Overexpression Of Sftpb In Alveolar Type Ⅱ Epithelial Cells Induces Idiopathic Pulmonary Fibrosis In Adult Mouse

Idiopathic pulmonary fibrosis(IPF)is a typical chronic lung disease,mainly caused by smoking,herpes virus infection,air pollution and other factors.The pathogenesis of IPF is not yet clear.Because it is difficult to cure,it poses a serious threat to the physical and mental health of patients.Exploring the pathological molecular mechanism underlying IPF plays an important role in preventing and treating the disease.In recent years,human genome-wide association studies have found that human IPF disease is closely related to the lung surfactant protein SFTPB gene.To explore the role of SFTPB in the lungs,this study constructed SP-C-rt TA,(tet O)7-Cre,pMes-Sftpb transgenic mice,which using the tunable Tet-on system to evaluate the effect of overexpression of Sftpb in alveolar type Ⅱ epithelial cells of adult mice.Firstly,we successfully constructed effective pMes-Sftpb transgenic mice using prokaryotic microinjection technology.Then,a mouse model of SP-C-rt TA;(tet O)7-Cre;pMes-Sftpb mice was constructed by Tet-on system to specifically overexpress the Sftpb gene in alveolar type Ⅱ epithelial cells.By regulating the feeding time of doxycycline(Dox),the Sftpb gene is able to be continuously overexpressed in the lungs of adult mice.The lung tissues of mice were obtained at 7 days,14 days,1 month,and 2 months after Dox administration.Histomorphological analysis revealed that the alveolar structure of the mice was overwhelmed and collapsed from the outer edge to the center of the lung lobe.Moreover,the abnormal lung morphology also manifested as thickened alveoli septum and increased lung mesenchymal cells.Secondly,through the detection of pathological indexes,it was found that overexpression of Sftpb in alveolar type Ⅱ epithelial cells resulted in massive diffuse extracellular matrix(ECM)deposition,macrophage infiltration,accumulation of inflammatory factors,and a large amount of cell proliferation and apoptosis in alveoli.These results are consistent with the pathological features of clinical IPF.We further examined the expression of SP-C-rt TA;(tet O)7-Cre;pMes-Sftpb mouse alveolar epithelial cells and fibroblasts,and found that alveolar type Ⅱ epithelial cell proliferation and a large number of fibroblasts were abnormally activated.Finally,we examined and found that the expression of lung surfactant protein components in the lung tissue was unbalanced.We further found that the TGF-β signaling pathway that plays a key role in the process of pulmonary fibrosis,was activated by Sftpb overexpression,which is evidenced by detecting the expression level of its downstream member p-Smad2 in lung tissue.The above results indicate that overexpression of Sftpb in alveolar type Ⅱ epithelial cells leads to an imbalance of pulmonarysurfactant protein secretion in the lung tissue of the mouse,which may lead to the inactivation of the lung surfactant and increased surface tension in the alveoli,which prevents the alveoli from expanding completely,causing induration and collapse,and damage to the alveolar structure.Overexpression of Sftpb in alvoelar type Ⅱ epithelial cells can directly upregulate the activity of TGF-β signaling,causing the disorder of this pathway in the lung,which leads to abnormal activation of a large number of fibroblasts,and abnormal deposition of ECM in the lung tissue.This study provides a new effective and reliable animal genetic model of IPF for finding the underlying disease mechanisms,and also provide a potential drug target for the prevention and treatment of the disease in the future.