The effect of endothelial cell overexpression of plasminogen activator inhibitor-1 on smooth muscle cell migration

Introduction: Plasminogen activator inhibitor-1 (PAI-1), a known inhibitor of plasminogen activators, may regulate smooth muscle cell migration (SMC) through alteration in matrix metalloproteinase (MMP) activity. Methods:To study the effect of endothelial cell (EC) PAI-1 overexpression on SMC migration, RT-PCR was used to clone the full length PAI-1 gene, which was ligated into the pCMV/myc/ER expression vector. With electroporation, bovine aortic ECs were transfected with either the PAI-1 construct or the empty vector as control. EC PAI-1 overexpression was shown with a specific PAI-1 activity assay and enzyme-linked immunosorbent assay. The effect of EC PAI-1 overexpression on SMC migration was measured with a modified Boyden-chamber assay. SMC MMP expression was measured with zymography. Results: Selected clones (EC9, EC21) had a three-fold to five-fold increase in PAI-1 activity compared with untransfected EC and empty vector EC (ECC). Similarly, enzyme-linked immunosorbent assay results showed a 3.5-fold to 5.5-fold increase in PAI-1 levels in EC9 and EC21 versus ECC. Untransfected EC and ECC had similar effects on SMC migratory patterns. Migration of SMC exposed to PAI-1 overexpressing EC was inhibited by 35% to 57% compared with ECC. This inhibitory effect was reversed with addition of exogenous urokinase-type plasminogen activator (uPA). Zymography showed downregulation of MMP-2 and MMP-9 in SMCs exposed to PAI-1 overexpressing EC. Conclusion: PAI-1 overexpression with transfected EC inhibits SMC migration. This effect may be mediated through decreased SMC MMP activity.