LPS induces major changes in the extracellular proteolytic balance in the murine kidney

Bioanalytical approaches to assess the proteolytic stability of therapeutic fusion proteins

Therapeutic fusion proteins (TFPs) are designed to improve the therapeutic profile of an endogenous protein or protein fragment with a limited dose frequency providing the desired pharmacological activity in vivo. Fusion of a therapeutic protein to a half-life extension or targeting domain can improve the disposition of the molecule or introduce a novel mechanism of action. Prolonged exposure and altered biodistribution of an endogenous protein through fusion technology increases the potential for local protein unfolding during circulation increasing the chance for partial proteolysis of the therapeutic domain. Characterizing the proteolytic liabilities of a TFP can guide engineering efforts to inhibit or hinder partial proteolysis. This review focuses on considerations and techniques for evaluating the stability of a TFP both in vivo and in vitro.

Sepsis-associated disseminated intravascular coagulation and thromboembolic disease

Sepsis is almost invariably associated with haemostatic abnormalities ranging from subclinical activation of blood coagulation (hypercoagulability), which may contribute to localized venous thromboembolism, to acute disseminated intravascular coagulation (DIC), characterized by massive thrombin formation and widespread microvascular thrombosis, partly responsible of the multiple organ dysfunction syndrome (MODS), and subsequent consumption of platelets and coagulation proteins causing, in most severe cases, bleeding manifestations. There is general agreement that the key event underlying this life-threatening sepsis complication is the overwhelming inflammatory host response to the infectious agent leading to the overexpression of inflammatory mediators. Mechanistically, the latter, together with the micro-organism and its derivatives, causes DIC by 1) up-regulation of procoagulant molecules, primarily tissue factor (TF), which is produced mainly by stimulated monocytes-macrophages and by specific cells in target tissues; 2) impairment of physiological anticoagulant pathways (antithrombin, protein C pathway, tissue factor pathway inhibitor), which is orchestrated mainly by dysfunctional endothelial cells (ECs); and 3) suppression of fibrinolysis due to increased plasminogen activator inhibitor-1 (PAI-1) by ECs and likely also to thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor (TAFI). Notably, clotting enzymes non only lead to microvascular thrombosis but can also elicit cellular responses that amplify the inflammatory reactions. Inflammatory mediators can also cause, directly or indirectly, cell apoptosis or necrosis and recent evidence indicates that products released from dead cells, such as nuclear proteins (particularly extracellular histones), are able to propagate further inflammation, coagulation, cell death and MODS. These insights into the pathogenetic mechanisms of DIC and MODS may have important implications for the development of new therapeutic agents that could be potentially useful particularly for the management of severe sepsis.

Novel actions of tissue-type plasminogen activator in chronic kidney disease

Tissue-type plasminogen activator (tPA) is traditionally viewed as a simple serine protease whose main function is to convert plasminogen into biologically active plasmin. As a protease, tPA plays a crucial role in regulating blood fibrinolysis, in maintaining the homeostasis of extracellular matrix and in modulating the post-translational activation of growth factors. However, emerging evidence indicates that tPA also functions as a cytokine that transmits its signal across the cell membrane, initiates a diverse array of intracellular signaling, and dictates gene expression in the nuclei. tPA binds to the cell membrane LDL receptor-related protein 1 (LRP-1), triggers its tyrosine phosphorylation. As a cytokine, tPA plays a pivotal role in the pathogenesis of renal interstitial fibrosis through diverse mechanisms. It facilitates tubular epithelial to mesenchymal transition, potentiates myofibroblast activation, and protects renal interstitial fibroblasts/myofibroblasts from apoptosis. Together, growing evidence has implicated tPA as a fibrogenic cytokine that promotes the progression of kidney diseases. These new findings have radically changed our conception of tPA in renal fibrogenesis and represent a paradigm shift towards uncovering its cytokine function.

Synergistic effect of hypoxia and TNF-alpha on production of PAI-1 in human proximal renal tubular cells

BACKGROUND

Chronic hypoxia has been newly proposed as a common mechanism of tubulointerstitial fibrosis in the progression of various chronic inflammatory renal diseases, where plasminogen activator inhibitor-1 (PAI-1) plays an important role in the accumulation of extracellular matrix (ECM) through inhibition of plasmin-dependent ECM degradation. In the present study, we investigated the presence of PAI-1 in renal tubular cells by immunostaining renal biopsy samples. We also closely examined the effects of hypoxia and tumor necrosis factor-alpha (TNF-alpha) on PAI-1 expression in cultured human proximal renal tubular cells (HPTECs).

METHODS

Confluent cells growth-arrested in Dulbecco's modified Eagle's medium (DMEM) for 24 hours were exposed to hypoxia (1% O(2)) and/or TNF-alpha at 10 ng/mL for up to 48 hours. Amounts of PAI-1 protein and mRNA after stimulation were measured by enzyme-linked immunosorbent assay (ELISA) and TaqMan quantitative polymerase chain reaction (PCR) or cDNA array analysis, respectively, and compared to those in cells incubated under control conditions (18% O(2) without TNF-alpha). Hypoxia-inducible factor-1alpha (HIF-1alpha) was demonstrated by immunoblot and immunofluorescence analyses. Human PAI-1 promoter activity was estimated by luciferase reporter gene assay.

RESULTS

In crescentic glomerulonephritis, clusters of proximal tubules were specifically stained for PAI-1. cDNA array analysis identified PAI-1 as a major gene highly induced by hypoxia in HPTECs. Treatment of 24 hours with hypoxia, TNF-alpha, and their combination induced a 2.8-fold, a 1.8-fold, and a 4.6-fold increase in PAI-1 protein secretion, and produced a 3.6-fold, a 3.3-fold, and a 12.1-fold increase at the PAI-1 mRNA level, respectively. Immunoblot analysis and immunocytochemistry revealed that hypoxia-inducible factor-1alpha (HIF-1alpha) was markedly accumulated in the cell lysates and exclusively translocated to nuclei after 16 hours' exposure of HPTECs to hypoxia but not to TNF-alpha. Luciferase reporter gene assay showed that hypoxia, TNF-alpha, and their combination increased PAI-1 transcription activity by 1.8-fold, 1.4-fold, and 2.2-fold, respectively. A dominant-negative form of HIF-1alpha significantly suppressed PAI-1 transcription activity induced by hypoxia. Inhibition of nuclear factor-kappaB (NF-kappaB) caused a moderate decrease in PAI-1 production under hypoxia.

CONCLUSION

Hypoxia induces PAI-1 expression via remarkable nuclear accumulation of HIF-1alpha and partially via NF-kappaB activation in HPTECs. TNF-alpha can synergistically enhance this hypoxia-induced PAI-1 expression.

Renal synthesis of urokinase type-plasminogen activator, its receptor, and plasminogen activator inhibitor-1 in diabetic nephropathy in rats: modulation by angiotensin-converting-enzyme inhibitor

Plasmin is an important factor in the degradation of extracellular matrix. In the study reported here we examined the expression of plasminogen-activator inhibitor-1 (PAI-1), urokinase-type plasminogen activator (uPA), and uPA receptor (uPAR), as well as the relevance of such expression to the production of type IV collagen, a major component of extracellular matrix, in the renal tissue of rats with streptozotocin-induced diabetes. Because angiotensin II is involved in the synthesis of PAI-1 and uPA, we also examined the effect of benazepril, an angiotensin-converting-enzyme inhibitor, on the expression of PAI-1, uPA, and uPAR messenger RNAs (mRNAs) and type IV collagen protein. Rats with streptozocin-induced diabetes-some untreated and some treated with 30 mg/L benazepril-and nondiabetic control rats were sacrificed at 4, 12, or 24 weeks after induction of diabetes. We examined the expression of PAI-1, uPA, and uPAR mRNAs through the use of in situ hybridization and that of type IV collagen by means of immunohistochemical methods. In control rats, we detected weak signals for PAI-1, uPA, and uPAR mRNAs in glomeruli. Diabetic rats exhibited high levels of expression of PAI-1, uPA, and uPAR mRNAs and type IV collagen protein, mainly in mesangial cells. These mRNAs were synthesized in various renal cells (epithelial, mesangial, and endothelial cells and Bowman's capsule). Benazepril inhibited increases in all 3 mRNAs, especially in the mesangium; reduced type IV collagen expression; and attenuated mesangial expansion. Our results indicated that altered expression of PAI-1, uPA, and uPAR in diabetic nephropathy was associated with mesangial expansion and that the beneficial effects of ACE-I may be at least associated with such expression.

Ethyl pyruvate decreases sepsis-induced acute renal failure and multiple organ damage in aged mice

BACKGROUND

Sepsis is a common cause of acute renal failure (ARF). The incidence of sepsis increases dramatically after 50 years of age; however, most ARF studies are performed in young mice.

METHODS

We performed two common sepsis models, lipopolysaccharide (LPS) administration and cecal ligation puncture (CLP) in aged mice. We developed a fully treated CLP model in aged mice by treating mice with fluid resuscitation and antibiotics.

RESULTS

LPS induced renal injury in aged but not young mice. However, volume resuscitation starting within 6 hours decreased renal injury. We then used this fluid resuscitation scheme, along with antibiotics, to develop a fully treated CLP model in aged mice. Mice subjected to CLP developed functional and histologic ARF and multiple organ damage. Treatment with ethyl pyruvate, even when started 12 hours after surgery, decreased serum creatinine, tubular damage, and multiple organ injury at 24 hours. Ethyl pyruvate decreased plasma tumor necrosis factor-alpha (TNF-alpha), and kidney mRNA for TNF alpha, tissue factor, and plasminogen activator inhibitor-1 (PAI-1), and increased mRNA for urokinase-like plasminogen activator.

CONCLUSION

CLP in aged mice causes functional and histologic changes consistent with human ARF. A single dose of ethyl pyruvate inhibits renal and multiple organ damage, and is still effective when given 12 hours after surgery.

Expression of type-1 plasminogen activator inhibitor in the kidney of diabetic rat models

INTRODUCTION

Intrarenal coagulation and fibrinolysis are thought to be involved in the pathogenesis of diabetic nephropathy. However, gene expression of fibrinolytic factors in diabetic nephropathy has not been clearly defined. Therefore we determined the gene expression of fibrinolytic factors in the kidneys of diabetic rats.

MATERIALS AND METHODS

As a model of type1 diabetes male Sprague-Dawley rats were used. They were divided into three groups: control, streptozotocin (STZ)-induced diabetic, and insulin-treated diabetic. Otsuka Long-Evans Tokushima Fatty (OLETF) rats were used as a model of type 2 diabetes; and Long-Evans Tokushima Otsuka (LETO) rats, as the control. Renal gene expressions of type-1 plasminogen activator inhibitor (PAI-1), tissue-type PA (tPA), and urokinase-type PA (uPA) were examined by real-time PCR. Localization of PAI-1 mRNA was investigated by in situ hybridization.

RESULTS

Renal PAI-1 mRNA levels (versus control) were increased by 60-80% in STZ-induced diabetic rats (10 days or 3 weeks post STZ injection); and insulin treatment reduced this increased expression to the control level. In OLETF rats (38 weeks old), the renal PAI-1 mRNA level was 2.5-fold higher than that in age-matched LETO rats. Both tPA and uPA mRNA levels were significantly lower than those in LETO rats. PAI-1 mRNA was observed in intraglomerular cells and tubular epithelial cells of both models.

CONCLUSIONS

Renal PAI-1 gene expression is up-regulated in both type 1 and type 2 diabetic rats, and changes in gene expressions of fibrinolytic factors may play important roles in the development and pathogenesis of diabetic nephropathy.

Plasminogen activator inhibitor-1 and the kidney

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor that was isolated 20 years ago. First recognized as an inhibitor of intravascular fibrinolysis, it is now evident that PAI-1 is a multifunctional protein with actions that may be dependent on or independent of its protease inhibitory effects. The latter often involve interactions between PAI-1 and vitronectin or the urokinase receptor. The protease-inhibitory actions of PAI-1 extend beyond fibrinolysis and include extracellular matrix turnover and activation of several proenzymes and latent growth factors. PAI-1 has been implicated in several renal pathogenetic processes, including thrombotic microangiopathies and proliferative and/or crescentic glomerulopathies. Most recently, it has become clear that PAI-1 also plays a pivotal role in progressive renal disease, both glomerulosclerosis and tubulointerstitial fibrosis. An active area of present research interest, untold stories are likely to be uncovered soon.

Control elements between -9.5 and -3.0 kb in the human tissue-type plasminogen activator gene promoter direct spatial and inducible expression to the murine brain

Tissue-type plasminogen activator (t-PA) participates in the control of synaptic plasticity and memory formation in the central nervous system (CNS). Transgenic mice harbouring either 9.5, 3.0 or 1.4 kb of the human t-PA promoter fused to the LacZ reporter gene were used to assess t-PA promoter-directed expression in vivo. The 9.5 kb t-PA promoter directed expression to the brain, most notably to the dentate gyrus, superior colliculus, hippocampus, thalamus and piriform cortex. Staining was also observed in the retrosplenial and somatosensory cortex. The 3.0 kb t-PA promoter directed generalized and poorly defined expression to the cortex and hippocampus, while the 1.4 kb t-PA promoter directed expression selectively to the medial habenula. Intravenous administration of lipopolysaccharide into mice harbouring the 9.5 kb t-PA promoter resulted in an increase in reporter gene activity in the lateral orbital cortex and thalamus. Results of in vitro transfection experiments of NT2 cells with a series of t-PA promoter deletion constructs confirmed the presence of regulatory elements throughout the 9.5 kb promoter region. Finally, we describe a cis-acting element related to the NFAT recognition site that provides a protein-binding site and which may play a role in the selective expression of the 1.4 t-PA promoter in the medial habenula. These results indicate that elements between -3.0 and -9.5 kb of the t-PA promoter confer constitutive and inducible expression to specific regions of the CNS.

Plasminogen activator inhibitor type 1 is a potential target in renal fibrogenesis

Plasminogen activator inhibitor type 1 is a potential target in renal fibrogenesis. The progression of renal lesions to fibrosis involves several mechanisms, among which the inhibition of extracellular matrix (ECM) degradation appears to play an important role. Two interrelated proteolytic systems are involved in matrix degradation: the plasminogen activation system and the matrix metalloproteinase system. The plasminogen activator inhibitor type 1 (PAI-1), as the main inhibitor of plasminogen activation, regulates fibrinolysis and the plasmin-mediated matrix metalloproteinase activation. PAI-1 is also a component of the ECM, where it binds to vitronectin. PAI-1 is not expressed in the normal human kidney but is strongly induced in various forms of kidney diseases, leading to renal fibrosis and terminal renal failure. Thrombin, angiotensin II, and transforming growth factor-beta are potent in vitro and in vivo agonists in increasing PAI-1 synthesis. Several experimental and clinical studies support a role for PAI-1 in the renal fibrogenic process occurring in chronic glomerulonephritis, diabetic nephropathy, focal segmental glomerulosclerosis, and other fibrotic renal diseases. Experimental models of renal diseases in PAI-1-deficient animals are in progress, and preliminary results indicate a role for PAI-1 in renal fibrogenesis. Inhibition of PAI-1 activity or of PAI-1 synthesis by specific antibodies, peptidic antagonists, antisense oligonucleotides, or decoy oligonucleotides has been obtained in vitro, but needs to be evaluated in vivo for the prevention or the treatment of renal fibrosis.

Complement is activated in kidney by endotoxin but does not cause the ensuing acute renal failure

BACKGROUND

Acute renal failure (ARF) in sepsis occurs when the release of multiple inflammatory mediators is induced by bacterial endotoxins. C3 mRNA is markedly up-regulated in mouse kidney after exposure to lipopolysaccharide (LPS). We hypothesized that LPS could induce tubular synthesis and secretion of C3, leading to activation of the complement cascade and direct renal tubular injury.

METHODS

ARF was induced in mice by intravenous injection of LPS and was confirmed by an acute rise in blood urea nitrogen (BUN) and histologically by acute tubular necrosis. Three separate strategies were used to investigate the role of the complement system in this model of ARF: (1) Crry-Ig, a recombinant protein containing the potent murine complement C3 activation inhibitor Crry was injected at the same time as LPS (N = 8). (2) LPS was injected into transgenic mice overexpressing Crry in glomeruli and tubules (N = 8), and (3) LPS was injected into C3-deficient mice (N = 5).

RESULTS

Compared with unmanipulated mice, C3 staining by immunofluorescence (IF) microscopy in mice injected with LPS was greater in renal cortical tubular cells (IF score of 2. 1 +/- 0.1 vs. 1.4 +/- 0.2 in controls, P = 0.013), most prominently at the basolateral surface. LPS injection led to a 16- to 42-fold increase in urinary C3 excretion. Despite reduction or complete elimination of renal C3 with maneuvers suppressing complement activation, BUN values were not statistically different across all groups. In no experiment did BUN values correlate with the extent of C3 staining.

CONCLUSION

Although LPS up-regulates renal C3 synthesis, resulting in basolateral tubular C3 deposition, this is not responsible for LPS-induced ARF in mice.

Endogenous plasminogen activator expression after embolic focal cerebral ischemia in mice

Urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA) play important roles in fibrinolysis, cell migration, tissue destruction, angiogenesis and tissue remodeling. u-PA and t-PA activity in tissue are tightly regulated by plasminogen activator inhibitor-1 (PAI-1). However, little is known of the activity of endogenous plasminogen activators (PAs) and PAI-1 in ischemic brain. To evaluate whether cerebral ischemic injury induces endogenous PAs and PAI-1, we measured PA activity from brain homogenates, and examined the expression of t-PA mRNA, u-PA mRNA and PAI-1 mRNA from brain homogenates in C57BL/6J mice (n=45) weighing 29-35 g in which the middle cerebral artery (MCA) was occluded by a fibrin-rich clot. Brain homogenates were prepared for direct casein zymography from control non-ischemic mice (n=4) and mice at 2 h (n=5), 4 h (n=5), and 24 h (n=4) after MCA occlusion (MCAO). Also, u-PA and t-PA knockout mice at 4 h (n=2, each) after MCAO were used as a negative control for direct casein zymography. Frozen sections for in situ zymography were obtained from control mice (n=2) and mice at 2 h, 4 h, and 24 h (n=2, per time point) after clot occlusion. Brain homogenates were prepared for reverse transcriptase-polymerase chain reaction (RT-PCR) to examine t-PA mRNA, u-PA mRNA and PAI-1 mRNA expression from control non-ischemic mice (n=4) and mice at 2 h (n=5), 4 h (n=5), and 24 h (n=5) after MCAO. By direct casein zymography, u-PA activity increased at 4 h (P<0.05), and 24 h (P<0.05) after stroke in the ischemic hemisphere compared with the non-ischemic mice. Activity of t-PA in ischemic brain was not significantly different from the control group. As measured by in situ zymography, PA activity, most likely u-PA, was present in the ischemic hemisphere. By RT-PCR, expression of PAI-1 mRNA, but not u-PA mRNA and t-PA mRNA, increased 3-, 15- and 25-folds in the ischemic hemisphere at 2 h, 4 h and 24 h after stroke, respectively, compared with control mice. This study demonstrates that PAI-1 mRNA and u-PA activity increase in mouse brain after stroke.

Interstitial fibrosis in hypercholesterolemic rats: role of oxidation, matrix synthesis, and proteolytic cascades

Uninephrectomized rats with diet-induced hypercholesterolemia develop interstitial inflammation and fibrosis after 8 to 12 weeks. Fibrosis has been associated with the accumulation of lipid peroxidation products within the tubulointerstitium, along with increased renal mRNA levels for transforming growth factor beta-1 (TCF-beta 1), some matrix proteins, and the tissue inhibitor of metalloproteinases (TIMP-1). However, mRNA levels for urokinase-type plasminogen activator (uPA) have been found to be decreased. The purpose of the present study was to determine whether antioxidant therapy could attenuate interstitial fibrosis in hypercholesterolemic rats and to determine changes in the pattern of renal gene expression induced by antioxidant therapy. Three groups of uninephrectomized rats were studied after 12 weeks of feeding standard rat chow, an atherogenic diet (standard chow plus 4% cholesterol/1% cholic acid), or an atherogenic diet supplemented with high doses of the antioxidants probucol and vitamin E. Rats fed the atherogenic diet developed hypercholesterolemia and a 56% increase in total kidney collagen compared with rats fed standard chow. In comparison, the hypercholesterolemic rats treated with antioxidants had normal levels of renal lipid peroxidation products and a normal kidney collagen content. In contrast, there were no significant differences in urinary albumin excretion rates or the number of interstitial macrophages between the two hypercholesterolemic groups. Compared with the untreated hypercholesterolemic group, antioxidant therapy induced significant reductions in renal mRNA levels for procollagen III (to 60% of untreated levels), collagen IV (60%), and TIMP-1 (20%), while uPA levels were significantly increased (to 210%). Paradoxically, antioxidant therapy was associated with a significant increase in renal TGF-beta 1 mRNA levels (to 150%), although TGF-beta 1 protein expression shifted from interstitial to tubular epithelial cells in predominance. The results of the present study demonstrate the efficiency of antioxidant therapy in preventing renal interstitial fibrosis in hypercholesterolemic rats with a single kidney. Based on changes in renal gene expression at the mRNA level, impaired matrix protein synthesis and increased intrarenal activity of the metalloproteinases and uPA/plasmin may play a role in the attenuation of fibrosis.

The human plasminogen activator inhibitor type I gene promoter targets to kidney

The plasminogen activator inhibitor type 1 (PAI-1) gene encodes the physiological inhibitor of tissue-type and urokinase-type plasminogen activators and is induced by cytokines such as transforming growth factor-beta (TGF-beta). Studies have identified DNA sequence elements within the first 1.3 kb of the 5'-upstream DNA that mediate cytokine responsiveness in transfected cells in vitro. However, the DNA sequences that mediate PAI-1 expression in vivo have not yet been delineated. To define these regulatory sequences, we generated transgenic mice that expressed a hybrid gene comprising sequences between -1,272 and +75 of the human PAI-1 gene ligated to a LacZ reporter gene. Transgene expression detected in two independent lines was observed only in kidney from embryonic day 13 to adult and was seen primarily in proximal tubule cells of the outer medulla. Transgene expression and activity were unchanged in response to TGF-beta and remained restricted to kidney. Thus we have identified a promoter region within the PAI-1 gene that targets transgene expression to kidney but, unlike the native promoter, is unresponsive to TGF-beta in the experimental protocol used.

Modulation of plasminogen activator inhibitor-1 in vivo: a new mechanism for the anti-fibrotic effect of renin-angiotensin inhibition

We examined the potential of in vivo linkage of plasminogen activator inhibitor-1 (PAI-1) and angiotensin II (Ang II) in the setting of endothelial injury and sclerosis following radiation injury in the rat. PAI-1 is a major physiological inhibitor of the plasminogen activator (PA)/plasmin system, a key regulator of fibrinolysis and extracellular matrix (ECM) turnover. PAI-1 mRNA expression in the kidney was markedly increased (9-fold) at 12 weeks after irradiation (P < 1.001 vs. normal control). In situ hybridization revealed significant association of PAI-1 expression with sites of glomerular injury (signal intensity in injured vs. intact glomeruli, P < 0.001). Angiotensin converting enzyme inhibitors (ACEI, captopril or enalapril) or angiotensin II receptor antagonist (AIIRA, L158,809) markedly reduced glomerular lesions (thrombosis, mesangiolysis, and sclerosis; sclerosis index, 0 to 4+ scale, 0.49 +/- 0.20 in untreated vs. 0.05 +/- 0.02, 0.02 +/- 0.01, 0.04 +/- 0.02 in captopril, enalapril and AIIRA, respectively, all P < 0.01 vs untreated). Further, ACEI and AIIRA markedly attenuated increased PAI-1 mRNA expression in the irradiated kidney (36, 19 and 20% expression, respectively, for captopril, enalapril and AIIRA, compared to untreated irradiated kidney, P < 0.05, < 0.01, < 0.01). This effect was selective in that neither tissue-type nor urokinase-type PA mRNA expression was affected by these interventions. Thus, we speculate that inhibition of the renin-angiotensin system may ameliorate injury following radiation by accelerating fibrinolysis and ECM degradation, at least in part, via suppression of PAI-1 expression. In summary, inhibition of Ang II, in addition to its known effects on vascular sclerosis, may also by its novel effect to inhibit PAI-1, lessen fibrosis following endothelial/thrombotic injury.

Protease nexin 1 in the murine kidney: glomerular localization and up-regulation in glomerulopathies

Protease nexin 1 (PN-1), a potent serpin-class antiprotease, is thought to be synthesized in the murine kidney. However, neither the cellular localization of PN-1 synthesis nor its role has yet been defined. To address these questions, we determined by in situ hybridizations RNase protection assay and immunoblotting, the sites of PN-1 mRNA accumulation in normal mouse kidneys and the modulation of PN-1 expression in several pathological conditions. In normal kidneys, PN-1 mRNA was detected primarily in glomeruli, most likely in mesangial cells. The glomerular expression of PN-1 was substantially enhanced not only in lupus-like glomerulonephritis (induced by IgG3 monoclonal rheumatoid factors or occurring spontaneously in lupus-prone mice), but also in mild glomerular lesions associated with intracapillary thrombi induced by IgG3 anti-trinitrophenyl monoclonal antibodies. In contrast, no modulation of PN-1 mRNA levels was observed during the course of lipopolysaccharide-induced acute tubular necrosis. A constitutive PN-1 gene expression and its up-regulation during glomerular injury suggest a possible role for PN-1 in glomerular biology. In view of its high inhibitory activity towards thrombin, mesangial PN-1 may be involved in the control of glomerular coagulation following initial glomerular injuries.

The kidney is a major site of alpha(2)-antiplasmin production

The serpin alpha2-antiplasmin (alpha2-AP) is the major circulating inhibitor of plasmin; it plays a determining role in the regulation of intravascular fibrinolysis, In addition to blood plasma, plasmin formation occurs in various organs where it is thought to fulfill a spectrum of functions not restricted to clot lysis. Alpha2-AP is synthesized by hepatocytes, but other possible sites of production have not been investigated. To explore the potential extravascular contribution of alpha2-AP in the regulation of proteolysis, we have isolated the murine alpha2-AP cDNA and determined its mRNA distribution in adult tissues. In addition to liver, kidneys are major sites of alpha2-AP mRNA accumulation in the mouse. The transcript is present in epithelial cells lining the convoluted portion of proximal tubules, and its accumulation is under androgen control. Human kidneys also contain high levels of alpha2-AP mRNA. Moderate amounts Of alpha2-AP mRNA are detected in other murine tissues such as muscle, intestine, central nervous system, and placenta. Our observations indicate that alpha2-AP can be synthesized in a number of tissues, where it could function as a distal regulator of plasmin-mediated extracellular proteolysis.

Fibrin deposition in tissues from endotoxin-treated mice correlates with decreases in the expression of urokinase-type but not tissue-type plasminogen activator

The primary hypothesis of this report is that the formation and subsequent removal of fibrin in specific tissues during pathologic processes reflects temporal changes in the local expression of key procoagulant and fibrinolytic genes. To begin to test this hypothesis, we have used quantitative PCR assays and in situ hybridization analysis to examine the effects of endotoxin on the expression of specific genes in murine tissues, and to relate these changes to fibrin deposition/dissolution using immunohistochemical approaches. Endotoxin caused large increases in plasminogen activator inhibitor-1 mRNA and modest increases in tissue factor mRNA in most tissues examined. However, fibrin was only detected in the kidneys and adrenals of endotoxin-treated mice, and it was transient. Unexpectedly, changes in urokinase-type plasminogen activator mRNA but not tissue-type plasminogen activator mRNA correlated with fibrin deposition/dissolution in these tissues. Pretreatment of mice with the fibrinolytic inhibitor epsilon-aminocaproic acid before endotoxin increased both the number of fibrin-positive tissues and the duration of fibrin deposition in the kidneys and adrenals. These results suggest that the absence of fibrin in some tissues reflects ongoing local fibrinolysis, and that increases in plasminogen activator inhibitory and tissue fac- tor gene expression and decreases in urokinase-type plasminogen activator expression are necessary for tissue-specific fibrin deposition. Changes in tissue-type plasminogen activator gene expression do not appear to be essential for fibrin deposition/dissolution in this murine model of sepsis.

Up-regulation of type 1 plasminogen activator inhibitor messenger RNA with thrombotic changes in renal grafts

Small vessel thrombosis is a prominent feature in kidneys undergoing vascular rejection. Type I and type 2 plasminogen activator inhibitors (PAI-1 and PAI-2, respectively) are known to mediate thrombosis. To examine the potential role of PAI-1 and PAI-2 in the mediation of vascular injury, the relationship and the time course of gene expression of PAI-1 and PAI-2 with the thrombotic changes in renal grafts were investigated in an unmodified rejection model in rats. Orthotopic renal transplantation was performed from Lewis to dark agouti (DA) rats and from DA to DA isografts; untreated normal rat kidneys were used as controls. The rats were killed on days 1-9 posttransplantation (n=18 in each allograft and isograft group). The grafts were analyzed by histopathology, in situ mRNA hybridization and Northern blot methods. The results show that PAM mRNA was first detected at day 4, when the thrombotic changes in the grafts were first seen, and that this relationship persisted during the time course observed to day 9. There was no detectable PAI-1 mRNA in the control groups and no PAI-2 in either group. In situ hybridization showed that PAI-1 positive cells were predominantly located in the cortical interstitium, consistent with the distribution of interstitial microthrombi. These results provide experimental evidence that the thrombotic changes in rejecting allografts are associated with the up-regulation of PAI-1 in the donor tissue, whereas PAI-2, from our results, does not seem to influence these changes. The data are consistent with a role for PAI-1 in the pathogenesis of vascular rejection.

Induction of plasminogen activator inhibitor type 1 in murine lupus-like glomerulonephritis

Three major components of the plasminogen activators (PA)/plasmin system are synthesized physiologically in glomeruli, and can be involved in glomerular proteolysis and extracellular matrix metabolism: tissue-type PA (tPA), urokinase (uPA) and PA inhibitor type 1 (PAI-1). To explore the possible role of a dysregulation of the plasmin protease system in the development and progression of lupus-like glomerulonephritis, we studied the expression of the renal plasmin protease components during the course of the disease, either acute, induced by IgG3 monoclonal cryoglobulins, or chronic, occurring spontaneously in three different lupus-prone mice: (NZBxNZW)F1, BXSB and MRL-lpr/lpr. RNase protection assays and in situ hybridizations revealed a marked glomerular induction of PAI-1 mRNA abundance without any significant changes in renal tPA and uPA mRNA levels in the two different types of lupus-like glomerulonephritis. The overexpression of PAI-1 mRNA occurred in parallel with a significant decrease in glomerular tPA-catalyzed enzymatic activity as determined by zymographic analysis. In addition, a concomitant increase in glomerular expression of transforming growth factor beta 1 (TGF-beta 1) mRNA was observed. The demonstration of a close correlation between the PAI-1 and TGF-beta 1 mRNA levels and the severity of lupus-like glomerular lesions suggests that a pertubation of the glomerular PA/PAI balance, resulting from a marked TGF-beta 1-mediated induction of PAI-1 gene expression, plays an important role in the progression of lupus-like glomerular lesions, leading to glomerulosclerosis.

Regulation of proteolytic activity in tissues

Degradation of tissue proteins is controlled by multiple means. These include regulation of the synthesis of proteinases, activation of the zymogen forms, the activity of the mature proteinase, and the degradation of these enzymes and the substrates. Mature proteinases can be controlled by pH, calcium ions, ATP, lipids and the formation of complexes with other proteinases, proteoglycans, and inhibitors.