Urokinase is required for the pulmonary inflammatory response to Cryptococcus neoformans. A murine transgenic model

The Protective Pathways Activated in Kidneys of αMUPA Transgenic Mice Following Ischemia\Reperfusion-Induced Acute Kidney Injury

Despite the high prevalence of acute kidney injury (AKI), the therapeutic approaches for AKI are disappointing. This deficiency stems from the poor understanding of the pathogenesis of AKI. Recent studies demonstrate that αMUPA, alpha murine urokinase-type plasminogen activator (uPA) transgenic mice, display a cardioprotective pathway following myocardial ischemia. We hypothesize that these mice also possess protective renal pathways. Male and female αMUPA mice and their wild type were subjected to 30 min of bilateral ischemic AKI. Blood samples and kidneys were harvested 48 h following AKI for biomarkers of kidney function, renal injury, inflammatory response, and intracellular pathways sensing or responding to AKI. αMUPA mice, especially females, exhibited attenuated renal damage in response to AKI, as was evident from lower SCr and BUN, normal renal histology, and attenuated expression of NGAL and KIM-1. Notably, αMUPA females did not show a significant change in renal inflammatory and fibrotic markers following AKI as compared with wild-type (WT) mice and αMUPA males. Moreover, αMUPA female mice exhibited the lowest levels of renal apoptotic and autophagy markers during normal conditions and following AKI. αMUPA mice, especially the females, showed remarkable expression of PGC1α and eNOS following AKI. Furthermore, MUPA mice showed a significant elevation in renal leptin expression before and following AKI. Pretreatment of αMUPA with leptin-neutralizing antibodies prior to AKI abolished their resistance to AKI. Collectively, the kidneys of αMUPA mice, especially those of females, are less susceptible to ischemic I/R injury compared to WT mice, and this is due to nephroprotective actions mediated by the upregulation of leptin, eNOS, ACE2, and PGC1α along with impaired inflammatory, fibrotic, and autophagy processes.

Urokinase plasminogen activator surface receptor restricts HIV-1 replication by blocking virion release from the cell membrane

The urokinase-type plasminogen activator (uPA) system consists of the proteinase uPA, its receptor (PLAUR/uPAR). Under physiological conditions, uPA and PLAUR are predominantly expressed by blood cells, including neutrophils, monocytes, and macrophages, and play important roles in cell activation, adhesion, migration, and extravasation. Here, we report that PLAUR, which is highly expressed in macrophages and dendritic cells (DCs) but hardly expressed in CD4⁺ T cells, inhibits the release of HIV-1 progeny virions from the cell membrane. Silencing PLAUR markedly enhanced the transmission of HIV-1 in macrophages and DCs. We further demonstrated that PLAUR is localized at the cell membrane to block the release of HIV-1 virions. Interestingly, we found that uPA compromises the PLAUR-mediated inhibition to slightly enhance HIV-1 production in primary macrophages and DCs. In the absence of PLAUR, this enhanced effect induced by uPA is abrogated. In conclusion, PLAUR is a new anti-HIV-1 protein produced in both macrophages and DCs where it inhibits HIV-1 transmission. This discovery may provide a novel therapeutic target for combating HIV.

Immunomodulatory responses of differentially polarized macrophages to fungal infections

Macrophages, the first line of defense against invasive fungi in the innate immune system, are widely distributed in the blood and tissues of the body. In response to various internal and external stimulators, macrophages can polarize into classically activated macrophages (M1) and alternatively activated macrophages (M2). These two types of polarized macrophages play different roles in antifungal activity and in maintaining the steady-state balance between inflammation and tissue repair. However, the antifungal mechanisms of M1- and M2-type macrophages have not been fully described. In this review, the immune regulatory mechanisms against pathogenic fungi of these two classical types of macrophages in various tissues are summarized. The effects of antifungal factors on macrophage differentiation are also highlighted. The description of these data, on the one hand provides valuable insight for future investigations and also highlights new strategies for the treatment of pathogenic fungal infections.

Prognostic Significance and Gene Co-Expression Network of PLAU and PLAUR in Gliomas

The urokinase-type plasminogen activator(PLAU) and its receptor PLAUR participate in a series of cell physiological activities on the extracellular surface. Abnormal expression of PLAU and PLAUR is associated with tumorigenesis. This study aims to evaluate the prognostic value of PLAU/PLAUR transcription expression in glioma and to explore how they affect the generation and progression of glioma. In this study, online databases are applied, such as Oncomine, GEPIA, CGGA, cBioPortal, and LinkedOmics. Overexpression of PLAU/PLAUR was found to be significantly associated with clinical variables including age, tumor type, WHO grade, histology, IDH-1 mutation, and 1p19q status. PLAU and PLAUR had a high correlation in transcriptional expression levels. High expression of PLAU and PLAUR predicted a poor prognosis in primary glioma and recurrent glioma patients, especially in lower grade gliomas. Cox regression analysis indicated that high expression of PLAU and PLAUR were independent prognostic factors for shorter overall survival in glioma patients. In gene co-expression network analysis PLAU and PLAUR and their co-expression genes were found to be involved in inflammatory activities and tumor-related signaling pathways. In conclusion, PLAU and PLAUR could be promising prognostic biomarkers and potential therapeutic targets of glioma patients.

Multifaceted Role of the Urokinase-Type Plasminogen Activator (uPA) and Its Receptor (uPAR): Diagnostic, Prognostic, and Therapeutic Applications

The plasminogen activator (PA) system is an extracellular proteolytic enzyme system associated with various physiological and pathophysiological processes. A large body of evidence support that among the various components of the PA system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) play a major role in tumor progression and metastasis. The binding of uPA with uPAR is instrumental for the activation of plasminogen to plasmin, which in turn initiates a series of proteolytic cascade to degrade the components of the extracellular matrix, and thereby, cause tumor cell migration from the primary site of origin to a distant secondary organ. The components of the PA system show altered expression patterns in several common malignancies, which have identified them as ideal diagnostic, prognostic, and therapeutic targets to reduce cancer-associated morbidity and mortality. This review summarizes the various components of the PA system and focuses on the role of uPA-uPAR in different biological processes especially in the context of malignancy. We also discuss the current state of knowledge of uPA-uPAR-targeted diagnostic and therapeutic strategies for various malignancies.

Regulatory Mechanism of Collagen Degradation by Keratocytes and Corneal Inflammation: The Role of Urokinase-Type Plasminogen Activator

Keratocytes, corneal resident cells in the corneal stroma, exist between collagen lamellae and maintain the corneal stromal structure. When the corneal stroma is damaged, keratocytes are transformed to myofibroblasts to aid corneal wound healing by phagocytizing debris. Keratocytes and extracellular collagen influence each other because keratocytes cultured in a 3D collagen gel undergo morphological changes and keratocytes produce metalloproteases that degrade extracellular collagen. IL-1 and plasminogen are critical mediators for collagen degradation. The plasminogen system contributes to tissue repair by activating matrix metalloproteinases (MMPs), releasing growth factors from the extracellular matrix and extracellular matrix degradation. Urokinase-type plasminogen activator (uPA) is thought to be involved in corneal disorders and regulates corneal wound healing. uPA is a serine protease synthesized by various cells such as corneal epithelial cells, corneal fibroblasts, vascular endothelial cells, smooth muscle cells, monocytes, macrophages, and malignant tumor cells of different origins. Here, we review the role of uPA in corneal stromal wound healing. uPA is expressed in leukocytes and corneal fibroblasts in the corneas of patients with corneal ulcerations suggesting it is a key regulator of corneal stromal wound healing. uPA is directly involved in plasmin-mediated collagen degradation induced by IL-1. Moreover, uPA is critically involved in promoting leukocyte infiltration in corneal inflammation by activating MMP-9. This activation is presumably directly and indirectly mediated by the plasminogen/plasmin cascade. Moreover, uPA mediates the release of inflammatory cytokines from corneal fibroblasts to promote leukocyte infiltration.

Plasminogen activator inhibitor-1 stimulates macrophage activation through Toll-like Receptor-4

While inflammation is often associated with increased Plasminogen Activator Inhibitor-1 (PAI-1), the functional consequences of PAI-1 in inflammation have yet to be fully determined. The aim of this study was to establish the in vivo relevance of PAI-1 in inflammation. A mouse model of systemic inflammation was employed in wild-type (WT) and PAI-1 deficient (PAI-1(-/-)) mice. Mice survival, macrophage infiltration into the lungs, and plasma levels of pro-inflammatory cytokines were assessed after lipopolysaccharide (LPS) infusion. In vitro experiments were conducted to examine changes in LPS-induced inflammatory responses after PAI-1 exposure. PAI-1 was shown to regulate inflammation, in vivo, and affect macrophage infiltration into lungs. Further, PAI-1 activated macrophages, and increased pro-inflammatory cytokines at both the mRNA and protein levels in these cells. The effect of PAI-1 on macrophage activation was dose-dependent and LPS-independent. Proteolytic inhibitory activity and Lipoprotein Receptor-related Protein (LRP) and vitronectin (VN) binding functions, were not involved in PAI-1-mediated activation of macrophages. However, the effect of PAI-1 on macrophage activation was partially blocked by a TLR4 neutralizing antibody. Furthermore, PAI-1-induced Tumor Necrosis Factor-alpha (TNF-α) and Macrophage Inflammatory Protein-2 (MIP-2) expression was reduced in TLR4(-/-) macrophages compared to WT macrophages. These results demonstrate that PAI-1 is involved in the regulation of host inflammatory responses through Toll-like Receptor-4 (TLR4)-mediated macrophage activation.

Cytokines in cerebrospinal fluid of neurosyphilis patients: Identification of Urokinase plasminogen activator using antibody microarrays

Little is known regarding protein responses to syphilis infection in cerebrospinal fluid (CSF) of patients presenting with neurosyphilis. Protein and antibody arrays offer a new opportunity to gain insights into global protein expression profiles in these patients. Here we obtained CSF samples from 46 syphilis patients, 25 of which diagnosed as having central nervous system involvement based on clinical and laboratory findings. The CSF samples were then analyzed using a RayBioH L-Series 507 Antibody Array system designed to simultaneously analyze 507 specific cytokines. The results indicated that 41 molecules showed higher levels in patients with neurosyphilis in comparison with patients without neural involvement. For validation by single target ELISA, we selected five of them (MIP-1a, I-TAC/CXCL11, Urokinase plasminogen activator [uPA], and Oncostatin M) because they have previously been found to be involved in central nervous system (CNS) disorders. The ELISA tests confirmed that uPA levels were significantly higher in the CSF of neurosyphilis patients (109.1±7.88pg/ml) versus patients without CNS involvement (63.86±4.53pg/ml, p<0.0001). There was also a clear correlation between CSF uPA levels and CSF protein levels (p=0.0128) as well as CSF-VDRL titers (p=0.0074) used to diagnose neurosyphilis. No significant difference between the two groups of patients, however, was found in uPA levels in the serum, suggesting specific activation of the inflammatory system in the CNS but not the periphery in neurosyphilis patients. We conclude that measurements of uPA levels in CSF may be an additional parameter for diagnosing neurosyphilis.

Increased Soluble Urokinase-Type Plasminogen Activator Receptor (suPAR) Levels in Plasma of Suicide Attempters

The soluble form of the urokinase receptor, suPAR, has been suggested as a novel biomarker of low-grade inflammation. Activation of the immune system has been proposed to contribute to the development of depression and suicidal behavior. In order to identify depressed and suicidal individuals who could benefit from an anti-inflammatory treatment, a reliable biomarker of low-grade inflammation is vital. This study evaluates plasma suPAR levels as a biomarker of low-grade inflammation in patients with major depressive disorder and in patients who recently attempted suicide. The plasma suPAR and an established biomarker, C reactive protein (CRP) of suicide attempters (n = 54), depressed patients (n = 19) and healthy controls (n = 19) was analyzed with enzyme-linked immunosorbent assays. The biomarker attributes of sensitivity and sensibility were evaluated using ROC curve analysis. Both the depressed patients and suicide attempters had increased plasma suPAR. The levels of suPAR discriminated better between controls and suicide attempters than did CRP. In the future, plasma suPAR might be a superior prognosticator regarding outcome of treatment applying conventional antidepressants in conjunction with anti-inflammatory drugs.

The mRNA expression of soluble urokinase plasminogen activator surface receptor in human adipose tissue is positively correlated with body mass index

suPLAUR is the transcript variant that encodes the soluble form of the urokinase plasminogen activator surface receptor (suPLAUR). This soluble protein has been shown to enhance leukocyte migration and adhesion, and its circulatory level is increased in inflammatory states. In this pilot study, we used RNA-Seq to examine the splicing pattern of PLAUR in omental adipose tissues from obese and lean individuals. Of the three transcript variants of the PLAUR gene, only the proportion of suPLAUR (transcript variant 2) increases in obesity. After removing the effects of gender and age, the expression of suPLAUR is positively correlated with body mass index. This observation was validated using RT-qPCR with an independent cohort of samples. Additionally, in our RNA-Seq differential expression analysis, we also observed, in obese adipose tissues, an up-regulation of genes encoding other proteins involved in the process of chemotaxis and leukocyte adhesion; of particular interest is the integrin beta 2 (ITGB2) that is known to interact with suPLAUR in leukocyte adhesion. These findings suggest an important role for suPLAUR in the recruitment of immune cells to obese adipose tissue, in the pathogenesis of obesity.

Analysis of soluble urokinase plasminogen activator receptor in multiple myeloma for predicting prognosis

Multiple myeloma is a type of malignancy, which affects the plasma cells of the bone marrow. Recent studies have found that malignant plasma cells may express urokinase plasminogen activator (uPA) and uPA receptor (uPAR), and that initiation of proteolytic events by this system contributes to the process of invasion and destruction of the bone marrow. Studies have also suggested that the level of the soluble form of uPAR (suPAR) may act as a marker for prognosis in patients with multiple myeloma, and that there is an association between uPAR/suPAR expression, and clinical characteristics, efficacy of treatment in disease control and patient survival. In order to investigate this, the present study used flow cytometry to detect the monoclonal antibodies associated with multiple myeloma, specifically, uPAR (CD87), CD56 and CD38. Patients with multiple myeloma were divided into the following groups: The effective groups (remission and stable disease) and the ineffective group (progressive disease). suPAR expression in the effective groups was 257.6±32.47 pg/ml and 331.0±99.80 pg/ml respectively, which was not significantly different from that of the normal control group (P>0.05). By contrast, the suPAR level in the invalid group was 562.2±291.0 pg/ml, which was significantly different from the levels in the normal control group (P<0.01) and the effective groups (P<0.05). suPAR levels were positively correlated with disease stage (P<0.01), renal function (P<0.05), C-reactive protein (P<0.005), β2-microglobulin (P<0.001), extramedullary involvement (P<0.001), chromosome 13 deletion (P<0.01) and survival >2 years (P<0.01). They were was negatively correlated with hemoglobin concentration. No correlation was observed between uPAR expression and suPAR levels. The present study also indicated that the stage of disease and suPAR expression were independent factors, which predicted survival of <2 years. In conclusion, high suPAR expression appears to predict disease progression, a shortened survival period and early extramedullary infiltration.

Soluble urokinase-type plasminogen activator receptor levels in patients with schizophrenia

BACKGROUND

The etiology of schizophrenia remains largely unknown but alterations in the immune system may be involved. In addition to the psychiatric symptoms, schizophrenia is also associated with up to 20 years reduction in life span. Soluble urokinase-type plasminogen activator receptor (suPAR) is a protein that can be measured in blood samples and reflects the levels of inflammatory activity. It has been associated with mortality and the development of type 2 diabetes and cardiovascular disease.

METHODS

suPAR levels in patients with schizophrenia were compared to healthy controls from the Danish Blood Donor Study. SuPAR levels were dichotomized at >4.0 ng/ml, which is considered the threshold for low grade inflammation. A multiple logistic regression model was used and adjusted for age, sex, and current smoking.

RESULTS

In total we included 1009 subjects, 105 cases with schizophrenia (10.4%) and 904 controls (89.6%). The mean suPAR values were 4.01 ng/ml (SD = 1.43) for the cases vs 1.91 ng/ml (SD = 1.35) for the controls (P < .001). Multiple logistic regression with odds ratio (OR) for suPAR levels >4.0 ng/ml yielded: schizophrenia, OR: 46.15 95% CI 22.69-93.87, P < .001; age, OR: 1.02 95% CI 0.99-1.02, P = .15; male sex, OR: 0.70 95% CI 0.35-1.36, P = .29; and current smoking, OR: 3.51 95% CI 1.78-6.94, P < .001.

CONCLUSIONS

Patients with schizophrenia had significantly higher suPAR levels than healthy controls. Further studies are warranted to clarify if elevated suPAR levels are involved in the pathophysiology of schizophrenia and/or the increased mortality found in patients with schizophrenia.

Urokinase-type plasminogen activator deficiency has little effect on seizure susceptibility and acquired epilepsy phenotype but reduces spontaneous exploration in mice

Urokinase-type plasminogen activator (uPA), a serine protease, converts plasminogen to plasmin. Activation of plasmin leads to degradation of the extracellular matrix, which is critical for tissue recovery, angiogenesis, cell migration, and axonal and synaptic plasticity. We hypothesized that uPA deficiency would cause an abnormal neurophenotype and would lead to exacerbated epileptogenesis after brain injury. Wild-type (Wt) and uPA-/- mice underwent a battery of neurologic behavioral tests evaluating general reactivity, spontaneous exploratory activity, motor coordination, pain threshold, fear and anxiety, and memory. We placed particular emphasis on the effect of uPA deficiency on seizure susceptibility, including the response to convulsants (pentylenetetrazol, kainate, or pilocarpine) and kainate-induced epileptogenesis and epilepsy. The uPA-/- mice showed no motor or sensory impairment compared with the Wt mice. Hippocampus-dependent spatial memory also remained intact. The uPA-/- mice, however, exhibited reduced exploratory activity and an enhanced response to a tone stimulus (p<0.05 compared with the Wt mice). The urokinase-type plasminogen activator deficient mice showed no increase in spontaneous or evoked epileptiform electrographic activity. Rather, the response to pilocarpine administration was reduced compared with the Wt mice (p<0.05). Also, the epileptogenesis and the epilepsy phenotype after intrahippocampal kainate injection were similar to those in the Wt mice. Taken together, uPA deficiency led to diminished interest in the environmental surroundings and enhanced emotional reactivity to unexpected aversive stimuli. Urokinase-type plasminogen activator deficiency was not associated with enhanced seizure susceptibility or worsened poststatus epilepticus epilepsy phenotype.

Mechanisms of antitumor and immune-enhancing activities of MUC1/sec, a secreted form of mucin-1

Mucin 1 (MUC1) is a polymorphic type 1 transmembrane protein found on the apical surface of normal cells lining the lumen of ducts and glands. Mucins are thought to provide mucosal protection from environmental exposures and carcinogens. An altered form of the MUC1 glycoprotein, which is hypoglycosylated, is expressed in several types of human cancers. In our laboratory, we have found that transfection of a murine mammary tumor cell line with a human secreted isoform of MUC1 rendered these DA-3 cells (DA-3/sec) incapable of growing in intact BALB/c mice. In contrast, implantation of DA-3 cells transfected with the human transmembrane isoform of MUC1 (DA-3/TM), resulted in tumor formation and ultimately death of the animals, similar to the DA-3 parental line. Importantly, inoculation of the DA-3/sec cells in immunodeficient nude mice resulted in tumor formation, indicating that the MUC1/sec molecule's antitumor activity is immunologically controlled. In this review, we summarize the studies we have performed to elucidate possible mechanisms for the immune-mediated antitumor effect of MUC1/sec and/or a unique peptide present in this mucin. Understanding these mechanisms may provide new immunotherapeutic approaches that could be used to target different types of cancer.

Protein kinase C-δ mediates sepsis-induced activation of complement 5a and urokinase-type plasminogen activator signaling in macrophages

OBJECTIVE AND DESIGN

Activations of the complement C5a (C5a) and the urokinase-type plasminogen activator (uPA) are commonly seen together during sepsis. However, the mechanism linking these two important pathways remains elusive.

MATERIAL, METHODS AND TREATMENT

We used the C57BL/6 J mice model of sepsis induced by cecal ligation puncture (CLP) procedure, injected anti-C5aR or rottlerin through the tail vein to neutralize C5aR or PKC-δ, and then isolated peritoneal macrophages. Total RNA was isolated from the cells and analyzed by quantitative PCR.

RESULTS

Our study revealed that neutralizing C5aR markedly inhibited sepsis-induced uPA receptor (uPAR) expression and its downstream signaling in macrophage. Similarly, neutralizing uPAR suppressed sepsis activation of C5a signaling. Importantly, inhibition of PKC-δ largely blocked sepsis-induced expression of C5aR and uPAR.

CONCLUSIONS

Our study demonstrates a crosstalk between the complement C5a signaling and the fibrinolytic uPA pathways, which may depend on each other to maintain their expression and signaling, and reveals a central role of PKC-δ in mediating sepsis-induced activation of these pathways.

The intracellular life of Cryptococcus neoformans

Cryptococcus neoformans is a fungal pathogen with worldwide distribution. Serological studies of human populations show a high prevalence of human infection, which rarely progresses to disease in immunocompetent hosts. However, decreased host immunity places individuals at high risk for cryptococcal disease. The disease can result from acute infection or reactivation of latent infection, in which yeasts within granulomas and host macrophages emerge to cause disease. In this review, we summarize what is known about the cellular recognition, ingestion, and killing of C. neoformans and discuss the unique and remarkable features of its intracellular life, including the proposed mechanisms for fungal persistence and killing in phagocytic cells.

Levels of components of the urokinase-type plasminogen activator system are related to chronic obstructive pulmonary disease parenchymal destruction and airway remodelling

OBJECTIVE

Retrospective study to investigate levels of components of the urokinase-type plasminogen activator (uPA) system in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Peripheral lung tissue was obtained from patients who underwent surgical resection for benign lung diseases: 16 patients with COPD, 10 controls without lung function impairment who were smokers, and 10 controls without lung function impairment who were nonsmokers. Immunohistochemical staining for uPA, uPA receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) was quantified. Airway remodelling (collagen; detected by Sirius red staining), lung function (determined by spirometry) and emphysema (alveolar destruction; percentage of low attenuation areas on computed tomography scan) were evaluated.

RESULTS

uPA, uPAR and PAI-1 were significantly different in structural lung cells and pulmonary macrophages from patients with COPD compared with controls. There were significant positive correlations between collagen levels and uPA and PAI-1, and between uPA and degree of emphysema. There were significant inverse correlations between lung function and uPA, uPAR and PAI-1.

CONCLUSION

Correlations between components of the uPA system and lung function, small airway fibrosis and emphysema indicate a role for the uPA system in COPD.

Induction of brain microvascular endothelial cell urokinase expression by Cryptococcus neoformans facilitates blood-brain barrier invasion

The invasive ability of the blood-borne fungal pathogen Cryptococcus neoformans can be enhanced through interactions with host plasma components, such as plasminogen. Previously we showed by in vitro studies that plasminogen coats the surface of C. neoformans and is converted to the active serine protease, plasmin, by host plasminogen activators. Viable, but not formaldehyde- or sodium azide-killed, cryptococcal strains undergo brain microvascular endothelial cell-dependent plasminogen-to-plasmin activation, which results in enhanced, plasmin-dependent cryptococcal invasion of primary bovine brain microvascular endothelial cells and fungal ability to degrade plasmin substrates. In the present work, brain microvascular endothelial cells cultured with viable, but not killed, cryptococcal strains led to significant increases in both urokinase mRNA transcription and cell-associated urokinase protein expression. Soluble urokinase was also detected in conditioned medium from brain microvascular endothelial cells cultured with viable, but not killed, C. neoformans. Exposure of plasminogen pre-coated viable C. neoformans to conditioned medium from strain-matched brain microvascular endothelial cell-fungal co-cultures resulted in plasminogen-to-plasmin activation and plasmin-dependent cryptococcal invasion. siRNA-mediated silencing of urokinase gene expression or the use of specific inhibitors of urokinase activity abrogated both plasminogen-to-plasmin activation on C. neoformans and cryptococcal-brain microvascular endothelial cell invasion. Our results suggest that pathogen exploitation of the host urokinase-plasmin(ogen) system may contribute to C. neoformans virulence during invasive cryptococcosis.

At the interface of fibrinolysis and inflammation: the role of urokinase-type plasminogen activator in the leukocyte extravasation cascade

Leukocyte recruitment to the site of inflammation is a key event in the pathogenesis of cardiovascular diseases. This highly regulated process is tightly controlled by a variety of adhesion/signaling molecules, chemokines, and proteases specifically mediating the sequential steps in the leukocyte extravasation cascade. In addition to its prominent role in the fibrinolytic system, urokinase-type plasminogen activator (uPA) has been implicated in different physiological and pathophysiological processes, including cell adhesion and migration. This review focuses on the emerging role of uPA in the leukocyte recruitment process.

Soluble urokinase receptor and focal segmental glomerulosclerosis

PURPOSE OF REVIEW

We discuss recent work on the pathogenetic mechanism of focal segmental glomerulosclerosis (FSGS) and its relationship to soluble urokinase receptor (suPAR).

RECENT FINDINGS

Primary FSGS can affect both children and adults. The disease can recur after kidney transplantation suggesting the involvement of a causative circulating factor. Recent work suggests that approximately two-thirds of FSGS patients have elevated levels of serum suPAR, which confers risk to both native and posttransplant FSGS.

SUMMARY

Future studies that are geared to understand the clinical implications of high suPAR levels in native FSGS as well as in the pretransplant and posttransplant setting will allow for better patient risk stratification and more targeted treatment options.

Urokinase plasminogen activator regulates pulmonary arterial contractility and vascular permeability in mice

The concentration of urokinase plasminogen activator (uPA) is elevated in pathological settings such as acute lung injury, where pulmonary arterial contractility and permeability are disrupted. uPA limits the accretion of fibrin after injury. Here we investigated whether uPA also regulates pulmonary arterial contractility and permeability. Contractility was measured using isolated pulmonary arterial rings. Pulmonary blood flow was measured in vivo by Doppler and pulmonary vascular permeability, according to the extravasation of Evans blue. Our data show that uPA regulates the in vitro pulmonary arterial contractility induced by phenylephrine in a dose-dependent manner through two receptor-dependent pathways, and regulates vascular contractility and permeability in vivo. Physiological concentrations of uPA (≤1 nM) stimulate the contractility of pulmonary arterial rings induced by phenylephrine through the low-density lipoprotein receptor-related protein receptor. The procontractile effect of uPA is independent of its catalytic activity. At pathophysiological concentrations, uPA (20 nM) inhibits contractility and increases vascular permeability. The inhibition of vascular contractility and increase of vascular permeability is mediated through a two-step process that involves docking to N-methyl-d-aspartate receptor-1 (NMDA-R1) on pulmonary vascular smooth muscle cells, and requires catalytic activity. Peptides that specifically inhibit the docking of uPA to NMDA-R, or the uPA variant with a mutated receptor docking site, abolished both the effects of uPA on vascular contractility and permeability, without affecting its catalytic activity. These data show that uPA, at concentrations found under pathological conditions, reduces pulmonary arterial contractility and increases permeability though the activation of NMDA-R1. The selective inhibition of NMDAR-1 activation by uPA can be accomplished without a loss of fibrinolytic activity.

Activation of urokinase plasminogen activator and its receptor axis is essential for macrophage infiltration in a prostate cancer mouse model

Macrophages within the tumor microenvironment promote angiogenesis, extracellular matrix breakdown, and tumor cell migration, invasion, and metastasis. Activation of the urokinase plasminogen activator (uPA) and its receptor (uPAR) axis promotes prostate cancer tumorigenicity, invasion, metastasis, and survival within the tumor microenvironment. The link between macrophage infiltration and the uPA/uPAR axis in prostate cancer development has not been established, although it has been reported that uPA plays a critical role inmonocyte and macrophage chemotaxis. In this study, murine prostate cancer RM-1 cells were subcutaneously inoculated into wild-type (WT), uPA(-/-), and uPAR(-/-) mice. Tumor volume was significantly diminished in both uPA(-/-) and uPAR(-/-) mice compared with WT controls. Greater inhibition of tumor volume was also observed in uPA(-/-) mice compared with uPAR(-/-) mice, suggesting the important contribution of stromal-derived uPA to sustain the tumor growth. Immunohistochemical staining revealed that tumors in uPA(-/-) and uPAR(-/-) mice displayed significantly lower proliferative indices, higher apoptotic indices, and less neovascularity compared with the tumors in WT mice. Tumors in uPA(-/-) and uPAR(-/-) mice displayed significantly less macrophage infiltration as demonstrated by F4/80 staining and MAC3(+) cell numbers by flow cytometry compared with the tumors from WT mice. These findings suggest that the uPA/uPAR axis acts in both autocrine and paracrine manners in the tumor microenvironment, and activation of uPA/uPAR axis is essential for macrophage infiltration into prostate tumors.

Single-chain urokinase in empyema induced by Pasturella multocida

Intrapleural fibrin deposition and subsequent fibrosis characterize evolving empyema and contribute to the morbidity associated with this condition. Single-chain urokinase (scuPA) is proenzyme form of the urokinase plasminogen activator, which has recently been shown to effectively clear intrapleural loculation in tetracycline-induced pleurodesis in rabbits. The authors therefore hypothesized that scuPA could likewise improve intrapleural injury associated with empyema. The authors used a rabbit model of empyema induced by intrapleural administration of Pasturella multocida to test this hypothesis and determined the effects of intrapleural scuPA on pleural fluids indices of inflammation and intrapleural fibrosis. The authors found that intrapleural administration of scuPA was well tolerated, generated readily detectable fibrinolytic activity in the empyema fluids and did not induce intrapleural or systemic bleeding. Pleural fluid volume, intrapleural protein, and D-dimer concentrations were increased at 24 and 48 hours (P < .01, respectively) after induction of empyema. Intrapleural loculation did not occur in the scuPA- or vehicle control-treated animals and there was no significant change in the pleural empyema or thickening scores. These findings confirm that intrapleural scuPA generates fibrinolysis in empyema fluids but does not alter fibrotic repair at the pleural surface or the intensity of intrapleural inflammation in this empyema model.

Regulation of airway contractility by plasminogen activators through N-methyl-D-aspartate receptor-1

Reactive airway disease is mediated by smooth muscle contraction initiated through several agonist-dependent pathways. Activation of type 1 N-methyl-D-aspartate receptors (NMDA-R1s) by plasminogen activators (PAs) has been linked to control of vascular tone, but their effect on airway smooth muscle contractility has not previously been studied to our knowledge. We observed that NMDA-R1s are expressed by human airway smooth muscle cells and constitutively inhibit the contraction of isolated rat tracheal rings in response to acetylcholine (Ach). Both tissue-type PA (tPA) and urokinase-type PA (uPA) bind to NMDA-R1 and reverse this effect, thereby enhancing Ach-induced tracheal contractility. Tracheal contractility initiated by Ach is reduced in rings isolated from tPA(-/-) and uPA(-/-) mice compared with their wild-type counterparts. The procontractile effect of uPA or tPA was mimicked and augmented by the nitric oxide synthase inhibitor, l-NAME. uPA and tPA further enhanced the contractility of rings denuded of epithelium, an effect that was inhibited by the NMDA-R antagonist, MK-801. Binding of PAs to NMDA-R1 and the subsequent activation of the receptor were inhibited by PA inhibitor type 1, by a PA inhibitor type 1-derived hexapeptide that recognizes the tPA and uPA docking domains, as well as by specific mutations within the docking site of tPA. These studies identify involvement of PAs and NMDA-R1 in airway contractility, and define new loci that could lead to the development of novel interventions for reactive airway disease.

Elevated PAI-1 is associated with poor clinical outcomes in pediatric patients with acute lung injury

Purpose

Deposition of fibrin in the alveolar space is a hallmark of acute lung injury (ALI). Plasminogen activator inhibitor-1 (PAI-1) is an antifibrinolytic agent that is activated during inflammation. Increased plasma and pulmonary edema fluid levels of PAI-1 are associated with increased mortality in adults with ALI. This relationship has not been examined in children. The objective of this study was to test whether increased plasma PAI-1 levels are associated with worse clinical outcomes in pediatric patients with ALI.

Design/methods

We measured plasma PAI-1 levels on the first day of ALI among 94 pediatric patients enrolled in two separate prospective, multicenter investigations and followed them for clinical outcomes. All patients met American European Consensus Conference criteria for ALI.

Results

A total of 94 patients were included. The median age was 3.2 years (range 16 days–18 years), the PaO₂/F_iO₂ was 141 ± 72 (mean ± SD), and overall mortality was 14/94 (15%). PAI-1 levels were significantly higher in nonsurvivors compared to survivors (P < 0.01). The adjusted odds of mortality doubled for every log increase in the level of plasma PAI-1 after adjustment for age and severity of illness.

Conclusions

Higher PAI-1 levels are associated with increased mortality and fewer ventilator-free days among pediatric patients with ALI. These findings suggest that impaired fibrinolysis may play a role in the pathogenesis of ALI in pediatric patients and suggest that PAI-1 may serve as a useful biomarker of prognosis in patients with ALI.

Soluble urokinase receptor conjugated to carrier red blood cells binds latent pro-urokinase and alters its functional profile

Coupling plasminogen activators to carrier red blood cells (RBC) prolongs their life-time in the circulation and restricts extravascular side effects, thereby allowing their utility for short-term thromboprophylaxis. Unlike constitutively active plasminogen activators, single chain urokinase plasminogen activator (scuPA) is activated by plasmin proteolysis or binding to its receptor, uPAR. In this study we conjugated recombinant soluble uPAR (suPAR) to rat RBC, forming RBC/suPAR complex. RBC carrying suPAR circulated in rats similarly to naïve RBC and markedly prolonged the circulation time of suPAR. RBC/suPAR carrying approximately 3x10(4) suPAR molecules per RBC specifically bound up to 2x10(4) molecules of scuPA, retained approximately 75% of scuPA-binding capacity after circulation in rats and markedly altered the functional profile of bound scuPA. RBC carrying directly conjugated scuPA adhered to endothelial cells, while showing no appreciable fibrinolytic activity. In contrast, RBC/suPAR loaded with scuPA did not exhibit increased adhesion to endothelium, while effectively dissolving fibrin clots. This molecular design, capitalizing on unique biological features of the interaction of scuPA with its receptor, provides a promising modality to deliver a pro-drug for prevention of thrombosis.

Urokinase receptor mediates lung fibroblast attachment and migration toward provisional matrix proteins through interaction with multiple integrins

Fibroblasts from patients with pulmonary fibrosis express higher levels of the receptor for urokinase, and the extent of fibrosis in some animal models exhibits a dependence on the urokinase receptor. Recent observations have identified the urokinase receptor as a trans-interacting receptor with consequences on signaling and cell responses that vary depending on its interacting partner, the relative levels of expression, and the state of cellular transformation. We undertook this study to define the urokinase-type plasminogen activator cellular receptor (u-PAR)-integrin interactions and to determine the functional consequences of such interactions on normal human lung fibroblast attachment and migration. u-PAR colocalizes in lammelipodia/filopodia with relevant integrins that mediate fibroblast attachment and spreading on the provisional matrix proteins vitronectin, fibronectin, and collagens. Inhibitory antibody studies have revealed that human lung fibroblasts utilize alpha(v)beta(5) to attach to vitronectin, predominantly alpha(5)beta(1) (and alpha(v)beta(3)) to attach to fibronectin, and alpha(1)beta(1), alpha(2)beta(1), and alpha(3)beta(1) to attach to collagen. Blocking studies with alpha-integrin subunit decoy peptides and u-PAR neutralizing antibodies indicate that u-PAR modulates the integrin-mediated attachment to purified provisional matrix proteins, to anti-integrin antibodies, or to fibroproliferative lesions from fibrotic lungs. Furthermore, these decoy peptides blunt fibroblast spreading and migration. We show that u-PAR can interact with multiple alpha-integrins but with a preference for alpha(3). Taken together, these data demonstrate that u-PAR may interact with multiple integrins in normal human lung fibroblasts thereby promoting attachment, spreading, and migration. Modulation of fibroblast invasion would be expected to lead to amelioration of fibroproliferative diseases of the lung.

4G/5G polymorphism of plasminogen activator inhibitor-1 gene is associated with mortality in intensive care unit patients with severe pneumonia

BACKGROUND

Higher plasma and pulmonary edema fluid levels of plasminogen activator inhibitor-1 (PAI-1) are associated with increased mortality in patients with pneumonia and acute lung injury. The 4G allele of the 4G/5G polymorphism of the PAI-1 gene is associated with higher PAI-1 levels and an increased incidence of hospitalizations for pneumonia. The authors hypothesized that the 4G allele would be associated with worse clinical outcomes (mortality and ventilator-free days) in patients with severe pneumonia.

METHODS

The authors enrolled patients admitted with severe pneumonia in a prospective cohort. Patients were followed until hospital discharge. DNA was isolated from blood samples, and genotyping detection for the PAI-1 4G/5G polymorphism was carried out using Taqman-based allelic discrimination.

RESULTS

A total of 111 patients were available for analysis. Distribution of genotypes was 4G/4G 26 of 111 (23%), 4G/5G 59 of 111 (53%), and 5G/5G 26 of 111 (23%). Of 111 patients, 32 (29%) died before hospital discharge and 105 patients (94%) received mechanical ventilation. Patients with the 4G/4G and the 4G/5G genotypes had higher mortality (35% vs. 8%, P = 0.007) and fewer ventilator-free days (median 4 vs. 13, P = 0.04) compared to patients with the 5G/5G genotype.

CONCLUSIONS

The 4G allele of the 4G/5G polymorphism in the PAI-1 gene is associated with fewer ventilator-free days and increased mortality in hospitalized patients with severe pneumonia. These findings suggest that PAI-1 may have a role in pathogenesis and that the 4G/5G polymorphism may be an important biomarker of risk in patients with severe pneumonia.

Post-transcriptional regulation of urokinase-type plasminogen activator receptor expression in lipopolysaccharide-induced acute lung injury

RATIONALE

Urokinase-type plasminogen activator (uPA) receptor (uPAR) is required for the recruitment of neutrophils in response to infection. uPA induces its own expression in lung epithelial cells, which involves its interaction with cell surface uPAR. Regulation of uPAR expression is therefore crucial for uPA-mediated signaling in infectious acute lung injury (ALI).

OBJECTIVES

To determine the role of uPA in uPAR expression during ALI caused by sepsis.

METHODS

We used Western blot, Northern blot, Northwestern assay, and immunohistochemistry. Phosphate-buffered saline- and lipopolysaccharide (LPS)-treated wild-type and uPA(-/-) mice were used.

MEASUREMENTS AND MAIN RESULTS

Biological activities of uPA, including proteolysis, cell adhesion, migration, proliferation, and differentiation, are dependent on its association with uPAR. Bacterial endotoxin (LPS) is a major cause of pulmonary dysfunction and infection-associated mortality. The present study shows that LPS induces uPAR expression both in vitro and in vivo, and that the mechanism involves post-transcriptional stabilization of uPAR mRNA by reciprocal interaction of phosphoglycerate kinase (PGK) and heterogeneous nuclear ribonucleoprotein C (hnRNPC) with uPAR mRNA coding region and 3' untranslated region determinants, respectively. The process involves tyrosine phosphorylation of PGK and hnRNPC. uPA(-/-) mice failed to induce uPAR expression after LPS treatment. In these mice, LPS treatment failed to alter the binding of PGK and hnRNPC protein with uPAR mRNA due to lack of tyrosine phosphorylation.

CONCLUSIONS

Our study shows that induction of LPS-mediated uPAR expression is mediated through tyrosine phosphorylation of PGK and hnRNPC. This involves expression of uPA as an obligate intermediary.

Enhanced levels of urokinase plasminogen activator and its soluble receptor in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by defective immunoglobulin production and high frequency of bacterial infections, autoimmunity and manifestations of chronic inflammation. The urokinase plasminogen activator (uPA), its cell bound and soluble receptor (uPAR, suPAR) have complex biological functions involving innate immune defense mechanisms and regulation of inflammation. Based on this dual role, we hypothesized that the uPA system could be affected in CVID, and examined expression of components of the uPA system in subgroups of CVID. All CVID-patients had increased plasma levels of suPAR with particularly high levels in those with splenomegaly and thrombocytopenia. Plasma uPA levels were also raised in these patients, and both suPAR and uPA levels correlated with the monocyte activation marker neopterin. Monocytes from CVID patients had increased expression of uPAR. We show an increased activation of the uPA system possibly contributing to the inflammatory phenotype seen in subgroups of CVID patients.

Urokinase-mediated recruitment of myeloid-derived suppressor cells and their suppressive mechanisms are blocked by MUC1/sec

The transmembrane isoform of mucin 1 (MUC1/TM) is a well-recognized tumor antigen, contributing to tumorigenesis and immune evasion. Although MUC1/TM has been correlated with malignancy, we have previously reported on antitumor properties and prevention of tumor development by a secreted splice variant of MUC1 (MUC1/sec). Because myeloid-derived suppressor cells (MDSCs) play a critical role in tumor-induced immunosuppression, we investigated their recruitment by tumor cells expressing either MUC1/TM or MUC1/sec. DA-3 tumor cells expressing MUC1/sec recruit dramatically lower levels of MDSCs, relative to MUC1/TM-expressing DA-3 cells. Because MUC1/sec was previously shown to down-regulate tumor expression of urokinase plasminogen activator (uPA), a protease linked to tumor aggressiveness and metastasis, the potential role of uPA in MDSC recruitment was investigated. Tumor-derived uPA is capable of recruiting MDSCs, and correlates with tumor development. In addition to diminishing recruitment of MDSCs, the effect of MUC1/sec on MDSC-suppressive mechanisms was investigated. MUC1/sec, or its unique immunoenhancing peptide, is capable of blocking expression of arginase 1 and production of reactive oxygen species in MDSCs, implicated in the suppression of T cells. These findings demonstrate a new mechanism of MDSC recruitment, and provide evidence that MUC1/sec has antitumor properties affecting MDSCs.

Chemotactically active proteins of neutrophils

Polymorphonuclear leukocytes (neutrophils) are the first cells that arrive at sites of infection or injury. There, besides their microorganism-targeted effector functions, activated neutrophils secrete numerous chemoattractants that recruit other leukocyte subtypes into the inflamed tissue. First, neutrophil activation leads to the upregulation of the gene expression of several classical chemokines of the CXC and CC families. Second, neutrophil granules contain preformed intracellular storage pools of chemotactically active proteins that are rapidly released upon neutrophil degranulation. The third pathway of generation of chemotactically active proteins by activated neutrophils--shedding and concomitant proteolytic processing of a membrane protein--has recently been demonstrated in our laboratory. In this review, we summarize the essential features of chemoattractant production by neutrophils and their contribution to orchestrating the recruitment of leukocyte subtypes during inflammatory response.

Urokinase-type plasminogen activator plays essential roles in macrophage chemotaxis and skeletal muscle regeneration

Although macrophages are thought to play important roles in tissue repair, the molecular mechanisms involved remain to be elucidated. Mice deficient in urokinase-type plasminogen activator (uPA-/-) exhibit decreased accumulation of macrophages following muscle injury and severely impaired muscle regeneration. We tested whether macrophage-derived uPA plays essential roles in macrophage chemotaxis and skeletal muscle regeneration. Macrophage uPA was required for chemotaxis, even when invasion through matrix was not necessary. The mechanism by which macrophage uPA promoted chemotaxis was independent of receptor binding but appeared to depend on proteolytic activity. Exogenous uPA restored chemotaxis to uPA-/- macrophages and rescued muscle regeneration in uPA-/- mice. Macrophage depletion in wild-type (WT) mice using clodronate liposomes resulted in impaired muscle regeneration, confirming that macrophages are required for efficient healing. Furthermore, transfer of WT bone marrow cells to uPA-/- mice restored macrophage accumulation and muscle regeneration. In this rescue, transferred WT cells appeared to contribute to IGF-1 expression but did not fuse to regenerating fibers. These data indicate that WT leukocytes, including macrophages, that express uPA were sufficient to rescue muscle regeneration in uPA-/- mice. Overall, the results indicate that uPA plays a fundamental role in macrophage chemotaxis and that macrophage-derived uPA promotes efficient muscle regeneration.

A urokinase-type plasminogen activator deficiency diminishes the frequency of intestinal adenomas in ApcMin/+ mice

The interaction of urokinase-type plasminogen activator (uPA) and its receptor, uPAR, on cell surfaces facilitates the generation of cell-bound plasmin, thus allowing cells to establish a proteolytic front that enables their migration through protein barriers. This complex also activates cell signalling pathways that influence cell functions. Clinical studies have identified uPA as an indicator of poor overall survival in patients with colorectal cancer. In the current study, a mouse model of colon cancer, Apc(Min/+), with an additional deficiency of uPA (Apc(Min/+)/Plau-/-) was used to determine the effects of uPA on tumour initiation and growth. Utilizing this model, it was found that the number of tumours was diminished in these mice relative to Apc(Min/+) mice, which correlated with the decreased leukocyte infiltration in the tumours. However, tumour growth was not impeded in Apc(Min/+)/Plau-/- mice, and proliferation and tumour vascularization were, in fact, enhanced in Apc(Min/+)/Plau-/- mice. These latter effects are consistent with a mechanism involving up-regulation of COX-2 expression and Akt pathway activation in Apc(Min/+)/Plau-/- mice. The results from this study suggest that uPA plays dual and opposing roles in regulating lesion development: one early, during the transition from normal epithelia to dysplastic lesions, and another later during tumour growth.

Chronic plasminogen activator inhibitor-1 (PAI-1) overexpression dampens CD25+ lymphocyte recruitment after lipopolysaccharide endotoxemia in mouse lung

BACKGROUND

Plasma plasminogen activator inhibitor-1 (PAI-1) level rises during sepsis and confers a worse prognosis. PAI-1 participation to sepsis has been poorly documented and was mainly associated with fibrin deposits. Beside fibrin deposits, increased tissue PAI-1 expression may contribute to the poor outcome of endotoxemia through other mechanisms.

OBJECTIVE AND METHODS

During lipopolysaccharide (LPS) challenge, the role of PAI-1 in the early phase of inflammation was examined in the lungs of transgenic mice that either overexpress or lack the PAI-1 gene (PAI-1Tg or PAI-1(-/-)).

RESULTS

Analysis of leukocytes revealed that neutrophil and macrophage infiltrations did not differ for PAI-1Tg and wild-type (WT) mice. Remarkably, CD25+ lymphocyte infiltration was totally blunted in PAI-1Tg lungs and inversely correlated with fibrin depositions. In parallel, mRNA levels of the regulatory T cell (Treg) markers FoxP3, CTLA-4, and GITR were significantly lower in PAI-1Tg than in WT lungs after LPS challenge. These data are supported by opposite results in PAI-1(-/-) lungs. The systemic compartments (spleen and peripheral blood) showed no decrease in CD25+, CD4+ CD25+ lymphocytes, and Treg markers in PAI-1Tg mice after LPS injection compared with WT mice. In addition, plasma and lung concentrations of interleukin-6 (IL-6) and macrophage inflammatory protein-1alpha (MIP-1alpha) were significantly higher in PAI-1Tg mice than WT mice.

CONCLUSION

Our results suggest that chronic tissue PAI-1 overexpression influences the early phase of the inflammatory response during endotoxemia through the control of T lymphocyte traffic.

NKT cell-derived urokinase-type plasminogen activator promotes peripheral tolerance associated with eye

In a model of peripheral tolerance called anterior chamber-associated immune deviation (ACAID), the differentiation of the T regulatory cells depends on NKT cells and occurs in the spleen. In this study, we show that NKT cells that express the invariant (i) TCR and are the CD1d-reactive NKT cells (required for development of peripheral tolerance) actually produced urokinase-type plasminogen activator (uPA) during tolerance induction. The RT-PCR and in vitro plasmin assay showed that splenic iNKT cells derived uPA-converted plasminogen to plasmin. Moreover, uPA was required for tolerance induction because uPA knockout (KO) mice did not develop peripheral tolerance or develop CD8(+) T regulatory cells after Ag inoculation into the anterior chamber. In contrast, other aspects of ACAID-induced tolerance, including recruitment of iNKT cells to the spleen and production of IL-10 by iNKT cells, were unchanged in uPA-deficient mice. The adoptive transfer of splenic NKT cells from wild-type mice restored ACAID in Jalpha18 KO mice (iNKT cell deficient), but NKT cells from uPA KO mice did not. We postulate that the mechanism of action of uPA is through its binding to the uPAR receptor, and enzymatic cleavage of plasminogen to plasmin, which in turn activates latent TGFbeta. In conclusion, uPA derived from iNKT cells is required to induce peripheral tolerance via the eye.

4G/5G plasminogen activator inhibitor-1 polymorphisms and haplotypes are associated with pneumonia

RATIONALE

Plasminogen activator inhibitor (PAI)-1 inhibits urokinase and tissue plasminogen activator, required for host response to infection. Whether variation within the PAI-1 gene is associated with increased susceptibility to infection is unknown.

OBJECTIVES

To ascertain the role of the 4G/5G polymorphism and other genetic variants within the PAI-1 gene. We hypothesized that variants associated with increased PAI-1 expression would be associated with an increased occurrence of community-acquired pneumonia (CAP).

METHODS

Longitudinal analysis (>12 yr) of the Health, Aging, and Body Composition cohort, aged 65-74 years at start of analysis.

MEASUREMENTS AND MAIN RESULTS

We genotyped the 4G/5G PAI-1 polymorphism and six additional single nucleotide polymorphisms. Of the 3,075 subjects, 272 (8.8%) had at least one hospitalization for CAP. Among whites, variants at the PAI4G,5G, PAI2846, and PAI7343 sites had higher risk of CAP (P = 0.018, 0.021, and 0.021, respectively). At these sites, variants associated with higher PAI-1 expression were associated with increased CAP susceptibility. Compared with the 5G/5G genotypes at PAI4G,5G site, the 4G/4G and 4G/5G genotypes were associated with a 1.98-fold increased risk of CAP (95% confidence interval, 1.2-3.2; P = 0.006). In whole blood stimulation assay, subjects with a 4G allele had 3.3- and 1.9-fold increased PAI-1 expression (P = 0.043 and 0.034, respectively). In haplotype analysis, the 4G/G/C/A haplotype at the PAI4G,5G, PAI2846, PAI4588, and PAI7343 single nucleotide polymorphisms was associated with higher CAP susceptibility, whereas the 5G/G/C/A haplotype was associated with lower CAP susceptibility. No associations were seen among blacks.

CONCLUSIONS

Genotypes associated with increased expression of PAI-1 were associated with increased susceptibility to CAP in elderly whites.

A guide to murine fibrinolytic factor structure, function, assays, and genetic alterations

The components and functions of the murine fibrinolytic system are quite similar to those of humans. Because of these similarities and the adaptability of mice to genetic manipulation, murine fibrinolysis has been studied extensively. These studies have yielded important information regarding the function of the several components of fibrinolysis. This review presents information on the structure, function and assay of mouse fibrinolytic parameters and it discusses the results of the extensive studies of genetically modified mice. It is intended to be a convenient reference resource for investigators of fibrinolysis.

Plasminogen activator inhibitor type-1-deficient mice have an enhanced IFN-gamma response to lipopolysaccharide and staphylococcal enterotoxin B

Plasminogen activator inhibitor type-1 (PAI-1) is a major inhibitor of fibrinolysis by virtue of its capacity to inhibit urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA). Systemic inflammation is invariably associated with elevated circulating levels of PAI-1, and during human sepsis plasma PAI-1 concentrations predict an unfavorable outcome. Knowledge about the functional role of PAI-1 in a systemic inflammatory response syndrome is highly limited. In this study, we determined the role of endogenous PAI-1 in cytokine release induced by administration of LPS or staphylococcal enterotoxin B (SEB). Both LPS and SEB elicited secretion of PAI-1 into the circulation of normal wild-type (Wt) mice. Relative to Wt mice, PAI-1 gene-deficient (PAI-1(-/-)) mice demonstrated strongly elevated plasma IFN-gamma concentrations after injection of either LPS or SEB. In addition, PAI-1(-/-) splenocytes released more IFN-gamma after incubation with LPS or SEB than Wt splenocytes. Both PAI-1(-/-) CD4+ and CD8+ T cells produced more IFN-gamma upon stimulation with SEB. LPS-induced IFN-gamma release in mice deficient for uPA, the uPA receptor, or tPA was not different from IFN-gamma release in LPS-treated Wt mice. These results identify a novel function of PAI-1 during systemic inflammation, where endogenous PAI-1 serves to inhibit IFN-gamma release by a mechanism that does not depend on its interaction with uPA/uPA receptor or tPA.

Inhibition of Urokinase-Type Plasminogen Activator or Matrix Metalloproteinases Prevents Cardiac Injury and Dysfunction During Viral Myocarditis

Background— Acute viral myocarditis is an important cause of cardiac failure in young adults for which there is no effective treatment apart from general heart failure therapy. The present study tested the hypothesis that increased expression of the proteinases urokinase-type plasminogen activator (uPA) and matrix metalloproteinases (MMPs) is implicated in cardiac inflammation, injury, and subsequent failure during Coxsackievirus-B3 (CVB3)–induced myocarditis.

Methods and Results— First, we showed increased expression and activity of uPA and MMP-9 in wild-type mice at 7 days of CVB3-induced myocarditis. Targeted deletion of uPA, which resulted in reduced MMP activity and cytokine expression or inhibition of MMPs by adenoviral gene overexpression of tissue inhibitor of metalloproteinases-1, decreased cardiac inflammation and reduced myocardial necrosis at 7 days and decreased cardiac fibrosis at 35 days after CVB3 infection. Importantly, loss of uPA or MMP activity prevented CVB3-induced cardiac dilatation and dysfunction, as determined by serial echocardiography.

Conclusions— Loss of uPA or MMP activity reduces the cardiac inflammatory response after CVB3 infection, thereby protecting against cardiac injury, dilatation, and failure during CVB3-induced myocarditis.

Mactinin treatment promotes wound-healing-associated inflammation in urokinase knockout mice

Mactinin, a 31 kDa fragment from the amino-terminal end of alpha-actinin, is chemotactic for monocytes and can promote monocyte/macrophage maturation. Macrophages are essential for wound healing, in which they play key roles in debridement, angiogenesis, fibroblast proliferation, and collagen metabolism. We have previously determined that urokinase is necessary to form mactinin from extracellular alpha-actinin, which may be present at sites of inflammation as a result of cell movement. Thus, urokinase knockout mice are unable to form mactinin and therefore are an ideal model to study mactinin's effects on wound healing. Saline- and mactinin-treated wounds were analyzed in a subcutaneous sponge wound model in both wild-type and urokinase knockout mice. The wounded urokinase knockout mice had markedly decreased leukocyte infiltration compared with wounded wild-type mice. In addition, production of the proinflammatory cytokine, interleukin-12, and of collagen was also decreased in knockouts. Treatment of knockout mice with mactinin resulted in leukocyte infiltration numbers, interleukin-12 levels, and hydroxyproline measurements similar to those in wild-type mice. The results suggest that impaired wound healing in urokinase-deficient mice can be restored by administration of mactinin.

Fibrin-induced skin fibrosis in mice deficient in tissue plasminogen activator

The deposition of fibrin is an integral part of the tissue repair process, but its persistence is also associated with a number of fibrotic conditions. This study addressed the hypothesis that reduced fibrinolysis and fibrin persistence are associated with an enhanced accumulation of collagen and the development of skin fibrosis. Decreased fibrinolysis was confirmed in fibrin gel cultures that contained human dermal fibroblasts plus the specific plasmin inhibitor alpha(2)-antiplasmin or dermal fibroblasts isolated from plasminogen activator (PA)-deficient mice. Collagen accumulation was significantly increased in the presence of inhibitor and in tPA-deficient, but not uPA-deficient, fibroblasts compared with controls. These findings were also confirmed using a skin fibrosis model in which multiple injections of fibrin were given subcutaneously to PA-deficient mice. Injection sites from tPA-deficient mice displayed significantly increased collagen levels compared with uPA-deficient mice and wild-type controls. Up-regulation of fibroblast procollagen gene expression and reduced activation of pro-MMP-1 appeared to mediate the increase in collagen by human dermal fibroblasts in the presence of alpha2-antiplasmin. These findings suggest that persistent fibrin is associated with enhanced collagen accumulation that may result in the development of fibrotic skin disorders in which reduced fibrinolysis is a feature.

Urokinase-induced activation of the gp130/Tyk2/Stat3 pathway mediates a pro-inflammatory effect in human mesangial cells via expression of the anaphylatoxin C5a receptor

Glomerular mesangial cells (MCs) are central to the pathogenesis of progressive glomeruli-associated renal diseases. However, molecular mechanisms underlying changes in MC functions still remain poorly understood. Here, we show that in MCs, the urokinase-type plasminogen activator (uPA) induces, via its specific receptor (uPAR, CD87), upregulated expression of the complement anaphylatoxin C5a receptor (C5aR, CD88), and modulates C5a-dependent functional responses. This effect is mediated via the interaction of the uPA-specific receptor (uPAR, CD87) and gp130, a signal transducing subunit of the receptor complexes for the IL-6 cytokine family. The Janus kinase Tyk2 and the transcription factor Stat3 serve as downstream components in the signaling cascade resulting in upregulation of C5aR expression. In vivo, expression of C5aR and uPAR was increased in the mesangium of wild-type mice in a lipopolysaccharide (LPS)-induced model of inflammation, whereas in uPAR(-/-) animals C5aR expression remained unchanged. This is the first demonstration in vitro and in vivo that uPA acts in MCs as a modulator of immune responses via control of immune-competent receptors. The data suggest a novel role for uPA/uPAR in glomeruli-associated renal failure via a signaling cross-talk between the fibrinolytic and immune systems.

Mice deficient in plasminogen activator inhibitor-1 have improved skeletal muscle regeneration

Skeletal muscle possesses a remarkable capacity for regeneration. Although the regulation of this process at the molecular level remains largely undefined, the plasminogen system appears to play a critical role. Specifically, mice deficient in either urokinase-type plasminogen activator (uPA−/−mice) or plasminogen demonstrate markedly impaired muscle regeneration after injury. In the present study, we tested the hypothesis that loss of the primary inhibitor of uPA, plasminogen activator inhibitor-1 (PAI-1), would improve muscle regeneration. Repair of the extensor digitorum longus muscle was assessed after cardiotoxin injury in wild-type, uPA−/−, and PAI-1-deficient (PAI-1−/−) mice. As expected, there was no uPA activity in the injured muscles of uPA−/−mice, and muscles from these transgenic animals demonstrated impaired regeneration. On the other hand, uPA activity was increased in injured muscle from PAI-1−/−mice to a greater extent than in wild-type controls. Furthermore, PAI-1−/−mice demonstrated increased expression of MyoD and developmental myosin after injury as well as accelerated recovery of muscle morphology, protein levels, and muscle force compared with wild-type animals. The injured muscles of PAI-1-null mice also demonstrated increased macrophage accumulation, contrasting with impaired macrophage accumulation in uPA-deficient mice. The extent of macrophage accumulation correlated with both the clearance of protein after injury and the efficiency of regeneration. Taken together, these results indicate that PAI-1 deficiency promotes muscle regeneration, and this protease inhibitor represents a therapeutic target for enhancing muscle regeneration.

The role of urokinase in innate immunity against Staphylococcus aureus

Urokinase (uPA) is a serine protease that not only displays fibrinolytic function but also promotes host leukocytes to home to inflammatory sites. We have recently demonstrated that staphylokinase (SAK), which is a fibrinolytic protein secreted by Staphylococcus aureus, forms complexes with human neutrophil peptides (HNPs), which are members of the defensin family and have anti-microbial properties, thereby inhibiting the bactericidal effects of the HNPs. The aim of this study was to assess whether endogenous uPA, which has fibrinolytic properties similar to those of SAK, binds to HNPs and interferes with SAK/HNPs interaction. To this end, an ELISA was used to analyze the interactions between uPA and HNPs. HMW uPA had the ability to bind to both HNP types. The biological consequences of the formation of this complex were analyzed with respect to its bactericidal properties. HMW uPA killed S. aureus, albeit at relatively high doses (50-100 mug/ml). In contrast, the binding of HMW uPA to HNPs had no impact on the bactericidal functions of the HNPs. Importantly, the addition of HMW uPA to SAK eliminated the ability of SAK to neutralize HNPs. Our results demonstrate that endogenous HMW uPA inhibits S. aureus growth both directly, by cytolysis, and indirectly, by abrogation of the neutralizing effect of SAK on the bactericidal activities of HNPs. These findings indicate novel functions of HMW uPA in the host defense against staphylococcal infections.

Pathogenesis of pleural fibrosis

Pleural fibrosis resembles fibrosis in other tissues and can be defined as an excessive deposition of matrix components that results in the destruction of normal pleural tissue architecture and compromised function. Pleural fibrosis may be the consequence of an organised haemorrhagic effusion, tuberculous effusion, empyema or asbestos-related pleurisy and can manifest itself as discrete localised lesions (pleural plaques) or diffuse pleural thickening and fibrosis. Although the pathogenesis is unknown, it is likely that the complex interactions between resident and inflammatory cells, profibrotic mediators and coagulation, and fibrinolytic pathways are integral to pleural remodelling and fibrosis. It is generally considered that the primary target cell for pleural fibrosis is the subpleural fibroblast. However, increasing evidence suggests that mesothelial cells may also play a significant role in the pathogenesis of this condition, both by initiating inflammatory responses and producing matrix components. A greater understanding of the interactions between pleural and inflammatory cells, cytokines and growth factors, and blood derived proteins is required before adequate therapies can be developed to prevent pleural fibrosis from occurring.