Inhibition of the prostaglandin D2\u2013GPR44/DP2 axis improves human islet survival and function

Shadab Abadpour,Björn Tyrberg,Tina Rydén-Bergsten,Olle Korsgren,Simen W Schive,Hanne Scholz,Maria Sörhede Winzell,David M Smith,Erik Ryberg,Charlotte Wennberg Huldt,Peter Gennemark,Stanko Skrtic

doi:10.1007/s00125-020-05138-z

Abstract

Aims/hypothesisInflammatory signals and increased prostaglandin synthesis play a role during the development of diabetes. The prostaglandin D2 (PGD2) receptor, GPR44/DP2, is highly expressed in human islets and activation of the pathway results in impaired insulin secretion. The role of GPR44 activation on islet function and survival rate during chronic hyperglycaemic conditions is not known. In this study, we investigate GPR44 inhibition by using a selective GPR44 antagonist (AZ8154) in human islets both in vitro and in vivo in diabetic mice transplanted with human islets.MethodsHuman islets were exposed to PGD2 or proinflammatory cytokines in vitro to investigate the effect of GPR44 inhibition on islet survival rate. In addition, the molecular mechanisms of GPR44 inhibition were investigated in human islets exposed to high concentrations of glucose (HG) and to IL-1β. For the in vivo part of the study, human islets were transplanted under the kidney capsule of immunodeficient diabetic mice and treated with 6, 60 or 100 mg/kg per day of a GPR44 antagonist starting from the transplantation day until day 4 (short-term study) or day 17 (long-term study) post transplantation. IVGTT was performed on mice at day 10 and day 15 post transplantation. After termination of the study, metabolic variables, circulating human proinflammatory cytokines, and hepatocyte growth factor (HGF) were analysed in the grafted human islets.ResultsPGD2 or proinflammatory cytokines induced apoptosis in human islets whereas GPR44 inhibition reversed this effect. GPR44 inhibition antagonised the reduction in glucose-stimulated insulin secretion induced by HG and IL-1β in human islets. This was accompanied by activation of the Akt–glycogen synthase kinase 3β signalling pathway together with phosphorylation and inactivation of forkhead box O-1and upregulation of pancreatic and duodenal homeobox-1 and HGF. Administration of the GPR44 antagonist for up to 17 days to diabetic mice transplanted with a marginal number of human islets resulted in reduced fasting blood glucose and lower glucose excursions during IVGTT. Improved glucose regulation was supported by increased human C-peptide levels compared with the vehicle group at day 4 and throughout the treatment period. GPR44 inhibition reduced plasma levels of TNF-α and growth-regulated oncogene-α/chemokine (C-X-C motif) ligand 1 and increased the levels of HGF in human islets.Conclusions/interpretationInhibition of GPR44 in human islets has the potential to improve islet function and survival rate under inflammatory and hyperglycaemic stress. This may have implications for better survival rate of islets following transplantation.

Highlights

GPR44 is a transmembrane G-protein coupled receptor for prostaglandin D2 (PGD2), shown to be highly expressed in human beta cells through proteomics screening analysis [1]
We demonstrated increased cell death in human islets treated with high concentrations of glucose (HG) + IL-1β for 48 h (Fig. 1c), and the GPR44 antagonist
Inhibition of GPR44 in human islets has the following effects: (1) reduced PGD2- and proinflammatory cytokine-induced apoptosis; (2) preserved islet grafts; and (3) improved glucose regulation in vivo in human islets exposed to a type 1 diabetes-like milieu

Summary

Introduction

GPR44 ( known as PTGDR2, DP2 or CRTh2) is a transmembrane G-protein coupled receptor for prostaglandin D2 (PGD2), shown to be highly expressed in human beta cells through proteomics screening analysis [1]. It has been identified as a useful imaging biomarker for visualising of human beta cell mass [2]. The physiological role of GPR44 in human islet function and survival in the diabetic milieu is unknown One hallmark of both type 1 and type 2 diabetes is the loss of functional beta cell mass resulting in an insufficient release of insulin and development of hyperglycaemia [3]. IL-1β, a proinflammatory cytokine known to induce beta cell injury and loss, has been found to increase prostaglandin production in islets through activation of NF-κB [6]

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Results

Conclusion