Insulin secretion in islets from mice with a double knockout for the dense core vesicle proteins islet antigen-2 (IA-2) and IA-2beta.
Islet antigen-2 (IA-2 or ICA 512) and IA-2beta (or phogrin) are major autoantigens in type 1 diabetes. They are located in dense core secretory vesicles including insulin granules, but their role in beta-cell function is unclear. Targeted disruption of either IA-2 or IA-2beta, or both, impaired glucose tolerance, an effect attributed to diminution of insulin secretion. In this study, we therefore characterized the dynamic changes in cytosolic Ca2+([Ca2+](c)) and insulin secretion in islets from IA-2/IA-2beta double knockout (KO) mice. High glucose (15 mM) induced biphasic insulin secretion in IA-2/IA-2beta KO islets, with a similar first phase and smaller second phase compared with controls. Since the insulin content of IA-2/IA-2beta KO islets was approximately 45% less than that of controls, fractional insulin secretion (relative to content) was thus increased during first phase and unaffected during second phase. This peculiar response occurred in spite of a slightly smaller rise in [Ca2+](c), could not be attributed to an alteration of glucose metabolism (NADPH fluorescence) and also was observed with tolbutamide. The dual control of insulin secretion via the K(ATP) channel-dependent triggering pathway and K(ATP) channel-independent amplifying pathway was unaltered in IA-2/IA-2beta KO islets, and so were the potentiations by acetylcholine or cAMP (forskolin). Intriguingly, amino acids, in particular the cationic arginine and lysine, induced larger fractional insulin secretion in IA-2/IA-2beta KO than control islets. In conclusion, IA-2 and IA-2beta are dispensable for exocytosis of insulin granules, but are probably more important for cargo loading and/or stability of dense core vesicles.
Henquin
Jean-Claude
JC
Unit of Endocrinology and Metabolism, Faculty of Medicine, University of Louvain, UCL 55.30, Avenue Hippocrate 55, B-1200 Brussels, Belgium.
Nenquin
Myriam
M
Szollosi
Andras
A
Kubosaki
Atsutaka
A
Notkins
A L
AL
D000109:Acetylcholine / Q000494:pharmacology; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D001324:Autoantigens / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D018678:Cholinergic Agents / Q000494:pharmacology; D005089:Exocytosis / Q000502:physiology; D005260:Female; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D011189:Potassium Chloride / Q000494:pharmacology; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8 / Q000235:genetics* / Q000378:metabolism; D022142:Secretory Vesicles / Q000502:physiology*
D000596:Amino Acids; D001324:Autoantigens; D018678:Cholinergic Agents; D007328:Insulin; D011189:Potassium Chloride; D001120:Arginine; C516863:Ptprn protein, mouse; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D005947:Glucose; D000109:Acetylcholine; D002118:Calcium