寻常型银屑病发病机制尚不清楚，角质形成细胞过度增殖和异常分化是重要的病理特征；研究表明，DNA甲基化与其密切相关，但机制尚未阐明。本课题组前期对寻常型银屑病皮损组织、非皮损组织及正常皮肤组织进行全基因组DNA甲基化测序（MeDIP-Seq）发现，与正常皮肤组织和非皮损区组织相比，基因PDCD5在寻常型银屑病皮损区呈高甲基化状态（原因不明），且甲基化状态和患者PASI评分正相关；皮损组织中PDCD5 mRNA表达水平亦显著降低。文献报道称，IL-23/-17是寻常型银屑病中重要的炎症介质，且可能受到基因PDCD5的负调控。因此，我们提出如下假说：DNA甲基转移酶在某转录因子的招募下作用于基因PDCD5→基因PDCD5调控序列发生高甲基化→PDCD5表达下调→IL-23/-17表达增高→角质形成细胞过度增殖和异常分化→形成银屑病的特征性皮损。本项目将有助于进一步阐明寻常型银屑病的发病机制。

The mechanisms of psoriasis vulgaris remain unknown, characterized by abnormal keratinocytes proliferation and differentiation. Studies showed that DNA methylation is closed related, with many mysteries to be illuminated. Our previous investigation of genomic DNA methylation status between involved lesions, uninvolved lesions from patients with psoriasis vulgaris and normal skin tissues demonstrated that compared to normal control and non-skin lesions, hypermethylation of gene PDCD5 was observed in psoriatic skin lesions （mechanism unknown）. Correlation analysis showed that methylation levels of gene PDCD5 was positively correlated with patients' PASI scores. mRNA expression of PDCD5 was significantly down-regulated in psoriatic skin lesions. It was reported that IL-23/-17 are important inflammatory mediators in psoriasis, probably regulated by PDCD5. Therefore, based on the previous findings, we assume that DNMTs recruited by unknown TF to gene PDCD5 results in PDCD5 hypermethylation and decreased expression, which leads to increased IL-23/-17 expression, abnormal keratinocytes proliferation and psoriatic lesions. The project will provide further information on the mechanisms of psoriasis vulgaris.

背景：前期研究结果显示，PDCD5在寻常型银屑病皮损区呈高甲基化状态，与患者PASI评分正相关，且皮损中mRNA表达显著降低。但其发生机制尚不清楚。主要研究内容：寻找寻常型银屑病患者皮损组织中与PDCD5甲基化异常修饰相关的转录因子，明确该转录因子与基因PDCD5及DNA甲基化转移酶之间的相互作用关系。通过在HaCaT细胞中过表达/抑制表达基因PDCD5，观察角质形成细胞增殖与分化相关分子的表达是否发生改变。重要结果及关键数据：1）RUNX1是寻常型银屑病患者皮损组织中与PDCD5甲基化异常修饰相关的转录因子，RUNX1与DNMT1及HDAC1存在相互结合关系；2）HaCaT 细胞中促进RUNX1的表达，PDCD5 mRNA 和蛋白质表达水平显著降低；HaCaT 细胞中抑制RUNX1的表达，PDCD5 mRNA 和蛋白质表达水平显著升高；3）HaCaT 细胞中促进RUNX1的表达，PDCD5 启动子区RUNX1及DNMT1的结合明显增多，其DNA甲基化水平显著升高。HaCaT 细胞中抑制RUNX1的表达，PDCD5 启动子区RUNX1及DNMT1的结合明显减少，其DNA甲基化水平明显降低；4）分别转染pCDNA3.1(+)-PDCD5及对照质粒进入HaCaT 细胞后，用UVB照射诱导细胞凋亡，发现PDCD5能显著增强UVB诱导凋亡引起的细胞活力下降，但HaCaT 细胞的早期分化标记（involucrin 和 cytokeratin 10）、晚期分化标记（filaggrin）和基底细胞标记（cytokeatin 5）表达水平无显著改变。科学意义：本课题揭示了寻常型银屑病患者皮损组织中与PDCD5甲基化异常修饰相关的转录因子RUNX1，并发现PDCD5能显著增强UVB诱导凋亡引起的细胞活力下降，进一步揭示了PDCD5在寻常型银屑病发病中的作用。