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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

Exendin-4 (Ex-4) reduced the expression of palmitic acid (PA)-induced endoplasmic reticulum stress markers. HepG2 cells were incubated in the presence or absence of PA-containing medium, and treated with or without 100 nM exendin-4 for 24 hours. Protein expression of inositol-requiring enzyme-1α (IRE1α), PKR-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and CCAAT/enhancer binding homologous protein (CHOP) were analyzed by Western blotting. P-IRE1α, phosphor-IRE1α; P-PERK, phosphor-PERK.
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Figure 2: Exendin-4 (Ex-4) reduced the expression of palmitic acid (PA)-induced endoplasmic reticulum stress markers. HepG2 cells were incubated in the presence or absence of PA-containing medium, and treated with or without 100 nM exendin-4 for 24 hours. Protein expression of inositol-requiring enzyme-1α (IRE1α), PKR-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and CCAAT/enhancer binding homologous protein (CHOP) were analyzed by Western blotting. P-IRE1α, phosphor-IRE1α; P-PERK, phosphor-PERK.

Mentions: PA, a saturated fatty acid, disrupts ER homeostasis [17], potentially leading to diabetes and hepatic steatosis. To evaluate the effect of exendin-4 on PA-induced ER stress in hepatocyte cells, we examined the effect of exendin-4 on the expression of the ER stress markers IRE1α, PERK, ATF6, and CHOP. Cells exposed to PA displayed higher P-IRE1α, P-PERK, ATF6, and CHOP protein levels, whereas PA-induced increases in the ER stress marker protein levels were reversed in cells treated with exendin-4 (Fig. 2). These results suggest that exendin-4 reduces the expression of PA-induced increases in SEPP1 and fetuin-A, and that exendin-4 improves PA-induced 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)

Exendin-4 (Ex-4) reduced the expression of palmitic acid (PA)-induced endoplasmic reticulum stress markers. HepG2 cells were incubated in the presence or absence of PA-containing medium, and treated with or without 100 nM exendin-4 for 24 hours. Protein expression of inositol-requiring enzyme-1α (IRE1α), PKR-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and CCAAT/enhancer binding homologous protein (CHOP) were analyzed by Western blotting. P-IRE1α, phosphor-IRE1α; P-PERK, phosphor-PERK.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Exendin-4 (Ex-4) reduced the expression of palmitic acid (PA)-induced endoplasmic reticulum stress markers. HepG2 cells were incubated in the presence or absence of PA-containing medium, and treated with or without 100 nM exendin-4 for 24 hours. Protein expression of inositol-requiring enzyme-1α (IRE1α), PKR-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and CCAAT/enhancer binding homologous protein (CHOP) were analyzed by Western blotting. P-IRE1α, phosphor-IRE1α; P-PERK, phosphor-PERK.
Mentions: PA, a saturated fatty acid, disrupts ER homeostasis [17], potentially leading to diabetes and hepatic steatosis. To evaluate the effect of exendin-4 on PA-induced ER stress in hepatocyte cells, we examined the effect of exendin-4 on the expression of the ER stress markers IRE1α, PERK, ATF6, and CHOP. Cells exposed to PA displayed higher P-IRE1α, P-PERK, ATF6, and CHOP protein levels, whereas PA-induced increases in the ER stress marker protein levels were reversed in cells treated with exendin-4 (Fig. 2). These results suggest that exendin-4 reduces the expression of PA-induced increases in SEPP1 and fetuin-A, and that exendin-4 improves PA-induced 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