Age-related macular degeneration (AMD) is the leading cause of blindness in the industrialised world affecting over 50 million people worldwide; 5% of over 70’s suffer from AMD. AMD is characterised by degeneration of the retinal pigment epithelial cells (RPE) in the macula leading to destruction of photoreceptors in the eye. There is currently no effective treatment for the most common atrophic form of AMD. Since the prevalence of AMD is increasing with the expansion of the ageing population discovering novel drug targets is a priority.
Circulating mediators regulate RPE proliferation and integrity, which in turn is vital for the survival of photoreceptors1. G protein-coupled receptors are a family of cell-surface receptors, which respond to various extracellular mediators and regulate an array of physiological processes. The accessibility of GPCRs on the plasma membrane and their tissue-selective distribution make them excellent pharmacological targets2. However, the endogenous ligands of a large number of GPCRs remain unidentified, leaving their physiological role unknown. Studying these GPCRs, namely orphan GPCRs, could advance the understanding of disease.
GPR75 (retinal GPCR) is an orphan GPCR that is highly expressed in human RPEs3. Six potential pathogenic variants of GPR75 have been identified in AMD patients, however their functional significance has yet to be determined3. Our lab has begun to elucidate the function of GPR75 by creating GPR75 over-expressing HEK-293 cells, using CRISPR/Cas technology in-vitro and in-vivo and developing a screen to identify ligands. Uncovering ligands or developing functional or neutralising antibodies would provide useful research tools to target GPR75 and even offer potential therapeutics. Using cutting edge technologies such as molecular biology, signalling and G-protein binding assays, CRISPR/Cas technology, antibody generation, chemistry to synthesis and modify ligands and an animal model reflecting the early pathology of AMD, the specific aims of the studentship are to:
1. Uncover the pharmacology of GPR75, in part through the identification of ligands and the generation of functional or neutralising GPR75 antibodies.
2. Investigate the significance of GPR75 variants that are associated with AMD on receptor function by site-directed mutagenesis of wild-type GPR75.
3. Determine the physiological relevance of GPR75 in RPEs in a model of AMD using CRISPR/Cas GPR75-knockout mice, novel ligands and GPR75 functional antibodies.
This proposed PhD project brings together areas of expertise in pharmacology, immunology, chemistry and the blood–ocular barrier from the University of Aberdeen with those from local industry. Expertise and training in the generation of an antibody targeting GPR75 will be given by Elasmogen, a biologics drug discovery company that specialises in antibody-like proteins called soloMERs, which due to their small size allows for both site-specific delivery and penetration, which is ideal to cross the ocular barrier in-vivo. Completion of the specific aims will reveal the pharmacology of GPR75 and functional effects of receptor variants. Furthermore, understanding the role of GPR75 in RPE cells could uncover the biological mechanisms of the ageing process in the eye that predispose patients to AMD, thereby highlight this receptor as a new target for the disease, thus providing translational impact.
1.Devarajan G, Niven J, Forrester JV, Crane IJ. Retinal Pigment Epithelial Cell Apoptosis is Influenced by a Combination of Macrophages and Soluble Mediators Present in Age-Related Macular Degeneration. Curr Eye Res. 2016; 25:1-10.
2. Insel PA, Snead A, Murray F, Zhang L, Yokouchi H, Katakia T, Kwon O, Dimucci D, Wilderman A. GPCR expression in tissues and cells: are the optimal receptors being used as drug targets? Br J Pharmacol. 2012; 165(6):1613-6.
3. Sauer CG1, White K, Stöhr H, Grimm T, Hutchinson A, Bernstein PS, Lewis RA, Simonelli F, Pauleikhoff D, Allikmets R, Weber BH. Evaluation of the G protein coupled receptor-75 (GPR75) in age related macular degeneration. Br J Ophthalmol. 2001; 85(8):969-75.