Mathematical modelling of nitric oxide regulation of rete peg formation in psoriasis.

Recent experiments have shown that in patients with psoriasis, highly elevated levels of nitric oxide (NO) are released at the surface of psoriatic plaques. Nitric oxide is a central biological regulator of many aspects of physiology, and it is a natural possibility that the high nitric oxide levels in psoriasis play a causal role in the onset of the disease. Here, we use mathematical modelling to investigate this possibility. We begin by discussing a simple model consisting of a single equation for nitric oxide concentration, which enables nitric oxide secretion rates in the basal epidermis to be calculated from the observed NO release rates at the skin surface. Using this key parameter value, we then develop an extended model that tests the hypothesis that nitric oxide regulates the formation of the extended rete pegs seen in psoriatic plaques. This occurs via the peroxynitrite-dependent activation of the collagenase MMP-8, which is produced by neutrophils present at high levels in psoriatic plaques. The plausibility of the hypothesis is demonstrated and specific testable quantitative predictions about the roles of the various cell types and signalling molecules are made.     

Elevated interleukin-18 protein expression in early active and progressive plaque-type psoriatic lesions

Psoriasis is a T cell-mediated inflammatory skin disease characterized by an elevated IFN-gamma and IL-12p70 expression in skin lesions. Interleukin-18 (IL-18) synergizes with IL-12 to induce IFN-gamma production and a strong T-helper-1-mediated immune response, or to induce Th2 polarization depending on the immunological context. We have previously shown that keratinocytes in normal skin produce and store large amounts of pro-IL-18. In this study, we hypothesized that the expression of IL-18 in psoriatic lesional skin might be altered compared to normal skin. Therefore, IL-18 expression was assessed in psoriatic, stable, plaque-type lesions and early active and progressive lesions. IL-18 mRNA and protein concentrations were constitutively high, and did not differ between normal and stable, plaque-type epidermis. In active and progressive lesions an elevated expression of total IL-18 protein relative to normal and stable, plaque-type epidermis was detected using ELISA, while on Western blot, the differences in pro- or mature IL-18 were less clear. Our results indicate that the role of IL-18 in the pathogenesis of early phases of psoriasis may be more prominent than in established psoriatic lesions.     

Psoriasis pathogenesis — Pso p27 is generated from SCCA1 with chymase

Psoriasis is a chronic inflammatory skin disease with unknown aetiology. Infiltration of inflammatory cells as the initial event in the development of new psoriatic plaques together with the defined inflamed areas of such lesions argues for an immunological disease with a local production of a causal antigen. The auto-antigen Pso p27 is a protein expressed in the skin lesions. We recently demonstrated that Pso p27 is homologous to the core amino acid sequences of squamous cell carcinoma antigens 1 and 2 (SCCA1/2) and it is apparently generated from SCCA molecules by digestion with highly specific endoproteases. In this communication we demonstrate the generation of Pso p27 from SCCA1 with extracts from psoriatic scale and even more remarkably, the generation of Pso p27 from SCCA1 in the presence of mast cell associated chymase. These findings open up for new therapeutic strategies in psoriasis and probably also in other autoimmune diseases as Pso p27 epitopes have been detected in diseased tissues from patients with various chronic inflammatory diseases.     

The role of LncRNA MALAT-1 and MiRNA-9 in Psoriasis

BackgroundPsoriasis is a chronic skin disorder manifested by recurrent episodes of scaly, red, itchy skin patches that occur within apparently normal skin.ObjectivesThis study was performed to detect the expression of serum and tissue (lesion and non-lesion) LncRNA MALAT-1 and MiRNA-9 that might be used as biomarkers for psoriasis.MethodsBlood samples were obtained from 60 psoriasis patients and 40 controls, as well as 4 mm punch biopsy from lesional and non lesional skin of psoriatic patient and normal skin of healthy controls. Expression of LncRNA MALAT-1 and miRNNA-9 in serum and tissues was detected by real time qRT-PCR.Resultsa statistically significant increase in the expression of MALAT-1 in lesional and non-lesional skin and serum of psoriatic patients in comparison to controls were detected. Moreover, there was statistically significant increase in serum MiRNA-9 in patients in comparison to controls, while its tissue level was significantly lower in patients.ConclusionThis study highlights the dysregulation of LncRNA MALAT-1 and miRNA-9 in psoriasis. Elevated expression of MALAT-1 in lesional skin of psoriatic patients compared to non-lesional skin may possibly contribute to the development of psoriatic plaques.     

Psoriatic hair follicle cells I. Biochemistry and behaviour in culture

It is generally accepted that in psoriasis there is an alteration of epidermal cell proliferation. It has been reported that an increased rate of thymidine incorporation into keratinocytes is found in the upper part of the hair follicle in involved skin, but this is not the case in the lower part. Here we show that cells from psoriatic hair follicles could be brought in culture under the same conditions as those of normal hair follicles. Cells, whether originating from the upper or lower part of the hair follicle sheath either from involved or uninvolved psoriatic skin, show a faster rate of outgrowth in the first days of culture. Moreover, a large number of psoriatic cells have an increased motility in the early stages of culture, as compared to control cells. These properties can no longer be observed after several days in culture. The activity of glucose-6-phosphate dehydrogenase known to be increased in psoriatic plaques is normal in hair follicles isolated from these plaques. Protein gel electrophoretic investigations showed that there is no difference in gel patterns between normal and psoriatic hair follicles.In conclusion, the isolation of human hair follicles represents a simple method that allows psoriatic keratinocytes to be brought in culture and permits the study of certain aspects of the disease.     

Psoriasis pathogenesis – Pso p27 constitutes a compact structure forming large aggregates

Psoriasis is a chronic inflammatory skin disease. The absence of microbial organisms as potential causal agents has given rise to the hypothesis that the inflammation is due to an autoimmune reaction. The defined inflamed areas of the skin lesions argue for an immunological disease with a local production of a causal antigen. Pso p27 is a protein generated in mast cells in psoriatic plaques, but not in uninvolved skin. We recently demonstrated that the Pso p27 is generated by cleavage of SerpinB3 (SCCA1) in the presence of mast cell associated chymase.In this communication we demonstrate by X-ray crystallographic analysis that the cleavage products associate into a complex similar to SCCA1, but with the reactive centre loop inserted into a 5-stranded central β-sheet.Native gel electrophoresis show that these Pso p27 complexes form large aggregates which may be of significance with respect to an immunogenic role of Pso p27.     

Alterations of prostaglandin E2-9-ketoreductase activity in proliferating skin.

The activity of an NADPH-dependent PGE2-9-ketoreductase has been demonstrated in rat and human skin. This activity is localized in the high speed supernatant fraction, indicating the presence of an active PGE2-9-ketoreductase associated with the cytoplasmic fraction of the skin. Transformation of PGE2 into PGF2alpha is enhanced by skin specimens from psoriatic plaques and EFA-deficient rats, both characterized by excessive cellular proliferation and increased NADPH production. Incubations of the 105,000 g supernatant fractions from normal and EFA-deficient rats demonstrated that the activity of the PGE2-9-ketoreductase was elevated in high speed preparations from EFA-deficient rats. Results from these studies suggest that the increased activity of PGE2-9-ketoreductase observed in skin from human psoriatic plaques and EFA-deficient rats may be due in part to the increased generation of NADPH by these tissues and in part to alteration of the PGE2-9-ketoreductase by the excessive proliferation of the tissues.     

Transforming growth factor-beta 1 localization in normal and psoriatic epidermal keratinocytes in situ.

Transforming growth factor-beta 1 (TGF beta 1) is a potent inhibitor of epithelial cell proliferation and its effects on growth and differentiation have been extensively characterized in cultured keratinocytes. We used two TGF beta 1-specific polyclonal antibodies (anti-LC and anti-CC) to determine the presence of TGF beta 1 peptide in keratinocytes in sections of normal human skin in situ and in both plaque and nonplaque skin from individuals with psoriasis. In contrast to the differentiation phenotype expressed by keratinocytes in normal epidermis, keratinocytes in the psoriatic plaque exhibit a hyperproliferative/regenerative differentiation phenotype. Anti-TGF beta 1 staining was observed primarily in the epidermis. Anti-LC TGF beta 1 antibody stained nonproliferating, differentiated suprabasal keratinocytes intracellularly in normal skin but did not stain psoriatic plaques from five of seven patients. In contrast, anti-CC TGF beta 1 antibody stained suprabasal keratinocytes extracellularly in psoriatic plaques, but did not stain normal skin. Both anti-LC and anti-CC stained suprabasal keratinocytes intracellularly in nonplaque psoriatic skin. Thus, the conformation or structure of TGF beta 1 and its localization vary in keratinocytes with distinct differentiation phenotypes suggesting that TGF beta 1 is a potential modulator of keratinocyte differentiation in vivo. Selective association of TGF beta 1 with nonproliferating keratinocytes in the suprabasal layers of the epidermis and its exclusion from the proliferating keratinocytes in the basal layer suggest that it may be a physiological regulator of keratinocyte proliferation. In addition, the intracellular localization of TGF beta 1 peptide in both normal and psoriatic keratinocytes suggests that it is constitutively synthesized by epidermal keratinocytes in vivo.     

Substantial alterations of the cutaneous bacterial biota in psoriatic lesions

For psoriasis, an idiopathic inflammatory disorder of the skin, the microbial biota has not been defined using cultivation-independent methods. We used broad-range 16S rDNA PCR for archaea and bacteria to examine the microbiota of normal and psoriatic skin. From 6 patients, 19 cutaneous samples (13 from diseased skin and 6 from normal skin) were obtained. Extracted DNA was subjected to the broad range PCR, and 1,925 cloned products were compared with 2,038 products previously reported from healthy persons. Using 98% sequence identity as a species boundary, 1,841 (95.6%) clones were similar to known bacterial 16S rDNA, representing 6 phyla, 86 genera, or 189 species-level operational taxonomic unit (SLOTU); 84 (4.4%) clones with <98% identity probably represented novel species. The most abundant and diverse phylum populating the psoriatic lesions was Firmicutes (46.2%), significantly (P<0.001) overrepresented, compared to the samples from uninvolved skin of the patients (39.0%) and healthy persons (24.4%). In contrast, Actinobacteria, the most prevalent and diverse phylum in normal skin samples from both healthy persons (47.6%) and the patients (47.8%), was significantly (P<0.01) underrepresented in the psoriatic lesion samples (37.3%). Representation of Propionibacterium species were lower in the psoriatic lesions (2.9+/-5.5%) than from normal persons (21.1+/-18.2%; P<0.001), whereas normal skin from the psoriatic patients showed intermediate levels (12.3+/-21.6%). We conclude that psoriasis is associated with substantial alteration in the composition and representation of the cutaneous bacterial biota.     

Physical characterization of the stratum corneum of an in vitro psoriatic skin model by ATR-FTIR and Raman spectroscopies

The stratum corneum is an important permeability barrier for the skin. The disorganization of the skin protective barrier characterizes some skin diseases such as psoriasis. Indeed, psoriatic skin is known to be more permeable than normal human skin. An in vitro human skin substitute may be obtained by the auto-assembly method. This method was adapted to produce psoriatic substitutes. FTIR spectroscopy is a well-established method to evaluate the order of hydrocarbon chains in terms of population of trans and gauche conformers. Using ATR-FTIR, we have compared the physicochemical properties of the stratum corneum in skin models derived from uninvolved and involved psoriatic cells with those derived from normal cells. Our results suggest that the stratum corneum of involved psoriatic skin substitutes is less organized than that of normal skin substitutes. Also, it seems that the properties of uninvolved psoriatic skin may vary with seriousness of the disease. The development of a new psoriatic skin model would be helpful in the design of new treatments and to increase the understanding of the mechanisms of this pathology.     

Neutrophil chemoattractant and IL-1-like activity in samples from psoriatic skin lesions. Further characterization

The IL-1-like neutrophil chemoattractant activity previously reported by us to be present in the stratum corneum of psoriatic skin lesions has now been characterized further. Aqueous extracts of stratum corneum samples from psoriatic lesions and from the heels of normal volunteers were ultrafiltered to yield 10- to 30-kDa fractions. The ultrafiltered psoriatic preparations consistently contained greater neutrophil chemokinetic activity than the normal heel preparations, but in contrast the latter contained markedly greater IL-1 activity than the former. Successive chromatographic purification of psoriatic lesional stratum corneum extracts showed that the neutrophil chemokinetic material previously reported to co-elute with IL-1 activity on reversed phase HPLC, but to be distinct from C5a des arg, could now be separated by anion exchange HPLC into at least four different chemokinetic compounds that were also resolved from the IL-1 activity. The reversed phase HPLC-purified chemokinetic material from psoriatic stratum corneum was also active in a neutrophil chemotaxis assay. These findings show that samples from psoriatic skin lesions contain a group of novel 10- to 30-kDa neutrophil chemoattractant compounds that are distinct from both C5a des arg and IL-1. The contrasting neutrophil chemokinetic and IL-1 activities in psoriatic lesional and normal heel stratum corneum preparations support the finding that the two activities are produced by different compounds. These neutrophil chemoattractant and IL-1-like compounds may be of pathogenic importance in inflammatory skin disease.     

Psoriasis: hyperproliferation cannot induce characteristic epidermal morphology

Abstract A mathematical model of cell renewal in epidermis is proposed for describing how psoriatic lesions might develop, based on available cell kinetic data for normal and psoriatic epidermis. Our simulations clearly demonstrate that an increase in the turnover rate in the germinative cell population cannot alone induce the typical psoriatic tissue architecture (i.e. increased number of germinative cells). Two perturbations are needed to account for the morphology of clinically-stable psoriatic lesions. The first corresponds to a temporary disturbance of the steady state of the germinative layer, resulting in limited growth of this compartment; the second perturbation corresponds to a reduction in transit time in the differentiated compartment. Moreover, our simulation, based on a widely-accepted hypothesis of homeostatic control of tissue kinetics, demonstrates that the primary cause of typical psoriatic morphology is probably an alteration in epidermal maturation. In this view, depletion of differentiated cells at the surface is the stimulus for the increased cell production rate in the germinative population.     

Psoriasis: hyperproliferation cannot induce characteristic epidermal morphology

A mathematical model of cell renewal in epidermis is proposed for describing how psoriatic lesions might develop, based on available cell kinetic data for normal and psoriatic epidermis. Our simulations clearly demonstrate that an increase in the turnover rate in the germinative cell population cannot alone induce the typical psoriatic tissue architecture (i.e. increased number of germinative cells). Two perturbations are needed to account for the morphology of clinically-stable psoriatic lesions. The first corresponds to a temporary disturbance of the steady state of the germinative layer, resulting in limited growth of this compartment; the second perturbation corresponds to a reduction in transit time in the differentiated compartment. Moreover, our simulation, based on a widely-accepted hypothesis of homeostatic control of tissue kinetics, demonstrates that the primary cause of typical psoriatic morphology is probably an alteration in epidermal maturation. In this view, depletion of differentiated cells at the surface is the stimulus for the increased cell production rate in the germinative population.     

Lipid lymphocyte chemoattractants in psoriasis

In view of the evidence that lymphocyte infiltrates are a constant feature of the skin lesions of psoriasis and the demonstration that certain hydroxylated metabolites of arachidonic acid are present in lesional psoriatic skin and possess lymphocyte chemoattractant properties, lipid extracts of samples from lesional and normal skin were assayed to determine which are the predominant lipid lymphocyte chemoattractants in psoriasis. Dilution-related lymphocyte chemoattractant activity was found in lipid extracts of stratum corneum samples from psoriatic lesions, but not in similar extracts the samples from both sources contained equivalent amounts of this activity. Subsequent purification of lesional stratum corneum lipid extracts by straight and reversed phase high performance liquid chromatography (HPLC) revealed the presence of at least two different lipid chemoattractants, one major component being identified as 12-(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12[R]-HETE) by its biological and chromatographic properties. These compounds may play a role in the pathogenesis of the lymphocyte infiltrates in psoriatic lesions.     

Leukotrienes C4 and D4 in psoriatic skin lesions

Chemoattractant arachidonate lipoxygenase products have been recovered from the skin lesions of psoriasis, and may play a role in eliciting the intra-epidermal neutrophil infiltrate that characterises this disease. In view of evidence for lipoxygenase activity in psoriasis, the characteristic vasodilation in psoriatic lesions, and the vasodilator properties of leukotriene (LT) C4 and D4 in human skin, the presence of these LTs in psoriatic lesions has been investigated. Skin chamber fluid from abraded psoriatic lesions contained significantly greater amounts of immunoreactive material than that from clinically normal skin, as determined by a double antibody radioimmunoassay (RIA) that uses antiserum cross-reacting with both LTC4 and LTD4. Purification of lesional chamber fluid and scale extracts by high performance liquid chromatography (HPLC) and RIA of fractions showed immunoreactivity which co-eluted with standard LTC4 and LTD4. These findings suggest that LTC4 and LTD4 may play a role in mediating the vasodilation and increased blood flow that characterise psoriatic skin lesions.     

The role of the Duffy antigen-related chemokine receptor in psoriasis vulgaris

Chemokines represent a family of potent biological mediators. Within the group of receptors mediating their effects, a promiscuous receptor has been found which is able to bind and inactivate diverse chemokines of both C-C and C-X-C families. It is co-localized with blood group antigens of the Duffy system on the same glycoprotein and expressed on red blood cells as well as post-capillary blood vessels. In the present study three aspects of Duffy pathophysiology were studied: firstly the amount of IL-8 and RANTES binding to red blood cells and its correlation to disease activity of psoriatic patients, secondly the distribution of Duffy phenotype among psoriatic patients and thirdly the expression of Duffy antigen in normal vs psoriatic skin. Red blood cells from psoriatic patients (n=50) were lysed by triton X (1%) and supernatants tested in IL-8- and RANTES sandwich-ELISA. Duffy phenotype of psoriatic patients (n=50) was assessed by typing red blood cells with specific antisera in indirect Coombs technique. For immunohistochemical detection in normal and psoriatic skin (n=10 respectively) a specific monoclonal antibody (Fy6) was used. Neither IL-8- nor RANTES-levels on red blood cells correlated to disease activity and distribution of Duffy phenotype in psoriatics was not significantly altered when compared to the normal population. Furthermore, Duffy antigen was expressed in a similar pattern in normal and psoriatic skin at all parts of vasculature, albeit much more abundantly in diseased skin. Altogether, chemokine binding to red blood cells seems of minor importance in psoriasis. However, Duffy antigen together with other binding mechanisms like proteoglycans may play a role at local level by binding locally produced chemokines. Thus biological effects of chemokines are both restricted and focussed to dermal tissue.