Bedeutung von Interleukin-6, Oncostatin M und Interleukin-31 für die biochemische und immunologische Barrierefunktion der Haut
The barrier function of the human skin involves biochemical as well as immunological processes. The family of multidrug resistance-associated proteins (MRP) are efflux transporters which protect skin cells from xenobiotica and promote inflammatory defence responses against pathogens through the export of prostaglandins and leukotrienes. In the first part of this thesis we investigated the effect of interleukin-6 (IL-6) and oncostatin M (OSM) on the expression of MRP-1, -3, -4 and -5 in normal human epidermal keratinocytes and primary dermal fibroblasts. Using real-time PCR, RT-PCR, cDNA microarray, immunostaining and efflux assays we found that IL-6 in combination with its soluble receptor enhances MRP expression and activity in keratinocytes. Despite the expression of the OSM receptor (OSMR) we could not observe an increased expression of MRP-3 in keratinocytes while MRP-1 mRNA levels were elevated. On the other hand OSM turned out to be a more effective stimulator of MRP synthesis in dermal fibroblasts. Both cytokines induced a strong activation of STAT1 and STAT3 (signal transducer and activator of transcription) as well as the MAPK (mitogen-activated protein kinase) Erk1/2. In contrast to IL-6, OSM additionally activated protein kinase B/Akt and the stress-activated MAPK p38. While the activation of MAPK occurred transiently with a peak at 30 minutes, the tyrosine phosphorylation of STAT factors persisted over a time period of 24 hours. Using the MEK1 (MAPK/extracellular signal-regulated kinase kinase 1)-specific inhibitor U0126 we could exclude a stimulatory effect of MAPK on MRP gene expression. Inhibition of the phosphatidylinositol 3-kinase, however, indicated that this pathway might be involved in the OSM-mediated up-regulation of MRP-4 in dermal fibroblasts. It was known before that several inflammatory skin diseases show an enhanced expression of IL-6-type cytokines. This fact correlates well with the observed up-regulation of MRP-1 expression in lesional skin from patients with psoriasis. The second part of this thesis focussed on some aspects of the immunological skin barrier function and its dysregulation. We characterised the signalling capacities of the interleukin-31 receptor, which forms a receptor complex in combination with the OSMR for the recently identified cytokine IL-31. Furthermore the relevance of IL-31 for Th1/Th2-mediated inflammatory skin diseases was examined. Using a chimeric receptor system based on the extracellular parts of the IL-5 receptor as well as the transmembrane and intracellular regions of gp130, OSMR and IL-31R we identified the recruitment sites for STAT3 and STAT5 by site-directed mutagenesis of individual tyrosine residues. The activation of STAT1 was also dependent on tyrosine motifs, yet mutation of a single tyrosine residue was insufficient to abrogate STAT1 phosphorylation. Unlike gp130, LIFR or OSMR the IL-31R is unable to initiate ERK1/2 phosphorylation due to the lack of recruitment of the tyrosine phosphatase SHP2 or the adaptor protein Shc. The strong expression of IL-31 in many skin biopsies from patients with atopic dermatitis is in line with the severe pruritic skin phenotype of IL-31 transgenic mice. The very strong expression of IL-31 in some biopsies from patients with allergic contact dermatitis indicates an involvement of IL-31 in the pathogenesis of this disease. IL-31 expression correlates with increased IL-4 expression and is found only in biopsies from patients with atopic and allergic contact dermatitis, but not in biopsies taken from patients suffering from the Th1-lymphocyte mediated skin disease psoriasis. Therefore, the most likely candidate cells for the secretion of IL-31 are Th2-lmphocytes. In addition to the constitutive expression of IL-31R as well as the OSMR in primary human keratinocytes, we could show for the first time an expression of this receptor complex in dermal fibroblasts.
info:eu-repo/classification/ddc/570, Biowissenschaften, Biologie, Signaltransduktion, Cytokine, Dermatitis, Haut, MRP-Proteine, Interleukin-31, Oncostatin M, skin, multidrug resistance-associated proteins, signal transduction, cytokines
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