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Deng L, Kersten S, Stienstra R. Triacylglycerol uptake and handling by macrophages: From fatty acids to lipoproteins. Prog Lipid Res 2023; 92:101250. [PMID: 37619883 DOI: 10.1016/j.plipres.2023.101250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Revised: 08/18/2023] [Accepted: 08/21/2023] [Indexed: 08/26/2023]
Abstract
Macrophages are essential innate immune cells and form our first line of immune defense. Also known as professional phagocytes, macrophages interact and take up various particles, including lipids. Defective lipid handling can drive excessive lipid accumulation leading to foam cell formation, a key feature of various cardiometabolic conditions such as atherosclerosis, non-alcoholic fatty liver disease, and obesity. At the same time, intracellular lipid storage and foam cell formation can also be viewed as a protective and anti-lipotoxic mechanism against a lipid-rich environment and associated elevated lipid uptake. Traditionally, foam cell formation has primarily been linked to cholesterol uptake via native and modified low-density lipoproteins. However, other lipids, including non-esterified fatty acids and triacylglycerol (TAG)-rich lipoproteins (very low-density lipoproteins and chylomicrons), can also interact with macrophages. Recent studies have identified multiple pathways mediating TAG uptake and processing by macrophages, including endocytosis and receptor/transporter-mediated internalization and transport. This review will present the current knowledge of how macrophages take up different lipids and lipoprotein particles and address how TAG-rich lipoproteins are processed intracellularly. Understanding how macrophages take up and process different lipid species such as TAG is necessary to design future therapeutic interventions to correct excessive lipid accumulation and associated co-morbidities.
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Affiliation(s)
- Lei Deng
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition and Health, Wageningen University, Wageningen, the Netherlands
| | - Sander Kersten
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition and Health, Wageningen University, Wageningen, the Netherlands
| | - Rinke Stienstra
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition and Health, Wageningen University, Wageningen, the Netherlands; Department of Internal Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.
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Macrophages take up VLDL-sized emulsion particles through caveolae-mediated endocytosis and excrete part of the internalized triglycerides as fatty acids. PLoS Biol 2022; 20:e3001516. [PMID: 36026438 PMCID: PMC9455861 DOI: 10.1371/journal.pbio.3001516] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 09/08/2022] [Accepted: 07/09/2022] [Indexed: 11/26/2022] Open
Abstract
Triglycerides are carried in the bloodstream as part of very low-density lipoproteins (VLDLs) and chylomicrons, which represent the triglyceride-rich lipoproteins. Triglyceride-rich lipoproteins and their remnants contribute to atherosclerosis, possibly by carrying remnant cholesterol and/or by exerting a proinflammatory effect on macrophages. Nevertheless, little is known about how macrophages process triglyceride-rich lipoproteins. Here, using VLDL-sized triglyceride-rich emulsion particles, we aimed to study the mechanism by which VLDL triglycerides are taken up, processed, and stored in macrophages. Our results show that macrophage uptake of VLDL-sized emulsion particles is dependent on lipoprotein lipase (LPL) and requires the lipoprotein-binding C-terminal domain but not the catalytic N-terminal domain of LPL. Subsequent internalization of VLDL-sized emulsion particles by macrophages is carried out by caveolae-mediated endocytosis, followed by triglyceride hydrolysis catalyzed by lysosomal acid lipase. It is shown that STARD3 is required for the transfer of lysosomal fatty acids to the ER for subsequent storage as triglycerides, while NPC1 likely is involved in promoting the extracellular efflux of fatty acids from lysosomes. Our data provide novel insights into how macrophages process VLDL triglycerides and suggest that macrophages have the remarkable capacity to excrete part of the internalized triglycerides as fatty acids. How do macrophages take up and process very low density lipoprotein (VLDL) particles? This study reveals that endocytic uptake of VLDLs depends on lipoprotein lipase and caveolae; internalized VLDLs are then processed by lysosomes, and the lipids are hydrolyzed and translocated to the ER for storage as triglycerides.
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Alajbegovic A, Holmberg J, Daoud F, Rippe C, Kalliokoski G, Ekman M, Daudi S, Ragnarsson S, Swärd K, Albinsson S. MRTFA overexpression promotes conversion of human coronary artery smooth muscle cells into lipid-laden foam cells. Vascul Pharmacol 2021; 138:106837. [PMID: 33516965 DOI: 10.1016/j.vph.2021.106837] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 12/22/2020] [Accepted: 01/21/2021] [Indexed: 01/26/2023]
Abstract
OBJECTIVE Smooth muscle cells contribute significantly to lipid-laden foam cells in atherosclerotic plaques. However, the underlying mechanisms transforming smooth muscle cells into foam cells are poorly understood. The purpose of this study was to gain insight into the molecular mechanisms regulating smooth muscle foam cell formation. APPROACH AND RESULTS Using human coronary artery smooth muscle cells we found that the transcriptional co-activator MRTFA promotes lipid accumulation via several mechanisms, including direct transcriptional control of LDL receptor, enhanced fluid-phase pinocytosis and reduced lipid efflux. Inhibition of MRTF activity with CCG1423 and CCG203971 significantly reduced lipid accumulation. Furthermore, we demonstrate enhanced MRTFA expression in vascular remodeling of human vessels. CONCLUSIONS This study demonstrates a novel role for MRTFA as an important regulator of lipid homeostasis in vascular smooth muscle cells. Thus, MRTFA could potentially be a new therapeutic target for inhibition of vascular lipid accumulation.
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Affiliation(s)
- Azra Alajbegovic
- Department of Experimental Medical Science, Lund University, Sweden.
| | - Johan Holmberg
- Department of Experimental Medical Science, Lund University, Sweden
| | - Fatima Daoud
- Department of Experimental Medical Science, Lund University, Sweden
| | - Catarina Rippe
- Department of Experimental Medical Science, Lund University, Sweden
| | | | - Mari Ekman
- Department of Experimental Medical Science, Lund University, Sweden
| | - Sébastien Daudi
- Department of Clinical Science, Lund University, Lund, Sweden
| | | | - Karl Swärd
- Department of Experimental Medical Science, Lund University, Sweden
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4
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Li J, Meng Q, Fu Y, Yu X, Ji T, Chao Y, Chen Q, Li Y, Bian H. Novel insights: Dynamic foam cells derived from the macrophage in atherosclerosis. J Cell Physiol 2021; 236:6154-6167. [PMID: 33507545 DOI: 10.1002/jcp.30300] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Revised: 12/22/2020] [Accepted: 01/15/2021] [Indexed: 12/12/2022]
Abstract
Atherosclerosis can be regarded as a chronic disease derived from the interaction between disordered lipoproteins and an unsuitable immune response. The evolution of foam cells is not only a significant pathological change in the early stage of atherosclerosis but also a key stage in the occurrence and development of atherosclerosis. The formation of foam cells is mainly caused by the imbalance among lipids uptake, lipids treatment, and reverse cholesterol transport. Although a large number of studies have summarized the source of foam cells and the mechanism of foam cells formation, we propose a new idea about foam cells in atherosclerosis. Rather than an isolated microenvironment, the macrophage multiple lipid uptake pathways, lipid internalization, lysosome, mitochondria, endoplasmic reticulum, neutral cholesterol ester hydrolase (NCEH), acyl-coenzyme A-cholesterol acyltransferase (ACAT), and reverse cholesterol transport are mutually influential, and form a dynamic process under multi-factor regulation. The macrophage takes on different uptake lipid statuses depending on multiple uptake pathways and intracellular lipids, lipid metabolites versus pro-inflammatory factors. Except for NCEH and ACAT, the lipid internalization of macrophages also depends on multicellular organelles including the lysosome, mitochondria, and endoplasmic reticulum, which are associated with each other. A dynamic balance between esterification and hydrolysis of cholesterol for macrophages is essential for physiology and pathology. Therefore, we propose that the foam cell in the process of atherosclerosis may be dynamic under multi-factor regulation, and collate this study to provide a holistic and dynamic idea of the foam cell.
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Affiliation(s)
- Jun Li
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Qinghai Meng
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Yu Fu
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Xichao Yu
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Tingting Ji
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Ying Chao
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Qi Chen
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
| | - Yu Li
- School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China
| | - Huimin Bian
- Jiangsu Key Laboratory for Pharmacology and Safety Evaluation of Chinese Materia Medica, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China.,Jiangsu Key Laboratory of Therapeutic Material of Chinese Medicine, School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, China
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5
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Polyhistidine facilitates direct membrane translocation of cell-penetrating peptides into cells. Sci Rep 2019; 9:9398. [PMID: 31253836 PMCID: PMC6599048 DOI: 10.1038/s41598-019-45830-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Accepted: 06/14/2019] [Indexed: 12/27/2022] Open
Abstract
The bovine lactoferricin L6 (RRWQWR) has been previously identified as a novel cell-penetrating peptide (CPP) that is able to efficiently internalize into human cells. L6 interacts with quantum dots (QDs) noncovalently to generate stable L6/QD complexes that enter cells by endocytosis. In this study, we demonstrate a modified L6 (HL6; CHHHHHRRWQWRHHHHHC), in which short polyhistidine peptides are introduced into both flanks of L6, has enhanced cell-penetrating ability in human bronchoalveolar carcinoma A549 cells. The mechanism of cellular uptake of HL6/QD complexes is primarily direct membrane translocation rather than endocytosis. Dimethyl sulfoxide (DMSO), but not pyrenebutyrate (PB), ethanol, oleic acid, or 1,2-benzisothiazol-3(2 H)-one (BIT), slightly enhances HL6-mediated protein transduction efficiency. Neither HL6 nor HL6/QD complexes are cytotoxic to A549 or HeLa cells. These results indicate that HL6 could be a more efficient drug carrier than L6 for biomedical as well as biotechnological applications, and that the function of polyhistidine peptides is critical to CPP-mediated protein transduction.
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Maguire EM, Pearce SWA, Xiao Q. Foam cell formation: A new target for fighting atherosclerosis and cardiovascular disease. Vascul Pharmacol 2018; 112:54-71. [PMID: 30115528 DOI: 10.1016/j.vph.2018.08.002] [Citation(s) in RCA: 187] [Impact Index Per Article: 31.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Revised: 07/17/2018] [Accepted: 08/03/2018] [Indexed: 12/23/2022]
Abstract
During atherosclerosis, the gradual accumulation of lipids into the subendothelial space of damaged arteries results in several lipid modification processes followed by macrophage uptake in the arterial wall. The way in which these modified lipoproteins are dealt with determines the likelihood of cholesterol accumulation within the monocyte-derived macrophage and thus its transformation into the foam cell that makes up the characteristic fatty streak observed in the early stages of atherosclerosis. The unique expression of chemokine receptors and cellular adhesion molecules expressed on the cell surface of monocytes points to a particular extravasation route that they can take to gain entry into atherosclerotic site, in order to undergo differentiation into the phagocytic macrophage. Indeed several GWAS and animal studies have identified key genes and proteins required for monocyte recruitment as well cholesterol handling involving lipid uptake, cholesterol esterification and cholesterol efflux. A re-examination of the previously accepted paradigm of macrophage foam cell origin has been called into question by recent studies demonstrating shared expression of scavenger receptors, cholesterol transporters and pro-inflammatory cytokine release by alternative cell types present in the neointima, namely; endothelial cells, vascular smooth muscle cells and stem/progenitor cells. Thus, therapeutic targets aimed at a more heterogeneous foam cell population with shared functions, such as enhanced protease activity, and signalling pathways, mediated by non-coding RNA molecules, may provide greater therapeutic outcome in patients. Finally, studies targeting each aspect of foam cell formation and death using both genetic knock down and pharmacological inhibition have provided researchers with a clearer understanding of the cellular processes at play, as well as helped researchers to identify key molecular targets, which may hold significant therapeutic potential in the future.
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Affiliation(s)
- Eithne M Maguire
- Centre for Clinical Pharmacology, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, EC1M 6BQ, UK
| | - Stuart W A Pearce
- Centre for Clinical Pharmacology, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, EC1M 6BQ, UK
| | - Qingzhong Xiao
- Centre for Clinical Pharmacology, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, EC1M 6BQ, UK.
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7
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Vocelle D, Chesniak OM, Malefyt AP, Comiskey G, Adu-Berchie K, Smith MR, Chan C, Walton SP. Dextran functionalization enhances nanoparticle-mediated siRNA delivery and silencing. TECHNOLOGY 2016; 4:42. [PMID: 27774502 PMCID: PMC5072529 DOI: 10.1142/s2339547816400100] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Understanding the endocytosis and intracellular trafficking of short interfering RNA (siRNA) delivery vehicle complexes remains a critical bottleneck in designing siRNA delivery vehicles for highly active RNA interference (RNAi)-based therapeutics. In this study, we show that dextran functionalization of silica nanoparticles enhanced uptake and intracellular delivery of siRNAs in cultured cells. Using pharmacological inhibitors for endocytotic pathways, we determined that our complexes are endocytosed via a previously unreported mechanism for siRNA delivery in which dextran initiates scavenger receptor-mediated endocytosis through a clathrin/caveolin-independent process. Our findings suggest that siRNA delivery efficiency could be enhanced by incorporating dextran into existing delivery platforms to activate scavenger receptor activity across a variety of target cell types.
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Affiliation(s)
- Daniel Vocelle
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824-1226, USA
| | - Olivia M Chesniak
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1226, USA
| | - Amanda P Malefyt
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824-1226, USA
| | - Georgina Comiskey
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1226, USA
| | - Kwasi Adu-Berchie
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824-1226, USA
| | - Milton R Smith
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1226, USA
| | - Christina Chan
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824-1226, USA; Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-1226, USA
| | - S Patrick Walton
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824-1226, USA
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8
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Park YM. Oxidized LDL induces phosphorylation of non-muscle myosin IIA heavy chain in macrophages. BMB Rep 2015; 48:48-53. [PMID: 25322953 PMCID: PMC4345642 DOI: 10.5483/bmbrep.2015.48.1.186] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Revised: 09/23/2014] [Accepted: 10/16/2014] [Indexed: 11/20/2022] Open
Abstract
Oxidized LDL (oxLDL) performs critical roles in atherosclerosis by inducing macrophage foam cell formation and promoting inflammation. There have been reports showing that oxLDL modulates macrophage cytoskeletal functions for oxLDL uptake and trapping, however, the precise mechanism has not been clearly elucidated. Our study examined the effect of oxLDL on non-muscle myosin heavy chain IIA (MHC-IIA) in macrophages. We demonstrated that oxLDL induces phosphorylation of MHC-IIA (Ser1917) in peritoneal macrophages from wild-type mice and THP-1, a human monocytic cell line, but not in macrophages deficient for CD36, a scavenger receptor for oxLDL. Protein kinase C (PKC) inhibitor-treated macrophages did not undergo the oxLDL-induced MHC-IIA phosphorylation. Our immunoprecipitation revealed that oxLDL increased physical association between PKC and MHC-IIA, supporting the role of PKC in this process. We conclude that oxLDL via CD36 induces PKC-mediated MHC-IIA (Ser1917) phosphorylation and this may affect oxLDL-induced functions of macrophages involved in atherosclerosis.
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Affiliation(s)
- Young Mi Park
- Department of Molecular Medicine, Ewha Womans University School of Medicine; Global Top 5 Research Program, Ewha Womans University, Seoul 158-710, Korea
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9
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Rivera J, Walduck AK, Thomas SR, Glaros EN, Hooker EU, Guida E, Sobey CG, Drummond GR. Accumulation of serum lipids by vascular smooth muscle cells involves a macropinocytosis-like uptake pathway and is associated with the downregulation of the ATP-binding cassette transporter A1. Naunyn Schmiedebergs Arch Pharmacol 2013; 386:1081-93. [PMID: 23989929 DOI: 10.1007/s00210-013-0909-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 08/12/2013] [Indexed: 01/01/2023]
Abstract
Vascular smooth muscle cells (VSMC) are present in arterial intima before atherosclerotic plaques develop and are likely to be exposed to unmodified serum lipids as they enter the vessel wall. We examined the effects of sera from mice on the morphology and function of mouse VSMC. Incubation of a mouse VSMC line (MOVAS) with sera from normocholesterolemic (C57BL/6J) or hypercholesterolemic (APOE(-/-)) mice caused concentration-dependent increases in lipid accumulation as measured by AdipoRed, with the extent of lipid uptake significantly greater with the latter sera type. Inhibition of c-Jun N-terminal kinases (SP600125), Src kinases (AG1879), and clathrin-dependent endocytosis (monodansylcadaverine) to disrupt scavenger receptor-mediated uptake of lipids had no effect on serum-induced lipid accumulation by VSMC. By contrast, inhibition of macropinocytosis with antagonists of PI-3 kinase (LY294002) and actin (cytochalasin D) markedly reduced lipid accumulation. Serum exposure reduced the expression of the ATP-binding cassette transporter A1, consistent with impaired cholesterol efflux, but had no effect on the expression of markers of VSMC differentiation. Moreover, the expression of several inflammation and foam cell markers was unchanged (CCL2, CCL5, and CD68) by mouse sera. The accumulation of unmodified serum lipids by VSMC involves a macropinocytosis-like uptake pathway and is associated with the downregulation of the ATP-binding cassette transporter. We speculate that VSMC may play an atheroprotective role in arterial intima by acting as a "sink" for unmodified lipids.
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Affiliation(s)
- Jennifer Rivera
- Vascular Biology and Immunopharmacology Group, Department of Pharmacology, Monash University, Building 13E, Wellington Road, Clayton, VIC, 3800, Australia
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10
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Michael DR, Ashlin TG, Davies CS, Gallagher H, Stoneman TW, Buckley ML, Ramji DP. Differential regulation of macropinocytosis in macrophages by cytokines: implications for foam cell formation and atherosclerosis. Cytokine 2013; 64:357-61. [PMID: 23791479 PMCID: PMC3779350 DOI: 10.1016/j.cyto.2013.05.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Revised: 04/29/2013] [Accepted: 05/17/2013] [Indexed: 01/25/2023]
Abstract
Macrophages can internalise LDL through scavenger receptor-independent mechanisms. Macropinocytosis has been shown to contribute significantly to foam cell formation. Cytokines such as TGF-β, IL-33, IFN-γ and IL-17A can modulate macropinocytosis. TGF-β mediated inhibition of macropinocytosis is a Smad-2/-3-independent process. Macropinocytosis is a promising target for therapeutic intervention of atherosclerosis.
A key event during the formation of lipid-rich foam cells during the progression of atherosclerosis is the uptake of modified low-density lipoproteins (LDL) by macrophages in response to atherogenic mediators in the arterial intima. In addition to scavenger receptor-dependent uptake of LDL, macropinocytosis is known to facilitate the uptake of LDL through the constitutive and passive internalization of large quantities of extracellular solute. In this study we confirm the ability of macropinocytosis to facilitate the uptake of modified LDL by human macrophages and show its modulation by TGF-β, IFN-γ, IL-17A and IL-33. Furthermore we show that the TGF-β-mediated inhibition of macropinocytosis is a Smad-2/-3-independent process.
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Affiliation(s)
- Daryn R Michael
- Cardiff School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, United Kingdom.
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11
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Bazaz R, Marriott HM, Francis SE, Dockrell DH. Mechanistic links between acute respiratory tract infections and acute coronary syndromes. J Infect 2013; 66:1-17. [DOI: 10.1016/j.jinf.2012.09.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 09/22/2012] [Accepted: 09/26/2012] [Indexed: 12/27/2022]
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12
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Kruth HS. Receptor-independent fluid-phase pinocytosis mechanisms for induction of foam cell formation with native low-density lipoprotein particles. Curr Opin Lipidol 2011; 22:386-93. [PMID: 21881499 PMCID: PMC4174540 DOI: 10.1097/mol.0b013e32834adadb] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
PURPOSE OF REVIEW Because early findings indicated that native low-density lipoprotein (LDL) did not substantially increase macrophage cholesterol content during in-vitro incubations, investigators presumed that LDL must be modified in some way to trigger its uptake by the macrophage. The purpose of this review is to discuss recent findings showing that native unmodified LDL can induce massive macrophage cholesterol accumulation mimicking macrophage foam cell formation that occurs within atherosclerotic plaques. RECENT FINDINGS Macrophages that show high rates of fluid-phase pinocytosis also show similar high rates of uptake of native unmodified LDL through nonreceptor mediated uptake within both macropinosomes and micropinosomes. Nonsaturable fluid-phase uptake of LDL by macrophages converts the macrophages into foam cells. Different macrophage phenotypes demonstrate either constitutive fluid-phase pinocytosis or inducible fluid-phase pinocytosis. Fluid-phase pinocytosis has been demonstrated by macrophages within mouse atherosclerotic plaques indicating that this pathway contributes to plaque macrophage cholesterol accumulation. SUMMARY Contrary to what has been believed previously, macrophages can take up large amounts of native unmodified LDL by receptor-independent, fluid-phase pinocytosis converting these macrophages into foam cells. Thus, targeting macrophage fluid-phase pinocytosis should be considered when investigating strategies to limit macrophage cholesterol accumulation in atherosclerotic plaques.
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Affiliation(s)
- Howard S Kruth
- Section of Experimental Atherosclerosis, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland 20892-1422, USA.
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13
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Eicosapentaenoic Acid and Docosahexaenoic Acid Regulate Modified LDL Uptake and Macropinocytosis in Human Macrophages. Lipids 2011; 46:1053-61. [DOI: 10.1007/s11745-011-3598-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Accepted: 07/13/2011] [Indexed: 11/26/2022]
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14
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McLaren JE, Michael DR, Ashlin TG, Ramji DP. Cytokines, macrophage lipid metabolism and foam cells: implications for cardiovascular disease therapy. Prog Lipid Res 2011; 50:331-47. [PMID: 21601592 DOI: 10.1016/j.plipres.2011.04.002] [Citation(s) in RCA: 257] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Revised: 04/14/2011] [Accepted: 04/14/2011] [Indexed: 12/23/2022]
Abstract
Cardiovascular disease is the biggest killer globally and the principal contributing factor to the pathology is atherosclerosis; a chronic, inflammatory disorder characterized by lipid and cholesterol accumulation and the development of fibrotic plaques within the walls of large and medium arteries. Macrophages are fundamental to the immune response directed to the site of inflammation and their normal, protective function is harnessed, detrimentally, in atherosclerosis. Macrophages contribute to plaque development by internalizing native and modified lipoproteins to convert them into cholesterol-rich foam cells. Foam cells not only help to bridge the innate and adaptive immune response to atherosclerosis but also accumulate to create fatty streaks, which help shape the architecture of advanced plaques. Foam cell formation involves the disruption of normal macrophage cholesterol metabolism, which is governed by a homeostatic mechanism that controls the uptake, intracellular metabolism, and efflux of cholesterol. It has emerged over the last 20 years that an array of cytokines, including interferon-γ, transforming growth factor-β1, interleukin-1β, and interleukin-10, are able to manipulate these processes. Foam cell targeting, anti-inflammatory therapies, such as agonists of nuclear receptors and statins, are known to regulate the actions of pro- and anti-atherogenic cytokines indirectly of their primary pharmacological function. A clear understanding of macrophage foam cell biology will hopefully enable novel foam cell targeting therapies to be developed for use in the clinical intervention of atherosclerosis.
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Affiliation(s)
- James E McLaren
- Cardiff School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, UK
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15
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Liu BR, Huang YW, Winiarz JG, Chiang HJ, Lee HJ. Intracellular delivery of quantum dots mediated by a histidine- and arginine-rich HR9 cell-penetrating peptide through the direct membrane translocation mechanism. Biomaterials 2011; 32:3520-37. [PMID: 21329975 DOI: 10.1016/j.biomaterials.2011.01.041] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2010] [Accepted: 01/13/2011] [Indexed: 11/25/2022]
Abstract
Functional peptides that transfer biomaterials, such as semiconductor quantum dots (QDs), into cells in biomaterial research have been developed in recent years. Delivery of QDs conjugated with cell-penetrating peptides (CPPs) into cells by the endocytic pathway was problematic in biomedical applications because of lysosomal trapping. Here, we demonstrate that histidine- and arginine-rich CPPs (HR9 peptides) stably and noncovalently combined with QDs are able to enter into cells in an extremely short period (4 min). Interrupting both F-actin polymerization and active transport did not inhibit the entry of HR9/QD complexes into cells, indicating that HR9 penetrates cell membrane directly. Subcellular colocalization studies indicated that QDs delivered by HR9 stay in cytosol without any organelle capture. Dimethyl sulphoxide, ethanol and oleic acid, but not pyrenebutyrate, enhanced HR9-mediated intracellular delivery of QDs by promoting the direct membrane translocation pathway. HR9 and HR9/QDs were not cytotoxic. These findings suggest that HR9 could be an efficient carrier to deliver drugs without interfering with their therapeutic activity.
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Affiliation(s)
- Betty R Liu
- Department of Natural Resources and Environmental Studies, National Dong Hwa University, Shoufeng, Hualien, Taiwan
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16
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Napotnik TB, Rebersek M, Kotnik T, Lebrasseur E, Cabodevila G, Miklavcic D. Electropermeabilization of endocytotic vesicles in B16 F1 mouse melanoma cells. Med Biol Eng Comput 2010; 48:407-13. [PMID: 20361267 PMCID: PMC2855809 DOI: 10.1007/s11517-010-0599-9] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 03/18/2010] [Indexed: 12/11/2022]
Abstract
It has been reported previously that electric pulses of sufficiently high voltage and short duration can permeabilize the membranes of various organelles inside living cells. In this article, we describe electropermeabilization of endocytotic vesicles in B16 F1 mouse melanoma cells. The cells were exposed to short, high-voltage electric pulses (from 1 to 20 pulses, 60 ns, 50 kV/cm, repetition frequency 1 kHz). We observed that 10 and 20 such pulses induced permeabilization of membranes of endocytotic vesicles, detected by release of lucifer yellow from the vesicles into the cytosol. Simultaneously, we detected uptake of propidium iodide through plasma membrane in the same cells. With higher number of pulses permeabilization of the membranes of endocytotic vesicles by pulses of given parameters is accompanied by permeabilization of plasma membrane. However, with lower number of pulses only permeabilization of the plasma membrane was detected.
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Affiliation(s)
- Tina Batista Napotnik
- Faculty of Electrical Engineering, University of Ljubljana, Trzaska 25, 1000, Ljubljana, Slovenia
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17
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Collins RF, Touret N, Kuwata H, Tandon NN, Grinstein S, Trimble WS. Uptake of oxidized low density lipoprotein by CD36 occurs by an actin-dependent pathway distinct from macropinocytosis. J Biol Chem 2009; 284:30288-97. [PMID: 19740737 DOI: 10.1074/jbc.m109.045104] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The class B scavenger receptor CD36 has numerous ligands that include modified forms of low density lipoprotein, fibrillar amyloid, apoptotic cells, and Plasmodium falciparum-infected red blood cells, linking this molecule to atherosclerosis, Alzheimer disease, malaria, and other diseases. We studied the signaling events that follow receptor engagement and lead to CD36 and ligand internalization. We show that oxidized low density lipoprotein or antibody-induced clustering of CD36 triggers macropinocytosis and internalization of the receptor-ligand complex. Remarkably, however, CD36 internalization is independent of macropinocytosis and occurs by a novel endocytic mechanism that depends on actin, but not dynamin. This actin-driven endocytosis requires the activation Src family kinases, JNK, and Rho family GTPases, but, unlike macropinocytosis, it is not affected by inhibitors of phosphatidylinositol 3-kinase or Na/H exchange. Manipulation of this unique mode of internalization may prove helpful in the prevention and management of the wide range of diseases in which CD36 is implicated.
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Affiliation(s)
- Richard F Collins
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
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18
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Lin LM, Ricucci D, Lin J, Rosenberg PA. Nonsurgical root canal therapy of large cyst-like inflammatory periapical lesions and inflammatory apical cysts. J Endod 2009; 35:607-15. [PMID: 19410070 DOI: 10.1016/j.joen.2009.02.012] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 02/12/2009] [Accepted: 02/17/2009] [Indexed: 12/21/2022]
Abstract
It is a general belief that large cyst-like periapical lesions and apical true cysts caused by root canal infection are less likely to heal after nonsurgical root canal therapy. Nevertheless, there is no direct evidence to support this assumption. A large cyst-like periapical lesion or an apical true cyst is formed within an area of apical periodontitis and cannot form by itself. Therefore, both large cyst-like periapical lesions and apical true cysts are of inflammatory and not of neoplastic origin. Apical periodontitis lesions, regardless of whether they are granulomas, abscesses, or cysts, fail to heal after nonsurgical root canal therapy for the same reason, intraradicular and/or extraradicular infection. If the microbial etiology of large cyst-like periapical lesions and inflammatory apical true cysts in the root canal is removed by nonsurgical root canal therapy, the lesions might regress by the mechanism of apoptosis in a manner similar to the resolution of inflammatory apical pocket cysts. To achieve satisfactory periapical wound healing, surgical removal of an apical true cyst must include elimination of root canal infection.
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Affiliation(s)
- Louis M Lin
- Department of Endodontics, New York University College of Dentistry, New York, New York 10010, USA.
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19
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Pennings M, Meurs I, Ye D, Out R, Hoekstra M, Van Berkel TJC, Van Eck M. Regulation of cholesterol homeostasis in macrophages and consequences for atherosclerotic lesion development. FEBS Lett 2006; 580:5588-96. [PMID: 16935283 DOI: 10.1016/j.febslet.2006.08.022] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Revised: 07/28/2006] [Accepted: 08/06/2006] [Indexed: 11/25/2022]
Abstract
Foam cell formation due to excessive accumulation of cholesterol by macrophages is a pathological hallmark of atherosclerosis. Macrophages cannot limit the uptake of cholesterol and therefore depend on cholesterol efflux pathways for preventing their transformation into foam cells. Several ABC-transporters, including ABCA1 and ABCG1, facilitate the efflux of cholesterol from macrophages. These transporters, however, also affect membrane lipid asymmetry which may have important implications for cellular endocytotic pathways. We propose that in addition to the generally accepted role of these ABC-transporters in the prevention of foam cell formation by induction of cholesterol efflux from macrophages, they also influence the macrophage endocytotic uptake.
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Affiliation(s)
- Marieke Pennings
- Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
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20
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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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21
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Kruth HS, Jones NL, Huang W, Zhao B, Ishii I, Chang J, Combs CA, Malide D, Zhang WY. Macropinocytosis Is the Endocytic Pathway That Mediates Macrophage Foam Cell Formation with Native Low Density Lipoprotein. J Biol Chem 2005; 280:2352-60. [PMID: 15533943 DOI: 10.1074/jbc.m407167200] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Previously, we reported that fluid-phase endocytosis of native LDL by PMA-activated human monocytederived macrophages converted these macrophages into cholesterol-enriched foam cells (Kruth, H. S., Huang, W., Ishii, I., and Zhang, W. Y. (2002) J. Biol. Chem. 277, 34573-34580). Uptake of fluid by cells can occur either by micropinocytosis within vesicles (<0.1 microm diameter) or by macropinocytosis within vacuoles ( approximately 0.5-5.0 microm) named macropinosomes. The current investigation has identified macropinocytosis as the pathway for fluid-phase LDL endocytosis and determined signaling and cytoskeletal components involved in this LDL endocytosis. The phosphatidylinositol 3-kinase inhibitor, LY294002, which inhibits macropinocytosis but does not inhibit micropinocytosis, completely blocked PMA-activated macrophage uptake of fluid and LDL. Also, nystatin and filipin, inhibitors of micropinocytosis from lipid-raft plasma membrane domains, both failed to inhibit PMA-stimulated macrophage cholesterol accumulation. Time-lapse video phase-contrast microscopy and time-lapse digital confocal-fluorescence microscopy with fluorescent DiI-LDL showed that PMA-activated macrophages took up LDL in the fluid phase by macropinocytosis. Macropinocytosis of LDL depended on Rho GTPase signaling, actin, and microtubules. Bafilomycin A1, the vacuolar H+-ATPase inhibitor, inhibited degradation of LDL and caused accumulation of undegraded LDL within macropinosomes and multivesicular body endosomes. LDL in multivesicular body endosomes was concentrated >40-fold over its concentration in the culture medium consistent with macropinosome shrinkage by maturation into multivesicular body endosomes. Macropinocytosis of LDL taken up in the fluid phase without receptor-mediated binding of LDL is a novel endocytic pathway that generates macrophage foam cells. Macropinocytosis in macrophages and possibly other vascular cells is a new pathway to target for modulating foam cell formation in atherosclerosis.
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Affiliation(s)
- Howard S Kruth
- Section of Experimental Atherosclerosis, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1422, USA.
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22
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Krysko DV, Brouckaert G, Kalai M, Vandenabeele P, D'Herde K. Mechanisms of internalization of apoptotic and necrotic L929 cells by a macrophage cell line studied by electron microscopy. J Morphol 2004; 258:336-45. [PMID: 14584035 DOI: 10.1002/jmor.10161] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Rapid and efficient phagocytic removal of dying cells is a key feature of apoptosis. In necrotic caspase-independent modes of death, the role and extent of phagocytosis is not well documented. To address this issue, we studied at the ultrastructural level the phagocytic response to dying cells in an in vitro phagocytosis assay with a mouse macrophage cell line (Mf4/4). As target cells, murine L929sAhFas cells were induced to die by TNFR1-mediated necrosis or by Fas-mediated apoptosis. Apoptotic L929sAhFas cells are taken up by complete engulfment of apoptotic bodies as single entities forming a tight-fitting phagosome, thus resembling the "zipper"-like mechanism of internalization. In contrast, primary and secondary necrotic cells were internalized by a macropinocytotic mechanism with formation of multiple ruffles by the ingesting macrophage. Ingestion of necrotic cellular material was invariably taking place after the integrity of the cell membrane was lost and did not occur as discrete particles, in contrast to apoptotic material that is surrounded by an intact membrane. Although nuclei of necrotic cells have been observed in the vicinity of macrophages, no uptake of necrotic nuclei was observed. The present report provides a basis for future studies aimed at discovering molecular pathways that precede these diverse mechanisms of uptake.
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Affiliation(s)
- Dmitri V Krysko
- Department of Human Anatomy, Embryology, Histology and Medical Physics, Ghent University, Godshuizenlaan 4, B-9000 Ghent, Belgium.
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Marsche G, Zimmermann R, Horiuchi S, Tandon NN, Sattler W, Malle E. Class B scavenger receptors CD36 and SR-BI are receptors for hypochlorite-modified low density lipoprotein. J Biol Chem 2003; 278:47562-70. [PMID: 12968020 DOI: 10.1074/jbc.m308428200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The presence of HOCl-modified epitopes inside and outside monocytes/macrophages and the presence of HOCl-modified apolipoprotein B in atherosclerotic lesions has initiated the present study to identify scavenger receptors that bind and internalize HOCl-low density lipoprotein (LDL). The uptake of HOCl-LDL by THP-1 macrophages was not saturable and led to cholesterol/cholesteryl ester accumulation. HOCl-LDL is not aggregated in culture medium, as measured by dynamic light scattering experiments, but internalization of HOCl-LDL could be inhibited in part by cytochalasin D, a microfilament disrupting agent. This indicates that HOCl-LDL is partially internalized by a pathway resembling phagocytosis-like internalization (in part by fluid-phase endocytosis) as measured with [14C]sucrose uptake. In contrast to uptake studies, binding of HOCl-LDL to THP-1 cells at 4 degrees C was specific and saturable, indicating that binding proteins and/or receptors are involved. Competition studies on THP-1 macrophages showed that HOCl-LDL does not compete for the uptake of acetylated LDL (a ligand to scavenger receptor class A) but strongly inhibits the uptake of copper-oxidized LDL (a ligand to CD36 and SR-BI). The binding specificity of HOCl-LDL to class B scavenger receptors could be demonstrated by Chinese hamster ovary cells overexpressing CD36 and SR-BI and specific blocking antibodies. The lipid moiety isolated from the HOCl-LDL particle did not compete for cell association of labeled HOCl-LDL to CD36 or SR-BI, suggesting that the protein moiety of HOCl-LDL is responsible for receptor recognition. Experiments with Chinese hamster ovary cells overexpressing scavenger receptor class A, type I, confirmed that LDL modified at physiologically relevant HOCl concentrations is not recognized by this receptor.
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Affiliation(s)
- Gunther Marsche
- Karl-Franzens University Graz, Institute of Medical Biochemistry and Molecular Biology, Austria
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Haberland ME, Mottino G, Le M, Frank JS. Sequestration of aggregated LDL by macrophages studied with freeze-etch electron microscopy. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31170-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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25
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Intracellular trafficking of pigeon β-very low density lipoprotein and low density lipoprotein at low and high concentrations in pigeon macrophages. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)31976-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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26
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Jones NL, Reagan JW, Willingham MC. The pathogenesis of foam cell formation: modified LDL stimulates uptake of co-incubated LDL via macropinocytosis. Arterioscler Thromb Vasc Biol 2000; 20:773-81. [PMID: 10712403 DOI: 10.1161/01.atv.20.3.773] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Previously, modified LDLs were shown to stimulate macropinocytosis in pigeon macrophages. Simultaneous intracellular trafficking of LDL and AcLDL, differentially labeled with colloidal gold, was done to determine whether uptake of LDL, which does not cause foam cell formation, was internalized via a separate route from AcLDL, which stimulates foam cell formation. AcLDL and LDL were followed at either low (12 microg/mL) concentrations near the saturation of high affinity binding sites or high (50 to 150 microg/mL) lipoprotein concentrations used to induce foam cell formation. The colloidal gold distribution and percentage of co-labeling as observed by transmission electron microscopy were determined for organelles involved with coated-pit endocytosis or macropinocytosis. LDL simultaneously incubated with AcLDL on macrophages at the low concentration was predominately internalized via coated-pit endocytosis. AcLDL was internalized via both coated-pit endocytosis and macropinocytosis at low concentration. At higher lipoprotein concentrations (50 to 150 microg/mL), AcLDL continued to be internalized via macropinocytosis. Interestingly, a significant portion of the co-incubated LDL, at high concentrations, also trafficked via macropinocytosis. LDL internalized by macropinosomes at high lipoprotein concentrations suggests that AcLDL-stimulated macropinocytosis might increase uptake of co-incubated lipoproteins. When (125)I-LDL was incubated with cold AcLDL, LDL degradation at 37 degrees C doubled, without a corresponding increase in cell association or total binding of LDL at 4 degrees C. These studies suggest that modified LDL-stimulated macropinocytosis is a mechanism for increased degradation of co-incubated LDL potentially leading to foam cell formation.
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Affiliation(s)
- N L Jones
- Department of Pathology, Wake Forest University School of Medicine of Wake Forest University, Medical Center Boulevard, Winston-Salem, NC 27157-1092, USA.
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