Inhibition of miR-155-5p Exerts Anti-Fibrotic Effects in Silicotic Mice by Regulating Meprin α

Silicosis is a fatal profession-related disease linked to long-term inhalation of silica. The present study aimed to determine whether meprin α, a master regulator of anti-fibrotic peptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), is diminished by miR-155-5p in silicotic and control lung macrophages and fibroblasts upon activation. NR8383 macrophages, primary lung fibroblasts, and mouse embryonic fibroblasts were used to evaluate the expression and function of meprin α and miR-155-5p. In vitro meprin α manipulation was performed by recombinant mouse meprin α protein, actinonin (its inhibitor), and small interfering RNA knockdown. Macrophage and fibroblast activation was assessed by western blotting, real-time PCR, matrix deposition, and immunohistochemical staining. The roles of meprin α and miR-155-5p were also investigated in mice exposed to silica. We found that the meprin α level was stably repressed in silicotic rats. In vitro, silica decreased meprin α, and exogenous meprin α reduced activation of macrophages and fibroblasts induced by profibrotic factors. miR-155-5p negatively regulated Mep1a by binding to the 3′ untranslated region. Treatment with anti-miR-155-5p elevated meprin α, ameliorated macrophage and fibroblast activation, and attenuated lung fibrosis in mice induced by silica. The sustained repression of meprin α and beneficial effects of its rescue by inhibition of miR-155-5p during silicosis indicate that miR-155-5p/meprin α are two of the major regulators of silicosis.