HDL-mediated cholesterol uptake and targeting to lipid droplets in adipocytes

Abstract

Adipocytes express high levels of the HDL scavenger receptor class B type I in a differentiation-dependent manner. We thus have analyzed the routes of HDL cholesterol trafficking at different phases of adipocyte differentiation in the 3T3-L1 cell line. One novel and salient feature of this paper is the observation of a widespread distribution in the cell cytoplasm of Golgi markers, caveolin-2, and a fluorescent cholesterol analog NBD-cholesterol (NBD-chol), observed in the early phases of adipocyte formation, clearly distinct from that observed in mature fat cells (i.e., with fully formed lipid vesicles). Thus, in cells without visible lipid droplets, Golgi markers (Golgi 58K, Golgin 97, trans-Golgi network 38, Rab 6, and BODIPY-ceramide), caveolin-2, and NBD-chol all colocalize in a widespread distribution in the cell. In contrast, when lipid droplets are fully formed at latter stages, these markers clearly are distributed to distinct cell compartments: a compact juxtanuclear structure for the Golgi markers and caveolin-2, while NDB-chol concentrates in lipid droplets.In addition, disorganization of the Golgi using three different agents (Brefeldin, monensin, and N-ethyl-maleimide) drastically reduces NBD-chol uptake at different phases of adipocyte formation, strongly suggesting that the Golgi apparatus plays a critical role in HDL-mediated NBD uptake and routing to lipid droplets. Adipocytes express high levels of the HDL scavenger receptor class B type I in a differentiation-dependent manner. We thus have analyzed the routes of HDL cholesterol trafficking at different phases of adipocyte differentiation in the 3T3-L1 cell line. One novel and salient feature of this paper is the observation of a widespread distribution in the cell cytoplasm of Golgi markers, caveolin-2, and a fluorescent cholesterol analog NBD-cholesterol (NBD-chol), observed in the early phases of adipocyte formation, clearly distinct from that observed in mature fat cells (i.e., with fully formed lipid vesicles). Thus, in cells without visible lipid droplets, Golgi markers (Golgi 58K, Golgin 97, trans-Golgi network 38, Rab 6, and BODIPY-ceramide), caveolin-2, and NBD-chol all colocalize in a widespread distribution in the cell. In contrast, when lipid droplets are fully formed at latter stages, these markers clearly are distributed to distinct cell compartments: a compact juxtanuclear structure for the Golgi markers and caveolin-2, while NDB-chol concentrates in lipid droplets. In addition, disorganization of the Golgi using three different agents (Brefeldin, monensin, and N-ethyl-maleimide) drastically reduces NBD-chol uptake at different phases of adipocyte formation, strongly suggesting that the Golgi apparatus plays a critical role in HDL-mediated NBD uptake and routing to lipid droplets. Cholesterol is a crucial component of cell membranes, and as such plays a key role in the regulation of signal transduction (1Simons K. Toomre D. Lipid rafts and signal transduction.Nat. Rev. Mol. Cell Biol. 2000; 1: 31-39Google Scholar) and gene expression (2Goldstein J.L. Brown M.S. Regulation of the mevalonate pathway.Nature. 1990; 343: 425-430Google Scholar). The homeostasis of cell cholesterol is maintained through complex mechanisms that imply biosynthesis, uptake, and constant recycling between membranes. Many intracellular organelles take part in the regulation of cholesterol trafficking. Among these, the endosomal lysosomal pathway is involved in the uptake of exogenous cholesterol from LDL; caveolae are engaged in cholesterol trafficking to and from the plasma membrane; the endoplasmic reticulum (ER), where some of the enzymes of the cholesterol biosynthetic pathway reside, is of particular importance because it includes a cell cholesterol sensor system linked to the cleavage activating protein sterol-regulatory element binding proteins (SREBP) system (3Brown M.S. Goldstein J.L. The SREBP pathway: regulation of cholesterol metabolism by proteolysis of a membrane-bound transcription factor.Cell. 1997; 89: 331-340Google Scholar); and the Golgi apparatus plays a crucial role in sorting processes (4Anderson R.G. Pathak R.K. Vesicles and cisternae in the trans Golgi apparatus of human fibroblasts are acidic compartments.Cell. 1985; 40: 635-643Google Scholar, 5Fielding P.E. Fielding C.J. Intracellular transport of low density lipoprotein derived free cholesterol begins at clathrin-coated pits and terminates at cell surface caveolae.Biochemistry. 1996; 35: 14932-14938Google Scholar, 6Mendez A. Uint L. Apolipoprotein-mediated cellular cholesterol and phospholipid efflux depend on a functional Golgi apparatus.J. Lipid Res. 1996; 37: 2510-2524Google Scholar, 7Mendez A.J. Monensin and Brefeldin A inhibit high density lipoprotein-mediated cholesterol efflux from cholesterol-enriched cells.J. Biol. Chem. 1995; 270: 5891-5900Google Scholar). Recently, previously unrecognized organelles have been identified as new players in cholesterol traffic: the cytoplasmic lipid droplets (8Murphy D.J. The biogenesis and functions of lipid bodies in animals, plants and microorganisms.Prog. Lipid Res. 2001; 40: 325-438Google Scholar). The adipocyte is the unique cell type in which triglyceride-rich lipid droplets are present continuously and physiologically in the cytoplasm. Free cholesterol is also found in adipocyte lipid droplets (9Le Lay S. Robichon C. Le Liepvre X. Dagher G. Ferre P. Dugail I. Regulation of ABCA1 expression and cholesterol efflux during adipose differentiation of 3T3–L1 cells.J. Lipid Res. 2003; 44: 1499-1507Google Scholar, 10Prattes S. Horl G. Hammer A. Blaschitz A. Graier W.F. Sattler W. Zechner R. Steyrer E. Intracellular distribution and mobilization of unesterified cholesterol in adipocytes: triglyceride droplets are surrounded by cholesterol-rich ER-like surface layer structures.J. Cell Sci. 2000; 113: 2977-2989Google Scholar). On the other hand, the intracellular distribution of cholesterol between the plasma membrane and the lipid droplet is altered in pathological states such as obesity, as pointed out by previous studies from our laboratory (11Boizard M. Le Liepvre X. Lemarchand P. Foufelle F. Ferre P. Dugail I. Obesity-related overexpression of fatty-acid synthase gene in adipose tissue involves sterol regulatory element-binding protein transcription factors.J. Biol. Chem. 1998; 273: 29164-29171Google Scholar). As a signature of this defect, we have shown that the cholesterol-regulated transcription factor SREBP-2 was selectively activated in hypertrophied adipocytes from obese rodents. In addition, we have shown that some metabolic abnormalities that characterize adipocyte dysfunction in obesity can be mimicked in normal fat cells by altering their intracellular cholesterol balance (12Le Lay S. Krief S. Farnier C. Lefrere I. Le Liepvre X. Bazin R. Ferre P. Dugail I. Cholesterol, a cell size-dependent signal that regulates glucose metabolism and gene expression in adipocytes.J. Biol. Chem. 2001; 276: 16904-16910Google Scholar). For these reasons, we thought that the adipocyte cell type might provide useful information on the intracellular cholesterol trafficking. We took advantage of the existence of committed adipose cell lines that undergo adipose differentiation in culture to investigate the targeting of cholesterol to lipid droplets. Because adipocytes accumulate cholesterol from exogenous sources and express high levels of the HDL scavenger receptor class B type I (SR-BI) (13Babitt J. Trigatti B. Rigotti A. Smart E.J. Anderson R.G. Xu S. Krieger M. Murine SR-BI, a high density lipoprotein receptor that mediates selective lipid uptake, is N-glycosylated and fatty acylated and colocalizes with plasma membrane caveolae.J. Biol. Chem. 1997; 272: 13242-13249Google Scholar, 14Graf G.A. Connell P.M. van der Westhuyzen D.R. Smart E.J. The class B, type I scavenger receptor promotes the selective uptake of high density lipoprotein cholesterol ethers into caveolae.J. Biol. Chem. 1999; 274: 12043-12048Google Scholar), we examined the targeting of an HDL-associated fluorescent cholesterol analog, NBD-cholesterol (NBD-chol), to the lipid droplets at different stages of the adipocyte differentiation program. The results of this study show that the distribution of the Golgi complex, caveolin-2, and cholesterol exhibit marked changes in distribution during the differentiation process of adipocytes. The Golgi complex and caveolin-2 exhibit a dispersed distribution and colocalization with cholesterol in the first phase of adipocyte formation. In contrast, in fully differentiated lipid laden cells, the Golgi complex, as well as caveolin-2, occupies a juxtanuclear location, while cholesterol distributes preferentially in lipid droplets. These data suggest that the intracellular routes of HDL cholesterol significantly differ during fat cell differentiation, and that different mechanisms targeting cholesterol to the lipid droplets might exist, depending on its maturation. Human plasma HDLs were obtained from Calbiochem, La Jolla, CA. NBD-chol, [22-(N-7-nitrobenz-2-oxa-1,3-diazo-4-yl)-amino-23,24-bisnor-5-cholen-3-ol)], LysoTracker Red DND-99, cholera toxin subunit B Alexa Fluor 594 conjugate, monoclonal antibody to Golgin 97, calnexin, BODIPY FLC5 ceramide, and Alexa Fluor 488 and 546 goat anti-mouse goat were by Golgi antibody was from and monoclonal were from and were from other were from A monoclonal antibody to Rab was by L. and a goat monoclonal antibody to the trans-Golgi network was by M. J. M. Golgi apparatus in changes in its distribution during and Sci. 3T3-L1 were to on in with and of as was by and to the the culture was with with and of for As previously cytoplasmic triglyceride droplets were visible by and to of cells were fully differentiated by S. differentiation and Rev. Cell Biol. 1997; Scholar). were at three different phases of adipocyte I of differentiation this lipid droplets be observed in the cytoplasm. and phase to and of these latter cells were fully differentiated and the lipid droplets of adipocytes. HDLs with NBD-chol were as previously to fibroblasts from in by 1: Scholar). In NBD-chol was into human HDL and the HDLs were obtained and culture The protein of HDL was to using as a A and for the of of protein the of Scholar). the uptake and of NBD-chol, adipocytes were in and at in the of HDL with was by as (12Le Lay S. Krief S. Farnier C. Lefrere I. Le Liepvre X. Bazin R. Ferre P. Dugail I. Cholesterol, a cell size-dependent signal that regulates glucose metabolism and gene expression in adipocytes.J. Biol. Chem. 2001; 276: 16904-16910Google Scholar). NBD-chol uptake were using on A on the cells was and the of the was to the of the were analyzed from a of differentiated were for Cholesterol was by of NBD-chol and was by of at different using a The of as a of was using and as The of NBD-chol uptake was analyzed by the using from The were analyzed using tissue low levels of K. M. L. expression and cholesterol regulation of in Biol. Chem. 1995; 270: Scholar) and P. of cholesterol in and adipose J. Scholar). that adipocytes have a low to and that 3T3-L1 adipocytes free cholesterol (9Le Lay S. Robichon C. Le Liepvre X. Dagher G. Ferre P. Dugail I. Regulation of ABCA1 expression and cholesterol efflux during adipose differentiation of 3T3–L1 cells.J. Lipid Res. 2003; 44: 1499-1507Google Scholar), intracellular is to be by In some cellular NBD-chol efflux was as cells were in the of HDL NBD-chol for efflux cells were three with NBD-chol and efflux were using on A on the cells was and the of the was to the of the were analyzed from a three of differentiated were for Cholesterol efflux was by the of HDL and was by of at different using a The of cell as a of was using and as as for the uptake The NBD-chol was in the of HDL and from that observed in the of study the of cellular in the uptake of NBD-chol, adipocytes were of their intracellular by in with cholesterol uptake is by the Golgi complex, we NBD-chol uptake in the of Brefeldin and of These are to the of the Golgi complex and were for the to The of a to the network I. F. S. K. S. between of different on cellular and cellular and on in Cell Biol. Scholar), and a in structure and Scholar), on NBD-chol were also were to on and differentiated as intracellular NBD-chol cells were to HDL NBD-chol for at were three with and with in by to and were with in For the cells were in of the Golgi Golgin and monoclonal antibody were with the at a of were with and observed with a was as previously of of in Scholar). cells were with BODIPY at for and the was and cells three with The was to the cells were analyzed by the of NBD-chol in membranes, we the of In fluorescent in a are by an and through the of for is using are derived from the of as previously J. J. and of proteins in and cells by fluorescent protein 1999; Scholar). The are and the data are to the for where is the as a of of is as the of the is the is the and is the The constant can be obtained by using The constant for NBD-chol was for lipid droplets and cytoplasmic in cells and with that obtained for a fluorescent for intracellular As a of NBD-chol to was in these of be was also from the as a of a fluorescent The of NBD-chol uptake from HDL a of a first a of to and an of The of a and a between the and was also analyzed in and in these the were and of NBD-chol uptake in cells a constant from with a of NBD-chol efflux from cells with fluorescent lipid first with a constant of of HDL HDL NBD-chol uptake of a antibody to significantly NBD-chol uptake the of in the uptake of The distribution of NBD-chol in 3T3-L1 cells on the phase of of with NBD-chol, cells in phase I clearly lipid the cytoplasm In differentiated adipocytes and fluorescent lipid droplets be observed The of NBD-chol distribution in these cells that of lipid droplets visible by with a selective lipid droplet In to the of cellular in the trafficking of cells in phase were of by with These agents drastically the uptake efflux of These data that cholesterol uptake in adipocytes is an On the other hand, to with I. F. S. K. S. between of different on cellular and cellular and on in Cell Biol. Scholar) significantly HDL cholesterol uptake The routes of to the adipocyte lipid droplet are In this we to the of cell in this trafficking. we that our the routing of NBD-chol the lysosomal which is to be involved in this cells were with LysoTracker and NBD-chol uptake from HDL was for a of colocalization of cholesterol be observed during this lysosomal distribution and NBD-chol at of NBD-chol uptake, with colocalization between these fluorescent These results suggest that uptake and routing of sterol from HDL a pathway different from that of We to the role of the Golgi complex in the uptake, intracellular and of NBD-chol in adipocytes. were with agents to Golgi and These Brefeldin A for Brefeldin Scholar) and monensin, which the Golgi As shown in with drastically cholesterol uptake by these cells, thus the Golgi complex in this process and in intracellular trafficking. A in the of NBD-chol uptake was observed with to inhibit the factor involved in the transport of from the to other cell organelles E. M. C. K. for and Rab proteins in and transport in 1995; Scholar). We the colocalization of NBD-chol with the Golgi complex using to Golgin in phase when visible lipid droplets have in cells, fluorescent with antibody to Golgin a dispersed Golgi complex all the and NBD-chol was found to be these Golgi The of cholesterol with Golgi in phase I was while that of was In phase antibody to Golgin was dispersed in the and NBD-chol was in lipid droplets and cytoplasm. the Golgi complex formed a compact juxtanuclear structure in phase cells NBD-chol is present in lipid droplets with colocalization In to the of the Golgi complex in phase we a of the Golgi complex FLC5 to Golgi Golgi 58K, Rab 6, As shown in 6, a of all of these was observed in the strongly suggesting a dispersed Golgi complex in cells in phase I of the differentiation process were obtained using BODIPY in cells thus the distribution observed by in from the juxtanuclear of the Golgi complex in phase cells with lipid droplets of of cells in phase I that the different fluorescent Golgi markers were the of the the and were with NBD-chol These data that the distribution of Golgi complex marked changes during the differentiation A dispersed distribution with cholesterol was observed in phase in fully differentiated lipid laden cells, cholesterol from the juxtanuclear Golgi complex and distributes preferentially in lipid droplets. are cholesterol binding proteins and have been shown to be distributed at the plasma membrane and also in the Golgi as three distinct caveolin-2 the in adipocytes B. and and functional Cell Res. 2001; Scholar, A. The caveolae cholesterol and signal Rev. 2001; Scholar). In to the of cholesterol and Golgi markers during the of adipocyte differentiation, we cells for In phase I cells, caveolin-2 was by with a monoclonal antibody human caveolin-2 a distribution and with NBD-chol NBD-chol was present in lipid droplets while caveolin-2 a marked juxtanuclear distribution and was also observed at the cell membrane Thus, the distribution of caveolin-2 at different phases that of Golgi Because NBD-chol was found to be distributed the cytoplasm and with the Golgi complex in cells at phase we to the was to in in the was to the at which NBD-chol into of were by an and through of for was in the cytoplasm and in lipid droplets. As a an of the of NBD-chol was also The of constant was as in the and The of in the cytoplasm was for lipid droplets, it was and for cytoplasm These are of a to observed for such as receptor J. J. and of proteins in and cells by fluorescent protein 1999; Scholar, L. A. F. G. P. and of the formed by and in lipid 1999; Scholar, D. and the of in the plasma membrane of Cell Res. 1997; Scholar, Regulation of and cellular trafficking of the receptor by a J. 1999; 276: Scholar). In contrast, from of was in with obtained for of in phase As be observed in cells, which the of the in the which was of a fluorescent In this we to investigate the intracellular routes through which exogenous cholesterol is to lipid droplets in an adipocyte cell. For this we a cell system in which cells to mature adipocytes. the results of the present provide novel for of Golgi markers, caveolin-2, and NBD-chol during the fat cell differentiation On the other hand, of NBD-chol into adipocytes is an process that a functional Golgi study that in 3T3-L1 the uptake of NBD-chol from HDL SR-BI, as an antibody to this latter significantly this receptor functions as a receptor for is in cells, and was found to the selective uptake of HDL cholesterol to cells (13Babitt J. Trigatti B. Rigotti A. Smart E.J. Anderson R.G. Xu S. Krieger M. Murine SR-BI, a high density lipoprotein receptor that mediates selective lipid uptake, is N-glycosylated and fatty acylated and colocalizes with plasma membrane caveolae.J. Biol. Chem. 1997; 272: 13242-13249Google Scholar, 14Graf G.A. Connell P.M. van der Westhuyzen D.R. Smart E.J. The class B, type I scavenger receptor promotes the selective uptake of high density lipoprotein cholesterol ethers into caveolae.J. Biol. Chem. 1999; 274: 12043-12048Google Scholar). by differentiated fat cells, NBD-chol distributes the cytoplasm and lipid droplets through a that is of targeting a functional Golgi as it is by monensin, and all to the Golgi complex, and is an One novel and salient feature of the present study is that during the early phase of adipose a unique distribution of Golgi markers, caveolin-2, and NBD-chol clearly distinct from that observed in mature fat cells (i.e., with fully formed lipid vesicles). Thus, in the first fat cell differentiation in cells without visible lipid droplets, a of the Golgi apparatus the cytoplasm is observed using different to Golgi 38, Rab 6, Golgin 97, and Golgi results were obtained in cells using NBD-chol was found to be with the widespread Golgi in the first phase of differentiation, caveolin-2 a cytoplasmic distribution and a high colocalization with a when lipid droplets are fully NBD-chol concentrates in these droplets, while the Golgi complex an juxtanuclear also concentrates the in the Golgi Golgi were to and during J. Cell and biogenesis of the Golgi Cell Biol. 2000; Scholar, E. in of the Golgi complex and other organelles during Cell Biol. Scholar, J. K. E. J. Golgi are into and from the during 1999; Scholar). In cell the process of Golgi and during cell in the present study in 3T3-L1 differentiated cells, the is present for suggesting that it might be to The adipocyte differentiation is to distinct As a that to be a for cell is by and Thus, of the differentiation a of and a high of the cells the cell and undergo to three of to as regulation of gene expression during adipocyte Rev. 1995; Scholar). studies have that cell in 3T3-L1 during the first of differentiation (i.e., of S. B. J. K. a of the receptor functions as an early signal in the adipocyte differentiation Biol. Chem. 2000; Scholar, during of Biol. Chem. 2000; Scholar, M. J. K. and is a for 3T3–L1 differentiation into adipocytes.J. Biol. Chem. 2001; 276: Scholar). The results in this study show that the of Golgi in phase I is observed at through of is to be to the cell stages to be The role of the of the Golgi in cell processes is The colocalization of NBD-chol with the Golgi at the first phase of adipocyte differentiation, with the on NBD-chol of monensin, and strongly that the Golgi in the and routing of cholesterol to lipid droplets. A of studies have that the Golgi apparatus an role in intracellular cholesterol For the Golgi apparatus to the transport of cholesterol to the plasma membrane (4Anderson R.G. Pathak R.K. Vesicles and cisternae in the trans Golgi apparatus of human fibroblasts are acidic compartments.Cell. 1985; 40: 635-643Google Scholar). studies that the Golgi apparatus is involved in cholesterol efflux A. Uint L. Apolipoprotein-mediated cellular cholesterol and phospholipid efflux depend on a functional Golgi apparatus.J. Lipid Res. 1996; 37: 2510-2524Google Scholar, 7Mendez A.J. Monensin and Brefeldin A inhibit high density lipoprotein-mediated cholesterol efflux from cholesterol-enriched cells.J. Biol. Chem. 1995; 270: 5891-5900Google Scholar). studies that cholesterol is from clathrin-coated into that markers for the plasma membrane caveolae P.E. Fielding C.J. Intracellular transport of low density lipoprotein derived free cholesterol begins at clathrin-coated pits and terminates at cell surface caveolae.Biochemistry. 1996; 35: 14932-14938Google Scholar). The present study novel data suggesting that the Golgi a role in NBD-chol uptake from and their trafficking to the lipid droplets. of the Golgi is for in lipid NBD-chol was to be a useful for HDL-mediated cholesterol and efflux A. A. F. high density lipoprotein-mediated cholesterol Biol. Chem. 2000; Scholar, A. A. E. G. F. density lipoprotein-mediated cholesterol uptake and targeting to lipid droplets in A and Biol. Chem. 2000; Scholar); some have been the of NBD-chol to cholesterol distribution A. M. of a cholesterol analog from the cholesterol-rich phase in 2001; Scholar, S. X. I. Cholesterol distribution in using as a fluorescent cholesterol J. 1998; Scholar). In this that NBD-chol and a fluorescent in cells S. X. I. Cholesterol distribution in using as a fluorescent cholesterol J. 1998; Scholar). In contrast, a distribution of these fluorescent in fibroblasts A. A. E. G. F. density lipoprotein-mediated cholesterol uptake and targeting to lipid droplets in A and Biol. Chem. 2000; Scholar). In addition, NBD-chol by uptake as well as in cell fibroblasts and cells S. Horl G. Hammer A. Blaschitz A. Graier W.F. Sattler W. Zechner R. Steyrer E. Intracellular distribution and mobilization of unesterified cholesterol in adipocytes: triglyceride droplets are surrounded by cholesterol-rich ER-like surface layer structures.J. Cell Sci. 2000; 113: 2977-2989Google Scholar, A. A. F. high density lipoprotein-mediated cholesterol Biol. Chem. 2000; Scholar, A. A. E. G. F. density lipoprotein-mediated cholesterol uptake and targeting to lipid droplets in A and Biol. Chem. 2000; Scholar, S. J. M. J. A fluorescent cholesterol analog cholesterol in and is in and in Lipid Res. 1999; 40: Scholar). In this a distribution in the cytoplasm of and NBD-chol On the other hand, were to the of fluorescent to membranes. The and of the of NBD-chol in these R. A. Cholesterol in at low of and membrane J. 2001; Scholar). the of of to the cell its to plasma D. F. and unique of sterol in of cells.J. Biol. Chem. 2003; Scholar), to our is fluorescent analog that cholesterol distribution and are clearly to the of NBD-chol, this some and be cholesterol and the component of caveolae in B. and and functional Cell Res. 2001; Scholar, A. The caveolae cholesterol and signal Rev. 2001; Scholar). been that in trafficking and signal transduction processes by as proteins to and cholesterol and R.G. The caveolae membrane Rev. 1998; Scholar). Lipid rafts are at the of the plasma can also membrane such as the Golgi apparatus I. B. E. D. K. F. at the Golgi Biol. 2001; Scholar). is that and caveolin-2 are present at the Golgi complex R. E. A. M. R.G. of with the Golgi of a targeting in the Cell Biol. 1999; Scholar, P. Anderson in its intracellular Cell Biol. 2000; Scholar, R. A. P.E. Brown D. E. to the Golgi complex to plasma and rafts when with Biol. Chem. 1999; 274: Scholar). results are in with this as colocalizes with NBD-chol and is all the cytoplasm in the first phase of adipocyte formation. phases of adipocyte formation, it concentrates at a juxtanuclear in the Golgi Recently, lipid rafts and caveolae have as and for signal transduction and membrane trafficking In this that caveolin-2 is to the surface of lipid droplets K. K. R. is to lipid droplets, a new in the Cell Biol. 2001; Scholar). These results suggest that lipid droplets are involved in the trafficking of cholesterol by obtained results and that targeting of to be to lipid droplets, its caveolae at the of the plasma membrane S. Brown of in the endoplasmic reticulum the protein to lipid Cell Biol. 2001; Scholar). is of particular in to our present which out that targeting of cholesterol to the lipid droplets in the phase of their involves a process of the Golgi the routing of NBD-chol to lipid droplets from the Golgi apparatus the was in this into HDL-mediated cholesterol uptake and trafficking have been obtained the the mechanisms for these have to be in S. of membrane and membrane in lipid 2000; 1: In this study out distinct routing mechanisms of cholesterol in the early and phases of adipocyte in which the structure of the Golgi complex plays a critical such changes in the distribution of the Golgi apparatus might from cholesterol to the of lipid droplets, to be The to for