An mRNA atlas of G protein-coupled receptor expression during primary human monocyte/macrophage differentiation and lipopolysaccharide-mediated activation identifies targetable candidate regulators of inflammation

摘要

G protein-coupled receptors (GPCRs) are among the most important targets in drug discovery. In this study, we used TaqMan Low Density Arrays to profile the full GPCR repertoire of primary human macrophages differentiated from monocytes using either colony stimulating factor-1 (CSF-1/M-CSF) (CSF-1 Mφ) or granulocyte macrophage colony stimulating factor (GM-CSF) (GM-CSF Mφ). The overall trend was a downregulation of GPCRs during monocyte to macrophage differentiation, but a core set of 10 genes (e.g. LGR4, MRGPRF and GPR143) encoding seven transmembrane proteins were upregulated, irrespective of the differentiating agent used. Several of these upregulated GPCRs have not previously been studied in the context of macrophage biology and/or inflammation. As expected, CSF-1 Mφ and GM-CSF Mφ exhibited differential inflammatory cytokine profiles in response to the Toll-like Receptor (TLR)4 agonist lipopolysaccharide (LPS). Moreover, 15 GPCRs were differentially expressed between these cell populations in the basal state. For example, EDG1 was expressed at elevated levels in CSF-1 Mφ versus GM-CSF Mφ, whereas the reverse was true for EDG6. 101 GPCRs showed differential regulation over an LPS time course, with 65 of these profiles being impacted by the basal differentiation state (e.g. GPRC5A, GPRC5B). Only 14 LPS-regulated GPCRs showed asynchronous behavior (divergent LPS regulation) with respect to differentiation status. Thus, the differentiation state primarily affects the magnitude of LPS-regulated expression, rather than causing major reprogramming of GPCR gene expression profiles. Several GPCRs showing differential profiles between CSF-1 Mφ and GM-CSF Mφ (e.g. P2RY8, GPR92, EMR3) have not been widely investigated in macrophage biology and inflammation. Strikingly, several closely related GPCRs displayed completely opposing patterns of regulation during differentiation and/or activation (e.g. EDG1 versus EDG6, LGR4 versus LGR7, GPRC5A versus GPRC5B). We propose that selective regulation of GPCR5A and GPCR5B in CSF-1 Mφ contributes to skewing toward the M2 macrophage phenotype. Our analysis of the GPCR repertoire expressed during primary human monocyte to macrophage differentiation and TLR4-mediated activation provides a valuable new platform for conducting future functional analyses of individual GPCRs in human macrophage inflammatory pathways.