beta cells sense glucose through its metabolism and the resulting increase in ATP, which subsequently stimulates insulin secretion. Uncoupling protein-2 (UCP2) mediates mitochondrial proton leak, decreasing ATP production. In the present study, we assessed UCP2's role in regulating insulin secretion. UCP2-deficient mice had higher islet ATP levels and increased glucose-stimulated insulin secretion, establishing that UCP2 negatively regulates insulin secretion. Of pathophysiologic significance, UCP2 was markedly upregulated in islets of ob/ob mice, a model of obesity-induced diabetes. Importantly, ob/ob mice lacking UCP2 had restored first-phase insulin secretion, increased serum insulin levels, and greatly decreased levels of glycemia. These results establish UCP2 as a key component of beta cell glucose sensing, and as a critical link between obesity, beta cell dysfunction, and type 2 diabetes.

OBJECTIVEZinc ions are essential for the formation of hexameric insulin and hormone crystallization. A nonsynonymous single nucleotide polymorphism rs13266634 in the SLC30A8 gene, encoding the secretory granule zinc transporter ZnT8, is associated with type 2 diabetes. We describe the effects of deleting the ZnT8 gene in mice and explore the action of the at-risk allele.RESEARCH DESIGN AND METHODSSlc30a8 null mice were generated and backcrossed at least twice onto a C57BL/6J background. Glucose and insulin tolerance were measured by intraperitoneal injection or euglycemic clamp, respectively. Insulin secretion, electrophysiology, imaging, and the generation of adenoviruses encoding the low- (W325) or elevated- (R325) risk ZnT8 alleles were undertaken using standard protocols.RESULTSZnT8−/− mice displayed age-, sex-, and diet-dependent abnormalities in glucose tolerance, insulin secretion, and body weight. Islets isolated from null mice had reduced granule zinc content and showed age-dependent changes in granule morphology, with markedly fewer dense cores but more rod-like crystals. Glucose-stimulated insulin secretion, granule fusion, and insulin crystal dissolution, assessed by total internal reflection fluorescence microscopy, were unchanged or enhanced in ZnT8−/− islets. Insulin processing was normal. Molecular modeling revealed that residue-325 was located at the interface between ZnT8 monomers. Correspondingly, the R325 variant displayed lower apparent Zn2+ transport activity than W325 ZnT8 by fluorescence-based assay.CONCLUSIONSZnT8 is required for normal insulin crystallization and insulin release in vivo but not, remarkably, in vitro. Defects in the former processes in carriers of the R allele may increase type 2 diabetes risks.

The clonal isolation of putative adult pancreatic precursors has been an elusive goal of researchers seeking to develop cell replacement strategies for diabetes. We report the clonal identification of multipotent precursor cells from the adult mouse pancreas. The application of a serum-free, colony-forming assay to pancreatic cells enabled the identification of precursors from pancreatic islet and ductal populations. These cells proliferate in vitro to form clonal colonies that coexpress neural and pancreatic precursor markers. Upon differentiation, individual clonal colonies produce distinct populations of neurons and glial cells, pancreatic endocrine beta-, alpha- and delta-cells, and pancreatic exocrine and stellate cells. Moreover, the newly generated beta-like cells demonstrate glucose-dependent Ca(2+) responsiveness and insulin release. Pancreas colonies do not express markers of embryonic stem cells, nor genes suggestive of mesodermal or neural crest origins. These cells represent a previously unidentified adult intrinsic pancreatic precursor population and are a promising candidate for cell-based therapeutic strategies.

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Aims/hypothesis Zinc is highly concentrated in pancreatic beta cells, is critical for normal insulin storage, and may regulate glucagon secretion from alpha cells. ZnT8 is a zinc efflux transporter highly expressed in beta cells and polymorphisms in the ZnT8 (slc30a8) gene in man are associated with increased risk of type 2 diabetes. Whilst global ZnT8 knockout (ZnT8KO) mice have been characterized, ZnT8 is also expressed in other islet cell types and extra-pancreatic tissues. Therefore, it is important to devise strategies to understand the role of ZnT8 in beta and alpha cells without the confounding effects of ZnT8 in these other tissues. Methods We have generated beta and alpha cell specific ZnT8 knockout (ZnT8BKO and ZnT8AKO) mice and performed in vivo and in vitro characterization of the phenotypes to determine the functional and anatomical impact of ZnT8 in these cells. Thus we assessed zinc accumulation, insulin granule morphology, insulin biosynthesis and secretion, and glucose homeostasis. Results ZnT8BKO mice are glucose intolerant, have reduced beta cell zinc accumulation and atypical insulin granules. They also display reduced first phase glucose-stimulated insulin secretion, reduced insulin processing enzyme transcripts and increased proinsulin levels. In contrast, ZnT8AKO mice show no evident abnormalities in plasma glucagon and glucose homeostasis. Conclusion/interpretation We provide the first report of specific beta and alpha cell deletion of ZnT8. Our data indicate that while ZnT8 is absolutely required for proper beta cell function, under the conditions studied, it is largely dispensable for alpha cell function.