Effects Of Cyclic Stretch Preconditioning On Excessive Cyclic Stretch-induced Alveolar And Its Mechanism

Part Ⅰ The effects of excessive cyclic stretch on alveolar epithelial cell injuryObjectives:To investigate the effects of excessive cyclic stretch on alveolar epithelial cell.Methods:A549cells were randomly divided into two groups (n=5); control group and20%CS group.20%CS group conditioned by20%cyclic stretch for2hour,4hour,6hour and8hour respectively marked S2, S4, S6and S8. All cells were examined the apoptosis, the expression of RhoA and Rac mRNA and cytoskeleton F-actin.Results:Compared with group C, the apoptosis ratio significantly increased in S2、S4、S6and S8group (P<0.05). The F-actin staining in20%CS group showed that filaments rearrangement and break and the formation of intracellular stress fiber with time went. Compared with group C, RhoA mRNA expression in S2and S4group did not change significantly (P>0.05), but in S6and S8group RhoA mRNA expression was significantly increased (P<0.01). And RhoA mRNA expression reached the peak in six hours. Rac mRNA expression reduced with the extension of time (P<0.05).Conclusions:excessive cyclic stretch induced the increase of apoptosis and barrier dysfunction via regulation of the expression of Rho and Rac. Objectives:To investigate the effects of cyclic stretch preconditioning on excessive cyclic stretch-induced alveolar epithelial cell and its mechanism.Methods:A549cells were randomly divided into three groups (n=5); control group, S6group and P-S6group. P-S6group preconditioned by5%cyclic stretch for15min,30min,60min,120min respectively, then stimulated by20%CS for6hours, marked P15-S6、 P30-S6. P60-S6and P120-S6. All cells were examined the apoptosis, the expression of RhoA and Rac mRNA and cytoskeleton F-actin.Results:Compared with group S6, the apoptosis ratio decreased (P <0.05) at30min、60min and120min of precondition P-S6group. The F-actin staining in S6group showed that filaments rearrangement and break and the formation of intracellular stress fiber. Compared with S6group, the F-actin staining in5%pre-stretch the groups showed:the reduction of F-actin rearrangement and breaking, gradual clearing of peripheral actin ribbons and so on, particularly better in the pre-stretch60min. Compared with S6group, the expression of RhoA mRNA reduced in P-S6group, which reached the peak at60min of precondition. Only at30min and60min of precondition P-S6group, the expression of Rac mRNA increased significantly compared with S6group (P<0.05).Conclusions:Preconditioning physiologic (5%) cyclic stretch reduces the apoptosis and barrier dysfunction of CS-induced alveolar type II epithelial cell to varying degree via regulation of the expression of Rho and Rac.