E4 structure and its receptor binding mechanism determined by a combined cross-linking coupled to mass spectrometry and molecular dynamics approach. PLoS Comput Biol 2018; 14:e1006165. [PMID: 29933361 PMCID: PMC6033463 DOI: 10.1371/journal.pcbi.1006165] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 07/05/2018] [Accepted: 04/30/2018] [Indexed: 11/18/2022] Open
Abstract
Apolipoprotein E (apoE) is a forefront actor in the transport of lipids and the maintenance of cholesterol homeostasis, and is also strongly implicated in Alzheimer’s disease. Upon lipid-binding apoE adopts a conformational state that mediates the receptor-induced internalization of lipoproteins. Due to its inherent structural dynamics and the presence of lipids, the structure of the biologically active apoE remains so far poorly described. To address this issue, we developed an innovative hybrid method combining experimental data with molecular modeling and dynamics to generate comprehensive models of the lipidated apoE4 isoform. Chemical cross-linking combined with mass spectrometry provided distance restraints, characterizing the three-dimensional organization of apoE4 molecules at the surface of lipidic nanoparticles. The ensemble of spatial restraints was then rationalized in an original molecular modeling approach to generate monomeric models of apoE4 that advocated the existence of two alternative conformations. These two models point towards an activation mechanism of apoE4 relying on a regulation of the accessibility of its receptor binding region. Further, molecular dynamics simulations of the dimerized and lipidated apoE4 monomeric conformations revealed an elongation of the apoE N-terminal domain, whereby helix 4 is rearranged, together with Arg172, into a proper orientation essential for lipoprotein receptor association. Overall, our results show how apoE4 adapts its conformation for the recognition of the low density lipoprotein receptor and we propose a novel mechanism of activation for apoE4 that is based on accessibility and remodeling of the receptor binding region. Among the proteins involved in the transport of lipids and their distribution to the cells, apolipoprotein E (apoE) mediates the internalization of cholesterol rich lipoproteins by acting as a ligand for cell-surface receptors. In the central nervous system, while apoE is the major cholesterol transport protein, a dysfunction of apoE in the transport and metabolism of lipids is associated with Alzheimer’s disease. A molecular understanding of the mechanisms underlying the receptor binding abilities of apoE is crucial to address its biological functions, but is so far hindered by the dynamic and complex nature of these assemblies. We have designed an original hybrid approach combining experimental data and bioinformatics tools to generate high resolution models of lipidated apoE. Based on these models, we can propose how apoE adapts its conformation at the surface of lipid nanoparticles. Further, we propose a novel mechanism of regulation of the activation and receptor recognition of apoE that could prove valuable to interpret its role in Alzheimer and apoE-related cardiovascular diseases.
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Affiliation(s)
- Nicolas Henry
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Eva-Maria Krammer
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Florian Stengel
- Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
- Department of Biology, University of Konstanz, Konstanz, Germany
| | - Quentin Adams
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - François Van Liefferinge
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Ellen Hubin
- Structural Biology Research Center, VIB, Brussels, Belgium
- Structural Biology Brussels, Department of Biotechnology (DBIT), Vrije Universiteit Brussel (VUB), Brussels, Belgium
- Nanobiophysics Group, MIRA Institute for Biomedical Technology and Technical Medicine, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands
| | - Rui Chaves
- Structural Biology Research Center, VIB, Brussels, Belgium
- Structural Biology Brussels, Department of Biotechnology (DBIT), Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - Rouslan Efremov
- Structural Biology Research Center, VIB, Brussels, Belgium
- Structural Biology Brussels, Department of Biotechnology (DBIT), Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - Ruedi Aebersold
- Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
- Faculty of Science, University of Zurich, Zurich, Switzerland
| | - Guy Vandenbussche
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Martine Prévost
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Vincent Raussens
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
- * E-mail: (SD); (VT)
| | - Stéphanie Deroo
- Center for Structural Biology and Bioinformatics, Structure and Function of Biological Membranes, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
- * E-mail: (SD); (VT)
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11
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Frieden C, Wang H, Ho CMW. A mechanism for lipid binding to apoE and the role of intrinsically disordered regions coupled to domain-domain interactions. Proc Natl Acad Sci U S A 2017; 114:6292-6297. [PMID: 28559318 PMCID: PMC5474821 DOI: 10.1073/pnas.1705080114] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Relative to the apolipoprotein E (apoE) E3 allele of the APOE gene, apoE4 strongly increases the risk for the development of late-onset Alzheimer's disease. However, apoE4 differs from apoE3 by only a single amino acid at position 112, which is arginine in apoE4 and cysteine in apoE3. It remains unclear why apoE3 and apoE4 are functionally different. Described here is a proposal for understanding the functional differences between these two isoforms with respect to lipid binding. A mechanism is proposed that is based on the full-length monomeric structure of the protein, on hydrogen-deuterium exchange mass spectrometry data, and on the role of intrinsically disordered regions to control protein motions. It is proposed that lipid binds between the N-terminal and C-terminal domains and that separation of the two domains, along with the presence of intrinsically disordered regions, controls this process. The mechanism explains why apoE3 differs from apoE4 with respect to different lipid-binding specificities, why lipid increases the binding of apoE to its receptor, and why specific residues are conserved.
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Affiliation(s)
- Carl Frieden
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110;
| | - Hanliu Wang
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130
| | - Chris M W Ho
- Drug Design Methodologies LLC, St. Louis, MO 63103
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12
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Plasma levels of apolipoprotein E, APOE genotype and risk of dementia and ischemic heart disease: A review. Atherosclerosis 2016; 255:145-155. [DOI: 10.1016/j.atherosclerosis.2016.10.037] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 10/08/2016] [Accepted: 10/19/2016] [Indexed: 12/12/2022]
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13
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Ganesh HV, Chow AM, Kerman K. Recent advances in biosensors for neurodegenerative disease detection. Trends Analyt Chem 2016. [DOI: 10.1016/j.trac.2016.02.012] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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14
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Mizuguchi C, Hata M, Dhanasekaran P, Nickel M, Phillips MC, Lund-Katz S, Saito H. Fluorescence analysis of the lipid binding-induced conformational change of apolipoprotein E4. Biochemistry 2012; 51:5580-8. [PMID: 22730894 DOI: 10.1021/bi300672s] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Apolipoprotein (apo) E is thought to undergo conformational changes in the N-terminal helix bundle domain upon lipid binding, modulating its receptor binding activity. In this study, site-specific fluorescence labeling of the N-terminal (S94) and C-terminal (W264 or S290) helices in apoE4 by pyrene maleimide or acrylodan was employed to probe the conformational organization and lipid binding behavior of the N- and C-terminal domains. Guanidine denaturation experiments monitored by acrylodan fluorescence demonstrated the less organized, more solvent-exposed structure of the C-terminal helices compared to the N-terminal helix bundle. Pyrene excimer fluorescence together with gel filtration chromatography indicated that there are extensive intermolecular helix-helix contacts through the C-terminal helices of apoE4. Comparison of increases in pyrene fluorescence upon binding of pyrene-labeled apoE4 to egg phosphatidylcholine small unilamellar vesicles suggests a two-step lipid-binding process; apoE4 initially binds to a lipid surface through the C-terminal helices followed by the slower conformational reorganization of the N-terminal helix bundle domain. Consistent with this, fluorescence resonance energy transfer measurements from Trp residues to acrylodan attached at position 94 demonstrated that upon binding to the lipid surface, opening of the N-terminal helix bundle occurs at the same rate as the increase in pyrene fluorescence of the N-terminal domain. Such a two-step mechanism of lipid binding of apoE4 is likely to apply to mostly phospholipid-covered lipoproteins such as VLDL. However, monitoring pyrene fluorescence upon binding to HDL(3) suggests that not only apoE-lipid interactions but also protein-protein interactions are important for apoE4 binding to HDL(3).
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Affiliation(s)
- Chiharu Mizuguchi
- Institute of Health Biosciences and Graduate School of Pharmaceutical Sciences, The University of Tokushima, 1-78-1 Shomachi, Tokushima 770-8505, Japan
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15
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Structural differences between apoE3 and apoE4 may be useful in developing therapeutic agents for Alzheimer's disease. Proc Natl Acad Sci U S A 2012; 109:8913-8. [PMID: 22615372 DOI: 10.1073/pnas.1207022109] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Apolipoproteins E3 and E4, proteins with a molecular mass of 34.15 kDa, differ by a single amino acid change. ApoE4 contains an arginine residue at position 112, whereas apoE3 has a cysteine at this position. ApoE4 is the major risk factor for late-onset Alzheimer's disease, whereas apoE3, the common isoform, is neutral with respect to this disease. Here, using literature data from both hydrogen-deuterium exchange and site-directed mutations, we suggest structural differences between these two isoforms that are distant from the site of the arginine-to-cysteine change. These structural differences involve sequences from both the N- and C-terminal domains, sequentially far apart but structurally close. In addition, these regions are close to regions that bind lipid and to a region involved in association of apoE monomers to higher molecular weight forms. We discuss the possibility that these regions could be targeted preferentially to affect the function of apoE4 relative to apoE3.
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16
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Castellano JM, Kim J, Stewart FR, Jiang H, DeMattos RB, Patterson BW, Fagan AM, Morris JC, Mawuenyega KG, Cruchaga C, Goate AM, Bales KR, Paul SM, Bateman RJ, Holtzman DM. Human apoE isoforms differentially regulate brain amyloid-β peptide clearance. Sci Transl Med 2011; 3:89ra57. [PMID: 21715678 DOI: 10.1126/scitranslmed.3002156] [Citation(s) in RCA: 826] [Impact Index Per Article: 63.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The apolipoprotein E (APOE) ε4 allele is the strongest genetic risk factor for late-onset, sporadic Alzheimer's disease (AD). The APOE ε4 allele markedly increases AD risk and decreases age of onset, likely through its strong effect on the accumulation of amyloid-β (Aβ) peptide. In contrast, the APOE ε2 allele appears to decrease AD risk. Most rare, early-onset forms of familial AD are caused by autosomal dominant mutations that often lead to overproduction of Aβ(42) peptide. However, the mechanism by which APOE alleles differentially modulate Aβ accumulation in sporadic, late-onset AD is less clear. In a cohort of cognitively normal individuals, we report that reliable molecular and neuroimaging biomarkers of cerebral Aβ deposition vary in an apoE isoform-dependent manner. We hypothesized that human apoE isoforms differentially affect Aβ clearance or synthesis in vivo, resulting in an apoE isoform-dependent pattern of Aβ accumulation later in life. Performing in vivo microdialysis in a mouse model of Aβ-amyloidosis expressing human apoE isoforms (PDAPP/TRE), we find that the concentration and clearance of soluble Aβ in the brain interstitial fluid depends on the isoform of apoE expressed. This pattern parallels the extent of Aβ deposition observed in aged PDAPP/TRE mice. ApoE isoform-dependent differences in soluble Aβ metabolism are observed not only in aged but also in young PDAPP/TRE mice well before the onset of Aβ deposition in amyloid plaques in the brain. Additionally, amyloidogenic processing of amyloid precursor protein and Aβ synthesis, as assessed by in vivo stable isotopic labeling kinetics, do not vary according to apoE isoform in young PDAPP/TRE mice. Our results suggest that APOE alleles contribute to AD risk by differentially regulating clearance of Aβ from the brain, suggesting that Aβ clearance pathways may be useful therapeutic targets for AD prevention.
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Affiliation(s)
- Joseph M Castellano
- Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA
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17
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Petrlova J, Hong HS, Bricarello DA, Harishchandra G, Lorigan GA, Jin LW, Voss JC. A differential association of Apolipoprotein E isoforms with the amyloid-β oligomer in solution. Proteins 2011; 79:402-16. [PMID: 21069870 DOI: 10.1002/prot.22891] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The molecular pathogenesis of disorders arising from protein misfolding and aggregation is difficult to elucidate, involving a complex ensemble of intermediates, whose toxicity depends upon their state of progression along distinct processing pathways. To address the complex misfolding and aggregation that initiates the toxic cascade resulting in Alzheimer's disease (AD), we have developed a 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid spin-labeled amyloid-β (Aβ) peptide to observe its isoform-dependent interaction with the apoE protein. Although most individuals carry the E3 isoform of apoE, ∼15% of humans carry the E4 isoform, which is recognized as the most significant genetic determinant for Alzheimer's. ApoE is consistently associated with the amyloid plaque marker for AD. A vital question centers on the influence of the two predominant isoforms, E3 and E4, on Aβ peptide processing and hence Aβ toxicity. We used electron paramagnetic resonance (EPR) spectroscopy of incorporated spin labels to investigate the interaction of apoE with the toxic oligomeric species of Aβ in solution. EPR spectra of the spin-labeled side chain report on side chain and backbone dynamics as well as the spatial proximity of spins in an assembly. Our results indicate oligomer binding involves the C-terminal domain of apoE, with apoE3 reporting a much greater response through this conformational marker. Coupled with SPR binding measurements, apoE3 displays a higher affinity and capacity for the toxic Aβ oligomer. These findings support the hypothesis that apoE polymorphism and Alzheimer's risk can largely be attributed to the reduced ability of apoE4 to function as a clearance vehicle for the toxic form of Aβ.
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Affiliation(s)
- Jitka Petrlova
- Department of Biochemistry and Molecular Medicine, University of California Davis, California, USA
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18
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Leduc V, Domenger D, De Beaumont L, Lalonde D, Bélanger-Jasmin S, Poirier J. Function and comorbidities of apolipoprotein e in Alzheimer's disease. Int J Alzheimers Dis 2011; 2011:974361. [PMID: 21559182 PMCID: PMC3089878 DOI: 10.4061/2011/974361] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Accepted: 02/09/2011] [Indexed: 11/20/2022] Open
Abstract
Alzheimer's disease (AD)—the most common type of dementia among the elderly—represents one of the most challenging and urgent medical mysteries affecting our aging population. Although dominant inherited mutation in genes involved in the amyloid metabolism can elicit familial AD, the overwhelming majority of AD cases, dubbed sporadic AD, do not display this Mendelian inheritance pattern. Apolipoprotein E (APOE), the main lipid carrier protein in the central nervous system, is the only gene that has been robustly and consistently associated with AD risk. The purpose of the current paper is thus to highlight the pleiotropic roles and the structure-function relationship of APOE to stimulate both the functional characterization and the identification of novel lipid homeostasis-related molecular targets involved in AD.
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Affiliation(s)
- Valérie Leduc
- Department of Psychiatry, Douglas Mental Health University Institute, Perry Pavilion, E-3207.1, 6875 Lasalle Boulevard, Verdun, QC, Canada H4H1R3
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19
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Hauser PS, Narayanaswami V, Ryan RO. Apolipoprotein E: from lipid transport to neurobiology. Prog Lipid Res 2010; 50:62-74. [PMID: 20854843 DOI: 10.1016/j.plipres.2010.09.001] [Citation(s) in RCA: 222] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 09/04/2010] [Accepted: 09/12/2010] [Indexed: 12/17/2022]
Abstract
Apolipoprotein (apo) E has a storied history as a lipid transport protein. The integral association between cholesterol homeostasis and lipoprotein clearance from circulation are intimately related to apoE's function as a ligand for cell-surface receptors of the low-density lipoprotein receptor family. The receptor binding properties of apoE are strongly influenced by isoform specific amino acid differences as well as the lipidation state of the protein. As understanding of apoE as a structural component of circulating plasma lipoproteins has evolved, exciting developments in neurobiology have revitalized interest in apoE. The strong and enduring correlation between the apoE4 isoform and age of onset and increased risk of Alzheimer's disease has catapulted apoE to the forefront of neurobiology. Using genetic tools generated for study of apoE lipoprotein metabolism, transgenic "knock-in" and gene-disrupted mice are now favored models for study of its role in a variety of neurodegenerative diseases. Key structural knowledge of apoE and isoform-specific differences is driving research activity designed to elucidate how a single amino acid change can manifest such profoundly significant pathological consequences. This review describes apoE through a lens of structure-based knowledge that leads to hypotheses that attempt to explain the functions of apoE and isoform-specific effects relating to disease mechanism.
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Affiliation(s)
- Paul S Hauser
- Center for Prevention of Obesity, Cardiovascular Disease and Diabetes, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA
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20
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Lee Y, Kockx M, Raftery MJ, Jessup W, Griffith R, Kritharides L. Glycosylation and sialylation of macrophage-derived human apolipoprotein E analyzed by SDS-PAGE and mass spectrometry: evidence for a novel site of glycosylation on Ser290. Mol Cell Proteomics 2010; 9:1968-81. [PMID: 20511397 DOI: 10.1074/mcp.m900430-mcp200] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein E (apoE) is a 34-kDa glycoprotein secreted from various cells including hepatocytes and macrophages and plays an important role in remnant lipoprotein clearance, immune responses, Alzheimer disease, and atherosclerosis. Cellular apoE and plasma apoE exist as multiple glycosylated and sialylated glycoforms with plasma apoE being less glycosylated/sialylated than cell-derived apoE. Some of the glycan structures on plasma apoE are characterized; however, the more complicated structures on plasma and cellular/secreted apoE remain unidentified. We investigated glycosylation and sialylation of cellular and secreted apoE from primary human macrophages by one- and two-dimensional gel electrophoresis and mass spectrometry. Our results identify eight different glycoforms with (HexNAc)(2)-Hex(2)-(NeuAc)(2) being the most complex glycan detected on Thr(194) in both cellular and secreted apoE. Four additional glycans were identified on apoE(283-299), and using beta-elimination/alkylation by methylamine in vitro, we identified Ser(290) as a novel site of glycan attachment. Comparison of plasma and cellular/secreted apoE from the same donor confirmed that cell-derived apoE is more extensively sialylated than plasma apoE. Given the importance of the C terminus of apoE in regulating apoE solubility, stability, and lipid binding, these results may have important implications for our understanding of apoE biochemistry.
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Affiliation(s)
- Youra Lee
- Centre for Vascular Research, School of Medical Sciences, University of New South Wales, Sydney, Australia
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21
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Abstract
High density lipoprotein (HDL) possesses important anti-atherogenic properties and this review addresses the molecular mechanisms underlying these functions. The structures and cholesterol transport abilities of HDL particles are determined by the properties of their exchangeable apolipoprotein (apo) components. ApoA-I and apoE, which are the best characterized in structural terms, contain a series of amphipathic alpha-helical repeats. The helices located in the amino-terminal two-thirds of the molecule adopt a helix bundle structure while the carboxy-terminal segment forms a separately folded, relatively disorganized, domain. The latter domain initiates lipid binding and this interaction induces changes in conformation; the alpha-helix content increases and the amino-terminal helix bundle can open subsequently. These conformational changes alter the abilities of apoA-I and apoE to function as ligands for their receptors. The apoA-I and apoE molecules possess detergent-like properties and they can solubilize vesicular phospholipid to create discoidal HDL particles with hydrodynamic diameters of ~10 nm. In the case of apoA-I, such a particle is stabilized by two protein molecules arranged in an anti-parallel, double-belt, conformation around the edge of the disc. The abilities of apoA-I and apoE to solubilize phospholipid and stabilize HDL particles enable these proteins to be partners with ABCA1 in mediating efflux of cellular phospholipid and cholesterol, and the biogenesis of HDL particles. ApoA-I-containing nascent HDL particles play a critical role in cholesterol transport in the circulation whereas apoE-containing HDL particles mediate cholesterol transport in the brain. The mechanisms by which HDL particles are remodeled by lipases and lipid transfer proteins, and interact with SR-BI to deliver cholesterol to cells, are reviewed.
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22
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Tetali SD, Budamagunta MS, Simion C, den Hartigh LJ, Kálai T, Hideg K, Hatters DM, Weisgraber KH, Voss JC, Rutledge JC. VLDL lipolysis products increase VLDL fluidity and convert apolipoprotein E4 into a more expanded conformation. J Lipid Res 2009; 51:1273-83. [PMID: 19965582 DOI: 10.1194/jlr.m000406] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Our previous work indicated that apolipoprotein (apo) E4 assumes a more expanded conformation in the postprandial period. The postprandial state is characterized by increased VLDL lipolysis. In this article, we tested the hypothesis that VLDL lipolysis products increase VLDL particle fluidity, which mediates expansion of apoE4 on the VLDL particle. Plasma from healthy subjects was collected before and after a moderately high-fat meal and incubated with nitroxyl-spin labeled apoE. ApoE conformation was examined by electron paramagnetic resonance spectroscopy using targeted spin probes on cysteines introduced in the N-terminal (S76C) and C-terminal (A241C) domains. Further, we synthesized a novel nitroxyl spin-labeled cholesterol analog, which gave insight into lipoprotein particle fluidity. Our data revealed that the order of lipoprotein fluidity was HDL approximately LDL<VLDL<VLDL+lipoprotein lipase. Moreover, the conformation of apoE4 depended on the lipoprotein fraction: VLDL-associated apoE4 had a more linear conformation than apoE4 associated with LDL or HDL. Further, by changing VLDL fluidity, VLDL lipolysis products significantly altered apoE4 into a more expanded conformation. Our studies indicate that after every meal, VLDL fluidity is increased causing apoE4 associated with VLDL to assume a more expanded conformation, potentially enhancing the pathogenicity of apoE4 in vascular tissue.
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Affiliation(s)
- Sarada D Tetali
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India.
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