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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 in cells treated with exendin-4 (Ex-4) was regulated by AMP-activated protein kinase (AMPK). (A) HepG2 cells were treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, for 24 hours. (B-D) Cells were transfected with the specific small interfering RNA (siRNA) for AMPK or scrambled siRNA (Scr) for 24 hours, and then added to a container with or without 100 nM Ex-4 for 24 hours. The expression of AMPK, SEPP1, and fetuin-A messenger RNA (mRNA) was measured using quantitative real-time reverse transcription polymerase chain reaction. Con, control. aP<0.05; bP<0.01.
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Figure 4: Expression of selenoprotein P (SEPP1) and fetuin-A in cells treated with exendin-4 (Ex-4) was regulated by AMP-activated protein kinase (AMPK). (A) HepG2 cells were treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, for 24 hours. (B-D) Cells were transfected with the specific small interfering RNA (siRNA) for AMPK or scrambled siRNA (Scr) for 24 hours, and then added to a container with or without 100 nM Ex-4 for 24 hours. The expression of AMPK, SEPP1, and fetuin-A messenger RNA (mRNA) was measured using quantitative real-time reverse transcription polymerase chain reaction. Con, control. aP<0.05; bP<0.01.

Mentions: The AMPK activator AICAR can inhibit fatty acid-induced ER stress [18]. SIRT1-AMPK signaling induces a potent pro-tective effect of exendin-4 against fatty liver disease [19]. In this study, we have demonstrated that AICAR downregulates the expression of the SEPP1 and fetuin-A genes (Fig. 4A). We also examined whether the inhibitory effect of exendin-4 on the expression of ER stress-induced SEPP1 and fetuin-A is mediated by AMPK. The expression of AMPK increased in HepG2 cells treated with exendin-4 [19]. However, when the expression of AMPK was inhibited by AMPK siRNA, the expression of SEPP1 and fetuin-A in cells treated with exendin-4 did not decrease (Fig. 4B-D). These results suggest that exen-din-4 inhibits expression of ER stress-induced SEPP1 and fetuin-A via stimulation of AMPK. Activation of AMPK may mediate an inhibitory effect of exendin-4 on ER stress-induced hepatokines, such as SEPP1 and fetuin-A.


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 in cells treated with exendin-4 (Ex-4) was regulated by AMP-activated protein kinase (AMPK). (A) HepG2 cells were treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, for 24 hours. (B-D) Cells were transfected with the specific small interfering RNA (siRNA) for AMPK or scrambled siRNA (Scr) for 24 hours, and then added to a container with or without 100 nM Ex-4 for 24 hours. The expression of AMPK, SEPP1, and fetuin-A messenger RNA (mRNA) was measured using quantitative real-time reverse transcription polymerase chain reaction. Con, control. aP<0.05; bP<0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Expression of selenoprotein P (SEPP1) and fetuin-A in cells treated with exendin-4 (Ex-4) was regulated by AMP-activated protein kinase (AMPK). (A) HepG2 cells were treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, for 24 hours. (B-D) Cells were transfected with the specific small interfering RNA (siRNA) for AMPK or scrambled siRNA (Scr) for 24 hours, and then added to a container with or without 100 nM Ex-4 for 24 hours. The expression of AMPK, SEPP1, and fetuin-A messenger RNA (mRNA) was measured using quantitative real-time reverse transcription polymerase chain reaction. Con, control. aP<0.05; bP<0.01.
Mentions: The AMPK activator AICAR can inhibit fatty acid-induced ER stress [18]. SIRT1-AMPK signaling induces a potent pro-tective effect of exendin-4 against fatty liver disease [19]. In this study, we have demonstrated that AICAR downregulates the expression of the SEPP1 and fetuin-A genes (Fig. 4A). We also examined whether the inhibitory effect of exendin-4 on the expression of ER stress-induced SEPP1 and fetuin-A is mediated by AMPK. The expression of AMPK increased in HepG2 cells treated with exendin-4 [19]. However, when the expression of AMPK was inhibited by AMPK siRNA, the expression of SEPP1 and fetuin-A in cells treated with exendin-4 did not decrease (Fig. 4B-D). These results suggest that exen-din-4 inhibits expression of ER stress-induced SEPP1 and fetuin-A via stimulation of AMPK. Activation of AMPK may mediate an inhibitory effect of exendin-4 on ER stress-induced hepatokines, such as SEPP1 and fetuin-A.

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