51
|
Dahlhoff M, Fröhlich T, Arnold GJ, Müller U, Leonhardt H, Zouboulis CC, Schneider MR. Characterization of the sebocyte lipid droplet proteome reveals novel potential regulators of sebaceous lipogenesis. Exp Cell Res 2014; 332:146-55. [PMID: 25523620 DOI: 10.1016/j.yexcr.2014.12.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2014] [Revised: 12/03/2014] [Accepted: 12/05/2014] [Indexed: 01/06/2023]
Abstract
Lipid metabolism depends on lipid droplets (LD), cytoplasmic structures surrounded by a protein-rich phospholipid monolayer. Although lipid synthesis is the hallmark of sebaceous gland cell differentiation, the LD-associated proteins of sebocytes have not been evaluated systematically. The LD fraction of SZ95 sebocytes was collected by density gradient centrifugation and associated proteins were analyzed by nanoliquid chromatography/tandem mass spectrometry. 54 proteins were significantly enriched in LD fractions, and 6 of them have not been detected previously in LDs. LD fractions contained high levels of typical LD-associated proteins as PLIN2/PLIN3, and most proteins belonged to functional categories characteristic for LD-associated proteins, indicating a reliable dataset. After confirming expression of transcripts encoding the six previously unidentified proteins by qRT-PCR in SZ95 sebocytes and in another sebocyte line (SebE6E7), we focused on two of these proteins, ALDH1A3 and EPHX4. While EPHX4 was localized almost exclusively on the surface of LDs, ALDH1A3 showed a more widespread localization that included additional cytoplasmic structures. siRNA-mediated downregulation revealed that depletion of EPHX4 increases LD size and sebaceous lipogenesis. Further studies on the roles of these proteins in sebocyte physiology and sebaceous lipogenesis may indicate novel strategies for the therapy of sebaceous gland-associated diseases such as acne.
Collapse
Affiliation(s)
- Maik Dahlhoff
- Institute of Molecular Animal Breeding and Biotechnology, Gene Center, LMU Munich, Germany
| | - Thomas Fröhlich
- Laboratory for Functional Genome Analysis LAFUGA, Gene Center, LMU Munich, Germany
| | - Georg J Arnold
- Laboratory for Functional Genome Analysis LAFUGA, Gene Center, LMU Munich, Germany
| | - Udo Müller
- Human Biology and BioImaging, Department of Biology II, LMU Munich, Germany
| | - Heinrich Leonhardt
- Human Biology and BioImaging, Department of Biology II, LMU Munich, Germany
| | - Christos C Zouboulis
- Departments of Dermatology, Venereology, Allergology and Immunology, Dessau Medical Center, Dessau, Germany
| | - Marlon R Schneider
- Institute of Molecular Animal Breeding and Biotechnology, Gene Center, LMU Munich, Germany.
| |
Collapse
|
52
|
Khor VK, Ahrends R, Lin Y, Shen WJ, Adams CM, Roseman AN, Cortez Y, Teruel MN, Azhar S, Kraemer FB. The proteome of cholesteryl-ester-enriched versus triacylglycerol-enriched lipid droplets. PLoS One 2014; 9:e105047. [PMID: 25111084 PMCID: PMC4128735 DOI: 10.1371/journal.pone.0105047] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 07/19/2014] [Indexed: 12/20/2022] Open
Abstract
Within cells, lipids are stored in the form of lipid droplets (LDs), consisting of a neutral lipid core, surrounded by a phospholipid monolayer and an outer layer of protein. LDs typically accumulate either triacylglycerol (TAG) and diacylglycerol or cholesteryl ester (CE), depending on the type of tissue. Recently, there has been an increased interest in the proteins that surround LDs. LD proteins have been found to be quite diverse, from structural proteins to metabolic enzymes, proteins involved in vesicular transport, and proteins that may play a role in LD formation. Previous proteomics analyses have focused on TAG-enriched LDs, whereas CE-enriched LDs have been largely ignored. Our study has compared the LD proteins from CE-enriched LDs to TAG-enriched LDs in steroidogenic cells. In primary rat granulosa cells loaded with either HDL to produce CE-enriched LDs or fatty acids to produce TAG-enriched LDs, 61 proteins were found to be elevated in CE-enriched LDs and 40 proteins elevated in TAG-enriched LDs with 278 proteins in similar amounts. Protein expression was further validated by selected reaction monitoring (SRM) mass spectrometry (MS). SRM verified expression of 25 of 27 peptides that were previously detected by tandem mass tagging MS. Several proteins were confirmed to be elevated in CE-enriched LDs by SRM including the intermediate filament vimentin. This study is the first to compare the proteins found on CE-enriched LDs with TAG-enriched LDs and constitutes the first step in creating a better understanding of the proteins found on CE-enriched LDs in steroidogenic cells.
Collapse
Affiliation(s)
- Victor K. Khor
- Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California, United States of America
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
| | - Robert Ahrends
- Department of Chemical and Systems Biology, Stanford University, Stanford, California, United States of America
| | - Ye Lin
- Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California, United States of America
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
| | - Wen-Jun Shen
- Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California, United States of America
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
| | - Christopher M. Adams
- Mass Spectrometry Center, Stanford University, Stanford, California, United States of America
| | - Ann Nomoto Roseman
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
| | - Yuan Cortez
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
| | - Mary N. Teruel
- Department of Chemical and Systems Biology, Stanford University, Stanford, California, United States of America
| | - Salman Azhar
- Division of Gastroenterology and Hepatology, Department of Medicine, Stanford University, Stanford, California, United States of America
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
| | - Fredric B. Kraemer
- Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California, United States of America
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America
- * E-mail:
| |
Collapse
|
53
|
Arrese EL, Saudale FZ, Soulages JL. Lipid Droplets as Signaling Platforms Linking Metabolic and Cellular Functions. Lipid Insights 2014; 7:7-16. [PMID: 25221429 PMCID: PMC4161058 DOI: 10.4137/lpi.s11128] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The main cells of the adipose tissue of animals, adipocytes, are characterized by the presence of large cytosolic lipid droplets (LDs) that store triglyceride (TG) and cholesterol. However, most cells have LDs and the ability to store lipids. LDs have a well-known central role in storage and provision of fatty acids and cholesterol. However, the complexity of the regulation of lipid metabolism on the surface of the LDs is still a matter of intense study. Beyond this role, a number of recent studies have suggested that LDs have major functions in other cellular processes, such as protein storage and degradation, infection, and immunity. Thus, our perception of LDs has been radically transformed from simple globules of fat to highly dynamic organelles of unexpected complexity. Here, we compiled some recent evidence supporting the emerging view that LDs act as platforms connecting a number of relevant metabolic and cellular functions.
Collapse
Affiliation(s)
- Estela L Arrese
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| | - Fredy Z Saudale
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| | - Jose L Soulages
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| |
Collapse
|
54
|
Mannik J, Meyers A, Dalhaimer P. Isolation of cellular lipid droplets: two purification techniques starting from yeast cells and human placentas. J Vis Exp 2014:50981. [PMID: 24747783 PMCID: PMC4160924 DOI: 10.3791/50981] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Lipid droplets are dynamic organelles that can be found in most eukaryotic and certain prokaryotic cells. Structurally, the droplets consist of a core of neutral lipids surrounded by a phospholipid monolayer. One of the most useful techniques in determining the cellular roles of droplets has been proteomic identification of bound proteins, which can be isolated along with the droplets. Here, two methods are described to isolate lipid droplets and their bound proteins from two wide-ranging eukaryotes: fission yeast and human placental villous cells. Although both techniques have differences, the main method-- density gradient centrifugation--is shared by both preparations. This shows the wide applicability of the presented droplet isolation techniques. In the first protocol, yeast cells are converted into spheroplasts by enzymatic digestion of their cell walls. The resulting spheroplasts are then gently lysed in a loose-fitting homogenizer. Ficoll is added to the lysate to provide a density gradient, and the mixture is centrifuged three times. After the first spin, the lipid droplets are localized to the white-colored floating layer of the centrifuge tubes along with the endoplasmic reticulum (ER), the plasma membrane, and vacuoles. Two subsequent spins are used to remove these other three organelles. The result is a layer that has only droplets and bound proteins. In the second protocol, placental villous cells are isolated from human term placentas by enzymatic digestion with trypsin and DNase I. The cells are homogenized in a loose-fitting homogenizer. Low-speed and medium-speed centrifugation steps are used to remove unbroken cells, cellular debris, nuclei, and mitochondria. Sucrose is added to the homogenate to provide a density gradient and the mixture is centrifuged to separate the lipid droplets from the other cellular fractions. The purity of the lipid droplets in both protocols is confirmed by Western Blot analysis. The droplet fractions from both preps are suitable for subsequent proteomic and lipidomic analysis.
Collapse
Affiliation(s)
- Jaana Mannik
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee
| | - Alex Meyers
- Department of Chemical and Biomolecular Engineering, University of Tennessee
| | - Paul Dalhaimer
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee; Department of Chemical and Biomolecular Engineering, University of Tennessee;
| |
Collapse
|
55
|
Kiss RS, Nilsson T. Rab proteins implicated in lipid storage and mobilization. J Biomed Res 2014; 28:169-77. [PMID: 25013400 PMCID: PMC4085554 DOI: 10.7555/jbr.28.20140029] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 02/28/2014] [Indexed: 12/28/2022] Open
Abstract
Abnormal intracellular accumulation or transport of lipids contributes greatly to the pathogenesis of human diseases. In the liver, excess accumulation of triacylglycerol (TG) leads to fatty liver disease encompassing steatosis, steatohepatitis and fibrosis. This places individuals at risk of developing cirrhosis, hepatocellular carcinoma or hepatic decompensation and also contributes to the emergence of insulin resistance and dyslipidemias affecting many other organs. Excessive accumulation of TG in adipose tissue contributes to insulin resistance as well as to the release of cytokines attracting leucocytes leading to a pro-inflammatory state. Pathological accumulation of cholesteryl ester (CE) in macrophages in the arterial wall is the progenitor of atherosclerotic plaques and heart disease. Overconsumption of dietary fat, cholesterol and carbohydrates explains why these diseases are on the increase yet offers few clues for how to prevent or treat individuals. Dietary regimes have proven futile and barring surgery, no realistic alternatives are at hand as effective drugs are few and not without side effects. Overweight and obesity-related diseases are no longer restricted to the developed world and as such, constitute a global problem. Development of new drugs and treatment strategies are a priority yet requires as a first step, elucidation of the molecular pathophysiology underlying each associated disease state. The lipid droplet (LD), an up to now overlooked intracellular organelle, appears at the heart of each pathophysiology linking key regulatory and metabolic processes as well as constituting the site of storage of both TGs and CEs. As the molecular machinery and mechanisms of LDs of each cell type are being elucidated, regulatory proteins used to control various cellular processes are emerging. Of these and the subject of this review, small GTPases belonging to the Rab protein family appear as important molecular switches used in the regulation of the intracellular trafficking and storage of lipids.
Collapse
Affiliation(s)
- Robert Scott Kiss
- Department of Medicine, McGill University, Montreal, Canada; ; Research Institute of McGill University Health Centre, Montreal, Canada
| | - Tommy Nilsson
- Department of Medicine, McGill University, Montreal, Canada; ; Research Institute of McGill University Health Centre, Montreal, Canada
| |
Collapse
|
56
|
Barber E, Sinclair AJ, Cameron-Smith D. Comparative actions of omega-3 fatty acids on in-vitro lipid droplet formation. Prostaglandins Leukot Essent Fatty Acids 2013; 89:359-66. [PMID: 24012207 DOI: 10.1016/j.plefa.2013.07.006] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Revised: 07/18/2013] [Accepted: 07/25/2013] [Indexed: 01/24/2023]
Abstract
Storage of fat into lipid droplets (LDs) is the key step in adipogenesis. Previously the omega-3 polyunsaturated fatty acid (n-3PUFA) eicosapentaenoic acid (EPA; C20:5n-3) has been shown to suppress LD formation, yet the actions of other n-3PUFA is unknown. Here, we examined the impact of the three major long chain n-3PUFA; EPA, docosapentaenoic acid (DPA; C22:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) on LD formation in 3T3-L1 adipocytes. Cells were supplemented with 100µM fatty acid during differentiation. All n-3PUFA significantly reduced LD formation and the metabolic disorder marker, SCD1, in comparison to stearic acid (STA; C18:0). This action was more potent for DHA than either EPA or DPA. Furthermore, DHA significantly increased lipolysis and ATGL gene and protein expression but reduced the gene expression of three proteins related to LD formation (Perilipin A, Caveolin-1 and Cidea), compared with other n-3PUFA. Thus, DHA, above EPA and DPA, markedly suppressed fat storage in LDs in in-vitro adipocytes.
Collapse
Affiliation(s)
- Elizabeth Barber
- Department of Nutrition and Dietetics, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton 3800, Victoria, Australia.
| | | | | |
Collapse
|
57
|
Crunk AE, Monks J, Murakami A, Jackman M, MacLean PS, Ladinsky M, Bales ES, Cain S, Orlicky DJ, McManaman JL. Dynamic regulation of hepatic lipid droplet properties by diet. PLoS One 2013; 8:e67631. [PMID: 23874434 PMCID: PMC3708958 DOI: 10.1371/journal.pone.0067631] [Citation(s) in RCA: 58] [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: 02/11/2013] [Accepted: 05/20/2013] [Indexed: 12/21/2022] Open
Abstract
Cytoplasmic lipid droplets (CLD) are organelle-like structures that function in neutral lipid storage, transport and metabolism through the actions of specific surface-associated proteins. Although diet and metabolism influence hepatic CLD levels, how they affect CLD protein composition is largely unknown. We used non-biased, shotgun, proteomics in combination with metabolic analysis, quantitative immunoblotting, electron microscopy and confocal imaging to define the effects of low- and high-fat diets on CLD properties in fasted-refed mice. We found that the hepatic CLD proteome is distinct from that of CLD from other mammalian tissues, containing enzymes from multiple metabolic pathways. The hepatic CLD proteome is also differentially affected by dietary fat content and hepatic metabolic status. High fat feeding markedly increased the CLD surface density of perilipin-2, a critical regulator of hepatic neutral lipid storage, whereas it reduced CLD levels of betaine-homocysteine S-methyltransferase, an enzyme regulator of homocysteine levels linked to fatty liver disease and hepatocellular carcinoma. Collectively our data demonstrate that the hepatic CLD proteome is enriched in metabolic enzymes, and that it is qualitatively and quantitatively regulated by diet and metabolism. These findings implicate CLD in the regulation of hepatic metabolic processes, and suggest that their properties undergo reorganization in response to hepatic metabolic demands.
Collapse
Affiliation(s)
- Amanda E. Crunk
- Graduate Program of Molecular Biology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- Division of Basic Reproductive Sciences, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Jenifer Monks
- Division of Basic Reproductive Sciences, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Aya Murakami
- Graduate Program of Molecular Biology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Matthew Jackman
- Division of Endocrinology and Metabolism, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- The Center for Human Nutrition, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- The Colorado Obesity Research Initiative, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Paul S. MacLean
- Division of Endocrinology and Metabolism, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- The Center for Human Nutrition, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- The Colorado Obesity Research Initiative, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Mark Ladinsky
- The Boulder Laboratory for 3D Electron Microscopy, University of Colorado Boulder, Boulder Colorado, United States of America
| | - Elise S. Bales
- Division of Basic Reproductive Sciences, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Shannon Cain
- The Colorado Obesity Research Initiative, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - David J. Orlicky
- Department of Pathology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - James L. McManaman
- Graduate Program of Molecular Biology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- Division of Basic Reproductive Sciences, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- The Center for Human Nutrition, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- The Colorado Obesity Research Initiative, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- * E-mail:
| |
Collapse
|
58
|
Konige M, Wang H, Sztalryd C. Role of adipose specific lipid droplet proteins in maintaining whole body energy homeostasis. Biochim Biophys Acta Mol Basis Dis 2013; 1842:393-401. [PMID: 23688782 DOI: 10.1016/j.bbadis.2013.05.007] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Revised: 04/10/2013] [Accepted: 05/03/2013] [Indexed: 12/15/2022]
Abstract
Excess or insufficient lipid storage in white adipose tissue lipid droplets is associated with dyslipidemia, insulin resistance and increased risk for diabetes type 2. Thus, maintenance of adipose lipid droplet growth and function is critical to preserve whole body insulin sensitivity and energy homeostasis. Progress in understanding biology of lipid droplets has underscored the role of proteins that interact with lipid droplets. Here, we review the current knowledge of adipose specific lipid droplet proteins, which share unique functions controlling adipocyte lipid storage, limiting lipid spill-over and lipotoxic effects thought to contribute to disease. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.
Collapse
Affiliation(s)
- Manige Konige
- Department of Medicine, Division of Endocrinology, School of Medicine, University of Maryland, Baltimore, MD 21201, USA
| | - Hong Wang
- Department of Medicine, Division of Endocrinology, School of Medicine, University of Maryland, Baltimore, MD 21201, USA
| | - Carole Sztalryd
- Department of Medicine, Division of Endocrinology, School of Medicine, University of Maryland, Baltimore, MD 21201, USA; Geriatric Research, Education, and Clinical Center, Baltimore Veterans Affairs Health Care Center, Baltimore, MD 21201, USA.
| |
Collapse
|
59
|
Renes J, Mariman E. Application of proteomics technology in adipocyte biology. MOLECULAR BIOSYSTEMS 2013; 9:1076-91. [PMID: 23629546 DOI: 10.1039/c3mb25596d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Obesity and its associated complications have reached epidemic proportions in Western-type societies. Concomitantly, the obesity incidence in developing countries is increasing. One hallmark of obesity is the differentiation of pre-adipocytes into mature triglyceride-loaded adipocytes present in subcutaneous and visceral adipose tissue depots. This may ultimately lead to dysfunctional adipose tissue together with detrimental changes in the profiles of (pre-)adipocyte-secreted proteins, known as adipokines. Obesity-induced alterations in adipokine profiles contribute to the development of obesity-associated disorders. Consequently, the interest in the molecular events responsible for adipose tissue modifications during weight gain and weight loss as well as in the aetiology of obesity-associated disorders is growing. Molecular mechanisms involved in pre-adipocyte differentiation and alterations in adipokine profiles have been examined at the gene and protein level by high-throughput technologies. Independent proteomics studies have contributed significantly to further insight into adipocyte biology, particularly with respect to adipokine profiling. In this review novel findings obtained with adipo-proteomics studies are highlighted and the relevance of proteomics technologies to further understand molecular aspects of adipocyte biology is discussed.
Collapse
Affiliation(s)
- Johan Renes
- Department of Human Biology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
| | | |
Collapse
|
60
|
Krahmer N, Hilger M, Kory N, Wilfling F, Stoehr G, Mann M, Farese RV, Walther TC. Protein correlation profiles identify lipid droplet proteins with high confidence. Mol Cell Proteomics 2013; 12:1115-26. [PMID: 23319140 DOI: 10.1074/mcp.m112.020230] [Citation(s) in RCA: 123] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Lipid droplets (LDs) are important organelles in energy metabolism and lipid storage. Their cores are composed of neutral lipids that form a hydrophobic phase and are surrounded by a phospholipid monolayer that harbors specific proteins. Most well-established LD proteins perform important functions, particularly in cellular lipid metabolism. Morphological studies show LDs in close proximity to and interacting with membrane-bound cellular organelles, including the endoplasmic reticulum, mitochondria, peroxisomes, and endosomes. Because of these close associations, it is difficult to purify LDs to homogeneity. Consequently, the confident identification of bona fide LD proteins via proteomics has been challenging. Here, we report a methodology for LD protein identification based on mass spectrometry and protein correlation profiles. Using LD purification and quantitative, high-resolution mass spectrometry, we identified LD proteins by correlating their purification profiles to those of known LD proteins. Application of the protein correlation profile strategy to LDs isolated from Drosophila S2 cells led to the identification of 111 LD proteins in a cellular LD fraction in which 1481 proteins were detected. LD localization was confirmed in a subset of identified proteins via microscopy of the expressed proteins, thereby validating the approach. Among the identified LD proteins were both well-characterized LD proteins and proteins not previously known to be localized to LDs. Our method provides a high-confidence LD proteome of Drosophila cells and a novel approach that can be applied to identify LD proteins of other cell types and tissues.
Collapse
Affiliation(s)
- Natalie Krahmer
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520, USA
| | | | | | | | | | | | | | | |
Collapse
|
61
|
Abstract
Neonates of most species depend on milk lipids for calories, fat-soluble vitamins, and bioactive lipid components for growth and development during the postnatal period. To meet neonatal nutrition and development needs, the mammary gland has evolved efficient mechanisms for synthesizing and secreting large quantities of lipid during lactation. Although the biochemical steps involved in milk lipid synthesis are understood, the identities of the genes mediating these steps and the molecular physiology of milk lipid production and secretion have only recently begun to be understood in detail through advances in mouse genetics, gene expression analysis, protein structural properties, and the cell biology of lipid metabolism. This review discusses emerging data about the molecular, cellular, and structural determinants of milk lipid synthesis and secretion within the context of physiological functions.
Collapse
Affiliation(s)
- James L McManaman
- Division of Reproductive Sciences, Department of Obstetrics and Gynecology, Graduate Programs in Cell Biology, Stem Cells and Development, Molecular Biology and Reproductive Sciences, University of Colorado, School of Medicine, Aurora, CO 80045, USA
| |
Collapse
|
62
|
Ivashov VA, Grillitsch K, Koefeler H, Leitner E, Baeumlisberger D, Karas M, Daum G. Lipidome and proteome of lipid droplets from the methylotrophic yeast Pichia pastoris. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:282-90. [PMID: 23041514 PMCID: PMC3787741 DOI: 10.1016/j.bbalip.2012.09.017] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 09/11/2012] [Accepted: 09/28/2012] [Indexed: 11/24/2022]
Abstract
Lipid droplets (LD) are the main depot of non-polar lipids in all eukaryotic cells. In the present study we describe isolation and characterization of LD from the industrial yeast Pichia pastoris. We designed and adapted an isolation procedure which allowed us to obtain this subcellular fraction at high purity as judged by quality control using appropriate marker proteins. Components of P. pastoris LD were characterized by conventional biochemical methods of lipid and protein analysis, but also by a lipidome and proteome approach. Our results show several distinct features of LD from P. pastoris especially in comparison to Saccharomyces cerevisiae. P. pastoris LD are characterized by their high preponderance of triacylglycerols over steryl esters in the core of the organelle, the high degree of fatty acid (poly)unsaturation and the high amount of ergosterol precursors. The high phosphatidylinositol to phosphatidylserine of ~ 7.5 ratio on the surface membrane of LD is noteworthy. Proteome analysis revealed equipment of the organelle with a small but typical set of proteins which includes enzymes of sterol biosynthesis, fatty acid activation, phosphatidic acid synthesis and non-polar lipid hydrolysis. These results are the basis for a better understanding of P. pastoris lipid metabolism and lipid storage and may be helpful for manipulating cell biological and/or biotechnological processes in this yeast.
Collapse
Affiliation(s)
- Vasyl A Ivashov
- Institute of Biochemistry, Graz University of Technology, Austria
| | | | | | | | | | | | | |
Collapse
|