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Decrease in membrane phospholipid unsaturation induces unfolded protein response.

Ariyama H, Kono N, Matsuda S, Inoue T, Arai H - J. Biol. Chem. (2010)

Bottom Line: In this study we showed that stearoyl-CoA desaturase 1 (SCD1) knockdown increased the amount of saturated fatty acids and decreased that of monounsaturated fatty acids in phospholipids without affecting the amount or the composition of free fatty acid and induced unfolded protein response (UPR), evidenced by increased expression of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) mRNAs and splicing of Xbox-binding protein 1 (XBP1) mRNA.Finally we showed that palmitic acid-induced UPR was significantly enhanced by LPCAT3 knockdown as well as SCD1 knockdown.These results suggest that a decrease in membrane phospholipid unsaturation induces UPR.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.

ABSTRACT
Various kinds of fatty acids are distributed in membrane phospholipids in mammalian cells and tissues. The degree of fatty acid unsaturation in membrane phospholipids affects many membrane-associated functions and can be influenced by diet and by altered activities of lipid-metabolizing enzymes such as fatty acid desaturases. However, little is known about how mammalian cells respond to changes in phospholipid fatty acid composition. In this study we showed that stearoyl-CoA desaturase 1 (SCD1) knockdown increased the amount of saturated fatty acids and decreased that of monounsaturated fatty acids in phospholipids without affecting the amount or the composition of free fatty acid and induced unfolded protein response (UPR), evidenced by increased expression of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) mRNAs and splicing of Xbox-binding protein 1 (XBP1) mRNA. SCD1 knockdown-induced UPR was rescued by various unsaturated fatty acids and was enhanced by saturated fatty acid. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), which incorporates preferentially polyunsaturated fatty acids into phosphatidylcholine, was up-regulated in SCD1 knockdown cells. Knockdown of LPCAT3 synergistically enhanced UPR with SCD1 knockdown. Finally we showed that palmitic acid-induced UPR was significantly enhanced by LPCAT3 knockdown as well as SCD1 knockdown. These results suggest that a decrease in membrane phospholipid unsaturation induces UPR.

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LPCAT3 knockdown cells are susceptible to palmitic acid exposure. HeLa cells were transfected with the indicated siRNA. At 60 h after transfection cells were further incubated for 12 h in media supplemented with 16:0 (100 μm) and then harvested. A and B, expressions of CHOP (A) and GRP78 (B) mRNAs were detected by quantitative real-time PCR. The expression level of each gene was normalized to the GAPDH gene and is represented as -fold induction over siControl treated with ethanol. C, semiquantitative reverse transcription-PCR analysis of XBP1 spliced and unspliced mRNA is shown. The positions of the unspliced form (u) and spliced form (s) are indicated. Thapsigargin-treated cells (Tg) were used as a positive control. The asterisks indicate significant differences compared with siControl-transfected cells, which were treated with ethanol (p < 0.01).
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Figure 8: LPCAT3 knockdown cells are susceptible to palmitic acid exposure. HeLa cells were transfected with the indicated siRNA. At 60 h after transfection cells were further incubated for 12 h in media supplemented with 16:0 (100 μm) and then harvested. A and B, expressions of CHOP (A) and GRP78 (B) mRNAs were detected by quantitative real-time PCR. The expression level of each gene was normalized to the GAPDH gene and is represented as -fold induction over siControl treated with ethanol. C, semiquantitative reverse transcription-PCR analysis of XBP1 spliced and unspliced mRNA is shown. The positions of the unspliced form (u) and spliced form (s) are indicated. Thapsigargin-treated cells (Tg) were used as a positive control. The asterisks indicate significant differences compared with siControl-transfected cells, which were treated with ethanol (p < 0.01).

Mentions: To test the possibility that decreases of unsaturated fatty acids in phospholipids increase the susceptibility to exogenous palmitic acid toxicity, we examined the effect of LPCAT3 knockdown on 16:0-induced UPR signaling. LPCAT3 knockdown alone did not induce UPR activation in control cells but greatly enhanced the CHOP and GRP78 mRNA expressions and splicing of XBP1 mRNA in 16:0-treated cells (Fig. 8, A–C). Lipid analysis showed that LPCAT3 knockdown reduced the amounts of unsaturated fatty acids, especially 18:1n-9, 18:1n-7, and 20:4 in phospholipids of 16:0-treated cells (Table 2). These results indicate that decreases of unsaturated fatty acids in phospholipids make cells more susceptible to palmitic acid toxicity.


Decrease in membrane phospholipid unsaturation induces unfolded protein response.

Ariyama H, Kono N, Matsuda S, Inoue T, Arai H - J. Biol. Chem. (2010)

LPCAT3 knockdown cells are susceptible to palmitic acid exposure. HeLa cells were transfected with the indicated siRNA. At 60 h after transfection cells were further incubated for 12 h in media supplemented with 16:0 (100 μm) and then harvested. A and B, expressions of CHOP (A) and GRP78 (B) mRNAs were detected by quantitative real-time PCR. The expression level of each gene was normalized to the GAPDH gene and is represented as -fold induction over siControl treated with ethanol. C, semiquantitative reverse transcription-PCR analysis of XBP1 spliced and unspliced mRNA is shown. The positions of the unspliced form (u) and spliced form (s) are indicated. Thapsigargin-treated cells (Tg) were used as a positive control. The asterisks indicate significant differences compared with siControl-transfected cells, which were treated with ethanol (p < 0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2903364&req=5

Figure 8: LPCAT3 knockdown cells are susceptible to palmitic acid exposure. HeLa cells were transfected with the indicated siRNA. At 60 h after transfection cells were further incubated for 12 h in media supplemented with 16:0 (100 μm) and then harvested. A and B, expressions of CHOP (A) and GRP78 (B) mRNAs were detected by quantitative real-time PCR. The expression level of each gene was normalized to the GAPDH gene and is represented as -fold induction over siControl treated with ethanol. C, semiquantitative reverse transcription-PCR analysis of XBP1 spliced and unspliced mRNA is shown. The positions of the unspliced form (u) and spliced form (s) are indicated. Thapsigargin-treated cells (Tg) were used as a positive control. The asterisks indicate significant differences compared with siControl-transfected cells, which were treated with ethanol (p < 0.01).
Mentions: To test the possibility that decreases of unsaturated fatty acids in phospholipids increase the susceptibility to exogenous palmitic acid toxicity, we examined the effect of LPCAT3 knockdown on 16:0-induced UPR signaling. LPCAT3 knockdown alone did not induce UPR activation in control cells but greatly enhanced the CHOP and GRP78 mRNA expressions and splicing of XBP1 mRNA in 16:0-treated cells (Fig. 8, A–C). Lipid analysis showed that LPCAT3 knockdown reduced the amounts of unsaturated fatty acids, especially 18:1n-9, 18:1n-7, and 20:4 in phospholipids of 16:0-treated cells (Table 2). These results indicate that decreases of unsaturated fatty acids in phospholipids make cells more susceptible to palmitic acid toxicity.

Bottom Line: In this study we showed that stearoyl-CoA desaturase 1 (SCD1) knockdown increased the amount of saturated fatty acids and decreased that of monounsaturated fatty acids in phospholipids without affecting the amount or the composition of free fatty acid and induced unfolded protein response (UPR), evidenced by increased expression of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) mRNAs and splicing of Xbox-binding protein 1 (XBP1) mRNA.Finally we showed that palmitic acid-induced UPR was significantly enhanced by LPCAT3 knockdown as well as SCD1 knockdown.These results suggest that a decrease in membrane phospholipid unsaturation induces UPR.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.

ABSTRACT
Various kinds of fatty acids are distributed in membrane phospholipids in mammalian cells and tissues. The degree of fatty acid unsaturation in membrane phospholipids affects many membrane-associated functions and can be influenced by diet and by altered activities of lipid-metabolizing enzymes such as fatty acid desaturases. However, little is known about how mammalian cells respond to changes in phospholipid fatty acid composition. In this study we showed that stearoyl-CoA desaturase 1 (SCD1) knockdown increased the amount of saturated fatty acids and decreased that of monounsaturated fatty acids in phospholipids without affecting the amount or the composition of free fatty acid and induced unfolded protein response (UPR), evidenced by increased expression of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) mRNAs and splicing of Xbox-binding protein 1 (XBP1) mRNA. SCD1 knockdown-induced UPR was rescued by various unsaturated fatty acids and was enhanced by saturated fatty acid. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), which incorporates preferentially polyunsaturated fatty acids into phosphatidylcholine, was up-regulated in SCD1 knockdown cells. Knockdown of LPCAT3 synergistically enhanced UPR with SCD1 knockdown. Finally we showed that palmitic acid-induced UPR was significantly enhanced by LPCAT3 knockdown as well as SCD1 knockdown. These results suggest that a decrease in membrane phospholipid unsaturation induces UPR.

Show MeSH
Related in: MedlinePlus