During their lifespan, dendritic cells (DCs) are exposed to different pO₂ levels that affect their differentiation and functions. Autophagy is one of the adaptive responses to hypoxia with important implications for cell survival. While the autophagic machinery in DCs was shown to impact signaling of TLRs, its regulation by the MD-2/TLR4 ligand LPS is still unclear. The aim of this study was to evaluate whether LPS can induce autophagy in DCs exposed to either aerobic or hypoxic conditions. Using human monocyte-derived DCs and the combination of immunofluorescence confocal analysis, measure of mitochondrial membrane potential, Western blotting, and RT-qPCR, we showed that the ability of LPS to modulate autophagy was strictly dependent upon pO₂ levels. Indeed, LPS inhibited autophagy in aerobic conditions whereas the autophagic process was induced in a hypoxic environment. Under hypoxia, LPS treatment caused a significant increase of functional lysosomes, LC3B and Atg protein upregulation, and reduction of SQSTM1/p62 protein levels. This selective regulation was accompanied by activation of signalling pathways and expression of cytokines typically associated with DC survival. Bafilomycin A1 and chloroquine, which are recognized as autophagic inhibitors, confirmed the induction of autophagy by LPS under hypoxia and its impact on DC survival. In conclusion, our results show that autophagy represents one of the mechanisms by which the activation of the MD-2/TLR4 ligand LPS promotes DC survival under hypoxic conditions.

在其生命周期中，树突状细胞 (DC) 暴露于影响其分化和功能的不同 pO _2水平。自噬是对缺氧的适应性反应之一，对细胞存活具有重要意义。虽然 DC 中的自噬机制被证明会影响 TLR 的信号传导，但其通过 MD-2/TLR4 配体 LPS 的调节仍不清楚。本研究的目的是评估 LPS 是否可以在暴露于有氧或缺氧条件下的 DC 中诱导自噬。使用人单核细胞衍生的 DC 以及免疫荧光共聚焦分析、线粒体膜电位测量、蛋白质印迹和 RT-qPCR 的组合，我们表明 LPS 调节自噬的能力严格依赖于 pO ₂水平。事实上，LPS 在有氧条件下抑制自噬，而自噬过程是在缺氧环境中诱导的。在缺氧条件下，LPS 处理导致功能性溶酶体显着增加，LC3B 和 Atg 蛋白上调，以及 SQSTM1/p62 蛋白水平降低。这种选择性调节伴随着信号通路的激活和通常与 DC 存活相关的细胞因子的表达。被认为是自噬抑制剂的巴弗洛霉素 A1 和氯喹证实了 LPS 在低氧条件下诱导自噬及其对 DC 存活的影响。总之，我们的结果表明自噬代表了 MD-2/TLR4 配体 LPS 的激活促进缺氧条件下 DC 存活的机制之一。