Biogenesis of the multifunctional lipid droplet: Lipids, proteins, and sites

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Abstract

Lipid droplets (LDs) are ubiquitous dynamic organelles that store and supply lipids in all eukaryotic and some prokaryotic cells for energy metabolism, membrane synthesis, and production of essential lipid-derived molecules. Interest in the organelle’s cell biology has exponentially increased over the last decade due to the link between LDs and prevalent human diseases and the discovery of new and unexpected functions of LDs. As a result, there has been significant recent progress toward understanding where and how LDs are formed, and the specific lipid pathways that coordinate LD biogenesis.

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FAT SIGNALS - Lipases and Lipolysis in Lipid Metabolism and Signaling

Rudolf Zechner, Robert Zimmermann, Thomas O. Eichmann … (2012)

Lipolysis is defined as the catabolism of triacylglycerols stored in cellular lipid droplets. Recent discoveries of essential lipolytic enzymes and characterization of numerous regulatory proteins and mechanisms have fundamentally changed our perception of lipolysis and its impact on cellular metabolism. New findings that lipolytic products and intermediates participate in cellular signaling processes and that “lipolytic signaling” is particularly important in many nonadipose tissues unveil a previously underappreciated aspect of lipolysis, which may be relevant for human disease.

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Triacylglycerol synthesis enzymes mediate lipid droplet growth by relocalizing from the ER to lipid droplets.

Florian Wilfling, Huajin Wang, Joel T. Haas … (2013)

Lipid droplets (LDs) store metabolic energy and membrane lipid precursors. With excess metabolic energy, cells synthesize triacylglycerol (TG) and form LDs that grow dramatically. It is unclear how TG synthesis relates to LD formation and growth. Here, we identify two LD subpopulations: smaller LDs of relatively constant size, and LDs that grow larger. The latter population contains isoenzymes for each step of TG synthesis. Glycerol-3-phosphate acyltransferase 4 (GPAT4), which catalyzes the first and rate-limiting step, relocalizes from the endoplasmic reticulum (ER) to a subset of forming LDs, where it becomes stably associated. ER-to-LD targeting of GPAT4 and other LD-localized TG synthesis isozymes is required for LD growth. Key features of GPAT4 ER-to-LD targeting and function in LD growth are conserved between Drosophila and mammalian cells. Our results explain how TG synthesis is coupled with LD growth and identify two distinct LD subpopulations based on their capacity for localized TG synthesis. Copyright © 2013 Elsevier Inc. All rights reserved.

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The lipodystrophy protein seipin is found at endoplasmic reticulum lipid droplet junctions and is important for droplet morphology.

Kimberly Szymanski, Derk D. Binns, René Bartz … (2007)

Lipodystrophy is a disorder characterized by a loss of adipose tissue often accompanied by severe hypertriglyceridemia, insulin resistance, diabetes, and fatty liver. It can be inherited or acquired. The most severe inherited form is Berardinelli-Seip Congenital Lipodystrophy Type 2, associated with mutations in the BSCL2 gene. BSCL2 encodes seipin, the function of which has been entirely unknown. We now report the identification of yeast BSCL2/seipin through a screen to detect genes important for lipid droplet morphology. The absence of yeast seipin results in irregular lipid droplets often clustered alongside proliferated endoplasmic reticulum (ER); giant lipid droplets are also seen. Many small irregular lipid droplets are also apparent in fibroblasts from a BSCL2 patient. Human seipin can functionally replace yeast seipin, but a missense mutation in human seipin that causes lipodystrophy, or corresponding mutations in the yeast gene, render them unable to complement. Yeast seipin is localized in the ER, where it forms puncta. Almost all lipid droplets appear to be on the ER, and seipin is found at these junctions. Therefore, we hypothesize that seipin is important for droplet maintenance and perhaps assembly. In addition to detecting seipin, the screen identified 58 other genes whose deletions cause aberrant lipid droplets, including 2 genes encoding proteins known to activate lipin, a lipodystrophy locus in mice, and 16 other genes that are involved in endosomal-lysosomal trafficking. The genes identified in our screen should be of value in understanding the pathway of lipid droplet biogenesis and maintenance and the cause of some lipodystrophies.

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Author and article information

Journal

Journal ID (nlm-ta): J Cell Biol

Journal ID (iso-abbrev): J. Cell Biol

Journal ID (hwp): jcb

Journal ID (publisher-id): jcb

Title: The Journal of Cell Biology

Publisher: The Rockefeller University Press

ISSN (Print): 0021-9525

ISSN (Electronic): 1540-8140

Publication date (Print): 3 March 2014

Volume: 204

Issue: 5

Pages: 635-646

Affiliations

[1 ]Equip de Compartiments Cellulars i Senyalització, Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain

[2 ]Departament de Biologia Cellular, Immunologia i Neurociències, Facultat de Medicina, Universitat de Barcelona, 08036 Barcelona, Spain

[3 ]Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain

[4 ]Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697

[5 ]The Institute for Molecular Bioscience and [6 ]Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia

Author notes

Correspondence to Robert G. Parton: r.parton@ 123456imb.uq.edu.au ; or Albert Pol: apols@ 123456ub.edu

Article

Publisher ID: 201311051

DOI: 10.1083/jcb.201311051

PMC ID: 3941045

PubMed ID: 24590170

SO-VID: 5a9baab2-8a40-4f19-b3ab-2ab42fff177b

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This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

Biogenesis of the multifunctional lipid droplet: Lipids, proteins, and sites

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Most cited references 123

FAT SIGNALS - Lipases and Lipolysis in Lipid Metabolism and Signaling

Triacylglycerol synthesis enzymes mediate lipid droplet growth by relocalizing from the ER to lipid droplets.

The lipodystrophy protein seipin is found at endoplasmic reticulum lipid droplet junctions and is important for droplet morphology.

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