Lipidomic and proteomic analysis of Caenorhabditis elegans lipid droplets and identification of ACS-4 as a lipid droplet-associated protein

Abstract

Lipid droplets are cytoplasmic organelles that store neutral lipids for membrane synthesis and energy reserves. In this study, we characterized the lipid and protein composition of purified C. elegans lipid droplets. These lipid droplets are composed mainly of triacylglycerols, surrounded by a phospholipid monolayer composed primarily of phosphatidylcholine and phosphatidylethanolamine. The fatty acid composition of the triacylglycerols is rich in fatty acid species obtained from the dietary E. coli, including cyclopropane fatty acids and cis-vaccenic acid. Unlike other organisms, C. elegans lipid droplets contain very little cholesterol or cholesterol esters. Comparison of the lipid droplet proteomes of wild type and high-fat daf-2 mutant strains shows a very similar proteome in both strains, except that the most abundant protein in the C. elegans lipid droplet proteome, MDT-28, is relatively less abundant in lipid droplets isolated from daf-2 mutants. Functional analysis of lipid droplet proteins identified in our proteomic studies indicated an enrichment of proteins required for growth and fat homeostasis in C. elegans. Finally, we confirmed the localization of one of the newly identified lipid droplet proteins, ACS-4. We found that ACS-4 localizes to the surface of lipid droplets in the C. elegans intestine and skin. This study bolsters C. elegans as a model to study the dynamics and functions of lipid droplets in a multicellular organism.

Integrated omics study of lipid droplets from Plasmodiophora brassicae

“…3, Table S1). This diversity of lipid droplets-associated protein was also observed in earlier reported proteomics studies of multiple species, including oleaginous bacterium24, green algae35, Drosophila 2728, C. elegans 25, adult mice19 and mammalian cells26. The number of enzymes present in lipid droplets is greater in mice than in P. brassicae 19, which is greater in P. brassicae than that of the oleaginous bacterium PD63024.…”

“…14 enzymes were involved in lipid synthesis and degradation, including 3 transferases, 2 ligases, 7 dehydrogenases, 1 reductase and 1 synthase. 83 enzymes were involved in metabolic processes, while 28 were involved in biosynthetic processes ribosome, chaperone and histone proteins are abundant in the lipid droplets of P. brassicae , which had been identified in the lipid droplet proteomes of oleaginous bacterium24, Caenorhabditis elegans 25, mammalian cells26, adult mice19 and Drosophila embryos2728. Rab GTPase29, dynein, kinesin30, kinesin motor domain containing protein, actin31, 14-3-3 signaling proteins17 and heat shock protein 7032 were previously reported to play important roles in maintaining the functions of lipid droplets, and these proteins were identified in the lipid droplets proteome of P. brassicae .…”

Iron Overload Coordinately Promotes Ferritin Expression and Fat Accumulation in Caenorhabditis elegans

“…Although the reduced fat accumulation may be due to reduced yolk production, an alternative interpretation is that vitellogenins play a role in intracellular lipid transport. VIT-2 was recently identified as a lipid dropletassociated protein Vrablik et al 2015), and here we found that iron promoted the accumulation of VIT-2 protein in LDs (Figure 5,D and E). Meanwhile, the expression of VIT-2::GFP is also brighter in cyp-23A1(gk253) mutant, but not in acs-20(tm3232) mutants compared to N2 regardless of treatment with FAC ( Figure S9).…”

“…The expression of VIT-2::GFP is also brighter in cyp-23A1(gk253) mutant, but not in acs-20(tm3232) mutant compared to N2 under both FAC treatment and no FAC (Figure S9). VIT-2 is a yolk lipoprotein, but it has also been reported to be a C. elegans lipid droplet-associated protein Vrablik et al 2015). After isolating lipid droplets and other cellular fractions of vit-2::gfp worms treated with FAC 0 and 5.0 mg/ml, Western blot analysis using anti-GFP antibody showed that the level of VIT-2 protein was significantly increased in LD, total membrane (TM), and postnuclear supernatant (PNS) under FAC 5.0 mg/ml compared to FAC 0 mg/ml ( Figure 5, D and E).…”

Lipid droplet functions beyond energy storage

“…Lipidomics reveals that the core of an LD can contain over 100 different species of neutral lipids [22-26]. This repertoire is sure to expand over the next few years with the development of increasingly sophisticated lipidomics methods as well as imaging techniques based on Raman and mass spectrometry [27-34].…”