Extracellular Succinate Hyperpolarizes M2 Macrophages through SUCNR1/GPR91-Mediated Gq Signaling. Extracellular Succinate Hyperpolarizes M2 Macrophages through SUCNR1/GPR91-Mediated Gq Signaling

Succinate functions both as a classical TCA cycle metabolite and as an extracellular metabolic stress signal sensed by the mainly Gi-coupled succinate receptor, SUCNR1. In the present study, we characterize and compare effects and signaling pathways activated by succinate and both classes of non-metabolite SUCNR1 agonists. By use of specific receptor and pathway inhibitors, rescue in G protein depleted cells and monitoring of receptor G protein activation by BRET we surprisingly identify Gq rather than Gi signaling, to be responsible for SUCNR1-mediated effects on basic transcriptional regulation. Importantly, in primary human M2 macrophages, where SUCNR1 is highly expressed, we demonstrate that physiological concentrations of extracellular succinate act through SUCNR1 activated Gq signaling to efficiently regulate transcription of immune function genes in a manner that hyperpolarizes their M2 versus M1 phenotype. Thus, sensing of stress-induced extracellular succinate by SUCNR1 is an important transcriptional regulator in human M2 macrophages through Gq signaling. Overall design: RNA-seq of primary human monocyte-derived macrophages from healthy adult donors. Macrophages were polarised to the M2 state and treated with succinate +/- a SUCNR1 antagonist or a Gq inhibitor and compared with a vehicle control.

琥珀酸（succinate）既是经典的三羧酸循环（TCA cycle）代谢物，同时也是一种胞外代谢应激信号，可通过主要以Gi偶联的琥珀酸受体SUCNR1（succinate receptor）感知。本研究中，我们对琥珀酸以及两类非代谢型SUCNR1激动剂所激活的生物学效应与信号通路进行了表征与对比分析。通过使用特异性受体与通路抑制剂、在G蛋白缺失细胞中开展功能挽救实验，并借助生物发光共振能量转移（Bioluminescence Resonance Energy Transfer, BRET）技术监测受体G蛋白激活状态，我们意外发现，介导SUCNR1调控基础转录活性的信号通路并非Gi信号，而是Gq信号通路。尤为重要的是，在SUCNR1高表达的原代人M2巨噬细胞中，我们证实：生理浓度的胞外琥珀酸可通过SUCNR1激活的Gq信号通路，有效调控免疫功能相关基因的转录，进而使巨噬细胞偏向M2表型而非M1表型极化。综上，SUCNR1感知应激诱导产生的胞外琥珀酸，是通过Gq信号通路调控人M2巨噬细胞转录活性的重要机制。总体实验设计：采集健康成年供者的原代人单核细胞衍生巨噬细胞，开展RNA测序（RNA-seq）实验。将巨噬细胞极化为M2表型后，分别给予琥珀酸、琥珀酸联合SUCNR1拮抗剂或Gq抑制剂处理，并以溶剂对照组作为对照进行比较分析。