Investigating G protein-coupled receptor 35 signalling and its role in cardiovascular disease

Divorty, Nina (2017) Investigating G protein-coupled receptor 35 signalling and its role in cardiovascular disease. PhD thesis, University of Glasgow.

Abstract

G protein-coupled receptors (GPCRs) are an important source of drug targets with diverse therapeutic applications. Orphan GPCRs, which have unknown endogenous ligands or physiological functions, represent a pool of potential therapeutic targets that could provide novel or improved treatments for a wide range of diseases. G protein-coupled receptor 35 (GPR35) is an orphan receptor that has been associated with several diseases and physiological processes, including gastrointenstinal disease, pain transduction, inflammation and cardiovascular disease. However, the precise function of GPR35 in these processes is yet to be elucidated. Cardiovascular disease, including hypertension and heart failure, remains a large global disease burden, suggesting that current treatments are inadequate and that novel insights might be beneficial. Therefore, the role of GPR35 in cardiovascular disease was investigated in order to assess its potential as a therapeutic target.

To provide insight into the potential mechanisms of GPR35 actions in the cardiovascular system, GPR35 signalling was investigated in detail in vitro. Agonist-dependent phosphorylation was observed at five sites in the GPR35 C‑terminal tail, which differentially influenced β‑arrestin recruitment. Both agonist-dependent phosphorylation and β‑arrestin‑1/2, but not Gα12/13, were essential for agonist-induced internalisation of GPR35, an important process in the desensitisation of the G protein-mediated response. Conversely, agonist-induced reorganisation of the actin cytoskeleton was dependent on Gα12/13, but not phosphorylation or β‑arrestin.

To assess the role of GPR35 in cardiovascular disease, its actions were investigated in three in vivo models. A GPR35 knockout mouse had no abnormal cardiovascular phenotype under basal conditions, with no detectable differences in blood pressure, cardiac function, vascular reactivity or end-organ morphology compared with the wild type background strain. However, GPR35 knockout mice were resistant to hypertension and cardiac dysfunction induced by 2‑week infusion of angiotensin II. Furthermore, administration of the GPR35 agonist amlexanox exacerbated both hypertension and end-organ damage in the stroke-prone spontaneously hypertensive rat.

These findings demonstrate a pathological role for GPR35 in the development of hypertension and its associated end-organ damage. It is likely that this is a result of Gα13-mediated effects of GPR35 on the actin cytoskeleton in cardiovascular tissues, although this requires further investigation in primary cell models. These studies suggest that antagonism of GPR35 could be a novel therapeutic strategy to treat hypertension and/or heart failure. The findings must now be validated by antagonising GPR35 in in vivo disease models, in order to evaluate the therapeutic value of this strategy.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: GPR35, orphan, GPCR; cardiovascular, hypertension.
• Subjects: Q Science > QH Natural history > QH301 Biology; Q Science > QH Natural history > QH345 Biochemistry
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
• Funder's Name: Wellcome Trust (WELLCOTR)
• Supervisor's Name: Milligan, Professor Graeme, Nicklin, Dr. Stuart A. and Graham, Dr. Delyth
• Date of Award: 2017
• Depositing User: Nina Divorty
• Unique ID: glathesis:2017-8235
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 01 Jun 2017 08:06
• Last Modified: 28 Nov 2017 08:39
• URI: https://theses.gla.ac.uk/id/eprint/8235