THE LOCALIZATION OF PLASMINOGEN-ACTIVATOR INHIBITOR-1 IN GLOMERULAR SUBEPITHELIAL DEPOSITS IN MEMBRANOUS NEPHROPATHY

In this study, the localization of plasminogen activator inhibitor-1 ( PAI-1) and its association with glomerular subepithelial deposits of v itronectin (VN) in membranous nephropathy (MN) was evaluated. Renal bi opsy tissue from 30 patients with MN along with specimens of normal ki dney removed from six patients with renal tumors were examined for glo merular deposits of urokinase-type plasminogen activator, tissue-type plasminogen activator (t-PA), PAI-1, VN, and fibrinogen by using immun ofluorescence and immunoelectron microscopic techniques. Deposits were characterized by pretreating the frozen sections with arginine, glyci ne, and t-PA to dissociate the VN-PAI-1 complexes, thus providing evid ence of PAI-1 binding to VN. Glomeruli isolated from normal frozen kid ney and from frozen kidney tissue with MN were subjected to immunoblot analysis. VN was found in the mesangial area and t-PA was observed al ong the capillary wall of normal glomeruli. Coarse granular deposits o f VN, PAI-1, and t-PA were observed along the glomerular basement memb rane in MN. Immunoelectron microscopy showed the presence of VN, PAI-1 , and t-PA in the subepithelial immune deposits. Pretreating the sampl es with arginine decreased or abolished immunofluorescence staining fo r PAI-1 and t-PA, but not for VN. Pretreatment with t-PA decreased the immunofluorescence staining for PAI-1, but not for VN. Pretreatment w ith glycine decreased or abolished the staining for all three proteins . Immunoblot analysis revealed the presence of VN, PAI-1, t-PA, acid t -PA-PAI-1 complex in glomeruli with MN as well as the presence of VN, but not of PAI-1, t-PA, or complex in the normal glomeruli. The findin gs from this study strongly suggest that PAI-1 was deposited in the gl omeruli in MN as a result of binding to VN. Thus, VN-associated PAI-1 may injure the integrity of the fibrinolytic system in glomeruli affec ted by MN.