1095-OR: β Cell Ca2+ Extrusion through PMCA1 Reduces Insulin Secretion and Glucose Tolerance

Introduction and Objective: While glucose-dependent Ca²+ influx is central to pancreatic β cell insulin secretion, the mechanisms that control Ca²+ extrusion and their impact on insulin secretion have yet to be elucidated. As plasma membrane Ca²+ ATPase 1 (PMCA1) is the most highly expressed Ca²+ extrusion protein in β cells, we sought to determine how it regulates Ca²+ handling, insulin secretion, and glucose homeostasis. Methods: PMCA1 function was assessed in β cell-specific PMCA1 knockout mice (βPMCA1KO) and human pseudoislets with β cell-specific PMCA1 knockdown (βPMCA1KD). qPCR and Immunofluorescence were utilized to determine expression and subcellular localization of PMCA1. Islet Ca²+ was assessed to quantify glucose-stimulated Ca2+ dynamics. Insulin secretion was measured under basal and secretagogue-stimulated conditions. Additionally, intraperitoneal glucose tolerance testing was performed. Results: Mouse and human pancreata showed strong β cell PMCA1 staining specifically at the plasma membrane, which was lost in βPMCA1KO sections. βPMCA1KO islets showed a 73.9±34% increased glucose-stimulated Ca²+ oscillation period (P<.05), 46±23% reduction in peak-to-trough decay slope (P<.01), and a 51±32% increase in Ca²+ amplitude spike (P<.05). Consistent with enhanced Ca²+ signaling, βPMCA1KO mice displayed improved glucose tolerance (34±32% decrease in AUC; P<.001). This was further examined in human βPMCA1KD pseudoislets with a 93±3.6% reduction in ATP2B1, the mRNA encoding PMCA1 (P<.0001). βPMCA1KD pseudoislets showed elevated basal, first-phase, and KCl-stimulated insulin secretion (205±62%; P<.05, 69±19%; P<.05, 72±21%; P<.05, respectively). Interestingly, βPMCA1KD reduced insulin content 80±4.5% (P<.0001). Conclusion: PMCA1 is a key regulator of β-cell Ca²+ extrusion that reduces basal and glucose-stimulated Ca²+ influx and insulin secretion. Loss of human β cell PMCA1 promoted basal and glucose-stimulated insulin secretion, which likely depleted insulin content. Lastly, glucose tolerance was greatly improved in βPMCA1KO mice.