A cullin 4B-RING E3 ligase complex fine-tunes pancreatic δ cell paracrine interactions

Figure 1. CUL4B deficiency in pancreatic cells impairs glucose metabolism. (A and B) Western blots and quantitative data for CUL4A and CUL4B protein levels in islets from 12-week-old diabetic db/db mice and their heterozygous littermates (db/+). n = 6 mice per group. Representative Western blots from at least 3 independent experiments are shown. (C) Immunostaining for CUL4B (green) and somatostatin (SST, red) in pancreatic sections from db/db and db/+ mice. Scale bar: 100 m. n = 6 mice per group; 4-7 random areas were selected from each islet section, and 10 sections were randomly selected from each mouse. (D) Confirmation of pancreatic cell-specific CUL4B deficiency (Sst-Cre +/-Cul4b fl/Y ) through immunofluorescence. The colocalization of somatostatin (red) and CUL4B (green) in cells of WT mice was absent in Sst-Cre +/-Cul4b fl/Y mice. Scale bar: 100 m. (E) Immunostaining for insulin (red) and somatostatin (green) in WT and Sst-Cre +/-Cul4b fl/Y mice. Scale bar: 50 m. (F) Quantitative data for islet density, pancreatic cell number, and cell mass. n = 6 mice per group; 4-10 random areas were selected from each section, and 12 sections were randomly selected from each mouse. (G) The fasting and fed blood glucose levels of Sst-Cre +/-Cul4b fl/Y mice and their WT littermates. n = 8 mice per group. (H) Glucose tolerance test for Sst-Cre +/-Cul4b fl/Y mice and their WT littermates (n = 11-12). (I) Insulin tolerance test for Sst-Cre +/-Cul4b fl/Y mice and their WT littermates. Insulininduced decreases in blood glucose levels were significantly lower in Sst-Cre +/-Cul4b fl/Y mice than in their WT littermates, and they did not return to baseline levels at the 2-hour time point, whereas the levels of their WT littermates did (n = 9-11). *P < 0.05; **P < 0.01; ***P < 0.001. db/db mice were compared with their db/+ littermates, and Sst-Cre +/-Cul4b fl/Y mice were compared with their WT littermates. Error bars in F represent mean SD; other bars represent mean SEM. All data were analyzed using 1-way ANOVA.