151
|
Lu Y, Guo J, Di Y, Zong Y, Qu S, Tian J. Proteomic analysis of the triglyceride-rich lipoprotein-laden foam cells. Mol Cells 2009; 28:175-81. [PMID: 19756395 DOI: 10.1007/s10059-009-0120-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2009] [Revised: 07/01/2009] [Accepted: 07/22/2009] [Indexed: 11/29/2022] Open
Abstract
In hypertriglyceridaemic individuals, atherosclerogenesis is associated with the increased concentrations of very low density lipoprotein (VLDL) and VLDL-associated remnant particles. In vitro studies have suggested that VLDL induces foam cells formation. To reveal the changes of the proteins expression in the process of foam cells formation induced by VLDL, we performed a proteomic analysis of the foam cells based on the stimulation of differentiated THP-1 cells with VLDL. Using two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, 14 differentially expressed proteins, containing 8 up-regulated proteins and 6 down-regulated proteins were identified. The proteins are involved in energy metabolism, oxidative stress, cell growth, differentiation and apoptosis, such as adipose differentiation-related protein (ADRP), enolase, S100A11, heat shock protein 27 and so on. In addition, the expression of some selected proteins was confirmed by Western blot and RT-PCR analysis. The results suggest that VLDL not only induces lipid accumulation, but also brings about foam cells diverse characteristics by altering the expression of various proteins.
Collapse
Affiliation(s)
- Yanjun Lu
- Department of Biochemistry and Molecular Biology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China
| | | | | | | | | | | |
Collapse
|
152
|
Rankin EB, Rha J, Selak MA, Unger TL, Keith B, Liu Q, Haase VH. Hypoxia-inducible factor 2 regulates hepatic lipid metabolism. Mol Cell Biol 2009; 29:4527-38. [PMID: 19528226 PMCID: PMC2725738 DOI: 10.1128/mcb.00200-09] [Citation(s) in RCA: 255] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 03/22/2009] [Accepted: 06/08/2009] [Indexed: 12/14/2022] Open
Abstract
In mammals, the liver integrates nutrient uptake and delivery of carbohydrates and lipids to peripheral tissues to control overall energy balance. Hepatocytes maintain metabolic homeostasis by coordinating gene expression programs in response to dietary and systemic signals. Hepatic tissue oxygenation is an important systemic signal that contributes to normal hepatocyte function as well as disease. Hypoxia-inducible factors 1 and 2 (HIF-1 and HIF-2, respectively) are oxygen-sensitive heterodimeric transcription factors, which act as key mediators of cellular adaptation to low oxygen. Previously, we have shown that HIF-2 plays an important role in both physiologic and pathophysiologic processes in the liver. HIF-2 is essential for normal fetal EPO production and erythropoiesis, while constitutive HIF-2 activity in the adult results in polycythemia and vascular tumorigenesis. Here we report a novel role for HIF-2 in regulating hepatic lipid metabolism. We found that constitutive activation of HIF-2 in the adult results in the development of severe hepatic steatosis associated with impaired fatty acid beta-oxidation, decreased lipogenic gene expression, and increased lipid storage capacity. These findings demonstrate that HIF-2 functions as an important regulator of hepatic lipid metabolism and identify HIF-2 as a potential target for the treatment of fatty liver disease.
Collapse
Affiliation(s)
- Erinn B Rankin
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | | | | | | | | | | | | |
Collapse
|
153
|
Fan B, Ikuyama S, Gu JQ, Wei P, Oyama JI, Inoguchi T, Nishimura J. Oleic acid-induced ADRP expression requires both AP-1 and PPAR response elements, and is reduced by Pycnogenol through mRNA degradation in NMuLi liver cells. Am J Physiol Endocrinol Metab 2009; 297:E112-23. [PMID: 19383873 DOI: 10.1152/ajpendo.00119.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Fatty acids stimulate lipid accumulation in parallel with increased expression of adipose differentiation-related protein (ADRP) in liver cells. Although it is generally considered that the fatty acid effect on ADRP expression is mediated by peroxisome proliferator-activated receptors (PPARs), we identified here an additional molecular mechanism using the NMuLi mouse liver nonparenchymal cell line, which expresses PPARgamma and delta but not alpha. Oleic acid (OA) and specific ligands for PPARgamma and -delta stimulated ADRP expression as well as the -2,090-bp ADRP promoter activity which encompasses the PPAR response element (PPRE) adjacent to an Ets/activator protein (AP)-1 site. When the AP-1 site was mutated, OA failed to stimulate the activity despite the presence of the PPRE, whereas ligands for PPARgamma and -delta did stimulate it and so did a PPARalpha ligand under the coexpression of PPARalpha. DNA binding of AP-1 was stimulated by OA but not by PPAR ligands. Because we previously demonstrated that Pycnogenol (PYC), a French maritime pine bark extract, suppressed ADRP expression in macrophages partly by suppression of AP-1 activity, we tested the effect of PYC on NMuLi cells. PYC reduced the OA-induced ADRP expression along with suppression of lipid droplet formation. However, PYC neither suppressed the OA-stimulated ADRP promoter activity nor DNA binding of AP-1 but, instead, reduced the ADRP mRNA half-life. All these results indicate that the effect of OA on ADRP expression requires AP-1 as well as PPRE, and PYC suppresses the ADRP expression in part by facilitating mRNA degradation. PYC, a widely used dietary supplement, could be beneficial for the prevention of excessive lipid accumulation such as hepatic steatosis.
Collapse
Affiliation(s)
- Bin Fan
- Division of Clinical Immunology, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, Beppu 874-0838, Japan
| | | | | | | | | | | | | |
Collapse
|
154
|
PAT proteins, an ancient family of lipid droplet proteins that regulate cellular lipid stores. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:419-40. [PMID: 19375517 DOI: 10.1016/j.bbalip.2009.04.002] [Citation(s) in RCA: 508] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 02/24/2009] [Accepted: 04/08/2009] [Indexed: 02/07/2023]
Abstract
The PAT family of lipid droplet proteins includes 5 members in mammals: perilipin, adipose differentiation-related protein (ADRP), tail-interacting protein of 47 kDa (TIP47), S3-12, and OXPAT. Members of this family are also present in evolutionarily distant organisms, including insects, slime molds and fungi. All PAT proteins share sequence similarity and the ability to bind intracellular lipid droplets, either constitutively or in response to metabolic stimuli, such as increased lipid flux into or out of lipid droplets. Positioned at the lipid droplet surface, PAT proteins manage access of other proteins (lipases) to the lipid esters within the lipid droplet core and can interact with cellular machinery important for lipid droplet biogenesis. Genetic variations in the gene for the best-characterized of the mammalian PAT proteins, perilipin, have been associated with metabolic phenotypes, including type 2 diabetes mellitus and obesity. In this review, we discuss how the PAT proteins regulate cellular lipid metabolism both in mammals and in model organisms.
Collapse
|
155
|
Sapiro JM, Mashek MT, Greenberg AS, Mashek DG. Hepatic triacylglycerol hydrolysis regulates peroxisome proliferator-activated receptor alpha activity. J Lipid Res 2009; 50:1621-9. [PMID: 19304987 DOI: 10.1194/jlr.m800614-jlr200] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Recent evidence suggests that fatty acids generated from intracellular triacylglycerol (TAG) hydrolysis may have important roles in intracellular signaling. This study was conducted to determine if fatty acids liberated from TAG hydrolysis regulate peroxisome proliferator-activated receptor alpha (PPARalpha). Primary rat hepatocyte cultures were treated with adenoviruses overexpressing adipose differentiation-related protein (ADRP) or adipose triacylglycerol lipase (ATGL) or treated with short interfering RNA (siRNA) targeted against ADRP. Subsequent effects on TAG metabolism and PPARalpha activity and target gene expression were determined. Overexpressing ADRP attenuated TAG hydrolysis, whereas siRNA-mediated knockdown of ADRP or ATGL overexpression resulted in enhanced TAG hydrolysis. Results from PPARalpha reporter activity assays demonstrated that decreasing TAG hydrolysis by ADRP overexpression resulted in a 35-60% reduction in reporter activity under basal conditions or in the presence of fatty acids. As expected, PPARalpha target genes were also decreased in response to ADRP overexpression. However, the PPARalpha ligand, WY-14643, was able to restore PPARalpha activity following ADRP overexpression. Despite its effects on PPARalpha, overexpressing ADRP did not affect PPARgamma activity. Enhancing TAG hydrolysis through ADRP knockdown or ATGL overexpression increased PPARalpha activity. These results indicate that TAG hydrolysis and the consequential release of fatty acids regulate PPARalpha activity.
Collapse
Affiliation(s)
- Jessica M Sapiro
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108, USA
| | | | | | | |
Collapse
|
156
|
Shaw CS, Sherlock M, Stewart PM, Wagenmakers AJM. Adipophilin distribution and colocalization with lipid droplets in skeletal muscle. Histochem Cell Biol 2009; 131:575-81. [PMID: 19169702 DOI: 10.1007/s00418-009-0558-4] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/03/2009] [Indexed: 01/14/2023]
Abstract
Intramyocellular lipids (IMCL) are stored as discrete lipid droplets which are associated with a number of proteins. The lipid droplet-associated protein adipophilin (the human orthologue of adipose differentiation-related protein) is ubiquitously expressed and is one of the predominant lipid droplet-proteins in skeletal muscle. The aim of this study was to investigate the subcellular distribution of adipophilin in human muscle fibres and to measure the colocalization of adipophilin with IMCL. Muscle biopsies from six lean male cyclists (BMI 23.4 +/- 0.4, aged 31 +/- 2 years, W (max) 346 +/- 8) were stained for myosin heavy chain type 1, IMCL, adipophilin and mitochondria using immunofluorescence and viewed with widefield and confocal fluorescence microscopy. The present study shows that like IMCL, the adipophilin content is ~twofold greater in type I skeletal muscle fibres and is situated in the areas between the mitochondrial network. Colocalization analysis demonstrated that 61 +/- 2% of IMCL contain adipophilin. Although the majority of adipophilin is contained within IMCL, 36 +/- 4% of adipophilin is not associated with IMCL. In conclusion, this study indicates that the IMCL pool is heterogeneous, as the majority but not all IMCL contain adipophilin.
Collapse
Affiliation(s)
- Christopher S Shaw
- Exercise Metabolism Research Group, School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
| | | | | | | |
Collapse
|
157
|
Association of Polymorphisms of Chicken Adipose Differentiation-related Protein Gene with Carcass Traits. J Poult Sci 2009. [DOI: 10.2141/jpsa.46.87] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
|
158
|
Endolysosomal phospholipidosis and cytosolic lipid droplet storage and release in macrophages. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:524-39. [PMID: 19146988 DOI: 10.1016/j.bbalip.2008.12.007] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 12/08/2008] [Accepted: 12/11/2008] [Indexed: 12/12/2022]
Abstract
This review summarizes the current knowledge of endolysosomal and cytoplasmic lipid storage in macrophages induced by oxidized LDL (Ox-LDL), enzymatically degraded LDL (E-LDL) and other atherogenic lipoprotein modifications, and their relation to the adapter protein 3 (AP-3) dependent ABCA1 and ABCG1 cellular lipid efflux pathways. We compare endolysosomal lipid storage caused either through drug induced phospholipidosis, inheritable endolysosomal and cytosolic lipid storage disorders and Ox-LDL or E-LDL induced phagosomal uptake and cytosolic lipid droplet storage in macrophages. Ox-LDL is resistant to rapid endolysosomal hydrolysis and is trapped within the endolysosomal compartment generating lamellar bodies which resemble the characteristics of phospholipidosis. Various inherited lysosomal storage diseases including sphingolipidosis, glycosphingolipidosis and cholesterylester storage diseases also present a phospholipidosis phenotype. In contrast E-LDL resembling coreless unesterified cholesterol enriched LDL-particles, with a multilamellar, liposome-like structure, lead to rapid phagosomal degradation and cytosolic lipid droplet accumulation. As a consequence the uptake of E-LDL through type I and type II phagocytosis leads to increased lipid droplet formation and moderate upregulation of ABCA1 and ABCG1 while uptake of Ox-LDL leads to a rapid expansion of the lysosomal compartment and a pronounced upregulation of the ABCA1/ABCG1/AP-3 lipid efflux pathway.
Collapse
|
159
|
Gu JQ, Ikuyama S, Wei P, Fan B, Oyama JI, Inoguchi T, Nishimura J. Pycnogenol, an extract from French maritime pine, suppresses Toll-like receptor 4-mediated expression of adipose differentiation-related protein in macrophages. Am J Physiol Endocrinol Metab 2008; 295:E1390-400. [PMID: 18854426 DOI: 10.1152/ajpendo.90543.2008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Adipose differentiation-related protein (ADRP) is highly expressed in macrophages and human atherosclerotic lesions. We demonstrated that Toll-like receptor (TLR) 4-mediated signals, which are involved in atherosclerosis formation, enhanced the expression of ADRP in macrophages. Lipopolysaccharide (LPS) enhanced the ADRP expression in RAW264.7 cells or peritoneal macrophages from wild-type mice, but not in macrophages from TLR4-deficient mice. Actinomycin D almost completely abolished the LPS effect, whereas cycloheximide decreased the expression at 12 h, indicating that the LPS-induced ADRP expression was stimulated at the transcriptional level and was also mediated by new protein synthesis. LPS enhanced the ADRP promoter activity, in part, by stimulating activator protein (AP)-1 binding to the Ets/AP-1 element. In addition, preceding the increase of the ADRP mRNA, LPS induced the expression of interleukin (IL)-6, IL-1alpha, and interferon-beta mRNAs, all of which stimulated the ADRP expression. Antibodies against these cytokines or inhibitors of c-Jun NH(2)-terminal kinase and nuclear factor (NF)-kappaB suppressed the ADRP mRNA level. Thus TLR4 signals stimulate the ADRP expression both in direct and indirect manners. Pycnogenol (PYC), an extract of French maritime pine, suppressed the expression of ADRP and the above-mentioned cytokines. PYC suppressed the ADRP promoter activity and enhancer activity of AP-1 and NF-kappaB, whereas it did not affect the LPS-induced DNA binding of these factors. In conclusion, TLR4-mediated signals stimulate the ADRP expression in macrophages while PYC antagonizes this process. PYC, a widely used dietary supplement, might be useful for prevention of atherosclerosis.
Collapse
Affiliation(s)
- Jian-Qiu Gu
- Dept. of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu Univ., Beppu 874-0838, Japan
| | | | | | | | | | | | | |
Collapse
|
160
|
Anderson N, Borlak J. Molecular Mechanisms and Therapeutic Targets in Steatosis and Steatohepatitis. Pharmacol Rev 2008; 60:311-57. [DOI: 10.1124/pr.108.00001] [Citation(s) in RCA: 291] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
|
161
|
Olofsson SO, Boström P, Andersson L, Rutberg M, Levin M, Perman J, Borén J. Triglyceride containing lipid droplets and lipid droplet-associated proteins. Curr Opin Lipidol 2008; 19:441-7. [PMID: 18769224 DOI: 10.1097/mol.0b013e32830dd09b] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
PURPOSE OF REVIEW Cytosolic lipid droplets are now recognized as dynamic organelles. This review summarizes our current understanding of the mechanisms involved in the formation of lipid droplets, the importance of lipid droplet-associated proteins and the link between lipid droplet accumulation and development of insulin resistance. RECENT FINDINGS Lipid droplets are formed as primordial droplets and they increase in size by fusion. This fusion process requires the alpha-soluble N-ethylmaleimide-sensitive factor adaptor protein receptor SNAP23, which is also involved in the insulin-dependent translocation of a glucose transporter to the plasma membrane. Recent data suggest that SNAP23 is the link between increased lipid droplet accumulation and development of insulin resistance. Lipid droplets also form tight interactions with other organelles. Furthermore, additional lipid droplet-associated proteins have been identified and shown to play a role in droplet assembly and turnover, and in sorting and trafficking events. SUMMARY Recent studies have identified a number of key proteins that are involved in the formation and turnover of lipid droplets, and SNAP23 has been identified as a link between accumulation of lipid droplets and development of insulin resistance. Further understanding of lipid droplet biology could indicate potential therapeutic targets to prevent accumulation of lipid droplets and associated complications.
Collapse
Affiliation(s)
- Sven-Olof Olofsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Gothenburg, Sweden.
| | | | | | | | | | | | | |
Collapse
|
162
|
Varela GM, Antwi DA, Dhir R, Yin X, Singhal NS, Graham MJ, Crooke RM, Ahima RS. Inhibition of ADRP prevents diet-induced insulin resistance. Am J Physiol Gastrointest Liver Physiol 2008; 295:G621-8. [PMID: 18669627 PMCID: PMC2536783 DOI: 10.1152/ajpgi.90204.2008] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Diets with high fat content induce steatosis, insulin resistance, and type 2 diabetes. The lipid droplet protein adipose differentiation-related protein (ADRP) mediates hepatic steatosis, but whether this affects insulin action in the liver or peripheral organs in diet-induced obesity is uncertain. We fed C57BL/6J mice a high-fat diet and simultaneously treated them with an antisense oligonucleotide (ASO) against ADRP for 4 wk. Glucose homeostasis was assessed with clamp and tracer techniques. ADRP ASO decreased the levels of triglycerides and diacylglycerol in the liver, but fatty acids, long-chain fatty acyl CoAs, ceramides, and cholesterol were unchanged. Insulin action in the liver was enhanced after ADRP ASO treatment, whereas muscle and adipose tissue were not affected. ADRP ASO increased the phosphorylation of insulin receptor substrate (IRS)1, IRS2, and Akt, and decreased gluconeogenic enzymes and PKCepsilon, consistent with its insulin-sensitizing action. These results demonstrate an important role for ADRP in the pathogenesis of diet-induced insulin resistance.
Collapse
Affiliation(s)
- Gladys M. Varela
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Daniel A. Antwi
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Ravindra Dhir
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Xiaoyan Yin
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Neel S. Singhal
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Mark J. Graham
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Roseanne M. Crooke
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| | - Rexford S. Ahima
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and Isis Pharmaceuticals, Carlsbad, California
| |
Collapse
|
163
|
Murphy S, Martin S, Parton RG. Lipid droplet-organelle interactions; sharing the fats. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:441-7. [PMID: 18708159 DOI: 10.1016/j.bbalip.2008.07.004] [Citation(s) in RCA: 186] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Revised: 06/09/2008] [Accepted: 07/18/2008] [Indexed: 12/20/2022]
Abstract
Lipid droplets (LDs) are key cellular organelles involved in lipid storage and mobilisation. While the major signalling cascades and many of the regulators of lipolysis have been identified, the cellular interactions involved in lipid mobilisation and release remain largely undefined. In non-adipocytes, LDs are small, mobile and interact with other cellular compartments. In contrast, adipocytes primarily contain very large, immotile LDs. The striking morphological differences between LDs in adipocytes and non-adipocytes suggest that key differences must exist in the manner in which LDs in different cell types interact with other organelles. Recent studies have highlighted the complexity of LD interactions, which can be both homotypic, with each other, and heterotypic, with other organelles. The molecules involved in these interactions are also now emerging, including Rab proteins, key regulators of membrane traffic, and caveolin, an integral membrane protein providing a functional link between the cell surface and LDs. Here we summarise recent insights into the cell biology of the LD particularly focussing on the homotypic and heterotypic interactions in both adipocytes and non-adipocytes. We speculate that these interactions may involve inter-organelle membrane contact sites or a hemi-fusion type mechanism to facilitate lipid transfer.
Collapse
Affiliation(s)
- Samantha Murphy
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia
| | | | | |
Collapse
|
164
|
Imanishi Y, Sun W, Maeda T, Maeda A, Palczewski K. Retinyl ester homeostasis in the adipose differentiation-related protein-deficient retina. J Biol Chem 2008; 283:25091-102. [PMID: 18606814 DOI: 10.1074/jbc.m802981200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The retinal pigmented epithelium (RPE) plays an essential role in vision, including storing and converting retinyl esters of the visual chromophore, 11-cis-retinal. Retinyl ester storage structures (RESTs), specialized lipid droplets within the RPE, take up retinyl esters synthesized in the endoplasmic reticulum. Here we report studies of mice lacking exons 2 and 3 of the gene encoding adipose differentiation-related protein (Adfp), a structural component of RESTs. We found that dark adaptation was slower in Adfp(Delta2-3/Delta2-3) than in Adfp+/+ mice and that Adfp(Delta2-3/Delta2-3) mice had consistently delayed clearances of all-trans-retinal and all-trans-retinol from rod photoreceptor cells. Two-photon microscopy revealed aberrant trafficking of all-trans-retinyl esters in the RPE of Adfp(Delta2-3/Delta2-3) mice, a problem caused by abnormal maintenance of RESTs in the dark-adapted state. Retinyl ester accumulation was also reduced in Adfp(Delta2-3/Delta2-3) as compared with Adfp+/+ mice. These observations suggest that Adfp plays a unique role in vision by maintaining proper storage and trafficking of retinoids within the eye.
Collapse
Affiliation(s)
- Yoshikazu Imanishi
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
| | | | | | | | | |
Collapse
|
165
|
Kobayashi K, Inoguchi T, Maeda Y, Nakashima N, Kuwano A, Eto E, Ueno N, Sasaki S, Sawada F, Fujii M, Matoba Y, Sumiyoshi S, Kawate H, Takayanagi R. The lack of the C-terminal domain of adipose triglyceride lipase causes neutral lipid storage disease through impaired interactions with lipid droplets. J Clin Endocrinol Metab 2008; 93:2877-84. [PMID: 18445677 DOI: 10.1210/jc.2007-2247] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
CONTEXT The molecular mechanisms by which triglycerides in lipid droplets (LDs) are synthesized, stored, and degraded need to be elucidated. OBJECTIVE The objectives were to report siblings with neutral lipid storage disease with myopathy (NLSDM) with a novel mutation of adipose triglyceride lipase (ATGL) and determine whether the C-terminal part of ATGL containing the hydrophobic region plays a role in the interaction with LDs. DESIGN AND PATIENTS Skin fibroblasts and peripheral blood leukocytes were obtained from NLSDM patients. In vitro experiments were performed with fibroblasts and COS7 cells. MAIN OUTCOME MEASURES Transfection studies were used to assess the effects of various recombinant ATGL proteins on lipase activities and lipid contents. Fluorescence microscopy were used for determination of intracellular distribution of ATGL proteins. RESULTS The direct sequence of ATGL cDNA reveals that a patient is a homozygote for the 4-bp deletion, leading to a premature stop codon and causes the lack of the C terminus of the protein including the hydrophobic domain. Overexpressed control ATGL in NLSDM fibroblasts was found around the rims of LDs and caused significantly reduced cellular lipid accumulation. In contrast, NLSDM ATGL was homogeneously located in the cytoplasm despite the presence of LDs and had almost no effect on LD degradation despite its similar lipase activity. A series of C-terminal truncated ATGLs without the intact hydrophobic domain failed to localize around and degrade LDs. CONCLUSIONS These findings indicate that the domain including the hydrophobic region of ATGL was essential for association with LDs.
Collapse
Affiliation(s)
- Kunihisa Kobayashi
- Department of Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Japan.
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
166
|
Paul A, Chang BHJ, Li L, Yechoor VK, Chan L. Deficiency of adipose differentiation-related protein impairs foam cell formation and protects against atherosclerosis. Circ Res 2008; 102:1492-501. [PMID: 18483409 DOI: 10.1161/circresaha.107.168070] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Foam cells are a hallmark of atherosclerosis. However, it is unclear whether foam cell formation per se protects against atherosclerosis or fuels it. In this study, we investigated the role of adipose differentiation-related protein (ADFP), a major lipid droplet protein (LDP), in the regulation of foam cell formation and atherosclerosis. We show that ADFP expression facilitates foam cell formation induced by modified lipoproteins in mouse macrophages in vitro. We show further that Adfp gene inactivation in apolipoprotein E-deficient (ApoE(-/-)) mice reduces the number of lipid droplets in foam cells in atherosclerotic lesions and protects the mice against atherosclerosis. Moreover, transplantation of ADFP-null bone marrow-derived cells effectively attenuated atherosclerosis in ApoE(-/-) mice. Deficiency of ADFP did not cause a detectable compensatory increase in the other PAT domain proteins in macrophages in vitro or in vivo. Mechanistically, ADFP enables the macrophage to maintain its lipid content by hindering lipid efflux. We detected no significant difference in lesion composition or in multiple parameters of inflammation in macrophages or in their phagocytic activity between mice with and without ADFP. In conclusion, Adfp inactivation in ApoE(-/-) background protects against atherosclerosis and appears to be a relatively pure model of impaired foam cell formation.
Collapse
Affiliation(s)
- Antoni Paul
- Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | | | | | | | | |
Collapse
|
167
|
Listenberger LL, Brown DA. Fluorescent detection of lipid droplets and associated proteins. ACTA ACUST UNITED AC 2008; Chapter 24:Unit 24.2. [PMID: 18228510 DOI: 10.1002/0471143030.cb2402s35] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Most eukaryotic cells can store excess lipid in cytosolic lipid droplets. This unit discusses techniques for the visualization of lipid droplets and associated proteins in cultured mammalian cells. Protocols for the detection of lipid droplets with nile red and BODIPY 493/503 are included. The differences in the spectral properties of these two lipophilic dyes and advantages of each are discussed. The best method for combining visualization of intracellular lipid droplets with indirect immunofluorescent detection of lipid droplet-associated proteins is described. Techniques for sample fixation and permeabilization must be chosen carefully to avoid alterations to lipid droplet morphology. Immunofluorescent detection of adipophilin, a broadly expressed, lipid droplet-associated protein, widely used as a marker for lipid droplet accumulation, is presented as an example. Finally, a simple protocol for enhancing lipid droplet accumulation through supplementation with excess fatty acid is included.
Collapse
|
168
|
Keller P, Petrie JT, De Rose P, Gerin I, Wright WS, Chiang SH, Nielsen AR, Fischer CP, Pedersen BK, MacDougald OA. Fat-specific protein 27 regulates storage of triacylglycerol. J Biol Chem 2008; 283:14355-65. [PMID: 18334488 DOI: 10.1074/jbc.m708323200] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
FSP27 (fat-specific protein 27) is a member of the cell death-inducing DNA fragmentation factor-alpha-like effector (CIDE) family. Although Cidea and Cideb were initially characterized as activators of apoptosis, recent studies have demonstrated important metabolic roles for these proteins. In this study, we investigated the function of another member of this family, FSP27 (Cidec), in apoptosis and adipocyte metabolism. Although overexpression of FSP27 is sufficient to increase apoptosis of 293T and 3T3-L1 cells, more physiological levels of expression stimulate spontaneous lipid accumulation in several cell types without induction of adipocyte genes. Increased triacylglycerol is likely due to decreased beta-oxidation of nonesterified fatty acids. Altered flux of fatty acids into triacylglycerol may be a direct effect of FSP27 function, which is localized to lipid droplets in 293T cells and 3T3-L1 adipocytes. Stable knockdown of FSP27 during adipogenesis of 3T3-L1 cells substantially decreases lipid droplet size, increases mitochondrial and lipid droplet number, and modestly increases glucose uptake and lipolysis. Expression of FSP27 in subcutaneous adipose tissue of a human diabetes cohort decreases with total fat mass but is not associated with measures of insulin resistance (e.g. homeostasis model assessment). Together, these data indicate that FSP27 binds to lipid droplets and regulates their enlargement.
Collapse
Affiliation(s)
- Pernille Keller
- Department of Molecular and Integrative Physiology and Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
169
|
Abstract
Organisms store energy for later use during times of nutrient scarcity. Excess energy is stored as triacylglycerol in lipid droplets during lipogenesis. When energy is required, the stored triacylglycerol is hydrolyzed via activation of lipolytic pathways. The coordination of lipid storage and utilization is regulated by the perilipin family of lipid droplet coat proteins [perilipin, adipophilin/adipocyte differentiation-related protein (ADRP), S3-12, tail-interacting protein of 47 kilodaltons (TIP47), and myocardial lipid droplet protein (MLDP)/oxidative tissues-enriched PAT protein (OXPAT)/lipid storage droplet protein 5 (LSDP5)]. Lipid droplets are dynamic and heterogeneous in size, location, and protein content. The proteins that coat lipid droplets change during lipid droplet biogenesis and are dependent upon multiple factors, including tissue-specific expression and metabolic state (basal vs. lipogenic vs. lipolytic). New data suggest that proteins previously implicated in vesicle trafficking, including Rabs, soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), and motor and cytoskeletal proteins, likely orchestrate the movement and fusion of lipid droplets. Thus, rather than inert cytoplasmic inclusions, lipid droplets are now appreciated as dynamic organelles that are critical for management of cellular lipid stores. That much remains to be discovered is suggested by the recent identification of a novel lipase [adipocyte triglyceride lipase (ATGL)] and lipase regulator [Comparative Gene Identification-58 (CGI-58)], which has led to reconsideration of the decades-old model of lipolysis. Future discovery likely will be driven by the exploitation of model organisms and by human genetic studies.
Collapse
Affiliation(s)
- Nicole A Ducharme
- Center for Diabetes and Obesity Research, Brown Foundation Institute of Molecular Medicine, 1825 Pressler Street, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA
| | | |
Collapse
|
170
|
McManaman JL, Russell TD, Schaack J, Orlicky DJ, Robenek H. Molecular determinants of milk lipid secretion. J Mammary Gland Biol Neoplasia 2007; 12:259-68. [PMID: 17999166 DOI: 10.1007/s10911-007-9053-5] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2007] [Accepted: 10/24/2007] [Indexed: 12/20/2022] Open
Abstract
Mammary epithelial cells secrete lipids by an envelopment process that produces lipid droplets coated by membranes derived from the plasma membrane and possibly secretory vesicles. This secretion process, which resembles viral budding, is hypothesized to be mediated by specific interactions between molecules on the surface of intracellular lipids and membrane elements of the cell. Multiple lines of evidence indicate that milk lipid secretion occurs through a tripartite complex between the integral transmembrane protein, butyrophilin (BTN); the soluble metabolic enzyme, xanthine oxidoreductase (XOR); and the lipid droplet surface protein, adipophilin (ADPH). However, topological evidence from freeze-fracture replica immunolabelling (FRIL) challenge this model and suggests that milk lipid secretion is mediated by butyrophilin alone. Advances in our understanding of the molecular, structural, and functional properties of these proteins now make it possible to understand the physiological functions of each of these molecules in detail and to identify the specific molecular determinants that mediate milk lipid secretion.
Collapse
Affiliation(s)
- James L McManaman
- Department of Obstetrics and Gynecology, University of Colorado Denver and Health Sciences Center, Aurora, CO, USA.
| | | | | | | | | |
Collapse
|
171
|
Brasaemle DL. Thematic review series: Adipocyte Biology. The perilipin family of structural lipid droplet proteins: stabilization of lipid droplets and control of lipolysis. J Lipid Res 2007; 48:2547-59. [PMID: 17878492 DOI: 10.1194/jlr.r700014-jlr200] [Citation(s) in RCA: 734] [Impact Index Per Article: 43.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The majority of eukaryotic cells synthesize neutral lipids and package them into cytosolic lipid droplets. In vertebrates, triacylglycerol-rich lipid droplets of adipocytes provide a major energy storage depot for the body, whereas cholesteryl ester-rich droplets of many other cells provide building materials for local membrane synthesis and repair. These lipid droplets are coated with one or more of five members of the perilipin family of proteins: adipophilin, TIP47, OXPAT/MLDP, S3-12, and perilipin. Members of this family share varying levels of sequence similarity, lipid droplet association, and functions in stabilizing lipid droplets. The most highly studied member of the family, perilipin, is the most abundant protein on the surfaces of adipocyte lipid droplets, and the major substrate for cAMP-dependent protein kinase [protein kinase A (PKA)] in lipolytically stimulated adipocytes. Perilipin serves important functions in the regulation of basal and hormonally stimulated lipolysis. Under basal conditions, perilipin restricts the access of cytosolic lipases to lipid droplets and thus promotes triacylglycerol storage. In times of energy deficit, perilipin is phosphorylated by PKA and facilitates maximal lipolysis by hormone-sensitive lipase and adipose triglyceride lipase. A model is discussed whereby perilipin serves as a dynamic scaffold to coordinate the access of enzymes to the lipid droplet in a manner that is responsive to the metabolic status of the adipocyte.
Collapse
Affiliation(s)
- Dawn L Brasaemle
- Department of Nutritional Sciences and the Rutgers Center for Lipid Research, Rutgers, the State University of New Jersey, New Brunswick, NJ 08901, USA.
| |
Collapse
|
172
|
Llorente-Cortés V, Royo T, Juan-Babot O, Badimon L. Adipocyte differentiation-related protein is induced by LRP1-mediated aggregated LDL internalization in human vascular smooth muscle cells and macrophages. J Lipid Res 2007; 48:2133-40. [PMID: 17620659 DOI: 10.1194/jlr.m700039-jlr200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Aggregated LDL (agLDL) is internalized by LDL receptor-related protein (LRP1) in vascular smooth muscle cells (VSMCs) and human monocyte-derived macrophages (HMDMs). AgLDL is, therefore, a potent inducer of massive intracellular cholesteryl ester accumulation in lipid droplets. The adipocyte differentiation-related protein (ADRP) has been found on the surface of lipid droplets. The objectives of this work were to analyze whether agLDL uptake modulates ADRP expression levels and whether the effect of agLDL internalization on ADRP expression depends on LRP1 in human VSMCs and HMDMs. AgLDL strongly upregulates ADRP mRNA (real-time PCR) and protein expression (Western blot) in human VSMCs (mRNA: by 3.06-fold; protein: 8.58-fold) and HMDMs (mRNA: by 3.5-fold; protein: by 3.71-fold). Treatment of VSMCs and HMDMs with small anti-LRP1-interfering RNA (siRNA-LRP1) leads to specific inhibition of LRP1 expression. siRNA-LRP1 treatment significantly reduced agLDL-induced ADRP overexpression in HMDMs (by 69%) and in VSMCs (by 53%). Immunohystochemical studies evidence a colocolocalization between ADRP/macrophages and ADRP/VSMCs in advanced lipid-enriched atherosclerotic plaques. These results demonstrate that agLDL-LRP1 engagement induces ADRP overexpression in both HMDMs and human VSMCs and that ADRP is highly expressed in advanced lipid-enriched human atherosclerotic plaques. Therefore, LRP1-mediated agLDL uptake might play a pivotal role in vascular foam cell formation.
Collapse
Affiliation(s)
- V Llorente-Cortés
- Cardiovascular Research Center, Consejo Superior de Investigaciones Científicas-Instituto Catalán de Ciencias Cardiovasculares, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | | | | | | |
Collapse
|
173
|
Listenberger LL, Ostermeyer-Fay AG, Goldberg EB, Brown WJ, Brown DA. Adipocyte differentiation-related protein reduces the lipid droplet association of adipose triglyceride lipase and slows triacylglycerol turnover. J Lipid Res 2007; 48:2751-61. [PMID: 17872589 DOI: 10.1194/jlr.m700359-jlr200] [Citation(s) in RCA: 241] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Although neutral lipid storage droplets are ubiquitous in eukaryotic cells, very little is known about how their synthesis and turnover are controlled. Adipocyte differentiation-related protein (ADRP; also known as adipophilin) is found on the surface of lipid droplets in most mammalian cell types. To learn how ADRP affects lipid storage, we stably expressed the protein in human embryonic kidney 293 (HEK 293) cells, which express little endogenous ADRP. As expected, ADRP was targeted to the surface of lipid droplets and caused an increase in triacylglycerol (TAG) mass under both basal and oleate-supplemented conditions. At least part of the increased mass resulted from a 50% decrease in the rate of TAG hydrolysis in ADRP-expressing cells. Furthermore, ADRP expression increased the fraction of total cellular TAG that was stored in lipid droplets. ADRP expression induced a striking decrease in the association of adipose triglyceride lipase (ATGL) and mannose-6-phosphate receptor tail-interacting protein of 47 kDa with lipid droplets and also decreased the lipid droplet association of several other unknown proteins. Transient expression of ADRP in two other cell lines also reduced the lipid droplet association of catalytically inactive ATGL. We conclude that the reduced lipid droplet association of ATGL and/or other lipases may explain the decrease in TAG turnover observed in ADRP-expressing HEK 293 cells.
Collapse
Affiliation(s)
- Laura L Listenberger
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, USA
| | | | | | | | | |
Collapse
|
174
|
Gao JG, Simon M. A comparative study of human GS2, its paralogues, and its rat orthologue. Biochem Biophys Res Commun 2007; 360:501-6. [PMID: 17603008 DOI: 10.1016/j.bbrc.2007.06.089] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Accepted: 06/19/2007] [Indexed: 10/23/2022]
Abstract
We have previously shown that human GS2 (hGS2) catalyzes keratinocyte retinylester and triglyceride hydrolysis. hGS2 and its rat orthologue, rGS2, are 80% homologous and share a proline insertion at residue 56 and a C-terminal truncation compared to the hGS2 paralogues. Both changes are required for hGS2 function. However, the catalytic capabilities of hGS2 are more similar to the paralogue, TTS-2.2, than to rGS2. Only hGS2 and hTTS-2.2 transfer fatty acid from triglyceride to retinol, hydrolyze retinylesters, and generate 1,3-diacylglycerol from triglycerides. Rat-human chimeras containing either the N- or C-terminus of rGS2 are without activity and single substitutions of rat for human residues cause activity loss. The differences between orthologues suggest that GS2 has a unique function in humans or has a function that is fulfilled by other enzymes in rodents. Since retinoid and triglyceride metabolites are transcription factor ligands, we expect that these enzymes will coordinately regulate epidermal homeostasis.
Collapse
Affiliation(s)
- Jay G Gao
- Department of Oral Biology and Pathology, School of Dental Medicine, State University of New York at Stony Brook, Stony Brook, NY 11794-8702, USA
| | | |
Collapse
|
175
|
Kotokorpi P, Ellis E, Parini P, Nilsson LM, Strom S, Steffensen KR, Gustafsson JA, Mode A. Physiological differences between human and rat primary hepatocytes in response to liver X receptor activation by 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy]phenylacetic acid hydrochloride (GW3965). Mol Pharmacol 2007; 72:947-55. [PMID: 17628011 DOI: 10.1124/mol.107.037358] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The liver is central to the maintenance of glucose and lipid homeostasis, and liver X receptors (LXRs) are key regulators of expression of the genes involved. So far, effects of activation of LXR in human hepatocytes have not been well characterized. Here we show that treatment of primary human hepatocytes with the synthetic LXR ligand 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy]phenylacetic acid hydrochloride (GW3965) results in reduced output of bile acids and very low density lipoprotein triglycerides and induced expression of adipose differentiation-related protein accompanied by increased lipid storage. Genome wide-expression profiling identified novel human LXR target genes in the glycolytic and lipogenic pathways and indicated that LXR activation reduced hepatic insulin sensitivity. Comparative experiments showed significant differences in the response to GW3965 between human and rat hepatocytes, raising the question as to how well rodent models reflect the human situation. In summary, the risk of hepatic steatosis upon pharmaceutical targeting of LXR may be a particularly serious consequence in humans.
Collapse
Affiliation(s)
- Pia Kotokorpi
- Dept of Biosciences and Nutrition, Karolinska Institutet, Novum, S-141 57 Huddinge, Sweden
| | | | | | | | | | | | | | | |
Collapse
|
176
|
Russell TD, Palmer CA, Orlicky DJ, Fischer A, Rudolph MC, Neville MC, McManaman JL. Cytoplasmic lipid droplet accumulation in developing mammary epithelial cells: roles of adipophilin and lipid metabolism. J Lipid Res 2007; 48:1463-75. [PMID: 17452747 DOI: 10.1194/jlr.m600474-jlr200] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PAT proteins (perilipin, adipophilin, and TIP47) are hypothesized to be critical regulators of lipid accumulation in eukaryotic cells. We investigated the developmental relationships between the expression of these proteins and cytoplasmic lipid droplet (CLD) accumulation in differentiating secretory epithelial cells in mouse mammary glands. Adipophilin (ADPH) specifically localized to CLD in differentiating and lactating mammary glands and was found exclusively in the secreted lipid droplet fraction of mouse milk. ADPH transcripts were selectively detected in secretory epithelial cells, and steady-state levels of both ADPH mRNA and protein increased during secretory differentiation in patterns consistent with functional linkage to CLD accumulation. TIP47 also was detected in secretory epithelial cells; however, it had a diffuse punctate appearance, and its mRNA and protein expression patterns did not correlate with CLD accumulation. Perilipin-positive adipose cells and steady-state levels of perilipin mRNA and protein decreased during mammary gland differentiation, suggesting a progressive loss of adipose lipid storage during this process. Collectively, these data demonstrate that increased ADPH expression is a specialized property of differentiated secretory epithelial cells and provide developmental evidence specifically linking increased ADPH expression to increased CLD accumulation. In addition, evidence is presented that the epithelial and adipose compartments of the mammary gland undergo concerted, developmentally regulated shifts in lipid metabolism that increase the availability of fatty acids necessary for lipid synthesis by milk-secreting cells.
Collapse
Affiliation(s)
- Tanya D Russell
- Graduate Programs in Molecular Biology, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Aurora, CO, USA
| | | | | | | | | | | | | |
Collapse
|
177
|
Imai Y, Varela GM, Jackson MB, Graham MJ, Crooke RM, Ahima RS. Reduction of hepatosteatosis and lipid levels by an adipose differentiation-related protein antisense oligonucleotide. Gastroenterology 2007; 132:1947-54. [PMID: 17484887 DOI: 10.1053/j.gastro.2007.02.046] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Accepted: 02/15/2007] [Indexed: 02/06/2023]
Abstract
BACKGROUND & AIMS Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive triglyceride accumulation in hepatocytes. Expression of the lipid droplet protein adipose differentiation-related protein (ADRP) is increased in NAFLD, but whether this is causally linked to hepatic lipid metabolism is unclear. We postulated that a reduction in ADRP would ameliorate hepatic steatosis and improve insulin action. METHODS Leptin deficient Lep(ob/ob) and diet-induced obese (DIO) mice were treated with antisense oligonucleotide (ASO) against ADRP, and effects on hepatic and serum lipids and glucose homeostasis were examined. RESULTS ADRP ASO specifically decreased ADRP mRNA and protein levels in the livers of Lep(ob/ob) and DIO mice, without altering the levels of other lipid droplet proteins, that is, S3-12 and TIP47. ADRP ASO suppressed expression of lipogenic genes, reduced liver triglyceride content without affecting cholesterol, attenuated triglyceride secretion, and decreased serum triglyceride and alanine aminotransaminase levels. The reduction in hepatic steatosis by ADRP ASO was associated with improvement in glucose homeostasis in both Lep(ob/ob) and DIO mice. CONCLUSIONS This study demonstrates a crucial role for the lipid droplet protein ADRP in regulation of lipid metabolism. Reduction in hepatic ADRP level using an antisense oligonucleotide reverses hepatic steatosis, hypertriglyceridemia, and insulin resistance in obese mice, suggesting that ADRP may be targeted for the treatment of NAFLD and associated lipid and glucose abnormalities.
Collapse
Affiliation(s)
- Yumi Imai
- Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19010, USA
| | | | | | | | | | | |
Collapse
|
178
|
Kessler F, Vidi PA. Plastoglobule lipid bodies: their functions in chloroplasts and their potential for applications. ADVANCES IN BIOCHEMICAL ENGINEERING/BIOTECHNOLOGY 2007; 107:153-72. [PMID: 17522825 DOI: 10.1007/10_2007_054] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Plastoglobules are plant lipid bodies localized inside plastids. They have long been considered as mere lipid storage compartments. However, ultrastructural and proteomic data now suggest their involvement in various metabolic pathways, notably the biosynthesis of tocopherols. In this work, the current knowledge on the structure and functions of plastoglobules is reviewed. On the basis of similarities between plastoglobules and seed oleosomes, the potential of plastoglobules for bioengineering applications is discussed.
Collapse
Affiliation(s)
- Felix Kessler
- Institute of Botany, University of Neuchâtel, Emile-Argand 11, CP158, 2009, Neuchâtel, Switzerland.
| | | |
Collapse
|
179
|
Wolins NE, Quaynor BK, Skinner JR, Tzekov A, Croce MA, Gropler MC, Varma V, Yao-Borengasser A, Rasouli N, Kern PA, Finck BN, Bickel PE. OXPAT/PAT-1 is a PPAR-induced lipid droplet protein that promotes fatty acid utilization. Diabetes 2006; 55:3418-28. [PMID: 17130488 DOI: 10.2337/db06-0399] [Citation(s) in RCA: 251] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Lipid droplet proteins of the PAT (perilipin, adipophilin, and TIP47) family regulate cellular neutral lipid stores. We have studied a new member of this family, PAT-1, and found that it is expressed in highly oxidative tissues. We refer to this protein as "OXPAT." Physiologic lipid loading of mouse liver by fasting enriches OXPAT in the lipid droplet tissue fraction. OXPAT resides on lipid droplets with the PAT protein adipophilin in primary cardiomyocytes. Ectopic expression of OXPAT promotes fatty acid-induced triacylglycerol accumulation, long-chain fatty acid oxidation, and mRNAs associated with oxidative metabolism. Consistent with these observations, OXPAT is induced in mouse adipose tissue, striated muscle, and liver by physiological (fasting), pathophysiological (insulin deficiency), pharmacological (peroxisome proliferator-activated receptor [PPAR] agonists), and genetic (muscle-specific PPARalpha overexpression) perturbations that increase fatty acid utilization. In humans with impaired glucose tolerance, PPARgamma agonist treatment induces adipose OXPAT mRNA. Further, adipose OXPAT mRNA negatively correlates with BMI in nondiabetic humans. Our collective data in cells, mice, and humans suggest that OXPAT is a marker for PPAR activation and fatty acid oxidation. OXPAT likely contributes to adaptive responses to the fatty acid burden that accompanies fasting, insulin deficiency, and overnutrition, responses that are defective in obesity and type 2 diabetes.
Collapse
Affiliation(s)
- Nathan E Wolins
- Department of Medicine, 660 S. Euclid Ave., Campus Box 8127, St. Louis, MO 63110, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
180
|
Fukushima M, Enjoji M, Kohjima M, Sugimoto R, Ohta S, Kotoh K, Kuniyoshi M, Kobayashi K, Imamura M, Inoguchi T, Nakamuta M, Nawata H. Adipose differentiation related protein induces lipid accumulation and lipid droplet formation in hepatic stellate cells. In Vitro Cell Dev Biol Anim 2006; 41:321-4. [PMID: 16448220 DOI: 10.1007/s11626-005-0002-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The function of adipose differentiation-related protein (ADRP) is known to be the uptake of long-chain fatty acids and formation of lipid droplets in lipid-accumulating cells. We hypothesized that ADRP might stimulate activated hepatic stellate cells (HSCs) to accumulate lipids, resulting in their transition to the quiescent state. In this study, cultured HSCs in fifth passages isolated from rat were infected by adenovirus vector expressing ADRP (Ad.GFP-ADRP), and morphologic and functional changes were evaluated in comparison with control HSCs infected by recombinant adenovirus-expressing beta-galactosidase (Ad.LacZ). In Ad.GFP-ADRP-infected cells only, many tiny lipid droplets were apparent in the cytoplasm, while the outline of the cells was not changed. The ADRP was detected around the lipid droplets. In HSCs with intracellular actin filaments, the staining pattern of the filaments before and after infection with Ad.GFP-ADRP or Ad.LacZ did not differ. The cell proliferation rate was not influenced by infection with Ad.LacZ or Ad.GFP-ADRP. Type I collagen secretion from cells overexpressing ADRP was not significantly different from that of Ad.LacZ-infected cells. In our in vitro study, ADRP overexpression induced the formation of cytoplasmic lipid droplets in activated HSCs but could not convert other characteristics of the activated form into those of the quiescent form.
Collapse
Affiliation(s)
- Marie Fukushima
- Department of Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
181
|
McManaman JL, Reyland ME, Thrower EC. Secretion and fluid transport mechanisms in the mammary gland: comparisons with the exocrine pancreas and the salivary gland. J Mammary Gland Biol Neoplasia 2006; 11:249-68. [PMID: 17136613 DOI: 10.1007/s10911-006-9031-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Milk is a complex fluid composed of proteins, sugars, lipids and minerals, in addition to a wide variety of bioactive molecules including vitamins, trace elements and growth factors. The composition of these components reflects the integrated activities of distinct synthetic, secretion and transport processes found in mammary epithelial cells, and mirrors the differing nutritional and developmental requirements of mammalian neonates. Five general pathways have been described for secretion of milk components. With the exception of lipids, which are secreted a unique pathway, milk components are thought to be secreted by adaptations of pathways found in other secretory organs. However little is known about the molecular and cellular mechanisms that constitute these pathways or the physiological mechanisms by which they are regulated. Comparisons of current secretion and transport models in the mammary gland, exocrine pancreas and salivary gland indicate that significant differences exist between the mammary gland and other exocrine organs in how proteins and lipids are packaged and secreted, and how fluid is transported.
Collapse
Affiliation(s)
- James L McManaman
- Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center at Fitzsimons, Mail Stop 8309, P.O. Box 6511, Aurora, CO 80045, USA.
| | | | | |
Collapse
|
182
|
Larigauderie G, Cuaz-Pérolin C, Younes AB, Furman C, Lasselin C, Copin C, Jaye M, Fruchart JC, Rouis M. Adipophilin increases triglyceride storage in human macrophages by stimulation of biosynthesis and inhibition of beta-oxidation. FEBS J 2006; 273:3498-510. [PMID: 16884492 DOI: 10.1111/j.1742-4658.2006.05357.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Lipid accumulation alters macrophage biology and contributes to lipid retention within the vessel wall. In this study, we investigated the role of adipophilin on triglyceride accumulation and lipid-droplet formation in THP-1-derived macrophages (THP-1 macrophages). In the presence of acetylated low-density lipoprotein, macrophages infected with an adenovirus expressing human adipophilin showed a 31% increase in triglyceride content and a greater number of lipid droplets compared with control cells. Incubation of macrophages with very low-density lipoprotein (VLDL) dramatically increased cellular triglyceride content similarly in control and adipophilin-overexpressing cells. By itself, VLDL increased adipophilin expression, which explains the lack of effect of adipophilin overexpression on cellular triglyceride content in macrophages loaded with VLDL. The lipid-droplet content of macrophages was increased by overexpression of adipophilin and/or loading with VLDL. In contrast, inhibition of adipophilin expression using siRNA prevented lipid-droplet formation and significantly reduced intracellular triglyceride content. Using inhibitors of beta-oxidation and acyl-coenzyme A synthetase, results were obtained which suggest that adipophilin elevates cellular lipids by inhibition of beta-oxidation and stimulation of long-chain fatty acid incorporation into triglycerides. Adipophilin expression in THP-1 macrophages altered the cellular content of different lipids and enhanced the size of lipid droplets, consistent with a role for adipophilin in human foam cell formation.
Collapse
|
183
|
Wolins NE, Brasaemle DL, Bickel PE. A proposed model of fat packaging by exchangeable lipid droplet proteins. FEBS Lett 2006; 580:5484-91. [PMID: 16962104 DOI: 10.1016/j.febslet.2006.08.040] [Citation(s) in RCA: 309] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Revised: 08/22/2006] [Accepted: 08/22/2006] [Indexed: 01/10/2023]
Abstract
Humans have evolved mechanisms of efficient fat storage to survive famine, but these mechanisms contribute to obesity in our current environment of plentiful food and reduced activity. Little is known about how animals package fat within cells. Five related structural proteins serve roles in packaging fat into lipid droplets. The proteins TIP47, S3-12, and OXPAT/MLDP/PAT-1 move from the cytosol to coat nascent lipid droplets during rapid fat storage. In contrast, perilipin and adipophilin constitutively associate with lipid droplets and play roles in sustained fat storage and regulation of lipolysis. Different tissues express different complements of these lipid droplet proteins. Thus, the tissue-specific complement of these proteins determines how tissues manage lipid stores.
Collapse
Affiliation(s)
- Nathan E Wolins
- Department of Medicine, Division of Endocrinology, Metabolism and Lipid Research, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | | | | |
Collapse
|
184
|
Bozza PT, Melo RCN, Bandeira-Melo C. Leukocyte lipid bodies regulation and function: contribution to allergy and host defense. Pharmacol Ther 2006; 113:30-49. [PMID: 16945418 DOI: 10.1016/j.pharmthera.2006.06.006] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Accepted: 06/20/2006] [Indexed: 12/21/2022]
Abstract
Lipid bodies are lipid-rich organelles found in the cytoplasm of a variety of cells, including leukocytes. Lipid body morphology, its ability to interact with other organelles and its functions are dictated by its lipid arrangement, as well as its protein composition. Both may vary according to the cell type and with the specific lipid body biogenic stimulatory pathways. Nascent lipid bodies, which are formed in vivo in the course of a variety of immunopathological conditions, are sites of enzyme localization, eicosanoid production, as well as, sites for cytokine storage in inflammatory leukocytes, suggesting that lipid bodies function as inducible intracellular platforms for spatial segregation and organization of signaling leading to inflammatory mediator secretion during inflammation. The emerging role of lipid bodies as inflammatory organelles raises lipid body status to critical regulators of different inflammatory diseases, key markers of leukocyte activation and attractive targets for novel anti-inflammatory therapies.
Collapse
Affiliation(s)
- Patricia T Bozza
- Laboratório de Imunofarmacologia, Departamento de Fisiologia e Farmacodinâmica, IOC, Fundação Oswaldo Cruz, Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21045-900, Brazil.
| | | | | |
Collapse
|
185
|
Gao JG, Simon M. Molecular Screening for GS2 Lipase Regulators: Inhibition of Keratinocyte Retinylester Hydrolysis by TIP47. J Invest Dermatol 2006; 126:2087-95. [PMID: 16741517 DOI: 10.1038/sj.jid.5700327] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Retinoic acid at nanomolar concentrations modulates epidermal functions by serving as a transcription factor ligand. Under conditions of retinol sufficiency, it is imperative to limit retinoic acid biosynthesis from serum-derived retinol. In the epidermis, this is accomplished by esterifying retinol with long-chain fatty acids. Retinylester (RE) pools serve as a source of retinol for retinoic acid production under retinol deficiency and when required for proper differentiation. We have recently reported that GS2 lipase is expressed in keratinocytes and has the enzymatic properties of keratinocyte RE hydrolase. As GS2 lipase has a robust activity that can affect the intracellular retinol levels, we postulated that its activity must be regulated. Therefore, we screened keratinocyte cDNA expression libraries for the putative inhibitor. Herein, we report the identity of an inhibitor, TIP47, which prevents RE hydrolysis catalyzed by GS2 lipase and hormone-sensitive lipase. This protein was known to transport mannose-6-phosphate receptors from endosome to trans-Golgi and to be distributed between the cytoplasm and lipid droplets. Using a series of deletion mutants, we found two regions involved in the inhibitory activity. Residues within the carboxyl alpha3-alpha4 helices are essential in the context of the full-length protein. Residues within the amino-terminal also contribute depending on the context.
Collapse
Affiliation(s)
- Jay G Gao
- Department of Oral Biology and Pathology, School of Dental Medicine, State University of New York at Stony Brook, USA
| | | |
Collapse
|
186
|
Abstract
Lipid droplets form the main lipid store in eukaryotic cells. Although all cells seem to be able to generate lipid droplets, their biogenesis, regulatory mechanisms and interactions with other organelles remain largely elusive. In this article, we outline some of the recent developments in lipid droplet cell biology. We show the mobile and dynamic nature of this organelle, and advocate the adoption of a unified nomenclature to consolidate terminology in this emerging field.
Collapse
Affiliation(s)
- Sally Martin
- Institute for Molecular Bioscience, and Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, QLD 4072, Australia
| | | |
Collapse
|
187
|
Boström P, Magnusson B, Svensson PA, Wiklund O, Borén J, Carlsson LMS, Ståhlman M, Olofsson SO, Hultén LM. Hypoxia converts human macrophages into triglyceride-loaded foam cells. Arterioscler Thromb Vasc Biol 2006; 26:1871-6. [PMID: 16741148 DOI: 10.1161/01.atv.0000229665.78997.0b] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVE Atherosclerotic lesions have regions that are hypoxic. Because the lesion contains macrophages that are loaded with lipid, we investigated whether hypoxia can influence the accumulation of lipids in these cells. METHODS AND RESULTS Exposure of human macrophages to hypoxia for 24 hours resulted in an increased formation of cytosolic lipid droplets and an increased accumulation of triglycerides. Exposure of the macrophages to oxidized low-density lipoprotein (oxLDL) increased the accumulation of cytosolic lipid droplets because of an increase in cellular cholesterol esters. The accumulation of lipid droplets in oxLDL-treated cells was further increased after hypoxia, caused by an increased level of triglycerides. Expression analyses combined with immunoblot or RT-PCR demonstrated that hypoxia increased the expression of several genes that could promote the accumulation of lipid droplets. Hypoxia increased the mRNA and protein levels of adipocyte differentiation-related protein (ADRP). It is well known that an increased expression of ADRP increases the formation of lipid droplets. Hypoxia decreased the expression of enzymes involved in beta-oxidation (acyl-coenzyme A synthetase and acyl-coenzyme A dehydrogenase) and increased the expression of stearoyl-coenzyme A desaturase, an important enzyme in the fatty acid biosynthesis. Moreover, exposure to hypoxia decreased the rate of beta-oxidation, whereas the accumulation of triglycerides increased. CONCLUSIONS The results demonstrate that exposure of human macrophages to hypoxia causes an accumulation of triglyceride-containing cytosolic lipid droplets. This indicates that the hypoxia present in atherosclerotic lesions can contribute to the formation of the lipid-loaded macrophages that characterize the lesion and to the accumulation of triglycerides in such lesions.
Collapse
Affiliation(s)
- Pontus Boström
- Wallenberg Laboratory for Cardiovascular Research, Sahlgrenska Academy, Göteborg, Sweden
| | | | | | | | | | | | | | | | | |
Collapse
|
188
|
Yan J, Luo D, Luo Y, Gao X, Zhang G. Induction of G1 arrest and differentiation in MDA-MB-231 breast cancer cell by boehmeriasin A, a novel compound from plant. Int J Gynecol Cancer 2006; 16:165-70. [PMID: 16445628 DOI: 10.1111/j.1525-1438.2006.00291.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Boehmeriasin A is a new phenanthroquinolizidine alkaloid recently isolated from the Boehmeria siamensis Craib (Urticaceae). In vitro biological activity assay demonstrated that this novel compound has wide-range, strong antitumor activity. This study is aimed to determine the effects of boehmeriasin A on breast cancer cell (MDA-MB-231 cell line). Proliferation assay and fluorescence activated cell sorter (FACS) showed that cell growth inhibition and G1 phase arrest of cell cycle were caused by boehmeriasin A. The concentrations resulting in total and 50% growth inhibition are 0.007 and 0.0035 microg/mL, respectively. Exposed in 0.007 microg/mL boehmeriasin A for 12 h, the G1 phase cell percent increased from 44.8% pre-drug treatment to 66.3%. Consistent with G1 arrest and cell growth inhibition, cyclin E2 and cyclin D1 messenger RNA expression in the cell was down-regulated with drug treatment. Then, few apoptotic cells were detected, and most other cells underwent differentiation, which is characterized by specific changes in cell morphology, lots of lipid droplet accumulation, and increasing expression of adipocyte differentiation-related protein. The result first demonstrates that boehmeriasin A potently inhibits the proliferation of breast cancer cell MDA-MB-231 via the G1 phase cell cycle arrest and differentiation induction, and as such, may be considered as candidate chemotherapeutic and/or chemopreventive agent for breast cancer.
Collapse
Affiliation(s)
- J Yan
- Institute of materia medica, Di Ao Pharmaceutical Group, Chengdu 610041, People's Republic of China
| | | | | | | | | |
Collapse
|
189
|
Magnusson B, Asp L, Boström P, Ruiz M, Stillemark-Billton P, Lindén D, Borén J, Olofsson SO. Adipocyte differentiation-related protein promotes fatty acid storage in cytosolic triglycerides and inhibits secretion of very low-density lipoproteins. Arterioscler Thromb Vasc Biol 2006; 26:1566-71. [PMID: 16627799 DOI: 10.1161/01.atv.0000223345.11820.da] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE We investigated the role of adipocyte differentiation-related protein (ADRP) in triglyceride turnover and in the secretion of very low-density lipoprotein (VLDL) from McA-RH7777 cells and primary rat hepatocytes. METHODS AND RESULTS An increase in the expression of ADRP increased triglyceride accumulation in cytosolic lipid droplets and prevented the incorporation of fatty acids into secretable triglycerides, thereby reducing the secretion of triglycerides as well as of apolipoprotein B-100 (apoB-100) and apoB-48 VLDL. The ability of ADRP to block the secretion of apoB-100 VLDL1 decreased with increasing quantities of fatty acids in the medium, indicating a saturable process and emphasizing the importance of sequestering of fatty acids for the effect of ADRP on VLDL secretion. Knockdown (small interfering RNA) of ADRP decreased the pool of cytosolic lipid droplets but increased only the secretion of apoB-48 VLDL1. Additionally, there was an increased flow of fatty acids into beta-oxidation. CONCLUSIONS ADRP is essential for the accumulation of triglycerides in cytosolic lipid droplets. An increase in ADRP prevents the formation of VLDL by diverting fatty acids from the VLDL assembly pathway into cytosolic triglycerides, whereas a decrease of the protein increases the sorting of fatty acids to beta-oxidation and promotes the secretion of apoB-48 VLDL1.
Collapse
Affiliation(s)
- Björn Magnusson
- Wallenberg Laboratory for Cardiovascular Research, Göteborg University, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden
| | | | | | | | | | | | | | | |
Collapse
|
190
|
Yamaguchi T, Matsushita S, Motojima K, Hirose F, Osumi T. MLDP, a novel PAT family protein localized to lipid droplets and enriched in the heart, is regulated by peroxisome proliferator-activated receptor alpha. J Biol Chem 2006; 281:14232-40. [PMID: 16571721 DOI: 10.1074/jbc.m601682200] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Cytosolic lipid droplets (LDs) are multifunctional organelles that exist in all types of eukaryotic cells and control lipid homeostasis. In mammalian cells LDs contain a class of proteins in their surface layers that share a homologous sequence called the PAT domain, including perilipin, adipose differentiation-related protein (ADRP), a tail-interacting protein of 47 kDa (TIP47), and S3-12, which are distributed tissue- or cell type-selectively. Expression in some cases is regulated by peroxisome proliferator-activated receptors (PPARs). In this study we identified a new PAT family member named MLDP (myocardial LD protein) in a murine cDNA data base and showed the mRNA and protein to be highly enriched in the heart and also expressed at lower levels in the liver and adrenals. Upon subcellular fractionation, a substantial amount of MLDP was detected in the top fraction enriched with LDs. Furthermore, overexpressed MLDP tagged with green fluorescent protein accumulated at the surfaces of LDs and co-localized with perilipin and ADRP. Deletion analysis demonstrated the N-terminal region containing a PAT-1 domain and the following 33-mer domain to be required for targeting of MLDP to LDs. MLDP was found to be up-regulated at both mRNA and protein levels in the heart and liver by a selective ligand for PPARalpha, Wy14,643, but not in PPARalpha knock-out mice. MLDP expression was also increased upon fasting in parallel with ADRP. These results indicate that MLDP is a bona fide new PAT family member localized in LDs. Its expression depends on the physiological conditions and the action of PPARalpha.
Collapse
Affiliation(s)
- Tomohiro Yamaguchi
- Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo, 678-1297, Japan
| | | | | | | | | |
Collapse
|
191
|
Wei P, Taniguchi S, Sakai Y, Imamura M, Inoguchi T, Nawata H, Oda S, Nakabeppu Y, Nishimura J, Ikuyama S. Expression of adipose differentiation-related protein (ADRP) is conjointly regulated by PU.1 and AP-1 in macrophages. J Biochem 2006; 138:399-412. [PMID: 16272134 DOI: 10.1093/jb/mvi136] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
ADRP is associated with intracellular lipid droplets. We demonstrate the regulatory mechanism for ADRP expression in RAW264.7 macrophages. The ADRP mRNA expression was stimulated by PMA, and synergistically enhanced in association with its protein level in the presence of lipids. A proteasome inhibitor protected the protein from degradation under the lipid-free conditions. One of the possible sites of the PMA action was proved to be an Ets/AP-1 element in the promoter, since mutations of this site reduced the PMA-induced promoter activity, and ligation of this element led to a significant increase in the PMA-responsiveness of homologous or heterologous promoters. Mutations of this site diminished the synergistic effect on the promoter activity induced by PMA and oleic acid, suggesting a possible interaction between this site and the downstream PPARdelta site. EMSA revealed that PU.1 and AP-1 conjointly bound to this site. The juxtaposition of the two sequences was requisite for full activity, since spacer sequences between them decreased the PMA-induced activity. PI3 kinase inhibitor was found to reduce the PMA-induced mRNA expression and promoter activity in parallel with PU.1/AP-1 complex formation on EMSA. From these results, we concluded that the Ets/AP-1 site is an important cis-acting element that regulates the ADRP gene expression in macrophages.
Collapse
Affiliation(s)
- Ping Wei
- Division of Clinical Immunology, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, Beppu 874-0838, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
192
|
Dalen KT, Ulven SM, Arntsen BM, Solaas K, Nebb HI. PPARalpha activators and fasting induce the expression of adipose differentiation-related protein in liver. J Lipid Res 2006; 47:931-43. [PMID: 16489205 DOI: 10.1194/jlr.m500459-jlr200] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT (for perilipin, ADFP, and TIP47) proteins that associate on the surface of lipid droplets (LDs). Except for LD association, a clear role for ADFP has not been found. We demonstrate that ADFP is transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPARalpha) in mouse liver and rat and human hepatoma cells through a highly conserved direct repeat-1(DR-1) element. Although the ADFP mRNA is highly increased by a synthetic PPARalpha agonist, the ADFP protein is only substantially increased in cells containing LDs, such as hepatocytes incubated with fatty acids, and in livers of fasted mice. ADFP is induced by fasting even in the absence of a functional PPARalpha, in marked contrast to the PPARalpha target gene acyl-coenzyme A oxidase-1. Activation of LXRs, which stimulates LD formation through the activation of lipogenesis, does not affect ADFP mRNA levels. TIP47, another PAT member known to be expressed in liver, was unaffected by all treatments. This constitutively expressed PAT member seems to be less transcriptionally regulated than ADFP. These observations suggest that ADFP is primarily a fasting-induced protein in liver that coats the newly synthesized triacylglycerol-containing LDs formed during fasting.
Collapse
Affiliation(s)
- Knut Tomas Dalen
- Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Norway
| | | | | | | | | |
Collapse
|
193
|
Chang BHJ, Li L, Paul A, Taniguchi S, Nannegari V, Heird WC, Chan L. Protection against fatty liver but normal adipogenesis in mice lacking adipose differentiation-related protein. Mol Cell Biol 2006; 26:1063-76. [PMID: 16428458 PMCID: PMC1347045 DOI: 10.1128/mcb.26.3.1063-1076.2006] [Citation(s) in RCA: 247] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2005] [Accepted: 11/09/2005] [Indexed: 01/19/2023] Open
Abstract
Adipose differentiation-related protein (ADFP; also known as ADRP or adipophilin), is a lipid droplet (LD) protein found in most cells and tissues. ADFP expression is strongly induced in cells with increased lipid load. We have inactivated the Adfp gene in mice to better understand its role in lipid accumulation. The Adfp-deficient mice have unaltered adipose differentiation or lipolysis in vitro or in vivo. Importantly, they display a 60% reduction in hepatic triglyceride (TG) and are resistant to diet-induced fatty liver. To determine the mechanism for the reduced hepatic TG content, we measured hepatic lipogenesis, very-low-density lipoprotein (VLDL) secretion, and lipid uptake and utilization, all of which parameters were shown to be similar between mutant and wild-type mice. The finding of similar VLDL output in the presence of a reduction in total TG in the Adfp-deficient liver is explained by the retention of TG in the microsomes where VLDL is assembled. Given that lipid droplets are thought to form from the outer leaflet of the microsomal membrane, the reduction of TG in the cytosol with concomitant accumulation of TG in the microsome of Adfp-/- cells suggests that ADFP may facilitate the formation of new LDs. In the absence of ADFP, impairment of LD formation is associated with the accumulation of microsomal TG but a reduction in TG in other subcellular compartments.
Collapse
Affiliation(s)
- Benny Hung-Junn Chang
- Division of Diabetes, Endocrinology, and Metabolism, Departments of Medicine and Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
| | | | | | | | | | | | | |
Collapse
|
194
|
Tobin KAR, Harsem NK, Dalen KT, Staff AC, Nebb HI, Duttaroy AK. Regulation of ADRP expression by long-chain polyunsaturated fatty acids in BeWo cells, a human placental choriocarcinoma cell line. J Lipid Res 2006; 47:815-23. [PMID: 16391323 DOI: 10.1194/jlr.m500527-jlr200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Transplacental transfer of maternal fatty acids is critical for fetal growth and development. In the placenta, a preferential uptake of fatty acids toward long-chain polyunsaturated fatty acids (LCPUFAs) has been demonstrated. Adipose differentiation-related protein (ADRP) is a lipid droplet-associated protein that has been ascribed a role in cellular fatty acid uptake and storage. However, its role in placenta is not known. We demonstrate that ADRP mRNA and protein are regulated by fatty acids in a human placental choriocarcinoma cell line (BeWo) and in primary human trophoblasts. LCPUFAs of the n-3 and n-6 series [arachidonic acid (20:4n-6), docosahexaenoic acid (22:6n-3), and eicosapentaenoic acid (20:5n-3)] were more efficient than shorter fatty acids at stimulating ADRP mRNA expression. The fatty acid-mediated increase in ADRP mRNA expression was not related to the differentiation state of the cells. Synthetic peroxisome proliferator-activated receptor and retinoic X receptor agonists increased ADRP mRNA level but had no effect on ADRP protein level in undifferentiated BeWo cells. Furthermore, we show that incubation of BeWo cells with LCPUFAs, but not synthetic agonists, increased the cellular content of radiolabeled oleic acid, coinciding with the increase in ADRP mRNA and protein level. These studies provide new information on the regulation of ADRP in placental trophoblasts and suggest that LCPUFA-dependent regulation of ADRP could be involved in the metabolism of lipids in the placenta.
Collapse
Affiliation(s)
- Kari Anne Risan Tobin
- Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
| | | | | | | | | | | |
Collapse
|
195
|
Vernet N, Dennefeld C, Rochette-Egly C, Oulad-Abdelghani M, Chambon P, Ghyselinck NB, Mark M. Retinoic acid metabolism and signaling pathways in the adult and developing mouse testis. Endocrinology 2006; 147:96-110. [PMID: 16210368 DOI: 10.1210/en.2005-0953] [Citation(s) in RCA: 188] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
As a first step in investigating the role of retinoic acid (RA) in mouse testis, we analyzed the distribution pattern of the enzymes involved in vitamin A storage (lecithin:retinol acyltransferase), RA synthesis (beta-carotene 15,15'-monoxygenase and retinaldehyde dehydrogenases) and RA degradation (cytochrome P450 hydroxylases) as well as those of all isotypes of receptors transducing the RA signal [RA receptors (RARs) and rexinoid receptors (RXRs)]. Our data indicate that in adult testis 1) cytochrome P450 hydroxylase enzymes may generate in peritubular myoid cells a catabolic barrier that prevents circulating RA and RA synthesized by Leydig cells to enter the seminiferous epithelium; 2) the compartmentalization of RA synthesis within this epithelium may modulate, through paracrine mechanisms, the coupling between spermatogonia proliferation and spermatogenesis; 3) retinyl esters synthesized in round spermatids by lecithin:retinol acyltransferase may be transferred and stored in Sertoli cells, in the form of adipose differentiation-related protein-coated lipid droplets. We also show that RARalpha and RXRbeta are confined to Sertoli cells, whereas RARgamma is expressed in spermatogonia and RARbeta, RXRalpha, and RXRgamma are colocalized in step 7-8 spermatids. Correlating these expression patterns with the pathological phenotypes generated in response to RAR and RXR mutations and to postnatal vitamin A deficiency suggests that spermiation requires RXRbeta/RARalpha heterodimers in Sertoli cells, whereas spermatogonia proliferation involves, independently of RXR, two distinct RAR-mediated signaling pathways in both Sertoli cells and spermatogonia. Our data also suggest that the involvement of RA in testis development starts when primary spermatogonia first appear.
Collapse
Affiliation(s)
- Nadège Vernet
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique/Université Louis Pasteur de Strasbourg (ULP)/Collège de France, 67404 Illkirch Cedex, Communauté Urbaine de Strasbourg, France
| | | | | | | | | | | | | |
Collapse
|
196
|
Edvardsson U, Ljungberg A, Lindén D, William-Olsson L, Peilot-Sjögren H, Ahnmark A, Oscarsson J. PPARalpha activation increases triglyceride mass and adipose differentiation-related protein in hepatocytes. J Lipid Res 2005; 47:329-40. [PMID: 16282640 DOI: 10.1194/jlr.m500203-jlr200] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adipose differentiation-related protein (ADRP) is a lipid droplet-associated protein that is expressed in various tissues. In mice treated with the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist Wy14,643 (Wy), hepatic mRNA and protein levels of ADRP as well as hepatic triglyceride content increased. Also in primary mouse hepatocytes, Wy increased ADRP expression and intracellular triglyceride mass. The triglyceride mass increased in spite of unchanged triglyceride biosynthesis and increased palmitic acid oxidation. However, Wy incubation decreased the secretion of newly synthesized triglycerides, whereas apolipoprotein B secretion increased. Thus, decreased availability of triglycerides for VLDL assembly could help to explain the cellular accumulation of triglycerides after Wy treatment. We hypothesized that this effect could be mediated by increased ADRP expression. Similar to PPARalpha activation, adenovirus-mediated ADRP overexpression in mouse hepatocytes enhanced cellular triglyceride mass and decreased the secretion of newly synthesized triglycerides. In ADRP-overexpressing cells, Wy incubation resulted in a further decrease in triglyceride secretion. This effect of Wy was not attributable to decreased cellular triglycerides after increased fatty acid oxidation because the triglyceride mass in Wy-treated ADRP-overexpressing cells was unchanged. In summary, PPARalpha activation prevents the availability of triglycerides for VLDL assembly and increases hepatic triglyceride content in part by increasing the expression of ADRP.
Collapse
Affiliation(s)
- Ulrika Edvardsson
- Wallenberg Laboratory for Cardiovascular Research, Sahlgrenska University Hospital, Göteborg, Sweden.
| | | | | | | | | | | | | |
Collapse
|
197
|
Masuda Y, Itabe H, Odaki M, Hama K, Fujimoto Y, Mori M, Sasabe N, Aoki J, Arai H, Takano T. ADRP/adipophilin is degraded through the proteasome-dependent pathway during regression of lipid-storing cells. J Lipid Res 2005; 47:87-98. [PMID: 16230742 DOI: 10.1194/jlr.m500170-jlr200] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Adipose differentiation-related protein (ADRP) is a major protein associated with lipid droplets in various types of cells, including macrophage-derived foam cells and liver cells. However, the role of ADRP in the processes of formation and regression of these cells is not understood. When J774 murine macrophages were incubated with either VLDL or oleic acid, their content of both ADRP and triacylglycerol (TG) increased 3- to 4-fold. Induction of ADRP during TG accumulation was also observed in oleic acid-treated HuH-7 human liver cells. Addition of triacsin C, a potent inhibitor of acyl-CoA synthase, for 6 h decreased the amount of TG in VLDL-induced foam cells and oleic acid-treated liver cells; it decreased the amount of ADRP protein in parallel, indicating the amount of ADRP reduced during regression of the lipid-storing cells. Addition of a proteasome inhibitor during triacsin C treatment abolished the ADRP decrease and accumulated polyubiquitinated ADRP. In addition, the proteasome inhibitor reversed not only the degradation of ADRP but also TG reduction by triacsin C. These results suggest that cellular amounts of ADRP and TG regulate each other and that the ubiquitin-proteasome system is involved in degradation of ADRP during regression of lipid-storing cells.
Collapse
Affiliation(s)
- Yutaka Masuda
- Department of Biological Chemistry, School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
198
|
Jelinsky SA, Miyashiro JS, Saraf KA, Tunkey C, Reddy P, Newcombe J, Oestreicher JL, Brown E, Trepicchio WL, Leonard JP, Marusic S. Exploiting genotypic differences to identify genes important for EAE development. J Neurol Sci 2005; 239:81-93. [PMID: 16214174 DOI: 10.1016/j.jns.2005.08.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2005] [Revised: 07/08/2005] [Accepted: 08/09/2005] [Indexed: 10/25/2022]
Abstract
Experimental autoimmune encephalomyelitis (EAE) is an animal model of the human autoimmune disease multiple sclerosis (MS) and is primarily driven by T helper type 1 (Th1) cells. Interleukin (IL)-12 and interferon (IFN)-gamma are important cytokines involved in the differentiation and amplification of Th1 cells, however mice deficient in either IFN-gamma or IL-12 still develop EAE. We have used microarray analysis of EAE-affected CNS tissues in wild-type, IFN-gamma -/- and IL-12 -/- animals to identify genes critical for development of EAE. Over 500 genes were regulated in at least one genotype and over 94 genes were regulated in all three. Of those, 17 were also upregulated in spleen during the disease. We show that a majority of the genes regulated in EAE are also regulated in diseased regions of human MS tissues. The genes in the pool of 94 are more likely to be found regulated in MS patients than the genes regulated in only one or two of the mouse strains suggesting that analyzing gene expression under these multiple genetic conditions may lead to better identification of the genes critical for disease development.
Collapse
Affiliation(s)
- Scott A Jelinsky
- Molecular Profiling and Biomarker Discover, Biological Technologies Department, Wyeth Research, 87 Cambridge Park Drive, Cambridge MA 02140, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
199
|
Hanlon PR, Cimafranca MA, Liu X, Cho YC, Jefcoate CR. Microarray analysis of early adipogenesis in C3H10T1/2 cells: cooperative inhibitory effects of growth factors and 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol Appl Pharmacol 2005; 207:39-58. [PMID: 16054899 DOI: 10.1016/j.taap.2004.12.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2004] [Revised: 11/24/2004] [Accepted: 12/09/2004] [Indexed: 11/17/2022]
Abstract
C3H10T1/2 mouse embryo fibroblasts differentiate into adipocytes when stimulated by a standard hormonal mixture (IDMB). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), via the aryl hydrocarbon receptor (AhR), inhibits induction of the key adipogenic gene peroxisome proliferator-activated receptor gamma (PPARgamma) and subsequent adipogenesis. This TCDD-mediated inhibition requires activation of the extracellular signal-regulated kinase (ERK) pathway, which can be accomplished by serum, epidermal growth factor (EGF), or fibroblast growth factor (FGF). In the absence of serum or growth factors, IDMB induced adipogenesis without mitosis. Microarray analysis identified 200 genes that exhibited expression changes of at least twofold after 24 h of IDMB treatment. This time precedes most PPARgamma stimulation but follows the period of TCDD/ERK cooperation and periods of increased cell contraction and DNA synthesis. Functionally related gene clusters include genes associated with cell structure, triglyceride and cholesterol metabolism, oxidative regulation, and secreted proteins. In the absence of growth factors TCDD inhibited 30% of these IDMB responses without inhibiting the process of differentiation. A combination of EGF and TCDD that blocks differentiation cooperatively blocked a further 44 IDMB-responsive genes, most of which have functional links to differentiation, including PPARgamma. Cell cycle regulators that are stimulated by EGF were substantially inhibited by IDMB but these responses were unaffected by TCDD. By contrast, TCDD and EGF cooperatively reversed IDMB-induced changes in cell adhesion complexes immediately prior to increases in PPARgamma1 expression. Changes in adhesion-linked signaling may play a key role in TCDD affects on differentiation.
Collapse
Affiliation(s)
- Paul R Hanlon
- Molecular and Environmental Toxicology Center, University of Wisconsin-Madison, WI 53706, USA
| | | | | | | | | |
Collapse
|
200
|
Boström P, Rutberg M, Ericsson J, Holmdahl P, Andersson L, Frohman MA, Borén J, Olofsson SO. Cytosolic Lipid Droplets Increase in Size by Microtubule-Dependent Complex Formation. Arterioscler Thromb Vasc Biol 2005; 25:1945-51. [PMID: 16051877 DOI: 10.1161/01.atv.0000179676.41064.d4] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Objectives—
Adipocyte differentiation-related protein (ADRP)-containing lipid droplets have an essential role in the development of insulin resistance and atherosclerosis. Such droplets form in a cell-free system with a diameter of 0.1 to 0.4 μm, while the droplets present in cells vary in size, from small to very large, suggesting that the droplets can increase in size after being assembled. We have addressed this possibility.
Methods and Results—
Experiments in NIH 3T3 cells demonstrated that the lipid droplets could increase in size independently of triglyceride biosynthesis. NIH 3T3 cells were either microinjected with ADRP–GFP (green fluorescent protein) or stained with Nile Red and followed by confocal microscopy and time-lapse recordings. The results showed that lipid droplets formed complexes with each other, with a volume equal to the sum of the merging particles. The formation of complexes could be inhibited by the nocodazole-induced depolymerization of the microtubules; thus, the process is dependent on microtubules. The presence of dynein on ADRP-containing droplets supports a role for this motor protein.
Conclusions—
Lipid droplets can grow after they have been assembled. This increase in size is independent of triglyceride biosynthesis and involves formation of complexes, which requires intact microtubules.
Collapse
Affiliation(s)
- Pontus Boström
- Wallenberg Laboratory for Cardiovascular Research, Göteborg University, Göteborg, Sweden
| | | | | | | | | | | | | | | |
Collapse
|