1
|
Knaack DA, Chang J, Thomas MJ, Sorci-Thomas MG, Chen Y, Sahoo D. Scavenger receptor class B type I is required for efficient glucose uptake and metabolic homeostasis in adipocytes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.21.554190. [PMID: 37662321 PMCID: PMC10473602 DOI: 10.1101/2023.08.21.554190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
Obesity is a worldwide epidemic and places individuals at a higher risk for developing comorbidities that include cardiovascular disease and type 2 diabetes. Adipose tissue contains adipocytes that are responsible for lipid metabolism and reducing misdirected lipid storage. Adipocytes facilitate this process through insulin-mediated uptake of glucose and its subsequent metabolism into triglycerides for storage. During obesity, adipocytes become insulin resistant and have a reduced ability to mediate glucose import, thus resulting in whole-body metabolic dysfunction. Scavenger receptor class B type I (SR-BI) has been implicated in glucose uptake in skeletal muscle and adipocytes via its native ligands, apolipoprotein A-1 and high-density lipoproteins. Further, SR-BI translocation to the cell surface in adipocytes is sensitive to insulin stimulation. Using adipocytes differentiated from ear mesenchymal stem cells isolated from wild-type and SR-BI knockout (SR-BI -/- ) mice as our model system, we tested the hypothesis that SR-BI is required for insulin-mediated glucose uptake and regulation of energy balance in adipocytes. We demonstrated that loss of SR-BI in adipocytes resulted in inefficient glucose uptake regardless of cell surface expression levels of glucose transporter 4 compared to WT adipocytes. We also observed reduced glycolytic capacity, increased lipid biosynthesis, and dysregulated expression of lipid metabolism genes in SR-BI -/- adipocytes compared to WT adipocytes. These results partially support our hypothesis and suggest a novel role for SR-BI in glucose uptake and metabolic homeostasis in adipocytes.
Collapse
|
2
|
Lemus Silva EG, Delgadillo Y, White RE, Lucin KM. Beclin 1 regulates astrocyte phagocytosis and phagosomal recruitment of retromer. Tissue Cell 2023; 82:102100. [PMID: 37182392 DOI: 10.1016/j.tice.2023.102100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 04/21/2023] [Accepted: 04/26/2023] [Indexed: 05/16/2023]
Abstract
Phagocytosis plays an important role in maintaining brain homeostasis and when impaired can result in the accumulation of unwanted cellular material. While microglia are traditionally considered the phagocytes of the brain, astrocytes are also capable of phagocytosis and are the most numerous cells in the brain. In Alzheimer's disease (AD), astrocytes can be found surrounding β-amyloid (Aβ) plaques yet they seem unable to eliminate these deposits, suggesting phagocytosis may be impaired in AD. Mechanisms that might diminish astrocyte phagocytosis in AD are currently unclear. Here, we demonstrate that the autophagy protein beclin 1, which is reduced in AD, plays a role in regulating astrocyte phagocytosis. Specifically, we show that reducing beclin 1 in C6 astrocytes impairs the phagocytosis of latex beads, reduces retromer levels, and impairs retromer recruitment to the phagosomal membrane. Furthermore, we show that these beclin 1-mediated changes are accompanied by reduced expression of the phagocytic receptor Scavenger Receptor Class B type I (SR-BI). Collectively, these findings suggest a critical role for the protein beclin 1 in both receptor trafficking and receptor-mediated phagocytosis in astrocytes. Moreover, these findings provide insight into mechanisms by which astrocytes may become impaired in AD.
Collapse
Affiliation(s)
| | | | - Robin E White
- Westfield State University, Westfield, MA 01086, USA
| | - Kurt M Lucin
- Eastern Connecticut State University, Willimantic, CT 06226, USA.
| |
Collapse
|
3
|
Juhl AD, Wüstner D. Pathways and Mechanisms of Cellular Cholesterol Efflux-Insight From Imaging. Front Cell Dev Biol 2022; 10:834408. [PMID: 35300409 PMCID: PMC8920967 DOI: 10.3389/fcell.2022.834408] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Accepted: 02/04/2022] [Indexed: 12/24/2022] Open
Abstract
Cholesterol is an essential molecule in cellular membranes, but too much cholesterol can be toxic. Therefore, mammalian cells have developed complex mechanisms to remove excess cholesterol. In this review article, we discuss what is known about such efflux pathways including a discussion of reverse cholesterol transport and formation of high-density lipoprotein, the function of ABC transporters and other sterol efflux proteins, and we highlight their role in human diseases. Attention is paid to the biophysical principles governing efflux of sterols from cells. We also discuss recent evidence for cholesterol efflux by the release of exosomes, microvesicles, and migrasomes. The role of the endo-lysosomal network, lipophagy, and selected lysosomal transporters, such as Niemann Pick type C proteins in cholesterol export from cells is elucidated. Since oxysterols are important regulators of cellular cholesterol efflux, their formation, trafficking, and secretion are described briefly. In addition to discussing results obtained with traditional biochemical methods, focus is on studies that use established and novel bioimaging approaches to obtain insight into cholesterol efflux pathways, including fluorescence and electron microscopy, atomic force microscopy, X-ray tomography as well as mass spectrometry imaging.
Collapse
Affiliation(s)
- Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, Odense, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, Odense, Denmark
| |
Collapse
|
4
|
Li H, Yu XH, Ou X, Ouyang XP, Tang CK. Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis. Prog Lipid Res 2021; 83:101109. [PMID: 34097928 DOI: 10.1016/j.plipres.2021.101109] [Citation(s) in RCA: 76] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 05/31/2021] [Accepted: 06/02/2021] [Indexed: 12/12/2022]
Abstract
Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.
Collapse
Affiliation(s)
- Heng Li
- Institute of Cardiovascular Disease, Key Laboratory for Arteriosclerology of Hunan Province, Hunan International Scientific and Technological Cooperation Base of Arteriosclerotic Disease, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang Medical College, University of South China, Hengyang, Hunan 421001, China
| | - Xiao-Hua Yu
- Institute of Clinical Medicine, The Second Affiliated Hospital of Hainan Medical University, Haikou, Hainan 460106, China
| | - Xiang Ou
- Department of Endocrinology, the First Hospital of Changsha, Changsha, Hunan 410005, China
| | - Xin-Ping Ouyang
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang Medical College, University of South China, Hengyang, Hunan 421001, China.
| | - Chao-Ke Tang
- Institute of Cardiovascular Disease, Key Laboratory for Arteriosclerology of Hunan Province, Hunan International Scientific and Technological Cooperation Base of Arteriosclerotic Disease, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang Medical College, University of South China, Hengyang, Hunan 421001, China.
| |
Collapse
|
5
|
Wang D, Yang Y, Lei Y, Tzvetkov NT, Liu X, Yeung AWK, Xu S, Atanasov AG. Targeting Foam Cell Formation in Atherosclerosis: Therapeutic Potential of Natural Products. Pharmacol Rev 2019; 71:596-670. [PMID: 31554644 DOI: 10.1124/pr.118.017178] [Citation(s) in RCA: 114] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of atherosclerotic lesions. Targeting foam cell formation in the atherosclerotic lesions can be a promising approach to treat and prevent atherosclerosis. The formation of foam cells is determined by the balanced effects of three major interrelated biologic processes, including lipid uptake, cholesterol esterification, and cholesterol efflux. Natural products are a promising source for new lead structures. Multiple natural products and pharmaceutical agents can inhibit foam cell formation and thus exhibit antiatherosclerotic capacity by suppressing lipid uptake, cholesterol esterification, and/or promoting cholesterol ester hydrolysis and cholesterol efflux. This review summarizes recent findings on these three biologic processes and natural products with demonstrated potential to target such processes. Discussed also are potential future directions for studying the mechanisms of foam cell formation and the development of foam cell-targeted therapeutic strategies.
Collapse
Affiliation(s)
- Dongdong Wang
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Yang Yang
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Yingnan Lei
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Nikolay T Tzvetkov
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Xingde Liu
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Andy Wai Kan Yeung
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Suowen Xu
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| | - Atanas G Atanasov
- The Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, Guiyang, China (D.W., X.L.); Department of Molecular Biology, Institute of Genetics and Animal Breeding of the Polish Academy of Sciences, Jastrzębiec, Poland (D.W., Y.Y., Y.L., A.G.A.); Department of Pharmacognosy, University of Vienna, Vienna, Austria (A.G.A.); Institute of Clinical Chemistry, University Hospital Zurich, Schlieren, Switzerland (D.W.); Institute of Molecular Biology "Roumen Tsanev," Department of Biochemical Pharmacology and Drug Design, Bulgarian Academy of Sciences, Sofia, Bulgaria (N.T.T.); Pharmaceutical Institute, University of Bonn, Bonn, Germany (N.T.T.); Aab Cardiovascular Research Institute, Department of Medicine, University of Rochester, Rochester, New York (S.X.); Oral and Maxillofacial Radiology, Applied Oral Sciences and Community Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China (A.W.K.Y.); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (A.G.A.)
| |
Collapse
|
6
|
Zanoni P, Velagapudi S, Yalcinkaya M, Rohrer L, von Eckardstein A. Endocytosis of lipoproteins. Atherosclerosis 2018; 275:273-295. [PMID: 29980055 DOI: 10.1016/j.atherosclerosis.2018.06.881] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 06/04/2018] [Accepted: 06/22/2018] [Indexed: 02/06/2023]
Abstract
During their metabolism, all lipoproteins undergo endocytosis, either to be degraded intracellularly, for example in hepatocytes or macrophages, or to be re-secreted, for example in the course of transcytosis by endothelial cells. Moreover, there are several examples of internalized lipoproteins sequestered intracellularly, possibly to exert intracellular functions, for example the cytolysis of trypanosoma. Endocytosis and the subsequent intracellular itinerary of lipoproteins hence are key areas for understanding the regulation of plasma lipid levels as well as the biological functions of lipoproteins. Indeed, the identification of the low-density lipoprotein (LDL)-receptor and the unraveling of its transcriptional regulation led to the elucidation of familial hypercholesterolemia as well as to the development of statins, the most successful therapeutics for lowering of cholesterol levels and risk of atherosclerotic cardiovascular diseases. Novel limiting factors of intracellular trafficking of LDL and the LDL receptor continue to be discovered and to provide drug targets such as PCSK9. Surprisingly, the receptors mediating endocytosis of high-density lipoproteins or lipoprotein(a) are still a matter of controversy or even new discovery. Finally, the receptors and mechanisms, which mediate the uptake of lipoproteins into non-degrading intracellular itineraries for re-secretion (transcytosis, retroendocytosis), storage, or execution of intracellular functions, are largely unknown.
Collapse
Affiliation(s)
- Paolo Zanoni
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Srividya Velagapudi
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Mustafa Yalcinkaya
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Lucia Rohrer
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Arnold von Eckardstein
- Institute for Clinical Chemistry, University and University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
| |
Collapse
|
7
|
Velagapudi S, Yalcinkaya M, Piemontese A, Meier R, Nørrelykke SF, Perisa D, Rzepiela A, Stebler M, Stoma S, Zanoni P, Rohrer L, von Eckardstein A. VEGF-A Regulates Cellular Localization of SR-BI as Well as Transendothelial Transport of HDL but Not LDL. Arterioscler Thromb Vasc Biol 2017; 37:794-803. [DOI: 10.1161/atvbaha.117.309284] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Accepted: 03/20/2017] [Indexed: 11/16/2022]
Abstract
Objective—
Low- and high-density lipoproteins (LDL and HDL) must pass the endothelial layer to exert pro- and antiatherogenic activities, respectively, within the vascular wall. However, the rate-limiting factors that mediate transendothelial transport of lipoproteins are yet little known. Therefore, we performed a high-throughput screen with kinase drug inhibitors to identify modulators of transendothelial LDL and HDL transport.
Approach and Results—
Microscopy-based high-content screening was performed by incubating human aortic endothelial cells with 141 kinase-inhibiting drugs and fluorescent-labeled LDL or HDL. Inhibitors of vascular endothelial growth factor (VEGF) receptors (VEGFR) significantly decreased the uptake of HDL but not LDL. Silencing of VEGF receptor 2 significantly decreased cellular binding, association, and transendothelial transport of
125
I-HDL but not
125
I-LDL. RNA interference with VEGF receptor 1 or VEGF receptor 3 had no effect. Binding, uptake, and transport of HDL but not LDL were strongly reduced in the absence of VEGF-A from the cell culture medium and were restored by the addition of VEGF-A. The restoring effect of VEGF-A on endothelial binding, uptake, and transport of HDL was abrogated by pharmacological inhibition of phosphatidyl-inositol 3 kinase/protein kinase B or p38 mitogen-activated protein kinase, as well as silencing of scavenger receptor BI. Moreover, the presence of VEGF-A was found to be a prerequisite for the localization of scavenger receptor BI in the plasma membrane of endothelial cells.
Conclusions—
The identification of VEGF as a regulatory factor of transendothelial transport of HDL but not LDL supports the concept that the endothelium is a specific and, hence, druggable barrier for the entry of lipoproteins into the vascular wall.
Collapse
Affiliation(s)
- Srividya Velagapudi
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Mustafa Yalcinkaya
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Antonio Piemontese
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Roger Meier
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Simon Flyvbjerg Nørrelykke
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Damir Perisa
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Andrzej Rzepiela
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Michael Stebler
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Szymon Stoma
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Paolo Zanoni
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Lucia Rohrer
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| | - Arnold von Eckardstein
- From the Institute of Clinical Chemistry, University and University Hospital of Zurich, Schlieren, Switzerland (S.V., M.Y., A.P., D.P., P.Z., L.R., A.v.E.); Competence Center for Integrated Human Physiology, University of Zurich, Switzerland (S.V., M.Y., D.P., P.Z., L.R., A.v.E.); Department of Pharmacy, University of Parma, Italy (A.P.); and Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland (R.M., S.F.N., A.R., M.S., S.S.)
| |
Collapse
|
8
|
Juks C, Lorents A, Arukuusk P, Langel Ü, Pooga M. Cell‐penetrating peptides recruit type A scavenger receptors to the plasma membrane for cellular delivery of nucleic acids. FASEB J 2016; 31:975-988. [DOI: 10.1096/fj.201600811r] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 11/14/2016] [Indexed: 12/12/2022]
Affiliation(s)
- Carmen Juks
- Institute of Molecular and Cell BiologyUniversity of Tartu Tartu Estonia
| | - Annely Lorents
- Institute of Molecular and Cell BiologyUniversity of Tartu Tartu Estonia
| | - Piret Arukuusk
- Laboratory of Molecular BiotechnologyInstitute of TechnologyUniversity of Tartu Tartu Estonia
| | - Ülo Langel
- Laboratory of Molecular BiotechnologyInstitute of TechnologyUniversity of Tartu Tartu Estonia
- Department of NeurochemistryStockholm University Stockholm Sweden
| | - Margus Pooga
- Institute of Molecular and Cell BiologyUniversity of Tartu Tartu Estonia
| |
Collapse
|
9
|
Kardassis D, Gafencu A, Zannis VI, Davalos A. Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational. Handb Exp Pharmacol 2015; 224:113-179. [PMID: 25522987 DOI: 10.1007/978-3-319-09665-0_3] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.
Collapse
Affiliation(s)
- Dimitris Kardassis
- Department of Biochemistry, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology of Hellas, Heraklion, Crete, 71110, Greece,
| | | | | | | |
Collapse
|
10
|
Chulsky S, Paland N, Lazarovich A, Fuhrman B. Urokinase-type plasminogen activator (uPA) decreases hepatic SR-BI expression and impairs HDL-mediated reverse cholesterol transport. Atherosclerosis 2014; 233:11-8. [DOI: 10.1016/j.atherosclerosis.2013.11.070] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 11/05/2013] [Accepted: 11/27/2013] [Indexed: 11/29/2022]
|
11
|
Wu J, Xiao Y, Liu J, Yang H, Dong X, Hu S, Jin S, Wu D. Potential role of ATM in hepatocyte endocytosis of ApoE-deficient, ApoB48-containing lipoprotein in ApoE-deficient mice. Int J Mol Med 2013; 33:462-8. [PMID: 24276232 PMCID: PMC4035781 DOI: 10.3892/ijmm.2013.1566] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2013] [Accepted: 11/07/2013] [Indexed: 11/21/2022] Open
Abstract
Individuals carrying mutations at both ataxia telangiectasia mutated (ATM) gene alleles reportedly have increased plasma cholesterol and triglyceride levels. Previous studies have demonstrated that defective ATM function promotes atherosclerosis. We previously demonstrated that ATM facilitates the clearance of plasma apolipoprotein (Apo)E-deficient, ApoB48-containing (E−/B48) lipoproteins in ApoE-deficient mice (ApoE−/− mice). However, to date there is no exact explanation available as to the mechanism(s) through which ATM is involved in the removal of E−/B48 lipoprotein in ApoE−/− mice. In this study, to our knowledge, we demonstrate for the first time that heterozygous ATM mutation reduces the hepatocyte uptake of E−/B48 lipoproteins in ApoE−/− mice; however, heterozygous ATM mutation did not affect hepatocyte binding to E−/B48 lipoproteins. Moreover, our results revealed that ATM proteins were localized in the nucleus, early endosomes and late endosomes, but not in the plasma membrane in the hepatocytes of ApoE−/− mice. In addition, following treatment with the ATM activator, chloroquine, and E−/B48 lipoproteins, ATM interacted with class III phosphatidylinositol-3-kinases (PI3Ks) and the activated ATM protein enhanced class III PI3K activity. Furthermore, treatment with a class III PI3K inhibitor (LY290042 and 3-MA) attenuated the intracellular total cholesterol accumulation induced by ATM activation. These results provide insight into the mechanisms behind the involvment of ATM in the process of endocytosis of E−/B48 lipoprotein in ApoE−/− mice, demonstrating the role of class III PI3K protein.
Collapse
Affiliation(s)
- Jianhua Wu
- Department of Pharmacy, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| | - Yanhong Xiao
- Department of Pharmacy, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| | - Juang Liu
- Department of Pharmacy, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| | - Hong Yang
- Department of Cardiovascular Biology, Meharry Medical College, Nashville, TN 37208, USA
| | - Xiaomin Dong
- Department of Osteology, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| | - San Hu
- Department of Pharmacy, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| | - Shanrui Jin
- Department of Pharmacy, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| | - Dongfang Wu
- Department of Pharmacy, Zhongnan Hospital of Wuhan University, Wuhan, Hubei 430071, P.R. China
| |
Collapse
|
12
|
Wang L, Jia XJ, Jiang HJ, Du Y, Yang F, Si SY, Hong B. MicroRNAs 185, 96, and 223 repress selective high-density lipoprotein cholesterol uptake through posttranscriptional inhibition. Mol Cell Biol 2013; 33:1956-64. [PMID: 23459944 PMCID: PMC3647964 DOI: 10.1128/mcb.01580-12] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Accepted: 02/25/2013] [Indexed: 01/05/2023] Open
Abstract
Hepatic scavenger receptor class B type I (SR-BI) plays an important role in selective high-density lipoprotein cholesterol (HDL-C) uptake, which is a pivotal step of reverse cholesterol transport. In this study, the potential involvement of microRNAs (miRNAs) in posttranscriptional regulation of hepatic SR-BI and selective HDL-C uptake was investigated. The level of SR-BI expression was repressed by miRNA 185 (miR-185), miR-96, and miR-223, while the uptake of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-HDL was decreased by 31.9% (P < 0.001), 23.9% (P < 0.05), and 15.4% (P < 0.05), respectively, in HepG2 cells. The inhibition of these miRNAs by their anti-miRNAs had opposite effects in these hepatic cells. The critical effect of miR-185 was further validated by the loss of regulation in constructs with mutated miR-185 target sites. In addition, these miRNAs directly targeted the 3' untranslated region (UTR) of SR-BI with a coordinated effect. Interestingly, the decrease of miR-96 and miR-185 coincided with the increase of SR-BI in the livers of ApoE KO mice on a high-fat diet. These data suggest that miR-185, miR-96, and miR-223 may repress selective HDL-C uptake through the inhibition of SR-BI in human hepatic cells, implying a novel mode of regulation of hepatic SR-BI and an important role of miRNAs in modulating cholesterol metabolism.
Collapse
Affiliation(s)
- Li Wang
- Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences, Beijing, China
| | | | | | | | | | | | | |
Collapse
|
13
|
Huang CX, Zhang YL, Wang JF, Jiang JY, Bao JL. MCP-1 impacts RCT by repressing ABCA1, ABCG1, and SR-BI through PI3K/Akt posttranslational regulation in HepG2 cells. J Lipid Res 2013; 54:1231-40. [PMID: 23402987 DOI: 10.1194/jlr.m032482] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Monocyte chemoattractant protein-1 (MCP-1) plays crucial roles at multiple stages of atherosclerosis. We hypothesized that MCP-1 might impair the reverse cholesterol transport (RCT) capacity of HepG2 cells by decreasing the cell-surface protein expression of ATP binding cassette A1 (ABCA1), ATP binding cassette G1 (ABCG1), and scavenger receptor class B type I (SR-BI). MCP-1 reduced the total protein and mRNA levels of ABCA1 and SR-BI, but not of ABCG1. MCP-1 decreased the cell-surface protein expression of ABCA1, ABCG1, and SR-BI in dose-dependent and time-dependent manners, as measured using cell-surface biotinylation. We further studied the phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase Akt pathway in regulating receptor trafficking. Both the translation and transcription of ABCA1, ABCG1, and SR-BI were not found to be regulated by the PI3K/Akt pathway. However, the cell-surface protein expression of ABCA1, ABCG1, and SR-BI could be regulated by PI3K activity, and PI3K activation corrected the MCP-1-induced decreases in the cell-surface protein expression of ABCA1, ABCG1, and SR-BI. Moreover, we found that MCP-1 decreased the lipid uptake by HepG2 cells and the ABCA1-mediated cholesterol efflux to apoA-I, which could be reversed by PI3K activation. Our data suggest that MCP-1 impairs RCT activity in HepG2 cells by a PI3K/Akt-mediated posttranslational regulation of ABCA1, ABCG1, and SR-BI cell-surface expression.
Collapse
Affiliation(s)
- Can-Xia Huang
- Department of Cardiology, Sun Yat-sen Memorial Hospital, University of Sun Yat-sen, Guangzhou, China
| | | | | | | | | |
Collapse
|
14
|
Kilpinen L, Tigistu-Sahle F, Oja S, Greco D, Parmar A, Saavalainen P, Nikkilä J, Korhonen M, Lehenkari P, Käkelä R, Laitinen S. Aging bone marrow mesenchymal stromal cells have altered membrane glycerophospholipid composition and functionality. J Lipid Res 2012; 54:622-635. [PMID: 23271708 DOI: 10.1194/jlr.m030650] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Human mesenchymal stem/stromal cells (hMSC) are increasingly used in advanced cellular therapies. The clinical use of hMSCs demands sequential cell expansions. As it is well established that membrane glycerophospholipids (GPL) provide precursors for signaling lipids that modulate cellular functions, we studied the effect of the donor's age and cell doublings on the GPL profile of human bone marrow MSC (hBMSC). The hBMSCs, which were harvested from five young and five old adults, showed clear compositional changes during expansion seen at the level of lipid classes, lipid species, and acyl chains. The ratio of phosphatidylinositol to phosphatidylserine increased toward the late-passage samples. Furthermore, 20:4n-6-containing species of phosphatidylcholine and phosphatidylethanolamine accumulated while the species containing monounsaturated fatty acids (FA) decreased during passaging. Additionally, in the total FA pool of the cells, 20:4n-6 increased, which happened at the expense of n-3 polyunsaturated FAs, especially 22:6n-3. The GPL and FA correlated with the decreased immunosuppressive capacity of hBMSCs during expansion. Our observations were further supported by alterations in the gene expression levels of several enzymes involved in lipid metabolism and immunomodulation. The results show that extensive expansion of hBMSCs harmfully modulates membrane GPLs, affecting lipid signaling and eventually impairing functionality.
Collapse
Affiliation(s)
- Lotta Kilpinen
- Advanced Therapies and Product Development, Finnish Red Cross Blood Service, Helsinki, Finland
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Abstract
Eukaryotes possess seven different phosphoinositides (PIPs) that help form the unique signatures of various intracellular membranes. PIPs serve as docking sites for the recruitment of specific proteins to mediate membrane alterations and integrate various signaling cascades. The spatio-temporal regulation of PI kinases and phosphatases generates distinct intracellular hubs of PIP signaling. Hepatitis C virus (HCV), like other plus-strand RNA viruses, promotes the rearrangement of intracellular membranes to assemble viral replication complexes. HCV stimulates enrichment of phosphatidylinositol 4-phosphate (PI4P) pools near endoplasmic reticulum (ER) sites by activating PI4KIIIα, the kinase responsible for generation of ER-specific PI4P pools. Inhibition of PI4KIIIα abrogates HCV replication. PI4P, the most abundant phosphoinositide, predominantly localizes to the Golgi and plays central roles in Golgi secretory functions by recruiting effector proteins involved in transport vesicle generation. The PI4P effector proteins also include the lipid-transfer and structural proteins such as ceramide transfer protein (CERT), oxysterol binding protein (OSBP) and Golgi phosphoprotein 3 (GOLPH3) that help maintain Golgi-membrane composition and structure. Depletion of Golgi-specific PI4P pools by silencing PI4KIIIβ, expression of dominant negative CERT and OSBP mutants, or silencing GOLPH3 perturb HCV secretion. In this review we highlight the role of PIPs and specifically PI4P in the HCV life cycle.
Collapse
Affiliation(s)
- Bryan Bishé
- Division of Biological Sciences, University of California, San Diego. 9500 Gilman Dr., San Diego, CA, 92093, USA;
- Division of Infectious Diseases, University of California, San Diego. 9500 Gilman Dr., San Diego, CA, 92093, USA;
| | - Gulam Syed
- Division of Infectious Diseases, University of California, San Diego. 9500 Gilman Dr., San Diego, CA, 92093, USA;
| | - Aleem Siddiqui
- Division of Infectious Diseases, University of California, San Diego. 9500 Gilman Dr., San Diego, CA, 92093, USA;
- Author to whom correspondence should be addressed; ; Tel.: +858-822-1750; Fax: +858-822-1749
| |
Collapse
|
16
|
Su K, Sabeva NS, Liu J, Wang Y, Bhatnagar S, van der Westhuyzen DR, Graf GA. The ABCG5 ABCG8 sterol transporter opposes the development of fatty liver disease and loss of glycemic control independently of phytosterol accumulation. J Biol Chem 2012; 287:28564-75. [PMID: 22715101 DOI: 10.1074/jbc.m112.360081] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
ABCG5 and ABCG8 form a complex (G5G8) that opposes the absorption of plant sterols but is also expressed in liver where it promotes the excretion of cholesterol into bile. Hepatic G5G8 is transcriptionally regulated by a number of factors implicated in the development of insulin resistance and nonalcoholic fatty liver disease. Therefore, we hypothesized that G5G8 may influence the development of diet-induced obesity phenotypes independently of its role in opposing phytosterol absorption. G5G8 knock-out (KO) mice and their wild type (WT) littermates were challenged with a plant sterol-free low fat or high fat (HF) diet. Weight gain and the rise in fasting glucose were accelerated in G5G8 KO mice following HF feeding. HF-fed G5G8 KO mice had increased liver weight, hepatic lipids, and plasma alanine aminotransferase compared with WT controls. Consistent with the development of nonalcoholic fatty liver disease, macrophage infiltration, the number of TUNEL-positive cells, and the expression of proinflammatory cytokines were also increased in G5G8 KO mice. Hepatic lipid accumulation was associated with increased peroxisome proliferator activated receptor γ, CD36, and fatty acid uptake. Phosphorylation of eukaryotic translation initiation factor 2α (eiF2α) and expression of activating transcription factor 4 and tribbles 3 were elevated in HF-fed G5G8 KO mice, a pathway that links the unfolded protein response to the development of insulin resistance through inhibition of protein kinase B (Akt) phosphorylation. Phosphorylation of Akt and insulin receptor was reduced, whereas serine phosphorylation of insulin receptor substrate 1 was elevated.
Collapse
Affiliation(s)
- Kai Su
- Department of Pharmaceutical Sciences, University of Kentucky, Lexington, Kentucky 40536, USA
| | | | | | | | | | | | | |
Collapse
|
17
|
Jourdan T, Demizieux L, Gresti J, Djaouti L, Gaba L, Vergès B, Degrace P. Antagonism of peripheral hepatic cannabinoid receptor-1 improves liver lipid metabolism in mice: evidence from cultured explants. Hepatology 2012; 55:790-9. [PMID: 21987372 DOI: 10.1002/hep.24733] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Accepted: 09/26/2011] [Indexed: 12/07/2022]
Abstract
UNLABELLED It is well established that inactivation of the central endocannabinoid system (ECS) through antagonism of cannabinoid receptor 1 (CB1R) reduces food intake and improves several pathological features associated with obesity, such as dyslipidemia and liver steatosis. Nevertheless, recent data indicate that inactivation of peripheral CB1R could also be directly involved in the control of lipid metabolism independently of central CB1R. To further investigate this notion, we tested the direct effect of the specific CB1R antagonist, SR141716, on hepatic carbohydrate and lipid metabolism using cultured liver slices. CB1R messenger RNA expression was strongly decreased by SR141716, whereas it was increased by the CB1R agonist, arachidonic acid N-hydroxyethylamide (AEA), indicating the effectiveness of treatments in modulating ECS activity in liver explants both from lean or ob/ob mice. The measurement of O(2) consumption revealed that SR141716 increased carbohydrate or fatty acid utilization, according to the cellular hormonal environment. In line with this, SR141716 stimulated ß-oxidation activity, and the role of CB1R in regulating this pathway was particularly emphasized when ECS was hyperactivated by AEA and in ob/ob tissue. SR141716 also improved carbohydrate and lipid metabolism, blunting the AEA-induced increase in gene expression of proteins related to lipogenesis. In addition, we showed that SR141716 induced cholesterol de novo synthesis and high-density lipoprotein uptake, revealing a relationship between CB1R and cholesterol metabolism. CONCLUSION These data suggest that blocking hepatic CB1R improves both carbohydrate and lipid metabolism and confirm that peripheral CB1R should be considered as a promising target to reduce cardiometabolic risk in obesity.
Collapse
Affiliation(s)
- Tony Jourdan
- UMR 866 INSERM-UB, Team Physiopathology of Dyslipidemia, Faculty of Sciences, Dijon, France
| | | | | | | | | | | | | |
Collapse
|
18
|
Mechanisms regulating hepatic SR-BI expression and their impact on HDL metabolism. Atherosclerosis 2011; 217:299-307. [DOI: 10.1016/j.atherosclerosis.2011.05.036] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 05/11/2011] [Accepted: 05/26/2011] [Indexed: 11/22/2022]
|
19
|
Hayashi AA, Webb J, Choi J, Baker C, Lino M, Trigatti B, Trajcevski KE, Hawke TJ, Adeli K. Intestinal SR-BI is upregulated in insulin-resistant states and is associated with overproduction of intestinal apoB48-containing lipoproteins. Am J Physiol Gastrointest Liver Physiol 2011; 301:G326-37. [PMID: 21546579 DOI: 10.1152/ajpgi.00425.2010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Intestinal lipid dysregulation is a common feature of insulin-resistant states. The present study investigated alterations in gene expression of key proteins involved in the active absorption of dietary fat and cholesterol in response to development of insulin resistance. Studies were conducted in two diet-induced animal models of insulin resistance: fructose-fed hamster and high-fat-fed mouse. Changes in the mRNA abundance of lipid transporters, adenosine triphosphate cassette (ABC) G5, ABCG8, FA-CoA ligase fatty acid translocase P4, Niemann-Pick C1-Like1 (NPC1L1), fatty acid transport protein 4 (FATP4), and Scavenger Receptor Class B Type I (SR-BI), were assessed in intestinal fragments (duodenum, jejunum, and ileum) using quantitative real-time PCR. Of all the transporters evaluated, SR-B1 showed the most significant changes in both animal models examined. A marked stimulation of SR-B1 expression was observed in all intestinal segments examined in both insulin-resistant animal models. The link between SR-BI expression and intestinal lipoprotein production was then examined in the Caco-2 cell model. SR-B1 overexpression in Caco-2 cells increased apolipoprotein B (apoB) 100 and apoB48 secretion, whereas RNAi knock down of SR-B1 decreased secretion of both apoB100 and apoB48. We also observed changes in subcellular distribution of SR-B1 in response to exogenous lipid and insulin. Confocal microscopy revealed marked changes in SR-BI subcellular distribution in response to both exogenous lipids (oleate) and insulin. In summary, marked stimulation of intestinal SR-BI occurs in vivo in animal models of diet-induced insulin resistance, and modulation of SR-BI in vitro regulates production of apoB-containing lipoprotein particles. We postulate that apical and/or basolateral SR-BI may play an important role in intestinal chylomicron production and may contribute to chylomicron overproduction normally observed in insulin-resistant states.
Collapse
Affiliation(s)
- Amanda A Hayashi
- Molecular Structure & Function, Research Institute, The Hospital for Sick Children, University of Toronto, Canada
| | | | | | | | | | | | | | | | | |
Collapse
|
20
|
Wood P, Mulay V, Darabi M, Chan KC, Heeren J, Pol A, Lambert G, Rye KA, Enrich C, Grewal T. Ras/mitogen-activated protein kinase (MAPK) signaling modulates protein stability and cell surface expression of scavenger receptor SR-BI. J Biol Chem 2011; 286:23077-92. [PMID: 21525007 DOI: 10.1074/jbc.m111.236398] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mitogen-activated protein kinase (MAPK) Erk1/2 has been implicated to modulate the activity of nuclear receptors, including peroxisome proliferator activator receptors (PPARs) and liver X receptor, to alter the ability of cells to export cholesterol. Here, we investigated if the Ras-Raf-Mek-Erk1/2 signaling cascade could affect reverse cholesterol transport via modulation of scavenger receptor class BI (SR-BI) levels. We demonstrate that in Chinese hamster ovary (CHO) and human embryonic kidney (HEK293) cells, Mek1/2 inhibition reduces PPARα-inducible SR-BI protein expression and activity, as judged by reduced efflux onto high density lipoprotein (HDL). Ectopic expression of constitutively active H-Ras and Mek1 increases SR-BI protein levels, which correlates with elevated PPARα Ser-21 phosphorylation and increased cholesterol efflux. In contrast, SR-BI levels are insensitive to Mek1/2 inhibitors in PPARα-depleted cells. Most strikingly, Mek1/2 inhibition promotes SR-BI degradation in SR-BI-overexpressing CHO cells and human HuH7 hepatocytes, which is associated with reduced uptake of radiolabeled and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyane-labeled HDL. Loss of Mek1/2 kinase activity reduces SR-BI expression in the presence of bafilomycin, an inhibitor of lysosomal degradation, indicating down-regulation of SR-BI via proteasomal pathways. In conclusion, Mek1/2 inhibition enhances the PPARα-dependent degradation of SR-BI in hepatocytes.
Collapse
Affiliation(s)
- Peta Wood
- Faculty of Pharmacy, University of Sydney, Sydney, New South Wales 2006, Australia
| | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Ji A, Meyer JM, Cai L, Akinmusire A, de Beer MC, Webb NR, van der Westhuyzen DR. Scavenger receptor SR-BI in macrophage lipid metabolism. Atherosclerosis 2011; 217:106-12. [PMID: 21481393 DOI: 10.1016/j.atherosclerosis.2011.03.017] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 03/07/2011] [Accepted: 03/11/2011] [Indexed: 12/15/2022]
Abstract
OBJECTIVE To investigate the mechanisms by which macrophage scavenger receptor BI (SR-BI) regulates macrophage cholesterol homeostasis and protects against atherosclerosis. METHODS AND RESULTS The expression and function of SR-BI was investigated in cultured mouse bone marrow-derived macrophages (BMM). SR-BI, the other scavenger receptors SRA and CD36 and the ATP-binding cassette transporters ABCA1 and ABCG1 were each distinctly regulated during BMM differentiation. SR-BI levels increased transiently to significant levels during culture. SR-BI expression in BMM was reversibly down-regulated by lipid loading with modified LDL; SR-BI was shown to be present both on the cell surface as well as intracellularly. BMM exhibited selective HDL CE uptake, however, this was not dependent on SR-BI or another potential candidate glycosylphosphatidylinositol anchored high density lipoprotein binding protein 1 (GPIHBP1). SR-BI played a significant role in facilitating bidirectional cholesterol flux in non lipid-loaded cells. SR-BI expression enhanced both cell cholesterol efflux and cholesterol influx from HDL, but did not lead to altered cellular cholesterol mass. SR-BI-dependent efflux occurred to larger HDL particles but not to smaller HDL(3). Following cholesterol loading, ABCA1 and ABCG1 were up-regulated and served as the major contributors to cholesterol efflux, while SR-BI expression was down-regulated. CONCLUSION Our results suggest that SR-BI plays a significant role in macrophage cholesterol flux that may partly account for its effects on atherogenesis.
Collapse
Affiliation(s)
- Ailing Ji
- Department of Internal Medicine, University of Kentucky, Lexington, KY 40536, USA.
| | | | | | | | | | | | | |
Collapse
|
22
|
Modulators of Protein Kinase C Affect SR-BI-Dependent HDL Lipid Uptake in Transfected HepG2 Cells. CHOLESTEROL 2011; 2011:687939. [PMID: 21490774 PMCID: PMC3065880 DOI: 10.1155/2011/687939] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 12/02/2010] [Indexed: 11/17/2022]
Abstract
SR-BI is a cell surface HDL receptor that mediates selective uptake of the lipid cargo of HDL, an important process in hepatocytes, driving reverse cholesterol transport from cells in the artery wall. To facilitate examination of factors that modulate SR-BI activity in hepatocytes, we have generated fluorescent protein-tagged versions of SR-BI that allow for facile monitoring of SR-BI protein levels and distribution in transfected cells. We show that deletion of the C-terminal cytosolic tail does not affect the distribution of SR-BI in HepG2 cells, nor is the C-terminal cytosolic tail required for SR-BI-mediated uptake of HDL lipids. We also demonstrate that the phorbol ester, PMA, increased, while protein kinase C inhibitors reduced SR-BI-mediated HDL lipid uptake in HepG2 cells. These data suggest that protein kinase C may modulate selective uptake of HDL lipids including cholesterol in hepatocytes, thereby influencing hepatic HDL cholesterol clearance and reverse cholesterol transport.
Collapse
|
23
|
Perez-Tilve D, Hofmann SM, Basford J, Nogueiras R, Pfluger PT, Patterson JT, Grant E, Wilson-Perez HE, Granholm NA, Arnold M, Trevaskis JL, Butler AA, Davidson WS, Woods SC, Benoit SC, Sleeman MW, DiMarchi RD, Hui DY, Tschöp MH. Melanocortin signaling in the CNS directly regulates circulating cholesterol. Nat Neurosci 2010; 13:877-82. [PMID: 20526334 DOI: 10.1038/nn.2569] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2010] [Accepted: 04/28/2010] [Indexed: 01/02/2023]
Abstract
Cholesterol circulates in the blood in association with triglycerides and other lipids, and elevated blood low-density lipoprotein cholesterol carries a risk for metabolic and cardiovascular disorders, whereas high-density lipoprotein (HDL) cholesterol in the blood is thought to be beneficial. Circulating cholesterol is the balance among dietary cholesterol absorption, hepatic synthesis and secretion, and the metabolism of lipoproteins by various tissues. We found that the CNS is also an important regulator of cholesterol in rodents. Inhibiting the brain's melanocortin system by pharmacological, genetic or endocrine mechanisms increased circulating HDL cholesterol by reducing its uptake by the liver independent of food intake or body weight. Our data suggest that a neural circuit in the brain is directly involved in the control of cholesterol metabolism by the liver.
Collapse
Affiliation(s)
- Diego Perez-Tilve
- Metabolic Diseases Institute, Division of Endocrinology, Department of Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Abstract
PURPOSE OF REVIEW Remnant lipoproteins that persist in the bloodstream after each meal have become increasingly important contributors to atherosclerotic vascular disease, owing to the spread of overnutrition, underexertion, obesity, insulin resistance, and type 2 diabetes. Here, we review recent work that clarified long-standing controversies over the molecular mediators of remnant clearance by the liver, as well as their dysregulation - but possible correction - during alterations in caloric balance. RECENT FINDINGS Two endocytic receptors, the syndecan-1 heparan sulfate proteoglycan (HSPG) and the LDL receptor, plus one docking receptor, SR-BI, significantly contribute to normal hepatic remnant catabolism. Compelling evidence exists for dysfunction of the syndecan-1 HSPG in diabetic states. The major molecular defect identified so far in poorly controlled type 1 diabetes is impaired hepatic HSPG assembly. In contrast, the primary defect in hepatic HSPGs in type 2 diabetes appears to arise from accelerated de-sulfation, owing to the induction of a sulfatase. Moreover, short-term caloric restriction restores hepatic expression of this sulfatase towards normal. SUMMARY Correct identification of hepatic remnant receptors has finally allowed investigations of their molecular dysregulation in diabetes and related conditions. New work points to novel therapeutic targets to correct postprandial dyslipoproteinemia and its consequent arterial damage.
Collapse
Affiliation(s)
- Kevin Jon Williams
- Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
| | | |
Collapse
|
25
|
Adachi H, Tsujimoto M. Adaptor protein sorting nexin 17 interacts with the scavenger receptor FEEL-1/stabilin-1 and modulates its expression on the cell surface. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:553-63. [PMID: 20226821 DOI: 10.1016/j.bbamcr.2010.02.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Revised: 02/23/2010] [Accepted: 02/25/2010] [Indexed: 11/28/2022]
Abstract
The scavenger receptor FEEL-1/stabilin-1 is known as the marker of alternatively activated macrophage and sinusoidal endothelial cell. FEEL-1/stabilin-1 is a multifunctional transmembrane glycoprotein that is implicated in bacterial infection, diabetes, atherosclerosis, wound healing, and innate immunity. In the current study, we have identified the phox-homology domain containing protein SNX17 as a novel interaction partner of FEEL-1/stabilin-1 in endothelial cells. SNX17 directly interacts with FEEL-1/stabilin-1 and regulates its trafficking. Studies using the cytoplasmic domain of truncated or mutant FEEL-1/stabilin-1 suggest that the NPxF motif of the FEEL-1/stabilin-1 cytoplasmic tail is required for its interaction with SNX17. By transfecting cells with small interfering RNA targeting SNX17, total cellular FEEL-1/stabilin-1 expression and FEEL-1/stabilin-1-mediated ligand uptake were significantly decreased due to the enhancement of FEEL-1/stabilin-1 protein degradation. Our results identify SNX17 as a novel interaction partner of FEEL-1/stabilin-1 in endothelial cells.
Collapse
Affiliation(s)
- Hideki Adachi
- Laboratory of Cellular Biochemistry, RIKEN, Saitama 351-0198, Japan.
| | | |
Collapse
|
26
|
Cholewa J, Nikolic D, Post SR. Regulation of class A scavenger receptor-mediated cell adhesion and surface localization by PI3K: identification of a regulatory cytoplasmic motif. J Leukoc Biol 2009; 87:443-9. [PMID: 19952357 DOI: 10.1189/jlb.0509318] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The importance of cytoplasmic motifs in differentially regulating SR-A function was demonstrated by deleting the first 49 cytoplasmic aa (SR-A(Delta1-49)), which abolished SR-A-mediated ligand internalization without reducing cell adhesion. To identify additional cytoplasmic motifs within the first 49 aa that regulate SR-A function, the acidic residues in a conserved motif (EDAD) were changed to their amide derivatives (SR-A(QNAN)). The function and regulation of SR-A(QNAN) were compared with that of SR-A(Delta1-49) and SR-A in transfected HEK-293 cells. Blocking PI3K activation inhibited SR-A, but not SR-A(Delta1-49)- or SR-A(QNAN)-mediated cell adhesion. Although deleting (SR-A(Delta1-49)) or mutating (SR-A(QNAN)) the EDAD motif abolished the PI3K sensitivity of SR-A-mediated cell adhesion, these mutations did not affect ligand internalization or PI3K activation during cell adhesion. To define the mechanism by which PI3K regulates SR-A-mediated cell adhesion, the cellular localization of wild-type and mutant SR-A was examined. PI3K inhibition reduced surface localization of SR-A but not of SR-A(Delta1-49) or SR-A(QNAN). The regulation of SR-A surface localization by PI3K was confirmed in peritoneal macrophages, which endogenously express SR-A. Together, these results suggest a pathway in which SR-A binding to an immobilized ligand activates PI3K to recruit more receptor to the plasma membrane and enhances cell adhesion.
Collapse
Affiliation(s)
- Jill Cholewa
- Graduate Center for Nutritional Sciences, The University of Kentucky, Lexington, Kentucky, USA
| | | | | |
Collapse
|
27
|
Kim SI, Shin D, Lee H, Ahn BY, Yoon Y, Kim M. Targeted delivery of siRNA against hepatitis C virus by apolipoprotein A-I-bound cationic liposomes. J Hepatol 2009; 50:479-88. [PMID: 19155084 DOI: 10.1016/j.jhep.2008.10.029] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Revised: 10/20/2008] [Accepted: 10/21/2008] [Indexed: 12/04/2022]
Abstract
BACKGROUND/AIMS Hepatitis C virus (HCV) is one of the major human hepatic RNA viruses. Recently, we developed a liver-specific siRNA delivery technology using DTC-Apo composed of cationic liposomes (DTC) and apolipoprotein A-I (apo A-I). Here, we investigated whether DTC-Apo nanoparticles can systemically deliver siRNA into mouse hepatocytes expressing HCV proteins and inhibit their expression efficiently. METHODS A transient HCV model was constructed by hydrodynamic injection of plasmid DNA expressing viral structural proteins under hepatic control region and alpha1-antitrypsin promoter elements. Using this model, DTC-Apo containing HCV-core-specific siRNA was intravenously injected to assess antiviral activity as well as the duration of silencing. RESULTS Post-administration of DTC-Apo/HCV-specific siRNA at a dose of 2mg siRNA/kg inhibited viral gene expression by 65-75% in the liver on day 2. Improved activity (95% knockdown on day 2) without immunotoxicity was obtained by 2'-OMe-modification at two U sequences on its sense strand. Notably, the gene silencing effect of the modified siRNA was still maintained at day 6, while the unmodified one lost RNAi activity after day 4. CONCLUSIONS Our results suggest that DTC-Apo liposome is a highly potential delivery vehicle to transfer therapeutic siRNA especially targeting HCV to the liver.
Collapse
Affiliation(s)
- Soo In Kim
- Virus Research Laboratory, Mogam Biotechnology Research Institute, Giheung-Gu, Gyeonggi-Do, South Korea
| | | | | | | | | | | |
Collapse
|
28
|
Robichaud JC, Francis GA, Vance DE. A role for hepatic scavenger receptor class B, type I in decreasing high density lipoprotein levels in mice that lack phosphatidylethanolamine N-methyltransferase. J Biol Chem 2008; 283:35496-506. [PMID: 18842588 DOI: 10.1074/jbc.m807433200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Phosphatidylethanolamine N-methyltransferase (PEMT) is a liver-specific enzyme that converts phosphatidylethanolamine to phosphatidylcholine (PC). Mice that lack PEMT have reduced plasma levels of PC and cholesterol in high density lipoproteins (HDL). We have investigated the mechanism responsible for this reduction with experiments designed to distinguish between a decreased formation of HDL particles by hepatocytes or an increased hepatic uptake of HDL lipids. Therefore, we analyzed lipid efflux to apoA-I and HDL lipid uptake using primary cultured hepatocytes isolated from Pemt(+/+) and Pemt(-/-) mice. Hepatic levels of the ATP-binding cassette transporter A1 are not significantly different between Pemt genotypes. Moreover, hepatocytes isolated from Pemt(-/-) mice released cholesterol and PC into the medium as efficiently as did hepatocytes from Pemt(+/+) mice. Immunoblotting of liver homogenates showed a 1.5-fold increase in the amount of the scavenger receptor, class B, type 1 (SR-BI) in Pemt(-/-) compared with Pemt(+/+) livers. In addition, there was a 1.5-fold increase in the SR-BI-interacting protein PDZK1. Lipid uptake experiments using radiolabeled HDL particles revealed a greater uptake of [(3)H]cholesteryl ethers and [(3)H]PC by hepatocytes derived from Pemt(-/-) compared with Pemt(+/+) mice. Furthermore, we observed an increased association of [(3)H]cholesteryl ethers in livers of Pemt(-/-) compared with Pemt(+/+) mice after tail vein injection of [(3)H]HDL. These results strongly suggest that PEMT is involved in the regulation of plasma HDL levels in mice, mainly via HDL lipid uptake by SR-BI.
Collapse
Affiliation(s)
- Julie C Robichaud
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
| | | | | |
Collapse
|
29
|
Abstract
The origins of cholesterol utilized by intestinal ABCA1 were investigated in the human intestinal cell line Caco-2. Influx of apical membrane cholesterol increases ABCA1 mRNA and mass, resulting in enhanced efflux of HDL-cholesterol. Luminal (micellar) cholesterol and newly synthesized cholesterol are not transported directly to ABCA1 but reach the ABCA1 pool after incorporation into the apical membrane. Depleting the apical or the basolateral membrane of cholesterol by cyclodextrin attenuates the amount of cholesterol transported by ABCA1 without altering ABCA1 expression. Filipin added to the apical side but not the basal side attenuates ABCA1-mediated cholesterol efflux, suggesting that apical membrane "microdomains," or rafts, supply cholesterol for HDL. Preventing cholesterol esterification increases the amount of cholesterol available for HDL. Ezetimibe, a Niemann-Pick C1-like 1 protein inhibitor, does not alter ABCA1-mediated cholesterol efflux. U18666A and imipramine, agents that mimic cholesterol trafficking defects of Neimann-Pick type C disease, attenuate cholesterol efflux without altering ABCA1 expression; thus, intestinal NPC1 may facilitate cholesterol movement to ABCA1. ABCA1-mediated cholesterol efflux is independent of cholesterol synthesis. The results suggest that following incorporation into plasma membrane and rafts of the apical membrane, dietary/biliary and newly synthesized cholesterol contribute to the ABCA1 pool and HDL-cholesterol. NPC1 may have a role in this process.
Collapse
Affiliation(s)
- F Jeffrey Field
- Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA.
| | | | | |
Collapse
|
30
|
Ashraf MZ, Kar NS, Chen X, Choi J, Salomon RG, Febbraio M, Podrez EA. Specific oxidized phospholipids inhibit scavenger receptor bi-mediated selective uptake of cholesteryl esters. J Biol Chem 2008; 283:10408-14. [PMID: 18285332 DOI: 10.1074/jbc.m710474200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have recently demonstrated that specific oxidized phospholipids (oxPC(CD36)) accumulate at sites of oxidative stress in vivo such as within atherosclerotic lesions, hyperlipidemic plasma, and plasma with low high-density lipoprotein levels. oxPC(CD36) serve as high affinity ligands for the scavenger receptor CD36, mediate uptake of oxidized low density lipoprotein by macrophages, and promote a pro-thrombotic state via platelet scavenger receptor CD36. We now report that oxPC(CD36) represent ligands for another member of the scavenger receptor class B, type I (SR-BI). oxPC(CD36) prevent binding to SR-BI of its physiological ligand, high density lipoprotein, because of the close proximity of the binding sites for these two ligands on SR-BI. Furthermore, oxPC(CD36) interfere with SR-BI-mediated selective uptake of cholesteryl esters in hepatocytes. Thus, oxidative stress and accumulation of specific oxidized phospholipids in plasma may have an inhibitory effect on reverse cholesterol transport.
Collapse
Affiliation(s)
- Mohammad Z Ashraf
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA
| | | | | | | | | | | | | |
Collapse
|
31
|
Murao K, Yu X, Imachi H, Cao WM, Chen K, Matsumoto K, Nishiuchi T, Wong NCW, Ishida T. Hyperglycemia suppresses hepatic scavenger receptor class B type I expression. Am J Physiol Endocrinol Metab 2008; 294:E78-87. [PMID: 17957039 DOI: 10.1152/ajpendo.00023.2007] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Hyperglycemia is a major risk factor for atherosclerotic disease. Hepatic scavenger receptor class B type I (SR-BI) binds HDL particles that mediate reverse cholesterol transport and thus lowers the risk of atherosclerosis. Here we examined glucose regulation of SR-BI gene expression in both HepG2 cells and whole animals. Results showed that hepatic SR-BI mRNA, protein, and uptake of cholesterol from HDL were halved following 48 h of exposure to 22.4 vs. 5.6 mM glucose. As in the case of the cell culture model, hepatic expression of SR-BI was lower in diabetic rats than in euglycemic rats. Transcriptional activity of the human SR-BI promoter paralleled endogenous expression of the gene, and this activity was dependent upon the dose of glucose. Next, we used inhibitors of select signal transduction pathways to demonstrate that glucose suppression of SR-BI was sensitive to the p38 MAPK inhibitor. Expression of a constitutively active p38 MAPK inhibited SR-BI promoter activity in the presence or absence of glucose. A dominant-negative p38 MAPK abolished the inhibitory effect of glucose on promoter activity. Deletional analysis located a 50-bp fragment of the promoter that mediated the effects of glucose. Within this DNA fragment there were several specificity protein-1 (Sp1) binding sites, and cellular knockdown of Sp1 abrogated its suppression by glucose. Together, these results indicate that the glucose suppression of SR-B1 expression is partially mediated by the activation of the p38 MAPK-Sp1 pathway and raise the possibility that the inhibition of hepatic SR-BI expression under high-glucose conditions provides a mechanism for accelerated atherosclerosis in diabetics.
Collapse
Affiliation(s)
- Koji Murao
- Div. of Endocrinology and Metabolism, Dept. of Internal Medicine, Faculty of Medicine, Kagawa University, 1750-1, Miki-cho, Kita-gun, Kagawa, 761-0793, Japan.
| | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Zhang Y, Ahmed AM, Tran TL, Lin J, McFarlane N, Boreham DR, Igdoura SA, Truant R, Trigatti BL. The inhibition of endocytosis affects HDL-lipid uptake mediated by the human scavenger receptor class B type I. Mol Membr Biol 2007; 24:442-54. [PMID: 17710648 DOI: 10.1080/09687680701300410] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The scavenger receptor SR-BI plays an important role in the hepatic clearance of HDL cholesterol and other lipids, driving reverse cholesterol transport and contributing to protection against atherosclerosis in mouse models. We characterized the role of endocytosis in lipid uptake from HDL, mediated by the human SR-BI, using a variety of approaches to inhibit endocytosis, including hypertonic shock, potassium or energy depletion and disassembly of the actin cytoskeleton. Our studies revealed that unlike mouse SR-BI, human SR-BI-mediated HDL-lipid uptake was reduced by inhibition of endocytosis. This was not dependent on the cytoplasmic C-terminus of SR-BI. Monitoring the uptake of both the protein and lipid components of HDL revealed that although overall lipid uptake was decreased, the degree of selective lipid uptake was increased. These data suggest that that endocytosis is a dynamic regulator of SR-BI's selective lipid uptake activity.
Collapse
Affiliation(s)
- Yi Zhang
- Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada
| | | | | | | | | | | | | | | | | |
Collapse
|
33
|
Saraswathi V, Gao L, Morrow JD, Chait A, Niswender KD, Hasty AH. Fish oil increases cholesterol storage in white adipose tissue with concomitant decreases in inflammation, hepatic steatosis, and atherosclerosis in mice. J Nutr 2007; 137:1776-82. [PMID: 17585030 DOI: 10.1093/jn/137.7.1776] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Although fish oil has hypolipidemic and antiatherosclerotic properties, the potential for white adipose tissue (WAT) to mediate these effects has not been studied. LDL-receptor deficient (LDLR-/-) mice were fed high fat, olive oil-containing diets supplemented with additional olive oil or with fish oil for 12 wk. Fish oil feeding significantly reduced plasma lipid levels. In contrast, lipid storage in WAT was increased in fish oil-fed mice as evidenced by increased total fat (P < 0.05) and perigonadal WAT mass (P < 0.05), increased cholesterol storage (P < 0.001), and adipocyte hypertrophy. Despite increased adipose tissue mass, WAT-specific inflammation and insulin sensitivity were improved (P < 0.05), concomitant with reduced macrophage infiltration. Furthermore, fish oil increased WAT and plasma levels of adiponectin. In addition, fish oil feeding decreased the formation of proinflammatory F2- isoprostanes, markers of oxidative stress (P < 0.05). The increased WAT lipid storage in fish oil-fed mice was associated with reduced lipid accumulation in liver (P < 0.05) and decreased atherosclerotic lesion area (P < 0.05). Taken together, these data highlight the specific role of WAT in regulating dietary fish oil-mediated improvement in systemic lipid homeostasis and atherosclerosis.
Collapse
Affiliation(s)
- Viswanathan Saraswathi
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | | | | | | | | | | |
Collapse
|
34
|
Orlowski S, Coméra C, Tercé F, Collet X. Lipid rafts: dream or reality for cholesterol transporters? EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:869-85. [PMID: 17576551 DOI: 10.1007/s00249-007-0193-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Revised: 05/11/2007] [Accepted: 05/15/2007] [Indexed: 01/12/2023]
Abstract
As a key constituent of the cell membranes, cholesterol is an endogenous component of mammalian cells of primary importance, and is thus subjected to highly regulated homeostasis at the cellular level as well as at the level of the whole body. This regulation requires adapted mechanisms favoring the handling of cholesterol in aqueous compartments, as well as its transfer into or out of membranes, involving membrane proteins. A membrane exhibits functional properties largely depending on its lipid composition and on its structural organization, which very often involves cholesterol-rich microdomains. Then there is the appealing possibility that cholesterol may regulate its own transmembrane transport at a purely functional level, independently of any transcriptional regulation based on cholesterol-sensitive nuclear factors controling the expression level of lipid transport proteins. Indeed, the main cholesterol "transporters" presently believed to mediate for instance the intestinal absorption of cholesterol, that are SR-BI, NPC1L1, ABCA1, ABCG1, ABCG5/G8 and even P-glycoprotein, all present privileged functional relationships with membrane cholesterol-containing microdomains. In particular, they all more or less clearly induce membrane disorganization, supposed to facilitate cholesterol exchanges with the close aqueous medium. The actual lipid substrates handled by these transporters are not yet unambiguously determined, but they likely concern the components of membrane microdomains. Conversely, raft alterations may provide specific modulations of the transporter activities, as well as they can induce indirect effects via local perturbations of the membrane. Finally, these cholesterol transporters undergo regulated intracellular trafficking, with presumably some relationships to rafts which remain to be clarified.
Collapse
Affiliation(s)
- Stéphane Orlowski
- SB2SM/IBTS and URA 2096 CNRS, CEA, Centre de Saclay, 91191, Gif-sur-Yvette cedex, France.
| | | | | | | |
Collapse
|
35
|
Yvan-Charvet L, Bobard A, Bossard P, Massiéra F, Rousset X, Ailhaud G, Teboul M, Ferré P, Dagher G, Quignard-Boulangé A. In vivo evidence for a role of adipose tissue SR-BI in the nutritional and hormonal regulation of adiposity and cholesterol homeostasis. Arterioscler Thromb Vasc Biol 2007; 27:1340-5. [PMID: 17363694 DOI: 10.1161/atvbaha.106.136382] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVES This study examines the role of insulin and angiotensin II in high-density lipoprotein (HDL) metabolism by focusing on the regulation and function of scavenger receptor type-BI (SR-BI) in adipose tissue. METHODS AND RESULTS Insulin or angiotensin II injection in wild-type mice induced a decrease in circulating HDL and it was associated with the translocation of SR-BI from intracellular sites to the plasma membrane of adipose tissue. Refeeding upregulated adipose HDL selective cholesteryl esters uptake and SR-BI proteins through transcriptional and posttranscriptional mechanisms. This occurred along with a decrease in serum HDL and an increase in adipose cholesterol content. Similar results were obtained with transgenic mice overexpressing locally angiotensinogen in adipose tissue. In adipose 3T3-L1 cell line, HDL induced lipogenesis by increasing liver X receptor binding activity. This mechanism was dependent of insulin and angiotensin II. CONCLUSIONS Our results raise the possibility that adipose tissue SR-BI translocation might be a link between adipose tissue lipid storage and HDL clearance.
Collapse
|