Ataxia Telangiectasia in the CNS - Cause and Effect

描述（由申请人提供）：共济失调毛细血管扩张症（AT）是一种遗传性疾病，令人惊讶的是仅在某些组织中表现出来。这种组织偏好与at影响的中枢神经系统特别相关，其中小脑皮层的退化及其随后的许多传入和传出神经元通路是病理的主要目标部位。浦肯野神经元的明显丧失是该疾病的一个标志，这导致研究主要集中在ATM在这种神经元群中的作用，而对胶质隔室的关注相当少。虽然ATM的功能丧失可能直接影响神经元群的存活，但越来越明显的是，许多已定义的神经系统疾病是由胶质细胞缺陷引起的，尤其是星形胶质细胞间室的胶质细胞缺陷，从而间接影响周围神经元成分的存活。为了确定星形胶质细胞是否以及在多大程度上促成了AT中观察到的病理，我们从纯合子ATM缺陷小鼠大脑中分离出星形胶质细胞，并将其与野生型对照进行比较。从人类病理的主要部位小脑组织中分离出来的星形胶质细胞被高度氧化，产生抗氧化反应的能力下降，并以组织和年龄特异性的方式显示谷氨酸转运体GLAST的失调。这些功能变化表明，突变的星形胶质细胞群可能在为邻近细胞维持保护环境的能力方面受到严重损害。谷氨酸转运体GLAST的解除管制似乎特别重要，因为小脑含有不成比例的谷氨酰胺能神经元，这些神经元依赖于星形胶质细胞控制的谷氨酸稳态。有趣的是，突变型星形胶质细胞的损伤不是全球性的，而是区域特异性的，我们的初步结果表明，从同一动物的皮质组织中分离出来的星形胶质细胞在测试参数上与野生型对照组没有区别。这一发现与人类病理一致，其中小脑功能最严重和逐渐受到疾病的影响。综上所述，我们的观察结果导致了星形胶质细胞有助于AT小脑病理表型的假设。为了验证这一假设，我们将在体内诱导特定中枢神经系统细胞群的AT功能丧失，并确定特定突变细胞类型对小脑神经变性的贡献。由于细胞过早死亡和AT功能的全面丧失，目前可用的动物模型不适合进行这项研究。此外，我们将确定是否存在一个关键的易损窗口，在此期间AT缺乏导致星形胶质细胞功能受损。公共卫生相关性：本提案的目的是确定星形胶质细胞在共济失调毛细血管扩张（AT）中的作用。根据我们的初步研究，我们认为星形胶质细胞在病理中起主要作用，我们显示了小脑特异性星形胶质细胞功能损伤，这与人类病理一致。在没有严重限制现有AT敲除动物寿命的癌症发展的情况下，为了表征这种星形胶质细胞室损伤的后果，我们建议产生中枢神经系统组织特异性诱导的AT突变动物，这些动物发展出与人类患者相似的中枢神经系统病理，并且具有寿命，使我们能够表征星形胶质细胞在疾病进展中的作用。

DESCRIPTION (provided by applicant): Ataxia Telangiectasia (AT) is a genetic disorder that surprisingly manifests itself only in certain tissues. This tissue preference is especially relevant to the AT-affected CNS, in which degeneration of the cerebellar cortex and subsequently many of its afferent and efferent neuronal pathways are the major target site for pathology. The obvious loss of Purkinje neurons that is a hallmark of the disease has resulted in studies that mainly focus on the role of ATM in this neuronal population with considerable less attention paid to the glial compartment. While the functional loss of ATM might affect the survival of neuronal populations directly, it is becoming increasingly evident that many defined neurological disorders are caused by glial deficiencies, especially in the astrocyte compartment, which then indirectly affect the survival of surrounding neuronal components. In an attempt to determine whether and to what extend astrocytes contribute to the pathology observed in AT, we isolated astrocytes from homozygous ATM deficient mouse brains and compared them to their wildtype controls. Astrocytes isolated from cerebellar tissue, the major site of human pathology, were highly oxidized, had a decreased ability to mount an anti-oxidant response and showed deregulation of the glutamate transporter GLAST in a tissue and age specific manner. These functional changes suggest that the mutant astrocyte population is likely to be significantly impaired in the ability to maintain a protective environment for neighboring cells. The deregulation of the glutamate transporter GLAST seems particular significant as the cerebellum contains a disproportionate ratio of glutaminergic neurons that rely on proper glutamate homeostasis controlled by astrocytes. Interestingly, the impairment of mutant astrocytes was not global but region specific and our preliminary results show that astrocytes isolated from cortical tissue of the same animals did not differ from wildtype controls in the tested parameters. This finding is consistent with the human pathology in which cerebellar functions are most severely and progressively affected by the disease. Taken together, our observations lead to the hypothesis that astrocytes contribute to the pathological phenotype of the cerebellum in AT. To test this hypothesis we will induce loss of AT function in specific CNS cell populations in vivo and determine the contribution of specific mutant cell types to the neurodegeneration in the cerebellum. Currently available animal models are not suitable to conduct this research due to premature cell death and global loss of AT function. In addition, we will determine whether there is a critical window of vulnerability during which the deficiency in AT leads to impairment of function in astrocytes. PUBLIC HEALTH RELEVANCE: The aim of this proposal is to establish the role of astrocytes in Ataxia Telangiectasia (AT). Based on our preliminary studies we suggest that astrocytes play a major role in the pathology and we show a cerebellar specific impairment of astrocyte function that is consistent with the human pathology. To characterize the consequence of this impairment in the astrocyte compartment in the absence of the cancer development that severely restricts the lifespan of existing AT knockout animals, we propose to generate CNS tissue specific inducible AT mutant animals that develop a CNS pathology similar to the human patients and with a live span that allows us to characterize the role of astrocytes in the disease progression.