The mitogen-activated protein kinases p38 and ERK1/2 are increased in lesional psoriatic skin

BACKGROUND: Alterations in specific signal transduction pathways may explain the hyperproliferation and abnormal differentiation of the keratinocytes as well as the increased expression of inflammatory cytokines seen in psoriasis. Major signalling pathways used by eukaryotic cells to transduce extracellular signals into cellular responses impinge on the mitogen-activated protein kinases (MAPKs). OBJECTIVES: To investigate the expression of the MAPK p38, extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) in psoriatic skin. METHODS: Keratome biopsies were taken from patients with plaque-type psoriasis. Western blot analysis was used to determine p38, ERK and JNK activity and protein levels, whereas kinase assays were used to examine the kinase activity of p38. RESULTS: We demonstrated increased levels of the phosphorylated forms of p38 and ERK1/2 in lesional psoriatic skin compared with nonlesional psoriatic skin. No abnormality was found in the activation and expression of JNK1/2. Ex vivo kinase assays confirmed the increased activation of p38, and furthermore demonstrated increased kinase activity of the p38 isoforms p38alpha, p38beta and p38delta in lesional compared with nonlesional psoriatic skin. p38gamma was not detected in the psoriatic skin. Clearance of the psoriatic lesions, induced by climatotherapy at the Dead Sea for 4 weeks, led to a normalization in the activity of both p38 and ERK1/2. CONCLUSIONS: Taken together, our results demonstrate that the activity of the MAPKs p38alpha, p38beta and p38delta and ERK1/2 are increased in lesional psoriatic skin compared with nonlesional psoriatic skin, and that clearance of psoriasis normalizes the p38 and ERK1/2 activity. Thus, p38 and ERK1/2 might be potential targets in the treatment of psoriasis.     

The activity of caspase-1 is increased in lesional psoriatic epidermis

Caspase-1 belongs to the group of inflammatory caspases and is the activating enzyme for the proinflammatory cytokine IL-18, a cytokine known to play an important role in the pathogenesis of psoriasis. The purpose of this study was to determine the expression of caspase-1 in psoriatic skin and the signaling mechanisms involved in stress-induced activation of caspase-1 and IL-18. Interestingly, increased caspase-1 activity in lesional compared with non-lesional psoriatic skin was seen. In vitro experiments in cultured human keratinocytes demonstrated anisomycin-induced, p38 mitogen-activated protein kinase (p38 MAPK)-dependent increased secretion of procaspase-1 and active caspase-1. Furthermore, anisomycin increased the mRNA expression of IL-18 through a p38 MAPK-dependent but caspase-1-independent mechanism, reaching a maximum level after 12 hours of stimulation. Finally, anisomycin caused a rapid (4 hours) increase in the secretion of proIL-18 and active IL-18. Secretion of active IL-18 was mediated through a p38 MAPK/caspase-1-dependent mechanism, whereas secretion of proIL-18 was mediated by a p38 MAPK-dependent but caspase-1-independent mechanism. These data demonstrate that the activity of caspase-1 is increased in psoriatic skin and that IL-18 secretion is regulated by a p38 MAPK/caspase-1-dependent mechanism, making caspase-1 a potential target in the treatment of psoriasis.     

The mesenchymal stem cell profile in psoriasis

Background The expression of inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor (VEGF) and the level of total oxyradical scavenging capacity have been evaluated extensively in the cutaneous cells of patients with psoriasis. As yet, no indications are available about the undifferentiated cells, the mesenchymal stem cells (MSCs), isolated from skin. Objectives To isolate MSCs in patients with psoriasis and to compare them with those obtained from atopic and healthy subjects, in order to analyse whether MSCs show some typical psoriatic profiles and to understand whether pathophysiological events leading to psoriasis start early at the stem cell level. Methods MSCs isolated from seven patients with psoriasis, seven patients with acute atopic dermatitis and seven healthy subjects were characterized by fluorescence‐activated cell sorting analysis. VEGF and nitric oxide (NO) content was measured in conditioned medium, the expression of VEGF and iNOS was analysed by immunohistochemistry, and the total oxyradical scavenging capacity towards peroxynitrite was tested. Results VEGF content was highest in the medium conditioned by psoriatic perilesional MSCs, whereas NO concentration was maximally increased in medium conditioned by MSCs isolated from lesional psoriatic skin. The ability to neutralize the oxidizing effects of peroxynitrite was lower for MSCs isolated from lesional psoriatic skin compared with other MSCs, except for MSCs of lesional atopic skin. Conclusions The microenvironment in psoriasis differs from those of atopic dermatitis and healthy skin; it could induce resident MSCs to produce angiogenic and proinflammatory mediators which lead to a reduction in the antioxidant capacity of these cells, contributing to the development of skin lesions in psoriasis.     

Expression of CCL1 and CCL18 in atopic dermatitis and psoriasis

Background.  Recent studies have shown that chemoattractive proteins play an important role in the organization of the innate and adaptive immune responses. There are some reports that chemokine (C‐C motif) ligand (CCL)1 and CCL18, members of a family of chemoattractive proteins, have increased expression in atopic dermatitis (AD). Aim.  To evaluate the quantity and pattern of CCL1 and CCL18 expression in lesions and blood of patients with AD, and compare them with those of patients with psoriasis. Methods.  Biopsy specimens were taken from atopic skin and normal‐appearing skin of patients with AD and from the psoriatic skin only of patients with psoriasis. Quantitative real‐time PCR analysis and immunohistochemistry of CCL1 and CCL18 expression were performed, and the quantities of expressed CCL1 and CCL18 in acute AD were compared with those of normal‐appearing atopic skin and psoriatic skin. The serum level of CCL1 and CCL18 was assessed by ELISA. Results.  Expression of CCL1 mRNA and protein was significantly higher in the acute lesional skin of patients with AD than in their nonlesional skin or in the lesional skin of patients with psoriasis. Both CCL18 mRNA and protein were abundant in acute AD lesions and in psoriatic lesions, but were lower in the nonlesional skin of patients with AD. The serum levels of CCL1 and CCL18 were not different in patients with AD and patients with psoriasis. Conclusions.  CCL1 is a chemokine that is associated with AD. Both CCL1 and CCL18 may play important roles in the initiation and progression of atopic skin inflammation.     

CCL7 contributes to the TNF‐alpha‐dependent inflammation of lesional psoriatic skin

Chemokines are small chemotactic proteins that have a crucial role in leukocyte recruitment into tissue. Targeting these mediators has been suggested as a potential therapeutic option in inflammatory skin diseases such as psoriasis. Using quantitative RT‐PCR, we found CCL7, a chemokine ligand known to interact with multiple C‐C chemokine receptors, to be markedly increased in lesional psoriasis as opposed to atopic dermatitis, lichen planus, non‐lesional psoriatic and normal control skin. Surprisingly, this increase in CCL7 mRNA expression exceeded that of all other chemokines investigated, and keratinocytes and dermal blood endothelial cells were identified as its likely cellular sources. In an imiquimod‐induced psoriasis‐like mouse model, CCL7 had a profound impact on myeloid cell inflammation as well as on the upregulation of key pro‐psoriatic cytokines such as CCL20, IL‐12p40 and IL‐17C, while its blockade led to an increase in the antipsoriatic cytokine IL‐4. In humans receiving the TNF‐α‐blocker infliximab, CCL7 was downregulated in lesional psoriatic skin already within 16 hours after a single intravenous infusion. These data suggest that CCL7 acts as a driver of TNF‐α‐dependent Th1/Th17‐mediated inflammation in lesional psoriatic skin.     

TNFα‐ and IL‐17A‐mediated S100A8 expression is regulated by p38 MAPK

The antimicrobial peptide S100A8 is known to be upregulated in lesional psoriatic skin compared with non‐lesional psoriatic skin and is believed to play a role in the pathogenesis of psoriasis. However, little is known about the signalling pathways involved in the regulation of S100A8 expression. Using quantitative real‐time RT‐PCR analysis, we demonstrated that stimulation with TNFα and IL‐17A in combination resulted in a significant and synergistic induction of S100A8 mRNA in human keratinocytes. TNFα and IL‐17A also induced the S100A8 promoter activity synergistically. This was demonstrated by a gene reporter assay in cells transfected with a luciferase plasmid construct, consisting of 3502 base pairs of the human S100A8 promoter. The TNFα‐ and IL‐17A‐mediated induction of S100A8 mRNA and protein was mediated by a p38 MAPK‐dependent mechanism, as demonstrated by the use of a p38 MAPK inhibitor. Finally, adalimumab treatment for patients with psoriasis significantly decreased S100A8 mRNA at day fourteen after start of treatment, but not at day four. Taken together, this study demonstrates that the p38 MAPK signalling pathway plays a key role in the TNFα‐ and IL‐17A‐induced expression of S100A8 in cultured human keratinocytes.     

Very late antigen-1 in psoriasis: an immunohistochemical study

Background Currently, psoriasis is thought to be an inflammatory response to an antigenic stimulation, in which angiogenesis plays a fundamental role. Very late antigen‐1 (VLA‐1) is a β₁ integrin collagen receptor that is up‐regulated in many angiogenic processes. Data on its role in psoriasis are sparse. Objective In a prospective study, we evaluated the staining of VLA‐1 in lesional skin from patients with psoriasis and atopic dermatitis. Material and methods Frozen sections from skin biopsies of patients with chronic plaque‐type psoriasis (n = 18) and chronic atopic dermatitis (n = 7) were stained with a monoclonal antibody to VLA‐1. The number of blood vessels stained with VLA‐1 and the staining intensity were evaluated. These were correlated with the histologic features. Results The absolute number of blood vessels was found to be similar in the atopic and psoriatic samples. However, the number of vessels stained with anti‐VLA‐1, as well as the staining intensity, was shown to be significantly higher in the psoriasis group (P < 0.05). Differences between psoriatic lesions showing typical histological features of psoriasis and those showing features that overlap with dermatitis were found as well. Conclusions Expression of VLA‐1 was found significantly higher in lesional dermal blood vessels of psoriatic patients compared with atopic patients. These findings suggest a possible role for VLA‐1 in the pathological angiogenesis of psoriasis. It may be an additional tool for establishing the diagnosis of psoriasis and provide a basis for new strategies in the treatment of psoriasis.     

High expression levels of keratinocyte antimicrobial proteins in psoriasis compared with atopic dermatitis

Recently, it was shown that lesional skin of atopic dermatitis patients expresses low levels of some antimicrobial peptides, compared with psoriasis patients. Here we performed microarray analysis on mRNA from purified lesional epidermal cells of patients with chronic plaque psoriasis and chronic atopic dermatitis, to investigate whether this is a general phenomenon for host defense proteins, and how specific it is for this class of molecules. Microarray data were confirmed on a selected set of genes by quantitative PCR and at the protein level by immunohistochemistry. We found overexpression of many antimicrobial proteins in keratinocytes from psoriatic skin compared with atopic dermatitis skin. Interestingly, we observed that markers of normal differentiation and the activated/hyperproliferative epidermal phenotype were expressed at equal levels. Chronic lesions of psoriasis and atopic dermatitis patients are remarkably similar with respect to cellular proliferation. We conclude that psoriatic epidermis expresses high levels of host defense proteins compared with atopic dermatitis epidermis, and this phenomenon appears to be specific for these proteins. It remains to be investigated whether this is caused by genetic polymorphisms in pathways leading to an epidermal antimicrobial response, or by differences in the cellular infiltrate in psoriasis compared with atopic dermatitis.     

Increased expression of the aryl hydrocarbon receptor in patients with chronic inflammatory skin diseases

Polychlorinated biphenyls (PCBs) and 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) are major environmental pollutants, and their effects on the human body critically depend on the aryl hydrocarbon receptor (AhR). The aim of this study was to evaluate the significance of the AhR and its ligands in chronic inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis. Expression of AhR‐related mRNA was increased in lesional skin from patients with AD and psoriasis compared to those of normal skin from healthy controls. The AhR and aryl hydrocarbon receptor nuclear translocator were colocalized in the nuclei of keratinocytes at the lower epidermis of psoriatic lesions, which suggested activation of the AhR pathway. After treatment of normal human epidermal keratinocytes with TCDD or PCBs, IL‐6 and IL‐8 production were increased. The results of this study suggest that AhR is highly expressed in the acute lesional skin of patients with AD and psoriasis, and the AhR pathway is activated especially in psoriasis.     

Reduced oxazolone-induced skin inflammation in MAPKAP kinase 2 knockout mice

Mitogen-activated protein kinase (MAPK) AP kinase 2 (MK2) is a serine/threonine kinase that is phosphorylated and activated by p38 MAPK. MK2 regulates the expression of various proinflammatory cytokines including TNF-alpha, IL-1beta, IL-6, and IL-8. Recently, MK2 was demonstrated to be activated in lesional psoriatic epidermis. This study investigates for the first time the role of MK2 in skin inflammation using the model of oxazolone-induced acute allergic contact dermatitis in mice. We show that oxazolone treatment leads to increased expression and sustained activation of both p38 MAPK and MK2. The inflammatory response was determined by ear thickness, myeloperoxidase activity, and histology after oxazolone challenge. Pretreatment with the p38 MAPK inhibitor SB202190 and genetic ablation of MK2 inhibit this inflammatory response. In particular, IL-1beta and, to a smaller but significant extent, also TNF-alpha and IFN-gamma expression were decreased in MK2 knockout mice compared with wild-type mice. These results indicate that MK2 is a potential target for the treatment of inflammatory skin diseases.     

Surfactant protein D in atopic dermatitis and psoriasis

The collectin surfactant protein-D (SP-D) shows antimicrobial and immuno-regulatory properties and has recently been detected in the basal layers of normal human skin. This molecule potentially plays an important role in inflammatory skin diseases and therefore SP-D content and location was examined using immunohistochemistry on skin biopsies from patients with the two major dermatologic diseases, psoriasis and atopic dermatitis. SP-D was located in the stratum basale of all biopsies with similar intense staining in both diseased and normal skin. Differences were detected in stratum spinosum where involved psoriatic skin showed intense staining through the entire region significantly different from uninvolved and normal skin. Lesional atopic skin showed moderate staining extending through the basal three-fourths of stratum spinosum. Using real time polymerase chain reaction analysis, no substantial up-regulation of SP-D mRNA was detected in lesional psoriatic skin, and a comparison of serum levels of SP-D between patients with atopic dermatitis or psoriasis and a group of age matched healthy controls did not show significant differences. In conclusion SP-D was significantly more abundant in the stratum spinosum of lesional psoriatic and atopic skin due to more cells producing the molecule rather than up-regulation of production in single cells of diseased skin. Further studies are needed to show if SP-D plays a role in the protection against skin infections or modulation of the inflammatory process in these common skin diseases.     

Key component of inflammasome,NLRC4, was identified in the lesional epidermis of psoriatic patients

Inflammasomes are multimolecular complexes that control the inflammatory response. The function of inflammasomes in the pathogenesis of psoriasis is still unclear. To clarify the relationship between inflammasomes and the pathophysiology of psoriasis, and in particular, to identify molecules interacting with caspase‐1, a crucial component of inflammasomes, scale extracts obtained from patients with psoriasis were immunoprecipitated with anti‐caspase‐1 antibody and analyzed by liquid chromatography coupled with electrospray tandem mass spectrometry (LC‐MS/MS). The expression of the inflammasome component was assessed by immunohistochemical analysis and an in vitro assay. We identified several candidates for caspase‐1‐interacting proteins from the psoriatic scale extracts by immunoprecipitation and LC‐MS/MS. Nucleotide‐binding oligomerization domain‐containing protein‐like receptor family CARD domain‐containing protein 4 (NLRC4) was the only inflammasome component among the candidates; thus, the protein is considered to be a key factor of inflammasomes in psoriasis. No inflammasome component was found in the extracts of atopic dermatitis or normal skin by LC‐MS/MS. Immunohistochemical analysis demonstrated upregulation of NLRC4 in the lesional epidermis of some psoriatic patients whereas weak expression of NLRC4 was detected in the normal and non‐lesional epidermis. The mRNA expression of the NLRC4 gene increased in keratinocytes at confluency, 48 h after air exposure and after the addition of 1.5 mmol/L calcium chloride. Our findings suggest that NLRC4 may be involved in the exacerbation or modification of psoriatic lesions.     

Kinetics and differential expression of the skin-related chemokines CCL27 and CCL17 in psoriasis, atopic dermatitis and allergic contact dermatitis

CCL27 and CCL17 are chemokines believed to be involved in the process of establishing the inflammatory infiltrate, characteristic for the various inflammatory skin diseases. The skin-specific CCL27 binds the chemokine receptor-10 (CCR10), and CCL17 is a chemokine receptor-4 (CCR4) ligand. The purpose of our study was to characterize the expression of CCL27 and CCL17 in the inflammatory skin diseases: psoriasis, atopic dermatitis (AD) and acute allergic contact dermatitis (ACD) induced in nickel-sensitive individuals. Surprisingly, our studies revealed a markedly decreased CCL27 mRNA and protein expression in psoriatic lesions compared with non-lesional psoriatic skin. A minor CCL17 mRNA increase was measured in lesional psoriatic skin. No alterations were found in AD. In ACD, we found a pronounced (90-fold) raise in CCL17 mRNA and a 50-fold increase in CCL17 protein compared with normal skin. A kinetic ACD study of CCL17 expression showed the highest mean value 24 h after hapten application. Furthermore, we found the mRNA levels of CCR10 and CCR4 paralleling the results of their corresponding ligands. Overall, our principal findings were a distinct decrease in CCL27 in lesional psoriatic skin and a marked upregulation of CCL17 in ACD. These findings underscore the differential cutaneous T-cell recruitment in different inflammatory diseases.