Analysis of the plasminogen activator activity of the human glomerulus

Expression of glomerular plasminogen activator inhibitor type 1 in glomerulonephritis

Plasminogen activator inhibitor type 1 (PAI-1) and tissue plasminogen activator (tPA) are the major regulators of plasmin generation. Glomerular PAI-1/tPA balance is involved in extracellular matrix turnover, as well as fibrin deposition in glomeruli. Renal biopsy specimens were obtained from 80 patients with either primary or secondary glomerulonephritis (10 patients, minimal change nephrotic syndrome; 6 patients, focal segmental glomerulosclerosis [FSGS]; 10 patients, membranous nephropathy [MN]; 24 patients, mesangial proliferative glomerulonephritis; 15 patients, lupus nephritis; 14 patients, diabetic nephropathy; and 1 patient, membranoproliferative glomerulonephritis). We quantified glomerular PAI-1 and tPA messenger RNA (mRNA) by competitive polymerase chain reaction. We also determined PAI-1 mRNA localization by in situ hybridization. Glomerular PAI-1 mRNA levels in patients with FSGS and MN were significantly greater than those of controls. There was a sixfold increase in PAI-1-tPA mRNA ratio in patients with MN compared with the control group. In addition, glomerular PAI-1 mRNA level correlated with level of proteinuria. Conversely, there was no difference in tPA mRNA levels among types of glomerulonephritis. These results suggest that suppressed glomerular fibrinolytic and proteolytic activity may be associated with the pathogenesis of glomerulonephritis, especially in FSGS and MN.

Plasminogen and plasminogen activators protect against renal injury in crescentic glomerulonephritis

The plasminogen/plasmin system has the potential to affect the outcome of inflammatory diseases by regulating accumulation of fibrin and other matrix proteins. In human and experimental crescentic glomerulonephritis (GN), fibrin is an important mediator of glomerular injury and renal impairment. Glomerular deposition of matrix proteins is a feature of progressive disease. To study the role of plasminogen and plasminogen activators in the development of inflammatory glomerular injury, GN was induced in mice in which the genes for these proteins had been disrupted by homologous recombination. Deficiency of plasminogen or combined deficiency of tissue type plasminogen activator (tPA) and urokinase type plasminogen activator (uPA) was associated with severe functional and histological exacerbation of glomerular injury. Deficiency of tPA, the predominant plasminogen activator expressed in glomeruli, also exacerbated disease. uPA deficiency reduced glomerular macrophage infiltration and did not significantly exacerbate disease. uPA receptor deficiency did not effect the expression of GN. These studies demonstrate that plasminogen plays an important role in protecting the glomerulus from acute inflammatory injury and that tPA is the major protective plasminogen activator.

Quantification of glomerular TGF-beta 1 mRNA in patients with diabetes mellitus

Transforming growth factor-beta 1 (TGF-beta 1) is a primary determinant of the mesangial expansion observed in diabetic nephropathy. In this study, we quantitated the levels of intraglomerular TGF-beta 1 mRNA in patients with diabetes mellitus using a competitive polymerase chain reaction (PCR) method. Renal biopsy specimens were obtained from 29 patients with non-insulin-dependent diabetes mellitus. Total RNA was extracted from the glomeruli and reverse transcribed into cDNA with reverse transcriptase. To prepare samples containing identical amounts of beta-actin cDNA (8 pg), we performed competitive PCR by co-amplifying mutant templates of beta-actin with a unique EcoRI site. We also used this competitive PCR method to measure TGF-beta 1 cDNA by co-amplifying mutant templates of TGF-beta 1. We observed higher expression of TGF-beta 1 mRNA in glomeruli of patients with diabetic nephropathy as compared with normal glomeruli. Intraglomerular TGF-beta 1 mRNA was elevated, even in the early stage of diabetic nephropathy. Moreover, levels of intraglomerular TGF-beta 1 mRNA correlated with values of HbA1c. These data suggest that hyperglycemia induces intraglomerular TGF-beta 1 mRNA expression in vivo, and that TGF-beta 1 overproduction may be associated with the progression of diabetic nephropathy.

ECM degradation by cultured human mesangial cells is mediated by a PA/plasmin/MMP-2 cascade

We examined the role of the plasminogen activator/plasmin system in extracellular matrix (ECM) degradation by human mesangial cells cultured on thin films of 125I-labeled ECM (Matrigel). ECM degradation (release of 125I into the medium) was dependent on exogenous plasminogen, proportional to the number of mesangial cells and amount of plasminogen added, and coincident with the appearance of plasmin in the medium. ECM degradation was completely blocked (P < 0.001) by two plasmin inhibitors, alpha-2-antiplasmin (40 micrograms/ml) and aprotinin (216 KIU/ml), and partially reduced (-33 +/- 1.8%, P < 0.01) by TIMP-1 (40 micrograms/ml), a specific inhibitor of matrix metalloproteinases. Zymography of medium obtained from cells cultured in the absence of plasminogen revealed the presence of latent matrix metalloproteinase-2 (MMP-2) which was converted to a lower molecular weight, active form in the presence of mesangial cells and plasminogen. Northern analysis of poly A+RNA prepared from cultured human mesangial cells revealed mRNA for tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1), and uPA receptor (uPAR). The presence of uPA protein in medium obtained from cultured human mesangial cells was demonstrated by Western blotting and ELISA which revealed a large molar excess of PAI-1 (1.2 +/- 0.1 x 10(-9) M) over uPA (1.2 +/- 0.1 x 10(-12) M) and tPA (0.19 +/- 0.04 x 10(-9) M). ECM degradation was reduced by a monoclonal antibody (MAb) against human tPA (-54 +/- 8.6%) or human uPA (-39 +/- 5.2%) compared to cells treated with identical amounts of non-specific monoclonal IgG (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Intraglomerular expression of transforming growth factor-beta 1 (TGF-beta 1) mRNA in patients with glomerulonephritis: quantitative analysis by competitive polymerase chain reaction

TGF-beta 1 is involved in the pathogenesis of glomerular sclerosis. We studied the intraglomerular expression of TGF-beta 1 mRNA in patients with glomerulonephritis using competitive polymerase chain reaction (PCR). This method is sensitive enough to quantify cDNA copies of mRNA present in small amounts of samples. Renal biopsy specimens were obtained from 42 patients with various kinds of glomerulonephritis. Ten glomeruli were dissected from renal biopsy specimens. Normal glomeruli were also obtained from the resected kidneys of eight patients with renal cell cancer. Total RNA was extracted from the glomeruli and reverse transcribed into cDNA with reverse transcriptase. To prepare samples containing identical amounts of beta-actin cDNA (8 pg), we performed competitive PCR by co-amplifying mutant templates of beta-actin with a unique EcoRI site. Next, to measure TGF-beta 1 cDNA, we performed competitive PCR by co-amplifying mutant templates of TGF-beta 1. We observed a higher glomerular expression of TGF-beta 1 mRNA in cases of mesangial proliferative glomerulonephritis having a moderate increase in mesangial matrix, diabetic nephropathy and diffuse proliferative lupus nephritis, compared with normal glomeruli. Results suggest that the intraglomerular synthesis of TGF-beta 1 may be involved in the progression of glomerulonephritis in humans.

Role of plasminogen-activator inhibitor type 1 in the pathogenesis and outcome of the hemolytic uremic syndrome

BACKGROUND

Deposition of fibrin in glomeruli and renal failure are characteristic features of the hemolytic uremic syndrome. An inhibitor of glomerular fibrinolysis has been detected in plasma from children with this disorder. In this study, we define the inhibitor and show that its plasma level is correlated with the outcome of the disease.

METHODS AND RESULTS

Plasminogen-activator inhibitor type 1 (PAI-1) in plasma was measured with an assay employing a specific monoclonal antibody in 40 consecutive children hospitalized with the hemolytic uremic syndrome: 12 who recovered adequate renal function (serum creatinine, less than or equal to 2.0 mg per deciliter [177 mumol per liter]) without dialysis, 23 who recovered adequate renal function after peritoneal dialysis, and 5 who did not recover adequate renal function after undergoing dialysis. At presentation, plasma PAI-1 levels were higher in the patients with the hemolytic uremic syndrome than in nine children with other forms of acute renal failure. That the inhibitor was PAI-1 was indicated by the fact that it was a potent inhibitor of tissue plasminogen activator, was acid-resistant, and was not inhibited by denaturation (all unique traits of PAI-1) and that it was neutralized by an antibody specific for PAI-1. Multivariate discriminant-function analysis revealed that the duration of elevated PAI-1 activity was strongly correlated with the outcome of the disease (P less than 0.001). Peritoneal dialysis reduced plasma PAI-1 levels dramatically.

CONCLUSIONS

Our studies suggest that PAI-1 is the circulating inhibitor of fibrinolysis in the hemolytic uremic syndrome. Normalization of plasma PAI-1 levels (e.g., by peritoneal dialysis) is correlated with improvement in renal function. However, the possibility that increased plasma levels of PAI-1 are either causes or effects of the hemolytic uremic syndrome is not unequivocally established by these studies.

Tissue-type plasminogen activator and its inhibitor in human glomerulonephritis

We carried out an immunohistochemical study of tissue-type plasminogen activator (PA) and urokinase-type PA, and their inhibitors, PA inhibitor-1 and PA inhibitor-2, using renal biopsy specimens obtained from 86 patients with various forms of glomerulonephritis. The controls were four normal renal tissue specimens. On immunofluorescent observation, granular staining for tissue-type PA was found to be distributed along the glomerular capillary walls. The fluorescence was weak in the normal renal tissue and occasionally intense in the tissues of patients with IgA nephritis, minimal change nephrotic syndrome, and lupus nephritis. PA inhibitor-1 was abundant in the glomerular epithelial cells and scarce in the mesangial area and glomerular capillary lumens of the normal renal tissues. This was confirmed by immunoelectron microscopy using gold staining. The fluorescence of PA inhibitor-1 was weaker in some specimens of nephritic tissues than in the normal renal tissues. Urokinase-type PA and PA inhibitor-2 were negative within the glomeruli in all the specimens. In the glomerulonephritic tissues which were fibrin deposition-positive, tissue-type PA expression in the glomeruli tended to be strong. An association between fibrin deposition and PA inhibitor-1 staining was not clear. These data suggest that expression of tissue-type PA in the glomeruli increases in association with fibrin deposition.

Sites of synthesis of urokinase and tissue-type plasminogen activators in the murine kidney

Kidneys have long been recognized as a major source of plasminogen activators (PAs). However, neither the sites of synthesis of the enzymes nor their role in renal function have been elucidated. By the combined use of zymographies on tissue sections and in situ hybridizations, we have explored the cellular distribution of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators and of their mRNAs in developing and adult mouse kidneys. In 17.5-d old embryos, renal tubules synthesize u-PA, while S-shaped bodies produce t-PA. In the adult kidney, u-PA is synthesized and released in urine by the epithelial cells lining the straight parts of both proximal and distal tubules. In contrast, t-PA is produced by glomerular cells and by epithelial cells lining the distal part of collecting ducts. The precise segmental distribution of PAs suggests that both enzymes may be implicated in the maintenance of tubular patency, by catalyzing extracellular proteolysis to prevent or circumvent protein precipitation.

Glomerular fibrin deposition and removal

Glomerular fibrin deposits may occur within vessels or in extracapillary crescents. Studies suggest that intravascular thrombosis is promoted by endothelial cell activation/injury, resulting in the release of endothelial-cell-derived tissue factor procoagulant, fibrinolytic inhibitors, platelet activating factor, and large multimers of von Willebrand factor. Fibrin in crescents may arise from coagulation of plasma in Bowman's space mediated by the release of tissue factor from infiltrating macrophages. Glomerular fibrin may be removed by fibrinolytic or phagocytic mechanisms or persist and lead to glomerular obsolescence. Suppression or elimination of factors that promote glomerular fibrin deposition and enhancement of mechanisms that remove glomerular fibrin may be important in the recovery from several forms of human kidney disease.

Tissue plasminogen activator therapy of glomerular thrombi in the Shwartzman reaction

To study the effect of tissue plasminogen activator (TPA) therapy on glomerular fibrin deposition in the generalized Shwartzman reaction, rabbits were given an intravenous injection of TPA immediately following or three, four, or five hours after the second injection of endotoxin. Animals were sacrificed six hours after the second dose of endotoxin. Glomerular fibrin deposition was reduced in animals receiving TPA four hours after the second injection of endotoxin and was absent in animals receiving TPA five hours after the second dose of endotoxin. Glomerular fibrinolytic activity was reduced following development of the generalized Shwartzman reaction but was normal in animals that received TPA five hours after the second injection of endotoxin. TPA did not produce a systemic fibrinolytic state and did not prevent the decline in hematologic and coagulation factors typical of the Shwartzman reaction, despite the elimination of glomerular fibrin. These results suggest that TPA effectively removes glomerular thrombi in the generalized Shwartzman reaction and infers that TPA may be of value in the treatment of human diseases with similar pathology, such as the hemolytic uremic syndrome.