Novel regulatory role of nuclear miRNAs in repatterning the transcriptional and post-transcriptional dynamics in MDD brain

基因x环境相互作用对转录调控的微调是适应不良的核心 与重度抑郁症（MDD）相关的过程。过去十年的研究提供了 强烈支持表观遗传机制在MDD发病机制中的重要性。microRNAs（miRNAs）， 一类小的非编码RNA，产生了巨大的兴趣，不仅作为表观遗传的大型调控因子， 基因表达，但也为他们的作用，疾病的病理生理学和治疗目标。我们和其他 研究人员已经显示了MDD个体脑中miRNA的差异调节。人们普遍认为 miRNAs通过miRNAs种子序列介导细胞质中转录后基因沉默 通过Argonaute（Ago）- RNA诱导沉默复合物（miRISC）。近年来，一种范式转换现象被提出 选择成熟的miRNAs的“核定位”概念。这些miRNAs，包含独特的一组（或多组） 3'末端的核信号，可以从细胞质穿梭回到细胞核，在那里它们可以调节 表达选择核池的编码和非编码RNA转录后，但更多 在转录上非常明显。在转录水平上，有证据表明，成熟的 在基因启动子区的miRNAs具有部分或完全的序列互补性，这使得核 调节基因转录的miRNAs，包括初级miRNAs。转录后，核miRNA 与核酸内切酶Drosha结合，可以靶向pri-miRNA或可以结合核编码3’UTR区 通过miRISC进行转录。新发现的机制提出了一种有趣的可能性，即在细胞核内， miRNAs可能具有显著的基因转录动力学重新模式化的独特能力， 不仅可以在初级和前体（前）-miRNA水平上调节自身的表达， 转录水平。这可能与MDD相关的适应不良过程高度相关。我们提出了一个 总体假设是成熟miRNAs的动态变化和核富集由特定的核转录因子驱动， 信号及其对细胞核内关键的初级、前和成熟miRNA以及编码基因的调节，以及 因此，功能属性将是MDD发病机制的核心。采用高度创新的方法， 从MDD和非精神病对照受试者中获得了良好表征和匹配的大脑样本，我们的目标是 确定：1）miRNA的核富集、胞质向核的转移及其功能相关性; 2） miRNA易位的可能机制; 3）核miRNA独特的转录调控作用 Ago 1复合物在改变靶基因启动子动力学中的作用;以及4）Ago 1复合物的独特作用 作为Drosha微处理器复合体的功能，核miRNA在修饰pri-miRNA加工中的作用。 我们的研究具有高度创新性，有可能揭示核miRNA在重新定义细胞中的独特作用 转录组作为MDD病因学的机制，并确定治疗干预的新靶点。

The fine-tuning of transcriptional regulation by gene x environment interaction is central to maladaptive processes associated with major depressive disorder (MDD). Research over the past decade has provided strong support for the importance of epigenetic mechanisms in MDD pathogenesis. microRNAs (miRNAs), a class of small noncoding RNAs, are generating enormous interest not only as epigenetic mega-regulators of gene expression, but also for their role in disease pathophysiology and treatment targets. We and other investigators have shown differential regulation of miRNAs in the brain of MDD individuals. It is generally agreed that miRNAs mediate post-transcriptional gene silencing in the cytoplasm through seed sequence of miRNAs and complementary sequences in the 3′-untranslated regions (UTR) of target mRNAs via Argonaute (Ago)- based-RNA-induced silencing complex (miRISC). Recently, a paradigm-shifting phenomenon has been put forth with the concept of “nuclear localization” of select mature miRNAs. These miRNAs, containing unique set(s) of nuclear signals in the 3’ terminus, can shuttle back to nucleus from cytoplasm where they can regulate the expression of select nuclear pool of coding and non-coding RNA transcripts post-transcriptionally, but more remarkably, transcriptionally. At the transcription level, there is evidence of putative binding sites of mature miRNAs in the gene promoter regions with partial or perfect sequence complementarity, which enables nuclear miRNAs to regulate gene transcription, including primary(pri-)-miRNAs. Post-transcriptionally, nuclear miRNAs in conjunction with endonuclease Drosha, can target pri-miRNAs or can bind to 3’UTR region of nuclear coding transcripts via miRISC. The newly discovered mechanism poses an interesting possibility that within the nucleus, miRNAs may have the distinct capability of repatterning the gene transcription dynamics dramatically where they can not only regulate their own expression at pri- and precursor(pre)-miRNA levels, but also at the nuclear coding transcript level. This could be highly relevant in MDD-associated maladaptation processes. We propose an overarching hypothesis that a dynamic shift and nuclear enrichment of mature miRNAs driven by specific nuclear signals and their regulation of key pri-, pre-, and mature miRNAs, and coding genes within the nucleus, and consequent functional attributes, will be central to MDD pathogenesis. Using highly innovative approaches and well characterized and matched brain samples from MDD and non-psychiatric control subjects, we aim to determine: 1) the nuclear enrichment of miRNAs, cytosolic to nuclear shift, and their functional relevance; 2) possible mechanism(s) of miRNA translocation; 3) the unique transcriptional regulatory role of nuclear miRNAs in changing the promoter dynamics of target genes as a function of Ago1 complex; and 4) the unique role of nuclear miRNAs in modifying the processing of pri-miRNAs as a function of Drosha microprocessor complex. Our study is highly innovative and has the potential to uncover the unique role of nuclear miRNAs in redefining transcriptome as a mechanism in MDD etiology and identifying novel targets for therapeutic intervention.