Investigating the molecular pharmacology of the short chain fatty acid receptor FFA2

Sergeev, Eugenia (2018) Investigating the molecular pharmacology of the short chain fatty acid receptor FFA2. PhD thesis, University of Glasgow.

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Abstract

The G protein-coupled receptor FFA2 is a key mediator of short chain fatty acid signalling, which are produced in the gut via fermentation of poorly digested carbohydrates by the gut microbiota. Therefore, FFA2 has attracted interest as a potential therapeutic target for metabolic and inflammatory diseases. However, several limitations have hindered validation of FFA2 as a drug target, including the limited understanding of the molecular determinants of ligand binding and species-specific differences in pharmacology. Herein, novel tool compounds and assay systems were developed for FFA2 and utilised to address some of these limitations. Following the characterisation of functional assays for detection of FFA2 signalling, these were employed to examine the structure-activity relationship and pharmacology of FFA2 agonists versus antagonists. To assess how the pharmacology of FFA2 ligands is defined by their mode of binding, a radioligand binding assay was developed using a tritiated form of FFA2 antagonist GLPG0974 that was utilised in combination with site-directed mutagenesis and homology modelling to explore FFA2 ligand binding sites. These studies showed that FFA2 agonist binding was defined by an essential interaction between the ligand carboxylate and an orthosteric Arg-His-Arg triad. In contrast, FFA2 antagonists only required one orthosteric arginine for high-affinity binding and could tolerate modifications of the carboxylate moiety. This knowledge was applied to develop an antagonist-based fluorescent tracer for FFA2 that was utilised in BRET binding assays but displayed complex pharmacological behaviour that was shown to be based on the bitopic nature of FFA2 antagonists. The secondary binding site of FFA2 antagonists was also related to their lack of action at rodent orthologues of FFA2, whose molecular basis was explored using homology models of human and murine FFA2. This facilitated the identification of a single lysine to arginine variation at position 2.60 that might provide a basis for antagonist selectivity. Extending these studies to agonist function demonstrated that removal of the positive charge at this position produced a signalling-biased form of FFA2, in which only coupling to Gi G proteins was fully maintained. In summary, these findings contribute to understanding the complex pharmacology of FFA2 ligands and the underlying mechanisms that define their function, and conclusions drawn from these studies may help advance future efforts to validate the therapeutic potential of targeting FFA2.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Molecular pharmacology, GPCR, FFA2.
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QH Natural history > QH345 Biochemistry
R Medicine > RM Therapeutics. Pharmacology
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Supervisor's Name: Milligan, Professor Graeme and Hudson, Dr. Brian
Date of Award: 2018
Depositing User: Miss Eugenia Sergeev
Unique ID: glathesis:2018-8963
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 26 Apr 2018 13:34
Last Modified: 24 May 2018 09:24
URI: http://theses.gla.ac.uk/id/eprint/8963
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