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 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 Zebrafish lipid droplets regulate embryonic ATP homeostasis to power early development

Open Biology ◽  
2017 ◽  
Vol 7 (7) ◽  
pp. 170063 ◽  
Author(s):  
Asmita Dutta ◽  
Deepak Kumar Sinha
Keyword(s):  
Fatty Acids ◽  
Early Development ◽  
Lipid Droplets ◽  
Developmental Stages ◽  
Fatty Acyl ◽  
Zebrafish Embryos ◽  
Early Developmental Stages ◽  
Successful Execution ◽  
Acyl Coenzyme A ◽  
Early Developmental

In zebrafish embryos, the maternally supplied pool of ATP is insufficient to power even the earliest of developmental events (0–3 hpf) such as oocyte-to-embryo transition (OET). The embryos generate an additional pulse (2.5 h long) of ATP (1.25–4 hpf) to achieve the embryonic ATP homeostasis. We demonstrate that the additional pulse of ATP is needed for successful execution of OET. The maternally supplied yolk lipids play a crucial role in maintaining the embryonic ATP homeostasis. In this paper, we identify the source and trafficking routes of free fatty acids (FFAs) that feed the mitochondria for synthesis of ATP. Interestingly, neither the maternally supplied pool of yolk-FFA nor the yolk-FACoA (fatty acyl coenzyme A) is used for ATP homeostasis during 0–5 hpf in zebrafish embryos. With the help of lipidomics, we explore the link between lipid droplet (LD)-mediated lipolysis and ATP homeostasis in zebrafish embryos. Until 5 hpf, the embryonic LDs undergo extensive lipolysis that generates FFAs. We demonstrate that these newly synthesized FFAs from LDs are involved in the maintenance of embryonic ATP homeostasis, rather than the FFAs/FACoA present in the yolk. Thus, the LDs are vital embryonic organelles that maintain the ATP homeostasis during early developmental stages (0–5 hpf) in zebrafish embryos. Our study highlights the important roles carried on by the LDs during the early development of the zebrafish embryos.

scholarly journals Snx14 proximity labeling reveals a role in saturated fatty acid metabolism and ER homeostasis defective in SCAR20 disease

2020 ◽  
Author(s):  
Sanchari Datta ◽  
Jade Bowerman ◽  
Hanaa Hariri ◽  
Rupali Ugrankar ◽  
Kaitlyn M. Eckert ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Fatty Acid ◽  
Lipid Droplet ◽  
Saturated Fatty Acids ◽  
Disease Patient ◽  
Metabolic Energy ◽  
Functional Interaction ◽  
Over Expression ◽  
Er Homeostasis

AbstractFatty acids (FAs) are central cellular metabolites that contribute to lipid synthesis, and can be stored or harvested for metabolic energy. Dysregulation in FA processing and storage causes toxic FA accumulation or altered membrane compositions and contributes to metabolic and neurological disorders. Saturated lipids are particularly detrimental to cells, but how lipid saturation levels are maintained remains poorly understood. Here, we identify the cerebellar ataxia SCAR20-associated protein Snx14, an endoplasmic reticulum (ER)-lipid droplet (LD) tethering protein, as a novel factor required to maintain the lipid saturation balance of cell membranes. We show that SNX14KO cells and SCAR20 disease patient-derived cells are hypersensitive to saturated FA (SFA)-mediated lipotoxic cell death that compromises ER integrity. Using APEX2-based proximity labeling, we reveal the protein composition of Snx14-associated ER-LD contacts and define a functional interaction between Snx14 and Δ-9 FA desaturase SCD1. Lipidomic profiling reveals that SNX14KO cells increase membrane lipid saturation following exposure to palmitate, phenocopying cells with reduced SCD1 activity. In line with this, SNX14KO cells manifest delayed FA processing and lipotoxicity, which can be rescued by SCD1 over-expression. Altogether these mechanistic insights reveal a role for Snx14 in FA and ER homeostasis, defects in which may underlie the neuropathology of SCAR20.Significance StatementSCAR20 disease is an autosomal recessive spinocerebellar ataxia primarily affecting children, and results from loss-of-function mutations in the SNX14 gene. Snx14 is an endoplasmic reticulum (ER)-localized protein that localizes to ER-lipid droplet (LD) contacts and promotes LD biogenesis following exogenous FA treatment, but why Snx14 loss causes SCAR20 is unclear. Here, we demonstrate that following exposure to saturated fatty acids, Snx14-deficient cells have defective ER homeostasis and altered lipid saturation profiles. We reveal a functional interaction between Snx14 and fatty acid (FA) desaturase SCD1. Lipidomics shows Snx14-deficient cells contain elevated saturated lipids, closely mirroring SCD1-defective cells. Furthermore, SCD1 over-expression can rescue Snx14 loss. We propose that Snx14 maintains cellular lipid homeostasis, the loss of which underlies the cellular basis for SCAR20 disease.

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 A conserved family of proteins facilitates nascent lipid droplet budding from the ER

2015 ◽  
Vol 211 (2) ◽  
pp. 261-271 ◽  
Author(s):  
Vineet Choudhary ◽  
Namrata Ojha ◽  
Andy Golden ◽  
William A. Prinz
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Caenorhabditis Elegans ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
De Novo ◽  
Fat Storage ◽  
Higher Eukaryotes ◽  
Er Membrane

Lipid droplets (LDs) are found in all cells and play critical roles in lipid metabolism. De novo LD biogenesis occurs in the endoplasmic reticulum (ER) but is not well understood. We imaged early stages of LD biogenesis using electron microscopy and found that nascent LDs form lens-like structures that are in the ER membrane, raising the question of how these nascent LDs bud from the ER as they grow. We found that a conserved family of proteins, fat storage-inducing transmembrane (FIT) proteins, is required for proper budding of LDs from the ER. Elimination or reduction of FIT proteins in yeast and higher eukaryotes causes LDs to remain in the ER membrane. Deletion of the single FIT protein in Caenorhabditis elegans is lethal, suggesting that LD budding is an essential process in this organism. Our findings indicated that FIT proteins are necessary to promote budding of nascent LDs from the ER.

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 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 Seipin-Mediated Contacts as Gatekeepers of Lipid Flux at the Endoplasmic Reticulum–Lipid Droplet Nexus 

Contact ◽  
2020 ◽  
Vol 3 ◽  
pp. 251525642094582
Author(s):  
Veijo T. Salo ◽  
Maarit Hölttä-Vuori ◽  
Elina Ikonen
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Recent Work ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Intimate Relationship

Lipid droplets (LDs) are dynamic cellular hubs of lipid metabolism. While LDs contact a plethora of organelles, they have the most intimate relationship with the endoplasmic reticulum (ER). Indeed, LDs are initially assembled at specialized ER subdomains, and recent work has unraveled an increasing array of proteins regulating ER-LD contacts. Among these, seipin, a highly conserved lipodystrophy protein critical for LD growth and adipogenesis, deserves special attention. Here, we review recent insights into the role of seipin in LD biogenesis and as a regulator of ER-LD contacts. These studies have also highlighted the evolving concept of ER and LDs as a functional continuum for lipid partitioning and pinpointed a role for seipin at the ER-LD nexus in controlling lipid flux between these compartments.

scholarly journals Functional Role of Fatty Acyl-Coenzyme A Synthetase in the Transmembrane Movement and Activation of Exogenous Long-chain Fatty Acids

2002 ◽  
Vol 277 (33) ◽  
pp. 29369-29376 ◽  
Author(s):  
James D. Weimar ◽  
Concetta C. DiRusso ◽  
Raymond Delio ◽  
Paul N. Black
Keyword(s):  
Fatty Acids ◽  
Functional Role ◽  
Coenzyme A ◽  
Fatty Acyl ◽  
Long Chain Fatty Acids ◽  
Acyl Coenzyme A ◽  
Long Chain ◽  
Chain Fatty Acids
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