Increased lung vascular permeability and neutrophilic inflammation are hallmarks of acute lung injury. Alveolar macrophages (AMϕ), the predominant sentinel cell type in the airspace, die in massive numbers while fending off pathogens. Recent studies indicate that the AMϕ pool is replenished by airspace-recruited monocytes, but the mechanisms instructing the conversion of recruited monocytes into reparative AMϕ remain elusive. Cyclic AMP (cAMP) is a vascular barrier protective and immunosuppressive second messenger in the lung. Here, we subjected mice expressing GFP under the control of the Lysozyme-M promoter (LysM-GFP mice) to the LPS model of rapidly resolving lung injury to address the impact of mechanisms determining cAMP levels in AMϕ and regulation of mobilization of the reparative AMϕ-pool. RNA-seq analysis of flow-sorted Mϕ identified phosphodiesterase 4b (PDE4b) as the top LPS-responsive cAMP-regulating gene. We observed that PDE4b expression markedly increased at the time of peak injury (4 h) and then decreased to below the basal level during the resolution phase (24 h). Activation of transcription factor NFATc2 was required for transcription of PDE4b in Mϕ. Inhibition of PDE4 activity at the time of peak injury, using i.t. rolipram, increased cAMP levels, augmented the reparative AMϕ pool, and resolved lung injury. This response was not seen following conditional depletion of monocytes, thus establishing airspace-recruited PDE4b-sensitive monocytes as the source of reparative AMϕ. Interestingly, adoptive transfer of rolipram-educated AMϕ into injured mice resolved lung edema. We propose suppression of PDE4b as an effective approach to promote reparative AMϕ generation from monocytes for lung repair.

中文翻译：

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通过靶向 PDE4b 在体内将单核细胞重编程为修复性肺泡巨噬细胞的证据

肺血管通透性增加和中性粒细胞炎症是急性肺损伤的标志。肺泡巨噬细胞 (AMφ) 是领空中的主要哨兵细胞类型，在抵御病原体的同时大量​​死亡。最近的研究表明 AMφ 池由空域招募的单核细胞补充，但指示招募的单核细胞转化为修复性 AMφ 的机制仍然难以捉摸。环 AMP (cAMP) 是肺中的血管屏障保护和免疫抑制第二信使。在这里，我们将在溶菌酶-M 启动子（LysM-GFP 小鼠）控制下表达 GFP 的小鼠置于快速解决肺损伤的 LPS 模型中，以解决确定 AMφ 中 cAMP 水平的机制的影响和调节修复性 AMφ 的动员-水池。流式分选 Mϕ 的 RNA-seq 分析将磷酸二酯酶 4b (PDE4b) 鉴定为顶级 LPS 响应 cAMP 调节基因。我们观察到 PDE4b 表达在损伤高峰时（4 小时）显着增加，然后在消退阶段（24 小时）降低至基础水平以下。Mφ 中 PDE4b 的转录需要激活转录因子 NFATc2。在损伤高峰时抑制 PDE4 活性，使用咯利普兰，增加了 cAMP 水平，增加了修复性 AMφ 池，并解决了肺损伤。在单核细胞条件性耗竭后没有看到这种反应，因此建立了空域招募的 PDE4b 敏感单核细胞作为修复性 AMφ 的来源。有趣的是，将经过咯利普兰的 AMϕ 过继转移到受伤的小鼠中可以解决肺水肿。