Natural biased signaling of hydroxycarboxylic acid receptor 3 and G protein-coupled receptor 84

BACKGROUND: Medium-chain fatty acids and their 3-hydroxy derivatives are metabolites endogenously produced in humans, food-derived or originating from bacteria. They activate G protein-coupled receptors, including GPR84 and HCA(3), which regulate metabolism and immune functions. Although both receptors are coupled to G(i) proteins, share at least one agonist and show overlapping tissue expression, GPR84 exerts pro-inflammatory effects whereas HCA(3) is involved in anti-inflammatory responses. Here, we analyzed signaling kinetics of both HCA(3) and GPR84, to unravel signal transduction components that may explain their physiological differences. METHODS: To study the signaling kinetics and components involved in signal transduction of both receptors we applied the label-free dynamic mass redistribution technology in combination with classical cAMP, ERK signaling and β-arrestin-2 recruitment assays. For phenotypical analyses, we used spheroid cell culture models. RESULTS: We present strong evidence for a natural biased signaling of structurally highly similar agonists at HCA(3) and GPR84. We show that HCA(3) signaling and trafficking depends on dynamin-2 function. Activation of HCA(3) by 3-hydroxyoctanoic acid but not 3-hydroxydecanoic acid leads to β-arrestin-2 recruitment, which is relevant for cell-cell adhesion. GPR84 stimulation with 3-hydroxydecanoic acid causes a sustained ERK activation but activation of GPR84 is not followed by β-arrestin-2 recruitment. CONCLUSIONS: In summary, our results highlight that biased agonism is a physiological property of HCA(3) and GPR84 with relevance for innate immune functions potentially to differentiate between endogenous, non-pathogenic compounds and compounds originating from e.g. pathogenic bacteria. GRAPHICAL ABSTRACT: [Image: see text]