Reduced peripheral blood miR-140 may be a biomarker for acute lung injury by targeting Toll-like receptor 4 (TLR4)

Acute lung injury (ALI) is a common complication of sepsis to which patients often succumb due to poor effective pharmacological interventions. Recent studies have focused on the potential application of circulating microRNAs (miRs or miRNAs) as novel prognostic and therapeutic biomarkers. The present study focuses mainly on miR-140, the role of which is poorly understood in the progression of ALI. The results of the present study revealed that toll-like receptor 4 (TLR4) expression was upregulated the lungs of rats with ALI. Meanwhile, serum levels of tumor necrosis factor-, interleukin (IL)-6 and IL-1 were significantly increased in rats with ALI compared with normal control rats. These data indicated the successful establishment of LPS-induced ALI. Furthermore, miR-140 was decreased in the peripheral blood of patients with ALI compared with control subjects. Receiver operator characteristic analysis indicated that miR-140 could be used to screen ALI patients and distinguish them from healthy controls. MiR-140 was demonstrated to be downregulated in the plasma and lungs of rats with ALI compared with the normal control group. A dual luciferase reporter assay indicated that TLR4 was a target gene of miR-140. To investigate whether miR-140 exerted its role via TLR4, a specific TLR4-targeting small interfering RNA was selected. It was revealed that TLR4 silencing was able to suppress the phosphorylation of NF-B even in cells transfected with miR-140 inhibitor. In summary, reduced miR-140 expression and increased TLR4 signaling activation may serve a key role in the progression of ALI.