Acute D-Serine Co-Agonism of ß-Cell NMDA Receptors Potentiates Glucose-Stimulated Insulin Secretion and Excitatory ß-Cell Membrane Activity.

ABSTRACT

Insulin-secreting pancreatic ß-cells express proteins characteristic of D-serine regulated synapses, but the acute effect of D-serine co-agonism on its presumptive ß-cell target, N-methyl D-aspartate receptors (NMDARs), is unclear. We used multiple models to evaluate glucose homeostasis and insulin secretion in mice with a systemic increase in D-serine (intraperitoneal injection or DAAO mutants without D-serine catabolism) or tissue-specific loss of Grin1-encoded GluN1, the D-serine binding NMDAR subunit. We also investigated the effects of D-serine ± NMDA on glucose-stimulated insulin secretion (GSIS) and ß-cell depolarizing membrane oscillations, using perforated patch electrophysiology, in ß-cell-containing primary isolated mouse islets. In vivo models of elevated D-serine correlated to improved blood glucose and insulin levels. In vitro, D-serine potentiated GSIS and ß-cell membrane excitation, dependent on NMDAR activating conditions including GluN1 expression (co-agonist target), simultaneous NMDA (agonist), and elevated glucose (depolarization). Pancreatic GluN1-loss females were glucose intolerant and GSIS was depressed in islets from younger, but not older, ßGrin1 KO mice. Thus, D-serine is capable of acute antidiabetic effects in mice and potentiates insulin secretion through excitatory ß-cell NMDAR co-agonism but strain-dependent shifts in potency and age/sex-specific Grin1-loss phenotypes suggest that context is critical to the interpretation of data on the role of D-serine and NMDARs in ß-cell function.