The role of orphan receptor GPR84 in macrophage biology and inflammation

Thesis

GPR84 is a Class A orphan GPCR expressed primarily by innate immune cells. Despite significant advances in our understanding of GPR84 in the past 23 years the endogenous agonist(s) remain unknown. Current evidence suggests a primary role for this receptor in inflammation, though its pathophysiological role and the best strategy to exploit its activity therapeutically also remain unknown. This is true at both the physiological level, exemplified by disease models and clinical studies, but also at the molecular level, exemplified by a lack of understanding of downstream pathways and their relationship to cellular function. Surrogate agonists acting at this receptor have been shown to promote the mobilisation of inflammatory mediators, chemotaxis, and phagocytosis in a cell and context-dependent manner. However, the influence of agonist bias via the transducer proteins Gαi and β-arrestin-2 on these cellular responses are unclear. The development of chemical and biological tools to study the function of GPR84 are described herein, including two probes suitable for use in vivo and recombinant cell lines that phenocopy the response of macrophages. A detailed assessment of the signalling and kinetics of responses elicited by the agonists 6-OAU and DL-175 revealed that DL-175 exhibits a delayed impedance response, a delayed and suppressed activation of Akt, and an impaired ability to internalise the receptor. Finally, through the development of a screening set of chemically and biologically diverse agonists a relationship between agonist desensitisation potency and cAMP potency was found, but only a weak relationship between level of internalisation and level of bias. The lack of strong explanatory correlations between compounds in each assay highlights the potential to ‘dial’ receptor signalling in or out based on chemical structure. This work has furthered our molecular understanding of GPR84 signalling and supports research for the development of novel compounds with novel properties.

Authors: Luscombe, VB

• DOI: 10.5287/ora-keovxdkmy
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: G-protein coupled receptor; molecular pharmacology; GPR84; inflammation; macrophage
• Subjects: Inflammation; Macrophages--Activation; Molecular pharmacology