Human S100A7 peptide

Human keratinocytes produce several antimicrobial peptides and proteins (AMP) which contribute to the protection of human skin against infection. RNase 7 is a major AMP involved in cutaneous defense with a high expression in keratinocytes and a broad spectrum of antimicrobial activity. The cytokine IL-17A has been recently identified as a potent inducer of several AMP in keratinocytes. Since the role of IL-17A to induce RNase 7 expression is unknown we analyzed IL-17A alone and in combination with other cytokines to induce RNase 7 expression in keratinocytes. Whereas IL-17A alone only weakly induced RNase 7 expression, the synergistic combination of IL-17A and IFN-gamma (IL-17A/IFN-gamma) was identified as a potent inducer of RNase 7 expression. This combination was more effective in inducing RNase 7 than the combination of IL-17A/TNF-alpha, a combination previously identified as a strong inducer of psoriasis-related immune response genes including several AMP. IFN-gamma and IL-17A both have been reported to activate the transcription factor STAT3 (Signal transducer and activator of transcription 3). Therefore we investigated the influence of STAT3 on the IL-17A/IFN-gamma -mediated RNase 7 induction. The use of a STAT3 inhibitor as well as siRNA-mediated downregulation of STAT3 resulted in a diminished IL-17A/IFN-gamma mediated RNase 7 induction in keratinocytes indicating that STAT3 is involved in this process. Similarly as seen with RNase 7, treatment of keratinocytes with IL-17A/IFN-c revealed also a synergistic induction of gene expression of the AMP human beta-defensin (hBD)-2 and -3 as well as the S100 protein psoriasin (S100A7) indicating that the combination of IL-17A/IFN-gamma is a potent inducer of various AMP classes in general. This was also reflected by an increase of the Staphylococcus aureus-killing activity of IL-17A/IFN-gamma -treated keratinocytes.

Psoriasis is a chronic inflammatory skin disease characterized by altered proliferation and differentiation of keratinocytes as well as infiltration of immune cells. Increased expression of Th17 cells and cytokines secreted by them provides evidence for its central role in the pathogenesis of psoriasis. IL-17A, signature cytokine of Th17 cells was found to be highly differentially expressed in psoriatic lesional skin. However, cellular and molecular mechanism by which IL-17A exerts its function on keratinocyte is incompletely understood. To understand IL-17A mediated signal transduction pathways, gene expression profiling was done and differentially expressed genes were analysed by IPA software. Here, we demonstrate that during IL-17A signaling total cholesterol levels were elevated, which in turn resulted in the suppression of genes of cholesterol and fatty acid biosynthesis. We found that accumulation of cholesterol was essential for IL-17A signaling as reduced total cholesterol levels by methyl beta cyclodextrin (MBCD), significantly decreased IL-17A induced secretion of CCL20, IL-8 and S100A7 from the keratinocytes. To our knowledge this study for the first time unveils that high level of intracellular cholesterol plays a crucial role in IL-17A signaling in keratinocytes and may explain the strong association between psoriasis and dyslipidemia.