Experimental pulmonary fibrosis was suppressed by microRNA-506 through NF-kappa-mediated apoptosis and inflammation

Fibrosis in the lungs usually occurs in the initial phase of acute respiratory distress syndrome (ARDS), which exacerbates poor prognosis among patients. MicroRNAs (miRs) have the ability to modulate the expression profiles of many genes, thus essentially altering cell phenotypes. We hypothesize that miRs may be involved in the development of lung fibrosis in mice. In this study, mice were treated with lipopolysaccharide (LPS) to establish the lung fibrosis animal model. Hematoxylin and eosin (H&E) staining and western blot (WB) were performed to confirm the successful establishment of the model. Quantitative PCR (qPCR) and WB were utilized to monitor the expression of miRs and proteins. A dual-luciferase reporter assay was used to detect the interaction between miR and genes. We observed miR-506 downregulation in lung tissues during lung fibrosis after ARDS rat modeling by LPS exposure. We also observed that its expression level was similar to that observed in TGF-β1-induced human MRC-5 cells. The proportion of apoptotic cells decreased, while levels of inflammatory cytokines were upregulated in lung tissues during lung fibrosis and in fibroblasts after TGF-β1 treatment. In order to elucidate the possible role of miR-506, it was overexpressed in mice with ARDS. It was revealed that miR-506 significantly ameliorated the degree and spread of pulmonary damage stimulated by LPS. miR-506 also induced apoptosis in vivo and in vitro, while also ameliorating the inflammatory response. Notably, p65, a subunit of NF-κB, acts as a target of miR-506. p65 expression was downregulated in TGF-β1-treated MRC-5 cells upon transfection with miR-506 mimic. Indeed, the 3′-UTR of human p65 contained functional human miR-506-responsive sequences. LPS induction and TGF-β1 stimulation in mice led to p65 upregulation. In addition, p65 knockdown in the ARDS mouse model partially ameliorated the severity of lung lesions, induced apoptosis and reduced inflammation in lung tissue. Our findings revealed that miR-506 could be an important modulator of apoptosis and inflammation and a regulator of lung fibrosis.