Tissue plasminogen activator in psoriasis

Reduction in tissue plasmin: a new mechanism of action of narrowband ultraviolet B in psoriasis

BACKGROUND

Plasmin (PL) is a potent inflammatory cell activator, and ultraviolet (UV)B has immunomodulatory effects on cutaneous inflammatory responses. There are no previous studies comparing the effect of narrowband (NB)-UVB on tissue PL levels in psoriasis.

AIM

To estimate the possible role of PL in the pathogenesis of psoriasis, and to evaluate the effect of NB-UVB on tissue PL in psoriasis.

METHODS

This case-control study enrolled 21 patients with psoriasis and 20 clinically healthy volunteers matched for age and sex. Patients underwent 24 sessions of NB-UVB radiation. Biopsy samples using a 4 mm punch were taken from all patients before and after treatment and from the controls for estimation of tissue PL level by ELISA.

RESULTS

Tissue PL was significantly upregulated in psoriasis before treatment (mean ± SD 1.73 ± 1.23 ng/mg protein) compared with controls (0.21 ± 0.15 ng/mg protein) (P < 0.001). A statistically significant positive correlation (P = 0.02) was found between the tissue PL before treatment and the Psoriasis Area and Severity Index. Patients received 24 sessions of NB-UVB, with a mean cumulative dose of 23.25 ± 8.14 mJ/cm(2) . Tissue PL levels were reduced by a mean of 30.3% post-treatment compared with baseline (P < 0.001). The reduction in Pl levels was significantly correlated with the cumulative dose of NB-UVB, and with the percentage reduction in PASI (P < 0.001).

CONCLUSIONS

Our study highlights the possible role played by tissue PL level in the pathogenesis of psoriasis. PL level appears to reflect disease severity, and is a possible marker of therapeutic efficacy of NB-UVB on psoriatic skin.

Plasmin plays an essential role in amplification of psoriasiform skin inflammation in mice

Background

Although increased levels of plasminogen activators have been found in psoriatic lesions, the role of plasmin converted from plasminogen by plasminogen activators in pathogenesis of psoriasis has not been investigated.

Methodology/Principal Findings

Here we examined the contribution of plasmin to amplification of inflammation in patients with psoriasis. We found that plasminogen was diminished, but that the amount and activity of its converted product plasmin were markedly increased in psoriasis. Moreover, annexin II, a receptor for plasmin was dramatically increased in both dermis and epidermis in psoriasis. Plasmin at sites of inflammation was pro-inflammatory, eliciting production of inflammatory factors, including CC chemokine ligand 20 (CCL20) and interleukin-23 (IL-23), that was mediated by the nuclear factor-kappaB (NF-κB) signaling pathway and that had an essential role in the recruitment and activation of pathogenic C-C chemokine receptor type 6 (CCR6)⁺ T cells. Moreover, intradermal injection of plasmin or plasmin together with recombinant monocyte/macrophage chemotactic protein-1 (MCP-1) resulted in induction of psoriasiform skin inflammation around the injection sites with several aspects of human psoriasis in mice.

Conclusions/Significance

Plasmin converted from plasminogen by plasminogen activators plays an essential role in amplification of psoriasiform skin inflammation in mice, and targeting plasmin receptor - annexin II - may harbor therapeutic potential for the treatment of human psoriasis.

Upregulation of cathepsin S in psoriatic keratinocytes

Cathepsin S (CATS) is a cysteine protease, well known for its role in MHC class II-mediated antigen presentation and extracellular matrix degradation. Disturbance of the expression or metabolism of this protease is a concomitant feature of several diseases. Given this importance we studied the localization and regulation of CATS expression in normal and pathological human/mouse skin. In normal human skin CATS-immunostaining is mainly present in the dermis and is localized in macrophages, Langerhans, T- and endothelial cells, but absent in keratinocytes. In all analyzed pathological skin biopsies, i.e. atopic dermatitis, actinic keratosis and psoriasis, CATS staining is strongly increased in the dermis. But only in psoriasis, CATS-immunostaining is also detectable in keratinocytes. We show that cocultivation with T-cells as well as treatment with cytokines can trigger expression and secretion of CATS, which is involved in MHC II processing in keratinocytes. Our data provide first evidence that CATS expression (i) is selectively induced in psoriatic keratinocytes, (ii) is triggered by T-cells and (iii) might be involved in keratinocytic MHC class II expression, the processing of the MHC class II-associated invariant chain and remodeling of the extracellular matrix. This paper expands our knowledge on the important role of keratinocytes in dermatological disease.

Tissue plasminogen activator (t-PA) and placental plasminogen activator inhibitor (PAI-2) in gingival crevicular fluid from patients with Papillon-Lefevre syndrome

OBJECTIVES

Numerous patients with Papillon-Lefèvre syndrome (PLS) express a severe periodontal inflammation that results in premature loss of deciduous and permanent teeth. The plasminogen activating (PA) system is involved in physiological and pathological processes including epithelial healing, extracellular proteolysis and local inflammatory reactions. The aim of the study was to explore a possible role of the PA system in patients with PLS.

MATERIAL AND METHODS

Samples of gingival crevicular fluid (GCF) were collected from areas with gingival infection in 20 patients with PLS and in 20 healthy controls. The concentration of tissue plasminogen activator (t-PA) and inhibitor (PAI-2) was measured with ELISA.

RESULTS

The median level of PAI-2 was significantly higher (p < 0.01) in PLS patients than in the controls, while the median value of t-PA did not differ between the groups. No difference in t-PA or PAI-2 levels was found regarding age, gender or presence of active periodontal disease.

CONCLUSION

The findings indicate an atypical activity of the PA system with a disturbed epithelial function in PLS patients, suggesting that the periodontal destruction seen in patients with PLS is secondary to a hereditary defect in the defense system.

Plasminogen mediates the pathological effects of urokinase-type plasminogen activator overexpression

Increased expression of urokinase-type plasminogen activator (uPA) and its receptor (uPAR) is associated with different pathological conditions. Both uPAR-mediated signaling and plasmin-catalyzed extracellular proteolysis may contribute to pathogenesis. To evaluate the involvement of plasminogen in such circumstances, we have taken advantage of transgenic mouse models in which overexpression of uPA and/or uPAR in enamel epithelium, basal epidermis, and hair follicles leads to a pathological phenotype; uPA transgenic mice have chalky-white incisors and, when uPAR is co-expressed, develop extensive alopecia, epidermal thickening, and subepidermal blisters. We report here that when these transgenic mice were backcrossed into a plasminogen-deficient (Plg-/-) background, the dental and skin phenotypes appeared completely normal. Heterozygous Plg+/- transgenic mice exhibited a haplo-insufficiency, with an intermediate or normal phenotype. These results do not argue in favor of a role for uPAR-mediated signaling in our experimental model; rather, they demonstrate an essential, dose-dependent, requirement for plasminogen in uPA-mediated tissue alterations. They also support the hypothesis that plasminogen could play a part in certain skin diseases.

Urokinase-type plasminogen activator and its receptor synergize to promote pathogenic proteolysis

Urokinase-type plasminogen activator (uPA) is a potent catalyst of extracellular proteolysis, which also binds to a high-affinity plasma membrane receptor (uPAR). Binding of uPA may influence pericellular proteolysis and/or activate intracellular signal transduction. Transgenic mice overexpressing either uPA or uPAR in basal epidermis and hair follicles had no detectable cutaneous alterations. In contrast, bi-transgenic mice overexpressing both uPA and uPAR, obtained by crossing the two transgenic lines, developed extensive alopecia induced by involution of hair follicles, epidermal thickening and sub-epidermal blisters. The phenotype was due to uPA catalytic activity since combined overexpression of uPAR and uPAR-binding but catalytically inactive uPA in the same tissue was not detrimental in another bi-transgenic line. It was accompanied by increased plasmin-generating capacity, up-regulation and activation of matrix metalloproteinases type-2 and -9, and cleavage of uPAR. Thus, combined overexpression of uPA and uPAR acts in synergy to promote pathogenic extracellular proteolysis.

trans-4-(Aminomethyl)cyclohexane carboxylic acid (T-AMCHA), an anti-fibrinolytic agent, accelerates barrier recovery and prevents the epidermal hyperplasia induced by epidermal injury in hairless mice and humans

Because wounding the epidermis increases proteolytic activity and because disorders associated with barrier dysfunction have elevated protease activity, we studied the effect of protease inhibitors on the time course of barrier recovery and on the development of epidermal hyperplasia induced by repeated injury. After injuries to the epidermis produced by tape stripping, acetone treatment, or detergent (SDS) treatment that disrupt the barrier, a single application of 5% tranexamic acid [4-(aminomethyl)cyclohexane carboxylic acid, t-AMCHA], a well known anti-plasmin reagent, accelerated barrier recovery in both hairless mouse and human skin. In contrast, neither aminocaproic acid nor aminobutyric acid, inactive analogs of t-AMCHA, affected the time course of barrier recovery. Several trypsin-like serine protease inhibitors, e.g., leupeptin, TLCK, and PMSF, also accelerated barrier repair. In contrast other types of protease inhibitors, e.g., EDTA, pepstatin, N-ethylmaleimide, chymostatin, and TPCK, did not accelerate barrier recovery. We next evaluated the effects of daily topical application of t-AMCHA on epidermal hyperplasia, induced by repeated tape stripping or acetone treatment for 7 d. The degree of hyperplasia, quantified by the measurement of epidermal thickness, was reduced in both models by repeated applications of t-AMCHA. Finally, proteolytic activity in both human and mouse epidermis increased 1-2 h after epidermal injuries that disrupt the barrier. These results demonstrate that the inhibition of plasmin, a serine protease, accelerates barrier recovery and inhibits the epidermal hyperplasia induced by repeated barrier disruption, perhaps by decreasing the extent of attendant epidermal injury.

tPA of human keratinocytes: contribution to cell surface-associated plasminogen activation and upregulation by retinoic acid

We tested distinct variants of a human keratinocyte line (HaCaT) for the expression of tissue-type plasminogen activator (tPA)-specific mRNA, as well as cell surface-associated and secreted tPA. Cells of early passages (passage no. 22) only expressed urokinase plasminogen activator (uPA)- but not tPA-specific mRNA. Cells after prolonged culture (passage no. 44) expressed uPA- and tPA-specific mRNA, but did not release tPA in the extracellular space and did not display surface-associated tPA. HaCaT cells transformed with the c-Ha-ras oncogene (HaCaTras) showed both secreted and surface-associated tPA antigen. The secreted and the surface-associated plasminogen activator (PA)-activity of HaCaTras cells were in part inhibitable by anticatalytic anti-tPA antibodies, thus indicating that tPA contributes to extracellular and surface-associated plasminogen activation. Finally, we demonstrate that tPA secretion of HaCaT 44 cells can be induced by retinoic acid, most likely via interaction of retinoic acid with nuclear-associated retinoic acid-receptor(s).

Plasminogen activation by human keratinocytes: molecular pathways and cell-biological consequences

Keratinocytes are the major cellular constituent of stratified epithelia. Defects in these epithelia are re-epithelialized by keratinocytes migrating from the edge of the defect into the wound. The cells form a monolayer with subsequent differentiation into a multilayered epithelium. It is thought that plasminogen activation by migrating keratinocytes is an important event during re-epithelialization. In the present report we summarize the studies on plasminogen activation by human keratinocytes in vitro and in vivo. Under the aspect of pericellular proteolysis the discussion is focused on the molecular mechanisms of plasminogen activation at the keratinocyte surface and on the cell-biological consequences of pericellular plasmin formation. We describe a cell surface-associated pathway of plasminogen activation which crucially depends on cell surface receptors for (pro)-uPA and plasmin(ogen). uPA bound to its receptor converts cell-bound plasminogen into the active protease plasmin. Compared to plasminogen activation in solution, activation at the keratinocyte cell surface is accelerated by a factor of approx. 7-10, and the plasmin generated and bound at the cell surface is protected against its specific inhibitor alpha 2-antiplasmin. Plasmin thus provided in the pericellular space leads to detachment of cultured keratinocytes from the growth substratum. Plasmin interferes with the adhesion of keratinocytes to fibrin, but not with the adhesion to collagen type I. By demonstrating that keratinocytes of the epithelial outgrowth in healing skin wounds express uPA and the uPA-R and that plasmin(ogen) is colocalized with uPA and/or uPA-R, indirect evidence is provided that this pathway may be operative in vivo. In view of previous findings that plasminogen activation is also observed under certain pathologic conditions in the epidermis, we conclude that plasminogen activation by keratinocytes is rather related to tissue damage and subsequent repair mechanisms than to a specific pathologic situation.

Levels of skin-derived antileukoproteinase (SKALP)/elafin in serum correlate with disease activity during treatment of severe psoriasis with cyclosporin A

The epidermal serine proteinase inhibitor SKALP (also known as elafin), directed against human leukocyte elastase and proteinase 3, is strongly induced in suprabasal keratinocytes during inflammation. The presence of SKALP/elafin in urine has been demonstrated for several inflammatory skin disorders, such as psoriasis, erythroderma, and erysipelas. In this study we investigated whether SKALP/elafin levels in serum and urine of psoriatic patients can be used as a marker for disease activity during treatment. Patients with severe chronic disabling psoriasis were treated for 16 weeks with cyclosporin A, which resulted in a marked clinical improvement as measured with the PASI score. SKALP/elafin levels both in serum and urine were determined with an enzyme-linked immunosorbent assay (ELISA). Measurements were performed at the start of the cyclosporin A treatment, and after regular intervals up to 16 weeks. The results indicate that 1) SKALP/elafin determination in serum rather than in urine is the preferred method, because the decrease in serum SKALP levels during therapy is more pronounced and correlated better with the clinical course of the patients; 2) SKALP/elafin levels in serum decreased during cyclosporin A treatment (p < 0.05); and 3) SKALP/elafin levels in serum correlate with the PASI score (p < 0.01). We conclude that SKALP/elafin measurement in serum of patients with severe psoriasis provides a tool for monitoring disease activity.

Immunohistochemical characterization of the plasminogen activator system in psoriatic epidermis

The relative topographical distribution of urokinase-type plasminogen activator (uPA), tissue-type PA (tPA), PA-inhibitor-1 (PAI-1), PA-inhibitor-2 (PAI-2), plasmin(ogen), alpha 2-antiplasmin, and alpha 2-macroglobulin was studied in lesional epidermis of psoriasis vulgaris, and in normal epidermis, by immunohistochemistry. In psoriatic epidermis, tPA predominated, although uPA was found in some biopsies. PAs were not detected in normal epidermis. PAI-1 was not detected in normal epidermis and was only present in a proportion of biopsies of psoriatic lesions. PAI-2 was found in normal and psoriatic epidermis. Plasmin(ogen) was confined to the basal cell layer of normal epidermis, whereas in lesional psoriatic skin it was scattered throughout the epidermis. Alpha 2-antiplasmin and alpha 2-macroglobulin were not found in the epidermis of normal skin. In psoriatic epidermis alpha 2-antiplasmin was confined to the subcorneal layer, whereas staining for alpha 2-macroglobulin was found only in a proportion of biopsies, in the upper epidermis. Our immunohistological findings indicate that colocalization of tPA and its substrate plasminogen may allow efficient generation of plasmin, and that the focal absence of plasmin inhibitors may then favour the persistence of plasmin activity.

Plasminogen activation in lesional skin of Pemphigus vulgaris type Neumann

Zymographic and immunological studies revealed that primarily tissue-type plasminogen activator and to a lesser extent urokinase-type plasminogen activator were present in fluids of pemphigus vulgaris (type Neumann) skin blisters. Furthermore, plasmin activity was detected in pemphigus blister fluids using chromogenic peptide substrate assays. In pemphigus, but not in control, suction blister fluids plasmin/alpha 2-antiplasmin and plasmin/alpha 2-macroglobulin complexes were found by immunoprecipitation or by testing in immunoassays after fractionation by molecular-sieve chromatography. Plasmin activity, detected by a low molecular weight chromogenic peptide assay, was ascribed to plasmin/alpha 2-macroglobulin complexes. Since formation of plasmin/inhibitor complexes requires active plasmin, the finding indicates previous activation of plasminogen in pemphigus lesions.