Abstract
Epithelial-mesenchymal transition (EMT) of alveolar epithelial cells is an important mechanism for the onset and development of broncho-pulmonary dysplasia (BPD).The role of FGF-2 in BPD is currently unclear. The aim of our study is to investigate the expression of FGF-2 in lung tissue of BPD mice, to further clarify the effect of FGF-2 on EMT in alveolar epithelial cells and to actively search for possible signaling pathways. The BPD model was induced by exposure to hyperoxia. Lung tissue samples were collected and Hematoxylin and eosin (HE) staining was used to determine the modelling effect. Quantitative Real-time Polymerase Chain Reaction (QRT-PCR), immunohistochemistry were used to detect FGF-2 expression in BPD mice. To further investigate the effect of FGF-2 supplementation and deficiency on EMT in alveolar epithelial cells, A549 cells were cryopreserved, resuspended, cultured and passaged. Transforming growth factor-β1 (TGFβ1) was used to induce EMT. FGF-2 small interfering RNA fragments were synthesised and screened. Fbroblast growth factor receptor1 (FGFR1) expression was inhibited by BGJ398. (3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H tetrazolium) (MTS) assay was used to detect the effect of FGF-2 and Infigratinib (BGJ398) on cell proliferation. We used qRT-PCR and Western blot to detect the expression of epithelial cell markers, mesenchymal cell markers and EMT-related signaling pathway proteins. Our results showed that the successful established hyperoxia mice model were characteristic by BPD. Hyperoxia decreased FGF-2 on day 4, upregulated FGF-2 on day 21, which resulted in EMT. In vitro, we found that FGF-2 alone increased the expression of mesenchymal markers, decreased the expression of epithelial markers and activated Phosphatidylinositol 3-kinase/Protein kinase B (PI3K/AKT), Small mother against decapentaplegic (Smad), mitogen-activated protein kinase (P38) and extracellular signal-regulated kinase (ERK) signaling pathways. FGF-2 could not reverse but synergistically promote TGF-β1-induced EMT of alveolar epithelial cells. Silencing FGF-2 increased the expression of epithelial marker E-cadherin, inhibited the PI3K/AKT, Smad, and P38 signaling pathways activated by TGF-β1, but activated ERK signaling. FGF-2 receptor inhibitor BGJ398 reversed TGF-β1-induced EMT, decreased the expression of FGFR1, and inhibited ERK signaling pathway activation. FGF2 was closely associated with EMT in BPD mice. Both high and low levels of FGF2 promoted EMT in A549. The FGF-2 receptor inhibitor BGJ398 reversed TGF-β1-induced EMT in A549 by inhibiting the FGFR1/P-ERK signaling pathway.
Published Version
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