Opposing effects of prostaglandin E 2 receptors EP3 and EP4 on mouse and human β-cell survival and proliferation

Abstract

ObjectiveHyperglycemia and systemic inflammation, hallmarks of Type 2 Diabetes (T2D), can induce the production of the inflammatory signaling molecule Prostaglandin E2 (PGE2) in islets. The effects of PGE2 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, Gi and GS, respectively. We previously found that EP3 and EP4 expression are reciprocally regulated by activation of the FoxM1 transcription factor, which promotes β-cell proliferation and survival. Our goal was to determine if EP3 and EP4 regulate β-cell proliferation and survival and, if so, to elucidate the downstream signaling mechanisms.Methodsβ-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). β-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.ResultsBlockade of EP3 enhanced β-cell proliferation in young, but not old, mouse islets in part through phospholipase C (PLC)-γ1 activity. Blocking EP3 also increased human β-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, β-cell proliferation. In both mouse and human islets, EP3 blockade or EP4 activation enhanced β-cell survival in the presence of cytokines. EP4 acts in a protein kinase A (PKA)-dependent manner to increase mouse β-cell survival. In addition, the positive effects of FoxM1 activation on β-cell survival are inhibited by EP3 and dependent on EP4 signaling.ConclusionsOur results identify EP3 and EP4 as novel regulators of β-cell proliferation and survival in mouse and human islets ex vivo.

The role of Cox‐2 and prostaglandin E 2 receptor EP3 in pancreatic β‐cell death

“…In accordance with the findings in rats (51) and in humans (29), the most prevalent receptor in human islets is EP3. Consistent with previous observation, a selective elevated expression in T2D islets was observed only in EP3 and not in the additional PGE 2 receptors EP1, EP2, and EP4 (29, 30). In the present study, we could not establish a correlation between the body mass index of the donors and the expression of EP3 in islets isolated from both diabetics and nondiabetics.…”

“…However, the role of PGE 2 and EP3 in lipotoxicity‐induced apoptosis has never been addressed. Elevated expression of the EP3 receptor in islets isolated from individuals with T2D has previously been reported (29, 30); in the present study we support these findings and bring evidence of elevated expression of the EP3 receptor in β‐cells exposed to palmitate or PGE 2 . Moreover, down‐regulation of the pathway using pharmacological tools (inhibitor or antagonist) and the RNA interference approach to either COX‐2 or EP3 decreased the levels of palmitate‐induced apoptosis.…”

“…It was proposed that multiple signaling pathways such as Akt and mTOR activities are inhibited by EP3 signaling reducing β‐cell proliferation. Interestingly, increased expression of EP3 and more specifically that of the spliced variant EP3‐ γ gene with age was observed, suggesting that enhanced PGE 2 signaling via EP3 results in impaired β‐cell proliferation in old mice (30). Neuman et al .…”

“…*P , 0.05, palmitate-or PGE 2 -treated vs. untreated cells. PGE 2 signaling via EP3 results in impaired b-cell proliferation in old mice (30). Neuman et al (52) presented a different approach of showing the involvement of EP3 in b-cell function.…”

Cardiac injury modulates critical components of prostaglandin E2 signaling during zebrafish heart regeneration

“…There are four membrane-bound PGE 2 receptors. Signaling through these receptors has pleiotropic effects; however upregulation of Prostaglandin E 2 receptor 2 (EP2) and EP4 is frequently associated with cancer progression, cell survival and proliferation [20][21][22][23][24] , while activation of EP3 often stimulates opposing cellular responses [25][26][27] .…”