The Effect Of Heme Oxygenase-1 In Regulating Proliferation Of Alveolar Epithelial Type Ⅱ Cells In Improvement Of Seawater Drowning Induced-acute Lung Injury

Drowning is currently the leading cause of accidental death worldwide and an very important public health problem in the world,with seawater drowning being the most serious.Seawater inhalation into the lungs can directly and severely damage alveolar epithelial cells,resulting in pathological processes such as swelling,necrosis and shedding,which in turn cause seawater drowning induced-acute lung injury(SWD-ALI)and even acute respiratory distress syndrome(ARDS).At present,the treatment methods used in clinical practice have limited improvement of lung injury.Therefore,lung tissue repair after seawater drowning,especially the repair of alveolar epithelial cells,is particularly important.Heme oxygenase-1(HO-1)plays an extremely important role in the repair of lung injury.Previous studies by our group have found that HO-1 and its metabolites have a protective effect on lung injury induced by seawater drowning,but the specific pathway of its action is not clear.The aim of this study was to investigate the role of alveolar epithelial cell proliferation in the repair of lung injury induced by seawater drowning and the effect of HO-1 on epithelial cell proliferation.In this study,we used mouse alveolar epithelial cell line MLE-12 to establish a cell injury model with seawater stimulation.By observing the cell morphology,detecting the cell viability,q PCR and western blot and other experimental methods,it was found that seawater intervention would cause damage to the cells,and the cell number and proliferation were reduced,but the cell state,number and proliferation were recovered after 24 hours,and HO-1showed a high expression state.This shows that alveolar epithelial type II cell(AT2)is in a state of proliferative repair after SW24 h,in which HO-1 plays a key role.To verify the effect of HO-1 on AT2 proliferation,seawater stimulated MLE-12 cells were treated with HO-1 agonist hemin and inhibitor zinc protoporphyrin(Zn PP)in this study.The results showed that HO-1 agonist Hemin promoted HO-1 expression and cell proliferation,improved cellular inflammation and oxidative stress injury after intervention in MLE-12 cells;while HO-1 inhibitor Zn PP inhibited HO-1 expression and cell proliferation and aggravated cell injury.This suggests that HO-1 promotes AT2 proliferation repair ameliorating cell injury.For further studies,HO-1 conditional knockout mice of alveolar epithelial type II cells(AT2)were constructed to establish a mouse model of seawater drowning lung injury,which was used to simulate the occurrence of seawater drowning in the natural environment.Detection of lung wet/dry ratio,lung injury score,total cell count and total protein concentration in bronchoalveolar lavage fluid and oxidative stress indicators in mice revealed that knockdown of HO-1 in AT2 aggravated lung tissue injury,pulmonary edema and weakened lung function,and aggravated inflammation and oxidative stress injury in mice with seawater drowning lung injury;next,immunohistochemical and immunofluorescence techniques revealed that the loss of HO-1 aggravated AT2 injury induced by seawater drowning.The results of animal experiments showed that HO-1 in specific knockout mice AT2 aggravated SWD-ALI and inhibited epithelial cell proliferation and repair.In summary,this study found that HO-1 promotes type II alveolar epithelial cell proliferation to ameliorate seawater drowning lung injury from the animal and cellular levels.