Development of new therapeutic approaches based on GPR120 and GPR55 activation for type 2 diabetes

Abstract

G-protein coupled receptors (GPCRs) are a 7-transmembrane family of receptors expressed in regions of the brain, pancreas, and the gut. Activation of GPCRs is associated with many processes in the body including energy metabolism. New anti-diabetic therapies that can improve beta cell survival and increase proliferation along with glucoregulatory properties are of interest with much focus on targeting free fatty acid and cannabinoid receptors. The aim of this study was to investigate the therapeutic potential of GPR120 and GPR55 activation. The effects of GPR55 and GPR120 endogenous and synthetic agonists were studied in vitro focusing on insulin release, cytotoxicity, gene expression and signalling in clonal pancreatic BRIN-BD11 cells. GPR120 and GPR55 agonist specificity was examined in knockout cells generated from BRIN-BD11 cells using CRISPR Cas9 gene-editing. Gene expression studies were conducted to investigate the compensatory expression of other cannabinoid and free fatty acid receptors in the absence of GPR55 and GPR120. In vivo studies were conducted to investigate the metabolic effects of GPR120 and GPR55 agonist treatments in high fat fed mice. Agonist activation of GPR55 and GPR120 augmented insulin release with no cytotoxic effects in BRIN-BD11 cells, increased ERK and Akt MAPK signalling were also observed. GPR55 agonists AM251, Abn-CBD and ML184, and GPR120 agonists, ALA, GSK137647 and Compound A were shown to be highly specific with no insulinotropic activity following the abolishment of the receptors in CRISPR engineered knockout cells. Expression of GPR120 and GPR55 was confirmed in isolated mouse islets and clonal beta cells, along with the demonstration of areas of co-localisation with insulin. Oral administration of GPR120 and GPR55 agonists enhanced glucose tolerance and increased insulin release plus an additive effect in combination with DPP-4 inhibitor, Sitagliptin in high fat fed mice. Treatment (21-days) with Compound A and ML184 improved glucose tolerance with increased insulin secretion, insulin sensitivity, islet cell renewal and decreased food intake. Biochemical studies showed increased circulating GLP-1 and GIP hormones and changes in MAPK signalling. This
investigative study has revealed the targeting of GPR55 and GPR120 as a novel therapeutic strategy in the treatment of diabetes and related metabolic diseases.

Date of Award	May 2022
Original language	English
Supervisor	Peter Flatt (Supervisor) & Aine McKillop (Supervisor)