Down-regulation of lncRNA CASC9 aggravates sepsis-induced acute lung injury by regulating miR-195-5p/PDK4 axis

Background Long non-coding RNA (lncRNA) cancer susceptibility candidate 9 (CASC9) is reported to be linked to cancers. This research aims to explore the role and possible mechanism of CASC9 in lung injury induced by sepsis. Methods Lipopolysaccharide (LPS) induced human small airway epithelial cells (HSAECs) were established in vitro to mimic sepsis-induced lung injury. The effects of CASC9 and miR-195-5p on HSAECs viability were studied by CCK-8 assay. Interactions between CASC9 and miR-195-5p were determined by bioinformatics analysis, RT-PCR, dual luciferase reporter assay, and RNA immunoprecipitation assay. Pyruvate dehydrogenase kinase 4 (PDK4) and apoptosis-related molecules including Bcl2 and Bad were detected by western blot. Additionally, sepsis-induced lung injury model in rats was established by intraperitoneal injection of LPS in vivo to validate the demonstrations of in vitro studies. Results CASC9 was markedly down-regulated while miR-195-5p was significantly up-regulated in HSAECs treated by LPS and lung tissues of rats with sepsis. CASC9 interacted with miR-195-5p, and negatively regulated its expression level. Overexpression of CASC9 or transfection of miR-195-5p inhibitors significantly promoted the viability of HSAECs. The transfection of miR-195-5p mimics effected oppositely. For mechanism, miR-195-5p targeted the 3 ' UTR of pyruvate dehydrogenase kinase 4 (PDK4) gene and depressed the protein level, and PDK4 was regulated indirectly by CASC9. Restoration of CASC9 in the lung tissues of rats with sepsis ameliorated lung injury. Conclusion CASC9 protects lung epithelial cells from sepsis-induced injury via regulating miR-195-5p/PDK4 axis.