Immunometabolism has been unveiled in the last decade to play a major role in controlling macrophage metabolism and inflammation. There has been a constant effort to understand the immunomodulating properties of regulated metabolites during inflammation with the aim of controlling and re-wiring aberrant macrophages in inflammatory diseases. M-CSF and GM-CSF-differentiated macrophages play a key role in mounting successful innate immune responses. When a resolution phase is not achieved however, GM-CSF macrophages contribute substantially more towards an adverse inflammatory milieu than M-CSF macrophages, consequently driving disease progression. Whether there are specific immunometabolites that determine the homoeostatic or inflammatory nature of M-CSF and GM-CSF-differentiated macrophages is still unknown. As such, we performed metabolomics analysis on LPS and IL-4-stimulated M-CSF and GM-CSF-differentiated human macrophages to identify differentially accumulating metabolites. Adenine was distinguished as a metabolite significantly higher in M-CSF-differentiated macrophages after both LPS or IL-4 stimulation. Human macrophages treated with adenine before LPS stimulation showed a reduction in inflammatory gene expression, cytokine secretion and surface marker expression. Adenine caused macrophages to become more quiescent by lowering glycolysis and OXPHOS which resulted in reduced ATP production. Moreover, typical metabolite changes seen during LPS-induced macrophage metabolic reprogramming were absent in the presence of adenine. Phosphorylation of metabolic signalling proteins AMPK, p38 MAPK and AKT were not responsible for the suppressed metabolic activity of adenine-treated macrophages. Altogether, in this study we highlight the immunomodulating capacity of adenine in human macrophages and its function in driving cellular quiescence.

近十年来，免疫代谢已被揭示在控制巨噬细胞代谢和炎症方面发挥着重要作用。人们一直在努力了解炎症过程中受调节代谢物的免疫调节特性，目的是控制和重新连接炎症疾病中的异常巨噬细胞。M-CSF 和 GM-CSF 分化的巨噬细胞在成功建立先天免疫反应中发挥着关键作用。然而，当未达到缓解阶段时，GM-CSF 巨噬细胞比 M-CSF 巨噬细胞对不良炎症环境的贡献更大，从而推动疾病进展。是否存在决定 M-CSF 和 GM-CSF 分化巨噬细胞的稳态或炎症性质的特异性免疫代谢物仍不清楚。因此，我们对 LPS 和 IL-4 刺激的 M-CSF 和 GM-CSF 分化的人类巨噬细胞进行代谢组学分析，以鉴定差异积累的代谢物。在 LPS 或 IL-4 刺激后，腺嘌呤是 M-CSF 分化的巨噬细胞中显着升高的代谢物。在 LPS 刺激前用腺嘌呤处理的人巨噬细胞显示炎症基因表达、细胞因子分泌和表面标志物表达减少。腺嘌呤通过降低糖酵解和 OXPHOS 导致巨噬细胞变得更加静止，从而导致 ATP 产量减少。此外，在腺嘌呤存在的情况下，LPS诱导的巨噬细胞代谢重编程期间观察到的典型代谢变化不存在。代谢信号蛋白 AMPK、p38 MAPK 和 AKT 的磷酸化与腺嘌呤处理的巨噬细胞代谢活性的抑制无关。总而言之，在这项研究中，我们强调了腺嘌呤在人类巨噬细胞中的免疫调节能力及其驱动细胞静止的功能。