Dexamethasone induces cell death in insulin-secreting cells, an effect reversed by exendin-4.
Glucocorticoid excess induces hyperglycemia, which may result in diabetes. The present experiments explored whether glucocorticoids trigger apoptosis in insulin-secreting cells. Treatment of mouse beta-cells or INS-1 cells with the glucocorticoid dexamethasone (0.1 micromol/l) over 4 days in cell culture increased the number of fractionated nuclei from 2 to 7 and 14%, respectively, an effect that was reversed by the glucocorticoid receptor antagonist RU486 (1 micromol/l). In INS-1 cells, dexamethasone increased the number of transferase-mediated dUTP nick-end labeling-staining positive cells, caspase-3 activity, and poly-(ADP-) ribose polymerase protein cleavage; decreased Bcl-2 transcript and protein abundance; dephosphorylated the proapoptotic protein of the Bcl-2 family (BAD) at serine155; and depolarized mitochondria. Dexamethasone increased PP-2B (calcineurin) activity, an effect abrogated by FK506. FK506 (0.1 micromol/l) and another calcineurin inhibitor, deltamethrin (1 micromol/l), attenuated dexamethasone-induced cell death. The stable glucagon-like peptide 1 analog, exendin-4 (10 nmol/l), inhibited dexamethasone-induced apoptosis in mouse beta-cells and INS-1 cells. The protective effect of exendin-4 was mimicked by forskolin (10 micromol/l) but not mimicked by guanine nucleotide exchange factor with the specific agonist 8CPT-Me-cAMP (50 micromol/l). Exendin-4 did not protect against cell death in the presence of cAMP-dependent protein kinase (PKA) inhibition by H89 (10 micromol/l) or KT5720 (5 micromol/l). In conclusion, glucocorticoid-induced apoptosis in insulin-secreting cells is accompanied by a downregulation of Bcl-2, activation of calcineurin with subsequent dephosphorylation of BAD, and mitochondrial depolarization. Exendin-4 protects against glucocorticoid-induced apoptosis, an effect mimicked by forskolin and reversed by PKA inhibitors.
Ranta
Felicia
F
Institut für Physiologie, University of Tübingen, Gmelinstrasse 5, D-72076 Tübingen, Germany.
Avram
Diana
D
Berchtold
Susanne
S
Düfer
Martina
M
Drews
Gisela
G
Lang
Florian
F
Ullrich
Susanne
S
D000818:Animals; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology*; D000077270:Exenatide; D006801:Humans; D007306:Insecticides / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008116:Lizards; D051379:Mice; D008856:Microscopy, Fluorescence; D015735:Mifepristone / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D011722:Pyrethrins / Q000494:pharmacology; D016559:Tacrolimus / Q000494:pharmacology; D014688:Venoms / Q000494:pharmacology*
D007306:Insecticides; D007328:Insulin; D009570:Nitriles; D010455:Peptides; D011722:Pyrethrins; D014688:Venoms; C017180:decamethrin; D015735:Mifepristone; D003907:Dexamethasone; D000077270:Exenatide; D016559:Tacrolimus