Exendin-4 protects murine pancreatic β-cells from dexamethasone-induced apoptosis through PKA and PI-3K signaling.
OBJECTIVE
To explore the effect and mechanism of exendin-4 on dexamethasone-induced apoptosis in pancreatic β-cells.


METHODS
Murine MIN6 pancreatic β-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 β-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 β-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.


CONCLUSIONS
PI-3K and PKA signaling are involved in the exendin-4-mediated modulation of β-cell apoptosis.
Wang
Lin-Xi
LX
Department of Endocrinology, Fujian Institute of Endocrinology, Union Hospital of Fujian Medical University, Fuzhou, Fujian, People's Republic of China.
Wang
Yan-Ping
YP
Chen
Zhou
Z
Liu
Xiao-Ying
XY
Liu
Xiao-Hong
XH
Liu
Liang
L
Chen
Wen-Jia
WJ
Liu
Li-Bin
LB
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D061945:Caspase Inhibitors; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D045304:Cytochromes c / Q000037:antagonists & inhibitors; D003907:Dexamethasone / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000077270:Exenatide; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D010455:Peptides / Q000494:pharmacology*; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D014688:Venoms / Q000494:pharmacology*; D051025:bcl-Associated Death Protein / Q000378:metabolism
D061945:Caspase Inhibitors; D010455:Peptides; D014688:Venoms; D051025:bcl-Associated Death Protein; D003907:Dexamethasone; D045304:Cytochromes c; D000077270:Exenatide; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases