microRNA参与狼疮低甲基化调控机制
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中国科学院上海生命科学研究院健康科学研究所沈南教授领导的研究组整合上海交通大学附属仁济医院风湿科的临床优势和健康所的基础研究力量，继2009年在风湿病学领域最有影响力的杂志ARTHRITIS & RHEUMATISM上报道了miRNA作为负反馈调节分子在狼疮关键致病通路中起了重要作用后，近日又在国际学术期刊Journal of immunology发表了有关miRNA参与狼疮T细胞低甲基化调控的最新研究成果。该工作揭示了miRNA参与狼疮发病的新机制，为今后发展miRNA为靶点的干预治疗提供了重要依据。
系统性红斑狼疮(systemic lupus erythematosus, SLE) 发病机理复杂，被认为是自身免疫病的原型，T淋巴细胞异常低甲基化在SLE的发病中起着重要作用。但狼疮T细胞异常低甲基化的机制尚未阐明。MicroRNA(miRNA)是近年来广为关注的重要的基因表达调控因子，SLE患者T细胞异常低甲基化可能与某些miRNA异常表达有关。
为探索这一关键问题，研究人员通过高通量和特异性的miRNA表达谱分析、筛选发现，miR-21和miR-148a在SLE小鼠模型T淋巴细胞异常高表达。探索miR-21和miR-148a的表达与疾病临床表型的相关性，发现在SLE患者T细胞中这两个miRNA的表达水平与疾病的活动性以及免疫相关的甲基化敏感基因的表达呈正相关。进一步机制研究发现，狼疮T细胞中高表达的miR-21通过直接抑制DNMT1上游信号分子RASGRP1而间接调控DNMT1的表达，miR-148a通过直接靶向DNMT1的编码区来调控DNMT1的表达，加速细胞内低甲基化状态，诱导自身免疫相关的甲基化敏感基因启动子区域去甲基化，上调敏感基因的表达，介导疾病发生。使用这两个miRNA特异性抑制剂对SLE病人T淋巴细胞进行干预处理，发现能够有效逆转低甲基化状态。
该项研究表明，miR-21和miR-148a有望成为调控SLE患者T淋巴细胞异常低甲基化的新靶点，改变SLE患者T淋巴细胞内的miR-21和miR-148a表达水平可作为潜在的干预治疗手段。
该项工作得到国家科技部、国家自然科学基金和上海市科委的经费支持。
MicroRNA-21 and MicroRNA-148a Contribute to DNA Hypomethylation in Lupus CD4+ T Cells by Directly and Indirectly Targeting DNA Methyltransferase
Wen Pan~undefined Shu Zhu, Min Yuan~undefined Huijuan Cui~undefined Lijia Wang~undefined Xiaobing Luo~undefined Jia Li~undefined Haibo Zhou~undefined, Yuanjia Tang~undefined, and Nan Sheundefined,
【Abstract】Systemic lupus erythematosus is a complex autoimmune disease caused by genetic and epigenetic alterations. DNA methylation abnormalities play an important role in systemic lupus erythematosus disease processes. MicroRNAs (miRNAs) have been implicated as fine-tuning regulators controlling diverse biological processes at the level of posttranscriptional repression. Dysregulation of miRNAs has been described in various disease states, including human lupus. Whereas previous studies have shown miRNAs can regulate DNA methylation by targeting the DNA methylation machinery, the role of miRNAs in aberrant CD4+ T cell DNA hypomethylation of lupus is unclear. In this study, by using high-throughput microRNA profiling, we identified that two miRNAs (miR-21 and miR-148a) overexpressed in CD4+ T cells from both patients with lupus and lupus-prone MRL/lpr mice, which promote cell hypomethylation by repressing DNA methyltransferase 1 (DNMT1) expression. This in turn leads to the overexpression of autoimmune-associated methylation-sensitive genes, such as CD70 and LFA-1, via promoter demethylation. Further experiments revealed that miR-21 indirectly downregulated DNMT1 expression by targeting an important autoimmune gene, RASGRP1, which mediated the Ras–MAPK pathway upstream of DNMT1; miR-148a directly downregulated DNMT1 expression by targeting the protein coding region of its transcript. Additionally, inhibition of miR-21 and miR-148a expression in CD4+ T cells from patients with lupus could increase DNMT1 expression and attenuate DNA hypomethylation. Together, our data demonstrated a critical functional link between miRNAs and the aberrant DNA hypomethylation in lupus CD4+ T cells and could help to develop new therapeutic approaches.
