Different expression of the plasminogen activation system in renal thrombotic microangiopathy and the normal human kidney.

Renal thrombotic microangiopathy is characterized by glomerular and vascular thrombosis. The persistancy of fibrin deposits may result from imbalance between plasminogen activation and inhibition. In the present study, we used immunohistochemistry and in situ hybridization techniques to determine the localization of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators, type 1 plasminogen activator inhibitor (PAI-1) and membrane receptor for u-PA (uPA-R) antigen and their sites of synthesis in renal thrombotic microangiopathy (N = 10) as compared to acute tubular necrosis (N = 5) and normal human kidneys (N = 7). We found an induction of PAI-1 and uPA-R expression in glomeruli and in arterial walls in renal thrombotic microangiopathy. In addition, the induction of uPA-R expression was also found in some tubular epithelial cells. In most case, local synthesis of PAI-1 and uPA-R was confirmed by in situ hybridization with the corresponding cDNA probes. In contrast, using similar techniques PAI-1 and uPA-R antigens and messenger RNAs could not be detected in normal kidneys. In both renal thrombotic microangiopathy and normal kidneys, t-PA mRNA was detected in large amounts in all glomeruli and in vascular endothelial cells, but t-PA antigen was only detected in a limited number of glomerular and arterial endothelial cells, whereas it was strongly expressed by all venous endothelial cells. Although u-PA antigen was found in almost all tubular sections, u-PA mRNA was only found in tubular epithelial cells in the deep cortex and the outer medulla. Our results indicate that there is an up-regulation of PAI-1 and u-PA-R expression in the glomeruli and in the arterial walls of thrombotic microangiopathy. The local release of PAI-1 could play a role in the persistancy of fibrin deposition and the further development of fibrotic lesions. Whether uPA-R plays a pathogenic role in the development of glomerular and vascular lesions, or is involved in the repair process of these lesion, remains to be elucidated.