EZH2-mediated H3K27 trimethylation mediates neurodegeneration in ataxia-telangiectasia

The symptoms of ataxia-telangiectasia (A-T) include a progressive neurodegeneration caused by ATM protein deficiency. We previously found that nuclear accumulation of histone deacetylase-4, HDAC4, contributes to this degeneration; we now report that increased histone H3K27 trimethylation (H3K27me3) mediated by polycomb repressive complex 2 (PRC2) also plays an important role in the A-T phenotype. Enhancer of zeste homolog 2 (EZH2), a core catalytic component of PRC2, is identified as a new ATM kinase target, and its S734 phosphorylation reduces protein stability. Thus, PRC2 formation is elevated along with H3K27me3in ATM deficiency. ChIP-sequencing shows a significant increase in H3K27me3 'marks' and a dramatic shift in their location. The change of H3K27me3 chromatin-binding pattern is directly related to cell cycle re-entry and cell death of ATM-deficient neurons. Lentiviral knockdown of EZH2 rescues Purkinje cell degeneration and behavioral abnormalities in Atm / mice, demonstrating that EZH2-mediated H3K27me3 is another key factor in A-T neurodegeneration. Two samples each were run of brain total RNA from Atm+/+ and Atm-/- mice.共济失调毛细血管扩张症（ataxia-telangiectasia, A-T）的病症表现为ATM蛋白缺陷引发的进行性神经退行性变。我们此前的研究发现，组蛋白去乙酰化酶4（histone deacetylase-4, HDAC4）的核聚集参与了该退行性病变过程；本研究进一步证实，由多梳抑制复合体2（polycomb repressive complex 2, PRC2）介导的组蛋白H3K27三甲基化（histone H3K27 trimethylation, H3K27me3）水平升高，同样在A-T表型中发挥重要作用。作为PRC2的核心催化组分，zeste同源增强子2（Enhancer of zeste homolog 2, EZH2）被鉴定为ATM激酶的新型底物，其S734位点的磷酸化可降低自身蛋白质稳定性。因此，在ATM缺陷的细胞中，PRC2的组装水平与H3K27me3水平均显著升高。染色质免疫共沉淀测序（ChIP-sequencing）结果显示，H3K27me3的修饰标记数量显著增加，且其基因组定位发生了显著偏移。H3K27me3的染色质结合模式改变，与ATM缺陷神经元的细胞周期重激活及细胞死亡直接相关。慢病毒介导的EZH2敲低可挽救Atm敲除小鼠的浦肯野细胞退行性变与行为异常，证实EZH2介导的H3K27me3是A-T神经退行性变的另一关键调控因子。本研究对Atm+/+与Atm-/-小鼠的脑组织总RNA各设置两份样本完成检测。