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Individual stearoyl-coa desaturase 1 expression modulates endoplasmic reticulum stress and inflammation in human myotubes and is associated with skeletal muscle lipid storage and insulin sensitivity in vivo.

Peter A, Weigert C, Staiger H, Machicao F, Schick F, Machann J, Stefan N, Thamer C, Häring HU, Schleicher E - Diabetes (2009)

Bottom Line: Stearoyl-CoA desaturase 1 (SCD1) plays a key role in preventing lipotoxic effects, as it converts SFAs to less harmful monounsaturated fatty acids.In primary human myotubes, high SCD1 inducibility was associated with a low inflammatory (interleukin [IL]-6, IL-8, and chemokine [CXC motif] ligand 3 [CXCL3]) and ER stress (CCAAT/enhancer binding protein [C/EBP] homologous protein, activating transcription factor 3 [ATF3], and X-box binding protein 1 [XBP1]) response to palmitate exposure.This may describe individuals with increased capability of innoxious free fatty acid handling and benign triglyceride storage.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Medicine, Nephrology, and Clinical Chemistry, University of Tübingen, Tübingen, Germany. andreas.peter@med.uni-tuebingen.de

ABSTRACT

Objective: Increased plasma levels of free fatty acids occur in obesity and type 2 diabetes and contribute to the development of insulin resistance. Saturated fatty acids (SFAs) such as palmitate especially have lipotoxic effects leading to endoplasmatic reticulum (ER) stress, inflammation, and insulin resistance. Stearoyl-CoA desaturase 1 (SCD1) plays a key role in preventing lipotoxic effects, as it converts SFAs to less harmful monounsaturated fatty acids. Here, we tested the hypothesis that individual differences in the regulation of SCD1 expression by palmitate exist and influence insulin sensitivity and the cellular response to palmitate.

Research design and methods: Palmitate-induced gene expression was studied in primary human myotubes of 39 metabolically characterized individuals, as well as in an SCD1-overexpressing cell culture model.

Results: SCD1 mRNA expression and inducibility by palmitate in cultured myotubes showed a broad interindividual variation, presumably due to inheritable characteristics of the donors. Overexpression of SCD1 prevented the inflammatory and ER stress response to palmitate exposure. In primary human myotubes, high SCD1 inducibility was associated with a low inflammatory (interleukin [IL]-6, IL-8, and chemokine [CXC motif] ligand 3 [CXCL3]) and ER stress (CCAAT/enhancer binding protein [C/EBP] homologous protein, activating transcription factor 3 [ATF3], and X-box binding protein 1 [XBP1]) response to palmitate exposure. Finally, palmitate-stimulated SCD1 mRNA expression, positively correlated with intramyocellular lipid (IMCL) content of the donors, was measured by (1)H-magnetic resonance spectroscopy. After adjustment for IMCL, SCD1 expression and inducibility were positively correlated with insulin sensitivity.

Conclusions: We hypothesize that myocellular SCD1 inducibility by palmitate is an individual characteristic that modulates lipid storage, palmitate-induced inflammation, ER stress, and insulin resistance. This may describe individuals with increased capability of innoxious free fatty acid handling and benign triglyceride storage.

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Characterization of an SCD1 overexpression model in HEK293 cells. HEK293 cells were stably transfected with HA-tagged human SCD1. A: Endogenous SCD1 and overexpressed SCD1-HA protein expression is visualized by Western blotting using an anti–human-SCD1 antibody. The strongly overexpressed SCD1-HA is visible above the endogenous SCD1. The cytosolic protein glutamine:fructose-6-phosphate aminotransferase was used as a loading control. B: Analysis of the cellular fatty acid composition revealed a significantly higher fatty acid ratio of SCD1 product to substrate (C16:1/C16:0) in SCD1 than in control cells. Means ± SE of n = 4 are displayed. *Significantly different between the groups, P < 0.01.
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Figure 2: Characterization of an SCD1 overexpression model in HEK293 cells. HEK293 cells were stably transfected with HA-tagged human SCD1. A: Endogenous SCD1 and overexpressed SCD1-HA protein expression is visualized by Western blotting using an anti–human-SCD1 antibody. The strongly overexpressed SCD1-HA is visible above the endogenous SCD1. The cytosolic protein glutamine:fructose-6-phosphate aminotransferase was used as a loading control. B: Analysis of the cellular fatty acid composition revealed a significantly higher fatty acid ratio of SCD1 product to substrate (C16:1/C16:0) in SCD1 than in control cells. Means ± SE of n = 4 are displayed. *Significantly different between the groups, P < 0.01.

Mentions: Next, we established a cell culture model to study the role of SCD1 in fatty acid–induced inflammation and ER stress. We generated a cell line with stable overexpression of HA-tagged human SCD1 in HEK293 cells. In the Western blot, overexpressed SCD1-HA can be detected above the endogenous SCD1 protein due to the added HA tag (Fig. 2A). Fatty acid analysis revealed a significantly higher proportion of the MUFA (C16:1) and the SCD1 product-to-substrate ratio (C16:1/C16:0) in SCD1-overexpressing cells compared with controls (Fig. 2B). As overexpression of SCD1 has been shown to prevent lipotoxicity (10,11), the SCD1-overexpressing cells showed increased viability in a WST-1 assay (+42%, P = 0.007) after extended exposure to palmitate (0.6 mmol/l, 48 h). These results indicate a detoxifying effect of overexpressed SCD1 in our cell model.


Individual stearoyl-coa desaturase 1 expression modulates endoplasmic reticulum stress and inflammation in human myotubes and is associated with skeletal muscle lipid storage and insulin sensitivity in vivo.

Peter A, Weigert C, Staiger H, Machicao F, Schick F, Machann J, Stefan N, Thamer C, Häring HU, Schleicher E - Diabetes (2009)

Characterization of an SCD1 overexpression model in HEK293 cells. HEK293 cells were stably transfected with HA-tagged human SCD1. A: Endogenous SCD1 and overexpressed SCD1-HA protein expression is visualized by Western blotting using an anti–human-SCD1 antibody. The strongly overexpressed SCD1-HA is visible above the endogenous SCD1. The cytosolic protein glutamine:fructose-6-phosphate aminotransferase was used as a loading control. B: Analysis of the cellular fatty acid composition revealed a significantly higher fatty acid ratio of SCD1 product to substrate (C16:1/C16:0) in SCD1 than in control cells. Means ± SE of n = 4 are displayed. *Significantly different between the groups, P < 0.01.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2712792&req=5

Figure 2: Characterization of an SCD1 overexpression model in HEK293 cells. HEK293 cells were stably transfected with HA-tagged human SCD1. A: Endogenous SCD1 and overexpressed SCD1-HA protein expression is visualized by Western blotting using an anti–human-SCD1 antibody. The strongly overexpressed SCD1-HA is visible above the endogenous SCD1. The cytosolic protein glutamine:fructose-6-phosphate aminotransferase was used as a loading control. B: Analysis of the cellular fatty acid composition revealed a significantly higher fatty acid ratio of SCD1 product to substrate (C16:1/C16:0) in SCD1 than in control cells. Means ± SE of n = 4 are displayed. *Significantly different between the groups, P < 0.01.
Mentions: Next, we established a cell culture model to study the role of SCD1 in fatty acid–induced inflammation and ER stress. We generated a cell line with stable overexpression of HA-tagged human SCD1 in HEK293 cells. In the Western blot, overexpressed SCD1-HA can be detected above the endogenous SCD1 protein due to the added HA tag (Fig. 2A). Fatty acid analysis revealed a significantly higher proportion of the MUFA (C16:1) and the SCD1 product-to-substrate ratio (C16:1/C16:0) in SCD1-overexpressing cells compared with controls (Fig. 2B). As overexpression of SCD1 has been shown to prevent lipotoxicity (10,11), the SCD1-overexpressing cells showed increased viability in a WST-1 assay (+42%, P = 0.007) after extended exposure to palmitate (0.6 mmol/l, 48 h). These results indicate a detoxifying effect of overexpressed SCD1 in our cell model.

Bottom Line: Stearoyl-CoA desaturase 1 (SCD1) plays a key role in preventing lipotoxic effects, as it converts SFAs to less harmful monounsaturated fatty acids.In primary human myotubes, high SCD1 inducibility was associated with a low inflammatory (interleukin [IL]-6, IL-8, and chemokine [CXC motif] ligand 3 [CXCL3]) and ER stress (CCAAT/enhancer binding protein [C/EBP] homologous protein, activating transcription factor 3 [ATF3], and X-box binding protein 1 [XBP1]) response to palmitate exposure.This may describe individuals with increased capability of innoxious free fatty acid handling and benign triglyceride storage.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Medicine, Nephrology, and Clinical Chemistry, University of Tübingen, Tübingen, Germany. andreas.peter@med.uni-tuebingen.de

ABSTRACT

Objective: Increased plasma levels of free fatty acids occur in obesity and type 2 diabetes and contribute to the development of insulin resistance. Saturated fatty acids (SFAs) such as palmitate especially have lipotoxic effects leading to endoplasmatic reticulum (ER) stress, inflammation, and insulin resistance. Stearoyl-CoA desaturase 1 (SCD1) plays a key role in preventing lipotoxic effects, as it converts SFAs to less harmful monounsaturated fatty acids. Here, we tested the hypothesis that individual differences in the regulation of SCD1 expression by palmitate exist and influence insulin sensitivity and the cellular response to palmitate.

Research design and methods: Palmitate-induced gene expression was studied in primary human myotubes of 39 metabolically characterized individuals, as well as in an SCD1-overexpressing cell culture model.

Results: SCD1 mRNA expression and inducibility by palmitate in cultured myotubes showed a broad interindividual variation, presumably due to inheritable characteristics of the donors. Overexpression of SCD1 prevented the inflammatory and ER stress response to palmitate exposure. In primary human myotubes, high SCD1 inducibility was associated with a low inflammatory (interleukin [IL]-6, IL-8, and chemokine [CXC motif] ligand 3 [CXCL3]) and ER stress (CCAAT/enhancer binding protein [C/EBP] homologous protein, activating transcription factor 3 [ATF3], and X-box binding protein 1 [XBP1]) response to palmitate exposure. Finally, palmitate-stimulated SCD1 mRNA expression, positively correlated with intramyocellular lipid (IMCL) content of the donors, was measured by (1)H-magnetic resonance spectroscopy. After adjustment for IMCL, SCD1 expression and inducibility were positively correlated with insulin sensitivity.

Conclusions: We hypothesize that myocellular SCD1 inducibility by palmitate is an individual characteristic that modulates lipid storage, palmitate-induced inflammation, ER stress, and insulin resistance. This may describe individuals with increased capability of innoxious free fatty acid handling and benign triglyceride storage.

Show MeSH
Related in: MedlinePlus