Exendin-4 protects murine pancreatic ß-cells from dexamethasone-induced apoptosis through PKA and PI-3K signaling.

Diabetes research and clinical practice

PubMedID: 20889222

Wang LX, Wang YP, Chen Z, Liu XY, Liu XH, Liu L, Chen WJ, Liu LB. Exendin-4 protects murine pancreatic ß-cells from dexamethasone-induced apoptosis through PKA and PI-3K signaling. Diabetes Res Clin Pract. 2010;90(3):297-304.
AIMS
To explore the effect and mechanism of exendin-4 on dexamethasone-induced apoptosis in pancreatic ß-cells.

METHODS
Murine MIN6 pancreatic ß-cells were treated with dexamethasone (100 nmol/l) over 48h following pretreatment with exendin-4 (100 nmol/l). Cell viability was determined using an MTT assay. The percentage of apoptotic cells was determined through fluorescence microscopy analysis after Hochest/PI staining and a flow cytometric assay after Annexin V-FITC/PI staining. Caspase 3 activity was measured using the caspase 3 activity assay kit. Expression of cyt-c, bcl-2, bax, AKT, and phosphorylated AKT was detected by western blot.

RESULTS
Exendin-4 reduced the percentage of cells undergoing apoptosis when ß-cells were exposed to dexamethasone. Exendin-4 down-regulated caspase 3 activity, reduced cytochrome c levels in cytoplasm, and increased Bcl-2 protein levels and the Bcl-2 to Bax ratio in dexamethasone-treated ß-cells. These exendin-4 effects were blocked in the presence of an inhibitor of the phosphoinositide-3 kinase (PI-3K) pathway or of the protein kinase A (PKA) pathway. Exendin-4 reversed dexamethasone-mediated inhibition of Akt phosphorylation, which was abrogated by the PI-3K and PKA inhibitors.

CONCLUSION
PI-3K and PKA signaling are involved in the exendin-4-mediated modulation of ß-cell apoptosis.