Crucial Role of P2X7 Receptor in Regulating Exocytosis of Single-Walled Carbon Nanotubes in Macrophages

Authors

  • Xuejing Cui,

    1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
    2. University of Chinese Academy of Sciences, Beijing, China
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  • Bin Wan,

    Corresponding author
    1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
    2. University of Chinese Academy of Sciences, Beijing, China
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  • Yu Yang,

    1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
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  • Xiaomin Ren,

    1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
    2. University of Chinese Academy of Sciences, Beijing, China
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  • Liang-Hong Guo,

    Corresponding author
    1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
    2. University of Chinese Academy of Sciences, Beijing, China
    3. Institute of Environment and Health, Jianghan University, Wuhan, Hubei, China
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  • Hui Zhang

    1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
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Abstract

Exocytosis of single-walled carbon nanotubes (SWCNTs) determines therapeutic efficiency and toxicity of nanoproducts but its underlying mechanism remains elusive. In this study, it is found that the exocytosis mechanism of SWCNTs is mediated mainly through the activation of P2X7 receptor (P2X7R), an ATP-gated membrane receptor highly expressed in macrophages. Inhibition of P2X7R signaling by either a specific inhibitor (oxidized ATP) or small interfering RNA targeting P2X7R largely prevents the exocytosis of SWCNTs from Raw264.7 cells, resulting in significant accumulation of SWCNTs within cells. In contrast, activation of P2X7R with ATP promotes exocytosis of SWCNTs. Specifically, it is elucidated that internalized SWCNTs are accumulated in lysosomes and induce transitional release of ATP into extracellular space, which further activates P2X7R, leading to the influx of calcium ions, phosphorylation of protein kinase C, ERK1/2, p38, and JNK, as well as alkalization of lysosomes. SWCNTs exposure also induces microtubules reorganization that facilitates the secretion of SWCNTs-containing lysosomes. It is also found that P2X7R simultaneously mediates secretion of IL-1β from Raw264.7 cells during the process of SWCNTs exocytosis. The combined data reveals that P2X7R-mediated pathway is the predominant molecular mechanism for exocytosis of SWCNTs in Raw264.7 cells. Moreover, SWCNT-induced inflammation is closely coupled with the exocytosis of SWCNTs through P2X7R.

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