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TNFα-, IL-23- and IL-17-targeting drugs are highly effective in the treatment of psoriasis. However, the precise molecular mechanism remains unknown. In psoriatic skin, the presence of Langerhans cells ( LCs) is reduced, but the role of LC is poorly understood. The purpose of this study was to investigate the impact of TNFα and IL-23/ IL-17 on the presence of LC in the skin during treatment. Therefore, psoriatic skin was investigated before and after 4 days of adalimumab or ustekinumab treatment. Furthermore, TNFα and IL-17A stimulation was investigated in an ex vivo model of epidermis and dermis from healthy normal skin kept in cultures at an air-liquid interphase for 4 days. In a gene array analysis, we found that the two LC markers, CD1a and CD207, were among the most up- or downregulated genes in psoriatic skin after anti- TNFα therapy. Validation showed that both mRNA expression and protein level followed the same pattern and became significantly upregulated after 4 days of treatment. No changes were seen after ustekinumab treatment. In the ex vivo skin model, a decrease in the CD1a level was seen after TNFα stimulation and it was caused by LC migration from epidermis. No response in LC migration was seen after IL-17A stimulation. Taken together, we demonstrated that changes in the LC level in epidermis precede the histological and clinical changes during adalimumab treatment in psoriatic skin. Furthermore, TNFα plays a prominent role in orchestrating LC migration in the skin. This seems not to be the true for the IL-23/ IL-17A pathway. [ABSTRACT FROM AUTHOR]

Although biological drugs in psoriasis treatment show clinical efficacy, there are still a proportion of patients in whom little treatment response is obtained. The aim of this study was to identify molecular biomarkers for treatment response and to investigate the molecular effects of ustekinumab treatment of psoriasis. The mRNA expression of various genes in skin biopsies was analysed by quantitative polymerase chain reaction (qPCR). At baseline, there was no significant clinical difference between responders and non-responders. Ten patients were clinical responders, with a mean baseline Psoriasis Area and Severity Index (PASI) score of 15.4 and a mean percentage improvement of 89.6%. No significant reduction in PASI during treatment was seen among the 5 non-responders. In the responder group, ustekinumab therapy reduced the mRNA expression of the majority of the studied genes in lesional psoriatic skin. 1I,-20, IL-21 and p40 mRNA expression in lesional psoriatic skin at baseline were significantly upregulated by factors of 2.7, 2.4 and 2.3, respectively, among non-responders compared with responders. The mRNA levels of p40, IL-20 and IL-21 at baseline may serve as potential predictors of treatment response to ustekinumab treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

p38 mitogen-activated protein kinase plays a pivotal role in skin inflammation. The purpose of this study was to investigate the role of the various p38 isoforms. p38β/δ-knockout-C57BL/6 mice were generated, studied in a 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced skin inflammation model and compared with wild-type mice. The inflammatory response was determined by ear thickness, myeloperoxidase activity and histology. mRNA and protein expression of interleukin (IL)-1β and IL-6 was determined by quantitative real-time reverse transcription PCR and enzyme-linked immunoassay. In both groups application of TPA resulted in a significant increase in inflammation, and pretreatment with the p38α/β inhibitor, SB202190 resulted in a significant inhibition. A significantly slower onset but prolonged duration of the response was seen in p38β/δ knockout mice. This was paralleled by a significant, but transient, lower IL-1β and IL-6 protein expression in p38β/δ knockout mice. Although the p38α isoform is important, our data also demonstrate an important role of the p38β and/or δ isoforms in the regulation of TPA-induced skin inflammation. [ABSTRACT FROM AUTHOR]

Mitogen- and stress-activated protein kinase (MSK)1/2 are two kinases involved in inflammation as well as in cell transformation. Purpose: To examine the role of MSK1/2 in skin tumor development. Results: MSK1/2 knockout mice developed significantly fewer skin tumors compared with wild-type mice. The myeloperoxidase activity in TPA-treated skin from MSK1/2 knockout mice was significantly elevated compared with wild-type mice. Furthermore, the mRNA and protein levels of IL-1ββ as well as the mRNA expression of TNF-αα were significantly increased in MSK1/2 knockout mice. Conclusion: These data provide in vivo evidence that MSK1/2 signaling represents a novel tumor-promoting axis in skin carcinogenesis. [ABSTRACT FROM AUTHOR]

Background: IL-24 (melanoma differentiation-associated gene-7 (mda-7)), a member of the IL-10 cytokine family, possesses the properties of a classical cytokine as well as tumor suppressor effects. The exact role of IL-24 in the immune system has not been defined but studies have indicated a role for IL-24 in inflammatory conditions such as psoriasis. The tumor suppressor effects of IL-24 include inhibition of angiogenesis, sensitization to chemotherapy, and p38 mitogen-activated protein kinase (MAPK)- mediated apoptosis. Current knowledge on the regulation of IL-24 expression is sparse. Previous studies have suggested that mRNA stabilization is of major importance to IL-24 expression. Yet, the mechanisms responsible for the regulation of IL-24 mRNA stability remain unidentified. As p38 MAPK is known to regulate gene expression by interfering with mRNA degradation we examined the role of p38 MAPK in the regulation of IL-24 gene expression in cultured normal human keratinocytes. Methodology/Principal Findings: In the present study we show that anisomycin- and IL-1β- induced IL-24 expression is strongly dependent on p38 MAPK activation. Studies of IL-24 mRNA stability in anisomycin-treated keratinocytes reveal that the p38 MAPK inhibitor SB 202190 accelerates IL-24 mRNA decay suggesting p38 MAPK to regulate IL-24 expression by mRNA-stabilizing mechanisms. The insertion of the 39 untranslated region (UTR) of IL-24 mRNA in a tet-off reporter construct induces degradation of the reporter mRNA. The observed mRNA degradation is markedly reduced when a constitutively active mutant of MAPK kinase 6 (MKK6), which selectively activates p38 MAPK, is co-expressed. Conclusions/Significance: Taken together, we here report p38 MAPK as a regulator of IL-24 expression and determine interference with destabilization mediated by the 39 UTR of IL-24 mRNA as mode of action. As discussed in the present work these findings have important implications for our understanding of IL-24 as a tumor suppressor protein as well as an immune modulating cytokine. [ABSTRACT FROM AUTHOR]

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.Journal of Investigative Dermatology (2007) 127, 2857–2864; doi:10.1038/sj.jid.5700922; published online 28 June 2007 [ABSTRACT FROM AUTHOR]

We previously demonstrated that m RNA for the pro-inflammatory cytokine interleukin 20 ( IL-20) is expressed in suprapapillary keratinocytes of lesional psoriatic skin ( LS). Here, we describe the distribution of IL-20 protein and the identity of the IL-20-positive cells in LS. We found that the main part of IL-20 immunoreactivity is present in mononuclear cells of the dermal papillae, and that the IL-20-positive cells located in the papillae were langerin+, CD1a+, CD4+ and CD303+. These cells might be immature dendritic cell. In situ hybridization for IL-20 m RNA on non- LS, ex vivo stimulated with IL-1 β revealed a colocalization between IL-20 m RNA and the keratinocyte marker CK14. No IL-20 m RNA was detected in the dermal mononuclear cells. Our results suggest that IL-20 is produced by keratinocytes, released into the epidermis and then possibly taken up by papillary mononuclear cells. Our study supports that IL-20 is involved in the pathogenesis of psoriasis. [ABSTRACT FROM AUTHOR]

Abnormal epidermal proliferation and differentiation characterize the inflammatory skin disease psoriasis. Here we demonstrate that expression of PPARδ mRNA and protein is markedly upregulated in psoriatic lesions and that lipoxygenase products accumulating in psoriatic lesions are potent activators of PPARδ. The expression levels of NF-κB p50 and p65 were not significantly altered in lesional compared with nonlesional psoriatic skin. In the basal layer of normal epidermis both p50 and p65 were sequestered in the cytoplasm, whereas p50, but not p65, localized to nuclei in the suprabasal layers, and this distribution was maintained in lesional psoriatic skin. In normal human keratinocytes PPAR agonists neither impaired IL-1β-induced translocation of p65 nor IL-1β-induced NF-κB DNA binding. We show that PPARδ physically interacts with the N-terminal Rel homology domain of p65. Irrespective of the presence of agonists none of the PPAR subtypes decreased p65-mediated transactivation in keratinocytes. In contrast p65, but not p50, was a potent repressor of PPAR-mediated transactivation. The p65-dependent repression of PPARδ- but not PPARα- or PPARγ-mediated transactivation was partially relieved by forced expression of the coactivators p300 or CBP. We suggest that deficient NF-κB activation in chronic psoriatic plaques permitting unabated PPARδ-mediated transactivation contributes to the pathologic phenotype of psoriasis. [ABSTRACT FROM AUTHOR]