miR-26a-5p alleviates lipopolysaccharide-induced acute lung injury by targeting the connective tissue growth factor

The aim of the present study was to investigate the regulatory functions of microRNA (miR)-26a-5p on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and its molecular mechanisms. The role of miR-26a-5p on an ALI mouse model was evaluated by examining the histological changes, wet/dry (W/D) ratio, myeloperoxidase (MPO) activity, malondialdehyde (MDA) expression levels in lung tissues and the survival of ALI mice. Moreover, the protein concentration and the number of neutrophils and lymphocytes in bronchoalveolar lavage fluid (BALF) was analyzed. To explore the effect of miR-26a-5p on inflammatory responses and apoptosis, the expression levels of tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta and IL-6 and apoptosis were measured by ELISA, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling staining and flow cytometry in BALF, A549 cells and lung tissues. B-cell lymphoma-2 (Bcl-2), Bax and cleaved caspase-3 in lung tissues were measured by western blotting and reverse transcription-quantitative PCR. Connective tissue growth factor (CTGF) was predicted as a direct target of miR-26a-5p using dual luciferase reporter assay. The present study sought to determine whether CTGF overexpression reversed the effect of miR-26a-5p on apoptosis and inflammatory responses in LPS-induced A549 cells. The data revealed that miR-26a-5p overexpression ameliorated LPS-induced ALI, which was implicated by fewer histopathological changes, W/D ratio, apoptosis in lung tissues and the survival of ALI mice. Moreover, miR-26a-5p overexpression alleviated LPS-induced inflammatory responses in ALI mice via the reduction of total protein, neutrophil and lymphocyte counts and the expression levels of TNF-alpha, IL-1 beta, IL-6, MDA and MPO activity in BALF. Similarly, miR-26a-5p overexpression decreased apoptosis and the expression of TNF-alpha, IL-1 beta and IL-6 in LPS-induced A549 cells. CTGF was a direct target of miR-26a-5p. CTGF overexpression reversed the effect of miR-26a-5p on cell apoptosis and inflammatory responses in LPS-induced A549 cells. The present study demonstrated that miR-26a-5p could attenuate lung inflammation and apoptosis in LPS-induced ALI by targeting CTGF.