Evaluation of GPR55 and GPR120 as novel therapeutic targets for the treatment of type 2 diabetes

Abstract

G-protein coupled receptors (GPCRs) are expressed in the gut-brain-pancreatic axis and regulate energy metabolism through a range of cellular responses, including hormone release, cell proliferation, neurological signalling and immune responses. Novel therapies that maintain glucose homeostasis and enhance islet cell proliferation are required with research focusing on cannabinoid and free fatty acid receptors. This research study aims to evaluate the therapeutic potential of two GPCRs, namely GPR55 and GPR120. BRIN-BD11 cells were used to assess the effects of endogenous and synthetic GPR55 and GPR120 agonists on insulin release, cell proliferation and cytotoxicity, followed by GPCR expression and intracellular signalling analysis. CRISPR/Cas9 gene editing was utilised to assess agonist specificity. Metabolic effects of GPCR agonist therapies in-vivo were explored in high fat fed (HFF) induced diabetic mice. GPR55 and GPR120 activation exhibited insulinotropic and proliferative effects on pancreatic BRIN-BD11 cells, with modulations in intracellular Ca2+ and MAPK signalling. Assessment of agonist specificity using knockout beta cell lines developed by CRISPR/Cas9 revealed that ALA (GPR120) and Abn-CBD (GPR55) were the most potent selective agonists. Expression and localisation of GPR55 and GPR120 were demonstrated in clonal beta cells and murine islets with areas of co-localisation observed with insulin. Orally administered GPR55/GPR120 agonists improved glucose tolerance and circulating insulin, GLP-1 and GIP in HFF mice, with further improvements in combination with DPP-IV inhibitor (Sitagliptin). Long term administration of ALA and Abn-CBD based therapies improved glycaemic control, bodyweight, insulin sensitivity and enhanced islet cell regeneration. Biochemical analysis revealed improvements towards circulating insulin, dyslipidaemia and CVD risk markers. Collectively, this study highlights GPR55 and GPR120 as novel therapeutic targets for the treatment of diabetes and obesity related diseases.

Date of Award	May 2019
Original language	English
Sponsors	Diabetes UK
Supervisor	Peter Flatt (Supervisor) & Aine McKillop (Supervisor)