Korean J Physiol Pharmacol.  2014 Aug;18(4):333-339. 10.4196/kjpp.2014.18.4.333.

Exendin-4 Improves Nonalcoholic Fatty Liver Disease by Regulating Glucose Transporter 4 Expression in ob/ob Mice

• Kim S
• Jung J
• Kim H
• Heo RW
• Yi CO
• Lee JE
• Jeon BT
• Kim WH
• Hahm JR
• Roh GS

• KMID: 2285528
• DOI: http://doi.org/10.4196/kjpp.2014.18.4.333

Abstract

Exendin-4 (Ex-4), a glucagon-like peptide-1 receptor (GLP-1R) agonist, has been known to reverse hepatic steatosis in ob/ob mice. Although many studies have evaluated molecular targets of Ex-4, its mechanism of action on hepatic steatosis and fibrosis has not fully been determined. In the liver, glucose transporter 4 (GLUT4) is mainly expressed in hepatocytes, endothelial cells and hepatic stellate cells (HSCs). In the present study, the effects of Ex-4 on GLUT4 expression were determined in the liver of ob/ob mice. Ob/ob mice were treated with Ex-4 for 10 weeks. Serum metabolic parameters, hepatic triglyceride levels, and liver tissues were evaluated for hepatic steatosis. The weights of the whole body and liver in ob/ob mice were reduced by long-term Ex-4 treatment. Serum metabolic parameters, hepatic steatosis, and hepatic fibrosis in ob/ob mice were reduced by Ex-4. Particularly, Ex-4 improved hepatic steatosis by enhancing GLUT4 via GLP-1R activation in ob/ob mice. Ex-4 treatment also inhibited hepatic fibrosis by decreasing expression of connective tissue growth factor in HSCs of ob/ob mice. Our data suggest that GLP-1 agonists exert a protective effect on hepatic steatosis and fibrosis in obesity and type 2 diabetes.

Keyword

Exendin-4; Glucose transporter 4; Nonalcoholic fatty liver disease; ob/ob

MeSH Terms

Animals
Connective Tissue Growth Factor
Endothelial Cells
Fatty Liver*
Fibrosis
Glucagon-Like Peptide 1
Glucagon-Like Peptide-1 Receptor
Glucose Transport Proteins, Facilitative*
Hepatic Stellate Cells
Hepatocytes
Liver
Mice*
Obesity
Triglycerides
Weights and Measures
Connective Tissue Growth Factor
Glucagon-Like Peptide 1
Glucose Transport Proteins, Facilitative

Figure

• 

  Fig. 1 Effect of long-term Ex-4 treatment on the weight of body, liver, and epididymal fat padsin ob/ob mice. (A) The change in body weight for 10 weeks after Ex-4 injection. (B) Representative photographs of WT, ob/ob, ob/ob+Ex-4, and WT+Ex-4 mice. Scale bar=1 cm. (C) Representative photographs of the liver, perirenal fat pads, and epididymal fat pads from each experimental group. Scale bar=0.5 cm. The asterisk indicates kidney within perirenal fat. (D) Graphs showing weights of the liver, perirenal fat pad, and epididymal fat pad, and total fat (perirenal+epididymal fat) from each experimental group. Data (n=10 mice per group) are presented as the mean±SEM. *p<0.05; vs. WT; †p<0.05 vs. ob/ob.

• 

  Fig. 2 Effect of Ex-4 on insulin and glucose tolerance in ob/ob mice. (A) Insulin glucose tolerance test. Blood glucose levels after insulin (0.75 U/kg) injection. (B) Glucose tolerance test. Blood glucose levels after D-glucose (2 g/kg) injection. Data (n=10 mice per group) are presented as the mean±SEM. *p<0.05; vs. WT; †p<0.05 vs. ob/ob.

• 

  Fig. 3 Effect of Ex-4 on hepatic function and steatosis in ob/ob mice. (A) Representative microphotographs of H&E and Oil red O staining of liver sections from WT or ob/ob with or without Ex-4. Scale bar=100 µm. (B) Serum levels of AST, ALT, and liver TG from each experimental group. Data (n=10 mice per group) are presented as the mean±SEM. *p<0.05; vs. WT; †p<0.05 vs. ob/ob.

• 

  Fig. 4 Effect of Ex-4 on hepatic fibrosis in ob/ob mice. (A) Representative microphotographs of Masson trichrome staining of liver sections from WT (a), ob/ob (b), ob/ob+Ex-4 (c), and WT+Ex-4 (d) mice. Scale bar=100 µm. The asterisk indicates fibrosis. (B) Western blots showing hepatic CTGF expression and its quantification. Densitometry values for CTGF expression were normalized to β-actin expression and are represented as arbitrary units. Data are shown as the mean±SEM. *p<0.05; vs. WT; †p<0.05 vs. ob/ob.

• 

  Fig. 5 Effect of Ex-4 on PPAR-α, GLP-1R, GLUT2, and GLUT4 expression in the liver of ob/ob mice. Western blots and quantifications showing hepatic PPAR-α (A), GLP-1R (B), GLUT2 (C), GLUT4 (D) expression. Densitometry values for each protein were normalized to β-actin expression and are represented as arbitrary units. Data are shown as the mean±SEM. *p<0.05 vs. WT; †p<0.05 vs. ob/ob. (E) Representative microphotographs of immunostained GLUT4 in liver sections from WT (a), ob/ob (b), ob/ob+Ex-4 (c), and WT+Ex-4 (d) mice. Scale bar=100 µm.

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