BACKGROUND Mesenchymal stem cells (MSCs) have been shown to alleviate acute lung injury (ALI) via paracrine hepatocyte growth factor (HGF) and to induce the differentiation of dendritic cells (DCs) into tolerogenic dendritic cells (DCregs) and participate in the immune response. However, whether MSCs induce the production of DCregs by secreting HGF to alleviate early ALI remains unclear. We observed that the protective effect of mouse bone marrow-derived MSCs against lipopolysaccharide (LPS)-induced ALI was achieved by inducing mature DCs (mDCs) to differentiate into DCregs, and its mechanism is related to the activation of the HGF/Akt pathway. METHODS MSCs or MSCs with overexpression or knockdown of HGF were cocultured with DCs derived from mouse bone marrow using a Transwell system for 3 days. Moreover, we used MSCs or MSCs with overexpression or knockdown of HGF to treat LPS-induced ALI mice for 24 h. Flow cytometry was performed to measure the phagocytosis, accumulation, and maturation of DCs, as well as proliferation of T cells. Lung injury was estimated by lung wet weight to body weight ratio (LWW/BW) and histopathological analysis. Furthermore, we used the Akt inhibitor MK-2206 in a coculture system to elucidate the role of the HGF/Akt pathway in regulating the differentiation of DCs into regulatory DCs and relieving lung injury in early ALI mice. RESULTS Immature DCs (imDCs) were induced to mature after 24 h of LPS (50 ng/ml) stimulation. MSCs or HGF induced the differentiation of mDCs into regulatory DCs characterized by low expression of MHCII, CD86, and CD40 molecules, strong phagocytic function, and the ability to inhibit T cell proliferation. The effect of MSCs on DCregs was enhanced with the increase in HGF secretion and was weakened with the decrease in HGF secretion. DCregs induced by recombinant HGF were attenuated by the Akt inhibitor MK-2206. Lung DC aggregation and mDC ratio increased in LPS-induced ALI mice, while treatment with MSCs decreased lung DC aggregation and maturation and alleviated lung pathological injury. High expression of the HGF gene enhanced the above effect of MSCs, while decreased expression of HGF weakened the above effect of MSCs. CONCLUSIONS MSCs alleviate early ALI via paracrine HGF by inducing mDCs to differentiate into regulatory DCs. Furthermore, the mechanism of HGF-induced differentiation of mDCs into DCregs is related to the activation of the Akt pathway.

中文翻译：

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间充质干细胞通过旁分泌肝细胞生长因子诱导树突状细胞免疫耐受，以减轻急性肺损伤。

背景技术间充质干细胞（MSCs）已显示通过旁分泌肝细胞生长因子（HGF）减轻急性肺损伤（ALI）并诱导树突状细胞（DCs）分化为致耐受性树突状细胞（DCregs）并参与免疫应答。但是，MSC是否通过分泌HGF减轻早期ALI诱导DCregs的产生尚不清楚。我们观察到，小鼠骨髓间充质干细胞对脂多糖（LPS）诱导的ALI的保护作用是通过诱导成熟的DC（mDC）分化为DCreg而实现的，其机制与HGF / Akt途径的激活有关。方法用Transwell系统将MSC或HGF过表达或敲低的MSC与源自小鼠骨髓的DC共培养3天。而且，我们使用过表达或抑制HGF的MSC或MSCs治疗LPS诱导的ALI小鼠24小时。进行流式细胞术以测量DC的吞噬作用，积累和成熟以及T细胞的增殖。通过肺湿重与体重之比（LWW / BW）和组织病理学分析评估肺损伤。此外，我们在共培养系统中使用了Akt抑制剂MK-2206，以阐明HGF / Akt通路在调节DC分化为调节DC以及减轻ALI早期小鼠肺损伤中的作用。结果LPS（50 ng / ml）刺激24 h后，未成熟的DC（imDC）诱导成熟。MSC或HGF诱导mDC分化为调节性DC，其特征在于MHCII，CD86和CD40分子的低表达，强吞噬功能，以及抑制T细胞增殖的能力。MSCs对DCregs的作用随着HGF分泌的增加而增强，而随着HGF分泌的减少而减弱。重组HGF诱导的DCregs被Akt抑制剂MK-2206减毒。LPS诱导的ALI小鼠的肺DC聚集和mDC比增加，而MSCs处理可降低肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC分化为DCregs的机制与Akt途径的激活有关。MSCs对DCregs的作用随着HGF分泌的增加而增强，而随着HGF分泌的减少而减弱。重组HGF诱导的DCregs被Akt抑制剂MK-2206减毒。LPS诱导的ALI小鼠的肺DC聚集和mDC比增加，而MSCs处理可降低肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC分化为DCregs的机制与Akt途径的激活有关。MSCs对DCregs的作用随着HGF分泌的增加而增强，而随着HGF分泌的减少而减弱。重组HGF诱导的DCregs被Akt抑制剂MK-2206减毒。LPS诱导的ALI小鼠的肺DC聚集和mDC比增加，而MSCs处理可降低肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC分化为DCregs的机制与Akt途径的激活有关。重组HGF诱导的DCregs被Akt抑制剂MK-2206减毒。LPS诱导的ALI小鼠的肺DC聚集和mDC比增加，而MSCs处理可降低肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC分化为DCregs的机制与Akt途径的激活有关。重组HGF诱导的DCregs被Akt抑制剂MK-2206减毒。LPS诱导的ALI小鼠的肺DC聚集和mDC比增加，而MSCs处理可降低肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC向DCregs分化的机制与Akt途径的激活有关。而用MSCs治疗可减少肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC分化为DCregs的机制与Akt途径的激活有关。而用MSCs治疗可减少肺DC聚集和成熟并减轻肺病理损伤。HGF基因的高表达增强了MSCs的上述作用，而HGF表达的降低则减弱了MSCs的上述作用。结论MSC通过诱导mDCs分化为调节DCs，通过旁分泌HGF减轻早期ALI。此外，HGF诱导的mDC向DCregs分化的机制与Akt途径的激活有关。