Knockdown of circ_0026579 ameliorates lipopolysaccharide (bacterial origin)-induced inflammatory injury in bronchial epithelium cells by targeting miR-338-3p/TBL1XR1 axis

Background: Circular RNAs (circRNAs) play an important regulatory role in human diseases including organ allograft rejection. The aim of this study is to clarify the functional role and molecular mechanism of circ_0026579 RNA in lipopolysaccharide (LPS)-induced bronchopneumonia injury. Materials and methods: Bronchial epithelial BEAS-2B cells were treated with LPS to mimic an in vitro model for bronchopneumonia. Cell viability and proliferation were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and 5-ethynyl-2 '-deoxyuridine (EdU) assay. Flow cytometry assay was used to assess cell apoptosis. Caspase-3 activity was analyzed by Caspase-3 activity assay kit. The expression levels of circ_0026579 RNA, miR-338-3p, and transducin beta-like 1x related protein 1 (TBL1XR1) RNA were determined by RT-qPCR. The protein level was quantified by western blot assay. The correlation between miR-338-3p and circ_0026579 or TBL1XR1 was confirmed by dual-luciferase reporter and RNA immunoprecipitation assays. Results: LPS treatment repressed proliferation but induced apoptosis and inflammatory response in BEAS-2B cells. Circ_0026579 RNA was highly expressed in patients with pneumonia. Besides, the expression levels of circ_0026579 RNA and TBL1XR1 RNA/protein were upregulated, while miR-338-3p level was decreased in LPStreated BEAS-2B cells. Knockdown of circ_0026579 RNA or TBL1XR1 protein could abolish LPS-induced cell injury in BEAS-2B cells. Furthermore, we found that circ_0026579 RNA functioned as a "sponge" for miR-338-3p to regulate TBL1XR1 expression. Additionally, silencing circ_0026579 RNA protected BEAS-2B cells from LPSinduced bronchopneumonia injury by regulating TBL1XR1 expression. Conclusion: Circ_0026579 RNA knockdown promoted cell proliferation but inhibited apoptosis and inflammation in LPS-induced BEAS-2B cells through regulating miR-338-3p RNA/TBL1XR1 protein axis.