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Kentala H, Weber-Boyvat M, Olkkonen VM. OSBP-Related Protein Family: Mediators of Lipid Transport and Signaling at Membrane Contact Sites. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 321:299-340. [PMID: 26811291 DOI: 10.1016/bs.ircmb.2015.09.006] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Oxysterol-binding protein (OSBP) and its related protein homologs, ORPs, constitute a conserved family of lipid-binding/transfer proteins (LTPs) expressed ubiquitously in eukaryotes. The ligand-binding domain of ORPs accommodates cholesterol and oxysterols, but also glycerophospholipids, particularly phosphatidylinositol-4-phosphate (PI4P). ORPs have been implicated as intracellular lipid sensors or transporters. Most ORPs carry targeting determinants for the endoplasmic reticulum (ER) and non-ER organelle membrane. ORPs are located and function at membrane contact sites (MCSs), at which ER is closely apposed with other organelle limiting membranes. Such sites have roles in lipid transport and metabolism, control of Ca(2+) fluxes, and signaling events. ORPs are postulated either to transport lipids over MCSs to maintain the distinct lipid compositions of organelle membranes, or to control the activity of enzymes/protein complexes with functions in signaling and lipid metabolism. ORPs may transfer PI4P and another lipid class bidirectionally. Transport of PI4P followed by its hydrolysis would in this model provide the energy for transfer of the other lipid against its concentration gradient. Control of organelle lipid compositions by OSBP/ORPs is important for the life cycles of several pathogenic viruses. Targeting ORPs with small-molecular antagonists is proposed as a new strategy to combat viral infections. Several ORPs are reported to modulate vesicle transport along the secretory or endocytic pathways. Moreover, antagonists of certain ORPs inhibit cancer cell proliferation. Thus, ORPs are LTPs, which mediate interorganelle lipid transport and coordinate lipid signals with a variety of cellular regimes.
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Affiliation(s)
- Henriikka Kentala
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland
| | - Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland
| | - Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland
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Olkkonen VM. OSBP-Related Protein Family in Lipid Transport Over Membrane Contact Sites. Lipid Insights 2015; 8:1-9. [PMID: 26715851 PMCID: PMC4685180 DOI: 10.4137/lpi.s31726] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/03/2015] [Accepted: 09/06/2015] [Indexed: 12/12/2022] Open
Abstract
Increasing evidence suggests that oxysterol-binding protein-related proteins (ORPs) localize at membrane contact sites, which are high-capacity platforms for inter-organelle exchange of small molecules and information. ORPs can simultaneously associate with the two apposed membranes and transfer lipids across the interbilayer gap. Oxysterol-binding protein moves cholesterol from the endoplasmic reticulum to trans-Golgi, driven by the retrograde transport of phosphatidylinositol-4-phosphate (PI4P). Analogously, yeast Osh6p mediates the transport of phosphatidylserine from the endoplasmic reticulum to the plasma membrane in exchange for PI4P, and ORP5 and -8 are suggested to execute similar functions in mammalian cells. ORPs may share the capacity to bind PI4P within their ligand-binding domain, prompting the hypothesis that bidirectional transport of a phosphoinositide and another lipid may be a common theme among the protein family. This model, however, needs more experimental support and does not exclude a function of ORPs in lipid signaling.
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Affiliation(s)
- Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland. ; Department of Anatomy, Faculty of Medicine, University of Helsinki, Finland
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Gadella BM, Boerke A. An update on post-ejaculatory remodeling of the sperm surface before mammalian fertilization. Theriogenology 2015; 85:113-24. [PMID: 26320574 DOI: 10.1016/j.theriogenology.2015.07.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Revised: 07/07/2015] [Accepted: 07/12/2015] [Indexed: 11/17/2022]
Abstract
The fusion of a sperm with an oocyte to form new life is a highly regulated event. The activation-also termed capacitation-of the sperm cell is one of the key preparative steps required for this process. Ejaculated sperm has to make a journey through the female uterus and oviduct before it can approach the oocyte. The oocyte at that moment also has become prepared to facilitate monospermic fertilization and block immediately thereafter the chance for polyspermic fertilization. Interestingly, ejaculated sperm is not properly capacitated and consequently is not yet able to fertilize the oocyte. During the capacitation process, the formation of competent lipid-protein domains on the sperm head enables sperm-cumulus and zona pellucida interactions. This sperm binding allows the onset for a cascade reaction ultimately resulting in oocyte-sperm fusion. Many different lipids and proteins from the sperm surface are involved in this process. Sperm surface processing already starts when sperm are liberated from the seminiferous tubules and is followed by epididymal maturation where the sperm cell surface is modified and loaded with proteins to ensure it is prepared for its fertilization task. Although cauda epididymal sperm can fertilize the oocyte IVF, they are coated with so-called decapacitation factors during ejaculation. The seminal plasma-induced stabilization of the sperm surface permits the sperm transit through the cervix and uterus but prevents sperm capacitation and thus inhibits fertilization. For IVF purposes, sperm are washed out of seminal plasma and activated to get rid of decapacitation factors. Only after capacitation, the sperm can fertilize the oocyte. In recent years, IVF has become a widely used tool to achieve successful fertilization in both the veterinary field and human medicine. Although IVF procedures are very successful, scientific knowledge is still far from complete when identifying all the molecular players and processes during the first stages the fusion of two gametes into a new life. A concise overview in the current understanding of the process of capacitation and the sperm surface changes is provided. The gaps in knowledge of these prefertilization processes are critically discussed.
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Affiliation(s)
- B M Gadella
- Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, The Netherlands; Department of Biochemistry & Cell Biology, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
| | - A Boerke
- Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, The Netherlands; Department of Biochemistry & Cell Biology, Faculty of Veterinary Medicine, Utrecht University, The Netherlands
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Kentala H, Pfisterer SG, Olkkonen VM, Weber-Boyvat M. Sterol liganding of OSBP-related proteins (ORPs) regulates the subcellular distribution of ORP-VAPA complexes and their impacts on organelle structure. Steroids 2015; 99:248-58. [PMID: 25681634 DOI: 10.1016/j.steroids.2015.01.027] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 01/21/2015] [Accepted: 01/22/2015] [Indexed: 01/20/2023]
Abstract
Oxysterol-binding protein (OSBP) and its homologues (ORPs) are lipid-binding/transfer proteins with affinity for oxysterols, cholesterol and glycerophospholipids. In addition to a ligand-binding domain, a majority of the ORPs carry a pleckstrin homology domain that targets organelle membranes via phosphoinositides, and a motif targeting the endoplasmic reticulum (ER) via VAMP-associated proteins (VAPs). We employed here Bimolecular Fluorescence Complementation (BiFC) to systematically assess the effects of sterol manipulation of HuH7 cells on complexes of established sterol-binding ORPs with their ER receptor, VAMP-associated protein A (VAPA). Depletion of cellular cholesterol with lipoprotein-deficient medium and Mevastatin caused concentration of OSBP-VAPA complexes and Golgi complex markers at a juxtanuclear position, an effect reversed by low-density lipoprotein treatment. A similar redistribution of OSBP-VAPA but not of sterol-binding deficient mutant OSBP(ΔELSK)-VAPA, occurred upon treatment with the high-affinity ligand, 25-hydroxycholesterol (25OHC), which reduced total and free cholesterol. ORP2-VAPA complexes, which localize in untreated cells at blob-like ER structures with associated lipid droplets, were redistributed upon treatment with the ORP2 ligand 22(R)OHC to a diffuse cytoplasmic/ER pattern and the plasma membrane. Analogously, distribution of ORP4L-VAPA complexes between the plasma membrane and vimentin intermediate filament associated compartments was modified by statin or 25OHC treatment. The treatments resulted in loss of vimentin co-localization, and sterol-binding deficient ORP4L(ΔELSR)-VAPA localized predominantly to the plasma membrane. In conclusion, treatment with statin or oxysterol ligands modify the subcellular targeting of ORP-VAPA complexes, consistent with the notion that this machinery controls lipid homeostasis and signaling at organelle interfaces.
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Affiliation(s)
- Henriikka Kentala
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
| | - Simon G Pfisterer
- Institute of Biomedicine, Anatomy, FI-00014 University of Helsinki, Finland
| | - Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland; Institute of Biomedicine, Anatomy, FI-00014 University of Helsinki, Finland
| | - Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland.
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Weber-Boyvat M, Kentala H, Peränen J, Olkkonen VM. Ligand-dependent localization and function of ORP-VAP complexes at membrane contact sites. Cell Mol Life Sci 2015; 72:1967-87. [PMID: 25420878 PMCID: PMC11114005 DOI: 10.1007/s00018-014-1786-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 10/17/2014] [Accepted: 11/17/2014] [Indexed: 01/08/2023]
Abstract
Oxysterol-binding protein/OSBP-related proteins (ORPs) constitute a conserved family of sterol/phospholipid-binding proteins with lipid transporter or sensor functions. We investigated the spatial occurrence and regulation of the interactions of human OSBP/ORPs or the S. cerevisiae orthologs, the Osh (OSBP homolog) proteins, with their endoplasmic reticulum (ER) anchors, the VAMP-associated proteins (VAPs), by employing bimolecular fluorescence complementation and pull-down set-ups. The ORP-VAP interactions localize frequently at distinct subcellular sites, shown in several cases to represent membrane contact sites (MCSs). Using established ORP ligand-binding domain mutants and pull-down assays with recombinant proteins, we show that ORP liganding regulates the ORP-VAP association, alters the subcellular targeting of ORP-VAP complexes, or modifies organelle morphology. There is distinct protein specificity in the effects of the mutants on subcellular targeting of ORP-VAP complexes. We provide evidence that complexes of human ORP2 and VAPs at ER-lipid droplet interfaces regulate the hydrolysis of triglycerides and lipid droplet turnover. The data suggest evolutionarily conserved, complex ligand-dependent functions of ORP-VAP complexes at MCSs, with implications for cellular lipid homeostasis and signaling.
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Affiliation(s)
- Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Henriikka Kentala
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Johan Peränen
- Cell and Molecular Biology Program, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, Tukholmankatu 8, 00290 Helsinki, Finland
- Institute of Biomedicine, Anatomy, University of Helsinki, 00014 Helsinki, Finland
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Rhinovirus uses a phosphatidylinositol 4-phosphate/cholesterol counter-current for the formation of replication compartments at the ER-Golgi interface. Cell Host Microbe 2014; 16:677-90. [PMID: 25525797 DOI: 10.1016/j.chom.2014.10.003] [Citation(s) in RCA: 163] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 08/19/2014] [Accepted: 09/23/2014] [Indexed: 12/19/2022]
Abstract
Similar to other positive-strand RNA viruses, rhinovirus, the causative agent of the common cold, replicates on a web of cytoplasmic membranes, orchestrated by host proteins and lipids. The host pathways that facilitate the formation and function of the replication membranes and complexes are poorly understood. We show that rhinovirus replication depends on host factors driving phosphatidylinositol 4-phosphate (PI4P)-cholesterol counter-currents at viral replication membranes. Depending on the virus type, replication required phosphatidylinositol 4-kinase class 3beta (PI4K3b), cholesteryl-esterase hormone-sensitive lipase (HSL) or oxysterol-binding protein (OSBP)-like 1, 2, 5, 9, or 11 associated with lipid droplets, endosomes, or Golgi. Replication invariably required OSBP1, which shuttles cholesterol and PI4P between ER and Golgi at membrane contact sites. Infection also required ER-associated PI4P phosphatase Sac1 and phosphatidylinositol (PI) transfer protein beta (PITPb) shunting PI between ER-Golgi. These data support a PI4P-cholesterol counter-flux model for rhinovirus replication.
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Zhu F, Shi L, Li H, Eksi R, Engel JD, Guan Y. Modeling dynamic functional relationship networks and application to ex vivo human erythroid differentiation. ACTA ACUST UNITED AC 2014; 30:3325-33. [PMID: 25115705 DOI: 10.1093/bioinformatics/btu542] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
MOTIVATION Functional relationship networks, which summarize the probability of co-functionality between any two genes in the genome, could complement the reductionist focus of modern biology for understanding diverse biological processes in an organism. One major limitation of the current networks is that they are static, while one might expect functional relationships to consistently reprogram during the differentiation of a cell lineage. To address this potential limitation, we developed a novel algorithm that leverages both differentiation stage-specific expression data and large-scale heterogeneous functional genomic data to model such dynamic changes. We then applied this algorithm to the time-course RNA-Seq data we collected for ex vivo human erythroid cell differentiation. RESULTS Through computational cross-validation and literature validation, we show that the resulting networks correctly predict the (de)-activated functional connections between genes during erythropoiesis. We identified known critical genes, such as HBD and GATA1, and functional connections during erythropoiesis using these dynamic networks, while the traditional static network was not able to provide such information. Furthermore, by comparing the static and the dynamic networks, we identified novel genes (such as OSBP2 and PDZK1IP1) that are potential drivers of erythroid cell differentiation. This novel method of modeling dynamic networks is applicable to other differentiation processes where time-course genome-scale expression data are available, and should assist in generating greater understanding of the functional dynamics at play across the genome during development. AVAILABILITY AND IMPLEMENTATION The network described in this article is available at http://guanlab.ccmb.med.umich.edu/stageSpecificNetwork.
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Affiliation(s)
- Fan Zhu
- Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA
| | - Lihong Shi
- Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA
| | - Hongdong Li
- Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA
| | - Ridvan Eksi
- Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA
| | - James Douglas Engel
- Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA
| | - Yuanfang Guan
- Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA Department of Computational Medicine and Bioinformatics, Department of Cell and Developmental Biology, Department of Internal Medicine and Department of Computer Science and Engineering, University of Michigan, MI48109, USA
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Identification of OSBPL2 as a novel candidate gene for progressive nonsyndromic hearing loss by whole-exome sequencing. Genet Med 2014; 17:210-8. [PMID: 25077649 DOI: 10.1038/gim.2014.90] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 06/11/2014] [Indexed: 01/10/2023] Open
Abstract
PURPOSE Various forms of hearing loss have genetic causes, but many of the responsible genes have not yet been identified. Here, we describe a large seven-generation Chinese family with autosomal dominant nonsyndromic hearing loss that has been excluded as being caused by known deafness gene mutations associated with autosomal dominant nonsyndromic hearing loss with the aim of identifying a novel causative gene involved in deafness. METHODS Whole-exome sequencing was conducted in three affected family members, and cosegregation analysis was performed on other members of the family. RESULTS Whole-exome sequencing and subsequent segregation analysis identified a heterozygous frameshift mutation (c.153_154delCT, p.Gln53Argfs*100) in the oxysterol binding protein-like 2 (OSBPL2) gene in 25 affected family members. The deletion mutation is predicted to lead to premature truncation of the OSBPL2 protein. Modeling and structure-based analysis support the theory that this gene deletion is functionally deleterious. Our finding was further confirmed by the detection of another missense mutation, a c.583C>A transversion (p.Leu195Met) in exon 7 of OSBPL2, in an additional sporadic case of deafness. CONCLUSION Based on this study, OSBPL2 was identified as an excellent novel candidate gene for autosomal dominant nonsyndromic hearing loss; this study is the first to implicate OSBPL2 mutations in autosomal dominant nonsyndromic hearing loss.
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Sakai-Kato K, Un K, Nanjo K, Nishiyama N, Kusuhara H, Kataoka K, Kawanishi T, Goda Y, Okuda H. Elucidating the molecular mechanism for the intracellular trafficking and fate of block copolymer micelles and their components. Biomaterials 2014; 35:1347-58. [DOI: 10.1016/j.biomaterials.2013.11.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 11/08/2013] [Indexed: 01/14/2023]
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Un K, Sakai-Kato K, Kawanishi T, Okuda H, Goda Y. Effects of Liposomal Phospholipids and Lipid Transport-Related Protein on the Intracellular Fate of Encapsulated Doxorubicin. Mol Pharm 2014; 11:560-7. [DOI: 10.1021/mp400505a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Keita Un
- Division
of Drugs, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Kumiko Sakai-Kato
- Division
of Drugs, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Toru Kawanishi
- National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Haruhiro Okuda
- National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Yukihiro Goda
- Division
of Drugs, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
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Association of oxysterol binding protein-related protein 9 polymorphism with cerebral infarction in Hunan Han population. Ir J Med Sci 2013; 183:439-48. [PMID: 24190612 DOI: 10.1007/s11845-013-1035-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Accepted: 10/22/2013] [Indexed: 12/16/2022]
Abstract
BACKGROUND Oxysterol binding protein-related protein 9 (ORP9) may be related to the pathogenesis of cerebral infarction since it is closely related with glucose and lipid metabolism. The present study was designed to investigate the genetic relationship between ORP9 gene polymorphisms and cerebral infarction (CI) in Hunan Han population. METHODS Total 544 cerebral infarction patients (60.0 ± 10.3 years) and 284 healthy controls (59.0 ± 9.5 years) were enrolled. Sociodemographic and clinical data of the subjects, such as age, gender, body mass index, smoking, drinking, diabetes mellitus, hypertension, systolic and diastolic blood pressures, fasting blood glucose, triglycerides, total cholesterol, low-density and high-density lipoprotein were recorded, and two single-nucleotide polymorphisms (SNPs) of ORP9 gene including rs856600 and rs768529 with high mutation annotation format (MAF) values of 0.103 and 0.485 were studied by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). RESULTS No statistical difference was observed in allele distributions and frequencies of the two SNPs between control and CI groups. However, the percentage of atherosclerosis in CI group was significantly higher than that in the control group (p < 0.001). The frequencies of the TT genotype and T allele of rs768529 were significantly higher in patients with vulnerable plaque than those in patients with stable plaque (p < 0.001, p = 0.002). Logistic association analysis showed no correlations between cerebral infarction and different alleles (p > 0.05). CONCLUSION T allele of rs768529 may be a risk factor for the formation of the carotid vulnerable plaque in Chinese Hunan Han population.
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OSBP-related proteins: liganding by glycerophospholipids opens new insight into their function. Molecules 2013; 18:13666-79. [PMID: 24196413 PMCID: PMC6270239 DOI: 10.3390/molecules181113666] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 11/01/2013] [Accepted: 11/01/2013] [Indexed: 12/12/2022] Open
Abstract
Oxysterol-binding protein (OSBP) and its homologs designated OSBP-related (ORP) or OSBP-like (OSBPL) proteins constitute a conserved family of lipid binding/transfer proteins (LTP) in eukaryotes. The mechanisms of ORP function have remained incompletely understood, but they have been implicated as intracellular sterol sensors or transporters. A number of studies have provided evidence for the roles of ORPs at membrane contact sites (MCS), where endoplasmic reticulum is closely apposed with other organelle limiting membranes. ORPs are postulated to either transport sterols over MCSs or control the activity of enzymatic effectors or assembly of protein complexes with functions in signaling and lipid metabolism. Studies of yeast Saccharomyces cerevisiae ORPs Osh4p, Osh3p, Osh6p and Osh7p have revealed that ORPs do not exclusively bind sterols within their OSBP-related ligand-binding domain (ORD): The Osh4p ORD accommodates either sterols or phosphatidylinositol-4-phosphate (PI4P), and the Osh3p ORD was shown to specifically bind PI4P, the binding cavity being too narrow for a sterol to fit in. Most recently, Osh6p and Osh7p were demonstrated to show specific affinity for phosphatidylserine (PS), and to play a role in the intracellular transport of this glycerophospholipid; Additionally, two mammalian ORPs were shown to bind PS. Thus, the term frequently used for ORPs/OSBPLs, oxysterol-binding proteins, is a misnomer. While a number of ORPs bind oxysterols or cholesterol, other family members appear to interact with phospholipid ligands to regulate lipid fluxes, organelle lipid compositions and cell signaling. As a conclusion, ORPs are LTPs with a wide ligand spectrum and marked functional heterogeneity.
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63
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Olkkonen VM, Li S. Oxysterol-binding proteins: Sterol and phosphoinositide sensors coordinating transport, signaling and metabolism. Prog Lipid Res 2013; 52:529-38. [DOI: 10.1016/j.plipres.2013.06.004] [Citation(s) in RCA: 126] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Revised: 06/15/2013] [Accepted: 06/22/2013] [Indexed: 01/27/2023]
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Thiel K, Heier C, Haberl V, Thul PJ, Oberer M, Lass A, Jäckle H, Beller M. The evolutionarily conserved protein CG9186 is associated with lipid droplets, required for their positioning and for fat storage. J Cell Sci 2013; 126:2198-212. [PMID: 23525007 DOI: 10.1242/jcs.120493] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Lipid droplets (LDs) are specialized cell organelles for the storage of energy-rich lipids. Although lipid storage is a conserved feature of all cells and organisms, little is known about fundamental aspects of the cell biology of LDs, including their biogenesis, structural assembly and subcellular positioning, and the regulation of organismic energy homeostasis. We identified a novel LD-associated protein family, represented by the Drosophila protein CG9186 and its murine homolog MGI:1916082. In the absence of LDs, both proteins localize at the endoplasmic reticulum (ER). Upon lipid storage induction, they translocate to LDs using an evolutionarily conserved targeting mechanism that acts through a 60-amino-acid targeting motif in the center of the CG9186 protein. Overexpression of CG9186, and MGI:1916082, causes clustering of LDs in both tissue culture and salivary gland cells, whereas RNAi knockdown of CG9186 results in a reduction of LDs. Organismal RNAi knockdown of CG9186 results in a reduction in lipid storage levels of the fly. The results indicate that we identified the first members of a novel and evolutionarily conserved family of lipid storage regulators, which are also required to properly position LDs within cells.
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Affiliation(s)
- Katharina Thiel
- Department of Molecular Developmental Biology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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Béaslas O, Metso J, Nissilä E, Laurila PP, Kaiharju E, Batchu KC, Kaipiainen L, Mäyränpää MI, Yan D, Gylling H, Jauhiainen M, Olkkonen VM. Osbpl8 deficiency in mouse causes an elevation of high-density lipoproteins and gender-specific alterations of lipid metabolism. PLoS One 2013; 8:e58856. [PMID: 23554939 PMCID: PMC3598917 DOI: 10.1371/journal.pone.0058856] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Accepted: 02/08/2013] [Indexed: 11/24/2022] Open
Abstract
OSBP-related protein 8 (ORP8) encoded by Osbpl8 is an endoplasmic reticulum sterol sensor implicated in cellular lipid metabolism. We generated an Osbpl8−/− (KO) C57Bl/6 mouse strain. Wild-type and Osbpl8KO animals at the age of 13-weeks were fed for 5 weeks either chow or high-fat diet, and their plasma lipids/lipoproteins and hepatic lipids were analyzed. The chow-fed Osbpl8KO male mice showed a marked elevation of high-density lipoprotein (HDL) cholesterol (+79%) and phospholipids (+35%), while only minor increase of apolipoprotein A-I (apoA-I) was detected. In chow-fed female KO mice a less prominent increase of HDL cholesterol (+27%) was observed, while on western diet the HDL increment was prominent in both genders. The HDL increase was accompanied by an elevated level of HDL-associated apolipoprotein E in male, but not female KO animals. No differences between genotypes were observed in lecithin:cholesterol acyltransferase (LCAT) or hepatic lipase (HL) activity, or in the fractional catabolic rate of fluorescently labeled mouse HDL injected in chow-diet fed animals. The Osbpl8KO mice of both genders displayed reduced phospholipid transfer protein (PLTP) activity, but only on chow diet. These findings are consistent with a model in which Osbpl8 deficiency results in altered biosynthesis of HDL. Consistent with this hypothesis, ORP8 depleted mouse hepatocytes secreted an increased amount of nascent HDL into the culture medium. In addition to the HDL phenotype, distinct gender-specific alterations in lipid metabolism were detected: Female KO animals on chow diet showed reduced lipoprotein lipase (LPL) activity and increased plasma triglycerides, while the male KO mice displayed elevated plasma cholesterol biosynthetic markers cholestenol, desmosterol, and lathosterol. Moreover, modest gender-specific alterations in the hepatic expression of lipid homeostatic genes were observed. In conclusion, we report the first viable OsbplKO mouse model, demonstrating a HDL elevating effect of Osbpl8 knock-out and additional gender- and/or diet-dependent impacts on lipid metabolism.
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Affiliation(s)
- Olivier Béaslas
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Jari Metso
- Department of Chronic Disease Prevention, Public Health Genomics Research Unit, National Institute for Health and Welfare, and Institute for Molecular Medicine Finland (FIMM), Helsinki, Finland
| | - Eija Nissilä
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
- Institute of Biomedicine, Anatomy, University of Helsinki, Helsinki, Finland
| | - Pirkka-Pekka Laurila
- Department of Chronic Disease Prevention, Public Health Genomics Research Unit, National Institute for Health and Welfare, and Institute for Molecular Medicine Finland (FIMM), Helsinki, Finland
| | - Essi Kaiharju
- Department of Chronic Disease Prevention, Public Health Genomics Research Unit, National Institute for Health and Welfare, and Institute for Molecular Medicine Finland (FIMM), Helsinki, Finland
| | - Krishna Chaithanya Batchu
- Institute of Biomedicine, Department of Biochemistry and Developmental Biology, University of Helsinki, Helsinki, Finland
| | - Leena Kaipiainen
- Division of Internal Medicine, Department of Medicine, University of Helsinki, Helsinki, Finland
| | - Mikko I. Mäyränpää
- Department of Pathology, Haartman Institute, University of Helsinki and HUSLAB Division of Pathology, Meilahti Laboratories of Pathology, Helsinki University Central Hospital, Helsinki, Finland
| | - Daoguang Yan
- Department of Biology, Jinan University, Guangzhou, China
| | - Helena Gylling
- Division of Internal Medicine, Department of Medicine, University of Helsinki, Helsinki, Finland
| | - Matti Jauhiainen
- Department of Chronic Disease Prevention, Public Health Genomics Research Unit, National Institute for Health and Welfare, and Institute for Molecular Medicine Finland (FIMM), Helsinki, Finland
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
- Institute of Biomedicine, Anatomy, University of Helsinki, Helsinki, Finland
- * E-mail:
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Weber-Boyvat M, Zhong W, Yan D, Olkkonen VM. Oxysterol-binding proteins: functions in cell regulation beyond lipid metabolism. Biochem Pharmacol 2013; 86:89-95. [PMID: 23428468 DOI: 10.1016/j.bcp.2013.02.016] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 02/08/2013] [Accepted: 02/11/2013] [Indexed: 12/12/2022]
Abstract
Oxysterol-binding (OSBP)-related proteins (ORPs) constitute a family of sterol and phosphoinositide binding/transfer proteins in eukaryotes from yeast to man. While their functions have mainly been addressed in cellular lipid metabolism or sterol transport, increasing evidence points to more versatile regulatory roles in a spectrum of cellular regimes. In fact ORPs do not appear to be robust controllers of lipid homeostasis. Several ORPs localize at membrane contacts sites (MCS), where endoplasmic reticulum (ER) is apposed with other organelle limiting membranes. Apparently, ORPs have the capacity to control the formation of MCS or activity of enzymatic machineries at these sites. Thereby, ORPs most likely affect organelle membrane lipid compositions, with impacts on signaling and vesicle transport, but also cellular lipid metabolism. Moreover, an increasing number of protein interaction partners of ORPs have been identified, connecting these proteins with various aspects of cell regulation. Small molecular anti-proliferative compounds, ORPphilins, were recently found to target two members of the ORP family, OSBP and ORP4, revealing an essential function of ORPs in cancer cell proliferation and survival. Further functions assigned for ORPs include regulation of extracellular signal regulated kinase (ERK) activity (OSBP), control of ER-late endosome MCS and late endosome motility (ORP1L), regulation of β1-integrin activity (ORP3), modulation of hepatocyte insulin signaling and macrophage migration (ORP8), as well as post-Golgi vesicle transport, phosphatidylinositol-4-phosphate and target of rapamycin complex 1 signaling and nitrogen sensing (Saccharomyces cerevisiae Osh4p). These and other recent observations shed light on the ORPs as integrators of lipid signals with an unforeseen variety of vital cellular processes.
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Affiliation(s)
- Marion Weber-Boyvat
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
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67
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Un K, Sakai-Kato K, Oshima Y, Kawanishi T, Okuda H. Intracellular trafficking mechanism, from intracellular uptake to extracellular efflux, for phospholipid/cholesterol liposomes. Biomaterials 2012; 33:8131-41. [DOI: 10.1016/j.biomaterials.2012.07.030] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 07/15/2012] [Indexed: 01/27/2023]
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Zhou Y, Robciuc MR, Wabitsch M, Juuti A, Leivonen M, Ehnholm C, Yki-Järvinen H, Olkkonen VM. OSBP-related proteins (ORPs) in human adipose depots and cultured adipocytes: evidence for impacts on the adipocyte phenotype. PLoS One 2012; 7:e45352. [PMID: 23028956 PMCID: PMC3448648 DOI: 10.1371/journal.pone.0045352] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2012] [Accepted: 08/15/2012] [Indexed: 01/28/2023] Open
Abstract
Oxysterol-binding protein (OSBP) homologues, ORPs, are implicated in lipid homeostatic control, vesicle transport, and cell signaling. We analyzed here the quantity of ORP mRNAs in human subcutaneous (s.c.) and visceral adipose depots, as well as in the Simpson-Golabi-Behmel syndrome (SGBS) adipocyte cell model. All of the ORP mRNAs were present in the s.c and visceral adipose tissues, and the two depots shared an almost identical ORP mRNA expression pattern. SGBS adipocytes displayed a similar pattern, suggesting that the adipose tissue ORP expression pattern mainly derives from adipocytes. During SGBS cell adipogenic differentiation, ORP2, ORP3, ORP4, ORP7, and ORP8 mRNAs were down-regulated, while ORP11 was induced. To assess the impacts of ORPs on adipocyte differentiation, ORP3 and ORP8, proteins down-regulated during adipogenesis, were overexpressed in differentiating SGBS adipocytes, while ORP11, a protein induced during adipogenesis, was silenced. ORP8 overexpression resulted in reduced expression of the aP2 mRNA, while down-regulation of adiponectin and aP2 was observed in ORP11 silenced cells. Furthermore, ORP8 overexpression or silencing of ORP11 markedly decreased cellular triglyceride storage. These data identify the patterns of ORP expression in human adipose depots and SGBS adipocytes, and provide the first evidence for a functional impact of ORPs on the adipocyte phenotype.
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Affiliation(s)
- You Zhou
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Marius R. Robciuc
- National Institute for Health and Welfare, Public Health Genomics Unit, Helsinki, Finland
| | - Martin Wabitsch
- Division of Paediatric Endocrinology and Diabetes, Department of Paediatrics and Adolescent Medicine, University of Ulm, Ulm, Germany
| | - Anne Juuti
- Department of Surgery, Helsinki University Central Hospital, Helsinki, Finland
| | - Marja Leivonen
- Department of Surgery, Helsinki University Central Hospital, Helsinki, Finland
| | - Christian Ehnholm
- National Institute for Health and Welfare, Public Health Genomics Unit, Helsinki, Finland
| | - Hannele Yki-Järvinen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
- Department of Medicine, University of Helsinki, Helsinki, Finland
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
- Institute of Biomedicine, Anatomy, University of Helsinki, Helsinki, Finland
- * E-mail:
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69
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Mitić T, Andrew R, Walker BR, Hadoke PWF. 11β-Hydroxysteroid dehydrogenase type 1 contributes to the regulation of 7-oxysterol levels in the arterial wall through the inter-conversion of 7-ketocholesterol and 7β-hydroxycholesterol. Biochimie 2012; 95:548-55. [PMID: 22940536 PMCID: PMC3585959 DOI: 10.1016/j.biochi.2012.08.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 08/13/2012] [Indexed: 11/29/2022]
Abstract
The atherogenic 7-oxysterols, 7-ketocholesterol (7-KC) and 7β-hydroxycholesterol (7βOHC), can directly impair arterial function. Inter-conversion of 7-KC and 7βOHC has recently been shown as a novel role for the glucocorticoid-metabolizing enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Since this enzyme is expressed in vascular smooth muscle cells, we addressed the hypothesis that inter-conversion of 7-KC and 7βOHC by 11β-HSD1 may contribute to regulation of arterial function. Incubation (4–24 h) of aortic rings with either 7-KC (25 μM) or 7βOHC (20 μM) had no effect on endothelium-dependent (acetylcholine) or -independent (sodium nitroprusside) relaxation. In contrast, exposure to 7-KC (but not to 7βOHC) attenuated noradrenaline-induced contraction (Emax) after 4 h (0.78 ± 0.28 vs 0.40 ± 0.08 mN/mm; p < 0.05) and 24 h (2.28 ± 0.34 vs 1.56 ± 0.48 mN/mm; p < 0.05). Both 7-oxysterols were detected by GCMS in the aortic wall of chow-fed C57Bl6/J mice, with concentrations of 7-KC (1.41 ± 0.81 ng/mg) higher (p = 0.05) than 7βOHC (0.16 ± 0.06 ng/mg). In isolated mouse aortic rings 11β-HSD1 was shown to act as an oxo-reductase, inter-converting 7-KC and 7βOHC. This activity was lost in aorta from 11β-HSD1−/− mice, which had low oxysterol levels. Renal homogenates from 11β-HSD1−/− mice were used to confirm that the type 2 isozyme of 11β-HSD does not inter-convert 7-KC and 7βOHC. These results demonstrate that 7-KC has greater effects than 7βOHC on vascular function, and that 11β-HSD1 can inter-convert 7-KC and 7βOHC in the arterial wall, contributing to the regulation of 7-oxysterol levels and potentially influencing vascular function. This mechanism may be important in the cardioprotective effects of 11β-HSD1 inhibitors.
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Affiliation(s)
- Tijana Mitić
- Endocrinology Unit, University/BHF Centre for Cardiovascular Science, College of Medicine and Veterinary Medicine, University of Edinburgh, The Queen's Medical Research Institute, Edinburgh, Scotland, UK
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70
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Nissilä E, Ohsaki Y, Weber-Boyvat M, Perttilä J, Ikonen E, Olkkonen VM. ORP10, a cholesterol binding protein associated with microtubules, regulates apolipoprotein B-100 secretion. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1472-84. [PMID: 22906437 DOI: 10.1016/j.bbalip.2012.08.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Revised: 07/31/2012] [Accepted: 08/03/2012] [Indexed: 12/30/2022]
Abstract
ORP10/OSBPL10 is a member of the oxysterol-binding protein family, and genetic variation in OSBPL10 is associated with dyslipidemias and peripheral artery disease. In this study we investigated the ligand binding properties of ORP10 in vitro as well as its localization and function in human HuH7 hepatocytes. The pleckstrin homology (PH) domain of ORP10 selectively interacts with phosphatidylinositol-4-phosphate, while the C-terminal ligand binding domain binds cholesterol and several acidic phospholipids. Full-length ORP10 decorates microtubules (MT), while the ORP10 N-terminal fragment (aa 1-318) localizes at Golgi membranes. Removal of the C-terminal aa 712-764 of ORP10 containing a predicted coiled-coil segment abolishes the MT association, but allows partial Golgi targeting. A PH domain-GFP fusion protein is distributed mainly in the cytosol and the plasma membrane, indicating that the Golgi affinity of ORP10 involves other determinants in addition to the PH domain. HuH7 cells expressing ORP10-specific shRNA display increased accumulation of apolipoprotein B-100 (apoB-100), but not of albumin, in culture medium, and contain reduced levels of intracellular apoB-100. Pulse-chase analysis of cellular [(35)S]apoB-100 demonstrates enhanced apoB-100 secretion by cells expressing ORP10-specific shRNA. The apoB-100 secretion phenotype is replicated in HepG2 cells transduced with the ORP10 shRNA lentiviruses. As a conclusion, the present study dissects the determinants of ORP10 association with MT and the Golgi complex and provides evidence for a specific role of this protein in β-lipoprotein secretion by human hepatocytes.
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Affiliation(s)
- Eija Nissilä
- Institute of Biomedicine, Anatomy, PO Box 63, FI-00014 University of Helsinki, Finland
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71
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Lee S, Wang PY, Jeong Y, Mangelsdorf DJ, Anderson RGW, Michaely P. Sterol-dependent nuclear import of ORP1S promotes LXR regulated trans-activation of apoE. Exp Cell Res 2012; 318:2128-42. [PMID: 22728266 DOI: 10.1016/j.yexcr.2012.06.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 05/30/2012] [Accepted: 06/08/2012] [Indexed: 01/30/2023]
Abstract
Oxysterol binding protein related protein 1S (ORP1S) is a member of a family of sterol transport proteins. Here we present evidence that ORP1S translocates from the cytoplasm to the nucleus in response to sterol binding. The sterols that best promote nuclear import of ORP1S also activate the liver X receptor (LXR) transcription factors and we show that ORP1S binds to LXRs, promotes binding of LXRs to LXR response elements (LXREs) and specifically enhances LXR-dependent transcription via the ME.1 and ME.2 enhancer elements of the apoE gene. We propose that ORP1S is a cytoplasmic sterol sensor, which transports sterols to the nucleus and promotes LXR-dependent gene transcription through select enhancer elements.
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Affiliation(s)
- Sungsoo Lee
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, United States.
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72
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Saka HA, Valdivia R. Emerging roles for lipid droplets in immunity and host-pathogen interactions. Annu Rev Cell Dev Biol 2012; 28:411-37. [PMID: 22578141 DOI: 10.1146/annurev-cellbio-092910-153958] [Citation(s) in RCA: 158] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Lipid droplets (LDs) are neutral lipid storage organelles ubiquitous to eukaryotic cells. It is increasingly recognized that LDs interact extensively with other organelles and that they perform functions beyond passive lipid storage and lipid homeostasis. One emerging function for LDs is the coordination of immune responses, as these organelles participate in the generation of prostaglandins and leukotrienes, which are important inflammation mediators. Similarly, LDs are also beginning to be recognized as playing a role in interferon responses and in antigen cross presentation. Not surprisingly, there is emerging evidence that many pathogens, including hepatitis C and Dengue viruses, Chlamydia, and Mycobacterium, target LDs during infection either for nutritional purposes or as part of an anti-immunity strategy. We here review recent findings that link LDs to the regulation and execution of immune responses in the context of host-pathogen interactions.
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Affiliation(s)
- Hector Alex Saka
- Department of Molecular Genetics and Microbiology and Center for Microbial Pathogenesis, Duke University Medical Center, Durham, North Carolina 27710, USA
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73
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Olkkonen VM, Zhou Y, Yan D, Vihervaara T. Oxysterol-binding proteins-emerging roles in cell regulation. EUR J LIPID SCI TECH 2012. [DOI: 10.1002/ejlt.201200044] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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74
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Abstract
Among organelles, lipid droplets (LDs) uniquely constitute a hydrophobic phase in the aqueous environment of the cytosol. Their hydrophobic core of neutral lipids stores metabolic energy and membrane components, making LDs hubs for lipid metabolism. In addition, LDs are implicated in a number of other cellular functions, ranging from protein storage and degradation to viral replication. These processes are functionally linked to many physiological and pathological conditions, including obesity and related metabolic diseases. Despite their important functions and nearly ubiquitous presence in cells, many aspects of LD biology are unknown. In the past few years, the pace of LD investigation has increased, providing new insights. Here, we review the current knowledge of LD cell biology and its translation to physiology.
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Affiliation(s)
- Tobias C Walther
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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75
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Transcriptomic profiles of peripheral white blood cells in type II diabetes and racial differences in expression profiles. BMC Genomics 2011; 12 Suppl 5:S12. [PMID: 22369568 PMCID: PMC3287494 DOI: 10.1186/1471-2164-12-s5-s12] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Background Along with obesity, physical inactivity, and family history of metabolic disorders, African American ethnicity is a risk factor for type 2 diabetes (T2D) in the United States. However, little is known about the differences in gene expression and transcriptomic profiles of blood in T2D between African Americans (AA) and Caucasians (CAU), and microarray analysis of peripheral white blood cells (WBCs) from these two ethnic groups will facilitate our understanding of the underlying molecular mechanism in T2D and identify genetic biomarkers responsible for the disparities. Results A whole human genome oligomicroarray of peripheral WBCs was performed on 144 samples obtained from 84 patients with T2D (44 AA and 40 CAU) and 60 healthy controls (28 AA and 32 CAU). The results showed that 30 genes had significant difference in expression between patients and controls (a fold change of <-1.4 or >1.4 with a P value <0.05). These known genes were mainly clustered in three functional categories: immune responses, lipid metabolism, and organismal injury/abnormaly. Transcriptomic analysis also showed that 574 genes were differentially expressed in AA diseased versus AA control, compared to 200 genes in CAU subjects. Pathway study revealed that "Communication between innate and adaptive immune cells"/"Primary immunodeficiency signaling" are significantly down-regulated in AA patients and "Interferon signaling"/"Complement System" are significantly down-regulated in CAU patients. Conclusions These newly identified genetic markers in WBCs provide valuable information about the pathophysiology of T2D and can be used for diagnosis and pharmaceutical drug design. Our results also found that AA and CAU patients with T2D express genes and pathways differently.
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Vihervaara T, Jansen M, Uronen RL, Ohsaki Y, Ikonen E, Olkkonen VM. Cytoplasmic oxysterol-binding proteins: sterol sensors or transporters? Chem Phys Lipids 2011; 164:443-50. [DOI: 10.1016/j.chemphyslip.2011.03.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 03/04/2011] [Accepted: 03/04/2011] [Indexed: 12/13/2022]
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Fu Q, Lynn-Miller A, Lan Q. Characterization of the oxysterol-binding protein gene family in the yellow fever mosquito, Aedes aegypti. INSECT MOLECULAR BIOLOGY 2011; 20:541-52. [PMID: 21699592 PMCID: PMC3139008 DOI: 10.1111/j.1365-2583.2011.01087.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The oxysterol-binding protein (OSBP) and OSBP-related proteins (ORPs) are sterol-binding proteins that may be involved in cellular sterol transportation, sterol metabolism and signal transduction pathways. Four ORP genes were cloned from Aedes aegypti. Based on amino acid sequence homology to human proteins, they are AeOSBP, AeORP1, AeORP8 and AeORP9. Splicing variants of AeOSBP and AeORP8 were identified. The temporal and spatial transcription patterns of members of the AeOSBP gene family through developmental stages and the gonotrophic cycle were profiled. AeORP1 transcription seemed to be head tissue-specific, whereas AeOSBP and AeORP9 expression was induced by a bloodmeal. Furthermore, over-expression of AeORPs facilitated [(3)H]-cholesterol uptake in Ae. aegypti cultured Aag -2 cells.
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Affiliation(s)
- Qiang Fu
- Department of Entomology, University of Wisconsin-Madison, Madison, WI 53705
| | - Ace Lynn-Miller
- Department of Entomology, University of Arkansas, Fayetteville, AR 72701
| | - Que Lan
- Department of Entomology, University of Wisconsin-Madison, Madison, WI 53705
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Heo GY, Bederman I, Mast N, Liao WL, Turko IV, Pikuleva IA. Conversion of 7-ketocholesterol to oxysterol metabolites by recombinant CYP27A1 and retinal pigment epithelial cells. J Lipid Res 2011; 52:1117-1127. [PMID: 21411718 DOI: 10.1194/jlr.m014217] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Of the different oxygenated cholesterol metabolites, 7-ketocholesterol (7KCh) is considered a noxious oxy-sterol implicated in the development of certain pathologies, including those found in the eye. Here we elucidated whether sterol 27-hydroxylase cytochrome P450 27A1 (CYP27A1) is involved in elimination of 7KCh from the posterior part of the eye: the neural retina and underlying retinal pigment epithelium (RPE). We first established that the affinities of purified recombinant CYP27A1 for 7KCh and its endogenous substrate cholesterol are similar, yet 7KCh is metabolized at a 4-fold higher rate than cholesterol in the reconstituted system in vitro. Lipid extracts from bovine neural retina and RPE were then analyzed by isotope dilution GC-MS for the presence of the 7KCh-derived oxysterols. Two metabolites, 3β,27-dihydroxy-5-cholesten-7-one (7KCh-27OH) and 3β-hydroxy-5-cholesten-7-one-26-oic acid (7KCh-27COOH), were detected in the RPE but not in the neural retina. 7KCh-27OH was also formed when RPE homogenates were supplemented with NADPH and the mitochondrial redox system. Quantifications in human RPE showed that CYP27A1 is indeed expressed in the RPE at 2-4-fold higher levels than in the neural retina. The data obtained represent evidence for the role of CYP27A1 in retinal metabolism of 7KCh and suggest that, in addition to cholesterol removal, the functions of this enzyme could also include elimination of toxic endogenous compounds.
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Affiliation(s)
- Gun-Young Heo
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Ilya Bederman
- Pediatrics, Case Western Reserve University, Cleveland, OH
| | - Natalia Mast
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Wei-Li Liao
- Institute for Bioscience and Biotechnology Research, Rockville, MD
| | - Illarion V Turko
- Institute for Bioscience and Biotechnology Research, Rockville, MD; Division Analytical Chemistry, National Institute of Standards and Technology, Gaithersburg, MD
| | - Irina A Pikuleva
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH.
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Vihervaara T, Uronen RL, Wohlfahrt G, Björkhem I, Ikonen E, Olkkonen VM. Sterol binding by OSBP-related protein 1L regulates late endosome motility and function. Cell Mol Life Sci 2011; 68:537-51. [PMID: 20690035 PMCID: PMC11114714 DOI: 10.1007/s00018-010-0470-z] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 06/24/2010] [Accepted: 07/14/2010] [Indexed: 11/26/2022]
Abstract
ORP1L is an oxysterol binding homologue that regulates late endosome (LE) positioning. We show that ORP1L binds several oxysterols and cholesterol, and characterize a mutant, ORP1L Δ560-563, defective in oxysterol binding. While wild-type ORP1L clusters LE, ORP1L Δ560-563 induces LE scattering, which is reversed by disruption of the endoplasmic reticulum (ER) targeting FFAT motif, suggesting that it is due to enhanced LE-ER interactions. Endosome motility is reduced upon overexpression of ORP1L. Both wild-type ORP1L and the Δ560-563 mutant induce the recruitment of both dynactin and kinesin-2 on LE. Most of the LE decorated by overexpressed ORP1L fail to accept endocytosed dextran or EGF, and the transfected cells display defective degradation of internalized EGF. ORP1L silencing in macrophage foam cells enhances endosome motility and results in inhibition of [(3)H]cholesterol efflux to apolipoprotein A-I. These data demonstrate that LE motility and functions in both protein and lipid transport are regulated by ORP1L.
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Affiliation(s)
- Terhi Vihervaara
- Minerva Foundation Institute for Medical Research, Biomedicum Helsinki 2U, Tukholmankatu 8, 00290 Helsinki, Finland
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum 1, 00290 Helsinki, Finland
| | - Riikka-Liisa Uronen
- Institute of Biomedicine/Anatomy, University of Helsinki, P.O. Box 63, 00014 Helsinki, Finland
| | - Gerd Wohlfahrt
- Computer-Aided Drug Design, Orion Pharma, Orionintie 1, 02101 Espoo, Finland
| | - Ingemar Björkhem
- Karolinska Institutet, Karolinska University Hospital Huddinge, 14186 Stockholm, Sweden
| | - Elina Ikonen
- Institute of Biomedicine/Anatomy, University of Helsinki, P.O. Box 63, 00014 Helsinki, Finland
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum Helsinki 2U, Tukholmankatu 8, 00290 Helsinki, Finland
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum 1, 00290 Helsinki, Finland
- Institute of Biomedicine/Anatomy, University of Helsinki, P.O. Box 63, 00014 Helsinki, Finland
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80
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Jansen M, Ohsaki Y, Rega LR, Bittman R, Olkkonen VM, Ikonen E. Role of ORPs in sterol transport from plasma membrane to ER and lipid droplets in mammalian cells. Traffic 2010; 12:218-31. [PMID: 21062391 DOI: 10.1111/j.1600-0854.2010.01142.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In this study, we investigated the mechanisms of sterol transport from the plasma membrane (PM) to the endoplasmic reticulum (ER) and lipid droplets (LDs) in HeLa cells. By overexpressing all mammalian oxysterol-binding protein-related proteins (ORPs), we found that especially ORP1S and ORP2 enhanced PM-to-LD sterol transport. This reflected the stimulation of transport from the PM to the ER, rather than from the ER to LDs. Double knockdown of ORP1S and ORP2 inhibited sterol transport from the PM to the ER and LDs, suggesting a physiological role for these ORPs in the process. A two phenylalanines in an acidic tract (FFAT) motif in ORPs that mediates interaction with VAMP-associated proteins (VAPs) in the ER was not necessary for the enhancement of sterol transport by ORPs. However, VAP-A and VAP-B silencing slowed down PM-to-LD sterol transport. This was accompanied by enhanced degradation of ORP2 and decreased levels of several FFAT motif-containing ORPs, suggesting a role for VAPs in sterol transport by stabilization of ORPs.
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Affiliation(s)
- Maurice Jansen
- Institute of Biomedicine, University of Helsinki, Finland
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81
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Abstract
Normally macrophages localized in the arterial vessel wall perform the "reverse transfer" of cholesterol, which includes endocytosis of low density lipoproteins (LDL), cholesterol transfer to newly formed high density lipoprotein particles, and their following elimination by the liver. The homeostatic function of macrophages for cholesterol involves a system of lipid sensors. Oxysterol sensors LXRs, oxysterol and cholesterol sensors INSIG and SCAP acting through controlled transcription factors SREBP, as well as sensors for oxidized fatty acids and their derivatives, PPAR, are the best studied. Activation of LXR and PPAR is also accompanied by inhibition of macrophage functions related to inflammation. Accumulation of oxidized and otherwise modified LDL in the subendothelial space induced by endothelium injury, infection, or other pathogenic factors instead of stimulation of the homeostatic functions of macrophages leads to their weakening with a concurrent increase in the inflammatory potential of these cells. These shifts seem to drive the transformation of macrophages into foam cells, which form the core of sclerotic plaques. The intervention of another lipid sensor, TLR4, can trigger such a radical change in the functional activity of macrophages. The interaction of modified LDL with this signaling receptor results in inhibition of the homeostatic oxysterol signaling, induction of additional LDL transporters, and activation of the phagocytic function of macrophages. The re-establishment of cholesterol homeostasis under these circumstances can be achieved by administration of LXR and PPARgamma agonists. Therefore, it is urgent to design ligands with reduced side effects.
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Abstract
Oxysterol-binding protein (OSBP)-related proteins (ORPs) are lipid-binding proteins that are conserved from yeast to humans. They are implicated in many cellular processes including signaling, vesicular trafficking, lipid metabolism, and nonvesicular sterol transport. All ORPs contain an OSBP-related domain (ORD) that has a hydrophobic pocket that binds a single sterol. ORDs also contain additional membrane-binding surfaces, some of which bind phosphoinositides and may regulate sterol binding. Studies in yeast suggest that ORPs function as sterol transporters, perhaps in regions where organelle membranes are closely apposed. Yeast ORPs also participate in vesicular trafficking, although their role is unclear. In mammalian cells, some ORPs function as sterol sensors that regulate the assembly of protein complexes in response to changes in cholesterol levels. This review will summarize recent advances in our understanding of how ORPs bind lipids and membranes and how they function in diverse cellular processes.
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Affiliation(s)
- Sumana Raychaudhuri
- Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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83
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Functional implications of sterol transport by the oxysterol-binding protein gene family. Biochem J 2010; 429:13-24. [PMID: 20545625 DOI: 10.1042/bj20100263] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Cholesterol and its numerous oxygenated derivatives (oxysterols) profoundly affect the biophysical properties of membranes, and positively and negatively regulate sterol homoeostasis through interaction with effector proteins. As the bulk of cellular sterols are segregated from the sensory machinery that controls homoeostatic responses, an important regulatory step involves sterol transport or signalling between membrane compartments. Evidence for rapid, energy-independent transport between organelles has implicated transport proteins, such as the eukaryotic family of OSBP (oxysterol-binding protein)/ORPs (OSBP-related proteins). Since the founding member of this family was identified more than 25 years ago, accumulated evidence has implicated OSBP/ORPs in sterol signalling and/or sterol transport functions. However, recent evidence of sterol transfer activity by OSBP/ORPs suggests that other seemingly disparate functions could be the result of alterations in membrane sterol distribution or ancillary to this primary activity.
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84
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Maxfield FR, van Meer G. Cholesterol, the central lipid of mammalian cells. Curr Opin Cell Biol 2010; 22:422-9. [PMID: 20627678 DOI: 10.1016/j.ceb.2010.05.004] [Citation(s) in RCA: 261] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 04/25/2010] [Accepted: 05/03/2010] [Indexed: 12/18/2022]
Abstract
Despite its importance for mammalian cell biology and human health, there are many basic aspects of cholesterol homeostasis that are not well understood. Even for the well-characterized delivery of cholesterol to cells via lipoproteins, a novel regulatory mechanism has been discovered recently, involving a serum protein called PCSK9, which profoundly affects lipoproteins and their receptors. Cells can export cholesterol by processes that require the activity of ABC transporters, but the molecular mechanisms for cholesterol transport remain unclear. Cholesterol levels in different organelles vary by 5-10-fold, and the mechanisms for maintaining these differences are now partially understood. Several proteins have been proposed to play a role in the inter-organelle movement of cholesterol, but many aspects of the mechanisms for regulating intracellular transport and distribution of cholesterol remain to be worked out. The endoplasmic reticulum is the main organelle responsible for regulation of cholesterol synthesis, and careful measurements have shown that the proteins responsible for sterol sensing respond over a very narrow range of cholesterol concentrations to provide very precise, switch-like control over cholesterol synthesis.
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Affiliation(s)
- Frederick R Maxfield
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA.
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85
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Abstract
In eukaryotic cells, membranes of the late secretory pathway contain a disproportionally large amount of cholesterol in relation to the endoplasmic reticulum, nuclear envelope and mitochondria. At one extreme, enrichment of the plasma membrane with cholesterol and sphingolipids is crucial for formation of liquid ordered domains (rafts) involved in cell communication and transport. On the other hand, regulatory machinery in the endoplasmic reticulum is maintained in a relatively cholesterol-poor environment, to ensure appropriate rapid responses to fluctuations in cellular sterol levels. Thus, cholesterol homeostasis is absolutely dependent on its distribution along an intracellular gradient. It is apparent that this gradient is maintained by a combination of sterol-lipid interactions, vesicular transport and sterol-binding/transport proteins. Evidence for rapid, energy-independent transport between organelles has implicated transport proteins, in particular the eukaryotic oxysterol binding protein (OSBP) family. Since the founding member of this family was identified more than 25 years ago, accumulated evidence implicates the 12-member family of OSBP and OSBP-related proteins (ORPs) in sterol signalling and/or sterol transport functions. The OSBP/ORP gene family is characterized by a conserved beta-barrel sterol-binding fold but is differentiated from other sterol-binding proteins by the presence of additional domains that target multiple organelle membranes. Here we will discuss the functional and structural characteristics of the mammalian OSBP/ORP family that support a 'dual-targeting' model for sterol transport between membranes.
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Affiliation(s)
- Neale D Ridgway
- Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, B3H 4H7, Canada.
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86
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Affiliation(s)
- Norihito Shibata
- Department of Cellular and Molecular Medicine, University of California
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87
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Abstract
Long underappreciated as important cellular organelles, lipid droplets are finally being recognized as dynamic structures with a complex and interesting biology. In light of this newfound respect, we discuss emerging views on lipid droplet biology and speculate on the major advances to come.
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Affiliation(s)
- Robert V Farese
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA.
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88
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Perttilä J, Merikanto K, Naukkarinen J, Surakka I, Martin NW, Tanhuanpää K, Grimard V, Taskinen MR, Thiele C, Salomaa V, Jula A, Perola M, Virtanen I, Peltonen L, Olkkonen VM. OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism. J Mol Med (Berl) 2009; 87:825-35. [PMID: 19554302 PMCID: PMC2707950 DOI: 10.1007/s00109-009-0490-z] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Revised: 05/14/2009] [Accepted: 05/25/2009] [Indexed: 11/25/2022]
Abstract
Analysis of variants in three genes encoding oxysterol-binding protein (OSBP) homologues (OSBPL2, OSBPL9, OSBPL10) in Finnish families with familial low high-density lipoprotein (HDL) levels (N = 426) or familial combined hyperlipidemia (N = 684) revealed suggestive linkage of OSBPL10 single-nucleotide polymorphisms (SNPs) with extreme end high triglyceride (TG; >90th percentile) trait. Prompted by this initial finding, we carried out association analysis in a metabolic syndrome subcohort (Genmets) of Health2000 examination survey (N = 2,138), revealing association of multiple OSBPL10 SNPs with high serum TG levels (>95th percentile). To investigate whether OSBPL10 could be the gene underlying the observed linkage and association, we carried out functional experiments in the human hepatoma cell line Huh7. Silencing of OSBPL10 increased the incorporation of [(3)H]acetate into cholesterol and both [(3)H]acetate and [(3)H]oleate into triglycerides and enhanced the accumulation of secreted apolipoprotein B100 in growth medium, suggesting that the encoded protein ORP10 suppresses hepatic lipogenesis and very-low-density lipoprotein production. ORP10 was shown to associate dynamically with microtubules, consistent with its involvement in intracellular transport or organelle positioning. The data introduces OSBPL10 as a gene whose variation may contribute to high triglyceride levels in dyslipidemic Finnish subjects and provides evidence for ORP10 as a regulator of cellular lipid metabolism.
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MESH Headings
- Cell Line, Tumor
- Cholesterol, HDL/blood
- Cholesterol, HDL/genetics
- Cholesterol, HDL/metabolism
- Female
- Finland
- Gene Silencing
- Hepatocytes/metabolism
- Humans
- Hyperlipidemia, Familial Combined/genetics
- Hyperlipidemia, Familial Combined/metabolism
- Lipid Metabolism
- Male
- Microtubules/chemistry
- Polymorphism, Single Nucleotide
- Receptors, Steroid/analysis
- Receptors, Steroid/genetics
- Receptors, Steroid/metabolism
- Triglycerides/blood
- Triglycerides/genetics
- Triglycerides/metabolism
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Affiliation(s)
- Julia Perttilä
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
- Institute of Biomedicine/Anatomy, University of Helsinki, P.O. Box 63, 00014 Helsinki, Finland
| | - Krista Merikanto
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
| | - Jussi Naukkarinen
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
| | - Ida Surakka
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
| | - Nicolas W. Martin
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- Queensland Institute of Medical Research, 300 Herston Road, Brisbane, 4029 Australia
| | - Kimmo Tanhuanpää
- Light microscopy Unit, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Vinciane Grimard
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Marja-Riitta Taskinen
- Department of Medicine, Division of Cardiology, Helsinki University Hospital and Biomedicum, Haartmaninkatu 8, 00290 Helsinki, Finland
| | - Christoph Thiele
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Veikko Salomaa
- Department of Chronic Disease Prevention, National Institute for Health and Welfare, P.O. Box 30, 00271 Helsinki, Finland
| | - Antti Jula
- National Institute for Health and Welfare, 20720 Turku, Finland
| | - Markus Perola
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
| | - Ismo Virtanen
- Institute of Biomedicine/Anatomy, University of Helsinki, P.O. Box 63, 00014 Helsinki, Finland
| | - Leena Peltonen
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
- Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA UK
- Department of Medical Genetics, University of Helsinki, 00014 Helsinki, Finland
- The Broad Institute, Boston, MA 02142 USA
| | - Vesa M. Olkkonen
- National Institute for Health and Welfare/Public Health Genomics Unit, Biomedicum, P.O. Box 104, 00251 Helsinki, Finland
- FIMM, Institute for Molecular Medicine Finland, University of Helsinki, P.O. Box 20, 00014 Helsinki, Finland
- Institute of Biomedicine/Anatomy, University of Helsinki, P.O. Box 63, 00014 Helsinki, Finland
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