Hypervirulent Klebsiella pneumoniae (hvKp) infection-induced sepsis-associated acute lung injury (ALI) has emerged as a significant clinical challenge. Increasing evidence suggests that activated inflammatory macrophages contribute to tissue damage in sepsis. However, the underlying causes of widespread macrophage activation remain unclear. BALB/c mice were intravenously injected with inactivated hvKp (iHvKp) to observe lung tissue damage, inflammation, and M1 macrophage polarization. In vitro, activated RAW264.7 macrophage-derived exosomes (iHvKp-exo) were isolated and their role in ALI formation was investigated. RT-PCR was conducted to identify changes in exosomal miRNA. Bioinformatics analysis and dual-luciferase reporter assays were performed to validate MSK1 as a direct target of miR-155-5p. Further in vivo and in vitro experiments were conducted to explore the specific mechanisms involved. iHvKp successfully induced ALI in vivo and upregulated the expression of miR-155-5p. In vivo, injection of iHvKp-exo induced inflammatory tissue damage and macrophage M1 polarization. In vitro, iHvKp-exo was found to promote macrophage inflammatory response and M1 polarization through the activation of the p38-MAPK pathway. RT-PCR revealed exposure time-dependent increased levels of miR-155-5p in iHvKp-exo. Dual-luciferase reporter assays confirmed the functional role of miR-155-5p in mediating iHvKp-exo effects by targeting MSK1. Additionally, inhibition of miR-155-5p reduced M1 polarization of lung macrophages in vivo, resulting in decreased lung injury and inflammation induced by iHvKp-exo or iHvKp. The aforementioned results indicate that exosomal miR-155-5p drives widespread macrophage inflammation and M1 polarization in hvKp-induced ALI through the MSK1/p38-MAPK Axis.

中文翻译：

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外泌体 miR-155-5p 通过 MSK1/p38-MAPK 轴在高毒力肺炎克雷伯菌诱导的急性肺损伤中驱动广泛的巨噬细胞 M1 极化

高毒力肺炎克雷伯菌 (hvKp) 感染引起的脓毒症相关急性肺损伤 (ALI) 已成为一项重大的临床挑战。越来越多的证据表明，活化的炎症巨噬细胞会导致脓毒症中的组织损伤。然而，巨噬细胞广泛激活的根本原因仍不清楚。BALB/c小鼠静脉注射灭活的hvKp（iHvKp），观察肺组织损伤、炎症和M1巨噬细胞极化情况。在体外，分离了活化的 RAW264.7 巨噬细胞衍生的外泌体 (iHvKp-exo)，并研究了它们在 ALI 形成中的作用。进行 RT-PCR 来鉴定外泌体 miRNA 的变化。进行生物信息学分析和双荧光素酶报告基因测定以验证 MSK1 作为 miR-155-5p 的直接靶标。进一步进行体内和体外实验以探索所涉及的具体机制。iHvKp 成功诱导体内 ALI 并上调 miR-155-5p 的表达。在体内，注射 iHvKp-exo 诱导炎症组织损伤和巨噬细胞 M1 极化。在体外，iHvKp-exo 通过激活 p38-MAPK 通路促进巨噬细胞炎症反应和 M1 极化。RT-PCR 显示 iHvKp-exo 中 miR-155-5p 水平呈暴露时间依赖性增加。双荧光素酶报告基因测定证实了 miR-155-5p 通过靶向 MSK1 介导 iHvKp-exo 效应的功能作用。此外，抑制 miR-155-5p 可减少体内肺巨噬细胞的 M1 极化，从而减少 iHvKp-exo 或 iHvKp 诱导的肺损伤和炎症。上述结果表明，外泌体 miR-155-5p 通过 MSK1/p38-MAPK 轴驱动 hvKp 诱导的 ALI 中广泛的巨噬细胞炎症和 M1 极化。