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

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. Single‐walled carbon nanotubes (SWCNTs) induce the accumulation of extracellular ATP that activates P2X7 receptor‐mediated signaling pathways and elevates lysosomal pH. The alkalized lysosomes move along reorganized microtubules to fuse with plasma membrane and ultimately are released from cells, along with which SWCNTs are exocytosed.