Department of Pharmacology & Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, United States.
The Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States.
Front Immunol. 2023 Dec 12;14:1235936. doi: 10.3389/fimmu.2023.1235936. eCollection 2023.
Circulating monocytes are important players of the inflammatory response to ionizing radiation (IR). These IR-resistant immune cells migrate to radiation-damaged tissues and differentiate into macrophages that phagocytize dying cells, but also facilitate inflammation. Besides the effect of damage-associated molecular patterns, released from irradiated tissues, the inflammatory activation of monocytes and macrophages is largely dependent on IR-induced DNA damage and aberrant transcriptional activity, which may facilitate expression of type I interferons (IFN-I) and numerous inflammation-related genes. We analyzed the accumulation of dsRNA, dsDNA fragments, and RNA:DNA hybrids in the context of induction of RNA-triggered MAVS-mediated and DNA-triggered STING-mediated signaling pathways, in primary human monocytes and a monocytic cell line, THP1, in response to various doses of gamma IR. We found that exposure to lower doses (<7.5 Gy) led to the accumulation of dsRNA, along with dsDNA and RNA:DNA hybrids and activated both MAVS and STING pathway-induced gene expression and signaling activity of IFN-I. Higher doses of IR resulted in the reduced dsRNA level, degradation of RNA-sensing mediators involved in MAVS signaling and coincided with an increased accumulation of dsDNA and RNA:DNA hybrids that correlated with elevated STING signaling and NF-κB-dependent gene expression. While both pathways activate IFN-I expression, using MAVS- and STING-knockout THP1 cells, we identified differences in the spectra of interferon-stimulated genes (ISGs) that are associated with each specific signaling pathway and outlined a large group of STING signaling-associated genes. Using the RNAi technique, we found that increasing the dose of IR activates STING signaling through the DNA sensor cGAS, along with suppression of the DDX41 helicase, which is known to reduce the accumulation of RNA:DNA hybrids and thereby limit cGAS/STING signaling activity. Together, these results indicate that depending on the applied dose, IR leads to the activation of either dsRNA-induced MAVS signaling, which predominantly leads to the expression of both pro- and anti-inflammatory markers, or dsDNA-induced STING signaling that contributes to pro-inflammatory activation of the cells. While RNA:DNA hybrids boost both MAVS- and STING-mediated signaling pathways, these structures being accumulated upon high IR doses promote type I interferon expression and appear to be potent enhancers of radiation dose-dependent pro-inflammatory activation of monocytes.
循环单核细胞是对电离辐射 (IR) 产生炎症反应的重要参与者。这些对 IR 有抵抗力的免疫细胞迁移到受辐射损伤的组织中，并分化为巨噬细胞，吞噬死亡细胞，但也促进炎症。除了受损组织释放的损伤相关分子模式的影响外，单核细胞和巨噬细胞的炎症激活在很大程度上取决于 IR 诱导的 DNA 损伤和异常转录活性，这可能促进 I 型干扰素 (IFN-I) 和许多炎症相关基因的表达。我们分析了双链 RNA(dsRNA)、双链 DNA 片段和 RNA:DNA 杂交在诱导主要组织相容性复合体 (MHC) 相关病毒信号转导物 (MAVS) 介导的 RNA 触发和 STING 介导的 DNA 触发信号通路中的积累情况，在原代人单核细胞和单核细胞系 THP1 中，以响应各种剂量的γIR。我们发现，暴露于较低剂量（<7.5Gy）会导致 dsRNA 以及 dsDNA 和 RNA:DNA 杂交的积累，并激活 MAVS 和 STING 通路诱导的 IFN-I 基因表达和信号活性。更高剂量的 IR 导致 dsRNA 水平降低，参与 MAVS 信号的 RNA 感应介质降解，同时 dsDNA 和 RNA:DNA 杂交的积累增加，与 STING 信号的升高和 NF-κB 依赖性基因表达相关。虽然两条途径都能激活 IFN-I 的表达，但使用 MAVS 和 STING 敲除 THP1 细胞，我们确定了与每种特定信号通路相关的干扰素刺激基因 (ISG) 的谱存在差异，并概述了一大组与 STING 信号相关的基因。使用 RNAi 技术，我们发现增加 IR 剂量会通过 DNA 传感器 cGAS 激活 STING 信号，同时抑制 DDX41 解旋酶，这已知会减少 RNA:DNA 杂交的积累，从而限制 cGAS/STING 信号活性。总之，这些结果表明，根据应用的剂量，IR 会导致 dsRNA 诱导的 MAVS 信号的激活，这主要导致促炎和抗炎标志物的表达，或者 dsDNA 诱导的 STING 信号的激活，这有助于细胞的促炎激活。虽然 RNA:DNA 杂交增强了 MAVS 和 STING 介导的信号通路，但这些结构在高 IR 剂量下积累，促进了 I 型干扰素的表达，并且似乎是辐射剂量依赖性促炎激活单核细胞的有效增强剂。
