Abstract
Long-term exposure to a high-fat diet (HFD) causes glucotoxicity and lipotoxicity in islet β cells and leads to the development of metabolic dysfunctions. Reductions in pancreatic and duodenal homeobox-1 (PDX-1) expression have been shown to induce type 2 diabetes mellitus by causing impairments to islet β cells. Glucagon-like peptide 1 (GLP-1) treatment reduces endogenous insulin resistance in HFD-induced type 2 diabetes mellitus. In the present study, the underlying mechanism by which GLP-1 exerts its function in type 2 diabetes mellitus was investigated. The effect of liraglutide (GLP-1 receptor agonist) administration on glucose tolerance, insulin release, and glucose-dependent insulinotropic polypeptide level was detected in a HFD-induced diabetes C57/BL6 mouse model. Moreover, the role of liraglutide administration on the activity of PDX-1 was quantified to demonstrate the association between the two indicators. The results showed that administration of liraglutide could ameliorate the impairments to β cells due to HFD consumption. Liraglutide restored the insulin capacity and stimulated glucose disposal by improving the function and increasing the number of islet β cells. Furthermore, the hyperplasia and redundant function of islet α cells were inhibited by liraglutide treatment as well. At the molecular level, administration of liraglutide induced the expression of PDX-1, MafA, p-JAK2 and p-Stat3 in HFD model to relatively normal levels. It was suggested that the effect of liraglutide-induced activation of GLP-1 was exerted via activation of PDX-1 rather than its function in decreasing body weight. The study demonstrated that GLP-1 played an essential role in type 2 diabetes mellitus.