Liraglutide Enhances Autophagy and Promotes Pancreatic β Cell Proliferation to Ameliorate Type 2 Diabetes in High-Fat-Fed and Streptozotocin-Treated Mice

Abstract

BACKGROUND Clinical and experimental studies have revealed that liraglutide has multiple anti-diabetes biological effects. However, little is known about its role in autophagy and pancreatic β cell proliferation. This study aimed to assessed the effects of liraglutide on pancreatic b cell proliferation and autophagy in a mouse model of type 2 diabetes. MATERIAL AND METHODS The effect of liraglutide on autophagy and proliferation in pancreatic β cells was investigated using a high-fat-fed and streptozotocin-induced mouse model of type 2 diabetes. RESULTS Liraglutide significantly improved the symptoms of high-fat-fed (HFD) and streptozotocin (STZ)-induced type 2 diabetic mice, as indicated by body weight gain, reduction of blood glucose and plasma insulin, and enhanced sensitivity to insulin. The results of quantitative real-time polymerase chain reaction and Western blot analysis showed that liraglutide upregulated AGT5 expression and promoted the conversion of LC3-I to LC3-II, thus improving the defective autophagy. In addition, we observed that both mRNA and protein expressions of PCNA and Ki-67 were upregulated by liraglutide treatment. Immunocytochemical staining results showed that the number of PCNA- or Ki-67-positive cells in pancreatic islet tissues in the HFD + STZ + liraglutide group were increased compared with the HFD + STZ group. CONCLUSIONS These results strongly suggest that liraglutide is able to enhance autophagy and promote pancreatic β cell proliferation. This study improves our insights into the mechanism by which liraglutide treatment relieves diabetes, and provides experimental evidence for clinical utilization of liraglutide in type 2 diabetes treatment.

Figure 1

Liraglutide relieves diabetes in HFD and STZ-treated mice. Effects of liraglutide on body weight (A), blood glucose (B), plasma insulin (C), glucose tolerance (D), and insulin tolerance (E). (F) The area under the glucose or insulin tolerance curve generated in D and E. Data are presented as mean ±SD (n=6). * P<0.05 vs. control, ** P<0.01 vs. control, *** P<0.001 vs. control, ^# P<0.05 vs. HFD + STZ group, ^## P<0.01 vs. HFD + STZ group.

Figure 2

Liraglutide treatment enhances autophagy in HFD and STZ-treated mice. (A, B) ATG5 and LC3 mRNA expression levels were detected by qRT-PCR. (C) Western blot analysis was conducted to detect ATG5 and LC3 protein expression. (D) Liraglutide upregulated the protein expression of ATG5 and accelerated the conversion of LC3-I to LC3-II. Data are presented as mean ±SD (n=6). ** P<0.01 vs. control, *** P<0.001 vs. control, ^# P<0.05 vs. HFD + STZ group, ^## P<0.01 vs. HFD + STZ group.

Figure 3

Liraglutide promotes pancreatic β cell proliferation. (A, B) PCNA and Ki-67 mRNA expression levels in pancreatic tissues were detected by qRT-PC. (C) Western blot results of PCNA and Ki-67 protein are shown. (D, E) Quantification of the protein levels of PCNA and Ki-67 shown in C. (F, H) Representative images of IHC are shown (magnification 200×). (G, I) Quantification of PCNA and Ki-67-positive cells in F and H. Data are presented as mean ±SD (n=6). ** P<0.01 vs. control, *** P<0.001 vs. control, ^# P<0.05 vs. HFD + STZ group, ^## P<0.01 vs. HFD + STZ.