Lack of TRPM2 impaired insulin secretion and glucose metabolisms in mice

OBJECTIVE-TRPM2 is a Ca²⁺-permeable nonselective cation channel activated by adenosine dinucleotides. We previously demonstrated that TRPM2 is activated by coapplication of heat and intracellular cyclic adenosine 5'-diphosphoribose, which has been suggested to be involved in intracellular Ca²⁺ increase in immunocytes and pancreatic β-cells. To clarify the involvement of TRPM2 in insulin secretion, we analyzed TRPM2 knockout (TRPM2-KO) mice. RESEARCH DESIGN AND METHODS-Oral and intraperitoneal glucose tolerance tests (OGTT and IPGTT) were performed in TRPM2-KO and wild-type mice. We also measured cytosolic free Ca²⁺ in single pancreatic cells using fura-2 microfluorometry and insulin secretion from pancreatic islets. RESULTS-Basal blood glucose levels were higher in TRPM2-KO mice than in wild-type mice without any difference in plasma insulin levels. The OGTT and IPGTT demonstrated that blood glucose levels in TRPM2-KO mice were higher than those in wild-type mice, which was associated with an impairment in insulin secretion. In isolated β-cells, smaller intracellular Ca²⁺ increase was observed in response to high concentrations of glucose and incretin hormone in TRPM2-KO cells than in wildtype cells. Moreover, insulin secretion from the islets of TRPM2-KO mice in response to glucose and incretin hormone treatment was impaired, whereas the response to tolbutamide, an ATP-sensitive potassium channel inhibitor, was not different between the two groups. CONCLUSIONS-These results indicate that TRPM2 is involved in insulin secretion stimulated by glucose and that further potentiated by incretins. Thus, TRPM2 may be a new target for diabetes therapy.