Malfunctioning DDR and metabolism drive cerebellar pathologies in genetic instability disorders

基因组不断受到内源性和外源性损伤的挑战。细胞进化出两种关键的DNA损伤反应（DDR）途径，分别由ATM和ATR介导。MRN （MRE11/RAD50/NBS1）复合体的功能主要是在DNA双链断裂（DSBs）时激活ATM，并在复制应激时调节ATR的激活。ATM、ATR、NBS1和MRE11基因突变分别导致共济失调-毛细血管扩张症（A-T）、Seckel综合征（SS）、奈梅根断裂综合征（NBS）和A-T样疾病（A-TLD）。A-T和A-TLD与小脑变性有关，NBS和ATR-SS以小头畸形和智力迟钝为特征。众所周知，DDR分子和修复途径的突变引起神经系统症状，这些症状通常与小脑缺陷有关，导致人类患者和小鼠模型中的共济失调；然而，为什么小脑而不是大脑皮层容易受到DDR功能障碍的影响是一个长期未解之谜。为了了解这些疾病的分子通路，我们建立了Nbs1、Mre11、Atm和Atr突变小鼠模型。我们发现，尽管Atr、Nbs1和Mre11不是有丝分裂后神经元存活所必需的，但它们具有其他新的生理功能，例如线粒体和代谢、血管完整性和突触前活动。我们假设这些基因组不稳定性障碍A-T、SS、A-TLD和NBS的神经缺陷是发育和代谢障碍，这些疾病是由这些DDR参与者的规范和非规范功能的失败引起的。因此，我们的目标是：(1)研究使小脑神经祖细胞易受DDR功能障碍影响的分子途径；(2)阐明代谢在DDR缺乏症小脑耗损中的调节作用；(3)发现和表征血管完整性等环境因素在预防小脑缺陷中的作用。(1) DDR在小脑发育和维持中的分子和遗传学解剖。（ii）集成组学，包括神经元和非神经元细胞以及神经元活性的靶向代谢分析和单细胞RNA-seq。（iii）小脑与大脑皮层血管完整性的分子和影像学分析。我们的研究将导致在神经病变中DDR蛋白控制的分子通路的新发现，特别是在基因组不稳定综合征中小脑的特异性。了解共济失调相关疾病的本质不仅可以为个体提供药物策略，还可以揭示小脑发育，功能及其维护的基础生物学。

The genome is constantly challenged by endogenous and exogenous damaging insults. Cells evolve two key DNA damage response (DDR) pathways, which are mediated by ATM and ATR. The MRN (MRE11/RAD50/NBS1) complex functions mainly to activate ATM in response to DNA double strand breaks (DSBs) and also regulates the ATR activation in response to replication stress. Mutations of ATM, ATR, NBS1 and MRE11 cause Ataxia-Telangiectasia (A-T), Seckel Syndrome (SS), Nijmegen Breakage Syndrome (NBS) and A-T Like Disorder (A-TLD), respectively. A-T and A-TLD are associated with cerebellar degeneration, NBS and ATR-SS are characterized by microcephaly and mental retardation. It is well known yet puzzling that mutations of DDR molecules and repair pathways cause neurological symptoms, which are often associated with defects in the cerebellum, leading to ataxia in human patients and mouse models; however, why cerebella, but not cerebral cortex, are vulnerable to DDR malfunction is a long-term unsolved mystery. To understand the molecular pathways of these disorders, Nbs1, Mre11, Atm, and Atr mutant mouse models have been generated. We found that although surprisingly Atr, Nbs1 and Mre11 are not required for survival of postmitotic neurons, they have other novel physiological functions, for example in mitochondria and metabolism, vascular integrity and presynaptic activities. We hypotheses that neurological defects of these genomic instability disorders A-T, SS, A-TLD and NBS are developmental as well as metabolic disorders and that these disorders are caused by the failure of the canonical as well as the non-canonical functions of these DDR players. We therefore set up the following objectives: (1) To study the molecular pathways that render the cerebellar neuroprogenitors susceptible to the DDR malfunction (2) To elucidate the function of metabolism as a regulator of cerebellar attrition of DDR deficiency(3) To discover and characterize the environmental factors such as vascular integrity in preventing cerebellar defects We will take the following approaches: (i) Molecular and genetic dissection of the DDR in cerebellar development and maintenance. (ii) Integrated omics including targeted metabolic analysis and single cell RNA-seq in neuron and non-neuronal cells as well as neuronal activity. (iii) Molecular and imaging analyses of vascular integrity in cerebella in comparison with cerebral cortices.Our study will lead to new discovery of molecular pathways that under control by the DDR proteins in neuropathies particularly the specificity of cerebella in genomic instability syndromes. The understanding of the nature of the ataxia related disorders will not only deliver pharmaceutical strategies for the individuals, but also shed light on the fundamental biology of the cerebellum development, functionality and its maintenance.