1515-P: Pyruvate Kinase Amplifies Insulin Secretion Downstream of the ß-Cell GLP1 Receptor

The advent of GPCR agonists and co-agonists that target the β-cell incretin receptors - GLP1R and GIPR - have revolutionized therapeutics for diabetes, though the signaling pathways downstream of these receptors have yet to be fully understood. Previous work in our lab has demonstrated the critical role of the glycolytic enzyme pyruvate kinase (PK) in the closure of K_ATP channels. However, PK activators also potentiate insulin secretion independent of K_ATP channel closure, suggesting additional roles for PK. We therefore sought to determine if PK potentiates insulin secretion downstream of GPCRs by modulating cAMP signaling. To elucidate the role of PK downstream of GPCRs, we employed live-cell imaging with subcellularly-targeted biosensors to track cAMP signaling over time in intact human and mouse islets in response to glucagon, GLP1, GIP, and tirzepatide. To further characterize the role of GLP1R and GCGR, chemical antagonism and mice deficient in β-cell GLP1R/GCGR were utilized in combination with TEPP-46, a pharmacologic activator of PKm2 and PKL. Our data demonstrates that PK amplifies cAMP signaling at the plasma membrane downstream of β-cell GPCRs. Specifically, there is enhanced protein kinase A (PKA) activity and increased insulin secretion in the presence of a PK activator with glucagon as a ligand. PK did not potentiate insulin secretion or PKA activity in response to GIP, indicating a receptor specific effect. Chemical antagonists and knockout experiments show that PK potentiates PKA activity primarily downstream GLP1R more than GCGR. These studies, which link glycolysis to GPCR signaling, suggest that biased GLP1R agonists that work via PK will more efficiently increase insulin secretion.