Molecular Pathogenesis of Myotonic Dystrophy

描述（由申请人提供）：强直性肌营养不良（DM）是肌营养不良的第二大最常见原因，也是成人型肌营养不良的最常见原因。该疾病是显性遗传的，多系统的，表型可变的。导致DM的突变是位于转录基因的非翻译区内的扩展的三（CTG）和四（CCTG）核苷酸重复。发病机制涉及一种新的机制，其中从扩增的等位基因转录的RNA发挥毒性功能获得性。最近的证据表明，RNA功能获得性是其他微卫星扩增疾病的重要组成部分，如脊髓小脑共济失调8（SCA 8），脆性X相关震颤/共济失调综合征（FXTAS）和亨廷顿病样2（HDL 2）。扩展的重复RNA在DM中发挥功能获得的一种机制是通过隔离RNA结合蛋白如肌盲样（MBNL）家族，导致功能丧失。我们已经确定了第二种机制，其中扩增的重复RNA激活蛋白激酶C（PKC），并诱导第二种RNA结合蛋白，CUG结合蛋白1（CUGBP 1）的PKC依赖性磷酸化，导致其稳定和上调。MBNL和CUGBP 1通常在发育过程中调节前体mRNA选择性剪接，并且它们在DM中的功能的破坏导致先前与疾病症状的起因相关的剪接缺陷。来自微卫星扩增的RNA诱导信号事件的发现对发病机制具有广泛的意义。本提案的目标是确定扩展重复RNA激活信号事件的机制，研究对CUGBP 1功能的直接影响，确定更广泛的后果，并将扩展重复序列的这些影响与细胞培养中抑制骨骼肌分化和骨骼肌组织消耗的机制联系起来。研究的后一个方面将使用新开发的DM 1小鼠模型进行，该模型再现了该疾病的特征，包括严重的骨骼肌萎缩。在这些研究完成后，我们将建立一个新发现的信号事件刺激微卫星衍生的RNA的疾病发病机制的贡献。这些结果将为预防或规避导致肌肉萎缩的分子事件提供新的治疗靶点。 公共卫生相关性：强直性肌营养不良症是第二个最常见的原因肌肉萎缩症在美国。它是由一种不寻常的突变和以前未知的机制引起的。我们将使用细胞培养和小鼠模型来确定疾病的机制。这些信息将用于开发治疗方法，以逆转或规避疾病过程。

DESCRIPTION (provided by applicant): Myotonic dystrophy (DM) is the second most common cause of muscular dystrophy and the most common cause of adult onset muscular dystrophy. The disease is dominantly inherited, multisystemic, and phenotypically variable. The mutations that cause DM are expanded tri- (CTG) and tetra- (CCTG) nucleotide repeats located within untranslated regions of transcribed genes. Pathogenesis involves a novel mechanism in which RNA transcribed from the expanded allele exerts a toxic gain-of-function. Recent evidence indicates that an RNA gain-of-function is an important component of other microsatellite expansion disorders such as Spinocerebellar Ataxia 8 (SCA8), Fragile X-associated Tremor/Ataxia Syndrome (FXTAS), and Huntington Disease-Like 2 (HDL2). One mechanism by which the expanded repeat RNA exerts a gain-of-function in DM is by sequestration of RNA binding proteins such as the muscleblind-like (MBNL) family, resulting in a loss-of-function. We have identified a second mechanism in which expanded repeat RNA activates protein kinase C (PKC) and induces PKC-dependent phosphorylation of a second RNA binding protein, CUG-binding protein 1 (CUGBP1), resulting in its stabilization and up-regulation. MBNL and CUGBP1 normally regulate pre-mRNA alternative splicing during development and the disruption of their functions in DM results in the splicing defects that have previously been linked with causation of disease symptoms. The finding that RNA from a microsatellite expansion induces a signaling event has broad implications to the mechanism of pathogenesis. The goals of this proposal are to determine the mechanism by which expanded repeat RNA activates a signaling event, investigate the immediate effects on CUGBP1 function, determine the broader consequences, and relate these effects of the expanded repeats to mechanisms of inhibited skeletal muscle differentiation in cell culture and wasting of skeletal muscle tissue. The latter aspect of the investigation will be performed using a newly developed DM1 mouse model that reproduces features of the disease including severe skeletal muscle wasting. At the completion of these studies, we will have established the contributions to disease pathogenesis of a newly discovered signaling event stimulated by microsatellite-derived RNA. These results will provide new therapeutic targets to prevent or circumvent the molecular events leading to muscle wasting. PUBLIC HEALTH RELEVANCE: Myotonic dystrophy is the second most common cause of muscular dystrophy in the United States. It is caused by an unusual kind of mutation and a previously unknown mechanism. We will use cell culture and mouse models of the to determine the mechanism of disease. This information will be used to develop therapeutic approaches to reverse or circumvent disease processes.