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Electroporation-mediated transfer of plasmids to the lung results in reduced TLR9 signaling and inflammation

Abstract

Electroporation can deliver DNA efficiently and safely to tissues in live animals, including the lung where it causes little inflammation or lung injury. In contrast, cationic lipid-mediated gene transfer has been shown to induce an inflammatory response caused by unmethylated plasmid CpG residues, which activate the toll-like receptor (TLR9) signaling pathway. As TLR9 is located in the endosomal/lysosomal compartment, we hypothesized that plasmids do not activate TLR9 during electroporation because they enter the cytoplasm directly through transient pores in the plasma membrane. To test this, plasmids were transfected into kidney epithelial cells overexpressing TLR9 (HEK293-TLR9+) and cells lacking TLR9 (HEK293-TLR9-null). Interleukin (IL)-8 expression, an indicator of TLR9 activation, increased more than 10-fold at 24 h post-liposome transfection in HEK293-TLR9+ cells, but showed no significant increase in electroporated cells, compared with untransfected cells. In vivo liposome-mediated gene transfer caused increases in IL-6, IL-12, tumor necrosis factor α and interferon γ in mouse bronchial alveolar lavage fluid, whereas the levels of these cytokines were more than 10-fold lower by comparison following electroporation. Depletion of alveolar macrophages suggested that this inflammatory response is mediated by resident pulmonary epithelial cells. These results suggest that electroporation-mediated gene transfer bypasses the TLR-9 pathway, thus accounting for the low levels of inflammation seen with this approach.

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Acknowledgements

We thank Gokhan Mutlu, John Christman and Amy Bellmeyer for helpful discussions and technical advice. This work was supported in part by grants HL59956, HL71643 and HL81148 from the National Institutes of Health.

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Correspondence to D A Dean.

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Zhou, R., Norton, J., Zhang, N. et al. Electroporation-mediated transfer of plasmids to the lung results in reduced TLR9 signaling and inflammation. Gene Ther 14, 775–780 (2007). https://doi.org/10.1038/sj.gt.3302936

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