Effect of miR-130a-3p targeting PPAR-γ on epithelial-mesenchymal transition in silica-induced pulmonary fibrosis

Background At present, the treatment of silicosis is still limited, and no method is available to cure the disease. miRNAs are involved in the process of fibrosis at the transcriptional level by directly degrading target gene mRNA or inhibiting its translation. However, how miR-130a-3p regulates silicosis fibrosis has not been fully elucidated yet.

Objective To investigate whether miR-130a-3p promotes epithelial-mesenchymal transition (EMT) by inhibiting peroxisome proliferators-activated receptors gamma (PPAR-γ), thereby pro-moting the process of silicotic fibrosis. To identify effective new targets for the treatment of silicotic fibrosis.

Methods (1) Animal experiments: C57BL/6J mice were intratracheally injected with a one-time dose of 10 mg silica suspension (dissolved in 100 μL saline) as positive lung exposure. A silicosis model group was established 28 d after the exposure. A control group was injected with the same amount of normal saline into the trachea. Hematoxylin-eosin staining and Sirius red staining were used to observe the pathological changes and collagen deposition in lung tissues respectively. Realtime fluorescence-based quantitative polymerase chain reaction (RT-qPCR) was used to assay the expression of miR-130a-3p and PPAR-γ mRNA in lung tissues. Western blotting was used to detect the protein expression of PPAR-γ, transforming growth factor (TGF)-β1, E-cadherin, α-smooth muscle actin (α-SMA), and Collagen Ⅰ in lung tissues. (2) Cells experiments: Mouse lung epithelial cells (MLE-12) were induced with 5 µg·L⁻¹ TGF-β1 for different time (0, 12, 24, 48 h). RT-qPCR was used to detect the expression of miR-130a-3p and PPAR-γ mRNA in cells. The binding relationship between miR-130a-3p and PPAR-γ mRNA was verified by dual luciferase reporter gene assay. MLE-12 cells were stimulated by 5 µg·L⁻¹ TGF-β1 after transfection of miR-130a-3p inhibitor, and Western blotting was used to measure the protein expression of PPAR-γ, E-cadherin, and α-SMA in the TGF-β1-induced cells.

Results In the silicosis model group, the alveolar septum was widened and the pulmonary nodules were formed. The Sirius red staining collagen deposition in pulmonary nodules indicated that a silicosis fibrosis model was successfully established. The expressions of TGF-β1, α-SMA, and Collagen Ⅰ proteins were increased, and the expressions of E-cadherin and PPAR-γ proteins were decreased in lung tissues of the silicosis group, compared with the control group (P<0.05 or P<0.01). The expression of miR-130a-3p was increased and the expression of PPAR-γ mRNA was decreased in lung tissues of the silicosis model (P<0.01). The expression of miR-130a-3p was significantly increased, while the expression of PPAR-γ mRNA was decreased in the TGF-β1 induced MLE-12 cells (P<0.05 or P<0.01). The dual luciferase reporter assay showed a direct relationship between miR-130a-3p and PPAR-γ mRNA in MLE-12 cells. The transfection of miR-130a-3p inhibitor in the TGF-β1 induced MLE-12 cells inhibited the decrease of PPAR-γ and E-cadherin proteins, and the increase of α-SMA protein in the MLE-12 cells induced by TGF-β1 (P<0.05 or P<0.01).

Conclusion miR-130a-3p promotes the development of silicosis fibrosis by targeting PPAR-γ to increase pulmonary EMT.