Targeting GluN2B-containing NMDA receptors to interact with stress pathways and Ca2+-regulated K+ channels in murine islets of Langerhans

Long-term activation of NMDA receptors of pancreatic islet-cells increases oxidative stress and alters insulin secretion. Previously, we demonstrated that inhibition of GluN2B-containing NMDA receptors protects against islet-cell death. The aim of our current study was to further characterize the pathways influenced by modulating the receptors via the GluN2B subunit. To target GluN2B, the subtype-specific antagonists WMS-1410 and Ro 25-6981 were tested in mouse islet- and MIN6-cells. Our data reveal that sustained activation of NMDA receptors increases oxidative stress not only by mitochondrial dysfunction but also by stimulation of NADPH oxidases. Moreover, activation of NMDA receptors induces a K⁺ current in islet-cells. Inhibition of GluN2B but not of GluN2A prevents this. K_Ca3.1 and K_Ca1.1 channels were identified as main constituents of the NMDA-induced K⁺ current by specific inhibition with senicapoc or paxilline. Importantly, these two K_Ca channel blockers partly protect against glucolipotoxicity-mediated apoptosis. GluN2B-subunit antagonists reduce oxidative stress produced by mitochondria and NADPH oxidases, improve the mitochondrial oxygen consumption rate, downregulate the mRNA of Chop and have a protective effect on insulin secretion in islets challenged by NMDA. The latter was partially mimicked by the ER-stress chaperon and mitochondrial stabilizer tauroursodeoxycholic acid but not by solely scavenging mitoROS or unselective inhibition of NADPH oxidases. In summary, prolonged stimulation of GluN2B-containing NMDA receptors mediates β-cell dysfunction on the level of ion channel coupling and multiple stress responses. Targeting this subunit protects against most of these islet-cell damaging effects and could be an additional option for the treatment of type 2 diabetes.