MicroRNA‑421 attenuates macrophage‑mediated inflammation by inhibiting PDCD4 in vitro

The exact pathogenesis of acute lung injury (ALI) has not been fully clarified. Previous studies have demonstrated that ALI is associated with inflammation. Recent studies have demonstrated that microRNA‑421 (miR‑421) prevents inflammation in cerebellar ischemia reperfusion injury. However, the role of miR‑421 in ALI remains unclear. The present study investigated the role of miR‑421 in ALI and the mechanism underlying this. ALI was induced in vitro by treatment of RAW 264.7 macrophages with lipopolysaccharide (LPS). Cells were then transfected with miR‑421 mimic, miR‑421 mimic control, programmed cell death 4 (PDCD4) siRNA and PDCD4 siRNA control using Lipofectamine 2000. Cell viability was measured using the Cell Counting kit‑8. Reverse transcription‑quantitative polymerase chain reaction was used to detect the expression of miR‑421 and PDCD4 in RAW 264.7 macrophages. The concentrations of IL‑1β and TNF‑α were detected by ELISA. Dual‑luciferase reporter assays were used to investigate the interaction between miR‑421 and PDCD4 mRNA. LPS inhibited cell viability and miR‑421 expression. The miR‑421 mimic promoted RAW 264.7 cell viability and inhibited the expression of iNOS and COX‑2 as well as the release of IL‑1β and TNF‑α. PDCD4 siRNA inhibited the expression of iNOS and COX‑2 expression as well as the release of IL‑1β and TNF‑α. In addition, miR‑421 mimic and PDCD4 siRNA inhibit the expression of p‑NF‑κB (p65) in RAW 264.7 cells. In conclusion, the present study demonstrated the protective effect of miR‑421 on ALI and showed that miR‑421 attenuates LPS‑induced ALI by inhibiting PDCD4 and NF‑κB. These findings provided a theoretical basis for the treatment of ALI.