SIDT2 is involved in the NAADP-mediated release of calcium from insulin secretory granules

Abstract

The Sidt2 global knockout mouse (Sidt2−/−) has impaired insulin secretion. The aim of this study was to assess the role of SIDT2 protein in glucose-induced insulin secretion in primary cultured mouse β-cells. The major metabolic and electrophysiological steps of glucose-induced insulin secretion of primary cultured β-cells from Sidt2−/− mice were investigated. The β-cells from Sidt2−/− mice had normal NAD(P)H responses and KATP and KV currents. However, they exhibited a lower [Ca2+]i peak height when stimulated with 20mM glucose compared with those from WT mice. Furthermore, it took a longer time for the [Ca2+]i of β-cell from Sidt2−/− mice to reach the peak. Pretreatment with ryanodine or 2-aminoethoxydiphenyl borate (2-APB) did not change [Ca2+]i the response pattern to glucose in Sidt2−/− cells. Extraordinarily, pretreatment with bafilomycin A1(Baf-A1) led to a comparable [Ca2+]i increase pattern between these two groups, suggesting that calcium traffic from the intracellular acidic compartment is defective in Sidt2−/− β-cells. Bath-mediated application of 50nM nicotinic acid adenine dinucleotide phosphate (NAADP) normalized the [Ca2+]i response of Sidt2−/− β-cells. Finally, glucose-induced CD38 expression increased to a comparable level between Sidt2−/− and WT islets, suggesting that Sidt2−/− islets generated NAADP normally. We conclude that Sidt2 is involved in NAADP-mediated release of calcium from insulin secretory granules and thus regulates insulin secretion.