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The proteome of cholesteryl-ester-enriched versus triacylglycerol-enriched lipid droplets.

Khor VK, Ahrends R, Lin Y, Shen WJ, Adams CM, Roseman AN, Cortez Y, Teruel MN, Azhar S, Kraemer FB - PLoS ONE (2014)

Bottom Line: 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.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.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.

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California, United States of America; Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America.

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.

No MeSH data available.


Treatment of cultured granulosa cells with FA or HDL leads to lipid droplet formation.Granulosa cells untreated (A) or treated with 240 µM FA (B) or 500 µg/ml HDL (C) form lipid droplets. C. Quantification of total cellular cholesterol (TC) and TAG in granulosa cells following incubation with either FA or HDL. *, p<0.001 versus HDL-loaded; †, p<0.001 versus FA-loaded.
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pone-0105047-g001: Treatment of cultured granulosa cells with FA or HDL leads to lipid droplet formation.Granulosa cells untreated (A) or treated with 240 µM FA (B) or 500 µg/ml HDL (C) form lipid droplets. C. Quantification of total cellular cholesterol (TC) and TAG in granulosa cells following incubation with either FA or HDL. *, p<0.001 versus HDL-loaded; †, p<0.001 versus FA-loaded.

Mentions: Granulosa cells from estrogen-primed female naïve rats were untreated (Figure 1A) or treated with either 240 µM FA or 500 µg/ml HDL for 48 hrs to induce the formation of TAG-enriched (Figure 1B) or CE-enriched LDs (Figure 1C), respectively, as detected by light microscopy. Cellular total cholesterol content was elevated (p<0.001) in cells incubated with HDL to induce formation of 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). Using electron microscopy, it is apparent that only rare LDs were detected in cells cultured in the absence of either 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.


The proteome of cholesteryl-ester-enriched versus triacylglycerol-enriched lipid droplets.

Khor VK, Ahrends R, Lin Y, Shen WJ, Adams CM, Roseman AN, Cortez Y, Teruel MN, Azhar S, Kraemer FB - PLoS ONE (2014)

Treatment of cultured granulosa cells with FA or HDL leads to lipid droplet formation.Granulosa cells untreated (A) or treated with 240 µM FA (B) or 500 µg/ml HDL (C) form lipid droplets. C. Quantification of total cellular cholesterol (TC) and TAG in granulosa cells following incubation with either FA or HDL. *, p<0.001 versus HDL-loaded; †, p<0.001 versus FA-loaded.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4128735&req=5

pone-0105047-g001: Treatment of cultured granulosa cells with FA or HDL leads to lipid droplet formation.Granulosa cells untreated (A) or treated with 240 µM FA (B) or 500 µg/ml HDL (C) form lipid droplets. C. Quantification of total cellular cholesterol (TC) and TAG in granulosa cells following incubation with either FA or HDL. *, p<0.001 versus HDL-loaded; †, p<0.001 versus FA-loaded.
Mentions: Granulosa cells from estrogen-primed female naïve rats were untreated (Figure 1A) or treated with either 240 µM FA or 500 µg/ml HDL for 48 hrs to induce the formation of TAG-enriched (Figure 1B) or CE-enriched LDs (Figure 1C), respectively, as detected by light microscopy. Cellular total cholesterol content was elevated (p<0.001) in cells incubated with HDL to induce formation of 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). Using electron microscopy, it is apparent that only rare LDs were detected in cells cultured in the absence of either 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.

Bottom Line: 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.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.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.

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California, United States of America; Veterans Affairs Palo Alto Health Care System, Palo Alto, California, United States of America.

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.

No MeSH data available.