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Abstract
Perilipin proteins were discovered in the adipocyte, where they regulate lipid storage and lipolysis. Animal knockout models provided initial evidence of the critical role of perilipin 1, the most abundant of the adipocyte proteins, in energy and glucose metabolism. During a decade of study, genetic variation in perilipin 1 has been consistently but not invariably associated with body weight and obesity-related complications. Related phenotypes such as postprandial lipid metabolism and aerobic fitness are also modulated by perilipin 1 genotype, consistent with earlier metabolic studies. Investigations of gene-diet interactions, together with gene expression studies, have yielded increased understanding, but important questions about causal variants and mechanisms remain. The newest work examines perilipin 4, an adipocyte regulator of triglyceride synthesis and packaging. The novel discovery that a perilipin 4 variant creates a binding site for regulation of the perilipin gene (PLIN) by microRNA suggests intriguing new possibilities for additional mechanistic investigations of other perilipin proteins.
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Affiliation(s)
- Caren E Smith
- Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, Massachusetts, USA
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52
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Hashimoto T, Segawa H, Okuno M, Kano H, Hamaguchi HO, Haraguchi T, Hiraoka Y, Hasui S, Yamaguchi T, Hirose F, Osumi T. Active involvement of micro-lipid droplets and lipid-droplet-associated proteins in hormone-stimulated lipolysis in adipocytes. J Cell Sci 2012; 125:6127-36. [PMID: 23108672 DOI: 10.1242/jcs.113084] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The regulation of lipolysis in adipocytes involves coordinated actions of many lipid droplet (LD)-associated proteins such as perilipin, hormone sensitive lipase (HSL), adipose triglyceride lipase (ATGL), and its activator protein, CGI-58. Here, we describe the cellular origin and physiological significance of micro LDs (mLDs) that emerge in the cytoplasm during active lipolysis, as well as the roles of key lipolytic proteins on mLDs in differentiated 3T3-L1 adipocytes. Multiplex coherent anti-Stokes Raman scattering (CARS) microscopy demonstrated that mLDs receive the fatty acid (FA) moiety of triglyceride from pre-existing LDs during lipolysis. However, when FA re-esterification was blocked, mLDs did not emerge. Time-lapse imaging of GFP-tagged LD-associated proteins and immunocytochemical analyses showed that particulate structures carrying LD-associated proteins emerged throughout the cells upon lipolytic stimulation, but not when FA re-esterification was blocked. Overall lipolysis, as estimated by glycerol release, was significantly lowered by blocking re-esterification, whereas release of free FAs was enhanced. ATGL was co-immunoprecipitated with CGI-58 from the homogenates of lipolytically stimulated cells. Following CGI-58 knockdown or ATGL inhibition with bromoenol lactone, release of both glycerol and FA was significantly lowered. AICAR, an activator of AMP-activated protein kinase, significantly increased FA release, in accordance with increased expression of ATGL, even in the absence of CGI-58. These results suggest that, besides on the surface of pre-existing central LDs, LD-associated proteins are actively involved in lipolysis on mLDs that are formed by FA re-esterification. Regulation of mLDs and LD-associated proteins may be an attractive therapeutic target against lipid-associated metabolic diseases.
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Affiliation(s)
- Takeshi Hashimoto
- Faculty of Sport and Health Science, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan.
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53
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Ogasawara J, Sakurai T, Kizaki T, Ishibashi Y, Izawa T, Sumitani Y, Ishida H, Radak Z, Haga S, Ohno H. Higher levels of ATGL are associated with exercise-induced enhancement of lipolysis in rat epididymal adipocytes. PLoS One 2012; 7:e40876. [PMID: 22815850 PMCID: PMC3397928 DOI: 10.1371/journal.pone.0040876] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Accepted: 06/18/2012] [Indexed: 01/18/2023] Open
Abstract
BACKGROUND In adipose cells, adipose triglyceride lipase (ATGL) catalyzes the first step in adipocyte triacylglyceride hydrolysis, thereby regulating both basal and hormone-stimulated lipolysis. However, little is known about the molecular mechanism(s) underlying habitual exercise-induced adaptive modulation of ATGL in white adipocytes via alteration in transcription regulator and lipolytic cofactors. METHODOLOGY/PRINCIPAL RESULTS Male Wistar rats were randomly divided into 2 groups a sedentary control group (CG) and a habitual exercise group (EG). The EG was subjected to running on a treadmill set at 5 days per week for 9 weeks. The CG was not subjected to running on a treadmill. In the EG, levels of ATGL mRNA and protein were elevated with a significant increase in lipolysis compared with the CG, accompanied by a significant increase in associations of CGI-58 with ATGL protein. Under these conditions, an upregulation of peroxisome proliferation-activated receptorg-2 (PPARg-2) was observed. In the EG, the addition of rosiglitazone further significantly increased the levels of ATGL protein compared with the CG. However, attenuated levels of the ATGL protein in adipocytes were obtained by the addition of insulin, which is known to inhibit the expression of ATGL, in both types of groups. Actually, levels of plasma insulin were significantly reduced in the EG compared with the CG. CONCLUSIONS These data suggest that elevated levels of ATGL are involved in the exercise-induced enhancement of lipolysis in primary adipocytes. The exact mechanism(s) underlying this phenomenon is associated, at least in part, with upregulated transcriptional activation of PPARg-2. In addition, exercise-induced lower circulation levels of insulin also correlate with habitual exercise-induced higher levels of ATGL in primary adipocytes.
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Affiliation(s)
- Junetsu Ogasawara
- Department of Molecular Predictive Medicine and Sport Science, Kyorin University, School of Medicine, Tokyo, Japan.
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54
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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: 170] [Impact Index Per Article: 14.2] [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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55
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Bartholomew SR, Bell EH, Summerfield T, Newman LC, Miller EL, Patterson B, Niday ZP, Ackerman WE, Tansey JT. Distinct cellular pools of perilipin 5 point to roles in lipid trafficking. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1821:268-78. [PMID: 22063271 PMCID: PMC3740563 DOI: 10.1016/j.bbalip.2011.10.017] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2010] [Revised: 10/11/2011] [Accepted: 10/17/2011] [Indexed: 11/16/2022]
Abstract
The PAT family of lipid storage droplet proteins comprised five members, each of which has become an established regulator of cellular neutral lipid metabolism. Perilipin 5 (also known as lsdp-5, MLDP, PAT-1, and OXPAT), the most recently discovered member of the family, has been shown to localize to two distinct intracellular pools: the lipid storage droplet (LD), and a poorly characterized cytosolic fraction. We have characterized the denser of these intracellular pools and find that a population of perilipin 5 not associated with large LDs resides in complexes with a discrete density (~1.15 g/ml) and size (~575 kDa). Using immunofluorescence, western blotting of isolated sucrose density fractions, native gradient gel electrophoresis, and co-immunoprecipitation, we have shown that these small (~15 nm), perilipin 5-encoated structures do not contain the PAT protein perilipin 2 (ADRP), but do contain perilipin 3 and several other as of yet uncharacterized proteins. The size and density of these particles as well as their susceptibility to degradation by lipases suggest that like larger LDs, they have a neutral lipid rich core. When treated with oleic acid to promote neutral lipid deposition, cells ectopically expressing perilipin 5 experienced a reorganization of LDs in the cell, resulting in fewer, larger droplets at the expense of smaller ones. Collectively, these data demonstrate that a portion of cytosolic perilipin 5 resides in high density lipid droplet complexes that participate in cellular neutral lipid accumulation.
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Affiliation(s)
- Sadie R Bartholomew
- Department of Chemistry and Biochemistry, Otterbein University, Westerville, OH 43081, USA
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56
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Kühnlein RP. The contribution of the Drosophila model to lipid droplet research. Prog Lipid Res 2011; 50:348-56. [DOI: 10.1016/j.plipres.2011.04.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 04/20/2011] [Accepted: 04/28/2011] [Indexed: 12/18/2022]
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57
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Abstract
A wealth of information related to lipid metabolism and signaling has been revealed in recent years using mass spectrometric-based lipidomics methods. Although quantitatively sensitive, these compositional profiling methods rely on conventional tissue extractions of total lipids which results in a loss of original cellular context of lipid metabolites. We described the development of direct organelle mass spectrometry (DOMS), a high resolution MS profiling method providing the capability to directly visualize, extract, and analyze the lipid compositions in single, individual lipid droplets (LDs) from plant tissues. DOMS of lipid droplets isolated from mature cotton embryos demonstrated a surprising lipid droplet-to-droplet variability in triacylglycerol (TAG) composition that would have been concealed through conventional profiling methods and might be important for the understanding of LD biogenesis in oilseeds. Additional applications directed toward the identification of lipid and protein compositions of other organelles could have a significant impact on our general understanding of metabolism and suggest new ideas about how cells coordinate the functions of their subcellular compartments.
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Affiliation(s)
- Patrick J Horn
- University of North Texas, Center for Plant Lipid Research, Department of Biological Sciences, Denton, TX, USA
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58
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Mottillo EP, Granneman JG. Intracellular fatty acids suppress β-adrenergic induction of PKA-targeted gene expression in white adipocytes. Am J Physiol Endocrinol Metab 2011; 301:E122-31. [PMID: 21505145 PMCID: PMC3129835 DOI: 10.1152/ajpendo.00039.2011] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
β-Adrenergic receptor (β-AR) activation elevates cAMP levels in fat cells and triggers both metabolic and transcriptional responses; however, the potential interactions between these pathways are poorly understood. This study investigated whether lipolysis affects β-AR-mediated gene expression in adipocytes. Acute β(3)-adrenergic receptor (β(3)-AR) stimulation with CL 316,243 (CL) increased expression of PKA-targeted genes PCG-1α, UCP1, and NOR-1 in mouse white fat. Limiting lipolysis via inhibition of hormone-sensitive lipase (HSL), a direct target of PKA, sharply potentiated CL induction of PCG-1α, UCP1, and NOR-1. CL also induced greater expression of PKA-targeted genes in white fat of HSL-null mice compared with wild-type littermates, further indicating that HSL activity limits PKA-mediated gene expression. Inhibiting HSL in 3T3-L1 adipocytes also potentiated the induction of PGC-1α, UCP1, and NOR-1 by β-AR activation, as did siRNA knockdown of adipose triglyceride lipase, the rate-limiting enzyme for lipolysis. Conversely, treatments that promote intracellular fatty acid accumulation suppressed induction of PGC-1α and UCP1 through β-AR stimulation. Analysis of β-adrenergic signaling indicated that excessive intracellular fatty acid production inhibits adenylyl cyclase activity and thereby reduces PKA signaling to the nucleus. Lastly, partially limiting lipolysis by inhibition of HSL increased the induction of oxidative gene expression and mitochondrial electron transport chain activity in white adipose tissue and facilitated fat loss in mice treated for 5 days with CL. Overall, our results demonstrate that fatty acids limit the upregulation of β-AR-responsive genes in white adipocytes and suggest that limiting lipolysis may be a novel means of enhancing β-AR signaling.
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MESH Headings
- 3T3-L1 Cells
- Adipocytes, White/drug effects
- Adipocytes, White/metabolism
- Animals
- Coenzyme A Ligases/antagonists & inhibitors
- Cyclic AMP-Dependent Protein Kinases/physiology
- Down-Regulation/drug effects
- Enzyme Inhibitors/pharmacology
- Fatty Acids/metabolism
- Fatty Acids/pharmacology
- Female
- Gene Expression/drug effects
- Intracellular Space/metabolism
- Lipolysis/drug effects
- Lipolysis/genetics
- Male
- Mice
- Mice, Inbred C57BL
- Receptors, Adrenergic, beta/genetics
- Receptors, Adrenergic, beta/metabolism
- Receptors, Adrenergic, beta-3/genetics
- Receptors, Adrenergic, beta-3/metabolism
- Triazenes/pharmacology
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Affiliation(s)
- Emilio P Mottillo
- Center for Integrative Metabolic and Endocrine Research, Department of Pathology and Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
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59
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Oberer M, Boeszoermenyi A, Nagy HM, Zechner R. Recent insights into the structure and function of comparative gene identification-58. Curr Opin Lipidol 2011; 22:149-58. [PMID: 21494142 PMCID: PMC5808844 DOI: 10.1097/mol.0b013e328346230e] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
PURPOSE OF REVIEW Comparative gene identification-58 (CGI-58) is an important player in lipid metabolism. It acts as activator of triglyceride hydrolases and as acyl-CoA-dependent lysophosphatidic acid acyltransferase. This review aims at establishing a structure-function relationship of this still rather enigmatic protein based on recent studies characterizing different functions of CGI-58. RECENT FINDINGS Novel studies confirm the important regulatory role of CGI-58 as activator of the triglyceride hydrolase adipose triglyceride lipase. New evidence, corroborated by the characterization of a CGI-58 knockout mouse model, also suggests the existence of yet unknown lipases that are activated by CGI-58. Additionally, CGI-58 was identified to exert acyl-CoA-dependent lysophosphatidic acid acyltransferase activity, which implies possible roles in triglyceride or phospholipid synthesis or signaling processes. Unlike mammalian CGI-58 proteins, orthologs from plants and yeast additionally act as weak triglyceride and phospholipid hydrolases. A first three-dimensional model was calculated and allows preliminary structural considerations for the functions of CGI-58. SUMMARY Despite important progress concerning the different biochemical functions of CGI-58, the physiological importance of these activities requires better characterization. Furthermore, three-dimensional structural data for CGI-58 are required to unveil the molecular mechanism of how CGI-58 acts as activator of lipases and exerts its enzymatic functions.
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Affiliation(s)
- Monika Oberer
- Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50/3, 8010 Graz, Austria
| | - Andras Boeszoermenyi
- Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50/3, 8010 Graz, Austria
| | - Harald Manuel Nagy
- Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50/3, 8010 Graz, Austria
| | - Rudolf Zechner
- Institute of Molecular Biosciences, University of Graz, Heinrichstrasse 31, 8010 Graz, Austria
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60
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Adeyo O, Horn PJ, Lee S, Binns DD, Chandrahas A, Chapman KD, Goodman JM. The yeast lipin orthologue Pah1p is important for biogenesis of lipid droplets. ACTA ACUST UNITED AC 2011; 192:1043-55. [PMID: 21422231 PMCID: PMC3063132 DOI: 10.1083/jcb.201010111] [Citation(s) in RCA: 223] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Pah1p promotes lipid droplet assembly independent of its role in triacylglycerol synthesis. Lipins are phosphatidate phosphatases that generate diacylglycerol (DAG). In this study, we report that yeast lipin, Pah1p, controls the formation of cytosolic lipid droplets. Disruption of PAH1 resulted in a 63% decrease in droplet number, although total neutral lipid levels did not change. This was accompanied by an accumulation of neutral lipids in the endoplasmic reticulum (ER). The droplet biogenesis defect was not a result of alterations in neutral lipid ratios. No droplets were visible in the absence of both PAH1 and steryl acyltransferases when grown in glucose medium, even though the strain produces as much triacylglycerol as wild type. The requirement of PAH1 for normal droplet formation can be bypassed by a knockout of DGK1. Nem1p, the activator of Pah1p, localizes to a single punctum per cell on the ER that is usually next to a droplet, suggesting that it is a site of droplet assembly. Overall, this study provides strong evidence that DAG generated by Pah1p is important for droplet biogenesis.
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Affiliation(s)
- Oludotun Adeyo
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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61
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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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62
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Ho PC, Chuang YS, Hung CH, Wei LN. Cytoplasmic receptor-interacting protein 140 (RIP140) interacts with perilipin to regulate lipolysis. Cell Signal 2011; 23:1396-403. [PMID: 21504789 DOI: 10.1016/j.cellsig.2011.03.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 03/28/2011] [Accepted: 03/28/2011] [Indexed: 01/14/2023]
Abstract
Receptor-interacting protein 140 (RIP140) is abundantly expressed in mature adipocyte and modulates gene expression involved in lipid and glucose metabolism. Protein kinase C epsilon and protein arginine methyltransferase 1 can sequentially stimulate RIP140 phosphorylation and then methylation, thereby promoting its export to the cytoplasm. Here we report a lipid signal triggering cytoplasmic accumulation of RIP140, and a new functional role for cytoplasmic RIP140 in adipocyte to regulate lipolysis. Increased lipid content, particularly an elevation in diacylglycerol levels, promotes RIP140 cytoplasmic accumulation and increased association with lipid droplets (LDs) by its direct interaction with perilipin. By interacting with RIP140, perilipin more efficiently recruits hormone-sensitive lipase (HSL) to LDs and enhances adipose triglyceride lipase (ATGL) forming complex with CGI-58, an activator of ATGL. Consequentially, HSL can more readily access its substrates, and ATGL is activated, ultimately enhancing lipolysis. In adipocytes, blocking cytoplasmic RIP140 accumulation reduces basal and isoproterenol-stimulated lipolysis and the pro-inflammatory potential of their conditioned media (i.e. activating NF-κB and inflammatory genes in macrophages). These results show that in adipocytes with high lipid contents, RIP140 increasingly accumulates in the cytoplasm and enhances triglyceride catabolism by directly interacting with perilipin. The study suggests that reducing nuclear export of RIP140 might be a useful means of controlling adipocyte lipolysis.
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Affiliation(s)
- Ping-Chih Ho
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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63
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Lafontan M. Rein, tissu adipeux, adipocytes – quelles nouveautés ? Nephrol Ther 2011; 7:69-79. [DOI: 10.1016/j.nephro.2010.11.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2010] [Revised: 11/07/2010] [Accepted: 11/07/2010] [Indexed: 12/21/2022]
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64
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Horn PJ, Ledbetter NR, James CN, Hoffman WD, Case CR, Verbeck GF, Chapman KD. Visualization of lipid droplet composition by direct organelle mass spectrometry. J Biol Chem 2010; 286:3298-306. [PMID: 21118810 DOI: 10.1074/jbc.m110.186353] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
An expanding appreciation for the varied functions of neutral lipids in cellular organisms relies on a more detailed understanding of the mechanisms of lipid production and packaging into cytosolic lipid droplets (LDs). Conventional lipid profiling procedures involve the analysis of tissue extracts and consequently lack cellular or subcellular resolution. Here, we report an approach that combines the visualization of individual LDs, microphase extraction of lipid components from droplets, and the direct identification of lipid composition by nanospray mass spectrometry, even to the level of a single LD. The triacylglycerol (TAG) composition of LDs from several plant sources (mature cotton (Gossypium hirsutum) embryos, roots of cotton seedlings, and Arabidopsis thaliana seeds and leaves) were examined by direct organelle mass spectrometry and revealed the heterogeneity of LDs derived from different plant tissue sources. The analysis of individual LDs makes possible organellar resolution of molecular compositions and will facilitate new studies of LD biogenesis and functions, especially in combination with analysis of morphological and metabolic mutants. Furthermore, direct organelle mass spectrometry could be applied to the molecular analysis of other subcellular compartments and macromolecules.
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Affiliation(s)
- Patrick J Horn
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203, USA
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65
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Grisouard J, Bouillet E, Timper K, Radimerski T, Dembinski K, Frey DM, Peterli R, Zulewski H, Keller U, Müller B, Christ-Crain M. Both inflammatory and classical lipolytic pathways are involved in lipopolysaccharide-induced lipolysis in human adipocytes. Innate Immun 2010; 18:25-34. [DOI: 10.1177/1753425910386632] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
High fat diet-induced endotoxaemia triggers low-grade inflammation and lipid release from adipose tissue. This study aims to unravel the cellular mechanisms leading to the lipopolysaccharide (LPS) effects in human adipocytes. Subcutaneous pre-adipocytes surgically isolated from patients were differentiated into mature adipocytes in vitro. Lipolysis was assessed by measurement of glycerol release and mRNA expression of pro-inflammatory cytokines were evaluated by real-time PCR. Treatment with LPS for 24 h induced a dose-dependent increase in interleukin (IL)-6 and IL-8 mRNA expression. At 1 µg/ml LPS, IL-6 and IL-8 were induced to 19.5 ± 1.8-fold and 662.7 ± 91.5-fold ( P < 0.01 vs basal), respectively. From 100 ng/ml to 1 µg/ml, LPS-induced lipolysis increased to a plateau of 3.1-fold above basal level ( P < 0.001 vs basal). Co-treatment with inhibitors of inhibitory kappa B kinase kinase beta (IKKβ) or NF-κB inhibited LPS-induced glycerol release. Co-treatment with the protein kinase A (PKA) inhibitor H-89, the lipase inhibitor orlistat or the hormone-sensitive lipase (HSL) inhibitor CAY10499 abolished the lipolytic effects of LPS. Co-treatment with the MAPK inhibitor, U0126 also reduced LPS-induced glycerol release. Inhibition of lipolysis by orlistat or CAY10499 reduced LPS-induced IL-6 and IL-8 mRNA expression. Induction of lipolysis by the synthetic catecholamine isoproterenol or the phosphodiesterase type III inhibitor milrinone did not alter basal IL-6 and IL-8 mRNA expression after 24 treatments whereas these compounds enhanced LPS-induced IL-6 and IL-8 mRNA expression. Both the inflammatory IKKβ/NF-κB pathway and the lipolytic PKA/HSL pathways mediate LPS-induced lipolysis. In turn, LPS-induced lipolysis reinforces the expression of pro-inflammatory cytokines and, thereby, triggers its own lipolytic activity.
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Affiliation(s)
- Jean Grisouard
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
| | - Elisa Bouillet
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
| | - Katharina Timper
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
- Division of Endocrinology, Diabetes and Clinical Nutrition, University Hospital Basel, Basel, Switzerland
| | - Tanja Radimerski
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
| | - Kaethi Dembinski
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
| | - Daniel M Frey
- Department of Surgery, University Hospital Basel, Basel, Switzerland
| | - Ralph Peterli
- Department of Surgery, St Claraspital Basel, Basel, Switzerland
| | - Henryk Zulewski
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
- Division of Endocrinology, Diabetes and Clinical Nutrition, University Hospital Basel, Basel, Switzerland
| | - Ulrich Keller
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
- Division of Endocrinology, Diabetes and Clinical Nutrition, University Hospital Basel, Basel, Switzerland
| | - Beat Müller
- Department of Internal Medicine, Kantonsspital Aarau, Aarau, Switzerland
| | - Mirjam Christ-Crain
- Department of Biomedicine, Metabolism Group, University Hospital Basel, Basel, Switzerland
- Division of Endocrinology, Diabetes and Clinical Nutrition, University Hospital Basel, Basel, Switzerland
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Disruption of the Arabidopsis CGI-58 homologue produces Chanarin-Dorfman-like lipid droplet accumulation in plants. Proc Natl Acad Sci U S A 2010; 107:17833-8. [PMID: 20876112 DOI: 10.1073/pnas.0911359107] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
CGI-58 is the defective gene in the human neutral lipid storage disease called Chanarin-Dorfman syndrome. This disorder causes intracellular lipid droplets to accumulate in nonadipose tissues, such as skin and blood cells. Here, disruption of the homologous CGI-58 gene in Arabidopsis thaliana resulted in the accumulation of neutral lipid droplets in mature leaves. Mass spectroscopy of isolated lipid droplets from cgi-58 loss-of-function mutants showed they contain triacylglycerols with common leaf-specific fatty acids. Leaves of mature cgi-58 plants exhibited a marked increase in absolute triacylglycerol levels, more than 10-fold higher than in wild-type plants. Lipid levels in the oil-storing seeds of cgi-58 loss-of-function plants were unchanged, and unlike mutations in β-oxidation, the cgi-58 seeds germinated and grew normally, requiring no rescue with sucrose. We conclude that the participation of CGI-58 in neutral lipid homeostasis of nonfat-storing tissues is similar, although not identical, between plant and animal species. This unique insight may have implications for designing a new generation of technologies that enhance the neutral lipid content and composition of crop plants.
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67
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Granneman JG, Kimler VA, Moore HPH. Cell Biology Symposium: imaging the organization and trafficking of lipolytic effectors in adipocytes. J Anim Sci 2010; 89:701-10. [PMID: 20852075 DOI: 10.2527/jas.2010-3370] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The storage and mobilization of lipid energy are central functions of adipocytes. Lipid energy is stored as triglyceride in lipid droplet structures that are now recognized as bona fide organelles and whose functions are greatly influenced by members of the perilipin family of lipid droplet scaffolds. Recent work indicates that the signaling events underlying fatty acid mobilization involve protein trafficking to a specialized subset of lipid droplets. Furthermore, the core lipolytic machinery is composed of evolutionarily conserved proteins whose functions are conserved in avian and mammalian production species. Lipolysis affects many aspects of animal nutrition and physiology, which can have an important influence on growth efficiency, lactation, and meat quality. This review focuses on recent research that addresses the organization and trafficking of key players in hormone-stimulated lipolysis, and the central role of perilipin1A in adipocyte lipolysis. The review emphasizes recent work from the laboratories of the authors that utilizes imaging techniques to explore the organization and interactions among lipolytic effectors in live cells during lipolytic activation. A mechanistic understanding of lipolysis may lead to new strategies for promoting human and animal health.
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Affiliation(s)
- J G Granneman
- Center for Integrative Metabolic and Endocrine Research, Wayne State University School of Medicine, Detroit, MI 48201, USA.
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68
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Neuschwander-Tetri BA. Nontriglyceride hepatic lipotoxicity: the new paradigm for the pathogenesis of NASH. Curr Gastroenterol Rep 2010; 12:49-56. [PMID: 20425484 DOI: 10.1007/s11894-009-0083-6] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Lipid droplet accumulation and oxidant stress, once thought to play essential roles in the pathogenesis of nonalcoholic steatohepatitis (NASH), may actually represent parallel epiphenomena. Emerging data now point to nontriglyceride lipotoxicity and complex mechanisms of hepatocyte injury and apoptosis as the major contributors to the disease phenotype currently recognized as NASH. Although specific mediators of hepatic lipotoxicity have not been identified with certainty, abundant evidence from animal studies and recent data in humans indicate that free fatty acids in the liver can serve as substrates for formation of nontriglyceride lipotoxic metabolites that cause liver injury. The accumulation of triglyceride in droplets may actually be protective, and thus therapeutic efforts directed at fat accumulation as a sole endpoint may be misguided. This review examines the new evidence supporting the role of nontriglyceride fatty acid metabolites in causing NASH and how adipose and muscle insulin resistance contribute to hepatic lipotoxicity.
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Affiliation(s)
- Brent A Neuschwander-Tetri
- Division of Gastroenterology and Hepatology, Saint Louis University School of Medicine, St. Louis, MO 63110, USA.
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69
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Neuschwander-Tetri BA. Hepatic lipotoxicity and the pathogenesis of nonalcoholic steatohepatitis: the central role of nontriglyceride fatty acid metabolites. Hepatology 2010; 52:774-88. [PMID: 20683968 DOI: 10.1002/hep.23719] [Citation(s) in RCA: 779] [Impact Index Per Article: 55.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
A significant body of evidence now forces us to rethink the causes of NASH. Once thought to be a disease caused by triglyceride accumulation in hepatocytes with subsequent oxidant stress and lipid peroxidation causing inflammation and fibrosis, new data from animal studies and a limited number of human studies now provide convincing evidence that triglyceride accumulation does not cause insulin resistance or cellular injury in the liver. The lipotoxic liver injury hypothesis for the pathogenesis of NASH suggests that we need to focus our therapeutic efforts on reducing the burden of fatty acids going to the liver or being synthesized in the liver. This can be accomplished by improving insulin sensitivity at the level of adipose tissue to prevent inappropriate peripheral lipolysis and by preventing unnecessary de novo lipogenesis in the liver. Excess carbohydrates are the major substrates for de novo lipogenesis, and thus, reducing carbohydrate consumption through dietary changes and increasing muscle glucose uptake through exercise remain important cornerstones of treatment and prevention of lipotoxic liver injury, a disease hitherto called NASH.
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70
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Krintel C, Klint C, Lindvall H, Mörgelin M, Holm C. Quarternary structure and enzymological properties of the different hormone-sensitive lipase (HSL) isoforms. PLoS One 2010; 5:e11193. [PMID: 20567594 PMCID: PMC2887374 DOI: 10.1371/journal.pone.0011193] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2010] [Accepted: 05/26/2010] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Hormone-sensitive lipase (HSL) is a key enzyme in the mobilization of energy in the form of fatty acids from intracellular stores of neutral lipids. The enzyme has been shown to exist in different isoforms with different molecular masses (84 kDa, 89 kDa and 117 kDa) expressed in a tissue-dependent manner, where the predominant 84 kDa form in adipocytes is the most extensively studied. METHODOLOGY/PRINCIPAL FINDINGS In this study we employed negative stain electron microscopy (EM) to analyze the quarternary structure of the different HSL isoforms. The results show that all three isoforms adopt a head-to-head homodimeric organization, where each monomer contains two structural domains. We also used enzymatic assays to show that despite the variation in the size of the N-terminal domain all three isoforms exhibit similar enzymological properties with regard to psychrotolerance and protein kinase A (PKA)-mediated phosphorylation and activation. CONCLUSIONS/SIGNIFICANCE We present the first data on the quaternary structure and domain organization of the three HSL isoforms. We conclude that despite large differences in the size of the N-terminal, non-catalytic domain all three HSL isoforms exhibit the same three-dimensional architecture. Furthermore, the three HSL isoforms are very similar with regard to two unique enzymological characteristics of HSL, i.e., cold adaptation and PKA-mediated activation.
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Affiliation(s)
- Christian Krintel
- Department of Experimental Medical Science, Lund University, Lund, Sweden
- Division of Diabetes, Metabolism and Endocrinology, Department of Molecular Biophysics, Lund University, Lund, Sweden
| | - Cecilia Klint
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Håkan Lindvall
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Matthias Mörgelin
- Division of Infection Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden
| | - Cecilia Holm
- Department of Experimental Medical Science, Lund University, Lund, Sweden
- * E-mail:
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71
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Ahmed K, Tunaru S, Tang C, Müller M, Gille A, Sassmann A, Hanson J, Offermanns S. An autocrine lactate loop mediates insulin-dependent inhibition of lipolysis through GPR81. Cell Metab 2010; 11:311-9. [PMID: 20374963 DOI: 10.1016/j.cmet.2010.02.012] [Citation(s) in RCA: 268] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2009] [Revised: 12/29/2009] [Accepted: 02/17/2010] [Indexed: 02/07/2023]
Abstract
Lactate is an important metabolic intermediate released by skeletal muscle and other organs including the adipose tissue, which converts glucose into lactate under the influence of insulin. Here we show that lactate activates the G protein-coupled receptor GPR81, which is expressed in adipocytes and mediates antilipolytic effects through G(i)-dependent inhibition of adenylyl cyclase. Using GPR81-deficient mice, we demonstrate that the receptor is not involved in the regulation of lipolysis during intensive exercise. However, insulin-induced inhibition of lipolysis and insulin-induced decrease in adipocyte cAMP levels were strongly reduced in mice lacking GPR81, although insulin-dependent release of lactate by adipocytes was comparable between wild-type and GPR81-deficient mice. Thus, lactate and its receptor GPR81 unexpectedly function in an autocrine and paracrine loop to mediate insulin-induced antilipolytic effects. These data show that lactate can directly modulate metabolic processes in a hormone-like manner, and they reveal a new mechanism underlying the antilipolytic effects of insulin.
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Affiliation(s)
- Kashan Ahmed
- Department of Pharmacology, Max-Planck-Institute for Heart and Lung Research, Ludwigstrasse 43, 61231 Bad Nauheim, Germany
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72
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Koh YJ, Park BH, Park JH, Han J, Lee IK, Park JW, Koh GY. Activation of PPAR gamma induces profound multilocularization of adipocytes in adult mouse white adipose tissues. Exp Mol Med 2010; 41:880-95. [PMID: 19745605 DOI: 10.3858/emm.2009.41.12.094] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We sought to determine the effects of activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) on multilocularization of adipocytes in adult white adipose tissue (WAT). Male C57BL/6 normal, db/db, and ob/ob mice were treated with agonists of PPAR-gamma, PPAR-alpha, or beta(3)-adrenoceptor for 3 weeks. To distinguish multilocular adipocytes from unilocular adipocytes, whole- mounted adipose tissues were co-immunostained for perilipin and collagen IV. PPAR-gamma activation with rosiglitazone or pioglitazone induced a profound change of unilocular adipocytes into smaller, multilocular adipocytes in adult WAT in a time-dependent, dose-dependent, and reversible manner. PPAR-alpha activation with fenofibrate did not affect the number of locules or remodeling. db/db and ob/ob obese mice exhibited less multilocularization in response to PPAR-gamma activation compared to normal mice. Nevertheless, all adipocytes activated by PPAR-gamma contained a single nucleus regardless of locule number. Multilocular adipocytes induced by PPAR-gamma activation contained substantially increased mitochondrial content and enhanced expression of uncoupling protein-1, PPAR-gamma coactivator-1-alpha, and perilipin. Taken together, PPAR-gamma activation induces profound multilocularization and enhanced mitochondrial biogenesis in the adipocytes of adult WAT. These changes may affect the overall function of WAT.
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Affiliation(s)
- Young Jun Koh
- National Research Laboratory of Vascular Biology and Graduate School of Medical Science and Engineering, Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea
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73
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He H, Yang D, Ma L, Luo Z, Ma S, Feng X, Cao T, Yan Z, Liu D, Tepel M, Zhu Z. Telmisartan prevents weight gain and obesity through activation of peroxisome proliferator-activated receptor-delta-dependent pathways. Hypertension 2010; 55:869-79. [PMID: 20176998 DOI: 10.1161/hypertensionaha.109.143958] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Telmisartan shows antihypertensive and several pleiotropic effects that interact with metabolic pathways. In the present study we tested the hypothesis that telmisartan prevents adipogenesis in vitro and weight gain in vivo through activation of peroxisome proliferator-activated receptor (PPAR)-delta-dependent pathways in several tissues. In vitro, telmisartan significantly upregulated PPAR-delta expression in 3T3-L1 preadipocytes in a time- and dose-dependent manner. Other than enhancing PPAR-delta expression by 68.2+/-17.3% and PPAR-delta activity by 102.0+/-9.0%, telmisartan also upregulated PPAR-gamma expression, whereas neither candesartan nor losartan affected PPAR-delta expression. In vivo, long-term administration of telmisartan significantly reduced visceral fat and prevented high-fat diet-induced obesity in wild-type mice and hypertensive rats but not in PPAR-delta knockout mice. Administration of telmisartan did not influence food intake in mice. Telmisartan influenced several lipolytic and energy uncoupling related proteins (UCPs) and enhanced phosphorylated protein kinase A and hormone sensitive lipase but reduced perilipin expression and finally inhibited adipogenesis in 3T3-L1 preadipocytes. Telmisartan-associated reduction of adipogenesis in preadipocytes was significantly blocked after PPAR-delta gene knockout. Chronic telmisartan treatment upregulated the expressions of protein kinase A, hormone-sensitive lipase, and uncoupling protein 1 but reduced perilipin expression in adipose tissue and increased uncoupling protein 2 and 3 expression in skeletal muscle in wild-type mice but not in PPAR-delta knockout mice. We conclude that telmisartan prevents adipogenesis and weight gain through activation of PPAR-delta-dependent lipolytic pathways and energy uncoupling in several tissues.
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Affiliation(s)
- Hongbo He
- Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing 400042, People's Republic of China
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74
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Gruber A, Cornaciu I, Lass A, Schweiger M, Poeschl M, Eder C, Kumari M, Schoiswohl G, Wolinski H, Kohlwein SD, Zechner R, Zimmermann R, Oberer M. The N-terminal region of comparative gene identification-58 (CGI-58) is important for lipid droplet binding and activation of adipose triglyceride lipase. J Biol Chem 2010; 285:12289-98. [PMID: 20164531 DOI: 10.1074/jbc.m109.064469] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In mammals, excess energy is stored in the form of triacylglycerol primarily in lipid droplets of white adipose tissue. The first step of lipolysis (i.e. the mobilization of fat stores) is catalyzed by adipose triglyceride lipase (ATGL). The enzymatic activity of ATGL is strongly enhanced by CGI-58 (comparative gene identification-58), and the loss of either ATGL or CGI-58 function causes systemic triglyceride accumulation in humans and mice. However, the mechanism by which CGI-58 stimulates ATGL activity is unknown. To gain insight into CGI-58 function using structural features of the protein, we generated a three-dimensional homology model based on sequence similarity with other proteins. Interestingly, the model of CGI-58 revealed that the N terminus forms an extension of the otherwise compact structure of the protein. This N-terminal region (amino acids 1-30) harbors a lipophilic tryptophan-rich stretch, which affects the localization of the protein. (1)H NMR experiments revealed strong interaction between the N-terminal peptide and dodecylphosphocholine micelles as a lipid droplet-mimicking system. A role for this N-terminal region of CGI-58 in lipid droplet binding was further strengthened by localization studies in cultured cells. Although wild-type CGI-58 localizes to the lipid droplet, the N-terminally truncated fragments of CGI-58 are dispersed in the cytoplasm. Moreover, CGI-58 lacking the N-terminal extension loses the ability to stimulate ATGL, implying that the ability of CGI-58 to activate ATGL is linked to correct localization. In summary, our study shows that the N-terminal, Trp-rich region of CGI-58 is essential for correct localization and ATGL-activating function of CGI-58.
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Affiliation(s)
- Astrid Gruber
- Institute of Molecular Biosciences, University of Graz, Humboldtstrasse, A-8010 Graz, Austria
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75
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Hodges BDM, Wu CC. Proteomic insights into an expanded cellular role for cytoplasmic lipid droplets. J Lipid Res 2010; 51:262-73. [PMID: 19965608 PMCID: PMC2803228 DOI: 10.1194/jlr.r003582] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 11/02/2009] [Indexed: 12/11/2022] Open
Abstract
Cytoplasmic lipid droplets (CLDs) are cellular structures composed of a neutral lipid core surrounded by a phospholipid monolayer of amphipathic lipids and a variety of proteins. CLDs have classically been regarded as cellular energy storage structures. However, recent proteomic studies reveal that, although many of the proteins found to associate with CLDs are connected to lipid metabolism, storage, and homeostasis, there are also proteins with no obvious connection to the classical function and typically associated with other cellular compartments. Such proteins are termed refugee proteins, and their presence suggests that CLDs may serve an expanded role as a dynamic protein storage site, providing a novel mechanism for the regulation of protein function and transport.
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Affiliation(s)
| | - Christine C. Wu
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO
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76
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Liu Y, Zhou D, Abumrad NA, Su X. ADP-ribosylation factor 6 modulates adrenergic stimulated lipolysis in adipocytes. Am J Physiol Cell Physiol 2010; 298:C921-8. [PMID: 20107045 DOI: 10.1152/ajpcell.00541.2009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
ADP-ribosylation factor 6 (Arf6) is a small GTPase that influences membrane receptor trafficking and the actin cytoskeleton. In adipocytes, Arf6 regulates the trafficking of the glucose transporter type 4 (GLUT4) and consequently insulin-stimulated glucose transport. Previous studies also indicated a role of Arf6 in adrenergic receptor trafficking, but whether this contributes to the control of lipolysis in adipocytes remains unknown. This was examined in the present study by using RNA interference (RNAi) and pharmaceutical inhibition in murine cultured 3T3-L1 adipocytes. Downregulation of Arf6 by RNAi impairs isoproterenol-stimulated lipolysis specifically but does not alter triacylglycerol (TAG) synthesis or the insulin signaling pathway. Neither total TAG amounts nor TAG fatty acid compositions are altered. The inhibitory effect on lipolysis is mimicked by dynasore, a specific inhibitor for dynamin, which is required for endocytosis. In contrast, lipolysis triggered by reagents that bypass events at the plasma membrane (e.g., forskolin, isobutylmethylxanthine or 8-bromo-cAMP) is not affected. Moreover, Arf6 protein levels in white adipose tissues are markedly increased in ob/ob mice, whereas they are decreased in obesity-resistant CD36 null mice. These changes reflect at least in part alterations in Arf6 mRNA levels. Collectively, these results suggest a role of the endocytic pathway and its regulation by Arf6 in adrenergic stimulation of lipolysis in adipocytes and potentially in the development of obesity.
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Affiliation(s)
- Yingqiu Liu
- Dept. of Internal Medicine, Center for Human Nutrition, Washington Univ. School of Medicine, 660 S. Euclid, St. Louis, MO 63110, USA
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77
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Nagayama M, Shimizu K, Taira T, Uchida T, Gohara K. Shrinking and development of lipid droplets in adipocytes during catecholamine-induced lipolysis. FEBS Lett 2010; 584:86-92. [PMID: 19896941 DOI: 10.1016/j.febslet.2009.10.088] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2009] [Revised: 09/30/2009] [Accepted: 10/31/2009] [Indexed: 12/29/2022]
Abstract
Time-lapse observation of adipocytes during catecholamine-induced lipolysis clearly shows that shrinking of existing lipid droplets (LDs) occurs in some adipocytes and that small LDs are newly developed in almost all cells. Immunofluorescence imaging reveals that activation and localization of hormone-sensitive lipase (HSL) on the surface of LDs, which are required for conferring maximal lipolysis, are necessary for the shrinking of the LDs. However, not all adipocytes in which phosphorylated HSL is localized on LDs exhibit shrinking of LDs. The simultaneous shrinking and development of LDs yield apparent fragmentation and dispersion of LDs in adipocytes stimulated with catecholamine.
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Affiliation(s)
- Masafumi Nagayama
- Division of Applied Physics, Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo, Japan.
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78
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Liu K, Zhou S, Kim JY, Tillison K, Majors D, Rearick D, Lee JH, Fernandez-Boyanapalli RF, Barricklow K, Houston MS, Smas CM. Functional analysis of FSP27 protein regions for lipid droplet localization, caspase-dependent apoptosis, and dimerization with CIDEA. Am J Physiol Endocrinol Metab 2009; 297:E1395-413. [PMID: 19843876 DOI: 10.1152/ajpendo.00188.2009] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The adipocyte-specific protein FSP27, also known as CIDEC, is one of three cell death-inducing DFF45-like effector (CIDE) proteins. The first known function for CIDEs was promotion of apoptosis upon ectopic expression in mammalian cells. Recent studies in endogenous settings demonstrated key roles for CIDEs in energy metabolism. FSP27 is a lipid droplet-associated protein whose heterologous expression enhances formation of enlarged lipid droplets and is required for unilocular lipid droplets typical of white adipocytes in vivo. Here, we delineate relationships between apoptotic function and lipid droplet localization of FSP27. We demonstrate that ectopic expression of FSP27 induces enlarged lipid droplets in multiple human cell lines, which is indicative that its mechanism involves ubiquitously present, rather than adipocyte-specific, cellular machinery. Furthermore, promotion of lipid droplet formation in HeLa cells via culture in exogenous oleic acid offsets FSP27-mediated apoptosis. Using transient cotransfections and analysis of lipid droplets in HeLa cells stably expressing FSP27, we show that FSP27 does not protect lipid droplets from action of ATGL lipase. Domain mapping with eGFP-FSP27 deletion constructs indicates that lipid droplet localization of FSP27 requires amino acids 174-192 of its CIDE C domain. The apoptotic mechanism of FSP27, which we show involves caspase-9 and mitochondrial cytochrome c, also requires this 19-amino acid region. Interaction assays determine the FSP27 CIDE C domain complexes with CIDEA, and Western blot reveals that FSP27 protein levels are reduced by coexpression of CIDEA. Overall, our findings demonstrate the function of the FSP27 CIDE C domain and/or regions thereof for apoptosis, lipid droplet localization, and CIDEA interaction.
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Affiliation(s)
- Kun Liu
- Department of Biochemistry and Cancer Biology and Center for Diabetes and Endocrine Research, The University of Toledo College of Medicine, Toledo, Ohio 43614, USA
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79
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PKA phosphorylates and inactivates AMPKalpha to promote efficient lipolysis. EMBO J 2009; 29:469-81. [PMID: 19942859 DOI: 10.1038/emboj.2009.339] [Citation(s) in RCA: 209] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 10/26/2009] [Indexed: 12/27/2022] Open
Abstract
The mobilization of metabolic energy from adipocytes depends on a tightly regulated balance between hydrolysis and resynthesis of triacylglycerides (TAGs). Hydrolysis is stimulated by beta-adrenergic signalling to PKA that mediates phosphorylation of lipolytic enzymes, including hormone-sensitive lipase (HSL). TAG resynthesis is associated with high-energy consumption, which when inordinate, leads to increased AMPK activity that acts to restrain hydrolysis of TAGs by inhibiting PKA-mediated activation of HSL. Here, we report that in primary mouse adipocytes, PKA associates with and phosphorylates AMPKalpha1 at Ser-173 to impede threonine (Thr-172) phosphorylation and thus activation of AMPKalpha1 by LKB1 in response to lipolytic signals. Activation of AMPKalpha1 by LKB1 is also blocked by PKA-mediated phosphorylation of AMPKalpha1 in vitro. Functional analysis of an AMPKalpha1 species carrying a non-phosphorylatable mutation at Ser-173 revealed a critical function of this phosphorylation for efficient release of free fatty acids and glycerol in response to PKA-activating signals. These results suggest a new mechanism of negative regulation of AMPK activity by PKA that is important for converting a lipolytic signal into an effective lipolytic response.
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80
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Ahmadian M, Duncan RE, Sul HS. The skinny on fat: lipolysis and fatty acid utilization in adipocytes. Trends Endocrinol Metab 2009; 20:424-8. [PMID: 19796963 PMCID: PMC2764815 DOI: 10.1016/j.tem.2009.06.002] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2009] [Revised: 06/03/2009] [Accepted: 06/03/2009] [Indexed: 01/01/2023]
Abstract
Lipolysis for the provision of fatty acids (FA) for other organs during times of energy demand occurs uniquely in white adipose tissue (WAT). Recent findings have identified a bona fide TAG hydrolase and the major adipose phospholipase A(2), AdPLA. By controlling PGE(2) levels, AdPLA dominantly regulates lipolysis in an autocrine/paracrine manner. Moreover, recent findings demonstrate that, surprisingly, increasing lipolysis in adipose tissue does not necessarily increase serum FA levels, which are usually correlated with insulin resistance. Rather, increasing lipolysis in adipose tissue causes a shift within adipocytes towards increased FA utilization and energy expenditure and thus protects against obesity. Here, we discuss the regulation of lipolysis and its effects on FA utilization within WAT and on insulin resistance.
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Affiliation(s)
- Maryam Ahmadian
- Department of Nutritional Science and Toxicology, University of California, Berkeley, California 9472, USA
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81
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Granneman JG, Moore HPH, Krishnamoorthy R, Rathod M. Perilipin controls lipolysis by regulating the interactions of AB-hydrolase containing 5 (Abhd5) and adipose triglyceride lipase (Atgl). J Biol Chem 2009; 284:34538-44. [PMID: 19850935 DOI: 10.1074/jbc.m109.068478] [Citation(s) in RCA: 276] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mobilization of stored lipid by hormones is a fundamental function of fat cells, and there is strong evidence that perilipin (Plin), a lipid droplet scaffold, and adipose tissue triglyceride lipase (Atgl), a triglyceride-specific lipase, play critical roles. Previous work suggested that Abhd5, a protein activator of Atgl, coordinates with Plin in controlling basal and stimulated lipolysis; however, the underlying mechanism is controversial. The present experiments investigated protein trafficking and interactions among Plin, Atgl, and Abhd5 in live cells. The results demonstrate that Plin binds Abhd5 with high affinity and thereby suppresses the interaction of Abhd5 with Atgl. Sequestration of Abhd5 appears to a major mechanism by which Plin reduces basal lipolysis. Phosphorylation of Plin on serine 492 or serine 517 rapidly releases Abhd5 from Plin, allowing Abhd5 to directly interact with Atgl. Imaging experiments demonstrated that the Plin-dependent interaction of Abhd5 and Atgl occurs mainly, but not exclusively, on lipid droplets that contain Plin.
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Affiliation(s)
- James G Granneman
- Center for Integrative Metabolic and Endocrine Research, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
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82
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Miyoshi H, Souza SC, Endo M, Sawada T, Perfield JW, Shimizu C, Stancheva Z, Nagai S, Strissel KJ, Yoshioka N, Obin MS, Koike T, Greenberg AS. Perilipin overexpression in mice protects against diet-induced obesity. J Lipid Res 2009; 51:975-82. [PMID: 19797618 DOI: 10.1194/jlr.m002352] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Perilipin A is the most abundant phosphoprotein on adipocyte lipid droplets and is essential for lipid storage and lipolysis. Perilipin null mice exhibit diminished adipose tissue, elevated basal lipolysis, reduced catecholamine-stimulated lipolysis, and increased insulin resistance. To understand the physiological consequences of increased perilipin expression in vivo, we generated transgenic mice that overexpressed either human or mouse perilipin using the adipocyte-specific aP2 promoter/enhancer. Phenotypes of female transgenic and wild-type mice were characterized on chow and high-fat diets (HFDs). When challenged with an HFD, transgenic mice exhibited lower body weight, fat mass, and adipocyte size than wild-type mice. Expression of oxidative genes was increased and lipogenic genes decreased in brown adipose tissue of transgenic mice. Basal and catecholamine-stimulated lipolysis was decreased and glucose tolerance significantly improved in transgenic mice fed a HFD. Perilipin overexpression in adipose tissue protects against HFD-induced adipocyte hypertrophy, obesity, and glucose intolerance. Alterations in brown adipose tissue metabolism may mediate the effects of perilipin overexpression on body fat, although the mechanisms by which perilipin overexpression alters brown adipose tissue metabolism remain to be determined. Our findings demonstrate a novel role for perilipin expression in adipose tissue metabolism and regulation of obesity and its metabolic complications.
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Affiliation(s)
- Hideaki Miyoshi
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA
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83
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Abstract
Human obesity and its complications are an increasing burden in developed and underdeveloped countries. Adipose tissue mass and the mechanisms that control it are central to elucidating the aetiology of obesity and insulin resistance. Over the past 15 years tremendous progress has been made in several avenues relating to adipose tissue. Knowledge of the lipolytic machinery has grown with the identification of new lipases, cofactors and interactions between proteins and lipids that are central to the regulation of basal and stimulated lipolysis. The dated idea of an inert lipid droplet has been appropriately revamped to that of a dynamic and highly-structured organelle that in itself offers regulatory control over lipolysis. The present review provides an overview of the numerous partners and pathways involved in adipose tissue lipolysis and their interaction under various metabolic states. Integration of these findings into whole adipose tissue metabolism and its systemic effects is also presented in the context of inflammation and insulin resistance.
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84
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Goodman JM. Demonstrated and inferred metabolism associated with cytosolic lipid droplets. J Lipid Res 2009; 50:2148-56. [PMID: 19696439 DOI: 10.1194/jlr.r001446] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Cytosolic lipid droplets were considered until recently to be rather inert particles of stored neutral lipid. Largely through proteomics is it now known that droplets are dynamic organelles and that they participate in several important metabolic reactions as well as trafficking and interorganellar communication. In this review, the role of droplets in metabolism in the yeast Saccharomyces cerevisiae, the fly Drosophila melanogaster, and several mammalian sources are discussed, particularly focusing on those reactions shared by these organisms. From proteomics and older work, it is clear that droplets are important for fatty acid and sterol biosynthesis, fatty acid activation, and lipolysis. However, many droplet-associated enzymes are predicted to span a membrane two or more times, which suggests either that droplet structure is more complex than the current model posits, or that there are tightly bound membranes, particularly derived from the endoplasmic reticulum, which account for the association of several of these proteins.
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Affiliation(s)
- Joel M Goodman
- Department of Pharmacology University of Texas Southwestern Medical School Dallas TX 75390-9041, USA.
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85
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Bézaire V, Mairal A, Anesia R, Lefort C, Langin D. Chronic TNFα and cAMP pre-treatment of human adipocytes alter HSL, ATGL and perilipin to regulate basal and stimulated lipolysis. FEBS Lett 2009; 583:3045-9. [DOI: 10.1016/j.febslet.2009.08.019] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 07/31/2009] [Accepted: 08/11/2009] [Indexed: 10/20/2022]
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86
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Schittmayer M, Birner-Gruenberger R. Functional proteomics in lipid research: Lipases, lipid droplets and lipoproteins. J Proteomics 2009; 72:1006-18. [DOI: 10.1016/j.jprot.2009.05.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Revised: 05/06/2009] [Accepted: 05/19/2009] [Indexed: 01/22/2023]
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87
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Krintel C, Mörgelin M, Logan DT, Holm C. Phosphorylation of hormone-sensitive lipase by protein kinase A in vitro promotes an increase in its hydrophobic surface area. FEBS J 2009; 276:4752-62. [PMID: 19664063 DOI: 10.1111/j.1742-4658.2009.07172.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hormone-sensitive lipase (EC 3.1.1.79; HSL) is a key enzyme in the mobilization of fatty acids from stored triacylglycerols. HSL activity is controlled by phosphorylation of at least four serines. In rat HSL, Ser563, Ser659 and Ser660 are phosphorylated by protein kinase A (PKA) in vitro as well as in vivo, and Ser660 and Ser659 have been shown to be the activity-controlling sites in vitro. The exact molecular events of PKA-mediated activation of HSL in vitro are yet to be determined, but increases in both Vmax and S0.5 seem to be involved, as recently shown for human HSL. In this study, the hydrophobic fluorescent probe 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (bis-ANS) was found to inhibit the hydrolysis of triolein by purified recombinant rat adipocyte HSL, with a decrease in the effect of bis-ANS upon PKA phosphorylation of HSL. The interaction of HSL with bis-ANS was found to have a Kd of 1 microM in binding assays. Upon PKA phosphorylation, the interactions of HSL with both bis-ANS and the alternative probe SYPRO Orange were increased. By negative stain transmission electron microscopy, phosphorylated HSL was found to have a closer interaction with phospholipid vesicles than unphosphorylated HSL. Taken together, our results show that HSL increases its hydrophobic nature upon phosphorylation by PKA. This suggests that PKA phosphorylation induces a conformational change that increases the exposed hydrophobic surface and thereby facilitates binding of HSL to the lipid substrate.
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Affiliation(s)
- Christian Krintel
- Department of Experimental Medical Science, Division of Diabetes, Metabolism and Endocrinology, Lund University, Sweden
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88
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Ahmed K, Tunaru S, Langhans CD, Hanson J, Michalski CW, Kölker S, Jones PM, Okun JG, Offermanns S. Deorphanization of GPR109B as a receptor for the beta-oxidation intermediate 3-OH-octanoic acid and its role in the regulation of lipolysis. J Biol Chem 2009; 284:21928-21933. [PMID: 19561068 DOI: 10.1074/jbc.m109.019455] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The orphan G-protein-coupled receptor GPR109B is the result of a recent gene duplication of the nicotinic acid and ketone body receptor GPR109A being found in humans but not in rodents. Like GPR109A, GPR109B is predominantly expressed in adipocytes and is supposed to mediate antilipolytic effects. Here we show that GPR109B serves as a receptor for the beta-oxidation intermediate 3-OH-octanoic acid, which has antilipolytic activity on human but not on murine adipocytes. GPR109B is coupled to Gi-type G-proteins and is activated by 2- and 3-OH-octanoic acid with EC50 values of about 4 and 8 microM, respectively. Interestingly, 3-OH-octanoic acid plasma concentrations reach micromolar concentrations under conditions of increased beta-oxidation rates, like in diabetic ketoacidosis or under a ketogenic diet. These data suggest that the ligand receptor pair 3-OH-octanoic acid/GPR109B mediates in humans a negative feedback regulation of adipocyte lipolysis to counteract prolipolytic influences under conditions of physiological or pathological increases in beta-oxidation rates.
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Affiliation(s)
- Kashan Ahmed
- Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
| | - Sorin Tunaru
- Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
| | - Claus-Dieter Langhans
- Department of General Pediatrics, Division of Inherited Metabolic Disease, University Childrens Hospital Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany
| | - Julien Hanson
- Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany; Department of Medicinal Chemistry, Centre Interfacultaire de Recherche du Médicament, University of Liège, 4000 Liège, Belgium
| | - Christoph W Michalski
- Department of Surgery, Technical University Munich, Ismaninger Strasse 22, 81675 Munich, Germany
| | - Stefan Kölker
- Department of General Pediatrics, Division of Inherited Metabolic Disease, University Childrens Hospital Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany
| | - Patricia M Jones
- Department of Pathology, University of Texas Southwestern Medical Center, Childrens Medical Center, Dallas, Texas 75235
| | - Jürgen G Okun
- Department of General Pediatrics, Division of Inherited Metabolic Disease, University Childrens Hospital Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany
| | - Stefan Offermanns
- Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany; Department of Pharmacology, Max-Planck-Institute for Heart and Lung Research, Parkstrasse 1, 61231 Bad Nauheim, Germany
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89
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Bezaire V, Mairal A, Ribet C, Lefort C, Girousse A, Jocken J, Laurencikiene J, Anesia R, Rodriguez AM, Ryden M, Stenson BM, Dani C, Ailhaud G, Arner P, Langin D. Contribution of adipose triglyceride lipase and hormone-sensitive lipase to lipolysis in hMADS adipocytes. J Biol Chem 2009; 284:18282-91. [PMID: 19433586 DOI: 10.1074/jbc.m109.008631] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Lipolysis is the catabolic pathway by which triglycerides are hydrolyzed into fatty acids. Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) have the capacity to hydrolyze in vitro the first ester bond of triglycerides, but their respective contributions to whole cell lipolysis in human adipocytes is unclear. Here, we have investigated the roles of HSL, ATGL, and its coactivator CGI-58 in basal and forskolin-stimulated lipolysis in a human white adipocyte model, the hMADS cells. The hMADS adipocytes express the various components of fatty acid metabolism and show lipolytic capacity similar to primary cultured adipocytes. We show that lipolysis and fatty acid esterification are tightly coupled except in conditions of stimulated lipolysis. Immunocytochemistry experiments revealed that acute forskolin treatment promotes HSL translocation from the cytosol to small lipid droplets and redistribution of ATGL from the cytosol and large lipid droplets to small lipid droplets, resulting in enriched colocalization of the two lipases. HSL or ATGL overexpression resulted in increased triglyceride-specific hydrolase capacity, but only ATGL overexpression increased whole cell lipolysis. HSL silencing had no effect on basal lipolysis and only partially reduced forskolin-stimulated lipolysis. Conversely, silencing of ATGL or CGI-58 significantly reduced basal lipolysis and essentially abolished forskolin-stimulated lipolysis. Altogether, these results suggest that ATGL/CGI-58 acts independently of HSL and precedes its action in the sequential hydrolysis of triglycerides in human hMADS adipocytes.
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Affiliation(s)
- Véronic Bezaire
- INSERM U858, Laboratoire de Recherches sur les Obésités, F-31432 Toulouse, France
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90
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PAT proteins, an ancient family of lipid droplet proteins that regulate cellular lipid stores. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:419-40. [PMID: 19375517 DOI: 10.1016/j.bbalip.2009.04.002] [Citation(s) in RCA: 494] [Impact Index Per Article: 32.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 02/24/2009] [Accepted: 04/08/2009] [Indexed: 02/07/2023]
Abstract
The PAT family of lipid droplet proteins includes 5 members in mammals: perilipin, adipose differentiation-related protein (ADRP), tail-interacting protein of 47 kDa (TIP47), S3-12, and OXPAT. Members of this family are also present in evolutionarily distant organisms, including insects, slime molds and fungi. All PAT proteins share sequence similarity and the ability to bind intracellular lipid droplets, either constitutively or in response to metabolic stimuli, such as increased lipid flux into or out of lipid droplets. Positioned at the lipid droplet surface, PAT proteins manage access of other proteins (lipases) to the lipid esters within the lipid droplet core and can interact with cellular machinery important for lipid droplet biogenesis. Genetic variations in the gene for the best-characterized of the mammalian PAT proteins, perilipin, have been associated with metabolic phenotypes, including type 2 diabetes mellitus and obesity. In this review, we discuss how the PAT proteins regulate cellular lipid metabolism both in mammals and in model organisms.
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91
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Miyoshi H, Perfield JW, Obin MS, Greenberg AS. Adipose triglyceride lipase regulates basal lipolysis and lipid droplet size in adipocytes. J Cell Biochem 2009; 105:1430-6. [PMID: 18980248 DOI: 10.1002/jcb.21964] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In adipocytes, lipid droplet (LD) size reflects a balance of triglyceride synthesis (lipogenesis) and hydrolysis (lipolysis). Perilipin A (Peri A) is the most abundant phosphoprotein on the surface of adipocyte LDs and has a crucial role in lipid storage and lipolysis. Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) are the major rate-determining enzymes for lipolysis in adipocytes. Each of these proteins (Peri A, ATGL, and HSL) has been demonstrated to regulate lipid storage and release in the adipocyte. However, in the absence of protein kinase A (PKA) stimulation (basal state), the lipases (ATGL and HSL) are located mainly in the cytoplasm, and their contribution to basal rates of lipolysis and influence on LD size are poorly understood. In this study, we utilize an adenoviral system to knockdown or overexpress ATGL and HSL in an engineered model system of adipocytes in the presence or absence of Peri A. We are able to demonstrate in our experimental model system that in the basal state, LD size, triglyceride storage, and fatty acid release are mainly influenced by the expression of ATGL. These results demonstrate for the first time the relative contributions of ATGL, HSL, and Peri A on determination of LD size in the absence of PKA stimulation.
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Affiliation(s)
- Hideaki Miyoshi
- Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111, USA
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92
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Beller M, Sztalryd C, Southall N, Bell M, Jäckle H, Auld DS, Oliver B. COPI complex is a regulator of lipid homeostasis. PLoS Biol 2009; 6:e292. [PMID: 19067489 PMCID: PMC2586367 DOI: 10.1371/journal.pbio.0060292] [Citation(s) in RCA: 268] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Accepted: 10/14/2008] [Indexed: 11/19/2022] Open
Abstract
Lipid droplets are ubiquitous triglyceride and sterol ester storage organelles required for energy storage homeostasis and biosynthesis. Although little is known about lipid droplet formation and regulation, it is clear that members of the PAT (perilipin, adipocyte differentiation related protein, tail interacting protein of 47 kDa) protein family coat the droplet surface and mediate interactions with lipases that remobilize the stored lipids. We identified key Drosophila candidate genes for lipid droplet regulation by RNA interference (RNAi) screening with an image segmentation-based optical read-out system, and show that these regulatory functions are conserved in the mouse. Those include the vesicle-mediated Coat Protein Complex I (COPI) transport complex, which is required for limiting lipid storage. We found that COPI components regulate the PAT protein composition at the lipid droplet surface, and promote the association of adipocyte triglyceride lipase (ATGL) with the lipid droplet surface to mediate lipolysis. Two compounds known to inhibit COPI function, Exo1 and Brefeldin A, phenocopy COPI knockdowns. Furthermore, RNAi inhibition of ATGL and simultaneous drug treatment indicate that COPI and ATGL function in the same pathway. These data indicate that the COPI complex is an evolutionarily conserved regulator of lipid homeostasis, and highlight an interaction between vesicle transport systems and lipid droplets.
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Affiliation(s)
- Mathias Beller
- Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
- Max-Planck-Institut für biophysikalische Chemie, Abteilung für Molekulare Entwicklungsbiologie, Göttingen, Germany
- * To whom correspondence should be addressed. E-mail: (M. Beller); (C. Sztalryd); (B. Oliver)
| | - Carole Sztalryd
- Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
- GRECC/Geriatrics, Veterans Affairs Medical Center, Department of Medicine, School of Medicine, University of Maryland, Baltimore, Maryland, United States of America
- * To whom correspondence should be addressed. E-mail: (M. Beller); (C. Sztalryd); (B. Oliver)
| | - Noel Southall
- NIH Chemical Genomics Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Ming Bell
- GRECC/Geriatrics, Veterans Affairs Medical Center, Department of Medicine, School of Medicine, University of Maryland, Baltimore, Maryland, United States of America
| | - Herbert Jäckle
- Max-Planck-Institut für biophysikalische Chemie, Abteilung für Molekulare Entwicklungsbiologie, Göttingen, Germany
| | - Douglas S Auld
- NIH Chemical Genomics Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Brian Oliver
- Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
- * To whom correspondence should be addressed. E-mail: (M. Beller); (C. Sztalryd); (B. Oliver)
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93
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Granneman JG, Moore HPH, Mottillo EP, Zhu Z. Functional interactions between Mldp (LSDP5) and Abhd5 in the control of intracellular lipid accumulation. J Biol Chem 2008; 284:3049-3057. [PMID: 19064991 DOI: 10.1074/jbc.m808251200] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellular lipid metabolism is regulated in part by protein-protein interactions near the surface of intracellular lipid droplets. This work investigated functional interactions between Abhd5, a protein activator of the lipase Atgl, and Mldp, a lipid droplet scaffold protein that is highly expressed in oxidative tissues. Abhd5 was highly targeted to individual lipid droplets containing Mldp in microdissected cardiac muscle fibers. Mldp bound Abhd5 in transfected fibroblasts and directed it to lipid droplets in proportion to Mldp concentration. Analysis of protein-protein interactions in situ demonstrated that the interaction of Abhd5 and Mldp occurs mainly, if not exclusively, on the surface of lipid droplets. Oleic acid treatment rapidly increased the interaction between Abhd5 and Mldp, and this effect was suppressed by pharmacological inhibition of triglyceride synthesis. The functional role of the Abhd5-Mldp interaction was explored using a mutant of mouse Abhd5 (E262K) that has greatly reduced binding to Mldp. Mldp promoted the subcellular colocalization and interaction of Atgl with wild type, but not mutant, Abhd5. This differential interaction was reflected in cellular assays of Atgl activity. In the absence of Mldp, wild type and mutant Abhd5 were equally effective in reducing lipid droplet formation. In contrast, mutant Abhd5 was unable to prevent lipid droplet accumulation in cells expressing Mldp despite considerable targeting of Atgl to lipid droplets containing Mldp. These results indicate that the interaction between Abhd5 and Mldp is dynamic and essential for regulating the activity of Atgl at lipid droplets containing Mldp.
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Affiliation(s)
- James G Granneman
- Center for Integrative Metabolic and Endocrine Research, the Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan 48201.
| | - Hsiao-Ping H Moore
- Center for Integrative Metabolic and Endocrine Research, the Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Emilio P Mottillo
- Center for Integrative Metabolic and Endocrine Research, the Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Zhengxian Zhu
- Center for Integrative Metabolic and Endocrine Research, the Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan 48201
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94
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Zechner R, Kienesberger PC, Haemmerle G, Zimmermann R, Lass A. Adipose triglyceride lipase and the lipolytic catabolism of cellular fat stores. J Lipid Res 2008; 50:3-21. [PMID: 18952573 DOI: 10.1194/jlr.r800031-jlr200] [Citation(s) in RCA: 391] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Fatty acids (FAs) are essential components of all lipid classes and pivotal substrates for energy production in all vertebrates. Additionally, they act directly or indirectly as signaling molecules and, when bonded to amino acid side chains of peptides, anchor proteins in biological membranes. In vertebrates, FAs are predominantly stored in the form of triacylglycerol (TG) within lipid droplets of white adipose tissue. Lipid droplet-associated TGs are also found in most nonadipose tissues, including liver, cardiac muscle, and skeletal muscle. The mobilization of FAs from all fat depots depends on the activity of TG hydrolases. Currently, three enzymes are known to hydrolyze TG, the well-studied hormone-sensitive lipase (HSL) and monoglyceride lipase (MGL), discovered more than 40 years ago, as well as the relatively recently identified adipose triglyceride lipase (ATGL). The phenotype of HSL- and ATGL-deficient mice, as well as the disease pattern of patients with defective ATGL activity (due to mutation in ATGL or in the enzyme's activator, CGI-58), suggest that the consecutive action of ATGL, HSL, and MGL is responsible for the complete hydrolysis of a TG molecule. The complex regulation of these enzymes by numerous, partially uncharacterized effectors creates the "lipolysome," a complex metabolic network that contributes to the control of lipid and energy homeostasis. This review focuses on the structure, function, and regulation of lipolytic enzymes with a special emphasis on ATGL.
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Affiliation(s)
- Rudolf Zechner
- Institute of Molecular Biosciences, University of Graz, Austria.
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95
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Abstract
The ability to store energy in the form of energy-dense TAG (triacylglycerol) and to mobilize these stores rapidly during times of low carbohydrate availability (fasting or famine) or during heightened metabolic demand (exercise or cold-stress) is a highly conserved process essential for survival. Today, in the presence of nutrient excess and sedentary lifestyles, the regulation of this pathway is viewed as an important therapeutic target for disease prevention, as elevated circulating fatty acids in obesity contribute to many aspects of the metabolic syndrome including hepatic steatosis, atherosclerosis and insulin resistance. In the present review, we discuss the metabolic regulation and function of TAG lipases with a focus on HSL (hormone-sensitive lipase), ATGL (adipose triacylglycerol lipase) and newly identified members of the lipolytic proteome.
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96
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Adipocyte dysfunctions linking obesity to insulin resistance and type 2 diabetes. Nat Rev Mol Cell Biol 2008; 9:367-77. [PMID: 18401346 DOI: 10.1038/nrm2391] [Citation(s) in RCA: 1580] [Impact Index Per Article: 98.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Acquired resistance to the action of insulin to stimulate glucose transport in skeletal muscle is associated with obesity and promotes the development of type 2 diabetes. In skeletal muscle, insulin resistance can result from high levels of circulating fatty acids that disrupt insulin signalling pathways. However, the severity of insulin resistance varies greatly among obese people. Here we postulate that this variability might reflect differences in levels of lipid-droplet proteins that promote the sequestration of fatty acids within adipocytes in the form of triglycerides, thereby lowering exposure of skeletal muscle to the inhibitory effects of fatty acids.
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