Psoriasis is a common immune-mediated, chronic, inflammatory skin disease characterized by hyperproliferation and abnormal differentiation of keratinocytes and infiltration of inflammatory cells. Although TNFα-and IL-17A-targeting drugs have recently proven to be highly effective, the molecular mechanism underlying the pathogenesis of psoriasis remains poorly understood. We found that expression of the atypical IκB member IκB (inhibitor of NF-κB) ζ, a selective coactivator of particular NF-κB target genes, was strongly increased in skin of patients with psoriasis. Moreover, in human keratinocytes IκBζ was identified as a direct transcriptional activator of TNFα/IL-17A-inducible psoriasis-associated proteins. Using genetically modified mice, we found that imiquimod-induced psoriasis-like skin inflammation was completely absent in IκBζ-deficient mice, whereas skin inflammation was still inducible in IL-17A-and TNFα-deficient mice. IκBζ deficiency also conferred resistance against IL-23-induced psoriasis. In addition, local abrogation of IκBζ function by intradermal injection of IκBζ siRNA abolished psoriasis-like skin inflammation. Taken together, we identify IκBζ as a hitherto unknown key regulator of IL-17A-driven effects in psoriasis. Thus, targeting IκBζ could be a future strategy for treatment of psoriasis, and other inflammatory diseases for which IL-17 antagonists are currently tested in clinical trials.
Background: IkBz plays a key role in psoriasis by mediating IL-17A-driven effects, but the molecular mechanism by which IL-17A regulates IkBz expression is not clarified. Objective: We sought to explore the molecular transformation in patients with psoriasis during anti-IL-17A (secukinumab) treatment with a focus on IkBz. Methods: The study was an open-label, single-arm, single-center secukinumab treatment study that included 14 patients with plaque psoriasis. Skin biopsy specimens and blood samples were collected on days 0, 4, 14, 42, and 84 and processed for microarray gene expression analysis. Furthermore, in vitro experiments with human keratinocytes and synovial fibroblasts were conducted. Results: Secukinumab improved clinical scores and histologic psoriasis features. Moreover, secukinumab altered the skin transcriptome. The major transcriptional shift appeared between day 14 and day 42 after treatment initiation, although 80 genes were differentially expressed already at day 4. Expression of nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor (IkB) z (NFKBIZ, the gene encoding IkBz) was reduced already after 4 days of treatment in the skin. NFKBIZ expression correlated to Psoriasis Area and Severity Index score, and NFKBIZ mRNA levels in the skin decreased during anti-IL-17A treatment. Moreover, specific NFKBIZ signature genes were significantly altered during anti-IL-17A treatment. Finally, we identified NF-kB activator 1 (Act1), p38 mitogen-activated protein kinase (MAPK), Jun NH2-terminal kinase (JNK), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) as key signaling pathways in NFKBIZ/IkBz regulation. Conclusion: Our results define a crucial role for IkBz in the antipsoriatic effect of secukinumab. Because IkBz signature genes were regulated already after 4 days of treatment, this strongly indicates that IkBz plays a crucial role in the antipsoriatic effects mediated by anti-IL-17A treatment. (J Allergy Clin Immunol 2020;145:379-90.)
Psoriasis is a common chronic inflammatory and immune-mediated skin disease. Antagonists of TNF-α and, recently, IL-17 have proven to be highly effective in the treatment for psoriasis; however, the molecular mechanisms involved in the pathogenesis of psoriasis are poorly understood. Recently, we presented evidence that IκBζ is a key regulator in the development of psoriasis through its role in mediating IL-17A-driven effects. Like IL-17A, IL-17F is produced by a variety of immune cells, and the expression of IL-17F is increased in psoriatic skin. The purpose of this study was to characterize the role of IL-17F in the regulation of IκBζ expression and to investigate whether IL-17F regulates psoriasis-associated genes in human keratinocytes through IκBζ. Here, we demonstrate that IL-17F stimulation induces IκBζ expression at both the mRNA and the protein levels in normal human keratinocytes. Moreover, silencing IκBζ by siRNA revealed that IκBζ is a key regulator of specific IL-17F-inducible psoriasis-associated genes and proteins, including DEFB4/hBD2, S100A7, CCL20, IL-8 and CHI3L1. In addition, IL-17F-induced IκBζ expression is mediated by a mechanism involving the p38 MAPK and NF-κB signalling pathways, as shown by the clear reduction in IL-17F-mediated expression of IκBζ during chemical inhibition of these two signalling pathways. In summary, we present IκBζ as a novel key regulator of IL-17F-driven effects in psoriasis. Thus, antagonists to IκBζ could potentially provide a more targeted approach for treating psoriasis as well as for treating the other inflammatory and immune-mediated diseases for which IL-17-targeting drugs have recently been approved.
Human β-defensin 2 (hBD2), encoded by the DEFB4 gene, is an antimicrobial peptide playing an essential role in inflammatory processes in the skin. hBD2 expression is regulated synergistically by tumor necrosis factor-α (TNF-α) and IL-17A; however, the underlying regulatory mechanisms are unknown. The purpose of this study was to characterize the molecular mechanism by which TNF-α and IL-17A synergistically induce hBD2 expression. In cultured human keratinocytes we show that a constitutive noninducible binding of the transcription factor organic cation transporter 1 (OCT1) to the DEFB4 promoter is crucial for IL-17A/TNF-α-mediated synergistic induction of hBD2 but not the synergistic induction of CCL20, IL8, IL17C and LCN2. Interestingly, stimulation with IL-17A results in a p38 mitogen-activated protein kinase-dependent accumulation of inhibitor of nuclear factor κB ζ (IκBζ), which is a necessity for synergistic induction of hBD2. Finally, co-stimulation with TNF-α induces DNA binding of NF-κB and activator protein 1 (AP-1) to two specific sites in the DEFB4 promoter region. Hence, our study shows how two inflammatory stimuli are integrated by three different signaling pathways into the regulation of one specific target gene involving the three specific transcription factors OCT1, NF-κB, and AP-1 as well as the transcriptional cofactor IκBζ. These findings may be important in psoriasis, where TNF-α and IL-17A have been identified as key pathogenic cytokines.
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