151
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Berger JH, Charron MJ, Silver DL. Major facilitator superfamily domain-containing protein 2a (MFSD2A) has roles in body growth, motor function, and lipid metabolism. PLoS One 2012; 7:e50629. [PMID: 23209793 PMCID: PMC3510178 DOI: 10.1371/journal.pone.0050629] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 10/22/2012] [Indexed: 12/24/2022] Open
Abstract
The metabolic adaptations to fasting in the liver are largely controlled by the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARα), where PPARα upregulates genes encoding the biochemical pathway for β-oxidation of fatty acids and ketogenesis. As part of an effort to identify and characterize nutritionally regulated genes that play physiological roles in the adaptation to fasting, we identified Major facilitator superfamily domain-containing protein 2a (Mfsd2a) as a fasting-induced gene regulated by both PPARα and glucagon signaling in the liver. MFSD2A is a cell-surface protein homologous to bacterial sodium-melibiose transporters. Hepatic expression and turnover of MFSD2A is acutely regulated by fasting/refeeding, but expression in the brain is constitutive. Relative to wildtype mice, gene-targeted Mfsd2a knockout mice are smaller, leaner, and have decreased serum, liver and brown adipose triglycerides. Mfsd2a knockout mice have normal liver lipid metabolism but increased whole body energy expenditure, likely due to increased β-oxidation in brown adipose tissue and significantly increased voluntary movement, but surprisingly exhibited a form of ataxia. Together, these results indicate that MFSD2A is a nutritionally regulated gene that plays myriad roles in body growth and development, motor function, and lipid metabolism. Moreover, these data suggest that the ligand(s) that are transported by MFSD2A play important roles in these physiological processes and await future identification.
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Affiliation(s)
- Justin H. Berger
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Maureen J. Charron
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Medicine, Division of Endocrinology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Obstetrics and Gynecology and Women’s Health, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - David L. Silver
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Signature Research Program in Cardiovascular & Metabolic Disorders, Duke-NUS Graduate Medical School, Singapore, Singapore
- * E-mail:
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152
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Moir RD, Gross DA, Silver DL, Willis IM. SCS3 and YFT2 link transcription of phospholipid biosynthetic genes to ER stress and the UPR. PLoS Genet 2012; 8:e1002890. [PMID: 22927826 PMCID: PMC3426550 DOI: 10.1371/journal.pgen.1002890] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Accepted: 06/19/2012] [Indexed: 11/21/2022] Open
Abstract
The ability to store nutrients in lipid droplets (LDs) is an ancient function that provides the primary source of metabolic energy during periods of nutrient insufficiency and between meals. The Fat storage-Inducing Transmembrane (FIT) proteins are conserved ER–resident proteins that facilitate fat storage by partitioning energy-rich triglycerides into LDs. FIT2, the ancient ortholog of the FIT gene family first identified in mammals has two homologs in Saccharomyces cerevisiae (SCS3 and YFT2) and other fungi of the Saccharomycotina lineage. Despite the coevolution of these genes for more than 170 million years and their divergence from higher eukaryotes, SCS3, YFT2, and the human FIT2 gene retain some common functions: expression of the yeast genes in a human embryonic kidney cell line promotes LD formation, and expression of human FIT2 in yeast rescues the inositol auxotrophy and chemical and genetic phenotypes of strains lacking SCS3. To better understand the function of SCS3 and YFT2, we investigated the chemical sensitivities of strains deleted for either or both genes and identified synthetic genetic interactions against the viable yeast gene-deletion collection. We show that SCS3 and YFT2 have shared and unique functions that connect major biosynthetic processes critical for cell growth. These include lipid metabolism, vesicular trafficking, transcription of phospholipid biosynthetic genes, and protein synthesis. The genetic data indicate that optimal strain fitness requires a balance between phospholipid synthesis and protein synthesis and that deletion of SCS3 and YFT2 impacts a regulatory mechanism that coordinates these processes. Part of this mechanism involves a role for SCS3 in communicating changes in the ER (e.g. due to low inositol) to Opi1-regulated transcription of phospholipid biosynthetic genes. We conclude that SCS3 and YFT2 are required for normal ER membrane biosynthesis in response to perturbations in lipid metabolism and ER stress. The ability to form lipid droplets is a conserved property of eukaryotic cells that allows the storage of excess metabolic energy in a form that can be readily accessed. In adipose tissue, the storage of excess calories in lipid droplets normally protects other tissues from lipotoxicity and insulin resistance, but this protection is lost with chronic over-nutrition. The FAT storage-inducing transmembrane (FIT) proteins were recently identified as a conserved family of proteins that reside in the lipid bilayer of the endoplasmic reticulum and are implicated in lipid droplet formation. In this work we show that specific functions of the FIT proteins are conserved between yeast and humans and that SCS3 and YFT2, the yeast homologs of mammalian FIT2, are part of a large genetic interaction network connecting lipid metabolism, vesicle trafficking, transcription, and protein synthesis. From these interactions we determined that yeast strains lacking SCS3 and YFT2 are defective in their response to chronic ER stress and cannot induce the unfolded protein response pathway or transcription of phospholipid biosynthetic genes in low inositol. Our findings suggest that the mammalian FIT genes may play an important role in ER stress pathways, which are linked to obesity and type 2 diabetes.
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Affiliation(s)
- Robyn D. Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - David A. Gross
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Signature Research Program in Cardiovascular and Metabolic Disorders, Duke–NUS Graduate Medical School Singapore, Singapore, Singapore
| | - David L. Silver
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Signature Research Program in Cardiovascular and Metabolic Disorders, Duke–NUS Graduate Medical School Singapore, Singapore, Singapore
- * E-mail: (IMW); (DLS)
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- * E-mail: (IMW); (DLS)
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153
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Sun Z, Miller RA, Patel RT, Chen J, Dhir R, Wang H, Zhang D, Graham MJ, Unterman TG, Shulman GI, Sztalryd C, Bennett MJ, Ahima RS, Birnbaum MJ, Lazar MA. Hepatic Hdac3 promotes gluconeogenesis by repressing lipid synthesis and sequestration. Nat Med 2012; 18:934-42. [PMID: 22561686 PMCID: PMC3411870 DOI: 10.1038/nm.2744] [Citation(s) in RCA: 279] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Accepted: 03/16/2011] [Indexed: 12/18/2022]
Abstract
Fatty liver disease is associated with obesity and type 2 diabetes, and hepatic lipid accumulation may contribute to insulin resistance. Histone deacetylase 3 (Hdac3) controls the circadian rhythm of hepatic lipogenesis. Here we show that, despite severe hepatosteatosis, mice with liver-specific depletion of Hdac3 have higher insulin sensitivity without any changes in insulin signaling or body weight compared to wild-type mice. Hdac3 depletion reroutes metabolic precursors towards lipid synthesis and storage within lipid droplets and away from hepatic glucose production. Perilipin 2, which coats lipid droplets, is markedly induced upon Hdac3 depletion and contributes to the development of both steatosis and improved tolerance to glucose. These findings suggest that the sequestration of hepatic lipids in perilipin 2–coated droplets ameliorates insulin resistance and establish Hdac3 as a pivotal epigenomic modifier that integrates signals from the circadian clock in the regulation of hepatic intermediary metabolism.
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Affiliation(s)
- Zheng Sun
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA
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154
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Yang H, Galea A, Sytnyk V, Crossley M. Controlling the size of lipid droplets: lipid and protein factors. Curr Opin Cell Biol 2012; 24:509-16. [DOI: 10.1016/j.ceb.2012.05.012] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 05/23/2012] [Indexed: 01/23/2023]
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155
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Lehner R, Lian J, Quiroga AD. Lumenal lipid metabolism: implications for lipoprotein assembly. Arterioscler Thromb Vasc Biol 2012; 32:1087-93. [PMID: 22517367 DOI: 10.1161/atvbaha.111.241497] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Overproduction of apolipoprotein B (apoB)-containing lipoproteins by the liver and the intestine is 1 of the hallmarks of insulin resistance and type 2 diabetes and a well-established risk factor of cardiovascular disease. The assembly of apoB lipoproteins is regulated by the availability of lipids that form the neutral lipid core (triacylglycerol and cholesteryl ester) and the limiting lipoprotein monolayer (phospholipids and cholesterol). Although tremendous advances have been made over the past decade toward understanding neutral lipid and phospholipid biosynthesis and neutral lipid storage in cytosolic lipid droplets (LDs), little is known about the mechanisms that govern the transfer of lipids to the lumen of the endoplasmic reticulum for apoB lipidation. ApoB-synthesizing organs can deposit synthesized neutral lipids into at least 3 different types of LDs, each decorated with a subset of specific proteins: perilipin-decorated cytosolic LDs, and 2 types of LDs formed in the lumen of the endoplasmic reticulum, the secretion-destined LDs containing apoB, and resident lumenal LDs coated with microsomal triglyceride transfer protein and exchangeable apolipoproteins. This brief review will address the current knowledge of lumenal lipid metabolism in the context of apoB assembly and lipid storage.
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Affiliation(s)
- Richard Lehner
- Department of Pediatrics and Cell Biology, Group on Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada.
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156
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Murphy DJ. The dynamic roles of intracellular lipid droplets: from archaea to mammals. PROTOPLASMA 2012; 249:541-85. [PMID: 22002710 DOI: 10.1007/s00709-011-0329-7] [Citation(s) in RCA: 271] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Accepted: 09/28/2011] [Indexed: 05/02/2023]
Abstract
During the past decade, there has been a paradigm shift in our understanding of the roles of intracellular lipid droplets (LDs). New genetic, biochemical and imaging technologies have underpinned these advances, which are revealing much new information about these dynamic organelles. This review takes a comparative approach by examining recent work on LDs across the whole range of biological organisms from archaea and bacteria, through yeast and Drosophila to mammals, including humans. LDs probably evolved originally in microorganisms as temporary stores of excess dietary lipid that was surplus to the immediate requirements of membrane formation/turnover. LDs then acquired roles as long-term carbon stores that enabled organisms to survive episodic lack of nutrients. In multicellular organisms, LDs went on to acquire numerous additional roles including cell- and organism-level lipid homeostasis, protein sequestration, membrane trafficking and signalling. Many pathogens of plants and animals subvert their host LD metabolism as part of their infection process. Finally, malfunctions in LDs and associated proteins are implicated in several degenerative diseases of modern humans, among the most serious of which is the increasingly prevalent constellation of pathologies, such as obesity and insulin resistance, which is associated with metabolic syndrome.
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Affiliation(s)
- Denis J Murphy
- Division of Biological Sciences, University of Glamorgan, Cardiff, CF37 4AT, UK.
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157
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Sturley SL, Hussain MM. Lipid droplet formation on opposing sides of the endoplasmic reticulum. J Lipid Res 2012; 53:1800-10. [PMID: 22701043 DOI: 10.1194/jlr.r028290] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In animal cells, the primary repositories of esterified fatty acids and alcohols (neutral lipids) are lipid droplets that form on the lumenal and/or cytoplasmic side of the endoplasmic reticulum (ER) membrane. A monolayer of amphipathic lipids, intermeshed with key proteins, serves to solubilize neutral lipids as they are synthesized and desorbed. In specialized cells, mobilization of the lipid cargo for delivery to other tissues occurs by secretion of lipoproteins into the plasma compartment. Serum lipoprotein assembly requires an obligate structural protein anchor (apolipoprotein B) and a dedicated chaperone, microsomal triglyceride transfer protein. By contrast, lipid droplets that form on the cytoplasmic face of the ER lack an obligate protein scaffold or any required chaperone/lipid transfer protein. Mobilization of neutral lipids from the cytosol requires regulated hydrolysis followed by transfer of the products to different organelles or export from cells. Several proteins play a key role in controlling droplet number, stability, and catabolism; however, it is our premise that their formation initiates spontaneously, solely as a consequence of neutral lipid synthesis. This default pathway directs droplets into the cytoplasm where they accumulate in many lipid disorders.
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Affiliation(s)
- Stephen L Sturley
- Institute of Human Nutrition and Department of Pediatrics, Columbia University Medical Center, New York, NY 10032, USA.
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158
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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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159
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Lainscak M, von Haehling S, Doehner W, Anker SD. The obesity paradox in chronic disease: facts and numbers. J Cachexia Sarcopenia Muscle 2012; 3:1-4. [PMID: 22450395 PMCID: PMC3302984 DOI: 10.1007/s13539-012-0059-5] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 02/14/2012] [Indexed: 12/01/2022] Open
Abstract
Body size, particularly large, is a matter of concern among the lay public. Whether this is justified depends upon the state of health and should be judged individually. For patients with established chronic disease, there is sufficient evidence to support the benefits of large body size, i.e., the obesity paradox. This uniform finding is shared over a variety of cardiovascular, pulmonary, and renal diseases and is counterintuitive to the current concepts on ideal body weight. The scientific community has to increase the awareness about differences for optimal body size in health and disease. Simultaneously, clinicians have to be aware about body weight dynamics implications and should interpret the changes in the context of an underlying disease in order to implement the best available management.
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Affiliation(s)
- Mitja Lainscak
- Division of Cardiology; University Clinic of Pulmonary and Allergic Diseases Golnik; Golnik 36 SI-4204 Golnik
- Applied Cachexia Research, Department of Cardiology; Charité Medical School, Campus Virchow-Klinikum; Berlin
| | - Stephan von Haehling
- Applied Cachexia Research, Department of Cardiology; Charité Medical School, Campus Virchow-Klinikum; Berlin
- Center for Cardiovascular Research (CCR); Charité Medical School, Campus Mitte; Berlin
| | - Wolfram Doehner
- Center for Stroke Research, Berlin; Charite Medical School; Berlin
| | - Stefan D. Anker
- Applied Cachexia Research, Department of Cardiology; Charité Medical School, Campus Virchow-Klinikum; Berlin
- Center for Clinical and Basic Research; IRCCS San Raffaele; Rome
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160
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Ding Y, Yang L, Zhang S, Wang Y, Du Y, Pu J, Peng G, Chen Y, Zhang H, Yu J, Hang H, Wu P, Yang F, Yang H, Steinbüchel A, Liu P. Identification of the major functional proteins of prokaryotic lipid droplets. J Lipid Res 2012; 53:399-411. [PMID: 22180631 PMCID: PMC3276463 DOI: 10.1194/jlr.m021899] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 12/15/2011] [Indexed: 11/20/2022] Open
Abstract
Storage of cellular triacylglycerols (TAGs) in lipid droplets (LDs) has been linked to the progression of many metabolic diseases in humans, and to the development of biofuels from plants and microorganisms. However, the biogenesis and dynamics of LDs are poorly understood. Compared with other organisms, bacteria seem to be a better model system for studying LD biology, because they are relatively simple and are highly efficient in converting biomass to TAG. We obtained highly purified LDs from Rhodococcus sp. RHA1, a bacterium that can produce TAG from many carbon sources, and then comprehensively characterized the LD proteome. Of the 228 LD-associated proteins identified, two major proteins, ro02104 and PspA, constituted about 15% of the total LD protein. The structure predicted for ro02104 resembles that of apolipoproteins, the structural proteins of plasma lipoproteins in mammals. Deletion of ro02104 resulted in the formation of supersized LDs, indicating that ro02104 plays a critical role in cellular LD dynamics. The putative α helix of the ro02104 LD-targeting domain (amino acids 83-146) is also similar to that of apolipoproteins. We report the identification of 228 proteins in the proteome of prokaryotic LDs, identify a putative structural protein of this organelle, and suggest that apolipoproteins may have an evolutionarily conserved role in the storage and trafficking of neutral lipids.
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Affiliation(s)
- Yunfeng Ding
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Li Yang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Shuyan Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China
| | - Yang Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Yalan Du
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Department of Histology and Embryology, University of South China, Hengyang, Hunan Province, China
| | - Jing Pu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Gong Peng
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Yong Chen
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China
| | - Huina Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China
| | - Jinhai Yu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China; National Laboratory of Biomacromolecules, Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Haiying Hang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China
| | - Peng Wu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China
| | - Fuquan Yang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China
| | - Hongyuan Yang
- National Laboratory of Biomacromolecules, School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
| | - Alexander Steinbüchel
- National Laboratory of Biomacromolecules, Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, D-48149 Münster, Germany, and King Abdulaziz University, Jeddah, Saudi Arabia.
| | - Pingsheng Liu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, China.
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161
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Grasselli E, Voci A, Demori I, Canesi L, De Matteis R, Goglia F, Lanni A, Gallo G, Vergani L. 3,5-Diiodo-L-thyronine modulates the expression of genes of lipid metabolism in a rat model of fatty liver. J Endocrinol 2012; 212:149-58. [PMID: 22107956 DOI: 10.1530/joe-11-0288] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Recent reports demonstrated that 3,5-diiodo-l-thyronine (T(2)) was able to prevent lipid accumulation in the liver of rats fed a high-fat diet (HFD). In this study, we investigated how the rat liver responds to HFD and T(2) treatment by assessing the transcription profiles of some genes involved in the pathways of lipid metabolism: oxidation, storage and secretion. The mRNA levels of the peroxisome proliferator-activated receptors (PPARα, PPARγ and PPARδ), and of their target enzymes acyl-CoA oxidase and stearoyl-CoA desaturase were evaluated by real-time RT-PCR. Moreover, the expression of the adipose triglyceride lipase involved in lipid mobilisation, of the main PAT proteins acting in lipid droplet (LD) turnover, and of apoprotein B (apo B), the major protein component of very low-density lipoproteins (VLDLs) were analysed. Overall, our data demonstrated that T(2) administration to HFD rats counteracts most of the hepatic transcriptional changes that occurred in response to the excess exogenous fat. In particular, our results suggest that T(2) may prevent the pathways leading to lipid storage in LDs, promote the processes of lipid mobilisation from LDs and secretion as VLDL, in addition to the stimulation of pathways of lipid oxidation. In conclusion, our findings might give an insight into the mechanisms underlying the anti-steatotic ability of T(2) and help to define the potential therapeutic role of T(2) for preventing or treating liver steatosis.
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162
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Bui A, Xiao R, Perveen Z, Kleinow K, Penn A. Zebrafish embryos sequester and retain petrochemical combustion products: developmental and transcriptome consequences. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2012; 108:23-32. [PMID: 22055752 DOI: 10.1016/j.aquatox.2011.09.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Revised: 09/16/2011] [Accepted: 09/29/2011] [Indexed: 05/31/2023]
Abstract
Zebrafish embryos are a model for studying effects of environmental stressors on development. Incomplete combustion of the environmentally relevant volatile petrochemical, 1,3-butadiene (BD) yields butadiene soot (BDS) nanoparticles, to which polynuclear aromatic hydrocarbons (PAHs) are adsorbed. In mammalian cells these PAHs are concentrated in lipid droplets and trigger up-regulation of biotransformation, oxidative stress and inflammatory genes. The present study was designed to determine whether: (a) PAH-rich BDS elicits alterations in zebrafish embryo development; (b) BDS-exposed zebrafish embryos sequester PAHs in select tissues; and (c) developmental abnormalities are correlated with altered gene expression patterns. 1-day old zebrafish embryos were exposed for 48 h to BDS (0, 6, 30 or 60 μg/ml) sprinkled on the water surface. PAH localization was tracked by fluorescence. Developmental responses (pericardial edema, yolk sac swelling, axial malformations) were monitored by microscopy. Gene expression changes were assessed by gene microarray and qRT-PCR. Our results show that PAHs localized with endogenous lipids in the yolk sac and in hatching gland cells. PAHs were retained at least 8 days after exposures ended. Dose-dependent pericardial and yolk sac edema and axial malformations were prominent and accompanied by up-regulation of biotransformation and oxidative stress gene cascades. Thus, zebrafish embryos should be useful for predicting the potential for developmental toxicity following exposure to PAH-rich petrochemical soots, e.g., those arising from attempts at oil spill remediation by combustion.
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Affiliation(s)
- Allen Bui
- Department of Comparative Biomedical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA 70803, USA.
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163
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Mormeneo E, Jimenez-Mallebrera C, Palomer X, De Nigris V, Vázquez-Carrera M, Orozco A, Nascimento A, Colomer J, Lerín C, Gómez-Foix AM. PGC-1α induces mitochondrial and myokine transcriptional programs and lipid droplet and glycogen accumulation in cultured human skeletal muscle cells. PLoS One 2012; 7:e29985. [PMID: 22272266 PMCID: PMC3260188 DOI: 10.1371/journal.pone.0029985] [Citation(s) in RCA: 284] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Accepted: 12/09/2011] [Indexed: 11/24/2022] Open
Abstract
The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) is a chief activator of mitochondrial and metabolic programs and protects against atrophy in skeletal muscle (skm). Here we tested whether PGC-1α overexpression could restructure the transcriptome and metabolism of primary cultured human skm cells, which display a phenotype that resembles the atrophic phenotype. An oligonucleotide microarray analysis was used to reveal the effects of PGC-1α on the whole transcriptome. Fifty-three different genes showed altered expression in response to PGC-1α: 42 upregulated and 11 downregulated. The main gene ontologies (GO) associated with the upregulated genes were mitochondrial components and processes and this was linked with an increase in COX activity, an indicator of mitochondrial content. Furthermore, PGC-1α enhanced mitochondrial oxidation of palmitate and lactate to CO2, but not glucose oxidation. The other most significantly associated GOs for the upregulated genes were chemotaxis and cytokine activity, and several cytokines, including IL-8/CXCL8, CXCL6, CCL5 and CCL8, were within the most highly induced genes. Indeed, PGC-1α highly increased IL-8 cell protein content. The most upregulated gene was PVALB, which is related to calcium signaling. Potential metabolic regulators of fatty acid and glucose storage were among mainly regulated genes. The mRNA and protein level of FITM1/FIT1, which enhances the formation of lipid droplets, was raised by PGC-1α, while in oleate-incubated cells PGC-1α increased the number of smaller lipid droplets and modestly triglyceride levels, compared to controls. CALM1, the calcium-modulated δ subunit of phosphorylase kinase, was downregulated by PGC-1α, while glycogen phosphorylase was inactivated and glycogen storage was increased by PGC-1α. In conclusion, of the metabolic transcriptome deficiencies of cultured skm cells, PGC-1α rescued the expression of genes encoding mitochondrial proteins and FITM1. Several myokine genes, including IL-8 and CCL5, which are known to be constitutively expressed in human skm cells, were induced by PGC-1α.
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Affiliation(s)
- Emma Mormeneo
- CIBER de Diabetes y Enfermedades Metabólicas, Barcelona, Spain.
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164
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Re-evaluating lipotoxic triggers in skeletal muscle: Relating intramyocellular lipid metabolism to insulin sensitivity. Prog Lipid Res 2012; 51:36-49. [DOI: 10.1016/j.plipres.2011.11.003] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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165
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Cho YS, Chen CH, Hu C, Long J, Ong RTH, Sim X, Takeuchi F, Wu Y, Go MJ, Yamauchi T, Chang YC, Kwak SH, Ma RC, Yamamoto K, Adair LS, Aung T, Cai Q, Chang LC, Chen YT, Gao Y, Hu FB, Kim HL, Kim S, Kim YJ, Lee JJM, Lee NR, Li Y, Liu JJ, Lu W, Nakamura J, Nakashima E, Ng DPK, Tay WT, Tsai FJ, Wong TY, Yokota M, Zheng W, Zhang R, Wang C, So WY, Ohnaka K, Ikegami H, Hara K, Cho YM, Cho NH, Chang TJ, Bao Y, Hedman ÅK, Morris AP, McCarthy MI, DIAGRAM consortium, MuTHER consortium, Takayanagi R, Park KS, Jia W, Chuang LM, Chan JC, Maeda S, Kadowaki T, Lee JY, Wu JY, Teo YY, Tai ES, Shu XO, Mohlke KL, Kato N, Han BG, Seielstad M. Meta-analysis of genome-wide association studies identifies eight new loci for type 2 diabetes in east Asians. Nat Genet 2011; 44:67-72. [PMID: 22158537 PMCID: PMC3582398 DOI: 10.1038/ng.1019] [Citation(s) in RCA: 483] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2011] [Accepted: 11/02/2011] [Indexed: 12/14/2022]
Abstract
We conducted a three-stage genetic study to identify susceptibility loci for type 2 diabetes (T2D) in east Asian populations. We followed our stage 1 meta-analysis of eight T2D genome-wide association studies (6,952 cases with T2D and 11,865 controls) with a stage 2 in silico replication analysis (5,843 cases and 4,574 controls) and a stage 3 de novo replication analysis (12,284 cases and 13,172 controls). The combined analysis identified eight new T2D loci reaching genome-wide significance, which mapped in or near GLIS3, PEPD, FITM2-R3HDML-HNF4A, KCNK16, MAEA, GCC1-PAX4, PSMD6 and ZFAND3. GLIS3, which is involved in pancreatic beta cell development and insulin gene expression, is known for its association with fasting glucose levels. The evidence of an association with T2D for PEPD and HNF4A has been shown in previous studies. KCNK16 may regulate glucose-dependent insulin secretion in the pancreas. These findings, derived from an east Asian population, provide new perspectives on the etiology of T2D.
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Affiliation(s)
- Yoon Shin Cho
- Center for Genome Science, National Institute of Health, Osong Health Technology Administration Complex, Chungcheongbuk-do, The Republic of Korea
| | - Chien-Hsiun Chen
- Institute of Biomedical Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang, Taipei, Taiwan
- School of Chinese Medicine, China Medical University, 91 Hsueh-Shih Road, Taichung, Taiwan
| | - Cheng Hu
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, 600 Yishan Road, Shanghai, 200233, PR China
| | - Jirong Long
- Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
| | - Rick Twee Hee Ong
- NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore
| | - Xueling Sim
- Centre for Molecular Epidemiology, National University of Singapore, Singapore 117597, Singapore
| | - Fumihiko Takeuchi
- Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, 162-8655, JAPAN
| | - Ying Wu
- Department of Genetics, University of North Carolina, Chapel Hill, NC, USA
| | - Min Jin Go
- Center for Genome Science, National Institute of Health, Osong Health Technology Administration Complex, Chungcheongbuk-do, The Republic of Korea
| | - Toshimasa Yamauchi
- Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo 113-8655, Japan
| | - Yi-Cheng Chang
- Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
| | - Soo Heon Kwak
- Department of Internal Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Korea
| | - Ronald C.W. Ma
- Dept of Medicine and Therapeutics, Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong
| | - Ken Yamamoto
- Division of Genome Analysis, Research Center for Genetic Information, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582 Japan
| | - Linda S. Adair
- Department of Nutrition, University of North Carolina, Chapel Hill, NC, USA
| | - Tin Aung
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 168751, Singapore
- Department of Ophthalmology, National University of Singapore, Singapore 119074, Singapore
| | - Qiuyin Cai
- Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
| | - Li-Ching Chang
- Institute of Biomedical Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang, Taipei, Taiwan
| | - Yuan-Tsong Chen
- Institute of Biomedical Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang, Taipei, Taiwan
| | - Yutang Gao
- Department of Epidemiology, Shanghai Cancer Institute, Shanghai 200032, China
| | - Frank B. Hu
- Department of Nutrition and Epidemiology, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Hyung-Lae Kim
- Center for Genome Science, National Institute of Health, Osong Health Technology Administration Complex, Chungcheongbuk-do, The Republic of Korea
- Department of Biochemistry, School of Medicine, Ewha Womans University, Seoul, The Republic of Korea
| | - Sangsoo Kim
- School of Systems Biomedical Science, Soongsil University, Sangdo-5-dong 1-1, Dongjak-gu, Seoul 156-743, The Republic of Korea
| | - Young Jin Kim
- Center for Genome Science, National Institute of Health, Osong Health Technology Administration Complex, Chungcheongbuk-do, The Republic of Korea
| | - Jeannette Jen-Mai Lee
- Department of Epidemiology and Public Health, National University of Singapore, Singapore 117597, Singapore
| | - Nanette R. Lee
- Office of Population Studies Foundation Inc., University of San Carlos, Cebu City, Philippines
| | - Yun Li
- Department of Genetics, University of North Carolina, Chapel Hill, NC, USA
- Department of Biostatistics, University of North Carolina, Chapel Hill, NC 27599
| | - Jian Jun Liu
- Genome Institute of Singapore, Agency for Science, Technology and Research, Singapore 138672, Singapore
| | - Wei Lu
- Shanghai Institute of Preventive Medicine, Shanghai 200336, China
| | - Jiro Nakamura
- Division of Endocrinology and Diabetes, Department of Internal Medicine, Nagoya University Graduate School of Medicine, Nagoya, 466-8560 JAPAN
| | - Eitaro Nakashima
- Division of Endocrinology and Diabetes, Department of Internal Medicine, Nagoya University Graduate School of Medicine, Nagoya, 466-8560 JAPAN
- Department of Diabetes and Endocrinology, Chubu Rosai Hospital, Nagoya, 455-8530 Japan
| | - Daniel Peng-Keat Ng
- Department of Epidemiology and Public Health, National University of Singapore, Singapore 117597, Singapore
| | - Wan Ting Tay
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 168751, Singapore
| | - Fuu-Jen Tsai
- School of Chinese Medicine, China Medical University, 91 Hsueh-Shih Road, Taichung, Taiwan
| | - Tien Yin Wong
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore 168751, Singapore
- Department of Ophthalmology, National University of Singapore, Singapore 119074, Singapore
- Centre for Eye Research Australia, University of Melbourne, East Melbourne VIC, 3002 Australia
| | - Mitsuhiro Yokota
- Department of Genome Science, Aichi-Gakuin University, School of Dentistry, Nagoya, 464-8651 Japan
| | - Wei Zheng
- Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
| | - Rong Zhang
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, 600 Yishan Road, Shanghai, 200233, PR China
| | - Congrong Wang
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, 600 Yishan Road, Shanghai, 200233, PR China
| | - Wing Yee So
- Dept of Medicine and Therapeutics, Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong
| | - Keizo Ohnaka
- Department of Geriatric Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582 Japan
| | - Hiroshi Ikegami
- Dept Endocrinology, Metabolism and Diabetes, Kinki University School of Medicine 377-2 Ohno-higashi, Osaka-sayama, Osaka, 589-8511 Japan
| | - Kazuo Hara
- Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo 113-8655, Japan
| | - Young Min Cho
- Department of Internal Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Korea
| | - Nam H Cho
- Department of Preventive Medicine, Ajou University School of Medicine, Suwon, The Republic of Korea
| | - Tien-Jyun Chang
- Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
| | - Yuqian Bao
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, 600 Yishan Road, Shanghai, 200233, PR China
| | - Åsa K. Hedman
- Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Andrew P. Morris
- Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Mark I. McCarthy
- Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
| | | | | | - Ryoichi Takayanagi
- Department of Geriatric Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582 Japan
| | - Kyong Soo Park
- Department of Internal Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Korea
- WCU Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology and College of Medicine, Seoul National University, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Korea
| | - Weiping Jia
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, 600 Yishan Road, Shanghai, 200233, PR China
| | - Lee-Ming Chuang
- Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
- Graduate Institute of Clinical Medicine, National Taiwan University School of Medicine, Taipei, Taiwan
| | - Juliana C.N. Chan
- Dept of Medicine and Therapeutics, Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong
| | - Shiro Maeda
- Laboratory for Endocrinology and Metabolism, RIKEN Center for Genomic Medicine, Yokohama 230-0045, Japan
| | - Takashi Kadowaki
- Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo 113-8655, Japan
| | - Jong-Young Lee
- Center for Genome Science, National Institute of Health, Osong Health Technology Administration Complex, Chungcheongbuk-do, The Republic of Korea
| | - Jer-Yuarn Wu
- Institute of Biomedical Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang, Taipei, Taiwan
- School of Chinese Medicine, China Medical University, 91 Hsueh-Shih Road, Taichung, Taiwan
| | - Yik Ying Teo
- Department of Epidemiology and Public Health, National University of Singapore, Singapore 117597, Singapore
- Department of Biostatistics, University of North Carolina, Chapel Hill, NC 27599
- Department of Statistics and Applied Probability, National University of Singapore, Singapore 117546, Singapore
- Centre for Molecular Epidemiology, National University of Singapore, Singapore 117597, Singapore
- NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore
| | - E Shyong Tai
- Department of Medicine, National University of Singapore, Singapore 119228 Singapore
- Department of Epidemiology and Public Health, National University of Singapore, Singapore 117597, Singapore
- Duke-National University of Singapore Graduate Medical School, Singapore 169857, Singapore
| | - Xiao Ou Shu
- Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
| | - Karen L. Mohlke
- Department of Genetics, University of North Carolina, Chapel Hill, NC, USA
| | - Norihiro Kato
- Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, 162-8655, JAPAN
| | - Bok-Ghee Han
- Center for Genome Science, National Institute of Health, Osong Health Technology Administration Complex, Chungcheongbuk-do, The Republic of Korea
| | - Mark Seielstad
- Genome Institute of Singapore, Agency for Science, Technology and Research, Singapore 138672, Singapore
- Institute for Human Genetics, University of California, 513 Parnassus Avenue, San Francisco, CA 94143-0794, USA
- Blood Systems Research Institute, 270 Masonic Avenue, San Francisco, California, 94118, USA
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166
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Gong J, Sun Z, Wu L, Xu W, Schieber N, Xu D, Shui G, Yang H, Parton RG, Li P. Fsp27 promotes lipid droplet growth by lipid exchange and transfer at lipid droplet contact sites. ACTA ACUST UNITED AC 2011; 195:953-63. [PMID: 22144693 PMCID: PMC3241734 DOI: 10.1083/jcb.201104142] [Citation(s) in RCA: 273] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The lipid droplet–associated protein Fsp27 mediates lipid droplet growth by promoting directional lipid transfer from smaller to larger lipid droplets. Lipid droplets (LDs) are dynamic cellular organelles that control many biological processes. However, molecular components determining LD growth are poorly understood. Genetic analysis has indicated that Fsp27, an LD-associated protein, is important in controlling LD size and lipid storage in adipocytes. In this paper, we demonstrate that Fsp27 is focally enriched at the LD–LD contacting site (LDCS). Photobleaching revealed the occurrence of lipid exchange between contacted LDs in wild-type adipocytes and Fsp27-overexpressing cells but not Fsp27-deficient adipocytes. Furthermore, live-cell imaging revealed a unique Fsp27-mediated LD growth process involving a directional net lipid transfer from the smaller to larger LDs at LDCSs, which is in accordance with the biophysical analysis of the internal pressure difference between the contacting LD pair. Thus, we have uncovered a novel molecular mechanism of LD growth mediated by Fsp27.
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Affiliation(s)
- Jingyi Gong
- Peking-Tsinghua Center for Life Sciences, Tsinghua University, Beijing 100084, China
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167
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Direct binding of triglyceride to fat storage-inducing transmembrane proteins 1 and 2 is important for lipid droplet formation. Proc Natl Acad Sci U S A 2011; 108:19581-6. [PMID: 22106267 DOI: 10.1073/pnas.1110817108] [Citation(s) in RCA: 133] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The process of lipid droplet (LD) formation is an evolutionarily conserved process among all eukaryotes and plays an important role in both cellular physiology and disease. Recently, fat storage-inducing transmembrane proteins 1 and 2 (FIT1/FITM1 and FIT2/FITM2) were discovered as an evolutionarily conserved family of proteins involved in fat storage. In mammals, FIT1 is expressed primarily in skeletal muscle and FIT2 is expressed primarily in adipose, raising the possibility that FIT1 and FIT2 have unique functions. These proteins are exclusively localized to the endoplasmic reticulum (ER) and mediate triglyceride-rich LD accumulation when overexpressed in cells, mouse liver, or muscle. Unlike the ER-resident diacylglycerol O-acyltransferase family of triglyceride-synthesizing enzymes, FITs do not synthesize triglyceride, but rather partition triglyceride into LDs. The mechanism by which FIT proteins mediate this process has not been determined. A simple hypothesis was tested that FIT proteins bind to triglyceride to mediate LD formation. Here, it is shown that FIT proteins purified in detergent micelles directly bind triolein with specificity and saturation-binding kinetics. A FIT2 gain-of-function mutant that formed larger LDs, FLL(157-9)AAA, showed increased binding to triolein relative to wild-type FIT2, whereas FIT1 and a FIT2 partial loss-of-function mutant, N80A, had significantly lower triolein binding and produced smaller LDs. In summary, FIT proteins are transmembrane domain-containing proteins shown to bind triglyceride. These findings indicate that FITs have a unique biochemical mechanism in mediating LD formation and implicates triglyceride binding as important for FIT-mediated LD formation.
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168
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Brasaemle DL, Wolins NE. Packaging of fat: an evolving model of lipid droplet assembly and expansion. J Biol Chem 2011; 287:2273-9. [PMID: 22090029 DOI: 10.1074/jbc.r111.309088] [Citation(s) in RCA: 174] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Lipid droplets (LDs) are organelles found in most types of cells in the tissues of vertebrates, invertebrates, and plants, as well as in bacteria and yeast. They differ from other organelles in binding a unique complement of proteins and lacking an aqueous core but share aspects of protein trafficking with secretory membrane compartments. In this minireview, we focus on recent evidence supporting an endoplasmic reticulum origin for LD formation and discuss recent findings regarding LD maturation and fusion.
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Affiliation(s)
- Dawn L Brasaemle
- Rutgers Center for Lipid Research and Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
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169
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Miranda DA, Koves TR, Gross DA, Chadt A, Al-Hasani H, Cline GW, Schwartz GJ, Muoio DM, Silver DL. Re-patterning of skeletal muscle energy metabolism by fat storage-inducing transmembrane protein 2. J Biol Chem 2011; 286:42188-42199. [PMID: 22002063 DOI: 10.1074/jbc.m111.297127] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Triacylglyceride stored in cytosolic lipid droplets (LDs) constitutes a major energy reservoir in most eukaryotes. The regulated turnover of triacylglyceride in LDs provides fatty acids for mitochondrial β-oxidation and ATP generation in physiological states of high demand for energy. The mechanisms for the formation of LDs in conditions of energy excess are not entirely understood. Fat storage-inducing transmembrane protein 2 (FIT2/FITM2) is the anciently conserved member of the fat storage-inducing transmembrane family of proteins implicated to be important in the formation of LDs, but its role in energy metabolism has not been tested. Here, we report that expression of FIT2 in mouse skeletal muscle had profound effects on muscle energy metabolism. Mice with skeletal muscle-specific overexpression of FIT2 (CKF2) had significantly increased intramyocellular triacylglyceride and complete protection from high fat diet-induced weight gain due to increased energy expenditure. Mass spectrometry-based metabolite profiling suggested that CKF2 skeletal muscle had increased oxidation of branched chain amino acids but decreased oxidation of fatty acids. Glucose was primarily utilized in CKF2 muscle for synthesis of the glycerol backbone of triacylglyceride and not for glycogen production. CKF2 muscle was ATP-deficient and had activated AMP kinase. Together, these studies indicate that FIT2 expression in skeletal muscle plays an unexpected function in regulating muscle energy metabolism and indicates an important role for lipid droplet formation in this process.
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Affiliation(s)
- Diego A Miranda
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461
| | - Timothy R Koves
- Sarah W. Stedman Nutrition and Metabolism Center, Department of Medicine, Duke University, Durham, North Carolina 27704
| | - David A Gross
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461
| | - Alexandra Chadt
- Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, 40225 Dusseldorf, Germany
| | - Hadi Al-Hasani
- Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, 40225 Dusseldorf, Germany
| | - Gary W Cline
- Diabetes Endocrinology Research Center, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Gary J Schwartz
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461
| | - Deborah M Muoio
- Sarah W. Stedman Nutrition and Metabolism Center, Department of Medicine, Duke University, Durham, North Carolina 27704
| | - David L Silver
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461.
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170
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Ottaviani E, Malagoli D, Franceschi C. The evolution of the adipose tissue: a neglected enigma. Gen Comp Endocrinol 2011; 174:1-4. [PMID: 21781968 DOI: 10.1016/j.ygcen.2011.06.018] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 06/22/2011] [Accepted: 06/30/2011] [Indexed: 12/19/2022]
Abstract
The complexity of the anatomical distribution and functions of adipose tissue (AT) has been rarely analyzed in an evolutionary perspective. From yeast to man lipid droplets are stored mainly in the form of triglycerides in order to provide energy during periods when energy demands exceed caloric intake. This simple scenario is in agreement with the recent discovery of a highly conserved family of proteins for fat storage in both unicellular and multicellular organisms. However, the evolutionary history of organs such as the fat body in insects, playing a role in immunity and other functions besides energy storage and thermal insulation, and of differently distributed subtypes of AT in vertebrates is much less clear. These topics still await a systematic investigation using up-to-date technologies and approaches that would provide information useful for understanding the role of different AT subtypes in normal/physiological conditions or in metabolic pathologies of humans.
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Affiliation(s)
- Enzo Ottaviani
- Department of Biology, University of Modena and Reggio Emilia, Modena, Italy.
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171
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Choi SH, Ginsberg HN. Increased very low density lipoprotein (VLDL) secretion, hepatic steatosis, and insulin resistance. Trends Endocrinol Metab 2011; 22:353-63. [PMID: 21616678 PMCID: PMC3163828 DOI: 10.1016/j.tem.2011.04.007] [Citation(s) in RCA: 272] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2011] [Revised: 04/18/2011] [Accepted: 04/19/2011] [Indexed: 12/14/2022]
Abstract
Insulin resistance (IR) affects not only the regulation of carbohydrate metabolism but all aspects of lipid and lipoprotein metabolism. IR is associated with increased secretion of VLDL and increased plasma triglycerides, as well as with hepatic steatosis, despite the increased VLDL secretion. Here we link IR with increased VLDL secretion and hepatic steatosis at both the physiologic and molecular levels. Increased VLDL secretion, together with the downstream effects on high density lipoprotein (HDL) cholesterol and low density lipoprotein (LDL) size, is proatherogenic. Hepatic steatosis is a risk factor for steatohepatitis and cirrhosis. Understanding the complex inter-relationships between IR and these abnormalities of liver lipid homeostasis will provide insights relevant to new therapies for these increasing clinical problems.
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Affiliation(s)
- Sung Hee Choi
- Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seoul, Korea
| | - Henry N Ginsberg
- Columbia University College of Physicians and Surgeons, New York, NY, USA
- whom correspondence should be addressed.
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172
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Promlek T, Ishiwata-Kimata Y, Shido M, Sakuramoto M, Kohno K, Kimata Y. Membrane aberrancy and unfolded proteins activate the endoplasmic reticulum stress sensor Ire1 in different ways. Mol Biol Cell 2011; 22:3520-32. [PMID: 21775630 PMCID: PMC3172275 DOI: 10.1091/mbc.e11-04-0295] [Citation(s) in RCA: 212] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Eukaryotic cells activate the unfolded-protein response (UPR) upon endoplasmic reticulum (ER) stress, where the stress is assumed to be the accumulation of unfolded proteins in the ER. Consistent with previous in vitro studies of the ER-luminal domain of the mutant UPR initiator Ire1, our study show its association with a model unfolded protein in yeast cells. An Ire1 luminal domain mutation that compromises Ire1's unfolded-protein-associating ability weakens its ability to respond to stress stimuli, likely resulting in the accumulation of unfolded proteins in the ER. In contrast, this mutant was activated like wild-type Ire1 by depletion of the membrane lipid component inositol or by deletion of genes involved in lipid homeostasis. Another Ire1 mutant lacking the authentic luminal domain was up-regulated by inositol depletion as strongly as wild-type Ire1. We therefore conclude that the cytosolic (or transmembrane) domain of Ire1 senses membrane aberrancy, while, as proposed previously, unfolded proteins accumulating in the ER interact with and activate Ire1.
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Affiliation(s)
- Thanyarat Promlek
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
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173
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Candida parapsilosis fat storage-inducing transmembrane (FIT) protein 2 regulates lipid droplet formation and impacts virulence. Microbes Infect 2011; 13:663-72. [DOI: 10.1016/j.micinf.2011.02.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 02/23/2011] [Accepted: 02/24/2011] [Indexed: 11/19/2022]
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174
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McCollum CW, Ducharme NA, Bondesson M, Gustafsson JA. Developmental toxicity screening in zebrafish. ACTA ACUST UNITED AC 2011; 93:67-114. [DOI: 10.1002/bdrc.20210] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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175
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Somwar R, Roberts CT, Varlamov O. Live-cell imaging demonstrates rapid cargo exchange between lipid droplets in adipocytes. FEBS Lett 2011; 585:1946-50. [PMID: 21575639 DOI: 10.1016/j.febslet.2011.05.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Revised: 04/26/2011] [Accepted: 05/04/2011] [Indexed: 11/30/2022]
Abstract
Lipid droplets form the storage reservoirs for lipids in adipocytes, and their stable appearance suggests a static nature of lipid storage. A stable lipid store, however, may be maintained through the dynamic recycling of lipid cargo between the cytoplasmic compartment and the lipid droplet. In this study, we applied live-cell microscopy to follow intracellular transport steps of fluorescently labeled fatty acids in differentiated 3T3-L1 adipocytes. We demonstrate that intracellular lipids continuously exit and re-enter lipid droplets, and that individual lipid droplets exchange their content on a timescale of minutes. These data demonstrate a surprisingly high rate of intracellular lipid turnover in adipocytes and support the novel concept that lipid storage is achieved by dynamic recycling rather than static retention.
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Affiliation(s)
- Romel Somwar
- Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, United States
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176
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WU J, JIAO ZY, LU HL, Zhang J, Lin HH, Cianflone K. The molecular mechanism of acylation stimulating protein regulation of adipophilin and perilipin expression: Involvement of phosphoinositide 3-kinase and phospholipase C. J Cell Biochem 2011; 112:1622-9. [DOI: 10.1002/jcb.23076] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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177
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The unfolded protein response transducer IRE1α prevents ER stress-induced hepatic steatosis. EMBO J 2011; 30:1357-75. [PMID: 21407177 DOI: 10.1038/emboj.2011.52] [Citation(s) in RCA: 283] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Accepted: 01/28/2011] [Indexed: 12/21/2022] Open
Abstract
The endoplasmic reticulum (ER) is the cellular organelle responsible for protein folding and assembly, lipid and sterol biosynthesis, and calcium storage. The unfolded protein response (UPR) is an adaptive intracellular stress response to accumulation of unfolded or misfolded proteins in the ER. In this study, we show that the most conserved UPR sensor inositol-requiring enzyme 1 α (IRE1α), an ER transmembrane protein kinase/endoribonuclease, is required to maintain hepatic lipid homeostasis under ER stress conditions through repressing hepatic lipid accumulation and maintaining lipoprotein secretion. To elucidate physiological roles of IRE1α-mediated signalling in the liver, we generated hepatocyte-specific Ire1α-null mice by utilizing an albumin promoter-controlled Cre recombinase-mediated deletion. Deletion of Ire1α caused defective induction of genes encoding functions in ER-to-Golgi protein transport, oxidative protein folding, and ER-associated degradation (ERAD) of misfolded proteins, and led to selective induction of pro-apoptotic UPR trans-activators. We show that IRE1α is required to maintain the secretion efficiency of selective proteins. In the absence of ER stress, mice with hepatocyte-specific Ire1α deletion displayed modest hepatosteatosis that became profound after induction of ER stress. Further investigation revealed that IRE1α represses expression of key metabolic transcriptional regulators, including CCAAT/enhancer-binding protein (C/EBP) β, C/EBPδ, peroxisome proliferator-activated receptor γ (PPARγ), and enzymes involved in triglyceride biosynthesis. IRE1α was also found to be required for efficient secretion of apolipoproteins upon disruption of ER homeostasis. Consistent with a role for IRE1α in preventing intracellular lipid accumulation, mice with hepatocyte-specific deletion of Ire1α developed severe hepatic steatosis after treatment with an ER stress-inducing anti-cancer drug Bortezomib, upon expression of a misfolding-prone human blood clotting factor VIII, or after partial hepatectomy. The identification of IRE1α as a key regulator to prevent hepatic steatosis provides novel insights into ER stress mechanisms in fatty liver diseases associated with toxic liver injuries.
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178
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Fujimoto T, Parton RG. Not just fat: the structure and function of the lipid droplet. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a004838. [PMID: 21421923 DOI: 10.1101/cshperspect.a004838] [Citation(s) in RCA: 359] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Lipid droplets (LDs) are independent organelles that are composed of a lipid ester core and a surface phospholipid monolayer. Recent studies have revealed many new proteins, functions, and phenomena associated with LDs. In addition, a number of diseases related to LDs are beginning to be understood at the molecular level. It is now clear that LDs are not an inert store of excess lipids but are dynamically engaged in various cellular functions, some of which are not directly related to lipid metabolism. Compared to conventional membrane organelles, there are still many uncertainties concerning the molecular architecture of LDs and how each function is placed in a structural context. Recent findings and remaining questions are discussed.
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Affiliation(s)
- Toyoshi Fujimoto
- Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Japan.
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179
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Imrie D, Sadler KC. White adipose tissue development in zebrafish is regulated by both developmental time and fish size. Dev Dyn 2011; 239:3013-23. [PMID: 20925116 DOI: 10.1002/dvdy.22443] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Adipocytes are heterogeneous. Whether their differences are attributed to anatomical location or to different developmental origins is unknown. We investigated whether development of different white adipose tissue (WAT) depots in zebrafish occurs simultaneously or whether adipogenesis is influenced by the metabolic demands of growing fish. Like mammals, zebrafish adipocyte morphology is distinctive and adipocytes express cell-specific markers. All adults contain WAT in pancreatic, subcutaneous, visceral, esophageal, mandibular, cranial, and tail-fin depots. Unlike most zebrafish organs that form during embryogenesis, WAT was not found in embryos or young larvae. Instead, WAT was first identified in the pancreas on 12 days postfertilization (dpf), and then in visceral, subcutaneous, and cranial stores in older fish. All 30 dpf fish exceeding 10.6 mm standard length contained the adult repertoire of WAT depots. Pancreatic, esophageal, and subcutaneous WAT appearance correlated with size, not age, as found for other features appearing during postembryonic zebrafish development.
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Affiliation(s)
- Dru Imrie
- Department of Medicine/Division of Liver Diseases, Mount Sinai School of Medicine, New York, New York 10029, USA
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180
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Abstract
The lipid droplet (LD), an organelle that exists ubiquitously in various organisms, from bacteria to mammals, has attracted much attention from both medical and cell biology fields. The LD in white adipocytes is often treated as the prototype LD, but is rather a special example, considering that its size, intracellular localization and molecular composition are vastly different from those of non-adipocyte LDs. These differences confer distinct properties on adipocyte and non-adipocyte LDs. In this article, we address the current understanding of LDs by discussing the differences between adipocyte and non-adipocyte LDs.
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Affiliation(s)
- Michitaka Suzuki
- Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
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181
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Eyre NS, Drummer HE, Beard MR. The SR-BI partner PDZK1 facilitates hepatitis C virus entry. PLoS Pathog 2010; 6:e1001130. [PMID: 20949066 PMCID: PMC2951368 DOI: 10.1371/journal.ppat.1001130] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Accepted: 09/02/2010] [Indexed: 01/01/2023] Open
Abstract
Entry of hepatitis C virus (HCV) into hepatocytes is a multi-step process that involves a number of different host cell factors. Following initial engagement with glycosaminoglycans and the low-density lipoprotein receptor, it is thought that HCV entry proceeds via interactions with the tetraspanin CD81, scavenger receptor class B type I (SR-BI), and the tight-junction proteins claudin-1 (CLDN1) and occludin (OCLN), culminating in clathrin-dependent endocytosis of HCV particles and their pH-dependent fusion with endosomal membranes. Physiologically, SR-BI is the major receptor for high-density lipoproteins (HDL) in the liver, where its expression is primarily controlled at the post-transcriptional level by its interaction with the scaffold protein PDZK1. However, the importance of interaction with PDZK1 to the involvement of SR-BI in HCV entry is unclear. Here we demonstrate that stable shRNA-knockdown of PDZK1 expression in human hepatoma cells significantly reduces their susceptibility to HCV infection, and that this effect can be reversed by overexpression of full length PDZK1 but not the first PDZ domain of PDZK1 alone. Furthermore, we found that overexpression of a green fluorescent protein chimera of the cytoplasmic carboxy-terminus of SR-BI (amino acids 479-509) in Huh-7 cells resulted in its interaction with PDZK1 and a reduced susceptibility to HCV infection. In contrast a similar chimera lacking the final amino acid of SR-BI (amino acids 479-508) failed to interact with PDZK1 and did not inhibit HCV infection. Taken together these results indicate an indirect involvement of PDZK1 in HCV entry via its ability to interact with SR-BI and enhance its activity as an HCV entry factor.
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Affiliation(s)
- Nicholas S. Eyre
- Centre for Cancer Biology, SA Pathology, Adelaide, South Australia, Australia
- School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, Australia
| | - Heidi E. Drummer
- Burnet Institute, Melbourne, Victoria, Australia
- Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria, Australia
- Department of Microbiology, Monash University, Clayton, Victoria, Australia
| | - Michael R. Beard
- Centre for Cancer Biology, SA Pathology, Adelaide, South Australia, Australia
- School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, Australia
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182
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Identification of novel inhibitors of dietary lipid absorption using zebrafish. PLoS One 2010; 5:e12386. [PMID: 20811635 PMCID: PMC2928291 DOI: 10.1371/journal.pone.0012386] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Accepted: 06/11/2010] [Indexed: 11/19/2022] Open
Abstract
Pharmacological inhibition of dietary lipid absorption induces favorable changes in serum lipoprotein levels in patients that are at risk for cardiovascular disease and is considered an adjuvant or alternative treatment with HMG-CoA reductase inhibitors (statins). Here we demonstrate the feasibility of identifying novel inhibitors of intestinal lipid absorption using the zebrafish system. A pilot screen of an unbiased chemical library identified novel compounds that inhibited processing of fluorescent lipid analogues in live zebrafish larvae. Secondary assays identified those compounds suitable for testing in mammals and provided insight into mechanism of action, which for several compounds could be distinguished from ezetimibe, a drug used to inhibit cholesterol absorption in humans that broadly inhibited lipid absorption in zebrafish larvae. These findings support the utility of zebrafish screening assays to identify novel compounds that target complex physiological processes.
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183
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Abstract
Zebrafish are an increasingly popular vertebrate model organism in which to study biological phenomena. It has been widely used, especially in developmental biology and neurobiology, and many aspects of its development and physiology are similar to those of mammals. The popularity of zebrafish relies on its relatively low cost, rapid development and ease of genetic manipulation. Moreover, the optical transparency of the developing fish together with novel imaging techniques enable the direct visualization of complex phenomena at the level of the entire organism. This potential is now also being increasingly appreciated by the lipid research community. In the present review we summarize basic information on the lipid composition and distribution in zebrafish tissues, including lipoprotein metabolism, intestinal lipid absorption, the yolk lipids and their mobilization, as well as lipids in the nervous system. We also discuss studies in which zebrafish have been employed for the visualization of whole-body lipid distribution and trafficking. Finally, recent advances in using zebrafish as a model for lipid-related diseases, including atherosclerosis, obesity, diabetes and hepatic steatosis are highlighted. As the insights into zebrafish lipid metabolism increase, it is likely that zebrafish as a model organism will become an increasingly powerful tool in lipid research.
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184
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Cellular retinol-binding protein type I (CRBP-I) regulates adipogenesis. Mol Cell Biol 2010; 30:3412-20. [PMID: 20498279 DOI: 10.1128/mcb.00014-10] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Adipogenesis is governed by a well-documented cascade of transcription factors. However, less is known about non-transcription factors that govern early stages of adipogenesis. Here we show that cellular retinol-binding protein type I (CRBP-I), a small cytosolic binding protein for retinol and retinaldehyde, is specifically restricted to preadipocytes in white adipose tissue. The absence of CRBP-I in mice (CRBP-I-KO mice) leads to increased adiposity. Despite increased adiposity, CRBP-I-KO mice remain more glucose tolerant and insulin sensitive during high-fat-diet feeding. 3T3-L1 cells deficient in CRBP-I or mouse embryonic fibroblasts derived from CRBP-I-KO mice had increased adipocyte differentiation and triglyceride (TG) accumulation. This was due to increased expression and activity of PPAR gamma, while other transcription factor pathways in early and late differentiation remained unchanged. Conversely, the overexpression of CRBP-I in 3T3-L1 cells results in decreased TG accumulation. In conclusion, CRBP-I is a cytosolic protein specifically expressed in preadipocytes that regulates adipocyte differentiation in part by affecting PPAR gamma activity.
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185
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Gross DA, Snapp EL, Silver DL. Structural insights into triglyceride storage mediated by fat storage-inducing transmembrane (FIT) protein 2. PLoS One 2010; 5:e10796. [PMID: 20520733 PMCID: PMC2875400 DOI: 10.1371/journal.pone.0010796] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Accepted: 05/03/2010] [Indexed: 11/19/2022] Open
Abstract
Fat storage-Inducing Transmembrane proteins 1 & 2 (FIT1/FITM1 and FIT2/FITM2) belong to a unique family of evolutionarily conserved proteins localized to the endoplasmic reticulum that are involved in triglyceride lipid droplet formation. FIT proteins have been shown to mediate the partitioning of cellular triglyceride into lipid droplets, but not triglyceride biosynthesis. FIT proteins do not share primary sequence homology with known proteins and no structural information is available to inform on the mechanism by which FIT proteins function. Here, we present the experimentally-solved topological models for FIT1 and FIT2 using N-glycosylation site mapping and indirect immunofluorescence techniques. These methods indicate that both proteins have six-transmembrane-domains with both N- and C-termini localized to the cytosol. Utilizing this model for structure-function analysis, we identified and characterized a gain-of-function mutant of FIT2 (FLL(157-9)AAA) in transmembrane domain 4 that markedly augmented the total number and mean size of lipid droplets. Using limited-trypsin proteolysis we determined that the FLL(157-9)AAA mutant has enhanced trypsin cleavage at K86 relative to wild-type FIT2, indicating a conformational change. Taken together, these studies indicate that FIT2 is a 6 transmembrane domain-containing protein whose conformation likely regulates its activity in mediating lipid droplet formation.
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Affiliation(s)
- David A. Gross
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Erik L. Snapp
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - David L. Silver
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- * E-mail:
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186
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LI DZ, HE JX, LEI MG, XU DQ, JIANG SW, XIONG YZ. Polymorphism in exon 2 of pig FIT1 gene and its association with fat-deposition-related traits. YI CHUAN = HEREDITAS 2010; 32:375-80. [DOI: 10.3724/sp.j.1005.2010.00375] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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187
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188
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Es-x/Ces1 prevents triacylglycerol accumulation in McArdle-RH7777 hepatocytes. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:1133-43. [DOI: 10.1016/j.bbalip.2009.07.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2009] [Revised: 06/25/2009] [Accepted: 07/17/2009] [Indexed: 02/08/2023]
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189
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Fernández-Murray JP, Gaspard GJ, Jesch SA, McMaster CR. NTE1-encoded phosphatidylcholine phospholipase b regulates transcription of phospholipid biosynthetic genes. J Biol Chem 2009; 284:36034-36046. [PMID: 19841481 DOI: 10.1074/jbc.m109.063958] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The Saccharomyces cerevisiae NTE1 gene encodes an evolutionarily conserved phospholipase B localized to the endoplasmic reticulum (ER) that degrades phosphatidylcholine (PC) generating glycerophosphocholine and free fatty acids. We show here that the activity of NTE1-encoded phospholipase B (Nte1p) prevents the attenuation of transcription of genes encoding enzymes involved in phospholipid synthesis in response to increased rates of PC synthesis by affecting the nuclear localization of the transcriptional repressor Opi1p. Nte1p activity becomes necessary for cells growing in inositol-free media under conditions of high rates of PC synthesis elicited by the presence of choline at 37 degrees C. The specific choline transporter encoded by the HNM1 gene is necessary for the burst of PC synthesis observed at 37 degrees C as follows: (i) Nte1p is dispensable in an hnm1Delta strain under these conditions, and (ii) there is a 3-fold increase in the rate of choline transport via the Hnm1p choline transporter upon a shift to 37 degrees C. Overexpression of NTE1 alleviated the inositol auxotrophy of a plethora of mutants, including scs2Delta, scs3Delta, ire1Delta, and hac1Delta among others. Overexpression of NTE1 sustained phospholipid synthesis gene transcription under conditions that normally repress transcription. This effect was also observed in a strain defective in the activation of free fatty acids for phosphatidic acid synthesis. No changes in the levels of phosphatidic acid were detected under conditions of altered expression of NTE1. Consistent with a synthetic impairment between challenged ER function and inositol deprivation, increased expression of NTE1 improved the growth of cells exposed to tunicamycin in the absence of inositol. We describe a new role for Nte1p toward membrane homeostasis regulating phospholipid synthesis gene transcription. We propose that Nte1p activity, by controlling PC abundance at the ER, affects lateral membrane packing and that this parameter, in turn, impacts the repressing transcriptional activity of Opi1p, the main regulator of phospholipid synthesis gene transcription.
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Affiliation(s)
- J Pedro Fernández-Murray
- Department of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada
| | - Gerard J Gaspard
- Department of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada
| | - Stephen A Jesch
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Christopher R McMaster
- Department of Pediatrics and Biochemistry and Molecular Biology, Atlantic Research Centre, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
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190
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Soni KG, Mardones GA, Sougrat R, Smirnova E, Jackson CL, Bonifacino JS. Coatomer-dependent protein delivery to lipid droplets. J Cell Sci 2009; 122:1834-41. [PMID: 19461073 DOI: 10.1242/jcs.045849] [Citation(s) in RCA: 215] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Lipid droplets (LDs) are cytoplasmic organelles that store neutral lipids for use as an energy supply in times of nutrient deprivation and for membrane assembly. Misregulation of LD function leads to many human diseases, including lipodystrophy, obesity and neutral lipid storage disorders. A number of proteins have been shown to localize to the surface of lipid droplets, including lipases such as adipose triglyceride lipase (ATGL) and the PAT-domain proteins ADRP (adipophilin) and TIP47, but the mechanism by which they are targeted to LDs is not known. Here we demonstrate that ATGL and ADRP, but not TIP47, are delivered to LDs by a pathway mediated by the COPI and COPII coatomer proteins and their corresponding regulators.
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Affiliation(s)
- Krishnakant G Soni
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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191
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Yamahama Y, Muranaka Y, Kumakiri Y, Tamotsu S, Hariyama T. Ultrastructural analysis of lipid incorporation in the embryonic silkworm, Bombyx mori. Zoolog Sci 2009; 26:321-4. [PMID: 19715500 DOI: 10.2108/zsj.26.321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Insect eggs store many lipid droplets as an energy source for embryonic development. We previously reported that lipid droplets are incorporated into embryos in three steps in the silkworm, Bombyx mori. The midgut plays important roles in lipid incorporation during the second and third steps, whereas the manner of lipid incorporation during the first step is still unknown. In this study, we focused on how lipids were incorporated into the embryo in the first step, compared with the mechanisms used in the second step, by means of transmission electron microscopy using the high-pressure freezing and freeze substitution method. At the beginning of the first step (blastoderm formation stage), some lipid droplets were observed in each cell of the embryonic tissues. Lipid droplets were seen to be derived from the oocyte peripheral cytoplasm by superficial cleavage. At the end of the first step (late appendage formation stage), some lipid droplets were attached to the elongated rough endoplasmic reticulum (rER). It seemed that formation of the lipid droplets occurred in embryonic cells at the end of the first step, because the rER is the site of biogenesis of lipid droplets. The incorporation of lipid droplets in the first step may be subdivided into two stages: the blastoderm formation stage and the subsequent stage before blastokinesis.
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Affiliation(s)
- Yumi Yamahama
- Department of Biology, Faculty of Medicine, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan.
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192
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Cobbe N, Marshall KM, Gururaja Rao S, Chang CW, Di Cara F, Duca E, Vass S, Kassan A, Heck MMS. The conserved metalloprotease invadolysin localizes to the surface of lipid droplets. J Cell Sci 2009; 122:3414-23. [PMID: 19706689 DOI: 10.1242/jcs.044610] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Invadolysin is a metalloprotease conserved in many different organisms, previously shown to be essential in Drosophila with roles in cell division and cell migration. The gene seems to be ubiquitously expressed and four distinct splice variants have been identified in human cells but not in most other species examined. Immunofluorescent detection of human invadolysin in cultured cells reveals the protein to be associated with the surface of lipid droplets. By means of subcellular fractionation, we have independently confirmed the association of invadolysin with lipid droplets. We thus identify invadolysin as the first metalloprotease located on these dynamic organelles. In addition, analysis of larval fat-body morphological appearance and triglyceride levels in the Drosophila invadolysin mutant suggests that invadolysin plays a role in lipid storage or metabolism.
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Affiliation(s)
- Neville Cobbe
- University of Edinburgh, Queen's Medical Research Institute, Centre for Cardiovascular Science, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
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193
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Two novel SNPs in coding region of the caprine Fat-inducing transcript gene and their association with growth traits. Mol Biol Rep 2009; 37:485-90. [DOI: 10.1007/s11033-009-9672-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Accepted: 07/27/2009] [Indexed: 02/05/2023]
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194
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Xu D, Sillaots S, Davison J, Hu W, Jiang B, Kauffman S, Martel N, Ocampo P, Oh C, Trosok S, Veillette K, Wang H, Yang M, Zhang L, Becker J, Martin CE, Roemer T. Chemical genetic profiling and characterization of small-molecule compounds that affect the biosynthesis of unsaturated fatty acids in Candida albicans. J Biol Chem 2009; 284:19754-64. [PMID: 19487691 DOI: 10.1074/jbc.m109.019877] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The balance between saturated and unsaturated fatty acids plays a crucial role in determining the membrane fluidity. In the diploid fungal pathogen Candida albicans, the gene for fatty acid Delta9 desaturase, OLE1, is essential for viability. Using a reverse genetic approach, termed the fitness test, we identified a group of structurally related synthetic compounds that induce specific hypersensitivity of the OLE1(+/-) strain. Genetic repression of OLE1 and chemical inhibition by two selected compounds, ECC145 and ECC188, resulted in a marked decrease in the total unsaturated fatty acids and impaired hyphal development. The resulting auxotroph of both was suppressed by the exogenous monounsaturated fatty acids (16:1Delta9 and 18:1Delta9). These correlations suggest that both compounds affect the level of unsaturated fatty acids, likely by impairing Ole1p directly or indirectly. However, the residual levels of monounsaturated fatty acids (MUFAs) resulted from chemical inhibition were significantly higher than OLE1 repression, indicating even partial inhibition of MUFAs is sufficient to stop cellular proliferation. Although the essentiality of OLE1 was suppressed by MUFAs in vitro, we demonstrated that it was required for virulence in a murine model of systemic candidiasis even when the animals were supplemented with a high fat diet. Thus, the fungal fatty acid desaturase is an attractive antifungal drug target. Taking advantage of the inhibitors and the relevant conditional shut-off strains, we validated several chemical genetic interactions observed in the fitness test profiles that reveal novel genetic interactions between OLE1/unsaturated fatty acids and other cellular processes.
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Affiliation(s)
- Deming Xu
- Center of Fungal Genetics, Merck-Frosst Canada Ltd., Montreal, Quebec H9H 3L1, Canada.
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195
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Le TT, Cheng JX. Non-Linear Optical Imaging of Obesity-Related Health Risks: Review. JOURNAL OF INNOVATIVE OPTICAL HEALTH SCIENCES 2009; 2:9-25. [PMID: 19784384 PMCID: PMC2750900 DOI: 10.1142/s1793545809000371] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
This review highlights the recent applications of non-linear optical (NLO) microscopy to study obesity-related health risks. A strong emphasis is given to the applications of coherent anti-Stokes Raman scattering (CARS) microscopy where multiple non-linear optical imaging modalities including CARS, sum-frequency generation (SFG), and two-photon fluorescence are employed simultaneously on a single microscope platform. Specific examples on applications of NLO microscopy to study lipid-droplet biology, obesity-cancer relationship, atherosclerosis, and lipid-rich biological structures are discussed.
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Affiliation(s)
- Thuc T. Le
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, USA,
| | - Ji-Xin Cheng
- Department of Chemistry and Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, USA,
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196
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Rutkowski DT, Wu J, Back SH, Callaghan MU, Ferris SP, Iqbal J, Clark R, Miao H, Fornek J, Katze MG, Hussain MM, Song B, Swathirajan J, Wang J, Yau GDY, Kaufman RJ. UPR pathways combine to prevent hepatic steatosis caused by ER stress-mediated suppression of transcriptional master regulators. Dev Cell 2008; 15:829-40. [PMID: 19081072 PMCID: PMC2923556 DOI: 10.1016/j.devcel.2008.10.015] [Citation(s) in RCA: 454] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 09/05/2008] [Accepted: 10/31/2008] [Indexed: 12/14/2022]
Abstract
The unfolded protein response (UPR) is linked to metabolic dysfunction, yet it is not known how endoplasmic reticulum (ER) disruption might influence metabolic pathways. Using a multilayered genetic approach, we find that mice with genetic ablations of either ER stress-sensing pathways (ATF6alpha, eIF2alpha, IRE1alpha) or of ER quality control (p58(IPK)) share a common dysregulated response to ER stress that includes the development of hepatic microvesicular steatosis. Rescue of ER protein processing capacity by the combined action of UPR pathways during stress prevents the suppression of a subset of metabolic transcription factors that regulate lipid homeostasis. This suppression occurs in part by unresolved ER stress perpetuating expression of the transcriptional repressor CHOP. As a consequence, metabolic gene expression networks are directly responsive to ER homeostasis. These results reveal an unanticipated direct link between ER homeostasis and the transcriptional regulation of metabolism, and suggest mechanisms by which ER stress might underlie fatty liver disease.
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Affiliation(s)
- D. Thomas Rutkowski
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Jun Wu
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Sung-Hoon Back
- Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Michael U. Callaghan
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
- Department of Pediatrics, Wayne State University, Detroit, MI, 48201
| | - Sean P. Ferris
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Jahangir Iqbal
- Department of Anatomy and Cell Biology, State University of New York Downstate Medical Center, Brooklyn, NY 11203
| | - Robert Clark
- Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Hongzhi Miao
- Department of Pediatrics, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Jamie Fornek
- Department of Microbiology, University of Washington, Seattle, WA, 98195
| | - Michael G. Katze
- Department of Microbiology, University of Washington, Seattle, WA, 98195
| | - M. Mahmood Hussain
- Department of Anatomy and Cell Biology, State University of New York Downstate Medical Center, Brooklyn, NY 11203
| | - Benbo Song
- Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Jayanth Swathirajan
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Junying Wang
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Grace D.-Y. Yau
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
| | - Randal J. Kaufman
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109
- Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109
- Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI 48109
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197
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Babin PJ, Gibbons GF. The evolution of plasma cholesterol: direct utility or a "spandrel" of hepatic lipid metabolism? Prog Lipid Res 2008; 48:73-91. [PMID: 19049814 DOI: 10.1016/j.plipres.2008.11.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Revised: 11/06/2008] [Accepted: 11/07/2008] [Indexed: 02/07/2023]
Abstract
Fats provide a concentrated source of energy for multicellular organisms. The efficient transport of fats through aqueous biological environments raises issues concerning effective delivery to target tissues. Furthermore, the utilization of fatty acids presents a high risk of cytotoxicity. Improving the efficiency of fat transport while simultaneously minimizing the cytotoxic risk confers distinct selective advantages. In humans, most of the plasma cholesterol is associated with low-density lipoprotein (LDL), a metabolic by-product of very-low-density lipoprotein (VLDL), which originates in the liver. However, the functions of VLDL are not clear. This paper reviews the evidence that LDL arose as a by-product during the natural selection of VLDL. The latter, in turn, evolved as a means of improving the efficiency of diet-derived fatty acid storage and utilization, as well as neutralizing the potential cytotoxicity of fatty acids while conserving their advantages as a concentrated energy source. The evolutionary biology of lipid transport processes has provided a fascinating insight into how and why these VLDL functions emerged during animal evolution. As causes of historical origin must be separated from current utilities, our spandrel-LDL theory proposes that LDL is a spandrel of VLDL selection, which appeared non-adaptively and may later have become crucial for vertebrate fitness.
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Affiliation(s)
- Patrick J Babin
- Université Bordeaux 1, Génomique et Physiologie des Poissons, UMR NuAGe, 33405 Talence, France
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198
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Abstract
Fat-specific protein of 27 kDa (FSP27) is a highly expressed adipocyte protein that promotes triglyceride accumulation within lipid droplets. In this issue of the JCI, Nishino et al. show that FSP27 also helps to maintain the characteristically large unilocular lipid droplet structure within each white adipocyte (see the related article beginning on page 2808). Fragmentation of lipid droplets in white adipocytes from FSP27-KO mice caused both increased lipolysis and upregulation of genes enhancing mitochondrial oxidative metabolism. This increased energy expenditure in turn protected the mice from diet-induced obesity and insulin resistance. These new results highlight powerful mechanisms that tightly coordinate rates of triglyceride storage in lipid droplets with mitochondrial fatty acid oxidation in white adipocytes.
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Affiliation(s)
- Vishwajeet Puri
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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199
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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: 13.0] [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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200
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Iqbal J, Rudel LL, Hussain MM. Microsomal triglyceride transfer protein enhances cellular cholesteryl esterification by relieving product inhibition. J Biol Chem 2008; 283:19967-80. [PMID: 18502767 DOI: 10.1074/jbc.m800398200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cholesteryl ester synthesis by the acyl-CoA:cholesterol acyltransferase enzymes ACAT1 and ACAT2 is, in part, a cellular homeostatic mechanism to avoid toxicity associated with high free cholesterol levels. In hepatocytes and enterocytes, cholesteryl esters are secreted as part of apoB lipoproteins, the assembly of which is critically dependent on microsomal triglyceride transfer protein (MTP). Conditional genetic ablation of MTP reduces cholesteryl esters and enhances free cholesterol in the liver and intestine without diminishing ACAT1 and ACAT2 mRNA levels. As expected, increases in hepatic free cholesterol are associated with decreases in 3-hydroxy-3-methylglutaryl-CoA reductase and increases in ATP-binding cassette transporter 1 mRNA levels. Chemical inhibition of MTP also decreases esterification of cholesterol in Caco-2 and HepG2 cells. Conversely, coexpression of MTP and apoB in AC29 cells stably transfected with ACAT1 and ACAT2 increases cholesteryl ester synthesis. Liver and enterocyte microsomes from MTP-deficient animals synthesize lesser amounts of cholesteryl esters in vitro, but addition of purified MTP and low density lipoprotein corrects this deficiency. Enrichment of microsomes with cholesteryl esters also inhibits cholesterol ester synthesis. Thus, MTP enhances cellular cholesterol esterification by removing cholesteryl esters from their site of synthesis and depositing them into nascent apoB lipoproteins. Therefore, MTP plays a novel role in regulating cholesteryl ester biosynthesis in cells that produce lipoproteins. We speculate that non-lipoprotein-producing cells may use different mechanisms to alleviate product inhibition and modulate cholesteryl ester biosynthesis.
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Affiliation(s)
- Jahangir Iqbal
- Department of Anatomy and Cell Biology and Pediatrics, State University of New York Downstate Medical Center, Brooklyn, NY 11203, USA
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