Delineating a role for histone modifications in Down syndrome using human cellular models

总结 唐氏综合症（DS），由21号染色体的额外拷贝驱动，与以下方面的深刻变化有关： 全基因组基因表达和DNA甲基化，但潜在的机制仍然不完全 解决了利用人类诱导多能干细胞（iPSC）模型来捕获分子机制 与人类发展相关，我们以前发现一种特定的 组蛋白修饰，组蛋白H3赖氨酸36二甲基化（H3 K36 me 2），与 整倍体对照;这一结果在一组DS患者和整倍体对照中也具有高度重现性 淋巴母细胞样细胞系，表明该发现延伸到一些外周细胞类型。H3 K36 me 2定位于 常染色质，它影响转录调控，并对维持DNA甲基化至关重要 通过DNMT 3A募集，特别是在基因间区域。值得注意的是， 催化H3 K36 me 2的甲基转移酶驱动一种称为Sotos综合征的神经发育障碍， 其特征在于减少的H3 K36 me 2、转录失调和DNA低甲基化。的深刻 Sotos综合征中H3 K36 me 2减少的发育后果支持了新的假设， 我们在DS中发现的H3 K36 me 2的减少也可能导致这种疾病的发育异常 上下文我们的总体假设是DS中H3 K36 me 2的减少驱动DNA低甲基化， 转录失调，H3 K36 me 2的正常化将部分挽救这些 表型在目的I中，我们将测试H3 K36 me 2减少驱动DNA低甲基化的假设， DS，通过生成全基因组DNA甲基化图谱并将其与现有的H3 K36 me 2基因整合 占据和转录数据集，均来自相同的DS患者和同基因整倍体对照iPSC。 衍生的神经元。重要的是，这些实验的目的是连接一个良好的特点， DS表型（异常DNA甲基化）与新的分子机制（减少H3 K36 me 2）。在Aim中 II中，我们将检验DS患者iPSC衍生的神经元中的H3 K36 me 2水平正常化可以抑制H3 K36 me 2表达的假设。 拯救DNA甲基化表型。这些数据将作为原理证明，抑制或激活 特定的表观遗传修饰剂可以逆转DS中充分表征的表型， 相关的人类细胞模型。总的来说，我们严格的分子分析将阐明新的机制， DS的表观遗传失调，这可能最终为DS患者提供新的治疗策略; 他们还将为未来的研究提供必要的路线图，以进一步研究如何减少H3 K36 me 2 并且其正常化影响iPSC衍生的和外周血细胞表型。

SUMMARY Down syndrome (DS), driven by an extra copy of chromosome 21, is associated with profound changes in genome-wide gene expression and DNA methylation, but underlying mechanisms remain incompletely resolved. Leveraging human induced pluripotent stem cell (iPSC) models to capture molecular mechanisms relevant for human development, we previously identified a significant decrease in the abundance of a specific histone modification, histone H3 lysine 36 dimethylation (H3K36me2), in DS patient cells compared with euploid controls; this finding was also highly reproducible across a panel of DS patient and euploid control lymphoblastoid cell lines, indicating the finding extends to some peripheral cell types. H3K36me2 is localized to euchromatin where it impacts transcriptional regulation and is essential for maintenance of DNA methylation via DNMT3A recruitment, particularly at intergenic regions. Notably, haploinsufficiency of the histone methyltransferase which catalyzes H3K36me2 drives a neurodevelopmental disorder called Sotos syndrome, characterized by reduced H3K36me2, transcriptional dysregulation and DNA hypomethylation. The profound developmental consequences of reduced H3K36me2 in Sotos syndrome supports the novel hypothesis that the reduced H3K36me2 we found in DS could also contribute to developmental abnormalities in this disease context. Our overall hypothesis is that reduced H3K36me2 in DS drives DNA hypomethylation and transcriptional dysregulation, and that normalization of H3K36me2 will partially rescue these phenotypes. In Aim I, we will test the hypothesis that decreased H3K36me2 drives DNA hypomethylation in DS, by generating genome-wide DNA methylation maps and integrating them with existing H3K36me2 gene occupancy and transcriptional datasets, all from the same DS patient and isogenic euploid control iPSC- derived glutamatergic neurons. Importantly, these experiments are designed to connect a well-characterized phenotype in DS (aberrant DNA methylation) with a novel molecular mechanism (reduced H3K36me2). In Aim II, we will test the hypothesis that normalizing H3K36me2 levels in DS patient iPSC-derived neurons can rescue DNA methylation phenotypes. These data would serve as proof-of-principle that inhibition or activation of specific epigenetic modifiers can reverse well-characterized phenotypes in DS, using physiologically relevant human cellular models. Collectively, our rigorous molecular analyses will elucidate novel mechanisms of epigenetic dysregulation in DS, which may ultimately inform on new therapeutic strategies for DS patients; they will also generate an essential roadmap for future studies to further investigate how reduced H3K36me2 and its normalization impacts iPSC-derived and peripheral blood cell phenotypes.