A Preliminary Study Of Atg7 Defect On Alveolar Type ? Cells Function And Lamellar Bodies Formation

Objective:Autophagy is a highly evolutionarily conservative lysosome-dependent degradation process existing in all eukaryotic cells.Autophagosome is mainly formed by wrapping"waste"such as abnormal proteins and damaged organelles in cells.Followingly,it can fuse with lysosomes to form autophagosomes to degrade and recycle the decomposed products.In recent years,it has been found that compromised autophagic activity can result in some lung diseases.Previously,we found that Atg7?autophagy-related gene 7?global knockout mice were characterized by smaller size and cyanosis in comparison to those littermate controls.Moreover,they died within 12 hours after birth.This is very similar neonatal respiratory distress syndrome.Pulmonary surfactant?PS?is secreted by alveolar type II?ATII?cells into the alveolar cavity.The organelles that synthesize,store,and secrete PS in ATII cells are lamellar bodies?LBs?.Since Atg7 global knockout mice died shortly after birth,we bred bronchioalveolar epithelium-specific Atg7-deficient mice.The morphology of lung tissue,ATII cells maturity and lamellar bodies formation in mice at the first day?P0?and 3 months?P90?were studied.Methods:The alveolar wall thickness and alveolar area of four genotypes[Atg7^flox/+,Atg7^flox/+/?tetO?₇-Cre,Atg7^flox/+/SP-C-rtTA and Atg7^SPC]were compared by HE staining.ABCA3 staining of lamellar bodies in alveolar type II cells was compared by immunohistochemistry.Western blot analysis of SP-B in lung tissue lysate was carried out.The lung tissue of mice?P90?was subjected to Masson's trichrome staining to analyze the degree of pulmonary fibrosis,and lung function was measured.Results:The results of the HE staining showed that the thickness of alveoli increased and the area of alveoli decreased in bronchioalveolar epithelium-specific Atg7-deficient mice at P0 and P90.The results of immunohistochemistry showed that the lamellar bodies of the Atg7^SPC newborn mice became smaller,and the lamellar bodies expanded abnormally at 90 days.Western blot demonstrated the decrease of SP-B expression in bronchioalveolar epithelium-specific Atg7-deficient mice.There was no difference in fibrosis level or pulmonary function among the four genotypes.Conclusion:The bronchioalveolar epithelium-specific Atg7-deficient mice leads to the change of lung tissue morphology and the formation of lamellar bodies.