VAMP4 facilitates the fusion of iISGs and resorted vesicles with lysosomes for granule cargo degradation. (A–D) The state of ISG-lysosome contact events (A), ISG-lysosome fusion events (B), ISG-lysosome engulfment events (C), and ISG-lysosome degradation events (D) were observed in the region of interest in EM images of pancreatic β cells from WT mice (indicated by arrows). The EM images were captured at 120 kV and a magnification of 23,000×. Triangle: lysosome; asterisk: ISG. Scale bars, 0.5 μm. (E–G) The number of ISGs per β cell (E), cytoplasmic area of β cells (F), and number of ISG-lysosome interactions (G) in β cells of the WT and KO mice were quantified from EM images shown in Fig. 7 A. (H–J) Line charts showing the expression levels of PC1 (H), PC2 (I), and proinsulin (J) quantified as fold changes with respect to the average values measured at 0 h for the WT based on the Western blot bands shown in Fig. 7 H (n = 3 biological independent experiments). The data used for the analyses in E–G were based on 25 β cells in two islets isolated from one WT male mouse and 24 β cells in three islets isolated from two VAMP4 KO male mice. The WT and KO mice were 16 wk of age. The data are presented as the mean ± SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001; and ****, P < 0.0001. The statistical analyses were performed with two-tailed unpaired Student’s t test (E–G) and two-way ANOVA (H–J).