Altered cAMP and Ca2+ signaling in mouse pancreatic islets with glucagon-like peptide-1 receptor null phenotype.
1-Cells from rodents and humans express different receptors recognizing hormones of the secretin-glucagon family, which--when activated--synergize with glucose in the control of insulin release. We have recently reported that isolated islets from mice homozygous for a GLP-1 receptor null mutation (GLP-1R(-/-)) exhibit a well-preserved insulin-secretory response to glucose. This observation can be interpreted in two different ways: 1) the presence of GLP-1R is not essential for the secretory response of isolated islets to glucose alone; 2) beta-cells in GLP-1R(-/-) pancreases underwent compensatory changes in response to the null mutation. To explore these possibilities, we studied islets from control GLP-IR(+/+) mice in the absence or presence of 1 pmol/l exendin (9-39)amide, a specific and potent GLP-1R antagonist. Exendin (9-39)amide (15-min exposure) reduced glucose-induced insulin secretion from both perifused and statically incubated GLP-1R(+/+) islets by 50% (P < 0.05), and reduced islet cAMP production in parallel (P < 0.001). Furthermore, GLP-1R(-/-) islets exhibited: 1) reduced cAMP accumulation in the presence of 20 mmol/l glucose (knockout islets versus control islets, 12 +/- 1 vs. 27 +/- 3 fmol x islet(-1) x 15 min(-1); P < 0.001) and exaggerated acceleration of cAMP production by 10 nmol/l glucose-dependent insulinotropic peptide (GIP) (increase over 20 mmol/l glucose by GIP in knockout islets versus control islets: 66 +/- 5 vs. 14 +/- 3 fmol x islet(-1) x 15 min(-1); P < 0.001); 2) increased mean cytosolic [Ca2+] ([Ca2+]c) at 7, 10, and 15 mmol/l glucose in knockout islets versus control islets; and 3) signs of asynchrony of [Ca2+]c oscillations between different islet subregions. In conclusion, disruption of GLP-1R signaling is associated with reduced basal but enhanced GIP-stimulated cAMP production and abnormalities in basal and glucose-stimulated [Ca2+]c. These abnormalities suggest that GLP-1R signaling is an essential upstream component of multiple beta-cell signaling pathways.
Flamez
D
D
Diabetes Research Center, Vrije Universiteit Brussel, Brussels, Belgium.
Gilon
P
P
Moens
K
K
Van Breusegem
A
A
Delmeire
D
D
Scrocchi
L A
LA
Henquin
J C
JC
Drucker
D J
DJ
Schuit
F
F
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology*; D003981:Diazoxide / Q000494:pharmacology; D005260:Female; D000067757:Glucagon-Like Peptide-1 Receptor; D005947:Glucose / Q000494:pharmacology; D007515:Islets of Langerhans / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010446:Peptide Fragments / Q000494:pharmacology; D010641:Phenotype; D018027:Receptors, Glucagon / Q000502:physiology*; D015398:Signal Transduction
C000593833:GLP1R protein, human; C000593834:Glp1r protein, mouse; D000067757:Glucagon-Like Peptide-1 Receptor; D010446:Peptide Fragments; D018027:Receptors, Glucagon; C083773:exendin (9-39); D000242:Cyclic AMP; D005947:Glucose; D000109:Acetylcholine; D003981:Diazoxide; D002118:Calcium