EP3 signaling is decoupled from the regulation of glucose-stimulated insulin secretion in β-cells compensating for obesity and insulin resistance

• Published in: Islets 2023-12, Vol.15 (1), p.2223327-2223327
• Main Authors: Schaid, Michael D., Harrington, Jeffrey M., Kelly, Grant M., Sdao, Sophia M., Merrins, Matthew J., Kimple, Michelle E.
• Format: Article
• Language: English
• Subjects: Animals; cAMP; Diabetes; Diabetes Mellitus, Type 2 - metabolism; EP3 receptor; Glucose - metabolism; Glucose - pharmacology; hyperglycemia; Insulin - metabolism; Insulin Resistance; Insulin Secretion; Islets of Langerhans - metabolism; Leptin - metabolism; Leptin - pharmacology; Mice; Mice, Inbred C57BL; Obesity; prostaglandins; Rap1gap; Signal Transduction; β-cell
• ISSN: 1938-2014; 1938-2022
• DOI: 10.1080/19382014.2023.2223327

Of the β-cell signaling pathways altered by obesity and insulin resistance, some are adaptive while others contribute to β-cell failure. Two critical second messengers are Ca 2+ and cAMP, which control the timing and amplitude of insulin secretion. Previous work has shown the importance of the cAMP-inhibitory Prostaglandin EP3 receptor (EP3) in mediating the β-cell dysfunction of type 2 diabetes (T2D). Here, we used three groups of C57BL/6J mice as a model of the progression from metabolic health to T2D: wildtype, normoglycemic Leptin Ob (NGOB), and hyperglycemic Leptin Ob (HGOB). Robust increases in β-cell cAMP and insulin secretion were observed in NGOB islets as compared to wildtype controls; an effect lost in HGOB islets, which exhibited reduced β-cell cAMP and insulin secretion despite increased glucose-dependent Ca 2+ influx. An EP3 antagonist had no effect on β-cell cAMP or Ca 2+ oscillations, demonstrating agonist-independent EP3 signaling. Finally, using sulprostone to hyperactivate EP3 signaling, we found EP3-dependent suppression of β-cell cAMP and Ca 2+ duty cycle effectively reduces insulin secretion in HGOB islets, while having no impact insulin secretion on NGOB islets, despite similar and robust effects on cAMP levels and Ca 2+ duty cycle. Finally, increased cAMP levels in NGOB islets are consistent with increased recruitment of the small G protein, Rap1GAP, to the plasma membrane, sequestering the EP3 effector, Gɑ z , from inhibition of adenylyl cyclase. Taken together, these results suggest that rewiring of EP3 receptor-dependent cAMP signaling contributes to the progressive changes in β cell function observed in the Leptin Ob model of diabetes.