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

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 [Ca(2+)]i peak height when stimulated with 20mM glucose compared with those from WT mice. Furthermore, it took a longer time for the [Ca(2+)]i of β-cell from Sidt2(-/-) mice to reach the peak. Pretreatment with ryanodine or 2-aminoethoxydiphenyl borate (2-APB) did not change [Ca(2+)]i the response pattern to glucose in Sidt2(-/-) cells. Extraordinarily, pretreatment with bafilomycin A1(Baf-A1) led to a comparable [Ca(2+)]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 [Ca(2+)]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.