Analysis of Fibroblast Growth Factor 2 Impact and Mechanism on Broncho-Pulmonary Dysplasia

Objective: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. Methods: 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. Results: 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. Conclusions: 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.