Truchan, N. A. | Search bioRxiv

bioRxiv2021

Human islet expression levels of Prostaglandin E2 synthetic enzymes, but not prostaglandin EP3 receptor, are positively correlated with markers of β-cell function and mass in non-diabetic obesity

Elevated islet production of prostaglandin E2 (PGE2), an arachidonic acid metabolite, and expression of Prostaglandin E2 Receptor subtype EP3 (EP3) are well-known contributors to the {beta}-cell dysfunction of type 2 diabetes (T2D). Yet, many of the same pathophysiological conditions exist in obesity, and little is known about how the PGE2 production and signaling pathway influences non-diabetic beta-cell function. In this work, plasma arachidonic acid and PGE2 metabolite levels were quantified in a cohort of non-diabetic and T2D human subjects to identify their relationship with glycemic control, obesity, and systemic inflammation. In order to link these findings to processes happening at the islet level, cadaveric human islets were subject to gene expression and functional assays. Interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2) mRNA levels, but not those of EP3, positively correlated with donor body mass index (BMI). IL-6 expression also strongly correlated with the expression of COX-2 and other PGE2 synthetic pathway genes. Insulin secretion assays using an EP3-specific antagonist confirmed functionallyrelevant up-regulation of PGE2 production. Yet, islets from obese donors were not dysfunctional, secreting just as much insulin in basal and stimulatory conditions as those from non-obese donors as a percent of content. Islet insulin content, on the other hand, was increased with both donor BMI and islet COX-2 expression, while EP3 expression was unaffected. We conclude up-regulated islet PGE2 production may be part of the {beta}-cell adaption response to obesity and insulin resistance that only becomes dysfunctional when both ligand and receptor are highly expressed in T2D.

pharmacology and toxicology↗

bioRxiv2019

Differential Effects of Prostaglandin E2 Production and Signaling through the Prostaglandin EP3 Receptor on Human Beta-cell Compensation

ObjectiveSignaling through Prostaglandin E3 Receptor (EP3), a G protein-coupled receptor for E series prostaglandins such as prostaglandin E2 (PGE2), has been linked to the beta-cell dysfunction and loss of beta-cell mass in type 2 diabetes (T2D). In the beta-cell, EP3 is specifically coupled to the unique cAMP-inhibitory G protein, Gz. Divergent effects of EP3 agonists and antagonists or Gz loss on beta-cell function, replication, and survival depending on whether islets are isolated from mice or humans in the lean and healthy, type 1 diabetic, or T2D state suggest a divergence in biological effects downstream of EP3/Gz dependent on the physiological milieu in which the islets reside.\n\nMethodsWe determined the expression of a number of genes in the EP3/Gz signaling pathway; PGE2 production pathway; and the beta-cell metabolic, proliferative, and survival responses to insulin resistance and its corresponding metabolic and inflammatory derangements in a panel of 80 islet preparations from non-diabetic human organ donors spanning a BMI range of approximately 20-45. In a subset of islet preparations, we also performed glucose-stimulated insulin secretion assays with and without the addition of an EP3 agonist, L798,106, and a glucagon-like peptide 1 receptor agonist, exendin-4, allowing us to compare the gene expression profile of each islet preparation with its (1) total islet insulin content (2), functional responses to glucose and incretin hormones, and (3) intrinsic influence of endogenous EP3 signaling in regulating these functional responses. We also transduced two independent islet preparations from three human organ donors with adenoviruses encoding human Gz or a GFP control in order to determine the impact of Gz hyperactivity (a mimic of the T2D state) on human islet insulin content and functional response to glucose.\n\nResultsIn contrast to results from islets isolated from T2D mice and human organ donors, where PGE2-mediated EP3 signaling actively contributes to beta-cell dysfunction, PGE2 production and EP3 expression appeared positively associated with various measurements of functional beta-cell compensation. While Gz mRNA expression was negatively associated with islet insulin content, that of each of the Gz-sensitive adenylate cyclase (AC) isoforms were positively associated with BMI and cyclin A1 mRNA expression, suggesting increased expression of AC1, AC5, and AC6 is a compensatory mechanism to augment beta-cell mass. Human islets over-expressing Gz via adenoviral transduction had reduced islet insulin content and secretion of insulin in response to stimulatory glucose as a percent of content, consistent with the effects of hyperactivation of Gz by PGE2/EP3 signaling observed in islets exposed to the T2D physiological milieu.\n\nConclusionsOur work sheds light on critical mechanisms in the human beta-cell compensatory response, before the progression to frank T2D.

molecular biology↗