Abstract
Within cells, lipids are stored in the form of lipid droplets (LDs), consisting of a neutral lipid core, surrounded by a phospholipid monolayer and an outer layer of protein. LDs typically accumulate either triacylglycerol (TAG) and diacylglycerol or cholesteryl ester (CE), depending on the type of tissue. Recently, there has been an increased interest in the proteins that surround LDs. LD proteins have been found to be quite diverse, from structural proteins to metabolic enzymes, proteins involved in vesicular transport, and proteins that may play a role in LD formation. Previous proteomics analyses have focused on TAG-enriched LDs, whereas CE-enriched LDs have been largely ignored. Our study has compared the LD proteins from CE-enriched LDs to TAG-enriched LDs in steroidogenic cells. In primary rat granulosa cells loaded with either HDL to produce CE-enriched LDs or fatty acids to produce TAG-enriched LDs, 61 proteins were found to be elevated in CE-enriched LDs and 40 proteins elevated in TAG-enriched LDs with 278 proteins in similar amounts. Protein expression was further validated by selected reaction monitoring (SRM) mass spectrometry (MS). SRM verified expression of 25 of 27 peptides that were previously detected by tandem mass tagging MS. Several proteins were confirmed to be elevated in CE-enriched LDs by SRM including the intermediate filament vimentin. This study is the first to compare the proteins found on CE-enriched LDs with TAG-enriched LDs and constitutes the first step in creating a better understanding of the proteins found on CE-enriched LDs in steroidogenic cells.
Highlights
Over the past decade, there has been a rise in interest in the interactions of and proteins surrounding intracellular lipid droplets (LDs)
Cellular total cholesterol content was elevated (p,0.001) in cells incubated with high density lipoproteins (HDL) to induce formation of cholesteryl ester (CE)-enriched LDs, whereas cellular TAG was markedly elevated (p,0.001) in cells incubated with fatty acids to induce TAG-enriched LDs (Figure 1D)
It is apparent that only rare LDs were detected in cells cultured in the absence of either fatty acids (FA) or HDL (Figure 2A), whereas abundant LDs are observed in cells incubated either with FA (Figure 2B) or with HDL (Figure 2C), with the LDs appearing to be in close apposition to mitochondria and ribosomes
Summary
There has been a rise in interest in the interactions of and proteins surrounding intracellular lipid droplets (LDs). A wide array of proteins has been found on the LD surface, from lipid structural proteins to enzymes involved in metabolism, vesicular transport machinery, and several cytoskeletal proteins [1,2,3,4,5,6] These surrounding proteins have many diverse functions, ranging from LD formation, fusion, binding, and may serve as markers of cellular signaling [7]. Changes in LD binding proteins were seen between normal chow and western diet fed Ldlr2/2 or Apoe 2/2 mice, suggesting the ability LD proteins to alter cellular function and pathogenesis [2] Both approaches have highlighted the importance of LD proteins in both cellular and LD physiology
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
