Znt8 Haploinsufficiency Impacts Min6 Cell Zinc Content And Beta-Cell Phenotype Via Zip-Znt8 Coregulation

The zinc transporter ZnT8 (SLC30A8) localises to insulin secretory granules of beta -cells where it facilitates zinc uptake for insulin crystallisation. ZnT8 abundance has been linked to beta -cell survival and functional phenotype. However, the consequences of ZnT8 haploinsufficiency for beta -cell zinc trafficking and function remain unclear. Since investigations in human populations have shown SLC30A8 truncating polymorphisms to decrease the risk of developing Type 2 Diabetes, we hypothesised that ZnT8 haploinsufficiency would improve beta -cell function and maintain the endocrine phenotype. We used CRISPR/Cas9 technology to generate ZnT8 haploinsufficient mouse MIN6 beta -cells and showed that ZnT8 haploinsufficiency is associated with downregulation of mRNAs for Slc39a8 and Slc39a14, which encode for the zinc importers, Znt- and Irt-related proteins 8 (ZIP8) and 14 (ZIP14), and with lowered total cellular zinc content. ZnT8 haploinsufficiency disrupts expression of a distinct array of important beta -cell markers, decreases cellular proliferation via mitogen-activated protein (MAP) kinase cascades and downregulates insulin gene expression. Thus, ZnT8 cooperates with zinc importers of the ZIP family to maintain beta -cell zinc homeostasis. In contrast to the hypothesis, lowered ZnT8 expression reduces MIN6 cell survival by affecting zinc-dependent transcription factors that control the beta -cell phenotype.