Inhibition of importin-7 attenuates ventilator-induced lung injury by targeting nuclear translocation of p38.

ABSTRACT

BACKGROUND: The ability of p38 to phosphorylate substrates in the nucleus and the role of nuclear p38 in the regulation of inflammation have focused attention on the subcellular localization of the kinase. Although it is clear that p38 shuttles to the nucleus upon stimulation, the mechanisms that regulate p38 nuclear input in response to mechanical stretch remain to be determined. METHODS: Cyclic stretch (CS)-induced nuclear translocation of p38 was determined by Western blotting and immunofluorescence. The p38 interacting protein was identified using endogenous pull-down and protein binding assays. The potential role of importin-7 (Imp7) in CS-induced nuclear translocation of p38 and p38-dependent gene expression was confirmed using a series of in vitro and in vivo experiments. Furthermore, we tested the therapeutic potential of intratracheal administration of Imp7 siRNA-loaded nanoparticles in the ventilator-induced lung injury (VILI) mouse model. RESULTS: We show that CS induced phosphorylation-dependent nuclear translocation of p38, which required the involvement of microtubules and dynein. Endogenous pull-down assay revealed Imp7 to be a potential p38-interacting protein, and the direct interaction between p38 and Imp7 was confirmed by in vitro and in vivo binding assays. Furthermore, silencing Imp7 inhibited CS-induced nuclear translocation of p38 and subsequent cytokine production. Notably, intratracheal administration of Imp7 siRNA nanoparticles attenuated lung inflammation and histological damage in the VILI mouse model. CONCLUSIONS: Our findings uncover a key role for Imp7 in the process of p38 nuclear import after CS stimulation and highlight the potential of preventing p38 nuclear translocation in treatment of VILI.