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

Epithelial-mesenchymal transition (EMT) of alveolar epithelial cells is an important mechanism for the onset and development of broncho-pulmonary dysplasia (BPD). Fibroblast growth factor 2 (FGF2) is involved in the development and repair of injury in many organs, particularly the lung. The role of FGF2 in BPD is currently unclear. The aim of our study was to investigate the expression of FGF2 in lung tissue of BPD mice, to further clarify the effect of FGF2 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 staining was used to determine the modeling effect. Quantitative real-time polymerase chain reaction (QRT-PCR), immunohistochemistry was used to detect FGF2 expression in BPD mice. To further investigate the effect of FGF2 supplementation and deficiency on EMT in alveolar epithelial cells, A549 cells were cryopreserved, resuspended, cultured, and passaged. Transforming growth factor-β1 (TGF-β1) was used to induce EMT. FGF2 small interfering RNA fragments were synthesized and screened. Fibroblast growth factor receptor 1 (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 FGF2 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 FGF2 on day 4, upregulated FGF2 on day 21, which resulted in EMT. In vitro, we found that FGF2 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. FGF2 could not reverse but synergistically promote Transforming growth factor-β1 (TGF-β1)-induced EMT of alveolar epithelial cells. Silencing FGF2 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. FGF2 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 FGF2 receptor inhibitor BGJ398 reversed TGF-β1-induced EMT in A549 by inhibiting the FGFR1/P-ERK signaling pathway.