Fig. 4: Both PDX1LOW/MAFALOW and PDX1HIGH/MAFAHIGH β-cells are required for islet dynamics and insulin secretion.
From: PDX1LOW MAFALOW β-cells contribute to islet function and insulin release
a–c Hub cell proportion (red circles) (a) (n = 7 islets/3 animals; unpaired t-test), mRNA for Gjd2 (b) (n = 7 animals; paired t-test) and coordinated β-cell activity (connectivity) (c) (n = 7 islets/3 animals; unpaired t-test) are all decreased in B-MAT islets. d, e Raster plots showing β-cell activity profiles in B-NORM (d) and B-MAT islets (e). f–h Loss of PDXLOW/MAFALOW β-cells leads to reductions in glucose (f)- and Exendin-4 (g)-stimulated insulin secretion (n = 10 replicates/4 animals; two-way ANOVA, Bonferroni’s multiple comparison) (G16.7: F = 7.89, DF = 1) (Ex4: F = 13.40, DF = 1), despite an increase in insulin content (h) (n = 8 replicates/4 animals; Mann–Whitney U-test). Samples were run together, but due to the relative magnitude of the Exendin-4 response, results are displayed separately (G3, 3 mM glucose; G16.7, 16.7 mM glucose; Ex4, 20 nM Exendin-4). i Images and summary bar graph showing insulin granule density at the membrane in B-NORM and B-MAT islets (scale bar = 6 µm) (n = 12 islets/6 animals; unpaired t-test). j No differences in Stx1a, Snap25 and Vamp2 expression are detected in B-MAT islets (n = 5 animals; paired t-test). k, l Ins1 (k) and Ins2 (l) levels are unchanged in B-MAT islets (n = 4 animals; paired t-test). m, n GLP1R mRNA (m) (n = 5 animals, paired t-test) and protein (n) (n = 20 islets/4 animals, unpaired t-test) expression are reduced in B-MAT islets (scale bar = 25 µm). o–q Maximal Exendin-4-stimulated cAMP rises are blunted in B-MAT islets, shown by mean traces (o) and summary bar graph (p), as well as representative images (scale bar = 25 µm) (q) (n = 17 islets/2 animals; unpaired t-test) (G11, 11 mM glucose; Ex4, 20 nM Exendin-4). r, s Exendin-4-stimulated Ca2+-spiking is blunted in B-MAT islets (r), confirmed using wavelet analysis (s) (mean wave shown) (n = 6 islets/3 animals; two-way ANOVA, Bonferroni’s multiple comparison) (F = 4.40, DF = 1) (G16.7, 16.7 mM glucose; Ex4, 20 nM Exendin-4). Bar graphs and traces show the mean ± SEM. All tests are two-sided where relevant.
