Baicalin relieves Mycoplasma pneumoniae infection-induced lung injury through regulating microRNA-221 to inhibit the TLR4/NF-κB signaling pathway

Mycoplasma pneumoniae (MP) is a common pathogen that can cause respiratory infections. MP pneumonia (MPP) leads to numerous complications, including lung injury and even death. The present study aimed to investigate the protective effects of Baicalin treatment on MP infection-induced lung injury and the molecular mechanism underlying these effects. Briefly, after mice were infected intranasally by MP and treated with Baicalin (80 mg/kg), serum levels of MP-immunoglobulin M (IgM) were detected by ELISA. The expression levels of C-reactive protein (CRP) in lung tissue were detected by immunohistochemistry and the bronchoalveolar lavage fluid (BALF) was examined by ELISA. Inflammatory factors and inflammatory cells in the BALF were assessed. The expression levels of microRNA (miR)-221 in lung tissue were examined by reverse transcription-quantitative PCR and pathological changes in lung tissue were detected by H&E staining. Cell apoptosis was evaluated by TUNEL assay and the protein expression levels of TLR4, MyD88 and NF-κB were detected by western blotting. Baicalin treatment significantly reduced serum levels of MP-IgM and CRP expression in lung tissue during MP infection. In addition, Baicalin decreased the levels of IL-1β, IL-6, IL-18 and TNF-α in the BALF, and the number of inflammatory cells. Baicalin also reduced the inflammatory infiltration in lung tissue induced by MP infection, improved the pathological changes detected in lung tissue, reduced apoptosis, and downregulated the protein expression levels of TLR4, MyD88 and NF-κB. Furthermore, Baicalin treatment downregulated the expression of miR-221 and the protective effects of Baicalin were attenuated by miR-221 overexpression. In conclusion, Baicalin has a therapeutic effect on mice with MP infection-induced lung injury, which may be related to inhibition of miR-221 expression and regulation of the TLR4/NF-κB signaling pathway.