UBE3A modulates Angelman syndrome transcriptome via retrovirus like GAG domain containing protein PEG10

Angelman syndrome (AS) is a rare severe neurodevelopmental disorder caused by neuronal loss of ubiquitin ligase UBE3A. Despite therapies for AS that reinstate the paternal UBE3A allele entering clinics, our understanding of relevant UBE3A targets particularly in humans has been severely limited. We established human patient derived neuron (hiPSC) models for AS and demonstrate specific and reciprocal modulation of UBE3A using anti-sense oligonucleotides (ASOs) in AS patient derived neurons. Through unbiased proteomic analysis we identified UBE3A targets, including the novel human specific retrotransposon derived GAG domain containing protein PEG10. PEG10 protein but not RNA was elevated in AS hiPSC-derived neurons as well in an AS patient brain. Its upregulation in AS was proteasome and UBE3A dependent. Functional analysis revealed that PEG10 binds both RNA and ataxia associated proteins, ATXN2 and ATXN10. PEG10 localizes to stress granules and is secreted in extracellular vesicles where it affects vesicle content in AS neurons. AS neurons in which either UBE3A was reinstated or PEG10 was reduced, showed a striking similarity in transcriptome changes implicating PEG10 as a central driver in transcriptomic alterations downstream of UBE3A. Subsequently, overexpression of human PEG10 in mice dramatically affected cortical neuronal migration. These findings imply that PEG10 is a secreted UBE3A target involved inAS pathophysiology.

安格尔曼综合征（Angelman syndrome, AS）是一种罕见的重度神经发育障碍，由神经元泛素连接酶UBE3A缺失所导致。尽管可恢复父源性UBE3A等位基因的AS治疗手段已进入临床阶段，但我们对相关UBE3A靶点的认知仍存在严重局限，尤其是在人类样本中的相关研究更为匮乏。我们构建了AS患者来源的人类诱导多能干细胞（human induced pluripotent stem cell, hiPSC）神经元模型，并证实利用反义寡核苷酸（anti-sense oligonucleotides, ASOs）可对AS患者来源神经元中的UBE3A实现特异性双向调控。通过无偏蛋白质组学分析，我们鉴定出多个UBE3A靶点，其中包括新型人类特异性逆转录转座子衍生的含GAG结构域蛋白PEG10。在AS的hiPSC来源神经元以及AS患者大脑组织中，PEG10蛋白（而非其RNA转录本）的水平显著升高，且该上调效应依赖于蛋白酶体与UBE3A的调控。功能分析结果显示，PEG10可同时结合RNA以及共济失调相关蛋白ATXN2与ATXN10。PEG10定位于应激颗粒，并可通过细胞外囊泡进行分泌，进而影响AS神经元内的囊泡内容物组成。在恢复UBE3A表达或降低PEG10水平的AS神经元中，二者的转录组变化呈现显著相似性，这表明PEG10是UBE3A下游转录组改变的核心驱动因子。后续实验中，在小鼠体内过表达人类PEG10会显著干扰皮层神经元的迁移过程。上述研究结果表明，PEG10是一种分泌型UBE3A靶点，参与了安格尔曼综合征的病理生理过程。