Fig. 5: α-IAPP-O stimulates macrophage-dependent clearance of hIAPP oligomers.

Representative images (a) and quantitative analysis (b–d) of islets from 50-week-old transgenic rats treated with ^chα-IAPP-O (1 mg/kg, 3 mg/kg, 10 mg/kg), inert ^chα-IAPP-O (10 mg/kg) and vehicle for 38 weeks. Pancreatic islets were stained for α-IAPP-O-positive oligomers (blue), ThioS-positive amyloid fibrils (green) and CD68-positive rat macrophages (red). Scale bars: 100 and 20 µm. b Quantification of hIAPP oligomer and amyloid fibrils in relation to islet area. c Quantification of CD68-immunoreactive macrophages associated with hIAPP oligomers and amyloid. d Quantitative analysis of insulin-immunoreactive beta cells in pancreatic islets. Final group numbers in (a–d) were n = 10 vehicle, n = 10 1 mg/kg, n = 7 3 mg/kg, n = 8 10 mg/kg ^chα-IAPP-O, n = 9 inert ^chα-IAPP-O 10 mg/kg. e Uptake of hIAPP oligomers conjugated to the pH-sensitive dye pHrodo (hIAPP-pHrodo) by PBMC-derived human macrophages in the presence of α-IAPP-O, inert α-IAPP-O, and IgG control antibodies at increasing concentrations using flow cytometry. Blocking of Fc receptors expressed on macrophages was used to inhibit phagocytosis induced by α-IAPP-O at 12 nM (+Fc block, represented by a dashed line). Scatterplots of viable singlet macrophages plotted as a function of hIAPP-pHrodo versus forward scatter height (FSC-H) fluorescence intensities, and selection of hIAPP-pHrodo-negative (gray) or -positive (black) populations (left). Dose-response curves (right) showing increased phagocytosis of hIAPP oligomers by macrophages. Data are from three biological replicates. Similar data for (e) has been obtained in two independent experiments. All data are expressed as means ± s.e.m. Statistical analysis was done using one-way ANOVA followed by Dunnett’s post hoc test for with indicated p values derived from multiple group comparison vs vehicle (b, c, d), or ****p < 0.0001 by two-way ANOVA with Dunnett’s test (e).