Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI, United States.
Institute for Integrative Toxicology, Michigan State University, East Lansing, MI, United States.
Front Immunol. 2020 Oct 6;11:2179. doi: 10.3389/fimmu.2020.02179. eCollection 2020.
Airway exposure of lupus-prone NZBWF1 mice to crystalline silica (cSiO), a known trigger of human autoimmune disease, elicits sterile inflammation and alveolar macrophage death in the lung that, in turn, induces early autoimmune onset and accelerates lupus progression to fatal glomerulonephritis. Dietary supplementation with docosahexaenoic acid (DHA), a marine ω-3 polyunsaturated fatty acid (PUFA), markedly ameliorates cSiO-triggered pulmonary, systemic, and renal manifestations of lupus. Here, we tested the hypothesis that DHA influences both cSiO-induced death and efferocytotic clearance of resultant cell corpses using three murine macrophage models: (i) primary alveolar macrophages (AM) isolated from NZBWF1 mice; (ii) self-renewing AM-like Max Planck Institute (MPI) cells isolated from fetuses of C57BL/6 mice, and (iii) RAW 264.7 murine macrophages, a virus-transformed cell line derived from BALB/c mice stably transfected with the inflammasome adaptor protein ASC (RAW-ASC). Incubation with cSiO at 25 and 50 μg/ml for 6 h was found to dose-dependently induce cell death ( < 0.05) in all three models as determined by both acridine orange/propidium iodide staining and release of lactate dehydrogenase into cell culture supernatant. Pre-incubation with DHA at a physiologically relevant concentration (25 μM) significantly reduced cSiO-induced death ( < 0.05) in all three models. Cell death induction by cSiO alone and its suppression by DHA were primarily associated with caspase-3/7 activation, suggestive of apoptosis, in AM, MPI, and RAW-ASC cells. Fluorescence microscopy revealed that all three macrophage models were similarly capable of efferocytosing RAW-ASC target cell corpses. Furthermore, MPI effector cells could likewise engulf RAW-ASC target cell corpses elicited by treatment with staurosporine (apoptosis), LPS, and nigericin (pyroptosis), or cSiO. Pre-incubation of RAW-ASC target cells with 25 μM DHA prior to death induced by these agents significantly enhanced their efferocytosis ( < 0.05) by MPI effector cells. In contrast, pre-incubating MPI effector cells with DHA did not affect engulfment of RAW-ASC target cells pre-incubated with vehicle. Taken together, these findings indicate that DHA at a physiologically relevant concentration was capable of attenuating macrophage death and could potentiate efferocytosis, with the net effect of reducing accumulation of cell corpses capable of eliciting autoimmunity.
空气通道暴露于狼疮易感 NZBWF1 小鼠的结晶二氧化硅 (cSiO),一种已知的人类自身免疫性疾病的触发因素,会引发肺部的无菌性炎症和肺泡巨噬细胞死亡,进而诱导早期自身免疫发作,并加速狼疮进展为致命的肾小球肾炎。用二十二碳六烯酸 (DHA),一种海洋 ω-3 多不饱和脂肪酸 (PUFA) 进行饮食补充,可显著改善 cSiO 引发的肺部、全身和肾脏狼疮表现。在这里,我们使用三种鼠巨噬细胞模型来测试 DHA 影响 cSiO 诱导的死亡和由此产生的细胞尸体的吞噬清除的假设:(i) 从 NZBWF1 小鼠中分离的原代肺泡巨噬细胞 (AM);(ii) 从 C57BL/6 小鼠胎儿中分离的自我更新的 AM 样马克斯·普朗克研究所 (MPI) 细胞,以及 (iii) RAW 264.7 鼠巨噬细胞,一种源自 BALB/c 小鼠的病毒转化细胞系,稳定转染了炎症小体衔接蛋白 ASC(RAW-ASC)。用 25 和 50 μg/ml 的 cSiO 孵育 6 小时被发现可剂量依赖性地诱导所有三种模型中的细胞死亡 ( < 0.05),这是通过吖啶橙/碘化丙啶染色和乳酸脱氢酶释放到细胞培养上清液中确定的。在所有三种模型中,用生理相关浓度 (25 μM) 的 DHA 预先孵育可显著降低 cSiO 诱导的死亡 ( < 0.05)。cSiO 诱导的细胞死亡和 DHA 的抑制主要与 caspase-3/7 激活有关,提示凋亡,在 AM、MPI 和 RAW-ASC 细胞中。荧光显微镜显示,所有三种巨噬细胞模型均能够以类似的方式吞噬 RAW-ASC 靶细胞尸体。此外,MPI 效应细胞也能够吞噬由 staurosporine(凋亡)、LPS 和 Nigericin(焦亡)或 cSiO 处理诱导的 RAW-ASC 靶细胞尸体。在这些试剂诱导的 RAW-ASC 靶细胞死亡之前,用 25 μM DHA 预先孵育显著增强了 MPI 效应细胞的吞噬作用 ( < 0.05)。相比之下,用 DHA 预先孵育 MPI 效应细胞不会影响对用载体预孵育的 RAW-ASC 靶细胞的吞噬作用。总之,这些发现表明,生理相关浓度的 DHA 能够减轻巨噬细胞死亡,并能够增强吞噬作用,其净效应是减少能够引发自身免疫的细胞尸体的积累。