scholarly journals Postlipolytic insulin-dependent remodeling of micro lipid droplets in adipocytes

2012 ◽  
Vol 23 (10) ◽  
pp. 1826-1837 ◽  
Author(s):  
Nicholas Ariotti ◽  
Samantha Murphy ◽  
Nicholas A. Hamilton ◽  
Lizhen Wu ◽  
Kathryn Green ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplets ◽  
Electron Tomography ◽  
Morphological Changes ◽  
Quantitative Imaging ◽  
The Reformation ◽  
Fundamental Process ◽  
Insulin Dependent ◽  
Fat Pads

Despite the lipolysis–lipogenesis cycle being a fundamental process in adipocyte biology, very little is known about the morphological changes that occur during this process. The remodeling of lipid droplets to form micro lipid droplets (mLDs) is a striking feature of lipolysis in adipocytes, but once lipolysis ceases, the cell must regain its basal morphology. We characterized mLD formation in cultured adipocytes, and in primary adipocytes isolated from mouse epididymal fat pads, in response to acute activation of lipolysis. Using real-time quantitative imaging and electron tomography, we show that formation of mLDs in cultured adipocytes occurs throughout the cell to increase total LD surface area by ∼30% but does not involve detectable fission from large LDs. Peripheral mLDs are monolayered structures with a neutral lipid core and are sites of active lipolysis. Electron tomography reveals preferential association of mLDs with the endoplasmic reticulum. Treatment with insulin and fatty acids results in the reformation of macroLDs and return to the basal state. Insulin-dependent reformation of large LDs involves two distinct processes: microtubule-dependent homotypic fusion of mLDs and expansion of individual mLDs. We identify a physiologically important role for LD fusion that is involved in a reversible lipolytic cycle in adipocytes.

scholarly journals Mdm1 maintains endoplasmic reticulum homeostasis by spatially regulating lipid droplet biogenesis

2019 ◽  
Vol 218 (4) ◽  
pp. 1319-1334 ◽  
Author(s):  
Hanaa Hariri ◽  
Natalie Speer ◽  
Jade Bowerman ◽  
Sean Rogers ◽  
Gang Fu ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Fatty Acyl ◽  
Nutrient Depletion ◽  
Coenzyme A Ligase ◽  
Response To Stress ◽  
Acyl Coenzyme A ◽  
Er Homeostasis

Lipid droplets (LDs) serve as cytoplasmic reservoirs for energy-rich fatty acids (FAs) stored in the form of triacylglycerides (TAGs). During nutrient stress, yeast LDs cluster adjacent to the vacuole/lysosome, but how this LD accumulation is coordinated remains poorly understood. The ER protein Mdm1 is a molecular tether that plays a role in clustering LDs during nutrient depletion, but its mechanism of function remains unknown. Here, we show that Mdm1 associates with LDs through its hydrophobic N-terminal region, which is sufficient to demarcate sites for LD budding. Mdm1 binds FAs via its Phox-associated domain and coenriches with fatty acyl–coenzyme A ligase Faa1 at LD bud sites. Consistent with this, loss of MDM1 perturbs free FA activation and Dga1-dependent synthesis of TAGs, elevating the cellular FA level, which perturbs ER morphology and sensitizes yeast to FA-induced lipotoxicity. We propose that Mdm1 coordinates FA activation adjacent to the vacuole to promote LD production in response to stress, thus maintaining ER homeostasis.

scholarly journals Spatiotemporal dynamics of triglyceride storage in unilocular adipocytes

2014 ◽  
Vol 25 (25) ◽  
pp. 4096-4105 ◽  
Author(s):  
Michael Chu ◽  
Harini Sampath ◽  
David Y. Cahana ◽  
Christoph A. Kahl ◽  
Romel Somwar ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Adipose Tissue ◽  
Free Fatty Acids ◽  
Lipid Droplets ◽  
Ex Vivo ◽  
Spatiotemporal Dynamics ◽  
Biological Features ◽  
Adipocyte Hypertrophy ◽  
Cellular Organelles

The spatiotemporal dynamics of triglyceride (TG) storage in unilocular adipocytes are not well understood. Here we applied ex vivo technology to study trafficking and metabolism of fluorescent fatty acids in adipose tissue explants. Live imaging revealed multiple cytoplasmic nodules surrounding the large central lipid droplet (cLD) of unilocular adipocytes. Each cytoplasmic nodule harbors a series of closely associated cellular organelles, including micro–lipid droplets (mLDs), mitochondria, and the endoplasmic reticulum. Exogenously added free fatty acids are rapidly adsorbed by mLDs and concurrently get esterified to TG. This process is greatly accelerated by insulin. mLDs transfer their content to the cLD, serving as intermediates that mediate packaging of newly synthesized TG in the large interior of a unilocular adipocyte. This study reveals novel cell biological features that may contribute to the mechanism of adipocyte hypertrophy.

scholarly journals Cerebellar ataxia disease–associated Snx14 promotes lipid droplet growth at ER–droplet contacts

2019 ◽  
Vol 218 (4) ◽  
pp. 1335-1351 ◽  
Author(s):  
Sanchari Datta ◽  
Yang Liu ◽  
Hanaa Hariri ◽  
Jade Bowerman ◽  
W. Mike Henne
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Cerebellar Ataxia ◽  
Lipid Droplets ◽  
Fatty Acyl ◽  
Droplet Growth ◽  
Sorting Nexin ◽  
Coa Ligase ◽  
In Trans ◽  
Time Point

Lipid droplets (LDs) are nutrient reservoirs used by cells to maintain homeostasis. Nascent droplets form on the endoplasmic reticulum (ER) and grow following an influx of exogenous fatty acids (FAs). The budding of LDs requires extensive ER–LD crosstalk, but how this is regulated remains poorly understood. Here, we show that sorting nexin protein Snx14, an ER-resident protein associated with the cerebellar ataxia SCAR20, localizes to ER–LD contacts following FA treatment, where it promotes LD maturation. Using proximity-based APEX technology and topological dissection, we show that Snx14 accumulates specifically at ER–LD contacts independently of Seipin, where it remains ER-anchored and binds LDs in trans. SNX14KO cells exhibit perturbed LD morphology, whereas Snx14 overexpression promotes LD biogenesis and extends ER–LD contacts. Multi–time point imaging reveals that Snx14 is recruited to ER microdomains containing the fatty acyl-CoA ligase ACSL3, where nascent LDs bud. We propose that Snx14 is a novel marker for ER–LD contacts and regulates FA-stimulated LD growth.

scholarly journals Raman Study on Lipid Droplets in Hepatic Cells Co-Cultured with Fatty Acids

2021 ◽  
Vol 22 (14) ◽  
pp. 7378
Author(s):  
Pradjna N. Paramitha ◽  
Riki Zakaria ◽  
Anisa Maryani ◽  
Yukako Kusaka ◽  
Bibin B. Andriana ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Cell Death ◽  
Linoleic Acid ◽  
Hepg2 Cells ◽  
Lipid Droplets ◽  
Morphological Changes ◽  
Growth Curves ◽  
Nonalcoholic Fatty Liver ◽  
Hepatic Cells ◽  
Oleic And Linoleic Acids

The purpose of the present study was to investigate molecular compositions of lipid droplets changing in live hepatic cells stimulated with major fatty acids in the human body, i.e., palmitic, stearic, oleic, and linoleic acids. HepG2 cells were used as the model hepatic cells. Morphological changes of lipid droplets were observed by optical microscopy and transmission electron microscopy (TEM) during co-cultivation with fatty acids up to 5 days. The compositional changes in the fatty chains included in the lipid droplets were analyzed via Raman spectroscopy and chemometrics. The growth curves of the cells indicated that palmitic, stearic, and linoleic acids induced cell death in HepG2 cells, but oleic acid did not. Microscopic observations suggested that the rates of fat accumulation were high for oleic and linoleic acids, but low for palmitic and stearic acids. Raman analysis indicated that linoleic fatty chains taken into the cells are modified into oleic fatty chains. These results suggest that the signaling pathway of cell death is independent of fat stimulations. Moreover, these results suggest that hepatic cells have a high affinity for linoleic acid, but linoleic acid induces cell death in these cells. This may be one of the causes of inflammation in nonalcoholic fatty liver disease (NAFLD).

scholarly journals Endoplasmic reticulum remains continuous and undergoes sheet-to-tubule transformation during cell division in mammalian cells

2007 ◽  
Vol 179 (5) ◽  
pp. 895-909 ◽  
Author(s):  
Maija Puhka ◽  
Helena Vihinen ◽  
Merja Joensuu ◽  
Eija Jokitalo
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Division ◽  
3D Modeling ◽  
Mammalian Cells ◽  
Structural Changes ◽  
Electron Tomography ◽  
Morphological Changes ◽  
Homogenous Distribution ◽  
Membrane Bound ◽  
Cycle Dependent

The endoplasmic reticulum (ER) is a multifaceted cellular organelle both structurally and functionally, and its cell cycle–dependent morphological changes are poorly understood. Our quantitative confocal and EM analyses show that the ER undergoes dramatic reorganization during cell division in cultured mammalian cells as mitotic ER profiles become shorter and more branched. 3D modeling by electron tomography reveals that the abundant interphase structures, sheets, are lost and subsequently transform into a branched tubular network that remains continuous. This is confirmed by observing the most prominent ER subdomain, the nuclear envelope (NE). A NE marker protein spreads to the mitotic ER tubules, although it does not show a homogenous distribution within the network. We mimicked the mitotic ER reorganization using puromycin to strip the membrane-bound ribosomes from the interphase ER corresponding to the observed loss of ribosomes normally occurring during mitosis. We propose that the structural changes in mitotic ER are linked to ribosomal action on the ER membranes.

scholarly journals Dictyostelium Lipid Droplets Host Novel Proteins

2013 ◽  
Vol 12 (11) ◽  
pp. 1517-1529 ◽  
Author(s):  
Xiaoli Du ◽  
Caroline Barisch ◽  
Peggy Paschke ◽  
Cornelia Herrfurth ◽  
Oliver Bertinetti ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Unsaturated Fatty Acids ◽  
Neutral Lipids ◽  
Saturated Fatty Acids ◽  
Endoplasmic Reticulum Membrane ◽  
Hydrophobic Core ◽  
Content Type

ABSTRACT Across all kingdoms of life, cells store energy in a specialized organelle, the lipid droplet. In general, it consists of a hydrophobic core of triglycerides and steryl esters surrounded by only one leaflet derived from the endoplasmic reticulum membrane to which a specific set of proteins is bound. We have chosen the unicellular organism Dictyostelium discoideum to establish kinetics of lipid droplet formation and degradation and to further identify the lipid constituents and proteins of lipid droplets. Here, we show that the lipid composition is similar to what is found in mammalian lipid droplets. In addition, phospholipids preferentially consist of mainly saturated fatty acids, whereas neutral lipids are enriched in unsaturated fatty acids. Among the novel protein components are LdpA, a protein specific to Dictyostelium , and Net4, which has strong homologies to mammalian DUF829/Tmem53/NET4 that was previously only known as a constituent of the mammalian nuclear envelope. The proteins analyzed so far appear to move from the endoplasmic reticulum to the lipid droplets, supporting the concept that lipid droplets are formed on this membrane.

scholarly journals Acyl-CoA synthetase 3 promotes lipid droplet biogenesis in ER microdomains

2013 ◽  
Vol 203 (6) ◽  
pp. 985-1001 ◽  
Author(s):  
Adam Kassan ◽  
Albert Herms ◽  
Andrea Fernández-Vidal ◽  
Marta Bosch ◽  
Nicole L. Schieber ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Copy Number ◽  
Storage Capacity ◽  
Neutral Lipids ◽  
Electron Tomography ◽  
Lipid Storage ◽  
Lipid Concentration ◽  
Stable Core

Control of lipid droplet (LD) nucleation and copy number are critical, yet poorly understood, processes. We use model peptides that shift from the endoplasmic reticulum (ER) to LDs in response to fatty acids to characterize the initial steps of LD formation occurring in lipid-starved cells. Initially, arriving lipids are rapidly packed in LDs that are resistant to starvation (pre-LDs). Pre-LDs are restricted ER microdomains with a stable core of neutral lipids. Subsequently, a first round of “emerging” LDs is nucleated, providing additional lipid storage capacity. Finally, in proportion to lipid concentration, new rounds of LDs progressively assemble. Confocal microscopy and electron tomography suggest that emerging LDs are nucleated in a limited number of ER microdomains after a synchronized stepwise process of protein gathering, lipid packaging, and recognition by Plin3 and Plin2. A comparative analysis demonstrates that the acyl-CoA synthetase 3 is recruited early to the assembly sites, where it is required for efficient LD nucleation and lipid storage.

scholarly journals The Step-Wise C-Truncation and Transport of ESyt3 to Lipid Droplets Reveals a Mother Primordial Cisterna

2020 ◽  
Author(s):  
Vasiliki Lalioti ◽  
Galina V. Beznoussenko ◽  
Alexander A. Mironov ◽  
Ignacio V. Sandoval
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
3D Reconstruction ◽  
Lipid Droplets ◽  
Adipocyte Differentiation ◽  
Electron Tomography ◽  
Close Contact ◽  
C2 Domains ◽  
Lipid Exchange ◽  
Main Component

AbstractExtended synaptotagmins (E-Syts) are endoplasmic reticulum (ER) proteins consisting of an SMP domain and multiple C2 domains that bind phospholipids and Ca2+. E-Syts create contact junctions between the ER and plasma membrane to facilitate lipid exchange. During adipocyte differentiation, the proteasome-based removal of the C2C domain results in targeting of E-Syt3 to the primordial cisterna, a previously undescribed giant annular organelle that mothers the LDs. Further cleavage causes the E-Syt3 relocation to the surface of LDs. Fragmentation of the primordial cisterna and LD budding into its lumen are early events in the biogenesis of LDs in the 3T3-L1 adipocyte. Electron tomography-based 3D reconstruction of the fragmented primordial cisterna revealed patches of a tightly packed E-Syt3-rich network of varicose tubules in close contact with young LDs. Esyt3 binds avidly phosphatidylethanolamine through its SMP domain, a main component of the LD membrane that fosters LD biogenesis. Repression of E-Syt3 effectively inhibits LD biogenesis and growth.

scholarly journals Metabolism of palmitate in perfused rat liver. Computer models of subcellular triacylglycerol metabolism

1979 ◽  
Vol 184 (1) ◽  
pp. 73-81 ◽  
Author(s):  
Jens Kondrup ◽  
Stig E. Damgaard ◽  
Peter Fleron
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplets ◽  
Preceding Paper ◽  
Computer Models ◽  
The Other ◽  
Triacylglycerol Metabolism ◽  
Cytoplasmic Lipid Droplets ◽  
Hepatic Triacylglycerol ◽  
Hydrolysis Of

1. In the preceding paper [Kondrup (1979) Biochem. J.184, 63–71] the separation of two major fractions of hepatic triacylglycerol was described. One fraction contained triacylglycerol from the endoplasmic reticulum and from the Golgi apparatus. The other fraction contained triacylglycerol from the cytoplasmic lipid droplets. In the present paper possible precursor–product relationships between the two fractions were investigated by means of computer models. 2. The fatty acids present in di- and tri-acylglycerol in the fractions isolated in the time studies were analysed by gas chromatography. From this analysis the relative specific radioactivities, and contents, of palmitate in acylglycerols in the two fractions at the various time points were calculated. 3. A computer was used to predict relative specific radioactivities of pools in defined models of hepatic triacylglycerol metabolism. The acceptability of the models was evaluated by comparing predicted with measured relative specific radioactivities. 4. It is suggested that triacylglycerol in cytoplasmic lipid droplets does not originate (a) directly from triacylglycerol in the endoplasmic reticulum, (b) from a sub-pool of it or (c) directly from non-esterified fatty acids entering the cell. Rather, it is formed from diacylglycerol (and acyl-CoA) in the endoplasmic reticulum. Diacylglycerol, on the other hand, is furnished in part by hydrolysis of triacylglycerol in the endoplasmic reticulum. 5. This suggestion is discussed in relation to previous models of hepatic fatty acid metabolism.

scholarly journals The endoplasmic reticulum-resident protein TMEM-120/TMEM120A promotes fat storage in C. elegans and mammalian cells

2021 ◽  
Author(s):  
Yan Li ◽  
Siwei Huang ◽  
Xuesong Li ◽  
Xingyu Yang ◽  
Ningyi Xu ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Lipid Droplets ◽  
Stimulated Raman Scattering ◽  
Transmembrane Helices ◽  
Fat Storage ◽  
Over Expression ◽  
C Elegans

The synthesis of triacylglycerol (TAG) is essential for the storage of excess fatty acids, which can subsequently be used for energy or cell growth. A series of enzymes act in the endoplasmic reticulum (ER) to synthesize TAG, prior to its transfer to lipid droplets (LDs), which are conserved organelles for fat storage. Here, we report that the deficiency of TMEM-120/TMEM120A, a protein with 6-transmembrane helices, retards TAG synthesis and LD expansion in C. elegans. GFP fusion proteins of TMEM-120, expressed at the endogenous level in live worms, were observed throughout the ER network. Using Stimulated Raman Scattering, we demonstrated the specific requirement of TMEM-120 in the storage of exogenous fatty acids in LDs. Knockdown of TMEM120A impedes adipogenesis of pre-adipocytes in vitro, while its over-expression is sufficient to promote LD expansion in mammalian cells. Our results suggest that TMEM-120/TMEM120A plays a conserved role in increasing the efficiency of TAG synthesis.

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