Fig. 1Exendin-4 (Ex-4) reduced the expression of selenoprotein P (SEPP1) and fetuin-A in HepG2 cells treated with palmitic acid (PA). HepG2 cells were incubated in the presence or absence of PA-containing medium, and treated with or without 100 nM Ex-4 for 24 hours. (A, B) The expression of SEPP1 and fetuin-A was analyzed using quantitative real-time reverse transcription polymerase chain reaction and Western blotting, and the data were normalized based on the β-actin. Con, control; mRNA, messenger RNA. aP<0.05; bP<0.01.
Fig. 2Exendin-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.
Fig. 3Expression 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.
Fig. 4Expression 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.