| Psoriasis is a chronic inflammatory skin disease whose pathogenesis remains unclear. Recent researches indicate that psoriasis is an autoimmune disorder mediated by Thl/Th17 cells. Different types of cells and cytokines are considered to be involved in this procedure.Expression of keratins changes significantly in skin lesions as epidermal proliferation happens in psoriasis. Keratin 17(K17), also known as "psoriasis related keratin", is not expressed in healthy epidermis but is highly expressed in psoriatic skin lesions, with its level of expression closely related to the severity of the disease. Former researches of our group on K17 and psoriasis found out that there might be a "T cell—cytokin—K17 autoimmune loop" in the pathogenesis of psoriasis. In psoriasis, K17 induces the activation and proliferation of T cells. T cells then produce inflammatory cytokines such as Interferon-y(IFN-y) and Interleukin-17(IL-17), while both IFN-y and IL-17 can induce the production of K17, forming a self-facilitating circle, leading to pathological changes such as proliferation and inflammatory responses.Interleukin-22(IL-22) is one of the major effect cytokine of Th17 cells. Being the "pro-inflammatory cytokine" of psoriasis, its level is positively correlated with the severity of psoriasis. IL-22 can regulate the expression of genes of differentiation-associated proteins, thus inhibit the differentiation of keratinocytes, leading to epidermal proliferation and acanthosis in psoriasis.Objective:Considering the important role of both IL-22 and K17 in psoriasis, as well as the similarities they share in relationship with immunocytes and diseases, we focused on the relationship between them two. Our research mainly concerned with the relationship between IL-22 stimulation and K17 expression in keratinocytes and the possible molecular mechanism in this procedure.Methods:In vitro cultivated HaCaT cells were treated with IL-22 in different concentrations of Ong/mL,12.5ng/mL,25ng/mL,50ng/mL and 100ng/mL for 48 hours. The Ong/mL IL-22 treated group was set as blank control, while a 250U/mL IFN-y treated group was set as positive control. Real-time PCR, ELISA, Western blot and immunofluorescence staining were employed to analyze the mRNA and protein level of K17, the effective concentration of IL-22 stimulation, and the relationship between them.HaCaT cells were then treated with an effective concentration of IL-22 for Omin,15min,30min,60min respectively. Real-time PCR and immunofluorescence staining were used to determine the tyrosine phosphorylation of signaling molecules.In blocking experiments, HaCaT cells were treated first with relevant antagonists of signaling pathways for 2 hours and then with IL-22 for 12-24 hours. Real-time PCR and immunofluorescence staining were used to examine the effect of antagonists on IL-22 induced K17 expression.Results:HaCaT cells treated with IL-22 of 12.5ng/mL,25ng/mL,50ng/mL and 100ng/mL for 48 hours all exhibited K17 expression to varying degrees. Compared with blank control, no statistical difference was detected in the K17 mRNA and protein expression of the 12.5ng/mL group, while significant differences were found between the 25ng/mL,50ng/mL, 100ng/mL groups and the blank control group (P<0.05). A dose-dependent relationship was found between IL-22 stimulation and K17 expression. Signal transducer and activator of transcription 3(STAT3) and extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylation were detected since 15min after 25ng/mL IL-22 stimulation. HaCaT cells being pretreated with STAT3 and ERK1/2 specific inhibitor Piceatannol and PD-98059 for 2h, K17 expression significantly decreased after 25ng/mL IL-22 stimulation.Conclusion:Our research proved that IL-22 can induce K17 expression in HaCaT cells in a dose-dependent way, and that the involved signaling pathways are STAT3 and ERK1/2. These findings indicate that the role IL-22 played in the pathogenesis of psoriasis can be at least partly attributed to its induction of K17 expression. Being an enrichment of our former "T cell—cytokin—K17 autoimmune loop" hypothesis, our findings provided us with new targets for the cure of psoriasis and laid a foundation for further researches on more effective and more specific treatments of psoriasis. |
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