Abstract
Objectives. This study aimed to explore the effect of exendin-4 on t-BHP-induced apoptosis in pancreatic β cells and the mechanism of action. Methods. Murine MIN6 pancreatic β cells were treated with exendin-4 in the presence or absence of tert-butyl hydroperoxide (t-BHP). Cell survival was assessed by MTT staining. The percentage of apoptotic cells was determined by fluorescence microscopy analysis after Hoechst/PI staining and flow cytometric assay after Annexin V-FITC/PI staining. The activity of caspase-3 was determined using a caspase-3 activity kit. Expression of P-IRE1α, IRE1α, C-Jun N-terminal kinase (JNK), P-JNK, C-JUN, and P-C-JUN was detected by western blotting. Results. Exendin-4 was found to inhibit t-BHP-induced apoptosis in pancreatic β-cells by downregulating caspase-3 activity. Exendin-4 also inhibited the endoplasmic reticulum transmembrane protein IRE1, the apoptosis-related signaling molecule JNK, and c-Jun activation. Conclusions. Our findings suggest that exendin-4 ultimately reduces t-BHP-induced β-cell apoptosis. IRE1-JNK-c-Jun signaling is involved in the exendin-4-mediated modulation of β-cell apoptosis.
Highlights
Type 2 diabetes is caused by complex interactions between insulin resistance in the peripheral tissues and impaired insulin secretion by pancreatic β-cells
The treatment of β-cells with 25 μmol/L tertbutyl hydroperoxide (t-BHP) produced the maximal apoptotic response after 1 h as evidenced by results of the Hoechst/propidium iodide (PI) and Annexin V-FITC/PI assays. β cells treated with 25 μmol/L t-BHP for 1 h clearly exhibited staining that was indicative of apoptosis (Figure 1(A)(b))
An Annexin V-FITC/PI quantification assay demonstrated that t-BHP-induced MIN6 cell death was mediated by apoptosis (Figure 1(B)(b)) and that exendin-4 protected MIN6 cells from t-BHP-induced apoptosis (Figure 1(B)(d))
Summary
Type 2 diabetes is caused by complex interactions between insulin resistance in the peripheral tissues and impaired insulin secretion by pancreatic β-cells. There is a general consensus that the latter results from both impaired βcell function and decreased β-cell mass. The high activity of molecules, such as reactive oxygen species (ROS) and clusters of reactive nitrogen species (RNS), could cause oxidative damage, leading to tissue injury. Recent studies have revealed that the endoplasmic reticulum (ER) is an organelle that can sense various stresses and transmit apoptotic signals [1, 2]. One characteristic feature of β-cells is a highly developed ER, which arises from the large amounts of insulin secretion [3]. Abnormal oxidation and impaired protein folding can lead to endoplasmic reticulum stress (ERS)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
