Figure 3.

Daily oral spermidine treatment did not alter insulin granule homeostasis in female nondiabetic mice. (a) A stitched micrograph including 25 single micrographs (V: vessel, N: nucleus, I: immune cell), scale bar: 5 µm. (b1) Black arrowhead indicates mature granules with a condensed core containing insulin. (b2) White asterisk marks immature transforming granules with a white halo. (b3) White arrow indicates rod-like insulin granules—crystallized structure surrounded by a bright halo, scale bar: 0.5 µm. (c1) Black arrowhead indicates a phagophore (dilated membrane) enwrapping a mature granule with a dark core. (c2) White arrowhead marks autophagosome (double bilayer) surrounding a mature granule. (c3) Autolysosome: white arrow indicates enclosed digested granule without a halo—membrane stacks within the autolysosome. (c4) Crinophagy: black arrows indicate a fusion of mature granules with electron-bright lysosomes, scale bar: 0.5 µm. (d) Insulin granule types normalized to filled vesicles. (e) pancreatic insulin content measured by ELISA (ctrl n = 7, spd n = 3). (f) Number of autophagy pathway structures (phagophore, autophagosome, autolysosome) per µ${\mathrm{m}}^2$. (g) Number of vesicophagic vesicles per µm². (h) Number of crinophagic vesicles per µ${\mathrm{m}}^2$. Mice with blood glucose levels less than 200 mg/dl in two consecutive measurements were determined as nondiabetic at 35 weeks of age. Each datapoint represents the average of 3 islets from one mouse; area of 332 µ${\mathrm{m}}^2$–2272 µ${\mathrm{m}}^2$ from each islet was analyzed. Nondiabetic ctrl mice (n = 3) and nondiabetic spd mice (n = 3). Data is shown as mean ± SD. Mann–Whitney U test was used as statistical analysis.