Objective To investigate the effect and mechanism of microRNA (miR)-146a-3p on acute lung injury (ALI) and inflammation induced by lipopolysaccharide (LPS) in mice.Methods Thirty-two BALB/c mice were randomly divided into sham group, ALI group, ALI+agomiR-negative control (NC) group, ALI+miR-146a-3p agonist (agomiR-146a-3p) group, with 8 mice in each group. The ALI model was established by instilling 5 mg/kg LPS into the lungs through the trachea, and the same amount of saline was instilled slowly in the sham group. The mice in the ALI+agomiR-146a-3p group/NC group were injected with 8 mg/kg agomiR-146a-3p or agomiR-NC respectively through the tail vein, once a day, for 3 days. The sham group and the model group were given the same amount of normal saline injection through the tail vein. After 24 hours, they were sacrificed and lung tissues were collected. The expressions of miR-146a-3p and toll-like receptor 4 (TLR4) mRNA in lung tissue were detected by RT-qPCR, the expression levels of TLR4, cleaved caspase-3, Bcl-2 related X protein (Bax), B cell lymphoma-2 (Bcl-2) protein in lung tissue were detected by Western blot. The changes of lung pathology were observed by hematoxylin-eosin staining. The apoptosis of lung tissue was detected by TdT-mediated dUTP nick-end labeling. The expression levels of IL-1β, IL-6 and TNF-α in lung tissue were detected by enzyme-linked immunosorbent assay (ELISA). The dual luciferase reporting system verified the targeting relationship between miR-146a-3p and TLR4 in MRC-5 cells. MRC-5 cells were divided into control group, LPS group, LPS+miR-146a-3p mimic group, LPS+pcDNA3.1(pc)-TLR4 group, LPS+miR-146a-3p mimic+pc-TLR4 group. 100 nmol/L miR-146a-3p mimic and pc-TLR4 plasmids were transfected into MRC-5 cells separately or jointly for 24 hours, and then treated with 1000 ng/mL LPS or normal saline for 72 hours. The apoptosis rate was detected by flow cytometry. The expression levels of TLR4, cleaved caspase-3, Bax, and Bcl-2 proteins were detected by Western blot. The levels of IL-1β, IL-6 and TNF-α were detected by ELISA.Results Compared with the ALI group, the expression of miR-146a-3p was up-regulated, the expressions of TLR4 mRNA and protein were down-regulated, the apoptotic rate was decreased, the expressions of cleaved caspase-3 and Bax protein was down-regulated, the expression of Bcl-2 protein was up-regulated, and the levels of TNF-α, IL-6 and IL-1β in lung tissue were decreased in the lung tissues of the ALI+agomiR-146a-3p group (P<0.05). Dual-luciferase reporter assay confirmed that miR-146a-3p regulates transcription by targeting TLR4 3’UTR sequence (P<0.05). Compared with the LPS group, the expression of TLR4 protein in MRC-5 cells of the LPS+miR-146a-3p mimic group was down-regulated, the apoptosis was reduced, the expressions of cleaved caspase-3 and Bax protein were down-regulated, and the levels of TNF-α, IL-6 and IL-1β in lung tissue were decreased (P<0.05). Overexpression of TLR4 reversed the effect of miR-146a-3p mimic overexpression on LPS-induced apoptosis and inflammation of MRC-5 cells (P<0.05).Conclusion miR-146a-3p alleviates LPS-induced ALI in mice by down-regulating TLR4.

Citation： XU Xiaorong, WANG Haibin, BAI Xiaoyue, SU Xinyun, GUO Ran. miR-146a-3p alleviates LPS-induced acute lung injury in mice by targeting TLR4. Chinese Journal of Respiratory and Critical Care Medicine, 2021, 20(7): 495-502. doi: 10.7507/1671-6205.202005034 Copy