Prostaglandin EP3 Receptor signaling is required to prevent insulin hypersecretion and metabolic dysfunction in a non-obese mouse model of insulin resistance

Abstract

Objective: Black and Tan Brachyury (BTBR) mice have underlying defects in insulin sensitivity and beta-cell function, even when lean. When homozygous for the Leptin Ob mutation (BTBR-Ob), hyperphagia leads to morbid obesity, and by 10 weeks of age, a type 2 diabetes (T2D) phenotype is fully penetrant. The second messenger molecule, cyclic AMP (cAMP), promotes glucose-stimulated and incretin-potentiated insulin secretion, beta-cell proliferation, and betacell survival. We have previously shown that a key player in the loss of functional beta-cell mass in the BTBR-Ob strain is Prostaglandin EP3 receptor (EP3); dysfunctionally up-regulated in the islet by the pathophysiological conditions of T2D. EP3 transmits a signal from its ligand, prostaglandin E2 (PGE2), to the unique cAMP-inhibitory G protein alpha-subunit, Gαz, reducing beta-cell cAMP production. Our objective in this study was to study the effect of beta-cell EP3 and Gαz loss on the metabolic phenotype of both BTBR-lean and -Ob mice, providing support for targeting this pathway in a genetically-susceptible population before and after the progression to frank T2D. Methods: EP3 or Gαz-floxed BTBR mice were bred with BTBR mice expressing Cre recombinase under the control of the rat insulin promoter in order to design beta-cell-specific knockout mice. A final cross into the BTBR-Ob strain provided both lean and obese experimental animals. To our surprise, the EP3 deleted allele was transferred via the germline, making full-body EP3null mice, as confirmed by qPCR. Beta-cell-specific Gαz loss in Gαz-flox-RIP-Cre mice (Gαz βKO) was confirmed; yet, these mice were poor breeders, particularly in the context of the Leptin Ob mutation; therefore, only BTBR-lean mice were phenotyped. Full-body metabolic and ex vivo islet assays were conducted in wild-type and EP3-null BTBR-lean and Ob mice and wild-type and Gαz βKO BTBR-lean mice, linking any islet phenotype with observed effects on glucose homeostasis. Results: Systemic EP3 loss accelerated the early T2D phenotype of BTBR-Ob mice and caused insulin resistance and glucose intolerance in BTBR-lean mice, likely due to the extra-pancreatic effects described previously in other mouse models. Even so, islets from EP3-null BTBR-Ob mice had significantly increased insulin-positive pancreas area, supportive of an increased proliferation response. Gαz βKO BTBR-lean mice, on the other hand, had significantly improved glucose tolerance due to elevated glucose-stimulated and incretin-potentiated insulin secretion, with no apparent effect of beta-cell Gαz loss on beta-cell proliferation. Combined, our findings suggest a divergence in signaling downstream of EP3/Gαz depending on the (patho)physiologic conditions to which the islet is exposed. Conclusions: Our work sheds light on G protein-mediated mechanisms by which beta-cells compensate for systemic insulin resistance and how these become dysfunctional in the T2D state.The second messenger molecule, cyclic AMP (cAMP), has been well-characterized as a potentiator of glucose-stimula...

PTGER3 and MMP-2 play potential roles in diabetic nephropathy via competing endogenous RNA mechanisms

“…Additionally, elevated production of prostaglandin E 2 (PE2) and PTGER3 can be targeted to improve insulin secretion from islets [24]. Pathologically, PTGER3 negatively regulates the production of cyclic AMP (cAMP), a potentiator of GSIS [22,25]. Rankin et al [21] showed that agonist (sulprostone) and antagonist of EP3r both significantly reduced GSIS and fasting plasma glucagon in non-human primates with noninsulin-dependent diabetes mellitus.…”