Figure 5.

Insulin secretion is increased in GIPR-Q350 islets. A. Immunofluorescence of pancreatic islets. Staining shows Glucagon (green) and Insulin (magenta). Scale bar, 50 μm. B&C. GSIS performed on 8 to 10 technical replicates per condition of pooled islets of similar sizes isolated from GIPR-E350 and GIPR-Q350 mice (n = 3 male mice/genotype, 20–27 weeks old fed a normal chow diet). Islets were incubated for 45 min in 2.7 mM or 16.7 mM Glucose (B), or in 16.7 mM Glucose with or without [D-Ala²]-GIP (50 nM or 100 nM), Tirzepatide (100 nM), Exendin-4 (100 nM) (C). Graphs show Insulin secretion corrected to islets protein content (representative graphs of n = 3 independent experiments). D&E. cAMP production was measured on 3 technical replicates per condition of pooled islets of similar sizes isolated from GIPR-E350 (n = 3–5) and GIPR-Q350 (n = 3–5) female (D) and male (E) mice. Islets were incubated for 30 min in 16.7 mM Glucose with or without GIP (100 nM) or Forskolin (10 μM). Graph shows cAMP production corrected to total protein content. F. Electron microscopy images of pancreatic islets isolated from GIPR-E350 and GIPR-Q350 animals at 22–26 weeks of age. Scale bar, 2 μm. G. Granule density per β-cell frame in GIPR-E350 and GIPR-Q350 mice (2–5 β-cell frame per animal, 5 mice per group). H&I. Distance of insulin granule center to the plasma membrane was measured in GIPR-E350 and GIPR-Q350 female (H) and male (I) mice. Insulin granules were grouped with respect to their distance to the plasma membrane. (2–5 β-cell frame per animal, 5 mice per group). Data are mean ± SEM. Two tailed unpaired t-tests for B-E. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)