Opposing effects of prostaglandin E2 receptors EP3 and EP4 on mouse and human β-cell survival and proliferation

Objective: Hyperglycemia and systemic inflammation, hallmarks of Type 2 Diabetes (T2D), can induce the production of the inflammatory signaling molecule Prostaglandin E-2 (PGE(2)) in islets. The effects of PGE(2) are mediated by its four receptors, E-Prostanoid Receptors 1-4 (EP1-4). EP3 and EP4 play opposing roles in many cell types due to signaling through different G proteins, G(i) and G(S), respectively. We previously found that EP3 and EP4 expression are reciprocally regulated by activation of the FoxM1 transcription factor, which promotes beta-cell proliferation and survival. Our goal was to determine if EP3 and EP4 regulate beta-cell proliferation and survival and, if so, to elucidate the downstream signaling mechanisms. Methods: beta-cell proliferation was assessed in mouse and human islets ex vivo treated with selective agonists and antagonists for EP3(sulprostone and DG-041, respectively) and EP4 (CAY10598 and L-161,982, respectively). beta-cell survival was measured in mouse and human islets treated with the EP3- and EP4-selective ligands in conjunction with a cytokine cocktail to induce cell death. Changes in gene expression and protein phosphorylation were analyzed in response to modulation of EP3 and EP4 activity in mouse islets. Results: Blockade of EP3 enhanced beta-cell proliferation in young, but not old, mouse islets in part through phospholipase C (PLC)-gamma 1 activity. Blocking EP3 also increased human beta-cell proliferation. EP4 modulation had no effect on ex vivo proliferation alone. However, blockade of EP3 in combination with activation of EP4 enhanced human, but not mouse, beta-cell proliferation. In both mouse and human islets, EP3 blockade or EP4 activation enhanced beta-cell survival in the presence of cytokines. EP4 acts in a protein kinase A (PKA)-dependent manner to increase mouse beta-cell survival. In addition, the positive effects of FoxM1 activation on beta-cell survival are inhibited by EP3 and dependent on EP4 signaling. Conclusions: Our results identify EP3 and EP4 as novel regulators of beta-cell proliferation and survival in mouse and human islets ex vivo. (C) Published by Elsevier GmbH.