Abstract
Silicosis is an occupational disease characterized by extensive pulmonary fibrosis, and the underlying pathological process remains uncertain. Herein, we explored the molecular mechanism by which microRNA-205-5p (miR-205-5p) affects the autophagy of alveolar macrophages (AMs) and pulmonary fibrosis in mice with silicosis through the E2F transcription factor 1 (E2F1)/S-phase kinase-associated protein 2 (SKP2)/Beclin1 axis. Alveolar macrophages (MH-S cells) were exposed to crystalline silica (CS) to develop an in vitro model, and mice were treated with CS to establish an in vivo model. Decreased Beclin1 and increased SKP2 and E2F1 were identified in mice with silicosis. We silenced or overexpressed miR-205-5p, E2F1, SKP2 and Beclin1 to investigate their potential roles in pulmonary fibrosis in vivo and autophagy in vitro. Recombinant adenovirus mRFP-GFP-LC3 was transduced into the MH-S cells to assay autophagic flow. Knocking down Beclin1 promoted pulmonary fibrosis and suppressed the autophagy. Co-immunoprecipitation and ubiquitination assays suggested that SKP2 induced K48-linked ubiquitination of Beclin1. Furthermore, chromatin immunoprecipitation-PCR revealed the site where E2F1 bound to the SKP2 promoter between 1638 bp and 1645 bp. As shown by dual-luciferase reporter gene assay, the transfection with miR-205-5p mimic inhibited the luciferase activity of the wild-type E2F1 3'untranslated region, suggesting that miR-205-5p targeted E2F1. Additionally, miR-205-5p overexpression increased autophagy and reduced the pulmonary fibrosis, while overexpression of E2F1 or SKP2 or inhibition of Beclin1 could annul this effect. The current study elucidated that miR-205-5p targeted E2F1, thereby inhibiting SKP2-mediated Beclin1 ubiquitination to promote macrophage autophagy and inhibit pulmonary fibrosis in mice with silicosis.