Bleomycin-induced pulmonary fibrosis in transgenic mice that either lack or overexpress the murine plasminogen activator inhibitor-1 gene

Elevated levels of plasminogen activator inhibitor-1 in pulmonary edema fluid are associated with mortality in acute lung injury

The alveolar fibrinolytic system is altered in acute lung injury (ALI). Levels of the fibrinolytic protease inhibitor, plasminogen activator inhibitor-1 (PAI-1), are too low in bronchoalveolar lavage to address its prognostic significance. This study was performed to assess whether PAI-1 antigen in undiluted pulmonary edema fluid levels can identify patients with ALI and predict their outcome. PAI-1 antigen levels in both plasma and edema fluid were higher in ALI compared with hydrostatic edema, and edema fluid PAI-1 values identified those with ALI with high sensitivity and specificity. Both the high plasma and edema fluid PAI-1 antigen values were associated with a higher mortality rate and fewer days of unassisted ventilation in patients with ALI. Differences in PAI-1 activity were concordant with levels of PAI-1 antigen. Although the fibrin-derived alveolar D-dimer levels were strikingly similar in both groups, ALI patients had a higher relative proportion of D-monomer. In conclusion, PAI-1 levels in edema fluid and plasma identify those with ALI that have a poor prognosis. The data indicate that fibrin turnover in early ALI is a consequence of a rapid fibrinogen influx and fractional fibrinolytic inhibition.

The upregulation of type I plasminogen activator inhibitor in oral submucous fibrosis

Type I plasminogen activator inhibitor (PAI-1) is a 50 kDa glycoprotein belonging to the serine protease superfamily. PAI-1 is consistently and dramatically upregulated in a variety of fibrotic diseases. The aim of this study was to compare PAI-1 expression in normal human buccal mucosa and oral submucous fibrosis (OSF) specimens and further explore the potential mechanism that may lead to induced PAI-1 expression. Twenty-five OSF specimens and six normal buccal mucosa were examined by immunohistochemistry. The activity of PAI-1 from cells cultured from OSF and normal buccal mucosa were assayed using reverse-transcriptase polymerase chain reaction (RT-PCR) and Western blots. PAI-1 expression was significantly higher in OSF specimens and expressed mainly by fibroblasts, endothelial cells, and inflammatory cells. In addition, OSF exhibited higher PAI-1 expression than normal buccal mucosa fibroblast (BMF) both in mRNA and protein levels. To verify whether arecoline, a major areca nut alkaloid, could affect PAI-1 expression by human BMFs, RT-PCR and Western blots were used. The results demonstrated highly elevated PAI-1 mRNA and protein expression in normal human BMFs stimulated by arecoline. Taken together, these results suggest that PAI-1 expression is significantly upregulated in OSF tissues from areca quid chewers, and arecoline may be responsible for the enhanced PAI-1 expression in vivo.

Plasminogen activator inhibitor-1 is a significant determinant of renal injury in experimental crescentic glomerulonephritis

Crescentic glomerulonephritis is characterized by glomerular fibrin deposition, and experimental crescentic glomerulonephritis has been shown to be fibrin-dependent. Net fibrin deposition is a balance between activation of the coagulation system causing glomerular fibrin deposition and fibrin removal by the plasminogen-plasmin (fibrinolytic) system. Plasminogen activator inhibitor-1 (PAI-1) inhibits fibrinolysis by inhibiting plasminogen activators and has effects on leukocyte recruitment and matrix deposition. To test the hypothesis that the presence of PAI-1 and its levels were a determinant of injury in crescentic glomerulonephritis, accelerated anti-glomerular basement membrane glomerulonephritis was induced in mice genetically deficient in PAI-1 (PAI-1 -/-), PAI-1 heterozygotes (PAI-1 +/-), and mice engineered to overexpress PAI-1 (PAI-1 tg). Compared with strain-matched genetically normal animals, PAI-1 -/- mice with glomerulonephritis developed fewer glomerular crescents, less glomerular fibrin deposition, fewer infiltrating leukocytes, and less renal collagen accumulation at day 14 of disease. The reduction in disease persisted at day 28, when injury had become more established. In contrast, mice overexpressing the PAI-1 gene (PAI-1 tg), that have basal plasma and renal PAI-1 levels several times, normal developed increased glomerular crescent formation, more glomerular fibrin deposition, increased numbers of infiltrating leukocytes, and more renal collagen at both time points. These studies demonstrate that PAI-1 is a determinant of glomerular fibrin deposition and renal injury in crescentic glomerulonephritis.

Mapping of a conformational epitope on plasminogen activator inhibitor-1 by random mutagenesis. Implications for serpin function

The mechanism for the conversion of plasminogen activator inhibitor-1 (PAI-1) from the active to the latent conformation is not well understood. Recently, a monoclonal antibody, 33B8, was described that rapidly converts PAI-1 to the latent conformation (Verhamme, I., Kvassman, J. O., Day, D., Debrock, S., Vleugels, N., Declerck, P. J., and Shore, J. D. (1999) J. Biol. Chem. 274, 17511-17517). In an attempt to understand this interaction, and more broadly to understand the mechanism of the natural transition of PAI-1 to the latent conformation, we have used random mutagenesis to identify the 33B8 epitope in PAI-1. This site involves at least 8 amino acids scattered over more than two-thirds of the linear sequence that form a compact epitope on the PAI-1 three-dimensional structure. Surface plasmon resonance studies indicate a high affinity interaction between latent PAI-1 and 33B8 that is approximately 100-fold higher than comparable binding to active PAI-1. Structural modeling results together with surface plasmon resonance analysis of parental and site-directed PAI-1 mutants with disrupted 33B8 binding suggest the existence of a specific PAI-1 intermediate structure that is stabilized by 33B8 binding. These analyses strongly suggest that this intermediate form of PAI-1 has a partial insertion of the reactive center loop into beta-sheet A, and together, these data have significant implications for the general serpin mechanism of proteinase inhibition.

Urokinase receptor deficiency accelerates renal fibrosis in obstructive nephropathy

The urokinase cellular receptor (uPAR) recognizes the N-terminal growth factor domain of urokinase-type plasminogen activator (uPA) and is expressed by several cell types. The present study was designed to test the hypothesis that uPAR regulates the renal fibrogenic response to chronic injury. Groups of uPAR wild-type (+/+) and deficient (-/-) mice were investigated between 3 and 14 d after unilateral ureteral obstruction (UUO) or sham surgery. Not detected in normal kidneys, uPAR mRNA was expressed in response to UUO in the +/+ mice. By in situ hybridization, uPAR mRNA transcripts were detected in renal tubules and interstitial cells of the obstructed uPAR+/+ kidneys. The severity of renal fibrosis, based on the measurement of total collagen (13.5 +/- 1.5 versus 9.8 +/- 1.0 microg/mg kidney on day 14; -/- versus +/+) and interstitial area stained by Masson trichrome (22 +/- 4% versus 14 +/- 3% on day 14; -/- versus +/+) was significantly greater in the uPAR-/- mice. In the absence of uPAR, renal uPA activity was significantly decreased compared with the wild-type animals after UUO (62 +/- 20 versus 135 +/- 13 units at day 3 UUO; 74 +/- 17 versus 141 +/- 16 at day 7 UUO; 98 +/- 20 versus 165 +/- 10 at day 14 UUO; -/- versus +/+). In contrast, renal expression of several genes that regulate plasmin activity were similar in both genotypes, including uPA, tPA, PAI-1, protease nexin-1, and alpha2-antiplasmin. Worse renal fibrosis in the uPAR-/- mice appears to be TGF-beta-independent, as TGF-beta activity was actually reduced by 65% in the -/- mice despite similar renal TGF-beta1 mRNA levels. Significantly lower levels of the major 2.3-kb transcript and the 69-kd active protein of hepatocyte growth factor (HGF), a known anti-fibrotic growth factor, in the uPAR-/- mice suggests a potential link between HGF and the renoprotective effects of uPAR. These data suggest that renal uPAR attenuates the fibrogenic response to renal injury, an outcome that is mediated in part by urokinase-dependent but plasminogen-independent functions.

Increased plasminogen activator inhibitor-1 in keloid fibroblasts may account for their elevated collagen accumulation in fibrin gel cultures

Proteolytic degradation of the provisional fibrin matrix and subsequent substitution by fibroblast-produced collagen are essential features of injury repair. Immunohistochemical studies revealed that although dermal fibroblasts of normal scars and keloids expressed both urokinase type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1), keloid fibroblasts had a much higher PAI-1 expression. In long-term three-dimensional fibrin gel cultures (the in vitro fibroplasia model), normal fibroblasts expressed moderate and modulated activity levels of uPA and PAI-1. In contrast, keloid fibroblasts expressed a persistently high level of PAI-1 and a low level of uPA. The high PAI-1 activity of keloid fibroblasts correlated with their elevated collagen accumulation in fibrin gel cultures. Substituting collagen for fibrin in the gel matrix resulted in increased uPA activity and reduced collagen accumulation of keloid fibroblasts. Furthermore, decreasing PAI-1 activity of keloid fibroblasts in fibrin gel cultures with anti-PAI-1-neutralizing antibodies also resulted in a reduction in collagen accumulation by keloid fibroblasts. Cumulatively, these results suggest that PAI-1 overexpression is a consistent feature of keloid fibroblasts both in vitro and in vivo, and PAI-1 may play a causative role in elevated collagen accumulation of keloid fibroblasts.

Coagulation, fibrinolysis, and fibrin deposition in acute lung injury

OBJECTIVES

To review: a) the role of extravascular fibrin deposition in the pathogenesis of acute lung injury; b) the abnormalities in the coagulation and fibrinolysis pathways that promote fibrin deposition in the acutely injured lung; and c) the pathways that contribute to the regulation of the fibrinolytic system via the lung epithelium, including newly recognized posttranscriptional and urokinase-dependent pathways. Another objective was to determine how novel anticoagulant or fibrinolytic strategies may be used to protect against acute inflammation or accelerated fibrosis in acute lung injury.

DATA SOURCES

Published medical literature.

DATA SUMMARY

Alveolar fibrin deposition is characteristic of diverse forms of acute lung injury. Intravascular thrombosis or disseminated intravascular coagulation can also occur in the acutely injured lung. Extravascular fibrin deposition promotes lung dysfunction and the acute inflammatory response. In addition, transitional fibrin in the alveolar compartment undergoes remodeling leading to accelerated pulmonary fibrosis similar to the events associated with wound healing, or desmoplasia associated with solid neoplasms. In acute lung injury, alveolar fibrin deposition is potentiated by consistent changes in endogenous coagulation and fibrinolytic pathways. Procoagulant activity is increased in conjunction with depression of fibrinolytic activity in the alveolar compartment. Initiation of the procoagulant response occurs as a result of local overexpression of tissue factor associated with factor VII. Depression of fibrinolytic activity occurs as a result of inhibition of urokinase plasminogen activator (uPA) by plasminogen activators, or series inhibition of plasmin by antiplasmins. Locally increased amplification of plasminogen activator inhibitor-1 (PAI-1) is largely responsible for this fibrinolytic defect. Newly described pathways by which lung epithelial cells regulate expression of uPA, its receptor uPAR, and PAI-1 at the posttranscriptional level have been identified. These pathways operate by cis-trans interactions between mRNA binding proteins; regulatory sequences within these mRNAs control their stability. The regulatory mechanisms seem to involve multiple protein-mRNA interactions, and the phosphorylation state of the proteins appears to determine whether complex formation of, or dissociation from, the regulatory sequences occurs. uPA is capable of inducing its own expression in lung epithelial cells as well as that of uPAR and PAI-1-the effects involve posttranscriptional regulatory components. These and related observations have led to the implementation of anticoagulant or fibrinolytic strategies to protect the lung against acute lung injury. The success of new fibrinolytic strategies to block pleural loculation suggests that a similar approach might be used to prevent accelerated pulmonary fibrosis, which can occur in association with many forms of acute lung injury.

CONCLUSIONS

Disordered coagulation and fibrinolysis promote extravascular fibrin deposition in acute lung injury. It is this deposition that characterizes acute lung injury and repair. Expression of uPA, uPAR, and PAI-1 by the lung epithelium, as well as the ability of uPA to induce other components of the fibrinolytic system, involves posttranscriptional regulation. These pathways may contribute to disordered fibrin turnover in the injured lung. The success of anticoagulant or fibrinolytic strategies designed to reverse the abnormalities of local fibrin turnover in acute lung injury supports the inference that abnormalities of coagulation, fibrinolysis, and fibrin deposition have a critical role in the pathogenesis of acute lung injury.

Hypoxia-inducible factor-1 and hypoxia response elements mediate the induction of plasminogen activator inhibitor-1 gene expression by insulin in primary rat hepatocytes

The expression of the plasminogen activator inhibitor-1 (PAI-1) gene is enhanced by insulin both in vivo and in various cell types. Because insulin exerts a number of its biologic activities via the phosphatidylinositol 3-kinase and protein kinase B (PI3K/PKB) signaling pathway, it was the aim of the present study to investigate the role of the PI3K/PKB pathway in the expression of the PAI-1 gene and to identify the insulin responsive promoter sequences. It was shown that the induction of PAI-1 mRNA and protein expression by insulin and mild hypoxia could be repressed by the PI3K inhibitor wortmannin. Overexpression of a constitutively active PKB led to induction of PAI-1 mRNA expression and of luciferase (Luc) activity from a gene construct containing 766 bp of the rat PAI-1 promoter. Mutation of the hypoxia response elements (HRE-1 and HRE-2) in rat PAI-1 promoter, which could bind hypoxia inducible factor-1 (HIF-1), abolished the induction of PAI-1 by insulin and PKB. Insulin and the constitutive active PKB also induced Luc expression in cells transfected with the pGl3EPO-HRE Luc construct, containing 3 copies of the HRE from the erythropoietin gene in front of the SV40 promoter. Furthermore, insulin and the active PKB enhanced all 3 HIF alpha-subunit protein levels and HIF-1 DNA-binding activity, as shown by electrophoretic mobility shift assays (EMSAs). Thus, the insulin-dependent activation of the PAI-1 gene expression can be mediated via the PI3K/PKB pathway and the transcription factor HIF-1 binding to the HREs in the PAI-1 gene promoter.

A plasminogen activator inhibitor-1 promoter polymorphism and idiopathic interstitial pneumonia

The normal fibrinolytic activity within the alveolar space is suppressed in fibrotic lung diseases in part because of increased levels of plasminogen activator inhibitor-1 (PAI-1). Studies with animals have shown that inhibition of the plasminogen system by PAI-1 increases the generation of pulmonary fibrosis. To determine if a similar relationship occurs in human fibrotic lung diseases, we took advantage of a polymorphism (4G/5G) that occurs in the promoter region of the human PAI-1 gene and influences the expression of PAI-1. We hypothesized that the 4G/4G genotype, because of its association with higher levels of PAI-1, would occur in patients with idiopathic interstitial pneumonia more frequently than in a control population. PAI-1 promoter genotype was determined in 88 well-characterized patients with idiopathic interstitial pneumonia consisting of 62 patients with usual interstitial pneumonia and 26 with nonspecific interstitial pneumonia. DNA was extracted from paraffin-embedded biopsy tissue and the genotype identified by polymerase chain reaction and restriction endonuclease digestion. We found that the distribution of PAI-1 genotypes in the idiopathic interstitial pneumonia population was similar to that of a large control population. However, subgroup analysis showed that patients with nonspecific interstitial pneumonia were more likely than the control population to have the promoter genotype (4G/4G) that is associated with higher levels of PAI-1. A similar pattern in PAI-1 polymorphism was not seen in the usual interstitial pneumonia subgroup. The results of this study support the conclusion that PAl-1 expression influences the development of nonspecific interstitial pneumonia in a similar manner to what occurs in animal models of pulmonary fibrosis. Patients with usual interstitial pneumonia did not show the same relationship with PAl-1 genotype.

Differential expression of urokinase-type plasminogen activator and plasminogen activator inhibitor-1 in early and late gestational mouse skin and skin wounds

Early gestation fetal mouse skin heals without scars. Plasminogen activator inhibitor-1 (PAI-1) has been associated with postnatal organ fibrosis. We hypothesized that the relative balance between urokinase-type plasminogen activator (uPA) and PAI-1 expression in favor of uPA prevents scarring in early fetal skin wounds, whereas a change in favor of PAI-1 in late gestation results in wound scarring. To evaluate uPA and PAI-1 expression, 1-mm skin wounds were made in E14.5 and E18 mice and harvested 24, 48, or 96 hours postwounding. Aprotinin (2 mg/ml)-coated beads were injected into selected E14.5 wounds. Normal skin and skin wounds were evaluated for uPA, PAI-1, and collagen expression. We showed that in normal skin uPA level is higher in E14.5 than in E18 mice, while PAI-1 is lower in E14.5 than in E18 mice. After wounding, E14.5 wounds show a moderate increase in uPA and a minimal increase in PAI-1. E18 wounds show a transient increase in uPA but a significant, sustained increase in PAI-1. Addition of aprotinin to E14.5 wounds causes an increase in collagen deposition. We conclude that the differential expression of uPA and PAI-1 in the skin of early vs. late gestation mice may contribute to the degree of scar formation seen after cutaneous injury.

Inducible lung-specific urokinase expression reduces fibrosis and mortality after lung injury in mice

Plasminogen activator inhibitor-1 (PAI-1)-deficient transgenic mice have improved survival and less fibrosis after intratracheal bleomycin instillation. We hypothesize that PAI-1 deficiency limits scarring through unopposed plasminogen activation. If this is indeed true, then we would expect increased urokinase-type plasminogen activator (uPA) expression to result in a similar reduction in scarring and improvement in mortality. To test our hypothesis, using the tetracycline gene regulatory system, we have generated a transgenic mouse model with the features of inducible, lung-specific uPA production. After doxycycline administration, these transgenic animals expressed increased levels of uPA in their bronchoalveolar lavage (BAL) fluid that accelerated intrapulmonary fibrin clearance. Importantly, this increased plasminogen activator production led to a reduction in both lung collagen accumulation and mortality after bleomycin-induced injury. These results suggest that PAI-1 deficiency does protect against the effects of bleomycin-induced lung injury through unopposed plasmin generation. By allowing the manipulation of plasminogen activation at different phases of the fibrotic process, this model will serve as a powerful tool in further investigations into the pathogenesis of pulmonary fibrosis.

Effects of inhaled plasminogen activator on the balance between coagulation and fibrinolysis in traumatized pigs

A profibrinolytic state is normal in the alveoli, but this may change as a result of trauma, possibly leading to fibrin deposition, a characteristic of acute lung injury/acute respiratory distress syndrome. Therefore, the present study investigated in a double-blind, placebo-controlled manner the effect of severe trauma on the alveolar fibrinolytic/coagulation balance, and the effect here-upon of inhalation of single-chain urokinase plasminogen activator (scu-PA) in pigs. The study shows an increased concentration of scu-PA in the bronchoalveolar lavage fluid of the treated animals in association with an increased plasmin-dependent fibrinolytic activity without increased systemic fibrinolytic activity, the transient increase in the concentration of scu-PA in the plasma being minimal. In conclusion, the study shows that activatable scu-PA can be nebulized to the lower respiratory tract and can increase the alveolar fibrinolysis without any significant systemic effects.

The renin-angiotensin-aldosterone system and fibrinolysis in progressive renal disease

Renal glomerular and interstitial fibrosis is widely viewed as the final common pathway to renal failure, regardless of the initiating injury. Similarly, the renin-angiotensin-aldosterone system (RAAS) plays an important role in the progression of renal disease. This review explores the hypothesis that the RAAS causes injury and fibrosis, in part, through effects on plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of plasminogen activators in vivo. PAI-1, by inhibiting the production of plasmin from plasminogen, tips the balance in favor of extracellular matrix accumulation and promotes fibrosis. Interruption of the RAAS decreases both PAI-1 expression and fibrosis in animal models. These findings have implications for the clinical management of renal disease.

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.

Age-dependent spontaneous coronary arterial thrombosis in transgenic mice that express a stable form of human plasminogen activator inhibitor-1

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) regulates fibrinolysis and has been reported to be an independent risk factor for ischemic cardiovascular events. This study describes the age-dependent development of spontaneous coronary arterial thrombi that are associated with evidence of subendocardial myocardial infarction in mice transgenic for human PAI-1.

METHODS AND RESULTS

We generated two independent transgenic mice founder lines that express a stable variant of active human PAI-1 under control of the murine preproendothelin-1 (mPPET-1) promoter. Backcrossed homozygous transgenic animals from founder line I had plasma PAI-1 levels of 23+/-12 ng/mL. PAI-1 transgenic animals younger than 4 months do not exhibit any evidence of arterial or venous thrombosis. Ninety percent of transgenic animals (n=10) older than 6 months developed spontaneous occlusions of typically multiple, penetrating coronary arteries, with histological evidence of subendocardial infarction identified in 50% of animals.

CONCLUSIONS

This study shows that chronically elevated levels of PAI-1 are associated with age-dependent coronary arterial thrombosis in mice transgenic for human PAI-1. This is the first study of a murine model of coronary thrombosis that occurs in the absence of severe hypercholesterolemia or multiple genetic manipulations. These findings provide new evidence to support the hypothesis that PAI-1 excess contributes to the development of coronary arterial thrombosis.

Future research directions in idiopathic pulmonary fibrosis: summary of a National Heart, Lung, and Blood Institute working group

Idiopathic pulmonary fibrosis (IPF) is an insidious inflammatory fibroproliferative disease whose cause and course before diagnosis are unknown, and for which existing treatments are of limited benefit. The National Heart, Lung, and Blood Institute convened a working group to develop specific recommendations for future IPF research. Inflammatory and immune processes are involved in IPF pathogenesis, and current therapeutic strategies are aimed at suppressing the inflammation. Recent data suggest that the molecular processes underlying the fibrogenesis may provide new opportunities for therapeutic intervention. Specific areas of future research recommended by the working group include studies to elucidate the etiology of IPF, to develop novel diagnostic techniques and molecular diagnostics, to establish a program for identification of molecular targets for IPF treatment and identification and generation of agonists or antagonists that inhibit fibrogenesis, to foster investigations that couple the use of new technologies (e.g., laser capture microdissection, microarrays, and mass spectroscopic analysis of proteins) with data from the human genome project, to establish a national consortium of Clinical Centers of Excellence to conduct coordinated clinical and laboratory studies of well-characterized patients and patient-derived materials, and to stimulate research to develop animal models of persistent and progressive pulmonary fibrosis for evaluation of new intervention approaches.

PAI-1 promotes extracellular matrix deposition in the airways of a murine asthma model

Dysregulation of matrix metalloproteinases (MMPs) and ineffective fibrinolysis are associated with the deposition of extracellular matrix (ECM). We hypothesized that elevated plasminogen activator inhibitor (PAI)-1 promotes ECM deposition in the asthmatic airway by inhibiting MMP-9 activity and fibrinolysis. Degree of airway inflammation was similar in PAI-1(-/-) and wild type (WT) mice after ovalbumin (OVA) challenge. PAI-1 production, deposition of collagen and fibrin, and MMP-9 activity in the lung tissue or airways were greater after OVA challenge compared with saline challenge. However, in PAI-1(-/-) mice, collagen deposition was 2-fold less, fibrin deposition was 4-fold less, and MMP-9 activity was 3-fold higher. This is the first direct evidence that the plasmin system regulates ECM deposition in the airways of a murine asthma model, independently of the effect of PAI-1 on inflammatory cells. The results suggest that the PAI-1-dependent inhibition of MMP-9 activity and fibrinolysis is a major mechanism by which ECM deposition occurs.

A pivotal role of cytosolic phospholipase A(2) in bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is an interstitial disorder of the lung parenchyma whose mechanism is poorly understood. Potential mechanisms include the infiltration of inflammatory cells to the lungs and the generation of pro-inflammatory mediators. In particular, idiopathic pulmonary fibrosis is a progressive and fatal form of the disorder characterized by alveolar inflammation, fibroblast proliferation and collagen deposition. Here, we investigated the role of cytosolic phospholipase A(2) (cPLA(2)) in pulmonary fibrosis using cPLA(2)-null mutant mice, as cPLA(2) is a key enzyme in the generation of pro-inflammatory eicosanoids. Disruption of the gene encoding cPLA(2) (Pla2g4a) attenuated IPF and inflammation induced by bleomycin administration. Bleomycin-induced overproduction of thromboxanes and leukotrienes in lung was significantly reduced in cPLA(2)-null mice. Our data suggest that cPLA(2) has an important role in the pathogenesis of pulmonary fibrosis. The inhibition of cPLA(2)-initiated pathways might provide a novel therapeutic approach to pulmonary fibrosis, for which no pharmaceutical agents are currently available.

Endothelium and disordered fibrin turnover in the injured lung: newly recognized pathways

OBJECTIVES

To review derangements of pathways of fibrin turnover that promote pathologic fibrin deposition in the acute respiratory distress syndrome and to review the contribution of the endothelium and parenchymal lung cells to the derangements. In addition, to review how these pathways can be exploited in specific clinical circumstances, including sepsis and acute lung injury. Lastly, to review newly recognized posttranscriptional and urokinase-dependent pathways by which the fibrinolytic system is regulated in the lung.

DATA SOURCES

Medical literature published in English from 1966 to present.

DATA SUMMARY

Local abnormalities of fibrin turnover in the injured lung recapitulate the systemic changes observed in sepsis. In both circumstances, the procoagulant response is increased, whereas fibrinolytic activity is concurrently depressed. The increased procoagulant activity is related to tissue factor associated with factor VII/VIIa. Fibrinolytic activity in the vasculature is mainly attributable to tissue plasminogen activator, whereas extravascular fibrinolytic activity in the lung is mainly attributable to urokinase plasminogen activator (uPA). Depressed fibrinolytic activity is in large part attributable to plasminogen activator inhibitor-1. In sepsis, activated protein C is also deficient, potentiating the inflammatory response, coagulopathy, and depressed fibrinolysis. Recombinant human activated protein C (drotrecogin alfa [activated]) was successful as an intervention for sepsis in a recent phase 3 clinical trial (PROWESS). Recently, novel posttranscriptional pathways that regulate expression of uPA, its receptor (uPAR), and plasminogen activator inhibitor-1 have been identified. The responsible mechanisms involve cis-trans interactions between newly recognized messenger RNA (mRNA) binding sequences and mRNA binding proteins. A 51 nucleotide mRNA binding sequence within the coding region of uPAR mRNA interacts with a novel 50-kDa mRNA binding protein to destabilize the message. Sequences within the 3' untranslated region of uPA or plasminogen activator inhibitor-1 mRNA interact with 30- and 60-kDa proteins, respectively, to regulate message stability. All of these pathways operate in lung epithelial cells, and endothelial cells regulate uPA expression through a similar pathway. In addition, uPA itself is capable of inducing expression of other components of the fibrinolytic system, including uPAR. This observation defines another feedback loop that could amplify local fibrinolysis and other uPA- or uPAR-mediated cellular responses, including cellular proteolysis, proliferation, and directed cellular migration.

CONCLUSIONS

Novel posttranscriptional pathways regulate expression of uPA, uPAR, and plasminogen activator inhibitor-1. uPA itself is capable of inducing other components of the fibrinolytic system. Some or all of these newly recognized pathways are operative in endothelial and parenchymal lung cells and may influence disordered fibrin turnover in the injured lung.

Keratinocyte and hepatocyte growth factors in the lung: roles in lung development, inflammation, and repair

A growing body of evidence indicates that the epithelial-specific growth factors keratinocyte growth factor (KGF), fibroblast growth factor (FGF)-10, and hepatocyte growth factor (HGF) play important roles in lung development, lung inflammation, and repair. The therapeutic potential of these growth factors in lung disease has yet to be fully explored. KGF has been best studied and has impressive protective effects against a wide variety of injurious stimuli when given as a pretreatment in animal models. Whether this protective effect could translate to a treatment effect in humans with acute lung injury needs to be investigated. FGF-10 and HGF may also have therapeutic potential, but more extensive studies in animal models are needed. Because HGF lacks true epithelial specificity, it may have less potential than KGF and FGF-10 as a targeted therapy to facilitate lung epithelial repair. Regardless of their therapeutic potential, studies of the unique roles played by these growth factors in the pathogenesis and the resolution of acute lung injury and other lung diseases will continue to enhance our understanding of the complex pathophysiology of inflammation and repair in the lung.

Expression of glomerular plasminogen activator inhibitor type 1 in glomerulonephritis

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

Plasminogen activator inhibitor type-1 deficiency attenuates murine antigen-induced arthritis

OBJECTIVE

To examine the role of plasminogen activator inhibitor type-1 (PAI-1), the major fibrinolytic inhibitor, in vivo during murine antigen-induced arthritis (AIA).

METHODS

AIA was induced in PAI-1-deficient mice and control wild-type mice. Arthritis severity was evaluated by technetium 99m (99mTc) uptake in the knee joints and by histological scoring. Intra-articular fibrin deposition was examined by immunohistochemistry and synovial fibrinolysis quantitated by tissue D-dimer measurements and zymograms.

RESULTS

Joint inflammation, quantitated by 99mTc uptake, was significantly reduced in PAI-1(-/-) mice on day 7 after arthritis onset (P<0.01). Likewise, synovial inflammation, evaluated by histological scoring, was significantly decreased in PAI-1-deficient mice on day 10 after arthritis onset (P<0.001). Articular cartilage damage was significantly decreased in PAI-1(-/-) mice, as shown by histological grading of safranin-O staining on day 10 after arthritis onset (P<0.005). Significantly decreased synovial accumulation of fibrin was observed by day 10 in arthritic joints of PAI-1(-/-) mice (P<0.005). Accordingly, the synovial tissue content of D-dimers, the specific fibrin degradation products generated by plasmin, were increased in PAI-1(-/-) mice (P<0.02). Finally, as expected, PA activity was increased in synovial tissues from PAI-1(-/-) mice, as shown by zymographic analysis.

CONCLUSIONS

These results indicate that deficiency of PAI-1 results in increased synovial fibrinolysis, leading to reduced fibrin accumulation in arthritic joints and reduced severity of AIA.

Spironolactone abolishes the relationship between aldosterone and plasminogen activator inhibitor-1 in humans

Recent studies have defined a link between the renin-angiotensin-aldosterone system and fibrinolysis. The present study tests the hypothesis that endogenous aldosterone regulates plasminogen activator inhibitor-1 (PAI-1) production in humans. Hemodynamic parameters, PAI-1 and tissue-type plasminogen activator (t-PA) antigen, potassium, PRA, angiotensin II, and aldosterone were measured in nine male hypertensive subjects after a 3-wk washout, after 2 wk of hydrochlorothiazide (HCTZ; 25 mg plus 20 mmol KCl/d), and after 2 wk of spironolactone (100 mg/d plus KCl placebo). Spironolactone (P = 0.04), but not HCTZ (P = 0.57 vs. baseline; P = 0.1 vs. spironolactone), significantly lowered systolic blood pressure. Angiotensin II increased from baseline during both HCTZ (P = 0.02) and spironolactone (P = 0.02 vs. baseline; P = 0.19 vs. HCTZ) treatments. Although both HCTZ (P = 0.004) and spironolactone (P < 0.001 vs. baseline) increased aldosterone, the effect was greater with spironolactone (P < 0.001 vs. HCTZ). HCTZ increased PAI-1 antigen (P = 0.02), but did not alter t-PA antigen. In contrast, there was no effect of spironolactone on PAI-1 antigen (P = 0.28), whereas t-PA antigen was increased (P = 0.01). There was a significant correlation between PAI-1 antigen and serum aldosterone during both baseline and HCTZ study days (r(2) = 0.57; P = 0.0003); however, treatment with spironolactone abolished this correlation (r(2) = 0.13; P = 0.33). This study provides evidence that endogenous aldosterone influences PAI-1 production in humans.

Microarray profile of differentially expressed genes in a monkey model of allergic asthma

BACKGROUND

Inhalation of Ascaris suum antigen by allergic monkeys causes an immediate bronchoconstriction and delayed allergic reaction, including a pulmonary inflammatory infiltrate. To identify genes involved in this process, the gene-expression pattern of allergic monkey lungs was profiled by microarrays. Monkeys were challenged by inhalation of A. suum antigen or given interleukin-4 (IL-4) treatment; lung tissue was collected at 4, 18 or 24 h after antigen challenge or 24 h after IL-4. Each challenged monkey lung was compared to a pool of normal, unchallenged monkey lungs.

RESULTS

Of the approximately 40,000 cDNAs represented on the microarray, expression levels of 169 changed by more than 2.5-fold in at least one of the pairwise probe comparisons; these cDNAs encoded 149 genes, of which two thirds are known genes. The largest number of regulated genes was observed 4 h after challenge. Confirmation of differential expression in the original tissue was obtained for 95% of a set of these genes using real-time PCR. Cluster analysis revealed at least five groups of genes with unique expression patterns. One cluster contained genes for several chemokine mediators including eotaxin, PARC, MCP-1 and MCP-3. Genes involved in tissue remodeling and antioxidant responses were also identified as regulated by antigen and IL-4 or by antigen only.

CONCLUSION

This study provides a large-scale profile of gene expression in the primate lung following allergen or IL-4 challenge. It shows that microarrays, with real-time PCR, are a powerful tool for identifying and validating differentially expressed genes in a disease model.

The molecular basis for anti-proteolytic and non-proteolytic functions of plasminogen activator inhibitor type-1: roles of the reactive centre loop, the shutter region, the flexible joint region and the small serpin fragment

The serine proteinase inhibitor plasminogen activator inhibitor type-1 (PAI-1) is the primary physiological inhibitor of the tissue-type and the urokinase-type plasminogen activator (tPA and uPA, respectively) and as such an important regulator of proteolytic events taking place in the circulation and in the extracellular matrix. Moreover, a few non-proteolytic functions have been ascribed to PAI-1, mediated by its interaction with vitronectin or the interaction between the uPA-PAI-1 complex bound to the uPA receptor and members of the low density lipoprotein receptor family. PAI-1 belongs to the serpin family, characterised by an unusual conformational flexibility, which governs its molecular interactions. In this review we describe the anti-proteolytic and non-proteolytic functions of PAI-1 from both a biological and a biochemical point of view. We will relate the various biological roles of PAI-1 to its biochemistry in general and to the different conformations of PAI-1 in particular. We put emphasis on the intramolecular rearrangements of PAI-1 that are required for its antiproteolytic as well as its non-proteolytic functions.

Blood transfer: the use of autologous blood as a chromophore and tissue augmentation agent

BACKGROUND

Atrophic scars, whether traumatic, postsurgical, or postacne, are distressing and difficult to treat. A freely available autologous agent that provides medium- to long-term correction of this problem would be welcome. There are very few endogenous chromophores in the skin for laser or light energy to target. A benign exogenous pigment implanted in superficial scars may be useful in presenting such a target for light energy, allowing selective injury to these scars and the possibility of new collagen formation.

OBJECTIVE

To report five representative case reports that describe elements of two new techniques that may be useful in the management of atrophic acne scarring.

METHODS

After drawing blood from the patient, this was immediately reinjected into premarked areas of atrophic scars. If there was substantial tissue deficit, this was either followed by repeated injections of whole blood at monthly intervals on three occasions or until adequate correction was attained and oral antifibrinolysis medication dispensed in addition to the blood transfer (hematogenous augmentation of tissue or the HAT technique). In the other circumstance, where the deficit was superficial, blood was implanted high in the tissue and used as a target for vascular laser or intense pulsed light in a technique termed the blood augmentation (with or without) stimulation of tissues by irradiation with light or laser energy or the Bastille technique. This is again repeated as required.

RESULTS

Reasonable short- to medium-term correction has been attained in all five cases and there seemed to be a progressive improvement with each injection session. With the Bastille technique case there seemed to be progressive improvement with time, with the result at 4 weeks being substantially better than that at 2 weeks or at baseline.

CONCLUSION

These case reports suggest that blood may be a worthwhile augmentation agent and chromophore. Both these techniques deserve further investigation to determine the optimum parameters. They are so simple in their concept and technique that should they help to provide a medium- to long-term correction for atrophic scars and other depressions, such as expression lines and wrinkles, they would be worthwhile additions to existing dermatologic techniques.

Direct thrombin inhibition reduces lung collagen, accumulation, and connective tissue growth factor mRNA levels in bleomycin-induced pulmonary fibrosis

Dramatic activation of the coagulation cascade has been extensively documented for pulmonary fibrosis associated with acute and chronic lung injury. In addition to its role in hemostasis, thrombin exerts profibrotic effects via activation of the major thrombin receptor, protease-activated receptor-1. In this study, we examined the effect of the direct thrombin inhibitor, UK-156406 on fibroblast responses in vitro and on bleomycin-induced pulmonary fibrosis in rats. UK-156406 significantly inhibited thrombin-induced fibroblast proliferation, procollagen production, and connective tissue growth factor (CTGF) mRNA levels when used at equimolar concentration to the protease. Thrombin levels in bronchoalveolar lavage fluid and expression of thrombin and protease-activated receptor-1 in lung tissue were increased after intratracheal instillation of bleomycin. The characteristic doubling in lung collagen in bleomycin-treated animals (38.4 +/- 2.0 mg versus 17.1 +/- 1.4 mg, P < 0.01) was preceded by significant elevations in alpha1(I) procollagen and CTGF mRNA levels (3.0 +/- 0.4-fold and 6.3 +/- 0.4-fold respectively, (P < 0.01), and total inflammatory cell number. UK-156406, administered at an anticoagulant dose, attenuated lung collagen accumulation in response to bleomycin by 35 +/- 12% (P < 0.05), inhibited alpha1(I) procollagen and CTGF mRNA levels by 50% and 35%, respectively (P < 0.05), but had no effect on inflammatory cell recruitment. This is the first report showing that direct thrombin inhibition abrogates lung collagen accumulation in bleomycin-induced pulmonary fibrosis.

Specific tissue distribution of megsin, a novel serpin, in the glomerulus and its up-regulation in IgA nephropathy

Mesangial cells play critical roles in maintaining a structure and function of the glomerulus. We previously cloned a novel mesangium-predominant gene, megsin, a new serine protease inhibitor. To clarify localization and roles of megsin protein, we raised polyclonal antibodies to megsin. By immunohistochemistry, megsin protein was specifically identified in the mesangial area. The amount of megsin protein was increased in glomeruli of patients with IgA nephropathy than in those of normal individuals and of patients with minimal change nephrotic syndrome or membranous nephropathy, suggesting a pathophysiological role of megsin as a functional modulator of mesangial functions in situ.

Plasminogen activator inhibitor-1 deficiency prevents hypertension and vascular fibrosis in response to long-term nitric oxide synthase inhibition

BACKGROUND

Long-term inhibition of nitric oxide synthase (NOS) is known to induce hypertension and perivascular fibrosis. Recent evidence also suggests that long-term NOS inhibition induces expression of plasminogen activator inhibitor-1 (PAI-1) in vascular tissues and that PAI-1 may contribute to the development of fibrosis after chemical or ionizing injury. On the basis of these observations, we hypothesized that PAI-1 may influence the vascular response to long-term NOS inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME).

METHODS AND RESULTS

We compared the temporal changes in systolic blood pressure and coronary perivascular fibrosis in PAI-1-deficient (PAI-1(-/-)) and wild-type (WT) male mice (N=6 per group). At baseline, there were no significant differences in blood pressure between groups. After initiation of L-NAME, systolic blood pressure increased in both groups at 2 weeks. Over an 8-week study period, systolic blood pressure increased to 141+/-3 mm Hg in WT animals versus 112+/-4 mm Hg in PAI-1(-/-) mice (P<0.0001). The extent of coronary perivascular fibrosis increased significantly in L-NAME-treated WT mice (P<0.01 versus PAI-1(-/-) mice). Cardiac type I collagen mRNA expression was greater in control (P<0.01) and L-NAME-treated PAI-1(-/-) (P<0.05) groups than in control WT mice, indicating that PAI-1 deficiency prevents the increase of collagen deposition by promoting matrix degradation.

CONCLUSIONS

These findings suggest that PAI-1 deficiency alone is sufficient to protect against the structural vascular changes that accompany hypertension in the setting of long-term NOS inhibition. Direct inhibition of vascular PAI-1 activity may provide a new therapeutic strategy for the prevention of arteriosclerotic cardiovascular disease.

Development of pulmonary fibrosis in fibrinogen-deficient mice

Bleomycin is an antineoplastic drug commonly used for the treatment of many carcinomas and lymphomas. Its toxic side effect on lung tissue is a major limitation to its use, with approximately 3-5% of patients affected. Although the number of affected patients is small, the damage incurred by bleomycin in these patients is often irreversible and, at times, fatal. A number of therapies have been shown to be effective in animal studies to minimize damage, but to date no "magic bullet" has been identified. Many proteins of the fibrinolytic system have been implicated as playing a role in the progression of the disease, one of which is fibrinogen (Fg) acting in the context of a fibroproliferative agent. Its presence correlates with an upregulation of plasminogen activator inhibitor-1 and tissue factor in alveolar cells surrounding the lesion area. It is believed that Fg participates in the activation and migration of fibroblasts and provides a scaffold, in the form of fibrin, for cell migration following induction of acute lung injury. To further understand the mechanism of injury following bleomycin treatment and the possible role of fibrinogen therein, mice have been generated with a targeted deletion of the gamma-chain of Fg, which resulted in the absence of detectable circulating Fg. The offsprings of Fg heterozygous mice (FG+/-) mice follow Mendelian distributions indicating no embryonic lethality with this deletion. Approximately one-half of the Fg-deficient (FG-/-) neonates exhibited bleeding episodes, approximately one-half of which were fatal. For the pulmonary fibrosis study, FG-/- mice and wildtype littermates were administered a bleomycin solution intratracheally and the disease was allowed to progress for two weeks. The mice were then sacrificed, the left lung was excised for hydroxyproline analysis, the right lung was processed for histologic profiling. Examination of trichrome stained sections, surprisingly, revealed no qualitative difference between wildtype and FG-/- animals. The extent and pattern of the deposition of collagen were also similar. These results were quantitatively confirmed by hydroxyproline analysis, which revealed equivalent increases in collagen content between wildtype and FG-/- animals when compared to appropriate saline controls. Analysis of the early acute inflammatory stage of the disease showed a difference in the neutrophil population between days three and five of the disease. These studies suggest that, although fibrinogen is not required for collagen deposition at the later stage of the disease, it may play a role in the early acute inflammation stage.

Genetic manipulation of fibrinogen and fibrinolysis in mice

Vascular integrity is maintained by a sophisticated system of circulating and cell associated hemostatic factors that control local platelet deposition, the conversion of soluble fibrinogen to an insoluble fibrin polymer, and the dissolution of fibrin matrices. However, hemostatic factors are likely to be biologically more important than merely maintaining vascular patency and controlling blood loss. Specific hemostatic factors have been associated with a wide spectrum of physiological processes, including development, reproduction, tissue remodeling, wound repair, angiogenesis, and the inflammatory response. Similarly, it has been proposed that hemostatic factors are important determinants of a variety of pathological processes, including vessel wall disease, tumor dissemination, infectious disease, and inflammatory diseases of the joint, lung, and kidney. The development of gene targeted mice either lacking or expressing modified forms of selected hemostatic factors has provided a valuable opportunity to test prevailing hypotheses regarding the biological roles of key coagulation and fibrinolytic system components in vivo. Genetic analyses of fibrin(ogen) and its interacting factors in transgenic mice have proven to be particularly illuminating, often challenging long standing concepts. This review summarizes the key findings made in recent studies of gene targeted mice with single and combined deficits in fibrinogen and fibrinolytic factors. Studies illustrating the role and interplay of these factors in disease progression are highlighted.

Fibrin and wound healing

Although hemostasis is the major role of fibrin in wound repair, once the clot is present the wound cells must deal with it. The invasion and clearing of fibrin by these cells involves multiple complex processes that may go array XXX and delay wound repair. A good example, of the latter is leg ulcers. These chronic wounds contain a plethora of proteases that digest fibronectin and growth factors in the fibrin clot resulting in a corrupt provisional matrix that no longer supports reepithelialization or granulation tissue formation. Every good wound care provider knows that these wounds will not heal unless the corrupt matrix is removed by vigorous debridement that stimulates the accumulation of a competent provisional matrix.

PAI-1 deficiency attenuates the fibrogenic response to ureteral obstruction

BACKGROUND

Progressive renal disease is characterized by the induction of plasminogen activator inhibitor-1 (PAI-1), suggesting that impaired activity of the renal plasmin cascade may play a role in renal fibrosis.

METHODS

To test this hypothesis, the severity of renal fibrosis caused by unilateral ureteral obstruction (UUO) was compared in PAI-1 wild-type (+/+) and PAI-1 deficient (-/-) mice. The extent of interstitial inflammation and fibrosis, renal plasminogen activator and plasmin activity, and renal expression of profibrotic genes was evaluated after 3, 7, and 14 days of UUO.

RESULTS

Renal PAI-1 mRNA levels increased 8- to 16-fold in the +/+ mice after UUO surgery, and PAI-1 protein was detected in kidney homogenates. Interstitial fibrosis was significantly attenuated in -/- mice compared with +/+ mice at day 7 and day 14, based on the interstitial area stained with picrosirius red and total kidney collagen content. However, neither the mean renal plasminogen activator nor plasmin activities were increased in -/- mice compared with +/+ mice. The number of interstitial macrophages were significantly lower in the -/- mice three and seven days after UUO; interstitial myofibroblasts were significantly fewer at three days. At the same time points, this altered interstitial cellularity was associated with a significant reduction in renal mRNA levels for transforming growth factor-beta and procollagens alpha 1(I) and alpha 1(III).

CONCLUSIONS

These studies establish an important fibrogenic role for PAI-1 in the renal fibrogenic response. The results demonstrate that one important fibrosis-promoting function of PAI-1 is its role in the recruitment of fibrosis-inducing cells, including myofibroblasts and macrophages.

Cloning of rodent megsin revealed its up-regulation in mesangioproliferative nephritis

BACKGROUND

We recently cloned a new human mesangium-predominant gene, megsin. Megsin is a novel member of the serine protease inhibitor (serpin) superfamily. To elucidate functional roles of this gene, we cloned megsin in rodents and investigated its role in a rat nephritis model.

METHODS

Megsin homologues were cloned from cultured rat and mouse mesangial cDNAs utilizing polymerase chain reaction (PCR) with degenerative primers. Expression of megsin in three different types of resident glomerular cells was investigated by PCR. Levels of megsin mRNA expression at various time points in the anti-Thy1 rat nephritis model were studied by semiquantitative PCR and Northern blotting analysis. In order to investigate megsin protein expression in anti-Thy1 nephritis rats, we raised antibody against rat megsin-specific synthetic peptide, with which immunohistochemical studies were performed.

RESULTS

Rat and mouse megsins were composed of 380 amino acids, which revealed 75.3 and 73.9% identity, respectively, with human megsin at the amino acid level. Characteristic features as an inhibitory serpin were conserved in both rat and megsin megsins. PCR analysis revealed expression of megsin in cultured mesangial cells but not in glomerular epithelial or endothelial cells. In anti-Thy1 nephritis rats, semiquantitative PCR and Northern blotting showed that expression of megsin mRNA was up-regulated in glomeruli at day 8. Immunohistochemical studies demonstrated the prominent accumulation of megsin in glomeruli at the same time point. Megsin was mainly localized in mesangial area. The megsin expression level returned to the basal level at day 28.

CONCLUSION

Sequences of megsin were well conserved among different species. Rat megsin was also predominantly expressed in mesangial cells. Expression of megsin was up-regulated at the peak of hypercellularity and matrix accumulation in the mesangioproliferative glomerulonephritis model, suggesting that megsin may participate in the process of glomerulosclerosis by modulating extracellular matrix deposition or cell survival.

Delayed branching of endothelial capillary-like cords in glycated collagen I is mediated by early induction of PAI-1

Development of micro- and macrovascular disease in diabetes mellitus (DM) warrants a thorough investigation into the repertoire of endothelial cell (EC) responses to diabetic environmental cues. Using human umbilical vein EC (HUVEC) cultured in three-dimensional (3-D) native collagen I (NC) or glycated collagen I (GC), we observed capillary cord formation that showed a significant reduction in branching when cells were cultured in GC. To gain insight into the molecular determinants of this phenomenon, HUVEC subjected to GC vs. NC were studied using a PCR-selected subtraction approach. Nine different genes were identified as up- or downregulated in response to GC; among those, plasminogen activator inhibitor-1 (PAI-1) mRNA was found to be upregulated by GC. Western blot analysis of HUVEC cultured on GC showed an increase in PAI-1 expression. The addition of a neutralizing anti-PAI-1 antibody to HUVEC cultured in GC restored the branching pattern of formed capillary cords. In contrast, supplementation of culture medium with the constitutively active PAI-1 reproduced defective branching patterns in HUVEC cultured in NC. Ex vivo capillary sprouting in GC was unaffected in PAI-1 knockout mice but was inhibited in wild-type mice. This difference persisted in diabetic mice. In conclusion, the PCR-selected subtraction technique identified PAI-1 as one of the genes characterizing an early response of HUVEC to the diabetic-like interstitial environment modeled by GC and responsible for the defective branching of endothelial cells. We propose that an upregulation of PAI-1 is causatively linked to the defective formation of capillary networks during wound healing and eventual vascular dropout characteristic of diabetic nephropathy.

Release of urokinase plasminogen activator receptor during urosepsis and endotoxemia

BACKGROUND

The urokinase receptor (uPAR; CD87) is a multifunctional molecule involved in fibrinolysis, in proteolysis, in renal tubular functions, and in migration and adhesion of inflammatory cells to the site of infection.

METHODS

To gain insight into systemic and local release of uPAR and into its regulation during urosepsis, which is one of the leading causes of chronic renal failure, uPAR was measured in urine and plasma of healthy human controls (N = 20), patients with culture-proven urosepsis (N = 30), and healthy human volunteers intravenously injected with endotoxin (N = 7).

RESULTS

Patients had elevated uPAR levels in both plasma and urine. Three hours after endotoxin challenge in volunteers, there was also a significant increase of uPAR in plasma and in urine. The urine/plasma ratio for uPAR was highly elevated during urosepsis and experimental endotoxemia, suggesting local production in the kidney. Accordingly, damaged tubuli strongly expressed uPAR during pyelonephritis. Moreover, tubular epithelial cells produced uPAR in vitro, and this secretion was strongly up-regulated after stimulation with interleukin-1 beta or tumor necrosis factor-alpha.

CONCLUSIONS

We found that uPAR is released systemically and in the urinary tract during urosepsis and experimental endotoxemia. This systemic and renal production of uPAR during pyelonephritis may play a central role in eliminating the infection and protecting renal function.

Increased D allele frequency of the angiotensin-converting enzyme gene in pulmonary fibrosis

An insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme has previously been studied extensively in relationship to cardiovascular and renal disease. The deletion/deletion (D/D) genotype is associated with a poor outcome in immunoglobulin (Ig) A nephropathy. However, the association of this genetic marker in cardiovascular and renal disease has generated controversy, with the exception of the rate of progression and therapeutic responsiveness in IgA nephropathy. Many of the same cytokines and polypeptide mediators involved in fibrosis of the cardiovascular and renal systems have been shown to be involved in pulmonary fibrosis. We examined the I/D polymorphism of the angiotensin-converting enzyme in a group of 24 patents with interstitial pneumonia and moderate to severe pulmonary fibrosis defined by radiographic studies, pulmonary function tests, and histologic findings. The incidence of the D allele in this study population was 69.0%, which is approximately 15.0% higher than the incidence in the general population of 54.0%. The incidence of the D/D genotype was 42.0%, which is approximately 11.0% greater than that in the general population (31.0%). The distribution of the D/D, I/D, and insertion/insertion genotypes of these 24 patients was not significantly different from that of historical controls (P =.1; chi(2) test); there were marginally significantly more D alleles among the 48 observed alleles than would be expected (P =.04).

The upstream stimulatory factor-2a inhibits plasminogen activator inhibitor-1 gene expression by binding to a promoter element adjacent to the hypoxia-inducible factor-1 binding site

Plasminogen activator inhibitor-1 (PAI-1) expression is induced by hypoxia (8% O(2)) via the PAI-1 promoter region -175/-159 containing a hypoxia response element (HRE-2) binding the hypoxia-inducible factor-1 (HIF-1) and an adjacent response element (HRE-1) binding a so far unknown factor. The aim of the present study was to identify this factor and to investigate its role in the regulation of PAI-1 expression. It was found by supershift assays that the upstream stimulatory factor-2a (USF-2a) bound mainly to the HRE-1 of the PAI-1 promoter and to a lesser extent to HRE-2. Overexpression of USF-2a inhibited PAI-1 messenger RNA and protein expression and activated L-type pyruvate kinase expression in primary rat hepatocytes under normoxia and hypoxia. Luciferase (Luc) gene constructs driven by 766 and 276 base pairs of the 5'-flanking region of the PAI-1 gene were transfected into primary hepatocytes together with expression vectors encoding wild-type USF-2a and a USF-2a mutant lacking DNA binding and dimerization activity (DeltaHU2a). Cotransfection of the wild-type USF-2a vector reduced Luc activity by about 8-fold, whereas cotransfection of DeltaHU2a did not influence Luc activity. Mutation of the HRE-1 (-175/-168) in the PAI-1 promoter Luc constructs decreased USF-dependent inhibition of Luc activity. Mutation of the HRE-2 (-165/-158) was less effective. Cotransfection of a HIF-1alpha vector could compete for the binding of USF at HRE-2. These results indicated that the balance between 2 transcriptional factors, HIF-1 and USF-2a, which can bind adjacent HRE sites, appears to be involved in the regulation of PAI-1 expression in many clinical conditions.

Expression and function of peroxisome proliferator-activated receptor-gamma in mesangial cells

P:eroxisome proliferator-activated receptor-gamma (PPARgamma) is a novel nuclear receptor, which enhances insulin-mediated glucose uptake. Ligands to PPARgamma are currently used as therapy for type II diabetes. Using Western blot analysis, RNase protection assay, and immunostaining, we identified the presence of PPARgamma message and protein in cultured primary rat mesangial cells. Electrophoretic mobility of a labeled PPARgamma response element (PPRE) was retarded in the presence of mesangial cell nuclear extract, suggesting that PPARgamma is functional in these cells. The addition of unlabeled PPRE efficiently competed away the PPARgamma-PPRE protein complex, confirming specificity of binding of the PPARgamma to the PPRE. PPARgamma ligands rosiglitazone (1 to 10 micromol/L) and troglitazone (1 to 10 micromol/L) inhibited platelet-derived growth factor-induced DNA synthesis, measured as bromodeoxyuridine incorporation (P<0.01). This inhibition was dose dependent. When administered in antidiabetic doses to streptozotocin-induced diabetic rats, troglitazone substantially normalized albumin excretion at 3 months (from 687.1 to 137.6 microgram urinary albumin/mg creatinine, P:<0.05) but did not affect hyperglycemia or blood pressure in this model. This treatment also decreased glomerular plasminogen activator inhibitor-1 (PAI-1) expression. These data suggest that PPARgamma activation may directly attenuate diabetic glomerular disease, possibly by inhibiting mesangial growth, which occurs early in the process of diabetic nephropathy, or by inhibiting PAI-1 expression. PAI-1 inhibits the activation of plasmin and matrix metalloproteinase, which degrade extracellular matrix in the glomerulus. Excess glomerular PAI-1 allows the accumulation of extracellular matrix, leading to glomerulosclerosis. These results have therapeutic implications for diabetic nephropathy as well as for proliferative mesangial diseases of the kidney.