Molecular Pathogenesis of Myotonic Dystrophy

描述(申请人提供)：强直性肌营养不良(DM)是肌肉营养不良的第二个最常见的原因，也是成人起病的最常见的原因。这种疾病主要是遗传性的，多系统的，表型多变的。导致糖尿病的突变是位于转录基因的非翻译区内的扩大的三(CTG)和四(CCTG)核苷酸重复。发病机制涉及一种新的机制，在这种机制中，从扩展的等位基因转录的RNA施加了有毒的功能获得。最近的证据表明，RNA功能增强是其他微卫星扩张性疾病的重要组成部分，如脊髓小脑性共济失调8(SCA8)、脆性X相关震颤/共济失调综合征(FXTAS)和亨廷顿病样2(HDL2)。扩展的重复RNA在DM中发挥功能增益的一种机制是通过隔离RNA结合蛋白，如肌肉样(MBNL)家族，导致功能丧失。我们已经确定了第二种机制，在这种机制中，扩展的重复RNA激活蛋白激酶C(PKC)，并诱导第二个RNA结合蛋白CUG结合蛋白1(CUGBP1)依赖于PKC的磷酸化，从而导致其稳定和上调。MBNL和CUGBP1通常在发育过程中调节前mRNA的选择性剪接，它们在糖尿病中的功能中断会导致剪接缺陷，而剪接缺陷以前被认为与疾病症状的原因有关。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。该方案的目的是确定扩展的重复RNA激活信号事件的机制，调查对CUGBP1功能的直接影响，确定更广泛的后果，并将这些影响与细胞培养中抑制骨骼肌分化和骨骼肌组织浪费的机制联系起来。后一方面的研究将使用新开发的DM1小鼠模型进行，该模型复制了包括严重骨骼肌萎缩在内的疾病特征。在这些研究完成后，我们将确定一种新发现的信号事件在疾病发病机制中的作用，该信号事件由微卫星衍生的RNA刺激。这些结果将提供新的治疗靶点，以防止或绕过导致肌肉萎缩的分子事件。公共卫生相关性：强直性肌营养不良是美国肌肉营养不良的第二大常见原因。它是由一种不寻常的突变和以前未知的机制引起的。我们将利用细胞培养和小鼠模型来确定疾病的发病机制。这些信息将被用来开发逆转或规避疾病过程的治疗方法。

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.