Macrophage plasminogen activator: modulation of enzyme production by anti-inflammatory steroids, mitotic inhibitors, and cyclic nucleotides

Thrombosis and inflammatory bowel disease: a call for improved awareness and prevention

Thrombotic complications in patients with inflammatory bowel disease (IBD) are common and require improved awareness and prevention. In this review the interface between IBD and thrombosis is discussed, with emphasis on risk assessment and data to aid clinical decision making. Thromboembolic complications are 3-fold more likely in IBD patients than controls and the relative risk exceeds 15 during disease flares. Improved assessment of thrombosis risk for an individual patient includes thorough personal and family history and awareness of prothrombotic medications and lifestyle choices. Patients with the highest risk of thrombosis are those with active colonic disease, personal or strong family history of thrombosis, and those with significant acquired risk factors. Combined risk factors or hospitalization should prompt mechanical thromboprophylaxis. Indications for prophylactic anticoagulation are not defined currently by clinical studies, especially in pediatric patients, although some groups now advocate prophylactic anticoagulation for all hospitalized IBD patients and even some outpatients with disease flares. Thrombosis management requires a multidisciplinary therapeutic approach to balance anticoagulation and bleeding risk. While bleeding may occur with anticoagulation in IBD, data and experience indicate that therapeutic heparin is safe and bleeding manifestations can be managed supportively in most patients. Until prospective trials of prophylactic anticoagulation are published, management of thrombotic risk and prophylaxis in IBD will remain a clinical challenge.

Urokinase-type plasminogen activator increases hepatocyte growth factor activity required for skeletal muscle regeneration

The plasminogen system plays a crucial role in the repair of a variety of tissues, including skeletal muscle. We hypothesized that urokinase-type plasminogen activator (uPA) promotes muscle regeneration by activating hepatocyte growth factor (HGF), which, in turn, stimulates proliferation of myoblasts required for regeneration. In our studies, levels of active HGF and phosphorylation of the HGF receptor c-met were increased after muscle injury in wild-type mice. Compared with wild-type animals, mice deficient in uPA (uPA(-/-)) had markedly reduced HGF levels and c-met activation after muscle damage. This reduced HGF activity in uPA(-/-) animals was associated with decreased cell proliferation, myoblast accumulation, and new muscle fiber formation. On the other hand, HGF activity was enhanced at early time points in PAI-1(-/-) mice compared with wild-type mice and the PAI-1(-/-) animals exhibited accelerated muscle fiber regeneration. Furthermore, administration of exogenous uPA rescued HGF levels and muscle regeneration in uPA(-/-) mice, and an HGF-blocking antibody reduced HGF activity and muscle regeneration in wild-type mice. We also found that uPA promotes myoblast proliferation in vitro through its proteolytic activity, and this process was inhibited by an HGF-blocking antibody. Together, our findings demonstrate that uPA promotes muscle regeneration through HGF activation and subsequent myoblast proliferation.

Neutral proteinases of leucocytes and the inflammatory process

Plasminogen, the inactive precursor of plasmin, a general trypsin-like proteinase, is present at high concentration in blood and in body fluids. Most cells can recruit this proteolytic potential by secreting plasminogen activator (PA) to generate localized proteolysis in the surrounding microenvironment. PA and plasmin are serine enzymes whose pH optima match extracellular pH; further, in view of the large amount of circulating proenzyme and the broad substrate range of plasmin, the possibility that this proteolytic system can initiate a variety of proteolytic reactions or sequences should be kept in mind. PA production is precisely regulated by hormones, temporal programming, or both; and enzyme synthesis is correlated with some physiological and pathological processes requiring proteolysis. Thus PA production is coordinately regulated with ovulation, trophoblast implantation, spermatogenesis, polypeptide hormone synthesis, and some developmental phenomena; and with inflammation, tumour promotion, and neoplasia. Tissue remodelling and cell migration are common to many of these processes. Macrophage (monocyte) and polymorphonuclear leucocyte PA production is modulated by many biologically active substances. Enzyme synthesis is induced and stimulated by stimuli that recruit these cells to sites of inflammation, and it is repressed by anti-inflammatory agents, notably by glucocorticoids.

Naproxen, meloxicam and methylprednisolone inhibit urokinase plasminogen activator and inhibitor and gelatinases expression during the early stage of osteoarthritis

BACKGROUND

To test the hypothesis that naproxen, meloxicam and methylprednisolone down-regulate the plasminogen activator (PA)/plasmin system and gelatinases [matrix metalloproteinase (MMP)-2 and MMP-9] expression during early development of osteoarthritis (OA).

METHODS

Samples of human OA articular cartilage, meniscus and synovium were obtained at knee arthroscopy and cultured ex vivo with or without naproxen, meloxicam or methylprednisolone. MMP-2 and MMP-9 levels were evaluated by gelatin zymography and urokinase-type PA (u-PA) and PA inhibitor-1 (PAI-1) levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Gelatin zymography revealed that naproxen, meloxicam and methylprednisolone could suppress MMP-2 secretion in all tissue cultures and MMP-9 production in meniscal and synovial cultures. ELISA showed that naproxen and meloxicam reduced u-PA secretion in chondral and synovial cultures at 48 h except in naproxen-treated chondral cultures. On PAI-1 secretion, naproxen and meloxicam had the suppressive effects in all cultures at 48 h but not in naproxen-treated meniscal cultures. Methylprednisolone also decreased u-PA secretion in chondral and synovial cultures and PAI-1 production in synovial cultures at 48 h.

CONCLUSION

Naproxen, meloxicam and methylprednisolone can down-regulate the PA/plasmin system and gelatinases expression in the early osteoarthritic knee of humans, thereby possibly have a potential structure-modifying activity in a limited use.

Studies on mRNA expression of tissue-type plasminogen activator in bruises for wound age estimation

We investigated mRNA expression of tissue-type plasminogen activator (tPA) and inflammatory cell dynamics for wound age estimation of bruises in mice. Neutrophils were detected from 1 h post-injury. Up to 8 h, they accumulated in subcutaneous tissue and the lower part of the dermis, and thereafter they extended to all the layers. Macrophages became detectable 3 h post-injury, and moderate infiltration of lymphocytes was seen from 144 h. In addition, epidermal thickening was also seen from 72 h. tPA mRNA expression peaked at 1 h, and increased slightly at 72 h post-injury. tPA mRNA was detected in epidermal cells, fibroblasts, and endothelial cells before and after injury, from 3 h in neutrophils and from 72 h in macrophages, respectively. This study presents the time-dependent expression of tPA mRNA in bruises in relation to temporal histologic characteristics during wound healing, which was considered to be useful for wound age estimation. Furthermore, it is suggested that tPA plays an important role in the first step of tissue remodeling.

Elimination of hydrocortisone from the medium enables tissue plasminogen activator gene expression by normal and immortalized nonmalignant human epithelial cells

Human cervical epithelial cells transfected and immortalized with human papillomavirus type 16 DNA (HCE16/3) can be, like many other epithelial cells, normally grown in medium supplemented with epidermal growth factor, cholera toxin, hydrocortisone, insulin, transferrin, thyroid hormone and serum. We found that hydrocortisone diminished tissue plasminogen activator (tPA) production to an undetectable level. The removal of hydrocortisone increased urokinase plasminogen activator (uPA) activity within 24-48 h and tPA activity within 48-72 h, and converted the cells to a more elongated and fibroblastic phenotype. Upregulation of uPA mRNA was seen as early as at 3 h and of tPA mRNA within 48-72 h. Higher molecular weight forms (97-110 kDa) of plasminogen activators were seen in zymograms, apparently complexed with PAI-1, starting at 6 h both in the presence and absence of hydrocortisone. Immunoprecipitation with a PAI-1 monoclonal antibody confirmed that both uPA and tPA were complexed. We also studied normal diploid human bronchial epithelial cells (NHBE) and NHBE cells transformed with an adeno-12/SV40 hybrid virus (BEAS-2B). In both types of nonmalignant epithelial cells, the removal of hydrocortisone increased uPA activity. The omission of hydrocortisone increased tPA levels significantly in BEAS-2B cell cultures, and in NHBE cell cultures tPA became detectable at 72 h. No PA complexes were seen in these two cell types. We conclude that normal and immortalized nonmalignant epithelial cells produce tPA, but only if hydrocortisone is omitted in the growth medium.

Dental extraction wound management: medicating postextraction sockets

The rather impressive percentage of extraction sites undergoing clot loss and deranged healing results in significant morbidity for the patient and frequent visits to the surgeon to effect relief of discomfort, most often by the use of anodyne dressings. The amount of work lost by patients needing such palliative treatment, and loss of productive time for the surgeon, translate into an unknown, but potentially large, economic loss to society. This would mandate that economical methods of ensuring normal extraction socket healing with minimal morbidity be developed. The most useful socket medicaments to prevent socket healing derangements would include broad-spectrum antibiotics, specifically clindamycin and tetracycline. Not discussed in this article, but possibly germane to the subject of clot stabilization and healing, is consideration of resorbable substances such as gelatin sponge, polylactic acid, and methylcellulose as clot-stabilizing socket implants. The record of such substances in preventing AO is mixed, but the combinations of these inexpensive materials with topical socket medicaments may yield a decreased tendency for clot lysis and greater mechanical strength to the bulk blood clot, as has been demonstrated with difficult mandibular third molar impactions in one study involving polylactic acid, tetracycline, and hydrocortisone.

Inhibition of gelatinase activity in human airway epithelial cells and fibroblasts by dexamethasone and beclomethasone

The effects of dexamethasone and beclomethasone on gelatinase activity released from lung epithelial cells (A549, NCI-H292 and Calu-3 cell lines and NHBE primary cultures) and human lung fibroblasts (HLF) were investigated. All cells spontaneously released gelatin-degrading activity but the amounts were unaffected by treatment with glucocorticoids. Phorbol myristate acetate (PMA) increased the amount of gelatinase activity in conditioned media prepared from all cell types examined. In epithelial cells, PMA induced the expression of gelatinase B, whereas in HLF the increased gelatinase activity resulted from increased activation of gelatinase A. Dexamethasone and beclomethasone produced concentration-dependent inhibition of PMA-induced gelatinase activity in HLF and epithelial cell lines. In the epithelial cell lines, the inhibition of activity was associated with an attenuation of enzyme induction by PMA. In contrast, primary cultures of human bronchial epithelial cells were unresponsive to dexamethasone at concentrations that were maximally effective at inhibiting gelatinase activity induced in other cells.

Urinary tissue factor: a potential marker of disease

Tissue factor (TF) is the main physiological initiator of blood coagulation and may be important in the biology of a variety of solid malignancies, particularly where angiogenesis is a critical factor. TF is frequently encrypted in the plasma membrane of cells in contact with blood, and is exposed only after stimulation by certain agonists. Cancer cells variably express TF and cancer cell lines which exhibit multidrug resistance contain more TF than parental cells. TF is increased in both tumour-associated macrophages and blood monocytes and has been implicated in abnormal coagulation activation seen in patients with inflammatory conditions and cancer. TF is also found in urine (uTF) in a lipid-associated form, probably of kidney origin. uTF levels can be assayed in a cost-effective manner and may be clinically important, particularly in patients with renal disorders and malignancy. uTF levels are not significantly affected by age, gender or cigarette smoking.

De novo synthesis of glucocorticoid hormone regulated inner ear proteins in rats

Changes of rat inner ear de novo protein synthesis in response to dexamethasone (DEX), a synthetic glucocorticoid, have been analyzed by high resolution two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (2D-SDS-PAGE) and fluorography. Two proteins (M(r) 41,000 and 35,000) were amplified and one protein (M(r) 47,000) was suppressed by DEX in a cochlear culture medium. In the culture medium conditioned by vestibular tissue, three proteins (M(r) 67,000, 57,000 and 50,000) were amplified after DEX administration. In cochlear and vestibular tissues, glucocorticoid-responsive protein synthesis was down-regulated by DEX, including two proteins (M(r) 39,000 and 35,000) in the cochlea and five proteins (M(r) 80,000, 64,000, 59,000, 56,000 and 40,000) in the vestibule. The regulation of these inner ear proteins by DEX suggests that glucocorticoid may play an important role in normal inner ear microhomeostasis, as well as in the treatment of some inner ear disorders.

Leukemia inhibitory factor (LIF) inhibits angiogenesis in vitro

Using an in vitro model in which endothelial cells can be induced to invade a three-dimensional collagen gel to form capillary-like tubular structures, we demonstrate that leukemia inhibitory factor (LIF) inhibits angiogenesis in vitro. The inhibitory effect was observed on both bovine aortic endothelial (BAE) and bovine microvascular endothelial (BME) cell, and occurred irrespective of the angiogenic stimulus, which included basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), the synergistic effect of the two in combination, or the tumor promoter phorbol myristate acetate. LIF inhibited bFGF- and VEGF-induced proliferation in BAE and BME cells. In addition, LIF inhibited BAE but not BME cell migration in a conventional two-dimensional assay. Finally, LIF decreased the proteolytic activity of BAE and BME cells and increased their expression of plasminogen activator inhibitor-1. These results demonstrate that LIF inhibits angiogenesis in vitro, an effect that can be correlated with a LIF-mediated decrease in endothelial cell proliferation, migration and extracellular proteolysis.

High-dose glucocorticosteroids increase the procoagulant effects of OKT3

The use of OKT3 as prophylaxis in renal transplantation carries an increased risk of intragraft thrombosis, which is related to the systemic activation of the coagulation system that consistently occurs after the first dose of OKT3. As only a few patients develop thrombosis after OKT3 therapy, we searched for possible additional risk factor by comparing the demographic and clinical parameters of the 13 patients who developed thrombosis in our institution to those of 218 patients who did not. Multivariate analysis showed a relationship between the dose of methylprednisolone (mPDS) given before the first OKT3 injection and the risk of thrombosis: 6 out of 42 patients (14%) who received high (30 mg/kg) mPDS experienced a thrombotic event, as compared to 7 out of the 189 patients (3.7%) who received < or = 8 mg/kg of mPDS (P < 0.01). This led us to study the effects of mPDS on the procoagulant activity induced by OKT3 on peripheral blood mononuclear cells (PBMC) in vitro. The procoagulant activity of unstimulated PBMC (mean +/- SEM: 0.6 +/- 0.1 mU/ml) reached 3.0 +/- 0.7 mU/ml after OKT3 stimulation (P = 0.0062) and further increased to 7.4 +/- 2.0 mU/ml when PBMC were first preincubated overnight with mPDS before OKT3 stimulation (P = 0.018 as compared to OKT3 alone). This process involved the tissue factor/factor VII pathway, as shown by increased membrane expression of tissue factor on monocytes as well as by a marked reduction of the induced procoagulant activity when the clotting assay was performed with factor VII-deficient plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosteroids: do they damage the cardiovascular system?

Since their introduction for the treatment of rheumatoid arthritis, corticosteroids have become widely used as effective agents in the control of inflammatory diseases. Although there have been undoubted benefits upon mortality in diseases such as systemic lupus erythematosus, many patients survive only to suffer a high incidence of premature atherosclerosis. There is also evidence of increased rates of vascular mortality in other corticosteroid-treated diseases, such as rheumatoid arthritis, reversible airways obstruction and transplant recipients. Possible mechanisms of damage include elevated blood pressure, impaired glucose tolerance, dyslipidaemia, and imbalances in thrombosis and fibrinolysis. This paper reviews the clinical evidence supporting the contention that there is an excess cardiovascular mortality in steroid-treated patients and the underlying mechanisms, and points to further areas of research.

U937 cells can utilize plasminogen activator to regulate human interferon-gamma

Urokinase-type plasminogen activator (uPA) converts the proenzyme plasminogen to plasmin and thereby contributes to processes like cell migration, tissue remodeling, and cytokine processing. We report here that uPA produced by the human U937 promonocytic cell line also initiated the inactivation of recombinant interferon-gamma (rIFN-gamma) by plasmin-mediated proteolysis. When cultured serum-free with plasminogen, U937 promonocytic cells generated measurable levels of plasmin activity and destroyed the antiviral activity of exogenously added rIFN-gamma. This effect was not seen in the absence of plasminogen, was prevented by inhibitors of uPA and plasmin, and was accompanied by changes in the electrophoretic mobility of rIFN-gamma on polyacrylamide gels, consistent with limited proteolysis of the lymphokine. Culturing U937 cells or blood monocytes for 48 h led to an elevated expression of their surface uPA and an increase in their capacity to produce plasmin and inactivate rIFN-gamma. The ability of rIFN-gamma to induce Fc receptors on U937 cells could also be prevented by providing the cells with a source of exogenous plasminogen, indicating that U937 cells could control their own activation in vitro through the action of uPA. The results of these studies support the conclusion that mononuclear phagocytes have the capacity to use uPA to regulate cytokine activity in vitro.

Effect of glucocorticoids on TPA-induced inhibition of gap-junctional communication and morphological transformation in Syrian hamster embryo cells

The effect of glucocorticoids on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inhibition of gap-junctional intercellular communication (GJIC) and morphological transformation in Syrian hamster embryo (SHE) cells was examined. Fluocinolone acetonide (FA) and dexamethasone (DEX) almost completely suppressed the effect of TPA on induction of transformed morphology. On the other hand, up to 1000 times higher FA and DEX concentrations did not influence the inhibitory effect of TPA on GJIC. Neither treatment with these glucocorticoids for 4, 24 or 48 h before TPA exposure nor 24 h co-exposure with TPA altered the effect of TPA on GJIC. Thus the potent effect of glucocorticoids as inhibitors of the promotional effect of TPA on morphological transformation in SHE cells does not result in alterations of TPA-induced inhibition of GJIC.

Characterization of immunotrap assays for urokinase plasminogen activator and its inhibitors and measurements of these molecules in human plasma and mouse macrophage in culture

1. Immunotrap assays that can measure the activities of urokinase-type plasminogen activator (uPA) and its inhibitors (PAIs) were characterized. 2. Both human plasma and mouse macrophages in culture were found to contain much higher inhibitor activity than uPA-like activity. 3. The balance between pro- and anti-fibrinolytic activities was quantitatively changed in the murine macrophages after the injection of thioglycollate. uPA-like materials were synthesized by the macrophages and secreted to the conditioned medium continuously, while PAI activity was unchanged during the same time period.

Molecular control of glutamine synthetase expression in the developing retina tissue

Glutamine synthetase is a differentiation marker of the neural retina, whose expression is restricted to Müller glia cells, is inducible by glucocorticoids and is dependent on tissue development. The retina tissue acquires the competence to express GS in response to glucocorticoids with development, although the level of hormone binding activity in the cells does not alter with age. Using CAT constructs that are controlled by "simple GRE" promoters we demonstrated that glucocorticoid receptor transcription activity in retina cells increases with development. The increase in receptor activity correlates directly with the increase in inducibility of the glutamine synthetase gene and inversely with the rate of retina cell proliferation. At early developmental ages, when retina cells are still proliferating, the glucocorticoid receptor is transcriptionally inactive and glutamine synthetase expression cannot be induced. Receptor activity increases progressively with development and by day 12, when cell proliferation ceases, competence for glutamine synthetase induction is high. This competence for glutamine synthetase induction can be repressed by overexpressing the oncogene v-src, which stimulates retina cell proliferation. We discuss possible mechanisms for developmental-dependent modulation of glucocorticoid receptor transcriptional activity.

Modulation of the plasminogen activation system in murine macrophages

We have dissected the state of fibrinolytic balance in the C57/BL mouse macrophages, by means of immunotrap assays and zymography. We have monitored the individual changes of plasminogen activator (PA) and plasminogen activator inhibitor (PAI) activities of cellular lysates and secretions of these macrophages, after they were stimulated by various exogenous agents. The resident peritoneal macrophages were found to have very little PA but high level of PAI, and are therefore highly anti-fibrinolytic in nature. Upon stimulation by thioglycollate, PA activity increased and PAI activity decreased, thus raising the fibrinolytic balance in these macrophages. Upon incubation of resident or thioglycollate-activated macrophages by lipopolysaccharide (LPS), the PA level was depressed while the PAI level was increased, resulting in a large drop in the total fibrinolytic balance of the activated cells. When resident or thioglycollate-activated macrophages were incubated with the anti-inflammatory agent dexamethasone, the drug depressed both the expressions of PA and PAI, in the lysate and conditioned medium of both cell types. Thus cell-bound or secreted forms of macrophage PA and PAI activities were either increased or decreased in response to thioglycollate, LPS or dexamethasone challenge. The changes in PA and PAI resulted in different state of fibrinolytic balance in macrophages, and could be related to the different functions of these macrophages at different stages of their development.

Intra-articular corticosteroid reduces joint stiffness after an experimental periarticular fracture

Early care after surgery or trauma to the extremities often includes a period of immobilization. The resultant joint stiffness may require extensive rehabilitation and may permanently limit function of the limb. Posttraumatic joint stiffness is particularly vexing in the small joints. In an experimental model, we tested the effects of intra-articular corticosteroid injections on stiffness in a joint at risk of posttraumatic joint stiffness. Triamcinolone was injected into ankle joints of rabbits after distal tibial fractures. Three weeks after injury, joint stiffness increased 34% in ankles injected with the steroid. Stiffness in ankles injected with saline solution and in ankles treated with no injection increased 133% and 224%, respectively. Limb swelling and tibial torsional strength to failure were not significantly affected by either of the treatments.

Plasminogen activator regulation in osteoblasts: parathyroid hormone inhibition of type-1 plasminogen activator inhibitor and its mRNA

In order to determine the mechanism by which parathyroid hormone (PTH) stimulates plasminogen activator (PA) activity in rat osteoblasts, we investigated the effect of human PTH(1-34) [hPTH(1-34)] on the synthesis of mRNAs for tissue-type PA (tPA), urokinase-type PA (uPA), and PA inhibitor-1 (PAI-1), and on release of PA activity and PAI-1 protein in both normal rat calvarial osteoblasts and UMR 106-01 osteogenic sarcoma cells. hPTH(1-34) (0.25-25 nM) decreased PAI-1 mRNA and protein, and increased PA activity in both cell types in a dose-dependent manner with ED50 of about 1 nM for both responses. Forskolin and isobutylmethylxanthine also stimulated PA activity and decreased PAI-1 protein and mRNA in both cell types. hPTH(1-34) did not show any consistent effect on tPA and uPA mRNA in calvarial osteoblasts, but a modest (two-fold) increase of both mRNAs was observed in UMR 106-01 cells treated with 25 nM hPTH(1-34). However, when protein synthesis was inhibited with 100 microM cycloheximide, the increase of tPA and uPA mRNA by hPTH(1-34) was enhanced in UMR 106-01 cells and became evident in calvarial osteoblasts. Fibrin autography also revealed that hPTH(1-34) increases tPA and uPA activity, especially after cycloheximide treatment in UMR 106-01 cells. These results strongly suggest that PTH increases PA activity predominantly by decreasing PAI-1 protein production through a cyclic adenosine monophosphate (cAMP)-dependent mechanism in rat osteoblasts. The reduction of PAI-1 protein by PTH results in enhanced action of both tPA and uPA, and would contribute to the specific roles of these PAs in bone.

In vivo inflammatory stimulation induces a transient change in the binding of thrombin to rat peritoneal macrophages

The binding of 125I-labeled thrombin to rat peritoneal macrophages isolated 20 h after the ip injection of thioglycollate broth or lipopolysaccharide decreased to 20% of the value found in resident macrophages due to a decrease in the number of receptors. The binding returned to normal values within a week after the injection. The decline parallelled more or less the Vmax for the 5'-nucleotidase activity. This decrease in the binding of thrombin could not be explained by an immigration of monocytes into the peritoneal cavity, since the binding of 125I-labeled alpha 2-macroglobulin-trypsin complex increased 4.5-fold in the same cell population due to an increase in the number of receptors, and blood monocytes do not bind alpha 2-macroglobulin-trypsin complex. The increase in the binding of alpha 2-macroglobulin-protease complex parallelled an increase in the incorporation of glucosamine, although the latter did not increase to the same extent. Engulfment of plasma membrane after phagocytosis did not result in a decreased binding of thrombin, but preincubation at 37 degrees C with concanavalin A caused a minor reduction in the binding. There was a positive correlation between the binding of alpha 2-macroglobulin-trypsin complex and the fraction of polymorphonuclear leukocytes in the peritoneal exudate and a negative correlation between the binding of thrombin and the fraction of polymorphonuclear leukocytes in the exudate, when the inflammation was induced by a milder stimulus, sterile NaCl, indicating a common signal for the polymorphonuclear leukocyte chemotaxis and the macrophage differentiation.

Vascularization and endochondral bone development: changes in plasminogen activator activity

Changes in plasminogen activator activity were studied during the sequential developmental stages of matrix-induced cartilage, bone, and bone marrow development. The morphological transitions were correlated with biochemical parameters. Morphologic evidence of vascularization of calcified hypertrophic cartilage was accompanied by a concomitant rise in plasminogen activator activity. Thereafter, a steady decline during mineralization and deposition of new bone was observed. Maximal plasminogen activator activity occurs at approximately the same time as peak activity of alkaline and acid phosphatase. These results imply a role for plasminogen activator during angiogenesis, vascular invasion, and attendant bone differentiation.

Variable response of tissue parameters of the fibrinolytic system to unilateral or bilateral adrenalectomy and unilateral or bilateral adrenal demedullation

The effect of unilateral and bilateral adrenalectomy, unilateral and bilateral demedullation or unilateral adrenalectomy/unilateral demedullation on tissue plasminogen activator activity (PAA), plasminogen activator inhibition (PAI) and plasmin inhibition (PI) was studied in the rat. All the above treatments induced an increase of PAA in lungs. Increased PAA was also noted in brain after bilateral adrenalectomy or demedullation, as well as unilateral adrenalectomy/unilateral demedullation. In kidneys the PAA was decreased after bilateral adrenalectomy or demedullation and unilateral adrenalectomy/unilateral demedullation. In aorta only after bilateral adrenalectomy a decreased PAA was induced. In heart and liver no changes in PAA were noted. A decreased PAI expressed against tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) was found in lungs of all treated rats compared to controls. However, an increased PAI was noted in heart, liver and aorta against t-PA or u-PA after bilateral adrenalectomy and in liver after bilateral demedullation as well as after unilateral adrenalectomy/unilateral demedullation (rats with only one adrenal cortex). A dissociation between anti-t-PA and anti-u-PA response was seen in heart, liver and aorta. A variable change in PI was induced in kidneys, aorta, lungs and brain in all treatments except unilateral demedullation or unilateral adrenalectomy. Therefore, the effect of adrenalectomy or demedullation on tissue PAA, PAI and PI was variable and dependent on the extent of the treatment (unilateral or bilateral), the organ as well as the time after the treatment.

Transforming growth factor beta inhibits plasminogen activator (PA) activity and stimulates production of urokinase-type PA, PA inhibitor-1 mRNA, and protein in rat osteoblast-like cells

Transforming growth factor beta (TGF beta) treatment of rat osteoblast-rich calvarial cells or of the clonal osteogenic sarcoma cells, UMR 106-01, resulted in dose-dependent inhibition of plasminogen activator (PA) activity, and increased production of 3.2 kb mRNA and protein for PA inhibitor -1 (PAI-1). Although tissue-type PA (tPA) protein was not measured, TGF beta did not influence production of mRNA for tPA. Production of 2.3 kb mRNA for urokinase-type PA (uPA) was also increased by TGF beta in a dose-dependent manner. The effects of TGF beta on synthesis of mRNA for PAI-1 and uPA were maintained when protein synthesis was inhibited, and were abolished by inhibition of RNA synthesis. Although uPA had not been detected previously as a product of rat osteoblasts, treatment of lysates of osteoblast-like cells with plasmin yielded a band of PA activity on reverse fibrin autography, corresponding to a low Mr form of uPA. Untreated conditioned media from normal osteoblasts or UMR 106-01 cells contained no significant TGF beta activity, but activity could be detected in acidified medium. Treatment of conditioned media with plasmin resulted in activation of approximately 50% of the TGF beta detectable in acidified media. The results identify several effects of TGF beta on the PA-PA inhibitor system in osteoblasts. Net regulation of tPA activity through the stimulatory actions of several calciotropic hormones and the promotion of PAI-1 formation by TGF beta could determine the amount of osteoblast-derived TGF beta activated locally in bone. Stimulation of osteoblast production of mRNA for uPA could reflect effects on the synthesis of sc-uPA, a precursor for the active form of the enzyme.

Generation of procoagulant (thromboplastin) and plasminogen activator activities in peripheral blood monocytes after total hip replacement surgery. Effects of high doses of corticosteroids

Development of thromboplastin (tpl) and plasminogen activator (PA) activity in monocytes and the effects of high doses of corticosteroids (HCD) on these activities were studied in patients undergoing a standardized surgical trauma. Twelve patients who received uncemented total hip prostheses were divided into a nonsteroid group (n = 6) and a steroid group (n = 6). We found no significant differences between the two patient groups regarding tpl or PA activities of peripheral blood mononuclear cells (PBM) isolated during the postoperative phase. However, in the nonsteroid group there was a tendency for increased expression of procoagulant activity and decreased fibrinolytic activity on the 1st postoperative day, favoring the formation of fibrin in the monocyte microenvironment. Further, PBM isolated on the 1st and 2nd day after surgery were significantly less capable of generating tpl activity on endotoxin stimulation than cells isolated preoperatively. This was not the case in the steroid group. These patients had also a tendency for decreased fibrinolysis at the end of the 1st postoperative week, indicating increased imbalance towards a more thrombotic stage after surgery.

An assay system for the modulators of plasminogen activation on the cell surface

Plasminogen activation on the cell surface is regulated by a variety of modulators which balance surface-bound plasminogen activators (PAs) and plasminogen activator inhibitors (PAIs). In this study, we developed as assay system to assess modulation of cell-associated plasminogen activation. Plasmin generation by endogenous plasminogen activators was measured with a combination of exogenously added plasminogen and a chromogenic substrate, S-2251, in the presence of living cells. A cell surface PA activity was quantitated by adopting a rate of plasmin generation. We used HT-1080, a human fibrosarcoma cell line, as representative of cells which have both PAs and PAIs on their cell surface. A basal level of cell surface PA activity was specifically reduced by anti-urokinase-type PA IgG and enhanced by anti-PAI-1 IgG, suggesting that the basal level is determined by a balance between uPA and PAI-1 on the cell surface. We examined effects of dexamethasone and thrombin on cell surface PA activity in the assay system. Dexamethasone appeared to suppress the cell surface PA activity by enhancing de novo synthesis of PAI-1, whereas thrombin suppressed it by inactivating single-chain urokinase-type plasminogen activators. These results indicate that our assay system can be adapted for the screening of various types of PA modulators.

Calcitriol-mediated modulation of urokinase-type plasminogen activator and plasminogen activator inhibitor-2

Calcitriol-induced differentiation of U937 mononuclear phagocytes is known to have divergent effects on the synthesis of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-2 (PAI-2). In this study, we sought to determine whether calcitriol affects the expression of these proteins by modulating intermediate signal transduction involving intracellular calcium and protein kinase C (PKC). U937 cells were stimulated with calcitriol (50 nM) for 6-72 hr, inducing a transient increase in specific binding of [3H]phorbol dibutyrate ([3H]PDBu), seen only after 24 hr. Staurosporine (2 nM), a PKC inhibitor, had no effect on calcitriol-induced secretion of plasminogen activator (PA) activity. However, staurosporine significantly (P less than 0.05) inhibited the ability of calcitriol to enhance phorbol myristate acetate (PMA)-induced secretion of PA inhibitor activity, indicating that this priming effect of calcitriol requires expression of PKC. The calcium ionophore A23187 (0.1 microM) induced a modest increase in secreted PA inhibitor activity, in contrast to the secretion of PA activity which is consistently seen in response to calcitriol. Northern blot analysis demonstrated that A23187 induced an increase in PAI-2 mRNA and a marked reduction in uPA mRNA, while calcitriol induced opposite changes in both mRNA species. We conclude that calcitriol modulates uPA and PAI-2 expression by multiple mechanisms that are both PKC dependent and PKC independent. Our studies also demonstrated that increased intracellular calcium alters the synthesis of both uPA and PAI-2 in a manner which favors expression of PA inhibitor activity.

Effect of high-dose corticosteroids on the incidence of deep vein thrombosis after total hip replacement

Fifty patients receiving uncemented total hip prostheses were examined by venography of the legs on the 2nd postoperative day. The patients were randomly divided into two groups, a non-steroid group (n = 26) and a steroid group (n = 24). Both groups received dextran thrombo-prophylaxis. The patients in the steroid group were treated with high-dose corticosteroids. The incidence of deep vein thrombosis (DVT) was 38% (19/50). No patients had clinical signs or symptoms of DVT. All thrombi were located distally in the leg. DVT was bilateral in nine patients, in the operated leg in three, and in the non-operated leg in seven. The administration of high-dose corticosteroids did not influence the incidence or pattern of DVT. All patients were followed up clinically and plethysmographically up to 12 months after surgery. Distally located asymptomatic DVT were not given specific treatment. The postoperative course was uneventful except for one patient in each group who developed clinically, apparent DVT more than 3 weeks after operation, although the initial venographic studies were normal.

Osteoblasts display receptors for and responses to leukemia-inhibitory factor

Specific binding of leukemia-inhibitory factor (LIF) to osteoblasts, but not multinucleated osteoclasts, was demonstrated by receptor autoradiography by using cells isolated from newborn rat long bones. The clonal rat osteogenic sarcoma cells, UMR 106-06, which have several phenotypic properties of osteoblasts, expressed 300 LIF receptors per cell, with an apparent KD of 60 pM. Treatment of calvarial osteoblasts or UMR 106-01 cells with LIF resulted in a dose-dependent inhibition of plasminogen activator (PA) activity. Both calvarial osteoblasts and osteogenic sarcoma cells were shown by Western blotting and reverse fibrin autography to produce plasminogen activator inhibitor-1 (PAI-1), the production of which was increased by LIF treatment. Northern blot analysis revealed that LIF treatment resulted in a rapid (peak 1 hour), dose-dependent increase in mRNA for PAI-1. LIF treatment of the preosteoblast cell line, UMR 201, enhanced the alkaline phosphatase response of these cells to retinoic acid. Each of the osteoblast-like cell types (calvarial osteoblasts, UMR 106-06, and UMR 201) was shown to produce LIF by bioassay and, by using the polymerase chain reaction (PCR), was shown to express low levels of mRNA for LIF. These data establish that cells of the osteoblast lineage are targets for LIF action. The reported anabolic effects of this cytokine on bone formation in vivo could be related to inhibition of protease activity. LIF may be an important paracrine modulator in bone, or perhaps an autocrine one, based on the evidence for its production by osteoblasts and osteoblast-like cells.

Regulation of plasminogen receptor expression on human monocytes and monocytoid cell lines

The capacity of human monocytoid cell lines and peripheral blood monocytes to modulate their expression of plasminogen receptors has been assessed. After PMA stimulation, THP-1 or U937 monocytoid cells were separated into adherent and nonadherent populations. Plasminogen bound to adherent cells with similar capacity and affinity as to nonstimulated cells. In contrast, the nonadherent cells bound plasminogen with 5-17-fold higher capacity (without a change in affinity). This increase was selective as urokinase bound with similar affinity and capacity to the adherent and nonadherent populations. Upregulation of plasminogen receptors on the nonadherent monocytoid cells was rapid, detectable within 30 min, and reversible, adhesion of the nonadherent cells resulted in a sixfold decrease in plasminogen binding within 90 min. The increase in plasminogen binding to the nonadherent cells was associated with a marked increase in their capacity to generate plasmin activity from cell-bound plasminogen. PMA stimulation of human peripheral blood monocytes increased their expression of plasminogen receptors by two- to fourfold. This increase was observed in both adherent and nonadherent monocytes. Freshly isolated monocytes maximally bound 5.0 x 10(5) plasminogen molecules per cell, whereas monocytes cultured for 18 h or more maximally bound 1.7 x 10(7) molecules per cell, a 30-fold difference in receptor number. These results indicate that both monocytes and monocytoid cell lines can rapidly and markedly regulate their expression of plasminogen binding sites. As enhanced plasminogen binding is correlated with an increased capacity to generate plasmin, an enzyme with broad substrate recognition, modulation of plasminogen receptors may have profound functional consequences.

Antitumor promotion and antiinflammation: down-modulation of AP-1 (Fos/Jun) activity by glucocorticoid hormone

Glucocorticoid hormones counteract inflammation and phorbol ester tumor promotion and drastically decrease the expression of several extracellular proteases, including collagenase I. Glucocorticoid hormone inhibits basal and induced transcription of collagenase by interfering with AP-1, the major enhancer factor of the collagenase promoter. The mechanism of interference is novel in that it does not require protein synthesis, it depends on the hormone receptor but not its binding to DNA, it occurs at hormone doses one order of magnitude below those required for gene activation, and it involves down-modulation of the trans-activating function of preexisting unbound and DNA-bound AP-1. Coprecipitation experiments suggest direct AP-1-hormone receptor interaction, which also possibly explains the reverse experiment: overexpression of Fos or Jun inhibits the expression of hormone-dependent genes.

Increased proteolytic activity is responsible for the aberrant morphogenetic behavior of endothelial cells expressing the middle T oncogene

Expression of the polyoma virus middle T (mT) oncogene in vivo is associated with a profound subversion of normal vascular development, which results in the formation of endothelial tumors (hemangiomas). In an attempt to understand the molecular mechanisms responsible for this phenomenon, we have investigated, in an in vitro system, the morphogenetic properties of endothelial cells expressing this oncogene. mT-expressing endothelioma (End) cells grown within fibrin gels formed large hemangioma-like cystic structures. All End cell lines examined expressed high levels of fibrinolytic activity resulting from increased production of urokinase-type plasminogen activator and decreased production of plasminogen activator inhibitors. Neutralization of excess proteolytic activity by exogenously added serine protease inhibitors corrected the aberrant in vitro behavior of End cells and allowed the formation of capillary-like tubules. These results suggest that tightly controlled proteolytic activity is essential for vascular morphogenesis and that physiological protease inhibitors play an important regulatory role in angiogenesis.

Plasminogen activator is involved in the hCG-induced neutrophil extravasation and vasopermeability increase in the rat testis

The role of proteolytic enzymes in the hCG-induced increase in testicular vasopermeability and neutrophil extravasation was studied using protease inhibitors. An intra-testicular injection of hCG together with incubation medium conditioned by polymorphonuclear leucocytes (PMNs) caused a significant increase in vasopermeability and a coincident extravasation of PMN's from the postcapillary venules in the rat testis. When p-aminobenzamidine, a serine protease inhibitor which inhibits urokinase-type plasminogen activator, was administered together with hCG in the incubation medium, both the permeability increase and PMN extravasation were prevented. Aprotinin, another serine protease inhibitor, and Eglin C, a specific neutrophil elastase and cathepsin G inhibitor were, however, without effect. None of these inhibitors caused any non-specific vascular effects in the testis at the concentrations used. These results support the concept that the hCG-induced increase in vasopermeability in the rat testis is related to extravasation of PMNs and suggest that urokinase-type plasminogen activator is involved in migration of these cells through the postcapillary venular walls.

Human and murine urokinase cDNAs linked to the murine alpha A-crystallin promoter exhibit lens and non-lens expression in transgenic mice

cDNAs encoding either the human or the murine urokinase-type plasminogen activator (uPA) were fused downstream from the promoter-enhancer element of the murine gene encoding alpha A-crystallin, a protein found exclusively in the ocular lens. The DNAs were microinjected into fertilized mouse eggs as linear fragments free of bacterial sequences, and for each construct one line of transgenic mice was generated. In both lines transgenic uPA activity was detected in the ocular lens, in agreement with previous results reported on transgenic mice bearing genes fused to the same regulatory region. Unexpectedly however relatively high levels of this activity were found also in the retina, and furthermore, human uPA activity was found also in different parts of the brain and in the bone marrow, and to a lesser extent in the spleen, thymus and optic nerve. Transgenic uPA transcript was found in the lens, retina, brain and thymus of mice carrying the murine cDNA. Such a pattern of expression was different from that exhibited by the endogenous murine uPA gene and, excluding the lens, it appeared to be conferred by the cDNAs. The putative regulation by uPA cDNAs is suggested to be mediated through an internal enhancer-like element functioning in combination with the alpha A-crystallin promoter in a fashion independent of the specific nature of the promoter.