Tissue plasminogen activator and its receptor in the human amnion, chorion, and decidua at preterm and term

The plasminogen activator system consists of two proteins: tissue plasminog en activator (tPA) and urokinase plasminogen activator (uPA), which act upo n their specific receptors to generate plasmin from plasminogen located on the cell surface. Plasmin then acts directly and indirectly to degrade the components of the extracellular matrix (ECM), This process is likely to be important in the normal turnover of the ECM of fetal membranes and in its p remature weakening in preterm premature rupture of the fetal membranes. Quantitative Northern analysis and in situ hybridization have shown that th e decidua expresses mRNA for PPA. However, the immunolocalized tPA protein was most strongly associated with the amnion and chorion, as was its recept or annexin II, suggesting that the amnion and chorion are the targets for d ecidual tPA. At term, decidual tPA expression was unaffected by labor, and the tPA recep tor was elevated both before and after labor. At preterm, the converse was found: decidual tPA expression was significantly (p < 0.05) up-regulated by labor, but the tPA receptor was not. The results suggest that the generati on of plasmin at term would be controlled by an increased concentration of the tPA receptor in the amnion and chorion, whereas at preterm a pathologic al increase in plasmin would be generated by an overexpression of tPA, init iated by labor.