Molecular genetic regulation of Slc30a8/ZnT8 reveals a positive association with glucose tolerance

Zinc Transporter 8 (ZnT8), encoded by SLC30A8, is chiefly expressed within pancreatic islet cells where it mediates zinc (Zn(2+)) uptake into secretory granules. Whilst a common non-synonymous polymorphism (R325W), which lowers activity, is associated with increased type 2 diabetes (T2D) risk, rare inactivating mutations in SLC30A8 have been reported to protect against T2D. Here, we generate and characterise new mouse models to explore the impact on glucose homeostasis of graded changes in ZnT8 activity in the β cell. Firstly, Slc30a8 was deleted highly selectively in these cells using the novel deleter strain, Ins1Cre. The resultant Ins1CreZnT8KO mice displayed significant (p<0.05) impairments in glucose tolerance at 10 weeks of age versus littermate controls and glucose-induced increases in circulating insulin were inhibited in vivo. Whilst insulin release from Ins1CreZnT8KO islets was normal, Zn(2+) release was severely impaired. Conversely, transgenic ZnT8Tg mice, over-expressing the transporter inducibly in the adult β cell using an insulin promoter-dependent Tet-On system, showed significant (p<0.01) improvements in glucose tolerance compared to control animals. Glucose-induced insulin secretion from ZnT8Tg islets was severely impaired, whereas Zn(2+) release was significantly enhanced. Our findings demonstrate that glucose homeostasis in the mouse improves as β cell ZnT8 activity increases and, remarkably, these changes track Zn(2+) rather than insulin release in vitro. Activation of ZnT8 in β cells might therefore provide the basis of a novel approach to treating type 2 diabetes.