Endocrine Abstracts

GPR56 is an adhesion G-protein coupled receptor (GPCR), which we have shown to be the most abundant GPCR in mouse and human islets. The extracellular N-terminal domain of adhesion GPCRs contains a tethered agonist, buried within the GPCR autoproteolysis-inducing domain. Synthetic peptides mimicking tethered agonist sequences can activate a variety of adhesion GPCRs including GPR56. Here we investigated the effect of a GPR56 tethered agonist peptide, P7, on β-cell function. A stable GPR56KO MIN6 β-cell line, in which GPR56 had been deleted, was established by CRISPR-Cas9 technology and GPR56 deletion was confirmed by Sanger sequencing and Western blotting. Administration of P7 significantly increased intracellular calcium in native MIN6 β-cells, as measured by single cell calcium microfluorimetry, while this effect was lost in GPR56KO MIN6 β-cells (basal to peak ratio; native β-cells, 2 mM glucose: 0.02±0.01, +P7: 0.13±0.01, n=3, P<0.01; GPR56KO β-cells, 2mM glucose: 0.01±0.003,+P7: 0.02±0.001, P>0.2). In addition, P7 protected mouse islets and native MIN6 β-cells from cytokine-induced apoptosis, as assessed by luminescent quantification of caspase 3/7 activities, but it did not reduce apoptosis in GPR56KO MIN6 β-cells (% relative to maximum cytokine-induced apoptosis: mouse islets, +P7: 34±4.6%, P<0.0001; native β-cells, +P7: 87±4.2%, P<0.01; GPR56KO β-cells, +P7: 105±5.4%, P>0.1). P7 also potentiated glucose induced insulin secretion from human islets (2.32±0.72 fold, P<0.05). These studies indicate that P7-induced activation of GPR56 stimulates insulin secretion and protects β-cells from apoptosis, and this could have implications in developing novel therapies for type 2 diabetes.