OSBP-related protein 2 is a sterol receptor on lipid droplets that regulates the metabolism of neutral lipids

Adipocyte differentiation-related protein (ADrP) is an intrinsic lipid storage droplet protein that is highly expressed in lung. ADrP localizes to lipid storage droplets within lipofibroblasts, pulmonary cells characterized by high triacylglycerol, which is a precursor for surfactant phospholipid synthesis by alveolar type II epithelial (EPII) cells. The developmental pattern of ADrP mRNA and protein expression in lung tissue parallels triacylglycerol accumulation in rat lung. ADrP mRNA levels are relatively high in isolated lipofibroblasts, accounting for the high ADrP expression in lung. Isolated EPII cells, which do not store neutral lipids but derive them from lipofibroblasts, have low levels of ADrP mRNA expression. ADrP is found around lipid droplets in cultured lipofibroblasts, but not in EPII cells isolated from developing rat lung. After coculture with lipofibroblasts, EPII cells acquired ADrP, which associates with lipid droplets. Furthermore,3H-labeled triolein in isolated ADrP-coated lipid droplets is a tenfold better substrate for surfactant phospholipid synthesis by cultured EPII cells than 3H-labeled synthetic triolein alone. Antibodies to ADrP block transfer of neutral lipid. These data suggest a role for ADrP in this novel mechanism for the transfer of lipid between lipofibroblasts and EPII cells.

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A Molecular Logic Gate Enables Super-Resolved Imaging of Intracellular Lipid Droplets

10.26434/chemrxiv.9784799.v1 ◽

2019 ◽

Author(s):

Adam Eördögh ◽

Carolina Paganini ◽

Dorothea Pinotsi ◽

Paolo Arosio ◽

Pablo Rivera-Fuentes

Keyword(s):

Single Molecule ◽

Lipid Droplets ◽

Neutral Lipids ◽

Logic Gate ◽

Living Cells ◽

Three Dimensions ◽

Single Molecule Imaging ◽

Molecular Logic Gate ◽

Molecular Logic ◽

Cellular Compartments

<div>Photoactivatable dyes enable single-molecule imaging in biology. Despite progress in the development of new fluorophores and labeling strategies, many cellular compartments remain difficult to image beyond the limit of diffraction in living cells. For example, lipid droplets, which are organelles that contain mostly neutral lipids, have eluded single-molecule imaging. To visualize these challenging subcellular targets, it is necessary to develop new fluorescent molecular devices beyond simple on/off switches. Here, we report a fluorogenic molecular logic gate that can be used to image single molecules associated with lipid droplets with excellent specificity. This probe requires the subsequent action of light, a lipophilic environment and a competent nucleophile to produce a fluorescent product. The combination of these requirements results in a probe that can be used to image the boundary of lipid droplets in three dimensions with resolutions beyond the limit of diffraction. Moreover, this probe enables single-molecule tracking of lipids within and between droplets in living cells.</div>

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Interactions of Lipid Droplets with the Intracellular Transport Machinery

International Journal of Molecular Sciences ◽

10.3390/ijms22052776 ◽

2021 ◽

Vol 22 (5) ◽

pp. 2776

Author(s):

Selma Yilmaz Dejgaard ◽

John F. Presley

Keyword(s):

Membrane Trafficking ◽

Lipid Droplets ◽

Intracellular Transport ◽

Neutral Lipids ◽

Small Gtpases ◽

Lipid Phase ◽

Intracellular Organelles ◽

And Function ◽

Lipid Phase Separation ◽

Endocytic Pathways

Historically, studies of intracellular membrane trafficking have focused on the secretory and endocytic pathways and their major organelles. However, these pathways are also directly implicated in the biogenesis and function of other important intracellular organelles, the best studied of which are peroxisomes and lipid droplets. There is a large recent body of work on these organelles, which have resulted in the introduction of new paradigms regarding the roles of membrane trafficking organelles. In this review, we discuss the roles of membrane trafficking in the life cycle of lipid droplets. This includes the complementary roles of lipid phase separation and proteins in the biogenesis of lipid droplets from endoplasmic reticulum (ER) membranes, and the attachment of mature lipid droplets to membranes by lipidic bridges and by more conventional protein tethers. We also discuss the catabolism of neutral lipids, which in part results from the interaction of lipid droplets with cytosolic molecules, but with important roles for both macroautophagy and microautophagy. Finally, we address their eventual demise, which involves interactions with the autophagocytotic machinery. We pay particular attention to the roles of small GTPases, particularly Rab18, in these processes.

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Adipose differentiation-related protein has two independent domains for targeting to lipid droplets

Biochemical and Biophysical Research Communications ◽

10.1016/s0006-291x(03)00979-3 ◽

2003 ◽

Vol 306 (2) ◽

pp. 333-338 ◽

Cited By ~ 57

Author(s):

Noriko Nakamura ◽

Toyoshi Fujimoto

Keyword(s):

Lipid Droplets ◽

Related Protein ◽

Adipose Differentiation

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Intracellular Lipid Droplets: From Structure to Function

Lipid Insights ◽

10.1177/1178635317745518 ◽

2017 ◽

Vol 10 ◽

pp. 117863531774551 ◽

Cited By ~ 13

Author(s):

Stefano Vanni

Keyword(s):

Lipid Droplets ◽

Neutral Lipids ◽

Interfacial Structure ◽

Aqueous Environment ◽

Sterol Esters ◽

Computational Approaches ◽

Main Site ◽

Natural Surfactant ◽

Oil Emulsions ◽

Function Relationship

Lipid droplets (LDs) are unique intracellular organelles that are mainly constituted by neutral lipids (triglycerides, sterol esters). As such they serve as the main site of energy storage in the cell and they are akin to oil emulsions in water. To prevent the direct exposure of the hydrophobic neutral lipids to the aqueous environment of the cytosol, LDs are surrounded by a monolayer of phospholipids that thus behave as a natural surfactant. This interfacial structure is rather unique inside the cell, but a molecular understanding of how the LD structure modulates its functions is still lacking, mainly due to technical challenges in both experimental and computational approaches to investigate oil-in-water emulsions. Recently, we have investigated the structure of LDs using a combination of existing and newly developed computational approaches that are optimized to study oil-water interfaces.1 Our simulations provide a comprehensive molecular characterization of the unique surface properties of LDs, suggesting structure-function relationship in several LD-related metabolic processes.

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Multifunctional pyrazoline based AIEgens: real-time tracking and specific protein “fishing” of lipid droplets

Chemical Science ◽

10.1039/c9sc03111a ◽

2019 ◽

Vol 10 (39) ◽

pp. 9009-9016 ◽

Cited By ~ 10

Author(s):

Na Zhao ◽

Yan Li ◽

Weiyao Yang ◽

Jiabao Zhuang ◽

Yue Li ◽

...

Keyword(s):

Lipid Metabolism ◽

Real Time ◽

Intracellular Ph ◽

Lipid Droplet ◽

Lipid Droplets ◽

Specific Protein ◽

Related Protein ◽

Dual Color ◽

Real Time Tracking

A series of multifunctional pyrazoline based AIEgens were developed for real-time tracking of lipid metabolism, reversibly monitoring intracellular pH in dual-color mode and specific labeling of lipid droplet related protein.

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In Close Proximity: The Lipid Droplet Proteome and Crosstalk With the Endoplasmic Reticulum

Contact ◽

10.1177/2515256418768996 ◽

2018 ◽

Vol 1 ◽

pp. 251525641876899 ◽

Cited By ~ 5

Author(s):

Kirill Bersuker ◽

James A. Olzmann

Keyword(s):

Mass Spectrometry ◽

Endoplasmic Reticulum ◽

Lipid Droplets ◽

Neutral Lipids ◽

26S Proteasome ◽

High Confidence ◽

Close Proximity ◽

Bona Fide ◽

A Site ◽

High Degree

Lipid droplets (LDs) are conserved, endoplasmic reticulum (ER)-derived organelles that act as a dynamic cellular repository for neutral lipids. Numerous studies have examined the composition of LD proteomes by using mass spectrometry to identify proteins present in biochemically isolated buoyant fractions that are enriched in LDs. Although many bona fide LD proteins were identified, high levels of non-LD proteins that contaminate buoyant fractions complicate the detection of true LD proteins. To overcome this problem, we recently developed a proximity-labeling proteomic method to define high-confidence LD proteomes. Moreover, employing this approach, we discovered that ER-associated degradation impacts the composition of LD proteomes by targeting select LD proteins for clearance by the 26S proteasome as they transit between the ER and LDs. These findings implicate the ER as a site of LD protein degradation and underscore the high degree of crosstalk between ER and LDs.

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The yeast lipin orthologue Pah1p is important for biogenesis of lipid droplets

The Journal of Cell Biology ◽

10.1083/jcb.201010111 ◽

2011 ◽

Vol 192 (6) ◽

pp. 1043-1055 ◽

Cited By ~ 167

Author(s):

Oludotun Adeyo ◽

Patrick J. Horn ◽

SungKyung Lee ◽

Derk D. Binns ◽

Anita Chandrahas ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Neutral Lipid ◽

Strong Evidence ◽

Lipid Droplets ◽

Neutral Lipids ◽

Glucose Medium ◽

Wild Type ◽

Lipid Levels ◽

Total Neutral Lipid ◽

A Site

Lipins are phosphatidate phosphatases that generate diacylglycerol (DAG). In this study, we report that yeast lipin, Pah1p, controls the formation of cytosolic lipid droplets. Disruption of PAH1 resulted in a 63% decrease in droplet number, although total neutral lipid levels did not change. This was accompanied by an accumulation of neutral lipids in the endoplasmic reticulum (ER). The droplet biogenesis defect was not a result of alterations in neutral lipid ratios. No droplets were visible in the absence of both PAH1 and steryl acyltransferases when grown in glucose medium, even though the strain produces as much triacylglycerol as wild type. The requirement of PAH1 for normal droplet formation can be bypassed by a knockout of DGK1. Nem1p, the activator of Pah1p, localizes to a single punctum per cell on the ER that is usually next to a droplet, suggesting that it is a site of droplet assembly. Overall, this study provides strong evidence that DAG generated by Pah1p is important for droplet biogenesis.

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YPR139c/LOA1encodes a novel lysophosphatidic acid acyltransferase associated with lipid droplets and involved in TAG homeostasis

Molecular Biology of the Cell ◽

10.1091/mbc.e11-07-0650 ◽

2012 ◽

Vol 23 (2) ◽

pp. 233-246 ◽

Cited By ~ 26

Author(s):

Sophie Ayciriex ◽

Marina Le Guédard ◽

Nadine Camougrand ◽

Gisèle Velours ◽

Mario Schoene ◽

...

Keyword(s):

Lysophosphatidic Acid ◽

Lipid Droplets ◽

Neutral Lipids ◽

In Vitro Assays ◽

Metabolic Labeling ◽

Lysophosphatidic Acid Acyltransferase ◽

Escherichia Coli Cells ◽

Type Strains

For many years, lipid droplets (LDs) were considered to be an inert store of lipids. However, recent data showed that LDs are dynamic organelles playing an important role in storage and mobilization of neutral lipids. In this paper, we report the characterization of LOA1 (alias VPS66, alias YPR139c), a yeast member of the glycerolipid acyltransferase family. LOA1 mutants show abnormalities in LD morphology. As previously reported, cells lacking LOA1 contain more LDs. Conversely, we showed that overexpression results in fewer LDs. We then compared the lipidome of loa1Δ mutant and wild-type strains. Steady-state metabolic labeling of loa1Δ revealed a significant reduction in triacylglycerol content, while phospholipid (PL) composition remained unchanged. Interestingly, lipidomic analysis indicates that both PLs and glycerolipids are qualitatively affected by the mutation, suggesting that Loa1p is a lysophosphatidic acid acyltransferase (LPA AT) with a preference for oleoyl-CoA. This hypothesis was tested by in vitro assays using both membranes of Escherichia coli cells expressing LOA1 and purified proteins as enzyme sources. Our results from purification of subcellular compartments and proteomic studies show that Loa1p is associated with LD and active in this compartment. Loa1p is therefore a novel LPA AT and plays a role in LD formation.

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A Unique Junctional Interface at Contact Sites Between the Endoplasmic Reticulum and Lipid Droplets

Frontiers in Cell and Developmental Biology ◽

10.3389/fcell.2021.650186 ◽

2021 ◽

Vol 9 ◽

Author(s):

Vineet Choudhary ◽

Roger Schneiter

Keyword(s):

Endoplasmic Reticulum ◽

Lipid Droplets ◽

Neutral Lipids ◽

Close Contact ◽

Lipid Storage ◽

Metabolic Energy ◽

Lipid Monolayer ◽

Storage Diseases ◽

Contact Sites ◽

Ordered Assembly

Lipid droplets (LDs) constitute compartments dedicated to the storage of metabolic energy in the form of neutral lipids. LDs originate from the endoplasmic reticulum (ER) with which they maintain close contact throughout their life cycle. These ER–LD junctions facilitate the exchange of both proteins and lipids between these two compartments. In recent years, proteins that are important for the proper formation of LDs and localize to ER–LD junctions have been identified. This junction is unique as it is generally believed to invoke a transition from the ER bilayer membrane to a lipid monolayer that delineates LDs. Proper formation of this junction requires the ordered assembly of proteins and lipids at specialized ER subdomains. Without such a well-ordered assembly of LD biogenesis factors, neutral lipids are synthesized throughout the ER membrane, resulting in the formation of aberrant LDs. Such ectopically formed LDs impact ER and lipid homeostasis, resulting in different types of lipid storage diseases. In response to starvation, the ER–LD junction recruits factors that tether the vacuole to these junctions to facilitate LD degradation. In addition, LDs maintain close contacts with peroxisomes and mitochondria for metabolic channeling of the released fatty acids toward beta-oxidation. In this review, we discuss the function of different components that ensure proper functioning of LD contact sites, their role in lipogenesis and lipolysis, and their relation to lipid storage diseases.

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