Abstract 413: A Dominant Negative Mutant of Plasminogen Activator Inhibitor-1 Does Not Inhibit Intimal Hyperplasia After Balloon Coronary Angioplasty in Pigs

Background. Plasminogen activator inhibitor 1 (PAI-1) regulates arterial remodeling and intimal hyperplasia after vascular injury. PAI-1-R is a recombinant mutant that completely lacks anti-protease activity yet binds vitronectin (VN) with normal affinity. PAI-1-R inhibits cell migration in vitro and neointima formation in rodents by binding VN and competitively blocking its binding to integrins.

Objective and Methods. To determine if PAI-1-R inhibits intimal hyperplasia under experimental conditions highly relevant to human coronary artery disease we performed balloon angioplasty of the left circumflex coronary artery (LCX) of male pigs and administered PAI-1-R by direct coronary infusion immediately after angioplasty and by peripheral intravenous infusion on each of the next two days (5 mg/infusion; total dose 15 mg/pig). Thirteen pigs (weight 24±4.3 kg) received PAI-1-R and 13 pigs (weight 24 ± 4.7 kg) received identical infusions of vehicle control. Animals were euthanized 14 days after angioplasty and neointima formation in the injured LCX was determined by microscopic morphometric analysis.

Results. Plasma PAI-1-R concentrations assessed 1 hr after each infusion were 32±18, 89±60, and 59±16 ng/mL, respectively, in PAI-1-R-treated pigs and undetectable in controls. There was no significant difference in LCX neointima formation between PAI-1-R- vs. vehicle-treated pigs (maximal intima thickness 523±47 vs. 581±49 μm, p=0.41; intima area/media area normalized to media rupture length 3.7±0.3 vs 3.8±0.3, p=0.8).

Conclusion. Short-term, bolus infusions of a dominant negative form of PAI-1 do not significantly inhibit neointima formation in pigs after coronary angioplasty. These results contrast with rodent data and suggest that alternative strategies that achieve higher concentrations of PAI-1-R at vascular injury sites will be required to assess the efficacy of this strategy under clinically relevant conditions.

Matrix-bound PAI-1 supports cell blebbing via RhoA/ROCK1 signaling

The microenvironment of a tumor can influence both the morphology and the behavior of cancer cells which, in turn, can rapidly adapt to environmental changes. Increasing evidence points to the involvement of amoeboid cell migration and thus of cell blebbing in the metastatic process; however, the cues that promote amoeboid cell behavior in physiological and pathological conditions have not yet been clearly identified. Plasminogen Activator Inhibitor type-1 (PAI-1) is found in high amount in the microenvironment of aggressive tumors and is considered as an independent marker of bad prognosis. Here we show by immunoblotting, activity assay and immunofluorescence that, in SW620 human colorectal cancer cells, matrix-associated PAI-1 plays a role in the cell behavior needed for amoeboid migration by maintaining cell blebbing, localizing PDK1 and ROCK1 at the cell membrane and maintaining the RhoA/ROCK1/MLC-P pathway activation. The results obtained by modeling PAI-1 deposition around tumors indicate that matrix-bound PAI-1 is heterogeneously distributed at the tumor periphery and that, at certain spots, the elevated concentrations of matrix-bound PAI-1 needed for cancer cells to undergo the mesenchymal-amoeboid transition can be observed. Matrix-bound PAI-1, as a matricellular protein, could thus represent one of the physiopathological requirements to support metastatic formation.

Platelet-derived growth factor C deficiency in C57BL/6 mice leads to abnormal cerebral vascularization, loss of neuroependymal integrity, and ventricular abnormalities

Platelet-derived growth factors (PDGFs) and their tyrosine kinase receptors (PDGFRs) are known to play important roles during development of the lungs, central nervous system (CNS), and skeleton and in several diseases. PDGF-C is a ligand for the tyrosine kinase receptor PDGFRα. Mutations in the gene encoding PDGF-C have been linked to clefts of the lip and/or palate in humans, and ablation of PDGF-C in 129/Sv background mice results in death during the perinatal period. In this study, we report that ablation of PDGF-C in C57BL/6 mice results in a milder phenotype than in 129/Sv mice, and we present a phenotypic characterization of PDGF-C deficiency in the adult murine CNS. Multiple congenital defects were observed in the CNS of PDGF-C-null C57BL/6 mice, including cerebral vascular abnormalities with abnormal vascular smooth muscle cell coverage. In vivo imaging of mice deficient in PDGF-C also revealed cerebral ventricular abnormalities, such as asymmetry of the lateral ventricles and hypoplasia of the septum, reminiscent of cavum septum pellucidum in humans. We further noted that PDGF-C-deficient mice displayed a distorted ependymal lining of the lateral ventricles, and we found evidence of misplaced neurons in the ventricular lining. We conclude that PDGF-C plays a critical role in the development of normal cerebral ventricles and neuroependymal integrity as well as in normal cerebral vascularization.

Impaired fibrinolytic system in ApoE gene-deleted mice with hyperlipidemia augments deep vein thrombosis

BACKGROUND

Hyperlipidemia increases the level of blood plasminogen activator inhibitor-1 (PAI-1) that is responsible for regulating fibrinolysis by inhibiting both urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA). While this fibrinolytic pathway is well known, the role of PAI-1 in venous thrombosis (VT) under hyperlipidemic conditions has not been fully established. We sought to determine the effects of PAI-1 in an in vivo hyperlipidemic model of VT.

METHODS

C57BL/6 wild-type (WT) mice, apolipoprotein E gene-deleted mice (ApoE-/-) having hyperlipidemia, and PAI-1 gene-deleted (PAI-1-/-) mice were used in this study. Inferior vena cava (IVC) ligation below the level of the renal veins was performed to create a stasis VT. Endpoints included measuring acute thrombosis (day 2) and chronic thrombosis (days 6 and 14). At euthanasia, blood samples were collected for plasmin and PAI-1 activity. In addition, the IVC and its thrombus were evaluated for thrombus weight (TW), u-PA activity, and differential leukocyte count while the vein wall only was analyzed for monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinase (MMP) 2, and MMP-9.

RESULTS

Compared to WT at day 2, ApoE-/-mice demonstrated a statistically significant 14% increase in TW (P < .05) and a significant 41% increase in circulating PAI-1 activity (P < .05), while showing a trend of decreased plasmin activity. In addition, TW in ApoE-/-mice was 45% higher than PAI-1-/-mice at day 2 (P < .05), 33% at day 6 (P < .01), and 41% at day 14 (P < .01). ApoE-/-mice exhibited undetectable levels of u-PA in both vein wall and thrombus, compared to WT, at all time points. Also, vein wall MMP-2 was significantly decreased by 64% at day 6 (P < .01) and 58% at day 14 (P < .05). MMP-9 was significantly decreased by 71% at day 2 (P < .01) and 48% at day 6 (P < .01), in ApoE-/-mice compared to WT mice. In addition, in ApoE-/-mice, MCP-1 was significantly decreased by 38% at day 2 (P < .01) and 67% at day 6 (P < .01) vs WT mice. As expected in ApoE mice, following a decrease in MCP-1, monocyte recruitment was significantly decreased at days 6 (P < .01) and 14 (P < .05).

CONCLUSIONS

A significant increase of circulating PAI-1 levels in hyperlipidemic mice correlated with an early increase in TW due to impaired fibrinolysis. The undetectable levels of u-PA in ApoE-/-mice correlated to a decrease in vein wall MMP-2, MMP-9, MCP-1, and a decrease in monocyte recruitment diminishing thrombus resolution.

The thrombomodulin analog Solulin promotes reperfusion and reduces infarct volume in a thrombotic stroke model

BACKGROUND

 Currently there is no approved anticoagulant for treating acute stroke. This is largely because of concern for hemorrhagic complications, and suggests a critical need for safer anticoagulants. Solulin is a soluble analog of the endothelial cell receptor thrombomodulin, able to bind free thrombin and convert it to an activator of the anticoagulant, protein C.

OBJECTIVE

 Solulin was tested for its ability to inhibit middle cerebral artery occlusion (MCAO) induced by photothrombosis, and to restore MCA patency after establishment of stable occlusion.

METHODS

 Cerebral blood flow (CBF) was monitored by laser Doppler for 1.5 h after occlusion and again 72 h later.

RESULTS

 Solulin treatment 30 min before thrombosis resulted in an approximately 50% increase in time to form a stable occlusion. When administered 30 or 60 min after MCAO, Solulin significantly improved CBF within 90 min of treatment. In contrast, none of the vehicle-treated mice showed restoration of CBF in the first 90 min and only 17% did so by 72 h. Solulin treatment was associated with a significant reduction in infarct volume, and was well tolerated with no overt hemorrhage observed in any treatment group. Mechanistic studies in mice homozygous for the factor (F)V Leiden mutation, suggest that Solulin's efficacy derives primarily from the anticoagulant activity of the thrombin-Solulin complex and not from direct anti-inflammatory or neuroprotective effects of Solulin or activated protein C.

CONCLUSIONS

 Our data indicate that Solulin is a safe and effective anticoagulant that is able to antagonize active thrombosis in acute ischemic stroke, and to reduce infarct volume.

Multifaceted role of plasminogen activator inhibitor-1 in regulating early remodeling of vein bypass grafts

OBJECTIVE

The role of plasminogen activator inhibitor-1 (PAI-1) in vein graft (VG) remodeling is undefined. We examined the effect of PAI-1 on VG intimal hyperplasia and tested the hypothesis that PAI-1 regulates VG thrombin activity.

METHODS AND RESULTS

VGs from wild-type (WT), Pai1(-/-), and PAI-1-transgenic mice were implanted into WT, Pai1(-/-), or PAI-1-transgenic arteries. VG remodeling was assessed 4 weeks later. Intimal hyperplasia was significantly greater in PAI-1-deficient mice than in WT mice. The proliferative effect of PAI-1 deficiency was retained in vitronectin-deficient mice, suggesting that PAI-1's antiproteolytic function plays a key role in regulating intimal hyperplasia. Thrombin-induced proliferation of PAI-1-deficient venous smooth muscle cells (SMC) was significantly greater than that of WT SMC, and thrombin activity was significantly higher in PAI-1-deficient VGs than in WT VGs. Increased PAI-1 expression, which has been associated with obstructive VG disease, did not increase intimal hyperplasia.

CONCLUSIONS

Decreased PAI-1 expression (1) promotes intimal hyperplasia by pathways that do not require vitronectin and (2) increases thrombin activity in VG. PAI-1 overexpression, although it promotes SMC migration in vitro, did not increase intimal hyperplasia. These results challenge the concept that PAI-1 drives nonthrombotic obstructive disease in VG and suggest that PAI-1's antiproteolytic function, including its antithrombin activity, inhibits intimal hyperplasia.

Proteomic analysis of the Vibrio cholerae type II secretome reveals new proteins, including three related serine proteases

The type II secretion (T2S) system is responsible for extracellular secretion of a broad range of proteins, including toxins and degradative enzymes that play important roles in the pathogenesis and life cycle of many gram-negative bacteria. In Vibrio cholerae, the etiological agent of cholera, the T2S machinery transports cholera toxin, which induces profuse watery diarrhea, a hallmark of this life-threatening disease. Besides cholera toxin, four other proteins have been shown to be transported by the T2S machinery, including hemagglutinin protease, chitinase, GbpA, and lipase. Here, for the first time, we have applied proteomic approaches, including isotope tagging for relative and absolute quantification coupled with multidimensional liquid chromatography and tandem mass spectrometry, to perform an unbiased and comprehensive analysis of proteins secreted by the T2S apparatus of the V. cholerae El Tor strain N16961 under standard laboratory growth conditions. This analysis identified 16 new putative T2S substrates, including sialidase, several proteins participating in chitin utilization, two aminopeptidases, TagA-related protein, cytolysin, RbmC, three hypothetical proteins encoded by VCA0583, VCA0738, and VC2298, and three serine proteases VesA, VesB, and VesC. Focusing on the initial characterization of VesA, VesB, and VesC, we have confirmed enzymatic activities and T2S-dependent transport for each of these proteases. In addition, analysis of single, double, and triple protease knock-out strains indicated that VesA is the primary protease responsible for processing the A subunit of cholera toxin during in vitro growth of the V. cholerae strain N16961.

Plasminogen activator inhibitor-1 and vitronectin expression level and stoichiometry regulate vascular smooth muscle cell migration through physiological collagen matrices

BACKGROUND

Vascular smooth muscle cell (VSMC) migration is a critical process in arterial remodeling. Purified plasminogen activator inhibitor-1 (PAI-1) is reported to both promote and inhibit VSMC migration on two-dimensional (D) surfaces.

OBJECTIVE

To determine the effects of PAI-1 and vitronectin (VN) expressed by VSMC themselves on migration through physiological collagen matrices.

METHODS

We studied migration of wild-type (WT), PAI-1-deficient, VN-deficient, PAI-1/VN doubly-deficient (DKO) and PAI-1-transgenic (Tg) VSMC through three-D collagen gels.

RESULTS

WT VSMC migrated significantly slower than PAI-1- and VN-deficient VSMC, but significantly faster than DKO VSMC. Experiments with recombinant PAI-1 suggested that basal VSMC PAI-1 expression inhibits migration by binding VN, which is secreted by VSMC and binds collagen. However, PAI-1-over-expressing Tg VSMC migrated faster than WT VSMC. Reconstitution experiments with recombinant PAI-1 mutants suggested that the pro-migratory effect of PAI-1 over-expression required its anti-plasminogen activator (PA) and LDL receptor-related protein (LRP) binding functions, but not VN binding. While promoting VSMC migration in the absence of PAI-1, VN inhibited the pro-migratory effect of active PAI-1.

CONCLUSIONS

In isolation, VN and PAI-1 are each pro-migratory. However, via formation of a high-affinity, non-motogenic complex, PAI-1 and VN each buffers the other's pro-migratory effect. The level of PAI-1 expression by VSMC and the concentration of VN in extracellular matrix are critical determinants of whether PAI-1 and VN promote or inhibit migration. These findings help to rectify previously conflicting reports and suggest that PAI-1/VN stoichiometry plays an important role in VSMC migration and vascular remodeling.

Low density lipoprotein receptor-related protein-1 (LRP1) regulates thrombospondin-2 (TSP2) enhancement of Notch3 signaling

Intracellular trafficking of Notch and Notch ligands modulates signaling, suggesting that choreography of ligand and receptor translocation is essential for optimal Notch activity. Indeed, a major model for Notch signaling posits that Notch trans-endocytosis into the ligand-expressing (signal sending) cell is a key driving force for Notch signal transduction. The extracellular protein thrombospondin-2 (TSP2) enhances Notch signaling and binds to both Jagged1 and Notch3 ectodomains, potentially bridging two essential extracellular components of Notch signaling. We investigated the role of low density lipoprotein receptor-related protein-1 (LRP1), a TSP2 receptor, in the regulation of Notch3 signaling. TSP2 potentiation of Notch is blocked by the receptor-associated protein (an inhibitor of low density lipoprotein receptor-related protein function) and requires LRP1 expression in the signal-sending cell. TSP2 stimulates Notch3 endocytosis into wild type fibroblasts but not LRP1-deficient fibroblasts. Finally, recombinant Notch3 and Jagged1 interact with the LRP1 85-kDa B-chain, a subunit that lacks known ligand binding function. Our data suggest that LRP1 and TSP2 stimulate Notch activity by driving trans-endocytosis of the Notch ectodomain into the signal-sending cell and demonstrate a novel, non-cell autonomous function of LRP1 in cell-cell signaling.

Sex effects of interleukin-6 deficiency on neuroinflammation in aged C57Bl/6 mice

High levels of Interleukin-6 (IL-6) are associated with an increased risk of dementia in the elderly and can increase neuroinflammation in mice. Dementia is more frequent in females, and IL-6 is regulated by estrogen, suggesting that elevated IL-6 levels may contribute to neuroinflammation and dementia particularly in women. Therefore we hypothesized that IL-6 deficient ((-/-)) female mice would have lower aging-related neuroinflammation than wild type (WT). We quantified neuroinflammatory markers which are affected by aging, and regulated by both estrogen and IL-6; glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), interferon gamma (IFNgamma), lipid peroxidation (MDA), and synaptic density (SNAP25) and in IL-6(-/-) and WT C57Bl/6 mice. To determine age effects we used mid-age (18months) and old-age (24months) mice, and to determine region specific effects we used the hippocampus which is impaired in dementia and the cerebellum which is unimpaired in dementia. Unexpectedly, there were no effects of IL-6 deficiency on GFAP, MDA or SNAP25 levels in females, but IL-6 deficiency was associated with lower cerebellar MBP (p<0.05) levels. Interestingly, the old-aged IL-6(-/-) males had higher GFAP and MDA levels (p<0.05) in both the hippocampus and cerebellum, in addition to a greater body weight than WT. We suggest that IL-6 is important for promoting myelin synthesis in aged females, and that drugs which inhibit the synthesis of IL-6 in males may inadvertently affect fatty acid metabolism and augment aging-related neuroinflammation.

Characterization of a novel class of polyphenolic inhibitors of plasminogen activator inhibitor-1

Plasminogen activator inhibitor type 1, (PAI-1) the primary inhibitor of the tissue-type (tPA) and urokinase-type (uPA) plasminogen activators, has been implicated in a wide range of pathological processes, making it an attractive target for pharmacologic inhibition. Currently available small-molecule inhibitors of PAI-1 bind with relatively low affinity and do not inactivate PAI-1 in the presence of its cofactor, vitronectin. To search for novel PAI-1 inhibitors with improved potencies and new mechanisms of action, we screened a library selected to provide a range of biological activities and structural diversity. Five potential PAI-1 inhibitors were identified, and all were polyphenolic compounds including two related, naturally occurring plant polyphenols that were structurally similar to compounds previously shown to provide cardiovascular benefit in vivo. Unique second generation compounds were synthesized and characterized, and several showed IC(50) values for PAI-1 between 10 and 200 nm. This represents an enhanced potency of 10-1000-fold over previously reported PAI-1 inactivators. Inhibition of PAI-1 by these compounds was reversible, and their primary mechanism of action was to block the initial association of PAI-1 with a protease. Consistent with this mechanism and in contrast to previously described PAI-1 inactivators, these compounds inactivate PAI-1 in the presence of vitronectin. Two of the compounds showed efficacy in ex vivo plasma and one blocked PAI-1 activity in vivo in mice. These data describe a novel family of high affinity PAI-1-inactivating compounds with improved characteristics and in vivo efficacy, and suggest that the known cardiovascular benefits of dietary polyphenols may derive in part from their inactivation of PAI-1.

Novel bis-arylsulfonamides and aryl sulfonimides as inactivators of plasminogen activator inhibitor-1 (PAI-1)

Inactivators of plasminogen activator inhibitor-1 (PAI-1) have been identified as possible treatments for a range of conditions, including atherosclerosis, venous thrombosis, and obesity. We describe the synthesis and inhibitory activity of a novel series of compounds based on bis-arylsulfonamide and aryl sulfonimide motifs that show potent and specific activity towards PAI-1. Inhibitors containing short linking units between the sulfonyl moieties and a 3,4-dihydroxy aryl substitution pattern showed the most potent inhibitory activity, and retained high specificity for PAI-1 over the structurally-related serpin anti-thrombin III (ATIII).

Antimetastatic potential of PAI-1-specific RNA aptamers

The serine protease inhibitor plasminogen activator inhibitor-1 (PAI-1) is increased in several cancers, including breast, where it is associated with a poor outcome. Metastatic breast cancer has a dismal prognosis, as evidenced by treatment goals that are no longer curative but are largely palliative in nature. PAI-1 competes with integrins and the urokinase plasminogen activator receptor on the surface of breast cancer cells for binding to vitronectin. This results in the detachment of tumor cells from the extracellular matrix, which is critical to the metastatic process. For this reason, we sought to isolate RNA aptamers that disrupt the interaction between PAI-1 and vitronectin. Through utilization of combinatorial chemistry techniques, aptamers have been selected that bind to PAI-1 with high affinity and specificity. We identified two aptamers, WT-15 and SM-20, that disrupt the interactions between PAI-1 and heparin, as well as PAI-1 and vitronectin, without affecting the antiprotease activity of PAI-1. Furthermore, SM-20 prevented the detachment of breast cancer cells (MDA-MB-231) from vitronectin in the presence of PAI-1, resulting in an increase in cellular adhesion. Therefore, the PAI-1 aptamer SM-20 demonstrates therapeutic potential as an antimetastatic agent and could possibly be used as an adjuvant to traditional chemotherapy for breast cancer.

Mechanisms underlying the antifibrotic properties of noninhibitory PAI-1 (PAI-1R) in experimental nephritis

Administration of a mutant, noninhibitory PAI-1 (PAI-1R), reduces disease in experimental glomerulonephritis. Here we investigated the importance of vitronectin (Vn) binding, PAI-1 stability and protease binding in this therapeutic effect using a panel of PAI-1 mutants differing in half-life, protease binding, and Vn binding. PAI-1R binds Vn normally but does not inhibit proteases. PAI-1AK has a complete defect in Vn binding but retains full inhibitory activity, with a short half-life similar to wild-type (wt)-PAI-1. Mutant 14-lb is identical to wt-PAI-1 but with a longer half-life. PAI-1K has defective Vn binding, inhibits proteases normally, and has a long half-life. In vitro wt-PAI-1 dramatically inhibited degradation of mesangial cell ECM while the AK mutant had much less effect. Mutants 14-1b and PAI-1K, like wt-PAI-1, inhibited matrix degradation but PAI-1R failed to reverse this inhibition although PAI-1R reversed the wt-PAI-1-induced inhibition of ECM degradation in a plasmin-, time-, and dose-dependent manner. Thus the ability of PAI-1 to inhibit ECM degradation is dependent both on its antiproteinase activity and on maintaining an active conformation achieved either by Vn binding or mutation to a stable form. Administration of these PAI-1 mutants to nephritic rats confirmed the in vitro data; only PAI-1R showed therapeutic effects. PAI-1K did not bind to nephritic kidney, indicating that Vn binding is essential to the therapeutic action of PAI-1R. The ability of PAI-1R to remain bound to Vn even in a high-protease environment is very likely the key to its therapeutic efficacy. Furthermore, because both PAI-1R and 14-1b bound to the nephritic kidney in the same pattern and differ only in their ability to bind proteases, lack of protease inhibition is also keyed to PAI-1R's therapeutic action.

Recombinant plasminogen activator inhibitor-1 inhibits intimal hyperplasia

OBJECTIVE

Plasminogen activator inhibitor-1 (PAI-1) overexpression is implicated in vascular disease. However, the effects of a primary increase in PAI-1 expression on arterial remodeling are poorly defined. We tested the hypothesis that recombinant PAI-1 inhibits intimal hyperplasia after vascular injury.

METHODS AND RESULTS

Rats underwent carotid artery injury and received intraperitoneal injections of saline or mutant forms of PAI-1 for 14 days, including an active stable mutant (PAI-1-14-1b), a mutant lacking anti-PA activity (PAI-1-R), or a mutant defective in vitronectin (VN) binding (PAI-1-K). All forms of PAI-1 significantly inhibited neointima formation, whereas elastase-cleaved PAI-1, which lacks both anti-PA and VN-binding functions, did not. Similar effects were observed in a murine model. However, the antiproliferative effect of PAI-1-R was lost in Vn(-/-) mice, suggesting that PAI-1 can inhibit intimal hyperplasia in vivo by a VN-dependent pathway not involving direct inhibition of proteases. In vitro, recombinant PAI-1 inhibited wild-type vascular smooth muscle cell (VSMC) proliferation, promoted apoptosis, and inhibited migration. These effects were lost in VN-deficient VSMCs.

CONCLUSIONS

Recombinant PAI-1 inhibits intimal hyperplasia by inhibiting proteases and binding VN. VN is a key determinant of the antiproliferative effect of PAI-1 overexpression. PAI-1-R has therapeutic potential to inhibit vascular restenosis without promoting thrombosis.

Tissue plasminogen activator-mediated PDGF signaling and neurovascular coupling in stroke

The use of tissue plasminogen activator (tPA) as a thrombolytic treatment in ischemic stroke is limited largely due to concerns for hemorrhagic complications. The underlying mechanisms are still unknown, but evidence is beginning to emerge that tPA interacts with key regulators of the neurovascular unit (NVU), and that these interactions may contribute to the undesirable side effects associated with the use of tPA in ischemic stroke. Understanding these connections and tPA's normal function within the NVU may offer new insights into future therapeutic approaches.

Reduced glutathione is highly expressed in white matter and neurons in the unperturbed mouse brain--implications for oxidative stress associated with neurodegeneration

Oxidative stress is implicated in the pathogenesis of many neurodegenerative diseases, including Parkinson's disease and Alzheimer's disease. The depletion of glutathione (GSH) a powerful antioxidant renders cells particularly vulnerable to oxidative stress. Isolated neuronal and glial cell culture studies suggest that glia rather than neurons have greatest reserves of GSH, implying that neurons are most sensitive to oxidative stress. However, pathological in vivo studies suggest that GSH associated enzymes are elevated in neurons rather than astrocytes. The active, reduced form of GSH is rapidly degraded thus making it difficult to identify the location of GSH in post-mortem tissue. Therefore, to determine whether GSH is more highly expressed in neurons or astrocytes we perfused mouse brains with a solution containing NEM which reacts with the sulfhydryl group of GSH, thus locking the active form in situ, prior to immunostaining with an anti-GS-NEM antibody. We obtained brightfield and fluorescent digital images of sections stained with DAPI and antibodies directed against GS-NEM, glial fibrillary acidic protein (GFAP) in regions containing the hippocampus, striatum, frontal cortex, midbrain nuclei, cerebellum and reticular formation neurons. GSH was most abundant in neurons and white matter in all brain regions, and only in occasional astrocytes lining the third and fourth ventricles. High levels of GSH in neurons and white matter, suggests astrocytes rather than neurons may be particularly vulnerable to oxidative stress.

Self-regulation of inflammatory cell trafficking in mice by the leukocyte surface apyrase CD39

Leukocyte and platelet accumulation at sites of cerebral ischemia exacerbate cerebral damage. The ectoenzyme CD39 on the plasmalemma of endothelial cells metabolizes ADP to suppress platelet accumulation in the ischemic brain. However, the role of leukocyte surface CD39 in regulating monocyte and neutrophil trafficking in this setting is not known. Here we have demonstrated in mice what we believe to be a novel mechanism by which CD39 on monocytes and neutrophils regulates their own sequestration into ischemic cerebral tissue, by catabolizing nucleotides released by injured cells, thereby inhibiting their chemotaxis, adhesion, and transmigration. Bone marrow reconstitution and provision of an apyrase, an enzyme that hydrolyzes nucleoside tri- and diphosphates, each normalized ischemic leukosequestration and cerebral infarction in CD39-deficient mice. Leukocytes purified from Cd39-/- mice had a markedly diminished capacity to phosphohydrolyze adenine nucleotides and regulate platelet reactivity, suggesting that leukocyte ectoapyrases modulate the ambient vascular nucleotide milieu. Dissipation of ATP by CD39 reduced P2X7 receptor stimulation and thereby suppressed baseline leukocyte alphaMbeta2-integrin expression. As alphaMbeta2-integrin blockade reversed the postischemic, inflammatory phenotype of Cd39-/- mice, these data suggest that phosphohydrolytic activity on the leukocyte surface suppresses cell-cell interactions that would otherwise promote thrombosis or inflammation. These studies indicate that CD39 on both endothelial cells and leukocytes reduces inflammatory cell trafficking and platelet reactivity, with a consequent reduction in tissue injury following cerebral ischemic challenge.

PAI-1 and functional blockade of SNAI1 in breast cancer cell migration

Introduction

Snail, a family of transcriptional repressors implicated in cell movement, has been correlated with tumour invasion. The Plasminogen Activation (PA) system, including urokinase plasminogen activator (uPA), its receptor and its inhibitor, plasminogen activator inhibitor type 1(PAI-1), also plays a key role in cancer invasion and metastasis, either through proteolytic degradation or by non-proteolytic modulation of cell adhesion and migration. Thus, Snail and the PA system are both over-expressed in cancer and influence this process. In this study we aimed to determine if the activity of SNAI1 (a member of the Snail family) is correlated with expression of the PA system components and how this correlation can influence tumoural cell migration.

Methods

We compared the invasive breast cancer cell-line MDA-MB-231 expressing SNAI1 (MDA-mock) with its derived clone expressing a dominant-negative form of SNAI1 (SNAI1-DN). Expression of PA system mRNAs was analysed by cDNA microarrays and real-time quantitative RT-PCR. Wound healing assays were used to determine cell migration. PAI-1 distribution was assessed by immunostaining.

Results

We demonstrated by both cDNA microarrays and real-time quantitative RT-PCR that the functional blockade of SNAI1 induces a significant decrease of PAI-1 and uPA transcripts. After performing an in vitro wound-healing assay, we observed that SNAI1-DN cells migrate more slowly than MDA-mock cells and in a more collective manner. The blockade of SNAI1 activity resulted in the redistribution of PAI-1 in SNAI1-DN cells decorating large lamellipodia, which are commonly found structures in these cells.

Conclusions

In the absence of functional SNAI1, the expression of PAI-1 transcripts is decreased, although the protein is redistributed at the leading edge of migrating cells in a manner comparable with that seen in normal epithelial cells.

Tissue-type plasminogen activator requires a co-receptor to enhance NMDA receptor function

Glutamate is the main excitatory neurotransmitter of the CNS. Tissue-type plasminogen activator (tPA) is recognized as a modulator of glutamatergic neurotransmission. This attribute is exemplified by its ability to potentiate calcium signaling following activation of the glutamate-binding NMDA receptor (NMDAR). It has been hypothesized that tPA can directly cleave the NR1 subunit of the NMDAR and thereby potentiate NMDA-induced calcium influx. In contrast, here we show that this increase in NMDAR signaling requires tPA to be proteolytically active, but does not involve cleavage of the NR1 subunit or plasminogen. Rather, we demonstrate that enhancement of NMDAR function by tPA is mediated by a member of the low-density lipoprotein receptor (LDLR) family. Hence, this study proposes a novel functional relationship between tPA, the NMDAR, a LDLR and an unknown substrate which we suspect to be a serpin. Interestingly, whilst tPA alone failed to cleave NR1, cell-surface NMDARs did serve as an efficient and discrete proteolytic target for plasmin. Hence, plasmin and tPA can affect the NMDAR via distinct avenues. Altogether, we find that plasmin directly proteolyses the NMDAR whilst tPA functions as an indirect modulator of NMDA-induced events via LDLR engagement.

Structural differences between active forms of plasminogen activator inhibitor type 1 revealed by conformationally sensitive ligands

Plasminogen activator inhibitor type 1 (PAI-1) is a serine protease inhibitor (serpin) in which the reactive center loop (RCL) spontaneously inserts into a central beta-sheet, beta-sheet A, resulting in inactive inhibitor. Available x-ray crystallographic studies of PAI-1 in an active conformation relied on the use of stabilizing mutations. Recently it has become evident that these structural models do not adequately explain the behavior of wild-type PAI-1 (wtPAI-1) in solution. To probe the structure of native wtPAI-1, we used three conformationally sensitive ligands: the physiologic cofactor, vitronectin; a monoclonal antibody, 33B8, that binds preferentially to RCL-inserted forms of PAI-1; and RCL-mimicking peptides that insert into beta-sheet A. From patterns of interaction with wtPAI-1 and the stable mutant, 14-1B, we propose a model of the native conformation of wtPAI-1 in which the bottom of the central sheet is closed, whereas the top of the beta-sheet A is open to allow partial insertion of the RCL. Because the incorporation of RCL-mimicking peptides into wtPAI-1 is accelerated by vitronectin, we further propose that vitronectin alters the conformation of the RCL to allow increased accessibility to beta-sheet A, yielding a structural hypothesis that is contradictory to the current structural model of PAI-1 in solution and its interaction with vitronectin.

A PAI-1 mutant, PAI-1R, slows progression of diabetic nephropathy

Plasminogen activator inhibitor-1 (PAI-1) has been implicated in renal fibrosis. In vitro, PAI-1 inhibits plasmin generation, and this decreases mesangial extracellular matrix turnover. PAI-1R, a mutant PAI-1, increases glomerular plasmin generation, reverses PAI-1 inhibition of matrix degradation, and reduces disease in experimental glomerulonephritis. This study sought to determine whether short-term administration of PAI-1R could slow the progression of glomerulosclerosis in the db/db mouse, a model of type 2 diabetes in which mesangial matrix accumulation is evident by 20 wk of age. Untreated uninephrectomized db/db mice developed progressive albuminuria and mesangial matrix expansion between weeks 20 and 22, associated with increased renal mRNA encoding alpha1(I) and (IV) collagens and fibronectin. Treatment with PAI-1R prevented these changes without affecting body weight, blood glucose, glycosylated hemoglobin, creatinine, or creatinine clearance; therefore, PAI-1R may prevent progression of glomerulosclerosis in type 2 diabetes.

Visceral adipose tissue inflammation accelerates atherosclerosis in apolipoprotein E-deficient mice

BACKGROUND

Fat inflammation may play an important role in comorbidities associated with obesity such as atherosclerosis.

METHODS AND RESULTS

To first establish feasibility of fat transplantation, epididymal fat pads were harvested from wild-type C57BL/6J mice and transplanted into leptin-deficient (Lep(ob/ob)) mice. Fat transplantation produced physiological leptin levels and prevented obesity and infertility in Lep(ob/ob) mice. However, the transplanted fat depots were associated with chronically increased macrophage infiltration with characteristics identical to those observed in fat harvested from obese animals. The inflammation in transplanted adipose depots was regulated by the same factors that have been implicated in endogenous fat inflammation such as monocyte chemoattractant protein-1. To determine whether this inflamed adipose depot could affect vascular disease in mice, epididymal fat depots were transplanted into atherosclerosis-prone apolipoprotein E-deficient ApoE(-/-) mice. Plasma from ApoE(-/-) mice receiving fat transplants contained increased leptin, resistin, and monocyte chemoattractant protein-1 compared with plasma from sham-operated ApoE(-/-) mice. Furthermore, mice transplanted with visceral fat developed significantly more atherosclerosis compared with sham-operated animals, whereas transplants with subcutaneous fat did not affect atherosclerosis despite a similar degree of fat inflammation. Treatment of transplanted ApoE(-/-) mice with pioglitazone decreased macrophage content of the transplanted visceral fat pad and reduced plasma monocyte chemoattractant protein-1. Importantly, pioglitazone also reduced atherosclerosis triggered by inflammatory visceral fat but had no protective effect on atherosclerosis in the absence of the visceral fat transplantation.

CONCLUSIONS

Our results indicate that visceral adipose-related inflammation accelerates atherosclerosis in mice. Drugs such as thiazolidinediones might be a useful strategy to specifically attenuate the vascular disease induced by visceral inflammatory fat.

Neuroserpin polymorphisms and stroke risk in a biracial population: the stroke prevention in young women study

BACKGROUND

Neuroserpin, primarily localized to CNS neurons, inhibits the adverse effects of tissue-type plasminogen activator (tPA) on the neurovascular unit and has neuroprotective effects in animal models of ischemic stroke. We sought to evaluate the association of neuroserpin polymorphisms with risk for ischemic stroke among young women.

METHODS

A population-based case-control study of stroke among women aged 15-49 identified 224 cases of first ischemic stroke (47.3% African-American) and 211 age-matched control subjects (43.1% African-American). Neuroserpin single nucleotide polymorphisms (SNPs) chosen through HapMap were genotyped in the study population and assessed for association with stroke.

RESULTS

Of the five SNPs analyzed, the A allele (frequency; Caucasian = 0.56, African-American = 0.42) of SNP rs6797312 located in intron 1 was associated with stroke in an age-adjusted dominant model (AA and AT vs. TT) among Caucasians (OR = 2.05, p = 0.023) but not African-Americans (OR = 0.71, p = 0.387). Models adjusting for other risk factors strengthened the association. Race-specific haplotype analyses, inclusive of SNP rs6797312, again demonstrated significant associations with stroke among Caucasians only.

CONCLUSION

This study provides the first evidence that neuroserpin is associated with early-onset ischemic stroke among Caucasian women.

Structure-function relationships of plasminogen activator inhibitor-1 and its potential as a therapeutic agent

Plasminogen activator inhibitor-1 (PAI-1) is the primary inhibitor of tissue-type and urokinase-type plasminogen activators (tPA and uPA, respectively). PAI-1 also interacts with non-proteinase targets such as vitronectin, heparin, and several endocytic receptors of the low-density lipoprotein-receptor family, including the low-density lipoprotein-receptor related protein (LRP) and the very low-density lipoprotein receptor (VLDLr). PAI-1 is a multifunctional protein that is not only a physiologic regulator of fibrinolysis and cell migration but is also associated with several acute and chronic pathologic conditions. PAI-1 is involved in the pathophysiology of renal, pulmonary, cardiovascular, and metabolic diseases, and in vitro experiments and animal studies have elucidated PAI-1's contribution to the physiology or pathology of some of these conditions. PAI-1 is normally present at low levels in plasma, but acute and chronic diseases are strongly associated with increased PAI-1 expression and release. At sites of vascular injury and inflammation, local PAI-1 levels are even higher, due to its concentration in extracellular matrix through association with vitronectin. Elevated local or systemic PAI-1 is not only a marker of disease; it can also exacerbate pathologic conditions. Thus, interventions that directly target PAI-1 may be useful for the treatment of a number of chronic and acute disorders. Typically, such interventional strategies would involve the identification of small molecule inhibitors of PAI-1, and several recent reviews have covered this topic. However, it may also be possible or even potentially advantageous, to exploit the diverse functional interactions of PAI-1 to create highly specific and targeted therapeutic agents based on the PAI-1 protein itself. To understand how PAI-1 could be developed as a therapeutic agent, it is first necessary to discuss its structural and functional characteristics in depth.

The Contributions of Integrin Affinity and Integrin-Cytoskeletal Engagement in Endothelial and Smooth Muscle Cell Adhesion to Vitronectin

The serine proteinase inhibitor, plasminogen activator inhibitor type-1 (PAI-1), binds to the adhesion protein vitronectin with high affinity at a site that is located directly adjacent to the vitronectin RGD integrin binding sequence. The binding of PAI-1 to vitronectin sterically blocks integrin access to this site and completely inhibits the binding of purified integrins to vitronectin; however, its inhibition of endothelial and smooth muscle cell adhesion to vitronectin is at most 50-75%. Because PAI-1 binds vitronectin with approximately 10-100-fold higher affinity than purified integrins, we have analyzed the mechanism whereby these cells are able to overcome this obstacle. Our studies exclude proteolytic removal of PAI-1 from vitronectin as the mechanism, and show instead that cell adhesion in the presence of PAI-1 is dependent on integrin-cytoskeleton engagement. Disrupting endothelial or smooth muscle cell actin polymerization and/or focal adhesion assembly reduces cell adhesion to vitronectin in the presence of PAI-1 to levels similar to that observed for the binding of purified integrins to vitronectin. Furthermore, endothelial cell, but not smooth muscle cell adhesion to vitronectin in the presence of PAI-1 requires both polymerized microtubules and actin, further demonstrating the importance of the cytoskeleton for integrin-mediated adhesion. Finally, we show that cell adhesion in the presence of PAI-1 leads to colocalization of PAI-1 with the integrins alphavbeta3 and alphavbeta5 at the cell-matrix interface.

Mechanism of inactivation of plasminogen activator inhibitor-1 by a small molecule inhibitor

The inactivation of plasminogen activator inhibitor-1 (PAI-1) by the small molecule PAI-1 inhibitor PAI-039 (tiplaxtinin) has been investigated using enzymatic analysis, direct binding studies, site-directed mutagenesis, and molecular modeling studies. Previously PAI-039 has been shown to exhibit in vivo activity in various animal models, but the mechanism of inhibition is unknown. PAI-039 bound specifically to the active conformation of PAI-1 and exhibited reversible inactivation of PAI-1 in vitro. SDS-PAGE indicated that PAI-039 inactivated PAI-1 predominantly through induction of PAI-1 substrate behavior. Preincubation of PAI-1 with vitronectin, but not bovine serum albumin, blocked PAI-039 activity while analysis of the reciprocal experiment demonstrated that preincubation of PAI-1 with PAI-039 blocked the binding of PAI-1 to vitronectin. Together, these data suggest that the site of interaction of the drug on PAI-1 is inaccessible when PAI-1 is bound to vitronectin and may overlap with the PAI-1 vitronectin binding domain. This was confirmed by site-directed mutagenesis and molecular modeling studies, which suggest that the binding epitope for PAI-039 is localized adjacent to the previously identified interaction site for vitronectin. Thus, these studies provide a detailed characterization of the mechanism of inhibition of PAI-1 by PAI-039 against free, but not vitronectin-bound PAI-1, suggesting for the first time a novel pool of PAI-1 exists that is vulnerable to inhibition by inactivators that bind at the vitronectin binding site.

Effects of murine endotoxemia on lymphocyte subsets and clearance of staphylococcal pulmonary infection

In a model of staphylococcal pneumonia initiated during systemic endotoxemia in BALB/c mice, a significant reduction of the number of circulating CD4+ and CD8+ T-lymphocytes, B-lymphocytes, and NK cells, as well as lung-resident total T- and CD4+ T-lymphocytes was demonstrated. Staphylococcus aureus exposure only induced a similar decrease of lymphocyte subsets in the blood. However, the number of lung-resident total T- and CD4+ T-lymphocytes was increased. More viable bacteria were recovered from the lungs of S. aureus-infected mice than from those animals previously treated with lipopolysaccharide (LPS) followed by a staphylococcal challenge. These results indicate that LPS-induced reduction in the number of circulating lymphocyte subsets and lung-resident total T- and CD4+ T-lymphocytes do not increase susceptibility to staphylococcal respiratory infection. Moreover, LPS challenge prior to S. aureus exposure significantly improves clearance of the bacteria in the lung.

Molecular regulation of the PAI-1 gene by hypoxia: contributions of Egr-1, HIF-1alpha, and C/EBPalpha

Hypoxia, as occurs during tissue ischemia, tips the natural anticoagulant/procoagulant balance of the endovascular wall to favor activation of coagulation. Plasminogen activator inhibitor-1 (PAI-1) is an important factor suppressing fibrinolysis under conditions of low oxygen tension. We previously reported that hypoxia induced PAI-1 mRNA and antigen expression in murine macrophages secondary to increased de novo transcription as well as increased mRNA stability. We now show in RAW264.7 murine macrophages that the transcription factors early growth response gene-1 (Egr-1), hypoxia-inducible factor-1alpha (HIF-1alpha), and CCAAT/enhancer binding protein alpha (C/EBPalpha) are quickly activated in hypoxia and are responsible for transcription and expression of PAI-1. Murine PAI-1 promoter constructs, including Egr, HIF-1alpha, and/or C/EBPalpha binding sites, were transfected into RAW 264.7 murine macrophages. To identify the relative importance of each of these putative hypoxia-responsive elements, cells were exposed to normobaric hypoxia, and transcriptional activity was recorded. At 16 h of hypoxic exposure, murine PAI-1 promoter deletion constructs that included Egr, HIF-1alpha, and/or C/EBPalpha binding sites demonstrated increased transcriptional activity. Mutation of each of these three murine PAI-1 promoter sites (or a combination of them) resulted in a marked reduction in hypoxia sensitivity as detected by transcriptional analysis. Functional data obtained using 32P-labeled Egr, HIF-1alpha response element (HRE), and C/EBPalpha oligonucleotides revealed induction of DNA binding activity in nuclear extracts from hypoxic RAW cells, with supershift analysis confirming activation of Egr-1, HIF-1alpha, or C/EBPalpha. ChIP analysis confirmed the authenticity of these interactions as each of these transcription factors binds to chromatin under hypoxic conditions. Further, the induction of PAI-1 by Egr-1, HIF-1alpha, or C/EBPalpha was replicated in primary peritoneal macrophages. These data suggest that although HIF-1alpha appears to dominate the PAI-1 transcriptional response in hypoxia, Egr-1 and C/EBPalpha greatly augment this response and can do so independent of HIF-1alpha or each other. These studies are relevant to ischemic up-regulation of the PAI-1 gene and consequent accrual of microvascular thrombus under ischemic conditions.

Dual role for plasminogen activator inhibitor type 1 as soluble and as matricellular regulator of epithelial alveolar cell wound healing

Epithelium repair, crucial for restoration of alveolo-capillary barrier integrity, is orchestrated by various cytokines and growth factors. Among them keratinocyte growth factor plays a pivotal role in both cell proliferation and migration. The urokinase plasminogen activator (uPA) system also influences cell migration through proteolysis during epithelial repair. In addition, the complex formed by uPAR-uPA and matrix-bound plasminogen activator inhibitor type-1 (PAI-1) exerts nonproteolytic roles in various cell types. Here we present new evidence about the dual role of PAI-1 under keratinocyte growth factor stimulation using an in vitro repair model of rat alveolar epithelial cells. Besides proteolytic involvement of the uPA system, the availability of matrix-bound-PAI-1 is also required for an efficient healing. An unexpected decrease of healing was shown when PAI-1 activity was blocked. However, the proteolytic action of uPA and plasmin were still required. Moreover, immediately after wounding, PAI-1 was dramatically increased in the newly deposited matrix at the leading edge of wounds. We thus propose a dual role for PAI-1 in epithelial cell wound healing, both as a soluble inhibitor of proteolysis and also as a matrix-bound regulator of cell migration. Matrix-bound PAI-1 could thus be considered as a new member of the matricellular protein family.

Tissue-type plasminogen activator-mediated shedding of astrocytic low-density lipoprotein receptor-related protein increases the permeability of the neurovascular unit

The low-density lipoprotein receptor-related protein (LRP) is a member of the LDL receptor gene family that binds several ligands, including tissue-type plasminogen activator (tPA). tPA is found in blood, where its primary function is as a thrombolytic enzyme, and in the central nervous system where it mediates events associated with cell death. Cerebral ischemia induces changes in the neurovascular unit (NVU) that result in brain edema. We investigated whether the interaction between tPA and LRP plays a role in the regulation of the permeability of the NVU during cerebral ischemia. We found that the ischemic insult induces shedding of LRP's ectodomain from perivascular astrocytes into the basement membrane. This event associates with the detachment of astrocytic end-feet processes and the formation of areas of perivascular edema. The shedding of LRP's ectodomain is significantly decreased in tPA deficient (tPA(-/-)) mice, is increased by incubation with tPA, and is inhibited by the receptor-associated protein (RAP). Furthermore, treatment with either RAP or anti-LRP IgG results in a faster recovery of motor activity and protection of the integrity of the NVU following middle cerebral artery occlusion (MCAO). Together, these results implicate tPA/LRP interactions as key regulators of the integrity of the NVU.

Effect of pharmacologic plasminogen activator inhibitor-1 inhibition on cell motility and tumor angiogenesis

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) is integrally involved in tumorigenesis by impacting on both proteolytic activity and cell migration during angiogenesis.

OBJECTIVES

We hypothesized that an orally active small molecule inhibitor of PAI-1 (PAI-039; tiplaxtinin) could affect smooth muscle cell (SMC) attachment and migration in vitro on a vitronectin matrix, and exhibit antiangiogenic activity in vivo.

METHODS

In vitro assays were used to assess the mechanism of inhibition of PAI-1 by PAI-039 using wild-type PAI-1 in the presence or absence of vitronectin and wild-type PAI-1 and specific PAI-1 mutants in SMC adhesion and migration assays. An in vivo tumor angiogenesis model was used to assess the effect of PAI-039 administration on neovascularization in a Matrigel implant.

RESULTS

PAI-039 dose-dependently inhibited soluble, but not vitronectin-bound, PAI-1. Cell adhesion assays using PAI-1 mutants unable to bind vitronectin (PAI-1K) or inactivate proteases (PAI-1R) further suggested that PAI-039 inactivated PAI-1 by binding near its vitronectin domain. In a tumor angiogenesis model, PAI-039 treatment of wild-type mice dose-dependently decreased hemoglobin concentration and endothelial cell staining within the Matrigel implant, indicating reduced angiogenesis, but exhibited no in vivo efficacy in PAI-1 null mice.

CONCLUSIONS

Administration of an orally active PAI-1 inhibitor prevented angiogenesis in a Matrigel implant. The lack of activity of PAI-039 against wild-type PAI-1 bound to vitronectin and PAI-1K suggests PAI-039 binding near the vitronectin-binding site. Our studies further substantiate a role for PAI-1 in cellular motility and tumor angiogenesis, and suggest for the first time that these effects can be modulated pharmacologically.

Noninhibitory PAI-1 enhances plasmin-mediated matrix degradation both in vitro and in experimental nephritis

Plasminogen activator inhibitor-type 1 (PAI-1) is thought to be profibrotic by inhibiting plasmin generation, thereby decreasing turnover of pathological extracellular matrix (ECM). A mutant, noninhibitory PAI-1 (PAI-1R) was recently shown by us to increase glomerular plasmin generation and reduce disease in anti-thy-1 nephritis. Here, in vitro and in vivo studies were performed to determine whether enhanced plasmin-dependent ECM degradation underlies the therapeutic effect of PAI-1R. 3H-labeled ECM was produced by rat mesangial cells (MCs). The effect of wild-type PAI-1 (wt-PAI-1) and PAI-1R on ECM degradation by newly plated MCs was measured by the release of 3H into medium. In vivo, anti-thy-1 nephritis was assessed in normal, untreated diseased and PAI-1R treated rats with or without the plasmin/plasminogen inhibitor, tranexamic acid (TA). wt-PAI-1 totally inhibited plasmin generation and reduced ECM degradation by 76% when exogenous plasminogen was added. Although PAI-1R alone had no effect, PAI-1R in the presence of wt-PAI-1 reversed the wt-PAI-1 inhibition of ECM degradation in a time- and dose-dependent manner (P<0.001). Plasmin activity and zymography were consistent with ECM degradation. Plasmin inhibitors: alpha2-antiplasmin, aprotinin, and TA completely blocked PAI-1R's ability to normalize ECM degradation (P<0.001). Consistent with the in vitro results, TA reversed PAI-1R-induced reductions in glomerular fibrin and ECM accumulation. Other measures of disease severity were either unaltered or partially reversed. PAI-1R reduces pathological ECM accumulation, in large part through effectively competing with native PAI-1 thereby restoring plasmin generation and increasing plasmin-dependent degradation of matrix components.

Endocytic receptor LRP together with tPA and PAI-1 coordinates Mac-1-dependent macrophage migration

Migration of activated macrophages is essential for resolution of acute inflammation and the initiation of adaptive immunity. Here, we show that efficient macrophage migration in inflammatory environment depends on Mac-1 recognition of a binary complex consisting of fibrin within the provisional matrix and the protease tPA (tissue-type plasminogen activator). Subsequent neutralization of tPA by its inhibitor PAI-1 enhances binding of the integrin-protease-inhibitor complex to the endocytic receptor LRP (lipoprotein receptor-related protein), triggering a switch from cell adhesion to cell detachment. Genetic inactivation of Mac-1, tPA, PAI-1 or LRP but not the protease uPA abrogates macrophage migration. The defective macrophage migration in PAI-1-deficient mice can be restored by wild-type but not by a mutant PAI-1 that does not interact with LRP. In vitro analysis shows that tPA promotes Mac-1-mediated adhesion, whereas PAI-1 and LRP facilitate its transition to cell retraction. Our results emphasize the importance of ordered transitions both temporally and spatially between individual steps of cell migration, and support a model where efficient migration of inflammatory macrophages depends on cooperation of three physiologically prominent systems (integrins, coagulation and fibrinolysis, and endocytosis).

A mechanism for assembly of complexes of vitronectin and plasminogen activator inhibitor-1 from sedimentation velocity analysis

Plasminogen activator inhibitor-1 (PAI-1) and vitronectin are cofactors involved in pathological conditions such as injury, inflammation, and cancer, during which local levels of PAI-1 are increased and the active serpin forms complexes with vitronectin. These complexes become deposited into surrounding tissue matrices, where they regulate cell adhesion and pericellular proteolysis. The mechanism for their co-localization has not been elucidated. We hypothesize that PAI-1-vitronectin complexes form in a stepwise and concentration-dependent fashion via 1:1 and 2:1 intermediates, with the 2:1 complex serving a key role in assembly of higher order complexes. To test this hypothesis, sedimentation velocity experiments in the analytical ultracentrifuge were performed to identify different PAI-1-vitronectin complexes. Analysis of sedimentation data invoked a novel multisignal method to discern the stoichiometry of the two proteins in the higher-order complexes formed (Balbo, A., Minor, K. H., Velikovsky, C. A., Mariuzza, R. A., Peterson, C. B., and Schuck, P. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 81-86). Our results demonstrate that PAI-1 and vitronectin assemble into higher order forms via a pathway that is triggered upon saturation of the two PAI-1-binding sites of vitronectin to form the 2:1 complex. This 2:1 PAI-1-vitronectin complex, with a sedimentation coefficient of 6.5 S, is the key intermediate for the assembly of higher order complexes.

A specific role of integrin Mac-1 in accelerated macrophage efflux to the lymphatics

In response to injury, monocytes migrate to the site of inflammation, where they differentiate into macrophages and participate in various biologic processes. However, their fate during the resolution of acute inflammation is not fully understood. Here, we show that inflammatory macrophages do not die locally by apoptosis; rather, they migrate across the peritoneal mesothelium to the lymphatics, through which they further migrate to the lymph nodes and to the blood circulation. Macrophage efflux is enhanced considerably on cell activation, and such accelerated macrophage migration is dependent specifically on integrin Mac-1, and can be blocked by addition of its antagonist. Thus, genetic inactivation of Mac-1 in mice inhibits the accelerated macrophage efflux from the inflammatory site to the lymphatics, but it does not compromise the accumulation of blood monocytes into the inflammatory site. Together, our study demonstrates that Mac-1 is involved specifically in the efflux of activated macrophages to the lymphatics, suggesting that Mac-1 may play an important role in the removal of local inflammatory macrophages and in their subsequent migration to the lymph nodes, a process that is critical to the development of the adaptive immunity.

A soluble Fn14-Fc decoy receptor reduces infarct volume in a murine model of cerebral ischemia

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily. TWEAK acts on responsive cells via binding to a small cell surface receptor named Fn14. Recent studies have demonstrated that TWEAK can stimulate numerous cellular responses including cell proliferation, migration, and proinflammatory molecule production, but the role of this cytokine in cardiovascular disease and stroke has not been established. The present study investigated whether TWEAK or Fn14 expression was regulated in a murine model of cerebral ischemia and whether TWEAK played a role in ischemia-mediated cell death. We found that TWEAK and Fn14 were expressed by primary mouse cerebral cortex-derived astrocytes and neurons cultured in vitro. Also, both the TWEAK and Fn14 proteins were present at elevated levels in the ischemic penumbra region after middle cerebral artery occlusion. Finally, we report that intracerebroventricular injection of a soluble Fn14-Fc decoy receptor immediately after middle cerebral artery occlusion significantly reduced infarct volume and the extent of microglial cell activation and apoptotic cell death in the ischemic penumbra. We conclude that the cytokine TWEAK may play an important role in ischemia-induced brain injury and that inhibition of TWEAK expression or function in the brain may represent a novel neuroprotective strategy to treat ischemic stroke.

New functions for an old enzyme: nonhemostatic roles for tissue-type plasminogen activator in the central nervous system

Tissue-type plasminogen activator (tPA) is a highly specific serine proteinase that activates the zymogen plasminogen to the broad-specificity proteinase plasmin. Tissue-type plasminogen activator is found not only in the blood, where its primary function is as a thrombolytic enzyme, but also in the central nervous system (CNS), where it promotes events associated with synaptic plasticity and acts as a regulator of the permeability of the neurovascular unit. Tissue-type plasminogen activator has also been associated with pathological events in the CNS such as cerebral ischemia and seizures. Neuroserpin is an inhibitory serpin that reacts preferentially with tPA and is located in regions of the brain where either tPA message or tPA protein are also found, indicating that neuroserpin is the selective inhibitor of tPA in the CNS. There is a growing body of evidence demonstrating the participation of tPA in a number of physiological and pathological events in the CNS, as well as the role of neuroserpin as the natural regulator of tPA's activity in these processes. This review will focus on nonhemostatic roles of tPA in the CNS with emphasis on its newly described function as a regulator of permeability of the neurovascular unit and on the regulatory role of neuroserpin in these events.

Serpin mutagenesis

Mutagenesis represents a powerful methodology for the analysis of protein structural and functional relationships and dissection of complex protein-protein interactions. The suicide substrate-like inhibitory mechanism of the proteins of the serpin superfamily offers unique challenges for the design of mutagenesis studies. All serpins share a well-characterized core structure and most adopt a metastable conformation that is required for inhibitory activity. Mutagenesis studies focused on the reactive center loop, the hinge region, protease-binding exo-sites, conformational stability, and accessory ligand binding domains have led to a well-established serpin inhibitory mechanism and have defined specific biological interactions and functions for a number of serpins in development, homeostasis, and host defense. Nonetheless, great care must be taken in the design and interpretation of serpin mutagenesis studies, since the rapid conformational changes that occur during serpin inhibition can be affected at many levels.

Mouse DESC1 is located within a cluster of seven DESC1-like genes and encodes a type II transmembrane serine protease that forms serpin inhibitory complexes

We report the identification and functional analysis of a type II transmembrane serine protease encoded by the mouse differentially expressed in squamous cell carcinoma (DESC) 1 gene, and the definition of a cluster of seven homologous DESC1-like genes within a 0.5-Mb region of mouse chromosome 5E1. This locus is syntenic to a region of human chromosome 4q13.3 containing the human orthologues of four of the mouse DESC1-like genes. Bioinformatic analysis indicated that all seven DESC1-like genes encode functional proteases. Direct cDNA cloning showed that mouse DESC1 encodes a multidomain serine protease with an N-terminal signal anchor, a SEA (sea urchin sperm protein, enterokinase, and agrin) domain, and a C-terminal serine protease domain. The mouse DESC1 mRNA was present in epidermal, oral, and male reproductive tissues and directed the translation of a membrane-associated 60-kDa N-glycosylated protein with type II topology. Mouse DESC1 was synthesized in insect cells as a zymogen that could be activated by exposure to trypsin. The purified activated DESC1 hydrolyzed synthetic peptide substrates, showing a preference for Arg in the P1 position. DESC1 proteolytic activity was abolished by generic inhibitors of serine proteases but not by other classes of protease inhibitors. Most interestingly, DESC1 formed stable inhibitory complexes with both plasminogen activator inhibitor-1 and protein C inhibitor that are expressed in the same tissues with DESC1, suggesting that type II transmembrane serine proteases may be novel targets for serpin inhibition. Together, these data show that mouse DESC1 encodes a functional cell surface serine protease that may have important functions in the epidermis, oral, and reproductive epithelium.

Characterization and comparative evaluation of a structurally unique PAI-1 inhibitor exhibiting oral in-vivo efficacy

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of both tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). Elevated levels of PAI-1 are associated with thrombosis and vascular disease, suggesting that high plasma PAI-1 may promote a hypercoagulable state by disrupting the natural balance between fibrinolysis and coagulation. In this study, we identify WAY-140312 as a structurally novel small molecule inactivator of PAI-1, compare its inhibitory activity with other previously identified small molecule inhibitors, and investigate the mechanism of inactivation of PAI-1 in the presence of both tPA and uPA. In an immunofunctional assay, WAY-140312 inhibited PAI-1 with an estimated inhibitory concentration (IC(50)) of 11.7 micro m, which was the lowest value obtained of the four different PAI-1 inactivators tested. Surface activity profiling indicated that the critical micelle concentration for WAY-140312 was 95.8 micro m, and that each inhibitor exhibited unique physical chemical properties. Using a sensitive direct activity assay, the IC(50) for WAY-140312 was similar when either tPA or uPA was used as the target protease. Immunoblot analysis demonstrated that WAY-140312 near the IC(50) inhibited the complex formation between either tPA or uPA and PAI-1. After oral administration, WAY-140312 exhibited 29% bioavailability with a plasma half-life of approximately 1 h. In an in-vivo model of vascular injury, a 10 mg kg(-1) oral dose of WAY-140312 was associated with improvement in arterial blood flow and reduction in venous thrombosis. Thus, WAY-140312 represents a structurally novel small molecule inhibitor of PAI-1, and is the first such molecule to exhibit efficacy in animal models of vascular disease following oral administration.

Tissue plasminogen activator and neuroserpin are widely expressed in the human central nervous system

Tissue plasminogen activator (tPA) is increasingly recognized to play important roles in various physiological and pathological processes in the central nervous system (CNS). Much of the data on the involvement of plasminogen activators in neurophysiology and -pathology have been derived from studies on experimental animals. We have now performed a systematic characterization of the expression of tPA and its inhibitor, neuroserpin, in normal human CNS. Brain and spinal cord samples from 30-36 anatomic locations covering all major brain regions were collected at 9 autopsies of donors with no neurological disease. Tissues were embedded in paraffin and tissue arrays were constructed. In two cases parallel samples were snap-frozen for biochemical analysis. Expression and activity profiling of tPA and neuroserpin were performed by immunohistochemistry, in situ hybridization, immunocapture and zymography assays. In the adult CNS, tPA was expressed at the mRNA and protein levels in many types of neurons, in particular in thalamus, cortex of cerebellum, pontine nuclei, neocortex, limbic system, and medulla oblongata. Interestingly, tPA was often co-expressed with its CNS inhibitor, neuroserpin. Despite overlapping expression of tPA and neuroserpin, zymography and immunocapture assays demonstrated that human neural tissue is a rich source of active tPA. Our analysis documents a detailed map of expression of tPA and its inhibitor in the human CNS and is compatible with the view that tPA is a key player in CNS physiology and pathology.

Tissue-type plasminogen activator and neuroserpin: a well-balanced act in the nervous system?

Tissue-type plasmingen activator (tPA) is a highly specific serine proteinase that activates the zymogen plasminogen to the broad-specificity proteinase plasmin. tPA is found in the blood, where its primary function is as a thrombolytic enzyme, as well as in the central nervous system (CNS), where it promotes events associated with synaptic plasticity and cell death in a number of settings, such as cerebral ischemia and seizures. Neuroserpin is a fully inhibitory serine proteinase inhibitor (serpin) that reacts preferentially with tPA, and is located in regions of the brain where either tPA message or tPA protein are also found, suggesting that neuroserpin is the selective inhibitor of tPA in the CNS. There is a growing body of evidence demonstrating the participation of tPA in a number of physiologic and pathologic events in the CNS, and the role of neuroserpin as the natural regulator of tPA's activity in these processes.

Mutants of plasminogen activator inhibitor-1 designed to inhibit neutrophil elastase and cathepsin G are more effective in vivo than their endogenous inhibitors

Neutrophil elastase and cathepsin G are abundant intracellular neutrophil proteinases that have an important role in destroying ingested particles. However, when neutrophils degranulate, these proteinases are released and can cause irreparable damage by degrading host connective tissue proteins. Despite abundant endogenous inhibitors, these proteinases are protected from inhibition because of their ability to bind to anionic surfaces. Plasminogen activator inhibitor type-1 (PAI-1), which is not an inhibitor of these proteinases, possesses properties that could make it an effective inhibitor of neutrophil proteinases if its specificity could be redirected. PAI-1 efficiently inhibits surface-sequestered proteinases, and it efficiently mediates rapid cellular clearance of PAI-1-proteinase complexes. Therefore, we examined whether PAI-1 could be engineered to inhibit and clear neutrophil elastase and cathepsin G. By introducing specific mutations in the reactive center loop of wild-type PAI-1, we generated PAI-1 mutants that are effective inhibitors of both proteinases. Kinetic analysis shows that the inhibition of neutrophil proteinases by these PAI-1 mutants is not affected by the sequestration of neutrophil elastase and cathepsin G onto surfaces. In addition, complexes of these proteinases and PAI-1 mutants are endocytosed and degraded by lung epithelial cells more efficiently than either the neutrophil proteinases alone or in complex with their physiological inhibitors, alpha1-proteinase inhibitor and alpha1-antichymotrypsin. Finally, the PAI-1 mutants were more effective in reducing the neutrophil elastase and cathepsin G activities in an in vivo model of lung inflammation than were their physiological inhibitors.

Neuroserpin: a selective inhibitor of tissue-type plasminogen activator in the central nervous system

Neuroserpin is a member of the serine proteinase inhibitor (serpin) gene family that reacts preferentially with tissue-type plasminogen activator (tPA) and is primarily localized to neurons in regions of the brain where tPA is also found. Outside of the central nervous system (CNS) tPA is predominantly found in the blood where its primary function is as a thrombolytic enzyme. However, tPA is also expressed within the CNS where it has a very different function, promoting events associated not only with synaptic plasticity but also with cell death in a number of settings, such as cerebral ischemia and seizures. Neuroserpin is released from neurons in response to neuronal depolarization and plays an important role in the development of synaptic plasticity. Following the onset of cerebral ischemia there is an increase in both tPA activity and neuroserpin expression in the area surrounding the necrotic core (ischemic penumbra), and treatment with neuroserpin following ischemic stroke or overexpression of the neuroserpin gene results in a significant decrease in the volume of the ischemic area as well as in the number of apoptotic cells. TPA activity and neuroserpin expression are also increased in specific areas of the brain by seizures, and treatment with neuroserpin slows the progression of seizure activity throughout the CNS and results in significant neuronal survival in the hippocampus. Mutations in human neuroserpin result in a form of autosomal dominant inherited dementia which is characterized by the presence of intraneuronal inclusion bodies and is known as Familial Encephalopathy with Neuroserpin Inclusion Bodies.

Conservation of critical functional domains in murine plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 is the main physiological regulator of tissue-type plasminogen activator in normal plasma. In addition to its critical function in fibrinolysis, plasminogen activator inhibitor-1 has been implicated in roles in other physiological and pathophysiological processes. To investigate structure-function aspects of mouse plasminogen activator inhibitor-1, the recombinant protein was expressed in Escherichia coli and purified. Five variant recombinant murine proteins (R76E, Q123K, R346A, R101A, and Q123K/R101A) were also generated using site-directed mutagenesis. The variant (R346A) was found to be defective in its inhibitory activity against tissue plasminogen activator relative to its wild-type counterpart. Enzyme-linked immunosorbent assay and surface plasmon resonance experiments demonstrated reduced vitronectin-binding affinity of the (Q123K) variant (K(D) = 1800 nm) relative to the wild-type protein (K(D) = 5.4 nm). Kinetic analyses indicated that the (Q123K) variant had a slower association (k(on) = 2.92 x 10(4) m(-1) s(-1)) to, and a faster dissociation from, vitronectin (k(off) = 5.3 x 10(-2) s(-1)), (wild-type k(on) = 1.03 x 10(6) m(-1) s(-1) and k(off) = 5.27 x 10(-3) s(-1)). The Q123K/R101A variant demonstrated an even lower vitronectin-binding ability. Low density lipoprotein receptor-related protein binding was decreased for the (R76E) variant. It was also demonstrated that the plasminogen activator inhibitor-1/vitronectin complex decreased the interaction of plasminogen activator inhibitor-1 with low density lipoprotein receptor-related protein. These results indicate that the complex interactions traditionally associated with different plasminogen activator inhibitor-1 functions apply to the murine system, thus showing a commonality of subtle functions among different species and evolutionary conservation of this protein. Further, this study provides additional evidence that the human hemostasis system can be studied effectively in the mouse, which is a great asset for investigations with gene-altered mice.

The low density lipoprotein receptor-related protein modulates protease activity in the brain by mediating the cellular internalization of both neuroserpin and neuroserpin-tissue-type plasminogen activator complexes

Proteases contribute to a variety of processes in the brain; consequently, their activity is carefully regulated by protease inhibitors, such as neuroserpin. This inhibitor is thought to be secreted by axons at synaptic regions where it controls tissue-type plasminogen activator (tPA) activity. Mechanisms regulating neuroserpin are not known, and the current studies were undertaken to define the cellular pathways involved in neuroserpin catabolism. We found that both active neuroserpin and neuroserpin.tPA complexes were internalized by mouse cortical cultures and embryonic fibroblasts in a process mediated by the low density lipoprotein receptor-related protein (LRP). Surprisingly, despite the fact that active neuroserpin is internalized by LRP, this form of the molecule does not directly bind to LRP on its own, indicating the requirement of a cofactor for neuroserpin internalization. Our studies ruled out the possibility that endogenously produced plasminogen activators (i.e. tPA and urokinase-type plasminogen activator) are responsible for the LRP-mediated internalization of active neuroserpin, but could not rule out the possibility that another cell-associated proteases capable of binding active neuroserpin functions in this capacity. In summary, neuroserpin levels appear to be carefully regulated by LRP and an unidentified cofactor, and this pathway may be critical for maintaining the balance between proteases and inhibitors.