Effects Of Sftpc Overexpression In Alveolar Type ? Epithelial Cells On Lung Homeostasis Maintenance In Mice

During the development of the lungs,pulmonary surfactants have an irreplaceable role.Pulmonary surfactant protein is one of its components,the content is only 10%,but it is an important material guarantee to maintain the stability of the lung organ structure and ensure the smooth exchange of gas.Pulmonary surfactant protein includes SP-A,SP-B,SP-C and SP-D four proteins.Among them,SP-C is an important protein to maintain the balance of alveolar tension,maintain the stability of the alveolar membrane structure,and ensure the normal function of the alveoli.Loss of expression of Sftpc gene encoding SP-C protein can cause abnormal lung development and related lung diseases.However,there are relatively few studies on the effect of overexpression of the Sftpc gene on lung development.Therefore,based on the Tet-on system,this project constructed SP-C-rt TA;(tet O)₇-Cre;pMes-Sftpc transgenic mice to realize the specificity of Sftpc gene in mouse alveolar type II epithelial cells at different times.To further study the effect of Sftpc gene on the development of lung organs in mice.Firstly,pMes-Sftpc transgenic mice was constructed and its effectiveness was verified.The SP-C-rt TA;(tet O)₇-Cre;pMes-Sftpc transgenic mice were constructed using the Tet-on system and induced by doxycycline DOX to achieve the specificity of Sftpc gene in mouse alveolar type II epithelial cells expression.Through the observation of the overall lung morphology and tissue section staining,it was found that local alveolar expansion occurred in the alveolar structure of mice overexpressing the Sftpc gene,mainly concentrated at the edge of the lung lobe.The alveolar interval at the edge of the lung lobe is broken,and adjacent alveoli merge with each other to form irregular and uneven cysts.Furthermore,SP-C-rt TA;(tet O)₇-Cre;pMes-Sftpc transgenic mice were tested for extracellular matrix proteins,inflammatory factors,and cell proliferation and apoptosis levels.The results showed that the extracellular matrix content in the alveolar tissue of mice overexpressing the Sftpc gene was abnormal,mainly manifested as a significant decrease in the expression of collagen,elastin,and fibronectin,which may be a cause of alveolar expansion.The expression levels of inflammatory factors in the alveolar tissues of mice were detected.It was found that the expression levels of IL-13,IL-18 and TNF-a in the alveolar tissues of mice overexpressing the Sftpc gene increased,indicating that the alveolar tissues of the mice had inflammation.The immune system is abnormal.By analyzing the proliferation and apoptosis levels of mouse alveolar tissue cells,it was found that the proliferation level of alveolar tissue cells in mice overexpressing the Sftpc gene did not change significantly,and the apoptosis level was significantly increased.This may be related to the rupture of the alveolar compartment and the confluence of adjacent alveoli,causing the alveoli to expand.Pulmonary surfactant protein is an important component to maintain the structure and function of the alveoli.At the same time,there are interactions between the expression levels of various lung surfactant proteins.By detecting the expression level of related lung surfactant protein.We found that the expression of SP-C in lung tissue increased,while the expression of SP-A decreased.SP-B,as the synthetic precursor protein of SP-C protein,did not change its expression and the content of SP-D protein did not change.Changes in lung surfactant protein content are related to the appearance of related phenotypes in mouse alveolar tissue.Increased expression of SP-C leads to disorder of alveolar morphology,destruction of alveolar surface tension balance,and local alveolar expansion.SP-A is an important protein responsible for alveolar immune function,and the decrease of its expression is related to the occurrence of inflammation in the alveoli.Pulmonary function index detection is an important means to reflect the condition of lung function and evaluate disease.Functional Residual Capacity(FRC),Inspiratory Capacity(IC)and Vital Capacity(VC)these three indicators are more representative detection indicators,Its can reflect the gas exchange process in the lungs of mice and assess the level of lung function in mice.We use the animal lung function detection system to explore the effect of overexpression of the Sftpc gene on the lung function of mice.Among them,the three lung function indexes of FRC,IC and VC have all improved.This may be due to the decrease in alveolar elasticity of the mutant mice during the exhalation or inhalation process of the mouse,which caused the air in the lungs to not be completely eliminated,resulting in an increase in the functional residual volume.At the same time,the decrease in alveolar elasticity and the expansion of the alveoli also caused the mutant mice to inhale and exhale more air during the breathing process,which was manifested as an increase in the maximum inspiratory capacity and vital capacity.This experiment successfully constructed SP-C-rt TA;(tet O)₇-Cre;pMes-Sftpc transgenic mouse model.The mouse's alveolar structure was broken,and the alveoli expanded locally.The change of this morphological structure is closely related to the large number of cell apoptosis,the decrease of extracellular matrix protein expression and the decrease of alveolar elasticity.The mice showed obvious lung function abnormalities.This topic provides a certain theoretical support and data basis for further in-depth study of Sftpc gene on mouse lung development and related lung function.