Rudolf Schönheimer Institute of Biochemistry, Faculty of Medicine, Leipzig University, Johannisallee 30, 04103 Leipzig, Germany.
Swedish Metabolomics Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Linnaeus väg 6, 901 87 Umeå, Sweden.
Pharmacol Res. 2022 Feb;176:106047. doi: 10.1016/j.phrs.2021.106047. Epub 2021 Dec 27.
G protein-coupled receptors (GPCRs) are key regulatory proteins of immune cell function inducing signaling in response to extracellular (pathogenic) stimuli. Although unrelated, hydroxycarboxylic acid receptor 3 (HCA) and GPR84 share signaling via Gα proteins and the agonist 3-hydroxydecanoic acid (3HDec). Both receptors are abundantly expressed in monocytes, macrophages and neutrophils but have opposing functions in these innate immune cells. Detailed insights into the molecular mechanisms and signaling components involved in immune cell regulation by GPR84 and HCA are still lacking. Here, we report that GPR84-mediated pro-inflammatory signaling depends on coupling to the hematopoietic cell-specific Gα protein in human macrophages, while HCA exclusively couples to Gα protein. We show that activated GPR84 induces Gα-dependent ERK activation, increases intracellular Ca and IP levels as well as ROS production. In contrast, HCA activation shifts macrophage metabolism to a less glycolytic phenotype, which is associated with anti-inflammatory responses. This is supported by an increased release of anti-inflammatory IL-10 and a decreased secretion of pro-inflammatory IL-1β. In primary human neutrophils, stimulation with HCA agonists counteracts the GPR84-induced neutrophil activation. Our analyses reveal that 3HDec acts solely through GPR84 but not HCA activation in macrophages. In summary, this study shows that HCA mediates hyporesponsiveness in response to metabolites derived from dietary lactic acid bacteria and uncovers that GPR84, which is already targeted in clinical trials, promotes pro-inflammatory signaling via Gα protein in macrophages.
G 蛋白偶联受体（GPCRs）是免疫细胞功能的关键调节蛋白，能在外源（致病）刺激下诱导信号转导。虽然 HCA3 受体（hydroxycarboxylic acid receptor 3）和 G 蛋白偶联受体 84（GPR84）无关联，但它们通过 Gα 蛋白和激动剂 3-羟基癸酸（3-hydroxydecanoic acid，3HDec）共享信号转导。这两种受体在单核细胞、巨噬细胞和中性粒细胞中大量表达，但在这些固有免疫细胞中具有相反的功能。尽管人们对 GPR84 和 HCA 调节免疫细胞的分子机制和信号成分有了一定的了解，但仍存在一些细节上的空白。在这里，我们报告 GPR84 介导的促炎信号取决于人巨噬细胞中造血细胞特异性 Gα 蛋白的偶联，而 HCA 则专门与 Gα 蛋白偶联。我们发现，激活的 GPR84 诱导 Gα 依赖性 ERK 激活，增加细胞内 Ca 和 IP 水平以及 ROS 产生。相反，HCA 激活使巨噬细胞代谢向更少糖酵解表型转变，这与抗炎反应有关。这一结果得到了以下证据的支持：抗炎性细胞因子 IL-10 释放增加，促炎性细胞因子 IL-1β 分泌减少。在原代人中性粒细胞中，HCA 激动剂刺激可拮抗 GPR84 诱导的中性粒细胞激活。我们的分析表明，在巨噬细胞中，3HDec 仅通过 GPR84 而不是 HCA 激活起作用。总之，本研究表明，HCA 介导对膳食乳酸菌衍生代谢物的低反应性，并揭示 GPR84 在临床试验中已被靶向，它通过 Gα 蛋白在巨噬细胞中促进促炎信号转导。
