| Background Chronic obstructive pulmonary disease is characterized by airflow limitation that is not fully reversible.The airflow limitation is usually progressive and associated with an abnormal inflammatory respose of the lung to noxious particles or gases.Chronic obstructive pulmonary disease is the fourth leading cause of death worldwide.It is mainly caused by exposure to cigarettes smoke,environmental or occupational pollutants,chronic infection or an interaction of these factors.It involves two major processes simultaneously,chronic airway inflammation and remodeling.The disbalance of proteinase and anti-proteinase is presumed important pathogenesis.Matrix metalloproteinase system(MMPs) plays an important role in the pathogenesie of COPD.Plasminogen activator inhibitor-1(PAI-1) can inhibit the activation of plasminogen to plasmin through urokinase type plasminogen activator (uPA) directly and MMPs indirectly.PAI-1 can regulate extracellular matrix (ECM) degradation,cell migration and levels of inflammatory factors.In this research,we study the effect of PAI-1 on the process of inflammation in COPD through exposuring alveolar epithelial cells(AECs) to cigarette smoke extraction(CSE) or lipopolysaccharides(LPS) and silencing the expression of PAI-1.Method CSE was prepared according to the method described by Carp H..Alveolar epithelial cells(A549 cells,AECs) were cultured and stimulated by different concentration of CSE or LPS.The levels of PAI-1 in supernatants were detected by ELISA.The concentration of CSE and LPS which induced the most PAI-1 expression was chosen and used in the next experiments.The mRNA and protein expression of PAI-1 in AECs were detected by RT-PCR and western blotting.The levels of PAI-1,interleukin-8(IL-8),leukotriene B4 (LTB4) in the supernatants of AECs were evaluated quantitatively by ELISA. Monocytes and neutrophils were separated from normal human veinous blood samples by Lymphoprep.Transwells were used to assess migration of monocytes and neutrophils to AECs.The AECs were transfected by siRNA that specially targeted PAI-1 or negative control RNA(ncRNA).RT-PCR was used to analysis the efficiency of transfection.After transfection,the AECs were exposured to CSE or LPS.The mRNA and protein expression of PAI-1 in AECs was evaluated by RT-PCR and western blotting.The levels of PAI-1, IL-8 and LTB4 in the supernatants of AECs were evaluated by ELISA. Transwells were used to assess migration of monocytes and neutrophils to AECs transfected by siRNA targeted PAI-1 or ncRNA and stimulated by CSE or LPS.Results The 10%CSE and 75μg/ml LPS can induce the most expression of PAI-1.The exposure to 10%CSE or 75μg/ml LPS enhanced expression of PAI-1,IL-8,LTB4 significantly(P＜0.05)and migration of monocytes and neutrophils to AECs(2.8±0.1fold,P＜0.01,2.45±0.12 fold, P＜0.01,2.25±0.11fold,P＜0.01 and 2.9±0.15 fold,P＜0.01,respectively). Through AECs transfection with siRNA targeted PAI-1,the expression of PAI-1 was inhibited significantly.Through silencing the expression of PAI-1, IL-8 and LTB4 induced by 10%CSE or 75μg/ml LPS were significantly attenuated compared to those without silencing the expression of PAI-1 under the same stimulation conditions(P＜0.05,P＜0.01,P＜0.01 and P＜0.01, respectively).The migration of inflammatory cells was attenuated significantly compared to those transfected by ncRNA under the same stimulation conditions(P＜0.01).Conclusion Through stimulation by CSE or LPS,the inflammation was induced in AECs,the expression of inflammatory factors(IL-8 and LTB4) was induced and inflammatory cells(monocytes and neutrophils) were recruited.PAI-1 promotes inflammation process induced by CSE or LPS in AECs through regulating expression of some inflammatory factors and chemotaxis of inflammatory cells.PAI-1 may play a proinflammatory role in the inflammation of AECs and the inflammation may be attenuated through silencing its expression. Inhibiting the expression of PAI-1 could be considered as a novel therapeutic strategy in COPD.
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