Department of Internal Medicine, East Tennessee State University College of Medicine, Johnson City, Tennessee, USA.
Department of Biomedical Sciences, East Tennessee State University College of Medicine, Johnson City, Tennessee, USA.
Infect Immun. 2014 Sep;82(9):3816-25. doi: 10.1128/IAI.01495-14. Epub 2014 Jun 30.
The sepsis initial hyperinflammatory reaction, if not treated early, shifts to a protracted state of immunosuppression that alters both innate and adaptive immunity and is associated with elevated mortality. Myeloid-derived suppressor cells (MDSCs) are myeloid progenitors and precursors that fail to differentiate into mature innate-immunity cells and are known for their potent immunosuppressive activities. We previously reported that murine MDSCs expand dramatically in the bone marrow during late sepsis, induced by cecal ligation and puncture, and demonstrated that they contribute to late-sepsis immunosuppression. However, the molecular mechanism responsible for generating these immature Gr1(+) CD11b(+) myeloid cells during sepsis remains unknown. We show here that sepsis generates a microRNA (miRNA) signature that expands MDSCs. We found that miRNA 21 (miR-21) and miR-181b expression is upregulated in early sepsis and sustained in late sepsis. Importantly, we found that simultaneous in vivo blockade of both miRNAs via antagomiR (a chemically modified miRNA inhibitor) injection after sepsis initiation decreased the bone marrow Gr1(+) CD11b(+) myeloid progenitors, improved bacterial clearance, and reduced late-sepsis mortality by 74%. Gr1(+) CD11b(+) cells isolated from mice injected with antagomiRs were able to differentiate ex vivo into macrophages and dendritic cells and produced smaller amounts of the immunosuppressive interleukin 10 (IL-10) and transforming growth factor β (TGF-β) after stimulation with bacterial lipopolysaccharide, suggesting that immature myeloid cells regained their maturation potential and have lost their immunosuppressive activity. In addition, we found that the protein level of transcription factor NFI-A, which plays a role in myeloid cell differentiation, was increased during sepsis and that antagomiR injection reduced its expression. Moreover, knockdown of NFI-A in the Gr1(+) CD11b(+) cells isolated from late-septic mice increased their maturation potential and reduced their production of the immunosuppressive mediators, similar to antagomiR injection. These data support the hypothesis that sepsis reprograms myeloid cells and thus alters the innate immunity cell repertoire to promote immunosuppression, and they demonstrate that this process can be reversed by targeting miR-21 and miR-181b to improve late-sepsis survival.
脓毒症初始的过度炎症反应，如果不早期治疗，会转变为持续的免疫抑制状态，改变固有免疫和适应性免疫，并与死亡率升高相关。髓系来源的抑制细胞（MDSCs）是髓样祖细胞和前体细胞，它们不能分化为成熟的固有免疫细胞，其具有强大的免疫抑制活性。我们之前报道过，在盲肠结扎和穿刺诱导的晚期脓毒症中，鼠 MDSC 在骨髓中大量扩增，并证明它们有助于晚期脓毒症的免疫抑制。然而，导致这些不成熟 Gr1(+)CD11b(+)髓样细胞在脓毒症中产生的分子机制尚不清楚。我们在这里表明，脓毒症产生了一个 miRNA（miRNA）特征，该特征可扩增 MDSC。我们发现，miR-21 和 miR-181b 的表达在早期脓毒症中上调，并在晚期脓毒症中持续上调。重要的是，我们发现，在脓毒症发作后通过注射反义 miRNA（一种化学修饰的 miRNA 抑制剂）同时阻断这两种 miRNA，可减少骨髓 Gr1(+)CD11b(+)髓样祖细胞，提高细菌清除率，并将晚期脓毒症的死亡率降低 74%。从注射反义 miRNA 的小鼠中分离出的 Gr1(+)CD11b(+)细胞能够在体外分化为巨噬细胞和树突状细胞，并在受到细菌脂多糖刺激后产生较少的免疫抑制性白细胞介素 10（IL-10）和转化生长因子-β（TGF-β），这表明不成熟的髓样细胞恢复了其成熟潜能并丧失了其免疫抑制活性。此外，我们发现，转录因子 NFI-A 的蛋白水平在脓毒症期间升高，而反义 miRNA 注射降低了其表达。此外，在从晚期脓毒症小鼠中分离的 Gr1(+)CD11b(+)细胞中敲低 NFI-A 可增加其成熟潜能并减少其免疫抑制介质的产生，这类似于反义 miRNA 注射。这些数据支持这样一种假设，即脓毒症重新编程髓样细胞，从而改变固有免疫细胞谱系以促进免疫抑制，并且它们表明，通过靶向 miR-21 和 miR-181b 来改善晚期脓毒症的存活率，可以逆转这一过程。
