ObjectiveTo investigate effects of high expression of miR-499a-5p on lung injury in rats with acute respiratory distress syndrome (ARDS) by targeting matrix metallopeptidase-16 (MMP-16).MethodsThe experiment set up sham operation group, model group, miR-499a-5p mimic group, MMP-16 group, miR-499a-5p mimic+MMP-16 group, D-ribofuranosylbenzimidazole (DRB, Nrf2 signaling pathway inhibitor) group, miR-499a-5p mimic+DRB group. A rat model of ARDS was constructed by cecal puncture. One hour before surgery, the transfection complex (50 μL) was injected into the trachea with a micro-syringe. DRB (5 mg/kg) was intraperitoneally injected 30 min before surgery. The expression levels of miR-499a-5p and MMP-16 in lung tissue were detected by RT-qPCR; Alveolar type Ⅱ epithelial cells of model group rats were separated and MMP-16 3 'UTR WT and MUT luciferase report plasmid were transfected into alveolar type Ⅱ epithelial cells with miR-499 respectively to verify the targeting relationship between miR-499 and MMP-16; the targeted relationship was verified by the dual luciferase reporter gene; lung injury was observed by hematoxylin-eosin staining; The level of inflammatory factors in bronchoalveolar lavage fluid (BALF) and the level of oxidative stress in lung tissue were detected by enzyme-linked immunosorbent assay; The expression levels of NAD(P)H: quinone oxidoreductase 1 (NQO1), heme oxygenase (HO)-1, and nuclear factor-erythroid 2-related factor 2 (Nrf2) proteins in lung tissues were analyzed by Western blotting.ResultsmiR-499a-5p was down-regulated in the lungs of ARDS model rats (P<0.01), while MMP-16 was highly expressed (P<0.01); miR-499a-5p and MMP-16 3'UTR regions had binding sites, and miR-499a-5p directly targeted negative regulation of MMP-16 expression (P<0.01); overexpression of miR-499a-5p significantly reduced the right lung wet-to-dry weight ratio in the ARDS rats (P<0.05), reduced lung tissue damage (P<0.01), and reduced tumor necrosis factor α, interleukin (IL)-1β and IL-6 levels in BALF (P<0.01), decreased malondialdehyde and myeloperoxidase levels in lung tissue, increased total anti-oxidant capacity (P<0.01), and up-regulated NQO1, HO-1, Nrf2 protein expression in lung tissue (P<0.01). However, this phenomenon was significantly reversed after the addition of MMP-16 and DRB.ConclusionOverexpression of miR-499a-5p attenuates lung injury in rats with ARDS by targeting negative regulation of MMP-16 via activating the Nrf2 signaling pathway.