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Exendin-4 Inhibits the Expression of SEPP1 and Fetuin-A via Improvement of Palmitic Acid-Induced Endoplasmic Reticulum Stress by AMPK.

Lee J, Hong SW, Park SE, Rhee EJ, Park CY, Oh KW, Park SW, Lee WY - Endocrinol Metab (Seoul) (2014)

Bottom Line: Exendin-4 reduced the expression of SEPP1, fetuin-A, and ER stress markers including PKR-like ER kinase, inositol-requiring kinase 1α, activating transcription factor 6, and C/EBP homologous protein in HepG2 cells.Exendin-4 also reduced the expression of SEPP1 and fetuin-A in cells treated with tunicamycin, an ER stress inducer.In addition, exendin-4 treatment did not decrease SEPP1 and fetuin-A expression in cells transfected with AMPK siRNA.

View Article: PubMed Central - PubMed

Affiliation: Institute of Medical Research, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.

ABSTRACT

Background: Selenoprotein P (SEPP1) and fetuin-A, both circulating liver-derived glycoproteins, are novel biomarkers for insulin resistance and nonalcoholic fatty liver disease. However, the effect of exendin-4 (Ex-4), a glucagon-like peptide-1 receptor agonist, on the expression of hepatokines, SEPP1, and fetuin-A, is unknown.

Methods: The human hepatoma cell line HepG2 was treated with palmitic acid (PA; 0.4 mM) and tunicamycin (tuni; 2ug/ml) with or without exendin-4 (100 nM) for 24 hours. The change in expression of PA-induced SEPP1, fetuin-A, and endoplasmic reticulum (ER) stress markers by exendin-4 treatment were evaluated using quantitative real-time reverse transcription polymerase chain reaction and Western blotting. Transfection of cells with AMP-activated protein kinase (AMPK) small interfering RNA (siRNA) was performed to establish the effect of exendin-4-mediated AMPK in the regulation of SEPP1 and fetuin-A expression.

Results: Exendin-4 reduced the expression of SEPP1, fetuin-A, and ER stress markers including PKR-like ER kinase, inositol-requiring kinase 1α, activating transcription factor 6, and C/EBP homologous protein in HepG2 cells. Exendin-4 also reduced the expression of SEPP1 and fetuin-A in cells treated with tunicamycin, an ER stress inducer. In cells treated with the AMPK activator 5-aminoidazole-4-carboxamide ribonucleotide (AICAR), the expression of hepatic SEPP1 and fetuin-A were negatively related by AMPK, which is the target of exendin-4. In addition, exendin-4 treatment did not decrease SEPP1 and fetuin-A expression in cells transfected with AMPK siRNA.

Conclusion: These data suggest that exendin-4 can attenuate the expression of hepatic SEPP1 and fetuin-A via improvement of PA-induced ER stress by AMPK.

No MeSH data available.


Related in: MedlinePlus

Expression of selenoprotein P (SEPP1) and fetuin-A increased by endoplasmic reticulum (ER) stress was reversed by exendin-4 (Ex-4). HepG2 cells were treated with tunicamycin (Tuni), an ER stress inducer, for 24 hours, after which tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, or Ex-4 was added for 24 hours. The gene expression levels of X-box binding protein 1 (XBP-1), SEPP1, and fetuin-A were analyzed using quantitative real-time reverse transcription polymerase chain reaction, and the data were normalized based on the β-actin. Con, control; mRNA, messenger RNA. aP<0.05; bP<0.01.
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Figure 3: Expression of selenoprotein P (SEPP1) and fetuin-A increased by endoplasmic reticulum (ER) stress was reversed by exendin-4 (Ex-4). HepG2 cells were treated with tunicamycin (Tuni), an ER stress inducer, for 24 hours, after which tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, or Ex-4 was added for 24 hours. The gene expression levels of X-box binding protein 1 (XBP-1), SEPP1, and fetuin-A were analyzed using quantitative real-time reverse transcription polymerase chain reaction, and the data were normalized based on the β-actin. Con, control; mRNA, messenger RNA. aP<0.05; bP<0.01.

Mentions: To examine whether increased expression of SEPP1 and fetuin-A secondary to PA treatment is associated with ER stress, HepG2 cells were pretreated with Tuni, an ER stress inducer, followed by the addition of TUDCA, an ER stress inhibitor, or exendin-4. As shown in Fig. 3, the expression of SEPP1 and fetuin-A mRNA as well as XBP-1, a marker for ER stress, was significantly higher in cells treated with Tuni than in the untreated controls. In contrast, supplementation of TUDCA in cells exposed to Tuni completely abolished the effect of Tuni on the expression of these genes. Interestingly, the expression of XBP-1, SEPP1, and fetuin-A in cells treated with exendin-4 exhibited levels similar to those in cells treated with TUDCA. These data suggest that exendin-4 has a protective effect against ER stress, and that exendin-4 attenuates the expression of the SEPP1 and fetuin-A genes by relieving ER stress.


Exendin-4 Inhibits the Expression of SEPP1 and Fetuin-A via Improvement of Palmitic Acid-Induced Endoplasmic Reticulum Stress by AMPK.

Lee J, Hong SW, Park SE, Rhee EJ, Park CY, Oh KW, Park SW, Lee WY - Endocrinol Metab (Seoul) (2014)

Expression of selenoprotein P (SEPP1) and fetuin-A increased by endoplasmic reticulum (ER) stress was reversed by exendin-4 (Ex-4). HepG2 cells were treated with tunicamycin (Tuni), an ER stress inducer, for 24 hours, after which tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, or Ex-4 was added for 24 hours. The gene expression levels of X-box binding protein 1 (XBP-1), SEPP1, and fetuin-A were analyzed using quantitative real-time reverse transcription polymerase chain reaction, and the data were normalized based on the β-actin. Con, control; mRNA, messenger RNA. aP<0.05; bP<0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508262&req=5

Figure 3: Expression of selenoprotein P (SEPP1) and fetuin-A increased by endoplasmic reticulum (ER) stress was reversed by exendin-4 (Ex-4). HepG2 cells were treated with tunicamycin (Tuni), an ER stress inducer, for 24 hours, after which tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, or Ex-4 was added for 24 hours. The gene expression levels of X-box binding protein 1 (XBP-1), SEPP1, and fetuin-A were analyzed using quantitative real-time reverse transcription polymerase chain reaction, and the data were normalized based on the β-actin. Con, control; mRNA, messenger RNA. aP<0.05; bP<0.01.
Mentions: To examine whether increased expression of SEPP1 and fetuin-A secondary to PA treatment is associated with ER stress, HepG2 cells were pretreated with Tuni, an ER stress inducer, followed by the addition of TUDCA, an ER stress inhibitor, or exendin-4. As shown in Fig. 3, the expression of SEPP1 and fetuin-A mRNA as well as XBP-1, a marker for ER stress, was significantly higher in cells treated with Tuni than in the untreated controls. In contrast, supplementation of TUDCA in cells exposed to Tuni completely abolished the effect of Tuni on the expression of these genes. Interestingly, the expression of XBP-1, SEPP1, and fetuin-A in cells treated with exendin-4 exhibited levels similar to those in cells treated with TUDCA. These data suggest that exendin-4 has a protective effect against ER stress, and that exendin-4 attenuates the expression of the SEPP1 and fetuin-A genes by relieving ER stress.

Bottom Line: Exendin-4 reduced the expression of SEPP1, fetuin-A, and ER stress markers including PKR-like ER kinase, inositol-requiring kinase 1α, activating transcription factor 6, and C/EBP homologous protein in HepG2 cells.Exendin-4 also reduced the expression of SEPP1 and fetuin-A in cells treated with tunicamycin, an ER stress inducer.In addition, exendin-4 treatment did not decrease SEPP1 and fetuin-A expression in cells transfected with AMPK siRNA.

View Article: PubMed Central - PubMed

Affiliation: Institute of Medical Research, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.

ABSTRACT

Background: Selenoprotein P (SEPP1) and fetuin-A, both circulating liver-derived glycoproteins, are novel biomarkers for insulin resistance and nonalcoholic fatty liver disease. However, the effect of exendin-4 (Ex-4), a glucagon-like peptide-1 receptor agonist, on the expression of hepatokines, SEPP1, and fetuin-A, is unknown.

Methods: The human hepatoma cell line HepG2 was treated with palmitic acid (PA; 0.4 mM) and tunicamycin (tuni; 2ug/ml) with or without exendin-4 (100 nM) for 24 hours. The change in expression of PA-induced SEPP1, fetuin-A, and endoplasmic reticulum (ER) stress markers by exendin-4 treatment were evaluated using quantitative real-time reverse transcription polymerase chain reaction and Western blotting. Transfection of cells with AMP-activated protein kinase (AMPK) small interfering RNA (siRNA) was performed to establish the effect of exendin-4-mediated AMPK in the regulation of SEPP1 and fetuin-A expression.

Results: Exendin-4 reduced the expression of SEPP1, fetuin-A, and ER stress markers including PKR-like ER kinase, inositol-requiring kinase 1α, activating transcription factor 6, and C/EBP homologous protein in HepG2 cells. Exendin-4 also reduced the expression of SEPP1 and fetuin-A in cells treated with tunicamycin, an ER stress inducer. In cells treated with the AMPK activator 5-aminoidazole-4-carboxamide ribonucleotide (AICAR), the expression of hepatic SEPP1 and fetuin-A were negatively related by AMPK, which is the target of exendin-4. In addition, exendin-4 treatment did not decrease SEPP1 and fetuin-A expression in cells transfected with AMPK siRNA.

Conclusion: These data suggest that exendin-4 can attenuate the expression of hepatic SEPP1 and fetuin-A via improvement of PA-induced ER stress by AMPK.

No MeSH data available.


Related in: MedlinePlus