101
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Pavlic M, Xiao C, Szeto L, Patterson BW, Lewis GF. Insulin acutely inhibits intestinal lipoprotein secretion in humans in part by suppressing plasma free fatty acids. Diabetes 2010; 59:580-7. [PMID: 20028946 PMCID: PMC2828667 DOI: 10.2337/db09-1297] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
OBJECTIVE Intestinal lipoprotein production has recently been shown to be increased in insulin resistance, but it is not known whether it is regulated by insulin in humans. Here, we investigated the effect of acute hyperinsulinemia on intestinal (and hepatic) lipoprotein production in six healthy men in the presence and absence of concomitant suppression of plasma free fatty acids (FFAs). RESEARCH DESIGN AND METHODS Each subject underwent the following three lipoprotein turnover studies, in random order, 4-6 weeks apart: 1) insulin and glucose infusion (euglycemic-hyperinsulinemic clamp) to induce hyperinsulinemia, 2) insulin and glucose infusion plus Intralipid and heparin infusion to prevent the insulin-induced suppression of plasma FFAs, and 3) saline control. RESULTS VLDL1 and VLDL2-apoB48 and -apoB100 production rates were suppressed by 47-62% by insulin, with no change in clearance. When the decline in FFAs was prevented by concomitant infusion of Intralipid and heparin, the production rates of VLDL1 and VLDL2-apoB48 and -apoB100 were intermediate between insulin and glucose infusion and saline control. CONCLUSIONS This is the first demonstration in humans that intestinal apoB48-containing lipoprotein production is acutely suppressed by insulin, which may involve insulin's direct effects and insulin-mediated suppression of circulating FFAs.
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Affiliation(s)
- Mirjana Pavlic
- Division of Endocrinology and Metabolism, Department of Medicine and Physiology, University of Toronto, Toronto, Canada
| | - Changting Xiao
- Division of Endocrinology and Metabolism, Department of Medicine and Physiology, University of Toronto, Toronto, Canada
| | - Linda Szeto
- Division of Endocrinology and Metabolism, Department of Medicine and Physiology, University of Toronto, Toronto, Canada
| | - Bruce W. Patterson
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Gary F. Lewis
- Division of Endocrinology and Metabolism, Department of Medicine and Physiology, University of Toronto, Toronto, Canada
- Corresponding author: Gary F. Lewis,
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102
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The assembly of lipid droplets and its relation to cellular insulin sensitivity. Biochem Soc Trans 2009; 37:981-5. [PMID: 19754436 DOI: 10.1042/bst0370981] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The assembly of lipid droplets is dependent on PtdIns(4,5)P(2) that activates PLD(1) (phospholipase D(1)), which is important for the assembly process. ERK2 (extracellular-signal-regulated kinase 2) phosphorylates the motor protein dynein and sorts it to lipid droplets, allowing them to be transported on microtubules. Lipid droplets grow in size by fusion, which is dependent on dynein and the transfer on microtubules, and is catalysed by the SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) proteins SNAP-23 (23 kDa synaptosome-associated protein), syntaxin-5 and VAMP-4 (vesicle-associated protein 4). SNAP-23 is also involved in the insulin-dependent translocation of the glucose transporter GLUT4 to the plasma membrane. Fatty acids induce a missorting of SNAP-23, from the plasma membrane to the interior of the cell, resulting in cellular insulin resistance that can be overcome by increasing the levels of SNAP-23. The same missorting of SNAP-23 occurs in vivo in skeletal-muscle biopsies from patients with T2D (Type 2 diabetes). Moreover, there was a linear relation between the amount of SNAP-23 in the plasma membrane from human skeletal-muscles biopsies and the systemic insulin-sensitivity. Syntaxin-5 is low in T2D patients, which leads to a decrease in the insulin-dependent phosphorylation of Akt (also known as protein kinase B). Thus both SNAP-23 and syntaxin-5 are highly involved in the development of insulin resistance.
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103
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Silva AR, Pacheco P, Vieira-de-Abreu A, Maya-Monteiro CM, D'Alegria B, Magalhães KG, de Assis EF, Bandeira-Melo C, Castro-Faria-Neto HC, Bozza PT. Lipid bodies in oxidized LDL-induced foam cells are leukotriene-synthesizing organelles: a MCP-1/CCL2 regulated phenomenon. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:1066-75. [DOI: 10.1016/j.bbalip.2009.06.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Revised: 06/09/2009] [Accepted: 06/23/2009] [Indexed: 12/01/2022]
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104
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Olofsson SO, Boström P, Andersson L, Li L, Højlund K, Adiels M, Perkins R, Borén J. Lipid droplets and their role in the development of insulin resistance and diabetic dyslipidemia. ACTA ACUST UNITED AC 2009. [DOI: 10.2217/clp.09.54] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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105
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Abstract
Lipid droplets are intracellular organelles that play central roles in lipid metabolism. In many cells, lipid droplets undergo active motion, typically along microtubules. This motion has been proposed to aid growth and breakdown of droplets, to allow net transfer of nutrients from sites of synthesis to sites of need and to deliver proteins and lipophilic signals. This review summarizes the current understanding of where, why and how lipid droplets move.
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106
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Zehmer JK, Huang Y, Peng G, Pu J, Anderson RGW, Liu P. A role for lipid droplets in inter-membrane lipid traffic. Proteomics 2009; 9:914-21. [PMID: 19160396 DOI: 10.1002/pmic.200800584] [Citation(s) in RCA: 205] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
All cells have the capacity to accumulate neutral lipids and package them into lipid droplets. Recent proteomic analyses indicate that lipid droplets are not simple lipid storage depots, but rather complex organelles that have multiple cellular functions. One of these proposed functions is to distribute neutral lipids as well as phospholipids to various membrane-bound organelles within the cell. Here, we summarize the lipid droplet-associated membrane-trafficking proteins and review the evidence that lipid droplets interact with endoplasmic reticulum, endosomes, peroxisomes, and mitochondria. Based on this evidence, we present a model for how lipid droplets can distribute lipids to specific membrane compartments.
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Affiliation(s)
- John K Zehmer
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
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107
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Jägerström S, Polesie S, Wickström Y, Johansson BR, Schröder HD, Højlund K, Boström P. Lipid droplets interact with mitochondria using SNAP23. Cell Biol Int 2009; 33:934-40. [PMID: 19524684 DOI: 10.1016/j.cellbi.2009.06.011] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Revised: 03/30/2009] [Accepted: 06/03/2009] [Indexed: 12/17/2022]
Abstract
Triglyceride-containing lipid droplets (LD) are dynamic organelles stored on demand in all cells. These droplets grow through a fusion process mediated by SNARE proteins, including SNAP23. The droplets have also been shown to be highly motile and interact with other cell organelles, including peroxisomes and the endoplasmic reticulum. We have used electron and confocal microscopy to demonstrate that LD form complexes with mitochondria in NIH 3T3 fibroblasts. Using an in vitro system of purified LD and mitochondria, we also show the formation of the LD-mitochondria complex, in which cytosolic factors are involved. Moreover, the presence of LD markers in mitochondria isolated by subcellular fractionations is demonstrated. Finally, ablation of SNAP23 using siRNA reduced complex formation and beta oxidation, which suggests that the LD-mitochondria complex is functional in the cell.
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Affiliation(s)
- Sara Jägerström
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Lab 1, Bruna Stråket 16, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden
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108
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PAT proteins, an ancient family of lipid droplet proteins that regulate cellular lipid stores. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:419-40. [PMID: 19375517 DOI: 10.1016/j.bbalip.2009.04.002] [Citation(s) in RCA: 508] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 02/24/2009] [Accepted: 04/08/2009] [Indexed: 02/07/2023]
Abstract
The PAT family of lipid droplet proteins includes 5 members in mammals: perilipin, adipose differentiation-related protein (ADRP), tail-interacting protein of 47 kDa (TIP47), S3-12, and OXPAT. Members of this family are also present in evolutionarily distant organisms, including insects, slime molds and fungi. All PAT proteins share sequence similarity and the ability to bind intracellular lipid droplets, either constitutively or in response to metabolic stimuli, such as increased lipid flux into or out of lipid droplets. Positioned at the lipid droplet surface, PAT proteins manage access of other proteins (lipases) to the lipid esters within the lipid droplet core and can interact with cellular machinery important for lipid droplet biogenesis. Genetic variations in the gene for the best-characterized of the mammalian PAT proteins, perilipin, have been associated with metabolic phenotypes, including type 2 diabetes mellitus and obesity. In this review, we discuss how the PAT proteins regulate cellular lipid metabolism both in mammals and in model organisms.
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109
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Abstract
The intracellular storage and utilization of lipids are critical to maintain cellular energy homeostasis. During nutrient deprivation, cellular lipids stored as triglycerides in lipid droplets are hydrolysed into fatty acids for energy. A second cellular response to starvation is the induction of autophagy, which delivers intracellular proteins and organelles sequestered in double-membrane vesicles (autophagosomes) to lysosomes for degradation and use as an energy source. Lipolysis and autophagy share similarities in regulation and function but are not known to be interrelated. Here we show a previously unknown function for autophagy in regulating intracellular lipid stores (macrolipophagy). Lipid droplets and autophagic components associated during nutrient deprivation, and inhibition of autophagy in cultured hepatocytes and mouse liver increased triglyceride storage in lipid droplets. This study identifies a critical function for autophagy in lipid metabolism that could have important implications for human diseases with lipid over-accumulation such as those that comprise the metabolic syndrome.
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110
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Walther TC, Farese RV. The life of lipid droplets. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:459-66. [PMID: 19041421 DOI: 10.1016/j.bbalip.2008.10.009] [Citation(s) in RCA: 349] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Revised: 10/14/2008] [Accepted: 10/28/2008] [Indexed: 12/12/2022]
Abstract
Lipid droplets are the least characterized of cellular organelles. Long considered simple lipid storage depots, these dynamic and remarkable organelles have recently been implicated in many biological processes, and we are only now beginning to gain insights into their fascinating lives in cells. Here we examine what we know of the life of lipid droplets. We review emerging data concerning their cellular biology and present our thoughts on some of the most salient questions for investigation.
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Affiliation(s)
- Tobias C Walther
- Organelle Architecture and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany.
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111
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Grimard V, Massier J, Richter D, Schwudke D, Kalaidzidis Y, Fava E, Hermetter A, Thiele C. siRNA screening reveals JNK2 as an evolutionary conserved regulator of triglyceride homeostasis. J Lipid Res 2008; 49:2427-40. [DOI: 10.1194/jlr.m800168-jlr200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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112
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Nikonova L, Koza RA, Mendoza T, Chao PM, Curley JP, Kozak LP. Mesoderm-specific transcript is associated with fat mass expansion in response to a positive energy balance. FASEB J 2008; 22:3925-37. [PMID: 18644838 PMCID: PMC2574032 DOI: 10.1096/fj.08-108266] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2008] [Accepted: 06/19/2008] [Indexed: 12/20/2022]
Abstract
A 50-fold variation in mRNA and protein levels of the mesoderm-specific transcript gene (Mest) in white fat of C57BL/6J (B6) mice fed an obesogenic diet is positively correlated with expansion of fat mass. MEST protein was detected only in adipocytes, in which its induction occurred with both unsaturated and saturated dietary fat. To test the hypothesis that MEST modulates fat mass expansion, its expression was compared to that of stearoyl CoA desaturase (Scd1) in B6 mice exposed to diets and environmental temperatures that generated conditions separating the effects of food intake and adiposity. Under a range of conditions, Mest expression was always associated with variations in adiposity, whereas Scd1 expression was associated with the amount of saturated fat in the diet. Mest mRNA was expressed at its highest levels during early postnatal growth at the onset of the most rapid phase of fat mass expansion. MEST is localized to the endoplasmic reticulum/Golgi apparatus where its putative enzymatic properties as a lipase or acyltransferase, predicted from sequence homology with members of the alpha/beta fold hydrolase superfamily, can enable it to function in lipid accumulation under conditions of positive energy balance. Variations in adiposity and Mest expression in genetically identical mice also provides a model of epigenetic regulation.
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Affiliation(s)
- Larissa Nikonova
- Pennington Biomedical Research Center, 6400 Perkins Rd., Baton Rouge, LA 70808, USA
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113
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Biogenesis of cytoplasmic lipid droplets: from the lipid ester globule in the membrane to the visible structure. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:399-407. [PMID: 18996222 DOI: 10.1016/j.bbalip.2008.10.002] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 08/09/2008] [Accepted: 10/06/2008] [Indexed: 01/22/2023]
Abstract
The cytoplasmic lipid droplet (CLD) and very low-density lipoprotein are generated from the lipid ester synthesized in the endoplasmic reticulum. The lipid ester deposited between the two membrane leaflets is supposed to bulge toward the cytoplasm to make a nascent CLD, but its size must be below the resolution limit of conventional techniques and the detectable CLD should only form after acquisition of additional lipid esters. The CLD is different from vesicular organelles in that the internal content is highly hydrophobic and the shape is invariably spherical. Due to its unique characteristics, quantitative discordance between the surface and the volume may occur in the growth and/or involution processes of the CLD. The possibility that these processes may give rise to the structural and functional diversities of the CLD is discussed.
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114
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Olofsson SO, Boström P, Andersson L, Rutberg M, Levin M, Perman J, Borén J. Triglyceride containing lipid droplets and lipid droplet-associated proteins. Curr Opin Lipidol 2008; 19:441-7. [PMID: 18769224 DOI: 10.1097/mol.0b013e32830dd09b] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
PURPOSE OF REVIEW Cytosolic lipid droplets are now recognized as dynamic organelles. This review summarizes our current understanding of the mechanisms involved in the formation of lipid droplets, the importance of lipid droplet-associated proteins and the link between lipid droplet accumulation and development of insulin resistance. RECENT FINDINGS Lipid droplets are formed as primordial droplets and they increase in size by fusion. This fusion process requires the alpha-soluble N-ethylmaleimide-sensitive factor adaptor protein receptor SNAP23, which is also involved in the insulin-dependent translocation of a glucose transporter to the plasma membrane. Recent data suggest that SNAP23 is the link between increased lipid droplet accumulation and development of insulin resistance. Lipid droplets also form tight interactions with other organelles. Furthermore, additional lipid droplet-associated proteins have been identified and shown to play a role in droplet assembly and turnover, and in sorting and trafficking events. SUMMARY Recent studies have identified a number of key proteins that are involved in the formation and turnover of lipid droplets, and SNAP23 has been identified as a link between accumulation of lipid droplets and development of insulin resistance. Further understanding of lipid droplet biology could indicate potential therapeutic targets to prevent accumulation of lipid droplets and associated complications.
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Affiliation(s)
- Sven-Olof Olofsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Gothenburg, Sweden.
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115
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Olofsson SO, Boström P, Andersson L, Rutberg M, Perman J, Borén J. Lipid droplets as dynamic organelles connecting storage and efflux of lipids. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:448-58. [PMID: 18775796 DOI: 10.1016/j.bbalip.2008.08.001] [Citation(s) in RCA: 181] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2008] [Revised: 06/24/2008] [Accepted: 08/05/2008] [Indexed: 02/06/2023]
Abstract
Neutral lipids are stored in the cytosol in so-called lipid droplets. These are dynamic organelles with neutral lipids as the core surrounded by a monolayer of amphipathic lipids (phospholipids and cholesterol) and specific proteins (PAT proteins and proteins involved in the turnover of lipids and in the formation and trafficking of the droplets). Lipid droplets are formed at microsomal membranes as primordial droplets with a diameter of 0.1-0.4 microm and increase in size by fusion. In this article, we review the assembly and fusion of lipid droplets, and the processes involved in the secretion of triglycerides. Triglycerides are secreted from cells by two principally different processes. In the mammary gland, lipid droplets interact with specific regions of the plasma membrane and bud off with an envelope consisting of the membrane, to form milk globules. In the liver and intestine, very low-density lipoproteins (VLDL) and chylomicrons are secreted by using the secretory pathway of the cell. Finally, we briefly review the importance of lipid droplets in the development of insulin resistance and atherosclerosis.
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Affiliation(s)
- Sven-Olof Olofsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
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116
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Murphy S, Martin S, Parton RG. Lipid droplet-organelle interactions; sharing the fats. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:441-7. [PMID: 18708159 DOI: 10.1016/j.bbalip.2008.07.004] [Citation(s) in RCA: 186] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Revised: 06/09/2008] [Accepted: 07/18/2008] [Indexed: 12/20/2022]
Abstract
Lipid droplets (LDs) are key cellular organelles involved in lipid storage and mobilisation. While the major signalling cascades and many of the regulators of lipolysis have been identified, the cellular interactions involved in lipid mobilisation and release remain largely undefined. In non-adipocytes, LDs are small, mobile and interact with other cellular compartments. In contrast, adipocytes primarily contain very large, immotile LDs. The striking morphological differences between LDs in adipocytes and non-adipocytes suggest that key differences must exist in the manner in which LDs in different cell types interact with other organelles. Recent studies have highlighted the complexity of LD interactions, which can be both homotypic, with each other, and heterotypic, with other organelles. The molecules involved in these interactions are also now emerging, including Rab proteins, key regulators of membrane traffic, and caveolin, an integral membrane protein providing a functional link between the cell surface and LDs. Here we summarise recent insights into the cell biology of the LD particularly focussing on the homotypic and heterotypic interactions in both adipocytes and non-adipocytes. We speculate that these interactions may involve inter-organelle membrane contact sites or a hemi-fusion type mechanism to facilitate lipid transfer.
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Affiliation(s)
- Samantha Murphy
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia
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117
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Gubern A, Casas J, Barceló-Torns M, Barneda D, de la Rosa X, Masgrau R, Picatoste F, Balsinde J, Balboa MA, Claro E. Group IVA phospholipase A2 is necessary for the biogenesis of lipid droplets. J Biol Chem 2008; 283:27369-27382. [PMID: 18632668 DOI: 10.1074/jbc.m800696200] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Lipid droplets (LD) are organelles present in all cell types, consisting of a hydrophobic core of triacylglycerols and cholesteryl esters, surrounded by a monolayer of phospholipids and cholesterol. This work shows that LD biogenesis induced by serum, by long-chain fatty acids, or the combination of both in CHO-K1 cells was prevented by phospholipase A(2) inhibitors with a pharmacological profile consistent with the implication of group IVA cytosolic phospholipase A(2) (cPLA(2)alpha). Knocking down cPLA(2)alpha expression with short interfering RNA was similar to pharmacological inhibition in terms of enzyme activity and LD biogenesis. A Chinese hamster ovary cell clone stably expressing an enhanced green fluorescent protein-cPLA(2)alpha fusion protein (EGFP-cPLA(2)) displayed higher LD occurrence under basal conditions and upon LD induction. Induction of LD took place with concurrent phosphorylation of cPLA(2)alpha at Ser(505). Transfection of a S505A mutant cPLA(2)alpha showed that phosphorylation at Ser(505) is key for enzyme activity and LD formation. cPLA(2)alpha contribution to LD biogenesis was not because of the generation of arachidonic acid, nor was it related to neutral lipid synthesis. cPLA(2)alpha inhibition in cells induced to form LD resulted in the appearance of tubulo-vesicular profiles of the smooth endoplasmic reticulum, compatible with a role of cPLA(2)alpha in the formation of nascent LD from the endoplasmic reticulum.
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Affiliation(s)
- Albert Gubern
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona
| | - Javier Casas
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas, E-47003 Valladolid, Spain
| | - Miquel Barceló-Torns
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona
| | - David Barneda
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona
| | - Xavier de la Rosa
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona
| | - Roser Masgrau
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona
| | - Fernando Picatoste
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona
| | - Jesús Balsinde
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas, E-47003 Valladolid, Spain
| | - María A Balboa
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas, E-47003 Valladolid, Spain
| | - Enrique Claro
- Institut de Neurociències and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, E-08193 Barcelona.
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118
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Affiliation(s)
- Joel M Goodman
- Department of Pharmacology, University of Texas Southwestern Medical School, Dallas, Texas 75390-9041, USA.
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119
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Thiele C, Spandl J. Cell biology of lipid droplets. Curr Opin Cell Biol 2008; 20:378-85. [PMID: 18606534 DOI: 10.1016/j.ceb.2008.05.009] [Citation(s) in RCA: 221] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 05/27/2008] [Accepted: 05/27/2008] [Indexed: 02/01/2023]
Abstract
Lipid storage has attracted much attention in the past years, both by the broader public and the biomedical scientific community. Driven by concerns about the obesity epidemic that affects most industrialized countries and even substantial parts of the population in less and least developed countries, work from researchers of many disciplines has shed light on the genetics, the physiology, and the cellular mechanisms of fat accumulation. This review focuses on the actual organelle of fat deposition, the lipid droplet (LD), and on the recent progress in mechanistic understanding of processes like LD biogenesis, LD growth and degradation, protein targeting to LDs and LD fusion.
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Affiliation(s)
- Christoph Thiele
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, D-01307 Dresden, Germany.
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120
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Fujimoto T, Ohsaki Y, Cheng J, Suzuki M, Shinohara Y. Lipid droplets: a classic organelle with new outfits. Histochem Cell Biol 2008; 130:263-79. [PMID: 18546013 PMCID: PMC2491702 DOI: 10.1007/s00418-008-0449-0] [Citation(s) in RCA: 247] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/23/2008] [Indexed: 12/28/2022]
Abstract
Lipid droplets are depots of neutral lipids that exist virtually in any kind of cell. Recent studies have revealed that the lipid droplet is not a mere lipid blob, but a major contributor not only to lipid homeostasis but also to diverse cellular functions. Because of the unique structure as well as the functional importance in relation to obesity, steatosis, and other prevailing diseases, the lipid droplet is now reborn as a brand new organelle, attracting interests from researchers of many disciplines.
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Affiliation(s)
- Toyoshi Fujimoto
- Department of Anatomy and Molecular Cell Biology, Graduate School of Medicine, Nagoya University, 65 Tsurumai, Showa, Nagoya, 466-8550, Japan.
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121
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Takeda Y, Nakano A. In vitro formation of a novel type of membrane vesicles containing Dpm1p: putative transport vesicles for lipid droplets in budding yeast. J Biochem 2008; 143:803-11. [PMID: 18343875 DOI: 10.1093/jb/mvn034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A novel type of membrane vesicles was formed in vitro from microsomes of Saccharomyces cerevisiae, which carries Dpm1p, an enzyme involved in dolichol-sugar synthesis, but not a typical secretory cargo. While COPII vesicles formed in vitro were sedimentable by centrifugation at 200,000g(max) for 15 min, the novel vesicles were not. However, they were sedimented by additional centrifugation at the same speed for 1 h. Immunoelectron microscopy showed that the Dpm1p-containing vesicles had small vesicular/saccular structures of around 40-50 nm in diameter. The addition of glycerol-3-phosphate and oleoyl-CoA, substrates for lipid biosynthesis, significantly enhanced the efficiency of vesicle budding in an ATP-dependent fashion. Dpm1p was localized to lipid droplets as well as endoplasmic reticulum. Fluorescence microscopy further showed that Dpm1p-GFP was present in restricted subregions in isolated lipid droplets. The possibility that the vesicles were intermediates from the endoplasmic reticulum to lipid droplets was examined, and their possible role is discussed.
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Affiliation(s)
- Yuichi Takeda
- Molecular Membrane Biology Laboratory, RIKEN Discovery Research Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan.
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122
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Abstract
Organisms store energy for later use during times of nutrient scarcity. Excess energy is stored as triacylglycerol in lipid droplets during lipogenesis. When energy is required, the stored triacylglycerol is hydrolyzed via activation of lipolytic pathways. The coordination of lipid storage and utilization is regulated by the perilipin family of lipid droplet coat proteins [perilipin, adipophilin/adipocyte differentiation-related protein (ADRP), S3-12, tail-interacting protein of 47 kilodaltons (TIP47), and myocardial lipid droplet protein (MLDP)/oxidative tissues-enriched PAT protein (OXPAT)/lipid storage droplet protein 5 (LSDP5)]. Lipid droplets are dynamic and heterogeneous in size, location, and protein content. The proteins that coat lipid droplets change during lipid droplet biogenesis and are dependent upon multiple factors, including tissue-specific expression and metabolic state (basal vs. lipogenic vs. lipolytic). New data suggest that proteins previously implicated in vesicle trafficking, including Rabs, soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), and motor and cytoskeletal proteins, likely orchestrate the movement and fusion of lipid droplets. Thus, rather than inert cytoplasmic inclusions, lipid droplets are now appreciated as dynamic organelles that are critical for management of cellular lipid stores. That much remains to be discovered is suggested by the recent identification of a novel lipase [adipocyte triglyceride lipase (ATGL)] and lipase regulator [Comparative Gene Identification-58 (CGI-58)], which has led to reconsideration of the decades-old model of lipolysis. Future discovery likely will be driven by the exploitation of model organisms and by human genetic studies.
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Affiliation(s)
- Nicole A Ducharme
- Center for Diabetes and Obesity Research, Brown Foundation Institute of Molecular Medicine, 1825 Pressler Street, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA
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Martin S, Parton RG. Characterization of Rab18, a lipid droplet-associated small GTPase. Methods Enzymol 2008; 438:109-29. [PMID: 18413244 DOI: 10.1016/s0076-6879(07)38008-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Lipid droplets are the major intracellular store of lipids in eukaryotic cells. Understanding lipid storage and regulated mobilization of lipids from lipid droplets is essential for understanding the syndromes and diseases associated with excess lipid accumulation. Lipid droplets have been traditionally considered relatively inert structures. However, in recent years it has become apparent that lipid droplets are highly dynamic regulated organelles, which show complex interactions with other cellular compartments. The cellular components involved in regulation of lipid accumulation and release from lipid droplets, and in mediating the complex interactions with other organelles, are only now starting to be unraveled. A particularly important family of proteins in this respect is the Rab GTPases, crucial regulators of membrane traffic. Here we describe the techniques that we used to characterize the regulated association of Rab18 with the surface of lipid droplets. Rab18 provides an excellent marker to follow the dynamics of lipid droplets in living cells. In addition, the study of Rab18 provides insights into the mechanisms involved in the release of lipids from lipid droplets in adipocytes. In 3T3-L1 adipocytes, stimulation of lipolysis increases the association of Rab18 with lipid droplets, suggesting that recruitment of Rab18 is regulated by the metabolic state of individual lipid droplets. The study of Rab18 and its interacting proteins will provide new insights into the complex regulatory mechanisms involved in lipid storage and release.
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Affiliation(s)
- Sally Martin
- Institute for Molecular Bioscience and Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia
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Pacheco P, Vieira-de-Abreu A, Gomes RN, Barbosa-Lima G, Wermelinger LB, Maya-Monteiro CM, Silva AR, Bozza MT, Castro-Faria-Neto HC, Bandeira-Melo C, Bozza PT. Monocyte Chemoattractant Protein-1/CC Chemokine Ligand 2 Controls Microtubule-Driven Biogenesis and Leukotriene B4-Synthesizing Function of Macrophage Lipid Bodies Elicited by Innate Immune Response. THE JOURNAL OF IMMUNOLOGY 2007; 179:8500-8. [DOI: 10.4049/jimmunol.179.12.8500] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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125
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Adiels M, Westerbacka J, Soro-Paavonen A, Häkkinen AM, Vehkavaara S, Caslake MJ, Packard C, Olofsson SO, Yki-Järvinen H, Taskinen MR, Borén J. Acute suppression of VLDL1 secretion rate by insulin is associated with hepatic fat content and insulin resistance. Diabetologia 2007; 50:2356-65. [PMID: 17849096 DOI: 10.1007/s00125-007-0790-1] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Accepted: 06/21/2007] [Indexed: 12/11/2022]
Abstract
AIMS/HYPOTHESIS Overproduction of VLDL(1) seems to be the central pathophysiological feature of the dyslipidaemia associated with type 2 diabetes. We explored the relationship between liver fat and suppression of VLDL(1) production by insulin in participants with a broad range of liver fat content. METHODS A multicompartmental model was used to determine the kinetic parameters of apolipoprotein B and TG in VLDL(1) and VLDL(2) after a bolus of [(2)H(3)]leucine and [(2)H(5)]glycerol during a hyperinsulinaemic-euglycaemic clamp in 20 male participants: eight with type 2 diabetes and 12 control volunteers. The participants were divided into two groups with low or high liver fat. All participants with diabetes were in the high liver-fat group. RESULTS The results showed a rapid drop in VLDL(1)-apolipoprotein B and -triacylglycerol secretion in participants with low liver fat during the insulin infusion. In contrast, participants with high liver fat showed no significant change in VLDL(1) secretion. The VLDL(1) suppression following insulin infusion correlated with the suppression of NEFA, and the ability of insulin to suppress the plasma NEFA was impaired in participants with high liver fat. A novel finding was an inverse response between VLDL(1) and VLDL(2) secretion in participants with low liver fat: VLDL(1) secretion decreased acutely after insulin infusion whereas VLDL(2) secretion increased. CONCLUSIONS/INTERPRETATION Insulin downregulates VLDL(1) secretion and increases VLDL(2) secretion in participants with low liver fat but fails to suppress VLDL(1) secretion in participants with high liver fat, resulting in overproduction of VLDL(1). Thus, liver fat is associated with lack of VLDL(1) suppression in response to insulin.
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Affiliation(s)
- M Adiels
- Sahlgrenska Center for Cardiovascular and Metabolic Research/Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Göteborg University, Gothenburg, Sweden
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126
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Gustafsson M, Levin M, Skålén K, Perman J, Fridén V, Jirholt P, Olofsson SO, Fazio S, Linton MF, Semenkovich CF, Olivecrona G, Borén J. Retention of Low-Density Lipoprotein in Atherosclerotic Lesions of the Mouse. Circ Res 2007; 101:777-83. [PMID: 17761930 DOI: 10.1161/circresaha.107.149666] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Direct binding of apolipoprotein (apo)B-containing lipoproteins to proteoglycans is the initiating event in atherosclerosis, but the processes involved at later stages of development are unclear. Here, we investigated the importance of the apoB–proteoglycan interaction in the development of atherosclerosis over time and investigated the role of lipoprotein lipase (LPL) to facilitate low-density lipoprotein (LDL) retention at later stages of development. Atherosclerosis was analyzed in apoB transgenic mice expressing LDL with normal (control LDL) or reduced proteoglycan-binding (RK3359-3369SA LDL) activity after an atherogenic diet for 0 to 40 weeks. The initiation of atherosclerosis was delayed in mice expressing RK3359-3369SA LDL, but they eventually developed the same level of atherosclerosis as mice expressing control LDL. Retention studies in vivo showed that although higher levels of
131
I-tyramine cellobiose–labeled control LDL (
131
I-TC-LDL) were retained in nonatherosclerotic aortae compared with RK3359-3369SA
131
I-TC-LDL, the retention was significantly higher and there was no difference between the groups in atherosclerotic aortae. Lower levels of control
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I-TC-LDL and RK3359-3369SA
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I-TC-LDL were retained in atherosclerotic aortae from
ldlr
−/−
mice transplanted with
lpl
−/−
compared with
lpl
+/+
bone marrow. Uptake of control LDL or RK3359-3369SA LDL into macrophages with specific expression of human catalytically active or inactive LPL was increased compared with control macrophages. Furthermore, transgenic mice expressing catalytically active or inactive LPL developed the same extent of atherosclerosis. Thus, retention of LDL in the artery wall is initiated by direct LDL–proteoglycan binding but shifts to indirect binding with bridging molecules such as LPL.
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Affiliation(s)
- Maria Gustafsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research/Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Göteborg University, Sweden
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127
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SNARE proteins mediate fusion between cytosolic lipid droplets and are implicated in insulin sensitivity. Nat Cell Biol 2007; 9:1286-93. [PMID: 17922004 DOI: 10.1038/ncb1648] [Citation(s) in RCA: 267] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2007] [Accepted: 09/06/2007] [Indexed: 11/09/2022]
Abstract
The accumulation of cytosolic lipid droplets in muscle and liver cells has been linked to the development of insulin resistance and type 2 diabetes. Such droplets are formed as small structures that increase in size through fusion, a process that is dependent on intact microtubules and the motor protein dynein. Approximately 15% of all droplets are involved in fusion processes at a given time. Here, we show that lipid droplets are associated with proteins involved in fusion processes in the cell: NSF (N-ethylmaleimide-sensitive-factor), alpha-SNAP (soluble NSF attachment protein) and the SNAREs (SNAP receptors), SNAP23 (synaptosomal-associated protein of 23 kDa), syntaxin-5 and VAMP4 (vesicle-associated membrane protein 4). Knockdown of the genes for SNAP23, syntaxin-5 or VAMP4, or microinjection of a dominant-negative mutant of alpha-SNAP, decreases the rate of fusion and the size of the lipid droplets. Thus, the SNARE system seems to have an important role in lipid droplet fusion. We also show that oleic acid treatment decreases the insulin sensitivity of heart muscle cells, and this sensitivity is completely restored by transfection with SNAP23. Thus, SNAP23 might be a link between insulin sensitivity and the inflow of fatty acids to the cell.
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128
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Yan D, Lehto M, Rasilainen L, Metso J, Ehnholm C, Ylä-Herttuala S, Jauhiainen M, Olkkonen VM. Oxysterol Binding Protein Induces Upregulation of SREBP-1c and Enhances Hepatic Lipogenesis. Arterioscler Thromb Vasc Biol 2007; 27:1108-14. [PMID: 17303778 DOI: 10.1161/atvbaha.106.138545] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Oxysterol binding protein (OSBP) has previously been implicated as a sterol sensor that regulates sphingomyelin synthesis and the activity of extracellular signal-regulated kinases (ERK). METHODS AND RESULTS We determined the effects of adenovirus-mediated hepatic overexpression of OSBP and its homologues ORP1L and ORP3 on mouse serum lipids. Whereas ORP1L and ORP3 had no effect on serum lipids, OSBP induced a marked increase of VLDL triglycerides (TG). Also, the liver tissue TG were elevated in the AdOSBP-injected mice, and their TG secretion rate was increased by 70%. The messenger RNAs for enzymes of fatty acid synthesis and their transcriptional regulator, SREBP-1c, as well as the Insig-1 mRNA, were upregulated two-fold in the OSBP-expressing livers. No change occurred in the messages of liver X receptor target genes ABCA1, ABCG5, and CYP7A1, and the Insig-2a mRNA was reduced. The phosphorylation of ERK was decreased in AdOSBP-infected liver and cultured hepatocytes. Importantly, silencing of OSBP in hepatocytes suppressed the induction of SREBP1-c by insulin and resulted in a reduction of TG synthesis. CONCLUSION Our results demonstrate that OSBP regulates hepatic TG metabolism and suggest the involvement of OSBP in the insulin signaling pathways that control hepatic lipogenesis.
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MESH Headings
- Animals
- Blotting, Western
- Carcinoma, Hepatocellular/metabolism
- Carcinoma, Hepatocellular/pathology
- Carrier Proteins/biosynthesis
- Carrier Proteins/genetics
- Cells, Cultured
- Cholesterol, VLDL/blood
- Fatty Acid-Binding Proteins
- Female
- Gene Silencing
- Humans
- Insulin/metabolism
- Lipogenesis/physiology
- Liver/metabolism
- Liver/pathology
- Liver Neoplasms, Experimental/metabolism
- Liver Neoplasms, Experimental/pathology
- Mice
- Mice, Inbred C57BL
- RNA, Messenger/genetics
- Rabbits
- Receptors, Steroid/biosynthesis
- Receptors, Steroid/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Triglycerides/biosynthesis
- Up-Regulation
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Affiliation(s)
- Daoguang Yan
- Department of Molecular Medicine, National Public Health Institute, Biomedicum, P.O.Box 104, FI-00251 Helsinki, Finland
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129
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Wolins NE, Brasaemle DL, Bickel PE. A proposed model of fat packaging by exchangeable lipid droplet proteins. FEBS Lett 2006; 580:5484-91. [PMID: 16962104 DOI: 10.1016/j.febslet.2006.08.040] [Citation(s) in RCA: 309] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Revised: 08/22/2006] [Accepted: 08/22/2006] [Indexed: 01/10/2023]
Abstract
Humans have evolved mechanisms of efficient fat storage to survive famine, but these mechanisms contribute to obesity in our current environment of plentiful food and reduced activity. Little is known about how animals package fat within cells. Five related structural proteins serve roles in packaging fat into lipid droplets. The proteins TIP47, S3-12, and OXPAT/MLDP/PAT-1 move from the cytosol to coat nascent lipid droplets during rapid fat storage. In contrast, perilipin and adipophilin constitutively associate with lipid droplets and play roles in sustained fat storage and regulation of lipolysis. Different tissues express different complements of these lipid droplet proteins. Thus, the tissue-specific complement of these proteins determines how tissues manage lipid stores.
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Affiliation(s)
- Nathan E Wolins
- Department of Medicine, Division of Endocrinology, Metabolism and Lipid Research, Washington University School of Medicine, Saint Louis, MO 63110, USA
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130
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Boström P, Magnusson B, Svensson PA, Wiklund O, Borén J, Carlsson LMS, Ståhlman M, Olofsson SO, Hultén LM. Hypoxia converts human macrophages into triglyceride-loaded foam cells. Arterioscler Thromb Vasc Biol 2006; 26:1871-6. [PMID: 16741148 DOI: 10.1161/01.atv.0000229665.78997.0b] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVE Atherosclerotic lesions have regions that are hypoxic. Because the lesion contains macrophages that are loaded with lipid, we investigated whether hypoxia can influence the accumulation of lipids in these cells. METHODS AND RESULTS Exposure of human macrophages to hypoxia for 24 hours resulted in an increased formation of cytosolic lipid droplets and an increased accumulation of triglycerides. Exposure of the macrophages to oxidized low-density lipoprotein (oxLDL) increased the accumulation of cytosolic lipid droplets because of an increase in cellular cholesterol esters. The accumulation of lipid droplets in oxLDL-treated cells was further increased after hypoxia, caused by an increased level of triglycerides. Expression analyses combined with immunoblot or RT-PCR demonstrated that hypoxia increased the expression of several genes that could promote the accumulation of lipid droplets. Hypoxia increased the mRNA and protein levels of adipocyte differentiation-related protein (ADRP). It is well known that an increased expression of ADRP increases the formation of lipid droplets. Hypoxia decreased the expression of enzymes involved in beta-oxidation (acyl-coenzyme A synthetase and acyl-coenzyme A dehydrogenase) and increased the expression of stearoyl-coenzyme A desaturase, an important enzyme in the fatty acid biosynthesis. Moreover, exposure to hypoxia decreased the rate of beta-oxidation, whereas the accumulation of triglycerides increased. CONCLUSIONS The results demonstrate that exposure of human macrophages to hypoxia causes an accumulation of triglyceride-containing cytosolic lipid droplets. This indicates that the hypoxia present in atherosclerotic lesions can contribute to the formation of the lipid-loaded macrophages that characterize the lesion and to the accumulation of triglycerides in such lesions.
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Affiliation(s)
- Pontus Boström
- Wallenberg Laboratory for Cardiovascular Research, Sahlgrenska Academy, Göteborg, Sweden
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