Downregulated Smad4 Affects Extracellular Matrix Remodeling In Ventilator-induced Lung Injury

Objective:Mechanical ventilation(MV)plays a pivot role in the process of curing critically ill patients,the improper use of ventilator can cause and aggravate lung injury,which is called ventilator-induced lung injury(VILI).It is of great clinical importance to know the mechanism of VILI for improving treatment level and survival rate in critical care unit.This experiment established the models of VILI to explore the effect and underlying mechanism of TGF-?/Smad signaling pathway on the extracellular matrix remodeling in ventilator-induced lung injury.Methods:We randomized 24 C57BL/6 mice aged 6-8 weeks to 4 groups for treatment(n=6/group):control,ventilation,non-targeted(scramble)lentivirus transfection plus ventilation,and Smad4 small interfering RNA(siRNA)lentivirus transfection plus ventilation.Lentivirus was delivered by intranasal instillation to lung tissue after fully anesthesia.Four weeks later,the 3 ventilated groups underwent high tidal volume(VT 40mL/kg)ventilation to induce lung injury.Anesthesia mice were connected to ventilator after skin degerming and intubation,tidal volume was set to 40mL/kg and ventilation time was set to 4 hr.After 72 hr,lungs were collected from the anesthesia mice,the chests should be fully exposed and mice were bleeding to death through abdominal aorta,lungs should be fully washed using saline.Real Time PCR and Western blotting respectively detect Smad4 mRNA and protein to verify if the virus infected successfully.Histological changes in lungs were evaluated by hematoxylin and eosin(HE)and Masson's staining.The expression of a-smooth muscle actin(?-SMA)was determined by immunohistochemistry,and the mRNA and protein levels of ?-SMA,collagen I and III were detected by quantitative real-time PCR and western blotting analysis.Results:Smad4 mRNA and protein expression was more severe in ventilation group and scramble lentivirus transfection plus ventilation group as compared with control treatment and siRNA lentivirus transfection plus ventilation group(P<0.05).The results showed that the virus was successfully infected in the lung tissue of mice.Inflammatory cell infiltration and collagen deposition of ventilation group and scramble lentivirus transfection plus ventilation group were more severe than normal group.There was a marked improvement in siRNA lentivirus transfection plus ventilation group.It also inhibited accumulation of a-SMA-positive myofibroblasts and pulmonary fibrosis,as seen by reduced collagen I and III expression,induced by ventilation(P<0.05).Scramble siRNA treatment had no effect(P>0.05),so it may have no effect on the gene expression of lung tissue in mice.Conclusion:VILI can be caused by high VT,and there will be a large amount of inflammatory cellular infiltration,collagen deposition and extracellular matrix remodeling after the lung injury.VILI and pulmonary fibrosis may be regulated by TGF-?/Smad signaling pathway.Smad4 expression in the lung tissue was successfully interfered by lentivirus infection,which reduced the severity of ventilator-induced lung injury and fibrosis.