TFNAs induce autophagy via activation of the nonclassical cGAS-STING signalling pathway to attenuate acute lung injury in mice.

BACKGROUND: Acute lung injury is a common and fatal inflammatory condition in critically ill patients. Tetrahedral framework nucleic acids (TFNAs) have good potential for treating inflammatory diseases. The aim of this study was to use TFNAs in the treatment of acute lung injury (ALI) in mice to investigate the effect and possible mechanism. METHOD: The characteristics of the TFNAs, including particle size and cellular uptake, were detected. TFNAs were subsequently used to treat an ALI mouse lung epithelial cells (MLE12) model with or without an autophagy inhibitor. Flow cytometry and Western blotting (WB) were performed to detect apoptosis and autophagy. The oxidative stress level was assessed by measuring the malondialdehyde (MDA) content, superoxide dismutase (SOD) activity and reactive oxygen species (ROS) content. A survival curve of the ALI model mice treated with TFNAs was constructed, and the lung injury score was assessed through pathological staining. The lung wet/dry weight ratio and inflammatory cytokine content in bronchoalveolar lavage fluid were measured and recorded. Transcription sequencing was performed to elucidate the biological processes associated with TFNA treatment. Finally, the regulatory effect of the cGAS-STING signalling pathway on TFNA-induced autophagy was explored. RESULT: The synthesized TFNAs are typical nanomaterials. TFNAs significantly reduced the apoptosis rate according to flow cytometry and decreased the BAX/BCL2 ratio in MLE12 cells. Meanwhile, the autophagy level increased, as indicated by the increased expression of the ATG5, ATG7 and LC3II proteins when the cells were incubated with TFNAs. TFNAs could also inhibit the accumulation of ROS, increasing SOD activity and reducing the MDA content. Autophagy inhibitors can significantly inhibit the autophagy and antiapoptotic effects of TFNAs. In the ALI mouse model, TFNAs effectively reduced mortality, BALF inflammatory factor levels, pulmonary oedema, lung injury scores and neutrophil infiltration. The protective effect was significantly reduced with the use of autophagy inhibitors. In addition to autophagy, antigen processing and presentation, antiviral biological processes, and cytoplasmic membrane signal receptor complex functions were significantly upregulated, indicating that TFNAs might activate the cGAS-STING signalling pathway. Inhibition of the cGAS-STING signalling pathway effectively suppressed TFNA-induced autophagy. CONCLUSION: This study is the first to demonstrate that TFNAs protect MLE-12 cells against LPS-induced oxidative stress injury via autophagy activated by the nonclassical cGAS-STING signalling pathway. Therefore, TFNAs can attenuate ALI and improve patient prognosis in mice. These findings indicate that the cGAS-STING signalling pathway may be a basic mechanism contributing to various therapeutic immunologic effects. This study demonstrated the value of TFNAs in the treatment of ALI, with potential clinical translational value.