Expression of tissue type plasminogen activator and type 1 plasminogen activator inhibitor, and persistent fibrin deposition in chronic renal allograft failure

Renal transplant and hemostasis: early postoperative changes in recipients and donors

Background

The benefit of administering pharmacologic thromboprophylaxis following renal transplantation remains uncertain.

Objectives

To compare hemostatic parameters before and after renal transplant surgery in both recipients and their donors at predetermined time points.

Methods

Blood samples were collected at baseline (T1), immediately after surgery (T2), and at 24 hours after surgery (T3) in both recipients and donors and at 72 (T4) and 120 hours (T5) from recipients only. Assays included in vitro thrombin generation, factor VIII (FVIIIc) activity, von Willebrand factor (VWF) antigen, D-dimer, antithrombin activity, prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin complexes, and plasminogen activator inhibitor-1 (PAI-1) antigen.

Results

Fifty-two patients (28 recipients and 24 donors) were enrolled. Both donors and recipients had increased FVIIIc, VWF, F1 + 2, D-dimer, and PAI immediately after surgery but reduced antithrombin. Mixed-model analysis showed that the magnitude of change over time (between T1 and T3) for FVIIIc (mean estimated difference [MED], 72; 95% CI, 41-102; P < .0001), VWF (MED, 89; 95% CI, 35-142; P = .001), F1 + 2 (MED, 283; 95% CI, 144-422; P < .0001), thrombin-antithrombin complexes (MED, 3.5; 95% CI, 1.9-5.1; P < .0001), D-dimer (MED, 2.2; 95% CI, 1.0-3.3; P < .0001), PAI-1 (MED, 9.2; 95% CI, 3.4-14.9; P = .002), and time to peak thrombin generation (MED, 1.5; 95% CI, 0.35-2.7; P = .01) was more significant in recipients than in donors.

Conclusion

Persistence of a hypercoagulable state was more prominent in recipients after 24 hours despite recovery in renal function and initiation of thromboprophylaxis.

Factor Xa inhibitor, edoxaban ameliorates renal injury after subtotal nephrectomy by reducing epithelial-mesenchymal transition and inflammatory response

Chronic kidney disease (CKD) is an increasing and life-threatening disease worldwide. Recent evidence indicates that blood coagulation factors promote renal dysfunction in CKD patients. Activated factor X (FXa) inhibitors are safe and first-line drugs for the prevention of thrombosis in patients with atrial fibrillation. Here, we investigated the therapeutic effects of edoxaban on CKD using the mouse 5/6 nephrectomy model. Eight-week-old wild-type mice were subjected to 5/6 nephrectomy surgery and randomly assigned to two groups, edoxaban or vehicle admixture diet. Edoxaban treatment led to reduction of urinary albumin excretion and plasma UN levels compared with vehicle group, which was accompanied with reduced glomerular cross-sectional area and cell number. Edoxaban treatment also attenuated fibrinogen positive area in the remnant kidneys after subtotal nephrectomy. Moreover, edoxaban treatment resulted in attenuated tubulointerstitial fibrosis after 5/6 nephrectomy, which was accompanied by reduced expression levels of epithelial-mesenchymal transition (EMT) markers, inflammatory mediators, and oxidative stress markers in the remnant kidneys. Treatment of cultured proximal tubular cells, HK-2 cells, with FXa protein led to increased expression levels of EMT markers, inflammatory mediators, and oxidative stress markers, which were abolished by pretreatment with edoxaban. Treatment of HK-2 cells with edoxaban attenuated FXa-stimulated phosphorylation levels of extracellular signal-regulated kinase (ERK) and NF-κB. Our findings indicate that edoxaban can improve renal injury after subtotal nephrectomy by reducing EMT and inflammatory response, suggesting that FXa inhibition could be a novel therapeutic target for CKD patients with atrial fibrillation.

PAR2-Induced Tissue Factor Synthesis by Primary Cultures of Human Kidney Tubular Epithelial Cells Is Modified by Glucose Availability

Coagulopathies common to patients with diabetes and chronic kidney disease (CKD) are not fully understood. Fibrin deposits in the kidney suggest the local presence of clotting factors including tissue factor (TF). In this study, we investigated the effect of glucose availability on the synthesis of TF by cultured human kidney tubular epithelial cells (HTECs) in response to activation of protease-activated receptor 2 (PAR2). PAR2 activation by peptide 2f-LIGRLO-NH₂ (2F, 2 µM) enhanced the synthesis and secretion of active TF (~45 kDa) which was blocked by a PAR2 antagonist (I-191). Treatment with 2F also significantly increased the consumption of glucose from the cell medium and lactate secretion. Culturing HTECs in 25 mM glucose enhanced TF synthesis and secretion over 5 mM glucose, while addition of 5 mM 2-deoxyglucose (2DOG) significantly decreased TF synthesis and reduced its molecular weight (~40 kDa). Blocking glycosylation with tunicamycin also reduced 2F-induced TF synthesis while reducing its molecular weight (~36 kDa). In conclusion, PAR2-induced TF synthesis in HTECs is enhanced by culture in high concentrations of glucose and suppressed by inhibiting either PAR2 activation (I-191), glycolysis (2DOG) or glycosylation (tunicamycin). These results may help explain how elevated concentrations of glucose promote clotting abnormities in diabetic kidney disease. The application of PAR2 antagonists to treat CKD should be investigated further.

PAR2 Activation on Human Kidney Tubular Epithelial Cells Induces Tissue Factor Synthesis, That Enhances Blood Clotting

Coagulation abnormalities and increased risk of atherothrombosis are common in patients with chronic kidney diseases (CKD). Mechanisms that alter renal hemostasis and lead to thrombotic events are not fully understood. Here we show that activation of protease activated receptor-2 (PAR2) on human kidney tubular epithelial cells (HTECs), induces tissue factor (TF) synthesis and secretion that enhances blood clotting. PAR-activating coagulation-associated protease (thrombin), as well as specific PAR2 activators (matriptase, trypsin, or synthetic agonist 2f-LIGRLO-NH2 (2F), induced TF synthesis and secretion that were potently inhibited by PAR2 antagonist, I-191. Thrombin-induced TF was also inhibited by a PAR1 antagonist, Vorapaxar. Peptide activators of PAR1, PAR3, and PAR4 failed to induce TF synthesis. Differential centrifugation of the 2F-conditoned medium sedimented the secreted TF, together with the exosome marker ALG-2 interacting protein X (ALIX), indicating that secreted TF was associated with extracellular vesicles. 2F-treated HTEC conditioned medium significantly enhanced blood clotting, which was prevented by pre-incubating this medium with an antibody for TF. In summary, activation of PAR2 on HTEC stimulates synthesis and secretion of TF that induces blood clotting, and this is attenuated by PAR2 antagonism. Thrombin-induced TF synthesis is at least partly mediated by PAR1 transactivation of PAR2. These findings reveal how underlying hemostatic imbalances might increase thrombosis risk and subsequent chronic fibrin deposition in the kidneys of patients with CKD and suggest PAR2 antagonism as a potential therapeutic strategy for intervening in CKD progression.

Coagulation and Fibrinolysis in Kidney Graft Rejection

Coagulation system is currently considered an integrated part of innate immunity. Clotting activation in response to bacterial surface along with complement cascade priming represents the first line of defense against pathogens. In the last three decades, we learned that several coagulation factors, including factor II or thrombin and factor X, can interact with specific cell surface receptors activated by an unusual proteolytic mechanism and belonging to a novel class of G-protein-coupled receptors known as protease-activated receptors (PARs). PARs are expressed by a variety of cells, including monocytes, dendritic cells, and endothelial cells and may play a key role in the modulation of innate immunity and in the regulation of its interaction with the adaptive branch of the immune system. Also, the fibrinolytic system, in which activation is controlled by coagulation, can interact with innate immunity, and it is a key modulator of extracellular matrix deposition eventually leading to scarring and fibrosis. In the setting of kidney transplantation, coagulation and fibrinolytic systems have been shown to play key roles in the ischemia/reperfusion injury featuring delayed graft function and in the pathogenesis of tissue damage following acute and chronic rejection. In the present review, we aim to describe the mechanisms leading to coagulation and fibrinolysis activation in this setting and their interaction with the priming of the innate immune response and their role in kidney graft rejection.

Apolipoprotein E and plasminogen activator inhibitor 1 gene polymorphism in children with chronic renal insufficiency associated with cardiovascular disease

Background

Cardiovascular disease (CVD) is considered a major cause of death in renal insufficiency (RI). Contributing genetic factors is a recent focus of research. This study aims to elucidate apolipoprotein E (APO-E) and plasminogen activator inhibitor 1 (PAI-1) gene polymorphisms in RI children associated with CVD.

Methods

We studied 50 cases with chronic kidney disease (CKD) associated with CVD, and 30 healthy controls. Study sample was grouped as one on conservative treatment, the second on hemodialysis and the third was posttransplant. PAI-1 and APO-E gene polymorphisms were investigated using allele-specific polymerase chain reaction (AS-PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) respectively.

Results

4G4G and 4G5G were the most common PAI-1 polymorphism denoting high association of 4 G allele in renal insufficiency associated with CVD with absent link to dyslipidemia, echocardiography changes or thrombosis. E3E3 was the most common among APO-E polymorphism without relation to dyslipidemia or thrombosis. Dyslipidemia was significantly linked to thrombosis. The study confirmed the role of dyslipidemia and hemodialysis in promoting thrombosis.

Conclusion

Although PAI 4G Genotyping did not show significant association with echocardiography severity or thrombotic severity, yet genetic expression for high levels of PAI in plasma is expected in response to CRI factors known to trigger its release, in addition to those related to dialysis. APO-E3E3 genotyping showed a significant association with echocardiography severity as it enhances APO-A which contributes to CVD. The current study confirmed a significant association between dyslipidemia and CVD; however, the prevalent patterns 4G and E3E3 did not show a significant association with dyslipidemia. The genetic role for APO-A, B, O, or even other isomers for APO-E should be further studied as well.

Pharmacological and genetic depletion of fibrinogen protects from kidney fibrosis

Fibrinogen (Fg) has been implicated in the pathogenesis of several fibrotic disorders by acting as a profibrotic ligand for a variety of cellular surface receptors and by modulating the provisional fibrin matrix formed after injury. We demonstrated increased renal Fg expression after unilateral ureteral obstruction and folic acid (FA) nephropathy in mice, respectively. Urinary Fg excretion was also increased in FA nephropathy. Using in vitro and in vivo approaches, our results suggested that IL-6 mediates STAT3 activation in kidney fibrosis and that phosphorylated (p)STAT3 binds to Fgα, Fgβ, and Fgγ promoters in the kidney to regulate their transcription. Genetically modified Fg heterozygous mice (∼75% of normal plasma Fg levels) exhibited only 3% kidney interstitial fibrosis and tubular atrophy after FA nephropathy compared with 24% for wild-type mice. Fibrinogenolysis through Ancrod administration after FA reduced interstitial fibrosis more than threefold compared with vehicle-treated control mice. Mechanistically, we show that Fg acts synergistically with transforming growth factor (TGF)-β1 to induce fibroblast proliferation and activates TGF-β1/pSMAD2 signaling. This study offers increased understanding of Fg expression and molecular interactions with TGF-β1 in the progression to kidney fibrosis and, importantly, indicates that fibrinogenolytics like Ancrod present a treatment opportunity for a yet intractable disease.

Plasminogen activator inhibitor-1 in kidney pathology (Review)

Plasminogen activator inhibitor type-1 (PAI-1) inhibits tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), which convert plasminogen to plasmin, a strong proteolytic enzyme. Thus, PAI-1 is a primary and negative regulator of plasmin-driven proteolysis. In addition to its main role as an inhibitor of fibrinolysis, PAI‑1 has been implicated as a mediator in other processes, including fibrosis, rheumatoid arthritis, atherosclerosis, tumor angiogenesis and bacterial infections. It also significantly modulates cellular adhesion or migration, wound healing, angiogenesis and tumor cell metastasis. However, in the present study, we have reviewed the literature in relation to different kidney diseases where PAI-1 regulates fibrinolysis and acts independently of proteolysis. PAI-1 is normally produced in trace amounts in healthy kidneys but is synthesized in a wide variety of both acute and chronic diseased kidneys. We reviewed the role of PAI-1 in diabetic kidney nephropathy, chronic kidney disease, hemodialysis, peritoneal dialysis and in kidney transplantation. Increased PAI-1 expression results in accumulation of extracellular matrix (ECM) leading to numerous kidney diseases. Predisposition to some diseases is due to the genetic role of PAI-1 in their development. A number of studies demonstrated that the inhibition of PAI-1 activity or therapy with a mutant PAI-1 increases matrix turnover and reduces glomerulosclerosis by competing with endogenous PAI-1. This strongly suggests that PAI-1 is a valid target in the treatment of fibrotic renal disease. However, net proteolytic activity depends on the delicate balance between its negative regulation by PAI-1 and activation by uPA and tPA. Also, plasmin activated by its inhibitors upregulates activity of other enzymes. Thus, assessment of prognosis for the diseased kidney should include a variety of proteolysis regulators and enzymes.

Thrombin stimulates synthesis of macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor by human proximal tubular epithelial cells in culture

Background/Aims

Colony-stimulating factors (CSFs) are well-known hematopoietic growth factors. Although recent studies revealed that CSFs are involved in many inflammatory conditions, the local production of CSFs and its regulation in the kidney is not well elucidated. Therefore, using cultured human proximal tubular epithelial cells (PTEC), we examined the effect of thrombin on CSFs production, since thrombin has been suggested to play an important role in tubulointerstitial injury.

Methods

PTEC were incubated with thrombin (0.5–5.0 U/ml) and the effects on the production of macrophage CSF (M-CSF), granulocyte-macrophage CSF (GM-CSF) and granulocyte CSF (G-CSF) were measured in the cell supernatant by enzyme-linked immunosorbent assay, and the expressions of mRNA were analyzed by quantitative real-time reverse transcription polymerase chain reaction. Using argatroban, a direct thrombin inhibitor, we also examined the specific effect of thrombin.

Results

Thrombin 5.0 U/ml significantly stimulated the production of M-CSF (p < 0.01) and G-CSF (p < 0.01), and 1.0 and 5.0 U/ml thrombin significantly stimulated GM-CSF (p < 0.02 and p < 0.01) in a dose-dependent manner. Thrombin 5.0 U/ml increased CSFs (M-CSF, p < 0.005; GM-CSF, p < 0.0005; G-CSF, p < 0.005) in a time-dependent manner. Thrombin also significantly enhanced the mRNA expressions of M-CSF (p < 0.01), GM-CSF (p < 0.05) and G-CSF (p < 0.01). These effects of thrombin were significantly reduced by the addition of argatroban (M-CSF, p < 0.01; GM-CSF, p < 0.01; G-CSF, p < 0.05).

Conclusion

We demonstrated that thrombin significantly increased the production of CSFs by PTEC. These data suggest that the local production of CSFs in the tubulointerstitium may affect tubulointerstitial lesions in kidney injury.

Anti-thrombin therapy during warm ischemia and cold preservation prevents chronic kidney graft fibrosis in a DCD model

Ischemia reperfusion injury (IRI) is pivotal for renal fibrosis development via peritubular capillaries injury. Coagulation represents a key mechanism involved in this process. Melagatran (M), a thrombin inhibitor, was evaluated in an autotransplanted kidney model, using Large White pigs. To mimic deceased after cardiac death donor conditions, kidneys underwent warm ischemia (WI) for 60 min before cold preservation for 24 h in University of Wisconsin solution. Treatment with M before WI and/or in the preservation solution drastically improved survival at 3 months, reduced renal dysfunction related to a critical reduction in interstitial fibrosis, measured by Sirius Red staining. Tissue analysis revealed reduced expression of transforming growth factor-beta (TGF-beta) and activation level of its effectors phospho-Smad3, Smad4 and connective tissue growth factor (CTGF) after M treatment. Fibrinolysis activation was also observed, evidenced by downregulation of PAI-1 protein and gene expression. In addition, M reduced S100A4 expression and vimentin staining, which are markers for epithelial mesenchymal transition, a major pathway to chronic kidney fibrosis. Finally, expression of oxidative stress markers Nox2 and iNOS was reduced. We conclude that inhibition of thrombin is an effective therapy against IRI that reduces chronic graft fibrosis, with a significantly positive effect on survival.

Do distinct populations of dorsal root ganglion neurons account for the sensory peptidergic innervation of the kidney?

Peptidergic afferent renal nerves (PARN) have been linked to kidney damage in hypertension and nephritis. Neither the receptors nor the signals controlling local release of neurokinines [calcitonin gene-related peptide (CGRP) and substance P (SP)] and signal transmission to the brain are well-understood. We tested the hypothesis that PARN, compared with nonrenal afferents (Non-RN), are more sensitive to acidic stimulation via transient receptor potential vanilloid type 1 (TRPV1) channels and exhibit a distinctive firing pattern. PARN were distinguished from Non-RN by fluorescent labeling (DiI) and studied by in vitro patch-clamp techniques in dorsal root ganglion neurons (DRG; T11-L2). Acid-induced currents or firing due to current injection or acidic superfusion were studied in 252 neurons, harvested from 12 Sprague-Dawley rats. PARN showed higher acid-induced currents than Non-RN (transient: 15.9 ± 5.1 vs. 0.4 ± 0.2* pA/pF at pH 6; sustained: 20.0 ± 4.5 vs. 6.2 ± 1.2* pA/pF at pH 5; * P < 0.05). The TRPV1 antagonist capsazepine inhibited sustained, amiloride-transient currents. Forty-eight percent of PARN were classified as tonic neurons (TN = sustained firing during current injection), and 52% were phasic (PN = transient firing). Non-RN were rarely tonic (15%), but more frequently phasic (85%), than PARN ( P < 0.001). TN were more frequently acid-sensitive than PN (50–70 vs. 2–20%, P < 0.01). Furthermore, renal PN were more frequently acid-sensitive than nonrenal PN (20 vs. 2%, P < 0.01). Confocal microscopy revealed innervation of renal vessels, tubules, and glomeruli by CGRP- and partly SP-positive fibers coexpressing TRPV1. Our data show that PARN are represented by a very distinct population of small-to-medium sized DRG neurons exhibiting more frequently tonic firing and TRPV1-mediated acid sensitivity. These very distinct DRG neurons might play a pivotal role in renal physiology and disease.

PAI-1 donor polymorphism influences long-term kidney graft survival

BACKGROUND

The type 1 plasminogen activator inhibitor (PAI-1) is involved in the development of fibrosis, and its intrarenal expression is increased in interstitial fibrosis and tubular atrophy (IFTA). Moreover, a 4G/5G polymorphism of the PAI-1 gene has been described associating 4G haplotype with higher PAI-1 plasma activity. We investigated the relationship between the donor and recipient PAI-1 polymorphism and kidney graft survival.

METHODS

The PAI-1 genotype was determined for both the 304 donors and the 337 corresponding recipients. In recipients, PAI-1 antigen levels were also determined. We compared 4G/4G donors versus donors with other genotypes.

RESULTS

Donor or recipient genotype did not influence the PAI-1 plasma level in recipients. Actuarial kidney graft survival was significantly reduced in the 4G/4G donor group (107 months versus 147.5 months, P = 0.013), while recipient PAI-1 genotype did not show any influence on graft survival. Moreover, graft loss due to IFTA proved significantly higher in the 4G/4G donor group (13% versus 6%, P = 0.03). Multivariate analysis showed that the significant independent variables associated with graft loss were the donor 4G/4G genotype, acute clinical rejection and donor age.

CONCLUSION

Our study suggests that donor PAI-1 polymorphism influences kidney graft survival and that the donor 4G/4G genotype is an independent risk factor for graft loss. Prospective studies are needed to confirm these results.

Rapamycin inhibits PAI-1 expression and reduces interstitial fibrosis and glomerulosclerosis in chronic allograft nephropathy

BACKGROUND

Chronic allograft nephropathy (CAN) is characterized by deposition of extracellular matrix (ECM) in all renal compartments. PAI-1 seems to play a pivotal role in ECM turnover in CAN. Rapamycin has been shown to improve long-term graft survival in patients with CAN. The aim of the study was to evaluate the molecular mechanisms underlying the beneficial effects of rapamycin on CAN progression at glomerular and tubulointerstitial level.

METHODS

After a biopsy-proven CAN diagnosis (T0), 18 patients on calcineurin inhibitors (CNI) were randomly assigned in a 2:1 ratio to continue CNI (6 patients) or to receive rapamycin (RAPA; 12 patients). After 2 years of treatment (T24), all patients underwent a second renal biopsy. Morphometric analysis was conducted at T0 and at T24. PAI-1 expression was evaluated at T0 and T24 by immunohistochemistry. We evaluated the effect of rapamycin on PAI-1 gene expression in cultured proximal tubular cells incubated with CD40L or thrombin, two potential CAN pathogenic mediators.

RESULTS

The RAPA group showed a significant regression of glomerulosclerotic lesions and only a 26% increase in interstitial fibrosis after 2 years compared to baseline, whereas the CNI group showed progression of glomerulosclerosis and 112% increase in fibrosis. Glomerular and tubulointerstitial PAI-1 expression was reduced compared to the baseline in the RAPA group, while they were unchanged in the CNI group. In vitro data showed that rapamycin significantly reduced PAI-1 gene expression induced by both CD40L and thrombin in proximal tubular epithelial cells.

CONCLUSIONS

These data suggest that rapamycin may modulate ECM deposition in CAN reducing PAI-1 expression.

The value of D-dimer in lung transplant recipients with bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) following lung transplantation is common and potentially devastating. Its exact cause is undefined, but multiple immune and nonimmune processes contribute to its pathogenesis. The diagnosis of BOS syndrome is based on clinical presentation of progressive decline in the lung functions together with appropriate pathological findings. Severe acute rejection and recurrent acute rejection have been shown to confer the greatest risk for obliterative bronchiolitis, signifying the central importance of alloimmunity in the disease process. BOS is associated with activation of the coagulation system, and is a major cause of lung allograft loss. The aim of the study was to determine if there is an association between D-dimer levels and functional exercise capacity in lung transplant recipients with BOS. This prospective group comparison study was conducted at a tertiary-care, university-affiliated medical center. The sample included 46 patients (29%) who underwent lung transplantation between January 1997 and May 2006 and had positive findings on screening for BOS. Blood samples were collected for measurement of plasma D-dimer levels by the rapid MiniQuant assay. Correlational analysis was used to determine the association of D-dimer levels with demographic clinical data, pulmonary function, and functional exercise capacity parameters, including the 6-min walk test and cardiopulmonary exercise testing. D-dimer levels were associated with FEV1 (r=-0.43, p=0.001), 6-min walk test (r=-0.53, p=0.04), and VO2/kg/min (r=-0.36, p=0.04). No correlations were noted between D-dimer levels and total lung capacity, diffusion capacity, and oxygen saturation. On multivariate logistic regression, only FEV1 was a significant predictor of BOS (OR 0.885, CI: 0.812-0.965). We conclude that in lung transplant recipients with BOS, D-dimer levels are highly associated with functional exercise capacity and may serve as a useful marker for noninvasive monitoring. Further coagulation assays are needed to complete our observations.

The interface between coagulation and immunity

Coagulation proteases are involved in generating fibrin after vascular injury (hemostasis) but they also have multiple other effects, many of which are mediated independently of fibrin generation, via interactions with specific cell membrane-expressed "protease activated receptors". In inflammation, this family of proteins has a complex influence, the facets of which are still incompletely understood, though a common feature in different models appears to be amplification of innate signals that are initially generated by pathogenic elements or, in the context of transplantation, ischemia or anti-graft antibodies, for instance. There is increasing evidence that these proteases may also have specific effects on cells involved in adaptive immunity and on cells that mediate chronic inflammation and fibrosis. Understanding whether these effects are relevant in the responses generated against transplanted organs is important, as it could lead ultimately to the development of novel ways to promote long-term graft survival.

Regulation of TGF-beta1/MAPK-mediated PAI-1 gene expression by the actin cytoskeleton in human mesangial cells

The importance of transforming growth factor-beta1 (TGF-beta1) in plasminogen activator inhibitor-1 (PAI-1) gene expression has been established, but the precise intracellular mechanisms are not fully understood. Our hypothesis is that the actin cytoskeleton is involved in TGF-beta1/MAPK-mediated PAI-1 expression in human mesangial cells. Examination of the distributions of actin filaments (F-actin), alpha-actinin, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) by immunofluorescence and immunoprecipitation revealed that ERK and JNK associate with alpha-actinin along F-actin and that TGF-beta1 stimulation promote the dissociation of ERK and JNK with F-actin. Disassembly of the actin cytoskeleton inhibited phosphorylation of ERK and JNK and modulated PAI-1 expression and promoter activity under both basal and TGF-beta1-stimulated conditions. Stabilizing actin prevented dephosphorylation of ERK and JNK. ERK and JNK inhibitors and overexpressed dominant negative mutants antagonized the ability of TGF-beta1 to increase PAI-1 expression and promoter activity. Disassembly of F-actin also inhibited AP-1 DNA binding activity as determined by electrophoretic mobility shift assay using AP-1 consensus oligonucleotides derived from human PAI-1 promoter. F-actin stabilization prevented loss of AP-1 DNA binding activity. Therefore, changes in actin cytoskeleton modulate the ability of TGF-beta1 to stimulate PAI-1 expression through a mechanism dependent on the activation of MAPK/AP-1 pathways.

The aetiology and pathogenesis of chronic allograft nephropathy

Renal transplantation is the ultimate form of renal replacement therapy, and is the treatment of choice for many patients with end-stage renal failure. The advent of calcineurin inhibitor based immunosuppression resulted in the 1-year renal allograft failure rate dropping from around 50% twenty years ago to less than 10% in more recent times. Despite a massive improvement in renal allograft survival in the first year following transplantation 10-year graft survival can be as low as 50%. Chronic allograft nephropathy (CAN) is recognised as the main cause of renal allograft failure following the first year after transplantation. The diagnosis of CAN can only be made histologically. Typically biopsy specimens in grafts with CAN demonstrate an overall fibrotic appearance effecting the vascular endothelium, renal tubules, interstitium, and glomerulus. The risk factors for CAN are divided into alloimmune and alloimmune independent. Alloimmune dependent factors include acute cellular rejection, severity of rejection, subclinical rejection and HLA mismatch. Alloimmune independent factors such as delayed graft function, donor age, Cytomegalovirus infection, donor/recipient co-morbidity and of course calcineurin inhibitor toxicity are important in the development of CAN. The pathogenesis of CAN is complex, multifactorial, and unfortunately incompletely understood. There are a number of pivotal steps in the initiation and propagation of the fibrosis seen in biopsy specimens from kidneys with CAN. Endothelial activation in response to one or more of the aforementioned risk factors stimulates leukocyte activation and recruitment. Recruited leukocytes subsequently infiltrate through the endothelium and induce key effector cells to secrete excessive and abnormal extracellular matrix (ECM). Enhanced deposition of ECM is a histological hallmark of CAN. This paper aims to present a concise yet accurate and up-to-date review of the literature concerning the aetiological factors and pathological processes which are present in the generation of CAN.

CD40L proinflammatory and profibrotic effects on proximal tubular epithelial cells: role of NF-kappaB and lyn

Chronic allograft nephropathy (CAN) is the main cause of renal graft loss, but its pathogenic mechanisms are still unclear. Immune system activation has been suggested as a key event in the development of CAN. CD40 is a co-stimulatory protein whose expression is upregulated in proximal tubular epithelial cells (PTEC) in acute rejection. This receptor interacts with CD40L, expressed by activated T cells. CD40L induces the production by PTEC of different proinflammatory cytokines, but very little is known of its profibrotic effects. The aim of this study was to investigate the effect of CD40/CD40L interaction on PTEC expression of plasminogen activator inhibitor-1 (PAI-1), a powerful profibrotic mediator, and monocyte chemoattractant protein-1 (MCP-1), a proinflammatory cytokine, and to investigate the signaling pathways that lead to these effects. Soluble CD40L induced a time-dependent increase in both PAI-1 and MCP-1 gene expression and protein production in PTEC. CD40 cross-linking on PTEC caused TNF-R-associated factors 2 and 6 membrane translocation. This event led to NF-kappaB activation, through the NF-kappaB-inducing kinase, and to a significant increase in the phosphorylation of lyn, a src-related tyrosine kinase. Lyn, upon phosphorylation, became strictly associated with caveolin-1, a scaffolding protein enriched in caveolae. Lyn inhibition did not have any effect on CD40L-induced NF-kappaB activation and MCP-1 expression but abolished PAI-1 induction. On the contrary, NF-kappaB inhibition significantly reduced only MCP-1 expression. In conclusion, CD40L could play a key role in the pathogenesis of CAN through PAI-1 induction. CD40L profibrotic and proinflammatory effects are mediated by different signaling pathways, suggesting that drugs that inhibit inflammation may not be equally effective in reducing fibrosis.

Differential expression of tissue factor (TF) in calcineurin inhibitor-induced nephrotoxicity and rejection—implications for development of a possible diagnostic marker

Deposition of fibrin in the form of fibrinoid necrosis is a common feature of severe acute renal allograft rejection. The role of the coagulation system and its initiator tissue factor (TF) during this process is, however, still poorly understood. In this study, we analyzed the expression of TF in 88 renal transplants afflicted with different forms of rejection and calcineurin inhibitor-induced nephrotoxicity, to see whether there was differential expression of this protein. TF immunoreactivity was evaluated semiquantitatively in six different renal structures: the podocytes, Bowman epithelium, the endothelium of the glomeruli, the brush border of tubular cells, the thin ascending loop of Henle, and small arteries/arterioles. The TF expression of normal renal tissue (n=6) was restricted to the glomerular podocytes and Bowman epithelium, and to some extent the ascending loop of Henle. Renal allografts undergoing acute rejection (AR) of grades I-III, (n=13, n=17 and n=12, respectively) did not show any altered TF expression in the glomeruli or vascular endothelium. In the ascending loop of Henle, a reduced expression could be seen (ARI, p=0.015; and ARII, p=0.043). TF staining of the brush border of renal transplants undergoing acute cyclosporin A (CsA) nephrotoxicity (n=18) was significantly higher than in normal kidneys (p=0.0003), as well as in transplants undergoing various degrees of acute rejection (ARI, p=0.027; ARII, p=0.0012; and ARIII, p=0.0001). Tubular brush border-expressed TF was also evident in 10 of 15 allografts suffering from chronic CsA nephrotoxicity, compared to 4 out of 13 cases with chronic allograft vasculopathy (CAV), but the increase was not statistically significant relative to normal kidneys. The majority of the grafts afflicted with either of the two chronic conditions displayed a TF-positive arterial endothelium (CAV, p=0.0034; and chronic CsA nephrotoxicity, p=0.0026) relative to controls. In conclusion, these results indicate that vascular TF expression is not altered during acute rejection, but may be of importance in chronic allograft nephropathy. Furthermore, TF immunoreactivity in the tubular brush border may be specific to acute CsA nephrotoxicity and might be used as a biomarker for this condition. Further studies are required to evaluate the possible role of brush border-expressed TF in the pathogenesis of CsA nephrotoxicity.

Thrombin stimulates proinflammatory and proliferative responses in primary cultures of human proximal tubule cells

BACKGROUND

Fibrin deposition is frequently observed within the tubulointerstitium in various forms of chronic renal disease. This suggests the presence of active components of the coagulation pathway, which may contribute to the progressive deterioration in renal function. The aim of this study was to investigate the proinflammatory and fibroproliferative effects of the coagulation protease thrombin on human proximal tubular cells (PTC) in culture.

METHODS

Primary cultures of PTC were established from normal kidney tissue and grown under serum-free conditions with or without thrombin or the protease-activated receptor (PAR) activating peptides TFLLRN-NH(2), SLIGKV-NH(2), and SFLLRN-NH(2) (100 to 400 micromol/L). DNA synthesis (thymidine incorporation), intracellular Ca(2+) mobilization (fura-2 fluorimetry), fibronectin secretion [enzyme-linked immunosorbent assay (ELISA), immunoblotting], monocyte chemoattractant protein-1 (MCP-1) secretion (ELISA), and transforming growth factor-beta1 (TGF-beta1) secretion (ELISA) were measured. Reverse transcription-polymerase chain reaction (RT-PCR) was used to assess PAR mRNA expression in these cells.

RESULTS

Thrombin enhanced DNA synthesis, fibronectin secretion, MCP-1 secretion, and TGF-beta1 secretion in a concentration-dependent manner. Cell injury [lactate dehydrogenase (LDH) release] and cellular protein levels were unaffected. RT-PCR showed that cultures of PTC expressed mRNA transcripts for the thrombin receptors PAR-1 and PAR-3, but not PAR-4. Thrombin and each of the PAR activating peptides enhanced intracellular calcium mobilization. However, the other effects of thrombin were only fully reproduced by the PAR-2-specific peptide, SLIGKV-NH(2), only partially by SFLLRN-NH(2), (a PAR-1 peptide that can activate PAR-2), and not at all by the PAR-1-specific peptide, TFLLRN-NH(2). Thrombin-induced DNA synthesis, fibronectin, and MCP-1 secretion were unaffected by a TGF-beta neutralizing antibody, the matrix metalloproteinase (MMP) inhibitor, GM6001 and the epidermal growth factor (EGF) receptor kinase inhibitor AG1478.

CONCLUSION

Thrombin initiates both proinflammatory and fibroproliferative responses in human PTC. These responses which are dependent on its protease activity appear not to be mediated by PAR-1 activation, the autocrine action of thrombin-induced TGF-beta1 secretion, MMP activation, or EGF receptor transactivation. The proinflammatory and fibroproliferative actions of thrombin on human PTC may help explain the extent of tubulointerstitial fibrosis observed in kidney diseases where fibrin deposition is evident.

jun-N-terminal kinase regulates thrombin-induced PAI-1 gene expression in proximal tubular epithelial cells

BACKGROUND

Interstitial activation of the coagulation cascade is a common finding in acute and chronic tubulointerstitial damage. We previously demonstrated that thrombin may induce proximal tubular epithelial cells (PTEC) proliferation and regulate, through plasminogen activator inhibitor (PAI)-1 and urokinase-type plasminogen activator (u-PA), their profibrotic activity. The signaling pathways leading to these effects are still unknown. The PAI-1 promoter contains several activator protein-1 (AP-1) consensus sequences. AP-1 activation is induced by different agonists through jun-N-terminal kinase (JNK). Thus, we investigated the role of the JNK-AP-1 axis on thrombin-induced PAI-1 and u-PA expression in immortalized PTEC and its modulation by PKC and src, two key signaling enzymes.

METHODS

JNK and src activation was investigated by Western blotting, PAR-1 cellular surface expression by flow cytometry, PAI-1 and u-PA gene expression by Northern blotting, AP-1 activation by transient transfection, and DNA synthesis by (3)H-thymidine uptake.

RESULTS

Thrombin and PMA induced a time-dependent increase of JNK phosphorylation in immortalized PTEC that was inhibited by PKC down-regulation. Both thrombin and PMA caused AP-1 activation, significantly reduced by src inhibition. Phorbol 12-myristate 13-acetate (PMA), indeed, induced an increase in src phosphorylation. Both PMA- and thrombin-stimulated PAI-1 gene expression was abolished by JNK, protein kinase C (PKC), and src inhibition, and this effect was regulated at the trascriptional level. PKC, but not src or JNK inhibition, abolished thrombin-elicited u-PA expression. Finally, JNK inhibition did not influence thrombin-induced proliferation.

CONCLUSION

Our data suggest that thrombin activates the JNK-AP-1 axis in a PKC- and src-dependent manner in PTEC. This axis, necessary for thrombin-stimulated PAI-1 expression, but not for its fibrinolytic and regenerative effect, may represent a therapeutic target in acute and chronic tubulointerstitial damage.

Glycoxidation and inflammation in renal failure patients

BACKGROUND

Inflammation is common in patients with chronic renal failure and has been associated with the increased risk for cardiovascular disease (CVD) in this condition. Advanced glycoxidation end products (AGEs) are among the factors implicated in the inflammatory state of chronic renal failure.

METHODS

In a cross-sectional study of 189 dialysis patients, we measured circulating levels of C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-alpha), vascular adhesion molecule-1 (VCAM-1), vascular endothelial growth factor (VEGF), and plasminogen activator inhibitor-1 (PAI-1) to test for possible relationships between them and serum AGE levels. In addition, these parameters were measured in a subgroup of 18 patients with chronic renal failure randomly assigned to a 4-week diet, either low (L-AGE) or high (H-AGE) in AGE content. AGEs were measured by means of a monoclonal antibody against epsilonN-carboxymethyllysine.

RESULTS

At baseline, serum AGE levels, as well as those for CRP, TNF-alpha, VCAM-1, and VEGF, were markedly elevated, although no correlation was found between AGE levels and the other markers. Dietary AGE modulation resulted in a significant decrease in levels of serum AGEs, CRP, and PAI-1 in the L-AGE group (approximately 35%, 44%, and 17%, respectively; P < 0.03), whereas only serum AGE levels increased significantly in the H-AGE group. VCAM-1 and TNF-alpha levels, although similar at baseline, became significantly lower in patients on an L-AGE compared with H-AGE diet (P < 0.05) at the end of the study.

CONCLUSION

Data from the interventional phase of the study suggest that AGEs have a role in the initiation of the inflammatory state of chronic renal failure, which eventually leads to increased CVD. This finding opens the possibility for using anti-AGE strategies in the prevention and treatment of CVD in patients with chronic renal failure.

Nontransgenic hyperexpression of a complement regulator in donor kidney modulates transplant ischemia/reperfusion damage, acute rejection, and chronic nephropathy

Complement activation during ischemia and reperfusion contributes to the development of tissue injury with severe negative impact on outcomes in transplantation. To counter the effect of complement, we present a strategy to deliver a novel complement regulator stabilized on cell surfaces within donor organs. The membrane-bound complement regulator is able to inhibit complement activation when the donor organ is revascularized and exposed to host-circulating complement. Application of this construct to donor kidneys protected transplanted tissues from ischemia/reperfusion injury and reduced the deposition of activated complement and histological signs of damage under conditions in which a nontargeted control construct was ineffective. Treatment of donor organs in this way improved graft performance in the short and long term. An analysis of the immune response in allograft recipients showed that reducing graft damage at the time of transplantation through complement regulation also modulated the alloresponse. Additionally, the results of perfusion studies with human kidneys demonstrated the feasibility of targeting endothelial and epithelial surfaces with this construct, to allow investigation in clinical transplantation.

Protease-activated receptor-2 expression in IgA nephropathy: a potential role in the pathogenesis of interstitial fibrosis

An increasing body of evidence suggests that proteases may play a key role in the pathogenesis of tissue fibrosis. Protease-activated receptor-2 (PAR-2) is cleaved and activated by trypsin-like proteolytic enzymes, including tryptase and activated coagulation factor X (FXa). Both these soluble mediators have been demonstrated, directly or indirectly, at the interstitial level in progressive renal diseases, including IgA nephropathy (IgAN). PAR-2 mRNA and protein levels were investigated by RT-PCR and immunohistochemistry, respectively, in 17 biopsies from IgAN patients and 10 normal kidneys. PAR-2 expression was also evaluated, by RT-PCR and western blotting, in cultured human mesangial and proximal tubular cells. Finally, gene expression of plasminogen activator inhibitor-1 (PAI-1) and TGF-beta, two powerful fibrogenic factors, was evaluated in FXa-, trypsin-, and PAR-2 activating peptide-stimulated human proximal tubular cells by Northern blot. In normal kidneys, PAR-2 gene expression was barely detectable, whereas in IgAN biopsies the mRNA levels for this protease receptor were strikingly increased and directly correlated with the extent of interstitial fibrosis. Immunohistochemical staining demonstrated that PAR-2 protein expression in IgAN biopsies was mainly localized in the proximal tubuli and within the interstitial infiltrate. Proximal tubular cells in culture expressed PAR-2. Activation of this receptor by FXa in tubular cells induced a striking increase in intracellular calcium concentration. In addition, incubation of both cell lines with trypsin, FXa, or PAR-2 activating peptide caused a marked upregulation of PAI-1 gene expression that was not counterbalanced by an increased expression of plasminogen activators. Finally, PAR-2 activation induced a significant upregulation of TGF-beta gene and protein expression in both mesangial and tubular cells. On the basis of our data, we can suggest that PAR-2 expressed by renal resident cells and activated by either mast cell tryptase or FXa may induce extracellular matrix deposition modifying the PAI-1/PA balance and inducing TGF-beta expression. These molecular mechanisms may underlie interstitial fibrosis in IgAN.

Tissue factor pathway inhibitor production by human proximal tubular epithelial cells in culture

Fibrin deposition in the peritubular capillaries and along the tubular basement membrane is commonly observed in several renal diseases and suggests the involvement of blood coagulation in tubulointerstitial damage. It has been demonstrated that tissue factor (TF) is present in tubular epithelial cells of animal models of nephritis. Tissue factor pathway inhibitor (TFPI) regulates the extrinsic pathway of blood coagulation through its ability to inhibit TF activity and it is now thought to be produced mainly by the vascular endothelial cells. We examined whether human proximal tubular epithelial cells (PTEC) could produce TFPI and attempted to clarify the regulatory factors affecting TFPI production. Cultured human PTEC were used. The procoagulant activity (PCA) in PTEC lysate was quantified by measurement of the one-stage recalcification time. TFPI in the cell supernatants was measured by ELISA. The mRNA of TF and TFPI in PTEC was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). PCA which is compatible with TF activity was present in the PTEC lysate. TF mRNA and TFPI mRNA were detected in PTEC. The amount of TFPI increased over time in the cell supernatants. Immnoblot analysis revealed 40 kD protein of TFPI, and TFPI antigen was demonstrated in PTEC by immunofluorescence. The concentration of TFPI was significantly increased following incubation with thrombin and heparin in a dose- and time-dependent manner, although the amount of TFPI mRNA was not changed. Our study showed that TFPI is produced in cultured PTEC and added one more cell type that produced TFPI other than endothelial cells. Thrombin and heparin stimulated TFPI secretion from PTEC. TFPI of PTEC may act against generation of thrombin and tubular fibrin formation induced by tissue factor activation. The augmentation of TFPI secretion by heparin may play an important role in the modulation of anticoagulant properties of PTEC.

Plasma fibrinolytic capacity in renal transplant recipients: effect of steroid-free immunosuppression therapy

BACKGROUND

Cardiovascular disease is the most common cause of death among renal transplant recipients (RTRs). Impaired fibrinolytic capacity caused by an increase in plasminogen activator inhibitor type 1 (PAI-1) levels is involved in the onset of atherosclerosis and thrombotic complications. Long-term steroid treatment may induce arterial hypertension and metabolic and prothrombotic changes (including up-regulation of PAI-1 synthesis), which increase the cardiovascular risk. We evaluated plasma fibrinolytic behavior in two groups of RTRs treated with different immunosuppressive regimens.

METHODS

Twenty-seven RTRs were randomized to receive long-term (17 patients) or perioperative short-term (10 patients) steroids in addition to immunosuppression with cyclosporine A plus everolimus (Certican; Novartis, Basel, Switzerland) (7 patients) or FK506 plus mycophenolate mofetil (20 patients). In each patient, fibrinolytic capacity was studied with the 20-min venous occlusion test 1 and 6 months after transplantation. The following were assayed: euglobulin lysis time, tissue-type plasminogen activator antigen, and PAI-1 antigen and activity.

RESULTS

One month after transplantation, a severe impairment of fibrinolytic capacity, mainly caused by an increase in PAI-1 antigen and activity levels, was seen in patients with and without steroid treatment. Six months after transplantation, an improvement in fibrinolytic potential as the result of a decrease in PAI-1 levels was observed only in patients without steroid therapy. None of the steroid-treated patients demonstrated PAI-1 values correlating with body mass index, blood pressure, and metabolic parameters, thus confirming the effect of exogenous factors on PAI-1 expression. Moreover, all patients revealed a slight impairment of stimulated endothelial tissue-type plasminogen activator release, regardless of any steroid treatment, which was probably attributable to calcineurin inhibitor-induced endothelial dysfunction.

CONCLUSIONS

Our study suggests that steroid-free immunosuppression is associated with a better fibrinolytic capacity in RTRs. This finding may contribute toward reducing the risk of cardiovascular events.

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.

Protease-activated receptor 1 and plasminogen activator inhibitor 1 expression in chronic allograft nephropathy: the role of coagulation and fibrinolysis in renal graft fibrosis

BACKGROUND

Chronic allograft nephropathy (CAN), the major cause of renal graft failure, frequently displays extensive interstitial fibrin deposition. Little is known in regard to the cause of the altered coagulation/fibrinolysis balance and its relevance in the pathogenesis of CAN. Thrombin, present within the fibrin clots, can interact with a specific receptor, protease-activated receptor 1 (PAR-1), and modulate a variety of cell functions. On the other hand, the derangement of the fibrinolytic system may directly affect extracellular matrix (ECM) degradation.

METHODS

In the present study, we investigated, by in situ hybridization, PAR-1 gene expression and the mRNA levels for tissue factor and plasminogen activator inhibitor 1 (PAI-1), two key regulatory molecules of coagulation and fibrinolysis, in 16 CAN biopsies and in 10 normal human kidney grafts. The thrombin-induced transforming growth factor beta (TGF-beta) gene and protein expression in proximal tubular cells (PTC) was investigated by Northern blotting and ELISA, respectively.

RESULTS

Fibrin deposits, absent in normal grafts, were observed in the interstitial space and arterial wall of CAN. Tissue factor gene expression was not increased either at the vascular or at the interstitial level in CAN. On the contrary, PAI-1 gene expression, barely detectable in control tissue, was strikingly increased in CAN, with a distribution resembling the pattern of fibrin deposition. Note that PAI-1 gene expression was directly correlated with the degree of interstitial fibrosis. In addition, fibrin deposits were strictly associated with a marked increase of PAR-1 gene expression in endothelial cells and PTC. The tubular expression of PAR-1 was significantly higher in Banff grade II-III than in grade I. In vitro, incubation of PTC with thrombin caused a significant up-regulation of TGF-beta gene expression, followed by an increased TGF-beta release into the supernatant. Interestingly, urine from CAN patients contained significantly higher levels of TGF-beta.

CONCLUSIONS

Fibrin deposits in CAN may result from the increased expression of PAI-1 and the subsequent inhibition of fibrinolysis. The reduced fibrinolysis may cause, in turn, a decreased ECM turnover. Finally, thrombin, preserved in the active form within the fibrin clots, may interact with PAR-1 highly expressed on PTC and induce an up-regulation of ECM deposition in a TGF-beta-dependent manner.

Prognostic value of plasminogen activator inhibitor type 1 mRNA in microdissected glomeruli from transplanted kidneys

BACKGROUND

Plasminogen activator inhibitor type 1 (PAI-1) exerts antifibrinolytic and profibrotic activities. Inside the glomerulus, PAI-1 is mainly synthesized by mesangial cells. We hypothesized that thrombin, via its receptor protease activated receptor type 1 (PAR-1), present on the membrane of glomerular cells, is an important mediator of PAI-1 synthesis.

METHODS

Using the technique of Peten et al., we microdissected the glomeruli of 23 kidney transplanted patients admitted in our department from 1993 to 1997, and we followed-up these patients for up to 5 years, with sometimes iterative renal biopsies. With this technique, we also microdissected the glomeruli of three patients who have had a nephrectomy for cancer (control patients). We investigated mRNA expression of the PAI-1, the thrombin receptor PAR-1, the alpha2 chain of type IV (alpha2 IV) collagen, and of a housekeeping gene (cyclophilin) by reverse transcription-polymerase chain reaction. The results were correlated with the renal function and the histological findings classified into acute rejection (9 biopsies), chronic rejection (22 biopsies), or normal (8 biopsies).

RESULTS

A significant up-regulation of PAI-1 and alpha2 IV collagen mRNA was observed in acute rejection (P<0.05) when compared to normal kidneys. A positive correlation exists between alpha2 IV collagen mRNA level and the degree of cellular infiltration. A negative correlation was found between the level of mRNA of PAR-1 and the degree of vascular thrombosis (P=0.005) and glomerulosclerosis (P=0.04). A positive correlation was found between the degradation of renal function and the mRNA level of PAI-1 at the time of the renal biopsy (P<0.05).

CONCLUSIONS

These results suggest that glomerular PAI-1 mRNA may be predictive of the long-term renal graft function.

Initial inhibition of tissue factor signalling reduces chronic vascular changes in isogenic rat aortic transplants

Vascular changes are considered the major histopathological indicator of chronic allograft dysfunction. These changes are characterized by intimal thickening caused by accumulation of primarily smooth muscle cells. Contributing factors may be of both immunological and nonimmunological origin. Cold ischemia has been shown to trigger intimal proliferation in the absence of alloantigen in an isogenic rat aortic transplant model. We have used this model to investigate the impact of inhibition of tissue factor (TF) signalling on the progression of intimal thickening. Group 1 was treated with recombinant FVIIa inhibited in its active site (rFVIIai), and group 2 served as untreated controls. At 8 weeks the intimal area was measured with image analysis. Medial areas and the proportion of medial necrosis were determined. Animals treated with rFVIIai showed significantly less intimal thickening compared with controls: median 0.147 vs. 0.256 mm2, respectively (p = 0.008). A positive correlation between intimal hyperplasia and medial necrosis (r(s) = 0.79, p = 0.01), as well as adventitial inflammation (r(s) = 0.83, p = 0.009), was found. TF mRNA was not detected in the neointima at 8 weeks, as determined by in situ hybridization. We conclude that active site inhibited FVIIa (rFVIIai) given prior to and directly after implantation of aortic transplants significantly reduces intimal hyperplasia caused by nonimmunological factors in this model.

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.

Regenerative and proinflammatory effects of thrombin on human proximal tubular cells

Interstitial fibrin deposition is a common histologic feature of tubulointerstitial diseases, which suggests that the coagulation system is activated. Thrombin, generated during the activation of the coagulation cascade, is a powerful activating factor for different cell types. Although proximal tubular cells are potential targets for this coagulation factor, no information is available on the effect of thrombin on these cells. Thus, the expression of protease-activated receptor-1 (PAR-1), the main thrombin receptor, was investigated in human proximal tubular cells (hPTC) in vivo and in vitro. A diffuse expression of PAR-1 was observed by immunohistochemistry along the basolateral membrane of PTC in normal human kidney. This observation was confirmed in vitro in cultured hPTC. Because tubular damage and monocyte infiltration are two hallmarks of tubulointerstitial injury, the effect of thrombin on DNA synthesis and monocyte chemotactic peptide-1 (MCP-1) gene and protein expression was evaluated in cultured hPTC. Thrombin induced a significant and dose-dependent increase in thymidine uptake and a striking upregulation of MCP-1 mRNA expression and protein release into the supernatant. Although PAR-1 is a G protein-coupled receptor, its activation in hPTC, as in other cell systems, resulted in a transient increase in cellular levels of tyrosine-phosphorylated proteins. An increased level of tyrosine-phosphorylated c-src suggested the activation of this cytoplasmic tyrosine kinase in response to thrombin and its potential role in thrombin-induced protein-tyrosine phosphorylation. Interestingly, thrombin-induced DNA synthesis and MCP-1 gene expression were completely blocked by genistein, a specific tyrosine kinase inhibitor, but not by its inactive analogue daidzein, demonstrating a central role for tyrosine kinase activation in the thrombin effects on hPTC. Moreover, the specific src inhibitor PP1 abolished the thrombin effect on DNA synthesis. In conclusion, thrombin might represent a powerful regenerative and proinflammatory stimulus for hPTC in acute and chronic tubulointerstitial diseases.

Improved fibrinolytic capacity after withdrawal of steroid immunosuppression in renal transplant recipients

BACKGROUND

Long-term steroid immunosuppression has been associated with the prothrombotic state observed in renal transplant (RT) patients, in whom both hypercoagulability due to an increase of von Willebrand factor/factor VIII complex, and impaired fibrinolysis due to PAI-1 excess have been demonstrated. Our aim was to investigate the effect of steroid withdrawal on fibrinolytic capacity in a group of RT patients.

METHODS

The fibrinolytic study was performed in 28 RT patients under stable immunosuppression therapy with cyclosporine, azathioprine, and methylprednisolone; only 12 of these patients could repeat the study 6 months after steroid withdrawal. Euglobulin lysis time (ELT), tissue plasminogen activator activity (t-PA:act) and antigen (t-PA:Ag), PAI-1 activity (PAI-1:act), and antigen (PAI-1:Ag) were assayed on blood samples drawn before and 20 min after the venous occlusion test (VO).

RESULTS

An hypofibrinolytic state due to a significant increase in PAI-1 levels was confirmed in RT patients receiving triple immunosuppression therapy. RT patient who stayed off steroids showed a significant shortening of ELT both before (P=0.01) and 20' after VO (P=0.005) at the 6-month control. Moreover, after steroid withdrawal, PAI-1:Ag levels decreased significantly (P=0.002) and normalized; in a similar manner PAI-1:act levels also showed a significant decrease both before (P=0.001), and after VO (P=0.0001). The prevalence of RT patients with impaired fibrinolytic capacity was as high as 83.3% during steroid treatment, and dropped to 16.7% after steroid withdrawal.

CONCLUSIONS

Our findings confirm that steroid withdrawal may normalize impaired fibrinolytic capacity in RT patients; this improvement may further contribute to reduce the thrombotic risk associated with renal transplantation.

Angiotensin IV stimulates plasminogen activator inhibitor-1 expression in proximal tubular epithelial cells

BACKGROUND

Angiotensin II (Ang II) has been shown to be implicated in the development of renal fibrosis in several forms of chronic glomerulonephritides, but the precise mechanisms of its effects remain unclear. It has recently been reported that Ang II stimulates the expression of plasminogen activator inhibitor-1 (PAI-1) in several cell lines. PAI-1 is a major physiological inhibitor of the plasminogen activator/plasmin system, a key regulator of fibrinolysis and extracellular matrix (ECM) turnover. PAI-1 induction by Ang II in endothelial cells seems to be mediated by Ang IV via a receptor that is different from Ang II type 1 and 2 receptors (AT1 and AT2).

METHODS

In this study, we sought to evaluate the effects of Ang IV on PAI-1 gene and protein expression in a well-characterized and immortalized human proximal tubular cell line (HK2) by Northern blot and enzyme-linked immunosorbent assay.

RESULTS

Ang IV stimulated PAI-1 mRNA expression, whereas it did not induce a significant increase in tritiated thymidine uptake after 24 hours of incubation. This effect was dose and time dependent. Ang IV (10 nM) induced a 7.8 +/- 3.3-fold increase in PAI-1 mRNA expression. The PAI-1 antigen level was significantly higher in conditioned media and the ECM of cells treated with Ang II and Ang IV than in control cells (both P < 0.02). Although Ang II induced a 4.2 +/- 2. 1-fold increase in PAI-1 mRNA expression, its effect underwent a dose-dependent reduction when amastatin, a potent inhibitor of the endopeptidases that catalyzes the conversion of Ang II to Ang IV, was added. In contrast, amastatin was not able to prevent the expression of PAI-1 mRNA induced by Ang IV. Finally, pretreatment of HK2 cells with losartan and N-Nicotinoyl-Tyr-N3-(Nalpha-CBZ-Arg)-Lys-His-Pro-Ile, the specific antagonists of AT1 and AT2 receptors, failed to modify PAI-1 mRNA expression as induced by Ang II.

CONCLUSIONS

Our results demonstrate that Ang II stimulates PAI-1 mRNA expression and the production of its protein in human proximal tubular cells. This is mainly-if not exclusively-due to Ang IV, which acts on a receptor that is different than AT1 or AT2. Therefore, it can be hypothesized that the induction of PAI-1 by Ang IV may be implicated in the pathogenesis of renal interstitial fibrosis in several forms of chronic glomerulonephritides.