Department of Biology, Central Michigan University, Mount Pleasant, MI, United States.
Front Immunol. 2022 Jul 29;13:949451. doi: 10.3389/fimmu.2022.949451. eCollection 2022.
In response to several types of bacteria, as well as pharmacological agents, neutrophils produce extracellular vesicles (EVs) and release DNA in the form of neutrophil extracellular traps (NETs). However, it is unknown whether these two neutrophil products cooperate to modulate inflammation. Consistent with vital NETosis, neutrophils challenged with , as well as those treated with A23187, released significantly more DNA relative to untreated or fMLF-treated neutrophils, with no lysis occurring for any condition. To test the hypothesis that EVs generated during NETosis caused macrophage inflammation, we isolated and characterized EVs from A23187-treated neutrophils (A23187-EVs). A23187-EVs associated with neutrophil granule proteins, histone H3, transcription factor A, mitochondrial (TFAM), and nuclear and mitochondrial DNA (mtDNA). We showed that DNA from A23187-EVs, when transfected into macrophages, led to production of IL-6 and IFN-α2, and this response was blunted by pre-treatment with the STING inhibitor H151. Next, we confirmed that A23187-EVs were engulfed by macrophages, and showed that they induced cGAS-STING-dependent IL-6 production. In contrast, neither EVs from untreated or fMLF-treated cells exhibited pro-inflammatory activity. Although detergent-mediated lysis of A23187-EVs diminished IL-6 production, removal of surface-associated DNA with DNase I treatment had no effect, and A23187-EVs did not induce IFN-α2 production. Given these unexpected results, we investigated whether macrophage mtDNA activated the cGAS-STING signaling axis. Consistent with mitochondrial outer membrane permeabilization (MOMP), a defined mechanism of mtDNA release, we observed macrophage mitochondrial membrane depolarization, a decrease in cytosolic Bax, and a decrease in mitochondrial cytochrome c, suggesting that macrophage mtDNA may initiate this EV-dependent signaling cascade. All together, these data demonstrate that A23187-EVs behave differently than transfected NET- or EV-DNA, and that neutrophil-derived EVs could be used as a model to study NF-κB-dependent STING activation.
针对多种类型的细菌以及药理学制剂,中性粒细胞会产生细胞外囊泡 (EVs) 并以中性粒细胞细胞外陷阱 (NETs) 的形式释放 DNA。然而,尚不清楚这两种中性粒细胞产物是否协同调节炎症。与重要的 NETosis 一致,与 或 A23187 一起受到刺激的中性粒细胞相对于未处理或 fMLF 处理的中性粒细胞释放出显著更多的 DNA,任何情况下都不会发生裂解。为了测试 EVs 在 NETosis 过程中产生是否会导致巨噬细胞炎症的假设,我们从 A23187 处理的中性粒细胞中分离和表征了 EVs (A23187-EVs)。A23187-EVs 与中性粒细胞颗粒蛋白、组蛋白 H3、转录因子 A、线粒体 (TFAM) 以及核和线粒体 DNA (mtDNA) 相关。我们表明,从 A23187-EVs 转染到巨噬细胞中会导致产生 IL-6 和 IFN-α2,而用 STING 抑制剂 H151 预处理会减弱这种反应。接下来,我们证实 A23187-EVs 被巨噬细胞吞噬,并表明它们诱导 cGAS-STING 依赖性的 IL-6 产生。相比之下,未经处理或 fMLF 处理的细胞的 EVs 均未表现出促炎活性。尽管去污剂介导的 A23187-EVs 裂解会降低 IL-6 的产生,但用 DNase I 处理去除表面相关 DNA 则没有影响,并且 A23187-EVs 也不会诱导 IFN-α2 的产生。鉴于这些意外的结果,我们研究了巨噬细胞 mtDNA 是否激活了 cGAS-STING 信号通路。与线粒体外膜通透性 (MOMP) 一致,这是 mtDNA 释放的一种明确机制,我们观察到巨噬细胞线粒体膜去极化、细胞质 Bax 减少和线粒体细胞色素 c 减少,表明巨噬细胞 mtDNA 可能启动这种 EV 依赖性信号级联。综上所述,这些数据表明 A23187-EVs 的行为不同于转染的 NET 或 EV-DNA,并且中性粒细胞衍生的 EVs 可用作研究 NF-κB 依赖性 STING 激活的模型。