Direct Stimulatory Effects of the CB2 Ligand JTE 907 in Human and Mouse Islets.

Inmaculada Ruz-Maldonado,Bo Liu,Guo Cai Huang,Patricio Atanes,Shanta J Persaud

doi:10.3390/cells10030700

Abstract

Aims: The endocannabinoid system is a complex cell-signaling network through which endogenous cannabinoid ligands regulate cell function by interaction with CB1 and CB2 cannabinoid receptors, and with the novel cannabinoid receptor GPR55. CB1, CB2, and GPR55 are expressed by islet β-cells where they modulate insulin secretion. We have previously shown that administration of the putative CB2 antagonist/inverse agonist JTE 907 to human islets did not affect the insulinotropic actions of CB2 agonists and it unexpectedly stimulated insulin secretion on its own. In this study, we evaluated whether the lack of antagonism could be related to the ability of JTE 907 to act as a GPR55 agonist. Materials and Methods: We used islets isolated from human donors and from Gpr55+/+ and Gpr55−/− mice and quantified the effects of incubation with 10 μM JTE 907 on dynamic insulin secretion, apoptosis, and β-cell proliferation by radioimmunoassay, luminescence caspase 3/7 activity, and immunofluorescence, respectively. We also measured islet IP1 and cAMP accumulation using fluorescence assays, and monitored [Ca2+]i elevations by Fura-2 single cell microfluorometry. Results: JTE 907 significantly stimulated insulin secretion from islets isolated from human donors and islets from Gpr55+/+ and Gpr55−/− mice. These stimulatory effects were accompanied by significant elevations of IP1 and [Ca2+]i, but there were no changes in cAMP generation. JTE 907 also significantly reduced cytokine-induced apoptosis in human and mouse islets and promoted human β-cell proliferation. Conclusion: Our observations show for the first time that JTE 907 acts as a Gq-coupled agonist in islets to stimulate insulin secretion and maintain β-cell mass in a GPR55-independent fashion.

Highlights

Islets of Langerhans contain specialised β-cells that are capable of synthesising and secreting insulin into the bloodstream to rapidly counteract high blood glucose levels.Failure of appropriate β-cell function causes type 2 diabetes (T2D), a chronic disease that results in severe hyperglycaemia [1]
We analysed dynamic insulin secretion from human and mouse islets perifused with buffers supplemented with 2 mM glucose followed by 20 mM glucose in the absence or presence of
To evaluate whether this direct stimulation of insulin release could be related to the ability of JTE 907 to act as a GPR55 agonist in islets, we examined dynamic insulin profiles using wild-type mice and those null for GPR55, and found that JTE 907 significantly promoted glucose-stimulated insulin secretion in both Gpr55+/+ and Gpr55−/− mouse islets (Figure 1B)

Summary

Introduction

Islets of Langerhans contain specialised β-cells that are capable of synthesising and secreting insulin into the bloodstream to rapidly counteract high blood glucose levels.Failure of appropriate β-cell function causes type 2 diabetes (T2D), a chronic disease that results in severe hyperglycaemia [1]. The mechanisms underlying the regulation of βcell function and mass are of major research interest as advances in understanding will underpin development of novel pharmacological therapies for T2D [2]. In this context, the endocannabinoid system (ECS) is of particular interest since it was targeted by the cannabinoid (CB) receptor type 1 (CB1 ) antagonist rimonabant to aid weight loss and improve glycaemic control [3,4,5]. Phospholipid-derived endocannabinoids such as 2-arachidonoylglycerol and anandamide act as activators of the canonical CB1 and CB2 receptors [6]. Both receptors belong to the seven-transmembrane G protein-coupled receptor (GPCR) conserved family and they are distributed centrally and peripherally in active metabolic tissues [6,9]

Methods

Results

Conclusion