GPR84 is a member of the metabolic G protein-coupled receptor family, and its expression has been described predominantly in immune cells. GPR84 activation is involved in the inflammatory response, but the mechanisms by which it modulates inflammation have been incompletely described. In this study, we investigated GPR84 expression, activation, and function in macrophages to establish the role of the receptor during the inflammatory response. We observed that GPR84 expression in murine tissues is increased by endotoxemia, hyperglycemia, and hypercholesterolemia. Ex vivo studies revealed that GPR84 mRNA expression is increased by LPS and other pro-inflammatory molecules in different murine and human macrophage populations. Likewise, high glucose concentrations and the presence of oxidized LDL increased GPR84 expression in macrophages. Activation of the GPR84 receptor with a selective agonist, 6-(octylamino) pyrimidine-2,4(1H,3H)-dione (6-n-octylaminouracil, 6-OAU), enhanced the expression of phosphorylated Akt, p-ERK, and p65 nuclear translocation under inflammatory conditions and elevated the expression levels of the inflammatory mediators TNFα, IL-6, IL-12B, CCL2, CCL5, and CXCL1. In addition, GPR84 activation triggered increased bacterial adhesion and phagocytosis in macrophages. The enhanced inflammatory response mediated by 6-OAU was not observed in GPR84−/− cells nor in macrophages treated with a selective GPR84 antagonist. Collectively, our results reveal that GPR84 functions as an enhancer of inflammatory signaling in macrophages once inflammation is established. Therefore, molecules that antagonize the GPR84 receptor may be potential therapeutic tools in inflammatory and metabolic diseases.

GPR84 is an orphan G-protein-coupled receptor that is expressed on immune cells and implicated in several inflammatory diseases. The validation of GPR84 as a therapeutic target is hindered by the narrow range of available chemical tools and consequent poor understanding of GPR84 pathophysiology. Here we describe the discovery and characterization of DL-175, a potent, selective, and structurally novel GPR84 agonist and the first to display significantly biased signaling across GPR84-overexpressing cells, primary murine macrophages, and human U937 cells. By comparing DL-175 with reported GPR84 ligands, we show for the first time that biased GPR84 agonists have markedly different abilities to induce chemotaxis in human myeloid cells, while causing similar levels of phagocytosis enhancement. This work demonstrates that biased agonism at GPR84 enables the selective activation of functional responses in immune cells and delivers a high-quality chemical probe for further investigation.

Aims/hypothesis Microvascular complications in the heart and kidney are strongly associated with an overall rise in inflammation. Annexin A1 (ANXA1) is an endogenous anti-inflammatory molecule that limits and resolves inflammation. In this study, we have used a bedside to bench approach to investigate: (1) ANXA1 levels in individuals with type 1 diabetes; (2) the role of endogenous ANXA1 in nephropathy and cardiomyopathy in experimental type 1 diabetes; and (3) whether treatment with human recombinant ANXA1 attenuates nephropathy and cardiomyopathy in a murine model of type 1 diabetes. Methods ANXA1 was measured in plasma from individuals with type 1 diabetes with or without nephropathy and healthy donors. Experimental type 1 diabetes was induced in mice by injection of streptozotocin (STZ; 45 mg/kg i.v. per day for 5 consecutive days) in C57BL/6 or Anxa1 −/− mice. Diabetic mice were treated with human recombinant (hr)ANXA1(1 μg, 100 μl, 50 mmol/l HEPES; 140 mmol/l NaCl; pH 7.4, i.p.) or vehicle (100 μl, 50 mmol/l HEPES; 140 mmol/l NaCl; pH 7.4, i.p.).Results Plasma levels of ANXA1 were elevated in individuals with type 1 diabetes with/without nephropathy compared with healthy individuals (66.0 ± 4.2/64.0 ± 4 ng/ml vs 35.9 ± 2.3 ng/ml; p < 0.05). Compared with diabetic wild-type (WT) mice, diabetic Anxa1 −/− mice exhibited a worse diabetic phenotype and developed more severe cardiac (ejection fraction; 76.1 ± 1.6% vs 49.9 ± 0.9%) and renal dysfunction (proteinuria; 89.3 ± 5.0 μg/ mg vs 113.3 ± 5.5 μg/mg). Mechanistically, compared with nondiabetic WT mice, the degree of the phosphorylation of mitogenactivated protein kinases (MAPKs) p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) was significantly higher in non-diabetic Anxa1 −/− mice in both the heart and kidney, and was further enhanced after STZ-induced type 1 diabetes. Prophylactic treatment with hrANXA1 (weeks 1-13) attenuated both cardiac (ejection fraction; 54.0 ± 1.6% vs 72.4 ± 1.0%) and renal (proteinuria; 89.3 ± 5.0 μg/mg vs 53.1 ± 3.4 μg/mg) dysfunction associated with STZ-induced diabetes, while therapeutic administration of hrANXA1 (weeks 8-13), after significant cardiac and renal dysfunction had already developed, halted the further functional decline in cardiac and renal function seen in diabetic mice administered vehicle. In addition, administration of hrANXA1 attenuated the increase in phosphorylation of p38, JNK and ERK, and restored phosphorylation of Akt in diabetic mice. Conclusions/interpretationOverall, these results demonstrate that ANXA1 plasma levels are elevated in individuals with Christoph Thiemermann and Egle Solito contributed equally to this work.Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00125-017-4469-y) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Annexin-A1 (ANXA1) was first discovered in the early 1980's as a protein, which mediates (some of the) anti-inflammatory effects of glucocorticoids. Subsequently, the role of ANXA1 in inflammation has been extensively studied. The biology of ANXA1 is complex and it has many different roles in both health and disease. Its effects as a potent endogenous anti-inflammatory mediator are well-described in both acute and chronic inflammation and its role in activating the pro-resolution phase receptor, FPR2, has been described and is now being exploited for therapeutic benefit. In the present mini review, we will endeavor to give an overview of ANXA1 biology in relation to inflammation and functions that mediate pro-resolution that are independent of glucocorticoid induction. We will focus on the role of ANXA1 in diseases with a large inflammatory component focusing on diabetes and microvascular disease. Finally, we will explore the possibility of exploiting ANXA1 as a novel therapeutic target in diabetes and the treatment of microvascular disease.