Hypoxia lowers SLC30A8/ZnT8 expression and free cytosolic Zn2+ in pancreatic beta cells

Hypoxic damage complicates islet isolation for transplantation and may contribute to beta cell failure in type 2 diabetes. Polymorphisms in the SLC30A8 gene, encoding the secretory granule zinc transporter 8 (ZnT8), influence type 2 diabetes risk, conceivably by modulating cytosolic Zn2+ levels. We have therefore explored the role of ZnT8 and cytosolic Zn2+ in the response to hypoxia of pancreatic islet cells. Human, mouse or rat islets were isolated and exposed to varying O-2 tensions. Cytosolic free zinc was measured using the adenovirally expressed recombinant targeted zinc probe eCALWY4. Gene expression was measured using quantitative (q)RT-PCR, western (immuno-) blotting or immunocytochemistry. Beta cells were identified by insulin immunoreactivity. Deprivation of O-2 (1% vs 5% or 21%) for 24 h lowered free cytosolic Zn2+ concentrations by 40% (p < 0.05) and similar to 30% (p < 0.05) in mouse and human islet cells, respectively. Hypoxia similarly decreased SLC30A8 mRNA expression in islets, and immunoreactivity in beta cells. Implicating lowered ZnT8 levels in the hypoxia-induced fall in cytosolic Zn2+, genetic ablation of Slc30a8 from mouse islets lowered cytosolic Zn2+ by similar to 40% (p < 0.05) and decreased the induction of metallothionein (Mt1, Mt2) genes. Cell survival in the face of hypoxia was enhanced in small islets of older (> 12 weeks) Slc30a8 null mice vs controls, but not younger animals. The response of pancreatic beta cells to hypoxia is characterised by decreased SLC30A8 expression and lowered cytosolic Zn2+ concentrations. The dependence on ZnT8 of hypoxia-induced changes in cell survival may contribute to the actions of SLC30A8 variants on diabetes risk in humans.