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Staurenghi E, Leoni V, Lo Iacono M, Sottero B, Testa G, Giannelli S, Leonarduzzi G, Gamba P. ApoE3 vs. ApoE4 Astrocytes: A Detailed Analysis Provides New Insights into Differences in Cholesterol Homeostasis. Antioxidants (Basel) 2022; 11:2168. [PMID: 36358540 PMCID: PMC9686673 DOI: 10.3390/antiox11112168] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 10/28/2022] [Accepted: 10/29/2022] [Indexed: 07/30/2023] Open
Abstract
The strongest genetic risk factor for sporadic Alzheimer's disease (AD) is the presence of the ε4 allele of the apolipoprotein E (ApoE) gene, the major apolipoprotein involved in brain cholesterol homeostasis. Being astrocytes the main producers of cholesterol and ApoE in the brain, we investigated the impact of the ApoE genotype on astrocyte cholesterol homeostasis. Two mouse astrocytic cell lines expressing the human ApoE3 or ApoE4 isoform were employed. Gas chromatography-mass spectrometry (GC-MS) analysis pointed out that the levels of total cholesterol, cholesterol precursors, and various oxysterols are altered in ApoE4 astrocytes. Moreover, the gene expression analysis of more than 40 lipid-related genes by qRT-PCR showed that certain genes are up-regulated (e.g., CYP27A1) and others down-regulated (e.g., PPARγ, LXRα) in ApoE4, compared to ApoE3 astrocytes. Beyond confirming the significant reduction in the levels of PPARγ, a key transcription factor involved in the maintenance of lipid homeostasis, Western blotting showed that both intracellular and secreted ApoE levels are altered in ApoE4 astrocytes, as well as the levels of receptors and transporters involved in lipid uptake/efflux (ABCA1, LDLR, LRP1, and ApoER2). Data showed that the ApoE genotype clearly affects astrocytic cholesterol homeostasis; however, further investigation is needed to clarify the mechanisms underlying these differences and the consequences on neighboring cells. Indeed, drug development aimed at restoring cholesterol homeostasis could be a potential strategy to counteract AD.
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Affiliation(s)
- Erica Staurenghi
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
| | - Valerio Leoni
- Laboratory of Clinical Biochemistry, Hospital Pius XI of Desio, ASST-Brianza, University of Milano-Bicocca, 20126 Monza, Italy
- Department of Medicine and Surgery, University of Milano-Bicocca, 20126 Monza, Italy
| | - Marco Lo Iacono
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
| | - Barbara Sottero
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
| | - Gabriella Testa
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
| | - Serena Giannelli
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
| | - Gabriella Leonarduzzi
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
| | - Paola Gamba
- Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
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2
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Rueter J, Rimbach G, Huebbe P. Functional diversity of apolipoprotein E: from subcellular localization to mitochondrial function. Cell Mol Life Sci 2022; 79:499. [PMID: 36018414 PMCID: PMC9418098 DOI: 10.1007/s00018-022-04516-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 07/27/2022] [Accepted: 08/07/2022] [Indexed: 11/26/2022]
Abstract
Human apolipoprotein E (APOE), originally known for its role in lipid metabolism, is polymorphic with three major allele forms, namely, APOEε2, APOEε3, and APOEε4, leading to three different human APOE isoforms. The ε4 allele is a genetic risk factor for Alzheimer's disease (AD); therefore, the vast majority of APOE research focuses on its role in AD pathology. However, there is increasing evidence for other functions of APOE through the involvement in other biological processes such as transcriptional regulation, mitochondrial metabolism, immune response, and responsiveness to dietary factors. Therefore, the aim of this review is to provide an overview of the potential novel functions of APOE and their characterization. The detection of APOE in various cell organelles points to previously unrecognized roles in mitochondria and others, although it is actually considered a secretory protein. Furthermore, numerous interactions of APOE with other proteins have been detected, providing indications for new metabolic pathways involving APOE. The present review summarizes the current evidence on APOE beyond its original role in lipid metabolism, to change the perspective and encourage novel approaches to future research on APOE and its isoform-dependent role in the cellular metabolism.
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Affiliation(s)
- Johanna Rueter
- Devision of Food Science, Institute of Human Nutrition and Food Science, University of Kiel, Hermann-Rodewald-Strasse 6, 24118, Kiel, Germany
| | - Gerald Rimbach
- Devision of Food Science, Institute of Human Nutrition and Food Science, University of Kiel, Hermann-Rodewald-Strasse 6, 24118, Kiel, Germany.
| | - Patricia Huebbe
- Devision of Food Science, Institute of Human Nutrition and Food Science, University of Kiel, Hermann-Rodewald-Strasse 6, 24118, Kiel, Germany
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3
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Marais AD. Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease. Pathology 2018; 51:165-176. [PMID: 30598326 DOI: 10.1016/j.pathol.2018.11.002] [Citation(s) in RCA: 176] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 10/31/2018] [Accepted: 11/01/2018] [Indexed: 12/16/2022]
Abstract
Apolipoprotein E (apoE), a 34 kDa circulating glycoprotein of 299 amino acids, predominantly synthesised in the liver, associates with triglyceride-rich lipoproteins to mediate the clearance of their remnants after enzymatic lipolysis in the circulation. Its synthesis in macrophages initiates the formation of high density-like lipoproteins to effect reverse cholesterol transport to the liver. In the nervous system apoE forms similar lipoproteins which perform the function of distributing lipids amongst cells. ApoE accounts for much of the variation in plasma lipoproteins by three common variants (isoforms) that influence low-density lipoprotein concentration and the risk of atherosclerosis. ApoE2 generally is most favourable and apoE4 least favourable for cardiovascular and neurological health. The apoE variants relate to different amino acids at positions 112 and 158: cysteine in both for apoE2, arginine at both sites for apoE4, and respectively cysteine and arginine for apoE3 that is viewed as the wild type. Paradoxically, under metabolic stress, homozygosity for apoE2 may result in dysbetalipoproteinaemia in adults owing to impaired binding of remnant lipoproteins to the LDL receptor and related proteins as well as heparan sulphate proteoglycans. This highly atherogenic condition is also seen with other mutations in apoE, but with autosomal dominant inheritance. Mutations in apoE may also cause lipoprotein glomerulopathy. In the central nervous system apoE binds amyloid β-protein and tau protein and fragments may incur cellular damage. ApoE4 is a strong risk factor for the development of Alzheimer's disease. ApoE has several other physiological effects that may influence health and disease, including supply of docosahexaenoic acid for the brain and modulating immune and inflammatory responses. Genotyping of apoE may have application in disorders of lipoprotein metabolism as well as glomerulopathy and may be relevant to personalised medicine in understanding cardiovascular risk, and the outcome of nutritional and therapeutic interventions. Quantitation of apoE will probably not be clinically useful. ApoE is also of interest as it may generate peptides with biological function and could be employed in nanoparticles that may allow crossing of the blood-brain barrier. Therapeutic options may emerge from these newer insights.
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Affiliation(s)
- A David Marais
- Chemical Pathology Division, Pathology Department, University of Cape Town Health Science Faculty and National Health Laboratory Service, Cape Town, South Africa.
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4
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Gao H. Perspectives on Dual Targeting Delivery Systems for Brain Tumors. J Neuroimmune Pharmacol 2016; 12:6-16. [PMID: 27270720 DOI: 10.1007/s11481-016-9687-4] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 05/31/2016] [Indexed: 12/30/2022]
Abstract
Brain tumor remains one of the most serious threats to human beings. Different from peripheral tumors, drug delivery to brain tumor is largely restricted by the blood brain barrier (BBB). To fully conquer this barrier and specifically deliver drugs to brain tumor, dual targeting delivery systems were explored, which are functionalized with two active targeting ligands: one to the BBB and the other to the brain tumor. The development of dual targeting delivery system is still in its early stage, and attentions need to be paid to issues and concerns that remain unresolved in future studies.
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Affiliation(s)
- Huile Gao
- Key Laboratory of Drug Targeting and Drug Delivery Systems, West China School of Pharmacy, Sichuan University, Chengdu, China.
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5
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Fan J, Stukas S, Wong C, Chan J, May S, DeValle N, Hirsch-Reinshagen V, Wilkinson A, Oda MN, Wellington CL. An ABCA1-independent pathway for recycling a poorly lipidated 8.1 nm apolipoprotein E particle from glia. J Lipid Res 2011; 52:1605-16. [PMID: 21705806 DOI: 10.1194/jlr.m014365] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Lipid transport in the brain is coordinated by glial-derived lipoproteins that contain apolipoprotein E (apoE) as their primary protein. Here we show that apoE is secreted from wild-type (WT) primary murine mixed glia as nascent lipoprotein subspecies ranging from 7.5 to 17 nm in diameter. Negative-staining electron microscropy (EM) revealed rouleaux, suggesting a discoidal structure. Potassium bromide (KBr) density gradient ultracentrifugation showed that all subspecies, except an 8.1 nm particle, were lipidated. Glia lacking the cholesterol transporter ABCA1 secreted only 8.1 nm particles, which were poorly lipidated and nondiscoidal but could accept lipids to form the full repertoire of WT apoE particles. Receptor-associated-protein (RAP)-mediated inhibition of apoE receptor function blocked appearance of the 8.1 nm species, suggesting that this particle may arise through apoE recycling. Selective deletion of the LDL receptor (LDLR) reduced the level of 8.1 nm particle production by approximately 90%, suggesting that apoE is preferentially recycled through the LDLR. Finally, apoA-I stimulated secretion of 8.1 nm particles in a dose-dependent manner. These results suggest that nascent glial apoE lipoproteins are secreted through multiple pathways and that a greater understanding of these mechanisms may be relevant to several neurological disorders.
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Affiliation(s)
- Jianjia Fan
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada
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Kuo CL, Oyler G, Shoemaker CB. Lipid and cationic polymer based transduction of botulinum holotoxin, or toxin protease alone, extends the target cell range and improves the efficiency of intoxication. Toxicon 2009; 55:619-29. [PMID: 19852976 DOI: 10.1016/j.toxicon.2009.10.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2009] [Revised: 10/09/2009] [Accepted: 10/14/2009] [Indexed: 10/20/2022]
Abstract
Botulinum neurotoxin (BoNT) heavy chain (Hc) facilitates receptor-mediated endocytosis into neuronal cells and transport of the light chain (Lc) protease to the cytosol where neurotransmission is inhibited as a result of SNARE protein cleavage. Here we show that the role of BoNT Hc in cell intoxication can be replaced by commercial lipid-based and polycationic polymer DNA transfection reagents. BoNT "transduction" by these reagents permits efficient intoxication of neuronal cells as well as some non-neuronal cell lines normally refractory to BoNT. Surprisingly, the reagents facilitate delivery of recombinant BoNT Lc protease to the cytosol of both neuronal and non-neuronal cells in the absence of BoNT Hc, and with sensitivities approaching that of BoNT holotoxin. Transduction of BoNT, as with natural intoxication, is inhibited by bafilomycin A1, methylamine and ammonium chloride indicating that both pathways require endosome acidification. DNA transfection reagents facilitate intoxication by holotoxins, or isolated Lc proteases, of all three BoNT serotypes tested (A, B, E). These results suggest that lipid and cationic polymer transfection reagents facilitate cytosolic delivery of BoNT holotoxins and isolated Lc proteases by an endosomal uptake pathway.
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Affiliation(s)
- Chueh-Ling Kuo
- Tufts Cummings School of Veterinary Medicine, Department of Biomedical Sciences, 200 Westboro Road, North Grafton, MA 01536, USA
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7
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Sabaretnam T, Harris MJ, Kockx M, Witting PK, Le Couteur DG, Kritharides L. Effects of hydrogen peroxide and apolipoprotein E isoforms on apolipoprotein E trafficking in HepG2 cells. Clin Exp Pharmacol Physiol 2009; 36:e96-102. [PMID: 19793104 DOI: 10.1111/j.1440-1681.2009.05306.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
1. The major source of apolipoprotein E (apoE) is the liver. In the present study, the effects of oxidative stress and apoE isoforms on apoE distribution and trafficking were established using the HepG2 liver tumour cell line. 2. Hydrogen peroxide (0, 25, 250 and 1000 micromol/L) was associated with rapid and concentration-dependent redistribution of apoE into the early endosomal compartment. This redistribution was achieved with a much lower concentration (25 micromol/L) than that needed to induce changes in intracellular apoE mRNA expression, apoE protein levels and markers of oxidative stress (250-1000 micromol/L). 3. Live cell imaging of apoE3-green fluorescent protein revealed a significant decrease in traffic velocity in response to oxidative stress. 4. The E4 isoform was associated with reduced trafficking velocity compared with the E3 isoform under basal conditions. 5. The results indicate that oxidative stress and apoE isoforms influence apoE trafficking and distribution within HepG2 cells. Altered apoE hepatocyte trafficking may provide a mechanistic link between oxidative stress, ageing and some diseases in older people.
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8
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The effect of aging on the response of isolated hepatocytes to hydrogen peroxide and tert-butyl hydroperoxide. Toxicol In Vitro 2009; 24:123-8. [PMID: 19720132 DOI: 10.1016/j.tiv.2009.08.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Revised: 07/24/2009] [Accepted: 08/26/2009] [Indexed: 11/23/2022]
Abstract
Aging is associated with increased susceptibility to oxidative stress. To study this in the liver and to elucidate underlying mechanisms, hepatocytes from young (4-6 months) and old (24-26 months) rats were exposed to two oxidants, hydrogen peroxide and tert-butyl hydroperoxide. ATP content and mitochondrial activity were lower in old hepatocytes and decreased further with oxidative stress. Expression of Cu/Zn superoxide dismutase, Mn superoxide dismutase and catalase was not substantially influenced by oxidative stress in young and old hepatocytes, whereas glutathione peroxidase 1 expression was markedly increased only in young hepatocytes. Oxidative stress in young hepatocytes led to increased expression of apoE and movement of apoE to the early endosomes. In old hepatocytes, oxidative stress did not increase apoE expression and apoE was co-localized with early endosomes under control conditions. The results show that old age is associated with impaired hepatocyte responses of mitochondria, ATP, glutathione peroxidase 1 and apoE to oxidative stress.
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9
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Mosher MJ, Lange LA, Howard BV, Lee ET, Best LG, Fabsitz RR, Maccluer JW, North KE. Sex-specific interaction between APOE genotype and carbohydrate intake affects plasma HDL-C levels: the Strong Heart Family Study. GENES & NUTRITION 2008; 3:87-97. [PMID: 18850190 PMCID: PMC2467448 DOI: 10.1007/s12263-008-0075-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Accepted: 12/05/2007] [Indexed: 10/22/2022]
Abstract
Low plasma levels of high-density lipoprotein cholesterol (HDL-C) are identified as a risk factor for cardiovascular disease (CVD). Sexual dimorphism, however, is widely reported in both HDL-C and CVD, with the underlying explanations of these sexual differences not fully understood. HDL-C is a complex trait influenced by both genes and dietary factors. Here we examine evidence for a sex-specific effect of APOE and the macronutrient carbohydrate on HDL-C, triglycerides (TG) and apoprotein A-1 (ApoA-1) in a sample of 326 male and 423 female participants of the Strong Heart Family Study (SHFS). Using general estimating equations in SAS to account for kinship correlations, stratifying by sex, and adjusting for age, body mass index (BMI) and SHS center, we examine the relationship between APOE genotype and carbohydrate intake on circulating levels of HDL-C, TG, and ApoA-1 through a series of carbohydrate-by-sex interactions and stratified analyses. APOE-by-carbohydrate intake shows significant sex-specific effects. All males had similar decreases in HDL-C levels associated with increased carbohydrate intake. However, only those females with APOE-4 alleles showed significantly lower HDL-C levels as their percent of carbohydrate intake increased, while no association was noted between carbohydrate intake and HDL-C in those females without an APOE-4 allele. These findings demonstrate the importance of understanding sex differences in gene-by-nutrient interaction when examining the complex architecture of HDL-C variation.
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Affiliation(s)
- M J Mosher
- Department of Anthropology, Western Washington University, Bellingham, WA, USA,
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10
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Chou CY, Jen WP, Hsieh YH, Shiao MS, Chang GG. Structural and functional variations in human apolipoprotein E3 and E4. J Biol Chem 2006; 281:13333-13344. [PMID: 16540478 DOI: 10.1074/jbc.m511077200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
There are three major apolipoprotein E (apoE) isoforms. Although APOE-epsilon3 is considered a longevity gene, APOE-epsilon4 is a dual risk factor to atherosclerosis and Alzheimer disease. We have expressed full-length and N- and C-terminal truncated apoE3 and apoE4 tailored to eliminate helix and domain interactions to unveil structural and functional disturbances. The N-terminal truncated apoE4-(72-299) and C-terminal truncated apoE4-(1-231) showed more complicated or aggregated species than those of the corresponding apoE3 counterparts. This isoformic structural variation did not exist in the presence of dihexanoylphosphatidylcholine. The C-terminal truncated apoE-(1-191) and apoE-(1-231) proteins greatly lost lipid binding ability as illustrated by the dimyristoylphosphatidylcholine turbidity clearance. The low density lipoprotein (LDL) receptor binding ability, determined by a competition binding assay of 3H-LDL to the LDL receptor of HepG2 cells, showed that apoE4 proteins with N-terminal (apoE4-(72-299)), C-terminal (apoE4-(1-231)), or complete C-terminal truncation (apoE4-(1-191)) maintained greater receptor binding abilities than their apoE3 counterparts. The cholesterol-lowering abilities of apoE3-(72-299) and apoE3-(1-231) in apoE-deficient mice were decreased significantly. The structural preference of apoE4 to remain functional in solution may explain the enhanced opportunity of apoE4 isoform to display its pathophysiologic functions in atherosclerosis and Alzheimer disease.
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Affiliation(s)
- Chi-Yuan Chou
- Faculty of Life Sciences, Institute of Biochemistry, Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Wei-Ping Jen
- Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan
| | - Yi-Hui Hsieh
- Faculty of Life Sciences, Institute of Biochemistry, Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Ming-Shi Shiao
- Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan
| | - Gu-Gang Chang
- Faculty of Life Sciences, Institute of Biochemistry, Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan.
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Braun NA, Mohler PJ, Weisgraber KH, Hasty AH, Linton MF, Yancey PG, Su YR, Fazio S, Swift LL. Intracellular trafficking of recycling apolipoprotein E in Chinese hamster ovary cells. J Lipid Res 2006; 47:1176-86. [PMID: 16534141 DOI: 10.1194/jlr.m500503-jlr200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have investigated apolipoprotein E (apoE) recycling in Chinese hamster ovary (CHO) cells, a peripheral cell that does not produce lipoproteins or express apoE. Using a pulse-chase protocol in which cells were pulsed with 125I-apoE-VLDL and chased for different periods, approximately 30% of the apoE internalized during the pulse was resecreted within a 4 h chase in a relatively lipid-free state. The addition of lysosomotropic agents or brefeldin A had no effect on apoE recycling. Unlike previous results with hepatocytes and macrophages, neither apoA-I nor upregulation of ABCA1 stimulated apoE recycling. However, cyclodextrin, which extracts cholesterol from plasma membrane lipid rafts, increased recycling. Confocal studies revealed that apoE, internalized during a 1 h pulse, colocalizes with early endosomal antigen-1, Rab5, Rab11a, and lysobisphosphatidic acid but not with lysosomal-associated membrane protein-1. Colocalization of apoE and Rab11a persisted even after cells had been chased for 1 h, suggesting a pool of apoE within the endosomal recycling compartment (ERC). Our data suggest that apoE recycling in CHO cells is linked to cellular cholesterol removal via the ERC and phospholipid-containing acceptors in a pathway alternative to the ABCA1-apoA-I axis.
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Affiliation(s)
- Nicole A Braun
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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12
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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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13
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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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14
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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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15
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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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16
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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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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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18
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Chou CY, Lin YL, Huang YC, Sheu SY, Lin TH, Tsay HJ, Chang GG, Shiao MS. Structural variation in human apolipoprotein E3 and E4: secondary structure, tertiary structure, and size distribution. Biophys J 2004; 88:455-66. [PMID: 15475580 PMCID: PMC1305022 DOI: 10.1529/biophysj.104.046813] [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: 12/30/2022] Open
Abstract
Human apolipoprotein E (apoE) is a 299-amino-acid protein with a molecular weight of 34 kDa. The difference between the apoE3 and apoE4 isoforms is a single residue substitution involving a Cys-Arg replacement at residue 112. ApoE4 is positively associated with atherosclerosis and late-onset and sporadic Alzheimer's disease (AD). ApoE4 and its C-terminal truncated fragments have been found in the senile plaques and neurofibrillary tangles in the brain of AD patients. However, detail structural information regarding isoform and domain interaction remains poorly understood. We prepared full-length, N-, and C-terminal truncated apoE3 and apoE4 proteins and studied their structural variation. Sedimentation velocity and continuous size distribution analysis using analytical ultracentrifugation revealed apoE3(72-299) as consisting of a major species with a sedimentation coefficient of 5.9. ApoE4(72-299) showed a wider and more complicated species distribution. Both apoE3 and E4 N-terminal domain (1-191) existed with monomers as the major component together with some tetramer. The oligomerization and aggregation of apoE protein increased when the C-terminal domain (192-271) was incorporated. The structural influence of the C-terminal domain on apoE is to assist self-association with no significant isoform preference. Circular dichroism and fluorescence studies demonstrated that apoE4(72-299) possessed a more alpha-helical structure with more hydrophobic residue exposure. The structural variation of the N-terminal truncated apoE3 and apoE4 protein provides useful information that helps to explain the greater aggregation of the apoE4 isoform and thus has implication for the involvement of apoE4 in AD.
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Affiliation(s)
- Chi-Yuan Chou
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Yi-Ling Lin
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Yu-Chyi Huang
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Sheh-Yi Sheu
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Ta-Hsien Lin
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Huey-Jen Tsay
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Gu-Gang Chang
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
| | - Ming-Shi Shiao
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei 112, Taiwan; and Faculty of Life Sciences, Institute of Biochemistry, Institute of Neuroscience, and Structural Biology Program, National Yang-Ming University, Taipei 112, Taiwan
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