Mechanism of neurodegeneration in dystonia musculorum

描述(由申请人提供)： 突变的小鼠肌张力障碍(DT)患有严重的遗传性感觉神经病。这些小鼠从出生第二周开始出现肢体协调能力的进行性丧失。DT小鼠的背根神经节比野生型小得多，细胞器和空泡聚集在感觉神经轴突内。局灶性轴突肿胀充满神经丝、线粒体和膜结合的致密小体，是这些小鼠的病理特征。在突变小鼠中，细胞骨架的解体先于神经退化。在DT小鼠中突变的基因被称为dysttin，也被称为大疱性类天疱疮抗原1(BPAG1)。BPAG1是细胞骨架连接蛋白plakin家族的成员。Plakin家族成员有一个特有的plakin结构域，它可以与多种细胞黏附分子相互作用，也可以与含有Aradillo-Repeat结构域的蛋白家族(连环蛋白家族)的成员相互作用。此外，各种Plakin蛋白都有能与肌动蛋白微丝、微管和中间丝结合的结构域。在上皮细胞中，BPAG1-e参与将角蛋白中间丝锚定到半桥粒上。为什么半桥粒蛋白的缺失会导致神经元变性？为了研究这个问题，我们对BPAG1基因座进行了详细的分析。我们发现，通过组织特异性剪接，它以不同的相互作用结构域的不同组合编码各种异构体。在神经系统中有两种亚型表达：主要的亚型BPAG1-a和BPAG1-n，其表达水平低于BPAG1-a。BPAG1-b是最大的异构体，在肌肉中高度表达。或者，分别影响ABD和MTBD的5‘和3’末端的拼接可以导致BPAG1-a、BPAG1-b和BPAG1-n的额外亚型。在这个提议中，我们将更详细地研究神经元异构体的功能，以了解为什么这种蛋白质的突变会导致神经元退化。这项建议集中在小鼠突变的肌张力障碍(DT)的原因上，因此属于计划宣布倡议PA-02-156的领域：“研究肌张力障碍的原因和机制。”特别是，该提案符合PA瞄准的第二个研究领域的标准：“鉴定与肌张力障碍相关的细胞因子(基因、蛋白质)相互作用的蛋白质，并确定它们的协调功能。”

DESCRIPTION (provided by applicant): The mutant mouse dystonia musculorum (dt) suffers from a severe hereditary sensory neuropathy. The mice display progressive loss of limb coordination starting in the second week of life. Dorsal root ganglia of dt mice are considerably smaller in size than those of wild type mice with organelles and empty vacuoles accumulating within sensory axons. Focal axonal swellings filled with neurofilaments, mitochondria and membrane bound dense bodies are hallmarks of the pathology of these mice. The disorganization of the cytoskeleton precedes neurodegeneration in the mutant mice. The gene that is mutated in dt mice is called dystonin, and is also known as bullous pemphigoid antigen 1 (BPAG1). BPAG1 is a member of the plakin family of cytoskeletal linker proteins. Plakin family members have a characteristic plakin domain that can interact with a variety of cell adhesion molecules, as well as members of the armadillo-repeat domain containing protein family (catenin family). In addition, various plakins have domains that can bind to actin microfilaments, microtubules and intermediate filaments. In epithelial cells, BPAG1-e is involved in anchoring keratin intermediate filaments to the hemidesmosomes. Why does the deletion of a hemidesmosomal protein cause neuronal degeneration? To investigate this question, we have analyzed the BPAG1 locus in detail. We found that by tissue specific splicing, it encodes a variety of isoforms with different combinations of the various interacting domains. There are two isoforms expressed in the nervous system: the major isoform, BPAG1-a and BPAG1-n, which is expressed at lower levels than BPAG1-a. BPAG1-b is the largest isoform and is highly expressed in muscles. Alternatively spliced 5' and 3' ends that affect the ABD and MTBD respectively can lead to additional isoforms of BPAG1-a, BPAG1-b and BPAG1-n. In this proposal, we will study the function of the neuronal isoforms in more detail to understand why mutations of this protein result in neuronal degeneration. This proposal focuses on the cause for the mouse mutant dystonia musculorum (dt) and is therefore in the realm of the Program Announcement initiative PA- 02-156: "Studies into the causes and mechanisms of dystonia." In particular, the proposal meets the criteria of the second research area targeted by the PA: "Identification of proteins that interact with dystonia-related cellular factors (genes, proteins) and determination of their coordinated function."