Modelling the pharmacodynamics of the Adenosine A1 receptor

Anthony Knight1,2, Krasimira Tsaneva-Atanasova3, Manuel Alejandro Esparza-Franco1,2, John Davey2, Graham Ladds2. 1Systems Biology Doctoral Training Centre, University of Warwick, Coventry, CV4 7AL, UK, 2Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK, 3Department of Engineering Mathematics, University of Bristol, Queen's Building, Bristol, BS8 1TR, UK

G protein-coupled receptors (GPCRs) are the most abundant class of eukaryotic receptor and govern a wide range of physiological processes. GPCRs mediate cellular signalling via heterotrimeric G proteins. Ligand binding to the GPCR causes nucleotide exchange on the G alpha subunit, dissociation of G protein complex and stimulating downstream signalling via a variety of secondary messengers. GPCRs are capable of coupling to various G alpha subunits. It is thought that the G alpha subunit stimulated depends on the ligand bound to the GPCR. This selective activation is known as “agonist-directed trafficking”. Here we use the well-characterised Saccharomyces cerevisiae pheromone response as a model GPCR signalling pathway with which to explore human GPCR-G alpha interactions. This is possible due to chimeric G alpha subunits. Only the 5 C-terminal amino acids are required for GPCR-G protein interactions. In these strains (kindly provided by Dr Simon Dowell, GlaxoSmithKline) these amino acids have been replaced with their human counterparts, coupling a human GPCR to a model pathway via a human GPCR-G protein interaction. We use this system to investigate the pharmacodynamics of the adenosine A1 receptor. We explore agonist-directed trafficking using a variety of adenosine receptor agonists and antagonist combinations. We then extend the biological experiments by adopting an iterative systems biology approach. By modelling this pathway using a system of ordinary differential equations we can begin to determine the kinetic parameters of GPCR-G protein coupling in response to differing agonists and antagonists.