神经发育障碍性疾病的新机制：SNRPN通过抑制Nr4a1影响神经元兴奋性突触发育

Neurodevelopmental disorders are impairments of the growth and development of the brain or central nervous system. The term refers to a disorder of brain function that affects emotion, learning ability, self-control and memory and that unfolds as the individual grows. For poor adaptability, neonates with neurodevelopmental disorders have high perinatal mortality. Small Nuclear Ribonucleoprotein Polypeptide N (SNRPN), highly expressed in brain, is taking part in the alternative splicing of pre-mRNA. SNRPN is an important gene in 15q11-13 region, which is one of most common cause of neurodevelopmental disorders. The molecular and cell biological mechanisms by which SNRPN acts in neurodevelopment are largely unexplored..Li et al used massive parallel sequencing to analyze total RNA from untreated and SNRPN overexpressed HeLa cells. Nuclear receptor subfamily 4, group A, member 1, Nr4a1, showed a more than two-flod decrease after SNRPN induction. Nr4a1 belongs to a family of three immediate early genes that encode three orphan nuclear receptors, which are key regulators of synaptic function. Downregulation Nr4a1 leads to massive clustering of spines at the ends of dendrites in the neurons and impairs synaptic potentiation induced by chronic hyperactivity..Previously, we overexpressed SNRPN in neuron and found Nr4a1 mRNA level decreased significantly. Our hypothesis is SNRPN regulates excitatory synapse development through inhibition Nr4a1. In this project, we will: 1. Study how SNRPN regulates dendritic spine morphlogy and synaptic density by molecular clone, utero electroporation and so on. 2. Determine whether SNRPN regulates synapse development through downregulated Nr4a1. 3. Mouse models carrying SNRPN overexpression will be used to investigate the molecular and synaptic consequences of SNRPN..This project is focused on study the new mechanism of neurodevelopmental disorders via understanding the role of SNRPN in neurodevelopment. We believe that our study will help towards our understanding of biological alterations associated with neurodevelopmental disorders as well as the development of knowledge-based treatments.

神经发育障碍性疾病（NDDs）是多以认知障碍为特征的一组疾病，在新生儿脑病及不明原因死亡中占较高比例，突触发育是认知功能的结构基础。SNRPN表达异常可引起多种NDDs，我们前期研究中也得到了证实。SNRPN在大脑中特异性表达，但其如何影响神经发育的机制尚不明确。最新文献报道肿瘤细胞过表达SNRPN后，一系列基因发生改变。在此线索提示下，我们在神经元中过表达SNRPN，并检测了多个基因表达水平，其中和突触发育密切相关的Nr4a1明显降低。Nr4a1影响突触的结构及功能，突触发育异常是NDDs的重要病理特征。因此我们提出合理的科学设想：SNRPN通过抑制Nr4a1影响神经元兴奋性突触发育，是NDDs致病机制之一。本项目拟通过分子克隆、胚胎电转术、染色体工程小鼠模型等手段，检测SNRPN过表达对突触发育的影响，进一步明确Nr4a1在此过程中的角色。为理解SNRPN在NDDs中的作用提供新思路。

神经发育障碍性疾病（Neurodevelopmental disorders, NDDs)是一组由于非正常神经发育导致的神经行为异常疾病，影响到社交、认知、语言、运动等多个方面。小核核糖体蛋白多肽N（Small Nuclear Ribonucleoprotein Polypeptide N, SNRPN）是神经元特异性剪切蛋白编码基因，位于15号染色体长臂 11-13（15q11-13）区域，与多种神经发育障碍性疾病有关。SNRPN在大脑中选择性高表达，被认为参与大脑可变剪切，但其在神经发育中的作用及机制尚不清楚。我们通过分子生物学技术操控神经元SNRPN表达水平，观察发育中神经元形态功能变化，进一步探索其调控机制，为寻找NDDs靶向治疗药物提供理论依据。项目从SNRPN基因表达及对皮层神经发育的影响、SNRPN影响神经元发育的分子机制、药物治疗初探三部分开展研究。结果发现：SNRPN在大脑不同发育时期及不同功能区特异性表达，在大脑皮层、海马区域随着发育进程表达量增高，而小脑中则降低。体内体外研究发现，SNRPN过度表达抑制皮层神经元神经突生长，延缓胚胎期皮层神经元的正常放射状迁移。对于突触发育，SNRPN过表达神经元树突棘密度增高，树突棘过度堆积于树突末端。进一步检测SNRPN对神经元发育影响的分子机制，体外培养皮层神经元上调SNRPN表达水平可降低核受体亚家族4，A组，成员1（Nr4a1）表达水平，在高表达SNRPN小鼠大脑皮层同样发现Nr4a1表达水平降低。同时转染SNRPN过表达质粒及Nr4a1过表达质粒，可逆转树突棘密度异常增高及在树突末梢的过度堆积。敲减Nr4a1可抑制低SNRPN表达引起的神经突过度生长。此外，SNRPN调节剂3,3’-二吲哚基甲烷（3, 3’- Diindolylmethane, DIM）对低表达SNRPN神经元神经突的影响与敲减Nr4a1相似。初步探讨DIM在SNRPN表达异常动物模型中的作用，给予高表达SNRPN小鼠口服DIM 90天，可纠正小鼠体重的异常过度增长。综上所述，SNPRN基因表达水平改变影响正常神经元发育，SNRPN调控Nr4a1是影响神经元发育、树突棘密度及分布的机制之一。本研究在了解SNRPN功能及机制的基础上，尝试开展初步的治疗药物研究，对疾病的治疗干预具有重要探索意义。