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Asiamah EA, Feng B, Guo R, Yaxing X, Du X, Liu X, Zhang J, Cui H, Ma J. The Contributions of the Endolysosomal Compartment and Autophagy to APOEɛ4 Allele-Mediated Increase in Alzheimer's Disease Risk. J Alzheimers Dis 2024; 97:1007-1031. [PMID: 38306054 DOI: 10.3233/jad-230658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2024]
Abstract
Apolipoprotein E4 (APOE4), although yet-to-be fully understood, increases the risk and lowers the age of onset of Alzheimer's disease (AD), which is the major cause of dementia among elderly individuals. The endosome-lysosome and autophagy pathways, which are necessary for homeostasis in both neurons and glia, are dysregulated even in early AD. Nonetheless, the contributory roles of these pathways to developing AD-related pathologies in APOE4 individuals and models are unclear. Therefore, this review summarizes the dysregulations in the endosome-lysosome and autophagy pathways in APOE4 individuals and non-human models, and how these anomalies contribute to developing AD-relevant pathologies. The available literature suggests that APOE4 causes endosomal enlargement, increases endosomal acidification, impairs endosomal recycling, and downregulates exosome production. APOE4 impairs autophagy initiation and inhibits basal autophagy and autophagy flux. APOE4 promotes lysosome formation and trafficking and causes ApoE to accumulate in lysosomes. APOE4-mediated changes in the endosome, autophagosome and lysosome could promote AD-related features including Aβ accumulation, tau hyperphosphorylation, glial dysfunction, lipid dyshomeostasis, and synaptic defects. ApoE4 protein could mediate APOE4-mediated endosome-lysosome-autophagy changes. ApoE4 impairs vesicle recycling and endosome trafficking, impairs the synthesis of autophagy genes, resists being dissociated from its receptors and degradation, and forms a stable folding intermediate that could disrupt lysosome structure. Drugs such as molecular correctors that target ApoE4 molecular structure and enhance autophagy may ameliorate the endosome-lysosome-autophagy-mediated increase in AD risk in APOE4 individuals.
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Affiliation(s)
- Ernest Amponsah Asiamah
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Department of Biomedical Sciences, College of Health and Allied Sciences, University of Cape Coast, PMB UCC, Cape Coast, Ghana
| | - Baofeng Feng
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
- Hebei Technology Innovation Center for Stem Cell and Regenerative Medicine, Hebei, China
| | - Ruiyun Guo
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
| | - Xu Yaxing
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
| | - Xiaofeng Du
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
| | - Xin Liu
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
| | - Jinyu Zhang
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
| | - Huixian Cui
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
- Hebei Technology Innovation Center for Stem Cell and Regenerative Medicine, Hebei, China
| | - Jun Ma
- Hebei Medical University-Galway University of Ireland Stem Cell Research Center, Hebei Medical University, Hebei, China
- Hebei Research Center for Stem Cell Medical Translational Engineering, Hebei, China
- Hebei Technology Innovation Center for Stem Cell and Regenerative Medicine, Hebei, China
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2
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Bornfeldt KE. Apolipoprotein C3: form begets function. J Lipid Res 2024; 65:100475. [PMID: 37972731 PMCID: PMC10805671 DOI: 10.1016/j.jlr.2023.100475] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 11/02/2023] [Accepted: 11/04/2023] [Indexed: 11/19/2023] Open
Abstract
Increased circulating levels of apolipoprotein C3 (APOC3) predict cardiovascular disease (CVD) risk in humans, and APOC3 promotes atherosclerosis in mouse models. APOC3's mechanism of action is due in large part to its ability to slow the clearance of triglyceride-rich lipoproteins (TRLs) and their remnants when APOC3 is carried by these lipoproteins. However, different pools and forms of APOC3 exert distinct biological effects or associations with atherogenic processes. Thus, lipid-free APOC3 induces inflammasome activation in monocytes whereas lipid particle-bound APOC3 does not. APOC3-enriched LDL binds better to the vascular glycosaminoglycan biglycan than does LDL depleted of APOC3. Patterns of APOC3 glycoforms predict CVD risk differently. The function of APOC3 bound to HDL is largely unknown. There is still much to learn about the mechanisms of action of different forms and pools of APOC3 in atherosclerosis and CVD, and whether APOC3 inhibition would prevent CVD risk in patients on LDL-cholesterol lowering medications.
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Affiliation(s)
- Karin E Bornfeldt
- Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, UW Medicine Diabetes Institute and Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA.
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3
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Pohlkamp T, Xian X, Wong CH, Durakoglugil MS, Werthmann GC, Saido TC, Evers BM, White CL, Connor J, Hammer RE, Herz J. NHE6 depletion corrects ApoE4-mediated synaptic impairments and reduces amyloid plaque load. eLife 2021; 10:72034. [PMID: 34617884 PMCID: PMC8547963 DOI: 10.7554/elife.72034] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 09/19/2021] [Indexed: 11/13/2022] Open
Abstract
Apolipoprotein E4 (ApoE4) is the most important and prevalent risk factor for late-onset Alzheimer’s disease (AD). The isoelectric point of ApoE4 matches the pH of the early endosome (EE), causing its delayed dissociation from ApoE receptors and hence impaired endolysosomal trafficking, disruption of synaptic homeostasis, and reduced amyloid clearance. We have shown that enhancing endosomal acidification by inhibiting the EE-specific sodium-hydrogen exchanger 6 (NHE6) restores vesicular trafficking and normalizes synaptic homeostasis. Remarkably and unexpectedly, loss of NHE6 (encoded by the gene Slc9a6) in mice effectively suppressed amyloid deposition even in the absence of ApoE4, suggesting that accelerated acidification of EEs caused by the absence of NHE6 occludes the effect of ApoE on amyloid plaque formation. NHE6 suppression or inhibition may thus be a universal, ApoE-independent approach to prevent amyloid buildup in the brain. These findings suggest a novel therapeutic approach for the prevention of AD by which partial NHE6 inhibition reverses the ApoE4-induced endolysosomal trafficking defect and reduces plaque load.
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Affiliation(s)
- Theresa Pohlkamp
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States
| | - Xunde Xian
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States.,Institute of Cardiovascular Sciences and Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Peking University, Beijing, China
| | - Connie H Wong
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States
| | - Murat S Durakoglugil
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States
| | - Gordon Chandler Werthmann
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States
| | - Takaomi C Saido
- Laboratory for Proteolytic Neuroscience, Riken Center for Brain Science, Wako, Japan
| | - Bret M Evers
- Center for Translational Neurodegeneration Research, Dallas, United States
| | - Charles L White
- Pathology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Jade Connor
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States
| | - Robert E Hammer
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
| | - Joachim Herz
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.,Center for Translational Neurodegeneration Research, Dallas, United States.,Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, United States
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4
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Yang H, Zhang N, Okoro EU, Guo Z. Transport of Apolipoprotein B-Containing Lipoproteins through Endothelial Cells Is Associated with Apolipoprotein E-Carrying HDL-Like Particle Formation. Int J Mol Sci 2018; 19:ijms19113593. [PMID: 30441770 PMCID: PMC6274886 DOI: 10.3390/ijms19113593] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Revised: 11/09/2018] [Accepted: 11/11/2018] [Indexed: 12/15/2022] Open
Abstract
Passage of apolipoprotein B-containing lipoproteins (apoB-LPs), i.e., triglyceride-rich lipoproteins (TRLs), intermediate-density lipoproteins (IDLs), and low-density lipoproteins (LDLs), through the endothelial monolayer occurs in normal and atherosclerotic arteries. Among these lipoproteins, TRLs and IDLs are apoE-rich apoB-LPs (E/B-LPs). Recycling of TRL-associated apoE has been shown to form apoE-carrying high-density lipoprotein (HDL)-like (HDLE) particles in many types of cells. The current report studied the formation of HDLE particles by transcytosis of apoB-LPs through mouse aortic endothelial cells (MAECs). Our data indicated that passage of radiolabeled apoB-LPs, rich or poor in apoE, through the MAEC monolayer is inhibited by filipin and unlabeled competitor lipoproteins, suggesting that MAECs transport apoB-LPs via a caveolae-mediated pathway. The cholesterol and apoE in the cell-untreated E/B-LPs, TRLs, IDLs, and LDLs distributed primarily in the low-density (LD) fractions (d ≤ 1.063). A substantial portion of the cholesterol and apoE that passed through the MAEC monolayer was allotted into the high-density (HD) (d > 1.063) fractions. In contrast, apoB was detectable only in the LD fractions before or after apoB-LPs were incubated with the MAEC monolayer, suggesting that apoB-LPs pass through the MAEC monolayer in the forms of apoB-containing LD particles and apoE-containing HD particles.
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Affiliation(s)
- Hong Yang
- Department of Microbiology, Immunology and Physiology, Meharry Medical College, Nashville, TN 37208, USA.
| | - Ningya Zhang
- Department of Microbiology, Immunology and Physiology, Meharry Medical College, Nashville, TN 37208, USA.
| | - Emmanuel U Okoro
- Department of Microbiology, Immunology and Physiology, Meharry Medical College, Nashville, TN 37208, USA.
| | - Zhongmao Guo
- Department of Microbiology, Immunology and Physiology, Meharry Medical College, Nashville, TN 37208, USA.
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5
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Zanoni P, Velagapudi S, Yalcinkaya M, Rohrer L, von Eckardstein A. Endocytosis of lipoproteins. Atherosclerosis 2018; 275:273-295. [PMID: 29980055 DOI: 10.1016/j.atherosclerosis.2018.06.881] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 06/04/2018] [Accepted: 06/22/2018] [Indexed: 02/06/2023]
Abstract
During their metabolism, all lipoproteins undergo endocytosis, either to be degraded intracellularly, for example in hepatocytes or macrophages, or to be re-secreted, for example in the course of transcytosis by endothelial cells. Moreover, there are several examples of internalized lipoproteins sequestered intracellularly, possibly to exert intracellular functions, for example the cytolysis of trypanosoma. Endocytosis and the subsequent intracellular itinerary of lipoproteins hence are key areas for understanding the regulation of plasma lipid levels as well as the biological functions of lipoproteins. Indeed, the identification of the low-density lipoprotein (LDL)-receptor and the unraveling of its transcriptional regulation led to the elucidation of familial hypercholesterolemia as well as to the development of statins, the most successful therapeutics for lowering of cholesterol levels and risk of atherosclerotic cardiovascular diseases. Novel limiting factors of intracellular trafficking of LDL and the LDL receptor continue to be discovered and to provide drug targets such as PCSK9. Surprisingly, the receptors mediating endocytosis of high-density lipoproteins or lipoprotein(a) are still a matter of controversy or even new discovery. Finally, the receptors and mechanisms, which mediate the uptake of lipoproteins into non-degrading intracellular itineraries for re-secretion (transcytosis, retroendocytosis), storage, or execution of intracellular functions, are largely unknown.
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Affiliation(s)
- Paolo Zanoni
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Srividya Velagapudi
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Mustafa Yalcinkaya
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Lucia Rohrer
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Arnold von Eckardstein
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
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6
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Ramakrishnan VM, Yang JY, Tien KT, McKinley TR, Bocard BR, Maijub JG, Burchell PO, Williams SK, Morris ME, Hoying JB, Wade-Martins R, West FD, Boyd NL. Restoration of Physiologically Responsive Low-Density Lipoprotein Receptor-Mediated Endocytosis in Genetically Deficient Induced Pluripotent Stem Cells. Sci Rep 2015; 5:13231. [PMID: 26307169 PMCID: PMC4549683 DOI: 10.1038/srep13231] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2015] [Accepted: 07/14/2015] [Indexed: 11/09/2022] Open
Abstract
Acquiring sufficient amounts of high-quality cells remains an impediment to cell-based therapies. Induced pluripotent stem cells (iPSC) may be an unparalleled source, but autologous iPSC likely retain deficiencies requiring correction. We present a strategy for restoring physiological function in genetically deficient iPSC utilizing the low-density lipoprotein receptor (LDLR) deficiency Familial Hypercholesterolemia (FH) as our model. FH fibroblasts were reprogrammed into iPSC using synthetic modified mRNA. FH-iPSC exhibited pluripotency and differentiated toward a hepatic lineage. To restore LDLR endocytosis, FH-iPSC were transfected with a 31 kb plasmid (pEHZ-LDLR-LDLR) containing a wild-type LDLR (FH-iPSC-LDLR) controlled by 10 kb of upstream genomic DNA as well as Epstein-Barr sequences (EBNA1 and oriP) for episomal retention and replication. After six months of selective culture, pEHZ-LDLR-LDLR was recovered from FH-iPSC-LDLR and transfected into Ldlr-deficient CHO-a7 cells, which then exhibited feedback-controlled LDLR-mediated endocytosis. To quantify endocytosis, FH-iPSC ± LDLR were differentiated into mesenchymal cells (MC), pretreated with excess free sterols, Lovastatin, or ethanol (control), and exposed to DiI-LDL. FH-MC-LDLR demonstrated a physiological response, with virtually no DiI-LDL internalization with excess sterols and an ~2-fold increase in DiI-LDL internalization by Lovastatin compared to FH-MC. These findings demonstrate the feasibility of functionalizing genetically deficient iPSC using episomal plasmids to deliver physiologically responsive transgenes.
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Affiliation(s)
- Venkat M Ramakrishnan
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Department of Physiology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA
| | - Jeong-Yeh Yang
- Regenerative Bioscience Center, University of Georgia, Athens, Georgia 30602, USA.,Department of Animal and Dairy Sciences, University of Georgia, Athens, GA 30206, USA
| | - Kevin T Tien
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA
| | - Thomas R McKinley
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA
| | - Braden R Bocard
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Georgetown College, Georgetown, KY 40324, USA
| | - John G Maijub
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Department of Surgery, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Patrick O Burchell
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA
| | - Stuart K Williams
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Department of Physiology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA
| | - Marvin E Morris
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Department of Surgery, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - James B Hoying
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Department of Physiology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA
| | - Richard Wade-Martins
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3QX, UK
| | - Franklin D West
- Regenerative Bioscience Center, University of Georgia, Athens, Georgia 30602, USA.,Department of Animal and Dairy Sciences, University of Georgia, Athens, GA 30206, USA
| | - Nolan L Boyd
- Cardiovascular Innovation Institute, University of Louisville School of Medicine and Jewish Hospital, Louisville, Kentucky 40202, USA.,Department of Physiology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA
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7
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van Rahden VA, Brand K, Najm J, Heeren J, Pfeffer SR, Braulke T, Kutsche K. The 5-phosphatase OCRL mediates retrograde transport of the mannose 6-phosphate receptor by regulating a Rac1-cofilin signalling module. Hum Mol Genet 2012; 21:5019-38. [PMID: 22907655 DOI: 10.1093/hmg/dds343] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mutations in the OCRL gene encoding the phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) 5-phosphatase OCRL cause Lowe syndrome (LS), which is characterized by intellectual disability, cataracts and selective proximal tubulopathy. OCRL localizes membrane-bound compartments and is implicated in intracellular transport. Comprehensive analysis of clathrin-mediated endocytosis in fibroblasts of patients with LS did not reveal any difference in trafficking of epidermal growth factor, low density lipoprotein or transferrin, compared with normal fibroblasts. However, LS fibroblasts displayed reduced mannose 6-phosphate receptor (MPR)-mediated re-uptake of the lysosomal enzyme arylsulfatase B. In addition, endosome-to-trans Golgi network (TGN) transport of MPRs was decreased significantly, leading to higher levels of cell surface MPRs and their enrichment in enlarged, retromer-positive endosomes in OCRL-depleted HeLa cells. In line with the higher steady-state concentration of MPRs in the endosomal compartment in equilibrium with the cell surface, anterograde transport of the lysosomal enzyme, cathepsin D was impaired. Wild-type OCRL counteracted accumulation of MPR in endosomes in an activity-dependent manner, suggesting that PI(4,5)P(2) modulates the activity state of proteins regulated by this phosphoinositide. Indeed, we detected an increased amount of the inactive, phosphorylated form of cofilin and lower levels of the active form of PAK3 upon OCRL depletion. Levels of active Rac1 and RhoA were reduced or enhanced, respectively. Overexpression of Rac1 rescued both enhanced levels of phosphorylated cofilin and MPR accumulation in enlarged endosomes. Our data suggest that PI(4,5)P(2) dephosphorylation through OCRL regulates a Rac1-cofilin signalling cascade implicated in MPR trafficking from endosomes to the TGN.
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Affiliation(s)
- Vanessa A van Rahden
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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8
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Zhao GJ, Yin K, Fu YC, Tang CK. The interaction of ApoA-I and ABCA1 triggers signal transduction pathways to mediate efflux of cellular lipids. Mol Med 2012; 18:149-58. [PMID: 22064972 DOI: 10.2119/molmed.2011.00183] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Accepted: 11/01/2011] [Indexed: 12/17/2022] Open
Abstract
Reverse cholesterol transport (RCT) has been characterized as a crucial step for antiatherosclerosis, which is initiated by ATP-binding cassette A1 (ABCA1) to mediate the efflux of cellular phospholipids and cholesterol to lipid-free apolipoprotein A-I (apoA-I). However, the mechanisms underlying apoA-I/ABCA1 interaction to lead to the lipidation of apoA-I are poorly understood. There are several models proposed for the interaction of apoA-I with ABCA1 as well as the lipidation of apoA-I mediated by ABCA1. ApoA-I increases the levels of ABCA1 protein markedly. In turn, ABCA1 can stabilize apoA-I. The interaction of apoA-I with ABCA1 could activate signaling molecules that modulate posttranslational ABCA1 activity or lipid transport activity. The key signaling molecules in these processes include protein kinase A (PKA), protein kinase C (PKC), Janus kinase 2 (JAK2), Rho GTPases and Ca²⁺, and many factors also could influence the interaction of apoA-I with ABCA1. This review will summarize these mechanisms for the apoA-I interaction with ABCA1 as well as the signal transduction pathways involved in these processes.
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Affiliation(s)
- Guo-Jun Zhao
- Institute of Cardiovascular Research, Key Laboratory for Atherosclerology of Hunan Province, Life Science Research Center, University of South China, Hengyang, China
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9
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Laatsch A, Panteli M, Sornsakrin M, Hoffzimmer B, Grewal T, Heeren J. Low density lipoprotein receptor-related protein 1 dependent endosomal trapping and recycling of apolipoprotein E. PLoS One 2012; 7:e29385. [PMID: 22238606 PMCID: PMC3251589 DOI: 10.1371/journal.pone.0029385] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Accepted: 11/28/2011] [Indexed: 11/19/2022] Open
Abstract
Background Lipoprotein receptors from the low density lipoprotein (LDL) receptor family are multifunctional membrane proteins which can efficiently mediate endocytosis and thereby facilitate lipoprotein clearance from the plasma. The biggest member of this family, the LDL receptor-related protein 1 (LRP1), facilitates the hepatic uptake of triglyceride-rich lipoproteins (TRL) via interaction with apolipoprotein E (apoE). In contrast to the classical LDL degradation pathway, TRL disintegrate in peripheral endosomes, and core lipids and apoB are targeted along the endocytic pathway for lysosomal degradation. Notably, TRL-derived apoE remains within recycling endosomes and is then mobilized by high density lipoproteins (HDL) for re-secretion. The aim of this study is to investigate the involvement of LRP1 in the regulation of apoE recycling. Principal Findings Immunofluorescence studies indicate the LRP1-dependent trapping of apoE in EEA1-positive endosomes in human hepatoma cells. This processing is distinct from other LRP1 ligands such as RAP which is efficiently targeted to lysosomal compartments. Upon stimulation of HDL-induced recycling, apoE is released from LRP1-positive endosomes but is targeted to another, distinct population of early endosomes that contain HDL, but not LRP1. For subsequent analysis of the recycling capacity, we expressed the full-length human LRP1 and used an RNA interference approach to manipulate the expression levels of LRP1. In support of LRP1 determining the intracellular fate of apoE, overexpression of LRP1 significantly stimulated HDL-induced apoE recycling. Vice versa LRP1 knockdown in HEK293 cells and primary hepatocytes strongly reduced the efficiency of HDL to stimulate apoE secretion. Conclusion We conclude that LRP1 enables apoE to accumulate in an early endosomal recycling compartment that serves as a pool for the intracellular formation and subsequent re-secretion of apoE-enriched HDL particles.
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Affiliation(s)
- Alexander Laatsch
- Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Malamatenia Panteli
- Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Marijke Sornsakrin
- Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Britta Hoffzimmer
- Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Thomas Grewal
- Faculty of Pharmacy A15, The University of Sydney, Sydney, Australia
| | - Joerg Heeren
- Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- * E-mail:
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10
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Mechanics and dynamics of triglyceride-phospholipid model membranes: Implications for cellular properties and function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:1947-56. [PMID: 21545789 DOI: 10.1016/j.bbamem.2011.04.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 04/10/2011] [Accepted: 04/11/2011] [Indexed: 11/21/2022]
Abstract
We demonstrate here that triolein alters the mechanical properties of phospholipid membranes and induces extraordinary conformational dynamics. Triolein containing membranes exhibit fluctuations up to size range of 100μm and with the help of these are e.g. able to squeeze through narrow passages between neighbouring structures. Triolein-phosphatidylcholine membranes were found to have bending rigidity significantly lower than that of corresponding pure phosphatidylcholine membrane. Moreover, the triolein containing membranes were found to be reluctant to fuse, which is in good accordance with larger lamellar distances observed in the TOPOPC membranes. These findings suggest repulsion between adjacent membranes. We provide a comprehensive discussion on the possible explanations for the observed mechanics and dynamics in the TOPOPC system and on their potential cellular implications.
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11
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Pakkanen KI, Duelund L, Vuento M, Ipsen JH. Phase coexistence in a triolein-phosphatidylcholine system. Implications for lysosomal membrane properties. Chem Phys Lipids 2009; 163:218-27. [PMID: 19962372 DOI: 10.1016/j.chemphyslip.2009.11.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2009] [Revised: 10/10/2009] [Accepted: 11/25/2009] [Indexed: 10/20/2022]
Abstract
The effects of tri- and monoglycerides on phospholipid (POPC) membranes were studied using spectroscopical methods. Triolein was found to form two types of POPC-rich membranes, both with POPC or as a three-component system with monopalmitin. These two membrane types were determined as co-existing phases based on their spontaneous and stable separation and named heavy and light phase according to their sedimentation behaviour. Marked differences were seen in the physical properties of these phases, even though only minor compositional variation was detected. The light, less polar phase was found to be less ordered and more fluid and seemed to allow significantly lower amount of water penetration into the membrane-water interface than pure POPC membrane. The heavy phase, apart from their slightly altered water penetration, resembled more a pure POPC membrane. As triglycerides are present in lysosomal membranes, the present results can be seen as an implication for polarity-based water permeability barrier possibly contributing to the integrity of lysosomes.
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Affiliation(s)
- Kirsi I Pakkanen
- Nanoscience Center, Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
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12
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Conde-Vancells J, Rodriguez-Suarez E, Embade N, Gil D, Matthiesen R, Valle M, Elortza F, Lu SC, Mato JM, Falcon-Perez JM. Characterization and comprehensive proteome profiling of exosomes secreted by hepatocytes. J Proteome Res 2009; 7:5157-66. [PMID: 19367702 DOI: 10.1021/pr8004887] [Citation(s) in RCA: 440] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Exosomes represent a discrete population of vesicles that are secreted from various cell types to the extracellular media. Their protein and lipid composition are a consequence of sorting events at the level of the multivesicular body, a central organelle which integrates endocytic and secretory pathways. Characterization of exosomes from different biological samples has shown the presence of common as well as cell-type specific proteins. Remarkably, the protein content of the exosomes is modified upon pathological or stress conditions. Hepatocytes play a central role in the body response to stress metabolizing potentially harmful endogenous substances as well as xenobiotics. In the present study, we described and characterized for the first time exosome secretion in nontumoral hepatocytes, and with the use of a systematic proteomic approach, we establish the first extensive proteome of a hepatocyte-derived exosome population which should be useful in furthering our understanding of the hepatic function and in the identification of components that may serve as biomarkers for hepatic alterations. Our analysis identifies a significant number of proteins previously described among exosomes derived from others cell types as well as proteins involved in metabolizing lipoproteins, endogenous compounds and xenobiotics, not previously described in exosomes. Furthermore, we demonstrated that exosomal membrane proteins can constitute an interesting tool to express nonexosomal proteins into exosomes with therapeutic purposes.
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Affiliation(s)
- Javier Conde-Vancells
- Metabolomics Unit, CICbioGUNE, CIBERehd, Bizkaia Technology Park, Derio, 48160, Bizkaia, Spain
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13
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Rellin L, Heeren J, Beisiegel U. Recycling of apolipoprotein E is not associated with cholesterol efflux in neuronal cells. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1781:232-8. [PMID: 18359298 DOI: 10.1016/j.bbalip.2008.02.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Revised: 02/13/2008] [Accepted: 02/14/2008] [Indexed: 01/27/2023]
Abstract
After receptor-mediated endocytosis of apolipoprotein E (apoE)-containing lipoproteins in hepatocytes, the isoform apoE3 is efficiently recycled in a process which is associated with cholesterol efflux. Recycling and cholesterol efflux are greatly reduced when apoE4 is the only isoform present. ApoE is the main apolipoprotein in cerebrospinal fluid, and it plays a pivotal role in maintaining cholesterol homeostasis in the brain. The isoform apoE4 is associated with an increased risk of Alzheimer's disease and it has been postulated that high intracellular cholesterol levels promote the amyloidogenic processing of amyloid precursor protein. Therefore we investigated the cellular processing of different apoE isoforms as well as the associated cholesterol efflux in the murine neuronal cell line HT-22. Uptake of apoE3-containing lipoproteins resulted in the expected recycling while, as seen in non-neuronal cells, recycling of apoE4 was significantly reduced. However, despite these differences in apoE recycling, there was no difference in rates of cholesterol efflux. Therefore we conclude that in this neuronal cell model the reduced recycling of apoE4 does not affect cellular cholesterol metabolism.
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Affiliation(s)
- Lars Rellin
- University Medical Center Hamburg-Eppendorf, Department of Biochemistry and Molecular Biology II: Molecular Cell Biology, Martinistrasse 52, Hamburg, Germany
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14
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Abstract
The classic concept of self-non-self discrimination by the immune system focused on the recognition of fragments from proteins presented by classical MHC molecules. However, the discovery of MHC-class-I-like CD1 antigen-presentation molecules now explains how the immune system also recognizes the abundant and diverse universe of lipid-containing antigens. The CD1 molecules bind and present amphipathic lipid antigens for recognition by T-cell receptors. Here, we outline the recent advances in our understanding of how the processes of CD1 assembly, trafficking, lipid-antigen binding and T-cell activation are achieved and the new insights into how lipid antigens differentially elicit CD1-restricted innate and adaptive T-cell responses.
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Affiliation(s)
- Duarte C Barral
- Division of Rheumatology, Immunology and Allergy, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, 1 Jimmy Fund Way, Boston, Massachusetts 02115, USA
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15
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Kontush A, Chapman MJ. Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis. Pharmacol Rev 2006; 58:342-74. [PMID: 16968945 DOI: 10.1124/pr.58.3.1] [Citation(s) in RCA: 533] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.
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Affiliation(s)
- Anatol Kontush
- Dyslipoproteinemia and Atherosclerosis Research Unit, National Institute for Health and Medical Research, Hôpital de la Pitié, 83 boulevard de l'Hôpital, 75651 Paris Cedex 13, France.
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16
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Gonzalez JB, Orth M, Schaefer M, Tauber R. Endocytosis and intracellular trafficking of fatty acid esters of phenylaminopropanediol, the putative etiologic agents of the toxic oil syndrome (TOS). Toxicol Lett 2006; 163:206-12. [PMID: 16343824 DOI: 10.1016/j.toxlet.2005.10.025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2005] [Revised: 10/26/2005] [Accepted: 10/28/2005] [Indexed: 11/25/2022]
Abstract
The toxic oil syndrome (TOS) caused by ingestion of rapeseed oil adulterated with aniline is characterized by symptoms of an allergic and/or autoimmune illness associated with vessel wall lesions similar to those of atherosclerosis. Fatty acid esters of 3-(N-phenylamino)-1,2-propanediol (PAP) have been incriminated as the etiologic agents of TOS. However, the pathogenesis of TOS is yet unknown. Here, we addressed whether PAP fatty acid esters are incorporated into lipoproteins, which after transport to vascular endothelial cells are taken up to initiate TOS vasculopathy. After loading (14)C-dioleyl-ester of PAP into LDL labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindolcarbocyanine (DiI) we assessed receptor mediated endocytosis and intracellular localization of these lipopoproteins in vascular endothelial cells. Our data suggest that these lipoprotein-derivatives are internalized into endothelial cells by LDL receptor mediated endocytosis. Confocal microscopy revealed that DiI-LDL loaded with dioleyl-ester of PAP and incubated for 60 min with endothelial cells colocalizes with the lysosomotropic compound LysoTracker Green, indicating that internalized PAP-loaded LDL are targetted to the endolysosomal compartment for further processing. Subcellular fractionation of endothelial-like ECV-304 cells after incubation with LDL loaded with the (14)C-dioleyl-ester of PAP for 6h showed that the radioactive label accumulated in fractions containing endosomes, the Golgi apparatus and the endoplasmic reticulum.
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Affiliation(s)
- Jose B Gonzalez
- Institut für Klinische Chemie und Pathobiochemie, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany.
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17
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Sun B, Eckhardt ERM, Shetty S, van der Westhuyzen DR, Webb NR. Quantitative analysis of SR-BI-dependent HDL retroendocytosis in hepatocytes and fibroblasts. J Lipid Res 2006; 47:1700-13. [PMID: 16705213 DOI: 10.1194/jlr.m500450-jlr200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Previous studies have suggested that HDL retroendocytosis may play a role in scavenger receptor class B type I (SR-BI)-dependent selective lipid uptake in a cell-specific manner. To investigate this possibility, we developed methods to quantitatively measure HDL uptake and resecretion in fibroblast (COS-7) and hepatocyte (HepG2) cells expressing exogenous SR-BI. Approximately 17% and 24% of HDL associated in an SR-BI-dependent manner with COS-7 and HepG2 cells, respectively, accumulates intracellularly after a 10 min incubation. To determine whether this intracellular HDL undergoes retroendocytosis, we developed a pulse-chase assay whereby internalized biotinylated (125)I-HDL(3) secreted from cells is quantitatively precipitated from cell supernatants using immobilized streptavidin. Our results show a rapid secretion of a portion of intracellular HDL from both cell types (representing 4-7% of the total cell-associated HDL) that is almost complete within 30 min (half-life approximately 10 min). In COS-7 cells, the calculated rate of HDL secretion ( approximately 0.5 ng HDL/mg/min) was >30-fold slower than the rate of SR-BI-dependent selective cholesteryl ester (CE) uptake ( approximately 17 ng HDL/mg/min), whereas the rate of release of HDL from the cell surface ( approximately 19 ng HDL/mg/min) was similar to the rate of selective CE uptake. Notably, the rate of SR-BI-dependent HDL resecretion in COS-7 and HepG2 cells was similar. BLT1, a compound that inhibits selective CE uptake, does not alter the amount of SR-BI-mediated HDL retroendocytosis in COS-7 cells. From these data, we conclude that HDL retroendocytosis in COS-7 and HepG2 cells is similar and that the vast majority of SR-BI-dependent selective uptake occurs at the cell surface in both cell types.
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Affiliation(s)
- Bing Sun
- Department of Internal Medicine, Graduate Center for Nutritional Sciences, University of Kentucky Medical Center, Lexington, 40536, USA
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18
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Wüstner D. Steady State Analysis and Experimental Validation of a Model for Hepatic High-Density Lipoprotein Transport. Traffic 2006; 7:699-715. [PMID: 16637891 DOI: 10.1111/j.1398-9219.2006.00421.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Transport of high-density lipoprotein (HDL) in the hepatocyte plays a fundamental role in reverse cholesterol transport and regulation of plasma HDL levels. On the basis of a recently developed kinetic model, the steady state distribution of HDL was analyzed. Fractional fluorescence of labeled HDL in the basolateral membrane, sorting endosomes (SE), the subapical compartment/ apical recycling compartment, the biliary canaliculus and in late endosomes and lysosomes (LE/LYS) including expected standard deviation is predicted. Improved parameter estimation was obtained by including kinetic data of apical endocytosis of fluorescent markers for LE/LYS, asialoorosomucoid and Rhodamine-dextran, in the regression. Predicted values using the refined kinetic parameters are in good agreement with experimental values of compartmental steady state fluorescence of Alexa488-HDL in polarized hepatic HepG2 cells. From calculated steady state fluxes, it is suggested that export of HDL from basolateral SE is the key step for determining the transport of HDL through the hepatocyte. The analysis provides testable predictions for high-throughput fluorescence microscopy screening experiments on potential inhibitors of hepatic HDL processing. By quantitative fluorescence imaging and model analysis, it is shown that the phosphoinositide kinase inhibitor wortmannin prevents apical transport of fluorescent HDL from basolateral SE. The results support that endosomes of polarized hepatic cells have different sorting functions and that apical endocytosis is an integrative trafficking step in hepatocytes.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230, Odense M, Denmark.
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19
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Heeren J, Beisiegel U, Grewal T. Apolipoprotein E recycling: implications for dyslipidemia and atherosclerosis. Arterioscler Thromb Vasc Biol 2005; 26:442-8. [PMID: 16373604 DOI: 10.1161/01.atv.0000201282.64751.47] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
After receptor-mediated endocytosis, the intracellular fate of triglyceride-rich lipoproteins (TRLs) is far more complex than the classical degradation pathway of low-density lipoproteins. Once internalized, TRLs disintegrate in peripheral endosomes, followed by a differential sorting of TRL components. Although core lipids and apolipoprotein B are targeted to lysosomes, the majority of TRL-derived apolipoprotein E (apoE) remains in peripheral recycling endosomes. This pool of TRL-derived apoE is then mobilized by high-density lipoproteins (HDLs) or HDL-derived apoA-I to be recycled back to the plasma membrane, followed by apoE resecretion and the subsequent formation of apoE-containing HDL. The HDL-induced recycling of apoE is accompanied by cholesterol efflux and involves the internalization and targeting of HDL-derived apoA-I to endosomes containing both apoE and cholesterol. These findings point to a yet unknown intracellular link between TRL-derived apoE, cellular cholesterol transport, and HDL metabolism. Recent studies provide first evidence that impaired recycling of TRL-derived apoE4, but not apoE3, is associated with intracellular cholesterol accumulation, which might explain some well-documented effects of apoE4 on HDL metabolism. This review summarizes the current understanding of apoE recycling and its potential role in the regulation of plasma apoE levels in the postprandial state.
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Affiliation(s)
- Joerg Heeren
- Institute for Biochemistry and Molecular Biology II, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
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20
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Zhu MY, Hasty AH, Harris C, Linton MF, Fazio S, Swift LL. Physiological relevance of apolipoprotein E recycling: studies in primary mouse hepatocytes. Metabolism 2005; 54:1309-15. [PMID: 16154429 DOI: 10.1016/j.metabol.2005.04.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2004] [Accepted: 04/30/2005] [Indexed: 10/25/2022]
Abstract
Studies in our laboratory have shown that a fraction of apolipoprotein (apo) E internalized by hepatocytes escapes degradation and is resecreted. Although the intracellular routing is not fully understood, our studies suggest that a portion of apoE recycles through the Golgi apparatus. Given the role of the Golgi apparatus in lipoprotein secretion and the fact that apoE modulates the hepatic secretion of very low-density lipoprotein, we hypothesized that recycling apoE has an effect on hepatic very low-density lipoprotein assembly and/or secretion. To test this hypothesis, apoE-/- mice were transplanted with bone marrow from wild-type mice. In this model, extrahepatic (macrophage-derived) apoE is internalized by the hepatocytes in vivo and is resecreted when the hepatocytes are placed in culture. Unexpectedly, our studies demonstrate that recycling apoE has little effect on hepatic lipid content or hepatocyte triglyceride secretion. In addition, recycling apoE has little effect on the expression of enzymes and proteins involved in lipid synthesis as well as plasma lipoprotein apoproteins. We conclude that the physiological relevance of apoE recycling may not be related to cell-specific functions, such as lipoprotein assembly in the liver. Rather, recycling may provide a mechanism for modulating general cellular effects such as intracellular cholesterol transport or cholesterol efflux.
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Affiliation(s)
- Mei-Ying Zhu
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, TN 37232-2561, USA
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21
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Hasty AH, Plummer MR, Weisgraber KH, Linton MF, Fazio S, Swift LL. The recycling of apolipoprotein E in macrophages. J Lipid Res 2005; 46:1433-9. [PMID: 15805547 DOI: 10.1194/jlr.m400418-jlr200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability of apolipoprotein E (apoE) to be spared degradation in lysosomes and to recycle to the cell surface has been demonstrated by our group and others, but its physiologic relevance is unknown. In this study, we characterized apoE recycling in primary murine macrophages and probed the effects of HDL and apoA-I on this process. In cells pulsed with (125)I.apoE bound to VLDL, intact apoE was found in the chase medium for up to 24 h after the pulse. Approximately 27 +/- 5% of the apoE internalized during the pulse was recycled after 4 h of chase. Addition of apoA-I and HDL increased apoE recycling to 45 +/- 3% and 46 +/- 3%, respectively, similar to the amount of apoE recycled after pulsing the cells with (125)I.apoE.HDL. In addition, apoA-I-producing macrophages from transgenic mice showed increased apoE recycling at 4 h (38 +/- 3%). Increased ABCA1 expression potentiated apoE recycling, suggesting that recycling occurs via ABCA1. Finally, in the presence of apoA-I, recycled apoE exited the cells on HDL-like particles. These results suggest that apoE recycling in macrophages may be part of a larger signaling loop activated by HDL and directed at maximizing cholesterol losses from the cell.
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Affiliation(s)
- Alyssa H Hasty
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
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22
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Zager RA, Johnson ACM, Hanson SY. Renal tubular triglyercide accumulation following endotoxic, toxic, and ischemic injury. Kidney Int 2005; 67:111-21. [PMID: 15610234 DOI: 10.1111/j.1523-1755.2005.00061.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
BACKGROUND Cholesterol accumulates in renal cortical proximal tubules in response to diverse forms of injury or physiologic stress. However, the fate of triglycerides after acute renal insults is poorly defined. This study sought new insights into this issue. METHODS CD-1 mice were subjected to three diverse models of renal stress: (1) endotoxemia [Escherichia coli lipopolysaccharide (LPS), injection]; (2) ischemia/reperfusion (I/R); or (3) glycerol-induced rhabdomyolysis. Renal cortical, or isolated proximal tubule, triglyceride levels were measured approximately 18 hours later. To gain mechanistic insights, triglyceride levels were determined in (1) proximal tubules following exogenous phospholipase A(2) (PLA(2)) treatment; (2) cultured HK-2 cells after mitochondrial blockade (antimycin A) +/- serum; or (3) HK-2 cells following "septic" (post-LPS) serum, or exogenous fatty acid (oleate) addition. RESULTS Each form of in vivo injury evoked three-to fourfold triglyceride increases in renal cortex and/or proximal tubules. PLA(2) treatment of proximal tubules evoked acute, dose-dependent, triglyceride formation. HK-2 cell triglyceride levels rose with antimycin A. With serum present, antimycin A induced an exaggerated triglyceride loading state (vs. serum alone or antimycin A alone). "Septic" serum stimulated HK-2 triglyceride formation (compared to control serum). Oleate addition caused striking HK-2 cell triglyceride accumulation. Following oleate washout, HK-2 cells were sensitized to adenosine triphosphate (ATP) depletion or oxidant attack. CONCLUSION Diverse forms of renal injury induce dramatic triglyceride loading in proximal tubules/renal cortex, suggesting that this is a component of a cell stress response. PLA(2) activity, increased triglyceride/triglyceride substrate (e.g., fatty acid) uptake, and possible systemic cytokine (e.g., from LPS) stimulation, may each contribute to this result. Finally, in addition to being a marker of prior cell injury, accumulation of triglyceride (or of its constituent fatty acids) may predispose tubules to superimposed ATP depletion or oxidant attack.
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Affiliation(s)
- Richard A Zager
- Department of Medicine, University of Washington, and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
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23
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Greenow K, Pearce NJ, Ramji DP. The key role of apolipoprotein E in atherosclerosis. J Mol Med (Berl) 2005; 83:329-42. [PMID: 15827760 DOI: 10.1007/s00109-004-0631-3] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2004] [Accepted: 11/08/2004] [Indexed: 01/17/2023]
Abstract
Apolipoprotein E is a multifunctional protein that is synthesized by the liver and several peripheral tissues and cell types, including macrophages. The protein is involved in the efficient hepatic uptake of lipoprotein particles, stimulation of cholesterol efflux from macrophage foam cells in the atherosclerotic lesion, and the regulation of immune and inflammatory responses. Apolipoprotein E deficiency in mice leads to the development of atherosclerosis and re-expression of the protein reduces the extent of the disease. This review presents evidence for the potent anti-atherogenic action of apolipoprotein E and describes our current understanding of its multiple functions and regulation by factors implicated in the pathogenesis of cardiovascular disease.
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Affiliation(s)
- Kirsty Greenow
- Cardiff School of Biosciences, Cardiff University, Museum Avenue, P.O. Box 911, Cardiff CF10 3US, Wales, UK
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24
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Van Hoof D, Rodenburg KW, Van der Horst DJ. Intracellular fate of LDL receptor family members depends on the cooperation between their ligand-binding and EGF domains. J Cell Sci 2005; 118:1309-20. [PMID: 15741231 DOI: 10.1242/jcs.01725] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The insect low-density lipoprotein (LDL) receptor (LDLR) homologue LpR mediates endocytosis of an insect lipoprotein (lipophorin) that is structurally related to LDL. Despite these similarities, lipophorin and LDL follow distinct intracellular routes upon endocytosis by their receptors. Whereas LDL is degraded in lysosomes, lipophorin is recycled in a transferrin-like manner. We constructed several hybrid receptors composed of Locusta migratoria LpR and human LDLR regions to identify the domains implicated in LpR-mediated ligand recycling. Additionally, the triadic His562 residue of LDLR, which is putatively involved in ligand uncoupling, was mutated to Asn, corresponding to Asn643 in LpR, to analyse the role of the His triad in receptor functioning. The familial hypercholesterolaemia (FH) class 5 mutants LDLRH562Y and LDLRH190Y were also analysed in vitro. Fluorescence microscopic investigation and quantification suggest that LpR-mediated ligand recycling involves cooperation between the ligand-binding domain and epidermal growth factor (EGF) domain of LpR, whereas its cytosolic tail does not harbour motifs that affect this process. LDLR residue His562 appears to be essential for LDLR recycling after ligand endocytosis but not for constitutive receptor recycling. Like LDLRH562N, LDLRH562Y did not recycle bound ligand; moreover, the intracellular distribution of both mutant receptors after ligand incubation coincides with that of a lysosomal marker. The LDLR mutant characterization in vitro suggests that LDLR FH class 5 mutations might be divided into two subclasses.
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MESH Headings
- Animals
- Asparagine/chemistry
- Blotting, Western
- CHO Cells
- Cell Membrane/metabolism
- Cricetinae
- DNA, Complementary/metabolism
- Endocytosis
- ErbB Receptors/metabolism
- Histidine/chemistry
- Hydrogen-Ion Concentration
- Ligands
- Lipoproteins/chemistry
- Locusta migratoria
- Microscopy, Fluorescence
- Models, Chemical
- Models, Molecular
- Mutation
- Phenotype
- Protein Structure, Tertiary
- Receptors, LDL/chemistry
- Receptors, LDL/genetics
- Receptors, LDL/metabolism
- Receptors, Lipoprotein/chemistry
- Time Factors
- Transfection
- Transferrin/chemistry
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Affiliation(s)
- Dennis Van Hoof
- Department of Biochemical Physiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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25
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Niemeier A, Kassem M, Toedter K, Wendt D, Ruether W, Beisiegel U, Heeren J. Expression of LRP1 by human osteoblasts: a mechanism for the delivery of lipoproteins and vitamin K1 to bone. J Bone Miner Res 2005; 20:283-93. [PMID: 15647823 DOI: 10.1359/jbmr.041102] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2004] [Revised: 07/27/2004] [Accepted: 08/31/2004] [Indexed: 01/31/2023]
Abstract
UNLABELLED Accumulating clinical and experimental data show the importance of dietary lipids and lipophilic vitamins, such as vitamin K1, for bone formation. The molecular mechanism of how they enter the osteoblast is unknown. Here we describe the expression of the multifunctional LRP1 by human osteoblasts in vitro and in vivo. We provide evidence that LRP1 plays an important role in the uptake of postprandial lipoproteins and vitamin K1 by human osteoblasts. INTRODUCTION Chylomicrons (CM) and their remnants (CR) represent the postprandial plasma carriers of dietary lipids. Dietary vitamin K1 is known to be transported in the circulation as part of CM/CR and is required by osteoblasts as an essential co-factor for the gamma-carboxylation of bone matrix proteins. The molecular mechanisms underlying the delivery of lipophilic substances to bone are not understood. In this study, the expression and function of CM/CR receptors was examined in human osteoblasts. MATERIALS AND METHODS Four human osteoblast-like cell lines were analyzed: two osteosarcoma lines (MG63, SaOS-2) and two telomerase-immortalized human bone marrow stromal cell lines (hMSC-TERT [4] and [20]) after 1,25(OH)2 vitamin D3 induction of osteoblastic differentiation (hMSC-TERT-OB). Receptor expression was examined by Western blotting and immunohistochemistry of normal human bone sections. Endocytotic receptor function was analyzed by cellular uptake assays using fluorescent and radiolabeled human CR. Vitamin K1-enriched CR (CR-K1) were generated in vivo after oral vitamin administration and vitamin K1 uptake by osteoblasts was measured by HPLC. The effect of CR-K1 uptake on osteocalcin carboxylation was measured by ELISA. RESULTS Osteoblasts exhibit high levels of protein expression of the CR receptors LRP1 and LDLR. VLDLR is expressed to a lower degree. Immunohistochemistry of normal human bone sections showed strong LRP1 expression by osteoblasts and marrow stromal cells. Uptake of fluorescent CR by osteoblasts resulted in the typical pattern of receptor-mediated endocytosis. CR uptake was stimulated by the exogenous addition of the lipoprotein receptor ligands apolipoprotein E and lipoprotein lipase. Uptake was reduced by the known LRP1 inhibitors RAP, lactoferrin, and suramin, but not by LDL, which exclusively binds to the LDLR. Vitamin K1 uptake by hMSC-TERT-OB after incubation with CR-K1 was also shown to be sensitive to LPL stimulation and the LRP1 specific inhibitor lactoferrin. CR-K1 uptake into osteoblasts stimulated the gamma-carboxylation of osteocalcin. CONCLUSION Human osteoblasts express receptors of the LDLR family with a capacity for vitamin K1 uptake through CR endocytosis, a novel mechanism for the delivery of dietary lipids and lipophilic vitamins to human bone. The current data suggest that, among the expressed receptors, LRP1 plays a predominant role.
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Affiliation(s)
- Andreas Niemeier
- Department of Orthopaedics, University Hospital Hamburg-Eppendorf, Hamburg, Germany.
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26
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Heeren J, Grewal T, Laatsch A, Becker N, Rinninger F, Rye KA, Beisiegel U. Impaired Recycling of Apolipoprotein E4 Is Associated with Intracellular Cholesterol Accumulation. J Biol Chem 2004; 279:55483-92. [PMID: 15485881 DOI: 10.1074/jbc.m409324200] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
After internalization of triglyceride-rich lipoproteins (TRL) in hepatoma cells, TRL particles are immediately disintegrated in the early endosomal compartment. This involves the targeting of lipids and apoprotein B along the degradative pathway and the recycling of TRL-derived apoE through recycling endosomes. Re-secretion of apoE is accompanied by the concomitant association of apoE and cellular cholesterol with high-density lipoproteins (HDL). Since epidemiological data showed that apoE3 and apoE4 have differential effects on HDL metabolism, we investigated whether the intracellular processing of TRL-derived apoE4 differs from apoE3-TRL. In this study, we demonstrated by radioactive and immunofluorescence uptake experiments that cell-surface binding and internalization of TRL-derived apoE4 are increased compared with apoE3 in hepatoma cells. Pulse-chase experiments revealed that HDL-induced recycling, but not disintegration and degradation, of apoE4-enriched TRL is strongly reduced in these cells. Furthermore, impaired HDL-induced apoE4 recycling is associated with reduced cholesterol efflux. Studies performed in Tangier fibroblasts showed that apoE recycling does not depend on ATP-binding cassette transporter A1 activity. These studies provide initial evidence that impaired recycling of apoE4 could interfere with intracellular cholesterol transport and contribute to the pathophysiological lipoprotein profile observed in apoE4 homozygotes.
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Affiliation(s)
- Joerg Heeren
- Institute for Biochemistry and Molecular Biology II: Molecular Cell Biology and Department of Internal Medicine, University Hospital Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
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Farkas MH, Weisgraber KH, Shepherd VL, Linton MF, Fazio S, Swift LL. The recycling of apolipoprotein E and its amino-terminal 22 kDa fragment: evidence for multiple redundant pathways. J Lipid Res 2004; 45:1546-54. [PMID: 15145976 DOI: 10.1194/jlr.m400104-jlr200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A portion of apolipoprotein E (apoE) internalized by hepatocytes is spared degradation and is recycled. To investigate the intracellular routing of recycling apoE, primary hepatocyte cultures from LDL receptor-deficient mice and mice deficient in receptor-associated protein [a model of depressed expression of LDL receptor-related protein (LRP)] were incubated with human VLDL containing 125I-labeled human recombinant apoE3. Approximately 30% of the internalized intact apoE was recycled after 4 h. The N-terminal 22 kDa fragment of apoE was also resecreted, demonstrating that this apoE domain contains sufficient sequence to recycle. The 22 kDa fragment has reduced affinity for lipoproteins, suggesting that apoE recycling is linked to the ability of apoE to bind directly to a recycling receptor. Finally, apoE was found to recycle equally well in the presence of brefeldin A, a drug that blocks transport from the endoplasmic reticulum and leads to collapse of the Golgi stacks. Our studies demonstrate that apoE recycling occurs 1) in the absence of the LDL receptor or under conditions of markedly reduced LRP expression; 2) when apoE lacks the carboxyl-terminal domain, which allows binding to the lipoprotein; and 3) in the absence of an intact Golgi apparatus. We conclude that apoE recycling occurs through multiple redundant pathways.
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Affiliation(s)
- Monica H Farkas
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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Brundert M, Heeren J, Greten H, Rinninger F. Hepatic lipase mediates an increase in selective uptake of HDL-associated cholesteryl esters by cells in culture independent from SR-BI. J Lipid Res 2003; 44:1020-32. [PMID: 12611911 DOI: 10.1194/jlr.m300058-jlr200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Scavenger receptor class B type I (SR-BI) mediates the selective uptake of HDL cholesteryl esters (CEs) by the liver. Hepatic lipase (HL) promotes this lipid uptake independent from lipolysis. The role of SR-BI in this HL-mediated increase in selective CE uptake was explored. Baby hamster kidney (BHK) cells were transfected with the SR-BI cDNA yielding cells with SR-BI expression, whereas no SR-BI was detected in control cells. These cells were incubated in medium containing 125I [3H]cholesteryl oleyl ether-labeled HDL3 (d = 1.125-1.21 g/ml) and HL was absent or present. Tetrahydrolipstatin (THL) blocked lipolysis. In control BHK cells and in BHK cells with SR-BI, HDL3 selective CE uptake (3H-125I) was detectable and SR-BI promoted this uptake. In both cell types, HL mediated an increase in selective CE uptake from HDL3. Quantitatively, this HL effect was similar in control BHK cells and in BHK cells with SR-BI. These results suggest that HL promotes selective uptake independent from SR-BI. To investigate the role of cell surface proteoglycans on the HL-mediated HDL3 uptake, proteoglycan deficiency was induced by heparinase digestion. Proteoglycan deficiency decreased the HL-mediated promotion of selective CE uptake. In summary, the stimulating HL effect on HDL selective CE uptake is independent from SR-BI and lipolysis. Proteoglycans are a requisite for the HL action on selective uptake. Results suggest that (a) pathway(s) distinct from SR-BI mediate(s) selective CE uptake from HDL.
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Affiliation(s)
- May Brundert
- Universitaetsklinikum Hamburg-Eppendorf, Department for Internal Medicine, Martinistrasse 52, 20246 Hamburg, Germany
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29
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Heeren J, Grewal T, Laatsch A, Rottke D, Rinninger F, Enrich C, Beisiegel U. Recycling of apoprotein E is associated with cholesterol efflux and high density lipoprotein internalization. J Biol Chem 2003; 278:14370-8. [PMID: 12584196 DOI: 10.1074/jbc.m209006200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
After receptor-mediated endocytosis of triglyceride-rich lipoproteins (TRL) into the liver, TRL particles are immediately disintegrated in peripheral endosomal compartments. Whereas core lipids and apoprotein B are delivered for degradation into lysosomes, TRL-derived apoE is efficiently recycled back to the plasma membrane. This is followed by apoE re-secretion and association of apoE with high density lipoproteins (HDL). Because HDL and apoE can independently promote cholesterol efflux, we investigated whether recycling of TRL-derived apoE in human hepatoma cells and fibroblasts could be linked to intracellular cholesterol transport. In this study we demonstrate that HDL(3) does not only act as an extracellular acceptor for recycled apoE but also stimulates the recycling of internalized TRL-derived apoE. Furthermore, radioactive pulse-chase experiments indicate that apoE recycling is accompanied by cholesterol efflux. Confocal imaging reveals co-localization of apoE and cholesterol in early endosome antigen 1-positive endosomes. During apoE re-secretion, HDL(3)-derived apoA-I is found in these early endosome antigen 1, cholesterol-containing endosomes. As shown by time-lapse fluorescence microscopy, apoE recycling involves the intracellular trafficking of apoA-I to pre-existing and TRL-derived apoE/cholesterol-containing endosomes in the periphery. Thus, these studies provide evidence for a new intracellular link between TRL-derived apoE, cellular cholesterol transport, and HDL metabolism.
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Affiliation(s)
- Joerg Heeren
- Institute for Medical Biochemistry and Molecular Biology, the Department of Molecular Cell Biology, University Hospital Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
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Farkas MH, Swift LL, Hasty AH, Linton MF, Fazio S. The recycling of apolipoprotein E in primary cultures of mouse hepatocytes. Evidence for a physiologic connection to high density lipoprotein metabolism. J Biol Chem 2003; 278:9412-7. [PMID: 12524433 DOI: 10.1074/jbc.m208026200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Internalization of apoE-containing very low density protein (VLDL) by hepatocytes in vivo and in vitro leads to apoE recycling and resecretion. Because of the role of apoE in VLDL metabolism, apoE recycling may influence lipoprotein assembly or remnant uptake. However, apoE is also a HDL protein, and apoE recycling may be related to reverse cholesterol transport. To investigate apoE recycling, apoE(-/-) mouse hepatocytes were incubated (pulsed) with wild-type mouse lipoproteins, and cells and media were collected at chase periods up to 24 h. When cells were pulsed with VLDL, apoE was resecreted within 30 min. Although the mass of apoE in the media decreased with time, it could be detected up to 24 h after the pulse. Intact intracellular apoE was also detectable 24 h after the pulse. ApoE was also resecreted when cells were pulsed with HDL. When apoA-I was included in the chase media after a pulse with VLDL, apoE resecretion increased 4-fold. Furthermore, human apoE was resecreted from wild-type mouse hepatocytes after a pulse with human VLDL. Finally, apoE was resecreted from mouse peritoneal macrophages after pulsing with VLDL. We conclude that 1) HDL apoE recycles in a quantitatively comparable fashion to VLDL apoE; 2) apoE recycling can be modulated by extracellular apoA-I but is not affected by endogenous apoE; and 3) recycling occurs in macrophages as well as in hepatocytes, suggesting that the process is not cell-specific.
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Affiliation(s)
- Monica H Farkas
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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31
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Van Hoof D, Rodenburg KW, Van der Horst DJ. Insect lipoprotein follows a transferrin-like recycling pathway that is mediated by the insect LDL receptor homologue. J Cell Sci 2002; 115:4001-12. [PMID: 12356906 DOI: 10.1242/jcs.00113] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The lipoprotein of insects, high-density lipophorin (HDLp), is homologous to that of mammalian low-density lipoprotein (LDL) with respect to its apolipoprotein structure. Moreover, an endocytic receptor for HDLp has been identified (insect lipophorin receptor, iLR) that is homologus to the LDL receptor. We transfected LDL-receptor-expressing CHO cells with iLR cDNA to study the endocytic uptake and intracellular pathways of LDL and HDLp simultaneously. Our studies provide evidence that these mammalian and insect lipoproteins follow distinct intracellular routes after receptor-mediated endocytosis. Multicolour imaging and immunofluorescence was used to visualize the intracellular trafficking of fluorescently labeled ligands in these cells. Upon internalization, which can be completely inhibited by human receptor-associated protein (RAP), mammalian and insect lipoproteins share endocytic vesicles. Subsequently, however, HDLp evacuates the LDL-containing endosomes. In contrast to LDL, which is completely degraded in lysosomes after dissociating from its receptor, both HDLp and iLR converge in a nonlysosomal juxtanuclear compartment. Colocalization studies with transferrin identified this organelle as the endocytic recycling compartment via which iron-depleted transferrin exits the cell. Fluorescently labeled RAP is also transported to this recycling organelle upon receptor-mediated endocytosis by iLR. Internalized HDLp eventually exits the cell via the recycling compartment, a process that can be blocked by monensin, and is re-secreted with a t(1/2) of approximately 13 minutes. From these observations, we conclude that HDLp is the first non-exchangeable apolipoprotein-containing lipoprotein that follows a transferrin-like recycling pathway despite the similarities between mammalian and insect lipoproteins and their receptors.
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Affiliation(s)
- Dennis Van Hoof
- Department of Biochemical Physiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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32
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Heeren J, Grewal T, Jäckle S, Beisiegel U. Recycling of apolipoprotein E and lipoprotein lipase through endosomal compartments in vivo. J Biol Chem 2001; 276:42333-8. [PMID: 11546820 DOI: 10.1074/jbc.m107461200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have recently described a novel recycling pathway of triglyceride-rich lipoprotein (TRL)-associated apolipoprotein (apo) E in human hepatoma cells. We now demonstrate that not only TRL-derived apoE but also lipoprotein lipase (LPL) is efficiently recycled in vitro and in vivo. Similar recycling kinetics of apoE and LPL in normal and low density lipoprotein receptor-negative human fibroblasts also indicate that the low density lipoprotein receptor-related protein seems to be involved. Intracellular sorting mechanisms are responsible for reduced lysosomal degradation of both ligands after receptor-mediated internalization. Immediately after internalization in rat liver, TRLs are disintegrated, and apoE and LPL are found in endosomal compartments, whereas TRL-derived phospholipids accumulate in the perinuclear region of hepatocytes. Subsequently, substantial amounts of both proteins can be found in purified recycling endosomes, indicating a potential resecretion of these TRL components. Pulse-chase experiments of perfused rat livers with radiolabeled TRLs demonstrated a serum-induced release of internalized apoE and LPL into the perfusate. Analysis of the secreted proteins identified approximately 80% of the recycled TRL-derived proteins in the high density lipoprotein fractions. These results provide the first evidence that recycling of TRL-derived apoE and LPL could play an important role in the modulation of lipoproteins in vivo.
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Affiliation(s)
- J Heeren
- Department of Medical Biochemistry and Molecular Biology, University Hospital Eppendorf, D-20246 Hamburg, Germany.
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33
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Santamarina-Fojo S, Remaley AT, Neufeld EB, Brewer HB. Regulation and intracellular trafficking of the ABCA1 transporter. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)30266-2] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
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34
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Von Eckardstein A, Langer C, Engel T, Schaukal I, Cignarella A, Reinhardt J, Lorkowski S, Li Z, Zhou X, Cullen P, Assmann G. ATP binding cassette transporter ABCA1 modulates the secretion of apolipoprotein E from human monocyte-derived macrophages. FASEB J 2001; 15:1555-61. [PMID: 11427487 DOI: 10.1096/fj.00-0798com] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Apolipoprotein E (apoE) produced by macrophages in the arterial wall protects against atherosclerosis, but the regulation of its secretion by these cells is poorly understood. Here we investigated the contribution of the adenosine triphosphate binding cassette transporters ABCA1 and ABC8 to the secretion of apoE from either primary human monocyte-derived macrophages (HMDM) or human THP1 macrophages. During incubations of up to 6 h, apoE secretion from both THP1 macrophages and HMDM was stimulated by 8-Br-cAMP, which activates ABCA1 expression. The putative ABCA1 inhibitor glyburide and antisense oligonucleotides directed against ABCA1 mRNA significantly reduced apoE secretion from THP1 macrophages and HMDM. Antisense oligonucleotides directed against ABC8 mRNA also inhibited apoE secretion, although this inhibition was less pronounced and consistent than in the case of ABCA1. ApoE secretion from HMDM of ABCA1-deficient patients with Tangier disease was also decreased. ApoE mRNA expression was not affected by inhibition of ABCA1 or ABC8 in normal HMDM or the lack of functional ABCA1 in HMDM from Tangier disease patients. Inhibition of ABCA1 in HMDM prevented the occurrence of anti-apoE-immunoreactive granular structures in the plasma membrane. We conclude that ABCA1 and, to a lesser extent, ABC8 both promote secretion of apoE from human macrophages.
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Affiliation(s)
- A Von Eckardstein
- Institute of Clinical Chemistry and Laboratory Medicine, Central Laboratory, Westphalian Wilhelms University, D-48129 Münster, Germany.
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35
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Swift LL, Farkas MH, Major AS, Valyi-Nagy K, Linton MF, Fazio S. A recycling pathway for resecretion of internalized apolipoprotein E in liver cells. J Biol Chem 2001; 276:22965-70. [PMID: 11304532 DOI: 10.1074/jbc.m100172200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have investigated the recycling of apoE in livers of apoE(-)/- mice transplanted with wild type bone marrow (apoE(+/+) --> apoE(-)/-), a model in which circulating apoE is derived exclusively from macrophages. Nascent Golgi lipoproteins were recovered from livers of apoE(+/+) --> apoE(-)/- mice 8 weeks after transplantation. ApoE was identified with nascent d < 1.006 and with d 1.006-1.210 g/ml lipoproteins at a level approximately 6% that of nascent lipoproteins from C57BL/6 mice. Hepatocytes from apoE(+/+) --> apoE(-)/- mice were isolated and cultured in media free of exogenous apoE. ApoE was found in the media primarily on the d < 1.006 g/ml fraction, indicating a resecretion of internalized apoprotein. Secretion of apoE from C57BL/6 hepatocytes was consistent with constitutive production, whereas the majority of apoE secreted from apoE(+/+) --> apoE(-)/- hepatocytes was recovered in the last 24 h of culture. This suggests that release may be triggered by accumulation of an acceptor, such as very low density lipoproteins, in the media. In agreement with the in vivo data, total recovery of apoE from apoE(+/+) --> apoE(-)/- hepatocytes was approximately 6% that of the apoE recovered from C57BL/6 hepatocytes. Since plasma apoE levels in the transplanted mice are approximately 10% of control levels, the findings indicate that up to 60% of the internalized apoE may be reutilized under physiologic conditions. These studies provide definitive evidence for the sparing of apoE and its routing through the secretory pathway and demonstrate that internalized apoE can be resecreted in a quantitatively significant fashion.
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Affiliation(s)
- L L Swift
- Departments of Pathology, Medicine, and Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
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36
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Abstract
Over the past 10 years, many advances have been made in our understanding of the intravascular metabolism of triglyceride-rich lipoproteins. It is now known that the complex extracellular interactions of triglyceride-rich lipoprotein-associated apolipoprotein E, lipoprotein lipase and hepatic lipase with heparan sulfate proteoglycans and lipoprotein receptors facilitate the hepatocellular uptake of triglyceride-rich lipoproteins. Recent studies have also revealed that the intracellular fate of internalized triglyceride-rich lipoproteins is highly complex. The dissociation of triglyceride-rich lipoprotein components within intracellular endosomal compartments involves the recycling of apolipoprotein E, whereas the remaining lipid core associated with apolipoprotein B is susceptible to lysosomal degradation. Apolipoprotein E recycling is an important newly discovered feature of lipoprotein metabolism, and will be discussed in the context of its intracellular transport mechanisms and cholesterol efflux. Current concepts concerning its potential relevance with regard to lipoprotein metabolism and atherosclerosis will also be discussed.
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Affiliation(s)
- J Heeren
- Department of Internal Medicine, University Hospital Hamburg-Eppendorf, Hamburg, Germany.
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37
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Neufeld EB, Remaley AT, Demosky SJ, Stonik JA, Cooney AM, Comly M, Dwyer NK, Zhang M, Blanchette-Mackie J, Santamarina-Fojo S, Brewer HB. Cellular localization and trafficking of the human ABCA1 transporter. J Biol Chem 2001; 276:27584-90. [PMID: 11349133 DOI: 10.1074/jbc.m103264200] [Citation(s) in RCA: 267] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
ABCA1, the ATP-binding cassette protein mutated in Tangier disease, mediates the efflux of excess cellular sterol to apoA-I and thereby the formation of high density lipoprotein. The intracellular localization and trafficking of ABCA1 was examined in stably and transiently transfected HeLa cells expressing a functional human ABCA1-green fluorescent protein (GFP) fusion protein. The fluorescent chimeric ABCA1 transporter was found to reside on the cell surface and on intracellular vesicles that include a novel subset of early endosomes, as well as late endosomes and lysosomes. Studies of the localization and trafficking of ABCA1-GFP in the presence of brefeldin A or monensin, agents known to block intracellular vesicular trafficking, as well as apoA-I-mediated cellular lipid efflux, showed that: (i) ABCA1 functions in lipid efflux at the cell surface, and (ii) delivery of ABCA1 to lysosomes for degradation may serve as a mechanism to modulate its surface expression. Time-lapse fluorescence microscopy revealed that ABCA1-GFP-containing early endosomes undergo fusion, fission, and tubulation and transiently interact with one another, late endocytic vesicles, and the cell surface. These studies establish a complex intracellular trafficking pathway for human ABCA1 that may play important roles in modulating ABCA1 transporter activity and cellular cholesterol homeostasis.
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Affiliation(s)
- E B Neufeld
- NHLBI, National Institutes of Health and the NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
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38
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Abstract
Apolipoprotein E (apoE) plays a role in the distribution of lipid within many organs and cell types in the human body, including neurons and astrocytes of the central nervous system (CNS). The apoE4 isoform is also a genetic risk factor for late onset Alzheimer's disease (AD). However, the mechanism by which apoE is involved in AD is largely unknown. In order to understand how apoE is involved in the distribution of lipid in the CNS, we sought to investigate not only the origin of intraneuronal apoE, but the pathway by which it is processed once synthesized. We have established that human neurons can synthesize apoE in the presence of astrocytes, and that intracellular neuronal apoE is processed through the rough endoplasmic reticulum, golgi, and CD63-positive lysosomes where it may be stored before secretion. Our results also suggest that apoE synthesis is regulated by a feedback mechanism, controlled by the neuron itself. This regulatory mechanism may be essential to the maintenance of neuronal cholesterol concentrations and in turn membrane stability.
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Affiliation(s)
- R M Dekroon
- Neuroscience Unit, School of Biological Sciences, University of Sydney, Sydney, NSW 2006, Australia
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von Eckardstein A, Nofer JR, Assmann G. High density lipoproteins and arteriosclerosis. Role of cholesterol efflux and reverse cholesterol transport. Arterioscler Thromb Vasc Biol 2001; 21:13-27. [PMID: 11145929 DOI: 10.1161/01.atv.21.1.13] [Citation(s) in RCA: 511] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
High density lipoprotein (HDL) cholesterol is an important risk factor for coronary heart disease, and HDL exerts various potentially antiatherogenic properties, including the mediation of reverse transport of cholesterol from cells of the arterial wall to the liver and steroidogenic organs. Enhancement of cholesterol efflux and of reverse cholesterol transport (RCT) is considered an important target for antiatherosclerotic drug therapy. Levels and composition of HDL subclasses in plasma are regulated by many factors, including apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors, and cellular transporters. In vitro experiments as well as genetic family and population studies and investigation of transgenic animal models have revealed that HDL cholesterol plasma levels do not necessarily reflect the efficacy and antiatherogenicity of RCT. Instead, the concentration of HDL subclasses, the mobilization of cellular lipids for efflux, and the kinetics of HDL metabolism are important determinants of RCT and the risk of atherosclerosis.
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Affiliation(s)
- A von Eckardstein
- Institut für Klinische Chemie und Laboratoriumsmedizin, Zentrallaboratorium, Westfälische Wilhelms-Universität Münster, Germany.
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40
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Kokotos G, Kotsovolou S, Constantinou-Kokotou V, Wu G, Olivecrona G. Inhibition of lipoprotein lipase by alkanesulfonyl fluorides. Bioorg Med Chem Lett 2000; 10:2803-6. [PMID: 11133096 DOI: 10.1016/s0960-894x(00)00566-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
A number of alkanesulfonyl halides (chlorides and fluorides) and esters were synthesized and their effect on the activity of lipoprotein lipase (LPL) was studied. Sulfonyl fluorides proved to be efficient inhibitors of LPL when the enzyme was incubated with a 10-fold molar excess of the inhibitors in a buffer containing bile salts (deoxycholate). Hexadecane- and dodecanesulfonyl fluorides caused 50% inhibition of LPL activity at concentrations of 10 to 20 microM.
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Affiliation(s)
- G Kokotos
- Department of Chemistry, University of Athens, Greece.
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41
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Abstract
A low level of high-density lipoprotein (HDL) cholesterol is an important risk factor for coronary heart disease. Levels of HDL cholesterol and composition of HDL subclasses in plasma are regulated by many factors, including apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors, and cellular transporters. Reverse transport of cholesterol from cells of the arterial wall to the liver is an important mechanism by which HDL exerts its anti-atherogenic properties. Enhancement of reverse cholesterol transport is considered as a potential target for anti-atherosclerotic drug therapy. It is suggested, however, that the serum level of HDL cholesterol does not necessarily reflect the efficacy of reverse cholesterol transport.
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Affiliation(s)
- A von Eckardstein
- Institut für Klinische Chemie und Laboratoriumsmedizin, Zentrallaboratorium, Westfälische Wilhelms-Universität Münster, Germany.
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42
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Rensen PC, Jong MC, van Vark LC, van der Boom H, Hendriks WL, van Berkel TJ, Biessen EA, Havekes LM. Apolipoprotein E is resistant to intracellular degradation in vitro and in vivo. Evidence for retroendocytosis. J Biol Chem 2000; 275:8564-71. [PMID: 10722695 DOI: 10.1074/jbc.275.12.8564] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Apolipoprotein E (apoE) is an important determinant for the uptake of triglyceride-rich lipoproteins and emulsions by the liver, but the intracellular pathway of apoE following particle internalization is poorly defined. In the present study, we investigated whether retroendocytosis is a unique feature of apoE as compared with apoB by studying the intracellular fate of very low density lipoprotein-sized apoE-containing triglyceride-rich emulsion particles and LDL after LDLr-mediated uptake. Incubation of HepG2 cells with [(3)H]cholesteryl oleate-labeled particles at 37 degrees C led to a rapid release of [(3)H]cholesterol within 30 min for both LDL and emulsion particles. In contrast, emulsion-derived (125)I-apoE was more resistant to degradation (>/=120 min) than LDL-derived (125)I-apoB (30 min). Incubation at 18 degrees C, which allows endosomal uptake but prevents lysosomal degradation, with subsequent incubation at 37 degrees C resulted in a time-dependent release of intact apoE from the cells (up to 14% of the endocytosed apoE at 4 h). The release of apoE was accelerated by the presence of protein-free emulsion (20%) or high density lipoprotein (26%). Retroendocytosis of intact particles could be excluded since little intact [(3)H]cholesteryl oleate was released (<3%). In contrast, the degradation of LDL was complete with virtually no secretion of intact apoB into the medium. The intracellular stability of apoE was also demonstrated after hepatic uptake in C57Bl/6 mice. Intravenous injection of (125)I-apoE and [(3)H]cholesteryl oleate-labeled emulsions resulted in efficient LDLr-mediated uptake of both components by the liver (45-50% of the injected dose after 20 min). At 1 h after injection, only 15-20% of the hepatic (125)I-apoE was degraded, whereas 75% of the [(3)H]cholesteryl oleate was hydrolyzed. From these data we conclude that following LDLr-mediated internalization by liver cells, apoE can escape degradation and can be resecreted. This sequence of events may allow apoE to participate in its hypothesized intracellular functions such as mediator of the post-lysosomal trafficking of lipids and very low density lipoprotein assembly.
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Affiliation(s)
- P C Rensen
- Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, University of Leiden, Sylvius Laboratory, P. O. Box 9503, 2300 RA Leiden, The Netherlands.
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43
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Enrich C, Pol A, Calvo M, Pons M, Jäckle S. Dissection of the multifunctional "Receptor-Recycling" endocytic compartment of hepatocytes. Hepatology 1999; 30:1115-20. [PMID: 10534329 DOI: 10.1002/hep.510300505] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- C Enrich
- Departament de Biologia Cellular, Institut de Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain.
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Takahashi Y, Smith JD. Cholesterol efflux to apolipoprotein AI involves endocytosis and resecretion in a calcium-dependent pathway. Proc Natl Acad Sci U S A 1999; 96:11358-63. [PMID: 10500181 PMCID: PMC18038 DOI: 10.1073/pnas.96.20.11358] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
We previously have described the cAMP-mediated induction of cholesterol and phospholipid efflux from the murine macrophage RAW264 cell line to lipid-free apolipoprotein acceptors. This induction of cholesterol efflux is associated with increased binding and association of apolipoprotein to the cells. In the present study, using primarily apolipoprotein AI (apoAI) as the acceptor, cAMP-dependent cholesterol efflux to apolipoprotein acceptors was associated with apoAI binding to coated pits, cellular uptake, and resecretion. After cell association and washing, 58% of the apoAI was resecreted during a 90-min chase period. In addition, after apoAI uptake and washing, cholesterol efflux was observed during a chase period without additional acceptors. Cholesterol efflux was partially blocked by chlorpromazine and hypertonic media, two inhibitors of coated pit endocytosis. Cholesterol efflux to apoAI was found to depend on extracellular calcium. By temporally separating the cAMP induction phase from the apoAI chase phase, calcium was found to be required during the apoAI chase phase rather than during the cAMP induction period. In the absence of calcium the 8-Br-cAMP-mediated induction of apoAI binding was maintained, but the specific apoAI cellular association was inhibited. The data are consistent with a model for cholesterol efflux to apolipoproteins that involves a calcium-dependent endocytic pathway, followed by recycling and the subsequent release of the nascent lipoprotein particle from the cell.
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Affiliation(s)
- Y Takahashi
- The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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